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Scattering Signal (scattering + signal)

Distribution by Scientific Domains
Chemistry75%

Kinds of Scattering Signal

  • anomalous scattering signal
    		•

    Selected Abstracts

    Use of Reversal Nanoimprinting of Nanoparticles to Prepare Flexible Waveguide Sensors Exhibiting Enhanced Scattering of the Surface Plasmon Resonance

    ADVANCED FUNCTIONAL MATERIALS, Issue 11 2010
    Dehui Wan
    Abstract A flexible surface plasmon resonance (SPR)-based scattering waveguide sensor is prepared by directly imprinting hollow gold nanoparticles (NPs) and solid gold NPs onto flexible polycarbonate (PC) plates,without any surface modification,using a modified reversal nanoimprint lithography technology. Controlling the imprinting conditions, including temperature and pressure, allows for the fine adjustment of the depths of the embedded metal NPs and their SPR properties. This patterning approach exhibits a resolution down to the submicrometer level. A 3D finite-difference time domain simulation is used to examine the optical behavior of light propagating parallel to the air/substrate interface within the near-field regime. Consistent with the simulations, almost an order of magnitude enhancement in the scattering signal after transferring the metal NPs from the glass mold to the PC substrate is obtained experimentally. The enhanced signal is attributed to the particles' strong scattering of the guiding-mode waves (within the waveguide) and the evanescent wave (above the waveguide) simultaneously. Finally, the imprinting conditions are optimized to obtain a strongly scattering bio/chemical waveguide sensor. [source]

    Precipitation analysis using the Advanced Microwave Sounding Unit in support of nowcasting applications

    METEOROLOGICAL APPLICATIONS, Issue 2 2002
    Ralf Bennartz
    We describe a method to remotely sense precipitation and classify its intensity over water, coasts and land surfaces. This method is intended to be used in an operational nowcasting environment. It is based on data obtained from the Advanced Microwave Sounding Unit (AMSU) onboard NOAA-15. Each observation is assigned a probability of belonging to four classes: precipitation-free, risk of precipitation, precipitation between 0.5 and 5 mm/h, and precipitation higher than 5 mm/h. Since the method is designed to work over different surface types, it relies mainly on the scattering signal of precipitation-sized ice particles received at high frequencies. For the calibration and validation of the method we use an eight-month dataset of combined weather radar and AMSU data obtained over the Baltic area. We compare results for the AMSU-B channels at 89 GHz and 150 GHz and find that the high frequency channel at 150 GHz allows for a much better discrimination of different types of precipitation than the 89 GHz channel. While precipitation-free areas, as well as heavily precipitating areas (>5 mm/h), can be identified to high accuracy, the intermediate classes are more ambiguous. This stems from the ambiguity of the passive microwave observations as well as from the non-perfect matching of the different data sources and sub-optimal radar adjustment. In addition to a statistical assessment of the method's accuracy, we present case studies to demonstrate its capabilities to classify different types of precipitation and to work over highly structured, inhomogeneous surfaces. Copyright © 2002 Royal Meteorological Society [source]

    Away from the edge II: in-house Se-SAS phasing with chromium radiation

    ACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2005
    Hao Xu
    Recently, the demands of high-throughput macromolecular crystallography have driven continuous improvements in phasing methods, data-collection protocols and many other technologies. Single-wavelength anomalous scattering (SAS) phasing with chromium X-ray radiation opens a new possibility for phasing a protein with data collected in-house and has led to several successful examples of de novo structure solution using only weak anomalous scatterers such as sulfur. To further reduce data-collection time and make SAS phasing more robust, it is natural to combine selenomethionine-derivatized protein (SeMet protein) with Cr,K, radiation to take advantage of the larger anomalous scattering signal from selenium ( = 2.28 e,) compared with sulfur ( = 1.14 e,). As reported herein, the crystal structure of a putative chorismate mutase from Clostridium thermocellum was determined using Se-SAS with Cr,K, radiation. Each protein molecule contains eight selenomethionine residues in 148 amino-acid residues, providing a calculated Bijvoet ratio of about 3.5% at the Cr,K, wavelength. A single data set to 2.2,Å resolution with approximately ninefold redundancy was collected using an imaging-plate detector coupled with a Cr source. Structure solution, refinement and deposition to the Protein Data Bank were performed within 9,h of the availability of the scaled diffraction data. The procedure used here is applicable to many other proteins and promises to become a routine pathway for in-house high-throughput crystallography. [source]

    Monitoring the anomalous scattering signal and noise levels in X-ray diffraction of crystals

    ACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2004
    Zheng-Qing Fu
    A statistical index Ras is proposed in order to monitor the overall signal-to-noise ratio in an anomalous scattering data set. In this approach, symmetry-equivalent reflections are merged and grouped into centric and non-centric subsets. Reflections in the centric subset, which in theory should be equal, are used to estimate the noise level in the data. This approach differs from that used by most data-processing programs, in which the centric reflections are merged and averaged. By preserving the differences in centric reflections during data processing, an internal measure of the noise level can be estimated and used to analyze the quality of the anomalous signal in the data. An index Ras is defined as the ratio of the average Bijvoet difference of merged acentric reflections to merged centric reflections. Test results on a variety of data show that Ras has good correlation with the capability to determine the anomalous scattering substructure from the data. Ras can also be useful in monitoring the quality of the data in terms of the data-collection strategy, instrument settings and data-processing software used. Ras analysis has been implemented in the program 3DSCALE as part of a data-processing program suite that is under development in our laboratory. [source]

    Novel approach to phasing proteins: derivatization by short cryo-soaking with halides

    ACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2000
    Zbigniew Dauter
    A quick (less than 1,min) soak of protein crystals in a cryo-solution containing bromide or iodide anions leads to incorporation of these anomalous scatterers into the ordered solvent region around the protein molecules. These halide anions provide a convenient way of phasing through their anomalous scattering signal: bromides using multiwavelength anomalous dispersion (MAD) and bromides and/or iodides using single-wavelength anomalous dispersion (SAD) or single isomorphous replacement with anomalous scattering (SIRAS) methods. This approach has been tested successfully on four different proteins and has been used to solve the structure of a new protein of molecular weight 30,kDa. [source]

    Use of thallium to identify monovalent cation binding sites in GroEL

    ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 10 2009
    Philip D. Kiser
    GroEL is a bacterial chaperone protein that assembles into a homotetradecameric complex exhibiting D7 symmetry and utilizes the co-chaperone protein GroES and ATP hydrolysis to assist in the proper folding of a variety of cytosolic proteins. GroEL utilizes two metal cofactors, Mg2+ and K+, to bind and hydrolyze ATP. A K+ -binding site has been proposed to be located next to the nucleotide-binding site, but the available structural data do not firmly support this conclusion. Moreover, more than one functionally significant K+ -binding site may exist within GroEL. Because K+ has important and complex effects on GroEL activity and is involved in both positive (intra-ring) and negative (inter-ring) cooperativity for ATP hydrolysis, it is important to determine the exact location of these cation-binding site(s) within GroEL. In this study, the K+ mimetic Tl+ was incorporated into GroEL crystals, a moderately redundant 3.94,Å resolution X-ray diffraction data set was collected from a single crystal and the strong anomalous scattering signal from the thallium ion was used to identify monovalent cation-binding sites. The results confirmed the previously proposed placement of K+ next to the nucleotide-binding site and also identified additional binding sites that may be important for GroEL function and cooperativity. These findings also demonstrate the general usefulness of Tl+ for the identification of monovalent cation-binding sites in protein crystal structures, even when the quality and resolution of the diffraction data are relatively low. [source]

    Enhancing effect of chemically reduced gold on surface Raman scattering for organic sulfides chemisorbed on iron

    JOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2001
    Yun Lu
    Chemically reduced gold particles on an organic sulfide-covered plate can effectively enhance surface Raman scattering signals. This method was used to investigate the adsorption states of 4-aminophenyl disulfide and benzyl disulfide attached to the iron surface by Fourier transform surface-enhanced Raman scattering. The results indicate that these sulfide molecules can be chemisorbed perpendicularly and form a self-assembled film dotted with ferric hydroxide on the iron surface. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Analysis of time-resolved X-ray scattering data from solution-state systems

    ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2010
    Kristoffer Haldrup
    As ultrafast time-resolved studies of liquid systems with the laser pump/X-ray scattering probe method have come of age over the past decade, several groups have developed methods for the analysis of such X-ray scattering data. The present article describes a method developed primarily with a focus on determining structural parameters in the excited states of medium-sized molecules (~30 atoms) in solution. The general methodology is set in a maximum-likelihood framework and is introduced through the analysis of the photoactive platinum compound PtPOP, in particular the structure of its lowest triplet excited state (3A2u). Emphasis is put on structure determination in terms of model comparisons and on the information content of difference scattering signals as well as the related experimental variables. Several suggestions for improving the accuracy of these types of measurements are presented. [source]