Vaccination strategies when vaccines are scarce: on conflicts between reducing the burden and avoiding the evolution of escape mutants

When vaccine supply is limited but population immunization urgent, theallocation of the available doses needs to be carefully considered. Oneaspect of dose allocation is the time interval between the first and thesecond injections in two-dose vaccines. By stretching this interval, more indi-viduals can be vaccinated with the first dose more quickly, which can bebeneficial in reducing case numbers, provided a single dose is sufficientlyeffective. On the other hand, there has been concern that intermediatelevels of immunity in partially vaccinated individuals may favour theevolution of vaccine escape mutants. In that case, a large fraction of half-vaccinated individuals would pose a risk—but only if they encounter thevirus. This raises the question whether there is a conflict between reducingthe burden and the risk of vaccine escape evolution or not. We develop anSIR-type model to assess the population-level effects of the timing of thesecond dose. Trade-offs can occur both if vaccine escape evolution is morelikely or if it is less likely in half-vaccinated than in unvaccinated individ-uals. Their presence or absence depends on the efficacies for susceptibilityand transmissibility elicited by a single dose

Cloud optical thickness and liquid water path – does the <i>k</i> coefficient vary with droplet concentration?

Cloud radiative transfer calculations in general circulation models involve a link between cloud microphysical and optical properties. Indeed, the liquid water content expresses as a function of the mean volume droplet radius, while the light extinction is a function of their mean surface radius. There is a small difference between these two parameters because of the droplet spectrum width. This issue has been addressed by introducing an empirical multiplying correction factor to the droplet concentration. Analysis of in situ sampled data, however, revealed that the correction factor decreases when the concentration increases, hence partially mitigating the aerosol indirect effect. <br><br> Five field experiments are reanalyzed here, in which standard and upgraded versions of the droplet spectrometer were used to document shallow cumulus and stratocumulus topped boundary layers. They suggest that the standard probe noticeably underestimates the correction factor compared to the upgraded versions. The analysis is further refined to demonstrate that the value of the correction factor derived by averaging values calculated locally along the flight path overestimates the value derived from liquid water path and optical thickness of a cloudy column, and that there is no detectable relationship between the correction factor and the droplet concentration. It is also shown that the droplet concentration dilution by entrainment-mixing after CCN activation is significantly stronger in shallow cumuli than in stratocumulus layers. These various effects are finally combined to produce the today best estimate of the correction factor to use in general circulation models

High-throughput data mined prediction of inorganic compounds and computational discovery of new lithium-ion battery cathode materials

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from PDF version of thesis.Includes bibliographical references (p. 117-129).The ability to computationally predict the properties of new materials, even prior to their synthesis, has been made possible due to the current accuracy of modern ab initio techniques. In some cases, high-throughput computations can be used to create large data sets of potential compounds and their computed properties. However, regardless of the field of application, such a computational high-throughput approach faces a major problem: to be relevant, the properties need to be computed on compounds (i.e., stoichiometries and crystal structures) that will be stable enough to be synthesized. In this thesis, we address this compound prediction problem through a combination of data mining and high-throughput Density Functional Theory. We first describe a method based on correlations between crystal structure prototypes that can be used with a limited computational budget to search for new ternary oxides. In addition, for the treatment of sparser data regions such as quaternaries, a new algorithm based on the data mining of ionic substitutions is proposed and analyzed. The second part of this thesis demonstrates the application of this highthroughput ab initio computing technique to the lithium-ion battery field. Here, we describe a large-scale computational search for novel cathode materials with specific battery properties, which enables experimentalists to focus on only the most promising chemistries. Finally, to illustrate the potential of new compound computational discovery using this approach, a novel chemical class of cathode materials, the carbonophosphates, is presented along with synthesis and electrochemical results.by Geoffroy Hautier.Ph.D

Critical point network for drainage between rough surfaces

In this paper, we present a network method for computing two-phase flows between two rough surfaces with significant contact areas. Low-capillary number drainage is investigated here since one-phase flows have been previously investigated in other contributions. An invasion percolation algorithm is presented for modeling slow displacement of a wetting fluid by a non wetting one between two rough surfaces. Short-correlated Gaussian process is used to model random rough surfaces.The algorithm is based on a network description of the fracture aperture field. The network is constructed from the identification of critical points (saddles and maxima) of the aperture field. The invasion potential is determined from examining drainage process in a flat mini-channel. A direct comparison between numerical prediction and experimental visualizations on an identical geometry has been performed for one realization of an artificial fracture with a moderate fractional contact area of about 0.3. A good agreement is found between predictions and observations

CARACTERISATION D'UN LASER Nd : YAG CONTINU A MODES COUPLES

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Pre-cruise and site surveys : a synthesis of marine geological and geophysical data on the Côte d'Ivoire-Ghana transform margin

ODP Leg 159 is the first drilling cruise dedicated to assess the sedimentary, tectonic, and thermal processes as well as the subsidence history operating during and after continental transform margin formation, the challenge being to improve and develop geological models applied to this specific type of ocean-continent boundary. The location of the Côte d'Ivoire-Ghana Transform Margin, within an equatorial region and located between two different oceanic basins (Central and South Atlantic) of different ages, also provided paleoceanographic potential for Leg 159. The marine geological and geophysical surveys briefly presented above, and with which Leg 159 was planned, have already provided noteworthy data making this segment of transform margin a well-investigated example of this type. It is anticipated that continuous coring and logging at all selected Leg 159 sites will answer many of the questions still in discussion and open new trends of investigation. (Résumé d'auteur

Potential of ensiling for efficient management of spent residue from solid state fermentation system

Studies on ensiling of spent solids from solid state fermentation process for production of cellulases by #Trichoderma harzianum$ showed that good quality ensiled solids can be obtained by using about 43% initial substrate dry matter with 0.3% ensiling additive. (Résumé d'auteur