6,924 research outputs found
Heterogenous treatment effects: secrets for a reliable treat-to-target trial?
No abstract available
Pulsations as a Driver for LBV Variability
Among the most spectacular variable stars are the Luminous Blue Variables
(LBVs), which can show three types of variability. The LBV phase of evolution
is poorly understood, and the driving mechanisms for the variability are not
known. The most common type of variability, the S Dor instability, occurs on
timescales of tens of years. During an S Dor outburst, the visual magnitude of
the star increases, while the bolometric magnitude stays approximately
constant. In this work, we investigate pulsation as a possible trigger for the
S Dor type outbursts. We calculate the pulsations of envelope models using a
nonlinear hydrodynamics code including a time-dependent convection treatment.
We initialize the pulsation in the hydrodynamic model based on linear
non-adiabatic calculations. Pulsation properties for a full grid of models from
20 to 85 M were calculated, and in this paper we focus on the few
models that show either long-period pulsations or outburst-like behaviour, with
photospheric radial velocities reaching 70-80 km/s. At the present time, our
models cannot follow mass loss, so once the outburst event begins, our
simulations are terminated. Our results show that pulsations alone are not able
to drive enough surface expansion to eject the outer layers. However, the
outbursts and long-period pulsations discussed here produce large variations in
effective temperature and luminosity, which are expected to produce large
variations in the radiatively driven mass-loss rates.Comment: 9 pages, 10 figures, accepted for publication in MNRA
Inhomogeneous systematic signals in cosmic shear observations
We calculate the systematic errors in the weak gravitational lensing power
spectrum which would be caused by spatially varying calibration (i.e.
multiplicative) errors, such as might arise from uncorrected seeing or
extinction variations. The systematic error is fully described by the angular
two-point correlation function of the systematic in the case of the 2D lensing
that we consider here. We investigate three specific cases: Gaussian,
``patchy'' and exponential correlation functions. In order to keep systematic
errors below statistical errors in future LSST-like surveys, the spatial
variation of calibration should not exceed 3% rms. This conclusion is
independently true for all forms of correlation function we consider. The
relative size the E- and B-mode power spectrum errors does, however, depend
upon the form of the correlation function, indicating that one cannot repair
the E-mode power spectrum systematics by means of the B-mode measurements.Comment: 8 pages, 3 figures. Changes reflect PRD published versio
Efficiency of energy funneling in the photosystem II supercomplex of higher plants
The investigation of energy transfer properties in photosynthetic
multi-protein networks gives insight into their underlying design
principles.Here, we discuss excitonic energy transfer mechanisms of the
photosystem II (PS-II) CSM supercomplex, which is the largest
isolated functional unit of the photosynthetic apparatus of higher
plants.Despite the lack of a decisive energy gradient in CSM, we
show that the energy transfer is directed by relaxation to low energy states.
CSM is not organized to form pathways with strict energetic
downhill transfer, which has direct consequences on the transfer efficiency,
transfer pathways and transfer limiting steps. The exciton dynamics is
sensitive to small structural changes, which, for instance, are induced by the
reorganization of vibrational coordinates. In order to incorporate the
reorganization process in our numerical simulations, we go beyond rate
equations and use the hierarchically coupled equation of motion approach
(HEOM). While transfer from the peripherical antenna to the proteins in
proximity to the reaction center occurs on a faster time scale, the final step
of the energy transfer to the RC core is rather slow, and thus the limiting
step in the transfer chain. Our findings suggest that the structure of the
PS-II supercomplex guarantees photoprotection rather than optimized efficiency.Comment: 23 pages, 6 figure
Exciton-phonon information flow in the energy transfer process of photosynthetic complexes
Non-Markovian and non-equilibrium phonon effects are believed to be key
ingredients in the energy transfer in photosynthetic complexes, especially in
complexes which exhibit a regime of intermediate exciton-phonon coupling. In
this work, we utilize a recently-developed measure for non-Markovianity to
elucidate the exciton-phonon dynamics in terms of the information flow between
electronic and vibrational degrees of freedom. We study the measure in the
hierarchical equation of motion approach which captures strong system-bath
coupling effects and non-equilibrium molecular reorganization. We propose an
additional trace-distance measure for the information flow that could be
extended to other master equations. We find that for a model dimer system and
the Fenna-Matthews-Olson complex that non-Markovianity is significant under
physiological conditions.Comment: 4 pages, 2 figure
Epigenetics and immunometabolism in diabetes and aging
Significance: A strong relationship between hyperglycemia, impaired insulin pathway and cardiovascular disease in type 2 diabetes (T2D) is linked to oxidative stress and inflammation. Immunometabolic pathways link these pathogenic processes and pose important potential therapeutic targets. Recent Advances: The link between immunity and metabolism is bi-directional and includes the role of inflammation in the pathogenesis of metabolic disorders such as T2D, obesity, metabolic syndrome and hypertension as well as the role of metabolic factors in regulation of immune cell functions. Low-grade inflammation, oxidative stress, balance between superoxide and nitric oxide, and the infiltration of macrophages, T cells, B cells in insulin-sensitive tissues, leads to metabolic impairment and accelerated ageing. Critical Issues: Inflammatory infiltrate and altered immune cell phenotype precede development of metabolic disorders. Inflammatory changes are tightly linked to alterations in metabolic status and energy expenditure and are controlled by epigenetic mechanisms. Future directions: A better comprehension of these mechanistic insights is of utmost importance to identify novel molecular targets. Here, we describe a complex scenario of epigenetic changes and immunometabolism linking to diabetes and aging-associated vascular disease
Perivascular adipose tissue inflammation in vascular disease
Perivascular adipose tissue (PVAT) plays a critical role in the pathogenesis of cardiovascular disease. In vascular pathologies, perivascular adipose tissue increases in volume and becomes dysfunctional, with altered cellular composition and molecular characteristics. PVAT dysfunction is characterized by its inflammatory character, oxidative stress, diminished production of vaso-protective adipocyte-derived relaxing factors and increased production of paracrine factors such as resistin, leptin, cytokines (IL-6 and TNF-α) and chemokines [RANTES (CCL5) and MCP-1 (CCL2)]. These adipocyte-derived factors initiate and orchestrate inflammatory cell infiltration including primarily T cells, macrophages, dendritic cells, B cells and NK cells. Protective factors such as adiponectin can reduce NADPH oxidase superoxide production and increase NO bioavailability in the vessel wall, while inflammation (e.g. IFN-γ or IL-17) induces vascular oxidases and eNOS dysfunction in the endothelium, vascular smooth muscle cells and adventitial fibroblasts. All of these events link the dysfunctional perivascular fat to vascular dysfunction. These mechanisms are important in the context of a number of cardiovascular disorders including atherosclerosis, hypertension, diabetes and obesity. Inflammatory changes in PVAT's molecular and cellular responses are uniquely different from classical visceral or subcutaneous adipose tissue or from adventitia, emphasizing the unique structural and functional features of this adipose tissue compartment. Therefore, it is essential to develop techniques for monitoring the characteristics of PVAT and assessing its inflammation. This will lead to a better understanding of the early stages of vascular pathologies and the development of new therapeutic strategies focusing on perivascular adipose tissue
Environment-assisted quantum transport in ordered systems
Noise-assisted transport in quantum systems occurs when quantum
time-evolution and decoherence conspire to produce a transport efficiency that
is higher than what would be seen in either the purely quantum or purely
classical cases. In disordered systems, it has been understood as the
suppression of coherent quantum localisation through noise, which brings
detuned quantum levels into resonance and thus facilitates transport. We report
several new mechanisms of environment-assisted transport in ordered systems, in
which there is no localisation to overcome and where one would naively expect
that coherent transport is the fastest possible. Although we are particularly
motivated by the need to understand excitonic energy transfer in photosynthetic
light-harvesting complexes, our model is general---transport in a tight-binding
system with dephasing, a source, and a trap---and can be expected to have wider
application
Path integral Monte Carlo with importance sampling for excitons interacting with an arbitrary phonon bath
The reduced density matrix of excitons coupled to a phonon bath at a finite
temperature is studied using the path integral Monte Carlo method. Appropriate
choices of estimators and importance sampling schemes are crucial to the
performance of the Monte Carlo simulation. We show that by choosing the
population-normalized estimator for the reduced density matrix, an efficient
and physically-meaningful sampling function can be obtained. In addition, the
nonadiabatic phonon probability density is obtained as a byproduct during the
sampling procedure. For importance sampling, we adopted the Metropolis-adjusted
Langevin algorithm. The analytic expression for the gradient of the target
probability density function associated with the population-normalized
estimator cannot be obtained in closed form without a matrix power series. An
approximated gradient that can be efficiently calculated is explored to achieve
better computational scaling and efficiency. Application to a simple
one-dimensional model system from the previous literature confirms the
correctness of the method developed in this manuscript. The displaced harmonic
model system within the single exciton manifold shows the numerically exact
temperature dependence of the coherence and population of the excitonic system.
The sampling scheme can be applied to an arbitrary anharmonic environment, such
as multichromophoric systems embedded in the protein complex. The result of
this study is expected to stimulate further development of real time
propagation methods that satisfy the detailed balance condition for exciton
populations.Comment: 16 pages, 5 figure
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