7,030 research outputs found
Lineaments and Mineral Occurrences in Pennsylvania
The author has identified the following significant results. A conservative lineament map of Pennsylvania interpreted from ERTS-1 channel 7 (infrared) imagery and Skylab photography was compared with the distribution of known metallic mines and mineral occurrences. Of 383 known mineral occurrences, 116 show a geographical association to 1 km wide lineaments, another 24 lie at the intersection of two lineaments, and one lies at the intersection of three lineaments. The Perkiomen Creek lineament in the Triassic Basin is associated with 9 Cu-Fe occurrences. Six Pb-Zn occurrences are associated with the Tyrone-Mount Union lineament. Thirteen other lineaments are associated with 3, 4, or 5 mineral occurrences each
Relation of lineaments to sulfide deposits: Bald Eagle Mountain, Centre County, Pennsylvania
The author has identified the following significant results. Discrete areas of finely-fractured and brecciated sandstone float are present along the crest of Bald Mountain and are commonly sites of sulfide mineralization, as evidenced by the presence of barite and limonite gossans. The frequency distributions of the brecciated float as the negative binomial distribution supports the interpretation of a separate population of intensely fractured material. Such zones of concentrated breccia float have an average width of one kilometer with a range from 0.4 to 1.6 kilometers and were observed in a quarry face to have subvertical dips. Direct spatial correlation of the Landsat-derived lineaments to the fractured areas on the ridge is low; however, the mineralized and fracture zones are commonly assymetrical to the lineament positions. Such a systematic dislocation might result from an inherent bias in the float population or could be the product of the relative erosional resistance of the silicified material in the mineralized areas in relation to the erosionally weak material at the stream gaps
Evolution of Quantum Criticality in CeNi_{9-x}Cu_xGe_4
Crystal structure, specific heat, thermal expansion, magnetic susceptibility
and electrical resistivity studies of the heavy fermion system
CeNi_{9-x}Cu_xGe_4 (0 <= x <= 1) reveal a continuous tuning of the ground state
by Ni/Cu substitution from an effectively fourfold degenerate non-magnetic
Kondo ground state of CeNi_9Ge_4 (with pronounced non-Fermi-liquid features)
towards a magnetically ordered, effectively twofold degenerate ground state in
CeNi_8CuGe_4 with T_N = 175 +- 5 mK. Quantum critical behavior, C/T ~ \chi ~
-ln(T), is observed for x about 0.4. Hitherto, CeNi_{9-x}Cu_xGe_4 represents
the first system where a substitution-driven quantum phase transition is
connected not only with changes of the relative strength of Kondo effect and
RKKY interaction, but also with a reduction of the effective crystal field
ground state degeneracy.Comment: 15 pages, 9 figure
The Active Traveling Wave in the Cochlea
A sound stimulus entering the inner ear excites a deformation of the basilar
membrane which travels along the cochlea towards the apex. It is well
established that this wave-like disturbance is amplified by an active system.
Recently, it has been proposed that the active system consists of a set of
self-tuned critical oscillators which automatically operate at an oscillatory
instability. Here, we show how the concepts of a traveling wave and of
self-tuned critical oscillators can be combined to describe the nonlinear wave
in the cochlea.Comment: 5 pages, 2 figure
Magnetic Energy and Helicity Budgets in the Active-Region Solar Corona. I. Linear Force-Free Approximation
We self-consistently derive the magnetic energy and relative magnetic
helicity budgets of a three-dimensional linear force-free magnetic structure
rooted in a lower boundary plane. For the potential magnetic energy we derive a
general expression that gives results practically equivalent to those of the
magnetic Virial theorem. All magnetic energy and helicity budgets are
formulated in terms of surface integrals applied to the lower boundary, thus
avoiding computationally intensive three-dimensional magnetic field
extrapolations. We analytically and numerically connect our derivations with
classical expressions for the magnetic energy and helicity, thus presenting a
so-far lacking unified treatment of the energy/helicity budgets in the
constant-alpha approximation. Applying our derivations to photospheric vector
magnetograms of an eruptive and a noneruptive solar active regions, we find
that the most profound quantitative difference between these regions lies in
the estimated free magnetic energy and relative magnetic helicity budgets. If
this result is verified with a large number of active regions, it will advance
our understanding of solar eruptive phenomena. We also find that the
constant-alpha approximation gives rise to large uncertainties in the
calculation of the free magnetic energy and the relative magnetic helicity.
Therefore, care must be exercised when this approximation is applied to
photospheric magnetic field observations. Despite its shortcomings, the
constant-alpha approximation is adopted here because this study will form the
basis of a comprehensive nonlinear force-free description of the energetics and
helicity in the active-region solar corona, which is our ultimate objective.Comment: 44 pages, 8 figures, 2 tables. The Astrophysical Journal, in pres
Expert chess memory: Revisiting the chunking hypothesis
After reviewing the relevant theory on chess expertise, this paper re-examines experimentally the finding of Chase and Simon (1973a) that the differences in ability of chess players at different skill levels to copy and to recall positions are attributable to the experts' storage of thousands of chunks (patterned clusters of pieces) in long-term memory. Despite important differences in the experimental apparatus, the data of the present experiments regarding latencies and chess relations between successively placed pieces are highly correlated with those of Chase and Simon. We conclude that the 2-second inter-chunk interval used to define chunk boundaries is robust, and that chunks have psychological reality. We discuss the possible reasons why Masters in our new study used substantially larger chunks than the Master of the 1973 study, and extend the chunking theory to take account of the evidence for large retrieval structures (templates) in long-term memory
Vanishing Fe 3d orbital moments in single-crystalline magnetite
We show detailed magnetic absorption spectroscopy results of an in situ
cleaved high quality single crystal of magnetite. In addition the experimental
setup was carefully optimized to reduce drift, self absorption, and offset
phenomena as far as possible. In strong contradiction to recently published
data, our observed orbital moments are nearly vanishing and the spin moments
are quite close to the integer values proposed by theory. This very important
issue supports the half metallic full spin polarized picture of magnetite.Comment: 7 pages, 4 figure
Gold alignment & internal dissipation
The measures of mechanical alignment were obtained for both prolate and
oblate grains when their temperature is comparable with grain kinetic energy
devided by k, the Boltzmann constant. For such grains, the alignment of angular
momentum, J, with the axis of maximal inertia, a, is only partial. This
substantially alters the alignment as compared with the results in Lazarian
(1995) and Roberge, Hanany & Messinger (1996) obtained on the assumption of
perfect alignment.
We also describe the Gold alignment when the Barnett dissipation is
suppressed and derive an analytical expression which relates the measure of
alignment with parameters of grain nonsphericity and the direction of the gas -
grain drift. This solution provides the lower limit for the alignment measure,
while the upper limit is given by the analytics derived in Lazarian (1994).
Using results of a recent study of incomplete internal relaxation in Lazarian &
Roberge (1996), we find measures of alignment for the whole range of ratios of
grain rotational energy to k over T_s, where T_s is the grain temperature. To
describe alignment for mildly supersonic drifts, we suggest an analytical
approach which provides good correspondence with the results of direct
numerical simulations in Roberge, Hanany & Messinger (1995). We also extend our
approach to account for the simultaneous action of the Gold and
Davis-Greenstein mechanisms.Comment: 25 pages, 14 figures. Accepted to Ap
Spatial representation of temporal information through spike timing dependent plasticity
We suggest a mechanism based on spike time dependent plasticity (STDP) of
synapses to store, retrieve and predict temporal sequences. The mechanism is
demonstrated in a model system of simplified integrate-and-fire type neurons
densely connected by STDP synapses. All synapses are modified according to the
so-called normal STDP rule observed in various real biological synapses. After
conditioning through repeated input of a limited number of of temporal
sequences the system is able to complete the temporal sequence upon receiving
the input of a fraction of them. This is an example of effective unsupervised
learning in an biologically realistic system. We investigate the dependence of
learning success on entrainment time, system size and presence of noise.
Possible applications include learning of motor sequences, recognition and
prediction of temporal sensory information in the visual as well as the
auditory system and late processing in the olfactory system of insects.Comment: 13 pages, 14 figures, completely revised and augmented versio
- …