arXiv subjects

Xin Qian

Publications and source records attributed to Xin Qian.

At least 37 records · Page 2Linked to original sources

arXiv2025

On exact overlaps of integrable matrix product states: inhomogeneities, twists and dressing formulas

Invoking a quantum dressing procedure as well as the representation theory of twisted Yangians we derive a number of summation formulas for the overlap between integrable matrix product states and Bethe eigenstates which involve only eigenvalues of fused transfer matrices and which are valid in the presence of inhomogeneities as well as twists. Although the method is general we specialize to the $SO(6)$ spin chain for which integrable matrix product states corresponding to evaluation representations of the twisted Yangian $Y^+(4)$ encode the information about one-point functions of the D3-D5 domain wall version of ${\cal N}=4$ SYM. Considering the untwisted and homogeneous limit of our summation formulas we finally fill the last gap in the analytical understanding of the overlap formula for the $SO(6$) sector of the D3-D5 domain wall system.

hep-th↗

arXiv2024

Rigidity and regularity for almost homogeneous spaces with Ricci curvature bounds

We say that a metric space $X$ is $(ε,G)$-homogeneous if $G<Iso(X)$ is a discrete group of isometries with $diam(X/G)<ε$.\ A sequence of $(ε_i,G_i)$-homogeneous spaces $X_i$ with $ε_i\to0$ is called a sequence of almost homogeneous spaces. In this paper we show that the Gromov-Hausdorff limit of a sequence of almost homogeneous RCD$(K,N)$ spaces must be a nilpotent Lie group with $Ric\geqslant K$. We also obtain a topological rigidity theorem for $(ε,G)$-homogeneous RCD$(K,N)$ spaces, which generalizes a recent result by Wang. Indeed, if $X$ is an $(ε,G)$-homogeneous RCD$(K,N)$ space and $G$ is an almost-crystallographic group, then $X/G$ is bi-Hölder to an infranil orbifold. Moreover, we study $(ε,G)$-homogeneous spaces in the smooth setting and prove rigidity and $ε$-regularity theorems for Riemannian orbifolds with Einstein metrics and bounded Ricci curvatures respectively.

math.DG↗

arXiv2024

API Phonons: Python Interfaces for Phonon Transport Modeling

API Phonons is a Python software package to predict the transport dynamics of heat-carrying phonons. Using the powerful syntax of Python, this package provides modules and functions interfacing between different packages for atomistic simulations, lattice dynamics, and phonon-phonon interaction calculations including LAMMPS, Quippy, Phonopy, and ShengBTE. API Phonons enabled complex phonon calculations, including (1) extracting harmonic and anharmonic force constants from arbitrary interatomic potentials, which can be used as inputs for solving Boltzmann transport equations; (2) predicting thermal conductivity using Kubo's linear response theory, which captures both quasiparticle transport and inter-band coherent transport; and (3) modeling of ultrafast pump-probe thermal responses using a Green's function approach based on mode-resolved phonon properties for studying ballistic, hydrodynamic, and diffusive transport dynamics. The package provides a flexible, easy-to-use, and extensive platform for modeling phonon transport physics through Python programming.

cond-mat.mtrl-sci↗

arXiv2024

Analytical Green's Function of Multidimensional Boltzmann Transport Equation for Modeling Hydrodynamic Second Sound

Hydrodynamic second sound can be generated by heat pulses when the phonon-phonon interaction is dominantly momentum conserving, and the propagation of the temperature field becomes wavelike rather than diffusive. While the Boltzmann transport equation (BTE) has been widely applied to study phonon dynamics and thermal transport at the nanoscale, modeling the hydrodynamic transport regime remains challenging. The widely used relaxation time approximation (RTA) treats all phonon interactions as resistive without considering momentum conservation, resulting in the absence of phonon hydrodynamics. Rigorously solving BTE by inverting the full scattering matrix, however, is extremely computationally demanding and has been only applied to model one-dimensional temperature variations. Here, we present an analytical Green's function formalism for solving multidimensional Boltzmann transport equation (BTE) using phonon properties from first-principles calculations. This formalism involves Callaway's scattering approximation with separate relaxation times for momentum-conserving and momentum-destroying scattering events. The Green's function captures phonon dynamics in a wide range of temperature, spatial, and temporal scales, and successfully reproduces the transition from ballistic, hydrodynamic, to diffusive transport regimes. Our method avoids the computationally demanding inversion of large scattering matrices and shows good accuracies in predicting the temperature oscillation in ultrafast pump-probe characterizations with different geometries of thermal excitation.

cond-mat.mtrl-sci↗

arXiv2024

Nonreciprocal reflection of mid-infrared light by highly doped InAs at low magnetic fields

We report an experimental observation of room-temperature nonreciprocal reflection of mid-infrared light from planar highly doped InAs surfaces at low magnetic fields ranging from 0.07 T to 0.16 T. Using ellipsometry, we demonstrate that the amplitude ratio and phase shift of reflected light are nonreciprocal in the Voigt configuration. We also demonstrate using Fourier-transform infrared spectroscopy that the nonreciprocal reflectance contrast (the difference in reflectance in opposite directions) increases with the magnitude of the magnetic field for p-polarized light. Our work is a step toward the practical implementation of nonreciprocal thermal emitters and absorbers and applications such as remote magnetic field sensing.

physics.optics↗

arXiv2024

Waveform resampling with LMN method

Resampling is a common technique applied in digital signal processing. Based on the Fast Fourier Transformation (FFT), we apply an optimization called here the LMN method to achieve fast and robust re-sampling. In addition to performance comparisons with some other popular methods, we illustrate the effectiveness of this LMN method in a particle physics experiment: re-sampling of waveforms from Liquid Argon Time Projection Chambers.

hep-ex↗

arXiv2024

Reactor antineutrino flux and anomaly

Reactor antineutrinos have played a significant role in establishing the standard model of particle physics and the theory of neutrino oscillations. In this article, we review the reactor antineutrino flux and in particular the reactor antineutrino anomaly (RAA) coined over a decade ago. RAA refers to a deficit of the measured antineutrino inverse beta decay rates at very short-baseline reactor experiments compared to the theoretically improved predictions (i.e. the Huber-Mueller model). Since the resolution of several previous experimental anomalies have led to the discovery of non-zero neutrino mass and mixing, many efforts have been invested to study the origin of RAA both experimentally and theoretically. The progress includes the observation of discrepancies in antineutrino energy spectrum between data and the Huber-Mueller model, the re-evaluation of the Huber-Mueller model uncertainties, the potential isotope-dependent rate deficits, and the better agreement between data and new model predictions using the improved summation method. These developments disfavor the hypothesis of a light sterile neutrino as the explanation of RAA and supports the deficiencies of Huber-Mueller model as the origin. Looking forward, more effort from both the theoretical and experimental sides is needed to fully understand the root of RAA and to make accurate predictions of reactor antineutrino flux and energy spectrum for future discoveries.

hep-ph↗

arXiv2024

Thermodynamics of Ionic Thermoelectrics for Low-Grade Heat Harvesting

More than half of the waste heat rejected into the environment has temperatures lower than 100 $^\circ C$, which accounts for nearly 85 PWh/year worldwide. Efficiently harvesting low-grade heat could be a promising step toward carbon neutrality. Recent developments of ionic thermoelectrics (i-TE) with giant thermopower have provoked intensive interest in using ions as energy and charge carriers for efficient thermal energy harvesting. However, current literature primarily focuses on improving thermopower only, while the ion transport and thermodynamics affecting the efficiencies have been largely neglected. This review article clarifies the fundamentals of electrochemistry and thermodynamics for developing highly efficient i-TE devices. Two major types of i-TE devices, thermo-ionic capacitors (TIC) and thermogalvanic cells (TGC), are discussed in detail. The article analyzes the methods of enhancing ionic thermopower in the literature by taking an entropic point of view. We also derived modified thermoelectric factor Z for both TICs and TGCs that fully incorporate the dynamics of ion transport and electrochemical reactions. Recent developments of hybrid devices showing improved efficiencies, power density, and multifunctionality are reviewed. Finally, we comment on the remaining challenges and provide an outlook on future directions.

physics.chem-ph↗

arXiv2023

Imitation of Life: A Search Engine for Biologically Inspired Design

Biologically Inspired Design (BID), or Biomimicry, is a problem-solving methodology that applies analogies from nature to solve engineering challenges. For example, Speedo engineers designed swimsuits based on shark skin. Finding relevant biological solutions for real-world problems poses significant challenges, both due to the limited biological knowledge engineers and designers typically possess and to the limited BID resources. Existing BID datasets are hand-curated and small, and scaling them up requires costly human annotations. In this paper, we introduce BARcode (Biological Analogy Retriever), a search engine for automatically mining bio-inspirations from the web at scale. Using advances in natural language understanding and data programming, BARcode identifies potential inspirations for engineering challenges. Our experiments demonstrate that BARcode can retrieve inspirations that are valuable to engineers and designers tackling real-world problems, as well as recover famous historical BID examples. We release data and code; we view BARcode as a step towards addressing the challenges that have historically hindered the practical application of BID to engineering innovation.

cs.CL↗

arXiv2023

Singular sets on spaces with integral curvature bounds and diffeomorphism finiteness for manifolds

In this paper, we are concerned with noncollapsed Riemannian manifolds $(M^{n},g)$ with integral curvature bounds, as well as their Gromov-Hausdorff limits $(M^{n}_{i},g_{i})\xrightarrow{GH}(X,d)$. Our main result generalizes Cheeger's Hausdorff dimension estimate for the singular set in [7] and improve it into Minkowski dimension estimate in the spirit of Cheeger-Naber [12]. We also prove a difffeomorphism finiteness theorem for manifolds in the critical case, using Cheeger-Naber's methods in [13].

math.DG↗

arXiv2023

RCD(0,N)-spaces with small linear diameter growth

In this paper, we study some structure properties on the (revised) fundamental group of RCD(0,N) spaces. Our main result generalizes earlier work of Sormani on Riemannian manifolds with nonnegative Ricci curvature and small linear diameter growth. We prove that the revised fundamental group is finitely generated if assuming small linear diameter growth on RCD(0,N) spaces.

math.MG↗

arXiv2023

Glass-like Cross-plane Thermal Conductivity of Kagome Metals RbV3Sb5 and CsV3Sb5

This work reports the thermal conductivity of RbV3Sb5 and CsV3Sb5 with three-dimensional charge density wave phase transitions from 80 K to 400 K measured by pump-probe thermoreflectance techniques. The in-plane (basal plane) thermal conductivities are found moderate, i.e., 12 W/mK of RbV3Sb5 and 8.8 W/mK of CsV3Sb5 at 300 K. Low cross-plane (stacking direction) thermal conductivities are observed, with 0.72 W/mK of RbV3Sb5 and 0.49 W/mK of CsV3Sb5 at 300 K. A unique glass-like temperature dependence in the cross-plane thermal conductivity is observed, which decreases monotonically even lower than the Cahill-Pohl limit as the temperature decreases below the phase transition point TCDW. This temperature dependence is found to obey the hopping transport picture. In addition, a peak in cross-plane thermal conductivity is observed at TCDW as a fingerprint of the modulated structural distortion along the stacking direction.

cond-mat.mtrl-sci↗

arXiv2023

Machine learning reconstruction of depth-dependent thermal conductivity profile from pump-probe thermoreflectance signals

Characterizing materials with spatially varying thermal conductivities is significant to unveil the structure-property relation for a wide range of functional materials, such as chemical-vapor-deposited diamonds, ion-irradiated materials, nuclear materials under radiation, and battery electrode materials. Although the development of thermal conductivity microscopy based on time/frequency-domain thermoreflectance (TDTR/FDTR) enabled in-plane scanning of thermal conductivity profile, measuring depth-dependent thermal conductivity remains challenging. This work proposed a machine-learning-based reconstruction method for extracting depth-dependent thermal conductivity K(z) directly from frequency-domain phase signals. We demonstrated that the simple supervised-learning algorithm kernel ridge regression (KRR) can reconstruct K(z) without requiring pre-knowledge about the functional form of the profile. The reconstruction method can not only accurately reproduce typical K(z) distributions such as the pre-assumed exponential profile of chemical-vapor-deposited (CVD) diamonds and Gaussian profile of ion-irradiated materials, but also complex profiles artificially constructed by superimposing Gaussian, exponential, polynomial, and logarithmic functions. In addition to FDTR, the method also shows excellent performances of reconstructing K(z) of ion-irradiated semiconductors from TDTR signals. This work demonstrates that combining machine learning with pump-probe thermoreflectance is an effective way for depth-dependent thermal property mapping.

physics.app-ph↗

arXiv2023

Effect of solvation shell structure on thermopower of liquid redox pairs

Recent advancements in thermogalvanic batteries offer a promising route to efficient harvesting of low-grade heat with temperatures below 100 °C. The thermogalvanic temperature coefficient α, usually referred to as effective thermopower, is the key parameter determining the power density and efficiency of thermogalvanic batteries. However, the current understanding of improving α of redox pairs remains at the phenomenological level without microscopic insights, and the development of electrolytes with high α largely relies on experimental trial and error. This work applies the free energy perturbation method based on molecular dynamics simulations to predict the α of the {Fe^{3+}/Fe^{2+}} redox pair in aqueous and acetone solutions. We showed that α of the {Fe^{3+}/Fe^{2+}} redox pair can be increased from 1.5{\pm}0.3 mV/K to 4.1{\pm}0.4 mV/K with the increased acetone to water fraction. The predicted α of {Fe^{3+}/Fe^{2+}} both in pure water and acetone show excellent agreement with experimental values. By monitoring the fluctuation of dipole orientations in the first solvation shell, we discovered a significant change in the variance of solvent dipole orientation between Fe^{3+} and Fe^{2+}, which can be a microscopic indicator for large magnitudes of α. The effect of acetone weight fraction in the mixed acetone-water solvent on the α of {Fe^{3+}/Fe^{2+}} is also studied. Acetone molecules are found to intercalate into the first solvation shell of the {Fe^{2+}} ion at high acetone fractions, while this phenomenon is not observed in the solvation shell of the Fe^{3+} ion. Such solvation shell structure change of {Fe^{2+}} ions contributes to the enhanced α at high acetone fractions. Our discovery provides atomistic insights into how solvation shell order can be leveraged to develop electrolytes with high thermopower.

physics.chem-ph↗

arXiv2023

Thermo-optic phase shifter based on hydrogen-doped indium oxide microheater

Thermo-optic (TO) phase shifters are very fundamental units in large-scale active silicon photonic integrated circuits (PICs). However, due to the limitation of microheater materials with a trade-off between heating efficiency and absorption loss, designs reported so far typically suffer from slow response time, high power consumption, low yields, and so on. Here, we demonstrate an energy-efficient, fast-response, and low-loss TO phase shifter by introducing hydrogen-doped indium oxide (IHO) films as microheater, and the optimized electron concentration with enhanced mobility endows the IHO high conductivity as well as high near-infrared (NIR) transparency, which allow it to directly contact the silicon waveguide without any insulating layer for efficient tuning and fast response. The TO phase shifter achieves a sub-microsecond response time (970 ns/980 ns) with a π phase shift power consumption of 9.6 mW. And the insertion loss introduced by the IHO microheater is ~ 0.5 dB. The proposed IHO-based microheaters with compatible processing technology illustrate the great potential of such material in the application of large-scale silicon PICs.

physics.optics↗

arXiv2022

Augmenting Scientific Creativity with an Analogical Search Engine

Analogies have been central to creative problem-solving throughout the history of science and technology. As the number of scientific papers continues to increase exponentially, there is a growing opportunity for finding diverse solutions to existing problems. However, realizing this potential requires the development of a means for searching through a large corpus that goes beyond surface matches and simple keywords. Here we contribute the first end-to-end system for analogical search on scientific papers and evaluate its effectiveness with scientists' own problems. Using a human-in-the-loop AI system as a probe we find that our system facilitates creative ideation, and that ideation success is mediated by an intermediate level of matching on the problem abstraction (i.e., high versus low). We also demonstrate a fully automated AI search engine that achieves a similar accuracy with the human-in-the-loop system. We conclude with design implications for enabling automated analogical inspiration engines to accelerate scientific innovation.

cs.HC↗

arXiv2022

DUNE Software and High Performance Computing

DUNE, like other HEP experiments, faces a challenge related to matching execution patterns of our production simulation and data processing software to the limitations imposed by modern high-performance computing facilities. In order to efficiently exploit these new architectures, particularly those with high CPU core counts and GPU accelerators, our existing software execution models require adaptation. In addition, the large size of individual units of raw data from the far detector modules pose an additional challenge somewhat unique to DUNE. Here we describe some of these problems and how we begin to solve them today with existing software frameworks and toolkits. We also describe ways we may leverage these existing software architectures to attack remaining problems going forward. This whitepaper is a contribution to the Computational Frontier of Snowmass21.

hep-ex↗

arXiv2021

Confinement Effect on Thermopower of Electrolytes

Ionic Seebeck effect of electrolytes has shown promising applications in harvesting energy from low-grade waste-heat sources with small temperature difference from the environment, which can power sensors and Internet-of-Things devices. Recent experiments have demonstrated giant thermopower (~ 10 mV/K) of electrolytes under confinement due to the overlapping of electric double layer (EDL). Nonetheless, there has been no consensus on the theory of the ionic Seebeck effect, especially whether the thermopower depends on ionic diffusivities, imposing confusion on the theoretical interpretation of experimental discovery on giant thermopower of confined electrolytes. This article presents a linear perturbative solution of Poisson-Nernst-Planck (PNP) equations to describe the ionic Seebeck effect of confined liquid electrolytes. We provide both analytical and numerical solutions to the PNP equations for closed systems and open systems connected to reservoirs of electrolytes. The analytical solution captured the confinement effect both along and perpendicular to the temperature gradient, and showed excellent agreement with numerically solved PNP equations for a wide range of EDL potentials, channel widths, and lengths. Finally, we show that for polyelectrolytes with largely mismatched diffusivities, thermopower can only be enhanced for closed system through confinement perpendicular to the temperature gradient.

cond-mat.soft↗