911 research outputs found
Graph-based Mumford-Shah segmentation of dynamic PET with application to input function estimation
Convergence of energy-dependent incommensurate antiferromagnetic neutron scattering peaks to commensurate resonance in underdoped bilayer cuprates
The recently discovered coexistence of incommensurate antiferromagnetic
neutron scattering peaks and commensurate resonance in underdoped
YBaCuO is calling for an explanation. Within the t-J model, the
doping and energy dependence of the spin dynamics of the underdoped bilayer
cuprates in the normal state is studied based on the fermion-spin theory by
considering the bilayer interactions. Incommensurate peaks are found at
and at low energies with
initially increasing with doping at low dopings and then saturating at
higher dopings. These incommensurate peaks are suppressed, and the parameter
is reduced with increasing energy. Eventually it converges to the
resonance peak. Thus the recently observed coexistence is
interpreted in terms of bilayer interactions.Comment: 15 pages, Revtex, five figures are included, accepted for publication
in Phys. Rev.
The effects of weather on oilseed rape (OSR) yield in China: future implications of climate change
Understanding the role of climatic factors on crop yields is essential in predicting the future impact of climate change. In order to understand the influence of climatic factors on OSR, detailed farm-level panel data from 2566 farms across 67 counties of the 6 major OSR production regions in China, from the surveys conducted by the national OSR industry project between 2008 and 2013, were used to examine the contribution of changes in selected climatic variables between 2008 and 2013 to yield variation. Spatial and temporal patterns of the relationships between OSR yield, climatic factors were estimated together with the effects of farmer adaptation and management practices on yield variability. The analysis revealed that yields in the low-latitude production regions were more sensitive to temperature increases and likely to decline. Precipitation was the most influential factor on yield at the first two growth stages; temperature and sunshine hours were most important at the third and fourth growth stages, respectively. Labour input was the most influential management factor affecting yields compared with fertilizer and other inputs. The study concludes that projection of future climate change impacts will need inter alia to incorporate more sophisticated and detailed measures of climatic variables than simple means of temperature and precipitation, incorporating timing in relation to plant growth and yield
Hydrogen-bonded Silica Gels Dispersed in a Smectic Liquid Crystal: A Random Field XY System
The effect on the nematic to smectic-A transition in octylcyanobiphenyl (8CB)
due to dispersions of hydrogen-bonded silica (aerosil) particles is
characterized with high-resolution x-ray scattering. The particles form weak
gels in 8CB creating a quenched disorder that replaces the transition with the
growth of short range smectic correlations. The correlations include thermal
critical fluctuations that dominate at high temperatures and a second
contribution that quantitatively matches the static fluctuations of a random
field system and becomes important at low temperatures.Comment: 10 pages, 4 postscript figures as separate file
On Nonlinear Stochastic Balance Laws
We are concerned with multidimensional stochastic balance laws. We identify a
class of nonlinear balance laws for which uniform spatial bounds for
vanishing viscosity approximations can be achieved. Moreover, we establish
temporal equicontinuity in of the approximations, uniformly in the
viscosity coefficient. Using these estimates, we supply a multidimensional
existence theory of stochastic entropy solutions. In addition, we establish an
error estimate for the stochastic viscosity method, as well as an explicit
estimate for the continuous dependence of stochastic entropy solutions on the
flux and random source functions. Various further generalizations of the
results are discussed
Coherent quantum transport in narrow constrictions in the presence of a finite-range longitudinally polarized time-dependent field
We have studied the quantum transport in a narrow constriction acted upon by
a finite-range longitudinally polarized time-dependent electric field. The
electric field induces coherent inelastic scatterings which involve both
intra-subband and inter-sideband transitions. Subsequently, the dc conductance
G is found to exhibit suppressed features. These features are recognized as the
quasi-bound-state (QBS) features which are associated with electrons making
transitions to the vicinity of a subband bottom, of which the density of states
is singular. Having valley-like instead of dip-like structures, these QBS
features are different from the G characteristics for constrictions acted upon
by a finite-range time-modulated potential. In addition, the subband bottoms in
the time-dependent electric field region are shifted upward by an energy
proportional to the square of the electric field and inversely proportional to
the square of the frequency. This effective potential barrier is originated
from the square of the vector potential and it leads to the interesting
field-sensitive QBS features. An experimental set-up is proposed for the
observation of these features.Comment: 8 pages, 4 figure
Dynamics of a large extra dimension inspired hybrid inflation model
In low scale quantum gravity scenarios the fundamental scale of nature can be
as low as TeV, in order to address the naturalness of the electroweak scale. A
number of difficulties arise in constructing specific models; stabilisation of
the radius of the extra dimensions, avoidance of overproduction of Kaluza Klein
modes, achieving successful baryogenesis and production of a close to
scale-invariant spectrum of density perturbations with the correct amplitude.
We examine in detail the dynamics, including radion stabilisation, of a hybrid
inflation model that has been proposed in order to address these difficulties,
where the inflaton is a gauge singlet residing in the bulk. We find that for a
low fundamental scale the phase transition, which in standard four dimensional
hybrid models usually ends inflation, is slow and there is second phase of
inflation lasting for a large number of e-foldings. The density perturbations
on cosmologically interesting scales exit the Hubble radius during this second
phase of inflation, and we find that their amplitude is far smaller than is
required. We find that the duration of the second phase of inflation can be
short, so that cosmologically interesting scales exit the Hubble radius prior
to the phase transition, and the density perturbations have the correct
amplitude, only if the fundamental scale takes an intermediate value. Finally
we comment briefly on the implications of an intermediate fundamental scale for
the production of primordial black holes and baryogenesis.Comment: 9 pages, 2 figures version to appear in Phys. Rev. D, additional
references and minor changes to discussio
Interaction of N solitons in the massive Thirring model and optical gap system: the Complex Toda Chain Model
Using the Karpman-Solov''ev quasiparticle approach for soliton-soliton
interaction I show that the train propagation of N well separated solitons of
the massive Thirring model is described by the complex Toda chain with N nodes.
For the optical gap system a generalised (non-integrable) complex Toda chain is
derived for description of the train propagation of well separated gap
solitons. These results are in favor of the recently proposed conjecture of
universality of the complex Toda chain.Comment: RevTex, 23 pages, no figures. Submitted to Physical Review
Global epidemiology of avian influenza A H5N1 virus infection in humans, 1997–2015: a systematic review of individual case data
Avian influenza A H5N1 viruses have caused many, typically severe, human infections since the first human case was reported in 1997. However, no comprehensive epidemiological analysis of global human cases of H5N1 from 1997 to 2015 exists. Moreover, few studies have examined in detail the changing epidemiology of human H5N1 cases in Egypt, especially given the outbreaks since November, 2014, which have the highest number of cases ever reported worldwide in a similar period. Data on individual patients were collated from different sources using a systematic approach to describe the global epidemiology of 907 human H5N1 cases between May, 1997, and April, 2015. The number of affected countries rose between 2003 and 2008, with expansion from east and southeast Asia, then to west Asia and Africa. Most cases (67·2%) occurred from December to March, and the overall case-fatality risk was 483 (53·5%) of 903 cases which varied across geographical regions. Although the incidence in Egypt has increased dramatically since November, 2014, compared with the cases beforehand, there were no significant differences in the fatality risk, history of exposure to poultry, history of patient contact, and time from onset to hospital admission in the recent cases
4pi Models of CMEs and ICMEs
Coronal mass ejections (CMEs), which dynamically connect the solar surface to
the far reaches of interplanetary space, represent a major anifestation of
solar activity. They are not only of principal interest but also play a pivotal
role in the context of space weather predictions. The steady improvement of
both numerical methods and computational resources during recent years has
allowed for the creation of increasingly realistic models of interplanetary
CMEs (ICMEs), which can now be compared to high-quality observational data from
various space-bound missions. This review discusses existing models of CMEs,
characterizing them by scientific aim and scope, CME initiation method, and
physical effects included, thereby stressing the importance of fully 3-D
('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication
in Solar Physics (SUN-360 topical issue
- …