The fractional free volume of the sorbed vapor in modeling the viscoelastic contribution to polymer-coated surface acoustic wave vapor sensor responses

Surface acoustic wave (SAW) vapor sensors with polymeric sorbent layers can respond to vapors on the basis of mass loading and modulus decreases of the polymer film. The modulus changes are associated with volume changes that occur as vapor is sorbed by the film. A factor based on the fractional free volume of the vapor as a liquid has been incorporated into a model for the contribution of swelling-induced modulus changes to observed SAW vapor sensor responses. In this model, it is not the entire volume added to the film by the vapor that contributes to the modulus effect; it is the fractional free volume associated with the vapor molecules that causes the modulus to decrease in a manner that is equivalent to free volume changes from thermal expansion. The amplification of the SAW vapor sensor response due to modulus effects that are predicted by this model has been compared to amplification factors determined by comparing the responses of polymer-coated SAW vapor sensors with the responses of similarly coated thickness shear mode (TSM) vapor sensors, the latter being gravimetric. Results for six to eight vapors on each of two polymers, poly(isobutylene) and poly(epichlorohydrin), were examined. The model predicts amplification factors of the order of about 1.5-3, and vapor-dependent variations in the amplification factors are related to the specific volume of the vapor as a liquid. The fractional free volume factor provides a physically meaningful addition to the model and is consistent with conventional polymer physics treatments of the effects of temperature and plasticization on polymer modulus.     

Study of interactions in supercritical fluids and supercritical fluid chromatography by solvatochromic linear solvation energy relationships

Linear solvation energy relationships were used to study the retention process in supercritical fluid chromatography (SFC) and to gain a better understanding of intermolecular interactions in supercritical fluids. Correlation of SFC retention data with a set of solute solvatochromic parameters, which are also applicable to gas and liquid chromatography, yields information regarding the relative contributions of dispersion, cavity formation, dipolar, and hydrogen-bonding processes to retention. Dispersion interactions and cavity formation processes dominate retention on an open tubular poly(dimethylsiloxane) stationary phase with pure carbon dioxide as the mobile phase. Dipolar interactions and hydrogen-bonding interactions are of decidedly less importance but do contribute significantly to retention. Based on prior solvatochromic studies of poly(dimethylsiloxane) and carbon dioxide, the changes in the regression coefficients with temperature and pressure are interpreted chemically. The relative importance of these contributions changes with temperature and pressure. As pressure increases, the carbon dioxide becomes more dense, and dispersion interactions between the solute and the mobile phase increase. A temperature increase at constant pressure decreases dispersion interactions with the stationary phase, as in gas chromatography, but also decreases dispersion interactions with the mobile phase, due to a decrease in carbon dioxide density. On the basis of the solvatochromic coefficients, carbon dioxide acts as both a Lewis base and a Lewis acid. The quality of fit for these correlations is very high and compares favorably with similar studies in gas chromatography and liquid chromatography, permitting the prediction of retention behavior from a solute's solvatochromic parameters.     

Comparative study of hydrocarbon, fluorocarbon, and aromatic bonded RP-HPLC stationary phases by linear solvation energy relationships.

The retention properties of eight alkyl, aromatic, and fluorinated reversed-phase high-performance liquid chromatography bonded phases were characterized through the use of linear solvation energy relationships (LSERs). The stationary phases were investigated in a series of methanol/water mobile phases. LSER results show that solute molecular size and hydrogen bond acceptor basicity under all conditions are the two dominant retention controlling factors and that these two factors are linearly correlated when either different stationary phases at a fixed mobile-phase composition or different mobile-phase compositions at a fixed stationary phase are considered. The large variation in the dependence of retention on solute molecular volume as only the stationary phase is changed indicates that the dispersive interactions between nonpolar solutes and the stationary phase are quite significant relative to the energy of the mobile-phase cavity formation process. PCA results indicate that one PCA factor is required to explain the data when stationary phases of the same chemical nature (alkyl, aromatic, and fluoroalkyl phases) are individually considered. However, three PCA factors are not quite sufficient to explain the whole data set for the three classes of stationary phases. Despite this, the average standard deviation obtained by the use of these principal component factors are significantly smaller than the average standard deviation obtained by the LSER approach. In addition, selectivities predicted through the LSER equation are not in complete agreement with experimental results. These results show that the LSER model does not properly account for all molecular interactions involved in RP-HPLC. The failure could reside in the V2 solute parameter used to account for both dispersive and cohesive interactions since "shape selectivity" predictions for a pair of structural isomers are very bad.     

Comparisons of polymer/gas partition coefficients calculated from responses of thickness shear mode and surface acoustic wave vapor sensors

Apparent partition coefficients, K, for the sorption of toluene by four different polymer thin films on thickness shear mode (TSM) and surface acoustic wave (SAW) devices are compared. The polymers examined were poly(isobutylene) (PIB), poly(epichlorohydrin) (PECH), poly(butadiene) (PBD), and poly(dimethylsiloxane) (PDMS). Independent data on partition coefficients for toluene in these polymers were compiled for comparison, and TSM sensor measurements were made using both oscillator and impedance analysis methods. K values from SAW sensor measurements were about twice those calculated from TSM sensor measurements when the polymers were PIB and PECH, and they were also at least twice the values of the independent partition coefficient data, which is interpreted as indicating that the SAW sensor responds to polymer modulus changes as well as to mass changes. K values from SAW and TSM measurements were in agreement with each other and with independent data when the polymer was PBD. Similarly, K values from the PDMS-coated SAW sensor were not much larger than values from independent measurements. These results indicate that modulus effects were not contributing to the SAW sensor responses in the cases of PBD and PDMS. However, K values from the PDMS-coated TSM device were larger than the values from the SAW device or independent measurements, and the impedance analyzer results indicated that this sensor using our sample of PDMS at the applied thickness did not behave as a simple mass sensor. Differences in behavior among the test polymers on SAW devices are interpreted in terms of their differing viscoelastic properties.     

Fuzzy modeling of measurement data acquired from physical sensors

The measurement uncertainty in physical sensors is often represented by a probabilistic approach, but such a representation is not always adapted to new intelligent systems. Therefore, a fuzzy representation, based on the possibility theory, can sometimes be preferred. We previously proposed a truncated triangular probability-possibility transformation to be applied to any unimodal and symmetric probability distribution which can be assimilated to one of the four most encountered probability laws (Gaussian, double-exponential, triangular, uniform). In this paper, we propose to build a fuzzy model of data acquired from physical sensors by applying this transformation. For this purpose, a minimum of knowledge about the probabilistic modeling of sensors is required. Three main situations are considered and for each situation, an adapted fuzzy modeling is proposed. Examples of these three situations are based on FM-chirped ultrasonic sensors     

Frequency encoding of resonant mass sensors for chemical vapor detection

Chemical vapors can be detected by a resonant mass sensor array with selective absorption coatings implementing a frequency encoding method. The sensor array consists of sensor elements with different frequencies for their identifications in the frequency response obtained with a pulse Fourier transform detection scheme. Zero-loading resonance frequencies are chosen so that frequency shift due to absorption is bounded within a predefined region so that there is no overlap of peaks and all peaks can be assigned to the correct elements at any operation conditions. Mechanical oscillations of all or selected numbers of the sensor elements are excited by application of an excitation signal. Free oscillation decay signals from all or selectively excited sensor elements are detected and digitized. The free oscillation decay signal is subjected to a spectral analysis routine converting into a frequency spectrum, in which frequency shifts due to absorption of chemical vapors can be obtained. The implementation of the frequency encoding method with pulse Fourier transform detection to resonant mass sensors allows simultaneous multisensor detection, fast data acquisition speed, high signal-to-noise ratio by coaddition of raw data, flexible excitation, reduced complexity of electronic hardware, application of advanced data/spectral analysis algorithms, and realization of many other advantages by the introduction of the pulse Fourier transform method. A practical chemical vapor sensing system is demonstrated experimentally by use of nine frequency-encoded and polymer-coated sensors.     

Use of a pulsed electron beam for air cleaning from methyl methacrylate vapor

The results of experiments on methyl methacrylate (MMA) vapor decomposition in nitrogen-oxygen mixtures under the action of a pulsed electron beam are reported. It is established that there are two competitive mechanisms of MMA removal, with and without participation of active oxygen species.     

A study of a high-resolution linear circuit for capacitive sensors

A circuit for capacitance measurements is described. The circuit permits offset capacitance compensation using a dc voltage. The electronic circuitry with its testing is described. The output voltage is a linear function of the capacitance measured. Experimental data show good agreement with values predicted by the linear formula. Experiments show it is possible to measure capacitance changes with a resolution of a few femtofarads (fF)     

Decoupling features and virtual sensors for diagnosis of faults in vapor compression air conditioners

This paper describes the development and evaluation of features and virtual sensors that form the basis of a methodology for detecting and diagnosing multiple-simultaneous faults in vapor compression air conditioning equipment. The features were developed based upon a physical understanding of the system, cost considerations, and heuristics derived from experimental data and modeling results. Virtual sensors were developed in order to reduce the cost of implementation. The validity of the features and virtual sensors was evaluated using measurements from a variety of different air conditioners tested in a laboratory environment. More detailed evaluation results are presented in separate papers.     

Optimal selection of commercial sensors for linear model representation of daylight spectra

The average spectral power distribution of a set of measured daylight spectra, E(av)(lambda), is used for preliminary screening to select optimal sensor sets for daylight recovery. Spectra quite different from E(av)(lambda) are applied to the screened sets to obtain minimum total spectral error, which is closely related to recovery metrics but not to the coefficient of error. All basis functions should be utilized to make these two errors equal, to predict precisely the best sensor set, and to extend a set of few sensors to a set of many sensors. These are not acquirable by an exhaustive full search method.     

A Brownian motion algorithm for tow scale modeling of chemical vapor infiltration

Chemical vapor infiltration (CVI) is a frequent processing method for the tailoring of high-quality ceramic–matrix composites. It involves rarefied gas transfer in a disordered fibrous array and heterogeneous deposition reactions. Optimization of CVI by experimental means is prohibited by important fabrication costs and duration; triggering the need for a numerical model. Our tow scale computational tool reproduces gas transport by an Itō-Taylor random walk scheme whilst chemical reaction is handled by a Monte Carlo routine. Numerical validations of the code with respect to analytical estimates are presented. Finally, applications to 3D images are depicted and the influence of operating conditions on matrix deposition is discussed.     

Chemical vapor deposition of thin semiconductor films for solar energy conversion

The surfaces intercepting the incident radiation in solar energy converters must have a spectral profile that is properly matched to the solar emission and thermal reradiation properties, they must withstand high temperatures without harmful changes of their optoelectronic characteristics and they must operate for long enough to be economically viable. Multilayer systems deposited by chemical vapor deposition offer attractive features. The paper reviews methods of preparation and the optical performance of thin semiconductor films deposited from the vapor phase that meet all three requirements, in particular for applications at temperatures of 500°C. If developed further, chemical vapor deposition will be particularly well adapted to the requirements imposed on the thin semiconductor films used in photothermal converters.     

面向企业能效评估的能源消耗过程建模方法研究

针对企业能效评估对能源消耗系统模型的需求,在分析企业能耗过程的组成因素及其相互作用关系的基础上,提出了一种将企业的生产过程、物料移动、资源配置、余能回收利用等数字化的,基于模糊高级Petri网的企业能源消耗过程建模方法,并详细地给出了模型的形式化定义、运行规则以及建模原则.实例分析表明,该方法独立于特定的能源类型和用能设备,实现了能耗过程结构和动态行为方面信息的全面描述,是企业能源消耗过程分析与优化的基础.     

Characterization and modeling of transition edge sensors for high resolution X-ray calorimeter arrays

Characterizing and understanding, in detail, the behavior of a Transition Edge Sensor (TES) is required for achieving an energy resolution of 2 eV at 6 keV desired for future X-ray observatory missions. This paper will report on a suite of measurements (e.g. impedance and I–V among others) and simulations that were developed to extract a comprehensive set of TES parameters such as heat capacity, thermal conductivity, and R(T,I), (T,I), and β_i(T,I) surfaces. These parameters allow for the study of the TES calorimeter behavior at and beyond the small signal regime.     

Selecting algorithms, sensors, and linear bases for optimum spectral recovery of skylight

In a previous work [Appl. Opt.44, 5688 (2005)] we found the optimum sensors for a planned multispectral system for measuring skylight in the presence of noise by adapting a linear spectral recovery algorithm proposed by Maloney and Wandell [J. Opt. Soc. Am. A3, 29 (1986)]. Here we continue along these lines by simulating the responses of three to five Gaussian sensors and recovering spectral information from noise-affected sensor data by trying out four different estimation algorithms, three different sizes for the training set of spectra, and various linear bases. We attempt to find the optimum combination of sensors, recovery method, linear basis, and matrix size to recover the best skylight spectral power distributions from colorimetric and spectral (in the visible range) points of view. We show how all these parameters play an important role in the practical design of a real multispectral system and how to obtain several relevant conclusions from simulating the behavior of sensors in the presence of noise.     

Application of the holographic interferometer for modeling of processes in a vapor phase epitaxy reactor

Using holographic interferometry techniques, it is possible to visualize flows in the gas phase and obtain quantitative data about vapor phase density distribution in a given volume. The possibility of using this approach for monitoring processes in a vapor phase epitaxy (VPE) reactor has been studied using an experimental setup comprising a reactor chamber with two transparent windows, a real-time holographic interferometer, a gas supply system, and a system for visual observation of the gas flows. The results show good prospects of this method for optimization of the reactor design and the VPE process parameters.     

Use of mathematical modeling for measurements of nanodimensions in microelectronics

An “exact” mathematical model and a “simplified” mathematical model that each model video signals in a scanning electron microscope are developed. It is shown that the simplified model practically conforms to the exact model while requiring substantially lesser overhead of computational resources. Examples of the use of the models in the development of a new generation of application algorithms for precision measurement of the nanodimensional elements of modern integrated circuits are given.