1,567 research outputs found
Nutrition During Long Flight
The nutrition of astronautics during long flights is discussed, especially with respect to the changes brought about in the body by the condition of weightlessness
Photon collimator system for the ILC Positron Source
High energy e+e- linear colliders are the next large scale project in
particle physics. They need intense sources to achieve the required luminosity.
In particular, the positron source must provide about 10E+14 positrons per
second. The positron source for the International Linear Collider (ILC) is
based on a helical undulator passed by the electron beam to create an intense
circularly polarized photon beam. With these photons a longitudinally polarized
positron beam is generated; the degree of polarization can be enhanced by
collimating the photon beam. However, the high photon beam intensity causes
huge thermal load in the collimator material. In this paper the thermal load in
the photon collimator is discussed and a flexible design solution is presented.Comment: 22 pages, 19 figures, 8 tables, cross-reference to table 4 fixe
Orbital structure and magnetic ordering in stoichiometric and doped crednerite CuMnO2
The exchange interactions and magnetic structure in layered system CuMnO2
(mineral crednerite) and in nonstoichiometric system Cu1.04Mn0.96O2, with
triangular layers distorted due to orbital ordering of the Mn3+ ions, are
studied by ab-initio band-structure calculations, which were performed within
the GGA+U approximation. The exchange interaction parameters for the Heisenberg
model within the Mn-planes and between the Mn-planes were estimated. We explain
the observed in-plane magnetic structure by the dominant mechanism of the
direct d-d exchange between neighboring Mn ions. The superexchange via O ions,
with 90 degree Mn-O-Mn bonds, plays less important role for the in-plane
exchange. The interlayer coupling is largely dominated by one exchange path
between the half-filled 3z^2-r^2 orbitals of Mn3+. The change of interlayer
coupling from antiferromagnetic in pure CuMnO2 to ferromagnetic in doped
material is also explained by our calculations
CONTROL SYSTEM DEPENDING ON A PARAMETER
A nonlinear control system depending on a parameter is considered in a finite-dimensional Euclidean space and on a finite time interval. The dependence on the parameter of the reachable sets and integral funnels of the corresponding differential inclusion system is studied. Under certain conditions on the control system, the degree of this dependence on the parameter is estimated. Problems of targeting integral funnels to a target set in the presence of an obstacle in strict and soft settings are considered. An algorithm for the numerical solution of this problem in the soft setting has been developed. An estimate of the error of the developed algorithm is obtained. An example of solving a specific problem for a control system in a two-dimensional phase space is given
Electronic structure of VO: charge ordering, metal-insulator transition and magnetism
The low and high-temperature phases of VO have been studied by
\textit{ab initio} calculations. At high temperature, all V atoms are
electronically equivalent and the material is metallic. Charge and orbital
ordering, associated with the distortions in the V pseudo-rutile chains, occur
below the metal-insulator transition. Orbital ordering in the low-temperature
phase, different in V and V chains, allows to explain the
distortion pattern in the insulating phase of VO. The in-chain magnetic
couplings in the low-temperature phase turn out to be antiferromagnetic, but
very different in the various V and V bonds. The V dimers
formed below the transition temperature form spin singlets, but V ions,
despite dimerization, apparently participate in magnetic ordering.Comment: 10 pages, 6 figures, 2 table
Geomagnetic control of the spectrum of traveling ionospheric disturbances based on data from a global GPS network
In this paper an attempt is made to verify the hypothesis on the role of
geomagnetic disturbances as a factor determining the intensity of traveling
ionospheric disturbances (TIDs). To improve the statistical validity of the
data, we have used the based on the new GLOBDET technology method involving a
global spatial averaging of disturbance spectra of the total electron content
(TEC). To characterize the TID intensity quantitatively, we suggest that a new
global index of the degree of disturbance should be used, which is equal to the
mean value of the rms variations in TEC within the selected range of spectral
periods (of 20-60 min in the present case). It was found that power spectra of
daytime TEC variations in the range of 20-60 min periods under quiet conditions
have a power-law form, with the slope index k = -2.5. With an increase of the
level of magnetic disturbance, there is an increase in total intensity of TIDs,
with a concurrent kink of the spectrum caused by an increase in oscillation
intensity in the range of 20-60 min. It was found that an increase in the level
of geomagnetic activity is accompanied by an increase in total intensity of
TEC; however, it correlates not with the absolute level of Dst, but with the
value of the time derivative of Dst (a maximum correlation coefficient reaches
-0.94). The delay of the TID response of the order of 2 hours is consistent
with the view that TIDs are generated in auroral regions, and propagate
equatorward with the velocity of about 300-400 m/s.Comment: LaTeX2.09, 16 pages, 5 figures, 1 table, egs.cls, egs.bst (the style
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