6,478 research outputs found
A Wire Position Monitor System for the 1.3 GHZ Tesla-Style Cryomodule at the Fermilab New-Muon-Lab Accelerator
The first cryomodule for the beam test facility at the Fermilab New-Muon-Lab
building is currently under RF commissioning. Among other diagnostics systems,
the transverse position of the helium gas return pipe with the connected 1.3
GHz SRF accelerating cavities is measured along the ~15 m long module using a
stretched-wire position monitoring system. An overview of the wire position
monitor system technology is given, along with preliminary results taken at the
initial module cool down, and during further testing. As the measurement system
offers a high resolution, we also discuss options for use as a vibration
detector.Comment: 4 pp. 15th International Conference on RF Superconductivity
(SRF2011). 25-29 Jul 2011. Chicago, Illinois, US
Self-Consistent Field Theory of Brushes of Neutral Water-Soluble Polymers
The Self-Consistent Field theory of brushes of neutral water-soluble polymers
described by two-state models is formulated in terms of the effective Flory
interaction parameter that depends on both temperature, T
and the monomer volume fraction, . The concentration profiles,
distribution of free ends and compression force profiles are obtained in the
presence and in the absence of a vertical phase separation. A vertical phase
separation within the layer leads to a distinctive compression force profile
and a minimum in the plot of the moments of the concentration profile vs. the
grafting density. The analysis is applied explicitly to the Karalstrom model.
The relevance to brushes of Poly(N-isopropylacrylamide)(PNIPAM) is discussed.Comment: Accepted for publication in the Journal of Chemical Physic
Detection of quantum light in the presence of noise
Detection of quantum light in the presence of dark counts and background
radiation noise is considered. The corresponding positive operator-valued
measure is obtained and photocounts statistics of quantum light in the presence
of noise is studied.Comment: 4 pages, 1 figure; misprints correcte
Symmetric Exclusion Process with a Localized Source
We investigate the growth of the total number of particles in a symmetric
exclusion process driven by a localized source. The average total number of
particles entering an initially empty system grows with time as t^{1/2} in one
dimension, t/log(t) in two dimensions, and linearly in higher dimensions. In
one and two dimensions, the leading asymptotic behaviors for the average total
number of particles are independent on the intensity of the source. We also
discuss fluctuations of the total number of particles and determine the
asymptotic growth of the variance in one dimension.Comment: 7 pages; small corrections, references added, final versio
A consistent model for \pi N transition distribution amplitudes and backward pion electroproduction
The extension of the concept of generalized parton distributions leads to the
introduction of baryon to meson transition distribution amplitudes (TDAs),
non-diagonal matrix elements of the nonlocal three quark operator between a
nucleon and a meson state. We present a general framework for modelling nucleon
to pion () TDAs. Our main tool is the spectral representation for \pi N
TDAs in terms of quadruple distributions. We propose a factorized Ansatz for
quadruple distributions with input from the soft-pion theorem for \pi N TDAs.
The spectral representation is complemented with a D-term like contribution
from the nucleon exchange in the cross channel. We then study backward pion
electroproduction in the QCD collinear factorization approach in which the
non-perturbative part of the amplitude involves \pi N TDAs. Within our two
component model for \pi N TDAs we update previous leading-twist estimates of
the unpolarized cross section. Finally, we compute the transverse target single
spin asymmetry as a function of skewness. We find it to be sizable in the
valence region and sensitive to the phenomenological input of our \pi N TDA
model.Comment: 39 pages, 9 figure
Bootstrap and the physical values of resonance parameters
This is the 6th paper in the series developing the formalism to manage the
effective scattering theory of strong interactions. Relying on the theoretical
scheme suggested in our previous publications we concentrate here on the
practical aspect and apply our technique to the elastic pion-nucleon scattering
amplitude. We test numerically the pion-nucleon spectrum sum rules that follow
from the tree level bootstrap constraints. We show how these constraints can be
used to estimate the tensor and vector coupling constants. At last, we
demonstrate that the tree-level low energy expansion coefficients computed in
the framework of our approach show nice agreement with known experimental data.
These results allow us to claim that the extended perturbation scheme is quite
reasonable from the computational point of view.Comment: 41 pages, 7 figure
A discrete time relativistic Toda lattice
Four integrable symplectic maps approximating two Hamiltonian flows from the
relativistic Toda hierarchy are introduced. They are demostrated to belong to
the same hierarchy and to examplify the general scheme for symplectic maps on
groups equiped with quadratic Poisson brackets. The initial value problem for
the difference equations is solved in terms of a factorization problem in a
group. Interpolating Hamiltonian flows are found for all the maps.Comment: 32 pages, LaTe
High Resolution BPM Upgrade for the ATF Damping Ring at KEK
A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility
(ATF) damping ring has been accomplished, carried out by a KEK/FNAL/SLAC
collaboration under the umbrella of the global ILC R&D effort. The upgrade
consists of a high resolution, high reproducibility read-out system, based on
analog and processing, and also implements a new automatic gain error
correction schema. The technical concept and realization as well as results of
beam studies are presented.Comment: 3 pp. 10th European Workshop on Beam Diagnostics and Instrumentation
for Particle Accelerators DIPAC 2011, 16-18 May 2011. Hamburg, German
The Slowly Formed Guiselin Brush
We study polymer layers formed by irreversible adsorption from a polymer
melt. Our theory describes an experiment which is a ``slow'' version of that
proposed by Guiselin [Europhys. Lett., v. 17 (1992) p. 225] who considered
instantaneously irreversibly adsorbing chains and predicted a universal density
profile of the layer after swelling with solvent to produce the ``Guiselin
brush.'' Here we ask what happens when adsorption is not instantaneous. The
classic example is chemisorption. In this case the brush is formed slowly and
the final structure depends on the experiment's duration, . We find
the swollen layer consists of an inner region of thickness with approximately constant density and an outer region
extending up to height which has the same density decay as for the Guiselin case.Comment: 7 pages, submitted to Europhysics Letter
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