3,601 research outputs found
Indices of Upper Atmospheric Disturbance Phenomena in Auroral Zone
The earlier orbits and ephemerides for the Soviet satellites were not sufficiently
accurate to be very useful in making observations in Alaska. Extrapolations
from our own observations gave better predictions. This merely pointed out the fact
that rough observations of meridian transits at high latitudes will give better values
of the inclination of the orbit than precision observations at low latitudes. Hence,
it was decided to observe visually the meridian transits estimating the altitude by
noting the position with respect to the stars or using crude alidade measurements.
The times of the earlier observations were observed on a watch or clock and the clock
correction obtained from WWV. Later the times were determined with the aid of stop
watches, taking time intervals from WWV signals.
This rather meager program of optical observations of the Soviet satellites was
undertaken to give supplementary data for use of the radio observations, and particularly
to assist in the prediction of position of the satellite so that the 61-foot
radar of Stanford Research Institute could be set accurately enough to observe it
(the beam width at the half-power points is about 3°).
This report contains primarily the visual observations made at the Geophysical
Institute by various members of the staff, and a series of observations by Olaf
Halverson at Nome, Alaska. In addition there is a short discussion of the geometry
of the trajectory, the illumination of a circumpolar satellite, and a note on the
evaluation of Brouwer's moment factors.IGY Project No. I.14
NSF Grant No. Y/l.14/1771. INTRODUCTION / C. T. Elvey and M. Sugiura -- KEY TO GRAPH
DISTURBANCE INDICES -- 2. HOURLY RADAR INDICES OF AURORAL ACTIVITY / R. S. Leonard -- 3. HOURLY INDICES OF GEOELECTRIC AND MAGNETIC ACTIVITY
/ V. P. Hessler --
4. HOURLY IONOSPHERIC ABSORPTION / H. Leinbach --
5. HOURLY PHOTOMETRIC INDICES OF AURORAL ACTIVITY / W. Murcray --
6. HOURLY SPECTROSCOPIC INDICES OF AURORAL ACTIVITY
/ G. J. Romick --
7. AURORAL INDICES USING THE ALL-SKY CAMERA FILM / G. H. StanleyYe
Random Hamiltonian in thermal equilibrium
A framework for the investigation of disordered quantum systems in thermal
equilibrium is proposed. The approach is based on a dynamical model--which
consists of a combination of a double-bracket gradient flow and a uniform
Brownian fluctuation--that `equilibrates' the Hamiltonian into a canonical
distribution. The resulting equilibrium state is used to calculate quenched and
annealed averages of quantum observables.Comment: 8 pages, 4 figures. To appear in DICE 2008 conference proceeding
Finite-temperature phase transitions in quasi-one-dimensional molecular conductors
Phase transitions in 1/4-filled quasi-one-dimensional molecular conductors
are studied theoretically on the basis of extended Hubbard chains including
electron-lattice interactions coupled by interchain Coulomb repulsion. We apply
the numerical quantum transfer-matrix method to an effective one-dimensional
model, treating the interchain term within mean-field approximation.
Finite-temperature properties are investigated for the charge ordering, the
"dimer Mott" transition (bond dimerization), and the spin-Peierls transition
(bond tetramerization). A coexistent state of charge order and bond
dimerization exhibiting dielectricity is predicted in a certain parameter
range, even when intrinsic dimerization is absent.Comment: to be published in J. Phys. Soc. Jpn., Vol. 76 (2007) No. 1 (5 pages,
4 figures); typo correcte
Metastability in Interacting Nonlinear Stochastic Differential Equations II: Large-N Behaviour
We consider the dynamics of a periodic chain of N coupled overdamped
particles under the influence of noise, in the limit of large N. Each particle
is subjected to a bistable local potential, to a linear coupling with its
nearest neighbours, and to an independent source of white noise. For strong
coupling (of the order N^2), the system synchronises, in the sense that all
oscillators assume almost the same position in their respective local potential
most of the time. In a previous paper, we showed that the transition from
strong to weak coupling involves a sequence of symmetry-breaking bifurcations
of the system's stationary configurations, and analysed in particular the
behaviour for coupling intensities slightly below the synchronisation
threshold, for arbitrary N. Here we describe the behaviour for any positive
coupling intensity \gamma of order N^2, provided the particle number N is
sufficiently large (as a function of \gamma/N^2). In particular, we determine
the transition time between synchronised states, as well as the shape of the
"critical droplet", to leading order in 1/N. Our techniques involve the control
of the exact number of periodic orbits of a near-integrable twist map, allowing
us to give a detailed description of the system's potential landscape, in which
the metastable behaviour is encoded
Neural networks for action representation: a functional magnetic-resonance imaging and dynamic causal modeling study
Automatic mimicry is based on the tight linkage between motor and perception action representations in which internal models play a key role. Based on the anatomical connection, we hypothesized that the direct effective connectivity from the posterior superior temporal sulcus (pSTS) to the ventral premotor area (PMv) formed an inverse internal model, converting visual representation into a motor plan, and that reverse connectivity formed a forward internal model, converting the motor plan into a sensory outcome of action. To test this hypothesis, we employed dynamic causal-modeling analysis with functional magnetic-resonance imaging (fMRI). Twenty-four normal participants underwent a change-detection task involving two visually-presented balls that were either manually rotated by the investigator's right hand (“Hand”) or automatically rotated. The effective connectivity from the pSTS to the PMv was enhanced by hand observation and suppressed by execution, corresponding to the inverse model. Opposite effects were observed from the PMv to the pSTS, suggesting the forward model. Additionally, both execution and hand observation commonly enhanced the effective connectivity from the pSTS to the inferior parietal lobule (IPL), the IPL to the primary sensorimotor cortex (S/M1), the PMv to the IPL, and the PMv to the S/M1. Representation of the hand action therefore was implemented in the motor system including the S/M1. During hand observation, effective connectivity toward the pSTS was suppressed whereas that toward the PMv and S/M1 was enhanced. Thus, the action-representation network acted as a dynamic feedback-control system during action observation
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Upwelling O+ ion source characteristics
Recent observations from the Dynamics Explorer 1 (DE-1) spacecraft have shown that the dayside auroral zone is an important source of very low-energy superthermal O^+ ions for the polar magnetosphere. When observed at 2000- to 5000-km altitude, the core of the O^+ distribution exhibits transverse heating to energies on the order of 10 eV, significant upward heat flux, and subsonic upward flow at significant flux levels exceeding 10^8 cm^{-2}s^{-1}. The term "upwelling ions" has been adopted to label these flows, which stand out in sharp contrast to the light ion polar wind flows observed in the same altitude range in the polar cap and subauroral magnetosphere. We have chosen a typical upwelling ion event for detailed study, correlating retarding ion mass spectrometer observations of the low-energy plasma with energetic ion observations and local electromagnetic field observations. The upwelling ion signature is colocated with the magnetospheric cleft as marked by precipitating energetic magnetosheath ions. The apparent ionospheric heating is clearly linked with the magnetic field signatures of strong field-aligned currents in the vicinity of the dayside polar cap boundary. Electric field and ion plasma measurements indicate that a very strong and localized convection channel or jet exists coincident with the other signatures of this event. These observations indicate that transverse ion heating to temperatures on the order of 10^5 K in the 2000- to 5000-km ionosphere is an important factor in producing heavy ion outflows into the polar magnetosphere. This result contrasts with recent suggestions that electron heating to temperatures of order 10^4 K is the most important parameter with regard to O^+ outflow
Terrestrial exposure of a fresh Martian meteorite causes rapid changes in hydrogen isotopes and water concentrations
Determining the hydrogen isotopic compositions and H2O contents of meteorites and their components is important for addressing key cosmochemical questions about the abundance and source(s) of water in planetary bodies. However, deconvolving the effects of terrestrial contamination from the indigenous hydrogen isotopic compositions of these extraterrestrial materials is not trivial, because chondrites and some achondrites show only small deviations from terrestrial values such that even minor contamination can mask the indigenous values. Here we assess the effects of terrestrial weathering and contamination on the hydrogen isotope ratios and H2O contents of meteoritic minerals through monitored terrestrial weathering of Tissint, a recent Martian fall. Our findings reveal the rapidity with which this weathering affects nominally anhydrous phases in extraterrestrial materials, which illustrates the necessity of sampling the interiors of even relatively fresh meteorite falls and underlines the importance of sample return missions
Selection of tuning parameters in bridge regression models via Bayesian information criterion
We consider the bridge linear regression modeling, which can produce a sparse
or non-sparse model. A crucial point in the model building process is the
selection of adjusted parameters including a regularization parameter and a
tuning parameter in bridge regression models. The choice of the adjusted
parameters can be viewed as a model selection and evaluation problem. We
propose a model selection criterion for evaluating bridge regression models in
terms of Bayesian approach. This selection criterion enables us to select the
adjusted parameters objectively. We investigate the effectiveness of our
proposed modeling strategy through some numerical examples.Comment: 20 pages, 5 figure
Competition of Dimerization and Charge Ordering in the Spin-Peierls State of Organic Conductors
The effect of the charge ordering on the spin-Peierls (SP) state has been
examined by using a Peierls-Hubbard model at quarter-filling with dimerization,
on-site and nearest-neighbor repulsive interactions. By taking account of the
presence of dimerization, a bond distortion is calculated variationally with
the renormalization group method based on bosonization. When the charge
ordering appears at V=V_c with increasing the nearest-neighbor interaction (V),
the distortion exhibits a maximum due to competition between the dimerization
and the charge ordering. It is shown that the second-order phase transition
occurs from the SP state with the bond alternation to a mixed state with an
additional component of the site alternationat V = V_c.Comment: 11 pages, 13 figures, to be published in J. Phys. Soc. Jpn. 72 No.6
(2003
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