2,891 research outputs found
Effect of heat treatment on mechanical dissipation in TaO coatings
Thermal noise arising from mechanical dissipation in dielectric reflective
coatings is expected to critically limit the sensitivity of precision
measurement systems such as high-resolution optical spectroscopy, optical
frequency standards and future generations of interferometric gravitational
wave detectors. We present measurements of the effect of post-deposition heat
treatment on the temperature dependence of the mechanical dissipation in
ion-beam sputtered tantalum pentoxide between 11\,K and 300\,K. We find the
temperature dependence of the dissipation is strongly dependent on the
temperature at which the heat treatment was carried out, and we have identified
three dissipation peaks occurring at different heat treatment temperatures. At
temperatures below 200\,K, the magnitude of the loss was found to increase with
higher heat treatment temperatures, indicating that heat treatment is a
significant factor in determining the level of coating thermal noise.Comment: accepted Classical and Quantum Gravity 201
Structural Invariance of Sunspot Umbrae Over the Solar Cycle: 1993-2004
Measurements of maximum magnetic flux, minimum intensity, and size are
presented for 12 967 sunspot umbrae detected on the NASA/NSO
spectromagnetograms between 1993 and 2004 to study umbral structure and
strength during the solar cycle. The umbrae are selected using an automated
thresholding technique. Measured umbral intensities are first corrected for a
confirming observation of umbral limb-darkening. Log-normal fits to the
observed size distribution confirm that the size spectrum shape does not vary
with time. The intensity-magnetic flux relationship is found to be steady over
the solar cycle. The dependence of umbral size on the magnetic flux and minimum
intensity are also independent of cycle phase and give linear and quadratic
relations, respectively. While the large sample size does show a low amplitude
oscillation in the mean minimum intensity and maximum magnetic flux correlated
with the solar cycle, this can be explained in terms of variations in the mean
umbral size. These size variations, however, are small and do not substantiate
a meaningful change in the size spectrum of the umbrae generated by the Sun.
Thus, in contrast to previous reports, the observations suggest the equilibrium
structure, as testified by the invariant size-magnetic field relationship, as
well as the mean size (i.e. strength) of sunspot umbrae do not significantly
depend on solar cycle phase.Comment: 17 pages, 6 figures. Published in Solar Physic
Landlord Tenant Relations: A Report of the Landlord Tenant Relations Subcommittee of the North-Central Regional Land Tenure Committee
Acute pancreatitis and hyperamylasemia in renal homograft recipients.
In a series of 301 renal homograft recipients, 17 (5.6%) had acute pancreatitis at some time after transplantation. Eleven of these patients died, for a mortality of 64.7%. In each instance, pancreatitis was a major factor in a complex chain of lethal events to which immunosuppression invariably contributed. An additional 43 patients (14.3%) developed asymptomatic hyperamylasemia after transplantation and, undoubtedly, some of these recipients also had pancreatitis. The factors causing pancreatitis in the renal transplantation patient include uremia, hyperparathyroidism, pancreatic injury by drugs, infections resulting from chronic immunosuppression, gallstones, and operative trauma to the pancreas. In cases of preexisting pancreatitis, transplantation is not necessarily precluded, but efforts should be made to find a specific cause of the pancreatitis and take corrective measures, such as biliary tract surgery or parathyroidectomy if indicated, in advance of transplantation
Assessing Student Progress and Performance across the Curriculum
Evaluation of student learning is of paramount importance to the educational community and allows reflection on program successes and weaknesses; however, best practices are hotly debated. This project designed and implemented an assessment system in which an identical, mixed-format assessment was given to all levels of students in the Georgia Gwinnett College biology program at the start of the semester for academic years 2014-15, 2015-16 and Fall of 2016. The assessment contained multiple choice and free-response questions, and evaluated lab reports from core courses in the biology program. This system allows for longitudinal assessment of students, provides quick results for timely action, and can allow analysis of interesting demographic questions. We found student achievement on program goals was lower than previously assessed and student performance on multiple choice questions was higher than free-response questions. There was a modest, but temporary, gain in performance on the ability to effectively communicate science. Additionally, males outperformed their female counterparts and Hispanics underperformed their non-Hispanic peers
Unsuccessful attempts to control hyperacute rejection of human renal homografts with f(ab')<inf>2</inf> and citrate organ pretreatme
Hole dynamics in noble metals
We present a detailed analysis of hole dynamics in noble metals (Cu and Au),
by means of first-principles many-body calculations. While holes in a
free-electron gas are known to live shorter than electrons with the same
excitation energy, our results indicate that d-holes in noble metals exhibit
longer inelastic lifetimes than excited sp-electrons, in agreement with
experiment. The density of states available for d-hole decay is larger than
that for the decay of excited electrons; however, the small overlap between d-
and sp-states below the Fermi level increases the d-hole lifetime. The impact
of d-hole dynamics on electron-hole correlation effects, which are of relevance
in the analysis of time-resolved two-photon photoemission experiments, is also
addressed.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let
Measurements of a low temperature mechanical dissipation peak in a single layer of Ta2O5 doped with TiO2
Thermal noise arising from mechanical dissipation in oxide coatings is a
major limitation to many precision measurement systems, including optical
frequency standards, high resolution optical spectroscopy and interferometric
gravity wave detectors. Presented here are measurements of dissipation as a
function of temperature between 7 K and 290 K in ion-beam sputtered Ta2O5 doped
with TiO2, showing a loss peak at 20 K. Analysis of the peak provides the first
evidence of the source of dissipation in doped Ta2O5 coatings, leading to
possibilities for the reduction of thermal noise effects
Silica suspension and coating developments for Advanced LIGO
The proposed upgrade to the LIGO detectors to form the Advanced LIGO detector system is intended to incorporate a low thermal noise monolithic fused silica final stage test mass suspension based on developments of the GEO 600 suspension design. This will include fused silica suspension elements jointed to fused silica test mass substrates, to which dielectric mirror coatings are applied.
The silica fibres used for GEO 600 were pulled using a Hydrogen-Oxygen flame system. This successful system has some limitations, however, that needed to be overcome for the more demanding suspensions required for Advanced LIGO. To this end a fibre pulling machine based on a CO2 laser as the heating element is being developed in Glasgow with funding from EGO and PPARC.
At the moment a significant limitation for proposed detectors like Advanced LIGO is expected to come from the thermal noise of the mirror coatings. An investigation on mechanical losses of silica/tantala coatings was carried out by several labs involved with Advanced LIGO R&D. Doping the tantala coating layer with titania was found to reduce the coating mechanical dissipation. A review of the results is given here
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