1,440 research outputs found
Microscopic and Macroscopic Signatures of Antiferromagnetic Domain Walls
Magnetotransport measurements on small single crystals of Cr, the elemental
antiferromagnet, reveal the hysteretic thermodynamics of the domain structure.
The temperature dependence of the transport coefficients is directly correlated
with the real-space evolution of the domain configuration as recorded by x-ray
microprobe imaging, revealing the effect of antiferromagnetic domain walls on
electron transport. A single antiferromagnetic domain wall interface resistance
is deduced to be of order at a
temperature of 100 K.Comment: 3 color figure
Global entangling properties of the coupled kicked tops
We study global entangling properties of the system of coupled kicked tops
testing various hypotheses and predictions concerning entanglement in quantum
chaotic systems. In order to analyze the averaged initial entanglement
production rate and the averaged asymptotic entanglement different ensembles of
initial product states are evolved. Two different ensembles with natural
probability distribution are considered: product states of independent
spin-coherent states and product states of arbitrary states. It appears that
the choice of either of these ensembles results in significantly different
averaged entanglement behavior. We investigate also a relation between the
averaged asymptotic entanglement and the mean entanglement of the eigenvectors
of an evolution operator. Lower bound on the averaged asymptotic entanglement
is derived, expressed in terms of the eigenvector entanglement.Comment: 11 pages, 7 figures, RevTe
Quantum dynamics, dissipation, and asymmetry effects in quantum dot arrays
We study the role of dissipation and structural defects on the time evolution
of quantum dot arrays with mobile charges under external driving fields. These
structures, proposed as quantum dot cellular automata, exhibit interesting
quantum dynamics which we describe in terms of equations of motion for the
density matrix. Using an open system approach, we study the role of asymmetries
and the microscopic electron-phonon interaction on the general dynamical
behavior of the charge distribution (polarization) of such systems. We find
that the system response to the driving field is improved at low temperatures
(and/or weak phonon coupling), before deteriorating as temperature and
asymmetry increase. In addition to the study of the time evolution of
polarization, we explore the linear entropy of the system in order to gain
further insights into the competition between coherent evolution and
dissipative processes.Comment: 11pages,9 figures(eps), submitted to PR
Recoherence in the entanglement dynamics and classical orbits in the N-atom Jaynes-Cummings model
The rise in linear entropy of a subsystem in the N-atom Jaynes-Cummings model
is shown to be strongly influenced by the shape of the classical orbits of the
underlying classical phase space: we find a one-to-one correspondence between
maxima (minima) of the linear entropy and maxima (minima) of the expectation
value of atomic excitation J_z. Since the expectation value of this operator
can be viewed as related to the orbit radius in the classical phase space
projection associated to the atomic degree of freedom, the proximity of the
quantum wave packet to this atomic phase space borderline produces a maximum
rate of entanglement. The consequence of this fact for initial conditions
centered at periodic orbits in regular regions is a clear periodic recoherence.
For chaotic situations the same phenomenon (proximity of the atomic phase space
borderline) is in general responsible for oscillations in the entanglement
properties.Comment: 15 pages (text), 6 figures; to be published in Physical Review
Bosonization in d=2 from finite chiral determinants with a Gauss decomposition
We show how to bosonize two-dimensional non-abelian models using finite
chiral determinants calculated from a Gauss decomposition. The calculation is
quite straightforward and hardly more involved than for the abelian case. In
particular, the counterterm , which is normally motivated from gauge
invariance and then added by hand, appears naturally in this approach.Comment: 4 pages, Revte
Functional Integral Construction of the Thirring model: axioms verification and massless limit
We construct a QFT for the Thirring model for any value of the mass in a
functional integral approach, by proving that a set of Grassmann integrals
converges, as the cutoffs are removed and for a proper choice of the bare
parameters, to a set of Schwinger functions verifying the Osterwalder-Schrader
axioms. The corresponding Ward Identities have anomalies which are not linear
in the coupling and which violate the anomaly non-renormalization property.
Additional anomalies are present in the closed equation for the interacting
propagator, obtained by combining a Schwinger-Dyson equation with Ward
Identities.Comment: 55 pages, 9 figure
Increased angiogenic factor secretion by decidual natural killer cells from pregnancies with high uterine artery resistance alters trophoblast function.
STUDY QUESTION
Are the concentrations of factors secreted by decidual natural killer (dNK) cells from pregnancies at high risk of poor spiral artery remodelling different to those secreted from pregnancies at low risk?
SUMMARY ANSWER
Expression levels of PLGF, sIL-2R, endostatin and angiogenin were significantly increased by dNK cells from high-risk pregnancies, and angiogenin and endostatin were found to alter trophoblast function.
WHAT IS KNOWN ALREADY
During early pregnancy, maternal uterine spiral arteries are remodelled from small diameter, low-flow, high-resistance vessels into larger diameter, higher flow vessels, with low-resistance. This change is essential for the developing fetus to obtain sufficient oxygen and nutrients. dNK cells have been implicated in this process.
STUDY DESIGN, SIZE, DURATION
dNK cells were isolated from first trimester terminations of pregnancies (obtained with local ethical approval) screened for normal- or high-resistance index, indicative of cases least (21%) likely to have developed pre-eclampsia had the pregnancy not been terminated (n = 18 each group). Secreted factors and the effects of these on the trophoblast cell line, SGHPL-4, were assessed in vitro.
PARTICIPANTS/MATERIALS, SETTING, METHODS
A multiplex assay was used to assess dNK cell-secreted factors. SGHPL-4 cell functions were assessed using time-lapse microscopy, 3D invasion assays, endothelial-like tube formation ability and western blot analysis.
MAIN RESULTS AND THE ROLE OF CHANCE
The expression levels of PLGF (P < 0.01), sIL-2R (P < 0.01), endostatin (P < 0.05) and angiogenin (P < 0.05) were significantly increased by dNK cells from high-risk pregnancies. Endostatin significantly decreased SGHPL-4 invasion (P < 0.05), SGHPL-4 tube formation (P < 0.05) and SGHPL-4 Aktser473 phosphorylation (P < 0.05). Angiogenin significantly decreased SGHPL-4 invasion (P < 0.05), but increased SGHPL-4 tube formation (P < 0.01) and decreased SGHPL-4 Aktser473 phosphorylation (P < 0.05).
LIMITATIONS, REASONS FOR CAUTION
The culture of dNK cells and protein concentrations in vitro may not fully represent the in vivo situation. Although SGHPL-4 cells are extravillous trophoblast derived, further studies would be needed to confirm the roles of angiogenin and endostatin in vivo.
WIDER IMPLICATIONS OF THE FINDINGS
The altered expression of secreted factors of dNK cells may contribute to pregnancy disorders associated with poor spiral artery remodelling.
STUDY FUNDING/COMPETING INTEREST(S)
This study was supported by the Wellcome Trust (project reference 091550). R.F. was a recipient of a PhD studentship from the Division of Biomedical Sciences, St. George's, University of London. The authors have no conflict of interests
Entangling power of quantized chaotic systems
We study the quantum entanglement caused by unitary operators that have
classical limits that can range from the near integrable to the completely
chaotic. Entanglement in the eigenstates and time-evolving arbitrary states is
studied through the von Neumann entropy of the reduced density matrices. We
demonstrate that classical chaos can lead to substantially enhanced
entanglement. Conversely, entanglement provides a novel and useful
characterization of quantum states in higher dimensional chaotic or complex
systems. Information about eigenfunction localization is stored in a graded
manner in the Schmidt vectors, and the principal Schmidt vectors can be scarred
by the projections of classical periodic orbits onto subspaces. The eigenvalues
of the reduced density matrices are sensitive to the degree of wavefunction
localization, and are roughly exponentially arranged. We also point out the
analogy with decoherence, as reduced density matrices corresponding to
subsystems of fully chaotic systems are diagonally dominant.Comment: 21 pages including 9 figs. (revtex
Entanglement production in Quantized Chaotic Systems
Quantum chaos is a subject whose major goal is to identify and to investigate
different quantum signatures of classical chaos. Here we study entanglement
production in coupled chaotic systems as a possible quantum indicator of
classical chaos. We use coupled kicked tops as a model for our extensive
numerical studies. We find that, in general, presence of chaos in the system
produces more entanglement. However, coupling strength between two subsystems
is also very important parameter for the entanglement production. Here we show
how chaos can lead to large entanglement which is universal and describable by
random matrix theory (RMT). We also explain entanglement production in coupled
strongly chaotic systems by deriving a formula based on RMT. This formula is
valid for arbitrary coupling strengths, as well as for sufficiently long time.
Here we investigate also the effect of chaos on the entanglement production for
the mixed initial state. We find that many properties of the mixed state
entanglement production are qualitatively similar to the pure state
entanglement production. We however still lack an analytical understanding of
the mixed state entanglement production in chaotic systems.Comment: 16 pages, 5 figures. To appear in Pramana:Journal of Physic
- âŠ