423,330 research outputs found
Predicting the conformations of peptides and proteins in early evolution. A review article submitted to Biology Direct
Considering that short, mainly heterochiral, polypeptides with a high glycine content are expected to have played a prominent role in evolution at the earliest stage of life before nucleic acids were available, we review recent knowledge about polypeptide three-dimensional structure to predict the types of conformations they would have adopted. The possible existence of such structures at this time leads to a consideration of their functional significance, and the consequences for the course of evolution
Renewal-anomalous-heterogeneous files
Renewal-anomalous-heterogeneous files are solved. A simple file is made of
Brownian hard spheres that diffuse stochastically in an effective 1D channel.
Generally, Brownian files are heterogeneous: the spheres' diffusion
coefficients are distributed and the initial spheres' density is non-uniform.
In renewal-anomalous files, the distribution of waiting times for individual
jumps is exponential as in Brownian files, yet obeys: {\psi}_{\alpha}
(t)~t^(-1-{\alpha}), 0<{\alpha}<1. The file is renewal as all the particles
attempt to jump at the same time. It is shown that the mean square displacement
(MSD) in a renewal-anomalous-heterogeneous file, , obeys,
~[_{nrml}]^{\alpha}, where _{nrml} is the MSD in the
corresponding Brownian file. This scaling is an outcome of an exact relation
(derived here) connecting probability density functions of Brownian files and
renewal-anomalous files. It is also shown that non-renewal-anomalous files are
slower than the corresponding renewal ones.Comment: Accepted for publication (August, 2010
Dielectron widths of the S-, D-vector bottomonium states
The dielectron widths of and vector decay
constants are calculated using the Relativistic String Hamiltonian with a
universal interaction. For the dielectron widths and
their ratios are obtained in full agreement with the latest CLEO data. For
and a good agreement with experiment is
reached only if the 4S--3D mixing (with a mixing angle ) and 6S--5D mixing (with ) are taken into
account. The possibility to observe higher "mixed -wave" resonances,
with is discussed. In particular,
, originating from the pure state,
can acquire a rather large dielectron width, eV, so that this
resonance may become manifest in the experiments. On the contrary, the
widths of pure -wave states are very small,
eV.Comment: 13 pages, no figure
High-Latitude HI in the Low Surface Brightness Galaxy UGC7321
From the analysis of sensitive HI 21-cm line observations, we find evidence
for vertically extended HI emission (|z|<~2.4 kpc) in the edge-on, low surface
brightness spiral galaxy UGC7321. Three-dimensional modelling suggests that the
HI disk of UGC7321 is both warped and flared, but that neither effect can fully
reproduce the spatial distribution and kinematics of the highest z-height gas.
We are able to model the high-latitude emission as an additional HI component
in the form of a ``thick disk'' or ``halo'' with a FWHM~3.3 kpc. We find
tentative evidence that the vertically extended gas declines in rotational
velocity as a function of z, although we are unable to completely rule out
models with constant V(z). In spite of the low star formation rate of UGC7321,
energy from supernovae may be sufficient to sustain this high-latitude gas.
However, alternative origins for this material, such as slow, sustained infall,
cannot yet be excluded.Comment: to appear in the August 20 Astrophysical Journal; 17 pages; version
with full resolution figures available at
http://cfa-www.harvard.edu/~lmatthew
Regional marketing for organic retailers: Status quo and capabilities
The market for organic food is still growing. The entrance of conventional supermarkets as well as discounters into the market and the increase of organic supermarkets are responsible for the organic boom in Germany and more price competition. These developments raise the question of new competitive strategies for small and medium sized organic retailers. The combination of organic and regional marketing might provide an opportunity to render small organic shops more successful again. The following paper discusses the opportunities for regional organic marketing strategies.
First, this contribution gives an impression of the current situation and problems in the organic food branch, before continuing with theoretical research concerned with regional marketing. In the conclusion, the authors will underline different aspects with the aid of empirical results
The Multiple Origin of Blue Straggler Stars: Theory vs. Observations
In this chapter we review the various suggested channels for the formation
and evolution of blue straggler stars (BSSs) in different environments and
their observational predictions. These include mass transfer during binary
stellar evolution - case A/B/C and D (wind Roche-lobe overflow) mass transfer,
stellar collisions during single and binary encounters in dense stellar
cluster, and coupled dynamical and stellar evolution of triple systems. We also
explore the importance of the BSS and binary dynamics in stellar clusters. We
review the various observed properties of BSSs in different environments (halo
and bulge BSSs, BSSs in globular clusters and BSSs in old open clusters), and
compare the current observations with the theoretical predictions for BSS
formation. We try to constrain the likely progenitors and processes that play a
role in the formation of BSSs and their evolution. We find that multiple
channels of BSS formation are likely to take part in producing the observed
BSSs, and we point out the strengths and weaknesses of each the formation
channel in respect to the observational constraints. Finally we point out
directions to further explore the origin of BSS, and highlight eclipsing binary
BSSs as important observational tool.Comment: Chapter 11, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Baryon states with hidden charm in the extended local hidden gauge approach
The s-wave interaction of and , is studied within a unitary coupled channels scheme
with the extended local hidden gauge approach. In addition to the
Weinberg-Tomozawa term, several additional diagrams via the pion-exchange are
also taken into account as box potentials. Furthermore, in order to implement
the full coupled channels calculation, some of the box potentials which mix the
vector-baryon and pseudoscalar-baryon sectors are extended to construct the
effective transition potentials. As a result, we have observed six possible
states in several angular momenta. Four of them correspond to two pairs of
admixture states, two of - with , and two of - with . Moreover, we find a resonance which couples to
the channel and one spin degenerated bound state of
with .Comment: 24 pages, 6 figure
- …