16,767 research outputs found
Kinetics of in situ epoxidation of hemp oil under heterogeneous reaction conditions: an overview with preliminary results
Epoxidised hemp oil (EHO) was synthesised in the laboratory by reacting hemp oil (HO) with peroxyacetic acid (PA) in a batch reactor. The peroxyacetic acid was formed in situ from acetic acid (AA) and hydrogen peroxide (H2O2) in the presence on an acidic ion exchange resin (Amberlite IR-120) as catalyst. The overall reaction can be thought of as having two components. The first being epoxidation, a homogenous reaction which occurs at the interface of the aqueous phase and the HO phase while the second is the formation of PA, a heterogeneous reaction at the interface of the aqueous phase and the solid catalyst phase. The overall reaction kinetics were modelled by applying the Langmuir-Hinshelwood-Hougen-Watson (LHHW) model to heterogeneous reactions. Of the steps in the reaction it is postulated that the formation of PA is rate limiting, while the epoxidation occurs comparatively fast negating the requirement for an additional homogenous model. The diffusion steps in the reaction are also ignored in the kinetic model as it is believed that their effects are negligible due to intensive mixing in the batch reactor. Experiments were used to determine the optimal molar ratios of reactants and it was found that at these conditions 88% conversion of double bonds to epoxy groups occurred. The kinetic model was found to be in good agreement with the experimental results
Supergravity duals of gauge theories from F(4) gauged supergravity in six dimensions
We construct supergravity solutions dual to twisted field theories that are
the worldvolume theories of D4-branes wrapped on 2, 3-cycles, and NS-fivebranes
on 3-cycles. We first obtain the solutions for the Romans' six-dimensional
gauged supergravity theories and then up-lift them to ten dimensions. In
particular, we find solutions for field configurations with either non-Abelian
fields or B-fields being excited. One of these solutions, in the massless case,
is up-lifted to the massless type IIA string theory. This is the first example
of such a kind. The cases studied provide new examples of the AdS/CFT duality
involving twisted field theories.Comment: 26 pages, 3 figures, minor changes and references added to match the
published versio
Looking for a charge asymmetry in cosmic rays
We combine the data from PAMELA and FERMI-LAT cosmic ray experiments by
introducing a simple sum rule. This allows to investigate whether the lepton
excess observed by these experiments is charge symmetric or not. We also show
how the data can be used to predict the positron fraction at energies yet to be
explored by the AMS-02 experiment.Comment: Contribution to the proceedings of DISCRETE 2010, 5 pages, 2 figure
Immunity of intersubband polaritons to inhomogeneous broadening
We demonstrate that intersubband (ISB) polaritons are robust to inhomogeneous
effects originating from the presence of multiple quantum wells (MQWs). In a
series of samples that exhibit mid-infrared ISB absorption transitions with
broadenings varying by a factor of 5 (from 4 meV to 20meV), we have observed
polariton linewidths always lying in the 4 - 7 meV range only. We have
experimentally verified the dominantly inhomogeneous origin of the broadening
of the ISB transition, and that the linewidth reduction effect of the polariton
modes persists up to room-temperature. This immunity to inhomogeneous
broadening is a direct consequence of the coupling of the large number of ISB
oscillators to a single photonic mode. It is a precious tool to gauge the
natural linewidth of the ISB plasmon , that is otherwise masked in such MQWs
system , and is also beneficial in view of perspective applications such as
intersubband polariton lasers
Temporal fluctuation of multidrug resistant salmonella typhi haplotypes in the mekong river delta region of Vietnam.
BACKGROUND: typhoid fever remains a public health problem in Vietnam, with a significant burden in the Mekong River delta region. Typhoid fever is caused by the bacterial pathogen Salmonella enterica serovar Typhi (S. Typhi), which is frequently multidrug resistant with reduced susceptibility to fluoroquinolone-based drugs, the first choice for the treatment of typhoid fever. We used a GoldenGate (Illumina) assay to type 1,500 single nucleotide polymorphisms (SNPs) and analyse the genetic variation of S. Typhi isolated from 267 typhoid fever patients in the Mekong delta region participating in a randomized trial conducted between 2004 and 2005. PRINCIPAL FINDINGS: the population of S. Typhi circulating during the study was highly clonal, with 91% of isolates belonging to a single clonal complex of the S. Typhi H58 haplogroup. The patterns of disease were consistent with the presence of an endemic haplotype H58-C and a localised outbreak of S. Typhi haplotype H58-E2 in 2004. H58-E2-associated typhoid fever cases exhibited evidence of significant geo-spatial clustering along the Sông H u branch of the Mekong River. Multidrug resistance was common in the established clone H58-C but not in the outbreak clone H58-E2, however all H58 S. Typhi were nalidixic acid resistant and carried a Ser83Phe amino acid substitution in the gyrA gene. SIGNIFICANCE: the H58 haplogroup dominates S. Typhi populations in other endemic areas, but the population described here was more homogeneous than previously examined populations, and the dominant clonal complex (H58-C, -E1, -E2) observed in this study has not been detected outside Vietnam. IncHI1 plasmid-bearing S. Typhi H58-C was endemic during the study period whilst H58-E2, which rarely carried the plasmid, was only transient, suggesting a selective advantage for the plasmid. These data add insight into the outbreak dynamics and local molecular epidemiology of S. Typhi in southern Vietnam
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