Influence of Structural Anisotropy on the Irreversibility Line of High-T c Cuprates

From zero-field-cooled and field-cooled magnetic response, we have determined the irreversibility lines for a number of high-T _c oxides, viz., La(Sr)-214, Nd-223, Dy(Tb)-124, (Tl, Pb)-1212, and Tl-11112, in the H–T plane, which fit the relation H=A(1 –T/T _c ) ⁿ . Our results are consistent with a correlation between the anisotropy of the structure and the value of n, is in agreement with the Josephson decoupling model [1].     

SBS suppression using a depolarized source for high power fiberapplications

A depolarized source for fiber applications is demonstrated using a traveling wave LiNbO₃ phase modulator. The source suppresses stimulated Brillouin scattering (SBS) in the fiber when operated at high drive frequencies, enabling more power to be delivered to a remote location. The threshold for SBS is examined in detail using optical powers up to 150 mW and drive frequencies up to 4 GHz. A resonant enhancement technique is demonstrated which reduces the drive power requirement for frequencies <2 GHz by up to 7.6 dB     

Nonlinear analysis of reinforced concrete hyperboloid cooling towers—II. Parametric study and results

In this second and final part of this series of papers the details of parametric studies conducted to assess the influence of various geometric and material parameters on the load-displacement response of three reinforced concrete hyperboloid cooling towers are presented. The material model adopted for the nonlinear finite element analysis is described in part I of this paper.     

Microstructural Evolution during the Sintering of Nanostructured Ceramic Oxides

Using small-angle scattering, together with density measurements, X-ray diffraction, nitrogen adsorption, and both transmission and scanning electron microscopy, the microstructural evolution during sintering in nanostructured ceramic oxides has been studied. The availability of samples with sufficient size and uniformity has permitted absolute calibration of the scattering data and made possible determinations of microstructural parameters and surface areas that are statistically representative of the undisturbed nanophase morphologies. A fully quantitative microstructural model has been developed, and the effects of varying processing parameters during powder synthesis and sintering have been assessed. Predictions are made regarding the achievable sintered full-density microstructures.     

Doppler-broadened positron annihilation studies in Y-Ba-Cu-O,Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O superconductors

Doppler-broadened annihilation radiation spectra have been measured as a function of temperature from 77 K to 300 K, for several high temperature oxide superconductors viz single-phase YBCO, single- and mixed-phase Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O compounds. The temperature-dependent parameters extracted respond to a change at the onset of superconducting transition. The observations point to involvement of oxygen valence electrons at the onset of superconducting transition. Also a possible structural change and/or increase in electron density at the oxygen vacancy/defect sites seem to accompany the transition. In addition, the parameters derived are seen to be sensitive to the presence of more than one superconducting phases in mixed phase samples.     

On arrival of paths in fading multipath indoor radio channels

Arrival of the paths in fading multipath channels obtained from several manufacturing floors and college campus laboratories at 910 MHz are studied. The discrepancies between the empirical distribution of the arriving paths and Poisson arrivals are discovered. The modified Poisson process is shown to fit the arriving paths closely.<>     

Carrier backscattering characteristics of strained silicon-on-insulator n-MOSFETs featuring silicon–carbon source/drain regions

This work investigates for the first time, the physics of carrier transport in a sub-90 nm strained silicon-on-insulator (SOI) n-MOSFET with silicon–carbon (Si:C) source/drain (S/D) regions. The insertion of Si:C in the S/D exerts a lateral tensile strain in the transistor channel, leading to appreciable drive current enhancement. Significant improvement in both carrier backscattering r_sat and source injection velocity υ_inj were observed, accounting for the large drive current I_Dsat enhancement in Si:C S/D transistors. This improvement becomes more appreciable as the gate length is reduced. The reduction in r_sat is related to a shorter critical length ℓ₀ for carrier backscattering. On the other hand, the splitting of six-fold degenerate conduction band valleys due to strain-induced effects results in a reduced in-plane transport mass and thus contributes to significant υ_inj enhancement. In addition, the dependence of drive current performance on source injection velocity and ballistic efficiency in a short channel MOSFET is also discussed.     

Performance evaluation of a switch using priority-based dynamic capacity allocation scheme

Performance-analysis of a switching system using priority-based dynamic capacity allocation is presented. The system provides connectivity between a number of point-to-multipoint communication access clusters. The scheduling of traffic transmission at each access cluster is based on a priority scheme with priority given to real-time (rt) traffic over nonreal-time (nrt) traffic. An analytical model is developed to evaluate the covariance functions of both rt and nrt traffic arriving at the output ports. Aggregate traffic arrival streams are approximated to 2-state Markov-modulated Poisson processes (MMPPs) by matching their statistical characteristics. Analytical and simulation results on performance of an example 4 /spl times/ 4 switch for different traffic loads are discussed.     

Laser power coupling efficiency in conduction and keyhole welding of austenitic stainless steel

Laser welding of thin sheets of AISI 304 stainless steel was carried out with high power CW CO₂ laser. The laser power utilized in the welding process was estimated using the experimental results and the dimensionless parameter model for laser welding; and also the energy balance equation model. Variation of laser welding efficiency with welding speed and mode of welding was studied. Welding efficiency was high for high-speed conduction welding of thin sheets and also in keyhole welding process at high laser powers. Effect of pre-oxidization of the surface and powder as filler material on laser power coupling is also reported. The paper also discusses effect of microstructure on the cracking susceptibility of laser welds.