Robust Stability Analysis of Delayed Stochastic Neural Networks via Wirtinger-Based Integral Inequality.

We discuss stability analysis for uncertain stochastic neural networks (SNNs) with time delay in this letter. By constructing a suitable Lyapunov-Krasovskii functional (LKF) and utilizing Wirtinger inequalities for estimating the integral inequalities, the delay-dependent stochastic stability conditions are derived in terms of linear matrix inequalities (LMIs). We discuss the parameter uncertainties in terms of norm-bounded conditions in the given interval with constant delay. The derived conditions ensure that the global, asymptotic stability of the states for the proposed SNNs. We verify the effectiveness and applicability of the proposed criteria with numerical examples.

Localized Surface Plasmon Resonance in Au Nanoparticles Embedded dc Sputtered ZnO Thin Films.

The plasmonic behavior of metallic nanoparticles is explicitly dependent on their shape, size and the surrounding dielectric space. This study encompasses the influence of ZnO matrix, morphology of Au nanoparticles (AuNPs) and their organization on the optical behavior of ZnO/AuNPs-ZnO/ZnO/GP structures (GP: glass plate). These structures have been grown by a multiple-step physical process, which includes dc sputtering, thermal evaporation and thermal annealing. Different analytical techniques such as scanning electron microscopy, glancing angle X-ray diffraction, Rutherford backscattering spectrometry and optical absorption have been used to study the structures. In-situ rapid thermal treatment during dc sputtering of ZnO film has been found to induce subtle changes in the morphology of AuNPs, thereby altering the profile of the plasmon band in the absorption spectra. The results have been contrasted with a recent study on the spectral response of dc magnetron sputtered ZnO films embedded with AuNPs. Initial simulation results indicate that AuNPs-ZnO/Au/GP structure reflects/absorbs UV and infrared radiations, and therefore can serve as window coatings.

Mean square delay dependent-probability-distribution stability analysis of neutral type stochastic neural networks.

The aim of this manuscript is to investigate the mean square delay dependent-probability-distribution stability analysis of neutral type stochastic neural networks with time-delays. The time-delays are assumed to be interval time-varying and randomly occurring. Based on the new Lyapunov-Krasovskii functional and stochastic analysis approach, a novel sufficient condition is obtained in the form of linear matrix inequality such that the delayed stochastic neural networks are globally robustly asymptotically stable in the mean-square sense for all admissible uncertainties. Finally, the derived theoretical results are validated through numerical examples in which maximum allowable upper bounds are calculated for different lower bounds of time-delay.

Monitoring plasma treatment of thin films by surface plasmon resonance.

We report the surface plasmon resonance (SPR) measurements during plasma treatment of thin films by an indigenously designed setup. From the measurements on Al (6.3 nm)/Ag (38 nm) bi-layer at a pressure of 0.02 mbar, the SPR position was found to be shifted by ~20° after a plasma treatment of ~7 h. The formation of oxide layers during plasma oxidation was confirmed by glancing angle x-ray diffraction (GXRD) measurements. Combined analysis of GXRD and SPR data confirmed that while top Al layer enables controlling plasma oxidation of Ag, the setup enables monitoring the same. The setup designed is a first of its kind for in situ SPR studies where creation of low pressure is a prerequisite.

Electrocatalytic Properties of Nanocrystalline Calcium-Doped Lanthanum Cobalt Oxide for Bifunctional Oxygen Electrodes.

Calcium-doped lanthanum cobalt oxide is a promising electrocatalyst for oxygen evolution and oxygen reduction in rechargeable metal-air batteries and water electrolyzers operating with alkaline electrolyte. Nanocrystalline perovskite of composition La0.6Ca0.4CoO3 with a unique cellular internal structure was prepared at 350 °C and then annealed in air at progressively higher temperatures in the range of 600-750 °C. The samples were characterized by electrochemical techniques and X-ray photoelectron spectroscopy. The area-specific electrocatalytic activity for oxygen evolution/oxygen reduction, the oxidation state of cobalt, and the crystallite size increased with annealing temperature, while the Tafel slope remained constant. These trends provide new insights into the role of the cobalt center in oxygen evolution and oxygen reduction, and how preparation conditions can be altered to tune the activity of the cobalt center for electrocatalysis. We expect these findings to guide the design of electrocatalysts for bifunctional oxygen electrodes, in general.

The scanning laser ophthalmoscope--a review of its role in bioscience and medicine.

The scanning laser ophthalmoscope (SLO) offers the potential for retinal imaging that is complementary both to that of the fundus camera and also the newly developing technique of optical coherence tomography (OCT). It has the ability to produce rapid images at low light levels using light of specific wavelengths. This permits temporal studies of fluorescent-labelled cells which offer a unique insight into inflammatory processes in the eye. The facility to image with several different wavelengths simultaneously offers the potential for spectral imaging of retinal tissue with the aim of revealing those early changes in tissue perfusion that indicate the onset of retinal disease, so increasing the probability of successful therapy.

Improved leukocyte tracking in mouse retinal and choroidal circulation.

The purpose of this study is to develop a new method with which to visualize leukocyte dynamics in murine choroidal and retinal circulation. Both pigmented (B10.RIII) and non-pigmented (BALB/c) mice were used in this study. One hundred microl of 0.05% sodium fluorescein was injected via the mice tail vein to outline the vessel, followed by 150 microl (10(7) cells) C-AM labelled leukocytes. Fundus images were obtained with a confocal scanning laser ophthalmoscope. The dynamic image sequences were recorded simultaneously on videotape (S-VHS) and digitally at 25 frames per sec. The digital images were later analysed with a custom-made personal computer-based image analysis system. Both the choroidal and retinal circulation can be visualized in non-pigmented mice in the first few seconds of fluorescein angiography. However, the view of the choroidal and the retinal capillary circulation is soon blurred due to the rapid fluorescein leakage in the choroid. In contrast, in pigmented mice, retinal circulation is clear against the dark background of the choroid, while choroidal circulation is masked behind the pigment epithelial layer and cannot be seen at all. C-AM labelled leukocytes were clearly seen in the retinal circulation of all experimental mice and in the choroidal circulation of non-pigmented mice for as long as 30 min. The number of labelled circulating cells decreased as time clasped. Cells moved rapidly in the retinal arteries, slowing down or even stopping for a few seconds in the capillary system, and then moved slightly faster again through the postcapillary venules and veins. In non-pigmented mice, significant number of cells were seen to have arrested in the choroidal circulation. There was no difference between B10.RIII mice and BALB/c mice in vessel diameters, leukocyte velocities and shear stresses. This method allows the visualization of leukocytes and provides data on their behavior as they move through the choroidal and retinal circulation of non-pigmented mice, and in the retinal circulation of pigmented mice. It provides a valuable new tool for the investigation of real time leukocyte dynamics in murine retinal and choroidal microcirculations both under physiological conditions and during the development of ocular disease.

True colour imaging of the fundus using a scanning laser ophthalmoscope.

Currently retinal imaging is performed with the fundus camera. This has a number of limitations, in particular the high level of illuminations required for imaging. The scanning laser ophthalmoscope (SLO) has been proposed as an alternative imaging device but to date one of its main limitations has been that it gives only monochromatic images. In this paper we describe an SLO which uses low power red, green and blue lasers to image the human fundus. Using three lasers simultaneously to produce a colour image will increase the fundus exposure by a factor of three. To overcome this problem, a technique has been developed for multiplexing the lasers so that each point on the retina is imaged by the three lasers pulsed rapidly in sequence. The total exposure is thus kept to the same level as for a single laser and total imaging time is not increased. An example is shown of the image from a patient with diabetic retinopathy.

Clinical investigation of a true color scanning laser ophthalmoscope.

OBJECTIVE: To show true color scanning laser ophthalmoscope (SLO) images produced by simultaneously imaging the retina with red, green, and blue lasers. METHODS: Low-power red, green, and blue lasers were combined using fiber optics. By rapidly pulsing the lasers, each point on the fundus is illuminated by the 3 colors in quick succession, with the total power level being similar to that from a single laser. The reflected light is then decoded to extract the red, green, and blue color information and the true color fundus image is displayed live on a computer monitor. RESULTS: Comparison was made between the color SLO images from 5 patients and their digitized fundus photographs. The background fundus and retinal vasculature showed a similar appearance. The SLO gave better quality information in patients with ocular histoplasmosis, macular dystrophy, and optic disc drusen. By operating the color SLO in the indirect mode, macular edema could be clearly seen as lines and ridges surrounding the fovea. CONCLUSION: The color SLO offers all the advantages of the present commercially available monochromatic device, with the added advantage of true color representation of the fundus without increasing either imaging time or the level of exposure.

Characterization of fine particulate matter produced by combustion of residual fuel oil.

Combustion experiments were carried out on four different residual fuel oils in a 732-kW boiler. PM emission samples were separated aerodynamically by a cyclone into fractions that were nominally less than and greater than 2.5 microns in diameter. However, examination of several of the samples by computer-controlled scanning electron microscopy (CCSEM) revealed that part of the PM2.5 fraction consists of carbonaceous cenospheres and vesicular particles that range up to 10 microns in diameter. X-ray absorption fine structure (XAFS) spectroscopy data were obtained at the S, V, Ni, Fe, Cu, Zn, and As K-edges and at the Pb L-edge. Deconvolution of the X-ray absorption near edge structure (XANES) region of the S spectra established that the dominant molecular forms of S present were sulfate (26-84% of total S) and thiophene (13-39% of total S). Sulfate was greater in the PM2.5 samples than in the PM2.5+ samples. Inorganic sulfides and elemental sulfur were present in lower percentages. The Ni XANES spectra from all of the samples agreed fairly well with that of NiSO4, while most of the V spectra closely resembled that of vanadyl sulfate (VO.SO4.xH2O). The other metals investigated (i.e., Fe, Cu, Zn, and Pb) also were present predominantly as sulfates. Arsenic was present as an arsenate (As+5). X-ray diffraction patterns of the PM2.5 fraction exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca, etc.) superimposed on broad peaks due to amorphous carbons. All of the samples contain a significant organic component, with the loss on ignition (LOI) ranging from 64 to 87% for the PM2.5 fraction and from 88 to 97% for the PM2.5+ fraction. Based on 13C nuclear magnetic resonance (NMR) analysis, the carbon is predominantly condensed in graphitic structures. Aliphatic structure was detected in only one of seven samples examined.

Tomographic reconstruction of the retina using a confocal scanning laser ophthalmoscope.

Retinal imaging with a confocal scanning laser ophthalmoscope (cSLO) involves scanning a small laser beam over the retina and constructing an image from the reflected light. By applying the confocal principle, tomographic images can be produced. However, the thickness of such slices, when compared with the retinal thickness, is too large to give useful 3D retinal images. In this study an algorithm has been developed which fits a double Gaussian curve to the axial intensity profiles generated from a stack of image slices. The underlying assumption is that the laser light has mainly been reflected by two structures in the retina, the internal limiting membrane and the retinal pigment epithelium. From the fitted curve, topographic images and novel thickness images of the retina can be generated. The technique has been applied to three normal volunteers and seven patients with macular pathology (cystoid macular oedema and macular hole) demonstrating the clinical value of the technique. The improvement in accuracy achieved by using a double rather than a single Gaussian is also demonstrated.

In vivo cell tracking by scanning laser ophthalmoscopy: quantification of leukocyte kinetics.

PURPOSE: To image peripheral blood leukocyte traffic in the normal retinal and choroidal vasculature and to quantify the differences in the circulation dynamics between normal and concanavalin A (ConA)-activated leukocytes. METHODS: Normal or ConA-activated splenocytes were fluorescently labeled in vitro with 6-carboxyfluorescein diacetate (CFDA) and reinfused in vivo where they were tracked in the retinal and choroidal circulations of syngeneic rats by means of a scanning laser ophthalmoscope (SLO). Simultaneous digital and video images were captured for as long as 30 minutes, and the initial 15 seconds of image sequences and leukocyte dynamics were analyzed from digitized images by recording the velocity of trafficking cells and the number of stationary cells that accumulated with time, using a customized software package. RESULTS: Mean velocity (+/-SD) was 29.8 +/- 15.3 mm/sec in the retinal arteries, 14.7 +/- 7.2 mm/sec in the retinal veins, and 3.0 +/- 3.6 mm/sec in the retinal capillaries. Mean velocity in the choroidal vessels was 6.1 +/- 6.0 mm/sec. No significant difference in leukocyte velocity was found between activated and normal leukocytes in any of the vessel systems. However, activated leukocytes were observed to accumulate more within the choroidal vasculature (P < 0.001) and the retinal capillaries (P < 0.001) than in control animals, but not in larger retinal vessels. CONCLUSIONS: A technique to measure the kinetics of circulating leukocytes in vivo has been developed. Although leukocyte activation itself is insufficient to cause slowing of leukocyte velocity, the data indicate that leukocyte adherence to endothelium can be induced in the absence of local or systemic activating stimuli.

Novel approach towards colour imaging using a scanning laser ophthalmoscope.

AIMS: Conventional fundus imaging using a fundus camera produces colour fundus pictures. The scanning laser ophthalmoscope (SLO) has the advantages of lower levels of light exposure, improved contrast, and direct digital imaging but until now has produced monochromatic images as a laser of single wavelength is used. True representation of the fundus is possible by combining images taken using blue, green, and red lasers. METHODS: A custom built SLO was used to capture blue, green, and red fundus images from suitable volunteers and patients with fundus disease. Images were corrected for eye movement and combined to form a colour image. Colour fundus photographs were taken using a fundus camera for comparison with the SLO image. RESULTS: The background fundus and retinal vasculature had similar appearances with the two imaging modalities. Internal limiting membrane reflections were prominent with the SLO. Identification of new vessels in the diabetic fundus was easier with the SLO than the colour fundus photographs. CONCLUSION: A colour SLO offers all the advantages of the present monochromatic imaging system with the added advantage of true colour representation of the fundus.

Quantifying changes in retinal circulation: the generation of parametric images from fluorescein angiograms.

Fluorescein angiography is an established technique for examining the functional integrity of the retinal circulation. The ability to quantify this function offers the possibility of early detection of changes due to retinopathy. We have developed a technique to generate functional, parametric images of the retinal circulation. A given angiogram is first registered to align consecutive frames. At each point in the retina, a graph of fluorescein intensity versus time is then constructed and fitted with a gamma variate curve. Parameters are extracted from these curves and formed into parametric images showing the variation in fluorescein passage across the entire area of the angiogram. Parameters examined to date include time to maximum intensity, time of arrival and rise time. The technique has been demonstrated using photographic and scanning laser ophthalmoscopic angiograms of both normal subjects and patients with a variety of retinopathies. The time to maximum images of the normal subjects reveals a similar fillings pattern in each case, whilst the pathologies present in the abnormal angiograms are clearly identified. The generation of functional time to maximum images enables the health of the retinal circulation to be quantified with respect to the rate at which the vasculature fills with fluorescein. This offers a potential tool for detecting the onset of retinopathy and monitoring its progression.

Imaging of optic nerve head drusen with the scanning laser ophthalmoscope.

BACKGROUND: Optic nerve head drusen may present diagnostic difficulties in cases of disc swelling. Imaging of the nerve in a search for drusen is often inconclusive, especially in children, where drusen may be buried below the surface of the nerve head. METHODS: A small study was carried out using a scanning laser ophthalmoscope (SLO) with an infrared confocal facility to scan deep within optic discs in an attempt to image drusen. RESULTS: The SLO was able to demonstrate superficial and buried drusen (using the infrared confocal facility). The superiority of the SLO over ultrasound in the presence of lens opacity was revealed, as the SLO simultaneously demonstrated both drusen and the associated anomalous disc features which are not detected by ultrasound. CONCLUSION: The SLO can help in the diagnosis of optic disc drusen especially in difficult cases where lens opacity or buried drusen hinders their definitive diagnosis.

The scanning laser ophthalmoscope.

The imaging of the fundus of the eye poses two major technical challenges. First, it is necessary for both the illuminating and reflected beams to pass through the same aperture, the iris. In some commonly used instruments this leads to the use of levels of illumination close to the maximum tolerable by a patient. Second, in order to visualize the different structures present in the various layers of the fundus it is necessary to perform tomographic imaging. The scanning laser ophthalmoscope provides an answer to these particular problems. By scanning the fundus with a narrow laser beam most of the area of the iris is then available for the reflected light and so the intensity of the illuminating beam can be kept low, making it more acceptable for patients. The use of confocal imaging allows 3D images to be produced. In this short review the performance of the instrument will be discussed and its application to a number of clinical problems in ophthalmology considered. Finally there will be a brief description of other instrumentation currently under development.

Fundus imaging in patients with cataract: role for a variable wavelength scanning laser ophthalmoscope.

AIMS: An investigation was carried out to compare the image quality of the ocular fundus obtained clinically, photographically, and with the scanning laser ophthalmoscope (SLO) at visible and infrared wavelengths in patients with significant cataract. METHODS: Nineteen patients admitted for routine cataract extraction were examined clinically by two independent observers to ascertain cataract type and clarity of fundus view with an indirect ophthalmoscope. Fundus photography and both confocal and direct (non-confocal) SLO imaging at 590 nm, 670 nm, and 830 nm were carried out after pupillary dilatation. Images obtained were graded independently using a recognised grading system. RESULTS: Quality of SLO images appeared to be superior to indirect ophthalmoscopy (p < 0.01) and fundus photography (p < 0.001) when graded subjectively. Quantitative analysis of contrast of retinal vessels demonstrated significantly higher contrast for the SLO compared with digitised fundus photographs at all wavelengths tested (p < 0.001), with highest contrast at 590 nm. Use of a confocal aperture significantly improved vessel contrast but may reduce overall image intensity. CONCLUSIONS: Scanning laser ophthalmoscopy may offer a method to observe and record fine fundus detail in patients who have marked cataract.

Quantitative image analysis of macular drusen from fundus photographs and scanning laser ophthalmoscope images.

Drusen are common features in the ageing macula and are associated with exudative age-related macular degeneration (ARMD). They appear as characteristic structures in indirect mode infrared scanning laser ophthalmoscope (SLO) images. Manual counting of drusen area in SLO images has shown no significant difference from that in standard fundus photographs in 6 eyes of 5 patients (p > 0.5). Computerised image processing techniques have been applied to digitised colour fundus photographs and indirect mode images to quantify the area of the macula affected by drusen in an automated fashion. Application of these methods may permit objective and repeatable assessment of the natural history of macular drusen. For a specificity of 90%, a sensitivity of 60% for colour fundus photographs and 35% for SLO images has been achieved, when compared with manual counting. The colour fundus photograph method also showed superior reproducibility compared with the SLO technique.

Performance measurements of an infrared digital scanning laser ophthalmoscope.

Direct digital acquisition of images using a scanning laser ophthalmoscope (SLO) offers several advantages over the conventional fundus camera; in particular, the ability to produce tomographic images using a confocal aperture. This note describes measurements of the performance of an SLO. Spatial resolution, measured by the modulation transfer function, MTF, was shown to be worse along the direction of scan. As expected, image uniformity was good, with a coefficient of variation of 1.9%. While the effect of using a 100 microns diameter confocal aperture instead of one with a 400 microns diameter was to reduce slice thickness from 2600 microns to 975 microns, image intensity was reduced by a factor of 30.