Study of Thin Films and Multilayers using Energy-Dispersive Diffraction of Synchrotron Radiation

We present the results of a preliminary study of the use of polychromatic synchrotron radiation in energy-dispersive mode for the rapid characterization of thin film and multilayer materials. This technique takes advantage of the high intensity and excellent collimation properties of white beam synchrotron radiation. The glancing angle diffraction geometry allows structural depth probing as well as enhanced signal-to-noise by suppressing substrate contributions. The technique was successfully applied to metallic films a few hundred Angstroms thick, and to W-C multilayers.

Ethical Use and Impact of Participatory Approaches to Research in Post-Disaster Environments: An Australian Bushfire Case Study

This paper presents a case study of Beyond Bushfires, a large, multisite, mixed method study of the psychosocial impacts of major bushfires in Victoria, Australia. A participatory approach was employed throughout the study which was led by a team of academic investigators in partnership with service providers and government representatives and used on-site visits and multiple methods of communication with communities across the state to inform decision-making throughout the study. The ethics and impacts of conducting and adapting the approach within a post-disaster context will be discussed in reference to theories and models of participatory health research. The challenges of balancing local interests with state-wide implications will also be explored in the description of the methods of engagement and the study processes and outcomes. Beyond Bushfires demonstrates the feasibility of incorporating participatory methods in large, post-disaster research studies and achieving rigorous findings and multilevel impacts, while recognising the potential for some of the empowering aspects of the participatory experience to be reduced by the scaled-up approach.

Bunch mode specific rate corrections for PILATUS3 detectors

PILATUS X-ray detectors are in operation at many synchrotron beamlines around the world. This article reports on the characterization of the new PILATUS3 detector generation at high count rates. As for all counting detectors, the measured intensities have to be corrected for the dead-time of the counting mechanism at high photon fluxes. The large number of different bunch modes at these synchrotrons as well as the wide range of detector settings presents a challenge for providing accurate corrections. To avoid the intricate measurement of the count rate behaviour for every bunch mode, a Monte Carlo simulation of the counting mechanism has been implemented, which is able to predict the corrections for arbitrary bunch modes and a wide range of detector settings. This article compares the simulated results with experimental data acquired at different synchrotrons. It is found that the usage of bunch mode specific corrections based on this simulation improves the accuracy of the measured intensities by up to 40% for high photon rates and highly structured bunch modes. For less structured bunch modes, the instant retrigger technology of PILATUS3 detectors substantially reduces the dependency of the rate correction on the bunch mode. The acquired data also demonstrate that the instant retrigger technology allows for data acquisition up to 15 million photons per second per pixel.

The (3 + 1)-dimensional superspace description of the commensurately modulated structure of p-chlorobenzamide (α-form) and its relation to the γ-form

The room temperature structure (α-form) of the organic compound p-chlorobenzamide, C7H6ClNO, can be described as a classical three-dimensional periodic superstructure (α S) and also as a commensurately modulated structure (α M) in (3 + 1)-dimensional superspace. The diffraction pattern is characterized by a clear difference in intensity between main and satellite reflections. All reflections can be indexed with four indices hklm in a triclinic unit cell and one modulation vector in the superspace group P1̅(αβγ) with the modulation vector q⃗ = 1/3·a⃗*. The structure undergoes a phase transition at higher temperature. In this phase transition the modulation vanishes as indicated by the disappearance of the satellite reflections. The resulting high temperature phase (γ-form) contains one molecule in the asymmetric unit, the space group is P1̅. The high temperature structure (γ) is very close to the reference structure of the modulated model at room temperature. The phase transition can therefore be understood as a loss of the modulation at high temperature.

3D imaging of the Fermi surface by thermal diffuse scattering

We use thermal diffuse scattering of x rays to visualize the lens-shaped portions of the Fermi surface in metallic zinc. Our interpretation of the nature of the observed scattered intensity anomalies is supported by the incorporation of inelastic x-ray scattering measurements as well as ab initio calculations of the electronic structure and lattice dynamics. Our work demonstrates that thermal diffuse scattering complements well-established techniques and is a powerful tool in its own right for studying the shape of the Fermi surface through the associated electron-phonon coupling.

Using X-ray absorption spectra to monitor specific radiation damage to anomalously scattering atoms in macromolecular crystallography

Radiation damage in macromolecular crystals is not suppressed even at 90 K. This is particularly true for covalent bonds involving an anomalous scatterer (such as bromine) at the 'peak wavelength'. It is shown that a series of absorption spectra recorded on a brominated RNA faithfully monitor the extent of cleavage. The continuous spectral changes during irradiation preserve an 'isosbestic point', each spectrum being a linear combination of 'zero' and 'infinite' dose spectra. This easily yields a good estimate of the partial occupancy of bromine at any intermediate dose. The considerable effect on the near-edge features in the spectra of the crystal orientation versus the beam polarization has also been examined and found to be in good agreement with a previous study. Any significant influence of the (C-Br bond/beam polarization) angle on the cleavage kinetics of bromine was also searched for, but was not detected. These results will be useful for standard SAD/MAD experiments and for the emerging 'radiation-damage-induced phasing' method exploiting both the anomalous signal of an anomalous scatterer and the 'isomorphous' signal resulting from its cleavage.

Polarization-dependence of anomalous scattering in brominated DNA and RNA molecules, and importance of crystal orientation in single- and multiple-wavelength anomalous diffraction phasing

In this paper the anisotropy of anomalous scattering at the BrK-absorption edge in brominated nucleotides is investigated, and it is shown that this effect can give rise to a marked directional dependence of the anomalous signal strength in X-ray diffraction data. This implies that choosing the correct orientation for crystals of such molecules can be a crucial determinant of success or failure when using single- and multiple-wavelength anomalous diffraction (SAD or MAD) methods to solve their structure. In particular, polarized absorption spectra on an oriented crystal of a brominated DNA molecule were measured, and were used to determine the orientation that yields a maximum anomalous signal in the diffraction data. Out of several SAD data sets, only those collected at or near that optimal orientation allowed interpretable electron density maps to be obtained. The findings of this study have implications for instrumental choices in experimental stations at synchrotron beamlines, as well as for the development of data collection strategy programs.

Crystal and electronic structures of magnesium(II), copper(II), and mixed magnesium(II)-copper(II) complexes of the quinoline half of styrylquinoline-type HIV-1 integrase inhibitors

A new target in AIDS therapy development is HIV-1 integrase (IN). It was proven that HIV-1 IN required divalent metal cations to achieve phosphodiester bond cleavage of DNA. Accordingly, all newly investigated potent IN inhibitors contain chemical fragments possessing a high ability to chelate metal cations. One of the promising leads in the polyhydroxylated styrylquinolines (SQLs) series is (E)-8-hydroxy-2-[2-(4,5-dihydroxy-3-methoxyphenyl)-ethenyl]-7-quinoline carboxylic acid (1). The present study focuses on the quinoline-based progenitor (2), which is actually the most probable chelating part of SQLs. Conventional and synchrotron low-temperature X-ray crystallographic studies were used to investigate the chelating power of progenitor 2. Mg2+ and Cu2+ cations were selected for this purpose, and three types of metal complexes of 2 were obtained: Mg(II) complex (4), Cu(II) complex (5) and mixed Mg(II)-Cu(II) complexes (6 and 7). The analysis of the crystal structure of complex 4 indicates that two tridentate ligands coordinate two Mg2+ cations, both in octahedral geometry. The Mg-Mg distance was found equal to 3.221(1) A, in agreement with the metal-metal distance of 3.9 A encountered in the crystal structure of Escherichia coli DNA polymerase I. In 5, the complex is formed by two bidentate ligands coordinating one copper ion in tetrahedral geometry. Both mixed Mg(II)-Cu(II) complexes, 6 and 7 exhibit an original arrangement of four ligands linked to a central heterometallic cluster consisting of three octahedrally coordinated magnesium ions and one tetrahedrally coordinated copper ion. Quantum mechanics calculations were also carried out in order to display the electrostatic potential generated by the dianionic ligand 2 and complex 4 and to quantify the binding energy (BE) during the formation of the magnesium complex of progenitor 2. A comparison of the binding energies of two hypothetical monometallic Mg(II) complexes with that found in the bimetallic magnesium complex 4 was made.

Individual characteristics are less important than event characteristics in predicting protected and unprotected anal intercourse among homosexual and bisexual men in Melbourne, Australia

OBJECTIVE

To describe individual, social network and encounter specific factors associated with protected anal intercourse (PAI) and unprotected anal intercourse (UAI).

METHODS

This was a cross sectional survey conducted between April and November 2002. A total of 733 sexual encounters were reported by 202 men recruited from the gay community in Melbourne, Australia. Predictors of self reported PAI and UAI were examined.

RESULTS

Of the 733 sexual events most (56.3%) did not involve anal intercourse, and more involved PAI than UAI (30.6% versus 13.1%). PAI was more likely than no anal intercourse (NAI) if the participant's social network was mostly homosexual, the partner was an occasional or casual partner, or was HIV positive. PAI was less likely if sex took place at a "beat" but more likely if it took place at a sauna. PAI was more likely if the partner was affected by drugs or alcohol. UAI was more likely than NAI if the participant had injected drugs in the year before interview. It was less likely if the partner was occasional or casual or was HIV positive but more likely if the partner's HIV status was unknown. UAI was much more likely than NAI if the encounter took place at a "sex on premises" venue.

CONCLUSIONS

In this analysis it is the characteristics of the sexual encounter that predict whether PAI or UAI rather than NAI takes place.

X-ray absorption, refraction and resonant scattering tensors in selenated protein crystals: implications for data collection strategies in macromolecular crystallography

Polarized fluorescence spectra were recorded in the vicinity of the Se and BrKedges on crystals of the selenated protein aldose reductase in complex with a brominated inhibitor molecule. The X-ray absorption, refraction and resonant scattering tensors as a function of X-ray energy were derived from these data. Substantial dichroism and anisotropy of resonant scattering were observed in these crystals. It is predicted that these effects are present in many resonant scattering experiments in macromolecular crystallography and are likely to affect the diffraction data. As a consequence, the anomalous phasing signal in single- or multi-wavelength anomalous diffraction experiments can be optimized simply by choosing a judicious orientation of the crystal with respect to the polarization direction of the incident X-ray beam. A simple procedure is presented to achieve this, prior to any knowledge about the selenium sites.

Associations between the sexual behaviour of men who have sex with men and the structure and composition of their social networks

OBJECTIVE

This exploratory study identified associations between the number of sexual partners reported by men who have sex with men (MSM) and the structure and composition of their social networks.

METHODS

A cross sectional survey was conducted of men recruited as key informants, through advertising and chain referral. A face to face interview was conducted with 206 MSM. The interview included information on the number of sexual partners in the previous year and sociodemographic and behavioural characteristics of the participant. Social networks were enumerated and network size and density were calculated. Ordered logistic regression was used to assess the associations between number of sexual partners and personal and network characteristics.

RESULTS

The number of anal sex partners reported was higher if the participant had injected drugs in the past year rather than never having injected (odds ratio, 95% confidence interval: 3.23, 1.28 to 8.15), decreased with network density (0.014, 0.002 to 0.008) and increased if the network did not comprise only HIV negative people (1.77, 1.05 to 2.99). The number of additional oral sex partners increased with network size (1.06, 1.02 to 1.10) and decreased with increased network density (0.034, 0.006 to 0.205). In addition to similar effects of network size (1.05, 1.01 to 1.09) and network density (0.086, 0.013 to 0.563) the model for the number of additional manual sex partners also included age (1.03, 1.01 to 1.05).

CONCLUSION

The density of the social networks of MSM appears strongly and consistently associated with patterns of sexual behaviour. This underlines the importance of using network approaches to understanding the sexual behaviour of MSM and their potential value in identifying novel strategies for intervention.

N-Z-Pro-D-Leu using synchrotron radiation data from a very small crystal

The crystal structure of the neuroactive artificial dipeptide N-benzyloxycarbonylprolyl-D-leucine, C(19)H(26)N(2)O(5), was solved using synchrotron radiation data collected on a very small crystal (20 x 20 x 380 microm). The molecules form hydrogen-bonded 2(1) helices. The acid carbonyl group does not participate in strong hydrogen bonds. This is interpreted as a consequence of close-packing requirements.

Reduction of dioxygen by a dimanganese unit bonded inside a cavity provided by a pyrrole-based dinucleating ligand

A novel class of dinucleating ligands has been introduced into manganese chemistry to study the reactivity of this metal towards dioxygen under strictly controlled conditions. Such N4 ligands combine some of the major peculiarities of tetradentate Schiff bases and the porphyrin skeleton. They are derived from the condensation between 2-pyrrolaldehyde and ethylenediamine or o-phenylenediamine, leading to pyrenH2 (LH2, 1), pyrophenH2 (L'H2, 2) and Me2pyrophenH2, (L"H2, 3), respectively. Their metallation with [Mn3-(Mes)6] (Mes = 2,4,6-trimethylphenyl) led to [Mn2L2] (4), [MnL'(thf)2] (5) and [MnL"(thf)2] (6). Complex 4 displays a double-stranded helical structure, while 5 and 6 are mononuclear complexes containing hexacoordinated metals. Regardless of their structure, complexes 5 and 6 behave in a similar manner to 4 in their reaction with dioxygen, namely, as a dimetallic unit inside a cavity defined by two dinucleating ligands. These reactions led to dinuclear MnIII/MnIV oxo-hydroxo derivatives, [Mn2L2(mu-O)(mu-OH)] (7), [Mn2L'2(mu-O)(mu-OH)] (8) and [Mn2L"2(mu-O)(mu-OH)] (9), in which the two Mn ions are strongly antiferromagnetically coupled [J = -53 (7), J = -64 (8), J = -60 cm(-1) (9)]. The crystal structure of 7 could only be solved with synchrotron radiation as the crystals diffracted very poorly and suffered from twisting and disorder. The formation of 7-9 has been proposed to occur through the formation of an intermediate dinuclear hydroperoxo species.

Statistical Evaluation of Algebraic Constraints for Social Networks

A multirelational social network on a set of individuals may be represented as a collection of binary relations. Compound relations constructed from this collection represent various labeled paths linking individuals in the network. Since many models of interest for social networks can be formulated in terms of orderings among these labeled paths, we consider the problem of evaluating an hypothesized set of orderings, termed algebraic constraints. Each constraint takes the form of an hypothesized inclusion relation for a pair of labeled paths. In this paper, we establish conditions under which sets of such constraints may be regarded as partial algebras. We describe the structure of constraint sets and show that each corresponds to a subset of consistent relation bundles between pairs of individuals. We thereby construct measures of fit for a given constraint set. Then, we show how, in combination with the assumption of various conditional uniform multigraph distributions, these measures lead to a flexible approach to the evaluation of fit of an hypothesized constraint set. Several applications are presented and some possible extensions of the approach are briefly discussed. Copyright 2000 Academic Press.

N-methyl-DL-aspartic acid monohydrate

The title compound, C(5)H(9)NO(4).H(2)O, has been synthesized and crystallized. It crystallizes in Cc with one molecule in the asymmetric unit. The compound is found in its zwitterionic form. D and L forms of the compound are linked in the crystal via O-H...O and N-H.O hydrogen bonds, both directly between the aspartic acid-derivative entities and to the crystal water molecule. A weak intramolecular N-H...O interaction is found. The carbon skeleton is slightly twisted with C-C-C-C = 166.83 (11) degrees. A comparison with other derivatives of aspartic acid shows only two rotamers--one with a near planar carbon skeleton and one with a significantly twisted carbon skeleton.

Rapid characterization of complex structural phase transitions using powder diffraction and an area detector

The use of a high-intensity and well collimated X-ray beam from a third-generation synchrotron source, combined with an area detector with online readout capabilities, allows high-quality powder patterns to be obtained with exposure times of only a few seconds. Powder measurements of a rare-earth manganate perovskite (Nd(0.43)Sr(0.57)MnO(3)) were performed in the temperature range 105-200 K, and the data were of sufficient quality to be able to extract, via Rietveld refinement, accurate values for the lattice constants and atomic parameters. The temperature dependence of the Mn-O-Mn bond angles and Mn-O distances obtained in this manner illustrate the well known correlation between the distortion of the MnO(6) octahedra and the onset of orbital ordering. The success of this study, for which only two hours of synchrotron beam time was required, indicates the enormous improvements in efficiency and throughput which area detectors are bringing to powder diffraction experiments.

Logit models and logistic regressions for social networks: II. Multivariate relations

The research described here builds on our previous work by generalizing the univariate models described there to models for multivariate relations. This family, labelled p*, generalizes the Markov random graphs of Frank and Strauss, which were further developed by them and others, building on Besag's ideas on estimation. These models were first used to model random variables embedded in lattices by Ising, and have been quite common in the study of spatial data. Here, they are applied to the statistical analysis of multigraphs, in general, and the analysis of multivariate social networks, in particular. In this paper, we show how to formulate models for multivariate social networks by considering a range of theoretical claims about social structure. We illustrate the models by developing structural models for several multivariate networks.

The structure and function of the 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase from Haemophilus influenzae

The gene encoding the 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase of Haemophilus influenzae has been cloned and expressed in Escherichia coli. A complex of the purified protein with a substrate analog has been crystallized and its structure solved by multiple anomalous dispersion using phase information obtained from a single crystal of selenomethione-labeled protein. The enzyme folds into a four-stranded antiparallel beta-sheet flanked on one side by two alpha-helices and on the other by three consecutive alpha-helices, giving a novel beta1alpha1beta2beta3alpha2beta4alpha3alpha4alpha5 polypeptide topology. The three-dimensional structure of a binary complex has been refined at 2.1 A resolution. The location of the substrate analog and a sulfate ion gives important insight into the molecular mechanism of the enzyme.

Vaccine preventable diseases and immunisations: a qualitative study of mothers' perceptions of severity, susceptibility, benefits and barriers

This study investigated mothers' perceptions of vaccine-preventable diseases and associated vaccines in terms of perceived susceptibility, severity, benefits and barriers. A purposive sampling strategy was used to choose mothers whose only or youngest child was completely, incompletely (behind the recommended immunisation schedule) or partially (parents chose or advised not to have a specific immunisation) immunised or had no immunisations. Semi-structured interviews found that complete immunisers believed the risk of vaccines was lower than the risk from disease and that the likelihood of contracting many of these diseases was low. Incomplete immunisers perceived vaccines to be less effective in preventing disease and were often confused about which diseases the vaccines would protect against. Non-immunisers were more concerned about unknown, long-term side effects of vaccines than the diseases. Many mothers who did immunise believed that preventing diseases was not always possible and for diseases such as measles, mumps and rubella, it was not always necessary nor desirable. Vaccines were perceived as placing stress on the immune system rather than strengthening it. Important themes relating to barriers to the decision to immunise were a lack of 'balanced', detailed information and poor communication between health providers and parents. The major barrier to timely, age-appropriate immunisations was the occurrence of minor illnesses in the target child or the family. This study found that many mothers were balancing the risks of immunising with the risks of not immunising and this must be taken into account, along with factors such as difficulties in obtaining immunisations.

The representation of tonality and meter in children aged 7 and 9

The aim of this study was to explore the development of the representations of tonality and meter in children. Eighty children with a mean age of 7 (Grade 2) and 9 years (Grade 4) were compared on both melodic and rhythmic discrimination and classification tasks. The findings were considered in relation to their specificity to both task and age effects. The results revealed a developmental progression in the representation of tonality that was consistent across tasks. The rhythmic results also supported the existence of a representation of meter that developed with age, however these findings were more subject to task effects. The influence of stimulus length and likeableness on subject performance was also examined. Increased length was found to assist discrimination performance particularly with tonal, nontonal, and nonmetrical stimuli. No effects of stimulus likeableness were observed in the data.

Reaction to trauma: A cognitive processing model

We integrated existing cognitive processing models of posttrauma reactions into a longitudinal model. Data were obtained after a multiple shooting in a city office block. The subject group comprised 158 office workers who were in the building at the time of the shootings. The methodology of this research was a repeated measures survey, with data collection at 4, 8, and 14 months posttrauma. Measures included the Impact of Events Scale (IES) and the Symptom Checklist-90-Revised. A path analysis was performed with the IES as an indication of cognitive processing. Intrusion and avoidance were shown to mediate between exposure to trauma and symptom development. Intrusion was also found to be negatively related to subsequent symptom levels. The findings provide provisional support for a cognitive processing model.