Extending the internet of things (IoT) networks to remote areas under extreme conditions or for serving sometimes unpredictable mobile applications has increased the need for satellite technology to provide effective connectivity. However, existent medium access control (MAC) protocols deployed in commercial satellite networks were not designed to offer scalable solutions for the increasing number of devices predicted for IoT in the near future, nor do they consider other specific IoT characteristics. In particular, CubeSats—a low-cost solution for space technology—have the potential to become a wireless access network for the IoT, if additional requirements, including simplicity and low demands in processing, storage, and energy consumption are incorporated into MAC protocol design for satellite IoT systems. Here we review MAC protocols employed or proposed for satellite systems and evaluate their performance considering the IoT scenario along with the trend of using CubeSats for IoT connectivity. Criteria include channel load, throughput, energy efficiency, and complexity. We have found that Aloha-based protocols and interference cancellation-based protocols stand out on some of the performance metrics. However, the tradeoffs among communications performance, energy consumption, and complexity require improvements in future designs, for which we identify specific challenges and open research areas for MAC protocols deployed with next low-cost nanosatellite IoT systems. From the beginnings of space exploration, satellites were large objects that took years to construct and cost billions of dollars for a single unit. With more advanced and smaller technologies, cheaper spacecraft  have evolved for diverse applications, telecommunication applications being most prominent. Commercial satellite companies like Iridium, Intelsat, O3b, and others offer a portfolio of products, including voice services, broadband, and sensor data collection, with extensive coverage of the Earth’s surface. For example, With the internet of things (IoT), the paradigm that promises to revolutionize our world with the collection of enormous quantities of data, the connectivity demands are being increased around the globe. It is estimated that the IoT communications market will have an impact in the economy close to three to 11 trillion dollars per year in 2025 [With the need for more coverage of the IoT networks and the search for cheaper solutions, nanosatellites may be the best answer for the global connectivity that the IoT demands. The nanosatellite standard, the CubeSat with a volume of less than one liter and a weight of less than one kilogram, also offers access to space and satellite development for countries that previously had no experience in space sciences. Nevertheless, the performance of such a solution will largely depend on the low-level protocols selected for the network architecture.At the core of network architecture are the medium access control (MAC) protocols. Given the broadcast nature of channels in satellite communications, a MAC protocol ensures the proper coordination of frame transmissions, together with the logic for retransmissions and the recovery of data in case of collisions. In the past, there have been comprehensive reviews related to MAC protocols for satellite technology and also in the context of IoT. Peyravi  compiledA more recent survey by De Sanctis et al.  makes thThe contributions of this paper are threefold: (1) we review MAC protocols employed or proposed for satellite systems from a novel viewpoint that considers the restricted characteristics of CubeSat technology for wireless communications together with the particular requirements of IoT services and applications; (2) we provide a comparative quantitative and qualitative evaluation of the current protocols with metrics including communications performance , dependency of network topology, implementation complexity, and energy consumption; and (3) we discuss the open research and implementation challenges to address by the next generation of nanosatellite networks for IoT environments.The remainder of this paper is organized into seven sections. In In the 1950s, the Soviet Union launched Sputnik I, the first artificial satellite that orbited the Earth. This milestone marked the beginning of a competition between two powerful countries that had, as one of its consequences, an accelerated technological development in aerospace sciences. Satellites created in the decades after the beginning of this competition were designed for very specific missions, and each development had its own subsystems—energy, command and data handling, attitude control, etc.—which allowed the particular requirements of a given project to be met. Such a design methodology involved an extremely expensive process due to the constant iterations necessary to create a new device, and the difficulties in reusing previous versions and designs.One early shift occurred when, due to the use of modular systems, the main bus was designed to be flexible and reconfigurable according to the goal of each mission. As a result of reducing the costs in developing one unit, constellations of these spacecraft began to be feasibly designed and used by those countries and companies that could afford the still enormous cost of development. Depending on the configuration, these formations could increase the instantaneous global coverage and reducing revisiting times, among others benefits.Positioning systems: constellation of satellites located in medium height orbits  that make it possible to determine the position of an object on the Earth’s surface in a given coordinate system. There are several systems belonging to different countries, namely: GPS (USA—24 satellites), global orbiting navigation satellite system (GLONASS) , GALILEO (European Union—24 satellites), BEIDOU .Earth observation: Several satellites with a wide variety of cameras in different spectral bands have been sent to space. Defense and security, cartography, and meteorology are some of the disciplines that have benefited from these types of missions.Communications: Satellite systems that provide voice services, satellite television service, and narrowband/broadband connectivity through standalone satellites or constellations.A large number of satellites now dot the skies for diverse applications such as navigation, imaging, meteorology, and communications. Some of the most significant applications are the following:The Union of Concerned Scientists (UCS) maintains a count of operational satellites orbiting the Earth. In One of the areas in which satellites have been relevant is in communication networks. Due to the innate capacity of these spacecraft to cover the whole terrestrial surface, satellite systems are able to provide connectivity to remote or isolated areas that by other means are almost impossible to connect.There are three main types of architecture used in satellite communication systems: store and forward, bent-pipe, and crosslink . In the Geosynchronous equatorial orbit (GEO): This corresponds to an orbit whose rotation period is the same as the Earth’s. Consequently, the satellite seems to “stand still” to an observer at one point on the planet. To achieve this effect, the satellites are placed at a distance of approximately 35,786 km from Earth. Given such a long distance, the communication delays are considerable, in the order of 120 ms, in the satellite-ground direction or vice versa, for the best scenario; also, the transmission power required to establish effective links is high. Nevertheless, these systems have an excellent and broad coverage, reaching a 30% of the Earth’s surface. The placement process of a satellite into this orbit is an expensive task, and in order to remain at that position, the crew on the ground must perform orbital maneuvers from time to time.Low Earth orbit (LEO): Most of the satellites in space today are placed in this type of orbit. Its height ranges from 300–2000 km and, therefore, the delay in communications is low, in the order of tens of milliseconds for the worst case. The transmission power required to establish the links from this orbit are as low as hundreds of milliwatts . SatelliMedium Earth orbit (MEO): Heights are between the low and geostationary orbits—2000–35,786 km. One example system, the O3b network, is placed at a height of 8000 km and has a theoretical minimum delay of 26 ms satellite-ground, or vice versa. All global navigation satellite systems (GNSS) constellations are placed in this orbit.Highly elliptical orbit (HEO): Orbits with a large apogee and a small perigee. The most famous of this kind is the Molniya orbit, which offers large coverage for high latitudes. Another example is the Tundra orbit. In Molniya, the apogee is greater than a geostationary—about 40,000 km. Satellites in this particular orbit have an approximate period of 12 h. The Soviet Union was the first country to use it to provide communication services throughout its territory and also to obtain meteorological images.Satellite communication systems can be deployed in different orbits, offering a different set of services according to the channel/network conditions derived from the characteristics of the orbit of deployment. The types of orbits are the following:Broadband communications: The commercial satellite networks providing this service offer connectivity with broadband data rates. For example, the new Iridium’s NEXT constellation offers connectivity at 1.5 Mbps , whereasVoice services: Using small devices such as satellite telephones, these satellite systems offer voice connectivity on almost any part of the planet.Signaling services: In this area, some of the highlight services are the reception of automatic identification system (AIS) and automatic dependent surveillance broadcast (ADS-B) signals, which can track the path of vessels and aircraft, respectively.Sensor data collection: These satellite systems offer services at low data transfer rates, which allow data to be retrieved from small sensors placed on the ground.The classical services provided by satellite communication systems are the following:Traditionally, most of the projects for designing and building satellites have been excessively expensive. They involved complex designs and, consequently, long development time spans. However, starting in the 1980s, a new paradigm was established that significantly reduced the size of some satellites, leading to the appearance of microsatellites and, in the 2000s, the creation of nanosatellites or CubeSats: aircraft whose weight is equal to or less than one kilogram.The CubeSat standard was created in 1999 at the California Polytechnic State University in conjunction with the Stanford University’s Space Systems Development Lab. The development of this standard aimed at improving access to space by providing opportunities for satellite development, design, and construction to institutions that could not do so with the classical paradigm. The basic design of a CubeSat consists of a 10-cm cube—called 1U—which must contain the primary subsystems for the operation: an onboard computer, batteries, transmitters and receivers for communication, and attitude determination and control system (ADCS), among others. The cubic shape and volume defined for this new standard considerably reduce launching costs, but, at the same time, incorporate restrictions regarding availability of computational resources, energy, and volume, among others.Initially, the development of nanosatellites was intended to test components and study their behavior in the space environment. Nowadays, applications have spread widely with projects led by universities, governments, and commercial entities. Moreover, and of interest to the authors, this technology represents an excellent opportunity for developing countries to exploit space resources in addition to providing a tool to democratize the use of space .In South America, for example, several countries have taken advantage of nanosatellite technology to promote educational initiatives within universities, including, the Libertad-1 in Colombia (Sergio Arboleda University) , PUCPSATCisco forecasts that by the year 2020 the number of devices connected to the internet will exceed 50 billion , an incrEfficient performance against explosive trafficsLow data rates in terminalsEnergy efficiencyLow cost terminalsMobility and scalabilityMinimization in the use of spectrumMinimum signalingData securityData integrityReliabilityRobustnessFlexibilityThe IoT and machine-to-machine networks are characterized by their intention to meet one or more of the following requirements:In the case of terrestrial wireless access networks, various solutions have been developed to meet the above requirements. For low consumption sensor arrays deployed across extensive areas, technologies such as LoRaWAN  and SigfOne of the challenges of these new massive networks is to enable the many terminals to share a physical resource—the broadcast communications channel—in an efficient and orderly manner. Such a challenge would necessarily make use of the medium access control layer, which corresponds to a sub-layer of the link layer of the open system interconnection (OSI) model and is responsible for coordinating frame transmissions in broadcast links. The specific MAC protocol used for IoT applications will need to fulfil a number of requirements including increased average throughput, to meet a minimum level of fairness as well as to comply with the resources, requirements, and limitations of the access technology in use. Another critical aspect to consider in the choice of a MAC protocol is the network topology and how much knowledge the nodes have or need about that topology.To examine the fulfillment of the IoT and M2M networks requirements, from a MAC layer perspective in the case of this study, together with the restrictions imposed by the capabilities of the CubeSats, will shed light about the viability to provide IoT connectivity using nanosatellites. The reviews and discussion presented in the coming sections address all of the IoT and M2M requirements listed above, except the ones related to data security and data integrity. Whilst security aspects are of paramount importance in the IoT ecosystem, we direct the interested reader to specialized works on this subject discussing security threats and mitigations for a variety of IoT technologies and architectures ,30,31,32In order to exploit the full capabilities of the IoT, connectivity is a major issue to be solved in the task of recovering the amount of data generated by the—expected—billions of sensors forecasted to be deployed in coming years. Although some existent IoT technologies, like LoRa and SigFox, claim to have large coverage—40 and 20 km in rural environments, respectively —they areIn this context, the scenario to be considered in this review corresponds to a CubeSat constellation, with no inter-satellite connectivity, whose main purpose is retrieving small amounts of data from sensors placed on the ground at a low data rate. The constellation will be deployed in several orbital planes belonging to the Low Earth orbit; each orbit with a height ranging between 500–600 km and with an inclination close to The satellite communication system uses the 400 MHz band, which has low propagation losses compared with the typical bands employed by commercial companies offering satellite broadband services. Such frequencies are in the range of the amateur frequency band used and proven to work by most of the CubeSat projects deployed to date . The comAs mentioned above, the sensors are distributed randomly in any geographical area on Earth. A sensor node is not aware of the network topology, and the spacecraft does not know in advance how many devices needs to serve in an area of coverage. Each sensor generates a quantity of data independent of the others. It is also assumed there is no temporal synchronization among the sensors nodes, nor between the sensor nodes and the nanosatellite.MAC layer groups a set of protocols and mechanisms in order to distribute the resources for the nodes to make an effective (and efficient) use of the communications channel. The resources are typically distributed in terms of time assignment, frequency assignment or code assignment. In the particular case of broadcast links, a MAC protocol is in charge of coordinating the frame transmission.Each MAC protocol is designed to cover different requirements, and its performance can be quantified with different metrics. In some cases, the priority is set to the performance concerning data transmission rate, for which the normalized offered load and the normalized throughput are measured. Other priorities may include measurements of delays in sending data or the packet loss ratio (PLR). In the particular case of IoT applications, there may be limitations regarding processing capabilities, available storage, hardware complexity, and energy consumption.In this section, the authors provide a set of metrics that can quantify the fulfillment of the different requirements objectively. We also present the traditional categorization employed to classify the existent MAC protocols for broadcast channels.i, The normalized offered load (C) is the quotient between all the data injected into the network and the maximum data that could be sent at the transmission rate of the link. The latter corresponds to the product of the transmission rate and the total transmission time. The normalized offered load is calculated according to the following formula:t is an arbitrary time.The normalized throughput is the quotient between the data received by the satellite in a given time and all the data that could be sent continuously at the transmission rate of the link. It can be interpreted as how effective is the use of the channel. It is always true that PLR corresponds to the proportion of data lost or received with errors due to miscoordinations of frame transmissions, and that cannot be recovered over the total amount of data sent. The PLR is calculated as follows:The relation among the three metrics presented above is described by the following equation:From the point of view of MAC protocols, energy consumption is directly affected by the length of time in which data is being sent and received; to a lesser degree, energy consumption is also affected by the amount of processing required by the protocol. To evaluate the energy consumption, the length of time the transceiver is in transmission, reception, and idle modes should be compared. The consumption on each state depends specifically on the model of transmitter/receiver that is being used and the chosen MAC protocol. For example, in SigFox, the current consumption is 11 mA in reception mode and 125 mA in transmission mode . The peaIn general scenarios, the main energy limitation is found in the terminal nodes, since in most cases the receiving station has a virtually infinite energy source . In our study scenario, the case is different since CubeSats may also have energy limitations. Nevertheless, it is expected that energy limitation in the sensor nodes will be considerably higher than in the spacecraft.In the context of CubeSats and low-cost satellite solutions, the complexity of implementation turns out to be a relevant factor. For this reason, aspects such as the need of high processing availability, the presence of very specialized hardware, and large amounts of required storage, should be considered as directly impacting the complexity of a given MAC protocol.Usually, on-board computers (OBC) employed on CubeSats are microcontrollers such as the Microchip PIC24 or the Texas Instruments MSP430, which are very limited in terms of computational resources. Newer OBCs using the ARM Cortex family or ATMEL devices are already available in the market for nanosatellites, but they still are in the category of modest processors.Fixed Assignment: Protocols in this category are characterized by assigning a limited resource equitably and fixedly between different interlocutors. The resource can be a frequency channel, a time interval or a code, deriving in the well-known mechanisms frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). These protocols are characterized by being easy to implement, as well as being efficient in link usage when they occupy all or most of their resources. However, protocols following a fixed assignment are not very flexible to changes in data rates, nor are they tolerant to variations in the number of stations since they require a coordinated allocation among all the stations involved.Random Access: These protocols are characterized by having a non-fixed number of users that, without prior coordination, make use of the same channel . Since the allocation of resources is random, more than one device may win the right to use the channel at the same time, causing frame collisions. Therefore, protocols in this category cannot guarantee the successful arrival of frames. Depending on the scenario, these protocols may waste system capacity in failed transmissions (and retransmissions). However, they have a fundamental role in networks whose previous characteristics  are not known in advance.On-demand: These protocols are designed for scenarios in which the terminals require sending an unequal and variable amount of data; in that case, on-demand protocols can vary the allocation of resources depending on the nodes requirements. For example, a TDMA-based protocol may assign additional time-slots to nodes with higher requirements regarding data rate. To manage the variable assignment of resources, these protocols usually require extra control signaling, such as the incorporation of the packet generation rate of each terminal as additional control information in every message.Adaptive: These correspond to protocols designed to manage variable network conditions. These protocols are intended to change the MAC logic dynamically. For example, when communication is carried out among a few terminals, the MAC employs a random access scheme; conversely, when the number of devices increases, it uses a fixed allocation scheme.Reservation: The goal of these protocols is to achieve a collision-free allocation of resources. A typical way to achieve the collision-free scheme is the use of a subchannel dedicated to the coordination of access for each station, in such a way that only one station transmits at a given time. In that subchannel, the devices may rotate a testimony  that indicates who has the right to transmit on the channel. Most of these protocols make use of TDMA or variations of Aloha to assign the token.A brief categorization of the MAC protocols is provided as follows :Fixed AsThe last three categories are, in a general way, hybrids of the first two. This is mainly because the network characteristics—number of nodes, data generation rates, network explosiveness, etc.—have a nature that is essentially either random or deterministic. In this way, the dominant categories that match the network characteristics are either random access or fixed assignment protocols.In this work, the MAC protocols selected for review corresponded mainly to random access and its derivations. These schemes were selected because, in the study scenario, it is infeasible to predict the state of channel congestion at all times, which and how many nodes are within nanosatellite coverage, and the amount of data each node wants to transmit.The early satellite solutions traditionally employed protocols mainly based on fixed assignment . In some cases, the protocol was combined with a random access scheme to perform the adaptive assignment according to the demand of the nodes. An example of an early protocol is the demand assignment multiple access . NonetheThe protocols selected in this section included several descendants of the well-known Aloha protocol, since such derivations are present in current satellite systems and modern IoT technologies such as LoRa and Sigfox. The selection also included other significant—and more modern—random access protocols that were considered suitable for the IoT scenario described in The most representative random access protocol—and the inspiration for many other MAC protocols—is Aloha, developed in 1970. Although this protocol is quite old and simple, in current IoT developments Aloha plays a fundamental role. For example, leading IoT technologies that use variations of this protocol are LoRa and SigFox. Furthermore, there are several applications and modifications to Aloha reported for satellite environments in the literature. Some of them can be found in ,42,43,44In Pure Aloha, nodes send data when they have data to send, hoping that a collision does not occur. When the reception of a packet is successful, the receiver sends an acknowledgement (ACK); otherwise, nodes retransmit the same packet after a random time ,46. The ignaling . When thThe most similar version to Aloha is S-Aloha. It consists of discretizing the channel, where each time slot has the duration of a packet transmission time . The purS-Aloha achieves a low normalized throughput of For IoT aplications, S-Aloha is a good option in scenarios where the offered load is low and the delays between nodes and base station do not have a large variation, but it becomes impractical if the delays imposed on a satellite link are considered. An application of this protocol on the recent Weightless-N IoT technology is reported in .This protocol is considered for systems that have large transmission delays  and for which confirmations of packet reception are impractical . In the The maximum performance of this protocol is reported to be lower than for slotted Aloha. In DSA, a maximum normalized throughput of DA/DSA is suitable for links with large delays and offered loads less than The protocol is proposed to provide random multiple access over an unsynchronized channel. SS-Aloha uses spread spectrum techniques to send messages; it is similar to a CDMA protocol where each terminal uses the same code to spread the signal and accesses the channel without coordination (like in Aloha) . The mulRegarding the performance of SS-Aloha, thanks to the use of proper error correction codes, the protocol achieves a maximum normalized throughput close to The simplicity required in transmitters in addition to the good performance of SS-Aloha, compared to previous protocols, may make this protocol suitable for IoT scenarios. However, when employed in LEO satellite links, where the expected power imbalance is high, the performance of this protocol drops drastically, behaving similarly to S-Aloha.When sensor nodes of a telemetry application transmit data readings, they are usually configured to send packets in a periodical way, with a fixed time interval between messages. In this scenario, the E-Aloha protocol has been proposed as a simplified version of Aloha. At the time of sending, nodes simply initiate transmission, with no additional control to avoid collisions; a confirmation of reception is also not considered in the protocol. For some applications, nodes may end up with the same time interval between packets, in which case the nodes will collide permanently, with no effective communication. To avoid this situation, E-Aloha defines a time window—considerably longer than the packet transmission time—located around the fixed sending time. Within this window, each node selects randomly a new sending time, thus reducing the chances of permanent collisions among nodes using the same time interval.The performance evaluation of this protocol considered the periodic traffic characteristic of typical telemetry systems . The repThe simplicity of this protocol is desirable for the implementation on the IoT terminal node. It actually behaves well for the reported channel loads found in the systems where the protocol has been implemented. However, E-Aloha may lack the necessary scalability to support the future IoT networks.Despite not being reported in satellite environments, this protocol has an important relevance in low power wide area (LPWA) technologies, more precisely for its use in SigFox. Considering the ultra narrowband (UNB) technology, this protocol acquires prominence when low cost transmitters that do not require expensive oscillators are required to perform a precise adjustment of the carrier frequency. Taking this into account, random frequency time division multiple access (RFTDMA) uses the time and frequency to send messages without discretization (as in pure Aloha) . Figure C.The performance of this protocol is calculated in . Its maxm slots, each with the duration of a packet transmission time. The slots are grouped in frames, and the nodes randomly choose one slot per frame to send a packet. If a node successfully sends a packet, it proceeds to reserve the same slot in future frames. At the end of each frame, the receiver responds with an ACK, also indicating what the available slots for the next cycle are. An example of the operation of reservation Aloha (R-Aloha) is shown in This protocol divides the time into S approaches to 1 [The throughput of this protocol depends mainly on the number of packets sent by each node during a reservation. In the worst case, the performance of R-Aloha is similar to the S-Aloha. When the protocol holds reservations for a large number of frames, the normalized throughput hes to 1 .Although R-Aloha reports having a normalized throughput that tends to 1, it may not meet the requirements of IoT scenarios: the protocol has a good performance when the nodes disputing the channel resemble the number of slots in each frame, and also when the reservations made by each terminal last a large number of frames. However, when the scenario does not comply with these assumptions, R-Aloha turns out to be an unscalable protocol. Moreover, for IoT applications where nodes typically have small and/or infrequent amounts of data to send, the reservation mechanism of R-Aloha may result impractical.A classical protocol in wireless network, the carrier sense multiple access with collision avoidance (CSMA/CA) defines the monitoring of the channel before sending a message. If a node senses the channel is busy, it refrains from transmitting and enters an exponential backoff stage; otherwise, it issues a reservation request by means of a small broadcast message  packet). When there are no collisions and the receiver decodes the RTS correctly, another broadcast message granting the reservation  is sent by the receiver. Upon reception of the CTS, the sender proceeds to send the data packet . Figure The maximum performance regarding throughput of this protocol varies between orted in , for an In terms of complexity, CSMA/CA is still a simple protocol: it does not impose high processing demands on the nodes beyond the ability to transmit and receive. Conversely, the power consumption of CSMA/CA is high, since each node must permanently listen and monitor the channel.CSMA/CA is widely used in wireless IoT technologies, such as ZigBee, D7AP, and other short-range wireless sensor networks ,61. Howem slots grouped in frames. In each frame, the nodes select a slot for transmission in a pseudo-random manner [Similar to R-Aloha, the fixed competitive TDMA (FC-TDMA) protocol defines a set of m manner . To calcshown in . The recThe theoretical maximum normalized throughput of the protocol is Similar to R-Aloha, the maximum normalized throughput of FC-TDMA is achieved under very specific conditions: (a) when the number of devices is constant; and (b) when there are no conflicting IDs among all users. However, FC-TDMA could potentially match the traffic characteristics of an IoT application as long as the estimation of the number of nodes under its coverage is accurate and fast.As the name indicates, contention resolution diversity slotted Aloha (CRDSA) is based on the DSA protocol. In addition to sending two or more copies of a packet, CRDSA iteratively resolves the collisions that occur at the receiver through the use of a successive interference cancellation (SIC) mechanism . For a gIn terms of communication performance, when CRDSA uses two copies per packet, it achieves a maximum performance of To address the drawbacks reported for CRDSA, the protocol has evolved with adaptations such as multi-frequency CRDSA (MF-CRDSA) and spread spectrum CRDSA (SS-CRDSA) . The forThis protocol represents an improvement over CRDSA. Although it also requires the nodes to send copies of packets in randomly chosen slots, the difference lies in that the number of duplicates for each packet varies depending on an optimized distribution probability. The protocol is intended to improve the performance over uplink satellite channels .Irregular repetition slotted Aloha (IRSA) achieves a maximum performance of k parts of the same length. Each one of these sub-packets is then encoded with an error correction code and sent through the discrete channel [A protocol inspired by IRSA and CRDSA in which the nodes divide packets before transmission into  channel . Upon re channel  identifiThe communications performance of the CSA protocol indicates a normalized throughput of Similar to CRDSA and other interference cancellation-based protocols, CSA is also energy efficient due to its low duced in .This protocol generalizes the CRDSA protocol. By employing adequate error correction codes given a proper SNIR, multi slot coded Aloha (MuSCA) is able to decode packets even when there are collisions for all the transmissions in a frame . In the MuSCA achieves a maximum normalized throughput of This protocol is similar to SSA on the transmitter side. On the receiver side, enhanced spread spectrum Aloha (E-SSA) employs an iterative soft interference cancellation (ISIC) algorithm with a sliding window that captures the messages received on an unsynchronized channel. The main difference with the previous protocols is that E-SSA does not require sending multiple copies of packets, nor synchronization; thus, achieving a greater efficiency with a reduced complexity. The E-SSA protocol has been designed for integrated satellite/terrestrial mobile systems ,68. FiguIn terms of performance, the maximum normalized throughput reported for this protocol is The interference-cancellation protocols presented in this section are designed mostly to solve the multiple access for the uplink of satellite systems. However, most of the control information required by the protocols is actually acquired/exchanged on the downlink. For example, a correct channel estimation is a key element for the proper operation of E-SSA. Such an estimation takes place over the downlink. Similarly, the code sharing process of CSA also takes place on the downlink. In half-duplex systems, the interference-cancellation based protocol’s feasibility requires careful examination.Regarding the suitability of this category for IoT services, it can be mentioned that despite the great performance reported for these protocols, the complexity of their correct implementation makes them hard to adapt given the capabilities of CubeSats in a LEO orbit. Among the reviewed protocols, E-SSA stands out in performance compared to the others, and significantly reduces the complexity at the ground terminal; however, it is still highly demanding of resources on the nanosatellite side.This category corresponds to protocols whose MAC mechanisms are based on a mix of protocols belonging to the other categories previously discussed in this section. The ones already mentioned and that also match this category are SS-CRDSA, MF-CRDSA, FC-TDMA, and R-Aloha; all of them employ a mix of fixed allocation techniques in conjunction with random access mechanisms.Class A: The lowest power consumption type of device. Transmits data when is necessary using Pure Aloha. To receive messages from the gateway, a listening window is open after each transmission.Class B: For these devices there is a schedule to transmit, which is defined through beacons.Class C: These nodes are always in reception mode, except during transmission.Despite not being reported in satellite environments, another protocol that is worth mentioning due to its wide use in LPWA technologies is the one employed in LoRa. In this technology, the bandwidth is divided into several channels, where the number is dependent on the regulation  902–928 MHz band under federal communications commission (FCC) regulation). In these channels, nodes transmit modulating the signal with the chirp spread spectrum (CSS) and make use of different spreading factors (SF). The channels are further divided into 6 subchannels (from SF = 7 to SF = 12). The MAC behavior depends on the LoRa class of device:In the case of Class A nodes, the MAC protocol performs a fixed allocation of resources (in bandwidth and code) together with a random access scheme .To summarize our review, In this section, we discuss the performance evaluation provided in In terms of network topology, the Aloha-based protocols can benefit from the power imbalance among nodes because of the so-called capture effect. In such a case, the receiver can correctly receive a packet with a high signal strength despite the existence of interference with other transmissions with lower power levels. Among the protocols in this category, the E-Aloha is the current solution for commercial telemetry satellite systems, has been extensively tested, and is operative. The performance of E-Aloha is similar to that of S-Aloha, with no need of synchronization. However, the main problem with E-Aloha is it may lack scalability for massive applications, due to its poor performance even for moderate traffic loads, as shown in When examining the protocols based on interference cancellation . A visual evaluation of the suitability of each protocol derived from our comparative analysis is shown in To address the specific challenges derived from the utilization of nanosatellites for providing effective and cost-efficient IoT connectivity, we envision open research and implementation aspects from three perspectives: from the network protocols perspective, from the integration capabilities of CubeSats and from the evolution of the nanosatellites industry.When existing network protocols are evaluated in the context of nanosatellites technology for IoT connectivity, it is common to encounter difficulties in finding one protocol that meets all the requirements. In the case of MAC protocols, The IoT ecosystem will benefit from a more integrated communications platform. In many cases, a global nanosatellite network integrated to an LPWA technology would boost the possibilities for improving connectivity at reduced costs. In recent years, there have been proposals for such a hierarchical architecture: the connected devices send data to an LPWA gateway, which in turn forwards data via the satellite network ,69. HoweThe enormous growth foreseen for the IoT market is highly related to the rapid evolution of low-cost wireless access technologies. In particular, with the introduction of LPWA technologies such as LoRa, Sigfox, and NB-IoT, to mention some, the massification of connected devices seems more plausible in the near future. Although nanosatellite connectivity is being identified as part of the IoT technologies ecosystem ,7,8,9, iThe evolution of satellite systems and the introduction of CubeSats as low-cost satellite technology has made it possible to provide massive communications services for IoT applications, opening the opportunity for countries with no experience in space science and small corporations to participate competitively in the growing satellite communications market. However, the existent protocols in satellite technology, in particular for medium access control, were not designed with the IoT scenario, nor the low-cost technology constraints in mind.This paper has presented a thorough review of MAC protocols designed for satellite environments, considering the specific characteristics of the IoT networks and applications together with the conditions of a wireless network served by CubeSats deployed in a low earth orbit. The study has shown that many of the reviewed protocols are not suitable for deployment in the scenario of interest, although they have been successfully implemented and deployed in other satellite systems. From the comparative evaluation, the protocols employing interference cancellation techniques are shown to have the best communications performance, but they behave poorly with regards to the demands of processing/channel resources and energy consumption. Furthermore, the Aloha-based protocols are good candidates for the MAC layer in nanosatellites devoted to IoT connectivity due to their simplicity of implementation and their minimum hardware requirements. However, these protocols report having poor communications performance when the traffic load—related to the growing number of expected nodes in the IoT—increases, and also when the delays vary greatly due to variable link lengths.From our analysis, a better balance among performance, complexity, energy consumption, and sensitivity to topology should drive the design of future MAC protocols for nanosatellite IoT solutions. Aspects related to the network protocol design, the integration capabilities of CubeSat connectivity with other wireless technologies, and the evolution of the nanosatellites industry are some of the open challenges identified and discussed in this review.


A better understanding of stable changes in regulation of gene expression that result from epigenetic events is of great relevance in the development of strategies to prevent and treat infectious diseases. Histone modification and DNA methylation are key epigenetic mechanisms that can be regarded as marks, which ensure an accurate transmission of the chromatin states and gene expression profiles over generations of cells. There is an increasing list of these modifications, and the complexity of their action is just beginning to be understood. It is clear that the epigenetic landscape plays a fundamental role in most biological processes that involve the manipulation and expression of DNA. Although the molecular mechanism of gene regulation is relatively well understood, the hierarchical order of events and dependencies that lead to protection against infection remain largely unknown. In this review, we propose that host epigenetics is an essential, though relatively under studied, factor in the protection or susceptibility to malaria. Complex infectious diseases such as malaria, in which environmental and clinical features along with genetic susceptibility factors contribute significantly to the pathology of the disease, pose a great challenge for the identification of relevant biomarkers for protection against the disease. In the human host, the disease outcome is determined by a complex relationship between the host, the parasite, and the environment . For exaOur understanding of the role of epigenetics in complex disease is rapidly emerging. Epigenetics play an important role in hematopoiesis, for example, proliferation of hematopoietic stem cells, as well as the successive stages of differentiation into more committed progenitors, are regulated at the transcriptional level through epigenetic modifications . AlthougIn this review, we present and discuss the potential role of epigenetic factors in the protection/susceptibility to diseases. Particularly, we reviewed how the current knowledge on how epigenetic regulation contributes to protective immunity and susceptibility to disease can be applied to address the challenge of malaria.Plasmodium has been a major cause of morbidity and mortality throughout human history. As a result of this, malaria is believed to have exerted evolutionary pressure on the human genome by selecting genetic polymorphisms that provide protection against severe disease . Other epigenetic DNA modifications consist of the conversion of 5-methylcytosine to 5-hydroxymethylcytosine, and adenine methylation  DNA methylation, arising from transfer of a methyl moiety from hylation . The DNAhylation . “Writerhromatin .CD4 gene was hypermethylated in CD8+ T-cells and hypomethylated in CD4+ T-cells  or decreased (“tolerized”) response to a second challenge in comparison to naïve cells. This altered state can persist for weeks to months following the initial stimuli and results in cells of the innate immune system, including monocytes and macrophages, being more or less capable of producing inflammatory cytokines, and/or phagocytizing and killing microorganisms, in response to a second unrelated stimuli. On one side, “tolerance” can arise following high bacterial burden, preventing responsiveness to an additional challenge, or the immunosuppressive phenotype observed in late sepsis and is viewed as a strategy to limit inflammation . At the Plasmodium biology, and how this may be exploited to combat malaria, has been comprehensively covered by recent reviews, and will not be discussed in depth here  with Plasmodium falciparum, both in vivo and in vitro, results in subsequent toll-like receptor specific stimuli driving significantly higher proinflammatory responses  gene promoter , malaria remains a major cause of morbidity and mortality, causing an estimated 445,000 deaths globally in 2016 . Sub-SahThe development of new strategies that will explore new research avenues and hypotheses on biological factors of malaria susceptibility or resistance are urgently needed. This should be a priority if the goal of eradication is to be achieved by 2030.Plasmodium parasite have already been considered as an antimalarial strategy (Interestingly, growing evidence suggests that epigenetics play a key role to multiple levels of this complex disease, including immune evasion by the parasite, tolerance, training, and adaptive responses. The tools and frameworks are readily available to investigate the impact of epigenetics in the protection from or susceptibility to malaria in more depth. In other fields, drugs targeting epigenetic enzymes and processes have already advanced to clinic. For example, the DNMT inhibitors and HDAC inhibitors have proven efficacious in the treatment of cancer, particularly hematopoietic cancers , 113. Instrategy . UnderstThere are several challenges that epigenetic epidemiological studies have to address to elucidate fully the role of epigenetics in susceptibility or protection to malaria. One of these challenges is to understand how the parasite alters the host immune responses by exerting a strong selective pressure on population genetics in endemic regions. A better understanding of the mechanisms that underlie the chromatin and DNA methylation changes are topics of scientific interest. Such studies will generate more evidence in the role of epigenetics in the acquisition of protective immunity against infectious disease such as malaria. As we gain insight into the functional significance of changes in DNA methylation events and other epigenetic mechanisms, there will be a push to manipulate these processes, as tools and strategies to develop vaccines and target for therapeutic discoveries.CA: conceptualization, writing—original draft, writing—review and editing; BK and JQ: writing—review and editing; MT-B, A-KF, and OD: conceptualization, writing—review and editing. All authors read and approved the final manuscript and agreed to be accountable for all aspects of the work.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Bipolar clavicular fractures are extremely rare with no consensus on management. No previous cases of bipolar clavicular fracture on an ipsilateral reverse shoulder prosthesis have been reported.We report a case of a 78y.o female patient with left bipolar clavicular fracture on ipsilateral reverse shoulder prosthesis, associated with multiple ribs fracture, that was treated with open reduction and internal fixation using k-wires and endobutton for the lateral part, while as the medial part was fixed with plate and screws.Any patient with a clavicle fracture, with a history of sequential forces to the clavicle, a bipolar injury should always be suspected. Attention should be given if any implants are present on the ipsilateral side of the injury, which could affect surgical planning and outcome. Howev2rd to 7th ribs fracture that were treated conservatively.We report the case of a 78y.o female patient suffering from trauma to the left shoulder due to a car accident with the car tumbling multiple times, X-rays  and CT sA shoulder immobilizer sling was placed initially, and she was scheduled for open reduction and internal fixation of the clavicle fracture.Patient was taken to the operating room, under general anesthesia, beach chair position with arm rest, scrubbing and draping done. Using two k-wires under fluoroscopy, reduction and fixation of the lateral part of the fracture to the midshaft of the clavicle. Incision over medial aspect of the clavicle, dissection reaching the bone, reduction and fixation with plate and screws construct. Instability remained over the lateral part so decision to open reduction and internal fixation with fiberwire and endobuttons was taken. Using a small incision over acromioclavicular joint and distal clavicle, reduction and fixation was done with two endobuttons and fiberwire in three planes. Closure was done in the usual fashion, shoulder immobilizer was placed and post operative radiographs were done . The patPostoperatively, the patient was immobilized for 3 weeks then, gentle passive range of motion was initiated for two weeks followed by progressive active range of motion. Follow up radiographs were done at one month post op .Fig. 5RaAt three months post-op follow up, the percutaneous pins have been removed. The patient recovered most of her range of motion and is pain free, with satisfactory follow up imaging .Fig. 6Ra3Clavicle fractures are prevalent, accounting for 2.6–4% of all adult fractures and 44% of shoulder girdle injuries. ,2 Of allBipolar clavicle injuries are caused by the rotation of the clavicle about its midpoint, leading to posterior dislocation of the AC joint and anterior dislocation of the sternoclavicular joint. If dislocation occurs at both ends, then probably it is due to a major trauma whereby the deforming force acts on the lateral aspect of the shoulder or a powerful force pressing the shoulders together with trunk torsion .Their management is difficult and no consensus exist on the matter. In few cases, it has been treated conservatively , in otheThe increase in detection of these cases may be due to an increase in usage of CT scan imaging which reveals fractures of the medial part of the clavicle not easily visible on a plain X-ray. It points out that in any patient with a clavicle fracture, with a history of sequential forces to the clavicle, a bipolar injury should always be suspected. Our case is special in that it is the first reported, to our knowledge, whereby a bipolar fracture of the clavicle occurs with ribs fractures on the same side of the reverse shoulder prosthesis. We opted for a surgical fixation due to the inherent instability of the fracture in the current situation. Good functional and clinical outcomes were found after multiple physiotherapy sessions. To note, this article has been reported in line with the SCARE 2018 criteria .4This is the first case reported in the literature which shows a bipolar clavicle fracture on an ipsilateral reverse shoulder prosthesis associated with multiple ribs fracture. Surgical treatment was opted due to the nature and pattern of fracture. Post operative follow up showed satisfactory results. No consensus on management exists, but when surgical option is opted for it is best to consider the fracture in its two separate parts and treat each one individually with the construct of choice.No funds were received in support of this study.Ethics committee has given approval for publication.Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.No identity identifiers are present whatsoever in the manuscriptJoseph Maalouly: contributed to the writing and editing of this article.Dany Aouad: contributed to the writing of this article and the submission process.Jamal Saade: contributed to the editing of the figures and of the text.Ghadi Abboud: contributed to the radiological images, and editing of the final text.Georges El Rassi: contributed with the case, surgical management and editing of the article.This case has been registered in the IRB committee of St Georges Hospital University Hospital.Dr Georges El Rassi.Not commissioned, externally peer-reviewed.The authors declare no conflict of interest regarding the publication of this article.


This paper describes a dataset about institutional and interpersonal trust, life satisfaction and health in Cali, one of the major cities in Colombia, South America. Data was collected with the purpose of monitoring trust levels in the population and to serve as baseline information to monitor changes in population trust after the implementation of government interventions aimed at increasing institutional trust. Data was collected in 2017 with subsequent waves in 2018 and 2019, this manuscript presents data collected in 2017, which corresponds to the data analyzed in the paper related to this manuscript. The information was gathered through a population survey to over 1200 adults' city residents, randomly selected in face to face interviews. Data described also reports information on life satisfaction, physical and mental health, and socioeconomic characteristics. This information is useful for policy making purposes insofar as allow the monitoring of outcomes that are relevant for local and national governments that implement programs that affect trust, subjective well-being and health. Taken as a whole, data also allow to build composite indicators for interpersonal and institutional trust and social capital. This research was fully financed by Universidad Icesi through the Observatorio de Políticas Públicas –POLIS- to monitor citizens' perceptions of a different array of government interventions that affect the outcomes in which data was collected. Measures on trust, life satisfaction, and health follow international measurement standards set by the OEDC and Centers for Disease Control and Prevention to allow international comparisons. For data collection, a structured survey was designed  by the Observatorio of Políticas Públicas –POLIS- of Universidad Icesi. POLIS has established a population survey collected annually called CaliBRANDO [Another important feature of this project is the possibility to link the data with secondary sources of information. Respondents were asked about neighborhood of residency. This variable can be used to be linked with the provision of public services and goods that may be related with the outcome under study.The module of life satisfaction was constructed using questions from OECD guidelines to measure subjective well-being . In totaThe questionnaire was piloted 20 times prior implementation and language adjustment were made to correspond to the local context where data was gathered. In 2017, a total of 1217 surveys were collected. Analysis using the data described, are published in an article assessing whether two factors of wellbeing, social capital  and subjective well-being are associated with frequent mental distress and if there are any mediating effects by gender .2The dataset described in this manuscript is representative of the socioeconomic, gender, and racial/ethnic composition of the city with a margin error of 2.8% and a confidence level of 95%. This is a representative sample for the adult population in the city. The sample size of the survey, was estimated using the population reports of the national statics office in Colombia . The surFor field work, pollsters received intensive training about data collection and the language to be used during the survey. In total, 38 points in the city were selected to collect the data. Central points were used for field work instead of household surveys. Generally speaking, through household surveys the major share of the population responding the survey is older, retired or housekeepers. The aim of the study was to collect information representative to the general population and sociodemographic composition of the city. Fieldwork was conducted in parks, shopping malls, bus stations, recreational centers, open commercial areas, and central points in downtown. Where necessary, permission for data collection was solicited prior fieldwork. The survey lasted about 20 minutes. Pollsters approached respondents explaining the purpose of the study and assuring confidentiality, participation in the study was voluntary and respondents received a bookmark with the project information. Field supervisors revised each survey after pollsters filled completely the survey. Each day, a log data entry was updated with information about gender, socioeconomic strata, and race/ethnicity to keep track of the quotas in which the study is representative. Fieldwork lasted about three weeks.


Driving automation has been developing rapidly during the latest decade. However, all current technologies of driving automation still require human drivers’ monitoring and intervention. This means that during driving automation, the control by human driver and by the driving automation system are blended. In this case, if the human driver loses the sense of agency over the vehicle, he/she may not be able to actively engage in driving, and may excessively rely on the driving automation system. This review focuses on the subjective feeling of agency of the human driver over the vehicle in such situations. We address the possible measures of agency in driving automation, and discuss the insights from literatures on the sense of agency in joint control, robotics, automation, and driving assistance. We suggest that maintaining the sense of agency for human driver is important for ethical and safety reasons. We further propose a number of avenues for further research, which may help to better design an optimized driving automation considering human sense of agency. The sense of agency refers to the experience of controlling one’s own actions, and through this, external events . In pastIn this review, we focus on the field of driving automation. The technology of driving automation has gained explosive attention in the past decade, and the technology is maturing for practical use. The Society of Automobile Engineers (SAE) International defined six levels of driving automation from level 0 to 5 as follows, depending on the extent to which the driver is involved in driving  (cited from SAE J3016):SAE Level 0: No automation. The full-time performance by the human driver of all aspects of the dynamic driving taskSAE Level 1: Driver assistance. The driving mode-specific executionSAE Level 2: Partial automation. The driving mode-specific execution by one or more driver assistance systems of both steering and acceleration/deceleration using information about the driving environment, with the expectation that the human driver will perform all remaining aspects of the dynamic driving task.SAE Level 3: Conditional automation. The driving mode-specific performance by an automated driving system of all aspects of the dynamic driving task with the expectation that the human driver will respond appropriately to a request to intervene.SAE Level 4: High automation. The driving mode-specific performance by an automated driving system of all aspects of the dynamic driving task, even if a human driver does not respond appropriately to a request to intervene.SAE Level 5: Full automation. The full-time performance by an automated driving system of all aspects of the dynamic driving task under all roadway and environmental conditions that can be managed by a human driver.The commercial extent of driving automation is currently at or below Level 2, likely not only because of technical issues but also because of the legal and ethical role of “the driver” . In partIn this review, we aim to provide a fundamental understanding of the concept and measures of the sense of agency along with the role of the sense of agency in engineering fields, such as robotics. Furthermore, we discuss the possible link between the sense of agency and the development of driving automation, suggesting potential research focuses and the direction of an optimized driving automation system which accounts for the human sense of agency. We also reviewed literature that provided useful insights for measuring and maintaining the sense of agency in driving automation. Finally, in the discussion of the importance of the sense of agency in driving automation, we suggest two directions for future research on this topic.The sense of agency refers to the subjective feeling that one is controlling their own actions, and through them, external events . This deThe comparator model was the most dominant account of the sense of agency in recent decades. It suggests that the sense of agency emerges from comparisons between predicted sensory feedback, which is generated through motor commands, with actual sensory feedback . When thThe measurement of a subjective feeling is always challenging for scientists. In psychology, the most common method is self-reporting. Experimenters ask questions such as “Do you feel that you controlled the object on the screen (yes or no)?” and “How much control did you feel that you have over the motion of the object (rate between 1 and 7)?” To answer such questions, participants usually need to retrospect on what they had done and felt to make a judgment. Self-reporting a sense of agency may of course introduce individual judgment bias. However, with sufficient sample size, the individual difference in judgment criteria can be diluted. The subjective judgment of agency includes (1) binary judgment (no control vs. control); (2) categorical judgment ; and (3) rating . The different methods of self-reporting may result in slightly different response patterns. For instance, employing a rating system with many levels may result in a more linear response compared to binary judgment. Importantly, when using subjective report, researchers also need to consider human tendencies in classification behaviors. Specifically, when people notice that there are several different experimental conditions, they tend to attribute different responses to them , even if their sense of agency is comparable in all of the conditions. For example, in many studies using delayed feedback, agency ratings gradually decreased along with the increases in delay, despite the fact that participants’ perception of the causal relation between their actions and the feedback is intact .via the skin, it undergoes a process of “central cancellation” in the brain and therefore, this stimulus tickles less than another’s touch  at a time of their own choice, and judge the time at which they performed the action by reporting the number on the clock face. Participants’ response in the voluntary action block provides a baseline of participants’ time perception of an action when the action does not cause any effect. In the stimulus only condition, participants are presented with a stimulus  at a random time and report the onset of the stimulus. This provides a baseline of time perception for an event when the event is not caused by participants themselves . In the action-operant condition, participants perform an action, and the action causes an event at an interval of 250 ms. Participants only report the onset of their action. On the other hand, in the stimulus-operant condition, participants perform an action that causes an event, and they report the onset of the event. The two operant conditions indicate participants’ time perception of their voluntary action and the event caused by the action, which is compared with the above two baselines. The extents to which the action and event are perceived to shift toward each other are called action binding and effect binding, respectively.The intentional binding effect is another well-known implicit measure of the sense of agency. It refers to the phenomenon in which the perceived time codes of an action and its consequence are attracted to each other when people feel a sense of agency over the consequence . The expaction binding from effect binding, but can be used for continuous action tasks  signals.EEG signals are weak electric signals we can measure on the scalp using precise electrodes and amplifiers. The signals derive from neuron activities in the human brain. After passing through and spreading on the skull and scalp, the signals greatly decay relative to their strength on the surface of the cortex and contain significant noise from muscle activities and the environment. However, thanks to the progress in development of hardware and signal processing methods, the quality of EEG signals and usability of EEG devices have been greatly improved. Neuroscientists found many useful features in EEG signals that are linked to sensory processing, attention, arousal, motor imagination, and error detection. EEG signals can be continuously measured from a person; therefore, they are very useful anchors to examine humans’ perceptions without interrupting their behavior or asking a person to engage in introspection. Numerous prior studies have proposed brain-machine interfaces using EEG signals, decoding a human’s intention to control the machine. However, because of the noisy nature of EEG signals, such decoding techniques are far less accurate than a human’s voluntary control.Research on measuring individuals’ sense of agency using EEG is in its infancy. Neuroscientists are currently mainly employing hypothesis-driven approaches to determine candidate features in EEG signals that may be linked to the sense of agency. For example, previous studies reported that the N1 and P3 event-related components (ERPs), which are negative and positive potentials observed 100 and 300 ms after the onset of an action consequence, respectively, are attenuated in the condition when there is a sense of agency compared to the conditions when the sense of agency diminishes . The expFew studies have examined how EEG signals may be linked to the sense of agency during continuous actions. During many daily circumstances such as driving, people receive a stream of feedback while continuously performing a series of actions. People may receive both positive and negative evidence of the sense of agency. When the accumulated evidence reaches a threshold, people conclude a sense of agency or non-agency. During such continuous action and feedback cycles, ERP for each single event may interfere and overlay with each other, making it impossible to measure. Instead, time-frequency analysis provides a better monitoring of mental status relating to the sense of agency. Hypothesis-driven approaches provide clear theoretical accounts for phenomena but do not identify an inevitable phenomenon. In laboratory experiments, researchers designed conditions with and without the sense of agency, compared the EEG signals between the conditions, and reported the differences in some proposed features. However, this does not mean that if we observe a difference in these EEG features, we can make certain conclusions about the human sense of agency. The same feature may also be influenced by numerous other cognitive functions. It is very challenging to decode the sense of agency from brain activities, as the experience of agency is integrated from multiple cognitive processes, both at high and low levels. A recent study reported a high accuracy in decoding subliminal prediction errors . PredictGiven the circumstances of driving, the methods used in psychological experiments to measure the sense of agency face certain obstacles. Subjective judgment  is the easiest way to measure agency. However, as discussed in section “Measurement of the Sense of Agency,” subjective judgment can be easily biased or influenced by the categorization of experimental conditions. Besides these issues, asking a driver to report his/her sense of agency might interrupt driving. Therefore, it may be useful for measuring the overall sense of agency after each driving trial, but less applicable in a situation where the sense of agency dynamically changes.Sensory attenuation and the intentional binding effect are even more difficult to apply in a driving task, principally because these two methods are mainly designed for single instead of continuous feedback. Intentional binding also requires an interval between an action and its effect. Such delay is unnatural for a driving task and can greatly disturb driving performance.To measure the sense of agency in driving automation, especially when the sense of agency may dynamically change, we suggest three potentially useful approaches. The first approach is to use physiological signals to decode the sense of agency. As introduced in section “Physiological Signals Linked to the Sense of Agency,” studies in neuroscience and psychology have reported some useful features of the signals linked to a sense of agency. However, physiological signals were usually used as dependent variables in most of the previous studies, and as these features can be also influenced by other extraneous variables that were controlled in the previous studies, they might not provide high accuracy as indices of agency if the extraneous variables are not sufficiently controlled. Nevertheless, future studies to decode agency using physiological signals would be necessary for this approach.The second approach is to use attention as a proxy for the sense of agency. Previous studies showed that the sense of agency captures human attention . A recenFinally, control-motivated action may be another useful proxy for the sense of agency . PreviouIn the past decade, joint actions have become a research interest in social interaction. Joint actions affect both the predictive and postdictive processes underlying the sense of agency. Because actors in joint actions do not have access to co-actors’ intentions, motor commands, or sensory feedback, the accurate matching between sensory feedback and the self’s and co-actors’ action becomes impossible, and the attribution of control is vague. predictable effects produced by cooperative co-actors also increased the sense of agency, even when the effects  were not correlated with self-generated joystick movements. This indicates that the sense of agency during joint actions is evaluated with respect to both egocentric and group-level intentions  reported that when a user controlled a humanoid robot through BCI-SSVEPs , the additional feedback of audio-visual synchrony between a footstep sound and an actual humanoid’s walk reduced the time required for steering the robot and increased the feeling of control over the robot . This stvia a robot. Recent studies showed that when a BCI successfully decoded operators’ motor commands and provided corresponding visual feedback of the movement of a humanlike robot hand , people not only experienced a sense of agency over the robot hand, but also felt an illusion of bodily ownership over it  in different driving circumstances. Having said this, the establishment of the model of human sense of agency in driving automation is important. With such a model, researchers can estimate the threshold of sense of agency in different situations, and provide a good solution that ensures both safety and human agency according to the situation.In this paper, we discussed the importance of the sense of agency in driving automation. Two main questions remain to be solved in future research on this topic: (1) how to monitor the sense of agency when people use driving automation and (2) how to design the driving automation to ensure the compatibility of driving safety and the sense of agency. These questions are important for human-machine interaction in driving automation when the human is considered as a In this review, we focused on the role of the sense of agency in driving automation within its current commercial context, in which driver-automation joint control is required. Usually, the more reliable the driving automation, the less the driver might be engaged. The lack of a sense of agency is considered a reason for driver disengagement, which can be problematic when the driver’s decision-making is required. For research on driving automation, we suggest first that monitoring drivers’ sense of agency under different circumstances of use of driving automation is important. Physiological signals, attention , and control-motivated actions  may be more useful to measure the sense of agency than the traditional methods used in psychological experiments such as self-report, sensory attenuation, and intentional binding effect. Second, we suggest that in order to maintain a sense of agency at a good level, generating a “we-mode” is essential for driver-automation joint control. To achieve this, techniques decoding the driver’s intention are critical. Recent research in engineering is attempting to do so using onboard vehicle sensors . HoweverWW drafted the manuscript. WW, YK, and HA reviewed and revised the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Chlorhexidine compounds and their different formulations have been investigated several times, especially in the dentistry field. Chlorhexidine application for mouth rinsing immediately underwent oral contraindications, linked to the possibility of causing pigmentation to the teeth or relating to possible cytotoxic events after oral surgery. The positive effects, however, are considerable and its topical antiseptic action has been widely demonstrated by in vitro and clinical research. That’s the reason for its large application in different fields of dentistry. The aim of this study is to collect all the literature regarding the use of chlorhexidine gel in dentistry and all the numerous applications. The initial search on search engines obtained 232 results; then, following the application of the inclusion criteria there were 24 selected articles. The chlorhexidine gel appliance in the dental daily practice is direct to oral surgery, conservative endodontics, prevention and prophylaxis. The use of chlorhexidine has shown some positive effects, also in the case of systemic diseases prevention. Surely, this topical medicine used both professionally and prescribed for home use, can be considered a great help for the prevention of several oral pathologies with systemic implications too. In recent years, the use of chlorhexidine has been increasingly common in different fields of medicine. Chlorhexidine is often present in different formulations such as mouthwashes, gels, galenic preparations, creams or dentifrices. The numerous compositions reflect the several applications and the different fields of use ,2. Chlorhexidine is a chemical synthesis disinfectant with a broad-spectrum antiseptic action, active against Gram-positive and Gram-negative bacteria and also against fungi ,4,5,6. IIn the field of dentistry, an initial criticism has been created against this antiseptic because it could cause the formation of pigmentations on the enamel of the teeth, this is because chlorhexidine is able to attack the enamel film to remove it and thus makes the enamel susceptible to pigments in food or beverages. The purpose of this review is to evaluate in all the randomized studies on the advantages or disadvantages of the use of chlorhexidine and above all, which and how many fields it is used in . The funUsing the search parameters expressed in the materials and methods section, it was possible to filter the results until 24 jobs was obtained . These wIt is necessary to report that some articles, despite dealing with the topic of the study, do not fit our topic precisely. Some of the resulting articles deal with modified chlorhexidine-based gels or with samples that have pathologies or with experimental treatments ,18,19.Powerful bactericide: Chlorhexidine alters the protein structure of the bacterial cell membrane: by exaggeratingly increasing its permeability, the substance promotes the precipitation of cytoplasmic proteins and the consequent cell death by bacterial lysis.Bacteriostatic: Once it was believed that chlorhexidine could block the replication of bacteria; today it is well known that it is also able to kill them.As can be seen from the results, the uses of chlorhexidine are multiple, often this is used following oral surgery or for the treatment of periodontal or peri-implant lesions . CertainAccording to Coello-Gomez et al.  there ar2Cl2). On the contrary, the gluconate anion is soluble in water and is therefore an excellent counter-ion for the counter-chlorhexidine, making the compound moderately water-soluble . It is inactivated by sodium lauryl sulphate  and by triclosan, both possible components of toothpaste, which is why chlorhexidine treatment should be performed away from tooth cleaning with toothpaste. Chemically chlorhexidine is a bis-biguanide and is available as a counter-cation generally associated with three counter-anionic species such as: acetate, chloride and gluconate; the latter is the most used form in dentistry. Globally, the organic chlorhexidine molecule is therefore neutral, apolar and of medium-large dimensions (due to the strongly apolar benzene groups and arranged at the extremes of the molecule which occurs mainly in linear or unfolded form) and this explains its poor direct solubility in water. Chlorhexidine is deactivated by all ionic compounds, such as some anionic compounds present in dentifrices. For this reason, it can be seen from the literature that low chlorhexidine products should be used at least 30 minutes after normal oral/dental hygiene products. Its effectiveness can also be influenced by nutrition, so it is good to avoid civi or drinks for at least an hour. Furthermore, the function of chlorhexidine is influenced by the presence of blood or inflammatory fluid or soaps. Studies show that only 30% of the active ingredient of chlorhexidine-based products remains present in the oral cavity [The molecule, poorly soluble in an aqueous solution, has a double charge as a salt and behaves like a positive cation, generally associated with a pair of water-soluble negative anions such as chloride, acetate or gluconate (anion of gluconic acid); moreover, it is a symmetric molecule that contains two strongly apolar benzene groups. It is commercially available for various applications, such as chloride or acetate, for medical applications digluconate is usually used . Chlorhexidine as such is a practically apolar organic compound and therefore poorly soluble in water but also in poorly polar organic solvents such as dichloromethane . In the urine, less than 1% of chlorhexidine gluconate ingested was excreted. The remarkable antibacterial properties of chlorhexidine are due to the ability to alter the structure of the cell membrane with consequent precipitation of cytoplasmic proteins. It has a greater antibacterial effect on Gram-positive cocci and lesser on Gram-negatives . It alsoChlorhexidine gluconate, in oral rinsing, acts as an antimicrobial throughout the duration of the rinse; the clinical significance of this antimicrobial activity in oral rinsing is not entirely clear. Some microbiological tests have shown a general reduction of the bacterial load with the use of chlorhexidine. Tested, aerobic and anaerobic bacteria were reduced from 54 to 97% after a use of 6 chlorhexidine drugs. No bacterial resistance has been shown following the use of chlorhexidine, nor for the realization of opportunistic infections or negative characteristics for the oral microbiota. ,65. AfteChlorhexidine for this reason is used in different fields of medicine, such as dermatology, dentistry, gynecology, urology ,70,71,72The study takes into consideration a considerable number of jobs and many of these have a low risk of bias. Unfortunately, the works taken into consideration, however, cannot be related to each other and often chlorhexidine is compared to other materials and used in different formulations and dosages.From what can be seen from the results, chlorhexidine is used in different areas of dentistry. It is used for the treatment of mucositis, peri-implantitis, for the prevention of alveolitis or for conservative or endodontic treatment. The results are clearly in favor of the use of chlorhexidine rather than nothing, despite this there are also other oral cavity topical antiseptics that have similar effects to chlorhexidine. A unique fact cannot yet emerge from this study but the positive effects of chlorhexidine are well demonstrated.This review is in PROSPERO database with ID number 233453. It is an international database of prospectively registered systematic reviews. The following focus question was developed according to the population, intervention, comparison and outcome (PICO) study design.For dental patients, does the use of chlorhexidine gel reduce the future risk of complications compared with other topical oral antiseptics?And as alternative question:Do dental patients, who use chlorhexidine gel, have a decreased risk of oral and post-surgical complications?The search strategy incorporated examinations of electronic databases, supplemented by hand searches. A search of PubMed and Dentistry and Oral Sciences Source ,75, for The keywords used in the search of the selected electronic databases included the following: “(“chlorhexidine gel”) AND “oral”Keywords was selected by author with the aim to collect all articles about this topic.All results, inclusion and exclusion criteria have been verified by the author. For the stage of reviewing of full-text articles, a revision was performed.The review included studies on humans published in the English language. Letters, editorials and PhD theses were excluded. The review included all human RCTs about use of chlorhexidine gels in different formulations.Chlorhexidine gel use in randomized clinical trials (RCTs)Roles of chlorhexidine gelHuman RCTsThe full text of all studies of possible relevance was obtained for assessment against the following inclusion criteria:Studies involving patients with other specific diseases, immunologic disorders or other oral risk related systemic conditionsNot enough information regarding the selected topicNo access to the title and abstract in English languageNot older than 10 years RCTsThe applied exclusion criteria for studies were as follows:After the search and the exclusion of all the non-relevant articles thanks to the search filters, a manual review of the resulting articles was conducted. Articles that did not contain sufficient information were removed and the full text was read to highlight whether or not there was sufficient information to support the review. Articles more than 10 years old have been excluded.The data were independently extracted from studies in the form of variables, according to the aims and themes of the present review, as listed onwards.“Author (Year)”—Revealed the author and year of publication“Features”—Results and features evaluated about chlorhexidine gel“Field”—Field of use of chlorhexidine gel“Statistics”—Significative or not results“Type”—Type of articleData were collected from the included articles and arranged in the following fields :“Author Assessment of risk of bias was undertaken during data extraction process. The Cochrane tools were used to carry out the bias risk assessment of the items considered. The level of bias risk, in accordance with the above, was defined as low, moderate, high or unclear . Bias is


SqueezeMeta can be downloaded from https://github.com/jtamames/SqueezeMeta.The improvement of sequencing technologies has facilitated generalization of metagenomic sequencing, which has become a standard procedure for analyzing the structure and functionality of microbiomes. Bioinformatic analysis of sequencing results poses a challenge because it involves many different complex steps. SqueezeMeta is a fully automatic pipeline for metagenomics/metatranscriptomics, covering all steps of the analysis. SqueezeMeta includes multi-metagenome support that enables co-assembly of related metagenomes and retrieval of individual genomes via binning procedures. SqueezeMeta features several unique characteristics: co-assembly procedure or co-assembly of unlimited number of metagenomes via merging of individual assembled metagenomes, both with read mapping for estimation of the abundances of genes in each metagenome. It also includes binning and bin checking for retrieving individual genomes. Internal checks for the assembly and binning steps provide information about the consistency of contigs and bins. Moreover, results are stored in a MySQL database, where they can be easily exported and shared, and can be inspected anywhere using a flexible web interface that allows simple creation of complex queries. We illustrate the potential of SqueezeMeta by analyzing 32 gut metagenomes in a fully automatic way, enabling retrieval of several million genes and several hundreds of genomic bins. One of the motivations in the development of SqueezeMeta was producing a software capable of running in small desktop computers and thus amenable to all users and settings. We were also able to co-assemble two of these metagenomes and complete the full analysis in less than one day using a simple laptop computer. This reveals the capacity of SqueezeMeta to run without high-performance computing infrastructure and in absence of any network connectivity. It is therefore adequate for  The improvement of sequencing technologies has permitted the generalization of metagenomic sequencing, which has become standard procedure for analyzing the structure and functionality of microbiomes. Many novel bioinformatic tools and approaches have been developed to deal with the vast numbers of short read sequences produced by a metagenomic experiment. Aside from the simply overwhelming amount of data, a metagenomic analysis is a complex task comprising several non-standardized steps, involving different software tools whose results are often not directly compatible.in situ sequencing in scenarios where the need to obtain quick results is paramount, for instance clinical scenarios of disease control or epidemics . Recently, some tools have been developed to reassemble the portion of reads not assembled in the first instance, increasing the performance of this step . Co-asseAssembly is also advisable because it facilitates the recovery of quasi-complete genomes via binning methods. The retrieval of genomes is a major step forward in the study of a microbiome, since it enables linking organisms and functions, thereby contributing to a much more accurate ecologic description of the community’s functioning. It is possible, for instance, to determine the key members of the microbiome (involved in particularly important functions), to infer potential interactions between members , and to advance in the understanding of the effect of ecologic perturbations.The best strategy for binning is co-assembly of related metagenomes. By comparing the abundance and composition of the contigs in different samples, it is possible to determine which contigs belong to the same organism: these contigs have similar oligonucleotide composition, similar abundances in individual samples, and a co-varying pattern between different samples. In this way, it is possible to retrieve tens or hundreds of genomic bins with different levels of completion that can be used as the starting point for a more in-depth analysis of the microbiome’s functioning.SqueezeMeta is a fully automatic pipeline for metagenomics/metatranscriptomics, covering all steps of the analysis. It includes multi-metagenome support allowing co-assembly of related metagenomes and the retrieval of individual genomes via binning procedures.A comparison of the capabilities of SqueezeMeta and other pipelines is shown in Table SqueezeMeta offers several advanced characteristics that make it different to existing pipelines, for instance:1.Co-assembly procedure coupled with read mapping for the estimation of the abundances of individual genes in each metagenome.2.An alternative co-assembly approach enabling the processing of an unlimited number of metagenomes via merging of individual metagenomes.3.Support for nanopore long reads.4.Binning and bin checking for retrieving individual genomes.5.Internal checks for the taxonomic annotation of contigs and bins.6.Metatranscriptomic support via mapping of cDNA reads against reference metagenomes, or via co-assembly of metagenomes and metatranscriptomes.7.Inclusion of MySQL database for storing results, where they can be easily exported and shared and inspected anywhere using a web interface.in situ metagenomic sequencing experiments. By adequately setting all the pipeline’s components, we were able to fully analyze completely individual metagenomes and even co-assemble related metagenomes using a desktop computer with only 16 GB RAM. The fully automatic nature of our system, not requiring any technical or bioinformatic knowledge, also makes it very easy to use. It is also completely independent of the availability of any Internet connection.We have designed SqueezeMeta to be able to run in scarce computer resources, as expected for https://github.com/jtamames/SqueezeMeta.SqueezeMeta can be downloaded from SqueezeMeta is aimed to perform the analysis of several metagenomes in a single run. It can be run in three different modes . For each query sequence, we select a range of hits having at least 80% of the bit-score of the best hit and differing by less than 10% of its identity percentage. The LCA is the lower rank taxon common to most hits, since a small number of hits belonging to other taxa are allowed to add resilience against, for instance, annotation errors. Importantly, our algorithm includes strict cut-off identity values for the various taxonomic ranks. This means that hits must pass a minimum amino acid identity level to be used for assigning to a particular taxonomic rank. These thresholds are 85, 60, 55, 50, 46, 42, and 40% for species, genus, family, order, class, phylum, and superkingdom ranks, respectively . Hits beGenes in COGs and KEGG IDs can be annotated using the classical best hit approach or a more sensitive one considering the consistency of all hits . In shorThe taxonomic assignments of individual genes are used to produce consensus assignments for the contigs. A contig is annotated to the taxon to which most of their genes belong  a gene table, with all the information regarding genes . (2) A contig table, gathering all data for the contigs , and (3) A bin table with all information related to the bins .These three tables and the optional metadata will be used to create a MySQL database for easy inspection of the data arising from the analysis. The database includes a web-based user interface that enables easy creation of queries, so that the user does not need to have any knowledge on database usage to operate it Figure . The intWhen combining metagenomes and metatrancriptomes, the latter can be analyzed in a straightforward way by just mapping the cDNA reads against the reference metagenomes. In this way, we can obtain and compare the abundances of the same genes in both the metagenome and the metatranscriptome. However, this will obviate these genes present only in the latter, for instance genes belonging to rare species in the metagenome (therefore unassembled) and that happen to be very active. SqueezeMeta can deal with this situation using the merged mode. Metagenomes and metatranscriptomes are assembled separately and then merged so that contigs can come from DNA from the metagenome, cDNA from the metatranscriptome or both. Normalization of read counts makes it possible to compare presence and expression values within or between different samples.To illustrate the use of the SqueezeMeta software, we analyzed 32 metagenomic samples corresponding to gut microbiomes of Hadza and Italian subjects , using tThe improvement of gene recovery for the smaller samples is also noticeable by the percentage of mapped reads. The individual assembly for small samples achieves barely 35% of read mapping to the assembled metagenome, indicating that most reads could not be used. The small size (and therefore low coverage) of the metagenome prevented these reads from being assembled. When co-assembling these samples with the rest, more than 85% of the reads could then be mapped to the reference metagenome, indicating that co-assembly is able to capture most of the diversity found in these small samples.Table Binning results have been analyzed according to the completeness and contamination values provided by CheckM Table . Again, Bacteoides and Faecalibacterium are more abundant in these individuals than in Hadza individuals. The Hadza have increased diversity and fall into different groups corresponding to the presence of diverse species, in accordance with the distinctions found using functional profiles (Allistipes or Prevotella not present in the Italian metagenomes. Moreover, Spirochaetes from the genera Treponema are only present in Hadza subjects, which are supposedly not associated with pathogenesis. This information is directly retrieved from SqueezeMeta results and offers a revealing view of the genomic composition and differences between the samples. A similar result can be obtained for the functional annotations. The original functions represented in the bins can be used to infer the presence of metabolic pathways using the MinPath algorithm (Figure profiles . The miclgorithm , that dein situ metagenomic sequencing (1, summing 581 MB in less than 4 h. These experiments reveal that SqueezeMeta can be run even with scarce computational resources, and it is suitable for its intended use of in situ sequencing where the metagenomes will be moderate in size.One of the motivations for the development of SqueezeMeta was making it capable of performing a full metagenomic analysis on a limited computing infrastructure, such as the one that can be expected in the course of quencing . We creaSqueezeMeta is a highly versatile pipeline that enables analyzing a large number of metagenomes or metatranscriptomes in a very straightforward way. All analysis steps are included, starting with assembly, subsequent taxonomic/functional assignment of the resulting genes, abundance estimation and binning to obtain as many genomes as possible in the samples. SqueezeMeta is designed to run in moderately-sized computational infrastructures, relieving the burden of co-assembling tens of metagenomes by using sequential metagenomic assembly and ulterior merging of resulting contigs. The software includes specific software and adjustments to be able to process MinION sequences.The program includes several verifications on the results, such as the detection of possible inconsistent contigs and bins, and estimation of the latter’s completion using the checkM software. Finally, results can easily be inspected and managed since SqueezeMeta includes a built-in MySQL database that can be queried via a web-based interface, allowing the creation of complex queries in a very simple way.in situ sequencing will likely produce a moderate and manageable data size.One of the most remarkable features of this software is its capability to operate in limited computing infrastructure. We were able to analyze several metagenomes in a few hours using a virtual machine with just 16 GB RAM. Therefore, SqueezeMeta is apt to be used in scenarios in which computing resources are limited, such as remote locations in the course of metagenomic sampling campaigns. Also, it does not require the availability of any Internet connection. Obviously, complex, sizeable metagenomes cannot be analyzed with these limited resources. However, the intended use of SqueezeMeta will be further expanded by the creation of new tools allowing in-depth analyses of the functions and metabolic pathways represented in the samples.JT conceived and designed the tool and wrote the manuscript. JT and FP-S created the software and performed all necessary testing and read and approved the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.