24,037 research outputs found
Monte Carlo simulation of the transmission of measles: Beyond the mass action principle
We present a Monte Carlo simulation of the transmission of measles within a
population sample during its growing and equilibrium states by introducing two
different vaccination schedules of one and two doses. We study the effects of
the contact rate per unit time as well as the initial conditions on the
persistence of the disease. We found a weak effect of the initial conditions
while the disease persists when lies in the range 1/L-10/L ( being
the latent period). Further comparison with existing data, prediction of future
epidemics and other estimations of the vaccination efficiency are provided.
Finally, we compare our approach to the models using the mass action
principle in the first and another epidemic region and found the incidence
independent of the number of susceptibles after the epidemic peak while it
strongly fluctuates in its growing region. This method can be easily applied to
other human, animals and vegetable diseases and includes more complicated
parameters.Comment: 15 pages, 4 figures, 1 table, Submitted to Phys.Rev.
Cosmological neutrino bounds for non-cosmologists
I briefly review cosmological bounds on neutrino masses and the underlying
gravitational physics at a level appropriate for readers outside the field of
cosmology. For the case of three massive neutrinos with standard model
freezeout, the current 95% upper limit on the sum of their masses is 0.42 eV. I
summarize the basic physical mechanism making matter clustering such a
sensitive probe of massive neutrinos. I discuss the prospects of doing still
better in coming years using tools such as lensing tomography, approaching a
sensitivity around 0.03 eV. Since the lower bound from atmospheric neutrino
oscillations is around 0.05 eV, upcoming cosmological measurements should
detect neutrino mass if the technical and fiscal challenges can be met.Comment: 4 pages, 2 figs, in "Neutrino Physics", Proceedings of Nobel
Symposium 129, eds., L Bergstrom, O. Botner, P. Carlson, P. O. Hulth, and T.
Ohlsso
Evolution of an elliptical bubble in an accelerating extensional flow
Mathematical models that describe the dynamical behavior of a thin gas bubble embedded in a glass fiber during a fiber drawing process have been discussed and analyzed.
The starting point for the mathematical modeling was the equations presented in [1] for a glass fiber with a hole undergoing extensional flow. These equations were reconsidered here with the additional reduction that the hole, i.e. the gas bubble, was thin as compared to the radius of the fiber and of finite extent. The primary model considered was one in which the mass of the gas inside the bubble was fixed. This fixed-mass model involved equations for the axial velocity and fiber radius, and equations for the radius of the bubble and the gas pressure inside the bubble. The model equations assumed that the temperature of the furnace of the drawing tower was known.
The governing equations of the bubble are hyperbolic and predict that the bubble cannot extend beyond the limiting characteristics specified by the ends of the initial bubble shape. An analysis of pinch-off was performed, and it was found that pinch-off can occur, depending on the parameters of the model, due to surface tension when the bubble radius is small.
In order to determine the evolution of a bubble, a numerical method of solution was presented. The method was used to study the evolution of two different initial bubble shapes, one convex and the other non-convex. Both initial bubble shapes had fore-aft symmetry, and it was found that the bubbles stretched and elongated severely during the drawing process. For the convex shape, fore-aft symmetry was lost in the middle of the drawing process, but the symmetry was re-gained by the end of the drawing tower. A small amount of pinch-off was observed at each end for this case, so that the final bubble length was slightly shorter than its theoretical maximum length. For the non-convex initial shape, pinch-off occurred in the middle of the bubble resulting in two bubbles by the end of the fiber draw.
The two bubbles had different final pressures and did not have fore-aft symmetry.
An extension of the fixed-mass model was considered in which the gas in the bubble was allowed to diffuse into the surrounding glass. The governing equations for this leaky-mass model were developed and manipulated into a form suitable for a numerical treatment
Unitarization of Gluon Exchange Amplitudes and Rapidity Gaps at the Tevatron
Rapidity gaps between two hard jets at the Tevatron have been interpreted as
being due to the exchange of two gluons which are in an overall color-singlet
state. We show that this simple picture involves unitarity violating
amplitudes. Unitarizing the gluon exchange amplitude leads to qualitatively
different predictions for the fraction of -channel color singlet exchange
events in forward , or scattering, which better fit Tevatron
data.Comment: 21 pages, Revtex, 7 postscript figures included via epsf.sty.
Compressed postscript file of complete paper also available at
http://pheno.physics.wisc.edu/pub/preprints/1998/madph-98-1024.ps.Z or at
ftp://pheno.physics.wisc.edu/pub/preprints/1998/madph-98-1024.ps.
Neutrino Coherent Scattering Rates at Direct Dark Matter Detectors
Neutrino-induced recoil events may constitute a background to direct dark
matter searches, particularly for those detectors that strive to reach the
ton-scale and beyond. This paper discusses the expected neutrino-induced
background spectrum due to several of the most important sources, including
solar, atmospheric, and diffuse supernova neutrinos. The largest rate arises
from B produced solar neutrinos, providing upwards of events
per ton-year over all recoil energies for the heaviest nuclear targets. However
the majority of these B events are expected to be below the recoil
threshold of modern detectors. The remaining neutrino sources are found to
constitute a background to the WIMP-induced recoil rate only if the
WIMP-nucleon cross section is less than pb. Finally the sensitivity
to diffuse supernova neutrino flux for non-electron neutrino flavors is
discussed, and projected flux limits are compared with existing flux limits
A Homogenization Approach for Turbulent Channel Flows over Porous Substrates: Formulation and Implementation of Effective Boundary Conditions
The turbulent flow through a plane channel bounded by a single permeable wall is considered; this is a problem of interest since a carefully chosen distribution of grains and voids in the porous medium can result in skin friction reduction for the flow in the channel. In the homogenization approach followed here, the flow is not resolved in the porous layer, but an effective velocity boundary condition is developed (and later enforced) at a virtual interface between the porous bed and the channel flow. The condition is valid up to order two in terms of a small gauge factor, the ratio of microscopic to macroscopic length scales; it contains slip coefficients, plus surface and bulk permeability coefficients, which arise from the solution of microscale problems solved in a representative elementary volume. Using the effective boundary conditions, free of empirical parameters, direct numerical simulations are then performed in the channel, considering a few different porous substrates. The results, examined in terms of mean values and turbulence statistics, demonstrate the drag-reducing effects of porous substrates with streamwise-preferential alignment of the solid grains
Bio-oxidation of a low grade chalcopyrite ore by mixed culture of acidophilic bacteria
A study on the extent of biooxidation of a low grade Chalcopyrite ore using a mixed acidophilic bacterial consortium predominantly of the Acidithiobacillus ferrooxidans strain has been carried out. The influence of additive and pH on the bio-oxidation of the ore has been examined. The results of the investigations showed that bio-oxidation was enhanced by the addition of nutrient broth at lower pH. The enhancement in biooxidation of a chalcopyrite ore was 54% and 19% with and without addition of broth in 10 days incubation time, respectively. The study showed that at a lower pH (≤ 4.0), the biooxidation of the ore was higher in presence of broth. Consequently, in presence of nutrient broth, the concentration of Fe and Cu leached were 1200 mg/L and 350 mg/L; and without nutrient broth yielded 580 mg/L and 220 mg/L, respectively within 10 days of incubation and decreases afterwards
Étude de la dégradation d’une canalisation de conduite d’eau en béton armé
Dans ce travail nous nous sommes intéressés à l’étude des causes de dégradation d’une canalisation en béton armé dans la région de l’oriental au Maroc. Cet ouvrage est utilisé pour transporter de l’eau potable. L’altération de l’ouvrage n’a été constatée et de manière sévère que sur un tronçon bien situé. Dans ce cadre on a procédé à la détermination des causes de dégradation. Pour cela nous avons effectué un prélèvement d’échantillons du tronçon dégradé et de part et d’autre. Des échantillons témoins ont été réalisés à l’usine de fabrication des canalisations.Nous avons effectué le dosage de la teneur en chlorure et en ciment, étudié l’impact de la carbonatation et déterminé les pourcentages en silice et carbonates. Nous avons aussi mis au point la présence des ionschlorures en pourcentage assez important pouvant être responsable de la corrosion des aciers de frettage des tuyaux en béton précontraint et par conséquent des dégradations affectant ces tuyaux. La présence d’unenvironnement humide aurait favorisé la dégradation. Par ailleurs, la détermination de la teneur en chlorures par rapport à la masse de ciment a nécessité la détermination du pourcentage de ciment contenu dans le béton. Nous avons utilisé la méthode dite des inertes. La détermination de la teneur en anhydre carbonique CO2 a été réalisée par calcimétrie. Les résultats obtenus montrent que nous sommes en présence d’un béton ayant subi une légère carbonatation et contenant à la fois des teneurs en chlorures dépassant largement le seuil d’amorçage de la corrosion.Mots-clés : dégradation, canalisation, béton armé, corrosion, carbonatation
Universality of the preasymptotics in the hadron and photon diffraction
We note that it is premature to make a conclusion on the multiplicity of the
Pomerons on the basis of the available experimental data since the interactions
have a preasymptotic natureComment: 4 pages, latex, no figure
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