Asymmetric Profile Research Articles

Endplate effect in an open-cathode proton exchange membrane fuel cell stack: Phenomenon and resolution

Proton exchange membrane fuel cells (PEMFCs) have garnered substantial attention as highly promising devices for energy conversion. The operational lifespan and overall output performance of such stacks are inherently governed by the performance of the weakest fuel cell, a phenomenon often referred to as the “Bucket Effect.” Evidently, cells located proximate to the hydrogen inlet endplate exhibit poor performance in comparison to the remaining cells in a 95 cells open-cathode fuel cell stack. In response to this challenge, an innovative approach involving endplate heating has been proposed to mitigate the observed endplate effects. Experimental validation of this approach has been conducted, yielding pertinent results. Furthermore, the internal temperature distribution across the stack exhibits an asymmetric parabolic profile, largely attributed to the intricate interplay of the endplate effects. Comparative analysis against a counterpart stack without endplate heating indicates that an application of 80 W heating power leads to a prolongation of operational duration by 156 s, while 100 W heating extends the operational period by 333 s. 80 W heating increased stack power by 31.5 W while improving output power efficiency by 1.9%, and 100 W heating increased stack power by 45.6 W while improving output power efficiency by 2.74%.

Non-Diffraction Self-Acceleration Beams With Customized Transverse Intensity Profiles Based on 3-D-Printed Meta-Structure

In this article, two 3-D-printed all-dielectric meta-structures that can produce diffraction-free self-acceleration beams with different transverse intensity profiles are proposed in the microwave frequency band. The first single-layer meta-structure, combining the Fourier lens phase and cubic phase distributions, is engineered to generate Airy beams with highly asymmetric transverse intensity profiles. In order to flexibly customize the propagation trajectory and transverse spot shape, Bessel-like beams with symmetric transverse profiles along arbitrary trajectories are realized by the second compact meta-structure based on phase synthesis. Calculating the phase mask of the metasurface is the most critical part. In this work, phase-modulated meta-structures can map the phase information to height distribution of the cube elements that can be precisely controlled. To verify the validity, two prototypes are printed and measured. From the beam intensities at different cross sections along the propagation trajectory, the oscillating multilobe intensity pattern of the 2-D Airy beam and the symmetric non-spreading central main lobe of the Bessel-like beam can be observed in simulation and measurement. Besides that, two kinds of beams have transverse acceleration behavior and self-reconstruction property. Therefore, the proposed meta-structures have great potential in numerous challenging fields, like microwave power transmission, secure communication, imaging, and detection.

Measuring local physical parameters in coronal loops with spatial seismology

Context. The method of spatial seismology can be applied to the amplitude profile of transverse coronal loop oscillations to constrain the distributions of physical parameters, such as the loop density, magnitude of the magnetic field, and so on. Aims. We intend to develop and apply a practical spatial seismology technique to detect physical parameters of plasma and validate its effectiveness by comparing it with other methods. Methods. A spatial seismology inversion was conducted by numerically optimizing a parametric dynamic model of the loop’s density stratification and magnetic field variation to best fit the measured amplitude profile of the loop. Results. The spatial seismology inversion technique developed here was applied to a transverse coronal loop oscillation that occurred on 2013 April 11, whose oscillation amplitude profile of both the fundamental mode and first overtone was reported in previous work. The consistency between the time domain analysis and spatial seismology has been verified. Meanwhile, we accounted for the asymmetric profile of the fundamental mode by forward modeling and we derived the magnetic field distribution by inverse modeling, which is coincident with that of the extrapolated one. In addition, spatial seismology inversion was applied to the transverse oscillation event on 2022 March 30 to obtain the distribution of the loop’s density and magnetic field, which are compared with the results derived from the differential emission measure (DEM) diagnostics and the direct potential field extrapolation. Conclusions. Spatial seismology inversion can be used as an effective method to independently measure various physical parameters, for example the density and magnetic field of coronal loops, which are consistent with the results obtained by DEM diagnostics and potential field extrapolation.

Analysis of the stress-strain state when straightening asymmetric profiles

Analysis of the stress-strain state when straightening asymmetric profiles

Modeling and performance analysis of rotary compressor considering multi-body coupling and bearing deformation

Rotary compressor, which contains different types of friction pairs, is widely applied in refrigeration equipment. With its development towards high power density and long life, the multi-body interactions and the surface deformation have increasing impacts on the compressor performance. To reveal the working state of the compressor comprehensively and conduct optimal design, a new tribo-dynamic model considering multi-body coupling and bearing deformation is established in this study. Based on the analysis under high ambient pressure, the moving characteristics of the rolling piston and the effects of the crankshaft shoulder profile are presented. It is found that the direction and magnitude of the piston rotation speed highly depend on the working frequency, and an asymmetric crankshaft shoulder profile can dramatically increase the minimum oil film thickness and reduce the wear load. In addition, the impacts of the oil supply structures for the crank, the main bearing and the sub bearing are also given. By comparing different design schemes, the optimized oil supply structures are determined. This work provides a comprehensive analysis method for optimizing the lubrication design of high-performance compressors.

Accurate determination of line intensity of H[formula omitted]O near 7181 cm−1 : SI-traceable measurement using primary trace-moisture standard in N[formula omitted] gas

The absorption spectra of trace water vapor in N2 gas with a mole fraction of 500 nmol/mol in the pressure range of 20 kPa to 140 kPa were obtained near 7181 cm−1 using wavelength-meter-controlled cavity ring-down spectroscopy (WMC-CRDS). The reference gas (water vapor in N2 gas) was produced using a generation system of primary measurement standards for trace moisture in gases, where the amount of water vapor was measured using a gravimetric method. The obtained spectra of H2O were analyzed using a multispectrum fitting technique with a speed-dependent asymmetric Voigt profile (SDAVP). The values of the line intensity were determined with traceability to the International System of Units (SI). We could achieve the expanded uncertainty below 2 % for the line intensities of the strong lines.

Shaping magnetization dynamics in a planar square dot by adjusting its surface anisotropy

A planar square dot is one of the simplest structures confined to three dimensions. Despite its geometrical simplicity, the description of the spin wave modes in this structure is not trivial due to the competition of dipolar and exchange interactions. An additional factor that makes this description challenging are the boundary conditions depend both on non-local dipolar interactions and local surface parameters such as surface anisotropy. In the presented work, we showed how the surface anisotropy applied at the lateral faces of the dot can tune the frequency of fundamental mode in the planar CoFeB dot, magnetized in an out-of-plane direction. Moreover, we analyzed the spin wave profile of the fundamental mode and the corresponding dynamic stray field. We showed that the asymmetric application of surface anisotropy produces an asymmetric profile of dynamic stray field for square dot and can be used to tailor inter-dot coupling. The calculations were performed with the use of the finite-element method.

Formation mechanism of the double contact bands on the wheel and rail treads of a metro system

The contact band on the wheel and rail is an intuitive representation of the wheel–rail contact relationship that affects the dynamic performance of rail vehicles. In this paper, a vehicle dynamics model and the Archard wear model are established in an integrated way using the actual parameters of a metro train. The mechanism of formation of double contact bands on the wheel and rail in a metro line in China is studied by analysing the geometric combination based on the measured data. The influence of double contact bands on the dynamic performance of the metro vehicle is investigated. To suppress the formation of double contact bands, an optimisation method for asymmetric rail profiles in small radius curves is proposed based on the Kriging Surrogate Model (KSM) and the Particle Swarm Optimisation (PSO) algorithm. Through numerical simulations, it is proved that the optimised rail profiles can improve the curving performance and effectively reduce wheel wear. The methodology proposed in this paper can provide useful information on the mitigation of severe double contact bands on wheel and rail.

An asymmetric graded indexed helical structured optical fibre for enhanced optical delays

Optical fibres are generally used to provide a guided path to optical signals. Optical fibres are classified as multi-mode or single-mode fibres. Multi-mode graded index (GRIN) optical fibres have been prevalent in short-range optical networks, while single-mode GRIN fibres are used for long-range links. Another potential application of optical fibre is the optical delays in numerous applications, such as quantum computing, network buffering, data synchronization, pattern correlation, etc. This paper conceptualizes a novel application of an asymmetric GRIN optical fibre for possible enhanced optical delays. An asymmetric GRIN parabolic profile with helical structure geometry has been proposed for this task. A detailed analysis has been presented to investigate the effects of various parameters of the proposed geometry. Further, a guided propagation has also been demonstrated with the help of ray optics and the Helmholtz wave equation to assess the feasibility of the proposal. The presented investigations revealed that the geometrical length of the proposed structure is significantly compact compared with the traditional GRIN fibre, proving it beneficial for optical delays.

Momentum boundary layers in transcritical channel flows

We present well-resolved large-eddy simulations (LES) of a channel flow solving the fully compressible Navier–Stokes equations in conservative form. An adaptive look-up table method is used for thermodynamic and transport properties. We apply a physically consistent subgrid-scale turbulence model, that is based on the Adaptive Local Deconvolution Method (ALDM) for implicit LES. The wall temperatures are set to enclose the pseudo-boiling temperature at a supercritical pressure, leading to strong property variations within the channel geometry. In total seven cases are computed covering different Reynolds numbers, pseudo-boiling positions and pressure values. The hot wall at the top and the cold wall at the bottom produce asymmetric mean velocity and temperature profiles which result in different momentum layer thicknesses. All cases feature a turbulent mass flux which is essential in turbulence modelling. Furthermore, we analyse the turbulent kinetic energy budgets, perform a quadrant and octant analysis of the Reynolds shear stress and employ an invariant map to study the anisotropy in transcritical turbulent channel flows.

Surface Roughness of Enamel and Dentin after Preparation Finishing with Rotary Burs or Piezoelectric Instruments

This study compares the effect of different handpieces (turbine, high-speed electric handpiece and piezoelectric device) on surface roughness of enamel and dentin when using diamond-coated working tips and burs of the same grit size. The experiment was conducted on 15 extracted first molars from patients aged 45 to 60 years. The occlusal portion was removed using a diamond-coated water wheel and then refined with a 120–130 μm grit bur in order to obtain a flat surface with an adequate exposition of the dentin core. Each surface was divided into three portions and every portion was finished with one of the three tested instruments. The rotary burs and piezoelectric tips had the same grit size (60 μm), and the load on handpiece during preparation never exceeded 150 g. Roughness parameters (Ra, Rsk, Rku) were recorded with a profilometer, and a SEM analysis of treated surfaces and working tips was conducted. Ra and Rsk differed significantly between enamel and dentin only after using turbine (p = 0.004 and p = 0.007, respectively). No significant differences were observed in Ra, Rsk and Rku between enamel and dentin when using a high-speed electric handpiece or piezoelectric device. The turbine produced higher Ra and Rsk values on dentin than the other devices, while no significant differences were found between piezoelectric handpiece and high-speed electric contra-angle on both substrates. Summarizing, the findings of the present study demonstrated that turbine generated rougher surfaces on dentin compared to the other handpieces. Moreover, the turbine produced more asymmetrical surface profiles on both enamel and dentin. However, it should be considered that these differences in roughness (Ra) were within the range of 0.25–0.30 μm: it is still unclear if these variations, although statistically significant, will influence final clinical outcomes.

How Do Earthquakes Stop? Insights From a Minimal Model of Frictional Rupture

AbstractThe question “what arrests an earthquake rupture?” sits at the heart of any potential prediction of earthquake magnitude. Here, we use a one‐dimensional, thin‐elastic‐strip, minimal model, to illuminate the basic physical parameters that may control the arrest of large ruptures. The generic formulation of the model allows for wrapping various earthquake arrest scenarios into the variations of two dimensionless variables (initial dimensionless stress parameter on the fault) and (dimensionless fracture energy), valid for both in‐plane and antiplane shear loading. Our continuum model is equivalent to the standard Burridge‐Knopoff model, with an added characteristic length scale, H, that corresponds to either the thickness of the damage zone for strike‐slip faults or to the thickness of the downward moving plate for subduction settings. We simulate the propagation and arrest of frictional ruptures and derive closed‐form expressions to predict rupture arrest under different conditions. Our generic model illuminates the different energy budget that mediates crack‐ and pulse‐like rupture propagation and arrest. It provides additional predictions such as generic stable pulse‐like rupture solutions, stress drop independence of the rupture size, the existence of back‐propagating fronts, and predicts that asymmetric slip profiles arise under certain pre‐stress conditions. These diverse features occur also in natural earthquakes, and the fact that they can all be predicted by a single minimal framework is encouraging and pave the way for future developments of this model.

Interfacial Structural and Dynamical Properties of [BMI+] [PF6 -] Ionic Liquids on the MXene Electrode: A Molecular Dynamics Simulation Study

Two-dimensional MXene nanomaterials are attracting more and more research interests as electrodes in energy storage applications. In this work, the interfacial structural and dynamical properties of solvent-free ionic liquids ([BMI+] [PF6 -]) on the MXene electrode are investigated using molecular dynamics simulation. Multiple alternating structures of [BMI+] cation and [PF6 -] anions on the MXene surface are observed. Interestingly, the ion diffusion coefficients are remarkably reduced (by 30~40%) in the interfacial Helmholtz layer. Importantly, an asymmetric bell-shaped differential capacitance profile with a maximum capacitance of ~7.04 μF/cm2 is observed. This is chiefly correlated with the structural properties of counterions rather than coins in the interfacial areas.

Revealing cholesterol effects on PEGylated HSPC liposomes using AF4-MALS and simultaneous small- and wide-angle X-ray scattering.

Liposome development is of great interest owing to increasing requirements for efficient drug carriers. The structural features and thermal stability of such liposomes are crucial in drug transport and delivery. Reported here are the results of the structural characterization of PEGylated liposomes via small- and wide-angle X-ray scattering and an asymmetric flow field-flow fractionation (AF4) system coupled with differential refractive-index detection, multi-angle light scattering (MALS) and dynamic light scattering. This integrated analysis of the exemplar PEGylated liposome formed from hydrogenated soy phosphatid-yl-choline (HSPC) with the addition of cholesterol reveals an average hydro-dynamic radius (R h) of 52 nm with 10% polydispersity, a comparable radius of gyration (R g) and a major liposome particle mass of 118 kDa. The local bilayer structure of the liposome is found to have asymmetric electronic density profiles in the inner and outer leaflets, sandwiched by two PEGylated outer layers ca 5 nm thick. Cholesterol was found to effectively intervene in lipid chain packing, resulting in the thickening of the liposome bilayer, an increase in the area per lipid and an increase in liposome size, especially in the fluid phase of the liposome. These cholesterol effects show signs of saturation at cholesterol concentrations above ca 1:5 cholesterol:lipid molar ratio.

H i Absorption in Low-power Radio AGNs Detected by FAST

We report the discovery of three H i absorbers toward low-power radio active galactic nuclei (AGNs) in a pilot H i absorption survey with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Compared to past studies, FAST observations have explored lower radio powers by ∼0.4 dex and detected these weakest absorbers at given redshifts. By comparing the gas properties and kinematics of sources along radio powers, we aim to explore the interplay between AGN and the surrounding interstellar medium (ISM). Compared to brighter sources at similar redshifts, our observations suggest a slightly lower detection rate of H i absorption lines (∼11.5%) in low-power radio AGNs with . The low-power sources with have a lower detection rate of ∼6.7%. Due to the incompleteness of the sample, these detection rates may represent the lower limits. The selection of more extended sources and dilution by H i emission at lower redshifts may contribute to the lower detection rate of H i absorption lines. These detected absorbers present relatively narrow line widths and comparable column densities consistent with previous observations. One absorber has a symmetric profile with a large velocity offset, while the other two show asymmetric profiles that can be decomposed into multiple components, suggesting various possibilities of gas origins and kinematics. These H i absorbers may have connections with rotating disks, gas outflows, galactic gas clouds, gas fueling of the AGN, and jet–ISM interactions, which will be further investigated with the upcoming systematic survey and spatially resolved observations.

Coupling rare earth element analyses and high-resolution topography along fault scarps to investigate past earthquakes: A case study from the Southern Apennines (Italy)

AbstractThe systematic study of faults that have released strong earthquakes in the past is a challenge for seismic hazard assessment. In carbonate landscapes, the use of rare earth element (REE) concentrations on slickensides may aid the reconstruction of fault slip history. We applied this methodology to the Caggiano normal fault (Southern Apennines, Italy), cropping out southeast of the Irpinia 1980 CE earthquake fault (Mw 6.9), which was responsible for both the 1561 CE and partly the 1857 CE Basilicata earthquakes (Mw 6.7 and 7.1). We integrated the REE analysis approach with a high-resolution topographic analysis along 98 serial topographic profiles to measure vertical separations attributable to faulting since the Last Glacial Maximum (LGM). The asymmetric scarp height profiles suggest fault-lateral propagation and along-strike variations in the fault evolution. Our results indicate the occurrence of 7 to 11 earthquakes with variable slip between ~40 cm and ~70 cm within post-LGM times. We estimated the magnitudes of the respective earthquakes, between 5.5 and 7.0, and most commonly between 6.3 and 6.5. The results suggest a recurrence time between 1.6 k.y. and 2.3 k.y. and a slip rate ranging between 0.6 mm/yr and 0.9 mm/yr. This approach may be useful for application to carbonate fault planes in similar tectonic contexts worldwide.

A cylindrical skiving tool design method based on a conjugate surface for internal gear manufacture

Power skiving is a highly productive method for manufacturing gears, especially internal gears. However, due to the resharpening errors of the conical skiving tool, the insufficient tool life hinders the large-scale applications of power skiving. This work proposes a novel design method of the cylindrical skiving tool based on deriving the mathematical model of two-parameters conjugate tooth surface of an internal gear. The error-free cutting-edge of the skiving tool is obtained from the intersection curve of the conjugate tooth surface and the rake face with an offset along the tool axis. In the present study, a helical internal gear with 97 teeth, module of 1.5875 mm and helix angle of 23.5° is used for the design of a cylindrical skiving tool with 37 teeth. The numerical analysis results show that the tool axial offset zoff, crossed shaft angle Σ and geometric rake angle of tool γ0 result in the asymmetrical tool profile and the uneven clearance angles on both flanks. However, the change of the tool helix angle by 0.7° can obtain an even clearance angles on both flanks when zoff is −30 mm. The noninterference height of the cylindrical tool is 48 % more than the conical tool when machining the same workpiece, which means the cylindrical tool is expected to be a longer tool life. Experiments are conducted on a Profilator Type H skiving machine by using the cylindrical skiving tool by the accuracy of DIN 3. The results show the tool design method is effective and applicable to machine a gear by the accuracy of ISO1328-1 level 7.

Transmission and Reflection properties of the incident Light via SW coherent laser field

The relative phase of the applied lights has been used to explore the position dependence of the transmitted and reflected light from a defective dielectric medium. The duplicated two-level atomic system that makes up the dielectric medium interacts with a position-dependent standing wave (SW) coupling light and a weak probe laser field. We found that identical behaviors can be produced for the transmitted and reflected light in various directions due to the relative phase of the applied light. Furthermore, we understood that the transmitted and reflected spectra of the incident light become asymmetric for the asymmetric profile of the coupling light, and that these circumstances will cause the probing field to be amplified. In this instance, we found that altering the relative phase of the applied lights can modify the position of the subluminal and superluminal light.

Ultrasound Speckle Decorrelation-Based Blood Flow Measurements.

Ultrasound imaging is the preferred noninvasive technique to measure blood flow to diagnose cardiovascular disease such as heart failure, carotid stenosis, and renal failure. Conventional ultrasound techniques such as Doppler ultrasound, ultrasound imaging velocimetry, vector Doppler and transverse oscillation beamforming have been used for blood flow velocity profile measurement. However, these techniques were limited to measuring blood flow velocities within the 2-D lateral (across the ultrasound beam) plane of a vessel, and the blood flow velocity profile was derived by assuming that blood vessels have a circular cross-section with axis symmetry. This assumption is incorrect because most vessels have complex geometries, such as tortuosity and branches, and an asymmetric flow profile in the presence of vascular plaque. Consequently, ultrasound speckle decorrelation has been proposed to measure blood flow from transverse views of blood vessels wherein the ultrasound beam is perpendicular to the vessel axis. In this review, we present a summary of recent progress in ultrasound speckle decorrelation-based blood flow measurement techniques.

Study of red blood cells and particles in stenosed microvessels using coupled discrete and continuous forcing immersed boundary methods

A computational study of the blood flow in a stenosed microvessel is presented using coupled discrete ghost-cell and continuous-forcing immersed boundary methods. This study focuses on studying platelet behaviors near the stenosis with deformable red blood cells (RBCs). The influence of varying hematocrit, area blockage, stenosis shape, and driving force on flow characteristics, RBCs, and particle behaviors is considered. Distinct flow characteristics are observed in stenosed microvessels in the presence of RBCs. The motion of RBCs is the major cause of time-dependent oscillations in flow rates, while the contribution of particles to the fluctuations is negligible. However, this effect decreases when the stenosis is elongated in the axial direction. Interestingly, as the hematocrit level increases, downstream particles move closer to the vessel wall due to the enhanced shear-induced lift force resulting from the interaction among RBCs and particles. Furthermore, it is observed that geometrical changes in the stenosis have a more significant impact on the axial profile of particle concentration compared to changes in hematocrit or driving force. An asymmetric stenosis leads to asymmetric profiles in the flow velocity and the distribution of cells and particles due to the geometric focusing effect of the stenosis. There is no significant change in flow rates until a blockage of 0%–50%, but a sudden increase in the root mean square of flow rates occurs at an 80% blockage. This study contributes to our understanding of the rheological behaviors of RBCs and rigid particles in a stenosed microvessel under various hemodynamic conditions.