Investigation of craze development using small-angle X-ray scattering of synchrotron radiation

The development of crazes in polycarbonate was investigated with the method of ultra-small-angle X-ray scattering (USAXS) of synchrotron radiation. Measurements at different temperatures and with different draw rates were carried out. The two-dimensional scattering patterns were analyzed by means of a fibrillar model of the craze. The geometrical parameters of the craze as a function of the macroscopic draw ratio were determined by using a curve-fitting procedure. From the measured values of the diameter and the mean distance of the fibrils, it is possible to calculate the volume fraction v_f of the fibrils directly. Additional scattering caused by submicrocracks is discussed.     

Investigation of the topological shape of bovine serum albumin in solution by small-angle x-ray scattering at Beijing synchrotron radiation facility

This paper reports that at a newly constructed small-angle x-ray scattering station of Beijing Synchrotron Radia- tion Facility, the topological shape of ligand-free bovine serum albumin in solution has been investigated. An appropriate scattering curve is obtained and the calculated value of the gyration radius is 31.2~=t=0.25 ~_ （11=0.1 nm） which is co- incident with other ones＇ results. It finds that the low-resolution structure models obtained by making use of ab initio reconstruction methods are fitting the crystal structure of human serum albumin very well. All of these results perform the potential of the beamline to apply to structural biology studies. The characteristics, the defects, and the improving measures of the station in future are also discussed.     

Self—assembly behaviour of amphiphilic diblock copolymer in selective solvents studied by synchrotron small—angle x—ray scattering

The aggregation behaviour of styrene-vinyl benzoic acid (PS_m-b-PVBA_n) amphiphilic diblock copolymers in selective solvents with different m and n was investigated by synchrotron small-angle x-ray scattering (SAXS). We have carried out a detailed analysis of scattering intensity, dimension, shape and microstructure of the diblock copolymers of narrow distribution in water, methanol, ethanol and isopropanol selective solvents, respectively. We have found that the aggregation behaviour of the copolymer depends on the nature of the solvent and the micelle forms flat disc objects with the ratio of radius ω=0.4. The average radius gyration R_g of the copolymer decreases as solvents change from isopropanol to ethanol and to methanol, and increases with increasing pH in aqueous solution, but decreases with the addition of CoCl_2 in ethanol solvent. The scattering intensity of diblock copolymer micelle follows I(h)∝h^{-α} in different selective solutions, suggesting that the PS_m-b-PVBA_n coils have self-similar structure behaviour or a fractal structure in the selective solvents. All of these revealed that the aggregation behaviour of the diblock copolymer changes dramatically with experimental condition in the selective solvent. The increase of mass fractal dimension (D_m) from 2.12 to 2.47 indicates that the copolymer chain changes from a swollen coil to a rather compact disc in the course of changing solvents, decreasing surface fractal dimension (D_s) from 2.98 to 2.58 indicates that the copolymer micelle change from a rather rough surface to a smooth form in the course of increasing pH in aqueous solutions, and increasing D_m and D_s from 2.29 to 2.35 and 2.70 to 2.90, respectively, indicates the shrinkage of copolymer micelle to a rather compact and rough disc form by adding CoCl_2 in ethanol solvents.     

High pressure x-ray diffraction techniques with synchrotron radiation

This article summarizes the developments of experimental techniques for high pressure x-ray diffraction(XRD) in diamond anvil cells(DACs) using synchrotron radiation. Basic principles and experimental methods for various diffraction geometry are described, including powder diffraction, single crystal diffraction, radial diffraction, as well as coupling with laser heating system. Resolution in d-spacing of different diffraction modes is discussed. More recent progress, such as extended application of single crystal diffraction for measurements of multigrain and electron density distribution, timeresolved diffraction with dynamic DAC and development of modulated heating techniques are briefly introduced. The current status of the high pressure beamline at BSRF(Beijing Synchrotron Radiation Facility) and some results are also presented.     

High-pressure studies with nuclear scattering of synchrotron radiation

Hyperfine Interactions - The nuclear forward scattering (NFS) of synchrotron radiation is especially suited for probing magnetism at high pressure (h.p.), here in the Mbar range, by the nuclear...     

Introduction to nuclear resonant scattering with synchrotron radiation

The concepts leading to the application of synchrotron radiation to elastic and inelastic nuclear resonant scattering are discussed. The resulting new experimental techniques are compared to conventional Mössbauer spectroscopy. A survey of situations that favor experiments with synchrotron radiation is offered.

     

Positive deviation from debye‘s theory in small—angle x—ray scattering

The small-angle x-ray scattering (SAXS) resulting from a non-ideal two-phase system having sharply defined phase boundaries but with micro-fluctuations of electron density within any phase shows a positive deviation from Debye's theory. We have found a simple method suitable for fitting the slit-smeared SAXS data and correcting the positive deviation. The validity of this procedure is tested on porous ZrO_2 xerogel prepared using the sol-gel process.     

Nuclear resonant scattering of synchrotron radiation

Hyperfine Interactions -     

Nuclear resonant scattering of synchrotron radiation

The principal ideas of the theory and the main results of the experimental studies of the coherent resonant scattering of-radiation by nuclear ensembles in matter are briefly over-viewed. An analysis of transmission of the Mössbauer-radiation and of synchrotron radiation through a nuclear resonant medium is suggested using an approach based on the optical theory. The feasibilities of the nuclear resonant scattering of synchrotron radiation as a new technique for studying the hyperfine interactions and some other phenomena of the physics of condensed matter are considered.     

Nuclear resonant scattering using synchrotron radiation

A one-dimensional quantum model for nuclear resonant scattering using synchrotron radiation has been developed. This model gives a clear physical interpretation of the most prominent features of the coherent forward scattering process namely, the “speed-up” and “dynamical beat” effects. The form of the solution, for the time-dependent forward scattered intensity of the resonant radiation from the resonant medium after synchrotron radiation excitation, is a finite series. This unique solution can be interpreted in terms of a summation over all multiple forward scattering paths the radiation takes in reaching the detector. The resonant medium is represented by a linear chain of N effective resonant nuclei. The analysis starts from a coupled set of quantum mechanical equations for the relevant amplitudes in frequency space. Transformation to the time domain gives an analytical expression for the forward scattered intensity. The contribution of every order of the multiple scattering processes from the N effective nuclei appears naturally. The expression gives a clear physical understanding of all relevant aspects of resonant forward nuclear scattering. Furthermore, the present formalism allows the consideration of incoherent processes. This permits the study of processes in which there is gamma emission with recoil or emission of internal-conversion electrons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Perturbed nuclear scattering of synchrotron radiation

Mössbauer spectroscopy in the time domain with SR as a source may become a powerful tool in investigations of time-dependent hyperfine interactions caused by external perturbations. This is firstly due to the easy possibility to synchronize the excitation of the nuclei with an external perturbation and secondly due to the insensitivity of Mössbauer time spectra to mechanical vibrations which are generated in samples by these perturbations. As a particular case of perturbed nuclear scattering, the coherent scattering under conditions of 90°- and 180°-switching of the magnetic hyperfine field direction is considered. The results of the first experimental studies are discussed.     

Fixed-exit channel-cut crystal x-ray monochromators for synchrotron radiation

Two types of fixed-exit channel-cut crystal x-ray monochromators are proposed. In both monochromators the groove walls are not parallel. The fixed position of exit beam is achieved by coupling the rotation of crystal with its radial or axial translation.The author is indebted to Dr. S. Mobilio from INFN Frascati and Dr. V. Holý from University J. E. Purkyn Brno for valuable discussion.     

Nuclear Resonant scattering experiments with synchrotron radiation at KEK

Experiments of nuclear Resonant scattering carried out at PF and TRISTAN-AR of KEK are described, which include nuclear Bragg scattering in time domain as well as energy domain, time-resolved nuclear resonant forward scattering, and interferometric studies.     

Structural modeling of proteins by integrating small-angle x-ray scattering data

Elucidating the structure of large biomolecules such as multi-domain proteins or protein complexes is challenging due to their high flexibility in solution. Recently, an "integrative structural biology" approach has been proposed, which aims to determine the protein structure and characterize protein flexibility by combining complementary high- and lowresolution experimental data using computer simulations. Small-angle x-ray scattering(SAXS) is an efficient technique that can yield low-resolution structural information, including protein size and shape. Here, we review computational methods that integrate SAXS with other experimental datasets for structural modeling. Finally, we provide a case study of determination of the structure of a protein complex formed between the tandem SH3 domains in c-Cb1-associated protein and the proline-rich loop in human vinculin.