bluuebunny/crossref_metadata_2025 huggingface dataset:
On the use of Taylor's translation hypothesis for diffusion in the mixed layer
Authors: Willis G. E. , Deardorff J. W.
Published: February 2007

Diffusion measurements in a modelled mixed layer support the equivalence of an instantaneous line‐source concentration field without a mean wind and a continuous point source with a mean wind when use is made of Taylor's translation hypothesis. Taylor's hypothesis as applied to mixed‐layer diffusion appears to break down in this type of flow for values of s̀u/U > 0.5, where s̀u is the horizontal turbulence velocity component and U is the uniform mean wind. Variations in expected levels of cross‐wind integrated concentration are presented as a function of height and distance downstream from the source for a sampling duration of 4zi/U, where zi is the mixed‐layer depth.
An analysis of Manley's central England temperature data: I
Authors: Dyer T. G. J.
Published: February 2007

Manley's (1974) temperature data for central England are subjected to analyses which suggest that they should be treated as a set of monthly time series. Secular variation is found for the months October to April inclusive. Extended methods dealing with spectral analysis are used to focus attention on the mainly longer‐period oscillations. Oscillations of lengths 10–12 and 22–25 years are suggested for some months. Burg's maximum entropy spectral method has been used to resolve signals in the very low frequencies. The combined variance associated with these oscillations is shown to increase for months near mid‐year when the sun has its maximum north declination and to decrease for months on either side of June and July to a minimum when the sun has greatest south declination. Furthermore, the variance associated with months when the sun changes direction in declination and crosses the equator appears to receive boosts.
Intensity plots of the parhelia
Authors: White R.
Published: February 2007

A simple model is used to give a closed expression for the distribution of intensity in the parhelia, in terms of elementary functions of position on the celestial sphere. Some numerical values are given in the form of intensity contour maps. the frequently observed appearance of the parhelia ‘on the slant’ for large elevations is explained. Brief remarks are made on the under‐parhelia and the arcs of Lowitz.
Investigation into the factors affecting accuracy of mass measurements on a time‐of‐flight mass spectrometer using Design of Experiment
Authors: Laures Alice M.‐F. , Wolff Jean‐Claude , Eckers Christine , Borman Phil J. , Chatfield Marion J.
Published: February 2007

The results of an investigation of the parameters which have the most significant effect on the accuracy of mass measurements on a quadrupole orthogonal acceleration time‐of‐flight mass spectrometer (q‐oaToF) are reported. The influence of eight factors is investigated: ion abundances of reference and analyte compounds, mass difference between analyte and reference compounds, quality of calibration, number of reference acquisitions averaged and TDC (time‐to‐digital converter) settings (resolution, Np multiplier (number of pushes correction factor), minimum number of points, i.e. minimum acquisition width which defines a peak). To extract the maximum information from as few experiments as possible, a Design of Experiment approach was used. The data will be used as a basis for developing guidance on accurate mass measurement on q‐oaToF instruments. Copyright © 2007 John Wiley & Sons, Ltd.
Point source effects on density, biomass and diversity of benthic macroinvertebrates in a Mediterranean stream
Authors: Ortiz J. D. , Puig M. A.
Published: February 2007

We sampled benthic macroinvertebrates above and below a point source effluent in La Tordera stream (NE, Spain) over 2001–2002 to assess the effects of nutrient enrichment on the structure, and taxonomic composition of the benthic macroinvertebrate community. Below the point source, discharge, specific conductance and nutrient concentrations were higher than at the upstream reach, while dissolved oxygen (DO) decreased. Macroinvertebrate density was higher at the downstream reach than at the upstream reach on most dates but the two reaches did not differ in macroinvertebrate biomass.

On average, taxa richness at the upstream reach was 20% higher than at the downstream reach. Several taxa, especially mayflies, stoneflies and caddisflies, were present only at the upstream reach. Shannon diversity was similar between the two reaches on 50% of the dates. Ordination analysis clearly separated the samples of the upstream reach from the samples of the downstream reach in the first axis and corroborated the effect of the point source on the benthic community. The two reaches followed a similar temporal pattern with respect to the distribution of taxa along the second axis of the ordination analysis. Higher similarities between the two reaches in taxa composition, densities and biomass after the spates of April and May 2002, suggest that flooding events may act as a reset mechanism for benthic communities and play an important role in stream restoration. Copyright © 2007 John Wiley & Sons, Ltd.
Estimating a survival curve with unlinked entry and failure times
Authors: Wu Yujun , Shih Weichung J. , Moore Dirk F.
Published: February 2007

In monitoring a clinical trial or other observational study with a survival endpoint, sometimes the numbers of patients entering and dying at each time point are presented, but the connections between them are kept confidential. Hence, the exact time to failure or censoring for each individual is missing. We refer to such a study monitoring table with missing pairing information between the entry and death times as a ‘broken’ survival data set. In this paper we study the problem of estimating the survival distribution from a broken survival data set. We have developed two methods, likelihood‐based estimation and self‐consistency estimation, to estimate the survival curve parametrically and empirically, respectively. We use simulations to study the properties of these methods, and illustrate them with data from the STELLAR‐3 trial. Copyright © 2007 John Wiley & Sons, Ltd.
Managerial ownership and corporate diversification: a longitudinal view
Authors: Goranova Maria , Alessandri Todd M. , Brandes Pamela , Dharwadkar Ravi
Published: February 2007

Strategy and finance research suggests that managerial ownership results in increased incentive alignment and therefore is negatively related to corporate diversification. Using a longitudinal approach, we develop arguments to examine whether managerial ownership is associated with subsequent changes in diversification and/or if diversification is associated with subsequent changes in ownership. The results indicate that levels of managerial ownership in one time period are not associated with subsequent changes in corporate diversification, which raises incentive alignment questions. We also find that higher levels of corporate diversification are associated with changes in managerial ownership, which suggests support for the employment risk‐reduction perspective. This study provides important reasons to reassess the longitudinal implications of the managerial ownership‐corporate diversification link from both theoretical and managerial perspectives. Copyright © 2007 John Wiley & Sons, Ltd.
Effect of Interesterification of Palmitic Acid‐rich Triacylglycerol on Postprandial Lipid and Factor VII Response
Authors: Berry Sarah E. E. , Woodward Rebecca , Yeoh Christabelle , Miller George J. , Sanders Thomas A. B.
Published: February 2007

The process of interesterification results in changes in triacylglycerol (TAG) structure and is used to increase the melting point of dietary fats. The acute health effects of this process on palmitic acid‐rich fats are uncertain with regard to postprandial lipemia, insulin and factor VII activated (FVIIa) concentrations. Two randomized crossover trials in healthy male subjects compared the effects of meals containing 50 g fat [interesterified palm oil (IPO) versus native palm oil (NPO); n = 20, and IPO versus high‐oleic sunflower oil (HOS); n = 18], on postprandial changes in lipids, glucose, insulin, chylomicron composition and FVIIa. Compared with NPO, IPO decreased postprandial TAG and insulin concentrations. Both NPO and IPO increased FVIIa concentrations postprandially; mean increases at 6 h were 21 and 19%, respectively. Compared with HOS, IPO decreased postprandial TAG (47% lower incremental area under the curve) and reduced the postprandial increase in FVIIa concentration by 64% at 6 h; no significant differences in hepatic and total lipase activities or insulin concentrations were noted. All three test meals increased postprandial leukocyte counts (average 26% at 6 h). The fatty acid composition of the chylomicron TAG was similar to the test fats following all test meals. It is concluded that interesterification of palm oil does not result in adverse changes in postprandial lipids, insulin or FVIIa compared to high oleate and native palm oils.
Systematic screening of LNA/2′‐O‐methyl chimeric derivatives of a TAR RNA aptamer
Authors: Di Primo Carmelo , Rudloff Ivo , Reigadas Sandrine , Arzumanov Andrey A. , Gait Michael J. , Toulmé Jean-Jacques
Published: February 2007

We synthesized and evaluated by surface plasmon resonance 64 LNA/2′‐O‐methyl sequences corresponding to all possible combinations of such residues in a kissing aptamer loop complementary to the 6‐nt loop of the TAR element of HIV‐1. Three combinations of LNA/2′‐O‐methyl nucleoside analogues where one or two LNA units are located on the 3′ side of the aptamer loop display an affinity for TAR below 1 nM, i.e. one order of magnitude higher than the parent RNA aptamer. One of these combinations inhibits the TAR‐dependent luciferase expression in a cell assay.
Labour segmentation in the Spanish fish-canning industry: a historical perspective, 1880–1960
Authors: MUÑOZ ABELEDO LUISA
Published: February 2007

This article makes use of linkage of many different sources – official population censuses, wage books, interviews, the correspondence of many canning companies, notarial records, documents from canning unions – in order to investigate labour market segmentation between 1880 and 1960 in the Spanish fish-canning industry, a sector that employed mainly female labour. I explore some social and economic factors that explain why women were placed in the ‘secondary’ segment of the labour market in the fish-canning sector. The study also considers the earning differentials between men and women and the different types of contracts offered to male and female workers.
Early visual experience prevents but cannot reverse
deprivation-induced loss of refinement in adult superior colliculus
Authors: CARRASCO MARÍA MAGDALENA , PALLAS SARAH L.
Published: February 2007

The role of sensory experience in the development and plasticity of
the visual system has been widely studied. It has generally been reported
that once animals reach adulthood, experience-dependent visual plasticity
is reduced. We have found that visual experience is not needed for the
refinement of receptive fields (RFs) in the superior colliculus (SC) but
instead is necessary to maintain them in adulthood (Carrasco et al., 2005). Without light exposure, RFs in SC of hamsters
refine by postnatal day 60 as usual but then enlarge, presumably reducing
visual acuity. In this study we examine whether a brief period of light
exposure during early postnatal development would be sufficient to prevent
RF enlargement in adulthood, and whether prolonged light exposure in
adulthood could reverse the deprivation-induced increase in RF size. We
found that an early postnatal period of at least 30 days of visual
experience was sufficient to maintain refined RFs in the adult SC.
Prolonged visual experience in adulthood could not reverse the RF
enlargement resulting from long-term dark rearing, reflecting a loss of
plasticity at this age. Our results suggest that, unlike in visual cortex,
dark rearing does not indefinitely extend the critical period of
plasticity in SC. Rather, there is a limited time window when early
experience can protect RFs from the detrimental effects of visual
deprivation in adulthood. These results contribute to understanding adult
brain plasticity and argue for the importance of early visual experience
in protecting the adult visual system.
Postreceptoral adaptation abnormalities in early age-related
maculopathy
Authors: FEIGL B. , BROWN B. , LOVIE-KITCHIN J. , SWANN P.
Published: February 2007

Age-related maculopathy (ARM) has become the major cause of blindness
in the Western World. Currently its pathogenesis and primary site of
functional damage is not fully understood but ischemia is believed to play
a major role. Early detection and precise monitoring of progression of ARM
are main goals of current research due to lack of sufficient treatment
options, especially in the dry, atrophic form of this disease. We applied
the multifocal electroretinogram (mfERG) that can detect any local
functional deficit objectively in the central retina. We recorded two
paradigms in early ARM patients, the fast flicker and the slow flash
paradigm which both represent fast adaptation processes of the proximal
retina but under differing photopic conditions and stimulation rates. By
subtracting the waveform responses we extracted a late component in the
difference waveform that was significantly reduced in the early ARM group
compared to a healthy control group (p ≤ 0.05). We propose
that this multifocal nonlinear analysis permits the detection of
adaptative deficits and provides topographic mapping of retinal
dysfunction in early ARM. The difference waveform component we extracted
with this novel approach might indicate early functional loss in ARM
caused by ischemia in postreceptoral layers such as bipolar cells and
inner plexiform regions.
Topographic analysis of the ganglion cell layer in the retina of the four-eyed fishAnableps anableps
Authors: OLIVEIRA FRANCISCO GILBERTO , COIMBRA JOÃO PAULO , YAMADA ELIZABETH SUMI , MONTAG LUCIANO FOGAÇA DE ASSIS , NASCIMENTO FRANCYLLENA L. , OLIVEIRA VALÉRIA A. , MOTA DIÓGENES LUÍS DA , BITTENCOURT ALEXANDRE MOTTA , SILVA VALDIR LUNA DA , COSTA BELMIRA LARA DA SILVEIRA ANDRADE DA
Published: February 2007

Fish of the genusAnableps(Anablepidae, Cyprinodontiformes) have eyes that are adapted for simultaneous aerial and aquatic vision. In this study we investigate some of the corresponding retinal specializations of the adultAnableps anablepseye using retinal transverse sections and wholemounts. The linear dimensions of the retina were found to be asymmetric with a greater representation of the dorsal compared to the ventral visual field. The total number of neurons in the ganglion cell layer of the ventral hemiretina was on average 3.6 times greater than the values obtained in the dorsal hemiretina. Isodensity contour maps revealed a prominent horizontal visual streak in the ventral hemiretina with an average peak cell density of 18,286 cells/mm2. A second less-well-developed horizontal visual streak was also observed in the dorsal hemiretina. A sub-population of large cells with soma areas between 74 and 188 μm2was identified and found to be distributed evenly across both hemiretinas. Together, these results show that the sampling gain of the ventral retina is significantly greater than the dorsal segment, that retinal specializations important for mediating acute vision are present in the parts of the visual field immediately above and below the surface of the water, and that visual functions related with the large ganglion cells require more even sampling across the visual field. The relevance of these retinal specializations to the feeding and other behavioral strategies adopted byAnablepsis discussed.
Differences in the pharmacological activation of visual opsins
Authors: ISAYAMA T. , CHEN Y. , KONO M. , DEGRIP W.J. , MA J.-X. , CROUCH R.K. , MAKINO C.L.
Published: February 2007

Opsins, like many other G-protein-coupled receptors, sustain constitutive activity in the absence of ligand. In partially bleached rods and cones, opsin's activity closes cGMP-gated channels and produces a state of “pigment adaptation” with reduced sensitivity to light and accelerated flash response kinetics. The truncated retinal analogue, β-ionone, further desensitizes partially bleached green-sensitive salamander rods, but enables partially bleached red-sensitive cones to recover dark-adapted physiology. Structural differences between rod and cone opsins were proposed to explain the effect. Rods and cones, however, also contain different transducins, raising the possibility that G-protein type determines the photoreceptor-specific effects of β-ionone. To test the two hypotheses, we applied β-ionone to partially bleached blue-sensitive rods and cones of salamander, two cells that couple the same cone-like opsin to either rod or cone transducin, respectively. Immunocytochemistry confirmed that all salamander rods contain one form of transducin, whereas all cones contain another. β-Ionone enhanced pigment adaptation in blue-sensitive rods, but it also did so in blue- and UV-sensitive cones. Furthermore, all recombinant salamander rod and cone opsins, with the exception of the red-sensitive cone opsin, activated rod transducin upon the addition of β-ionone. Thus opsin structure determines the identity of β-ionone as an agonist or an inverse agonist and in that respect distinguishes the red-sensitive cone opsin from all others.
G protein coupling profile of mGluR6 and expression of Gα proteins in retinal ON bipolar cells
Authors: TIAN LIANTIAN , KAMMERMEIER PAUL J.
Published: February 2007

Metabotropic glutamate receptor 6 (mGluR6) is a group III, pertussis toxin (PTX)-sensitive G protein coupled mGluR that plays a specialized role in the retina. Retinal ON bipolar cells, which receive direct glutamatergic input from photoreceptor cells, express mGluR6 as their primary postsynaptic glutamate receptor. Activation of mGluR6 in these cells initiates an intracellular signaling cascade ultimately leading to inhibition of a cation channel and cell hyperpolarization. The primary mediator of this pathwayin vivois Gαo, but the potential roles of other G proteins from the Gαi/ofamily in the regulation of this or other signaling pathways in ON bipolar cells are unclear. To determine which specific G proteins from the Gαi/ofamily are able to couple to mGluR6, a Gα reconstitution system was employed using PTX-insensitive Gα mutants expressed with mGluR6 in PTX-treated sympathetic neurons from the rat superior cervical ganglion (SCG). The efficiency of coupling to mGluR6 was Goa> Gob, Gi1> Gi2, Gi3, whereas no coupling was observed with Gαz, nor with the retinal Gα proteins, rod (GNAT2) or cone (GNAT1) transducin (GαTr-R, GαTr-C). Finally, the expression of Gα proteins determined to couple with mGluR6 was examined in rat ON bipolar cells using single cell RT-PCR. Co-expression of mGluR6 message was used to distinguish ON from OFF bipolar cells. Expression of Gαowas detected in every ON bipolar cell examined. Message for Gαi1, which coupled moderately to mGluR6, was not detected in ON bipolar cells, nor was Gαi3, which coupled to mGluR6 in only a few cells but on average did not exhibit statistically significant coupling. Finally, though Gαi2was detectable in ON bipolar cells, its coupling to mGluR6 in the SCG system was not significant. Together, these data indicate that signaling through mGluR6 in mammalian ON bipolar cells is highly focused, apparently acting through a single Gα protein subtype.
Talking About My Generation: the Date of the West Kennet Long Barrow
Authors: Bayliss Alex , Whittle Alasdair , Wysocki Michael
Published: February 2007

Thirty-one radiocarbon results are now available from the West Kennet long barrow, and are presented within an interpretive Bayesian statistical framework. Two alternative archaeological interpretations of the sequence are given, each with a separate Bayesian model. In our preferred interpretation, the barrow is seen as a unitary construction (given the lack of dating samples from the old ground surface, ditches or constructional features themselves), with a series of deposits of human remains made in the chambers following construction. Primary deposition in the chambers is followed by further secondary deposition of some human remains, including children, and layers of earth and chalk, the latest identifiable finds in which are Beaker sherds. In the Bayesian model for this sequence, the construction of the monument at West Kennet, as dated from the primary mortuary deposits, occurred in 3670–3635 cal. bc, probably in the middle decades of the thirty-seventh century cal. bc. The last interments of this initial use of the chambers probably occurred in 3640–3610 cal. bc. The difference between these two distributions suggests that this primary mortuary activity probably continued for only 10–30 years. After a hiatus probably lasting for rather more than a century, the infilling of the chambers began in 3620–3240 cal. bc and continued into the second half of the third millennium cal. bc. In an alternative interpretation, we do not assume that all the people dated from the primary mortuary deposits were placed in the monument in a fleshed or partially articulated condition; they could therefore have died before the monument was built, although they must have died before the end of the formation of the mortuary deposit. In the Bayesian model for this interpretation, the monument appears to belong either to the thirty-seventh century cal. bc or the mid-thirty-sixth century cal. bc, and deposition again appears short-lived, but the model is unstable. Results are discussed in relation to the setting and sequence of the local region.
Is the sperm centrosome to blame for the complex polyploid chromosome patterns observed in cleavage stage embryos from an OAT patient?
Authors: Chatzimeletiou K. , Rutherford A. J. , Griffin D. K. , Handyside A. H.
Published: February 2007

Oligoasthenoteratozoospermia (OAT) is defined by a combined low count < 20 × 106 sperm/ml, poor motility < 50 % forward progression or < 25 % rapid linear progression and abnormal morphology (5–8 % normal using Kruger strict criteria) and has been associated with increased levels of sperm aneuploidy. Here we report on the cytogenetic findings from three ‘spare’ embryos from a couple that were referred for ICSI because of OAT. The embryos were processed for sequential FISH in three hybridization rounds using probes for chromosomes 3, 7, 9, 13, 17, 18, 21, X and Y. Molecular cytogenetic analysis of nine chromosomes revealed that all three embryos were female polyploid. One of them was uniformly tetraploid for all chromosomes tested, while the remaining two embryos showed evidence of abnormal postzygotic segregation of chromosomes, causing the derivative blastomeres to have uneven chromosomal constitution. In one of them in particular, the non-disjoining chromosomes showed preferential segregation to the same pole, rather than randomly moving towards either pole, suggesting an abnormal spindle and causing the derivative blastomeres to have significantly uneven chromosomal constitutions. The possible scenarios leading to polyploidy and chromosomal imbalance through cytokinetic failure and subsequent abnormal centrosomal distribution are outlined.
Trends in overweight by socio-economic status in Vietnam: 1992 to 2002
Authors: Nguyen Minh Duc , Beresford Shirley AA , Drewnowski Adam
Published: February 2007

Objective

To explore socio-economic factors associated with rising rates of overweight among Vietnamese adults.

Design

The study was based on three national surveys of socio-economic factors and health conducted over a 10-year period. The studies were: the Vietnamese Living Standard Survey 1992–1993 (11 982 participants); the Vietnamese Living Standard Survey 1997–1998 (15 975 participants); and the Vietnamese National Health Survey 2001–2002 (94 656 participants).

Subjects

Male and female adults >18 years old were stratified by gender, age group, area of residence, occupation, education and relative food expenditures. Overweight was defined using body mass index (BMI) ≥ 25 kg m− 2.

Results

Overweight rates in Vietnam more than doubled between 1992 and 2002 (from 2.0 to 5.7%). Significant increases were observed for men and women, in urban and rural areas, and for all age groups. In univariate analyses, both age and higher socio-economic status were associated with higher rates of overweight. Using the most recent survey, urban populations were more likely to be overweight than rural ones (odds ratio (OR) = 1.79), white-collar workers were more likely to be overweight than manual labourers (OR = 1.95) and persons in the top level of food expenditures were more likely to be overweight than persons in the bottom level (OR = 4.96) after adjustment for other factors. Education was inversely associated with overweight after adjusting for covariates.

Conclusion

Economic growth and improved standard of living are associated with higher rates of overweight in nations in early stages of economic development. In Vietnam, higher rates of overweight were observed among the higher income and occupation groups.
Environmental impacts of the expected increase in sea transportation, with a particular focus on oil and gas scenarios for Norway and northwest Russia
Authors: Dalsøren Stig B. , Endresen Øyvind , Isaksen Ivar S. A. , Gravir Gjermund , Sørgård Eirik
Published: February 2007

We have complemented existing global sea transportation emission inventories with new regional emission data sets and scenarios for ship traffic and coastal activity in 2015. Emission inventories for 2000 and 2015 are used in a global Chemical Transport Model (CTM) to quantify environmental atmospheric impacts with particular focus on the Arctic region. Although we assume that ship emissions continue to increase from 2000 to 2015, reductions are assumed for some chemical components and regions because of implementation of new regulations. Current ship traffic (2000) is estimated to contribute significantly to coastal pollution. Norwegian coastal ship traffic is responsible for more than 1/3 and 1/6 of the Norwegian NOx and SO2 emissions, respectively. For these short‐lived components the impact of Norwegian coastal emissions is regionally important. For most components the international ship transportation outside coastal waters dominates the effects. Ship emissions increase wet deposition in Scandinavia with 30–50% for nitrate and 10–25% for sulfate. In general, coastal regions with prevailing onshore winds show substantial increases in deposition of acid components. Maximum surface increase in ozone is in excess of 10 ppbv. Column ozone increases are also significant. Assuming no changes in nonshipping emissions, scenarios for shipping activities in 2015 lead to more than 20% increase in NO2 from 2000 to 2015 in some coastal areas. Ozone increases are in general small. Wet deposition of acidic species increases up to 10% in areas where current critical loads are exceeded. Regulations limiting the sulfur content in the fuel in the North Sea and English Channel will be an efficient measure to reduce sulfate deposition in nearby coastal regions. The expected oil and gas transport by ships from Norway and northwest Russia, sea transport along the Northern Sea Route and new Norwegian coastal gas power plants will have a significant regional effect by increases of acid deposition in north Scandinavia and the Kola Peninsula. Augmented levels of particles in the Arctic are calculated, and thus the contribution from ship traffic to phenomena like Arctic haze could be increasing.
Assimilation of POLDER aerosol optical thickness into the LMDz‐INCA model: Implications for the Arctic aerosol burden
Authors: Generoso S. , Bréon F.‐M. , Chevallier F. , Balkanski Y. , Schulz M. , Bey I.
Published: February 2007

The large spatial and temporal variability of atmospheric aerosol load makes it a challenge to quantify aerosol effect on climate. This study is one of the first attempts to apply data assimilation for the analysis of global aerosol distribution. Aerosol optical thickness (AOT) observed from the Polarization and Directionality of the Earth Reflectances (POLDER) spaceborne instrument are assimilated into a three‐dimensional chemistry model. POLDER capabilities to distinguish between fine and coarse AOT are used to constrain them separately in the model. Observation and model errors are a key component of such a system and are carefully estimated on a regional basis using some of the high‐quality surface observations from the Aerosol Robotic Network (AERONET). Other AERONET data provide an independent evaluation of the a posteriori fields. Results for the fine mode show improvements, in terms of reduction of root‐mean‐square errors, in most regions with the largest improvements found in the Mediterranean Sea and Eurasia. We emphasize the results for the Arctic, where there is growing evidence of a strong aerosol impact on climate, but a lack of regional and continuous aerosol monitoring. The a posteriori fields noticeably well reproduce the winter‐spring “Arctic Haze” peak measured in Longyearbyen (15°E, 78°N) and typical seasonal variations in the Arctic region, where AOT increase by up to a factor of three between a posteriori and a priori. Enhanced AOT are found over a longer period in spring 2003 than in 1997, suggesting that the large Russian fires in 2003 have influenced the Arctic aerosol load.
Influence of ridge migration and proximity to hot spots on the morphology of slow‐ and intermediate‐spreading centers
Authors: Supak S. , Carbotte S. M. , Macdonald K. C.
Published: February 2007

Recent observations of ridge bathymetry suggest magmatic segmentation at fast‐ and intermediate‐spreading centers is linked to the migration of the spreading axis over the mantle. At fast‐ and intermediate‐spreading centers, Carbotte et al. (2004) observed that leading segments, those that are offset in the direction of ridge migration, are typically shallower (interpreted to be magmatically robust) relative to trailing segments across first‐ and second‐order discontinuities. The model set forth for this correlation invokes asymmetrical mantle upwelling in response to the absolute motion of the ridge axis and the entrainment of melt from across discontinuities. In this investigation, differences in ridge axis depth across first‐ and second‐order discontinuities are examined within the context of absolute plate motions for portions of the slow‐spreading Mid‐Atlantic Ridge (MAR 22–36°N and 25–35°S latitude), intermediate‐spreading Galápagos Spreading Center (GSC 83–98°W), and intermediate‐spreading South East Indian Ridge (SEIR 77–114°E). Portions of each of these areas display chemical and/or physical anomalies resulting from hot spot–ridge interaction. Along non–hot spot–influenced sections of intermediate‐spreading ridges, leading segments coincide with shallower segments across 72% of the first‐ and second‐order discontinuities (86% of transform faults and 55% of second‐order discontinuities). Depth asymmetries vary with ridge offset length, with maximum asymmetries for ridge offset lengths of 50–100 km. A weaker correlation is observed between ridge migration direction and ridge morphology at the slow‐spreading MAR, where leading segments are shallower across ∼60% of first‐ and second‐order discontinuities. For hot spot–influenced spreading centers, hot spot proximity dominates ridge morphology at intermediate‐spreading centers, but it is not a consistent predictor of axial depth asymmetries at slow‐spreading centers. This spreading‐rate‐dependent influence of ridge migration and hot spot proximity on axial morphology may reflect a more limited entrainment of melt from across slow‐spreading discontinuities due to the predominance of three‐dimensional upwelling and melt focusing to segment centers.
Diurnal cycle of dust and cirrus over West Africa as seen from Meteosat Second Generation satellite and a regional forecast model
Authors: Chaboureau Jean‐Pierre , Tulet Pierre , Mari Céline
Published: February 2007

A brightness temperature difference (BTD) technique is used to evaluate the dust and cirrus forecasts of a regional meteorological model. The technique based on a contrasted absorption property of dust and cirrus at two wavelengths within the atmospheric infrared window is applied to 3‐hourly Meteosat Second Generation (MSG) observations in the 10.8‐ and 12‐μm bands over West Africa. The satellite observation of dust coverage over the Sahara shows a well marked diurnal cycle associated with the boundary layer activity peaking at 15 UTC. A similar signature is obtained from the regional model when the dust scheme is activated. The cirrus cover over West Africa is maximum at 12 UTC as seen both from MSG and the model. The use of prognostic dust aerosol, instead of climatology, furthermore better captures the observed convective activity.
Diurnal variation and radiative influence of Martian water ice clouds
Authors: Wilson R. John , Neumann Gregory A. , Smith Michael D.
Published: February 2007

We have identified regions in the Martian tropics with anomalously warm nighttime surface temperatures. The seasonal evolution of these anomalies is strongly correlated with the waxing and waning of the tropical cloud belt that is most prominent during Northern Hemisphere summer. We attribute the anomalies to enhanced downward infrared radiation from water ice clouds. The close agreement with spatial maps of atmospheric extinction derived from Mars Orbiter Laser Altimeter radiometry strongly supports this interpretation. We show that a Mars general circulation model simulation with radiatively active water ice clouds is able to reasonably match the observed spatial pattern and amplitude of the surface temperature anomaly. The nighttime clouds are most prominent in the Tharsis and Arabia regions and are thicker (optical depth ∼ 1) and more extensive than daytime clouds. Our cloud retrievals are the first to spatially map the nighttime clouds and provide an estimate of their thermal influence.
Time‐resolved ducting of atmospheric acoustic‐gravity waves by analysis of the vertical energy flux
Authors: Yu Yonghui , Hickey Michael P.
Published: February 2007

A new 2‐D time‐dependent model is used to simulate the propagation of an acoustic‐gravity wave packet in the atmosphere. A Gaussian tropospheric heat source is assumed with a forcing period of 6.276 minutes. The atmospheric thermal structure creates three discrete wave ducts in the stratosphere, mesosphere, and lower thermosphere, respectively. The horizontally averaged vertical energy flux is derived over altitude and time in order to examine the time‐resolved ducting. This ducting is characterized by alternating upward and downward energy fluxes within a particular duct, which clearly show the reflections occurring from the duct boundaries. These ducting simulations are the first that resolve the time‐dependent vertical energy flux. They suggest that when ducted gravity waves are observed in the mesosphere they may also be observable at greater distances in the stratosphere.
Simulation of the effects of critical factors on ozone formation and accumulation in the greater Athens area
Authors: Bossioli Elissavet , Tombrou Maria , Dandou Aggeliki , Soulakellis Nikos
Published: February 2007

In the present study, the temporal and spatial dynamics of the ozone production in the greater Athens area (GAA) is examined by using the photochemical UAM‐V model coupled with the meteorological MM5 model. Several numerical experiments were performed in order to investigate and to quantify the effect of critical factors that conduce to the ozone formation and accumulation during ozone episodes. The initial scenario is able to reproduce the observed ozone patterns, but it underestimates the observed peaks in most of the downwind suburban stations. Using process analysis, we demonstrate the contribution of chemical and physical processes to ozone formation and destruction. The inclusion of biogenic emissions and their distribution based on a satellite vegetation index, as well as the adjustment of the speciation of the anthropogenic NMVOC emissions according to specific characteristics measured in street and aged city plumes, lead to a more realistic description of the urban mixture and thus of the ozone production. The effect of the urban sector introduced via a simplified urbanized meteorological data set, provoke a differentiation of the spatial pattern attributed to the accumulation of the primary NOX pollutants inside the city center and to the consequent limited horizontal advection toward the peripheral zone. Finally, the ozone background turned out to be a key factor for the model performance. The statistical evaluation of the results reveals the importance and the necessity of implementing all the above modifications; the persistence of some discrepancies is associated with meteorological or modeling coupling limitations.
Chemical cycling and deposition of atmospheric mercury: Global constraints from observations
Authors: Selin Noelle E. , Jacob Daniel J. , Park Rokjin J. , Yantosca Robert M. , Strode Sarah , Jaeglé Lyatt , Jaffe Daniel
Published: February 2007

We use a global 3‐D model of atmospheric mercury (GEOS‐Chem) to interpret worldwide observations of total gaseous mercury (TGM) and reactive gaseous mercury (RGM) in terms of the constraints they provide on the chemical cycling and deposition of mercury. Our simulation including a global mercury source of 7000 Mg yr−1 and a TGM lifetime of 0.8 years reproduces the magnitude and large‐scale variability of TGM observations at land sites. However, it cannot capture observations of high TGM from ship cruises, implying a problem either in the measurements or in our fundamental understanding of mercury sources. Observed TGM seasonal variation at northern midlatitudes is consistent with a photochemical oxidation for Hg(0) partly balanced by photochemical reduction of Hg(II). Observations of increasing RGM with altitude imply a long lifetime of Hg(II) in the free troposphere. We find in the model that Hg(II) dominates over Hg(0) in the upper troposphere and stratosphere and that subsidence is the principal source of Hg(II) at remote surface sites. RGM observations at Okinawa Island (Japan) show large diurnal variability implying fast deposition, which we propose is due to RGM uptake by sea‐salt aerosols. Observed mercury wet deposition fluxes in the United States show a maximum in the southeast, which we attribute to photochemical oxidation of the global Hg(0) pool. They also show a secondary maximum in the industrial Midwest due to regional emissions that is underestimated in the model, possibly because of excessive dry deposition relative to wet (dry deposition accounts for 68% of total mercury deposition in the United States in the model, but this is sensitive to the assumed phase of Hg(II)). We estimate that North American anthropogenic emissions contribute on average 20% to U.S. mercury deposition.
A Mössbauer spectral study of the GdCo4−xFexB compounds
Authors: Grandjean Fernande , Hermann Raphaël P. , Popiel E. , Long Gary J.
Published: February 2007

The iron-57 Mössbauer spectra of the GdCo4−xFexB compounds, where x is 0.10, 0.15, 0.20, 0.25, 1, 2, 2.5, and 2.6, have been measured at room temperature and reveal relatively small iron hyperfine fields of approximately 12–18T, relatively large quadrupole interactions of approximately +0.9 and −1mm∕s, and three very different types of spectra for x=0.10 and 0.15, x=0.25, 1, and 2, and x=2.5 and 2.6. The differences result from both the different easy magnetization directions in these compounds and the different cobalt and∕or iron occupancies of the crystallographic 2c and 6i sites. The spectra have been fitted by calculating the spectral absorption with the complete iron-57 nuclear excited state Hamiltonian for the iron 2c and 6i sites. The fits have used an asymmetry parameter η and Euler angles θ and ϕ that relate the hyperfine field to the iron electric field gradient axes of each crystallographic site in an orientation that is consistent with the structural and magnetic properties of the site. The results of the fits indicate both that the full Hamiltonian approach is required for physically reasonable spectral fits and that the small observed fields result from the presence of large orbital contributions which subtract from the Fermi contact contributions to the magnetic hyperfine fields of the two sites. The iron 2c occupancy obtained from the Mössbauer spectral area has been used to model the compositional dependence of the magnetic anisotropy constant in the GdCo4−xFexB compounds.
Integrable lattices and their sublattices: From the discrete Moutard (discrete Cauchy-Riemann) 4-point equation to the self-adjoint 5-point scheme
Authors: Doliwa A. , Grinevich P. , Nieszporski M. , Santini P. M.
Published: February 2007

We present the sublattice approach, a procedure to generate, from a given integrable lattice, a sublattice which inherits its integrability features. We consider, as illustrative example of this approach, the discrete Moutard 4-point equation and its sublattice, the self-adjoint 5-point scheme on the star of the square lattice, which are relevant in the theory of the integrable discrete geometries and in the theory of discrete holomorphic and harmonic functions (in this last context, the discrete Moutard equation is called discrete Cauchy-Riemann equation). Therefore an integrable, at one energy, discretization of elliptic two-dimensional operators is considered. We use the sublattice point of view to derive, from the Darboux transformations and superposition formulas of the discrete Moutard equation, the Darboux transformations and superposition formulas of the self-adjoint 5-point scheme. We also construct, from algebro-geometric solutions of the discrete Moutard equation, algebro-geometric solutions of the self-adjoint 5-point scheme. In particular, we show that the corresponding restrictions on the finite-gap data are of the same type as those for the fixed energy problem for the two-dimensional Schrödinger operator. We finally use these solutions to construct explicit examples of discrete holomorphic and harmonic functions, as well as examples of quadrilateral surfaces in R3.
The transport of a passive scalar in magnetohydrodynamic turbulence subjected to mean shear and frame rotation
Authors: Kassinos S. C. , Knaepen B. , Carati D.
Published: February 2007

We consider the transport of a passive scalar under the influence of homogeneous turbulence in a conducting fluid that is exposed to a uniform external magnetic field while being sheared in fixed and rotating frames. The mean scalar gradient is assumed to be uniform and aligned with the transverse direction within the plane of the mean shear, while both the frame-rotation axis and the applied magnetic field are aligned in the direction normal to the plane of the mean shear. For any given frame rotation rate, we find that a key parameter determining the structural morphology of the flow is the ratio of the time scale of the mean shear to the Joule time, τshear∕τm. The most drastic modifications to passive scalar transport are observed when τshear≥τm, and these are shown to be linked to changes in the structure of the velocity and scalar fields. In most cases, the observed evolution of the scalar flux coefficients can be explained in terms of structural information provided by the one-point structure tensors, except for high magnetic Reynolds numbers flows, where the alignment of the velocity fluctuation field with the spatially varying local mean magnetic field can, under certain conditions, lead to loss of coherence and suppression of the correlation between the velocity and scalar fields.
Atomic quantum similarity indices in position and momentum spaces
Authors: Angulo J. C. , Antolín J.
Published: February 2007

Quantum similarity for atoms is investigated using electron densities in position and momentum spaces. Contrary to the results in position space, the analysis in the momentum space shows how the momentum density carries fundamental information about periodicity and structure of the system and reveals the pattern of Mendeleev’s table. A global analysis in the joint r-p space keeps this result.
Electron parallel velocity and temperature gradient driven electrostatic fluctuations in nonuniform magnetoplasmas
Authors: Shukla P. K. , Coppi B. , Eliasson B.
Published: February 2007

The combined effects of the electron-temperature (ET) and parallel electron velocity (PEV) gradients on electrostatic instabilities in a nonuniform magnetoplasma are investigated. For this purpose, a hybrid approach is used, in which the electrons are treated as a magnetized fluid, while the ions are described by means of a kinetic description. A new dispersion relation is derived, which shows how different plasma modes are linear coupled in the presence of the ET and PEV gradients. The dispersion relation is analyzed analytically (numerically) to demonstrate the instability of long- and short-wavelength electrostatic modes (to examine the combined effects of ET and PEV gradients) in nonuniform magnetoplasmas. The present results may be useful in understanding the salient features of nonthermal fluctuations and associated anomalous cross-field electron fluxes in forthcoming laboratory experiments.
Reaction of Cl with CD4 excited to the second C–D stretching overtone
Authors: Martin Marion R. , Ankeny Brown Davida J. , Chiou Albert S. , Zare Richard N.
Published: February 2007

The effects of vibrational excitation on the Cl+CD4 reaction are investigated by preparing three nearly isoenergetic vibrational states: ∣3000⟩ at 6279.66cm−1, ∣2100⟩ at 6534.20cm−1, and ∣1110⟩ at 6764.24cm−1, where ∣D1D2D3D4⟩ identifies the number of vibrational quanta in each C–D oscillator. Vibrational excitation of the perdeuteromethane is via direct infrared pumping. The reaction is initiated by photolysis of molecular chlorine at 355nm. The nascent methyl radical product distribution is measured by 2+1 resonance-enhanced multiphoton ionization at 330nm. The resulting CD3 state distributions reveal a preference to remove all energy available in the most excited C–D oscillator. Although the energetics are nearly identical, the authors observe strong mode specificity in which the CD3 state distributions markedly differ between the three Cl-atom reactions. Reaction with CD4 prepared in the ∣3000⟩ mode leads to CD3 products populated primarily in the ground state, reaction with CD4 prepared in the ∣2100⟩ mode leads primarily to CD3 with one quantum of stretch excitation, and reaction with CD4 prepared in the ∣1110⟩ mode leads primarily to CD3 with one quantum of C–D stretch excitation in two oscillators. There are some minor deviations from this behavior, most notably that the Cl atom is able to abstract more energy than is available in a single C–D oscillator, as in the case of ∣2100⟩, wherein a small population of ground-state CD3 is observed. These exceptions likely result from the mixings between different second overtone stretch combination bands. They also measure isotropic and anisotropic time-of-flight profiles of CD3 (ν1=1,2) products from the Cl+CD4 ∣2100⟩ reaction, providing speed distributions, spatial anisotropies, and differential cross sections that indicate that energy introduced as vibrational energy into the system essentially remains as such throughout the course of the reaction.