Accurate determination of the Gaussian transition in spin-1 chains with single-ion anisotropy

The Gaussian transition in the spin-one Heisenberg chain with single-ion anisotropy is extremely difficult to treat, both analytically and numerically. We introduce an improved DMRG procedure with strict error control, which we use to access very large systems. By considering the bulk entropy, we determine the Gaussian transition point to 4-digit accuracy, $D_{c}/J = 0.96845(8)$, resolving a long-standing debate in quantum magnetism. With this value, we obtain high-precision data for the critical behavior of quantities including the ground-state energy, gap, and transverse string-order parameter, and for the critical exponent, $\nu = 1.472(2)$. Applying our improved technique at $J_{z} = 0.5$ highlights essential differences in critical behavior along the Gaussian transition line.Comment: 4 pages and 4 figure

Dark-state sideband cooling in an atomic ensemble

We utilize the dark state in a {\Lambda}-type three-level system to cool an ensemble of 85Rb atoms in an optical lattice [Morigi et al., Phys. Rev. Lett. 85, 4458 (2000)]. The common suppression of the carrier transition of atoms with different vibrational frequencies allows them to reach a subrecoil temperature of 100 nK after being released from the optical lattice. A nearly zero vibrational quantum number is determined from the time-of-flight measurements and adiabatic expansion process. The features of sideband cooling are examined in various parameter spaces. Our results show that dark-state sideband cooling is a simple and compelling method for preparing a large ensemble of atoms into their vibrational ground state of a harmonic potential and can be generalized to different species of atoms and molecules for studying ultracold physics that demands recoil temperature and below

MiniSeg: An Extremely Minimum Network for Efficient COVID-19 Segmentation

The rapid spread of the new pandemic, i.e., COVID-19, has severely threatened global health. Deep-learning-based computer-aided screening, e.g., COVID-19 infected CT area segmentation, has attracted much attention. However, the publicly available COVID-19 training data are limited, easily causing overfitting for traditional deep learning methods that are usually data-hungry with millions of parameters. On the other hand, fast training/testing and low computational cost are also necessary for quick deployment and development of COVID-19 screening systems, but traditional deep learning methods are usually computationally intensive. To address the above problems, we propose MiniSeg, a lightweight deep learning model for efficient COVID-19 segmentation. Compared with traditional segmentation methods, MiniSeg has several significant strengths: i) it only has 83K parameters and is thus not easy to overfit; ii) it has high computational efficiency and is thus convenient for practical deployment; iii) it can be fast retrained by other users using their private COVID-19 data for further improving performance. In addition, we build a comprehensive COVID-19 segmentation benchmark for comparing MiniSeg to traditional methods

Experimental Investigation on the Influence of Refrigerant Charge on the Performance of Trans-critical CO2 Water-Water Heat Pump

Natural refrigerant CO2 is widely used in refrigeration and heat pump systems. It is of great significance for reductions of ozone depletion and global warming. The efficiency of heat pump system is affected by many factors. The amount of refrigerant charge in the heat pump is a primary parameter that influences the energy efficiency. Undercharge or overcharge of refrigerant degrade its performance and deteriorate system reliability. Therefore, heat pump should be charged with an optimum amount of refrigerant to achieve high performance. However, it is difficult to calculate the optimum charge accurately because of the various components and operating parameters. Â In this paper, a trans-critical CO2Â heat pump system is set up to investigate the influence of refrigerant charge on the performance of a small-sized heat pump water heater. The trans-critical CO2Â heat pump system is composed of a rotary compressor, a tube-in-tube evaporator and gas cooler, an electronic expansion valve (EEV), and an internal heat exchanger (IHX). The objective of this study is to analyze the characteristics of the CO2 heat pump under various refrigerant charging conditions. Therefore, the performance of the CO2Â system was measured and discussed on the basis of refrigerant charge amount. Â Based on the experimental results, the effects of refrigerant charge on the power of system, rejection pressure, evaporating pressure, mass flow rate and coefficient of performance (COP) were analyzed with different EEV openings. The experimental results show that the COP was strongly related to CO2 mass charge and that the formation of the trans-critical cycle depended on CO2 mass charge greatly. The pressures in the gas cooler and the evaporator increased with the rise of refrigerant charge. The compression ratio decreased with the increase of the refrigerant charge. The COP has a maximum value at a specific CO2 mass charge. Undercharged CO2 systems could result in a fast decrease of the heating capacity and COP. However, overcharged CO2 systems could cause an abrupt increase of compressor power consumption. The heating cycle displayed different characteristics with different CO2 mass charges. The optimum CO2 mass charges varied with different EEV openings, and it could be determined according to several parameters

Investigation of the Frequency Shift of a SAD Circuit Loop and the Internal Micro-Cantilever in a Gas Sensor

Micro-cantilever sensors for mass detection using resonance frequency have attracted considerable attention over the last decade in the field of gas sensing. For such a sensing system, an oscillator circuit loop is conventionally used to actuate the micro-cantilever, and trace the frequency shifts. In this paper, gas experiments are introduced to investigate the mechanical resonance frequency shifts of the micro-cantilever within the circuit loop(mechanical resonance frequency, MRF) and resonating frequency shifts of the electric signal in the oscillator circuit (system working frequency, SWF). A silicon beam with a piezoelectric zinc oxide layer is employed in the experiment, and a Self-Actuating-Detecting (SAD) circuit loop is built to drive the micro-cantilever and to follow the frequency shifts. The differences between the two resonating frequencies and their shifts are discussed and analyzed, and a coefficient α related to the two frequency shifts is confirmed