10,998 research outputs found
Towards a new determination of the QCD Lambda parameter from running couplings in the three-flavour theory
We review our new strategy and current status towards a high precision
computation of the Lambda parameter from three-flavour simulations in QCD. To
reach this goal we combine specific advantages of the Schr\"odinger functional
and gradient flow couplings.Comment: 7 pages, 3 figures; Proceedings of the 32nd International Symposium
on Lattice Field Theory; 23-28 June, 2014, Columbia University, New Yor
Monte Carlo simulations of random copolymers at a selective interface
We investigate numerically using the bond--fluctuation model the adsorption
of a random AB--copolymer at the interface between two solvents. From our
results we infer several scaling relations: the radius of gyration of the
copolymer in the direction perpendicular to the interface () scales
with , the interfacial selectivity strength, as
where is the usual Flory exponent and
is the copolymer's length; furthermore the monomer density at the interface
scales as for small . We also determine numerically the
monomer densities in the two solvents and discuss their dependence on the
distance from the interface.Comment: Latex text file appended with figures.tar.g
High efficiency thermionic converter studies
The objective is to improve thermionic converter performance by means of reduced interelectrode losses, greater emitter capabilities, and lower collector work functions until the converter performance level is suitable for out-of-core space reactors and radioisotope generators. Electrode screening experiments have identified several promising collector materials. Back emission work function measurements of a ZnO collector in a thermionic diode have given values less than 1.3 eV. Diode tests were conducted over the range of temperatures of interest for space power applications. Enhanced mode converter experiments have included triodes operated in both the surface ionization and plasmatron modes. Pulsed triodes were studied as a function of pulse length, pulse potential, inert gas fill pressure, cesium pressure, spacing, emitter temperature and collector temperature. Current amplifications (i.e., mean output current/mean grid current) of several hundred were observed up to output current densities of one amp/sq cm. These data correspond to an equivalent arc drop less than 0.1 eV
Copolymer adsorption kinetics at a selective liquid-liquid interface: Scaling theory and computer experiment
We consider the adsorption kinetics of a regular block-copolymer of total
length and block size at a selective liquid-liquid interface in the
limit of strong localization. We propose a simple analytic theory based on
scaling considerations which describes the relaxation of the initial coil into
a flat-shaped layer. The characteristic times for attaining equilibrium values
of the gyration radius components perpendicular and parallel to the interface
are predicted to scale with chain length and block length as
(here is the Flory exponent)
and as , although initially the rate of coil
flattening is expected to decrease with block size as . Since
typically for multiblock copolymers, our results suggest that the
flattening dynamics proceeds faster perpendicular rather than parallel to the
interface. We also demonstrate that these scaling predictions agree well with
the results of extensive Monte Carlo simulations of the localization dynamics.Comment: 4 pages, 4 figures, submited to Europhys. Let
The -parameter in 3-flavour QCD and by the ALPHA collaboration
We present results by the ALPHA collaboration for the -parameter in
3-flavour QCD and the strong coupling constant at the electroweak scale,
, in terms of hadronic quantities computed on the CLS gauge
configurations. The first part of this proceedings contribution contains a
review of published material \cite{Brida:2016flw,DallaBrida:2016kgh} and yields
the -parameter in units of a low energy scale, . We
then discuss how to determine this scale in physical units from experimental
data for the pion and kaon decay constants. We obtain MeV which translates to
using perturbation theory to match between 3-, 4- and 5-flavour QCD.Comment: 21 pages. Collects contributions of A. Ramos, S. Sint and R. Sommer
to the 34th annual International Symposium on Lattice Field Theory; LaTeX
input encoding problem fixe
Avalanche Size Scaling in Sheared Three-Dimensional Amorphous Solid
We have studied the statistics of plastic rearrangement events in a simulated
amorphous solid at T=0. Events are characterized by the energy release and the
``slip volume'', the product of plastic strain and system volume. Their
distributions for a given system size appear to be exponential, but a
characteristic event size cannot be inferred, because the mean values of these
quantities increase as with . In contrast to
results obtained in 2D models, we do not see simply connected avalanches. The
exponent suggests a fractal shape of the avalanches, which is also evidenced by
the mean fractal dimension and participation ratio.Comment: Accepted for publication in Physical Review Letter
Localization transition of random copolymers at interfaces
We consider adsorption of random copolymer chains onto an interface within
the model of Garel et al. Europhysics Letters 8, 9 (1989). By using the replica
method the adsorption of the copolymer at the interface is mapped onto the
problem of finding the ground state of a quantum mechanical Hamiltonian. To
study this ground state we introduce a novel variational principle for the
Green's function, which generalizes the well-known Rayleigh-Ritz method of
Quantum Mechanics to nonstationary states. Minimization with an appropriate
trial Green's function enables us to find the phase diagram for the
localization-delocalization transition for an ideal random copolymer at the
interface.Comment: 5 page
Disturbance-diversity relationships in two lakes of similar nutrient chemistry but contrasting disturbance regimes
Phytoplankton diversity was studied in two North German lakes of comparable nutrient chemistry but different exposure to winds. In both lakes, phytoplankton was primarily N-limited but diatoms were Si-limited. Plußsee had a very constant mixing depth during summer, while week-to-week changes of several meters were quite common in the more exposed Behler See. In Plußsee, phytoplankton biomass during summer came closer to the carrying capacity as defined by the available total N. In Plußsee there was a marked decline of diversity during the summer maximum of biomass, while this decline was less pronounced in Behler See. It is concluded that disturbances which prevented phytoplankton from reaching the carrying capacity also maintained a high level of diversity. A negative response of diversity to undisturbed conditions became apparent, after phytoplankton biomass had exceeded about 5% of the carrying capacity
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