Fermi gas in harmonic oscillator potentials

Assuming the validity of grand canonical statistics, we study the properties of a spin-polarized Fermi gas in harmonic traps. Universal forms of Fermi temperature $T_F$, internal energy $U$ and the specific heat per particle of the trapped Fermi gas are calculated as a {\it function} of particle number, and the results compared with those of infinite number particles.Comment: 8 pages, 1 figure, LATE

Exploiting Cognitive Structure for Adaptive Learning

Adaptive learning, also known as adaptive teaching, relies on learning path recommendation, which sequentially recommends personalized learning items (e.g., lectures, exercises) to satisfy the unique needs of each learner. Although it is well known that modeling the cognitive structure including knowledge level of learners and knowledge structure (e.g., the prerequisite relations) of learning items is important for learning path recommendation, existing methods for adaptive learning often separately focus on either knowledge levels of learners or knowledge structure of learning items. To fully exploit the multifaceted cognitive structure for learning path recommendation, we propose a Cognitive Structure Enhanced framework for Adaptive Learning, named CSEAL. By viewing path recommendation as a Markov Decision Process and applying an actor-critic algorithm, CSEAL can sequentially identify the right learning items to different learners. Specifically, we first utilize a recurrent neural network to trace the evolving knowledge levels of learners at each learning step. Then, we design a navigation algorithm on the knowledge structure to ensure the logicality of learning paths, which reduces the search space in the decision process. Finally, the actor-critic algorithm is used to determine what to learn next and whose parameters are dynamically updated along the learning path. Extensive experiments on real-world data demonstrate the effectiveness and robustness of CSEAL.Comment: Accepted by KDD 2019 Research Track. In Proceedings of the 25th ACM SIGKDD International Conference on Knowledge Discovery & Data Mining (KDD'19

Supported Au nanoparticles as efficient catalysts for aerobic homocoupling of phenylboronic acid

Au nanoparticles with small sizes (1–4 nm) were effectively formed on Mg–Al mixed oxides (Au/MAO), which showed superior catalytic performances and good recyclability in aerobic homocoupling of phenylboronic acid

Neutron scattering study of commensurate magnetic ordering in single crystal CeSb2_2

Temperature and field-dependent magnetization $M(H,T)$ measurements and neutron scattering study of a single crystal CeSb$_2$ are presented. Several anomalies in the magnetization curves have been confirmed at low magnetic field, i.e., 15.6 K, 12 K, and 9.8 K. These three transitions are all metamagnetic transitions (MMT), which shift to lower temperatures as the magnetic field increases. The anomaly at 15.6 K has been suggested as paramagnetic (PM) to ferromagnetic (FM) phase transition. The anomaly located at around 12 K is antiferromagnetic-like transition, and this turning point will clearly split into two when the magnetic field $H\geq0.2$ T. Neutron scattering study reveals that the low temperature ground state of CeSb$_2$ orders antiferromagnetically with commensurate propagation wave vectors $\textbf{k}=(-1,\pm1/6,0)$ and $\textbf{k}=(\pm1/6,-1,0)$, with N\'eel temperature $T_N\sim9.8$ K. This transition is of first-order, as shown in the hysteresis loop observed by the field cooled cooling (FCC) and field cooled warming (FCW) processes.Comment: 7 pages,9 figure

The 13N(d,n)14O Reaction and the Astrophysical 13N(p,g)14O Reaction Rate

$^{13}$N($p,\gamma$)$^{14}$O is one of the key reactions in the hot CNO cycle which occurs at stellar temperatures around $T_9$ $\geq$ 0.1. Up to now, some uncertainties still exist for the direct capture component in this reaction, thus an independent measurement is of importance. In present work, the angular distribution of the $^{13}$N($d,n$)$^{14}$O reaction at $E_{\rm{c.m.}}$ = 8.9 MeV has been measured in inverse kinematics, for the first time. Based on the distorted wave Born approximation (DWBA) analysis, the nuclear asymptotic normalization coefficient (ANC), $C^{^{14}O}_{1,1/2}$, for the ground state of $^{14}$O $\to$ $^{13}$N + $p$ is derived to be $5.42 \pm 0.48$ fm$^{-1/2}$. The $^{13}$N($p,\gamma$)$^{14}$O reaction is analyzed with the R-matrix approach, its astrophysical S-factors and reaction rates at energies of astrophysical relevance are then determined with the ANC. The implications of the present reaction rates on the evolution of novae are then discussed with the reaction network calculations.Comment: 17 pages and 8 figure

A New Experimental Technique for Applying Impulse Tension Loading

This paper deals with a new experimental technique for applying impulse tension loads. Briefly, the technique is based on the use of pulsed-magnetic-driven tension loading. Electromagnetic forming (EMF) can be quite effective in increasing the forming limits of metal sheets, such as aluminium and magnesium alloys. Yet, why the forming limit is increased is still an open question. One reason for this is the difficulty to let forming proceed on a certain influence monotonically: the main phenomena causing this increase in formability are considered to due to “body force” effect, inertia effect, changes in strain rate sensitivity. In this study, an impulse tension loading setup is presented. “Body force” effect and strain rate, which are known to be the two key factors leading to higher formability, can now be separated freely by our designed device. Reproducible and adjustable loading rate (80s-1~3267s-1) can be achieved by adjusting the discharge voltage and capacitance. The relation between the discharge voltage and strain rate was obtained with the help of finite element calculations and high-camera measurement results. The results of an exploratory experiment carried out on the designed device are presented for aluminum alloy AA5052 sheet. It shows that this technique could be used to study the dynamic response of sheets

Role of the van Hove Singularity in the Quantum Criticality of the Hubbard Model

A quantum critical point (QCP), separating the non-Fermi liquid region from the Fermi liquid, exists in the phase diagram of the 2D Hubbard model [Vidhyadhiraja et. al, Phys. Rev. Lett. 102, 206407 (2009)]. Due to the vanishing of the critical temperature associated with a phase separation transition, the QCP is characterized by a vanishing quasiparticle weight. Near the QCP, the pairing is enhanced since the real part of the bare d-wave p-p susceptibility exhibits algebraic divergence with decreasing temperature, replacing the logarithmic divergence found in a Fermi liquid [Yang et. al, Phys. Rev. Lett. 106, 047004 (2011)]. In this paper we explore the single-particle and transport properties near the QCP. We focus mainly on a van Hove singularity (vHS) coming from the relatively flat dispersion that crosses the Fermi level near the quantum critical filling. The flat part of the dispersion orthogonal to the antinodal direction remains pinned near the Fermi level for a range of doping that increases when we include a negative next-near-neighbor hopping t' in the model. For comparison, we calculate the bare d-wave pairing susceptibility for non-interacting models with the usual two-dimensional tight binding dispersion and a hypothetical quartic dispersion. We find that neither model yields a vHS that completely describes the critical algebraic behavior of the bare d-wave pairing susceptibility. The resistivity, thermal conductivity, thermopower, and the Wiedemann-Franz Law are examined in the Fermi liquid, marginal Fermi liquid, and pseudo-gap doping regions. A negative next-near-neighbor hopping t' increases the doping region with marginal Fermi liquid character. Both T and negative t' are relevant variables for the QCP, and both the transport and the motion of the vHS with filling suggest that they are qualitatively similar in their effect.Comment: 15 pages, 17 figure

A comparative study on the hepatoprotective action of bear bile and coptidis rhizoma aqueous extract on experimental liver fibrosis in rats

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