24,208 research outputs found
Recommended from our members
Organic Geochemistry of a Hydrocarbon-rich Calcarenite from the Chicxulub Scientific Drilling Program
The organic geochemistry of hydrocarbon-rich core material recovered by the CSDP is examined to establish whether hydrocarbons are associated with the migration and emplacement of organic matter by post-impact hydrothermal activity
Control of scroll wave turbulence using resonant perturbations
Turbulence of scroll waves is a sort of spatio-temporal chaos that exists in
three-dimensional excitable media. Cardiac tissue and the Belousov-Zhabotinsky
reaction are examples of such media. In cardiac tissue, chaotic behaviour is
believed to underlie fibrillation which, without intervention, precedes cardiac
death. In this study we investigate suppression of the turbulence using
stimulation of two different types, "modulation of excitability" and "extra
transmembrane current". With cardiac defibrillation in mind, we used a single
pulse as well as repetitive extra current with both constant and feedback
controlled frequency. We show that turbulence can be terminated using either a
resonant modulation of excitability or a resonant extra current. The turbulence
is terminated with much higher probability using a resonant frequency
perturbation than a non-resonant one. Suppression of the turbulence using a
resonant frequency is up to fifty times faster than using a non-resonant
frequency, in both the modulation of excitability and the extra current modes.
We also demonstrate that resonant perturbation requires strength one order of
magnitude lower than that of a single pulse, which is currently used in
clinical practice to terminate cardiac fibrillation. Our results provide a
robust method of controlling complex chaotic spatio-temporal processes.
Resonant drift of spiral waves has been studied extensively in two dimensions,
however, these results show for the first time that it also works in three
dimensions, despite the complex nature of the scroll wave turbulence.Comment: 13 pages, 12 figures, submitted to Phys Rev E 2008/06/13. Last
version: 2008/09/18, after revie
Energy Density Functionals From the Strong-Coupling Limit Applied to the Anions of the He Isoelectronic Series
Anions and radicals are important for many applications including
environmental chemistry, semiconductors, and charge transfer, but are poorly
described by the available approximate energy density functionals. Here we test
an approximate exchange-correlation functional based on the exact
strong-coupling limit of the Hohenberg-Kohn functional on the prototypical case
of the He isoelectronic series with varying nuclear charge , which
includes weakly bound negative ions and a quantum phase transition at a
critical value of , representing a big challenge for density functional
theory. We use accurate wavefunction calculations to validate our results,
comparing energies and Kohn-Sham potentials, thus also providing useful
reference data close to and at the quantum phase transition. We show that our
functional is able to bind H and to capture in general the physics of
loosely bound anions, with a tendency to strongly overbind that can be proven
mathematically. We also include corrections based on the uniform electron gas
which improve the results.Comment: Accepted for the JCP Special Topic Issue "Advances in DFT
Methodology
Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub
Accepted versio
Jastrow correlation factor for atoms, molecules, and solids
A form of Jastrow factor is introduced for use in quantum Monte Carlo
simulations of finite and periodic systems. Test data are presented for atoms,
molecules, and solids, including both all-electron and pseudopotential atoms.
We demonstrate that our Jastrow factor is able to retrieve a large fraction of
the correlation energy
Examination of the factor structure of the Schizotypal Personality Questionnaire (SPQ) among British and Trinidadian adults
Much debate in schizotypal research has centred on the factor structure of the Schizotypal Personality Questionnaire (SPQ), with research variously showing higher-order dimensionality consisting of two to seven dimensions. In addition, cross-cultural support for the stability of those factors remains limited. Here, we examined the factor structure of the SPQ among British and Trinidadian adults. Participants from a White British sub-sample (n = 351) resident in the UK and from an African Caribbean sub-sample (n = 284) resident in Trinidad completed the SPQ. The higher-order factor structure of the SPQ was analysed through confirmatory factor analysis, followed by multiple-group analysis for the model of best-fit. Between-group differences for sex and ethnicity were investigated using multivariate analysis of variance in relation to the higher-order domains. The model of best-fit was the four-factor structure, which demonstrated measurement invariance across groups. Additionally, these data had an adequate fit for two alternative models: a) 3 factors and b) a modified 4-factor. The British sub-sample had significantly higher scores across all domains than the Trinidadian group, and men scored significantly higher on the disorganised domain than women. The four-factor structure received confirmatory support and, importantly, support for use with populations varying in ethnicity and culture
Transport properties of annealed CdSe nanocrystal solids
Transport properties of artificial solids composed of colloidal CdSe
nanocrystals (NCs) are studied from 6 K to 250 K, before and after annealing.
Annealing results in greatly enhanced dark and photocurrent in NC solids, while
transmission electron microscopy (TEM) micrographs show that the inter-dot
separation decreases. The increased current can be attributed to the
enhancement of inter-dot tunneling caused by the decreased separation between
NCs and by chemical changes in their organic cap. In addition, the absorption
spectra of annealed solids are slightly red-shifted and broadened. These
red-shifts may result from the change of the dielectric environment around the
NCs. Our measurements also indicate that Coulomb interactions between charges
on neighboring NCs play an important role in the tunneling current.Comment: 24 pages,4 figures, 1 tabl
Electro-hydrodynamics of binary electrolytes driven by modulated surface potentials
We study the electro-hydrodynamics of the Debye screening layer that arises
in an aqueous binary solution near a planar insulating wall when applying a
spatially modulated AC-voltage. Combining this with first order perturbation
theory we establish the governing equations for the full non-equilibrium
problem and obtain analytic solutions in the bulk for the pressure and velocity
fields of the electrolyte and for the electric potential. We find good
agreement between the numerics of the full problem and the analytics of the
linear theory. Our work provides the theoretical foundations of circuit models
discussed in the literature. The non-equilibrium approach also reveals
unexpected high-frequency dynamics not predicted by circuit models.Comment: 9 pages including 4 figures. Accepted for PRE
Frequency response in surface-potential driven electro-hydrodynamics
Using a Fourier approach we offer a general solution to calculations of slip
velocity within the circuit description of the electro-hydrodynamics in a
binary electrolyte confined by a plane surface with a modulated surface
potential. We consider the case with a spatially constant intrinsic surface
capacitance where the net flow rate is in general zero while harmonic rolls as
well as time-averaged vortex-like components may exist depending on the spatial
symmetry and extension of the surface potential. In general the system displays
a resonance behavior at a frequency corresponding to the inverse RC time of the
system. Different surface potentials share the common feature that the
resonance frequency is inversely proportional to the characteristic length
scale of the surface potential. For the asymptotic frequency dependence above
resonance we find a 1/omega^2 power law for surface potentials with either an
even or an odd symmetry. Below resonance we also find a power law omega^alpha
with alpha being positive and dependent of the properties of the surface
potential. Comparing a tanh potential and a sech potential we qualitatively
find the same slip velocity, but for the below-resonance frequency response the
two potentials display different power law asymptotics with alpha=1 and
alpha~2, respectively.Comment: 4 pages including 1 figure. Accepted for PR
- …