4,670 research outputs found
Slow energy relaxation of macromolecules and nano-clusters in solution
Many systems in the realm of nanophysics from both the living and inorganic
world display slow relaxation kinetics of energy fluctuations. In this paper we
propose a general explanation for such phenomenon, based on the effects of
interactions with the solvent. Within a simple harmonic model of the system
fluctuations, we demonstrate that the inhomogeneity of coupling to the solvent
of the bulk and surface atoms suffices to generate a complex spectrum of decay
rates. We show for Myoglobin and for a metal nano-cluster that the result is a
complex, non-exponential relaxation dynamics.Comment: 5 pages, 3 figure
A Beam Driven Plasma-Wakefield Linear Collider: From Higgs Factory to Multi-TeV
Plasma wakefield acceleration (PWFA) holds much promise for advancing the
energy frontier because it can potentially provide a 1000-fold or more increase
in acceleration gradient with excellent power efficiency in respect with
standard technologies. Most of the advances in beam-driven plasma wakefield
acceleration were obtained by a UCLA/USC/SLAC collaboration working at the SLAC
FFTB[ ]. These experiments have shown that plasmas can accelerate and focus
both electron and positron high energy beams, and an accelerating gradient in
excess of 50 GeV/m can be sustained in an 85 cm-long plasma. The FFTB
experiments were essentially proof-of-principle experiments that showed the
great potential of plasma accelerators.
The FACET[ ] test facility at SLAC will in the period 2012-2016 further study
several issues that are directly related to the applicability of PWFA to a
high-energy collider, in particular two-beam acceleration where the witness
beam experiences high beam loading (required for high efficiency), small energy
spread and small emittance dilution (required to achieve luminosity).
The PWFA-LC concept presented in this document is an attempt to find the best
design that takes advantage of the PWFA, identify the critical parameters to be
achieved and eventually the necessary R&D to address their feasibility. It best
benefits from the extensive R&D that has been performed for conventional rf
linear colliders during the last twenty years, especially ILC[ ] and CLIC[ ],
with a potential for a comparably lower power consumption and cost.Comment: Submitted to the proceedings of the Snowmass Process CSS2013. Work
supported in part by the U.S. Department of Energy under contract number
DE-AC02-76SF0051
Finding instabilities in the community structure of complex networks
The problem of finding clusters in complex networks has been extensively
studied by mathematicians, computer scientists and, more recently, by
physicists. Many of the existing algorithms partition a network into clear
clusters, without overlap. We here introduce a method to identify the nodes
lying ``between clusters'' and that allows for a general measure of the
stability of the clusters. This is done by adding noise over the weights of the
edges of the network. Our method can in principle be applied with any
clustering algorithm, provided that it works on weighted networks. We present
several applications on real-world networks using the Markov Clustering
Algorithm (MCL).Comment: 4 pages, 5 figure
Warm and Cold Denaturation in the Phase Diagram of a Protein Lattice Model
Studying the properties of the solvent around proteins, we propose a much
more sophisticated model of solvation than temperature-independent pairwise
interactions between monomers, as is used commonly in lattice representations.
We applied our model of solvation to a 16-monomer chain constrained on a
two-dimensional lattice. We compute a phase diagram function of the temperature
and a solvent parameter which is related to the pH of the solution. It exhibits
a native state in which the chain coalesces into a unique compact conformation
as well as a denatured state. Under certain solvation conditions, both warm and
cold denaturations occur between the native and the denatured states. A good
agreement is found with the data obtained from calorimetric experiments,
thereby validating the proposed model.Comment: 7 pages, 2 figure
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