电阻-时间线性转换电路

基于电阻的传感器,如应力规和压阻器件,常用于测量多种物理参数.对于使用数字处理器或微控制器进行数据采集和信号处理的设备来说,传感器的响应必须表现为一种适合于转换成数字格式的形式.把这类传感器的电阻变化转换成一个与之成比例的频率或时间间隔是可取的,所以你就能用一个计数器或定时器来方便地得到数字形式的输出信号.图1所示电路把传感器的电阻RS线性地转换成与之成比例的时间间隔.这一电路实际上是一个张驰振荡器,由一个电流源、一个桥式放大器、一个比较器和一个触发器组成.电流IS分成两路,分别通过R1和R2,就如同这两个电阻并联在一起一样.假定运算放大器是理想放大器,则当RX(R4+RS)大于R1R3/R2时,该电路就起一个振荡器的作用.     

Crystallization of Polymer-Derived Silicon Carbonitride at 1873 K under Nitrogen Overpressure

The chemical stability of an amorphous silicon carbonitride ceramic, having the composition 0.57SiC·0.43Si₃N₄·0.49C is studied as a function of nitrogen overpressure at 1873 K. The ceramic suffers a weight loss at p _N2 < 3.5 bar (1 bar = 100 kPa), does not show a weight change from 3.5 to 11 bar, and gains weight above 11 bar. The structure of the ceramic changes with pressure: it is crystalline from 1 to 6 bar, amorphous at ∼10 bar, and is crystalline above ∼10 bar. The weight-loss transition, at 3.5 bar, is in excellent agreement with the prediction from thermodynamic analysis when the activities of carbon, SiC, and Si₃N₄ are set equal to those of the crystalline forms; this implies that the material crystallizes before decomposition. The amorphous to crystalline transition that occurs at ∼10 bar, and which is accompanied by weight gain, is likely to have taken place by a different mechanism. A nucleation and growth reaction with the atmospheric nitrogen is proposed as the likely mechanism. The supersaturation required to nucleate α-Si₃N₄ crystals is calculated to be 30 kJ/mol.     

Acoustic emission technique for leak detection in an end shield of a pressurised heavy water reactor

This paper discusses the successful application of the Acoustic Emission Technique (AET) for detection and location of leak paths present on the inaccessible side of an end shield of a Pressurised Heavy Water Reactor (PHWR). The methodology was based on the fact that air and water leak AE signals have different characteristic features. Baseline data was generated from a sound end-shield of a PHWR for characterizing the background noise. A mock up end-shield system with saw cut leak paths was used to verify the validity of the methodology. It was found that air leak signals under pressurisation (as low as 3 psi) could be detected by frequency domain analysis. Signals due to air leaks from various locations of a defective end-shield were acquired and analysed. It was possible to detect and locate leak paths. Presence of detected leak paths were further confirmed by alternate test.     

Upper-bound analysis of the pressure-assisted injection forging of thick-walled tubular components with hollow flanges

An upper-bound analysis of the pressure-assisted injection forging (PAIF) of thick-walled tubular components with hollow flanges was conducted to predict the maximum forming-pressure requirements. The polymeric pressurizing material and the pure aluminium work material employed were assumed to obey the von-Mises’ yield criterion, the two materials being divided into three and six zones, respectively, and described using kinematically admissible velocity fields. An upper-bound solution was derived based on this model. Experiments were conducted to validate the solution. The results suggest that the upper-bound analysis has sufficient accuracy for the prediction of the forming-pressure requirements. Subsequently, a parametric analysis was conducted to study the effects of variation of the principal parameters of the process and the geometry, such as tube thicknesses, flange dimensions and friction, on the forming-force requirements, which showed other useful applications of the upper-bound solutions.     

Stabilization and termination of severe accidents in LWRs

The last 20 years of research on severe accident safety for light water reactors (LWRs) has resolved a number of issues. However, the issue of melt/debris coolability is still unresolved. At stake is the stabilization and termination of a severe accident, if ever it would occur. The stabilization and termination can be established only through the coolability of the melt or the particulate debris, which are found in-vessel, or ex-vessel, depending upon the extent of the progression of a postulated accident.This paper will review the state of the art of coolability during a severe accident for the current light water reactors (LWRs). It will also review whether the accident management actions will be effective in terminating a postulated severe accident. The attention paid to the stabilization and coolability in future LWRs will be discussed and the design solutions will be evaluated.     

Heterogeneity in endothelium-derived nitric oxide-mediated relaxation of different sized pulmonary arteries of newborn lambs

Extensive documentation has validated the role of UV irradiation as a tumor initiator and promoter, inducing both squamous and basal cell carcinomas. Human epidermis is a tissue which undergoes active metabolism of arachidonic acid to prostaglandins which is regulated by the action of prostaglandin H synthase (also known as cyclooxygenase). One mechanism for the promotional activity of UV light may involve its ability to induce prostaglandin formation. Work in our laboratory has demonstrated that acute exposure of human keratinocytes to UVB irradiation results in increased production of prostaglandin E2 (PGE2). When cultured human keratinocytes were examined after irradiation with 30 mJ/cm2 UVB in vitro, Western blot analysis showed a 6-fold increase in COX-2 protein which was evident at 6 h and peaked 24 h after irradiation. Furthermore, when human subjects were irradiated on sun-protected skin with up to four times their minimal erythema dosage (MED) and biopsied 24 h later, upregulation of COX-2 protein expression was observed via immunofluorescence microscopy. RNAase protection assays supported this observation, showing induction of COX-2 message which peaked at approximately 12 h following irradiation in vitro. Furthermore, human squamous cell carcinoma biopsies exhibited strongly enhanced staining for COX-2 protein via immunohistochemistry and Western analysis when compared to normal non-sun-exposed control skin. Together, these data demonstrate acute upregulation of COX-2 via UVB irradiation and suggest the need for further studies of COX-2 expression as a potential pharmacological target mediating human skin tumor development.     

On the application of CAD technology for the synthesis of spatial revolute–revolute dyads

This work presents a method based on Computer Aided Design or CAD for facilitating the synthesis of Revolute–Revolute (R–R) dyads with adjustable moving pivots. The CAD-based method presented in this work ensures that all prescribed rigid-body parameters used to synthesize the R–R dyad satisfy particular kinematic requirements of an R–R dyad. Through the application of this CAD method, five of the six general R–R dyad constraint equations are satisfied and therefore not essential for the synthesis of the R–R dyad. By reducing the number of dyad design constraints from six to one, the user can synthesize R–R links with adjustable moving pivots for multi-phase motion and path generation applications. The example included demonstrates the use of the CAD method in the synthesis of an RRSS path generator with adjustable moving pivots.     

Analytical Modelling and Simulation of Si-Ge Hetero-Junction Dual Material Gate Vertical T-Shaped Tunnel FET

Silicon - In this paper, a compact 2D analytical modelling of surface potential and simulation of Si-Ge hetero-junction Dual Material Gate Vertical t-shape T-FET is presented. In the proposed...     

Design of Dual-Gate P-type IMOS Based Industrial Purpose Pressure Sensor

Silicon - In this treatise, we have proposed a Single Material Gate–Dual Gate Impact Ionization Metal Oxide Semiconductor (SMG DG-IMOS) based Pressure Sensor. The pressure sensor has the most...     

Enhancing the design and performance of a gate-all-around (GAA) charge plasma nanowire field-effect transistor with the help of the negative-capacitance technique

A gate-all-around charge plasma nanowire field-effect transistor (GAA CP NW FET) device using the negative-capacitance technique is introduced, termed the GAA CP NW negative-capacitance (NC) FET. In the face of bottleneck issues in nanoscale devices such as rising power dissipation, new techniques must be introduced into FET structures to overcome their major limitations. Negative capacitance is an efficient effect that can be incorporated into a device to enhance its performance for low-power applications and help to reduce the operating voltage. The Landau–Khalatnikov equation can be applied in such cases to obtain the effective bias. To determine the effects of negative capacitance, lead zirconate titanate (PZT) ferroelectric material, a ceramic material with perovskite properties, is adopted as a gate insulator. This approach diminishes the supply voltage and reduces the power dissipation in the device. Excluding their polarization properties, ferroelectric materials are similar to dielectric materials, and PZT offers abundant polarization with improved reliability and a higher dielectric capacitance. Without proper tuning of the thickness of the PZT material, hysteresis behavior mat occur. Hence, the thickness of the PZT material (t_FE) is an essential parameter to optimize the device performance and achieve a reduced threshold voltage for the GAA CP NW NC-FET device proposed herein. Furthermore, varying the thickness of the PZT ferroelectric material can also enhance the performance. When using the highest values of t_FE, improved outcomes with an analogously lower operating voltage are observed. The effects of varying t_FE on the performance characteristics of the device including the drain current, transconductance, polarized charge, etc. are also interpreted herein.