1,718 research outputs found
Vibrational States of Glassy and Crystalline Orthotherphenyl
Low-frequency vibrations of glassy and crystalline orthoterphenyl are studied
by means of neutron scattering. Phonon dispersions are measured along the main
axes of a single crystal, and the corresponding longitudinal and transversal
sound velocities are obtained. For glassy and polycrystalline samples, a
density of vibrational states is determined and cross-checked against other
dynamic observables. In the crystal, low-lying zone-boundary modes lead to an
excess over the Debye density of states. In the glass, the boson peak is
located at even lower frequencies. With increasing temperature, both glass and
crystal show anharmonicity.Comment: 7 pages of LaTeX (svjour), 2 tables, 10 figures accepted in Eur.
Phys. J.
Lösung der stationären Neutronentransportgleichung bei Kugelsymmetrie
Das in diesem Bericht behandelte Problem trat im Institut für Reaktorentwicklung der Kernforschungsanlage Jülich GmbH im Zusamnenhang mit der Entwicklung des Kugelhaufenreaktors auf. Da es sich hier um den Kugelhaufenreaktor handelt, wird im folgenden die kugelsymmetrische Form von (1.1) (vgl. (2.1)) mit der Randbedingung (1.2) behandelt und in eine Fredholmsche Integralgleichung zweiter Art transformiert. Es werden Existenzsätze, Eindeutigkeitssätze und ein Iterationsverfahren für die Lösung angegeben. Für den Fall der Abwärtsstreuung wird auch das diskretisierte Problem diskutiert. Hierfür wurden mehrere Beispiele gerechnet
Sintering characteristics of nanocrystalline TiO2—A study combining small angle neutron scattering and nitrogen absorption-BET
Small angle neutron scattering (SANS) was employed to characterize the pore structure of nanophase TiO2 ceramic materials compacted at different temperatures. Nanophase samples, produced by inert gas condensation, were compacted at 25, 290, 413, and 550 °C using a pressure of 1 GPa. The pore size distribution of the sample compacted at room temperature was very broad, with sizes ranging from 3-30 nm and pores comprising 38% of the sample volume. Compaction at 290 and 413 °C reduced the pore volume to 25% and 20%, respectively, by eliminating pores at both the small and large ends of the distribution. Compaction at 550 °C resulted in a pore volume that was less than 8%. Complications in the SANS analysis arising from the scattering from grain boundaries are discussed. The results from SANS are compared with those derived from nitrogen absorption, BET, measurement
Magnetic microstructure of nanostructured Fe, studied by small angle neutron scattering
Small angle neutron scattering (SANS) was applied to achieve insight into the magnetic correlations in nanostructured Fe. The results confirm the expected microstructure involving ferromagnetic grains and a nonmagnetic or weakly magnetic interface region, the interfaces occupying about half the specimen volume. The SANS measurements further reveal that in nanostructured Fe the magnetic correlations are not confined to single grains, but are extended across the interfaces and result in the alignment of the magnetization over several hundreds of grains. An external field of 1.5 kOe is not sufficient for complete magnetic alignment of the entire specimen. However, the long-range magnetic correlations are considerably disturbed by this field. Reducing the external magnetic field to zero causes the magnetic correlations to resume microstructural characteristics similar to what they had in the original stat
Annealing tests of in-pile irradiated oxide coated U–Mo/Al–Si dispersed nuclear fuel
Authors do acknowledge the MERARG team for their experimental work (CEA) and F. Charollais, J. Noirot and finally B. Kapusta for their advices and comments. This study was supported by a combined Grant (FRM0911) of the Bundesministerium für Bildung und Forschung (BMBF) and the Bayerisches Staatsministerium für Wissenschaft, Forschung und Kunst (StMWFK).U–Mo/Al based nuclear fuels have been worldwide considered as a promising high density fuel for the conversion of high flux research reactors from highly enriched uranium to lower enrichment. In this paper, we present the annealing test up to 1800°C of in-pile irradiated U–Mo/Al–Si fuel plate samples. More than 70% of the fission gases (FGs) are released during two major FG release peaks around 500°C and 670°C. Additional characterisations of the samples by XRD, EPMA and SEM suggest that up to 500°C FGs are released from IDL/matrix interfaces. The second peak at 670°C representing the main release of FGs originates from the interaction between U–Mo and matrix in the vicinity of the cladding
Outcome of renal grafts after simultaneous kidney/ pancreas transplantation
Nineteen patients with endstage renal failure due to Type 1 (insulin-dependent) diabetes mellitus received simultaneous pancreas/kidney transplants using bladder drainage technique. Another group of 25 Type 1 diabetic patients received pancreas/kidney transplants by the duct occlusion technique. We observed a higher incidence of rejection episodes in the patients of the bladder drainage group than those in the duct occlusion group, 14 of 19 patients (74%) vs 7 of 25 (28%) respectively. Anti CD3 antibodies (Orthoclone, OKT3) as a part of induction treatment was used more often in the bladder drainage group (58%) than in the control group (20%)
Harmonic behavior of metallic glasses up to the metastable melt
In two amorphous alloys ZrTiCuNiBe and ZrAlNiCu coherent neutron scattering has been measured over five decades in energy, including measurements in the metastable melt of a metallic alloy more than 80 K above Tg. In the vibrational spectra a pronounced "boson" peak is found: Even in crystallized samples the density of states exceeds the Debye ω2 model, and in the amorphous state low-frequency vibrations are further enhanced. The peak position shows no dispersion in q, while intensities are strongly correlated with the static structure factor. Over the full energy range the temperature dependence is strictly harmonic. From high-energy resolution measurements we establish lower bounds for the temperatures at which structural α and fast β relaxation become observable
Economic Feasibility of Utilizing Waste-Water Heat from Coal-Fired Electrical Generating Plants in Commercial Greenhouses in North Dakota
This study provides information on the economic feasibility of establishing commercial greenhouses utilizing waste-water heat in North Dakota.Production Economics, Resource /Energy Economics and Policy,
Uniform intensity in multifocal microscopy using a spatial light modulator
Multifocal microscopy (MFM) offers high-speed three-dimensional imaging
through the simultaneous image capture from multiple focal planes. Conventional
MFM systems use a fabricated grating in the emission path for a single emission
wavelength band and one set of focal plane separations. While a Spatial Light
Modulator (SLM) can add more flexibility, the relatively small number of pixels
in the SLM chip, cross-talk between the pixels, and aberrations in the imaging
system can produce non-uniform intensity in the different axially separated
image planes. We present an in situ iterative SLM calibration algorithm that
overcomes these optical- and hardware-related limitations to deliver
near-uniform intensity across all focal planes. Using immobilized gold
nanoparticles under darkfield illumination, we demonstrate superior intensity
evenness compared to current methods. We also demonstrate applicability across
emission wavelengths, axial plane separations, imaging modalities, SLM
settings, and different SLM manufacturers. Therefore, our microscope design and
algorithms provide an alternative to fabricated gratings in MFM, as they are
relatively simple and could find broad applications in the wider research
community.Comment: 15 page
Localization precision in chromatic multifocal imaging
Multifocal microscopy affords fast acquisition of microscopic 3D images. This
is made possible using a multifocal grating optic, however this induces
chromatic dispersion effects into the point spread function impacting image
quality and single-molecule localization precision. To minimize this effect,
researchers use narrow-band emission filters. However, the choice of optimal
emission filter bandwidth in such systems is, thus far, unclear. This work
presents a theoretical framework to investigate how the localization precision
of a point emitter is affected by the emission filter bandwidth. We calculate
the Cram\'er-Rao lower bound for the 3D position of a single emitter imaged
using a chromatic multifocal microscope. Results show that the localization
precision improves with broader emission filter bandwidth due to increased
photon throughput, despite a larger chromatic dispersion. This study provides a
framework for optimally designing chromatic multifocal optics and serves as a
theoretical foundation for interpretting results
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