Most online tool condition monitoring (TCM) methods easily cause machining interference. To solve this problem, we propose a method based on the analysis of the spindle motor current signal of a machine tool. Firstly, cutting experiments under multi-conditions were carried out at a Fanuc vertical machining center, using the Fanuc Servo Guide software to obtain the spindle motor current data of the built-in current sensor of the machine tool, which can not only apply to the actual processing conditions but, also, save costs. Secondly, we propose the variational mode decomposition (VMD) algorithm for feature extraction, which can describe the tool conditions under different cutting conditions due to its excellent performance in processing the nonstationary current signal. In contrast with the popular wavelet packet decomposition (WPD) method, the VMD method was verified as a more effective signal-processing technique according to the experimental results. Thirdly, the most indicative features that relate to the tool condition were fed into the ensemble learning (EL) classifier to establish a nonlinear mapping relationship between the features and the tool wear level. Compared with existing TCM methods based on current sensor signals, the operation process and experimental results show that using the proposed method for the monitoring signal acquisition is suitable for the actual processing conditions, and the established tool wear prediction model has better performance in both accuracy and robustness due to its good generalization capability. Compared with the traditional manufacturing industry, the advanced manufacturing industry is moving towards intelligent development; however, there are many problems to be solved in the development of modern manufacturing. One problem is whether the tool status can be accurately monitored in real time. Tool wear is a common problem in precision manufacturing, which affects the productivity of modern high-speed computer numerical control (CNC) manufacturing greatly . Severe The main TCM methods are direct and indirect, respectively. Since the direct methods need to be shut down to measure the tool wear value, they cannot meet the needs of industrial applications. The indirect methods analyze relevant information collected from one or more sensors to estimate tool wear conditions by using a machine-learning technique. Since the indirect methods can implement online monitoring, it has been widely adopted. The most commonly used indirect monitoring signals include cutting force signal ,3,4, vibAlthough the change of cutting force is closely related to tool wear conditions, the installation of the force measurement system on machine tools is difficult or unfeasible during their machining. In addition, the force measurement system is expensive—these shortcomings diminish its usefulness in real industrial applications. Compared to the force measurement system, the vibration sensor can be installed easily on machine tools. Due to the source of the vibration signal, including the impact of cutting in and out, the friction between the workpiece and cutting tool, the chip fracture and the vibration of the machine tool, and so on, vibration information that is not related to the tool wear condition is difficult to filter. In addition, the position of sensor installation affects the monitoring result greatly. Due to this, it is difficult to use the vibration signal to monitor the tool wear state accurately. Compared with the vibration signal, the frequency of the acoustic emission signal is higher, and the interference of low-frequency vibration can be eliminated; however, the acoustic emission signal may exhibit nonstationary characteristics, even if the tool state and cutting parameters are unchanged. The chip fracture and the tool’s cutting in and out can affect the acoustic emission signal; therefore, the preprocessing and feature extraction of the acoustic emission signal related to the tool wear condition is exceedingly difficult. Since the characteristics of the machined surface image are closely related to the tool wear state, the feature extraction of the machined surface image can be used to judge the tool wear status. The machined surface image can be obtained by a vision-measuring instrument. For example, an industrial camera can be applied to capture the machined surface image. However, considering the influence of the cutting fluid and chips, it is difficult to achieve accurate online TCM.Compared with the above sensors, the motor current sensor is considered to be more suitable for the actual processing environment due to its relatively simple application and lack of installation effect on machining operations . In addiAlthough multiple sensors can get more information related to the tool wear condition than a single current sensor, the costs and the interference caused by sensors increases with an increasing amount of sensors; therefore, in recent years, some researchers have made some achievements in the application of single-current sensors for tool wear monitoring. For example, Akbari et al.  indicateAs one of the most commonly used signal-processing techniques, the wavelet packet decomposition (WPD) conducts a multi-level band division over the entire signal band and further decomposes the high-frequency band to increase the frequency resolution . Since tFor example, VMD has been used to extract features from the nonstationary Bluetooth transient signals to improve classification accuracy. According to the classification results, a higher classification performance is achieved when higher-order statistical features are extracted from band-limited modes in the implementation of VMD in the radio frequency fingerprinting of Bluetooth devices . RuichenThe commonly used classifiers for tool wear identification include artificial neural networks (ANNs) ,23, suppMany application cases have proved that the RF algorithm has higher prediction accuracy. Wu et al.  applied The remainder of this paper is organized as follows: Since the cutting experiment environment was a Fanuc vertical machining center, and Fanuc Servo Guide is a system debugging software, which can obtain the current amplitude of the spindle motor by setting the relevant conversion coefficient and conversion reference, the Fanuc Servo Guide software can be used to obtain the spindle motor current. One of the collected current signals based on Fanuc Servo Guide software is shown in Firstly, the Fanuc Servo Guide software was installed on the upper computer . Then, the upper computer communicates with the CNC machine tool through the ethernet-based transmission control protocol and internet protocol. As shown in The model of the Fanuc vertical machining center is CY-VMC850 , and the system is the Fanuc 0i-Mate MC system . The upper computer can read the internal data of the machine tool through the Ethernet interface of the system. Finally, after setting the sampling time and sampling frequency, the spindle motor current can be obtained by setting the relevant parameters of the current signal acquisition channel on the Fanuc Servo Guide debugging software. Compared with using the external current sensor to obtain the current, the upper computer directly reads the current data of the built-in current sensor of the machine tool through the transmission control protocol and internet protocol based on the Ethernet, which does not need to change the structure of the machine tool and does not affect the dynamic machining performance of the spindle. As shown in The signal with time as its independent variable is the most basic and intuitive form of expression. As the most basic detection method, the time–domain analysis can detect the status of some devices quickly and effectively.There is a correlation between the degree of tool wear and time–domain statistics features of the current signal. For example: under the same working conditions, the root mean square value of the alternating current (AC) signal increases with the increase of the tool wear degree; therefore, the statistical characteristics of the spindle motor current related to tool wear can be extracted by the time–domain analysis, and these statistical features can be analyzed and calculated to identify the tool wear condition to a certain extent.The output power of the spindle motor changes with the variation of tool wear degree, which is reflected in the spindle motor current signal. In our study, the time–domain statistics features of the current signal sensitive to tool wear were extracted as follows: mean value, root mean square value, kurtosis factor, and margin factor.Unlike the time–domain analysis, the frequency–domain analysis is performed to show the energy distribution of different frequency bands in the frequency–domain. There is also a correlation between the tool wear degree and frequency–domain statistics features of the current signal. For example, the frequency centroid reflects the position change of the spectrum centroid, the mean square frequency reflects the position change of the main frequency band of the signal, and the frequency variance reflects the energy distribution of a different spectrum. These frequency–domain statistics features change with the variation of tool wear degree. The frequency of the cutting vibration varies with the change of tool wear loss, which will be reflected in the frequency–domain of the current signal. In this study, the frequency–domain statistics features of the current signal sensitive to tool wear are extracted as follows: frequency centroid, mean square frequency, and frequency variance. The signal can be decomposed into several modal components by VMD. In the process of obtaining modal components, the frequency center and bandwidth of each modal component are determined by the iterative search for the optimal solution of the variational model, so that the signal can be adaptively divided in the frequency–domain and each component can be separated effectively. The constraint decomposition model of VMD can be expressed asThe iterative formula In Equation (3), Similarly, the center frequency in the frequency–domain is obtained, and the updated expression of According to the principle of VMD, the algorithm of VMD is to update all modal components in the frequency–domain and then transform them into the time–domain by inverse Fourier transformation. The procedure of the algorithm is as follows: The algorithm avoids the process of getting the local mean curve by using extreme points in the recursive adaptive decomposition algorithm, which results in evident inhibition on the phenomena of mode mixing among intrinsic mode function components after the empirical mode decomposition.Mode mixing means that similar characteristic time scales are distributed in different modal components. For example, adjacent modal components contain waveforms with the same or similar frequency components. In this study, the number of modal components was determined by combining the center frequency and waveform of the current signal after VMD. The results of the VMD show that the phenomenon of mode mixing occurs when the center frequency of each mode was close to each other or unevenly distributed.For one current signal sample decomposed by VMD, the central frequencies of the modal components corresponding to the number of different modal components are shown in For one current signal sample, the current signal waveforms after VMD under different K values are shown in When using VMD to decompose signals, the number of modal components should be set in advance. If the set number is too small, the signal cannot be effectively decomposed, which will affect the extraction of effective features. If the number is too big, it will cause mode mixing and also affect the extraction of effective features; therefore, it is necessary to ensure that the signal is decomposed sufficiently and that mode mixing cannot occur. The time–domain, frequency–domain, and VMD statistical features listed in In the time–domain analysis, four types of statistical features were extracted. The mean (The random forest (RF) algorithm is an EL method that builds a forest of decision trees from bootstrap samples of a training dataset. Every decision tree produces a response, given a group of predictor values. In every decision tree, each internal node represents a test on an attribute, each branch represents the outcome of the test, and each leaf node represents a class label for classification. Based on each decision tree and voting rules, the final classification result of RF is obtained.Since the training samples are randomly selected when the decision tree is generated, the optimal attributes when the nodes split in the decision tree are also randomly selected; taking into account the stochastic characteristics of the training samples and the randomness of feature selection, RF can ensure that it does not produce overfitting phenomenon in the classification.Many of the application cases described in Given the excellent recognition ability of RF, we implemented an RF classifier to identify the tool wear condition. The pattern recognition route is shown in The experimental setup is shown in The workpiece material and cutter material used in the experiment were low carbon steel and high-speed steel, respectively. The length, width, and height of the workpiece are 200, 100, and 40 mm, respectively. Cutting experiments under multi-conditions were conducted on a three-axis high-speed CNC machine (CY-VMC850). Since the material of the workpiece and cutter used in the experiment were low-carbon steel.The spindle motor current data were monitored in real time during each cutting test. The sampling frequency was 1000 Hz.During the test, new cutting tools were used to carry out the cutting test under experimental conditions. After each cutting test, the value of the tool wear was measured off-line using a microscope. Since the material of the workpiece and cutter used in the experiment were low-carbon steel and high-speed steel, respectively, and the processing condition was rough machining, the tool flank’s maximum width of the wear land (VB) reaching or above 0.5 mm was considered worn. The range of the tool wear value in different wear stages is shown in After the tool wear measurements, three different tool wear stages were obtained.A complete tool wear monitoring system includes the acquisition of monitoring data, feature extraction, and pattern recognition. Above all, the spindle motor current data collected by Fanuc Servo Guide software formed the raw data. The raw data were transformed into a set of statistical features supported by a machine-learning algorithm. The statistical features were input into the RF algorithm to identify the tool wear conditions.In machine learning, two-thirds of the input data samples were selected at random for model training. The remaining input data samples were used for model testing.In the process of tool wear recognition using RF, since the selection of training samples was random, it was necessary to carry out multiple classifications to evaluate the performance of the identification model. When the RF was used for classification, classification was repeated 10 times, the average value of 10 classification results was taken as the final classification result, and the variance of the 10 times identification results was calculated to evaluate the performance of the identification model.Under nine different experimental conditions, nine sets of tool wear condition recognition accuracy results were obtained. As an example, We know that various classifiers can obtain various characteristics in the area of pattern recognition. In this paper, the radial basis function (RBF)ANNs, SVM, and RF were used to identify the tool wear conditions, respectively. In this paper, the performance of the three classifiers was evaluated by the variance of the identification results and the recognition accuracy.In the existing research papers of online tool wear condition recognition, most researchers obtain the monitoring information related to tool wear through external sensors such as a stationary dynamometer, acoustic emission sensor, piezo accelerometers, industrial camera, and so on. Although they can realize the identification of tool wear conditions, the installation of these external sensors causes machining interference. Given this serious shortcoming, we propose a TCM method that can be applied to actual processing conditions and has a high prediction accuracy. Our work is summarized as follows:(1) We provided a deep review of past TCM methods. The analysis and comparison show that TCM based on the spindle motor current signal is an affordable, feasible, and effective monitoring method. Then, through experimentation, we compared our proposed method and other TCM methods based on the current signal analysis. The experimental results show that using our proposed approach for TCM is more suitable and effective for the actual processing environment.(2) The time–domain analysis, frequency–domain analysis, and VMD were jointly used to extract the sensitive features of the monitoring current signal, which is closely related to the tool wear condition. The experimental results show that the VMD has an excellent performance in processing the nonstationary current signal; the frequency band and energy features obtained by the VMD of the current signal are more sensitive to tool wear than that obtained by the frequently used WPD of the current signal.(3) Since RF can handle thousands of input variables without variable deletion, it improves the identification efficiency. Due to this, we chose RF for tool wear condition prediction. The prediction model was established by combining the sensitive features and RF. The results show that the established tool wear prediction model has a higher prediction accuracy, smaller variance, and better robustness.


The process of diffusion is central to the ever increasing entropic state of the universe and is fundamental in many branches of science and engineering. Although non-reciprocal metamaterials are well developed for wave systems, the studies of diffusive metamaterials have been limited by their characteristic spatial inversion symmetry and time inversion antisymmetry. Here, we achieve large spatial asymmetric diffusion characteristics inside a metamaterial whose material parameters are space- and time-modulated. Inside such a spatiotemporal metamaterial, diffusion occurs as if the material had an intrinsic flow velocity, whose direction is dictated by the relative phase between the modulations of the conductivity and capacity. This creates dramatic out-of-equilibrium concentrations and depletions, which we demonstrate experimentally for the diffusion of electric charges in a one-dimensional electrical system composed of an array of space-time-modulated variable capacitors and switches. These results may offer exciting possibilities in various fields, including electronics, thermal management, chemical mixing, etc. Being able to manipulate the temporal evolution and spatial distribution of diffusive quantities would provide exciting possibilities for applications. Here, the authors show that one can achieve large spatial asymmetric diffusion characteristics inside a metamaterial whose material parameters are space- and time-modulated. However, it can be shown that diffusion phenomena in homogeneous materials obey a parity symmetry, which means that diffusion, in homogeneous media, occurs identically along the positive and negative directions of a given axis2. One way to break such a symmetry has been shown to be the use of a moving medium; for instance, showing an asymmetric diffusion of chemical solutions within airflow3. Therefore, let us pose the following question: can we design an effectively homogenized material in which diffusion would have a spatially directional preference?Diffusion is a physical mechanism that dictates how a wide range of physical systems evolve in time. From the mixing of chemical solutions to the transfer of heat and the distribution of charge on a surface, all physical phenomena based on diffusion tend to an equilibrium. This steady state is ultimately dictated by the increase of entropy of the system with time. It has been established in the past that some special materials have the ability to diffuse differently along different axes, a phenomenon known as anisotropic diffusion4 or external magnetic fields for electromagnetic waves10. Also, the use of nonlinear materials provides a route towards nonreciprocity12. More recently, researchers in the field of electromagnetics have extensively explored the use of metamaterials whose effective constitutive parameters (permittivity and/or permeability) vary in space and time to allow non-reciprocal behavior17. These non-reciprocal wave systems can be used to achieve persistent near-field electromagnetic flow of thermal energy through coherent radiation18. However, in contrast to the laws that govern propagation of waves, the diffusion equation is inherently not symmetric with respect to a time reversal.In the context of wave propagation, researchers have achieved platforms that support the propagation of waves along a preferred direction by breaking the time-reversal symmetry of the wave equation. One way to do this is by introducing external mechanisms to bias the wave-supporting media such as medium velocity for the case of acoustic waves19 led researchers to explore the flow of heat through microscopically patterned structures, achieving effective infinite thermal conductivities with applications for cloaking20, negative effective thermal conductivities21, and heat flux guiding22. Exploiting a parallelism with transformation optics25, it was shown that, in general, heat can be manipulated analogously to light by microscopically designing the conductivity tensor of a metamaterial25. Recently, researchers have achieved motionless temperature profiles between two counter-moving fluids by exploiting the anti-time symmetry of the diffusion equation26.For the case of diffusion, the concept of metamaterialsIn this study, we introduce a paradigm to control those physical quantities that obey the diffusion equation. This is done using a metamaterial comprised of spatiotemporally modulated structures capable of breaking spatial symmetry. We apply homogenization techniques in such media to obtain effective parameters of conductivity and capacity. Such effectively homogenized material exhibits unprecedented control over diffusion features. Our proof-of-concept experiments demonstrate and verify our ideas. The concepts presented here may be applicable to any physical system governed by the diffusion equation.In the diffusion equation, the material capacity relates the potential  required to store a certain amount of the conserved quantity of interest  per unit volume and a conductivity term, which relates the transport of that quantity between two points of different potential. For the case of heat, the pertinent material quantities are heat capacity and thermal conductivity, whereas for the case of electric charge diffusion they are electrical capacitance and electrical conductivity.28, which in its most general form for the one-dimensional (1D) scenario can be written asDiffusion can be macroscopically understood in terms of Fick’s diffusion equationWe ask the following question: can we propose a medium over which the diffusion occurs in a “biased” asymmetric manner, thus breaking the diffusion spatial symmetry, as sketched in the right panel of Fig. t) and space . The parameters For that purpose, let us now consider a metamaterial composed of an infinite chain of miniaturized parallel capacitive elements connected by series finite-conductivity elements as depicted in Fig. mentclass2pt{minimmentclass2pt{minimmentclass2pt{minimThis homogenization results in two arguably unexpected outcomes. First, the effective velocity obtained in Eq.  depends 31.In the following, let us introduce two different mechanisms that take advantage of this effective velocity to produce large concentrations of the diffusive quantity. First, let us imagine a finite size metamaterial, which is insulated against the flow at both of its boundaries at which the electric current (or the heat flux) must therefore vanish. In the absence of biasing effective velocity, the charge density  will eventually come to equilibrium with a uniform distribution. However, if the biasing effective velocity is non-zero, charge  will be driven towards one end of the structure, accumulating until a balance is reached between the two forces acting on them: the diffusive force, which is trying to reduce the accumulation, and the force due to the biasing effective velocity, which pushes it towards the insulating interface. The stationary solution in this case takes the form of an exponential x direction, but in the following we shall prove that this fact will not play any role in the effective bias velocity of the metamaterial.To demonstrate experimentally a proof-of-concept of this phenomenon, we have constructed a 1D spatiotemporally varying metamaterial for the case of electric charge diffusion see Fig. . This stIn our setup, the first disk on one end of the sample  is connected to a voltage source that maintains a constant potential between the first rotor and the stators. The equations governing the temporal dynamics of the system comprised of a series of switches alternated with parallel capacitors can be derived analytically in terms of the Kirchhoff laws, with the spatiotemporally varying capacitances and switches following a traveling triangular function and a traveling square function, as summarized in Fig. Although the experimental setup is presented for the case of electric charge diffusion, an analogous device could be envisioned for the case of thermal energy diffusion. One way to achieve this would be to substitute the variable capacitors with closed gas reservoirs whose volumes can be externally controlled by means of a set of pistons. The reservoirs are connected by variable thermal resistors, whose value can be controlled by mechanically modifying the cross-section in contact with the neighboring gas reservoirs. In this case, the variable thermal capacitors would follow, in the limit of high modulation frequencies, a series of adiabatic compression and expansion cycles, which can be modeled using the specific heat ratio of the gas used.It is worth noting that due to the time modulation of the capacitance at any given node along the sample, the voltage at that point becomes also time-modulated even when the charge distribution has reached the steady state. However, we restrict our attention to the time-homogenized voltage, i.e., time-averaged voltage In the following, we investigate two elucidating cases of the degree of control over the charge diffusion in our experimental setup.In the first case, the effective velocity is chosen such that the charges are drawn from the source and accumulated at the opposite end of the sample. To achieve this, the relative phase between the spatiotemporal modulation of the capacitances and the switches has been chosen close to The theoretical prediction  effective velocity is the result of the time homogenization (over the modulation period) of the product of the oscillating terms from the two spatiotemporal variations of capacity and conductivity. If one considers the case in which these two have different frequencies and wavelengths, one can show that this would lead to a homogenized diffusion equation in which the effective velocity also presents a spatiotemporal dependence consistent with the difference in wavevector and frequency  between the spatiotemporal variations of the capacity and conductivity. With this, one can achieve sets of alternating points that accumulate/deplete any diffusive quantity  that can also move in time and space along the structure . As shown in Fig. Other exciting scenarios involve higher dimensions such as two- or three-dimensional metamaterials. One can imagine a planar spatiotemporal metastructure with the capability of accumulating diffusive quantities on a number of arbitrary points within the medium or at its boundaries. As a first proof of concept, we have simulated a two-dimensional, two-domain system in which a quarter of the plane presents a constant diagonal effective velocity, in the opposite direction to the other three quarters of the plane, as shown in Fig. 32.The approach presented here could be extended to systems in which the time-modulation is implemented via the propagation of waves, which interact with the medium modifying its properties as they advance. An example of this would be the propagation of pressure waves, which are already known to create thermoacoustic heat pumps when traveling through temperature gradientsIn summary, we have investigated a mechanism involving metamaterials with spatiotemporally variations of conductivity and capacity, allowing for the biasing and control of the diffusion phenomenon. By combining domains of these metamaterials, we have demonstrated the ability to create attractors and barriers for the diffusive quantities both at external and internal boundaries. This approach may find applications in various branches of science and technology involving diffusive quantities such as charges, thermal energy, and particles, among others.Supplementary InformationDescription of Additional Supplementary FilesSupplementary Movie 1Supplementary Movie 2


Finding genuine novelty in cellular structures is inherently difficult due to the numerous possible topological and geometrical configurations and their complex mechanical and physical interrelations. Here, we draw inspiration from the incredibly rich collection of crystallographic periodic networks that we interpret from a structural point of view to identify and design novel cellular structures with unique properties. We provide a ready-to-use catalog with more than 17,000 unique entries and show how crystallographic symmetries relate to their mechanical properties. Our work provides a foundation to support future applications in science and engineering, ranging from mechanical and optical metamaterials, over bone tissue engineering, to the design of electrochemical devices. The properties of periodic cellular structures strongly depend on the regular spatial arrangement of their constituent base materials and can be controlled by changing the topology and geometry of the repeating unit cell. Recent advances in three-dimensional (3D) fabrication technologies more and more expand the limits of fabricable real-world architected materials and strengthen the need of novel microstructural topologies for applications across all length scales and fields in both fundamental science and engineering practice. Here, we systematically explore, interpret, and analyze publicly available crystallographic network topologies from a structural point of view and provide a ready-to-use unit cell catalog with more than 17,000 unique entries in total. We show that molecular crystal networks with atoms connected by chemical bonds can be interpreted as cellular structures with nodes connected by mechanical bars. By this, we identify new structures with extremal properties as well as known structures such as the octet-truss or the Kelvin cell and show how crystallographic symmetries are related to the mechanical properties of the structures. Our work provides inspiration for the discovery of novel cellular structures and paves the way for computational methods to explore and design microstructures with unprecedented properties, bridging the gap between microscopic crystal chemistry and macroscopic structural engineering. Crystallographers were among the first to study the organizing principles behind the formation of patterns and distinct network topologies in solid materials and to relate them to their overall macroscopic properties , 2. Simi14To facilitate the design of novel microstructural architectures and to complement existing computational methods, in this work we systematically explore, interpret, and analyze the incredibly rich collection of crystallographic periodic network topologies from a structural point of view. We provide a ready-to-use unit cell catalog with 17,087 unique entries in total, offering a source of knowledge and inspiration for engineers and scientists by substantially extending the limited set of well-known unit cells from literature with crystal-network-based topologies. Our catalog and the results in this paper are based on the two publicly accessible databases Reticular Chemistry Structure Resource (RCSR) , 23 and In crystal chemistry, crystalline solids or crystals are solid materials with regular periodic microstructures. Their spatial arrangement is governed by the atomic forces between atoms, resulting in the formation of molecular networks. In theory, these molecular networks extend infinitely, and the representation of the intrinsic organizing principle of this microstructure is called the associated crystal network, or simply net . Due to The periodicity of an infinite crystal network allows for a compact encoding of its structural features based on the overall geometry of the unit cell and the position of the nodes and edges in the unit cell. The geometry of a 3D unit cell is specified by one of the 14 translational symmetry preserving Bravais lattices, which are spanned by three noncollinear base vectors describing the shape and the size of the unit cell. The spatial realization of a crystal network in the Euclidean space, i.e., the position of nodes and the edges connecting the nodes, is directly linked to the nodal positions of the atoms in the unit cell and the chemical bonds between them, and usually reflects the embedding with the highest symmetry possible. In the simplest case, the embedding is obtained by joining the nearest-neighbor nodes to form the edges, which corresponds to a sphere packing with ideally equal edge lengths. For more complex structures, the maximum symmetry embedding might be of lower symmetry, and equal edge lengths are not always possible. The sets of symmetry operations that constitute the final realizations of the nets are summarized in 230 space groups in 3D and are categorized with respect to point-symmetry operations and the underlying crystallographic systems. Since all possible configurations of periodic structures in the Euclidean space conform to one of the space groups, crystallography provides us with a comprehensive and concise mathematical description that we can use to construct and design cellular structures. In the this work, we use the program SYSTRE  with theThe two publicly accessible databases used in this work, the RCSR database  and the SI Appendix, Fig. S1). To estimate the property range of the cellular structures in the catalog and to identify topologies with extreme mechanical behavior, we compute and visualize the homogenized effective Young’s moduli, shear moduli, and Poisson’s ratios of all structures. The text-based unit cell catalog  shows an example from ref. Euplectella sp. The Euplectella sp. structure is composed of horizontal, vertical, and diagonal struts arranged in a square checkerboard pattern at the millimeter scale  shows a different type of hierarchical structure whose two-dimensional (2D) realization is the result of an inverse homogenization problem proposed in ref. er scale . The strSI Appendix). The inset at the top right in  crystal . Hence,  crystal , which i crystal . ConversInsets) show examples of structures with extreme deformation behavior under a compressive deformation in the z direction. The structure ort_Z04.0_R193 in the inset n1 expands in the y direction x direction y direction x direction y direction in this structure, while horizontal straight bars prevent large deformations in the x direction. Like the previously discussed decoupled stiffness, the combination of stretch-dominated elements such as straight bars and bending-dominated elements such as rhombic or scissorlike arrangements enables the decoupling of compliant deformation modes in anisotropic structures. The inset n3 shows the structure tet_Z03.8_E5841, which contracts in the x direction and in the y direction simultaneously. This structure is partly auxetic with Poisson’s ratios of Since structures with higher symmetry, that is with cubic or isotropic behavior, are of specific interest for researchers and engineers, we use the Zener index C11−C12)  to quantSI Appendix). The results show that the shear modulus and the bulk modulus, like in ref. We further search for structures with extremal properties for which the effective stiffness tensor e others . The eige others . These stafluids . The preIn summary, we explore the range of mechanical properties of cellular structures, which we obtain by interpreting the spatial arrangement of molecular crystal networks in the context of structural engineering. Our findings are based on the evaluation of 17,087 unique unit cells, which we provide as a ready-to-use catalog, including their geometrical and mechanical description, and visualizations of both. We show that the intrinsic organizing principles of microscopic nets provide a basis for finding well-known and novel cellular structures with tailored properties. We further show that extreme properties often originate from repetitive patterns based on simple geometrical features, which can be related to the underlying crystallographic symmetries. Finally, our work shows that crystallographic knowledge provides a rich source of inspiration for the discovery of novel cellular structures and creates search spaces whose exploration can motivate the design of architected structures with unprecedented properties for future applications across many research fields and length scales.SI Appendix). The global Cartesian coordinate system orientation is selected for convenience such that the three axes x, y, z coincide with what are the main crystallographic directions of a primitive cubic cell. Following this approach, our catalog of unit cell descriptions is created based on the decoding of a total of SI Appendix. The datasets generated and analyzed during the current study are available in the ETH Zurich Research Collection repository  . SYSTRE approach  based onpository , 27.Supplementary FileSupplementary File


The Medical Student Performance Evaluation (MSPE) is an important tool of communication used by program directors to make decisions in the residency application process. To understand the perspective and usage of the MSPE across multiple medical specialties now and in anticipation of the planned changes in USMLE Step 1 score-reporting. A survey instrument including quantitative and qualitative measures was developed and piloted. The final survey was distributed to residency programs across 28 specialties in 2020 via the main contact on the ACGME listserv. Of the 28 specialties surveyed, at least one response was received from 26 (93%). Eight percent of all programs (364/4675) responded to the survey, with most respondents being program directors. Usage of the MSPE varied among specialties. Approximately 1/3 of end-users stated that the MSPE is very or extremely influential in their initial screening process. Slightly less than half agreed or strongly agreed that they trust the information to be an accurate representation of applicants, though slightly more than half agree that the MSPE will become more influential once USMLE Step 1 becomes pass/fail. Professionalism was rated as the most important component and noteworthy characteristics among the least important in the decision-making process. Performance in the internal medicine clerkship was rated as the most influential while neurology and psychiatry performances were rated as less influential. Overwhelmingly, respondents suggested that including comparative performance and/or class rank would make the MSPE more useful once USMLE Step 1 becomes pass/fail. MSPE end-users across a variety of specialties utilize this complex document in different ways and value it differentially in their decision-making processes. Despite this, continued mistrust of the MSPE persists. A better understanding of end-users’ perceptions of the MSPE offers the UME community an opportunity to transform the MSPE into a highly valued, trusted document of communication. The residency selection process has never been so complex. Residency program leadership must sift through myriad resources about potential applicants in their decision-making process regarding whom to invite and rank for residency slots. In recent years, the total number of applicants, as well as the average number of applications per medical school graduate have increased in all specialties, making the process increasingly onerous . This inThe primary method by which undergraduate medical education (UME) institutions communicate with the graduate medical education (GME) community about student applicants is via the medical student performance evaluation (MSPE). The MSPE is one of the several resources used by program directors and others to make decisions regarding both interviewing and ranking candidates . The MSPAs a tool of communication between UME and GME, an important consideration for the MSPE is the perspective of the end-user, defined as a person who uses the document in the residency selection process. In 2019, we reported on a survey of MSPE end-users in Internal Medicine (IM) . Those fTM.The authors used responses from a survey distributed to IM programs directors to inform the development of a pilot survey. In addition to items on the utility of each section of the MSPE, questions about professionalism and the graphic presentation of clerkship grades were included. Items in the pilot survey consisted of both closed- and open-ended questions. A pilot survey was distributed via email to the GME community from the authors’ home institutions . The email included a description and an anonymous link to the survey, which was administered through QualtricsInfluence and Usage, Areas of Importance, and Suggestions for the future. During the time between the administration of the pilot survey and development of the final version, the USMLE announced the planned change in score-reporting for the Step 1 exam [The authors reviewed the results from the pilot survey (60 responses) and agreed on the final version of the survey through an iterative process (Appendix 1). Three sections of questions resulted: p 1 exam . TherefoTM in early 2020. A reminder was sent 10 days after the initial distribution, and 10 days following that. A single response per institution was included in the final analysis.To prepare for distribution of the survey to a wide audience, a panel of recipients was created using the 2019–20 program lists by specialty reports from the Accreditation Council for Graduate Medical Education (ACGME) website . All GMEDescriptive statistics are presented as the percent of respondents who chose the top two highest anchors on 5-point Likert questions. The data is presented as all respondents, as well as specialty-specific for the core clerkships (family medicine (FM), internal medicine (IM), neurology, obstetrics/gynecology (OB/GYN), pediatrics, psychiatry, and surgery) and specialties with a response rate of at least 15% of the programs surveyed. Two of the authors (JB and JBB) independently used content analysis to determine the presence of themes. Any differences were reconciled via conversation between JB and JBB. The data presented come from the final survey; pilot survey data is not included. Results of content analysis are presented by frequency of response.Of the 28 specialties surveyed, at least one response was received from 26 (93%) of them. A total of 364/4675 programs (8%) responded to the survey. Of the respondents, 24 (7%) were not directly involved in reviewing MSPEs and were thus removed from the analysis, leaving 340 included in the overall analysis. Of all programs listed on the ACGME website, response rates were the highest for physical medicine and rehabilitation (PM&R) (19%), emergency medicine (EM) (18%), pediatrics (15%), anesthesiology (13%), and OB/GYN (11%) . The majApproximately one third of all end-users stated that the MSPE is very or extremely influential in their initial screening process (32%), granting invitations for interviews (39%), and rank list decisions (35%). However, the priority of the MSPE in these roles varied amongst the specialties .Table 2.Trust of the MSPE’s ability to accurately represent an applicant varied considerably across specialties . SlightlThe importance of the individual MSPE components to the end user is displayed in . The proWithin the summary paragraph, the majority (79%) of respondents reported that the graphic representation of the applicant’s performance was very or extremely influential. Additionally, most end-users reported that the overall adjective or rank was very or extremely influential. Concluding comments of the MSPE is the least valued of the summary paragraph components .The importance of an applicant’s academic performance in the core clerkships varied by specialty . Every sRecommendations to make the MSPE more useful after USMLE Step 1 score reporting changes included: 1) reporting of comparative performance or class rank (54%); 2) greater transparency including comments addressing areas of improvement (21%); 3) inclusion of more objective measures  (21%); 4) broader standardization of the template (13%); 5) grades, including reporting of subcomponents (13%). Other suggestions mentioned, but with less frequency (<6%) included a request for earlier release, coinciding with opening of ERAS and the addition of more specific comments about clinical performance, possibly in a framework such as competency, EPA or RIME. The remaining comments were not able to be grouped into a theme due to low frequency.Despite the AAMC MSPE Task Force guidelines seeking to better standardize the preparation of MSPEs across institutions, this has not necessarily translated into standardized usage. The readers of the MSPE are a diverse group and our findings demonstrate that end-users from different specialties utilize the MSPE for different purposes and at different points along the residency recruitment process, from influencing initial screening of applications, to granting an interview, to preparing for the actual interview, and finally, when creating rank lists.In terms of the structure of the MSPE, end-users indicated that the noteworthy characteristics were not highly valued with approximately one-third of readers citing it as very or extremely influential. The identification of noteworthy characteristics is sometimes stressful for students, onerous for the MSPE writers, open to implicit bias, and not sufficiently consistent to allow for comparisons of students across schools . The infThe next section in many MSPEs, the academic history, is a snapshot of the academic program and outlines a timeline of the student’s advancement from matriculation to graduation, making it easy for end-users to identify gaps, adverse events, and remediation; thus it is not surprising that this information was valued to a great extent by respondents, more than double in comparison with noteworthy characteristics. With the overview that the academic history offers, readers are better equipped to search for explanations within the text for any student who diverges from the usual four-year progression.In many MSPEs, academic history is followed by a statement of the student’s professionalism. In responding to our survey, end-users across specialties identified professionalism as an element in which the MSPE could be most influential, particularly regarding lapses, but also when providing examples of positive behaviors. Our survey confirmed what is likely a fear of many medical school administrators – an acknowledgement that report of lapses could adversely impact a decision about the candidate . This diThe academic progress section offers readers a combination of grades, grading components, comparative performance, and narrative comments, typically focused on student performance in clerkships. In our survey, the academic progress section was valued more for the narrative comments and graphic representation of a student’s performance than how the grades were derived . This isrecommendation than a letter of evaluation. Omitting the summary may be a way to entice end-users to read and interpret the entirety of the letter rather than simply the conclusion [Finally, and in alignment with the literature , programnclusion ,23.In looking ahead, respondents overwhelmingly agree that the MSPE will become more influential following the change in USMLE Step 1 score reporting. Coincident with this, our data reveal that many end-users harbor a significant mistrust of the MSPE and have numerous suggestions for inclusion of additional data . Until tDespite the absolute number of survey respondents of 340, our study is limited by the low overall response rate as well as the variability amongst specialties that responded. Although our numbers per specialty were small, a strength of our study is the wide range of programs which responded, allowing a broad representation of specialties. We opted not to combine specialties into larger groups in order to best represent different approaches to the MSPE use. Our methodology of disseminating the survey to the contact person on the ACGME website was sound but identifying actual readers of the MSPE in each institution remains a challenge.Our study is the first to our knowledge to query end-users across a wide breadth of specialties to better understand how they use and value the components of the MSPE. It is also the first survey to look ahead and ask how the MSPE might change once USMLE Step 1 ends three-digit score reporting. End-users across a variety of specialties are a diverse group and utilize this complex letter in different ways and, depending on the specialty, value it differentially in their decision-making processes. Across all specialties, continued mistrust of the MSPE persists. With the impending loss of the USMLE Step 1 score as a discriminating metric, this tension may intensify. A better understanding of end-users’ perceptions of the MSPE offers the UME community an opportunity to transform the MSPE into a highly valued, trusted, and transparent method of communication as desired by the medical education community .


Osteoarthritis (OA) is a common problem in the older population. To reduce pain and stress in the affected knee joint compartment, a functional knee brace is often prescribed by physicians to protect it from high loads.An instrumented gait analysis should evaluate how the 4-point knee orthosis for varus or valgus load relief (M.4s OA) changes the kinematics of the knee, especially in the frontal plane.17 healthy participants took part and were analyzed with an inertial sensor system (MyoMotion) giving continuous, objective information on the anatomical angles. The measurements were made both without wearing a knee brace and with the brace in different settings.The results show a significant reduction in the maximum knee abduction and raised knee adduction. The knee brace, with a strong adjustment in varus or valgus orientation, caused a shift of maximum ab-/adduction in the proposed direction in 69% and 75% of the dynamic tests, respectively. The knee motion in the frontal plane shows individual movement patterns.The use of the brace leads to significant changes in the knee’s movement. Patient-specific movement patterns may explain different effects of functional knee braces on individual persons. Inertial sensors have been shown to be a low-cost, easy-to-use option for individual movement analysis and further personalized therapy. Osteoarthritis (OA) is the leading cause of musculoskeletal disability in most developed countries –4. The pSome patients of OA do not wish to undergo surgery, accordingly, it has been analyzed that after consultations with an adequate specialist and a biomechanical analysis, an effective, non-invasive treatment plan can be created ,6. CorreKnee kinematics is complex . It inclIn contrast to the knee, brace kinematics are less complex as it does not include a real floating axis . Braces Previous studies have pointed out that further dynamic investigation is necessary to prove the effectiveness of knee braces for OA treatment. In most cases, former investigations on this issue have only examined the immediate effect of valgus knee braces on aspects such as knee loading  and adduInertial Measurement Units (IMUs) are a low-cost and easy-to-use alternative method to complex static optoelectronic measurement systems for determining kinematic data . They coIn our study, the effects of a knee brace for the treatment of unicompartmental OA were investigated using an IMU approach, focusing on the brace’s influence on knee kinematics, especially in the frontal plane. Along with differences in kinematics, different varus and valgus adjustments and slippage of the knee brace can cause misalignment of the knee and brace rotation axes, which might influence the global knee motion. Our focus was on the frontal plane because this is where the ab-/ adduction manipulation took place and where the knee joint position change occurred. We hypothesized that the pressure relief provided by the varus and valgus knee braces causes adapted movement patterns like increased adduction in addition to movement restriction displayed by decreased knee flexion.2. Subjects with knee pain or problems or any other musculoskeletal or neurological diseases which could influence gait and posture were excluded. Healthy participants were chosen because in those cases the knee joint itself did not have any variations related to OA deformities ensuring our results would not be influenced by OA related parameters or effects. Without restrictions like pain, we were able to analyze the brace’s effect on the knee kinematics during activities like walking. Moreover, we were able to better compare our observations to the physiological knee function because testing on healthy patients allowed us to measure the effects of valgus and varus bracing on the same knee.A test setup was designed to study the influence a brace intended to reduce the load in the medial or lateral compartment of the knee joint has on the knee kinematics using an IMU system. There were 17 healthy participants with normal knee alignment included in this study; 13 men, 4 women, mean age of 28 ± 4 years. The mean weight was 77 ± 11 kg and the mean height was 180 ± 11 cm, resulting in a mean body mass index (BMI) of 24 ± 2 kg/ mWe used the 4-point knee orthosis M.4s  for varus or valgus pressure relief and stabilization . The M.4The tibiofemoral kinematic for both legs was acquired using MyoMotion, an IMU-system developed by Noraxon . The MyoMotion uses advanced, medical-grade IMUs that measure 3D motion with an accuracy level within 1 to 2 degrees of legacy camera-based systems –25. TheyTesting began with the calibration of the IMU-system by having the participant stand with their knees fully extended in a fixed and neutral position. Then, in the first step of dynamic testing, all subjects were instructed to walk 25 m at a self-selected, comfortable speed without a brace over a flat surface while the IMU-system collected kinematic data. Participants were advised to adopt a comfortable walking velocity instead of a default speed to minimize the amount of external influences and boundary conditions. In this way, the later addition of the brace would be the only difference between experiments. Dynamic testing with the brace was conducted in a similar manner. First, the brace was strapped in accordance with the manufacturer’s instructions. Then, the complete “system” (knee with a brace) was checked to ensure that both the femur and the tibia were correctly supported by the knee brace. Next, five different alterations of the brace were tested: one neutral, and a light or strong varus or valgus adjustment. The starting point for each adjustment was the neutral orientation, where no load should be applied to the knee. The light and strong adjustments were defined as a quarter and full rotation of the screw for pressure relief on the varus or valgus brace. The order of measurements was randomized and the brace was always worn on the right side. As a result of complete randomization, the numbers of participants with the same order of measurement conditions were unbalanced and in addition to their small number, no order effect was analyzed. All measurements were made individually for each participant by the same investigator, trained in using the MyoMotion system.Measurement data was systematically processed and analyzed using calculations made with self-written Matlab-scripts . In order to analyze the brace’s effect, it was critical to measure the knee’s kinematics, especially in the frontal plane (ab-/ adduction plane). First, the angle data  from all subjects was divided into single strides. Each stride began with the initial foot contact, followed by the stance phase, the toe-off, the swing phase, and ended with the following initial contact . Based oTo eliminate the influences of start and stop events, the first and last stride of each measurement was excluded. Since each subject took a different number of strides over the 25 m, 15 strides of each leg, were taken for analysis. Based on the mean angle curve of 15 strides over one gait cycle, the extrema were calculated for statistical analysis. Besides the statistical evaluation, these curves were also visually inspected and analyzed, in comparison with the angle course presented in previous literature and between the different participants.® SPSS Statistics . The normal distribution of the dependent variables was examined using the Shapiro-Wilks test and was not confirmed for most variables. Therefore, nonparametric tests were used. The effects of wearing a brace were evaluated by comparing results between measurements taken in a neutral adjustment, with and without the brace, using a Wilcoxon test. The effect size r is equal to Based on previous research reports, an appropriate sample size was determined ,16,17,19This research was approved by the Ethics Committee of the University Hospital RWTH Aachen and written informed consent was obtained. The research related to human use complies with all the relevant national regulations, institutional policies and was performed in accordance with the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board (EK 251/18).To evaluate our test setup and results, our data involving the right knee movement in the frontal plane during walking was compared with previous data from literature ,30–34 F.As the results of our test setup showed a strong correlation to existing data from previous literature, we concluded that using an IMU-system, a valid detection of the brace’s influence on the knee during walking was possible.In the first step of influence testing, to see the pure bracing effects, the movement of the right knee in a neutral position with and without the brace was compared . The desThe statistical pairwise comparison (Wilcoxon test) showed that the abduction  of the right knee was significantly reduced by the brace . In contIn order to analyze the effects of different brace adjustments in the frontal plane, the brace was tuned to light and strong valgus  or varusBy comparing the measurements obtained with the brace in neutral, light, and strong adjustments for valgus or varus pressure relief, we were able to analyze the effect of different brace adjustments on the gait cycle. When the brace was in a valgus setting, a significant effect on the maximum knee flexion, outward knee rotation, and ROM in the transverse plane was observed . A varusA valgus adjustment for the brace provides pressure relief by shifting load to the lateral condyles by increasing abduction and/or decreasing adduction. For a varus brace, the effect is reversed by load shifting to the medial condyles through increased adduction and/or decreased abduction. Adjusting the brace to different settings affects the kinematics of the knee, and in The first row presents the percent of cases where the maximum abduction is increased by a valgus adjustment and reduced by a varus adjustment. The second row lists the percent of cases where the opposite effects were observed for maximum adduction. The third row is the percent of all cases where any effect was measured. All cases are compared to measurements taken with the brace in a neutral setting.Analyzing the movement pattern of the knee in the frontal plane visually, we found individual patterns. Based on the curve progression of the ab-/ adduction angle, we were able to identify three different groups. The subjective classification is shown in Using a knee brace to support the mobility of OA patients is a common functional and clinical solution. This study provided a comprehensive description of the knee joint motion in a three-dimensional field while level walking without and with wearing a knee brace in different settings. Our hypothesis supports the observation of decreased knee flexion and adapted knee movement patterns in the frontal plane caused by varus or valgus pressure relief brought forth by the brace.To show the effectiveness of our measurement setup, we compared our reference data, measurements from healthy participants walking without a brace, to previously published data . The angOur results have shown us that wearing a knee brace significantly reduces the maximum knee abduction while increasing the maximum adduction. Consequently, the ROM of the knee in the frontal plane is reduced. Since this is the overall effect of the knee brace, the different effects with respect to either a varus or valgus manipulation can be explained Tables  and 3. ABy analyzing the effects of the knee brace on the complete knee movement in three dimensions, a significant reduction of the maximum abduction and in the ROM through the sagittal and transverse plane was discovered . These rWe analyzed the frontal knee movement in detail in an attempt to explain the different effects of the brace. As described before, the mean angle progression of the knee ab-/ adduction is comparable to previously published data . HoweverOur approach includes some inherent limitations. In contrast to previous studies, we decided to analyze healthy participants instead of ‘real’ patients. Therefore, we were able to analyze the effect of the brace and different brace adjustments on the knee joint itself, without confounding OA effects. However, we were not able to analyze the effectiveness of bracing on patients with OA or any accompanying long term effects. Since this was only a pilot study to analyze the bracing effect on healthy knee joints, the sample size was small with a majority of men. The limitations of our measurement setup using portable IMUs have already been discussed.As the number of patients with knee OA increases, finding an effective and low-cost treatment becomes more and more critical. Our results advocate the functionality and effectiveness of a knee brace for varus/ valgus pressure relief. Moreover, the measurement setup is shown to be a low-cost, easy-to-use option for detailed analysis of the individual effects of assistive devices. Such a solution is important, especially since our results show the individual effects of wearing a knee brace, like unique movement patterns and compensation strategies.S1 Appendix(DOCX)Click here for additional data file.S2 Appendix(DOCX)Click here for additional data file.


Transcatheter techniques for the treatment of tricuspid regurgitation (TR) are being more frequently used and several new devices are in development. Since 90% of patients with TR have secondary TR, catheter based systems which reduce the dilated tricuspid annulus area are of particular interest. In order to perform an annuloplasty procedure effectively and safely, knowledge about the anatomy of the tricuspid valve apparatus and especially of the annulus in relation to the important neighboring structures such as the aortic root, the RCA, the electrical pathways and the CS is fundamental. In addition, comprehensive understanding of the device itself, the delivery system, its maneuverability and the individual procedural steps is required. Furthermore, the use of multi-modality imaging is important. For each step of the procedure the appropriate imaging modality as well as the optimal; imaging planes are crucial to provide the necessary information to best guide the individual procedural step. In recent years, interest in the transcatheter treatment of tricuspid regurgitation (TR) has considerably increased. TR  is a common valve disorder that affects 65–85% of adults , 2. In ~. HoweverThe in-hospital mortality rate is currently 8.8% Isolated tricuspid valve procedures carry the highest risk of all valve surgeries Single center experiences with isolated tricuspid valve surgery are limited by small numbers The length-of-stay is relatively long: median 11 days (associated with higher costs) Pacemakers are utilized in a high number of patients undergoing TV replacement (26%) Tricuspid valve replacement, age >60 years, end-stage renal disease and coagulopathies are associated with greater in-hospital mortality In accordance with current guidelines , 17, 86%Since secondary  TR accounts for 90% of the cases in adults, annular dilation is a primary target for therapeutic transcatheter repair strategies. Consequently devices which reduce tricuspid annular dimensions are of interest.2; p < 0.01), and the mean vena contracta width by 28% ] with improvement in heart failure symptoms, quality of life and exercise tolerance after 6 months . The Cardioband is the only annuloplasty device with Conformitié Européenne (CE) mark approval. Results from the TRI-REPAIR (TrIcuspid Regurgitation RePAIr With CaRdioband Transcatheter System) study demonstrated a significant reduction in TR by reducing annular dimensions [the effective regurgitant orifice area was reduced by 50%  attached to the ventricular septum or to papillary muscles that, in turn arise from the ventricular wall. At the hinge of the leaflets, atrial myocardium may overlap the leaflet surface by 0.5–2 mm. Thus, normal valvular function requires not only normality of all the valvular components but also adjoining atrial and ventricular walls for sphincteric contraction and excursion of the orifice toward the ventricular apex, as well as interaction with the left ventricle through muscular continuity.It is underappreciated that the tricuspid annulus is not a robust fibrous ring which suspends the leaflets. Anatomically, the fibrous tricuspid annulus is indistinct and incomplete, especially at the segment corresponding to the RV “free wall” accounting for the potential dilatation in these regions whereas the “septal” segment is less prone to dilatation. The so-called annulus i.e., the hinge line of the leaflets normally circumscribes an almost oval and non-planar shape that becomes more circular as the RV dilates. Furthermore, its geometry can also be distorted e.g., in dilatation of right atrium (RA), RV as well as aortic root dilatation.Imaging protocols have arbitrarily divided into 5 segments the tricuspid annulus beginning with segment 1 in the region of the antero-septal commissure and going clockwise to segment 5 at the postero-septal commissure to assess the annulus  Figure . In thisThe border between RA and RV wall, the atrioventricular junction, is a wedge of tissue comprised mainly of epicardial fat intermingled with thin collagen and elastic fibers filling the atrioventricular groove . This tiThe atrial wall leading to the tricuspid orifice is termed the vestibule of the RA. Its endocardial surface is smooth, separating the pectinated appendage wall from the valve orifice . The porSupported by fan-shaped commissural chords, the commissures (or breach) do not reach the annulus but several millimeters of leaflet tissue remain sometimes in the form of small scallops. Although tricuspid by name, anatomically there are more commonly five leaflets . In addiAll leaflets have a basal clear zone usually devoid of chordal support and a rough zone where majority of tendinous chords insert to the ventricular surface. The rough zone occupying several millimeters from the free edge corresponds to the zone of coaptation that allows the leaflets to abut together and seal the tricuspid valve orifice .The septal leaflet, as its name implies, has multiple chordal attachments directly to the ventricular septum or to multiple small papillary muscles that insert to the septum that limit excursion of its movement to close the valvular orifice .As shown in From the postero-septal commissure, the annulus of the septal leaflet ascends superior to be anchored to the central fibrous body which comprises of the right fibrous trigone in the region of aortic-mitral continuity and the membranous septum. This part of the annulus marks the anterior border of the triangle of Koch which is the anatomical landmark for the location of the atrioventricular node and the penetrating bundle of His sitting at its apex. The posterior border of the triangle is marked by the tendon of Todaro while the inferior border is the vestibular wall anterior to the orifice of the coronary sinus (CS) . Where tNotably, where segment 6 transitions to segment 1, the septal leaflet extends laterally beyond the membranous septum at the antero-septal segment of the annulus, often appearing as a scallop that adjoins the anterior (aka antero-superior) leaflet at the commissure which is supported by the medial papillary muscle attached to the septomarginal trabeculation . Importantly, the annulus from the membranous septum to the antero-sepal commissure is related to the aortic root. On the epicardial side, the RA wall is only separated from the non- and right coronary aortic sinuses to varying extents by the transverse pericardial sinus b.The anterior leaflet is the most extensive around the annulus, covering segments 1 through 3, and also the largest, hence contributing the most to the closure of the valvular orifice. It is usually supported by a large anterior papillary muscle that attaches to the moderator band at its insertion to the RV free wall.Corresponding to segment 4, the posterior  leaflet is smaller, often supported by a cluster of slender papillary muscles. In some hearts the commissure between the anterior and posterior leaflets is indistinct, giving the impression of a bi-leaflet tricuspid valve while in some the leaflet is scalloped.In segment 5, the annulus from the postero-septal commissure to continue into the septal annulus runs anterior to the orifice of the CS separated by the vestibule. The distance of the CS orifice to the annulus varies from a few millimeters to 1.5 cm or more. The vestibule may give the impression of a shelf when the orifice is located more toward the septum. This segment of the vestibule is significant in that it marks the inferior border of the anatomical landmark used for locating the atrioventricular node of the cardiac conduction system. It is the target zone for slow pathway ablation in atrioventricular nodal reentry tachycardia as it harbors the rightward inferior extension of the atrioventricular node that usually runs close to the annulus  Figure b.The RCA runs within the tissues of the atrioventricular junction at variable levels relative to the level of the leaflet annulus. Its distance from the endocardial surface of the atrium tends to be closer when it courses into the inferior segment (1.8 ± 0.6 mm) compared to its antero-lateral course (5.3+1.3 mm) .The atrioventricular node at the apex of the triangle of Koch and the conduction bundle at the border of the membranous septum with the ventricular septum. Inferior extensions of the atrioventricluar node at the annulus close to CS orifice.Thin RA wall at vestibule surrounding the orifice.Location of the aortic root.The tricuspid Cardioband  con con28) cOnce all anchors are deployed, the implant delivery system (IDS) is detached from the band and removed. A leading wire stays in place and the size adjustment tool (SAT) is inserted over the wire and connected to the spool. The implant is then contracted stepwise depending on the band size between 3.5 and 5.5 cm under beating heart conditions. TR reduction is assessed in real-time (RT) by TEE monitoring until a satisfactory result is achieved. The implant is then detached from the SAT and the entire system is removed.Before a procedure the exact mechanism(s) of TR, the grade of TR severity, the precise dimensions of the tricuspid annulus, the localization and extension of calcification as well as relationships of the tricuspid annulus to surrounding structures (particularly the RCA), need to be evaluated. For each anchor position it should be confirmed, that tissue quality is adequate and that there is enough space between the hinge points of the leaflets and coronary vessels to guarantee safe anchoring. As a wire in the RCA is extremely useful for procedural navigation, patency of the RCA is important, and occlusion of this vessel should be excluded prior to the procedure. Furthermore, factors that may affect imaging quality during the procedure should be addressed see .The pre-procedural diagnostic work-up currently includes the following imaging modalities:TTE is the primary imaging modality to characterize tricuspid valve anatomy, valve lesion(s), valve function, to grade TR severity , 29, to The grading of TR is made according to current guidelines , 17 by uRT 3D echocardiography adds valuable information and supplements 2D echocardiography. By providing enface views of the tricuspid valve the number, size and mobility of leaflets, the attachment of the leaflets to the tricuspid annulus, leaflet coaptation, commissural opening, annular shape, and size can be evaluated during the cardiac cycle in a single view and 3D volumes can be provided –40.The imaging of the tricuspid valve with TEE is generally more difficult than the mitral valve (MV). The tricuspid valve is located more anterior and thus further away from the TEE probe. Secondly, the tricuspid valve inserts more apically than the MV. Deep esophageal views often have a poorer quality because the esophagus curves away from the heart in its distal segment. Thirdly, tricuspid valve leaflets are thinner than the MV leaflets and visualization is therefore more difficult and echo drop out artifact frequently occur. Furthermore, acoustic windows are limited and fibrous/lipomatous structures in the heart as well as any prosthetic material in the left heart , at the interatrial septum  or in the right heart  may cause acoustic shadowing or reverberations in the far field of the image and thus overshadow/obscure the tricuspid valve. Acoustic shadowing can usually be overcome in part by using trans-gastric windows, therefore it is important to check trans-gastric imaging quality and ensure, that the entire circumference of the annulus is visible prior to the procedure, optimally in supine position.2D and 3D TEE imaging of the tricuspid valve is described in detail in current guidelines  and statIn our experience, the most important TEE views to assess the tricuspid valve prior to a Cardioband procedure and to guide the procedure include mid- (4-chamber) and deep esophageal views at 0–10°, a mid-esophageal RV inflow-outflow view 50–70°), trans-gastric views and 3D enface views of the tricuspid valve as shown in 0°, transMDCT is the preferred imaging modality to depict degenerative calcium deposition in the tricuspid annulus. This is rare in the tricuspid compared to mitral valve disease and occurs usually secondary to diffuse cardiac calcinosis, in patients with longstanding severe kidney disease and chronic dialysis and in patients with chronic inflammatory diseases  , 43. HowFurthermore, MDCT is used prior to a tricuspid Cardioband procedure to measure annular dimensions, to define the position of the first anchor place, to select an appropriate band size, to evaluate the tissue quality and the distance to the hinge points of the leaflets and the RCA for each anchor region, to pre-define optimal fluoroscopic projections for a specific patient , and to CMR imaging is accurate and reproducible in the evaluation of RV morphology, size, and function and allows for the non-invasive assessment of blood flow, including stroke volume, cardiac output, pulmonary arterial distensibility and RV mass and can therefore play an important role in the decision-making process, particularly when TTE/TEE findings are ambiguous .2.A coronary angiography is needed prior to a procedure in order to exclude coronary artery disease. Especially the patency of the RCA should be ensured, since the placement of a coronary wire in this vessel considerably facilitates the navigation during the procedure Echocardiographic evaluation of pulmonary artery hypertension includes: a peak TR systolic velocity >2.9 m/s, an RV/LV basal diameter ratio >1, flattening of the interventricular septum in systole and/or diastole, an RV acceleration time <105 ms and/or mid-systolic notching, an early diastolic pulmonary regurgitation velocity >2.2 m/s, a pulmonary artery diameter >25 mm, an inferior cava diameter >21 mm with decreased inspiratory collapse and an end-systolic RA area >18 cmSevere TR may cause equalization of RA and RV pressures which can result in low TR systolic velocities, leading to underestimation of pulmonary artery systolic pressures by echocardiographic Doppler evaluation . ConsequIt can also result in underestimation of pulmonary artery mean pressures during right heart catheterization even in case of considerably elevated pulmonary vascular resistance. The measurement of pulmonary vascular resistance should therefore be included in the right heart catheter examination.The procedure is currently guided with 2D/3D TEE imaging in conjunction with fluoroscopy. Intracardiac echocardiography (ICE) has shown to be feasible for the guidance of some tricuspid procedures , 49 and Before starting the procedure 2D/3D TEE is used to re-assess annular dimensions and TR severity. This is of utmost importance as TR grade and annular dimensions are dynamic and can vary considerably in size depending on the volume status of the patient  which may be different at the moment of the procedure compared to the point in time when MDCT derived measurements for band size selection were made. Thus, the correct band size needs to be confirmed . In addiIn a first step, the transfemoral steerable sheath (TSS) with a dilator is introduced into the RA or directly into the superior caval vein (SVC) under fluoroscopic and TEE guidance by using a transfemoral venous access. In the next step, the implant delivery system (IDS) consisting of the steerable Guide catheter (GC) and the implantation catheter  is inserted and positioned in the SVC. These steps are best monitored by using 2D TEE bicaval views with x-plane imaging or alternatively 3D TEE views obtained from a bicaval view . The entIn general, 3D TEE enface views of the tricuspid valve are used to navigate the delivery system around the tricuspid annulus to the target region. Once an anchor point is reached, x-plane imaging or RT multi-planar reconstruction (RT-MPR) of a 3D data set is subsequently used to confirm contact of the IC tip to the annulus, adequate distance of the IC tip to the hinge point of the leaflets and coronary vessels, an adequate angulation of the delivery system in relation to the annular plane and satisfactory tissue quality for anchoring. After the correct position is confirmed by TEE and fluoroscopy, the anchor is screwed in and subsequently a tug- test is performed to ensure stable anchorage. During the tug- test attention must be paid to the annular tissue movement at the anchor point (visible in TEE), alternatively a relative movement between the GC and IC can be considered as an indirect sign of secure anchoring (visible in TEE and fluoroscopy). If the anchor position is satisfactory the anchor is released and by releasing the band the next anchor position is targeted. All further anchors are implanted in the same way along the tricuspid annulus. The procedural steps are illustrated in Once all anchors are implanted the IDS is retrieved and the SAT is inserted over the wire and connected to the spool. The contraction is performed step-wise and the effect on the TR grade and annular dimensions is monitored by TEE preferably by using x-plane imaging with color Doppler of the TR jet under beating heart conditions as shown in Before the device is detached from the SAT annular dimensions and the grade of TR are re-assessed in the same way as before and a coronary angiography is performed to confirm unlimited flow in the RCA. If needed, the band can be partially or completely released prior to detachment. If the result is satisfactory, the implant is detached from the SAT and the entire system is retrieved through the femoral vein.Complications may occur at any time point during the procedure. These include the formation of thrombi either in the cardiac chambers or attached to wires/catheters/devices, the occurrence of pericardial effusion/tamponade or a peri-device leak, anchor disengagement, injury of the RCA or cardiac veins including the CS, injury of tricuspid leaflets, arrhythmias, particularly higher grades of AV blocks, or RA/RV/defibrillator lead dislodgement. Thus, continuous, detailed and active TEE monitoring, as well as ECG and hemodynamic monitoring is required to immediately detect any of these complications.If pacemaker/defibrillator leads are present, certain questions must be answered:How many leads are present?Is one of the leads relevantly involved in the mechanism of TR?∘ If yes, the primary consideration should be to revise the lead to improve the TRIf a RA lead is present, where is the tip located?∘ Most RA leads are located in the anterior region close to the right atrial appendage. In this case it is usually easy to navigate the delivery system to the lateral side of the lead. If the RA lead is located at the lateral wall, it is necessary to insert the delivery system inferior to the RA lead to avoid any interference with the delivery systemWhere are the RV/defibrillator leads located at the level of the Tricuspid valve and are the leads mobile or attached to the annulus/to a tricuspid leaflet/to the RA lead?∘ In general, the delivery system should be navigated to the lateral/anterior side of the RV/defibrillator leads to avoid any interference∘ If a lead is mobile it is usually possible to push the leads toward the poster-septal commissure and to avoid any interference with the delivery system.∘ If it is not possible to navigate the system to the lateral/anterior side of the RV/defibrillator leads or if the lead(s) are attached to the annulus, to each other or to leaflets, a careful analysis should be done, to decide whether the procedure can be performed without endangering the pacemaker/defibrillator leads.Are there any thrombi attached to the leads?∘ Mobile thrombi attached to pacemaker leads are frequent and occur in up to 30% of patients undergoing ablation therapy . If a paSecondary TR is the most common etiology occurring in about 90% of patients with severe TR. Therefore, interventional approaches that target the mechanistic causes of secondary TR in the form of annulus reduction are particularly important. In order to perform an annuloplasty procedure effectively and safely, a good understanding of the anatomy of the complex tricuspid valve apparatus and especially of the annulus in relation to the important neighboring structures such as the aortic root, the RCA, the electrical pathways and the CS is fundamental. In addition, detailed knowledge of the device itself, the delivery system, its maneuverability and the individual procedural steps is required. Furthermore, the use of multi-modality imaging is extremely important. For each step of the procedure, the imaging modality and the optimal imaging planes that are best suited to provide the necessary information are essential to guide the individual procedural step and lead to a safe, successful, and effective procedure.All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.NW reports being a consultant and proctor for Edwards Lifesciences and a consultant for Bioventrix Inc. MA reports being a consultant for Edwards Lifesciences and Abbott Vascular and MS reports being a lecturer and proctor for Abbott Vascular, Boston Scientific, Philips Healthcare and Bioventrix Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Depth estimation of a single image presents a classic problem for computer vision, and is important for the 3D reconstruction of scenes, augmented reality, and object detection. At present, most researchers are beginning to focus on unsupervised monocular depth estimation. This paper proposes solutions to the current depth estimation problem. These solutions include a monocular depth estimation method based on uncertainty analysis, which solves the problem in which a neural network has strong expressive ability but cannot evaluate the reliability of an output result. In addition, this paper proposes a photometric loss function based on the Retinex algorithm, which solves the problem of pulling around pixels due to the presence of moving objects. We objectively compare our method to current mainstream monocular depth estimation methods and obtain satisfactory results. In contemporary research, the methods of monocular depth estimation based on deep learning are divided into the following six types: supervised, unsupervised, semi-supervised, conditional random field (CRF), joint semantic segmentation, and information-assisted depth estimation. In practical applications, the six methods overlap each other, and there are no strict boundaries. When monocular vision research emerged, many scholars trained neural networks in a supervised manner. In 2014, Eigen et al.  combinedConditional random fields (CRFs) have always performed well in the field of image semantic segmentation. Considering the continuity of depth values, researchers have begun to apply CRFs to solve depth estimation problems and have achieved some results in recent years . In addiDue to the particularity of monocular depth estimation, the supervised training of neural networks is often limited by the scene. Thus, to overcome the need for ground truth data, unsupervised training of a network is a popular research topic. The basic idea is to use either left and right images or inter-frame images, in combination with epipolar geometry and automatic encoders to solve the depth. Many scholars have begun to study the monocular depth estimation of unsupervised learning. Zhou et al.  proposedx and y represent two images to be compared, The current unsupervised monocular depth estimation studies used similar pixel value subtraction methods  in terms of photometric loss. The SSIM algorithm is shown in Equation (1)We think that photometric loss primarily affects the depth of the edge of the object in the image, which leads to an unclear depth map around the contour of the object. In addition, the current convolutional neural network used for monocular depth estimation has strong expressive ability, but it cannot evaluate the reliability of the output result. In this study, the variance of the training neural network was used to construct the uncertainty loss function equation. Uncertainty estimation has a long history in neural networks as well, starting with Bayesian neural networks. Different models are sampled from the distribution weights to estimate the mean and variance. This method is simple and effective. Many scholars have integrated uncertainty and neural networks ,23.An unsupervised depth estimation network based on uncertainty is proposed to improve the problem of low prediction depth accuracy in monocular depth estimation. This method of uncertainty learning solves the problem in which the convolutional neural network currently used for monocular depth estimation has a strong expressive ability but cannot evaluate the reliability of the output result. By modeling the uncertainty, the confidence of the estimated depth can be predicted while the model prediction accuracy is improved and the uncertainty of the output result is quantified.Retinex lighting theory is used to construct the photometric loss function to solve the interference problem caused by dynamic objects in the scene.In this paper, our main contributions are two-fold:Given two consecutive frames polation  is used polation . SimilarThe total loss function of the target network is:The basic theory of the Retinex algorithm is shown in The change in the moving object directly affects the reflected light of According to the basic theory of the Retinex algorithm, the expression is as follows:The single-scale Retinex algorithm is often used for image enhancement. We apply it here to the establishment of the monocular depth estimation loss function. The main principle of the single-scale Retinex algorithm is convolving the three channels of the image with the center surround function. The image after the convolution operation is regarded as an estimate of the illumination component of the original image.The process of using a low-pass filter to solve the incident component through a convolution operation can be expressed as:From a mathematical perspective, solving N represents pixels in the image.In summary, the photometric loss function can be transformed from Equations (7) and (8):Before regularizing the estimated depth map of the existing work, the smoothness loss needs to be added. We adopt the edge-aware smoothness loss used in , which iThe uncertainty of neural networks is generally divided into two categories: model uncertainty and random uncertainty. Model uncertainty mainly refers to the uncertainty of model parameters. When there are multiple models with good results, the final model parameters need to be selected from them. When the amount of input data is large enough, the model uncertainty is very low. In this paper, the training data were large enough, so the model uncertainty was not considered.Sensor noise and motion noise may cause the observation data to be inaccurate, resulting in random uncertainty. These observation noises cannot be eliminated by large-scale data training. We assume that the data have a Gaussian distribution when modeling random uncertainties, and the likelihood function is shown in Equation (10).According to Equation (10), we take the logarithm of both sides of the equation and solve the negative log likelihood function:N represents the number of pixels, The random uncertainty of heteroscedasticity assumes that the noise variance is variable under different inputs. For example, uncertainties such as the edges of objects and distant scenes are usually higher, while other positions are more reliable. Therefore, the objective function of learning is as follows:Depth estimation is a regression task. The most common loss functions for regression task optimization include the L2 loss function and the L1 loss function. The square operation makes the L2 loss function sensitive to outliers and it has a good optimization effect for large prediction errors, but has poor ability to further optimize for small prediction errors. The L1 loss function has a better optimization effect for smaller prediction errors, whereas the optimization effect for large prediction errors is general. The L1 loss function is slightly better in actual training. The uncertainty loss function proposed in this paper combines L1 loss and heteroscedastic random uncertainty in neural networks. In addition, the linear growth rate of the L1 loss makes it insensitive to loud noises, thus inhibiting adverse effects. The objective function of uncertainty can be expressed as Equation (14):To avoid the denominator being zero and to ensure the loss function has better numerical stability, the uncertainty loss function is transformed into:The software environment: Ubuntu 64-bit operating system, NVIDIA CUDA 9.1, NVIDIA CUDNN 7.1 and Python 3.7.0.Hardware environment: Intel(R) Core (TM) i7-7700 CPU@3.60GHz processor, Kingston 32 GB memory, and NVIDIA GeForce GTX 1080Ti GPU, 11 GB.For the depth network, we experimented with DispNet , which tTo objectively evaluate the proposed monocular depth estimation model, this paper uses the following five evaluation criteria to quantify the model:Average relative error (Rel):Root mean squared error (RMSE):Average log10 error (log10):Accuracy with threshold thr:We evaluate the evaluation model on the KITTI dataset . Figure The experimental results showed that the algorithm proposed in this paper is as effective as the state-of-the-art algorithms. Our algorithm is slightly inferior to  in termsIn this section, we verify the contributions of two innovations in this paper: luminosity loss and uncertainty analysis. We used the DispNet network for ablation study. The image resolution input in When the basic network part was optimized with Retinex, the error parameters of AbsRel, SqRel and RMS significantly reduced. We think that this occurred due to the reduction in the error rate of the proposed algorithm in the small part around the object, which also serves the purpose of constructing loss function Unlike the general regression task loss function, the uncertainty loss function proposed in this paper can not only estimate the depth, but also obtain the confidence of the estimated depth through the predicted variance. The smaller the noise variance, the closer the predicted depth to the real depth; the larger the noise variance, the higher the deviation between the predicted depth and the real depth. This paper proposed a method of monocular depth estimation based on uncertainty and a method of optical flow loss function based on the Retinex algorithm as a supervised network. The proposed method solves the problem of pulling around pixels due to the presence of moving objects. State-of-the-art performance is achieved on the KITTI dataset. In future work, we will focus on the effectiveness of unsupervised depth estimation in more complex scenarios.