1,391 research outputs found
CLIMATE CHANGE, AGRICULTURE AND POVERTY
Even though much has been written about climate change and poverty as distinct and complex problems, the link between them has received little attention. Understanding this link is vital for the formulation of effective policy responses to climate change. In this article, we focus on agriculture as a primary means by which the impacts of climate change are transmitted to the poor, and as a sector at the forefront of climate change mitigation efforts in developing countries. In so doing, we offer some important insights that may help shape future policies as well as ongoing research in this area.Agricultural and Food Policy, Environmental Economics and Policy, Food Security and Poverty, Resource /Energy Economics and Policy,
Optical Conductivity of Clean Metals
We briefly review some basic aspects of transport in clean metals focusing on
the role of electron-electron interactions and neglecting the effects of
impurities, phonons and interband transitions. Both for small Fermi surfaces of
two and three-dimensional metals and open Fermi surfaces of quasi
one-dimensional metals the dc conductivity sigma is largely dominated by
momentum and pseudo-momentum conservation, respectively. In general, the
frequency and temperature dependencies of sigma(w,T) have very little in
common. For small Fermi surfaces in three dimensions we find for example that
the scattering rate is quadratic in frequency, Gamma \propto w^2, even in the
absence of a T^2 contribution.Comment: invited paper for a special edition of Annalen der Physik
commemorating P. Drud
Mott transition of fermionic atoms in a three-dimensional optical trap
We study theoretically the Mott metal-insulator transition for a system of
fermionic atoms confined in a three-dimensional optical lattice and a harmonic
trap. We describe an inhomogeneous system of several thousand sites using an
adaptation of dynamical mean field theory solved efficiently with the numerical
renormalization group method. Above a critical value of the on-site
interaction, a Mott-insulating phase appears in the system. We investigate
signatures of the Mott phase in the density profile and in time-of-flight
experiments.Comment: 4 pages and 5 figure
Transport in Almost Integrable Models: Perturbed Heisenberg Chains
The heat conductivity kappa(T) of integrable models, like the one-dimensional
spin-1/2 nearest-neighbor Heisenberg model, is infinite even at finite
temperatures as a consequence of the conservation laws associated with
integrability. Small perturbations lead to finite but large transport
coefficients which we calculate perturbatively using exact diagonalization and
moment expansions. We show that there are two different classes of
perturbations. While an interchain coupling of strength J_perp leads to
kappa(T) propto 1/J_perp^2 as expected from simple golden-rule arguments, we
obtain a much larger kappa(T) propto 1/J'^4 for a weak next-nearest neighbor
interaction J'. This can be explained by a new approximate conservation law of
the J-J' Heisenberg chain.Comment: 4 pages, several minor modifications, title change
Lower bounds for the conductivities of correlated quantum systems
We show how one can obtain a lower bound for the electrical, spin or heat
conductivity of correlated quantum systems described by Hamiltonians of the
form H = H0 + g H1. Here H0 is an interacting Hamiltonian characterized by
conservation laws which lead to an infinite conductivity for g=0. The small
perturbation g H1, however, renders the conductivity finite at finite
temperatures. For example, H0 could be a continuum field theory, where momentum
is conserved, or an integrable one-dimensional model while H1 might describe
the effects of weak disorder. In the limit g to 0, we derive lower bounds for
the relevant conductivities and show how they can be improved systematically
using the memory matrix formalism. Furthermore, we discuss various applications
and investigate under what conditions our lower bound may become exact.Comment: Title changed; 9 pages, 2 figure
Kondo proximity effect: How does a metal penetrate into a Mott insulator?
We consider a heterostructure of a metal and a paramagnetic Mott insulator
using an adaptation of dynamical mean field theory to describe inhomogeneous
systems. The metal can penetrate into the insulator via the Kondo effect. We
investigate the scaling properties of the metal-insulator interface close to
the critical point of the Mott insulator. At criticality, the quasiparticle
weight decays as 1/x^2 with distance x from the metal within our mean field
theory. Our numerical results (using the numerical renormalization group as an
impurity solver) show that the prefactor of this power law is extremely small.Comment: 4 pages, 3 figure
Non-Equilibrium Transport through a Kondo-Dot in a Magnetic Field: Perturbation Theory and Poor Man's Scaling
We consider electron transport through a quantum dot described by the Kondo
model in the regime of large transport voltage V in the presence of a magnetic
field B with max(V,B) >> T_K. The electric current I and the local
magnetization M are found to be universal functions of V/T_K and B/T_K, where
T_K is the equilibrium Kondo temperature. We present a generalization of the
perturbative renormalization group to frequency dependent coupling functions,
as necessitated by the structure of bare perturbation theory. We calculate I
and M within a poor man's scaling approach and find excellent agreement with
experiment.Comment: version accepted in PRL, notations changed, parts rewritten, figures
modified, references and some corrections adde
Anionic lipids enriched at the ExPortal of Streptococcus pyogenes
The ExPortal of Streptococcus pyogenes is a membrane microdomain dedicated to the secretion and folding of proteins. We investigated the lipid composition of the ExPortal by examining the distribution of anionic membrane phospholipids. Staining with 10-N-nonyl-acridine orange revealed a single microdomain enriched with an anionic phospholipid whose staining characteristics and behavior in a cardiolipin-deficient mutant were characteristic of phosphatidylglycerol. Furthermore, the location of the microdomain corresponded to the site of active protein secretion at the ExPortal. These results indicate that the ExPortal is an asymmetric lipid microdomain, whose enriched content of anionic phospholipids may play an important role in ExPortal organization and protein trafficking
Transport in dimerized and frustrated spin systems
We analyze the Drude weight for both spin and thermal transport of
one-dimensional spin-1/2 systems by means of exact diagonalization at finite
temperatures. While the Drude weights are non-zero for finite systems, we find
indications of a vanishing of the Drude weights in the thermodynamic limit for
non-integrable models implying normal transport behavior.Comment: 2 pages, 1 figure. Proceedings of the ICM 2003, Rom
- …