Chemical processes in protoplanetary disks. II. On the importance of photochemistry and X-ray ionization

We investigate the impact of photochemistry and X-ray ionization on the molecular composition of, and ionization fraction in, a protoplanetary disk surrounding a typical T Tauri star. We use a sophisticated physical model, which includes a robust treatment of the radiative transfer of UV and X-ray radiation, and calculate the time-dependent chemical structure using a comprehensive chemical network. In previous work, we approximated the photochemistry and X-ray ionization; here, we recalculate the photoreaction rates using the explicit UV wavelength spectrum and wavelength-dependent reaction cross sections. We recalculate the X-ray ionization rate using our explicit elemental composition and X-ray energy spectrum. We find that photochemistry has a larger influence on the molecular composition than X-ray ionization. Observable molecules sensitive to the photorates include OH, HCO+, N2H+, H2O, CO2, and CH3OH. The only molecule significantly affected by the X-ray ionization is N2H+, indicating that it is safe to adopt existing approximations of the X-ray ionization rate in typical T Tauri star-disk systems. The recalculation of the photorates increases the abundances of neutral molecules in the outer disk, highlighting the importance of taking into account the shape of the UV spectrum in protoplanetary disks. A recalculation of the photoreaction rates also affects the gas-phase chemistry due to the adjustment of the H/H2 and C+/C ratios. The disk ionization fraction is not significantly affected by the methods adopted to calculate the photochemistry and X-ray ionization. We determine that there is a probable "dead zone" where accretion is suppressed, present in a layer, Z/R lsim 0.1-0.2, in the disk midplane, within R ˜ 200 AU.

Applying an XC6200 to real-time image processing

This implementation of a two-dimensional discrete cosine transform demonstrates the development of a suitable architectural style for a specific technology-in this case, the Xilinx XC6200 FPGA series. The design exploits distributed arithmetic, parallelism, and pipelining to achieve a high-performance custom-computing implementation.

Convergent evolutionary processes driven by foraging opportunity in two sympatric morph pairs of Arctic charr with contrasting post-glacial origins

The expression of two or more discrete phenotypes amongst individuals within a species (morphs) provides multiple modes upon which selection can act semi-independently, and thus may be an important stage in speciation. In the present study, we compared two sympatric morph systems aiming to address hypotheses related to their evolutionary origin. Arctic charr in sympatry in Loch Tay, Scotland, exhibit one of two discrete, alternative body size phenotypes at maturity (large or small body size). Arctic charr in Loch Awe segregate into two temporally segregated spawning groups (breeding in either spring or autumn). Mitochondrial DNA restriction fragment length polymorphism analysis showed that the morph pairs in both lakes comprise separate gene pools, although segregation of the Loch Awe morphs is more subtle than that of Loch Tay. We conclude that the Loch Awe morphs diverged in situ (within the lake), whereas Loch Tay morphs most likely arose through multiple invasions by different ancestral groups that segregated before post-glacial invasion (i.e. in allopatry). Both morph pairs showed clear trophic segregation between planktonic and benthic resources (measured by stable isotope analysis) but this was significantly less distinct in Loch Tay than in Loch Awe. By contrast, both inter-morph morphological and life-history differences were more subtle in Loch Awe than in Loch Tay. The strong ecological but relatively weak morphological and life-history divergence of the in situ derived morphs compared to morphs with allopatric origins indicates a strong link between early ecological and subsequent genetic divergence of sympatric origin emerging species pairs. The emergence of parallel specialisms despite distinct genetic origins of these morph pairs suggests that the effect of available foraging opportunities may be at least as important as genetic origin in structuring sympatric divergence in post-glacial fishes with high levels of phenotypic plasticity. (c) 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, , .

THE MARINE RADIOCARBON BOMB PULSE ACROSS THE TEMPERATE NORTH ATLANTIC: A COMPILATION OF Delta C-14 TIME HISTORIES FROM ARCTICA ISLANDICA GROWTH INCREMENTS

Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Delta C-14 excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromso, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of C-14 at the air-sea boundary, C-14 content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Delta C-14 excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic air-sea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses.

Epigenetics:Time to translate into transplantation

Substantial progress has been made in identifying genetic loci associated with multifactorial disorders, including variants that seem to impact outcomes following solid organ transplantation. Despite these advances, much of the heritability and susceptibility to chronic disease processes remains unexplained. Epigenetic modifications may exert their effect independently or complementary to genetic variants. Epigenetic modifications can change gene expression without altering the DNA sequence. These modifications are dynamic, potentially heritable, and can be induced by environmental stimuli or drugs. The impact of epigenetic phenomena on the outcomes of organ transplantation is currently poorly understood. Epigenetic modifications can occur during periods of illness; these may persist and potentially influence allograft outcomes. Epigenetic mechanisms influence the activation, proliferation, and differentiation of the immune cells involved in allograft rejection. The donor's epigenome may also impact transplant survival, and initial research has demonstrated that peritransplant conditions induce rapid epigenetic modification within the allograft. Further research will help to define the importance of epigenetic modifications in transplantation. This will potentially lead to the identification of useful biomarkers and the development of novel pharmacotherapies. This review explores the nature of epigenetic modification in disease and the emerging evidence for epigenetic influences on allograft survival.

Rapid design of discrete orthonormal wavelet transforms

A methodology which allows a non-specialist to rapidly design silicon wavelet transform cores has been developed. This methodology is based on a generic architecture utilizing time-interleaved coefficients for the wavelet transform filters. The architecture is scaleable and it has been parameterized in terms of wavelet family, wavelet type, data word length and coefficient word length. The control circuit is designed in such a way that the cores can also be cascaded without any interface glue logic for any desired level of decomposition. This parameterization allows the use of any orthonormal wavelet family thereby extending the design space for improved transformation from algorithm to silicon. Case studies for stand alone and cascaded silicon cores for single and multi-stage analysis respectively are reported. The typical design time to produce silicon layout of a wavelet based system has been reduced by an order of magnitude. The cores are comparable in area and performance to hand-crafted designs. The designs have been captured in VHDL so they are portable across a range of foundries and are also applicable to FPGA and PLD implementations.

Rapid silicon design of discrete orthonormal wavelet transforms based algorithms

A methodology has been developed which allows a non-specialist to rapidly design silicon wavelet transform cores for a variety of specifications. The cores include both forward and inverse orthonormal wavelet transforms. This methodology is based on efficient, modular and scaleable architectures utilising time-interleaved coefficients for the wavelet transform filters. The cores are parameterized in terms of wavelet type and data and coefficient word lengths. The designs have been captured in VHDL and are hence portable across a range of silicon foundries as well as FPGA and PLD implementations.

Preferences for a third-trimester ultrasound scan in a low-risk obstetric population: a discrete choice experiment

Objective: Establish maternal preferences for a third-trimester ultrasound scan in a healthy, low-risk pregnant population.

Design: Cross-sectional study incorporating a discrete choice experiment.

Setting: A large, urban maternity hospital in Northern Ireland.

Participants: One hundred and forty-six women in their second trimester of pregnancy.

Methods: A discrete choice experiment was designed to elicit preferences for four attributes of a third-trimester ultrasound scan: health-care professional conducting the scan, detection rate for abnormal foetal growth, provision of non-medical information, cost. Additional data collected included age, marital status, socio-economic status, obstetric history, pregnancy-specific stress levels, perceived health and whether pregnancy was planned. Analysis was undertaken using a mixed logit model with interaction effects.

Main outcome measures: Women's preferences for, and trade-offs between, the attributes of a hypothetical scan and indirect willingness-to-pay estimates.

Results: Women had significant positive preference for higher rate of detection, lower cost and provision of non-medical information, with no significant value placed on scan operator. Interaction effects revealed subgroups that valued the scan most: women experiencing their first pregnancy, women reporting higher levels of stress, an adverse obstetric history and older women.

Conclusions: Women were able to trade on aspects of care and place relative importance on clinical, non-clinical outcomes and processes of service delivery, thus highlighting the potential of using health utilities in the development of services from a clinical, economic and social perspective. Specifically, maternal preferences exhibited provide valuable information for designing a randomized trial of effectiveness and insight for clinical and policy decision makers to inform woman-centred care.

Stress processes in caring for an end-of-life family member:Application of a theoretical model

Objectives: Family caregivers play a vital role in maintaining the lives of individuals with advanced illness living in the community. However, the responsibility of caregiving for an end-of-life family member can have profound consequences on the psychological, physical and financial well-being of the caregiver. While the literature has identified caregiver stress or strain as a complex process with multiple contributing factors, few comprehensive studies exist. This study examined a wide range of theory-driven variables contributing to family caregiver stress. Method: Data variables from interviews with primary family caregivers were mapped onto the factors within the Stress Process Model theoretical framework. A hierarchical multiple linear regression analysis was used to determine the strongest predictors of caregiver strain as measured by a validated composite index, the Caregiver Strain Index. Results: The study included 132 family caregivers across south-central/western Ontario, Canada. About half of these caregivers experienced high strain, the extent of which was predicted by lower perceived program accessibility, lower functional social support, greater weekly amount of time caregivers committed to the care recipient, younger caregiver age and poorer caregiver self-perceived health. Conclusion: This study examined the influence of a multitude of factors in the Stress Process Model on family caregiver strain, finding stress to be a multidimensional construct. Perceived program accessibility was the strongest predictor of caregiver strain, more so than intensity of care, highlighting the importance of the availability of community resources to support the family caregiving role.

Modified Information Criteria and Selection of Long Memory Time Series Models

The problem of model selection of a univariate long memory time series is investigated once a semi parametric estimator for the long memory parameter has been used. Standard information criteria are not consistent in this case. A Modified Information Criterion (MIC) that overcomes these difficulties is introduced and proofs that show its asymptotic validity are provided. The results are general and cover a wide range of short memory processes. Simulation evidence compares the new and existing methodologies and empirical applications in monthly inflation and daily realized volatility are presented.

The use and meanings of 'time of wetness' in understanding stone decay

Moisture is a well documented, and crucial, control on the nature of stone decay. The term time of wetness has frequently been adopted to describe how long a stone block is wet, with a view to understanding the impact of this on decay processes. Although this term has proved conceptually useful, it has been used in different ways, by different groups to mean mean quite different things. For example, the time of wetness for a stone block surface (the traditional understanding) may be quite different from that of a block interior, controlled by the different dynamics of wetting and drying in those zones. Thus, surface wetting will occur regularly (sometimes swiftly followed by drying, depending on the time of year), with block interior wetting requiring the accumulation of surface moisture to penetrate to depth (more likely in autumn and winter months), and drying out much more slowly. This relatively new but important perspective, framed in the context of climate change, is crucial to understanding the length of time stone may remain damp at depth following a period of prolonged precipitation. The nature and speed of drying is also relevant in quantifying time of wetness of both surfaces and the interior of building stones.
These ideas related to time of wetness have implications for decay processes, specifically how a prolonged time of deep wetness may re-focus the emphasis of salt weathering in natural building stones toward chemical action. Literature on chemical change is discussed, suggesting that chemical change occurring during periods of prolonged wetness is likely to be significant in itself, with implications for weakening the stone (in terms of, for example, cement dissolution or grain boundary weakening) and exacerbating physical damage from salt crystallisation when blocks finally dry out.

A multiconfigurational time-dependent Hartree-Fock method for excited electronic states. I. General formalism and application to open-shell states

The solution of the time-dependent Schrodinger equation for systems of interacting electrons is generally a prohibitive task, for which approximate methods are necessary. Popular approaches, such as the time-dependent Hartree-Fock (TDHF) approximation and time-dependent density functional theory (TDDFT), are essentially single-configurational schemes. TDHF is by construction incapable of fully accounting for the excited character of the electronic states involved in many physical processes of interest; TDDFT, although exact in principle, is limited by the currently available exchange-correlation functionals. On the other hand, multiconfigurational methods, such as the multiconfigurational time-dependent Hartree-Fock (MCTDHF) approach, provide an accurate description of the excited states and can be systematically improved. However, the computational cost becomes prohibitive as the number of degrees of freedom increases, and thus, at present, the MCTDHF method is only practical for few-electron systems. In this work, we propose an alternative approach which effectively establishes a compromise between efficiency and accuracy, by retaining the smallest possible number of configurations that catches the essential features of the electronic wavefunction. Based on a time-dependent variational principle, we derive the MCTDHF working equation for a multiconfigurational expansion with fixed coefficients and specialise to the case of general open-shell states, which are relevant for many physical processes of interest. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3600397]

Is the number of species on earth increasing or decreasing? Time, chaos and the origin of species

Darwin's On the Origin of Species has led to a theory of evolution with a mass of empirical detail on population genetics below species level, together with heated debate on the details of macroevolutionary patterns above species level. Most of the main principles are clear and generally accepted, notably that life originated once and has evolved over time by descent with modification. Here, I review the fossil and molecular phylogenetic records of the response of life on Earth to Quaternary climatic changes. I suggest that the record can be best understood in terms of the nonlinear dynamics of the relationship between genotype and phenotype, and between climate and environments. 'The origin of species' is essentially unpredictable, but is nevertheless an inevitable consequence of the way that organisms reproduce through time. The process is 'chaotic', but not 'random'. I suggest that biodiversity is best considered as continuously branching systems of lineages, where 'species' are the branch tips. The Earth's biodiversity should thus (1) be in a state of continuous increase and (2) show continuous discrepancies between genetic and morphological data in time and space. © The Palaeontological Association.

In situ FTIRS investigations of surface processes of Rh electrode - Novel observation of geminal adsorbates of carbon monoxide on Rh electrode in acid solution

With the help of in situ multi-step FTIR Spectroscopy, two types of adsorbed geminal CO have been observed for the first time at an electrochemically modified Rh electrode. A doublet band of two broad peaks at 2166 and 2112cm is assigned to geminal CO on Rh surface oxide (or hydroxide) produced by the electrochemical modification process, and a doublet band of two peaks near 2103 and 2033cm is ascribed to geminal CO on surface clusters of Rh formed by reduction of Rh surface oxide. Based on the evolution of FTIR spectra with the electrode potential, the surface processes of a Rh electrode, subjected to a potential cycling treatment at 1.5Vs between -0.275 and 2.4V for 2min, have been elucidated. The present results at the solid/liquid electrochemical interface were compared with those obtained at the solid/gas interface, and consistent conclusions were achieved.