16,160 research outputs found
Meiotic recombination proteins localize to linear elements in Schizosaccharomyces pombe
Peer reviewedPostprin
Micellar Crystals in Solution from Molecular Dynamics Simulations
Polymers with both soluble and insoluble blocks typically self-assemble into
micelles, aggregates of a finite number of polymers where the soluble blocks
shield the insoluble ones from contact with the solvent. Upon increasing
concentration, these micelles often form gels that exhibit crystalline order in
many systems. In this paper, we present a study of both the dynamics and the
equilibrium properties of micellar crystals of triblock polymers using
molecular dynamics simulations. Our results show that equilibration of single
micelle degrees of freedom and crystal formation occurs by polymer transfer
between micelles, a process that is described by transition state theory. Near
the disorder (or melting) transition, bcc lattices are favored for all
triblocks studied. Lattices with fcc ordering are also found, but only at lower
kinetic temperatures and for triblocks with short hydrophilic blocks. Our
results lead to a number of theoretical considerations and suggest a range of
implications to experimental systems with a particular emphasis on Pluronic
polymers.Comment: 12 pages, 11 figures. Note that some figures are extremely low
quality to meet arXiv's file size limit
Heat transfer between elastic solids with randomly rough surfaces
We study the heat transfer between elastic solids with randomly rough
surfaces. We include both the heat transfer from the area of real contact, and
the heat transfer between the surfaces in the noncontact regions. We apply a
recently developed contact mechanics theory, which accounts for the
hierarchical nature of the contact between solids with roughness on many
different length scales. For elastic contact, at the highest (atomic)
resolution the area of real contact typically consists of atomic (nanometer)
sized regions, and we discuss the implications of this for the heat transfer.
For solids with very smooth surfaces, as is typical in many modern engineering
applications, the interfacial separation in the non-contact regions will be
very small, and for this case we show the importance of the radiative heat
transfer associated with the evanescent electromagnetic waves which exist
outside of all bodies.Comment: 23 pages, 19 figure
On the Incompleteness of Berger's List of Holonomy Representations
In 1955, Berger \cite{Ber} gave a list of irreducible reductive
representations which can occur as the holonomy of a torsion-free affine
connection. This list was stated to be complete up to possibly a finite number
of missing entries. In this paper, we show that there is, in fact, an infinite
family of representations which are missing from this list, thereby showing the
incompleteness of Berger's classification. Moreover, we develop a method to
construct torsion-free connections with prescribed holonomy, and use it to give
a complete description of the torsion-free affine connections with these new
holonomies. We also deduce some striking facts about their global behaviour.Comment: 20 pages, AMS-LaTeX, no figure
Radiation Generated by Charge Migration Following Ionization
Electronic many-body effects alone can be the driving force for an ultrafast
migration of a positive charge created upon ionization of molecular systems.
Here we show that this purely electronic phenomenon generates a characteristic
IR radiation. The situation when the initial ionic wave packet is produced by a
sudden removal of an electron is also studied. It is shown that in this case a
much stronger UV emission is generated. This emission appears as an ultrafast
response of the remaining electrons to the perturbation caused by the sudden
ionization and as such is a universal phenomenon to be expected in every
multielectron system.Comment: 5 pages, 4 figure
A normal form for excitable media
We present a normal form for travelling waves in one-dimensional excitable
media in form of a differential delay equation. The normal form is built around
the well-known saddle-node bifurcation generically present in excitable media.
Finite wavelength effects are captured by a delay. The normal form describes
the behaviour of single pulses in a periodic domain and also the richer
behaviour of wave trains. The normal form exhibits a symmetry preserving Hopf
bifurcation which may coalesce with the saddle-node in a Bogdanov-Takens point,
and a symmetry breaking spatially inhomogeneous pitchfork bifurcation. We
verify the existence of these bifurcations in numerical simulations. The
parameters of the normal form are determined and its predictions are tested
against numerical simulations of partial differential equation models of
excitable media with good agreement.Comment: 22 pages, accepted for publication in Chao
The Microbiological Flora of the Gemini 9 Spacecraft Before and After Flight
Microbiological contamination of Gemini 9 spacecraft before and after fligh
The Survival of Microorganisms in Space. Further Rocket and Balloon Borne Exposure Experiments
Rocket and balloon borne exposure experiments on survival of microorganisms in space environmen
Effect of inelasticity on the phase transitions of a thin vibrated granular layer
We describe an experimental and computational investigation of the ordered
and disordered phases of a vibrating thin, dense granular layer composed of
identical metal spheres. We compare the results from spheres with different
amounts of inelasticity and show that inelasticity has a strong effect on the
phase diagram. We also report the melting of an ordered phase to a homogeneous
disordered liquid phase at high vibration amplitude or at large inelasticities.
Our results show that dissipation has a strong effect on ordering and that in
this system ordered phases are absent entirely in highly inelastic materials.Comment: 5 pages, 5 figures, published in Physical Review E. Title of first
version slightly change
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