19,925 research outputs found
Geodetic Measurement of Deformation East of the San Andreas Fault in Central California
Triangulation and trilateration data from two geodetic networks located between the western edge of the Great Valley and the San Andreas fault have been used to calculate shear strain rates in the Diablo Range and to estimate the slip rate along the Calaveras and Paicines faults in Central California. Within the Diablo Range the average shear strain rate was determined for the time period between 1962 and 1982 to be 0.15 + or - 0.08 microrad/yr, with the orientation of the most compressive strain at N 16 deg E + or - 14 deg. The orientation of the principal compressive strain predicted from the azimuth of the major structures in the region is N 25 deg E. It is inferred that the measured strain is due to compression across the folds of this area: the average shear straining corresponds to a relative shortening rate of 4.5 + or - 2.4 mm/yr. From an examination of wellbore breakout orientations and the azimuths of P-axes from earthquake focal mechanisms the inferred orientation of maximum compressive stress was found to be similar to the direction of maximum compressive strain implied by the trend of local fold structures. Results do not support the hypothesis of uniform fault-normal compression within the Coast Ranges. From trilateration measurements made between 1972 and 1987 on lines that are within 10 km of the San Andreas fault, a slip rate of 10 to 12 mm/yr was calculated for the Calaveras-Paicines fault south of Hollister. The slip rate of the Paicines fault decreases to 4 mm/yr near Bitter
The essential signature of a massive starburst in a distant galaxy
Observations of carbon monoxide (CO) emission in high redshift (z>2) galaxies
indicate the presence of large amounts of molecular gas. Many of these galaxies
contain an active galactic nucleus (AGN) powered by accretion of gas onto a
supermassive black hole, and a key question is whether their extremely high
infrared luminosities result from the AGN, or from bursts of massive star
formation (associated with the molecular gas), or both. In the Milky Way,
high-mass stars form in the dense cores of interstellar molecular clouds; gas
densities are n(H2)>105 cm-3 in the cores. Recent surveys show that virtually
all galactic sites of high-mass star formation have similarly high densities.
The bulk of the cloud material traced by CO observations is at a much lower
density. In galaxies in the local Universe, the HCN(J=1-0) line is an effective
tracer of the high-density molecular gas. Here we report observations of HCN
emission in the early Universe from the infrared luminous 'Cloverleaf' quasar
(at a redshift z=2.5579). The HCN line luminosity indicates the presence of 10
billion solar masses of very dense gas, an essential feature of an immense
starburst that contributes, together with the AGN it harbors, to its high
infrared luminosity.Comment: PDF pape
Interference enhanced thermoelectricity in quinoid type structures
Quantum interference (QI) effects in molecular junctions may be used to
obtain large thermoelectric responses. We study the electrical conductance G
and the thermoelec- tric response of a series of molecules featuring a quinoid
core using density functional theory (DFT), as well as a semi-empirical
interacting model Hamiltonian describing the {\pi}-system of the molecule which
we treat in the GW approximation. Molecules with a quinoid type structure are
shown to have two distinct destructive QI features close to the frontier
orbital energies. These manifest themselves as two dips in the transmission,
that remain separated, even when either electron donating or withdraw- ing side
groups are added. We find that the position of the dips in the transmission and
the frontier molecular levels can be chemically controlled by varying the
electron donating or withdrawing character of the side groups as well as the
conjugation length inside the molecule. This feature results in a very high
thermoelectric power factor S^2G and figure of merit ZT, where S is the Seebeck
coefficient, making quinoid type molecules potential candidates for efficient
thermoelectric devices.Comment: 22 pages, 11 figure
Molecular hydrogen in the galaxy and galactic gamma rays
Recent surveys of 2.6 mm CO emission and 100 MeV gamma-radiation in the galactic plane reveal a striking correlation suggesting that both emissions may be primarily proportional to the line-of-sight column density of H2 in the inner galaxy. Both the gamma ray and CO data suggest a prominent ring or arm consisting of cool clouds of H2 at a galactocentric distance of approximately 5 kpc with a mean density of approximately 4 atoms/cu cm. The importance of H2 in understanding galactic gamma ray observations is also reflected in the correlation of galactic latitude distribution of gamma rays and dense dust clouds. A detailed calculation of the gamma ray flux distribution in the 0 deg to 180 deg range using the CO data to obtain the average distribution of molecular clouds in the galaxy shows that most of the enhancement in the inner galaxy is due to pion-decay radiation and the 5 kpc ring plays a major role. Detailed agreement with the gamma ray data is obtained with the additional inclusion of contributions from bremsstrahlung and Compton radiation of secondary electrons and Compton radiation from the intense radiation field near the galactic center
Quantum wires from coupled InAs/GaAs strained quantum dots
The electronic structure of an infinite 1D array of vertically coupled
InAs/GaAs strained quantum dots is calculated using an eight-band
strain-dependent k-dot-p Hamiltonian. The coupled dots form a unique quantum
wire structure in which the miniband widths and effective masses are controlled
by the distance between the islands, d. The miniband structure is calculated as
a function of d, and it is shown that for d>4 nm the miniband is narrower than
the optical phonon energy, while the gap between the first and second minibands
is greater than the optical phonon energy. This leads to decreased optical
phonon scattering, providing improved quantum wire behavior at high
temperatures. These miniband properties are also ideal for Bloch oscillation.Comment: 5 pages revtex, epsf, 8 postscript figure
Acceleration of Plasma Flows Due to Reverse Dynamo Mechanism
The "reverse-dynamo" mechanism - the amplification/generation of fast plasma
flows by micro scale (turbulent) magnetic fields via magneto-fluid coupling is
recognized and explored. It is shown that macro-scale magnetic fields and flows
are generated simultaneously and proportionately from micro scale fields and
flows. The stronger the micro-scale driver, the stronger are the macro-scale
products. Stellar and astrophysical applications are suggested.Comment: 16 pages including 3 figures. The Astrophys. J. (accepted);
additional material is given for clarification; terminology is change
Reporting Requirements Under the Animal Welfare Act: Their Inadequacies and the Public\u27s Right to Know
The Animal Welfare Act is the only federal statute designed to protect animals used in laboratory research. This law requires research facilities to register with the U.S. Department of Agriculture (USDA) and meet minimum housing standards, care, and treatment standards for most warm-blooded animals. The Act is administered by the Animal and Plant Health Inspection Service (APHIS), an agency of the USDA. Research institutions are required to file annual reports. However, the reports are frequently deficient. The authors argue that the USDA should issue clear definitions for what is meant by “pain” and “distress. ” They should also provide further explanation regarding what is meant by “routine procedures” and request additional information from those institutions reporting that they do not use pain-relieving drugs
Coherent pairing states for the Hubbard model
We consider the Hubbard model and its extensions on bipartite lattices. We
define a dynamical group based on the -pairing operators introduced by
C.N.Yang, and define coherent pairing states, which are combinations of
eigenfunctions of -operators. These states permit exact calculations of
numerous physical properties of the system, including energy, various
fluctuations and correlation functions, including pairing ODLRO to all orders.
This approach is complementary to BCS, in that these are superconducting
coherent states associated with the exact model, although they are not
eigenstates of the Hamiltonian.Comment: 5 pages, RevTe
Space and surface power for the space exploration initiative: Results from project outreach
The analysis and evaluations of the Space and Surface Power panel, one of eight panels created by RAND to screen and analyze submissions to the Space Exploration Initiative (SEI) Outreach Program, is documented. In addition to managing and evaluating the responses, or submissions, to this public outreach program, RAND conducted its own analysis and evaluation relevent to SEI mission concepts, systems, and technologies. The Power panel screened and analyzed submissions for which a substantial portion of the concepts involved power generation sources, transmission, distribution, thermal management, and handling of power (including conditioning, conversion, packaging, and enhancements in system components). A background discussion of the areas the Power panel covered and the issues the reviewers considered pertinent to the analysis of power submissions are presented. An overview of each of the highest-ranked submissions and then a discussion of these submissions is presented. The results of the analysis is presented
Impact of schizophrenia on anterior and posterior hippocampus during memory for complex scenes.
ObjectivesHippocampal dysfunction has been proposed as a mechanism for memory deficits in schizophrenia. Available evidence suggests that the anterior and posterior hippocampus could be differentially affected. Accordingly, we used fMRI to test the hypothesis that activity in posterior hippocampus is disproportionately reduced in schizophrenia, particularly during spatial memory retrieval.Methods26 healthy participants and 24 patients with schizophrenia from the UC Davis Early Psychosis Program were studied while fMRI was acquired on a 3 Tesla Siemens scanner. During encoding, participants were oriented to critical items through questions about item features (e.g., "Does the lamp have a square shade?") or spatial location (e.g., "Is the lamp on the table next to the couch?"). At test, participants determined whether scenes were changed or unchanged. fMRI analyses contrasted activation in a priori regions of interest (ROI) in anterior and posterior hippocampus during correct recognition of item changes and spatial changes.ResultsAs predicted, patients with schizophrenia exhibited reduced activation in the posterior hippocampus during detection of spatial changes but not during detection of item changes. Unexpectedly, patients exhibited increased activation of anterior hippocampus during detection of item changes. Whole brain analyses revealed reduced fronto-parietal and striatal activation in patients for spatial but not for item change trials.ConclusionsResults suggest a gradient of hippocampal dysfunction in which posterior hippocampus - which is necessary for processing fine-grained spatial relationships - is underactive, and anterior hippocampus - which may process context more globally - is overactive
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