37 research outputs found
Polymer Shape Anisotropy and the Depletion Interaction
We calculate the second and third virial coefficients of the effective
sphere-sphere interaction due to polymer depletion. By utilizing the anisotropy
of a typical polymer conformation, we can consider polymers that are roughly
the same size as the spherical inclusions. We argue that recent experiments can
confirm this anisotropy.Comment: 4 pages, 4 eps figures, RevTe
Irradiation of luminescence dosimeters in pulsed mixed radiation fields
UHDpulse - Metrology for Advanced Radiotherapy using beams with Ultra-High
Pulse Dose Rates is a European project aimed at developing novel dosimetry
standards, as well as improving existing ones, for FLASH radiotherapy, very
high energy electrons radiotherapy, and laser-driven medical accelerators.
Within the scope of this project, Thermoluminescence (TL) and Optically
Stimulated Luminescence (OSL) detectors are used to measure stray radiation
fields. Experiments performed with conventional pulsed particle-beams allow to
characterize the dosimeters in known and controllable radiation fields. In
turn, this allows to develop models and predict their behavior in complex
radiation fields, such as those at laser-driven and FLASH facilities. TL and
OSL detectors were irradiated at the Microtron MT25 electron accelerator in
Prague, Czech Republic. GAFChromicTM films and plastic nuclear track detectors
were used to study the beam profile and the neutron background respectively.
The responses of the different detector to the pulsed mixed radiation fields of
the Microtron MT25 are compared among each other and presented in this paper
Isotropic-nematic phase equilibria in the Onsager theory of hard rods with length polydispersity
We analyse the effect of a continuous spread of particle lengths on the phase
behavior of rodlike particles, using the Onsager theory of hard rods. Our aim
is to establish whether ``unusual'' effects such as isotropic-nematic-nematic
(I-N-N) phase separation can occur even for length distributions with a single
peak. We focus on the onset of I-N coexistence. For a log-normal distribution
we find that a finite upper cutoff on rod lengths is required to make this
problem well-posed. The cloud curve, which tracks the density at the onset of
I-N coexistence as a function of the width of the length distribution, exhibits
a kink; this demonstrates that the phase diagram must contain a three-phase
I-N-N region.
Theoretical analysis shows that in the limit of large cutoff the cloud point
density actually converges to zero, so that phase separation results at any
nonzero density; this conclusion applies to all length distributions with
fatter-than-exponentail tails. Finally we consider the case of a Schulz
distribution, with its exponential tail. Surprisingly, even here the long rods
(and hence the cutoff) can dominate the phase behaviour, and a kink in the
cloud curve and I-N-N coexistence again result. Theory establishes that there
is a nonzero threshold for the width of the length distribution above which
these long rod effects occur, and shows that the cloud and shadow curves
approach nonzero limits for large cutoff, both in good agreement with the
numerical results.Comment: 20 pages, 13 figure
FLASH Modalities Track (Oral Presentations) OVERVIEW AND CURRENT STATUS OF THE JOINT RESEARCH PROJECT UHDPULSE: “METROLOGY FOR ADVANCED RADIOTHERAPY USING PARTICLE BEAMS WITH ULTRA-HIGH PULSE DOSE RATES”
The syndrome of inappropriate secretion of antidiuretic hormone and the urinary excretion of aldosterone
Enhancement of Diffusion-Controlled Reaction Rates by Surface-Induced Orientational Restriction
We explore the means by which immobilization of a substrate on a surface can increase the rate of a diffusion-controlled enzymatic reaction. A quasichemical approach is developed and compared with Brownian dynamics simulations. We use these methods to show that restricting only the orientation of the enzyme by long-range interactions with the surface is sufficient for enhancing catalysis