1,534 research outputs found
alpha - HgS Nanocrystals: Synthesis, Structure and Optical Properties
Well-separated mercury sulfide (HgS) nanocrystals are synthesized by a wet
chemical route. Transmission electron microscopy studies show that nanocrystals
are nearly spherical in shape with average size of 9 nm. Grazing angle X-ray
diffraction confirms that HgS nanocrystals are in cinnabar phase. Particle
induced X-ray emission and Rutherford back scattering spectrometry analysis
reveal HgS nanocrystals are stoichiometric and free from foreign impurities.
The optical absorption measurements show two excitonic peaks corresponding to
electron-heavy hole and electron-light hole transitions, which are blue shifted
by 0.1 and 0.2 eV, respectively, from its bulk value, due to quantum size
effect. The experimental data obtained by optical absorption measurement is
simulated with a theoretical model considering the particle size distribution
as Gaussian
Editorial: Sustainable Production of Nutrient-Dense Foods
Feeding the world's growing population presents plant-based agriculture with enormous challenges as it is estimated that current agricultural production must increase 60 to 100 percent all else being unchanged (food waste levels, current trends in population growth and food consumption). The quantities and qualities of necessary food components, e.g., proteins, carbohydrates, lipids, and vitamins and minerals in plant products are highly relevant for human and animal consumption. These plant foods also contain a varied and limited range of bioactive compounds that have been associated with the prevention of chronic diseases including heart and circulation problems, cancer, diabetes, cataracts, and age-related functional decline
Pulsating flow in a planar diffuser upstream of automotive catalyst monoliths
The flow distribution across automotive exhaust catalysts has a significant effect on their conversion efficiency. The exhaust gas is pulsating and flow distribution is a function of engine operating condition, namely speed (frequency) and load (flow rate). This study reports on flow measurements made across catalyst monoliths placed downstream of a wide-angled planar diffuser presented with pulsating flow. Cycle-resolved particle image velocimetry (PIV) measurements were made in the diffuser and hot wire anemometry (HWA) downstream of the monoliths. The ratio of pulse period to residence time within the diffuser (defined as the J factor) characterises the flow distribution. During acceleration the flow remained attached to the diffuser walls for some distance before separating near the diffuser inlet later in the cycle. Two cases with J ∼ 3.5 resulted in very similar flow fields with the flow able to reattach downstream of the separation bubbles. With J = 6.8 separation occurred earlier with the flow field resembling, at the time of deceleration, the steady flow field. Increasing J from 3.5 to 6.8 resulted in greater flow maldistribution within the monoliths; steady flow producing the highest maldistribution in all cases for the same Re
Numerical Simulations of Magnetoacoustic-Gravity Waves in the Solar Atmosphere
We investigate the excitation of magnetoacoustic-gravity waves generated from
localized pulses in the gas pressure as well as in vertical component of
velocity. These pulses are initially launched at the top of the solar
photosphere that is permeated by a weak magnetic field. We investigate three
different configurations of the background magnetic field lines: horizontal,
vertical and oblique to the gravitational force. We numerically model
magnetoacoustic-gravity waves by implementing a realistic (VAL-C) model of
solar temperature. We solve two-dimensional ideal magnetohydrodynamic equations
numerically with the use of the FLASH code to simulate the dynamics of the
lower solar atmosphere. The initial pulses result in shocks at higher
altitudes. Our numerical simulations reveal that a small-amplitude initial
pulse can produce magnetoacoustic-gravity waves, which are later reflected from
the transition region due to the large temperature gradient. The atmospheric
cavities in the lower solar atmosphere are found to be the ideal places that
may act as a resonator for various oscillations, including their trapping and
leakage into the higher atmosphere. Our numerical simulations successfully
model the excitation of such wave modes, their reflection and trapping, as well
as the associated plasma dynamics
An assessment of CFD applied to steady flow in a planar diffuser upstream of an automotive catalyst
Flow maldistribution across automotive exhaust catalysts significantly affects their conversion efficiency. Flow behaviour can be predicted using computational fluid dynamics (CFD). This study investigates the application of CFD to modelling flow in a 2D system consisting of a catalyst monolith downstream of a wide-angled planar diffuser presented with steady flow. Two distinct approaches, porous medium and individual channels, are used to model monoliths of length 27 mm and 100 mm. Flow predictions are compared to particle image velocimetry (PIV) measurements made in the diffuser and hot wire anemometry (HWA) data taken downstream of the monolith. Both simulations compare favourably with PIV measurements, although the models underestimate the degree of mixing in the shear layer at the periphery of the emerging jet. Tangential velocities are predicted well in the central jet region but are overestimated elsewhere, especially at the closest measured distance, 2.5 mm from the monolith. The individual channels model is found to provide a more consistently accurate velocity profile downstream of the monolith. Maximum velocities, on the centre line and at the secondary peak near to the wall, are reasonably well matched for the cases where the flow is more maldistributed. Under these conditions, a porous medium model remains attractive because of low computational demand
Multiwavelength Observations of Supersonic Plasma Blob Triggered by Reconnection Generated Velocity Pulse in AR10808
Using multi-wavelength observations of Solar and Heliospheric Observatory
(SoHO)/Michelson Doppler Imager (MDI), Transition Region and Coronal Explorer
(TRACE) 171 \AA, and H from Culgoora Solar Observatory at Narrabri,
Australia, we present a unique observational signature of a propagating
supersonic plasma blob before an M6.2 class solar flare in AR10808 on 9th
September 2005. The blob was observed between 05:27 UT to 05:32 UT with almost
a constant shape for the first 2-3 minutes, and thereafter it quickly vanished
in the corona. The observed lower bound speed of the blob is estimated as
215 km s in its dynamical phase. The evidence of the blob with
almost similar shape and velocity concurrent in H and TRACE 171 \AA\
supports its formation by multi-temperature plasma. The energy release by a
recurrent 3-D reconnection process via the separator dome below the magnetic
null point, between the emerging flux and pre-existing field lines in the lower
solar atmosphere, is found to be the driver of a radial velocity pulse outwards
that accelerates this plasma blob in the solar atmosphere. In support of
identification of the possible driver of the observed eruption, we solve the
two-dimensional ideal magnetohydrodynamic equations numerically to simulate the
observed supersonic plasma blob. The numerical modelling closely match the
observed velocity, evolution of multi-temperature plasma, and quick vanishing
of the blob found in the observations. Under typical coronal conditions, such
blobs may also carry an energy flux of 7.0 ergs cm
s to re-balance the coronal losses above active regions.Comment: Solar Physics; 22 Pages; 8 Figure
Universal Equation for Efimov States
Efimov states are a sequence of shallow 3-body bound states that arise when
the 2-body scattering length is large. Efimov showed that the binding energies
of these states can be calculated in terms of the scattering length and a
3-body parameter by solving a transcendental equation involving a universal
function of one variable. We calculate this universal function using effective
field theory and use it to describe the three-body system of 4He atoms. We also
extend Efimov's theory to include the effects of deep 2-body bound states,
which give widths to the Efimov states.Comment: 8 pages, revtex4, 2 ps figures, table with numerical values of
universal function adde
Optical Activity From Extra Dimension
Optical activity, like Faraday effect, is a rotation of the plane of
polarization of propagating light in a medium and can be attributed to
different sources with distinct signatures. In this note we discuss the effect
of optical activity {\it{in vacuum}} due to Kaluza-Klein scalar field ,
in the presence of an external electro-magnetic field. The astrophysical
implication of this effect is indicated. We also point out the possibility of
observing the same in laboratory conditions.Comment: Four Page
Critical number of atoms for attractive Bose-Einstein condensates with cylindrically symmetrical traps
We calculated, within the Gross-Pitaevskii formalism, the critical number of
atoms for Bose-Einstein condensates with two-body attractive interactions in
cylindrical traps with different frequency ratios. In particular, by using the
trap geometries considered by the JILA group [Phys. Rev. Lett. 86, 4211
(2001)], we show that the theoretical maximum critical numbers are given
approximately by . Our results also show that, by
exchanging the frequencies and , the geometry with
favors the condensation of larger number of particles.
We also simulate the time evolution of the condensate when changing the ground
state from to using a 200ms ramp. A conjecture on higher order
nonlinear effects is also added in our analysis with an experimental proposal
to determine its signal and strength.Comment: (4 pages, 2 figures) To appear in Physical Review
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