bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel approach for the crystallization of soluble proteins using non-ionic surfactants
Authors: Mustafa Aziz O. , Derrick Jeremy P. , Tiddy Gordon J. T. , Ford Robert C.
Published: July 2002

Crystallization trials using three polyoxyethylene surfactants as precipitating agents are described. Of the eight soluble proteins screened, five were successfully crystallized at the first attempt. These included lysozyme, catalase, ferritin, ribonuclease A and ubiquitin. Further work suggested that these surfactants could also be suitable for cryo-crystallographic analysis of crystals. At the concentrations used in the crystallization trials [10–40%(v/v)], they are capable of promoting the formation of non-crystalline glasses at cryogenic temperatures (77 K). This would facilitate crystal mounting and allow the minimization of crystal irradiation damage. Results from this study also suggest that proteins remain stable at high concentrations of these surfactants [40%(w/v)] and over long time periods (>1 month). A number of membrane proteins were also screened for crystallization. These included photosystems I and II and light harvesting complexes I and II from spinach and bacteriorhodopsin from Halobacterium halobium. The trials were unsuccessful both in the absence and presence of heptane-1,2,3-triol and over a wide range of surfactant concentrations.
Crystallographic studies of casein kinase I δ: toward a structural understanding of auto-inhibition
Authors: Longenecker Kenton L. , Roach Peter J. , Hurley Thomas D.
Published: July 2002

A recombinant form of mammalian casein kinase I δ (CKIδ) containing the catalytic domain and an auto-inhibitory domain was expressed in Escherichia coli, purified and crystallized. X-ray data were collected to 2.4 Å resolution, and the crystals belong to space group C2221. Molecular replacement using the structure of the catalytic domain of CKIδ yielded strong electron density for residues in the model, but no interpretable density was found for the inhibitory domain. A conserved intermolecular contact suggests the formation of dimers which would inhibit the activity of this protein kinase.
Molecular Replacement: the Revival of the Molecular Fourier Transform Method
Authors: Rabinovich Dov , Rozenberg Haim , Shakked Zippora
Published: July 2002

The molecular Fourier transform method, perhaps the first application of the molecular-replacement approach, used in the 1950s for the two-dimensional structure determination of small molecules, has been modernised for the efficient solution of complex structures. In the modern application of the molecular Fourier transform (MFT), the three-dimensional transform of the molecular model is calculated and fitting is achieved by rotating the weighted reciprocal lattice with respect to the calculated transform. The fit between the transform and the weighted reciprocal lattice is gauged by three different criteria corresponding to R factor, correlation coefficient and product function. Since the procedure involves the rotation of indices and is, therefore, independent of the number of atoms, it is much faster than other methods which employ the rotation of the molecular model. This feature enabled the renovation of the rotation–translation search method ULTIMA, which utilizes low-order data and packing considerations for the efficient solution of large structures.
Expression, purification, crystallization and preliminary X-ray analysis of the κ-carrageenase from Pseudoalteromonas carrageenovora
Authors: Michel Gurvan , Barbeyron Tristan , Flament Didier , Vernet Thierry , Kloareg Bernard , Dideberg Otto
Published: July 2002

A recombinant form of His-tagged κ-carrageenase from Pseudoalteromonas carrageenovora has been expressed, purified and crystallized. Crystals have been obtained by the vapour-diffusion method using polyethylene glycol (Mr
= 4000) as a precipitant. These crystals belong to the space group P212121, with unit-cell parameters a  =  58.2, b  =  62.8, c  =  77.9 Å, and diffract to 2.2 Å resolution on a rotating-anode X-ray source.
Determination of a protein structure by iodination: the structure of iodinated acetylxylan esterase
Authors: Ghosh Debashis , Erman Mary , Sawicki Mark , Lala Puloma , Weeks Daniel R. , Li Naiyin , Pangborn Walter , Thiel Daniel J. , Jörnvall Hans , Gutierrez Rodrigo , Eyzaguirre Jaime
Published: July 2002

Enzymatic and non-enzymatic iodination of the amino acid tyrosine is a well known phenomenon. The iodination technique has been widely used for labeling proteins. Using high-resolution X-ray crystallographic techniques, the chemical and three-dimensional structures of iodotyrosines formed by non-enzymatic incorporation of I atoms into tyrosine residues of a crystalline protein are described. Acetylxylan esterase (AXE II; 207 amino-acid residues) from Penicillium purpurogenum has substrate specificities towards acetate esters of D-xylopyranose residues in xylan and belongs to a new class of α/β hydrolases. The crystals of the enzyme are highly ordered, tightly packed and diffract to better than sub-ångström resolution at 85 K. The iodination technique has been utilized to prepare an isomorphous derivative of the AXE II crystal. The structure of the enzyme determined at 1.10 Å resolution exclusively by normal and anomalous scattering from I atoms, along with the structure of the iodinated complex at 1.80 Å resolution, demonstrate the formation of covalent bonds between I atoms and C atoms at ortho positions to the hydroxyl groups of two tyrosyl moieties, yielding iodotyrosines.
Critical initial real-space refinement in the structure determination of arginine kinase
Authors: Zhou Genfa , Somasundaram Thayumanasamy , Blanc Eric , Chen Zhi , Chapman Michael S.
Published: July 2002

Arginine kinase (AK), a homologue of creatine kinase, catalyses the reversible transfer of a phosphoryl group between a guanidino phosphate and ADP. The family of phosphagen kinases eluded structure determination for over 25 years until an inactive form creatine kinase (CK) structure was determined [Fritz-Wolf et al. (1996). Nature (London), 381, 341–345]. The structure determination of the active-form transition-state complex was non-trivial, owing to the distant relatedness and domain reorientation of AK compared with CK. Phases from a molecular-replacement solution of the large domain, supplemented by single isomorphous replacement and inter-crystal averaging, did not reveal interpretable electron density for the small domain. Reciprocal-space refinement of the initial model (R
free = 0.54) by any of the commonly used methods, including post facto application of maximum-likelihood methods, led to overfitting without significant improvement of the partial initial model. By contrast, in the local real-space refinements which proved successful, the interdependence of atoms is limited to immediate neighbors, and atomic positions are not influenced by errors or omissions in remote parts of the structure. Modest improvement was possible without overfitting, and this was critical to the calculation of improved phases. Phases were refined and extended from 4.0 to 2.5 Å resolution by Fourier inversion of omit maps, combination with isomorphous replacement phases and averaging between crystal forms, after several batches of real- and reciprocal-space atomic refinement. The final structure refinement, against a 1.86 Å cryo data set yielded a high-quality model with R = 0.196 and R
free = 0.224.
Structure of mare apolactoferrin: the N and C lobes are in the closed form
Authors: Sharma A. K. , Rajashankar K. R. , Yadav M. P. , Singh T. P.
Published: July 2002

The structure of mare apolactoferrin (MALT) has been determined at 3.8 Å resolution by the molecular-replacement method, using the structure of mare diferric lactoferrin (MDLT) as the search model. The MDLT structure contains two iron-binding sites: one in the N-terminal lobe, lying between domains N1 and N2, and one in the C-terminal lobe between domains C1 and C2. Both lobes have a closed structure. MALT was crystallized using the microdialysis method with 10%(v/v) ethanol in 0.01 M Tris–HCl. The structure has been refined to a final R factor of 0.20 for all data to 3.8 Å resolution. Comparison of the structure of MALT with that of MDLT showed that the domain arrangements in these structures are identical. However, the structure of MALT is very different to the structures of human apolactoferrin (HALT) and duck apo-ovotransferrin (DAOT), in which the domain associations differ greatly. In HALT, the N lobe adopts an open conformation while the C lobe is in the closed form. On the other hand, in DAOT both the N and the C lobes adopt the open form. These results indicate the domain arrangements in these proteins to be an important structural feature related to their specific biological functions. Based on the structures of MALT, HALT and DAOT, it can be stated that the native apoproteins of the transferrin family adopt three forms: (i) with both the N and the C lobes in closed forms, as observed in MALT, (ii) with the N lobe open and the C lobe closed, as observed in HALT, and (iii) with both the N and the C lobes open, as found in DAOT. All these proteins attain a convergent form when iron is bound to them, suggesting an efficient and unique form of iron binding. The interface between the N and C lobes, which is formed by N1–C1 contact in the core of the molecule, does not change significantly.
Errors and reproducibility in electron-density map interpretation
Authors: Mowbray Sherry L. , Helgstrand Charlotte , Sigrell Jill A. , Cameron Alexander D. , Jones T. Alwyn
Published: July 2002

Three investigators, with varying levels of experience, independently built and refined the structure of Escherichia coli ribokinase at 2.6 Å resolution. At the end of the refinement/rebuilding processes the models had essentially converged, although each had its own particular pattern of remaining errors. The subsequent refinement of the same structure at 1.8 Å resolution allowed an overall quality check of each of the lower resolution models, and an analysis of which graphics-based tools were generally most efficient in locating these errors. Criteria which are useful in the application of Ramachandran, main-chain and side-chain database and real-space fit analyses are presented.
Protein crystallization with a combination of hard and soft precipitants
Authors: Huang Qing-qiu , Teng Mai-kun , Niu Li-wen
Published: July 2002

Much effort and progress have been made in understanding the nucleation and crystallization of globular proteins, and many techniques have been developed to crystallize proteins in the past decades. The advantages of the use of combined precipitants in protein crystallization have been much appreciated. Unfortunately, there is still no theory or empirical guide on how to combine so many precipitants and how to use combined precipitants, although many proteins have been crystallized successfully using combined precipitants. This report gives a proposal about how to use conventional precipitants to obtain protein crystals, based on a novel idea of hard and soft precipitant combinations.
Structures of the deoxy and CO forms of haemoglobin from Dasyatis akajei, a cartilaginous fish
Authors: Chong Khoon Tee , Miyazaki Gentaro , Morimoto Hideki , Oda Yutaka , Park Sam-Yong
Published: July 2002

The three-dimensional structures of the deoxy- and carbonmonoxyhaemoglobin (Hb) from Dasyatis akajei, a stingray, have been determined at 1.6 and 1.9 Å resolution, respectively. This is one of the most distantly related vertebrate Hbs to human HbA. Both structures resemble the respective forms of HbA, indicating that the α2β2-type tetramer and the mode of the quaternary structure change are common to Hbs of jawed vertebrates. Larger deviations between D. akajei Hb and human HbA are observed in various parts of the molecule, even in the E and F helices. Significant mutations and/or conformational changes are also observed around the haems, in the C-terminal region of the β subunit, in the α1β2 interface and in the organic phosphate-binding site of HbA. Despite these structural differences, the oxygen affinity, haem–haem interaction, Bohr effect and organic phosphate effect of D. akajei Hb are all only moderately reduced. Compared with human HbA, the overall r.m.s. deviation of main-chain atoms in the helical regions of bony fish Hbs is smaller than that of D. akajei Hb.
Crystallization of Pleurotus ostreatus (oyster mushroom) lectin
Authors: Chattopadhyay T. K. , Lisgarten J. N. , Brechtel R. , Rüdiger H. , Palmer R. A.
Published: July 2002

Crystals of Pleurotus ostreatus (oyster mushroom) lectin have been grown by the hanging-drop technique using ammonium sulfate as the precipitant at 293 K. Over a period of between two and three weeks, crystals of hexagonal bipyramidal morphology grew to maximum dimensions of 0.2 × 0.2 × 0.5 mm. The crystals belong to space group P6122 or P6522, with unit-cell parameters a = b = 155.9, c = 149.8 Å, V = 3153078 Å3, Z = 12 (assuming 50% solvent), and diffract to 4.1 Å at 293 K.
Dehydration leads to a phase transition in monoclinic factor XIII crystals
Authors: Weiss Manfred S. , Hilgenfeld Rolf
Published: July 2002

Monoclinic factor XIII crystals have been transferred to a solution containing increasing amounts of the precipitant PEG 6000. At a concentration of about 36%(w/v) PEG 6000, a phase transition was observed. The space group of the crystals was preserved on the transition, but half of the 21 screw axes were lost, which meant that the unit-cell volume and the content of the asymmetric unit were doubled. The structure of factor XIII in the new crystal form was solved by molecular replacement. About 80% of the changes accompanying the transition can be explained by a rigid-body rotation of half of the factor XIII dimers in the lattice by about 5°. The remaining changes are mostly small interdomain movements of the four domains which constitute one factor XIII monomer.
RSPS version 4.0: a semi-interactive vector-search program for solving heavy-atom derivatives
Authors: Knight Stefan D.
Published: July 2002

A program for inspection and interpretation of the Patterson function is described. The program is mainly intended for finding heavy-atom positions from difference Patterson maps, but may also be used to locate molecules with non-crystallographic symmetry when the local axis is nearly parallel to a crystallographic symmetry axis. Options are available for vector-based methods to locate heavy-atom sites, for finding sets from a list of possible heavy-atom positions and for checking of potential solutions. Both crystallographic and non-crystallographic symmetry may be used, either independently or in conjunction.
Crystallization and preliminary X-ray analysis of recombinant full-length human m-calpain
Authors: Masumoto Hajime , Nakagawa Kazuhiro , Irie Shota , Sorimachi Hiroyuki , Suzuki Koichi , Bourenkov Gleb P. , Bartunik Hans , Fernandez-Catalan Carlos , Bode Wolfram , Strobl Stefan
Published: July 2002

m-Calpain constitutes the prototype of the superfamily of neutral calcium-activated cysteine proteinases. It is a heterodimer consisting of an 80 and a 30 kDa subunit. Recombinant full-length human m-calpain has been crystallized using macro-seeding techniques and vapour-diffusion methods. Two different monoclinic crystal forms (space group P21) were obtained from a solution containing polyethylene glycol (MW
= 10 000) as a pecipitating agent. Complete data sets have been collected to 2.3 and 3.0 Å resolution using cryo-cooling conditions and synchrotron radiation. The unit-cell parameters are a = 64.86, b = 133.97, c = 78.00 Å, β = 102.43° and a = 51.80, b = 171.36, c = 64.66 Å, β = 94.78°, respectively. The Vm
values indicate that there is one heterodimer in each asymmetric unit.
Crystallization of the NADP-dependent β-keto acyl-carrier protein reductase from Brassica napus
Authors: Fisher Martin , Sedelnikova Svetlana E. , Martindale Wayne , Thomas Neil C. , Simon J. William , Slabas Antoni R. , Rafferty John B.
Published: July 2002

The NADP-dependent β-keto acyl-carrier protein reductase (BKR) from Brassica napus has been crystallized by the hanging-drop vapour-diffusion method using polyethylene glycol of average molecular weight 1500 as the precipitant. The crystals belong to the hexagonal space group P6422, with unit-cell parameters a = b = 129.9, c = 93.1 Å, α = β = 90, γ = 120°. Calculated values for Vm
, the use of rotation and translation functions and consideration of the packing suggest that the asymmetric unit contains a monomer. The crystals diffract to beyond 2.8 Å resolution and are more amenable to X-ray diffraction analysis than those reported previously for the Escherichia coli enzyme. The structure determination of B. napus BKR will provide important insights into the catalytic mechanism of the enzyme and into the evolution of the fatty-acid elongation cycle by comparisons with the other oxidoreductase of the pathway, enoyl acyl-carrier protein reductase (ENR).
Effects of microgravity on the crystal quality of a collagen-like polypeptide
Authors: Berisio R. , Vitagliano L. , Sorrentino G. , Carotenuto L. , Piccolo C. , Mazzarella L. , Zagari A.
Published: July 2002

(Pro-Pro-Gly)10 is one of the most widely studied collagen polypeptide models. Microgravity crystal growth of (Pro-Pro-Gly)10 was carried out in the Advanced Protein Crystallization Facility aboard the Space Shuttle Discovery during the STS-95 mission. Crystals were successfully grown in all experiments, using both dialysis and free-interface diffusion methods. The quality of the microgravity-grown crystals and of ground-grown counterparts was assessed by X-ray synchrotron diffraction. Microgravity-grown crystals exhibited a significant improvement in terms of dimensions and resolution limit. As previously reported, crystals were orthorhombic, space group P212121. However, the diffraction pattern showed weak reflections, never previously measured, that were consistent with new unit-cell parameters a = 26.9, b = 26.4, c = 182.5 Å. This allowed the derivation of a new model for the arrangement of the triple-helical molecules in the crystals.
Incorporation of Mn, Co and Zn cations into large-pore aluminophosphate molecular sieves MeAPO-50
Authors: Arčon Iztok , Tušar N. N. , Ristić Alenka , Kaučič Venceslav , Kodre Alojz , Helliwell Madeleine
Published: July 2002

Large-pore metal modified aluminophosphate molecular sieves MeAPO-50 (Me = Co,Zn,Mn) were synthesised by hydrothermal crystallisation using di-n-propylamine as structure directing agent. EXAFS and XRD analysis show that cobalt(II), manganese(II) and zinc(II) are incorporated into the non-phosphorus tetrahedral framework sites of MeAPO-50 on the threefold-axis site, and on a site in a general position in the unit cell. Results of both methods on distribution of the metal over the two sites are compared.
Determination of metal–metal distances: significance and accuracy
Authors: Mijovilovich Ana , Meyer-Klaucke W.
Published: July 2002

Nature utilises a variety of metal clusters as catalytic centers. Some of them make use of two or more metals in the catalytic site. The variation of metal-metal distances plays an important role in several processes like charge transfer and weakening of bonds. X-ray absorption spectroscopy can determine these metal-metal distances in several states (crystal, solution or amorphous). However sometimes backscattering from light elements hides the metal-metal contribution to the fine structure. Here we point out significance and accuracy of metal-metal distances in a model system. Therefore a number of different refinement protocols are applied to the data. These protocols will be discussed focusing on the significance and accuracy of the metal-metal distances extracted from the data.
The influence of experimental and model uncertainties on EXAFS results
Authors: Rossner Hermann , Krappe Hans
Published: July 2002

We analyze EXAFS oscillations in k-space with the FEFF code to obtain main-shell distances Rν and mean-square displacement parameters σi
2 for all single and multiple scattering paths i in the shells ν up to a maximum shell radius Rmax. To quantify the uncertainty in the determination of these model parameters we take into account experimental errors and uncertainties connected with background subtraction, with the approximate handling of the electronic many-body problem in FEFF, and with the truncation of the multiple scattering series. The impact of these uncertainties on the Rν and σi
2 is investigated in the framework of Bayesian methods. We introduce an a priori guess of these model parameters and consider two alternative strategies to control the weight of the a priori input relative to that of the experimental data. We can take a model parameter space of up to 250 dimensions. Optionally we can also fit the coordination numbers Nj (j≤ν) and the skewness of the distribution of the Rν besides the Rν and σi
2. The method is applied to 10K Cu K-edge and 300K Au L3-edge data to obtain model parameters and their a posteriori error correlation matrices.
In situ observation of pitting of stainless steel by XAFS
Authors: Kimura Masao , Kaneko Michio , Suzuki Tamaki
Published: July 2002

An in situ observation technique by XAFS (X-ray Absorption Fine Structures) has been developed for observation of metal corrosion. XAFS spectra were obtained with a special electrochemical cell to elucidate pitting: change of concentrations and structures of ions near the interface of solution and metal. It has been successfully shown that the concentrations of Cr and Br are linearly dependent on the distance from the interface. Also, salt formation at the interface and the hydrolysis reaction far from the interface are indicated.
A grating monochromator of BL23SU at SPring-8 covering silicon and oxygen K-edges
Authors: Yoshigoe Akitaka , Agui Akane , Nakatani Takeshi , Matsusita Tomohiro , Saitoh Yuji , Yokoya Akinari
Published: July 2002

We report the present performance of a grating monochromator at the newly constructed soft X-ray beamline ( BL23SU at the SPring-8 ), which can measure both silicon and oxygen K-edges. That provides new opportunities for XAFS measurements of solids up to 2100 eV.
APEX version 2.0: latest version of the cross-platform analysis program for EXAFS
Authors: Dimakis Nicholas , Bunker Grant
Published: July 2002

This report describes recent progress on APEX, a free, open source, cross platform set of EXAFS data analysis software. In a previous report we described APEX 1.0 (Dimakis, N. and Bunker, G., 1999), a free and open source code suite of basic X-Ray Absorption Fine Structure (XAFS) data analysis programs for classical data reduction and single scattering analysis. The first version of APEX was the only cross platform (linux/irix/windows/MacOS) EXAFS analysis program to our knowledge, but it lacked important features like multiple scattering fitting, generic format conversion from ASCII to University of Washington (UW) binary-type files, and user friendly interactive graphics. In the enhanced version described here we have added cross-platform interactive graphics based on the BLT package, which is an extension to TCL/TK. Some of the utilities have been rewritten in native TCL/TK, allowing for faster and more integrated functionality with the main package. The package also has been ported to SunOS. APEX 2.0 in its current form is suitable for routine data analysis and training. Addition of more advanced methods of data analysis are planned.
Reflection mode XAFS investigations of reactively sputtered thin films
Authors: Lützenkirchen-Hecht Dirk , Frahm Ronald
Published: July 2002

Amorphous Ta-oxide and Sn-nitride thin films were prepared by reactive sputter deposition on smooth float glass substrates and investigated ex situ using reflection mode XAFS. The absorption coefficient μ and its fine structure were extracted from the measured reflection mode XAFS spectra with a method based on the Kramers-Kronig transform. Bond distances, coordination numbers and Debye-Waller factors were determined by a detailed XAFS data analysis and compared to those of reference compounds. In addition, changes of the atomic short range order of the sputter deposited Ta2O5-films induced by a thermal heat treatment in ambient air were examined as a function of the annealing temperature.
Identification of the chemical states of phosphorus in atmospheric aerosols by XANES spectrometry
Authors: Tohno Susumu , Kawai Jun , Kitajima Yoshinori
Published: July 2002

Depth selective XAFS spectrometry was applied to determine the chemical states of phosphorus in atmospheric aerosols. Atmospheric aerosols were collected on aluminum foils and polyethylene films using a 4-stage cascade impactor and a 12-stage low pressure Andersen sampler, respectively. Samplings were performed at Uji (urban area) and Sakurajima (near a volcano). We measured X-ray fluorescence yield (XFY) and total electron yield (sample current) simultaneously to obtain the X-ray absorption near edge structure (XANES) spectra of the atmospheric aerosols. X-ray absorption in the vicinities of P K-edges was measured on the beamline BL-11B at the Photon Factory, High Energy Accelerator Research Organization, Tsukuba, Japan. The Sakurajima aerosol samples showed only a P5+ peak and the peak was remarkable in coarse mode. In case of the Uji samples, the P5+ peak was dominant and a slight P3+ peak was detected for sample current measurement.
Anharmonic effective pair potentials in CaTiO3, SrTiO3 and CaGeO3 perovskite
Authors: Yoshiasa Akira , Nakajima Kenji , Murai Kei-ichiro , Okube Maki
Published: July 2002

The temperature dependence of EXAFS Debye–Waller factors in CaTiO3, SrTiO3 and CaGeO3 perovskite was investigated with the cumulant expansion method. The CaGeO3 perovskite as an analogue of the Earth's lower-mantle mineral was synthesized in a cubic anvil type apparatus under 10 GPa 1250 K. The Ca, Ti and Ge K-edge EXAFS spectra were measured in transmission mode at temperature up to 1100 K. The effective pair potentials, V(u) = αu2/2 + βu3/3!, were evaluated and the Grüneisen parameter were calculated. The potential coefficients α and β for Ti—O bond in CaTiO3 are 6.9 eV Å−2 and −38 eV Å−3, respectively. Those for Ge—O bond in CaGeO3 are 9.8 eV Å−2 and −36 eV Å−3, respectively.
Structure of new porous compounds after annealing in vacuum
Authors: Erenburg S. B. , Bausk N. V. , Naumov N. G. , Chutornoi V. A. , Fedorov V. E. , Mazalov L. N.
Published: July 2002

Dehydration process in recently synthesized porous inorganic salts formed by large cluster anions [Re6X8(CN)6]4- (X= S, Se), transition metal cations and water molecules has been investigated. Desolvation process of the complex Co(DMF)6[Mo6Br8(NCS)6], where DMF - dimethylformamide, has been studied. CoK, MoK and ReL
3 XAFS measurements of these new complicated compounds before and after annealing in vacuum at temperature up to 250°C were performed. Changes of electronic and spatial structure of these compounds under the heating process have been established and adequate structural models of the amorphous compounds obtained are suggested and discussed.
X-ray absorption spectroscopy study of Co structure in the epitaxial Co/Pt multilayers on Al2O3(11-20) substrates
Authors: Lee Chih-Hao , Yu Kuan-Li , Cheng Pei-Yu , Huang J. C. A. , Pong W. F.
Published: July 2002

In this study, five epitaxial [Co(t nm)/Pt(1 nm)]30 multilayer samples (t=0.16-1.07 nm) were studied using polarized X-ray absorption spectroscopy method. These samples were prepared on Mo(110)/ Al2O3(11-20) substrates by MBE technique. The results show that the Co layer is more like an fcc pseudomorphic structure for the Co thickness of less than 0.3 nm. For Co layer thickness of 1 nm, the first shell distance is 0.25 nm, which is very close to the Co-Co distance of bulk hcp Co. On the other hand, for Co layer of less than 0.3 nm, the in plane first shell distance is expanded by 4% and most of the neighboring atoms are Pt atoms. The fitting results of the Co/Pt multilayers seem to support a sharp boundary model rather than an interdiffusion model.
Parabolic refractive X-ray lenses
Authors: Lengeler Bruno , Schroer Christian G. , Benner Boris , Gerhardus Achim , Günzler Til Florian , Kuhlmann Marion , Meyer Jannik , Zimprich Christiane
Published: July 2002

Parabolic refractive X-ray lenses are optical components, especially suitable for third-generation synchrotron radiation sources. This article describes the status of the development of our lenses and illustrates the possibilities for micrometre and submicrometre focusing and for X-ray imaging in absorption and phase contrast. The parabolic lens profile ensures distortion-free imaging of high quality. First characteristics of Be lenses are given. A microscope based on Be lenses is expected to have a lateral resolution below 80 nm.
Phase-contrast X-ray imaging based on interferometry
Authors: Momose Atsushi
Published: July 2002

Phase-contrast X-ray imaging including tomographic configuration using a crystal X-ray interferometer is reviewed. The imaging principle based on phase retrieval is described, and some demonstrations showing its high sensitivity are presented on the observations of animal and human cancerous tissues.
Design of Compact Absorbers for High-Heat-Load X-ray Undulator Beamlines at SPring-8
Authors: Mochizuki T. , Sakurai Y. , Shu D. , Kuzay T. M. , Kitamura H.
Published: July 2002

A compact and high-heat-load absorber for the SPring-8 X-ray undulator beamline has been developed and installed. It consists of an upper heat-absorber part and a lower photon duct part, which are configured together in a water-cooled GlidCop body. The absorber part has a horizontal notch shape and the photon duct part forms a rectangular open channel under the absorber part. Two types of absorber are designed: one, with wire mesh channels, is 486 mm long, 70 mm high and 64 mm wide; the other, with smooth-bore channels, is 610 mm long, 75 mm high and 70 mm wide. Thermal and stress analyses show that they withstand the 12.3 kW heat load and the maximum heat flux of 940 W mm−2 at normal incidence.
Conserving the Coherence and Uniformity of Third-Generation Synchrotron Radiation Beams: the Case of ID19, a `Long' Beamline at the ESRF
Authors: Espeso José I. , Cloetens Peter , Baruchel José , Härtwig Jürgen , Mairs Trevor , Biasci Jean Claude , Marot Gérard , Salomé-Pateyron Murielle , Schlenker Michel
Published: July 2002

The lateral coherence length is of the order of 100 µm at the `long' (145 m) ID19 beamline of the ESRF, which is mainly devoted to imaging. Most of the optical elements located along the X-ray path can thus act as `phase objects', and lead to spurious contrast and/or to coherence degradation, which shows up as an enhanced effective angular size of the source. Both the spurious contrast and the coherence degradation are detrimental for the images (diffraction topographs, tomographs, phase-contrast images) produced at this beamline. The problems identified and the way they were solved during the commissioning of ID19 are reported. More particularly, the role of the protection foils located in the front end, the beryllium windows, the filters and the monochromator defects (scratches, dust, small vibrations) is discussed.
Rare earth crown ether complexes: (15-crown-5)tris(nitrato)praseodymium(III)
Authors: McIntosh Nadine N. , Kahwa Ishenkumba A. , Mague Joel T.
Published: July 2002

The title compound, tris(nitrato-κ2O,O′)(1,4,7,10,13-pentaoxacyclopentadecane-κ5O)praseodymium(III), [Pr(NO3)3(C10H20O5)], was obtained from a reaction designed to explore CO2-fixation by lanthanide salts. The structure is the same as found previously for the La, Ce, Eu and Nd analogs.
{2,2′-[1,2-Phenylenebis(nitrilomethylidyne)]diphenolato}copper(II) dichloromethane solvate
Authors: Baggio Ricardo , Garland Maria Teresa , Atria Ana María , Hidalgo Oscar , Solezi Santiago
Published: July 2002

The title compound, [Cu(C20H14N2O2)]·CH2Cl2, crystallizes as a monomer, with the copper ion in a square-planar environment provided by the tetradentate 2,2′-[1,2-phenylenebis(nitrilomethylidyne)]diphenolate (L18) ligand. The planar molecules pack parallel to the (101) crystallographic planes.
Trends in library management
Authors: Layzell Ward Patricia
Published: July 2002

Provides a brief review of trends in library management in 2000, indicating issues of current concern.
“Fast track” transition to an electronic journal collection: a case study
Authors: Hansen Montgomery Carol
Published: July 2002

Describes the background and development of the migration to an electronic journal collection by the W.W. Hagerty Library of Drexel University, Philadelphia. Starting in 1998, this transition was a key component of the library’s strategic plan, and with a few exceptions, journals are purchased in electronic‐only format whenever possible. Drexel’s collection now consists of only 800 print subscriptions and 5,500 electronic journals. The transition has had a considerable impact on library staffing and workflow. Offsetting a decrease in the activity levels relating to the print format is a large increase in workload for serials’ acquisitions and management functions. A newly created position of electronic resources librarian acts as a focal point for the integrated development of all electronic resources.
Performance appraisal: principals’ perspectives and some implications
Authors: Timperley Helen S.
Published: July 2002

Performance appraisal and teacher evaluation systems in schools have been subject to criticism in many countries because they have not met perceived requirements of educators and/or the state. This study sought the views of New Zealand secondary school principals to whom responsibility for developing appraisal systems has been devolved since 1989. In general, principals developed systems that met their own requirements and were reasonably satisfied with their efforts. Some principals prioritised developmental purposes while others included accountability purposes. These two groups experienced different outcomes. In some cases, staff opposition prevented principals from developing accountable systems. Although the performance appraisal systems developed by principals mostly met their own requirements, most did not all meet the state’s requirements for accountability.
Quality in the sandwich year
Authors: Edmunds Mike
Published: July 2002

The aims and learning outcomes of the sandwich year are generally still loosely defined, poorly supported, rarely assessed and only in exceptional circumstances influence degree classification.The paper reports the findings of a major DfEE funded study into the BA Business Studies sandwich year. It concludes that if the potential for learning of the sandwich year is to be fully realised it needs to be defined in terms of knowledge, skills and competences. The definition of knowledge used must be carefully framed to include forms not always recognised by universities in the past. Developments outside the universities with Key Skills and Occupational Standards offer nationally recognised reference points “known” to employers that should not be ignored.
Structural basis of α‐amylase activation by chloride
Authors: Aghajari Nushin , Feller Georges , Gerday Charles , Haser Richard
Published: July 2002

To further investigate the mechanism and function of allosteric activation by chloride in some α‐amylases, the structure of the bacterial α‐amylase from the psychrophilic micro‐organism Pseudoalteromonas haloplanktis in complex with nitrate has been solved at 2.1 A˚, as well as the structure of the mutants Lys300Gln (2.5 A˚) and Lys300Arg (2.25 A˚). Nitrate binds strongly to α‐amylase but is a weak activator. Mutation of the critical chloride ligand Lys300 into Gln results in a chloride‐independent enzyme, whereas the mutation into Arg mimics the binding site as is found in animal α‐amylases with, however, a lower affinity for chloride. These structures reveal that the triangular conformation of the chloride ligands and the nearly equatorial coordination allow the perfect accommodation of planar trigonal monovalent anions such as NO3−, explaining their unusual strong binding. It is also shown that a localized negative charge such as that of Cl−, rather than a delocalized charge as in the case of nitrate, is essential for maximal activation. The chloride‐free mutant Lys300Gln indicates that chloride is not mandatory for the catalytic mechanism but strongly increases the reactivity at the active site. Disappearance of the putative catalytic water molecule in this weakly active mutant supports the view that chloride helps to polarize the hydrolytic water molecule and enhances the rate of the second step in the catalytic reaction.
Depolarization‐induced pH microdomains and their relationship to calcium transients in isolated snail neurones
Authors: Schwiening Christof J. , Willoughby Debbie
Published: July 2002

Neuronal electrical activity causes only modest changes in global intracellular pH (pHi). We have measured regional pHi differences in isolated patch‐clamped neurones during depolarization, using confocal imaging of 8‐hydroxypyrene‐1,3,6‐trisulfonic acid (HPTS) fluorescence. The pHi shifts in the soma were as expected; however, substantially larger shifts occurred in other regions. These regional differences were still observed in the presence of CO2‐HCO3−, they decayed over many seconds and were associated with changes in calcium concentration. Lamellipodial HPTS fluorescence fell by 8.7 ± 1.3 % (n= 9; ∼0.1 pH unit acidification) following a 1 s depolarization to 0 mV; this was more than 4‐fold greater than the relative shift seen in the soma. Depolarization to +40 mV for 1 s caused a 46.7 ± 7.0 % increase (n= 11; ∼0.4 pH unit alkalinization) in HPTS fluorescence in the lamellipodia, more than 6‐fold that seen in the soma. Application of 5 % CO2‐20 mm HCO3− did not significantly reduce the size of the +40 mV‐evoked local pH shifts despite carbonic anhydrase activity. The pHi gradient between regions ∼50 μm apart, resulting from acid shifts, took 10.3 ± 3.1 s (n= 6) to decay by 50 %, whereas the pHi gradient resulting from alkaline shifts took only 3.7 ± 1.4 s (n= 12) to decay by 50 %. The regional rates of acidification and calcium recovery were closely related, suggesting that the acidic pH microdomains resulted from Ca2+‐H+ pump activity. The alkaline pH microdomains were blocked by zinc and resulted from proton channel opening. It is likely that the microdomains result from transmembrane acid fluxes in areas with different surface area to volume ratios. Such neuronal pH microdomains are likely to have consequences for local receptor, channel and enzyme function in restricted regions.
A Mechanistic Force Model for Contour Turning
Authors: Reddy Rohit G. , Kapoor Shiv G. , DeVor Richard E.
Published: July 2002

In this paper a mechanistic force model for contour turning is presented. Analytical solutions are developed for evaluation of the mechanistic parameters (chip load, chip thickness, chip width, effective lead angle), as a function of the process parameters (tool geometry, workpiece geometry, and the tool path). The effect of these parameter variations on the cutting forces is analyzed. Simple straight turning tests are employed for model calibration. A workpiece with convex and concave contours is employed for model validation. Model simulations are found to match well with the experimental results. The analytical model is utilized to investigate the effect of process variables with a 26 full factorial design. [S1087-1357(00)01602-6]
Development of a Cutting Direction and Sensor Orientation Independent Monitoring Technique for End-Milling
Authors: Roth John T. , Pandit Sudhakar M.
Published: July 2002

In the authors’ previous work, univariate models were fit to acceleration data to predict impending tool failure. Numerous end-milling life tests, conducted under a wide variety of cutting conditions, demonstrated that the method could consistently warn of impending failure between 6 inches (15 cm) and 8 inches (20 cm) prior to the actual event. This paper presents an improved method that increases the warning time and allows the technique to function independent of the cutting direction or sensor orientation. Using multivariate autoregressive models fit to tri-axial accelerometer signals, monitoring indices are developed, verified and the results are compared with those from the univariate models. The multivariate models detected impending failure 30 inches (76 cm) prior to its occurrence, 23.5 inches (60 cm) earlier than with the univariate models. Furthermore, the multivariate models are able to monitor the condition of the tool, regardless of the cutting direction or sensor orientation. [S1087-1357(00)01003-0]
Implications of Inspection Updating on System Fatigue Reliability of Offshore Structures
Authors: Moan Torgeir , Song Ruxin
Published: July 2002

Offshore structures are considered as fail safe and inspections are carried out during their service lifetime to assess their actual condition. In this paper, the effect of inspection updating on fatigue reliability of offshore structures is investigated. In particular, the effect of inspection on the reliability of both inspected and uninspected joints is assessed dependent upon the correlation of properties of different joints. The effect of repeated inspections and inspection sample size on fatigue reliability is also investigated. The influence of inspection of certain joints on the reliability of a series system is studied and the effect of system-based updating policy on fatigue reliability is investigated. It is found that the system reliability is significantly affected by the inspection updating policy. [S0892-7219(00)00403-9]
Cryogenic Fracture Toughness Determination of a Structural Alloy Weldment by Notch Tensile Measurement and Finite Element Analysis
Authors: Shindo Y. , Mano Y. , Horiguchi K. , Sugo T.
Published: July 2002

This paper investigates the use of circumferentially notched bar specimens for the measurement of elastic-plastic fracture toughness JIC of structural alloys and weldments for superconducting magnets in fusion energy systems. Notch tensile tests were performed with small cylindrical notched bar specimens at liquid helium temperature (4 K) using crosshead rates of 0.2 mm/min and 20 mm/s. Test specimens were 5 mm in diameter with a 30-mm reduced section. In the mid-section of the specimen a 1 mm deep electro discharge machined (EDM) notch of 0.2 mm width was machined around the girth, thus maintaining a starting diameter of 3 mm. Correlations between notch tensile strength σNTS, failure energy absorption ENT, and JIC were assessed. The best data fit was found between the ratio σNTS/JIC and JIC. A finite element analysis was also performed to compute directly the J-values. Comparisons of the predicted JIC with results obtained from conventional JIS Z 2284 standard tests were made. Results of structural alloy weldment with a representatively wide range of JIC indicate that fracture toughness prediction accuracy is roughly equal to ±25 percent.
Relationship Between Visible Spray Observations and DI Diesel Engine Performance
Authors: Watanabe Takashi , Daidoji Susumu , Varde Keshav S.
Published: July 2002

This investigation was conducted to enhance understanding of combustion in a direct injection (DI) diesel engine with square combustion chamber. The investigation included a bench study of spray and its interaction with the chamber and correlation with engine performance. The bench study was conducted by using a liquid injection technique (LIT). The technique relies on the use of instantaneous photo images of emulsified fuel spray patterns to deduce spray behavior. It captures spray images in forced swirling flow on a positive film, which was used to deduce fuel-air mixing by scattering radiation technique. Three different chamber configurations, with different ratios of arc radius (r) to inscribed circle radius (R), and several spray deflecting angles were used in the study. The best parameters were found to be a deflecting angle of about 30 deg and a ratio of r/R of about 0.65. The results of the bench test were used to compare engine performance at similar design parameters. The engine performance was found to be superior at the above values of r/R and the deflecting angle. Engine exhaust of NOx and exhaust smoke were found to be lower at these design parameters. The experimental technique of using emulsified spray with LIT can be used qualitatively to evaluate effects of combustion chamber and fuel system design variables on engine performance. [S0742-4795(00)00104-6]
Global Warming: Is It Real?
Authors: Watts Robert G.
Published: July 2002

The atmospheric loading of several greenhouse gases is increasing. The most important of these is carbon dioxide, which is emitted to the atmosphere when fossil fuel is burned to supply energy. In this paper I discuss the implications of this in terms of global warming, and address the claims of the skeptics in the scientific community. [S0199-6231(00)00103-9]
Propagation of Focused and Multibeam Laser Energy in Biological Tissue
Authors: Fowler Alex J. , Pinar Menguc M.
Published: July 2002

The results of a Monte Carlo simulation of laser beam propagation in turbid media are presented. The study was performed to determine whether using a focused beam or multiple beams instead of a single collimated beam could improve subsurface laser energy delivery in biological tissue. A parametric study was carried out to determine both the laser fluence at a target depth and the ratio of fluence at the target over surface fluence as a function of tissue properties and the mode of energy delivery. It was found that the reduced scattering coefficient was the primary determinant as to whether multibeam or focused beam delivery could be effective. A focused beam was found to be extremely effective in increasing fluence at the target if the dimensionless reduced scattering coefficient was less than 2. The delivered fluence, however, was found to be extremely sensitive to tissue properties. A five-beam laser system was found to be less effective at increasing fluence at the target than a focused beam; but the fluence delivered by a five-beam system was far less sensitive to tissue properties, thereby making accurate dosimetry more feasible. [S0148-0731(00)01205-X]
Two-Dimensional Simulation of Wave Propagation in a Three-Pipe Junction
Authors: Pearson R. J. , Bassett M. D. , Batten P. , Winterbone D. E.
Published: July 2002

The modelling of wave propagation in complex pipe junctions is one of the biggest challenges for simulation codes, particularly those applied to flows in engine manifolds. In the present work an inviscid two-dimensional model, using an advanced numerical scheme, has been applied to the simulation of shock-wave propagation through a three-pipe junction; the results are compared with corresponding schlieren images and measured pressure-time histories. An approximate Riemann solver is used in the shock-capturing finite volume scheme and the influence of the order of accuracy of the solver and the use of adaptive mesh refinement are investigated. The code can successfully predict the evolution and reflection of the wave fronts at the junctions whilst the run time is such as to make it feasible to include such a model as a local multi-dimensional region within a one-dimensional wave-action simulation of flow in engine manifolds. [S0742-4795(00)01304-1]