Thermal stress cycling of GaAs solar cells

A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance

Composite materials for space applications

The objectives of the program were to: generate mechanical, thermal, and physical property test data for as-fabricated advanced materials; design and fabricate an accelerated thermal cycling chamber; and determine the effect of thermal cycling on thermomechanical properties and dimensional stability of composites. In the current program, extensive mechanical and thermophysical property tests of various organic matrix, metal matrix, glass matrix, and carbon-carbon composites were conducted, and a reliable database was constructed for spacecraft material selection. Material property results for the majority of the as-fabricated composites were consistent with the predicted values, providing a measure of consolidation integrity attained during fabrication. To determine the effect of thermal cycling on mechanical properties, microcracking, and thermal expansion behavior, approximately 500 composite specimens were exposed to 10,000 cycles between -150 and +150 F. These specimens were placed in a large (18 cu ft work space) thermal cycling chamber that was specially designed and fabricated to simulate one year low earth orbital (LEO) thermal cycling in 20 days. With this rate of thermal cycling, this is the largest thermal cycling unit in the country. Material property measurements of the thermal cycled organic matrix composite laminate specimens exhibited less than 24 percent decrease in strength, whereas, the remaining materials exhibited less than 8 percent decrease in strength. The thermal expansion response of each of the thermal cycled specimens revealed significant reduction in hysteresis and residual strain, and the average CTE values were close to the predicted values

A Wire Position Monitor System for the 1.3 GHZ Tesla-Style Cryomodule at the Fermilab New-Muon-Lab Accelerator

The first cryomodule for the beam test facility at the Fermilab New-Muon-Lab building is currently under RF commissioning. Among other diagnostics systems, the transverse position of the helium gas return pipe with the connected 1.3 GHz SRF accelerating cavities is measured along the ~15 m long module using a stretched-wire position monitoring system. An overview of the wire position monitor system technology is given, along with preliminary results taken at the initial module cool down, and during further testing. As the measurement system offers a high resolution, we also discuss options for use as a vibration detector.Comment: 4 pp. 15th International Conference on RF Superconductivity (SRF2011). 25-29 Jul 2011. Chicago, Illinois, US

High Resolution BPM Upgrade for the ATF Damping Ring at KEK

A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility (ATF) damping ring has been accomplished, carried out by a KEK/FNAL/SLAC collaboration under the umbrella of the global ILC R&D effort. The upgrade consists of a high resolution, high reproducibility read-out system, based on analog and processing, and also implements a new automatic gain error correction schema. The technical concept and realization as well as results of beam studies are presented.Comment: 3 pp. 10th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators DIPAC 2011, 16-18 May 2011. Hamburg, German

Influence of high-dose aprotinin treatment on blood loss and coagulation patterns in open-heart surgery

Intraoperative administration of the proteinase Inhibitor aprotinin causes reduction in blood loss and homologous blood requirement in patients undergoing cardiac surgery. To ascertain the blood-saving effect of aprotinin and to obtain further information about the mode of action, 40 patients undergoing primary myocardial revascularization were randomly assigned to receive either aprotinin or placebo treatment. Aprotinin was given as a bolus of 2 X 105 kallikrein inactivator units (KIU) before surgery followed by a continuous infusion of 5 X 105 KIU/h during surgery. Additionally, 2 X 105 KIU were added to the pump prime. Strict criteria were used to obtain a homogeneous patient selection. Total blood loss was reduced from 1,431 +/- 760 ml in the control group to 738 +/- 411 ml in the aprotinin group (P < 0.05) and the homologous blood requirement from 838 +/- 963 ml to 163 +/- 308 ml (P < 0.05). In the control group, 2.3 +/- 2.2 U of homologous blood or blood products were given, and in the aprotinin group, 0.63 +/- 0.96 U were given (P < 0.05). Twenty-five percent of patients in the control group and 63% in the aprotinin group did not receive banked blood or homologous blood products. The activated clotting time as an indicator of inhibition of the contact phase of coagulation was significantly Increased before heparinization in the aprotinin group (141 +/- 13 s vs. 122 +/- 25 s) and remained significantly Increased until heparin was neutralized after cardiopulmonary bypass (CPB). The concentration of the thrombin-antithrombin III complex was significantly decreased at the end of CPB in the aprotinin group, indicating less thrombin generation in the aprotinin-treated group. The total concentration of the fibrinogen-fibrin split products (FSP) and the split products of the cross-linked fibrin (D-dimers) were also significantly reduced due to attenuated proteolytic activities of thrombin and plasmin. The results of the fibrin plate assay revealed higher fibrinolytic activity during CPB in the control group. The results demonstrate the beneficial effect of high-dose aprotinin treatment on blood loss and homologous blood requirement. This effect can be attributed to the inhibition of the contact phase of coagulation and the consequently reduced thrombotic and fibrionolytic activity during and after CPB

QSO 0347-383 and the invariance of m_p/m_e in the course of cosmic time

The variation of the dimensionless fundamental physical constant mu = m_p/m_e (the proton to electron mass ratio) can be constrained via observation of Lyman and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha systems (DLAs) in the line of sight to distant QSOs. Drawing on VLT-UVES high resolution data sets of QSO 0347-383 and its DLA obtained in 2009 our analysis yields dmu/mu = (4.3 +/- 7.2) * 10^-6 at z_abs =3.025. We apply corrections for the observed offsets between discrete spectra and for the first time we find indications for inter-order distortions. Current analyses tend to underestimate the impact of systematic errors. Based on the scatter of the measured redshifts and the corresponding low significance of the redshift-sensitivity correlation we estimate the limit of accuracy of line position measurements to about 220 m/s, consisting of roughly 150 m/s due to the uncertainty of the absorption line fit and about 150 m/s allocated to systematics related to instrumentation and calibration.Comment: 9 pages, 9 figures, accepted for publication in A&

The relaxation dynamics of a simple glass former confined in a pore

We use molecular dynamics computer simulations to investigate the relaxation dynamics of a binary Lennard-Jones liquid confined in a narrow pore. We find that the average dynamics is strongly influenced by the confinement in that time correlation functions are much more stretched than in the bulk. By investigating the dynamics of the particles as a function of their distance from the wall, we can show that this stretching is due to a strong dependence of the relaxation time on this distance, i.e. that the dynamics is spatially very heterogeneous. In particular we find that the typical relaxation time of the particles close to the wall is orders of magnitude larger than the one of particles in the center of the pore.Comment: 9 pages of Latex, 4 figure