115,224 research outputs found
Phase behavior and interfacial properties of nonadditive mixtures of Onsager rods
Within a second virial theory, we study bulk phase diagrams as well as the
free planar isotropic-nematic interface of binary mixtures of nonadditive thin
and thick hard rods. For species of the same type the excluded volume is
determined only by the dimensions of the particles, whereas for dissimilar ones
it is taken to be larger or smaller than that, giving rise to a nonadditivity
that can be positive or negative. We argue that such a nonadditivity can result
from modelling of soft interactions as effective hard-core interactions. The
nonadditivity enhances or reduces the fractionation at isotropic-nematic ()
coexistence and may induce or suppress a demixing of the high-density nematic
phase into two nematic phases of different composition ( and ),
depending on whether the nonadditivity is positive or negative. The interfacial
tension between co-existing isotropic and nematic phases show an increase with
increasing fractionation at the interface, and complete wetting of the
interface by the phase upon approach of the triple point
coexistence. In all explored cases bulk and interfacial properties of the
nonadditive mixtures exhibit a striking and quite unexpected similarity with
the properties of additive mixtures of different diameter ratio.Comment: 12 pages, revised version, submitted to JC
The Horseshoe Estimator: Posterior Concentration around Nearly Black Vectors
We consider the horseshoe estimator due to Carvalho, Polson and Scott (2010)
for the multivariate normal mean model in the situation that the mean vector is
sparse in the nearly black sense. We assume the frequentist framework where the
data is generated according to a fixed mean vector. We show that if the number
of nonzero parameters of the mean vector is known, the horseshoe estimator
attains the minimax risk, possibly up to a multiplicative constant. We
provide conditions under which the horseshoe estimator combined with an
empirical Bayes estimate of the number of nonzero means still yields the
minimax risk. We furthermore prove an upper bound on the rate of contraction of
the posterior distribution around the horseshoe estimator, and a lower bound on
the posterior variance. These bounds indicate that the posterior distribution
of the horseshoe prior may be more informative than that of other one-component
priors, including the Lasso.Comment: This version differs from the final published version in pagination
and typographical detail; Available at
http://projecteuclid.org/euclid.ejs/141813426
Two-hadron single target-spin asymmetries: first measurement by HERMES
Single target-spin asymmetries in semi-inclusive two-pion production were
measured for the first time by the HERMES experiment, using a longitudinally
polarized deuterium target. These asymmetries relate to the unknown
transversity distribution function through, also unknown, interference
fragmentation functions. The presented results are compared with a model for
the dependence of one of these interference fragmentation functions on the
invariant mass of the pion pair.Comment: 4 pages, 4 figures, contribution to the proceedings for the 16th
international spin physics symposium (SPIN'2004
A Submillimeter Selected Quasar in the Field of Abell 478
We report the discovery of a z=2.83 quasar in the field of the cooling flow
galaxy cluster Abell 478. This quasar was first detected in a submm survey of
star forming galaxies at high redshifts, as the brightest source. We discuss
the optical spectrum and far-IR spectral energy distribution (SED) of this
object.Comment: 4 pages, 3 figures, in "Deep Millimeter Surveys: Implications for
Galaxy Formation and Evolution", ed. J. Lowenthal and D. Hughes, World
Scientific Publisher
Equilibrium and non-equilibrium concepts in forest genetic modelling: population- and individually-based approaches
The environment is changing and so are forests, in their functioning, in species composition, and in the species’ genetic composition. Many empirical and process-based models exist to support forest management. However, most of these models do not consider the impact of environmental changes and forest management on genetic diversity nor on the rate of adaptation of critical plant processes. How genetic diversity and rates of adaptation depend on management actions is a crucial next step in model development. Modelling approaches of genetic and demographic processes that operate in forests are categorized here in two classes. One approach assumes equilibrium conditions in phenotype and tree density, and analyses the characteristics of the demography and the genetic system of the species that determine the rate at which that equilibrium is attained. The other modelling approach does not assume equilibrium conditions and describes both the ecological —and genetic processes to analyse how environmental changes result in selection pressures on functional traits of trees and the consequences of that selection for tree— and ecosystem functioning. The equilibrium approach allows analysing the recovery rate after a perturbation in stable environments, i.e. towards the same pre-perturbation stable state. The nonequilibrium approach allows, in addition to the equilibrium approach, analysing consequences of ongoing environmental changes and forest management, i.e. non-stationary environments, on tree functioning, species composition, and genetic composition of the trees in forest ecosystem. In this paper we describe these two modelling approaches and discuss advantages and disadvantages of them and current knowledge gaps
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Material Issues of the Metal Printing Process, MPP
The metal printing process, MPP; is a novel Rapid Manufacturing process under development
at SINTEF and NTNU in Trondheim, Norway. The process, which aims at the manufacturing
of end-use products for demanding applications in metallic and CerMet materials, consists of
two separate parts; The layer fabrication, based on electrostatic attraction of powder materials,
and the consolidation, consisting of the compression and sintering of each layer in a heated
die. This approach leads to a number of issues regarding the interaction between the process
solutions and the materials. This paper addresses some of the most critical material issues at
the current development stage of MPP, and the present solutions to these.Mechanical Engineerin
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