bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of effects of U18666A and enantiomeric U18666A on sterol synthesis and induction of apoptosis
Authors: Cenedella Richard J. , Sexton Patricia S. , Krishnan Kathiresan , Covey Douglas F.
Published: November 2006

Treatment of animals or cells with the amphipathic tertiary amine U18666A {3β‐[2‐(diethylamino) ethoxy]androst‐5‐en‐17‐one} provides models for several human diseases (e.g., cataracts, Niemann‐Pick disease, and epilepsy). Although U18666A can inhibit several enzymes in the cholesterol synthesis pathway, we hypothesized that induction of these varied conditions was due to physical effects of the amine rather than to inhibition of specific proteins. To test this possibility we compared the capacity of U18666A and its enantiomer, ent‐U18666A, to inhibit net sterol synthesis and induce apoptosis in cultured bovine lens epithelial cells. Nonenantiospecific actions dependent on the physical properties of these mirror image molecules would be identical, but effects dependent upon enantiospecific interactions would be different for the enantiomers. At the same concentrations, both forms of the compound equally inhibited sterol synthesis and induced apoptosis. These observations supported a generalized mechanism of enzyme inhibition such as perturbation of the microenvironment of endoplasmic enzymes and alteration of membrane order, perhaps of the mitochondrial membrane, to explain induction of apoptosis.
Astonishing diversity of natural surfactants: 6. Biologically active marine and terrestrial alkaloid glycosides
Authors: Dembitsky Valery M.
Published: November 2006

This review article presents 209 alkaloid glycosides isolated and identified from plants, microorganisms, and marine invertebrates that demonstrate different biological activities. They are of great interest, especially for the medicinal and/or pharmaceutical industries. These biologically active glycosides have good potential for future chemical preparation of compounds useful as antioxidants, anticancer, antimicrobial, and antibacterial agents. These glycosidic compounds have been subdivided into several groups, including: acridone; aporphine; benzoxazinoid; ergot; indole; enediyne alkaloidal antibiotics; glycosidic lupine alkaloids; piperidine, pyridine, pyrrolidine, and pyrrolizidine alkaloid glycosides; glycosidic quinoline and isoquinoline alkaloids; steroidal glycoalkaloids; and miscellaneous alkaloid glycosides.
Overview of hemostatic factors involved in atherosclerotic cardiovascular disease
Authors: Kannel William B.
Published: November 2006

Hemostatic factors associated with the development of cardiovascular disease (CVD) include fibrinogen, von Willebrand factor, tissue plasminogen activator (tPA) antigen, plasminogen activator inhibitor‐1 (PAI‐1), and factor VII. Each SD increment of these increases the association by 24–30%. Most hemostatic factors are intercorrelated with inflammatory markers [e.g., C‐reactive protein (CRP)] and LDL cholesterol. Fibrinogen seems the most fundamental hemostatic risk factor for CVD. The Framingham Study reaffirms the significant linear risk factor trends across fibrinogen tertiles (P<0.001) for age, body mass index, smoking, diabetes mellitus, total cholesterol, HDL cholesterol, and TG in both sexes. Fibrinogen may also directly increase CVD risk because of its role in platelet aggregation, plasma viscosity, and fibrin formation. Fibrinogen is also an acute‐phase reactant that is elevated in inflammatory states. Fibrinogen mediates the thrombogenic effect of other risk factors. Fibrinogen levels increase with the number of cigarettes smoked and quickly fall after smoking cessation. This rapid fibrinogen decline may be a mechanism for CVD risk reduction after smoking cessation. Weight loss is accompanied by reduced fibrinogen. The correlation between fibrinogen and LDL cholesterol suggests that lipidimposed CVD risk is mediated partly through fibrinogen. Hyperreactive platelets of diabetics may result in part from their increased fibrinogen. Elevated fibrinogen and CRP of unstable angina suggest an acute‐phase reaction. Prevalence, case‐control, angiographic, and echocardiogram investigations incriminate hemostatic and inflammatory markers as strong independent risk factors for initial and recurrent CVD. Framingham Study data indicate that each SD increase in fibrinogen imposes a 20% independent increment in risk. It may be concluded that fibrinogen and CRP determination may be useful screening tools to identify individuals at added risk for thrombotic complications of CVD.
Lipolysis of different oils using crude enzyme isolate from the intestinal tract of rainbow trout,Oncorhynchus mykiss
Authors: Gøttsche Jesper R. , Nielsen Nina S. , Nielsen Henrik H. , Mu Huiling
Published: November 2006

Crude enzyme isolate was prepared from the intestine of rainbow trout. Positional specificity of the crude enzyme isolate was determined from both 1(3)‐ and 2‐MAG products afterin vitrolipolysis of radioactive‐labeled triolein. The ratio of 2‐MAG/1(3)‐MAG was 2∶1, suggesting that the overall lipase specificity of the enzyme isolate from rainbow trout tended to be 1,3‐specific; however, activity against thesn‐2 position also was shown.In vitrolipolysis of four different unlabeled oils was performed with the crude enzyme isolate. The oils were: structured lipid [SL; containing the medium‐chain FA (MCFA) 8∶0 in thesn‐1,3 positions and long‐chain FA (LCFA) in thesn‐2 position], DAG oil (mainly 1,3‐DAG), fish oil (FO), and triolein (TO). MCFA were rapidly hydrolyzed from the SL oil. LCFA including n−3 PUFA were, however, preserved in thesn‐2 position and therefore found in higher amounts in 2‐MAG of SL compared with 2‐MAG of FO, DAG, and TO. Lipolysis of the DAG oil produced higher amounts of MAG than the TAG oils, and 1(3)‐MAG mainly was observed after lipolysis of the DAG oil. The positional specificity determined and the results from the hydrolysis of the different oils suggest that n−3 very long‐chain PUFA from structured oils may be used better by aquacultured fish than that from fish oils.
Effects of duodenal seal oil administration in patients with inflammatory bowel disease
Authors: Arslan Gülen , Brunborg Linn Anne , Frøyland Livar , Brun Johan G. , Valen Merete , Berstad Arnold
Published: November 2006

Long‐chain n‐3 PUFA in fish oil have modulating effects on inflammatory responses. The aim of this open pilot study was to investigate whether duodenal seal oil administration would benefit patients with inflammatory bowel disease (IBD). Seal oil (10 mL) was administered three times a day directly into the distal part of the duodenum via a nasoduodenal feeding tube for 10 d in 10 patients, 5 of whom had Crohn's disease and 5 ulcerative colitis. Nine of the 10 patients suffered from IBD‐associated joint pain. Various parameters of disease activity and FA incorporation in tissues were analyzed before and after treatment. Following seal oil therapy, joint pain index, disease activity, and serum cholesterol level were significantly decreased, whereas the n‐3 to n‐6 ratio both in intestinal biopsies and blood was significantly increased. Measures of calprotectin concentration in gut lavage fluid, intestinal permeability, and lipid peroxidation were not significantly changed. The results suggest positive effects of seal oil in patients with IBD, especially on IBD‐associated joint pain. Further controlled studies are warranted.
Long‐chain PUFA supplementation improves PUFA profile in infants with cholestasis
Authors: Socha Piotr , Koletzko Berthold , Jankowska Irena , Pawlowska Joanna , Demmelmair Hans , Stolarczyk Anna , Świątkowska Elzbieta , Socha Jerzy
Published: November 2006

Long‐chain PUFA (LCP) deficiency is a frequent complication in cholestatic infants. We investigated the effects of LCP‐supplemented formula on EFA status in infants with cholestasis. Twenty‐three infants with cholestasis (biliary atresia after surgery, 8; intrahepatic cholestasis, 15) aged 1.9 to 4.9 mon (median 3.1 mon) were randomized to receive commercial infant formulas either without LCP or with LCP from egg phospholipids for 1 mon. Liver tests, nutrient intakes, and plasma phospholipid FA (%w/w) were determined at baseline and after intervention. At baseline, patients had high serum direct bilirubin levels (5.9 ± 3.0 mg/dL; mean ± SD), they were malnourished (body fat mass: 40 ± 13% of normal) and presented with PUFA deficiency [plasma phospholipid PUFA: 28.43%w/w (26.56–30.53) in patients vs. 37.02%w/w (34.53–39.58) in controls; median (1st–3rd quartile)] with elevated Mead acid and palmitoleic acid. LCP‐supplemented (n=11 and‐nonsupplemented groups (n=12) did not differ in age, indicators of liver function, and EFA status at baseline. After the intervention, LCP‐supplemented infants had higher levels of arachidonic acid [7.2 (5.9–8.8) vs. 4.2 (3.0–5.3) %w/w; P<0.001] and DHA [2.8 (2.2–3.2) vs. 1.6 (1.0–2.1) %w/w; P<0.05], accompanied by increased [BARS concentration: 1.9 (1.4–2.2) vs. 1.3 (1.1–1.6) nmol/mL; P<0.05]. We concluded that LCP‐supplemented formulae improve LCP status of infants with severe cholestasis but may enhance lipid peroxidation.
Divergent incorporation of dietary trans fatty acids in different serum lipid fractions
Authors: Vidgren Helvi M. , Louheranta Anne M. , Ågren Jyrki J. , Schwab Ursula S. , Uusitupa Matti I. J.
Published: November 2006

Trans fatty acids may be involved in atherosclerotic vascular diseases. We investigated the incorporation of dietary trans fatty acids and oleic acid into the serum triglycerides (TG), cholesterol esters (CE), and phospholipids (PL). Fourteen healthy female volunteers, aged 23.2±3.1 yr (mean±SD), body mass index 20.8±2.1 kg/m2 participated in this study. All subjects consumed both a trans fatty acid‐enriched diet (TRANS diet) and an oleic acid‐enriched diet (OLEIC diet) for 4 wk according to a randomized crossover design. Both experimental diet periods were preceded by consumption of a baseline diet for 2 wk which supplied 37% of total energy (E%) as fat: 18 E% from saturated fatty acids (SFA), 12 E% from monounsaturated fatty acids, and 6 E% from polyunsaturated fatty acids. Five E% of the SFA in the baseline diet was replaced by trans fatty acids (18∶1 t and 18∶2 c,t+18∶2t,t, where c is cis and t is trans) in the TRANS diet and by oleic acid (18∶1n‐9) in the OLEIC diet. After the TRANS diet, the proportions of 18∶1t and 18∶2t increased (P <0.001) in all serum lipid fractions analyzed. The increase of 18∶1 t in TG and PL (1.80±0.28 vs. 5.26±1.40; 1.07±0.34 vs. 3.39±0.76 mol% of total fatty acids, respectively) was markedly higher than that in CE (0.44±0.07 vs. 0.92±0.26), whereas that of 18∶2t was nearly the same in all three fractions. The proportions of palmitic, stearic, arachidonic, and eicosapentaenoic acids in TG, CE, and PL and that of oleic acid in TG and CE were decreased when compared with the baseline value. In contrast, the proportion of palmitoleic acid in TG and PL and that of linoleic acid in PL increased on the TRANS diet. After consumption of the OLEIC diet, the proportion of oleic acid increased in all three lipid fractions analyzed, and the percentage increase was nearly the same in all fractions. In contrast, the proportions of 18∶1 t in TG and PL and 18∶2 t in TG and CE decreased when compared with the baseline value. In conclusion, a moderate increase in dietary trans fatty acids resulted in a marked incorporation into serum lipids and decreased the conversion of linoleic acid to its more unsaturated long‐chain metabolites. Analysis of 18∶1 t from serum TG and PL seems to reflect reliably the dietary intake of this fatty acid.
Identification of conjugated linoleic acid isomers in cheese by gas chromatography, silver ion high performance liquid chromatography and mass spectral reconstructed ion profiles. Comparison of chromatographic elution sequences
Authors: Sehat Najibullah , Kramer John K. G. , Mossoba Magdi M. , Yurawecz Martin P. , Roach John A. G. , Eulitz Klaus , Morehouse Kim M. , Ku Youh
Published: November 2006

Commercial cheese products were analyzed for their composition and content of conjugated linoleic acid (CLA) isomers. The total lipids were extracted from cheese using petroleum ether/diethyl ether and methylated using NaOCH3. The fatty acid methyl esters (FAME) were separated by gas chromatography (GC), using a 100‐m polar capillary column, into nine minor peaks besides that of the major rumenic acid, 9c, 11t‐octadecadienoic acid (18∶2), and were attributed to 19 CLA isomers. By using silver ion‐high performance liquid chromatography (Ag+‐HPLC), CLA isomers were resolved into seven trans, trans (5–9%), three cis/trans (10–13%), and five cis, cis (<1%) peaks, totaling 15, in addition to that of the 9c, 11t‐18∶2 (78–84%). The FAME of total cheese lipids were fractionated by semipreparative Ag+‐HPLC and converted to their 4,4‐dimethyloxazoline derivatives after hydrolysis to free fatty acids. The geometrical configuration of the CLA isomers was confirmed by GC‐direct deposition‐Fourier transform infrared, and their double bond positions were established by GC‐electron ionization mass spectrometry. Reconstructed mass spectral ion profiles of the m+2 allylic ion and the m+3 ion (where m is the position of the second double bond in the parent conjugated fatty acid) were used to identify the minor CLA isomers in cheese. Cheese contained 7 t,9c‐18∶2 and the previously unreported 11t, 13c‐18∶2 and 12c, 14t‐18∶2, and their trans,trans and cis,cis geometric isomers. Minor amounts of 8,10‐, and 10, 12–18∶2 were also found. The predicted elution orders of the different CLA isomers on long polar capillary GC and Ag*‐HPLC columns are also presented.
Acid‐catalyzed isomerization of fucosterol and Δ5‐avenasterol
Authors: Kamal‐Eldin Afaf , Määttä Kaisu , Toivo Jari , Lampi Anna‐Maija , Piironen Vieno
Published: November 2006

This work shows that fucosterol, Δ5‐avenasterol, and similar ethylidene‐side chain sterols can undergo acid‐catalyzed isomerization to give a mixture of five isomers. Four isomers formed from fucosterol were analyzed, using gas chromatography‐mass spectrometry, and were characterized as Δ5‐avenasterol two Δ5,23‐stigmastadienols, and Δ5,24(250)‐stigmastadienol. When the unsaponifiables fraction from oat oil was subjected to acid hydrolysis, the two Δ5,23‐stigmastadienol isomers and Δ5,24(25)‐stigmastadienol were detected while fucosterol coeluted with sitosterol. Interisomerization of ethylidene‐side chain sterols represents a limitation to the use of the acid hydrolysis method in the determination of sterols in food and other plant materials rich in these sterols, e.g., oat lipids.
Low doses of eicosapentaenoic acid, docosahexaenoic acid, and hypolipidemic eicosapentaenoic acid derivatives have no effect on lipid peroxidation in plasma
Authors: Vaagenes Hege , Muna Ziad A. , Madsen Lise , Berge Rolf K.
Published: November 2006

It was of interest to investigate the influence of both high doses of eicosapentaenoic acid (EPA) and low doses of 2‐or 3‐methylated EPA on the antioxidant status, as they all cause hypolipidemia, but the dose required is quite different. We fed low doses (250 mg/d/kg body wt) of different EPA derivatives or high doses (1500 mg/d/kg body wt) of EPA and DHA to rats for 5 and 7 d, respectively. The most potent hypolipidemic EPA derivative, 2,2‐dimethyl‐EPA, did not change the malondialdehyde content in liver or plasma. Plasma vitamin E decreased only after supplementation of those EPA derivatives that caused the greatest increase in the fatty acyl‐CoA oxidase activity. Fatty acyl‐CoA oxidase activity increased after administration of both EPA and DHA at high doses. High doses of EPA and DHA decreased plasma vitamin E content, whereas only DHA elevated lipid peroxidation. In liver, however, both EPA and DHA increased lipid peroxidation, but the hepatic level of vitamin E was unchanged. The glutathione‐requiring enzymes and the glutathione level were unaffected, and no significant changes in the activities of xanthine oxidase and superoxide dismutase were observed in either low‐or high‐dose experiments. In conclusion, increased peroxisomal β‐oxidation in combination with high amounts of polyunsaturated fatty acids caused elevated lipid peroxidation. At low doses of polyunsaturated fatty acids, lipid peroxidation was unchanged, in spite of increased peroxisomal β‐oxidation, indicating that polyunsaturation is the most important factor for lipid peroxidation.
Proliferation of activated CD1d‐restricted NKT cells is down‐modulated by lymphocyte activation gene‐3 signaling via cell cycle arrest in S phase
Authors: Byun Hyun‐Jung , Jung Woon‐Won , Lee Dong‐Sup , Kim Sanghee , Kim Sang Joon , Park Chung‐Gyu , Chung Hee Yong , Chun Taehoon
Published: November 2006

Upon antigenic stimulation, CD1d‐restricted NKT cells quickly secrete large amounts of cytokines. This prompt response demonstrates that CD1d‐restricted NKT cells may potentially prove to be useful therapeutic agents for the treatment of many diseases. Despite the clinical importance of CD1d‐restricted NKT cells, the regulating mechanisms of this unique T cell population remain to be defined. We found murine LAG‐3 is inducible on CD1d‐restricted NKT cells as the result of a variety of stimulants such as concanavalin A (con A) and anti‐CD3. Also, antigen‐specific CD1d stimulation can elicit LAG‐3 in CD1d‐restricted NKT cells. Moreover, ectopic LAG‐3 expression on CD1d‐restricted NKT cells results in cell cycle arrest in the S phase. These results show that LAG‐3 signaling on activated CD1d‐restricted NKT cells may down‐modulate NKT cell proliferation.
Localisation and modulation of prostanoid receptors EP1 and EP4 in the rat chronic constriction injury model of neuropathic pain
Authors: Woodhams Peter L. , MacDonald Rachel E. , Collins Sue D. , Chessell Iain P. , Day Nicola C.
Published: November 2006

Immunohistochemistry was used to examine the expression of prostaglandin E2 receptors EP1 and EP4 in sciatic nerves from the rat chronic constriction injury (CCI) model of neuropathic pain. At 21 days post‐surgery the CCI rats had developed mechanical hyperalgesia on the operated side, and quantitative image analysis showed a highly significant doubling of the area occupied by EP1‐ and EP4‐positive pixels in sections from CCI nerves when compared to sham‐operated controls. Co‐localisation studies with the marker ED1 revealed that 73% of the EP1‐positive cells and 54% of the EP4‐positive cells in the injured nerves represented infiltrating macrophages. Cells negative for ED1 and positive for either EP1 or EP4 were characterised as Schwann cells from their morphology and expression of myelin basic protein and S100 antigens. Similar EP1‐ and EP4‐positive Schwann cell profiles were observed in sections of uninjured control nerves. Low levels of EP receptor expression were found in neurofilament‐immunostained axons, but no consistent differences were observed in the levels of axonal EP staining between CCI and control tissue. These data provide further evidence of the importance of prostaglandins in the pathogenesis of neuropathic pain, and suggest that not only infiltrating macrophages but also Schwann cells may be involved in the modulation of these mediators in response to nerve injury.
Pan‐genome isolation of low abundance transcripts using SAGE tag
Authors: Kim Yeong Cheol , Jung Yong-Chul , Xuan Zhenyu , Dong Hui , Zhang Michael Q. , Wang San Ming
Published: November 2006

The SAGE (serial analysis of gene expression) method is sensitive at detecting the lower abundance transcripts. More than a third of human SAGE tags identified are novel representing the low abundance unknown transcripts. Using the GLGI method (generation of longer 3′ EST from SAGE tag for gene identification), we converted 1009 low‐copy, human X chromosome‐specific SAGE tags into 10210 3′ ESTs. We identified 3418 unique 3′ ESTs, 46% of which are novel and originated from the lower abundance transcripts. However, nearly all 3′ ESTs were mapped to various regions across the genome but not X chromosome. Detailed analysis indicates that those 3′ ESTs were isolated by SAGE tag mis‐priming to the non‐parent transcripts. Replacing SAGE tags with non‐transcribed genomic DNA tags resulted in poor amplification, indicating that the sequence similarity between different transcripts contributed to the amplification. Our study shows the prevalence of novel low abundance transcripts that can be isolated efficiently through SAGE tags mis‐priming.
Airborne gravity over Lake Vostok and adjacent highlands of East Antarctica
Authors: Holt John W. , Richter Thomas G. , Kempf Scott D. , Morse David L. , Blankenship Donald D.
Published: November 2006

Lake Vostok and a 1200 km transect were the targets of aerogeophysical surveys in East Antarctica during the austral summer of 2000/2001. The measurement of gravity anomalies for geologic studies was the primary goal. A total of 24,459 line‐km of data were acquired. Favorable weather, aircraft navigation, and instrument performance contributed to excellent data quality. Multiple carrier‐phase GPS solutions to determine aircraft‐induced accelerations were available for each flight. Raw gravity and GPS position solutions were initially filtered to compensate for hardware filtering within the gravity meter. Filtering of remaining high‐frequency noise was accomplished with a spatial, moving average smoother. Due to upward continuation effects imposed by the ice cover, the theoretically estimated minimum resolvable gravity feature size for the Lake Vostok survey is 8 km, consistent with an analysis of power spectra comparing the gravity signal to noise calculated from geographically repeated lines. Comparison of gravity results with subice topography indicates that the gravity data are sensitive to real features including the existence of major crustal structures. Repeated lines and crossovers were analyzed to estimate uncertainties for the Lake Vostok data set, with both of these repeatability measures indicating relative accuracy in the 2 mGal range for the unleveled data and 1 mGal after leveling.
Prediction of sediment thickness in the Norwegian–Greenland Sea from gravity inversion
Authors: Engen Øyvind , Frazer L. Neil , Wessel Pål , Faleide Jan Inge
Published: November 2006

We explore the feasibility of inverting freely available altimetry‐derived gravity grids for sediment thickness on oceanic crust. A four‐layer Earth model is adopted, assuming that the gravity signal from the base of the sedimentary layer can be fully isolated from the observed free‐air gravity. The following additional data are required: (1) shipboard bathymetry for reliable Bouguer correction, (2) oceanic crustal ages to correct for gravity anomalies related to the thermal history of lithospheric breakup and seafloor spreading, and (3) some wide‐angle seismic observations of sediment thickness. A fixed relationship between the base of the sedimentary layer and the Moho is also required because of limited gravity resolution at large depths. The final inversion setup searches for three control parameter values (density of uppermost sediments, density of oceanic crystalline crust, and thermal diffusivity of mantle rock) that minimize misfit between the Earth model and observations. Applied to the Norwegian–Greenland Sea, the inversion successfully predicts locations of >20–25 km wide depocenters and crystalline crustal highs, yet ∼1 km thickness errors are common even in well‐constrained areas. The largest errors are associated with underplated crust, active mid‐ocean ridges, and the continent‐ocean boundary, indicating locally incorrect assumptions of mantle thermal structure and crystalline crustal thickness. The thicknesses of >4 km thick submarine fans are underpredicted, probably because of too low sedimentary densities in the Earth model. If these limitations are acceptable or do not apply because of simple crustal structure, gravity inversion may be used for mapping regional sedimentary patterns, e.g., in the Arctic Ocean.
A theoretical model for the distribution of latitudinal extents of field‐aligned electron acceleration
Authors: Yamamoto T.
Published: November 2006

We reassess the mathematical expression for statistical distributions of latitudinal extents of electron acceleration events; the distributions have been obtained by Newell et al. (1996, hereinafter referred to as N96) using precipitation data from all Defense Meteorological Satellite Program satellites. Paper N96 proposed a basic hypothesis that within a (given) large‐scale region of upward field‐aligned currents (FACs), any 1‐s spectrum has a constant probability, P, of experiencing electron acceleration independently of neighboring spectra. Directly from this hypothesis, the probability of observing n consecutive accelerated spectra, denoted by Qn, is newly derived as the correction of “Pn−1(1 − P)” that was assumed in N96. Necessarily, Qn is a function of the probability P and the latitudinal width W of a large‐scale FAC region; hence it is written as Qn(W, P). The occurrence frequency distribution (histogram) of latitudinal extents of observed acceleration events can be identified with a statistical superposition of a number of Qn(W, P) in relatively wide ranges of W and P. For fitting to the histograms obtained in N96, 0.1° ≲ W and 0.7 ≲ P ≲ 0.98 are appropriate. This prediction is quite in contrast with N96's supposition that P is nearly constant and that normally the width of a large‐scale FAC region is sufficiently large to accommodate many accelerated spectra. (The appearance of region 1 FACs of narrow widths has already been identified both observationally and theoretically.)
A two‐ejecta event associated with a two‐step geomagnetic storm
Authors: Farrugia C. J. , Jordanova V. K. , Thomsen M. F. , Lu G. , Cowley S. W. H. , Ogilvie K. W.
Published: November 2006

A new view on how large disturbances in the magnetosphere may be prolonged and intensified further emerges from a recently discovered interplanetary process: the collision/merger of interplanetary (IP) coronal mass ejections (ICMEs; ejecta) within 1 AU. As shown in a recent pilot study, the merging process changes IP parameters dramatically with respect to values in isolated ejecta. The resulting geoeffects of the coalesced (“complex”) ejecta reflect a superposition of IP triggers which may result in, for example, two‐step, major geomagnetic storms. In a case study, we isolate the effects on ring current enhancement when two coalescing ejecta reached Earth on 31 March 2001. The magnetosphere “senses” the presence of the two ejecta and responds with a reactivation of the ring current soon after it started to recover from the passage of the first ejection, giving rise to a double‐dip (DD) great storm (each min Dst < −250 nT). A drift‐loss global kinetic model of ring current buildup shows that in this case the major factor determining the intensity of the storm activity is the very high (up to ∼10 cm−3) plasma sheet density. The plasma sheet density, in turn, is found to correlate well with the very high solar wind density, suggesting the compression of the leading ejecta as the source of the hot, superdense plasma sheet in this case. This correlation is similar to that obtained in a previous investigation extending over several years, but the present case study extends the range of plasma sheet densities from ∼2 to ∼10 cm−3. Since the features of the ejecta interaction in this example are fairly general, we propose that interacting ejecta are a new, important IP source of DD major storms. Peculiarities in the behavior of the magnetopause current during these extreme events are briefly discussed in the light of recent work. In a brief discussion of a second example (21–23 October 2001), we suggest that by strengthening the leading shock, the ejecta merger may have added to the “shock‐driver gas” origin of DD geomagnetic storms by increasing the ability of the shock to compress preexisting Bz < 0 magnetic fields.
Ensemble‐based ozone forecasts: Skill and economic value
Authors: Pagowski Mariusz , Grell Georg A.
Published: November 2006

In the summer of 2004, seven air quality models provided forecasts of surface ozone concentrations over the eastern United States and southern Canada. Accuracy of these forecasts can be assessed against hourly ozone measurements at over 350 locations. The ensemble of the air quality models is used to issue deterministic and probabilistic forecasts of maximum daily 8‐hour and 1‐hour averaged ozone concentrations. For completeness, a short summary on performance of deterministic forecasts for this ensemble of models, obtained alternatively by averaging model concentrations or by using dynamic linear regression as described by Pagowski et al. (2006), is given on the basis of this work. In parallel, the skill of probabilistic forecasts is discussed. To remove the bias, the probabilistic forecasts are calibrated. The economic value of forecasts, which is calculated using Richardson's cost‐loss decision model, is evaluated for both deterministic and probabilistic cases. It is shown that deterministic forecasts obtained with the ensemble of models provide a greater benefit to decision makers than forecasts issued with individual models. Probabilistic forecasts demonstrate similar advantages over the deterministic forecasts.
A model of the ULF magnetic and electric field generated from a dust devil
Authors: Farrell W. M. , Marshall J. R. , Cummer S. A. , Delory G. T. , Desch M. D.
Published: November 2006

It has been demonstrated that terrestrial dust devils emit ULF magnetic radiation. On Mars, dust devils may also generate such magnetic emissions, which might be used as a hazard alert for manned missions. Specifically, grains in dust devils become charged via contact electrification, and it has been proposed that the cyclonic motion of these charged grains in the vortex wind fields accounts for the magnetic emission. To test this hypothesis in general and the possible Mars application, a computer simulation of the contact electrification/wind blowing phenomena was created, with the charge distribution and resulting magnetic fields monitored as a function of time. The results indicate that indeed a fluctuating charge distribution in a vortex wind can account for the ULF magnetic fields measured from a dust devil. The contact electrification process is a function of composition, and we demonstrate that the various compositions will give rise to different magnetic field responses from the dust devil. We also demonstrate that this system of swirling charged grains develops vertical currents and associated electric fields, as suggested in preceding works.
A new procedure for analyzing the nucleation kinetics of freezing in computer simulation
Authors: Bartell Lawrence S. , Wu David T.
Published: November 2006

A new method for deriving the size of the critical nucleus and the Zeldovich factor directly from kinetic data is presented. Moreover, in principle, the form of G(n), the free energy of formation of nuclei consisting of n molecules, can be inferred. The method involves measuring times of first appearance of nuclei of size n in the transient regime and applying the Becker-Döring theory. Times of first appearance exhibit the same characteristics as the conventional times associated with N(n,t), the number of nuclei of at least size n per unit volume that have materialized at time t. That is, they are well represented by three nucleation parameters, the reduced moment, the time lag, and the steady state nucleation rate. But unlike the conventional steady state rate which is independent of n, the steady state times of first appearance vary with n. In order to characterize the three nucleation parameters with precision, however, thousands of independent stochastic events with known n are required. Such sets of data are readily generated in molecular dynamic simulations but, so far, not in laboratory experiments. Results are illustrated by an analysis of simulations of the spontaneous freezing of large clusters of SeF6.
Measurement of interstrand conductance in multistrand superconducting cables
Authors: Lu Bing , Luongo Cesar
Published: November 2006

Multistrand superconducting cables are widely used in large scale applications to obtain large current carrying capacity. Stability is one of the key issues that ensure continuous and reliable operation of superconducting cables. Knowledge of interstrand conductance is essential for analysis of current distribution and redistribution processes that substantially influence the stability of multistrand superconducting cables. In this paper, an approach to measure interstrand conductance is developed using parametric estimation method as used in control theory. First, a distributed parameter circuit model is adopted to calculate the current and voltage distribution in superconducting cables. Then, strand voltage differences at cable ends are measured by experiment. Finally, least squares method is applied to estimate the interstrand conductance which gives the minimum error of the voltage difference at cable ends between calculated and measured data. The interstrand conductance between the subcables in different cabling stages in a cable-in-conduit conductor (CICC) has been studied under different conditions (different temperatures and different cable lengths). The results are consistent, accurate, and fit the distributed parameters circuit model well. This method provides a convenient approach to evaluate electrical coupling parameters in multistrand superconducting cables under different conditions. The estimated parameters can be used to improve the accuracy of analysis of current distribution and cable stability.
Calculation of nuclear magnetic resonance shieldings using frozen-density embedding
Authors: Jacob Christoph R. , Visscher Lucas
Published: November 2006

We have extended the frozen-density embedding (FDE) scheme within density-functional theory [T. A. Wesolowski and A. Warshel, J. Phys. Chem. 97, 8050 (1993)] to include external magnetic fields and applied this extension to the nonrelativistic calculation of nuclear magnetic resonance (NMR) shieldings. This leads to a formulation in which the electron density and the induced current are calculated separately for the individual subsystems. If the current dependence of the exchange-correlation functional and of the nonadditive kinetic-energy functional are neglected, the induced currents in the subsystems are not coupled and each of them can be determined without knowledge of the induced current in the other subsystem. This allows the calculation of the NMR shielding as a sum of contributions of the individual subsystems. As a test application, we have calculated the solvent shifts of the nitrogen shielding of acetonitrile for different solvents using small geometry-optimized clusters consisting of acetonitrile and one solvent molecule. By comparing to the solvent shifts obtained from supermolecular calculations we assess the accuracy of the solvent shifts obtained from FDE calculations. We find a good agreement between supermolecular and FDE calculations for different solvents. In most cases it is possible to neglect the contribution of the induced current in the solvent subsystem to the NMR shielding, but it has to be considered for aromatic solvents. We demonstrate that FDE can describe the effect of induced currents in the environment accurately.
Dynamic strength of molecularly bonded surfaces
Authors: Li Fang , Leckband Deborah
Published: November 2006

This study reports a theoretical analysis of the forced separation of two adhesive surfaces linked via a large number of parallel noncovalent bonds. To describe the bond kinetics, we implement a three-state reaction model with kinetic rates obtained from a simple integral expression of the mean first passage time for diffusive barrier crossing in a pulled-distance-dependent potential. We then compute the rupture force for the separation of adhesive surfaces at a constant rate. The results correspond well with a Brownian dynamics simulation of the same system. The separation rate relative to the intrinsic relaxation time of the bonds defines three loading regimes and the general dependence of the adhesion on kinetic or thermodynamic parameters of the bonds. In the equilibrium regime, the rupture force asymptotically approaches the equilibrium rupture force, which increases linearly with the equilibrium bond energy. In the near-equilibrium regime, the rupture force increases with the separation rate and increasingly correlates with the bond rupture barrier. In the far-from-equilibrium regime where rebinding is irrelevant, the rupture force varies linearly with the rupture barrier.
Time dependent diffusion in a disordered medium with partially absorbing walls: A perturbative approach
Authors: Qian Jiang , Sen Pabitra N.
Published: November 2006

We present an analytical study of the time dependent diffusion coefficient in a dilute suspension of spheres with partially absorbing boundary condition. Following Kirkpatrick [J. Chem. Phys. 76, 4255 (1982)] we obtain a perturbative expansion for the time dependent particle density using volume fraction f of spheres as an expansion parameter. The exact single particle t operator for partially absorbing boundary condition is used to obtain a closed form time dependent diffusion coefficient D(t) accurate to first order in the volume fraction f. Short and long time limits of D(t) are checked against the known short time results for partially or fully absorbing boundary conditions and long time results for reflecting boundary conditions. For fully absorbing boundary condition the long time diffusion coefficient is found to be D(t)=5a2∕(12fD0t)+O((D0t∕a2)−2) to the first order of perturbation theory. Here f is small but nonzero, D0 the diffusion coefficient in the absence of spheres, and a the radius of the spheres. The validity of this perturbative result is discussed.
Dynamics of a discotic liquid crystal in the isotropic phase
Authors: Li Jie , Fruchey Kendall , Fayer M. D.
Published: November 2006

Optically heterodyne-detected optical Kerr effect (OHD-OKE) experiments are conducted to study the orientational dynamics of a discotic liquid crystal 2,3,6,7,10,11-hexakis(pentyloxy)triphenylene (HPT) in the isotropic phase near the columnar-isotropic (C-I) phase transition. The OHD-OKE signal of HPT is characterized by an intermediate power law t−0.76±0.02 at short times (a few picoseconds), a von Schweidler power law t−0.26±0.01 at intermediate times (hundreds of picoseconds), and an exponential decay at long times (tens of nanoseconds). The exponential decay has Arrhenius temperature dependence. The functional form of the total time dependent decay is identical to the one observed previously for a large number of molecular supercooled liquids. The mode coupling theory schematic model based on the Sjögren [Phys. Rev. A 33, 1254 (1986)] model is able to reproduce the HPT data over a wide range of times from <1ps to tens of nanoseconds. The studies indicate that the HPT C-I phase transition is a strong first order transition, and the dynamics in the isotropic phase display a complex time dependent profile that is common to other molecular liquids that lack mesoscopic structure.
Dissociative and associative attachment of NO to iron clusters
Authors: Gutsev G. L. , Mochena M. D. , Johnson E. , Bauschlicher C. W.
Published: November 2006

Electronic and geometrical structures of iron clusters with associative (FeNO, Fe2NO, Fe3NO, Fe4NO, Fe5NO, and Fe6NO) and dissociative (OFeN, OFe2N, OFe3N, OFe4N, OFe5N, and OFe6N) attachments of NO, as well as the corresponding singly negatively and positively charged ions, are computed using density functional theory with generalized gradient corrections. Both types of isomers are found to be stable and no spontaneous dissociation was observed during the geometry optimizations. The ground states correspond to dissociative attachment of NO for all iron clusters Fen, except for Fe and Fe+. All of the OFenN clusters have ferrimagnetic ground states, except for OFe2N, OFe2N−, OFe4N, and OFe4N−, which prefer the ferromagnetic coupling. In the ferrimagnetic states, the excess spin density at one iron atom couples antiferromagnetically to the excess spin densities of all other iron atoms. Relative to the high-spin Fen ground state, the lowest energy ferrimagnetic state quenches the total magnetic moments of iron clusters by 7, which is to be compared with a reduction in the magnetic moment of one in the lowest energy ferromagnetic states. Dissociation of NO on the iron clusters has a pronounced impact on the energetics of reactions; the FenNO+CO→FenN+CO2 channels are exothermic while the OFe6N+CO→ Fe6N+CO2 channels are nearly thermoneutral.
Lattice dynamics investigations of phonon thermal conductivity of Si∕Ge superlattices with rough interfaces
Authors: Ren Shang-Fen , Cheng Wei , Chen Gang
Published: November 2006

Phonon thermal conductivities in both growth and in-plane directions of Si∕Ge superlattices (SLs) with perfect and rough interfaces are calculated by using a lattice dynamics model. In addition to the general trend, the results show that there exist fluctuations of thermal conductivity in both directions for SLs with even or odd number of layers when the layer thickness is small. Thermal conductivities in both directions of Si∕Ge SLs with rough interfaces are shown to be much lower than those of SLs with perfect interfaces. To understand the influences of rough interfaces, thermal conductivities of homogeneous alloy are further calculated and compared. The results show that along the in-plane direction, the thermal conductivity of SLs with rough interfaces is about the same as that of random alloy, while in the growth direction it is lower than that of the random alloy.
Increasing the Q factor in the constant-excitation mode of frequency-modulation atomic force microscopy in liquid
Authors: Ebeling D. , Hölscher H. , Anczykowski B.
Published: November 2006

By adding a Q-control electronics to the setup of the constant-excitation mode of the frequency-modulation atomic force microscope, the authors are able to increase the effective Q factor of a self-oscillated cantilever in liquid to values comparable to ambient conditions. During imaging of soft biological samples adsorbed on a mica substrate, the authors observed an increased corrugation of the topography with increased Q factors. This effect is caused by the reduction of tip-sample indentation forces as demonstrated by numerical simulations and an analytical approach.
Rotatoelectricity in cholesteric side-chain liquid single crystal elastomers
Authors: Menzel Andreas M. , Brand Helmut R.
Published: November 2006

We analyze the phenomenon of rotatoelectricity which is characteristic of cholesteric side-chain liquid single crystal elastomers. Using a linearized macroscopic continuum description and our previous work we show that if such a material is exposed to a static external electric field oriented parallel to the cholesteric helical axis, the director of the liquid crystalline phase will rotate around the helical axis. The material considered is assumed to be a perfect electric insulator. We propose an experiment in which the effect of rotatoelectricity should be directly observable and from which the ratio of the material parameters involved will be accessible.
Brewster angle phenomenon in two-dimensional metallic photonic crystals and its application to polarization beam splitting
Authors: Hu Xinhua , Ho Kai-Ming
Published: November 2006

The authors show the Brewster angle phenomenon of p waves in two-dimensional metallic photonic crystals of rectangular lattices with effective medium theory and accurate multiple-scattering calculations. The Brewster angle can be tuned over a wide range by varying the structure parameters. Based on this phenomenon, the authors propose a polarization beam splitter which can completely separate the p and s waves at an incident angle of 45°±10° in a very wide wavelength range (1∼500μm).
Resistive hystersis effects in perovskite oxide-based heterostructure junctions
Authors: Singh M. P. , Méchin L. , Prellier W. , Maglione M.
Published: November 2006

The electrical and structural properties of the oxide-based metal/ferroelectric/metal (MFM) junctions are reported. The heterostructures are composed of ultrathin layers of La0.7Ca0.3MnO3 (LCMO) as a metallic layer and BaTiO3 (BTO) as a ferroelectric layer. Junction based devices, having the dimensions of 400×200μm2, have been fabricated upon LCMO/BTO/LCMO heterostructures by photolithography and Ar-ion milling technique. The dc current-voltage (I-V) characteristics of the MFM junctions were carried out. At 300K, the devices showed the linear (I-V) characteristics, whereas at 77K, (I-V) curves exhibited some reproducible switching behaviors with well-defined remnant currents. The resulting resistance modulation is very different from what was already reported in ultrathin ferroelectric layers displaying resistive switching. A model is presented to explain the data.
Deep level transient spectroscopy study of Pd and Pt sputtering damage in n-type germanium
Authors: Simoen E. , Opsomer K. , Claeys C. , Maex K. , Detavernier C. , Van Meirhaeghe R. L. , Clauws P.
Published: November 2006

Defect formation during Pd and Pt germanidation of n-type germanium, using rapid thermal annealing in the range of 300–500°C, is investigated by deep level transient spectroscopy. Small concentrations of an electron trap at ∼EC−0.385eV are found, which is believed to be associated with vacancy-related sputtering damage. This is supported by the observation of much higher concentrations of vacancy-related deep levels on as-deposited Pt and Pd Schottky barriers. A steep concentration profile rising towards the surface confirms the assignment to Ar ion-related damage. The applied thermal budget points out that the defects observed in the germanide samples are more stable than simple vacancy-related point defects and could correspond to vacancy clusters formed during the deposition and/or the annealing step.
Analysis of defects in an electric and photonic double-layer substrate made by separation-by-implanted-oxygen three-dimensional sculpting
Authors: Kishima Koichiro
Published: November 2006

With a view to application to electric-device fabrication, the authors investigated a separation-by-implanted-oxygen (SIMOX) three-dimensional (3D) sculpting method [P. Koonath et al., Appl. Phys. Lett. 83, 4909 (2003)] that will integrate in three dimensions electric circuits and photonic circuits on a silicon-on-insulator substrate. The authors analyzed the defects in the first silicon layer for electric circuits and the second silicon layer for optical circuits made by SIMOX 3D sculpting. The authors found that a balance between an acceptable number of defects on the first silicon layer and the formation of a buried optical waveguide is achievable. The defect densities of the first silicon layer and the second silicon layer were 1.8×103∕cm2 and 5.0×107∕cm2, respectively.
Nonequilibrium thermal boundary layer in a capillary discharge with an ablative wall
Authors: Keidar Michael , Beilis Isak I.
Published: November 2006

A thermal nonequilibrium region near wall in a capillary discharge is considered. The proposed model suggests that nonequilibrium thermal boundary layer thickness strongly depends on the capillary wall ablation rate. It is shown that the applicability of the thermal equilibrium condition, widely employed in capillary models, is limited to a case with a large ablation rate.
Influence of contact effect on the performance of microcrystalline silicon thin-film transistors
Authors: Chan Kah-Yoong , Bunte Eerke , Stiebig Helmut , Knipp Dietmar
Published: November 2006

Microcrystalline silicon thin-film transistors were prepared by plasma-enhanced chemical vapor deposition at substrate temperatures below 200°C. The transistors exhibit electron mobilities of 38cm2∕Vs, threshold voltages in the range of 2V, and subthreshold slopes of 0.3V∕decade. Despite the realization of transistors with high carrier mobility, contact effects limit the performance of the transistors. The influence of the drain and source contacts on device parameters including the mobility, the threshold voltage, and the subthreshold slope will be discussed in detail.