162 research outputs found
Universal shape ratios for polymers grafted at a flat surface
We consider dilute non-adsorbed polymers grafted at an impenetrable surface
and compute several quantities which characterize the polymer shape: the
asphericity and the ratios of the eigenvalues of the radius-of-gyration tensor.
The results are only slightly different from those obtained for polymers in the
bulk, showing that the surface has little influence on the polymer shape.Comment: 10 pages, LaTe
Structure factor of dilute ring polymers
We consider ring polymers in good solvents in the dilute limit. We determine
the structure factor and the monomer-monomer distribution function. We compute
accurately the asymptotic behavior of these functions for small and large
momenta and distances by using field-theoretical methods. Phenomenological
expressions with the correct asymptotic behaviors are also given.Comment: 17 pages, 3 figure
Intra-chain correlation functions and shapes of homopolymers with different architectures in dilute solution
We present results of Monte Carlo study of the monomer-monomer correlation
functions, static structure factor and asphericity characteristics of a single
homopolymer in the coil and globular states for three distinct architectures of
the chain: ring, open and star. To rationalise the results we introduce the
dimensionless correlation functions rescaled via the corresponding mean-squared
distances between monomers. For flexible chains with some architectures these
functions exhibit a large degree of universality by falling onto a single or
several distinct master curves. In the repulsive regime, where a stretched
exponential times a power law form (de Cloizeaux scaling) can be applied, the
corresponding exponents and have been obtained. The exponent
is found to be universal for flexible strongly repulsive coils
and in agreement with the theoretical prediction from improved higher-order
Borel-resummed renormalisation group calculations. The short-distance exponents
of an open flexible chain are in a good agreement with the
theoretical predictions in the strongly repulsive regime also. However,
increasing the Kuhn length in relation to the monomer size leads to their fast
cross-over towards the Gaussian behaviour. Likewise, a strong sensitivity of
various exponents on the stiffness of the chain, or on the number
of arms in star polymers, is observed. The correlation functions in the
globular state are found to have a more complicated oscillating behaviour and
their degree of universality has been reviewed. Average shapes of the polymers
in terms of the asphericity characteristics, as well as the universal behaviour
in the static structure factors, have been also investigated.Comment: RevTeX 12 pages, 10 PS figures. Accepted by J. Chem. Phy
Dynamic Critical Behavior of an Extended Reptation Dynamics for Self-Avoiding Walks
We consider lattice self-avoiding walks and discuss the dynamic critical
behavior of two dynamics that use local and bilocal moves and generalize the
usual reptation dynamics. We determine the integrated and exponential
autocorrelation times for several observables, perform a dynamic finite-size
scaling study of the autocorrelation functions, and compute the associated
dynamic critical exponents . For the variables that describe the size of the
walks, in the absence of interactions we find in two dimensions
and in three dimensions. At the -point in two dimensions
we have .Comment: laTeX2e, 32 pages, 11 eps figure
Molecular Epidemiology of Early and Acute HIV Type 1 Infections in the United States Navy and Marine Corps, 2005–2010
The U.S. military represents a unique population within the human immunodeficiency virus 1 (HIV-1) pandemic. The last comprehensive study of HIV-1 in members of the U.S. Navy and Marine Corps (Sea Services) was completed in 2000, before large-scale combat operations were taking place. Here, we present molecular characterization of HIV-1 from 40 Sea Services personnel who were identified during their seroconversion window and initially classified as HIV-1 negative during screening. Protease/reverse transcriptase (pro/rt) and envelope (env) sequences were obtained from each member of the cohort. Phylogenetic analyses were carried out on these regions to determine relatedness within the cohort and calculate the most recent common ancestor for the related sequences. We identified 39 individuals infected with subtype B and one infected with CRF01_AE. Comparison of the pairwise genetic distance of Sea Service sequences and reference sequences in the env and pro/rt regions showed that five samples were part of molecular clusters, a group of two and a group of three, confirmed by single genome amplification. Real-time molecular monitoring of new HIV-1 acquisitions in the Sea Services may have a role in facilitating public health interventions at sites where related HIV-1 infections are identified
When the chickens come home to roost: The long‐term impact of party positions on religious voting
Polydisperse star polymer solutions
We analyze the effect of polydispersity in the arm number on the effective
interactions, structural correlations and the phase behavior of star polymers
in a good solvent. The effective interaction potential between two star
polymers with different arm numbers is derived using scaling theory. The
resulting expression is tested against monomer-resolved molecular dynamics
simulations. We find that the theoretical pair potential is in agreement with
the simulation data in a much wider polydispersity range than other proposed
potentials. We then use this pair potential as an input in a many-body theory
to investigate polydispersity effects on the structural correlations and the
phase diagram of dense star polymer solutions. In particular we find that a
polydispersity of 10%, which is typical in experimental samples, does not
significantly alter previous findings for the phase diagram of monodisperse
solutions.Comment: 14 pages, 7 figure
Reliability of low-energy electron diffraction for studies of surface order-disorder phenomena
It is shown that a determination of critical exponents in surface phase transformations based on a kinematic analysis of LEED peak intensities is subject to errors caused by multiple scattering that are large enough to prevent a clear assignment to a known universality class. The multiple-scattering contribution arises from short-range flucutations and has its maximum value at the transition temperature. The specific-heat exponent of the surface phase can be measured directly from the variation of the integral-order-beam intensity with temperature that is caused by the multiple scattering
TRY plant trait database - enhanced coverage and open access
Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
- …