964 research outputs found
Non-exponential relaxation and hierarchically constrained dynamics in a protein
A scaling analysis within a model of hierarchically constrained dynamics is
shown to reproduce the main features of non-exponential relaxation observed in
kinetic studies of carbonmonoxymyoglobin.Comment: 4 pages, 3 figures in text. Reference errors have been correcte
Potential climate change impacts on the water balance of subcatchments of the River Spree, Germany
Lusatia is considered one of the driest regions of Germany. The climatic water balance is negative even under current climate conditions. Due to global climate change, increased temperatures and a shift of precipitation from summer to winter are expected. Therefore, it is of major interest whether the excess water in winter can be stored and to which extent it is used up on increasing evapotranspiration.
Thus, this study focuses on estimating potential climate change impacts on the water balance of two subcatchments of the River Spree using the Soil and Water Integrated Model (SWIM). Climate input was taken from 100 realisations each of two scenarios of the STatistical Analogue Resampling scheme STAR assuming a further temperature increase of 0 K (scenario A) and 2 K by the year 2055 (scenario B) respectively. Resulting from increased temperatures and a shift in precipitation from summer to winter actual evapotranspiration is supposed to increase in winter and early spring, but to decrease in later spring and early summer. This is less pronounced for scenario A than for scenario B. Consequently, also the decrease in discharge and groundwater recharge in late spring is lower for scenario A than for scenario B. The highest differences of runoff generation and groundwater recharge between the two scenarios but also the highest ranges within the scenarios occur in summer and early autumn. It is planned to estimate potential climate change for the catchments of Spree, Schwarze Elster and Lusatian Neisse
Hydrogen and fuel cell technologies for heating: A review
The debate on low-carbon heat in Europe has become focused on a narrow range of technological options and has largely neglected hydrogen and fuel cell technologies, despite these receiving strong support towards commercialisation in Asia. This review examines the potential benefits of these technologies across different markets, particularly the current state of development and performance of fuel cell micro-CHP. Fuel cells offer some important benefits over other low-carbon heating technologies, and steady cost reductions through innovation are bringing fuel cells close to commercialisation in several countries. Moreover, fuel cells offer wider energy system benefits for high-latitude countries with peak electricity demands in winter. Hydrogen is a zero-carbon alternative to natural gas, which could be particularly valuable for those countries with extensive natural gas distribution networks, but many national energy system models examine neither hydrogen nor fuel cells for heating. There is a need to include hydrogen and fuel cell heating technologies in future scenario analyses, and for policymakers to take into account the full value of the potential contribution of hydrogen and fuel cells to low-carbon energy systems
Gluon Structure Function of a Color Dipole in the Light-Cone Limit of Lattice QCD
We calculate the gluon structure function of a color dipole in
near-light-cone SU(2) lattice QCD as a function of . The quark and
antiquark are external non-dynamical degrees of freedom which act as sources of
the gluon string configuration defining the dipole. We compute the color dipole
matrix element of transversal chromo-electric and chromo-magnetic field
operators separated along a direction close to the light cone, the Fourier
transform of which is the gluon structure function. As vacuum state in the pure
glue sector, we use a variational ground state of the near-light-cone
Hamiltonian. We derive a recursion relation for the gluon structure function on
the lattice similar to the perturbative DGLAP equation. It depends on the
number of transversal links assembling the Schwinger string of the dipole.
Fixing the mean momentum fraction of the gluons to the "experimental value" in
a proton, we compare our gluon structure function for a dipole state with four
links with the NLO \emph{MRST} 2002 and the \emph{CTEQAB-0} parameterizations
at . Within the systematic uncertainty we find rather
good agreement. We also discuss the low behavior of the gluon structure
function in our model calculation.Comment: 44 pages, 10 figures, to be in accordance with the variant submitted
to Phys. Rev.
Potential climate change impacts on the water balance of subcatchments of the River Spree, Germany
Lusatia is considered one of the driest regions of Germany. The climatic
water balance is negative even under current climate conditions. Due to
global climate change, increased temperatures and a shift of precipitation
from summer to winter are expected. Therefore, it is of major interest
whether the excess water in winter can be stored and to which extent it is
used up on increasing evapotranspiration.
Thus, this study focuses on estimating potential climate change impacts on
the water balance of two subcatchments of the River Spree using the Soil and
Water Integrated Model (SWIM). Climate input was taken from 100 realisations
each of two scenarios of the STatistical Analogue Resampling scheme STAR
assuming a further temperature increase of 0 K (scenario A) and 2 K by the
year 2055 (scenario B) respectively. Resulting from increased temperatures
and a shift in precipitation from summer to winter actual evapotranspiration
is supposed to increase in winter and early spring, but to decrease in later
spring and early summer. This is less pronounced for scenario A than for
scenario B. Consequently, also the decrease in discharge and groundwater
recharge in late spring is lower for scenario A than for scenario B. The
highest differences of runoff generation and groundwater recharge between
the two scenarios but also the highest ranges within the scenarios occur in
summer and early autumn. It is planned to estimate potential climate change
for the catchments of Spree, Schwarze Elster and Lusatian Neisse
Theory of Exciton Migration and Field-Induced Dissociation in Conjugated Polymers
The interplay of migration, recombination, and dissociation of excitons in
disordered media is studied theoretically in the low temperature regime. An
exact expression for the photoluminescence spectrum is obtained. The theory is
applied to describe the electric field-induced photoluminescence-quenching
experiments by Kersting et al. [Phys. Rev. Lett. 73, 1440 (1994)] and Deussen
et al. [Synth. Met. 73, 123 (1995)] on conjugated polymer systems. Good
agreement with experiment is obtained using an on-chain dissociation mechanism,
which implies a separation of the electron-hole pair along the polymer chain.Comment: 4 pages, RevTeX, 2 Postscript figure
Monte-Carlo Simulations of the Dynamical Behavior of the Coulomb Glass
We study the dynamical behavior of disordered many-particle systems with
long-range Coulomb interactions by means of damage-spreading simulations. In
this type of Monte-Carlo simulations one investigates the time evolution of the
damage, i.e. the difference of the occupation numbers of two systems, subjected
to the same thermal noise. We analyze the dependence of the damage on
temperature and disorder strength. For zero disorder the spreading transition
coincides with the equilibrium phase transition, whereas for finite disorder,
we find evidence for a dynamical phase transition well below the transition
temperature of the pure system.Comment: 10 pages RevTeX, 8 Postscript figure
Nonequilibrium relaxation and scaling properties of the two-dimensional Coulomb glass in the aging regime
We employ Monte Carlo simulations to investigate the two-time density
autocorrelation function for the two-dimensional Coulomb glass. We find that
the nonequilibrium relaxation properties of this highly correlated disordered
system can be described by a full aging scaling ansatz. The scaling exponents
are non-universal, and depend on temperature and charge density.Comment: 6 pages, 3 figures included; revised version: corrected exponents,
and some additional explanations and references added; to appear in EP
Quarnet Inference Rules for Level-1 Networks
An important problem in phylogenetics is the construction of phylogenetic trees. One way to approach this problem, known as the supertree method, involves inferring a phylogenetic tree with leaves consisting of a set X of species from a collection of trees, each having leaf-set some subset of X. In the 1980s, Colonius and Schulze gave certain inference rules for deciding when a collection of 4-leaved trees, one for each 4-element subset of X, can be simultaneously displayed by a single supertree with leaf-set X. Recently, it has become of interest to extend this and related results to phylogenetic networks. These are a generalization of phylogenetic trees which can be used to represent reticulate evolution (where species can come together to form a new species). It has recently been shown that a certain type of phylogenetic network, called a (unrooted) level-1 network, can essentially be constructed from 4-leaved trees. However, the problem of providing appropriate inference rules for such networks remains unresolved. Here, we show that by considering 4-leaved networks, called quarnets, as opposed to 4-leaved trees, it is possible to provide such rules. In particular, we show that these rules can be used to characterize when a collection of quarnets, one for each 4-element subset of X, can all be simultaneously displayed by a level-1 network with leaf-set X. The rules are an intriguing mixture of tree inference rules, and an inference rule for building up a cyclic ordering of X from orderings on subsets of X of size 4. This opens up several new directions of research for inferring phylogenetic networks from smaller ones, which could yield new algorithms for solving the supernetwork problem in phylogenetics
On dispersive energy transport and relaxation in the hopping regime
A new method for investigating relaxation phenomena for charge carriers
hopping between localized tail states has been developed. It allows us to
consider both charge and energy {\it dispersive} transport. The method is based
on the idea of quasi-elasticity: the typical energy loss during a hop is much
less than all other characteristic energies. We have investigated two models
with different density of states energy dependencies with our method. In
general, we have found that the motion of a packet in energy space is affected
by two competing tendencies. First, there is a packet broadening, i.e. the
dispersive energy transport. Second, there is a narrowing of the packet, if the
density of states is depleting with decreasing energy. It is the interplay of
these two tendencies that determines the overall evolution. If the density of
states is constant, only broadening exists. In this case a packet in energy
space evolves into Gaussian one, moving with constant drift velocity and mean
square deviation increasing linearly in time. If the density of states depletes
exponentially with decreasing energy, the motion of the packet tremendously
slows down with time. For large times the mean square deviation of the packet
becomes constant, so that the motion of the packet is ``soliton-like''.Comment: 26 pages, RevTeX, 10 EPS figures, submitted to Phys. Rev.
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