237 research outputs found
Turbulent Drag Reduction by Flexible and Rodlike Polymers: Crossover Effects at Small Concentrations
Drag reduction by polymers is bounded between two universal asymptotes, the
von-K\'arm\'an log-law of the law and the Maximum Drag Reduction (MDR)
asymptote. It is theoretically understood why the MDR asymptote is universal,
independent of whether the polymers are flexible or rodlike. The cross-over
behavior from the Newtonian von-K\'arm\'an log-law to the MDR is however not
universal, showing different characteristics for flexible and rodlike polymers.
In this paper we provide a theory for this cross-over phenomenology.Comment: 5 pages, 4 figures, submitted to Physical Review
Strategy for allocating the MSD magnets and vacuum chambers
An analogous strategy as applied for the MSI septum magnets allows an optimisation of the installation of the MSD septa regarding magnet and chamber allocation. Even if the gain in aperture is small, of the order of half a millimetre, it is not negligible and- being essentially for free - should nevertheless be implemented
A new concept in the design of the LHC beam dump
Recent Monte Carlo cascade simulations have shown that a reduction in the maximum of deposited energy density can be obtained by applying a uniform magnetic field over a front part of the graphite core of the LHC dump. This paper shows the effect of field strength on spatial distributions of absorbed energy and temperatures, and discusses problems to be solved when designing a suitable magnet
Apertures in the LHC Beam Dump System and Beam Losses During Beam Abort
The LHC beam dumping system (LBDS) is used to dispose accelerated protons and ions in a wide energy range from 450 GeV up to 7 TeV. An abort gap of s is foreseen to avoid sweeping particles through the LHC ring aperture. This paper gives a brief overview of the critical apertures in the extraction region and the two beam dump lines. MAD-X tracking studies have been made to investigate the impact of particles swept through the aperture due to extraction kicker failures or the presence of particles within the abort gap. The issue of failures during beam abort is a major concern for machine protection as well as a critical factor for safe operation of the experiments and their detectors
Resonant Third-Integer Extraction from the PS2
For the proposed PS2 accelerator several extraction systems are needed, including a slow third-integer resonant extraction. The requirements are presented together with the conceptual considerations for the sextupole locations and strengths, the separatrices at the extraction elements and the aperture implications for the overall machine. Calculations of the phase space separatrices have been computed with a new code for the physics of slow resonant extraction, which is briefly reviewed. Implications for the extraction equipment design and for the injection-extraction straight section optics are discussed
Delay of Disorder by Diluted Polymers
We study the effect of diluted flexible polymers on a disordered capillary
wave state. The waves are generated at an interface of a dyed water sugar
solution and a low viscous silicon oil. This allows for a quantitative
measurement of the spatio-temporal Fourier spectrum. The primary pattern after
the first bifurcation from the flat interface are squares. With increasing
driving strength we observe a melting of the square pattern. It is replaced by
a weak turbulent cascade. The addition of a small amount of polymers to the
water layer does not affect the critical acceleration but shifts the disorder
transition to higher driving strenghs and the short wave length - high
frequency fluctuations are suppressed
Dynamics of Strongly Deformed Polymers in Solution
Bead spring models for polymers in solution are nonlinear if either the
finite extensibility of the polymer, excluded volume effects or hydrodynamic
interactions between polymer segments are taken into account. For such models
we use a powerful method for the determination of the complete relaxation
spectrum of fluctuations at {\it steady state}. In general, the spectrum and
modes differ significantly from those of the linear Rouse model. For a tethered
polymer in uniform flow the differences are mainly caused by an inhomogeneous
distribution of tension along the chain and are most pronounced due to the
finite chain extensibility. Beyond the dynamics of steady state fluctuations we
also investigate the nonlinear response of the polymer to a {\em large sudden
change} in the flow. This response exhibits several distinct regimes with
characteristic decay laws and shows features which are beyond the scope of
single mode theories such as the dumbbell model.Comment: 7 pages, 3 figure
Influence of hepatitis G virus infection on liver disease
The influence of hepatitis G virus (HGV) infection on disease activity in hepatitis C related and unrelated liver disease was investigated in 254 individuals using an EIA polymerase chain reaction assay for HGV. One hundred patients had chronic hepatitis C, 26 primary biliary cirrhosis, and 30 alcoholic liver cirrhosis. In addition, 51 hepatitis B surface antigen (HBsAg)-positive and 47 anti-hepatitis C virus (HCV)-positive blood donors were screened. Hepatitis G virus was detected in 18% of patients with chronic hepatitis C, 13% of patients with alcoholic liver cirrhosis, 11 % of patients with primary biliary cirrhosis, 10% of anti-HCV-positive blood donors, and 2% of HBsAg-positive blood donors. Virus load and alanine aminotransferase (ALT) levels did not differ significantly in patients with HCV alone versus patients coinfected with HCV and HGV. However, mild liver fibrosis correlated with HGV coinfection. Hepatitis G virus did not influence ALT levels or liver damage in liver disease unrelated to viral infectio
Beam commissioning of injection into the LHC
The LHC injection tests and first turn beam commissioning took place in late summer 2008, after detailed and thorough preparation. The beam commissioning of the downstream sections of the SPS-to-LHC transfer lines and the LHC injection systems is described. The details of the aperture measurements in the injection regions are presented together with the performance of the injection related equipment. The measured injection stability is compared to the expectations. The operational issues encountered are discussed
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