5,355 research outputs found
POWTEX Neutron Diffractometer at FRM II - new perspectives for in-situ rock deformation analysis
EGU2012-13521
In Geoscience quantitative texture analysis here defined as the quantitative analysis of the crystallographic preferred orientation (CPO), is a common tool for the investigation of fabric development in mono- and polyphase rocks, their deformation histories and kinematics. Bulk texture measurements also allow the quantitative characterisation of the anisotropic physical properties of rock materials. A routine tool to measure bulk sample volumes is neutron texture diffraction, as neutrons have large penetration capabilities of several cm in geological sample materials.
The new POWTEX (POWder and TEXture) Diffractometer at the neutron research reactor FRM II in Garching, Germany is designed as a high-intensity diffractometer by groups from the RWTH Aachen, Forschungszentrum Jülich and the University of Göttingen. Complementary to existing neutron diffractometers (SKAT at Dubna, Russia; GEM at ISIS, UK; HIPPO at Los Alamos, USA; D20 at ILL, France; and the local STRESS-SPEC and SPODI at FRM II) the layout of POWTEX is focused on fast time-resolved experiments and the measurement of larger sample series as necessary for the study of large scale geological structures. POWTEX is a dedicated beam line for geoscientific research.
Effective texture measurements without sample tilting and rotation are possible firstly by utilizing a range of neutron wavelengths simultaneously (Time-of-Flight technique) and secondly by the high detector coverage (9.8 sr) and a high flux (�~1x10 7 n/cm2s) at the sample. Furthermore the instrument and the angular detector resolution is designed also for strong recrystallisation textures as well as for weak textures of polyphase rocks. These instrument characteristics allow in-situ time-resolved texture measurements during deformation experiments on rocksalt, ice and other materials as large sample environments will be implemented at POWTEX.
The in-situ deformation apparatus is operated by a uniaxial spindle drive with a maximum axial load of 250 kN, which will be redesigned to minimize shadowing effects inside the cylindrical detector. The HT deformatione experiments will be carried out in uniaxial compression or extension and an upgrade to triaxial deformation conditions is envisaged. The load frame can alternatively be used for ice deformation by inserting a cryostat cell for temperatures down to 77 K with a triaxial apparatus allowing also simple shear experiments on ice. Strain rates range between 10-8 and 10-3 s-1 reaching to at least 50% axial strain. The deformation apparatus is designed for continuous long-term deformation experiments and can be exchanged between in-situ and ex-situ placements during continuous operation inside and outside the neutron detector
On the Joint Distribution of Energy Levels of Random Schroedinger Operators
We consider operators with random potentials on graphs, such as the lattice
version of the random Schroedinger operator. The main result is a general bound
on the probabilities of simultaneous occurrence of eigenvalues in specified
distinct intervals, with the corresponding eigenfunctions being separately
localized within prescribed regions. The bound generalizes the Wegner estimate
on the density of states. The analysis proceeds through a new multiparameter
spectral averaging principle
Recommended from our members
University of Delaware Energy Institute
The main goal of this project funded through this DOE grant is to help in the establishment of the University of Delaware Energy Institute (UDEI) which is designed to be a long-term, on-going project. The broad mission of UDEI is to develop collaborative programs encouraging research activities in the new and emerging energy technologies and to partner with industry and government in meeting the challenges posed by the nationâÂÂs pressing energy needs
Model pathways in lignin thermolysis
Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1981.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCEIncludes bibliographical references.by Michael Tully Klein.Sc.D
Angular dependence of domain wall resistivity in SrRuO films
is a 4d itinerant ferromagnet (T 150 K) with
stripe domain structure. Using high-quality thin films of SrRuO we study
the resistivity induced by its very narrow ( nm) Bloch domain walls,
(DWR), at temperatures between 2 K and T as a function of the
angle, , between the electric current and the ferromagnetic domains
walls. We find that which provides the first experimental
indication that the angular dependence of spin accumulation contribution to DWR
is . We expect magnetic multilayers to exhibit a similar
behavior.Comment: 5 pages, 5 figure
Diet of Burbot and Implications for Sampling
Burbot (Lota lota) are an apex piscivore that were illegally introduced to the Green River drainage, Wyoming, raising concerns for the conservation and management of fishes throughout the basin. However, relatively little is known about the diet of non-native burbot. The objectives of this research were to characterize diet composition of burbot and identify differences in diet composition as a function of sampling gear. Diet composition was characterized using frequency of occurrence, percent by number, and percent by weight to identify the importance of each prey type to burbot. Diet composition was compared across gears to identify the relationship between gear and diet. Fishes were present in the stomach contents of nearly all burbot sampled and composed 62–100 percent of the stomach contents of burbot greater than 300 mm. Prey diversity was greatest in diets of burbot sampled with small-mesh hoop nets. Results from the current study provide important information on the diet of non-native burbot and highlight the potential influence of gear on diet studies
Detailed Radio Spectra of Selected Compact Sources in the Nucleus of M82
We have determined detailed radio spectra for 26 compact sources in the
starburst nucleus of M82, between 74 and 1.3 cm. Seventeen show low-frequency
turnovers. One other has a thermal emission spectrum, and we identify it as an
HII region. The low frequency turnovers are due to absorption by the
interstellar gas in M82. New information on the AGN candidate 44.01+595, shows
it to have a non-thermal falling powerlaw spectrum at the highest frequencies,
and that it is strongly absorbed below 2 GHz. We derive large magnetic fields
in the supernova remnants, of order 1-2 milliGauss, hence large pressures in
the sources suggest that the brightest ones are either expanding or are
strongly confined by a dense interstellar medium. From the largest source in
our sample, we derive a supernova rate of 0.016 SN/yr.Comment: 19 pages, 7 tables, 29 figures, LaTeX, requires AAS macros v. 4.0. To
appear in ApJ July 20, 199
Social Information Signaling by Neurons in Primate Striatum
Social decisions depend on reliable information about others. Consequently, social primates are motivated to acquire information about the identity, social status, and reproductive quality of others [1]. Neurophysiological [2] and neuroimaging [3 and 4] studies implicate the striatum in the motivational control of behavior. Neuroimaging studies specifically implicate the ventromedial striatum in signaling motivational aspects of social interaction [5]. Despite this evidence, precisely how striatal neurons encode social information remains unknown. Therefore, we probed the activity of single striatal neurons in monkeys choosing between visual social information at the potential expense of fluid reward. We show for the first time that a population of neurons located primarily in medial striatum selectively signals social information. Surprisingly, representation of social information was unrelated to simultaneously expressed social preferences. A largely nonoverlapping population of neurons that was not restricted to the medial striatum signaled information about fluid reward. Our findings demonstrate that information about social context and nutritive reward are maintained largely independently in striatum, even when both influence decisions to execute a single action.► Single neurons in striatum encode social information ► Typically, striatal neurons signal social or fluid information, but not both ► Topographically distinct information channels process social and fluid rewar
Wigner Crystalline Edges in nu < 1 Quantum Dots
We investigate the edge reconstruction phenomenon believed to occur in
quantum dots in the quantum Hall regime when the filling fraction is nu < 1.
Our approach involves the examination of large dots (< 40 electrons) using a
partial diagonalization technique in which the occupancies of the deep interior
orbitals are frozen. To interpret the results of this calculation, we evaluate
the overlap between the diagonalized ground state and a set of trial
wavefunctions which we call projected necklace (PN) states. A PN state is
simply the angular momentum projection of a maximum density droplet surrounded
by a ring of localized electrons. Our calculations reveal that PN states have
up to 99% overlap with the diagonalized ground states, and are lower in energy
than the states identified in Chamon and Wen's study of the edge
reconstruction.Comment: 8 pages, 8 figures, to be published in Phys. Rev.
- …