arXiv subjects

Nan Xie

Publications and source records attributed to Nan Xie.

12 recordsLinked to original sources

arXiv2026

Dynamics of a microroller under confinement

Rotating particles can translate when placed near a surface, forming microrollers with a wide range of biomedical and microfluidic applications. In this work, we investigate the dynamics of microrollers in confined microchannels with different geometries by combining experiments, numerical simulations, and scaling analysis. In constricted channels, we find that the translational velocity of a microroller decreases as it approaches the constricted region. In both rectangular and cylindrical channels, velocity reversal occurs as the characteristic channel width decreases. Using the force-free condition for free translation, we develop a systematic scaling framework that can be generalized to different channel geometries. The scaling analysis yields functional dependences of the translational velocity on the degree of confinement, which agree well with both experiments and simulations. Importantly, we demonstrate that the viscous stress generated by the far-field rotlet flow governs the observed velocity reduction and reversal, while the translational resistance resulting from the near-field shear flow suppresses translation under tight confinement. The distinct roles of these flow components revealed by our analysis may provide practical guidance for controlling microroller dynamics in confined fluid environments.

physics.flu-dyn↗

arXiv2025

Suppression and Regulation of Thermal Birefringence in Optical Voltage Sensor with Isomerism Electrodes and Arbitrary Electric Field Direction Modulation

The insufficient stability and reliability of Optical Voltage Sensor is primarily caused by thermal stress induced birefringence. In this paper, a method based on arbitrary electric field direction modulation and isomerism electrodes is proposed to suppress or regulate it. With the aid of multi-physics Finite Element Method, Jones Matrix and the theory of photoelastic effect, it is found that metal or transparent isomerism electrodes can generate a special thermal stress distribution, which regulates the birefringence in the optical path and their induced measurement error. The experiment is conducted on a 10mm cubic bismuth germanite crystal, with cutting directions 110, -110 and 001. The experiment result shows that Cu isomerism electrodes with electric field angle of 59.9 degrees could generate 37% less birefringence error compared to parallel plate electrodes, in the temperature range from 25 degrees Celsius to 40 degrees Celsius. However, the Indium Tin Oxide electrodes with field angle of 29.6 degrees produces approximately 7 times error because of its bad ductility and thermal conduction. The proposed modeling and suppression method for birefringence is beneficial to design of high accuracy optical voltage sensor or electro-optical modulator.

eess.SY↗

arXiv2024

AgentCourt: Simulating Court with Adversarial Evolvable Lawyer Agents

Current research in LLM-based simulation systems lacks comprehensive solutions for modeling real-world court proceedings, while existing legal language models struggle with dynamic courtroom interactions. We present AgentCourt, a comprehensive legal simulation framework that addresses these challenges through adversarial evolution of LLM-based agents. Our AgentCourt introduces a new adversarial evolutionary approach for agents called AdvEvol, which performs dynamic knowledge learning and evolution through structured adversarial interactions in a simulated courtroom program, breaking the limitations of the traditional reliance on static knowledge bases or manual annotations. By simulating 1,000 civil cases, we construct an evolving knowledge base that enhances the agents' legal reasoning abilities. The evolved lawyer agents demonstrated outstanding performance on our newly introduced CourtBench benchmark, achieving a 12.1% improvement in performance compared to the original lawyer agents. Evaluations by professional lawyers confirm the effectiveness of our approach across three critical dimensions: cognitive agility, professional knowledge, and logical rigor. Beyond outperforming specialized legal models in interactive reasoning tasks, our findings emphasize the importance of adversarial learning in legal AI and suggest promising directions for extending simulation-based legal reasoning to broader judicial and regulatory contexts. The project's code is available at: https://github.com/relic-yuexi/AgentCourt

cs.CL↗

arXiv2024

DeliLaw: A Chinese Legal Counselling System Based on a Large Language Model

Traditional legal retrieval systems designed to retrieve legal documents, statutes, precedents, and other legal information are unable to give satisfactory answers due to lack of semantic understanding of specific questions. Large Language Models (LLMs) have achieved excellent results in a variety of natural language processing tasks, which inspired us that we train a LLM in the legal domain to help legal retrieval. However, in the Chinese legal domain, due to the complexity of legal questions and the rigour of legal articles, there is no legal large model with satisfactory practical application yet. In this paper, we present DeliLaw, a Chinese legal counselling system based on a large language model. DeliLaw integrates a legal retrieval module and a case retrieval module to overcome the model hallucination. Users can consult professional legal questions, search for legal articles and relevant judgement cases, etc. on the DeliLaw system in a dialogue mode. In addition, DeliLaw supports the use of English for counseling. we provide the address of the system: https://data.delilegal.com/lawQuestion.

cs.CL↗

arXiv2022

Design of optical voltage sensor based on electric field regulation and rotating isomerism electrode

Temperature drift, stress birefringence and low frequency vibration lead to the randomness and fluctuation of the output of optical voltage sensor(OVS). In order to solve the problem, this study adopts the lock-in amplifier technology with the aid of a high-speed rotating electrode to realize electric field modulation. This technology could shift the measured signal frequency band from near 50 Hz moved to several kilometer Hz, so as to make the output signal avoid the interference from low-frequency temperature drift, stress birefringence and vibration, leading to higher stability and reliability. The electro-optic coupling wave theory and static electric field finite element method are utilized to investigate the shape of modulation wave. The simulation results proves that lock-in technology is able to prevent the measured voltage signal from the large step signal interference and restore the perfect original signal. While the sample rate is decreased to the value of the modulation frequency.

eess.SP↗

arXiv2022

IEC61850 Sample-Value Service Based on Reduced Application Service Data Unit for Energy IOT

With the development of 5G technology and low-power wireless communication technology, a large number of IOT devices are introduced into energy systems. Existing IOT communication protocols such as MQQT and COAP cannot meet the requirements of high reliability and real-time performance. However, the 61850-9-2 Sample value protocol is relatively complex and the message length is large, difficult to ensure real-time transmission for IOT devices with limited transmission rate. This paper proposes a 9-2 Sample Value protocol for IOT controller based on Application Service Data Unit. The communication protocol is strictly in accordance with IEC61850-9-2 and can be recognized by existing intelligent electronic devices such as merging units. The protocol simplifies and trims some parameters, and changes the floating point value to integer data. Considering the instability of wireless communication, uni-cast or multicast UDP/IP is utilized to send SV Payload based on the 2.4GHz WIFI. The maximum transmission rate can be up to 30 Mbps. The hardware to implement reduced SV adopts ESP32-S, which is a dual-core MCU supporting WIFI with frequency of 240MHz. Software is based on FreeRTOS, LWIP and Libiec61850. A PC or raspberry PI is used as the Host to receive and analyze packets, verifying feasibility of reduced SV protocols.

cs.NI↗

arXiv2022

A half-wave voltage regulation method of electro-optic crystal based on center-symmetric electrodes and arbitrary direction electric field

To solve the problems of instability and thermal stress birefringence of voltage divided medium in optical voltage sensor (OVS), a half-wave voltage regulation method based on a central symmetry electrode and an arbitrary directional electric field is proposed in this paper. The method uses a center-symmetric copper foil electrode or the ITO (Indium Tin Oxide) transparent electrode to apply voltage, which can arbitrarily adjust the direction of the average electric field in the crystal, so as to improve the half-wave voltage of the bismuth germanate (Bi4Ge3O12, or BGO) crystal directly without additional SF6 gas or quartz glass. The internal electric field of the BGO crystal is simulated by the finite element method, and the half-wave voltage is calculated by the coupling wave theory of electro-optic effect. The results show that the maximum regulated half-wave voltage, considering the 1° angle, can reach 2.67e3 kV. And this is consistent to the experimental results 1.72e3 kV with difference of 35.6%. For the measurement of 110kV line voltage, that is, 63.5kV phase voltage, to ensure a 0.2 accuracy class, the angle error of incident light, and the polarization direction and the electric field direction is required to be less than 3.9', which can be achieved by the existing technologies.

cond-mat.mtrl-sci↗

arXiv2017

Properties of an Aloha-like stability region

A well-known inner bound on the stability region of the finite-user slotted Aloha protocol is the set of all arrival rates for which there exists some choice of the contention probabilities such that the associated worst-case service rate for each user exceeds the user's arrival rate, denoted $Λ$. Although testing membership in $Λ$ of a given arrival rate can be posed as a convex program, it is nonetheless of interest to understand the properties of this set. In this paper we develop new results of this nature, including $i)$ an equivalence between membership in $Λ$ and the existence of a positive root of a given polynomial, $ii)$ a method to construct a vector of contention probabilities to stabilize any stabilizable arrival rate vector, $iii)$ the volume of $Λ$, $iv)$ explicit polyhedral, spherical, and ellipsoid inner and outer bounds on $Λ$, and $v)$ characterization of the generalized convexity properties of a natural ``excess rate'' function associated with $Λ$, including the convexity of the set of contention probabilities that stabilize a given arrival rate vector.

cs.IT↗

arXiv2017

Delay on broadcast erasure channels under random linear combinations

We consider a transmitter broadcasting random linear combinations (over a field of size $d$) formed from a block of $c$ packets to a collection of $n$ receivers, where the channels between the transmitter and each receiver are independent erasure channels with reception probabilities $\mathbf{q} = (q_1,\ldots,q_n)$. We establish several properties of the random delay until all $n$ receivers have recovered all $c$ packets, denoted $Y_{n:n}^{(c)}$. First, we provide lower and upper bounds, exact expressions, and a recurrence for the moments of $Y_{n:n}^{(c)}$. Second, we study the delay per packet $Y_{n:n}^{(c)}/c$ as a function of $c$, including the asymptotic delay (as $c \to \infty$), and monotonicity (in $c$) properties of the delay per packet. Third, we employ extreme value theory to investigate $Y_{n:n}^{(c)}$ as a function of $n$ (as $n \to \infty$). Several results are new, some results are extensions of existing results, and some results are proofs of known results using new (probabilistic) proof techniques.

cs.IT↗

arXiv2016

On the Aloha throughput-fairness tradeoff

A well-known inner bound of the stability region of the slotted Aloha protocol on the collision channel with n users assumes worst-case service rates (all user queues non-empty). Using this inner bound as a feasible set of achievable rates, a characterization of the throughput--fairness tradeoff over this set is obtained, where throughput is defined as the sum of the individual user rates, and two definitions of fairness are considered: the Jain-Chiu-Hawe function and the sum-user alpha-fair (isoelastic) utility function. This characterization is obtained using both an equality constraint and an inequality constraint on the throughput, and properties of the optimal controls, the optimal rates, and the fairness as a function of the target throughput are established. A key fact used in all theorems is the observation that all contention probability vectors that extremize the fairness functions take at most two non-zero values.

cs.IT↗

arXiv2013

Twisted Bilayer Graphene Superlattices

Twisted bilayer graphene (tBLG) provides us with a large rotational freedom to explore new physics and novel device applications, but many of its basic properties remain unresolved. Here we report the synthesis and systematic Raman study of tBLG. Chemical vapor deposition was used to synthesize hexagon- shaped tBLG with a rotation angle that can be conveniently determined by relative edge misalignment. Superlattice structures are revealed by the observation of two distinctive Raman features: folded optical phonons and enhanced intensity of the 2D-band. Both signatures are strongly correlated with G-line resonance, rotation angle and laser excitation energy. The frequency of folded phonons decreases with the increase of the rotation angle due to increasing size of the reduced Brillouin zone (rBZ) and the zone folding of transverse optic (TO) phonons to the rBZ of superlattices. The anomalous enhancement of 2D-band intensity is ascribed to the constructive quantum interference between two Raman paths enabled by a near-degenerate Dirac cone. The fabrication and Raman identification of superlattices pave the way for further basic study and new applications of tBLG.

cond-mat.mtrl-sci↗

arXiv2010

Geometric Approximations of Some Aloha-like Stability Regions

Most bounds on the stability region of Aloha give necessary and sufficient conditions for the stability of an arrival rate vector under a specific contention probability (control) vector. But such results do not yield easy-to-check bounds on the overall Aloha stability region because they potentially require checking membership in an uncountably infinite number of sets parameterized by each possible control vector. In this paper we consider an important specific inner bound on Aloha that has this property of difficulty to check membership in the set. We provide ellipsoids (for which membership is easy-to-check) that we conjecture are inner and outer bounds on this set. We also study the set of controls that stabilize a fixed arrival rate vector; this set is shown to be a convex set.

cs.IT↗