13,326 research outputs found
Theoretical investigations of the reactions of N and O containing species on a C(100):H 2×1 reconstructed diamond surface
Quantum
mechanical and hybrid quantum mechanical/molecular mechanical
cluster models were used to investigate possible reaction mechanisms
whereby gas-phase NH<sub><i>x</i></sub> (<i>x</i> = 0–2), CNH<sub><i>x</i></sub> (<i>x</i> = 0, 1), and OH radicals can add to, and incorporate in, a C–C
dimer bond on the C(100):H 2 × 1 diamond surface during chemical
vapor deposition (CVD) from microwave-activated C/H containing gas
mixtures containing trace amounts of added N or O. Three N incorporation
routes are identified, initiated by N, NH, and CNÂ(H) addition to a
surface radical site, whereas only OH addition was considered as the
precursor to O incorporation. Each is shown to proceed via a ring-opening/ring-closing
reaction mechanism analogous to that identified previously for the
case of CH<sub>3</sub> addition (and CH<sub>2</sub> incorporation)
in diamond growth from a pure C/H plasma. On the basis of the relative
abundances of N atoms and NH radicals close to the growing diamond
surface, the former is identified as the more probable carrier of
the N atoms appearing in CVD grown diamond, but fast H-shifting reactions
postaddition encourage the view that NH is the more probable migrating
and incorporating species. CN radical addition is deemed less probable
but remains an intriguing prospect, since, if the ring-closed structure
is reached, this mechanism has the effect of adding two heavy atoms,
with the N atom sitting above the current growth layer and thus offering
a potential nucleation site for next-layer growth
Simulations of Spinodal Nucleation in Systems with Elastic Interactions
Systems with long-range interactions quenched into a metastable state near
the pseudospinodal exhibit nucleation that is qualitatively different than the
classical nucleation observed near the coexistence curve. We have observed
nucleation droplets in our Langevin simulations of a two-dimensional model of
martensitic transformations and have determined that the structure of the
nucleating droplet differs from the stable martensite structure. Our results,
together with experimental measurements of the phonon dispersion curve, allow
us to predict the nature of the droplet. These results have implications for
nucleation in many solid-solid transitions and the structure of the final
state
Beta lives - some statistical perspectives on the capital asset pricing model
This note summarizes some technical issues relevant to the use of the idea of excess return in empirical modelling. We cover the case where the aim is to construct a measure of expected return on an asset and a model of the CAPM type is used. We review some of the problems and show examples where the basic CAPM may be used to develop other results which relate the expected returns on assets both to the expected return on the market and other factors
An investigation of the RWPE prostate derived family of cell lines using FTIR spectroscopy
Interest in developing robust, quicker and easier diagnostic tests for cancer has lead to an increased use of Fourier transform infrared (FTIR) spectroscopy to meet that need. In this study we present the use of different experimental modes of infrared spectroscopy to investigate the RWPE human prostate epithelial cell line family which are derived from the same source but differ in their mode of transformation and their mode of invasive phenotype. Importantly, analysis of the infrared spectra obtained using different experimental modes of infrared spectroscopy produces similar results. The RWPE family of cell lines can be separated into groups based upon the method of cell transformation rather than the resulting invasiveness/aggressiveness of the cell line. The study also demonstrates the possibility of using a genetic algorithm as a possible standardised pre-processing step and raises the important question of the usefulness of cell lines to create a biochemical model of prostate cancer progression
Electron cyclotron current drive in low collisionality limit: On parallel momentum conservation
Zeros of the Partition Function and Pseudospinodals in Long-Range Ising Models
The relation between the zeros of the partition function and spinodal
critical points in Ising models with long-range interactions is investigated.
We find the spinodal is associated with the zeros of the partition function in
four-dimensional complex temperature/magnetic field space. The zeros approach
the real temperature/magnetic field plane as the range of interaction
increases.Comment: 20 pages, 9 figures, accepted to PR
M-branes and N=2 Strings
The string field theory of N=(2,1) heterotic strings describes a set of
self-dual Yang-Mills fields coupled to self-dual gravity in 2+2 dimensions. We
show that the exact classical action for this field theory is a certain
complexification of the Green-Schwarz/Dirac-Born-Infeld string action, closely
related to the four dimensional Wess-Zumino action describing self-dual gauge
fields. This action describes the world-volume of a 2+2d ``M-brane'', which
gives rise upon different null reductions to critical strings and membranes. We
discuss a number of further properties of N=2 heterotic strings, such as the
geometry of null reduction, general features of a covariant formulation, and
possible relations to BPS and GKM algebras.Comment: 49 pages, harvmac; 1 figure (uses epsf.tex). References adde
Attempts to identify Cassava Brown Streak Virus in western Democratic Republic of Congo
Open Access ArticleRoot necrosis similar to those of the cassava brown streak disease (CBSD) were observed on cassava in western provinces of the Democratic Republic of Congo (DR.Congo) in the early 2000’s. However molecular laboratory diagnosis were not able to detect any causative agent responsible for the attacks, hence, the disease related to these symptoms was named CBSD-like disease.
In order to assess the distribution and the incidence of the CBSD-like disease, surveys were carried out in four western provinces, comprising, Kwango and Kwilu, Sud Ubangi, Kinshasa and Kongo Central. CBSD-like disease was observed in all surveyed provinces on the basis of root symptoms because foliar symptoms were different to those of the documented cases of CBSD in other parts of east Africa. CBSD-like disease incidence was high in Kongo Central and Sud Ubangi, exceeding an average of 50 %, but low in Kwango and Kwilu (32.8%) and in Kinshasa (19.1%).
During the surveys, cassava leaf samples were collected for lab identification of the causal agent. PCR diagnosis was done on these samples using primers specific for the two known CBSVs. All samples tested negative with no amplification of DNA fragments of the correct size. Thus, further analysis on the causative organism is needed using Next Generation Sequencing (NGS) approaches. NGS approaches will help also to identify the causative organism in other Central Africa countries (Angola, Congo-Brazzaville and Gabon) where such cassava root necrosis have been reported or are suspected
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