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abstracts
New and improved synchrotron radiation sources enable experiments that demand the ability to acquire successive hard (e.g., 10 keV) x-ray images at sub-microsecond rates or to quickly acquire x-ray patterns encompassing intensities that vary by 10^6 or more across single images. We describe two novel integrating Pixel Array Detectors (PADs) developed at Cornell University that accomplish these objectives. The Mixed-Mode PAD (MM-PAD) frames at > 1 KHz and can readily detect signals within a single image ranging from single x-rays to over 107 x-rays/pixel/frame. The Keck-PAD can acquire 8-12 successive images at frame rates approaching 10 MHz with a range of single x-rays up to about 10^4 x-rays/pixel/frame. The operating principles of the MM-PAD and Keck-PAD, respectively, are described. We also describe examples of experiments that have been performed at various synchrotron radiation sources.
abstracts
High pressures encountered in the biosphere (i.e., at the bottom of the oceans) have extraordinary effects on biological molecules and assemblies. These include pressure denaturation of proteins, as well as dramatic changes in protein monomer-multimer association, substrate binding, membrane ion transport, transcription/translation of DNA & RNA, virus infectivity, enzyme kinetics, and conformational states of proteins. Yet practically all the biomolecules involved are highly incompressible. The challenge is to understand how pressure affects structure and to elucidate the relevant physical mechanisms for the observed effects even though the volume changes are very small. X-ray crystallography of proteins under high pressure conditions will be described. It is seen that the key point is not the magnitude of the structural changes, but rather the way differential compressibility of different parts of the protein affect functionality.
