Neutron and Raman Scattering Studies of Hgba2CuO4+δ

The HgBa₂CuO₄₊ sample was characterized by Neutron diffraction and magnetic measurements. Both of the measurements indicate a high purity of the sample. Raman measurement was performed on a HgBa₂CuO₄₊ compound of T_c = 96 K. The apical oxygen vibration at 592 cm^–1 was found to show (a) an above T_c anomaly, and (b) frequency hardening and linewidth broadening below the superconducting phase transition. The latter is attributed to the coupling of the phonon to the electronic excitation and related to the opening of the superconducting gap below the phonon frequency.     

Brain Derived Vision Algorithm on High Performance Architectures

Even though computing systems have increased the number of transistors, the switching speed, and the number of processors, most programs exhibit limited speedup due to the serial dependencies of existing algorithms. Analysis of intrinsically parallel systems such as brain circuitry have led to the identification of novel architecture designs, and also new algorithms than can exploit the features of modern multiprocessor systems. In this article we describe the details of a brain derived vision (BDV) algorithm that is derived from the anatomical structure, and physiological operating principles of thalamo-cortical brain circuits. We show that many characteristics of the BDV algorithm lend themselves to implementation on IBM CELL architecture, and yield impressive speedups that equal or exceed the performance of specialized solutions such as FPGAs. Mapping this algorithm to the IBM CELL is non-trivial, and we suggest various approaches to deal with parallelism, task granularity, communication, and memory locality. We also show that a cluster of three PS3s (or more) containing IBM CELL processors provides a promising platform for brain derived algorithms, exhibiting speedup of more than 140 × over a desktop PC implementation, and thus enabling real-time object recognition for robotic systems.     

Wavelength blocking filter with flexible data rates and channel spacing

This work presents a high-resolution (13.2 GHz) channel-blocking optical filter, suitable for use as a reconfigurable optical add/drop multiplexer (ROADM), which seamlessly supports data rates from 2.5 to 160 Gb/s. The filter consists of a linear array of 64 MEMS micromirrors and a high-dispersion echelle grating. The demonstrated device had an insertion loss of 9 dB, a loss ripple of 1.2 dB, and a group delay ripple of 15 ps. Data transmission through the device with various mixed data rate scenarios ranging from 2.5 to 160 Gb/s showed negligible penalty, except at 40 Gb/s where a maximum penalty of 1.5 dB was observed due to a phase coherence with the blocker filter ripple.     

OFC 2004 workshop on optical and electronic mitigation of impairments

This paper provides an overview of OFC 2004 Workshop on Optical and Electronic Mitigation of Impairments from the perspective of the invited speakers. The workshop was held on February 23, 2004.     

Generation of correlated Rayleigh fading envelopes for spreadspectrum applications

A procedure for generating N Rayleigh fading envelopes with any desired covariance matrix is given. This method, numerical in nature, enables researchers to simulate correlated fading envelopes, for use in: (1) the study of the impact of correlation on diversity system performance and (2) the study of multicarrier CDMA (MC-CDMA), where the number of carriers notably exceeds the degree of system diversity     

ISI mitigation using decision feedback loop demonstrated with PMDdistorted 10 Gbit/s signals

Electrical polarisation mode dispersion (PMD) and receiver bandwidth generated intersymbol interference (ISI) mitigation using an analogue decision feedback loop for 10 Gbit/s NRZ signals is demonstrated. ISI caused by first-order (PMD) of up to 120 ps differential group delay was equalised. Error free recovery of signals with completely closed eye diagrams was achieved     

Compensation of intrachannel nonlinearities in 40-Gb/s pseudolinear systems using optical-phase conjugation

In this paper intrachannel nonlinearities in a return-to-zero differential-phase-shift-keyed (RZ-DPSK) 40-Gb/s 32/spl times/100-km system are compensated in the absence of signal power symmetry using a single LiNbO/sub 3/ conjugator and results in two decades of improvement in bit-error rate (BER). The reduction of transmission impairments enables the reach of the system to be extended from 5200 to 6400 km with a measured BER =5/spl times/10/sup -4/. This paper also presents a first-order perturbation analysis that describes the effects of optical-phase conjugation and dispersion mapping on the optical field of pulses.     

Substrate bias voltage influenced structural, electrical and optical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide (Ta₂O₅) films were formed on silicon (111) and quartz substrates by dc reactive magnetron sputtering of tantalum target in the presence of oxygen and argon gases mixture. The influence of substrate bias voltage on the chemical binding configuration, structural, electrical and optical properties was investigated. The unbiased films were amorphous in nature. As the substrate bias voltage increased to −50 V the films were transformed into polycrystalline. Further increase of substrate bias voltage to −200 V the crystallinity of the films increased. Electrical characteristics of Al/Ta₂O₅/Si structured films deposited at different substrate bias voltages in the range from 0 to −200 V were studied. The substrate bias voltage reduced the leakage current density and increased the dielectric constant. The optical transmittance of the films increased with the increase of substrate bias voltage. The unbiased films showed an optical band gap of 4.44 eV and the refractive index of 1.89. When the substrate bias voltage increased to −200 V the optical band gap and refractive index increased to 4.50 eV and 2.14, respectively due to the improvement in the crystallinity and packing density of the films. The crystallization due to the applied voltage was attributed to the interaction of the positive ions in plasma with the growing film.     

MEMS-based channelized dispersion compensator with flat passbands

This paper describes a continuously variable and independently addressable channelized dispersion compensator. The optical system is a free-space grating-based system used in a four-pass configuration to ensure flat passbands. The variable dispersion is produced by an array of thermally adaptable curvature micromechanical mirrors. A per-channel variable dispersion greater than +/-400 ps/nm has been demonstrated, with 58 GHz +/-0.4 dB flat passband on 85 GHz spacing. The group delay ripple is less than 7 ps and the penalty with 40 Gb/s CSRZ is 0.7 dB.     

Endoscopic closure of the eustachian tube for repair of cerebrospinal fluid leak

Techniques to repair cerebrospinal fluid (CSF) leak through the eustachian tube (ET) include temporary or permanent CSF diversion; middle fossa craniotomy and packing of the ET from above; and packing of the ET from behind, through the middle ear. We report a case of endoscopic closure of the ET in the nasopharynx (the front). A 26-year-old woman underwent a translabyrinthine removal of a 4.5-cm vestibular schwannoma. One year later, she developed CSF rhinorrhea and meningitis. Attempts at control of this leak included traditional approaches mentioned previously (shunting, middle fossa, middle ear packing). The leak recurred 2-3 months after each procedure. An endoscope was used transnasally to expose the ET orifice, which was incised, inverted, and cauterized. She has remained free of leak for 1 year. Our success in this difficult case suggests that this is a useful procedure for treatment of CSF rhinorrhea originating in the posterior fossa. Greater experience is needed to verify its long-term effectiveness and utility as a primary procedure for the treatment of CSF rhinorrhea.