6,071 research outputs found
On the Life and Work of S. Helgason
This article is a contribution to a Festschrift for S. Helgason. After a
biographical sketch, we survey some of his research on several topics in
geometric and harmonic analysis during his long and influential career. While
not an exhaustive presentation of all facets of his research, for those topics
covered we include reference to the current status of these areas.Comment: Final versio
Excited-state Forces within a First-principles Green's Function Formalism
We present a new first-principles formalism for calculating forces for
optically excited electronic states using the interacting Green's function
approach with the GW-Bethe Salpeter Equation method. This advance allows for
efficient computation of gradients of the excited-state Born-Oppenheimer
energy, allowing for the study of relaxation, molecular dynamics, and
photoluminescence of excited states. The approach is tested on photoexcited
carbon dioxide and ammonia molecules, and the calculations accurately describe
the excitation energies and photoinduced structural deformations.Comment: 2 figures and 2 table
Automatic holographic droplet analysis for liquid fuel sprays
The basic scheme for automated holographic analysis involves an optical system for reconstruction of the three dimensional real image of the droplet field, a spatial scanning system to transport a digitizing X-y image sensor through the real image, and processing algorithms for droplet recognition which establish the droplet sizes and positions. The hardware for system demonstrated includes the expanded and collimated beam from a 5 mW helium-neon laser for hologram reconstruction, an imaging lens for magnification of the real image field, and a video camera and digitizer providing 512-by-512 pixel resolution with 8-bit digitization. A mechanical stage is used to scan the hologram in three dimensional space, maintaining constant image magnification. A test droplet hologram is used for development and testing of the image processing algorithms
Behavioural compensation by drivers of a simulator when using a vision enhancement system
Technological progress is suggesting dramatic changes to the tasks of the driver, with the general aim of making driving environment safer. Before any of these technologies are implemented, empirical research is required to establish if these devices do, in fact, bring about the anticipated improvements. Initially, at least, simulated driving environments offer a means of conducting this research. The study reported here concentrates on the application of a vision enhancement (VE) system within the risk homeostasis paradigm. It was anticipated, in line with risk homeostasis theory, that drivers would compensate for the reduction in risk by increasing speed. The results support the hypothesis although, after a simulated failure of the VE system, drivers did reduce their speed due to reduced confidence in the reliability of the system
Mode coupling and multiquantum vibrational excitations in Feshbach-resonant positron annihilation in molecules
The dominant mechanism of low-energy positron annihilation in polyatomic
molecules is through positron capture in vibrational Feshbach resonances (VFR).
In this paper we investigate theoretically the effect of anharmonic terms in
the vibrational Hamiltonian on the positron annihilation rates. Such
interactions enable positron capture in VFRs associated with multiquantum
vibrational excitations, leading to enhanced annihilation. Mode coupling can
also lead to faster depopulation of VFRs, thereby reducing their contribution
to the annihlation rates. To analyze this complex picture, we use
coupled-cluster methods to calculate the anharmonic vibrational spectra and
dipole transition amplitudes for chloroform, chloroform-,
1,1-dichloroethylene, and methanol, and use these data to compute positron
resonant annihilation rates for these molecules. Theoretical predictions are
compared with the annihilation rates measured as a function of incident
positron energy. The results demonstrate the importance of mode coupling in
both enhancement and suppression of the VFR. There is also experimental
evidence for the direct excitation of multimode VFR. Their contribution is
analyzed using a statistical approach, with an outlook towards more accurate
treatment of this phenomenon.Comment: 16 pages, 10 figures, submitted to Phys. Rev.
16S rRNA gene sequencing of mock microbial populations- impact of DNA extraction method, primer choice and sequencing platform
peer-reviewedBackground
Next-generation sequencing platforms have revolutionised our ability to investigate the microbiota composition of complex environments, frequently through 16S rRNA gene sequencing of the bacterial component of the community. Numerous factors, including DNA extraction method, primer sequences and sequencing platform employed, can affect the accuracy of the results achieved. The aim of this study was to determine the impact of these three factors on 16S rRNA gene sequencing results, using mock communities and mock community DNA.
Results
The use of different primer sequences (V4-V5, V1-V2 and V1-V2 degenerate primers) resulted in differences in the genera and species detected. The V4-V5 primers gave the most comparable results across platforms. The three Ion PGM primer sets detected more of the 20 mock community species than the equivalent MiSeq primer sets. Data generated from DNA extracted using the 2 extraction methods were very similar.
Conclusions
Microbiota compositional data differed depending on the primers and sequencing platform that were used. The results demonstrate the risks in comparing data generated using different sequencing approaches and highlight the merits of choosing a standardised approach for sequencing in situations where a comparison across multiple sequencing runs is required.This publication has emanated from research supported in part by a research
grant from Science Foundation Ireland (SFI) under Grant Numbers SFI/12/RC/2273 and 11/PI/1137 and by FP7 funded CFMATTERS (Cystic Fibrosis
Microbiome-determined Antibiotic Therapy Trial in Exacerbations: Results Stratified, Grant Agreement no. 603038)
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