Displacement Of Center Research Articles

Comparison of stent displacement and displacement force after endovascular aneurysm repair with cross-limb or parallel-limb stent

This study aims to investigate whether displacement force on stents can accurately represents the displacement of the stent after endovascular aneurysm repair (EVAR) by comparing the measured stent displacement with the displacement forces calculated by computational fluid dynamics (CFD). And the effect of cross-limb and parallel-limb EVAR on stent displacements is further studied. Based on our objective, in this study, ten cross-limb EVAR patients and ten parallel-limb EVAR patients in West China Hospital of Sichuan University were enrolled. Patient-specific models were first reconstructed based on the computed tomography angiography images, then the stent displacements were measured, and the displacement forces acting on the stents were calculated by CFD. Finally, the value of the angle between the displacement force and the displacement vector was used to analyze the matching degree between the displacement and the displacement force. The results showed that the displacement forces on cross-limb stents and parallel-limb stents were (2.67 ± 2.14) N and (1.36 ± 0.48) N, respectively. Displacements of stent gravity center, stent displacements relative to vessel, and vessel displacements of cross-limb and parallel-limb stents were (4.43 ± 2.81) mm and (6.39 ± 2.62) mm, (0.88 ± 0.67) mm and (1.11 ± 0.71) mm, (3.55 ± 2.88) mm and (5.28 ± 2.52) mm, respectively. The mean for cross-limb and parallel-limb stents were 0.02 ± 0.66 and - 0.10 ± 0.73, respectively. This study indicates that the displacement force on the stent can't accurately represent the displacement of the stent after EVAR. In addition, the cross-limb EVAR is probably safer and more stable than the parallel-limb EVAR.

The Social Murder of Victoria Salazar: Neoliberal Capitalism and Working Class Precariousness in El Salvador

On March 27, 2021, a Salvadoran refugee named Victoria Salazar was brutally killed by police in the Mexican resort town of Tulum, Quintana Roo. In this article, I introduce a "proletarian feminist analysis" to the study of Central American displacement and forced migration to argue that Victoria Salazar's death is a "social murder." Although Mexican police murdered Victoria Salazar, I contend that the social degradation and working-class precariousness in El Salvador and Mexico, all shaped by neoliberal capitalist relations of exploitation and afflicting cisgender and trans women in distinctive ways, set the conditions for Ms Salazar's social murder.

Finite element analysis on impact response and damage mechanism of composite laminates under single and repeated low-velocity impact

Aerospace composite structures are subjected to not only single but also repeated low-velocity impact during service conditions. In this paper, the dynamic mechanical response and damage mechanism characterization of composite laminates under single and repeated low-velocity impact are investigated numerically by considering the thickness effect. A progressive damage finite element model is developed in ABAQUS with the help of a user-defined material subroutine. The Hou failure criteria are applied to simulate the intra-layer damage, while the cohesive zone model is adopted to describe the inter-layer damage. The validated model is used to study the effect of thickness. The composite plates with three kinds of thickness are analyzed and discussed in terms of contact force, central displacement, energy absorption and internal damage in detail. The numerical results indicate that for both single and repeated impact, the impact response parameters vary linearly with thickness for the chosen plates. Moreover, the damage patterns are inconsistent with each other in that the dominant damage mode changes from intra-laminar damage to inter-laminar damage as the thickness increases owing to the better load-bearing capacity of the thicker layer.

Brownian non-Gaussian diffusion of self-avoiding walks

Three-dimensional Monte Carlo simulations provide a striking confirmation to a recent theoretical prediction: the Brownian non-Gaussian diffusion of critical self-avoiding walks. Although the mean square displacement of the polymer center of mass grows linearly with time (Brownian behavior), the initial probability density function is strongly non-Gaussian and crosses over to Gaussianity only at large time. Full agreement between theory and simulations is achieved without the employment of fitting parameters. We discuss simulation techniques potentially capable of addressing the study of anomalous diffusion under complex conditions like adsorption- or Theta-transition.

Entropy of electrolytes with off-centre charge cations. Monte Carlo studies

Monte Carlo techniques including Inverse Grand Canonical Monte Carlo simulations are utilized to calculate the entropy of a restricted primitive model electrolyte with the caveat that the cation charge centre is displaced from the geographical centre of the cation sphere towards the surface of the sphere. Calculations have been performed for symmetric valency (1:1) and asymmetric valency (2:1) electrolytes at 298.15 K for a range of electrolyte concentrations. The cation charge centre displacement accompanied by an increase of temperature leads to an increase of entropy. For the 2:1 valency system the entropy as a function of the square root of concentration reveals a broad inflexion region that separates the domains of deformation due to the electrostatic and steric interactions. When the central ion is an anion, and the charge centres of the surrounding cations are oriented towards the anion then the electrostatic interactions are stronger than in the standard restricted primitive model and the entropy decreases, while a central cation deforms the ionic atmosphere surrounding it and the entropy increases. In the low concentration regime good agreement is seen between the results from the Debye-Hückel limiting law and the corresponding simulations.

Objective Evaluation of Neurogenic Intermittent Claudication for Patients With Lumbar Spinal Stenosis Based on Plantar Pressure Analysis.

A cross-sectional study. To quantify the severity of neurogenic intermittent claudication (NIC) for patients with lumbar spinal stenosis (LSS) based on the center of pressure trajectory. NIC is one of the typical symptoms of LSS. So far, the severity level of NIC is mainly evaluated by the subjective description of patients, which might be biased by patients' background differences and thus lead to an ineffective diagnosis or inappropriate treatment for LSS. Therefore, it remains necessary to develop a reliable clinical technique for quantitative evaluation of NIC to achieve more effective therapy for LSS. In the present study, the Footscan pressure system was used to detect the center of pressure trajectory. The real-time walking distance (rtWD) and the corresponding displacement of the medial-lateral center of pressure (ML-COP) were calculated based on the trajectory. The differences of ML-COP between LSS and control groups were analyzed using a one-way repeated measures analysis of variance. Regression and Pearson correlation analysis were used to investigate the correlation between rtWD and ML-COP, as well as the relation between the Oxford Claudication Score (OCS) and clinical evaluation indicators. The present study included 31 LSS patients and 31 healthy controls. There were no significant differences in demographic data between the two groups ( P >0.05). The results indicated that ML-COP would increase with the number of laps in the LSS group while not in the control group. Also, a linear relationship was identified between the ML-COP and rtWD for LSS patients ( R2 >0.80, P <0.05). Since the incremental rate of ML-COP for LSS patients was reflected by the regression coefficients of the linear regression analysis, thus the regression coefficients were defined as the claudication correlation coefficients (CCCs). In addition, it was indicated by the statistical analysis that there was a strong positive correlation between OCS and CCC ( r =0.96; P <0.001) and a medium negative correlation with final walking distance ( r =-0.67; P <0.001). It was also noticed that there was no significant correlation between the average ML-COP and OCS ( r =-0.03; P =0.864). The ML-COP of LSS patients would increase with the patients' walking distance. This incremental rate, characterized by the CCC, would be used as an effective indicator to quantify the severity level of the NIC for potentially more accurate and reliable diagnosis, evaluation, and treatment of LSS. 3.

Liquefaction of water on the hydrophobic surface of black phosphorene: A reactive molecular dynamics simulation

Numerous empirical and computational studies have been undertaken on the phenomenon of liquefaction on hydrophilic surfaces. However, recent experiments have demonstrated that some of the hydrophobic surfaces, e.g., black phosphorene, have the capacity for water vapor liquefaction. The current study uses reactive molecular dynamics simulation to model the water vapor molecules' conversion to the liquid water cluster on black phosphorene. First, some simulations are performed in the presence of one, two, and numerous water molecules on the black phosphorene surface, and their structures and dynamics are investigated. Afterward, the growth and formation mechanism of the water cluster on the surface is studied. According to the results, due to the difference in the energy level of the two zigzag and armchair directions of the black phosphorene, the trapped water molecule in the zigzag direction acts as the initial nucleus of the water molecule accumulation. The presence of other water molecules provides the opportunity for the water clusters' growth via the intermolecular hydrogen bonds of water molecules. To study the structure and dynamics of water molecules on the black phosphorene surface, the molecules' orientation and molecular dipole moment, the water molecules’ dipole moment profile, the mass center displacement of water molecules, hydrogen bonds, and their stability were calculated.

Validation of three-dimensional digital model superimpositions based on palatal structures in patients with maximum anterior tooth retraction following premolar extraction.

ObjectiveThis study aimed to evaluate the superimposition accuracy of digital modes for measuring tooth movement in patients requiring anterior retraction after premolar extraction based on the proposed reference regions.MethodsForty patients treated with bilateral maxillary first premolar extraction were divided into two groups moderate retraction (< 7.0 mm) and maximum retraction (≥ 7.0 mm). Central incisor displacement was measured using cephalometric superimpositions and three-dimensional (3D) digital superimpositions with the 3rd or 4th ruga as the reference point. The Wilcoxon signed-rank test and linear regression analyses were performed to test the significance of the differences and relationships between the two measurement techniques.ResultsIn the moderate retraction group, the central incisor anteroposterior displacement values did not differ significantly between 3D digital and cephalometric superimpositions. However, in the maximum-retraction group, significant differences were observed between the anteroposterior displacement evaluated by the 3rd ruga superimposition and cephalometric methods (p < 0.05).ConclusionsThis study demonstrated that 3D digital superimpositions were clinically as reliable as cephalometric superimpositions in assessing tooth movements in patients requiring moderate retraction. However, the reference point should be carefully examined in patients who require maximum retraction.

Measurement method of a microspring-supported force plate with an external laser displacement meter

Ground reaction force (GRF) is a significant factor for the evaluation of animal locomotion. Recently, micro force plates have been implemented as a GRF measurement method for tiny insects. Previous micro force plates were highly sensitive, but fragile and laborious to fabricate, because of the use of strain-sensing elements. Here, we applied high-resolution 3D printing and a noncontact displacement meter to a micro force plate for a fruit fly. 3D printing is suitable for easier, reproducible, and complex three-dimensional fabrication so that a force plate structure, which consists of a plate and four supporting 3D microsprings, is developed as an integrated unit. By detecting the displacement of the plate centre externally, when a fruit fly lands on the plate surface, the vertical GRF of the whole device is calculated via the spring constant. The force plate is sufficiently tough due to the supporting 3D microsprings. The spring constant of the microspring is designed to be approximately 5.98 N m−1, which enables a high-resolution external laser displacement meter to realize a force resolution of less than 1/50 of the body weight of a fruit fly. Providing that the four springs have the same spring constant and the displacement meter aligns at the plate centre, in principle, there is no positional error when converting from displacement to force. However, fabrication error does lead to spring constant differences. Here, we theoretically and experimentally determined the measurement point of the displacement sensor where the positional error caused by the difference in the spring constant of the four microsprings is compensated for. It was confirmed in the experiment that the calibration process improved the position error to be within ±1.5%. Finally, we demonstrated the GRF measurement of a fruit fly. The average GRF was 6.5 μN, which was equal to the weight of a fruit fly. Our proposed device can help evaluate the biomechanics of tiny insects.

Low-Velocity Impact Behavior of Sandwich Plates with FG-CNTRC Face Sheets and Negative Poisson’s Ratio Auxetic Honeycombs Core

The combination of auxetic honeycomb and CNT reinforcement composite is expected to further improve the impact protection performance of sandwich structures. This paper studies the low-velocity impact response of sandwich plates with functionally graded carbon nanotubes reinforced composite (FG-CNTRC) face sheets and negative Poisson’s ratio (NPR) auxetic honeycomb core. The material properties of FG-CNTRC were obtained by the rule of mixture theory. The auxetic honeycomb core is made of Ti-6Al-4V. The governing equations are derived based on the first-order shear deformation theory and Hamilton’s principle. The nonlinear Hertz contact law is used to calculate the impact parameters. The Ritz method with Newmark’s time integration schemes is used to solve the response of the sandwich plates. The (20/−20/20)s, (45/−45/45)s and (70/−70/70)s stacking sequences of FG-CNTRC are considered. The effects of the gradient forms of FG-CNTRC surfaces, volume fractions of CNTs, impact velocities, temperatures, ratio of plate length, width and thickness of surface layers on the value of the plate center displacement, the recovery time of deformation, contact force and contact time of low-velocity impact were analyzed in detail.

Mutual Coupling Compensation for Compact MIMO Radar

A calibration method to compensate for the mutual coupling and channel imbalance in a compact multi-input multi-output (MIMO) radar array based on turn table measurements is proposed. Two mutual coupling matrices, one for the transmit array and the other for the receive array, are used to model the relationship between the ideal manifold and the measured manifold. The practical factors such as the nonisotropic element pattern and the displacement of the array phase center are also taken into account. All the unknowns are determined by solving the nonlinear least-squares fitting problem iteratively. Using two coupling matrices consists of the mutual coupling mechanism in an MIMO array and has better calibration performance than using one matrix for the virtual array. It also reduces the dimension of the matrix and hence the computation load of calibration. Measurements by a microstrip array with two transmitters and four receivers are used to verify its effectiveness in angle estimation, beamforming, and superresolution of close targets.

The effect of expertise on postural control in elite sport ju-jitsu athletes

BackgroundDue to the high postural control demands of sport ju-jitsu, it is likely that long-term sport ju-jitsu training may induce sport-specific adaptations in postural control, especially in positions directly related to combat. The aim of the study was to assess the differences in postural control between elite sport ju-jitsu athletes and untrained controls in non-ecological and ecological conditions and to investigate the relative contribution of spinal and supraspinal mechanisms to postural control in expert athletes.MethodsThe study was conducted on eleven male elite ju-jitsu athletes and ten non-athletes. The data was collected with the use of a force plate under two conditions: quiet standing and ju-jitsu combat stance. Apart from the standard analysis of the spatial–temporal parameters of center of foot pressure, non-linear measures were used, namely rambling-trembling and sample entropy. The non-parametric Mann–Whitney U test was used to compare both groups.ResultsThe main findings of the study showed that in quiet standing, elite ju-jitsu athletes and non-athletes had comparable postural control in both the anterior–posterior and mediolateral planes. In contrast, in the combat stance, elite athletes had lower values of postural sway and rambling component (range and rms) and higher values of sample entropy in comparison to the non-athletes (p < 0.05). No differences were found in the trembling component of sway between groups in the combat stance (p < 0.05).ConclusionsSmaller postural sway and its rambling component in sport ju-jitsu athletes may indicate the more precise control of center of foot pressure and improved ability in estimating its position. The sample entropy results confirmed that the displacement of center of foot pressure for sport ju-jitsu athletes was more irregular, which demonstrates greater automatization in postural control. The results also confirm the importance of ecological validity in investigating postural adaptations associated with sports expertise.

Influence of material uncertainty on higher-order FG-GPLs reinforced porous spherical panels under blast loading

The present study investigates the influence of material uncertainty on the dynamic response of functionally graded graphene nanoplatelets (FG-GPLs) reinforced porous spherical panels under air blast loading. The uncertainty is included in various parameters such as Young’s moduli, mass density, Poisson’s ratios, porosity coefficient, and GPLs’ weight fraction. The microstructural gradation is accomplished by creating pores followed by symmetric, asymmetric, and uniform porosity distributions which lead to variation in the properties along the thickness direction. The metal matrix i.e., Aluminum is reinforced with graphene nano-platelets, and the effective Young’s modulus is estimated using the Halpin–Tsai model whereas the rule of the mixture is employed to determine effective mass density and Poisson’s ratio. A higher-order C0 — continuous structural kinematics is employed to find the dynamic response of the spherical panels. The Governing relations are developed using Euler–Lagrange’s equation and the finite element method in conjunction with the first-order perturbation technique and Newmark’s time integration scheme is applied to find the numerical results in terms of mean and standard deviation of center displacement. The influence of various parameter such as porosity coefficient, GPLs weight fraction, TNT-weight, stand-off stand, etc. are also presented in detail.

Certain Voicing Tasks Improve Balance in Postpartum Women Compared With Nulliparous Women

Background: Postpartum women are at an increased risk of falls. Maintaining standing balance is multifactorial, involving abdominal wall/pelvic floor muscle responsivity, quick generation of intra-abdominal pressure, and glottis position. Objective: To identify whether using voicing tasks improves balance in postpartum women. Study Design: Research report. Methods: Eleven postpartum women and 10 age-matched nulliparous controls stood on a force plate when balance was perturbed to the front or back of their bodies while performing 6 different breathing and voicing tasks. Tasks modified glottis position and lung volume. Primary outcome measure was maximal displacement of center of pressure immediately following perturbation. Results: When comparing the 2 groups' responses, postpartum women showed worse balance during the “Ah” sound and “normal exhale without breath hold” (P = .049 and P = .031, respectively). When comparing all responses to each task, participants in both groups showed no significantly different response to any tasks when they were perturbed anteriorly. The nulliparous group also had no significantly different responses when perturbed posteriorly. Postpartum women showed a significant difference in response to “normal exhale without breath hold” compared with “counting” (P = .01), with better balance for “counting.” Conclusion: Postpartum women showed improved balance during the “counting” task, which incorporates the glottis into the balance mechanism. Tasks that did not incorporate the glottis (exhalation) and relied more on the abdominal wall/pelvic floor produced worse balance in postpartum women. For recently postpartum women, counting may be a helpful strategy to improve balance and reduce fall risk.

Propulsion Calculated by Force and Displacement of Center of Mass in Treadmill Cross-Country Skiing.

This study evaluated two approaches for estimating the total propulsive force on a skier’s center of mass (COM) with double-poling (DP) and V2-skating (V2) skiing techniques. We also assessed the accuracy and the stability of each approach by changing the speed and the incline of the treadmill. A total of 10 cross-country skiers participated in this study. Force measurement bindings, pole force sensors, and an eight-camera Vicon system were used for data collection. The coefficient of multiple correlation (CMC) was calculated to evaluate the similarity between the force curves. Mean absolute force differences between the estimated values and the reference value were computed to evaluate the accuracy of each approach. In both DP and V2 techniques, the force–time curves of the forward component of the translational force were similar to the reference value (CMC: 0.832–0.936). The similarity between the force and time curves of the forward component of the ground reaction force (GRF) and the reference value was, however, greater (CMC: 0.879–0.955). Both approaches can estimate the trend of the force–time curve of the propulsive force properly. An approach by calculating the forward component of GRF is a more appropriate method due to a better accuracy.

Characterization of jet parameters related to cavitation bubble dynamics in a vicinity of a flat liquid-liquid interface

Presented study analyses different jet parameters that appear during and after bubble collapse, namely bubble center displacement, length of a jet-pierced bubble and size of the rebounded bubble and their relation to anisotropy parameter in a vicinity of a liquid–liquid interface. In experiments cavitation bubble was produced with a focused pulsed laser and its dynamics was recorded by a high-speed camera. Two different types of liquid-liquid interfaces consisting of distilled water and two types of silicone oil were used for the study in order to be able to compare the influence of anisotropy parameter on the magnitude of considered jet parameters. The elongation of the cavitation bubble during jet protrusion was analysed and compared for both interface types. The study exhibits systemic approach to jet parameter consideration and presents an important step in understanding the behaviour of cavitation bubble near liquid-liquid interfaces.

Pivot Point position determination and its use for manoeuvring a vessel

ABSTRACT The article deals with the use of Pivot Point to optimize vessel control. It is shown that the position of the Pivot Point should be calculated relative to the center of rotation, and not the center of gravity, as previously thought. For the first time, the dependence of the rotation center displacement on the longitudinal speed of the vessel has been obtained. For the linear model of the vessel, the subdomains of admissible controls are constructed, and the special positions of the Pivot Point are analyzed. The dependence of the control distribution coefficient on the position of the Pivot Point is obtained. Optimal controls are considered. The operability and efficiency of the methods have been verified by mathematical modeling.

Twisted photovoltaics at terahertz frequencies from momentum shift current

The bulk photovoltaic effect (BPVE) converts light into a coherent dc current at zero bias, through what is commonly known as the shift current. This current has previously been attributed to the displacement of the electronic wave function center in real space, when the sample is excited by light. We reveal that materials like twisted bilayer graphene (TBG) with a flatband dispersion are uniquely suited to maximize the BPVE because they lead to an enhanced shift in the momentum space, unlike any previously known shift current mechanism. We identify properties of quantum geometry, which go beyond the quantum geometric tensor, and are unrelated to Berry charges, as the physical origin of the large BPVE we observe in TBG. Our calculations show that TBG with a band gap of several meV exhibits a giant BPVE in a range of 0.2--1 THz, which represents the strongest BPVE reported so far at this frequency in a two-dimensional material and partially persists even a room temperature. Our paper provides a design principle for shift current generation, which applies to a broad range of twisted heterostructures with the potential to overcome the so-called ``terahertz gap'' in THz sensing.

Low-velocity impact response of axially moving functionally graded graphene platelet reinforced metal foam plates

This paper pays attention to the low-velocity impact response of axially moving graphene platelet (GPL) reinforced metal foam plates. Pores and graphene platelets (GPLs) can be unevenly or evenly distributed along the plate thickness direction. The equivalent Young's modulus is described by the Haplin-Tsai equation while the effective mass density and Poisson's ratio are calculated by the mixture rule. Based on the Hamilton's principle, governing equations and corresponding boundary conditions are established. Afterwards, the governing equations are transformed into a set of ordinary differential equations by using the Galerkin's method. In order to simulate the contact load, the time-dependent contact force between an axially moving GPL reinforced metal foam (GPLRMF) plate and an impactor is obtained by applying the single spring-mass model. The linearized contact law is introduced to acquire the contact force. The transverse central displacements of the plate are calculated by adopting the Duhamel integration. Results show that the foam distributions, the GPL patterns, the GPL weight fraction, the foam coefficient, the plate speed, the impactor mass and the impact velocity play important role on the impact response of axially moving GPLRMF plates.

Dynamic response of polypropylene honeycomb/polystyrene foam core sandwich composite panels: Experimental and numerical analysis

In this study, dynamically loaded sandwich panels with two different core materials and face sheets made of aluminum alloys (6061-T6) were investigated experimentally and numerically under low-velocity impact. Polypropylene, PP (C3H6)n honeycomb and extruded polystyrene foam, XPS (C8H8)n were preferred as core material. By using the contact force and kinetic energy changes, which were the impact test results of the sandwich panels, the contact and impact resistance was examined. As a result of the tests, damaged regions and permanent central displacement were determined and energy absorption capabilities were demonstrated for two different structures. The results obtained were compared with the results obtained by the open finite element method. In this study, it was shown that the face-sheet thickness of sandwich panels was an important parameter affecting the impact behavior. The behavior of the core material when the face-sheet loses its rigidity was investigated and it was found that polystyrene foam was more effective in preventing impact damage. However, it was found that using the PP honeycomb or XPS was affected the impact behavior in different points.