2,055 research outputs found
Local entropic effects of polymers grafted to soft interfaces
In this paper, we study the equilibrium properties of polymer chains
end-tethered to a fluid membrane. The loss of conformational entropy of the
polymer results in an inhomogeneous pressure field that we calculate for
gaussian chains. We estimate the effects of excluded volume through a relation
between pressure and concentration. Under the polymer pressure, a soft surface
will deform. We calculate the deformation profile for a fluid membrane and show
that close to the grafting point, this profile assumes a cone-like shape,
independently of the boundary conditions. Interactions between different
polymers are also mediated by the membrane deformation. This pair-additive
potential is attractive for chains grafted on the same side of the membrane and
repulsive otherwise.Comment: 10 pages, 9 figure
Depletion forces between two spheres in a rod solution
We study the depletion interaction between spherical particles of radius R
immersed in a dilute solution of rigid rods of length L. The computed
interaction potential is, within numerical accuracy, exact for any value of
L/R. In particular we find that for L of order R, the depth of the depletion
well is smaller than the prediction of the Derjaguin approximation. Our results
bring new light into the discussion on the lack of phase separation in
colloidal mixtures of spheres and rods.Comment: 12 pages including figures. 5 eps figures. LaTeX with REVTe
Monte Carlo Study of the Inflation-Deflation Transition in a Fluid Membrane
We study the conformation and scaling properties of a self-avoiding fluid
membrane, subject to an osmotic pressure , by means of Monte Carlo
simulations. Using finite size scaling methods in combination with a histogram
reweighting techniques we find that the surface undergoes an abrupt
conformational transition at a critical pressure , from low pressure
deflated configurations with a branched polymer characteristics to a high
pressure inflated phase, in agreement with previous findings
\cite{gompper,baum}. The transition pressure scales with the system
size as , with . Below
the enclosed volume scales as , in accordance with the
self-avoiding branched polymer structure, and for our data
are consistent with the finite size scaling form ,
where .
Also the finite size scaling behavior of the radii of gyration and the
compressibility moduli are obtained. Some of the observed exponents and the
mechanism behind the conformational collapse are interpreted in terms of a
Flory theory.Comment: 20 pages + postscript-file, Latex + Postscript, IFA Report No. 94/1
A detector for continuous measurement of ultra-cold atoms in real time
We present the first detector capable of recording high-bandwidth real time
atom number density measurements of a Bose Einstein condensate. Based on a
two-color Mach-Zehnder interferometer, our detector has a response time that is
six orders of magnitude faster than current detectors based on CCD cameras
while still operating at the shot-noise limit. With this minimally destructive
system it may be possible to implement feedback to stabilize a Bose-Einstein
condensate or an atom laser.Comment: 3 pages, 3 figures, submitted to optics letter
Getting Digitization Projects Done in a Medium-Sized Academic Library: a Collaborative Effort Between Technical Services, Systems, Special Collections, and Collection Development
Cleveland State University Library, a medium-sized academic library serving approximately 15,000 students, is engaged in large-scale efforts to digitize and make accessible online collections of unique Cleveland-related materials. The Cleveland State University Library Special Collections digitization and cataloging efforts use staff from several different library organizational units. The collaboration of staff with specific expertise in long-standing library functions -- special collections, cataloging, systems, archives, selection -- to create two Web databases is described. The collaborative effort has proven effective in getting resources processed, archived, digitized, described, promoted, and made accessible in a highly efficient and effective manner. The responsibilities of the different library units involved in the digitization project are described
Pulsed pumping of a Bose-Einstein condensate
In this work, we examine a system for coherent transfer of atoms into a
Bose-Einstein condensate. We utilize two spatially separate Bose-Einstein
condensates in different hyperfine ground states held in the same dc magnetic
trap. By means of a pulsed transfer of atoms, we are able to show a clear
resonance in the timing of the transfer, both in temperature and number, from
which we draw conclusions about the underlying physical process. The results
are discussed in the context of the recently demonstrated pumped atom laser.Comment: 5 pages, 5 figures, published in Physical Review
Achieving peak brightness in an atom laser
In this paper we present experimental results and theory on the first
continuous (long pulse) Raman atom laser. The brightness that can be achieved
with this system is three orders of magnitude greater than has been previously
demonstrated in any other continuously outcoupled atom laser. In addition, the
energy linewidth of a continuous atom laser can be made arbitrarily narrow
compared to the mean field energy of a trapped condensate. We analyze the flux
and brightness of the atom laser with an analytic model that shows excellent
agreement with experiment with no adjustable parameters.Comment: 4 pages, 4 black and white figures, submitted to Physical Revie
Novel enantiopure bis(pyrrolo)tetrathiafulvalene donors exhibiting chiral crystal packing arrangements
Two novel enantiopure bis(pyrrolo[3,4-d])tetrathiafulvalene derivatives, substrates for preparing chiral conducting materials, show chiral crystal packing arrangements in which successive layers are rotated in accordance with an exact or approximate 43 axis. The corresponding donors containing fused dihydropyrrolegroups, and thus four more hydrogen atoms, form stacks along a crystal axis
A multibeam atom laser: coherent atom beam splitting from a single far detuned laser
We report the experimental realisation of a multibeam atom laser. A single
continuous atom laser is outcoupled from a Bose-Einstein condensate (BEC) via
an optical Raman transition. The atom laser is subsequently split into up to
five atomic beams with slightly different momenta, resulting in multiple,
nearly co-propagating, coherent beams which could be of use in interferometric
experiments. The splitting process itself is a novel realization of Bragg
diffraction, driven by each of the optical Raman laser beams independently.
This presents a significantly simpler implementation of an atomic beam
splitter, one of the main elements of coherent atom optics
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