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Abstract: The structural response of the nootropic drug piracetam (2-oxo-pyrrolidineacetamide) to both direct compression and high-pressure recrystallization from aqueous solution is reported. Crystals obtained by these methods have been characterized in situ by single-crystal X-ray diffraction. Compression of form II between pressures of 0.45-0.70 GPa caused a reversible, single- crystal to single-crystal transition to give a new polymorph, form V. Crystallization from a dilute aqueous solution of piracetam at a pressure of 0.6 GPa via crystallization of high-pressure ice-VI resulted in the formation of a previously unreported dihydrate. The molecular packing arrangements of these new structures are compared with the known polymorphs and hydrates of piracetam. This study highlights how the systematic variation of pressure is a powerful method for the exploration of polymorphism and solvate formation and has the potential to add a further dimension to polymorph screening of pharmaceuticals.
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May 2007
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Abstract: We have used x-ray magnetic circular dichroism to study the element specific magnetic properties of ultrathin films of the Heusler alloy Co 2 MnGa
Co2MnGa
at room temperature. Nine films were grown by molecular beam epitaxy on GaAs substrates and engineered to vary in stoichiometry as Co 1.86 Mn 0.99 Ga 1
Co1.86Mn0.99Ga1
, Co 1.95 Mn 0.98 Ga 1
Co1.95Mn0.98Ga1
, and Co 1.97 Mn 0.96 Ga 1
Co1.97Mn0.96Ga1
, with thicknesses of 5.3, 7.6, and 9.7nm
9.7nm
, and were capped with Al to prevent oxidization. Sum rule analysis revealed magnetic moments significantly lower than the values predicted theoretically, especially in the case of the Mn total magnetic moment. The results do not support the hypothesis that a large magnetic moment is transferred from Co to Mn, and may suggest that diffusion and reacted layers at ultrathin thicknesses can effect the establishment of a full Heusler structure.
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May 2007
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Abstract: Ruthenium modified carbon supported platinum catalysts have been shown to have a similar activity towards carbon monoxide oxidation as conventionally prepared bimetallic PtRu alloy catalysts. In this study the effect of the applied electrode potential and potential cycles on the location and oxidation state of the Ru species in such Ru modified Pt/C catalysts was investigated using in situ EXAFS collected at both the Ru K and Pt L3 absorption edges. The as prepared catalyst was found to consist of a Pt core with a Ru oxy/hydroxide shell. The potential dependent data indicated alloying to form a PtRu phase at 0.05 V versus RHE and subsequent dealloying to return to the Ru oxy/hydroxide decorated Pt surface at potentials greater than 0.7 V. The Ru–O distances obtained indicate that both Ru3+ and Ru4+ species are present on the surface of the Pt particles at oxidising potentials; the former is characteristic of the as prepared Ru modified Pt/C catalyst and following extensive periods at potentials above 0.7 V and the latter of the Ru oxide species on the PtRu alloy.
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May 2007
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[1220]
Abstract: 1H-3-Hydroxy-4-oxoquinaldine 2,4-dioxygenase (HOD) is a cofactor-devoid dioxygenase that is involved in the anthranilate pathway of quinaldine degradation. HOD has been proposed to belong to the [alpha]/[beta]-hydrolase-fold superfamily of enzymes. N-terminally His6-tagged HOD has been crystallized by the hanging-drop vapour-diffusion method using sodium/potassium tartrate as a precipitant and CuCl2 as an additive. The structure was solved by the single anomalous dispersion (SAD) technique using data collected to 3.5 Å resolution at the Cu absorption peak wavelength. The crystals belong to the primitive tetragonal space group P43212, with unit-cell parameters a = b = 153.788, c = 120.872 Å.
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May 2007
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Accelerator Physics
Diagnostics
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Abstract: This paper describes the designs and initial tests of the transverse multibunch feedback system under development at Diamond. The system is designed to damp instabilities up to 200 MHz in both the vertical and horizontal planes. This will lead to an increase of effective instability thresholds which will permit a reduction of chromaticity and thus should improve dynamic aperture and lifetime.
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May 2007
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Accelerator Physics
Diagnostics
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Abstract: We present a set of four complementary measurements of the synchrotron visible light to characterise the stored electron beam at Diamond in the time domain. The electron bunch profiles and its evolution are measured with picosecond accuracy using a dual sweep streak camera. The beam dynamics are also given by a fast photodiode connected to a fast oscilloscope. The fill pattern is measured using a time correlated single photon counting system which has a high dynamic range for bunch purity measurement, and a fast averaging card which gives the fill structure with a high accuracy within a short integration time. We describe our set of instruments, discuss their performance and show first results from measurements at Diamond.
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May 2007
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Accelerator Physics
Controls
Diagnostics
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Abstract: We present our experience with the Libera Electron Beam Position Monitor (EBPM) during the first months of operation at Diamond. Measurement noise and beam current dependence with beam are compared to earlier lab measurements. Where discrepancies between the performance in the lab and in the application are observed, the causes have been investigated. Furthermore, results of the integration of the EBPMs into a Fast Orbit Feedback (FOFB) system are presented, uncluding measurements, of orbit motion spectra with and without FOFB.
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May 2007
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Diagnostics
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Abstract: Third generation Synchrotron Light Sources with vertical beam sizes down to few microns require beam resolutions on the submicron level. Study of different Beam Position Monitors (BPM) geometries has been done to reach such tight requirements. The used Matlab Graphical User Interface (GUI) is based on the simulation of a charged particle inside a selectable vacuum chamber type, computing the induced signal that it produces on the button feedthroughs. Needed parameters for the computation are the button electrode dimensions, vacuum chamber profile, electron beam current and measurement bandwidth. Output results from the GUI are the induced power on the feedthroughs, BPM sensitivity and intrinsic resolution of the analyzed geometry. As sensitivity and resolution are BPM geometry dependent terms, the Matlab GUI turned out to be an easy and fast way for first step geometry analysis.
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May 2007
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Abstract: Core/shell nanoparticles of M–B (M = Fe, Co) with amorphous and mixed amorphous + bcc-Fe core have been synthesized by chemical reduction of metallic salts by sodium borohydride. The XANES spectra show the existence of a surface layer consisting of metallic hydroxides in a percentage around 15 at.%. The EXAFS reveals the existence of short-range order in the amorphous core with a contribution from the M–O pairs of the shell and a variation of the coordination numbers with respect to bulk alloys. The existence of Fe-bcc in the mixed alloys is observed in the Fourier transform of the EXAFS data.
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Apr 2007
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Abstract: Cardiovascular stents are commonly made from 316L stainless steel and are deployed within stenosed arterial lesions using balloon expansion. Deployment involves inflating the balloon and plastically deforming the stent until the required diameter is obtained. This plastic deformation induces static stresses in the stent, which will remain for the lifetime of the device. In order to determine these stresses, finite element models of the unit cells of geometrically different, commercially available balloon expandable stents have been created, and deployment and elastic recoil have been simulated. In this work the residual stresses associated with deployment and recoil are compared for the various stent geometries, with a view to establishing appropriate initial stress states for fatigue loading for the stents. The maximum, minimum, and mean stresses induced in the stent due to systolic/diastolic pressure are evaluated, as are performance measures such as radial and longitudinal recoil.
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Apr 2007
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