bluuebunny/crossref_metadata_2025 huggingface dataset:
Procreation for Donation: The Moral and Political Permissibility
of “Having a Child to Save a Child”
Authors: AULISIO MARK P. , MAY THOMAS , BLOCK GEOFFREY D.
Published: July 2002

The crisis in donor organ and tissue supply is one of the most
difficult challenges for transplant today. New policy initiatives,
such as the driver's license option and required request,
have been implemented in many states, with other initiatives, such
as mandated choice and presumed consent, proposed
in the hopes of ameliorating this crisis. At the same time, traditional
acquisition of organs from human cadavers has been augmented by living
human donors, and nonheartbeating human donors, as well as experimental
animal and artificial sources. Despite these efforts, the crisis persists
and is perhaps most tragic when it threatens the lives of children,
driving parents to sometimes desperate measures. Herein, we address
one very controversial step some parents have taken to obtain matching
tissue or organs for their needy children—that is, having a child,
in part, for the purpose of organ or tissue procurement.
On the Subject(s) of Jack Kevorkian, M.D.: A Retrospective Analysis
Authors: KOCH TOM
Published: July 2002

To those defining euthanasia as a battle for the
principle of self-determination, persons seeking physician
assisted death (PAD) are soldiers in the fight for patient
autonomy. The reasons they seek it, or the potential of
other, non-life-threatening interventions is less important
than this principle: individuals have the right not only
to choose death (suicide), but to be assisted in dying.
They should not be second guessed or denied on the basis
of another's distaste for that decision. This paper
offers a general review of deaths attributed to Dr. Jack
Kevorkian's PAD practice in an attempt to answer two
questions: Why do persons seek physician assisted death,
and, to what extent does induced death seem, in retrospect,
a reasonable and perhaps necessary medical response to
specific patient complaints?
Political dimensions to leisure and cultural activities in Canadian cities, 1880–1940
Authors: Dagenais Michèle
Published: July 2002

Under what circumstances did Canadian municipalities, charged with ensuring the existence of services which encouraged the development of real property, come to be involved in the field of culture and leisure? By examining the process through which the Municipal Library and the Botanical Garden were established in Montreal, this article attempts to answer this question. Because these projects constituted precedents in relation to the usual areas of Canadian municipal intervention, they provoked vigorous debate. Each in their own way, the projects served to call into question the definition of public culture and the democratization of knowledge. They also raised the equally contentious issue of the role of municipal government in the fields of leisure and culture.
Sound, space, sculpture: some thoughts on the ‘what’, ‘how’ and ‘why’ of sound diffusion
Authors: HARRISON JONTY
Published: July 2002

Sound diffusion – the realtime (usually manual) control of the relative levels and spatial deployment during performance – is one of the most contentious issues in the field of electroacoustic music. There are parts of the world where the practice is virtually unknown; in other places it is the norm and appropriate facilities would be provided as a matter of course for any visiting composer or performer. These ‘local variations’ are not merely ripples on the surface of a standardised performance practice but stem from underlying attitudes to what composition and performance in this medium are about and, ultimately, to a definition of music itself. What follows summarises observations drawn from fifteen years of working with the BEAST concert diffusion system in numerous performance spaces in the UK and Europe, as well as experiencing, both as listener and performer, other systems in Europe and North America. Scientific rigour, in the normally accepted sense of tables of measurements etc., is not my goal – my portable measuring equipment has been my ears, and my conclusions are based on what I have heard.
A Neural Circuit Analysis of Visual Recognition Memory: Role of Perirhinal, Medial, and Lateral Entorhinal Cortex
Authors: Kesner Raymond P. , Ravindranathan Ajay , Jackson Pamela , Giles Ryan , Chiba Andrea A.
Published: July 2002

Using a continuous recognition memory procedure for visual object information, we sequentially presented rats with eight novel objects and four repeated objects (chosen from the 8). These were selected from 120 different three-dimensional objects of varying sizes, shapes, textures, and degree of brightness. Repeated objects had lags ranging from 0 to 4 (from 0 to 4 different objects between the first and repeated presentation). An object was presented on one side of a long table divided in half by an opaque Plexiglas guillotine door, and the latency between opening the door and the rat moving the object was measured. The first presentation of an object resulted in reinforcement, but repeated presentations did not result in a reinforcement. After completion of acquisition training (significantly longer latencies for repeated presentation compared with the first presentation of an object), rats received lesions of the perirhinal, medial, or lateral entorhinal cortex or served as sham operated controls. On the basis of postsurgery testing and additional tests, the results indicated that rats with perirhinal cortex lesions had a sustained impairment in performing the task. There were no sustained deficits with medial or lateral entorhinal cortex lesions. The data suggest that recognition memory for visual object information is mediated primarily by the perirhinal cortex but not by the medial or lateral entorhinal cortex.
Isolation and Characterization of Homogentisate Phytyltransferase Genes from Synechocystis sp. PCC 6803 and Arabidopsis
Authors: Savidge Beth , Weiss James D. , Wong Yun-Hua H. , Lassner Michael W. , Mitsky Timothy A. , Shewmaker Christine K. , Post-Beittenmiller Dusty , Valentin Henry E.
Published: July 2002

Tocopherols, synthesized by photosynthetic organisms, are micronutrients with antioxidant properties that play important roles in animal and human nutrition. Because of these health benefits, there is considerable interest in identifying the genes involved in tocopherol biosynthesis to allow transgenic alteration of both tocopherol levels and composition in agricultural crops. Tocopherols are generated from the condensation of phytyldiphosphate and homogentisic acid (HGA), followed by cyclization and methylation reactions. Homogentisate phytyltransferase (HPT) performs the first committed step in this pathway, the phytylation of HGA. In this study, bioinformatics techniques were used to identify candidate genes,slr1736 and HPT1, that encode HPT fromSynechocystis sp. PCC 6803 and Arabidopsis, respectively. These two genes encode putative membrane-bound proteins, and contain amino acid residues highly conserved with other prenyltransferases of the aromatic type. A Synechocystissp. PCC 6803 slr1736 null mutant obtained by insertional inactivation did not accumulate tocopherols, and was rescued by the Arabidopsis HPT1 ortholog. The membrane fraction of wild-type Synechocystis sp. PCC 6803 was capable of catalyzing the phytylation of HGA, whereas the membrane fraction from the slr1736 null mutant was not. The microsomal membrane fraction of baculovirus-infected insect cells expressing the Synechocystis sp. PCC 6803slr1736 were also able to perform the phytylation reaction, verifying HPT activity of the protein encoded by this gene. In addition, evidence that antisense expression of HPT1in Arabidopsis resulted in reduced seed tocopherol levels, whereas seed-specific sense expression resulted in increased seed tocopherol levels, is presented.
Molecular Responses to Aphid Feeding in Arabidopsis in Relation to Plant Defense Pathways
Authors: Moran Patrick J. , Thompson Gary A.
Published: July 2002

Little is known about molecular responses in plants to phloem feeding by insects. The induction of genes associated with wound and pathogen response pathways was investigated following green peach aphid (Myzus persicae) feeding on Arabidopsis. Aphid feeding on rosette leaves induced transcription of two genes associated with salicylic acid (SA)-dependent responses to pathogens (PR-1 and BGL2) 10- and 23-fold, respectively. Induction of PR-1 and BGL2mRNA was reduced in npr1 mutant plants, which are deficient in SA signaling. Application of the SA analog benzothiadiazole led to decreases in aphid reproduction on leaves of both wild-type plants and mutant plants deficient in responsiveness to SA, suggesting that wild-type SA-dependent responses do not influence resistance to aphids. Two-fold increases occurred in mRNA levels ofPDF1.2, which encodes defensin, a peptide involved in the jasmonate (JA)-/ethylene-dependent response pathway. Transcripts encoding JA-inducible lipoxygenase (LOX2) and SA/JA-inducible Phe-ammonia lyase increased 1.5- to 2-fold.PDF1.2 and LOX2 induction by aphids did not occur in infested leaves of the JA-resistant coi1-1mutant. Aphid feeding induced 10-fold increases in mRNA levels of a stress-related monosaccharide symporter gene, STP4. Phloem feeding on Arabidopsis leads to stimulation of response pathways associated with both pathogen infection and wounding.
Production of Dwarf Lettuce by Overexpressing a Pumpkin Gibberellin 20-Oxidase Gene
Authors: Niki Tomoya , Nishijima Takaaki , Nakayama Masayoshi , Hisamatsu Tamotsu , Oyama-Okubo Naomi , Yamazaki Hiroko , Hedden Peter , Lange Theo , Mander Lewis N. , Koshioka Masaji
Published: July 2002

We investigated the effect of overexpressing a pumpkin gibberellin (GA) 20-oxidase gene encoding an enzyme that forms predominantly biologically inactive products on GA biosynthesis and plant morphology in transgenic lettuce (Lactuca sativa cv Vanguard) plants. Lettuce was transformed with the pumpkin GA 20-oxidase gene downstream of a strong constitutive promoter cassette (El2–35S-Ω). The transgenic plants in which the pumpkin gene was detected by polymerase chain reaction were dwarfed in the T2generation, whereas transformants with a normal growth phenotype did not contain the transgene. The result of Southern-blot analysis showed that the transgene was integrated as a single copy; the plants segregated three dwarfs to one normal in the T2 generation, indicating that the transgene was stable and dominant. The endogenous levels of GA1 and GA4 were reduced in the dwarfs, whereas large amounts of GA17 and GA25, which are inactive products of the pumpkin GA 20-oxidase, accumulated in these lines. These results indicate that a functional pumpkin GA 20-oxidase is expressed in the transgenic lettuce, resulting in a diversion of the normal pathway of GA biosynthesis to inactive products. Furthermore, this technique may be useful for controlling plant stature in other agricultural and horticultural species.
Long-Distance Phloem Transport of Glucosinolates in Arabidopsis
Authors: Chen Sixue , Petersen Bent Larsen , Olsen Carl Erik , Schulz Alexander , Halkier Barbara Ann
Published: July 2002

Glucosinolates are a large group of plant secondary metabolites found mainly in the order Capparales, which includes a large number of economically important Brassica crops and the model plant Arabidopsis. In the present study, several lines of evidence are provided for phloem transport of glucosinolates in Arabidopsis. When radiolabeled p-hydroxybenzylglucosinolate (p-OHBG) and sucrose were co-applied to the tip of detached leaves, both tracers were collected in the phloem exudates at the petioles. Long-distance transport of [14C]p-OHBG was investigated in wild-type and transgenic 35S::CYP79A1 plants, synthesizing high amounts of p-OHBG, which is not a natural constituent of wild-type Arabidopsis. In both wild-type and 35S::CYP79A1 plants, radiolabeled p-OHBG was rapidly transported from the application site into the whole plant and intactp-OHBG was recovered from different tissues. The pattern of distribution of the radioactivity corresponded to that expected for transport of photoassimilates such as sucrose, and was consistent with translocation in phloem following the source-sink relationship. Radiolabeled p-OHBG was shown to accumulate in the seeds of wild-type and 35S::CYP79A1 plants, wherep-OHBG had been either exogenously applied or endogenously synthesized from Tyr in the leaves. p-OHBG was found in phloem exudates collected from cut petioles of leaves from both wild-type and 35S::CYP79A1 plants. Phloem exudates were shown to contain intact glucosinolates, and not desulphoglucosinolates, as the transport form. It is concluded that intact glucosinolates are readily loaded into and transported by the phloem.
Icosahedral quasicrystals applied as a harmonic-free crystal analyser
Authors: Capitan M. J. , Alvarez J.
Published: July 2002

The use of quasicrystals as crystal analysers has been studied in monochromatic X-ray synchrotron radiation applications. The quasiperiodicity of their structures gives a theoretical third-harmonic rejection factor of up to 5 × 10−4when the icosahedral (20,32) Bragg peak is used. This ratio is compared with the intrinsic value for silicon perfect crystals in Bragg configuration, namely 2 × 10−2. This rejection factor may be increased for some well defined configurations, as reported elsewhere for the case of periodic crystals.
Displacements from Cu4Ti in a Cu–Ti single crystal using small-angle and diffuse X-ray scattering: a synchrotron radiation study
Authors: Lyon O. , Servant C. , Simon J. P.
Published: July 2002

Single crystals of Cu–2.5 at.% Ti have been studied by small-angle and large-angle X-ray scattering to determine the displacements induced by the formation and the coarsening of ordered Cu4Ti precipitates. The variation of the atomic scattering factor of Cu near its absorption edge was used to confirm the nature of the precipitates and to show that the scattering appearing near Bragg peaks was due to the displacements of the atoms from their ideal positions, induced by the formation of the precipitates, and not to the segregation of the Ti atoms. The displacement field was found to be dependent on the precipitate mean size, with a single component aligned along a soft 〈100〉 direction: it is composed of a region of dilatation, where the Cu-atom positions follow the increase of the atomic distance induced by the Cu4Ti precipitate formation, followed by a region of contraction. This effect is responsible for the pile-up of the precipitates along the soft directions: the interaction between precipitates is repulsive at long distances and attractive at shorter distances.
Chemical and crystallographic investigations on the cracking of blue corundum, Al2O3, produced by the Verneuil technique
Authors: Rinaudo C. , Orione P. , Zarka A.
Published: July 2002

Corundum (Al2O3) boules grown by the Verneuil process generally crack along an irregular surface parallel to the elongation axis. In order to investigate the reasons for such cracking, a half boule of blue corundum, industrially produced following the Verneuil technique, was cut into slices (about 1 mm thick) parallel or normal to the elongation axis of the sample. All the slices were analysed by optical microscopy, energy dispersive spectrometry (EDS), flame atomic absorption spectrometry (FAAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and by X-ray transmission topography, using synchrotron radiation. The two most interesting phenomena observed were: (a) a blue colour, the location of which was not homogeneous in the boule, but concentrated in a narrow (∼2 mm) ring in the outer region of the sample; (b) the development of a single crystal during the first stages of the growth and the formation of a macromosaic crystal, with domains that were slightly misoriented and subparallel to one another, in the middle part and at the top of the boule.
FBR: a robust method to determine the basis matrix of the Bravais lattice from oscillation images
Authors: Döhring Klaus , Tavan Paul
Published: July 2002

The FBR (Fourier basis reconstruction) method described in this paper has been designed to determine the basis matrix of the Bravais lattice with respect to the laboratory frame of reference and without prior knowledge of cell constants, particularly for protein crystals of comparatively low quality. It is based on Fourier analysis of a three-dimensional intensity distribution in reciprocal space, which is directly obtained from observed intensity distributions, provided that they are recorded by the rotation method using a fixed X-ray wavelength, resulting in a direct-space determination of the basis vectors. After a description of the motivation and theory behind the method, it is tested by application to numerically generated images of a virtual sample crystal and to experimental data of a lysozyme crystal with well known cell constants. Finally, FBR is applied to a set of images of bacteriorhodopsin crystals suffering from strong anisotropic spot broadening; this case provided the original motivation for the present work.
LAPODS: a computer program for refinement of lattice parameters using optimal regression
Authors: Dong Cheng , Langford J. I.
Published: July 2002

LAPODSis an upgraded version of the programLAPODfor the refinement of lattice parameters using the method of Cohen [Langford (1971).J. Appl. Cryst.4, 259–260]. The improved version has a number of advanced features. It can detect the most significant systematic errors automatically by means of a statisticalFtest; it can also operate in a manual mode with corrections set by the user or input manually. The single-value decomposition (SVD) method is used so that the refinement is now more stable. The general formula to calculate the specimen-transparency error has been incorporated and a transparency correction can now be made when the absorption is intermediate between the limiting cases of `thick' or `thin' samples.
High-pressure studies of the cubic to rhombohedral transformation in NbO2F
Authors: Carlson Stefan
Published: July 2002

ThePm\bar{3}mtoR\bar{3}chigh-pressure transition of NbO2F has been studied in detail using diamond anvil cells and synchrotron X-ray radiation. The transition starts at 0.28 GPa and is complete at 0.65 GPa. The bulk modulus for the cubic phase became 24.8 (11) GPa, which is roughly two times higher than for the rhombohedral phase.
The number of good reflections in a powder pattern
Authors: Sivia D. S.
Published: July 2002

The number of `statistically independent' observations in a powder diffraction pattern has been the topic of some discussion over the past few years. It is argued that while this notion is tantalizing, it is illusory in principle, and it is suggested that a more appropriate measure of the quality of the data is the number of `good' reflections. By way of explanation, a tutorial on the underlying concepts of correlation and covariance, which are a surprisingly common source of confusion, is provided. A practical procedure for implementing the theoretical ideas is proposed.
Coupling between spatial and angular variables in surface X-ray diffraction: effects on the line shapes and integrated intensities
Authors: Jedrecy Nathalie
Published: July 2002

The intensity line shape, as provided by a rocking scan, and the derivation of the structure factor from the integrated intensity are reviewed in the context of surface X-ray diffraction, focusing on thez-axis geometry. In a first step, under the assumption of a Dirac-like rod and a point-like sample, the effects of the detector slit settings on the scan width and on the integrated rod height are described. In a second step, it is shown that it is incorrect to treat the integrated intensity as being proportional to the active areaAof the surface, defined as the sample area that is illuminated by the incident beam and viewed by the detector. Indeed, one must take account of the changes in the scattering direction that occur during the θ scan, and define at every θ the surface fractionA(θ) that scatters into the detector. In a third step, a rod with finite width is considered, and the spilling and travelling of the diffracted spot, arising from the centre of the sample, over the detector window is described. The spots emerging from any other sample position are then considered. By coupling spatial and angular variables, the scan line shape can be simulated quantitatively, by means of the in-plane intensity distribution of the rod. The resulting integrated intensity provides the correction factor to be applied to the raw data for the derivation of the structure-factor amplitude. This correction factor is compared to the usual correction (ALΔl), whereAis assumed to be constant,Lis the Lorentz factor and Δlis thelrange as integrated during the scan (in the context of the Dirac-like rod). Significant differences occur at largelvalues when using grazing-incidence conditions.
Diffraction measurements from crystals under electric fields: instrumentation
Authors: Guillot Régis , Allé Paul , Fertey Pierre , Hansen Niels K. , Elkaïm Eric
Published: July 2002

Based on the ideas of previous work, a device has been built for applying strong electric fields to a crystal during the measurement of diffracted intensities using a field-switching technique. It consists of a high-voltage supply, the electronics for switching the field, and synchronous counting on four chains combined with controls for step-scanning the diffraction profiles. By using this `stroboscopic' technique, it is possible to measure very small changes in Bragg angles arising from the strain induced by the converse piezoelectric effect, and also to measure minute changes in the Bragg intensities arising from polarizations of atomic structure and electron density.
The convergence of the van Cittert method of deconvolution
Authors: Ruland W.
Published: July 2002

The means of assessing the convergence of the van Cittert method of deconvolution is discussed with the help of the corresponding operation in Fourier space.
Examination of errors in the determination of phase boundary thickness by small-angle X-ray scattering
Authors: Roe R.-J.
Published: July 2002

The method of determining the thickness of a diffuse phase boundary with density profile governed by equilibrium conditions is proposed. It follows the well known procedure of analyzing the deviations from Porod's law. Errors in the obtained boundary thickness, owing to the statistical scatter in the intensity data and to the difficulty of separating the effect of density fluctuations within the phases, are examined. For this purpose, scattering curves are synthesized on the basis of a well defined model structure with known boundary thicknesses. These synthesized curves, when analyzed according to the proposed method, yield the correct boundary thickness under favorable conditions, but are also shown to lead to very erroneous results in some cases.
The determination of the crystallinity in glass-ceramic materials by the method of Ruland
Authors: Vonk C. G. , Fagherazzi G.
Published: July 2002

The method of Ruland [Acta Cryst. (1961). 14, 1180–1185] for the determination of crystallinity has been modified in order to take account of a difference in chemical composition of the crystallized and non-crystallized fractions, such as occurs in glass-ceramic materials. Application to two samples leads to higher crystallinities than found by other X-ray methods, and shows a large increase of disorder with decreasing crystallinity.
Kristallstrukturdaten von PdPb0.2As0.8(m)
Authors: Ellner M. , Kattner U. , Predel B.
Published: July 2002

The structure of the metastable phase PdPb0.2As0.8(m) is isotypic with NiAs. The hexagonal unit-cell parameters (293 K) are: P63/mmc, a = 3.803(1), c = 5.651(1) Å, U = 70.78 Å3; Z = 2, Dx
= 9.75 g cm−3; Cu Kα radiation. X-ray powder diffraction data are reported. The JCPDS Diffraction File No. for PdPb0.2As0.8(m) is 33-1490.
Polytypic structures of (Cr, Fe)7C3 carbides
Authors: Kowalski M.
Published: July 2002

A number of polytypes have been found in (Cr, Fe)7C3 carbides. The basic structure of these carbides and polytypes can be considered as a stacking of layers parallel to the {110} planes in the basic cell. The symmetry of all possible polytypes of M
7
C
3 carbides can be described by four space groups: Pb, P21/b, Pca21 and Pbca (Pca21 in two settings). A procedure for structure determination based on the analysis of electron diffraction patterns is proposed and applied to the polytypes: 2O, 3M, 4O, 4M, 5M
1, 5M
2, 5M
3, 6O, 6M
1, 6M
2 and 8O (in Ramsdell notation).
Report on a round-robin study of diffuse X-ray scattering
Authors: Ohshima K. , Harada J. , Morinaga M. , Georgopoulos P. , Cohen J. B.
Published: July 2002

The diffuse scattering in a volume in reciprocal space from NbC0.72 was measured on an absolute scale at two synchrotron sources (in the US and in Japan) and with a high-intensity rotating-anode source (in Japan). The shape and actual absolute intensities agreed to a few percent. Special problems associated with such measurements at a synchrotron are noted, especially with an insertion device. The high resolution possible at such sources reduces the need for an evacuated sample chamber. Detailed measurements can be completed in 1–2 d, making such studies much more accessible than is possible with sealed-tube X-ray generation.
New crystal data (neutron) for phase II rubidium nitrate at 513 K
Authors: Shamsuzzoha M. , Lucas B. W.
Published: July 2002

Indexed neutron powder diffraction data of phase II RbNO3 indicate a body-centred cubic unit cell [a = 8.84(3) Å at T = 513 K, V = 690.1(52) Å3, Z = 8, Dx
= 2.84(2) Mg m−3, λ = 1.083 Å, possible space groups include I23, I213, Im3, I432, I{\bar 4}3m or Im3m] in preference to the previously reported tetragonal cell {a = 6.19, c = 8.74 Å, Z = 4 [Brown & McLaren (1962). Acta Cryst.
15, 974–976]}, or trigonal cell {a ≃ 5.48, c ≃ 10.71 Å, Z = 3 [Ahtee & Hewat (1980). Phys. Status Solidi A, 58, 525–531]}.
Some computer drawings of molecular and solid-state structures
Authors: Keller E.
Published: July 2002

Drawings of molecular and solid-state structures generated by the computer program SCHAKAL88 are presented. Automatic atom labelling and some of the graphical techniques used for shading of line and raster drawings are briefly discussed.
CRYST – a system to display 3D images of crystal structure, symmetry operations and crystal forms
Authors: Sakurai T. , Kobayashi K. , Horiki T. , Furukawa M. , Naitou K.
Published: July 2002

CRYST is a three-dimensional computer graphics program to help the understanding of crystallographic procedures. The three-dimensional image of a crystal structure is displayed, together with the arrangement of the symmetry elements in the unit cell. The symmetry-related atoms can be generated successively on a graphics screen by designating symmetry elements with a pen and tablet. Changes in morphology of a growing crystal may also be drawn by computer. Several applications of the system are described.
RSPACE – a reciprocal-space modelling tool
Authors: Harris M. R. , Fitzgibbon M. , Hage F.
Published: July 2002

RSPACE is an interactive computer-graphics program that models the relationship between crystallographic data-collection hardware and reciprocal space. It is designed to help crystallographers plan efficient complex data-collection strategies for area detector systems, and as an educational tool. Because RSPACE models the interaction of crystal, detector and goniostat geometry in a general way, it is of particular interest to users of area detectors interfaced with multi-axis goniostats.
The effect of diffraction by the diamonds of a diamond-anvil cell on single-crystal sample intensities
Authors: Loveday J. S. , McMahon M. I. , Nelmes R. J.
Published: July 2002

The integrated intensities measured in X-ray single-crystal high-pressure structural studies using a diamond-anvil cell are shown to be reduced substantially when the diamonds diffract at the same setting as the sample – by as much as 50% in some cases. The pressure and wavelength dependence of this process have been studied and also the effect of changing the beam divergence by the use of a synchrotron beam. The consequences for the accuracy of structural information derived from data sets collected at high pressure are considered and a data-collection strategy for detecting and avoiding the effects of diamond diffraction is proposed.
Small-angle X-ray scattering at high energies
Authors: Siddons D. P. , Riekel C. , Hastings J. B.
Published: July 2002

Initial tests are described of a high-resolution small-angle X-ray scattering apparatus adapted for operation at high photon energies. The energy chosen was 50 keV, and was limited by the available source. All orders of scattering out to the seventh were observed from a sample of 0.9 μm diameter latex spheres in a 4 h experiment. Phase separation in a binary Al–Li alloy was studied by the observation of spherical Al3Li precipitates. This demonstrates that the use of perfect-crystal collimators and analyzers yields a resolution function which does not depend on photon energy. New sources of high-energy photons will make such an apparatus invaluable for the study of highly absorbing samples, or samples in difficult environments such as ovens or high-pressure cells.
Estimation of incoherent backgrounds in SANS studies of polymers
Authors: Dubner W. S. , Schultz J. M. , Wignall G. D.
Published: July 2002

Small- and intermediate-angle neutron scattering studies have been undertaken on mixtures of deuterated and protonated poly(ethylene terephthalate) (PET) molecules with a wide range of concentration. The samples were converted to random copolymers by transesterifying in the melt, thus removing the coherent component of the intensity associated with single-chain scattering. The transesterified samples were used to determine the level of incoherent scattering associated with each isotopic mixture which was compared with estimates from established background-correction techniques based on extra-polating from the scattering of fully protonated or deuterated blanks. Scaling via the measured sample transmission works well for predominantly protonated mixtures but fails when the fraction of deuterated polymer exceeds φ
D ~0.6. Scaling via the component of the sample transmission attributable to the incoherent scattering from H nuclei works well over the whole concentration range. This method involves calculations of the sample transmission via the bound-atom cross section and this is a good approximation at the wavelength employed (λ ~4.75 Å), where the hydrogen incoherent cross section is close to the bound-atom cross section (σ
H ~80 × 10−28 m2). However, σ
H is a strong function of wavelength and the method cannot be used where the measured and calculated transmissions diverge. A recently developed theory describing the scattering from random copolymers was used to analyze the residual coherent cross section of the copolymers and led to a statistical segment length b = 14.3 ± 1 Å, in good agreement with existing values for PET.
Converse-transformation analysis
Authors: Karen V. L. , Mighell A. D.
Published: July 2002

Converse-transformation theory and NIST*LATTICE open a new approach to study many theoretical and practical problems in crystallography. In this approach a new operator, the converse-transformation operator, is defined. The focus of this approach is based on the calculation of groups of matrices relating two lattices and subsequent analysis of these matrices to deduce crystallographic relationships. An efficient algorithm has been designed that has the ability to find all matrices (H) that relate ANY two cells (no matter how skewed) to within any specified tolerances (t) of the cell parameters. A Fortran program, NIST*LATTICE, that enables this new approach to be used is available to the scientific community. There are many immediate applications of converse-transformation analysis including the full automation of the single-crystal diffractometer and phase characterization using lattice-matching techniques.
The defects and intergrowth of lead oxides revealed by HRTEM
Authors: Wang Y. G. , Ye H. Q. , Kuo K. H. , Guo J. G.
Published: July 2002

High-resolution transmission electron microscopy (HRTEM) and electron diffraction were used to investigate the microstructure of natural lead oxides found in Panzhihua Mountain, China. The electron diffraction patterns showed crossing of diffraction spots along 〈110〉 directions in litharge and along 〈100〉 directions in massicot and the structural images showed the domain-like texture, probably constructed by arrays of planar defects in the fundamental structures. Based upon the structure of these oxides the possible structural models of planar defects are discussed and the orientation relationship of litharge and massicot is determined.
SIRPOW.91 - a direct-methods package optimized for powder data
Authors: Cascarano G. , Favia L. , Giacovazzo C.
Published: July 2002

A direct-methods package optimized for powder data is described. Omission of weak intensities and overlapping reflections can greatly influence the phasing process. Methods are proposed which reduce their adverse effects on the efficiency of direct procedures. The experimental tests prove that SIRPOW.91 is a useful tool for solving crystal structures from both neutron and X-ray powder data.
X-ray diffraction investigations of CaF2 at high pressure
Authors: Gerward L. , Olsen J. S. , Steenstrup S. , Malinowski M. , Åsbrink S. , Waskowska A.
Published: July 2002

Synchrotron-radiation X-ray diffraction studies of CaF2 at high pressures have been performed on a powder sample up to 45 GPa and on a single-crystal sample up to 9.4 GPa. The bulk modulus of the low-pressure phase was determined to be B
0 = 87 (5) GPa. A phase transition was observed at about 9.5 GPa. The transition is accompanied by a volume contraction of 11%. The high-pressure phase is orthorhombic PbCl2 type (space group Pbnm). The sample only partially reverts to the low-pressure phase upon release of pressure.
The half-widths of Bragg intensity profiles measured with a triple-crystal diffractometer at a synchrotron-radiation source. II. The half-widths of YIG and Si single crystals
Authors: Rossmanith E. , Werner M. , Kumpat G. , Ulrich G. , Eichhorn K.
Published: July 2002

The practical usefulness of the expressions for the half-width proposed in paper I [Rossmanith (1993). J. Appl. Cryst.
26, 753–755] are demonstrated for three examples: a spherical YIG (yttrium iron garnet) crystal, a spherical silicon crystal and a plane-parallel perfect silicon plate. The new concept for the calculation of the width results in theoretical widths that are in excellent agreement with experimental widths observed in parallel and antiparallel arrangements of the sample with respect to the second monochromator crystal.
Development of the computational procedures for simulation and indexing of back-reflection Laue patterns
Authors: Marín C. , Cintas A. , Diéguez E.
Published: July 2002

A method for the simulation of Laue-grams has been developed according to geometrical considerations and the equations for easy solution of the problem are given. At the same time, with the model proposed by Riquet & Bonet [J. Appl. Cryst. (1979), 12, 39–41] taken into account, an algorithm has been developed for indexing all the experimental spots obtained by Laue back reflection of an unknown orientation of any single-crystal material. In this work, the simulation and indexing have been successfully applied to LiNbO3 crystals.
XPLCHK – an extensible program for checking and validating X-PLOR input files
Authors: Laub P. B.
Published: July 2002

XPLCHK is a portable and user-extensible C-language program for checking and validating input files for X-PLOR, versions 2.1+. Motivating the development of this program was the frustration and waste of time resulting from X-PLOR runs that crash due to errors in the input file or that yield irrelevant results because of incorrect specification of key parameters. Consequently, XPLCHK scans the file for common errors, verifies that all needed files are accessible and warns the user of potential problems. In addition, symbol assignments are summarized, making it easy for the user to check that they are properly set. Coded in an open and well documented manner, XPLCHK makes it straightforward for users with a modest knowledge of to create modules specific to their use of X-PLOR. The source code is available by sending email to p_laub@fccc.edu.
High-Angular-Resolution Camera Coupled with an Undulator Source at the European Synchrotron Radiation Facility High-Brilliance Beamline
Authors: Diat O. , Bösecke P. , Lambard L. , de Moor P. P. E. A.
Published: July 2002

The performance of a high-angular-resolution small-angle X-ray camera combined with an undulator source is presented in the form of examples.
Small-Angle Neutron Scattering Studies of the Phase Behavior and Mesophases of Homopolymers, Block Copolymers and Complex Mixtures
Authors: Mortensen K. , Almdal K. , Schwahn D. , Bates F. S.
Published: July 2002

Small-angle scattering of X-rays and neutrons are particularly powerful techniques for studying complex materials such as polymers, micellar solutions and lyotropic mesophases of amphiphilic molecules. In the present paper, we review some of the recent progress on polymer complex fluids made using small-angle neutron scattering. These studies include examination of the phase behavior of binary polymers where fluctuations due to the free volume significantly renormalize the critical behavior. Block copolymers phase-separate on the microscopic level given by the length scale of the polymer coils and form a variety of mesoscopic ordered phases. Blends of homopolymers and diblock copolymers show new physical phenomena where different critical behavior meets in a Lifshitz point. Block copolymers in selected solutions self-assemble into micellar structures which provide the basis for ordered structures.
Phenomenological model of anisotropic peak broadening in powder diffraction
Authors: Stephens Peter W.
Published: July 2002

Anisotropic line-shape broadening (peak width which is not a smooth function ofd-spacing) is frequently observed in powder diffraction patterns, and can be a source of considerable difficulty for whole-pattern fitting or Rietveld analysis. A model of the multi-dimensional distribution of lattice metrics within a powder sample is developed, leading naturally to a few parameters which can be varied to achieve optimal line-shape fits. Conditions on these parameters are derived for all crystal systems, and the method is illustrated with two examples: sodiump-hydroxybenzoate and rubidium fulleride.
Isotope effects in solution small-angle X-ray scattering
Authors: Henderson Stephen J.
Published: July 2002

While the difference between using heavy and light water as solvents for small-angle neutron scattering experiments is well known, the lesser difference for the case of small-angle X-ray scattering with these same isotopes of water has, as yet, not been reported. This difference for the case of X-rays is discussed and quantified for several familiar materials: polystyrene latexes, proteins and lipids.
Condensation-free X-ray diffraction data collection with capillaries at 277 K
Authors: Lim Daniel , Ye Qilu , Jia Zongchao
Published: July 2002

Crystallization at 277 K is routinely practiced in most crystallography laboratories. Data collection from such crystals at this temperature has been facilitated by the widespread use of versatile cryocooling devices capable of maintaining crystals at cryogenic to near room temperatures. However, temperature gradients can potentially develop along a capillary cooled by a gas stream, which may result in condensation around the crystal. A convenient protocol has been developed and used successfully to prevent this problem. By the placement of oil plugs close to both sides of the crystal, the enclosed airspace is kept free of condensation, even while the capillary is cooled for extended periods of time by a gas stream flowing at an angle to the capillary. This technique eliminates the need to work with very short capillaries and can be implemented without modification to an existing cryostat configuration.
Crystalline and microstructure study of the AlN–Al2O3section in the Al–N–O system. II. φ′- and δ-AlON spinel phases
Authors: Tabary P. , Servant C.
Published: July 2002

Results from the crystalline and microstructure study of the φ′- and δ-AlON spinel phases by X-ray diffraction, neutron diffraction and standard-resolution transmission electron microscopy techniques are reported. Several samples having different compositions in mol % AlN were considered. A structural model is proposed to account for the double modulation of composition and displacement of the cations and anions, which has been determined for these two phases and for the relationship with the γ-AlON spinel phase. Some high-resolution transmission electron microscopy experiments have confirmed the present structural model. A discussion with reference to previous data is presented.
A standardless method of quantitative ceramic analysis using X-ray powder diffraction
Authors: Mazumdar Sujata
Published: July 2002

A new procedure using X-ray powder diffraction data for quantitative estimation of the crystalline as well as the amorphous phase in ceramics is described. Classification of the crystalline and amorphous X-ray scattering was achieved by comparison of the slopes at two successive points of the powder pattern at scattering angles at which the crystalline and amorphous phases superimpose. If the second slope exceeds the first by a stipulated value, the intensity is taken as crystalline; otherwise the scattering is considered as amorphous. Crystalline phase analysis is obtained by linear programming techniques using the concept that each observed X-ray diffraction peak has contributions fromncomponent phases, the proportionate analysis of which is required. The method does not require the measurement of calibration data for use as an internal standard, but knowledge of the approximate crystal structure of each phase of interest in the mixture is necessary. The technique is also helpful in qualitative analysis because each suspected phase is characterized by the probability that it will be present when a reflection zone is considered in which the suspected crystalline phase could contribute. The amorphous phases are determined prior to the crystalline ones. The method is applied to ceramic materials and some results are presented.
A method to stabilize reduced and/or gas-treated protein crystals by flash-cooling under a controlled atmosphere
Authors: Vernède Xavier , Fontecilla-Camps Juan Carlos
Published: July 2002

A customized glove box for protein crystallization under a controlled atmosphere is described along with a cryogenic technique adapted to freeze protein crystals inside the glove box and a very simple device for studying gas–protein complexes in the crystalline state at cryogenic temperatures. Using these techniques different redox states of oxygen-sensitive crystalline proteins have been stabilized and the interaction of hydrogenase with Xe, a model for the much lighter substrate molecular hydrogen, has been studied.
Second-order neutron optics of three-axis spectrometers. I. Quasielastic scattering
Authors: Stoica A. D. , Popovici M. , Yelon W. B.
Published: July 2002

The basics of second-order neutron optics for bent-crystal three-axis spectrometers are presented. Energy-transfer resolution for quasielastic scattering is examined in detail. Experimental data illustrating the effect of second-order aberrations are presented. The resolution of energy transfer at 5 meV neutron energy with bent monochromators made from commercial thin silicon wafers was improved to 8 µeV from a previous record of 16 µeV.
Determination of polarity in noncentrosymmetric layer/substrate systems
Authors: Meyer Dirk C. , Richter Kurt , Krane Hans-Georg , Morgenroth Wolfgang , Paufler Peter
Published: July 2002

Energy-dispersive anomalous X-ray scattering has been used for the determination of the polarity of a noncentrosymmetric layer/substrate system. The method was applied to an epitaxically grown (Ga,In)P layer on a (001) GaAs substrate as an example to show its applicability as a routine procedure for noncentrosymmetric thin-film systems. In the simplest case, four energy spectra of various orders of the 111 reflections were sufficient to identify polarity, without the need for intensity corrections.
Etude structurale par diffraction des RX et spectroscopie IR des hydrates 10 et 8.4 Å de kaolinite
Authors: Jemai S. , Ben Haj Amara A. , Ben Brahim J. , Plançon A.
Published: July 2002

Two hydrated kaolinites, characterized by 10 and 8.4 Å basal distances, were synthesized by treating the kaolinite KGa-1 with dimethyl sulfoxide (DMSO) and ammonium fluoride (NH4F). The X-ray diffraction study was based on a comparison between the experimental and calculated profiles. This study was conducted in two steps: firstly, the study of the 00lreflections enabled the determination of the stacking mode alongc*, the number of water molecules and their positions along the normal to the plane of the sheet structure; secondly, the study of thehkbands, withhand/ork≠ 0, enabled the determination of the stacking mode and the positions of the water molecules in the (a,b) plane. The 10 Å hydrated kaolinite is characterized by two water molecules per Al2Si2O5(OH)4unit, situated at 3 and 3.4 Å from the hydroxyl surface, over the octahedral sites. Two adjacent layers are translated with respect to each other, withT11= −0.38a− 0.37b+ 10n. The 8.4 Å hydrated kaolinite is characterized by one water molecule per Al2Si2O5(OH)4unit, situated at 2.4 Å from the hydroxyl surface and inserted between the vacant octahedral site and the ditrigonal cavity of the tetrahedral sheet. The corresponding interlayer shift isT11= −0.355a+ 0.35b+ 8.4n.
Interactive Web-based tools for an introductory course in crystallography
Authors: Chapuis Gervais , Hardaker Wesley
Published: July 2002

The new possibilities offered by the Java programming environment combined with the accessibility of the World Wide Web present new and interesting perspectives. It is thus now possible to perform simulations directly, using a Web browser, independently of the computer platform being used. Basic concepts of crystallography,i.e.crystal structures, point- and space-group symmetry, lattices, reciprocal lattices and diffraction principles can be illustrated utilizing interactive simulations written in Java. A number of such applications have been developed with the aim to facilitate the understanding of these crystallographic concepts to the newcomers in the field.
Origin of the optical activity of silver thiogallate
Authors: Etxebarria J. , Folcia C. L. , Ortega J.
Published: July 2002

Using a high-accuracy universal polarimeter, the birefringence and optical activity of AgGaS2have been determined between 300 and 500 K. The optical rotation has been found to be 94° mm−1at room temperature for a wavelength of 632.8 nm. This value is unexpectedly small if compared with values close to 1000° mm−1at 485 nm reported previously. The present optical data are well explained using a point-dipole model for the calculation of the refractive indices and optical activity. The main contributors to the optical rotation are the S atoms. However, these atoms are not at positions especially suitable to promote extremely large gyrations. Consequently, the size of the optical rotation reported before in the blue part of the spectrum is presumably due to the existence of a circular dichroism band close to that region. Using an optical system based on a photoelastic modulator, a strong linear dichroism peak has been measured in the range 450–500 nm. This fact has prevented reliable measurement of the circular dichroism.