52,966 research outputs found
Calculated elastic scattering cross sections for the liplus-he system
Elastic scattering cross sections of lithium plus helium syste
Performance characteristics of wind profiling radars
Doppler radars used to measure winds in the troposphere and lower stratosphere for weather analysis and forecasting are lower-sensitivity versions of mesosphere-stratosphere-troposphere radars widely used for research. The term wind profiler is used to denote these radars because measurements of vertical profiles of horizontal and vertical wind are their primary function. It is clear that wind profilers will be in widespread use within five years: procurement of a network of 30 wind profilers is underway. The Wave Propagation Laboratory (WPL) has operated a small research network of radar wind profilers in Colorado for about two and one-half years. The transmitted power and antenna aperture for these radars is given. Data archiving procedures have been in place for about one year, and this data base is used to evaluate the performance of the radars. One of the prime concerns of potential wind profilers users is how often and how long wind measurements are lacking at a given height. Since these outages constitute an important part of the performance of the wind profilers, they are calculated at three radar frequencies, 50-, 405-, and 915-MHz, (wavelengths of 6-, 0.74-, and 0.33-m) at monthly intervals to determine both the number of outages at each frequency and annual variations in outages
Conductance oscillations in mesoscopic rings: microscopic versus macroscopic picture
The phase of Aharonov-Bohm oscillations in mesoscopic metal rings in the
presence of a magnetic field can be modulated by application of a DC-bias
current I_DC. We address the question of how a variation of I_DC and hence of
the microscopic phases of the electronic wave functions results in the
macroscopic phase of the conductance oscillations. Whereas the first one can be
varied continuously the latter has to be quantized for a ring in two-wire
configuration by virtue of the Onsager symmetry relations. We observe a
correlation between a phase flip by +/- pi and the amplitude of the
oscillations.Comment: 4 pages, 4 figure
Feynman versus Bakamjian-Thomas in Light Front Dynamics
We compare the Bakamjian-Thomas (BT) formulation of relativistic few-body
systems with light front field theories that maintain closer contact with
Feynman diagrams. We find that Feynman diagrams distinguish Melosh rotations
and other kinematical quantities belonging to various composite subsystem
frames that correspond to different loop integrals. The BT formalism knows only
the rest frame of the whole composite system, where everything is evaluated.Comment: 5 page
[OII] emitters in the GOODS field at z~1.85: a homogeneous measure of evolving star formation
We present the results of a deep, near-infrared, narrow band imaging survey
at a central wavelength of 1.062 microns (FWHM=0.01 microns) in the GOODS-South
field using the ESO VLT instrument, HAWK-I. The data are used to carry out the
highest redshift search for [OII]3727 emission line galaxies to date. The
images reach an emission line flux limit (5 sigma) of 1.5 x 10^-17 erg cm^-2
s^-1, additionally making the survey the deepest of its kind at high redshift.
In this paper we identify a sample of [OII]3727 emission line objects at
redshift z~1.85 in a co-moving volume of ~4100 Mpc^3. Objects are selected
using an observed equivalent width (EW_obs) threshold of EW_obs = 50 angstroms.
The sample is used to derive the space density and constrain the luminosity
function of [OII] emitters at z=1.85. We find that the space density of objects
with observed [OII] luminosities in the range log(L_[OII]) > 41.74 erg s^-1 is
log(rho)=-2.45+/-0.14 Mpc^-3, a factor of 2 greater than the observed space
density of [OII] emitters reported at z~1.4. After accounting for completeness
and assuming an internal extinction correction of A_Halpha=1 mag (equivalent to
A_[OII]=1.87), we report a star formation rate density of rho* ~0.38+/-0.06
Msun yr^-1 Mpc^-3. We independently derive the dust extinction of the sample
using 24 micron fluxes and find a mean extinction of A_[OII]=0.98+/-0.11
magnitudes (A_Halpha=0.52). This is significantly lower than the A_Halpha=1
(A[OII]=1.86) mag value widely used in the literature. Finally we incorporate
this improved extinction correction into the star formation rate density
measurement and report rho*~0.24+/-0.06 Msun yr^-1 Mpc^-3.Comment: 11 pages, 10 figures, accepted for publication in MNRA
The influence of strength of hyperon-hyperon interactions on neutron star properties
An equation of state of neutron star matter with strange baryons has been
obtained. The effects of the strength of hyperon-hyperon interactions on the
equations of state constructed for the chosen parameter sets have been
analyzed. Numerous neutron star models show that the appearance of hyperons is
connected with the increasing density in neutron star interiors. The performed
calculations have indicated that the change of the hyperon-hyperon coupling
constants affects the chemical composition of a neutron star. The obtained
numerical hyperon star models exclude large population of strange baryons in
the star interior.Comment: 18 pages, 22 figures, accepted to be published in Journal of Physics
G: Nuclear and Particle Physic
Non-sequential triple ionization in strong fields
We consider the final stage of triple ionization of atoms in a strong
linearly polarized laser field. We propose that for intensities below the
saturation value for triple ionization the process is dominated by the
simultaneous escape of three electrons from a highly excited intermediate
complex. We identify within a classical model two pathways to triple
ionization, one with a triangular configuration of electrons and one with a
more linear one. Both are saddles in phase space. A stability analysis
indicates that the triangular configuration has the larger cross sections and
should be the dominant one. Trajectory simulations within the dominant symmetry
subspace reproduce the experimentally observed distribution of ion momenta
parallel to the polarization axis.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
A tunable, dual mode field-effect or single electron transistor
A dual mode device behaving either as a field-effect transistor or a single
electron transistor (SET) has been fabricated using silicon-on-insulator metal
oxide semiconductor technology. Depending on the back gate polarisation, an
electron island is accumulated under the front gate of the device (SET regime),
or a field-effect transistor is obtained by pinching off a bottom channel with
a negative front gate voltage. The gradual transition between these two cases
is observed. This dual function uses both vertical and horizontal tunable
potential gradients in non-overlapped silicon-on-insulator channel
Neutron Charge Radius: Relativistic Effects and the Foldy Term
The neutron charge radius is studied within a light-front model with
different spin coupling schemes and wave functions. The cancellation of the
contributions from the Foldy term and Dirac form factor to the neutron charge
form factor is verified for large nucleon sizes and it is independent of the
detailed form of quark spin coupling and wave function. For the physical
nucleon our results for the contribution of the Dirac form factor to the
neutron radius are insensitive to the form of the wave function while they
strongly depend on the quark spin coupling scheme.Comment: 12 pages, 5 figures, Latex, Int. J. Mod. Phys.
- …