381,307 research outputs found
Linear, third- and fifth-order nonlinear spectroscopy of a charge transfer system coupled to an underdamped vibration
We study hole, electron and exciton transport in a charge transfer system in
the presence of underdamped vibrational motion. We analyze the signature of
these processes in the linear and third-, and fifth-order nonlinear electronic
spectra. Calculations are performed with a numerically exact hierarchical
equations of motion method for an underdamped Brownian oscillator spectral
density. We find that combining electron, hole and exciton transfer can lead to
non-trivial spectra with more structure than with excitonic coupling alone.
Traces taken during the waiting time of a two-dimensional spectrum are
dominated by vibrational motion and do not reflect the electron, hole, and
exciton dynamics directly. We find that the fifth-order nonlinear response is
particularly sensitive to the charge transfer process. While third-order 2D
spectroscopy detects the correlation between two coherences, fifth-order 2D
spectroscopy (2D population spectroscopy) is here designed to detect
correlations between the excited states during two different time periods
Extracting Energy from Accretion into Kerr Black Hole
The highest efficiency of converting rest mass into energy by accreting
matter into a Kerr black hole is ~ 31% (Thorne 1974). We propose a new process
in which periods of accretion from a thin disk, and the associated spin-up of
the black hole, alternate with the periods of no accretion and magnetic
transfer of energy from the black hole to the disk. These cycles can repeat
indefinitely, at least in principle, with the black hole mass increasing by ~
66% per cycle, and up to ~ 43% of accreted rest mass radiated away by the disk.Comment: 4 pages, 1 figur
Control of black hole evaporation?
Contradiction between Hawking's semi-classical arguments and string theory on
the evaporation of black hole has been one of the most intriguing problems in
fundamental physics. A final-state boundary condition inside the black hole was
proposed by Horowitz and Maldacena to resolve this contradiction. We point out
that original Hawking effect can be also regarded as a separate boundary
condition at the event horizon for this scenario. Here, we found that the
change of Hawking boundary condition may affect the information transfer from
the initial collapsing matter to the outgoing Hawking radiation during
evaporation process and as a result the evaporation process itself,
significantly.Comment: Journal of High Energy Physics, to be publishe
Algebras, Hawking Radiation and Information Retention by Stringy Black Holes
We have argued previously, based on the analysis of two-dimensional stringy
black holes, that information in stringy versions of four-dimensional
Schwarzschild black holes (whose singular regions are represented by
appropriate Wess-Zumino-Witten models) is retained by quantum -symmetries
when the horizon area is not preserved due to Hawking radiation. It is key that
the exactly-marginal conformal world-sheet operator representing a massless
stringy particle interacting with the black hole requires a contribution from
generators in its vertex function. The latter correspond to
delocalised, non-propagating, string excitations that guarantee the transfer of
information between the string black hole and external particles. When
infalling matter crosses the horizon, these topological states are excited via
a process: (Stringy black hole) + infalling matter (Stringy
black hole), where the black hole is viewed as a stringy state with a
specific configuration of charges that are conserved. Hawking
radiation is then the reverse process, with conservation of the
charges retaining information. The Hawking radiation spectrum near the horizon
of a Schwarzschild or Kerr black hole is specified by matrix elements of
higher-order currents that form a phase-space algebra. We show
that an appropriate gauging of this algebra preserves the horizon
two-dimensional area classically, as expected because the latter is a conserved
Noether charge.Comment: 21 pages, no figure
Characteristics of heat exchange in the region of injection into a supersonic high-temperature flow
An experimental investigation of the local heat transfer coefficient distribution during gas injection into the supersonic-flow portion of a Laval nozzle is discussed. The controlling dimensionless parameters of the investigated process are presented in terms of a generalized relation for the maximum value of the heat transfer coefficient in the nozzle cross section behind the injection hole. Data on the heat transfer coefficient variation along the nozzle length as a function of gas injection rate are also presented, along with the heat transfer coefficient distribution over a cross section of the nozzle
A density matrix approach to photoinduced electron injection
Electron injection from an adsorbed molecule to the substrate (heterogeneous
electron transfer) is studied. One reaction coordinate is used to model this
process. The surface phonons and/or the electron-hole pairs together with the
internal degrees of freedom of the adsorbed molecule as well as possibly a
liquid surrounding the molecule provide a dissipative environment, which may
lead to dephasing, relaxation, and sometimes excitation of the relevant system.
In the process studied the adsorbed molecule is excited by a light pulse. This
is followed by an electron transfer from the excited donor state to the
quasi-continuum of the substrate. It is assumed that the substrate is a
semiconductor. The effects of dissipation on electron injection are
investigated
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