Paraffin/SiC as a Novel Composite Phase-Change Material for a Lithium-Ion Battery Thermal Management System

A lithium-ion battery thermal management system has always been a hot spot in the battery industry. In this study, a novel high-thermal-conductivity composite phase-change material(CPCM) made by paraffin wax and silicon was adopted to facilitate heat transfer. Moreover, high resistance or even insulation of CPCM is capable of preventing short circuits between the cells. The heat transfer mechanism of CPCMs was determined under a scanning electron microscope. A thermogravimetric analyzer was employed to determine the thermal stability. A diff erential scanning calorimeter was used to explore the thermophysical properties of the composite samples. By comparing the results of the experiment, it was reported that under the silicon carbide content of 5%, the parameters were better than others. The phase-change enthalpy of CPCM was 199.4 J/g, the leakage rate of liquid was 4.6%, and the melting point was 53.6℃. To verify the practicality of CPCM, a three-dimensional layered battery pack model was built in the COMSOL Multiphysics software. By simulating the thermal runaway inside the battery packs of various materials, it was reported that the addition of CPCM significantly narrowed the temperature range of the battery pack from 300–370 to 303–304 K. Therefore, CPCM can eff ectively increase the rate of heat transfer to prevent the chain of thermal runaway reactions. It also enables the battery pack to run at a stable temperature.

Curvature Compensated CMOS Bandgap Reference with Novel Process Variation Calibration Technique

A lowtemperature coefficient（ TC） bandgap reference（ BGR） with novel process variation calibration technique is proposed in this paper. This proposed calibration technique compensating both TC and output value of BGR achieves fine adjustment step towards the reference voltage,while keeping optimal TC by utilizing large resistance to help layout match. The high-order curvature compensation realized by poly and p-diffusion resistors is introduced into the design to guarantee the temperature characteristic. Implemented in 180 nm technology,the proposed BGR has been simulated to have a power supply rejection ratio（ PSRR） of 91 dB@100 Hz. The calibration technique covers output voltage scope of 0. 49 V-0. 56 Vwith TC of 9. 45 × 10^（-6）/℃-9. 56 × 10^（-6）/℃ over the temperature range of-40 ℃-120 ℃. The designed BGR provides a reference voltage of 500 mV,with measured TC of 10. 1 × 10^（-6）/℃.

Quantum-classical correspondence in integrable systems

We find that the quantum-classical correspondence in integrable systems is characterized by two time scales. One is the Ehrenfest time below which the system is classical;the other is the quantum revival time beyond which the system is fully quantum. In between, the quantum system can be well approximated by classical ensemble distribution in phase space. These results can be summarized in a diagram which we call Ehrenfest diagram. We derive an analytical expression for Ehrenfest time, which is proportional to h-1/2. According to our formula, the Ehrenfest time for the solar-earth system is about 1026 times of the age of the solar system. We also find an analytical expression for the quantum revival time, which is proportional to h-1. Both time scales involve ω(I), the classical frequency as a function of classical action. Our results are numerically illustrated with two simple integrable models. In addition, we show that similar results exist for Bose gases, where 1/N serves as an effective Planck constant.

AGING PROPERTIES OF THE LIFETIME IN SIMPLE ADDITIVE DEGRADATION MODELS

This paper deals with the simple additive degradation models with single random effect. The authors further study the link between the aging property of the implied lifetime and that of the random variation. It is found that both the aging property of the random variation and the analytical behavior of the mean degradation path influence the aging behavior of the implied lifetime.

Green challenges to system software in data centers

With the increasing demand and the wide application of high performance commodity multi-core processors, both the quantity and scale of data centers grow dramatically and they bring heavy energy consumption. Researchers and engineers have applied much effort to reducing hardware energy consumption, but software is the true consumer of power and another key in making better use of energy. System software is critical to better energy utilization, because it is not only the manager of hardware but also the bridge and platform between applications and hardware. In this paper, we summarize some trends that can affect the efficiency of data centers. Meanwhile, we investigate the causes of software inefficiency. Based on these studies, major technical challenges and corresponding possible solutions to attain green system software in programmability, scalability, efficiency and software architecture are discussed. Finally, some of our research progress on trusted energy efficient system software is briefly introduced.