Search Results - (Author, Cooperation:A. W. Thompson)

2014-01-11

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Bacteriophages ; Carbon/*metabolism ; Cell Membrane/*metabolism/ultrastructure ; DNA, Bacterial/analysis/*metabolism ; Prochlorococcus/*metabolism/ultrastructure/virology ; Seawater/chemistry/*microbiology

2012-09-22

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Calcification, Physiologic ; Carbon/metabolism ; Cyanobacteria/cytology/genetics/isolation & purification/*physiology ; Genes, rRNA ; Genome, Bacterial ; Haptophyta/cytology/genetics/isolation & purification/*physiology ; Molecular Sequence Data ; Nitrogen/metabolism ; *Nitrogen Fixation ; Pacific Ocean ; *Photosynthesis ; Phytoplankton/cytology/genetics/isolation & purification/*physiology ; Seawater/*microbiology ; *Symbiosis

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A new instrument (Station 9.5) has been established on the wiggler line at the Daresbury Synchrotron Radiation Source (SRS). It extends the experimental capability at Daresbury for macromolecular crystallography beyond what is provided for with Stations 7.2 (Ref. 1), 9.6 (Ref. 2), and 9.7 by providing a point focused white beam (from a Pt-coated toroid mirror) and/or a rapidly tunable monochromatic beam (using a water-cooled double-crystal monochromator (Ref. 3). The design principles of the new Station 9.5 have been published (Ref. 4). A CCD detector for the station is being developed (preliminary work is described in Ref. 5, or see the additional poster at this meeting) to allow time slices of part of a diffraction pattern to be measured. Laue patterns are currently recorded on film, but access to an image plate detector will shortly become available. Shutter speeds down to 50 μs are routinely available using a rotating disk shutter (Ref. 6). Fluorescence detectors are available for optimized anomalous dispersion data collection. The experimental bench is long enough to accommodate a camera system, and downstream from it an "on-line'' image plate scanner. Data collected on the instrument in various modes of operation will be described for a variety of macro and small molecule crystal systems.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Crystal structure solution by anomalous dispersion methods has been greatly facilitated using the rapidly tunable station 9.5 at the Daresbury SRS. Both SIROAS and MAD techniques, with IP data, have been used in the phasing of a brominated nucleotide and a seleno deaminase, respectively. The electron density maps in each case are interpretable. Throughput of projects could be improved upon with a better duty cycle detector. Another category of data collection is that at very high resolution. Detailed structure refinement pushes the limits of resolution and data quality. Station 9.5 has been used to collect high resolution (1.4 A(ring)) native data for the protein concanavalin A. This utilized very short wavelengths (0.7 A(ring)), the image plate, and crystal freezing. A total of 155 407 measurements from two crystals benefited from the on-line nature of the IP detector device, but a slow and quick pass are required to capture the full dynamic range of the data. There are data seen to 1.2 A(ring) and beyond for a pure Mn substituted form of the protein, but a higher intensity still is required to actually record these data. By comparison, trials at CHESS, on a multipole wiggler (station A1) with a CCD (without image intensifier) system, yield native concanavalin A data to 0.98 A(ring) and beyond. This demonstrates that the combination of yet higher intensity and the ease of use of a CCD offers worthwhile improvements; in this case an increase in the data by a factor of (1.4/0.98)3, thus at least doubling the data to parameter ratio for protein structure model refinement and potentially opening up direct structure determination of proteins of the size of concanavalin A (25 kDa).Finally, possibilities at ESRF and further detector developments, such as mosaic CCDs and scintillator coatings, offer further impetus for the field. These include more intense rapidly tunable beams for anomalous dispersion-based structure solution and "ideal'' higher resolution data collection and reactivity studies. ESRF BL19 is described; facilities on BL19 will include a system for freezing and storing crystals at cryogenic temperatures, so that data can be recorded from the same crystal on different runs. Overall, there have been tremendous strides made in this field in the last 15 years, and yet further improvements are to come. © 1995 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

There exists considerable promise for the use of charge-coupled device (CCD) imagers in the fast recording of parts of macromolecular crystal Laue diffraction patterns. As part of this development CCD tests have been made with direct detection of Laue patterns from a small molecule test crystal and a protein crystal. Merging R factors (on intensity), for strong reflections, of 3% have been obtained. A time-slicing scheme for a CCD camera is discussed based on the stacking of slices held in storage in the CCD in the submillisecond time resolution range.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

A focused white beam from existing synchrotrons has an intensity comparable with the monochromatic beams available from future undulator beamlines. The beam from station 9.5 on the SRS has therefore been used to examine the radiation damage caused within a protein crystal, cooled to near liquid nitrogen temperature. It was found that observable radiation damage occurred at doses comparable with those which have been observed in cryo-electron microscopy. It would be possible to collect many data sets from the test lysozyme crystal before radiation damage occurred under these conditions. However, it would not be possible to collect a good quality data set from a single protein crystal of a few tens of microns in size, even at liquid nitrogen temperature.

Electronic Resource

1460-2695

Blackwell Publishing Journal Backfiles 1879-2005

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Fundamental understanding of fracture requires accurate interpretation of fractography. Examples are drawn from recent work on titanium aluminide alloys based on both Ti3Al and TiAl. Although the fracture mode in these alloys is often characterized as “cleavage”, in reality the fracture surfaces are neither entirely cleavage-like, nor do the “cleavage” regions generally correspond to the classical description of cleavage. Implications of such fractographic observations, and of model fracture calculations, are discussed. Needs for further work to clarify fracture processes are also identified.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The white synchrotron radiation beam from a storage ring diverges from a small region at the tangent point of the beam line. A narrow wavelength band can be selected from this beam by reflection from a crystal monochromator; a cylindrically curved monochromator produces a converging X-ray beam. At ...

Electronic Resource

0035-8118

Romance Studies

REVIEWS

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Microstructural changes in Cu-2.5wt % Ti during ageing at 573 and 773 K have been studied by transmission electron microscopy. Ageing times ranged from 60 sec to 200 h. Ordering of theβ′ precipitates was observed after very short ageing treatments at 773 K, and coarsening according tot 1/3 was also observed from very early times. Theβ′ particles were observed to become increasingly aligned into rod-like groups along 〈10 0〉 as ageing progressed. These results permit a new interpretation of the strengthening mechanisms in this alloy.

Electronic Resource