3,354 research outputs found
Empiric Models of the Earth's Free Core Nutation
Free core nutation (FCN) is the main factor that limits the accuracy of the
modeling of the motion of Earth's rotational axis in the celestial coordinate
system. Several FCN models have been proposed. A comparative analysis is made
of the known models including the model proposed by the author. The use of the
FCN model is shown to substantially increase the accuracy of the modeling of
Earth's rotation. Furthermore, the FCN component extracted from the observed
motion of Earth's rotational axis is an important source for the study of the
shape and rotation of the Earth's core. A comparison of different FCN models
has shown that the proposed model is better than other models if used to
extract the geophysical signal (the amplitude and phase of FCN) from
observational data.Comment: 8 pages, 3 figures; minor update of the journal published versio
Grand Unification, Axion, and Inflation in Intermediate Scale Supersymmetry
A class of supersymmetric grand unified theories is introduced that has a
single scale below the cutoff, that of the supersymmetry breaking masses
. For a wide range of the dimensionless parameters, agreement with
the observed mass of the Higgs boson determines , yielding Intermediate Scale Supersymmetry. We show that within this
framework it is possible for seesaw neutrino masses, axions, and inflation to
be described by the scale , offering the possibility of a unified
origin of disparate phenomena. Neutrino masses allowing for thermal
leptogenesis can be obtained, and the axion decay constant lies naturally in
the range , consistent with a recent
observational suggestion of high scale inflation. A minimal model is
presented that illustrates these features. In this model, the only states at
the grand unified scale are those of the heavy gauge supermultiplet. The grand
unified partners of the Higgs doublets have a mass of order ,
leading to the dominant proton decay mode , which
may be probed in upcoming experiments. Dark matter may be winos, with mass
environmentally selected to the TeV scale, and/or axions. Gauge coupling
unification is found to be successful, especially if the wino is at the TeV
scale.Comment: 27 pages, 7 figures; minor corrections, references and discussion
adde
MnAs dots grown on GaN(0001)-(1x1) surface
MnAs has been grown by means of MBE on the GaN(0001)-(1x1) surface. Two
options of initiating the crystal growth were applied: (a) a regular MBE
procedure (manganese and arsenic were delivered simultaneously) and (b)
subsequent deposition of manganese and arsenic layers. It was shown that
spontaneous formation of MnAs dots with the surface density of 1
cm and cm, respectively (as observed by AFM),
occurred for the layer thickness higher than 5 ML. Electronic structure of the
MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led
to determination of the Mn 3d - related contribution to the total density of
states (DOS) distribution of MnAs. It has been proven that the electronic
structures of the MnAs dots grown by the two procedures differ markedly. One
corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to
that reported for half-metallic zinc-blende MnAs. Both system behave
superparamagnetically (as revealed by magnetization measurements), but with
both the blocking temperatures and the intra-dot Curie temperatures
substantially different. The intra-dot Curie temperature is about 260 K for the
former system while markedly higher than room temperature for the latter one.
Relations between growth process, electronic structure and other properties of
the studied systems are discussed. Possible mechanisms of half-metallic MnAs
formation on GaN are considered.Comment: 20+ pages, 8 figure
Conditional Intensity and Gibbsianness of Determinantal Point Processes
The Papangelou intensities of determinantal (or fermion) point processes are
investigated. These exhibit a monotonicity property expressing the repulsive
nature of the interaction, and satisfy a bound implying stochastic domination
by a Poisson point process. We also show that determinantal point processes
satisfy the so-called condition which is a general form of
Gibbsianness. Under a continuity assumption, the Gibbsian conditional
probabilities can be identified explicitly.Comment: revised and extende
Eigenfunctions decay for magnetic pseudodifferential operators
We prove rapid decay (even exponential decay under some stronger assumptions)
of the eigenfunctions associated to discrete eigenvalues, for a class of
self-adjoint operators in defined by ``magnetic''
pseudodifferential operators (studied in \cite{IMP1}). This class contains the
relativistic Schr\"{o}dinger operator with magnetic field
Detection of Phase Jumps of Free Core Nutation of the Earth and their Concurrence with Geomagnetic Jerks
We detected phase jumps of the Free Core Nutation (FCN) of the Earth directly
from the analysis of the Very Long Baseline Interferometer (VLBI) observation
of the Earth rotation for the period 1984-2003 by applying the Weighted Wavelet
Z-Transform (WWZ) method and the Short-time Periodogram with the Gabor function
(SPG) method. During the period, the FCN had two significant phase jumps in
1992 and 1998. These epochs coincide with the reported occurrence of
geomagnetic jerks.Comment: 8 pages, 4 figure
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