11,634 research outputs found
Interaction effects and transport properties of Pt capped Co nanoparticles
We studied the magnetic and transport properties of Co nanoparticles (NPs)
being capped with varying amounts of Pt. Beside field and temperature dependent
magnetization measurements we performed delta-M measurements to study the
magnetic interactions between the Co NPs. We observe a transition from
demagnetizing towards magnetizing interactions between the particles for an
increasing amount of Pt capping. Resistivity measurements show a crossover from
giant magnetoresistance towards anisotropic magnetoresistance
Phonon-mediated vs. Coulombic Back-Action in Quantum Dot circuits
Quantum point contacts (QPCs) are commonly employed to capacitively detect
the charge state of coupled quantum dots (QD). An indirect back-action of a
biased QPC onto a double QD laterally defined in a GaAs/AlGaAs heterostructure
is observed. Energy is emitted by non-equilibrium charge carriers in the leads
of the biased QPC. Part of this energy is absorbed by the double QD where it
causes charge fluctuations that can be observed under certain conditions in its
stability diagram. By investigating the spectrum of the absorbed energy, we
identify both acoustic phonons and Coulomb interaction being involved in the
back-action, depending on the geometry and coupling constants
Large antenna apertures and arrays for deep space communications
Effect of frequency on communications capability, single antennas and arrays, and economic balance between ground station and spacecraft developmen
Quantum measurement problem and cluster separability
A modified Beltrametti-Cassinelli-Lahti model of measurement apparatus that
satisfies both the probability reproducibility condition and the
objectification requirement is constructed. Only measurements on microsystems
are considered. The cluster separability forms a basis for the first working
hypothesis: the current version of quantum mechanics leaves open what happens
to systems when they change their separation status. New rules that close this
gap can therefore be added without disturbing the logic of quantum mechanics.
The second working hypothesis is that registration apparatuses for microsystems
must contain detectors and that their readings are signals from detectors. This
implies that separation status of a microsystem changes during both preparation
and registration. A new rule that specifies what happens at these changes and
that guarantees the objectification is formulated and discussed. A part of our
result has certain similarity with 'collapse of the wave function'.Comment: 31 pages, no figure. Published versio
Friction and wear in cryogenic liquids for composites of phenolic and of polytetrafluoroethylene of various particle sizes and concentrations
Friction and wear in cryogenic liquids for phenolic and polytetrafluoroethylene composites of various particle sizes and concentration
The New Transiting Planet OGLE-TR-56b: Orbit and Atmosphere
Motivated by the identification of the very close-in extrasolar giant planet
OGLE-TR-56b, we explore the implications of its existence on problems of tidal
dissipation, planet migration, and atmospheric stability. The small orbit of
OGLE-TR-56b makes the planet an interesting test particle case for tidal
dissipation in stellar convection zones. We show that it favors prescriptions
of suppressed convective eddy viscosity. Precise timing of the transits of
OGLE-TR-56b might place interesting constraints on stellar convection theory,
if orbital period change is detected in the near future.Comment: 12 pages, 1 figure, submitted to ApJ
Field-induced structural aging in glasses at ultra low temperatures
In non-equilibrium experiments on the glasses Mylar and BK7, we measured the
excess dielectric response after the temporary application of a strong electric
bias field at mK--temperatures. A model recently developed describes the
observed long time decays qualitatively for Mylar [PRL 90, 105501, S. Ludwig,
P. Nalbach, D. Rosenberg, D. Osheroff], but fails for BK7. In contrast, our
results on both samples can be described by including an additional mechanism
to the mentioned model with temperature independent decay times of the excess
dielectric response. As the origin of this novel process beyond the "tunneling
model" we suggest bias field induced structural rearrangements of "tunneling
states" that decay by quantum mechanical tunneling.Comment: 4 pages, 4 figures, accepted at PRL, corrected typos in version
Heating in the Accreted Neutron Star Ocean: Implications for Superburst Ignition
We perform a self-consistent calculation of the thermal structure in the
crust of a superbursting neutron star. In particular, we follow the
nucleosynthetic evolution of an accreted fluid element from its deposition into
the atmosphere down to a depth where the electron Fermi energy is 20 MeV. We
include temperature-dependent continuum electron capture rates and realistic
sources of heat loss by thermal neutrino emission from the crust and core. We
show that, in contrast to previous calculations, electron captures to excited
states and subsequent gamma-emission significantly reduce the local heat loss
due to weak-interaction neutrinos. Depending on the initial composition these
reactions release up to a factor of 10 times more heat at densities < 10^{11}
g/cc than obtained previously. This heating reduces the ignition depth of
superbursts. In particular, it reduces the discrepancy noted by Cumming et al.
between the temperatures needed for unstable 12C ignition on timescales
consistent with observations and the reduction in crust temperature from Cooper
pair neutrino emission.Comment: 10 pages, 11 figures, the Astrophysical Journal, in press (scheduled
for v. 662). Revised from v1 in response to referee's comment
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