1,026 research outputs found
Some Remarks on the Pade Unitarization of Low-Energy Amplitudes
We present a critical analysis of Pade-based methods for the unitarization of
low energy amplitudes. We show that the use of certain Pade Approximants to
describe the resonance region may lead to inaccurate determinations. In
particular, we find that in the Linear Sigma Model the unitarization of the low
energy amplitude through the inverse amplitude method produces essentially
incorrect results for the mass and width of the sigma. Alternative sequences of
Pades are studied and we find that the diagonal sequences (i.e., [N/N]) have
much better convergence properties.Comment: 12 pages, 4 fig
Giant magnetoresistance of multiwall carbon nanotubes: modeling the tube/ferromagnetic-electrode burying contact
We report on the giant magnetoresistance (GMR) of multiwall carbon nanotubes
with ultra small diameters. In particular, we consider the effect of the
inter-wall interactions and the lead/nanotube coupling. Comparative studies
have been performed to show that in the case when all walls are well coupled to
the electrodes, the so-called inverse GMR can appear. The tendency towards a
negative GMR depends on the inter-wall interaction and on the nanotube le ngth.
If, however, the inner nanotubes are out of contact with one of the electrodes,
the GMR remains positive even for relatively strong inter-wall interactions
regardless of the outer nanotube length. These results shed additional light on
recently reported experimental data, where an inverse GMR was found in some
multiwall carbon nanotube samples.Comment: 5 pages, 5 figure
A novel hybrid algorithm for mean-CVaR portfolio selection with real-world constraints
In this paper, we employ the Conditional Value at Risk (CVaR) to measure the portfolio risk, and propose a mean-CVaR portfolio selection model. In addition, some real-world constraints are considered. The constructed model is a non-linear discrete optimization problem and difficult to solve by the classic optimization techniques. A novel hybrid algorithm based particle swarm optimization (PSO) and artificial bee colony (ABC) is designed for this problem. The hybrid algorithm introduces the ABC operator into PSO. A numerical example is given to illustrate the modeling idea of the paper and the effectiveness of the proposed hybrid algorithm
The resonance in s wave scatterings
A new unitarization approach incorporated with chiral symmetry is established
and applied to study the elastic scatterings. We demonstrate that the
resonance exists, if the scattering length parameter in the I=1/2, J=0
channel does not deviate much from its value predicted by chiral perturbation
theory. The mass and width of the resonance is found to be
, , obtained by fitting the
LASS data up to 1430MeV. Better determination to the pole parameters is
possible if the chiral predictions on scattering lengths are taken into
account.Comment: Minor corrections made on discussions and typos. 1 ref. added version
to appear in Nuclear Physics
Hydraulic and photosynthetic limitations prevail over root non-structural carbohydrate reserves as drivers of resprouting in two Mediterranean oaks
Resprouting is an ancestral trait in angiosperms that confers resilience after perturbations. As climate change increases stress, resprouting vigor is declining in many forest regions, but the underlying mechanism is poorly understood. Resprouting in woody plants is thought to be primarily limited by the availability of non-structural carbohydrate reserves (NSC), but hydraulic limitations could also be important. We conducted a multifactorial experiment with two levels of light (ambient, 2–3% of ambient) and three levels of water stress (0, 50 and 80 percent losses of hydraulic conductivity, PLC) on two Mediterranean oaks (Quercus ilex and Q. faginea) under a rain-out shelter (n = 360). The proportion of resprouting individuals after canopy clipping declined markedly as PLC increased for both species. NSC concentrations affected the response of Q. ilex, the species with higher leaf construction costs, and its effect depended on the PLC. The growth of resprouting individuals was largely dependent on photosynthetic rates for both species, while stored NSC availability and hydraulic limitations played minor and non-significant roles, respectively. Contrary to conventional wisdom, our results indicate that resprouting in oaks may be primarily driven by complex interactions between hydraulics and carbon sources, whereas stored NSC play a significant but secondary role
A survey of partial differential equations in geometric design
YesComputer aided geometric design is an area
where the improvement of surface generation techniques
is an everlasting demand since faster and more accurate
geometric models are required. Traditional methods
for generating surfaces were initially mainly based
upon interpolation algorithms. Recently, partial differential
equations (PDE) were introduced as a valuable
tool for geometric modelling since they offer a number
of features from which these areas can benefit. This work
summarises the uses given to PDE surfaces as a surface
generation technique togethe
On the stability and uniqueness of the flow of a fluid through a porous medium
© 2016, The Author(s). In this short note, we study the stability of flows of a fluid through porous media that satisfies a generalization of Brinkman’s equation to include inertial effects. Such flows could have relevance to enhanced oil recovery and also to the flow of dense liquids through porous media. In any event, one cannot ignore the fact that flows through porous media are inherently unsteady, and thus, at least a part of the inertial term needs to be retained in many situations. We study the stability of the rest state and find it to be asymptotically stable. Next, we study the stability of a base flow and find that the flow is asymptotically stable, provided the base flow is sufficiently slow. Finally, we establish results concerning the uniqueness of the flow under appropriate conditions, and present some corresponding numerical results
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
Specific Heat of Liquid Helium in Zero Gravity very near the Lambda Point
We report the details and revised analysis of an experiment to measure the
specific heat of helium with subnanokelvin temperature resolution near the
lambda point. The measurements were made at the vapor pressure spanning the
region from 22 mK below the superfluid transition to 4 uK above. The experiment
was performed in earth orbit to reduce the rounding of the transition caused by
gravitationally induced pressure gradients on earth. Specific heat measurements
were made deep in the asymptotic region to within 2 nK of the transition. No
evidence of rounding was found to this resolution. The optimum value of the
critical exponent describing the specific heat singularity was found to be a =
-0.0127+ - 0.0003. This is bracketed by two recent estimates based on
renormalization group techniques, but is slightly outside the range of the
error of the most recent result. The ratio of the coefficients of the leading
order singularity on the two sides of the transition is A+/A- =1.053+ - 0.002,
which agrees well with a recent estimate. By combining the specific heat and
superfluid density exponents a test of the Josephson scaling relation can be
made. Excellent agreement is found based on high precision measurements of the
superfluid density made elsewhere. These results represent the most precise
tests of theoretical predictions for critical phenomena to date.Comment: 27 Pages, 20 Figure
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Supramolecular chemistry enables vat photopolymerization 3D printing of novel water-soluble tablets
YesVat photopolymerization has garnered interest from pharmaceutical researchers for the fabrication of personalised medicines, especially for drugs that require high precision dosing or are heat labile. However, the 3D printed structures created thus far have been insoluble, limiting printable dosage forms to sustained-release systems or drug-eluting medical devices which do not require dissolution of the printed matrix. Resins that produce water-soluble structures will enable more versatile drug release profiles and expand potential applications. To achieve this, instead of employing cross-linking chemistry to fabricate matrices, supramolecular chemistry may be used to impart dynamic interaction between polymer chains. In this study, water-soluble drug-loaded printlets (3D printed tablets) are fabricated via digital light processing (DLP) 3DP for the first time. Six formulations with varying ratios of an electrolyte acrylate
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