bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Au/TiO2 Nanocomposites by XPS
Authors: Armelao Lidia , Barreca Davide , Bottaro Gregorio , Bovo Antonia , Gasparotto Alberto , Tondello Eugenio
Published: April 2005

Au/TiO 2 nanocomposites were prepared by a hybrid route consisting in the rf sputtering of gold on porous titania xerogels [TiOx(OH)y(OR)z] obtained by means of the sol-gel route. In particular, titania substrates were prepared on silica slides by dip-coating starting from ethanolic solutions of Ti(OPri)4 (OPri=iso-propoxy) and Hacac (2,4-pentanedione). Subsequently, Au depositions were performed on the as-prepared xerogels in Ar plasmas at temperatures as low as 60 °C. The resulting systems were finally annealed in air for 1 h at 200, 400, and 600 °C, with the aim of tailoring gold distribution in the titania matrix. Their structure, composition and morphology were studied by glancing incidence x-ray diffraction (GIXRD), optical absorption spectroscopy, and x-ray photoelectron spectroscopy (XPS). This work is dedicated to the XPS characterization of a representative Au/TiO2 sample analyzed after annealing in air at 600 °C. In particular, detailed scans for the Au 4f, Ti 2p, O ls, and C 1s regions and related data are presented and discussed. The obtained results point to the presence of metallic gold and TiO2, with carbon contamination limited only to the outermost layers.
Beam Damage of Poly(vinyl chloride) [PVC] as observed by X-ray Photoelectron Spectroscopy at 143 K, 303 K, and 373 K
Authors: Engelhard Mark , Baer Don , Lea Scott
Published: April 2005

XPS spectra were obtained from PVC for ∼240 min in order to measure the effects of x-ray damage. The damage rates were measured with the sample maintained at three different temperatures, 143 K, 303 K, and 373 K. The data demonstrate that temperature does alter the rate of damage accumulation and may be a consideration in mounting of samples and in understanding how to minimize the damage process.
X-Ray Beam Damage of Nafion (perfluorosulfonate ionomer)
Authors: Militello Maria C. , Gaarenstroom Stephen W.
Published: April 2005

XPS spectra were obtained from a Nafion (perfluorosulfonate ionomer) membrane over a period of 15 h in order to measure the effects of x-ray beam exposure on the Nafion surface. This polymer has an aliphatic fluorocarbon backbone, fluoroalkoxy side chains, and sulfonic acid endgroups. Under the conditions used, 10% each of the S 2p, perfluoroether O 1s, and F 1s intensities are lost in 23, 98, and 656 min, respectively. The data also show the sulfonate O 1s loses intensity faster than the perfluoroether O 1s. This suggests that the perfluorosulfonate side chain, particularly the sulfonate endgroup, is susceptible to x-ray damage. In contrast, the perfluoroalkyl backbone of the Nafion is relatively immune from volatilization, although some bond-breaking and rearrangement may be occurring.
Chemical State of Semiconducting SmS Thin Film by XPS Measurement
Authors: Mori Yukimasa , Tanemura Sakae
Published: April 2005

Semiconducting SmS thin film was fabricated on a-SiO2/Si substrate at room temperature by dual targets (dc for metal Sm and rf for pressed powdered chalcogenide Sm2S3) magnetron sputtering of concurrent power control. X-ray photoelectron spectroscopy was applied to investigate the chemical state of semiconducting SmS phase.
Au/SiO2 Nanosystems by XPS
Authors: Barreca Davide , Bovo Antonia , Gasparotto Alberto , Tondello Eugenio
Published: April 2005

Au/SiO2 nanocomposites were prepared by rf-sputtering of gold on amorphous silica substrates. Deposition experiments were carried out in Ar plasmas at temperatures as low as 60 °C. Particular attention was devoted to the combined influence of the applied rf power and total pressure on the chemico-physical properties of the final nanosystems. In particular, low pressures (<0.2 mbar) and high rf powers (>20 W) resulted in a higher sputtering yield, allowing the deposition of continuous gold films on silica. Conversely, decreased sputtering yields (at higher pressures and lower powers) enabled the preparation of discontinuous Au/SiO2 nanosystems. A thorough investigation of the structure-properties relationships was attained by means of a multi-technique characterization. In particular, laser reflection interferometry (LRI) was employed for an in situ monitoring of growth processes, while glancing-incidence x-ray diffraction (GIXRD) and transmission electron microscopy (TEM) provided valuable information on the system nanostructure. Moreover, x-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, and atomic force microscopy (AFM) were used to investigate the chemical composition, optical properties, and surface morphology, respectively. This study is dedicated to an XPS investigation of the principal core levels (Au, Si, O) of Au/SiO2 nanosystems. In particular, detailed scans for the Au 4f, Si 2s, O 1s, and C 1s regions and related data for a gold film on silica and a discontinuous Au/SiO2 specimen are presented and discussed.
Introduction to Surface Science Spectra data on electron and x-ray damage: Sample degradation during XPS and AES measurements
Authors: Baer D. R. , Engelhard M. H. , Lea A. S.
Published: April 2005

The types of damage to sample surfaces that can occur during x-ray or electron irradiation used during Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) are summarized. The material and instrumental dependence of the rate and nature of damage formation or sample degradation are highlighted. Particular note is made of an enhanced susceptibility of thin films to damage. A simple method to enable comparison of published damage rates to what may be observed in a specific system is described and discussed in relation to data included in this journal volume. Strategies for detecting and minimizing damage are presented.
A Comparison of Plasma Enhanced Chemical Vapor Deposited and Thermally Deposited Hafnium Oxide and Hafnium Silicate Thin Film Using XPS
Authors: Bhandari Harish B. , Klein Tonya M.
Published: April 2005

Hafnium oxide and hafnium silicate films, 20 to 55 nm thick, were grown by chemical vapor deposition using hafnium(IV) tert-butoxide, O2 and 2% SiH4 in He on a 0.005–0.03 Ω cm, n-type Si<100> substrate doped with antimony. HfO2 films were deposited thermally at a substrate temperature of 425 °C, while hafnium silicate films were deposited both thermally and using remote plasma enhanced process, at the same substrate temperature. X-ray photoelectron spectroscopy survey spectra with 100 eV pass energy and high-resolution spectra for Hf 4f, Si 2p, O 1s, and C 1s core level transitions with 25 eV pass energy were obtained at 90° take off. The relative binding energies of these transitions corresponded to hafnium oxide and hafnium silicate chemical states. These spectra are useful for understanding the peak positions of hafnium, silicon and oxygen plasma enhanced chemical vapor deposited films.
LaCoO3 Nanosystems by a Hybrid CVD/Sol-Gel Route: An XPS Investigation
Authors: Armelao Lidia , Barreca Davide , Bottaro Gregorio , Gasparotto Alberto , Maragno Cinzia , Tondello Eugenio
Published: April 2005

Lanthanum cobaltite (LaCoO3) nanosystems were synthesised by an innovative combined use of the chemical vapor deposition (CVD) and sol-gel (SG) routes. In particular, a lanthanum oxyfluoride based layer was deposited by CVD on CoOx(OH)y SG substrates (xerogel). The subsequent thermal treatment in air, between 400 and 900 °C, was aimed at promoting the solid-state reaction between La-O and Co-O based layers, resulting in the complete formation of LaCoO3. The obtained samples were analyzed by glancing incidence x-ray diffraction (GIXRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), x-ray photoelectron (XPS) and x-ray excited Auger electron (XE-AES) spectroscopies, for a detailed determination of their microstructure, chemical composition, and surface morphology. The present work focuses on the XPS and XE-AES analysis of a selected lanthanum cobaltite (LaCoO3) thin film, annealed at 700 °C for 2 h. Besides the wide scan spectrum, detailed spectra for the La 3d, Co 2p, Co LMM, O 1s, and C 1s regions and related data are presented and discussed. Both the experimental Co 2p3/2-Co 2p1/2 energy splitting and the evaluation of the Auger parameter point out to the formation of single-phase lanthanum cobaltite thin film. The presence of fluorine was never detected, indicating its elimination after thermal treatment. Moreover, carbon contamination was merely limited to the outermost sample layers.
HfO2-doped Silica Thin Films by XPS
Authors: Armelao Lidia , Gross Silvia , Zattin Andrea , Tondello Eugenio
Published: April 2005

The development of molecularly homogeneous multicomponent oxide based glasses is a key concern in many fields of materials chemistry. Oxide nanoparticles covalently embedded in dielectric matrices represent a class of nanocomposite systems endowed with outstanding optical, mechanical, electronic, and thermal properties. In this study, silica thin films embedding HfO2 were prepared by dip-coating on silica glass via a modified sol-gel processing. This powerful synthetic method, mainly based on the hydrolysis and condensation of metal alkoxides, provides a reliable route to oxide materials which can be processed into a variety of different forms (thin films, powders, monoliths, etc.). The novel synthetic route here presented is based on the copolymerization of the organically modified oxohafnium clusters (Hf4O2(OMc)12 with OMc = OC(O)–C(CH3)=CH2)) with (methacryloxymethyl)triethoxysilane (MAMTES). The crystalline clusters, which are the precursors for the corresponding metal oxide (MO2) were prepared via the sol-gel route by reaction of hafnium butoxide with methacrylic acid. The copolymerization of the cluster with previously prehydrolysed methacrylate-functionalized siloxane, allows the anchoring of the oxocluster to the forming silica network. Thin films were prepared starting from a THF (tetrahydrofurane) solution with molar ratios Hf4O2(OMc)12:MAMTES of 1:44 and a MAMTES:THF molar ratio of 1:5, which was stirred at room temperature for 8 h. After deposition, the film was annealed 3 h at 800 °C in air to promote the decomposition of the hafnium oxocluster to give the corresponding HfO2. The obtained HfO2-SiO2 film resulted transparent and homogeneous. The composition of the film was investigated by secondary ionization mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS), which were used also to investigate the in-depth distribution. The depth profiles evidenced a very homogenous distribution of hafnium within the whole silica film and a sharp film-substrate interface. TEM micrographs revealed the formation of isolated nanocrystalline particles, thus ruling out the formation of a HfO2–SiO2 mixture. Concerning the herewith reported XPS analyses, the main XPS core-levels were analyzed for the sample annealed 3 h at 800 °C. The formation of hafnium oxide was evidenced. Furthermore, a very homogeneous distribution of the guest oxide in the host matrix was evidenced, in agreement with SIMS data.
TLR11 Activation of Dendritic Cells by a Protozoan Profilin-Like Protein
Authors: Yarovinsky Felix , Zhang Dekai , Andersen John F. , Bannenberg Gerard L. , Serhan Charles N. , Hayden Matthew S. , Hieny Sara , Sutterwala Fayyaz S. , Flavell Richard A. , Ghosh Sankar , Sher Alan
Published: April 2005

Mammalian Toll-like receptors (TLRs) play an important role in the innate recognition of pathogens by dendritic cells (DCs). Although TLRs are clearly involved in the detection of bacteria and viruses, relatively little is known about their function in the innate response to eukaryotic microorganisms. Here we identify a profilin-like molecule from the protozoan parasite
Toxoplasma gondii
that generates a potent interleukin-12 (IL-12) response in murine DCs that is dependent on myeloid differentiation factor 88.
T. gondii
profilin activates DCs through TLR11 and is the first chemically defined ligand for this TLR. Moreover, TLR11 is required in vivo for parasite-induced IL-12 production and optimal resistance to infection, thereby establishing a role for the receptor in host recognition of protozoan pathogens.
The book of life
Authors: Copland P
Published: April 2005

It has recently been suggested that the practice of bioethics in the area of biology and genetics has been hampered by the lack of an accurate and appropriate metaphor. Beginning with previous metaphors that have compared the genome with a static blueprint or “book of life”, I develop a dynamic metaphor that is compatible with our present understanding of the role of genetics in biology. The resulting metaphor is not only an accurate representation of current biology but of particular use to bioethicists and non-biologists in general.
Methodological quality and reporting of ethical requirements in phase III cancer trials
Authors: Tuech J J , Pessaux P , Moutel G , Thoma V , Schraub S , Herve C
Published: April 2005

Background:The approval of a research ethics committee (REC) and obtaining informed consent from patients (ICP) could be considered the main issues in the ethics of research with human beings. The aim of this study was to assess both methodological quality and ethical quality, and also to assess the relationship between these two qualities in randomised phase III cancer trials.

Method:Methodological quality (Jadad score) and ethical quality (Berdeu score) were assessed for all randomised controlled trials (RCTs) published in 10 international journals between 1999 and 2001 (n =  231).

Results:The mean Jadad score was 9.86 ± 1.117. The methodological quality was poor in 75 RCTs (Jadad score <9). The mean Berdeu score was 0.42 ± 0.133. The mean ethical quality score for poor methodological quality RCTs (n =  75) was 0.39 ± 0.133; it was 0.43 ± 0.133 for good (n =  156) methodological quality RCTs (p  =  0.07). There was improvement in ethical quality according to the year of commencement of the trials (p < 0.001). There was no correlation between methodological quality and the number of participating patients (R2  =  0.003, p  =  0.78), between ethical quality and the number of participating patients (R2  =  0.003, p  =  0.76 ), or between ethical quality and methodological quality (R2  =  0.012, p  =  0.1). ICP and REC approval were not obtained for 21 and 77 trials respectively.

Conclusion:The association between methodological quality and the reporting of ethical requirements probably reflects the respect shown for patients during the whole research process. These results suggest that closer attention to the conduct of clinical research, as well as the reporting of its ethical aspects, is needed.
Capabilities and health
Authors: Anand P
Published: April 2005

Sen’s capabilities approach offers a radical generalisation of the conventional approach to welfare economics. It has been highly influential in development and many researchers are now beginning to explore its implications for health care. This paper contributes to the emerging debate by discussing two examples of such applications: first, at the individual decision making level, namely the right to die, and second, at the social choice level. For the first application, which draws on Nussbaum’s list of capabilities, it is argued that many capabilities are ambiguously or indirectly related to the right to die, but the ability to form a concept of the good life and plan one’s own life provides a direct justification for such a right. In the second application, the focus is specifically on healthcare rationing and it is argued that, although not committed to age based rationing, the capabilities approach provides a more natural justification of age related access to health care than the fair innings argument, which is often used to justify the alleged ageism inherent in quality adjusted life years (QALY) maximisation.
The fable of the dragon tyrant
Authors: Bostrom N
Published: April 2005

This paper recounts the tale of a most vicious dragon that ate thousands of people every day, and of the actions that the king, the people, and an assembly of dragonologists took with respect thereof.
Use of conformationally restricted pyridinium α-D-N-acetylneuraminides to probe specificity in bacterial and viral sialidases
Authors: Watson Jacqueline N , Knoll Tara L , Chen Johnny H , Chou Doug T.H , Borgford Thor J , Bennet Andrew J
Published: April 2005

Investigations into subtle changes in the catalytic activity of sialidases have been performed using enzymes from several different origins, and their results have been compared. This work highlights the potential pitfalls encountered when extending conclusions derived from mechanistic studies on a single enzyme even to those with high-sequence homology. Specifically, a panel of 5 pyridinium N-acetylneuraminides were used as substrates in a study that revealed subtle differences in the catalytic mechanisms used by 4 different sialidase enzymes. The lowest reactivity towards the artificial (pyridinium) substrates was displayed by the Newcastle disease virus hemagglutinin-neuraminidase. Moreover, in reactions involving aryl N-acetylneuraminides, the activity of the Newcastle enzyme was competitively inhibited by the 3,4-dihydro-2H-pyrano[3,2-c]pyridinium compound with a Ki = 58 µmol/L. Alternatively, the 3 bacterial enzymes tested, from Salmonella typhimurium, Clostridium perfringens, and Vibrio cholerae, were catalytically active against all members of the panel of substrates. Based on the observed effect of leaving-group ability, it is proposed that the rate-determining step for kcat(and likely for kcat/Kmas well) with each bacterial enzyme is as follows: sialylation, which is concerted with conformational change for V. cholerae; and conformational change for S. typhimurium and C. perfringens.Key words: sialidases, neuraminidases, sialic acids, glycosidase, mechanism.
Differential effects of selenite and selenate on human melanocytes, keratinocytes, and melanoma cells
Authors: Bandura Laura , Drukala Justyna , Wolnicka-Glubisz Agnieszka , Björnstedt Mikael , Korohoda Wlodzimierz
Published: April 2005

Among the substances that attracted the attention of oncologists in recent years are selenium-containing compounds, both inorganic and organic. Several epidemiological studies have shown an inverse correlation between selenium intake and cancer incidence. In the experiments reported here, we compared the effects of 2 inorganic selenium- containing salts that differed in the level of selenium oxidation, selenite IV and selenate VI. We tested the effects of these 2 compounds on cell survival and growth, cell cycle processing, cell morphology, cytoskeleton, and lipid peroxidation in 3 human skin cell types: normal keratinocytes, melanocytes, and human melanoma cell line HTB140. The different effects of selenite and selenate on the viability, growth, and morphology of normal cells and tumor cells are reported and provide a base for future research and treatment of some neoplastic diseases. The attention is paid to cell apoptosis induced by selenite and not by selenate, and the effects of tested substances on thioredoxin reductase system are postulated.Key words: selenium, cell viability and growth, apoptosis, lipid oxidation, thioredixin reductase system, human skin cells, human melanoma.
Zinc-sensitive genes as potential new target genes of the metal transcription factor-1 (MTF-1)
Authors: Kindermann Birgit , Döring Frank , Budczies Jan , Daniel Hannelore
Published: April 2005

Zinc is an essential trace element that serves as a structural constituent of a large number of transcription factors, which explains its pivotal role in the control of gene expression. Previous studies investigating the effect of zinc deficiency and zinc supplementation on gene expression in the human adenocarcinoma cell line HT-29 led to the identification of a considerable number of genes responding to alterations in cellular zinc status with changes in steady state mRNA levels. For 9 of 20 genes from these previous screenings that were studied in more detail, mRNA steady state levels responded to both high and low media zinc concentrations. As they are primarily zinc-dependent, we assessed whether these genes are controlled by the zinc-finger metal transcription factor MTF-1. To test this hypothesis we generated a doxycyline-inducible Tet-On HT-29 cell line overexpressing MTF-1. Using this conditional expression system, we present evidence that Kruppel-like factor 4 (klf4), hepatitis A virus cellular receptor 1 (hhav), and complement factor B (cfbp) are 3 potential new target genes of MTF-1. To support this, we used in silico analysis to screen for metal-responsive elements (MREs) within promotors of zinc-sensitive genes. We conclude that zinc responsiveness of klf4, hhav, and cfbp in HT-29 cells is mediated at least in part by MTF-1.Key words: zinc-sensitive genes, target genes, MTF-1, HT-29 cells, metal-response element.
Optimal conditions and specific characteristics ofVentexo– DNA polymerase in ligation-mediated polymerase chain reaction protocols
Authors: Vigneault François , Drouin Régen
Published: April 2005

An optimized procedure for the ligation-mediated polymerase chain reaction (PCR) technique using Thermococcus litoralis exo– DNA polymerase (Vent exo–) was developed. The optimal dosage of Vent exo– at the primer extension and PCR amplification steps as well as the optimal DNA quantity to use were established. We showed that Vent exo– can efficiently create the blunt-ended termini required for subsequent linker ligation. Vent exo– proves to be more efficient than Pyrococcus furiosus exo– (Pfu exo–) for this task. Vent exo– resolves highly GC-rich sequence substantially better than Thermus aquaticus DNA polymerase (Taq) and with a similar efficiency as Pfu exo–. The DNA/DNA polymerase activity ratio is significantly higher for Vent exo– than for Pfu exo–, which is reflected by the sensibility of Vent exo– in efficiently amplifying genomic DNA. Furthermore, the range of efficiency of Vent exo– demonstrates the importance of conducting evaluative testing to identify the optimal dosage of use of this polymerase to obtain successful PCR amplification. Optimal MgSO4concentrations to use with Vent exo– were established. Our results show that Vent exo– DNA polymerase produces bands of uniform and strong intensity and can efficiently be used for the analysis of DNA in living cells by ligation-mediated PCR.Key words: Vent exo– DNA polymerase, Pfu exo– DNA polymerase, DNA sequence context, ligation-mediated polymerase chain reaction (PCR), PCR buffer.
Removal of the nitro and phenyl groups from NPPB decreases its inhibitory effect on cytoplasmic streaming in the alga Nitella hookeri
Authors: Graichen Florian , Giles Kristian R , Abell Andrew , Garrill Ashley
Published: April 2005

Structural analogues of the arylaminobenzoate 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), prepared using a simple reductive amination sequence, were tested for their effects on cytoplasmic streaming rates in the alga Nitella hookeri. Cytoplasmic streaming was sensitive to NPPB, with an IC50 value of 24 µmol/L. Removal of the nitro group from the benzoate ring decreased the IC50 to 455 µmol/L. The introduction of an extra carbon or double bond into the aliphatic chain had no effect on activity. Loss of the phenyl group decreased potency, with an IC50 of 6.4 mmol/L. These data are the first documenting the relative inhibitory effects of structural changes to arylaminobenzoates in algae. Patch-clamp data and the effects of tetrapentyl ammonium chloride on streaming suggest that the nitro and phenyl groups may act by inhibiting both K+ and Cl– channels. This is likely, through changes in the membrane potential, to affect Ca2+ fluxes and action potentials, thereby slowing cytoplasmic streaming.Key words: arylaminobenzoate, NPPB, cytoplasmic streaming, characian algae, ion channel blocker, reductive amination.
Targeted modification of the complete chicken lysozyme gene by poxvirus-mediated recombination
Authors: Losos Jan K , Evans David H , Gibbins Ann M. Verrinder
Published: April 2005

We have developed a novel ex vivo system for the rapid one-step targeted modification of large eucaryotic DNA sequences. The highly recombinant environment resulting from infection of rabbit cornea cells with the Shope fibroma virus was exploited to mediate precise modifications of the complete chicken lysozyme gene domain (21.5 kb). Homologous recombination was designed to occur between target DNA (containing the complete lysozyme gene domain) maintained in a λ bacteriophage vector and modified targeting DNA maintained in a plasmid. The targeting plasmids were designed to transfer exogenous sequences (for example, β-galactosidase α-complement, green fluorescent protein, and hydrophobic tail coding sequences) to specific sites within the lysozyme gene domain. Cotransfection of the target phage and a targeting plasmid into Shope fibroma virus infected cells resulted in the poxvirus-mediated transfer of the modified sequences from plasmid to phage. Phage DNA (recombinant and nonrecombinant) was then harvested from the total cellular DNA by packaging into λ phage particles and correct recombinants were identified. Four different gene-targeting pairings were carried out, and from 3% to 11% of the recovered phages were recombinant. Using this poxvirus-mediated targeting system, four different regions of the chicken lysozyme gene domain have been modified precisely by our research group overall with a variety of inserts (6–971 bp), deletions (584–3000 bp), and replacements. We have never failed to obtain the desired recombinant. Poxvirus-mediated recombination thus constitutes a routine, rapid, and remarkably efficient genetic engineering system for the precise modification of large eucaryotic gene domains when compared with traditional practices.Key words: chicken lysozyme, gene targeting, homologous recombination, poxvirus, avian bioreactor.
Phaseococcin, an antifungal protein with antiproliferative and anti-HIV-1 reverse transcriptase activities from small scarlet runner beans
Authors: Ngai Patrick H.K , Ng T B
Published: April 2005

From the seeds of small scarlet runner beans (Phaseolus coccineus 'Minor'), an antifungal protein with an N-terminal sequence homologous to those of defensins was isolated. The antifungal protein bound to Affi-gel blue gel and Mono S but it did not bind to DEAE-cellulose. It was further purified by gel filtration on a Superdex peptide column. It exhibited a molecular mass of 5422 Da as determined by mass spectrometry. The protein, designated as phaseococcin, suppressed mycelial growth in a number of fungi including Botrytis cinerea, Coprinus comatus, Fusarium oxysporum, Mycosphaerella arachidicola, Physalospora piricola, and Rhizoctonia solani. It also inhibited proliferation in several Bacillus species and the leukemia cell lines HL60 and L1210 and curtailed the activity of HIV-1 reverse transcriptase. It did not affect proliferation of mouse splenocytes and neither did it inhibit protein synthesis in a cell-free rabbit reticulocyte lysate system.Key words: antifungal proteins, runner beans, antiproliferative.
STABILITY OF PHOTOINDUCED SUPERCONDUCTING STATES IN STRONGLY CORRELATED TWO-DIMENSIONAL ELECTRON SYSTEMS
Authors: GOMI HIROKI , UEDA TOSHIHIRO , TAKAHASHI AKIRA , AIHARA MASAKI
Published: April 2005

We theoretically investigate the properties of multiphoton excited states in strongly correlated two-dimensional electron systems at half-filling using the extended Hubbard model in the strong correlation case. We find that the photoinduced d-wave superconducting states are stable against the nearest neighbor Coulomb interaction within the realistic Coulomb parameters.
NOVEL VORTEX STRIPE PHASE UNDER STRONG MAGNETIC FIELD IN HIGH TEMPERATURE SUPERCONDUCTORS
Authors: CHEN YAN , WANG Z. D. , TING C. S.
Published: April 2005

The nature of vortex structure in the mixed state of high-temperature superconductors (HTS) is investigated by solving the Bogoliubov-de Gennes equations with consideration of competition between antiferromagnetic (AF) and d-wave superconductivity (DSC) orders. By varying the applied magnetic field and temperature, the geometry of vortex structure can take two different forms: conventional vortex lattice (triangular or square), or vortex stripe phases where all the order parameters including spin density wave, charge density wave and superconducting order exhibit stripe-like behavior. This novel vortex stripe phases may show up at low temperature and adjacent to upper critical field H c2 Phase diagram of temperature dependence of H c2 will be presented. Our results may shed light on the understanding of the low-temperature H c2 anomalies in some HTS. New experiments are proposed to test our predictions.
ROBUST STATISTICAL MECHANISM FOR PHONON-DRIVEN HIGH-Tc SUPERCONDUCTIVITY
Authors: de LLANO M. , SEVILLA F. J. , SOLÍS M. A. , VALENCIA J. J.
Published: April 2005

Though commonly unrecognized, a superconducting BCS condensate consists of equal numbers of two-electron (2e) and two-hole (2h) Cooper pairs (CPs). A new complete (in the sense that 2h-CPs are not ignored) boson-fermion statistical ternary gas model, however, is able to depart from this perfect 2e-/2h-CP symmetry. It yields robustly higher Tc's without abandoning electron-phonon dynamics, and reduces to all the known statistical theories of superconductors, including the BCS-Bose "crossover" picture—but goes considerably beyond it.
THE DISCREPANCY BETWEEN MUON SPECTROSCOPY AND SCANNING TUNNELING MICROSCOPY AND PHOTOEMISSION: YBa2Cu3O7 AND Bi2Sr2CaCu2O8
Authors: DOW JOHN D. , HARSHMAN DALE R.
Published: April 2005

Muon spectroscopy of YBa 2 Cu 3 O 7 and Bi 2 Sr 2 CaCu 2 O 8 produces strong evidence that both materials are s-wave superconductors, while scanning tunneling microscopy (STM) and photoemission data seem to indicate that Bi 2 Sr 2 CaCu 2 O 8 in particular has d-wave character. The resolution of this apparent discrepancy is that the CuO 2 planes (which are responsible for the d-wave character reported by STM and photoemission) do not superconduct and are different from the superconducting BaO or SrO layers sensed by muons.
DISTINCTIVE FEATURES OF NOVEL SUPERCONDUCTING TRANSITIONS IN UNDERDOPED AND OVERDOPED HIGH-Tc CUPRATES
Authors: DZHUMANOV S. , FAN J. D.
Published: April 2005

It is argued that the new theory that combines the precursor BCS-like non-superconducting (SC) pairing and the Cooper-pair condensation into a superfluid Bose-liquid state is more plausible than the standard SC fluctuation approach in describing the distinctive features of the underdoped and overdoped high-Tc cuprates. We show that the scenarios for high-Tc superconductivity in these materials are quite different on the character of the Cooper-pair formation and SC phase transitions.
UNUSUAL c-AXIS CHARGE TRANSPORT IN THE ELECTRON DOPED COBALTATE
Authors: LIANG YING , LIU BIN , FENG SHIPING
Published: April 2005

The c-axis charge transport of the electron doped cobaltate is investigated within the t-J model by considering the incoherent interlayer hopping. It is shown that the c-axis charge transport of the electron doped cobaltate is essentially determined by the scattering from the in-plane fluctuation. The c-axis conductivity spectrum shows a low-energy peak and the unusual broad midinfrared band, which are qualitatively consistent with these of the doped square lattice antiferromagnet.
THE SOLITARY WAVE MODEL OF SUPERFLUIDITY
Authors: PENG KUANGDING
Published: April 2005

We propose the solitary wave model of superfluidity. According to harmonic oscillator model of quasi-lattice of liquid, it is proven that superfluid domains (SD) exist in He liquid, in which the resistanceless motion of liquid molecules (LM) can be carry out. At temperature lower than T c, all SD connect with each other and superflow in whole liquid takes place. Applying Toda's potential, under continuous conditions, we obtain the motion equation of LM, and its exact solution. Substituting these results into Schrödinger equation of LM, we can prove the existence of solitary waves of LM and the non-linear Schrödinger equation of LM. The motion of solitons of LM leads to a superflow. On the basis of coherent condition of wave of LM, we derive the formula of transition temperature Tc of superfluidity. From the formula, the relation of the onset temperature Tc of superflow on inert layers is explained.
CRUCIAL ROLE OF THE COULOMB INTERACTION IN HTSC MECHANISM
Authors: PASHITSKII E. A. , PENTEGOV V. I.
Published: April 2005

We present results of numerical calculations emphasizing the central role of the Coulomb interaction in the mechanism of d-wave Cooper pairing in layered cuprate metal-oxides. We demonstrate that many-particle Coulomb correlation described by the Coulomb vertex function Γ substantially enhances the effective electron-electron attraction in the d-wave Cooper-pairing channel in these compounds. Such a "Coulomb" mechanism of anisotropic Cooper pairing may provide high superconducting transition critical temperatures (Tc⩾100 K ) for optimum-doped cuprates.
PHASE DIAGRAM OF UNCONVENTIONAL SUPERCONDUCTORS ON TRIANGULAR LATTICES
Authors: CHEN HONG-WEI , HAN QIANG , WANG Z. D.
Published: April 2005

The superconducting system in the two dimensional triangular lattice is investigated by the mean-field treatment of a simple effective model. We calculate the phase diagram of this kind of superconductor for various pairing symmetries and interactions as well as electron occupancies. It is found that the px+ipy-, d+id′-, and f- wave superconducting states are stabilized in different doping regions, and there exist superconducting phase transitions by varying the carrier concentration in the system. The relevance of our results to the recently discovered superconductor, Na x CoO 2·y H 2 O , is briefly discussed.
OPTICAL CONDUCTIVITY OF OXIDES
Authors: GERVAIS FRANCOIS , TA PHUOC VINH , POIROT NATHALIE , COQUELET CEDRIC , GRUENER GISELE , LOBO RICARDO P. S. M.
Published: April 2005

Optical conductivity spectra of conducting oxides including high-TC cuprates - compared to non-superconducting nickelates in particular - deduced from infrared reflectivity spectroscopy in polarized light and their doping and temperature dependence, are discussed with emphasis on the signatures of intrinsic inhomogeneities of charge carrier concentration. The model of disordered metal is shown to be compatible with the general loss of spectral weight in the optical conductivity upon decreasing frequency, instead of a maximum conductivity at zero frequency as found within a Drude description. In high-TC multilayer cuprates, the discussion focuses upon the c-axis response and the inhomogeneity of the electronic concentration related to the conducting planes alternating with insulating sheets. The onset of stripes that are intrinsic inhomogeneities of the charge carrier distribution is discussed in the example of nickelates.
FIELD-INDUCED AND IMPURITY-INDUCED MAGNETIC ORDER IN La2-xSrxCuO4 STUDIED BY THE THERMAL CONDUCTIVITY AND μSR
Authors: KOIKE Y. , YAMAZAKI M. , KAWAMATA T. , TAKAHASHI N. , OKI N. , YAIRI S. , ADACHI T. , NOJI T. , KUDO K. , NISHIZAKI T. , KOBAYASHI N. , WATANABE I. , NAGAMINE K.
Published: April 2005

Our recent experimental works on the field-induced and impurity-induced magnetic order in La 2-x Sr x CuO 4 are reviewed. The muon-spin-relaxation (μSR) measurements of La 2-x Sr x Cu 1-y M y O 4 ( M = Zn , Ni ) have revealed that both Zn and Ni impurities develop the magnetic order around x=0.115, though the effect of Zn on the development of the magnetic order is more marked than that of Ni . The field-induced magnetic order around x=0.115 pointed out from the neutron scattering experiments has also been investigated by the thermal conductivity measurements in magnetic fields. Marked suppression of the thermal conductivity by the application of magnetic fields parallel to the c-axis has been observed in x=0.10 and x=0.13, which appears to be in good correspondence to the development of the magnetic order. In conclusion, not only impurities but also vortex cores in the CuO 2 plane seem to operate to pin the dynamical stripes of spins and holes, leading to the development of the magnetic order.
MAGNETIC NESTING AND COEXISTENCE OF FERROMAGNETISM AND SUPERCONDUCTIVITY
Authors: ELESIN V. F. , KAPAEV V. V. , KOPAEV Yu. V.
Published: April 2005

If the condition for magnetic nesting is fulfilled for the electron dispersion law with spin σ along a certain preferential direction n, ferromagnetism and the inhomogeneous superconducting state can coexist up to very high magnetization I. This fact was used to explain the coexistence of ferromagnetism and superconductivity for layered cuprates of the RuSr 2 GdCu 2 O 8 type, which possess a finite, though rather high critical magnetization, because the conditions for magnetic nesting are fulfilled only approximately.
SEPARATED SPIN AND CHARGE DEGREES OF FREEDOM IN HIGH-Tc SUPERCONDUCTORS
Authors: KRUSIN-ELBAUM L. , SHIBAUCHI T. , BLATTER G.
Published: April 2005

Recent Nernst and interlayer transport experiments in Bi 2 Sr 2 CaCu 2 O 8+y (BSCCO) high temperature superconductors report hugely different limiting magnetic fields. We demonstrate that both fields convert to the same pseudogap energy scale T* upon transformation as orbital and Zeeman critical fields, respectively. We suggest a consistent interpretation of this finding based on separation of spin and charge degrees of freedom residing in different regions of a truncated Fermi surface.
SPIN DEPENDENCE OF PAIR TUNNELING PROPERTIES OF Bi2Sr2CaCu2O8+x INTRINSIC JOSEPHSON JUNCTIONS
Authors: BANG DO , LEE HU-JONG , BAE MYUNG-HO , PARK WANG-HYUN
Published: April 2005

Detailed tunneling characteristics of a stack of intrinsic Josephson junctions in a Bi 2 Sr 2 CaCu 2 O 8+x single crystal were obtained both in spin-degenerate and spin-polarized bias configurations. Injection of the spin-polarized quasiparticles effectively weakened the in-plane superconducting strength and the interlayer Jospehson coupling. The superconducting gap and the Josephson critical current of the stack were, in general, further suppressed by an external field applied in parallel with the c-axis direction. Study of the spin-dependent tunneling characteristics may provide valuable information on clarifying the mechanism of high-Tc superconductivity as well as the interlayer phase fluctuation induced by the "pancake vortices" on CuO 2 layers.
ANISOTROPY OF THE ELECTRON-DOPED INFINITE-LAYER SUPERCONDUCTOR Sr0.9La0.1CuO2
Authors: KIM HEON-JUNG , PARK MIN-SEOK , JUNG C. U. , LEE SUNG-IK , KIM MUN-SEOG
Published: April 2005

Anisotropy of a c-axis aligned Sr 0.9 La 0.1 CuO 2 infinite-layer superconductor was studied by measuring the magnetization in different temperature (M(T)) and angle (M(θ)). The M(θ) and the critical temperature as a function of the angle (Tc2(θ)) deduced from M(T) was well described by the anisotropic Ginzburg-Landua theory with a moderate anisotropy value γ≈9. This low value, which is comparable to that of YBa 2 Cu 3 O 7-δ implied strong interlayer coupling between CuO 2 planes. In this compound, the strong interlayer coupling was thought to solely result from the crystal structure without charge reservoir blocks.
TWO-DIMENSIONAL QUARTER-FILLED EXTENDED HUBBARD MODEL AT STRONG COUPLING
Authors: LEE W. F. , LIN H. Q.
Published: April 2005

In this paper, we generalized the perturbation approach to study the quasi-two-dimension extended Hubbard model. This model is characterizing by intra-chain electron hopping t, on-site Column interaction U, nearest-neighbor interaction V, and inter-chain electron hopping t′ and nearest-neighbor interaction V′. An effective Hamiltonian up to sixth-order in t/U, t/V, t/V′, t′/U, t′/V and t′/V′ expansion was obtained and the spin-spin correlation functions were calculated. We presented results for t=t′, V=V′.
EFFECT OF INCREASING Cu CONTENT ON SUPERCONDUCTIVE TRANSITION OF Bi-BASED CUPRATE SUPERCONDUCTORS
Authors: LIN DEHUA , HU BINGQUAN , ZHANG JIE , LI SONGLIN , ZHONG CHAORONG , YANG DEZHI , LI LONGJIAN
Published: April 2005

For Bi -based cuprate superconductors, increasing its Cu content by heat-treatment is probably a beneficial way to its superconducting transition. In the paper, the corresponding methods and procedures of the experiment were proposed, and the theoretical analysis and explanation of the experimental results were conducted. The method of increasing Cu content by heat-treatment is innovative.
FexCu1-xBa2YCu2O7+y SUPERCONDUCTORS SYNTHESIZED BY HIGH PRESSURE
Authors: LIU Y. H. , CHE G. C. , LI K. Q. , ZHAO Z. X. , KOU Z. Q. , DI N. L. , CHENG Z. H.
Published: April 2005

Systematic studies of x-ray diffraction(XRD), superconductivity and Mössbauer effect on Fe x Cu 1-x Ba 2 YCu 2 O 7+y ( x =0.00~0.70) superconductors synthesized by high pressure (HP) were summarized. All the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples (synthesized by ambient pressure). The HP-samples have higher oxygen content than the AM-samples. Moreover, for the HP-sample with x =0.5, all of the Fe located in the CuO x chains have fivefold-oxygen coordination.
NONEQUILIBRIUM CHARACTERISTICS OF INTRINSIC Bi2.3Pb0.1Sr2CaCu2O8+y JOSEPHSON JUNCTIONS
Authors: NIE Y. , WANG Z. H. , QIU L. , GAO J.
Published: April 2005

Using photolithography and Ar ion milling, we fabricate small mesas on top of the Bi 2.3 Pb 0.1 Sr 2 CaCu 2 O 8+y single crystals to study the inherent tunnelling property of intrinsic Josephson junctions. The I-V characteristics of the mesas show a typical multiple branches with large hysteresis. The return current I r depends on the N-th branch. The relation of I r and N follows I r= I 0* N m, where -1< m <0 might be related to the Coulomb blockade effect. The McCumber parameter βc of the samples is also investigated.
ELECTRON DIFFRACTION STUDIES OF SUPERCONDUCTORS OF THE K-BA-BI-O SYSTEM AND RELATED OXIDES
Authors: NIKOLAICHIK V. I. , KLINKOVA L. A.
Published: April 2005

The application of transmission electron microscopy in combination with physical-chemical methods has made it possible to discover a large number of discrete oxides of ordered structures in the Ba - Bi - O system, which is the parent system for the K - Ba - Bi - O superconducting system. Cation-ordered superconductors Ba 1-x K x BiO 3 with the crystalline structure of a non-cubic and layered nature have been synthesized. This result removes the crystallographic contradiction between bismuthate and cuprate superconductors that provides support to the existence of a common non-magnetic pairing mechanism.
DOPING DEPENDENT ELECTRONIC STRUCTURE OF CUPRATES AND THE EFFECTIVE LOW ENERGY HAMILTONIAN FOR THE MAGNETIC PAIRING
Authors: GAVRICHKOV V. A. , KORSHUNOV M. M. , OVCHINNIKOV S. G.
Published: April 2005

The properties of the normal and superconducting phases of p- and n-type cuprates are investigated in the appropriate low-energy models in the approximation beyond Hubbard I considering spin fluctuations. Calculated chemical potential dependence on doping, Fermi surface and Tc(x) phase diagram for n-type cuprates are in remarkably good agreement with the experimental ones. Comparison of the singlet-triplet t-J model with simple t-J model shows that the spin-exciton mechanism originated from singlet-triplet hybridization leads to small contribution to the Tc(x) - optimal doping value becomes slightly lower and the maximum value of Tc become slightly higher.
THE BULGE IN THE BASAL PLANE AREA OF CUPRATE SUPERCONDUCTORS
Authors: RÖHLER J.
Published: April 2005

The bulge in the doping dependence of the basal plane area of cuprate superconductors is shown to be an effect of the particular inhomogenous electronic structure created by the dense packing of paired self-protected singlets (PSPS) in CuO 2 lattices.
EFFECTS OF MAGNETIC FIELD ON THE HYSTERESIS V-I CURVE
Authors: XU X. B. , ZHANG L. , LENG X. , DING S. Y. , WANG Z. H.
Published: April 2005

Hysteresis V-I curves were simulated based on flux creep model. The clockwise loop was found for a sample with homogenous flux pinning if a fast current sweeping rate is used. Moreover, it is shown that an applied magnetic field can suppress the loop. The results coincide qualitatively with the relevant measurements.
QUASIPARTICLE SPECTROSCOPY AND HIGH-FIELD PHASE DIAGRAMS OF CUPRATE SUPERCONDUCTORS – AN INVESTIGATION OF COMPETING ORDERS AND QUANTUM CRITICALITY
Authors: YEH N.-C. , CHEN C.-T. , ZAPF V. S. , BEYER A. D. , HUGHES C. R. , PARK M.-S. , KIM K.-H. , LEE S.-I.
Published: April 2005

We present scanning tunneling spectroscopic and high-field thermodynamic studies of hole- and electron-doped (p- and n-type) cuprate superconductors. Our experimental results are consistent with the notion that the ground state of cuprates is in proximity to a quantum critical point (QCP) that separates a pure superconducting (SC) phase from a phase comprised of coexisting SC and a competing order, and the competing order is likely a spin-density wave (SDW). The effect of applied magnetic field, tunneling current, and disorder on the revelation of competing orders and on the low-energy excitations of the cuprates is discussed.
EFFECT OF INTERMEDIATE DEFORMATION ON THE TEXTURING OF Bi-2223/Ag TAPES
Authors: YI H. P. , LIN D. , SONG X. H. , LIU W. , LIU Q. , HAN Z. , ZHENG Y. K.
Published: April 2005

The effect of intermediate deformation (ID) on texturing of Bi -2223 phase was studied by SEM and rocking curve. There exists a peak value for the degree of texturing as a function of ID reduction. The optimum reduction for intermediate rolling and intermediate pressing is 14.3% and 10.7%, respectively. The texturing of the Bi -2223 phase was further improved by the final heat treatment after ID. Moreover, the critical current density ( Jc ) of the tapes was directly proportional to the texturing of Bi -2223 phase.
SUPERCONDUCTING PROPERTY IN Mn DOPED La1.85Sr0.15CuO4 SYSTEM
Authors: ZHANG CHANGJIN , KIM J. S. , KIM B. H. , PARK Y. W.
Published: April 2005

In this paper the superconducting properties in La 1.85S Sr 0.15 Cu 1-x Mn x O 4 and La 1.85-2x Sr 0.15+2x Cu 1-x Mn x O 4 samples are discussed. The superconducting transition temperature keeps constantly at 37 K for all superconducting samples. The suppression of superconductivity in these systems does not fit the Arbrikosov and Gork'ov theory which predicts that Tc should decrease in the presence of magnetic impurities in the lattice. The magnetic pair-breaking effect is not the reason for the suppression of superconductivity in Mn doping systems. The localization of carriers in the CuO 2 plane induced by Mn doping should be responsible for the suppression of superconductivity.
ANOMALOUS THERMAL EFFECT OF Y1-xCaxBa2Cu3Oy
Authors: ZHANG L. , SUN X. F. , RUI X. F. , ZHANG H.
Published: April 2005

It is found in oxygen there are a weight loss and an endothermal anomaly in compound of Y 1-x Ca x Ba 2 Cu 3 O y starting at about 320 °C, while in nitrogen at about 370 °C and a mixed atmosphere, N 2(50%)+ O 2(50%), at about 350 °C. The results are different from those in undoped YBa 2 Cu 3 O y and some doped systems. It is suggested that Ca prefers a sixfold coordination, which causes the oxygen loss in Cu (2)- O plane and the weight and heat anomalies at different temperature in different atmospheres. The oxygen loss in Cu (2)- O plane is also responsible for Tc suppression in Y 1-x Ca x Ba 2 Cu 3 O y.
THE ENHANCED SUPERCONDUCTIVITY OF Cu-1234 UNDER HIGH PRESSURE
Authors: JIN C. Q. , QIN X. M. , SHIMIZU K. , NISHIYAMA M. , NAMIKI T. , YU Y.
Published: April 2005

The evolution of superconducting transition of CuBa 2 Ca 3 Cu 4 O 10+δ (i.e. Cu -1234) superconductor has been studied by using diamond anvil cell technique. The Tc of Cu -1234 can be enhanced continuously from ambient reaching to 123 K at 15 GPa. This seems the one more system besides Hg -12( n -1) n which demonstrate the positive pressure effect on Tc over a wide pressure range above 10 GPa.