Probing the momentum dependence of medium modifications of the nucleon-nucleon elastic cross sections

The momentum dependence of the medium modifications on nucleon-nucleon elastic cross sections is discussed with microscopic transport theories and numerically investigated with an updated UrQMD microscopic transport model. The semi-peripheral Au+Au reaction at beam energy $E_b=400A$ MeV is adopted as an example. It is found that the uncertainties of the momentum dependence on medium modifications of cross sections influence the yields of free nucleons and their collective flows as functions of their transverse momentum and rapidity. Among these observables, the elliptic flow is sensitively dependent on detailed forms of the momentum dependence and more attention should be paid. The elliptic flow is hardly influenced by the probable splitting effect of the neutron-neutron and proton-proton cross sections so that one might pin down the mass splitting effect of the mean-field level at high beam energies and high nuclear densities by exploring the elliptic flow of nucleons or light clusters.Comment: 13 pages, 6 figures, 1 tabl

Topological mechanics in quasicrystals

We study topological mechanics in two-dimensional quasicrystalline parallelogram tilings. Topological mechanics has been studied intensively in periodic lattices in the past a few years, leading to the discovery of topologically protected boundary floppy modes in Maxwell lattices. In this paper we extend this concept to quasicrystalline parallelogram tillings and we use the Penrose tiling as our example to demonstrate how these topological boundary floppy modes arise with a small geometric perturbation to the tiling. The same construction can also be applied to disordered parallelogram tilings to generate topological boundary floppy modes. We prove the existence of these topological boundary floppy modes using a duality theorem which relates floppy modes and states of self stress in parallelogram tilings and fiber networks, which are Maxwell reciprocal diagrams to one another. We find that, due to the unusual rotational symmetry of quasicrystals, the resulting topological polarization can exhibit orientations not allowed in periodic lattices. Our result reveals new physics about the interplay between topological states and quasicrystalline order, and leads to novel designs of quasicrystalline topological mechanical metamaterials.Comment: 16 pages, 8 figure

Joint Head Selection and Airtime Allocation for Data Dissemination in Mobile Social Networks

Mobile social networks (MSNs) enable people with similar interests to interact without Internet access. By forming a temporary group, users can disseminate their data to other interested users in proximity with short-range communication technologies. However, due to user mobility, airtime available for users in the same group to disseminate data is limited. In addition, for practical consideration, a star network topology among users in the group is expected. For the former, unfair airtime allocation among the users will undermine their willingness to participate in MSNs. For the latter, a group head is required to connect other users. These two problems have to be properly addressed to enable real implementation and adoption of MSNs. To this aim, we propose a Nash bargaining-based joint head selection and airtime allocation scheme for data dissemination within the group. Specifically, the bargaining game of joint head selection and airtime allocation is first formulated. Then, Nash bargaining solution (NBS) based optimization problems are proposed for a homogeneous case and a more general heterogeneous case. For both cases, the existence of solution to the optimization problem is proved, which guarantees Pareto optimality and proportional fairness. Next, an algorithm, allowing distributed implementation, for join head selection and airtime allocation is introduced. Finally, numerical results are presented to evaluate the performance, validate intuitions and derive insights of the proposed scheme

Physical limits to sensing material properties

Constitutive relations describe how materials respond to external stimuli such as forces. All materials respond heterogeneously at small scales, which limits what a localized sensor can discern about the global constitution of a material. In this paper, we quantify the limits of such constitutional sensing by determining the optimal measurement protocols for sensors embedded in disordered media. For an elastic medium, we find that the least fractional uncertainty with which a sensor can determine a material constant $\lambda_0$ is approximately \begin{equation*} \frac{\delta \lambda_0}{\lambda_0 } \sim \left( \frac{\Delta_{\lambda} }{ \lambda_0^2} \right)^{1/2} \left( \frac{ d }{ a } \right)^{D/2} \left( \frac{ \xi }{ a } \right)^{D/2} \end{equation*} for $a \gg d \gg \xi$, $\lambda_0 \gg \Delta_{\lambda}^{1/2}$, and $D>1$, where $a$ is the size of the sensor, $d$ is its spatial resolution, $\xi$ is the correlation length of fluctuations in the material constant, $\Delta_{\lambda}$ is the local variability of the material constant, and $D$ is the dimension of the medium. Our results reveal how one can construct microscopic devices capable of sensing near these physical limits, e.g. for medical diagnostics. We show how our theoretical framework can be applied to an experimental system by estimating a bound on the precision of cellular mechanosensing in a biopolymer network.Comment: 33 pages, 3 figure

A stochastic model for internal HIV dynamics

In this paper we analyse a stochastic model representing HIV internal virus dynamics. The stochasticity in the model is introduced by parameter perturbation which is a standard technique in stochastic population modelling. We show that the model established in this paper possesses non-negative solutions as this is essential in any population dynamics model. We also carry out analysis on the asymptotic behaviour of the model. We approximate one of the variables by a mean reverting process and nd out the mean and variance of this process. Numerical simulations conclude the paper

Situational Context and Marked Code-Switching

Based on Halliday’s theory of register, this paper concerns about marked code-switching from the perspective of sociolinguistic situational context. Marked code-switching does not happen at random, but a kind of rational behavior. The data are gathered from utterances occurred in different situational contexts, by which and based on the field, tenor and mode of register, this research has made a deep analysis on marked code-switch, its socio-pragmatic functions and psychological motivations as well. It does have some research value either in theory and application since there is seldom research done about the marked code-switching phenomenon from the perspective of register theory. Keywords: register theory; marked code-switching; socio-pragmatic functions Résumé: Sur la base de la théorie de registre de Halliday, cet article s’intéresse sur le code-switching marqué à partir de la perspective du contexte situationnel sociolinguistique. Le Code-switching marqué ne se fait pas au hasard. C’est une sorte de procédé rationnel. Les données sont recueillies à partir des énoncés produits dans de différents contextes situationnels et la recherche a fait une analyse profonde sur le code-switching marqué, ses fonctions socio-pragmatiques et aussi les motivations psychologiques. Elle possède une certaine valeur de recherche dans la théorie et dans l'application, car les recherches sur le phénomène de code-switching marqué sont rarement faites dans la perspective de la théorie de registre. Mots-clés: la théorie de register; le code-switching marqué; les fonctions socio-pragmatiques 摘 要：本文從社會語言學的情景語境角度，借助Halliday的語域理論探討在語言的使用中有標記語碼轉換現象。 有標記語碼轉換不是盲目隨意的，而是一種理性行為。本文以一些生活中的情景語境片段為語料，從語域理論的語場、語勢和語式三維變項角度分析了有標記語碼轉換現象、有標記語碼轉換的社會語用和心理動機。將語域理論用於研究有標記語碼轉換的研究不甚多見，因此本研究具有一定的理論和應用價值。 關鍵詞：語域理論；有標記語碼轉換；社會語用功