Comparative study on internally heated and adiabatic regenerators in liquid desiccant air conditioning system

Liquid desiccant regeneration has important effect on performance of a liquid desiccant air conditioning system. Compared with conventional packed regenerator, internally heated regenerator is proposed to achieve better regeneration performance. This study emphasized on both regeneration rate and regeneration thermal efficiency to evaluate the performance of both regenerators. A validated heat and mass transfer model was used to analyse and compare the performance of internally heated and adiabatic regenerators. The results indicated that internally heated regenerator not only could increase the regenerate rate, but also could exhibit higher energy utilization efficiency. Different from adiabatic regenerator, internally heated regenerator can provide comparable regeneration efficiency and regeneration rate at low desiccant flow rate, so it should be a good alternative to avoid carryover of desiccant droplets. Higher air flow rate would result in a deduction of regeneration thermal efficiency although achieving higher regeneration rate. Suitable flow rate of the air should be considered carefully in liquid desiccant regeneration. The internally regenerator could have considerable prospect in liquid desiccant air conditioning application.     

绿色材料在家电中的应用研究

在节能环保、低碳循环技术发展的大趋势下,绿色材料的开发应用已成为家电业发展的主流方向之一。本文介绍了绿色材料的概念,阐述分析了生物基材料、无毒性材料、抑霉抗菌材料等绿色材料在家电领域的应用现状,探讨了家电用绿色材料的发展前景。     

Deterministic Sensing Matrices Based on Multidimensional Pseudo-Random Sequences

An approach is proposed for producing compressed sensing (CS) matrices via multidimensional pseudo-random sequences. The columns of these matrices are binary Gold code vectors where zeros are replaced by ?1. This technique is mainly applied to restore sub-Nyquist-sampled sparse signals, especially image reconstruction using block CS. First, for the specific requirements of message length and compression ratio, a set Λ which includes all preferred pairs of m-sequences is obtained by a searching algorithm. Then a sensing matrix A _M×N is produced by using structured hardware circuits. In order to better characterize the correlation between any two columns of A, the average coherence is defined and the restricted isometry property (RIP) condition is described accordingly. This RIP condition has strong adaptability to different sparse signals. The experimental results show that with constant values of N and M, the sparsity bound of A is higher than that of a random matrix. Also, the recovery probability may have a maximum increase of 20 % in a noisy environment.     

Transient Charging and Discharging Behaviors of Border Traps in the Dual-Layer HfO2/SiO2 High- κ Gate Stack Observed by Using Low-Frequency Charge Pumping Method

Transient charging and discharging of border traps in the dual-layer HfO₂/SiO₂ high-kappa gate stack have been extensively studied by the low-frequency charge pumping method with various input pulse waveforms. It has been demonstrated that the exchange of charge carriers mainly occurs through the direct tunneling between the Si conduction band states and border traps in the HfO₂ high-kappa dielectric within the transient charging and discharging stages in one pulse cycle. Moreover, the transient charging and discharging behaviors could be observed in the time scale of 10^-8- 10^-4 s and well described by the charge trapping/detrapping model with dispersive capture/emission time constants used in static positive bias stress. Finally, the frequency and voltage dependencies of the border trap area density could also be transformed into the spatial and energetic distribution of border traps as a smoothed 3-D mesh profiling     

Building an Application-Aware IPsec Policy System

As a security mechanism at the network-layer, the IP security protocol (IPsec) has been available for years, but its usage is limited to virtual private networks (VPNs). The end-to-end security services provided by IPsec have not been widely used. To bring the IPsec services into wide usage, a standard IPsec API is a potential solution. However, the realization of a user-friendly IPsec API involves many modifications on the current IPsec and Internet key exchange (IKE) implementations. An alternative approach is to configure application-specific IPsec policies, but the current IPsec policy system lacks the knowledge of the context of applications running at upper layers, making it infeasible to configure application-specific policies in practice. In this paper, we propose an application-aware IPsec policy system on the existing IPsec/IKE infrastructure, in which a socket monitor running in the application context reports the socket activities to the application policy engine. In turn, the engine translates the application policies into the underlying security policies, and then writes them into the IPsec security policy database (SPD) via the existing IPsec policy management interface. We implement a prototype in Linux (Kernel 2.6) and evaluate it in our testbed. The experimental results show that the overhead of policy translation is insignificant, and the overall system performance of the enhanced IPsec is comparable to those of security mechanisms at upper layers. Configured with the application-aware IPsec policies, both secured applications at upper layers and legacy applications can transparently obtain IP security enhancements.     

Flexible and Highly Sensitive Pressure Sensors Based on Bionic Hierarchical Structures

The rational design of high‐performance flexible pressure sensors attracts attention because of the potential applications in wearable electronics and human–machine interfacing. For practical applications, pressure sensors with high sensitivity and low detection limit are desired. Here, ta simple process to fabricate high‐performance pressure sensors based on biomimetic hierarchical structures and highly conductive active membranes is presented. Aligned carbon nanotubes/graphene (ACNT/G) is used as the active material and microstructured polydimethylsiloxane (m‐PDMS) molded from natural leaves is used as the flexible matrix. The highly conductive ACNT/G films with unique coalescent structures, which are directly grown using chemical vapor deposition, can be conformably coated on the m‐PDMS films with hierarchical protuberances. Flexible ACNT/G pressure sensors are then constructed by putting two ACNT/G/PDMS films face to face with the orientation of the ACNTs in the two films perpendicular to each other. Due to the unique hierarchical structures of both the ACNT/G and m‐PDMS films, the obtained pressure sensors demonstrate high sensitivity (19.8 kPa^?1, <0.3 kPa), low detection limit (0.6 Pa), fast response time (<16.7 ms), low operating voltage (0.03 V), and excellent stability for more than 35 000 loading–unloading cycles, thus promising potential applications in wearable electronics.     

Probing into Reverse Bias Dark Current in Perovskite Photodiodes: Critical Role of Surface Defects

Minimizing reverse bias dark current density (J_dark) while retaining high external quantum efficiency is crucial for promising applications of perovskite photodiodes, and it remains challenging to elucidate the ultimate origin of J_dark. It is demonstrated in this study that the surface defects induced by iodine vacancies are the main cause of J_dark in perovskite photodiodes. In a targeted way, the surface defects are thoroughly passivated through a simple treatment with butylamine hydroiodide to form ultrathin 2D perovskite on its 3D bulk. In the passivated perovskite photodiodes, J_dark as low as 3.78 × 10^-10 A cm^-2 at -0.1 V is achieved, and the photoresponse is also enhanced, especially at low light intensities. A combination of the two improvements realizes high specific detectivity up to 1.46 × 10¹² Jones in the devices. It is clarified that the trap states induced by the surface defects can not only raise the generation-recombination current density associated with the Shockley–Read–Hall mechanisms in the dark (increasing J_dark), but also provide additional carrier recombination paths under light illumination (decreasing photocurrent). The critical role of surface defects on J_dark of perovskite photodiodes suggests that making trap-free perovskite thin films, for example, by fine preparation and/or surface engineering, is a top priority for high-performance perovskite photodiodes.     

Biomarker-Responsive Nanosystems for Chronic Disease Theranostics

Chronic diseases claim millions of lives every year, and it is of great significance to explore and develop advanced drugs to improve the cure rate of chronic diseases. Nanotheranostics are innovative strategies that enable the integration of diagnostic and therapeutic properties into a single nanosystem. Despite great success in nanotheranostics, their applications of nanotheranostics in nanomedicine are still in their infancy. This is because each disease has its corresponding characteristic pathological microenvironment, which motivates the development of endogenous biomarker-responsive nanosystems to meet the requirements of diagnosis and treatment. Herein, recent progress is presented in biomarker-responsive nanosystems and their biomedical applications. First, biomarker-responsive nanosystems are classified into eight subsections according to the type of chronic diseases, including tumors, cardiovascular diseases, neurological diseases, Wilson's diseases, chronic liver diseases, chronic kidney diseases, diabetes mellitus, and rheumatoid arthritis. In the following, a variety of intriguing applications of biomarkers-responsive nanosystems are briefly elaborated, such as biosensing, diagnosis, therapy, combined theranostics, and early evaluation of therapy effect, etc. Finally, the challenges and future directions from research to clinical translation of these responsive nanosystems are also presented.     

永磁同步电机矢量控制中死区补偿技术的研究

本文针对永磁同步电机矢量控制系统,分析了死区电压矢量对三相输出电压的影响以及死区电压矢量与定子电流方向的关系,提出了一种基于SVPWM矢量控制的死区补偿方法。定子电流矢量角根据计算得出,避免了传统方法在相电流过零处由于电流方向检测不准而影响补偿效果。该方案无需增加硬件电路,对软件进行修改即可实现。仿真试验结果证实了该方法的有效性。     

基于虚拟仪器的斯托克斯参量测试系统

采用旋转波片法搭建了一套偏振态斯托克斯参量自动检测系统,每秒可以处理和显示15个偏振椭圆。该系统采用数据采集卡和LabVIEW软件来组成虚拟仪器,通过数据插值与重采样技术对旋转角度进行精确定位,消除了电机转速不稳定带来的系统误差。根据米勒矩阵得出透射光强随旋转角度的变化方程,并与实时采集的测量数据进行对比拟合,通过傅里叶变换得出曲线方程中的待定系数,给出对应的斯托克斯参量,并计算光波的电场分量及相位差,确定出射光的椭圆偏振消光比、长轴方向与椭圆旋向。还考查了本底噪声对测量结果的影响,比较了旋转波片与旋转检偏器两种测试方法的优缺点。