787 research outputs found
Electrical transport and low-temperature scanning tunneling microscopy of microsoldered graphene
Using the recently developed technique of microsoldering, we perform a
systematic transport study of the influence of PMMA on graphene flakes
revealing a doping effect of up to 3.8x10^12 1/cm^2, but a negligible influence
on mobility and gate voltage induced hysteresis. Moreover, we show that the
microsoldered graphene is free of contamination and exhibits a very similar
intrinsic rippling as has been found for lithographically contacted flakes.
Finally, we demonstrate a current induced closing of the previously found
phonon gap appearing in scanning tunneling spectroscopy experiments, strongly
non-linear features at higher bias probably caused by vibrations of the flake
and a B-field induced double peak attributed to the 0.Landau level of graphene.Comment: 8 pages, 3 figure
Dynamical response of the nuclear pasta in neutron star crusts
The nuclear pasta -- a novel state of matter having nucleons arranged in a
variety of complex shapes -- is expected to be found in the crust of neutron
stars and in core-collapse supernovae at subnuclear densities of about
g/cm. Due to frustration, a phenomenon that emerges from the
competition between short-range nuclear attraction and long-range Coulomb
repulsion, the nuclear pasta displays a preponderance of unique low-energy
excitations. These excitations could have a strong impact on many transport
properties, such as neutrino propagation through stellar environments. The
excitation spectrum of the nuclear pasta is computed via a molecular-dynamics
simulation involving up to 100,000 nucleons. The dynamic response of the pasta
displays a classical plasma oscillation in the 1-2 MeV region. In addition,
substantial strength is found at low energies. Yet this low-energy strength is
missing from a simple ion model containing a single-representative heavy
nucleus. The low-energy strength observed in the dynamic response of the pasta
is likely to be a density wave involving the internal degrees of freedom of the
clusters.Comment: 4 pages, 3 figures, Phys Rev C in pres
Empathy and correct mental state inferences both promote prosociality
In a world with rapidly increasing population that competes for the earth's limited resources, cooperation is crucial. While research showed that empathizing with another individual in need enhances prosociality, it remains unclear whether correctly inferring the other's inner, mental states on a more cognitive level (i.e., mentalizing) elicits helping behavior as well. We applied a video-based laboratory task probing empathy and a performance measure of mentalizing in adult volunteers (N = 94) and assessed to which extent they were willing to help the narrators in the videos. We replicate findings that an empathy induction leads to more prosocial decisions. Crucially, we also found that correct mentalizing increases the willingness to help. This evidence helps clarify an inconsistent picture of the relation between mentalizing and prosociality
Floating Phase in 2D ANNNI Model
We investigate whether the floating phase (where the correlation length is
infinite and the spin-spin correlation decays algebraically with distance)
exists in the temperature() - frustration parameter () phase diagram
of 2D ANNNI model. To identify this phase, we look for the region where (i)
finite size effect is prominent and (ii) some relevant physical quantity
changes somewhat sharply and this change becomes sharper as the system size
increases. For , the low temperature phase is ferromagnetic and
we study energy and magnetization. For , the low temperature
phase is antiphase and we study energy, layer magnetization, length of domain
walls running along the direction of frustration, number of domain-intercepts
that are of length 2 along the direction of frustration, and the number of
domain walls that do not touch the upper and/or lower boundary. In agreement
with some previous studies, our final conclusion is that, the floating phase
exists, if at all, only along a line.Comment: 9 pages, 17 figure
Depressive Symptoms Affect Working Memory in Healthy Older Adult Hispanics
Objectives: Low and middle income nations will experience an unprecedented growth of the elderly population and subsequent increase in age-related neurological disorders. Worldwide prevalence and incidence of all-types of neurological disorders with serious mental health complications will increase with life expectancy across the globe. Onein- ten individuals over 75 has at least moderate cognitive impairment. Prevalence of cognitive impairment doubles every 5 years thereafter. Latin America’s population of older adult’s 65 years and older is growing rapidly, yet little is known about cognitive aging among healthy older Latinos. Clinically significant depressive symptomatology is common among community-dwelling older adults and is associated with deficits across multiple cognitive domains, however much of the literature has not modeled the unique effects of depression distinct from negative and low positive affect. Our objective was to understand how mental health affects cognitive health in healthy aging Latinos.
Methods: The present study used confirmatory factor analysis (CFA) and structural equation modeling (SEM) to examine the relative effects of Negative Affect, Positive Affect and Geriatric Depression on Verbal Memory, Verbal Reasoning, Processing Speed, and Working Memory in healthy aging Latinos. Data was collected from a sample of healthy community dwelling older adults living in San Jose, Costa Rica. Modeling of latent variables attenuated error and improved measurement reliability of cognition, affect, and depression variables.
Results: Costa Ricans enjoy a notoriety for being much happier than US citizens and are renowned as one of the happiest nations in the world in global surveys. This was born out in these data. Costa Rican affective profiles differed substantively from US profiles. Levels of negative affect and depression were similar to US samples, but their levels of positive affect were much higher. Cognitive performance of these Costa Rican older adults was similar to USage and education matched peers. CFA and SEM found that increased depressive symptomatology had deleterious effects on Working Memory made up of subtest scores sampling simple attention and vigilance for numbers. Verbal Memory, Verbal Reasoning, and Processing Speed were not affected by self-reported Positive Affect, Negative Affect or Depressive symptoms.
Conclusion: Costa Rican older adults were happy, as evidenced by the high ratio of positive affect to relatively low negative affect. Thus, we were somewhat surprised to find that depressive symptoms were selectively correlated to decrements in working memory and that negative and positive affect contributed negligible amounts of variance to any of the cognitive factors. Because of the methodological rigor of latent variable analysis, these results are very specific. The Working Memory factor is not contaminated with Speed of Processing or other measured cognitive factors. Likewise, the measured Geriatric Depression represents symptoms that are richly cognitive, not overtly affective
Adrenergic/Cholinergic Immunomodulation in the Rat Model—In Vivo Veritas?
For several years, our group has been studying the in vivo role of adrenergic and cholinergic
mechanisms in the immune-neuroendocrine dialogue in the rat model. The main results of these studies can be
summarized as follows: (1) exogenous or endogenous catecholamines suppress PBL functions through alpha-2-receptor-mediated
mechanisms, lymphocytes of the spleen are resistant to adrenergic in vivo stimulation,
(2) direct or indirect cholinergic treatment leads to enhanced ex vivo functions of splenic and thymic lymphocytes
leaving PBL unaffected, (3) cholinergic pathways play a critical role in the “talking back” of the immune system to the brain,
(4) acetylcholine inhibits apoptosis of thymocytes possibly via direct effects on thymic epithelial cells, and may
thereby influence T-cell maturation, (5) lymphocytes of the various immunological compartments were found to be
equipped with the key enzymes for the synthesis of both acetylcholine and norepinephrine, and to secrete these
neurotransmitters in culture supernatant
Wave function mapping in graphene quantum dots with soft confinement
Using low-temperature scanning tunneling spectroscopy, we map the local
density of states (LDOS) of graphene quantum dots supported on Ir(111). Due to
a band gap in the projected Ir band structure around the graphene K point, the
electronic properties of the QDs are dominantly graphene-like. Indeed, we
compare the results favorably with tight binding calculations on the honeycomb
lattice based on parameters derived from density functional theory. We find
that the interaction with the substrate near the edge of the island gradually
opens a gap in the Dirac cone, which implies soft-wall confinement.
Interestingly, this confinement results in highly symmetric wave functions.
Further influences of the substrate are given by the known moir{\'e} potential
and a 10% penetration of an Ir surface resonanceComment: 7 pages, 11 figures, DFT calculations directly showing the origin of
soft confinment, correct identification of the state penetrating from Ir(111)
into graphen
Two-dimensional periodic frustrated Ising models in a transverse field
We investigate the interplay of classical degeneracy and quantum dynamics in
a range of periodic frustrated transverse field Ising systems at zero
temperature. We find that such dynamics can lead to unusual ordered phases and
phase transitions, or to a quantum spin liquid (cooperative paramagnetic) phase
as in the triangular and kagome lattice antiferromagnets, respectively. For the
latter, we further predict passage to a bond-ordered phase followed by a
critical phase as the field is tilted. These systems also provide exact
realizations of quantum dimer models introduced in studies of high temperature
superconductivity.Comment: Revised introduction; numerical error in hexagonal section correcte
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Factors Influencing Optical Coherence Tomography Peripapillary Choroidal Thickness: A Multicenter Study.
Purpose:To quantify peripapillary choroidal thickness (PCT) and the factors that influence it in healthy participants who represent the racial and ethnic composition of the U.S. population. Methods:A total of 362 healthy participants underwent optical coherence tomography (OCT) enhanced depth imaging of the optic nerve head with a 24 radial B-scan pattern aligned to the fovea to Bruch's membrane opening axis. Bruch's membrane, anterior scleral canal opening (ASCO), and the anterior scleral surface were manually segmented. PCT was measured at 100, 300, 500, 700, 900, and 1100 ÎĽm from the ASCO globally and within 12 clock-hour sectors. The effects of age, axial length, intraocular pressure, ethnicity, sex, sector, and ASCO area on PCT were assessed by ANOVA and univariable and multivariable regressions. Results:Globally, PCT was thicker further from the ASCO border and thinner with older age, longer axial length, larger ASCO area, European descent, and female sex. Among these effectors, age and axial length explained the greatest proportion of variance. The rate of age-related decline increased further from the ASCO border. Sectorally, the inferior-temporal sectors were thinnest (10.7%-20.0% thinner than the thickest sector) and demonstrated a higher rate of age-related loss (from 15.6% to 20.7% faster) at each ASCO distance. Conclusions:In healthy eyes, PCT was thinnest in the inferior temporal sectors and thinner PCT was associated with older age, European descent, longer axial length, larger ASCO area, and female sex. Among these associations, age had the strongest influence, and its effect was greatest within the inferior temporal sectors
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