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

Study of the Effect of Anisotropic Gold Nanoparticles on Plasmonic Coupling with a Photosensitizer for Antimicrobial Film

Development of antimicrobial surfaces for sterilization is much needed to avoid the spreading of drug resistant bacteria. Light can activate antimicrobial surfaces by an interaction between nanoparticles and a photosensitizer dye to produce a steady and efficient killing of bacteria. The film studied in this work contains gold nanorods (AuNRs) of 32 nm length and 16 nm diameter and gold nanostars (AuNSs) of 50 nm of diameter, in combination with crystal violet (CV) dye. The surface plasmon resonance (SPR) of the nanoparticles used in the film was mathematically simulated and characterized to understand different SPR between the particles. Their effects on plasmonic coupling with the dye, and thus the production of reactive oxygen species (ROS) and consequently the activity of the film against bacteria, were studied. The films showed great antimicrobial activity against Gram-negative bacteria (E. coli) in 4 h of light exposure; when modified with AuNSs, it could kill E. coli with 5 orders of magnitude (5-log), and the one modified with AuNRs could kill with 4 order of magnitude (4-log), while maintaining partial activity against Gram-positive bacteria (S. aureus), i.e. being able to kill with 2.5 orders of magnitude by the film containing AuNSs and 3 orders of magnitude by those containing AuNRs. The differential response of Gram-negative and Gram-positive bacteria to the ROS generated by the films would allow a more targeted approach for specific bacterial species, for example, surfaces of bedpans or common contact surfaces (handles, handrails, etc.) that are contaminated principally by Gram-negative or Gram-positive bacteria, respectively

Nitrous oxide emissions increase exponentially when optimum nitrogen fertilizer rates are exceeded in the North China plain

The IPCC assume a linear relationship between nitrogen (N) application rate and nitrous oxide (N2O) emissions in inventory reporting, however, a growing number of studies show a nonlinear relationship under specific soil-climatic conditions. In the North China plain, a global hotspot of N2O emissions, covering a land as large as Germany, the correlation between N rate and N2O emissions remains unclear. We have therefore specifically investigated the N2O response to N applications by conducting field experiments with five N rates, and high-frequency measurements of N2O emissions across contrasting climatic years. Our results showed that cumulative and yield-scaled N2O emissions both increased exponentially as N applications were raised above the optimum rate in maize (Zea mays L.). In wheat (Triticum aestivum L.) there was a corresponding quadratic increase in N2O emissions with the magnitude of the response in 2012–2013 distinctly larger than that in 2013–2014 owing to the effects of extreme snowfall. Existing empirical models (including the IPCC approach) of the N2O response to N rate have overestimated N2O emissions in the North China plain, even at high N rates. Our study therefore provides a new and robust analysis of the effects of fertilizer rate and climatic conditions on N2O emissions

Biodegradation of a Nano-Hydroxyapatite/Collagen Composite by Peritoneal Monocyte-Macrophages

A nano-hydroxyapatite/collagen composite was prepared by precipitation of hydroxyapatite from an aqueous solution onto collagen. Mouse peritoneal macrophages were used to investigate the in vitro biodegradation of the composite. The results showed the mechanism of phagocytosis and extracellular degradation process. The cells that belong to the mononuclear phagocyte system showed some morphological characteristics similar to those of osteoclasts and made pits on the composite surface. The local modification of the material surface by the cell was another phenomenon distinguishable from the degradation process. The degradation and modification made the material porous with a widely varying Ca/P ratio

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

A possible disk mechanism for the 23d QPO in Mkn~501

Optically thin two-temperature accretion flows may be thermally and viscously stable, but acoustically unstable. Here we propose that the O-mode instability of a cooling-dominated optically thin two-temperature inner disk may explain the 23-day quasi-periodic oscillation (QPO) period observed in the TeV and X-ray light curves of Mkn~501 during its 1997 high state. In our model the relativistic jet electrons Compton upscatter the disk soft X-ray photons to TeV energies, so that the instability-driven X-ray periodicity will lead to a corresponding quasi-periodicity in the TeV light curve and produce correlated variability. We analyse the dependence of the instability-driven quasi-periodicity on the mass (M) of the central black hole, the accretion rate ($\rm{\dot{M}}$) and the viscous parameter ($\alpha$) of the inner disk. We show that in the case of Mkn~501 the first two parameters are constrained by various observational results, so that for the instability occurring within a two-temperature disk where $\alpha=0.05-1.0$, the quasi-period is expected to lie within the range of 8 to 100 days, as indeed the case. In particular, for the observed 23-day QPO period our model implies a viscosity coefficient $\alpha \leq 0.28$, a sub-Eddington accretion rate $\dot{M} \simeq 0.02 \dot{M}_{\rm Edd}$ and a transition radius to the outer standard disk of $r_0 \sim 60 r_g$, and predicts a period variation $\delta P/P \sim 0.23$ due to the motion of the instability region.Comment: 18 pages, 1 figure, accepted by AP

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