Drag Reduction by Bubble Oscillations

Drag reduction in stationary turbulent flows by bubbles is sensitive to the dynamics of bubble oscillations. Without this dynamical effect the bubbles only renormalize the fluid density and viscosity, an effect that by itself can only lead to a small percentage of drag reduction. We show in this paper that the dynamics of bubbles and their effect on the compressibility of the mixture can lead to a much higher drag reduction.Comment: 7 pages, 1 figure, submitted to Phys. Rev.

Small scale statistics of viscoelastic turbulence

The small scale statistics of homogeneous isotropic turbulence of dilute polymer solutions is investigated by means of direct numerical simulations of a simplified viscoelastic fluid model. It is found that polymers only partially suppress the turbulent cascade below the Lumley scale, leaving a remnant energy flux even for large elasticity. As a consequence, fluid acceleration in viscoelastic flows is reduced with respect to Newtonian turbulence, whereas its rescaled probability density is left unchanged. At large scales the velocity field is found to be unaffected by the presence of polymers.Comment: 7 pages, 4 figure

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

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

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 $3 \mu$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

Protecting LHC Components Against Radiation Resulting From an Unsynchronized Beam Abort

The effect of possible accidental beam loss in the LHC on the IP5 and IP6 insertion elements is studied via realistic Monte Carlo simulations. The scenario studied is beam loss due to unsynchronized abort at an accidental prefire of one of the abort kicker modules. Simulations show that this beam loss would result in severe heating of the IP5 and IP6 superconducting (SC) quadrupoles. Contrary to the previous considerations with a stationary set of collimators in IP5, collimators in IP6 close to the cause are proposed: a movable collimator upstream of the Q4 quadrupole and a stationary one upstream of the extraction septum MSD. The calculated temperature rise in the optimal set of collimators is quite acceptable. All SC magnets are protected by these collimators against damage

Role of Gastric Colonization in Nosocomial Infections and Endotoxemia: A Prospective Study in Neurosurgical Patients on Mechanical Ventilation

The role of gastric microbial colonization in nosocomial infections and endotoxemia was investigated prospectively in 40 neurosurgical patients requiring mechanical ventilation for >48 h. Each was studied up to 7 d. Swabs from the nose and oropharynx were cultured at admission, and aspirates from the stomach and trachea were cultured daily until enteral alimentation was started. Patients were evaluated every second day for endotoxemia and coagulation activation. Of 153 gastric aspirates, 66.7% contained microorganisms at a mean quantity of 107 cfu/ml, Nosocomial pneumonia occurred in 15 patients, septicemia in 5, and meningitis in 1. The stomach was the evident source of infection in only 1 patient with pneumonia. Of 140 plasma samples, 12 (8.6%) from 10 patients showed detectable endotoxin levels, but there was no association between endotoxemia or coagulation activation and the presence of microorganisms in the stomach. The stomach was not an important source for nosocomial infections or endotoxemia, even in patients with high gastric p

Dynamics of threads and polymers in turbulence: power-law distributions and synchronization

We study the behavior of threads and polymers in a turbulent flow. These objects have finite spatial extension, so the flow along them differs slightly. The corresponding drag forces produce a finite average stretching and the thread is stretched most of the time. Nevertheless, the probability of shrinking fluctuations is significant and is known to decay only as a power-law. We show that the exponent of the power law is a universal number independent of the statistics of the flow. For polymers the coil-stretch transition exists: the flow must have a sufficiently large Lyapunov exponent to overcome the elastic resistance and stretch the polymer from the coiled state it takes otherwise. The probability of shrinking from the stretched state above the transition again obeys a power law but with a non-universal exponent. We show that well above the transition the exponent becomes universal and derive the corresponding expression. Furthermore, we demonstrate synchronization: the end-to-end distances of threads or polymers above the transition are synchronized by the flow and become identical. Thus, the transition from Newtonian to non-Newtonian behavior in dilute polymer solutions can be seen as an ordering transition.Comment: 13 pages, version accepted to Journal of Statistical Mechanic

Salovum Egg Yolk Containing Antisecretory Factor As an Adjunct Therapy in Severe Cholera in Adult Males: A Pilot Study

Cholera involves stimulation of intestinal secretory process in response to cholera toxin leading to profuse watery diarrhoea that might cause death due to dehydration unless timely rehydration therapy is initiated. Efforts to identify and test potential antisecretory agents are ongoing. Antisecretory factor (AF) is a naturally-occurring protein produced in the human secretory organs, including the intestine, with antisectory properties demonstrated in animal and human models of secretory diarrhoea. Salovum egg yolk powder contains proteins with antisecretory properties in a much higher (500 times) concentration than that of normal hen eggs. This is achieved by feeding hens with specially-processed cereals, capable of inducing proteins with antisecretory properties in the yolk. The aim of the study was to examine the effect of Salovum egg yolk powder containing AF in the treatment of adult cholera patients. In an open, randomized controlled trial (pilot study), 40 adult male patients with severe cholera were studied: 20 received standard treatment (oral rehydration solution, antibiotic, and usual hospital diet) plus Salovum egg yolk powder (study group) and 20 received standard treatment alone (control group). All the patients received tablet doxycycline (300 mg) once immediately after randomization. Written informed consent was obtained from each subject before enrollment. The main outcome measures were stool weight and duration of diarrhoea. The demographic and baseline clinical characteristics of the study patients were comparable between the groups. No significant differences were found in the mean stool weight, g/kg of body-weight during the first 24 hours [study vs control group, mean±standard deviation (SD), 218±119 vs 195±136], second 24 hours (mean±SD, 23±39 vs 22±34), and cumulative up to 72 hours (mean±SD, 245±152 vs 218±169). The duration (hours) of diarrhoea after admission in the hospital was also similar in both the groups (mean±SD, 33±14 vs 32±10). No adverse effect was observed. Salovum egg powder containing AF as an adjunct therapy in the treatment of severe cholera could not demonstrate any beneficial effect. Further studies with higher doses of Salovum egg yolk powder might be considered in future to establish its antisecretory effect

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