Narrow-band correction of the residual amplitude modulation in frequency-modulation spectroscopy

We have developed a narrow-band controller in the MHz range, based on a field-programmable gate array. It is used to control the probe beam intensity in frequency-modulated spectroscopy experiments with an acoustooptic modulator. The residual amplitude modulation at the modulation frequency (2.5 MHz) is reduced by 50 dB. The first-harmonic detection of the signals is operated in saturation spectroscopy of I/sub 2/ at 514.5 nm and 501.7 nm. A reduction of the background noise and a large increase in the signal-to-noise ratio are obtained.     

Recognition by linear combinations of models

An approach to visual object recognition in which a 3D object is represented by the linear combination of 2D images of the object is proposed. It is shown that for objects with sharp edges as well as with smooth bounding contours, the set of possible images of a given object is embedded in a linear space spanned by a small number of views. For objects with sharp edges, the linear combination representation is exact. For objects with smooth boundaries, it is an approximation that often holds over a wide range of viewing angles. Rigid transformations (with or without scaling) can be distinguished from more general linear transformations of the object by testing certain constraints placed on the coefficients of the linear combinations. Three alternative methods of determining the transformation that matches a model to a given image are proposed     

Separation of Transparent Layers using Focus

Consider situations where the depth at each point in the scene is multi-valued, due to the presence of a virtual image semi-reflected by a transparent surface. The semi-reflected image is linearly superimposed on the image of an object that is behind the transparent surface. A novel approach is proposed for the separation of the superimposed layers. Focusing on either of the layers yields initial separation, but crosstalk remains. The separation is enhanced by mutual blurring of the perturbing components in the images. However, this blurring requires the estimation of the defocus blur kernels. We thus propose a method for self calibration of the blur kernels, given the raw images. The kernels are sought to minimize the mutual information of the recovered layers. Autofocusing and depth estimation in the presence of semi-reflections are also considered. Experimental results are presented.     

Immobilization of lipase on poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) hydrogel for the synthesis of butyl oleate

Lipase from Candida rugosa was immobilized by entrapment on poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) [poly(VP-co-HEMA)] hydrogel, cross-linked with ethylene glycol dimethacrylate (EDMA). The immobilized enzyme was used in the esterification of oleic acid with butanol in hexane. The activities of the immobilized enzyme preparations and the leaching of the enzyme from the hydrogel supports with respect to composition were investigated. The thermal, solvent, and storage stability of the immobilized preparations also were determined. Increasing the percentage VP from 0 to 90, which corresponds to the increase in the hydrophilicity of the hydrogels, increased the activity of the immobilized enzyme. Lipase immobilized onto VP(%):HEMA(%), 90:10 hydrogel had the highest activity. Increasing the hydrophobicity of the hydrogel (increasing the percentage HEMA) seemed to decrease leaching of the enzyme from the support. Immobilized lipase on 100% HEMA hydrogel indicated highest entrapment and lowest leaching by hexane washing. The lipase immobilized on VP(%):HEMA(%), 50:50 hydrogel showed highest thermal, solvent, and storage stability compared to lipase immobilized on other hydrogel compositions as well as the native lipase.     

Synthesis of medium-chain glycerides using lipase from Candida rugosa

Enzymatic synthesis of medium-chain glycerides (MCG) from capric acid and glycerol was studied using lipase from Candida rugosa. The effects of various reaction parameters such as time, molar ratio of substrates (mmol capric acid/mmol glycerol), amount of lipase, type of organic solvents, and initial water activity (a _w ) were studied. The best conditions tested for MCG synthesis at 37°C were, respectively, time, 24 h; molar ratio of substrates, 2.5; and amount of lipase, 100.0 mg. The use of organic solvents greatly influenced the activity of lipase in the synthesis of MCG. Generally, activity of lipase was high in nonpolar solvents with log P values from 3.50 to 4.50, where P is the partition coefficient between water and 1-octanol. The enzymatic synthesis of MCG was preferably carried out at an initial a _w of 0.328, which resulted in maximal yield. Analysis of the products of reaction using gas chromatography showed that lipase from Candida rugosa seemed to produce more dicaprin and tricaprin than monocaprin.     

Polyethersulfone (PES)–silver composite UF membrane: Effect of silver loading and PVP molecular weight on membrane morphology and antibacterial activity

Polyethersulfone–silver composite membranes were fabricated via a simple phase inversion method by using silver nitrate (AgNO₃) as an antibacterial agent and polyvinylpyrollidone (PVP) of molecular weight 10,000, 40,000 and 360,000 Da as dispersant in the dope formulation. The effect of AgNO₃ loading on the resulting membrane was studied using field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) techniques. The silver loss during fabrication and pure water filtration was measured using inductive-coupled plasma mass spectrometer (ICP-MS). From XPS and EDX examinations, it was observed that the resulting membrane prepared from 2 wt.% AgNO₃ and PVP of 360,000 Da exhibited high concentration of Ag mainly due to the high Ag-particle entrapment in the membrane structure. The uniform distribution of Ag particles has contributed significantly to 100% inhibition against Escherichia coli (E. coli) growth within 24 h incubation. In addition, the results of pure water filtration test showed minimum silver loss during operation, indicating better stability of membrane produced in terms of Ag-entrapment in membrane structure. Based on the findings, it can be concluded that PES–silver composite membrane with PVP of 360,000 MW offers huge potential membrane for bacteria removal and disinfection.     

Enhanced backstepping sliding mode controller for motion tracking of a nonlinear 2-DOF piezo-actuated micromanipulation system

Microsystem Technologies - In this paper a robust backstepping sliding mode controller is developed for tracking control of 2-DOF piezo-actuated micromanipulation system. The control approach is...     

Improved catalytic activity by catalase immobilization using γ‐cyclodextrin and electrospun PCL nanofibers

Nanofibrous structures are promising for biocatalyst immobilization due to their large surface area which facilitates the enzyme attachment, stability, ease of separation, and fine porous structure. There is limited research available on the change in enzyme activity following interaction with cyclodextrin. In this study, catalase enzyme was immobilized into nanofibrous structures by various techniques, with and without γ‐CD addition, and the enzymatic activity of catalase was evaluated. In addition, catalase‐γ‐CD complex containing PEO polymer solution was electrospun in between PCL nanofibrous layers as a newly developed technique. The enzyme immobilized nanofibrous structures were characterized by SEM, XRD, and FT‐IR analysis methods. Among all the activity tests, best enzyme activity was recorded with catalase‐γ‐CD physical mixture encapsulated PCL nanofibrous layers. Moreover, the test results indicated that the use of cyclodextrin in immobilization process considerably improves the catalytic activity of the enzyme. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44404.     

Recognition Using Region Correspondences

Recognition systems attempt to recover information about the identity of observed objects and their location in the environment. A fundamental problem in recognition is pose estimation. This is the problem of using a correspondence between some portions of an object model and some portions of an image to determine whether the image contains an instance of the object, and, in case it does, to determine the transformation that relates the model to the image. The current approaches to this problem are divided into methods that use global properties of the object (e.g., centroid and moments of inertia) and methods that use local properties of the object (e.g., corners and line segments). Global properties are sensitive to occlusion and, specifically, to self occlusion. Local properties are difficult to locate reliably, and their matching involves intensive computation.We present a novel method for recognition that uses region information. In our approach the model and the image are divided into regions. Given a match between subsets of regions (without any explicit correspondence between different pieces of the regions) the alignment transformation is computed. The method applies to planar objects under similarity, affine, and projective transformations and to projections of 3-D objects undergoing affine and projective transformations. The new approach combines many of the advantages of the previous two approaches, while avoiding some of their pitfalls. Like the global methods, our approach makes use of region information that reflects the true shape of the object. But like local methods, our approach can handle occlusion.