18,212 research outputs found
From Golden Spirals to Constant Slope Surfaces
In this paper, we find all constant slope surfaces in the Euclidean 3-space,
namely those surfaces for which the position vector of a point of the surface
makes constant angle with the normal at the surface in that point. These
surfaces could be thought as the bi-dimensional analogue of the generalized
helices. Some pictures are drawn by using the parametric equations we found.Comment: 11 pages, 8 figure
Influence of qubit displacements on quantum logic operations in a silicon-based quantum computer with constant interaction
The errors caused by qubit displacements from their prescribed locations in
an ensemble of spin chains are estimated analytically and calculated
numerically for a quantum computer based on phosphorus donors in silicon. We
show that it is possible to polarize (initialize) the nuclear spins even with
displaced qubits by using Controlled NOT gates between the electron and nuclear
spins of the same phosphorus atom. However, a Controlled NOT gate between the
displaced electron spins is implemented with large error because of the
exponential dependence of exchange interaction constant on the distance between
the qubits. If quantum computation is implemented on an ensemble of many spin
chains, the errors can be small if the number of chains with displaced qubits
is small
Temperature effects on the 15-85-micron spectra of olivines and pyroxenes
Far-infrared spectra of laboratory silicates are normally obtained at room
temperature even though the grains responsible for astronomical silicate
emission bands seen at wavelengths >20 micron are likely to be at temperatures
below ~150 K. In order to investigate the effect of temperature on silicate
spectra, we have obtained absorption spectra of powdered forsterite and
olivine, along with two orthoenstatites and diopside clinopyroxene, at 3.5+-0.5
K and at room temperature (295+-2K). To determine the changes in the spectra
the resolution must be increased from 1 to 0.25 cm^-1 at both temperatures
since a reduction in temperature reduces the phonon density, thereby reducing
the width of the infrared peaks. Several bands observed at 295 K split at 3.5
K. At 3.5 K the widths of isolated single bands in olivine, enstatites and
diopside are ~ 90% of their 295 K-widths. However, in forsterite the
3.5-K-widths of the 31-, 49- and 69-micron bands are, respectively, 90%, 45%
and 31% of their 295 K widths. Due to an increase in phonon energy as the
lattice contracts, 3.5-K-singlet peaks occur at shorter wavelengths than do the
corresponding 295-K peaks; the magnitude of the wavelength shift increases from
\~ 0-0.2 micron at 25 micron to ~0.9 micron at 80 micron. Changes in the
relative absorbances of spectral peaks are also observed. The temperature
dependence of lambda_pk and bandwidth shows promise as a means to deduce
characteristic temperatures of mineralogically distinct grain populations. In
addition, the observed changes in band strength with temperature will affect
estimates of grain masses and relative mineral abundances inferred using
room-temperature laboratory data.Comment: 11 pages, 7 figures including figures 3a and 3b. includes latex and
eps files. Accepted by MNRAS on 15th March 200
Magnetic structure of Ba(TiO)Cu(PO) probed using spherical neutron polarimetry
The antiferromagnetic compound Ba(TiO)Cu(PO) contains square
cupola of corner-sharing CuO plaquettes, which were proposed to form
effective quadrupolar order. To identify the magnetic structure, we have
performed spherical neutron polarimetry measurements. Based on symmetry
analysis and careful measurements we conclude that the orientation of the
Cu spins form a non-collinear in-out structure with spins approximately
perpendicular to the CuO motif. Strong Dzyaloshinskii-Moriya interaction
naturally lends itself to explain this phenomenon. The identification of the
ground state magnetic structure should serve well for future theoretical and
experimental studies into this and closely related compounds.Comment: 9 pages, 4 figure
The supercluster--void network III. The correlation function as a geometrical statistic
We investigate properties of the correlation function of clusters of galaxies
using geometrical models. On small scales the correlation function depends on
the shape and the size of superclusters. On large scales it describes the
geometry of the distribution of superclusters. If superclusters are distributed
randomly then the correlation function on large scales is featureless. If
superclusters and voids have a tendency to form a regular lattice then the
correlation function on large scales has quasi-regularly spaced maxima and
minima of decaying amplitude; i.e., it is oscillating. The period of
oscillations is equal to the step size of the grid of the lattice.
We calculate the power spectrum for our models and compare the geometrical
information of the correlation function with other statistics. We find that
geometric properties (the regularity of the distribution of clusters on large
scales) are better quantified by the correlation function. We also analyse
errors in the correlation function and the power spectrum by generating random
realizations of models and finding the scatter of these realizations.Comment: MNRAS LaTex style, 12 pages, 7 PostScript figures embedded, accepted
by MNRA
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