Radiation characteristics of prime focus paraboloids with square aperture

Radiation characteristics of a paraboloid with a square aperture are described in this paper. A systematic analysis of the principal plane radiation patterns of the dish employing the uniform geometrical theory of diffraction (UGTD) [3], [4] reveals that for the square paraboloid the backlobes are weak because there is no caustic at the rear boresight as in the case of circular apertures. Based on the method enunciated in [7] the front-to-back (F/B) ratio for different square paraboloids are also tabulated.     

An I/O-Conscious Tiling Strategy for Disk-Resident Data Sets

This paper describes a tiling technique that can be used by application programmers and optimizing compilers to obtain I/O-efficient versions of regular scientific loop nests. Due to the particular characteristics of I/O operations, a straightforward extension of the traditional tiling method to I/O-intensive programs may result in poor I/O performance. Therefore, the technique presented in this paper adapts iteration space tiling for I/O-performing loop nests to deliver high I/O performance. The generated code results in huge savings in the number of I/O calls as well as the volume of data transferred between the disk subsystem and main memory. Our experimental results on the IBM SP-2 distributed-memory message-passing multiprocessor demonstrate that the reduction in these two parameters, namely, the number of I/O calls and the transferred data volume, can lead to a marked decrease in overall execution times of I/O-intensive loop nests. In a number of loop nests extracted from several benchmarks and math libraries, we were able to improve the execution times by an average 42.5% for one data set and by an average 47.4% for another.     

Models and logics for true concurrency

A distributed computer system consists of different processes oragents that function largely autonomously and coordinate their actions by communicating with each other. In such a situation, actions may be performed by different agents of the system locally, in a concurrent manner. In this paper, we first discuss formal models of distributed systems in which concurrency is specifiedexplicitly, in contrast to more traditional approaches where concurrency is representedimplicitly as a nondeterministic choice between all possible sequentializations of concurrent actions. This naturally leads to models based on partially-ordered sets of actions rather than sequences of actions and is often called thetrue concurrency approach. The models we focus on are distributed transition systems, elementary net systems and event structures. In the second half of the paper, we develop a family of logics to specify and reason about the behavioural properties of the models we have described. The logics we define are extensions of temporal logic with new modalities to directly describe concurrency. This paper is essentially a survey of work done by the authors during the last few years on modelling distributed systems with true concurrency and using logic to reason about these models. The emphasis is on motivating definitions through examples and on presenting major results, without going into too many formal details. We provide pointers to the literature where these details can be found.     

Identification of embedded interlaminar flaw using inverse analysis

The integrity of a composite laminate can be greatly affected by an existence of embedded interlaminar flaw. In general, identification of such a flaw often requires expensive tools and tedious processes. The aim of the present work is to develop a novel method with the aid of an intelligent post-processing scheme, thereby not relying on those sophisticated experiments. Essentially the proposed procedure utilizes an inverse analysis to estimate unknown delamination parameters from limited measurements. The procedure first constructs approximate functions relating the delamination parameters to measurement parameters. Then, a multi-dimensional minimization technique is adopted to search for the best estimates of unknown parameters corresponding to the lowest value of error objective function. In the present verification and simulation analyses, surface strains at discrete locations on a composite laminate under three-point bending are selected as the input measurements. Although reasonable estimates are obtained with these measurements, to increase their accuracy, the deflection at load point is also included as measurement input. Additional improvements are observed when those measurements under multiple loading conditions are included. A detailed error sensitivity analysis is also carried out to confirm the methods robustness. These results suggest the current method to be one of the alternate identification approaches for detecting a single embedded delamination in composite laminates.     

Comparison of multiexcitation fluorescence and diffuse reflectance spectroscopy for the diagnosis of breast cancer (March 2003)

Nonmalignant (n = 36) and malignant (n = 20) tissue samples were obtained from breast cancer and breast reduction surgeries. These tissues were characterized using multiple excitation wavelength fluorescence spectroscopy and diffuse reflectance spectroscopy in the ultraviolet-visible wavelength range, immediately after excision. Spectra were then analyzed using principal component analysis (PCA) as a data reduction technique. PCA was performed on each fluorescence spectrum, as well as on the diffuse reflectance spectrum individually, to establish a set of principal components for each spectrum. A Wilcoxon rank-sum test was used to determine which principal components show statistically significant differences between malignant and nonmalignant tissues. Finally, a support vector machine (SVM) algorithm was utilized to classify the samples based on the diagnostically useful principal components. Cross-validation of this nonparametric algorithm was carried out to determine its classification accuracy in an unbiased manner. Multiexcitation fluorescence spectroscopy was successful in discriminating malignant and nonmalignant tissues, with a sensitivity and specificity of 70% and 92%, respectively. The sensitivity (30%) and specificity (78%) of diffuse reflectance spectroscopy alone was significantly lower. Combining fluorescence and diffuse reflectance spectra did not improve the classification accuracy of an algorithm based on fluorescence spectra alone. The fluorescence excitation-emission wavelengths identified as being diagnostic from the PCA-SVM algorithm suggest that the important fluorophores for breast cancer diagnosis are most likely tryptophan, NAD(P)H and flavoproteins.     

Weighted Random Routing on Torus Networks

In this paper, we introduce a new closed-form oblivious routing algorithm called W2TURN that is worst-case throughput optimal for 2D-torus networks. W2TURN is based on a weighted random selection of paths that contain at most two turns. In terms of average hop count, W2TURN outperforms the best previously known closed-form worst-case throughput optimal routing algorithm called IVAL. In addition, we present a new optimal weighted random routing algorithm for rings called WRD.     

Randomized Partially-Minimal Routing on Three-Dimensional Mesh Networks

This letter presents a new oblivious routing algorithm for 3D mesh networks called Randomized Partially- Minimal (RPM) routing that provably achieves optimal worstcase throughput for 3D meshes when the network radix k is even and within a factor of 1/k2 of optimal when k is odd. Although this optimality result has been achieved with the minimal routing algorithm O1TURN [9] for the 2D case, the worst-case throughput of O1TURN degrades tremendously in higher dimensions. Other existing routing algorithms suffer from either poor worst-case throughput (DOR [10], ROMM [8]) or poor latency (VAL [14]). RPM on the other hand achieves near optimal worst-case and good average-case throughput as well as good latency performance.     

Hydrodynamics in down flow jet loop reactor

Gas holdup and liquid circulation time were measured in a down flow jet loop reactor for air–water system. It was observed that the circulation time decreases with an increase in nozzle diameter, draft tube to column diameter ratio and liquid velocity. Th gas holdup increases with an increase in gas and liquid velocities. The optimum draft tube to column diameter ratio was found to be 0.438. Correlations for gas holdup and circulation time involving operational and geometrical variables are presented.     

Iron(III) chloride-benzotriazole adduct for oxygen reduction reaction in alkaline medium

Transition metal-nitrogen-carbon (MNC) based non-platinum metal catalysts obtained by pyrolysis of a transition metal, carbon and nitrogen sources were viewed as an inexpensive substitute for the platinum-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. Due to the pyrolysis step involved in synthesizing MNC catalysts, the exact active site structure responsible for ORR was not conclusively identified thereby limiting the efforts of scientists in identifying effective synthetic routes to achieve highly active MNC catalysts with required active site structure and site density. To alleviate the lack of clarity on the active site structure of MNC catalysts, as a substitute, copper, and cobalt-based metal-organic frameworks and complexes were synthesized recently and shown to be ORR active. In this study, we have synthesized an Iron(III) chloride-benzotriazole ($\left[{\text{FeCl}}_3{\left(\text{btaH}\right)}_2\right]$) adduct and demonstrated its ORR activity in alkaline medium, which primarily reduces oxygen by 4-electron reduction pathway. Single crystal XRD characterization revealed the crystal structure of $\left[{\text{FeCl}}_3{\left(\text{btaH}\right)}_2\right]$ unambiguously. The ORR onset potential, Tafel slopes, and methanol tolerance ability of $\left[{\text{FeCl}}_3{\left(\text{btaH}\right)}_2\right]$ were compared against commercial 20 wt% Pt/C. $\left[{\text{FeCl}}_3{\left(\text{btaH}\right)}_2\right]$ adduct shows complete methanol tolerance and ORR onset potential of 0.89 V vs. RHE, which is highest among the unpyrolyzed metal-organic frameworks/complexes.     

Offset spherical dual-reflector antenna

The dual offset spherical reflector antenna offers the advantage of a circularly symmetric main reflector together with a subreflector possessing an axis of symmetry. These features could lead to significant cost reductions in manufacture compared to existing offset designs. Initial results of a parametric study, using physical optics, show that 64% efficiency is possible with a peak crosspolar level below ?35 dB, together with very low sidelobes.