bluuebunny/crossref_metadata_2025 huggingface dataset:
Sol–gel transition behavior of biodegradable three‐arm and four‐arm star‐shaped PLGA–PEG block copolymer aqueous solution
Authors: Lee Su Jeong , Han Bo Ryeong , Park Sang Yeob , Han Dong Keun , Kim Sung Chul
Published: December 2005

Two types of temperature‐sensitive biodegradable three‐arm and four‐arm star‐shaped poly(DL‐lactic acid‐co‐glycolic acid‐b‐ethylene glycol) (3‐arm and 4‐arm PLGA–PEG) were successfully synthesized via the coupling reaction of 3‐arm and 4‐arm PLGA and α‐monocarboxyl‐ω‐monomethoxypoly(ethylene glycol) (CMPEG). In dilute aqueous solutions, star PLGA–PEGs showed the temperature‐ and concentration‐dependent formation and aggregation of micelles over specific concentration and specific temperature. With increasing the molecular weight and the relative hydrophobicity of hydrophobic PLGA block, critical micelle temperature (CMT) decreased. Aqueous solution of 4‐arm PLGA–PEG started to form micelles at lower temperature and showed sharper temperature‐dependent growth in micelle size. These results are due to the enhanced hydrophobicity of PLGA block. On the other hand, at high concentration, two types of 3‐arm and 4‐arm PLGA–PEG showed sol–gel–sol transition behavior as the temperature was increased. The 3‐arm and 4‐arm PLGA–PEG showed sol–gel transition at higher polymer concentrations (above 24 wt %) than the PEG–PLGA–PEG triblock copolymer. As the molecular weight and the relative hydrophobicity of PLGA block increased, the critical gel concentration (CGC) decreased. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 888–899, 2006
Biofunctionalized block copolymer nanoparticles based on ring‐opening metathesis polymerization
Authors: Carrillo Alvaro , Yanjarappa Mallinamadugu J. , Gujraty Kunal V. , Kane Ravi S.
Published: December 2005

We present an approach to the synthesis of biofunctionalized block copolymer nanoparticles based on ring‐opening metathesis polymerization; these nanoparticles may serve as novel scaffolds for the multivalent display of ligands. The nanoparticles are formed by the self‐assembly of diblock copolymers composed of a hydrophobic block and a hydrophilic activated block that can be functionalized with thiolated ligands in aqueous media. The activated block enables control over the orientation of the displayed ligands, which may be sugars, peptides, or proteins engineered to contain cysteine residues at suitable locations. The nanoparticle diameter can be varied over a wide range through changes in the composition of the block copolymer, and biofunctionalization of the nanoparticles has been demonstrated by the attachment of a peptide previously shown to inhibit the assembly of anthrax toxin. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 928–939, 2006
Synthesis and characterization of a series of thermotropic liquid crystalline copolyester nanocomposites
Authors: Chang Jin‐Hae , Ju Chul Ha , Kim Seong Hun
Published: December 2005

A series of aromatic thermotropic liquid crystalline copolyester (TLCP) nanocomposites were prepared by the in situ intercalation polymerization of p‐acetoxybenzoic acid (ABA), terephthalic acid (TPA), and diacetoxynaphthalene (DAN) isomers in the presence of the organoclay. The DAN isomers used in this study were 2,3‐ and 2,7‐naphthylene. We examined the variation of the liquid crystallinity, morphology, and thermal properties of the nanocomposites with organoclay content in the range 0–10 wt %. All the polymer nanocomposites were fabricated with a molar ratio of ABA:TPA:DAN = 2:1:1; they were shown to consist of a nematic liquid crystalline phase for low organoclay contents (≤5 wt %), whereas the hybrids with a higher concentration of organoclay (≥10 wt %) were found not to be mesomorphic. By using transmission electron microscopy, the clay layers in the 2,3‐DAN copolyester hybrids were found to be better dispersed in the matrix polymer than those in the 2,7‐DAN copolyester hybrids. The introduction of an organoclay into the matrix polymer was found to improve the thermal properties of the 2,3‐DAN copolyester hybrids. However, the thermal properties of the 2,7‐DAN copolyester hybrids were found to be worse than those of the pure matrix polymer for all organoclay compositions tested. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 387–397, 2006
Coupling of structural fluctuations to deamidation reaction in triosephosphate isomerase by Gaussian network model
Authors: Konuklar F. A. S. , Aviyente V. , Haliloğlu T.
Published: December 2005

We study the structural fluctuations of triosephosphate isomerase (TIM) by an elastic model, namely, the Gaussian network model (GNM), to identify a network of coupled motions in the allosteric communication between its deamidation and catalytic sites, and the promoting motions for the deamidation activity. For this, three TIM structures have been studied: one crystal structure and two model structures designed to describe different putative models for the deamidation reaction taking place at the subunit interface. The structural fluctuations have been mapped on the functional properties; then the differences in the fluctuations between the two models in relation to the deamidation reaction have been considered. The results demonstrate that the qualitative picture of the mean‐square fluctuations and the correlations between the fluctuations are similar in both, but the differences may affect the observed barrier height of the deamidation reaction. The higher packing density at regions close to deamidation sites, reflected by the high‐frequency fluctuating residues in the respective regions, the stronger positive correlation between the fluctuations of the deamidation sites, and enhanced positive correlation of the primary deamidation site with the extended vicinity of the catalytic region on the juxtaposed unit promote the probability of the deamidation reaction. The results in general emphasize the importance of structural fluctuations in enzyme reactions, as well as proposing the present methodology as a plausible approach for studies on the network of coupled promoting motions in protein functions. Proteins 2006. © 2005 Wiley‐Liss, Inc.
Microstructure and exchange coupling parameters of MTJ with CoFeB bottom electrode
Authors: Kanak J. , Stobiecki T. , Schebaum O. , Reiss G. , Brückl H.
Published: December 2005

In this study, we report the relationship between interface roughness, texture and the exchange bias and the interlayer‐Néel coupling fields of the spin‐valve magnetic tunnel junction (SV‐MTJ). SV‐MTJs with the structure: Si(100)/SiO2/buffer/IrMn/CoFeB/AlOx /NiFe/Ta were deposited on two buffers: Cu and Ta/Cu/Ta/Cu, and next the samples were annealed in vacuum and in a magnetic field. XRD analysis reveals that the texture degree of MTJ with Cu buffer is significantly lower than that of the sample with Ta/Cu/Ta/Cu buffer. The enhancement of IrMn and CoFeB texture leads to a higher amplitude of roughness and an increase of exchange bias and Néel coupling fields. The comparison of junctions with CoFe and CoFeB bottom electrodes shows that addition of 5% B in a CoFe layer makes the surface of the pinned layer smoother. This leads to a lower Néel coupling field, which is desirable for application of MTJ in MRAM technology. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic anisotropy changes in ultrathin Co films grown on vicinal sapphire substrates
Authors: Stupakiewicz A. , Gieniusz R. , Maziewski A. , Postava K. , Baczewski L. T. , Wawro A.
Published: December 2005

The aim of the work is to study the magnetic anisotropy changes in epitaxial ultrathin Co films grown on vicinal sapphire substrates with different miscut angles. Changes of the in‐plane magnetic anisotropy symmetry were deduced from magnetooptical hysteresis loops shape and angular dependence analysis of the resonance field measured in the sample plane. Two‐fold and four‐fold symmetry of the in‐plane anisotropy was observed for different miscut angles. The experimental data are discussed taking into account the following energy contributions: (i) demagnetization; (ii) perpendicular uniaxial anisotropy (iii) and step‐induced uniaxial anisotropy. Magnetic anisotropy constants are fitted to the experimental results for different miscut angles. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic structure of URuGa5 and UIrGa5
Authors: Morkowski J. A. , Szajek A.
Published: December 2005

As a part of a systematic study of the uranium isomorphic ternaries UTGa5 with transition metals results of calculations of the electronic structure for T = Ru and Ir are presented. The compounds crystallize in the HoCoGa5‐type structure, space group P4/mmm, and (except for T = Ni, Pd and Pt) are not magnetically ordered. The electronic structure was calculated by the full‐potential LMTO method. General features of the calculated densities of states show similarities to the ones for UCoGa5. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Grid connection of large offshore wind farms using HVDC
Authors: Xu Lie , Andersen Bjarne R.
Published: December 2005

This article describes the use of high‐voltage DC (HVDC) transmission systems for connection of large offshore wind farms using doubly fed induction generators (DFIGs) to the main grid. HVDC systems based on voltage source converters (VSC transmission) and on line‐commutated converters (LCC HVDC) are discussed. The article describes proposed system configurations, operating principles and controls for the two technologies. PSCAD/EMTDC simulations are presented to demonstrate the robust performance of the proposed systems during variation of generation and onshore AC fault conditions. Copyright © 2005 John Wiley & Sons, Ltd.
Sexual and seasonal differences in the frequency of beak marks on the wings of twoLethebutterflies
Authors: Ide Jun‐Ya
Published: December 2005

To assess bird predation pressure on butterflies, I investigated beak marks on the wings of twoLethebutterflies for 3 years in secondary temperate forests. If bird predation had significant effects on average longevity of butterflies, and if the number of specimens preyed upon was proportionate to the number of beak‐marked specimens, the beak mark frequency would be negatively correlated with average longevity of a butterfly. Bird predation pressure is generally thought to influence average longevity of butterflies. Therefore, if there is a negative correlation between beak mark frequency and average longevity, bird predation pressure would be reflected in beak mark frequency. Beak mark frequency was negatively correlated with longevity inLethe diana(Butler), the more abundant of the two species; thus, the beak mark frequency was considered to be a suitable index of bird predation pressure on the butterflies investigated in this study. In bothLethespecies, beak mark frequency was higher in females than in males. Because female butterflies have a relatively smaller thorax and flight muscles and a larger abdomen that contains eggs, they are presumably weaker or less agile fliers than males, and are probably attacked more easily by birds. In autumn, butterflies were heavily attacked by birds irrespective of sex and species. Because the numbers of lepidopteran larvae, which are the preferred prey of many birds, decreased in autumn, birds were thought to shift their diets to alternative prey such as adult butterflies.
Effect of quebracho tannin on faecal egg counts and worm burdens of temperate sheep with challenge nematode infections
Authors: MAX R. A. , WAKELIN D. , DAWSON J. M. , KIMAMBO A. E. , KASSUKU A. A. , MTENGA L. A. , CRAIGON J. , BUTTERY P. J.
Published: December 2005

Three animal experiments were carried out to investigate the effect of condensed tannins (CT) on parasitic gastrointestinal (GI) nematode infections of sheep. Experiment 1 investigated the long-term effect of varying dietary levels (0–80 g/kg diet) of quebracho tannin (QT) on faecal egg counts (FEC) and feed consumption of lambs with experimental Haemonchus contortus infection. Dietary QT did not cause significant reductions in FEC although at high inclusions of QT there was an indication of a reduction in FEC. Some undesirable effects of tannins were also observed; feed consumption was significantly reduced (P<0·001) by dietary QT, while faecal water content increased significantly (P<0·01). In order to reduce the undesirable effects of dietary tannins in the host, short-term exposure to tannins was adopted. QT was administered as a drench, for 3 consecutive days, to growing lambs infected with H. contortus (Experiment 2) or its mixed infection with Trichostrongylus colubriformis (Experiment 3) and its effect on FEC, worm burdens and the GI tract was investigated. Administration of QT drench to sheep infected with the abomasal H. contortus alone significantly (P<0·05) reduced FEC and worm burdens (P<0·01) compared with the control group. In Experiment 3 the drench had little effect (P>0·05) on small intestinal T. colubriformis although similar effects to those seen in Experiment 2 on H. contortus were observed, suggesting that the location of the nematodes in the gut might be important. Apart from reducing feed consumption, the drench caused some physiological changes in the gut, particularly an increase in faecal water and mucus content, which were more marked following the drench than seen in the dietary inclusion trial. In conclusion, unlike dietary inclusion, QT worked more quickly and more effectively against H. contortus when administered as drench; T. colubriformis may require a higher dose or a prolonged exposure to the drench. The present findings suggest that it may be possible, perhaps with limited use of synthetic anthelmintics, to design appropriate feeding strategies using tannins to alleviate the problem of nematode infections in small ruminants. This may be particularly relevant to the tropics and subtropics where many species of plants contain high levels of tannins and where extracts high in tannins are readily available.
Behaviour of Toxoplasma gondii RH Ankara strain tachyzoites during continuous production in various cell lines
Authors: DÖŞKAYA M. , DEGˇİRMENCİ A. , ÇİÇEK C. , AK M. , KORKMAZ M. , GÜRÜZ Y. , ÜNER A.
Published: December 2005

Toxoplasma gondii is an obligate intracellular protozoan parasite. The objective of the present study was to examine the behaviour of Toxoplasma gondii RH Ankara strain tachyzoites in a cell culture environment. The study represents the first step in determining whether T. gondii RH Ankara strain tachyzoites, grown in cell culture, are of sufficient quality to allow cessation of in vivo tachyzoite production for diagnostic assays. In the present study, T. gondii RH Ankara strain tachyzoites were continuously produced in myeloma X63.Ag8.653, HeLa, Hep-2, and Vero cell cultures for 2 months. The average size of the tachyzoites was 3×5·7 μm prior to the first inoculation but after continuous production, a marked decrease was noted in average tachyzoite size. The smallest tachyzoite size, was 1×2·1 μm after 2 months, in myeloma cell cultures even though the yield of tachyzoites increased. With other cell cultures, tachyzoite yields were not as high as myeloma cell culture although decrease in size was less. The smallest decrease in tachyzoite size, averaging 2×3·8 μm after 2 months, was observed in tachyzoites produced in HeLa cell cultures. A virulence assay in small groups of BALB/c mice, using tachyzoites derived from cell cultures, was also conducted. The preliminary results of the virulence assay suggest that as the size of the tachyzoites decreased, the virulence in mice decreased. Future research will focus on the effect of the size of cell culture-derived T. gondii RH Ankara strain tachyzoites on the virulence, protein expression, and the reliability of diagnostic assays. Ultimately, the behaviour of tachyzoites from various T. gondii strains will be observed in cell culture to determine if size is altered.
Responses of the surface membrane and excretory system ofSchistosoma mansonito damage and to treatment with praziquantel and other biomolecules
Authors: OLIVEIRA F. A. , KUSEL J. R. , RIBEIRO F. , COELHO P. M. Z.
Published: December 2005

Damage to the surface membrane of adultSchistosoma mansoni, and the activity of the excretory system, as shown by resorufin fluorescence, was observed following treatment with praziquantel and incubation with other molecules. Praziquantel treatment induced damage to the surface membrane as measured by the use of a variety of fluorescent compounds. The excretory system of the male worm was inhibited immediately after praziquantel treatment, but fully recovered after culture for 2 h following removal of praziquantel. The excretory system of the female, observed to be minimally active in untreated worm pairs, was often greatly activated in paired females, as shown by intense resorufin labelling, after praziquantel treatment, and this continued during recovery of the male excretory system. In experiments with normal worm pairs, the female could be activated by inhibiting the metabolic rate of the pair by a cooling procedure. The effects on the excretory system of changes in culture conditions (such as changes in pH, concentrations of bacterial lipopolysaccharide, cytokines, reactive oxygen species, compounds which remove cholesterol, such as beta-methyl cyclodextrin, and damaging basic poly-L-lysine) were also assessed. It is concluded that the extensive excretory system of the adult worm is responsive to drug treatment and to certain changes in environmental conditions. Its activity seems to be strongly linked to the integrity of the surface membrane.
Fitness effects and transmission routes of a microsporidian parasite infectingDrosophilaand its parasitoids
Authors: FUTERMAN P. H. , LAYEN S. J. , KOTZEN M. L. , FRANZEN C. , KRAAIJEVELD A. R. , GODFRAY H. C. J.
Published: December 2005

A microsporidian infection was discovered in laboratory cultures ofDrosophilaspecies. Ultrastructural examination suggested it belonged to the poorly characterized speciesTubulinosema kingi, and morphological and sequence data are presented. We explored howT. kingiaffected the fitness ofDrosophila melanogasterandD. subobscura, as well as the fitness of 2 of their parasitoids,Asobara tabidaandPachycrepoideus vindemiae. InDrosophila, infections caused changes in most of the traits we looked at that were associated with fitness, in particular causing a 34–55% reduction in early-life fecundity. Parasitoid fitness was affected more severely by infection than that of their hosts, with pupal mortality in particular increasing by 75–89%. We investigated the most important routes of transmission forT. kingiin a laboratory setting. LettingDrosophilalarvae feed on medium contaminated with spores from infected dead flies resulted in 100% infection. Low levels of transmission (<10%) were found between larvae, and vertically between mothers and their offspring. Parasitoids developing in infected hosts all became infected, but infected adults were neither able to transmit the pathogen to their offspring nor to their offspring'sDrosophilahost, either directly, or via contamination of the ovipositor or other body parts. A field survey ofDrosophilaand their parasitoids in southern England revealed no natural infections. We discuss the potential importance of Microsporidia in parasitoid-host interactions, and for those working withDrosophilain the laboratory.
The effect of macroeconomic variables on suicide
Authors: BERK MICHAEL , DODD SEETAL , HENRY MARGARET
Published: December 2005

Background. There are a large number of factors mediating suicide. Many studies have searched for a direct causal relationship between economic hardship and suicide, however, findings have been varied.

Method. Suicide data was obtained from the Australian Bureau of Statistics for the period between January 1968 and August 2002. These were correlated with a suite of macroeconomic data including housing loan interest rates, unemployment rates, days lost to industrial disputes, Consumer Price Index, gross domestic product, and the Consumer Sentiment Index.

Results. A total of 51845 males and 16327 females committed suicide between these dates. There were significant associations between suicide rates and eleven macroeconomic indicators for both genders in at least one age range. Data was divided into male and female and five age ranges and pooled ages. Analyses were conducted on these 132 datasets resulting in 80 significant findings. The data was generally stronger for indices measuring economic performance than indices measuring consumers' perceptions of the state of the economy. A striking difference between male and female trends was seen. Generally, male suicide rates increased with markers of economic adversity, while the opposite pattern was seen in females. There were significantly different patterns in age-stratified data, with for example higher housing loan interest rates having a positive association with suicide in younger people and a negative association in older age groups.

Conclusion. Macroeconomic trends are significantly associated with suicide. The patterns in males and females are very different, and there are further substantial age-related differences.
Methods and techniques for the evaluation of user-adaptive systems
Authors: GENA CRISTINA
Published: December 2005

This article presents a comprehensive overview of methods and techniques used for the evaluation of user-adaptive systems. It describes the methodologies derived both from the evaluation of human–computer interaction systems and from information retrieval and information filtering systems by giving examples of the application of these methodologies in the user-adaptive systems. The state of the art and the main results in the evaluation of these systems are reported. In particular, empirical evaluation and layered approaches are discussed in detail. Finally, focus on less explored methodologies, such as qualitative approaches (e.g. Grounded Theory), is proposed.
Evolutionary game theory and multi-agent reinforcement learning
Authors: TUYLS KARL , NOWÉ ANN
Published: December 2005

In this paper we survey the basics of reinforcement learning and (evolutionary) game theory, applied to the field of multi-agent systems. This paper contains three parts. We start with an overview on the fundamentals of reinforcement learning. Next we summarize the most important aspects of evolutionary game theory. Finally, we discuss the state-of-the-art of multi-agent reinforcement learning and the mathematical connection with evolutionary game theory.
Nationwide outbreak of listeriosis due to contaminated meat
Authors: MEAD P. S. , DUNNE E. F. , GRAVES L. , WIEDMANN M. , PATRICK M. , HUNTER S. , SALEHI E. , MOSTASHARI F. , CRAIG A. , MSHAR P. , BANNERMAN T. , SAUDERS B. D. , HAYES P. , DEWITT W. , SPARLING P. , GRIFFIN P. , MORSE D. , SLUTSKER L. , SWAMINATHAN B.
Published: December 2005

We used molecular subtyping to investigate an outbreak of listeriosis involving residents of 24 US states. We defined a case as infection with Listeria monocytogenes serotype 4b yielding one of several closely related patterns when subtyped by pulsed-field gel electrophoresis. Patients infected with strains yielding different patterns were used as controls. A total of 108 cases were identified with 14 associated deaths and four miscarriages or stillbirths. A case-control study implicated meat frankfurters as the likely source of infection (OR 17·3, 95% CI 2·4–160). The outbreak ended abruptly following a manufacturer-issued recall, and the outbreak strain was later detected in low levels in the recalled product. A second strain was recovered at higher levels but was not associated with human illness. Our findings suggest that L. monocytogenes strains vary widely in virulence and confirm that large outbreaks can occur even when only low levels of contamination are detected in sampled food. Standardized molecular subtyping and coordinated, multi-jurisdiction investigations can greatly facilitate detection and control of listeriosis outbreaks.
An outbreak of hepatitis A in Southern Italy: the case for vaccinating food handlers
Authors: PRATO R. , LOPALCO P. L. , CHIRONNA M. , GERMINARIO C. , QUARTO M.
Published: December 2005

We report an outbreak of hepatitis A that occurred in the city of Bari (Apulian region) in June 2002. Overall, 26 cases were observed over a 4-week period. These were traced back to the index case, a food handler who prepared various food products for sale over the counter at a store in the district (OR 5·36, CI 95% 1·58–19·25). Laboratory investigations confirmed that the outbreak was due to a point source and identified a new genotype IB variant. There is a possible indication for administration of hepatitis A vaccine to food handlers, although further evidence of an acceptable cost–benefit ratio needs to be ascertained.
EANA trail guide in astrobiology: search for a second genesis of life
Authors: Brack André , Ehrenfreund Pascale , von Kiedrowski Günter , Lammer Helmut , Prieur Daniel , Szuszkiewicz Ewa , Westall Frances
Published: December 2005

The European Astrobiology Network Association (EANA) coordinates and promotes astrobiology in the 17 European countries that are member of the organization. Astrobiology includes the study of the origin, evolution and distribution of life in the Universe. It is a multi-disciplinary science that encompasses the disciplines of chemistry, biology, palaeontology, geology, atmospheric physics, planetary physics and stellar physics. The open questions to be addressed and the steps ahead in cosmochemistry, star and planet formation, the chemistry of life's origin, the study of bacterial life as a reference and the search for habitats and biosignatures beyond the Earth are presented.
Detecting single atoms of calcium and iron in biological structures by electron energy‐loss spectrum‐imaging
Authors: Leapman R. D.
Published: December 2005

As techniques for electron energy‐loss spectroscopy (EELS) reach a higher degree of optimization, experimental detection limits for analysing biological structures are approaching values predicted by the physics of the electron scattering. Theory indicates that it should be possible to detect a single atom of certain elements like calcium and iron contained in a macromolecular assembly using a finely focused probe in the scanning transmission electron microscope (STEM). To test this prediction, EELS elemental maps have been recorded with the spectrum‐imaging technique in a VG Microscopes HB501 STEM coupled to a Gatan Enfina spectrometer, which is equipped with an efficient charge‐coupled device (CCD) array detector. By recording spectrum‐images of haemoglobin adsorbed onto a thin carbon film, it is shown that the four heme groups in a single molecule can be detected with a signal‐to‐noise ratio of ∼10 : 1. Other measurements demonstrate that calcium adsorbed onto a thin carbon film can be imaged at single atom sensitivity with a signal‐to‐noise ratio of ∼5 : 1. Despite radiation damage due to the necessarily high electron dose, it is anticipated that mapping single atoms of metals and other bound elements will find useful applications in characterizing large protein assemblies.
Successful application of spatial difference technique to electron energy‐loss spectroscopy studies of Mo/SrTiO3 interfaces
Authors: Gao M. , Scheu C. , Tchernychova E. , Rühle M.
Published: December 2005

The electron energy‐loss near‐edge structure (ELNES) of Mo/SrTiO3 interfaces has been studied using high spatial resolution electron energy‐loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. Thin films of Mo with a thickness of 50 nm were grown on (001)‐orientated SrTiO3 surfaces by molecular beam epitaxy at 600 °C. High‐resolution transmission electron microscopy revealed that the interfaces were atomically abrupt with the (110)Mo plane parallel to the substrate surface. Ti‐L2,3 (∼460 eV), O‐K (∼530 eV), Sr‐L2,3 (∼1950 eV) and Mo‐L2,3 (∼2500 eV) absorption edges were acquired by using the Gatan Enfina parallel EELS system with a CCD detector. The interface‐specific components of the ELNES were extracted by employing the spatial difference method. The interfacial Ti‐L2,3 edge shifted to lower energy values and the splitting due to crystal field became less pronounced compared to bulk SrTiO3, which indicated that the Ti atoms at the interface were in a reduced oxidation state and that the symmetry of the TiO6 octahedra was disturbed. No interfacial Sr‐L2,3 edge was observed, which may demonstrate that Sr atoms do not participate in the interfacial bonding. An evident interface‐specific O‐K edge was found, which differs from that of the bulk in both position (0.8 ± 0.2 eV positive shift) and shape. In addition, a positive shift (0.9 ± 0.3 eV) occurred for the interfacial Mo‐L2,3, revealing an oxidized state of Mo at the interface. Our results indicated that at the interface SrTiO3 was terminated with TiO2. The validity of the spatial difference technique is discussed and examined by introducing subchannel drift intentionally.
Advances in EELS spectroscopy by using new detector and new specimen preparation technologies
Authors: Scheu C. , Gao M. , Van Benthem K. , Tsukimoto S. , Schmidt S. , Sigle W. , Richter G. , Thomas J.
Published: December 2005

First results obtained with a Gatan UHV Enfina system, which was attached to a VG HB 501 UX dedicated STEM, are reported. The Enfina system is based on a CCD detector and offers, compared to the previously used photodiode array, a narrower point‐spread function, higher sensitivity, and faster read‐out capabilities. These improvements are demonstrated with electron energy‐loss measurements on various oxides, such as Al2O3, TiO2 and SrTiO3. It is shown that a better energy resolution is achieved and that acquisition of high‐energy absorption edges with a reasonable signal‐to‐noise ratio becomes possible. Furthermore, we report on the influence of the TEM specimen quality on the energy‐loss spectra. Thin amorphous layers at the specimen surfaces, which are induced by ion‐milling processes, can modify specific electron energy‐loss near‐edge structure features. We found that for the investigated ceramics the use of low‐energy ion‐milling systems is highly recommended, since the loss of energy‐loss near‐edge structure details by the presence of the amorphous layers is considerably reduced. This is especially true for very thin specimens.
Acid sphingomyelinase and inhibition by phosphate ion: role of inhibition by phosphatidyl‐myo‐inositol 3,4,5‐triphosphate in oligodendrocyte cell signaling
Authors: Testai F. D. , Landek M. A. , Goswami R. , Ahmed M. , Dawson G.
Published: December 2005

There is ample evidence that both acid (ASMase) and neutral (NSMase) sphingomyelinases play a role in cell death so inhibitors of either enzyme could have significant value as protectors against neurodegeneration. We used a fluorogenic sphingomyelinase substrate, 6‐hexadecanoylamino‐4‐methylumbelliferyl‐phosphorylcholine, and a [14C]choline‐labeled sphingomyelin substrate to screen large numbers of phosphocompounds for inhibition of ASMase in extracts of human oligodendroglioma cells (HOG) and neonatal rat oligodendrocytes. Non‐competitive inhibition was observed with inorganic phosphate and AMP, which was a more potent inhibitor of ASMase than cyclic AMP, ADP or ATP. However, other nucleotide phosphates, sugar phosphates, nucleotide sugars and glycerol phosphate did not inhibit ASMase. Our key finding was that phosphatidyl‐myo‐inositol 3,4,5‐triphosphate [PtdIns (3,4,5)P3] was a much more potent inhibitor of ASMase than lysophosphatidic acid or phosphatidyl‐myo‐inositol 4,5‐diphosphate [PtdIns(4,5)P2]. When PtdIns(3,4,5)P3 was added to cultured cells we observed 50% inhibition of ASMase but no inhibition of other lysosomal hydrolases. After transfection of HOG cells with the tumor supressor phosphatase and tensin homolog protein (PTEN), which hydrolyses PtdIns(3,4,5)P3 to PtdIns(4,5)P2, we observed a two‐fold increase in ASMase activity. Furthermore, the phosphatidylinositol‐3‐kinase inhibitor wortmannin (which reduces PtdIns(3,4,5)P3 levels) also resulted in activation of ASMase. We propose that the small amount of ASMase activity associated with detergent‐resistant cell membranes (Rafts) is regulated by PtdIns(3,4,5)P3 and is most likely involved in receptor clustering and capping.
Group I metabotropic glutamate receptors mediate the inhibition of phosphatidylserine synthesis in rat cerebellar slices: a possible role in physiology and pathology
Authors: Buratta Sandra , Mambrini Raffaela , Miniaci Maria Concetta , Tempia Filippo , Mozzi Rita
Published: December 2005

In cerebellar slices, the lowering of oxygen availability, obtained by bubbling N2 in the medium, reduced the incorporation of radioactive serine into phosphatidylserine (PtdSer). CPCCOEt, an antagonist of metabotropic glutamate receptors type 1 (mGluR1) counteracted the effect, whereas antagonists of NMDA or AMPA receptors were ineffective. In oxygenated slices, agonists of Group I mGluRs, which include mGluR1, inhibited PtdSer synthesis. This effect was also counteracted by CPCCOEt. These findings indicate that glutamate inhibits PtdSer synthesis by acting on mGluR1. This could be important in relation to the known release of glutamate in hypoxia–ischaemia conditions. In cerebellar Purkinje cells, mGluR1 are involved in the generation of mGluR‐EPSP evoked by parallel fibre stimulation. The administration of l‐serine to cerebellar slices reduced in a dose‐dependent manner the mGluR‐EPSP evoked by parallel fibre stimulation. The effect was mostly due to the increased synthesis of PtdSer. Thus inhibition of PtdSer synthesis, mediated by mGluR1, may participate in the generation of mGluR‐EPSP.
Coating carbon nanotubes with inorganic materials by pulsed laser deposition
Authors: Ikuno Takashi , Yasuda Tatsuro , Honda Shin-ichi , Oura Kenjiro , Katayama Mitsuhiro , Lee Jung-Goo , Mori Hirotaro
Published: December 2005

Using pulsed laser deposition (PLD), coaxial coating of carbon nanotubes (CNTs) with various inorganic materials (e.g., ZrOx,HfOx,AlOx,ZnOx, and Au) has been performed. The morphology and crystallinity of the coated layers were found to differ according to the materials used even at the same deposition temperature. For oxide materials, the deposits exhibited a uniform layer structure the composition of which was precisely controlled, while for Au, well-crystallized Au nanoparticles were observed on the CNT surface densely. Moreover, not only a single layer but also multiple layers were sequentially coated on CNTs by repeating PLD.
An equation-free probabilistic steady-state approximation: Dynamic application to the stochastic simulation of biochemical reaction networks
Authors: Salis Howard , Kaznessis Yiannis N.
Published: December 2005

Stochastic chemical kinetics more accurately describes the dynamics of “small” chemical systems, such as biological cells. Many real systems contain dynamical stiffness, which causes the exact stochastic simulation algorithm or other kinetic Monte Carlo methods to spend the majority of their time executing frequently occurring reaction events. Previous methods have successfully applied a type of probabilistic steady-state approximation by deriving an evolution equation, such as the chemical master equation, for the relaxed fast dynamics and using the solution of that equation to determine the slow dynamics. However, because the solution of the chemical master equation is limited to small, carefully selected, or linear reaction networks, an alternate equation-free method would be highly useful. We present a probabilistic steady-state approximation that separates the time scales of an arbitrary reaction network, detects the convergence of a marginal distribution to a quasi-steady-state, directly samples the underlying distribution, and uses those samples to accurately predict the state of the system, including the effects of the slow dynamics, at future times. The numerical method produces an accurate solution of both the fast and slow reaction dynamics while, for stiff systems, reducing the computational time by orders of magnitude. The developed theory makes no approximations on the shape or form of the underlying steady-state distribution and only assumes that it is ergodic. We demonstrate the accuracy and efficiency of the method using multiple interesting examples, including a highly nonlinear protein-protein interaction network. The developed theory may be applied to any type of kinetic Monte Carlo simulation to more efficiently simulate dynamically stiff systems, including existing exact, approximate, or hybrid stochastic simulation techniques.
Wire fixturing in high wire-number z pinches critical for high radiation power and reproducibility
Authors: Sanford T. W. L. , Mock R. C. , Seamen J. F. , Lopez M. R. , Watt R. G. , Idzorek G. C. , Peterson D. L.
Published: December 2005

The quality of high wire-number z-pinch implosions on Z using a dynamic hohlraum (DH) configuration [Sanford, et al., Phys. Plasmas 9, 3573 (2002)] is significantly affected by the method of holding the wires. The three arrangements discussed here have led to differences in radial and axial x-ray powers of factors of 1.6±0.2 and 1.5±0.2, respectively. An increase in power is accompanied by reductions in rise time and pulse width, and improvements in shot-to-shot reproducibility. Higher powers are produced by fixtures that enable the wires to be maintained taut, which also produce superior current contacts at the electrodes (and in particular at the cathode) prior to implosion. The increased axial power, and decreased variation in power and pulse shape, correlate with decreased wire-plasma material observed at the axial radiation exit holes of the DH.
Modeling and experimental studies of magnetron injection locking
Authors: Pengvanich P. , Neculaes V. B. , Lau Y. Y. , Gilgenbach R. M. , Jones M. C. , White W. M. , Kowalczyk R. D.
Published: December 2005

A phase-locking model has been developed from circuit theory to qualitatively explain the various regimes observed in magnetron injection-locking experiments. The experiments utilize two continuous-wave oven magnetrons: one functions as an oscillator and the other as a driver. The model includes both magnetron-specific electronic conductance and frequency-pulling parameter. Both time and frequency domain solutions are developed from the model, allowing investigations into the growth and saturation as well as the frequency response of the output signal. This simplified model recovers qualitatively many of the phase-locking frequency characteristics observed in the experiments.
Kinetic properties of shear Alfvén eigenmodes in tokamak plasmas
Authors: Lauber Ph. , Günter S. , Pinches S. D.
Published: December 2005

This work reports on numerical calculations concerning the kinetic properties of low-n, low-m toroidal Alfvén eigenmodes (TAEs) in tokamak plasmas for fusion relevant parameters. The self-consistent and nonperturbative code LIGKA [Ph. Lauber, Ph.D. thesis, TU München (2003)] is employed. It is based on a linear gyrokinetic model consisting of the quasineutrality equation and the moment equation for the perturbed current. It is shown that in a certain limit the underlying equations of LIGKA can be simplified to the equations known as the “reduced kinetic model.” An antenna-like version of LIGKA allows one to systematically find all shear-Alfvén-type modes in a given frequency interval, such as kinetic TAEs (KTAEs) and kinetically modified TAEs. The coupling to the kinetic Alfvén wave (KAW) is found in the form of continuum damping and radiative damping. For the cases examined here, no mode conversion in the centre is found. In the case of a large nonideal parameter, damping rates around 0.5%–1% are found, close to experimental measurements.
Intermolecular potentials based on symmetry-adapted perturbation theory with dispersion energies from time-dependent density-functional calculations
Authors: Misquitta Alston J. , Podeszwa Rafał , Jeziorski Bogumił , Szalewicz Krzysztof
Published: December 2005

Recently, three of us have proposed a method [Phys. Rev. Lett. 91, 33201 (2003)] for an accurate calculation of the dispersion energy utilizing frequency-dependent density susceptibilities of monomers obtained from time-dependent density-functional theory (DFT). In the present paper, we report numerical calculations for the helium, neon, water, and carbon dioxide dimers and show that for a wide range of intermonomer separations, including the van der Waals and short-range repulsion regions, the method provides dispersion energies with accuracies comparable to those that can be achieved using the current most sophisticated wave-function methods. If the dispersion energy is combined with (i) the electrostatic and first-order exchange interaction energies as defined in symmetry-adapted perturbation theory (SAPT) but computed using monomer Kohn-Sham (KS) determinants, and (ii) the induction energy computed using the coupled KS static response theory, (iii) the exchange-induction and exchange-dispersion energies computed using KS orbitals and orbital energies, the resulting method, denoted by SAPT(DFT), produces very accurate total interaction potentials. For the helium dimer, the only system with nearly exact benchmark values, SAPT(DFT) reproduces the interaction energy to within about 2% at the minimum and to a similar accuracy for all other distances ranging from the strongly repulsive to the asymptotic region. For the remaining systems investigated by us, the quality of the SAPT(DFT) interaction energies is so high that these energies may actually be more accurate than the best available results obtained with wave-function techniques. At the same time, SAPT(DFT) is much more computationally efficient than any method previously used for calculating the dispersion and other interaction energy components at this level of accuracy.
Making sense of nanocrystal lattice fringes
Authors: Fraundorf P. , Qin Wentao , Moeck Peter , Mandell Eric
Published: December 2005

The orientation dependence of thin-crystal lattice fringes can be gracefully quantified using fringe-visibility maps, a direct-space analog of Kikuchi maps [Nishikawa and Kikuchi, Nature (London) 121, 1019 (1928)]. As in navigation of reciprocal space with the aid of Kikuchi lines, fringe-visibility maps facilitate acquisition of crystallographic information from lattice images. In particular, these maps can help researchers to determine the three-dimensional lattice of individual nanocrystals, to “fringe-fingerprint” collections of randomly oriented particles, and to measure local specimen thickness with only a modest tilt. Since the number of fringes in an image increases with maximum spatial-frequency squared, these strategies (with help from more precise goniometers) will be more useful as aberration correction moves resolutions into the subangstrom range.
Postcollision interaction in noble gas clusters: Observation of differences in surface and bulk line shapes
Authors: Lindblad A. , Fink R. F. , Bergersen H. , Lundwall M. , Rander T. , Feifel R. , Öhrwall G. , Tchaplyguine M. , Hergenhahn U. , Svensson S. , Björneholm O.
Published: December 2005

The surface and bulk components of the x-ray photoelectron spectra of free noble gas clusters are shown to display differences in the influence of postcollision interaction between the photoelectron and the Auger electron on the spectral line shape; the bulk component is observed to be less affected than the surface and atomic parts of the spectra. A model for postcollision interaction in nonmetallic solids and clusters is also provided which takes the polarization screening into account. Core-level photoelectron spectra of Ar, Kr, and Xe have been recorded to verify the dependence of the postcollision interaction effect on the polarizability of the sample.
Formation and characteristics of dispersion layers of organofluorine compounds in poly(methyl methacrylate) using a vacuum process
Authors: Mochizuki Hiroyuki , Mizokuro Toshiko , Tanigaki Nobutaka , Hiraga Takashi
Published: December 2005

Dispersion layers of organofluorine compounds in poly(methyl methacrylate) (PMMA) were formed by a vacuum process, and their thickness increased with treatment temperature and time. Generally, dispersion of an additive into a polymer seems to follow Fick’s Law based on thermal diffusion. However, the dispersion layers formed in the present study could not have been governed by Fick’s Law. The concentration of organofluorine compounds was uniform throughout the dispersion layer, which showed a lower refractive index than the initial PMMA because the organofluorine compound used here showed a lower refractive index. The refractive index could be controlled by treatment temperature. The process used in the present study was favorable for preparation of the waveguide.
Significance of small voltage in impedance spectroscopy measurements on electrolytic cells
Authors: Barbero G. , Alexe-Ionescu A. L. , Lelidis I.
Published: December 2005

We investigate, theoretically, for what amplitude of the applied voltage to an electrolytic cell the concept of impedance is meaningful. The analysis is performed by means of a continuum model, by assuming the electrodes perfectly blocking. We show that, in the low-frequency range, the electrolytic cell behaves as a linear system only if the amplitude of the measurement voltage is small with respect to the thermal voltage VT=kBT∕q, where kBT is the thermal energy, and q is the modulus of the electrical charge of the ions, assumed identical except for the sign of the charge. On the contrary, for large frequency, we prove that the amplitude of the applied signal has to be small with respect to a critical voltage that is frequency dependent. The same kind of analysis is presented for the case in which the diffusion coefficients of the positive ions is different from that for negative ions, and for the case where surface adsorption takes place.
Enhancement of blue upconversion mechanism in YLiF4:Yb:Tm:Nd crystals
Authors: Courrol Lilia Coronato , Ranieri Izilda Marcia , Tarelho Luís Vicente Gomes , Baldochi Sônia Lícia , Gomes Laércio , Júnior Nilson Dias Vieira
Published: December 2005

In this paper we present a comparison between YLiF4:Yb:Tm and YLiF4:Yb:Tm:Nd systems identifying the most important processes that lead to a 20 times enhancement of thulium blue upconversion emission, under excitation around 792 nm, for the double sensitized system. Analysis of the 483 nm and 1030 nm emissions for the samples with different concentrations of Nd3+ ions showed that energy transfer between Nd3+ and Yb3+ is the main mechanism and responsible for the enhancement in upconversion.
Bridge-enhanced nanoscale impedance microscopy
Authors: Pingree L. S. C. , Hersam M. C.
Published: December 2005

A conductive atomic force microscopy (cAFM) technique has been developed that is capable of quantitatively measuring the magnitude and phase of alternating current flow through the tip/sample junction with a five order of magnitude improvement in sensitivity. Bridge-enhanced nanoscale impedance microscopy (BE-NIM) uses a tunable resistor/capacitor bridge circuit to null the spurious contribution to the tip/sample current caused by fringe capacitance between the cAFM cantilever and the sample. As a proof of principle, BE-NIM is used to characterize an array of electron-beam lithographically patterned metal-oxide-semiconductor capacitors and compared directly to conventional nanoscale impedance microscopy. In addition, BE-NIM is applied to a multiwalled carbon nanotube/poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) nanocomposite material, on which the alternating current behavior of individual nanoscale conductive pathways is quantitatively probed.