bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear stability of mixed convection
flow under non-Boussinesq conditions.
Part 1. Analysis and bifurcations
Authors: SUSLOV S. A. , PAOLUCCI S.
Published: July 2002

The weakly nonlinear theory for modelling flows away from the bifurcation point
developed by the authors in their previous work (Suslov & Paolucci 1997) is generalized
for flows of variable-density fluids in open systems. It is shown that special treatment
of the continuity equation is necessary to perform the analysis of such flows and
to account for the potential total fluid mass variation in the domain. The stability
analysis of non-Boussinesq mixed convection flow of air in a vertical channel is then
performed for a wide range of temperature differences between the walls, and Grashof
and Reynolds numbers. A cubic Landau equation, which governs the evolution of
a disturbance amplitude, is derived and used to identify regions of subcritical and
supercritical bifurcations to periodic flows. Equilibrium disturbance amplitudes are
computed for regions of supercritical bifurcations.
Determinism in new-dialect formation and the genesis of New Zealand English
Authors: TRUDGILL PETER , GORDON ELIZABETH , LEWIS GILLIAN , MACLAGAN MARGARET
Published: July 2002

In this paper we use an extensive archive of early New Zealand speakers, together
with comparisons with the other Southern Hemisphere varieties of English, to argue
that dialect mixture and new-dialect formation are not haphazard processes. We
demonstrate that, given sufficient linguistic information about the dialects which
contribute to a mixture, and sufficient demographic information about the
proportions of speakers of the different dialects, it is possible to make predictions
about what the outcome of the mixture will be. We also argue that we have arrived
at a probabilistic solution to the problem of randomness in the transmission of dialect
features from one generation to another in such situations.
The effect of a dust-size distribution on dust acoustic waves
Authors: BRATTLI A. , HAVNES O. , MELANDSØ F.
Published: July 2002

Using a kinetic model for low-frequency dust acoustic waves (DAW)
in a dusty

plasma, we have examined the effects of a dust-size distribution on their

propagation and damping. Both Landau damping and damping due to dust-charge variation are included. We consider Gaussian and power-law dust-size

distributions. In accordance with earlier results of Melandsø et al., we find that

the dust Landau damping dominates at short wavelengths. At wavelengths

longer than the Debye length λD0, the

dust-charge variation is generally

dominant. It is always dominant for the power-law size distributions that
we

have studied. We also find that if the upper and lower size limits of the
dust are

chosen so that the average dust size remains constant, regardless of the
power-law exponent γ, the wave properties are practically identical to
those of a

monosize distribution of the average dust size. For a Gaussian dust-size

distribution, Landau damping may be the dominant damping mechanism if the

dust plasma is tenuous (P[Lt ]1) and the width of the distribution
is large.
The Seizure of the Sta. Catarina Revisited: The Portuguese Empire in Asia, VOC Politics and the Origins of the Dutch-Johor Alliance (1602 – c.1616)
Authors: Borschberg Peter
Published: July 2002

The seizure of the Sta. Catarina took place off the east coast of Singapore in 1603 and was popularised by the Dutch lawyer and humanist Hugo Grotius. Based on Dutch and Portuguese sources, the article revisits the incident to critique Grotius' account and provide a snapshot of Portuguese trade and diplomacy in Asia at the time.
Infectivity of Himasthla spp. (Trematoda) in cockle (Cerastoderma edule) spat
Authors: Jensen K.Thomas , Castro Nora Fernández , Bachelet Guy
Published: July 2002

The common cockle Cerastoderma edule is intermediate host to several species of digenean trematodes. However, little is known about the factors influencing the settlement of trematode larvae in cockles as well as their effects on the host. Aspects of the transmission ecology, behaviour and effects on juvenile host specimens of trematode larvae belonging to the genus Himasthla and utilizing mudsnails Hydrobia ulvae as their first intermediate host and various waterbirds as their definitive host have been studied. Cercariae of Himasthla spp. (more than 90% of the metacercariae were identified as H. continua post-experimentally) exhibited a host size-dependent selection within the host size range from 2 to 6 mm. Infection efficiency was reduced by the presence of substratum allowing cockles to burrow, suggesting that the foot and visceral region may be attacked by cercariae. No increased mortality due to parasite infections could be demonstrated within 5 d after infestation. The metacercariae within experimentally infected cockles were primarily located in the connective tissue within the foot and visceral region. Although some cockles were completely filled with metacercariae only small functional effects were detected, such as a slightly prolonged burrowing time of infected specimens.
Production, respiration and ammonia excretion of two polychaete species in a north Norfolk saltmarsh
Authors: Nithart Mathilde , Alliot Elisabeth , Salen-Picard Chantal
Published: July 2002

The secondary production of Nereis diversicolor and Scoloplos armiger (Annelida, Polychaeta) was studied at Stiffkey saltmarshes (north Norfolk coast). Production estimation on the basis of monthly sampling (August 1992–July 1993) gives 17.91 g C m−2 y−1 for N. diversicolor, 3.37 g C m−2 y−1 for S. armiger. Oxygen consumption of individuals was studied using a respirometer at four temperatures (5, 10, 15 and 20°C). At 15 °C, the relationships between O2 consumption (mg h−1) and body dry weight (mg) is Y=0.003X0.695 for S. armiger and Y=0.003X0.498 for N. diversicolor. Ammonia excretion of S. armiger tends to increase with decreasing temperature whereas it increases from 5 to 15 °C for N. diversicolor. Carbon loss through respiration for the sampling period is estimated at 32 g C m−2 y−1 for S. armiger, and 31.7 g C m−2 y−1 for N. diversicolor. About 20% of the potential supply of phytobenthic carbon in the marsh would be converted by the populations of both species. Estimations of carbon and nitrogen budgets of S. armiger are discussed.
Educational consequences of mental disorders treated in hospital. A 31-year follow-up of the Northern Finland 1966 Birth Cohort
Authors: ISOHANNI I. , JONES P. B. , JÄRVELIN M.-R. , NIEMINEN P. , RANTAKALLIO P. , JOKELAINEN J. , CROUDACE T. J. , ISOHANNI M.
Published: July 2002

Background. Mental disorders often begin during the formative years of education. They may
disrupt education and lead to social underachievement.

Methods. We examined the impact of mental disorders treated in hospital (ages 16–29) on
educational attainment up to 31 years in the Northern Finland 1966 Birth Cohort (N = 10581).
People discharged due to mental illness were grouped by DSM-III-R diagnoses (of schizophrenia,
other psychoses and non-psychotic disorders) and were compared with those having no such
hospital treatment. Associations between diagnoses and educational outcome (completion of basic
level, upper secondary or tertiary education) were analysed stratified by age at onset (early onset
< 22 years v. later), and adjusted for confounding by perinatal risk, early motor development,
maternal education, family structure, parental social class, and school achievement using prospective
data from earlier assessments and logistic regression analysis.

Results. Twelve per cent of the comparison group completed basic level education, 62% upper
secondary, and 26% tertiary education. People with early onset disorder tended to stagnate in the
basic level. Early onset schizophrenia and all non-psychotic cases had 3- to 6-fold adjusted odds for
this outcome. Many with early onset schizophrenia completed secondary education, but none
completed the tertiary level. Hospitalization for non-psychotic disorder increased the risk of
underachievement in tertiary education for those with early onset.

Conclusions. Mental disorder treated in hospital truncates education. Failure to complete higher
education may contribute to the ‘social exclusion’ of the mentally ill through reduced opportunities
in later occupational life and failure to accumulate social capital.
Psychological distress and work and home roles: a focus on socio-economic differences in distress
Authors: MATTHEWS S. , POWER C. , STANSFELD S.
Published: July 2002

Background. Home and work factors have been linked to psychological status, but less is known about their contribution to social inequalities in psychological status. We examine whether social inequalities in psychological distress can be explained by work–home factors and whether the impact of these potential explanatory factors is similar for men and women.

Methods. Data are from the 1958 British birth cohort study. We sought to explain social class differences in psychological distress at age 33. Explanatory factors were classified as work–home roles: i.e. employment, marital status, domestic responsibility, children and elderly care; and work–home characteristics: i.e. job-strain, insecurity, unsocial working hours, youngest child's age, number of children and level of involvement in childcare.

Results. A social gradient in psychological distress was found: odds ratios for classes IV and V v. I and II were 2·65 (men) and 3·02 (women). Work factors had consistently stronger associations with psychological distress and with social class among men than women. Work factors had a greater impact on class differences in psychological distress in men. Associations for home roles and characteristics were less consistent and their combined effect on class differences in distress was negligible for both sexes.

Conclusion. Explanations for the social gradient differ for men and women. Work may be more important for men than women, but the impact of home factors was not strong during the early adulthood of this cohort.
In defence of a contented religious exclusivism
Authors: GELLMAN JEROME
Published: July 2002

In this paper I defend the possibility that a ‘contented religious
exclusivist’, will be fully rational and not neglectful of any of her epistemic duties
when faced with the world’s religious diversity. I present an epistemic strategy for
reflecting on one's beliefs and then present two features of religious belief that make
contented exclusivism a rational possibility. I then argue against the positions of
John Hick, David Basinger, and Steven Wykstra on contented exclusivism, and
criticize an overly optimistic conception of rationality. Finally, I describe a
contented exclusivist who might very well not be fully rational in the face of
religious diversity.
High-resolution measurements of X-ray emission from dense
quasi-1D plasma: Line merging and profile modification
Authors: RENNER O. , SONDHAUSS P. , PEYRUSSE O. , KROUSKÝ E. , RAMIS R. , EIDMANN K. , FÖRSTER E.
Published: July 2002

The precise measurements of the spectral line profiles
near the short-wavelength limit of the Lyman series of
Al are reported. The spatially resolved narrow-band spectra
were attributed to macroscopic plasma parameters by using
the results of 1D and 2D hydrodynamic plasma modeling.
The gradual merging and broadening of the spectral lines
Al Lyε–θ was compared to the
synthetic spectra produced by atomic physics codes. The
discrepancies between the experimental and theoretical data
indicate the limits for applicability of standard theoretical
models.
Knowledge Driven Planning and Multimodal Control of a Telerobot
Authors: Kazi Zunaid , Foulds Richard
Published: July 2002

The Multimodal User Supervised Interface and Intelligent Control (MUSIIC) project focuses on a multimodal human-machine interface which addresses user need to manipulate familiar objects in an unstructured environment. The control of a robot by individuals with
significant physical limitations presents a challenging problem of telemanipulation. This
is addressed by a unique user-interface integrating the user's command (speech) and gestures (pointing) with autonomous planning techniques (knowledge-bases and 3-D vision). The resultant test-bed offers the opportunity to study telemanipulation by individuals with physical disabilities, and can be generalized to an effective technique for other, including remote and time-delayed, telemanipulation. This paper focuses on the knowledge-driven planning mechanism that is central to the MUSIIC system.
BEHAVIOR OF DICKEY–FULLER t-TESTS WHEN THERE
IS A BREAK UNDER THE ALTERNATIVE HYPOTHESIS
Authors: Leybourne Stephen J. , Newbold Paul
Published: July 2002

This paper analyzes the limiting behavior of Dickey–Fuller
t-tests when the true generating model is stationary
around a broken linear trend. The cases of a break in level
and a break in slope are considered separately and found
to generate qualitatively different outcomes. In the asymptotic
analysis, appropriate normalizations are applied to the
break sizes. This leads to theoretical results that generate
interesting predictions for sample sizes and break amounts
of practical interest. Simulation evidence confirms the
value of this approach to an asymptotic theory.
High frequency asymptotic analysis of a string with rapidly oscillating density
Authors: CASTRO C. , ZUAZUA E.
Published: July 2002

We consider the eigenvalue problem associated with the vibrations of a string with rapidly
oscillating periodic density. In a previous paper we stated asymptotic formulae for the
eigenvalues and eigenfunctions when the size of the microstructure ε is shorter than the
wavelength of the eigenfunctions 1/√λε. On the other hand, it has been observed that
when the size of the microstructure is of the order of the wavelength of the eigenfunctions
(ε ∼ 1/√λε) singular phenomena may occur. In this paper we study the behaviour of the
eigenvalues and eigenfunctions when 1/√λε is larger than the critical size ε. We use the WKB
approximation which allows us to find an explicit formula for eigenvalues and eigenfunctions
with respect to ε. Our analysis provides all order correction formulae for the limit eigenvalues
and eigenfunctions above the critical size. Each term of the asymptotic expansion requires
one more derivative of the density. Thus, a full description requires the density to be C∞
smooth.
Source-type solutions to thin-film equations in

higher dimensions
Authors: FERREIRA RAUL , BERNIS FRANCISCO
Published: July 2002

We prove that the thin film equation

ht+div (hn grad

(Δh))=0 in dimension d[ges ]2 has

a unique C1 source-type radial self-similar non-negative
solution

if 0<n<3 and has no

solution of this type if n[ges ]3. When 0<n3 the solution

h has finite speed of propagation

and we obtain the first order asymptotic behaviour of h at the

interface or free boundary

separating the regions where h>0 and h=0. (The case

d=1 was already known [1]).
Avoiding Exploitation in Clinical Research
Authors: BENATAR SOLOMON R.
Published: July 2002

Clinical research has become a burgeoning activity
in recent years, largely stimulated by the pharmaceutical
industry's interest in new drugs with high marketing
profiles. Several other forces fuel this thrust: the increasing
dependence of academic medical institutions on research
funding from industry; the need for large, efficient multicenter
trials to obtain reliable and statistically significant
results in the shortest possible time for drug registration
purposes; and access to research subjects in “developing”
countries. The intense interest in HIV/AIDS research and
recent controversies about revisions to the Helsinki Declaration,
which have been seen by some to be motivated by the desire
to facilitate exploitative research in “developing”
countries, have stimulated renewed interest in the ethics
of clinical research.
Interdigitated Deletion Complexes on Mouse Chromosome 5 Induced by Irradiation of Embryonic Stem Cells
Authors: Schimenti John C. , Libby Brian J. , Bergstrom Rebecca A. , Wilson Lawriston A. , Naf Dieter , Tarantino Lisa M. , Alavizadeh Alireza , Lengeling Andreas , Bucan Maja
Published: July 2002

Chromosome deletions have several applications in the genetic analysis of complex organisms. They can be used as reagents in region-directed mutagenesis, for mapping of simple or complex traits, or to identify biological consequences of segmental haploidy, the latter being relevant to human contiguous gene syndromes and imprinting. We have generated three deletion complexes in ES (Embryonic Stem) cells that collectively span ∼ 40 cM of proximal mouse chromosome 5. The deletion complexes were produced by irradiation of F1 hybrid ES cells containing herpes simplex virus thymidine kinase genes (tk) integrated at the Dpp6, Hdh (Huntington disease locus), or Gabrb1 loci, followed by selection for tk-deficient clones. Deletions centered at the adjacent Hdh and Dpp6 loci ranged up to ∼ 20 cM or more in length and overlapped in an interdigitated fashion. However, the interval between Hdh and Gabrb1 appeared to contain a locus haploinsufficient for ES cell viability, thereby preventing deletions of either complex from overlapping. In some cases, the deletions resolved the order of markers that were previously genetically inseparable. A subset of the ES cell–bearing deletions was injected into blastocysts to generate germline chimeras and establish lines of mice segregating the deletion chromosomes. At least 11 of the 26 lines injected were capable of producing germline chimeras. In general, those that failed to undergo germline transmission bore deletions larger than the germline-competent clones, suggesting that certain regions of chromosome 5 contain haploinsufficient developmental genes, and/or that overall embryonic viability is cumulatively decreased as more genes are rendered hemizygous. Mice bearing deletions presumably spanning the semidominant hammertoe locus (Hm) had no phenotype, suggesting that the classic allele is a dominant, gain-of-function mutation. Overlapping deletion complexes generated in the fashion described in this report will be useful as multipurpose genetic tools and in systematic functional mapping of the mouse genome.
Sequencing a Genome by Walking with Clone-End Sequences: A Mathematical Analysis
Authors: Batzoglou Serafim , Berger Bonnie , Mesirov Jill , Lander Eric S.
Published: July 2002

One approach to sequencing a large genome is (1) to sequence a collection of nonoverlapping “seeds” chosen from a genomic library of large-insert clones [such as bacterial artificial chromosomes (BACs)] and then (2) to take successive “walking” steps by selecting and sequencing minimally overlapping clones, using information such as clone-end sequences to identify the overlaps. In this paper we analyze the strategic issues involved in using this approach. We derive formulas showing how two key factors, the initial density of seed clones and the depth of the genomic library used for walking, affect the cost and time of a sequencing project—that is, the amount of redundant sequencing and the number of steps to cover the vast majority of the genome. We also discuss a variant strategy in which a second genomic library with clones having a somewhat smaller insert size is used to close gaps. This approach can dramatically decrease the amount of redundant sequencing, without affecting the rate at which the genome is covered.
The Three-Dimensional Structure of Aspergillus niger Pectin Lyase B at 1.7-Å Resolution1
Authors: Vitali Jacqueline , Schick Brian , Kester Harry C.M. , Visser Jaap , Jurnak Frances
Published: July 2002

The three-dimensional structure of Aspergillus niger pectin lyase B (PLB) has been determined by crystallographic techniques at a resolution of 1.7 Å. The model, with all 359 amino acids and 339 water molecules, refines to a final crystallographic R factor of 16.5%. The polypeptide backbone folds into a large right-handed cylinder, termed a parallel β helix. Loops of various sizes and conformations protrude from the central helix and probably confer function. The largest loop of 53 residues folds into a small domain consisting of three antiparallel β strands, one turn of an α helix, and one turn of a 310 helix. By comparison with the structure ofErwinia chrysanthemi pectate lyase C (PelC), the primary sequence alignment between the pectate and pectin lyase subfamilies has been corrected and the active site region for the pectin lyases deduced. The substrate-binding site in PLB is considerably less hydrophilic than the comparable PelC region and consists of an extensive network of highly conserved Trp and His residues. The PLB structure provides an atomic explanation for the lack of a catalytic requirement for Ca2+ in the pectin lyase family, in contrast to that found in the pectate lyase enzymes. Surprisingly, however, the PLB site analogous to the Ca2+ site in PelC is filled with a positive charge provided by a conserved Arg in the pectin lyases. The significance of the finding with regard to the enzymatic mechanism is discussed.
Purification, Properties, and Molecular Cloning of a Novel Ca2+-Binding Protein in Radish Vacuoles
Authors: Yuasa Koji , Maeshima Masayoshi
Published: July 2002

To understand the roles of plant vacuoles, we have purified and characterized a major soluble protein from vacuoles of radish (Raphanus sativus cv Tokinashi-daikon) taproots. The results showed that it is a novel radish vacuole Ca2+-binding protein (RVCaB). RVCaB was released from the vacuolar membrane fraction by sonication, and purified by ion exchange and gel filtration column chromatography. RVCaB is an acidic protein and migrated on sodium dodecyl sulfate-polyacrylamide gel with an apparent molecular mass of 43 kD. The Ca2+-binding activity was confirmed by the 45Ca2+-overlay assay. RVCaB was localized in the lumen, as the protein was recovered in intact vacuoles prepared from protoplasts and was resistant to trypsin digestion. Plant vacuoles store Ca2+ using two active Ca2+ uptake systems, namely Ca2+-ATPase and Ca2+/H+ antiporter. Vacuolar membrane vesicles containing RVCaB accumulated more Ca2+ than sonicated vesicles depleted of the protein at a wide range of Ca2+concentrations. A cDNA (RVCaB) encoding a 248-amino acid polypeptide was cloned. Its deduced sequence was identical to amino acid sequences obtained from several peptide fragments of the purified RVCaB. The deduced sequence is not homologous to that of other Ca2+-binding proteins such as calreticulin. RVCaB has a repetitive unique acidic motif, but not the EF-hand motif. The recombinant RVCaB expressed in Escherichia coli-bound Ca2+ as evidenced by staining with Stains-all and migrated with an apparent molecular mass of 44 kD. These results suggest that RVCaB is a new type Ca2+-binding protein with high capacity and low affinity for Ca2+ and that the protein could function as a Ca2+-buffer and/or Ca2+-sequestering protein in the vacuole.
Ultraviolet B Radiation Enhances a Phytochrome-B-Mediated Photomorphogenic Response in Arabidopsis
Authors: Boccalandro Hernán E. , Mazza Carlos A. , Mazzella M. Agustina , Casal Jorge J. , Ballaré Carlos L.
Published: July 2002

Ultraviolet B radiation (UV-B, 290–315 nm) can cause damage and induce photomorphogenic responses in plants. The mechanisms that mediate the photomorphogenic effects of UV-B are unclear. In etiolated Arabidopsis seedlings, a daily exposure to 2.5 h of UV-B enhanced the cotyledon opening response induced by a subsequent red light (R) pulse. An R pulse alone, 2.5 h of UV-B terminated with a far-red pulse, or 2.5 h of continuous R caused very little cotyledon opening. The enhancing effect of UV-B increased with fluence rate up to approximately 7.58 μmol m−2 s−1; at higher fluence rates the response to UV-B was greatly reduced. ThephyA, phyA cry1, and cry1 cry2 mutants behaved like the wild type when exposed to UV-B followed by an R pulse. In contrast, phyB, phyB cry1, and phyB phyA mutants failed to open the cotyledons. Thus, phytochrome B was required for the cotyledon opening response to UV-B → R treatments, whereas phytochrome A and cryptochromes 1 and 2 were not necessary under the conditions of our experiments. The enhancing effect of low doses of UV-B on cotyledon opening in uvr1 uvr2 and uvr1 uvr3mutants, deficient in DNA repair, was similar to that found in the wild type, suggesting that this effect of UV-B was not elicited by signals derived from UV-B-induced DNA lesions (cyclobutane pyrimidine dimers and 6-4 photoproducts). We conclude that low doses of UV-B, perceived by a receptor system different from phytochromes, cryptochromes, or DNA, enhance a de-etiolation response that is induced by active phytochrome B.
Role of Nitric Oxide Synthase in the Light-Induced Development of Sporangiophores in Phycomyces blakesleeanus
Authors: Maier Josef , Hecker Rolf , Rockel Peter , Ninnemann Helga
Published: July 2002

Blue light controls the development of sporangiophores in the zygomycete Phycomyces blakesleeanus Burgeff. Light represses the production of microsporangiophores and enhances the development of macrosporangiophores. Inhibition of the biosynthesis of tetrahydrobiopterin, a cofactor of NO synthase, inhibits this photomorphogenesis. Light induces production of citrulline from arginine in the mycelium and in sporangiophores. The citrulline-forming activity is dependent on NADPH, independent of calcium, and inhibited by NO synthase inhibitors. It is reduced in tetrahydrobiopterin-depleted mycelium. Light induces emission of NO from the developing fungus in the same order of magnitude as citrulline formation from arginine. The NO donor sodium nitroprusside can replace the light effect on sporangiophore development, and inhibitors of NO synthase repress it. We suggest that a fungal NO synthase is involved in sporangiophore development and propose its participation in light signaling.
Structural study of monoclinic KGd(WO4)2and effects of lanthanide substitution
Authors: Pujol M. C. , Solé R. , Massons J. , Gavaldà Jna. , Solans X. , Zaldo C. , Díaz F. , Aguiló M.
Published: July 2002

The crystal structure of monoclinic KGd(WO4)2(KGW) has been refined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters area= 10.652 (4),b= 10.374 (6),c= 7.582 (2) Å, β = 130.80 (2)°, withZ= 4, in space groupC2/c. The linear thermal expansion tensor has been determined and the principal axes are [302], [010] and [106]. The principal axis with maximum thermal expansion (\boldalpha'_{33} = 23.44 × 10−6 K−1), {\bf X}'_{3}, was located 12° from thecaxis. Undoped crystals of KGW and crystals that were partially doped by Pr, Nd, Ho, Er, Tm and Yb were grown by the top-seeding-solution growth slow-cooling method. The effect of doping on the KGW structure was observed in the cell parameters and in morphological changes. The changes in parameters follow the changes in lanthanide ionic radii. The doped crystals show {021} and {\bar{2}21} faces in addition to the {110}, {\bar{1}11}, {010}, {130} and {310} faces which basically follow the habit of the undoped KGW crystals. The development of the faces is related to the number of the most important periodic bond chains parallel to them.
Aminoguanidinium hexafluorozirconate: a new ferroelectric
Authors: Bauer M. R. , Pugmire D. L. , Paulsen B. L. , Christie R. J. , Arbogast D. J. , Gallagher C. S. , Raveane W. V. , Nielson R. M. , Ross C. R. , Photinos P. , Abrahams S. C.
Published: July 2002

Analysis of the atomic arrangement in anhydrous aminoguanidinium hexafluorozirconate, CN4H8ZrF6, reported by Bukvetskii, Gerasimenko & Davidovich [Koord. Khim.(1990),16, 1479–1484], led to the prediction that it is a new ferroelectric [Abrahams, Mirsky & Nielson (1996).Acta Cryst.B52, 806–809]. Initial attempts to verify the prediction were inconclusive because of the variety of closely related materials produced under the original preparation conditions. Clarification of these conditions led to the formation of pure CN4H8ZrF6and the growth of single crystals with dimensions as large as 7 × 7 × 2 mm. Highly reproducible calorimetric and dielectric permittivity anomalies reveal the Curie temperatureTc= 383 (1) K. At this temperature, the heat capacityCpexhibits an entropy change of 0.7 (1) J mol−1 K−1, while the relative permittivity ∊rexhibits an inflection and the dielectric loss a distinct peak; the dielectric anomaly atTcis observed only at the lowest (0.1–1 kHz) frequencies used. Dielectric hysteresis is demonstrable at 295 K under the application of ∼1 MV m−1alternating fields and remains observable at allT<Tcbut not atT≥Tc; the prediction of ferroelectricity is hence confirmed. The value of the spontaneous polarizationPsis 0.45 (9) × 10−2 C m−2at 298 K, with piezoelectric coefficientd33= 1.9 (5) pC N−1and pyroelectric coefficientp3= 4 (1) µC m−2 K−1. Tilts of less than ∼11° by the two symmetry-independent CN4H{}_{8}^{2+} ions, combined with rotations of ∼20° or less by the N—NH3and C—(NH2)2groups about the central C—N bond in each cation, as all H atoms rotate into or become symmetrically distributed about the planes atz= 0 or ½, allow them to conform to mirror symmetryviapolar atomic displacements of ∼0.4 Å or less by N or C, and of 0.7 Å or less by H. Corresponding displacements of less than 0.08 Å within the two symmetry-independent ZrF{}_{6}^{2-} anions also result in mirror symmetry, satisfying the structural criteria required for the development of ferroelectricity.
Alternative algorithm for the correction of preferred orientation in Rietveld analysis
Authors: Bergmann J. , Monecke T. , Kleeberg R.
Published: July 2002

Texture effects caused by preferred orientation can be corrected in Rietveld analysis by an alternative algorithm presented in this contribution. This algorithm is equivalent to models using symmetrized linear combinations of spherical harmonic functions, but it is unique to all Laue classes and to all orders. Positive definiteness of the polar-axis density is achieved by the exponential method. The outlined algorithm was tested during Rietveld refinement of selected polycrystal samples. The algorithm was proven to be numerically robust and satisfactorily described deviations from the ideal intensity ratios of the Bragg reflections caused by the texture of the samples.
Structure of TiN
x
studied by electron diffraction and microscopy
Authors: Nagakura S. , Kusunoki T.
Published: July 2002

The crystal and internal structures of the non-stoichiometric compound TiNx (x = 0.61~0.999, δ-phase, NaCl type) have been studied by electron diffraction and microscopy. In general, interstitial N atoms produce only short-range order, but in TiN0.61 there is long-range order after aging at 500°C for one or three months. The ordered structure is tetragonal with lattice parameters a = 4.198 Å < a
0, and c = 8.591 Å > 2a
0 (a
0 = 4.221 Å: lattice parameter of disordered TiN0.61), and belongs to the space group I41/amd with the atom positions 8 Ti at 8(e) with z = ¼+0.018, 4 N at 4(a) and 0.88 N at 4(b). The ordered regions develop from small isolated regions and coalesce gradually with aging. The resulting structure contains antiphase and semi-antiphase domain boundaries with respect to the N atom arrangement. The appearance of the semi-antiphase domain boundaries is due to the structure being able to have both 41 and 43 screw axes. The structural difference between TiN
x
and γ (or ∊)-Ti2N is also discussed.
Error analysis of 2π powder data for cubic or uniaxial phases
Authors: Frevel L. K.
Published: July 2002

The likely error in the 2θ measurement of a particular powder reflection can be bracketed by a self-consistent error analysis. To a specific observed θm
value one assigns arbitrary increments {Δθm
} and calculates iteratively the corresponding increments of any other θn
according to the expression: \Delta \theta_{n} = \sin^{-1} {{{q \sin (\theta_{m} + \Delta \theta_{m})-\sin \theta_{n} \cos \Delta \theta_{n}}\over{\cos \theta_{n}}}}where q is the product of the square root of the ratio of the quadratic factors for (hmkmlm
) and (hnknln
) and a correction factor for refraction. By considering special coincidences for which the various Δθn
's are 0° or nil (0.000X°), one arrives at a likely bracketing interval for Δθm
. Continuing this process one computes the indicated errors for the remaining reflections. The intent of the error analysis is to induce the experimenter to seek the cause(s) of the indicated errors in the 2θ determinations, and to delimit more precisely the accuracy of lattice constants of cubic or uniaxial phases.
Unit-cell refinement from powder diffraction scans
Authors: Pawley G. S.
Published: July 2002

A procedure for the refinement of the crystal unit cell from a powder diffraction scan is presented. In this procedure knowledge of the crystal structure is not required, and at the end of the refinement a list of indexed intensities is produced. This list may well be usable as the starting point for the application of direct methods. The problems of least-squares ill-conditioning due to overlapping reflections are overcome by constraints. An example, using decafluorocyclohexene, C6F10, shows the quality of fit obtained in a case which may even be a false minimum. The method should become more relevant as powder scans of improved resolution become available, through the use of pulsed neutron sources.
A new high-resolution small-angle X-ray scattering apparatus using a fine-focus rotating anode, point-focusing collimation and a position-sensitive proportional counter
Authors: Yoda O.
Published: July 2002

A high-resolution small-angle X-ray scattering camera has been built, which has the following features. (i) The point collimation optics employed allows the scattering cross section of the sample to be directly measured without corrections for desmearing. (ii) A small-angle resolution better than 0.5 mrad is achieved with a camera length of 1.6 m. (iii) A high photon flux of 0.9 photons μs−1 is obtained on the sample with the rotating-anode X-ray generator operated at 40 kV–30 mA. (iv) Incident X-rays are monochromated by a bent quartz crystal, which makes the determination of the incident X-ray intensity simple and unambiguous. (v) By rotation of the position-sensitive proportional counter around the direct beam, anisotropic scattering patterns can be observed without adjusting the sample. Details of the design and performance are presented with some applications.
A Voigtian as profile shape function in Rietveld refinement
Authors: Ahtee M. , Unonius L. , Nurmela M. , Suortti P.
Published: July 2002

A modification of the Rietveld refinement program is introduced by replacing the Gaussian profile function with a Voigtian. The performance of the program is tested by an application to simulated and measured diffraction patterns of NaTaO3, and excellent results are obtained when the tails of the reflections are included at distances 10 to 20 times the half-width of the reflections. Comparison between Gaussian and Voigtian refinements show large differences in the thermal parameters. This is due to the high level of background that is assumed in the Gaussian refinement to compensate for the lack of tail overlap. Application of the Voigtian refinement to the measured pattern of Ni yields a thermal parameter that is close to the literature values, while the Gaussian analysis gives a value which is 35% too large. The isotropic temperature factors of the room-temperature structure of NaTaO3, respectively, drop down to the values B(Ta) = 0.09(2), B(Na) = 1.21(3), B(O1) = 0.59(3) and B(O2) = 0.61(3) Å2, when the Voigtian analysis with a proper background is carried out. The role of background in powder pattern refinement is discussed, and it is suggested that a calculation of the average TDS should be included in the refinement.
On the automatic extension of incomplete models by iterative Fourier calculation
Authors: Kinneging A. J. , de Graaff R. A. G.
Published: July 2002

A program is presented that solves crystal structures completely using advanced Fourier methods starting from a small known fraction (about 8%) of the structure. The program uses a statistical test based on the R
2 factor to check the correctness of the model obtained so far. The results obtained with four test structures are given.
An enhanced interactive PLUTO78 for molecular display
Authors: Crennell K. M. , Crisp G. M.
Published: July 2002

The well known molecular drawing program, PLUTO78, has been made more widely available in the UK by mounting it on the minicomputers of the Joint Academic Network (JANET) wide-area network. Enhancements include interaction, faster plotting, use of colour and simulated half tone, easy access to centrally maintained high-quality-output devices, and the provision of comprehensive documentation in the form of on-line help and a user manual.
Absorption corrections and digital filtering of X-ray diffraction profiles recorded with a position-sensitive detector
Authors: Burian A. , Lecante P. , Mosset A. , Galy J. , Van Dun J. , Mortier W. J.
Published: July 2002

Expressions for the absorption correction function are obtained in the form of integral equations for the case of a flat-plate sample and a position-sensitive detector. It is shown that the absorption correction used for both transmission and reflection geometries with a conventional diffractometer may be applied to a diffractometer equipped with a linear position-sensitive detector. The application of a Savitzky–Golay-type digital filter considerably facilitates the analysis of the data without losing pertinent information.
A HREM study of nonbasal twinning and superlattices in ilmenite
Authors: Wang Y. G. , Ye H. Q. , Ximen L. , Kuo K. H.
Published: July 2002

The microstructures of natural ilmenite found in Panzhihua district, China, were examined by high-resolution electron microscopy (HREM). The [{\bar 1}2{\bar 1}0] structural images showed clearly the (10{\bar 1}1) nonbasal twinning which seems to be coincident with the [{\bar 1}012] rotation twinning. The superlattices with periodicities of 16.8 and 12.6 Å, respectively, as well as the unit-cell twinning related to the ordering of (10{\bar 1}1) multiple twinnings were observed. The superlattice resulting from the ordering arrangement of (10{\bar 1}1) stacking faults related to the slip systems suggested by Heuer [Philos, Mag. (1966), 13, 379–893] were also detected. Possible genetic aspects are considered.
An elastically bent silicon crystal as a monochromator for thermal neutrons
Authors: Mikula P. , Krüger E. , Scherm R. , Wagner V.
Published: July 2002

Some experimental results are presented for an elastically bent perfect silicon crystal in a strongly asymmetric diffraction geometry as a neutron monochromator. The use of this unconventional geometry of the monochromator appears to be suitable for a wide (several centimetres) incident polychromatic beam, when, thanks to the spatial condensation of the diffracted neutrons (Fankuchen effect), a high monochromatic beam density may be obtained. Furthermore, when using focusing in real and in momentum space by adjusting an optimum bending radius, the intensity diffracted by a sample may be comparable even with the best mosaic monochromators such as highly oriented pyrolytic graphite (PG). A comparison is demonstrated on the rocking curves of a strongly mosaic Ni–Al(020) crystal obtained with the monochromatic beam from bent Si(111), Si(400) and from PG(002), Cu(220) mosaic monochromators.
Structures of Zr2Co11 and HfCo7 intermetallic compounds
Authors: Demczyk B. G. , Cheng S. F.
Published: July 2002

The crystal structures of Zr2CO11 and HfCo7 intermetallic compounds were examined by transmission electron microscopy using both selected-area and convergent-beam electron diffraction. Results show that both have an orthorhombic crystal structure, space group Pcna. The unit cells of both compounds appear to be comprised of two long-period superlattices in antiphase relation to one another along [001].
Profile fitting of X-ray diffraction lines and Fourier analysis of broadening
Authors: Balzar D.
Published: July 2002

The extraction of pure-specimen X-ray diffraction-line broadening is described using a convolution of the instrumental profile and an exact Voigt function. Real Fourier coefficients were computed from the Cauchy and Gauss integral breadths and were input for Warren–Averbach analysis. Smooth surface-weighted and volume-weighted column-length distribution functions were obtained and errors in root-mean-square strains as well as effective domain sizes were evaluated. The method was applied to two cubic structures with average volume-weighted domain sizes up to 3600 Å as well as patterns of tetragonal and orthorhombic (La, Sr)2CuO4, which exhibit weak line broadenings and highly overlapping reflections. Comparison with the integral-breadth methods is given. Reliability of the method is discussed in the case of a cluster of overlapping peaks.
iA program package for preprocessing of two-dimensional detector data
Authors: Lorenzen M. , Ferrero C. , Diat O. , Riekel C. , Mayerhofer U.
Published: July 2002

A set of macros based on CERN's program package PAW has been developed for interactive preprocessing of two-dimensional detector data at ESRF prior to more detailed data analysis. Various types of image operations (averaging, cuts, background correction etc.) are available. The main use of the package is at present in small- and wide-angle X-ray scattering (SAXS and WAXS). The flexibility of the package allows, however, easy adaptation to other areas such as fibre or powder diffraction.
GAMATCH – a genetic algorithm-based program for indexing crystal faces
Authors: Tam K. Y. , Compton R. G.
Published: July 2002

An intelligent genetic algorithm-based crystal-indexing program, GAMATCH, is described, by means of which the Miller indices of the relevant planes can be unambiguously identified using a set of interplanar angles. A two-step-divide-and-conquer strategy is employed and is found to speed up the convergence to the global solution. The program was tested using both hypothetical and centimetre-sized triphenylmethyl chloride crystals. The results obtained were compared to the expected indices and excellent agreement was noted.
The Monolithic Double-Crystal Spectrometer: Theory and Design Principles
Authors: Gang O. , Deutsch M.
Published: July 2002

The monolithic double-crystal spectrometer (MDCS) is a perfect-crystal device allowing X-ray spectroscopic measurements on an absolute energy scale with an accuracy of better than 1 in 106. This paper presents a detailed analysis of its properties using the dynamical theory of X-ray propagation in perfect crystals. The transmitted wavelength, the transmission window profile, the energy dispersion and the integrated intensity of the transmitted radiation and their dependence on the scanning angle of rotation are derived. The polarization mixing is shown to have a subtle yet important effect on the transmission of the MDCS. An example of a specific MDCS, designed for measuring the Cu Kβ emission spectra, is discussed in detail. The results of the study highlight the advantages and limitations of this device and yield tools for optimizing the MDCS for a wide class of X-ray spectroscopic measurements and for correcting the inevitable, although minimal, distortions introduced by the finite instrumental window of the device.
Simulations of femtosecond X-ray diffraction from unperturbed and rapidly heated single crystals
Authors: Wark J. S. , Lee R. W.
Published: July 2002

Simulations are presented of the dynamical diffraction of femtosecond pulses of X-rays from crystals whose structures are modified on similar time scales. Such simulations are of relevance to experiments in which short pulses of X-rays from synchrotron or laser sources are diffracted from rapidly laser-heated crystals.
On the problem of overlapping ω scans measured on thin films deposited on monocrystal substrates
Authors: Machajdík D. , Pevala A. , Rosová A. , Fröhlich K. , Šouc J. , Weiss F. , Figueras A.
Published: July 2002

CeO2thin films deposited on sapphire monocrystal substrates were used for an experimental study of the nature of extremely narrow overlapped maxima on X-ray diffraction ω scans. Full width at half-maximum (FWHM) values of such maxima typically reached the resolution function of the diffractometer. A comparative study of the influence of various diffractometer set-ups on the spectral characteristics of the X-ray beam in relation to the above-mentioned phenomenon was carried out. A surrounding (λmin− λmax) or (2θmin− 2θmax) of the strong substrate reflection was obtained, where a substrate contribution to an ω scan measured on thin-film reflection can be expected. Two possible origins of the narrow maxima are discussed: (a) a contribution of a part of the X-ray beam having λ ≠ λKαthat diffracts on a set of substrate crystallographic planes parallel to the thin-film crystallographic planes used for the ω-scan measurement; and (b) the presence in part of the thin film of a perfect monocrystal-like quality with practically no mosaicity. The principles of this approach and experimental procedure are reported, and on this basis it is possible to distinguish between the two possible origins of the narrow overlapped maxima. It is shown that under appropriate conditions, an extremely high quality CeO2thin film can be grown. The FWHM value of its ω scan can reach the value of diffractometer instrumental broadening obtained for a perfect monocrystal.
Gamma-ray sensitivity and shielding of a neutron imaging plate
Authors: Haga Y. Karasawa , Kumazawa S. , Niimura N.
Published: July 2002

The energy dependence of gamma-ray sensitivity of a neutron imaging plate (NIP) has been measured. The gamma-ray sensitivity is equivalent to one half that of a thermal neutron at a gamma-ray energy less than 300 keV, and 1/40 at greater than 300 keV. The shielding of the NIP, by lead, from gamma rays in the experimental hall of the reactor JRR-3M of the Japan Atomic Energy Research Institute (JAERI) was measured. It was found that lead of thickness 40 mm is sufficient to reduce the gamma-ray background to 1/10 on a normalized scale. Covering the NIP with lead foil of thickness 1 mm results in a decrease of the gamma-ray background without reduction of the neutron signal.
Measurement of sugar depletion from uncharged lamellar phases by SANS contrast variation
Authors: Demé B. , Zemb Th.
Published: July 2002

We applied small-angle neutron scattering (SANS) contrast variation to samples where a microphase separation occurred. The samples contain multilamellar vesicles in equilibrium with excess "solvent" that produce a very common powder pattern in SANS: a Debye-Sherrer ring produced by the regular bilayer packing superposed to a sharply decaying Porod behaviour. These two features of the SANS pattern have distinct contrast match points (CMP). We exploit here the small angle signal to determine the partition of sugars between two coexisting microphases. The net result is an exclusion of small sugar molecules from the liquid crystalline domains of the sample. We discuss this exclusion in relation with the observed maximum swelling, headgroup hydration and bilayer softening induced by the presence of the sugar molecules.
The classification of face-transitive periodic three-dimensional tilings
Authors: Dress A. W. M. , Huson D. H. , Molnár E.
Published: July 2002

It has long been known that there exists an infinite number of types of tile-transitive periodic three-dimensional tilings. Here, it is shown that, by contrast, the number of types of face-transitive periodic three-dimensional tilings is finite. The method of Delaney symbols and the properties of the 219 isomorphism classes of crystallographic space groups are used to find exactly 88 equivariant types that fall into seven topological families.