37,238 research outputs found
Kinetics of viral self-assembly: the role of ss RNA antenna
A big class of viruses self-assemble from a large number of identical capsid
proteins with long flexible N-terminal tails and ss RNA. We study the role of
the strong Coulomb interaction of positive N-terminal tails with ss RNA in the
kinetics of the in vitro virus self-assembly. Capsid proteins stick to
unassembled chain of ss RNA (which we call "antenna") and slide on it towards
the assembly site. We show that at excess of capsid proteins such
one-dimensional diffusion accelerates self-assembly more than ten times. On the
other hand at excess of ss RNA, antenna slows self-assembly down. Several
experiments are proposed to verify the role of ss RNA antenna.Comment: 4 pages, 3 figures, several experiments are proposed, a new idea of
experiment is adde
Sudden Expansion of a One-Dimensional Bose Gas from Power-Law Traps
We analyze free expansion of a trapped one-dimensional Bose gas after a
sudden release from the confining trap potential. By using the stationary phase
and local density approximations, we show that the long-time asymptotic density
profile and the momentum distribution of the gas are determined by the initial
distribution of Bethe rapidities (quasimomenta) and hence can be obtained from
the solutions to the Lieb-Liniger equations in the thermodynamic limit. For
expansion from a harmonic trap, and in the limits of very weak and very strong
interactions, we recover the self-similar scaling solutions known from the
hydrodynamic approach. For all other power-law traps and arbitrary interaction
strengths, the expansion is not self-similar and shows strong dependence of the
density profile evolution on the trap anharmonicity. We also characterize
dynamical fermionization of the expanding cloud in terms of correlation
functions describing phase and density fluctuations.Comment: Final published version with modified title and a couple of other
minor changes. 5 pages, 2 figures, and Supplemental Materia
Questions of quality in repositories of open educational resources: a literature review
Open educational resources (OER) are teaching and learning materials which are freely available and openly licensed. Repositories of OER (ROER) are platforms that host and facilitate access to these resources. ROER should not just be designed to store this content â in keeping with the aims of the OER movement, they should support educators in embracing open educational practices (OEP) such as searching for and retrieving content that they will reuse, adapt or modify as needed, without economic barriers or copyright restrictions. This paper reviews key literature on OER and ROER, in order to understand the roles ROER are said or supposed to fulfil in relation to furthering the aims of the OER movement. Four themes which should shape repository design are identified, and the following 10 quality indicators (QI) for ROER effectiveness are discussed: featured resources; user evaluation tools; peer review; authorship of the resources; keywords of the resources; use of standardised metadata; multilingualism of the repositories; inclusion of social media tools; specification of the creative commons license; availability of the source code or original files. These QI form the basis of a method for the evaluation of ROER initiatives which, in concert with considerations of achievability and long-term sustainability, should assist in enhancement and development.
Keywords: open educational resources; open access; open educational practice; repositories; quality assuranc
Kinetic limitations of cooperativity based drug delivery systems
We study theoretically a novel drug delivery system that utilizes the
overexpression of certain proteins in cancerous cells for cell specific
chemotherapy. The system consists of dendrimers conjugated with "keys" (ex:
folic acid) which "key-lock" bind to particular cell membrane proteins (ex:
folate receptor). The increased concentration of "locks" on the surface leads
to a longer residence time for the dendrimer and greater incorporation into the
cell. Cooperative binding of the nanocomplexes leads to an enhancement of cell
specificity. However, both our theory and detailed analysis of in-vitro
experiments indicate that the degree of cooperativity is kinetically limited.
We demonstrate that cooperativity and hence the specificity to particular cell
type can be increased by making the strength of individual bonds weaker, and
suggest a particular implementation of this idea. The implications of the work
for optimizing the design of drug delivery vehicles are discussed.Comment: 4 pages, 4 figures, v3: minor revision
Gluon fusion contribution to W+W- + jet production
We describe the computation of the process that contributes
to the production of two -bosons and a jet at the CERN Large Hadron Collider
(LHC). While formally of next-to-next-to-leading order (NNLO) in QCD, this
process can be evaluated separately from the bulk of NNLO QCD corrections
because it is finite and gauge-invariant. It is also enhanced by the large
gluon flux and by selection cuts employed in the Higgs boson searches in the
decay channel , as was first pointed out by Binoth {\it et al.}
in the context of production. For cuts employed by the ATLAS
collaboration, we find that the gluon fusion contribution to
enhances the background by about ten percent and can lead to moderate
distortions of kinematic distributions which are instrumental for the ongoing
Higgs boson searches at the LHC. We also release a public code to compute the
NLO QCD corrections to this process, in the form of an add-on to the package
{\tt MCFM}.Comment: 13 pages, 4 figures, 3 table
Development and application of a non-Gaussian atmospheric turbulence model for use in flight simulators
A method is described for generating time histories which model the frequency content and certain non-Gaussian probability characteristics of atmospheric turbulence including the large gusts and patchy nature of turbulence. Methods for time histories using either analog or digital computation are described. A STOL airplane was programmed into a 6-degree-of-freedom flight simulator, and turbulence time histories from several atmospheric turbulence models were introduced. The pilots' reactions are described
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