2,442,752 research outputs found
On the contribution of density perturbations and gravitational waves to the lower order multipoles of the Cosmic Microwave Background Radiation
The important studies of Peebles, and Bond and Efstathiou have led to the
formula C_l = const/[l(l +1)] aimed at describing the lower order multipoles of
the CMBR temperature variations caused by density perturbations with the flat
spectrum. Clearly, this formula requires amendments, as it predicts an
infinitely large monopole C_0, and a dipole moment C_1 only 6/2 times larger
than the quadrupole C_2, both predictions in conflict with observations. We
restore the terms omitted in the course of the derivation of this formula, and
arrive at a new expression. According to the corrected formula, the monopole
moment is finite and small, while the dipole moment is sensitive to
short-wavelength perturbations, and numerically much larger than the
quadrupole, as one would expect on physical grounds. At the same time, the
function l(l +1)C_l deviates from a horizontal line and grows with l, for l
\geq 2. We show that the inclusion of the modulating (transfer) function
terminates the growth and forms the first peak, recently observed. We fit the
theoretical curves to the position and height of the first peak, as well as to
the observed dipole, varying three parameters: red-shift at decoupling,
red-shift at matter-radiation equality, and slope of the primordial spectrum.
It appears that there is always a deficit, as compared with the COBE
observations, at small multipoles, l \sim 10. We demonstrate that a reasonable
and theoretically expected amount of gravitational waves bridges this gap at
small multipoles, leaving the other fits as good as before. We show that the
observationally acceptable models permit somewhat `blue' primordial spectra.
This allows one to avoid the infra-red divergence of cosmological
perturbations, which is otherwise present.Comment: prints to 25 pages including 14 figures, several additional sentences
on interpretation, new references, to appear in Int. Journ. Mod. Physics
Cooling system for high speed aircraft
The system eliminates the necessity of shielding an aircraft airframe constructed of material such as aluminum. Cooling is accomplished by passing a coolant through the aircraft airframe, the coolant acting as a carrier to remove heat from the airframe. The coolant is circulated through a heat pump and a heat exchanger which together extract essentially all of the added heat from the coolant. The heat is transferred to the aircraft fuel system via the heat exchanger and the heat pump. The heat extracted from the coolant is utilized to power the heat pump. The heat pump has associated therewith power turbine mechanism which is also driven by the extracted heat. The power turbines are utilized to drive various aircraft subsystems, the compressor of the heat pump, and provide engine cooling
Cooper Pairs with Broken Parity and Time-Reversal Symmetries in D-wave Superconductors
Paramagnetic effects are shown to result in the appearance of a triplet
component of order parameter in a vortex phase of a d-wave superconductor in
the absence of impurities. This component, which breaks both parity and
time-reversal symmetries of Cooper pairs, is expected to be of the order of
unity in a number of modern superconductors such as organic, high-Tc, and some
others. A generic phase diagram of such type-IV superconductors, which are
singlet ones at H=0 and characterized by singlet-triplet mixed Copper pairs
with broken time-reversal symmetry in a vortex phase, is discussed.Comment: 10 pages, 1 figures, Phys. Rev. Lett., submitted (July 25 2005
In-plane magnetic field phase diagram of superconducting Sr2RuO4
We develop the Ginzburg - Landau theory of the upper critical field in the
basal plane of a tetragonal multiband metal in two-component superconducting
state. It is shown that typical for the two component superconducting state the
upper critical field basal plane anisotropy and the phase transition splitting
still exist in a multiband case. However, the value of anisotropy can be
effectively smaller than in the single band case. The results are discussed in
the application to the superconducting Sr2RuO4.Comment: 4 pages, no figure
Scanning Gate Spectroscopy on Nanoclusters
A gated probe for scanning tunnelling microscopy (STM) has been developed.
The probe extends normal STM operations by means of an additional electrode
fabricated next to the tunnelling tip. The extra electrode does not make
contact with the sample and can be used as a gate. We report on the recipe used
for fabricating the tunnelling tip and the gate electrode on a silicon nitride
cantilever. We demonstrate the functioning of the scanning gate probes by
performing single-electron tunnelling spectroscopy on 20-nm gold clusters for
different gate voltages.Comment: 3 pages, 4 figure
- …