bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallization and preliminary crystallographic analysis of the Escherichia coli tyrosine aminotransferase
Authors: Ko Tzu-Ping , Wu Szu-Pei , Yang Wei-Zen , Tsai Hsin , Yuan Hanna S.
Published: July 2002

Tyrosine aminotransferase catalyzes transamination for both dicarboxylic and aromatic amino-acid substrates. The substrate-free Escherichia coli tyrosine aminotransferase (eTAT) bound with the cofactor pyridoxal 5′-phosphate (PLP) was crystallized in the trigonal space group P32. A low-resolution crystal structure of eTAT was determined by molecular-replacement methods. The overall folding of eTAT resembles that of the aspartate aminotransferases, with the two identical subunits forming a dimer in which each monomer binds a PLP molecule via a covalent bond linked to the ∊-NH2 group of Lys258. Comparison of the structure of eTAT with those of the open, half-open or closed form of chicken or E. coli aspartate aminotransferases shows the eTAT structure to be in the open conformation.
Crystallization and preliminary X-ray crystallographic studies of the D2 region of the skeletal muscle ryanodine receptor
Authors: Kim Seha , Shin Dong Wook , Kim Do Han , Eom Soo Hyun
Published: July 2002

The N-terminal portion (amino acids 1303–1367) of the type 1 ryanodine receptor D2 region is thought to be critical for excitation–contraction coupling in skeletal muscle. A segment of the D2 region (amino acids 1317–1355) was expressed as a glutathione S-transferase fusion protein (GST-D2) and then crystallized at room temperature using ammonium sulfate as precipitant. Using a newly developed cryo-soaking method, complete native data sets were measured to a resolution of 2.2 Å using synchrotron radiation. The crystal was found to be hexagonal, belonging to space group P6322, with unit-cell parameters a = b = 116.1, c = 77.9 Å.
Structure of the RWJ-51084–bovine pancreatic β-trypsin complex at 1.8 Å
Authors: Recacha Rosario , Carson Mike , Costanzo Michael J. , Maryanoff Bruce , DeLucas Lawrence J. , Chattopadhyay Debasish
Published: July 2002

The three-dimensional structure of bovine pancreatic trypsin complexed with the inhibitor RWJ-51084 has been determined at 1.8 Å resolution. These crystals belong to the trigonal space group P3121, with unit-cell parameters a = b = 53.43, c = 107.76 Å. The refined R and R
free values are 0.175 and 0.237, respectively. The carbonyl group bonded to the benzothiazole group of the inhibitor is covalently linked to the hydroxyl O atom of Ser195, forming a tetrahedral intermediate hemiketal structure. The other carbonyl O atom of the inhibitor forms a hydrogen bond with the Gln192 side-chain amide group. The benzothiazole group is oriented with the aromatic N atom of RWJ-51084 accepting a hydrogen bond from His57 NE2. The arginine side chain of the inhibitor extends into the deep and narrow pocket of the S1 specificity site of trypsin, forming a network of hydrogen bonds.
Lactoferrin–metal interactions: first crystal structure of a complex of lactoferrin with a lanthanide ion (Sm3+) at 3.4 Å resolution
Authors: Sharma Ashwani K. , Singh Tej P.
Published: July 2002

Lactoferrin is an important member of the transferrin family. A characteristic property of transferrins is their ability to bind very tightly (K
app ≃ 1020) but reversibly two Fe3+ ions. The structural consequences of binding a metal other than Fe3+ have been examined by crystallographic analysis at 3.4 Å resolution of mare samarium–lactoferrin (Sm2Lf). The structure was refined to an R factor of 0.219 for 8776 reflections in the resolution range 17.0–3.4 Å. The samarium geometry (distorted octahedral coordination) is similar in both lobes. However, the anion interactions are quite different in the two lobes. In the N lobe, the anion is able to form only two hydrogen bonds instead of the four observed in the C lobe of Sm2Lf and the six observed in Fe2Lf. This is because Arg121, Thr117 and Gly124 have moved away from the anion as a consequence of the binding of the Sm3+ ion. The protein ligands in the binding cleft of Sm2Lf show large displacements, but the overall protein structure remains the same. The binding of Sm3+ by lactoferrin shows that the protein is capable of sequestering ions of different sizes and charges, though with reduced affinity. This conclusion should be true of other transferrins also.
Crystallization and preliminary X-ray diffraction studies of C4-form phosphoenolpyruvate carboxylase from maize
Authors: Matsumura Hiroyoshi , Nagata Takahiro , Terada Mika , Shirakata Shunsuke , Inoue Tsuyoshi , Yoshinaga Takeo , Ueno Yoshihisa , Saze Hidetoshi , Izui Katsura , Kai Yasushi
Published: July 2002

Phosphoenolpyruvate carboxylase is a key enzyme in the fixation of atmospheric CO2 in C4 and crassulacean acid metabolism (CAM) plants. The enzyme catalyzes the irreversible carboxylation of phosphoenolpyruvate to form oxaloacetate and inorganic phosphate, the first committed step in the fixation of external CO2 in these plants. The enzyme has been isolated from maize leaves and crystallized using the hanging-drop vapour-diffusion method with PEG 8000 as a precipitant at pH 7.5. The crystals belong to space group C2221, with unit-cell dimensions a = 160.2, b = 175.6, c = 255.5 Å, and diffract to 3.2 Å resolution.
Structure of acutolysin-C, a haemorrhagic toxin from the venom of Agkistrodon acutus, providing further evidence for the mechanism of the pH-dependent proteolytic reaction of zinc metalloproteinases
Authors: Zhu Xue-yong , Teng Mai-kun , Niu Li-wen
Published: July 2002

The structure of acutolysin-C, a haemorrhagic zinc metalloproteinase from the venom of Agkistrodon acutus, has been analyzed and refined at 2.2 Å resolution. The space group of the crystal is P212121, with unit-cell dimensions a = 46.84, b = 49.52, c = 95.34 Å. One molecule was found in each asymmetric unit. The phasing problem was solved by the molecular-replacement program AMoRe. Crystallographic refinement was performed using X-PLOR, leading to final R and free R factors of 0.176 and 0.272, respectively. The residue sequence of acutolysin-C was determined mainly by electron density. No density was found for the first residue at the N-terminus and the last two residues at the C-terminus, which was also the case for most other P-I class snake-venom metalloproteinases (SVMPs). Acutolysin-C has two highly conserved characteristic sequences His142-Glu143-X-X-His146-X-X-Gly149-X-X-His152 and Cys162-Ile163-Met164. The enzyme has three disulfide bridges: Cys117–Cys195, Cys157–Cys179 and Cys159–Cys162. The entire structure shows good agreement with that of other reported P-I class SVMPs and has two subdomains with a cleft in which one catalytic zinc ion is localized. However, the local conformation (especially the disulfide configurations), the coordination of the catalytic water molecules and some residue side chains differ compared with other P-I class SVMPs. The proteolytic activities of SVMPs are sensitive to the pH value. The molecular superpositions around the proteolytic active sites of all the P-I class SVMP crystal structures show that the distances between the zinc ion and its ligands are not correlated with the crystallization pH values, although the contact distances between the catalytic water molecule and the O atoms of the Glu143 carboxylate group in the neutral and weakly alkaline structures are shorter than those in weakly acidic structures, and the closer the crystallization pH value of one enzyme is to its optimal activity pH value, the shorter the contact distances. Overall, all P-I class SVMPs have similar conformations in the active-site cleft. The size of the active site is not correlated with the crystallization pH values or the proteolytic activities. The disulfide bridge Cys117–Cys195 is conserved in all crystal structures of P-I class SVMPs, whereas the conformation and number of disulfide bridges in the C-terminal subdomain differ. Acutolysin-C has no structural calcium ion, which may not affect the proteolytic activity or haemorrhagic activity directly.
Initiating a structural study of 2-keto-3-deoxy-6-phosphogluconate aldolase from Escherichia coli
Authors: Buchanan Louise V. , Mehta Nupur , Pocivavsek Luka , Niranjanakumari S. , Toone Eric J. , Naismith James H.
Published: July 2002

2-Keto-3-deoxy-6-phosphogluconate aldolase (KDPG aldolase, E.C. 4.1.2.14) is a member of the pyruvate/phosphoenolpyruvate aldolase family. It is also a synthetically useful enzyme, capable of catalyzing the stereoselective aldol addition of pyruvate to a range of unnatural electrophilic substrates. The recombinant protein was purified by a two-step HPLC protocol involving anion-exchange and hydrophobic chromatography. Dynamic light-scattering experiments indicated the protein to be monodisperse. Crystals were obtained using the sitting-drop vapour-diffusion method, with PEG 6K as precipitant. Diffraction data were collected on a frozen crystal to a resolution of 2.26 Å on station PX9.6 at the Daresbury synchrotron. The crystal belongs to space group P212121, with unit-cell parameters a = 53.2, b = 77.9, c = 146.8 Å.
Structure of agkistrodotoxin in an orthorhombic crystal form with six molecules per asymmetric unit
Authors: Tang Liang , Zhou Yuan-Cong , Lin Zheng-Jiong
Published: July 2002

The structure of agkistrodotoxin crystallized under basic conditions has been determined at 2.8 Å resolution by the molecular-replacement technique and refined to a crystallographic R factor of 0.194 and a free R factor of 0.260 with good stereochemistry. The molecular packing in the crystal differs from other PLA2s. The six molecules in the asymmetric unit form three dimers linked by Ca2+ ions in a near-perfect six-ligand octahedral coordinating system. Extensive intermolecular hydrophobic interactions occur at the interfacial recognition site of each neurotoxin molecule, which provides an insight into phospholipase A2–membrane interactions. This hydrophobic interaction-induced molecular association along the interfacial recognition site suggests a self-protection mechanism of agkistrodotoxin.
Three-centre C—H...O hydrogen bonds in the DNA minor groove: analysis of oligonucleotide crystal structures
Authors: Ghosh Anirban , Bansal Manju
Published: July 2002

AA·TT and GA·TC dinucleotide steps in B-DNA-type oligomeric crystal structures and in protein-bound DNA fragments (solved using data with resolution <2.6 Å) show very small variations in their local dinucleotide geometries. A detailed analysis of these crystal structures reveals that in AA·TT and GA·TC steps the electropositive C2—H2 group of adenine is in very close proximity to the keto O atoms of both the pyrimidine bases in the antiparallel strand of the duplex structure, suggesting the possibility of intra-base pair as well as cross-strand inter-base pair C—H...O hydrogen bonds in the DNA minor groove. The C2—H2...O2 hydrogen bonds in the A·T base pairs could be a natural consequence of Watson–Crick pairing. However, the cross-strand interactions between the bases at the 3′-end of the AA·TT and GA·TC steps obviously arise owing to specific local geometry of these steps, since a majority of the H2...O2 distances in both data sets are considerably shorter than their values in the uniform fibre model (3.3 Å) and many are even smaller than the sum of the van der Waals radii. The analysis suggests that in addition to already documented features such as the large propeller twist of A·T base pairs and the hydration of the minor groove, these C2—H2...O2 cross-strand interactions may also play a role in the narrowing of the minor groove in A-tract regions of DNA and help explain the high structural rigidity and stability observed for poly(dA)·poly(dT).
Crystallization and preliminary crystallographic study of triple-helical DNA
Authors: Han Zong-Jin , Rhee Sangkee , Liu Keliang , Miles H. Todd , Davies David R.
Published: July 2002

Single crystals of d(CTCCTSCCGCGCG)·d(CGCGCGGAG) have been grown by the vapor-diffusion method using 2-methyl-2,4-pentanediol as a precipitant. The crystals are tetragonal, space group P42, with unit-cell parameters a = b = 53.8, c = 43.1 Å, and diffract to 1.8 Å resolution at a synchrotron X-ray beamline. In the crystal, the asymmetric unit contains one copy of the construct. The two halves of the structure are related by non-crystallographic twofold symmetry. These observations are consistent with the conclusion that the sequences of the 12-mer and 9-mer oligonucleotides form a duplex DNA at one end and a triplex DNA at the other end.
Experiences and expectations of a novel X-ray microsource with focusing mirror. I. Erratum
Authors: Bloomer A. C. , Arndt U. W.
Published: July 2002

The following are corrections to a paper by Bloomer & Arndt [(1999), Acta Cryst. D55, 1672–1680]. The entry in the second row of the I
MAR column of Table 1(b) on page 1674 should read 6.6 and not 16.6. In Table 4 on page 1677 the source diameter should be given as 15 µm and not 15 mm, and the units for the diameter of the sample should be given as µm instead of mm.
Characterization of Ti-Beta zeolites and their reactivity for the photocatalytic reduction of CO2 with H2O
Authors: Ikeue Keita , Yamashita Hiromi , Takewaki Takahiko , Davis Mark E. , Anpo Masakazu
Published: July 2002

A characterization of Ti-Beta zeolites synthesized under various conditions as well as an investigation of their photocatalytic properties for the reduction of CO2 with H2O at 323 K to produce CH4 and CH3OH were carried out. In situ XAFS spectra measurements indicated that a highly dispersed tetrahedral titanium oxide species was present in the zeolite framework and an increase in the coordination number of the titanium oxide species by the addition of H2O and CO2 molecules could be detected. The Ti-Beta zeolite having a hydrophilic property ( Ti-Beta(OH) ) exhibited a more dramatic increase in the coordination number than the Ti-Beta(F) zeolite which had a hydrophobic property. These results suggest that CO2 and H2O molecules can be adsorbed efficiently onto the highly dispersed tetrahedrally coordinated titanium oxide species. UV irradiation of these Ti-Beta zeolite catalysts in the presence of H2O and CO2 led to the formation of CH4 and CH3OH. Ti-Beta(OH) exhibited a higher reactivity than Ti-Beta(F), while the selectivity for the formation of CH3OH on Ti-Beta(F) was higher than that for Ti-Beta(OH). These results indicated that the reactivity and selectivity of the zeolite catalyst can be determined by the hydrophilic and hydrophobic properties of the zeolites.
Hydration of some large and highly charged metal ions
Authors: Sandström Magnus , Persson Ingmar , Jalilehvand Farideh , Lindquist-Reis Patric , Spångberg Daniel , Hermansson Kersti
Published: July 2002

EXAFS studies of metal ions with hydration numbers higher than six in aqueous solution, often show asymmetric distribution of the metal-oxygen bond distances. The hydration number can be determined from a correlation with the bond distance. The mean Ca-O distance 2.46(1) Å shows the calcium(II) ion to be eight-hydrated in a wide asymmetric distribution. Theoretically calculated EXAFS oscillations for individual snapshots from an MD simulation show large variations. The scandium(III) ion is surrounded by two groups of about eight water molecules, with the mean Sc-O distance 2.185(6) Å. The yttrium(III) ion coordinates eight waters in an asymmetric distribution at 2.368(5) Å, and the lanthanum(III) ion 6 + 3 water molecules at 2.52(2) and 2.65(3) Å, respectively. For the the uranium(IV) and thorium(IV) ions, the M-O distances 2.42(1) and 2.45(1) Å, respectively, indicate hydration numbers close to 10.
High-resolution soft X-ray absorption spectroscopy of solids
Authors: Saitoh Y. , Muro T. , Kotsugi M. , Iwasaki T. , Sekiyama A. , Imada S. , Suga S.
Published: July 2002

The present research deals with the high-resolution soft x-ray absorption spectra (XAS) of Si, Ce- and Sm- compounds measured at BL25SU of SPring-8. The spectra are compared with theoretical results. The Si 1s spectrum shows good agreement with the calculated empty density of states so far reported. The Ce 3d spectra are very sensitive to the local electronic structure. The Sm 3d XAS of SmS shows clear temperature dependence, which is partly explained by a calculation for Sm2+ ion.
XANES study on the valence transitions in cerium oxide nanoparticles
Authors: Zhang Jing , Wu Ziyu , Liu Tao , Hu Tiandou , Wu Zhonghua , Ju Xin
Published: July 2002

The aim of this work is the determination of Ce environment and valence state in cerium oxide nanoparticles prepared by the microemulsion method. X-ray absorption near-edge structure measurements at Ce L3 edge were performed on the nanoparticles as a function of annealing temperature, ranging from 298K to 873K under air condition. The experimental results support the conclusion that Ce ion, in the investigated systems, is in trivalence state when the annealing temperature is below 473K. As the temperature increases up to 623K, the XANES spectrum shows the coexistence of Ce3+ and Ce4+states. When the temperature is higher than 623K, the spectra become identical to that of CeO2 with a distinct double-peak structure, corresponding to the Ce4+ state.
Multiple ionization upon K-shell photoabsorption of the CO and N2 molecules
Authors: Yavna Victor , Nadolinsky Alexey , Hopersky Alexey , Yavna Svetlana
Published: July 2002

The spectra of multiple ionization of CO and N2 in the gas phase in the region of the K-shell ionization thresholds of C and N are studied theoretically. The processes of additional excitation/ionization from 1π and 5σ-shells are included. The effects of many-electron correlations on the extention of multiplet structure for some configurations of multiple excitations is studied. Absolute values of photoabsorption cross sections are calculated in some of the channels of multiple ionization.
The temperature dependence for the third shell's Fourier-peak of Nb-EXAFS in KNbO3 as additional source of information on the local atomic structure
Authors: Bugaev Lusegen A. , Shuvaeva Victoria A. , Zhuchkov Konstantin N. , Rusakova Elizaveta B. , Vedrinskii Rostislav V.
Published: July 2002

The information on the structure of tetragonal KNbO3 is extracted from the temperature dependence of the third shell's Fourier-peak of Nb-EXAFS. It is shown that this dependence can be explained by two effects: 1) rigid rotations of the O6-octahedron and 2) increase of the third shell's DW-parameter. However, diffraction data on the temperature dependence of the DW-parameter permit us to conclude that the last effect only is sufficient and the O6-octahedron rotation doesn't occur in the high-temperature phases of KNbO3. Using EXAFS it is revealed that in the neighboring cells Nb-atoms are parallel shifted closely to [211] direction in tetragonal phase.
Ni clay neoformation on montmorillonite surface
Authors: Dähn Rainer , Scheidegger André , Manceau Alain , Schlegel Michel , Baeyens Bart , Bradbury Michael H.
Published: July 2002

Polarized extended X-ray absorption fine structure spectroscopy (P-EXAFS) was used to study the sorption mechanism of Ni on the aluminous hydrous silicate montmorillonite at high ionic strength (0.3 M NaClO4), pH 8 and a Ni concentration of 0.66 mM. Highly textured self-supporting clay films were obtained by slowly filtrating a clay suspension after a reaction time of 14 days. P-EXAFS results indicate that sorbed Ni has a Ni clay-like structural environment with the same crystallographic orientation as montmorillonite layers.
Structural approach of CsCl-modified Ga2S3-La2S3 glasses
Authors: Alves M. C. M. , Ramos A.Y. , Watanabe N.
Published: July 2002

Gallium-lanthanum sulfide glasses have specific interesting physical properties, as semiconductor behavior and good transmission at long wavelengths. The addition of CsCl increases the thermal stability region of the glass making it suitable for many applications in optoelectronics. Ga2S3-La2S3 glasses modified by 10 to 40% CsCl have been studied by X-ray absorption spectroscopy, at the chlorine K edge and at the gallium K edge at 9 K, in order to get information about the actual structural role of CsCl. The chlorine environment is similar to that in CsCl. The gallium coordination sulfur polyhedra are weakly distorted tetrahedra, identical for all samples. The low temperature measurements shown that the polyhedral corner linkage is also unaltered by the addition of CsCl.
Determination of double decker sandwich structured La-substituted chlorophyll a by EXAFS
Authors: Tao Y. , Zhao G. , Yang J. , Ikeda S. , Jiang J. , Hu T. , Chen W. , Wei Z. , Hong F.
Published: July 2002

As a representative natural porphyrin derivative, it is interesting to know the chemical form of lanthanide in chlorophyll a. We select the natural fern dicranopteris dichotoma, the most lanthanide-concentrated plant known, to isolate the chlorophyll a for our study. It is found by EXAFS that lanthanum substitutes in the magnesium position in chlorophyll and coordinates with the porphyrin ring. The lanthanum is seen to have a similar coordination structure to a sandwich-type lanthanide complex, with the La surrounded by eight nitrogen atoms from two porphyrin rings with average La-N bond length of 2.65 Å.
X-ray absorption fine structure spectroscopy determination of the binding mechanism of tetrahedral anions to self assembled monolayers on mesoporous support
Authors: Kelly S. D. , Kemner K. M. , Fryxel G. E. , Liu J. , Mattigod S.
Published: July 2002

X-ray absorption fine structure (XAFS) spectroscopy is used to investigate the chemical interaction between the end member [Cu(NH2)6] of self-assembled monolayers on mesoporous supports (SAMMS) and the tetrahedral anion SO4. The local structure about Cu indicates monodentate bonding between the SO4 anion and the SAMMS.
Local structure of NiTi nanocrystals studied by EXAFS and XRD
Authors: Ju Xin , Su Yixi
Published: July 2002

A series of NiTi nanocrystals with different annealing temperatures, prepared by sputtering method, were investigated by extended x-ray absorption fine structure (EXAFS) and x-ray diffraction. It was found that the structure of nano-phase powder is different from bulk NiTi alloy with bcc structure as target materials. When increasing the annealing temperature, a small fraction of the (Ni,Ti) type nanocrystal with the hexagonal structure was presented except target materials and Ni, and it is atomic occupation in random. Finally there were four Ti and two Ni atoms around central Ni atoms, and the bond length of Ni-Ti and Ni-Ni were 0.2462nm and 0.2585nm at 800°C annealed.
Lattice softening in superconducting compositions of Ba(K)BiO3
Authors: Menushenkov A. P. , Klementev K. V. , Cortes R. , Purans J.
Published: July 2002

Temperature dependent X-ray absorption spectra investigation were measured for Ba1−x
K
x
BiO3 (Bi L3-edge) with x = 0.0, 0.25, 0.4, 0.5 and for BaPbO3 (Pb L3 edge). It was found that at low temperatures the Debye-Waller factor of the square diagonal Bi-Bi bond has the maximum value near the insulator-metal phase transition for the compound with x = 0.25 and x = 0.4. Temperature dependence of Debye-Waller factor of Bi-Bi bomnd strongly differs from the Einstein model curve that well describes the harmonic systems (for example BaPbO3). This behaviour is consistent with the strong anharmonicity of the Bi-O shell due to the double-well vibration potential reported by us earlier. Presented results point to the essential lattice softening of the superconducting compositions, which is important for the understanding of superconductivity mechanism in perovskite type oxides.
XAFS study on a pressure-induced superconductor Cs3C60 under high pressure
Authors: Fujiki Satoshi , Kubozono Yoshihiro , Takabayashi Yasuhiro , Kashino Setsuo , Emura Shuichi
Published: July 2002

Cs K-edge XAFS of Cs3C60 which is a pressure-induced superconductor were measured at 21 and 34 kbar by using a diamond anvil cell (DAC) in order to obtain the structural information under high pressure, and to clarify the origin of the pressure-induced superconductivity. The distances and the mean square displacements between the Cs and C atoms are consistent with those determined by X-ray powder diffraction. Consequently, the high-pressure XAFS can give the reliable structural-information on a fullerene superconductor under high pressure. We also show the procedure of the analysis of high-pressure XAFS with DAC in detail.
Growth induced magnetic and chemical anisotropy in CoPt3 alloy films
Authors: Cross J. O. , Newville M. , Hellman F. , Rooney P. W. , Shapiro A. L. , Harris V. G.
Published: July 2002

We report the results of polarized Co $K$ EXAFS experiments on a series of CoPt3 films grown by molecular beam epitaxy on (100) MgO single crystal substrates over a range of temperatures from 473 K to 1073 K. These samples exhibit substantial perpendicular magnetic anisotropy that is strongly dependent on the substrate growth temperature T

g
. We measure a preference for in-plane Co-Co pairs that is correlated with the magnetic properties.
A new approach for indexing powder diffraction data based on whole-profile fitting and global optimization using a genetic algorithm
Authors: Kariuki Benson M. , Belmonte Scott A. , McMahon Malcolm I. , Johnston Roy L. , Harris Kenneth D. M. , Nelmes Richard J.
Published: July 2002

This paper describes a new technique for indexing powder diffraction data. The lattice parameters (unit-cell dimensions) {a,b,c,α,β,γ} define the parameter space of the problem, and the aim is to find the optimal lattice parameters for a given experimental powder diffraction pattern. Conventional methods for indexing consider the measured positions of a limited number of peak maxima, whereas this new approach considers the whole powder diffraction profile. This new strategy offers several advantages, which are discussed fully. In this approach, the quality of a given set of lattice parameters is determined from the profile R-factor, R
wp, obtained following a Le Bail-type fit of the intensity profile. To find the correct lattice parameters (i.e. the global minimum in R
wp), a genetic algorithm has been used to explore the R
wp(a,b,c,α,β,γ) hypersurface. (Other methods for global minimization, such as Monte Carlo and simulated annealing, may also be effective.) Initially, a number of trial sets of lattice parameters are generated at random, and this `population' is then allowed to evolve subject to well defined evolutionary procedures for mating, mutation and natural selection (the fitness of each member of the population is determined from its value of R
wp). Examples are presented to demonstrate the success and underline the potential of this new approach for indexing powder diffraction data.
Azidoacetamide, a neutral small organic azide
Authors: Kumasaki Mieko , Kinbara Kazushi , Wada Yuji , Arai Mitsuru , Tamura Masamitsu
Published: July 2002

The structure of the title compound, C2H4N4O, was determined and found to be almost planar, excluding H atoms. The N—N bond lengths of 1.130 (2) and 1.231 (2) Å in the azide group exhibited a resonance effect and the characteristic organic azide structure.
A 2-styrylboronate ester
Authors: Clegg William , Marder Todd B. , Scott Andrew J. , Wiesauer Christian , Weissensteiner Walter
Published: July 2002

Molecules of the title compound, (E)-2-(2-phenylethenyl)-1,3,2-benzodioxaborole, C14H11BO2, are essentially completely planar with a high degree of conjugation. They pack with a herring-bone pattern in the crystal structure. The compound is synthesized with high regioselectivity by hydroboration of phenylacetylene with catecholborane.
(E)-1-(2-Thienyl)ethanone 8-quinolylhydrozone
Authors: Lynch Daniel E. , McClenaghan Ian
Published: July 2002

The structure of the title compound, C15H13N3S, comprises planar molecules. The dihedral angle between the quinoline and thiophene rings is 2.6 (2)°.
6-Amino-4-iminio-4H-1,3,5-dithiazole iodide
Authors: Lynch Daniel E. , McClenaghan Ian
Published: July 2002

The structure of the title compound, C3H6IN3S2, comprises a puckered ring that associates to the I−anionviaN—H...I interactions. In the asymmetric unit, two I−anions reside on special positions (twofold rotation axes) equivalent to one complete anion per cation. The cationic charge is delocalized between the two amines, as suggested by the similar bond lengths, across the heterocyclic N atom, between these two groups.
Developing turbulent duct flow: hybrid solution via integral transforms and algebraic model
Authors: Cotta R.M. , Pimentel L.C.G.
Published: July 2002

The integral transform method is employed for the hybrid numerical‐analytical solution of the boundary layer formulation in developing turbulent flow inside channels. An algebraic turbulence model due to Cebeci and Smith is adopted, in light of its popularity demonstrated in the recent numerical simulation literature. Numerical results for the velocity components in a parallel‐plates channel are obtained, and the automatic error control feature of the present approach is demonstrated. Critical comparisons with experimental works, as well as with previous simulations that employed differential turbulence models, are also performed.
Numerical Determination of Thermal Contact Resistance for Nonisothermal Forging Processes
Authors: Marchand A.-S. , Raynaud M.
Published: July 2002

A numerical study is conducted to estimate the thermal contact resistance (TCR) between the tool and the workpiece during slow nonisothermal forging processes. A finite difference method is used to determine the TCR from a thermomechanical microscopic model. Correlations of the numerical results are developed for the TCR as a function of the interface geometry and the thermal properties. The method used to introduce these correlations in forging softwares, to account for a time and space-dependent TCR instead of a constant arbitrary value, is given. The predictive capability of the correlations is partially validated by comparing their outputs with TCR results from the literature. [S0022-1481(00)00903-8]
Discussion: “The Impact of the Model of the Environment in Exergy Analyses” (Mun˜oz, J. R., and Michaelides, E. E., 1999, ASME J. Energy Resour. Technol., 121, pp. 268–276)
Authors: Szargut Jan
Published: July 2002

[S0195-0738(00)00104-7]
Free Response of Twisted Plates with Fixed Support Separation
Authors: Mockensturm Eric M. , Mote, C. D.
Published: July 2002

In previous work, Mockensturm and Mote investigated the effects of twist on steady motions of an axially moving plate. It was found that twisting produces compressive stresses that increase with twist, aspect ratio, and initial, longitudinal tension. In this work, we study the effects of the stresses and non-flat equilibrium produced by twist on the free response. To accomplish this, the equations of motion are linearized about the equilibrium configuration, yielding a set of three, coupled, linear partial differential equations. The equations are discretized and the free response is predicted from the resulting discrete eigenvalue problem. As a function of twist angle, the natural frequencies first increase and then decrease rapidly to zero as the compressive lateral stresses become sufficiently large to cause wrinkling. The effects of thickness, aspect ratio, and initial tension on natural frequencies are also studied.
Forced Convective Heat Transfer of Parallel-Mode Reciprocating Tube Fitted With a Twisted Tape With Application to Piston Cooling
Authors: Chang S. W.
Published: July 2002

This experimental study, motivated by the need to improve the cooling performance of a piston in a marine propulsive diesel engine, investigated turbulent flow heat transfer in a reciprocating tube fitted with a twisted-tape insert. The nonreciprocating experimental data, obtained from the tube fitted with twisted tape, confirmed that heat-transfer augmentation from plain-tube level occurs. When the test tube reciprocated, buoyancy effects became appreciable, and interacted with the reciprocating and inertial forces to provide considerable heat transfer modifications from nonreciprocating situation. When the reciprocating forces were relatively weak, a range of heat-transfer impediments, that could reduce local Nusselt numbers to levels of about 53% of nonreciprocating values, was observed. A further increase of the relative strength of the reciprocating force resulted in a subsequent heat-transfer recovery, and eventually led to heat-transfer enhancements relative to the nonreciprocating situation. For design considerations, heat-transfer enhancement due to the twisted-tape insert was confirmed, but the impediments from nonreciprocating levels at lower values of pulsating numbers needs particular attention in order to avoid overheating situations.
Numerical Simulation of Human Exposure to Aerosols Generated During Compressed Air Spray-Painting in Cross-Flow Ventilated Booths
Authors: Flynn Michael R. , Sills Eric D.
Published: July 2002

This paper examines the use of computational fluid dynamics as a tool for predicting human exposure to aerosols generated during compressed air spray painting in cross-flow ventilated booths. Wind tunnel experiments employing a mannequin and non-volatile oil provide data to evaluate the numerical predictions. Fidap (v8.01) is used to calculate the velocity field and particle trajectories, while in-house codes were developed to post-process the trajectory data into mass concentrations, size distributions, transfer efficiency, and over-spray generation rates. The predicted dimensionless breathing-zone concentration of 0.13±23 percent is in agreement with the measured value of 0.13±15 percent given the uncertainties involved in such comparisons. Computational fluid dynamics is a powerful tool capable of providing useful information to occupational hygiene engineers involved in controlling human exposures to toxic airborne contaminants.
On Using Unstable Electrohydraulic Valves for Control
Authors: Krishnaswamy Kailash , Li Perry Y.
Published: July 2002

High bandwidth, high flow rate electrohydraulic valves typically have two or more stages. Most multi-stage valves are expensive, require meticulously clean fluid, and introduce higher order dynamics. On the other hand, single-stage spool valves are cheaper and more reliable. However, a majority of them are not suitable for high bandwidth, high flow rate applications due to limitations of the electromechanical/solenoid spool-stroking actuators. In this paper, we investigate the feasibility of reducing this limitation by exploiting the transient flow forces in the valve so as to achieve spool dynamics that are intrinsically open-loop unstable. While conventional valves are designed to be open-loop stable, the unstable valve design has to be stabilized via closed-loop feedback. Simulation case studies are conducted to examine the potential dynamic and energetic advantages that an unstable valve may offer. These studies indicate that unstable valves provide faster response than the stable counterparts when stroking forces are limited. Moreover, unstable valves tend to require less positive power and energy to operate.
Turbomachinery Wakes: Differential Work and Mixing Losses
Authors: Rose M. G. , Harvey N. W.
Published: July 2002

In this paper the mixing of stator wakes in turbomachinery is considered. An extension is made to the existing model of Denton (1993, ASME J. Turbomach., 115, pp. 621–656) which addresses the effects of acceleration before mixing. Denton showed that if a total pressure wake was accelerated, mixing loss diminished, and vice versa. Here a total temperature wake is shown to exhibit a reverse trend. An attempt is also made to understand better the work transfer process between a stator wake and a rotor. The paper concentrates on axial turbines, but a brief look at compressors is included. It is argued that the free-stream work is not the same as the wake work, and the concept of “Differential Work” is introduced. A simple steady velocity triangle based model is proposed to give an estimate of the ratio of wake work to free-stream work (μ, see later). The model is compared to an unsteady CFD result to offer some verification of the assumptions. It is concluded that the rotodynamic work process tends to reduce total pressure wake depths in turbines and compressors and therefore mixing losses. The mixing loss due to total temperature wakes is less strongly affected by the differential work process. [S0889-504X(00)00801-1]
Depth profiling of an ion plated interface by ion scattering spectrometry
Authors: Hoffman D. W. , Nimmagadda R.
Published: July 2002

The depth profile of composition for gold films ion plated onto chromium has been investigated through the region of the interface by ion scattering spectrometry and compared with similar films formed by electron beam evaporation and rf sputtering. Significant grading of the composition at the interface is observed, but not uniquely in the ion plated films. Rather a gradual transition from pure chromium to pure gold occurs over the distance of 100 atomic layers in both the ion plated and evaporated films irrespective of bias voltage on the substrate. On the other hand, sharp interfaces with no composition grading are observed when the chromium substrates are not cleaned by sputter etching to remove the thin oxide layer immediately prior to coating. In no case is there any indication of composition grading on the scale of microns as reported in the literature for copper ion-plated onto steel.
Preparation and Properties of Pb1−xLnxTe (Ln=Eu, Yb) Films
Authors: Suryanarayanan R. , Paparoditis C.
Published: July 2002

We have adopted the technique of co-evaporation to prepare Pb1−xLnxTe films. Both amorphous and freshly cleaved NaCl substrates have been used. Structural, optical, and electrical properties of these films were studied. It is found that PbTe–EuTe alloys form single phase solid solutions over the entire range of composition and epitaxial films could be obtained. Electrical and optical properties are reported. n and p-type single-crystal films of PbTe with u77=5000 cm2/V-sec have been prepared. Transmission and reflection measurements of EuTe films indicate a band gap value of 2.25 eV with an absorption co-efficient of 105 cm−1 in the absorbing region. Electrical measurements of YbTe show it to be a wide band gap material. We also report optical and electrical properties of Pb1−xYbxTe films.
Piston Manometer as an Absolute Standard for Vacuum-Gauge Calibration
Authors: Warshawsky I.
Published: July 2002

Total pressure in a calibration volume is determined by measuring the force on a thin circular disk, of accurately known area, that is freely suspended in a hole in the container wall, so that the disk is substantially flush with the wall. The disk almost fills the hole, so that there is a narrow annular gap. A continuous flow of calibrating gas, injected into the container in order to maintain a desired pressure, passes through the annular gap to a diffusion pump. The ratio of pressures on the two faces of the disk is of the order of 100:1, so that downstream pressure need be known only nominally in order to deduce the upstream pressure. Force on the disk is measured by a balance that is calibrated in situ with dead weights. In one arrangement, pressures in the range of 10–500 μTorr were measured with an estimated probable error of (1μTorr+1%).
Structure of Silicon Films Evaporated onto a Clean NaCl Substrate
Authors: Shimaoka G. , Chang S. C.
Published: July 2002

Silicon films, 30–300 Å in thickness, evaporated (using an electron beam evaporation technique) onto NaCl substrates cleaved in ultrahigh vacuum and held at 25–500 °C at various deposition rates (0.1–8 Å/sec) have been investigated by reflection electron diffraction and transmission electron microscopy. It was found that the structure and epitaxy of films were markedly influenced by the purity of the Si source, ambient pressure during evaporation, substrate surface condition, deposition rate, and substrate temperature. Decoration of imperfections of the substrate surface was obtained with Si deposited at relatively slow rate (0.1–0.3 Å/sec). Films produced on the substrates at 25–300 °C were amorphous. The amorphous to crystalline transition temperature was in the range of 300–400 °C. Epitaxial orientation of films (001)Si‖(001)NaCl with [100]Si‖ [100]NaCl was observed on the substrates at 400 °C at the slow deposition rate. The epitaxial films included microtwins with the twinning planes of {111}. The growth and structure of films were also influenced considerably by an electron beam bombardment applied to the substrate during evaporation.
Effect of Gold Coating on Sorption Characteristics of CO, Sulphur, and Other Gases on Stainless-Steel Sheet
Authors: Komiya S. , Narusawa T. , Hayashi C.
Published: July 2002

Auger electron spectroscopic observations of the vacuum-deposited gold surface in comparison with bare stainless-steel surface have been made under varying vacuum conditions. The C and O peaks for the gold surface were negligibly small whereas those for the bare surface were rather intense and increased with time of exposure to primary electron bombardment. Decrease of the sulphur peak with increase of C and O peaks was observed for the bare surface which suggests that the impurity sulphur located on the stainless steel surface is covered by an adsorbed CO layer. Sulphur is the dominant impurity on a stainless steel surface after 700 °C flashing, but a very weak sulphur peak is observed for the surface covered by approximately 10 layers of vacuum-deposited gold film. Migration of sulphur from a bare stainless-steel surface to the gold-covered part of the surface has also been observed as a function of temperature.
Backstreaming of Hydrogen When Pumping Hydrocarbons with an Ion Pump
Authors: Williams F. , Boudart M. , Frennet A.
Published: July 2002

Ion pumps used for maintaining a stationary pressure of hydrocarbons in the range 10−9–10−6 Torr regurgitate hydrogen. With alkanes this hydrogen partial pressure is stationary and can be as high as that of the hydrocarbon. The amount of hydrogen regurgitated depends on the amount of hydrogen previously pumped (memory effect). With ethylene and acetylene, regurgitation of hydrogen by the pump varies with time and exhibits hysteresis. The mechanisms for hydrogen production from methane, ethane, propane, cyclopropane, neopentane, ethylene, and acetylene are discussed. As an example, LEED patterns observed during the exposure of W(100) to methane, propane, and cyclopropane in an ion pumped system are interpreted as due in whole or in part to mixed adsorption of hydrocarbon and of hydrogen backstreaming from the ion pump.
Contamination Threats to Critical Surfaces from Handling and Storage Practices
Authors: Poehlmann H. C. , Manning R. R. , Jackman R. W.
Published: July 2002

It is well known that in a thermal-vacuum or space environment, critical optical, electrical, or mechanical surfaces can be contaminated by the outgassed products of materials or by poor procedures in handling or vacuum testing. From contamination monitoring of recent spacecraft instrument thermal-vacuum tests it now appears that some of the materials and practices commonly used to protect critical surfaces from molecular or particulate contaminants can themselves represent significant threats. Included are clean room and clean tent materials, gloves, tissues, and covering or packaging materials. Mass and infrared spectral analyses of these materials and the environments and instruments exposed to them indicate the contaminants are largely plasticizers, slip or antistatic agents, and binders used in the manufacture of these products. Products of particular threat include vinyl gloves, booties, and clean tent walls and some polyethylene sheets and bags. Of the techniques investigated for reducing these threats, the use of alternate protective materials or the solvent cleaning of such materials and parts exposed to them appear more effective than does the vacuum baking of the contaminated parts.
Field Ion Microscope Combined with a Quadrupole Mass Analyzer and an Energy Analyzer
Authors: Utsumi Takao , Nishikawa O.
Published: July 2002

A field ion microscope is combined with a quadrupole mass analyzer for chemical identification of field ionized or desorbed ion species and with a retarding grid energy analyzer for determining the distance of ionization of these species relative to the surface atoms. With its present sensitivity this instrument is capable of detecting the image gas ions down to a partial pressure of 3×10−7 Torr at 78 K by scanning the mass range of 10 amu corresponding to 2 ions/sec/amu to the detector. The preliminary experimental results for field ionization of hydrogen on iridium (001) are discussed.
Investigation of the Surface Reaction of Germanium with Oxygen by LEED and Conductivity Measurements
Authors: Margoninski Y.
Published: July 2002

The oxidation process of clean germanium (100), (110), and (111) surfaces was studied by measuring simultaneously the beam and background intensities of the low-energy electron-diffraction pattern and the surface conductance during exposure of the surface to oxygen. Two distinct and separate phases of oxidation were observed. During the first phase and for the (100) and (110) surfaces, the intensity of the beams (half-order and integral) as well as that of the background decreased and reached a minimum at about 10×10−7 Torr min. The surface resistance decreased too, and its minimum almost coincided with that of the beam (or background) intensity. The second phase of the oxidation was marked by an increase in resistance and beam and background intensities. During this phase these intensity increases were caused by an increase in the yield of the elastically backscattered electrons and not by enhanced scattering from the disordered structure. Results for the (111) surface were similar, but here the minimum of surface resistance was reached after an oxygen adsorption of 200×10−7 Torr min and therefore did not coincide with the minimum of the LEED intensities.
A Spectroscopic Monitor for Sputter-Etching Processes
Authors: Bernstein T. , Labuda E. F.
Published: July 2002

Sputter-etching is a convenient technique for metal pattern generation on complex integrated circuits. It is particularly advantageous for multimetal systems because it completely eliminates the possibility of undercutting of the lower metal layers as can occur with chemical etching. A real-time monitoring system has been developed for monitoring the sputter-etching process when it is used for metal pattern generation with a beam lead metallization system consisting of titanium, platinum (or palladium), and gold. The intensity of the uv atomic radiation emitted by sputter-etched atoms which are excited in the sputtering discharge is monitored. The system has been used with both triode and diode types of sputter-etching systems and can reliably be used to tell when a given metal layer has been completely removed. A detailed description of the monitoring system and its performance is given.
Quantitative AES and LEED Study of Alkali Metal Overlayers on W(100)
Authors: Thomas S. , Haas T. W.
Published: July 2002

Experimental Auger calibration curves have been obtained for Cs, Rb, K, and Na adsorbed on a W(100) substrate, by monitoring the ratio of the adsorbate-substrate Auger peak-to-peak heights with coverage. A comparative study is made on such curves obtained in the four-grid LEED system and the cylindrical mirror analyzer. The adsorbate on a W substrate has an enhanced Auger yield over that on a Mo substrate due to the increase in the backscattering factor. The attenuation of the substrate Auger electrons is dependent on the atomic number of the alkali adsorbates. The first well-defined LEED pattern during the alkali adsorption revealed a C(2×2) structure. At higher coverages a two-domain hcp structure was observed with no change in the C(2×2) structure.