Direct Integration Research Articles

Engineering Epitaxial Interfaces for Topological Insulator — Superconductor Hybrid Devices with Al Electrodes

AbstractProximity‐induced superconductivity in hybrid devices of topological insulators and superconductors offers a promising platform for the pursuit of elusive topological superconductivity and its anticipated applications, such as fault‐tolerant quantum computing. To study and harness such hybrid devices, a key challenge is the realization of highly functional material interfaces with a suitable superconductor featuring 2‐periodic parity‐conserving transport to ensure a superconducting hard‐gap free of unpaired electrons, which is important for Majorana physics. A superconductor well‐known for this characteristic is Al, however, its direct integration into devices based on tetradymite topological insulators has so far been found to yield non‐transparent interfaces. By focusing on Bi2Te3‐Al heterostructures, this study identifies detrimental interdiffusion processes at the interface through atomically resolved structural and chemical analysis, and showcases their mitigation by leveraging different interlayers – namely Nb, Ti, Pd, and Pt – between Bi2Te3 and Al. Through structural transformation of the interlayer materials (X) into their respective tellurides (XTe2) atomically‐sharp epitaxial interfaces are engineered and further characterized in low‐temperature transport experiments on Al‐X‐Bi2Te3‐X‐Al Josephson junctions and in complementary density functional theory calculations. By demonstrating functional interfaces between Bi2Te3 and Al, this work provides key insights and paves the way for the next generation of sophisticated topological devices.

A Comparison of Medical Education Policies in Japan and Singapore with a Focus on Governance: Implications for Korea

Among Asian nations, Japan, Singapore, and South Korea exemplify countries with high standards of medical quality. This review explores the differences in medical education policies between Japan and Singapore, particularly concerning governance, and discusses the implications for South Korea’s medical education policies. Relevant documents were analyzed by referencing scholarly articles and data from governmental and expert organizations in each country. In Japan, advances in medical education policies include initiatives such as the regional quota system and the core curriculum model, which emphasize stakeholder engagement and transparency. However, challenges persist due to limited stakeholder participation, necessitating a transition toward a more equitable governance paradigm. Singapore’s model features robust public-private partnerships with minimal direct governmental intervention, emphasizing innovation and community integration, as seen in the Healthier SG project. These case studies demonstrate effective governance involving significant stakeholder collaboration and strategic financial investments. Conversely, South Korea’s medical education policies face challenges from a predominantly government-centric approach, with an absence of cohesive governance structures and inadequate involvement from essential professional stakeholders. This situation has led to policy inconsistencies and a deficit of strategic direction, exacerbated by insufficient financial support for educational infrastructure and program development. The experiences of Japan and Singapore indicate that it would be beneficial for South Korea to adopt integrated governance frameworks that prioritize transparency and collaboration. Furthermore, increasing financial investment in medical education could mitigate existing deficiencies and improve the quality and effectiveness of its healthcare education system.

Full‐Spectrum Light‐Harvesting Solar Thermal Electrocatalyst Boosts Oxygen Evolution

AbstractEnabling high‐efficiency solar thermal conversion (STC) at catalytic active site is critical but challenging for harnessing solar energy to boost catalytic reactions. Herein, we report the direct integration of full‐spectrum STC and high electrocatalytic oxygen evolution activity by fabricating a hierarchical nanocage architecture composed of graphene‐encapsulated CoNi nanoparticle. This catalyst exhibits a near‐complete 98 % absorptivity of solar spectrum and a high STC efficiency of 97 %, which is superior than previous solar thermal catalytic materials. It delivers a remarkable potential decrease of over 240 mV at various current densities for electrocatalytic oxygen evolution under solar illumination, which is practically unachievable via traditionally heating the system. The high‐efficiency STC is enabled by a synergy between the regulated electronic structure of graphene via CoNi‐carbon interaction and the multiple absorption of lights by the light‐trapping nanocage. Theoretical calculations suggest that high temperature‐induced vibrational free energy gain promotes the potential‐limiting *O to *OOH step, which decreases the overpotential for oxygen evolution.

A block-based numerical strategy for modeling the dynamic out-of-plane behavior of unreinforced brick masonry walls

AbstractIn this paper, a numerical procedure is proposed to simulate the dynamic out-of-plane response of unreinforced masonry (URM) walls. A state-of-the-art damaging block-based model, originally developed for quasi-static simulations, is extended for the first time in a dynamic regime. The blocks are represented using solid 3D finite elements governed by a plastic-damage constitutive law for both tension and compression. A cohesive-frictional contact-based formulation is used to account for interactions between the blocks. A simplified mechanical characterization is formulated to improve efficiency in wall-level analyses. Dynamic simulation is performed using a generalized HHT-$$\alpha$$ α direct integration implicit solver and by implementing Rayleigh damping in the bulk. Such consideration allows the use of both mass and stiffness proportional terms of the Rayleigh damping without compromising efficiency. The strategy is applied to simulate incremental dynamic experiments performed on full-scale walls, showing good agreement between numerical and experimental results. The calibrated numerical model is then optimized to reduce computational effort while maintaining accuracy. The optimized model is used to investigate the effect of relative support motion on the one-way bending out-of-plane seismic response of URM walls, demonstrating the potential of the modeling strategy to explore the effect of boundary conditions that occur in real buildings but are often overlooked in laboratory experiments. This investigation also explores the adequacy of simplifications in capturing the effect of relative support motion, which can be adopted for simple modeling strategies commonly used in standard engineering practice.

Analytical evaluation of the elastic stresses in a multilayer spherical pressure vessel

An explicit-form solution is constructed for a problem on elastic deformation of a multilayer spherical vessel due to uniform internal pressure. The vessel is assembled of perfectly connected elastic layers whose material properties may arbitrarily vary across their thickness. The solution is constructed through the use of the single solid approach along with the modified scheme of the direct integration method which allow for the consideration of the multilayer vessel as a composite sphere with piecewise-variable profiles of the material properties. As a result, the original problem is reduced to solving a governing integral equation of the second kind whose solution is constructed in the form of the explicit dependence on the internal pressure. The solution is verified by the comparison with exact solutions derived by making use the method of tailored solutions for specific benchmark problems. By comparing our with the one for a functionally-graded sphere, whose material properties are evaluated through the use of the micromodular homogenization technique, the specific features of the circumferential stress are analyzed.

Investigation of nonlinear dynamic behaviors of vertical rotor system supported by aerostatic bearings

Abstract A common issue associated with gas bearing-rotor systems is the tendency to generate self-excited vibrations, leading to instability. To address this problem, the fluid-structure coupling model of an aerostatic bearing-rotor system is established in this paper. Then a hybrid method combining the finite difference method and direct integration method, is employed to solve the bearing lubrication equation and rotor motion equation simultaneously. Furthermore, based on the orbit of rotor center,frequency spectrum diagram, Poincaré map, waterfall diagram and bifurcation diagram, the effects of rotational speed, rotor mass, orifice diameter and nominal clearance on the nonlinear dynamic behaviors of the bearing-rotor system are investigated. The results indicate that the system exhibits rich nonlinear behaviors with increasing rotational speed and rotor mass, including the occurrence of typical half-speed whirl. However, the nonlinear vibrations of the system can be restricted by selecting appropriate bearing structural parameters, providing theoretical guidance for the design of aerostatic bearing-rotor systems.

Ultra‐Thin Strain‐Relieving Si1−xGex Layers Enabling III‐V Epitaxy on Si

AbstractThe explosion of artificial intelligence, the possible end of Moore's law, dawn of quantum computing, and the continued exponential growth of data communications traffic have brought new urgency to the need for laser integration on the diversified Si platform. While diode lasers on group III‐V platforms have long‐powered internet data communications and other optoelectronic technologies, direct integration with Si remains problematic. A paradigm‐shifting solution requires exploring new and unconventional materials and integration approaches. In this work, it is shown that a sub‐10‐nm ultra‐thin Si1−xGex buffer layer fabricated by an oxidative solid‐phase epitaxy process can facilitate extraordinarily efficient strain relaxation. The Si1−xGex layer is formed by ion implanting Ge into Si(111) and selectively oxidizing Si atoms in the resulting ion‐damaged layer, precipitating a fully strain‐relaxed Ge‐rich layer between the Si substrate and surface oxide. The efficient strain relaxation results from the high oxidation temperature, producing a periodic network of dislocations at the substrate interface, coinciding with modulations of the Ge content in the Si1−xGex layer and indicating the presence of defect‐mediated diffusion of Si through the layer. The epitaxial growth of high‐quality GaAs is demonstrated on this ultra‐thin Si1−xGex layer, demonstrating a promising new pathway for integrating III‐V lasers directly on the Si platform.

Facilitating Absorption Spectroscopy of Strongly Absorbing Fluids: A High-Throughput Approach.

Measuring absorption spectra of strongly absorbing solutions is usually only possible by diluting the solution. However, the absorption spectra can be heavily influenced by concentration-dependent interactions, so dilution leads to misleading results. To enable reliable absorption measurements of concentrated solutions, we introduce in this work thinning fluid film spectroscopy (TFFS), a simple and highly automatable method. We present three exemplary measurement modes of TFFS suitable for many different applications and validate the TFFS measurements with control data obtained in specialized, low optical path length cuvettes. Additionally, we compare the suitability of the different measurement modes over a broad concentration range and demonstrate the automation possibilities with a spectroscopy robot. Beyond this automated approach for highly efficient and high-throughput lab work, we also show the possibility of direct integration into production systems with an in-line setup, which can be incorporated into a variety of pipe systems. The TFFS method is not limited to samples from material science but can be transferred to a broad variety of research and industry fields, including proteins, food, and pharmaceuticals or also agriculture and forensics.

Magnetic field calculation of a uniformly magnetized sphere using solid angles

A new method to calculate the magnetic field of a uniformly magnetized sphere or spherical shell with surface current density K=Kosinθ using the solid angle concept is presented. The field can be shown easily to be constant inside the shell and dipole-like outside with a direct integral of Biot-Savart’s law without invoking magnetic vector potential or special scalar functions typically used for this classical problem.

Quasi-Diabatization Based on Minimizing Derivative Couplings in a Limited Configuration Space: Elimination of Boundary Condition Dependence.

Due to the cuspidal ridges of adiabatic potential energy surfaces (PESs) and singularities of nonadiabatic couplings (NACs), obtaining an analytical expression for the adiabatic Hamiltonian is difficult. Thereby, nonadiabatic dynamics simulations are often carried out on-the-fly, which is time-consuming. This motivates us to construct quasi-diabatic representations, which have smooth PESs and diabatic couplings. In this study, we propose a new quasi-diabatization method based on minimizing derivative couplings (MDC) in a limited configuration space. The boundary conditions are first considered and finally released to obtain the adiabatic-to-diabatic rotation angles and transformation matrices. As demonstrated in representative one- and two-dimensional models and the widely studied linear H3 molecule, MDC performs significantly better than the direct integration quasi-diabatization approach. In particular, accurate diabatic potential energy matrices have been successfully obtained even when the NACs of all configurations in the considered space are nonnegligible.

A comprehensive proteogenomic pipeline for neoantigen discovery to advance personalized cancer immunotherapy.

The accurate identification and prioritization of antigenic peptides is crucial for the development of personalized cancer immunotherapies. Publicly available pipelines to predict clinical neoantigens do not allow direct integration of mass spectrometry immunopeptidomics data, which can uncover antigenic peptides derived from various canonical and noncanonical sources. To address this, we present an end-to-end clinical proteogenomic pipeline, called NeoDisc, that combines state-of-the-art publicly available and in-house software for immunopeptidomics, genomics and transcriptomics with in silico tools for the identification, prediction and prioritization of tumor-specific and immunogenic antigens from multiple sources, including neoantigens, viral antigens, high-confidence tumor-specific antigens and tumor-specific noncanonical antigens. We demonstrate the superiority of NeoDisc in accurately prioritizing immunogenic neoantigens over recent prioritization pipelines. We showcase the various features offered by NeoDisc that enable both rule-based and machine-learning approaches for personalized antigen discovery and neoantigen cancer vaccine design. Additionally, we demonstrate how NeoDisc's multiomics integration identifies defects in the cellular antigen presentation machinery, which influence the heterogeneous tumor antigenic landscape.

A novel iterative algorithm for nonlinear inelastic dynamic analysis of truss structures; MCB-Spline+Sp time integration method

The focus of this work is on the development of a novel algorithm for the nonlinear dynamic analysis of structures. In the sake of a general and easy-to-implement solution method, the tangential stiffness matrix is calculated by combining the Cauchy-Riemann equations derived from the differentiation of complex functions and using the nodal displacement perturbation vector. An implicit direct time integration method based on a cubic B-Spline is integrated with the incremental-iterative method using a quadrature rule based on the interpolation of spline functions, which is referred to as the MCB-Spline+Sp time integration method. A step-by-step algorithm for developing a computer code to implement this method is provided. The effectiveness of the proposed approach is evaluated through several nonlinear time history analyses, which demonstrate its accuracy and efficiency by observing less computational efforts and fast convergence rate. Moreover, a comparison is made between the developed method and well-established techniques such as the Newmark and Standard-Bathe time integration methods in combination with the iterative Newton-Raphson method.

Unraveling the Source of Self-Induced Diastereomeric Anisochronism in Chiral Dipeptides.

Mastering of analytical methods for accurate quantitative determinations of enantiomeric excess is a crucial aspect in asymmetric catalysis, chiral synthesis, and pharmaceutical applications. In this context, the phenomenon of Self-Induced Diastereomeric Anisochronism (SIDA) can be exploited in NMR spectroscopy for accurate determinations of enantiomeric composition, without using a chiral auxiliary that could interfere with the spectroscopic investigation. This phenomenon can be particularly useful for improving the quantitative analysis of mixtures with low enantiomeric excesses, where direct integration of signals can be tricky. Here, we describe a novel analysis protocol to correctly determine the enantiomeric composition of scalemic mixtures and investigate the thermodynamic and stereochemical features at the basis of SIDA. Dipeptide derivatives were chosen as substrates for this study, given their central role in drug design. By integrating the experiments with a conformational stochastic search that includes entropic contributions, we provide valuable information on the dimerization thermodynamics, the nature of non-covalent interactions leading to self-association, and the differences in the chemical environment responsible for the anisochronism, highlighting the importance of different stereochemical arrangement and tight association for the distinction between homochiral and heterochiral adducts. An important role played by the counterion was pointed out by computational studies.

Rapid-Learning Collaborative Pushing and Grasping via Deep Reinforcement Learning and Image Masking

When multiple objects are positioned close together or stacked, pre-grasp operations such as pushing objects can be used to create space for the grasp, thereby improving the grasping success rate. This study develops a model based on a deep Q-learning network architecture and introduces a fully convolutional network to accurately identify pixels in the workspace image that correspond to target locations for exploration. In addition, this study incorporates image masking to limit the exploration area of the robotic arm, ensuring that the agent consistently explores regions containing objects. This approach effectively addresses the sparse reward problem and improves the convergence rate of the model. Experimental results from both simulated and real-world environments show that the proposed method accelerates the learning of effective grasping strategies. When image masking is applied, the success rate in the grasping task reaches 80% after 600 iterations. The time required to reach 80% success rate is 25% shorter when image masking is used compared to when it is not used. The main finding of this study is the direct integration of image masking technique with a deep reinforcement learning (DRL) algorithm, which offers significant advancement in robotic arm control. Furthermore, this study shows that image masking technique can substantially reduce training time and improve the object grasping success rate. This innovation enables the robotic arm to better adapt to scenarios that conventional DRL methods cannot handle, thereby improving training efficiency and performance in complex and dynamic industrial applications.

Evaluating integration methods of a quantum random number generator in OpenSSL for TLS

The rapid advancement of quantum computing poses a significant threat to conventional cryptography. Whilst post-quantum cryptography (PQC) stands as the prevailing trend for fortifying the security of cryptographic systems, the coexistence of quantum and classical computing paradigms presents an opportunity to leverage the strengths of both technologies, for instance, nowadays the use of Quantum Random Number Generators (QRNGs)–considered as True Random Number Generators (TRNGs)–opens up the possibility of discussing hybrid systems. In this paper, we evaluate both aspects, on the one hand, we use hybrid TLS (Transport Layer Security) protocol that leverages the widely used secure protocol on the Internet and integrates PQC algorithms, and, on the other hand, we evaluate two approaches to integrate a QRNG, i.e., Quantis PCIe-240M, in OpenSSL 3.0 to be used by TLS. Both approaches are compared through a Nginx Web server, that uses OpenSSL’s implementation of TLS 1.3 for secure web communication. Our findings highlight the importance of optimizing such integration method, because while direct integration can lead to performance penalties specific to the method and hardware used, alternative methods demonstrate the potential for efficient QRNG deployment in cryptographic systems.

Extended King integral for modeling of parametric array loudspeakers with axisymmetric profiles.

Parametric array loudspeakers have been widely used in audio applications for generating directional audio beams. However, accurately calculating audio sound with a low computational load remains challenging, even for basic axisymmetric source profiles. This work addresses this challenge by extending the King integral in linear acoustics to incorporate both cumulative and local nonlinear effects, under the framework of the quasilinear solution without the paraxial approximation. The proposed method exploits the azimuthal symmetry in cylindrical coordinates to simplify modeling. To further improve computational efficacy, fast Hankel and Fourier transforms are employed for the radial and beam radiation directions, respectively. Numerical results with both uniform and focusing profiles demonstrate the advantages of the proposed approach over the traditional spherical wave expansion and direct integration methods, especially for larger aperture sizes. Specifically, for typical configurations with source aperture size of 0.2 m, we observe at least a 24-fold improvement in computational speed and a 227-fold reduction in memory requirements. These advancements allow us, for the first time, to present the sound field radiated by parametric array loudspeakers with a large aperture size of up to 0.5 m, without paraxial approximations. The implementation codes are available on https://github.com/ShaoZhe-LI/PAL_King.

Three-dimensional elasticity solutions for doubly-curved composite shells by extended differential quadrature method

This paper presents the three-dimensional (3D) stress analysis of doubly-curved composite shells with general boundary conditions using the strong sampling surfaces (SaS) formulation. The SaS method is based on the choice of SaS parallel to the middle surface and located at Chebyshev polynomial nodes to introduce the displacements of these surfaces as unknown functions that leads to a non-conventional shell formulation, in which strain–displacement and stress–strain relationships are represented in terms of SaS displacements. This is due to the use of Lagrange polynomials in approximating displacements, strains and stresses in the thickness direction. The outer surfaces are not included into a set of SaS that makes it possible to uniformly minimize the error ca used by Lagrange interpolation. The strong SaS formulation, based on direct integration of elasticity equilibrium equations in the thickness direction by the extended differential quadrature (EDQ) method, can be applied efficiently for high-precision calculations of doubly-curved composite shells with clamped and free edges. This is because in the SaS/EDQ formulation, displacements, strains and stresses of SaS are interpolated in a rectangular domain specified in a curvilinear coordinate system using a Chebyshev-Gauss-Lobatto grid and Lagrange polynomials are also used as basis functions. The proposed approach deals with equilibrium equations in terms of SaS stresses, avoiding the integration of second order differential equations in terms of SaS displacements, that greatly simplifies the implementation of the EDQ method.

Spherical image potentials for an N-charged particle system

The potential energy interaction between a system of N -charged particles and a spherical conducting surface is obtained by means of direct integration of the electrostatic energy density. Making use of the image charge method, we show that the full potential can be split into a sum of one-body central potentials and two-body contributions related to particle–particle and particle–sphere interactions. Analytical expressions are provided for all contributions. The spherical surface of radius R can be considered to correspond to a cavity inside a conductor or a metallic ball, with two different electric conditions, namely the grounded and isolated charged cases. By taking the limit R → ∞ of the spherical case, one recovers the image potential for an N -charged particle system interacting with a planar conductor. While the final results for the potential do not appear as unexpected, the provided analytical expressions should help in diverse physical applications modelled by a number of charged particles interacting close to a spherical surface.

Multi-stage control design for oscillating water column-based ocean wave energy conversion system

Despite the enormous global potential of ocean wave energy, it has yet to achieve a level of maturity and economic competitiveness that would result in a substantial impact. Challenges include direct integration into weak or isolated microgrids, a high proportion of uncertain marine environments, nonlinear dynamics, oscillating water column (OWC) device limitations, slower response times, unplanned power outages, power fluctuations, high capital and operational costs in ocean wave energy conversion (OWEC) systems. To this end, a new independent multi-stage design approach is proposed for the performance enhancement of an OWC-based OWEC system. Firstly, an airflow and rotational speed optimal control stage enhances power capture in the Wells turbine-based OWC plant. Secondly, compared to conventional control, the proposed permanent magnet synchronous generator control incorporates an adaptive nonlinear back-stepping control algorithm based on Lyapunov stability theory. Thirdly, introducing reconfigurable control into the conventional six-leg power converter ensures the uninterrupted operation of an OWEC system. Lastly, a model-predictive control-based energy management system is integrated with a bidirectional DC-DC converter that delivers steady power from the grid-connected OWC OWEC system. Hence, MATLAB simulations ensure the overall performance enhancement and feasibility of the OWEC system application and verify that the proposed multi-stage solution is efficient, robust, and reliable.

Ultracompact and Uniform Nanoemitter Array Based on Periodic Scattering.

As emerging gain materials, lead halide perovskites have drawn considerable attention in coherent light sources. With the development of patterning and integration techniques, a perovskite laser array has been realized by distributing perovskite microcrystals periodically. Nevertheless, the packing density is limited by the crystal size and the channel gap distance. More importantly, the lasing performance for individual laser units is quite random due to variation of size and crystal quality. Herein an ultracompact perovskite nanoemitter array with uniform emission has been demonstrated. Individual emitters are formed via scattering evanescent components from a shared Fabry-Perot laser, ensuring uniform lasing emission in a unit cell with a side length of 160 nm and lattice constant of 400 nm. And the periodic silicon scatterers do not deteriorate the lasing threshold dramatically. In addition, the surface emitting efficiency increased significantly. The direct integration of a densely packed nanoemitter array with a silicon platform promises high-throughput sensing and high-capacity optical interconnects.