bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of ions during stable impedance operation of the immersed-Bz diode at 4 to 5 MV
Authors: Rovang D. C. , Bruner N. , Maenchen J. E. , Oliver B. V. , Portillo S. , Puetz E. , Rose D. V. , Welch D. R.
Published: November 2007

The immersed-Bz diode is being developed as a high-brightness, flash x-ray radiography source at Sandia National Laboratories. This diode is a foil-less electron-beam diode with a long, thin, needlelike cathode that is inserted into the bore of a solenoid. The solenoidal magnetic field guides the electron beam emitted from the cathode to the anode while maintaining a small beam radius. The electron beam strikes a thin, high-atomic-number anode and produces forward-directed bremsstrahlung. In addition, electron beam heating of the anode produces surface plasmas allowing ion emission. Two different operating regimes for this diode have been identified: a nominal operating regime where the total diode current is characterized as classically bipolar and an anomalous operating regime characterized by a dramatic impedance collapse where the total diode current greatly exceeds the bipolar limit. Data from a comprehensive series of experiments fielded at 4 and 5MV, where the diode operates in the nominal or stable impedance regime, with beam currents ranging from 20–40kA on target are presented. In this mode, both the measured diode current and experimental radiation production are consistent with physics based models including two-dimensional particle-in-cell simulations. The analysis indicates that intermediate mass ions (e.g., 12–18amu) control the nominal impedance evolution rather than expected lighter mass ions such as hydrogen.
An extension of Liu procedure in weakly nonlocal thermodynamics
Authors: Cimmelli Vito Antonio
Published: November 2007

An extension of the celebrated Liu procedure for the exploitation of second law of thermodynamics is proposed. The new method is applied to investigate weakly nonlocal extended thermodynamics of rigid heat conductors. Thermodynamic restrictions on the constitutive functions are derived and compared with classical results.
Small-scale isotropy and universality of axisymmetric jets
Authors: Picano F. , Casciola C. M.
Published: November 2007

This paper addresses the long-standing debate about whether the asymptotic jet can be universal. It is argued that the ansatz of a universal spreading rate is inconsistent with more accurate and recent measurements where the scatter in the opening angle is found to exceed the experimental accuracy, implying a true lack of universality in these basic quantities. A universal scaling theory may still be proposed by including the spreading rate in the similarity transformations. We will show that this approach leads to a conflict with the presumed recovery of isotropy in the dissipative scales of the flow. The issue is addressed here by using direct numerical simulations of free-jets to finally show that a complete universality is also incompatible with the experimental data available in the literature.
Spatially convective global modes in a boundary layer
Authors: Alizard Frédéric , Robinet Jean-Christophe
Published: November 2007

The linear stability of a weakly nonparallel flow, the case of a flat plate boundary layer, is revisited by a linear global stability approach where the two spatial directions are taken as inhomogeneous, leading to a fully nonparallel stability method. The resulting discrete eigenvalues obtained by the fully nonparallel approach seem to be in agreement with classical Tollmien–Schlichting waves. Then the different modes are compared with classical linear stability approach and weakly nonparallel method based on linear parabolized stability equations (PSEs). It is illustrated that the nonparallel correction provided by the linear global stability approach is well matched by linear PSE. Furthermore, physical interpretation of these spatio-temporal global modes is given where a real pulsation, which has more physical interest, is considered. In particular the use of a Gaster transformation and the pseudospectrum illustrate the local and global properties of these Tollmien–Schlichting modes. Finally, the contribution of different components of global modes (normal and streamwise) in the transient amplifying behavior associated with the convectively unstable boundary layer is analyzed and compared with a classical steepest descent method. Then, a discussion of an equivalent of the continuous branch is given.
Nonstationary Rayleigh-Taylor instability in supernova ejecta
Authors: Ribeyre X. , Hallo L. , Tikhonchuk V. T. , Bouquet S. , Sanz J.
Published: November 2007

This paper studies the effect of a nonstationary shell acceleration on the development of the Rayleigh-Taylor instability (RTI) in supernovae remnants (SNRs). Two groups of solutions describing acceleration and deceleration phase of the SNR shell are obtained. Using a special transformation (co-moving coordinate frame), an exact dispersion relation for nonstationary RTI is derived. It is shown that compressible and incompressible branches are separated for the spherically symmetric flow and only the former is unstable. The exact analytic solution is compared to a simpler WKB-like analysis and a good agreement is shown, which proves that this analysis can be useful and easily extended to further applications.
Current driven low-frequency electrostatic waves in the solar corona: Linear theory and nonlinear saturation
Authors: Lee Kuang Wu , Büchner Jörg , Elkina Nina
Published: November 2007

Important solar physical problems such as the heating of the corona, reconnection, and electron acceleration might be related to current-driven plasma waves, especially at low frequencies, where, perhaps, most of the wave power is concentrated. Since a direct observation of plasma waves in the solar corona is impossible, theoretical investigations are needed to clarify the possibilities of their excitation, of their nonlinear evolution, and the possible macroscopic consequences of such waves. A multifluid linear dispersion analysis of current flows parallel to the magnetic field in the solar corona is carried out. For this reason, an appropriate linear dispersion solver is developed, considering all possible propagation directions of the waves with respect to the solar magnetic field. As for the assumed plasma model, an electron distribution drifting in the direction parallel to the ambient magnetic field while the background protons were at rest was considered. Thermal effects are taken into account by means of appropriate energy equations of state. Due to their importance for the heating and anomalous transport in the solar corona, the analysis of low-frequency electrostatic waves is studied. For the limiting cases of parallel and perpendicular propagation, the Buneman and the lower-hybrid waves due to a modified two-stream instability were recovered, respectively. For realistic coronal plasma parameters of the lower corona, the dispersion curves of the two basic unstable wave modes are found to approach each other very closely, and their possible nonlinear saturation level is estimated. It appeared that for solar conditions, the two basic modes contribute a comparable (within an order of magnitude) amount of anomalous dissipation, which is quantified by estimating an “effective collision rate.”
Velocity fluctuations of initially stratified sedimenting spheres
Authors: Tee Shang-You , Mucha P. J. , Brenner M. P. , Weitz D. A.
Published: November 2007

The study of velocity fluctuations in the sedimentation of spheres is complicated by the time evolution of the underlying particle distribution, both at the microscale and in the bulk. We perform a series of experiments and simulations to isolate the effect of an initial, stable stratification in the particle concentration. The directly observed dependence of velocity fluctuations on stratification agrees with a previously obtained scaling theory.
Operation of resonant-tunneling diodes beyond resonant-state-lifetime limit
Authors: Feiginov Michael N. , Roy Chowdhury Dibakar
Published: November 2007

We show, first, that the charge relaxation (response) time of resonant-tunneling diode (RTD) can be significantly shorter or longer than the resonant-state lifetime, depending on RTD operating point and RTD parameters. Coulomb interaction between electrons is responsible for the effect. Second, it is also demonstrated that the operating frequencies of RTDs are limited neither by resonant-state lifetime nor by relaxation time; particularly in the RTDs with heavily doped collector, the differential conductance can stay negative at the frequencies far beyond the limits imposed by the time constants. We provide experimental evidences for both effects.
Evolution of optical phonons in CdS nanowires, nanobelts, and nanosheets
Authors: Lee Kyoung-Yeon , Lim Jung-Ran , Rho Heesuk , Choi Young-Jin , Choi Kyoung Jin , Park Jae-Gwan
Published: November 2007

We report Raman scattering from single and ensemble CdS nanowires, nanobelts, and nanosheets. The Raman spectra of nanobelts and nanosheets are notably different from those of nanowires, exhibiting a strong enhancement of the multiphonon response. Moreover, the first-order longitudinal optical (LO) phonon energy systematically increases with increasing lateral size from nanowires to nanobelts, and to nanosheets. These results suggest that the optical phonons in the CdS nanostructures are influenced by strain, crystallinity, and exciton-LO phonon coupling.
Laser-dust interaction and dust size distribution measurements on DIII-D
Authors: Smirnov R. D. , West W. P. , Krasheninnikov S. I. , Pigarov A. Yu. , Rosenberg M. , Bray B. D.
Published: November 2007

The determination of dust radius distributions from the measurement of laser scattering intensity in tokamaks is presented. The analysis takes into account non-Rayleigh regimes of light scattering for different complex refractive indices of dust materials, as well as dust evaporation due to heating by laser radiation. The model is applied to calculate the dust particle radius distribution in tokamaks during normal plasma operation. It is shown that a relatively small amount of large dust particles in the distribution may play a significant role for estimation of the dust mass inventory in tokamaks.
Elegant SiOX heliotropes composed of assembled flexural SiOX nanowires
Authors: Wu Renbing , Li Baosheng , Gao Mingxia , Zhu Qimiao , Pan Yi , Yang Guangyi , Chen Jianjun
Published: November 2007

Silicon oxide nanowires assembled with elegant heliotrope-shape have been synthesized by the modified evaporation of Fe and Si mixture sources. Structures and morphologies of the obtained microheliotropes were thoroughly studied by field emission scanning electron microscopy and high resolution transmission electron microscopy. It is suggested that the multinucleation sites around the perimeter of Fe droplet are responsible for the growth of SiOX nanowires and then via self-assembly process, which results in the formation of microheliotropes. These interesting results and discussion may be beneficial to the understanding of complex nanostructures formation and hopefully enrich the conventional knowledge of vapor-liquid-solid growth phenomena.
Temperature induced single domain–vortex state transition in sub-100nm Fe nanodots
Authors: Dumas Randy K. , Liu Kai , Li Chang-Peng , Roshchin Igor V. , Schuller Ivan K.
Published: November 2007

Magnetization reversal in nanomagnets via a vortex state, although often investigated at the remanent state, may not necessarily display a zero remanence or a highly pinched hysteresis loop. In contrast, the irreversible nucleation/annihilation events are clear indications of a vortex state. In this work, temperature induced single domain–vortex state transition has been investigated in 67nm Fe nanodots using a first-order reversal curve (FORC) technique. The two phase coexistence is manifested as different features in the FORC distribution. At lower temperatures, it becomes harder to nucleate and annihilate vortices and the amount of single domain dots increases.
Multiple small angle neutron scattering: A new two-dimensional ultrasmall angle neutron scattering technique
Authors: Grünzweig C. , Hils T. , Mühlbauer S. , Ay M. , Lorenz K. , Georgii R. , Gähler R. , Böni P.
Published: November 2007

We report on the demonstration experiment of the multiple small angle neutron scattering (MSANS) technique at a 5.6m long neutron beam line, leading to a q resolution of 3×10−4Å−1. The MSANS technique is based on two two-dimensional multihole apertures placed at the front end of the collimator and close to the sample, respectively. By choosing the proper MSANS geometry, individual diffraction patterns are superimposed leading to a large gain in intensity. Using MSANS as an option for standard small angle neutron scattering beam lines, the q resolution could be increased to 10−5Å−1 without dramatically sacrificing intensity.
Deep level thermal evolution in Fe implanted InP
Authors: Cesca Tiziana , Gasparotto Andrea , Piana Erio , Fraboni Beatrice
Published: November 2007

We report on the thermal evolution of the deep levels in Fe implanted and annealed InP. The position and nature of the dominant traps have been assessed by current-voltage-temperature measurements analyzed in the framework of the space-charge-limited current model. For low temperature annealing the conduction properties of the material are controlled by a damage-related donor located at EC−0.21eV. A deep donor–deep acceptor electrical compensation mechanism has been assessed after high temperature annealing. The dominant traps are located at EC−0.55eV and EV+0.72eV. The latter is associated with the Fe2+∕3+ center which is responsible for the semi-insulating properties.
Very small-size and high-density β-FeSi2 nanocrystal assemblies grown on a Si(100) substrate using an embedded solid-phase epitaxy and bionanoprocess with protein ferritin
Authors: Nakama Yuji , Minakawa Kyousuke , Ohta Jun , Nunoshita Masahiro
Published: November 2007

An embedded solid-phase epitaxy technique has been studied to produce very small-size and high-density β-FeSi2 nanocrystal (NC) assemblies on a Si (100) substrate. In this procedure, a bionanoprocess is utilized, with protein “ferritin” containing Fe2O3 cores, for solid-phase epitaxial β-FeSi2-NC growth (at 500–800°C) embedded in an amorphous Si thin film. X-ray diffraction and transmission electron microscopy revealed β-FeSi2 NCs of uniform diameter (6.3±0.3nm) and high density (6.2×1011dots∕cm2). By measuring the photoluminescence spectra at 7K, a photoluminescence peak of 0.91eV is obtained as an excitonic emission from the β-FeSi2 NCs.
Microbial response to the addition of soluble organic substrates
Authors: Hoyle F. C. , Murphy D. V.
Published: November 2007

Soil microbial activity is often limited by the absence of readily available carbon (C) based substrates. Addition of a range of soluble organic substrates to soil has been shown to either accelerate or constrain the rate of CO2-C evolution. The aim of this study was to investigate the capacity of the microbial population to become activated in response to small additions of glucose-C (10–50 µg C/g soil) and 19 other soluble organic substrates (30 µg C/g soil) in soil either amended or not with cellulose. Rapid utilisation (equivalent to 25–35%) of added glucose was demonstrated in an initial flush of respiratory activity measured as CO2-C. However, the cumulative amount of respired C in 23 days indicated no additional release of CO2-C from the native soil organic matter (SOM) following application of glucose to soils, and a highly variable secondary phase of C mineralisation distinct from the initial glucose mineralisation phase. Although several C substrates resulted in the evolution of ‘extra’ CO2-C, no obvious association was observed between the response and the chemical structure of each substrate.
Influence of organic acid and amino acid on cadmium and lead desorption from soil
Authors: Chen S. , Sun L. N. , Chao L. , Zhou Q. X. , Sun T. H.
Published: November 2007

A study was conducted to investigate the influence of organic acid (citric acid, oxalic acid) and amino acid (histidine) on the desorption of cadmium and lead from artificial contaminated soil in north-east China. Results showed that when the concentration of organic acid and amino acid in desorption solution was relatively low, the presence of organic ligands inhibited the desorption behaviour of Cd. When organic acid and amino acid concentrations were higher (>2 mmol/L), the presence of organic acid and amino acid obviously promoted Cd desorption. The increment of citric acid, oxalic acid, and histidine concentration significantly (P < 0.01) accelerated the desorption of Pb. The influence of organic acid and amino acid on the desorption behaviour of Cd and Pb followed the same sequence: citric acid > oxalic acid > histidine. This revealed that the organic acids had stronger affinity with heavy metals than that of amino acids. Functional group positions and types were important in determining if an organic acid or an amino acid would complex metals and increase their potential leaching. The results of this work implicated that amendment of organic acid and amino acid would enhance conditionally the bioavailability of heavy metals adsorbed by soils, relying on the type and concentration of organic acid and amino acid in soil solution.
Vertical distribution of alkali and alkaline earth metals in the soil profile of a wetland - terrestrial ecosystem complex in India
Authors: Prusty B. Anjan Kumar , Azeez P. A.
Published: November 2007

We examined the ammonium acetate extractable forms of alkali (Na, K) and alkaline earth (Ca, Li, and Mg) metals in the soil system in a world heritage site, Keoladeo National Park, Bharatpur, India for 3 consecutive years—2003, 2004, and 2005. The metals were assessed along the soil profile, from surface to 1.00 m depth (as 5 layers, at 0, 0.25, 0.50, 0.75, and 1.00 m). Sodium and K were negatively correlated (P < 0.05) and were found in the range 40–4533 and 77–1802 mg/kg, respectively. The distributions of these metals were significantly different among habitats (Na: F = 17.035, K: F = 30.56; P < 0.05). The lowest and highest values of Ca were 548 and 5976 mg/kg, and for Mg 230 and 5654 mg/kg. The variation in Ca was significant among the soil layers (F = 11.9) and among the habitats (F = 117.3, P < 0.05). Li was found in the range 1.74–15.00 mg/kg soil and varied significantly among the soil layers (F = 71.7) as well as habitats (F = 105.9, P < 0.05). Potassium was positively correlated with Ca, Li, and Mg during 2004 and 2005 (P < 0.05). The terrestrial areas in the Park had higher values of Na/K ratio, indicating the dominating presence of Na salts. Calcium-type enrichment in the wetland and Na-type enrichment in the woodland and grassland differentiated the soil in the Park. A low Mg/Ca molar ratio with a range 0.089–1.681 suggests that CaCO3 rocks would not be the major source of Ca in this Park. Since some of the elements were comparatively higher in the soil, the phytocycling of biogenic elements such as Mg and Ca would ultimately improve the fertility status of the soil system in the Park. Although not addressed here, this issue needs to be considered.
The Brigalow Catchment Study: III. Productivity changes on brigalow land cleared for long-term cropping and for grazing
Authors: Radford B. J. , Thornton C. M. , Cowie B. A. , Stephens M. L.
Published: November 2007

Productivity of grain crops and grazed pastures inevitably declines without soil nutrient replacement and may eventually make these enterprises unprofitable. We monitored these declines in north-eastern Australia during 23 years after clearing 2 of 3 adjacent brigalow catchments, in order to define the productivity levels of developed brigalow land over time. One catchment (11.7 ha) was used for grain production and another (12.7 ha) for beef production from a sown buffel grass pasture. There was no upward or downward trend in annual rainfall amounts throughout the study period. In the cropped catchment, grain yield from 14 winter crops without added nutrients declined significantly in 20 years from 2.9 to 1.1 t/ha.year on the upper-slope clay soil (92 kg/ha.year) and from 2.4 to 0.6 t/ha.year on the Sodosol (88 kg/ha.year). Crop production per year declined by 20% between 2 successive 10-year periods. Wheat grain protein content also declined with time, falling below the critical value for adequate soil N supply (11.5%) 12 years after clearing on the Sodosol and 16 years after clearing on the clay soil. Such declines in grain quantity and quality without applied fertiliser reduce profitability. The initial pasture dry matter on offer of 8 t/ha had halved 3 years after clearing, and a decline in cattle liveweight gain of 4 kg/ha.year was observed over an 8-year period with constant stocking of 0.59 head/ha. Due to fluctuating stocking rate levels of 0.3–0.7 head/ha over the trial period, liveweight productivity trends are attributed to the multiple effects of stocking rate changes and fertility decline. The amount of nitrogen exported from the cleared catchments was 36.1 kg/ha.year in grain but only 1.6 kg/ha.year in cattle (as liveweight gain). Total soil N at 0–0.3 m declined by 84 kg/ha.year under cropping but there was no significant decline under grazing. The soil nutrients removed during grain and beef production need to be replaced in order to avert productivity decline post-clearing.
Title, Control, and Closure? The Experience of the Eritrea–Ethiopia Boundary Commission
Authors: Shaw Malcolm N
Published: November 2007

This article examines the establishment and work of the Eritrea–Ethiopia Boundary Commission with regard to its decision of 13 April 2002 concerning the delimitation of the border between Eritrea and Ethiopia and subsequent events. Apart from an examination of the substantive decision of the Commission in the light of the law relating to territory, the article will discuss certain unusual features of the process, including mandating the Commission both to delimit and demarcate the boundary and the involvement of third parties. The delimitation decision is significant in a number of ways, including its views as to the applicable law, treaty interpretation and the subsequent conduct of the parties in relation to title. The long-running and difficult process of demarcation is noted, together with the important role played by the UN and other international actors.
A Charter of Rights for the Island of Ireland: An Unknown Quantity in the Good Friday/Belfast Agreement
Authors: Egan Suzanne , Murray Rachel
Published: November 2007

The basic aim of the Good Friday/Belfast Agreement was to try to achieve a political settlement to the conflict in Northern Ireland. While the channels for the settlement were to be primarily institutional, the importance of safeguarding the rights of both communities in Northern Ireland by addressing equality and justice issues was recognized, to varying degrees, by all parties to the process that led to the drafting of the Agreement. As the negotiations progressed, the human rights section of the Agreement grew exponentially, moving ‘from the margins to the mainstream’ so that the final Agreement contains a whole section on human rights protections. Not only have these particular elements of the Agreement come to fruition, but they also have received a considerable amount of public and political interest as well as academic comment and analysis. Buried within the human rights chapter, however, is a concept that has so far received minimal interest or enthusiasm from any quarter. That is the reference in paragraph 10 of the ‘Rights, Safeguards and Equality of Opportunity’ chapter to the possibility of establishing an all-island Charter of Rights.

The purpose of this article is threefold. First, it traces the genesis of the Charter of Rights concept through to its inclusion in the Good Friday/Belfast Agreement; secondly, it examines the approach thus far taken by the Joint Committee of the two human rights commissions to the task entrusted to them in relation to the Charter by the Agreement; and finally, it explores some of the issues that need to be considered and the challenges faced by that Committee in future efforts to assist in the construction of any such Charter. In so doing, it describes the political and legal difficulties faced in attempts not only to formulate agreement on human rights but also to create a legal document which may be applicable to two jurisdictions. It concludes by suggesting ways in which the project may be progressed.
Rethinking the Role of Judicial Independence in Socialist-Transforming East Asia
Authors: Gillespie John
Published: November 2007

This article argues that judicial independence is a poor indicator of the capacity of courts effectively to resolve commercial disputes. Judicial power is a more accurate measure because it assesses whether courts have sufficient jurisdiction, discretionary authority and enforcement powers to make decisions over socially meaningful commercial problems. In fact, judicial independence may reduce the power of newly emerging commercial courts in socialist-transforming Asia, which need politics to protect them from interference by powerful governments and private investors. This article explores the trade-offs between judicial power and political patronage by inquiring into the circumstances where patronage may slide into interference. It also investigates the conditions in which judges are most likely to acquire or arrogate discretionary powers to understand politics on their terms. Finally, this article analyses the highly polarized views in this region about what constitutes valid judicial determinations. The message for international agencies contemplating judicial reforms is that reducing political influence and promoting law-based decisions will not uniformly generate popular support and legitimacy for courts.
International Arbitration and English Courts
Authors: Grant TD
Published: November 2007

The Court of Appeal, Civil Division, Longmore LJ, on 24 January 2007 handed down a decision in Fiona Trust v Privalov which clarifies the relation between sections 9 and 72 of the Arbitration Act 1996; affirms, again, in strong terms the separability (or severability) of an arbitration clause from the contract in which it is included; and, apparently for the first time in English courts, establishes that allegations of bribery may be subject to the jurisdiction of an arbitrator. The decision therefore holds interest in relation to the enforcement in the United Kingdom of agreements to arbitrate and, more generally, supports the position that arbitration has a role to play in international efforts to combat corruption.
Genocide as a Fact of Common Knowledge
Authors: Jørgensen Nina HB
Published: November 2007

Judicial notice has become a widely used tool in the practice of international criminal tribunals but its use has always been constrained by the fair trial rights of the accused. This article considers the possible impact on those rights of the decision of the International Criminal Tribunal for Rwanda (ICTR) Appeals Chamber to take judicial notice of the genocide in Rwanda as a notorious fact against the backdrop of the legal requirements for judicial notice as a fact of common knowledge and as an adjudicated fact. The question whether it would have been more appropriate to notice the Rwandan genocide as an adjudicated fact is addressed in the context of the implications for other instances of genocide, for example Srebrenica.
The ICJ in the 21st Century: Judicial Restraint, Judicial Activism, or Proactive Judicial Policy
Authors: Kooijmans He Judge Pieter
Published: November 2007

A court of law can take various approaches when dealing with a case before it: judicial restraint, judicial activism or a proactive policy. In the present article the recent case law of the International Court of Justice is analysed in this light. The author is of the view that the Court, as the principal judicial organ of the United Nations should, wherever possible, by a careful judicial policy, apart from deciding the case in hand, give guidance and provide clarification on a number of questions which are of primordial importance in present-day international society but still are largely obscure from a legal point of view.
Aspects of the modelling of the radial distribution function for small nanoparticles
Authors: I. Korsunskiy Vladimir , Neder Reinhard B. , Hofmann Andreas , Dembski Sofia , Graf Christina , Rühl Eckart
Published: November 2007

An approach to modelling radial distribution functions (RDFs) of nanoparticle samples over a wide range of interatomic distances is presented. Two different types of contribution to the model RDF are calculated. The first explicitly reflects the structure of the nanoparticle parts with more or less crystalline atomic structure. It can be calculated precisely and contains comparatively sharp peaks, which are produced by the set of discrete interatomic distances. The second includes RDF contributions from distances between weakly correlated atoms positioned within different nanoparticles or within different parts of a nanoparticle model. The calculation is performed using the approximation of a uniform distribution of atoms and utilizes the ideas of the characteristic functions of the particle shape known in small-angle scattering theory. This second RDF contribution is represented by slowly varying functions of interatomic distancer. The relative magnitude of this essential part of the model RDF increases with increasingrcompared with the part that represents the ordered structure. The method is applied to test several spherical and core/shell models of semiconductor nanoparticles stabilized with organic ligands. The experimental RDFs of ZnSe and CdSe/ZnS nanoparticle samples were obtained by high-energy X-ray diffraction at beamline BW5, HASYLAB, DESY. The ZnSe nanoparticles have a spherical core with approximately 26 Å diameter and zincblende structure. The RDF of the CdSe/ZnS nanoparticle sample shows resolved peaks of the first- and the second-neighbour distances characteristic for CdSe (2.62 and 4.27 Å) and for ZnS (2.33 and 3.86 Å) and for the first time clearly confirms the presence of CdSe and ZnS nanophases in such objects. The diameters of the CdSe and ZnS spherical cores are estimated as 27 and 15 Å. CdSe and ZnS are present in the sample for the most part as independent nanoparticles. A smaller amount of ZnS forms an irregularly shaped shell around the CdSe cores, which consists of small independently oriented ZnS particles.
A new design for the standard pinhole small-angle neutron scattering instrument D11
Authors: Lieutenant Klaus , Lindner Peter , Gahler Roland
Published: November 2007

Monte Carlo simulations have been performed to check ideas for improvements of the collimating guide system of the standard pinhole small-angle neutron scattering (SANS) instrument D11 at Institut Laue–Langevin, which reaches very lowQvalues by using long detector and collimation distances. According to the simulations, improved guide characteristics can increase the flux at the sample by about 10–15% for short collimation distances. Widening the guide width over the first few metres by 50% will yield a flux gain of about 40% for long and intermediate collimation distances, but a loss for short distances. A gain for all collimation distances can be achieved by a reduction of the guide cross section over the last few metres (in addition to the widening). The best performance was found for a quasi-elliptical exit that reduces width and height to 60% of its nominal size. The effect on divergence of the neutron arriving at the sample has been studied. The changes will be realized in the framework of the ongoing D11 renewal project.
Evidence for the presence of U–Mo–Al ternary compounds in the U–Mo/Al interaction layer grown by thermal annealing: a coupled micro X-ray diffraction and micro X-ray absorption spectroscopy study
Authors: Palancher Hervé , Martin Philippe , Nassif Vivian , Tucoulou Remi , Proux Olivier , Hazemann Jean-Louis , Tougait Olivier , Lahéra Eric , Mazaudier Fabrice , Valot Carole , Dubois Sylvie
Published: November 2007

The systematic presence of the ternary phases U6Mo4Al43and UMo2Al20is reported in a U–Mo/Al interaction layer grown by thermal annealing. This work shows, therefore, the low Mo solubility in UAl3and UAl4binary phases; it contradicts the hypothesis of the formation of (U,Mo)Al3and (U,Mo)Al4solid solutions often admitted in the literature. Using µ-XAS (micro X-ray absorption spectroscopy) at the MoKedge and µ-XRD (micro X-ray diffraction), the heterogeneity of the interaction layer obtained on a γ-U0.85Mo0.15/Al diffusion couple has been precisely investigated. The UMo2Al20phase has been identified at the closest location from the Al side. Moreover, µ-XRD mapping performed on an annealed fuel plate enabled the characterization of the four phases resulting from the γ-U0.85Mo0.15/Al and (U2Mo + α-U)/Al interactions. A strong correlation between the concentrations of UAl4and UMo2Al20and those of UAl3and U6Mo4Al43has been shown.
On the precision and accuracy of structural analysis of light-induced metastable states
Authors: Legrand Vincent , Pillet Sébastien , Weber Hans-Peter , Souhassou Mohamed , Létard Jean-François , Guionneau Philippe , Lecomte Claude
Published: November 2007

Bragg diffraction data were collected on single crystals of the spin-crossover complex [Fe(phen)2(NCS)2] in its low-spin and light-induced metastable high-spin states. Experimental variables included the temperature (32 and 15 K), the X-ray source (sealed tube and synchrotron), and the time interval between laser light excitation of the sample (λ = 647 nm). From a comparison of the structural parameters refined, it is shown that photo-crystallographic measurements suffer significantly and systematically from bias if the probed sample contains residual ground-state species, resulting from an incomplete photo-conversion or a significant metastable- to ground-state relaxation. It follows that a 4% population of species in a different spin state affects the Fe—N bond lengths by more than three standard deviations, and the FeN6polyhedron volume by as much as seven standard deviations, while the mean atomic position misfit exceeds 0.005 Å.
Application of white-beam X-ray microdiffraction for the study of mineralogical phase identification in ancient Egyptian pigments
Authors: Lynch P. A. , Tamura N. , Lau D. , Madsen I. , Liang D. , Strohschnieder M. , Stevenson A. W.
Published: November 2007

High-brightness synchrotron X-rays together with precision achromatic focusing optics on beamline 7.3.3 at the Advanced Light Source have been applied for Laue microdiffraction analysis of mineralogical phases in Egyptian pigments. Although this task is usually performed using monochromatic X-ray diffraction, the Laue technique was both faster and more reliable for the present sample. In this approach, white-beam diffraction patterns are collected as the sample is raster scanned across the incident beam (0.8 µm × 0.8 µm). The complex Laue diffraction patterns arising from illumination of multiple grains are indexed using the white-beam crystallographic software packageXMAS, enabling a mineralogical map as a function of sample position. This methodology has been applied to determine the mineralogy of colour pigments taken from the ancient Egyptian coffin of Tjeseb, a priestess of the Apis bull dating from the Third Intermediate to Late period, 25th Dynasty to early 26th Dynasty (747 to 600 BC). For all pigments, a ground layer of calcite and quartz was identified. For the blue pigment, cuprorivaite (CuCaSi4O10) was found to be the primary colouring agent with a grain size ranging from ∼10 to 50 µm. In the green and yellow samples, malachite [Cu2(OH)2CO3] and goethite [FeO(OH)] were identified, respectively. Grain sizes from these pigments were significantly smaller. It was possible to index some malachite grains up to ∼20 µm in size, while the majority of goethite grains displayed a nanocrystalline particle size. The inability to obtain a complete mineralogical map for goethite highlights the fact that the incident probe size is considerably larger than the grain size. This limit will continue to improve as the present trend is toward focusing optics approaching the diffraction limit (∼1000× smaller beam area).
A structural proteomics filter: prediction of the quaternary structural type of hetero-oligomeric proteins on the basis of their sequences
Authors: Carugo Oliviero
Published: November 2007

A protein chain can correspond to a monomeric protein or it can form, together with other chains, oligomeric assemblies, which can be either homo-oligomers or hetero-oligomers. In the latter case, the three-dimensional structure of the single protein chain is unlikely to be determined, since it will probably be difficult to express and crystallize. A computational method is presented here that allows one to predict if a chain participates in hetero-oligomeric assemblies, on the basis of its amino acid composition, with accuracy close to 80%. Such a technique should improve the success rate of structural biology projects.
X-ray extinction changes due to dislocations
Authors: Masimov M.
Published: November 2007

A correct interpretation of the diffraction phenomenon in crystals with low dislocation content, for which the kinematical scattering theory does not yield any reasonable results, was carried out by X-ray extinction treatments. Different approaches to investigating the dislocation-induced X-ray extinction changes are reviewed and the applicability of the statistical dynamical theory to analysis of the substructure characteristics of crystals is discussed. A relationship between the scattering amplitudes and the dislocation density in crystals is established by using pair correlation functions. A procedure for determination of the substructure characteristics by means of measurements of the integrated intensities is proposed. The tests illustrate satisfactory agreement of the investigated approaches with experimental data.
In situX-ray diffraction analysis of (CFx)nbatteries: signal extraction by multivariate analysis
Authors: Rodriguez Mark A. , Keenan Michael R. , Nagasubramanian Ganesan
Published: November 2007

(CFx)ncathode reaction during discharge has been investigated usingin situX-ray diffraction (XRD). Mathematical treatment of thein situXRD data set was performed using multivariate curve resolution with alternating least squares (MCR–ALS), a technique of multivariate analysis. MCR–ALS analysis successfully separated the relatively weak XRD signal intensity due to the chemical reaction from the other inert cell component signals. The resulting dynamic reaction component revealed the loss of (CFx)ncathode signal together with the simultaneous appearance of LiF by-product intensity. Careful examination of the XRD data set revealed an additional dynamic component which may be associated with the formation of an intermediate compound during the discharge process.
On the role of nitrogen in stiffening the diamond structure
Authors: Nailer Stuart Geoffrey , Moore Moreton , Chapman John , Kowalski Grzegorz
Published: November 2007

Three large (4–7 mm) natural diamonds, each half brown and half white, from the Argyle Diamond Mine in Western Australia, have been studied for growth history and crystal perfection. Scanning electron microscopy and X-ray single-crystal topography showed the diamonds to have good octahedral morphologies but poor internal perfection. X-ray double-crystal topography quantified this lack of perfection, rocking-curve widths taking unusually large values of 300 and 75 s of arc for the brown and white regions, respectively, in a diffraction geometry for which 3 s of arc would be expected for a perfect diamond. Fourier transform infrared spectroscopy revealed significant differences in nitrogen concentration between the brown and white regions of the diamonds. The white regions, with 400 to 600 p.p.m. nitrogen, contained over 1.6 times more nitrogen than the brown regions. It is concluded that the extra nitrogen (in A and B forms) in the white regions stiffens the lattice against distortion by natural plastic deformation.
Advances in spectroscopic methods for biological crystals. 2. Raman spectroscopy
Authors: Carpentier Philippe , Royant Antoine , Ohana Jérémy , Bourgeois Dominique
Published: November 2007

A Raman microspectrophotometer is described that allows the spectroscopic investigation of protein crystals under exactly the same conditions as those used for X-ray data collection. The concept is based on the integration of the Raman excitation/collection optics into a microspectrophotometer built around a single-axis diffractometer and a cooling device. It is shown that Raman spectra of outstanding quality can be recorded from crystallized macromolecules under non-resonant conditions. It is proposed that equipment developed in the context of macromolecular cryocrystallography, such as commonly used cryoloops, can be advantageously used to improve the quality of Raman spectra. In a few examples, it is shown that Raman microspectrophotometry provides crucial complementary information to X-ray crystallography,e.g.identifying the chemical nature of unknown features discovered in electron-density maps, or following ligand-binding kinetics in biological crystals. The feasibility of `online' Raman measurements performed directly on the ESRF macromolecular crystallography beamlines has been investigated and constitutes a promising perspective for the routine implementation of combined spectroscopic and crystallographic methods.In crystalloRaman spectroscopy efficiently complements absorption/fluorescence microspectrophotometry for the study of biological crystals and opens up new avenues for difficult structural projects with mechanistic perspectives in the field of protein crystallography.
Interpretation of small-angle X-ray scattering patterns of crystalline triglyceride nanoparticles in dispersion
Authors: Unruh T.
Published: November 2007

Triglyceride nanocrystals in aqueous dispersion produced by high-pressure melt homogenization exhibit platelet-like shapes and clear but broadened Bragg reflections in the small-angle scattering regime. Because the particle thickness, the thickness of the stabilizer layer, the length scale of the crystalline structure of the nanoparticles and often the interparticle distances are of the same order of magnitude, the scattering of these structures mutually interferes. This leads to complicated small-angle scattering patterns which exhibit a lot of features, but it is not straightforward to discover the contained information on the structure of the system. In this contribution, a scattering model for such systems will be described, which is based on the kinematic scattering theory of X-rays. Using this scattering model an X-ray powder pattern simulation analysis is introduced to gain information on tripalmitin nanosuspensions which have been investigated by synchrotron small-angle X-ray scattering. It will be demonstrated that the results of this method provide a consistent description of all structural details mentioned above. In particular, information on the extension and the molecular packing density of the stabilizer layers can be achieved because these layers exhibit a comparatively large scattering contrast.
On the intersection of grating truncation rods with the Ewald sphere studied by grazing-incidence small-angle X-ray scattering
Authors: Yan Minhao , Gibaud Alain
Published: November 2007

In this work a grating made of lines having a height of 55 nm and a period of 450 nm has been characterized by grazing-incidence small-angle X-ray scattering (GISAXS). The GISAXS patterns are characterized by a series of spots corresponding to the intersection of the Ewald sphere with the grating truncation rods (GTRs). When the grating lines are almost parallel to the direct beam, the location of these spots is very sensitive to any change in the azimuthal angle. The precise location of the intersection of the GTRs with the Ewald sphere can be calculated for any azimuthal angle. From this analysis we can estimate the statistical coverage of the grating, its period and the width of the lines. In addition, the anisotropy of the width of the spots in theqzdirection is interpreted in terms of wavelength spread and angular divergence of the incident beam.
Application of the constrained S-FFT direct-phasing method to powder diffraction data. XIII
Authors: Rius Jordi , Frontera Carles
Published: November 2007

Since its discovery, the direct-methods origin-free modulus sum functionS, originally denotedZRby Rius [Acta Cryst.(1993), A49, 406–409], has been used for solving some relatively complex crystal structures from powder X-ray diffraction data. In these applications, phase refinement was normally carried out by maximizing the functionSwith a modified tangent formula. However, further progress in the powder diffraction field was hampered by the complexity of combining the tangent formula refinement that makes explicit use of triple-phase sums, with the introduction of constraints in real space necessary to counterbalance the information loss produced by peak overlap in powder diffraction. Recently, a considerably simpler and completely general phasing procedure (S-FFT) has been developed that maximizesSby means of the FFT algorithm and considers the triple-phase sums implicitly [Rius, Crespi & Torrelles (2007),Acta Cryst.A63, 131–134]. As pointed out by the authors, this procedure could represent a source of progress in powder diffraction. Here, an algorithm combining the S-FFT procedure with real-space constraints according to theShake-and-Bakephilosophy [Weeks, de Titta, Miller & Hauptman (1993),Acta Cryst. D49, 179–181] is given and its capability to treat powder diffraction data is proved with some realistic test structures.
GenX: an extensible X-ray reflectivity refinement program utilizing differential evolution
Authors: Björck Matts , Andersson Gabriella
Published: November 2007

GenXis a versatile program using the differential evolution algorithm for fitting X-ray and neutron reflectivity data. It utilizes the Parratt recursion formula for simulating specular reflectivity. The program is easily extensible, allowing users to incorporate their own models into the program. This can be useful for fitting data from other scattering experiments, or for any other minimization problem which has a large number of input parameters and/or contains many local minima, where the differential evolution algorithm is suitable. In addition,GenXmanages to fit an arbitrary number of data sets simultaneously. The program is released under the GNU General Public License.