444 research outputs found
The sensitivity of Euro-Atlantic regimes to model horizontal resolution
There is growing evidence that the atmospheric dynamics of the Euro-Atlantic sector during winter is driven in part by the presence of quasi-persistent regimes. However, general circulation models typically struggle to simulate these with, for example, an overly weakly persistent blocking regime. Previous studies have showed that increased horizontal resolution can improve the regime structure of a model but have so far only considered a single model with only one ensemble member at each resolution, leaving open the possibility that this may be either coincidental or model dependent. We show that the improvement in regime structure due to increased resolution is robust across multiple models with multiple ensemble members. However, while the high-resolution models have notably more tightly clustered data, other aspects of the regimes may not necessarily improve and are also subject to a large amount of sampling variability that typically requires at least three ensemble members to surmount
Complete eigenstates of identical qubits arranged in regular polygons
We calculate the energy eigenvalues and eigenstates corresponding to coherent
single and multiple excitations of an array of N identical qubits or two-level
atoms (TLA's) arranged on the vertices of a regular polygon. We assume only
that the coupling occurs via an exchange interaction which depends on the
separation between the qubits. We include the interactions between all pairs of
qubits, and our results are valid for arbitrary distances relative to the
radiation wavelength. To illustrate the usefulness of these states, we plot the
distance dependence of the decay rates of the n=2 (biexciton) eigenstates of an
array of 4 qubits, and tabulate the biexciton eigenvalues and eigenstates, and
absorption frequencies, line widths, and relative intensities for polygons
consisting of N=2,...,9 qubits in the long-wavelength limit.Comment: Added a figure showing how these results can be used to compute
deviations from "equal collective decoherence" approximation
Activated platelets form protected zones of adhesion on fibrinogen and fibronectin-coated surfaces.
Leukocytes form zones of close apposition when they adhere to ligand-coated surfaces. Because plasma proteins are excluded from these contact zones, we have termed them protected zones of adhesion. To determine whether platelets form similar protected zones of adhesion, gel-filtered platelets stimulated with thrombin or ADP were allowed to adhere to fibrinogen- or fibronectin-coated surfaces. The protein-coated surfaces with platelets attached were stained with either fluorochrome-conjugated goat anti-human fibrinogen or anti-human fibronectin antibodies, or with rhodamine-conjugated polyethylene glycol polymers. Fluorescence microscopy revealed that F(ab')2 anti-fibrinogen (100 kD) did not penetrate into the contact zones between stimulated platelets and the underlying fibrinogen-coated surface, while Fab antifibrinogen (50 kD) and 10 kD polyethylene glycol readily penetrated and stained the substrate beneath the platelets. Thrombin- or ADP-stimulated platelets also formed protected zones of adhesion on fibronectin-coated surfaces. F(ab')2 anti-fibronectin and 10 kD polyethylene glycol were excluded from these adhesion zones, indicating that they are much less permeable than those formed by platelets on fibrinogen-coated surfaces. The permeability properties of protected zones of adhesion formed by stimulated platelets on surfaces coated with both fibrinogen and fibronectin were similar to the zones of adhesion formed on fibronectin alone. mAb 7E3, directed against the alpha IIb beta 3 integrin blocked the formation of protected adhesion zones between thrombin-stimulated platelets and fibrinogen or fibronectin coated surfaces. mAb C13 is directed against the alpha 5 beta 1 integrin on platelets. Stimulated platelets treated with this mAb formed protected zones of adhesion on surfaces coated with fibronectin. These protected zones were impermeable to F(ab')2 antifibronectin but were permeable to 10 kD polyethylene glycol. These results show that activated platelets form protected zones of adhesion and that the size of molecules excluded from these zones depends upon the composition of the matrix proteins to which the platelets adhere. They also show that formation of protected zones of adhesion by platelets requires alpha IIb beta 3 integrins while the permeability properties of these zones of adhesion are regulated by both alpha IIb beta 3 and alpha 5 beta 1 integrins
Generation of maximum spin entanglement induced by cavity field in quantum-dot systems
Equivalent-neighbor interactions of the conduction-band electron spins of
quantum dots in the model of Imamoglu et al. [Phys. Rev. Lett. 83, 4204 (1999)]
are analyzed. Analytical solution and its Schmidt decomposition are found and
applied to evaluate how much the initially excited dots can be entangled to the
remaining dots if all of them are initially disentangled. It is demonstrated
that the perfect maximally entangled states (MES) can only be generated in the
systems of up to 6 dots with a single dot initially excited. It is also shown
that highly entangled states, approximating the MES with a good accuracy, can
still be generated in systems of odd number of dots with almost half of them
being excited. A sudden decrease of entanglement is observed by increasing the
total number of dots in a system with a fixed number of excitations.Comment: 6 pages, 7 figures, to appear in Phys. Rev.
Photoinduced charge and spin dynamics in strongly correlated electron systems
Motivated by photoinduced phase transition in manganese oxides, charge and
spin dynamics induced by photoirradiation are examined. We calculate the
transient optical absorption spectra of the extended double-exchange model by
the density matrix renormalization group (DMRG) method. A charge-ordered
insulating (COI) state becomes metallic just after photoirradiation, and the
system tends to recover the initial COI state. The recovery is accompanied with
remarkable suppression of an antiferromagnetic correlation in the COI state.
The DMRG results are consistent with recent pump-probe spectroscopy data.Comment: 5 pages, 4 figure
A Cell of One’s Own? Incarceration and Other Turning Points in Women’s Journeys to Desistance
Research has shown the importance of turning points in desistance from criminal behavior. Using qualitative data from a sample of 100 formerly incarcerated mothers interviewed about their criminal behavior, this article explores their descriptions of transition moments and whether and how those moments affected their criminal behavior. The findings indicate that whereas parenting emerges as a turning point, the practical difficulties of reentry may reduce the impact of mothering on women’s desistance. More self-focused turning points, such as those due to incarceration, arrest, and sobriety appeared to be particularly important to the women’s desistance. This article emphasizes the need for research into the subjective and environmental factors that affect women’s desistance behaviors
Entanglement Entropy from a Holographic Viewpoint
The entanglement entropy has been historically studied by many authors in
order to obtain quantum mechanical interpretations of the gravitational
entropy. The discovery of AdS/CFT correspondence leads to the idea of
holographic entanglement entropy, which is a clear solution to this important
problem in gravity. In this article, we would like to give a quick survey of
recent progresses on the holographic entanglement entropy. We focus on its
gravitational aspects, so that it is comprehensible to those who are familiar
with general relativity and basics of quantum field theory.Comment: Latex, 30 pages, invited review for Classical and Quantum Gravity,
minor correction
A 4D-Var inversion system based on the icosahedral grid model (NICAM-TM 4D-Var v1.0) – Part 2: Optimization scheme and identical twin experiment of atmospheric CO<sub>2</sub> inversion
A four-dimensional variational method (4D-Var) is a popular technique for
source/sink inversions of atmospheric constituents, but it is not without
problems. Using an icosahedral grid transport model and the 4D-Var method, a
new atmospheric greenhouse gas (GHG) inversion system has been developed. The
system combines offline forward and adjoint models with a quasi-Newton
optimization scheme. The new approach is then used to conduct identical twin
experiments to investigate optimal system settings for an atmospheric
CO2 inversion problem, and to demonstrate the validity of the new
inversion system. In this paper, the inversion problem is simplified by
assuming the prior flux errors to be reasonably well known and by designing
the prior error correlations with a simple function as a first step. It is
found that a system of forward and adjoint models with smaller model errors
but with nonlinearity has comparable optimization performance to that of
another system that conserves linearity with an exact adjoint relationship.
Furthermore, the effectiveness of the prior error correlations is
demonstrated, as the global error is reduced by about 15 % by adding
prior error correlations that are simply designed when 65 weekly flask
sampling observations at ground-based stations are used. With the optimal
setting, the new inversion system successfully reproduces the spatiotemporal
variations of the surface fluxes, from regional (such as biomass burning) to
global scales. The optimization algorithm introduced in the new system does
not require decomposition of a matrix that establishes the correlation among
the prior flux errors. This enables us to design the prior error covariance
matrix more freely
Seasonal characteristics of trace gas transport into the extratropical upper troposphere and lower stratosphere
To investigate the seasonal characteristics of trace gas
distributions in the extratropical upper troposphere and lower stratosphere
(ExUTLS) as well as stratosphere–troposphere exchange processes, origin
fractions of air masses originating in the stratosphere, tropical
troposphere, midlatitude lower troposphere (LT), and high-latitude LT in the
ExUTLS are estimated using 10-year backward trajectories
calculated with European Centre for Medium-Range Weather Forecasts (ECMWF)
ERA-Interim data as the meteorological input. Time series of trace gases
obtained from ground-based and airborne observations are incorporated into
the trajectories, thus reconstructing spatiotemporal distributions of trace
gases in the ExUTLS. The reconstructed tracer distributions are analyzed with
the origin fractions and the stratospheric age of air (AoA) estimated using
the backward trajectories. The reconstructed distributions of SF6 and
CO2 in the ExUTLS are linearly correlated with those of AoA because of
their chemically passive behavior and quasi-stable increasing trends in the
troposphere. Distributions of CH4, N2O, and CO are
controlled primarily by chemical decay along the transport path from the
source region via the stratosphere and subsequent mixing of such stratospheric
air masses with tropospheric air masses in the ExUTLS.</p
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