27,653 research outputs found
Polydispersity Effects in the Dynamics and Stability of Bubbling Flows
The occurrence of swarms of small bubbles in a variety of industrial systems
enhances their performance. However, the effects that size polydispersity may
produce on the stability of kinematic waves, the gain factor, mean bubble
velocity, kinematic and dynamic wave velocities is, to our knowledge, not yet
well established. We found that size polydispersity enhances the stability of a
bubble column by a factor of about 23% as a function of frequency and for a
particular type of bubble column. In this way our model predicts effects that
might be verified experimentally but this, however, remain to be assessed. Our
results reinforce the point of view advocated in this work in the sense that a
description of a bubble column based on the concept of randomness of a bubble
cloud and average properties of the fluid motion, may be a useful approach that
has not been exploited in engineering systems.Comment: 11 pages, 2 figures, presented at the 3rd NEXT-SigmaPhi International
Conference, 13-18 August, 2005, Kolymbari, Cret
Electron bifurcation mechanism and homoacetogenesis explain products yields in mixed culture anaerobic fermentations
Anaerobic fermentation of organic wastes using microbial mixed cultures is a promising avenue to treat residues and obtain added-value products. However, the process has some important limitations that prevented so far any industrial application. One of the main issues is that we are not able to predict reliably the product spectrum (i.e. the stoichiometry of the process) because the complex microbial community behaviour is not completely understood. To address this issue, in this work we propose a new metabolic network of glucose fermentation by microbial mixed cultures that incorporates electron bifurcation and homoacetogenesis. Our methodology uses NADH balances to analyse published experimental data and evaluate the new stoichiometry proposed. Our results prove for the first time the inclusion of electron bifurcation in the metabolic network as a better description of the experimental results. Homoacetogenesis has been used to explain the discrepancies between observed and theoretically predicted yields of gaseous H2 and CO2 and it appears as the best solution among other options studied. Overall, this work supports the consideration of electron bifurcation as an important biochemical mechanism in microbial mixed cultures fermentations and underlines the importance of considering homoacetogenesis when analysing anaerobic fermentations
Triaxial Angular Momentum Projection and Configuration Mixing calculations with the Gogny force
We present the first implementation in the plane of the
generator coordinate method with full triaxial angular momentum and particle
number projected wave functions using the Gogny force. Technical details about
the performance of the method and the convergence of the results both in the
symmetry restoration and the configuration mixing parts are discussed in
detail. We apply the method to the study of Mg, the calculated energies
of excited states as well as the transition probabilities are compared to the
available experimental data showing a good overall agreement. In addition, we
present the RVAMPIR approach which provides a good description of the ground
and gamma bands in the absence of strong mixing.Comment: 40 pages,14 figure
The continuum description with pseudo-state wave functions
Benchmark calculations are performed aiming to test the use of two different
pseudo-state bases on the the Multiple Scattering expansion of the total
Transition amplitude (MST) scattering framework. Calculated differential cross
sections for p-6He inelastic scattering at 717 MeV/u show a good agreement
between the observables calculated in the two bases. This result gives extra
confidence on the pseudo-state representation of continuum states to describe
inelastic/breakup scattering.Comment: 4 pages, 2 figures. Published in Physical Review
Anomalous Roughening of Viscous Fluid Fronts in Spontaneous Imbibition
We report experiments on spontaneous imbibition of a viscous fluid by a model
porous medium in the absence of gravity. The average position of the interface
satisfies Washburn's law. Scaling of the interface fluctuations provides a
dynamic exponent z \simeq 3, indicative of global dynamics driven by capillary
forces. The complete set of exponents clearly shows that interfaces are not
self-affine, exhibiting distinct local and global scaling, both for time
(b=0.64\pm 0.02, b* =0.33 \pm 0.03) and space (a=1.94 \pm 0.20, a_loc=0.94 \pm
0.10). These values are compatible with an intrinsic anomalous scaling
scenario.Comment: 4 pages, 5 figure
Analysis and test of the central-blue-spot infall hallmark
The infall of material onto a protostar, in the case of optically thick line
emission, produces an asymmetry in the blue- and red-wing line emission. For an
angularly resolved emission, this translates in a blue central spot in the
first-order moment (intensity weighted velocity) map. An analytical expression
for the first-order moment intensity as a function of the projected distance
was derived, for the cases of infinite and finite infall radius. The effect of
a finite angular resolution, which requires the numerical convolution with the
beam, was also studied. This method was applied to existing data of several
star-forming regions, namely G31.41+0.31 HMC, B335, and LDN 1287, obtaining
good fits to the first-order moment intensity maps, and deriving values of the
central masses onto which the infall is taking place (G31.41+0.31 HMC: 70-120
; B335: 0.1 ; Guitar Core of LDN 1287: 4.8 ). The
central-blue-spot infall hallmark appears to be a robust and reliable indicator
of infall.Comment: Accepted for publication in A&
Quark pseudoscalar vertex and quark mass function with clover fermions : spontaneous symmetry breaking, OPE, symmetry restoration at small volume
We study the quark mass function on hypercubic lattices, in a large range of
physical volumes and cutoffs. To avoid the very large Wilson term artefact, we
exploit the relation between the quark mass function and the pseudoscalar
vertex in the continuum. We extrapolate to the chiral limit.
In function of the physical volume, we observe a striking discontinuity in
the properties of chiral extrapolation around a physical volume L_c 6
(GeV}^{-1}=1.2 fm. It is present in the quark mass function, which collapses
to zero, as well as in the pion mass and the quark condensate as directly
calculated from the pseudoscalar correlator. It is strongly reminiscent of the
phenomenon of chiral symmetry restoration observed by Neuberger and Narayanan
at around the same physical length.
In the case of spontaneous symmetry breaking, we confirm that the OPE of the
quark mass function, involving the quark condensate, is not operative at the
available momenta, even taking into account the unusually large high order
corrections to the Wilson coefficient calculated by Chetyrkin and Maier ; the
gap remains large, around a factor 2, even at the largest momenta available to
us (p \simeg GeV)Comment: 31 pages, 8 figures Comments added, one figure suppressed, various
typos correcte
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