3,312 research outputs found
Phase diagram of patchy colloids: towards empty liquids
We report theoretical and numerical evaluations of the phase diagram for
patchy colloidal particles of new generation. We show that the reduction of the
number of bonded nearest neighbours offers the possibility of generating liquid
states (i.e. states with temperature lower than the liquid-gas critical
temperature) with a vanishing occupied packing fraction (), a case which
can not be realized with spherically interacting particles. Theoretical results
suggest that such reduction is accompanied by an increase of the region of
stability of the liquid phase in the (-) plane, possibly favoring the
establishment of homogeneous disordered materials at small , i.e. stable
equilibrium gels.Comment: 4 pages, 4 figures, revised version, accepted in Phys. Rev. Let
Time to Organize the Bioinformatics Resourceome
The initial steps toward a bioinformatics resourceome are
clear. First, an overall ontology with the high-level concepts
(algorithms, databases, organizations, papers, people, etc.)
must be created, with a set of standard attributes and a
standard set of relations between these concepts (e.g., people
publish papers, papers describe algorithms or databases,
organizations house people, etc.). The initial ontology should
be compact and built for distributed collaborative extension.
Second, a mechanism for people to extend this ontology with
subconcepts in order to describe their own resources should
be designed. The precise location of a tool within a taxonomy
is not critical—the author will place it somewhere based on
the location of similar/competing resources or based on a
best-informed guess. Others may create links to the resource
from other appropriate locations in the taxonomy in order to
ensure that competing interpretations of the appropriate
conceptual location for the resource are accommodated.
Third, the formats for the ontologies and the resource
descriptions should be published so enterprising software
engineers can create interfaces for surfing, searching, and
viewing the resources. The resulting distributed system of
resource descriptions would be extensible, robust, and useful
to the entire biomedical research community
Self-Assembly of Patchy Particles into Polymer Chains: A Parameter-Free Comparison between Wertheim Theory and Monte Carlo Simulation
We numerically study a simple fluid composed of particles having a hard-core
repulsion, complemented by two short-ranged attractive (sticky) spots at the
particle poles, which provides a simple model for equilibrium polymerization of
linear chains. The simplicity of the model allows for a close comparison, with
no fitting parameters, between simulations and theoretical predictions based on
the Wertheim perturbation theory, a unique framework for the analytic
prediction of the properties of self-assembling particle systems in terms of
molecular parameter and liquid state correlation functions. This theory has not
been subjected to stringent tests against simulation data for ordering across
the polymerization transition. We numerically determine many of the
thermodynamic properties governing this basic form of self-assembly (energy per
particle, order parameter or average fraction of particles in the associated
state, average chain length, chain length distribution, average end-to-end
distance of the chains, and the static structure factor) and find that
predictions of the Wertheim theory accord remarkably well with the simulation
results
Shear-driven solidification of dilute colloidal suspensions
We show that the shear-induced solidification of dilute charge-stabilized
(DLVO) colloids is due to the interplay between the shear-induced formation and
breakage of large non-Brownian clusters. While their size is limited by
breakage, their number density increases with the shearing-time. Upon flow
cessation, the dense packing of clusters interconnects into a rigid state by
means of grainy bonds, each involving a large number of primary colloidal
bonds. The emerging picture of shear-driven solidification in dilute colloidal
suspensions combines the gelation of Brownian systems with the jamming of
athermal systems
CPT-conserving Hamiltonians and their nonlinear supersymmetrization using differential charge-operators C
A brief overview is given of recent developments and fresh ideas at the
intersection of PT and/or CPT-symmetric quantum mechanics with supersymmetric
quantum mechanics (SUSY QM). We study the consequences of the assumption that
the "charge" operator C is represented in a differential-operator form. Besides
the freedom allowed by the Hermiticity constraint for the operator CP,
encouraging results are obtained in the second-order case. The integrability of
intertwining relations proves to match the closure of nonlinear SUSY algebra.
In an illustration, our CPT-symmetric SUSY QM leads to non-Hermitian polynomial
oscillators with real spectrum which turn out to be PT-asymmetric.Comment: 25 page
Phytotoxic metabolites produced by fungi involvedin cork oak decline
Diplodia corticola, anamorph of Botryosphaeria corticola Phillips, Alves et Luque, and
Biscognauxia mediterranea (De Not.) O. Kuntze (= Hypoxylon mediterraneum) have often been
associated with serious decline phenomena, which have been affecting the cork oak forest in Italy
and other Mediterranean countries for several years. Diplodia corticola is widespread in Sardinian
oak forests, and can affect plants of different ages, inducing symptoms which include dieback,
cankers and vascular necrosis. These studies may provide information which could be useful for understanding the chemistry
and the biology governing the relationship between these fungi and their hosts. Further studies
should aim to also evaluate the ecological role of these substances
Soil Carbon in Agroforestry Systems: An Unexplored Treasure?
Soil organic matter (SOM), which contains more reactive organic carbon (C) than any other single terrestrial pool, plays a major role in determining C storage in ecosystems and regulating atmospheric concentrations of carbon dioxide (CO2)^1^. Agroforestry, the practice of growing trees and crops in interacting combinations on the same unit of land^2^, primarily by resource-poor smallholder farmers in developing countries, is recognized as a strategy for soil carbon sequestration (SCS) under the Clean Development Mechanism (CDM) of the Kyoto Protocol^3^. The understanding about C storage and dynamics under agroforestry systems (AFS), however, is minimal. Our studies under various AFS in diverse ecological conditions in five countries showed that tree-based agricultural systems, compared to treeless systems, stored more C in deeper soil layers up to 1 m depth under comparable conditions. More C is stored in soil near the tree than away from the tree; higher SOC content is associated with higher species richness and tree density; and C3 plants (trees) contribute to more C in the silt- + clay-sized (<53 µm) fractions that constitute more stable C, than C4 plants, in deeper soil profiles4 - 8. These results provide clear indications of the possibilities for climate change mitigation through SCS in AFS, and opportunities for economic benefit - through carbon trading - to millions of smallholder farmers in developing countries
Coarse Grained Density Functional Theories for Metallic Alloys: Generalized Coherent Potential Approximations and Charge Excess Functional Theory
The class of the Generalized Coherent Potential Approximations (GCPA) to the
Density Functional Theory (DFT) is introduced within the Multiple Scattering
Theory formalism for dealing with, ordered or disordered, metallic alloys. All
GCPA theories are based on a common ansatz for the kinetic part of the
Hohenberg-Kohn functional and each theory of the class is specified by an
external model concerning the potential reconstruction. The GCPA density
functional consists of marginally coupled local contributions, does not depend
on the details of the charge density and can be exactly rewritten as a function
of the appropriate charge multipole moments associated with each lattice site.
A general procedure based on the integration of the 'qV' laws is described that
allows for the explicit construction the same function. The coarse grained
nature of the GCPA density functional implies great computational advantages
and is connected with the O(N) scalability of GCPA algorithms. Moreover, it is
shown that a convenient truncated series expansion of the GCPA functional leads
to the Charge Excess Functional (CEF) theory [E. Bruno, L. Zingales and Y.
Wang, Phys. Rev. Lett. {\bf 91}, 166401 (2003)] which here is offered in a
generalized version that includes multipolar interactions. CEF and the GCPA
numerical results are compared with status of art LAPW full-potential density
functional calculations for 62, bcc- and fcc-based, ordered CuZn alloys, in all
the range of concentrations. These extensive tests show that the discrepancies
between GCPA and CEF are always within the numerical accuracy of the
calculations, both for the site charges and the total energies. Furthermore,
GCPA and CEF very carefully reproduce the LAPW site charges and the total
energy trends.Comment: 19 pages, 11 figure
Distributional Borel Summability of Odd Anharmonic Oscillators
It is proved that the divergent Rayleigh-Schrodinger perturbation expansions
for the eigenvalues of any odd anharmonic oscillator are Borel summable in the
distributional sense to the resonances naturally associated with the system
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