The palmaris longus (PL) muscle is considered by many to be a vestigial muscle due to it having little to no functional significance on the upper limb. This, however, made it highly valuable in surgical procedures, especially as a graft in plastic and reconstructive cases. Variations in the muscle’s morphology were discussed in the literature, but some are more rare than others. Those variations may have clinical implications on different pathologies such as Guyon’s syndrome or Carpal tunnel syndrome based on the nerves and vessels surrounding it, and thus demand a proper understanding of the variation’s anatomy. Here, we report a case of one of the rarer variations, a unilaterally reversed palmaris longus muscle in the left forearm of a 55-year-old male cadaver, discovered in a routine teaching session. Throughout the case, we will discuss the normal anatomy, the variation, and the clinical implications this variation may have. The palmaris longus is a small muscle that has a spindle-shaped belly and can be found on the anterior forearm. It originates via the common forearm flexor tendon from the medial epicondyle of the humerus and is located between the flexor carpi radialis and the flexor carpi ulnaris, with the palmar aponeurosis being the most common insertion site. Even though the structure of the palmaris longus varies widely, it can generally be divided into three parts: a proximal part made up of tendon, a middle part made up of muscle that is spindle-shaped, and a distal part made up of a slender long tendon , 2. The The palmaris longus muscle is primarily supplied by branches from the ulnar artery, and less commonly, through branches from the main brachial artery itself . EmbryolThe palmaris longus muscle is anatomically diverse, with unilateral agenesis being the most frequent of its variants. Other anatomical variants include bifid palmaris longus, triple-headed palmaris longus, accessory palmaris longus, several anomalous insertions at the wrist, and one of the more rare variants, a reversed palmaris longus . In thisDuring a regular educational anatomy session , an uncommon and interesting finding of the palmaris longus muscle was uncovered in the cadaver of a 55-year-old male. Throughout the dissection, we followed the Grant’s dissector manual. Digital pictures of the entire dissected area were taken. Of note, all the muscles in the forearm start with the belly proximally and end or taper into a tendon distally. Due to this, the tendon of the reversed muscle was easily discerned, standing out in contrast with and amongst the bellies of the flexors of the wrist and the fingers. Its upper end arises from the area over the common flexor origin and runs distally, immediately medial to the belly of the flexor carpi radialis (FCR) muscle. Tracing it downwards , the tendon was connected to a muscular belly, continuing downwards and medially to then disappear under a triangular tag of skin and fascia at the wrist Figure . Considering that the tendon of the reversed muscle is replacing the belly of a normal palmaris longus muscle, which is conventionally known to be the immediate medial structure to the FCR muscle, and since the palmaris longus muscle is renowned for its high tendency of variability, we concluded that the encountered reversed muscle is bound to an aberrant reversed and deviated palmaris longus muscle in the left forearm of that body. The skin tag covering the distal part of the aberrant palmaris longus muscle was reflected, and then meticulous dissection was carried out, separating the muscle from the surrounding fascia to trace the muscle attaching mostly to the pisiform bone; the end of the muscle was partly fused with the surrounding fascia. As the hand was already dissected, the carpal ligaments  were absent. The palmar aponeurosis was also resected, rendering it difficult to speculate upon its relation to the distal part of the belly Figure .Delicate dissection was carried out to expose the ulnar artery and nerve  while they were within the Guyon canal (Zone 1). The point of division of the ulnar nerve  was retrieved, but was found higher than usual. The radial border of the deviated palmaris longus muscle was 2 cm away from the median nerve at the distal part of the forearm. The distal part of the belly of the muscle was mobilized to trace the superficial and deep branches of the ulnar nerve to their origin point of division. On cutting the distal part of the belly at the point of division of the ulnar nerve, other anatomical structures, like the tendon of the flexor carpi ulnaris muscle reaching the pisiform, were revealed Figure .This aberrant palmaris longus muscle case presents an anomaly in which the hypertrophy of the medially-deviated reversed belly of the muscle could principally cause compressive ulnar nerve neuropathy, likely involving both of its divisions: the sensory and the motor. On dissection of the contralateral forearm, a normal palmaris longus muscle was revealed Figure .A video of our cadaver with the palmaris longus muscle on the right side showing a normal orientation, and the palmaris longus on the left side showing a reversed orientation with ulnar deviation, was shown in Video In 1973, Still and Kleinert were the first to describe a reversed palmaris longus muscle . A studyCarpal tunnel syndrome is caused by entrapment of the median nerve as it passes through the carpal tunnel and makes up 90% of all neuropathies. Pain, paresthesia, and numbness are considered early symptoms of this condition. The symptoms are felt specifically on the first three fingers radially, and on the radial half of the ring finger. As the severity of the compression increases, the patient will start to have additional symptoms, such as clumsiness, weakness in the affected hand, and atrophy of the thenar muscle. Symptoms of the disease most commonly appear at night while lying down and subside during the day in the initial phases. As the illness progresses, symptoms will appear during the day, particularly when performing repetitive tasks like painting, typing, or gaming. Symptoms can become continuous as the condition advances . The tenA study was done to evaluate three female patients who presented with swelling of the anterior region of their wrists and lower forearm. In all three cases, the swelling had impacted their digital flexor tendon, exhibiting carpal tunnel syndrome symptoms. Those patients all reported pain in the lower forearm-to-wrist area, with a minor bluish swelling proximal to the flexor retinaculum, and no obvious thenar wasting. After the tests for rheumatoid arthritis came back negative, the patients then underwent surgery for decompression. The swellings were discovered to be caused by distal bellies of the palmaris longus muscle overlaying a squeezed median nerve located between the belly of the muscle and the supporting tendons .In a study conducted in 2017 on 80 randomly selected and isolated upper limbs, the course and location of tendon insertion, as well as its relationship to the median nerve, were studied. It was found that the palmaris longus muscle can be divided into three major categories based on the morphology of its insertion. The most frequent was type I (78.8%), where the tendon attaches to the palmar aponeurosis. Type II showed a bifurcated tendon, where the lateral division was inserted in the palmar aponeurosis and the medial division in the flexor retinaculum, found in 10 upper limbs (12.5%). The third type was considered the rarest (having only been found in 1.2% of the cases), where the palmaris longus in one limb was found to be fused with the flexor carpi ulnaris muscle. In that group, the insertion was found in the pisiform bone and the palmar aponeurosis in the distal part of the tendon . The thiSince the reversed palmaris longus muscle can have an atypical insertion site, it can precipitate inflammation, edema, and blue-colored discoloration, consequently causing pain and numbness in the lower portion of the forearm. This decreases hand functionality, especially when performing hand flexion . HypertrGuyon canal syndrome is an infrequent peripheral ulnar nerve neuropathy in which the ulnar nerve is injured as it passes through a restricted anatomical pathway at the level of the wrist. The ulnar nerve enters the hand through Guyon's canal, a special spot where the ulnar nerve is susceptible to compression. Inflammation, compression, or trauma, such as hook of hamate fractures, can all result in distal ulnar nerve injury. Other causes include lipoma and excess fat tissue within the Guyon canal. In rare cases, an aberrant muscle can lead to ulnar nerve damage . The relIn the field of hand reconstruction surgery, the palmaris longus tendon is frequently used as it is thought to be the best source for grafting the hand's long flexors . Due to It is not uncommon to have different morphological variations of the palmaris longus muscle. These variations include different insertion sites, an absent, bifurcated, hypertrophied, and reversed muscle. Our case here discussed one of the rare variants, a unilaterally reversed palmaris longus muscle in the left forearm, and its clinical significance in the literature. In a reversed case, the orientation and position of the muscle can affect or compress the nerves surrounding it, contributing to various pathologies such as carpal tunnel syndrome and Guyon's canal syndrome, especially when the muscle hypertrophies with repetitive use. Despite having been deemed inert, the palmaris longus muscle has always been an important surgical landmark. Its variations play a critical role in surgical settings, as it is considered one of the best sources of grafts, especially in reconstructive surgeries. Carefully studying the variations in this muscle will also save the surgeons any unnecessary surgical complications.


Triboelectric charge transfer is complex and depends on contact properties such as material composition and contact area, as well as environmental factors including humidity, temperature, and air pressure. Saturation surface charge density on particles is inversely dependent on particle size and the number of nearby particles. Here we show that electrical breakdown of air is the primary cause of triboelectric charge saturation on single and multiple electrically insulating particles, which explains the inverse dependence of surface charge density on particle size and number of particles. We combine computational simulations with experiments under controlled humidity and pressure. The results show that the electric field contribution of multiple particles causes electrical breakdown of air, reducing saturation surface charge density for greater numbers of particles. Furthermore, these results show that particles can be discharged in a low pressure environment, yielding opportunities for improved industrial powder flows and dust mitigation from surfaces. In addition to reducing flowability, this charge build-up can cause clogging of fluidised bed reactors7 and pneumatic conveyers9. This agglomeration and segregation in powder flows causes problems for industrial products, leading to non-uniform dosage in pharmaceutical products for example10. Large charge build-up causes the creation of strong electric fields which can cause electrical discharge and arcing. Such arcing can cause damage to electronic devices12 and pose a significant fire and explosion hazard14.Electrical charge can be exchanged when two materials contact. This process is called triboelectric charging, and it is prevalent in many processes involving the contact of insulating materials, giving rise to a number of problems and opportunities. A key area affected by triboelectric charge build-up is that of industrial powder flow processes. Charge build-up can lead to increased friction and hence energy losses in such flows, reducing powder flowability15, electrostatic mineral separation21, and electrodynamic dust shields for solar farms22 and lunar exploration24. A better knowledge of triboelectric charging can improve the understanding of a number of natural processes, in addition to enabling new technological applications. Such natural processes include particle behaviour in dust storms28, electrification of volcanic plumes30 which leads to levitation of ash into the Earth’s ionosphere31, and the aggregation of dust particles in planetary formation34.Triboelectric charge build-up can be harnessed for a number of applications despite the negative impact it has on some processes. These applications include toner particle charging for electrophotography38. Particle saturation charge has been shown to be proportional to particle size39, but the surface charge density reduces with increasing particle size40.There are still many outstanding questions about which mechanisms dominate the behaviour of triboelectric charge transfer and saturation. Theory development and experimentation on the triboelectric charging of single particles under controlled conditions have been performed to understand these charge transfer mechanisms better. Experiments on the charge transferred per contact show that particles charge towards a saturation level in a manner similar to a capacitor, and that the rate of charging can be dependent on factors such as impact velocity and angle42. Surface potential altering43 and dielectric breakdown of air44 are the two primary mechanisms available for explaining this reduction in charge per particle. In the surface potential altering model, the electric field created by additional particles induces a charge in a conducting charging surface. This charge induction may alter the work function of the charging surface, in turn affecting the final saturation charge attainable by particles that contact it45. In the breakdown model, the electric field created by a particle or group of particles may become strong enough to cause the dielectric breakdown of the surrounding medium. This phenomenon has been considered as a saturation mechanism for single particle charging47 and the formation of nano-scale oppositely charged patches on the surface of materials48. It has also been proposed as a potential cause for reduction in charge saturation on larger groups of particles relative to a single particle, however this has yet to be definitively demonstrated49.The mechanism for charge saturation on groups of particles in close proximity is still not well understood. Increasing the number of particles in a mixture reduces the charge per particle at saturationIn this work, we determine whether the charge saturation mechanism for the triboelectric charging of multiple identical insulating particles is electrical breakdown. We describe a new method of simultaneous triboelectric charging and charge measurement. Theory for the charge saturation on single particles is discussed, then verified experimentally in a controlled humidity and temperature environment and under vacuum. The theory and experiments are then extended to multiple particles, using a combination of experimental results and simulations of the electric field build-up on multiple particles to determine the mechanism of charge saturation. Finally, we test the effect of pressure on saturation charge, resulting in a new method for electrostatic charge mitigation which can be applied to dust removal.38. The charge on a particle can be measured using a Faraday cup connected to a coulombmeter. Here we used a Faraday cup as one of the triboelectric charging surfaces. An identical stainless steel container to the inner cup of the Faraday cup was attached to the top of the Faraday cup, using a 2 mm thick 3D printed PLA ring to electrically insulate the two cups from each other, in a manner similar to Schella et al.42. This created an enclosed charging capsule, one half being the inside of a Faraday cup, the other half being an identical grounded stainless steel container. The charging capsule was then enclosed in a grounded stainless steel outer shell, serving as an electromagnetic shield to avoid background noise in charge measurements. The entire system was then mounted on a servo motor, controlled using an Arduino microcontroller so that it rotates 180° back and forth around the horizontal axis. Two 5 mm holes were drilled in the side of the shell and capsule to allow the air to vent when the system is placed in a vacuum. In addition, the capsule is detachable to allow the addition and removal of particles and cleaning of the charging surfaces. We used a Keithley 6517b electrometer which is fit with a coulombmeter for charge measurements.An automatic charging system was designed that can triboelectrically charge particles up to their saturation charge while simultaneously measuring their charge build-up over time. A schematic of this system is shown in Fig. A demonstration of the charge measurement process shown in Fig. 50. This required field strength reduces at first as the pressure reduces, due to the increase in the mean free path of an electron in low pressure air. The Paschen curve shows that there is a critical pressure at which the electric field strength required to ionise air is at a minimum51. The dielectric strength of air increases again below this pressure as a vacuum is approached, due to the low number density of molecules in the air. The mean free path of an electron will get shorter above this critical pressure, requiring a stronger electric field for ionisation on impact with an air molecule.Electrical breakdown of air the process whereby electrons generated by natural ionisation in air are accelerated enough to cause an avalanche of ionisations through impact with air molecules. This requires an electric field of ~ 3 MV/m at atmospheric pressureFull spark discharge only occurs in a uniform electric field between conducting electrodes. The presence of static charge on insulators, and curvature on charged surfaces, lead to non-uniform electric fields which cause localised ionisation in smaller regions close to the charged surface. These non-uniform fields cause corona or brush discharge.52 has been used to describe corona breakdown around high voltage wires53. The law is an empirical relationship relating the wire radius We consider the electric field at the surface of a spherical insulating particle next to a grounded flat conductor. The electric field is strongest near the curved surface of the particle, which is where partial discharge will occur if the charge is high enough. Peek’s law55. Here we adapt it to predict the saturation surface charge density Peek’s law can be used for the geometry of conducting spheres next to a grounded flat conductormentclass2pt{minim50. The electric field generated at a curved surface will decrease quickly as the distance above the surface increases, and the rate of decrease is inversely related to the radius of curvature. This inverse dependence between radius of curvature and electric field gradient holds true also for insulating particles, meaning that Peek’s law can also be used to approximate the surface charge density required on insulating particles of varying size to cause electrical breakdown. The distance over which the electric field is strong enough to cause ionisation will not be large enough if the electric field at the surface just exceeds the electrical breakdown limit. Any electrons arising from natural ionisation in this region do not gain enough energy to cause further ionisation of air. A stronger electric field is necessary at a curved surface in order to ensure that the region in which the electrical breakdown limit is exceeded is large enough for electrons to gain enough energy to cause ionisation.The non-uniform electric field at charged curved surfaces can explain the inverse radius dependence of this equation48. Gauss’ law cannot be used to calculate the electric field generated by an insulating particle if this is the case, as it relies on the surface charge density being uniform. Non-uniform charge density gives rise to tangential electric field components that do not cancel out at the surface of the particle. Local electric fields can thus be stronger, exceeding the value that would be calculated using Gauss’ law and the total charge on the particle. This deviation from Gauss’ law has implications for experimental measurements, where the electric field cannot be calculated accurately based on the measured total charge on an insulating particle. The true electric field at the surface will be higher than that calculated using Gauss’ law, and the difference will be relative to the non-uniformity of the surface charge density. As a result, it is expected that the electric field calculated based on experimental charge measurements will follow a trend similar to Eq.  and 30 °C. The experiments were repeated in a vacuum at 4 × 10There is excellent agreement between the electrical breakdown model and the measured saturation surface charge density of the PTFE particles at atmospheric pressure. The charge of the particles in a vacuum is much higher than at atmospheric pressure. The expected trend is seen at atmospheric pressure, and repeating the same experiment in a vacuum where the dielectric constant of the surrounding medium is higher leads to a much higher observed charge. This suggests that electrical breakdown is most likely the charge saturation mechanism.The experiments were repeated in air using different polymer materials to provide further evidence that electrical breakdown is the mechanism responsible for charge saturation. Particles of different material are expected to saturate as predicted by Eq.  if electThe experimentally measured saturation charges on the PVC and LDPE particles align closely with the electrical breakdown model which was fit to the PTFE data. In addition to the increased charge under vacuum observed in the previous section, this agreement between the model and multiple materials further confirms that electrical breakdown is the saturation mechanism for single polymeric insulating particles in air. The model also yields accurate predictions for saturation charge for sizes that the model was not fitted to. This is evident from the accurate prediction of the saturation charge on the 22.23 mm diameter PVC particle for example, which is almost twice as large as the largest of the PTFE particles.A simulation of the charging process was developed to determine whether electric field build-up is the saturation mechanism for charge in multiple-particle systems. Figure Here we consider two primary geometries for simulation as shown in Fig. The maximum electric field for both geometries is calculated by considering the closest packing possible using a hexagonal lattice. Dome-first geometry is simulated by adding one particle at a time until a complete hexagonal layer is formed, then creating new layers of particles on top until a complete dome is made using hexagonal close packing. With layer-first geometry, a single hexagonal packed layer of particles is built-out until a maximum diameter is reached instead of creating new layers of particles vertically. Both the dome-first and layer-first geometries are shown in Fig. The magnitude and distribution of the electric field created by a group of particles determines whether dielectric breakdown of air occurs, or if the Coulomb force is strong enough for particles to adhere to the grounded wall. In these simulations the electric field was calculated at the contact point between the centre particle in the lattice and the charging capsule, assuming the surface charge density of the particles is uniform. The total electric field 56) is being exceeded, leading to a cessation of further charge build-up. Only the normal component Equation  represenoth Eqs.  and 4)  56) is bentclass1pt{minimaPTFE spheres of 6.35 and 12.7 mm diameter were tribocharged in batches of 1 to 64 and 1 to 32 particles. A batch refers to the number of particles charged together at the same time. Each batch size was charged for 300 rotations of the charging capsule, and this was repeated 11 times, yielding over 1600 charge measurements per batch size. More information about the charge measurement is given in Note The maximum batch sizes of 64 and 32 for 6.35 and 12.7 mm particles is create 1–1.5 layers of particles at the base of the charging capsule. The small number of layers, combined with the 300 experimental rotations, suggest that most, if not all, particles will be in contact with the long side of the charging capsule as it rotates as shown in the schematic in Fig. Figure The data in Fig. The simulations match the observed logarithmic drop-off in charge per particle as the number of particles increases. The simulations match the single-particle experimental charge, while predicting a slightly smaller charge per particle for multiple particles. This is due to the simulations considering the closest packing possible, yielding a lower limit for saturation charge. Any variations from the simulation in particle dynamics and packing geometry, which are expected in the experiments, would require a larger electrical breakdown-inducing charge than the simulations predict.–4 mbar.These results provide evidence that electrical breakdown of air is the mechanism causing charge to saturate at lower values as the number of particles increases. The experiments were repeated under vacuum in order to further test this hypothesis. It was found that particles gain enough charge to adhere to the side of the charging capsule under vacuum, preventing further charge build-up. Figure The charging capsule is initially set to rotate back and forth by 180°, represented by the solid line in Fig. Figure The charge at which particles adhered to the charging capsule was measured experimentally for batches of 1, 4, 16 and 64 particles of 6.35 mm diameter. This experimental charge was then used to calculate the normal electric field strength at the contact point with the capsule wall using the layer-first model and Eq. . In these experiments, particles of 6.35 and 12.70 mm diameter were used in batches ranging from 1 to 64 particles.It was necessary to build a custom Faraday cup with the correct geometry and cup material while designing an automatic charging and measurement system. Cups of any geometry or conducting material can be used for construction, as Faraday cups works by charge induction.For these experiments, dimensions of 85 mm diameter × 85 mm height were used for the outer cup, and 60 mm diameter × 60 mm height for the inner cup. All cups used were made of 304 stainless steel, polished to a 0.4 μm finish (Pharma Hygiene Products COC4085P UK).To construct the Faraday cup a 1 cm hole was drilled in the side of the outer cup. A 75 Ω panel mount BNC connector was mounted on the drilled hole (RS pro 546-4904 UK). A 1 cm thick sheet of PTFE was cut out and placed at the bottom of the outer cup, on which the inner cup was mounted. The tip of the BNC connector was soldered to the surface of the inner cup using lead free silver solder (RS pro 756-8884 UK) and S26 fluid flux (Solders & Fluxes UK). The space between the cups was then filled with an electrically insulating polyurethane potting compound (RS pro 199-1395 UK). Immediately after potting, the cups were placed in a vacuum for 30 min to off-gas any bubbles in the compound. This is done to improve the resistive properties of the potting compound, and to ensure trapped bubbles do not expand and compromise the structure when the cup is used in a vacuum chamber.Experiments done in air were done under controlled humidity and temperature using a sealed glovebox. To control humidity, the glovebox was connected to two desiccant capsules via an air tube and a pump. This pump pulled air from the chamber, passing it through the desiccant capsules to dry it, before being pumped back into the main chamber. In addition, the chamber was connected to a feed of dry nitrogen gas which could be used to purge humid air. There were a number of valves attached to the chamber so that air would be forced out of the chamber with the introduction of nitrogen, maintaining ambient air pressure inside. Using nitrogen purging and desiccant, the humidity in the glovebox could be controlled in the range of 5–95%. For temperature control, a PID controlled heater was used in conjunction with a chiller. This allowed for temperature control from 12 to 60 °C.–4 mbar was achievable using this system. The automated charging system was placed in the vacuum chamber, and the BNC cable connecting the electrometer to the Faraday cup was fed in using a vacuum rated feedthrough (LewVac FH-BNC-D-40CF UK). The Arduino board was kept in the vacuum chamber, however the USB cable connecting to the computer to power and control the board was also separated and fed through using a custom-made electrical feedthrough. The vacuum chamber was fit with a built-in pressure transducer which was accurate at in the high vacuum–low pressure range (< 25 mbar). An additional pressure transducer (Omega PXM409-001BVUSBH UK) was mounted on the side of the vacuum chamber which was accurate in the low pressure–atmospheric pressure range. Combined, the two calibrated transducers allowed for a continuous logged pressure reading as air was pumped out of and reintroduced into the chamber.A vacuum chamber connected to three roughing pumps and two turbo pumps was used to perform charging experiments under low pressure and at vacuum. A high vacuum of 3 × 10Supplementary Information.


In the original published version of this article, the percentage in section 3.2 of ‘0.05%’ should be ‘0.5%’. This has been fixed in the correction. The authors apologize for the errors. Both the HTML and PDF versions of the article have been updated to correct the errorsThe authors declare no conflict of interest.


Pseudotropheus zebra. The expression of the protein pS6 was measured in 19 brain areas and compared between groups of individuals subjected to four different behavioral contexts . Control group individuals were sacrificed with minimal interactions. Fish in the avoidance group were chased with a net for an hour, after which they were sacrificed. Individuals in the trained group received daily training sessions to associate a visual object with a food reward. They were sacrificed the day they reached learning criterion. Fish in the novelty group were habituated to one set of visual stimuli, then faced a change in stimulus type (novelty stimulus) before they were sacrificed. Fish in the three treatment groups showed the largest activation of pS6 in the inferior lobes and the tectum opticum compared to the control group. The avoidance group showed additional activation in the preoptic area, several telencephalic regions, the torus semicircularis, and the reticular formation. The trained group that received a food reward, showed additional activation of the torus lateralis, a tertiary gustatory center. The only area that showed strong activation in all three treatment groups was the nucleus diffusus situated within the inferior lobe. The inferior lobe receives prominent visual input from the tectum via the nucleus glomerulosus but so far, nothing is known about the functional details of this pathway. Our study showed for the first time that the inferior lobes play an important role in visual learning and object recognition.The neural correlates of most cognitive functions in fish are unknown. This project aimed to identify brain regions involved in visual learning in the cichlid fish The online version contains supplementary material available at 10.1007/s00429-023-02627-w. Fish have been the subject of a large number of visual discrimination experiments, which have shown that fish possess many of the same cognitive abilities as birds and mammals  expression have been used during the last two decades to identify brain areas involved in different cognitive functions in fishes. C-fos and egr-1 are generally the two main proteins assessed, which can be detected by immunocytochemistry inside the nucleus of activated neurons. However, the availability of antibodies for fishes is problematic and many studies used in situ hybridization and PCR on micro dissected brain parts to localize the expression of genes correlated with the activation of neurons. More recently, the phosphorylated ribosome marker pS6 has become a popular alternative to visualize neural activation in fish  belong to the species Pseudotropheus zebra, also known as Zebra mbuna (Konings and Stauffer Metriaclima zebra or Maylandia zebra (Boulenger www.fishbase.org). Cichlids are teleosts and represent one of the most varied extant vertebrate radiations  or to being used in behavioral experiments . The isolation was necessary to avoid the activation of brain areas involved in social interactions. Walls and floor of each tank consisted of light grey PVC, while the front was made of white frosted plexiglass. A grey partition was inserted into the middle of the tank separating a back from a front compartment; the partition was fitted with a passage for the fish, that could be closed with the help of a transparent guillotine door during the training of the fish. In the back compartment of the tank, a fish shelter, a heating element, a filter system as well as a pump were placed. The water temperature was kept at about 25 °C.Figure N = 10) did not receive any treatment. They were fed once daily, except on the day of sacrifice to prevent any activation of sensory brain areas involved in olfactory and gustatory pathways. After being kept in isolation without any social contact for seven days, fish were taken out of the tank and sacrificed.Fish in the control group (N = 10), were fed once daily, except on the day of the behavioral procedure. After being kept for seven days in isolation and immediately prior to the behavioral procedure, they were moved to a new compartment. Fish were then chased with a net for one hour before being sacrificed 90 min after the chase ended.Fish in the avoidance group (N = 10) were kept in isolation for one week before the training started. On the inside of each plexiglass front wall of the tank, two food holders were installed, consisting of two small pieces of plastic pipe which were attached to the wall with suckers; in each pipe, a hose filled with food was inserted. On the other end, the hose was connected to a syringe through which the food delivery was controlled remotely. With the help of a plastic divider, the front compartment was divided into a right and left compartment. Parallel and 3 cm away from the frontal wall a line indicated the start of the decision-making area into which the fish had to swim in order for its choice to be valid. Please refer to Schluessel et al.  which was located in front of the tank and connected to a notebook. The stimuli were projected on the right and left side, just below the respective food holders and at the same height as the guillotine door to allow the fish to see them, even from the posterior area of the tank. For each of the ten trials within a session, the position of the positive stimulus was randomly determined prior to the experiments  during which the positive stimulus was shown five times on each side of the tank in total; however, it was never shown more than twice in a row on the same side. In total, four rotational schemes were used consecutively over every four sessions. Before each trial, the door was closed, restricting the fish to the back compartment. With the help of a webcam, positioned above the experimental tank, it was possible to observe the behavior of the animal in the tank, without affecting its decision. The guillotine door was then remotely opened and the fish allowed to enter the front compartment. Once the door was opened, the fish had to make a choice within 2 min, otherwise the trial was terminated. To prevent olfactory cues, both feeders were baited in each trial and always simultaneously re-baited to prevent unintentional cuing by the experimenter.Before the actual training commenced, the experimentally naive animals were given time to get used to the experimental setup and to feeding from the food holders in the decision area. The guillotine door was open so that the fish could freely swim throughout both compartments of the aquarium. After the fish had learned to swim through the open guillotine door and collect food from the dispenser at the front of the tank while the projector (no stimulus presentation) was on, training started. Experiments were conducted daily, twice a day always at the same time, during daylight hours. At the beginning of the experiment, the two training symbols (a black dot over a white background (positive stimulus) and a white background without a symbol , Fig. Trial time was taken from the time the individual passed through the guillotine door with the tip of its mouth, until crossing the decision line in front of the projector  were kept in isolation for one week before starting the experiment. For this group, a modification of the habituation-dishabituation experiment elaborated by Messina and colleagues was used . The brain was removed and fixed overnight in 4% paraformaldehyde (PFA) at 4 °C, then cryoprotected overnight in 30% sucrose at 4 °C. The following day, the brain was embedded in O.C.T. compound  and frozen at − 20 °C. Thirty- five µm thick sections were cut at − 20 °C with a cryostat (Leica CM1520) and mounted on gelatin-coated slides in three series, then stored until immunohistochemistry (IHC).To minimize differences in stain intensity, IHC was performed twice within three days, each time including 5 brains for each group .2Od) containing 1.5% H2O2 to deactivate endogenous peroxidase, followed by several washes in PBS. Slides were then blocked in 10% normal goat serum (NGS) for 1 h. The sections were transferred to a primary pS6-antibody solution  antibody, Cell Signalling 2211S: 1:1000) overnight at 4 °C, before being washed several times in PBS.During the IHC, sections were rehydrated by washes in PBS drops; then a post-fixation procedure was performed with 4% PFA drops for 10 min, followed by several washes in PBS. The sections were incubated for 30 min in distilled water  for ~ 15 min, resulting in a deep greyish reaction product confined to the cell bodies of activated neurons. The reaction was stopped by several washes in PBS. Subsequently, sections were dehydrated in ascending alcohols before coverslipping from xylene with Eukitt .The following day, the second antibody reaction  was performed in 5% NGS/1X PBS—0.3% Triton X-100, followed by repeated washes in PBS. Then, signal amplification was initiated using the ABC method , Vector Labs., USA) for 1 h at RT. Following several rinses in PBS, the antibody-Avidin–Biotin complex was visualized using the chromogen-solution  buffer tablet  dissolved in 10 ml HFor the current study, the specificity of pS6 antibody was checked by replacing either the primary or secondary antibodies with PBS, showing no reaction product. No other test of the specificity of the antibody was performed.Astatotilapia burtoni  was performed for each brain part comparing the learning groups with the control group to check for significant differences . Lastly, the activation in each brain area was calculated by dividing the pS6 stain level into the three learning groups by the staining level in the control group and log-transformed  according to a U-test.After the analysis of the potentially induced behavioral components, pS6 staining was analyzed in 19 brain areas  was measured relative to the baseline activity in the control group.In the stress/avoidance group, fish were moved to a different tank and were chased with a net for one hour. Many sensory areas were activated. Olfactory stimulation correlated with the activation of OB and Dp, and was likely induced by the presence of new water and the net. The latter also seemed to have caused activation of the visual system, reflected by the strong activity of pS6 in both TOp and TOs. The lateral line/hearing system also showed activation (indicated by the activity of pS6 in TS) possibly due to the movement of the net in the water or noises made by the experimenter. There was also activity of pS6 in the preoptic area, which appears to be a stress-related response. In addition, the enforced locomotion activated the reticular formation, a premotor area. The avoidance learning component likely caused activation of the dorsomedial part of the telencephalon and the inferior lobes.In the active training group, fish were trained every day to choose the correct target to get food. Once the fish reached the learning criterion (≥ 70% correct choices three times in a row), it was sacrificed. Compared to the control group, there was a little additional signal, possibly due to the continuous repetition of training. However, there was an increase in pS6 activity in the torus lateralis, a brain area associated with a taste that was likely activated by receiving a food reward. In addition, the inferior lobes together with both layers of the tectum opticum (TOp and TOs) were activated—possibly due to visual learning.In the habituation/novelty group, staining was also similar to the control group. During the habituation phase, the stimulus was shown to the fish for 5 days, followed by a food release. On the last day, the novelty stimulus was shown. The presentation of a novel stimulus appears to be associated with a small increase in the activity of pS6 in the tectum (vision) and the inferior lobes.The aim of this project was to investigate some of the neural substrates involved in visual learning in the cichlid The changes in activity in the different brain areas correlate with the different behavioral responses observed in the four groups. Common to all experimental groups is a strong activation of the inferior lobes. This may be explained by the fact that a visual learning component is present in all groups, except the control group. Higher cognitive functions are often thought to be located in the telencephalon, as is the case in mammals. However, lesion studies and further anatomical evidence have shown that the telencephalon of teleosts is less important for many sensory, motoric and cognitive tasks. Lesion studies have shown that the lesion/ablation of the telencephalon in teleosts has little effect on many behaviors Below is the link to the electronic supplementary material.


In recent years there has been public speculation about the breed, destination and number of horses being sold by public auction at livestock saleyards in Australia. Currently, there is little objective information available about the breed and condition of horses sold through this medium. With little publicly available objective data on these horses, the horse industry has been left vulnerable to misinformation. Accurate information regarding the composition and condition of horses attending saleyards is important to identify and address any welfare issues and to inform public debate.Data were collected on 312 horses and ponies presented for sale through the Pakenham Horse Sales between July 2019 and March 2020. All horses and ponies were inspected at the saleyards and information on breed, age, body condition score (BCS), purchaser and sale price were recorded as the animals were auctioned.Crossbred horses and ponies were the largest groups presented for sale. Ponies were more likely to be sold to private buyers. Quarter horses and riding ponies were as likely to be sent to slaughter as thoroughbreds and standardbreds. Entire males and females sold for lower prices than geldings. Most horses and ponies (64%) were sold to private buyers. More than three‐quarters (77%) of horses and ponies presented for sale had a BCS greater than or equal to three out of five.This pilot study challenges perceptions that thoroughbreds are the primary breed to attend public sales or that animals attending the sales are in poor condition. In recent years there has been an increased focus by the community, political parties and animal welfare organisations on the number of thoroughbred and standardbred horses being sent to the slaughterhouse.Previous research has indicated that recreational horse owners primarily buy and sell horses and ponies through private sales, only 2% of recreational owners reported that they use knackeries, and 3% sell through auctions/saleyards to dispose of horses or ponies when they are no longer needed.There is a perception amongst the public, animal welfare and rights organisations, and the media that majority of horses being sent to slaughter are thoroughbreds.The aim of this pilot study is to begin to fill the gaps in our knowledge about the number, type, breed and condition of horses and ponies attending public sales at the Pakenham Livestock Exchange. The sale price and purchaser were also recorded. The results of this study will provide insight into the numbers of horses and ponies being sold through this venue, the number of animals being sold to slaughterhouses, and an estimate of the age, body condition and breeds of the horses that are presented for sale. Our hypothesis was that thoroughbreds were not the majority breed group that attended the sales, nor were they the largest breed group that was purchased by slaughterhouse buyers.All horses presented for sale by Pakenham Horse Auctions at the Pakenham Livestock Exchange, from July 2019 to March 2020, were included in the study population to determine the total number, breed, sex and ages of the horses sold in this period. Sales were held once per month, with no sales held in January 2020. The sales ceased and data collection was suspended in April 2020 due to COVID‐19 restrictions. One researcher, with training in body condition scoring and written instructions, attended all eight sales to observe the horses and ponies, and collect data. Data were collected in two sets during each sale. The first set was collected prior to the auction and recorded the date of sale, pen number and horse details. The second set was collected during the auction and recorded the pen number, purchaser details, whether the horse was sold and purchase price. The two sets were matched using the pen number of the horse.The outcome of the sale was recorded, including the type of purchaser and purchase price in Australian dollars. The type of purchaser was categorised into four groups: buyers who were known to purchase horses to be processed at abattoirs or knackeries (slaughterhouse), buyers who on‐sell horses to third‐party private or commercial buyers , private buyers (private) or rescue organisations (rescue). The purchaser descriptions and subsequent categorisation were based on sale records and local business knowledge. Horses  sold to ‘dealers’ were included in the ‘slaughterhouse’ (n = 107) category because some dealers on‐sell horses to slaughterhouses if they cannot find a private buyer to purchase the horse; ‘slaughterhouse’ and ‘dealer’ buyers are reported under the collective heading of ‘slaughterhouse’ in the table but are detailed separately in the text. Rescue organisations (n = 2) were included with ‘private’ buyers (n = 192), because they were unlikely to be sold for slaughter, for reporting in the tables but are detailed separately in the text.Information on the horse breed, age and sex; details of body condition and hoof condition were also recorded. Microchip, registration and/or names were recorded if they were provided on the vendor declaration form. Brands were photographed. Individuals were categorised as ponies if they were at or below a height of 144 cm (14.2 hands high), measured from the ground to the top of the wither. Horses were those that measured greater than 144 cm high. Horse sex was determined from information provided by the vendor, information provided by the auctioneer, or after visual examination. ‘Females’ were all fillies and mares. ‘Males’ were any male horses attending the sales. Males were further sub‐classified as ‘Geldings’ if they had been castrated and ‘Entire male’ if they had not been castrated. The body condition score (BCS) of the horse was graded on a scale from 0 to 5.Horses were observed from all sides from the outside of the pen, to determine sex of horse, body condition and hoof condition. Researchers did not enter the pens with the horses for safety reasons. Age was broadly categorised as immature, young, mature, aged and unknown. Age was estimated using the visual appearance of the horse, presence of brands, and/or age on the information provided by the vendor or auctioneer. The visual inspection included identifying the equine as a foal or very young animal (immature), and conversely the presence of grey hair and other signs of advanced age (aged). Horses and ponies of foal up to 12 months of age were categorised as ‘Immature’. ‘Young’ horses and ponies were those aged 12 months to 4‐years. ‘Mature’ horses and ponies were those aged 5 to 16 years. Horses and ponies aged 17 years and over were categorised as ‘Aged’.Information provided by the vendor or auctioneer, the presence of brands and visual inspection were used to determine the breed of the horse. ‘Crossbred’ refers to horses and ponies were the breed information, included two or more breeds. This applies to both horses and ponies. Horse breeds with fewer than 10 individuals were categorised as other – horse or other – pony as appropriate. Appaloosa (n = 6), Paint (n = 7), Arab (n = 2), Clydesdale (n = 1), Warmblood (n = 1) were collapsed into ‘other – horse’. The breeds Brumby (n = 3), Hackney (n = 1), Miniature (n = 3) and Welsh pony (n = 7) were collapsed into ‘other – pony’.Continuous  and categorical variables  were compared using t‐tests and chi‐squared tests, respectively. Non‐normally distributed data  was log‐transformed prior to analysis. Percentages were calculated by dividing the number of horses and/or ponies of interest by the total number of study horses and ponies (n = 312), unless otherwise indicated. Analysis of variance was used to analyse the difference in sale price between breeds and Tukey's honestly significant difference test was used to compare the sale price of each breed category.There were 312 horses and ponies sold at eight sales between July 2019 and March 2020. The median number of horses and ponies to attend each sale was 33 . The lowest number of horses and ponies  attending a sale occurred in August 2019 and the largest number of horses and ponies  to attend a sale was in December 2019  were the largest group to attend the sales overall, ponies outnumbered horses at the July 2019 sale  and the December 2019 sale . The most frequent breed description for crossbreds was Shetland crosses . Thoroughbreds were the second most frequent breed  attending the sales .Overall, crossbred horses and ponies were the most frequent  breed group that attended the sales . Half of all the entire males  were ponies from one sale (Dec‐19). Horses  were more likely than ponies  to be geldings . There was no significant difference in the number of females between horses  and ponies , .Females were the most frequent  sex to attend the sales, followed in descending order by geldings  and entire males  or Standardbreds . Females  were more likely than males (19%. n = 7 of 37) to be of unknown breeding .There was no significant difference between males and females for thoroughbreds  and entire males  compared to geldings. There was no difference in the proportion of mature thoroughbreds  or mature Standardbreds  when compared to the rest of the study population.The majority  of the horses and ponies attending the sales were a mature age, followed by young, immature and aged with 5.8% (17 of 312) of unknown age .The majority 73%, 219 of 312) of horses and ponies attending the sales had a BCS of three, followed by those with a BCS of two and four . There was no significant difference between the sexes in the likelihood of having BCS of less than 3 when attending the sales  were as likely to have a BSC of less than three, compared to other breeds . Males (20% 29 of 145) were as likely as females  to be presented for sale with hooves in ‘poor’ condition . When the hoof condition for breed groups was investigated, quarter horses  were more likely to have ‘poor’ hoof conditions than other breeds .The majority 76%, 236 of 312) of horses and ponies had hooves that were either in ‘okay’ or ‘good’ condition  of horses and ponies presented for sale. Of the eight horses and ponies where the purchaser and/or sale price was unavailable, one was recorded as sold but the purchaser type and price were not available, one was sold to a slaughterhouse and the price was not recorded, one was unsold and five were passed in. These eight horses and ponies were excluded from further analysis.2 test statistic = 21.91, df = 1, P < 0.001, Table 2 test statistic = 22.84, df = 1, P < 0.001, Table 2 test statistic = 1.56, df = 3, P = 0.67) or hoof condition . There was no significant difference between the age categories of the horses and ponies purchased by private and slaughterhouse buyers . Females  were more likely than males  to be purchased by slaughterhouse buyers . Thoroughbreds and Standardbreds were more likely to be purchased by slaughterhouse buyers  when compared to non‐racing breeds  of the horses and ponies attending the sales . However, there was no significant difference in the likelihood of riding ponies , quarter horses  and standardbreds  being purchased by slaughterhouse buyers when compared to thoroughbreds  of horses and ponies attending the sales were purchased by private buyers . Eighty‐five percent of horses and ponies (259 of 304) sold for $500 or less, with nearly a quarter  sold for between $101 and $200  which was significantly less than the median sale price for horses of $335 , . Horses and ponies sold to slaughterhouse buyers  were purchased for lower prices than those sold to private buyers , . Entire males  and females were more likely to be sold at a lower price  than geldings  and 76% had okay or good hoof condition. This suggests that these horses and ponies had been kept at an adequate level of husbandry prior to coming to the sales. Thoroughbred horses were in similar body condition and hoof condition to other horses and ponies at the sale. The BCSs coupled with hoof husbandry in this study showed that the majority of thoroughbreds were not in racing condition when they passed through Pakenham. These findings suggest that these thoroughbreds are not being sent to the sales directly after retiring from racing but were more likely coming from spelling or a post‐racing home. There was no difference in BCS between horses and ponies sold to private buyers and slaughter. This suggests that there are factors other than body mass and condition that influence the destination of horses from the sales.The purchase price in this study was not a good predictor of purchaser type. The ponies sold in this study were more likely to be purchased by private buyers, horses were more likely to go to slaughter, despite horses being sold for a higher median price than ponies. This may be due to horses having a higher proportion of suitable body mass for use in meat compared to ponies, or other logistical factors such as the ability to transport safely. There is a perception that many horses sold through the saleyards are thoroughbreds and that the majority of these are sold to slaughter.The proportion of horses and ponies purchased by slaughterhouse buyers that were racing breeds (41%) in this study was lower than the 53% reported by previous research on horses going through a Queensland export abattoir.Female horses were more likely than males to be purchased for slaughter and were sold for a lower median price. This may be due to the perception that mares can be moody or ill‐tempered making them potentially less desirable as a riding prospect.While 64% of the entire males were ponies, the majority (72%) were from one vendor. Information provided by the vendor at the sale indicated that these ponies were from a deceased estate where the ponies had been left to breed and fend for themselves as the owner's health declined. This is likely to have biased the results on entire males and these results should therefore be interpreted with caution.One of the limitations of the current study was that the overall results for this study were potentially skewed by a large number of ponies entered from one vendor at the December sale. Due to the limited sample size, comparisons between the full dataset with the dispersal ponies in it and a reduced set without the ponies were not undertaken. It is unclear from this study if the inclusion of a large intake of animals from one vendor was a singular event or a more frequent occurrence. Future longitudinal studies are required to investigate homogeneity of the population attending sales.This pilot study provides valuable insight into the horses attending the mixed breed sales in Victoria. However, features unique to this saleyard may limit the application of results in other types of sales and sales in other locations. Further research is needed to better understand the demographic information and condition of horses attending sales throughout Australia and how this compares to the general horse population to identify risks for sale attendance and differences in outcomes when purchased at sale. Further research is needed to investigate the decision‐making process for people purchasing horses through a sale.With public concerns around the overbreeding of horses, the finding that the largest breed group was crossbreds warrants further investigation into the factors that influence the decision to breed and the intended uses and markets for the horses that are being produced.There are no sources of funding to declare for this study. The authors have read the journal's policy and have the following competing interests to declare: Racing Victoria Ltd. provided support for MLF in the form of a thesis stipend as part of a research contract (Racing Vic 045083 15/16) to conduct a separate project. AgriFutures provides support to MLF and JRG to work on another unrelated project. These external funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. There are no patents, products in development or marketed products associated with this research to declare.


Robot swarms are becoming popular in domains that require spatial coordination. Effective human control over swarm members is pivotal for ensuring swarm behaviours align with the dynamic needs of the system. Several techniques have been proposed for scalable human–swarm interaction. However, these techniques were mostly developed in simple simulation environments without guidance on how to scale them up to the real world. This paper addresses this research gap by proposing a metaverse for scalable control of robot swarms and an adaptive framework for different levels of autonomy. In the metaverse, the physical/real world of a swarm symbiotically blends with a virtual world formed from digital twins representing each swarm member and logical control agents. The proposed metaverse drastically decreases swarm control complexity due to human reliance on only a few virtual agents, with each agent dynamically actuating on a sub-swarm. The utility of the metaverse is demonstrated by a case study where humans controlled a swarm of uncrewed ground vehicles (UGVs) using gestural communication, and via a single virtual uncrewed aerial vehicle (UAV). The results show that humans could successfully control the swarm under two different levels of autonomy, while task performance increases as autonomy increases. The field of swarm robotics borrows lessons from biological swarms to enable the cooperation of multi-robot systems to carry out complex tasks . A groupDespite the potential of robot swarms in various application sectors, completely autonomous swarms are not anticipated to be operational in the near future due to numerous technical difficulties and accountability issues ,8. This Human–swarm interaction (HSI) studies the dynamics of interactions between human team members and robot swarms to enhance team performance. Human interaction with robot swarms is challenging due to the limited cognitive capacity of humans relative to both the amount of information generated by swarm members and the number of control signals needed to be sent concurrently to all swarm members ,11,12,13Since the early days of humankind, humans have managed to control very large swarms of sheep via shepherding, where a human communicates their intent to a sheepdog (control agent), which in turn chases swarm members to guide them along a path dictated by the human. Using a sheepdog facilitates controlling the swarm; thanks to the cognitive and physical superiority of the dog compared to the swarm members. Inspired by sheep herding, the concept of shepherding has been reproduced in robotic systems and has demonstrated its potential as a scalable mechanism for swarm control .Nevertheless, existing mechanisms for HSI, including shepherding, have mostly been developed and evaluated in simulated environments with minimal guidance on how to transfer these mechanisms to the control of physical robot swarms. The complexity of implementing HSI mechanisms in the real world slows down the advancement of this research area. For example, shepherding implementations require the availability of a physically and cognitively superior control agent, which imposes extra costs for the acquisition, maintenance, and personnel training required to operate the control agent. Any failure or loss of this control agent renders the whole swarm mission unattainable, creating a very costly environment to run, especially in an academic context running on a tight budget.metaverse, where the physical and virtual worlds are combined, may hold a proper solution to this issue. Our proposed metaverse incorporates a real-world component where the physical swarm interacts with its environment and a symbiotic simulation component containing digital twins for the swarm members. The parameters of the digital-twin swarm are updated and uploaded through a real-time data link with the real world. One or more virtual control agents are employed in the simulation component, through which the human can guide the swarm using shepherding guidance tactics. The user sees the world through a graphical user interface (GUI), such that the human could be unaware of what is physical/real and what is simulated/virtual. The main advantage of the proposed metaverse are twofold. First, it is a cost-effective solution to test shepherding as a swarm guidance tactic while waiving some of the expensive platforms that represent the physical control agent. Second, it makes it feasible to use powerful AI concepts as part of the virtual control agent to support high levels of autonomy.Interestingly, the concept of a Proposing a digital-twin enabled metaverse for scalable control of physical robot swarms by utilising the shepherding control strategy with a virtual control agent.Implementing the proposed metaverse in the control of a physical swarm of Turtlebot-3 UGVs. This is enabled by coupling the physical environment with a simulated Gazebo environment where the digital-twin swarm and the virtual control agent operate.Implementing two levels of autonomy (LoA) for the interaction between the human and the virtual control agent, and designing two gesture communication languages to support these LoA.Validating the proposed metaverse by presenting the results of using it to control the physical swarm under two LoA.To the best of our knowledge, this is the first study to propose a digital-twin-enabled metaverse for scalable HSI. The contributions of the paper can be summarised as follows:The rest of the paper is organised as follows. Robot swarms, as with other types of automation, lack the human-like intelligence required to handle unforeseen circumstances . BecauseThe creation of mechanisms that permit smooth interactions between humans and swarm members is a major issue that limits the potential of human–swarm teams ,9. The mbehaviour selection, (2) parameter selection, (3) control via environmental signals, and (4) control through few swarm members. Swarm control via behaviour selection requires the existence of a library of behaviours for the human to select from such that the human acts as a supervisor who can intermittently interact with the swarm to switch between its behaviours. Kolling et al. [behaviour selection where a human can select a subset of the swarm and issue a command for behaviour switching to one of seven programmed behaviours. The results showed that novice human operators could easily use behaviour selection for swarm control. Walker et al. [behaviour selection to offer a high level of autonomy for the swarm, which they showed to be important in obstacle-cluttered environments. Nagavalli et al. [behaviour selection to achieve a given swarm formation  in shape-changing tasks. The timing of issuing the behaviour switching command was shown to be critical for task success; however, the human operators were able to learn to improve the timing of their commands over time [behaviour selection in controlling swarms of UGVs; however, behaviour switches are triggered autonomously with no human input.Studies on HSI sought to address the scalability issue by proposing interaction mechanisms that take the inter-dependencies between swarm members into account. g et al.  investigr et al.  used behi et al.  studied ver time . More rever time ,23 used behaviour selection has a number of advantages, including high levels of autonomy and ease of use by novice human operators. Nonetheless, behaviour selection requires all swarm behaviours to be programmed ahead, and it lacks adaptability to changing environmental conditions [behaviour selection is sensitive to the human operator’s perception of the swarm state and the timing of issuing a command for behaviour switching [Overall, as a mechanism for swarm control, nditions . Moreovewitching .Parameter selection is another class of control method that aims to give the human more control over the behaviours executed by a swarm. Similar to behaviour selection, the set of allowed models for swarm interaction needs to be programmed offline. However, the swarm models can be parameterised in real-time by the human operator to allow for more flexibility. Behaviour parameterisation can enable a wide range of swarm operations; for instance, Couzin et al. [parameter selection can be very difficult, as it indirectly affects the swarm’s emerging properties. Usually, parameter selection is performed at the stage of system development to choose a suitable parameter setting for a given task, either by manual parameter selection [n et al.  showed telection  or throuelection .environmental signals enables a human supervisor to insert environmental influences for spatial control. That is, the control is applied to swarm members within the region of the environment where the influence is inserted. Previous studies have investigated variants of control by environmental signals. Kolling et al. [environmental signals and behaviour selection for swarm control. In their work, the human supervisor would select one of the available behaviours and send it to one of the beacons in the environment. Beacons are dynamically placed by the supervisor, who also configures their range. A beacon would keep transmitting the human command it received so that swarm members passing through its range can listen to the command. Kolling et al. found that the performance of control via beacons was inferior to the case where the supervisor directly selects a sub-swarm to execute the command.Swarm control via g et al.  used a cenvironmental signals [Pheromones have also been used as a bio-inspired mechanism for swarm control via  signals ,27. Pher signals  studied few swarm members, where the human sends their commands  such that the behaviour of the virtual control agents eventually influences the physical swarm members.One of the key concerns of using control via le swarm  by comprle swarm ,34,36. Fle swarm . A few sle swarm ,40; howele swarm . This meAnother gap in the literature relates to the type of control agents. The vast majority of HSI studies used leaders for control, which typically assumes that swarm members are clustered in one group such that the leader’s influence can easily propagate between swarm members. Nonetheless, many tasks require the swarm to be scattered during some phases, such as in environmental monitoring  and targDifferent roles can be assigned to humans in HSI. Scholtz  presentsHuman performance is improved when they function as supervisors rather than operators, according to previous HSI studies ,45. On tDesigning easy-to-use interfaces is an important factor affecting the performance of human–robot teams . ClassicGesture interfaces have been successfully applied in HSI settings. Podevijn et al.  designedThe gesture interface proposed in  allows tRegularly performed tasks should be given to gestures that are easy to repeat, whereas less-frequent tasks can be given less-comfortable gestures.Comfortable gestures are those where the hands are close to the lower chest region and the body’s mid-line without being too far from the torso. The hands should not be wider or higher than the shoulders and no more than 45 degrees of shoulder flexion should be allowed to separate the hands from the body.Gesturing should not be required at a high rate and should not include hands striking against each other or against hard objects.Postures and motions for the wrist and forearm should be neutral. The set of comfortable wrist and forearm gestures is listed in .Postures and motions for the hand and fingers should be relaxed and should avoid the need for full extension.To ensure the effectiveness of gesture interfaces, it is important to design intuitive gestures that do not impose a significant physical workload on the human. Rempel et al.  provide Swarm control can either be proximal where the human co-exists with the swarm in the physical environment , or remoTraditional remote control settings, shown in The control flow is shown in Algorithm 1 and can be described as follows. The physical robot swarm is deployed in the operation environment to achieve a given goal. The simulated environment is initialised with an equal-sized swarm of digital twins in addition to one or more virtual control agents (lines 1–3). The models of the digital twins are set based on Algorithm 1 Swarm control in the proposed metaverseInput:    1:   2:   3:t ← 0   4:while t do   5:    t ← t + 1   6:       7:    updateDigitialTwinsData. Based on the design decision, the simulated environment can send the physical environment either the new positions of the digital twins or only the new positions of the control agents, leaving it to the physical robots to determine their next movement (lines 15–23). This design decision would depend on the available communication resources. In either case, and after action execution, the position and orientation of each physical robot are estimated and sent to the simulated environment such that the position and orientation of the corresponding digital twin are set accordingly. The next subsection provides more details on the role of digital twins in the proposed metaverse. This is followed by a discussion on setting the level of autonomy in the interaction between the human and the control agents, and a description of the shepherding model to facilitate the interaction between the control agents and members of the swarm.The role of the digital twins in the simulation environment can be explained as follows. The interaction between the control agent and the digital twins acts as a safety-net  that allows for verifying the impact of human commands before executing them in the physical environment. For example, the detection of potential safety risks  among the digital-twin robots could be used to prevent the execution of commands in the physical environment. Thus, it is important to frequently update the digital twins’ position and orientation information using their physical counterparts to continuously calibrate the digital twins when deviations occur in the physical environment. This will help avoid the accumulation of errors due to approximations and will ensure that interactions happening in the simulated environment closely align to those occurring in the physical environment.In our proposed metaverse, the human indirectly influences swarm operation via the control agents. The human interaction with the control agents can have different levels of autonomy. On the one hand, for the lowest level of autonomy, a human would tele-operate the control agents and direct their low-level actions. Low levels of autonomy could impose a significant workload on the human as, even with one or few control agents, the human still needs to observe and assess the states of all the swarm members, which can be very cognitively demanding. On the other hand, the highest levels of autonomy would allow the human to communicate the task objective to the control agents and then have no further interactions with them till the end of the task. Such fully autonomous operation is, however, not possible in realistic environments given the current state of technology  and is nMid-level autonomy would allow the human to have more influence whilst not fully controlling the control agents. This can be very useful to ensure the human stays within the control loop while avoiding increasing their cognitive load. Semi-autonomous swarm operations with mid levels of autonomy can be operationalised in different ways within the proposed metaverse. For example, a human can select high-level behaviours for each control agent using a library of pre-defined behaviours, can assign sub-swarms to different control agents, or can command the control agents using waypoints. Designing a suitable set of commands for controlling the control agents is of the utmost importance to ensure the human can effectively control the swarm. As discussed in n sheep GCM of the flock and collects GCM. This is achieved by setting the dog’s target position as follows:x at time t, and Shepherding is a bio-inspired strategy for the guidance of large swarms using a few control agents. In shepherding, a human uses a dog A sheep agent In the proposed metaverse, the virtual control agents assume the role of the dogs that can be controlled by the human to guide the swarm members (sheep). As discussed in To validate the proposed metaverse, we present a case study where we implemented and tested the metaverse in a swarm control task, as shown in The physical environment is a square environment with a side length of 2.9 m. Three physical Turtlebot-3 UGVs have been deployed in the environment. Each UGV is equipped with a Raspbian Jessie single board computer (SBC) with a Rasberry Pi 2 processor. The SBCs run Raspbian Linux operating system with ROS Kinetic in order to support communication with other devices. An overhead camera has been used to calculate the positions and orientations of the UGVs, similar to the positioning system used in . To achiThe symbiotic simulation environment has been implemented using Gazebo 9, a high-fidelity simulator containing models for various commercially available robotic systems. Gazebo 9 was running on a desktop computer with Ubuntu 18.04 LTS and ROS Melodic-Desktop-Full. The simulated UAV model employed in this work is the open-source AR.Drone 2.0 from the TUM simulator . A rotarThe GUI provides visualisation of the task state including the position and heading information of the UAV and the UGVs as well as supporting information to assist the human with controlling the swarm. The GUI is written as a We implemented two levels of autonomy to allow for different levels of human influence on the UAV operation. In the low level of autonomy case, the human controls the UAV by continuously sending commands to control the altitude  and the movement in the x-y plane . In the high level of autonomy case, the human sends one of these high-level commands: collect, drive, and hover. The collect command directs the UAV to autonomously apply the algorithm for collecting astray UGVs towards the GCM of all the UGVs  performed the task under the two levels of autonomy. For each level of autonomy, each operator underwent a training session to become familiar with the gestures. Each training session consisted of ten episodes where the swarm was fully simulated  such that the task is to guide all the simulated UGVs to the target area. The decision to run the training sessions in a fully simulated environment is to focus the human attention on learning the gestures without becoming occupied or confused by the complexity of controlling physical UGVs and the associated actuation errors that occur in a real environment. After each training session, the human performed twenty episodes under the same level of autonomy where the task involved both the simulation and physical environments. The mission objective was to use the virtual UAV to guide all the physical UGVs inside the target area. It is worth noting that the interface, including the GUI and the gestural communication, is agnostic to whether the task is completed in the simulation environment, the physical world, or in a mix of simulation and physical settings.Success rate (%) is the percentage of successful mission completions, such that the mission is considered successful if the GCM of the UGVs is inside the target area within a maximum of 10,000 simulation steps.Number of steps is the number of steps taken before the GCM of the UGVs becomes inside the target area. This metric reflects the time efficiency of the mission.UGVs travel distance (m) is the average total distance travelled by the three UGVs. This metric reflects the energy efficiency of the mission.Number of switches is the average number of switches between gestures. This metric reflects the psycho-physical load imposed on the human due to the required rate of issuing commands. Fixing commands is easy to manage mentally, but will put a restraint on the joints repeating the commands to the robot, while fast switching commands could increase both cognitive and physical loads.Four metrics have been used for evaluating the performance of the proposed metaverse as listed below:p = 0.015). That is, considering only successful episodes, the low level of autonomy required significantly more time than the high level of autonomy. Similarly, the low level of autonomy had a considerably higher number of gesture switches  than the high level of autonomy , with the difference being statistically significant (p < 0.001).p = 0.21). It is worth noting that this metric is calculated only over successful episodes. For some episodes, the low level of autonomy recorded high distances by the UGVs; however, it could not reach success, hence these episodes are excluded when calculating this metric. From these results, it is clear that the high level of autonomy results in higher success, higher time efficiency, and less workload on the human (indicated by the number of task switches). Looking at energy efficiency, the distance travelled by the UGVs is slightly shorter for the low level of autonomy case  than the high level of autonomy case ; however, the difference is not statistically significant . A number of challenges need to be addressed to enable the adoption of shepherding in various swarm applications. First, the use of few control agents to guide the whole swarm has been shown to raise security threats as several techniques exist for the identification of swarm control agents. Once identified, these control agents can be compromised and used to spoof the swarm. Second, UAVs have been used by previous studies to perform the role of the dog due to their superior speed and navigation abilities as compared to UGVs. Nonetheless, the deployment of UAVs can be challenging in many scenarios due to the need for specialised licensing, safety pilots, and compliance with aviation regulations.Our proposed metaverse enables us to use shepherding for controlling physical swarms while addressing these challenges. We use a symbiotic simulation environment that contains digital twins for individuals in a swarm in addition to virtual control agents. The use of virtual control agents negates the possibility of attacking the swarm by identifying them and compromising their operation. Virtual control agents also enable a simple way of guiding the swarm without requiring the use of actual physical UAVs. An additional benefit of using symbiotic simulation environments is that constraints on swarm members’ movements can be enforced by adding obstacles to the simulated environment. In the case study presented in To manage the human workload during the interaction with the control agent, it is important to design an easy-to-use interface for authenticating human commands and to select an appropriate level of autonomy for the control agent. To enable natural communication between the human and the UAV, our case study used gestural communication due to its intuitiveness and ease of learning. Our case study investigated two levels of autonomy: the lower one required the human to fully control the UAV operation; whereas the higher one enabled the human to interact through high-level commands. Our results align with previously published results on this matter by showing that higher levels of autonomy improve performance and reduce the workload imposed on humans.Incorporating the human element into swarm operations is deemed necessary to account for the lack of human-like intelligence. A promising extension to our work is to utilise advanced artificial intelligence (AI) techniques to assist humans with swarm control. For example, reinforcement learning has been previously used to autonomously guide simulated swarms . HoweverAnother important research direction is evaluating the proposed metaverse with multiple UAVs. This setting will increase the number of joint behaviours performed by the UAVs and might require extending the set of commands accordingly to ensure efficient control. Along similar lines, extending the metaverse to allow simultaneous control by multiple humans/teams could prove useful for dealing with high-workload scenarios. This might require extending the interface to accommodate human-to-human coordination by incorporating multiple communication modalities .


Optical fiber is a component of the green and sustainable internet. This paper analyzes the energy loss induced by the attenuation effect of electromagnetic waves during optical fiber propagation. The dynamics of the Hamiltonian, which was derived using the dynamics of the solution the Nonlinear Schrödinger equation (NLS) problem, were used to investigate the energy drop. In this study, the Newton-Raphson (NR) approach was used to establish the stationary solution of the NLS problem, and the fourth order Runge-Kutta method was used to evaluate the dynamics of the solution (RK4). In this study, numerous parameters are adjusted, including group wave dispersion, nonlinearity, attenuation parameter, and potential trap. The solution of the NR approach is fairly close to the analytical solution based on the analytical solutions. The dynamics of the NLS equation solution are greatly influenced by parameters. The obtained results reveal that for large attenuation parameter values, the strength of the propagating electromagnetic waves decreases quite quickly. The result also shows that the other parameters studied must be maintained at the best conditions to support the attenuation parameters and potential trap. This condition is an indicator in the choice of the fundamental material for producing optical fiber, which should have a low attenuation and dispersion effect. The NLS equation that will be used in this study can be written in the form of,Hamiltonian is explained by deriving from basic physical laws, such as norms and the conservation of energy. The law of conservative energy leads to vertex conditions and generalized Kirchhoff's rules 2.1α is zero The analytical solution of the NLS equation can be constructed if the two parameters in Eq. 2.2Eq. 2.3The RK4 method can be applied to the NLS equation by transforming the NLS equation into the form,3The Hamiltonian dynamics in this study were constructed using the dynamics of the solution to the NLS equation using the RK4 method. Before getting the dynamics of the solution of the NLS equation, it is necessary to find a stationary solution of the NLS equation using the NR method. The stationary solution of the NLS equation is used as an input signal which is then entered in the RK4 method which represents the propagation of electromagnetic waves in the optical fiber. The Hamiltonian obtained in this study represents the energy of electromagnetic waves propagating in the optical fiber. Meanwhile, the Hamiltonian dynamics obtained in this study were analyzed in order to pay attention to the effect of the various parameters on the energy of electromagnetic waves propagating in the optical fiber. The parameter values that are varied in the study are dimensionless, so that each result listed in this paper does not have units.3.1β and parameter γ which has a fixed value has been simulated as shown in The solution to the NLS equation without a trap potential (β. The greater the value of β, the wider the pulse of electromagnetic waves entering the optical fiber. This difference is indicated by observing γ affects the amplitude of the electromagnetic wave without affecting the pulse width of the wave. This is indicated by observing β and γ values are more precisely displayed in two dimensions in this simulation, demonstrating that the β parameter magnifies the pulse and the γ parameter is connected to amplitude.Changes in 3.2β and a constant value of parameter γ has been simulated as shown in The solution of the NLS equation in the presence of a trap potential β affects the amplitude and pulse width of the electromagnetic wave in the optical fiber. It can be seen in β, the solution of the NLS equation with varying values of parameter γ and parameter β which has a fixed value has been shown in γ affects the amplitude height without affecting the pulse width of the electromagnetic wave in the optical fiber. It can be seen in 3.3α, β, and γ for the case α and β are obtained as shown in We numerically study the dynamics of solitons in the NLS equation with several values of α and β. Based on the results that have been illustrated in β and α greatly affect the condition of the electromagnetic waves that propagate in the optical fiber. The effect of parameter β with a relatively large value on electromagnetic waves causes the electromagnetic wave pulses that propagate in the optical fiber to widen. Meanwhile, parameter α is very influential on the height of the electromagnetic wave amplitude with its relation to the intensity of the electromagnetic wave. The greater the value of α, the faster the electromagnetic wave loses its intensity. After getting the results of the dynamics of the solutions of the NLS equations for variations α and β, the dynamics of the solutions of the NLS equations for variations in the values of α and γ are simulated as shown in α dan γ. Based on γ only affects the amplitude of the electromagnetic wave when it enters the optical fiber. The dynamics of the solution of the NLS equation simulated in γ parameter causes a decrease in the amplitude of the electromagnetic wave at the beginning of propagation.α, β, and γ. The dynamics of the solution of the NLS equation for the case of α and β are obtained as illustrated in The dynamics of the solution of the NLS equation for the case of α and β. As has been simulated in β without spreading in all directions as shown in α and γ have also been simulated as shown in α and γ. As shown in γ only causes a decrease in the amplitude at the beginning of the electromagnetic wave. However, the decrease in the intensity of electromagnetic waves that occur when propagating in an optical fiber requires the same time span for each value of γ.3.4α, β, and γ are obtained as shown in The dynamics of the Hamiltonian NLS equation are analyzed in this study to analyze the energy of electromagnetic waves in the optical fiber with attenuation and dispersion effects. The dynamics of the Hamiltonian for the case without trap potential (α, β, and γ. The Hamiltonian dynamics shown in α, β, and γ. As can be analyzed through α. The influence of parameter β in β indirectly causes the electromagnetic waves propagating in the fiber to increase in energy, but the decrease in energy also increases with time. Meanwhile, parameter γ in γ parameter value causes its energy to decrease slowly. Parameter α causes a decrease in energy that occurs along the propagation of electromagnetic waves. The tendency of a high value of α causes electromagnetic waves to lose energy so that the amplitude decreases during propagation. The decrease in energy that occurs is caused by various factors, including the effects of attenuation, dispersion, and the interaction of waves with the medium during propagation. This indicates that it is necessary to review the selection of the basic material for making optical fiber to maximize the propagation of electromagnetic waves.α, β, and γ. From the figure, it can be analyzed that there is a fluctuation in the energy of the electromagnetic wave that propagates in the optical fiber in the presence of a trap potential and an increase in the energy of the electromagnetic wave. Each parameter that is varied in this case has the same effect as for the case without potential traps. The greater the value of the parameter β (see γ (see α causes electromagnetic waves to lose energy so that the amplitude decreases during propagation. The amplitude of the NLS equation is closely related to the intensity of the electromagnetic wave propagating in the optical fiber. When compared to the simulation results obtained in The second case in Hamiltonian dynamics is that the trap potential The results obtained show that for large attenuation parameter values, the decrease in the intensity of the electromagnetic waves that propagate occurs very quickly. This is an indicator in the selection of the basic material for making optical fiber, which is recommended to have a fairly small attenuation and dispersion effect. The obtained Hamiltonian dynamics decreased during propagation. This indicates that the attenuation effect causes electromagnetic waves to not be able to maintain their energy as they propagate. With the trap potential, the dynamics of the Hamiltonian of the NLS equation represents the energy of the electromagnetic wave which increases at the beginning of propagation and fluctuates during propagation. The effect of the attenuation parameters and the trapping potential on the nonlinear part makes the wave distance longer. However, based on the explanation of the beta and gamma parameters, the influence of these two variables will affect the intensity and diversity of the waves at the source. This means that these four parameters must be maintained in their best condition on a particular medium. This is an indicator that the use of potential traps in optical fiber has a higher efficiency than optical fiber that does not use potential traps. Based on the results obtained, the use of the main material for making optical fiber cores needs to be further reviewed on the effects of attenuation, dispersion, and nonlinearity of materials in order to obtain maximum electromagnetic wave propagation.4β only affects the pulse width of the electromagnetic wave that is the input signal. Meanwhile, parameter γ only affects the high amplitude of electromagnetic waves. In the case of a potential trap, parameter β affects the pulse width and increases the amplitude of the electromagnetic wave that becomes the input signal. Meanwhile, parameter γ has the same effect as the case without potential traps.A study has been conducted on the dynamics of the solution to the NLS equation and its Hamiltonian dynamics. First of all, we search for solutions to the NLS equation using the NR method. Based on the results obtained, it appears that the NR method used in this study produces a solution that is very close to the analytical solution of the NLS equation. In the case without potential traps, parameter α and β Whereas in the case without trapping potential, the dynamics of the solution of the simulated NLS equation shows that the intensity decreases but the trapping potential can minimize the dispersion effect on the optical fiber. This is obtained by observing that the electromagnetic waves that propagate in the optical fiber do not experience pulse widening and do not experience wave propagation. Thus, the use of optical fiber with a potential trap is highly recommended when compared to optical fiber without a potential trap.The dynamics of the solution of the NLS equation has been studied in this study numerically using the RK4 method. The dynamics of the solution of the NLS equation is carried out by inputting a signal in the form of a stationary solution of the NLS equation determined using the NR method. Based on the results obtained, in the case without trapping potential, it was found that the dynamics of the solution to the NLS equation which represents the propagation of electromagnetic waves in the optical fiber are dispersed and experience a decrease in intensity for large values of The dynamics of the Hamiltonian NLS equation have been studied in this study numerically by taking into account each energy during the propagation of electromagnetic waves in the optical fiber. Interesting things arise in the case of potential pitfalls. In the case of a potential trap, the dynamics of the Hamiltonian fluctuates. This is not the case in the case without potential traps. The attenuation effect in optical fiber causes the wave energy to decrease over time. Further studies need to be carried out in this area. This is needed as the development of nonlinear optical theory in order to get the best quality optical fiber.Harish Abdillah Mardi; Muhammad Ikhwan; Marwan Ramli, Ph.D: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Wrote the paper.Nasaruddin Nasaruddin; Nurmaulidar Nurmaulidar: Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.The authors declare no competing interests.