Preparation of nanometre size oxide particles using filter expansion aerosol generator

Crystalline zinc oxide particles of nanometre size (< 20 nm) particles were produced from a zinc acetate solution by using a filter expansion aerosol generator (FEAG). The FEAG is an aerosol generator that is operated at 60 torr reactor pressure and produces droplets of around 2 m. The shape of the particles produced by the FEAG were distinctively different from those produced by the ultrasonic spray source (USS). Results from scanning electron microscopy (SEM) and X-ray diffractometry (XRD) indicated that crystalline zinc oxide particles of nanometre size were produced at 600 °C in 0.02 s residence time. Weight loss of these particles, determined by thermogravimetric analysis (TGA), was 3 wt%. Based on the morphology change as a function of the reactor temperature and solute concentration, we proposed that the nanometre particles were formed by uniform precipitation at the drying stage and decomposition followed by disintegration into nanometre particles. It was also shown that exothermic decomposition of the solute was not required for the disintegration of the primary particles in the FEAG process. This result opened up an opportunity for producing carbon-free nanometre particles from nitrate salts by using the FEAG.     

Utility function of TCP

Understanding the TCP congestion control mechanism from a global optimization point of view is not only important in its own right, but also crucial to the design of other transport layer traffic control protocols with provable properties. In this paper, we derive a global utility function and the corresponding optimal control law, known as TCP control law, which maximizes the global utility. The TCP control law captures the essential behaviors of TCP, including slow start, congestion avoidance, and the binary nature of congestion feedback in TCP. We find that the utility function of TCP is linear in the slow start phase and is proportional to the additive increase rate and approaches the well-known logarithm function as the data rate becomes large in the congestion avoidance phase. We also find that understanding the slow start phase with a fixed threshold is critical to the design of new transport layer control protocols to enable quality of service features. Finally, as an application, we design a Minimum Rate Guaranteed (MRG) traffic control law that shares the same utility function as the TCP control law. Our simulation study of the MRG control law indicates that it is indeed TCP friendly and can provide minimum rate guarantee as long as the percentage of network resource consumed by the MRG flows is moderately small.     

高校学生诚信教育体系构建

随着我国社会经济的进一步转型,如何更有效地进行诚信教育已成为高校德育教育的一项重要课题。本文从诚信的内涵出发,以大学生诚信现状为切入点,并在此基础上对大学生诚信缺失的现象和存在的问题进行深入分析,提出构建高校学生诚信体系的对策或建议。     

Cryogenic Exfoliation of 2D Stanene Nanosheets for Cancer Theranostics

Stanene(Sn)-based materials have been extensively applied in industrial production and daily life,but their potential biomedi-cal application remains largely un...     

Measurement of periodic micro flows using micro-particle image velocimetry with phase sampling

A phase-sampling method has been developed to measure periodic flows at a high temporal resolution using conventional micro-particle image velocimetry (PIV). In this technique, the sampling is set such that each velocimetry dataset represents a unique point in phase of a periodic flow. The flow characteristics over a single cycle are reconstructed from measurements over a number of cycles, thus allowing measurement at a higher temporal resolution than the PIV system. The flow measurements were performed for AC electroosmotic flows and verified with results from the phase-locking technique. The temporal resolution is limited by the shortest camera exposure time and the time separation between laser pulses. The theoretical sampling resolution can be as low as 20 μs for 100 Hz periodic flows. A resolution of 200 μs was obtained in the experiment using 40 velocimetry datasets.     

Spatial Wavefunction-Switched (SWS) InGaAs FETs with II–VI Gate Insulators

This paper presents the implementation of a novel InGaAs field-effect transistor (FET), using a ZnSe-ZnS-ZnMgS-ZnS stacked gate insulator, in a spatial wavefunction-switched (SWS) structural configuration. Unlike conventional FETs, SWS devices comprise two or more asymmetric coupled quantum wells (QWs). This feature enables carrier transfer vertically from one quantum well to another or laterally to the wells of adjacent SWS-FET devices by manipulation of the gate voltages (V _g). Observation of an extra peak (near both accumulation and inversion regions) in the capacitance–voltage data in an InGaAs-AlInAs two-quantum-well SWS structure is presented as evidence of spatial switching. The peaks are attributed to the appearance of carriers first in the lower well and subsequently their transfer to the upper well as the gate voltage is increased. The electrical characteristics of a fabricated SWS InGaAs FET are also presented along with simulations of capacitance–voltage (C–V) behavior, showing the effect of wavefunction switching between wells. Finally, logic operations involving simultaneous processing of multiple bits in a device, using coded spatial location of carriers in quantum well channels, are also described.     

Management of the variability of vibration response levels in mistuned bladed discs using robust design concepts. Part 2: Tolerance design

The mistuning pattern on a bladed disc is controlled in Part 2 of the two-part article either by (i) imposing a small maximum allowable mistune according to the small mistuning approach or (ii) incorporating non-identical blades of specific patterns, known as the intentional mistuning approach. These approaches resemble the tolerance design stage of the Taguchi method of robust design. The first-order maximum amplification factor sensitivity in a single-degree-of-freedom (DOF)-per-sector system is derived to support a new definition of the interblade coupling ratio and to illustrate the dependence of the maximum amplification factor sensitivity on design parameters of a bladed disc. It is found that the variability of the forced vibration response levels in flexible bladed discs can be reduced by controlling the degree of mistune within realistic levels. The potential of a “linear” mistuning pattern to become an effective intentional mistuning pattern is evaluated by observing the amplification factors of bladed discs with combined intentional mistuning and additional random mistuning. A tool based on the importance sampling method is used to reduce the computational effort in determining the magnitude of intentional mistuning. Guidelines of designing bladed discs with a lower variability of forced vibration response levels are given according to the findings in casting the blade mistuning problem as a robust design problem.     

An efficient algorithm for electromagnetic scattering from rough surfaces using a single integral equation and multilevel sparse-matrix canonical-grid method

An efficient algorithm for wave scattering from two-dimensional lossy rough surfaces is proposed. It entails the use of a single magnetic field integral equation (SMFIE) in conjunction with a multilevel sparse-matrix canonical-grid (MSMCG) method. The Rao-Wilton-Glisson (RWG) triangular discretization is adopted to better model the rough surface than the pulse basis functions used in the well-established SMCG method. Using the SMFIE formulation, only one unknown per interior edge of the triangular mesh approximating the rough surface is required, and the iterative solution to the moment equation converges more rapidly than that of the conventional coupled equations for dielectric rough surfaces. The MSMCG method extends the applicability of the SMCG method to rougher surfaces. Parallel implementation of the proposed method enables us to model dielectric surfaces up to a few thousand square wavelengths. Simulation results are presented as bistatic scattering coefficients for Gaussian randomly rough surfaces.     

Improved MPEG-4 still texture image coding under noisy environment

This paper describes the performance of the MPEG-4 still texture image codec in coding noisy images. As will be shown, when using the MPEG-4 still texture image codec to compress a noisy image, increasing the compression rate does not necessarily imply reducing the peak-signal-to-noise ratio (PSNR) of the decoded image. An optimal operating point having the highest PSNR can be obtained within the low bit rate region. Nevertheless, the visual quality of the decoded noisy image at this optimal operating point is greatly degraded by the so-called "cross" shape artifact. In this paper, we analyze the reason for the existence of the optimal operating point and the "cross" shape artifact when using the MPEG-4 still texture image codec to compress noisy images. We then propose an adaptive thresholding technique to remove the "cross" shape artifact of the decoded images. It requires only a slight modification to the quantization process of the traditional MPEG-4 encoder while the decoder remains unchanged. Finally, an analytical study is performed for the selection and validation of the threshold value used in the adaptive thresholding technique. It is shown that, the visual quality and PSNR of the decoded images are much improved by using the proposed technique comparing with the traditional MPEG-4 still texture image codec in coding noisy images.