Engineering students designing a statistical procedure for quantifying variability

The study examined first-year engineering students’ responses to a statistics task that asked them to generate a procedure for quantifying variability in a data set from an engineering context. Teams used technological tools to perform computations, and their final product was a ranking procedure. The students could use any statistical measures, and they needed to explain their ranking procedure in detail. The responses were first categorized by the statistical measures used. The responses were categorized using a cyclic model development perspective moving from primitive to more sophisticated responses. The modeling cycle framework provided a developmental view of students’ responses and use of statistics. The study raised questions related to the measurement of variability, the application of statistics, and the process teams go through when designing an analysis procedure.     

Strong Formulations of Robust Mixed 0–1 Programming

We introduce strong formulations for robust mixed 0–1 programming with uncertain objective coefficients. We focus on a polytopic uncertainty set described by a ``budget constraint' for allowed uncertainty in the objective coefficients. We show that for a robust 0–1 problem, there is an α–tight linear programming formulation with size polynomial in the size of an α–tight linear programming formulation for the nominal 0–1 problem. We give extensions to robust mixed 0–1 programming and present computational experiments with the proposed formulations.     

Modeling and simulation of planar SOFC to study the electrochemical properties

In this paper, modeling and simulations are carried out using COMSOL Multiphysics. A three-dimensional model is developed for a planar intermediate temperature (IT) solid oxide fuel cell (SOFC). A parametric study has been carried out to analyze the performance of SOFC.Simulations reveal some promising features and enhanced performance of SOFC. It is shown that the maximum value of power (4–3.3) kW/m² still remains higher with significant rise of temperature (600 °C–1000 °C), nearly 0.15 kW/m² is the very small loss of power per 100 °C rise of temperature. Results have shown that the electrolytic current density is (6700–5500) A/m² for peak value of power (4–3.3) kW/m² with increase of temperature (600 °C–1000 °C). For model validation we have plotted a comparison of average current density.     

氧碘化学激光中的增益光导效应

 发现和分析了氧碘化学激光中的增益光导效应。碘注入的不均匀等导致增益在该方向的不均匀。采用预混模型和Fabry Perot腔模型，推导了碘不均匀分布情况下的单重态氧的产额和激光束横向分布的解析表达式。计算结果表明，由于增益光导效应，引起激光横向分布的变化，可导致光束在碘注入方向的倾斜，以及输出功率的下降。     

Theoretical and experimental study of V–I characteristics of UV pre-ionized TEA CO2 laser for variety of laser gas mixtures

Experimental and theoretical study of V–I characteristics of UV pre-ionized TEA CO₂ laser has been carried out for a variety of gas mixtures emitting different optical pulse shapes suitable for various applications. Coupled differential equations have been solved to model the pulse excitation circuit using the numerically calculated values of ionization coefficient (α), attachment coefficient (β) and drift velocity (U_d) as functions of E/N (i.e. electric field to neutral particle density ratio) for chosen gas mixture. Calculated and experimental V–I characteristics for gas mixtures (CO₂:N₂:He::1:2:3, 1:1:4, 1:1:5 and 1:0:4.7) show a good agreement. It has been shown that gas mixture has a dominant effect on the delay between pre-ionization and main discharge; thus, determining the long-term stability of discharge. The excitation pulse duration increases with increase in molecular content of gas mixture (i.e. amount of CO₂ and N₂ in gas mixture).     

Physical meaning of the stretched exponential Kohlrausch function

In this paper the physical meaning of the empirical Kohlrausch-Williams-Watts (KWW) function is explained in terms of the linear oscillator theory. It is shown that the KWW function is a solution of the non-autonomous linear first order equation for an overdamped linear oscillator. From the linear oscillator model it follows that the KWW-type relaxation is the linear relaxation with a time (coordinate, stress, voltage, etc.) dependent dissipation of energy. The theoretical results are validated by measurements. A method for modeling KWW-type relaxation using simple electrical circuits is proposed.     

Computer simulations of a dielectric barrier discharge used for analytical spectrometry

A model developed for a dielectric barrier discharge (DBD) in helium, used as a new spectroscopic source in analytical chemistry, is presented in this paper. The model is based on the fluid approach and describes the behavior of electrons, He⁺ and ions, He metastable atoms, He atoms in higher excited levels, and He₂ dimers. The He ground-state atoms are regarded as background gas. The characteristic effect of charging/discharging of the dielectrics which cover both electrodes is also simulated. Typical results of the model include the distribution of potential inside the plasma (and the potential drop across the dielectrics), the electric current and gap voltage as a function of time for a given applied potential profile, the spatial and temporal number-density profiles of the different plasma species, and the relative contributions of the mechanisms of their production and loss. Figure Schematic diagram of the dielectric barrier discharge (left) and typical temporal profiles of voltage and current, as obtained from the simulations (right)     

A semi-empirical approach for predicting the performance of mixed matrix membranes containing selective flakes

A successful model for mixed matrix membrane performance must address the complex geometry of the problem and accurately treat the diffusion behavior of the host–guest systems being considered. Detailed calculations based on the Maxwell–Stefan equations provide a widely accepted means of treating the diffusion of gases within zeolites. However, a full numerical solution of these equations for a complex mixed matrix membrane geometry does not offer the convenience and transparency that comes with an analytical treatment. At the same time, existing analytical equations which were formulated specifically to address mixed matrix geometry do so under the assumption of very simplistic models for diffusion. Here, an approach is presented for predicting the permeability and selectivity of mixed matrix membranes containing zeolite flakes that combines well-known analytical expressions for mixed matrix membrane performance with Maxwell–Stefan modeling for zeolite diffusion. The constant permeabilities required by the analytical models are calculated by the Maxwell–Stefan equations as a function of operating conditions, and these calculated effective permeabilities are used to predict mixed matrix membrane performance at corresponding operating conditions. The method is illustrated through two case studies: normal- and iso-butane separation by a membrane containing silicalite-1 flakes and carbon dioxide/methane separation by membranes containing CHA-type zeolites. Predictions are compared to experimental results found in the literature for both cases. Also, the applicability of the Maxwell and Cussler analytical models for mixed matrix membrane performance is explored as a function of flake loading and aspect ratio.     

Quantitative characterization of tissue microstructure with temporal diffusion spectroscopy

The signals recorded by diffusion-weighted magnetic resonance imaging (DWI) are dependent on the micro-structural properties of biological tissues, so it is possible to obtain quantitative structural information non-invasively from such measurements. Oscillating gradient spin echo (OGSE) methods have the ability to probe the behavior of water diffusion over different time scales and the potential to detect variations in intracellular structure. To assist in the interpretation of OGSE data, analytical expressions have been derived for diffusion-weighted signals with OGSE methods for restricted diffusion in some typical structures, including parallel planes, cylinders and spheres, using the theory of temporal diffusion spectroscopy. These analytical predictions have been confirmed with computer simulations. These expressions suggest how OGSE signals from biological tissues should be analyzed to characterize tissue microstructure, including how to estimate cell nuclear sizes. This approach provides a model to interpret diffusion data obtained from OGSE measurements that can be used for applications such as monitoring tumor response to treatment in vivo.     

基于OSC-PLS算法对大麦蛋白质含量进行定量分析的研究

用色散扫描型仪器采集大麦样品的近红外光谱,扫描出的光谱携带了大量样品化学值信息,采用正交信号校正(OSC)预处理方法对这些原始光谱进行处理,剔除噪声等不相关因子以后建立偏最小二乘(PLS)近红外光谱分析模型(OSC-PLS),预测大麦蛋白质的含量,并与传统PLS建模方法进行对比。基于OSC-PLS算法的蛋白质含量近红外光谱分析模型的测定系数R2为0.901,检验集的化学值与模型预测值的相关系数r达到0.971 7,分析模型的预测标准偏差SD为0.545 0,相对标准偏差RSD为4.2%。结果表明,OSC-PLS回归方法能在较大程度上消除无关因素的影响,在简化模型的同时提高了模型的可解释性,能够建立准确的大麦蛋白质含量近红外预测模型,可代替经典分析方法,满足农产品快速分析的需要。