2,285 research outputs found
Wall influence on dynamics of a microbubble
The nonlinear dynamic behaviour of microscopic bubbles near a wall is
investigated. The Keller-Miksis-Parlitz equation is adopted, but modified to
account for the presence of the wall. This base model describes the time
evolution of the bubble surface, which is assumed to remain spherical, and
accounts for the effect of acoustic radiation losses owing to liquid
compressibility in the momentum conservation. Two situations are considered:
the base case of an isolated bubble in an unbounded medium; and a bubble near a
solid wall. In the latter case, the wall influence is modeled by including a
symmetrically oscillating image bubble. The bubble dynamics is traced using a
numerical solution of the model equation. Subsequently, Floquet theory is used
to accurately detect the bifurcation point where bubble oscillations stop
following the driving ultrasound frequency and undergo period-changing
bifurcations. Of particular interest is the detection of the subcritical period
tripling and quadrupling transition. The parametric bifurcation maps are
obtained as functions of non-dimensional parameters representing the bubble
radius, the frequency and pressure amplitude of the driving ultrasound field
and the distance from the wall. It is shown that the presence of the wall
generally stabilises the bubble dynamics, so that much larger values of the
pressure amplitude are needed to generate nonlinear responses.Comment: 25 pages, 14 figure
Detection, localization and quantification of the emissions of gas from the seabed in fieldwork and experimental studies using active sonar systems
Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins in NiFe / -FeO
We report studies of exchange bias and coercivity in ferromagnetic
NiFe layers coupled to antiferromagnetic (AF) (0001),
(110), and (112) -FeO layers. We show that AF
spin configurations which permit spin-flop coupling give rise to a strong
uniaxial anisotropy and hence a large coercivity, and that by annealing in
magnetic fields parallel to specific directions in the AF we can control either
coercivity or exchange bias. In particular, we show for the first time that a
reversible temperature-induced spin reorientation in the AF can be used to
control the exchange interaction.Comment: 15 pages, 5 figures, submitted to Phys. Rev. Let
The role of selenium supplementation in cardiovascular disease prevention: an in vitro study to identify the molecular mechanism(s).
Obesity is a worldwide epidemic, with two thirds of the UK population either overweight or obese (body mass index (BMI) 25–29·9 and >30 kg/m2 respectively). Obesity is characterised by systemic oxidative stress (OS), which itself results from chronically high levels of reactive oxidative species (ROS) and reduced antioxidant status. OS is considered to play a key role in cardiovascular disease (CVD) development by initiating atherosclerosis. In particular, increased monocyte ROS generation instigates atherosclerotic plaque formation by increasing the recruitment, binding and transmigration of monocytes across arterial endothelial cells into the arterial wall. An increased intake of dietary antioxidants or up-regulation of endogenous antioxidant enzymes may counteract this OS state and therefore lower CVD risk. Selenium is an essential dietary micronutrient which is incorporated within the catalytic site of endogenous antioxidant Glutathione Peroxidase (GPx) enzymes and protects cells from OS and consequent cell damage. There is, however, a lack of knowledge concerning both the effect of selenium supplementation in an OS state representative of sedentary overweight/obese individuals and the mechanisms involved. The aim of this work was to investigate the effect of selenium supplementation in modulating, in vitro, monocyte cell viability, ROS generation and antioxidant enzymes gene expression (GPx1/GPx4) when under OS. U937 monocyte cells were either supplemented, or not with sodium selenite (Na2SeO3; 100nM or 200nM) and cultured for 48 hours at 37°C. Paraquat (1 mM) and S-Nitroso-N-acetyl-DL-penicillamine (0·7 mM) (SNAP) were added to cells overnight to induce OS. Cell viability was assessed via MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay, ROS generation was determined by Flow Cytometry using CM-H2DC-FDA, while GPx1/GPx4 gene expression was quantified by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). PQ/SNAP treatment significantly reduced U937 cell viability and increased ROS generation compared to untreated control U937 cells; confirming the induction of OS. Supplementation with 100nM Na2SeO3, before PQ/SNAP treatment, significantly increased cell viability by 33% (p 0·05). Furthermore, 100nM Na2SeO3 supplementation significantly reduced ROS generation by 32% (p < 0·001) in cells treated with PQ/SNAP. Correspondingly, this increased GPx1 by 146% (p < 0·01) and GPx4 gene expression by 77% (p < 0·05), when compared to un-supplemented PQ/SNAP treated cells. This study indicates that selenium supplementation may be effective in counteracting the detrimental effects of OS by significantly increasing the expression of antioxidant genes; reinforcing endogenous antioxidant protection to quench ROS generation more effectively and improve cell viability. This preliminary data, in monocyte cells, indicates that GPx1 gene expression is affected considerably more by both selenium supplementation and OS when compared with GPx4. This suggests GPx1 may play a more important role in CVD prevention, with regards to selenium supplementation in overweight/obese individuals
On the Number of Iterations for Dantzig-Wolfe Optimization and Packing-Covering Approximation Algorithms
We give a lower bound on the iteration complexity of a natural class of
Lagrangean-relaxation algorithms for approximately solving packing/covering
linear programs. We show that, given an input with random 0/1-constraints
on variables, with high probability, any such algorithm requires
iterations to compute a
-approximate solution, where is the width of the input.
The bound is tight for a range of the parameters .
The algorithms in the class include Dantzig-Wolfe decomposition, Benders'
decomposition, Lagrangean relaxation as developed by Held and Karp [1971] for
lower-bounding TSP, and many others (e.g. by Plotkin, Shmoys, and Tardos [1988]
and Grigoriadis and Khachiyan [1996]). To prove the bound, we use a discrepancy
argument to show an analogous lower bound on the support size of
-approximate mixed strategies for random two-player zero-sum
0/1-matrix games
Sewage sludge composting in small towns, Station Bulletin, no.508
The Bulletin is a publication of the New Hampshire Agricultural Experiment Station, College of Life Sciences and Agriculture, University of New Hampshire, Durham, New Hampshire
The detection of tethered and rising bubbles using multiple acoustic techniques
There exists a range of acoustic techniques for characterizing bubble populations within liquids. Each technique has limitations, and complete characterization of a population requires the sequential or simultaneous use of several, so that the limitations of each find compensation in the others. Here, nine techniques are deployed using one experimental rig, and compared to determine how accurately and rapidly they can characterize given bubble populations. These are, specifically (i) two stationary bubbles attached to a wire; and (ii) injected, rising bubble
Amplification of simian retroviral sequences from human recipients of baboon liver transplants
Investigations into the use of baboons as organ donors for human transplant recipients, a procedure called xenotransplantation, have raised the specter of transmitting baboon viruses to humans and possibly establishing new human infectious diseases. Retrospective analysis of tissues from two human transplant recipients with end-stage hepatic disease who died 70 and 27 days after the transplantation of baboon livers revealed the presence of two simian retroviruses of baboon origin, simian foamy virus (SFV) and baboon endogenous virus (BaEV), in multiple tissue compartments. The presence of baboon mitochondrial DNA was also detected in these same tissues, suggesting that xenogeneic 'passenger leukocytes' harboring latent or active viral infections had migrated from the xenografts to distant sites within the human recipients. The persistence of SFV and BaEV in human recipients throughout the posttransplant period underscores the potential infectious risks associated with xenotransplantation
Resonance regimes of scattering by small bodies with impedance boundary conditions
The paper concerns scattering of plane waves by a bounded obstacle with
complex valued impedance boundary conditions. We study the spectrum of the
Neumann-to-Dirichlet operator for small wave numbers and long wave asymptotic
behavior of the solutions of the scattering problem. The study includes the
case when is an eigenvalue or a resonance. The transformation from the
impedance to the Dirichlet boundary condition as impedance grows is described.
A relation between poles and zeroes of the scattering matrix in the non-self
adjoint case is established. The results are applied to a problem of scattering
by an obstacle with a springy coating. The paper describes the dependence of
the impedance on the properties of the material, that is on forces due to the
deviation of the boundary of the obstacle from the equilibrium position
- …