1,336 research outputs found
Lunar science prior to Apollo 11
Evolutional aspects and geological interpretations in lunar scienc
A Scintillating Fiber Tracker With SiPM Readout
We present a prototype for the first tracking detector consisting of 250
micron thin scintillating fibers and silicon photomultiplier (SiPM) arrays. The
detector has a modular design, each module consists of a mechanical support
structure of 10mm Rohacell foam between two 100 micron thin carbon fiber skins.
Five layers of scintillating fibers are glued to both top and bottom of the
support structure. SiPM arrays with a channel pitch of 250 micron are placed in
front of the fibers. We show the results of the first module prototype using
multiclad fibers of types Bicron BCF-20 and Kuraray SCSF-81M that were read out
by novel 32-channel SiPM arrays from FBK-irst/INFN Perugia as well as
32-channel SiPM arrays produced by Hamamatsu. A spatial resolution of 88 micron
+/- 6 micron at an average yield of 10 detected photons per minimal ionizig
particle has been achieved.Comment: 5 pages, 7 figures, submitted as proceedings to the 11th Topical
Seminar on Innovative Particle and Radiation Detectors (IPRD08
Two-dimensional streptavidin crystals on giant lipid bilayer vesicles
Streptavidin was crystallized on giant bilayer vesicles (20-60 mum) in sucrose solution at various pH values. The streptavidin-coated vesicles exhibited unique roughened spherical and prolate ellipsoidal shapes, illustrating resistance to curvature of the two-dimensional crystals. Studies indicated that the spheroids and prolate ellipsoids correspond to different crystal morphologies. Through confocal microscopy, the various crystal morphologies on vesicle surfaces were observed under different solution conditions. Unlike two-dimensional (2D) streptavidin crystals grown in ionic buffer that assume the P1, P2, and C222 lattices at pH 4, 5.5, and 7, respectively (Wang et al. Langmuir 1999, 15, 154 1), crystals grown in sucrose with no added salt show only the lowest density C222 lattice due to strong electrostatic interactions
Critical phenomena in colloid-polymer mixtures: interfacial tension, order parameter, susceptibility and coexistence diameter
The critical behavior of a model colloid-polymer mixture, the so-called AO
model, is studied using computer simulations and finite size scaling
techniques. Investigated are the interfacial tension, the order parameter, the
susceptibility and the coexistence diameter. Our results clearly show that the
interfacial tension vanishes at the critical point with exponent 2\nu ~ 1.26.
This is in good agreement with the 3D Ising exponent. Also calculated are
critical amplitude ratios, which are shown to be compatible with the
corresponding 3D Ising values. We additionally identify a number of subtleties
that are encountered when finite size scaling is applied to the AO model. In
particular, we find that the finite size extrapolation of the interfacial
tension is most consistent when logarithmic size dependences are ignored. This
finding is in agreement with the work of Berg et al.[Phys. Rev. B, V47 P497
(1993)]Comment: 13 pages, 16 figure
Stability of Colloidal Quasicrystals
Freezing of charge-stabilized colloidal suspensions and relative stabilities
of crystals and quasicrystals are studied using thermodynamic perturbation
theory. Macroion interactions are modelled by effective pair potentials
combining electrostatic repulsion with polymer-depletion or van der Waals
attraction. Comparing free energies -- counterion terms included -- for
elementary crystals and rational approximants to icosahedral quasicrystals,
parameters are identified for which one-component quasicrystals are stabilized
by a compromise between packing entropy and cohesive energy.Comment: 6 pages, 4 figure
Silicon photomultiplier arrays - a novel photon detector for a high resolution tracker produced at FBK-irst, Italy
A silicon photomultiplier (SiPM) array has been developed at FBK-irst having
32 channels and a dimension of 8.0 x 1.1 mm^2. Each 250 um wide channel is
subdivided into 5 x 22 rectangularly arranged pixels. These sensors are
developed to read out a modular high resolution scintillating fiber tracker.
Key properties like breakdown voltage, gain and photon detection efficiency
(PDE) are found to be homogeneous over all 32 channels of an SiPM array. This
could make scintillating fiber trackers with SiPM array readout a promising
alternative to available tracker technologies, if noise properties and the PDE
are improved
Gel transitions in colloidal suspensions
The idealized mode coupling theory (MCT) is applied to colloidal systems
interacting via short-range attractive interactions of Yukawa form. At low
temperatures MCT predicts a slowing down of the local dynamics and ergodicity
breaking transitions. The nonergodicity transitions share many features with
the colloidal gel transition, and are proposed to be the source of gelation in
colloidal systems. Previous calculations of the phase diagram are complemented
with additional data for shorter ranges of the attractive interaction, showing
that the path of the nonergodicity transition line is then unimpeded by the
gas-liquid critical curve at low temperatures. Particular attention is given to
the critical nonergodicity parameters, motivated by recent experimental
measurements. An asymptotic model is developed, valid for dilute systems of
spheres interacting via strong short-range attractions, and is shown to capture
all aspects of the low temperature MCT nonergodicity transitions.Comment: 12 pages, LaTeX, 5 eps figures, uses ioplppt.sty, to appear in J.
Phys.: Condens. Matte
Flory-Huggins theory for athermal mixtures of hard spheres and larger flexible polymers
A simple analytic theory for mixtures of hard spheres and larger polymers
with excluded volume interactions is developed. The mixture is shown to exhibit
extensive immiscibility. For large polymers with strong excluded volume
interactions, the density of monomers at the critical point for demixing
decreases as one over the square root of the length of the polymer, while the
density of spheres tends to a constant. This is very different to the behaviour
of mixtures of hard spheres and ideal polymers, these mixtures although even
less miscible than those with polymers with excluded volume interactions, have
a much higher polymer density at the critical point of demixing. The theory
applies to the complete range of mixtures of spheres with flexible polymers,
from those with strong excluded volume interactions to ideal polymers.Comment: 9 pages, 4 figure
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