Sharp Profile Research Articles

An Implicit/Explicit dynamic context for brittle fracture using localized gradient damage model

In this work, an implicit/explicit framework for dynamic brittle fracture using localizing gradient damage model (LGDM) with monolithic and staggered solution schemes is presented. A predictive capability of the present approach is witnessed through accurate predictions of damage phenomena investigating various problems. First, a classical crack branching example is considered where the LGDM is shown to resolve the mesh sensitivity issue along with sharp crack profiles. Additionally, the robustness of different solutions schemes is demonstrated through mesh sensitivity analysis where the staggered explicit scheme is found to be computationally efficient. Next, the performance of the proposed model is investigated through the simulation of compact tension tests under different loading rates, to demonstrate the evolution from mode-I to mixed mode crack branching fracture. These tension tests demonstrate the capability of the model in capturing different failure patterns at different loading rates, which agree with the experimental data well. Finally, we considered a specimen with two dynamically propagating cracks located on opposite edges. These numerical simulations demonstrate the model’s capability in handling multiple crack propagation and effectively capturing the intricate mechanisms of damage growth.

A robust hybridizable discontinuous Galerkin scheme with harmonic averaging technique for steady state of real-world semiconductor devices

Solving real-world nonlinear semiconductor device problems modeled by the drift-diffusion equations coupled with the Poisson equation (also known as the Poisson-Nernst-Planck equations) necessitates an accurate and efficient numerical scheme which can avoid non-physical oscillations even for problems with extremely sharp doping profiles. In this paper, we propose a flexible and high-order hybridizable discontinuous Galerkin (HDG) scheme with harmonic averaging (HA) technique to tackle these challenges. The proposed HDG-HA scheme combines the robustness of finite volume Scharfetter-Gummel (FVSG) method with the high-order accuracy and hp-flexibility offered by the locally conservative HDG scheme. The coupled Poisson equation and two drift-diffusion equations are simultaneously solved by the Newton method. Indicators based on the gradient of net doping and solution variables are proposed to switch between cells with HA technique and high-order conventional HDG cells, utilizing the flexibility of HDG scheme. Numerical results suggest that the proposed scheme does not exhibit oscillations or convergence issues, even when applied to heavily doped and sharp PN-junctions. Devices with circular junctions and realistic doping profiles are simulated in two dimensions, qualifying this scheme for practical simulation of real-world semiconductor devices.

Effect of the sharp profile geometry ong the cutting forces of tire recycling tools

Objective: Study the impact of blade profile geometry on cutting forces during tire recycling, focusing on how variations in the shape and design of tools affect the efficiency and quality of the cut, as well as the tools' lifespan. Methodology: Through the construction and testing of three blade geometries, based on a prior numerical study and made from DF2 and 1.2363 steel, experiments were conducted on a Universal Testing Machine with samples of used tire rubber. Results: It was demonstrated that the hollow profile blade significantly reduces energy consumption and improves cutting performance compared to the 30° straight V profile blade, for both rubber-only samples and those with reinforcing textile fibers. Additionally, the study presented the evaluation of shear stresses using a 90° blade, indicating an average shear stress value of 8.67 MPa. Conclusion: This finding suggests that the appropriate selection of blade geometry can significantly contribute to the efficiency of the tire recycling process, offering important economic and environmental implications.

Positive solutions for a nonhomogeneous nonlocal logistic equation

In this paper, we deal with the nonhomogeneous nonlocal dispersal equation∫ΩJ(x−y)u(y)dy−u(x)+λu(x)−a(x)up(x)+Mf(x)=0,x∈Ω¯, where Ω is a bounded and smooth domain, p>1 and the parameters M,λ>0. The kernel function J(x) is nonnegative and symmetric, and the coefficients a,f∈C(Ω¯) are assumed to be nonnegative. We are interested in the existence, uniqueness and asymptotic profiles of positive solutions. It is shown that the structure of positive solutions makes a fundamental change due to the nonhomogeneous effect. Moreover, we study the sharp profiles of positive solutions when there is a spatial degeneracy of a(x). The result exhibits that the blow-up profiles are determined by the degeneracy of a(x).

Fluid resonance in narrow gaps formed by three-box system with sharp and round edge profiles under irregular wave actions

Fluid resonance within narrow gaps in multiple-box systems with sharp and round edge profiles under irregular wave actions are investigated by using a viscous fluid flow solver based on OpenFOAM® package. In difference to the two-peak behavior under regular wave actions, the variation of free surface amplitudes in narrow gaps with incident spectral peak frequencies show the single-peak behavior, including the sharp and round edge profiles. Spectral analysis indicates that the wave spectrums of fluid oscillations in narrow gaps mainly around the first- and/or second-order resonant frequencies. The second-order fluid resonance is easier to be aroused for round edge profiles than that for sharp edge profiles. Furthermore, the statistical and histogram results indicate the significant periods are always around the resonant frequencies; while the corresponding standard deviations approach to cover the region between two resonant frequencies. The above results confirm that the wave responses in narrow gaps mainly oscillate with two resonant frequencies under irregular wave actions.

Fluid simulations for a finite size plasma

Studies on finite-size plasma have attracted a lot of attention lately. They can form by ionizing liquid droplets by lasers. The dynamical behavior of such plasma droplets is, therefore, a topic of significant interest. In particular, questions related to the linear and nonlinear characteristics (associated with the inhomogeneous density typically at the edge of the droplet), the behavior of plasma expansion, etc., are of interest. A one-dimensional fluid simulation study has been carried out to investigate this behavior. It is observed that a slight imbalance in the charge density leads to oscillations that are concentrated and keep acquiring higher amplitude and sharper profiles at the inhomogeneous edge region. Such oscillations lead to the expansion of the droplet. Though the fluid description breaks when the sharpness of these structures becomes comparable to the grid size, it provides a reasonable estimate of wave-breaking time. The presence of dissipative effects such as diffusion is shown to arrest the sharpness of these structures. The dynamics of these structures in the presence of an externally applied oscillating electric field corresponding to long wavelength radiation have also been studied.

Probing Isolated Water Molecules in Aqueous Acetonitrile Solutions Using Oxygen K-Edge X-ray Absorption Spectroscopy.

Oxygen K-edge X-ray absorption spectroscopy (XAS) of an aqueous acetonitrile solution exhibited a sharp peak at approximately 537 eV, which was similar to that of water vapor and was not observed in liquid water. The inner-shell spectra of isolated water molecules and water clusters of different sizes surrounded by acetonitrile molecules were obtained by extracting these water structures from the liquid structures of aqueous acetonitrile solutions, as calculated using molecular dynamics simulations. The sharp peak profiles of the O K-edge XAS spectra were derived not from water clusters but from isolated water molecules surrounded by acetonitrile molecules. The present study proposes that isolated water molecules are easily formed in aqueous acetonitrile solutions and that the electronic structures of the isolated water molecules can be analyzed using O K-edge XAS spectra, which separates the contributions of small water clusters.

High capacity laminate adsorbers: Enhancing separation performance beyond packed beds

In response to the growing demand for more efficient adsorption processes, structured adsorbents have emerged as a promising solution as they offer improved mass transfer and pressure drop characteristics. However, they are often hampered by a lower volumetric capacity due the presence of support structures or a large bed void fraction. This research focuses on the manufacturing and evaluation of self-standing zeolitic laminates of various thickness and spacing, comparing their performance to a traditional packed bed. A shaping method to obtain laminates with a 84 wt% zeolite 13X content is described. Furthermore, a method for precise assembly and spacing of the laminates is detailed. Three such laminar adsorbers with different geometries were evaluated in breakthrough experiments and compared to a packed bed to assess their efficiency in the bulk separation of carbon dioxide. Superior performance of the laminar adsorbers was found, with one configuration employing 1.2 mm laminates and 0.4 mm spacing showing a significant 19 % increase in volumetric capacity compared to a packed bed of pellets. This enhanced capacity is achieved while maintaining efficient heat and mass transfer, resulting in sharp breakthrough profiles. Furthermore, using thinner (0.5 mm) laminates, the length of unused bed was further reduced. Additionally, pressure drop calculations were performed and experimentally validated. The pressure drop over the laminar adsorbers was shown to be significantly lower than over a packed bed. These findings underscore the potential of laminar adsorbers to intensify adsorptive separation processes, reduce energy consumption, and address the demand for more effective adsorption technologies.

Silicon x-ray backlighter improvement by targets with spike-like microstructures

In order to accurately probe high energy density matter states, it is vital to create powerful x-ray backlighters. One approach to create such x-ray sources is based on the usage of short-pulse, high-energy lasers, which greatly benefits from an optimization of the laser target coupling. Here, the spectral and temporal x-ray emission profiles of structured silicon targets with micron-sized spikes on the front surface are studied at laser intensities of 1017 W cm−2. The laser pulse length is varied between 1 and 20 ps with an energy of up to 1 kJ. The structured targets show an up to 13× enhancement of silicon Heα emission compared to flat foils with a well-defined, sharp emission pulse profile. Furthermore, the performance of the microstructured targets is compared to targets with a CH shield as well as foils irradiated with a UV prepulse.

Intermittent Kac's flights and the generalized telegrapher's equation.

A generalized one-dimensional telegrapher equationassociated with an intermittent change of sign in the velocity of a Kac's flight has been proposed. To solve this random differential equation, we used the enlarged master equationapproach to obtain the exact differential equationfor the evolution of a normalized positive distribution. This distribution is associated with a generalized finite-velocity diffusionlike process. We studied the robustness of the ballistic regime, the cutoff of its domain, and the time-dependent Gaussian convergence. The second moment for the evolution of the profile has been studied as a function of non-Poisson statistics (possibly intermittent) for the time intervals Δ_{ij} in the Kac's flight. Numerical results for the evolution of sharp and wide initial profiles have also been presented. In addition, for comparison with a non-Gaussian process at all times, we have revisited the non-Markov Poisson's flight with exponential pulses. A theory for generalized random flights with intermittent stochastic velocity and in the presence of a force is also presented, and the stationary distribution for two classes of potential has been obtained.

GeV Variability Properties of TeV Blazars Detected by Fermi-LAT

Variability is a prominent observational feature of blazars. The high-energy radiation mechanism of jets has always been important but is still unclear. In this work, we performed a detailed analysis using Fermi-LAT data across 15 yr and obtained GeV light-curve information for 78 TeV blazars detected by Fermi. We provided annual GeV fluxes and corresponding spectral indices for the 78 TeV blazars and thorough monthly GeV fluxes for a subsample of 41 bright blazars. Our results suggest a strong correlation between the γ-ray photon index and logLγ for the flat spectrum radio quasars (FSRQs) and high-energy peaked BL Lacs. Fourteen sources in our sample show significant GeV outbursts/flares above the relatively stable, low-flux light curve, with six of them showing a clear sharp peak profile in their 5 day binned light curves. We quantified the variability utilizing the fractional variability parameter F var, and found that the flux of the FSRQs showed significantly stronger variability than that of the BL Lacs. The 41 bright blazars in this work are best fit by a log-normal flux distribution. We checked the spectral behavior and found 11 out of the 14 sources show a bluer-when-brighter trend, suggesting this spectral behavior for these TeV blazars at the GeV band arises from the mechanism in which the synchrotron-self Compton process dominates the GeV emission. Our research offers a systematic analysis of the GeV variability properties of TeV blazars and serves as a helpful resource for further associated blazar studies.

Ion acceleration from the interaction of ultrahigh-intensity laser pulses with near-critical density, nonuniform gas targets

Using one-dimensional, long-timescale particle-in-cell simulations, we study the processes of ion acceleration from the interaction of ultraintense (1020 W cm−2), ultrashort (30 fs) laser pulses with near-critical, nonuniform gas targets. The considered initially neutral, nitrogen gas density profiles mimic those delivered by an already developed noncommercial supersonic gas shock nozzle: they have the generic shape of a narrow (20 μm wide) peak superimposed on broad (∼1 mm, ∼180 μm scale length), exponentially decreasing ramps. While keeping its shape constant, we vary its absolute density values to identify the interaction conditions leading to collisionless shock-induced ion acceleration in the gas density ramps. We find that collisionless electrostatic shocks (CES) form when the laser pulse is able to shine through the central density peak and deposit a few 10% of its energy into it. Under our conditions, this occurs for a peak electron density between 0.35 nc and 0.7 nc. Moreover, we show that the ability of the CES to reflect the upstream ions is highly sensitive to their charge state and that the laser-induced electron pressure gradients mainly account for shock generation, thus highlighting the benefit of using sharp gas profiles, such as those produced by shock nozzles.

Electric discharge aided surface post-treatment of laser powder bed fused non-planar metallic components for enhanced form accuracy

Laser powder bed fusion (LPBF) of metals is an advanced technology gaining popularity in the manufacturing domain for producing near net shape products. The feasibility in batch production and design freedom highlights the promising scope of LPBF over conventional fabrication methods. However, loss of geometrical and dimensional accuracy is a critical challenge in LPBF due to solidification induced volumetric shrinkage and formation of surface irregularities. The aforementioned challenge gets aggravated whenever the fabricated components are non-planar. Studies on post-processing induced modification of dimensional and form accuracy of LPBF components is limited in literature. Moreover, the existing post-treatment operations using laser source, chemicals and mechanical forces exhibit limitations in ensuring desired geometrical accuracy in LPBF components. Therefore, the feasibility evaluation of integrating an alternate post-processing method with LPBF in improving geometrical accuracy become meaningful and worth exploring. Thus, the present study investigates the efficacy of a low energy thermo-electric post-processing method called wire electrical discharge polishing (WEDP) in ensuring geometrical form and dimensional accuracy of LPBF components. The study proposes a mathematical model which discloses the factors to be considered for dimension compensation in computer aided design (CAD) model. The results of the present study indicate that the proposed approach can impart notable reduction in form deviation leading to improved geometrical accuracy. The substantial error in terms of circularity over LPBF curved specimens were drastically reduced after WEDP process. Moreover, the cylindricity of curved specimens was improved by ~80 %. Despite the reduction in flatness error to ~7 μm, the irregularities pertaining to the edges were successfully removed from inclined LPBF surfaces resulting in sharp edged profile. The polishing speed was observed to be strongly dependent on the stair-stepping effect over vertically built LPBF surface. The discharge energy in WEDP played a vital role in influencing the circularity and surface integrity of the processed surface. Furthermore, the thermal impact of WEDP process leads to microstructural modification near the surface, whereas residual stress state after WEDP remains similar to LPBF condition. In a nutshell, the WEDP method looks promising in improving the geometrical and dimensional accuracy of LPBF components thereby enhancing the acceptability of parts in industrial applications.

Interferometry analysis with fringe normalization and matrix Abel inversion for plasma diagnostics

In plasma diagnostics using interferometry, the phase shift caused by the plasma in the fringes is extracted to determine the plasma density. The common method to extract the phase shift from the fringes is the fast-Fourier-Transform (FFT), but this technique encounters challenges when dealing with insufficient fringe numbers, spatially varying fringe frequencies, or extremely sharp phase changes. These challenges result in errors and hinder the acquisition of precise phase measurements. To tackle this issue, we introduced the fringe normalization (FN) method. The simulations demonstrated that the FN method extracts accurate phase information, surpassing the capabilities of the FFT method. As a result, this advancement enables more precise plasma diagnostics by mitigating errors that arise during the phase data processing. Furthermore, we improved the code for the inverse matrix Abel inversion to convert phase information into density. The simulation employing this code showed that the developed code provides more accurate values in the analysis of plasmas with a sharp density profile, assisting in electron beam manipulation in laser-plasma acceleration.

Enhancing Tissue Equivalence in 7Li Heavy Ion Therapy with MC Algorithm Optimized Polymer-Based Bioinks.

The unique physical properties of heavy ion beams, particularly their distinctive depth-dose distribution and sharp lateral dose reduction profiles, have led to their widespread adoption in tumor therapy worldwide. However, the physical properties of heavy ion beams must be investigated to deliver a sufficient dose to tumors without damaging organs at risk. These studies should be performed on phantoms made of biomaterials that closely mimic human tissue. Polymers can serve as soft tissue substitutes and are suitable materials for building radiological phantoms due to their physical, mechanical, biological, and chemical properties. Extensive research, development, and applications of polymeric biomaterials have been encouraged due to these properties. In this study, we investigated the ionization, recoils, phonon release, collision events, and lateral straggle properties of polymeric biomaterials that closely resemble soft tissue using lithium-ion beams and Monte Carlo Transport of Ions in Matter simulation. The results indicated that the Bragg peak position closest to soft tissue was achieved with a 7.3% difference in polymethylmethacrylate, with an average recoils value of 10.5%. Additionally, average values of 33% were observed in collision events and 22.6% in lateral straggle. A significant contribution of this study to the existing literature lies in the exploration of secondary interactions alongside the assessment of linear energy transfer induced by the 7Li beam used for treatment. Furthermore, we analyzed the tissue-equivalent properties of polymer biomaterials using heavy ion beams, taking into account phonon release resulting from ionization, recoils, lateral straggle, and all other interactions. This approach allows for the evaluation of the most suitable polymeric biomaterials for heavy ion therapy while considering the full range of interactions involved.

Investigation of the interface state characteristics of the Al/Al2O3/Ge/p-Si heterostructure over a wide frequency range by capacitance and conductance measurements

In this work, Al/Al2O3/Ge/p-Si heterostructures were fabricated by e-beam thermal evaporation. The EDX (energy dispersive X-ray spectroscopy) map visually obtained the basic distribution information in a two-dimensional graph. Three-dimensional atomic Force Microscope (AFM) analysis of the roughness of the Al/Al2O3/Ge/p-Si heterostructure shows that the Al2O3 particle has approximately 4.35 nm. Quantitative analysis via histogram plots for Al2O3 interlayer grown on p-Si shows a Gaussian-like distribution, and it has a sharp profile between 0 and 2 nm on silicon, located around 1.2 nm. The current-voltage (I–V) and capacitance-conductance-voltage (C-G/ω-V) measurements were used to investigate the electrical properties of the structure at room temperature. The I–V measurements revealed two distinct linear regions, attributed to barrier inhomogeneity and distribution of interfacial state/trap densities (Dit). For this reason, we obtained Dit distributions by considering the voltage dependence of the ideality factor n(V) in two regions. Diode parameters acquired through different methods are comparatively presented with a brief literature review. Then, the C-G/ω-V measurements were conducted across a broad frequency range (from 0.3 kHz to 3 MHz), and these measurements revealed notable alterations in the electrical parameters with regard to frequency. In order to probe interface states/traps, we employed the conductance/admittance method, which provided satisfactory information about trap lifetime, following the low-high frequency (LF-HF) and Hill-Coleman methods. The effects of these states/traps on the measurements according to voltage, frequency, and energy level (Eit-Ev) are discussed in detail.

A robust staggered localizing gradient enhanced isotropic damage model for failure prediction in heterogeneous materials

In the present work, a robust and efficient staggered localizing gradient damage model (LGDM) with a simple isotropic damage variable is adopted to predict crack growth phenomena in bi-material and fiber reinforced composites under mixed-mode loading. We first consider a series of three-point bend experiments conducted by Lee and Krishnaswamy (2000) on bi-material specimens of PMMA/Al6061, where the staggered LGDM is shown to capture correct crack profiles under different boundary conditions. It is observed that the numerical crack paths are well compared with the experimental crack paths. Next, a fiber reinforced composite with a central fiber is considered where the effect of change in fiber sizes on the overall structural responses is investigated. It is seen that the increasing fiber size results in reduced load carrying capacity of fiber reinforced composites. Finally, we consider a fiber reinforced composite with fibers located on opposite edges of the specimen. Here, a parametric study on the strength ratio of the matrix phase is conducted to investigate their effect on crack initiation, propagation, and orientation. These simulations highlight the predictive capability of the present model in terms of structural responses as well as sharp crack profiles.

Sharp asymptotic profile of the solution to a West Nile virus model with free boundary

AbstractWe consider the long-time behaviour of a West Nile virus (WNv) model consisting of a reaction–diffusion system with free boundaries. Such a model describes the spreading of WNv with the free boundary representing the expanding front of the infected region, which is a time-dependent interval $[g(t), h(t)]$ in the model (Lin and Zhu, Spatial spreading model and dynamics of West Nile virus in birds and mosquitoes with free boundary. J. Math. Biol. 75, 1381–1409, 2017). The asymptotic spreading speed of the front has been determined in Wang et al. (Spreading speed for a West Nile virus model with free boundary. J. Math. Biol. 79, 433–466, 2019) by making use of the associated semi-wave solution, namely $\lim _{t\to \infty } h(t)/t=\lim _{t\to \infty }[\!-g(t)/t]=c_\nu$ , with $c_\nu$ the speed of the semi-wave solution. In this paper, by employing new techniques, we significantly improve the estimate in Wang et al. (Spreading speed for a West Nile virus model with free boundary. J. Math. Biol. 79, 433–466, 2019): we show that $h(t)-c_\nu t$ and $g(t)+c_\nu t$ converge to some constants as $t\to \infty$ , and the solution of the model converges to the semi-wave solution. The results also apply to a wide class of analogous Ross–MacDonold epidemic models.

On-chip plasmonic nanosensor based on multiple Fano resonances in rectangular coupled systems

The transmission characteristics of coupled multi-resonators integrated in metal-insulator-metal (MIM) waveguide systems are studied and used to design refractive nanosensors. The symmetry of this nanostructure can be easily broken by changing the relative distance between the multi-resonators, and the transmission spectrum for the system will exhibit double sharp Fano profiles. Simulation results show that the Fano profiles can be used for high-sensitivity refractive sensing with a sensitivity reaching ∼800nm/RIU and figure of merit (FOM) of ∼1.845×104. Moreover, the structure can be easily extended by adding another slender rectangular resonator, and multiple Fano resonances will appear in the spectrum. The new formed nanostructure can achieve a higher sensor sensitivity about ∼875 nm/RIU, and the FOM is 1.861×104. The proposed nanostructures will have great application prospects in on-chip information processing, biosensors and analytical chemistry.

Metal plasmon-enhanced lanthanide fluorescent nanoparticles for monitoring aqueous copper ions

Lanthanide-doped nanomaterials displaying intense, explicit, and long-lasting photoluminescence (PL) have gained much attention in sensing and imaging applications. In this work, europium complex Eu(dibenzoylmethane)3(1,10-phenanthroline) was integrated into core-shell magnetoplasmonic nanoparticles (Ag@Fe3O4 MagPlas NPs), forming a photoluminescent MagPlas nanostructure with uniform morphology, sharp PL emission profile, and distinct magnetic response. The Eu-doped MagPlas NPs (Eu-MagPs) with Ag-core exhibited an enhancement of PL intensity and lifetime compared to the non-plasmonic counterpart, owing to the metal plasmon-induced fluorescence enhancement. Moreover, the quenching phenomenon of the Eu-MagP probe was utilized as a platform for active quantification of metal ion concentration, exclusively Cu2+, in aqueous samples. The luminescence intensity from the Eu-doped MagPlas NP was proportionally quenched by Cu2+ in the working range of 0–2 ppm with negligible influences of other common cations and anions. Static quenching was investigated as the main mechanism for selective detection, in which the presence of quenchers did not affect the luminescent lifetime of the hybrid nanostructure. Moreover, Eu-MagPs were integrated into polyacrylamide hydrogels with enhanced customizability toward the varied amounts of Cu2+. This fluorescent MagPlas structure, therefore, can be utilized as versatile, waste-free, fully recoverable testing assays or chemical sensors for on-site environmental analysis, and water quality control.