4,095 research outputs found
Local Behavior of the First-Order Gradient Correction to the Thomas-Fermi Kinetic Energy Functional
The first order gradient correction to the Thomas-Fermi functional, proposed
by Haq, Chattaraj and Deb (Chem. Phys. Lett. vol. 81, 8031, 1984) has been
studied by evaluating both the total kinetic energy and the local kinetic
energy density. For testing the kinetic energy density we evaluate its
deviation from an exact result through a quality factor, a parameter that
reflects the quality of the functionals in a better way than their relative
errors. The study is performed on two different systems: light atoms (up to
Z=18) and a noninteracting model of fermions confined in a Coulombic-type
potential. It is found than this approximation gives very low relative errors
and a better local behavior than any of the usual generalized gradient
approximation semilocal kinetic density functionals.Comment: 7 pages, 2 tables, 4 figure
Gaussian-Charge Polarizable Interaction Potential for Carbon Dioxide
A number of simple pair interaction potentials of the carbon dioxide molecule
are investigated and found to underestimate the magnitude of the second virial
coefficient in the temperature interval 220 K to 448 K by up to 20%. Also the
third virial coefficient is underestimated by these models. A rigid,
polarizable, three-site interaction potential reproduces the experimental
second and third virial coefficients to within a few percent. It is based on
the modified Buckingham exp-6 potential, an anisotropic Axilrod-Teller
correction and Gaussian charge densities on the atomic sites with an inducible
dipole at the center of mass. The electric quadrupole moment, polarizability
and bond distances are set to equal experiment. Density of the fluid at 200 and
800 bars pressure is reproduced to within some percent of observation over the
temperature range 250 K to 310 K. The dimer structure is in passable agreement
with electronically resolved quantum-mechanical calculations in the literature,
as are those of the monohydrated monomer and dimer complexes using the
polarizable GCPM water potential. Qualitative agreement with experiment is also
obtained, when quantum corrections are included, for the relative stability of
the trimer conformations, which is not the case for the pair potentials.Comment: Error in the long-range correction fixed and three-body dispersion
introduced. 32 pages (incl. title page), 7 figures, 9 tables, double-space
Genetic Synthesis of Periodic Protein Materials
Genetic engineering offers a novel approach to the development of
advanced polymeric materials, in particular protein-based materials.
Biological synthesis provides levels of control of polymer chain architecture
that cannot yet be attained by current methods of chemical synthesis. In
addition to employing naturally occurring genetic templates artificial genes
can be designed to encode completely new materials with customized properties.
In the present paper we: 1) review the concepts and technology of creating
protein-based materials by genetic engineering, 2) discuss the merits of
producing crystalline lamellar proteins by this approach, and 3) review
progress made by our group in generating such materials by genetic strategies.
Full descriptions appear elsewhere about the parameters to be considered in
designing artificial protein genes of this type, the effectiveness of
different gene construction and expression strategies utilized by us thus far
and, the specific properties of the various materials derived from these
efforts (1,2).
Progress made by other groups involved in developing periodic proteins by
molecular biological strategies are described in refs. 3-8. The latter
studies include genetic engineering of artificial silk-like proteins (3,4),
poly-aspartylphenylalanine (5), an α/β barrel domain (octarellin; 6), the
collagen tripeptide GlyProPro (7) and human tropoelastin (8). Advances with
the silk-like proteins (SLP) have been particularly impressive. In addition
to producing multi-gram quantities of pure SLP homopolymers, this group has successfully generated block copolymers of SLP interspersed with core peptides of mammalian elastin and the human fibronectin cell attachment element. While publications are still lacking it appears that a numiber of groups are striving to create genetically engineered variants of the repetitive bioadhesive proteins produced by mussels and barnacles (9)
Recommended from our members
The Stardust – a successful encounter with the remarkable comet Wild 2
On January 2, 2004 the Stardust spacecraft completed a close flyby of comet Wild2 (P81). Flying at a relative speed of 6.1 km/s within 237km of the 5 km nucleus, the spacecraft took 72 close-in images, measured the flux of impacting particles and did TOF mass spectrometry
Permeation of CO2 and N2 through glassy poly(dimethyl phenylene) oxide under steady- and presteady-state conditions
Glassy polymers are often used for gas separations because of their high selectivity. Although the dual-mode permeation model correctly fits their sorption and permeation isotherms, its physical interpretation is disputed, and it does not describe permeation far from steady state, a condition expected when separations involve intermittent renewable energy sources. To develop a more comprehensive permeation model, we combine experiment, molecular dynamics, and multiscale reaction–diffusion modeling to characterize the time-dependent permeation of N2 and CO2 through a glassy poly(dimethyl phenylene oxide) membrane, a model system. Simulations of experimental time-dependent permeation data for both gases in the presteady-state and steady-state regimes show that both single- and dual-mode reaction–diffusion models reproduce the experimental observations, and that sorbed gas concentrations lag the external pressure rise. The results point to environment-sensitive diffusion coefficients as a vital characteristic of transport in glassy polymers
Observation and Spectral Measurements of the Crab Nebula with Milagro
The Crab Nebula was detected with the Milagro experiment at a statistical
significance of 17 standard deviations over the lifetime of the experiment. The
experiment was sensitive to approximately 100 GeV - 100 TeV gamma ray air
showers by observing the particle footprint reaching the ground. The fraction
of detectors recording signals from photons at the ground is a suitable proxy
for the energy of the primary particle and has been used to measure the photon
energy spectrum of the Crab Nebula between ~1 and ~100 TeV. The TeV emission is
believed to be caused by inverse-Compton up-scattering scattering of ambient
photons by an energetic electron population. The location of a TeV steepening
or cutoff in the energy spectrum reveals important details about the underlying
electron population. We describe the experiment and the technique for
distinguishing gamma-ray events from the much more-abundant hadronic events. We
describe the calculation of the significance of the excess from the Crab and
how the energy spectrum is fit. The fit is consistent with values measured by
IACTs between 1 and 20 TeV. Fixing the spectral index to values that have been
measured below 1 TeV by IACT experiments (2.4 to 2.6), the fit to the Milagro
data suggests that Crab exhibits a spectral steepening or cutoff between about
20 to 40 TeV.Comment: Submitted to Astrophysical Journa
Cardiovascular-renal axis disorders in the domestic dog and cat: a veterinary consensus statement
OBJECTIVES
There is a growing understanding of the complexity of interplay between renal and cardiovascular systems in both health and disease. The medical profession has adopted the term "cardiorenal syndrome" (CRS) to describe the pathophysiological relationship between the kidney and heart in disease. CRS has yet to be formally defined and described by the veterinary profession and its existence and importance in dogs and cats warrant investigation. The CRS Consensus Group, comprising nine veterinary cardiologists and seven nephrologists from Europe and North America, sought to achieve consensus around the definition, pathophysiology, diagnosis and management of dogs and cats with "cardiovascular-renal disorders" (CvRD). To this end, the Delphi formal methodology for defining/building consensus and defining guidelines was utilised.
METHODS
Following a literature review, 13 candidate statements regarding CvRD in dogs and cats were tested for consensus, using a modified Delphi method. As a new area of interest, well-designed studies, specific to CRS/CvRD, are lacking, particularly in dogs and cats. Hence, while scientific justification of all the recommendations was sought and used when available, recommendations were largely reliant on theory, expert opinion, small clinical studies and extrapolation from data derived from other species.
RESULTS
Of the 13 statements, 11 achieved consensus and 2 did not. The modified Delphi approach worked well to achieve consensus in an objective manner and to develop initial guidelines for CvRD.
DISCUSSION
The resultant manuscript describes consensus statements for the definition, classification, diagnosis and management strategies for veterinary patients with CvRD, with an emphasis on the pathological interplay between the two organ systems. By formulating consensus statements regarding CvRD in veterinary medicine, the authors hope to stimulate interest in and advancement of the understanding and management of CvRD in dogs and cats. The use of a formalised method for consensus and guideline development should be considered for other topics in veterinary medicine
- …