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11,767 items found (0 items not approved), displaying 11,601 to 11,610.[First/Prev] 1,157, 1,158, 1,159, 1,160, 1,161, 1,162, 1,163, 1,164 [Next/Last]

Instruments / Technical Area	Publication Details	Published
	Tracking the motion of charges in a terahertz light field by femtosecond X-ray diffraction A. Cavalleri , S. Wall , C. Simpson , E. Statz , D. W. Ward , K. A. Nelson , M. Rini , R. W. Schoenlein Nature 442 (7103), 664 - 666 DOI: 10.1038/nature05041 Show Abstract ▼ Abstract: In condensed matter, light propagation near resonances is described in terms of polaritons, electro-mechanical excitations in which the time-dependent electric field is coupled to the oscillation of charged masses. This description underpins our understanding of the macroscopic optical properties of solids, liquids and plasmas, as well as of their dispersion with frequency. In ferroelectric materials, terahertz radiation propagates by driving infrared-active lattice vibrations, resulting in phonon-polariton waves. Electro-optic sampling with femtosecond optical pulses3, 4, 5 can measure the time-dependent electrical polarization, providing a phase-sensitive analogue to optical Raman scattering6, 7. Here we use femtosecond time-resolved X-ray diffraction8, 9, 10, a phase-sensitive analogue to inelastic X-ray scattering11, 12, 13, to measure the corresponding displacements of ions in ferroelectric lithium tantalate, LiTaO3. Amplitude and phase of all degrees of freedom in a light field are thus directly measured in the time domain. Notably, extension of other X-ray techniques to the femtosecond timescale (for example, magnetic or anomalous scattering) would allow for studies in complex systems, where electric fields couple to multiple degrees of freedom	Aug 2006
	The life cycle of nanoparticles in Acid Mine Drainage: An in situ synchrotron study L. E. Davidson , L. G. Benning , S. Shaw , N. J. Terrill Geochimica Et Cosmochimica Acta 70 (18), A131 16th Annual V M Goldschmidt Conference DOI: 10.1016/j.gca.2006.06.278 Show Abstract ▼ Abstract: Owing to their high surface area and increased surface reactivity, iron oxyhydroxide nano-phases in natural and contaminated environments play an important role in many processes which control the cycling and bioavailability of trace contaminants (e.g., As). Schwertmannite (SW), a poorly ordered iron oxyhydroxy-sulphate that typically forms in low pH (2.5 < pH < 4.5), high [SO4] aqueous environments (i.e., Acid Mine Drainage, AMD), is known to effectively remove toxic species from solution. However, the pathways leading to its formation and crystallisation have so far not been quantified. Here, we present new data using in situ time-resolved synchrotron-based Small Angle X-ray Scattering (SAXS) and Energy Dispersive X-ray Diffraction (EDXRD) to characterise the nucleation, growth, and transformation of schwertmannite.	Aug 2006
	Blind crystal structure prediction of a novel second polymorph of 1-hydroxy-7-azabenzotriazole Harriott Nowell , Christopher S. Frampton , Julie Waite , Sarah L. Price Acta Crystallographica Section B Structural Science 62, 642-650 DOI: 10.1107/S0108768106012584 PMID: 16840814 Show Abstract ▼ Abstract: The commercially available peptide coupling reagent 1-hydroxy-7-azabenzotriazole has been shown to crystallize in two polymorphic forms. The two polymorphs differ in their hydrogen-bonding motif, with form I having an R-2(2)(10) dimer motif and form II having a C(5) chain motif. The previously unreported form II was used as an informal blind test of computational crystal structure prediction for flexible molecules. The crystal structure of form II has been successfully predicted blind from lattice-energy minimization calculations following a series of searches using a large number of rigid conformers. The structure for form II was the third lowest in energy with form I found as the global minimum, with the energy calculated as the sum of the ab initio intramolecular energy penalty for conformational distortion and the intermolecular lattice energy which is calculated from a distributed multipole representation of the charge density. The predicted structure was sufficiently close to the experimental structure that it could be used as a starting model for crystal structure refinement. A subsequent limited polymorph screen failed to yield a third polymorphic form, but demonstrated that alcohol solvents are implicated in the formation of the form I dimer structure.	Aug 2006
	Identification of CO adsorption sites in supported Pt catalysts using high-energy-resolution fluorescence detection X-ray spectroscopy Olga Safovova , Moniek Tromp , J A Van Bokhoven , Frank M.f. De Groot , John Evans , Pieter Glatzel Journal Of Physical Chemistry B 110 (33), 1616216164 DOI: 10.1021/jp063416t Show Abstract ▼ Abstract: High-energy-resolution fluorescence detection (HERFD) X-ray spectroscopy is presented as a new tool for the identification of the bonding sites of reactants in supported metal catalysts. The type of adsorption site of CO on an alumina-supported platinum catalyst and the orbitals involved in the bonding are identified. Because X-ray absorption spectroscopy (XAS) is element-specific and can be used under high pressures and temperatures, in situ HERFD XAS can be applied to a swathe of catalytic systems, including alloys.	Aug 2006
Controls Diagnostics	Bunch purity measurement for Diamond C. A. Thomas , G. Rehm , H. L. Owen , N. G. Wyles , S. W. Botchway , V. Schlott , M. Wahl Nuclear Instruments & Methods In Physics Research Section A-accelerators Spectrometers Detectors And Associated Equipment 566 (2), 762-766 DOI: 10.1016/j.nima.2006.07.059 Show Abstract ▼ Abstract: Measurement of the fill pattern of synchrotron storage rings is important for several reasons, including checking the quality of the injection system and the generation of special fill patterns for time-resolved experiments. For the new national X-ray facility based on the Diamond 3 GeV electron storage ring, it is planned to measure the beam quality in a short time of several minutes by using a time-correlated single photon counting method. The method has very good time resolution (50 ps) and high dynamic range (more than six orders of magnitude). In this paper, we describe our experimental setup, a series of tests to evaluate the system limitations using short pulse lasers on laboratory test benches, the existing SRS national X-ray facility, and the third-generation synchrotron radiation facility SLS. Taking all these results together, we are able to predict the system performance for Diamond.	Aug 2006
	Membrane's Eleven: heavy-atom derivatives of membrane-protein crystals Preben Morth , Thomas Sorensen , Poul Nissen Acta Crystallographica Section D Biological Crystallography 62 (8), 877 - 882 DOI: 10.1107/S0907444906023547 PMID: 16855303 Show Abstract ▼ Abstract: A database has been assembled of heavy-atom derivatives used in the structure determination of membrane proteins. The database can serve as a guide to the design of experiments in the search for heavy-atom derivatives of new membrane-protein crystals. The database pinpoints organomercurials, platinum(II) and trimethyllead compounds as being particularly useful. On the other hand, lanthanide and uranyl compounds are poorly represented, which may be a consequence of these compounds having aggressive effects in crystal-soaking procedures. Furthermore, the database highlights the variety of methods applied in the preparation of heavy-atom-derivatized crystals and in phasing. Cocrystallization can be further exploited. Phases have predominantly been obtained by SIRAS/MIRAS methods rather than SAD/MAD in recent structure determinations.	Aug 2006
	4-Fluoroproline derivative peptides: effect on PPII conformation and SH3 affinity Paolo Ruzza , Giuliano Siligardi , Arianna Donella-deana , Andrea Calderan , Rohanah Hussain , Chiara Rubini , Luca Cesaro , Alessio Osler , Andrea Guiotto , Lorenzo A. Pinna , Gianfranco Borin Journal Of Peptide Science 12 (7), 462-471 DOI: 10.1002/psc.750 PMID: 16506148 Show Abstract ▼ Abstract: Eukaryotic signal transduction involves the assembly of transient protein-protein complexes mediated by modular interaction domains. Specific Pro-rich sequences with the consensus core motif PxxP adopt the PPII helix conformation upon binding to SH3 domains. For short Pro-rich peptides, little or no ordered secondary structure is usually observed before binding interactions. The association of a Pro-rich peptide with the SH3 domain involves unfavorable binding entropy due to the loss of rotational freedom on forming the PPII helix. With the aim of stabilizing the PPII helix conformation in the Pro-rich HPKI decapeptide PPPLPPKPKF (P2), a series of P2 analogues was prepared, in which specific Pro positions were alternatively occupied by 4(S)- or 4(R)-4-fluoro-L-proline. The interactions of these peptides with the SH3 domain of the HPK1-binding partner HS1 were quantitatively analyzed by the NILIA-CD approach. A CD thermal analysis of the P2 analogues was performed to assess their propensity to adopt the PPII helix conformation. Contrary to our expectations, the K-d values of the analogues were lower than that of the parent peptide P2. These results clearly show that the induction of a stable PPII helix conformation in short Pro-rich peptides is not sufficient to increase their affinity toward the SH3 domain and that the effect of 4-fluoroproline strongly depends on the position of this residue in the sequence and the chirality of the substituent in the pyrrolidine ring. Copyright (c) 2006 European Peptide Society and John Wiley & Sons, Ltd.	Jul 2006
Power Supplies	Diamond Storage Ring Power Converters John Dobbing EPAC'06	Jul 2006
	X-ray polycapillary characterization and 3D imaging properties Dariush Hampai , Giorgio Cappuccio , Giannantonio Cibin , Sultan B. Dabagov , Vito Sessa International Conference on Charged and Neutral Particles Channeling Phenomena II Show Abstract ▼ Abstract: Radiation sources ; Channeling radiation ; Channeling ; X-ray sources ; X radiation ; Experimental study ; Experimental data ; Design ; Modelling ; Ray tracing ; Polycapillary optics ; Cylindrical lens ; Astrophysical plasma ; Angular measurement ; Optical focusing ;	Jul 2006
	High Throughput In Situ XAFS Screening of Catalysts Nikolaos Tsapatsaris , Angela M. Beesley , Norbert Weiher , Helen Tatton , Andy J. Dent , Frederick J. W. Mosselmans , Moniek Tromp , Sergio Russu , John Evans , Ian Harvey , Shusaku Hayama , Sven L. M. Schroeder 13th International Conference on X-ray Absorption Fine Structure (XAFS13) DOI: 10.1063/1.2644604 Show Abstract ▼ Abstract: We outline and demonstrate the feasibility of high?throughput (HT) in situ XAFS for synchrotron radiation studies. An XAS data acquisition and control system for the analysis of dynamic materials libraries under control of temperature and gaseous environments has been developed. The system is compatible with the 96?well industry standard and coupled to multi?stream quadrupole mass spectrometry (QMS) analysis of reactor effluents. An automated analytical workflow generates data quickly compared to traditional individual spectrum acquisition and analyses them in quasi?real time using an HT data analysis tool based on IFFEFIT. The system was used for the automated characterization of a library of 91 catalyst precursors containing ternary combinations of Cu, Pt, and Au on ??Al2O3, and for the in situ characterization of Au catalysts supported on Al2O3 and TiO2.	Jul 2006

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