Digital control of magnetic bearings supporting a multimass flexible rotor

The characteristics of magnetic bearings used to support a three mass flexible rotor operated at speeds up to 14,000 RPM are discussed. The magnetic components of the bearing are of a type reported in the literature previously, but the earlier analog controls were replaced by digital ones. Analog-to-digital and digital-to-analog converters and digital control software were installed in an AT&T PC. This PC-based digital controller was used to operate one of the magnetic bearings on the test rig. Basic proportional-derivative control was applied to the bearings, and the bearing stiffness and damping characteristics were evaluated. Particular attention is paid to the frequency dependent behavior of the stiffness and damping properties, and comparisons are made between the actual controllers and ideal proportional-derivative control

The Ginzburg-Landau Free Energy Functional of Color Superconductivity at Weak Coupling

We derive the Ginzburg-Landau free energy functional of color superconductivity in terms of the thermal diagrams of QCD in its perturbative region. The zero mode of the quadratic term coefficient yields the same transition temperature, including the pre-exponential factor, as the one obtained previously from the Fredholm determinant of the two quark scattering amplitude. All coefficients of the free energy can be made identical to those of a BCS model by setting the Fermi velocity of the latter equal to the speed of light. We also calculate the induced symmetric color condensate near $T_c$ and find that it scales as the cubic power of the dominant antisymmetric color component. We show that in the presence of an inhomogeneity and a nonzero gauge potential, while the color-flavor locked condensate dominates in the bulk, the unlocked condensate, the octet, emerges as a result of a simultaneous color-flavor rotation in the core region of a vortex filament or at the junction of super and normal phases.Comment: 32 pages, Plain Tex, 3 figure

Laparoscopy for small bowel obstruction: the reason for conversion matters

Background: Although laparoscopy is associated with reduced hospital stay, early recovery, and decreased morbidity compared with open surgery, it is not well established for the treatment of small bowel obstruction (SBO). Methods: This study analyzed a prospective nationwide database of the Swiss Association of Laparoscopic and Thoracoscopic Surgery. Results: From 1995 to 2006, 537 patients underwent laparoscopy for SBO. Matted adhesions were the main cause of obstruction (62.6%). Intraoperative complications occurred for 9.5% of the patients. Postoperative morbidity was 14% and mortality 0.6%. Within 30days, 13 patients (2.4%) were readmitted because of early recurrence or complications. The conversion rate was 32.4%. The conversions resulted from inability to visualize the site of obstruction or matted adhesions (53.4%), intraoperative complications (21.3%), and small target incisions for resection (25.3%). Emergency operations were associated with higher conversion rates (43.6% vs 19.8%; p<0.001) but not with significantly more postoperative complications (15.2% vs 11.9%; p=0.17). Intraoperative complications and conversion were associated with significantly increased postoperative morbidity (39.2% vs 11.3%; p<0.001 and 24.7% vs 8.3%; p<0.001, respectively). Reactive conversion due to intraoperative complications was associated with the highest postoperative complication rate (48.6%). Morbidity for preemptive conversion due to impaired visualization/matted adhesions or a small-target incision was significantly lower (20% and 26.1%; p=0.02 and p<0.001, respectively). American Society of Anesthesiology (ASA) scores higher than 2 also were associated with postoperative morbidity (p<0.001). However, multivariate regression analysis showed that reactive conversion was the only independent risk factor for postoperative morbidity (p<0.001; odds ratio, 3.97; 95% confidence interval, 1.83-8.64). Conclusions: Laparoscopic management of SBO is feasible with acceptable morbidity and low mortality but with a considerable conversion rate. Early conversion is recommended to reduce postoperative morbidit

A Statistical Method for Estimating Luminosity Functions using Truncated Data

The observational limitations of astronomical surveys lead to significant statistical inference challenges. One such challenge is the estimation of luminosity functions given redshift $z$ and absolute magnitude $M$ measurements from an irregularly truncated sample of objects. This is a bivariate density estimation problem; we develop here a statistically rigorous method which (1) does not assume a strict parametric form for the bivariate density; (2) does not assume independence between redshift and absolute magnitude (and hence allows evolution of the luminosity function with redshift); (3) does not require dividing the data into arbitrary bins; and (4) naturally incorporates a varying selection function. We accomplish this by decomposing the bivariate density into nonparametric and parametric portions. There is a simple way of estimating the integrated mean squared error of the estimator; smoothing parameters are selected to minimize this quantity. Results are presented from the analysis of a sample of quasars.Comment: 30 pages, 9 figures, Accepted for publication in Ap

Transient absorption and reshaping of ultrafast XUV light by laser-dressed helium

We present a theoretical study of transient absorption and reshaping of extreme ultraviolet (XUV) pulses by helium atoms dressed with a moderately strong infrared (IR) laser field. We formulate the atomic response using both the frequency-dependent absorption cross section and a time-frequency approach based on the time-dependent dipole induced by the light fields. The latter approach can be used in cases when an ultrafast dressing pulse induces transient effects, and/or when the atom exchanges energy with multiple frequency components of the XUV field. We first characterize the dressed atom response by calculating the frequency-dependent absorption cross section for XUV energies between 20 and 24 eV for several dressing wavelengths between 400 and 2000 nm and intensities up to 10^12 W/cm^2. We find that for dressing wavelengths near 1600 nm, there is an Autler-Townes splitting of the 1s ---> 2p transition that can potentially lead to transparency for absorption of XUV light tuned to this transition. We study the effect of this XUV transparency in a macroscopic helium gas by incorporating the time-frequency approach into a solution of the coupled Maxwell-Schr\"odinger equations. We find rich temporal reshaping dynamics when a 61 fs XUV pulse resonant with the 1s ---> 2p transition propagates through a helium gas dressed by an 11 fs, 1600 nm laser pulse.Comment: 13 pages, 8 figures, 1 table, RevTeX4, revise

Characterizaiton of Cold-formed Steel Shear Wall Behavior under Cyclic Loading for the CFS-NEES Building

The objective of this paper is to provide a full hysteretic characterization of OSB sheathed cold-formed steel (CFS) shear walls designed for use in the National Science Foundation funded Network for Earthquake Engineering Simulation (NEES) project: CFS-NEES (www.ce.jhu.edu/cfsnees). The shear walls were designed for a two-story ledger-framed building (i.e., the CFS-NEES building) that will undergo full-scale shake table testing at the University of Buffalo NEES site. Shear walls in real construction, such as the CFS-NEES building, have details that differ from the shear walls tested and provided for strength prediction in standards such as AISI-S213-07. Differences include: (a) ledger (rim track) members are attached across the interior face of the studs, (b) OSB panel seams, both horizontal and vertical, may not be aligned with the chord studs or only blocked with strap, (c) interior gypsum board is in place, (d) field studs may have a different thickness or grade from the chord studs, and other differences. In this work, these four highlighted differences (a-d) are specifically explored in a series of shear walls tests loaded via cyclic (CUREE) protocols to determine their hysteretic performance. The test results are compared with AISIS213-07 and hysteretic material characterizations utilizing an elastic-plastic model (EEEP) and a model capable of exhibiting pinching in the hysteretic loops (Pinching4). Recommendations are made with respect to modeling the shear walls

Carrier and Light Trapping in Graded Quantum Well Laser Structures

We investigated the carrier and light trapping in GaInAs/AlGaAs single quantum well laser structures by means of time resolved photoluminescence and Raman spectroscopy. The influence of the shape and depth of the confinement potential and of the cavity geometry was studied by using different AlGaAs/GaAs short-period superlattices as barriers. Our results show that grading the optical cavity improves considerably both carrier and light trapping in the quantum well, and that the trapping efficiency is enhanced by increasing the graded confining potential.Comment: PDF-format, 15 pages (including 4 figures), Applied Physics Letters (June 2000