arXiv subjects

Mingwei Zhang

Publications and source records attributed to Mingwei Zhang.

At least 19 recordsLinked to original sources

arXiv2026

A Novel Nb-Based Eutectic Superalloy with Exceptional Ultrahigh-Temperature Mechanical Properties

Refractory alloys operating above 1300 {\deg}C, beyond the limit of Ni-based superalloys, must balance high-temperature strength, thermal stability, low density, low cost, and room-temperature tensile ductility, a combination that existing refractory alloys have yet to achieve. Here we report a castable Nb-based eutectic superalloy, Nb-10Mo-9.5C (at. %, NMC-1), comprising a uniform lamellar structure of Nb-Mo solid solution and Nb2C carbide phases. NMC-1 achieves 0.2% yield strengths of ~300 MPa and ~200 MPa at 1300 {\deg}C and 1500 {\deg}C, respectively, among the highest reported for Nb-based alloys, with pronounced strain hardening, non-zero room-temperature tensile ductility, and no observed microstructural coarsening after 100 h at 1400 {\deg}C. Its low density (8.65 g/cc) and cost (~$85/kg) yield a specific-strength-per-cost merit index that far surpasses commercial Nb, Mo, Ta, and W alloys, establishing a new design paradigm for ultrahigh-temperature structural materials.

cond-mat.mtrl-sci↗

arXiv2026

The sharp curl-Sobolev inequality

We solve a longstanding problem, going back at least to Rivi\`ere 1998 and open even in the physically most relevant case $n=3$, by proving a sharp curl-Sobolev inequality on $\mathbb{S}^n$ when $n\equiv 3\pmod 4$: for every $\frac{n-1}{2}$-form $\alpha$, the conformally invariant quotient satisfies (with positive denominator) \[ \frac{\Big(\int_{\mathbb{S}^n}|{\rm curl}\alpha|^{\frac{2n}{n+1}}\,{\rm dV}\Big)^{\frac{n+1}{n}}}{\int_{\mathbb{S}^n}\langle{\rm curl}\alpha,\alpha\rangle\,{\rm dV}} \ge \frac{n+1}{2}\,\omega_n^{\frac1n}. \] We also classify all extremals in terms of Killing forms. By conformal invariance, the same result holds on $\mathbb{R}^n$. We then give geometric and variational applications that settle several open conjectures in geometry and mathematical physics. First, we show that on $\mathbb{S}^n$ the round metric is the unique optimizer for the conformal invariant $\mu([g_{{\rm st}}])$. Second, we prove that the unique minimizers of the $3$-energy $\int_{\mathbb{S}^3}|{\rm d} u|^3$ in the homotopy class of the Hopf map $\pi:\mathbb{S}^3\to\mathbb{S}^2$ are exactly $\pi\circ\Phi$ with $\Phi\in{\rm Conf}^+(\mathbb{S}^3)$, confirming a conjecture of Rivi\`ere. Third, for the Faddeev-Skyrme energy $\mathcal{FS}_\rho$ on $\mathbb{S}^3$, we establish global minimality of the Hopf map in the full predicted range: for every coupling constant $\rho\le \sqrt{2}$, the unique global minimizers in its homotopy class are precisely $\pi\circ R$ with $R\in\mathrm{SO}(4)$, as expected since Ward 1999. Fourth, in the presence of Dirac zero modes on $\mathbb{S}^3$, we prove the sharp lower bound $\|{\rm curl} A\|_{3/2} \ge 3\omega_3^{\frac 2 3}$ for the magnetic field and characterize equality in terms of Killing spinors; in particular, this yields a sharp criterion for the existence of zero modes and answers a question of Frank-Loss for $n=3$.

math.DG↗

arXiv2026

On the sharp constants in curl-Sobolev inequalities on $\mathbb{S}^n$

Let $n\equiv 3\ (\mathrm{mod}\ 4)$ and set $p=\frac{n-1}{2}$. On an oriented Riemannian $n$-manifold we consider the (middle-degree) curl operator, $\mathrm{curl}:*\mathrm{d}:\Omega^{p}\rightarrow\Omega^{p}$, and the associated conformally invariant Sobolev quotients on $(\mathbb{S}^n,g_{\mathrm{st}})$, \[ J_1(\alpha)=\frac{\big(\int|\mathrm{curl}\alpha|^{\frac{2n}{n+1}}\,\mathrm{dV}\big)^{\frac{n+1}{n}}}{\int\langle\mathrm{curl}\alpha,\alpha\rangle\,\mathrm{dV}}, \qquad J_2(\alpha)=\frac{\big(\int|\mathrm{curl}\alpha|^{\frac{2n}{n+1}}\,\mathrm{dV}\big)^{\frac{n+1}{n}}}{\inf_{\phi}\big(\int|\alpha-\mathrm{d}\phi|^{\frac{2n}{n-1}}\,\mathrm{dV}\big)^{\frac{n-1}{n}}}. \] Killing $p$-forms and their conformal images form a natural family of critical points for both functionals, analogous to the Aubin-Talenti family in the classical Sobolev inequality. We prove a quantitative local stability estimate for $J_1$ around this family, which in particular implies that every such form is a strict local minimizer in the conformally invariant space $W^{1,\frac{2n}{n+1}}$. In contrast, we show that these critical points are unstable for $J_2$ (and for related conformally invariant quotients), yielding a strict upper bound for the sharp constant of the $J_2$ inequality. By conformal invariance, the results on $\mathbb{S}^n$ transfer naturally to $\mathbb{R}^n$.

math.DG↗

arXiv2026

A conformal lower bound of weighted Dirac eigenvalues on manifolds with boundary

For the weighted Dirac eigenproblem on a compact spin manifold with the chiral boundary condition \begin{equation*} \left\{ \begin{array}{ll} D\varphi = \lambda f\varphi & \text{in } M, \\ \mathbf{B}\varphi = 0 & \text{on } \partial M, \end{array} \right. \end{equation*} we first give a lower bound of the eigenvalue using the relative Yamabe constant \begin{equation*} \lambda^2 \geq \frac{n}{4(n-1)} Y(M,\partial M,[g]), \end{equation*} then prove that equality holds if and only if (up to a conformal transformation) $M$ is a hemisphere and $\varphi$ is a Killing spinor. More generalizations are studied.

math.DG↗

arXiv2026

A Low-Cost, Strong, and Ductile Single-Phase Nb-Based Refractory Complex Concentrated Alloy

The development of structural materials capable of sustained operation above 1200 {\deg}C is critical for next-generation energy and aerospace systems; however, Ni-based superalloys are fundamentally constrained by their melting temperatures, while conventional Nb-based refractory alloys are limited by modest specific strength and high cost. Here, we report on the design and mechanical performance of a cost-effective, non-equiatomic refractory complex concentrated alloy (RCCA), Nb45Ta15Ti20V20, engineered to overcome these limitations. Specifically, its specific strength surpasses wrought C-103 and rivals additively manufactured (AM) C-103 at temperatures up to 1300 {\deg}C while maintaining extensive room temperature tensile ductility (>10 %). Coupled with a high melting point (~2167 {\deg}C), reduced density (8.67 g/cc), and a raw material cost of ~$130/kg compared to >$500/kg for wrought C-103 and >$2,500/kg for AM C-103, this alloy delivers superior specific strength-cost efficiency, highlighting the promise of non-equiatomic RCCAs as viable alternatives to commercial refractory alloys.

cond-mat.mtrl-sci↗

arXiv2026

Enhanced Elevated-Temperature Strength in Refractory Complex Concentrated Alloys via Temperature-Induced Transition from Screw-to-Edge Dislocation Control

Refractory complex concentrated alloys (RCCAs) show promise for high-temperature applications but often lose strength due to screw-dislocation-controlled plasticity. We demonstrate a temperature-driven transition from screw- to edge-dislocation-controlled deformation in a single-phase NbTaTiV RCCA. Tensile tests from 298-1573 K reveal a pronounced intermediate-temperature strength plateau and yield strengths surpassing other ductile RCCAs and the Ni-based superalloy CMSX-4 above 1273 K. In-situ neutron diffraction, TEM, and molecular dynamics identify a crossover near ~900 K, where edge dislocation glide stabilized by V-induced lattice distortion dominates, enabling enhanced strength retention and a clear design strategy for ultrahigh-temperature applications.

cond-mat.mtrl-sci↗

arXiv2025

Conformal invariants for the zero mode equation

For non-trivial solutions to the zero mode equation on a closed spin manifold \[D \varphi=iA\cdot \varphi,\] we first provide a simple proof for the sharp inequality \eq{ \norm{A}_{L^n}^2 \ge \frac {n}{4(n-1)} Y(M,[g]), } where $Y(M,[g])$ is the Yamabe constant of $(M,g)$, which was obtained by Frank-Loss and Reuss. Then we classify completely the equality case by proving that equality holds if and only if $\varphi$ is a Killing spinor, and if and only if $(M,g)$ is a Sasaki-Einstein manifold with $A$ (up to scaling) as its Reeb field and $\varphi$ a vacuum up to a conformal transformation. More generalizations have been also studied.

math.DG↗

arXiv2025

Creep Behavior of High-Entropy Alloys: A Critical Review

High-entropy alloys (HEAs) comprise a compositionally complex class of materials that in certain cases exhibit outstanding mechanical properties. While substantial progress has been made in understanding their phase stability, microstructure, and deformation mechanisms at room and cryogenic temperatures, the long-term creep behavior (>100 h) of HEAs at high temperatures (>0.6 Tm, where Tm is the melting temperature) remains relatively underexplored. This knowledge gap is critical, as many engineering applications, including those in aerospace, power generation, aero engines and nuclear energy, require materials with good creep resistance to maintain structural integrity over extended service lifetimes. This review provides a focused and critical assessment of the current understanding of high-temperature deformation and creep behavior of HEAs, with particular attention paid to face-centered cubic HEAs and body-centered cubic refractory HEAs. The underlying deformation mechanisms governing their creep response and the influence of phase stability at elevated temperatures are examined in detail. Recent studies reveal mechanistic differences between HEAs and conventional dilute alloys that do not always lead to improved creep resistance belying their initial promise. Based on these findings, we discuss the challenges in designing HEAs for high-temperature structural applications and outline future research directions that may lead to creep-resistant HEAs.

cond-mat.mtrl-sci↗

arXiv2025

Mechanistic Transition from Screw to Edge Dislocation Glide Enhances High-Temperature Strength in Refractory Complex Concentrated Alloys

The strength of body-centered cubic materials is traditionally known to be governed by screw dislocations. However, recent findings reveal that in certain refractory complex concentrated alloys, edge dislocations can instead control strength. This work integrates high-temperature mechanical testing, in-situ neutron scattering during heating and tension, scanning transmission electron microscopy, and molecular dynamics simulations to uncover the mechanism behind this behavior. In the Nb-Ta-Ti-V system, increasing the V content, due to its smaller atomic size, induces substantial atomic misfit that raises the glide barrier for edge dislocations relative to screw dislocations. This effect drives a gradual transition from screw to edge dislocation-controlled deformation, leading to markedly enhanced strength at elevated temperatures.

cond-mat.mtrl-sci↗

arXiv2025

Imitation Learning Policy based on Multi-Step Consistent Integration Shortcut Model

The wide application of flow-matching methods has greatly promoted the development of robot imitation learning. However, these methods all face the problem of high inference time. To address this issue, researchers have proposed distillation methods and consistency methods, but the performance of these methods still struggles to compete with that of the original diffusion models and flow-matching models. In this article, we propose a one-step shortcut method with multi-step integration for robot imitation learning. To balance the inference speed and performance, we extend the multi-step consistency loss on the basis of the shortcut model, split the one-step loss into multi-step losses, and improve the performance of one-step inference. Secondly, to solve the problem of unstable optimization of the multi-step loss and the original flow-matching loss, we propose an adaptive gradient allocation method to enhance the stability of the learning process. Finally, we evaluate the proposed method in two simulation benchmarks and five real-world environment tasks. The experimental results verify the effectiveness of the proposed algorithm.

cs.RO↗

arXiv2025

An Exhaustive DPLL Approach to Model Counting over Integer Linear Constraints with Simplification Techniques

Linear constraints are one of the most fundamental constraints in fields such as computer science, operations research and optimization. Many applications reduce to the task of model counting over integer linear constraints (MCILC). In this paper, we design an exact approach to MCILC based on an exhaustive DPLL architecture. To improve the efficiency, we integrate several effective simplification techniques from mixed integer programming into the architecture. We compare our approach to state-of-the-art MCILC counters and propositional model counters on 2840 random and 4131 application benchmarks. Experimental results show that our approach significantly outperforms all exact methods in random benchmarks solving 1718 instances while the state-of-the-art approach only computes 1470 instances. In addition, our approach is the only approach to solve all 4131 application instances.

cs.AI↗

arXiv2025

Stability of spinorial Sobolev inequalities on $\mathbb{S}^n$

The spinorial Sobolev inequality on the unit sphere states \begin{equation*} \Big(\int| D\psi|^{\frac{2n}{n+1}}\Big)^{\frac{n+1}{n}}-\frac{n}{2}\omega_{n}^{1/n}\int\langle D\psi,\psi\rangle \geq 0, \end{equation*} with equality if and only if $\psi \in {\mathcal M}$, the set of all $-\frac 12$-Killing spinors and their conformal transformations. Our main result in this paper is to refine this inequality by establishing a stability inequality \begin{equation*} \Big(\int| D\psi|^{\frac{2n}{n+1}}\Big)^{\frac{n+1}{n}}-\frac{n}{2}\omega_{n}^{1/n}\int\langle D\psi,\psi\rangle \geq {\bf c}_S\inf_{\phi\in\mathcal{M}}\Big(\int| D(\psi-\phi)|^{\frac{2n}{n+1}}\Big)^{\frac{n+1}{n}}. \end{equation*} As a by-product of our argument, we show that elements in set $\mathcal M$ are not optimizers of another spinorial Sobolev inequality \begin{equation*} \Big(\int| D\psi|^{\frac{2n}{n+1}}\Big)^{\frac{n+1}{n}} \geq C_S \Big(\int|\psi|^{\frac{2n}{n-1}}\Big)^{\frac{n-1}{n}}, \end{equation*} unlike expected by experts. They have in fact index $n+1$ and nullity $2^{[\frac n2]+2}$.

math.DG↗

arXiv2023

Multiple origins of extra electron diffractions in fcc metals

Diffuse intensities in the electron diffraction patterns of concentrated face-centered cubic solid solutions have been widely attributed to chemical short-range order, although this connection has been recently questioned. This article explores the many non-ordering origins of commonly reported features using a combination of experimental electron microscopy and multislice diffraction simulations, which suggest that diffuse intensities largely represent thermal and static displacement scattering. A limited number of observations may reflect additional contributions from planar defects, surface terminations incommensurate with bulk periodicity, or weaker dynamical effects

cond-mat.mtrl-sci↗

arXiv2023

Variants of Tagged Sentential Decision Diagrams

A recently proposed canonical form of Boolean functions, namely tagged sentential decision diagrams (TSDDs), exploits both the standard and zero-suppressed trimming rules. The standard ones minimize the size of sentential decision diagrams (SDDs) while the zero-suppressed trimming rules have the same objective as the standard ones but for zero-suppressed sentential decision diagrams (ZSDDs). The original TSDDs, which we call zero-suppressed TSDDs (ZTSDDs), firstly fully utilize the zero-suppressed trimming rules, and then the standard ones. In this paper, we present a variant of TSDDs which we call standard TSDDs (STSDDs) by reversing the order of trimming rules. We then prove the canonicity of STSDDs and present the algorithms for binary operations on TSDDs. In addition, we offer two kinds of implementations of STSDDs and ZTSDDs and acquire three variations of the original TSDDs. Experimental evaluations demonstrate that the four versions of TSDDs have the size advantage over SDDs and ZSDDs.

cs.AI↗

arXiv2023

Adaptive Distributed Filtering of DDoS Traffic on the Internet

Despite the proliferation of traffic filtering capabilities throughout the Internet, attackers continue to launch distributed denial-of-service (DDoS) attacks to successfully overwhelm the victims with DDoS traffic. In this paper, we introduce a distributed filtering system that leverages nodes distributed along the paths of DDoS traffic to filter the DDoS traffic. In particular, we focus on adaptive distributed filtering, a new direction in filtering DDoS traffic. In our design, a subscriber to the distributed filtering service can act on behalf of a DDoS victim and generate filtering rules that not only adapt to the most suitable and effective filtering granularity (e.g., IP source address and a port number vs. an individual IP address vs. IP prefixes at different lengths), but also adapt to the preferences of the subscriber (e.g., maximum coverage of DDoS traffic vs. minimum collateral damage from dropping legitimate traffic vs. minimum number of rules). We design an efficient algorithm that can generate rules adaptive toward filtering granularities and objectives, which can further help determine where to deploy generated rules for the best efficacy. We evaluated our system through both large-scale simulations based on real-world DDoS attack traces and pilot studies. Our evaluations confirm that our algorithm can generate rules that adapt to every distinct filtering objective and achieve optimal results. We studied the success rate and distribution of rule deployment under different Internet-scale rule deployment profiles, and found a small number of autonomous systems can contribute disproportionately to the defense. Our pilot studies also show our adaptive distributed filtering system can effectively defend against real-world DDoS attack traces in real time.

cs.NI↗

arXiv2023

Decentralized Threshold Signatures with Dynamically Private Accountability

Threshold signatures are a fundamental cryptographic primitive used in many practical applications. As proposed by Boneh and Komlo (CRYPTO'22), TAPS is a threshold signature that is a hybrid of privacy and accountability. It enables a combiner to combine t signature shares while revealing nothing about the threshold t or signing quorum to the public and asks a tracer to track a signature to the quorum that generates it. However, TAPS has three disadvantages: it 1) structures upon a centralized model, 2) assumes that both combiner and tracer are honest, and 3) leaves the tracing unnotarized and static. In this work, we introduce Decentralized, Threshold, dynamically Accountable and Private Signature (DeTAPS) that provides decentralized combining and tracing, enhanced privacy against untrusted combiners (tracers), and notarized and dynamic tracing. Specifically, we adopt Dynamic Threshold Public-Key Encryption (DTPKE) to dynamically notarize the tracing process, design non-interactive zero knowledge proofs to achieve public verifiability of notaries, and utilize the Key-Aggregate Searchable Encryption to bridge TAPS and DTPKE so as to awaken the notaries securely and efficiently. In addition, we formalize the definitions and security requirements for DeTAPS. Then we present a generic construction and formally prove its security and privacy. To evaluate the performance, we build a prototype based on SGX2 and Ethereum.

cs.CR↗

arXiv2022

Extra electron reflections in concentrated alloys do not necessitate short-range order

In many concentrated alloys of current interest, the observation of diffuse superlattice intensities by transmission electron microscopy has been attributed to chemical short-range order. We briefly review these findings and comment on the plausibility of widespread interpretations, noting the absence of expected peaks, conflicts with theoretical predictions, and the possibility of alternative explanations.

cond-mat.mtrl-sci↗

arXiv2021

CSSR: A Context-Aware Sequential Software Service Recommendation Model

We propose a novel software service recommendation model to help users find their suitable repositories in GitHub. Our model first designs a novel context-induced repository graph embedding method to leverage rich contextual information of repositories to alleviate the difficulties caused by the data sparsity issue. It then leverages sequence information of user-repository interactions for the first time in the software service recommendation field. Specifically, a deep-learning based sequential recommendation technique is adopted to capture the dynamics of user preferences. Comprehensive experiments have been conducted on a large dataset collected from GitHub against a list of existing methods. The results illustrate the superiority of our method in various aspects.

cs.IR↗