140 research outputs found
Dynamical tunneling in molecules: Quantum routes to energy flow
Dynamical tunneling, introduced in the molecular context, is more than two
decades old and refers to phenomena that are classically forbidden but allowed
by quantum mechanics. On the other hand the phenomenon of intramolecular
vibrational energy redistribution (IVR) has occupied a central place in the
field of chemical physics for a much longer period of time. Although the two
phenomena seem to be unrelated several studies indicate that dynamical
tunneling, in terms of its mechanism and timescales, can have important
implications for IVR. Examples include the observation of local mode doublets,
clustering of rotational energy levels, and extremely narrow vibrational
features in high resolution molecular spectra. Both the phenomena are strongly
influenced by the nature of the underlying classical phase space. This work
reviews the current state of understanding of dynamical tunneling from the
phase space perspective and the consequences for intramolecular vibrational
energy flow in polyatomic molecules.Comment: 37 pages and 23 figures (low resolution); Int. Rev. Phys. Chem.
(Review to appear in Oct. 2007
A cross-sectional study of vascular risk factors in a rural South African population : data from the Southern African Stroke Prevention Initiative (SASPI)
Background: Rural sub-Saharan Africa is at an early stage of economic and health transition. It is
predicted that the 21st century will see a serious added economic burden from non-communicable disease
including vascular disease in low-income countries as they progress through the transition. The stage of
vascular disease in a population is thought to result from the prevalence of vascular risk factors. Already
hypertension and stroke are common in adults in sub-Saharan Africa. Using a multidisciplinary approach
we aimed to assess the prevalence of several vascular risk factors in Agincourt, a rural demographic
surveillance site in South Africa.
Methods: We performed a cross sectional random sample survey of adults aged over 35 in Agincourt
(population ≈ 70 000). Participants were visited at home by a trained nurse who administered a
questionnaire, carried out clinical measurements and took a blood sample. From this we assessed
participants' history of vascular risk, blood pressure using an OMRON 705 CP monitor, waist
circumference, body mass index (BMI), ankle brachial index (ABI), and total and HDL cholesterol.
Results: 402 people (24% men) participated. There was a high prevalence of smoking in men, but the
number of cigarettes smoked was small. There was a striking difference in mean BMI between men and
women (22.8 kg/m2 versus 27.2 kg/m2), but levels of blood pressure were very similar. 43% of participants
had a blood pressure greater than 140/90 or were on anti-hypertensive treatment and 37% of participants
identified with measured high blood pressure were on pharmacological treatment. 12% of participants had
an ABI of < 0.9, sugesting the presence of sub-clinical atheroma. 25.6% of participants had a total
cholesterol level > 5 mmol/l.
Conclusion: We found a high prevalence of hypertension, obesity in women, and a suggestion of
subclinical atheroma despite relatively favourable cholesterol levels in a rural South African population.
South Africa is facing the challenge of an emerging epidemic of vascular disease. Research to establish the
social determinates of these risk factors and interventions to reduce both individual and population risk
are required
Structure–properties relationships in fibre drawing of bioactive phosphate glasses
New bioactive phosphate glasses suitable for continuous fibre production are investigated in this work. The structure of both bulk and fibres from Na2O–CaO–MgO–P2O5 glasses has been studied by means of Raman and 31P and 23Na nuclear magnetic resonance spectroscopies, and the structural results have been correlated with the mechanical properties of the fibres and the dissolution rate of the bulk glasses. It has been observed that the mechanical properties of the phosphate glass fibres are influenced by the glass network connectivity, while the dissolution rates are governed by the Qi speciation of the PO4 units. As seen in previous studies, molar volume seems to play an important role in the fragility behaviour of phosphate glasses. Here, a lower molar volume resulting from the increase in the oxygen packing density hinders the cooperative flow of the PO4 units throughout the glass network and, therefore, causes a reduction in the kinetic fragility
TRY plant trait database - enhanced coverage and open access
Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
Nr2e3 is a Genetic Modifier That Rescues Retinal Degeneration and Promotes Homeostasis in Multiple Models of Retinitis Pigmentosa
Recent advances in viral vector engineering, as well as an increased understanding of the cellular and molecular mechanism of retinal diseases, have led to the development of novel gene therapy approaches. Furthermore, ease of accessibility and ocular immune privilege makes the retina an ideal target for gene therapies. In this study, the nuclear hormone receptor gene Nr2e3 was evaluated for efficacy as broad-spectrum therapy to attenuate early to intermediate stages of retinal degeneration in five unique mouse models of retinitis pigmentosa (RP). RP is a group of heterogenic inherited retinal diseases associated with over 150 gene mutations, affecting over 1.5 million individuals worldwide. RP varies in age of onset, severity, and rate of progression. In addition, ~40% of RP patients cannot be genetically diagnosed, confounding the ability to develop personalized RP therapies. Remarkably, Nr2e3 administered therapy resulted in reduced retinal degeneration as observed by increase in photoreceptor cells, improved electroretinogram, and a dramatic molecular reset of key transcription factors and associated gene networks. These therapeutic effects improved retinal homeostasis in diseased tissue. Results of this study provide evidence that Nr2e3 can serve as a broad-spectrum therapy to treat multiple forms of RP
The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope: I. Overview of the instrument and its capabilities
We provide an overview of the design and capabilities of the near-infrared
spectrograph (NIRSpec) onboard the James Webb Space Telescope. NIRSpec is
designed to be capable of carrying out low-resolution () prism
spectroscopy over the wavelength range m and higher resolution
( or ) grating spectroscopy over
m, both in single-object mode employing any one of five fixed
slits, or a 3.13.2 arcsec integral field unit, or in multiobject
mode employing a novel programmable micro-shutter device covering a
3.63.4~arcmin field of view. The all-reflective optical chain of
NIRSpec and the performance of its different components are described, and some
of the trade-offs made in designing the instrument are touched upon. The
faint-end spectrophotometric sensitivity expected of NIRSpec, as well as its
dependency on the energetic particle environment that its two detector arrays
are likely to be subjected to in orbit are also discussed
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The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope: I. Overview of the instrument and its capabilities
We provide an overview of the design and capabilities of the near-infrared
spectrograph (NIRSpec) onboard the James Webb Space Telescope. NIRSpec is
designed to be capable of carrying out low-resolution () prism
spectroscopy over the wavelength range m and higher resolution
( or ) grating spectroscopy over
m, both in single-object mode employing any one of five fixed
slits, or a 3.13.2 arcsec integral field unit, or in multiobject
mode employing a novel programmable micro-shutter device covering a
3.63.4~arcmin field of view. The all-reflective optical chain of
NIRSpec and the performance of its different components are described, and some
of the trade-offs made in designing the instrument are touched upon. The
faint-end spectrophotometric sensitivity expected of NIRSpec, as well as its
dependency on the energetic particle environment that its two detector arrays
are likely to be subjected to in orbit are also discussed
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