bluuebunny/crossref_metadata_2025 huggingface dataset:
A Functional Module of Yeast Mediator That Governs the Dynamic Range of Heat-Shock Gene Expression
Authors: Singh Harpreet , Erkine Alexander M , Kremer Selena B , Duttweiler Harry M , Davis Donnie A , Iqbal Jabed , Gross Rachel R , Gross David S
Published: February 2006

We report the results of a genetic screen designed to identify transcriptional coregulators of yeast heat-shock factor (HSF). This sequence-specific activator is required to stimulate both basal and induced transcription; however, the identity of factors that collaborate with HSF in governing noninduced heat-shock gene expression is unknown. In an effort to identify these factors, we isolated spontaneous extragenic suppressors of hsp82-ΔHSE1, an allele of HSP82 that bears a 32-bp deletion of its high-affinity HSF-binding site, yet retains its two low-affinity HSF sites. Nearly 200 suppressors of the null phenotype of hsp82-ΔHSE1 were isolated and characterized, and they sorted into six expression without heat-shock element (EWE) complementation groups. Strikingly, all six groups contain alleles of genes that encode subunits of Mediator. Three of the six subunits, Med7, Med10/Nut2, and Med21/Srb7, map to Mediator's middle domain; two subunits, Med14/Rgr1 and Med16/Sin4, to its tail domain; and one subunit, Med19/Rox3, to its head domain. Mutations in genes encoding these factors enhance not only the basal transcription of hsp82-ΔHSE1, but also that of wild-type heat-shock genes. In contrast to their effect on basal transcription, the more severe ewe mutations strongly reduce activated transcription, drastically diminishing the dynamic range of heat-shock gene expression. Notably, targeted deletion of other Mediator subunits, including the negative regulators Cdk8/Srb10, Med5/Nut1, and Med15/Gal11 fail to derepress hsp82-ΔHSE1. Taken together, our data suggest that the Ewe subunits constitute a distinct functional module within Mediator that modulates both basal and induced heat-shock gene transcription.
Palmitoyl-Protein Thioesterase 1 Deficiency in Drosophila melanogaster Causes Accumulation of Abnormal Storage Material and Reduced Life Span
Authors: Hickey Anthony J , Chotkowski Heather L , Singh Navjot , Ault Jeffrey G , Korey Christopher A , MacDonald Marcy E , Glaser Robert L
Published: February 2006

Human neuronal ceroid lipofuscinoses (NCLs) are a group of genetic neurodegenerative diseases characterized by progressive death of neurons in the central nervous system (CNS) and accumulation of abnormal lysosomal storage material. Infantile NCL (INCL), the most severe form of NCL, is caused by mutations in the Ppt1 gene, which encodes the lysosomal enzyme palmitoyl-protein thioesterase 1 (Ppt1). We generated mutations in the Ppt1 ortholog of Drosophila melanogaster to characterize phenotypes caused by Ppt1 deficiency in flies. Ppt1-deficient flies accumulate abnormal autofluorescent storage material predominantly in the adult CNS and have a life span 30% shorter than wild type, phenotypes that generally recapitulate disease-associated phenotypes common to all forms of NCL. In contrast, some phenotypes of Ppt1-deficient flies differed from those observed in human INCL. Storage material in flies appeared as highly laminar spherical deposits in cells of the brain and as curvilinear profiles in cells of the thoracic ganglion. This contrasts with the granular deposits characteristic of human INCL. In addition, the reduced life span of Ppt1-deficient flies is not caused by progressive death of CNS neurons. No changes in brain morphology or increases in apoptotic cell death of CNS neurons were detected in Ppt1-deficient flies, even at advanced ages. Thus, Ppt1-deficient flies accumulate abnormal storage material and have a shortened life span without evidence of concomitant neurodegeneration.
Mismatch Tolerance by DNA Polymerase Pol4 in the Course of Nonhomologous End Joining in Saccharomyces cerevisiae
Authors: Pardo Benjamin , Ma Emilie , Marcand Stéphane
Published: February 2006

In yeast, the nonhomologous end joining pathway (NHEJ) mobilizes the DNA polymerase Pol4 to repair DNA double-strand breaks when gap filling is required prior to ligation. Using telomere–telomere fusions caused by loss of the telomeric protein Rap1 and double-strand break repair on transformed DNA as assays for NHEJ between fully uncohesive ends, we show that Pol4 is able to extend a 3′-end whose last bases are mismatched, i.e., mispaired or unpaired, to the template strand.
The C Terminus of Collagen SQT-3 Has Complex and Essential Functions in Nematode Collagen Assembly
Authors: Novelli Jacopo , Page Antony P , Hodgkin Jonathan
Published: February 2006

The nematode exoskeleton is a multilayered structure secreted by the underlying hypodermal cells and mainly composed of small collagens, which are encoded by a large gene family. In previous work, we reported analysis of the C. elegans dpy-31 locus, encoding a hypodermally expressed zinc-metalloprotease of the BMP-1/TOLLOID family essential for viability and cuticle deposition. We have generated a large set of extragenic suppressors of dpy-31 lethality, most of which we show here to be allelic to the cuticle collagen genes sqt-3 and dpy-17. We analyzed the interaction among dpy-31, sqt-3, and dpy-17 using a SQT-3-specific antiserum, which was employed in immunofluorescence experiments. Our results support a role for DPY-31 in SQT-3 extracellular processing and suggest that the SQT-3 C-terminal nontrimeric region serves multiple roles during SQT-3 assembly. Different missense mutations of this region have diverse phenotypic consequences, including cold-sensitive lethality. Furthermore, the biochemical and genetic data indicate that the extracellular assemblies of DPY-17 and SQT-3 are interdependent, most likely because the collagens are incorporated into the same cuticular substructure. We find that absence of DPY-17 causes extensive intracellular retention of SQT-3, indicating that formation of the SQT-3–DPY-17 polymer could begin in the intracellular environment before secretion.
Smc5p Promotes Faithful Chromosome Transmission and DNA Repair in Saccharomyces cerevisiae
Authors: Cost Gregory J , Cozzarelli Nicholas R
Published: February 2006

Heterodimers of structural maintenance of chromosomes (SMC) proteins form the core of several protein complexes involved in the organization of DNA, including condensation and cohesion of the chromosomes at metaphase. The functions of the complexes with a heterodimer of Smc5p and Smc6p are less clear. To better understand them, we created two S. cerevisiae strains bearing temperature-sensitive alleles of SMC5. When shifted to the restrictive temperature, both mutants lose viability gradually, concomitant with the appearance of nuclear abnormalities and phosphorylation of the Rad53p DNA damage checkpoint protein. Removal of Rad52p or overexpression of the SUMO ligase Mms21p partially suppresses the temperature sensitivity of smc5 strains and increases their survival at the restrictive temperature. At the permissive temperature, smc5-31 but not smc5-33 cells exhibit hypersensitivity to several DNA-damaging agents despite induction of the DNA damage checkpoint. Similarly, smc5-31 but not smc5-33 cells are killed by overexpression of the SUMO ligase-defective Mms21-SAp but not by overexpression of wild-type Mms21p. Both smc5 alleles are synthetically lethal with mms21-SA and exhibit Rad52p-independent chromosome fragmentation and loss at semipermissive temperatures. Our data indicate a critical role for the S. cerevisiae Smc5/6-containing complexes in both DNA repair and chromosome segregation.
De Novo Appearance and “Strain” Formation of Yeast Prion [PSI+] Are Regulated by the Heat-Shock Transcription Factor
Authors: Park Kyung-Won , Hahn Ji-Sook , Fan Qing , Thiele Dennis J , Li Liming
Published: February 2006

Yeast prions are non-Mendelian genetic elements that are conferred by altered and self-propagating protein conformations. Such a protein conformation-based transmission is similar to that of PrPSc, the infectious protein responsible for prion diseases. Despite recent progress in understanding the molecular nature and epigenetic transmission of prions, the underlying mechanisms governing prion conformational switch and determining prion “strains” are not understood. We report here that the evolutionarily conserved heat-shock transcription factor (HSF) strongly influences yeast prion formation and strain determination. An hsf1 mutant lacking the amino-terminal activation domain inhibits the yeast prion [PSI+] formation whereas a mutant lacking the carboxyl-terminal activation domain promotes [PSI+] formation. Moreover, specific [PSI+] strains are preferentially formed in these mutants, demonstrating the importance of genetic makeup in determining de novo appearance of prion strains. Although these hsf1 mutants preferentially support the formation of certain [PSI+] strains, they are capable of receiving and faithfully propagating nonpreferable strains, suggesting that prion initiation and propagation are distinct processes requiring different cellular components. Our findings establish the importance of HSF in prion initiation and strain determination and imply a similar regulatory role of mammalian HSFs in the complex etiology of prion disease.
Genomic Organization of gypsy Chromatin Insulators in Drosophila melanogaster
Authors: Ramos Edward , Ghosh Dolanchanpa , Baxter Ellen , Corces Victor G
Published: February 2006

Chromatin insulators have been implicated in the regulation of higher-order chromatin structure and may function to compartmentalize the eukaryotic genome into independent domains of gene expression. To test this possibility, we used biochemical and computational approaches to identify gypsy-like genomic-binding sites for the Suppressor of Hairy-wing [Su(Hw)] protein, a component of the gypsy insulator. EMSA and FISH analyses suggest that these are genuine Su(Hw)-binding sites. In addition, functional tests indicate that genomic Su(Hw)-binding sites can inhibit enhancer–promoter interactions and thus function as bona fide insulators. The insulator strength is dependent on the genomic location of the transgene and the number of Su(Hw)-binding sites, with clusters of two to three sites showing a stronger effect than individual sites. These clusters of Su(Hw)-binding sites are located mostly in intergenic regions or in introns of large genes, an arrangement that fits well with their proposed role in the formation of chromatin domains. Taken together, these data suggest that genomic gypsy-like insulators may provide a means for the compartmentalization of the genome within the nucleus.
A Mutation in Tac1p, a Transcription Factor Regulating CDR1 and CDR2, Is Coupled With Loss of Heterozygosity at Chromosome 5 to Mediate Antifungal Resistance in Candida albicans
Authors: Coste Alix , Turner Vincent , Ischer Françoise , Morschhäuser Joachim , Forche Anja , Selmecki Anna , Berman Judith , Bille Jacques , Sanglard Dominique
Published: February 2006

TAC1, a Candida albicans transcription factor situated near the mating-type locus on chromosome 5, is necessary for the upregulation of the ABC-transporter genes CDR1 and CDR2, which mediate azole resistance. We showed previously the existence of both wild-type and hyperactive TAC1 alleles. Wild-type alleles mediate upregulation of CDR1 and CDR2 upon exposure to inducers such as fluphenazine, while hyperactive alleles result in constitutive high expression of CDR1 and CDR2. Here we recovered TAC1 alleles from two pairs of matched azole-susceptible (DSY294; FH1: heterozygous at mating-type locus) and azole-resistant isolates (DSY296; FH3: homozygous at mating-type locus). Two different TAC1 wild-type alleles were recovered from DSY294 (TAC1-3 and TAC1-4) while a single hyperactive allele (TAC1-5) was isolated from DSY296. A single amino acid (aa) difference between TAC1-4 and TAC1-5 (Asn977 to Asp or N977D) was observed in a region corresponding to the predicted activation domain of Tac1p. Two TAC1 alleles were recovered from FH1 (TAC1-6 and TAC1-7) and a single hyperactive allele (TAC1-7) was recovered from FH3. The N977D change was seen in TAC1-7 in addition to several other aa differences. The importance of N977D in conferring hyperactivity to TAC1 was confirmed by site-directed mutagenesis. Both hyperactive alleles TAC1-5 and TAC1-7 were codominant with wild-type alleles and conferred hyperactive phenotypes only when homozygous. The mechanisms by which hyperactive alleles become homozygous was addressed by comparative genome hybridization and single nucleotide polymorphism arrays and indicated that loss of TAC1 heterozygosity can occur by recombination between portions of chromosome 5 or by chromosome 5 duplication.
Aberrant Nucleo-cytoplasmic Cross-Talk Results in Donor Cell mtDNA Persistence in Cloned Embryos
Authors: Lloyd Rhiannon E , Lee Joon-Hee , Alberio Ramiro , Bowles Emma J , Ramalho-Santos João , Campbell Keith H S , St. John Justin C
Published: February 2006

Mitochondrial DNA is an extranuclear genome normally maternally inherited through the oocyte. However, the use of nuclear transfer can result in both donor cell and recipient oocyte mitochondrial DNA persisting through to blastocyst and being transmitted to the offspring. The degree of donor mitochondrial DNA transmission appears to be random and currently no evidence exists to explain this phenomenon. To determine whether this is a dilution factor or directly related to the transcriptional status of the donor cell in respect of mitochondrial DNA transcription factors, we have generated sheep nuclear transfer embryos using donor cells: (1) possessing their full mitochondrial DNA complement, (2) those partially depleted, and (3) those depleted but containing residual levels. For each donor type, donor mitochondrial DNA persisted in some blastocysts. It is evident from the donor cells used that nuclear-encoded mitochondrial DNA transcription and replication factors persist even after mitochondrial DNA depletion, as do transcripts for some of the mitochondrial-encoded genes. These cells are therefore still programmed to drive mitochondrial DNA replication and transcription. In nuclear transfer-derived embryos, we have observed the persistence of these nuclear-encoded mitochondrial DNA transcription and replication factors but not in those embryos generated through in vitro fertilization. Consequently, nucleo-mitochondrial interaction following nuclear transfer is out of sequence as the onset of mitochondrial replication is a postimplantation event.
Endemic Iron Deficiency Associated With Helicobacter pylori Infection Among School-Aged Children in Alaska
Authors: Baggett Henry C. , Parkinson Alan J. , Muth Pam T. , Gold Benjamin D. , Gessner Bradford D.
Published: February 2006

OBJECTIVES. Rural Alaska Natives have a high prevalence of iron deficiency and Helicobacter pylori infection. The objective of this study was to estimate the prevalence of iron deficiency, iron-deficiency anemia, and active H pylori infection among school-aged children in rural Alaska.

METHODS. We enrolled 68% (688) of the 7- to 11-year-old children from 10 predominantly Alaska Native villages in southwestern Alaska. We collected venous blood samples to assess iron deficiency and anemia. Each child was tested for active H pylori infection by 13C-urea breath test (UBT). Evaluated risk factors included age, gender, village of residence, number of household members, number of household members who were younger than 5 years, recent antibiotic use, and household water source.

RESULTS. Of 688 enrolled children, iron deficiency was present in 38%, iron-deficiency anemia was present in 7.8%, and H pylori infection by UBT was present in 86%. Iron deficiency was independently associated with living in a household with >6 people and village of residence. H pylori infection by UBT was independently associated with child's age ≥10 years and village of residence. Ninety-one percent of children with iron deficiency had H pylori infection by UBT, and children with active H pylori infection were more likely to be iron deficient than uninfected children. Children with H pylori infection by UBT were also more likely to have iron-deficiency anemia than uninfected children.

CONCLUSIONS. In this study of nearly 700 children in 10 different villages in Alaska, we confirmed that the high prevalence of iron deficiency persists among school-aged children. We found that active H pylori infection was independently associated with iron deficiency and iron-deficiency anemia among children in this region. H pylori infection may account for a portion of the iron deficiency and iron-deficiency anemia in rural Alaska and other areas with high prevalences of both conditions. Innovative approaches are critically needed to address the iron deficiency in high prevalence areas such as rural Alaska and most of the developing world.
Sarcoidosis in Chronic Granulomatous Disease
Authors: De Ravin Suk See , Naumann Nora , Robinson Michael R. , Barron Karyl S. , Kleiner David E. , Ulrick Jean , Friend Julia , Anderson Victoria L. , Darnell Dirk , Kang Elizabeth M. , Malech Harry L.
Published: February 2006

In addition to increased susceptibility to infections in patients with chronic granulomatous disease (CGD), a higher incidence of sterile inflammatory disorders in these patients has been noted. However, sarcoidosis has not been reported previously in CGD. In this report, we describe two patients who have CGD and a disorder consistent with sarcoidosis on the basis of unequivocal clinical-radiographic presentations, their responses to treatment, and serum angiotensin-converting enzyme levels. Serum angiotensin-converting enzyme levels were measured in 26 other patients with CGD to establish an appropriate reference range. A possible relationship between CGD and sarcoidosis is discussed.
Erratum: “Nanoindentation of polydimethylsiloxane elastomers: Effect of crosslinking, work of adhesion,and fluid environment on elastic modulus” [J. Mater.Res. 20, 2820 (2005)]
Authors: Carrillo Fernando , Gupta Shikha , Balooch Mehdi , Marshall Sally J. , Marshall Grayson W. , Pruitt Lisa , Puttlitz Christian M.
Published: February 2006

The authors would like to take this opportunity to rectify a derivational error in our recently published research article. Equation (12) (p. 2824) in the original manuscript pertains to the calculation of the Young's modulus from nanoindentation data considering a Johnson, Kendall, Roberts (JKR) adhesion model:
Synthesis and characterization of nanocrystalline (Zr0.84Y0.16)O1.92–(Ce0.85Sm0.15)O1.925 heterophase thin films
Authors: Kulkarni Aniruddha , Bourandas Alexander , Dong Junhang , Fuierer Paul A. , Xiao Hai
Published: February 2006

A new type of nanocrystalline samarium-doped-ceria/yttrium-stabilized-zirconia (SDC/YSZ) heterophase thin film electrolytes was synthesized on MgO and Si substrates by spin coating and thermal treatment of SDC-nanoparticle-incorporated polymeric precursors. In the heterophase films, SDC nanoparticles were uniformly dispersed in a nanocrystalline YSZ matrix. The heterophase structure was stable when fired in air at temperatures up to 850 °C. The nanocrystalline heterophase thin films exhibited electrical conductivities significantly higher than that of the phase-pure YSZ and SDC nanocrystalline thin films at reduced temperatures. The effects of SDC grain size and volume fraction on the electrical conductivity of the heterophase films were also studied.
Solvothermal synthesis of titania-zirconia composite
Authors: Wang Xin M. , Xiao Ping
Published: February 2006

Nanocomposite particles of anatase-type titania (TiO2) and cubic/tetragonal zirconia were synthesized from hydrothermal processing of TiCl4 and ZrOCl2·8H2O or ZrCl4 alcohol solutions at 160–200 °C. It was found that the morphologies and composition of the composite particles were mainly controlled by the precursors and the sequence by which the precursors were added. The TiO2–ZrO2 composite particles with nanoscale uniformity can be obtained by solvothermal processing of TiCl4 or a ZrO2 precursor together with preformed ZrO2 or yttria stabilized zirconia (YSZ) nanoparticles in ethanol. A novel one-step and non-template method for preparing ZrO2–TiO2 core–shell structured composite particles with hollow interior was identified, and possible reaction mechanism was suggested.
Growth morphologies and mechanisms of non-equilibrium solidified MC carbide
Authors: Chen Y. , Wang H.M.
Published: February 2006

Growth morphologies and mechanisms of the carbide of group IVB and VB elements (MC carbide), a typical faceted crystal, were studied with an estimated cooling rate from 102 to 105 K/s. Results showed that although the growth morphologies of the MC carbide vary remarkably with solidification cooling rate, the solid/liquid interface is always atomically smooth, and the growth mechanisms are always lateral growth. The growth mechanism transition from lateral to continuous growth mode, which was predicted by the classic crystal growth theory, was not observed for the TiC type MC carbide within the estimated cooling rate range of 102–105 K/s.
Effects of aging conditions on the structural properties of mesoporous SiO2/TiO2 composite materials with crystallized framework
Authors: Li Hua , Shen Wei-hua , Shi Jian-lin , Xiong Liang-ming , Liang Jian , Ruan Meilin
Published: February 2006

Well-organized mesoporous SiO2/TiO2 materials with crystallized framework were synthesized. The resultant materials showed high surface area (180–300 m2/g), narrow pore-size distribution (3.5–6 nm), and nanocrystalline framework. The influences of aging conditions on the mesoporous 80TiO2–20SiO2 materials were investigated. The water in the initial solution is beneficial for the mesostructural organization of the as-prepared sample while air moisture (relative humidity) during the aging process plays a key role in the crystallization of the calcined sample. Low aging temperature is another decisive factor to the formation of the mesostructure.
Oxidation behavior of bulk Ti3SiC2 at intermediate temperatures in dry air
Authors: Zhang H.B. , Zhou Y.C. , Bao Y.W. , Wang J.Y.
Published: February 2006

The isothermal oxidation behavior of bulk Ti3SiC2 at intermediate temperatures from 500 to 900 °C in flowing dry air was investigated. An anomalous oxidation with higher kinetics at lower temperatures was observed. This phenomenon resulted from the formation of microcracks in the oxide scales at low temperatures. The generation of these microcracks was caused by a phase change in the oxide products, i.e., the transformation of anatase TiO2 to rutile TiO2. This phase transformation resulted in tensile stress, which provided the driving force for the formation of the microcracks during oxidation. Despite the existence of microcracks, the intermediate-temperature oxidation of Ti3SiC2 generally obeyed the parabolic rate law and did not exhibit catastrophic destruction due to the fact that cracks occurring in the oxide layers were partially filled with amorphous SiO2. Therefore, further high oxidation kinetics was prevented.
Variations of structure and composition in magnesium incorporated hydroxyapatite/β-tricalcium phosphate
Authors: Ryu Hyun-Seung , Hong Kug Sun , Lee Jung-Kun , Kim Deug Joong
Published: February 2006

The phase evolution of magnesium incorporated hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) ceramics of high purity prepared by solid-state reaction was investigated with the aid of x-ray diffraction and infrared spectroscopy (IR) in transmittance mode analysis. The dependence of the microstructure on the phase evolution of biphasic ceramics during natural sintering was also investigated as a function of Mg content. When sintered at 1100 °C, Mg is preferentially incorporated into the β-TCP phase rather than the HA phase. This Mg incorporation into the β-TCP effectively suppresses the phase transition from β- to α-TCP. With increasing sintering temperature, the solubility limit of the Mg in the β-TCP decreases and Mg starts to be either incorporated into the HA phase or segregated as free MgO. The decreased Mg content in the β-TCP facilitates the phase transition from β- into α-TCP, at 1300 °C or higher. Different processing methods on Mg addition show that the retarded phase transition from β- to α-TCP is the inherent property of Mg-doped HA/TCP. The variations in processing parameters mainly affect the microstructure instead of the phase evolution, leading to highly densified HA/β-TCP ceramics.
Deformation of a hard coating on ductile substrate system during nanoindentation: Role of the coating microstructure
Authors: Xie Z-H. , Hoffman M. , Moon R.J. , Munroe P.R.
Published: February 2006

Deformation and fracture of a columnar-grained, ∼1.3-μm-thick TiN coating on a stainless steel substrate was investigated using a spherical tipped conical indenter of 5-μm nominal tip radius. Structural analysis, performed with the support of focused ion beam (FIB) milling and imaging techniques, revealed that the microstructure of the TiN coating had a strong influence on the deformation behavior of the coating. Intergranular sliding in the coating, as well as plastic flow in the ductile substrate, was found to be the predominant processes during the indentation. Neither plastic deformation, in the form of plastic flow, within the coating nor delamination of the interface was observed. Coating deformation was observed to be controlled by the intergranular shear cracking and thus by the interfacial columbic frictional stress between columnar grains. An indentation-energy based model was developed, which deconvolutes the coating behavior from that of the substrate, allowing quantification of the intergranular sliding stress.
Preparation and properties of aluminium titanate-alumina composites with a corrugated microstructure
Authors: Dakskobler Aleš , Kosmač Tomaž
Published: February 2006

Repeated deformation processing was used to produce layered aluminium titanate (ATI)-alumina composites with a corrugated microstructure. Viscous nonpolar pastes of ATI and alumina powders were prepared using paraffin oil as the dispersing medium. These pastes were rolled into tapes 1 mm thick, which were then stacked together to form starting bi-material laminates in an A-B-A sequence. The laminates were then plastically deformed by repeated folding and rolling at room temperature. After a sufficiently large true plastic deformation, composites with corrugated microstructures were successfully produced. During sintering, part of the ATI decomposed; in the alumina layers large anisotropic grains were formed. The mechanical properties of the sintered composites improved with structural refinement, in spite of extensive microcracking observed during cooling from the sintering temperature. In addition, the thermal expansion coefficient along the rolling direction did not differ from that of the reference material.
Mechanisms for the enhancement of the thermal stability of organic thin films by aluminum oxide capping layers
Authors: Sellner S. , Gerlach A. , Schreiber F. , Kelsch M. , Kasper N. , Dosch H. , Meyer S. , Pflaum J. , Fischer M. , Gompf B. , Ulbricht G.
Published: February 2006

We present a detailed study of the thermal stability of organic thin films of diindenoperylene encapsulated by sputtered aluminum oxide layers. We studied the influence of capping layer thickness, stoichiometry, and heating rate on the thermal stability of capped films and their eventual breakdown. Under optimized encapsulation conditions (thick and stoichiometric capping layer), the organic films desorb only at temperatures 200 °C above the desorption of the uncapped film. Moreover, the capped organic films retain their crystalline order at these elevated temperatures, whereas they would normally (i.e., uncapped) be in the gas phase. This study therefore also shows a way of studying organic materials under temperature conditions normally inaccessible. Considering results from complementary techniques, we discuss possible scenarios for the eventual breakdown. The results have implications for the performance and long-term stability of organic devices for which stability against elevated temperatures as well as against exposure to ambient gases is crucial.
ZrO2-nucleated calcium aluminate glass-ceramics with mid-infrared transparency
Authors: Shyu Jiin-Jyh , Mai Hung-Chuan
Published: February 2006

A silica-free MgO–CaO–BaO–Al2O3–ZrO2 glass was converted into glass-ceramic by adding zirconia as a nucleating agent. The crystallization and properties of the glass-ceramics were investigated. It was found that ZrO2 is an efficient nucleating agent for the present calcium aluminate glass. Addition of an appropriate amount of ZrO2 changed the crystallization behavior from surface nucleation to internal nucleation. The primary crystalline phase was Ca3Al2O6, which exhibited bulk nucleation. When the crystallizing time was increased, BaAl2O4 formed as a surface layer that grew from the surface into the interior of the sample. The hardness was increased when the parent glass was converted into glass-ceramics. The glass-ceramics without BaAl2O4 surface layer have visible-to-infrared transparency comparable with the parent glass. The transparency was substantially reduced after the development of the surface layer.
Atomic force microscopy study of the role of molecular weight of poly(acrylic acid) in chemical mechanical planarization for shallow trench isolation
Authors: Cho Chae-Woong , Kim Sang-Kyun , Paik Ungyu , Park Jea-Gun , Sigmund Wolfgang M.
Published: February 2006

The influence of the molecular weight of poly(acrylic acid) (PAA) on chemical mechanical planarization (CMP) for shallow trench isolation (STI) was investigated. The adsorption behaviors of PAA as a function of molecular weight on deposited plasma-enhanced tetraethylorthosilicate and chemical vapor deposition Si3N4 films were analyzed by the force measurement using atomic force microscopy (AFM). The AFM results revealed that the affinity of PAA with the nitride film is higher than the affinity with the oxide film, and thus a denser adsorption layer on the nitride film is formed with higher molecular weight of PAA, which leads to higher selectivity in STI CMP. Additionally, to determine the correlation between the dispersion stability of the CeO2 resulting from the presence of PAA with different molecular weight and CMP performance, the colloidal properties of the slurry as a function of the molecular weight of PAA were examined.
Improved thermoelectric properties of gadolinium intercalated compounds GdxTiS2 at the temperaturesfrom 5 to 310 K
Authors: Li D. , Qin X.Y. , Zhang J.
Published: February 2006

The thermoelectric properties of Gd intercalated compounds GdxTiS2 have been investigated at the temperatures from 5 to 310 K. The results indicate that Gd intercalation into TiS2 leads to substantial decrease of both its electrical resistivity and its lattice thermal conductivity κL (κL is lowered by 20% and 46% at 300 K for x = 0.025 and 0.05, respectively). Specially, as compared to the pristine TiS2 the figure of merit ZT of the intercalated compound GdxTiS2 has been improved at all temperatures investigated, and specifically, the ZT value of Gd0.05TiS2 at 300 K is about three times as large as that of TiS2.
Optical and magnetic properties of EuSi2O2N2
Authors: Li Y.Q. , Ramanujachary K.V. , Lofland S.E. , de With G. , Hintzen H.T.
Published: February 2006

A new europium-silicon-oxynitride compound EuSi2O2N2 was obtained by a reaction of Eu2O3, SiO2, and α–Si3N4 at 1300 °C under a nitrogen atmosphere. EuSi2O2N2 is indexed on a monoclinic unit cell with a = 13.151(5) Å, b =17.311(5) Å, c = 7.956(2) Å, β = 104.12(4)°, and V = 1756.56 Å3. EuSi2O2N2 shows a highly pure yellow color associated with a very steep drop in the reflection spectrum with an optical absorption edge at about 512 nm (2.43 eV). On the other hand, EuSi2O2N2 can be efficiently excited in the visible range 370–485 nm and shows a broad band emission peaking at about 568 nm corresponding to the Eu2+ 4f65d1 → 4f7 transition. EuSi2O2N2 shows paramagnetic Curie behavior with an experimental magnetic moment of 7.89(3) μB in accordance with 7 unpaired spins of Eu2+. Additionally, no magnetic ordering can be observed down to 5 K. The divalent nature of the Eu ions in EuSi2O2N2 is evident from both luminescence and magnetic properties.
Concrete reinforced with irradiated nylon fibers
Authors: Martínez-Barrera Gonzalo , Menchaca-Campos Carmina , Hernández-López Susana , Vigueras-Santiago Enrique , Brostow Witold
Published: February 2006

Polymeric fibers have been used since the 1980s for improvement of the concrete. However, high mechanical performance has been obtained at high cost and using complex technologies. At least two parameters are important here: dimensions and surface characteristics of the fibers. We have modified nylon 6,12 fiber surfaces by 5, 10, 50, and 100 kGy gamma irradiation dosages. Tensile strength of the irradiated fibers was determined and then the fibers mixed at 1.5%, 2.0%, and 2.5% in volume with Portland cement, gravel, sand, and water. The compressive strength of the fiber reinforced concrete (FRC) was evaluated and the results were compared with results for similar materials reported before. The highest values of the compressive strength of FRC are seen for fibers at 50 kGy and 2.0% in volume of fiber; the strength is 122.2 MPa, as compared to 35 MPa for simple concrete without fibers. We advance a mechanism by which the fiber structure can be affected by gamma irradiation resulting in the compressive strength improvement of the concrete.
Shear localization of nanoscale W in metallic glass composites
Authors: Lee Min Ha , Sordelet Daniel J.
Published: February 2006

High-density tungsten/metallic glass composites were fabricated by warm extrusion of two different powders. The first powder was a physical blend of −45 μm tungsten and Hf-based metallic glass powders and produced a relatively coarse distribution of tungsten particles within a continuous metallic glass matrix. The second powder was synthesized by mechanical milling the −45 μm tungsten and Hf-based metallic glass powders into composite particles composed of 20–500-nm layers of tungsten and metallic glass. The amorphous structure of the starting glass powders did not change during milling. Some macroscopic plasticity during compression testing was observed due to the formation of multiple shear bands at the interface between the coarse tungsten particles and the metallic glass matrix in the composite produced from blended powders. In contrast, shear localization without a decrease in strength occurred uniformly throughout the nano-grained tungsten and metallic glass phases in the sample obtained from extruded composite powders.
Interfacial adhesion of nanoporous zeolite thin films
Authors: Hu Lili , Wang Junlan , Li Zijian , Li Shuang , Yan Yushan
Published: February 2006

Nanoporous silica zeolite thin films are promising candidates for future generation low-dielectric constant (low-k) materials. During the integration with metal interconnects, residual stresses resulting from the packaging processes may cause the low-k thin films to fracture or delaminate from the substrates. To achieve high-quality low-k zeolite thin films, it is important to carefully evaluate their adhesion performance. In this paper, a previously reported laser spallation technique is modified to investigate the interfacial adhesion of zeolite thin film-Si substrate interfaces fabricated using three different methods: spin-on, seeded growth, and in situ growth. The experimental results reported here show that seeded growth generates films with the highest measured adhesion strength (801 ± 68 MPa), followed by the in situ growth (324 ± 17 MPa), then by the spin-on (111 ± 29 MPa). The influence of the deposition method on film–substrate adhesion is discussed. This is the first time that the interfacial strength of zeolite thin films-Si substrates has been quantitatively evaluated. This paper is of great significance for the future applications of low-k zeolite thin film materials.
Enhanced yield strength in iron nanocomposite with in situ grown single-wall carbon nanotubes
Authors: Goyal A. , Wiegand D.A. , Owens F.J. , Iqbal Z.
Published: February 2006

The yield strength of iron-carbon nanotube composites fabricated by in situ chemical vapor deposition of 2.2 vol% single-wall carbon nanotubes (SWNTs) inside an iron matrix showed substantial enhancement up to 45%, relative to that of similarly treated pure iron samples without carbon nanotubes of the same piece density. The work hardening coefficient and the Vickers hardness coefficient also significantly increased in these composites relative to the reference samples. X-ray diffraction together with energy dispersive x-ray measurements and micro-Raman spectroscopy indicated no concomitant formation of carbides and very little amorphous carbon during the vapor deposition process. Micro-Raman spectroscopy and scanning and transmission electron microscopy showed spectral signatures and images, respectively, indicating the formation and dispersion of SWNTs within the cavities of the iron matrix. It is suggested that the increased strength of the nanocomposites was due to the mechanical support provided to these cavities by the extremely strong SWNTs.
High-temperature phase equilibria in the system Zr–O–N
Authors: Ermoline Alexandre , Schoenitz Mirko , Dreizin Edward L.
Published: February 2006

Powders of Zr, ZrO2, and ZrN were mixed and pressed to produce samples with different bulk stoichiometries in the ternary Zr–O–N systems. The samples were laser heated above melting, maintained at a high temperature, and quenched. The processed samples were cross-sectioned and studied using scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. The results pointed to the location of the ternary invariant point Liquid + Gas + ZrO2 + ZrN on the high-temperature portion of the Zr–ZrO2–ZrN phase diagram. The ternary liquidus in the Zr–O–N system was further constrained based on the comparison of the results obtained in this work with composition histories of zirconium particles burning in air reported earlier. Elemental analysis of nitrogen-rich inclusions found in the samples showed the existence of an extended compositional range for ternary solid Zr–O–N solutions. X-ray diffraction analysis of the quenched samples indicated that these solutions are likely to be derived from the ZrN phase. A preliminary outline of the subsolidus ternary Zr–ZrO2–ZrN phase diagram is constructed based on these findings and the interpretations of the well-known binary Zr–O and Zr–N phase diagrams.
Gluconate controls one-dimensional growth of tellurium nanostructures
Authors: Gao Feng , Lu Qingyi , Komarneni Sridhar
Published: February 2006

In this paper, we show for the first time that by using sodium gluconate-assisted solution route, fine, uniform, and single-crystalline tellurium nanorods and nanowires can be synthesized. Sodium gluconate is a green and safe chemical with strong chelating function, and this property may be useful in the fabrication of nanomaterials, especially one-dimensional (1D) nanomaterials. The sodium gluconate acts as both reducing agent and morphology-directing agent and by adjusting the experimental parameters, the lengths and the diameters of the tellurium nanorods could be further controlled in a certain range. This method is a simple and economical route for 1D nanostructure fabrication and might bring about a novel concept for the synthesis of 1D nanostructures with bio-ligand, sodium gluconate.
Preparation and characterization of Ag/AgO nanoshells on carboxylated polystyrene latex particles
Authors: Zhang Rongwei , Zhang Dan , Mao Hui , Song Wenlong , Gao Ge , Liu Fengqi
Published: February 2006

Smooth and uniform Ag/AgO nanoshells (about 3–4 nm) on carboxylated polystyrene latex particles were prepared by electrostatic attraction between negatively charged –COO− on the surface of carboxylated polystyrene latex particles and positively charged Ag(NH3)2+ in the solution, and subsequent decomposition of the silver complex. The resultant nanoparticles were characterized with Fourier transform infrared, transmission electron microscopy, scanning electron microscopy, and x-ray diffraction. The effects of reducing agents, the amount of NaOH and temperature on the morphology of hybrid latex particles were discussed.
C60 fullerene tubes as removable templates
Authors: Minato Jun-ichi , Miyazawa Kun'ichi
Published: February 2006

Crystalline microtubes (inner diameter 240–2100 nm) consisting of C60 fullerene molecules were prepared in the mixture of C60-saturated pyridine and isopropyl alcohol kept at 0 °C. Characterization by transmission electron microscopy showed a linear relationship between the outer diameter and the inner diameter for the C60 fullerene tubes. Optical observations suggested that the specimens already had tubular structure when they were grown in the solution. Deposition of guest crystals inside the C60 fullerene tubes was performed by the following procedure: (i) ultrasonic pulverization to obtain the C60 fullerene tubes with open ends, (ii) absorption of methyl alcohol solution of KBr into the tubes by the capillary attraction, and (iii) evaporation of methyl alcohol to precipitate KBr inside the tubes. Columnar KBr crystals were then obtained by dissolving the fullerene tube walls in toluene.
Formation and properties of Pr-based bulk metallic glasses
Authors: Zhao Z.F. , Wen P. , Wang R.J. , Zhao D.Q. , Pan M.X. , Wang W.H.
Published: February 2006

The data on the compositional dependence of glass-forming ability, glass transition, and properties of bulk metallic glasses (BMGs) are important for understanding the nature and glass-forming ability of metallic glasses and for their application. In this paper, we report the formation of rare-earth-based Pr–(Cu,Ni)–Al pseudo-ternary BMGs with a large bulk glass-forming composition range and distinct glass transition. The compositional dependence of glass-forming ability, glass transition, and properties were systematically studied. The contrasting effects of Al and Pr on glass formation and glass transition, unique elastic properties, and phonon softening of the BMGs are discussed from the structural point of view.
Influence of Human Serum Albumin on Photodegradation of Folic Acid in Solution
Authors: Vorobey Pavel , Steindal Arnfinn Engeset , Off Morten Kristian , Vorobey Alexander , Moan Johan
Published: February 2006

It has been proposed that photodegradation of folates may be the reason for the pigmentation of races living under high fluence rates of ultraviolet radiation. The photodegradation of folic acid (FA) induced by ultraviolet‐A (UV‐A) radiation, in solution and in the presence of human serum albumin (HSA), was studied with absorption and fluorescence spectroscopy. FA photodegradation, with formation of p‐aminobenzoyl‐L‐glutamic acid, 6‐formylpterin and pterin‐6‐carboxylic acid, was found to follow an exponential trend. A scheme of FA photodegradation, which involves photosensitization of FA degradation by its photoproducts, was proposed. The rate of FA photodegradation decreased drastically in the presence of HSA, whereas the spectral characteristics of the photo‐products remained constant. The reduction of the FA photo‐degradation rate by HSA was accompanied by degradation of tryptophan in HSA. Tryptophan, when added to solutions of FA, had a similar effect as HSA. In solutions of FA and HSA the FA photoproducts cause photodamage mainly to HSA rather than to FA itself. The oxygen dependence of FA photo‐degradation and the inhibition of this process by sodium azide indicate that singlet oxygen may participate in the photosensitizing activity of FA photoproducts.
Variation of Morphology among Juvenile Chinook Salmon of Hatchery, Hybrid, and Wild Origin
Authors: Wessel Maria Lang , Smoker William W. , Joyce John E.
Published: February 2006

Body morphology differed significantly between juvenile hatchery Chinook salmon Oncorhynchus tshawytscha that have experienced five generations of hatchery culture and juveniles derived from the wild founding stock and cultured in the same environment. All lines tested were raised in a similar hatchery environment. Thin‐plate spline analysis was used to characterize the morphometric variation among these lines of fish. Hatchery fish had a more compressed body, a narrower head, shorter maxillae, and a longer and narrower caudal peduncle than wild fish. Canonical discriminant analysis was able to correctly classify 88% of hatchery fish and 90% of wild fish. Second‐generation hybrids of the two lines were morphologically intermediate to but significantly different from both the hatchery and wild lines, and they appeared to be more similar to the wild line. These results suggest that the differences observed between lines are largely genetic in origin and may be a result of the divergence of the hatchery stock from the founding wild stock. In addition, family of origin had a significant effect on body morphology.
Patterns of Intra‐ and Interspecies Genetic Diversity in Klamath River Basin Suckers
Authors: Tranah Gregory J. , May Bernie
Published: February 2006

The Klamath River basin, Oregon, is home to four catostomid species: The Klamath smallscale suckerCatostomus rimiculus, the Klamath largescale suckerCatostomus snyderi, the shortnose suckerChasmistes brevirostris, and the Lost River suckerDeltistes luxatus. A decline in Lost River and shortnose sucker abundances resulted in these species being listed as endangered under the U.S. Endangered Species Act in 1988. The primary aims of this study were to measure interspecific and intraspecific genetic variation in Klamath River basin suckers by examining 15 microsatellite loci. Over 300 suckers were sampled from four subbasins within the Klamath River basin (Lost River, upper Klamath–Sprague rivers, lower Klamath River, and upper Williamson River) and one region outside of the basin (Rogue River). A hierarchical analysis of population subdivision based on groups generated from microsatellite genetic distance (RST) data was performed by use of analysis of molecular variance. Assignment of individuals to known populations was performed with the program WHICHLOCI. The program STRUCTURE was used to assign individuals probabilistically to homogeneous clusters without population or species identifiers. Klamath smallscale and Lost River suckers were genetically distinct from each other and from shortnose and Klamath largescale suckers. Sympatrically occurring shortnose and Klamath largescale suckers from the Lost and upper Klamath–Sprague River subbasins were genetically indistinguishable from one another, which indicates that interspecific hybridization has occurred between these two species. Managing for the long‐term survival and recovery of endangered Klamath River basin suckers should focus on preserving the genetic diversity of all four sucker species. Continued protection of endangered shortnose suckers requires the protection of Klamath largescale suckers, since each of these species may be a crucial contributor to the evolutionary legacy of the other. Maintenance of healthy and abundant sucker spawning and rearing habitat should minimize the chance of losing genetically unique populations while maintaining genetically diverse populations and facilitating the recovery of all Klamath River basin suckers.