bluuebunny/crossref_metadata_2025 huggingface dataset:
Focusing Monochromators for Neutron Diffraction
Authors: Popovici M. , Yelon W.B.
Published: July 2007

Recent advances in bent crystal monochromators for neutron powder diffraction are reviewed. As monochromators for high resolution instruments, bent perfect crystals may be superior to flat mosaic crystals. They can provide both real-space focusing on sample and scattering-space focusing in diffraction for a wide range of detector angles. Double crystal monochromators with anti-parallel (+,+) settings can condense large area neutron beams into millimeter-size spots. Their focusing range for diffraction is narrow, but the situation is of interest for microfocus stress profiling measurements. The design of single and double monochromators for stress measurements by neutron diffraction is discussed. To take full advantage of focusing, techniques for plastic bending of crystals will have to be developed.
Small Effects and Neutron Flux
Authors: Axmann Anton
Published: July 2007

The conversion of modern research reactor facilities or designs with high flux-to-power ratios (small cores) from high-enriched uranium (93%, which is weapons grade) to low-enriched uranium (less than 20% 235U) leads to a flux loss of up to 70% [l, 2]. This paper shows that the loss of flux is equivalent to a loss of financial investments and scientific output of the same magnitude.
Position Sensitive Detectors for Thermal Neutrons Using Image Intensifiers, CCDs and Image Plates
Authors: Rausch C. , Dietze M. , Felber J. , Hofmann J. , Schillinger B.
Published: July 2007

This paper describes novel detection techniques for thermal neutrons and the performance of prototype position sensitive detectors. The first detector, developed and built at our institute, is our so-called “Handmonitor”. It uses a scintillator and an image intensifier, optically coupled to a CCD camera for electronic readout. The second detector consists of a cooled CCD camera, equipped with a high aperture lens, looking at a large area scintillator. The third detector type uses an image plate, specially designed for neutron detection. It performs all necessary processing steps, like exposure, scanning and reconditioning in situ. Measurements of the relevant detector parameters, like the detective quantum efficiency, spatial resolution, dynamic range and gamma sensitivity are presented and discussed.
The Information Bandwidth of Neutron Scattering Instruments
Authors: Johnson M.W.
Published: July 2007

The concept of the information content of a scientific measurement is introduced, and a theory is presented which enables the information that may be obtained by a neutron scattering instrument to be calculated. When combined with the time taken to perform the measurement the bandwidth of the instrument is obtained. This bandwidth is effectively a figure of merit which is of use in three respects: in the design of neutron instrumentation, the optimisation of measurements, and in the comparison of one instrument with another.
Nexus — Proposal for a HDF-Based Data Exchange Standard for the Neutron Scattering Community
Authors: Könnecke Mark , Arends Patrick
Published: July 2007

The need to convert neutron scattering data from site specific data formats to a format understood by data analysis programs has exercised the users of neutron scattering facilities since the invention of neutron scattering and computers. Recent developments in computing, neutron scattering technology and politics have made this problem big enough to justify a proposal for a data exchange format (DEF) for neutron scattering. The proposed data standard is organized in four levels: The first is the physical file format, which will be the Hierarchical Data Format (HDF) [1] developed by the National Center for Super Computer Applications (NCSA). The second level gives guidelines for storing individual data items in the file. A common name convention and a common structure for an exchange file will significantly facilitate the implementation and reuse of software. Therefore the third level defines a recommended structure for arranging and classifying information in the file in a logical manner. The fourth level is a set of naming conventions and a glossary of names for neutron scattering related data items. The standard is extensible. Data items can be added to the file without interfering with the standard. The standard is suggested for voluntary adoption by the neutron scattering community. The authors invite comments from all interested parties.
Analysing Neutron Scattering Data with the Cambridge Crystallographic Subroutine Library (CCSL)
Authors: Brown P.J.
Published: July 2007

The Cambridge Crystallographic Subroutine Library (CCSL) is a library designed to facilitate crystallographic calculations. It defines a data format for describing both nuclear and magnetic structures. Procedures contained in the library use these data to calculate properties which depend on the structure. Subroutines are provided to evaluate quantities such as the structure factor and its differentials with respect to the crystallographic parameters, bond lengths and angles, the indices of magnetic reflections, fourier series etc. The library also includes a selection of main programs for carrying out common tasks; these call the subroutines as required. Examples are given of how the procedures of CCSL can be pieced together to construct powerful programs to analyse different kinds of neutron scattering data. In conclusion some developing ideas for a C++ class library with a similar purpose to CCSL are outlined.
Instrument Control and Data Acquisition for a Time-of-Flight Neutron Reflectometer
Authors: van Well A.A. , Beunes A.J.H. , de Blois J. , van der Ende P. , de Haan V.O. , Osterholt E.A. , Schipper M.N.
Published: July 2007

A description is given of the integrated instrument control and data-acquisition electronics and the software of the neutron reflectometer ROG. For the data acquisition, VME electronics is developed to perform time-of-flight and stroboscopic measurements, using a single 3He detector or a two-dimensional position-sensitive detector. For the latter pixel-dependent discrimination is implemented. The instrument control is performed via a distributed (field bus) system. A flexible integrated software system controls the complete instrument.
Crystalline Silicon Diodes as Neutron Detectors: Performances and Perspectives
Authors: Petrillo C. , Sacchetti F. , Toker O. , Rhodes N.J.
Published: July 2007

The design and development of crystalline silicon neutron detectors are discussed. Experimental results obtained on prototype systems, namely a diode and a microstrip device, are reported. The detector performances are discussed with special emphasis on detection efficiency, dead-time and positional resolution. Performances in signal-to-noise ratio when switching from medium-speed to fast VLSI readout electronics are reported for the prototype systems. Progress through various detection schemes is outlined and the expected performances of a position sensitive area detector for neutron scattering application are presented.
Neutron Scintillators Using Wavelength Shifting Fibers
Authors: Hutchinson D.P. , Miller V.C. , Ramsey J.A.
Published: July 2007

A proposed design for an optically-based, one-dimension scintillation detector to replace the gas-filled position-sensitive proportional counter currently used for a wide-angle neutron detector (WAND) at the High-Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) is presented. The scintillator, consisting of a mixture of 6LiF and ZnS(Ag) powders in an epoxy binder, is coupled to an array of wavelength shifting optical fibers which provide position resolution. The wide-angle neutron detector is designed to cover a 120 degree arc with a 75 cm radius of curvature. The final detector design provides for 600 optical fibers coupled to the scintillator screen with an angular resolution of 0.2 degrees. Each individual pixel of the detector will be capable of operating at count rates exceeding 1 MHz. Results are presented from the measurement of neutron conversion efficiencies for several screen compositions, gamma-ray sensitivity and spatial resolution of a 16 element one-dimensional array prototype.
Development of Position-Sensitive Neutron Detectors and Associated Electronics
Authors: Müller K.D. , Reinartz R. , Engels R. , Reinhart P. , Schelten J. , Schäfer W. , Jansen E. , Will G.
Published: July 2007

The paper presents the spectrum of solid state neutron scintillation detectors, which have been developed and manufactured at Jiilich with respect to use at neutron scattering instruments at steady state reactors and pulsed spallation sources. Design and physical characteristics of three types of linear and three types of area detectors are described. The detectors are designed for operation as standalone PC-based systems with integrated timing interface based on programmable logic cell arrays. The data acquisiton system within the EISA-PC is suitable for applications requiring huge amounts of memory, e.g. in position-sensitive time-of-flight experiments.
Ultracold Neutron Production, Storage, and Detection in 3He-Superfluid 4He Mixtures
Authors: Lamoreaux Steve K.
Published: July 2007

Recent theoretical and experimental progress on the development of new techniques for measuring the neutron electric dipole moment and neutron lifetime, and for producing ultracold neutrons in general, is reviewed, with emphasis on the electric dipole moment work. The basic idea is to produce and store ultracold neutrons in a superfluid 4He bath which has been doped with a low concentration of polarized 3He which serves as an ultracold neutron polarizer, analyzer, and magnetometer.
A High-Rate Detection System to Study Parity Violation with Polarized Epithermal Neutrons at LANSCE
Authors: Knudson J.N. , Bowman J.D. , Crawford B.E. , Delheij P.P.J. , Frankle C.M. , Gould C.R. , Haase D.G. , Iinuma M. , Lowie L.Y. , Masaike A. , Masuda Y. , Matsuda Y. , Mitchell G.E. , Penttila S.I. , Postma H. , Roberson N.R. , Seestrom S.J. , Sharapov E.I. , Shimizu H.M. , Stephenson S.L. , Yen Y.F. , Yuan V.W. , Yoo S.H.
Published: July 2007

We describe an apparatus for studies of parity violation in neuwn-nucleus scattering. This experiment requires longitudinally polarized neutrons from the Los Alamos Neutron Scattering Center over the energy range from 1 to l000 eV, the ability to reverse the neutron spin without otherwise affecting the apparatus, the ability to detect neutrons at rates up to 500 MHz and an appropriate data acquisition system. We will discuss the neutron polarizer, fast neutron spin reverser, detector for transmitted neutrons and high rate data acquisition system.
Dual Polarised Beam Polarimeter: A Highly Sensitive Tool for the Detection of Very Small Neutron Spin Rotation
Authors: Otake Yoshié , Zeyen Claude M.E. , Forte Mario
Published: July 2007

Antisymmetric interactions with respect to spin direction give rise to spin rotations in certain perfect crystals. A new perfect crystal technique, termed Dual-Polarised-Beam technique (DPB), can be used to boost the sensitivity of the spin rotation measurements by several orders of magnitude. The typical Zeeman splitting is shown and a future experiment of neutron EDM detection with DPB using new crystals is also discussed.
Future Opportunities and Present Possibilities for Coherent Inelastic Single Crystal Measurements on Pulsed Neutron Sources
Authors: Hagen M. , Steigenberger U. , Petrillo C. , Sacchetti F.
Published: July 2007

The triple axis spectrometer (TAS) has long been the mainstay for measuring excitations in single crystal samples. In a recent paper Dorner has claimed that the TAS would be the instrument of choice for such measurements at any future high flux spallation neutron source. However, a comparison of the operational characteristics of a TAS and those of direct and indirect geometry time of flight spectrometers for this type of measurement at a pulsed source shows that the TAS would not in fact be a particularly competitive instrument for this purpose.
Comparison of the Structure Factors of a Simple Fluid Measured with Time-of-Flight and Two-Axis Diffractometers
Authors: Bafile U. , Zoppi M. , Magli R. , Guarini E. , Barocchi F.
Published: July 2007

In two recent experiments the static center-of-mass structure factor of liquid deuterium has been measured using both time-of-flight neutron diffraction at a pulsed source and two-axis diffraction at a reactor source. The comparison of the two experimental results shows that a discrepancy is present, which is larger than the experimental errors and appears to be due to systematic effects. Here we show that, if physical constraints are imposed on the pair correlation function g(r), most of these effects can be removed and the two sets of data are brought to agree with each other within the statistical uncertainties.
A Comparison of Neutron Energy Spectra in Low-Enriched and High-Enriched Uranium Cores
Authors: Iqbal Masood , Ansari Saleem A. , Zafar M.S.
Published: July 2007

The Pakistan Research Reactor-1 has been converted from highly enriched uranium to low-enriched fuel. The reactor power was also upgraded from 5 to 9 MW. An experimental program was undertaken to measure the neutron energy spectra in the core and the irradiation facilities of the new reactor. The objectives of these measurements were to provide useful data to the reactor users and to determine the changes in neutron energy spectrum due to the core conversion. The results were also compared to the neutron energy spectrum measurements made in the highly enriched uranium core. For energy spectrum measurements, several threshold activation detectors were irradiated in the reactor, and their measured activities were analyzed using the spectrum adjustment code SANDBP, which is a modified version of SAND-II. A sample energy spectrum for the material test reactor was used for the input to the SANDBP code, and the final spectrum was obtained by iterative adjustment. It was observed that the design of the low-enriched uranium core results in a harder energy spectrum than that resulting from highly enriched uranium core.
Focus: Project of a Space and Time Focussing Time-of-Flight Spectrometer for Cold Neutrons at the Spallation Source SINQ of the Paul Scherrer Institute
Authors: Mesot J. , Janssen S. , Holitzner L. , Hempelmann R.
Published: July 2007

The physical design of FOCUS, a new time-of-flight (TOF) spectrometer for cold neutrons located at the continuous spallation source SINQ at the Paul Scherrer Institute/CH is presented. The main purpose of the instrument is to provide a versatile TOF machine being suited for a large variety of applications. The concept of the instrument consists in the combination of a doubly focussing monochromator with a Fermi-chopper. The monochromator will be provided with variable curvatures in both horizontal and vertical direction. By variable distances between the main spectrometer components FOCUS will have the option to be operated either in time focussing or monochromatic focussing mode for quasielastic and inelastic scattering applications, respectively. By means of two interchangeable monochromators a continuous wavelength band ranging from 2Å up to 18Å will be accessible. Monte Car10 simulations for an ideal Pb-target at SINQ show that for 4Å and 6Å and in its time focussing mode FOCUS will yield comparable energy resolutions in connection with 70–90% of the intensity of the time focussing TOF spectrometer IN6 at the ILL.
Progress Toward a Spin Exchange Pumped 3He Neutron Spin Filter
Authors: Chupp T.E. , Coulter K.P. , Hwang S.R. , Smith T.B. , Welsh R.C.
Published: July 2007

Polarization of 3He by spin exchange with laser optically pumped Rb vapor has advanced to a state of the art necessary for an effective, reliable, and relatively inexpensive broadband neutron spin filter. Over the past several years, many advances have led to the current state, most importantly advances in materials (glass), cell making including cleaning and gas purification, and the utilization of laser diode arrays. Most crucial, however, have been the many exciting experimental applications that motivate the technical developments. We provide details useful for implementing spin filter cell construction and filling and for optimal use of laser diode arrays, and we describe a neutron spin filter test set-up at the University of Michigan.
Neutron Optics with Gradient Crystals
Authors: Magerl A.
Published: July 2007

To date almost exclusively mosaic crystals are used on instruments employing Bragg optics. However, gradient crystals, which are distinguished by a local variation of the interplanar lattice spacing, are an alternative means to design optimized optical components. Recently, significant progress has been achieved in the make of Si-Ge gradient crystals. Some simple applications will be presented in this paper where longitudinal and lateral gradient crystals hold promise for increased instrument performance.
The Focussing Monochromator of IN4C
Authors: Mutka H. , Saccheti F.
Published: July 2007

The new version of the time of flight spectrometer IN4 to be installed at ILL has been designed in order to obtain a very high intensity at the sample position and good performances in terms of momentum and energy resolution. The increase of flux at the sample as well as the control of the time-focussing conditions are obtained using a large area (440 cm2) variable curvature monochromator consisting of 55 individual crystals of 2 × 4 cm2. Both the horizontal and vertical radii of curvature are independently and continuously adjustable from R = 1 m to infiity. The monochromator has four faces to allow a ready change of the monochromating crystals and all the movements are computer controlled. This monochromator provides notable increase of flux estimated by simulation to be up to a factor of ten in normal operation conditions.
Analysis and Simulation of a Small-Angle Neutron Scattering Instrument on a 1 MW Long Pulse Spallation Source
Authors: Olah Glenn A. , Hjelm Rex P.
Published: July 2007

We studied the design and performance of a small-angle neutron scattering (SANS) instrument for a proposed 1 MW, 60 Hz long pulsed spallation source at the Los Alamos Neutron Science Center (LANSCE). An analysis of the effects of source characteristics and chopper performance combined with instrument simulations using the LANSCE Monte Carlo instrument simulations package shows that the T0 chopper should be no more than 5m from the source with the frame overlap and frame definition choppers at 5.6 and greater than 7m, respectively. The study showed that an optimal pulse structure has an exponential decaying tail with τ ≈ 75O µs. The Monte Carlo simulations were used to optimize the LPSS SANS, showing that an optimal length is 18 m. The simulations show that an instrument with variable length is best to match the needs of a given measurement. The performance of the optimized LPSS instrument was found to be comparable with present world standard instruments.
Performance of a Spin Echo Spectrometer at a Long Pulse Spallation Source
Authors: Keller T. , Mezei F. , Guy C. , Schorr S. , Stride J.
Published: July 2007

Design criteria for a NSE spectrometer at a LPSS are discussed. First results of Monte Carlo simulations, which were performed to quantify the performance of the instrument in typical quasielastic experiments on soft matter samples, are presented. Typical quasielastic scattering functions in the small wave number range for this kind of samples lead to convenient matching between the wavelength dependence of the instrument parameters and the wave number dependence of the scattering.
Monte Carlo Simulations of Resolution Functions and Scan Profiles for Neutron Three-Axis Spectrometers
Authors: Šaroun J. , Kulda J.
Published: July 2007

The method of ray-tracing simulation of the resolution functions for neutron scattering experiments is described. The corresponding algorithm has been implemented in a resolution calculation program for conventional three-axis spectrometers and combined with an efficient Monte Carlo convolution algorithm to simulate the phonon scans. Used in data fitting procedures, this method permits adequate instrumental corrections to be made including second order effects, and thus to improve significantly the accuracy of experiments. The measurement of LO phonons in diamond is given as an example.
High-Resolution Fourier Diffractometry for Long Pulse Neutron Sources
Authors: Aksenov V.L. , Balagurov A.M. , Trounov V.A.
Published: July 2007

Application of the Fourier technique for diffraction experiments at long pulse neutron sources is discussed. The main parameters of a neutron Fourier diffractometer are reviewed. A comparison of the parameters of the conventional TOF diffractometers at SPS and LPS with the possible characteristics of the Fourier diffractometer is carried out. The experience of operating of the HRFD instrument, the first neutron Fourier diffractometer at the LPS-type source, the IBR-2 pulsed reactor in Dubna, is discussed.
Prospects of Single-Crystal Diffraction at a Long Pulse Spallation Source
Authors: Jauch W.
Published: July 2007

The expected performance of single-crystal time-of-flight diffraction at a potential long pulse spallation source is discussed for both small and large-unit-cell structures. The requirements and capabilities in biomacromolecular structure analysis at high, atomic resolution are focused on. Data collection times are predicted on the basis of a detailed evaluation of the counting-statistical quality of a complete data set. It is found that a long pulse source would excel the capabilities at the best existing steady state source. Most promising for advances in the more challenging structural problems, however, looks a short pulse spallation source with an intermediate-temperature coupled moderator.
Multilayer Neutron Polarizing Mirrors Working Under a Low External Magnetic Field Less Than 100 Gausses
Authors: Kawai Takeshi , Ebisawa Toru , Tasaki Seiji , Eguchi Yoshiaki , Hino Masahiro , Achiwa Norio
Published: July 2007

We have developed multilayer neutron polarizing mirrors which are controlled under an external magnetic field less than 100 gausses. Multilayers of Permalloy-Ge and Fe-Ge have been evaporated on Si wafers in the magnetic field of about 130 gausses parallel to the surface of the wafer. The polarizing efficiencies of Fe-Ge and Permalloy-Ge multilayer mirrors were 95% and 91% respectively under a low external magnetic field of 80 gausses. Under a very low external field of 50 gausses, the polarizing efficiency was 90% in case of Permalloy-Ge. A neutron pulse was obtained by applying a pulsed magnetic field of about 50 gausses parallel to the Permalloy-Ge polarizing mirror. The pulse rise time is the order of 100 μs in the present pulsed magnetic devices.
Total Cross Section Measurements with Cold Neutrons on Solid and Powder Samples and on Hydrogen Containing Compounds
Authors: Knopf K. , Waschkowski W.
Published: July 2007

Transmission measurements with cold neutrons of mean energy of 0.57 meV on solid and powder samples were performed to deduce the inelastic scattering cross sections σinel and the absorption cross sections σγ for 43 chemical elements and 27 of their isotopes. The Debye-temperature Θ, could be deduced from measurements. From similar experiments on water, alcohole and carbon hydrogen compounds the proton scattering cross section for cold neutrons was determined.
Performance of the High Resolution Fourier Diffractometer at the IBR-2 Pulsed Reactor
Authors: Aksenov V.L. , Balagurov A.M. , Simkin V.G. , Bulkin A.P. , Kudryashev V.A. , Trounov V.A. , Antson O. , Hiismäki P. , Tiitta A.
Published: July 2007

The first neutron Fourier diffractometer at the pulsed neutron source, the High Resolution Fourier Diffractometer (HRFD), is described. The HRFD combines both high neutron flux at the sample position, ∼107n/cm2/s, provided by the IBR-2 high flux pulsed reactor, and high resolution, very close to 0.001, over a wide range of d-spacings. The paper deals with the basic principles of HRFD, its design, and performance. Examples of structural experiments are also given.
Time of Flight- or Larmor Method for Neutron Reflectometry at a Steady State Reactor
Authors: Fredrikze Henk
Published: July 2007

Two methods to measure neutron specular reflectivity at a steady state reactor are considered: the time of flight (TOF) method, where the time of flight of neutrons from a chopper to a detector is used to determine the wavelength and the LARMOR method, where the precession of the polarization of a neutron beam around an applied magnetic induction is used to determine the wavelength. Using computer simulations Poisson distributed ‘experimental data’ are generated taking into account the wavelength dependent flux, transmissions and detector efficiencies. Statistical accuracies for the ‘experimental’ neutron reflectivities are estimated from ‘experimental’ numbers of counts. Resolution effects due to finite widths of time channels for TOF and due to the Fourier Transform algorithm for LARMOR are taken into account properly. Numerical results show that, although both methods are feasible, the TOF method has advantages over the LARMOR method.
An Instrument for Stress Measurement using Neutron Diffraction
Authors: Witte D.A. , Krawitz A.D. , Winholtz R.A. , Berliner R.R. , Popovici M.
Published: July 2007

An instrument for conducting neutron stress measurements is described. The instrument is designed to make depth profiling stress tensor measurements, studies of stress distributions through peak breadth analysis, measurements of small strains, and phase and texture studies. To achieve these objectives the instrument will be able to translate and orient small and large specimens, has a sophisticated specimen alignment capability, and can make measurements up to a diffraction angle of 130°. It employs focusing monochromators, a position-sensitive detector, a modular design with all components on air pads, a freestanding detector that can be decoupled for removal of the diffractometer and full translation and tilt capabilily for small or large specimens.
CFDF – A New Fourier RTOF-Diffractometer for Stress and Powder Diffraction Investigations
Authors: Maayouf R.M.A. , Abdel-Latif I.A. , El-Kady A.S.I. , El-Shafey A.S. , Khalil M.I. , El-Shaer Y.H.
Published: July 2007

The present work deals with the results of measurements performed recently with the Cairo Fourier diffractometer facility (CFDF). The CFDF is based on the reverse time-of-flight (RTOF) method and is optimized for neutron diffraction measurements at scattering angle 2θ=90°. The CFDF performance is assessed and the main parameters are given. The neutron guide system attached to the CFDF provides a thermal neutron flux of ∼106n/cm2s at the sample position which is free from fast neutron and gamma-ray background. It has been found, from measurements with different powder samples, that this value of the thermal neutron flux is adequate for neutron diffraction measurements, at scattering angle 2θ = 90° and d-spacing values between 0.7 and 2.5 Å; with 0.52% resolution.
Neutron Spectrometer for the Determination of Very Low Hydrogen Content in Metals
Authors: Santisteban J.R. , Granada J.R. , Mayer R.E.
Published: July 2007

The commonly available techniques for the determination of hydrogen dissolved in solids are usually destructive from the point of view of the sample. A new, nondestructive method for this kind of measurements has been developed, with the requirement of improved sensitivity for massive samples. The method is based on the use of epithemal neutrons together with time-of-flight techniques, and has been implemented through the design and construction of a spectrometer dedicated to that task. In this work we describe the basic concepts of this method, as well as the different stages of design, building, and characterization of the new spectrometer. A pulsed neutron source based on an electron LINAC has been employed to perform the measurements. Preliminary results showing the sensitivity achieved are presented.
The Optimization of Neutron Polarizing Transmission Filter Thickness
Authors: Cussen L.D.
Published: July 2007

For a neutron polarizing transmission filter the transmitted neutron beam polarization and intensity are determined by the filter thickness. It is possible to trade off polarization for intensity and vice versa. Thus, there is an optimum filter thickness which minimizes the errors in scattering cross sections measured on an instrument using such filters. Formulae expressing the errors in measured neutron scattering cross sections are given in terms of the polarization and transmission of the filters which enable the calculation of optimum filter thickness for any given filter type once the relationship between polarization and transmission is known. Formulae for optimum counting times in each polarization state are also presented. The optimum filter thickness for different types of measurements is discussed. An analysis of the effect of instrumental background on the optimization is also presented.
The Choice of the Most Convenient Instrumental Parameters of Angular Dispersive Neutron Powder Diffractometers
Authors: Grabcev B. , Tirziu A.
Published: July 2007

A unique resolution function of angular dispersive neutron powder diffractometers, properly parametrized to be valid for a conventional instrument as well as for any of its multicrystal variants, is derived. The general formulae enable the calculation of the shapes and amplitudes of diffraction peaks for any form of scattering cross section, crystal reflectivity or collimator transmission function. The reliant analytical expressions obtained in Gaussian approximation are used in computer simulations, with different samples and single crystal monochromators, for the determination of the most convenient instrumental parameters. The results of these case studies offer reliable information that may be very useful both for designing the diffractometers and for conducting the experiments.
Moderator Decoupling Options for Structural Biology at Spallation Neutron Sources
Authors: Schoenborn Benno P. , Court John D. , Larson Allen C. , Ferguson Phil
Published: July 2007

Suitable instruments on spallation neutron sources are ideal for diffraction studies of proteins and oriented molecular complexes (Schoenborn, 1992a). With spallation neutrons and their time dependent wavelength structure, diffraction data may be readily selected electronically with an optimal wavelength bandwidth and cover the whole Laue spectrum as time (wavelength) resolved spectra. This optimizes data quality with best peak-to-background ratios and provides adequate spatial and energy resolution to eliminate diffraction peak overlaps. To maximize flux within this energy range a partially decoupled moderator concept will be discussed using calculated flux profiles, and the impact on calculated diffraction data assessed.
Polarized Neutron Diffraction with an Area-Sensitive Detector
Authors: Lee S.-H. , Majkrzak C.F.
Published: July 2007

We have developed a new technique for polarized neutron diffraction utilizing a two-dimensional, area-sensitive detector. An area-sensitive detector, used in conjunction with a transmission polarizer in the scattered beam, allows us to simultaneously measure non-spin-flip (NSF) and spin-flip (SF) scattering processes and therefore increases the data collection rate by a factor of two. An experimental test was performed on a single crystal of La5/3Srl/3NiO4 which demonstrates the advantages of this method over conventional means of polarized neutron analysis.
Applications of Specular Neutron Reflectometry in Materials Science
Authors: Majkrzak C.F.
Published: July 2007

By counting the number of neutrons elastically and specularly reflected from a flat surface, as a function of glancing incidence angle, the in-plane average of the scattering density can be deduced at any specified distance along the normal from the surface. From this scattering length density profile, the concentration of atoms of a given type at a particular depth can, subsequently, be inferred. If, in addition, the incident beam is polarized and the resultant polarization of the reflected beam is analyzed, it also becomes possible to distinguish, in microscopic detail, possible magnetic contributions to the scattering density. In this paper the fundamentals of specular neutron reflectometry are described, including both experimental technique and analysis of the measured reflectivity data. Applications of neutron reflectometry to materials science problems are also illustrated by a number of specific examples involving the determination of the structure of polymer and superconducting thin films, magnetic multi-layers, and surfaces undergoing electrochemical reactions in contact with aqueous solutions.
Multiple Small-Angle Neutron Scattering
Authors: Long Gabrielle , Krueger Susan , Allen Andrew
Published: July 2007

Over the past decade, a multiple small-angle neutron scattering (MSANS) formalism has been developed to enable researchers to derive microstructural parameters from multiply-scattered small-angle neutron data. The MSANS formalism is particularly useful in ceramic science and materials research because it is applicable to samples that are thicker (> 2 mm) and have larger scattering volume fractions (> 2%) than are commonly used in small-angle neutron scattering studies. At the same time, the microstructural size range within which microstructures are determined is extended from 10–l000 Å for small-angle neutron scattering to 800 Å– 10 µm for MSANS. This extended size range is precisely the size regime where significant materials microstructure exists. Finally, the rapidity with which MSANS data can be accumulated (on the order of minutes) compared to the typical time for small-angle neutron scattering data accumulation (on the order of hours) offers an opportunity to explore the kinetics of microstructure development in sifu.
Time-of-Flight Neutron Powder Diffraction
Authors: Richardson James W.
Published: July 2007

Intergranular or type-2 stresses are stresses on the length scale of the grains which arise from the anisotropy of plastic, elastic and thermal deformation in different crystallite orientations or in different phases in the material. In general the strain measured in a diffraction experiment will be a superposition of macroscopic and intergranular strains so it is important to be able to identify the two contributions. The experimental methods for measuring the intergranular strains with high accuracy are discussed in detail. Three case studies of major interest in materials science are examined. Intergranular strains are generated between the phases present in composite materials because of differences in thermal expansion and different plastic and elastic response to applied loads. Intergranular strains are generated in zirconium alloys through the anisotropy of the coefficients of thermal expansion as the alloy cools from the fabrication temperature and by the anisotropy of plastic deformation. Finally, intergranular strains develop in nickel-based cubic alloys from plastic and elastic anisotropy when these are plastically deformed.
Neutron Scattering from Disordered Materials
Authors: Price David Long
Published: July 2007

Studies of the structure and dynamics of disordered materials with neutron scattering techniques are described, with reference to vitreous silica for specific examples. The range of disordered materials investigated by neutron scattering is described in summary form.
High-resolution Neutron Diffraction using Larmor Precession for Angular and Wavelength Labelling
Authors: Rekveldt M.TH. , Kraan W.H.
Published: July 2007

A new high-resolution diffraction method is introduced without the confinement of using a highly collimated beam, necessary in conventional high-resolution diffraction. Larmor precession of a polarised neutron beam is used to label each neutron of the incident and scattered neutron beam with its wavelength and scattering angle. Giving the Larmor precession device front and back faces inclined over an angle adjusted to the scattering angle used, the wavelength–transmission angle relation of the Larmor precession matches precisely with the wavelength–scattering angle relation of the scattering vector. In this way the Larmor precession phases of different momentum transfers and thus the scattering vectors, can be measured with extremely high resolution. It should be possible to measure lattice constants with relative accuracy of better than 10−5, while using a low resolution beam, which means an effective intensity gain of orders of magnitude. Applications of this method are discussed.
Oxygen Partial Pressure in Outer Layers of Skin: Simulation Using Three‐Dimensional Multilayered Models
Authors: WANG WEN
Published: July 2007

Objective: Papillary loops in dermal papillae are believed to facilitate oxygen delivery to the germinal layer in the epidermis. The study aims to simulate the distribution of the oxygen partial pressure, pO2, in superficial layers of skin and to quantify oxygen supply from different sources.

Methods: A theoretical model that considered heterogeneity in tissue properties was developed based on the anatomical arrangement of the upper skin. Distribution of pO2 in tissues and in blood was solved numerically. Effects of the blood flow rate and the skin surface condition were investigated.

Results: Under normal blood flow rate and skin surface conditions, approximately one‐quarter of the oxygen consumed in the upper skin came from papillary loops. Subpapillary plexus was the main supplier, which accounted for more than 60% of the total oxygen supply. Oxygen diffusion into the skin from the air was restricted to superficial regions of the germinal layer and accounted for approximately 10% of the total oxygen uptake.

Conclusions: Papillary loops in dermal papillae facilitate oxygen delivery to the germinal layer from the circulation. The flow rate in papillary loops affects pO2 distribution in dermal papillae. In the epidermis, however, pO2 is strongly affected by skin surface conditions.
Interactions of Platelets with Subendothelium and Endothelium
Authors: CHEN JUNMEI , LÓPEZ JOSÉ A.
Published: July 2007

In this review, the authors summarize how platelets interact with subendothelium when the vessel wall is damaged or with intact endothelium in the inflammatory state. When subendothelium is exposed to rapidly flowing blood upon vessel damage, platelets adhere rapidly to the exposed surface, decelerate, and aggregate to arrest bleeding. Under high shear stress, such as is found in the microcirculation, the interaction between subendothelial von Willebrand factor (VWF) and its platelet receptor, glycoprotein (GP) Ib‐IX‐V, is required to slow down platelets and allow the platelet collagen receptors α2β1 and GP VI to bind to collagen. GP VI and α2β1 play important roles to activate platelets in the early stage and work with GP Ib‐IX‐V to fully activate platelets to form thrombi. GP Ib‐IX‐V and GP VI employ similar signaling pathways for platelet activation and the signals from both receptors are down‐modulated by PECAM‐1 (platelet–endothelial–cell adhesion molecule 1) to prevent unnecessary platelet activation under high shear. During inflammatory states, intact endothelial cells release VWF and P‐selectin from their Weibel‐Palade bodies. Both molecules are ligands for GP Ib‐IX‐V. The newly released VWF is larger and stickier than the form normally found in plasma and binds platelets spontaneously. Normally, VWF is processed by proteolysis by the plasma metalloprotease ADAMTS‐13. Failure of this processing results in the microvascular thrombotic disorder thrombotic thrombocytopenic purpura. In this review, the authors also use available crystal structures of platelet receptors and ligands to explain the details of their interactions.
A Failed Experiment: The Exportation of Fascism to Albania
Authors: Villari Giovanni
Published: July 2007

Using Italian and Albanian archive sources, this essay analyses the effectiveness of Italian policy in Albania, during the years of its union with Italy (1939–1943), in the creation of a model Fascist state and in the generation of support for Italy among the Albanian population. Through the creation of party and state structures similar to those in Italy, Fascism intended to give voice to Albanian Nationalist demands, but Italian policy was undermined by a basic defect which helped to cool any initial enthusiasm: the loss of all semblance of Albanian independence and the exploitation of local resources to the benefit of the Italians alone. The Italy-Greece conflict cast a shadow on the Fascist fighting ability which not even the creation of ‘Great Albania’ (thanks to the help of the Germans) removed. As Italy's military fortunes changed for the worse, they were forced to address a growing resistance until the tragic conclusion of 8th September 1943 and the end of the occupation.
Exploring the effects of communication intervention for developmental pragmatic language impairments: a signal‐generation study
Authors: Adams Catherine , Lloyd Julian , Aldred Catherine , Baxendale Janet
Published: July 2007

Background: The remediation of pragmatic problems forms a significant part of the caseload for professionals working with children with communication problems. There is little systematic evidence that demonstrates the benefits of speech and language therapy for children whose difficulties lie primarily within the pragmatic domain or which indicates whether changes in pragmatic behaviours, which are a result of a specific intervention, can be measured over time.

Aims: To generate a signal of change in pragmatic and other language behaviours for children with pragmatic language impairments; to gauge the magnitude and nature of the signal and to make recommendations for future studies.

Methods and Procedures: A case series of six children with pragmatic language impairments without diagnosis of autism received 8 weeks of individual intensive speech and language therapy supported in a mainstream educational setting in the UK. Measures of pragmatic behaviours in conversation were made at seven data points before and after therapy using Bishop's ALICC procedure. Conversation coders were blind to the point of assessment. Inferential comprehension, narrative, sentence formulation and sentence recall skills were also tested before and after therapy. The opinions of teachers and parents were sought regarding any change in communication and social abilities of the children over time.

Outcomes and Results: All children showed change in communication behaviour on some conversational measures, even if the child functioned at the ceiling on standardized language testing. Some conversation measures had more utility as outcome measures than others. Most children showed substantial change on standardized language measures, but there are limitations on the use of these due to heterogeneity within the group. Overall, the intervention produced a signal for change in pragmatics and/or language behaviour in all children. Parent/teacher opinion reported demonstrable change in communication behaviour and engagement in the curriculum.

Conclusions: There is a strong signal that change in pragmatic language behaviour can be measured in well‐controlled intervention studies but this signal is complex. Outcome measures should take into account changes in language processing skills that are significantly impaired in many children with PLI. For those children within the PLI group who function at ceiling on language tests, conversational measures may have the potential to signal change, but this finding has not been subjected to group study or to testing in generalized settings. Qualitative data regarding behaviour, classroom engagement and generalization of language gains will be an essential supplement to measuring progress in a diverse population.
Neuroglobin Ligand Binding Kinetics
Authors: Kiger Laurent , Uzan Julien , Dewilde Sylvia , Burmester Thorsten , Hankeln Thomas , Moens Luc , Hamdane Djemel , Baudin‐Creuza Veronique , Marden Michael C.
Published: July 2007

Neuroglobin, cytoglobin, and hemoglobins from Drosophila melanogaster and Arabidopsis thaliana were studied for their ligand binding properties versus temperature. These globins have a common feature of being hexacoordinated (via the distal histidine) under deoxy conditions, displaying an enhanced amplitude for the alpha absorption band at 560 nm. External ligands can bind, but the transition from the hexacoordinated form to the ligand (L) bound species is slow, as expected for a replacement reaction Fe‐His ↔ Fe ↔ Fe‐L. Histidine binding is on the order of 1 ms; dissociation times are variable, and may be as long as 1 s for the highest histidine affinities. Oxygen binds rapidly but dissociates slowly, requiring as much as 1 s. These rates would correspond to a very high affinity for the pentacoordinated form; however, competition with the distal histidine leads decreases the affinity for the external ligand. The observed oxygen affinity remains in the range of 1 to 10 mm Hg. The low oxygen dissociation indicates a stabilization via H‐bonds as for certain globins from parasites (Ascaris, the trematodes). Other ligands such as CO, or CN for the ferric form, show a decreased affinity, since only the competition with the E7 histidine, but not the stabilizing H‐bond, plays a role. In addition, the competitive internal ligand leads to a weaker observed temperature dependence of the ligand affinity, since the difference in equilibrium energy for the two ligands is much lower than that of ligand binding to pentacoordinated hemoglobin. This effect could be of biological relevance for certain organisms, since it would lead to an oxygen affinity that is nearly independent of temperature.
IUBMB Life, 56: 709‐719, 2004
Fatty acid composition and chilling resistance in the green alga Caulerpa prolifera (forrskal) lamouroux (Chlorophyta, caulerpales)
Authors: Terrados Jorge , Lopez‐Jimenez Jose Angel
Published: July 2007

Plant resistance to chilling injury depends on the maintenance of membrane functions. An increase in the degree of unsaturation of membrane fatty acids can help maintain membrane function at low temperatures by reducing the temperature at which deleterious membrane phase‐transitions occur. The fatty acid composition of membranes of the chlorophycean Caulerpa prolifera was determined in summer and winter in the Mar Menor coastal Lagoon (SE Spain). In January the percentage of polyunsaturated fatty acids was higher than in August. Membrane content of mono‐ and diunsaturated fatty acids was similar in the two seasons. The unsaturation index of membranes changed from 76.15 ± 1.80 (mean ± standard error) in August to 128.05 ± 0.32 in January. It is suggested that this increase in the degree of unsaturation might be important to allow C. prolifera to decrease its lower threshold of survival temperature and acclimate net photosynthesis and dark respiration rates to winter temperatures in the Mar Menor.
Paraquat induced DNA damage by reactive oxygen species
Authors: Ali Shakir , Jain S. K. , Abdulla Mohamed , Athar Mohammad
Published: July 2007

The redox cycling contact herbicide paraquat (PQ) causes oxidative damage to pulmonary tissue. PQ is reduced enzymatically to PQ radical in lung where it reacts with molecular oxygen, generating reactive oxygen species (ROS). ROS damage various macromolecules including DNA. However, the ability of paraquat to mediate DNA damage is unknown. In this study, Bam H1 site (5′‐GGATCC‐3′) on pBR322 DNA was chosen as the target sequence for a study of the PQ‐mediated DNA damage. The incubation of PQ with plasmid DNA in the presence of freshly prepared rat lung microsomes and NADPH resulted in damage to the restriction site. The PQ‐treated DNA was not digested with the endonuclease reflected by the digestion pattern of DNA on agarose gels. The effect was dependent on the dose of PQ. The PQ‐mediated damage to DNA was comparable to DNA damage caused by ROS generated through the xanthine‐xanthine oxidase system. The results of the present study suggest that ROS generated by PQ in vitro under aerobic conditions may lead to a modification of the restriction site on DNA.