2,465 research outputs found
Rolling and sliding of a nanorod between two planes: Tribological regimes and control of friction
The motion of a cylindrical crystalline nanoparticle sandwiched between two
crystalline planes, one stationary and the other pulled at a constant velocity
and pressed down by a normal load, is considered theoretically using a planar
model. The results of our model calculations show that, depending on load and
velocity, the nanoparticle can be either rolling or sliding. At sufficiently
high normal loads, several sliding states characterized by different friction
forces can coexist, corresponding to different orientations of the
nanoparticle, and allowing one to have low or high friction at the same pulling
velocity and normal load.Comment: 5 figure
Slice Stretching at the Event Horizon when Geodesically Slicing the Schwarzschild Spacetime with Excision
Slice-stretching effects are discussed as they arise at the event horizon
when geodesically slicing the extended Schwarzschild black-hole spacetime while
using singularity excision. In particular, for Novikov and isotropic spatial
coordinates the outward movement of the event horizon (``slice sucking'') and
the unbounded growth there of the radial metric component (``slice wrapping'')
are analyzed. For the overall slice stretching, very similar late time behavior
is found when comparing with maximal slicing. Thus, the intuitive argument that
attributes slice stretching to singularity avoidance is incorrect.Comment: 5 pages, 2 figures, published version including minor amendments
suggested by the refere
Temperature cycling tests on a mixed Be/Li₄SiO₄ pebble bed in the HEBLO facility. (Final report)
Magnetism in one-dimensional quantum dot arrays
We employ the density functional Kohn-Sham method in the local spin-density
approximation to study the electronic structure and magnetism of quasi
one-dimensional periodic arrays of few-electron quantum dots. At small values
of the lattice constant, the single dots overlap, forming a non-magnetic
quantum wire with nearly homogenous density. As the confinement perpendicular
to the wire is increased, i.e. as the wire is squeezed to become more
one-dimensional, it undergoes a spin-Peierls transition. Magnetism sets in as
the quantum dots are placed further apart. It is determined by the electronic
shell filling of the individual quantum dots. At larger values of the lattice
constant, the band structure for odd numbers of electrons per dot indicates
that the array could support spin-polarized transport and therefore act as a
spin filter.Comment: 11 pages, 6 figure
Nonequilibrium fluctuation induced escape from a metastable state
Based on a simple microscopic model where the bath is in a non-equilibrium
state we study the escape from a metastable state in the over-damped limit.
Making use of Fokker-Planck-Smoluchowski description we derive the time
dependent escape rate in the non-stationary regime in closed analytical form
which brings on to fore a strong non-exponential kinetic of the system mode.Comment: 4 pages, no figures, EPJ class file include
Diffusion and Current of Brownian Particles in Tilted Piecewise Linear Potentials: Amplification and Coherence
Overdamped motion of Brownian particles in tilted piecewise linear periodic
potentials is considered. Explicit algebraic expressions for the diffusion
coefficient, current, and coherence level of Brownian transport are derived.
Their dependencies on temperature, tilting force, and the shape of the
potential are analyzed. The necessary and sufficient conditions for the
non-monotonic behavior of the diffusion coefficient as a function of
temperature are determined. The diffusion coefficient and coherence level are
found to be extremely sensitive to the asymmetry of the potential. It is
established that at the values of the external force, for which the enhancement
of diffusion is most rapid, the level of coherence has a wide plateau at low
temperatures with the value of the Peclet factor 2. An interpretation of the
amplification of diffusion in comparison with free thermal diffusion in terms
of probability distribution is proposed.Comment: To appear in PR
Spectral properties of rotating electrons in quantum dots and their relation to quantum Hall liquids
The exact diagonalization technique is used to study many-particle properties
of interacting electrons with spin, confined in a two-dimensional harmonic
potential. The single-particle basis is limited to the lowest Landau level. The
results are analyzed as a function of the total angular momentum of the system.
Only at angular momenta corresponding to the filling factors 1, 1/3, 1/5 etc.
the system is fully polarized. The lowest energy states exhibit spin-waves,
domains, and localization, depending on the angular momentum. Vortices exist
only at excited polarized states. The high angular momentum limit shows
localization of electrons and separation of the charge and spin excitations.Comment: 14 pages 18 figure
Magnetic phases of one-dimensional lattices with 2 to 4 fermions per site
We study the spectral and magnetic properties of one-dimensional lattices
filled with 2 to 4 fermions (with spin 1/2) per lattice site. We use a
generalized Hubbard model that takes account all interactions on a lattice
site, and solve the many-particle problem by exact diagonalization. We find an
intriguing magnetic phase diagram which includes ferromagnetism, spin-one
Heisenberg antiferromagnetism, and orbital antiferromagnetism.Comment: 8 pages, 6 figure
Development of HPD Clusters for MAGIC-II
MAGIC-II is the second imaging atmospheric Cherenkov telescope of the MAGIC
observatory, which has recently been inaugurated on Canary island of La Palma.
We are currently developing a new camera based on clusters of hybrid photon
detectors (HPD) for the upgrade of MAGIC-II. The photon detectors feature a
GaAsP photocathode and an avalanche diode as electron bombarded anodes with
internal gain, and were supplied by Hamamatsu Photonics K.K. (R9792U-40). The
HPD camera with high quantum efficiency will increase the MAGIC-II sensitivity
and lower the energy threshold. The basic performance of the HPDs has been
measured and a prototype of an HPD cluster has been developed to be mounted on
MAGIC-II. Here we report on the status of the HPD cluster and the project of
eventually using HPD clusters in the central area of the MAGIC-II camera.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
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