A field-portable,laser-diode spectrometer for the ultra-sensitive detection of hydrocarbon gases

We have developed a field-portable optical gas sensor for the ultra-sensitive detection of ethane. The system is based on an adaptation of a commercially available system, which uses a cryogenically cooled, lead-salt laser diode at 3.34 μm and a multi-pass astigmatic Herriott sample cell. We have adapted this system to a second derivative wavelength modulation scheme giving a lower detection limit of less than 100 parts per trillion for a one second measurement time. Our custom-designed software controls every aspect of the instrument operation from spectral scanning of the laser diode, to automatic calibration, optical alignment, spectral analysis and complete data logging.     

THE AGGLOMERATION AND AGING OF TEREPHTHALIC ACID PARTICLES IN LIQUID SOLUTION

ABSTRACT

Because of considerable experimental difficulties, the data on 4-carboxybenzaldehyde incorporation in the terephthalic acid crystal does not allow to determine the effects of the major parameters, such as the crystal growth rate, on the separation effectiveness, in this work, a theoretical analysis was done of co-crystallization of two iso-morphous organic substances (terephthalic acid and 4-earboxybenzaldehyde) based on the Monte Carlo simulation of crystal growth. In order to account for the limited solute diffusion velocity thru the boundary layer, analytical solution of a simple model of the boundary layer was combined via an iterative process with the Monte Carlo simulation of the interface. The distribution coefficient of the impurity (4-carboxybenzaldehyde) was found to be largely independent of the impurity level in the solution and an increasing function of the crystal growth rate. In order to compare the theoretical results of this work with experiment, it was suggested to carry out future experiments on entrainment of 4-carboxybenzaldehyde in the terephthalic acid crystal in aqueous dimethyl-sulfoxide solutions at room temperature. Such a system is believed to simulate well the behavior of aqueous terephthalic acid solutions at temperatures around 200°C where the experiments become prohibitive.     

Influence of Iron Solute on the Structure of Small-Angle [001] Twist Boundaries in Magnesium Oxide

The structure of small-angle [001] twist boundaries in pure and Fe-doped MgO was examined by electron imaging techniques in order to study the influence of solute on grain-boundary structure. In addition, the effect of the oxidation state of the Fe on the boundary structure was also examined. The [001] twist boundaries were produced in the form of bicrystals, by the hot-pressing of cleaved single crystals of pure MgO and MgO containing Fe. In pure MgO the [001] twist boundaries produced with small plastic strains are planar and contain a square array of screw dislocations with Burgers vectors of the type a /2<110>. In the presence of solute the original interface becomes wavy and dissociates into subboundaries. Distorted hexagonal dislocation networks as well as square arrays of screw dislocations are often observed in Fe-doped MgO. These observations are evidence that [001] twist boundaries in MgO whose production was accompanied by small amounts of plastic deformation undergo a structural transformation induced by the presence of Fe solute. The influence of the Fe oxidation state on boundary structure is less well understood. It appears that when the [001] twist boundaries are produced using crystals containing a substantial amount of Fe³⁺ ions, the resulting boundary structure is more likely to contain distorted hexagonal dislocation networks than when the boundary is produced from crystals containing predominantly Fe²⁺ ions.     

Control strategy for single-input single-output non-linear systems with time delays

A new controller design technique is developed for a general class of non-linear systems with delays. The proposed suboptimal controller consists of a generalized proportional-integral (PI) control structure plus a new time-delay compensator that is shown to be superior to the conventional Smith Predictor. Simulation results demonstrate the advantages of the new design method in comparison with conventional PID control and gain scheduling.     

基于割集功率空间上的静态电压稳定域局部可视化方法

提出了一种新型快速的割集功率空间上电压稳定域边界局部近似算法，以用于实现静态电压稳定域的可视化。该算法首先在电力系统状态空间上推导出求解电压稳定域边界局部的线性方程组，利用该方程组可快速地求解出状态空间上的一组近似电压稳定域边界点；然后通过潮流方程将边界映射到割集功率空间上，解决了电压稳定域可视化的降维问题。在此基础上，可利用最小二乘法拟合出割集功率空间上的一个超平面，用以近似地表达电压稳定域边界。IEEE118节点系统算例结果表明，该方法能在割集功率空间上以较小的误差快速地近似表达出电压稳定域边界的局部；算法对于实现电压稳定域的在线计算及可视化具有一定的实用价值。     

Quantum theory of preparation and measurement

The conventional postulate for the probabilistic interpretation of quantum mechanics is asymmetric in preparation and measurement, making retrodiction reliant on inference by use of Bayes' theorem. Here, a more fundamental symmetric postulate is presented, from which both predictive and retrodictive probabilities emerge immediately, even where measurement devices more general than those usually considered are involved. It is shown that the new postulate is perfectly consistent with the conventional postulate.     

A brief tutorial on the estimation of the process standard deviation

We consider the common SQC problem of estimating a process standard deviation based on several sample ranges or sample standard deviations. Simple, well-known facts that are used to produce “control chart constants” can also provide guidance in the combining of such ranges or standard deviations for normal processes. Root mean squared errors for both unbiased linear estimators common in the literature and some (biased) optimal estimators are shown to be simple functions of these constants.     

ETHYLENE CAPSULE PROMOTES EARLY RIPENING OF 'd'ANJOU' PEARS PACKED IN MODIFIED ATMOSPHERE BAGS

‘d'Anjou’ pears (Pyrus communis, L.) harvested commercially with flesh firmness of 64.5 N were incapable of ripening normally at 20C within 60 days of air storage at ‐1C (denoted as “under‐chilled” fruits). When under‐chilled ‘d'Anjou’ fruits (8 fruits, total fruit weight of 1.8 kg) were packed in a 3.8‐liter perforated bag inserted with an ethylene capsule, fruit would ripen normally at 20C. The ethylene concentration in the packed bag maintained no less than 100 ppm after 4 days at 20C, and declined to about 25 ppm on day 7. Regardless of the storage length, ripened fruit induced by the ethylene capsule developed high buttery and juicy texture. If ‘d’ Anjou’ fruit had been stored at ‐1C for less than 30 days, ripened fruit lacked high flavor quality. Flavor quality of ripened fruit improved rapidly when the fruit had been stored for longer than 30 days.