Heat and mass transfer in composite desiccant pore structures for dehumidification

A composite desiccant dehumidifier made of mixed inert and desiccant materials is investigated. A heat and mass transfer model that incorporates the composite nature of the structure is discussed. The model includes both gas-side and solid-side resistances for heat and mass transport. The solid-side resistance for the mass transport includes gas-phase diffusion and surface diffusion. The effectiveness for moisture removal and heat transfer during adsorption and desorption processes in such a dehumidifier during single blow operation is investigated. Results are presented for composite structures made of silica gel and inert materials of different compositions and thermophysical properties.     

Test generation for specification test of analog circuits using efficient test response observation methods

In this paper, a new automated test generation methodology for specification testing of analog circuits using test point selection and efficient analog test response waveform capture methods for enhancing the test accuracy is proposed. The proposed approach co-optimizes the construction of a multi-tone sinusoidal test stimulus and the selection of the best set of test response observation points. For embedded analog circuits, it uses a subsampling-based digitization method compatible with IEEE 1149.1 to accurately digitize the analog test response waveforms. The proposed specification approach uses ‘alternate test’ framework, in which the specifications of the analog circuit-under-test are computed (predicted) using statistical regression models that are constructed based on process variations and corresponding variations of test responses captured from different test observation points. The test generation process and the test point selection process aim to maximize the accuracy of specification prediction. Experimental results validating the proposed specification test approach are presented.     

利用FPGA实现多种串行拓扑结构

对更大带宽的需求在典型的太位级(Terabit)系统中，瓶颈通常存在于系统互联一级，即系统内不同器件间互相通信以及与外部其它系统通信的速度。业界曾试图通过生产越来越快的CPU来克服这一问题。然而这一方法，似乎已陷入了僵局，因为用户已经不能再感受到与CPU性能直接成比例的巨大系统性能提升。正如莫尔定律所表明的，处理器带宽每18个月翻一翻，但PC总线的性能却要每三年才能提高一倍。很明显，这是无法仅仅通过继续提高CPU速度来克服的巨大性能缺口。现在处理器速度已经达到2GHz，并将很快达到10GHz，需要一种新的系统互连技术来…     

Deterministic Test Vector Compression/Decompression for Systems-on-a-Chip Using an Embedded Processor

A novel approach for using an embedded processor to aid in deterministic testing of the other components of a system-on-a-chip (SOC) is presented. The tester loads a program along with compressed test data into the processor's on-chip memory. The processor executes the program which decompresses the test data and applies it to scan chains in the other components of the SOC to test them. The program itself is very simple and compact, and the decompression is done very rapidly, hence this approach reduces both the amount of data that must be stored on the tester and reduces the test time. Moreover, it enables at-speed scan shifting even with a slow tester (i.e., a tester whose maximum clock rate is slower than the SOC's normal operating clock rate). A procedure is described for converting a set of test cubes (i.e., test vectors where the unspecified inputs are left as X's) into a compressed form. A program that can be run on an embedded processor is then given for decompressing the test cubes and applying them to scan chains on the chip. Experimental results indicate a significant amount of compression can be achieved resulting in less data that must be stored on the tester (i.e., smaller tester memory requirement) and less time to transfer the test data from the tester to the chip.     

Role of shape-memory alloy reinforcements on strain evolution in lead-free solder joints

Microelectronic solder joints are exposed to aggressive thermomechanical cycling (TMC) during service, resulting in strain localization near solder/bond-pad interfaces, which eventually leads to low-cycle fatigue (LCF) failure of the joint. In order to mitigate these strain concentrations, a “smart solder” reinforced with a martensitic NiTi-based shape-memory alloy (SMA) has been proposed before. In the present work, the role of NiTi particles on strain evolution in composite solders was studied using a combination of experimental and numerical means. Finite element modeling showed that NiTi pariculate reinforcements can reduce inelastic strain levels in the solder via shape recovery associated with the B19′ → B2 transformation. In situ TMC studies in the scanning electron microscope (SEM), in conjunction with strain analysis via digital image correlation (DIC), showed evidence of reverse deformation in the solder commensurate with the NiTi phase transformation, demonstrating the conceptual viability of the smart solder approach. The SEM-DIC experiments also suggested that the presence of particulates mitigates shear localization, which is commonly observed in monolithic solder joints close to joint/bond-pad interfaces. Finally, TMC experiments on monolithic solder and NiTi/solder single-fiber composite joints highlighted the beneficial effect of shape-memory transformation in reducing inelastic strain range of solders.     

Effect of prestrain on the ductile fracture behavior of an interstitial-free steel

The effect of tensile prestrain on the ductile fracture behavior of an interstitial-free (IF) steel has been studied using primarily (1) the analysis of void density by optical microscopy, (2) characterization of the size of dimples by scanning electron microscope (SEM) and image analyzer, and (3) estimation of strain hardening behavior of a series of prestrained tensile specimens, loaded until fracture. The variation of void density with local plastic strain around the necked region of the specimens indicated the existence of two types of void nucleation pertaining to inclusions and precipitate particles. The critical strain for void nucleation (ε{inn}) for the precipitate particles initially increases and then decreases with the increase in percentage prestrain. This phenomenon has been explained using the strain hardening exponent and nature of dislocation-particle interaction. The nature of variation of the average size of the dimples and that of ε{inn} with prestrain are found to be similar. The dimple size thus bears a proportional relationship with the void, nucleation strain ε{inn} and hence the former can be used to predict (ε{inn}) for IF steel.     

Laser-Surface Alloying of Nimonic 80 with Silicon and Aluminum and its Oxidation Behavior

In the current study, laser-surface alloying (LSA) of Nimonic 80 (a Ni-based superalloy) was conducted using a high-power continuous wave (CW) CO₂ laser by simultaneous feeding of predetermined proportion of elemental Si and Al powders with an Ar shroud. After LSA, the microstructure of the alloyed zone was carefully analyzed and found to consist of several intermetallic phases of Ni and Si. The microhardness of the alloyed zone was significantly increased to 500?VHN compared with 250?VHN of the as-received substrate. The high-temperature oxidation resistance of the laser-surface-alloyed specimens (under isothermal conditions) was improved (at temperature ranges between 1223?K and 1423?K [950?°C and 1150?°C]) compared with as-received Nimonic. Even though LSA enhanced resistance to oxidation up to a limited period, continued exposure to extended hours (at a given temperature) led to spallation of scale. It seems that a SiO₂-rich adherent scale is responsible for enhanced protection against oxidation in the laser-surface-alloyed specimens. However, the presence of Al₂O₃ in the oxide film enhances the resistance to spallation by increasing the scale adherence at a higher temperature. The results are supported by a suitable thermodynamic calculation.     

Development of hydrophobic and optically transparent monolithic silica aerogels for window panel applications

In the present paper, highly transparent, monolithic and hydrophobic silica aerogel monoliths were prepared by using tetraethoxysilane (TEOS) as precursor and methyltriethoxysilane (MTES) as co-precursor with different MTES/TEOS molar ratios (M) by two-step acid–base catalyzed sol–gel process followed by supercritical alcohol drying. The molar ratio of TEOS, ethanol (EtOH), water (0.001 M oxalic acid catalyst) and ammonium hydroxide (1 M NH₄OH) was kept constant at 1:5:3.5:3.5 respectively, while the molar ratio of MTES/TEOS (M) was varied from 0 to 0.75. It has been observed that as the M value increases, the gelation time increases. It has been found that lower (0.25) M values resulted in highly transparent (optical transmission >90 % for a 10 mm thick sample at 700 nm wavelength) and negligible volume shrinkage (<10 %) but less hydrophobic aerogels, whereas higher (0.75) M values resulted in semitransparent (<25 % optical transmission at 700 nm for a 10 mm thick sample) aerogels with >10 % volume shrinkage but excellent hydrophobicity. A good compromise of acceptable optical transmittance (~87 % optical transmission at 700 nm wavelength for a 10 mm thick sample) with negligible volume shrinkage (6 %) were obtained at M = 0.50. The hydrophobicity of the aerogels was tested by measuring the contact angle between a water droplet and silica aerogel surface. The hydrophobicity was confirmed by Fourier transform infra-red spectroscopy and contact angle measurements. the aerogels have been characterized by percentage of volume shrinkage, optical transmittance, scanning electron microscopy, thermal conductivity measurements and thermogravimetric analysis and differential thermal analysis.     

Sensing throughput trade‐off for an energy efficient cognitive radio network under faded sensing and reporting channel

The trade‐off between sensing time and throughput is investigated in the context of an energy‐efficient cognitive radio network considering both the sensing and reporting channels are Rayleigh faded, while the existing literature considered the fading in sensing channel only. In this paper, such a trade‐off is re‐examined under Rayleigh faded sensing as well as reporting channel. Novel analytical expressions for overall detection probability and false alarm probability are developed under such scenario. The performance is investigated in terms of detection probability, false alarm probability, throughput and energy efficiency of the network for different sensing parameters such as sensing time, number of samples, sensing channel signal‐to‐noise ratio and reporting channel signal‐to‐noise ratio. Our analysis shows that the quality of the reporting channel significantly affects the trade‐off performance of the network. Copyright © 2015 John Wiley & Sons, Ltd.