22,501 research outputs found
The Wisconsin magmatic terrane: An Early Proterozoic greenstone-granite terrane formed by plate tectonic processes
The Wisconsin magmatic terrane (WMT) is an east trending belt of dominantly volcanic-plutonic complexes of Early Proterozoic age (approx. 1850 m.y.) that lies to the south of the Archean rocks and Early Proterozoic epicratonic sequence (Marquette Range Supergroup) in Michigan. It is separated from the epicratonic Marquette Range Supergroup by the high-angle Niagara fault, is bounded on the south, in central Wisconsin, by Archean gneisses, is truncated on the west by rocks of the Midcontinent rift system, and is intruded on the east by the post-orogenic Wolf river batholith. The overall lithologic, geochemical, metallogenic, metamorphic, and deformational characteristics of the WMT are similar to those observed in recent volcanic arc terranes formed at sites of plate convergence. It is concluded that the WMT represents an evolved oceanic island-arc terrane accreated to the Superior craton in the Early Proterozoic. This conclusion is strengthened by the apparent absence of Archean basement from most of the WMT, and the recent recognition of the passive margin character of the epicratonic Marquette Range Supergroup
Weak disorder expansion for localization lengths of quasi-1D systems
A perturbative formula for the lowest Lyapunov exponent of an Anderson model on a strip is presented. It is expressed in terms of an energy-dependent doubly stochastic matrix, the size of which is proportional to the strip width. This matrix and the resulting perturbative expression for the Lyapunov exponent are evaluated numerically. Dependence on energy, strip width and disorder strength are thoroughly compared with the results obtained by the standard transfer matrix method. Good agreement is found for all energies in the band of the free operator and this even for quite large values of the disorder strength
Differential effects of age on involuntary and voluntary autobiographical memory
"This article may not exactly replicate the final version published in the APA journal. It is not the copy of record." Original article can be found at: http://psycnet.apa.org/journals/pag/24/2/397/ Copyright American Psychological Association. DOI: 10.1037/a0015785Research on aging and autobiographical memory has focused almost exclusively on voluntary autobiographical memory. However, in everyday life, autobiographical memories often come to mind spontaneously without deliberate attempt to retrieve anything. In the present study, diary and word-cue methods were used to compare the involuntary and voluntary memories of 44 young and 38 older adults. The results showed that older adults reported fewer involuntary and voluntary memories than did younger adults. Additionally, the life span distribution of involuntary and voluntary memories did not differ in young adults (a clear recency effect) or in older adults (a recency effect and a reminiscence bump). Despite these similarities between involuntary and voluntary memories, there were also important differences in terms of the effects of age on some memory characteristics. Thus, older adults’ voluntary memories were less specific and were recalled more slowly than those of young adults, but there were no reliable age differences in the specificity of involuntary memories. Moreover, older adults rated their involuntary memories as more positive than did young adults, but this positivity effect was not found for voluntary memories. Theoretical implications of these findings for research on autobiographical memory and cognitive aging are discussedPeer reviewe
Collective Diffusion and a Random Energy Landscape
Starting from a master equation in a quantum Hamiltonian form and a coupling
to a heat bath we derive an evolution equation for a collective hopping process
under the influence of a stochastic energy landscape. There results different
equations in case of an arbitrary occupation number per lattice site or in a
system under exclusion. Based on scaling arguments it will be demonstrated that
both systems belong below the critical dimension to the same universality
class leading to anomalous diffusion in the long time limit. The dynamical
exponent can be calculated by an expansion. Above the
critical dimension we discuss the differences in the diffusion constant for
sufficient high temperatures. For a random potential we find a higher mobility
for systems with exclusion.Comment: 15 pages, no figure
Electron spin relaxation in organic semiconductors probed through muSR
Muon spin spectroscopy and in particular the avoided level crossing technique
is introduced, with the aim of showing it as a very sensitive local probe for
electron spin relaxation in organic semiconductors. Avoided level crossing data
on TMS-pentacene at different temperatures are presented, and they are analysed
to extract the electron spin relaxation rate, that is shown to increase on
increasing the temperature from 0.02 MHz to 0.33 MHz at 3 K and 300 K
respectively.Comment: International Conference TSN2010 "Trends in spintronics and
nanomagnetism
Localized electron state in a T-shaped confinement potential
We consider a simple model of an electron moving in a T-shaped confinement
potential. This model allows for an analytical solution that explicitly
demonstrates the existence of laterally bound electron states in quantum wires
obtained by the cleaved edge overgrowth technique.Comment: 6 pages, 5 figure
The dust morphology of the elliptical Galaxy M86 with SPIRE
We present Herschel-SPIRE observations at 250–500 μm of the giant elliptical galaxy M 86 and examine the distribution of the resolved cold dust emission and its relation with other galactic tracers. The SPIRE images reveal three dust components: emission from the central region; a dust lane extending north-south; and a bright emission feature 10 kpc to the south-east. We estimate that ~10^6 M_☉ of dust is spatially coincident with atomic and ionized hydrogen, originating from stripped material from the nearby spiral NGC 4438 due to recent tidal interactions with M 86. The gas-to-dust ratio of the cold gas component ranges from ~20–80. We discuss the different heating mechanisms for the dust features
Mapping the interstellar medium in galaxies with Herschel/SPIRE
The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies
M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies using both
methods. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies
Influence of adaptive mesh refinement and the hydro solver on shear-induced mass stripping in a minor-merger scenario
We compare two different codes for simulations of cosmological structure
formation to investigate the sensitivity of hydrodynamical instabilities to
numerics, in particular, the hydro solver and the application of adaptive mesh
refinement (AMR). As a simple test problem, we consider an initially spherical
gas cloud in a wind, which is an idealized model for the merger of a subcluster
or galaxy with a big cluster. Based on an entropy criterion, we calculate the
mass stripping from the subcluster as a function of time. Moreover, the
turbulent velocity field is analyzed with a multi-scale filtering technique. We
find remarkable differences between the commonly used PPM solver with
directional splitting in the Enzo code and an unsplit variant of PPM in the Nyx
code, which demonstrates that different codes can converge to systematically
different solutions even when using uniform grids. For the test case of an
unbound cloud, AMR simulations reproduce uniform-grid results for the mass
stripping quite well, although the flow realizations can differ substantially.
If the cloud is bound by a static gravitational potential, however, we find
strong sensitivity to spurious fluctuations which are induced at the cutoff
radius of the potential and amplified by the bow shock. This gives rise to
substantial deviations between uniform-grid and AMR runs performed with Enzo,
while the mass stripping in Nyx simulations of the subcluster is nearly
independent of numerical resolution and AMR. Although many factors related to
numerics are involved, our study indicates that unsplit solvers with advanced
flux limiters help to reduce grid effects and to keep numerical noise under
control, which is important for hydrodynamical instabilities and turbulent
flows.Comment: 23 pages, 18 figures, accepted for publication by Astronomy and
Computin
Spectral Properties near the Mott Transition in the One-Dimensional Hubbard Model
Single-particle spectral properties near the Mott transition in the
one-dimensional Hubbard model are investigated by using the dynamical
density-matrix renormalization group method and the Bethe ansatz. The
pseudogap, hole-pocket behavior, spectral-weight transfer, and upper Hubbard
band are explained in terms of spinons, holons, antiholons, and doublons. The
Mott transition is characterized by the emergence of a gapless mode whose
dispersion relation extends up to the order of hopping t (spin exchange J) in
the weak (strong) interaction regime caused by infinitesimal doping.Comment: 4 pages, 2 figure
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