Modern Geometry

n/

Hard Real Time Quick Exafs Data Acquisition With All Open Source Software on a Commodity Personal Computer.

We describe here the data acquisition subsystem of the Quick EXAFS (QEXAFS) experiment at the National Synchrotron Light Source of Brookhaven National Laboratory. For ease of future growth and flexibility, almost all software components are open source with very active maintainers. Among them, Linux running on x86 desktop computer, RTAI for real-time response, COMEDI driver for the data acquisition hardware, Qt and PyQt for graphical user interface, PyQwt for plotting, and Python for scripting. The signal (A/D) and energy-reading (IK220 encoder) devices in the PCI computer are also EPICS enabled. The control system scans the monochromator energy through a networked EPICS motor. With the real-time kernel, the system is capable of deterministic data-sampling period of tens of micro-seconds with typical timing-jitter of several micro-seconds. At the same time, Linux is running in other non-real-time processes handling the user-interface. A modern Qt-based controls-front end enhances productivity. The fast plotting and zooming of data in time or energy coordinates let the experimenters verify the quality of the data before detailed analysis. Python scripting is built-in for automation. The typical data-rate for continuous runs are around ten mega-bytes per minute

Spatiotemporal Response of Crystals in X-ray Bragg Diffraction

The spatiotemporal response of crystals in x-ray Bragg diffraction resulting from excitation by an ultra-short, laterally confined x-ray pulse is studied theoretically. The theory presents an extension of the analysis in symmetric reflection geometry [1] to the generic case, which includes Bragg diffraction both in reflection (Bragg) and transmission (Laue) asymmetric scattering geometries. The spatiotemporal response is presented as a product of a crystal-intrinsic plane wave spatiotemporal response function and an envelope function defined by the crystal-independent transverse profile of the incident beam and the scattering geometry. The diffracted wavefields exhibit amplitude modulation perpendicular to the propagation direction due to both angular dispersion and the dispersion due to Bragg's law. The characteristic measure of the spatiotemporal response is expressed in terms of a few parameters: the extinction length, crystal thickness, Bragg angle, asymmetry angle, and the speed of light. Applications to self-seeding of hard x-ray free electron lasers are discussed, with particular emphasis on the relative advantages of using either the Bragg or Laue scattering geometries. Intensity front inclination in asymmetric diffraction can be used to make snapshots of ultra-fast processes with femtosecond resolution

X-Ray Active Matrix Pixel Sensors Basedon J-FET Technology Developed for the Linac Coherent Light Source.

An X-ray Active Matrix Pixel Sensor (XAMPS) is being developed for recording data for the X-ray Pump Probe experiment at the Linac Coherent Light Source (LCLS). Special attention has to be paid to some technological challenges that this design presents. New processes were developed and refined to address problems encountered during previous productions of XAMPS. The development of these critical steps and corresponding tests results are reported here

Fishing for ecosystem services

Ecosystems are commonly exploited and manipulated to maximize certain human benefits. Such changes can degrade systems, leading to cascading negative effects that may be initially undetected, yet ultimately result in a reduction, or complete loss, of certain valuable ecosystem services. Ecosystembased management is intended to maintain ecosystem quality and minimize the risk of irreversible change to natural assemblages of species and to ecosystem processes while obtaining and maintaining long-term socioeconomic benefits. We discuss policy decisions in fishery management related to commonly manipulated environments with a focus on influences to ecosystem services. By focusing on broader scales, managing for ecosystem services, and taking a more proactive approach, we expect sustainable, quality fisheries that are resilient to future disturbances. To that end, we contend that: (1) management always involves tradeoffs; (2) explicit management of fisheries for ecosystem services could facilitate a transition from reactive to proactive management; and (3) adaptive co-management is a process that could enhance management for ecosystem services. We propose adaptive co-management with an ecosystem service framework where actions are implemented within ecosystem boundaries, rather than political boundaries, through strong interjurisdictional relationships

Fishing for ecosystem services

Ecosystems are commonly exploited and manipulated to maximize certain human benefits. Such changes can degrade systems, leading to cascading negative effects that may be initially undetected, yet ultimately result in a reduction, or complete loss, of certain valuable ecosystem services. Ecosystembased management is intended to maintain ecosystem quality and minimize the risk of irreversible change to natural assemblages of species and to ecosystem processes while obtaining and maintaining long-term socioeconomic benefits. We discuss policy decisions in fishery management related to commonly manipulated environments with a focus on influences to ecosystem services. By focusing on broader scales, managing for ecosystem services, and taking a more proactive approach, we expect sustainable, quality fisheries that are resilient to future disturbances. To that end, we contend that: (1) management always involves tradeoffs; (2) explicit management of fisheries for ecosystem services could facilitate a transition from reactive to proactive management; and (3) adaptive co-management is a process that could enhance management for ecosystem services. We propose adaptive co-management with an ecosystem service framework where actions are implemented within ecosystem boundaries, rather than political boundaries, through strong interjurisdictional relationships

Developments in synchrotron x-ray microtomography for application to flow in porous media

Microimaging capabilities at Brookhaven National Laboratory`s National Synchrotron Light Source have been enhanced to provide larger and higher resolution 3-D renderings of pore networks in reservoir rocks at a fraction of the time required in previous first Generation scanning methods. Computer Microtomography, CMT, volumes containing 16 million voxels have been acquired at 3 micron resolution with the aid of expansion optics in a matter of hours. Such data are used to model single and multiphase flow properties in digital images of real porous media. Advances in 3-D visualization, which are being implemented in Brookhaven National Laboratory`s 3-D theater, will allow even greater digestion and interpretation of phenomena dependent upon pore interconnectivity and multipore interactions. Pore networks are analyzed for tortuosity and connectivity measures, which have been elusive parameters in transport property models. We present examples of porosimetry simulation via network modeling to produce initial water saturation and residual oil distributions in a water-wet pore system. Furthermore, pore networks can provide the boundary condition framework for more rigorous simulations of displacement, such as in the lattice Boltzmann simulated water flood example provided

Strong tuning of Rashba spin orbit interaction in single InAs nanowires

A key concept in the emerging field of spintronics is the gate voltage or electric field control of spin precession via the effective magnetic field generated by the Rashba spin orbit interaction. Here, we demonstrate the generation and tuning of electric field induced Rashba spin orbit interaction in InAs nanowires where a strong electric field is created either by a double gate or a solid electrolyte surrounding gate. In particular, the electrolyte gating enables six-fold tuning of Rashba coefficient and nearly three orders of magnitude tuning of spin relaxation time within only 1 V of gate bias. Such a dramatic tuning of spin orbit interaction in nanowires may have implications in nanowire based spintronic devices.Comment: Nano Letters, in pres

Trends and Challenges in Experimental Macromolecular Crystallography

Macromolecular X-ray crystallography underpins the vigorous field of structural molecular biology having yielded many protein, nucleic acid and virus structures in fine detail. The understanding of the recognition by these macromolecules, as receptors, of their cognate ligands involves the detailed study of the structural chemistry of their molecular interactions. Also these structural details underpin the rational design of novel inhibitors in modern drug discovery in the pharmaceutical industry. Moreover, from such structures the functional details can be inferred, such as the biological chemistry of enzyme reactivity. There is then a vast number and range of types of biological macromolecules that potentially could be studied. The completion of the protein primary sequencing of the yeast genome, and the human genome sequencing project comprising some 105 proteins that is underway, raises expectations for equivalent three dimensional structural database