4,153 research outputs found
Electron-Nââș scattering and dynamics
Molecular nitrogen, Nâ, is the most abundant molecule in the terrestrial atmosphere. Its cation Nââș is therefore prevalent in the earth's ionosphere as well as in nitrogen plasmas produced for reasons varying from lightning strikes to combustion. Any model which seeks to describe plasmas in air must contain a description of nitrogen ion chemistry. Despite this, there is a distinct paucity of data describing electron-Nââș interactions and the resultant bound and quasi-bound electronic structure of Nâ. The characterisation of these states is essential for describing dissociative recombination which is the main destroyer of molecular ions in a plasma. This thesis aims to alleviate this problem by performing extensive ab initio R-matrix calculations to create a comprehensive map of the highly-excited electronic structure of Nâ which can the be used to perform a dissociative recombination cross-section calculation. Potential energy curves were found by performing resonant and bound state calculations for all singlet and triplet molecular symmetries of Nâ up to l †4. The use of a dense grid meant that highly-excited electronic states could be found with an unprecedented level of detail. Many of the states were previously unknown. A new fitting method was developed for the characterisation of resonant states using the time-delay method. It was shown that whilst the R-matrix method is not competitive with conventional quantum chemistry techniques for low lying valence states, it is particularly appropriate for highly-excited states, such as Rydberg states. The data gained from these calculations was then used as an input for a multichannel quantum defect theory calculation of a dissociative recombination cross-section. A description is given of how to prepare the data from the R-matrix calculation for input into a multichannel quantum defect theory dissociative recombination cross-section calculation. Cross-sections were found for v=0-3 including three ionic cores. Whilst previous studies of dissociative recombination using R-matrix data required some empirical intervention, the cross-section found in this thesis is completely ab initio and is in good agreement with experiment
Systematic review of statistical approaches to quantify, or correct for, measurement error in a continuous exposure in nutritional epidemiology.
BACKGROUND: Several statistical approaches have been proposed to assess and correct for exposure measurement error. We aimed to provide a critical overview of the most common approaches used in nutritional epidemiology. METHODS: MEDLINE, EMBASE, BIOSIS and CINAHL were searched for reports published in English up to May 2016 in order to ascertain studies that described methods aimed to quantify and/or correct for measurement error for a continuous exposure in nutritional epidemiology using a calibration study. RESULTS: We identified 126 studies, 43 of which described statistical methods and 83 that applied any of these methods to a real dataset. The statistical approaches in the eligible studies were grouped into: a) approaches to quantify the relationship between different dietary assessment instruments and "true intake", which were mostly based on correlation analysis and the method of triads; b) approaches to adjust point and interval estimates of diet-disease associations for measurement error, mostly based on regression calibration analysis and its extensions. Two approaches (multiple imputation and moment reconstruction) were identified that can deal with differential measurement error. CONCLUSIONS: For regression calibration, the most common approach to correct for measurement error used in nutritional epidemiology, it is crucial to ensure that its assumptions and requirements are fully met. Analyses that investigate the impact of departures from the classical measurement error model on regression calibration estimates can be helpful to researchers in interpreting their findings. With regard to the possible use of alternative methods when regression calibration is not appropriate, the choice of method should depend on the measurement error model assumed, the availability of suitable calibration study data and the potential for bias due to violation of the classical measurement error model assumptions. On the basis of this review, we provide some practical advice for the use of methods to assess and adjust for measurement error in nutritional epidemiology
Statistical analysis of dwarf galaxies and their globular clusters in the Local Volume
Morphological classification of dwarf galaxies into early and late type,
though can account for some of their origin and characteristics but does not
help to study their formation mechanism. So an objective classification using
Principal Component analysis together with K means Cluster Analysis of these
dwarf galaxies and their globular clusters is carried out to overcome this
problem. It is found that the classification of dwarf galaxies in the Local
Volume is irrespective of their morphological indices. The more massive (MV 0 <
-13.7) galaxies evolve through self-enrichment and harbor dynamically less
evolved younger globular clusters (GCs) whereas fainter galaxies (MV 0 > -13.7)
are influenced by their environment in the star formation process.Comment: 22 pages, 10 figures, 5 tables, published in Ap
Anti-LRP/LR specific antibody IgG1-iS18 impedes adhesion and invasion of liver cancer cells.
Two key events, namely adhesion and invasion, are pivotal to the occurrence of metastasis. Importantly, the 37 kDa/67 kDa laminin receptor (LRP/LR) has been implicated in enhancing these two events thus facilitating cancer progression. In the current study, the role of LRP/LR in the adhesion and invasion of liver cancer (HUH-7) and leukaemia (K562) cells was investigated. Flow cytometry revealed that the HUH-7 cells displayed significantly higher cell surface LRP/LR levels compared to the poorly-invasive breast cancer (MCF-7) control cells, whilst the K562 cells displayed significantly lower cell surface LRP/LR levels in comparison to the MCF-7 control cells. However, Western blotting and densitometric analysis revealed that all three tumorigenic cell lines did not differ significantly with regards to total LRP/LR levels. Furthermore, treatment of liver cancer cells with anti-LRP/LR specific antibody IgG1-iS18 (0.2 mg/ml) significantly reduced the adhesive potential of cells to laminin-1 and the invasive potential of cells through the ECM-like Matrigel, whilst leukaemia cells showed no significant differences in both instances. Additionally, Pearson's correlation coefficients suggested direct proportionality between cell surface LRP/LR levels and the adhesive and invasive potential of liver cancer and leukaemia cells. These findings suggest the potential use of anti-LRP/LR specific antibody IgG1-iS18 as an alternative therapeutic tool for metastatic liver cancer through impediment of the LRP/LR- laminin-1 interaction.National Research Foundation.NCS201
Wavelength conversion of QAM signals in a low loss CMOS compatible spiral waveguide
We demonstrate wavelength conversion of quadrature amplitude modulation (QAM)
signals,
including 32-GBd quadrature phase-shift keying and 10-GBd 16-QAM, in a 50-cm long high
index doped
glass spiral
waveguide. The quality of the generated idlers for up to 20 nm of
wavelength shift is sufficient to achieve a BER performance below the hard decision
forward error correction threshold BER performance (<3.8 Ă 103), with an
optical signal-to-noise ratio penalty of less than 0.3 dB compared to the original
signal.
Our results confirm that this is a promising platform for nonlinear
optical signal
processing, as a result of both very low linear propagation loss
(<0.07 dB/cm) and a large material bandgap, which in turn ensures negligible
nonlinear loss
at telecom
wavelengths
Wavelength Conversion of QPSK and 16-QAM Coherent Signals in a CMOS Compatible Spiral Waveguide
<p>
We characterize a wavelength converter based on a 50-cm long low-loss spiral Hydex waveguide. A 10-nm FWM bandwidth is shown over which low OSNR penalty (< 0.5dB) wavelength conversion of QPSK and 16-QAM is reported. © OSA 2016.</p
In Vitro Inhibition of Angiogenesis by Antibodies Directed against the 37kDa/67kDa Laminin Receptor
The 37kDa/67kDa laminin receptor (LRP/LR) is a central receptor mediating interactions between tumour cells and the basement membrane and is thereby a key player in adhesion and invasion, essential processes in metastatic cancer. To affect continued tumour growth, tumours induce angiogenesis for the constant delivery of nutrients and oxygen. This study aims to determine the blocking effect of the anti-LRP/LR specific antibody, W3 on the angiogenic potential of HUVE (human umbilical vein endothelial) cells. Flow cytometric analysis revealed that 97% of HUVE cells display cell surface LRP/LR. An angiogenesis assay was conducted employing HUVE cells seeded on the basement membrane reconstituent Matrigelâą supplemented with the pro-angiogenic factor vascular endothelial growth factor (VEGF). Post 18h incubation at 37°C tubular structures, namely tube lengths were assessed. Treatment of established tubular structures with 100 ÎŒg/ml anti-LRP/LR specific antibody completely blocked angiogenesis. Our findings suggest a central role of the 37kDa/67kDa LRP/LR in tube formation and recommends anti-LRP/LR specific antibodies as potential therapeutic tools for treatment of tumour angiogenesis.This work was supported by the National Research Foundation, the Republic of South Africa and the Medical Research Council, the Republic of South Africa.NCS201
Bayesian astrostatistics: a backward look to the future
This perspective chapter briefly surveys: (1) past growth in the use of
Bayesian methods in astrophysics; (2) current misconceptions about both
frequentist and Bayesian statistical inference that hinder wider adoption of
Bayesian methods by astronomers; and (3) multilevel (hierarchical) Bayesian
modeling as a major future direction for research in Bayesian astrostatistics,
exemplified in part by presentations at the first ISI invited session on
astrostatistics, commemorated in this volume. It closes with an intentionally
provocative recommendation for astronomical survey data reporting, motivated by
the multilevel Bayesian perspective on modeling cosmic populations: that
astronomers cease producing catalogs of estimated fluxes and other source
properties from surveys. Instead, summaries of likelihood functions (or
marginal likelihood functions) for source properties should be reported (not
posterior probability density functions), including nontrivial summaries (not
simply upper limits) for candidate objects that do not pass traditional
detection thresholds.Comment: 27 pp, 4 figures. A lightly revised version of a chapter in
"Astrostatistical Challenges for the New Astronomy" (Joseph M. Hilbe, ed.,
Springer, New York, forthcoming in 2012), the inaugural volume for the
Springer Series in Astrostatistics. Version 2 has minor clarifications and an
additional referenc
Critical role of gap junction communication, calcium and nitric oxide signaling in bystander responses to focal photodynamic injury
Ionizing and nonionizing radiation affect not only directly targeted cells but also
surrounding âbystanderâ cells. The underlying mechanisms and therapeutic role of
bystander responses remain incompletely deined. Here we show that photosentizer
activation in a single cell triggers apoptosis in bystander cancer cells, which are
electrically coupled by gap junction channels and support the propagation of a Ca2+
wave initiated in the irradiated cell. The latter also acts as source of nitric oxide
(NO) that diffuses to bystander cells, in which NO levels are further increased by
a mechanism compatible with Ca2+-dependent enzymatic production. We detected
similar signals in tumors grown in dorsal skinfold chambers applied to live mice.
Pharmacological blockade of connexin channels signiicantly reduced the extent of
apoptosis in bystander cells, consistent with a critical role played by intercellular
communication, Ca2+ and NO in the bystander effects triggered by photodynamic
therapy
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