2,197 research outputs found
Non-equilibrium transport through a disordered molecular nanowire
We investigate the non-equilibrium transport properties of a disordered
molecular nanowire. The nanowire is regarded as a quasi-one-dimensional organic
crystal composed of self-assembled molecules. One orbital and a single random
energy are assigned to each molecule while the intermolecular coupling does not
fluctuate. Consequently, electronic states are expected to be spatially
localized. We consider the regime of strong localization, namely, the
localization length is smaller than the length of the molecular wire.
Electron-vibron interaction, taking place in each single molecule, is also
taken into account. We investigate the interplay between disorder and
electron-vibron interaction in response to either an applied electric bias or a
temperature gradient. To this end, we calculate the electric and heat currents
when the nanowire is connected to leads, using the Keldysh non-equilibrium
Green's function formalism. At intermediate temperature, scattering by disorder
dominates both charge and heat transport. We find that the electron-vibron
interaction enhances the effect of the disorder on the transport properties due
to the exponential suppression of tunneling
Is statistical learning trainable?
Statistical learning (SL) is the ability to implicitly extract regularities in the environment, and likely supports various
higher-order behaviors, from language to music and vision. While specific patterns experience are likely to influence SL outcomes, this ability is tacitly conceptualized as a fixed construct, and few studies to date have investigated how
experience may shape statistical learning. We report one experiment that directly tested whether SL can be modulated by previous experience. We used a prepost treatment design allowing us to pinpoint what specific
aspects of \u201cprevious experience\u201d matter for SL. The results show that performance on an artificial grammar learning task at post-test depends on whether the grammar to be learned at post-test matches the underlying grammar structures learned during treatment. Our study is the first to adopt a pre-post test design to directly modulate the effects of learning on learning itself
Electron kinetics at the plasma interface
The most fundamental response of an ionized gas to a macroscopic object is
the formation of the plasma sheath. It is an electron depleted space charge
region, adjacent to the object, which screens the object's negative charge
arising from the accumulation of electrons from the plasma. The plasma sheath
is thus the positively charged part of an electric double layer whose
negatively charged part is inside the wall. In the course of the Transregional
Collaborative Research Center SFB/TRR24 we investigated, from a microscopic
point of view, the elementary charge transfer processes responsible for the
electric double layer at a floating plasma-wall interface and made first steps
towards a description of the negative part of the layer inside the wall. Below
we review our work in a colloquial manner, describe possible extensions, and
identify key issues which need to be resolved to make further progress in the
understanding of the electron kinetics across plasma-wall interfaces.Comment: 14 pages, 8 figure
Probing Evidence of Cerebral White Matter Microstructural Disruptions in Ischemic Heart Disease Before and Following Cardiac Rehabilitation: A Diffusion Tensor MR Imaging Study.
BACKGROUND: Ischemic heart disease (IHD) is linked to brain white matter (WM) breakdown but how age or disease effects WM integrity, and whether it is reversible using cardiac rehabilitation (CR), remains unclear.
PURPOSE: To assess the effects of brain aging, cardiovascular disease, and CR on WM microstructure in brains of IHD patients following a cardiac event.
STUDY TYPE: Retrospective.
POPULATION: Thirty-five IHD patients (9 females; mean age = 59 ± 8 years), 21 age-matched healthy controls (10 females; mean age = 59 ± 8 years), and 25 younger controls (14 females; mean age = 26 ± 4 years).
FIELD STRENGTH/SEQUENCE: 3 T diffusion-weighted imaging with single-shot echo planar imaging acquired at 3 months and 9 months post-cardiac event.
ASSESSMENT: Tract-based spatial statistics (TBSS) and tractometry were used to compare fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) in cerebral WM between: 1) older and younger controls to distinguish age-related from disease-related WM changes; 2) IHD patients at baseline (pre-CR) and age-matched controls to investigate if cardiovascular disease exacerbates age-related WM changes; and 3) IHD patients pre-CR and post-CR to investigate the neuroplastic effect of CR on WM microstructure.
STATISTICAL TESTS: Two-sample unpaired t-test (age: older vs. younger controls; IHD: IHD pre-CR vs. age-matched controls). One-sample paired t-test (CR: IHD pre- vs. post-CR). Statistical threshold: P \u3c 0.05 (FWE-corrected).
RESULTS: TBSS and tractometry revealed widespread WM changes in older controls compared to younger controls while WM clusters of decreased FA in the fornix and increased MD in body of corpus callosum were observed in IHD patients pre-CR compared to age-matched controls. Robust WM improvements (increased FA, increased AD) were observed in IHD patients post-CR.
DATA CONCLUSION: In IHD, both brain aging and cardiovascular disease may contribute to WM disruptions. IHD-related WM disruptions may be favorably modified by CR.
LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 2
Genome-wide meta-analysis associates HLA-DQA1/DRB1 and LPA and lifestyle factors with human longevity
Genomic analysis of longevity offers the potential to illuminate the biology
of human aging. Here, using genome-wide association meta-analysis of 606,059
parents’ survival, we discover two regions associated with longevity (HLA-
DQA1/DRB1 and LPA). We also validate previous suggestions that APOE, CHRNA3/5,
CDKN2A/B, SH2B3 and FOXO3A influence longevity. Next we show that giving up
smoking, educational attainment, openness to new experience and high-density
lipoprotein (HDL) cholesterol levels are most positively genetically
correlated with lifespan while susceptibility to coronary artery disease
(CAD), cigarettes smoked per day, lung cancer, insulin resistance and body fat
are most negatively correlated. We suggest that the effect of education on
lifespan is principally mediated through smoking while the effect of obesity
appears to act via CAD. Using instrumental variables, we suggest that an
increase of one body mass index unit reduces lifespan by 7 months while 1 year
of education adds 11 months to expected lifespan
- …