120,751 research outputs found
What is tested when experiments test that quantum dynamics is linear
Experiments that look for nonlinear quantum dynamics test the fundamental
premise of physics that one of two separate systems can influence the physical
behavior of the other only if there is a force between them, an interaction
that involves momentum and energy. The premise is tested because it is the
assumption of a proof that quantum dynamics must be linear. Here variations of
a familiar example are used to show how results of nonlinear dynamics in one
system can depend on correlations with the other. Effects of one system on the
other, influence without interaction between separate systems, not previously
considered possible, would be expected with nonlinear quantum dynamics. Whether
it is possible or not is subject to experimental tests together with the
linearity of quantum dynamics. Concluding comments and questions consider
directions our thinking might take in response to this surprising unprecedented
situation.Comment: 14 pages, Title changed, sentences adde
Radical pair intersystem crossing: Quantum dynamics or incoherent kinetics?
Magnetic field effects on radical pair reactions arise due to the interplay
of coherent electron spin dynamics and spin relaxation effects, a rigorous
treatment of which requires the solution of the Liouville-von Neumann equation.
However, it is often found that simple incoherent kinetic models of the radical
pair singlet-triplet intersystem crossing provide an acceptable description of
experimental measurements. In this paper we outline the theoretical basis for
this incoherent kinetic description, elucidating its connection to exact
quantum mechanics. We show in particular how the finite lifetime of the radical
pair spin states, as well as any additional spin-state dephasing, leads to
incoherent intersystem crossing. We arrive at simple expressions for the
radical pair spin state interconversion rates to which the functional form
proposed recently by Steiner et al. [J. Phys. Chem. C 122, 11701 (2018)] can be
regarded as an approximation. We also test the kinetic master equation against
exact quantum dynamical simulations for a model radical pair and for a series
of molecular
wires
Spin-selective electron transfer reactions of radical pairs: beyond the Haberkorn master equation
Radical pair recombination reactions are normally described using a quantum
mechanical master equation for the electronic and nuclear spin density
operator. The electron spin state selective (singlet and triplet) recombination
processes are described with a Haberkorn reaction term in this master equation.
Here we consider a general spin state selective electron transfer reaction of a
radical pair and use Nakajima-Zwanzig theory to derive the master equation for
the spin density operator, thereby elucidating the relationship between
non-adiabatic reaction rate theory and the Haberkorn reaction term. A second
order perturbation theory treatment of the diabatic coupling naturally results
in the Haberkorn master equation with an additional reactive scalar electron
spin coupling term. This term has been neglected in previous spin chemistry
calculations, but we show that it will often be quite significant. We also show
that beyond second order in perturbation theory, i.e., beyond the Fermi golden
rule limit, an additional reactive singlet-triplet dephasing term appears in
the master equation. A closed form expression for the reactive scalar electron
spin coupling in terms of the Marcus theory parameters that determine the
singlet and triplet recombination rates is presented. By performing simulations
of radical pair reactions with the exact Hierarchical Equations of Motion
(HEOM) method, we demonstrate that our master equations provide a very accurate
description of radical pairs undergoing spin-selective non-adiabatic electron
transfer reactions. The existence of a reactive electron spin coupling may well
have implications for biologically relevant radical pair reactions such as
those which have been suggested to play a role in avian magnetoreception
Sigma terms from an SU(3) chiral extrapolation
We report a new analysis of lattice simulation results for octet baryon
masses in 2+1-flavor QCD, with an emphasis on a precise determination of the
strangeness nucleon sigma term. A controlled chiral extrapolation of a recent
PACS-CS Collaboration data set yields baryon masses which exhibit remarkable
agreement both with experimental values at the physical point and with the
results of independent lattice QCD simulations at unphysical meson masses.
Using the Feynman-Hellmann relation, we evaluate sigma commutators for all
octet baryons. The small statistical uncertainty, and considerably smaller
model-dependence, allows a signifcantly more precise determination of the
pion-nucleon sigma commutator and the strangeness sigma term than hitherto
possible, namely {\sigma}{\pi}N=45 \pm 6 MeV and {\sigma}s = 21 \pm 6 MeV at
the physical point.Comment: 4 pages, 4 figure
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Intralesional corticosteroid-induced hypopigmentation and atrophy
Intralesional corticosteroids are associated with various, uncommon, local adverse events [1]. Atrophy and hypopigmentation most commonlyremain localized to sites of injection. However, outward radiation in a linear, streaky pattern has been reported and is termed “perilesional/perilymphatic hypopigmentation or atrophy [2].” We report a case of this rare adverse event
Crucial cross-talk of interleukin-1β and progesterone in human choriocarcinoma
Copyright @ 2012 Spandidos Publications Ltd. This article can be accessed from the links below.This article has been made available through the Brunel Open Access Publishing Fund.Choriocarcinoma is a highly malignant epithelial tumour that is most often associated with hydatidiform mole and presents the most common emergency medical problem in the management of trophoblast disease. We hypothesise that the hormones/cytokines present within the tumour microenvironment play key roles in the development of choriocarcinoma. In this study we assessed the effects of interleukin-1β (IL-1β) on cell death in the presence or absence of the sex hormone progesterone using two choriocarcinoma cell lines (BeWo and JEG-3) as in vitro experimental models. Although IL-1β induced cell death in both cell lines, the effect was more pronounced in JEG-3 cells, where cell death reached 40% compared to 15% in BeWo cells. Cell death of JEG-3 cells in response to IL-1β was significantly decreased by co-treatment with 100 nM and 1000 nM progesterone and completely abolished at a progesterone concentration of 1000 nM. Progesterone was also able to induce phosphorylation of ERK1/2 in these cells. Pretreatment of JEG-3 cells with a specific MAPK inhibitor (UO126) inhibited progesterone's inhibitory effect on cell death. Collectively, these data provide evidence of cross-talk between progesterone and IL-1β in this aggressive and poorly understood tumour that involves activation of a MAPK pathway and involvement of numerous progesterone receptors.This research was funded by a National Institutes of Health Grant ESO12961. This article is made available through the Brunel Open Access Publishing Fund
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