评价淬火介质换热特性的Grossmann法与集中热容法的比较

研究了用于估算纳米流体、盐水溶液和某洗涤剂基试验介质淬火烈度的Grossmann法和集中热容（ LHC）法的适用性,评价了探头截面厚度对不同淬火介质换热系数的影响。借助于计算机分析了304不锈钢探头在淬火过程中的冷却曲线,并分别采用Grossmann法和LHC法对所测得的冷却曲线进行了换热系数的估算。研究表明,采用矱10 mm不锈钢探头的LHC法适用于淬火烈度小于20 m-1介质的表征。虽然Grossmann法是基于平均换热系数这一假设的,但仍能应用于具有不同淬火烈度介质之间的评定。 Grossmann法能更敏感地反映探头截面厚度对换热的影响。     

Atomic layer deposition of HfO2 thin films and nanolayered HfO2–Al2O3–Nb2O5 dielectrics

Smooth, 4–6-nm thick hafnium oxide films were grown by atomic layer deposition from HfI₄ or HfCl₄ and H₂O on SiO₂/Si(1 0 0) substrates at 300 °C. Non-uniform films were obtained on hydrogen-terminated Si(1 0 0). The stoichiometry of the films corresponded to that of HfO₂. The films contained small amounts of residual chlorine and iodine. The films deposited on SiO₂/Si(1 0 0) were amorphous, but crystallized upon annealing at 1000 °C. In order to decrease the conductivity, the HfO₂ films were mixed with Al₂O₃, and to increase the capacitance, the films were mixed with Nb₂O₅. The capacitance–voltage curves of the Hf–Al–O mixture films showed hysteresis. The capacitance–voltage curves of HfO₂ films and mixtures of Hf–Al–Nb–O were hysteresis free.     

Casting/mold thermal contact heat transfer during solidification of Al-Cu-Si alloy (LM 21) plates in thick and thin molds

Heat flow at the casting/mold interface was assessed and studied during solidification of Al-Cu-Si (LM 21) alloy in preheated cast iron molds of two different thicknesses, coated with graphite and alumina based dressings. The casting and the mold were instrumented with thermocouples connected to a computer controlled temperature data acquisition system. The thermal history at nodal locations in the mold and casting obtained during experimentation was used to estimate the heat flux by solving the one-dimensional inverse heat conduction problem. The cooling rate and solidification time were measured using the computer-aided cooling curve analysis data. The estimated heat flux transients showed a peak due to the formation of a stable solid shell, which has a higher thermal conductivity compared with the liquid metal in contact with the mold wall prior to the occurrence of the peak. The high values of heat flux transients obtained with thin molds were attributed to mold distortion due to thermal stresses. For thin molds, assumption of Newtonian heating yielded reliable interfacial heat transfer coefficients as compared with one-dimensional inverse modeling. The time of occurrence of peak heat flux increased with a decrease in the mold wall thickness and increase in the casting thickness.     

TETRA-BUTYL-MALONAMIDE AND TETRA-ISOBUTYL MALONAMIDE AS EXTRACTANTS FOR URANIUM(VI) AND PLUTONIUM(IV)

ABSTRACT

Two new symmetrical diamides, namely straight-chain alkyl substituted neutral tetra-butyl-malonamide(TBMA) and sterlcally hindered branched-chain alkyl substituted tetra-isobutyl malonamide(TIBMA) were synthesised, characterised and used for the extraction of U(VI) and Pu(IV) from nitric acid media into n-dodecane. Both the cations were found to be extracted as their disolvates. Interestingly TBMA extracted more efficiently than TIBMA but afforded poor selectivity for Pu/U separation. The thermodynamic parameters involved in the extraction, determined by the temperature variation method, indicated the reactions in all cases to be enthalpy favoured. Entropy was found to be counteracting the extraction of U(VI) and favouring the extraction of Pu(IV). The recovery of diamides from the loaded actinides could be easily accomplished by using dilute oxalic acid or dilute U(IV) as the strippant for Pu(IV) and using dilute Na₂C0₃ as that for U(VI).     

Molecular Epidemiological Study of Pyrazinamide-Resistance in Clinical Isolates of Mycobacterium tuberculosis from South India

Pyrazinamide (PZA) has been in use for almost 50 years as a first-line drug for short-course chemotherapy against Mycobacterium tuberculosis. In this study, PCR mediated automated DNA sequencing is used to check the prevalence of PZA resistance among treatment failure cases of pulmonary tuberculosis. Out of 50 clinical isolates examined, 39 had mutations in the pncA gene that encodes Pyrazinamidase, an enzyme required to activate PZA. Of these, 31 (79.5%) were localized to three regions of pncA. We found two isolates with hitherto unreported mutation at amino acid 26 (Ala→Gly) of pncA.     

The effect of a non-Newtonian lubricant on piston ring lubrication

The effect of a non-Newtonian oil (shear thinning) on the lubrication of a piston ring is theoretically investigated. A variation of shear strain rate with shear stress that is cubic in form is used to obtain a modified form of the Reynolds equation (dynamic) applicable to a run-in ring profile which is considered to be a double parabola with a central straight portion. Numerical solutions are obtained for the film thickness, pressure and frictional force over a complete stroke for the case of a constant load. Results presented in non-dimensional form show that the effect of pseudo plasticity is to reduce slightly the minimum film thickness, peak pressure ratio and friction coefficient.     

A 1-V heterogeneous reconfigurable DSP IC for wireless basebanddigital signal processing

A heterogeneous reconfigurable platform enables the flexible implementation of baseband wireless functions at energy levels between 10 and 100 MOPS/mW, six times higher than traditional digital signal processors. A 5.2 mm×6.7 mm prototype processor, targeted for voice compression, is implemented in a 0.25-μm 6-metal CMOS process, and consumes 1.8 mW at an average operation rate of 40 MHz. It combines an embedded microprocessor with an array of computational units of different granularities, connected by a hierarchical reconfigurable interconnect network     

Effect of different plasticizer on structural and electrical properties of PEMA-based polymer electrolytes

Plasticized poly(vinyl chloride)/poly(ethyl methacrylate) PVC/PEMA-based blend polymer electrolyte films containing lithium perchlorate (LiClO₄) as a salt were prepared by solvent casting technique. The effects of the plasticization on structural, thermal and electrical properties of the plasticized polymer blend electrolytes were investigated. The changes in the structural and complex formation properties of the materials were studied by XRD and FTIR techniques. Dielectric relaxation studies of the polymer electrolyte have been undertaken, and the results are discussed. TG/DTA technique is used to study the thermal stability. Complex impedance analysis is used to calculate the bulk resistance of the complexes. The effect of different plasticizer on the structural and physical properties of polymer blend electrolyte is well correlated.     

Authentication of WSN for Secured Medical Data Transmission Using Diffie Hellman Algorithm

The applications of wireless sensor network (WSN) exhibits a significant rise in recent days since it is enveloped with various advantageous benefits. In the medical field, the emergence of WSN has created marvelous changes in monitoring the health conditions of the patients and so it is attracted by doctors and physicians. WSN assists in providing health care services without any delay and so it plays predominant role in saving the life of human. The data of different persons, time, places and networks have been linked with certain devices, which are collectively known as Internet of Things (IOT); it is regarded as the essential requirement of people in recent days. In the health care monitoring system, IOT plays a magnificent role, which has produced the real time monitoring of patient’s condition. However the medical data transmission is accomplished quickly with high security by the routing and key management. When the data from the digital record system (cloud) is accessed by the patients or doctors, the medical data is transferred quickly through WSN by performing routing. The Probabilistic Neural Network (PNN) is utilized, which authenticates the shortest path to reach the destination and its performance is identified by comparing it with the Dynamic Source Routing (DSR) protocol and Energy aware and Stable Routing (ESR) protocol. While performing routing, the secured transmission is achieved by key management, for which the Diffie Hellman key exchange is utilized, which performs encryption and decryption to secure the medical data. This enables the quick and secured transmission of data from source to destination with improved throughput and delivery ratio.