This study lays the foundation for multi-particle detection and imaging systems in the context of range verification in PT.Particle therapy (PT) used for cancer treatment can spare healthy tissue and reduce treatment toxicity. However, full exploitation of the dosimetric advantages of PT is not yet possible due to range uncertainties, warranting development of range-monitoring techniques. This study proposes a novel range-monitoring technique introducing the yet unexplored concept of simultaneous detection and imaging of fast neutrons and prompt-gamma rays produced in beam-tissue interactions. A quasi-monolithic organic detector array is proposed, and its feasibility for detecting range shifts in the context of proton therapy is explored through Monte Carlo simulations of realistic patient models and detector resolution effects. The results indicate that range shifts of  As of the end of 2021, about 325,000 cancer patients have been treated in about 116 clinical PT facilities worldwide. The current trend is likely to continue in the foreseeable future as more facilities are either under construction (36 PT centers) or are in the planning stage (32 centers) worldwiderange uncertainties, arise from many different sources such as anatomical and density changes in the non-static patient and uncertainties associated with the estimation of stopping power in tissue2. The main motivation for developing systems for real-time range monitoring in PT is therefore to mitigate such uncertainties and thereby unleash the full potential of PT.The advantage of PT compared to the state-of-the-art RT with photons is attributable to the physical properties of charged particles where the ionization density is highest within a narrow range of depth, i.e. the Bragg peak. The sharp dose fall-off at the distal end of the Bragg peak is one of the major motivations for treating cancer with PT, as it allows for more conformal dose distributions that spare healthy tissue and thereby reduce adverse effects. However, in practice, uncertainties in the exact positioning of the Bragg peak preclude the use of the sharp distal dose fall-off. These uncertainties, referred to as 3. This ensures that the prescribed dose is delivered to the tumour, but at the expense of an extra dose to the surrounding healthy tissue. In addition, selection of beam angles is limited to avoid the risk of overshoots to high-risk organs5. Thus, it is highly desirable to increase the accuracy and adaptation potential of PT, especially for moving tumors and patients with implants or target regions affected by anatomical changes. Ideally, this would be achieved through treatment verification where the dose delivered by the incident particle beam—or at least the range of the therapeutic particle beam—is monitored during treatment. For pencil beam scanning, measurements would ideally be performed for each particle beam spot individually.Robust treatment planning is the current approach to reduce adverse effects of range uncertaintiesDuring PT, particles are fully stopped inside the patient and cannot be used for monitoring purposes. However, several production channels contribute to the generation of secondary particles: (1) electrons that contribute to the local dose deposition; (2) collisions with target nuclei leaving them excited, followed almost instantly by the emission of high-energy gamma rays ; (3) collisions with target nuclei that directly eject nuclear constituents such as protons (mostly stopped inside the patient) and fast neutrons .7; they are commonly based on a one-dimensional slit collimation9. Systems based on the Compton camera principle have also been proposed11, where successive interactions of the PG in absorber and scatter layers of a detector lead to event cones, enabling two- or three-dimensional reconstruction of the production sites. Furthermore, PG timing and spectroscopy systems have been proposed and tested under clinical conditions13.Devices detecting PGs to estimate their production location have been evaluated in clinical settings14, detection and imaging of FNs have been proposed to assess the neutron dose distribution in the patient. In another study by Ytre-Hauge et al.15, the use of a proton recoil telescope setup has been proposed to facilitate secondary FN detection and to use the available information for range verification in proton therapy. In another recent study, Lerendegui-Marco et al.16 discuss the combined measurements of PGs and thermal/epi-thermal neutrons with a pinhole camera. The study provides, however, no quantifiable insights into the potential benefits for range assessment purposes.While the use of PGs as potential range probes has been explored extensively, the same is not true for secondary FNs. In a recent study by Marafini et al.17. Only very recently, the PT community started shifting its focus to multi-modal detection systems19 without regards to more compact, hybrid systems that can be used for detection and imaging of multiple particle species simultaneously, reducing overall complexity and the clinical footprint.An important point is that an overwhelming majority of the state-of-the-art systems intended for in-vivo particle beam range monitoring rely completely on the detection of a single particle species with resulting limitations in counting statistics, making these systems essentially incapable of monitoring the range of mono-energetic pencil beam spots comprising a limited number of protons  and high resolution (14-bit) digitizers supplied with custom front-end electronics for signal shaping and amplification. Imaging of incident FNs will rely on double coincident elastic scatters on hydrogen nuclei, i.e.  scatters. The time-of-flight information between the detector segments will be used for determining the energies of scattered neutrons. For PGs, the imaging will rely on triple coincident scatter events that occur in distinct scintillator bars.In view of the above observations, and to the best of our knowledge, the current literature contains no discussion of hybrid systems combining measurements of PGs and FNs for the purposes of range probing in PT. To this end, the NOVO  collaboration proposes a novel technology that provides hybrid imaging of PG and FN emissions in PT. The proposed system is expected to provide a sufficiently high sensitivity to FNs and PGs as well as a much smaller footprint than the other state-of-the-art systems. The main building block of the envisaged NOVO system is a compact detector array (NOVCoDA) consisting of densely stacked, optically segmented organic scintillator bars with dual-ended light readout  investigations of the feasibility of using the NOVCoDA to detect controlled range variations in a virtual 3D patient model, and to determine expected sensitivities as a function of the required number of protons for mono-energetic proton beam spots and (2) investigations of the potential applicability of the NOVCoDA to detect treatment deviations in an example, realistic patient case with a locally advanced non-small cell lung cancer, using FN data only, PG data only, as well as the sum of FN and PG data. For both, true collision parameters obtained directly from MC models and collision parameters accounting for detector resolution effects were used. When using true collision parameters, the sensitivities and the capabilities concerning identification of realistic range shifts are reported for all three orientations of the NOVCoDA whereas only the lateral orientation is considered for the data sets incorporating detector resolution. This is justified by the fact that FNs are mostly emitted in the forward directionground truth distributions, the true 3D spatial coordinates of where successfully detected FNs and PGs originated from within the patient model were then obtained directly from phase-space files generated in MC simulations. Representative two-dimensional as well as one-dimensional projections of FN, PG and the summed production yields are shown in Fig. Firstly, for any imaging device used for the purposes of range assessment, the expected relation between signals extracted from the device and true range shifts must be quantified. In the MC simulations, the NOVCoDA was placed anterior, obliquely and laterally to the patient model, and the overall response to incident FNs and PGs was examined in all three orientations. Successful detection of an FN event required the incident neutron to collide elastically on hydrogen nuclei at least twice, whereas a successfully detected PG event required the incident gamma ray to scatter at least three times in the sensitive volume of the NOVCoDA, where the third scatter can be absorption or another scatter. To obtain The FN production predominates at shallower depths, whereas the PG production is more dominant towards the end of the beam’s range in the patient. Thus, imaging the points of origins of FNs and PGs in the patient may reveal complementary information on the overall radiological path of therapeutic protons.ground-truth distributions, the one-dimensional projected production distributions were then reconstructed from the simulated detector response using the LM-MLEM method  classifier was trained on bootstrapped projections for proton beam intensities between For the anterior orientation of the NOVCoDA, the The presented results are clearly in favor of the lateral orientation and a combination of the information obtained by both PG and FN data. Therefore, for the more realistic case in which the true MC hit data are smeared taking into account detector resolution , the corresponding calculations were performed only for the lateral orientation. The results are shown in Fig. The 4D planning CT of a patient with locally advanced non-small cell lung cancer was used to determine parameters of the incident proton pencil beam such that the beam stopped inside the the target volume. This example case was distinguished by a baseline shift, i.e. a change in the patient’s breathing motion pattern causing a shift and deformation of the tissue and lymph node metastasis inside the target volume, that was captured on the repeat 4D CT scan performed during the first treatment week.planning CT and the one week CT data-sets in conjunction with the GNB classifier. Upon training the GNB classifier and repeated calculations, the discrimination capability of the NOVCoDA in terms of the It should be noted that, in this case, there is no explicit information on the magnitude of the true range shift caused by this baseline shift; however, there is a distortion in the delivered dose from the primary pencil beam due to a change in the position of the tumor and, therefore, a change in the overall production distributions of both PGs and FNs see Fig. . The obsAlso for the clinical example considered here, the lateral , as well as a bootstrapping procedure applied to enable statistical analyses of the resulting RL distributions, show that the NOVCoDA provides the highest sensitivity at the lateral orientations  which is a vital component of such systems providing real-time or near real-time information on the dose delivery to decision-support systems. Although a number of state-of-the-art range-monitoring systems are now being tested in clinical settings, their relatively large clinical footprint limit their applications to certain treatment sites. The NOVCoDA with its reduced clinical footprint . Then, a best estimate of the incident FN energy can be calculated as For FNs, the non-relativistic kinematic reconstruction of event cones relies on two successive elastic scatters on hydrogen nuclei, i.e.  scatters. In the first scatter, the incident neutron transfers part of its kinetic energy to the recoiling proton. The transferred energy depends on the scattering angle. The scattered neutron will have its energy reduced. The scattered neutron then needs to undergo another  scatter in the sensitive volume of the NOVCoDA. The second  collision is used to determine the FN c is the speed of light, For PGs, the corresponding reconstruction of event cones relies on triple coincident collisions, mostly in the form of Compton scatter, in the sensitive volume of the NOVCoDA. This is because the incident PGs will typically have high energies and because the NOVCoDA consists of low density, low atomic number materials, meaning that photoelectric absorption is less likely to occur. Using Compton collision kinematics, one can arrive at:n (n = 1000 in this work) equi-spaced rays  collision data are smeared using realistic resolution characteristics of organic glass scintillator (OGS) samples. The true detection time of each event is smeared using a coincident time resolution (FWHM) of We determine so-called range landmarks (RLs) by taking one-dimensional projections of both the reconstructed and Monte Carlo (MC) ground truth distributions of PGs and FNs as well as projections of the summed distributions see Fig. E. The pr30. The sub-sampling bootstrapping algorithm, as implemented in this work, is described as follows: N, from the ratio of proton intensities. If N, is calculated as: Determine bootstrap sample size, For the ground truth distributions: From the entire data set, randomly sample coordinate values to fill an array of size N with replacement, meaning that the same data points from the main data set can appear multiple times in the sampled array.For the reconstructed distributions: Reconstruct the FN and PG distributions with LM-MLEM for the entire dataset once and construct a one-dimensional profile by taking a slice through the reconstructed 2D images that coincides with the proton beam axis. Re-scale the bin values as described in step 1. Re-sample each bin value from a Poisson distribution with a mean, Depending on whether the dataset to be analyzed is the MC ground truth distributions or the reconstructed distributions, the following steps were implemented: Calculate the RL for the data set sampled in step 2 by calculating the weighted average of the one-dimensional histogram.Repeat steps 2 and 3 for a fixed number of iterations to generate a distribution of calculated RL values. In this work, we set the number of bootstrap iterations to N, for a different proton intensity and repeat steps 2, 3 and 4 to get the RL uncertainty at varying proton intensities.Go back to step 1, and re-determine the bootstrap sample size, It is important to point out that the method described herein predicts that RLs, in line with the Central Limit Theorem, follow a Gaussian distribution, To determine The range shift determination relies on the calculation of RLs as explained above. The calculated 31. The implementation was done using python’s scikit-learn library32. The calculated RL values for a given particle species or their combination were labelled as belonging to a class corresponding to “no range shift” or “range shift” as the true labels of each RL value. The bootstrapped “no range shift” RL values were obtained using the original dataset without any dilation or erosion, and the corresponding “range shift” RL values were obtained using the dilated and eroded datasets at different proton intensities. The labelled RL values were then split into a training (80%) and a test (20%) set, chosen randomly. To avoid potential bias due to unbalanced datasets, the training of the classifier is done individually in each case. This is also supported by the fact that we are interested in determining the classification performance with respect to the original dataset at different proton intensities. As we only have one feature per class, the likelihood of each RL value to belong to one of the two classes is given as:A probabilistic classification of bootstrapped RL values was performed through a binary Gaussian Naive Bayes classifier (GNB)Then, the MAP (maximum a posteriori) estimate of the posterior probability and the most likely class (“no range shift” versus “range shift”) to which a new observation of RL values can be assigned is given as:Area Under the Receiver Operating Characteristic Curve  Toolkit v 1.1.3 : The patient body was threshold-masked, and subsequently the mask was eroded/dilated in 37 together with GATE v. 8.238, configured with the QGSP_BIC_EMY physics building list as suggested by Wrońska et al.39  was studied. Informed written consent was obtained from the patient and research was performed in accordance with the Norwegian Health Research Act and the Declaration of Helsinki. A 10-phase 4DCT was aquired for radiotherapy planning and during the first radiotherapy treatment week for this patient. Imaging was performed on a Big Bore CT scanner , using a Posirest-2 support device  for fixation in the supine position with arms resting above the head. The breathing curve for the 4DCT was acquired using the Philips Bellows device. For the treatment simulations we used the average intensity projections of the 4DCTs generated in Eclipse .A central point in the delineated gross tumor volume (GTV) was chosen as the target, and the two time points were registered to that point accordingly. A single pencil beam with sufficient energy to stop in the center of the GTV, i.e. The ability to separate the FN/PG production using the RL analysis analogously to the range-shift study was then evaluated.40.It should be pointed out that for both the clinical example described here and the data set from the “Lung CT Segmentation Challenge”, the gantry angle was at Supplementary Figures.Supplementary Figure 7.


The prediction of damage and failure to fiber-reinforced polymer composites in extreme environments, particularly when subjected to impact loading, is a crucial issue for the application and design of protective structures. In this paper, based on the prototype microelastic brittle (PMB) model and the LaRC05 composite materials failure model, we proposed a bond-based peridynamic (BB-PD) model with the introduction of plastic hardening of the resin matrix for fiber-reinforced polymer composites. The PD constitutive relationships of the matrix bond and interlayer bond under compressive loading are considered to include two stages of linear elasticity and plastic hardening, according to the stress–strain relationship of the resin matrix in the LaRC05 failure model. The proposed PD model is employed to simulate the damage behaviors of laminated composites subjected to impact loading. The corresponding ballistic impact tests of composite laminates were carried out to observe their damage behaviors. The PD prediction results are in good agreement with the ballistic experimental results, which can verify the correctness and accuracy of the PD model developed in this study in describing the impact damage behaviors of composite materials. In addition, the characteristics and degree of damage in composite laminates are analyzed and discussed based on this PD model. The difference in the impact resistance of composite laminates with different stacking sequences is also studied using the numerical simulation results. Fiber-reinforced composite materials are extensively applied in aviation, shipbuilding, military equipment, and automobile manufacturing due to their wonderful mechanical properties, such as high strength, modulus, fatigue resistance, and impact resistance. However, composite materials under extreme conditions, especially when subjected to impact loading, will inevitably appear damaged and fracture during their service life. Therefore, the damage prediction and analysis of composite materials is a critical issue when designing and using protective structures made from them.Ballistic impact tests can be used to directly observe and study the complex damage phenomenon of composite materials. Gower et al.  researchIn order to more systematically investigate and describe the damage and fracture behaviors of fiber-reinforced composite materials, many theoretical failure models have been proposed. The first type of failure model is the fracture criterion approach, which mainly uses classical material strength theory and focuses on the ultimate fracture limit of composite materials. The Hoffman criterion  is appliIn addition to the failure models described above, a series of failure models for fiber-reinforced composites have been proposed by researchers from NASA. The first proposed failure model is called the LaRC03 model , which iThe LaRC05 failure model divides the failure modes of composite materials into three types, namely matrix cracking, fiber kinking failure, and fiber tensile fracture, and establishes the failure criteria corresponding to these three failure modes. In the matrix failure, the failure mechanism is a brittle fracture, and the constitutive equation is linearly elastic when the resin is subjected to a tensile load. When subjected to shear and compression loads, the failure mechanism of the resin is yield fracture; that is, the resin first shows linear elastic behavior, then shows plastic hardening behavior until the applied load exceeds the shear or compression strength of the resin, at which point the resin will fracture. Regarding fiber kinking failure, this model believes that the reason for its occurrence is as follows: when the composite laminates are under axial compression loading, the high shear stress caused by the failure between adjacent layers cracks the matrix between the fibers, and the matrix splitting promotes the further bending of the fibers, which in turn leads to more matrix cracking. As a result of the combination of bending and compressive stresses, the bent fiber eventually breaks at both ends and forms a kink zone. Fiber kinking failure can be determined using a failure index equation; when the index is greater than 1, fiber kink failure occurs. For fiber tensile failure, the authors believe that the results predicted using the classical maximum stress damage criterion are in good agreement with the experimental results and therefore predict the fiber tensile fracture based on this criterion. The LaRC05 failure model contains many physical phenomena related to the failure process of fiber-reinforced composites under three-dimensional stress states, so the failure prediction based on this model fits well with the experimental results.Based on the strength criteria and failure models for composite materials, the finite element method (FEM) has been applied to the study of the damage and fracture of composite materials under impact loading ,17,18,19In order to avoid the difficulties of treating discontinuity problems such as damage and fracture to materials in terms of continuum mechanics, Dr. Silling developed a non-local theory based on the idea of non-local action, called peridynamic (PD) theory ,24,25. UIn recent years, the peridynamics theory has widely been employed to model the damage and fracture of composite materials. Xu et al. ,27 used Although the peridynamic theory has been effectively employed in composite failure prediction, the current PD model requires the introduction of plastic behaviors, which is essential when describing impact damage in composite materials . The preIn this study, a bond-based PD model that considers the plastic hardening stage of the resin matrix under compression loading for composite materials is established based on the LaRC05 model  and the x owns an interaction domain Hx with a radius of δ called the horizon, as shown in x and any material point x′ located within the interaction domain Hx is characterized by a vector function f, which is called the pairwise force function . f is given as followsThe PD theory assumes that in a reference configuration R, each material point x at any instant of time t in the reference configuration R can be expressed as 6. Each unidirectional lamina is composed of Kevlar49/epoxy with mechanical properties of E1 = 78 GPa, E2 = 5.5 GPa, and A rectangular composite laminate with the size of 100 × 100 × 6 mmAs a target model, the laminate was divided into According to the damage evolution of the front and rear surfaces, it can be observed that the laminate damage first occurred at the center of the front surface, as the compression stress wave generated by the steel ball impacted the target plate. Until During the damage evolution of laminate, we noticed an obvious characteristic: the damage on the front and rear surfaces of laminate always propagated along the fiber direction during the impact process, showing significant anisotropy and consistent with the conclusion in the literature . This isAccording to the change in cross-sectional damage to the laminate over time, the process and characteristics of delamination can be observed. At the early stage, when the steel ball impacts the target plate, the center of the impact surface is penetrated by the steel ball to a certain extent, and delamination damage begins to appear. At laminate ,48. Undelaminate ,48. Whenlaminate ,48.Through the above work, we can obtain the damage on the front and rear surfaces and the delamination in the thickness direction over time using the proposed PD model, which will provide an important contribution to the in-depth understanding and investigation of the behavioral characteristics and mechanical mechanisms of impact-induced damage to composite materials.Based on the proposed PD model, the dynamic mechanical behavior of composite laminates under different impact velocities will subsequently be investigated. The size and properties of the composite laminate model are the same as those in The analysis of However, when subjected to higher impact velocities like 300 m/s, 500 m/s, and 700 m/s, the damage to the laminates is significant at both the front and rear surfaces and far more dramatic than that under the lower impact velocities. It was observed that at 500 m/s and 700 m/s impact velocities, the damage along the fiber direction on the front surface was extended to the edge of the laminates. A strip of delamination with a width equal to the diameter of the steel ball was observed on the rear surface of the laminate, extending along the fiber direction of terature . This daIn this section, the impact resistance of composite laminates with different stacking sequences is studied. The layup configurations of laminates are It can be seen that layup configuration has a significant influence on the impact resistance of composite laminate. The damage on the front and rear surfaces of Compared with  uniform . The steThe damaged area on the front and rear surfaces of the terature . A reasoIn this study, a bond-based peridynamic model that considers the plastic hardening of resin matrix for fiber-reinforced composite materials was developed based on the PMB model and the LaRC05 failure model. A pairwise-force-updating algorithm was put forward to calculate the true bond forces of the matrix bond and interlayer bond with the plastic-hardening behavior. This PD model was employed to investigate the damage evolution and failure characteristics of composite laminates subjected to impact loading. Ballistic impact tests of composite laminates were conducted to observe the phenomenon and characteristics of impact damage. The simulation results, based on the model established in this research, match the experimental results very well. In addition, this PD model was adopted to investigate the impact-induced damage features of composite laminates under different impact velocities and with different stacking sequences. Some conclusions are given as follows.The developed bond-based peridynamic model can accurately describe the impact-induced damage behavior and evolution of fiber-reinforced composite materials. The PD simulation results for impact damage showed a good match with the experimental phenomena.The damage to composite laminates under impact loading is distributed and propagated along the fiber orientation, which shows significant anisotropy.The damage to composite laminates will become more and more severe with the increase in impact velocity. Compared with a low-impact velocity, the damage to the rear surface of laminates is more serious under high-impact velocity, and a strip of delamination is formed along the fiber orientation.The stacking sequence has a distinct effect on the impact resistance of composite laminates under the same impact velocity. For the angle ply laminate, increasing the fiber layup orientation will significantly improve its impact resistance.


Longitudinal optical field modulation is very important for applications such as optical imaging, spectroscopy, and optical manipulation. It can achieve high-resolution imaging or manipulation of the target object, but it is also limited by its depth of focus. The depth of focus determines whether the target object can be clearly imaged or manipulated at different distances, so extending the depth of focus can improve the adaptability and flexibility of the system. However, how to extend the depth of focus is still a significant challenge. In this paper, we use a super-oscillation phase modulation optimization method to design a polarization-independent metalens with extended focal depth, taking the axial focal depth length as the optimization objective. The optimized metalens has a focal depth of 13.07 μm (about 22.3 λ), and in the whole focal depth range, the transverse full width at half maximum values are close to the Rayleigh diffraction limit, and the focusing efficiency is above 10%. The results of this paper provide a new idea for the design of a metalens with a long focal depth and may have application value in imaging, lithography, and detection. To improve the performance of imaging systems, precise manipulation of the optical field is required. The optical field produces longitudinal field components when it varies along the propagation direction; these components have extraordinary optical manipulation capabilities. In the past few decades, people have extensively studied the longitudinal field components. For example, when the focusing of radial polarization light is used to enhance longitudinal field components, a special beam, namely a longitudinal polarization light needle ,2, can bHowever, one of the challenges in optical imaging is to achieve a high resolution and a long depth of field simultaneously. The depth of field is the distance range over which the image is in focus. A long depth of field is desirable for capturing clear images of objects at different distances from the lens. However, conventional lenses have a trade-off between resolution and depth of field: increasing the numerical aperture (NA) of the lens can improve the resolution, but it also reduces the depth of field. Therefore, there is a need for novel lenses that can overcome this limitation and achieve both high resolution and long depth of field.The methods for achieving extended focal depth that have been reported so far include Fresnel lens arrays (FLAs), axial lenses (AXLs) and light sword optical elements (LSOEs) ,7. HowevSubwavelength metasurfaces ,34,35,36In this paper, we design a polarization-insensitive metasurface based on titanium dioxide dielectric cylindrical unit structures, and use an innovative super-oscillation phase modulation method, which enables the metasurface to achieve near-diffraction-limit focusing performance and 22.3 λ extended focal depth under any polarization light excitation. The metasurface design method overcomes the limitations of traditional geometric phase structures, providing subwavelength metasurfaces with greater design freedom and stronger functionality. The metasurface has long focal depth and polarization-insensitive characteristics and has broad application prospects in imaging, lithography, and detection.The phase shift of the metasurface designed in this paper, which consists of cylindrical dielectric nanocolumn structures with rotational symmetry, depends on the transmission phase with polarization-independent characteristics. Therefore, in order to match the ideal phase obtained by calculation, we need to construct a phase library of nanocolumns. We use the commercial software package “FDTD Solutions”  to perform finite-difference time-domain (FDTD) simulation of nanocolumns and obtain the phase shift of nanocolumns when each geometric parameter increases by 2 nm. Periodic boundary conditions are applied along the x and y directions, and perfectly matched layers (PMLs) are applied along the z direction. The height, H, is fixed at 600 nm; the scanning range of the diameter of the nanocolumns is 80–310 nm; and the period of the properly arranged nanocolumn array, P, is 320 nm. As can be seen from In this paper, we first design the phase function of the super-oscillation lens. The phase function of the device can be divided into two parts: the focusing phase function The schematic diagram of the design in this paper is shown in The first part is the focusing phase, which can focus the optical field. This part of the phase function can be expressed as:The super-oscillation modulation phase function The specific design principle: using the point source method to calculate the intensity distribution of the axial diffraction light field, taking the depth of the focus  length as the objective function and then selecting the appropriate structure from the unit structure database obtained from simulation via the optimization algorithm. The formula for calculating the light field distribution via the point source method can be expressed using the following formula :(2)Ex0,yThe specific optimization solution process is shown in As shown in the flow chart: First, a database of the transmission phase and transmittance of the unit structure needs to be established, and then the designed metasurface is divided into N equidistant rings along the radial direction; N is 10 in this paper. Then, the phase variables in the optimization algorithm are added to each ring to construct a new ideal phase distribution. The optimization algorithm can choose any one of these: particle swarm optimization algorithm, cuckoo search algorithm, simulated annealing algorithm, genetic algorithm, etc. This paper uses the genetic algorithm.Using phase matching, we select the appropriate unit structure from the database and place it at the corresponding position of the metasurface to construct the complete structure of the metasurface. We use the point source method to solve the axial electric field intensity distribution of the metasurface and take the axial electric field depth of focus as the optimization objective function. At the same time, in order to ensure the position of the focal point, we set the position of the maximum value as 30 μm as a constraint condition to ensure the rationality of the design. Then, using continuous iterative optimization, we obtain the corresponding parameters of the design. For comparison, we first use a metasurface structure without super-oscillation phase modulation for calculation and obtain the simulation results as shown in When the superoscillation phase modulation is added, the optimized result is shown in After obtaining the corresponding design parameters, the full-wave simulation software FDTD Solutions was used to verify and obtain the corresponding results as shown in the following figure:By comparing the axial electric field intensity distribution curves of When the modulation is not performed with the super-oscillation phase, the depth of focus of the metasurface is 4.3 μm, the depth of focus is about three times greater after adding the super-oscillation phase modulation, and the resolution is also improved.This paper proposes a polarization-independent long focal depth metasurface structure using the super-oscillation phase optimization method. By combining the focusing phase and the super-oscillation phase as optimization variables, the focal depth of the metasurface is successfully increased to 13.07 μm (about 22.3 λ). The lateral full width at half maximum values in the whole focal depth range are close to the Rayleigh diffraction limit, and the focusing efficiency is above 10%. At the same time, this method uses the data in the fixed unit structure; unlike the topology optimization method, it does not need to change the shape of the structure, has more advantages in processing, and meets the conditions for processing and manufacturing. Compared with the traditional forward design style of long focal depth metasurface, the design method in this paper has a greater degree of freedom and is easier to control in terms of the relevant performance of the metasurface.The results of this paper provide a new perspective for the design of long focal depth metasurface and may find potential applications in imaging, holography and optical manufacturing.


These observations could improve our understanding of the characteristics of visual search behavior in parking performance and how this behavior is related to quality of life in elderly drivers.The aim of this study was to assess the characteristics of visual search behavior in elderly drivers in reverse parking. Fourteen healthy elderly and fourteen expert drivers performed a perpendicular parking task. The parking process was divided into three consecutive phases  and the visual search behavior was monitored using an eye tracker (Tobii Pro Glasses 2). In addition, driving-related tests and quality of life were evaluated in elderly drivers. As a result, elderly drivers had a shorter time of gaze at the vertex of the parking space both in direct vision and reflected in the driver-side mirror during the Forward and the Reverse phases. In contrast, they had increased gaze time in the passenger-side mirror in the Straighten the wheel phase. Multiple regression analysis revealed that quality of life could be predicted by the total gaze time in the Straighten the wheel phase ( Reverse perpendicular parking is a type of parking in which the vehicle enters the parking space from the rear at a 90-degree angle. This parking type has the advantage of higher spatial efficiency compared to parallel or angle parking . On the Visual impairment is related to poor driving performance. For example, the shrinkage of the field of view decreases the amount of information available for visual searching, leading to difficulties in vehicle positioning, a longer duration of maneuvering, and more frequent trajectory adjustments . ImpaireIn addition to the visual impairment itself, visuospatial information processing is also a critical factor in safe driving . GeneralAlthough the importance of visuospatial information processing in road driving is widely recognized, there is limited evidence during reverse parking. It is still unknown whether visuospatial information processing is presented during parking and how it contributes to backward maneuvering.It has already been reported that elderly drivers have less visual search behavior ,24, and The research gaps of this study include the following:To identify the visual search behavior characteristics of elderly drivers during reverse parking and compare these characteristics between elderly and expert drivers.To clarify how the characteristics of visual search behavior in reverse parking contribute to parking performance as well as QOL in elderly drivers.The main contributions of this study include the following:The findings of this study may provide the fundamental basis for building specific strategies for improving parking performance, analyzing visual search behavior during automated driving, and understanding the role of visual search behavior in the maintenance of driving and QOL in elderly drivers.The rest of this paper is organized as follows: Fourteen healthy elderly drivers  who visited the local driving school to renew their licenses were recruited. The inclusion criteria were (1) holding a valid driver’s license, (2) being without eye diseases, and (3) having the ability to follow commands. The exclusion criteria were (1) a clinical diagnosis of dementia and (2) having physical issues that affect driving. To identify the characteristics of visual search behavior in elderly drivers, data on 14 expert drivers  were also collected. This study was approved by the University Ethical Review Board for Medical Research Involving Human Subjects.The parking task was conducted at a parking space in a right-hand-drive vehicle equipped with double pedal devices on the passenger side. The elderly participants sat in the driver’s seat and were asked to adjust the seat position and mirrors, and instructed to drive to the parking area, enter the parking space, and then, return to the starting point. A driving instructor sat in the passenger seat to evaluate parking performance. Expert drivers conducted the same task without the evaluation of parking performance.As shown in An eye-tracking device  was used to measure participants’ visual search behavior during the parking task. The device was designed with a high-precision, ultra-light, and non-invasive head-tracking module that ensures comfort and freedom of behavior . The driBased on the concepts of previous studies ,21 and oElderly drivers’ driving performance was evaluated using six items by a single driving instructor: S-shape curve, changing direction, left turn, right turn, curve driving, and control of the steering wheel. The score ranges from 1 to 4 points: 1 = driving was unsafe, 2 = exhibited a couple of hazardous maneuvers, 3 = exhibited a few minor driving errors, and 4 = no obvious driving errors. The minimum total score is 6 and the maximum is 24.Driving attitude was assessed using two items: driving attitude  and driving confidence . The score ranges from 1 to 4 points: 1 = strongly disagree, 2 = disagree, 3 = agree and 4 = strongly agree. The minimum total score is 2 and the maximum is 8.QOL was assessed using WHOQOL-26. WHOQOL-26 assesses QOL in four domains including physical health, psychological, social relationships, and environment. Although the instrument captures multiple aspects of QOL, we only used the environmental domain as our interest was focused on the relationships between driving and QOL ,37. The The assumption of distributional normality was tested using the Shapiro–Wilk test, and we found that the data were not normally distributed. As a result, non-parametric statistics were applied. Differences between the elderly and expert drivers were examined using the Mann–Whitney test. Associations between visuospatial parameters and the number of attempts to park by the elderly driver were examined via Spearman’s rank correlation.p < 0.05 were considered significant.As our research aim was to know the contribution of visual search behavior in reverse parking, we selected visuospatial parameters, driving performance, and driving attitude as independent variables, and the environmental domain of WHOQOL-26 as the dependent variable. The analysis, therefore, was performed via a forced-entry linear multiple regression analysis ,40. The The results of correlations between the total gaze time and the number of attempts to park in the elderly drivers are shown in β = −0.45, p < 0.02), driving attitude , and driving performance ; the adjusted R2 value was 0.87 (The multiple regression model identified that QOL could be predicted by the total gaze time in the Straighten the wheel phase (was 0.87 . It is wWe found that the visual search behavior while parking was different between the two groups. Elderly drivers had a shorter time of gaze at the vertex of the parking space both in direct vision and reflected in the driver-side mirror during the early phases. In contrast, they had increased gaze time in the passenger-side mirror in the late phase. Moreover, multiple regression analysis revealed that QOL could be predicted by the lower total gaze time in the late phase, implying that visual search behavior is related to QOL in elderly drivers.Significant differences between groups in visuospatial parameters differed in each phase of the parking process. This observation is consistent with a previous study that compared visual scanning in the intersection. The study found that elderly drivers had a lower proportion of time scanning to the right than middle-aged drivers while approaching and exiting the intersection, although there was no age difference while approaching the median . AnotherElderly drivers gazed significantly less at the vertex of the parking space than expert drivers. The vertex of the parking space may play the role of the tangent point in our experiment. Previous studies suggested that the tangent point provides the driver with a visual pivot for planning a trajectory in the traveling direction, and the inside of the curve plays the role of a tangent point on curved roads . We assuConsidering the negative correlation between the total gaze time in the Forward phase and the number of attempts to park in the elderly drivers, the active visual search behavior in the earlier approach may contribute to better parking performance. According to a previous study, appropriate preliminary behavior in perpendicular parking improves the performance of the final alignment to the parking space . SkilledAnother meaningful difference was found in the parameter of the sawtooth pattern. The sawtooth pattern indicates a reciprocation pattern of oculomotor movement ,50. The The multiple regression model identified that QOL can be predicted using the total gaze time in the Straighten the wheel phase, driving attitude, and driving performance. The positive influence of driving attitude and performance on QOL and the negative influence of driving cessation on general health conditions and QOL are widely acknowledged ,54,55,56Several limitations should be acknowledged. Firstly, the parking space was always located on the driver’s side in this study, and therefore, the influence of the approach side was not considered. When turning at an intersection, the approach side between the driver and passenger sides could make differences in driving performances, such as speed variation or the stability of vehicle position . Visual Elderly drivers had a shorter time of gaze at the vertex of the parking space both in direct vision and reflected in the driver-side mirror during the early phases, resulting in poor parking performance. On the other hand, they increased their gaze time in the passenger-side mirror in the late phase, implying that a compensatory strategy was used to counterbalance the insufficient visual scanning in the previous phases.The lower total gaze time in the late phase is related to QOL. This observation could improve our understanding of the characteristics of visual search behavior in parking performance and how this behavior is related to QOL in elderly drivers.There are two main contributions of this research:


Anterior cruciate ligament reconstruction (ACLR) performed via arthroscopy is the primary treatment for anterior cruciate ligament injury. In traditional ACLR, the surgeon must create bone tunnels in both the femur and tibia, which increases the risk of bleeding and pain. The advent of all-inside technology has introduced the concept of bone sockets. However, the femoral socket created by the traditional all-inside technique is not a true femoral socket since the tunnel ends are still connected to achieve suspensory fixation. We are dedicated to achieving a true femoral socket in the all-inside ACLR technique. The AperFix Implant fixation system offers the potential for a genuine femoral socket by securely holding the ligaments in place through compression fixation. In this report, we present an all-inside ACLR using the AperFix Implant fixation system, which allows for a single exit of the femur side tunnel. This technique effectively reduces “windshield wiper” effect, “bungee cord” effect, as well as surgical time and minimizes the risk of bleeding, pain, and local microfractures. Introduction of improved all-inside ACLR using the AperFix fixation system. Because the ACL is closely related to the mechanical structure of the knee joint, reconstructive surgery is the most common treatment for the current rupture of the ACL. The purpose of ACLR is to replace the anterior cruciate ligament with a graft to maintain knee stability. When autologous tendon is used for ACLR, tendon diameter, fixation mode, and bone tunnel morphology are the key factors affecting the effect of ACLR. In conventional ACLR, tendons are commonly fixed by a cortical suspensory fixation button at the anterior cruciate ligament on the femur side and by compression screw suspension at the tibia side.An overview of our improved technique is shown in We reconstructed the anterior cruciate ligament with single autogenous semitendinosus muscle. In contrast to the traditional all-inside technique, where both ends were used for suspensory fixation, in this technical report, the femur side was fixed by the AperFix system , and the tibia was fixed by the traditional all-inside suspension method . First, the tendon of the semitendinosus tendon was removed from the affected knee joint A. The meThen, we made a combination of AperFix implant System, Tendon Graft, and Tibial Loop Complex. The thinner end was first threaded through 1 of the 2 holes of the AperFix implant systemA. EnsureThen we performed knot fixation of tendon graft ring structure. First, one of the sutures at one of the free ends of the semitendinosus graft was threaded through the loop of the tendon graft A. The suFirst, the true femoral socket was prepared. We then proceeded to immobilize the femur side of the complex. After positioning with an offset positioner(6.5 mm), a 2-mm guide needle was drilled, until it approached the cortex , A and BThe AperFix graft suspension device composite structure was implanted into the femoral socket through the anteromedial approach under direct arthroscopic vision. The entire AperFix implant body should be fully inserted into the socket and reach the socket bottom, as far as possible , A-C. ThThe assistant tensioned the traction suture and pulled the graft into the tibial socket under the direct vision of the arthroscopy , A and BACLR is one of the most important knee arthroscopy operation. With the increasing attention to sports, more and more patients suffer from anterior cruciate ligament injury. Patients with ACL injury usually need ACLR because of knee instability. ACLR’s approach is to replace the anterior cruciate ligament with autologous, allogeneic, or artificial tendons to maintain knee stability. In conventional surgery, a bone tunnel is required in order for the tendon to be delivered and secured to the anterior cruciate ligament.


When the first human leucocyte blood group antigen was discovered by Dausset in 1958, nobody could anticipate that was the beginning of a new and exceedingly fruitful research field in human medicine. Firstly, it became clear that this and a large number of other leucocyte antigens belong to the same genetic system. This system is the human leukocyte antigen (HLA) system, which acts as a primary barrier in organ transplantation. It was later discovered, which was even more surprising, that HLA is heavily involved in the development of a group of diseases.The HLA system is determined by genes located on the short arm of chromosome no. 6. The HLA loci constitute a genetic region called the major histocompatibility complex (MHC). The MHC encompasses genes (including HLA) essential to the integrity of the immune response. The HLA antigens have the function of controlling self-recognition and defending against pathogens.The HLA system's clinical relevance extends beyond infectious diseases to include autoimmune disorders and organ transplantation.The HLA frequencies vary widely across populations. Demographic factors and selection are suggested to have figured HLA variations across continents.The first study on HLA in Iraq dates back to 1977 when population HLA frequency was reported.12The author did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.The author has no conflict of interest to declare.Not applicable.The author designed the manuscript, reviewed the literature, wrote and approved the final draft, and is responsible for the content and similarity index of the manuscript.


We report a non-resonant piezoelectric microelectromechanical cantilever system for the measurement of liquid viscosity. The system consists of two PiezoMEMS cantilevers in-line, with their free ends facing each other. The system is immersed in the fluid under test for viscosity measurement. One of the cantilevers is actuated using the embedded piezoelectric thin film to oscillate at a pre-selected non-resonant frequency. The second cantilever, the passive one, starts to oscillate due to the fluid-mediated energy transfer. The relative response of the passive cantilever is used as the metric for the fluid’s kinematic viscosity. The fabricated cantilevers are tested as viscosity sensors by carrying out experiments in fluids with different viscosities. The viscometer can measure viscosity at a single frequency of choice, and hence some important considerations for frequency selection are discussed. A discussion on the energy coupling between the active and the passive cantilevers is presented. The novel PiezoMEMS viscometer architecture proposed in this work will overcome several challenges faced by state-of-the-art resonance MEMS viscometers, by enabling faster and direct measurement, straightforward calibration, and the possibility of shear rate-dependent viscosity measurement. Elevated viscosity of whole blood is also associated with diminishing renal functions4. The estimation of viscosity is also essential for monitoring the quality of lubricants during operation5. In chemical processing industries, the viscosity of the byproducts and the end product is used as a quality control measure. Currently, most of these applications utilise a rotating cylinder-based bulky instrument for viscosity sensing which is expensive, time-consuming, and incompatible with the paradigm of internet-of-things (IOT) based distributed and online sensing. The use of bulky equipment for fluid-property measurement are expensive, require large operating power, and are slower. There is a need for cheaper, low cost and in-line measurement techniques for accurate viscosity measurement without any post-processing. Moreover, there is much emphasis on the fourth industrial revolution (Industry 4.0) led by a large number of interconnected smart devices for self-monitoring6.At a fixed temperature and pressure, the mass density and the viscosity have unique values for a given fluid. Accurate characterisation of fluids using these properties is of immense importance in healthcare, processing industries, and liquid (lubricant) health monitoring. For example, in healthcare applications, the viscosity of blood plasma can be a marker for several conditions such as cardiovascular diseases and autoimmune disorders like rheumatoid arthritis12. Moreover, PiezoMEMS devices offer low-voltage operation and high electromechanical coupling and hence are suitable for such applications.Micro-scale solutions have emerged in the last decade to overcome the above challenges because they offer low cost, small footprint, and on-site installation for monitoring many properties and parameters. Piezoelectric MEMS resonators have become popular devices for the measurement of fluid properties because of their excellent ability to operate at a reasonable quality factor in a fluidic environment as evident from several publications over the last few yearsfr, and quality factor, Q, to estimate the density and viscosity of the fluid12. The obtained values depend on the fluid density and viscosity through secondary parameters13,Most MEMS-based fluid-property sensors use a single resonator (such as a cantilever) and track its resonance frequency, g1 and g2 are the secondary parameters which are a series expansion in terms of density, viscosity, and their products. For example, 13. This method is time-consuming and demands extensive post-processing of the experimental data. These single-cantilever systems suffer from large errors, particularly for viscosity measurement13, because changes in quality factor can be due to a complex combination of several factors including density, viscosity, acoustic damping, substrate damping, and temperature14. Moreover, the resonators used in the current viscometers are operated in higher-order modes to achieve a better Q-factor15, since higher modes have less energy dissipation16. However, at very high frequencies, viscoelasticity can affect the measurement results.In Eq. , g1 and 4. To overcome these challenges associated with SAW-based sensors, flexural modes of cantilever devices are actively being explored17.Another popular category of sensors for liquid property measurement is acoustic wave sensors. However, the response of the SAW-based sensors depends on the square root of the product of density and viscosity (Q-factor and associated complexity in the estimation of viscosity.We report a unique tip-coupled two-cantilever (TCTC) sensing system where the kinematic viscosity of any fluid can be obtained directly from the output parameters (velocity/displacement) of the device. Such a measurement technique offers a quick and direct measurement of viscosity. The use of two cantilevers in the proposed tip-coupled configuration allows us to eliminate the need for measurement of the The design of the viscometer mimics a conventional rheometer/viscometer where the test fluid is subjected to shear between a fixed and a rotating object (plates or cylinders). In the conventional rheometer, the relationship between the applied torque and the velocity of the moving object is used as a measure of the liquid viscosity. The sensor design used in this study consists of two micro-cantilevers integrated with piezoelectric, lead zirconate titanate (PZT) thin film as the active element. Figure 3 and 2.59 cSt, respectively. The frequency response of each cantilever shows two peaks corresponding to the cantilevers’ resonance frequencies. We observe two peaks for each of the cantilevers because, at the respective resonance frequencies of the individual cantilevers, there is enhanced fluid movement, resulting in more fluidic coupling between the two cantilevers.Although split electrodes were designed and fabricated on the cantilevers for simultaneous actuation and sensing of the response, the sensor output was corrupted due to the capacitive feedthrough between actuation and sensing electrodes. Due to this difficulty, the cantilevers’ vibrational responses were measured using a laser Doppler vibrometer (LDV), Polytec MSA-400. The active cantilever was actuated by applying a unipolar electric potential of 0.75 V across the top  and bottom electrodes of the PZT thin film while the sample was placed in a liquid (test fluid) filled petri-dish. The responses of the cantilevers  solutions. Figure 21. A fit model, aηb with the exponent b = 0.12, fits the experimental results. Such power law dependence results allow for a straightforward calibration of the sensor. This is considerably easier than the current resonant sensors where a Taylor series expansion of the hydrodynamic function is utilised for calibration requiring three or more experimental points13.Figure Q-measurement, thereby enabling faster measurements. Moreover, a frequency sweep away from the resonance may provide information on the shear rate dependence of the viscosity of the fluid. Figure This method enables the viscosity measurement without the frequency sweep and the requirement of any peak fitting for Since the viscosity measurement can be carried out at a single actuation frequency, it is important to discuss the critical factors for the selection of the actuation frequency. The two most important considerations for frequency selection that are discussed in this section are, (i) sensitivity, and (ii) the penetration depth of the shear waves generated by the oscillating active cantilever.m1 and m2 represent the effective masses of the active and passive cantilevers, respectively. The springs, k1 and k2 represent effective spring constants for the active and passive cantilevers, respectively. The dampers, c1 and c2 represent the damping coefficients associated with the vibration energy dissipation of each of the cantilevers. The fluid coupling can be incorporated in the model by introducing a coupling spring, kf and a coupling damper, cf. For an incompressible flow of fluid, the presence of the coupling spring, kf can be ignored. The damping coefficient cf for the coupling damper depends on the fluid properties. Please refer to the The cantilever system can be modelled as a two-degree-of-freedom spring mass-damper system, as shown in Fig. R) were calculated and plotted for different parameters. Predominantly, fluid density contributes to the added mass and viscosity contributes to the damping. The mass sensitivity, R with respect to m2, this sensitivity is valid for added mass also . Specifically, c2). The sensitivity is calculated for a cantilever exhibiting a resonance frequency of 34 kHz. It is well known that the response of the vibrating system is dominated by the damper only near the resonance frequency and hence we see that the amplitude ratio also follows the same trend.To understand the effects of fluid density and viscosity on the amplitude ratio, the sensitivities of the amplitude ratio  for fluid-property measurement. However, the lowest frequency that can be used will be dictated by the noise-required sensitivity for that particular measurement. Fortunately, the sensitivity of the device can be varied (if the application demands) by just changing the operating frequency of the device and designing the resonance frequency of the cantilever.δ22,ω is the frequency of oscillations and η is the kinematic viscosity of the fluid. The penetration depth of the shear waves follows an increasing trend with kinematic viscosity and a decreasing trend with frequency. Since the gap between the cantilevers is always fixed for a previously fabricated system, there can be an upper limit on the frequency and a lower limit on the viscosity.The transfer of energy from the active cantilever to the passive cantilever is through the shear waves generated by the active cantilever. The flow of shear waves created by an oscillating plate is governed by the characteristic length The concept of penetration depth also governs the gap between the cantilevers. Since there is an inverse relationship between the actuation frequency and the depth of penetration, as we increase the actuation frequency, the gap has to be reduced, to ensure effective coupling. The gap should be decided based on the minimum desired viscosity and maximum operational frequency.axb (with b < 1) dependence on kinematic viscosity. Such nonlinear dependence results in variable sensitivity in different measurement ranges. Since the exponent term in viscosity dependence is always smaller than unity, the sensitivity will follow a strongly decaying The amplitude ratio, which is the metric for viscosity measurement for TCTC viscometer, follows an with b <  dependenaxb, the sensor can be calibrated by performing two calibration experiments to obtain the two coefficients “a” and “b”. The precision of the sensor will be governed by the ability of these coefficients to capture the true viscosity values for other experiments. The expected curve for the dependence of the amplitude ratio on the kinematic viscosity of the fluid is shown in Fig. 13.Since the experimental curve follows a power law There are three modes of energy transfer from the active cantilever to the passive cantilever, namely structural coupling, coupling due to fluid flow, and acoustic coupling. The structural coupling has no effect on the viscosity measurement because it just adds a constant bias in the measured response. Both the acoustic coupling and the viscous coupling, affect the response of the passive cantilever. Moreover, both of these coupling mechanisms are affected by the kinematic viscosity of the fluid medium.22. The acoustic pressure wave, on the other hand, follows an exponentially decaying curve. The origin of these expressions is explained in the From a basic Stokes-flow assumption, the force on the passive cantilever due to the oscillations of the active cantilever should follow a The corresponding fit along with the experimental data points are plotted in Fig. aηb dependence on the kinematic viscosity of the fluid. Such a dependence allows for calibrations of the sensor using only two data points as opposed to four or more in the current MEMS viscometer. Another significant advantage of the TCTC viscometer is its ability to measure the viscosity of the liquid at different operating frequencies thereby allowing shear rate-dependent measurement. Although the test fluid used in this paper is a Newtonian fluid, the viscometer’s ability to measure viscosity at different frequencies is explained. We believe these initial results are encouraging for the MEMS community to explore the avenues of viscometry using TCTC design.The TCTC viscometer design presented in this paper utilises a novel two-cantilever architecture, where the fluid coupling between the tips of the cantilevers is exploited for viscosity sensing. This unique approach is a significant improvement over the current MEMS viscosity sensors, since it enables a direct, faster, and potentially, more sensitive measurement. The relative response of the passive cantilever follows a power law, In this paper, we have also presented an understanding of the energy coupling mechanism between the two cantilevers. It is proposed that in addition to the shear flow of fluid, the energy transfer between the cantilevers can also be due to the structural coupling (originating because the two cantilevers share a common frame) and due to the flow of acoustic waves. This hypothesis has been validated by fitting the experimental data to the appropriate expression which includes all three coupling mechanisms.Supplementary Material


This article was migrated. The article was marked as recommended.Many concerns have been raised regarding the impact of the changes to medical education as a result of the coronavirus disease 2019 (COVID-19) pandemic, particularly the impact of these changes on student assessments. This paper suggests an assessment clock as a conceptual model to enable medical educators to decide which assessment method is suitable under challenging circumstances, such as the COVID-19 pandemic. The assessment clock has five numbers, representing the five principles of the utility of assessment formula, which are arranged from the principle with the lowest weight (cost = 1) to the principle with the highest weight . The numbers are repeated in each half of the clock, and the clock is placed in the middle of two overlapping axes. The vertical axis is related to exam stakes (high or low). The low stakes condition, which represents the normal situation of running assessments at the beginning of each academic year, is placed at the top of the clock. The horizontal axis is related to the type of situation . The high stakes condition is placed at the bottom of the clock. The right half of the clock represents the normal situation of planning and conducting assessments, while the left half represents an emergency situation, such as the current COVID-19 pandemic. The assessment clock offers assessment planners insights into how to determine the most important assessment principles on which they should focus during a crisis situation. Moreover, it provides practical guidance for educators to help them decide which assessment tool is suitable for use in which situation. The rapid change of the coronavirus disease 2019 (COVID-19) from outbreak to pandemic has had significant consequences on education sectors worldwide, including medical education. Country-specific protective measures, such as social distancing, which aim to stop the spread of the disease, have led to medical school responses ranging from the total cessation of formal teaching and learning activities to the use of online/distance learning approaches  formula suggested by Van Der Vleuten , which iThe model is composed of a clock with placing the five principles of assessment utility in corresponding to o’clock number. They are arranged from the principle with the lowest weight (cost = 1) to the principle with the highest weight . The principles are repeated in each half of the clock, with cost appearing at one and seven o’clock, and validity appearing at 5 and 11 o’clock. Since the principle of education impact is important, it is fixed at the position for each situation . The clock is placed in the middle of two overlapping axes. The vertical axis is related to exam stakes (high or low). The horizontal axis is related to the type of situation .The low stakes condition, which represents the normal situation of initiating assessments at the beginning of each academic year, is placed at the top of the clock. The high stakes condition is placed at the bottom of the clock. High stakes assessments are usually held at the end of each academic year. The right half of the clock represents the normal situation of planning and conducting assessments, while the left half represents an emergency situation, such as the current COVID-19 pandemic, and the obligation to perform distance learning and assessment.Developed by the authorsThe clock can be used using in two different kinds of scenarios, as discussed below.•The first scenario Medical schools are bound to an academic calendar, which includes many teaching and assessment activities, and assessments are assigned fixed dates in that calendar. When developing a low stakes exam, such as the formative assessment, which is usually done through e-learning platforms , attenti•The second scenario Many schools are struggling to make decisions on how to conduct high stakes exams remotely in the emergency situation created by the COVID-19 pandemic. First, attention of school leaders was on the acceptability of the tools that will be used by the assessors and the learners and cost issues . Regarding acceptability by students, it is an essential matter especially as there is a sudden shift to online summative eAssessment for the first time. So, it needs familiarization and explanation to students. Considering cost, conducting online assessment are costly because consideration of fidelity and security issue .In other words, they were concerned with selecting the most suitable and most cost-effective online assessment tool, which would provide a fair environment for all students. Validity and reliability , which are the most important principles for high stakes assessments, should not be neglected in an emergency situation. These principles could be maintained by using high-quality items from existing question banks at colleges.For example, regarding assessing clinical competencies, only the cognitive parts of clinical competencies-such as clinical reasoning and communication skills-could be assessed during this period. Some colleges have used an objective structured video exam (OSVE). Studies have shown that OSVE is efficient, quick to administer and reliable and have demonstrated some evidence of its validity .In the current COVID-19 pandemic situation, medical schools worldwide have been required to make major changes in assessments, e.g. conducting remote assessments. This shift represents a real challenge for medical educators, who must prioritize assessment criteria based on a conceptual framework in order to choose the most suitable assessment tools and instruments. The assessment clock model can help in applying that conceptual framework.In an emergency situation in which remote assessments must be conducted, assessment designers should use the assessment clock model to:•evaluate the resources available to conduct remote assessments;•focus on acceptability and feasibility, which are the first principles considered during a sudden transformation; and•.remember to consider validity and reliability.Majed Mohamed Saleh Wadi is a senior lecturer of Medical Education, College of Medicine, University of Qassim, KSA. He is the Head of Medical Education Department. Head of the Assessment Committee. ORCID iD:https://orcid.org/0000-0002-8117-770X.Mohamed Elhassan Abdalla is an Assistant Professor of Medical Education at the College of Medicine and Medical Education Centre, University of Sharjah, UAE. He is the director of Medical Education Centre, chair of the curriculum committee. ORCID iD:https://orcid.org/0000-0002-9241-1370.Husameldin Khalafalla is an Assistant Professor of Community Medicine and Medical Education at the College of Medicine, University of Jazan, KSA. ORCID iD:https://orcid.org/0000-0002-7643-6180.Mohamed Hassan Taha is a visiting Assistant Professor of Medical Education at the College of Medicine and Medical Education Centre, University of Sharjah, UAE. He is the head of the Faculty Development Committee. ORCID iD:https://orcid.org/0000-0003-0808-5590. This review has been migrated. The reviewer awarded 4 stars out of 5 This interesting article addresses the dilemma of the assessment during the COVID-19 pandemic, the developed "clock" helps in the planning of the assessment, however, it would be an added value to mention more examples.Reviewer Expertise:NANo decision status is available This review has been migrated. The reviewer awarded 3 stars out of 5 This is an interesting article describing the use of an assessment clock to prioritize the utility of principles of assessment formula in emergency situations like the current pandemic. Their diagram of and description of the clock is clear. The authors mention that the clock can be used for both low stakes and high stakes exams and in normal practice and in emergency situations. However, I am still not able to fully understand how the assessment clock can be used and the authors can clarify this using more concrete examples. This will significantly strengthen the paper.Reviewer Expertise:NANo decision status is available This review has been migrated. The reviewer awarded 3 stars out of 5 this is a very interesting paper, but I also got lost with the clock model. It woud be very helpfull if the authors give some examples to explain better their ideas!Reviewer Expertise:NANo decision status is available This review has been migrated. The reviewer awarded 3 stars out of 5 I am not sure that I fully understood this paper, perhaps because when using the van der Vleuten VA formula, I always thought that many of the assessment qualities were very context and diversity driven, hence I was not sure that the authors' assessment clock was not that universally acceptable. Plus I feel that within the Covid-19 pandemic, very little is universally acceptable and all of the VA qualities are justifiable. It would have been very helpful had the authors explored this and given more concrete examples to justify their points.Reviewer Expertise:NANo decision status is available This review has been migrated. The reviewer awarded 4 stars out of 5 The dilemma faced by medical educators around the world in conducting student assessments during the Covid-19 pandemic are well described by the authors. Given the common challenges encountered by most institutions in this unprecedented crisis situation, shared guidelines and practices among academic institutions are useful, however, should be further contextualised to the institutional needs and resources. The conceptual model of an assessment clock that is founded on the principles of assessment utility is practical, realistic and serves as a guide for rationalising assessment tools and platform during an emergency situation. In addition to acceptability by the examiners and learners, the acceptability of the alternative assessment tools by the accreditation and professional bodies should also be considered.Reviewer Expertise:NANo decision status is available This review has been migrated. The reviewer awarded 5 stars out of 5 this article is informative and challenging to medical educators .Reviewer Expertise:NANo decision status is available