A non-quasi-static small-signal model for metal-semiconductor junction diodes

The quasi-static approximation, which assumes that free-carrier propagation delay in the semiconductor device is zero, is often used in device modeling. Consequently, the quasi-static model is adequate only for low-frequency excitations for which free-carrier propagation delay is very small compared to the variation of the excitations. This paper develops a non-quasi-static model suitable for metal-semiconductor junction diodes subjected to small-signal excitation. We show that the predictions of the non-quasi-static model agree more favourably with experimental data taken from Al---Si diodes than that of the quasi-static model, particularly when the frequency of the excitation is high.     

MATLAB modelling and examination of the effect of heat capacity of basin and glass cover on performance of solar still by thermal models

There are numerous researcher-developed mathematical models for single slope passive solar stills which considered the effect of heat capacities of basin and glass cover as negligible. The negligence parameter also plays a vital role in the prediction of the thermal performance of the system. In this paper, an effort has been made to evaluate the cumulative yield, energy efficiency and exergy efficiency of a single slope passive solar still with and without considering the heat capacities of basin and glass cover by using various thermal models such as Dunkle’s model, Zheng Hongfei et al.’s model and Tsilingiris model. These models were studied and compared with and without considering the heat capacity of solar components such as basin and glass cover. The thermodynamic model of this system is developed, and executed in a MATLAB code. By comparing the theoretical values of the cumulative yield, energy efficiency and exergy efficiency, it was found that consideration of the heat capacities of glass cover and basin gives a higher output in all the thermal models.     

Synthesis and characterization of pH‐ and salt‐responsive hydrogels based on etherificated sodium alginate

Hydrogels composed of etherificated sodium alginate (ESA), sodium acrylic acid (NaAA), and poly (vinyl alcohol) (PVA) were synthesized by aqueous solution polymerization. The effects of reaction variables such as terminal pH, ions, and ionic strength on hydrogel swelling ratio (SR) were determined and compared. SR was influenced strongly by pH and ionic strength. SR increased with increasing pH but tended to decrease with PVA content. At a given ionic strength, SR of ESA/NaAA/PVA hydrogel was dependent on the valence of anion; SR was higher in multivalent anion salt solution than in monovalent anion salt solution, i.e., SR_K2SO4 > SR_KCl and SR_Na2SO4 > SR_NaCl. The swelling kinetic of the hydrogels showed Fickian kinetic diffusion in acidic media and non‐Fickian behavior in alkaline media. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modulation of stability properties of bovine trypsin after in vitro structural changes with a variety of chemical modifiers

Controlled chemical modification of enzymes, targeting groups not involved in the active site, can lead to modified catalysts that are intrinsically more efficient and resistant to heat and denaturing agents. Bovine pancreatic trypsin was covalently modified up to 75-85% with monomeric glutaraldehyde (MGA), polymeric glutaraldehyde (PGA), oxidized sucrose and oxidized sucrose polymers (OSP 70 and OSP 400). Virtually no loss in activity occurred upon modification. Temperature optima of trypsin shifts from 45-76 degrees C and T50 from 54-76 degrees C for the best modified sample made with OSP. The efficiency of the modifiers in stabilization was ranked in the order: OSP 400-T > OSP 70-T > PGA-T > MGA-T > Sucrose-T. Half-life of modified enzymes also followed the same trend. Both stabilization factor and t1/2 decreased with increasing temperatures. The free energy of activation for inactivation delta(deltaG*) varies from 12-20 kJ/mol and the activation enthalpy delta(deltaH*) of the modified trypsin by 80-120 kJ/mol indicating stabilization. Inactivation of modified trypsin by urea is less noticeable. The character of the two-step inactivation process of trypsin changes with the degree of stabilization in that the duration of phase I one increased noticeably as stabilization increases. Native trypsin fluoresces less intensely showing a red shift under the influence of denaturation. Such a fluorescence change is not so obvious for the modified enzymes indicating conformational stability acquired by modification.      

Factors affecting the long-term stability of Cu/Al ball bonds subjected to standard and extended high temperature storage

This paper presents the findings of work performed on 20-μm diameter copper wire of five different wire types from three suppliers. Gold wire is the control. The test die was mounted on BT (B (Bismaleimide) and T (Triazine)) resin substrates. The bonding parameters were optimized for each wire used. Part of the optimization process involved monitoring the flatness of the bonded ball and the amount of aluminum remaining under the bond. The crystal structure of each type of interconnect was examined using composite imaging techniques. Visual data such as ball size, thickness, and shape were collected. First and second bonds were subjected to destructive testing, such as ball shear and wire pull, throughout the preparation process. The samples were then subjected to an industry-standard, high temperature stress test to determine the long-term stability of the interface of each wire type. Data for all read points are presented on all tests performed and provide useful information on the material and process set best suited for long term reliability.     

High Temperature Millimeter Wave Radiometric and Interferometric Measurements of Slag-Refractory Interaction for Application to Coal Gasifiers

Millimeter wave (MMW) radiometry can be used for simultaneous measurement of emissivity and temperature of materials under extreme environments such as in slagging coal gasifiers, where sensors have been identified as a key enabling technology need for process optimization. We present a dual-channel MMW heterodyne radiometer with active interferometric capability that allows simultaneous measurements of sample temperature, emissivity, and flow dynamics. Interferometric capability at 137 GHz is supplied via a probe signal originating from a local oscillator allowing monitoring of sample dynamics such as volume expansion and thickness change. This capability has been used to monitor characteristic behavior between refractories and slag such as slag infiltration, slag melting, viscous flow, foaming, and crucible corrosion by the molten slag. These results show the promise of the MMW system for extracting process parameters from operating slagging coal gasifiers, providing valuable information for process efficiency, control, and increased productivity.     

Induced crystallization of cellulose in never-dried cotton fibers

In the present investigation, we have made a systematic study of the induced crystallization in never-dried cotton fiber, by allowing it to desiccate under different conditions of humidity and temperature. The resulting structural changes have been followed using x-ray diffraction and infrared absorption techniques. A slow rate of drying coupled with a high temperature was more conducive for maximum crystallization. Analysis of the effect of temperature on the induced crystallization showed possible existence of a thermal transition in cellulose around 30°C. The induced crystallization brought about by slow drying as well as those produced using intercrystalline swelling agents, have been shown to be resulting from a proper channelization of the interfibrillar mobility existing in the never-dried fibers.     

Electrochemical etching of highT c superconducting materials

HighT _c superconductor materials of yttrium barium copper oxide (YBCO) have been etched by a new electrochemical technique. In this technique, acids like hydrochloric, nitric and phosphoric have been used as an electrolyte and etching has been achieved with acid dilutions as high as 1:200 with water. It is observed that rapid and controlled etching is possible by this technique.     

Topological Patterns for Scalable Representation and Analysis of Dataflow Graphs

Tools for designing signal processing systems with their semantic foundation in dataflow modeling often use high-level graphical user interfaces (GUIs) or text based languages that allow specifying applications as directed graphs. Such graphical representations serve as an initial reference point for further analysis and optimizations that lead to platform-specific implementations. For large-scale applications, the underlying graphs often consist of smaller substructures that repeat multiple times. To enable more concise representation and direct analysis of such substructures in the context of high level DSP specification languages and design tools, we develop the modeling concept of topological patterns, and propose ways for supporting this concept in a high-level language. We augment the dataflow interchange format (DIF) language—a language for specifying DSP-oriented dataflow graphs—with constructs for supporting topological patterns, and we show how topological patterns can be effective in various aspects of embedded signal processing design flows using specific application examples.