346 research outputs found
Images of psychiatry and psychiatrists
Peer reviewedPublisher PD
Magnetic ground state and magnon-phonon interaction in multiferroic h-YMnO
Inelastic neutron scattering has been used to study the magneto-elastic
excitations in the multiferroic manganite hexagonal YMnO. An avoided
crossing is found between magnon and phonon modes close to the Brillouin zone
boundary in the -plane. Neutron polarization analysis reveals that this
mode has mixed magnon-phonon character. An external magnetic field along the
-axis is observed to cause a linear field-induced splitting of one of the
spin wave branches. A theoretical description is performed, using a Heisenberg
model of localized spins, acoustic phonon modes and a magneto-elastic coupling
via the single-ion magnetostriction. The model quantitatively reproduces the
dispersion and intensities of all modes in the full Brillouin zone, describes
the observed magnon-phonon hybridized modes, and quantifies the magneto-elastic
coupling. The combined information, including the field-induced magnon
splitting, allows us to exclude several of the earlier proposed models and
point to the correct magnetic ground state symmetry, and provides an effective
dynamic model relevant for the multiferroic hexagonal manganites.Comment: 12 pages, 10 figure
Shot noise of a quantum dot with non-Fermi liquid correlations
The shot noise of a one-dimensional wire interrupted by two barriers shows
interesting features related to the interplay between Coulomb blockade effects,
Luttinger correlations and discrete excitations. At small bias the Fano factor
reaches the lowest attainable value, 1/2, irrespective of the ratio of the two
junction resistances. At larger voltages this asymmetry is power-law
renormalized by the interaction strength. We discuss how the measurement of
current and these features of the noise allow to extract the Luttinger liquid
parameter.Comment: 4 pages, 3 figures,to be published in Phys. Rev. B. For high
resolution image of Fig.1 see http://server1.fisica.unige.it/~braggio/doc.ht
Full Counting Statistics of Charge Transfer in Coulomb Blockade Systems
Full counting statistics (FCS) of charge transfer in mesoscopic systems has
recently become a subject of significant interest, since it proves to reveal an
important information about the system which can be hardly assessed by other
means. While the previous research mostly addressed the FCS of non- interacting
systems, the present paper deals with the FCS in the limit of strong
interaction. In this Coulomb blockade limit the electron dynamics is known to
be governed by a master equation. We develop a general scheme to evaluate the
FCS in such case, this being the main result of the work presented. We
illustrate the scheme, by applying it to concrete systems. For generic case of
a single resonant level we establish the equivalence of scattering and master
equation approach to FCS. Further we study a single Coulomb blockade island
with two and three leads attached and compare the FCS in this case with our
recent results concerning an open dot either with two and three terminals. We
demonstrate that Coulomb interaction suppresses the relative probabilities of
large current fluctuations.Comment: 17 pages, 16 figure
Shot noise of coupled semiconductor quantum dots
The low-frequency shot noise properties of two electrostatically coupled
semiconductor quantum dot states which are connected to emitter/collector
contacts are studied. A master equation approach is used to analyze the bias
voltage dependence of the Fano factor as a measure of temporal correlations in
tunneling current caused by Pauli's exclusion principle and the Coulomb
interaction. In particular, the influence of the Coulomb interaction on the
shot noise behavior is discussed in detail and predictions for future
experiments will be given. Furthermore, we propose a mechanism for negative
differential conductance and investigate the related super-Poissonian shot
noise.Comment: submitted to PR
Distribution of transmitted charge through a double-barrier junction
The distribution function of transmitted charge through a double-barrier
junction is studied at zero temperature and at small applied voltage. Both a
semiclassical model, in which the transport is described by jump rates, and a
quantum mechanical model, which averages over resonant and non-resonant states,
are used to determine the characteristic function of the transmitted electrons.
It is demonstrated that for large times the logarithm of the characteristic
function is equal within the two approaches. The charge distribution is in
between a Gaussian and a Poissonian distribution if both barriers have equal
height and reduces to a Poissonian if one barrier is much higher than the
other.Comment: 6 pages, revtex, 2 figures include
Early and Middle Holocene Hunter-Gatherer Occupations in Western Amazonia: The Hidden Shell Middens
We report on previously unknown early archaeological sites in the Bolivian lowlands, demonstrating for the first time early and middle Holocene human presence in western Amazonia. Multidisciplinary research in forest islands situated in seasonally-inundated savannahs has revealed stratified shell middens produced by human foragers as early as 10,000 years ago, making them the oldest archaeological sites in the region. The absence of stone resources and partial burial by recent alluvial sediments has meant that these kinds of deposits have, until now, remained unidentified. We conducted core sampling, archaeological excavations and an interdisciplinary study of the stratigraphy and recovered materials from three shell midden mounds. Based on multiple lines of evidence, including radiocarbon dating, sedimentary proxies (elements, steroids and black carbon), micromorphology and faunal analysis, we demonstrate the anthropogenic origin and antiquity of these sites. In a tropical and geomorphologically active landscape often considered challenging both for early human occupation and for the preservation of hunter-gatherer sites, the newly discovered shell middens provide evidence for early to middle Holocene occupation and illustrate the potential for identifying and interpreting early open-air archaeological sites in western Amazonia. The existence of early hunter-gatherer sites in the Bolivian lowlands sheds new light on the region's past and offers a new context within which the late Holocene "Earthmovers" of the Llanos de Moxos could have emerged. © 2013 Lombardo et al
Cross-sectional associations between air pollution and chronic bronchitis: an ESCAPE meta-analysis across five cohorts
BACKGROUND: This study aimed to assess associations of outdoor air pollution on prevalence of chronic bronchitis symptoms in adults in five cohort studies (Asthma-E3N, ECRHS, NSHD, SALIA, SAPALDIA) participating in the European Study of Cohorts for Air Pollution Effects (ESCAPE) project. METHODS: Annual average particulate matter (PM10, PM2.5, PMabsorbance, PMcoarse), NO2, nitrogen oxides (NOx) and road traffic measures modelled from ESCAPE measurement campaigns 2008-2011 were assigned to home address at most recent assessments (1998-2011). Symptoms examined were chronic bronchitis (cough and phlegm for ≥3 months of the year for ≥2 years), chronic cough (with/without phlegm) and chronic phlegm (with/without cough). Cohort-specific cross-sectional multivariable logistic regression analyses were conducted using common confounder sets (age, sex, smoking, interview season, education), followed by meta-analysis. RESULTS: 15 279 and 10 537 participants respectively were included in the main NO2 and PM analyses at assessments in 1998-2011. Overall, there were no statistically significant associations with any air pollutant or traffic exposure. Sensitivity analyses including in asthmatics only, females only or using back-extrapolated NO2 and PM10 for assessments in 1985-2002 (ECRHS, NSHD, SALIA, SAPALDIA) did not alter conclusions. In never-smokers, all associations were positive, but reached statistical significance only for chronic phlegm with PMcoarse OR 1.31 (1.05 to 1.64) per 5 µg/m(3) increase and PM10 with similar effect size. Sensitivity analyses of older cohorts showed increased risk of chronic cough with PM2.5abs (black carbon) exposures. CONCLUSIONS: Results do not show consistent associations between chronic bronchitis symptoms and current traffic-related air pollution in adult European populations
Sprint interval and sprint continuous training increases circulating CD34+ cells and cardio-respiratory fitness in young healthy women
The improvement of vascular health in the exercising limb can be attained by sprint interval training (SIT).
However, the effects on systemic vascular function and on circulating angiogenic cells (CACs) which may contribute to endothelial repair have not been investigated. Additionally, a comparison between SIT and sprint continuous training (SCT) which is less time committing has not been made
- …