bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of maternal circulating cholesterol and gestational diabetes mellitus on lipid metabolism in human term placenta
Authors: Marseille‐Tremblay Charles , Ethier‐Chiasson Maude , Forest Jean‐Claude , Giguère Yves , Masse André , Mounier Catherine , Lafond Julie
Published: December 2007

Maternal hypercholesterolemia (HC) during pregnancy and gestational diabetes mellitus (GDM) are associated with disturbance of fetal development which may also modify key features of placental functions. In this study, we evaluated the impact of maternal hypercholesterolemia on placental cholesterol and lipid metabolism in 59 women classified in two groups according to the median concentration of plasma total cholesterol (6.42 mM). The impact of GDM was also evaluated on the metabolism of placentas obtained from 7 insulin‐treated GDM and 7 non‐GDM women. We showed that high maternal circulating cholesterol is associated with a significant increase in the LDL‐cholesterol, ApoB‐100 and triglyceride concentrations in the maternal blood. However the level of cholesterol in the venous cord blood and placenta remains unchanged in response to modification in maternal cholesterol profile. The levels of Fatty acid synthase (FAS) and SREBP‐2 expressions in placenta are significantly increased in the HC group while expression of both sterol regulatory element‐binding proteins‐1 (SREBP‐1) and HMG‐CoA reductase (HMGR) are not modified. GDM is not associated with modification in the maternal lipid profile but it increases the concentration of inflammatory cytokines (IL‐1β and TNF‐α) in placenta which correlates with a dramatic induction of FAS expression without affecting the expression of mature SREBPs proteins. In conclusion, our study suggests that in placenta, expressions of key proteins involved in de novo lipid synthesis are affected by changes in maternal metabolism (HC and GDM) that may subsequently affect fetal development. Mol. Reprod. Dev. 75: 1054–1062, 2007. © 2007 Wiley‐Liss, Inc.
Molecular cloning of Plk1 and Nek2 and their expression in mature gonads of the teleost fish Nile Tilapia (Oreochromis niloticus)
Authors: Matsuoka Yoh , Kobayashi Tohru , Kihara Kazunori , Nagahama Yoshitaka
Published: December 2007

Polo‐like kinase 1 (Plk1) and NIMA‐related kinase 2 (Nek2) are serine/threonine kinases that are involved in the G2/M phase transition of the cell cycle in vertebrates. Although they also play critical roles in the regulation of spermatogenesis and oogenesis, their characterization in meiosis has not been elucidated fully, particularly in teleost fish. To investigate the evolutionary significance of serine/threonine kinases in the reproductive system of fish, we cloned the cDNAs of Plk1 and Nek2 from a Nile tilapia (Oreochromis niloticus) testicular cDNA library. Tilapia Plk1 encodes a protein of 582 amino acids that shares 75% homology with human Plk1, while tilapia Nek2 encodes a putative protein of 446 amino acids that shares 70% homology with human Nek2. Analyses of tissue distribution by RT‐PCR and Southern blotting revealed that Plk1 and Nek2 are strongly expressed in the ovary and testis. Northern blot analysis revealed two Nek2 transcripts in the ovary and testis with different expression patterns, which indicates the presence of two structural variants for tilapia Nek2. Moreover, the localization of Plk1 and Nek2 mRNAs in tilapia gonads was determined by in situ hybridization analysis. In the ovary, Plk1 and Nek2 were expressed predominantly in oocytes. In the testis, on the other hand, Plk1 was expressed in primary spermatocytes, while Nek2 was generally expressed in primary and secondary spermatocytes. These results suggest that Plk1 and Nek2 are key factors in the progression of meiosis in fish. Mol. Reprod. Dev. 75: 989–1001, 2007. © 2007 Wiley‐Liss, Inc.
Phase diagram and entropic interaction parameter of athermal all‐polymer nanocomposites
Authors: de Luzuriaga Alaitz Ruiz , Etxeberria Agustín , Rodríguez Javier , Pomposo José A.
Published: December 2007

An entropic model is introduced for the prediction of the χ interaction parameter and phase diagram of athermal all‐polymer nanocomposites (chemically identical polymer‐nanoparticle/linear‐polymer blends). According to this model, dilution of contact (hard sphere‐like) nanoparticle/nanoparticle interactions upon mixing plays a key role in explaining the miscibility behavior of athermal all‐polymer nanocomposites in the presence of unfavorable chain expansion (or contraction) effects. The new model is valid both for the cases of chain stretching and chain contraction and provides an appropriate capture of entropy changes accompanying the mixing of chemically identical nanoparticles and polymers. A good agreement was found between predicted χ interaction parameter (χcal =  −2.3 × 10−3) and reported small angle neutron scattering (SANS) experimental data ($\bar \chi _{\exp } $ ∼ −2 × 10−3) for 211 kDa cross‐linked poly(styrene) (PS)‐nanoparticles dissolved in 473 kDa deuterated linear‐PS. In addition, the miscibility boundary calculated from the model for PS‐nanoparticle/linear‐PS nanocomposites (ϕ1 = 0.02) compared very favorably to that experimentally found. For this system, the spinodal line in the polymer radius of gyration (Rg) versus nanoparticle radius (a) phase diagram was found to follow the simple scaling law: $R_{\rm g}^{{\rm sp}} \approx 0.27a^{3/2} $, $R_{\rm g}^{{\rm sp}} $ being the polymer radius of gyration at which the second derivative of the free energy of mixing vanishes. Finally, the model has been employed for the prediction of the entropic χ interaction parameter, the miscibility behavior, and the melting point depression of athermal poly(ethylene) (PE)‐nanoparticle/linear‐PE nanocomposites using recent chain dimension data from Monte Carlo (MC) simulations, where chain stretching or chain contraction effects were observed depending on nanoparticle size. Copyright © 2007 John Wiley & Sons, Ltd.
Surface properties of hydrosilylated polyolefins annealed in supercritical carbon dioxide
Authors: Zhu S.‐H. , Tzoganakis C.
Published: December 2007

Two hydrosilylated polyolefin compounds are obtained by reacting polypropylene (PP) and polyethylene (PE) with di‐ and multi‐functional hydride‐terminated poly(dimethylsiloxane) (dH‐PDMS and mH‐PDMS), respectively. The PDMS‐rich surface layers on these two samples show different Si concentrations but similar thicknesses. Samples of these materials are annealed in supercritical carbon dioxide (scCO2) at various temperatures and pressures for different periods of time. On the PP/dH‐PDMS sample, an increase in the annealing temperature does not affect the Si concentration up to 120°C. However, the Si concentration is sharply reduced at T = 150°C at which point the surface appears to be covered by SiO2 particles. Annealing the PP/dH‐PDMS sample for short times leads to submicron scale SiO2 particle formation on the surface. The particles form aggregated clusters that spread all over the surface uniformly when the annealing time is extended. However, Si concentration on the PE/mH‐PDMS sample surface is enhanced as the annealing temperature increases, reaching a maximum at an annealing temperature of 100°C. No particle formation is observed on the PE/mH‐PDMS sample surface. The contact angle of both samples is found to increase with annealing temperature. Increasing the scCO2 pressure leads to a higher Si concentration on the surfaces of both samples. On the other hand, increasing the CO2 pressure leads to opposite trends in contact angle with the PP/dH‐PDMS sample exhibiting an increasing contact angle and the PE/mH‐PDMS sample exhibiting a decreasing one. Copyright © 2007 John Wiley & Sons, Ltd.
Development of catalyst‐transfer condensation polymerization. Synthesis of π‐conjugated polymers with controlled molecular weight and low polydispersity
Authors: Miyakoshi Ryo , Yokoyama Akihiro , Yokozawa Tsutomu
Published: December 2007

We describe the development of chain‐growth condensation polymerization for the synthesis of well‐defined π‐conjugated polymers via a new polymerization mechanism, catalyst‐transfer polymerization. We first studied the condensation polymerization of Grignard‐type hexylthiophene monomer with a Ni catalyst as a part of our research on chain‐growth condensation polymerization, and found that this polymerization also proceeded in a chain‐growth polymerization manner. However, the polymerization mechanism involving the Ni catalyst was different from that of previous chain‐growth condensation polymerizations based on substituent effects; the Ni catalyst catalyzed the coupling reaction of the monomer with the polymer, followed by the transfer of Ni(0) to the terminal CBr bond of the elongated molecule. This catalyst‐transfer condensation polymerization is generally applicable for the synthesis of polythiophene with an etheric side chain and poly(p‐pheneylene), as well as for the synthesis of polyfluorene via the Pd‐catalyzed Suzuki–Miyaura coupling reaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 753–765, 2008
Synthesis and characterization of highly stable blue‐light‐emitting hyperbranched conjugated polymers
Authors: Wang Rui , Wang Wei‐Zhi , Yang Gui‐Zhong , Liu Tianxi , Yu Junsheng , Jiang Yadong
Published: December 2007

Polyfluorene homopolymer (P1) and its carbazole derivatives (P2–P4) have been prepared with good yield by Suzuki coupling polymerization. P2 is an alternating copolymer based on fluorene and carbazole; P3 is a hyperbranched polymer with carbazole derivative as the core and polyfluorene as the long arms; P4 is a hyperbranched polymer with carbazole derivative as the core and the alternating fluorene and carbazole as the long arms. These polymers show highly thermal stability, and their structures and physical properties are studied using gel permeation chromatography, 1H NMR, 13C NMR, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetry, UV–vis absorption, photoluminescence, and cyclic voltammetry (CV). The influence of the incorporation of carbazole and the hyperbranched structures on the thermal, electrochemical, and electroluminescent properties has been investigated. Both carbazole addition and the hyperbranched structure increase the thermal and photoluminescent stability. The CV shows an increase of the HOMO energy levels for the derivatives, compared with polyfluorene homopolymer (P1). The EL devices fabricated by these polymers exhibit pure blue‐light‐emitting with negligible low‐energy emission bands, indicating that the hyperbranched structure has a strong effect on the PLED characteristics. The results imply that incorporating carbazole into polyfluorene to form a hyperbranched structure is an efficient way to obtain highly stable blue‐light‐emitting conjugated polymers, and it is possible to adjust the property of light‐emitting polymers by the amount of carbazole derivative incorporated into the polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 790–802, 2008
Polymerization ofo‐quinodimethanes. V. Ionic polymerization ofo‐quinodimethanes generated by thermal isomerization of corresponding benzocyclobutenes
Authors: Chino Keisuke , Endo Takeshi
Published: December 2007

The ionic polymerization of substitutedo‐quinodimethanes via thermal isomerization of benzocyclobutenes is described. In the cationic polymerizations of 1‐methoxy‐o‐quinodimethane in the presence of various cationic initiators at 110 °C for 12 h, chain transfer reactions also considerably underwent besides the polymerization. Meanwhile, cationic polymerizations of 1‐trimethylsilyloxy‐o‐quinodimethane under the same conditions gave good yields of the corresponding polymer. Anionic polymerizations of 1‐cyano‐o‐quinodimethane in the presence of anionic initiators such asn‐BuLi ort‐BuOK were performed at various temperatures for 12 h. Good yields of hexane‐insoluble polymer, which was produced by anionic polymerization of correspondingo‐quinodimethane as an intermediate, were obtained above 120 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 844–850, 2008
Chiral discrimination of α‐amino acids by DNA tetranucleotides under electrospray ionization conditions
Authors: Sivaleela T. , Kumar M. Ravi , Prabhakar S. , Bhaskar G. , Vairamani M.
Published: December 2007

A set of DNA tetranucleotides, which are 3′‐ or 5′‐end extended versions of GCA, was used as chiral selectors for the discrimination of enantiomers of α‐amino acids. The [X+Y–2H]2− ions of the 1:1 complexes were generated by electrospraying a mixture of tetranucleotide (X) and amino acid (Y) solution. Chiral discrimination was achieved by studying the collision‐induced dissociation spectra of the [X+Y–2H]2− ion and the ratio of relative abundance of precursor ion to that of the product ion was used to measure the extent of discrimination. Among the tetranucleotides used, GCAA and GGCA exhibited better discrimination, in which GCAA showed D‐selectivity and GGCA showed L‐selectivity for the studied amino acids. In addition, binding constants were measured for the 1:1 complexes of phenylalanine enantiomers with GCAA and GGCA. Copyright © 2007 John Wiley & Sons, Ltd.
A new in vitro approach for the simultaneous determination of phase I and phase II enzymatic activities of human hepatocyte preparations
Authors: Lahoz Agustín , Donato Maria Teresa , Montero Sandra , Castell José V. , Gómez‐Lechón Maria José
Published: December 2007

Primary hepatocytes are still the best qualified in vitro system to anticipate drug metabolism in man. Recent advances in hepatocytes cryopreservation have notably increased their use not only for drug metabolism studies, but also for other applications such as cell transplantation. Evaluation of the drug‐metabolizing competence of each hepatocytes preparation is needed. To date, the metabolic characterization of hepatocytes preparations relies on the assessment of phase I activities and the role of phase II enzymes receives little attention. A novel approach for the rapid assessment of the metabolic functionality of hepatocytes has been developed. A five‐probe cocktail was used to simultaneously determine the enzymatic activities of major human phase I CYPs (CYP1A2, CYP2A6, CYP2C9, CYP2E1, CYP3A4), as well as two phase II enzymes: glucuronidase (UGTs) and sulfotransferase (SULT). Liquid chromatography/tandem mass spectrometry was used as the technique of choice for the determination of the enzymatic activities in a single run. Results showed that the method described herein permits a rapid assessment of the metabolic capabilities of human hepatocyte preparations as well as an estimation of the quality of freshly isolated or cryopreserved hepatocytes. Copyright © 2007 John Wiley & Sons, Ltd.
Root causes of unsatisfactory performance of large and complex remediation projects: Lessons learned from the united states department of energy environmental management programs
Authors: Greenberg Michael , Powers Charles , Mayer Henry , Kosson David
Published: December 2007

The Consortium for Risk Evaluation with Stakeholder Participation (CRESP) was asked by the United States Department of Energy (US DOE) to consider the root causes of remediation projects that fail to entirely achieve their goals and then to offer suggestions to assist the Department. To begin this project, CRESP held several meetings at which the group defined problematic outcomes, the early symptoms of problematic outcomes, and the root causes of failing to meet expectations. The five root causes are complex science, engineering, and technology; ambiguous economics; project management shortcomings; political processes and credibility; and history and organizational culture. This article, while focusing on the US DOE, provides a larger context for many remediation projects that have failed to entirely live up to their sponsors' expectations. © 2007 Wiley Periodicals, Inc.
Zinc and cobalt phytoextraction by different plant species
Authors: Abdel‐Sabour M. F. , Al‐Salama Y. J.
Published: December 2007

Plant species sorghum (Sorghum vulgar L.), clover (Trifolium pratense L.), panikum (Panicum antidotal), and canola (Brassica napus) were tested to determine their phytoremediation potential. After a period of about 90 days, plant samples (shoots and roots) and soil samples (before and after cultivation) were collected for zinc and cobalt analyses using atomic absorption spectrometry. The highest zinc uptake was observed in canola, while panikum grass showed a high zinc accumulation affinity compared to sorghum and clover. Calculation of the recovery percentage, based on the amount of zinc removed from the soil after cultivation, ranged between 12.8 and 36.3 percent of the total initial zinc. Canola shoots exhibited the highest cobalt uptake compared to the other plant species. Calculation of the recovery percentage based on cobalt removed from the soil after cultivation ranged between 10.1 and 40.7 percent of the total initial cobalt concentration. © 2007 Wiley Periodicals, Inc.*

This article is a U.S. Government work and, as such, is in the public domain of the United States of America.
Estimating survival in newly diagnosed cancer patients: Use of computer simulations to evaluate performances of different approaches in a wide range of scenarios
Authors: Rashid Ivan , Marcheselli Luigi , Federico Massimo
Published: December 2007

Many empirical studies have proven the usefulness of period analysis in providing more up‐to‐date estimates of cancer patient survival than cohort‐based methods. The aim of this paper is to provide a non‐empirical evaluation of several survival approaches over a comprehensive range of scenarios using computer simulations. The simulation model included the following input parameters: number of annual patients, length of survival calculation, number of years of diagnosis, prognosis of cancer, follow‐up period, and two additional parameters for modeling assumption on incidence and survival trends. The current study also introduced alternative cohort‐ and period‐based approaches in addition to more traditional methods. Simulations showed that the choice of an appropriate survival approach is strongly dependent on the given scenario: period analysis was effective only for a limited number of circumstances, while alternative approaches appeared to be suitable for more realistic situations, when the follow‐up period is different from the incidence period. The results of simulations could be useful for a quick identification of the most appropriate approach when estimating up‐to‐date cancer survival rates. Copyright © 2007 John Wiley & Sons, Ltd.
Similar toxicity of the oligomeric molten globule state and the prefibrillar oligomers
Authors: Čeru Slavko , Žerovnik Eva
Published: December 2007

We report that a mutant of human stefin B is in a molten globule conformation. It has all the spectroscopic characteristics for such a state. We also demonstrate that the molten globule is oligomeric, eluting on SEC within a similar MW range than the higher order oligomers of the wild type protein, which is confirmed by DLS and AFM. Both, the higher oligomers and the molten globule state bind ANS, implying a high degree of hydrophobic patches exposure and partial opening of the structure. Finally, we demonstrate that the oligomeric molten globule is as toxic as the prefibrillar aggregates obtained at acid pH or the higher order oligomers prepared at neutral pH.
Proton transfer in the photosynthetic reaction center of Blastochloris viridis
Authors: Kozlova Maria A. , Juhnke Hanno D. , Cherepanov Dmitry A. , Lancaster C. Roy D. , Mulkidjanian Armen Y.
Published: December 2007

Photosynthetic reaction centers of Blastochloris viridis require two quanta of light to catalyse a two‐step reduction of their secondary ubiquinone QB to ubiquinol. We employed capacitive potentiometry to follow the voltage changes that were caused by the accompanying transmembrane proton displacements. At pH 7.5 and 20 °C, the QB‐related voltage generation after the first flash was contributed by a fast, temperature‐independent component with a time constant of ∼30 μs and a slower component of ∼200 μs with activation energy (E
a) of 50 kJ/mol. The kinetics after the second flash featured temperature‐independent components of 5 μs and 200 μs followed by a component of 600 μs with E
a
∼ 60 kJ/mol.
Single particle analysis of thylakoid proteins from Thermosynechococcus elongatus and Synechocystis 6803: Localization of the CupA subunit of NDH‐1
Authors: Folea I. Mihaela , Zhang Pengpeng , Nowaczyk Marc M. , Ogawa Teruo , Aro Eva-Mari , Boekema Egbert J.
Published: December 2007

The larger protein complexes of the cyanobacterial photosynthetic membrane of Thermosynechoccus elongatus and Synechocystis 6803 were studied by single particle electron microscopy after detergent solubilization, without any purification steps. Besides the “standard” L‐shaped NDH‐1L complex, related to complex I, large numbers of a U‐shaped NDH‐1MS complex were found in both cyanobacteria. In membranes from Synechocystis ΔcupA and ΔcupA/cupB mutants the U‐shaped complexes were absent, indicating that CupA is responsible for the U‐shape by binding at the tip of the membrane‐bound arm of NDH‐1MS. Comparison of membranes grown under air levels of CO2 or 3% CO2 indicates that the number of NDH‐1MS particles is 30‐fold higher under low‐CO2.
F2L, a peptide derived from heme‐binding protein, inhibits LL‐37‐induced cell proliferation and tube formation in human umbilical vein endothelial cells
Authors: Lee Sun Young , Lee Mi-Sook , Lee Ha Young , Kim Sang Doo , Shim Jae Woong , Jo Seong Ho , Lee Jae Won , Kim Joon Youn , Choi Young-Whan , Baek Suk-Hwan , Ryu Sung Ho , Bae Yoe-Sik
Published: December 2007

F2L, a peptide derived from heme‐binding protein, was originally identified as an endogenous ligand for formyl peptide receptor‐like (FPRL)2. Previously, we reported that F2L inhibits FPR and FPRL1‐mediated signaling in neutrophils. Since endothelial cells express functional FPRL1, we examined the effect of F2L on LL‐37 (an FPRL1 agonist)‐induced signaling in human umbilical vein endothelial cells (HUVECs). F2L stimulated the chemotactic migration in HUVECs. However, F2L inhibited FPRL1 activity, resulting in the inhibition of cell proliferation and tube formation induced by LL‐37 in HUVECs. We suggest that F2L will potentially be useful in the study of FPRL1 signaling and the development of drugs to treat diseases involving the FPRL1 in the vascular system.
The origin of life in comets
Authors: Napier W.M. , Wickramasinghe J.T. , Wickramasinghe N.C.
Published: December 2007

Mechanisms of interstellar panspermia have recently been identified whereby life, wherever it has originated, will disperse throughout the habitable zone of the Galaxy within a few billion years. This re-opens the question of where life originated. The interiors of comets, during their aqueous phase, seem to provide environments no less favourable for the origin of life than that of the early Earth. Their combined mass throughout the Galaxy overwhelms that of suitable terrestrial environments by about 20 powers of ten, while the lifetimes of friendly prebiotic environments within them exceeds that of localized terrestrial regions by another four or five powers of ten. We propose that the totality of comets around G-dwarf Sun-like stars offers an incomparably more probable setting for the origin of life than any that was available on the early Earth.
Verification of Enhancement of the CSF Space, not Parenchyma, in Acute Stroke Patients with Early Blood—Brain Barrier Disruption
Authors: Henning Erica C , Latour Lawrence L , Warach Steven
Published: December 2007

Enhancement on post-contrast fluid-attenuated inversion recovery (FLAIR) images after acute stroke has been attributed to early blood—brain barrier disruption. Using an estimate of parenchymal volume fraction and the apparent diffusion coefficient (ADC), we investigated the relative contributions of cerebral spinal fluid (CSF) and parenchyma to enhancement seen on postcontrast FLAIR. Enhancing regions were found to have low parenchymal volume fractions and high ADC values, approaching that of pure CSF. These findings suggest that contrast enhancement on FLAIR occurs predominately in the CSF space, not parenchyma.
Mislocalization of human transcription factor MOK2 in the presence of pathogenic mutations of lamin A/C
Authors: Dreuillet Caroline , Harper Maryannick , Tillit Jeanne , Kress Michel , Ernoult‐Lange Michèle
Published: December 2007

Background information. hsMOK2 (human MOK2) is a DNA‐binding transcriptional repressor. For example, it represses the IRBP (interphotoreceptor retinoid‐binding protein) gene by competing with the CRX (cone‐rod homeobox protein) transcriptional activator for DNA binding. Previous studies have shown an interaction between hsMOK2 and nuclear lamin A/C. This interaction could be important to explain hsMOK2 ability to repress transcription.

Results. In the present study, we have tested whether missense pathogenic mutations of lamin A/C, which are located in the hsMOK2‐binding domain, could affect the interaction with hsMOK2. We find that none of the tested mutations is able to disrupt hsMOK2 binding in vitro or in vivo. However, we observe an aberrant cellular localization of hsMOK2 into nuclear aggregates when pathogenic lamin A/C mutant proteins are expressed.

Conclusions. These results indicate that pathogenic mutations in lamin A/C lead to sequestration of hsMOK2 into nuclear aggregates, which may deregulate MOK2 target genes.
Stimulated emission at 474nm from an InGaN laser diode structure grown on a (112¯2) GaN substrate
Authors: Kojima K. , Funato M. , Kawakami Y. , Masui S. , Nagahama S. , Mukai T.
Published: December 2007

The stimulated emissions from semipolar InGaN laser diode (LD) structures grown on (112¯2) GaN substrates are observed at room temperature under photopumped conditions. The measured emission peaks are in the photon energy range from 2.62eV (474nm)to3.05eV (405nm), and the emission intensity has a threshold behavior with respect to the pumping power. A strong in-plane optical anisotropy is observed between the two perpendicular directions, [1¯1¯23] and [11¯00], due to anisotropic matrix elements, which depend on the crystal orientation; the stimulated emission measured along the [1¯1¯23] direction occurs with a lower threshold pumping power at a lower energy compared to that obtained along the [11¯00] direction. The experimental results and the valence band calculations indicate that the transverse-electric mode with an electric vector along the [11¯00] direction is dominant for gain formation in semipolar and nonpolar InGaN LDs. Compared to c-plane InGaN LDs, semipolar InGaN LDs have comparable or less threshold pumping powers.
Pathway to copolymer collapse in dilute solution: Uniform versus random distribution of comonomers
Authors: Dasmahapatra Ashok Kumar , Nanavati Hemant , Kumaraswamy Guruswamy
Published: December 2007

Monte Carlo simulations show that copolymers with uniformly (or periodically) distributed sticky comonomers collapse “cooperatively,” abruptly forming a compact intermediate comprising a monomer shell surrounding a core of the aggregated comonomers. In comparison, random copolymers collapse through a relatively less-compact intermediate comprising a comonomer core surrounded by a fluffy monomer shell that densifies over a wide temperature range. This difference between the collapse pathways for random and uniform copolymers persists to higher chain lengths, where uniform copolymers tend to form multiple comonomer cores. In this paper, we describe the formation of such an intermediate state, and the subsequent collapse, by recognizing that these arise from the expected balance between comonomer aggregation enthalpy and loop formation entropy dictated by the chain microstructure.
On the collective network of ionic liquid/water mixtures. I. Orientational structure
Authors: Schröder C. , Rudas T. , Neumayr G. , Benkner S. , Steinhauser O.
Published: December 2007

In this work, the collective structure of aqueous solutions of ionic liquids was studied by means of molecular dynamics simulations. Various concentrations of 1-butyl-3-methyl-imidazolium tetrafluoroborate and TIP3P water were simulated at the very same size of the simulation box. For the analysis, the ternary system cation/anion/water was subdivided into binary networks. The local structure of each of these six networks is investigated by atom-atom radial distribution functions as well as by the so-called g coefficients, which reveal the mutual orientation of the network constituting partners. Furthermore, the collective structure of the whole samples was characterized by the contribution of each species to the static dielectric constant ϵ(ω=0) and to the Kirkwood GK factor. The combination of the analysis tools mentioned above provides knowledge about the cross-linking of the ionic species with the dipolar water. Thereby, the interplay between charge-charge and hydrogen bond networks is analyzed in detail.
Surface species produced in the radiolysis of zirconia nanoparticles
Authors: Carrasco-Flores Eduardo A. , LaVerne Jay A.
Published: December 2007

Modifications to water-zirconia nanoparticle interfaces induced by γ irradiation have been examined using diffuse reflection infrared Fourier transform (DRIFT), Raman scattering, and electron paramagnetic resonance (EPR) techniques. Spectroscopy with in situ heating was used to probe variations in the dissociatively bound chemisorbed water on the zirconia nanoparticles following evaporation of the physisorbed water. DRIFT spectra show that the bridged Zr–OH–Zr species decreases relative to the terminal Zr–OH species upon irradiation. No variation is observed with Raman scattering, indicating that the zirconia morphology is unchanged. EPR measurements suggest the possible formation of the superoxide ion, presumably by modification of the surface OH groups. Trapped electrons and interstitial H atoms are also observed by EPR.
Hydrogen transfer dynamics in a photoexcited phenol/ammonia (1:3) cluster studied by picosecond time-resolved UV-IR-UV ion dip spectroscopy
Authors: Ishiuchi Shun-ichi , Sakai Makoto , Daigoku Kota , Hashimoto Kenro , Fujii Masaaki
Published: December 2007

The picosecond time-resolved IR spectra of phenol/ammonia (1:3) cluster were measured by UV-IR-UV ion dip spectroscopy. The time-resolved IR spectra of the reaction products of the excited state hydrogen transfer were observed. From the different time evolution of two vibrational bands at 3180 and 3250cm−1, it was found that two isomers of hydrogenated ammonia radical cluster ∙NH4(NH3)2 coexist in the reaction products. The time evolution was also measured in the near-IR region, which corresponds to 3p-3s Rydberg transition of ∙NH4(NH3)2; a clear wavelength dependence was found. From the observed results, we concluded that (1) there is a memory effect of the parent cluster, which initially forms a metastable product, ∙NH4–NH3–NH3, and (2) the metastable product isomerizes successively to the most stable product, NH3–∙NH4–NH3. The time constant for OH cleaving, the isomerization, and its back reaction were determined by rate-equation analysis to be 24, 6, and 9ps, respectively.
Electron binding energies and Dyson orbitals of Al5Om− (m=3,4,5) and Al5O5H2−
Authors: Guevara-García Alfredo , Martínez Ana , Ortiz J. V.
Published: December 2007

Photoelectron spectra of Al5Om− (m=3–5) and of the anion produced by the dissociative adsorption of a water molecule by Al5O4− are interpreted with density-functional geometry optimizations and electron-propagator calculations of vertical electron detachment energies. For Al5O3−, Al5O4−, and Al5O5H2−, the observed signals may be attributed to the most stable isomer of each anion. For Al5O5−, the features in the photoelectron spectrum are due to three almost isoenergetic isomers.
Excitations of atomic fragments arising in the exothermic (n;q) reactions of light atoms with slow neutrons
Authors: Frolov Alexei M. , Wardlaw David M.
Published: December 2007

We have developed the closed procedure for evaluating the final state probabilities in atomic fragments which arise during exothermic (n;t)-, (n;α)-, and (n;p)-nuclear reactions in some light atoms with slow neutrons. The procedure includes the two consecutive steps: (1) computation of the final state probabilities based on the sudden approximation and (2) evaluation of various transition probabilities between the states obtained at the first step.
On Nichols algebras over SL(2,Fq) and GL(2,Fq)
Authors: Freyre Sebastián , Graña Matías , Vendramin Leandro
Published: December 2007

We compute necessary conditions on Yetter-Drinfeld modules over the groups SL(2,Fq) and GL(2,Fq) to generate finite dimensional Nichols algebras. This is a first step toward a classification of pointed Hopf algebras with a group of grouplikes isomorphic to one of these groups.
Coherent state maps related to the bounded positive operators
Authors: Odzijewicz Anatol , Goliński Tomasz , Tereszkiewicz Agnieszka
Published: December 2007

We show that for any bounded positive operator H with the simple spectrum, one can canonically define two coherent state maps. The algebras generated by annihilation operators defined by these coherent state maps are studied. We describe also how the Toda isospectral deformation of H deforms the corresponding coherent state maps and the related operator algebras.
On the possibility of electric-current sheets in dense formation
Authors: Low B. C.
Published: December 2007

This is a mathematical study of the formation of tangential discontinuities, or current sheets, in a magnetic field evolving in an electrically perfectly conducting fluid in response to deformation of its domain, an effect first treated by Hahm and Kulsrud [Phys. Fluids 28, 2412 (1985)]. Explicit examples are presented of three-dimensional, untwisted fields, anchored to the boundary, that cannot assume a force-free state in the absence of current sheets. The underlying physics of this process is as described by the Parker theory of spontaneous current sheets, namely, that for most continuous magnetic fields in complex three-dimensional geometry, there is an incompatibility between the preservation of field topology and point-by-point force balance to achieve equilibrium. This incompatibility is removed through discontinuous plasma displacements that produce magnetic tangential discontinuities. In contrast to the twisted magnetic fields central to the Parker theory, fixing the connectivity between the anchored magnetic footpoints alone is sufficient to lead to current-sheet formation in untwisted fields. This mode of sheet formation may produce spatially dense multitudes of sheets to heat a plasma throughout its macroscopic volume such as implied by several phenomena in the solar corona.
Portable x-ray fluorescence spectrometer for coating thickness measurement
Authors: Carapelle Alain , Fleury-Frenette Karl , Collette Jean-Paul , Garnir Henri-Pierre , Harlet Philippe
Published: December 2007

A handheld x-ray spectrometer has been realized and tested. The purpose of the device is to measure the thickness of coated samples in the range of 1–1500nm in an industrial environment. Accuracy of ∼3% has been achieved in this range with a measurement time of 1min. Automated software has been implemented to allow utilization by a nonspecialist operator. An automated calibration procedure, based on measurements of reference samples, is used.
Interfacial coherency and ferroelectricity of BaTiO3∕SrTiO3 superlattice films
Authors: Li Y. L. , Hu S. Y. , Tenne D. , Soukiassian A. , Schlom D. G. , Chen L. Q. , Xi X. X. , Choi K. J. , Eom C. B. , Saxena A. , Lookman T. , Jia Q. X.
Published: December 2007

We studied the phase transitions, domain morphologies, and polarizations in BaTiO3∕SrTiO3 superlattices grown on SrTiO3 substrates. Using the phase field approach, we discovered the remarkable influence of film/substrate interfacial coherency on the ferroelectricity of the SrTiO3 layers within a superlattice: it is an orthorhombic ferroelectric for an incoherent interface while it exhibits only induced polarization by the adjacent BaTiO3 layers for a coherent interface. We presented the domain morphologies within individual BaTiO3 and SrTiO3 layers which have different ferroelectric symmetries. The results are compared to ultraviolet Raman spectroscopy and variable temperature x-ray diffraction measurements.
Microstructural effect on optical properties of Au:SiO2 nanocomposite waveguide films
Authors: Cho Sunghun , Lee Soonil , Lee Taek Sung , Cheong Byung-ki , Kim Won Mok , Lee Kyeong-Seok
Published: December 2007

Polarization-dependent optical properties of slab waveguide films, which are composed of Au nanoparticles dispersed in a SiO2 matrix, were investigated using a prism coupler. The optical spectra and the mode profiles of the nanocomposite films prepared by alternating sputtering were compared with those of cosputtered films, and the optical anisotropy of the films were modeled and analyzed on the basis of an effective medium theory with Maxwell–Garnett geometry and a layer-by-layer photonic band-gap structures.
Algebraic Bethe ansatz for the elliptic quantum group Eτ,η(A2(2))
Authors: Manojlović Nenad , Nagy Zoltán
Published: December 2007

We implement the Bethe ansatz method for the elliptic quantum group Eτ,η(A2(2)). The Bethe creation operators are constructed as polynomials of the Lax matrix elements expressed through a recurrence relation. We also give the eigenvalues of the family of commuting transfer matrices defined in the tensor product of fundamental representations.
Thermal stability of supercritical thickness-strained Si layers on thin strain-relaxed buffers
Authors: Escobedo-Cousin E. , Olsen S. H. , Dobrosz P. , Bull S. J. , O’Neill A. G. , Coulson H. , Claeys C. , Loo R. , Delhougne R. , Caymax M.
Published: December 2007

The structural reaction of sub- and supercritical thickness-strained Si layers on novel thin SiGe strain-relaxed buffers (SRBs) during high-temperature annealing used in device fabrication is investigated. Atomic force microscopy, chemical defect etching, scanning electron microscopy, optical profilometry, optical microscopy, and Raman spectroscopy are used to study defect formation and morphology on thin and thick Si0.82Ge0.18 SRBs grown using a C-induced relaxation technique. For subcritical thickness layers, the defect density was found to be similar in both thin and thick SRBs and both structures responded similarly to annealing, indicating good thermal stability of thin SRB technology. The root-mean-square surface roughness of strained Si grown on thin SRBs was ∼50% lower than on similarly grown thick SRBs and conventional step-graded thick SRBs, and was robust during annealing. The impact of strained Si layer thickness on surface morphology is also analyzed. Using detailed filtering techniques, macro- and microroughness are distinguishable. For the first time, we show that exceeding the critical thickness has a greater impact on microroughness than on macroroughness. Whereas macroroughness is similar for sub- and supercritical thickness-strained Si layers, the microroughness is ∼2× larger in supercritical layers than in subcritical thickness layers. Prominent surface defects were detected on supercritical strained Si layers. The defects align with the cross-hatch morphology and double in density following annealing. It is proposed that the defects originate from localized threading dislocations assisted by further strain relaxation in the metastable strained Si layers. This is substantiated through the observation of stacking faults in the strained Si. In contrast, surfaces of subcritical thickness-strained Si layers on thin SRBs are defect-free.
Three-dimensional chemical analysis of tungsten probes by energy dispersive x-ray nanotomography
Authors: Saghi Z. , Xu X. , Peng Y. , Inkson B. , Möbus G.
Published: December 2007

The chemical distribution of oxide layers around functional tungsten nanotips is studied using electron tomography. Three-dimensional element distribution functions are derived for such tips, giving insight into the subsurface chemistry. Energy dispersive x-ray (EDX) spectroscopy is coupled to computed tomography to reconstruct slices across the tip. It is finally shown how the surface reconstruction by geometric tomography from annular dark field scanning transmission electron microscopy images can be combined with EDX tomography reconstructions to reduce backprojection artefacts and improve the sharpness of the surface contours.
The lipodystrophy protein seipin is found at endoplasmic reticulum lipid droplet junctions and is important for droplet morphology
Authors: Szymanski Kimberly M. , Binns Derk , Bartz René , Grishin Nick V. , Li Wei-Ping , Agarwal Anil K. , Garg Abhimanyu , Anderson Richard G. W. , Goodman Joel M.
Published: December 2007

Lipodystrophy is a disorder characterized by a loss of adipose tissue often accompanied by severe hypertriglyceridemia, insulin resistance, diabetes, and fatty liver. It can be inherited or acquired. The most severe inherited form is Berardinelli-Seip Congenital Lipodystrophy Type 2, associated with mutations in the
BSCL2
gene.
BSCL2
encodes seipin, the function of which has been entirely unknown. We now report the identification of yeast
BSCL2
/seipin through a screen to detect genes important for lipid droplet morphology. The absence of yeast seipin results in irregular lipid droplets often clustered alongside proliferated endoplasmic reticulum (ER); giant lipid droplets are also seen. Many small irregular lipid droplets are also apparent in fibroblasts from a BSCL2 patient. Human seipin can functionally replace yeast seipin, but a missense mutation in human seipin that causes lipodystrophy, or corresponding mutations in the yeast gene, render them unable to complement. Yeast seipin is localized in the ER, where it forms puncta. Almost all lipid droplets appear to be on the ER, and seipin is found at these junctions. Therefore, we hypothesize that seipin is important for droplet maintenance and perhaps assembly. In addition to detecting seipin, the screen identified 58 other genes whose deletions cause aberrant lipid droplets, including 2 genes encoding proteins known to activate lipin, a lipodystrophy locus in mice, and 16 other genes that are involved in endosomal–lysosomal trafficking. The genes identified in our screen should be of value in understanding the pathway of lipid droplet biogenesis and maintenance and the cause of some lipodystrophies.
Molecular dynamics simulations suggest a mechanism for translocation of the HIV-1 TAT peptide across lipid membranes
Authors: Herce Henry D. , Garcia Angel E.
Published: December 2007

The recombinant HIV-1 Tat protein contains a small region corresponding to residues
47
YGRKKRRQRR
57
R, which is capable of translocating cargoes of different molecular sizes, such as proteins, DNA, RNA, or drugs, across the cell membrane in an apparently energy-independent manner. The pathway that these peptides follow for entry into the cell has been the subject of strong controversy for the last decade. This peptide is highly basic and hydrophilic. Therefore, a central question that any candidate mechanism has to answer is how this highly hydrophilic peptide is able to cross the hydrophobic barrier imposed by the cell membrane. We propose a mechanism for the spontaneous translocation of the Tat peptides across a lipid membrane. This mechanism involves strong interactions between the Tat peptides and the phosphate groups on both sides of the lipid bilayer, the insertion of charged side chains that nucleate the formation of a transient pore, followed by the translocation of the Tat peptides by diffusing on the pore surface. This mechanism explains how key ingredients, such as the cooperativity among the peptides, the large positive charge, and specifically the arginine amino acids, contribute to the uptake. The proposed mechanism also illustrates the importance of membrane fluctuations. Indeed, mechanisms that involve large fluctuations of the membrane structure, such as transient pores and the insertion of charged amino acid side chains, may be common and perhaps central to the functions of many membrane protein functions.
Embryonic stem cell-derived tissues are immunogenic but their inherent immune privilege promotes the induction of tolerance
Authors: Robertson Nathan J. , Brook Frances A. , Gardner Richard L. , Cobbold Stephen P. , Waldmann Herman , Fairchild Paul J.
Published: December 2007

Although human embryonic stem (ES) cells may one day provide a renewable source of tissues for cell replacement therapy (CRT), histoincompatibility remains a significant barrier to their clinical application. Current estimates suggest that surprisingly few cell lines may be required to facilitate rudimentary tissue matching. Nevertheless, the degree of disparity between donor and recipient that may prove acceptable, and the extent of matching that is therefore required, remain unknown. To address this issue using a mouse model of CRT, we have derived a panel of ES cell lines that differ from CBA/Ca recipients at defined genetic loci. Here, we show that even expression of minor histocompatibility (mH) antigens is sufficient to provoke acute rejection of tissues differentiated from ES cells. Nevertheless, despite their immunogenicityin vivo, transplantation tolerance may be readily established by using minimal host conditioning with nondepleting monoclonal antibodies specific for the T cell coreceptors, CD4 and CD8. This propensity for tolerance could be attributed to the paucity of professional antigen-presenting cells and the expression of transforming growth factor (TGF)-β2. Together, these factors contribute to a state of acquired immune privilege that favors the polarization of infiltrating T cells toward a regulatory phenotype. Although the natural privileged status of ES cell-derived tissues is, therefore, insufficient to overcome even mH barriers, our findings suggest it may be harnessed effectively for the induction of dominant tolerance with minimal therapeutic intervention.
EPLIN mediates linkage of the cadherin–catenin complex to F-actin and stabilizes the circumferential actin belt
Authors: Abe Kentaro , Takeichi Masatoshi
Published: December 2007

The cadherin–catenin complex is the major machinery for cell–cell adhesion in many animal species. This complex in general associates with actin fibers at its cytoplasmic side, organizing the adherens junction (AJ). In epithelial cells, the AJ encircles the cells near their apical surface and forms the “zonula adherens” or “adhesion belt.” The mechanism as to how the cadherin–catenin complex and F-actin cooperate to generate these junctional structures, however, remains unknown. Here, we show that EPLIN (epithelial protein lost in neoplasm; also known as Lima-1), an actin-binding protein, couples with α-catenin and, in turn, links the cadherin–catenin complex to F-actin. Without EPLIN, this linkage was unable to form. When EPLIN had been depleted in epithelial cells, the adhesion belt was disorganized and converted into zipper-like junctions in which actin fibers were radially arranged. However, nonjunctional actin fibers were not particularly affected by EPLIN depletion. As EPLIN is known to have the ability to suppress actin depolymerization, our results suggest that EPLIN functions to link the cadherin–catenin complex to F-actin and simultaneously stabilizes this population of actin fibers, resulting in the establishment of the adhesion belt.