1,937 research outputs found
IMECE2005-82897 MAGNETORHEOLOGICAL MEASUREMENTS IN SUSPENSIONS OF MAGNETIC NANOPARTICLES
ABSTRACT We report measurements of the torque required to restrain a polycarbonate spindle surrounded by ferrofluid in a cylindrical container and subjected to the rotating field generated by a two-pole magnetic induction motor stator, as a function of applied field amplitude and frequency, and for various values of the geometric aspect ratios of the problem. Simultaneously, an ultrasonic method was used to measure the azimuthal velocity profiles in the ferrofluid contained in the annular gap of our apparatus. These measurements are compared to a rigorous regular perturbation solution in the small parameter Ωτ (Ω = frequency and τ = ferrofluid magnetic relaxation time) of the ferrohydrodynamic flow problem in the zero spin viscosity and linear magnetization limits
Modulation theory of quantum tunneling into a Calogero-Sutherland fluid
Quantum hydrodynamics of interacting electrons with a parabolic single
particle spectrum is studied using the Calogero-Sutherland model. The effective
action and modulation equations, describing evolution of periodic excitations
in the fluid, are derived. Applications to the problem of a single electron
tunneling into the FQHE edge state are discussed
Many-particle correlations in non-equilibrium Luttinger liquid
We develop an operator-based approach to the problem of Luttinger liquid
conductor in a non-equilibrium stationary state. We show that the
coherent-state many-body fermionic density matrix as well as all fermionic
correlation functions out of equilibrium are given by one-dimensional
functional determinants of the Fredholm type. Thus, the model constitutes a
remarkable example of a many-body problem where all the correlation functions
can be evaluated exactly. On the basis of the general formalism we investigate
four-point correlation functions of the fermions coming out of the Luttinger
liquid wire. Obtained correlations in the fermionic distribution functions
represent the combined effect of interaction and non-equilibrium conditions.Comment: 23 pages,7 figure
Graphite in the bi-layer regime: in-plane transport
An interplay between the increase in the number of carriers and the decrease
in the scattering time is expected to result in a saturation of the in-plane
resistivity, , in graphite above room temperature. Contrary to this
expectation, we observe a pronounced increase in in the interval
between 300 and 900 K. We provide a theory of this effect based on intervalley
scattering of charge carriers by high-frequency, graphene-like optical phonons.Comment: 5 pages, 2 fi
Pumping current of a Luttinger liquid with finite length
We study transport properties in a Tomonaga-Luttinger liquid in the presence
of two time-dependent point like weak impurities, taking into account
finite-length effects. By employing analytical methods and performing a
perturbation theory, we compute the backscattering pumping current (I_bs) in
different regimes which can be established in relation to the oscillatory
frequency of the impurities and to the frequency related to the length and the
renormalized velocity (by the electron-electron interactions) of the charge
density modes. We investigate the role played by the spatial position of the
impurity potentials. We also show how the previous infinite length results for
I_bs are modified by the finite size of the system.Comment: 9 pages, 7 figure
Routine delivery of artemisinin-based combination treatment at fixed health facilities reduces malaria prevalence in Tanzania: an observational study
BACKGROUND Artemisinin-based combination therapy (ACT) has been promoted as a means to reduce malaria transmission due to their ability to kill both asexual blood stages of malaria parasites, which sustain infections over long periods and the immature derived sexual stages responsible for infecting mosquitoes and onward transmission. Early studies reported a temporal association between ACT introduction and reduced malaria transmission in a number of ecological settings. However, these reports have come from areas with low to moderate malaria transmission, been confounded by the presence of other interventions or environmental changes that may have reduced malaria transmission, and have not included a comparison group without ACT. This report presents results from the first large-scale observational study to assess the impact of case management with ACT on population-level measures of malaria endemicity in an area with intense transmission where the benefits of effective infection clearance might be compromised by frequent and repeated re-infection. METHODS A pre-post observational study with a non-randomized comparison group was conducted at two sites in Tanzania. Both sites used sulphadoxine-pyrimethamine (SP) monotherapy as a first-line anti-malarial from mid-2001 through 2002. In 2003, the ACT, artesunate (AS) co-administered with SP (AS + SP), was introduced in all fixed health facilities in the intervention site, including both public and registered non-governmental facilities. Population-level prevalence of Plasmodium falciparum asexual parasitaemia and gametocytaemia were assessed using light microscopy from samples collected during representative household surveys in 2001, 2002, 2004, 2005 and 2006. FINDINGS Among 37,309 observations included in the analysis, annual asexual parasitaemia prevalence in persons of all ages ranged from 11% to 28% and gametocytaemia prevalence ranged from <1% to 2% between the two sites and across the five survey years. A multivariable logistic regression model was fitted to adjust for age, socioeconomic status, bed net use and rainfall. In the presence of consistently high coverage and efficacy of SP monotherapy and AS + SP in the comparison and intervention areas, the introduction of ACT in the intervention site was associated with a modest reduction in the adjusted asexual parasitaemia prevalence of 5 percentage-points or 23% (p < 0.0001) relative to the comparison site. Gametocytaemia prevalence did not differ significantly (p = 0.30). INTERPRETATION The introduction of ACT at fixed health facilities only modestly reduced asexual parasitaemia prevalence. ACT is effective for treatment of uncomplicated malaria and should have substantial public health impact on morbidity and mortality, but is unlikely to reduce malaria transmission substantially in much of sub-Saharan Africa where individuals are rapidly re-infected.Financial support for IMPACT-Tz came primarily from CDC, the U.S. Agency for International Development and the Wellcome Trust
Time resolved particle dynamics in granular convection
We present an experimental study of the movement of individual particles in a
layer of vertically shaken granular material. High-speed imaging allows us to
investigate the motion of beads within one vibration period. This motion
consists mainly of vertical jumps, and a global ordered drift. The analysis of
the system movement as a whole reveals that the observed bifurcation in the
flight time is not adequately described by the Inelastic Bouncing Ball Model.
Near the bifurcation point, friction plays and important role, and the branches
of the bifurcation do not diverge as the control parameter is increased. We
quantify the friction of the beads against the walls, showing that this
interaction is the underlying mechanism responsible for the dynamics of the
flow observed near the lateral wall
Quantum fluctuations of one-dimensional free fermions and Fisher-Hartwig formula for Toeplitz determinants
We revisit the problem of finding the probability distribution of a fermionic
number of one-dimensional spinless free fermions on a segment of a given
length. The generating function for this probability distribution can be
expressed as a determinant of a Toeplitz matrix. We use the recently proven
generalized Fisher--Hartwig conjecture on the asymptotic behavior of such
determinants to find the generating function for the full counting statistics
of fermions on a line segment. Unlike the method of bosonization, the
Fisher--Hartwig formula correctly takes into account the discreteness of
charge. Furthermore, we check numerically the precision of the generalized
Fisher--Hartwig formula, find that it has a higher precision than rigorously
proven so far, and conjecture the form of the next-order correction to the
existing formula.Comment: 17 pages, 2 figures, Latex, iopart.cl
A Field Approach to 3D Gene Expression Pattern Characterization
We present a vector field method for obtaining the spatial organization of 3D
patterns of gene expression based on gradients and lines of force obtained by
numerical integration. The convergence of these lines of force in local maxima
are centers of gene expression, providing a natural and powerful framework to
characterize the organization and dynamics of biological structures. We apply
this novel methodology to analyze the expression pattern of the Enhanced Green
Fluorescent Protein (EGFP) driven by the promoter of light chain myosin II
during zebrafish heart formation.Comment: 9 pages, 2 figures, The following article has been submitted to
Applied Physics Letters. If it is published, it will be found online at
http://apl.aip.or
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