2,333 research outputs found
Carter's constant revealed
A new formulation of Carter's constant for geodesic motion in Kerr black
holes is given. It is shown that Carter's constant corresponds to the total
angular momentum plus a precisely defined part which is quadratic in the linear
momenta. The characterization is exact in the weak field limit obtained by
letting the gravitational constant go to zero. It is suggested that the new
form can be useful in current studies of the dynamics of extreme mass ratio
inspiral (EMRI) systems emitting gravitational radiation.Comment: Minor changes to match published versio
Random Boolean Network Models and the Yeast Transcriptional Network
The recently measured yeast transcriptional network is analyzed in terms of
simplified Boolean network models, with the aim of determining feasible rule
structures, given the requirement of stable solutions of the generated Boolean
networks. We find that for ensembles of generated models, those with canalyzing
Boolean rules are remarkably stable, whereas those with random Boolean rules
are only marginally stable. Furthermore, substantial parts of the generated
networks are frozen, in the sense that they reach the same state regardless of
initial state. Thus, our ensemble approach suggests that the yeast network
shows highly ordered dynamics.Comment: 23 pages, 5 figure
Quantum Spin Tomography in Ferromagnet-Normal Conductors
We present a theory for a complete reconstruction of non-local spin
correlations in ferromagnet-normal conductors. This quantum spin tomography is
based on cross correlation measurements of electric currents into ferromagnetic
terminals with controllable magnetization directions. For normal injectors,
non-local spin correlations are universal and strong. The correlations are
suppressed by spin-flip scattering and, for ferromagnetic injectors, by
increasing injector polarization.Comment: 4+ page
Quantum pump driven fermionic Mach-Zehnder interferometer
We have investigated the characteristics of the currents in a pump-driven
fermionic Mach-Zehnder interferometer. The system is implemented in a conductor
in the quantum Hall regime, with the two interferometer arms enclosing an
Aharonov-Bohm flux . Two quantum point contacts with transparency
modulated periodically in time drive the current and act as beam-splitters. The
current has a flux dependent part as well as a flux independent
part . Both current parts show oscillations as a function of frequency
on the two scales determined by the lengths of the interferometer arms. In the
non-adiabatic, high frequency regime oscillates with a constant
amplitude while the amplitude of the oscillations of increases
linearly with frequency. The flux independent part is insensitive to
temperature while the flux dependent part is exponentially
suppressed with increasing temperature. We also find that for low amplitude,
adiabatic pumping rectification effects are absent for semitransparent
beam-splitters. Inelastic dephasing is introduced by coupling one of the
interferometer arms to a voltage probe. For a long charge relaxation time of
the voltage probe, giving a constant probe potential, and the part
of flowing in the arm connected to the probe are suppressed with
increased coupling to the probe. For a short relaxation time, with the
potential of the probe adjusting instantaneously to give zero time dependent
current at the probe, only is suppressed by the coupling to the
probe.Comment: 10 pages, 4 figure
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Recoil-deposited Po-210 in radon dwellings
Short-lived decay products of Rn-222 plate out on all surfaces in a house containing radon gas. Following the subsequent alpha decays of the mother nuclei, the daughter products Pb-214 and Pb-210 are superficially and permanently absorbed. Due to its long half-life (22 y) the activity of absorbed Pb-210 accumulates in the surface. The activity of Pb-210, or its decay products, can thus reflect the past randon daughter and plate-out history of a house over several decades. Our results and experience from measurements of Po-210 and Rn-222 in 22 dwellings will be presented. In these studies the Po-210 surface activity of one plane glass sheet per dwelling (window panes were not used) has been determined and compared with the period of exposure times the mean radon concentration measured over a two-month period. Considering the large uncertainty in the integrated radon exposure estimate the surface {sup 210}Po correlates well (r=0.73) with the accumulated radon exposure. The {sup 210}Po activity of the glass samples has been measured non-destructively using an open-flow pulse ionization chamber and this detector has also been successfully applied in field exercises
Elastic Stars in General Relativity: II. Radial perturbations
We study radial perturbations of general relativistic stars with elastic
matter sources. We find that these perturbations are governed by a second order
differential equation which, along with the boundary conditions, defines a
Sturm-Liouville type problem that determines the eigenfrequencies. Although
some complications arise compared to the perfect fluid case, leading us to
consider a generalisation of the standard form of the Sturm-Liouville equation,
the main results of Sturm-Liouville theory remain unaltered. As an important
consequence we conclude that the mass-radius curve for a one-parameter sequence
of regular equilibrium models belonging to some particular equation of state
can be used in the same well-known way as in the perfect fluid case, at least
if the energy density and the tangential pressure of the background solutions
are continuous. In particular we find that the fundamental mode frequency has a
zero for the maximum mass stars of the models with solid crusts considered in
Paper I of this series.Comment: 22 pages, no figures, final version accepted for publication in
Class. Quantum Grav. The treatment of the junction conditions has been
improve
Quantum teleportation by particle-hole annihilation in the Fermi sea
A tunnel barrier in a degenerate electron gas was recently discovered as a
source of entangled particle-hole excitations. The entanglement is produced by
elastic tunneling events, without requiring electron-electron interactions.
Here we investigate the inverse process, the annihilation of an electron and a
hole by elastic scattering. We find that this process leads to teleportation of
the (unknown) state of the annihilated electron to a second, distant electron
-- if the latter was previously entangled with the annihilated hole. We propose
an experiment, involving low-frequency noise measurements on a two-dimensional
electron gas in a high magnetic field, to detect teleportation of electrons and
holes in the two lowest Landau levels.Comment: 5 pages including 2 figures; [2017: fixed broken postscript figures
Pump-probe scheme for electron-photon dynamics in hybrid conductor-cavity systems
Recent experiments on nanoscale conductors coupled to microwave cavities put
in prospect transport investigations of electron-photon interplay in the deep
quantum regime. Here we propose a pump-probe scheme to investigate the
transient dynamics of individual electron-photon excitations in a double
quantum dot-cavity system. Excitations pumped into the system decay via charge
tunneling at the double dot, probed in real time. We investigate theoretically
the short-time charge transfer statistics at the dot, for periodic pumping, and
show that this gives access to vacuum Rabi oscillations as well as excitation
dynamics in the presence of double dot dephasing and relaxation.Comment: 5 Pages, 5 figure
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