Development of a honeycomb gas proportional counter array for photon multiplicity measurements in high multiplicity environment

A novel gas-based detector using large arrays of honeycomb cells has been developed and tested for use as a pre-shower photon multiplicity detector (PMD) for STAR and ALICE experiments. The appropriate cell design was arrived at using GARFIELD simulations. Prototype chambers with cell dimensions corresponding to STAR and ALICE were fabricated and tested at CERN PS and SPS. The charged particle detection efficiency and the pre-shower characteristics have been studied using pion and electron beams.     

Photoisomerization of merocyanine 540 in polymer-surfactant aggregate

Photoisomerization of merocyanine 540 (MC540) in a polymer-surfactant aggregate is studied using picosecond time resolved emission spectroscopy. The aggregate consists of the polymer, poly(vinylpyrrolidone) (PVP) and the surfactant, sodium dodecyl sulphate (SDS). With increase in the concentration of SDS in an aqueous solution of MC540 containing PVP, the emission quantum yield and lifetime of MC540 increase markedly. This indicates marked retardation in the nonradiative photoisomerization process of MC540, when it binds to the polymer-surfactant aggregate. The critical association concentration of SDS for binding to PVP has been found to be 0.5 mM. This is about 16 times lower than the CMC of SDS in pure water (8 mM).     

Synthesis and characterization of a novel polyazomethine ether for NLO application

Polymer containing azomethine and ether linking groups between phenylene rings has been prepared. It is a polycondensation reaction of a single monomer containing nitro as well as hydroxyl group in p,p^′ position from 4-nitroaniline and 4-hydroxy benzaldehyde. The polymer has been characterized by elemental analysis, IR, UV and NMR spectroscopies, viscometry and thermal studies. The thermotropic liquid crystalline behaviour of the polymer is investigated by optical polarizing microscopy. The crystalline behaviour of the polymer is confirmed by XRD study. The polymer shows good second harmonic generation for non-linear optical application.     

Challenges in analog and mixed-signal fault models

The design and testing of mixed-signal integrated circuits have enjoyed a renaissance in recent years. As is customary with past developments, however, design outpaces testing, and the drive to integrate analog and digital circuits on the same chip exacerbates the test problems. This article reviews the recent results in analog fault modeling-a critical area of mixed-signal testing-and describes the coming challenges for both industrial and university researchers     

A physical and circuit level approach for modeling turn-offcharacteristics of GTOs

In this paper, we present physical and circuit models, which are related via their parameters, to characterize the gated turn-off characteristics of thyristors. The physical model provides physical insight to the mechanism of turn-off in single islands, and investigates analytically, the dependence of storage time on external variables (anode and gate currents) and physical device parameters and dimensions. Such a characterization is useful since the current crowding effect (that limits current controllability in a multi-emitter structure) depends on the turn-off behavior of the unit cells. The circuit level approach provides a model which can be incorporated into CAD programs (such as SPICE) that can be used by application engineers to design a variety of power electronic circuits such as static VAr compensators (SVCs), The parameters of the circuit model are based on the physical model parameters and thus reflect the physical device properties and dimensions     

Effects of active Q enhancement on oscillator phase noise: an analysis

This article describes the effects of active Q enhancement on the performance of monolithic LC oscillator. Phase noise being the most important parameter for oscillators used in communication circuits, a lot of research efforts have been put in the direction of improving phase noise of fully on-chip LC oscillators over the past few years. Poor quality factor (Q) of on-chip passive components, specially that of spiral inductors limit the phase noise performance of LC oscillators. Use of active Q enhancement techniques has been proposed to improve phase noise but has not been proved by rigorous theory or supported by conclusive measurement results and thus require further investigation. In this article, it has been shown that active Q enhancement using transformer coupling, in fact, degrades the phase noise. The conclusion was reached based on theoretical analysis supported by simulation results.     

Mobility Testbed for 3GPP2-Based Multimedia Domain Networks

Wireless service providers strive to preserve the quality of service and user experience for mobile users. Several standards bodies are defining architectures that can be used as a platform to provide secure and seamless services to these mobile users. These architectures aim to provide several required functions such as signaling, configuration, security association, encryption, and billing. However, the placement of several functional components and their interaction at several layers contributes to the operational complexity and thus affects the optimal results. Testbed realization of any standardized architecture can help investigate the underlying networking issues. In this article, we describe a mobility test bed implementation based on one of the architecture alternatives of 3GPP2, where the outbound signaling servers are distributed around the edges of the network. We experiment with three different hand-off techniques and analyze the associated experimental results. Analysis of these experimental results and experiences obtained from the testbed implementation can be helpful to any service provider that plans to deploy a version of the MMD (multimedia domain) architecture with distributed signaling servers.     

Crosstalk penalty in a two-channel ASK heterodyne detection system with non-negligible laser line width

Crosstalk penalties as a function of channel spacing were measured in a two-channel ASK heterodyne system using 1·55?m DFB lasers. For an IF linewidth/bit rate ratio of 0.5, the channel spacing in the IF domain must be greater than 13 times the bit rate for negligible crosstalk penalty.     

Group representations and the method of sections

The unitary representations of the Euclidean and Poincaré groups are analysed, using viewpoints suggested by the method of sections, as applied to the monopole problem, and by the method of induced representations.     

Sequence Elucidation of an Unknown Cyclic Peptide of High Doping Potential by ETD and CID Tandem Mass Spectrometry

Identification of an unknown substance without any information remains a daunting challenge despite advances in chemistry and mass spectrometry. However, an unknown cyclic peptide in a sample with very limited volume seized at a Pennsylvania racetrack has been successfully identified. The unknown sample was determined by accurate mass measurements to contain a small unknown peptide as the major component. Collision-induced dissociation (CID) of the unknown peptide revealed the presence of Lys (not Gln, by accurate mass), Phe, and Arg residues, and absence of any y-type product ion. The latter, together with the tryptic digestion results of the unusual deamidation and absence of any tryptic cleavage, suggests a cyclic structure for the peptide. Electron-transfer dissociation (ETD) of the unknown peptide indicated the presence of Gln (not Lys, by the unusual deamidation), Phe, and Arg residues and their connectivity. After all the results were pieced together, a cyclic tetrapeptide, cyclo[Arg-Lys-N(C₆H₉)Gln-Phe], is proposed for the unknown peptide. Observations of different amino acid residues from CID and ETD experiments for the peptide were interpreted by a fragmentation pathway proposed, as was preferential CID loss of a Lys residue from the peptide. ETD was used for the first time in sequencing of a cyclic peptide; product ions resulting from ETD of the peptide identified were categorized into two types and named pseudo-b and pseudo-z ions that are important for sequencing of cyclic peptides. The ETD product ions were interpreted by fragmentation pathways proposed. Additionally, multi-stage CID mass spectrometry cannot provide complete sequence information for cyclic peptides containing adjacent Arg and Lys residues. The identified cyclic peptide has not been documented in the literature, its pharmacological effects are unknown, but it might be a “designer” drug with athletic performance-enhancing effects.