4,946 research outputs found
Supersymmetry-Breaking Nonlinear Sigma Models
We consider a novel class of constraints on chiral superfields to obtain
supersymmetric nonlinear sigma models in four spacetime dimensions, which
strictly combine the internal symmetry breaking with spontaneous supersymmetry
breaking. The resultant massless modes can be exclusively Nambu-Goldstone
bosons without their complex partners and the goldstino that is charged under
the internal symmetry. The massive modes show a peculiar relation among their
masses and the scales of symmetry breakings.Comment: 9 pages, comments and references adde
Microfinance and Household Poverty Reduction: Empirical Evidence from Rural Pakistan
This study examines whether household access to microfinance reduces poverty in Pakistan and, if so, how and to what extent. It draws on primary empirical data gathered by interviewing 1,132 households in which both borrower and non-borrower households were interviewed in 2008-9. Sample selection biases have been controlled partially by using propensity score matching. The study reveals that microfinance programmes had a positive impact on the participating households. Poverty-reducing effects were observed on a number of indicators, including expenditure on healthcare, clothing, household income, and on certain dwelling characteristics, such as water supply and quality of roofing and walls
Symmetry breaking and other phenomena in the optimization of eigenvalues for composite membranes
We consider the following eigenvalue optimization problem: Given a bounded
domain and numbers , ,
find a subset of area for which the first Dirichlet
eigenvalue of the operator is as small as possible.
We prove existence of solutions and investigate their qualitative properties.
For example, we show that for some symmetric domains (thin annuli and dumbbells
with narrow handle) optimal solutions must possess fewer symmetries than
; on the other hand, for convex reflection symmetries are
preserved.
Also, we present numerical results and formulate some conjectures suggested
by them.Comment: 24 pages; 3 figures (as separate files); (shortened previous
version); to appear in Comm. Math. Phy
Timing of sea ice retreat can alter phytoplankton community structure in the western Arctic Ocean
This study assesses the response of phytoplankton assemblages to recent
climate change, especially with regard to the shrinking of sea ice in the
northern Chukchi Sea of the western Arctic Ocean. Distribution patterns of
phytoplankton groups in the late summers of 2008–2010 were analysed based
on HPLC pigment signatures and, the following four major algal groups were
inferred via multiple regression and cluster analyses: prasinophytes,
diatoms, haptophytes and dinoflagellates. A remarkable interannual
difference in the distribution pattern of the groups was found in the
northern basin area. Haptophytes dominated and dispersed widely in warm
surface waters in 2008, whereas prasinophytes dominated in cold water in
2009 and 2010. A difference in the onset date of sea ice retreat was evident
among years–the sea ice retreat in 2008 was 1–2 months earlier than in
2009 and 2010. The spatial distribution of early sea ice retreat matched the
areas in which a shift in algal community composition was observed.
Steel-Dwass's multiple comparison tests were used to assess the physical,
chemical and biological parameters of the four clusters. We found a
statistically significant difference in temperature between the
haptophyte-dominated cluster and the other clusters, suggesting that the
change in the phytoplankton communities was related to the earlier sea ice
retreat in 2008 and the corollary increase in sea surface temperatures.
Longer periods of open water during the summer, which are expected in the
future, may affect food webs and biogeochemical cycles in the western Arctic
due to shifts in phytoplankton community structure
Intra-Landau level polarization effect for a striped Hall gas
We calculate the polarization function including only intra-Landau level
correlation effects of striped Hall gas. Using the polarization function, the
dielectric function, the dispersion of the plasmon and the correlation energy
are computed in a random phase approximation (RPA) and generalized random phase
approximation (GRPA). The plasmon becomes anisotropic and gapless owing to the
anisotropy of the striped Hall gas and two dimensionality of the quantum Hall
system. The plasmon approximately agrees with the phonon derived before by the
single mode approximation. The (G)RPA correlation energy is compared with other
numerical calculations.Comment: 15 pages,15 figures, revtex4, published versio
Yellow fever in Asia - a risk analysis
Background There is concern about the risk of yellow fever (YF) establishment in Asia, owing to rising numbers of urban outbreaks in endemic countries and globalisation. Following an outbreak in Angola in 2016, YF cases were introduced into China. Prior to this, YF had never been recorded in Asia, despite climatic suitability and the presence of mosquitoes. An outbreak in Asia could result in widespread fatalities and huge economic impact. Therefore, quantifying the potential risk of YF outbreaks in Asia is a public health priority. Methods Using international flight data and YF incidence estimates from 2016, we quantified the risk of YF introduction via air travel into Asia. In locations with evidence of a competent mosquito population, the potential for autochthonous YF transmission was estimated using a temperature-dependent model of the reproduction number and a branching process model assuming a negative binomial distribution. Results In total, 25 cities across Asia were estimated to be at risk of receiving at least one YF viraemic traveller during 2016. At their average temperatures, we estimated the probability of autochthonous transmission to be <50% in all cities, which was primarily due to the limited number of estimated introductions that year. Conclusion Despite the rise in air travel, we found low support for travel patterns between YF endemic countries and Asia resulting in autochthonous transmission during 2016. This supports the historic absence of YF in Asia and suggests it could be due to a limited number of introductions in previous years. Future increases in travel volumes or YF incidence can increase the number of introductions and the risk of autochthonous transmission. Given the high proportion of asymptomatic or mild infections and the challenges of YF surveillance, our model can be used to estimate the introduction and outbreak risk and can provide useful information to surveillance systems
First-Principles Computation of YVO3; Combining Path-Integral Renormalization Group with Density-Functional Approach
We investigate the electronic structure of the transition-metal oxide YVO3 by
a hybrid first-principles scheme. The density-functional theory with the
local-density-approximation by using the local muffin-tin orbital basis is
applied to derive the whole band structure. The electron degrees of freedom far
from the Fermi level are eliminated by a downfolding procedure leaving only the
V 3d t2g Wannier band as the low-energy degrees of freedom, for which a
low-energy effective model is constructed. This low-energy effective
Hamiltonian is solved exactly by the path-integral renormalization group
method. It is shown that the ground state has the G-type spin and the C-type
orbital ordering in agreement with experimental indications. The indirect
charge gap is estimated to be around 0.7 eV, which prominently improves the
previous estimates by other conventional methods
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