Analysis of Dislocation Density in Pb<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se Grown on ZnTe/Si by MBE

The growth of (211) Pb_(1−x)Sn _x Se on Si is achieved with a thick ZnTe buffer layer. The obtained films are specular, but contain widely dispersed void defects. Because the lattice misfit between Pb_(1−x)Sn _x Se and ZnTe is small, dislocation density values on the order of 10⁶/cm² in the Pb_(1−x)Sn _x Se are obtained. The variation of the dislocation density as a function of Pb_(1−x)Sn _x Se thickness, h, is analyzed in terms of dislocation annihilation. The analysis predicts an inverse quadratic dependence of dislocation density on h, and quantitative agreement with experimental measurements of the dislocation density is obtained.     

Influence of Zn doping profiles on excitation dependence of photoluminescence intensity in InGaAsP heterostructures

It is known that the Zn doping profile in strained multi-quantum-well (MQW) InGaAsP lasers strongly affects the electro-optical characteristics of these devices and their temperature sensitivity. A systematic investigation of the excitation dependence of the active layer photoluminescence (PL) intensity from compressively strained InGaAsP MQW pin laser material with different Zn doping profiles is described. When the pn junction lies within the active region, the excitation dependence of the PL intensity is superlinear at low excitation and linear at higher excitation. As the Zn profile is set back from the heterointerface creating a displaced pn junction from the active region, the excitation dependence is superlinear and linear at 300 K but becomes linear for all excitation powers at 77 K. The implications of these observations are discussed.     

Synthesis of poly(1‐hexene)s end‐functionalized with phenols

Electrophilic alkylations of phenol/2,6‐dimethylphenol were performed with vinylidene‐terminated poly(1‐hexene)s using BF₃·OEt₂ catalyst. Vinylidene‐terminated poly(1‐hexene)s with M_n varying from 400 to 10000 were prepared by bulk polymerization of 1‐hexene at 50 to ?20 °C using Cp₂ZrCl₂/MAO catalysts. The phenol/2,6‐dimethylphenol‐terminated poly(1‐hexene)s was characterized by NMR (¹H, ¹³C), UV, IR and vapor phase osmometer (VPO). The isomer distribution (ortho, para and ortho/para) was determined by ¹³P NMR using a phosphitylating reagent, namely 2‐chloro‐1,3,2‐dioxaphospholane. The number‐average degree of functionality (F_n) >0.9 with >95% para selectivity could be achieved using low‐molecular‐weight oligomers of poly(1‐hexene)s. Copyright © 2005 Society of Chemical Industry     

Decolourization of reactive dyes by thin film immobilized surface photoreactor using solar irradiation

The photocatalytic degradation of four reactive dyes using TiO₂ was investigated in suspended and immobilized systems under solar irradiation. Batch degradation experiments were carried out at initial concentrations ranging from 25 to 100 mg l⁻¹ and at a catalyst loading of 0.5–1 g l⁻¹. The studies on batch photocatalytic degradation of four dyes, showed about 30–70% colour removal depending on the initial dye concentration, dye structure (functional group and reactivity of dyes) and the amount of catalyst. The thin film immobilized surface photoreactor was able to give nearly 90–98% colour removal depending on the initial concentration and exposure time. Flow rate has noticeable effect on colour removal particularly at higher concentration (100 mg l⁻¹). High colour removals obtained with solar radiation indicated effectiveness of this process and its potential for practical application.     

A technique to improve the performance of serial, matched-filter acquisition in direct-sequence spread-spectrum packet radio communications

In this paper, we examine a simple method to improve the performance of serial, matched-filter acquisition in direct-sequence spread-spectrum packet radio communications. Each packet transmission includes an acquisition preamble, and the preamble sequence is changed at the boundaries of predefined time epochs based on a pseudorandom sequence generator. It is shown in previous work that the presence of an intermediate-frequency filter and the characteristics of the automatic gain-control subsystem lead to a probability of not acquiring that is a nonmonotonic function of the signal-to-noise ratio if the acquisition algorithm uses a threshold-crossing detector with a fixed threshold. The acquisition algorithm presented in this paper employs an estimator to adaptively select the acquisition threshold for each test statistic. It is shown that this technique reduces the severity of the nonmonotonicity and substantially improves the acquisition performance.     

An efficient protocol for the green synthesis of quinoxaline and dipyridophenazine derivatives at room temperature using sulfated titania

Biologically active quinoxalines and dipyridophenazines were efficiently synthesized in excellent yield and less reaction time using inexpensive, easily recyclable sulfated titania (TiO₂–SO₄²⁻). TiO₂–SO₄²⁻, prepared by sol–gel method, was characterized by XRD, FT-IR and SEM techniques to confirm the sulfate loading. TiO₂–SO₄²⁻ has more acidic sites when compared to TiO₂ (prepared )and TiO₂–P25. Synthesis of quinoxalines with this catalyst can also be carried out in water.     

Algorithms for Data Migration

The data migration problem is the problem of computing a plan for moving data objects stored on devices in a network from one configuration to another. Load balancing or changing usage patterns might necessitate such a rearrangement of data. In this paper, we consider the case where the objects are fixed-size and the network is complete. Our results are both theoretical and empirical. Our main theoretical results are (1) a polynomial time algorithm for finding a near-optimal migration plan in the presence of space constraints when a certain number of additional nodes is available as temporary storage, and (2) a 3/2-approximation algorithm for the case where data must be migrated directly to its destination. We also run extensive experiments on several algorithms for various data migration problems and show that empirically, many algorithms perform better in practice than their theoretical bounds suggest. We conclude that many of the algorithms we present are both practical and effective for data migration.     

Nonmetric calibration of wide-angle lenses and polycameras

Images taken with wide-angle cameras tend to have severe distortions which pull points towards the optical center. This paper proposes a simple method for recovering the distortion parameters without the use of any calibration objects. Since distortions cause straight lines in the scene to appear as curves in the image, our algorithm seeks to find the distortion parameters that map the image curves to straight lines. The user selects a small set of points along the image curves. Recovery of the distortion parameters is formulated as the minimization of an objective function which is designed to explicitly account for noise in the selected image points. Experimental results are presented for synthetic data as well as real images. We also present the idea of a polycamera which is defined as a tightly packed camera cluster. Possible configurations are proposed to capture very large fields of view. Such camera clusters tend to have a nonsingle viewpoint. We therefore provide analysis of what we call the minimum working distance for such clusters. Finally, we present results for a polycamera consisting of four wide-angle sensors having a minimum working distance of about 4 m. On undistorting the acquired images using our proposed technique, we create real-time high resolution panoramas.