1,013 research outputs found
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X-ray optics developments at the APS for third-generation synchrotron radiation sources
High brilliance third-generation synchrotron radiation sources simultaneously provide both a need and an opportunity for the development of new x-ray optical components. The high power and power densities of the x-ray beams produced by insertion devices have forced researchers to consider novel, and what may seem like exotic, approaches to the mitigation of thermal distortions that can dilute the beam brilliance delivered to the experiment or next optical component. Once the power has been filtered by such high heat load optical elements, specialized components can be employed that take advantage of the high degree of brilliance. This presentation reviews the performance of optical components that have been designed, fabricated, and tested at the Advanced Photon Source, starting with high heat load components and followed by examples of several specialized devices such as a milli-eV resolution (in-line) monochromator, a high energy x-ray phase retarder, and a phase zone plate with submicron focusing capability
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Feasibility study into the use of mechanical choppers to alter the natural time structure of the APS
In a very general way, one can divide time-resolved experiments into two broad classes: (1) those that take advantage of techniques that permit data to be collected in a more rapid fashion and (2) those that take advantage of the natural time-structure or modulation of the radiation produced by storage ring sources. It is with the latter group of experiments that this report is primarily concerned. Researchers planning to use the time structure are considering both experiments that can be cyclically pumped and probed. The natural time-structure of the storage ring may not, unfortunately, be optimal for all time-resolved experiments
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Heat transfer issues in high-heat-load synchrotron x-ray beams
In this paper, a short description of the synchrotron radiation x-ray sources and the associated power loads is given, followed by a brief description of typical synchrotron components and their heat load. It is emphasized that the design goals for most of these components is to limit (a) temperature, (b) stresses, or (c) strains in the system. Each design calls for a different geometry, material selection, and cooling scheme. Cooling schemes that have been utilized so far are primarily single phase and include simple macrochannel cooling, microchannel cooling, contact cooling, pin-post cooling, porous-flow cooling, jet cooling, etc. Water, liquid metals, and various cryogenic coolants have been used. Because the trend in x-ray beam development is towards brighter (i.e., more powerful) beams and assuming that no radical changes in the design of x-ray generating machines occurs in the next few years, it is fair to state that the utilization of various effective cooling schemes and, in particular, two-phase flow (e.g., subcooled boiling) warrants further investigation. This, however, requires a thorough examination of stability and reliability of two-phase flows for high-heat-flux components operating in ultrahigh vacuum with stringent reliability requirements
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Further tests on liquid-nitrogen-cooled, thin silicon-crystal monochcromators using a focused wiggler synchrotron beam
A newly designed, cryogenically cooled, thin Si crystal monochromator was tested at the European Synchrotron Radiation Facility (ESRF) beamline BL3. It exhibited less than 1 arcsec of thermal strain up to a maximum incident power of 186 W and average power density of 521 W/mm{sup 2}. Data were collected for the thin (0.7 mm) portion of the crystal and for the thick (>25 mm) part. Rocking curves were measured as a function of incident power. With a low power beam, the Si(333) rocking curve at 30 keV for the thin and thick sections was < 1 arcsec FWHM at room temperature. The rocking curve of the thin section increased to 2.0 arcsec when cooled to 78 K, while the thick part was unaffected by the reduction in temperature. The rocking curve of the thin section broadened to 2.5 arcsec FWHM and that of the thick section broadened to 1.7 arcsec at the highest incident power. The proven range of performance for this monochromator has been extended to the power density, but not the absorbed power, expected for the Advanced Photon Source (APS) undulator A in closed-gap operation (first harmonic at 3.27 keV) at a storage-ring current of 300 mA
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Performance of cryogenically cooled, high-heat-load silicon crystal monochromators with porous media augmentation
The performance of two Si crystal x-ray monochromators internally cooled with liquid nitrogen was tested on the F2-wiggler beamline at the Cornell High Energy Synchrotron Source (CHESS). Both crystals were (111)-oriented blocks of rectangular cross section having identical dimensions. Seven 6.4-mm-diameter coolant channels were drilled through the crystals along the beam direction. In one of the crystals, porous Cu mesh inserts were bonded into the channels to enhance the heat transfer. The channels of the second crystal were left as drilled. Symmetric, double-crystal rocking curves were recorded simultaneously for both the first and third order reflections at 8 and 24 keV. The power load on the cooled crystal was adjusted by varying the horizontal beam size using slits. The measured Si(333) rocking curve of the unenhanced crystal at 24 keV at low power was 1.9 arcsec FWHM. The theoretical width is 0.63 arcsec. The difference is due to residual fabrication and mounting strain. For a maximum incident power of 601 W and an average power density of about 10 W/MM{sup 2}, the rocking curve was 2.7 arcsec. The rocking curve for the enhanced crystal at low power was 2.4 arcsec. At a maximum incident power of 1803 W and an average power density of about 19 W/mm{sup 2} the rocking curve width was 2.2 arcsec FWHM. The use of porous mesh augmentation is a simple, but very effective, means to improve the performance of cryogenically cooled Si monochromators exposed to high power x-ray beams
Ab initio study of the beta$-tin->Imma->sh phase transitions in silicon and germanium
We have investigated the structural sequence of the high-pressure phases of
silicon and germanium. We have focussed on the cd->beta-tin->Imma->sh phase
transitions. We have used the plane-wave pseudopotential approach to the
density-functional theory implemented within the Vienna ab-initio simulation
package (VASP). We have determined the equilibrium properties of each structure
and the values of the critical parameters including a hysteresis effect at the
phase transitions. The order of the phase transitions has been obtained
alternatively from the pressure dependence of the enthalpy and of the internal
structure parameters. The commonly used tangent construction is shown to be
very unreliable. Our calculations identify a first-order phase transition from
the cd to the beta-tin and from the Imma to the sh phase, and they indicate the
possibility of a second-order phase-transition from the beta-tin to the Imma
phase. Finally, we have derived the enthalpy barriers between the phases.Comment: 12 pages, 16 figure
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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