bluuebunny/crossref_metadata_2025 huggingface dataset:
Gestational carrier — A reproductive haven for offspring of mothers with phenylketonuria (PKU): An alternative therapy for maternal PKU
Authors: Fisch R. O. , Tagatz G. , Stassart J. P.
Published: November 2004

Maternal phenylketonuria, PKU, has a detrimental effect on embryogenesis. Infant pathology is independent of fetal genotype, but is directly correlated with excessive phenylalaninaemia throughout pregnancy. Although normal children have been delivered by affected mothers who either had benign hyperphenylalaninaemia or in whom strict diet has apparently maintained maternal phenylalaninaemia in the low normal range from before conception, more abnormal than normal births have been reported. In addition, attempts at dietary management are often unsuccessful; most reported cases documented various severe pathological consequences of maternal PKU. Currently available methods provide viable alternative treatment.In vitro fertilization using the parental gametes, followed by implantation of the pre‐embryo in a surrogate mother, would avoid a metabolic environment impairing normal development, and therefore should be recommended as alternative therapy for potential mothers with PKU.
Scottish frequency of the common G985 mutation in the medium‐chain acyl‐CoA dehydrogenase (MCAD) gene and the role of MCAD deficiency in sudden infant death syndrome (SIDS)
Authors: Dundar M. , Lanyon W. G. , Connor J. M.
Published: November 2004

Medium‐chain acyl‐CoA dehydrogenase (MCAD) deficiency, is an autosomal recessive inborn error of metabolism associated with various clinical presentations, including sudden unexplained death in young children. We have determined the Scottish frequency of the common G985 mutation found in Caucasians and in samples from Scottish patients with sudden infant death syndrome (SIDS). The heterozygote frequency of the mutation was found to be 1 in 276 (95% confidence interval: 1/76–1/2279) in 552 healthy controls and 1 in 74 (95% confidence interval: 1/27–1/377) in 233 SIDS patients: a difference that was not statistically significant (Fisher's exact test; two‐sided;p=0.316). None of the SIDS samples was found to be homozygous for the G985 mutation.
Identification of GM2‐gangliosidosis B1 variant carriers
Authors: Ribeiro M. G. , Pinto R. , Oliveira P. , Sá Miranda M. C.
Published: November 2004

GM2‐gangliosidosis B1 variant, considered a rare disorder with a wide geographical and ethnic distribution, appears to be exceptionally frequent in Portugal. In order to establish a carrier detection method for this disease we have determined the ratio of enzymatic activities against 4MUGS and 4MUG in urine from B1 variant obligate carriers and controls, using the total extract and the Hex A immunobound to a monoclonal antibody. The Hex A immunoassay was applied to the identification of carriers in B1 variant families and the results obtained were compared with those from DNA analysis. The reliability and feasibility of the Hex A immunoassay make it a suitable method for B1 variant carrier screening, which is particularly important for the prevention of this severe neurological disease in the population at risk.
Impaired degradation of phytanic acid in cells from patients with mitochondriopathies: Evidence for the involvement of ETF and the respiratory chain in phytanic acid α‐oxidation
Authors: Fingerhut R. , Schmitz W. , Garavaglia B. , Reichmann H. , Conzelmann E.
Published: November 2004

Phytanic acid α‐oxidation was studied in cultures of skin fibroblasts and myoblasts from patients with various defects of the respiratory chain in order to obtain information on the subcellular site and the mechanism of this pathway. In fibroblasts from patients with complex IV (cytochromec oxidase) deficiency or glutaricaciduria type II, phytanic acid α‐oxidation was reduced to 14% of normal, whereas in myoblasts from patients with complex I (NADH‐Q reductase) deficiency, it was normal. Apparently, at least one step of phytanic acid α‐oxidation occurs in mitochondria and in this process electrons are transferred to the respiratory chain via the electron‐transfer flavoprotein (ETF).
Plasmacis‐dec‐4‐enoic acid measured by isotope dilution mass spectrometry; an improved assay to diagnose medium‐chain acyl‐CoA dehydrogenase deficiency
Authors: Johnson D. W. , Harrison J. R. , Norton W. A. , Poulos A. , Robertson E. F.
Published: November 2004

An isotope dilution mass spectrometric assay for plasmacis‐dec‐4‐enoic acid is described. It is quicker, more reliable and more accurate than previous methods. It confirmed previous findings thatcis‐dec‐4‐enoic acid is a reliable indicator for medium‐chain acyl‐CoA dehydrogenase deficiency (MCAD). The plasmacis‐dec‐4‐enoic acid levels of both asymptomatic and symptomatic MCAD patients (3.5–71 µmol/L) are demonstrably higher than those of normal children (0.2–1.7 µmol/L), MCAD heterozygotes (0.1–1.5 µmol/L), those with other fatty acid oxidation defects (0.2–2.2 µmol/L) or those receiving high doses of valproic acid (0.2–0.4 µmol/L).
Effect of betaine onS‐adenosylmethionine levels in the cerebrospinal fluid in a patient with methylenetetrahydrofolate reductase deficiency and peripheral neuropathy
Authors: Kishi T. , Kawamura I. , Harada Y. , Eguchi T. , Sakura N. , Ueda K. , Narisawa K. , Rosenblatt D. S.
Published: November 2004

A 16‐year‐old Japanese girl with 5,10‐methylenetetrahydrofolate reductase deficiency showed peripheral neuropathy. There were no significant responses to vitamin B6, vitamin B12 or folate, given alone or in combination. With the addition of betaine monohydrate, she has been free from gait disturbance and muscle weakness. The concentration ofS‐adenosylmethionine in cerebrospinal fluid, which was undetectable before receiving betaine monohydrate, increased to about the normal level 24 months after treatment with betaine monohydrate.
Molecular genetic characterization and urinary excretion pattern of metabolites in two families with MCAD deficiency due to compound heterozygosity with a 13 base pair insertion in one allele
Authors: Gregersen N. , Winter V. , Lyonnet S. , Saudubray J. M. , Wendel U. , Jensen T. G. , Andresen B. S. , Kølvraa S. , Lehnert W. , Bolund L. , Christensen E. , Bross P.
Published: November 2004

Two families with medium‐chain acyl‐CoA dehydrogenase (MCAD) deficiency due to compound heterozygosity are described. All patients have a 13 bp insertion in exon 11 of one allele at the MCAD gene locus. In the other allele patients in one of the families harbour the prevalent G985 mutation, and the other family possess an unidentified mutation causing reduced levels of MCAD mRNA. We demonstrate that the disease in these families is inherited as an autosomal recessive trait. Individuals heterozygous for the mutations show heterozygous/control levels of β‐oxidation activities in cultured fibroblasts (9.1–16.3 pmol/min per mg protein; control 10–17 pmol/min per mg protein), and in the excretion of the ‘β‐oxidation metabolites’, hexanoylglycine (<2 µmol/mmol creatinine), suberylglycine (<2 µmol/mmol creatinine) and phenylpropionylglycine (<2 µmol/mmol creatinine). This shows that there is no ‘negative dominance’ from the mutant monomeric protein onto the normal ones, in accordance with the finding of low levels of MCAD mRNA from the allele harbouring the 13 bp insertion as well as the allele with the unidentified mutation, and the low steady‐state level of enzyme protein expressed from the G985‐bearing allele. In the family possessing the G985 and the 13 bp insertion mutations, two asymptomatic compound heterozygous individuals were detected. They exhibited elevated excretion of hexanoylglycine (5–15 µmol/mmol creatinine) and suberylglycine (4–13 µmol/mmol creatinine), together with β‐oxidation activity in fibroblasts in the homozygous range (2.9 pmol/min per mg protein), showing a lack of correlation between the genotype, some biochemical parameters and the clinical phenotype.
Vitamin‐responsive complex I deficiency in a myopathic patient with increased activity of the terminal respiratory chain and lactic acidosis
Authors: Bakker H. D. , Scholte H. R. , Jeneson J. A. L. , Busch H. F. M. , Abeling N. G. G. M. , van Gennip A. H.
Published: November 2004

An 11‐year‐old gril with exercise intolerance, fatiguability from early childhood, had high blood lactate levels. Histochemistry showed increased activity of succinate dehydrogenase at the periphery of the muscle fibres, whereas aggregates of mitochondria were seen by electron microscopy. Biochemical investigation of isolated mitochondria and homogenate from muscle showed evidence of a severe complex I deficiency. In contrast, succinate dehydrogenase, complex II + III and complex IV were increased in activity. Therapy with biotin, riboflavin, nicotinamide, carnitine and amino acids resulted in an improvement of her endurance.31P NMR spectroscopy of her forearm muscle showed a decreased ratio of phosphocreatine (PCr) over ATP. After exercise the PCr recovery rate was 26% of the average rate in 20 healthy untrained controls. When the therapy was suspended the PCr/ATP ratio at rest decreased from 2.60 to 2.34, and the PCr recovery rate after exercise decreased to 21% of the average control rate. The therapy was reinstituted but only riboflavin and carnitine were given. The PCr/ATP ratio increased to 2.60 and the PCr recovery rate increased to 32% of the control rate. Improvement of the energy metabolism in patients with defects in the oxidative phosphorylation may add to the quality of life;31P NMR spectroscopy can measure these improvements.
Possible high frequency of tetrahydrobiopterin deficiency in South Brazil
Authors: Jardim L. B. , Giugliani R. , Coelho J. C. , Dutra‐Filho C. S. , Blau N.
Published: November 2004

We report our experience with the deficiency of 6‐pyruvoyltetrahydropterin synthase, the most common form of tetrahydrobiopterin deficiency. We investigated 5200 patients suspected of having some inborn error of metabolism in a 10‐year period, and detected 30 cases (from 28 sibships) of hyperphenylalaninaemias, HPA. From these, 4 sibships (5 patients) were affected by deficiency of 6‐pyruvoyltetrahydropterin synthase. All of them were ethnically mixed, with some European ancestry detected in all. The age of diagnosis ranged from 2 to 9 years, and all were initially referred for investigation by having mental retardation and seizures. All of them showed low urinary biopterin levels and a marked elevation of neopterin. Although we detected only a few cases of HPA (30), 5 cases of 6‐pyruvoyltetrahydropterin account for almost 20% of this total. The literature, however, reports a proportion of around 0.5%. As the frequency of classical phenylketonuria in our region is similar to that found in Caucasians (1/12 500), we believe that the frequency of this disease in South Brazil may be higher than expected (of the order of 1/400 000). We speculate that this finding could be related to a genetic drift (or founder effect).
l‐2‐Hydroxyglutaric acidaemia: Clinical and biochemical findings in 12 patients and preliminary report onl‐2‐hydroxyacid dehydrogenase
Authors: Barth P. G. , Hoffmann G. F. , Jaeken J. , Wanders R. J. A. , Duran M. , Jansen G. A. , Jakobs C. , Lehnert W. , Hanefeld F. , Valk J. , Schutgens R. B. H. , Trefz F. K. , Hartung H. ‐P. , Chamoles N. A. , Sfaello Z. , Caruso U.
Published: November 2004

l‐2‐Hydroxyglutaric acidaemia represents a newly defined inborn error of metabolism, with increased levels ofl‐2‐hydroxyglutaric acid in urine, plasma and cerebrospinal fluid. The concentration in cerebrospinal fluid is higher than in plasma. The other consistent biochemical finding is an increase of lysine in blood and cerebrospinal fluid, but lysine loading does not increasel‐2‐hydroxyglutaric acid concentration in plasma. This autosomal recessively inherited disease is expressed as progressive ataxia, mental deficiency with subcortical leukoencephalopathy and cerebellar atrophy on magnetic resonance imaging. Since these features were described in 8 patients by Barth and co‐workers in 1992, 4 more patients with similar findings have been diagnosed and added to the present series.l‐2‐Hydroxyglutaric acid is found in only trace amounts on routine gas chromatographic screening in normal persons, and its origin, its fate and even its relevance to normal metabolism are unknown. Therefore its catabolism was studied in normal liver. Incubation of rat liver withl‐2‐hydroxyglutaric acid did not produce H2O2, which excluded (peroxisomal)l‐2‐hydroxyacid oxidase as the main route of catabolism. However,l‐2‐hydroxyglutaric acid is rapidly dehydrogenated if NAD+ is added as a co‐factor to the standard reaction medium. This could also be demonstrated in human liver. The preliminary evidence for this enzyme activity in rats and humans,l‐2‐hydroxyglutaric acid dehydrogenase, is given. Further investigations are required to clarify the possible relevance to the metabolic defect inl‐2‐hydroxyglutaric acidaemia.
A Model for Northern Hemisphere Continental Ice Sheet Variation
Authors: Johnson R.G. , McClure B.T.
Published: December 2004

The marine record shows that over the last 350 ka Northern Hemisphere ice sheet volumes have fluctuated widely and only on rare short occasions have they been reduced to the present interglacial state. The fluctuations are well synchronized with hemispheric average summer insolation variations of 20 ka periodicity caused by changing orbital parameters. The development of a model which explains the varied amplitudes of the fluctuations and is consistent with the geological record embodies the following arguments: The transition from an interglacial state like today's to a glacial state is initiated when a summer insolation deficit causes a southerly extension of the North Atlantic-Arctic pack ice to 60°N latitude. The extension alters the subpolar low pressure patterns and thus causes a southward diversion of the European Gulf Stream flow. It also produces an enhanced warm West Greenland current. This current causes open seas as far north as Baffin Bay which provides moisture for rapid northern Laurentide ice sheet growth. After several glacial fluctuations driven by insolation variations, the southern Laurentide ice front may reach an extreme extension. This diverts the westerlies and the Gulf Stream thus weakening a dominant subpolar North Atlantic gyre and consequently producing a prolonged cutoff of the West Greenland current and a reduction of high latitude glacial precipitation. The subsequent high insolation can then melt back the eastern pack ice and restore the northern European Gulf Stream. This warms the high latitudes for a time sufficient to melt the continental ice, thus causing the transition back to the interglacial state.

An analysis of the record in the context of model suggests that the threshold deficit in average summer insolation that is required to initiate major glacial growth is influenced by the cooling effect of the Greenland ice cap on the seas to the east. The threshold level under conditions like today's is found to lie between −7 and −17 ly/day relative to the present. This threshold will not be crossed for at least 54 millenia due to an interval of smaller orbital eccentricity. Probable melting of the Greenland ice cap about 30 ka AP would ensure the extension of the present interglacial beyond 120 ka AP.
Proneofiber, a New Genus of Vole (Cricetidae: Rodentia) from the Pleistocene Seymour Formation of Texas, and its Evolutionary and Stratigraphic Significance
Authors: Hibbard Claude W. , Dalquest Walter W.
Published: December 2004

A new genus and species of a microtine rodent, Proneofiber guildayi, is named on the basis of rooted teeth with cement from the warm Gilliland local fauna, Seymour Formation of Pleistocene age, Knox County, Texas. Proneofiber guildayi is considered to be ancestral to Neofiber, the round-tailed water rat, now living in the extreme southeastern United States. The presence of Pleistocene faunas prior to the first continental glaciation and the existence of three Pearlette-like volcanic ashes in the Plains Region suggest a revision of the age assignment of Pleistocene deposits from the nonglaciated region.
Correlation of the Quaternary Terrace Sequence in the Lower Rhine Valley and Northern Alpine Foothills of Central Europe
Authors: Brunnacker Karl , Löscher Manfred , Tillmanns Wolfgang , Urban Brigitte
Published: December 2004

Thirteen glacial terraces are known from the western part of the northern Alpine foothills between the Lech and Iller Rivers. In the Lower Rhine region of West Germany, a similar number of terraces are capped by interglacial floodloams and soils. Whereas the environment during individual interglaciations did not differ substantially, the glaciations were progressively more severe. The Main Terrace system of the Rhine may be an exception. The duration of the Quaternary, starting at the base of Praetiglian, is estimated at approximately 2 million yr by paleomagnetic dating. The major cold-warm climatic cycles of the earliest Pleistocene lasted approximately 100,000 yr, the same as those of the Brunhes Chron. The intervening Main Terrace system has not yet been climatically subdivided. Correlation with the Netherlands is possible because of an abundance of paleobotanic and paleomagnetic evidence. In the Alpine foothills, stratigraphically useful indicators of warm climates are missing, but analogies in terrace development permit comparison with the Lower Rhine and Danube. The terrace sequence in the Alpine foothills is incomplete, as are those along most of the other rivers in Europe. Some of the older terraces may have been eroded.
Sea-Level Estimates during the Last Deglaciation Based on δ18O and Accelerator Mass Spectrometry 14C Ages Measured in Globigerina bulloides
Authors: Bard Edouard , Fairbanks Richard , Arnold Maurice , Maurice Pierre , Duprat Josette , Moyes Jean , Duplessy Jean-Claude
Published: December 2004

Coupled measurements of δ18O and accelerator mass spectrometry (AMS) 14C in a particular species of planktonic foraminifera may be used to calculate sea-level estimates for the last deglaciation. Of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth, which can be provided by δ18O measurements of modern shells (core tops, plankton tows). Isotopic (δ18O, AMS-14C dating) and faunal records (transfer function sea surface temperature) were obtained from two cores in the North Atlantic at about 37°N. The locations were chosen to obtain high sedimentation rate records removed from the major ice-melt discharge areas of the last deglaciation. Based upon Globigerina bulloides data, four δ18O-based sea-level estimates were calculated: −67 ± 7 m at 12,200 yr B.P. and −24 ± 8 m at about 8200 yr B.P. for core SU 81-18; −83 ± 10 m at 12,200 yr B.P. and −13 ± 11 m at about 8500 yr B.P. for core SU 81-14. Using a second working hypothesis concerning the seasonability of G. bulloides growth, it is suggested that the sea-level rose by about 40 m during the millennium which followed 14,500 yr B.P.
Paleoecology of Late-Glacial Peats from the Bering Land Bridge, Chukchi Sea Shelf Region, Northwestern Alaska
Authors: Elias Scott A. , Short Susan K. , Phillips R. Lawrence
Published: December 2004

Insect fossils and pollen from late Pleistocene nonmarine peat layers were recovered from cores from the shelf region of the Chukchi Sea at depths of about 50 m below sea level. The peats date to 11,300−11,000 yr B.P. and provide a limiting age for the regional Pleistocene-Holocene marine transgression. The insect fossils are indicative of arctic coastal habitats like those of the Mackenzie Delta region (mean July temperatures = 10.6–14°C) suggesting that 11,000 yr ago the exposed Chukchi Sea shelf had a climate substantially warmer than modern coastal regions of the Alaskan north slope. The pollen spectra are consistent with the age assignment to the Birch Interval (14,000–9000 yr B.P.). The data suggest a meadow-like graminoid tundra with birch shrubs and some willow shrubs growing in sheltered areas.
Southern Ocean sea ice and its wider linkages: insights revealed from models and observations
Authors: PARKINSON CLAIRE L.
Published: November 2004

Early conceptual models and global climate model (GCM) simulations both indicated the likelihood of an enhanced sensitivity to climate change in the polar regions, derived from the positive feedbacks brought about by snow and ice. As GCMs developed, however, the expected enhanced sensitivity has been more robust in the North Polar Region than the South Polar Region. Some recent increased-CO2 simulations, for instance, show little change in Southern Ocean sea ice extent and thickness and much less warming in the Southern Ocean region than in the sea ice regions of the Northern Hemisphere. Observations show a highly variable Southern Ocean ice cover that decreased significantly in the 1970s but, overall, has increased since the late 1970s. The increases are non-uniform, and in fact decreases occurred in the last three years of the 1979–2002 satellite record highlighted here. Regionally, the positive trends since the late 1970s are strongest in the Ross Sea, while the trends are negative in the Bellingshausen and Amundsen seas, a pattern that appears in greater spatial detail in maps of trends in the length of the sea ice season. These patterns correspond well with patterns of temperature trends, but there is a substantial way to go before they are understood (and can be modelled) in the full context of global change.
ENSO-related impacts on Antarctic sea ice: a synthesis of phenomenon and mechanisms
Authors: YUAN XIAOJUN
Published: November 2004

Many remote and local climate variabilities influence Antarctic sea ice at different time scales. The strongest sea ice teleconnection at the interannual time scale was found between El Niño–Southern Oscillation (ENSO) events and a high latitude climate mode named the Antarctic Dipole. The Antarctic Dipole is characterized by an out-of-phase relationship between sea ice and surface temperature anomalies in the South Pacific and South Atlantic, manifesting itself and persisting 3–4 seasons after being triggered by the ENSO forcing. This study examines the life cycles of ENSO warm and cold events in the tropics and associated evolution of the ADP in high latitudes of the Southern Hemisphere. In evaluating the mechanisms that form the ADP, the study suggests a synthesized scheme that links these high latitude processes with ENSO teleconnection in both the Pacific and Atlantic basins. The synthesized scheme suggests that the two main mechanisms responsible for the formation/maintenance of the Antarctic Dipole are the heat flux due to the mean meridional circulation of the regional Ferrel Cell and regional anomalous circulation generated by stationary eddies. The changes in the Hadley Cell, the jet stream in the subtropics, and the Rossby Wave train associated with ENSO link the tropical forcing to these high latitude processes. Moreover, these two mechanisms operate in phase and are comparable in magnitude. The positive feedback between the jet stream and stationary eddies in the atmosphere, the positive feedback within the air-sea-ice system, and the seasonality all reinforce the anomalies, resulting in persistent Antarctic Dipole anomalies.
Large scale importance of sea ice biology in the Southern Ocean
Authors: ARRIGO KEVIN R. , THOMAS DAVID N.
Published: November 2004

Despite being one of the largest biomes on earth, sea ice ecosystems have only received intensive study over the past 30 years. Sea ice is a unique habitat for assemblages of bacteria, algae, protists, and invertebrates that grow within a matrix dominated by strong gradients in temperature, salinity, nutrients, and UV and visible radiation. A suite of physiological adaptations allow these organisms to thrive in ice, where their enormous biomass makes them a fundamental component of polar ecosystems. Sea ice algae are an important energy and nutritional source for invertebrates such as juvenile krill, accounting for up to 25% of total annual primary production in ice-covered waters. The ability of ice algae to produce large amounts of UV absorbing compounds such as mycosporine-like amino acids makes them even more important to organisms like krill that can incorporate these sunscreens into their own tissues. Furthermore, the nutrient and light conditions in which sea ice algae thrive induce them to synthesize enhanced concentrations of polyunsaturated fatty acids, a vital constituent of the diet of grazing organisms, especially during winter. Finally, sea ice bacteria and algae have become the focus of biotechnology, and are being considered as proxies of possible life forms on ice-covered extraterrestrial systems. An analysis of how the balance between sea ice and pelagic production might change under a warming scenario indicates that when current levels of primary production and changes in the areas of sea ice habitats are taken into account, the expected 25% loss of sea ice over the next century would increase primary production in the Southern Ocean by approximately 10%, resulting in a slight negative feedback on climate warming.
Particle export and the biological pump in the Southern Ocean
Authors: HONJO SUSUMU
Published: November 2004

The organic carbon particle export to the interior layers in the Southern Ocean in the New Zealand–Tasmania Sector was approximately 170 mmolC m−2 yr−1. The export of particulate inorganic carbon in CaCO3 was 110 mmolC m−2 yr−1 and was contributed mostly by pteropods shells in the Antarctic Zones. The Si flux from biogenic opal at the sub-Antarctic Zone was 67 mmolSi m−2 yr−1 and rapidly increased to the south up to nearly 1 molSi m−2 yr−1 in the Antarctic Zone. The Antarctic Polar Front clearly demarcated the area where the biological pump was driven by CaCO3 to the north and biogenic SiO2 particle export to the south. Summer stratification caused by the sub-zero winter water layer in the Seasonal Ice Zone (SIZ) curtails the zooplankton community and hinders the replenishment of Fe. This hypothesis explains the large organic carbon export with large f- and export ratios at the SIZ and extremely large opal production at the Antarctic Circumpolar Zone. Estimated regeneration rate of CO2 from the export production and settling particulate fluxes of organic carbon in the water column between 100 m to 1 km was about 13 mmolC m−2 d−1 in the Antarctic Zone and Polar Frontal Zone.
Midnight radial profiles of the quiet and growth‐phase plasma sheet: The Geotail observations
Authors: Wang Chih‐Ping , Lyons Larry R. , Nagai T. , Samson J. C.
Published: December 2004

To evaluate the plasma sheet transition from weak to strong convection, we investigate ion moments and magnetic field observed by Geotail. The Geotail data from 1995 to 1997 within the area −9 RE ≥ XGSM ≥ −30 RE and ∣YGSM∣ ≤ 5 RE were sorted for periods of quiet times and the substorm growth phase, which gives a better indication of convection strength than do global indexes. We find that the overall growth‐phase ion pressure is a factor of ∼1.55 higher than the quiet‐time ion pressure. Density is higher and temperature is lower during quiet times. Ions drift mainly earthward and duskward, and the drift speed is about twice stronger during the growth phase. The duskward drift is dominated by ions' diamagnetic drift. The ∣Bx∣ in the lobes increases strongly, while Bz near the current sheet at small radial distance decreases as convection increases, indicating that field lines become more stretched during the growth phase because of the earthward penetration of the plasma sheet. The increase in the lobe magnetic field is sufficient to maintain force balance in the z direction with the enhanced ion pressure in the plasma sheet. Intervals of negative Bz are observed during both quiet and growth‐phase conditions. The observed negative Bz intervals near the current sheet are short and are likely caused by perturbations, while those in the lobes are substantially longer and are likely associated with field line flaring.
Always look on the bright site of Rho: structural implications for a conserved intermolecular interface
Authors: Dvorsky Radovan , Ahmadian Mohammad Reza
Published: December 2004

The signalling functions of Rho‐family GTPases are based on the formation of distinctive protein–protein complexes. Invaluable insights into the structure–function relationships of the Rho GTPases have been obtained through the resolution of several of their structures in complex with regulators and downstream effectors. In this review, we use these complexes to compare the binding and specificity‐determining sites of the Rho GTPases. Although the properties that characterize these sites are diverse, some fundamental conserved principles that govern their intermolecular interactions have emerged. Notably, all of the interacting partners of the Rho GTPases, irrespective of their function, bind to a common set of conserved amino acids that are clustered on the surface of the switch regions. This conserved region and its specific structural characteristics exemplify the convergence of the Rho GTPases on a consensus binding site.
The Emergence of Smart Business Networks
Authors: Vervest Peter , Preiss Kenneth , van Heck Eric , Pau Louis-François
Published: November 2004

This article introduces the novel concept of smart business networks. The authors see the future as a developing web of people and organizations, bound together in a dynamic and unpredictable way, creating smart outcomes from quickly (re-) configuring links between actors. The question is: What should be done to make the outcomes of such a network ‘smart’, that is, just a little better than that of your competitor? More agile, with less pain, with more return to all the members of the network, now and over time? The technical answer is to create a ‘business operating system’ that should run business processes on different organizational platforms. Business processes would become portable: The end-to-end management of processes running across many different organizations in many different forms would become possible. This article presents an energizing discussion of smart business networks and the research challenges ahead.
Isotope branching and tunneling in O(3P)+HD→OH+D; OD+H reactions
Authors: Sultanov Renat A. , Balakrishnan N.
Published: November 2004

The O(3P)+HD and O(3P)+D2 reactions are studied using quantum scattering calculations and chemically accurate potential energy surfaces developed for the O(3P)+H2 system by Rogers et al. [J. Phys. Chem. A 104, 2308 (2000)]. Cross sections and rate coefficients for OH and OD products are calculated using accurate quantum methods as well as the J-shifting approximation. The J-shifting approach is found to work remarkably well for both O+HD and O+D2 collisions. The reactions are dominated by tunneling at low temperatures and for the O+HD reaction the hydrogen atom transfer leading to the OH product dominates at low temperatures. Our result for the OH/OD branching ratio is in close agreement with previous calculations over a wide range of temperatures. The computed OH/OD branching ratios are also in close agreement with experimental results of Robie et al. [Chem. Phys. Lett. 134, 579 (1987)] at temperatures above 400 K but the theoretical results do not reproduce the rapid rise in the experimental values of the branching ratio for temperatures lower than 350 K. We believe that new measurements could resolve the long-standing discrepancy between experiment and theory for this benchmark reaction.
Correlation energy extrapolation by intrinsic scaling. I. Method and application to the neon atom
Authors: Bytautas Laimutis , Ruedenberg Klaus
Published: November 2004

Remarkably accurate scaling relations are shown to exist between the correlation energy contributions from various excitation levels of the configuration interaction approach, considered as functions of the size of the correlating orbital space. These relationships are used to develop a method for extrapolating a sequence of smaller configuration interaction calculations to the full configuration-interaction energy. Calculations of the neon atom ground state with the Dunning’s quadruple ζ basis set demonstrate the ability of the method to obtain benchmark quality results.
HEAT: High accuracy extrapolated ab initio thermochemistry
Authors: Tajti Attila , Szalay Péter G. , Császár Attila G. , Kállay Mihály , Gauss Jürgen , Valeev Edward F. , Flowers Bradley A. , Vázquez Juana , Stanton John F.
Published: November 2004

A theoretical model chemistry designed to achieve high accuracy for enthalpies of formation of atoms and small molecules is described. This approach is entirely independent of experimental data and contains no empirical scaling factors, and includes a treatment of electron correlation up to the full coupled-cluster singles, doubles, triples and quadruples approach. Energies are further augmented by anharmonic zero-point vibrational energies, a scalar relativistic correction, first-order spin–orbit coupling, and the diagonal Born–Oppenheimer correction. The accuracy of the approach is assessed by several means. Enthalpies of formation (at 0 K) calculated for a test suite of 31 atoms and molecules via direct calculation of the corresponding elemental formation reactions are within 1 kJ mol−1 to experiment in all cases. Given the quite different bonding environments in the product and reactant sides of these reactions, the results strongly indicate that even greater accuracy may be expected in reactions that preserve (either exactly or approximately) the number and types of chemical bonds.
The triplet state of cytosine and its derivatives: Electron impact and quantum chemical study
Authors: Abouaf Robert , Pommier Jacqueline , Dunet Henri , Quan Phung , Nam Pham-Cam , Nguyen Minh Tho
Published: November 2004

The excitation of the lowest electronic states and vibrational excitation of cytosine (C) have been studied using electron energy loss spectroscopy (EELS, 0–100 eV) with angular analysis. The singlet states have been found to be in good agreement with UV-VIS absorption results on sublimed films, slightly blueshifted by about 0.1 eV. The EEL spectra recorded at residual energy below 2 eV show clear shoulders at energy losses of 3.50 and 4.25 eV (±0.1 eV). They are assigned to the lowest triplet electronic states of cytosine. Energies and molecular structures of the lowest-lying triplet state of C and its methylated and halogenated 5-X-C, 6-X-C, and 5-X, 6-X-C substituted derivatives (X=CH3, F, Cl, and Br) have been studied using quantum chemical calculations with both molecular orbital and density functional methods, in conjunction with the 6-311++G(d,p), 6-311++G(3df,2p), and aug-cc-pVTZ basis sets. The triplet-singlet energy gap obtained using coupled-cluster theory [CCSD(T)] and density functional theory (DFT) methods agrees well with those derived from EELS study. The first C’s vertical triplet state is located at 3.6 eV, in good agreement with experiment. The weak band observed at 4.25 eV is tentatively assigned to the second C’s vertical triplet excitation. For the substituted cytosines considered, the vertical triplet state is consistently centered at 3.0–3.2 eV above the corresponding singlet ground state but about 1.0 eV below the first excited singlet state. Geometrical relaxation involving out-of-plane distortions of hydrogen atoms leads to a stabilization of 0.6–1.0 eV in favor of the equilibrium triplet. The lowest-lying adiabatic triplet states are located at 2.3–3.0 eV. Halogen substitution at both C(5) and C(6) positions tends to reduce the triplet-singlet separations whereas methylation tends to enlarge it. The vibrational modes of triplet cytosine and the ionization energies of substituted derivatives were also evaluated.
HF(H
2
O
)
n
clusters with an excess electron: Ab initio study
Authors: Odde Srinivas , Mhin Byung Jin , Lee Han Myoung , Kim Kwang S.
Published: November 2004

The structures of electron-bound and neutral clusters of HF(H2O)n (n=1–3) were optimized at the level of second-order Møller–Plesset perturbation theory (MP2). Then, the energies were studied using the coupled cluster singles, doubles, and perturbative triples correction [CCSD(T)] method. The vertical detachment energies of the electron-bound clusters for n=1–3 are 60, 180, and ∼300 meV, respectively. In the case of the n=3, two structures are competing energetically. The electron-bound clusters for n=1 and 2 are 1.5 and 1.8 kcal/mol more stable than the neutral, while that for n=3 is 0.6–0.9 kcal/mol less stable. The excess electron is stabilized in the surface-bound state of the dipole oriented structures of the hydrated acid clusters. Vibrational spectra of the electron-bound clusters are discussed.
Nonperturbative vibrational energy relaxation effects on vibrational line shapes
Authors: Yang Shilong , Shao Jiushu , Cao Jianshu
Published: November 2004

A general formulation of nonperturbative quantum dynamics of solutes in a condensed phase is proposed to calculate linear and nonlinear vibrational line shapes. In the weak solute-solvent interaction limit, the temporal absorption profile can be approximately factorized into the population relaxation profile from the off-diagonal coupling and the pure-dephasing profile from the diagonal coupling. The strength of dissipation and the anharmonicity-induced dephasing rate are derived in Appendix A. The vibrational energy relaxation (VER) rate is negligible for slow solvent fluctuations, yet it does not justify the Markovian treatment of off-diagonal contributions to vibrational line shapes. Non-Markovian VER effects are manifested as asymmetric envelops in the temporal absorption profile, or equivalently as side bands in the frequency domain absorption spectrum. The side bands are solvent-induced multiple-photon effects which are absent in the Markovian VER treatment. Exact path integral calculations yield non-Lorentzian central peaks in absorption spectrum resulting from couplings between population relaxations of different vibrational states. These predictions cannot be reproduced by the perturbative or the Markovian approximations. For anharmonic potentials, the absorption spectrum shows asymmetric central peaks and the asymmetry increases with anharmonicity. At large anharmonicities, all the approximation schemes break down and a full nonperturbative path integral calculation that explicitly accounts for the exact VER effects is needed. A numerical analysis of the O–H stretch of HOD in D2O solvent reveals that the non-Markovian VER effects generate a small recurrence of the echo peak shift around 200 fs, which cannot be reproduced with a Markovian VER rate. In general, the nonperturbative and non-Markovian VER contributions have a stronger effect on nonlinear vibrational line shapes than on linear absorption.
Photodissociation of laboratory oriented molecules: Revealing molecular frame properties of nonaxial recoil
Authors: van den Brom Alrik J. , Rakitzis T. Peter , Janssen Maurice H. M.
Published: November 2004

We report the photodissociation of laboratory oriented OCS molecules. A molecular beam of OCS molecules is hexapole state-selected and spatially oriented in the electric field of a velocity map imaging lens. The oriented OCS molecules are dissociated at 230 nm with the linear polarization set at 45° to the orientation direction of the OCS molecules. The CO(ν=0,J) photofragments are quantum state-selectively ionized by the same 230 nm pulse and the angular distribution is measured using the velocity map imaging technique. The observed CO(ν=0,J) images are strongly asymmetric and the degree of asymmetry varies with the CO rotational state J. From the observed asymmetry in the laboratory frame we can directly extract the molecular frame angles between the final photofragment recoil velocity and the permanent dipole moment and the transition dipole moment. The data for CO fragments with high rotational excitation reveal that the dissociation dynamics is highly nonaxial, even though conventional wisdom suggests that the nearly limiting β parameter results from fast axial recoil dynamics. From our data we can extract the relative contribution of parallel and perpendicular transitions at 230 nm excitation.
Three-photon absorption in anthracene-porphyrin-anthracene triads: A quantum-chemical study
Authors: Zhu Lingyun , Yang Xia , Yi Yuanping , Xuan Pengfei , Shuai Zhigang , Chen Dezhan , Zojer Egbert , Brédas Jean-Luc , Beljonne David
Published: November 2004

We have applied correlated quantum-chemical methods to investigate the three-photon absorption (3PA) response of a porphyrin triad derivative, where the central macrocycle is linked in mesopositions to two anthracene units via acetylenic bridges. The 3PA frequency-dependent spectrum of this derivative is dominated by a single resonance feature in the transparent region, associated with charge-transfer states between porphyrin and anthracene. The calculations indicate a two order of magnitude enhancement in the 3PA cross section in the triad molecule with respect to the individual entities, which is attributed to close one-, two-, and three-photon resonances together with strong electronic couplings among the units.
Polymorphic transformation of dense ZnO nanoparticles: Implications for chair/boat-type Peierls distortions of AB semiconductor
Authors: Chen Shuei-Yuan , Shen Pouyan , Jiang Jianzhong
Published: November 2004

Peierls distortion path was proved experimentally for dense ZnO nanoparticles prepared by static compression. Electron irradiation caused rock salt (R) to wurtzite (W) transition, following preferential (11̄1)R//(01̄11)W; [011]R//[1̄21̄3]W and then transformation strain induced (111̄)R//(1̄011)W; [011]R//[011̄1]W. The two relationships can be rationalized by specified extent of chair- and boat-type Peierls distortions accompanied with band gap opening and intermediate {111}R slip for energetically favorable {111}R/(01̄11)W match.
Inelastic electron tunneling spectroscopy in molecular junctions: Peaks and dips
Authors: Galperin Michael , Ratner Mark A. , Nitzan Abraham
Published: November 2004

We study inelastic electron tunneling through a molecular junction using the nonequilibrium Green’s function formalism. The effect of the mutual influence between the phonon and the electron subsystems on the electron tunneling process is considered within a general self-consistent scheme. Results of this calculation are compared to those obtained from the simpler Born approximation and the simplest perturbation theory approaches, and some shortcomings of the latter are pointed out. The self-consistent calculation allows also for evaluating other related quantities such as the power loss during electron conduction. Regarding the inelastic spectrum, two types of inelastic contributions are discussed. Features associated with real and virtual energy transfer to phonons are usually observed in the second derivative of the current I with respect to the voltage Φ when plotted against Φ. Signatures of resonant tunneling driven by an intermediate molecular ion appear as peaks in the first derivative dI/dΦ and may show phonon sidebands. The dependence of the observed vibrationally induced lineshapes on the junction characteristics, and the linewidth associated with these features are also discussed.
Entangled polymers in condensed phases
Authors: Orlandini E. , Whittington S. G.
Published: November 2004

We present Monte Carlo results on a model of polymers in a condensed phase, over a range of monomer densities. We imagine cutting a cube out of the system. This cube will typically have several polymer molecules running through its interior, and starting and ending on the boundary. These subchains will be mutually entangled and we present a way to assess the extent of entanglement complexity as a function of the monomer density and the number of subchains in the cube. The model is a set of k self-avoiding and mutually avoiding walks, properly embedded in the cube.
A ground state potential energy surface for H2 using Monte Carlo methods
Authors: Alexander S. A. , Coldwell R. L.
Published: November 2004

Using variational Monte Carlo and a simple explicitly correlated wave function we have computed the Born–Oppenheimer energy of the H2 ground state (X 1Σg+) at 24 internuclear distances. We have also calculated the diagonal correction to the Born–Oppenheimer approximation and the lowest-order relativistic corrections at each distance using variational Monte Carlo techniques. The nonadiabatic values are evaluated from numerical derivatives of the wave function with respect to the nuclear coordinates. With this potential energy surface we have computed several of the lowest vibrational-rotational energies for this system. Our results are in good agreement with the best values found in the literature.
Curvy-steps approach to constraint-free extended-Lagrangian ab initio molecular dynamics, using atom-centered basis functions: Convergence toward Born–Oppenheimer trajectories
Authors: Herbert John M. , Head-Gordon Martin
Published: November 2004

A dynamical extension of the “curvy-steps” approach to linear-scaling self-consistent field calculations is presented, which yields an extended-Lagrangian formulation of ab initio molecular dynamics. An exponential parametrization of the one-electron density matrix, expressed in terms of atom-centered Gaussian basis functions, facilitates propagation along the manifold of density matrices in a geometrically correct fashion that automatically enforces idempotency constraints. The extended Lagrangian itself is constraint free, thus neither density matrix purification nor expensive, iterative solution for Lagrange multipliers is required. Propagation is highly efficient, and time steps compare favorably to those used in Car–Parrinello molecular dynamics simulations. The behavior of the method, especially with regard to the maintenance of adiabatic decoupling of nuclei and electrons, is examined for a sequence of diatomic molecules, and comparison is made to trajectories propagated on the converged Born–Oppenheimer surface. Certain claims to the contrary notwithstanding, our results demonstrate that vibrational frequencies may depend on the value of the fictitious mass parameter, even in an atom-centered basis. Light-atom stretching frequencies can be significantly redshifted, even when the nuclear and electronic energy scales are well separated. With a sufficiently small fictitious mass and a short time step, accurate frequencies can be obtained; we characterize appropriate values of these parameters for a wide range of vibrational frequencies.
Comment on: “Disentangling density and temperature effects in the viscous slowing down of glass forming liquids” [J. Chem. Phys. 120, 6135 (2004)]
Authors: Roland C. M. , Casalini R.
Published: November 2004

Recently, Tarjus et al. [G. Tarjus, D. Kivelson, S. Mossa, and C. Alba-Simionesco, J. Chem. Phys. 120, 6135 (2004)] concluded from a review of data for a variety of glass formers that the supercooled dynamics are almost invariably dominated by temperature T, rather than by density ρ. By including additional published data into such a compilation, we show that for van der Waals molecular liquids, the dynamics near Tg are in fact governed as much by density as by temperature. Moreover, relaxation times measured at various temperatures and pressures can be superimposed by plotting as a function ργ/T. This scaling form can arise from an assumed inverse power law for the intermolecular repulsive potential, with γ a material constant.