1,114 research outputs found
Coexisting Pulses in a Model for Binary-Mixture Convection
We address the striking coexistence of localized waves (`pulses') of
different lengths which was observed in recent experiments and full numerical
simulations of binary-mixture convection. Using a set of extended
Ginzburg-Landau equations, we show that this multiplicity finds a natural
explanation in terms of the competition of two distinct, physical localization
mechanisms; one arises from dispersion and the other from a concentration mode.
This competition is absent in the standard Ginzburg-Landau equation. It may
also be relevant in other waves coupled to a large-scale field.Comment: 5 pages revtex with 4 postscript figures (everything uuencoded
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Intracardiac echocardiography in the diagnosis of prosthetic valve endocarditis
These images illustrate a new use of ICE as a diagnostic modality for prosthetic valve endocarditis. Although a few studies have examined the role of ICE in the evaluation of valvular pathology, its clinical role has primarily been within the electrophysiology laboratory to guide catheter placement. As this technology continues to evolve, ICE may supplement other imaging modalities and find new clinical applications
Worm Structure in Modified Swift-Hohenberg Equation for Electroconvection
A theoretical model for studying pattern formation in electroconvection is
proposed in the form of a modified Swift-Hohenberg equation. A localized state
is found in two dimension, in agreement with the experimentally observed
``worm" state. The corresponding one dimensional model is also studied, and a
novel stationary localized state due to nonadiabatic effect is found. The
existence of the 1D localized state is shown to be responsible for the
formation of the two dimensional ``worm" state in our model
Yohimbine as a pharmacological probe for alcohol research: a systematic review of rodent and human studies
Alcohol use disorder (AUD) is a significant public health concern, contributing to a myriad of social, psychological, and physiological issues. Despite substantial efforts within the alcohol research field, promising preclinical findings have failed to translate to clinical use, highlighting the necessity to develop safe and effective pharmacological probes with the ability to be used in preclinical and clinical research. Yohimbine, an alpha 2 adrenergic receptor antagonist, is a well-validated pharmacological tool that has been widely employed in alcohol studies to evaluate noradrenergic activation. This scoping systematic review examines published literature in rodent and human studies involving the use of yohimbine relevant to alcohol research. We conducted a systematic literature review of MEDLINE, Embase, Web of Science Core Collection, CINAHL, PsycInfo, and Cochrane Central Register of Controlled Trials to identify: (1) Experimental Characteristics and Methodology, (2) Sex Differences, (3) Neurochemical Systems and Brain Regions, and (4) Discussion of Applications for Medication Development. Sixty-seven (62 preclinical and 5 clinical) studies were identified meeting the stated criteria, comprising extensive evidence supporting the use of yohimbine as a safe, titratable pharmacological agent for translational alcohol research. Support for the use of yohimbine as a fully translational tool, however, is hindered by limited available findings from human laboratory studies, as well as a dearth of studies examining sex differences in yohimbine's mechanistic actions. Additional consideration should be given to further translational modeling, ideally allowing for parallel preclinical and clinical assessment of yohimbine, methodological assessment of neurochemical systems and brain regions
Mutator Dynamics on a Smooth Evolutionary Landscape
We investigate a model of evolutionary dynamics on a smooth landscape which
features a ``mutator'' allele whose effect is to increase the mutation rate. We
show that the expected proportion of mutators far from equilibrium, when the
fitness is steadily increasing in time, is governed solely by the transition
rates into and out of the mutator state. This results is a much faster rate of
fitness increase than would be the case without the mutator allele. Near the
fitness equilibrium, however, the mutators are severely suppressed, due to the
detrimental effects of a large mutation rate near the fitness maximum. We
discuss the results of a recent experiment on natural selection of E. coli in
the light of our model.Comment: 4 pages, 3 figure
Convection in Binary Fluid Mixtures. II. Localized Traveling Waves. (Physical Review E, in press)
Nonlinear, spatially localized structures of traveling convection rolls are
investigated in quantitative detail as a function of Rayleigh number for two
different Soret coupling strengths (separation ratios) with Lewis and Prandtl
numbers characterizing ethanol-water mixtures. A finite-difference method was
used to solve the full hydrodynamic field equations numerically. Structure and
dynamics of these localized traveling waves (LTW) are dominated by the
concentration field. Like in the spatially extended convective states ( cf.
accompanying paper), the Soret-induced concentration variations strongly
influence, via density changes, the buoyancy forces that drive convection. The
spatio-temporal properties of this feed-back mechanism, involving boundary
layers and concentration plumes, show that LTW's are strongly nonlinear states.
Light intensity distributions are determined that can be observed in side-view
shadowgraphs. Detailed analyses of all fields are made using colour-coded
isoplots, among others. In the frame comoving with their drift velocity, LTW's
display a nontrivial spatio-temporal symmetry consisting of time-translation by
half an oscillation period combined with vertical reflection through the
horizontal midplane of the layer. A time-averaged concentration current is
driven by a phase difference between the waves of concentration and vertical
velocity in the bulk of the LTW state. The associated large-scale concentration
redistribution stabilizes the LTW and controls its drift velocity into the
quiescent fluid by generating a buoyancy-reducing concentration "barrier" ahead
of the leading LTW front. The selection of the width of the LTW's is
investigated and comparisons with experiments are presented.Comment: 18 pages and 6 figures as uuencoded Postscript file (using uufiles) 1
color figure as uuencoded Postscript file, a high resolution version of the
color figure (about 10MB) can be requested from [email protected] or
[email protected].: (Barten)present address: PSI, CH-5232 Villigen
PSI, Switzerlan
Subcritical instabilities in a convective fluid layer under a quasi-1D heating
The study and characterization of the diversity of spatiotemporal patterns
generated when a rectangular layer of fluid is locally heated beneath its free
surface is presented. We focus on the instability of a stationary cellular
pattern of wave number which undergoes a globally subcritical transition
to traveling waves by parity-breaking symmetry. The experimental results show
how the emerging traveling mode () switches on a resonant triad
(, , ) within the cellular pattern yielding a ``mixed''
pattern. The nature of this transition is described quantitatively in terms of
the evolution of the fundamental modes by complex demodulation techniques. The
B\' enard-Marangoni convection accounts for the different dynamics depending on
the depth of the fluid layer and on the vertical temperature difference. The
existence of a hysteresis cycle has been evaluated quantitatively. When the
bifurcation to traveling waves is measured in the vicinity of the codimension-2
bifurcation point, we measure a decrease of the subcritical interval in which
the traveling mode becomes unstable. From the traveling wave state the system
under goes a {\it new} global secondary bifurcation to an alternating pattern
which doubles the wavelength () of the primary cellular pattern, this
result compares well with theoretical predictions [P. Coullet and G. Ioss, {\em
Phys. Rev. Lett.} {\bf 64}, 8 66 (1990)]. In this cascade of bifurcations
towards a defect dynamics, bistability due to the subcritical behavior of our
system is the reason for the coexistence of two different modulated patterns
connected by a front. These fronts are stationary for a finite interval of the
control parameters.Comment: 13 pages, 12 figure
Epistemic roles of materiality within a collaborative invention project at a secondary school
In this study, we examined maker‐centred learning from an epistemic perspective, highlighting the agentic role of material engagement and artefacts in learning and creativity. The use of physical materials plays a crucial role in maker activities where the socio‐epistemic aspects of knowledge creation entangle with the designing and making of physical artefacts. By taking a case study perspective, we analysed video data from nine design sessions involving a team of students (aged 13 to 14) developing an invention. First, we analysed knowledge that was built during the process. Our analysis revealed how design ideas evolved from preliminary to final stages and, together with the expressed design problems and conversations preceding the ideas, formed an epistemic object pursued by the team. Next, we included non‐human agencies into the analysis to understand the role of materials in the process. Features of materials and human design intentions both constrained and enabled idea improvement and knowledge creation, intermixing meanings and materials. Material making invited the students to not only rely on human rationalisation, but also to think together with the materials.In this study, we examined maker-centred learning from an epistemic perspective, highlighting the agentic role of material engagement and artefacts in learning and creativity. The use of physical materials plays a crucial role in maker activities where the socio-epistemic aspects of knowledge creation entangle with the designing and making of physical artefacts. By taking a case study perspective, we analysed video data from nine design sessions involving a team of students (aged 13 to 14) developing an invention. First, we analysed knowledge that was built during the process. Our analysis revealed how design ideas evolved from preliminary to final stages and, together with the expressed design problems and conversations preceding the ideas, formed an epistemic object pursued by the team. Next, we included non-human agencies into the analysis to understand the role of materials in the process. Features of materials and human design intentions both constrained and enabled idea improvement and knowledge creation, intermixing meanings and materials. Material making invited the students to not only rely on human rationalisation, but also to think together with the materials.Peer reviewe
Convective Fingering of an Autocatalytic Reaction Front
We report experimental observations of the convection-driven fingering
instability of an iodate-arsenous acid chemical reaction front. The front
propagated upward in a vertical slab; the thickness of the slab was varied to
control the degree of instability. We observed the onset and subsequent
nonlinear evolution of the fingers, which were made visible by a {\it p}H
indicator. We measured the spacing of the fingers during their initial stages
and compared this to the wavelength of the fastest growing linear mode
predicted by the stability analysis of Huang {\it et. al.} [{\it Phys. Rev. E},
{\bf 48}, 4378 (1993), and unpublished]. We find agreement with the thickness
dependence predicted by the theory.Comment: 11 pages, RevTex with 3 eps figures. To be published in Phys Rev E,
[email protected], [email protected], [email protected]
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