12,004 research outputs found
Theory of Polaron Resonance in Quantum Dots and Quantum-Dot Molecules
The theory of exciton coupling to photons and LO phonons in quantum dots
(QDs) and quantum-dot molecules (QDMs) is presented. Resonant-round trips of
the exciton between the ground (bright) and excited (dark or bright) states
mediated by the LO-phonon alter the decay time and yield the Rabi oscillation.
The initial distributions of the population in the ground and the excited
states dominate the oscillating amplitude and frequency. This property provides
a detectable signature to the information stored in a qubit made from QD or QDM
for a wide range of temperature T. Our results presented herein provide an
explanation to the anomaly on T-dependent decay in self-assembled InGaAs/GaAs
QDMs recently reported by experiment.Comment: 30 pages, 8 figure
Black hole masses of tidal disruption event host galaxies
The mass of the central black hole in a galaxy that hosted a tidal disruption
event (TDE) is an important parameter in understanding its energetics and
dynamics. We present the first homogeneously measured black hole masses of a
complete sample of 12 optically/UV selected TDE host galaxies (down to
22 mag and =0.37) in the Northern sky. The mass estimates
are based on velocity dispersion measurements, performed on late time optical
spectroscopic observations. We find black hole masses in the range
310 MM210 M.
The TDE host galaxy sample is dominated by low mass black holes (10
M), as expected from theoretical predictions. The blackbody peak
luminosity of TDEs with M10 M is consistent
with the Eddington limit of the SMBH, whereas the two TDEs with M10 M have peak luminosities below their SMBH
Eddington luminosity, in line with the theoretical expectation that the
fallback rate for M10 M is sub-Eddington. In
addition, our observations suggest that TDEs around lower mass black holes
evolve faster. These findings corroborate the standard TDE picture in 10
M black holes. Our results imply an increased tension between
observational and theoretical TDE rates. By comparing the blackbody emission
radius with theoretical predictions, we conclude that the optical/UV emission
is produced in a region consistent with the stream self-intersection radius of
shallow encounters, ruling out a compact accretion disk as the direct origin of
the blackbody radiation at peak brightness.Comment: 16 pages, 9 figures. Submitted to MNRAS; including minor revisions
suggested by the refere
Interaction induced ferro-electricity in the rotational states of polar molecules
We show that a ferro-electric quantum phase transition can be driven by the
dipolar interaction of polar molecules in the presence a micro-wave field. The
obtained ferro-electricity crucially depends on the harmonic confinement
potential, and the resulting dipole moment persists even when the external
field is turned off adiabatically. The transition is shown to be second order
for fermions and for bosons of a smaller permanent dipole moment, but is first
order for bosons of a larger moment. Our results suggest the possibility of
manipulating the microscopic rotational state of polar molecules by tuning the
trap's aspect ratio (and other mesoscopic parameters), even though the later's
energy scale is smaller than the former's by six orders of magnitude.Comment: 4 pages and 4 figure
Carbonate mineral saturation states in the East China Sea: present conditions and future scenarios
To assess the impact of rising atmospheric CO<sub>2</sub> and eutrophication on the carbonate chemistry of the East China Sea shelf waters, saturation states (Ω) for two important biologically relevant carbonate minerals – calcite (Ω<sub>c</sub>) and aragonite (Ω<sub>a</sub>) – were calculated throughout the water column from dissolved inorganic carbon (DIC) and total alkalinity (TA) data collected in spring and summer of 2009. Results show that the highest Ω<sub>c</sub> (∼9.0) and Ω<sub>a</sub> (∼5.8) values were found in surface water of the Changjiang plume area in summer, whereas the lowest values (Ω<sub>c</sub> = ∼2.7 and Ω<sub>a</sub> = ∼1.7) were concurrently observed in the bottom water of the same area. This divergent behavior of saturation states in surface and bottom waters was driven by intensive biological production and strong stratification of the water column. The high rate of phytoplankton production, stimulated by the enormous nutrient discharge from the Changjiang, acts to decrease the ratio of DIC to TA, and thereby increases Ω values. In contrast, remineralization of organic matter in the bottom water acts to increase the DIC to TA ratio, and thus decreases Ω values. The projected result shows that continued increases of atmospheric CO<sub>2</sub> under the IS92a emission scenario will decrease Ω values by 40–50% by the end of this century, but both the surface and bottom waters will remain supersaturated with respect to calcite and aragonite. Nevertheless, superimposed on such Ω decrease is the increasing eutrophication, which would mitigate or enhance the Ω decline caused by anthropogenic CO<sub>2</sub> uptake in surface and bottom waters, respectively. Our simulation reveals that, under the combined impact of eutrophication and augmentation of atmospheric CO<sub>2</sub>, the bottom water of the Changjiang plume area will become undersaturated with respect to aragonite (Ω<sub>a</sub> = ∼0.8) by the end of this century, which would threaten the health of the benthic ecosystem
Quark-lepton mass unification at TeV scales
A scenario combining a model of early (TeV) unification of quarks and leptons
with the physics of large extra dimensions provides a natural mechanism linking
quark and lepton masses at TeV scale. This has been dubbed as early
quark-lepton mass unification by one of us (PQH) in one of the two models of
early quark-lepton unification, which are consistent with data, namely SU(4)_PS
\otimes SU(2)_L \otimes SU(2)_R \otimes SU(2)_H. In particular, it focused on
the issue of naturally light Dirac neutrino. The present paper will focus on
similar issues in the other model, namely SU(4)_PS \otimes SU(3)_L \otimes
SU(3)_H.Comment: Accepted for publication in PRD: The new version is in agreement with
the accepted manuscrip
Difference equation approach to two-thermocouple sensor characterization in constant velocity flow environments
Thermocouples are one of the most popular devices for temperature measurement due to their
robustness, ease of manufacture and installation, and low cost. However, when used in certain harsh
environments, for example, in combustion systems and engine exhausts, large wire diameters are
required, and consequently the measurement bandwidth is reduced. This article discusses a software
compensation technique to address the loss of high frequency fluctuations based on measurements
from two thermocouples. In particular, a difference equation sDEd approach is proposed and
compared with existing methods both in simulation and on experimental test rig data with constant
flow velocity. It is found that the DE algorithm, combined with the use of generalized total least
squares for parameter identification, provides better performance in terms of time constant
estimation without any a priori assumption on the time constant ratios of the thermocouples
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