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Physical Review Letters Jun 2022Wave frequency is a critical parameter for applications ranging from structural health monitoring, noise control, and medical imaging to quantum of energy in matter....
Wave frequency is a critical parameter for applications ranging from structural health monitoring, noise control, and medical imaging to quantum of energy in matter. Frequency conversion is an inevitable wave phenomenon in nonlinear or time-modulated media. However, frequency conversion in linear media holds the promise of breaking limits imposed by the physics laws of wave diffraction such as Snell's law and Rayleigh criterion. In this Letter, we physically introduce a linear active metalayer in a structural beam that can convert the wave frequency of an flexural incidence into arbitrary frequencies of transmitted waves, which is underpinned by time modulation of sensing signals and insensitive to incident amplitude. The active element, involving piezoelectric components and time-modulated transfer function, breaks energy conservation such that the generated harmonics can be fully decoupled, making the frequency conversion linear and independent. By leveraging the time-modulated unit, phase-gradient and frequency-gradient metalayers are proposed for frequency-converted wave steering and dynamic beam steering, respectively. The linear active metalayer proposed herein suggests a promising solution to fully control time-domain signals of flexural waves, in stark contrast with existing elastic metasurfaces, regardless of being passive or active.
PubMed: 35776457
DOI: 10.1103/PhysRevLett.128.244301 -
Proceedings of the National Academy of... Aug 2022Geometric compatibility constraints dictate the mechanical response of soft systems that can be utilized for the design of mechanical metamaterials such as the negative...
Geometric compatibility constraints dictate the mechanical response of soft systems that can be utilized for the design of mechanical metamaterials such as the negative Poisson's ratio Miura-ori origami crease pattern. Here, we develop a formalism for linear compatibility that enables explicit investigation of the interplay between geometric symmetries and functionality in origami crease patterns. We apply this formalism to a particular class of periodic crease patterns with unit cells composed of four arbitrary parallelogram faces and establish that their mechanical response is characterized by an anticommuting symmetry. In particular, we show that the modes are eigenstates of this symmetry operator and that these modes are simultaneously diagonalizable with the symmetric strain operator and the antisymmetric curvature operator. This feature reveals that the anticommuting symmetry defines an equivalence class of crease pattern geometries that possess equal and opposite in-plane and out-of-plane Poisson's ratios. Finally, we show that such Poisson's ratios generically change sign as the crease pattern rigidly folds between degenerate ground states and we determine subfamilies that possess strictly negative in-plane or out-of-plane Poisson's ratios throughout all configurations.
PubMed: 35921444
DOI: 10.1073/pnas.2202777119 -
Journal of Neurophysiology May 2018We examined differences between normal weight (NW) and overweight (OW) children aged 8-10 yr in strength, muscle composition, and motor unit (MU) behavior of the first...
We examined differences between normal weight (NW) and overweight (OW) children aged 8-10 yr in strength, muscle composition, and motor unit (MU) behavior of the first dorsal interosseous. Ultrasonography was used to determine muscle cross-sectional area (CSA), subcutaneous fat (sFAT), and echo intensity (EI). MU behavior was assessed during isometric muscle actions at 20% and 50% of maximal voluntary contraction (MVC) by analyzing electromyography amplitude (EMG) and relationships between mean firing rates (MFR), recruitment thresholds (RT), and MU action potential amplitudes (MUAP) and durations (MUAP). The OW group had significantly greater EI than the NW group ( P = 0.002; NW, 47.99 ± 6.01 AU; OW, 58.90 ± 10.63 AU, where AU is arbitrary units) with no differences between groups for CSA ( P = 0.688) or MVC force ( P = 0.790). MUAP was larger for NW than OW in relation to RT ( P = 0.002) and for MUs expressing similar MFRs ( P = 0.011). There were no significant differences ( P = 0.279-0.969) between groups for slopes or y-intercepts from the MFR vs. RT relationships. MUAP was larger in OW ( P = 0.015) and EMG was attenuated in OW compared with NW ( P = 0.034); however, there were no significant correlations ( P = 0.133-0.164, r = 0.270-0.291) between sFAT and EMG. In a muscle that does not support body mass, the OW children had smaller MUAP as well as greater EI, although anatomical CSA was similar. This contradicts previous studies examining larger limb muscles. Despite evidence of smaller MUs, the OW children had similar isometric strength compared with NW children. NEW & NOTEWORTHY Ultrasound data and motor unit action potential sizes suggest that overweight children have poorer muscle composition and smaller motor units in the first dorsal interosseous than normal weight children. Evidence is presented that suggests differences in action potential size cannot be explained by differences in subcutaneous fat alone.
Topics: Action Potentials; Child; Electromyography; Female; Fingers; Humans; Male; Motor Neurons; Muscle Fibers, Skeletal; Muscle Strength; Muscle, Skeletal; Overweight; Pediatric Obesity; Subcutaneous Fat; Ultrasonography
PubMed: 29412774
DOI: 10.1152/jn.00675.2017 -
Journal of Strength and Conditioning... Mar 2023Ryan, GA, Bunn, JA, and Eisenman, ML. How accurate are coaches in predicting perceived exertion of their athletes? J Strength Cond Res 37(3): 684-687, 2023-Ratings of...
Ryan, GA, Bunn, JA, and Eisenman, ML. How accurate are coaches in predicting perceived exertion of their athletes? J Strength Cond Res 37(3): 684-687, 2023-Ratings of perceived exertion (RPE) are used extensively to subjectively evaluate workload in sport. The purpose of this study was to compare season long player to coach perceptions of RPE loads (RPEL) in Division I men's soccer and women's lacrosse programs. Coach and player self-reported RPE were collected during the competitive seasons for both teams within 30 minutes of training sessions. Scores of RPE were multiplied by recorded training time to determine RPEL and averaged to create a daily coach and player RPEL. Accuracy of RPEL prediction between coaches and players was determined via mean bias, mean absolute percent error (MAPE), correlation, and an equivalence test. Soccer coaches underestimated RPEL (1,345 ± 410 arbitrary unit [AU]) compared with players (1,372 ± 435 AU). The coach mean bias was -27.3 ± 151.9 AU, wieth an MAPE of 7.4%, a strong correlation (r = 0.937, p < 0.001), and coach to player equivalence (p = 0.045). Lacrosse coaches overestimated RPELs (876 ± 349 AU) compared with players (829 ± 214 AU). The coach mean bias was 47 ± 189 AU, with an MAPE of 14.7%, a strong correlation (r = 0.883, p < 0.001), and coach to player equivalence (p = 0.010). Analyses indicated that coaches accurately predicted player RPEL within both sports. Variance occurred on days with high RPELs, with overestimations occurring in lacrosse and underestimation in soccer. Coaches can use RPELs to assess subjective training load but should consider objective measures, including microtechnology, to provide a comprehensive assessment.
Topics: Male; Humans; Female; Physical Exertion; Physical Conditioning, Human; Soccer; Athletes; Racquet Sports
PubMed: 36820706
DOI: 10.1519/JSC.0000000000004290 -
Advances in Neural Information... Nov 2022Training with backpropagation (BP) in standard deep learning consists of two main steps: a forward pass that maps a data point to its prediction, and a backward pass...
Training with backpropagation (BP) in standard deep learning consists of two main steps: a forward pass that maps a data point to its prediction, and a backward pass that propagates the error of this prediction back through the network. This process is highly effective when the goal is to minimize a specific objective function. However, it does not allow training on networks with cyclic or backward connections. This is an obstacle to reaching brain-like capabilities, as the highly complex heterarchical structure of the neural connections in the neocortex are potentially fundamental for its effectiveness. In this paper, we show how predictive coding (PC), a theory of information processing in the cortex, can be used to perform inference and learning on arbitrary graph topologies. We experimentally show how this formulation, called , can be used to flexibly perform different tasks with the same network by simply stimulating specific neurons. This enables the model to be queried on stimuli with different structures, such as partial images, images with labels, or images without labels. We conclude by investigating how the topology of the graph influences the final performance, and comparing against simple baselines trained with BP.
PubMed: 37090087
DOI: No ID Found -
Sensors (Basel, Switzerland) Nov 2023Most of the existing metasurfaces are effective for the incident wave with the specific circularly polarized (CP) or linearly polarized (LP) state, that is the...
Most of the existing metasurfaces are effective for the incident wave with the specific circularly polarized (CP) or linearly polarized (LP) state, that is the polarization-sensitive metasurface. This drawback dramatically hinders the practical use of the metasurface. Herein, this paper presents a strategy of polarization-insensitive transmissive microwave metasurfaces to manipulate the incident wave with arbitrary CP and LP states. The metasurface consists of polarization-insensitive unit cells. For the left circularly polarized (LCP) and right circularly polarized (RCP) incident waves, the same abrupt phase covering 0° to 360° can be realized by combining the Pancharatnam-Berry (PB) and resonant phases. As the arbitrary LP wave can decompose into the LCP and RCP waves, metasurfaces consisting of designed unit cells are valid for any polarization states. The polarization-insensitive transmissive microwave metalens and orbital angular momentum multiplexing metasurface working at 23 GHz are devised for verification. Simulation and measurement results verify the availability of the approach. The proposed method is suitable for designing microwave-transmissive metasurfaces capable of polarization insensitivity.
PubMed: 38067786
DOI: 10.3390/s23239413 -
Nursing & Health Sciences Mar 2022The study aimed to explore the conditions that accompany conflict of conscience experienced by nurses in intensive care units. A qualitative approach guided the study,...
The study aimed to explore the conditions that accompany conflict of conscience experienced by nurses in intensive care units. A qualitative approach guided the study, which was undertaken between April 2020 and April 2021. A total of 15 registered nurses working in intensive care units were recruited through purposive sampling. Individual semistructured interviews were conducted. The data were analyzed using a qualitative content analysis. The analysis revealed two themes: "conflict of conscience in relation to the structure" and "conflict of conscience based on context." Conflict of conscience in relation to the structure consisted of two categories: conflict of interest and conflict of conscience and law. Conflict of conscience based on context consisted of two categories: care dilemmas and arbitrary behaviors with end-stage patients. A variety of factors were accompanied by a conflict of conscience for nurses in intensive care units. Given that conflict of conscience has negative consequences for the health and quality of nursing care, health care managers need to tailor strategies to reduce the negative consequences considering the findings of the study.
Topics: Conscience; Humans; Intensive Care Units; Nurses; Nursing Care; Qualitative Research; Walking
PubMed: 35061324
DOI: 10.1111/nhs.12921 -
Hippocampus Jul 2020The encoding of information in spike phase relative to local field potential (LFP) oscillations offers several theoretical advantages over equivalent firing rate codes....
The encoding of information in spike phase relative to local field potential (LFP) oscillations offers several theoretical advantages over equivalent firing rate codes. One notable example is provided by place and grid cells in the rodent hippocampal formation, which exhibit phase precession-firing at progressively earlier phases of the 6-12 Hz movement-related theta rhythm as their spatial firing fields are traversed. It is often assumed that such phase coding relies on a high amplitude baseline oscillation with relatively constant frequency. However, sustained oscillations with fixed frequency are generally absent in LFP and spike train recordings from the human brain. Hence, we examine phase coding relative to LFP signals with broadband low-frequency (2-20 Hz) power but without regular rhythmicity. We simulate a population of grid cells that exhibit phase precession against a baseline oscillation recorded from depth electrodes in human hippocampus. We show that this allows grid cell firing patterns to multiplex information about location, running speed and movement direction, alongside an arbitrary fourth variable encoded in LFP frequency. This is of particular importance given recent demonstrations that movement direction, which is essential for path integration, cannot be recovered from head direction cell firing rates. In addition, we investigate how firing phase might reduce errors in decoded location, including those arising from differences in firing rate across grid fields. Finally, we describe analytical methods that can identify phase coding in the absence of high amplitude LFP oscillations with approximately constant frequency, as in single unit recordings from the human brain and consistent with recent data from the flying bat. We note that these methods could also be used to detect phase coding outside of the spatial domain, and that multi-unit activity can substitute for the LFP signal. In summary, we demonstrate that the computational advantages offered by phase coding are not contingent on, and can be detected without, regular rhythmicity in neural activity.
Topics: Action Potentials; Grid Cells; Hippocampus; Humans; Periodicity
PubMed: 32065488
DOI: 10.1002/hipo.23199 -
Physical Review Letters Dec 2023Overcoming the influence of noise and imperfections is a major challenge in quantum computing. Here, we present an approach based on applying a desired unitary...
Overcoming the influence of noise and imperfections is a major challenge in quantum computing. Here, we present an approach based on applying a desired unitary computation in superposition between the system of interest and some auxiliary states. We demonstrate, numerically and on the IBM Quantum Platform, that parallel applications of the same operation lead to significant noise mitigation when arbitrary noise processes are considered. We first design probabilistic implementations of our scheme that are plug and play, independent of the noise characteristic and require no postprocessing. We then enhance the success probability (up to deterministic) using adaptive corrections. We provide an analysis of our protocol performance and demonstrate that unit fidelity can be achieved asymptotically. Our approaches are suitable to both standard gate-based and measurement-based computational models.
PubMed: 38134783
DOI: 10.1103/PhysRevLett.131.230601 -
Minerva Anestesiologica Feb 2020This review aimed at summarizing the available evidence on liver transplantation from uncontrolled donation after circulatory death (uDCD) on differences in protocols,... (Review)
Review
This review aimed at summarizing the available evidence on liver transplantation from uncontrolled donation after circulatory death (uDCD) on differences in protocols, donor management, in and ex vivo perfusion techniques from center to center. Uncontrolled DCDs represent a unique, complex model of ischemia-reperfusion injury, so far not completely understood. Nevertheless, results on liver transplantation from uDCDs are promising in terms of long-term graft survival. True difficulties still remain since common/shared protocols are not achievable due to legal differences between countries (i.e. no touch period duration). To date, there is no reliable metrics to determine whether a liver is safe to be ex situ perfused or to be transplanted since existing criteria, as stated by investigators themselves, are so far arbitrary. Values and kinetics of transaminanes during normothermic regional perfusion (nRP) should not considered absolute contraindication at least for ex vivo perfusion. Intraoperative evaluation at organ recovery remains pivotal since macroscopic alterations (i.e. hepatic rupture, an abnormal appearance of gall bladder and choledocus) still represent contraindications for organ retrieval. Concerning ex vivo perfusion, the debate is still open, since the choice of type of machine perfusion (mainly hypothermic vs. normothermic) varies from center to center, mainly relying to the single center experience (especially in controlled DCD), surgeons' believes and/or criteria translated from animal models.
Topics: Death; Graft Survival; Humans; Ischemia; Liver Circulation; Liver Transplantation; Organ Preservation; Shock; Tissue Donors
PubMed: 31334618
DOI: 10.23736/S0375-9393.19.13746-7