bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Surface Properties of Poly(vinyl alcohol) Brush
Authors: Terayama Yuki , Kobayashi Motoyasu , Takahara Atsushi
Published: September 2007

Poly(vinyl alcohol) (PVA) brush was prepared by surface-initiated iodine-transfer polymerization of vinyl acetate (VAc) from a silicon wafer and successive hydrolysis of acetyl groups. The adhesion forces of PVA and PVAc brush surfaces were measured by atomic force microscopy.
Mineralogy, geochemistry and genesis of smectite in pliocene volcaniclastic rocks of the doğanbey formation, beyşehir basin, Konya, Turkey
Authors: Kadir Selahattin
Published: September 2007

Pliocene volcaniclastic lacustrine rocks of the Doğanbey formation in the Beyşehir region (central Anatolia) are composed of organic-matter-bearing claystone, clastic units and dolomite interbeds, suggesting an anaerobic, shallow swampy, lacustrine depositional environment. The depositional environment was subjected to periodic climatic change during which diagenesis occurred, and smectite, and locally palygorskite, were precipitated. Smectite flakes formed authigenically on feldspar and palygorskite fibers between dolomite rhombs and at the edges of smectite flakes. Increases in leaching of Na, K, Sr, Ba and Rb, increasing Al/Si ratios, and Fe with increasing degree of alteration reveal that hydration of volcaniclastic grains (feldspar, glass) by meteoric water — determined from O and H isotopic values — was the main cause of precipitation of beidellite and montmorillonite based on the tetrahedral charge/octahedral charge ratio, with average structural formulae of (Si7.72Al0.28)(Al3.20Fe0.53Mg0.25 Mn0.02Ti0.04) (Ca0.11Na0.09K0.11), and (Si7.88Al0.13)(Al3.18Fe0.53Mg0.18Mn0.02Ti0.05)(Ca0.11Na0.11K0.09), respectively. Therefore, the Doğanbey-area smectite is presumed to have formed by chemical weathering and dissolution-precipitation from feldspar and glass during diagenesis; palygorskite formed by direct precipitation from Mg-rich solutions during dolomitization, and by transformation from smectite in an alkaline lacustrine environment.
Antibodies against Synthetic Deamidated Gliadin Peptides as Predictors of Celiac Disease: Prospective Assessment in an Adult Population with a High Pretest Probability of Disease
Authors: Niveloni Sonia , Sugai Emilia , Cabanne Ana , Vazquez Horacio , Argonz Julio , Smecuol Edgardo , Moreno María L , Nachman Fabio , Mazure Roberto , Kogan Zulema , Gomez Juan C , Mauriño Eduardo , Bai Julio C
Published: September 2007

Background: Noninvasive serologic tests have shown high diagnostic accuracy for celiac disease (CD) in selected populations. Our aim was to determine prospectively the performance of CD-related serology in individuals undergoing intestinal biopsy because of clinical suspicion of small-bowel disorders.

Methods: We enrolled 141 unselected consecutive adult patients attending a small-bowel disease clinic. Patients underwent endoscopy and biopsy; serum samples were obtained at that time for measurements of anti–tissue transglutaminase (a-tTG), IgA and IgG anti–deamidated gliadin-related peptide (a-DGP), and IgA antiactin antibodies (AAAs). Characterization of patients was based on histological criteria (Marsh type II lesion or greater).

Results: The prevalence of CD was 42.5%. Sensitivity, specificity, and positive and negative predictive values were >90% for most assays. Diagnostic accuracy based on ROC curve analysis was similar for all assays [area under the curve (95% CI): 0.996 (0.967–0.998) for a-tTG, 0.995 (0.964–0.998) for IgA a-DGP, 0.989 (0.954–0.999) for IgG a-DGP, 0.996 (0.966–0.998) for blended conjugated of IgA + IgG a-DGP in a single assay, and 0.967 (0.922–0.990) for AAA]. The combinations of 2 tests, IgG a-DGP plus IgA a-tTG or the single blended conjugate detecting IgA + IgG a-DGP plus IgA a-tTG had 100% positive and negative predictive values if concentrations of both tests in either combination were above or below the cutoff.

Conclusions: In a population with high pretest probability, the newly developed a-DGP tests have diagnostic accuracy that is at least equivalent to that of established assays.
Developmental changes in the L-arginine/nitric oxide pathway from infancy to adulthood: plasma asymmetric dimethylarginine levels decrease with age
Authors: Lücke Thomas , Kanzelmeyer Nele , Kemper Markus J. , Tsikas Dimitrios , Das Anibh M.
Published: September 2007

Clin Chem Lab Med 2007;45:1525–30.
How useful are housekeeping genes? Variable expression in melanoma metastases
Authors: Kågedal Bertil , Farnebäck Malin , Håkansson Annika , Gustafsson Bertil , Håkansson Leif
Published: September 2007

Clin Chem Lab Med 2007;45:1481–7.
Precursor Adsorption of SbBr3 on Au(111) and Au(100) for Antimony Underpotential Deposition in a BMIBF4 Ionic Liquid – A Comparison with SbCl3
Authors: Fu Yong-Chun , Zhang Hai-Ming , Su Yu-Zhuan , Wu De-Ying , Xie Zhao-Xiong , Mao Bing-Wei
Published: September 2007

By employing in-situ STM, we have studied precursor adsorption and initial stage of Sb UPD on Au(111) and Au(100) in a SbBr3-containing BMIBF4 ionic liquid. It has been observed that the adsorption of SbBr3 selectively takes place on Au(100), in contrast to that of SbCl3, with formation of chains with structure as well as squares with structure. The chains are composed of pairs of SbBr3 molecules, which are bridged with the adjacent SbBr3 molecules in the chain to form the anisotropy along either of the two characteristic directions of Au(100). The square configured structure is composed of periodically arranged monomeric and dimeric SbBr3, which will gradually replace the chain structure. Regardless of the precursor adsorption, however, the initial stage of Sb UPD is characterized by the formation of atomic strips, like in the SbCl3-containing system, which reveals the consistency of discharging behavior of Sb(III) from the SbCl3 and SbBr3 molecules. Together with the findings from the SbCl3-containing system, the results are discussed in view of matching of structures between the pyramidal antimony tri-halides and the crystalline surfaces. The role of the ionic liquid as well as properties of the electrified interface will also be mentioned.
Carbon Nanotubes and Electrochemistry
Authors: Esplandiu Maria José , Pacios M. , Bellido E. , Valle M. del
Published: September 2007

Rigid carbon nanotube (CNT) polymer composites were characterized as bare electrochemical transducers and as support for (bio)functionalization. In order to accomplish that, cyclic voltammetry and impedance spectroscopy in presence of benchmark redox systems were performed. The response and sensitivity can be enhanced if the density of edges is increased in the CNT systems. Bamboo-like CNTs seem to be the best choice for composite electrodes. Additionally, the CNT electrodes result in a very robust support for chemical functionalization. Direct electron transfer of myoglobin has been verified without the need of electrochemical mediators and without compromising the biomolecule activity. Finally, some other exciting applications of CNT electrochemistry at the nanoscale regime are also highlighted.
Formation of a Molecular Glue Based on the Electrochemical Reduction of 4-Hydroxyphenyldiazonium for the Attachment of Thin Sol–Gel Film on Glassy Carbon
Authors: Shapiro Leora , Mandler Daniel
Published: September 2007

The covalent attachment of a sol–gel thin film onto a glassy carbon electrode has been accomplished through the electrochemical reduction of 4-hydroxyphenyldiazonium. The latter forms a very thin layer on the glassy carbon with hydroxyl groups, through which the sol–gel is attached. We find that this “molecular glue” improves the adhesion of thin layers of sol–gel to a carbonaceous surface.
Comparative Study of Thymine Adsorption on Cu- and Ag-Adlayers on Au(111) Electrodes
Authors: Thiel K.-O. , Vollmer A. , Hintze M. , Avci E. , Donner Constanze
Published: September 2007

The electronic attributes of an electrochemically deposited copper monolayer on Au(111) were compared to its bulk equivalent by XPS experiments. Due to the modified interaction between the Cu-Cu as well as Cu-Au atoms at the surface a core level shift to lower binding energies occurs, which exceeds the values found for surface core level shifts of Cu atoms on Cu(100) surfaces.

It could be shown that the thymine orientation on a copper layer depends on the externally applied potential in analogy to the adsorption behaviour on Au(111) and Ag(111) single crystals. The transition between a chemisorbed and a physisorbed phase occurs around the potential of zero charge. Independently of the adsorption state of thymine the electron density around the surface copper atoms is reduced by the interaction between thymine molecules and the copper surface.

At electrochemically deposited silver monolayers, bilayers as well as at bulk silver on Au(111) different orientations and adsorption states of thymine could be evaluated. A comparison between XPS and electrochemical data reveal an alteration of the thymine–Ag interaction within the chemisorbed thymine layer deposited on 1 ML Ag/Au(111). It is notable that the transformation between the chemisorbed and physisorbed thymine phase does not seem to be dependent on the thickness of the silver adlayers, while the potential of zero charge differs by about 200 mV. In contrast, the onset of the hydrogen evolution shifts to lower potentials with increasing thickness of the Ag layers.
Essential Art: Matthew of Linköping's Fourteenth-Century Poetics
Authors: Mehtonen Päivi
Published: September 2007

This article contributes to the study of medieval poetics and rhetoric by reassessing the Arabic-Aristotelian influence in the Poetria and Testa nucis of Matthew of Linköping (c. 1300–1350). In the Poetria Matthew applied a dichotomy between essential and accidental aspects (essencialia-accidentalia) which provided him with a historical, theoretical, and cultural perspective on conventional poetics. The appeal of the (Parisian teaching of) Arabic-Aristotelian poetics lay not merely in its theoretical ideas, but also in its novel multilingual and cultural aspects that differed from the self-conscious Latin legacy of the older medieval poetics based on Horace and Cicero.
The regulation of body mass and its relation to the development of obesity
Authors: Juhász Attila , Katona Evelin , Csongrádi Éva , Paragh György
Published: September 2007

A testtömeg, ezen belül a zsírtömeg regulálása egy visszacsatolásos rendszerben valósul meg, melyben a zsírtömeg nagyságáról adipositasszignálok (leptin, inzulin, amylin), a pillanatnyi tápláltsági állapotról intestinalis peptidhormonok (ghrelin, PYY, PP, GLP-1, OXM, CCK) és a n. vagus informálják a központi idegrendszert mint központi szabályozót. A hypothalamus nucleus arcuatusának két jól elkülöníthető neuroncsoportja fogadja a zsírtömeg nagyságával arányos mennyiségben termelődő leptin közvetítette afferens információt. A leptinkötődés a sejtek felszínén elhelyezkedő leptinreceptorokhoz intracelluláris szignálmechanizmusokon keresztül a targetgének aktiválódását és anorexigén (POMC, CART) neuropeptidek termelését, majd másodlagos központokon keresztül az energiafelvétel és -leadás folyamatainak efferens regulációs mechanizmusait generálja. A testtömeg-szabályozás összetett és redundáns rendszer, számos más neuroendokrin folyamattal (növekedés, mellékvese- és pajzsmirigyműködés, reproduktív funkciók stb.), memória-, valamint jutalmazási és függőségi mechanizmussal áll kapcsolatban, így a szabályozórendszer egyes elemeinek befolyásolása, pl. gyógyszerekkel, más rendszerek működésére is hatással lehet, mellékhatások felléptére lehet számítani. Az obesitas világméretű epidémiája – mely elsősorban a magas energiasűrűségű élelmiszerek bőségével és a mozgásszegény életmóddal áll összefüggésben, melyhez a testtömeg-szabályozó rendszerünk nem tud megfelelően alkalmazkodni – intenzív kutatásokra ösztönzi az akadémiai és gyógyszeripari kutatóközpontokat annak érdekében, hogy új gyógyszerek, hatékony testsúlycsökkentő kezelési eljárások álljanak rendelkezésre az életmód-változtatási stratégiákon (diéta, fizikai aktivitás, magatartásterápia) túlmenően.
The possibilities of fractionated external beam reirradiation of relapsed primary brain tumours. The first Hungarian experience
Authors: Mangel László , Sipos László , Fedorcsák Imre , Viola Árpád , Julow Jenő , Bajcsay András , Németh György , Fodor János
Published: September 2007

Bevezetés:
A háromdimenziós CT/MRI alapú besugárzástervezés és a konformális sugárterápiás technikák bevezetése lehetővé tette az elsődleges rosszindulatú agydaganatok újabb kezelési formáinak, például az újrabesugárzási (reirradiációs) módszereknek a kidolgozását.
Célkitűzés:
Az Országos Onkológiai Intézet Sugárterápiás Osztályán frakcionált külső reirradiációs kezelésben részesült agydaganatos betegeknél a túlélés és a kezelés mellékhatásainak vizsgálata.
Módszer:
A szerzők 2002 és 2006 között tizenegy, előzetesen teljes dózisú (50–64 Gy) sugárkezelésben részesített agydaganatos betegnél végeztek teljes (50–54 Gy) vagy csökkentett (34–40 Gy) dózisú ismételt frakcionált külső besugárzást. A kezelések között eltelt időszak 7 és 30 év között volt. Minden esetben kihasználták a háromdimenziós sugártervezés és besugárzás adta lehetőségeket, a frakcionálás konvencionális (napi 1,8–2 Gy) volt.
Eredmények:
A betegek az újrabesugárzást minden esetben jól tolerálták, a kezelés közben, illetve az azt követő napokban komoly (Grade 3–4) neurológiai toxicitást nem észleltünk, a későbbiekben az érdemi kontaktust is megnehezítő, és nem a daganatos progresszióval kapcsolatos Grade 3 mentális hanyatlás egy esetben mutatkozott. Szövettanilag igazolt és ismételt műtétet szükségessé tévő radionekrózis egyszer fordult elő, illetve egy esetben valószínűsíthettünk komoly funkciókárosodást okozó kiterjedt agyszöveti károsodást. A medián progressziómentes időszak 8 (2–33) hónap, a medián túlélés 13 (4,5–33) hónap volt. A vizsgálat lezárásakor 3 túlélő beteg volt.
Következtetések:
A központi idegrendszer elsődleges daganatainak kiújulásakor más terápiás alternatíva hiányában a közel teljes dózisú frakcionált reirradiáció megfelelő feltételek mellett elvégezhető. Az optimális kezelési stratégia kidolgozásához további klinikai vizsgálatok szükségesek.
Advanced credit: patient enrolling and therapy initiation in the ADVANCE trial
Authors: Nagy Viktor
Published: September 2007

Az új évezredben a hipertónia és a cukorbaj fenyegeti világszerte a leginkább a populáció egészségi állapotát. A cukorbaj (hemoglobin-A1c < 6,5%) és a hipertónia (vérnyomás < 130/80 Hgmm) együttes beállítása központi helyet foglal el a cukorbetegek macro- és microvascularis betegségének megelőzésében. Az „Action in Diabetes and Vascular Disease: PreterAx and DiamicroN” tanulmány az első nagy prospektív, multicentrikus, randomizált, kontrollált vizsgálat, amelyben 2 × 2 faktoriális elrendezésben állapítják meg a vérnyomáscsökkentés (perindopril/indapamid kombináció) és a gliclazide-MR-en alapuló intenzív vércukor-beállítás hasznosságát a macro- és microvascularis kimenetelre.
Solid-phase epitaxial regrowth of fine-grain polycrystalline silicon
Authors: Sinke W. , Saris F. W. , Barbour J. C. , Mayer J. W.
Published: September 2007

Fine-grain polycrystalline silicon has been produced by low-energy pulsed-laser irradiation of copper-implanted amorphous silicon. This fine-grained material can be regrown epitaxially on the (100) substrate using thermal annealing at temperatures ranging from 800°–1000 °C.
Elastic strain energy and forces on point defects in a two-phase medium
Authors: Jagannadham K. , Narayan J.
Published: September 2007

Elastic strain energy and forces on point defects in a two-phase medium with a planar interface are analyzed employing the surface dislocation analysis developed earlier for three-dimensional distortions. The important field components, namely, the tractions and the displacements arising due to the point source at the interface, are determined. Furthermore, the field components at the interface are used to determine the elastic strain energy associated with the point source in the two-phase medium and the elastic force exerted by the second phase on the point defect. The significance of these results to the force acting on a vacancy or an interstitial at the interface is emphasized.
Precipitation of Icosahedral Al–Mn during pulsed laser melting
Authors: Aziz Michael J. , Budai John D.
Published: September 2007

The icosahedral phase has been produced by pulsed laser melting of thin films of Mn-implanted Al. With increasing laser intensity, we observe a mixture of icosahedral and fee phases followed by a single phase fee region. Grains as large as 1 μm in diameter have been observed in 0.1 μm thick films. Electron diffraction studies of individual icosahedral grains indicate that the rapid growth direction from the melt is along the threefold symmetry axis.
Nucleation behavior of Al–Mn icosahedral phase
Authors: Bendersky L.A. , Ridder S.D.
Published: September 2007

Electrohydrodynamic (EHD) atomization has been used to rapidly solidify micron and submicron size droplets of Al-14 at. % Mn to study nucleation behavior of icosahedral phase. Icosahedral grain size has been found to decrease continuously with decreasing droplet size. Based on this result, formation of the icosahedral phase is explained by homogeneous nucleation. Extremely low resistance to nucleation of icosahedral phase can be understood if possible topological similarities between liquid and icosahedral quasicrystal are considered. Formation of glass as configurationally frozen liquid in Al-Mn and similar alloy systems is questionable, implying that the reported Al-Mn glass probably has a microquasicrystalline structure.
Higher nitrides of hafnium, zirconium, and titanium synthesized by dual ion beam deposition
Authors: Johansson B.O. , Hentzell H.T.G. , Harper J.M.E. , Cuomo J.J.
Published: September 2007

We report the preparation and properties of higher nitrides of Hf, Zr, and Ti synthesized by dual ion beam deposition. For Hf and Zr, evidence is given for the existence of a metastable nitride phase with composition of approximately Hf3 N4 and Zr3 N4. These two materials are insulating and transparent straw colored, in contrast to the well-known mononitrides, which are shiny, gold colored, and highly conducting. For Ti-N we do not reach as high an N content and do not obtain an insulating, transparent phase. The higher nitrides of Hf and Zr are synthesized under energetic nitrogen ion bombardment (200 e V) of a growing film and do not form in the presence of molecular nitrogen gas alone. Several variations of the ion beam deposition process are used to obtain a wide range of film composition and to study the transition from the mononitride to the higher nitride phase. Transmission electron diffraction shows the structure of Hf3N4 and Zr3N4 to be very close to the Bl (NaCl) structure of the mononitrides, but with a slight rhombohedral distortion. Additional evidence from noble gas incorporation (Ne, Ar, and Xe) supports a model of these higher nitrides as containing a large number of vacancies on the metal atom sites.
Raman scattering and x-ray diffraction characterization of amorphous semiconductor multilayer interfaces
Authors: Allred D.D. , Gonzalez-Hernandez J. , Nguyen O.V. , Martin D. , Pawlik D.
Published: September 2007

Raman spectroscopy (RS) and low-angle x-ray diffraction (LAXRD) have been used to characterize semiconductor multilayer interfaces. In the present study a model for Raman spectra of multilayers is developed and applied to the specific case of the interfaces of a-Si/a-Ge multilayers. Quantification of the “blurring” of interfaces is possible because peak heights in the Raman spectra of thin films are proportional to the number of scatterers, thus RS is capable of directly “counting” the total number of chemical bonds of a given type in the film. Multilayers, prepared by various deposition techniques, are compared. The relative roles of LAXRD and RS in investigating interfaces are contrasted. Several a-Si/a-Ge multilayers deposited by ultra-high vacuum (UHV) evaporation (MBD) are found to exhibit very regular periodicities and exceptionally sharp interfaces (<1.0 Å intermixing).
Formation of stable dopant interstitials during ion implantation of silicon
Authors: Pennycook S.J. , Culbertson R.J. , Narayan J.
Published: September 2007

High concentrations of self-interstitials are trapped by dopant atoms during ion implantation into Si. For group V dopants, these complexes are sufficiently stable to survive solid-phase-epitaxial (SPE) growth but break up on subsequent thermal processing and cause a transientenhanced diffusion. Dopant diffusion coefficients are enhanced by up to five orders of magnitude over tracer values and are characterized by an activation energy of approximately one half of the tracer values. In the case of group III dopants, any complexes formed during implantation do not survive SPE growth but a second source of self-interstitials becomes significant and leads to similar transient effects. This is the damaged layer underlying the original amorphous/crystalline interface. These observations provide direct evidence for longrange self-interstitial migration in Si, and we believe these are the first observations of the interstitialcy diffusion mechanism with no vacancy contribution. We propose that the complexes are simply interstitial dopant atoms (in a split <100> interstitialcy configuration) that are particularly stable in the case of group V dopants. As they decay self-interstitials are released and cause the transient-enhanced diffusion.
Electron-beam-stimulated processes at CdS surfaces observed by real-time atomic-resolution electron microscopy
Authors: Smith David J. , Ehrlich Daniel J.
Published: September 2007

Electron-beam-induced changes in the structure of partially amorphous CdS surfaces have been observed directly by atomic-resolution electron microscopy. A sequence of atomic rearrangements leading to nucleation and growth of cubic CdS and hexagonal Cd has been documented. Inelastic electron collisions lead to crystallization of overlying amorphous CdS material whereas electron-stimulated desorption of S from the underlying CdS crystal results in precipitation of Cd crystallites at the crystalline/amorphous interface. From 100 to 500 keV the events are almost energy-independent.
Alpha-recoil damage in zirconolite (CaZrTi2O7)
Authors: Lumpkin G.R. , Ewing R.C. , Chakoumakos B.C. , Greegor R.B. , Lytle F.W. , Foltyn E.M. , Clinard F.W. , Boatner L.A. , Abraham M.M.
Published: September 2007

Radiation effects in a natural, metamict zirconolite from Sri Lanka that has received an alpha-decay dose greater than 1026 alpha decays/m3 have been studied using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron paramagnetic resonance spectroscopy (EPR), extended x-ray absorption fine structure spectroscopy (EXAFS), and x-ray absorption near edge structure spectroscopy (XANES). The same techniques were applied to the sample annealed between 1000°and 1100°C. The heat of recrystallization was measured by differential thermal analysis (DTA) with values of 40 to 50J/g. In contrast to previous work [A. E. Ringwood, Am. Scientist 70, 201 (1982); Mineralog. Mag. 49, 159 (1985)], these results demonstrate that there are fundamental differences at the atomic level between the annealed, crystalline, and the natural, fully damaged zirconolite. We suggest that the most likely structure for the fully damaged state is that of a random, three-dimensional network with no atomic periodicity extending beyond the first coordination sphere. Even within the first coordination sphere, there is a reduction in coordination number and an associated decrease in bond length for principal cations (Ca and Ti). Despite this structural modification and the great age of the specimen (∼550 million years), the natural zirconolite shows only minor signs of geochemical alteration. The metamict structure is readily annealed, initially to a disordered, flourite-type structure, and finally, at higher temperatures, to a highly twinned, monoclinic zirconolite structure.
Factors influencing the stability of the tetragonal form of zirconia
Authors: Srinivasan Ramachandra , De Angelis Robert , Davis Burton H.
Published: September 2007

ThepH of the solution that zirconia is precipitated from defines the crystal phase formed after calcination of the material at 400°to 600°C. A metastable tetragonal form is obtained for either low (less than about 5) or high (greater than about 13)pH. The tetragonal phase formed at highpH is much more stable at the calcination temperature than the material obtained at a lowpH is. For a material obtained by precipitation at a lowpH, monoclinic crystallites, determined by x-ray line broadening, were obtained that were smaller than the tetragonal crystals that produced them. A crystallite size effect, based on x-ray line broadening, is not responsible for the formation or stabilization of the tetragonal phase.
Detection of a metallic glass layer by x-ray diffraction
Authors: McCamy J.W. , Godbole M.J. , Pedraza A.J. , Lowndes D.H.
Published: September 2007

A simple, precise method for obtaining the average thickness of an amorphous layer formed by any surface treatment has been developed. The technique uses an x-ray diffractoeter to measure the reduction in the integrated intensity of several diffracted x-ray lines due to the near surface amorphous layer. The target material for generation of x rays is selected so that the emitted x rays are strongly absorbed by the specimen. This method permits thickness measurements down to ∼ 100 nm. It has been tested on a specimen of Fe80B20 on which an amorphous layer was produced by pulsed XeCl (308 nm) laser irradiation; the amorphous layer thickness was found to be 1.34 (∼0.1) um.
Crack propagation thresholds: A measure of surface energy
Authors: Cook Robert F.
Published: September 2007

Crack propagation thresholds in brittle materials are explained by consideration of the work done by the applied loading and that needed to create new surfaces as a crack propagates. The threshold mechanical energy release rate is shown to be a measure of the equilibrium surface energy of the material, dependent on the chemical environment. For applied loadings greater than those needed to maintain equilibrium the surface energy term introduces nonlinearities into the crack propagation characteristics. Any surface force or lattice trapping behavior at the crack tip will not influence the observed threshold provided the crack tip remains invariant on crack extension. A simple indentation/strength technique is demonstrated that permits the surface energy in the equilibrium state to be estimated. The technique is applied to the propagation of cracks in sapphire and the surface energy in water estimated as 1.42 J m−2, suggesting that the surfaces in water are stabilized by interactions stronger than van der Waals forces or hydrogen bonding alone.
Application of the embedded atom method to Ni3Al
Authors: Foiles S. M. , Daw M. S.
Published: September 2007

The embedded atom method [M. S. Daw and M. I. Baskes, Phys. Rev.B 29, 6443 (1984) used to calculate phase stability, lattice vibrational frequencies, point defect properties, antiphase boundary energies, and surface energies and relaxations for Ni3Al. The empirical embedding functions and core-core repulsions used by this method are obtained. The equilibrium phases for the Ni-rich half of the composition range of Ni–Al are determined for 1000 K and compared with experiment. The elastic constants and vibrational modes of Ni3Al are calculated and the elastic constants are compared with experiment. The formation energy, formation volume, and migration energies of vacancies are computed, and it is found that the formation energy of vacancies on the Ni sublattice is less than that on the Al sublattice. The (100) antiphase boundary is shown to be significantly lower in energy than the (111) antiphase boundary. The surface energies and atomic relaxations of the low index faces are computed, and it is shown that for the (100) and (110) faces that the preferred surface geometry corresponds to the bulk lattice with the mixed composition plane exposed.
Laser radiation enhancement of the corrosion resistance of an amorphous ribbon alloy
Authors: Schulz Robert , Lee Natalia L. , Clemens Bruce M.
Published: September 2007

The effects of pulsed laser radiation on the corrosion resistance, surface morphology, and composition of liquid-quenched amorphous Fe32Ni36Cr14P12B6 (Allied Corporation Metglas¯ 2826A) are reported. Scanning electron microscopy, Auger depth profiling, and x-ray diffraction were used to characterize the surface, while the corrosion resistance was determined by anodic polarization in H2SO4. The surface of the as-received melt-spun ribbons exhibited many defects, including cracks, compositional irregularities, and microcrystals of Ni5P4. These microcrystals differ from those found upon bulk crystallization. Melting and rapid solidification by radiation with a Q-switched Nd–YAG laser [30 ns full width at half maximum (FWHM)] modified the surface morphology (leaving composition constant), removing the microcrystals and cracks and reducing the carbon and oxygen contamination. The reduction of these surface defects resulted in improved corrosion resistance of the Metglas¯ 2826A ribbon. For example, spontaneous passivation is observed for the laser-treated samples, as opposed to critical current densities of 10μA/cm2 and 1000μA/cm2 for the as-received amorphous and crystallized Metglas¯ alloy, respectively.
Constrained network model for predicting densification behavior of composite powders
Authors: Lange F. F.
Published: September 2007

Inert particles that do not contribute to the densification of a composite powder compact are visualized as located on network sites; the network is defined by the distribution of the particles in the powder matrix. Because the distances between neighboring network sites are not identical, the strain produced by the sintering powder between all inert particle pairs cannot be the same as that for the powder compact without the inert particles. The constrained network model is based on the hypothesis that the densification of the composite will be constrained by the network and will mimic that of the network. The shrinkage of the network, and thus the densification of the composite, is estimated with a periodic network. A distance between the minimum and maximum site pairs within the unit cell defines the distance between site pairs in the random network where the powder between the particles densifies in the same manner as that for the powder without the inert particle. When the particles form a continuous touching network, composite shrinkage and densification is nil. The chosen lattice must also conform to this condition. A simple relation was developed relating the densification behavior of the composite to that of the matrix without the inert particles and the parameter associated with the chosen lattice. By choosing the lattice formed by the tetrakaidecahedron unit cell (volume fraction of particles for a touching network = 0.277), remarkable agreement was achieved for the experimental data concerning the densification behavior of the ZnO/SiC composite system reported by De Jonghe et al. [L. C. De Jonghe, M. N. Rahaman, and C. H. Hsueh, Acta Metall. 34, 1467 (1986)]. The universal nature of this lattice for other composites is discussed with respect to site percolation theory. The application of this concept to powder compacts containing either whiskers or agglomerates is briefly discussed.
Recrystallization of ion-implanted α-SiC
Authors: Bohn H. G. , Williams J. M. , McHargue C. J. , Begun G. M.
Published: September 2007

The annealing behavior of ion-implanted α-SiC single crystal was determined for samples implanted with 62 keV 14N to doses of 5.5X1014/cm2 and 8.0X1016/cm2 and with 260 keV 52Cr to doses of 1.5X1014/cm2 and 1.0X1016/cm2. The high-dose samples formed amorphous surface layers to depths of 0.17 μm (N) and 0.28 μm (Cr), while for the low doses only highly damaged but not randomized regions were formed. The samples were isochronically annealed up to 1600°C, holding each temperature for 10 min. The remaining damage was analyzed by Rutherford backscattering of 2 MeV He+, Raman scattering, and electron channeling. About 15% of the width of the amorphous layers regrew cpitaxially from the underlying undamaged material up to 1500°C, above which the damage annealed rapidly in a narrow temperature interval. The damage in the crystalline samples annealed linearly with temperature and was unmeasurable above 1000°C.
An investigation of the Ni5Al3 phase
Authors: Khadkikar P. S. , Vedula K.
Published: September 2007

The crystallography of the phases obtained by heat treating a Ni-34.7 at. % Al alloy with 0.9 at. % Hf and 0.04 at. % B was studied in detail using x-ray diffraction techniques. Particular emphasis was placed on characterizing the Ni5Al3 phase, which is obtained by quenching the B2 NiAl phase and aging the resultant martensite. The structure of the Ni5Al3 phase is confirmed to be orthorhombic with space group D192h (Cmmm) and lattice parameters of a0 = 0.7475 nm, b0 = 0.6727 nm, and c0 = 0.3732 nm. The transformation from B2 NiAl to L10 martensite is shown to involve a Bain distortion of the c/a ratio from 0.707 to 0.853, and the further ordering transformation to Ni5Al3 involves a further increase of this c/a ratio to 0.900.
Characterization of a synthetic apatite sinter for study of diffusion processes during acidic dissolution of dental enamel and other porous solids
Authors: Dibdin G. H. , Elliott J. C. , Anderson P.
Published: September 2007

A sintered aggregate of hydroxyapatite, Ca10(PO4)(6(OH)2, designed for in vitro simulation of some of the physicochemical processes of dental decay is described and characterized. Diffusivity at 35°C (by tritiated water effusion) was (2.9 + 0.6) ⊠ 10−6 cm2/s. The apparent density (2.50 ± 0.04) g/cm3 gave a porosity of 20.8 ± 1.3 vol % based on the theoretical density of hydroxyapatitc. Estimates of the volume percent porosity from water vapor desorption and tritiated water effusion were 19.2 ± 2.9 and 20.7 ± 1.4, respectively Pore-size distribution measurements using mercury porosimetry showed that most of the porosity (approximately 17% of the sample volume) was concentrated between 30 and 60 nm equivalent pore radius. The material, which has been successfully used to simulate some aspects of the dental decay process, should find further application in this and related fields.
Effects of milling brominated P-100 graphite fibers
Authors: Gaier James R. , Dillehay Michael E. , Hambourger Paul D.
Published: September 2007

Preliminary procedures have been developed for the ball milling of pristine and brominated P-100 graphite fibers. Because of the lubricative properties of graphite, large ball loads (50% by volume) are required. Use of 2-propanol as a milling medium enhances the efficiency of the process. The fibers, when allowed to settle from the milling medium, tend to be preferentially aligned with rather few fibers standing up. Milled, brominated P-100 fibers have resistivities that are indistinguishable from their pristine counterparts, apparently because of loss of bromine. This suggests that bromine would not be the intercalate of choice in applications where milled fibers of this type are required. It was found that brominated graphite fibers are stable in a wide variety of organic solvents.
Mechanical properties of GaAs crystals
Authors: Yonenaga Ichiro , Onose Utako , Sumino Koji
Published: September 2007

Mechanical properties of GaAs crystals grown by the liquid encapsulated Czochralski technique and the boat technique are investigated by means of compression tests. Stressstrain characteristics of a GaAs crystal in the temperature range 400°–500°C are very similar to those of a Si crystal in the temperature range 800°–900°C. This seems to reflect the fact that the dislocation mobility in a GaAs crystal in the former temperature range is comparable to that in a Si crystal in the latter temperature range. Dislocations in GaAs crystals are found to be easily immobilized at an intermediate temperature due to gettering of impurities and/or impurity-point defect complexes. In comparison to a Si crystal, the surface of a GaAs crystal seems to involve irregularities that act easily as effective generation centers for dislocations. Thus the magnitude of the yield stress of an aged GaAs crystal is controlled by the surface condition and is not influenced by the density of dislocations involved in the crystal. The socalled steady state of deformation is realized in a GaAs crystal in the deformation stage after the lower yield point as in Si and Ge crystals. Dislocation distributions in a deformed GaAs crystal observed by transmission electron microscopy is very similar to those in deformed Si and Ge crystals.
Influence of In and Ag atoms on optical and electrical properties of some Ge–Sb–S glasses
Authors: Tichá H. , Tichy L. , Klikorka J.
Published: September 2007

The influence of In and Ag atoms on the dc electrical conductivity and optical properties in the short wavelength edge region in Ge20Sb10S70 and Ge30Sb10S60 glasses has been examined. Contrary to the effect of In atoms, the Ag atoms at concentration levels below 4 at. % of Ag significantly influence the dc conductivity. Changes of the optical properties are less significant, and they are affected in a similar way by incorporation of In and Ag atoms into a glassy matrix. It is supposed that some of the Ag atoms are positively ionized to an Ag+ species that remains in the network. The 5s1 electron of Ag interacts with D+ states making, in the final state, an increase of D− defect states. Thus the Fermi level is shifted to the valence band and the dc conductivity increases.
Four-mode behavior in an In1−xGaxAsyP1−yquaternary alloy
Authors: Gupta H. C. , Sood Geeta , Malhotra Jaishree , Gupta Vijay Baboo , Tripathi B. B.
Published: September 2007

Log wavelength optical photons in a quanternary In1−xGaxAsyP1−yalloy are investigated based on the Green's function technique utilizing the concentration-dependent modified rigid ion model (MRIM). In order to obtain four-mode behavior in an A1−xBxCyD1−yquaternary alloy, formation of two cells AB and CD has been considered. In addition to the interactions betwen A, B, C, and D in their concentration ratios with a nonrandom ness parameter, the intercell and the intracell interactions are also taken into account. The results for the In1−xGaxAsyP1−yquaternary alloy are found to be in satisfactory agreement with the available experimental results.
Amorphous phase formation in Al70Si17Fe13 alloy
Authors: Bendersky L. A. , Biancaniello F. S. , Schaefer R. J.
Published: September 2007

The alloy Al70Si17Fe13 was subjected to a range of rapid solidification conditions and the resulting microstructures were evaluated. It was found that when solidification was sufficiently rapid to bypass the formation of primary intermetallic phases, the alloy consisted of spherical regions of amorphous (or microquasicrystalline) material surrounded by a crystalline phase(s). This microstructure is interpreted as the result of solidification of the amorphous phase from the melt by a first-order transformation. The structure of the amorphous phase is different from that of a liquid (or usual metallic glass).
The role of ion-beam cleaning in the growth of strained-layer epitaxial thin transition metal films
Authors: Park Sung I. , Marshall A. , Hammond R. H. , Geballe T. H. , Talvacchio J.
Published: September 2007

Low-energy ion-beam cleaning of the substrates prior to a deposition greatly enhances the quality of ultrathin (< 100 Å) refractory superconducting (Nb, V) films. Using this technique Nb films as thin as 7 Å have been grown, from which good tunnel junctions have been fabricated. Both the native films and the tunnel junctions are sturdy and can be thermally recycled without any degradation. In-situ surface study along with transmission electron microscopy (TEM) results suggest the removal of the carbon atoms from the surface of the substrate without an apparent surface damage as the causes of the improvement. The TEM results indicate that the Nb films grow perfectly lattice matched to the sapphire substrate when the substrate is ion-beam cleaned. This strained-layer epitaxy is observed up to 40 Å, the maximum thickness investigated through TEM.
The use of thermodynamic models in the prediction of the glass-forming range of binary alloys
Authors: Schwarz R. B. , Nash P. , Turnbull D.
Published: September 2007

Analytical expressions describing the various thermodynamic phases in binary systems can be derived by the CALPHAD approach, whereby the parameters in these expressions are obtained from fits to measured phase equilibrium data. Extrapolations of these models can be used to predict metastable equilibria. Different thermodynamic models proposed for the Ni–Ti and the Cu–Ti systems are used to calculate the T0 curves that are relevant to the prediction of the glass-forming range in rapidly cooled molten alloys. Although all the models give acceptable fits for the equilibrium range for which they were derived, significant differences are found for the metastable regime. The problems that need to be addressed in order to improve the extrapolations into the metastable regime are discussed. Simple thermodynamic considerations predict that the glass-forming range for rapidly quenched alloys exceeds that for amorphous alloys synthesized by isothermal solid-state interdiffusion reactions.
Interfacial reaction-induced morphological instabilities in thin Al/Pt and Al/Pd films
Authors: Colgan E. G. , Li C.-Y. , Mayer J. W.
Published: September 2007

Aluminum films 1–6 kÅ thick deposited on Pt or Pd layers developed voids after annealing between 200 and 275°C. Void formation was also observed when the Pt layer was deposited above the Al film. The amount of Al surrounding the voids increased as the voids grew. The rate of void growth decreased as the thickness of the initial Al film increased. The driving force appears to be surface tension. The controlling mechanism is diffusion along the Al/Pt or Al/Pd interface made possible by compound formation there.
Properties and microstructure of thin LiNbO3 films prepared by a sol-gel process
Authors: Partlow D. P. , Greggi J.
Published: September 2007

Thin LiNbO3 films were prepared from polymerized sol-gel precursor solutions having various concentrations and water:alkoxide ratios in an effort to investigate the effects of these and other processing variables on the resultant film properties and microstructure. Films deposted on silicon substrates were mostly amorphous when pyrolyzed at 435°C for 30 min. Randomly oriented polycrystalline films having distinctive microstnietures were produced using longer heating times or higher temperatures. All of the films exhibited low refractive indices due to porosity, which was attributed to the low level of hydrolysis water required to produce stable polymeric precursor solutions. When single-crystal LiNbO4 was used as the substrate, epitaxial growth of the film resulted. This ideal case establishes the feasibility of producing epitaxial films via sol-gel processing. All films were characterized by transmission electron microscopy (TEM) and thin-film x-ray diffraction patterns.
Theory of chemically induced kink formation on cracks in silica. II. Force law calculations
Authors: Masuda-Jindo K. , Tewary V. K. , Thomson Robb
Published: September 2007

This article is this second of a pair on a theory of chemically assisted fracture. In it a simple bond orbital model of the force laws to be used in fracture is developed. In the bond orbital model, only a few of the atoms in the vicinity of the bond to be broken are considered and do not include interactions with the rest of the system, which is assumed to be Newtonian. Numerical accuracy is not required, but qualitative features of the force laws are believed to be valid. The silica bond is shown to rise quickly to a high peak, after which it develops a relatively long tail. When the bond is attacked by water, modeling by the same technique indicates that the bond has a “snapping” characteristic that is important in the theory developed in the first article. For bonds with smooth “back sides” the barriers to crack motion are shown to be low, but barriers are expected to be observable when the bond snaps. A tight binding treatment of a one-dimensional chain has been included in order to investigate the effect of including band effects in the force law. These effects are found to be small compared to the simple bond breaking of the bond orbital calculation.
In situ optical and structural studies of H2 chemisorption in C8K
Authors: Doll G. L. , Eklund P. C.
Published: September 2007

Results of in situ optical (reflectance, Raman scattering) and 00l x-ray diffraction studies of hydrogen chemisorption in Grafoil-based stage 1 C8K intercalation compounds are presented. Upon hydrogen uptake, stage 2 KC8H2/3 was found to coexist with C8K forming first in the optical skin depth. The intensities of the 00l x-ray diffraction peaks show quantitatively that the reaction C8K + 1/2xH2 ⇉ (1 − 3/2x)C8K + 3/2xC8KH2/3 occurs for x>0.4 in the bulk. The effects of the surface morphology of Grafoil on the near-normal incidence reflectance was investigated and found to be described by an energy (E) dependent function S(E) = exp[−aEn], such that the corrected spectrum Rc = SR, where R is the Grafoil reflectance. In this manner, reflectance spectra of C8K-Grafoil and C8KH2/3-Grafoil were quantitatively analyzed to determine the free carrier contribution. The free carrier lifetimes were found to be a factor of 2 shorter in Grafoil-based hosts, compared to highly oriented pyrolytic graphite-based hosts. The optical results for C8KH2/3 indicate the H(ls) band is full (or very nearly full).
Optical properties of amorphous hydrogenated carbon films: A spectroscopic ellipsometry study
Authors: Lin Shuhan , Chen Shuguang
Published: September 2007

Optical properties of plasma-deposited amorphous hydrogenated carbon films were studied by spectroscopic ellipsometry. From the ellipsometry data, the real and imaginary parts,nandk, of the complex index of refraction of the film have been deduced for photon energies between 2.0 and 4.0 eV for as-grown as well as for thermally annealed films. Herenandkshowed considerable variation with subsequent annealing, even under 400°C. A tentative explanation of the results is proposed.
Fabrication of oxide superconductors from multilayered metallic thin films
Authors: Nastasi M. , Arendt P. N. , Tesmer R. , Maggiore C. J. , Cordi R. C. , Bish D. L. , Thompson J. D. , Cheong S-W. , Bordes N. , Smith J. F. , Raistrick I. D.
Published: September 2007

Thin-film GdBa2Cu3Ox superconductors with an onset Tc > 90 K have been produced. The films were fabricated by thermal reaction in an oxidizing atmosphere of electron-beam deposited Ba/Gd/Cu multilayers. Attempts to produce the superconducting phase YBa2Cu3Ox by multilayer reaction were unsuccessful due to a positive heat of mixing between Y and Ba. The appearance of a wide superconducting transition in GdBa2Cu3Ox films may be the result of tunneling through a nonsuperconducting second phase.
Reoxygenation of vacuum-annealed YBa2Cu3O6.9
Authors: Ginley D. S. , Nigrey P. J. , Venturini E. L. , Morosin B. , Kwak J. F.
Published: September 2007

Vacuum-annealed samples of single-phase orthorhombic YBa2Cu3O6.9 have been reoxygenated. The vacuum-annealed material is tetragonal, semiconducting at room temperature, and shows no superconductivity. Upon annealing these samples in 640 Torr O2 at 200°C, a partial return of 90 K superconductivity is observed; complete restoration is achieved following 300°C anneals. Oxygen uptake in vacuum-annealed pellets follows an Arrhenius relation with an activation energy of −27 kcal/mol. Deoxygenation and reoxygenation does not seem to affect the structure of the grain interconnects in the material. The maximum oxygen uptake for vacuum-annealed material occurs at 450°C, while the maximum magnetic Meissner effect is observed following oxygen annealing at 350°C.