989 research outputs found
High Pressure Effects on Thermal Properties of MgO
Using the non-empirical Variational Induced Breathing (VIB) model, the
thermal properties of periclase (MgO) under high pressures and temperatures are
investigated using molecular dynamics, which includes all anharmonic effects.
Equations of state for temperatures up to 3000K and pressures up to 310 GPa
were calculated. Bulk modulus, thermal expansivity, Anderson-Gruneisen
parameter, thermal pressure, Gruneisen parameter and their pressure and
temperature dependencies are studied in order to better understand high
pressure effects on thermal properties. The results agree very well with
experiments and show that the thermal expansivity decreases with pressure up to
about 100 GPa (=0.73), and is almost pressure and temperature independent
above this compression. It is also effected by anharmonicity at zero pressure
and temperatures above 2500K. The thermal pressure changes very little with
increasing pressures and temperatures, and the Gruneisen parameter is
temperature independent and decreases slightly with pressure.Comment: Geophys. Res. Lett., in press, 7 pages, 4 figures, uuencoded ps fil
Complexity and hierarchical game of life
Hierarchical structure is an essential part of complexity, important notion
relevant for a wide range of applications ranging from biological population
dynamics through robotics to social sciences. In this paper we propose a simple
cellular-automata tool for study of hierarchical population dynamics
Tunneling magnetic force microscopy
We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording
A scanning tunneling microscopy based potentiometry technique and its application to the local sensing of the spin Hall effect
A scanning tunneling microscopy based potentiometry technique for the
measurements of the local surface electric potential is presented and
illustrated by experiments performed on current-carrying thin tungsten films.
The obtained results demonstrate a sub-millivolt resolution in the measured
surface potential. The application of this potentiometry technique to the local
sensing of the spin Hall effect is outlined and some experimental results are
reported.Comment: 9 pages and 4 figure
The SCUBA Bright Quasar Survey II: unveiling the quasar epoch at submillimetre wavelengths
We present results of the first systematic search for submillimetre continuum emission from z=2, radio-quiet, optically-luminous quasars, using the SCUBA/JCMT. We have observed a homogeneous sample of 57 quasars in the redshift range 1.54) redshift. The target sensitivity of the survey (3sigma=10mJy at 850um) was chosen to enable efficient identification of bright submm sources, suitable for detailed follow-up. 9 targets are detected, with fluxes in the range 7-17mJy. Although there is a suggestion of variation of submm detectability between z=2 and z=4, this is consistent with the K-correction of a characteristic far-infrared spectrum. Additionally, the weighted mean fluxes of non-detections at z=2 and z>4 are comparable
Radio Observations of Infrared Luminous High Redshift QSOs
We present Very Large Array (VLA) observations at 1.4 GHz and 5 GHz of a
sample of 12 Quasi-stellar Objects (QSOs) at z = 3.99 to 4.46. The sources were
selected as the brightest sources at 250 GHz from the recent survey of Omont et
al. (2001). We detect seven sources at 1.4 GHz with flux densities, S_{1.4} >
50 microJy. These centimeter (cm) wavelength observations imply that the
millimeter (mm) emission is most likely thermal dust emission. The
radio-through-optical spectral energy distributions for these sources are
within the broad range defined by lower redshift, lower optical luminosity
QSOs. For two sources the radio continuum luminosities and morphologies
indicate steep spectrum, radio loud emission from a jet-driven radio source.
For the remaining 10 sources the 1.4 GHz flux densities, or limits, are
consistent with those expected for active star forming galaxies. If the radio
emission is powered by star formation in these systems, then the implied star
formation rates are of order 1e3 M_solar/year. We discuss the angular sizes and
spatial distributions of the radio emitting regions, and we consider briefly
these results in the context of co-eval black hole and stellar bulge formation
in galaxies.Comment: to appear in the A
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