High temperature thermodynamic properties of iron-nickel alloys

A correlation is presented for the thermodynamic properties of alloys of iron and nickel at high temperatures. It covers both solid and liquid phases and is in good agreement with the available experimental information. The correlation is based on the assumption that the solutions consist of a mixture of chemical species in a state of thermodynamic equilibrium. The three-suffix Margules equations with zero ternary interactions and the regular solution assumption are used to describe the activity coefficients of the (assumed) species. The correlation is applicable over the full range of compositions, and is recommended for use at temperatures higher than 800 K. Values calculated for properties of interest are included.     

Mg@C72 MNDO/d evaluation of the isomeric composition

Temperature development of the relative stabilities of isomers of Mg@C72 (which has not yet been isolated) is computed using the recently introduced MNDO/d method. Four isomers originally considered for the Ca@C72 case are treated: one isolated-pentagon-rule (IPR) structure, two structures with a pair of adjacent pentagons, and one cage with a heptagon. The IPR structure comes as the lowest in MNDO/d potential energy, being rather closely followed by the two structures with a pentagon-pentagon pair. On the other hand, the structure with a heptagon is located too high in potential energy to be of any experimental significance. The entropy contributions are evaluated by the MNDO/d-based partition functions so that the relative concentrations can be treated accordingly. The computations suggest that if Mg@C72 is isolated, it should be a mixture of either two or three isomers. The prediction depends on temperature prehistory. If preparation takes place at temperatures of approximately 1000 K, two isomers should be produced. If temperatures are increased to approximately 2000 K, there will already be three isomers with significant relative concentrations. The study supplies a further interesting example of the profound role of enthalpy-entropy interplay in stabilities of isomeric fullerenic structures.     

基于氧化锆电解质的NOx传感器的检测系统设计

设计了一套用于测量汽车尾气排放的氮氧化物（NO与NO2）的车用传感器的检测装置。该装置能真实模拟汽车尾气的环境,测试了尾气温度、尾气流量、尾气中的O2浓度、NO浓度、NO2浓度等因素列代表NOx实际浓度的传感器极限电流IP2的影响,并对响应曲线进行了分析。该测试系统对所制作的NOx传感器内部结构及各电极的成分的改进具有重要的意义。     

Effects of nanoparticles on the nucleation and devitrification temperatures of polyol cryoprotectant solutions

To investigate the efficiency of nanoparticles as nucleation agents in polyol cryoprotectant solutions at cryogenic temperatures, the nucleation and devitrification temperatures of these solutions with different concentrations of diamond, gold, copper–nickel, and silicon nanoparticles were measured through differential scanning calorimetry. The results show that ice growth in these cryoprotectant solutions is prominently accelerated by nanoparticles and the devitrification temperatures of cryoprotectant solutions are significantly lowered by nanoparticles. These findings can be used to improve the efficiency of cell cryopreservation procedures and open numerous avenues of investigations regarding the application of nanoparticles in cryogenics.     

Effect of micro-electrode geometry on NO2 gas-sensing characteristics of one-dimensional tin dioxide nanostructure microsensors

Electrodes with micro-gaps are fabricated by using dc-sputtering and FIB techniques. SnO₂ nanowires are deposited on the micro-gap (1-30 μm) by suspension dropping method to fabricate a micro-gas sensor. The sensing ability of various SnO₂ micro-gap sensors is measured. A comparison between sensors reveals that the short-gap electrode has numerous advantages in terms of reliability, high sensitivity and detection of low concentrations of NO₂, while the large-gap electrode is relatively sensitive for high concentrations. Conductance measurements are carried out at different surface temperatures and NO₂ concentrations in order to investigate the effects that the gap size has on the overall sensor conductance. The results suggest that the interface between the electrode and sensitive layer has a very important role for the sensing mechanism of tin dioxide gas sensors.     

A BASIC program for the numerical solution of the transient kinetics of complex biochemical models

A highly optimized software for the kinetic analysis of complex chemical models is presented. The program is applied to the analysis of a vectorial biochemical reaction, where many species are linked by multiple equilibria of any order. The reaction stimulates the Ca2(+)-transport-linked ATPase reaction taking place in a suspension of vesicular fragments of isolated sarcoplasmic reticulum membranes, as described in many experimental reports. The model includes 12 reactants and intermediate chemical species, 14 kinetic constants, compartmentalization, and thermodynamic adjustment. The concentrations of all the model components, at any time, starting from a known initial condition, are calculated. The transient concentrations of the species are obtained by numerical integration of the appropriate differential equations, using an optimized version of the Runge-Kutta-Gill algorithm, with the aid of a Digital PDP11/23 computer and a standard BASIC-11 software, which could be fast and easily fitted to work with any microcomputer and/or alternative language or faster working compiled BASIC version. The errors of the calculations are evaluated.     

Impact of aerosol optical depth on seasonal temperatures in India: a spatio‐temporal analysis

The third assessment report of the Intergovernmental Panel on Climate Change (IPCC) describes the clear modulating effect of aerosols both directly and indirectly on the prevailing climatic conditions on the Earth's surface. Several studies have noted higher than average concentrations of aerosols over the densely populated Indian subcontinent and adjacent regions. The study focuses on seasonal‐level spatial patterns of aerosol optical depth (AOD) concentrations and their relationship with near‐surface air temperatures. The period of analysis includes the years 2000 to 2005 for the summer monsoon season, and 2001 to 2005 for the winter season. The overall patterns of AODs show higher concentrations over the densely populated and highly industrialized Gangetic basin for bot9h seasons. The AOD–temperature relationship was predominantly negative, meaning that higher AOD concentrations resulted in lower temperatures for both seasons over northeastern India and the west coast, in the vicinity of Mumbai. Temperatures in the interior northwestern sector of the subcontinent, extending northwards towards Kashmir, experienced positive forcing during the summer season. The winter‐season relationship was predominantly negative, whereas during the summer monsoon season it was neutral to positive. The differences in responses may be attributed to the impact of overcast skies and heavy precipitation during the summer monsoon season, leading to longwave radiation being trapped inside the Earth's atmosphere, producing higher minimum temperatures. However, predominantly clear skies during the winter season resulted in a negative forcing by aerosols on the surface temperatures.     

A reaction compiler for electrochemical kinetics

A computer code serving for an automatic translation of user-written source texts of electrochemical reaction mechanisms into corresponding target texts of mathematical equations that govern the kinetics of electrochemical systems under transient conditions is reported. The rules of the language enabling symbolic specification of the reaction mechanisms, the compiler options, and conventions regarding the target formulae are outlined and illustrated by examples. A considerable diversity of reaction mechanisms involving equilibrium, non-equilibrium reversible or irreversible reactions that can be electrochemical, heterogeneous non-electrochemical or homogeneous, is permitted. The reactions may involve bulk species (distributed in the electrolyte volume) and interfacial species (localized at the electrodes) of variable or constant concentrations, and electrons. The transient conditions may correspond to a number of electrochemical techniques, including potential-step method, linear potential scan voltammetry and chronopotentiometry. For kinetic problems in one-dimensional space geometry the generated governing equations take the general form of the reaction-advection-diffusion partial differential equations for the concentrations of bulk species (with initial and boundary conditions), optionally coupled with algebraic, ordinary differential or differential-algebraic equations for the concentrations of interfacial species. The governing equations can be obtained in the form of ELSIM problem definitions, enabling further solution by means of this simulation program.     

Development of a wet lime/limestone flue gas desulfurization process model. Phase I: Species distribution model

A new computer code is described which calculates the concentrations (or activities) of chemical species which are at chemical equilibrium. The species distribution model (SDM) is structured so that the user has essentially full control to define a wide variety of problems. Some of the capabilities allow the user (at run-time) to set up a virtually unlimited number and type of solutions and select the activity coefficient technique for each, omit species from consideration, limit the reactivity of species, and edit species and corresponding data (e.g., activity coefficient or equilibrium constant data). The code is highly modular and the routines are short with well-defined purposes and clean interfaces. The code and data structures are set up for ease of model enhancement.     

Solubility of CO2 in aqueous ammonia solution at low temperature

The solubility of carbon dioxide in aqueous ammonia solution with concentrations of 1.13, 2.18, 3.83, 6, and 8.11 molal was measured at atmospheric pressure and a range of temperatures from 268.15 to 288.15 K. The results showed that the solubility of carbon dioxide in ammonia aqueous solution increased with increasing temperature. The UNIQUAC-NRF model is applied to the experimental data for the present work. This modified model is used to calculate carbon dioxide solubility in aqueous ammonia solution at a range of temperatures from 268.15 to 288.15 K and atmospheric pressure. The results of AAD% (Absolute Average Deviation) show that the UNIQUAC-NRF model can accurately correlate the solubility of experimental data of carbon dioxide in aqueous ammonia solution over a wide range of low temperatures.     

Stabilization in a Two-Species Chemostat With Monod Growth Functions

We design feedback controllers for two species chemostats so that an equilibrium with arbitrary prescribed positive species concentrations becomes globally asymptotically stable. We use a new global explicit strict Lyapunov function construction, which allows us to quantify the effects of disturbances using the input-to-state stability paradigm. We assume that only a linear combination of the species concentrations is known. We illustrate our approach using a numerical example.      

基于SnO2气体传感器检测农药残留的表面动态响应特性

利用单个SnO2气体传感器在方波变化的温度条件下实现对敌百虫和乙酰甲胺磷及其混合气体的快速检测和识别.实验结果表面,SnO2气体传感器在温度范围为250～300℃、温度变化频率为20MHz的工作条件下对敌百虫和乙酰甲胺磷及其混合气体表现出高的灵敏度和清晰的动态响应特征.通过快速傅立叶变换(FFT)实现对敌百虫和乙酰甲胺磷及其混合气体的定量分析.     

Robust stabilization of competing species in the chemostat

This work addresses the problem of robust stabilization of the concentrations of two different species of living organisms, which compete for a single limiting substrate in a bioreactor. This stabilization is performed using discontinuous feedback control laws that ensure the coexistence of all species. The control laws are designed considering bounded parametric uncertainties on the kinetic rates.     

基于曲面拟合的NDIR单通道CO2气体传感器快速标定算法

为了提高非色散红外(NDIR,Non-Dispersion Infrared)二氧化碳(CO₂)气体传感器的标定效率,提出一种针对NDIR单通道CO₂气体传感器的高效快速标定算法。首先采集m个传感器节点在不同温度、不同浓度下对应的电压值;然后对于每个节点,将它的数据点(温度,浓度,输出电压)进行曲面拟合,拟合后的曲面作为候选曲面;测量待标定传感器的6个在不同温度、不同浓度下对应的输出电压数据点,选择一个与这6个数据点最优匹配的曲面,以此作为待标定传感器的标定曲面。实验结果表明,算法标定准确性和可靠性高,按照5%+50×10^-6的精度,算法标定的数据合格率达到99%。     

Thermal conductivity of doped polysilicon layers

The thermal conductivities of doped polysilicon layers depend on grain size and on the concentration and type of dopant atoms. Previous studies showed that layer processing conditions strongly influence the thermal conductivity, but the effects of grain size and dopant concentration were not investigated in detail. The current study provides thermal conductivity measurements for low-pressure chemical-vapor deposition (LPCVD) polysilicon layers of thickness near 1 μm doped with boron and phosphorus at concentrations between 2.0×10¹⁸ cm^-3 and 4.1×10¹⁹ cm^-3 for temperatures from 20 K to 320 K. The data show strongly reduced thermal conductivity values at all temperatures compared to similarly doped single-crystal silicon layers, which indicates that grain boundary scattering dominates the thermal resistance. A thermal conductivity model based on the Boltzmann transport equation reveals that phonon transmission through the grains is high, which accounts for the large phonon mean free paths at low temperatures. Algebraic expressions relating thermal conductivity to grain size and dopant concentration are provided for room temperature. The present results are important for the design of MEMS devices in which heat transfer in polysilicon is important     

The application of repro-modelling to a tropospheric chemical model

This paper describes the application of a parameterisation procedure to reduce a comprehensive atmospheric chemical mechanism to a set of algebraic polynomials. This is achieved here by the numerical fitting of orthonormal polynomial functions to changes in species concentrations from one time point to the next, using the Gram–Schmidt orthonormalisation technique. Polynomials are then optimised by the use of Horner equations. Some reduction of the number of species to only those which influence the concentration of the important species has been carried out previously by the removal of fast time-scale species and stable products, without significant loss of accuracy. Consequently the repro-model is fitted to a subset of the original mechanism, with polynomials generated for each of the species in the lower dimensional subspace. This method has been successfully applied to diurnal tropospheric cycles and several results are shown here. Deviations between the repro-model results and those of the original mechanism are consistently less than 1% across the scenario for all key species, with the repro-model running up to 25 times faster than the numerical solution of the original scheme. The repro-modelling technique is thus highly suited to replacing the system of ordinary differential equations in the chemical sub-model of a dispersion code—significantly reducing the computational burden without loss of accuracy.     

Stabilization of a chemostat model with Haldane growth functions and a delay in the measurements

The stabilization of equilibria in chemostats with measurement delays is a complex and challenging problem, and is of significant ongoing interest in bioengineering and population dynamics. In this paper, we solve an output feedback stabilization problem for chemostat models having two species, one limiting substrate, and either Haldane or Monod growth functions. Our feedback stabilizers depend on a given linear combination of the species concentrations, which are both measured with a constant time delay. The values of the delays are unknown. Instead, one only knows an upper bound on the delays, and we allow the upper bound to be arbitrarily large. The stabilizing feedback depends on the known upper bound for the delays as well. Our work is based on a Lyapunov-Krasovskii argument.     

Fractional differential equations in electrochemistry

Electrochemistry was one of the first sciences to benefit from the fractional calculus. Electrodes may be thought of as “transducers” of chemical fluxes into electricity. In a typical electrochemical cell, chemical species, such as ions or dissolved molecules, move towards the electrodes by diffusion. Likewise, other species are liberated into solution by the electrode reaction and diffuse away from the electrode into the bulk solution. It is demonstrated in this paper that the electric current is linearly related to the temporal semiderivative of the concentrations, at the electrode, of the species involved in the electrochemical reaction. More usefully, the semiintegral of the current provides immediate access information about concentrations.     

Modeling of ionization composition in argon plasma with fast electrons

Discharge and laser produced plasmas often have non-equilibrium electron distributions containing fast electrons that may have a profound effect on the ionization balance. The influence of high energy electrons on the ionization balance in the collisional-radiative equilibrium model for optically thin plasma is considered forthwith. A nonmaxwellian electron distribution with fast electrons at energies and concentrations is used for calculating collisional rates; this according to the Hartree-Fock-Slater (HFS) quantum-statistical model in the average atom approximation. The calculative approach is based on the distorted wave approximation along with numerical and semiclassical wave functions calculated in the self-consistent HFS potential. The results from ionization equilibrium modeling in argon plasma at temperatures T ∼ 5–1000 eV with fast electron energies ranging from 1 to 10 keV and their different relative concentrations (from 0.1–10%) are analyzed. It is shown that fast electrons increase the impact ionization rates and significantly change the ionization stage as compared with equilibrium plasma.     

Fabrication and mechanical testing of glass chips for high-pressure synthetic or analytical chemistry

The pressure strength of microfluidics glass chips for high-pressure chemistry has been examined. Internal pressures up to 320 bar have been measured, although variations are substantial. Long annealing steps at high temperatures did not show any improvement, but smoothening the powder blasted channel walls by isotropic etching did. Although macro cracks are observed at the bond interface it is believed that the formation of micro cracks in the channel wall and stress concentrations due to sharp corners in the channel cross-section geometry strongly limits the maximum applicable pressures.