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1

Electron Backscatter Diffraction (EBSD) Characterization of Uranium and Uranium Alloys  

SciTech Connect

Electron backscatter diffraction (EBSD) was used to examine the microstructures of unalloyed uranium, U-6Nb, U-10Mo, and U-0.75Ti. For unalloyed uranium, we used EBSD to examine the effects of various processes on microstructures including casting, rolling and forming, recrystallization, welding, and quasi-static and shock deformation. For U-6Nb we used EBSD to examine the microstructural evolution during shape memory loading. EBSD was used to study chemical homogenization in U-10Mo, and for U-0.75Ti, we used EBSD to study the microstructure and texture evolution during thermal cycling and deformation. The studied uranium alloys have significant microstructural and chemical differences and each of these alloys presents unique preparation challenges. Each of the alloys is prepared by a sequence of mechanical grinding and polishing followed by electropolishing with subtle differences between the alloys. U-6Nb and U-0.75Ti both have martensitic microstructures and both require special care in order to avoid mechanical polishing artifacts. Unalloyed uranium has a tendency to rapidly oxidize when exposed to air and a two-step electropolish is employed, the first step to remove the damaged surface layer resulting from the mechanical preparation and the second step to passivate the surface. All of the alloying additions provide a level of surface passivation and different one and two step electropolishes are employed to create good EBSD surfaces. Because of its low symmetry crystal structure, uranium exhibits complex deformation behavior including operation of multiple deformation twinning modes. EBSD was used to observe and quantify twinning contributions to deformation and to examine the fracture behavior. Figure 1 shows a cross section of two mating fracture surfaces in cast uranium showing the propensity of deformation twinning and intergranular fracture largely between dissimilarly oriented grains. Deformation of U-6Nb in the shape memory regime occurs by the motion of twin boundaries formed during the martensitic transformation. Deformation actually results in a coarsening of the microstructure making EBSD more practical following a limited amount of strain. Figure 2 shows the microstructure resulting from 6% compression. Casting of U-10Mo results in considerable chemical segregation as is apparent in Figure 2a. The segregation subsists through rolling and heat treatment processes as shown in Figure 2b. EBSD was used to study the effects of homogenization time and temperature on chemical heterogeneity. It was found that times and temperatures that result in a chemically homogeneous microstructure also result in a significant increase in grain size. U-0.75Ti forms an acicular martinsite as shown in Figure 4. This microstructure prevails through cycling into the higher temperature solid uranium phases.

McCabe, Rodney J. [Los Alamos National Laboratory; Kelly, Ann Marie [Los Alamos National Laboratory; Clarke, Amy J. [Los Alamos National Laboratory; Field, Robert D. [Los Alamos National Laboratory; Wenk, H. R. [University of California, Berkeley

2012-07-25

2

Advanced microstructural analysis of ferrite materials by means of electron backscatter diffraction (EBSD)  

NASA Astrophysics Data System (ADS)

The analysis of the achieved texture is of great importance for the performance of ferrite materials, either bulk or thin films. The recently developed electron backscatter diffraction (EBSD) technique enables a spatially resolved study of the crystallographic orientations by means of recording of Kikuchi patterns. To our knowledge, such a thorough EBSD analysis was not yet performed in any oxidic magnetic material, and only very recently on magnetite thin films by us. A good surface polishing/cleaning is essential for this analysis, as the method requires an undisturbed surface area for a high image quality (IQ). This information is recorded to each measured Kikuchi pattern, together with a parameter describing the quality of indexation. Here, the spatially highly resolved EBSD mappings provide additional information as compared to the standard analysis techniques, which can contribute to an optimization of the growth process. Furthermore, an analysis of the grain aspect ratio is possible which provides further insight to the microstructural dependence of the magnetic properties of ferrites.

Koblischka-Veneva, A.; Koblischka, M. R.; Mücklich, F.

2010-05-01

3

Application of electron backscatter diffraction (EBSD) to fracture studies of ferritic steels.  

PubMed

The application of electron backscatter diffraction (EBSD) to fracture studies has provided a new method for investigating the crystallography of fracture surfaces. The crystallographic indices of cleavage planes can be measured both directly from the fracture surface and indirectly from metallographic sections perpendicular to the plane of the adjoining fracture surfaces. The results of direct individual cleavage facet plane orientation measurements are presented for carbon-manganese (C-Mn) and low-alloy Mn-Mo-Ni (similar to ASTM A553 type-B). Pressure vessel steel weld metals, obtained from fracture surfaces of Charpy impact test specimens fractured at various test temperatures and for an ultra-low carbon steel (Fe-0.002C- 0.058P) fractured at -196 degrees C by impact. In addition to the direct measurement from the fracture surface, cleavage facet orientation measurements for the ultra-low carbon steel were complemented by the results obtained from the metallographic sections. Fractographic observations revealed that cleavage fracture is accommodated by a microvoid coalescence fracture micromechanism, which was induced by decohesion of second phase particles (inclusions). The correlation between the direct and indirect methodologies shows that the cleavage facet planes are dominated by the [001] plane orientations, and indicated that even when information concerning the full five degrees of freedom is inaccessible, the cleavage facet plane could still be determined. Finally, the advantages and disadvantages of direct orientation measurements from the fracture surface and indirectly by a destructive sectioning technique are discussed. PMID:11996192

Davies, P A; Novovic, M; Randle, V; Bowen, P

2002-03-01

4

Electron Back-Scatter Diffraction (EBSD) Analysis of Two Unusual Minerals in Carbonaceous Chondrites  

NASA Astrophysics Data System (ADS)

We report application of EBSD to identify two possible new minerals in carbonaceous chondrites (Fe-Cr phosphide in Kaidun and Ca-Al oxide in NWA470). The presence of these unique phases offers useful information on the formation of these meteorites.

Mikouchi, T.; Zolensky, M.; Tachikawa, O.; Komatsu, M.; Ivanova, M. A.; Le, L.; Gounelle, M.

2006-03-01

5

Characterisation of texture in Ti-6246 alloy fibre laser welds using Electron Backscattered Diffraction (EBSD)  

NASA Astrophysics Data System (ADS)

In this study, fibre laser welds of alloy Ti-6%Al-2%Sn-4%Zr-6%Mo have been characterised. It has been found that although the microstructure of the welds is important in predicting properties, it is not enough to simply characterise the welds based on the microstructure, as crystallographic texturing is also important in determining mechanical properties. The texturing of the fibre laser welds is being characterized using EBSD mapping, with light microscopy to characterize the microstructure. This has been carried out for a weld that has been heat treated for 3 hours at 550 °C. At this temperature, relaxation of residual stress will occur, but changes to the microstructure will be minimal. It is planned that EBSD will now be carried out on the as received sample, and the results will be presented, along with a comparison with the heat treated weld.

Merson, Eleanor; Hammond, Chris; Brydson, Rik

2006-02-01

6

Study of ferrous corrosion products on iron archaeological objects by electron backscattered diffraction (EBSD)  

NASA Astrophysics Data System (ADS)

The corrosion of iron-based archaeomaterials in anoxic environments leads mainly to Fe(II) compounds, like the hydroxychloride ?-Fe2(OH)3Cl, chukanovite Fe2(OH)2CO3 or siderite FeCO3. The understanding of the mechanisms then necessarily implies a thorough investigation of the chemical, mechanical and morphological characteristics of the Fe(II)-based layer that develops between the metal surface and the environment. In the peculiar case of Fe(II) compounds, generally very reactive towards O2, the main concern is to prevent any transformation by air during the analysis. The EBSD technique is adapted on a scanning electron microscope (SEM) where the samples are analysed under vacuum and consequently sheltered from air. Different options offered by EBSD for phase characterisation and microstructural study were tested for the first time on the rust layers of two archaeological iron nails. Results were confronted to those obtained by micro-Raman spectroscopy, which was used as reference method. Magnetite, Fe(II) hydroxychloride ?-Fe2(OH)3Cl and siderite were analysed successfully but improvements have to be brought for the study of other compounds such as iron oxyhydroxides and chukanovite. The choice of experimental parameters in our approach as well as the potentialities and limits of the technique for this kind of application are discussed.

Azoulay, Ilanith; Conforto, Egle; Refait, Philippe; Rémazeilles, Céline

2013-02-01

7

Towards a more comprehensive microstructural analysis of Zr-2.5Nb pressure tubing using image analysis and electron backscattered diffraction (EBSD)  

NASA Astrophysics Data System (ADS)

Zr-2.5Nb pressure tubes used in CANDU (CANada Deuterium Uranium) reactors have a very complex microstructure, with two major crystallographic phases, ? and ?. These phases include a fair amount of deformation from the extrusion process and the cold working (˜25%) performed at the end of the manufacturing process. This microstructure (texture, grain aspect ratio, etc.) changes along the tube's length and differs from tube to tube. In order to better understand the deformation mechanisms, these microstructural differences must be statistically characterized. Scanning electron microscopy combined with direct image analysis or with electron backscattered diffraction (EBSD) are good techniques for carrying out such a measurement. However it is not possible, using specimen preparation methods specific for each of these techniques, to reveal all of the grain and phase boundaries. We have thus developed post-treatment algorithms to be able to partially analyze the revealed Zr-2.5Nb microstructure. The first algorithm was used for image analysis treatments of micrographs taken at 5 kV on the radial-tangential plane of etched samples using a reactive ion etch (RIE, CF 4 + O 2). The second was developed for EBSD grain mapping and can be used to characterize ?-Zr grain shape and orientation. The two techniques are complementary: EBSD gives information about the micro-texture and the relationship between the microstructure and micro-texture while image analyses of SEM micrographs reveal the direction and distribution of the ?-Zr lamellae more easily and over a greater sample area than EBSD. However, the SEM micrographs that were used did not reveal any grain boundary (only phase boundary). An analysis of EBSD grain maps reveals that the average ?-Zr grain size, mainly in the elongated direction (tangential), is smaller than what is normally obtained from an image analysis of SEM micrographs. The grain size distribution of type I ?-Zr grains (deformed original (prior) ?-Zr) and type II (stress-induced ?-Zr ? ?-Zr phase transformation) is also shown to be different for sizes greater than 0.4 ?m 2.

Hovington, P.; Pinard, P. T.; Lagacé, M.; Rodrigue, L.; Gauvin, R.; Trudeau, M. L.

2009-08-01

8

Strain Determination Using Electron Backscatter Diffraction  

SciTech Connect

In the present paper we demonstrate the use of electron backscatter diffraction (EBSD) for high resolution elastic strain determination. Here, we focus on analysis methods based on determination of small shifts in EBSD pattern with respect to a reference pattern using cross-correlation algorithms. Additionally we highlight the excellent spatial and depth resolution of EBSD and introduce the use of simulated diffraction patterns based on dynamical diffraction theory for sensitivity estimation. Moreover the potential of EBSD for strain analysis of strained thin films with particular emphasis on appropriate target preparation which respect to occurring lattice defects is demonstrated.

Krause, M.; Graff, A.; Altmann, F. [Fraunhofer Institute for Mechanics of Materials, Walter-Huelse-Str.1, 06120 Halle (Germany)

2010-11-24

9

Electron Backscatter Diffraction (EBSD) Analysis and U-Pb Geochronology of the Oldest Lunar Zircon: Constraining Early Lunar Differentiation and Dating Impact-Related Deformation  

NASA Technical Reports Server (NTRS)

The evolution of the early moon was dominated by two processes (i) crystallization of the Lunar Magma Ocean (LMO) and differentiation of potassium-rare earth element-phosphorous-rich residual magma reservoir referred to as KREEP, and (ii) an intense meteorite bombardment referred to as lunar cataclysm . The exact timing of these processes is disputed, and resolution relies on collection and interpretation of precise age data. This study examines the microstructure and geochronology of zircon from lunar impact breccias collected during the Apollo 17 mission. A large zircon clast within lunar breccia 72215,195 shows sector zoning in optical microscopy, cathodoluminescence (CL) imaging and Raman mapping, and indicates that it was a relict fragment of a much larger magmatic grain. Sensitive high resolution ion microprobe (SHRIMP) U-Pb analysis of the zircon shows that U and Th concentration correlate with sector zoning, with darkest CL domains corresponding with high-U and Th (approx.150 and approx.100 ppm respectively), and the brightest-CL sectors containing approx.30-50 ppm U and approx.10-20 ppm Th. This indicates that variations in optical CL and Raman properties correspond to differential accumulation of alpha-radiation damage in each sector. Electron backscatter diffraction (EBSD) mapping shows that the quality of electron backscatter patterns (band contrast) varies with sector zoning, with the poorest quality patterns obtained from high-U and Th, dark-CL zones. EBSD mapping also reveals a deformation microstructure that is cryptic in optical, CL and Raman imaging. Two orthogonal sets of straight discrete and gradational low-angle boundaries accommodate approx.12 misorientation across the grain. The deformation bands are parallel to the crystallographic {a}-planes of the zircon, have misorientation axes parallel to the c-axis, and are geometrically consistent with formation by dislocation creep associated with <100>{010} slip. The deformation bands are unlike curved morphology of crystal-plastic microstructures in tectonically deformed terrestrial zircon, and geometrically similar to dislocation microstructures reported in experimentally shocked zircon. We interpret these crystal-plastic deformation microstructures to have resulted from a significant impact, either directly from impact shock, or during ductile flow directly following the impact. The deformation bands appear to continue undeflected through the non-indexed, radiation-damaged areas of the grain, which suggests that the orientation variation predates any significant mechanical weakening from radiation damage in the grain, and therefore occurred early in its history.

Timms, Nick; Nemchin, Alexander; Grange, Marion; Reddy, Steve; Pidgeon, Bob; Geisler, Thorsten; Meyer, Chuck

2009-01-01

10

Electron backscatter diffraction: Strategies for reliable data acquisition and processing  

SciTech Connect

In electron backscatter diffraction (EBSD) software packages there are many user choices both in data acquisition and in data processing and display. In order to extract maximum scientific value from an inquiry, it is helpful to have some guidelines for best practice in conducting an EBSD investigation. The purpose of this article therefore is to address selected topics of EBSD practice, in a tutorial manner. The topics covered are a brief summary on the principles of EBSD, specimen preparation, calibration of an EBSD system, experiment design, speed of data acquisition, data clean-up, microstructure characterisation (including grain size) and grain boundary characterisation. This list is not meant to cover exhaustively all areas where EBSD is used, but rather to provide a resource consisting of some useful strategies for novice EBSD users.

Randle, Valerie, E-mail: v.randle@swansea.ac.uk [Materials Research Centre, School of Engineering, Swansea University, Swansea SA2 8PP (United Kingdom)

2009-09-15

11

A channel plate detector for electron backscatter diffraction  

NASA Astrophysics Data System (ADS)

Electron backscatter diffraction (EBSD) using a scanning electron microscope has proven to be a valuable means for determining the crystal orientation of crystallites as small as ˜0.25 ?m. However, it is still not widely used. One deterrent is the high cost of the image intensified video camera system that is commonly used to record the weak EBSD images produced on a phosphor screen. A much less expensive detector system has been devised using a microchannel plate (MCP) electron multiplier to provide the necessary gain in image intensity and a standard video camera to record the image. Excitation of the MCP by secondary electrons and low energy backscattered electron is prevented by a thin aluminum foil on the MCP front surface. The benefits and disadvantages of this approach to EBSD are presented, together with typical EBSD images obtained from it.

Barr, D. L.; Brown, W. L.

1995-06-01

12

Recent developments in two fundamental aspects of electron backscatter diffraction  

NASA Astrophysics Data System (ADS)

Two very different aspects of electron backscatter diffraction (EBSD) are considered in this paper. Firstly, the use of the technique for the measurement of grain size is discussed with particular reference to the development of international standards to help ensure reproducible and repeatable measurements. In particular the lessons learnt for both calibration of the complete SEM-EBSD system and in choice of the correct data acquisition and processing parameters from an international round robin are summarized. Secondly, extending the capability of EBSD through development of new detectors is discussed. New shadow casting methods provide a means to achieve better accuracy in definition of sample-pattern geometry, while increased detail can be obtained by larger cameras and ultimately direct electron detection.

Mingard, K. P.; Day, A. P.; Quested, P. N.

2014-03-01

13

Orientation precision of electron backscatter diffraction measurements near grain boundaries.  

PubMed

Electron backscatter diffraction (EBSD) has become a common technique for measuring crystallographic orientations at spatial resolutions on the order of tens of nanometers and at angular resolutions <0.1°. In a recent search of EBSD papers using Google Scholar™, 60% were found to address some aspect of deformation. Generally, deformation manifests itself in EBSD measurements by small local misorientations. An increase in the local misorientation is often observed near grain boundaries in deformed microstructures. This may be indicative of dislocation pile-up at the boundaries but could also be due to a loss of orientation precision in the EBSD measurements. When the electron beam is positioned at or near a grain boundary, the diffraction volume contains the crystal lattices from the two grains separated by the boundary. Thus, the resulting pattern will contain contributions from both lattices. Such mixed patterns can pose some challenge to the EBSD pattern band detection and indexing algorithms. Through analysis of experimental local misorientation data and simulated pattern mixing, this work shows that some of the rise in local misorientation is an artifact due to the mixed patterns at the boundary but that the rise due to physical phenomena is also observed. PMID:24576405

Wright, Stuart I; Nowell, Matthew M; de Kloe, René; Chan, Lisa

2014-06-01

14

Present State of Electron Backscatter Diffraction and Prospective Developments  

SciTech Connect

Electron backscatter diffraction (EBSD), when employed as an additional characterization technique to a scanning electron microscope (SEM), enables individual grain orientations, local texture, point-to-point orientation correlations, and phase identification and distributions to be determined routinely on the surfaces of bulk polycrystals. The application has experienced rapid acceptance in metallurgical, materials, and geophysical laboratories within the past decade (Schwartz et al. 2000) due to the wide availability of SEMs, the ease of sample preparation from the bulk, the high speed of data acquisition, and the access to complementary information about the microstructure on a submicron scale. From the same specimen area, surface structure and morphology of the microstructure are characterized in great detail by the relief and orientation contrast in secondary and backscatter electron images, element distributions are accessed by energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS), or cathodoluminescence analysis, and the orientations of single grains and phases can now be determined, as a complement, by EBSD.

Schwarzer, R A; Field, D P; Adams, B L; Kumar, M; Schwartz, A J

2008-10-24

15

Electron backscatter diffraction in conservation science: phase identification of pigments in paint layers.  

PubMed

Electron backscatter diffraction (EBSD) was used in Conservation Science for characterization of ancient materials collected from works of art. The results demonstrate the feasibility of EBSD analysis on heterogeneous matrices as very small samples of paint layers collected from paintings. Two reference pigments were selected from those used by artists to investigate the relationship existing between EBSD pattern quality and properties of the investigated material (i.e., average atomic number, density, and Mohs hardness). The technique was also tested to investigate the pigment phases on two real samples collected from Romanino's Santa Giustina altarpiece, an oil on wood painting dated 1514 (Civic Museum, Padova, Italy). Results show for the first time the acquisition of EBSD patterns from painting samples mounted in resin, i.e., painting cross sections, opening a new powerful tool to elucidate the pigment phases avoiding large sampling on works of arts and to further study the complex mechanisms of pigment deterioration. PMID:23663448

Gambirasi, A; Peruzzo, L; Bianchin, S; Favaro, M

2013-08-01

16

Ultrasonic Characterization of Texture in Rolled Aluminium Correlated with Electron Backscatter Diffraction Measurements  

SciTech Connect

Electron Backscatter Diffraction (EBSD) is a microscopic technique that provides detailed crystallographic orientation and microstructural information, allowing for accurate measurement of such properties like average grain size. In order to validate and better understand what information an ultrasonic technique can give us we are correlating the ultrasonic measurements with those from EBSD. It generates an appreciation of the limitations of both techniques, and what each can reasonably deliver. We describe a technique to extrapolate the three independent orientation distribution coefficients (ODCs) for cubic structures W400, W420 and W440 from the Bunge-Euler angle data from EBSD scans. Preliminary EBSD results for thin rolled aluminium sheet are discussed and compared to the ODCs determined on the same sample using an ultrasonic EMAT-EMAT S0 Lamb wave measurement system.

Essex, S. D.; Potter, M. D. G.; Dixon, S. [University of Warwick, Dept. of Physics, Coventry. CV4 7AL (United Kingdom)

2007-03-21

17

An electron backscatter diffraction investigation of crystallographic orientations of embedded nanoparticles within melt-textured YBCO high temperature superconductors  

Microsoft Academic Search

Microstructures of melt-textured YBCO samples with embedded nanosized particles of Y2BaCuO5 (Y-211) and Y2Ba4CuMOx (M-2411 with M = U,Zr) are analysed by means of electron backscatter diffraction (EBSD). With the recent developments of the EBSD technique, we can directly measure the crystallographic orientation of the embedded nanoparticles, employing a spatial resolution of about 40 nm. The high image quality of

A. Koblischka-Veneva; M. R. Koblischka; N. Hari Babu; D. A. Cardwell; L. Shlyk; G. Krabbes

2006-01-01

18

Microstructure evolution of 6061 O Al alloy during ultrasonic consolidation: An insight from electron backscatter diffraction  

Microsoft Academic Search

6061 O Al alloy foils were welded to form monolithic and SiC fibre-embedded samples using the ultrasonic consolidation (UC) process. Contact pressures of 135, 155 and 175MPa were investigated at 20kHz frequency, 50% of the oscillation amplitude, 34.5mms?1 sonotrode velocity and 20°C. Deformed microstructures were analysed using electron backscatter diffraction (EBSD). At all contact pressures deformation occurs by non-steady state

E. Mariani; E. Ghassemieh

2010-01-01

19

Application of electron backscatter diffraction for crystallographic characterization of tin whiskers.  

PubMed

Understanding the growth of whiskers or high aspect ratio features on substrates can be aided when the crystallography of the feature is known. This study has evaluated three methods that utilize electron backscatter diffraction (EBSD) for the determination of the crystallographic growth direction of an individual whisker. EBSD has traditionally been a technique applied to planar, polished samples, and thus the use of EBSD for out-of-surface features is somewhat more difficult and requires additional steps. One of the methods requires the whiskers to be removed from the substrate resulting in the loss of valuable physical growth relationships between the whisker and the substrate. The other two techniques do not suffer this disadvantage and provide the physical growth information as well as the crystallographic growth directions. The final choice of method depends on the information required. The accuracy and the advantages and disadvantages of each method are discussed. PMID:22832083

Michael, Joseph R; McKenzie, Bonnie B; Susan, Donald F

2012-08-01

20

Large Area Stress Distribution in Crystalline Materials Calculated from Lattice Deformation Identified by Electron Backscatter Diffraction  

NASA Astrophysics Data System (ADS)

We report a method to obtain the stress of crystalline materials directly from lattice deformation by Hooke's law. The lattice deformation was calculated using the crystallographic orientations obtained from electron backscatter diffraction (EBSD) technology. The stress distribution over a large area was obtained efficiently and accurately using this method. Wurtzite structure gallium nitride (GaN) crystal was used as the example of a hexagonal crystal system. With this method, the stress distribution of a GaN crystal was obtained. Raman spectroscopy was used to verify the stress distribution. The cause of the stress distribution found in the GaN crystal was discussed from theoretical analysis and EBSD data. Other properties related to lattice deformation, such as piezoelectricity, can also be analyzed by this novel approach based on EBSD data.

Shao, Yongliang; Zhang, Lei; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Tian, Yuan; Huo, Qin

2014-08-01

21

Large area stress distribution in crystalline materials calculated from lattice deformation identified by electron backscatter diffraction.  

PubMed

We report a method to obtain the stress of crystalline materials directly from lattice deformation by Hooke's law. The lattice deformation was calculated using the crystallographic orientations obtained from electron backscatter diffraction (EBSD) technology. The stress distribution over a large area was obtained efficiently and accurately using this method. Wurtzite structure gallium nitride (GaN) crystal was used as the example of a hexagonal crystal system. With this method, the stress distribution of a GaN crystal was obtained. Raman spectroscopy was used to verify the stress distribution. The cause of the stress distribution found in the GaN crystal was discussed from theoretical analysis and EBSD data. Other properties related to lattice deformation, such as piezoelectricity, can also be analyzed by this novel approach based on EBSD data. PMID:25091314

Shao, Yongliang; Zhang, Lei; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Tian, Yuan; Huo, Qin

2014-01-01

22

Misorientation Mapping for Visualization of Plastic Deformation via Electron Back-Scattered Diffraction  

NASA Astrophysics Data System (ADS)

The ability to map plastic deformation around high strain gradient microstructural features is central in studying phenomena such as fatigue and stress corrosion cracking. A method for the visualization of plastic deformation in electron back-scattered diffraction (EBSD) data has been developed and is described in this article. This technique is based on mapping the intragrain misorientation in polycrystalline metals. The algorithm maps the scalar misorientation between a local minimum misorientation reference pixel and every other pixel within an individual grain. A map around the corner of a Vickers indentation in 304 stainless steel was used as a test case. Several algorithms for EBSD mapping were then applied to the deformation distributions around air fatigue and stress corrosion cracks in 304 stainless steel. Using this technique, clear visualization of a deformation zone around high strain gradient microstructural features (crack tips, indentations, etc.) is possible with standard EBSD data.

Brewer, L. N.; Othon, M. A.; Young, L. M.; Angeliu, T. M.

2006-02-01

23

Techniques for generating 3-D EBSD microstructures by FIB tomography  

Microsoft Academic Search

This work describes some techniques developed for focused ion beam (FIB) serial sectioning and electron backscatter diffraction (EBSD) mapping of partially and fully recrystallized metals. A DualBeam™ platform was used to sequentially mill submicron slices of a material by FIB with the crystallographic features of each newly created surface characterized by EBSD. Two promising milling procedures are described which involve:

W. Xu; M. Ferry; N. Mateescu; J. M. Cairney; F. J. Humphreys

2007-01-01

24

Electron Backscatter Diffraction: An Important Tool for Analyses of Structure-Property Relationships in Thin-Film Solar Cells  

NASA Astrophysics Data System (ADS)

The present work gives an overview of the application of electron backscatter diffraction (EBSD) in the field of thin-film solar cells, which consist of stacks of polycrystalline layers on various rigid or flexible substrates. EBSD provides access to grain-size and local-orientation distributions, film textures, and grain-boundary types. By evaluation of the EBSD patterns within individual grains of the polycrystalline solar cell layers, microstrain distributions also can be obtained. These microstructural properties are of considerable interest for research and development of thin-film solar cells. Moreover, EBSD may be performed three-dimensionally, by alternating slicing of cross sections in a focused ion-beam machine and EBSD acquisition. To relate the microstructural properties to the electrical properties of individual layers as well as to the device performances of corresponding solar cells, EBSD can be combined with electron-beam-induced current and cathodoluminescence measurements and with various scanning-probe microscopy methods such as Kelvin-probe force, scanning spreading resistance, or scanning capacitance microscopy on identical specimen positions. Together with standard device characterization of thin-film solar cells, these scanning microscopy measurements provide the means for extensive analysis of structure-property relationships in solar-cell stacks with polycrystalline layers.

Abou-Ras, D.; Kavalakkatt, J.; Nichterwitz, M.; Schäfer, N.; Harndt, S.; Wilkinson, A. J.; Tsyrulin, K.; Schulz, H.; Bauer, F.

2013-09-01

25

Plagioclase Preferred Orientation in Anorthosite by TOF Neutron Diffraction and SEM-EBSD  

NASA Astrophysics Data System (ADS)

Preferred Orientation analysis of the triclinic mineral plagioclase has traditionally relied on the measurements of the optical indicatrix, cleavages and twins with time-consuming U-stage methods. X-ray methods that are conventionally used for texture measurements proved to be unsatisfactory because of insufficient resolution to separate the closely spaced or overlapped diffraction peaks. This study reports a Time-of-Flight (TOF) neutron diffraction texture analysis of plagioclase. Results are compared with Electron Back Scatter Diffraction (EBSD) data. The sample investigated is a highly deformed anorthositic mylonite (Grenville Province, Quebec), composed of andesine. Neutron diffraction was performed with a Kappa-geometry texture goniometer at the Intense Pulsed Neutron Source (IPNS) of Argonne National Laboratory. Spectra were recorded in 16 sample orientations with 10 detectors, with a measurement time of 2.5 hours at each orientation. The texture was investigated with a modified Rietveld method, using many pole figures (56, in the d-range 2-3.5Å) and small number of sample orientations (16) with the Williams-Imhof-Matthies-Vinel (WIMV) algorithm implemented in the program package MAUD (Materials Analysis Using Diffraction). Electron Diffraction was performed by a digital SEM-EBSD system at Berkeley, relying on the Channel+ software for indexing diffraction patterns. 6561 diffraction patterns were measured. Analyses from neutron and electron diffraction data gave similar results. The principal pole figures show (010) roughly parallel to the rock foliation, (001) poles exhibiting a small angle ( ~15° ) to the pole to foliation, and (100) poles close to the Y-direction (the direction perpendicular to the lineation and foliation pole). The textures of the crystallographic directions [100], [010], and [001] were indirectly obtained by approximating the closest (hkl) poles (20-1), (010), and (-102) respectively. The [100] maximum is in the lineation direction, [010] directions concentrate near the foliation pole. The geological deformation conditions and the constructed pole figure patterns indicate that the preferred orientation could be attributed to intracrystalline slip dominantly on (010) with [100] as slip direction. The results demonstrate that neutron diffraction, as well as EBSD are reliable techniques to establish the orientation distribution of triclinic feldspars in deformed rocks.

Xie, Y.; Wenk, R.

2001-12-01

26

Electron Backscatter Diffraction of CdTe Thin Films: Effects of CdCl2 Treatment  

SciTech Connect

In this work, the authors describe procedures to prepare the surface of close-spaced sublimation CdTe thin films necessary for producing good electron backscatter diffraction (EBSD) data. They found that polishing resulted in an amorphous layer on the surface and no Kikuchi pattern; however, ion-beam milling produced a relatively flat and good-quality surface, resulting in high-quality patterns and, consequently, excellent EBSD data. The authors used a combination of polishing and ion-beam milling or etching to study the crystalline structure of the CdTe film at different depths. They also used EBSD, in conjunction with other analytical techniques, to investigate the effects of the CdCl{sub 2} treatment, performed at different temperatures and times, on the recrystallization process of physical vapor deposition CdTe thin films. The authors found that the untreated films were <111> oriented, with grain sizes smaller than 1 {micro}m. The CdCl{sub 2} at 350 C produced partially recrystallized films, whereas treatments at 400 C or 420 C produced completely recrystallized films, with no texture, and grains with grain sizes varying from about 1 {micro}m to more than 40{micro}m. These films were so flat that good EBSD data could be obtained without any surface preparation. Atomic force microscopy and scanning electron microscopy showed that large grains had different morphologies than smaller grains, and EBSD showed that these large grains had <111> texture. These results indicate that the (111) surface is the lowest energy surface in these films and, consequently, <111>-oriented grains grow at the expense of grains oriented in less-favorable directions. Regardless of the deposition method and treatment, the CdTe films have a high density of 60{sup o} <111> twin boundaries.

Moutinho, H. R.; Dhere, R. G.; Romero, M. J.; Jiang, C.-S.; To, B.; Al-Jassim, M. M.

2008-07-01

27

Dependence of the Electron Beam Energy and Types of Surface to Determine EBSD Indexing Reliability in Yttria-Stabilized Zirconia  

Microsoft Academic Search

Electron backscatter diffraction (EBSD) is a powerful technique for the surface microstructure analysis. EBSD analysis of cubic yttria-stabilized zirconia (YSZ) in two and three dimensions (2-D, 3-D) is demonstrated using sequential slicing from a focused ion beam (FIB) followed by EBSD mapping to represent 3-D reconstructed high density grain structure with random orientation. The statistics related to accuracy of EBSD

Saraf; Laxmikant V

2012-01-01

28

Some factors affecting EBSD pattern quality of Ga + ion-milled face centred cubic metal surfaces  

Microsoft Academic Search

Using a DualBeam™ platform, it is possible to generate crystallographic volumes of microstructure by sequentially milling submicron slices of a material using the focused ion beam (FIB) and mapping each newly created surface using electron backscatter diffraction (EBSD). The present work describes the influence of some FIB milling parameters on the quality of EBSD patterns obtained on ion-milled surfaces of

N. Mateescu; M. Ferry; W. Xu; J. M. Cairney

2007-01-01

29

Three-Dimensional EBSD Analysis of YSZ, NiO-YSZ and Ni-Alloy  

Microsoft Academic Search

In this report, a method is discussed to perform successive milling on yttria-stabilized zirconia (YSZ), NiO-YSZ and Ni-alloy at the intervals of 85 nm 50 nm and 100 nm, respectively using a focused ion beam (FIB) followed by electron backscatter diffraction (EBSD) analysis on each slice. The EBSD data is then reconstructed to generate 3D volume. The 3D-EBSD band quality

Saraf; Laxmikant V

2012-01-01

30

Electron backscatter diffraction analysis of ZnO:Al thin films  

NASA Astrophysics Data System (ADS)

Microstructural characterization and crystallographic orientation aspects of aluminium doped zinc oxide (ZnO:Al) thin films have been investigated by means of electron backscatter diffraction. ZnO:Al was produced by magnetron sputtering deposition from a ZnO ceramic target containing 2.0 wt% Al2O3 and 0.12 wt% Y2O3. Both top surface and cross-section analysis were performed. The experimental details concerning specific sample preparation procedures for EBSD investigations are presented. Crystalline texture was described by the inverse pole figure (IPF) maps. Strong texture on the basal plane orientation was observed on the analyzed thin film surface. In accordance with these results obtained from top surface investigations, a strong prismatic texture was found in cross-section analysis. From all these analyses a good description and quantification of the three dimensional configuration of the grains and of their crystallographic texture can be proposed.

Garcia, C. B.; Ariza, E.; Tavares, C. J.; Villechaise, P.

2012-10-01

31

X-Ray Bragg Diffraction in Asymmetric Backscattering Geometry  

Microsoft Academic Search

We observe three effects in the Bragg diffraction of x rays in backscattering geometry from asymmetrically cut crystals. First, exact Bragg backscattering takes place not at normal incidence to the reflecting atomic planes. Second, a well-collimated (â1 μrad) beam is transformed after the Bragg reflection into a strongly divergent beam (230 μrad) with reflection angle dependent on x-ray wavelength--an effect

J. Zhao; A. Alatas; H. D. Rueter; U. Kuetgens; M. Lerche; Yu. V. Shvydko

2006-01-01

32

X-Ray Bragg Diffraction in Asymmetric Backscattering Geometry  

Microsoft Academic Search

We observe three effects in the Bragg diffraction of x rays in backscattering geometry from asymmetrically cut crystals. First, exact Bragg backscattering takes place not at normal incidence to the reflecting atomic planes. Second, a well-collimated (~=1murad) beam is transformed after the Bragg reflection into a strongly divergent beam (230murad) with reflection angle dependent on x-ray wavelength---an effect of angular

Yu. V. Shvyd'Ko; M. Lerche; U. Kuetgens; H. D. Rüter; A. Alatas; J. Zhao

2006-01-01

33

Electron Backscatter Diffraction Analysis of a CZT Growth Tip from a Vertical Gradient Freeze Furnace  

SciTech Connect

Electronic backscatter diffraction (EBSD) was used to characterize the growth-tip region of a 4.2-cm diameter CdZnTe (CZT) boule grown using low-pressure Bridgman method in a vertical gradient freeze furnace. The boule was sectioned and polished and a section taken along the boule longitudinal centerline with an approximate surface area of 1-cm2 was used for optical and scanning electron microscopy. A collage was assembled using EBSD/SEM images to show morphological features, e.g., twin structure, grain structure, and overall crystal growth direction. Severely twinned regions originating from the tip and side walls were observed. The overall growth orientation was close to <110> and <112> directions. In some regions, the (001) poles of the CZT matrix aligned with the growth direction, while twins aligned such that (111) and (112) poles aligned with the growth direction. In some other areas, (112) or (011) poles of the CZT matrix aligned with the growth direction. New relationships between the CZT matrix and large Te polycrystalline particles were revealed: {11 }CZT??{1 00}Te and {001}CZT??{0 1}Te.

Sundaram, S. K.; Henager, Charles H.; Edwards, Danny J.; Schemer-Kohrn, Alan L.; Bliss, Mary; Riley, Brian J.

2011-08-15

34

Coupling Automated Electron Backscatter Diffraction with Transmission Electron and Atomic Force Microscopies  

SciTech Connect

Grain boundary network engineering is an emerging field that encompasses the concept that modifications to conventional thermomechanical processing can result in improved properties through the disruption of the random grain boundary network. Various researchers have reported a correlation between the grain boundary character distribution (defined as the fractions of special and random grain boundaries) and dramatic improvements in properties such as corrosion and stress corrosion cracking, creep, etc. While much early work in the field emphasized property improvements, the opportunity now exists to elucidate the underlying materials science of grain boundary network engineering. Recent investigations at LLNL have coupled automated electron backscatter diffraction (EBSD) with transmission electron microscopy (TEM) and atomic force microscopy (AFM) to elucidate these fundamental mechanisms. This investigation provides evidence that grain boundary network engineering and the formation of annealing twins disrupt the connectivity of the random grain boundary network and is likely responsible for the experimentally observed improvement in properties. This work illustrates that coupling of automated EBSD with other microstructural probes such as TEM and AFM provides data of greater value than any single technique in isolation. The coupled techniques have been applied to aid in understanding the underlying mechanisms of grain boundary network engineering and the corrosion properties of individual boundaries.

Schwartz, A.J.; Kumar, M.; Bedrossian, P.J.; King, W.E.

2000-01-26

35

Advances in EBSD and EBSD/EDS integration for the characterization of mineralogical samples  

NASA Astrophysics Data System (ADS)

Electron BackScatter Diffraction (EBSD) is a well-known powerful technique for petrofabric studies using Scanning Electron Microscope. By assessing the quantitative microstructural information, i.e. crystallographic orientation data, it allows a large variety of applications: understanding the deformation mechanisms, seismic properties, metamorphic processes; and more recently, performing phase identification and discrimination when combined with Energy Dispersive X-Ray Spectroscopy (EDS). However, it is known that for multiphase mineralogical samples, the information delivered either by EBSD or by EDS alone is not enough to successfully distinguish the present phases. Typical examples for EBSD related indexing issues are phases creating similar patterns; and for EDS technique alone, phases with similar chemical composition like calcite and aragonite, quartz and cristobalite. Recent software and hardware developments have significantly improved the data quality as well as the efficiency/productivity. This presentation aims to reveal the latest development in data processing that has transformed the combination of the two complementary techniques into a powerful tool for characterizing multiphase materials. Through geosciences application examples, we will present the advantages brought by this new approach which uses the quantified EDS results and EBSP to identify the correct phase, reducing the need of data cleaning, and without spending extra time at the SEM. We will also demonstrate how powerful EBSD indexing algorithm can overcome the limitation from sample preparation, with some examples of high hit rate achieved on polyphase mineralogical specimen and even on shock-metamorphosed minerals. Last but not least, recent developments also enable the investigation of nanostructured materials in the scanning electron microscope (SEM) by Transmission Kikuchi Diffraction (TKD). Through some mineralogical applications, we will demonstrate the high spatial resolution (<10 nm) of this technique compared to conventional EBSD. EBSD phase map of an oxide gabbro collected by the Integrated Ocean Drilling Program Expedition 304/305, U1309D. phases: clinopyroxene, clinohypersthene, magnetite, ilmenite, tremolite, plagioclase, quartz, pyrrhotite, apatite, clinochlore. Sample courtesy: Dr. Angela Halfpenny, CSIRO Perth, Australia.

Palasse, L.; Goran, D.; Schwager, T.

2013-12-01

36

Features of Transmission EBSD and its Application  

NASA Astrophysics Data System (ADS)

Features of transmission electron backscatter diffraction (EBSD) observation with a standard EBSD ( s-EBSD) detector are surveyed in this study. Heavily deformed Al and 8Cr tempered martensite transmission electron microscope (TEM) specimens were used for this study. It is shown that a specimen tilt angle of ~30°-40° in the opposite direction of the usual 70° and a smaller working distance in the range 4 mm-5 mm are recommended when using a s-EBSD detector. Specimen thickness and accelerating voltage (Acc.V) have a strong affect on the quality of transmission EBSD patterns and orientation maps. Higher Acc.Vs are generally recommended to get good quality orientation maps. In case of very thin specimens, lowering the Acc.Vs will give better results. In the observation of a thin film of an 8Cr tempered martensite steel specimen, it is confirmed that t-EBSD can provide images and detailed quantitative orientation data comparable with that obtained by TEM. It is also shown that small precipitates of Cr23C6 with sizes around 30 nm could be detected and their orientations measured.

Suzuki, Seiichi

2013-09-01

37

Dihedral corner reflector backscatter using higher order reflections and diffractions  

NASA Technical Reports Server (NTRS)

The uniform theory of diffraction (UTD) plus an imposed edge diffraction extension is used to predict the backscatter cross sections of dihedral corner reflectors which have right, obtuse, and acute included angles. The UTD allows individual backscattering mechanisms of the dihedral corner reflectors to be identified and provides good agreement with experimental cross-section measurements in the azimuthal plane. Multiply reflected and diffracted fields of up to third-order are included in the analysis for both horizontal and vertical polarizations. The coefficients of the uniform theory of diffraction revert to those of the geometrical theory of diffraction (GTD) in far-field cross-section analyses, but finite cross sections can be obtained everywhere by considering mutual cancellation of diffractions from parallel edges. Analytic calculations are performed using UTD coefficients; hence the accuracy required in angular measurements is more critical as the distance increases. The common far-field approximation that all rays to the observation point are parallel is too gross an approxiation for the angular parameters in the UTD coefficients in the far field.

Griesser, Timothy; Balanis, Constantine A.

1987-01-01

38

Electron backscatter diffraction (EBSD) as a tool for detection of coral diagenesis  

E-print Network

, as a consequence of the maximum life span of an individual colony, with dead (fossil) corals pro- viding evidence from subtropical oceans (Cohen et al. 2004; Kuhnert et al. 2005). Porites is reported to display

39

An electron backscatter diffraction investigation of crystallographic orientations of embedded nanoparticles within melt-textured YBCO high temperature superconductors  

NASA Astrophysics Data System (ADS)

Microstructures of melt-textured YBCO samples with embedded nanosized particles of Y2BaCuO5 (Y-211) and Y2Ba4CuMOx (M-2411 with M = U,Zr) are analysed by means of electron backscatter diffraction (EBSD). With the recent developments of the EBSD technique, we can directly measure the crystallographic orientation of the embedded nanoparticles, employing a spatial resolution of about 40 nm. The high image quality of the Kikuchi patterns allows true three-phase (YBCO, Y-211 and M-2411) scans to be performed. The Y-211 particles do not exhibit any preferred orientation, even if their size is considerably reduced, to the 100 nm range. The size reduction reduces the negative influence of the Y-211 particles on the YBCO matrix, however. U-2411 particles, which are formed during the processing stage, do not show any orientation, and with increasing concentration, some texture develops. In contrast to this, embedded Zr-2411 particles are fully oriented in the (001) orientation according to the surrounding superconducting matrix.

Koblischka-Veneva, A.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.; Shlyk, L.; Krabbes, G.

2006-07-01

40

Three-dimensional cathodoluminescence imaging and electron backscatter diffraction: tools for studying the genetic nature of diamond inclusions  

NASA Astrophysics Data System (ADS)

As a step towards resolving the genesis of inclusions in diamonds, a new technique is presented. This technique combines cathodoluminescence (CL) and electron backscatter diffraction (EBSD) using a focused ion beam-scanning electron microscope (FIB-SEM) instrument with the aim of determining, in detail, the three-dimensional diamond zonation adjacent to a diamond inclusion. EBSD reveals that mineral inclusions in a single diamond have similar crystallographic orientations to the host, within ±0.4°. The chromite inclusions record a systematic change in Mg# and Cr# from core to the rim of the diamond that corresponds with a ~80°C decrease of their formation temperature as established by zinc thermometry. A chromite inclusion, positioned adjacent to a boundary between two major diamond growth zones, is multi-faceted with preferred octahedral and cubic faces. The chromite is surrounded by a volume of non-luminescent diamond (CL halo) that partially obscures any diamond growth structures. The CL halo has apparent crystallographic morphology with symmetrically oriented pointed features. The CL halo is enriched in ~200 ppm Cr and ~80 ppm Fe and is interpreted to have a secondary origin as it overprints a major primary diamond growth structure. The diamond zonation adjacent to the chromite is complex and records both syngenetic and protogenetic features based on current inclusion entrapment models. In this specific case, a syngenetic origin is favoured with the complex form of the inclusion and growth layers indicating changes of growth rates at the diamond-chromite interface. Combined EBSD and 3D-CL imaging appears an extremely useful tool in resolving the ongoing discussion about the timing of inclusion growth and the significance of diamond inclusion studies.

Wiggers de Vries, D. F.; Drury, M. R.; de Winter, D. A. M.; Bulanova, G. P.; Pearson, D. G.; Davies, G. R.

2011-04-01

41

Scanning Electron Microscopy\\/Electron Backscatter Diffraction–Based Observations of Martensite Variant Selection and Slip Plane Activity in Supermartensitic Stainless Steels during Plastic Deformation at Elevated, Ambient, and Subzero Temperatures  

Microsoft Academic Search

The deformation-induced martensite variant selection in a supermartensitic stainless steel (SMSS) has been examined in the\\u000a temperature range from ?60 °C to 150 °C, using in-situ tensile testing in combination with electron backscatter diffraction (EBSD) analyses in the scanning electron microscope\\u000a (SEM). In the as-received (i.e., intercritically annealed) condition, the base material contains about 40 vol pct of retained austenite. At each

Morten Karlsen; Øystein Grong; Mario Søfferud; Jarle Hjelen; Gisle Rørvik; Remi Chiron

2009-01-01

42

Influence of Surface Preparation on Scanning Kelvin Probe Microscopy and Electron Backscatter Diffraction Analysis of Cross Sections of CdTe/CdS Solar Cells  

SciTech Connect

Electron backscatter diffraction (EBSD) provides information on the crystallographic structure of a sample, while scanning Kelvin probe microscopy (SKPM) provides information on its electrical properties. The advantage of these techniques is their high spatial resolution, which cannot be attained with any other techniques. However, because these techniques analyze the top layers of the sample, surface or cross section features directly influence the results of the measurements, and sample preparation is a main step in the analysis. In this work we investigated different methods to prepare cross sections of CdTe/CdS solar cells for EBSD and SKPM analyses. We observed that procedures used to prepare surfaces for EBSD are not suitable to prepare cross sections, and we were able to develop a process using polishing and ion-beam milling. This process resulted in very good results and allowed us to reveal important aspects of the cross section of the CdTe films. For SKPM, polishing and a light ion-beam milling resulted in cross sections that provided good data. We were able to observe the depletion region on the CdTe film and the p-n junction as well as the interdiffusion layer between CdTe and CdS. However, preparing good-quality cross sections for SKPM is not a reproducible process, and artifacts are often observed.

Moutinho, H. R.; Dhere, R. G.; Jiang, C. S.; Al-Jassim, M. M.

2011-01-01

43

CCMR: Study of Tailored Oriented Microstructures in Thin Metal Films using SEM and EBSD  

NSDL National Science Digital Library

Thin silver films have many important potential applications but are not presently well understood. Using scanning electron microscopy and electron backscatter diffraction (EBSD) mapping, the microstructure silver films created with a range of different thicknesses, titanium adhesion layers, and annealing temperatures, have been analyzed.

Little, Bethany

2007-08-29

44

Grain Growth Orientation and Anisotropy in Cu6Sn5 Intermetallic: Nanoindentation and Electron Backscatter Diffraction Analysis  

NASA Astrophysics Data System (ADS)

As the size of joints in micro/nano-electronics diminishes, the role of intermetallic (IMC) layers becomes more significant. It was shown that solder joint strength is controlled largely by IMC strength at higher strain rates. Additionally, there is a possibility that very small joints are completely composed of IMCs. Further miniaturization of joints may result in statistical grain size effects. Therefore, it is essential to characterize IMC materials and understand their anisotropic mechanical properties. One of the most common types of IMCs in microelectronic joints is Cu6Sn5, which is formed in a variety of bonding materials with different compositions of Sn, Cu, and Ag. This work studies through nanoindentation elastic-plastic properties of a single grain of Cu6Sn5 IMC in a Sn-3.5Ag/Cu system with reflow soldering. Elastic properties such as elastic modulus and hardness were determined from the nanoindentation load-depth curve. The reverse analysis model described by Dao et al. was used to extract plastic properties such as yield strength and strain hardening exponent from nanoindentation data. Care was taken to achieve indentation of single grains with sufficient accuracy and repeatability. Electron backscatter diffraction (EBSD) mapping was used to determine orientation of Cu6Sn5 grains and to relate the orientation with the load-depth curve results of nanoindentation and the corresponding elastic and plastic properties. The EBSD results indicated that the Cu6Sn5 crystal structure is hexagonal. Columnar growth of the Cu6Sn5 grains was observed as the grains mostly grew along the c-axis of the crystal. Indentation of different grains parallel to the basal plane showed no significant difference in mechanical properties.

Choudhury, Soud Farhan; Ladani, Leila

2014-04-01

45

Assessment of lattice strain, rotation and dislocation content using electron back-scatter diffraction  

NASA Astrophysics Data System (ADS)

Cross-correlation based analysis methods have been developed for electron back scatter diffraction (EBSD) patterns that improve the angular sensitivity to ~10-4 rads. This enables EBSD to be used to study the much smaller misorientations and even local elastic strain fields that are typical in semiconducting materials. Mapping of the lattice rotations and elastic strain variations provides sufficient detail for quantitative analysis of the threading dislocation density through the Nye tensor. The analysis will be briefly described and applications given to GaN and Si/SiGe based systems. Measurements of tilt, twist and elastic strain variations in GaN layers on basal plane sapphire will be reported and compared to results for some epitaxial lateral over grown (ELOG) GaN samples. The effects of misfit interfacial dislocations on the spatial distribution of the full strain and rotation tensors in a partially relaxed SiGe layer will also be shown.

Wilkinson, Angus J.

2011-11-01

46

Acquisition of an Electron Back Scatter Diffraction (EBSD) system for the Zeiss Sigma SEM at Portland State University -- Planetary Major Equipment  

NASA Astrophysics Data System (ADS)

To build on our parent Origins program award, entitled "Shock histories of chondrites as revealed by combined microstructural (TEM), petrographic, and X-ray microtomographic (micro-CT) analysis", we are requesting as Planetary Major Equipment the acquisition of an Electron Back Scatter Diffraction (EBSD) system, which will integrate with a Zeiss Sigma SEM that was installed at Portland State University last year (2010). This EBSD system will greatly augment the science return of the parent grant by allowing quantitative measurements of strain and textural fabrics in grains of all sizes and types across an entire thin section. Such measurements will help link data that are already being obtained with optical light microscopy, transmission electron microscopy, and micro- tomography methods. More generally, the EBSD system will augment the PI's research on the petrology of extraterrestrial materials by providing an additional tool for petrographic analyses, with data that can be used to evaluate strain, grain orientations, grain size distributions, phase proportions, and mineralogy. The equipment will enable quantitative characterization of the crystallography of primitive extraterrestrial materials, which will contribute to a better understanding of the formation and evolution of planetary systems, a major goal of NASA.

Ruzicka, Alex

47

Acquisition of an Electron Back Scatter Diffraction (EBSD) system for the Zeiss Sigma SEM at Portland State University Planetary Major Equipment  

NASA Astrophysics Data System (ADS)

To build on our parent Origins program award, entitled "Shock histories of chondrites as revealed by combined microstructural (TEM), petrographic, and X-ray microtomographic (micro-CT) analysis", we are requesting as Planetary Major Equipment the acquisition of an Electron Back Scatter Diffraction (EBSD) system, which will integrate with a Zeiss Sigma SEM that was installed at Portland State University last year (2010). This EBSD system will greatly augment the science return of the parent grant by allowing quantitative measurements of strain and textural fabrics in grains of all sizes and types across an entire thin section. Such measurements will help link data that are already being obtained with optical light microscopy, transmission electron microscopy, and micro- tomography methods. More generally, the EBSD system will augment the PI's research on the petrology of extraterrestrial materials by providing an additional tool for petrographic analyses, with data that can be used to evaluate strain, grain orientations, grain size distributions, phase proportions, and mineralogy. The equipment will enable quantitative characterization of the crystallography of primitive extraterrestrial materials, which will contribute to a better understanding of the formation and evolution of planetary systems, a major goal of NASA.

Ruzicka, Alex

48

Magnetic domain structure and crystallographic orientation of electrical steels revealed by a forescatter detector and electron backscatter diffraction.  

PubMed

The magnetic properties of non-oriented electrical steels (NOES) are an important factor in determining the efficiency of electric vehicle drivetrains. Due to the highly variable texture of NOES, the relationships between crystal orientation, the magnetic domain structure, and the final magnetic properties are complicated and not fully understood. In this study, a NOES sample was characterized with a method capable of imaging surface magnetic domains using scanning electron microscopy (SEM) with an electron backscatter diffraction (EBSD) system equipped with a forescatter detector. This method used type II magnetic contrast without a specialized SEM setup, and imaged with a resolution limit of approximately 250-300nm. The domain structure of the NOES sample was successfully related to ?, which was defined as the angle between the closest magnetic easy axis and the surface of the sample (the RD-TD plane). However, it was shown that if the easy axes were aligned between neighbouring grains with respect to the grain boundary normal, the domain structure could align with an easy axis that was not the closest to the surface, and complex domain structures could be become wider. This structure and width change of complex domain structures has not been previously observed from single crystal or large-grained material studies. The successful application of this method to reveal the influence of surrounding grains can be used to better understand the magnetic properties of NOES. PMID:24769020

Gallaugher, Matthew; Brodusch, Nicolas; Gauvin, Raynald; Chromik, Richard R

2014-07-01

49

An electron back-scattered diffraction study on the microstructure evolution of severely deformed aluminum AI6061 alloy  

NASA Astrophysics Data System (ADS)

In this paper dynamic strain ageing behavior in an Al-Mg-Si alloy related to equal channel angular pressing (ECAP) was investigated. In order to examine the combined plastic deformation and ageing effects on microstructure evolutions and strengthening characteristics, the Al6061 alloy were subjected to phi=90° ECAP die for up to 4 passes via route Bc at high temperatures. For investigating the effects of ageing temperature and strain rate in ECAP, Vickers hardness tests were performed. The combination of the ECAP process with dynamic ageing at higher temperatures resulted in a significant increase in hardness. The microstructural evolution of the samples was studied using electron back-scattering diffraction (EBSD). The grains of Al6061 aluminum alloy were refined significantly at 100 and 150 °C with greater pass numbers and the distributions of grain size tended to be more uniform with pass number increasing. Frequency of sub-boundaries and low angle grain boundaries (LAGBs) increased at initial stage of deformation, and sub-boundaries and LAGBs evolved into highangle grain boundaries (HAGBs) with further deformation, which resulted in the high frequency of HAGBs in the alloy after ECAP 4 passes.

Vaseghi, M.; Karimi Taheri, A.; Kim, H. S.

2014-08-01

50

Polymineralic orientation analysis of magmatic rocks using Electron Back-Scatter Diffraction: Implications for igneous fabric origin and evolution  

NASA Astrophysics Data System (ADS)

Electron Back-Scatter Diffraction (EBSD), which provides an easy way of acquiring large numbers of individual crystallographic orientation data from different phases, has been applied to the study of magmatic fabrics. Using this technique, the crystallographic preferred orientation (CPO) of plagioclase, biotite, orthopyroxene, hornblende and quartz in natural tonalites and quartzdiorites (from the Santa Olalla Igneous Complex, SW Iberia) deformed during the magmatic stage have been determined. Plagioclase is the coarser phase defining the main fabric in each sample, whereas biotite can display either the same fabric as plagioclase or a completely different one. The differences between these two phases occur because: (1) smaller phases interact with the larger ones to produce more random orientations, (2) under simple shear, finer phases can completely rotate giving a girdle included in the XZ plane, (3) finer phases can more easily preserve relict fabrics, while the coarser phases are completely reoriented by the last stress tensor. The last phases to crystallize show weak to completely random CPOs (hornblende) or completely random distributions (quartz). The study was completed with a shape preferred orientation analysis using the Intercept Method in order to detect weak magmatic lineations, and numerical modelling simulations of theoretically equivalent simple shear situations for each sample.

Romeo, I.; Capote, R.; Lunar, R.; Cayzer, N.

2007-11-01

51

Dependence of the Electron Beam Energy and Types of Surface to Determine EBSD Indexing Reliability in Yttria-Stabilized Zirconia  

SciTech Connect

Electron backscatter diffraction (EBSD) is a powerful technique for the surface microstructure analysis. EBSD analysis of cubic yttria-stabilized zirconia (YSZ) in two and three dimensions (2-D, 3-D) is demonstrated using sequential slicing from a focused ion beam (FIB) followed by EBSD mapping to represent 3-D reconstructed high density grain structure with random orientation. The statistics related to accuracy of EBSD band detection shows that probability of accurate grain orientation detection increased significantly when the electron beam energy is increased from 10 kV to 30 kV. As a result of better sampling with increased interaction volume, a disparity between local and average grain orientation angle also exhibited the dependence of the electron beam energy to determine the accuracy of grain orientation. To study the accuracy and quality of EBSD band detection as a function of surface roughness and over layer formation, rapid EBSD measurement tests are performed on (a) YSZ surfaces ion-polished at ion beam energies of 65 nA at 30 kV and 1 nA at 30 kV and (b) carbon coated versus uncoated YSZ surfaces. The EBSD results at both 10 kV and 30 kV electron beam energies indicate that EBSD band detection accuracy is negatively affected by surface roughness and amorphous over layer formation.

Saraf, Laxmikant V.

2012-04-01

52

Texture Analysis of Melt-Textured and Polycrystalline YBa 2 Cu 3 O y Using EBSD  

Microsoft Academic Search

We applied an electron backscatter diffraction (EBSD) technique to determine the texture and individual crystallite orientations on melt-textured and various polycrystalline YBa2Cu3Oy (YBCO) samples, doped with several Alkali metal additions (KClO3, K2CO3 and Rb2CO3). The EBSD analysis on melt-textured YBCO reveals a direct interplay between the crystal orientations of YBCO and the Y2BaCuO5 (Y-211) particles. The Y-211 particles do not

Anjela Koblischka-Veneva; Michael R. Koblischka

2003-01-01

53

Three-Dimensional Characterization of Microstructure by Electron Back-Scatter Diffraction  

NASA Astrophysics Data System (ADS)

The characterization of microstructures in three dimensions is reviewed, with an emphasis on the use of automated electron back-scatter diffraction techniques. Both statistical reconstruction of polycrystalline structures from multiple cross sections and reconstruction from parallel, serial sections are discussed. In addition, statistical reconstruction of second-phase particle microstructures from multiple cross sections is reviewed.

Rollett, Anthony D.; Lee, S.-B.; Campman, R.; Rohrer, G. S.

2007-08-01

54

Investigation of plastic deformation heterogeneities in duplex steel by EBSD  

SciTech Connect

An EBSD analysis of a duplex steel (austeno-ferritic) deformed in tension up to fracture is presented. The main purpose of the paper is to describe, qualitatively and quantitatively, the differences in the behavior of the two phases during plastic deformation. In order to do so, several topological maps are measured on the deformed state using the electron backscatter diffraction technique. Distributions of grain size, misorientation, image quality factor and texture are then analyzed in detail. - Highlights: Black-Right-Pointing-Pointer Heterogeneities in duplex steel is studied. Black-Right-Pointing-Pointer The behavior of the two phases during plastic deformation is studied. Black-Right-Pointing-Pointer IQ factor distribution and misorientation characteristics are examined using EBSD.

Wronski, S., E-mail: wronski@ftj.agh.edu.pl [Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow (Poland); Tarasiuk, J., E-mail: tarasiuk@ftj.agh.edu.pl [Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow (Poland); Bacroix, B., E-mail: brigitte.bacroix@univ-paris13.fr [LSPM-CNRS, Universite Paris 13, 99, Av. J.-B. Clement, 93430 Villetaneuse (France); Baczmanski, A., E-mail: baczman@ftj.agh.edu.pl [Faculty of Physics and Applied Computer Science, AGH-University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow (Poland); Braham, C., E-mail: chedly.braham@paris.ensam.fr [PIMM, Arts et Metiers ParisTech (ENSAM), 151 Bd de l'Hopital 75013 Paris (France)

2012-11-15

55

Effect of the surface preparation techniques on the EBSD analysis of a friction stir welded AA1100B 4C metal matrix composite  

Microsoft Academic Search

Aluminum based metal matrix composites (MMCs) have been used in various automobile, aerospace and military industries. Yet characterization of the microstructure in these materials remains a challenge. In the present work, the grain structure in the matrix of B4C particulate reinforced MMCs and their friction stir welds is characterized by using optical metallography and the electron backscatter diffraction (EBSD) technique.

J. Guo; S. Amira; P. Gougeon; X.-G. Chen

2011-01-01

56

EBSD for microstructure and property characterization of the SiC-coating in TRISO fuel particles  

Microsoft Academic Search

Tristructural-isotropic (TRISO)-coated particle fuel is being developed for use in the Next Generation Nuclear Plant. The reliable and precise characterization of the microstructure and properties of the SiC layer in the TRISO particle is essential for optimizing processing parameters to ensure reproducibility and performance of the coatings. Electron backscatter diffraction (EBSD) is a time-efficient analytical tool for obtaining a wealth

Lizhen Tan; Todd R. Allen; John D Hunn; James Henry Miller

2008-01-01

57

Microstructural Characterization Using 3-D Orientation Data Collected by an Automated FIB-EBSD System  

Microsoft Academic Search

In this work, a new technique utilizing an automated approach of combining a Focused Ion Beam (FIB) and Electron Back-Scatter Diffraction (EBSD) system was implemented for the collection of 3-D orientation data that can be used to more accurately model grain and sub-grain particle structures. The process is currently capable of sectioning a sample with inter-slice thicknesses as low as

M. Groeber; B. Haley; M. Uchic; S. Ghosh

2004-01-01

58

Phase analysis in duplex stainless steel: comparison of EBSD and quantitative metallography methods  

NASA Astrophysics Data System (ADS)

The purpose of the research was to work out the qualitative and quantitative analysis of phases in DSS in as-received state and after thermal aging. For quantitative purposes, SEM observations, EDS analyses and electron backscattered diffraction (EBSD) methods were employed. Qualitative analysis of phases was performed by two methods: EBSD and classical quantitative metallography. A juxtaposition of different etchants for the revealing of microstructure and brief review of sample preparation methods for EBSD studies were presented. Different ways of sample preparation were tested and based on these results a detailed methodology of DSS phase analysis was developed including: surface finishing, selective etching methods and image acquisition. The advantages and disadvantages of applied methods were pointed out and compared the accuracy of the analysis phase performed by both methods.

Michalska, J.; Chmiela, B.

2014-03-01

59

Characterization of microstructural damage due to low-cycle fatigue by EBSD observation  

SciTech Connect

Electron backscatter diffraction (EBSD) in conjunction with scanning electron microscopy was used to assess the damage due to cyclic or uniform strain. Samples of Type 316 stainless steel after fatigue and tensile tests were prepared for EBSD observation and the misorientation angle between neighboring points (local misorientation) was evaluated. It was shown that the local misorientation developed due to the cyclic and uniform strain and that its spatial distribution was not uniform. In fatigue samples, the area of large local misorientation tended to form clusters, whereas it localized to the grain boundaries in the tensile samples, and the magnitude of local misorientation and the degree of the localization increased with the strain amplitude. The degree of localization was quantified via statistical processing of the measured data. It was also shown that the source of damage (cyclic or uniform strain) and the loading direction could be deduced from the EBSD observations of the damaged sample.

Kamaya, Masayuki, E-mail: kamaya@inss.co.jp [Institute of Nuclear Safety System, Inc., 64 Sata, Mihama-cho, Mikata-gun, Fukui 919-1205 (Japan)

2009-12-15

60

Small area analysis using micro-diffraction techniques  

Microsoft Academic Search

An overall trend toward smaller electronic packages and devices makes it increasingly important and difficult to obtain meaningful diffraction information from small areas. X-ray micro-diffraction, electron back-scattered diffraction (EBSD) and Kossel are micro-diffraction techniques used for crystallographic analysis including texture, phase identification and strain measurements. X-ray micro-diffraction primarily is used for phase analysis and residual strain measurements. X-ray micro-diffraction primarily

RAYMOND P. GOEHNER; RALPH G. TISSOT JR; JOSEPH R. MICHAEL

2000-01-01

61

Need for Standardization of EBSD Measurements for Microstructural Characterization of Thin Film Structures  

NASA Astrophysics Data System (ADS)

Microstructural characterization of metal thin films includes measurement of grain size, crystallographic texture and misorientation angle across grain boundaries. All of these measurements can be made simultaneously by the use of electron backscatter diffraction (EBSD) in the scanning electron microscope. The use of EBSD measurements to characterize microstructure requires the collection and analysis of thousands of individual diffraction patterns, and the extraction of statistical quantities of interest from the data set. The results depend on the particular analytical procedures used. Since the grains in interconnect structures are often much smaller than those in bulk materials, the measurement and reporting protocols require adaptation of procedures developed for bulk materials. Here we demonstrate results from a specific procedure for collecting and analyzing EBSD data on electrodeposited copper films. We show that without careful controls, the apparent grain size can vary by a factor of two or more, and the time required to acquire the data can differ by hours. The demonstrated practical advantages of EBSD over previously available techniques and the severe effect of experimental parameters on the results support the need for standardization of the methods used for microstructural characterization by use of EBSD.

Geiss, Roy H.; Read, David T.

2007-09-01

62

Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Creep-Fatigue Conditions  

NASA Astrophysics Data System (ADS)

EBSD(Electron BackScatter Diffraction) analyses were conducted for studying the quantitative microstructural metrics of creep and creep-fatigue damage for austenitic SUS304HTB boiler tube steel and ferritic Mod.9Cr piping steel. KAM(Kernel Average Misorientation) maps and GOS(Grain Orientation Spread) maps were obtained for these samples and the area averaged values KAMave and GOSave were obtained. While the increasing trends of these misorientation metrics were observed for SUS304HTB steel, the decreasing trends were observed for damaged Mod.9Cr steel with extensive recovery of subgrain structure. To establish more universal parameter representing the accumulation of damage to compensate these opposite trends, the EBSD strain parameters were introduced for converting the misorientation changes into the quantities representing accumulated permanent strains during creep and creep-fatigue damage process. As KAM values were dependent on the pixel size (inversely proportional to the observation magnification) and the permanent strain could be expressed as the shear strain which was the product of dislocation density, Burgers vector and dislocation movement distance, two KAM strain parameters M?KAMnet and M??KAMave were introduced as the sum of product of the noise subtracted KAMnet and the absolute change from initial value ?KAMave with dislocation movement distance divided by pixel size. M??KAMave parameter showed better relationship both with creep strain in creep tests and accumulated creep strain range in creep-fatigue tests. This parameter can be used as the strain-based damage evaluation and detector of final failure.

Fujiyama, Kazunari; Kimachi, Hirohisa; Tsuboi, Toshiki; Hagiwara, Hiroyuki; Ogino, Shotaro; Mizutani, Yoshiki

63

Quantification of ridging in ferritic stainless steel sheets by electron backscattered diffraction R-value maps.  

PubMed

In ferritic stainless steel (FSS), undesirable surface defects of ridging appear during deep drawing. The formation of these defects is attributed to the inhomogeneous distribution of orientations of individual grains. In the present work, a new electron backscattered diffraction R(?)-value map was introduced, and the dependence of the tensile directions on the formation of ridging in an FSS sheet was discussed using this map. The results showed that large grain colonies in the R(?)-value maps lead to the formation of severe ridging in an FSS sheet. PMID:23920166

Lee, Kye-Man; Park, Jieon; Kim, Sangseok; Park, Sooho; Huh, Moo-Young

2013-08-01

64

Effect of the surface preparation techniques on the EBSD analysis of a friction stir welded AA1100-B{sub 4}C metal matrix composite  

SciTech Connect

Aluminum based metal matrix composites (MMCs) have been used in various automobile, aerospace and military industries. Yet characterization of the microstructure in these materials remains a challenge. In the present work, the grain structure in the matrix of B{sub 4}C particulate reinforced MMCs and their friction stir welds is characterized by using optical metallography and the electron backscatter diffraction (EBSD) technique. Optical metallography can partially reveal the grain structure in the matrix of AA1100-16 vol.% B{sub 4}C composite. The EBSD technique has been successfully applied to characterize the grain structure in the AA1100-16 vol.% B{sub 4}C friction stir welds, which provides a powerful tool to follow the microstructural evolution of MMC materials during friction stir welding (FSW). Both mechanical polishing and ion beam polishing are used for the EBSD sample preparation. The effect of the sample preparation on the EBSD data acquisition quality is studied. Some typical examples, such as the identification of grains and subgrains, grain size distribution, deformation fields and the texture components are given. - Highlights: {yields} EBSD has been used to characterize the grain structure of Al-B{sub 4}C MMCs. {yields} Mechanical and ion beam polishing are compared for EBSD sample preparation of MMCs. {yields} EBSD shows great advantages over optical microscopy for microtexture analysis of MMCs.

Guo, J., E-mail: junfeng.guo@cnrc-nrc.gc.ca [University of Quebec at Chicoutimi, Chicoutimi (QC), G7H 2B1 (Canada); Aluminium Technology Centre, National Research Council Canada, Chicoutimi (QC), G7H 8C3 (Canada); Amira, S.; Gougeon, P. [Aluminium Technology Centre, National Research Council Canada, Chicoutimi (QC), G7H 8C3 (Canada); Chen, X.-G. [University of Quebec at Chicoutimi, Chicoutimi (QC), G7H 2B1 (Canada)

2011-09-15

65

The application of electron backscatter diffraction and orientation contrast imaging in the SEM to textural problems in rocks  

Microsoft Academic Search

In a scanning electron microscope (SEM) an electron beam sets up an omni-directional source of scattered electrons within a specimen. Diffraction of these electrons will occur simultaneously on all lattice planes in the sample and the backscattered electrons (BSE), which escape from the specimen, will form a diffraction pattern that can be imaged on a phosphor screen. This is the

DAVID J. PRIOR; ALAN P. B OYLE; FRANK BRENKER; MICHAEL C. CHEADLE; AUSTIN DAY; GLORIA LOPEZ; LUCA PERUZZO; GRAHAM J. POTTS; STEVE REDDY; RICHARD SPIESS; NICK E. TIMMS; PAT TRIMBY; JOHN WHEELER; LENA ZETTERSTRÖM

1999-01-01

66

Combined electron backscatter diffraction and cathodoluminescence measurements on CuInS{sub 2}/Mo/glass stacks and CuInS{sub 2} thin-film solar cells  

SciTech Connect

Electron backscatter diffraction (EBSD) and cathodoluminescence (CL) measurements in a scanning electron microscope were performed on cross sections of CuInS{sub 2} thin films and ZnO/CdS/CuInS{sub 2}/Mo/glass thin-film solar cells. The CuInS{sub 2} layers analyzed for the present study were grown by a rapid thermal process. The regions of the CuInS{sub 2} layers emitting high CL intensity of band-band luminescence are situated near the top surface (or close to the interface with ZnO/CdS). This can be attributed to an enhanced crystal quality of the thin films in this region. The phenomenon may be related to the recrystallization via solid-state reactions with Cu{sub x}S phases, which is assumed to run from the top to the bottom of the growing CuInS{sub 2} layer. The distribution of CL intensities is independent of the sample temperature, the acceleration voltage of the electron beam, and of whether or not the ZnO/CdS window layers are present. When comparing CL images and EBSD maps on identical sample positions, pronounced intragrain CL contrast is found for individual grains. Also, it is shown that at random grain boundaries, the decreases in CL intensities are substantially larger than at {Sigma}3 grain boundaries.

Abou-Ras, D.; Nichterwitz, M.; Unold, T.; Klaer, J.; Schock, H.-W. [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Glienicker Strasse 100, 14109 Berlin (Germany); Jahn, U. [Paul-Drude Institute for Solid-State Electronics, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

2010-01-15

67

Ultraprecise studies of the thermal expansion coefficient of diamond using backscattering x-ray diffraction.  

SciTech Connect

The linear thermal expansion coefficient of diamond crystals of type IIa and type Ia was measured in the temperature range from 10 to 295 K. Neither negative thermal expansion nor any substantial difference in the thermal expansion coefficient in crystals of the different types were observed. An empirical expression was obtained that approximates the temperature dependence of the thermal expansion coefficient of diamond. The T{sup 3} temperature dependence of a Debye solid holds below {approx}100 K with an accuracy of {approx}10{sup -8} K{sup -1}. A slight increase in the value of the lattice parameter was found for the Ia-type crystal, which suggests lattice dilatation by nitrogen impurity. The measurements were performed using Bragg diffraction in backscattering from diamond crystals of highly monochromatic 23.7 keV x rays with the recently demonstrated high relative accuracy of 1.2 x 10{sup -8} in the determination of the lattice parameter.

Stoupin, S.; Shvyd'ko, Y. (X-Ray Science Division)

2011-03-17

68

Backscatter analysis of dihedral corner reflectors using physical optics and the physical theory of diffraction  

NASA Technical Reports Server (NTRS)

The backscatter cross-sections of dihedral corner reflectors in the azimuthal plane are presently determined by both physical optics (PO) and the physical theory of diffraction (PTD), yielding results for the vertical and horizontal polarizations. In the first analysis method used, geometrical optics is used in place of PO at initial reflections in order to maintain the planar character of the reflected wave and reduce the complexity of the analysis. In the second method, PO is used at almost every reflection in order to maximize the accuracy of the PTD solution at the expense of a rapid increase in complexity. Induced surface current densities and resulting cross section patterns are illustrated for the two methods.

Griesser, Timothy; Balanis, Constantine A.

1987-01-01

69

EBSD study of the microstructure evolution in a commercially pure aluminium severely deformed by ECAP  

NASA Astrophysics Data System (ADS)

Equal channel angular pressing (ECAP) is a promising technique for production of ultrafine-grain materials of a few hundred nanometres size. In the present paper commercially pure aluminium billets were processed by ECAP up to 8 passes using the route BC in which the samples were rotated about the longitudinal axis by 90° in the same direction after each consecutive pressing. Electron backscattered diffraction (EBSD) was used to evaluate the microstructure of the aluminium. EBSD scans revealed a fairly homogeneous ultrafine grained microstructure after 8 passes. This analysis also showed that the fraction of high angle grain boundaries and average grain size were about 70 % and 1500 nm, respectively. Then, tensile properties of the aluminium billets were evaluated. The results represent that the yield stress of aluminium is increased significantly by about four times after application of four consecutive passes of ECAP and then it remains approximately constant.

Tolaminejad, B.; Brisset, F.; Baudin, T.

2012-03-01

70

Hyperspectral Imaging at the Micro and Nanoscale using Energy-dispersive Spectroscopy (EDS) with Silicon Drift Detector (SDD) and EBSD Analysis  

Microsoft Academic Search

SDD systems have become state of the art technology in the field of EDS. The main characteristic of the SDDs is their extremely high pulse load capacity of up to 750,000 counts per second at good energy resolution (<123 eV Mn-Kalpha, <46 eV C-Kalpha at 100,000 counts per seconds). These properties in conjunction with electron backscatter diffraction (EBSD) technique and

T. Salge; D. Goran

2010-01-01

71

Embedded Y 2Ba 4CuNbO x nanoparticles in melt-textured YBCO studied by means of EBSD  

Microsoft Academic Search

Melt-textured YBCO samples with embedded nanosize particles of Y2Ba4CuNbOx (Nb-2411) have been studied by means of electron backscatter diffraction (EBSD). The microstructure of these samples shows some distinct and unusual features, not observed in melt-textured bulk samples of other compositions. The resulting texture of the superconducting YBCO matrix is found to be excellent. Y2BaCuO5 (Y-211) particles, which are also present

A. Koblischka-Veneva; M. R. Koblischka; N. Hari Babu; D. A. Cardwell; F. Mücklich

2006-01-01

72

EBSD and Nanoindentation-Correlated Study of Delamination Fracture in Al-Li Alloy 2090  

NASA Technical Reports Server (NTRS)

Al-Li alloys offer attractive combinations of high strength and low density. However, a tendency for delamination fracture has limited their use. A better understanding of the delamination mechanisms may identify methods to control delaminations through processing modifications. A combination of new techniques has been used to evaluate delamination fracture in Al-Li alloys. Both high quality electron backscattered diffraction (EBSD) information and valid nanoindentation measurements were obtained from fractured test specimens. Correlations were drawn between nano-scale hardness variations and local texture along delaminating boundaries. Intriguing findings were observed for delamination fracture through the combined analysis of grain orientation, Taylor factor, and kernel average misorientation.

Tayon, Wesley A.; Crooks, Roy E.; Domack, Marcia S.; Wagner, John A.; Elmustafa, A. A.

2008-01-01

73

A novel EBSD-based finite-element wave propagation model for investigating seismic anisotropy: Application to Finero Peridotite, Ivrea-Verbano Zone, Northern Italy  

NASA Astrophysics Data System (ADS)

novel electron backscatter diffraction (EBSD) -based finite-element (FE) wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples. The FE model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2D EBSD sections. The numerical model allows separation of the effects of crystallographic preferred orientation (CPO) and shape preferred orientation (SPO). The obtained seismic velocities with respect to specimen orientation are compared with Voigt-Reuss-Hill estimates and with laboratory measurements. The results of these three independent methods testify that CPO is the dominant factor controlling seismic anisotropy. Fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large (up to 23%). The SPO influence is minor compared to the other factors. The presented FE model is discussed with regard to its potential in simulating seismic wave propagation using EBSD data representing natural rock petrofabrics.

Zhong, Xin; Frehner, Marcel; Kunze, Karsten; Zappone, Alba

2014-10-01

74

Grain boundary studies of high temperature superconducting materials using electron backscatter Kikuchi diffraction  

SciTech Connect

Grain Orientation and gain boundary misorientation distributions in high critical current density, high temperature superconductors were determined using electron backscatter Kikuchi diffraction. It is found that depending on the type of superconductor and the processing method used to fabricate it, there exist different scales of biaxial texture from no biaxial texture, local biaxial texture, to complete biaxial texture. Experimentally obtained grain boundary misorientation distributions (GBMDs) were found to be skewed significantly to low angles in comparison to what is expected on the basis of macroscopic texture alone, suggesting that minimization of energy may be a driving force during the processing of high critical current density materials. In addition, a higher than expected fraction of coincident-site lattice boundaries is observed. Examination of maps of grain boundary misorientations in spatially correlated gains, i.e. the grain boundary mesotexture, suggests the presence percolative paths of high critical current density. A combination of orientation measurements, theoretical modeling of GBMDs and modeling of percolative current flow through an assemblage of gain boundaries is performed to gain an insight into the important microstructural features dictating the transport properties of high temperature superconductors. It is found that maximization of low energy, in particular, low angle boundaries is essential for higher critical currents. The combination of experimental and analytical techniques employed are applicable to other materials where physical properties are dominated by interganular characteristics.

Goyal, A.; Specht, E.D.; Wang, Z.L.; Kroeger, D.M.

1996-12-31

75

Comparison of nanoscale measurements of strain and stress using electron back scattered diffraction and confocal Raman microscopy  

NASA Astrophysics Data System (ADS)

Stresses in Si as small as 10 MPa have been measured using electron backscattered diffraction (EBSD) and confocal Raman microscopy (CRM) with spatial resolutions of 10 nm and 100 nm, respectively. In both techniques, data were collected across wedge indentations in (001) Si. EBSD measured the stress and strain tensors and CRM measured the uniaxial stress. The results agreed very well except close to the indentation, where the surface-sensitive EBSD results indicated larger stresses. Results converged when the CRM laser excitation wavelength was reduced, probing smaller depths. The stress profiles are consistent with the inverse-square power law predicted by Eshelby analysis.

Vaudin, Mark D.; Gerbig, Yvonne B.; Stranick, Stephan J.; Cook, Robert F.

2008-11-01

76

Garnet Deformation Microstructures: TEM vs. EBSD  

NASA Astrophysics Data System (ADS)

The development of electron backscatter diffraction (EBSD) and orientation contrast (OC) analysis enable us to study the microstructure of minerals and to measure the orientation of all crystallographic axes in thin sections with resolution down to sub micrometer scale. One of the great advantages of this methods is that it is now possible to study cubic crystals, such as garnet, which are isotropic for light. The application of this new technique to the study of garnets revealed an unexpected wide variety of microstructures, which are not all related to the deformation of garnet. The orientation distribution analyses help to distinguish between brittle or plastic deformation, grain or subgrain boundaries and growth defects. Garnet microstructures related to plastic deformation are characterized by the development of rotation axes if a transect across several garnet subgrains is measured with small crystallographic mismatches (<3° ) across cell boundaries. Each specific rotation axis is directly related to the activated slip system. If more than one slip system is involved, the identification of individual is not always possible. In order to fully characterize the deformation microstructure additional transmission electron microscopical (TEM) work is needed. Here we present new data on garnet deformation microstructures characterized by EBSD and TEM techniques. In some cases a connection between cell boundary and chemical composition is observed by comparing OC, BSE and element mapping. The same area is studied by analytical TEM and shows subgrain boundaries as well as indications for brittle failure with subsequent refilling of a newly grown garnet. In the case of subgrain boundaries a higher diffusivity is expected along dislocation cores. In order to get a more general view about the net effect of microstructuring of garnet, bulk diffusion calculations were performed for homogeneously distributed defects and a network of subgrain boundaries. Assuming the same enhancement of diffusion by microstructuring as in metal, garnet remains an open system for homogeneously distributed defects below 600 to 650° C at strain rates in the order of 10-12 s-1. A closely spaced network of subgrain boundaries will affect bulk diffusion at even higher temperatures. Our data suggest that deformation microstructures in garnet are more frequent than previously assumed and that microstructures may significantly enhance bulk diffusion coefficients. As a consequence the microstructure of garnet must be considered when applying geo-chronological or thermo-barometrical techniques.

Brenker, F. E.; Prior, D. J.

2003-12-01

77

Boundary identification in EBSD data with a generalization of fast multiscale clustering.  

PubMed

Electron backscatter diffraction (EBSD) studies of cellular or subgrain microstructures present problems beyond those in the study of coarse-grained polycrystalline aggregates. In particular, identification of boundaries delineating some subgrain structures, such as microbands, cannot be accomplished simply with pixel-to-pixel misorientation thresholding because many of the boundaries are gradual transitions in crystallographic orientation. Fast multiscale clustering (FMC) is an established data segmentation technique that is combined here with quaternion representation of orientation to segment EBSD data with gradual transitions. This implementation of FMC addresses a common problem with segmentation algorithms, handling data sets with both high and low magnitude boundaries, by using a novel distance function that is a modification of Mahalanobis distance. It accommodates data representations, such as quaternions, whose features are not necessarily linearly correlated but have known distance functions. To maintain the linear run time of FMC with such data, the method requires a novel variance update rule. Although FMC was originally an algorithm for two-dimensional data segmentation, it can be generalized to analyze three-dimensional data sets. As examples, several segmentations of quaternion EBSD data sets are presented. PMID:23751208

McMahon, Cullen; Soe, Brian; Loeb, Andrew; Vemulkar, Ayyappa; Ferry, Michael; Bassman, Lori

2013-10-01

78

Scanning Electron Microscopy/Electron Backscatter Diffraction-Based Observations of Martensite Variant Selection and Slip Plane Activity in Supermartensitic Stainless Steels during Plastic Deformation at Elevated, Ambient, and Subzero Temperatures  

NASA Astrophysics Data System (ADS)

The deformation-induced martensite variant selection in a supermartensitic stainless steel (SMSS) has been examined in the temperature range from -60 °C to 150 °C, using in-situ tensile testing in combination with electron backscatter diffraction (EBSD) analyses in the scanning electron microscope (SEM). In the as-received ( i.e., intercritically annealed) condition, the base material contains about 40 vol pct of retained austenite. At each testing temperature, this austenite transforms back to martensite during plastic deformation at a rate which is controlled by the accumulated plastic strain in the material. On the other hand, the applied strain rate and crystallographic orientations of the prior austenite grains do not affect the overall transformation rate. Moreover, the subsequent Schmid factor analysis reveals that the martensite variant selection is independent of the local slip activity within the austenite. Therefore, no new martensite variants, besides those already present in the parent steel, develop during the phase transformation. At the same time, their individual intensities remain approximately constant within each prior austenite grain. This means that the deformation-induced martensite variants nucleate from the same sites as those that are operative in the intercritically-annealed base material. Thus, the observed variant selection is another example of the inherent reversible nature of the martensite transformation.

Karlsen, Morten; Grong, Øystein; Søfferud, Mario; Hjelen, Jarle; Rørvik, Gisle; Chiron, Remi

2009-02-01

79

Crystal preferred orientations of garnet: comparison between numerical simulations and electron back-scattered diffraction (EBSD) measurements in naturally deformed eclogites  

NASA Astrophysics Data System (ADS)

Observations of dislocations, sub-grains and elongated crystal shapes support plastic deformation of garnet in laboratory experiments and naturally deformed eclogites. To evaluate the crystal preferred orientations (CPO) of garnet formed in axial shortening, pure shear and simple shear, we performed numerical simulations of CPO development during plastic flow using the visco-plastic self-consistent model. As input for the models we use the slip systems determined by transmission electron microscopy using experimentally deformed specimens. Although in garnet 66 slip systems are available, slip on the <111>{110} system provides over 86% of the total strain in the simulations. Characteristic CPO distributions are produced for the three deformation paths, with the CPO being strongest for axial shortening and weakest for simple shear. Compared with low-symmetry minerals, the pole figure densities of garnet, which has cubic symmetry, are weak. <100> axes tend to align with the shortening direction in all three deformation modes. The simulations are compared with CPO of naturally deformed garnet from nine eclogite samples from the Alps, Norway, and Mali, which contain 20-40% garnet. All samples show weak garnet CPO. Only two samples have a CPO pattern similar to the simulations for simple shear, no samples are similar to simulations for axial strain or pure shear. The presence of other weaker minerals, such as omphacite and quartz, with volume fractions higher than garnet, probably prevented garnet from becoming highly strained and developing characteristic CPOs in these eclogites. Higher volume fractions of garnet and higher temperature conditions may, however, allow the development of garnet CPO in the mantle transition zone, particularly within subducted oceanic material (MORB).

Mainprice, David; Bascou, Jérôme; Cordier, Patrick; Tommasi, Andréa

2004-11-01

80

First combined electron backscatter diffraction and transmission electron microscopy study of grain boundary structure of deformed quartzite.  

PubMed

The structures of boundaries in a deformed and dynamically recovered and recrystallized quartz polycrystal (mylonite) were characterized by transmission electron microscopy, after the misorientation angles across the same grain boundaries had been analysed using electron backscatter diffraction in a scanning electron microscope. In this new approach, a specific sample area is mapped with electron backscatter diffraction, and the mapped area is then attached to a foil, and by the ion beam thinned for transmission electron microscopy analysis. Dislocations in grain boundaries were recognized as periodic and parallel fringes. The fringes associated with dislocations are observed in boundaries with misorientations less than 9 degrees , whereas such fringes cannot be seen in the boundaries with misorientations larger than 17 degrees . Some boundaries with misorientations between 9 degrees and 17 degrees generally have no structures associated with dislocation. One segment of a boundary with a misorientation of 13.5 degrees has structures associated with dislocations. It is likely that the transition from low-angle to high-angle boundaries occurs at misorientations ranging from approximately 9 degrees to 14 degrees . Change in the grain boundary structure presumably influences the mobility of the boundaries. In the studied deformed quartz vein, a relative dearth of boundaries between misorientation angles of theta = 2 degrees and theta = 15 degrees has previously been reported, and high-angle boundaries form cusps where they intersect low-angle boundaries, suggesting substantial mobility of high-angle boundaries. PMID:17210063

Shigematsu, N; Prior, D J; Wheeler, J

2006-12-01

81

Assessing the precision of strain measurements using electron backscatter diffraction--part 2: experimental demonstration.  

PubMed

The residual impression after performing a microhardness indent in silicon has been mapped with high resolution EBSD to reveal residual elastic strain and lattice rotation fields. Mapping of the same area has been performed with variable pattern binning and exposure times to reveal the qualitative and quantitative differences resulting from reducing the pattern size and exposure time. Two dimension 'image' plots of these fields indicate that qualitative assessment of the shape and size of the fields can be performed with as much as 4×4 binning. However, quantitative assessment using line scans reveals that the smoothest profile can be obtained using minimal pattern binning and long exposure times. To compare and contrast with these experimental maps, finite element analysis has been performed using a continuum damage-plasticity material law which has been independently calibrated to Si [9]. The constitutive law incorporates isotropic hardening in compression, and isotropic hardening and damage in tension. To accurately capture the localised damage which develops during indentation via the nucleation and propagation of cracks around the indentation site cohesive elements were assigned along the interfaces between the planes which experience the maximum traction. The residual strain state around the indenter and the size of the cracks agree very well with the experimentally measured value. PMID:24034981

Britton, T B; Jiang, J; Clough, R; Tarleton, E; Kirkland, A I; Wilkinson, A J

2013-12-01

82

Electron Back-Scatter Diffraction Analysis of Pre and Post-Deformation Ti-6Al-4V Taylor Impact Specimens  

NASA Astrophysics Data System (ADS)

Titanium alloys have seen wide spread, and ever increasing, use in the aerospace industry, due to a high specific strength and good resistance to corrosion. However, current understanding of the deformation mechanisms of Titanium alloys under complex high strain rate loading is limited. In order to improve understanding in this area, post-deformation microstructural analyses of Titanium alloys loaded under well controlled, but complex, high strain rate loading conditions, such as the Taylor impact test, are required. This paper presents the results of Taylor impact experiments carried out on specimens cut from the rolling and transverse material directions of two heavily textured Ti-6Al-4V plates with different microstructures. Electron back-scatter diffraction analysis has been performed on pre and post-deformation specimens with comparisons made between the deformed microstructures of the two plates in the rolling and transverse material orientations.

Wielewski, Euan; Eggleston, Joshua; Siviour, Clive; Petrinic, Nik

2011-06-01

83

Fluvial suspended sediment characteristics by high-resolution, surrogate metrics of turbidity, laser-diffraction, acoustic backscatter, and acoustic attenuation  

NASA Astrophysics Data System (ADS)

Sedimentation is a primary and growing environmental, engineering, and agricultural issue around the world. However, collection of the data needed to develop solutions to sedimentation issues has declined by about three-fourths since 1983. Suspended-sediment surrogates have the potential to obtain sediment data using methods that are more accurate, of higher spatial and temporal resolution, and with less manually intensive, costly, and hazardous methods. The improved quality of sediment data from high-resolution surrogates may inform improved understanding and solutions to sedimentation problems. The field experiments for this research include physical samples of suspended sediment collected concurrently with surrogate metrics from instruments including 1.2, 1.5, and 3.0 megahertz frequency acoustic doppler current profilers, a nephelometric turbidity sensor, and a laser-diffraction particle size analyzer. This comprehensive data set was collected over five storms in 2009 and 2010 at Yellow River near Atlanta, Georgia. Fluvial suspended sediment characteristics in this study can be determined by high-resolution surrogate parameters of turbidity, laser-diffraction and acoustics with model errors 33% to 49% lower than traditional methods using streamflow alone. Hysteresis in sediment-turbidity relations for single storm events was observed and quantitatively related to PSD changes of less than 10 microns in the fine silt to clay size range. Suspended sediment particle size detection (PSD) is significantly correlated with ratios of measured acoustic attenuation at different frequencies; however the data do not fit the theoretical relations. Using both relative acoustic backscatter (RB) and acoustic attenuation as explanatory variables results in a significantly improved model of suspended sediment compared with traditional sonar equations using only RB. High resolution PSD data from laser diffraction provide uniquely valuable information; however the size detection limits of the instrument is a significant limitation.

Landers, Mark Newton

84

Metallographic Preparation of Space Shuttle Reaction Control System Thruster Electron Beam Welds for Electron Backscatter Diffraction  

NASA Technical Reports Server (NTRS)

A Space Shuttle Reaction Control System (RCS) thruster failed during a firing test at the NASA White Sands Test Facility (WSTF), Las Cruces, New Mexico. The firing test was being conducted to investigate a previous electrical malfunction. A number of cracks were found associated with the fuel closure plate/injector assembly (Fig 1). The firing test failure generated a flight constraint to the launch of STS-133. A team comprised of several NASA centers and other research institutes was assembled to investigate and determine the root cause of the failure. The JSC Materials Evaluation Laboratory was asked to compare and characterize the outboard circumferential electron beam (EB) weld between the fuel closure plate (Titanium 6Al-4V) and the injector (Niobium C-103 alloy) of four different RCS thrusters, including the failed RCS thruster. Several metallographic challenges in grinding/polishing, and particularly in etching were encountered because of the differences in hardness, ductility, and chemical resistance between the two alloys and the bimetallic weld. Segments from each thruster were sectioned from the outboard weld. The segments were hot-compression mounted using a conductive, carbon-filled epoxy. A grinding/polishing procedure for titanium alloys was used [1]. This procedure worked well on the titanium; but a thin, disturbed layer was visible on the niobium surface by means of polarized light. Once polished, each sample was micrographed using bright field, differential interference contrast optical microscopy, and scanning electron microscopy (SEM) using a backscatter electron (BSE) detector. No typical weld anomalies were observed in any of the cross sections. However, areas of large atomic contrast were clearly visible in the weld nugget, particularly along fusion line interfaces between the titanium and the niobium. This prompted the need to better understand the chemistry and microstructure of the weld (Fig 2). Energy Dispersive X-Ray Spectroscopy (EDS) was used to confirm the chemical composition of the variations in contrast in these areas. Niobium alloys generally require exposure to more aggressive chemical reagents than titanium alloys for etching because of niobium s chemical resistance; therefore, the titanium portion of the sample was etched first. A five second immersion in Kroll s reagent revealed a general microstructure on the titanium portion of the sample; however, the titanium heat affected zone closest to the weld, was over-etched due to higher concentrations of refined grains and an increase in eta-phase. The Kroll s etchant also revealed some microstructure in the weld nugget itself; the niobium portion of the sample remained unetched.

Martinez, James

2011-01-01

85

EBSD for microstructure and property characterization of the SiC-coating in TRISO fuel particles  

NASA Astrophysics Data System (ADS)

Tristructural-isotropic (TRISO)-coated particle fuel is being developed for use in the Next Generation Nuclear Plant. The reliable and precise characterization of the microstructure and properties of the SiC layer in the TRISO particle is essential for optimizing processing parameters to ensure reproducibility and performance of the coatings. Electron backscatter diffraction (EBSD) is a time-efficient analytical tool for obtaining a wealth of information on the SiC layer. In this study, we report the application of EBSD to the analysis of the SiC layer in a TRISO particle. The SiC layer identified as 3C-SiC with an average elastic stiffness of ˜402 GPa was mainly composed of random boundaries with a small fraction of low-? CSLBs. A few large grains, which were generally associated with local strains and tended to be columnar with the long axis oriented approximately along the TRISO particle radial direction, were observed in the SiC layer with an increased population from the IPyC-SiC to the SiC-OPyC interfaces.

Tan, L.; Allen, T. R.; Hunn, J. D.; Miller, J. H.

2008-01-01

86

EBSD study of substrate-mediated growth of hexagonal boron nitride  

NASA Astrophysics Data System (ADS)

Hexagonal Boron Nitride (h-BN) is a promising insulating material to complement and enable graphene electronics. Given the good lattice match to graphite, graphene/h-BN heterostructures may be grown with negligible amounts of strain and defect states, resulting in high carrier mobilities approaching values for suspended graphene. Chemical vapour deposition (CVD) has emerged as one of the preferred routes for the synthesis of 2D materials for electronic applications. Here we report on the growth of h-BN by low pressure CVD, using borazine as a precursor. Electron backscattered diffraction (EBSD) in conjunction with topographic imaging in the scanning electron microscope are used to investigate the change in crystal structure and orientation of three metallic catalyst substrates: Co, Ni and Cu, by high temperature processing and the growth of nanoscale h-BN domains. The behaviour of the metal foils is interpreted in light of the prevalent growth models. EBSD and imaging conditions are optimized to allow efficient acquisitions for these composite and nanostructured specimens.

Dias, J.; Kidambi, P. R.; Hofmann, S.; Ducati, C.

2014-06-01

87

Microstructural Characterization Using 3-D Orientation Data Collected by an Automated FIB-EBSD System  

NASA Astrophysics Data System (ADS)

In this work, a new technique utilizing an automated approach of combining a Focused Ion Beam (FIB) and Electron Back-Scatter Diffraction (EBSD) system was implemented for the collection of 3-D orientation data that can be used to more accurately model grain and sub-grain particle structures. The process is currently capable of sectioning a sample with inter-slice thicknesses as low as 100 nanometers and capturing an orientation map of each slice. Automation of this technique allowed for rapid data collection with the ability to update settings in real time. The orientation data obtained by the EBSD scans consists of each grid point's position, three Euler angles and phase. Reconstruction of the 3-D orientation data involves combining or "stacking" the 2-D slices obtained by the FIB-EBSD process. The orientation data of each slice is combined into one data file containing orientation information for each point on the 3-D grid, which can have spacing as little as 100 nanometers in all three directions. A program developed in this work, Micro-Mesher, uses the reconstructed orientation information to define microstructural features such as grains and second phase particles. Micro-Mesher constructs grain boundaries with line and plane segments using an error per unit length approach to approximate the complex grain boundaries. Important microstructural statistics that are used to define and characterize the 3-D microstructure are also calculated by Micro-Mesher. Such important parameters include: grain size, no. of neighboring grains, orientations and misorientations, second phase particles size and inter particle spacing as well as others. The 3-D statistical information gained from this process improves the ability to accurately characterize the microstructure.

Groeber, M.; Haley, B.; Uchic, M.; Ghosh, S.

2004-06-01

88

Lattice strain across Na-K interdiffusion fronts in alkali feldspar: an electron back-scatter diffraction study  

NASA Astrophysics Data System (ADS)

Cation exchange experiments between gem quality sanidine and KCl melt produced chemical alteration of alkali feldspar starting at the grain surface and propagating inwards by highly anisotropic Na-K interdiffusion on the alkali sublattice. Diffusion fronts developing in b-direction are very sharp, while diffusion fronts within the a- c-plane are comparatively broad. Due to the composition dependence of the lattice parameters of alkali feldspar, the diffusion induced compositional heterogeneity induces coherency stress and elastic strain. Electron back-scatter diffraction combined with the cross-correlation technique was employed to determine the lattice strain distribution across the Na-K interdiffusion fronts in partially exchanged single crystals of alkali feldspar. The strain changes gradually across the broad fronts within the a- c-plane, with a successive extension primarily in a-direction conferring to the composition strain in unstressed alkali feldspar. In contrast, lattice strain characterised by pronounced extension in b-direction is localised at the sharp diffusion fronts parallel to b, followed by a slight expansion in a-direction in the orthoclase-rich rim. This strain pattern does not confer with the composition induced lattice strain in a stress-free alkali feldspar. It may rather be explained by the mechanical coupling of the exchanged surface layer and the mechanically strong substratum. The lattice distortion localised at the sharp diffusion front may have an influence on the diffusion process and appears to produce a self-sharpening feedback, leading to a local reduction of component mobilities.

Schäffer, Anne-Kathrin; Jäpel, Tom; Zaefferer, Stefan; Abart, Rainer; Rhede, Dieter

2014-11-01

89

Insights to Meteorites and Impact Processes provided by Advanced EBSD Analysis  

NASA Astrophysics Data System (ADS)

Electron backscatter diffraction (EBSD) is a powerful analytical technique for assessing the petrographic texture of rocks and the crystallographic orientation of minerals therein using a scanning electron microscope (SEM). Innovations in EBSD technology include colour-coded forescattered electron (FSE) images, high resolution and highly sensitive EBSD detectors, together with advanced EDS integration. It allows to accurately identify and discriminate different phases, and to investigate microstructures related to shock metamorphism. As an example, shocked carbonates and shocked quartz reveal a complex thermal history during post-shock cooling. (A) EBSD studies of calcite ejecta particles from the Chicxulub impact event, at the K-Pg boundary of El Guayal, Mexico (~520 km SW of the Chicxulub crater centre) display various microstructures [1] and spherulitic calcite ejecta particles reveal a fibre texture of elongated crystals with a preferred orientation. This indicates the presence of carbonate melts which were ejected at T>1240°C and P>40 bar from upper target lithologies and crystallized at cooling rates of ~100´s °C/s [2]. The calcite particles of El Guayal and the K/Pg boundary of La Lajilla (~1000 km W of the crater centre) show distinct microstructures represented by unoriented, equiaxed crystals with random orientation distribution. It documents recrystallization upon impact induced thermal stress at T>550°C during prolonged atmospheric transport. (B) Combined EBSD, FSE and cathodoluminescence (CL) studies of semi-amorphous shocked quartz of Chicxulub, Ries and Popigai impactites, reveal various microstructures. Colour-coded FSE imaging reveal recrystallized/deformed bands in Ries and Popigai samples indicative of planar deformation features. EBSD studies of Popigai allow to distinguish twinned Qz, ?-Qz and ?-cristobalite along the transition zone between shocked gneiss clast and impact melt. Recrystallized Qz grains are associated with amorphous SiO2. For Chicxulub, the brecciated impact melt rock from borehole Yaxcopoil-1 (Unit 5, 861.72 m) [3] reveals that the ballen microstructure is only semi-amorphous and cross cuts a fine grained recrystallised microstructure. (C) CB chondrite Gujba: EDS and EBSD data were acquired simultaneously to study chemical and physical interactions between preexisting metal particles and the invading silicate-rich impact melt matrix. Metal particles appear to have different thermal histories. Some of them consist of many small grains (average diameter ~10 µm), which have a similar orientation when they are surrounded by arcuate Fe,Cr-sulfides. [4]. Acknowledgements: P. Claeys, R.H. Jones, ICDP and the Museum of Natural History Berlin for providing samples. References: [1] T. Salge (2007) PhD thesis, Humboldt Universität zu Berlin, 130p. [2] A. P. Jones et al. (2000) Lect. Notes in Earth Sciences 91: 343-361. [3] M. J. Nelson et al. (2012) GCA 86: 1-20. [4]. J. Berlin et al. (2013) 44th LPSC # 2439

Palasse, Laurie; Berlin, Jana; Goran, Daniel; Tagle, Roald; Hamers, Maartje; Assis Fernandes, Vera; Deutsch, Alexander; Schulte, Peter; Salge, Tobias

2013-04-01

90

Lattice strain across Na-K interdiffusion fronts in alkali feldspar: an electron back-scatter diffraction study  

NASA Astrophysics Data System (ADS)

Cation exchange experiments between gem quality sanidine (X_Or = 0.85) and KCl melt produced chemical alteration of alkali feldspar starting at the grain surface and propagating inwards by highly anisotropic Na-K interdiffusion on the alkali sublattice. Diffusion fronts developing in b-direction are very sharp, while diffusion fronts within the a-c-plane are comparatively broad. Due to the composition dependence of the lattice parameters of alkali feldspar, the diffusion induced compositional heterogeneity induces coherency stress and elastic strain. Electron back-scatter diffraction combined with the cross-correlation technique was employed to determine the lattice strain distribution across the Na-K interdiffusion fronts in partially exchanged single crystals of alkali feldspar. The strain changes gradually across the broad fronts within the a-c-plane, with a successive extension primarily in a-direction conferring to the composition strain in unstressed alkali feldspar. In contrast, lattice strain characterised by pronounced extension in b-direction is localised at the sharp diffusion fronts parallel to b, followed by a slight expansion in a-direction in the orthoclase-rich rim. This strain pattern does not confer with the composition induced lattice strain in a stress-free alkali feldspar. It may rather be explained by the mechanical coupling of the exchanged surface layer and the mechanically strong substratum. The lattice distortion localised at the sharp diffusion front may have an influence on the diffusion process and appears to produce a self-sharpening feedback, leading to a local reduction of component mobilities.

Schäffer, Anne-Kathrin; Jäpel, Tom; Zaefferer, Stefan; Abart, Rainer; Rhede, Dieter

2014-06-01

91

An ultrahigh-density digital data read-out method based on grazing-angle incidence x-ray backscattering diffraction  

Microsoft Academic Search

An ultrahigh-density x-ray optical data storage medium useful for terabyte-scale memory applications and named X-ROM is proposed. The X-ROM is a nanocrystalline semiconductor layer, in which non-diffracting nanosized reflectors of x-radiation are embedded. The procedure of digital data read-out from the X-ROM can be performed e.g. by the application of a grazing-angle incidence x-ray backscattering diffraction technique under conditions of

Hayk H. Bezirganyan Jr.; Siranush E. Bezirganyan; Petros H. Bezirganyan Jr.; Youri G. Mossikyan

2005-01-01

92

A simple algorithm to eliminate ambiguities in EBSD orientation map visualization and analyses: application to fatigue crack-tips/wakes in aluminum alloys.  

PubMed

A simple algorithm is developed and implemented to eliminate ambiguities, in both statistical analyses of orientation data (e.g., orientation averaging) and electron backscattered diffraction (EBSD) orientation map visualization, caused by symmetrically equivalent orientations and the wrap-around or umklapp effect. Using crystal symmetry operators and the lowest Euclidian-distance criterion, the orientation of each pixel within a grain is redefined. An advantage of this approach is demonstrated for direct determination of the representative orientation of a grain within an EBSD map by mean, median, or quaternion-based averaging methods that can be further used within analyses or visualization of misorientation or geometrically necessary dislocation (GND) density. If one also considers the lattice curvature tensor, five components of the dislocation density tensor-corresponding to a part of the GND content-may be inferred. The methodology developed is illustrated using EBSD orientation data obtained from the fatigue crack-tips/wakes in aerospace aluminum alloys 2024-T351 and 7050-T7451. PMID:20969812

Gupta, Vipul K; Agnew, Sean R

2010-12-01

93

A correlative approach to segmenting phases and ferrite morphologies in transformation-induced plasticity steel using electron back-scattering diffraction and energy dispersive X-ray spectroscopy.  

PubMed

Using a combination of electron back-scattering diffraction and energy dispersive X-ray spectroscopy data, a segmentation procedure was developed to comprehensively distinguish austenite, martensite, polygonal ferrite, ferrite in granular bainite and bainitic ferrite laths in a thermo-mechanically processed low-Si, high-Al transformation-induced plasticity steel. The efficacy of the ferrite morphologies segmentation procedure was verified by transmission electron microscopy. The variation in carbon content between the ferrite in granular bainite and bainitic ferrite laths was explained on the basis of carbon partitioning during their growth. PMID:25126753

Gazder, Azdiar A; Al-Harbi, Fayez; Spanke, Hendrik Th; Mitchell, David R G; Pereloma, Elena V

2014-12-01

94

Application of EBSD method for the investigation of microstructure and crystallographic orientation in RE2Zr2O7 TBC  

NASA Astrophysics Data System (ADS)

Modern aero engine turbine blades made of nickel-based superalloys are covered by thermal barrier coatings (TBC) for thermal and oxidation protection. A new generation of TBCs consist of a bond coat (thin layer of MCrAlY, where M may be Ni, Co, Fe) followed by a ceramic top coat of RE2Zr2O7 (RE - rare earth element). In this paper we present the possibility of the electron backscatter diffraction (EBSD) method for characterisation of the microstructure and crystallographic orientation of a new TBC consisting of a Gd2Zr2O7 top coat and a NiFeCrAlY bond coat after long thermal exposure (1100 °C, 500 h). During thermal exposure, a thermally grown oxide (TGO) layer forms at the bond coat/top coat interface. The TGO is mainly composed of Al2O3. But, there is a possible reaction between Gd2Zr2O7 and Al2O3, leading to Gd-Al-O phases. Phase composition plays an important role in controlling the stress evolution, TGO deformation and crack propagation. Application of SEM-EDS-EBSD techniques allows direct characterisation of the chemical composition, phase composition and crystallographic orientation in the ceramic top coat and TGO layers. This paper presents the possibilities of using the EBSD method for phase identification (Gd2Zr2O7, spinel Ni(Al,Cr)2O4, GdAlO3 and other phases) and orientation analysis of grains in the TGO layer.

Chmiela, B.; Soza?ska, M.; Moskal, G.

2012-03-01

95

Electron backscatter diffraction as a domain analysis technique in BiFeO(3)-PbTiO(3) single crystals.  

PubMed

xBiFeO(3)-(1-x)PbTiO(3) single crystals were grown via a flux method for a range of compositions. Presented here is a study of the domain configuration in the 0.5BiFeO(3)-0.5PbTiO(3) composition using electron backscatter diffraction to demonstrate the ability of the technique to map ferroelastic domain structures at the micron and submicron scale. The micron-scale domains exhibit an angle of approximately 85 degrees between each variant, indicative of a ferroelastic domain wall in a tetragonal system with a spontaneous strain, c/a - 1 of 0.10, in excellent agreement with the lattice parameters derived from x-ray diffraction. Contrast seen in forescatter images is attributed to variations in the direction of the electrical polarization vector, providing images of ferroelectric domain patterns. PMID:18519195

Burnett, T L; Comyn, T P; Merson, E; Bell, A J; Mingard, K; Hegarty, T; Cain, M

2008-05-01

96

Study of multi-carbide B4C-SiC/(Al, Si) reaction infiltrated composites by SEM with EBSD  

NASA Astrophysics Data System (ADS)

In the definition of conceptual developments and design of new materials with singular or unique properties, characterisation takes a key role in clarifying the relationships of composition, properties and processing that define the new material. B4C has a rare combination of properties that makes it suitable for a wide range of applications in engineering: high refractoriness, thermal stability, high hardness and abrasion resistance coupled to low density. However, the low self-diffusion coefficient of B4C limits full densification by sintering. A way to overturn this constraint is by using an alloy, for example Al-Si, forming composites with B4C. Multi-carbide B4C-SiC/(Al, Si) composites were produced by the reactive melt infiltration technique at 1200 - 1350 °C with up to 1 hour of isothermal temperature holds. Pressed preforms made from C-containing B4C were spontaneously infiltrated with Al-Si alloys of composition varying from 25 to 50 wt% Si. The present study involves the characterisation of the microstructure and crystalline phases in the alloys and in the composites by X-ray diffraction and SEM/EDS with EBSD. Electron backscatter diffraction is used in detail to look for segregation and spatial distribution of Si and Al containing phases during solidification of the metallic infiltrate inside the channels of the ceramic matrix when the composite cools down to the eutectic temperature (577 °C). It complements elemental maps of the SEM/EDS. The production of a flat surface by polishing is intrinsically difficult and the problems inherent to the preparation of EBSD qualified finishing in polished samples of such type of composites are further discussed.

Almeida, B. A.; Ferro, M. C.; Ravanan, A.; Grave, P. M. F.; Wu, H.-Y.; Gao, M.-X.; Pan, Y.; Oliveira, F. J.; Lopes, A. B.; Vieira, J. M.

2014-03-01

97

Assessment of local deformation using EBSD: Quantification of local damage at grain boundaries  

SciTech Connect

Electron backscatter diffraction (EBSD) in conjunction with scanning electron microscopy was used to assess localization of the local misorientation to grain boundary. In order to quantify the degree of localization, a parameter, which was referred to as the grain boundary local misorientation, was proposed. Through crystal orientation measurements using deformed Type 316 stainless steel, it was shown that the grain boundary local misorientation increased with the applied plastic strain. Particularly, at several grain boundaries, the grain boundary local misorientation was more than 3 times the local misorientation averaged for the whole area. Surface observations revealed that the large local misorientation near the grain boundaries was attributed to the impeded slip steps rather than the number of slip steps observed on the surface. The magnitude of the grain boundary local misorientation had a week correlation with grain boundary length or grain boundary misorientation, and no correlation was found for twin boundaries. Finally, it was shown that the maximum grain boundary local misorientation could be estimated statistically, and the estimated maximum value for the specimen surface with an area of 80 mm{sup 2} was 10.6 times the averaged value. - Highlights: Black-Right-Pointing-Pointer The grain boundary local misorientation was proposed. Black-Right-Pointing-Pointer The maximum grain boundary local misorientation could be estimated statistically. Black-Right-Pointing-Pointer The large local misorientation was attributed to the impeded slip steps.

Kamaya, Masayuki, E-mail: kamaya@inss.co.jp

2012-04-15

98

Comparison of recrystallisation kinetics determined by stress relaxation, double hit, optical metallography and EBSD approaches  

SciTech Connect

A comparison of the recrystallisation kinetics determined by stress relaxation (SR), double-hit (DH), optical metallography and scanning electron microscope/electron backscattered diffraction (SEM/EBSD) mapping experimental approaches has been conducted. Two different types of steel were used as experimental material: C-Mn and interstitial-free (IF). Tests were carried out in the austenitic region for C-Mn steel and just above the Ar{sub 1} temperature for IF steel. Both steels were investigated in static and postdynamic recrystallisation (SRx and PDRx, respectively) regions. The work indicates that some differences exist between the results given by these methods. The biggest correction to the experimental results in the SRx region has to be performed on the 'raw data' obtained by the SR method. The SR method, owing to its continually applied stress, tends to accelerate the recrystallisation kinetics. The estimation of the recrystallised fraction in the PDRx region by the DH test gives even higher error because of dynamic changes of microstructure during the second hit.

Dzubinsky, M.; Husain, Z.; Haaften, W.M. van

2004-05-15

99

Matrix grain characterisation by electron backscattering diffraction of powder metallurgy aluminum matrix composites reinforced with MoSi{sub 2} intermetallic particles  

SciTech Connect

Research highlights: Six extruded PM AA6061/MoSi{sub 2}/15p were processed with and without ball milling {yields} EBSD was used to characterise matrix grain size and grain orientation. {yields} Ball milling decreases matrix grain size to submicrometric level. {yields} Ball milling produces a more equiaxed microstructure and larger misorientation. {yields} Increasing milling time produces matrix texture randomization.

Corrochano, J., E-mail: javier.corrochano.flores@gmail.com; Hidalgo, P.; Lieblich, M.; Ibanez, J.

2010-11-15

100

Errors, Artifacts, and Improvements in EBSD Processing and Mapping  

NASA Astrophysics Data System (ADS)

Electron back scatter diffraction (EBSD) mapping and indexing has rapidly come into widespread use. However, inadequate attention has been paid to the details of the method. Many of the algorithms in current use were chosen because they were the first ones that were found to work, rather than because they were optimum. Results of systematic study are presented. It is shown that more than one method can successfully correct a sampling artifact, that there is an optimum binning ratio, that Gaussian filtering provides an alternative to "butterfly convolution," that better alternatives for mapping image quality than those in current use are available, and that saving all the original patterns is practical and advantageous.

Tao, Xiaodong; Eades, Alwyn

2005-02-01

101

Recrystallization, Grain Growth in Copper Foil at High Temperature Studied By Electron Back Scatter Diffraction  

NASA Astrophysics Data System (ADS)

As-received cold rolled and isothermally re-crystallized textures of high purity copper foil were studied using electron back-scattered diffraction patterns (EBSD) in a scanning electron microscope. The evolution of the re-crystallization texture was investigated as a function of annealing temperature. In as is sample, the Cu grains are small and equi-axed, but re-crystallization results in grains several microns in size. We observe a significant enhancement of the (311) texture by pole figure measurements till annealing temperatures of 400 °C and then enhancement of (200) texture at annealing temperatures of 600 °C. We propose that multiple twinning is the mechanism for this phenomenon.

Tiwari, Pragya; Srivastava, Himanshu; Rai, Sanjay; Deb, S. K.

2011-07-01

102

Subgrain boundary analyses in deformed orthopyroxene by TEM/STEM with EBSD-FIB sample preparation technique  

NASA Astrophysics Data System (ADS)

High-resolution structure analyses using electron beam techniques have been performed for the investigation of subgrain boundaries (SGBs) in deformed orthopyroxene (Opx) in mylonite from Hidaka Metamorphic Belt, Hokkaido, Japan, to understand ductile deformation mechanism of silicate minerals in shear zones. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analysis of Opx porphyroclasts in the mylonitic rock indicated that the crystal orientation inside the Opx crystals gradually changes by rotation about the b-axis by SGBs and crystal folding. In order to observe the SGBs along the b-axis by transmission electron microscopy (TEM) or scanning TEM (STEM), the following sample preparation protocol was adopted. First, petrographic thin sections were slightly etched with hydrofluoric acid to identify SGBs in SEM. The Opx crystals whose b-axes were oriented close to the normal of the surface were identified by EBSD, and the areas containing SGBs were picked and thinned for (S) TEM analysis with a focused ion beam instrument with micro-sampling system. High-resolution TEM imaging of the SGBs in Opx revealed various boundary structures from a periodic array of dissociated (100) [001] edge dislocations to partially or completely incoherent crystals, depending on the misorientation angle. Atomic-resolution STEM imaging clearly confirmed the formation of clinopyroxene (Cpx) structure between the dissociated partial dislocations. Moreover, X-ray microanalysis in STEM revealed that the Cpx contains a considerable amount of calcium replacing iron. Such chemical inhomogeneity may limit glide motion of the dislocation and eventually the plastic deformation of the Opx porphyroclasts at a low temperature. Chemical profiles across the high-angle incoherent SGB also showed an enrichment of the latter in calcium at the boundary, suggesting that SGBs are an efficient diffusion pathway of calcium out of host Opx grain during cooling.

Kogure, Toshihiro; Raimbourg, Hugues; Kumamoto, Akihito; Fujii, Eiko; Ikuhara, Yuichi

2014-12-01

103

An EBSD study on mapping of small orientation differences in lattice mismatched heterostructures  

NASA Astrophysics Data System (ADS)

Electron back scatter diffraction (EBSD) on a Scanning Electron Microscope (SEM) has experienced rapid development in recent years. However, inadequate attention has been paid to the details of the method. Many of the algorithms in current use were chosen because they were the first ones that were found to work, not because they were optimum. The long term aim of this study is mainly concerned with extending EBSD to characterizing threading dislocations in semiconductor materials. In working toward this objective, a systematic study on the EBSD technique was performed. The possibility of measuring small changes of orientation within grains by EBSD was explored. Conventional orientation maps (using EBSD) index the orientation of each position on the sample separately. This does not give accurate results for small differences of orientation. Therefore, methods of directly measuring small changes in orientation from one EBSD pattern to the others were examined. Previous workers have measured the change of position of zone axes in the EBSD pattern. A comparison between measuring changes of position of zone axes versus measuring the shift of the peaks in the Hough transform from one diffraction pattern to the next suggests that the latter method is superior. More over, it is possible, with a standard EBSD configuration, to measure the shift of the Kikuchi bands to a precision of about 0.1 pixels, which corresponds to a change of orientation of about 0.1 mrad. This method has been successfully applied on a GaN/Sapphire structure. Based on this method, ways to perform high precision orientation mapping are proposed. We have also shown that: (1) More than one method can successfully correct a sampling artifact, which is associated with the Hough transform; (2) There is an optimum binning ratio; (3) Gaussian filtering provides an alternative to "butterfly convolution"; (4) Better alternatives for mapping image quality than those in current use are available; (5) saving all the original patterns is practical and advantageous; and (6) Conventional usage of Monte-Carlo simulation for estimating the interaction volume of EBSD is flawed.

Tao, Xiaodong

104

The Influence of Sn Orientation on Intermetallic Compound Evolution in Idealized Sn-Ag-Cu 305 Interconnects: an Electron Backscatter Diffraction Study of Electromigration  

NASA Astrophysics Data System (ADS)

Previous research showed the relationship between Sn grain orientation and the intermetallic growth rate in Sn-Ag-Cu (SAC)305 interconnects. Samples with the Sn c-axis aligned parallel to the current flow have an intermetallic compound growth rate significantly faster than samples with the c-axis perpendicular to the current flow. This study continues the previous research by investigating intermetallic growth in polygranular joints and in joints that have a thin Ni layer at the cathodic or anodic interface of the interconnect. Planar SAC305 interconnects were sandwiched between two Cu pads (sometimes incorporating a thin Ni layer at the interface) and subjected to uniaxial current. The crystallographic orientation of Sn in these samples was characterized with electron backscatter diffraction before and after electromigration testing. The results show that polycrystalline joints have relatively slow intermetallic growth rates, close to those found in single-crystal joints with the c-axis perpendicular to the current. When a Ni layer was present on the anode side, the intermetallic grew at a rate comparable to that in samples without a Ni layer. However, when the Ni layer was on the cathode side, the intermetallic growth was significantly retarded. The measured growth rates of the intermetallic, combined with literature values for the diffusion of Cu in Sn, were used to calculate values for the effective charge, z *, which is significantly smaller for samples with current parallel to the c-axis than for either polycrystalline samples or samples with the c-axis perpendicular to the electron flow.

Linares, Xioranny; Kinney, Chris; Lee, Kyu-Oh; Morris, J. W.

2014-01-01

105

Analysis of EBSD Data Texture, Microstructure & Anisotropy  

E-print Network

EBSD system (Oxford INCA) Provides (2D regular grid) maps of crystal orientation from polished cross suppliers of software ­ Issues with Hexagonal materials · Important: the menus change as the software orientations provide the input data to which the coefficients of the generalized spherical harmonic functions

Rollett, Anthony D.

106

Analysis of EBSD Data Texture, Microstructure & Anisotropy  

E-print Network

of a typical EBSD system (Oxford INCA) Provides (2D regular grid) maps of crystal orientation from polished the input data to which the coefficients of the generalized spherical harmonic functions are fitted. · What on the fitted generalized spherical harmonic functions. · What is meant by the various different measures

Rollett, Anthony D.

107

The Weighted Burgers Vector: a new quantity for constraining dislocation densities and types using electron backscatter diffraction on 2D sections through crystalline materials.  

PubMed

The Weighted Burgers Vector (WBV) is defined here as the sum, over all types of dislocations, of [(density of intersections of dislocation lines with a map) x (Burgers vector)]. Here we show that it can be calculated, for any crystal system, solely from orientation gradients in a map view, unlike the full dislocation density tensor, which requires gradients in the third dimension. No assumption is made about gradients in the third dimension and they may be non-zero. The only assumption involved is that elastic strains are small so the lattice distortion is entirely due to dislocations. Orientation gradients can be estimated from gridded orientation measurements obtained by EBSD mapping, so the WBV can be calculated as a vector field on an EBSD map. The magnitude of the WBV gives a lower bound on the magnitude of the dislocation density tensor when that magnitude is defined in a coordinate invariant way. The direction of the WBV can constrain the types of Burgers vectors of geometrically necessary dislocations present in the microstructure, most clearly when it is broken down in terms of lattice vectors. The WBV has three advantages over other measures of local lattice distortion: it is a vector and hence carries more information than a scalar quantity, it has an explicit mathematical link to the individual Burgers vectors of dislocations and, since it is derived via tensor calculus, it is not dependent on the map coordinate system. If a sub-grain wall is included in the WBV calculation, the magnitude of the WBV becomes dependent on the step size but its direction still carries information on the Burgers vectors in the wall. The net Burgers vector content of dislocations intersecting an area of a map can be simply calculated by an integration round the edge of that area, a method which is fast and complements point-by-point WBV calculations. PMID:19250469

Wheeler, J; Mariani, E; Piazolo, S; Prior, D J; Trimby, P; Drury, M R

2009-03-01

108

Characterization of Recrystallization and Microstructure Evolution in Lead-Free Solder Joints Using EBSD and 3D-XRD  

NASA Astrophysics Data System (ADS)

Development of vulnerable high-angle grain boundaries (and cracks) from low-angle boundaries during thermal cycling by means of continuous recrystallization was examined in fine-pitch ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (wt.%) (SAC305) lead-free solder joints. Electron backscatter diffraction (EBSD) and differential-aperture x-ray microscopy (DAXM or 3D-XRD) were used for surface and subsurface characterization. A large number of subgrain boundaries were observed in the parent orientation using both techniques. However, unlike studies of anisotropic deformation in noncubic metals at much lower homologous temperatures, no streaked diffraction peaks were observed in DAXM Laue patterns within each 1 ?m3 voxel after thermal cycling, suggesting that geometrically necessary dislocations (GNDs) are effectively absorbed by the preexisting subgrain boundaries. Storage at room temperature (0.6 T m) prior to DAXM measurement may also facilitate recovery processes to reduce local GND contents. Heterogeneous residual elastic strains were found near the interface between a precipitated Cu6Sn5 particle and the Sn grain, as well as near particular subgrain boundaries in the parent orientation. Grain boundary migration associated with recrystallization resulted in regions without internal strains, subgrain boundaries, or orientation gradients. Development of new grain orientations by continuous recrystallization and subsequent primary recrystallization and grain growth occurred in the regions where the cracks developed. Orientation gradients and subgrain structure were observed within newly formed recrystallized grains that could be correlated with slip systems having high Schmid factors.

Zhou, Bite; Bieler, Thomas R.; Lee, Tae-Kyu; Liu, Wenjun

2013-02-01

109

High-resolution transmission electron microscopy and electron backscatter diffraction in nanoscaled ferritic and ferritic-martensitic oxide dispersion strengthened-steels  

NASA Astrophysics Data System (ADS)

For specific blanket and divertor applications in future fusion power reactors a replacement of presently considered reduced activation ferritic-martensitic (RAFM) steels as a structural material by suitable oxide dispersion strengthened ferritic-martensitic steels would allow a substantial increase of the operating temperature from ˜823 to about 923 K. Due to this reason the RAFM-alloy ODS-Eurofer has already been developed and produced with industrial partners. In the He-cooled modular divertor concept, where temperatures above 923 K will arise, an ODS-steel with a purely ferritic matrix is advantageous, because of missing phase transitions. Due to this reason, a special ferritic ODS-steel is being manufactured as well. In this work the microstructures of these two ODS-alloy types, analysed mainly by high resolution TEM are compared, with respect to different manufacturing processes. In addition first results of high resolution EBSD scans together with determined orientation maps of the RAFM steel ODS-Eurofer will also be presented.

Eiselt, Ch. Ch.; Klimenkov, M.; Lindau, R.; Möslang, A.; Sandim, H. R. Z.; Padilha, A. F.; Raabe, D.

2009-03-01

110

Infrared backscattering  

NASA Technical Reports Server (NTRS)

All particles in the atmosphere are not spherical. Moreover, the scattering properties of randomly oriented nonspherical particles are not equivalent to those of spherical particles no matter how the term equivalent is defined. This is especially true for scattering in the backward direction and at the infrared wavelengths at which some atmospheric particles have strong absorption bands. Thus calculations based on Mie theory of infrared backscattering by dry or insoluble atmospheric particles are suspect. To support this assertion, it was noted that peaks in laboratory-measured infrared backscattering spectra show appreciable shifts compared with those calculated using Mie theory. One example is ammonium sulfate. Some success was had in modeling backscattering spectra of ammonium sulfate particles using a simple statistical theory called the continuous distribution of ellipsoids (CDE) theory. In this theory, the scattering properties of an ensemble are calculated. Recently a modified version of this theory was applied to measured spectra of scattering by kaolin particles. The particles were platelike, so the probability distribution of ellipsoidal shapes was chosen to reflect this. As with ammonium sulfate, the wavelength of measured peak backscattering is shifted longward of that predicted by Mie theory.

Bohren, Craig F.; Nevitt, Timothy J.; Singham, Shermila Brito

1989-01-01

111

Hyperspectral Imaging at the Micro- and Nanoscale using Energy-dispersive Spectroscopy (EDS) with Silicon Drift Detector (SDD) and EBSD Analysis  

NASA Astrophysics Data System (ADS)

SDD systems have become state of the art technology in the field of EDS. The main characteristic of the SDDs is their extremely high pulse load capacity of up to 750,000 counts per second at good energy resolution (<123 eV Mn-K?, <46 eV C-K? at 100,000 counts per seconds). These properties in conjunction with electron backscatter diffraction (EBSD) technique and modern data processing allows not only high speed mapping but also hyperspectral analysis. Here, a database is created that contains an EDS spectrum and/or EBSD pattern for each pixel of the SEM image setting the stage for innovative analysis options: The Maximum Pixel Spectrum function [1] synthesizes a spectrum out of the EDS database, consisting of the highest count level found in each spectrum channel. Here, (trace) elements which occur in only one pixel can be detected qualitatively. Areas of similar EDS composition can be made visible with Autophase, a spectroscopic phase detection system. In cases where the crystallographic phase assessment by EBSD is problematic due to pattern similarity, the EDS signal can be used as additional information for phase separation. This paper presents geoscience applications with the QUANTAX system with EDS SDD and EBSD detector using the options described above: (1) Drill core analysis of a Chicxulub impact ejecta sequence from the K/Pg boundary at ODP leg 207 [2] using fast, high resolution element maps. (2) Detection of monazite in granite by the Maximum Pixel Spectrum function. (3) Distribution of elements with overlapping peaks by deconvolution at the example of rare earth elements in zoned monazite. (4) Spectroscopic phase analysis of a sulfate-carbonate-dominated impact matrix at borehole UNAM-7 from the Chicxulub impact crater [3]. (5) EBSD studies with examples of iron meteorites and impact-induced, recrystallized carbonate melts [4]. In addition, continuing technological advances require the elemental analysis of increasingly smaller structures in many fields, including geosciences. It will be demonstrated that using low accelerating voltages, the element distribution of structures at the nanoscale in bulk samples can be displayed in a short time due to optimized signal processing and solid angle. Peaks composed of contributions from several overlapping elements e.g. N-K (392 eV) and Ti-Ll (395 eV) can be deconvolved [6] using an improved atomic database with 250 additional L, M and N lines below 4 keV. Improved light element quantification allows the standardless quantification of features at the nanoscale such as rutile grains 200-500 nm in size. References: [1] Bright D S. & Newbury D. E. (2004) Journal of Microscopy 216:186-193. [2] Schulte P. et al. (2010) Science 327: 1214-1218. [3] Salge T. (2007) PhD thesis: 130p. http://edoc.huberlin.de/docviews/abstract.php?lang=ger&id=27753. [4] Deutsch A. et al. MAPS 45: A45. [6] Tunckan O. (2010) Joining ceramics using capacitor discharge technique and determination of metal ceramic interface reactions, PhD thesis, Anadolu University, Eskisehir, Turkey. Acknowledgements: We thank P. Schulte, A. Deutsch, ODP, L. Hecht, A. Kearsley, J. Urrutria-Fucugauchi, O. Tunckan and S. Turan for generously providing the samples.

Salge, T.; Goran, D.

2010-12-01

112

Area-preserving projections from hexagonal and triangular domains to the sphere and applications to electron back-scatter diffraction pattern simulations  

NASA Astrophysics Data System (ADS)

We construct two new area-preserving projections, which map regular hexagons and regular triangles onto circles. Combination of these projections with the inverse Lambert equal-area projection from the disc to the two hemispheres of a sphere provide bi-directional conversions between uniform planar grids with three-fold and six-fold rotational symmetry and corresponding uniform grids on the sphere. An application example is given for the representation of the channeling-modified back-scattered electron yield for hexagonal titanium.

Ro?ca, D.; De Graef, M.

2013-07-01

113

Electromagnetic backscattering by corner reflectors  

NASA Technical Reports Server (NTRS)

The Geometrical Theory of Diffraction (GTD), which supplements Geometric Optics (GO), and the Physical Theory of Diffraction (PTD), which supplements Physical Optics (PO), are used to predict the backscatter cross sections of dihedral corner reflectors which have right, obtuse, or acute included angles. These theories allow individual backscattering mechanisms of the dihedral corner reflectors to be identified and provide good agreement with experimental results in the azimuthal plane. The advantages and disadvantages of the geometrical and physical theories are discussed in terms of their accuracy, usefulness, and complexity. Numerous comparisons of analytical results with experimental data are presented. While physical optics alone is more accurate and more useful than geometrical optics alone, the combination of geometrical optics and geometrical diffraction seems to out perform physical optics and physical diffraction when compared with experimental data, especially for acute angle dihedral corner reflectors.

Balanis, C. A.; Griesser, T.

1986-01-01

114

Seismic velocities, anisotropy and deformation in Siberian cratonic mantle: EBSD data on xenoliths from the Udachnaya kimberlite  

NASA Astrophysics Data System (ADS)

The study presents microstructures and crystallographic preferred orientations (CPO) of minerals obtained by electron back-scattered diffraction (EBSD) in a suite of 23 fresh mantle xenoliths (20 peridotites, 2 eclogites and 1 pyroxenite) from the Udachnaya kimberlite in central Siberian craton. The suite includes coarse spinel- and garnet-facies peridotites equilibrated at 760-1000 °C from the upper part of the mantle lithosphere (45-160 km) and porphyroclastic garnet peridotites from the base of the lithosphere (160-210 km; 1200-1320 °C). The data indicate that dislocation creep is the main deformation mechanism in the peridotites and eclogites. The CPO patterns of olivine suggest a dominant activation of the (010) [100] slip system. Within this general pattern, coarse peridotites show a better alignment of [100]-olivine while porphyroclastic rocks have a better alignment of [010]-olivine. Recrystallization in the porphyroclastic peridotites reduces olivine grain size and facilitates the development of a mosaic matrix that leads to a decrease in the CPO strength. Orthopyroxene in peridotites slips parallel to (100) [001]; clinopyroxene shows a clear slip direction on [001] in both peridotites and eclogites. Seismic properties estimated from the CPO data and modal abundances of major minerals show significant differences between peridotites, eclogites and pyroxenites; some differences also exist between peridotite types. Importantly, coarse peridotites have much higher anisotropy than eclogites and may yield higher P-wave velocities in the fast direction (V p ? 8.8 km/s). Thus, the extremely high sub-Moho velocities (V p > 8.7 km/s) reported from some seismic profiles in the Siberian craton can be better explained by strong anisotropy of coarse peridotites in a horizontally foliated mantle rather than by the presence of abundant eclogites.

Bascou, Jérôme; Doucet, Luc S.; Saumet, Sylvaine; Ionov, Dmitri A.; Ashchepkov, Igor V.; Golovin, Alexander V.

2011-04-01

115

Electromagnetic backscattering by plates and disks  

NASA Technical Reports Server (NTRS)

With the recent development of diffraction coefficients for imperfectly conducting half-planes, it has become possible to analyze a wide variety of problems for which the impedance surface boundary condition applies. This impedance boundary condition, while approximate, was utilized to extend the usefulness of the Uniform Geometrical Theory of Diffraction (UTD) beyond the perfectly conducting geometries. These half-plane diffraction coefficients are used to analyze patterns of an antenna in the presence of an imperfectly conducting flat polygonal plate. The Geometrical Theory of Diffraction (GTD) techniques were also used to investigate the backscattering from perfectly conducting plates. To further improve the soft polarization results for wide angles, a model for the creeping wave or circulating current on the edge of the disk was obtained and used to find an additional component of the backscattered field. The backscattering from a square plate was then analyzed using GTD. Backscattering in both the principal and off-principal planes was examined.

Balanis, Constantine A.; Griesser, Timothy; Marsland, Diane M.

1987-01-01

116

The influence of in situ photoexcitation on a defect structure generation in Ar+ implanted GaAs(001) crystals revealed by high-resolution x-ray diffraction and Rutherford backscattering spectroscopy  

NASA Astrophysics Data System (ADS)

The influence of in situ photoexcitation on the defect structure generation in GaAs crystals implanted by Ar+ ions with energy of 200 keV and doses of 1×1013, 3×1013 and 5×1013 cm-2 was studied by high-resolution x-ray diffraction and Rutherford backscattering spectroscopy. The in situ photoexcitation is found to provide for annihilation of Frenkel pairs that decrease a residual concentration of radiation-induced point defects. The amorphization of the damaged layer is assumed to proceed by a generation and a growth of radiation-induced point defect clusters. The vacancy- and interstitial-type clusters are spatially separated: the former are located closer to the surface than the latter ones. The in situ photoexcitation is shown to hinder the cluster growth and to stimulate diffusion of interstitials towards undamaged substrate.

Chtcherbatchev, K. D.; Bublik, V. T.; Markevich, A. S.; Mordkovich, V. N.; Alves, E.; Barradas, N. P.; Sequeira, A. D.

2003-05-01

117

Electron back scattered diffraction study of SmCo magnets  

NASA Astrophysics Data System (ADS)

The remanence and energy product of permanent magnets is a strong function of their crystallographic texture. Electron back scattered diffraction (EBSD) is a tool for texture analysis providing information about the atomic layers up to 50 nm below the surface of the material. This paper discusses experimental requirements for performing EBSD measurements on rare-earth permanent magnets and presents results on commercial SmCo magnet material. EBSD measurements proved to be very sensitive to misaligned grains and were sensitive to texture in good agreement with information provided by X-ray diffraction scans. Results for nanostructured Sm(CoFeCuZr) z magnets are also discussed.

Yonamine, T.; Fukuhara, M.; Machado, R.; Missell, F. P.

118

Electromagnetic backscattering by corner reflectors  

NASA Technical Reports Server (NTRS)

The analysis of the backscatter cross section of a dihedral corner reflector, using Geometrical Theory of Diffraction (GTD) and Physical Theory of Diffraction (PTD), is completed in the azimuthal plane, and very good agreement with experimental results is obtained. The advantages and limitations of the GTD and PTD techniques are discussed specifically for radar cross section applications. The utilization of GTD and PTD in oblique incidence diffraction from conducting targets is discussed. Results for equivalent current off-axis diffraction from the flat rectangular plate are presented using the equivalent currents of Knott, Senior, and Michaeli. The rectangular subdivision technique of Sikta, and its extension by Sunatara, alleviate some of the limitations of the equivalent techniques. As yet, neither technique can be used in bistatic scattering or for multiple scattering of a complex target.

Balanis, C. A.; Griesser, T.

1986-01-01

119

In-situ EBSD Phase Transformation and Recrystallisation  

NASA Astrophysics Data System (ADS)

With the advent of in-situ heating stages that can fit into SEM's and the combination with EBSD, it is now possible to directly observe phenomenon such as phase transformations and recrystallisation at high spatial resolution and to link these processes to microstructural parameters. This presentation will report some results from preliminary in-situ EBSD heating experiments conducted in an SEM on the transformation of ausenite to ferrite in a plain carbon steel and recrystallisation in bronze alloy strip cast on a steel substrate. The microstructural changes observed during these experiments will be reported in terms of EBSD maps, grains size and crystallographic texture that evolves during a) a heating cycle from ferrite to austenite and cooling to ferrite and b) the recrystallisation microstructure for bronze and steel during isochronal heating.

Ubhi, H. S.; Parsons, J.; Othen, N.; Campbell, S.; Poole, R.; Gholinia, A.

2014-06-01

120

EBSD and TEM characterization of high burn-up mixed oxide fuel  

NASA Astrophysics Data System (ADS)

Understanding and studying the irradiation behavior of high burn-up oxide fuel is critical to licensing of future fast breeder reactors. Advancements in experimental techniques and equipment are allowing for new insights into previously irradiated samples. In this work dual column focused ion beam (FIB)/scanning electron microscope (SEM) was utilized to prepared transmission electron microscope samples from mixed oxide fuel with a burn-up of 6.7% FIMA. Utilizing the FIB/SEM for preparation resulted in samples with a dose rate of <0.5 mRem/h compared to ?1.1 R/h for a traditionally prepared TEM sample. The TEM analysis showed that the sample taken from the cooler rim region of the fuel pellet had ?2.5× higher dislocation density than that of the sample taken from the mid-radius due to the lower irradiation temperature of the rim. The dual column FIB/SEM was additionally used to prepared and serially slice ?25 ?m cubes. High quality electron back scatter diffraction (EBSD) were collected from the face at each step, showing, for the first time, the ability to obtain EBSD data from high activity irradiated fuel.

Teague, Melissa; Gorman, Brian; Miller, Brandon; King, Jeffrey

2014-01-01

121

Field Emission Gun Scanning Electron Microscopy with Electron Back Scatter Diffraction for Texture, Formability and Fatigue Studies of Advanced Materials.  

National Technical Information Service (NTIS)

An advanced field emission gun scanning electron microscope (FEGSEM Hitachi S-4300) equipped with energy dispersion spectroscopy (EDS PGT Spirit, presently a part of Bruker) and electron back scatter diffraction (EBSD HKL Channel 5, presently a part of Ox...

C. Man, J. Morris, T. Zhai

2007-01-01

122

EBSD and EDX analyses of a multiphase glass-ceramic obtained by crystallizing an yttrium aluminosilicate glass.  

PubMed

A glass with the mol % composition 23.82 Y2O3·39.82 Al2O3·28.50 SiO2·2.91AlF3·4.95 ZrO2 doped with 2 mol % CeF3 is crystallized at 1250 °C for 20 h. The crystallized samples are studied using X-ray diffraction (XRD), the SEM-based methods EBSD and EDX, as well as fluorescence microscopy. Six crystalline phases are detected in the residual glass including alumina, YAG, Y-stabilized zirconia (YSZ), and three different yttrium silicates of the composition Y2Si2O7. Chemistry-assisted indexing (ChI) is successfully applied to separate YAG and YSZ in EBSD-scans. YAG displays polygon as well as dendritic growth. Some crystals show both mechanisms at opposite ends, indicating that the growth mechanism is influenced by the chemistry of the surrounding glass matrix. PMID:23848162

Keshavarzi, Ashkan; Wisniewski, Wolfgang; Rüssel, Christian

2013-09-11

123

Diffraction-based study of fatigue crack initiation and propagation in aerospace aluminum alloys  

NASA Astrophysics Data System (ADS)

The crack initiation sites and microstructure-sensitive growth of small fatigue cracks are experimentally characterized in two precipitation-hardened aluminum alloys, 7075-T651 and 7050-T7451, stressed in ambient temperature moist-air (warm-humid) and -50°C dry N2 (cold-dry) environmental conditions. Backscattered electron imaging (BSE) and energy dispersive spectroscopy (EDS) of the fracture surfaces showed that Fe-Cu rich constituent particle clusters are the most common initiation sites within both alloys stressed in either environment. The crack growth within each alloy, on average, was observed to be slowed in the cold-dry environment than in the warm-humid environment, but only at longer crack lengths. Although no overwhelming effects of grain boundaries and grain orientations on small-crack growth were observed, crack growth data showed local fluctuations within individual grains. These observations are understood as crack propagation through the underlying substructure at the crack surface and frequent interaction with low/high-angle grain and subgrain boundaries, during cyclic loading, and, are further attributed to periodic changes in crack propagation path and multiple occurrences of crack-branching observed in the current study. SEM-based stereology in combination with electron backscattered diffraction (EBSD) established fatigue crack surface crystallography within the region from ˜1 to 50 mum of crack initiating particle clusters. Fatigue crack facets were parallel to a wide variety of crystallographic planes, with pole orientations distributed broadly across the irreducible stereographic triangle between the {001} and {101}-poles within both warm-humid and cold-dry environments. The results indicate environmentally affected fatigue cracking in both cases, given the similarity between the observed morphology and crystallography with that of a variety of aerospace aluminum alloys cracked in the presence of moist-air. There was no evidence of crystallographic {111} slip-plane cracking typical of the Stage I crack growth mode observed in single crystals and high purity polycrystals of face centered cubic metals, and which has presently been assumed for the present materials within fatigue crack initiation models. Rather, the facets tend to have near-Mode I spatial orientation, which is another indicator of the importance of environmentally affected fatigue damage. The results provide a physical basis to develop microstructurally-based next generation multi-stage fatigue (MSF) models that should include a new crack decohesion criteria based upon environmental fatigue cracking mechanisms. EBSD study of small-cracks in alloy 7050-T7451, stressed in warm-humid environment, showed that crack-path orientation changes and crack-branching occurred at both low/high-angle grain and subgrain boundaries. Single surface trace analysis suggests that the crack-path differs substantially from crystallographic slip-planes. EBSD-based observations of small-crack propagation through subgrain structure, either formed by cyclic plastic strain accumulation or pre-existing (typical of unrecrystallized grain structure in the present materials), suggest that subgrain structure plays a crucial role in small fatigue crack propagation. As mentioned earlier, local fluctuations in small-crack growth rates appear to be caused by frequent interaction with subgrain boundaries, and multiple occurrences of crack-branching and crack-path orientation changes at low/high-angle grain and subgrain boundaries. The aforementioned deviation from low-index {001}/{101}-planes and the occurrence of high-index cracking planes observed by EBSD/Stereology, in this study and others, are interpreted as trans-subgranular decohesion or inter-subgranular cracking, due to trapped hydrogen. In summary, the results provide a firmer experimental foundation for, and clearer understanding of, the mechanisms of environmental fatigue cracking of aluminum alloys, especially the role of inter-subgranular cracking, which had previously been advanced based upon fracture su

Gupta, Vipul K.

124

Extracting electron backscattering coefficients from backscattered electron micrographs  

SciTech Connect

Electron backscattering micrographs possess the so-called Z-contrast, carrying information about the chemical compositions of phases present in microstructures. The intensity at a particular point in the backscattered electron micrograph is proportional to the signal detected at a corresponding point in the scan raster, which is, in turn, proportional to the electron backscattering coefficient of a phase at that point. This article introduces a simple method for extracting the electron backscattering coefficients of phases present in the microstructure, from the backscattered electron micrographs. This method is able to convert the micrograph's greyscale to the backscattering-coefficient-scale. The prerequisite involves the known backscattering coefficients for two phases in the micrograph. In this way, backscattering coefficients of other phases can be determined. The method is unable to determine the chemical compositions of phases or the presence of an element only from analysing the backscattered electron micrograph. Nevertheless, this method was found to be very powerful when combined with energy dispersive spectroscopy, and the calculations of backscattering coefficients. - Research Highlights: {yields}A simple method for extracting the electron backscattering coefficients {yields}The prerequisite is known backscattering coefficients for two phases {yields}The information is complementary to the EDS-results. {yields}This method is especially useful when a phase contains a light element (H, Li, Be, and B)

Zupanic, F., E-mail: franc.zupanic@uni-mb.si

2010-12-15

125

Radial Reflection Diffraction Tomography Notes  

SciTech Connect

We are developing the theory behind a new imaging modality which uses a single transducer rotating about its center to launch a field radially outward and collect the backscattered (reflected) field. We use diffraction tomography techniques, based upon a linearized version of the field scattering equation, to form images of the medium surrounding the transducer. As there is one transducer which both transmits the incident field and measures the backscattered field, the operation mode is multimonostatic.

Lehman, S K; Norton, S J

2002-06-27

126

Anticollision backscatter sensor networks  

Microsoft Academic Search

This work analytically quantifies and attempts to alleviate the collision induced by a number of tags that operate via backscatter communication, i.e. modulate the reflection of a common carrier transmitted by a central hub. For omni hub antenna, it is shown that acceptable anti-collision performance can be engineered only when appropriate modulation at each tag is employed. When a beamforming

Aggelos Bletsas; Stavroula Siachalou; John N. Sahalos

2009-01-01

127

Radar backscatter modelling  

NASA Technical Reports Server (NTRS)

The terrain analysis software package was restructured and documentation was added. A program was written to test Johnson Space Center's four band scatterometer data for spurious signals data. A catalog of terrain roughness statistics and calibrated four frequency multipolarization scatterometer data is being published to support the maintenance of Death Valley as a radar backscatter calibration test site for all future airborne and spacecraft missions. Test pits were dug through sand covered terrains in the Eastern Sahara to define the depth and character of subsurface interfaces responsible for either backscatter or specular response in SIR-A imagery. Blocky sandstone bedrock surfaces at about 1 m depth were responsible for the brightest SIR-A returns. Irregular very dense CaCO3 cemented sand interfaces were responsible for intermediate grey tones. Ancient river valleys had the weakest response. Reexamination of SEASAT l-band imagery of U.S. deserts continues.

Schaber, G. G.; Kozak, R. C.; Gurule, R. L.

1984-01-01

128

Application of combined EBSD and 3D-SEM technique on crystallographic facet analysis of steel at low temperature.  

PubMed

Electron backscatter diffraction has been increasingly used to identify the crystallographic planes and orientation of cleavage facets with respect to the rolling direction in fracture surfaces. The crystallographic indices of cleavage planes can be determined either directly from the fracture surface or indirectly from metallographic sections perpendicular to the plane of the fracture surface. A combination of electron backscatter diffraction and 3D scanning electron microscopy imaging technique has been modified to determine crystallographic facet orientations. The main purpose of this work has been to identify the macroscopic crystallographic orientations of cleavage facets in the fracture surfaces of weld heat affected zones in a well-known steel fractured at low temperatures. The material used for the work was an American Petroleum Institute (API) X80 grade steel developed for applications at low temperatures, and typical heat affected zone microstructures were obtained by carrying out weld thermal simulation. The fracture toughness was measured at different temperatures (0°C, -30°C, -60°C and -90°C) by using Crack Tip Opening Displacement testing. Fracture surfaces and changes in microstructure were analyzed by scanning electron microscopy and light microscopy. Crystallographic orientations were identified by electron backscatter diffraction, indirectly from a polished section perpendicular to the major fracture surface of the samples. Computer assisted 3D imaging was used to measure the angles between the cleavage facets and the adjacent polished surface, and then these angles were combined with electron backscatter diffraction measurements to determine the macroscopic crystallographic planes of the facets. The crystallographic indices of the macroscopic cleavage facet planes were identified to be {100}, {110}, {211} and {310} at all temperatures. PMID:23692572

Mohseni, P; Solberg, J K; Karlsen, M; Akselsen, O M; Ostby, E

2013-07-01

129

Plasmonic backscattering enhanced inverted photovoltaics  

Microsoft Academic Search

A plasmonic nanoparticle incorporated inverted organic photovoltaic structure was demonstrated where a monolayer of Ag nanoparticles acted as a wavelength selective reflector. Enhanced light harvesting via plasmonic backscattering into the photovoltaic absorber was observed, resulting in a two-fold improvement in the photocurrent and increased open-circuit voltage. Further, utilizing an optical spacer, the plasmonic backscattering was spectrally controlled, thereby modulating the

D. M. N. M. Dissanayake; B. Roberts; P.-C. Ku

2011-01-01

130

Effect of the cortex on ultrasonic backscatter measurements of cancellous bone  

NASA Astrophysics Data System (ADS)

Ultrasonic backscatter techniques offer a promising new approach for detecting changes in bone caused by osteoporosis. However, several challenges impede clinical implementation of backscatter techniques. This study examines how the dense outer surface of bone (the cortex) affects backscatter measurements of interior regions of porous (cancellous) bone tissue. Fifty-two specimens of bone were prepared from 13 human femoral heads so that the same region of cancellous bone could be ultrasonically interrogated through the cortex or along directions that avoided the cortex. Backscatter signals were analyzed over a frequency range of 0.8-3.0 MHz to determine two ultrasonic parameters: apparent integrated backscatter (AIB) and frequency slope of apparent backscatter (FSAB). The term 'apparent' means that the parameters are sensitive to the frequency-dependent effects of diffraction and attenuation. Significant (p < 0.001) changes in AIB and FSAB indicated that measurements through the cortex decreased the apparent backscattered power and increased the frequency dependence of the power. However, the cortex did not affect the correlation of AIB and FSAB with the x-ray bone mineral density of the specimens. This suggests that results from many previous in vitro backscatter studies of specimens of purely cancellous bone may be extrapolated with greater confidence to in vivo conditions.

Hoffmeister, Brent K.; Holt, Andrew P.; Kaste, Sue C.

2011-10-01

131

Mapping strains at the nanoscale using electron back scatter diffraction  

NASA Astrophysics Data System (ADS)

In this paper, we describe the use of electron back scatter diffraction (EBSD) to study strain variations in crystalline samples at the nanoscale. The analysis relies on cross correlation measurements of small shifts in the EBSD pattern measured at many points dispersed across the pattern. The method allows the full strain tensor, and lattice rotations to be obtained at a sensitivity of ˜10 -4. The method is applied to study variations of strains and rotations near the surface of 200 nm thick epitaxial layers of Si 0.85Ge 0.15 grown on a Si substrate patterned with rectangular and square mesa. Linescans across rectangular mesas show that strain relaxation and accompanying lattice rotations are restricted to the edges of wide mesas but that the relaxation extends across the entirety of mesas narrower than ˜6 ?m. Two dimensional maps of the strain variation in a ˜3 ?m wide square mesa are also presented.

Wilkinson, Angus J.; Meaden, Graham; Dingley, David J.

2009-04-01

132

On the Spectral Analysis of Backscatter Data  

Microsoft Academic Search

Abstract: In this paper we explore the use of spectral analysis techniques applied to artifacts of denial of service attacks called backscatter packets. First, we detail how to partition backscatter data collected by a net- work sensor into logical attacks. Since backscatter packets are the result of spoofed packets sent to the target by the attacker, determining attack bound- aries

Kendall E. Giles; David J. Marchette; Carey E. Priebe

133

Diffracted S  

Microsoft Academic Search

Gutenberg and Richter1 commented in 1935 that diffracted S (the S wave diffracted around the Earth's core) was recorded more frequently than diffracted P, but they provided no observational data. To our knowledge, the only reference to observations of S beyond the shadow zone since that time was made by Lehmann2, who expressed doubt (on the score of amplitude) whether

J. Cleary; K. Porra; L. Read

1967-01-01

134

Backscatter measurements for NIF ignition targets (invited)  

SciTech Connect

Backscattered light via laser-plasma instabilities has been measured in early NIF hohlraum experiments on two beam quads using a suite of detectors. A full aperture backscatter system and near backscatter imager (NBI) instrument separately measure the stimulated Brillouin and stimulated Raman scattered light. Both instruments work in conjunction to determine the total backscattered power to an accuracy of {approx}15%. In order to achieve the power accuracy we have added time-resolution to the NBI for the first time. This capability provides a temporally resolved spatial image of the backscatter which can be viewed as a movie.

Moody, J. D.; Datte, P.; Krauter, K.; Bond, E.; Michel, P. A.; Glenzer, S. H.; Divol, L.; Suter, L.; Meezan, N.; MacGowan, B. J.; Hibbard, R.; London, R.; Kilkenny, J.; Wallace, R.; Knittel, K.; Frieders, G.; Golick, B.; Ross, G.; Widmann, K.; Jackson, J. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States); and others

2010-10-15

135

Spectral backscattering properties of marine phytoplankton cultures.  

PubMed

The backscattering properties of marine phytoplankton, which are assumed to vary widely with differences in size, shape, morphology and internal structure, have been directly measured in the laboratory on a very limited basis. This work presents results from laboratory analysis of the backscattering properties of thirteen phytoplankton species from five major taxa. Optical measurements include portions of the volume scattering function (VSF) and the absorption and attenuation coefficients at nine wavelengths. The VSF was used to obtain the backscattering coefficient for each species, and we focus on intra- and interspecific variability in spectral backscattering in this work. Ancillary measurements included chlorophyll-a concentration, cell concentration, and cell size, shape and morphology via microscopy for each culture. We found that the spectral backscattering properties of phytoplankton deviate from theory at wavelengths where pigment absorption is significant. We were unable to detect an effect of cell size on the spectral shape of backscattering, but we did find a relationship between cell size and both the backscattering ratio and backscattering cross-section. While particulate backscattering at 555 nm was well correlated to chlorophyll-a concentration for any given species, the relationship was highly variable between species. Results from this work indicate that phytoplankton cells may backscatter light at significantly higher efficiencies than what is predicted by Mie theory, which has important implications for closing the underwater and remotely sensed light budget. PMID:20639993

Whitmire, Amanda L; Pegau, W Scott; Karp-Boss, Lee; Boss, Emmanuel; Cowles, Timothy J

2010-07-01

136

EBSD coupled to SEM in situ annealing for assessing recrystallization and grain growth mechanisms in pure tantalum.  

PubMed

An in situ annealing stage has been developed in-house and integrated in the chamber of a Scanning Electron Microscope equipped with an Electron BackScattered Diffraction system. Based on the Joule effect, this device can reach the temperature of 1200°C at heating rates up to 100°C/s, avoiding microstructural evolutions during heating. A high-purity tantalum deformed sample has been annealed at variable temperature in the range 750°C-1030°C, and classical mechanisms of microstructural evolutions such as recrystallization and grain coarsening phenomena have been observed. Quantitative measurements of grain growth rates provide an estimate of the mean grain boundary mobility, which is consistent with the value estimated from physical parameters reported for that material. In situ annealing therefore appears to be suited for complementing bulk measurements at relatively high temperatures, in the context of recrystallization and grain growth in such a single-phase material. PMID:23521093

Kerisit, C; Logé, R E; Jacomet, S; Llorca, V; Bozzolo, N

2013-06-01

137

Higher order diffractions from a circular disk  

NASA Technical Reports Server (NTRS)

The backscattering from a circular disk is analyzed using the geometrical theory of diffraction. First-, second-, and third-order diffractions are included in the hard polarization analysis, while first-, second-, and third-order slope diffractions are included for soft polarization. Improvements in the prediction of the monostatic radar cross section over previous works are noted. For hard polarization, an excellent agreement is exhibited between experimental and theoretical results, while a very good agreement is noted for soft polarization. To further improve the soft polarization results for wide angles, a model for the creeping wave or circulating current on the edge of the disk is obtained and used to find an additional component of the backscattered field. The addition of this component significantly improves the results for wide angles, leading to excellent agreement for soft polarization also. An axial-caustic correction method using equivalent currents is also included in the analysis.

Marsland, Diane P.; Balanis, Constantine A.; Brumley, Stephen A.

1987-01-01

138

Inclusive diffraction  

E-print Network

Results are given on the measurements of the hard diffractive interactions at HERA $ep$ collider. The structure of the diffractive exchange in terms of partons and the factorisation properties are discussed, in particular by comparing the QCD predictions for dijets and $D^*$ with measurements both in the photo and electroproduction regimes.

L. Favart

2006-02-01

139

The coherent backscattering opposition effect  

NASA Technical Reports Server (NTRS)

We have measured the opposition effect, the nonlinear surge in reflectance seen in particulate materials as phase angle approaches zero degrees, in a suite of materials of varying particle size and reflectance. These samples were illuminated by linearly and circularly polarized monochromatic radiation at two wavelengths, 0.442 and 0.633 microns. By measuring the linear and circular polarization ratios for each sample, we have found that in highly reflective materials the behavior of the reflected radiation is consistent with the coherent backscattering process which has recently been proposed to explain the opposition surge that is seen in such media. The size and width of the coherent backscattering opposition peak vary as a function of reflectance of the sample. The opposition effect has been observed in particulate materials studied in the laboratory and it is also observed in the radiation reflected from solar system bodies which present a regolith to the earth based observer. The traditional explanation of the opposition effect, the shadow-hiding hypothesis, is that it was caused by the elimination of mutual shadows cast between the regolith grains as the phase angle of the observation became smaller. This shadow-hiding hypothesis, however, is unable to explain the opposition effect seen in highly reflective materials such as magnesium oxide and barium sulfate powders. This is because highly reflective media will multiply scatter the incident radiation between the regolith grains. This causes the shadows to be eliminated. We have measured the angular scattering properties of a suite of materials of different reflectivity. We have observed polarization ratios in reflective particulates that are consistent with coherent backscattering as the principal process which causes the opposition surge.

Nelson, R. M.; Hapke, B. W.; Smythe, W. D.; Gharakanian, V.; Herrera, P.

1993-01-01

140

EBSD investigation of the microstructure and texture characteristics of hot deformed duplex stainless steel.  

PubMed

The microstructure and crystallographic texture characteristics were studied in a 22Cr-6Ni-3Mo duplex stainless steel subjected to plastic deformation in torsion at a temperature of 1000 degrees C using a strain rate of 1 s(-1). High-resolution EBSD was successfully used for precise phase and substructural characterization of this steel. The austenite/ferrite ratio and phase morphology as well as the crystallographic texture, subgrain size, misorientation angles and misorientation gradients corresponding to each phase were determined over large sample areas. The deformation mechanisms in each phase and the interrelationship between the two are discussed. PMID:16774517

Cizek, P; Wynne, B P; Rainforth, W M

2006-05-01

141

Microstructure Evolution During Warm Working of Ti-6Al-4V with a Colony Alpha Microstructure (Preprint).  

National Technical Information Service (NTIS)

A high-resolution electron-backscatter-diffraction (EBSD) technique was employed to investigate microstructure evolution during warm working of Ti- 6Al-4V with a colony alpha microstructure. Particular emphasis was paid to the specific mechanisms governin...

G. A. Salishchev, M. Murzinova, S. Mironov, S. Zherebtsov, S. L. Semiatin

2008-01-01

142

Radial Reflection Diffraction Tomography  

SciTech Connect

We develop a wave-based tomographic imaging algorithm based upon a single rotating radially outward oriented transducer. At successive angular locations at a fixed radius, the transducer launches a primary field and collects the backscattered field in a ''pitch/catch'' operation. The hardware configuration, operating mode, and data collection method is identical to that of most medical intravascular ultrasound (IVUS) systems. IVUS systems form images of the medium surrounding the probe based upon ultrasonic B-scans, using a straight-ray model of sound propagation. Our goal is to develop a wave-based imaging algorithm using diffraction tomography techniques. Given the hardware configuration and the imaging method, we refer to this system as ''radial reflection diffraction tomography.'' We consider two hardware configurations: a multimonostatic mode using a single transducer as described above, and a multistatic mode consisting of a single transmitter and an aperture formed by multiple receivers. In this latter case, the entire source/receiver aperture rotates about the fixed radius. Practically, such a probe is mounted at the end of a catheter or snaking tube that can be inserted into a part or medium with the goal of forming images of the plane perpendicular to the axis of rotation. We derive an analytic expression for the multimonostatic inverse but ultimately use the new Hilbert space inverse wave (HSIW) algorithm to construct images using both operating modes. Applications include improved IVUS imaging, bore hole tomography, and non-destructive evaluation (NDE) of parts with existing access holes.

Lehman, S K; Norton, S J

2003-10-10

143

Beta Backscatter Measures the Hardness of Rubber  

NASA Technical Reports Server (NTRS)

Nondestructive testing method determines hardness, on Shore scale, of room-temperature-vulcanizing silicone rubber. Measures backscattered beta particles; backscattered radiation count directly proportional to Shore hardness. Test set calibrated with specimen, Shore hardness known from mechanical durometer test. Specimen of unknown hardness tested, and radiation count recorded. Count compared with known sample to find Shore hardness of unknown.

Morrissey, E. T.; Roje, F. N.

1986-01-01

144

Microstructure quantification and correlation with flow stress of ultrafine grained commercially pure Al fabricated by equal channel angular pressing (ECAP)  

Microsoft Academic Search

Commercial purity Al was severely deformed by equal channel angular pressing (ECAP) up to eight passes using route BC. The deformation microstructure was characterized quantitatively by electron-backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The microstructural homogeneity was investigated by EBSD at various locations from center to surface of the samples on a longitudinal section parallel to the pressing direction.

M. Reihanian; R. Ebrahimi; M. M. Moshksar; D. Terada; N. Tsuji

2008-01-01

145

Compositional averaging of backscatter intensities in compounds.  

PubMed

We present high-precision measurements of pure element stable isotope pairs that demonstrate mass has no influence on the backscattering of electrons at typical electron microprobe energies. The traditional prediction of average backscatter intensities in compounds was pragmatically based on elemental mass fractions. Our isotopic measurements establish that this approximation has no physical basis. We propose an alternative model to mass fraction averaging, based on the number of electrons or protons, termed "electron fraction," which predicts backscatter yield better than mass fraction averaging. We also present an improved backscatter (electron loss) factor based on a modified electron fraction average for the ZAF atomic number correction that provides a significant analytical improvement, especially where large atomic number corrections are required. PMID:12807672

Donovan, John J; Pingitore, Nicholas E; Westphal, Andrew

2003-06-01

146

Time domain attenuation estimation method from ultrasonic backscattered signals  

PubMed Central

Ultrasonic attenuation is important not only as a parameter for characterizing tissue but also for compensating other parameters that are used to classify tissues. Several techniques have been explored for estimating ultrasonic attenuation from backscattered signals. In the present study, a technique is developed to estimate the local ultrasonic attenuation coefficient by analyzing the time domain backscattered signal. The proposed method incorporates an objective function that combines the diffraction pattern of the source/receiver with the attenuation slope in an integral equation. The technique was assessed through simulations and validated through experiments with a tissue mimicking phantom and fresh rabbit liver samples. The attenuation values estimated using the proposed technique were compared with the attenuation estimated using insertion loss measurements. For a data block size of 15 pulse lengths axially and 15 beamwidths laterally, the mean attenuation estimates from the tissue mimicking phantoms were within 10% of the estimates using insertion loss measurements. With a data block size of 20 pulse lengths axially and 20 beamwidths laterally, the error in the attenuation values estimated from the liver samples were within 10% of the attenuation values estimated from the insertion loss measurements. PMID:22779499

Ghoshal, Goutam; Oelze, Michael L.

2012-01-01

147

Estimating backscatter spectra after deconvolution with Kalman smoothing  

NASA Astrophysics Data System (ADS)

In quantitative tissue characterization. Obtaining processed ultrasonic echoes with a direct relationship to local tissue response (backscatter spectrum) and that are free from systemic depth-dependent effects, such as diffraction, is essential. In general practice today, these unwanted distortions are eliminated by dividing short time power spectra. However, this method has its drawbacks; noise is not taken into account, and shorter time gates lead to an increasing bias within the relative spectra. To overcome these methodological issues, I propose a different approach as follows. Entire deconvolved A-scans are estimated by a Kalman smoothing deconvolution algorithm. These then serve as a basis for estimating the relative backscatter spectra. In addition, due to the principle of the deconvolution algorithm, it is possible to suppress additive noise to some degree. To examine the properties of the method proposed, this paper presents an analytical expression for the power spectrum of the deconvolved signals obtained by Kalman Smoothing. This result is then compared to the expectations of relative short time power spectra. Simulations demonstrate the behavior of the deconvolution method in a non-stationary environment.

Guenter, Armin I.

2001-05-01

148

EBSD as a tool to identify and quantify bainite and ferrite in low-alloyed Al-TRIP steels.  

PubMed

Bainite is thought to play an important role for the chemical and mechanical stabilization of metastable austenite in low-alloyed TRIP steels. Therefore, in order to understand and improve the material properties, it is important to locate and quantify the bainitic phase. To this aim, electron backscatter diffraction-based orientation microscopy has been employed. The main difficulty herewith is to distinguish bainitic ferrite from ferrite because both have bcc crystal structure. The most important difference between them is the occurrence of transformation induced geometrically necessary dislocations in the bainitic phase. To determine the areas with larger geometrically necessary dislocation density, the following orientation microscopy maps were explored: pattern quality maps, grain reference orientation deviation maps and kernel average misorientation maps. We show that only the latter allow a reliable separation of the bainitic and ferritic phase. The kernel average misorientation threshold value that separates both constituents is determined by an algorithm that searches for the smoothness of the boundaries between them. PMID:18503676

Zaefferer, S; Romano, P; Friedel, F

2008-06-01

149

EBSD and DTA Characterization of A356 Alloy Deformed by ECAP During Reheating and Partial Re-melting  

NASA Astrophysics Data System (ADS)

Recrystallization and partial re-melting processes have been developed for producing semi-solid feedstock in a solid state in which a globular microstructure is obtained by plastic deformation followed by reheating. In this research, to induce strain, a cast- and solution-treated Aluminum A356 (7 wt pct Si) alloy was subjected to a repetitive equal channel angular pressing process using a 90 deg die, up to a total accumulated strain of approximately 8 in route A (increasing strain through a sequence of passes with no rotation of the sample after each pass) at ambient temperature. The microstructural evolutions of deformed and reheated materials were studied by optical microscopy, scanning electron microscopy, and electron back-scattered diffraction analysis. In addition, the influences of pre-deformation on the recrystallization mechanism and liquid formation of A356 alloy were presented and discussed. The results are also supported by differential thermal analysis experiments. Evaluation of the observations indicated that the average cell boundary misorientation increased with increasing strain, so this increased misorientation accelerated the mobility of boundaries and recrystallization kinetics. Therefore, the recrystallization mechanism and kinetics affected by deformation, reheating condition, and intrinsic material properties determined the particle size in the semi-solid state.

Moradi, Marzyeh; Nili-Ahmadabadi, Mahmoud; Poorganji, Behrang; Heidarian, Bashir; Furuhara, Tadashi

2013-11-01

150

High-frequency asymptotic solutions for backscattering by cylinders with conic section directrixes  

Microsoft Academic Search

High-frequency asymptotic expansions are derived for electric and magnetic fields backscattered from a perfectly conducting smooth two-dimensional surface illuminated by a plane incident wave in two cases of TE and TM linear polarizations. Diffraction corrections up to the second order of the inverse large parameter p=ak (where a is a curvature radius at the specularly reflecting point, and k is

Iosif M. Fuks

2005-01-01

151

5 6 7 8 9 10 11 12 13 BackscatterCrossSection(1/(m*str))  

E-print Network

Diffraction Peak Scattering Lidar + + HSRL measurements of multiple scattering provide information., Madison WI 53706, e-mail: eloranta@lidar.ssec.wisc.edu HSRL measurements of backscatter cross section with the lidar cross section. + Assumed projected area volume relationship Provides ice water mass HSRL multiple

Eloranta, Edwin W.

152

Uniform PO and PTD solution for calculating plane wave backscattering from a finite cylindrical shell of arbitrary cross section  

Microsoft Academic Search

The plane wave backscattering from a perfectly conducting three-dimensional shell of arbitrary cross section has peen studied. A uniform physical optics (PO) solution, valid across the reflection limits, is derived. The solution, derived from an asymptotic evaluation of the PO integral, includes end-point contributions that account for the diffracted field on edges. It can be improved by the fringe fields

M. Martinez-Burdalo; A. Martin; R. Villar

1993-01-01

153

Photon diffraction  

NASA Astrophysics Data System (ADS)

In current light models, a particle-like model of light is inconsistent with diffraction observations. A model of light is proposed wherein photon inferences are combined with the cosmological scalar potential model (SPM). That the photon is a surface with zero surface area in the travel direction is inferred from the Michelson-Morley experiment. That the photons in slits are mathematically treated as a linear antenna array (LAA) is inferred from the comparison of the transmission grating interference pattern and the single slit diffraction pattern. That photons induce a LAA wave into the plenum is inferred from the fractal model. Similarly, the component of the photon (the hod) is treated as a single antenna radiating a potential wave into the plenum. That photons are guided by action on the surface of the hod is inferred from the SPM. The plenum potential waves are a real field (not complex) that forms valleys, consistent with the pilot waves of the Bohm interpretation of quantum mechanics. Therefore, the Afshar experiment result is explained, supports Bohm, and falsifies Copenhagen. The papers may be viewed at http://web.citcom.net/˜scjh/.

Hodge, John

2009-11-01

154

Materials Science: Diffraction  

NSDL National Science Digital Library

This suite of websites from the University of Liverpool comprises a learning module that focuses on diffraction. The website features sections on diffraction, the geometry of diffraction, the intensity of diffraction, electron diffraction and X-ray diffraction. Each section features text, images and animations as well as learning exercises. These sites aid in the exploration of the various aspects of diffraction.

Goodhew, Peter; Fretwell, Ann; Tanovic, Boban; Jones, Ian; Green, Andrew; Brook, David

155

On the use of EBSD analysis to investigate the microstructure of gold samples built by selective laser melting  

Microsoft Academic Search

In the selective laser melting process, the scanning strategies have a deep impact on the final microstructures. In this paper,\\u000a we point out the benefits of using EBSD techniques to characterize the scanning strategies on 18-carat gold samples. For a\\u000a given scanning strategy, different microstructures and orientation can be achieved, due to the change of the thermal gradients.\\u000a The results

Jamasp Jhabvala; Eric Boillat; Rémy Glardon

156

Bathymetry and acoustic backscatter: Estero Bay, California  

USGS Publications Warehouse

Between July 30 and August 9, 2012, scientists from the U.S. Geological Survey (USGS), Pacific Coastal and Marine Science Center (PCMSC), acquired bathymetry and acoustic-backscatter data from Estero Bay, San Luis Obispo, California, under PCMSC Field Activity ID S-05-12-SC. The survey was done using the R/V Parke Snavely outfitted with a multibeam sonar for swath mapping and highly accurate position and orientation equipment for georeferencing. This report provides these data in a number of different formats, as well as a summary of the mapping mission, maps of bathymetry and backscatter, and Federal Geographic Data Committee (FGDC) metadata.

Hartwell, Stephen R.; Finlayson, David P.; Dartnell, Peter; Johnson, Samuel Y.

2013-01-01

157

SAR backscatter from coniferous forest gaps  

NASA Technical Reports Server (NTRS)

A study is in progress comparing Airborne Synthetic Aperture Radar (AIRSAR) backscatter from coniferous forest plots containing gaps to backscatter from adjacent gap-free plots. Issues discussed are how do gaps in the range of 400 to 1600 sq m (approximately 4-14 pixels at intermediate incidence angles) affect forest backscatter statistics and what incidence angles, wavelengths, and polarizations are most sensitive to forest gaps. In order to visualize the slant-range imaging of forest and gaps, a simple conceptual model is used. This strictly qualitative model has led us to hypothesize that forest radar returns at short wavelengths (eg., C-band) and large incidence angles (e.g., 50 deg) should be most affected by the presence of gaps, whereas returns at long wavelengths and small angles should be least affected. Preliminary analysis of 1989 AIRSAR data from forest near Mt. Shasta supports the hypothesis. Current forest backscatter models such as MIMICS and Santa Barbara Discontinuous Canopy Backscatter Model have in several cases correctly predicted backscatter from forest stands based on inputs of measured or estimated forest parameters. These models do not, however, predict within-stand SAR scene texture, or 'intrinsic scene variability' as Ulaby et al. has referred to it. For instance, the Santa Barbara model, which may be the most spatially coupled of the existing models, is not truly spatial. Tree locations within a simulated pixel are distributed according to a Poisson process, as they are in many natural forests, but tree size is unrelated to location, which is not the case in nature. Furthermore, since pixels of a simulated stand are generated independently in the Santa Barbara model, spatial processes larger than one pixel are not modeled. Using a different approach, Oliver modeled scene texture based on an hypothetical forest geometry. His simulated scenes do not agree well with SAR data, perhaps due to the simple geometric model used. Insofar as texture is the expression of biological forest processes, such as succession and disease, and physical ones, such as fire and wind-throw, it contains useful information about the forest, and has value in image interpretation and classification. Forest gaps are undoubtedly important contributors to scene variance. By studying the localized effects of gaps on forest backscatter, guided by our qualitative model, we hope to understand more clearly the manner in which spatial heterogeneities in forests produce variations in backscatter, which collectively give rise to scene texture.

Day, John L.; Davis, Frank W.

1992-01-01

158

Radar Backscatter from Conducting Polyhedral Spheres  

Microsoft Academic Search

Electromagnetic backscatter characteristics of conducting polyhedral spheres, constructed of 12 pentagons and a large number of hexagons, were investigated. The polyhedral structures were classified by their number of vertices and by the width of the conducting edges in their frames. Polyhedral spheres with 60, 80, 180, 240, 320, 500, 540, 960, and 1500 vertices were evaluated for their ability to

Paul A. Bernhardt

2010-01-01

159

Rutherford backscattering analysis of contaminants in PET  

Microsoft Academic Search

Rutherford Backscattering Spectrometry (RBS) was used to understand the sorption and desorption of organic contaminants in the polymer Poly(ethylene terephthalate), or PET. Samples were exposed to a range of organics to simulate contamination of PET that can take place in the post-consumer waste stream. From RBS analysis, concentration depth profiles were shown to vary from a monolayer regime surface layer

D. E. Pierce; R. L. Pfeffer; G. D. Sadler

1997-01-01

160

Matej Mayer RBS -Rutherford Backscattering Spectrometry  

E-print Network

118 (1996) 52 #12;© Matej Mayer 2003 4 History Sir Ernest Rutherford (1871 - 1937) · 1911: Rutherford#12;#12;© Matej Mayer 2003 1 RBS - Rutherford Backscattering Spectrometry M. Mayer Max and kinematics · Rutherford cross section and limitations · RBS spectra from thin and thick films · Stopping

Smith, Richard J.

161

Window flaw detection by backscatter lighting  

NASA Technical Reports Server (NTRS)

Portable fiber-optic probe detects tiny flaws in transparent materials. Probe transmits light through surface to illuminate interior of material by backscattering off its edges. Light-sensitive contact paper records scratch pattern. Technique can be used for rapid visual checks. Flexible fiber optics are safely used in explosive or flammable areas; they present no hazard of breakage or contamination in controlled environments.

Crockett, L. K.; Minton, F. R.

1978-01-01

162

Efficient and reliable low-power backscatter networks  

E-print Network

There is a long-standing vision of embedding backscatter nodes like RFIDs into everyday objects to build ultra-low power ubiquitous networks. A major problem that has challenged this vision is that backscatter communication ...

Wang, Jue

163

Observation of high-temperature phase transformation in the Si-modified aluminide coating on mild steel using EBSD  

SciTech Connect

Mild steel was coated by hot-dipping in a molten bath containing Al-10 wt.% Si. The phase transformation in the aluminide layer during diffusion at 750 deg. C in static air was analyzed by Electron Backscatter Diffraction. The results showed that the aluminide layer of the as-coated specimen consisted of an outer Al-Si eutectic topcoat and the inner Fe-Al-Si and Fe-Al intermetallic layers. The formation of {tau}{sub 5}-Al{sub 7}Fe{sub 2}Si and {tau}{sub 6}-Al{sub 4}FeSi was observed with increasing exposure time at 750 deg. C, while the {tau}{sub 1}-(Al,Si){sub 5}Fe{sub 3} phase precipitated into the Fe{sub 2}Al{sub 5} phase. After 60 min of exposure, the {tau}{sub 5}-Al{sub 7}Fe{sub 2}Si and {tau}{sub 6}-Al{sub 4}FeSi phases disappeared. The FeAl phase not only formed at the interface between Fe{sub 2}Al{sub 5} and the steel substrate, but also transformed from {tau}{sub 1}-(Al,Si){sub 5}Fe{sub 3} after diffusion for 10 h. With prolonged exposure, the growing FeAl phase decreased the thickness of Fe{sub 2}Al{sub 5} and forced the formation of FeAl{sub 2} phase. Finally, the aluminide layer comprised only FeAl{sub 2} and FeAl.

Cheng, Wei-Jen, E-mail: d9603505@mail.ntust.edu.tw [Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei 10672, Taiwan (China); Wang, Chaur-Jeng [Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei 10672, Taiwan (China)

2010-04-15

164

Wave shadowing and modulation of microwave backscatter from the ocean  

NASA Astrophysics Data System (ADS)

Shadowing and modulation of microwave backscatter by ocean waves are studied using coherent X-band radars. Two types of shadowing are investigated: geometric shadowing (complete blockage of incident rays) and partial shadowing (polarization-dependent diffraction combined with weak scatterers). We point out that the frequency of occurrence of zero signal-to-noise ratio samples cannot depend on the incident power level or the polarization if geometric shadowing occurs but can if partial shadowing exists. We then compare this behavior with observations, and show that the data do not support the hypothesis that geometric shadowing plays a significant role in low-grazing-angle microwave scattering from the ocean surface. Furthermore, our data indicate that partial shadowing only depends significantly on polarization for the steep waves found near shorelines. We also study the modulation of microwave backscatter by ocean waves using these data by looking at the phase differences between received power and scatterer velocity. These phase differences appear to be rather well explained by standard composite surface theory at VV polarization, having values that are positive looking up wave and negative looking down wave. For HH polarization, however, breaking effects come into play and overshadow composite surface effects of free waves. They cause the phase difference to be near zero for up wave looks and near 180° for down-wave looks. A simple model that involves both breaking and freely propagating waves but does not include any shadowing effects is shown to account for observed phase differences at both polarizations to within about 10°.

Plant, William J.; Farquharson, Gordon

165

Independent measurement of extinction and backscatter profiles in cirrus clouds by using a combined Raman elastic-backscatter lidar  

Microsoft Academic Search

Height profiles of the extinction and the backscatter coefficients in cirrus clouds are determined independently from elastic- and inelastic- (Raman) backscatter signals. An extended error analysis is given. Examples covering the measured range of extinction-to-backscatter ratios (lidar ratios) in ice clouds are presented. Lidar ratios between 5 and 15 sr are usually found. A strong variation between 2 and 20

Albert Ansmann; Ulla Wandinger; Maren Riebesell; Claus Weitkamp; Walfried Michaelis

1992-01-01

166

Spectra of Particulate Backscattering in Natural Waters  

NASA Technical Reports Server (NTRS)

Hyperspectral profiles of downwelling irradiance and upwelling radiance in natural waters (oligotrophic and mesotrophic) are combined with inverse radiative transfer to obtain high resolution spectra of the absorption coefficient (a) and the backscattering coefficient (bb) of the water and its constituents. The absorption coefficient at the mesotrophic station clearly shows spectral absorption features attributable to several phytoplankton pigments (Chlorophyll a, b, c, and Carotenoids). The backscattering shows only weak spectral features and can be well represented by a power-law variation with wavelength (lambda): b(sub b) approx. Lambda(sup -n), where n is a constant between 0.4 and 1.0. However, the weak spectral features in b(sub b), suggest that it is depressed in spectral regions of strong particle absorption. The applicability of the present inverse radiative transfer algorithm, which omits the influence of Raman scattering, is limited to lambda < 490 nm in oligotrophic waters and lambda < 575 nm in mesotrophic waters.

Gordon, Howard, R.; Lewis, Marlon R.; McLean, Scott D.; Twardowski, Michael S.; Freeman, Scott A.; Voss, Kenneth J.; Boynton, Chris G.

2009-01-01

167

Microwave backscattering from an anisotropic soybean canopy  

NASA Technical Reports Server (NTRS)

Electromagnetic backscattering from a soybean canopy is modeled in the L band region of the spectrum. Mature soybean plants are taken as an ensemble of leaves and stems which are represented by lossy dielectric disks and rods respectively. Field data indicated that leaves and stems are not distributed uniformly in the azimuth coordinate. The plant has a tendency to grow out into the area between the rows. The effects on backscattered radar waves was computed by the distorted Born approximation. Results for look directions along the rows and perpendicular to the rows show that only a modest difference occurs in the L band frequency range. The use of another nonuniform distribution, different from those observed experimentally, results in a significant effect due to vegetation asymmetry.

Lang, R. H.; Saatchi, S.; Levine, D. M.

1986-01-01

168

Aerosol backscatter lidar calibration and data interpretation  

NASA Technical Reports Server (NTRS)

A treatment of the various factors involved in lidar data acquisition and analysis is presented. This treatment highlights sources of fundamental, systematic, modeling, and calibration errors that may affect the accurate interpretation and calibration of lidar aerosol backscatter data. The discussion primarily pertains to ground based, pulsed CO2 lidars that probe the troposphere and are calibrated using large, hard calibration targets. However, a large part of the analysis is relevant to other types of lidar systems such as lidars operating at other wavelengths; continuous wave (CW) lidars; lidars operating in other regions of the atmosphere; lidars measuring nonaerosol elastic or inelastic backscatter; airborne or Earth-orbiting lidar platforms; and lidars employing combinations of the above characteristics.

Kavaya, M. J.; Menzies, R. T.

1984-01-01

169

Backscattering from a randomly rough dielectric surface  

Microsoft Academic Search

A backscattering model for scattering from a randomly rough dielectric surface is developed. Both like- and cross-polarized scattering coefficients are obtained. The like-polarized scattering coefficients contain single scattering terms and multiple scattering terms. The single scattering terms are shown to reduce to the first-order solutions derived from the small perturbation method when the roughness parameters satisfy the slightly rough conditions.

A. K. Fung; Z. Li; K. S. Chen

1992-01-01

170

Aerosol Classification by Advanced Backscatter Lidar Techniques  

NASA Astrophysics Data System (ADS)

The high spectral resolution lidar (HSRL) method based on an iodine absorption filter and a frequency doubled pulsed Nd:YAG laser is presented. This method has the capability to directly measure the extinction and backscatter coefficients of aerosols and clouds. Measurements of an airborne HSRL system from four different field experiments are used to build up an aerosol classification. Two examples show the potential of this aerosol classification to distinguish between different aerosol types.

Groß, Silke; Wirth, Martin; Esselborn, Michael

171

The backscattering factor in appearance potential spectroscopy  

NASA Astrophysics Data System (ADS)

We have studied, through Monte Carlo simulations, the contribution of the elastic scattering of primary electrons ( RAPS) to the appearance potential yield for aluminum and tungsten, and compare the results with the backscattering effect on Auger electron spectroscopy ( RAES). We found that the RAPS contribution always diminishes the appearance potential yield, showing an inverse correlation with the elastic peak. This result points out a clear difference with the RAES contribution, which always increases the Auger yield.

Ferron, J.; del Barco, J. L.; Goldberg, E. C.

1990-12-01

172

Terahertz backscattering behavior of various absorbing materials  

NASA Astrophysics Data System (ADS)

The Submillimeter-Wave Technology Laboratory (STL) at the University of Massachusetts Lowell has investigated the electromagnetic scattering behavior of various broadband absorbers. Several absorbing materials were tested in a compact radar range operating at a center frequency of 160 GHz. The polarimetric radar cross section was measured at elevation angles from 15° to 75°. In addition to the backscattering behavior, the normal incidence transmittance of the materials was evaluated.

Wu, C.; Gatesman, A. J.; DeRoeck, L.; Horgan, T.; Giles, R. H.; Nixon, W. E.

2009-05-01

173

Fast in-situ annealing stage coupled with EBSD: A suitable tool to observe quick recrystallization mechanisms  

SciTech Connect

A heating stage has been developed to perform in-situ annealing in a SEM equipped with an EBSD system in order to study recrystallization mechanisms. High temperature treatments could then be performed inside the SEM, up to 1180 Degree-Sign C and with high heating and cooling rates ({approx} 100 Degree-Sign C s{sup -1}). Samples were cooled down to room temperature to perform EBSD orientation mapping in between successive short-duration heat treatments. Microstructure evolution snapshots obtained this way allow gaining an insight into recrystallization mechanisms. The interest of such experiments is shown for two examples: static recrystallization of cold deformed pure tantalum and post-dynamic evolution of hot-deformed Zircaloy4. - Highlights: Black-Right-Pointing-Pointer Heating stage for in-SEM annealing at high temperature (up to 1200 Degree-Sign C). Black-Right-Pointing-Pointer High heating and cooling rates (100 Degree-Sign C s{sup -1}), no temperature overshoot. Black-Right-Pointing-Pointer Sequential observation of very fast recrystallization mechanisms.

Bozzolo, N., E-mail: nathalie.bozzolo@mines-paristech.fr; Jacomet, S.; Loge, R.E.

2012-08-15

174

Photoelectron diffraction and holography: Some new directions  

SciTech Connect

Photoelectron diffraction has by now become a versatile and powerful technique for studying surface structures, with special capabilities for resolving chemical and magnetic states of atoms and deriving direct structural information from both forward scattering along bond directions and back-scattering path length differences. Further fitting experiment to theory can lead to structural accuracies in the {plus_minus}0.03 ){Angstrom} range. Holographic inversions of such diffraction data also show considerable promise for deriving local three-dimensional structures around a given emitter with accuracies of {plus_minus}0.2--0.3 {Angstrom}. Resolving the photoelectron spin in some way and using circularly polarized radiation for excitation provide added dimensions for the study of magnetic systems and chiral experimental geometries. Synchrotron radiation with the highest brightness and energy resolution, as well as variable polarization, is crucial to the full exploitation of these techniques.

Fadley, C.S. [Lawrence Berkeley Lab., CA (United States)]|[California Univ., Davis, CA (United States). Dept. of Physics

1993-08-01

175

Backscattering Differential Ghost Imaging in Turbid Media  

E-print Network

In this Letter we present experimental results concerning the retrieval of images of absorbing objects immersed in turbid media via differential ghost imaging (DGI) in a backscattering configuration. The method has been applied, for the first time to our knowledge, to the imaging of small thin black objects located at different depths inside a turbid solution of polystyrene nanospheres and its performances assessed via comparison with standard imaging techniques. A simple theoretical model capable of describing the basic optics of DGI in turbid media is proposed.

M. Bina; D. Magatti; M. Molteni; A. Gatti; L. A. Lugiato; F. Ferri

2012-08-22

176

Backscattering Differential Ghost Imaging in Turbid Media  

E-print Network

In this Letter we present experimental results concerning the retrieval of images of absorbing objects immersed in turbid media via differential ghost imaging (DGI) in a backscattering configuration. The method has been applied, for the first time to our knowledge, to the imaging of small thin black objects located at different depths inside a turbid solution of polystyrene nanospheres and its performances assessed via comparison with standard imaging techniques. A simple theoretical model capable of describing the basic optics of DGI in turbid media is proposed.

Bina, M; Molteni, M; Gatti, A; Lugiato, L A; Ferri, F

2012-01-01

177

Mudrocks examined by backscattered electron microscopy  

NASA Technical Reports Server (NTRS)

A method of studying mudrocks is developed using backscattered electrons (BSE) in scanning electron microscopy. Commercially available detectors are utilized to mix the BSE and secondary electron signals in order to obtain the optimum image for a particular material. Thin sections or polished rock chip surfaces are examined with BSE which provides both the atomic number contrast and topographic contrast. This technique provides very detailed information about the form and composition of individual grains in the mudrock thin sections and can be used in studies of the source, mode of deposition, diagenesis, and tectonic deformational history of mudrocks.

Pye, K.; Krinsley, D.

1983-01-01

178

Backscattering suppression in nonreciprocal ring resonators  

NASA Astrophysics Data System (ADS)

Faraday effect in ring resonators leads to the resonance splitting of clockwise and counter-clockwise propagating modes. Thus the backscattering into counter propagating mode of the ring resonator due to the roughness or periodical corrugation of the ring side walls can be suppressed by the Faraday effect. Based on that property, we propose here a novel ring resonator switch. The resonance of the corrugated resonator coupled to a waveguide can be switched off by the application of the external magnetic field. In this case, the resonance is not shifted, as what typically occurs at small perturbation, but suppressed.

Petrov, Alexander Yu.; Jalas, Dirk; Krause, Michael; Eich, Manfred

2010-10-01

179

A new technique for backscattering analysis  

NASA Astrophysics Data System (ADS)

We suggest a new technique for analyzing Rutherford backscattering spectra. By determining the ratio of the range of a particle of energy E, to that of a particle whose energy is a fraction of E, we convert two basic integral equations into a pair of linear equations that are easy to solve and manipulate. We demonstrate the applicability of this formalism by using it to measure the stopping power of gold for alpha particles with energies 1.2, 2.2, 3.7, 5.2 and 7.1 MeV.

Keaton, P. W.; Peercy, P. S.; Doyle, B. L.; Maggiore, C. J.

1980-01-01

180

Measured ionospheric Doppler spreading of HF ground backscatter  

NASA Astrophysics Data System (ADS)

Doppler spectra from ionospherically propagated ground backscatter are presented. These spectra show how the ionosphere distorts HF backscatter radio waves by frequency speading. The ground backscatter spectra presented here show that ionospheric Dopper spreading is so ubiquitous that its effect should never be disregarded, even when a narrow azimuth beam radar such as ours is used. Nevertheless, Doppler spreading varies so quickly that it usually pays to wait for it to diminish.

Jones, R. M.; Riley, J. P.; Georges, T. M.

1983-03-01

181

Analytical approach to backscattering of low-energy electrons  

NASA Astrophysics Data System (ADS)

The backscattered flux and energy of electrons when a monoenergetic electron is incident in a gas at any pitch angle are calculated using an approach based on spatial yield spectra. The four-dimensional yield spectrum function is defined and the equations for calculating the backscattered flux and energy are derived. The calculated backscattered flux and energy are compared to the data of Mantas and Walker (1976) and the data correlate well.

Haider, S. A.; Singhal, R. P.

1986-12-01

182

Rotational Raman scattering (Ring effect) in satellite backscatter ultraviolet measurements  

NASA Astrophysics Data System (ADS)

A detailed radiative transfer calculation has been carried out to estimate the effects of rotational Raman scattering (RRS) on satellite measurements of backscattered ultraviolet radiation. Raman-scattered light is shifted in frequency from the incident light, which causes filling in of solar Fraunhofer lines in the observed backscattered spectrum (also known as the Ring effect). The magnitude of the rotational Raman scattering filling in is a function of wavelength, solar zenith angle, surface reflectance, surface pressure, and instrument spectral resolution. The filling in predicted by our model is found to be in agreement with observations from the Shuttle Solar Backscatter Ultraviolet Radiometer and the Nimbus-7 Solar Backscatter Ultraviolet Radiometer.

Cebula, Richard P.; Joiner, Joanna; Bhartia, Pawan K.; Hilsenrath, Ernest; McPeters, Richard D.; Park, Hongwoo

1995-07-01

183

Measurement of high voltage using Rutherford backscattering spectrometry  

E-print Network

to be near channel 1550 when a 140 keV helium ion backscatters into the solid angle of the detector. Upon analyzing the backscattered spectra, an additional peak was observed below the energy of the bismuth peak, see Figure 11. Calibration Data- Helium... to be near channel 1550 when a 140 keV helium ion backscatters into the solid angle of the detector. Upon analyzing the backscattered spectra, an additional peak was observed below the energy of the bismuth peak, see Figure 11. Calibration Data- Helium...

Abrego, Celestino Pete

2007-04-25

184

Compton backscattered collmated X-ray source  

DOEpatents

A high-intensity, inexpensive and collimated x-ray source for applications such as x-ray lithography is disclosed. An intense pulse from a high power laser, stored in a high-finesse resonator, repetitively collides nearly head-on with and Compton backscatters off a bunched electron beam, having relatively low energy and circulating in a compact storage ring. Both the laser and the electron beams are tightly focused and matched at the interaction region inside the optical resonator. The laser-electron interaction not only gives rise to x-rays at the desired wavelength, but also cools and stabilizes the electrons against intrabeam scattering and Coulomb repulsion with each other in the storage ring. This cooling provides a compact, intense bunch of electrons suitable for many applications. In particular, a sufficient amount of x-rays can be generated by this device to make it an excellent and flexible Compton backscattered x-ray (CBX) source for high throughput x-ray lithography and many other applications.

Ruth, Ronald D. (Woodside, CA); Huang, Zhirong (Stanford, CA)

2000-01-01

185

Simulation of ultrasound backscatter images from fish  

NASA Astrophysics Data System (ADS)

The objective of this work is to investigate ultrasound (US) backscatter in the MHz range from fish to develop a realistic and reliable simulation model. The long term objective of the work is to develop the needed signal processing for fish species differentiation using US. In in-vitro experiments, a cod (Gadus morhua) was scanned with both a BK Medical ProFocus 2202 ultrasound scanner and a Toshiba Aquilion ONE computed tomography (CT) scanner. The US images of the fish were compared with US images created using the ultrasound simulation program Field II. The center frequency of the transducer is 10 MHz and the Full Width at Half Maximum (FWHM) at the focus point is 0.54 mm in the lateral direction. The transducer model in Field II was calibrated using a wire phantom to validate the simulated point spread function. The inputs to the simulation were the CT image data of the fish converted to simulated scatter maps. The positions of the point scatterers were assumed to be uniformly distributed. The scatter amplitudes were generated with a new method based on the segmented CT data in Hounsfield Units and backscatter data for the different types of tissues from the literature. The simulated US images reproduce most of the important characteristics of the measured US image.

Pham, An Hoai; Stage, Bjarne; Hemmsen, Martin Christian; Lundgren, Bo; Pedersen, Mads Møller; Pedersen, Tina Bock; Jensen, Jørgen Arendt

2011-03-01

186

The angular distribution of diffusely backscattered light  

NASA Astrophysics Data System (ADS)

The diffusion approximation predicts the angular distribution of light diffusely transmitted through an opaque slab to depend only on boundary reflectivity, independent of scattering anisotropy, and this has been verified by experiment(M.U. Vera and D.J. Durian, Phys. Rev. E 53) 3215 (1996). Here, by contrast, we demonstrate that the angular distribution of diffusely backscattered light depends on scattering anisotropy as well as boundary reflectivity. To model this observation scattering anisotropy is added to the diffusion approximation by a discontinuity in the photon concentration at the source point that is proportional to the average cosine of the scattering angle. We compare the resulting predictions with random walk simulations and with measurements of diffusely backscattered intensity versus angle for glass frits and aqueous suspensions of polystyrene spheres held in air or immersed in a water bath. Increasing anisotropy and boundary reflectivity each tend to flatten the predicted distributions, and for different combinations of anisotropy and reflectivity the agreement between data and predictions ranges from qualitatively to quantitatively good.

Vera, M. U.; Durian, D. J.

1997-03-01

187

Compton backscattered collimated x-ray source  

DOEpatents

A high-intensity, inexpensive and collimated x-ray source is disclosed for applications such as x-ray lithography is disclosed. An intense pulse from a high power laser, stored in a high-finesse resonator, repetitively collides nearly head-on with and Compton backscatters off a bunched electron beam, having relatively low energy and circulating in a compact storage ring. Both the laser and the electron beams are tightly focused and matched at the interaction region inside the optical resonator. The laser-electron interaction not only gives rise to x-rays at the desired wavelength, but also cools and stabilizes the electrons against intrabeam scattering and Coulomb repulsion with each other in the storage ring. This cooling provides a compact, intense bunch of electrons suitable for many applications. In particular, a sufficient amount of x-rays can be generated by this device to make it an excellent and flexible Compton backscattered x-ray (CBX) source for high throughput x-ray lithography and many other applications. 4 figs.

Ruth, R.D.; Huang, Z.

1998-10-20

188

Compton backscattered collimated x-ray source  

DOEpatents

A high-intensity, inexpensive and collimated x-ray source for applications such as x-ray lithography is disclosed. An intense pulse from a high power laser, stored in a high-finesse resonator, repetitively collides nearly head-on with and Compton backscatters off a bunched electron beam, having relatively low energy and circulating in a compact storage ring. Both the laser and the electron beams are tightly focused and matched at the interaction region inside the optical resonator. The laser-electron interaction not only gives rise to x-rays at the desired wavelength, but also cools and stabilizes the electrons against intrabeam scattering and Coulomb repulsion with each other in the storage ring. This cooling provides a compact, intense bunch of electrons suitable for many applications. In particular, a sufficient amount of x-rays can be generated by this device to make it an excellent and flexible Compton backscattered x-ray (CBX) source for high throughput x-ray lithography and many other applications.

Ruth, Ronald D. (Woodside, CA); Huang, Zhirong (Stanford, CA)

1998-01-01

189

EBSD characterisation of Y2Ba4CuUOx phase in melttextured YBCO with addition of depleted uranium oxide  

NASA Astrophysics Data System (ADS)

Melt-textured YBCO samples processed with added Y2O3 and depleted uranium oxide (DU) contain nano-particles, which have been identified previously as Y2Ba4CuUOx (U-411). This phase has a cubic unit cell, which is clearly distinct from the orthorhombic Y-123 and Y-211 phases within the YBCO system. In samples with a high amount of DU addition (0.8 wt-% DU), U-2411 particles have sizes between 200 nm and several µm, so identification of the Kikuchi patterns of this phase becomes possible. Together with a parallel EDX analysis, the particles embedded in the Y-123 matrix can be identified unambiguously. In this way, a three-phase EBSD scan becomes possible, allowing also the identification of nanometre-sized particles in the sample microstructure.

Koblischka-Veneva, A.; Mücklich, F.; Koblischka, M. R.; Babu, N. Hari; Cardwell, D. A.

2006-06-01

190

Beyond the random phase approximation: Stimulated Brillouin backscatter for finite laser coherence times  

E-print Network

We develop a statistical theory of stimulated Brillouin backscatter (BSBS) of a spatially and temporally partially incoherent laser beam for laser fusion relevant plasma. We find a new collective regime of BSBS (CBSBS) with intensity threshold controlled by diffraction, an insensitive function of the laser coherence time, $T_c$, once light travel time during $T_c$ exceeds a laser speckle length. The BSBS spatial gain rate is approximately the sum of that due to CBSBS, and a part which is independent of diffraction and varies linearly with $T_c$. We find that the bandwidth of KrF-laser-based fusion systems would be large enough to allow additional suppression of BSBS.

Alexander O. Korotkevich; Pavel M. Lushnikov; Harvey A. Rose

2013-11-25

191

X-Ray Diffraction.  

ERIC Educational Resources Information Center

Reviews applications in research and analytical characterization of compounds and materials in the field of X-ray diffraction, emphasizing new developments in applications and instrumentation in both single crystal and powder diffraction. Cites 414 references. (CS)

Smith, D. K.; Smith, K. L.

1980-01-01

192

Measurement of elastic strains and small lattice rotations using electron back scatter diffraction.  

PubMed

A method is presented for the determination of elastic strains from electron back scatter diffraction patterns, which are obtained at high spatial resolution, from bulk specimens in a scanning electron microscope. It is estimated that the method is sensitive to strains of the order of 0.02%. Strains in Si(1-x)Ge(x) epitaxial layers grown on planar Si substrates were measured for x from 0.2 to 0.015, there being excellent agreement with X-ray diffraction results. Small lattice rotations can also be measured, the technique being sensitive to rotations of 0.01 degrees, which offers an improvement of approximately two orders of magnitude from the more usual EBSD measurements of misorientation. Small lattice rotations were measured in Si(0.85)Geo(0.15) grown on a patterned Si substrate and were consistent with elastic relaxation of the epilayer strain energy. PMID:22666906

Wilkinson, A J

1996-03-01

193

Fading Characteristics of Panchromatic Radar Backscatter from Selected Agricultural Targets  

Microsoft Academic Search

An experiment was performed to determine the fading characteristics of backscattered radar signals from four agricultural targets at 9 GHz. The targets included two different row crops (corn and soybeans), a continuous canopy (alfalfa) and bare ground. After a short review of the statistics of Rayleigh fading backscatter, the data processing method and the results of the experiment are analyzed.

Thomas F. Bush; Fawwaz Uloby

1975-01-01

194

Discrimination of UXO in Soil Using Broadband Polarimetric GPR Backscatter  

E-print Network

of the target response relative to clutter from the rough surface scattering, without special processing beyond- 1 - Discrimination of UXO in Soil Using Broadband Polarimetric GPR Backscatter Kevin O'Neill Cold@crrel.usace.army.mil ABSTRACT Polarimetric analysis of ground penetrating radar (GPR) backscatter offers a new means

Shubitidze, Fridon

195

Azimuth Variation in Microwave Backscatter over the Greenland Ice Sheet  

E-print Network

ice sheet (see Fig. 2). For each sen- sor, different day ranges were used. SeaWinds uses 2 daysAzimuth Variation in Microwave Backscatter over the Greenland Ice Sheet Ivan S. Ashcraft and David ice sheet. However, most Greenland studies assume constant backscatter for varying azimuth angles

Long, David G.

196

Opposition Effect from Clementine Data and Mechanisms of Backscatter  

Microsoft Academic Search

An analysis of Clementine data obtained from a UVVIS camera and simulating laboratory photometric and polarimetric measurements is presented with the use of a new photometric three-parameter function combining the shadow-hiding and coherent backscatter mechanisms. The fit of calculated curves to the average brightness phase function of the Moon derived from Clementine data indicates that the coherent backscatter component is

Yu. G. Shkuratov; M. A. Kreslavsky; A. A. Ovcharenko; D. G. Stankevich; E. S. Zubko; C. Pieters; G. Arnold

1999-01-01

197

Backscattering limitation for fiber-optic quantum key distribution systems  

Microsoft Academic Search

We characterized backscattering effects in optical fiber using a photon counting technique and considered its implications for quantum key distribution (QKD). We found that Rayleigh (elastic) backscattering can put strong limitations on a two-way QKD system's performance. Raman (inelastic) scattering can restrict the ability of wavelength multiplexing of a quantum channel with strong classical data channel(s).

Darius Subacius; Anton Zavriyev; Alexei Trifonov

2005-01-01

198

Fading characteristics of panchromatic radar backscatter from selected agricultural targets  

NASA Technical Reports Server (NTRS)

An experiment was performed to empirically determine the fading characteristics of backscattered radar signals from four agricultural targets at 9 GHz. After a short review of the statistics of Rayleigh fading backscatter, the data processing method and results of the data are analyzed. Comparison with theory shows adequate agreement with the experimental results, provided of course, the targets are modeled in a correct manner.

Bush, T. F.; Ulaby, F. T.

1973-01-01

199

Tracking California seafloor seeps with bathymetry, backscatter and ROVs  

Microsoft Academic Search

The California (USA) margin includes two different tectonic regimes: subduction north of the Mendocino Triple Junction and translation south. Both margins include seeps, and their distribution can be inferred using seafloor bathymetry and backscatter as well as subsurface seismic data. Anomalous bathymetric and backscatter features related to fluid expulsion include headless submarine canyons, fault zones, anticlines, pockmarks, and mud volcanoes.

Daniel L. Orange; Janet Yun; Norman Maher; James Barry; Gary Greene

2002-01-01

200

DETECTION AND IMAGING IN STRONGLY BACKSCATTERING RANDOMLY LAYERED MEDIA  

E-print Network

DETECTION AND IMAGING IN STRONGLY BACKSCATTERING RANDOMLY LAYERED MEDIA R. ALONSO, L. BORCEA, G and difficult to distinguish from the medium backscatter. Detection and imaging with sensor arrays in such media the echoes that are useful in imaging. Key words. array imaging, randomly layered media, detection, filtering

Borcea, Liliana

201

Acoustic backscatter by schools of adult Atlantic mackerel  

Microsoft Academic Search

The extent of acoustic backscatter by schools of adult Atlantic mackerel (Scomber scombrus) is investigated to improve biomass estimates. Previous studies involving modelled scattering from individual mackerel showed that backscattering at high frequencies is dominated by the contribution from the backbone. Accurate predictions of the scattering spectra require consideration of back- scattering from the entire skeleton, including details of the

Natalia Gorska; Rolf J. Korneliussen; Egil On

202

Coherent Backscattering of Ultracold Atoms F. Jendrzejewski,1  

E-print Network

Coherent Backscattering of Ultracold Atoms F. Jendrzejewski,1 K. M¨uller,1 J. Richard,1 A. Date,1 T: November 12, 2012) We report on the direct observation of coherent backscattering (CBS) of ultracold atoms in a quasi-two-dimensional configuration. Launching atoms with a well-defined momentum in a laser speckle

Boyer, Edmond

203

Rayleigh backscattering in a fiber gyroscope with limited coherence sources  

Microsoft Academic Search

Noise due to temporal fluctuations of Rayleigh baekscattered light in fiber-optical gyroscopes is studied experimentally with various sources whose coherence length is less than the fiber length. The reduction of the coherent fraction of backscattered light and its fluctuation frequencies with reduced source coherence is demonstrated and fit to an analytical model. Measured backscatter parameters for the fiber and sources

W. Burns; R. Moeller

1983-01-01

204

Diffraction Metrology and Standards  

E-print Network

Diffraction Metrology and Standards CERAMICS Our objective is the development of Standard Reference vendors supply NIST Diffraction Metrology SRMs with the equipment they sell. One vendor includes SRM 1976 the previous value. · Calibration of equipment with NIST Diffraction Metrology SRMs is requisite for ISO

Perkins, Richard A.

205

Relationship between wind, waves and radar backscatter  

NASA Technical Reports Server (NTRS)

The aim of the research was to investigate the relationship between wind, waves, and radar backscatter from water surface. To this end, three field experiments with periods of 2 to 4 weeks were carried out during summer months in 1988, 1989 and 1990. For these periods, the University of Washington group provided (1) environmental parameters such as wind speed, wind stress, and atmospheric stratification through measurements of surface fluxes (of momentum, sensible heat and latent heat) and of air and water temperatures; and (2) wave height spectra including both the dominant waves and the short gravity-capillary waves. Surface flux measurements were performed by using our well tested instruments: a K-Gill twin propeller-vane anemometer and a fast response thermocouple psychrometer. Wave heights were measured by a resistance wire wave gauge. The University of Kansas group was responsible for the operation of the microwave radars.

Katsaros, Kristina B.; Ataktuerk, Serhad S.

1991-01-01

206

Rutherford backscattering analysis of contaminants in PET  

NASA Astrophysics Data System (ADS)

Rutherford Backscattering Spectrometry (RBS) was used to understand the sorption and desorption of organic contaminants in the polymer Poly(ethylene terephthalate), or PET. Samples were exposed to a range of organics to simulate contamination of PET that can take place in the post-consumer waste stream. From RBS analysis, concentration depth profiles were shown to vary from a monolayer regime surface layer to a saturation level, depending on the contaminant. Heat treatments were also applied to contaminated polymer to simulate thermal processing steps in the recycling of PET. Heating caused a dramatic decrease in contaminants and in some cases a complete removal of contamination was achieved to the limit of RBS detectability.

Pierce, D. E.; Pfeffer, R. L.; Sadler, G. D.

1997-05-01

207

A method for removing arm backscatter from EPID images  

SciTech Connect

Purpose: To develop a method for removing the support arm backscatter from images acquired using current Varian electronic portal imaging devices (EPIDs).Methods: The effect of arm backscatter on EPID images was modeled using a kernel convolution method. The parameters of the model were optimized by comparing on-arm images to off-arm images. The model was used to develop a method to remove the effect of backscatter from measured EPID images. The performance of the backscatter removal method was tested by comparing backscatter corrected on-arm images to measured off-arm images for 17 rectangular fields of different sizes and locations on the imager. The method was also tested using on- and off-arm images from 42 intensity modulated radiotherapy (IMRT) fields.Results: Images generated by the backscatter removal method gave consistently better agreement with off-arm images than images without backscatter correction. For the 17 rectangular fields studied, the root mean square difference of in-plane profiles compared to off-arm profiles was reduced from 1.19% (standard deviation 0.59%) on average without backscatter removal to 0.38% (standard deviation 0.18%) when using the backscatter removal method. When comparing to the off-arm images from the 42 IMRT fields, the mean {gamma} and percentage of pixels with {gamma} < 1 were improved by the backscatter removal method in all but one of the images studied. The mean {gamma} value (1%, 1 mm) for the IMRT fields studied was reduced from 0.80 to 0.57 by using the backscatter removal method, while the mean {gamma} pass rate was increased from 72.2% to 84.6%.Conclusions: A backscatter removal method has been developed to estimate the image acquired by the EPID without any arm backscatter from an image acquired in the presence of arm backscatter. The method has been shown to produce consistently reliable results for a wide range of field sizes and jaw configurations.

King, Brian W. [School of Mathematical and Physics Sciences, University of Newcastle, Newcastle, New South Wales 2308 (Australia); Greer, Peter B. [Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, New South Wales 2310 (Australia); School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, New South Wales 2308 (Australia)

2013-07-15

208

Case study of multiple-wavelength lidar backscatter from aerosols  

NASA Astrophysics Data System (ADS)

Range-resolved co-pointing multiple wavelength lidar backscatter from aerosols is analyzed for a summer day in the northeast United States. Lidar backscatter wavelengths are 355 nm, 532 nm, and 1064 nm and were measured at a vertical range gate of 60 meters. The altitude range of lidar measurement is from the surface to 4 km above ground level and the measurement period spanned five hours from late afternoon through several hours after sunset. Vertical profiles of temperature, relative humidity, and wind velocity, and surface visibility, were also measured to characterize the prevailing air mass. Lidar aerosol backscatter was significant through 3 km and diminished rapidly above. Several aerosol models selected on an a priori basis are used to compute backscatter ratios for wavelength pairs using scattering theory. These are compared with the profiles of measured backscatter ratios in an attempt to infer the type of aerosol present in the lower atmosphere and estimate multiple wavelength extinction. Measured backscatter ratios agreed with the ratios for soot, water-soluble, and haze aerosol models at the lowest altitudes with little agreement above 1 km for any model. Extinction estimates derived from lidar backscatter at 300 m were significantly higher than the corresponding values deduced from surface observations.

Roadcap, John R.; Dao, Phan D.; McNicholl, Patrick J.

2003-09-01

209

Microcontamination detection using Heavy Ion Backscattering Spectrometry  

SciTech Connect

Heavy Ion Backscattering Spectrometry (HIBS) is a new ion beam analysis tool using heavy, low-energy ions in backscattering mode which can detect very low levels of surface contamination. By taking advantage of the greatly increased scattering cross-section for such ion beams and eliminating unwanted substrate scattering with a thin carbon foil, our research system has achieved a sensitivity ranging from {approximately}5{times}10{sup 10} atoms/cm{sup 2} for Fe to {approximately}1{times}10{sup 9} atoms/cm{sup 2} for Au on Si, without preconcentration. A stand-alone HIBS prototype now under construction in collaboration with SEMATECH is expected to achieve detection limits of {approximately}5{times}10{sup 9} atoms/cm{sup 2} for Fe and {approximately}1{times}10{sup 8} atoms/cm{sup 2} for Au on Si, again without preconcentration. Since HIBS is standardless and has no matrix effects, it will be useful not only as a standalone tool, but also for benchmarking standards for other tools. This conference is testimony to the importance of controlling contamination in microelectronics manufacturing. By the turn of the century, very large scale integrated circuit processing is expected to require contamination levels well below 1{times}10{sup 9} atoms/cm{sup 2} in both starting materials and introduced by processing. One of the most sensitive of existing general-purpose tools is Total reflection X-Ray Fluorescence (TXRF), which can detect {approximately}1{times}10{sup 10} atoms/cm{sup 2} levels of some elements such as Fe and Cu, but for many elements it is limited to 1{times}10{sup 12} atoms/cm{sup 2} or worse. TXRF can achieve a sensitivity of 10{sup 8} atoms/cm{sup 2} through the use of synchrotron radiation or via pre-concentration using Vapor Phase Decomposition. HIBS provides an ion beam analysis capability with the potential for providing similar sensitivity at medium Z and higher sensitivity at larger Z, all without pre-concentration or matrix effects.

Knapp, J.A.; Banks, J.C. [Sandia National Labs., Albuquerque, NM (United States); Diebold, A.C. [SEMATECH, Austin, TX (United States)

1994-07-01

210

CO2 lidar backscatter profiles over Hawaii during fall 1988  

NASA Technical Reports Server (NTRS)

Aerosol and cloud backscatter data, obtained over a 24-day period in fall 1988 with the National Oceanic and Atmospheric Administration's Doppler lidar at 10.59-micron wavelength, are analyzed by using a new technique to lessen biases that are due to dropouts. Typical backscatter cross sections were significantly lower than those routinely observed over the continental United States, although episodic backscatter enhancements caused by cirrus and mineral dust also occurred. Implications of these data on the proposed Laser Atmospheric Wind Sounder wind profiling satellite sensor are discussed.

Post, Madison J.; Cupp, Richard E.

1992-01-01

211

Geophysical Diffraction Tomography  

Microsoft Academic Search

Diffraction tomography is the generalization of X-ray tomography to applications such as seismic exploration where diffraction effects must be taken into account. In this paper, the foundations of diffraction tomography for offset vertical seismic profiling and well-to-well tomography are presented for weakly inhomogeneous formations for which the Born or Rytov approximations can be employed. Reconstruction algorithms are derived for approximately

A. J. Devaney

1984-01-01

212

Asymptotic high frequency analysis of the electromagnetic backscattering from an inlet model consisting of piecewise linearly tapered sections  

NASA Technical Reports Server (NTRS)

Electromagnetic backscattering from an open ended three dimensional inlet model is analyzed and computed patterns are compared with results of experimental measurements. The model is comprised of two sections. The first section consists of a linearly tapered waveguide with a rectangular opening at one end and the other end is connected to the second section which is a uniform rectangular waveguide with a planar perfectly conducting termination. The model is electrically large so that many propagating modes are excited. The method of analysis contains conventional aperture integration and modal techniques combined with high frequency techniques, which employ concepts such as modal rays, geometrical theory of diffraction and equivalent currents. For the cases considered, it is shown that only a few of the many propagating modes contribute appreciably to the backscattered field. These modes are selected according to their modal ray angle directions.

Altintas, A.; Pathak, P. H.

1985-01-01

213

Statistical simulation of multiple Compton backscattering process  

NASA Astrophysics Data System (ADS)

A number of laboratories are currently developing monochromatic sources of X-rays and gamma quanta based on the Compton backscattering (CBS) of laser photons by relativistic electrons. Modern technologies are capable of providing a concentration of electrons and photons in the interaction point such that each primary electron can emit several hard photons. In contrast to the well-known nonlinear CBS process, in which an initial electron "absorbs" a few laser photons and emits a single hard one, the above-mentioned process can be called a multiple CBS process and is characterized by a mean number of emitted photons. The present paper is devoted to simulating the parameters of a beam of back scattered quanta based on the Monte Carlo technique. It is shown that, even in the case of strong collimation of a resulting photon beam, the radiation monochromaticity may deteriorate because of the contribution coming from the multiple photon emission, which is something that must be considered while designing new CBS sources.

Potylitsyn, A. P.; Kolchuzhkin, A. M.

2014-09-01

214

Radar backscatter from the sea controlled experiments  

NASA Astrophysics Data System (ADS)

This is the final report on ONR Grant N00014-89-J-3022. Since most of the work was in journal articles, conference proceedings, and reports, this report is brief. Work continued, and was largely concluded, on analysis of the TOWARD, SAXON-CLT, and NILDEX data sets. Comparison between optical and radio measurements of ripple spectra at TOWARD showed favorable results. Although the wind direction was usually unfavorable for SAXON-CLT, useful data was obtained on modulation in the crosswind direction. It was also demonstated that a vector slope gauge can work, but for logistic reasons its deployment made its footprint close to the tower. Hence, the data are useful only for proof of concept, not for oceanographic application. A new theory of SAR imaging of the ocean was developed. It incorporates elements of previous theories, but shows an improved way to find out the effects of signal modulations on the observed spectra. It confirms, by a different method, the results from several other theoretical and experimental studies on processor focus adjustment. These show optimum image contrast occurs for along-track wave motion when the processor is set to (phase velocity)/2. The method of analysis used allowed closer examination of the basis for the two-scale (Bragg resonance with slope modulation) model for ocean backscatter. The results cast some doubt on the validity of the Bragg-scatter model for explaining many observed phenomena.

Moore, Richard K.

1990-11-01

215

Estimating slash pine biomass using radar backscatter  

NASA Technical Reports Server (NTRS)

L-band HV multiple-incidence-angle aircraft synthetic aperture radar (SAR) data were analyzed in relation to average stand biomass, basal area, and tree height for 55 slash pine plantations located in northern Florida. This information was used to develop a system of equations to predict average stand biomass as a function of L-band (24.5-cm) radar backscatter. The system of equations developed in this study using three-stage least-squares and combinatorial screening accounted for 97 percent of the variability observed in average stand biomass per hectare. When applied to an independent data set, the biomass equations had an average bias of less than 1 percent with a standard error of approximately 3 percent. These results indicate that future Shuttle Imaging Radar Systems (e.g., SIR-C, which will have cross-polarized radar sensors) should be able to obtain better estimates of forest biomass than were obtained with previous satellite radar missions, which utilized only HH-polarized SAR data.

Hussin, Yousif Ali; Reich, Robin M.; Hoffer, Roger M.

1991-01-01

216

Electron back scattered diffraction characterization of Sm(CoFeCuZr)z magnets  

NASA Astrophysics Data System (ADS)

In permanent magnets based on the Sm2Co17 phase, the high coercivity depends on the presence of a complex microstructure, consisting of a Sm2(Co,Fe)17 cell phase, a cell boundary phase Sm(Co,Cu)5, and a Zr-rich platelet or lamellae phase. The aim of this work is to use electron back scatter diffraction (EBSD) in order to identify the different phases present in the isotropic magnets produced from cast alloys with the composition of Sm(CobalFe0.2Cu0.1Zrx)8, where x = 0, 0.02, or 0.06, and correlate them with the different phases observed in scanning electron microscopy (SEM) images. Due to the combination of careful surface preparation and high resolution microscopy, it was possible to observe the cellular structure characteristic of the 2:17 magnets in the SEM images. Until now, only transmission electron microscopy (TEM) had been used. Composition maps, energy dispersive spectroscopy (EDS), and EBSD measurements were used for doing the phase identification.

Yonamine, T.; Fukuhara, M.; Archanjo, B. S.; Missell, F. P.

2011-04-01

217

Polarimetric backscatter measurements of natural surfaces at millimeter wavelengths  

NASA Astrophysics Data System (ADS)

During the last four years, the Microwave Remote Sensing Laboratory of the University of Massachusetts has studied the polarimetric backscatter response of natural and man-made surfaces at 35, 95, and 225 GHz. These surfaces include grass, asphalt, snowcover, and trees. In addition, ground-based and airborne backscatter measurements of clouds and precipitation were made at 95 GHz. The results of these experiments are summarized by presenting histograms of normalized radar cross section for trees, snowcover, and clouds. The temporal dependence of the normalized radar cross section for snowcover is also presented for 95 and 225 GHz which shows a strong diurnal variation due to melting and refreezing. Also presented is the angular dependence of backscatter from grass and asphalt at 35, 95, and 225 GHz, as well as volume backscattering coefficients for airborne measurements of clouds and precipitation at 96 GHz.

Mead, James; Chang, Paul; McIntosh, Robert

1993-11-01

218

Simulation of coherent backscattering of light in nematic liquid crystals  

SciTech Connect

Multiple scattering of light by the fluctuations of the director in a nematic liquid crystal (NLC) aligned by a magnetic field is considered. A peak of coherent backscattering is calculated by numerical simulation. Since the indicatrix of single scattering for a liquid crystal (LC) is known exactly, the calculations are carried out without any simplifying assumptions on the parameters of the liquid crystal. Multiple scattering is simulated as a random walk of photons in the medium. A peak of coherent backscattering in such a medium is very narrow; therefore, the so-called semianalytical method is applied. The parameters of the backscattering peak obtained by numerical simulation are compared with the available experimental data and with the results of analytical approximations. It turns out that the experimental data are in good agreement with the results of simulation. The results of numerical simulation adequately describe the anisotropy and the width of the backscattering peak.

Aksenova, E. V., E-mail: aksev@mail.ru; Kokorin, D. I., E-mail: dmitry@kokorin.org; Romanov, V. P., E-mail: vpromanov@mail.ru [St. Petersburg State University (Russian Federation)

2012-08-15

219

Fractal property of backscattered acoustic signals from polycrystalline aluminium  

NASA Astrophysics Data System (ADS)

Backscattered acoustic signals from annealed polycrystalline aluminium are observed to possess fractal characteristics. Assuming this to be true a grain size distribution is deduced which is seen to match the distribution obtained experimentally in polycrystalline materials.

Barat, P.; De, Subhranil; Bandyopadhyay, S. K.

1998-08-01

220

BASIS: A New Backscattering Spectrometer at the SNS  

SciTech Connect

A new spectrometer named BASIS has recently entered the general user program at the Spallation Neutron Source. BASIS is an acronym for Backscattering Silicon Spectrometer. While there are several operational reactor-based spectrometers that utilize backscattering reflection from silicon single crystals, such as IN10 and IN16 [1] at the ILL, France; HFBS [2] at the NCNR, USA; and SPHERES [3] at the FRM-II, JCNS, Germany, BASIS is the first silicon backscattering spectrometer built on a spallation neutron source. Conceptually, it is similar to previously built time-of-flight backscattering spectrometers that utilize reflections from pyrolytic graphite or mica, such as IRIS [4] and OSIRIS [5] at the ISIS, UK; LAM-80 [6] at the KENS, Japan; or MARS [7] at the SINQ, Switzerland.

Mamontov, Eugene [ORNL; Zamponi, Michaela M [ORNL; Hammons, Stephanie E [ORNL; Keener, Wylie S [ORNL; Hagen, Mark E [ORNL; Herwig, Kenneth W [ORNL

2008-01-01

221

Interaction-induced backscattering in short quantum wires  

NASA Astrophysics Data System (ADS)

We study interaction-induced backscattering in clean quantum wires with adiabatic contacts exposed to a voltage bias. Particle backscattering relaxes such systems to a fully equilibrated steady state only on length scales exponentially large in the ratio of bandwidth of excitations and temperature. Here we focus on shorter wires in which full equilibration is not accomplished. Signatures of relaxation then are due to backscattering of hole excitations close to the band bottom which perform a diffusive motion in momentum space while scattering from excitations at the Fermi level. This is reminiscent to the first passage problem of a Brownian particle and, regardless of the interaction strength, can be described by an inhomogeneous Fokker-Planck equation. From general solutions of the latter we calculate the hole backscattering rate for different wire lengths and discuss the resulting length dependence of interaction-induced correction to the conductance of a clean single channel quantum wire.

Rieder, M.-T.; Micklitz, T.; Levchenko, A.; Matveev, K. A.

2014-10-01

222

Ultrasonic Backscattering from Suspended Erythrocytes: Dependence on Frequency and Size.  

NASA Astrophysics Data System (ADS)

The ultrasonic scattering properties of blood have been intensively investigated since the echo signal from red blood cells carries abundant diagnostic information for the study of blood flow and blood properties in the vessels. Recently, ultrasound of frequency higher than 20 MHz has been implemented in intravascular imaging to obtain better images of the vessel wall. In this research measurements were extended to 30 MHz to better understand the effect of blood on the operation of these intravascular devices. The experimentally measured backscatter of saline suspended porcine erythrocytes for frequency up to 30 MHz agrees very well with the theoretical analysis which indicate that Rayleigh scattering is still valid below this frequency. The analysis utilize the T-matrix method to calculate the backscattering cross section of an erythrocyte modeled as a fluid sphere, disk, and biconcave disk. Measurements on the backscattering coefficients of porcine, bovine, and lamb erythrocytes reveal that the backscatter has a square dependence on cell volume. The cell size dependent backscatter is also analyzed via a continuum approach. It is found that the echo intensity of high frequency ultrasound suffers greatly from the attenuation. The dilemma may be solved by using a spherically focused transducer. An analysis of the focused beam reflected from a perfect planar reflector leads to the modification of the standard substitution method for the backscatter measurement since the "image source" theory is found to be inappropriate for the focused beam. Reflection of the focused beam near the focal point is described based on Huygens' principle. Experimental and theoretical results indicate that the backscatter is dependent upon the position of the scatterer and the geometry of the transducer if a focused beam is used. Since ultrasound velocity information is needed for scattering measurements, an innovative method for measuring the acoustic speed and the attenuation coefficient without the knowledge of the thickness of a biological specimen is developed which may provide more accurate results for the measurement of backscattering coefficient.

Kuo, Ihyuan

223

Single Slit Diffraction  

NSDL National Science Digital Library

This web page includes a java illustration of single slit diffraction of light. The user can adjust the wavelength of the light and the size of the slit and observe the resultant changes in the diffraction pattern. Quantitative values for the wavelength and slit-width are given.

Kiselev, Sergey

2007-11-03

224

Diffraction by nanocrystals.  

PubMed

X-ray femtosecond nanocrystallography is a new, potentially powerful technique for imaging biological macromolecules that uses ensemble-averaged measurements of diffraction of x-ray free-electron laser pulses from nanocrytalline specimens. Nanocrystals have some diffraction characteristics that are distinct from those of macroscopic crystals, due to the presence of different kinds of unit cell in the crystal and of truncated unit cells on the crystal surface. Expressions are derived for diffraction by nanocrystals with variable and incomplete unit cells, averaged over a distribution of crystal sizes and shapes. The diffraction contains differently modulated Bragg components that are due to interference effects within and between the full and incomplete unit cells. Estimates are obtained for the relative magnitudes of the components. The nature of the diffraction is illustrated by two-dimensional simulations. Implications for molecular imaging are discussed. PMID:24323025

Chen, Joe P J; Millane, Rick P

2013-12-01

225

Single-Slit Diffraction  

NSDL National Science Digital Library

The Single-Slit Diffraction model simulates the diffraction pattern of light as it travels through a slit to a screen. The diffraction pattern is due to the difference in path length of the light from different parts of the slit as the light from the slit travels to the screen. The intensity of the light that reaches the screen is related to the wavelength of light, the slit width, and the angle away from the center of the screen. In the simulation one can change the wavelength, the slit separation, and whether the pattern is shown on a screen or on a photographic plate. Single-Slit Diffraction model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_diffraction.jar file will run the program if Java is installed.

Palop, Jose I.

2010-12-12

226

TCR backscattering characterization for microwave remote sensing  

NASA Astrophysics Data System (ADS)

A Trihedral Corner Reflector (TCR) is formed by three mutually orthogonal metal plates of various shapes and is a very important scattering structure since it exhibits a high monostatic Radar Cross Section (RCS) over a wide angular range. Moreover it is a handy passive device with low manufacturing costs and robust geometric construction, the maintenance of its efficiency is not difficult and expensive, and it can be used in all weather conditions (i.e., fog, rain, smoke, and dusty environment). These characteristics make it suitable as reference target and radar enhancement device for satellite- and ground-based microwave remote sensing techniques. For instance, TCRs have been recently employed to improve the signal-to-noise ratio of the backscattered signal in the case of urban ground deformation monitoring [1] and dynamic survey of civil infrastructures without natural corners as the Musmeci bridge in Basilicata, Italy [2]. The region of interest for the calculation of TCR's monostatic RCS is here confined to the first quadrant containing the boresight direction. The backscattering term is presented in closed form by evaluating the far-field scattering integral involving the contributions related to the direct illumination and the internal bouncing mechanisms. The Geometrical Optics (GO) laws allow one to determine the field incident on each TCR plate and the patch (integration domain) illuminated by it, thus enabling the use of a Physical Optics (PO) approximation for the corresponding surface current densities to consider for integration on each patch. Accordingly, five contributions are associated to each TCR plate: one contribution is due to the direct illumination of the whole internal surface; two contributions originate by the impinging rays that are simply reflected by the other two internal surfaces; and two contributions are related to the impinging rays that undergo two internal reflections. It is useful to note that the six contributions due to the doubly reflected rays define the leading term in the angular region around the boresight direction. The validity of the approach is well assessed by comparisons with experimental results, and its formulation is computer time inexpensive since in closed form. Moreover it is preferable to the model using near-field PO integrations for describing the interactions between the internal TCR's faces since this last requires the evaluation of multi-dimensional integrals, i.e., the expression of the final incident field contains a two-dimensional integral for each previous interaction. [1] Y. Qin, D. Perissin, and L. Lei, "The Design and Experiments on Corner Reflectors for Urban Ground Deformation Monitoring in Hong Kong," Int. J. Antennas Propagat., vol. 2013, pp. 1-8. [2] T. A. Stabile, A. Perrone, M. R. Gallipoli, R. Ditommaso, and F. C. Ponzo, "Dynamic Survey of the Musmeci Bridge by Joint Application of Ground-Based Microwave Radar Interferometry and Ambient Noise Standard Spectral Ratio Techniques," IEEE Geosci. Remote Sens. Lett., vol. 10, no. 4, pp. 870-874, 2013.

Riccio, Giovanni; Gennarelli, Claudio

2014-05-01

227

Bomb Detection Using Backscattered X-Rays  

SciTech Connect

Bomb Detection Using Backscattered X-rays* Currently the most common method to determine the contents of a package suspected of containing an explosive device is to use transmission radiography. This technique requires that an x-ray source and film be placed on opposite sides of the package. This poses a problem if the pachge is placed so that only one side is accessible, such as against a wall. There is also a threat to persomel and property since exTlosive devices may be "booby trapped." We have developed a method to x-ray a paclage using backscattered x-rays. This procedure eliminates the use of film behind the target. All of the detection is done from the same side as the source. When an object is subjected to x-rays, some of them iare scattered back towards the source. The backscattenng of x-rays is propordoml to the atomic number (Z) of the material raised to the 4.1 power. This 24"' dependence allows us to easily distinguish between explosives, wires, timer, batteries, and other bomb components. Using transmission radiography-to image the contents of an unknown package poses some undesirable risks. The object must have an x-ray film placed on the side opposite the x-ray source; this cannot be done without moving the package if it has been placed firmly against a wall or pillar. Therefore it would be extremely usefid to be able to image the contents of a package from only one side, without ever having to disturb the package itself. where E is the energy of the incoming x-ray. The volume of x-rays absorbed is important because it is, of course, directly correlated to the intensity of x-mys that will be scattered. Most of the x-rays that scatter will do so in a genemlly forward direction; however, a small percentage do scatter in a backward direction. Figure 1 shows a diagram of the various fates of x-rays directed into an object. The package that was examined in this ex~enment was an attache case made of pressed fiberboardwith a vinyl covering. It was approxirmtely 36 cm wide by 51 cm long by 13 cm deep. The case was placed on an aluminum sheet under the x-ray source. Because of the laborato~ setup, the attache case was rastered in the y-coordinate direction, while the x-ray source mstered in the x-coordinate direction. However, for field use, the x-ray source would of course raster in both the x- and y-coordinate directions, while the object under interrogation would remain stationary and undisturbed. A mobile system for use by law enforcement agencies or bomb disposal squads needs to be portable and somewhat durable. A 300 kV x-ray source should be sufficient for the task requirements and can be mounted on a mobile system. A robotic carriage could be used to transport the x-ray source and the CCD camera to the proximity of the suspect package. The controlling and data analyzing elements of the system' could then be maintained at a &tie distance from the possible explosive. F@re 8 shows a diagram of a conceptual design of a possible system for this type of use. The use of backscattered x-rays for interrogation of packages that may contain explosive devices has been shown to be feasible inthelaboratory. Usinga 150kVx-ray source anddetectors consisting of plastic scintillating material, all bomb components including the wiring were detectable. However, at this time the process requires more time than is desirable for the situations in which it will most likely be needed. Further development of the technology using CCD cameras, rather than the plastic stint illator detectors, shows promise of leading to a much faster system, as well as one with better resolution. Mounting the x- ray source and the CCD camera on a robotic vehicle while keeping the controlling and analyzing components and the opemting personnel a safe distance away from the suspect package will allow such a package to be examined at low risk to human life.

Jacobs, J.; Lockwood, G.; Selph, M; Shope, S.; Wehlburg, J.

1998-10-01

228

Exploring potential mechanisms responsible for observed changes of ultrasonic backscattered energy with temperature variations  

E-print Network

.1118/1.4870964] Key words: change in backscatter energy, ultrasonic thermometry 1. INTRODUCTION HyperthermiaExploring potential mechanisms responsible for observed changes of ultrasonic backscattered energy on probability variation of backscatter data Med. Phys. 39, 2369 (2012); 10.1118/1.3700235 Ultrasonic backscatter

Illinois at Urbana-Champaign, University of

229

ADCP backscatter measurements in the northeastern Gulf of Mexico: comparison of near-surface with near-bottom biological backscatter  

E-print Network

In the Gulf of Mexico, acoustic backscatter intensity (ABI) from an acoustic Doppler current profiler (ADCP) can be a proxy for zooplankton and micronekton biomass, and sperm whale abundance is correlated with regions of locally high ABI...

Sindlinger, Laurie R

2012-06-07

230

Combined raman elastic-backscatter LIDAR for vertical profiling of moisture, aerosol extinction, backscatter, and LIDAR ratio  

Microsoft Academic Search

A combined Raman elastic-backscatter lidar has been developed. A XeCl excimer laser is used as the radiation source. Inelastic Raman backscatter signals are spectrally separated from the elastic signal with a filter or grating polychromator. Raman channels can be chosen to register signals from CO2, O2, N2, and H2O. Algorithms for the calculation of the water-vapor mixing ratio from the

A. Ansmann; M. Riebesell; U. Wandinger; C. Weitkamp; E. Voss; W. Lahmann; W. Michaelis

1992-01-01

231

Radial reflection diffraction tomography  

DOEpatents

A wave-based tomographic imaging method and apparatus based upon one or more rotating radially outward oriented transmitting and receiving elements have been developed for non-destructive evaluation. At successive angular locations at a fixed radius, a predetermined transmitting element can launch a primary field and one or more predetermined receiving elements can collect the backscattered field in a "pitch/catch" operation. A Hilbert space inverse wave (HSIW) algorithm can construct images of the received scattered energy waves using operating modes chosen for a particular application. Applications include, improved intravascular imaging, bore hole tomography, and non-destructive evaluation (NDE) of parts having existing access holes.

Lehman, Sean K.

2012-12-18

232

Radial Reflection diffraction tomorgraphy  

DOEpatents

A wave-based tomographic imaging method and apparatus based upon one or more rotating radially outward oriented transmitting and receiving elements have been developed for non-destructive evaluation. At successive angular locations at a fixed radius, a predetermined transmitting element can launch a primary field and one or more predetermined receiving elements can collect the backscattered field in a "pitch/catch" operation. A Hilbert space inverse wave (HSIW) algorithm can construct images of the received scattered energy waves using operating modes chosen for a particular application. Applications include, improved intravascular imaging, bore hole tomography, and non-destructive evaluation (NDE) of parts having existing access holes.

Lehman, Sean K

2013-11-19

233

Multilayer dielectric diffraction gratings  

DOEpatents

The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.

Perry, Michael D. (Livermore, CA); Britten, Jerald A. (Oakley, CA); Nguyen, Hoang T. (Livermore, CA); Boyd, Robert (Livermore, CA); Shore, Bruce W. (Livermore, CA)

1999-01-01

234

Lead foil in dental X-ray film: Backscattering rejection or image intensifier?  

NASA Astrophysics Data System (ADS)

Dental X-ray films are still largely used due to sterilization issues, simplicity and, mainly, economic reasons. These films almost always are double coated (double emulsion) and have a lead foil in contact with the film for X-ray backscattering rejection. Herein we explore the use of the lead foil as an image intensifier. In these studies, spatial resolution was investigated when images were acquired on the dental X-ray films with and without the lead foil. Also, the lead foil was subjected to atomic analysis (fluorescent measurements) and structure analysis (X-ray diffraction). We determined that the use of the lead foil reduces the exposure time, however, does not affect the spatial resolution on the acquired images. This suggests that the fluorescent radiation spread is smaller than the grain sizes of the dental X-ray films.

Hönnicke, M. G.; Delben, G. J.; Godoi, W. C.; Swinka-Filho, V.

2014-11-01

235

X-Ray Diffraction  

NSDL National Science Digital Library

This site from the University of London presents a tutorial on several methods of X-ray diffraction, including the powder, rotating crystal, and Laue methods Each section includes interactive Java applets, exercises, and links to a glossary of terms.

Matter.org

236

Hard diffraction at CDF  

SciTech Connect

We present new evidence for events with a rapidity gap between jets in {bar p}-p collisions at {radical}s = 1.8 TeV based on data collected by triggering the Collider Detector at Fermilab on two high transverse momentum forward jets and results of a search for diffractive W{+-} and dijet production where diffraction is tagged by the rapidity gap technique. We also present the results of a search for diffractive dijets using data collected by triggering on a very forward particle in the recently installed roman-pot detectors. The dijet events exhibit additional diffractive characteristics such as rapidity gaps and boosted center of mass system, however the recoil antiproton measured in the roman-pots is in a regime in which the non- pomeron contribution is significant.

Melese, P.L. [Rockefeller Univ., New York, NY (United States); CDF Collaboration

1996-07-01

237

Diffraction with CMS  

SciTech Connect

The observation of diffraction at LHC with the CMS detector at {radical}(s) = 900 and 2360 GeV is presented, along with a comparison of the data with the predictions of the PYTHIA and PHOJET generators.

Pereira, Antonio Vilela [Universita degli Studi di Torino and INFN Torino, Via Pietro Giuria 1, 10125 Torino (Italy); CERN, CH-1211 Geneve 23, Switzerland - Mailbox: E25900 (Switzerland)

2011-07-15

238

Double Slit Diffraction  

NSDL National Science Digital Library

This resource illustrates the interference patterns for diffraction through double slits. A series of sources, electrons, protons, neutrons, photons, and pions, can be chosen for the virtual experiment. The energy of the source, the slit separation, and the flux rate can all be adjusted. The diffraction patterns are built from random flashes on a screen. The screens can be saved for comparison of different experiments.

Zollman, Dean

2010-08-06

239

Reflective diffraction grating  

DOEpatents

Reflective diffraction grating. A focused ion beam (FIB) micromilling apparatus is used to store color images in a durable medium by milling away portions of the surface of the medium to produce a reflective diffraction grating with blazed pits. The images are retrieved by exposing the surface of the grating to polychromatic light from a particular incident bearing and observing the light reflected by the surface from specified reception bearing.

Lamartine, Bruce C. (Los Alamos, NM)

2003-06-24

240

Light coupling and enhanced backscattering in layered plasmonic nanocomposites.  

PubMed

Peculiar enhanced backscattering of light as well as selective vapor sensing were recently observed in a layered plasmonic nanocomposite which consisted of gold nanospheres randomly distributed in a sol-gel glass thin film on top of a soda-lime glass substrate, including a buried leaky waveguide. In order to understand the underlying physical mechanisms, we performed three-dimensional transfer-matrix numerical simulations and calculated the reflectance in both backward and specular directions as functions of the incidence angle. First, assuming a layered periodic particle arrangement, we confirmed that backscattering took place at grazing incidence if the spatial period in the layers was chosen within an optimal range, in agreement with theoretical predictions. Then, using a pseudo-random particle arrangement to describe the actual nanocomposite, we revealed that strong backscattering could nevertheless persist for specific particle distributions, in spite of their randomness. This behavior was tentatively explained by putting backscattering in relation with the particle interdistance statistics. Finally, we showed that backscattered reflectance was much more sensitive than specular reflectance to the adsorption of water vapor either on the surface or inside the likely porous structure of the glass host. PMID:21263674

Deparis, Olivier; Beresna, Martynas; Vandenbem, Cédric; Kazansky, Peter G

2011-01-17

241

Modeling multi-frequency diurnal backscatter from a walnut orchard  

NASA Technical Reports Server (NTRS)

The Michigan Microwave Canopy Scattering Model (MIMICS) is used to model scatterometer data that were obtained during the August 1987 EOS (Earth Observing System) synergism study. During this experiment, truck-based scatterometers were used to measure radar backscatter from a walnut orchard in Fresno County, California. Multipolarized L- and X-band data were recorded for orchard plots for which dielectric and evapotranspiration characteristics were monitored. MIMICS is used to model a multiangle data set in which a single orchard plot was observed at varying impedance angles and a series of diurnal measurements in which backscatter from this same plot was measured continuously over several 24-h periods. MIMICS accounts for variations in canopy backscatter driven by changes in canopy state that occur diurnally as well as on longer time scales. L-band backscatter is dependent not only on properties of the vegetation but also on properties of the underlying soil surface. The behavior of the X-band backscatter is dominated by properties of the tree crowns.

Mcdonald, Kyle C.; Dobson, Myron C.; Ulaby, Fawwaz T.

1991-01-01

242

Probabilities and statistics for backscatter estimates obtained by a scatterometer  

NASA Technical Reports Server (NTRS)

Methods for the recovery of winds near the surface of the ocean from measurements of the normalized radar backscattering cross section must recognize and make use of the statistics (i.e., the sampling variability) of the backscatter measurements. Radar backscatter values from a scatterometer are random variables with expected values given by a model. A model relates backscatter to properties of the waves on the ocean, which are in turn generated by the winds in the atmospheric marine boundary layer. The effective wind speed and direction at a known height for a neutrally stratified atmosphere are the values to be recovered from the model. The probability density function for the backscatter values is a normal probability distribution with the notable feature that the variance is a known function of the expected value. The sources of signal variability, the effects of this variability on the wind speed estimation, and criteria for the acceptance or rejection of models are discussed. A modified maximum likelihood method for estimating wind vectors is described. Ways to make corrections for the kinds of errors found for the Seasat SASS model function are described, and applications to a new scatterometer are given.

Pierson, Willard J., Jr.

1989-01-01

243

Experimental results on the enhanced backscatter phenomenon and its dynamics  

NASA Astrophysics Data System (ADS)

Enhanced backscatter effects have long been predicted theoretically and experimentally demonstrated. The reciprocity of a turbulent channel generates a group of paired rays with identical trajectory and phase information that leads to a region in phase space with double intensity and scintillation index. Though simulation work based on phase screen models has demonstrated the existence of the phenomenon, few experimental results have been published describing its characteristics, and possible applications of the enhanced backscatter phenomenon are still unclear. With the development of commercially available high powered lasers and advanced cameras with high frame rates, we have successfully captured the enhanced backscatter effects from different reflection surfaces. In addition to static observations, we have also tilted and pre-distorted the transmitted beam at various frequencies to track the dynamic properties of the enhanced backscatter phenomenon to verify its possible application in guidance and beam and image correction through atmospheric turbulence. In this paper, experimental results will be described, and discussions on the principle and applications of the phenomenon will be included. Enhanced backscatter effects are best observed in certain levels of turbulence (Cn 2?10-13 m-2/3), and show significant potential for providing self-guidance in beam correction that doesn't introduce additional costs (unlike providing a beacon laser). Possible applications of this phenomenon include tracking fast moving object with lasers, long distance (>1km) alignment, and focusing a high-power corrected laser beam over long distances.

Wu, Chensheng; Nelson, William; Ko, Jonathan; Davis, Christopher C.

2014-10-01

244

Magnetic Force Microscopy and Electron Back Scatter Diffraction Study of Pseudo-Single-Domain Grains of Magnetite  

NASA Astrophysics Data System (ADS)

Magnetic domain structures in pseudo-single-domain (PSD) grains (5-20 ?m) of magnetite (Fe3O4) were studied using magnetic force microscopy (MFM) and correlated with grain shapes and with crystallographic orientations determined by electron back scatter diffraction (EBSD). The magnetite grains, produced by the glass-ceramic method, are randomly oriented and dispersed in a nonmagnetic silicate matrix. The studies were focused on grains with magnetization mainly parallel to the sample surface. Domain wall (DW) types and crystallographic orientation of wall planes were identified using MFM and EBSD data. For instance, for a triple wall junction where three wall types (180°, 71° and 109° DW) intersect, the wall orientations were identified as following: the 180° wall is parallel to (112) type plane, the 71° wall to (110) type plane and the 109° wall to (001). Most of the studied grains were subdivided into domains by 180° DWs, which cross the entire grain without formation of closure domain structures at grain edges. Domain structures remained qualitatively the same after repeated AF demagnetization cycles. Most of the observed 180° walls were parallel to (110) type planes, most likely because such planes contain two easy axes, which reduces wall energy density. Close to grain edges, 180° DWs often deviated from (110) orientations by twisting around a [111] axis parallel to the magnetization in adjacent domains. This allows optimization (minimization of total) of wall energy density, wall area and stray field (magnetic charge at grain edges) and indicates that stress is a subordinate factor in causing wall bending. Our wall bending analysis is consistent with published micromagnetic calculations. The combined MFM and EBSD study allows the conclusion that remanent 3-D domain structures in PSD grains result from combined magnetostatic effect of all grain surfaces (shape anisotropy of the grain) and magnetocrystalline anisotropy.

Pokhil, T.; Moskowitz, B. M.; Jackson, M. J.; Carter-Stiglitz, B. S.

2005-05-01

245

SEM/EDS/EBSD study of the behaviour of Ge, Mo and Al impurities in complex-doped crystals of higher manganese silicide  

NASA Astrophysics Data System (ADS)

The structure of Al, Ge, Mo doped higher manganese silicides (HMS) grown by the Bridgman technique has been studied by SEM/EDS/EBSD methods. It is shown that dopants are partially integrated into the HMS crystal lattice. Some inclusions with sizes of 0.1-100 ?m and different shapes (round, irregular, elongated) are formed. The precipitation of tetragonal MoSi2 and Si-Ge solid-solution has been observed. MoSi2 inclusions hundreds of microns in size form a multicomponent texture. The inclusions of Si-Ge solid solution have an irregular shape. The orientation relationship between these inclusions and matrix crystal is determined.

Orekhov, A. S.; Solomkin, F. Y.

2013-11-01

246

Backscattered deposition in Ar sputter etch of silicon dioxide  

NASA Astrophysics Data System (ADS)

Detailed mechanisms of sputter etch of silicon dioxide in argon plasma are studied using a novel test structure. We have found that a significant amount of the sputtered material (up to 50% of the sputter flux) returns, as an isotropic backscattered flux to the wafer. This backscattered flux results in significant deposition that cannot be accounted for by redeposition, i.e., line-of-sight deposition of the sputtered material, alone. A profile simulator is used to demonstrate a new physical model for the Ar sputter-etch process, based on the interaction of three simultaneous processes: (1) sputtering, (2) direct (i.e., line-of-sight) redeposition of sputtered material, and (3) isotropic deposition of sputtered material backscattered from the gas phase. Simulated profiles show good agreement with experimental results on the test structure and a common device structure.

Chang, C. Y.; McVittie, J. P.; Saraswat, K. C.; Lin, K. K.

1993-10-01

247

Backscatter signatures of biological aerosols in the infrared.  

PubMed

To develop a deeper understanding of the optical signatures of both biological aerosols and potential interferents, we made field measurements of optical cross sections and compared them to model-based predictions. We measured aerosol cross sections by conducting a hard-target calibration of a light detection and ranging system (LIDAR) based on the Frequency Agile Laser (FAL). The elastic backscatter cross sections are estimated at 19 long-wave infrared (LWIR) wavelengths spanning the range from 9.23 to 10.696 ?m. The theoretical modeling of the elastic backscatter cross sections is based on the measured refractive index and size distribution of the aerosols, which are used as inputs into Mie calculations. Both model calculations and experimental measurements show good agreement and also indicate the presence of spectral features based on single particle absorption in the backscatter cross sections that can be used as a basis for discrimination for both standoff and point sensors. PMID:22534887

Thrush, Evan; Salciccioli, Nicolas; Brown, David M; Siegrist, Karen; Brown, Andrea M; Thomas, Michael E; Boggs, Nathan; Carter, Christopher C

2012-04-20

248

Backscatter and attenuation properties of mammalian brain tissues  

NASA Astrophysics Data System (ADS)

Traumatic Brain Injury (TBI) is a common category of brain injuries, which contributes to a substantial number of deaths and permanent disability all over the world. Ultrasound technology plays a major role in tissue characterization due to its low cost and portability that could be used to bridge a wide gap in the TBI diagnostic process. This research addresses the ultrasonic properties of mammalian brain tissues focusing on backscatter and attenuation. Orientation dependence and spatial averaging of data were analyzed using the same method resulting from insertion of tissue sample between a transducer and a reference reflector. Apparent backscatter transfer function (ABTF) at 1 to 10 MHz, attenuation coefficient and backscatter coefficient (BSC) at 1 to 5 MHz frequency ranges were measured on ovine brain tissue samples. The resulting ABTF was a monotonically decreasing function of frequency and the attenuation coefficient and BSC generally were increasing functions of frequency, results consistent with other soft tissues such as liver, blood and heart.

Wijekularatne, Pushpani Vihara

249

Adaptive focus for deep tissue using diffuse backscatter  

NASA Astrophysics Data System (ADS)

A system integrating high density diffuse optical imaging with adaptive optics using MEMS for deep tissue interaction is presented. In this system, a laser source is scanned over a high density fiber bundle using Digital Micromirror Device (DMD) and channeled to a tissue phantom. Backscatter is then collected from the tissue phantom by a high density fiber array of different fiber type and channeled to CMOS sensor for image acquisition. Intensity focus is directly verified using a second CMOS sensor which measures intensity transmitted though the tissue phantom. A set of training patterns are displayed on the DMD and backscatter is numerically fit to the transmission intensity. After the training patterns are displayed, adaptive focus is performed using only the backscatter and fitting functions. Additionally, tissue reconstruction and prediction of interference focusing by photoacoustic and optical tomographic methods is discussed. Finally, potential NIR applications such as in-vivo adaptive neural photostimulation and cancer targeting are discussed.

Kress, Jeremy; Pourrezaei, Kambiz

2014-02-01

250

Multiple-Wave Diffraction in High Energy Resolution Back-Reflecting X-Ray Optics  

SciTech Connect

We have studied the effects of multiple-wave diffraction in a novel optical scheme recently published by Shvyd'ko et al. utilizing Bragg diffraction of x rays in backscattering geometry from asymmetrically cut crystals for achieving energy resolutions beyond the intrinsic width of the Bragg reflection. By numerical simulations based on dynamic x-ray diffraction and by experimentation involving two-dimensional angular scans of the back-reflecting crystal, multiple-wave diffraction was found to contribute up to several tens percent loss of efficiency but can be avoided without degrading the energy resolution of the original scheme by careful choice of azimuthal orientation of the diffracting crystal surface and by tilting of the crystal perpendicular to the dispersion plane.

Stetsko, Yuri P.; Keister, J. W.; Coburn, D. S.; Kodituwakku, C. N.; Cunsolo, A.; Cai, Y. Q. [National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973 (United States)

2011-10-07

251

Multipath analysis diffraction calculations  

NASA Technical Reports Server (NTRS)

This report describes extensions of the Kirchhoff diffraction equation to higher edge terms and discusses their suitability to model diffraction multipath effects of a small satellite structure. When receiving signals, at a satellite, from the Global Positioning System (GPS), reflected signals from the satellite structure result in multipath errors in the determination of the satellite position. Multipath error can be caused by diffraction of the reflected signals and a method of calculating this diffraction is required when using a facet model of the satellite. Several aspects of the Kirchhoff equation are discussed and numerical examples, in the near and far fields, are shown. The vector form of the extended Kirchhoff equation, by adding the Larmor-Tedone and Kottler edge terms, is given as a mathematical model in an appendix. The Kirchhoff equation was investigated as being easily implemented and of good accuracy in the basic form, especially in phase determination. The basic Kirchhoff can be extended for higher accuracy if desired. A brief discussion of the method of moments and the geometric theory of diffraction is included, but seems to offer no clear advantage in implementation over the Kirchhoff for facet models.

Statham, Richard B.

1996-01-01

252

A Parametric Study of Tillage Effects on Radar Backscatter  

NASA Technical Reports Server (NTRS)

Radar backscatter data for different field configurations and modulation function curves for angular and frequency variations are presented. A simplistic approach to modeling this effect is presented. It is concluded that: (1) row direction is a significant contributor to radar backscatter from cropland and must be considered when making radar measurements over bare or sparsely vegetated fields; (2) while the effect decrease with increasing frequency, it is still large (5 dB) at 13.3 GHz; (3) row effects are independent of linear polarization; (4) there is a strong aspect angle sensitivity which is a function of the scene and radar system parameters.

Fenner, R. G.; Pels, G. F.; Reid, S. C. (principal investigators)

1980-01-01

253

Newton's diffraction measurements  

NASA Astrophysics Data System (ADS)

This year marks the tercentenary of the publication of Newton's Opticks which contains his celebrated theory and experiments of light and colors as it evolved from the first published version in 1672. It is still fairly unknown, however, that in this book Newton also reported his experiments on diffraction fringes obtained from various "slender" objects placed in a beam of sunlight. These experiments posed an insurmountable difficulty to Newton's corpuscular theory of light, which failed to account for his observations. This failure explains the long delay in the publication of this book. In my talk I will compare Newton's experimental results on diffraction with the predictions of Fresnel's wave theory to demonstrate that his measurements were remarkable accurate. Eventually these measurements paved the way for Young's correct explanation of the diffraction fringes as a wave interference phenomenon.

Nauenberg, Michael

2004-05-01

254

Diffraction and holography of photoelectrons and fluorescent x-rays  

SciTech Connect

Photoelectron diffraction is by now a powerful technique for studying surface structures, with special capabilities for resolving chemical and magnetic states of atoms and deriving direct structural information from both forward scattering and backscattering. Fitting experiment to theory can lead to structural accuracies in the 0.03 {Angstrom} range. Holographic inversions of such diffraction data also show considerable promise for deriving local three-dimensional structures around a given emitter with accuracies of 0.2--0.3 {Angstrom}. Resolving the photoelectron spin in some way and using circularly polarized radiation for excitation provide added dimensions for the study of magnetic systems and chiral experimental geometries. Synchrotron radiation with the highest brightness and energy resolution, as well as variable polarization, is crucial to the full exploitation of these techniques. X-ray fluorescence holography also has promise for structural studies, but will require intense excitation sources and multichannel detection to be feasible.

Fadley, C.S. [Lawrence Berkeley Lab., CA (United States)]|[California Univ., Davis, CA (United States). Dept. of Physics

1993-04-01

255

Diffractive Interaction of Neutrinos  

NASA Astrophysics Data System (ADS)

Interactions of high-energy neutrinos expose hadronic properties, in particular, contain a strong diffractive channel. The Adler relation (AR) between soft interactions of neutrinos and pions, might look as a manifestation of pion dominance. However, neutrinos cannot fluctuate to pions because of conservation of the lepton current, and interact via much heavier hadronic components. This fact leads to nontrivial relations between interactions of different hadronic species, in particular, it links diagonal and off-diagonal diffractive interactions of pions. Absorptive corrections break these relations making the AR impossible to hold universally, for any target and at any energy.

Kopeliovich, B. Z.; Potashnikova, I. K.; Schmidt, Iván; Siddikov, M.

2013-06-01

256

Interference and Diffraction  

NSDL National Science Digital Library

In this video from the ICT Center, learn about interference and diffraction. See how the wave properties of light are used to explain interference patterns on a screen, and learn about related technologies such as the Fabry-Perot cavity, Bragg gratings, interference filters, and antireflection coatings. In addition, learn how diffraction patterns are produced, and study the grating equation.The video runs 4:12 and is accompanied by a background essay, standards alignment, and discussion questions. Users who sign up for a free account can save the resource and download the video as well.

2012-05-30

257

Biopolymer holographic diffraction gratings  

NASA Astrophysics Data System (ADS)

Surface-relief diffraction gratings are holographically recorded in dextran sensitized with ammonium dichromate (DCD). DCD was exposed with single-frequency 200 mW diode pumped ND-YAG laser, at 532 nm. The diffraction grating profiles were analyzed by atomic force microscopy (AFM). It was found that different surface profiles could be obtained. Gratings with 330 lines/mm spatial frequencies were made. Existence of higher harmonics in Fourier Transform of non-sinusoidal profiles shows that DCD is capable of recording spatial frequencies up to 1320 lines/mm (four times fundamental frequency). The measured maximum relief depth of the DCD grating is 402 nm.

Savi? Ševi?, Svetlana; Panteli?, Dejan

2008-03-01

258

Columnar to equiaxed transition of eutectic in hypoeutectic aluminium–silicon alloys  

Microsoft Academic Search

Directional solidification of unmodified and strontium modified binary, high-purity, aluminium–7 wt% silicon and commercial A356 alloys has been carried out to investigate the mechanism of eutectic solidification. The microstructure of the eutectic growth interface was investigated with optical microscopy and Electron Backscattering Diffraction (EBSD). In the commercial alloys, the eutectic solidification interface extends in the growth direction and creates a

G. Heiberg; K. Nogita; A. K. Dahle; L. Arnberg

2002-01-01

259

The {sigma} phase formation in annealed UNS S31803 duplex stainless steel: Texture aspects  

SciTech Connect

The influence of sigma phase precipitation on the texture of austenite in a duplex stainless steel UNS S31803 was investigated. Sigma phase quantification was precisely performed by electron backscattered scanning diffraction (EBSD) for some conditions. It was found that the increase of the sigma phase precipitation enhances the amount of Brass texture in the austenite phase.

Souza, C.M. [Universidade Federal do Rio de Janeiro, Departamento de Engenharia Metalurgica e de Materiais (Brazil)], E-mail: eng_marley@yahoo.com.br; Abreu, H.F.G. [Universidade Federal do Ceara, Departamento de Engenharia Metalurgica e de Materiais, Campus do Pici Bl. 702, Fortaleza, CE, CEP 60.455-760 (Brazil); Tavares, S.S.M. [Universidade Federal Fluminense, Departamento de Engenharia Mecanica (Brazil); Rebello, J.M.A. [Universidade Federal do Rio de Janeiro, Departamento de Engenharia Metalurgica e de Materiais (Brazil)

2008-09-15

260

Analysis of the mechanical properties and deformation behavior of nanostructured commercially pure Al processed by equal channel angular pressing (ECAP)  

Microsoft Academic Search

In the present paper commercially pure Al was processed by equal channel angular pressing (ECAP) up to 8 passes using route BC. For ECAP processing a proper die set was designed and constructed. Transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) were used to evaluate the microstructure of the pressed materials. Mechanical properties and the deformation behavior of the

M. Reihanian; R. Ebrahimi; N. Tsuji; M. M. Moshksar

2008-01-01

261

Novel Silver Nanostructures for Surface Enhanced Raman Spectroscopy  

NASA Astrophysics Data System (ADS)

Si/SiO2 channels filled with Ag clusters have been realized by applying of the swift heavy ion tracks and electroless wet-chemical deposition technologies. Microstructure and morphology have been investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). An exploitability of silver nanostructures in surface enhanced Raman spectroscopy (SERS) has been discussed.

Sivakov, V. A.; Zierbock, S.; Cialla, D.; Bochmann, A.; Petrov, A. V.; Kaniukov, E. Yu.; Demyanov, S. E.; Trautmann, C.

2013-05-01

262

Enhanced superplasticity in commercially pure titanium alloy X.J. Zhu, M.J. Tan *, W. Zhou  

E-print Network

Enhanced superplasticity in commercially pure titanium alloy X.J. Zhu, M.J. Tan *, W. Zhou School Available online 16 December 2004 Abstract The superplasticity of commercially pure titanium alloy at high. Keywords: Titanium; Dynamic recrystallization; Superplasticity; Electron backscattering diffraction (EBSD

Zhou, Wei

263

Modeling uniaxial tensile deformation of polycrystalline Al using CPFEM  

Microsoft Academic Search

The crystal plasticity finite element modeling (CPFEM) is realized in commercial finite element code ABAQUS with UMAT subroutine on the basis of the crystal plasticity theory of rate dependent polycrystal constitutive relations in the mesoscopic scale. The initial orientations obtained by electron backscatter diffraction (EBSD) are directly input into the CPFEM to simulate the mechanical response of polycrystalline 1050 pure

Huachun Pi; Jingtao Han; Chuanguo Zhang; A. Kiet Tieu; Zhengyi Jiang

2008-01-01

264

Experimental review of diffractive phenomena  

E-print Network

A review is given of the measurements of the hard diffractive interactions in recent years from two high-energy colliders, the HERA $ep$ collider and the Tevatron $p\\bar{p}$ collider. The structure of the diffractive exchange in terms of partons, the factorisation properties and the ratio of diffractive to non-diffractive cross sections are discussed.

L. Favart

2005-01-20

265

X-ray Diffraction  

NSDL National Science Digital Library

A series of laboratory activities on x-ray diffraction physics using the Teltron Tel-X-Ometer System. Detailed explanations on the production and delivery of the beam is included, as well as a very complete safety protocol for conducting the experiments.

Langan, Shawn

2012-03-08

266

Coherent backscattering of light by cold atoms: Theory meets experiment  

Microsoft Academic Search

Coherent backscattering (CBS) of quasi-resonant light by cold atoms presents some specific features due to the internal structure of the atomic scatterers. We present the first quantitative comparison between the experimentally observed CBS cones and Monte Carlo calculations which take into account the shape of the atomic cloud as well as the internal atomic structure.

G. Labeyrie; D. Delande; C. A. Müller; C. Miniatura; R. Kaiser

2003-01-01

267

Discrimination of UXO in soil using broadband polarimetric GPR backscatter  

Microsoft Academic Search

Polarimetric analysis of ground penetrating radar (GPR) backscatter offers a new means of discriminating subsurface metallic target shapes from one another. Such discrimination is urgently needed to distinguish buried unexploded ordnance (UXO) from other subsurface objects. To illuminate the underlying phenomenology of scattering from objects enveloped in soil, three-dimensional (3D) simulations are performed over a broad frequency band, characteristic of

Kevin O'Neill

2001-01-01

268

Rutherford backscattering analysis of gallium implanted 316 stainless steel  

E-print Network

Ion implantation of Ga ions into 316 stainless steel was performed at fluences ranging from 8x10¹? to 10¹? ions/cm². The depth profile of Ga in the steel was analyzed via Rutherford Backscattering and ToFSIMS. The surface effects were...

Ortensi, Javier

2012-06-07

269

Alpha particle backscattering measurements used for chemical analysis of surfaces  

NASA Technical Reports Server (NTRS)

Alpha particle backscattering performs a chemical analysis of surfaces. The apparatus uses a curium source and a semiconductor detector to determine the energy spectrum of the particles. This in turn determines the chemical composition of the surface after calibration to known samples.

Patterson, J. H.

1967-01-01

270

Analysis of meteors precipitation using ionospheric back-scatter radar  

Microsoft Academic Search

A 50 MHz coherent back-scatter radar also known by the anachronism RESCO has been operated since 1998 at S a o Lu i s Space Observatory 2 33 r S 44 2 r W DIP -0 5 near the dip equator The main purpose of RESCO is to study the equatorial electrojet dynamics through spectral analyses of the received echoes

H. C. Aveiro; L. P. Moor; C. M. Denardini; M. A. Abdu; N. J. Schuch

2006-01-01

271

RADIO-FREQUENCY BACKSCATTER OF ARTIFICIAL ELECTRON CLOUDS  

Microsoft Academic Search

Backscatter and forward-scatter reflection properties of chemically ; created electron clouds were measured throughout the HF spectrum. The ; measurements included radar cross sections, signal fading characteristics, and ; frequency-time-dependence. These quantities led to certain conclusions regarding ; the cloud model that describes in general the chemical releases. The model so ; presented appears to be a limited coherent type

Philip B. Gallagher; R. A. Barnes

1963-01-01

272

Bathymetry and acoustic backscatter: Elwha River Delta, Washington  

USGS Publications Warehouse

The surveys were conducted using the R/V Parke Snavely outfitted with an interferometric sidescan sonar for swath mapping and real-time kinematic navigation equipment for accurate shallow water operations. This report provides these data in a number of different formats, as well as a summary of the mapping mission, maps of bathymetry and backscatter, and Federal Geographic Data Committee (FGDC) metadata.

Finlayson, David P.; Miller, Ian M.; Warrick, Jonathan A.

2011-01-01

273

Quantum graphs where back-scattering is prohibited  

E-print Network

We describe a new class of scattering matrices for quantum graphs in which back-scattering is prohibited. We discuss some properties of quantum graphs with these scattering matrices and explain the advantages and interest in their study. We also provide two methods to build the vertex scattering matrices needed for their construction.

J. M. Harrison; U. Smilansky; B. Winn

2007-08-06

274

Simulation of Neutron Backscattering applied to organic material detection  

SciTech Connect

The Neutron Backscattering technique is tested when performing the task of localizing hydrogenated explosives hidden in soil. Detector system, landmine, soil and neutron source are simulated with Geant4 in order to obtain the number of neutrons detected when several parameters like mine composition, relative position mine-source and soil moisture are varied.0.

Forero, N. C.; Cruz, A. H.; Cristancho, F. [Departamento de Fisica, Universidad Nacional de Colombia, Bogota (Colombia); Centro Internacional de Fisica, Apartado Aereo 4948, Bogota (Colombia)

2007-10-26

275

Atic Backscatter Study Using Monte Carlo Methods in Fluka & Root  

Microsoft Academic Search

A Monte Carlo analysis, based upon FLUKA, of neutron backscatter albedoes is presented using the ATIC balloon experiment as a study case. Preparation of the FLUKA input geometry has been accomplished by means of a new semi-automatic procedure for converting GEANT3 simulations. Resultant particle fluences (neutrons, photons, and charged particles) produced by incident Carbon nuclei striking ATIC with energies up

T. Wilson; L. Pinsky; A. Empl; K. Lee; V. Andersen; J. Isbert; J. Wefel; F. Carminati; A. Fasso; A. Ferrari; P. Sala; E. Futo; J. Ranft

2002-01-01

276

Radar Backscatter Across the Gulf Stream Sea Surface Temperature Front  

NASA Technical Reports Server (NTRS)

Ocean backscatter signatures were measured by the Jet Propulsion Laboratory airborne NUSCAT K(sub u)-band scatterometer across the Gulf Stream sea surface temperature front. The measurements were made during the Surface Wave Dynamics Experiment (SWADE) off the coast of Virginia and Maryland in the winter of 1991.

Nghiem, S. V.; Li, F. K.; Walsh, E. J.; Lou, S. H.

1998-01-01

277

Estimating the Thermal Dose From Backscattered RF Echoes  

E-print Network

equation directly. The estimated thermal dose can then be used to monitor or plan ultrasound therapy-153, 2004. INTRODUCTION As the effectiveness of ultrasound thermal therapy continues to be demonstratedEstimating the Thermal Dose From Backscattered RF Echoes Bigelow, T.A., and O'Brien, W.D., Jr

Illinois at Urbana-Champaign, University of

278

Rutherford backscattering oscillation in scanning helium-ion microscopy  

SciTech Connect

Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface elemental analysis at the nanometer scale. Here we examine recently discovered SHIM backscattered intensity oscillations versus the target atomic number. These oscillations are contrary to the expected monotonic increase of the backscattered helium-ion (He{sup +}) rate with the atomic number of elemental samples. We explore the ion-sample interaction via numerical simulations for a variety of scattering geometries and confirm the presence of oscillations. The oscillations are attributed to the atomic rather than the nuclear structure of the target. To that end, we study the link (near anticorrelation) between backscatter rate and He{sup +} beam stopping power, both versus the target atomic number. This leads us to ascribe the origin of the backscatter oscillation to the ''Z{sub 2}-oscillations'' of the stopping power in ion-beam physics, with the latter being rooted in the valence electron configuration of elemental targets.

Kostinski, Sarah; Yao, Nan [Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544 (United States)

2011-03-15

279

Improving ozone profile retrieval from spaceborne UV backscatter  

E-print Network

to the South Atlantic Anomaly, low cloud fractions over deserts, desert dust outflow over the ocean layers start to contribute to the back-scattered radiance. Beyond 300­310 nm (depending on the solar zenith angle) a sizeable fraction of the solar light reaches the surface. Combining the radiances over

Haak, Hein

280

Orientation dependence of broadband acoustic backscattering from live squid  

E-print Network

Orientation dependence of broadband acoustic backscattering from live squid Wu-Jung Lee, Andone C squid (Loligo pealeii) was conducted using linear chirp signals (60­103 kHz) with data collected over with an analytical prolate spheroid model and a three-dimensional numerical model with randomized squid shape, both

Stanton, Tim

281

Coherent nonlinear backscattering by laser-plasma interactions  

Microsoft Academic Search

A theoretical analysis is carried out for the problem of coherent nonlinear backscattering of laser radiation by a high density plasma. A number of effects of direct interest to the DT-pellet fusion research are investigated. A simple physical description is introduced, which relies on a nonlinear potential formulation of the scattering equations. The simplicity and the unified nature of the

D. Anderson; H. Wilhelmsson

1975-01-01

282

Terahertz backscattering behavior of various absorbing materials , A. J. Gatesmana  

E-print Network

, absorbers, scattering, radar 1. INTRODUCTION Absorbing materials are commonly utilized in a wide variety the backscattering behavior of several absorbing materials in a compact radar range at terahertz frequencies. Several different types of structures were characterized including wedged, pyramidal, and bulk absorbers. The 160

Massachusetts at Lowell, University of

283

Dephasing Effect on Backscattering of Helical Surface States in 3D Topological Insulators  

NASA Astrophysics Data System (ADS)

We analyze the dephasing effect on the backscattering behavior of the helical surface states in 3D topological insulators. We show that the combination of dephasing and impurity scattering can cause backscattering in the helical states. Especially for the charge impurity case, the backscattering cross section becomes extremely large around the Dirac point. This large backscattering behavior can lead to the anomalous "gaplike" features found in recent experiments [T. Sato et al., Nat. Phys. 7, 840 (2011)].

Liu, Haiwen; Jiang, Hua; Sun, Qing-feng; Xie, X. C.

2014-07-01

284

Dephasing effect on backscattering of helical surface states in 3D topological insulators.  

PubMed

We analyze the dephasing effect on the backscattering behavior of the helical surface states in 3D topological insulators. We show that the combination of dephasing and impurity scattering can cause backscattering in the helical states. Especially for the charge impurity case, the backscattering cross section becomes extremely large around the Dirac point. This large backscattering behavior can lead to the anomalous "gaplike" features found in recent experiments [T. Sato et al., Nat. Phys. 7, 840 (2011)]. PMID:25105645

Liu, Haiwen; Jiang, Hua; Sun, Qing-Feng; Xie, X C

2014-07-25

285

Error caused by using a constant extinction\\/backscattering ratio in the lidar solution  

Microsoft Academic Search

The Bernoulli solution of the lidar equation with the assumption of a constant extinction\\/backscattering ratio can lead to errors in the derived aerosol extinction and backscattering profiles. This paper presents a general theoretical analysis of the errors that result from differences between the assumed and actual extinction\\/backscattering ratio profiles. Examples of the influence of the constant extinction\\/backscattering ratio assumption on

Yasuhiro Sasano; Edward V. Browell; Syed Ismail

1985-01-01

286

The effects of changes in forest biomass on radar backscatter from tree canopies  

Microsoft Academic Search

We validated a canopy backscatter model for loblolly pine forest stands at the Duke Forest, North Carolina, by comparing the observed and modelled SAR backscatter from the stands. Given the SAR backscatter data calibration uncertainty, the model made good predictions of C-HH, C-HV, L-HH, L-HV, L-VV, P-HH, and P-HV backscatter for most of 25 stands studied. The model overestimated C-VV

Y. WANG; F. W. Davies; J. M. MELACK; E. S. KASISCHKE; N. L. CHRISTENSEN JR

1995-01-01

287

Estimating Surface Oil Extent from the Deepwater Horizon Oil Spill using ASCAT Backscatter  

E-print Network

Estimating Surface Oil Extent from the Deepwater Horizon Oil Spill using ASCAT Backscatter Richard backscatter and observed backscatter indicate areas of the ocean surface affected by oil. The recent oil spill to estimate the spatial extent of surface oil. I. INTRODUCTION The oil spill from the Deepwater Horizon oil

Long, David G.

288

Direct Observations of Coherent Backscatter of Radar Waves in Precipitation A. R. JAMESON  

E-print Network

Direct Observations of Coherent Backscatter of Radar Waves in Precipitation A. R. JAMESON RJH the authors now present direct observations of radar coherent backscattered signals in precipitation, hereafter JK10a) the presence of radar coherent signals backscattered by precipitation was inferred from

Kostinski, Alex

289

Generalized Snell's law and its possible relation to coherent backscattering of ultrasonic waves  

Microsoft Academic Search

The cause of backscattering in the Rayleigh angle has first been explained by means of finite beam models in which there are inherently present backward traveling components that explain the backscattering effect. Later, the nature of backscattered sound was proved to consist mostly of incoherent sound due to material anomalies. The present work shows that besides the well known real

Nico F. Declercq; Joris Degrieck; Oswald Leroy

2004-01-01

290

Theoretical and experimental models of the diffuse radar backscatter from Mars  

Microsoft Academic Search

The general objective for this work was to develop a theoretically and experimentally consistent explanation for the diffuse component of radar backscatter from Mars. The strength, variability, and wavelength independence of Mars' diffuse backscatter are unique among our Moon and the terrestrial planets. This diffuse backscatter is generally attributed to wavelength-scale surface roughness and to rock clasts within the Martian

A. W. England

1995-01-01

291

Diffraction Studies of Multiferroics  

NASA Astrophysics Data System (ADS)

In multiferroics, magnetism is coupled to ferroelectricity so that the configuration of magnetic moments may be modified by an external electric field and, conversely, the electrically polar state may be magnetically switched. Such functionality has the potential for new technology such as energy-efficient, electrically written magnetic memories. Furthermore, multiferroics are of interest in fundamental research into quantum matter. Understanding the interplay between magnetism and ferroelectricity has posed a significant challenge to the scientific community. State-of-the-art diffraction experiments have played a unique role, as they are sensitive to both magnetic ordering and the atomic displacements associated with ferroelectricity. Exceptional insights have been gained from neutron polarimetry techniques complemented by X-ray magnetic scattering experiments, which, for the first time, have been applied to a large selection of related materials and problems. In this review, we discuss a broad selection of multiferroics and the diffraction experiments used to explain their phenomenology.

Johnson, Roger D.; Radaelli, Paolo G.

2014-07-01

292

Colored diffraction catastrophes.  

PubMed Central

On fine scales, caustics produced with white light show vividly colored diffraction fringes. For caustics described by the elementary catastrophes of singularity theory, the colors are characteristic of the type of singularity. We study the diffraction colors of the fold and cusp catastrophes. The colors can be simulated computationally as the superposition of monochromatic patterns for different wavelengths. Far from the caustic, where the luminosity contrast is negligible, the fringe colors persist; an asymptotic theory explains why. Experiments with caustics produced by refraction through irregular bathroom-window glass show good agreement with theory. Colored fringes near the cusp reveal fine lines that are not present in any of the monochromatic components; these lines are explained in terms of partial decoherence between rays with widely differing path differences. Images Fig. 1 Fig. 2 Fig. 3 Fig. 6 Fig. 8 Fig. 9 Fig. 10 PMID:11607642

Berry, M V; Klein, S

1996-01-01

293

SINGLE CRYSTAL NEUTRON DIFFRACTION.  

SciTech Connect

Single-crystal neutron diffraction measures the elastic Bragg reflection intensities from crystals of a material, the structure of which is the subject of investigation. A single crystal is placed in a beam of neutrons produced at a nuclear reactor or at a proton accelerator-based spallation source. Single-crystal diffraction measurements are commonly made at thermal neutron beam energies, which correspond to neutron wavelengths in the neighborhood of 1 Angstrom. For high-resolution studies requiring shorter wavelengths (ca. 0.3-0.8 Angstroms), a pulsed spallation source or a high-temperature moderator (a ''hot source'') at a reactor may be used. When complex structures with large unit-cell repeats are under investigation, as is the case in structural biology, a cryogenic-temperature moderator (a ''cold source'') may be employed to obtain longer neutron wavelengths (ca. 4-10 Angstroms). A single-crystal neutron diffraction analysis will determine the crystal structure of the material, typically including its unit cell and space group, the positions of the atomic nuclei and their mean-square displacements, and relevant site occupancies. Because the neutron possesses a magnetic moment, the magnetic structure of the material can be determined as well, from the magnetic contribution to the Bragg intensities. This latter aspect falls beyond the scope of the present unit; for information on magnetic scattering of neutrons see Unit 14.3. Instruments for single-crystal diffraction (single-crystal diffractometers or SCDs) are generally available at the major neutron scattering center facilities. Beam time on many of these instruments is available through a proposal mechanism. A listing of neutron SCD instruments and their corresponding facility contacts is included in an appendix accompanying this unit.

KOETZLE,T.F.

2001-03-13

294

Interactive Tutorial About Diffraction  

NSDL National Science Digital Library

The Interactive Tutorial About Diffraction is a joint effort by professors from Michigan State University, the University of Wuerzburg, and Ludwig-Maximilians University at Munich. A multitude of examples are used to present atom scattering, crystal structure, convolution theorem, Fourier transformations of crystal phase, and other topics. The interactive examples are simulations, using software developed by the authors, where students can input the number of atoms or atom type, etc. and view results as .gif images.

2007-12-27

295

Interactive Tutorial About Diffraction  

NSDL National Science Digital Library

The Interactive Tutorial About Diffraction is a joint effort by professors from Michigan State University, the University of Wuerzburg, and Ludwig-Maximilians University at Munich. A multitude of examples are used to present atom scattering, crystal structure, convolution theorem, Fourier transformations of crystal phase, and other topics. The interactive examples are simulations, using software developed by the authors, where students can input the number of atoms or atom type, etc. and view results as .gif images.

296

Diffraction before destruction  

PubMed Central

X-ray free-electron lasers have opened up the possibility of structure determination of protein crystals at room temperature, free of radiation damage. The femtosecond-duration pulses of these sources enable diffraction signals to be collected from samples at doses of 1000 MGy or higher. The sample is vaporized by the intense pulse, but not before the scattering that gives rise to the diffraction pattern takes place. Consequently, only a single flash diffraction pattern can be recorded from a crystal, giving rise to the method of serial crystallography where tens of thousands of patterns are collected from individual crystals that flow across the beam and the patterns are indexed and aggregated into a set of structure factors. The high-dose tolerance and the many-crystal averaging approach allow data to be collected from much smaller crystals than have been examined at synchrotron radiation facilities, even from radiation-sensitive samples. Here, we review the interaction of intense femtosecond X-ray pulses with materials and discuss the implications for structure determination. We identify various dose regimes and conclude that the strongest achievable signals for a given sample are attained at the highest possible dose rates, from highest possible pulse intensities. PMID:24914146

Chapman, Henry N.; Caleman, Carl; Timneanu, Nicusor

2014-01-01

297

Diffraction before destruction.  

PubMed

X-ray free-electron lasers have opened up the possibility of structure determination of protein crystals at room temperature, free of radiation damage. The femtosecond-duration pulses of these sources enable diffraction signals to be collected from samples at doses of 1000 MGy or higher. The sample is vaporized by the intense pulse, but not before the scattering that gives rise to the diffraction pattern takes place. Consequently, only a single flash diffraction pattern can be recorded from a crystal, giving rise to the method of serial crystallography where tens of thousands of patterns are collected from individual crystals that flow across the beam and the patterns are indexed and aggregated into a set of structure factors. The high-dose tolerance and the many-crystal averaging approach allow data to be collected from much smaller crystals than have been examined at synchrotron radiation facilities, even from radiation-sensitive samples. Here, we review the interaction of intense femtosecond X-ray pulses with materials and discuss the implications for structure determination. We identify various dose regimes and conclude that the strongest achievable signals for a given sample are attained at the highest possible dose rates, from highest possible pulse intensities. PMID:24914146

Chapman, Henry N; Caleman, Carl; Timneanu, Nicusor

2014-07-17

298

Comparison of reflectance with backscatter and absorption parameters for turbid waters  

NASA Technical Reports Server (NTRS)

The relation of reflectance to backscatter and absorption parameters is investigated for waters more turbid than those of previous investigations. Experimental data are examined for river waters in which beam attenuation values range from 8.9 to 18.9 per m at 550 nm. Attenuation, absorption, backscatter, and irradiance reflectance spectral properties are presented for wavelengths between 450 and 800 nm. Comparisons of reflectance with backscatter to absorption ratio and backscatter with absorption plus backscatter ratio indicate that data for turbid waters do not fit linear or polynomial models which are presently available in the literature.

Whitlock, C. H.; Poole, L. R.; Usry, J. W.; Houghton, W. M.; Witte, W. G.; Morris, W. D.; Gurganus, E. A.

1981-01-01

299

Encoding of efficient diffractive microlenses  

NASA Astrophysics Data System (ADS)

Different coding schemes for diffractive multilevel microlenses are compared. A simple method to code a lens to get the optimum diffraction efficiency is given. Furthermore, a straightforward way to estimate the achievable efficiency of a lens is presented.

Kuittinen, M.; Herzig, H. P.

1995-11-01

300

How to suppress the backscattering of conduction electrons?  

NASA Astrophysics Data System (ADS)

It is shown theoretically that the strong coupling of electrons to a high-frequency electromagnetic field results in the nulling of electron backscattering within the Born approximation. The conditions of the effect depend only on field parameters and do not depend on the concrete form of the scattering potential. As a consequence, this phenomenon is of universal physical nature and can take place in various conducting systems. Since the suppression of electron backscattering results in decreasing electrical resistance, the solved quantum-mechanical problem opens a new way to control electronic transport properties of conductors by a laser-generated field. Particularly, the elaborated theory is applicable to nanostructures exposed to a strong monochromatic electromagnetic wave.

Kibis, O. V.

2014-09-01

301

Bathymetry and Acoustic Backscatter: Northern Santa Barbara Channel, Southern California  

USGS Publications Warehouse

In the summer of 2008, as part of the California Seafloor Mapping Program (CSMP) the U.S. Geological Survey, Coastal and Marine Geology mapped a nearshore region of the northern Santa Barbara Channel in Southern California (fig 1). The CSMP is a cooperative partnership between Federal and State agencies, Universities, and Industry to create a comprehensive coastal/marine geologic and habitat basemap series to support the Marine Life Protection Act (MLPA) inititive. The program is supported by the California Ocean Protection Council and the California Coastal Conservancy. The 2008 mapping collected high resolution bathymetry and acoustic backscatter data using a bathymetric side scan system within State waters from about the 10-m isobath out over 3-nautical miles. This Open-File Report provides these data in a number of different formats, as well as a summary of the mapping mission, maps of bathymetry and backscatter, and FGDC metadata.

Dartnell, Pete; Finlayson, David; Conrad, Jamie; Cochrane, Guy; Johnson, Samuel

2010-01-01

302

Lidar extinction-to-backscatter ratio of the ocean.  

PubMed

Bio-optical models are used to develop a model of the lidar extinction-to-backscatter ratio applicable to oceanographic lidar. The model is based on chlorophyll concentration, and is expected to be valid for Case 1 waters. The limiting cases of narrow- and wide-beam lidars are presented and compared with estimates based on in situ optical measurements. Lidar measurements are also compared with the model using in situ or satellite estimates of chlorophyll concentration. A modified lidar ratio is defined, in which the properties of pure sea water are removed. This modified ratio is shown to be nearly constant for wide-beam lidar operating in low-chlorophyll waters, so accurate inversion to derive extinction and backscattering is possible under these conditions. This ratio can also be used for lidar calibration. PMID:25089487

Churnside, James H; Sullivan, James M; Twardowski, Michael S

2014-07-28

303

Azimuthal asymmetry of the coherent backscattering cone: Theoretical results  

NASA Astrophysics Data System (ADS)

The azimuthal asymmetry of the polarized backscattering cone and the intimately related polarization opposition effect (POE) are corollaries of the theory of coherent backscattering (CB) valid in the asymptotic limit of very small particle packing density. In this paper we use numerically exact solutions of the Maxwell equations to study the evolution of these and other manifestations of CB as the packing density in a multiparticle group increases from zero to values typical of actual particle suspensions and particulate surfaces. Our results reveal a remarkable robustness of virtually all effects predicted by the low-density concept of CB and allow us to conclude that the azimuthal asymmetry and POE observed in the laboratory for densely packed discrete random media are indeed caused by CB.

Mishchenko, Michael I.; Dlugach, Janna M.; Liu, Li

2009-11-01

304

Stimulated brillouin backscatter of a short-pulse laser  

SciTech Connect

Stimulated Brillouin backscattering (SBBS) from a short-pulse laser, where the pulse length is short compared to the plasma length, is found to be qualitatively different than in the long pulse regime, where the pulse length is long compared to the plasma length. We find that after an initial transient of order the laser pulse length transit time, the instability reaches a steady state in the variables x{prime} = x {minus} V{sub g}t, t{prime} = t, where V{sub g} is the pulse group velocity. In contrast, SBBS in a long pulse can be absolutely unstable and grows indefinitely, or until nonlinearities intervene. We find that the motion of the laser pulse induces Doppler related effects that substantially modify the backscattered spectrum at higher intensities, where the instability is strongly coupled (i.e. , has a growth rate large compared to the ion acoustic frequency).

Hinkel, D.E.; Williams, E.A.; Berger, R.L.

1994-11-03

305

Diffraction-Based Optical Switch  

NASA Technical Reports Server (NTRS)

Method and system for controllably redirecting a light beam, having a central wavelength lambda, from a first light-receiving site to a second light-receiving site. A diffraction grating is attached to or part of a piezoelectric substrate, which is connected to one or two controllable voltage difference sources. When a substrate voltage difference is changed and the diffraction grating length in each of one or two directions is thereby changed, at least one of the diffraction angle, the diffraction order and the central wavelength is controllably changed. A diffracted light beam component, having a given wavelength, diffraction angle and diffraction order, that is initially received at a first light receiving site (e.g., a detector or optical fiber) is thereby controllably shifted or altered and can be received at a second light receiving site. A polynomially stepped, chirped grating is used in one embodiment. In another embodiment, an incident light beam, having at least one of first and second wavelengths, lambda1 and lambda2, is received and diffracted at a first diffraction grating to provide a first diffracted beam. The first diffracted beam is received and diffracted at a second diffraction grating to produce a second diffracted beam. The second diffracted beam is received at a light-sensitive transducer, having at least first and second spaced apart light detector elements that are positioned so that, when the incident light beam has wavelength lambda1 or lambda2 (lambda1 not equal to lambda2), the second diffracted beam is received at the first element or at the second element, respectively; change in a selected physical parameter at the second grating can also be sensed or measured. A sequence of spaced apart light detector elements can be positioned along a linear or curvilinear segment with equal or unequal spacing.

Sperno, Stevan M. (Inventor); Fuhr, Peter L. (Inventor); Schipper, John F. (Inventor)

2005-01-01

306

Method and apparatus for measuring lung density by Compton backscattering  

DOEpatents

The density of the lung of a patient suffering from pulmonary edema is monitored by irradiating the lung by a single collimated beam of monochromatic photons and measuring the energies of photons compton back-scattered from the lung by a single high-resolution, high-purity germanium detector. A compact system geometry and a unique data extraction scheme are utilized to minimize systematic errors due to the presence of the chestwall and multiple scattering. 11 figs., 1 tab.

Loo, B.W.; Goulding, F.S.

1988-03-11

307

Effect of Corneal Hydration on Ultrasound Velocity and Backscatter  

PubMed Central

The cornea's acoustic properties (speed-of-sound, backscatter, attenuation) are related to its state of hydration. Our aim was to determine these properties as a function of corneal hydration using high frequency ultrasound. Bovine corneas were suspended in a Dexsol-equivalent corneal preservation medium at 33°C and then immersed successively in 75%, 50%, 25% medium and distilled water. Using a 38-MHz focused ultrasound transducer, we measured speed-of-sound and corneal thickness (n=8) and stromal backscatter (n=6) after 45-minutes immersion in each medium. Corneal speed-of-sound was modeled as a function of corneal thickness. We found the mean speed-of-sound to be 1605.4±2.9 m/s in normotensive medium. The maximum observed speed-of-sound was 1616 m/s. As we decreased medium tonicity, the cornea swelled and the speed-of-sound decreased, reaching 1563.0±2.2 m/s in water. Average corneal thickness increased from 969±93 ?m in 100% medium to 1579±104 ?m in water. Going from 100% medium to water, stromal backscatter (midband-fit) increased from -60.0±0.8 dBr to -52.5±3.5 dBr, spectral slope increased from -0.119±0.021 to -0.005±0.030 dB/MHz and attenuation coefficient decreased from 0.927±0.434 to 0.010±0.581 dB/cm-MHz. The observed correlation between acoustic backscatter and attenuation with the speed-of-sound offers a potential means for more accurate determination of speed-of-sound, and hence thickness, in edematous corneas. PMID:19195769

Silverman, Ronald H.; Patel, Monica S.; Gal, Omer; Sarup, Aman; Deobhakta, Avnish; Dababneh, Haitham; Reinstein, Dan Z.; Feleppa, Ernest J.; Coleman, D. Jackson

2009-01-01

308

Dependence of radar backscatter on coniferous forest biomass  

Microsoft Academic Search

Two independent experimental efforts have examined the dependence of radar backscatter on above-ground biomass of monospecie conifer forests using polarimetric airborne SAR data at P-, L- and C-bands. Plantations of maritime pines near Landes, France, range in age from 8 to 46 years with above-ground biomass between 5 and 105 tons\\/ha. Loblolly pine stands established on abandoned agricultural fields near

M. Craig Dobson; Fawwaz T. Ulaby; T. Letoan; A. Beaudoin; E. S. Kasischke; N. Christensen

1992-01-01

309

Forest biomass from combined ecosystem and radar backscatter modeling  

Microsoft Academic Search

Above-ground woody biomass is an important parameter for describing the function and productivity of forested ecosystems. Recent studies have demonstrated that synthetic aperture radar (SAR) can be used to estimate above-ground standing biomass. To date, these studies have relied on extensive ground-truth measurements to construct relationships between biomass and SAR backscatter. In this article we discuss the use of models

K. J. Ranson; G. Sun; J. F. Weishampel; R. G. Knox

1997-01-01

310

Ultrasonic characterization of tissues via backscatter frequency dependence  

Microsoft Academic Search

Phantom and patient studies were performed to assess the potential of backscatter frequency dependence as a useful parameter for tissue characterization. A commercial phased-array ultrasonic scanner was adapted to allow dignitization of the intermediate-frequency ultrasonic data. Studies of agar phantoms containing polystyrene microspheres with 3.5 and 5 MHz transducers indicated the ability for robust differentiation of phantoms having different scatterer

Paul Stetson; Graham Sommer

1997-01-01

311

Comparison of Modeled Backscatter using Measured Aerosol Microphysics with Focused CW Lidar Data over Pacific  

NASA Technical Reports Server (NTRS)

During NASA's GLObal Backscatter Experiment (GLOBE) II flight mission over the Pacific Ocean in May-June 1990, extensive aerosol backscatter data sets from two continuous wave, focused CO2 Doppler lidars and an aerosol microphysics data set from a laser optical particle counter (LOPC) were obtained. Changes in aerosol loading in various air masses with associated changes in chemical composition, from sulfuric acid and sulfates to dustlike crustal material, significantly affected aerosol backscatter, causing variation of about 3 to 4 orders of magnitude. Some of the significant backscatter features encountered in different air masses were the low backscatter in subtropical air with even lower values in the tropics near the Intertropical Convergence Zone (ITCZ), highly variable backscatter in the ITCZ, mid-tropospheric aerosol backscatter background mode, and high backscatter in an Asian dust plume off the Japanese coast. Differences in aerosol composition and backscatter for northern and southern hemisphere also were observed. Using the LOPC measurements of physical and chemical aerosol properties, we determined the complex refractive index from three different aerosol mixture models to calculate backscatter. These values provided a well-defined envelope of modeled backscatter for various atmospheric conditions, giving good agreement with the lidar data over a horizontal sampling of approximately 18000 km in the mid-troposphere.

Srivastava, Vandana; Clarke, Antony D.; Jarzembski, Maurice A.; Rothermel, Jeffry

1997-01-01

312

Evaluation of Ferroelectric Properties of Piezoelectric Ceramics Based on Crystallographic Homogenization Method and Crystal Orientation Analysis by SEM·EBSD Technique  

NASA Astrophysics Data System (ADS)

Macroscopic ferroelectric properties of piezoelectric polycrystals are strongly affected by microscopic inhomogeneous crystal structure. In our previous study, a multi-scale finite element method based on crystallographic homogenization method has been developed to estimate macroscopic properties considering microscopic crystal morphology. In this paper, the crystal orientation distribution of polycrystalline barium titanate has been measured by SEM·EBSD technique, and the measured crystal orientation distribution has been introduced to the microscopic finite element model. As the prediction of macroscopic properties depends on the sampling conditions of the measured crystal orientations, the effects of number of sampling points and sampling area have been investigated. As a result, the effective sampling conditions have been clarified to estimate macroscopic ferroelectric properties.

Uetsuji, Yasutomo; Yoshida, Toshihiro; Yamakawa, Takayuki; Tsuchiya, Kazuyoshi; Ueda, Sei; Nakamachi, Eiji

313

Diffraction measurements at the LHC  

E-print Network

Proton-proton collisions at the LHC can be classified as elastic, non-diffractive, and diffractive. In this paper we discuss various measurements of these above processes at various LHC experiments. We report about the total proton-proton cross-section measurements, about the analysis of diffractive events and also about the pseudorapidity distribution in inelastic events.

M. Csanad

2013-12-13

314

Molecular Expressions: Diffraction of Light  

NSDL National Science Digital Library

This item is an introductory tutorial on the topic of diffraction of light waves. It explains the phenomenon in a variety of ways and provides real-life examples of diffraction patterns. Related interactive simulations demonstrate basic properties of light being diffracted through a slit and allow users to explore more complex phenomena such as Airy disk patterns.

Davidson, Michael

2009-05-26

315

Visibility related to backscatter at 1.54 micron  

NASA Technical Reports Server (NTRS)

The lidar process was shown to have the necessary potential to fulfill the need for a remote measurement of visibility. Visibility can be inferred from a lidar return optical extinction. The wavelength 1.54 micron was chosen, being near the visible wavelength region and having a high eye safety threshol, 200,000 times higher than 1.06 micron; 1.54 is the erbium laser wavelength. This research utilized 105 measured height profiles of natural droplet size distributions data, taken in clouds, fog, and haze. These profiles were examined to determine the completeness of the droplet counting data. It was found that the particle spectrometer data were incomplete in the very light ford and haze so this portion of the data was eliminated. Utilizing the Mie theory, these droplet size distribution profiles were converted to backscatter at 1.54 micron and extinction in the visible region, 0.55 micron. Using Koschmeider's relationship, the extinction profiles were converted to visibility. The visibility and backscatter profiles were compared to develop a relationship between visibility and backscatter at 1.54 micron.

Barber, T. L.; Larson, D. R.

1986-01-01

316

Tracers in vascular casting resins enhance backscattering brightness.  

PubMed

Studying cast microvasculature with scanning electron microscopy has expanded our knowledge of many circulations, but need arises to determine the blood source of vascular beds that are supplied by two circulations. One way to do this is to mark the casting resin by adding a tracer compound that can be detected in the scanning electron microscope. A potential method of distinguishing different substances is to detect the backscattered electrons that are emitted from the tracer if the tracer is a heavier element, because heavier elements backscatter more electrons. To explore different tracers, we tested lead, titanium, iron, osmium, and uranium as solutions of different polarity and powders. The tracers were added to 1 ml of methyl methacrylate in log concentrations. Shrinkage, hardness, cast quality, and change in brightness from the tracer were compared with multivariate analysis at scanning electron microscopic working distances of 15 and 39 mm on carbon-coated and uncoated specimens. Several concentrations caused sedimentation of the tracer and prevented the resin from solidifying. Tetraethyl lead shortened the hardening time: uranyl acetate and osmium tetroxide prolonged it. Most tracers decreased shrinkage. When lead citrate and Reynolds solutions were removed, the brightness correlated with increasing atomic number, concentration of the tracer, and mean atomic number of the specimen (p <0.0001). The substances that increased contrast most were tetraethyl lead and uranium. Backscattering electron detection can distinguish methacrylate casts that have small amounts of heavier elements added to them, but an optimal tracer has not yet been established. PMID:12074492

Schraufnagel, Dean E; Ganesan, Dhanalakshmi P

2002-01-01

317

Simulation Studies of the Backscattering Signal in HSRL Technique  

E-print Network

The technique of High Spectral Resolution Lidar (HSRL) for atmospheric monitoring allows the determination of the aerosol to molecular ratio and can be used in UHECR Observatories using air fluorescence telescopes. By this technique a more accurate estimate of the Cherenkov radiation superimposed to the fluorescence signal can be achieved. A laboratory setup was developed to determine the backscattering coefficients using microparticles diluted in water and diffusion interfaces. In this setup we used a CW SLM laser at 532 nm and a 250 mm Newtonian telescope. Simulations of the above experimental configuration have been made using Scatlab\\c{opyright}, FINESSE\\c{opyright} 0.99.8 and MATLAB\\c{opyright} and are presented in this work. We compare the simulated 2-dimensional Fabry-Perot fringe images of the backscattering signal recorded in the CCD sensor with that of experimental ones. Additionally, we simulated the backscattering of the laser beam by the atmosphere at a height of 2000 m and we have studied the in...

Georgakopoulou, Angelika

2012-01-01

318

Relationships between multipolarized radar backscatter and slash pine stand parameters  

NASA Technical Reports Server (NTRS)

Multipolarized L-band (24.5 cm) aircraft radar data was obtained for a primarily forested area in northern Florida. Based on the results of previous studies by Hoffer and Hussin (1989), a swath of medium incidence angle (35-25 deg) data was defined. Three groups of slash pine stands were located in the data: 4- to 17-year-old plantations, 18- to 48-year-old plantations, and 16- to 53-year-old natural stands. Stand data obtained from the forest-products companies operating in the area include age, tree height, diameter-at-breast height, basal area, volume (cords/acre), and density (trees/acre). Each of these stand parameters were compared to each of the four polarizations (HH, VV, VH, and HV) of the radar data for each group of stands. Statistically significant relationships were found between the radar backscatter and the forest stand parameters only for the 4- to 17-year-old slash pine plantation stands. In general, the cross-polarized radar backscatter was more highly correlated with the various stand parameters than the like-polarized backscatter, and the VV-polarized data were more highly correlated than the HH-polarized data.

Hussin, Yousif Ali; Hoffer, Roger M.

1989-01-01

319

Spectroscopic diffraction phase microscopy.  

PubMed

We present spectroscopic diffraction phase microscopy (sDPM) as a method capable of measuring quantitative phase images at multiple wavelengths. sDPM uses a spatial light modulator at the Fourier plane of a lens to select desired wavelengths from the white light illumination of a grating. The quantitative phase information at different wavelengths allows us to decouple the refractive index and the thickness from the phase shift induced by biological cells. We demonstrate the capability of the setup by dispersion measurements of microsphere beads and RBCs. PMID:23381283

Pham, Hoa; Bhaduri, Basanta; Ding, Huafeng; Popescu, Gabriel

2012-08-15

320

Spectral diffraction efficiency characterization of broadband diffractive optical elements.  

SciTech Connect

Diffractive optical elements, with their thin profile and unique dispersion properties, have been studied and utilized in a number of optical systems, often yielding smaller and lighter systems. Despite the interest in and study of diffractive elements, the application has been limited to narrow spectral bands. This is due to the etch depths, which are optimized for optical path differences of only a single wavelength, consequently leading to rapid decline in efficiency as the working wavelength shifts away from the design wavelength. Various broadband diffractive design methodologies have recently been developed that improve spectral diffraction efficiency and expand the working bandwidth of diffractive elements. We have developed diffraction efficiency models and utilized the models to design, fabricate, and test two such extended bandwidth diffractive designs.

Choi, Junoh; Cruz-Cabrera, Alvaro Augusto; Tanbakuchi, Anthony

2013-03-01

321

Phase shifting diffraction interferometer  

DOEpatents

An interferometer which has the capability of measuring optical elements and systems with an accuracy of {lambda}/1000 where {lambda} is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about {lambda}/50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms. 8 figs.

Sommargren, G.E.

1996-08-29

322

Phase shifting diffraction interferometer  

DOEpatents

An interferometer which has the capability of measuring optical elements and systems with an accuracy of .lambda./1000 where .lambda. is the wavelength of visible light. Whereas current interferometers employ a reference surface, which inherently limits the accuracy of the measurement to about .lambda./50, this interferometer uses an essentially perfect spherical reference wavefront generated by the fundamental process of diffraction. This interferometer is adjustable to give unity fringe visibility, which maximizes the signal-to-noise, and has the means to introduce a controlled prescribed relative phase shift between the reference wavefront and the wavefront from the optics under test, which permits analysis of the interference fringe pattern using standard phase extraction algorithms.

Sommargren, Gary E. (Santa Cruz, CA)

1996-01-01

323

Ultrafast Powder Diffraction  

NASA Astrophysics Data System (ADS)

An overview is given of the use of powder synchrotron-X-ray and neutron diffraction to study very fast physical or chemical processes that require time resolution of 500 ms or less. The experimental requirements to obtain data of good quality are considered, including the incident flux, detector characteristics, and the different strategies possible for irreversible and reversible processes. The latter are accessible via a stroboscopic approach whereas the former require the maximum rates of data acquisition. Some recent studies are described, drawn from the areas of combustion synthesis, metallurgy and catalysis. The exploitation of the bunch structure of a synchrotron ring to obtain time resolution in the sub-ns range with the pump-probe stroboscopic approach is also illustrated.

Fitch, Andy; Curfs, Caroline

324

Dichroic Coherent Diffractive Imaging  

NASA Astrophysics Data System (ADS)

Understanding electronic structure at nanometer resolution is crucial to understanding physics such as phase separation and emergent behavior in correlated electron materials. Nondestructive probes which have the ability to see beyond surfaces on nanometer length and sub-picosecond time scales can greatly enhance our understanding of these systems and will impact development of future technologies, such as magnetic storage. Polarized x-rays are an appealing choice of probe due to their penetrating power, elemental and magnetic specificity, and high spatial resolution. The resolution of traditional x-ray microscopy is limited by the nanometer precision required to fabricate x-ray optics. In this thesis, a novel approach to lensless imaging of an extended magnetic nanostructure is presented. We demonstrate this approach by imaging ferrimagnetic "maze" domains in a Gd/Fe multilayer with perpendicular anisotropy. A series of dichroic coherent diffraction patterns, ptychographically recorded, are numerically inverted using non-convex and non-linear optimization theory, and we follow the magnetic domain configuration evolution through part of its magnetization hysteresis loop by applying an external magnetic field. Unlike holographic methods, it does not require a reference wave or precision optics, and so is a far simpler experiment. In addition, it enables the imaging of samples with arbitrarily large spatial dimensions, at a spatial resolution limited solely by the coherent x-ray flux and wavelength. It can readily be extended to other non-magnetic systems that exhibit circular or linear dichroism. This approach is scalable to imaging with diffraction-limited resolution, a prospect rapidly becoming a reality in view of the new generation of phenomenally brilliant x-ray sources.

Tripathi, Ashish

325

Dichroic coherent diffractive imaging  

PubMed Central

Understanding electronic structure at the nanoscale is crucial to untangling fundamental physics puzzles such as phase separation and emergent behavior in complex magnetic oxides. Probes with the ability to see beyond surfaces on nanometer length and subpicosecond time scales can greatly enhance our understanding of these systems and will undoubtedly impact development of future information technologies. Polarized X-rays are an appealing choice of probe due to their penetrating power, elemental and magnetic specificity, and high spatial resolution. The resolution of traditional X-ray microscopes is limited by the nanometer precision required to fabricate X-ray optics. Here we present a novel approach to lensless imaging of an extended magnetic nanostructure, in which a scanned series of dichroic coherent diffraction patterns is recorded and numerically inverted to map its magnetic domain configuration. Unlike holographic methods, it does not require a reference wave or precision optics. In addition, it enables the imaging of samples with arbitrarily large spatial dimensions, at a spatial resolution limited solely by the coherent X-ray flux, wavelength, and stability of the sample with respect to the beam. It can readily be extended to nonmagnetic systems that exhibit circular or linear dichroism. We demonstrate this approach by imaging ferrimagnetic labyrinthine domains in a Gd/Fe multilayer with perpendicular anisotropy and follow the evolution of the domain structure through part of its magnetization hysteresis loop. This approach is scalable to imaging with diffraction-limited resolution, a prospect rapidly becoming a reality in view of the new generation of phenomenally brilliant X-ray sources. PMID:21825152

Tripathi, Ashish; Mohanty, Jyoti; Dietze, Sebastian H.; Shpyrko, Oleg G.; Shipton, Erik; Fullerton, Eric E.; Kim, Sang Soo; McNulty, Ian

2011-01-01

326

Dichroic coherent diffractive imaging.  

PubMed

Understanding electronic structure at the nanoscale is crucial to untangling fundamental physics puzzles such as phase separation and emergent behavior in complex magnetic oxides. Probes with the ability to see beyond surfaces on nanometer length and subpicosecond time scales can greatly enhance our understanding of these systems and will undoubtedly impact development of future information technologies. Polarized X-rays are an appealing choice of probe due to their penetrating power, elemental and magnetic specificity, and high spatial resolution. The resolution of traditional X-ray microscopes is limited by the nanometer precision required to fabricate X-ray optics. Here we present a novel approach to lensless imaging of an extended magnetic nanostructure, in which a scanned series of dichroic coherent diffraction patterns is recorded and numerically inverted to map its magnetic domain configuration. Unlike holographic methods, it does not require a reference wave or precision optics. In addition, it enables the imaging of samples with arbitrarily large spatial dimensions, at a spatial resolution limited solely by the coherent X-ray flux, wavelength, and stability of the sample with respect to the beam. It can readily be extended to nonmagnetic systems that exhibit circular or linear dichroism. We demonstrate this approach by imaging ferrimagnetic labyrinthine domains in a Gd/Fe multilayer with perpendicular anisotropy and follow the evolution of the domain structure through part of its magnetization hysteresis loop. This approach is scalable to imaging with diffraction-limited resolution, a prospect rapidly becoming a reality in view of the new generation of phenomenally brilliant X-ray sources. PMID:21825152

Tripathi, Ashish; Mohanty, Jyoti; Dietze, Sebastian H; Shpyrko, Oleg G; Shipton, Erik; Fullerton, Eric E; Kim, Sang Soo; McNulty, Ian

2011-08-16

327

Knife Edge Diffraction Signal attenuation caused by diffraction of waves  

E-print Network

E E d i i d : Diffraction loss due to the presence of knife-edge wrt free space LOS E-field #12 The diffraction loss due to the presence of a knife edge, as compared to the free space E-field can be given of diffraction loss as a function of path difference around an obstruction, i.e. knife edge, is also explained

Cetiner, Bedri A.

328

Back-scattering channel-cut high-resolution monochromator for inelastic x-ray scattering  

SciTech Connect

We report on a design and on some experimental results for the performance of a new high energy resolution monochromator. It is a large channel-cut Si crystal with a 197 mm separation between the two faces designed to operate in a near-backscattering regime. The device was tested as a second monochromator on Sector 3 of the Synchrotron Radiation Instrumentation Collaborative Access Team (SRI-CAT) at the Advanced Photon Source using the Si(777) reflection at a photon energy of 13.84 keV. The same monochromator can be used for other energies with reflections of the type (hhh). Special care has been taken to equalize the temperature of the two faces by employing a Peltier heat pump. A Si(111) double-crystal pre-monochromator designed to withstand the high heat load of the undulator radiation was used upstream on the beamline. The measured throughput efficiency of the Si(777) channel-cut monochromator was less ideal by a factor of 1.9. Dynamical diffraction theory was used to calculate the throughput of an ideally perfect crystal.

Kushnir, V.I.; Abbamonte, P.M.; Macrander, A.T.; Schwoerer-Boehning, M.

1997-08-01

329

Backscattering from dental restorations and splint materials during therapeutic radiation  

SciTech Connect

Models were constructed to simulate as closely as possible the human oral cavity. Radiation absorbed doses were determined for controls and various test situations involving the presence of dental restorative and splint materials during cobalt-60 irradiation of the models. Adjacent gold full crowns and adjacent solid dental silver amalgam cores both increased the dose to the interproximal gingivae by 20%. Use of orthodontic full bands for splinting the jaws increased the dose to the buccal tissues by an average of 10%. Augmentation of dose through backscatter radiation was determined to be only slight for intracoronal amalgam fillings and stainless steel or plastic bracket splints.

Farman, A.G.; Sharma, S.; George, D.I.; Wilson, D.; Dodd, D.; Figa, R.; Haskell, B.

1985-08-01

330

Time-of-flight heavy ion backscattering spectrometry  

SciTech Connect

A new time-of-flight (TOF) ion detection system for Heavy Ion Backscattering Spectrometry (HIBS) is described. Examples are also given of the use of the system for measuring low-level contamination on Si wafers. Currently, the TOF-HBIS system has a sensitivity of 1 {times} 10{sup 9}/cm{sup 2} for the heaviest of surface impurity atoms and a mass resolution capable of separating Fe from Cu. The sensitivity is expected to improve by an additional order of magnitude on a industrial TOF-HIBS system being constructed for SEMATECH.

Knapp, J.A.; Banks, J.C.; Doyle, B.L.

1993-08-01

331

Implementation of Enhanced Image from Backscatter X-ray System.  

PubMed

Considerable attention has been focused on digital X-ray systems with transmission. However, only a few attempts have been made using X-ray backscatter system. It has difficulty that we have to reconstruct image from a little data in the image processing. Especially, it is necessary that the method correct error of detector effectively. That is the most important thing in the acquisition of X-ray data. In this paper, it is that propose some data processing methods that correct error of detector, and we can recognize that the image reconstruction from a little data is effective. PMID:17282576

Ryu, J S; Park, S W; Kim, M S; Yi, Y

2005-01-01

332

Relating the microwave backscattering coefficient to leaf area index  

NASA Technical Reports Server (NTRS)

This paper examines the relationship between the microwave backscattering coefficient of a vegetation canopy, sigma (can, 0) and the canopy's leaf area index (LAI). The relationship is established through the development of one model for corn and sorghum and another for wheat. Both models are extensions of the cloud model of Attema and Ulaby (1978). Analysis of experimental data measured at 8.6, 13.0, 17.0, and 35.6 GHz indicates that most of the temporal variations of sigma (can, 0) can be accounted for through variations in green LAI alone, if the latter is greater than 0.5.

Ulaby, F. T.; Allen, C. T.; Eger, G., III; Kanemasu, E.

1984-01-01

333

Relating the radar backscattering coefficient to leaf-area index  

NASA Technical Reports Server (NTRS)

The relationship between the radar backscattering coefficient of a vegetation canopy, sigma(0) sub can, and the canopy's leaf area index (LAI) is examined. The relationship is established through the development of a model for corn and sorghum and another for wheat. Both models are extensions of the cloud model of Attema and Ulaby (1978). Analysis of experimental data measured at 8.6, 13.0, 17.0, and 35.6 GHz indicates that most of the temporal variations of sigma(0) sub can can be accounted for through variations in green LAI alone, if the latter is greater than 0.5.

Ulaby, F. T. (principal investigator); Allen, C.; Eger, G.; Kanemasu, E.

1983-01-01

334

Confocal backscatter laser velocimeter with on-axis sensitivity.  

NASA Technical Reports Server (NTRS)

A confocal backscatter laser Doppler velocimeter (LDV) that measures two velocity components has been developed. This device requires only two incident beams polarized normally to one another. Moreover, the velocity components sensed are nearly orthogonal. The velocimeter employs a combined dual-scatter, local oscillator arrangement to obtain the bidirectional sensitivity. Two photodetectors are used, each sensing only one Doppler frequency proportional to one of the very nearly orthogonal velocity components. In addition, a single Bragg cell serves to frequency bias both velocity components in order to eliminate directional ambiguity. A differencing technique has also been incorporated to enhance the dual-scatter Doppler signal corresponding to the transverse velocity.

Orloff, K. L.; Logan, S. E.

1973-01-01

335

Statistical Parameter Estimation in Ultrasound Backscattering from Tissue Mimicking Media.  

NASA Astrophysics Data System (ADS)

Several tissue characterization parameters, including the effective scatterer number density and the backscatter coefficient, were derived from the statistical properties of ultrasonic echo signals. The effective scatterer number density is the actual scatterer number density in a medium multiplied by a frequency-dependent factor that depends on the differential scattering cross-sections of all scatterers. The method described in this thesis for determining the scatterer number density explicitly retains both the temporal nature of the data acquisition and the properties of the ultrasound field in the data reduction. Moreover, it accounts for the possibility that different sets of scatterers may dominate the echo signal at different frequencies. The random processes involved in forming ultrasound echo signals from random media give rise to an uncertainty in the estimated effective scatterer number density. This uncertainty is evaluated using error propagation. The statistical uncertainty depends on the effective number of scatterers contributing to the segmented echo signal, increasing when the effective number of scatterers increases. Tests of the scatterer number density data reduction method and the statistical uncertainty estimator were done using phantoms with known ultrasound scattering properties. Good agreement was found between measured values and those calculated from first-principles. The properties of the non-Gaussian and non-Rayleigh parameters of ultrasound echo signals are also studied. Both parameters depend on the measurement system, including the transducer field and pulse frequency content, as well as on the medium's properties. The latter is expressed in terms of the scatterer number density and the second and fourth moments of the medium's scattering function. A simple relationship between the non-Gaussian and non-Rayleigh parameters is derived and verified experimentally. Finally, a reference phantom method is proposed for measuring the effective scatterer number density in vivo. Various groups are using the frequency dependent backscatter coefficient (or the spatial autocorrelation function) to characterize scatterer sizes in biological tissue. Generally, sparse scatterer concentrations are assumed in relating scattering parameters to this tissue property. For dense scattering media, we study whether the frequency dependent backscatter coefficient changes with the scatterer volume fraction. Two scattering models suggested by Debye and Yagi are reviewed. In these models, the spatial autocorrelation function describing mass density and compressibility fluctuations in the scattering medium has a characteristic length that depends on the scatterer volume fraction as well as the scatterer size. The models predict the frequency dependence of the backscatter coefficient will vary with the scatterer volume fraction. Qualitative agreement between the model predictions and experimental results are seen for sephadex-in-agar phantoms.

Chen, Jian-Feng

336

Low-Frequency Electromagnetic Backscatter from Buried Tunnels  

SciTech Connect

This progress report is submitted under a contract between the Special Project Office of DARPA and Lawrence Livermore National Laboratory. The Project Manager at DARPA is Dr. Michael Zatman. Our purpose under this contract is to investigate interactions between electromagnetic waves and a class of buried targets located in multilayered media with rough interfaces. In this report, we investigate three preliminary problems. In each case our specific goal is to understand various aspects of the electromagnetic wave interaction mechanisms with targets in layered media. The first problem, discussed in Section 2, is that of low-frequency electromagnetic backscattering from a tunnel that is cut into a lossy dielectric half-space. In this problem, the interface between the upper (free space) region and the lower (ground) region is smooth. The tunnel is assumed to be a cylindrical free-space region of infinite extent in its axial direction and with a diameter that is small in comparison to the free-space wavelength. Because its diameter is small, the tunnel can be modeled as a buried ''wire'' described by an equivalent impedance per unit length. In Section 3 we extend the analysis to include a statistically rough interface between the air and ground regions. The interface is modeled as a random-phase screen. Such a screen reduces the coherent power in a plane wave that is transmitted through it, scattering some of the total power into an incoherent field. Our analysis of this second problem quantifies the reduction in the coherent power backscattered from the buried tunnel that is caused by the roughness of the air-ground interface. The problem of low-frequency electromagnetic backscattering from two buried tunnels, parallel to each other but at different locations in the ground, is considered in Section 4. In this analysis, we wish to determine the conditions under which the presence of more than one tunnel can be detected via backscattering. Section 5 concludes the report with a summary of the investigations discussed herein and recommendations for future work on problems of this class.

Casey, K; Pao, H

2006-06-21

337

Coherent phenomena in inelastic backscattering of electrons from disordered media  

SciTech Connect

The phenomenon of weak localization in an inelastic-scattering channel is considered in the context of the reflection of moderate-energy electrons with fixed energy loss from a disordered medium. The localization features in the backscattering angular spectrum are found to be manifested under the condition of strong interference, [omega][much lt][gamma] (here [h bar][omega] is the energy loss and [gamma] is the frequency of electron collisions). Unlike the elastic-scattering channel, the center of the enhanced peak is shown to be displaced relative to the exactly backward direction under the condition of oblique incidence of the electrons on a disordered sample surface.

Kanzieper, E.; Freilikher, V. (The Jack and Pearl Resnick Institute of Advanced Technology, Department of Physics, Bar-Ilan University, Ramat-Gan 52900 (Israel))

1995-02-01

338

ZEUS results on inclusive diffraction  

NASA Astrophysics Data System (ADS)

Deep inelastic diffractive scattering, ep ? e'?*p ? e'XN, has been studied at HERA with the ZEUS detector in a wide kinematic range in the ?*p centre-of-mass energy W, the photon virtually Q2 and the mass of the system X, MX. ZEUS results on diffraction have been obtained using the MX method and by identifying leading protons which carry a large fraction of the incoming proton beam energy. They are presented in terms of the diffractive cross section, d?(MX,W,Q2)/dMX and the diffractive structure function, xIPF2D(3)(?,xIP,Q2).

Lim, Heuijin

2005-10-01

339

Electrically-programmable diffraction grating  

DOEpatents

An electrically-programmable diffraction grating. The programmable grating includes a substrate having a plurality of electrodes formed thereon and a moveable grating element above each of the electrodes. The grating elements are electrostatically programmable to form a diffraction grating for diffracting an incident beam of light as it is reflected from the upper surfaces of the grating elements. The programmable diffraction grating, formed by a micromachining process, has applications for optical information processing (e.g. optical correlators and computers), for multiplexing and demultiplexing a plurality of light beams of different wavelengths (e.g. for optical fiber communications), and for forming spectrometers (e.g. correlation and scanning spectrometers).

Ricco, Antonio J. (Albuquerque, NM); Butler, Michael A. (Albuquerque, NM); Sinclair, Michael B. (Albuquerque, NM); Senturia, Stephen D. (Brookline, MA)

1998-01-01

340

In situ video and diffraction analysis of marine particles  

NASA Astrophysics Data System (ADS)

A design for a new underwater video-system to detect and observe suspended particles is presented. Particles are collected and isolated in a rectangular box where they are highly illuminated by a white light plane. The total field of view is determined. The camera, equipped with a remote controlled zoom, can resolve particles sizes ranging from 25 ?m to several millimetres. Real-time image analyses are therefore performed. Particle counts and size spectra are calculated and displayed. Total light intensity scattered by the illuminated particles is closely related to the back-scattering values determined by an optical back-scatter sensor. A particle size analyser using diffraction analysis is associated to this video-system on a custom profiler. Hydrological parameters are measured by a standard CTD probe associated to a chlorophyll sensor. Results are acquired and graphically presented in real time. This custom profiler presents numerous advantages in oceanographic research. Two examples of its use in different coastal areas are presented. In an estuary, temporal evolution of particle characteristics was described in relation to the tide cycle. While the video-system allows direct visualization and characterization of the largest particles, the particle-size analyser performs precise quantification of the finest ones. It was shown that the two methods were in accordance for quantification of large aggregates, which were observed around slack tide when salinity decreased. Video analyses cannot be performed above 25 mg l -1 dry weight equivalent. The system reliability, resolution and limits were also demonstrated during a cruise in the Gulf of Finland. A typical profile is presented here showing different layers, one characterized by the association of heterotrophic flagellates and detritals, and another dominated by zooplankton, the surface layer being characterized by cyanobacterial colonies. Video associated to diffraction analyses allows the study of flocculation processes in estuaries and a detailed description of thin layers.

Lunven, Michel; Gentien, P.; Kononen, K.; Le Gall, E.; Daniélou, M. M.

2003-08-01

341

Stochastization of backscattered laser radiation by whole blood during thrombus formation process  

NASA Astrophysics Data System (ADS)

The express method of laser diagnostics of thrombus formation process in a whole blood is presented. This method is based on experimental investigations of backscattered laser radiation by a whole blood. The technique of experimental researches of backscattered laser radiation by whole blood is shown. It is established that the stochastization of fluctuations of backscattered intensity decreases under the influence of thrombin, that gives the possibility to estimate continuance of thrombus formation process.

Gavrylyak, M. S.

2009-10-01

342

Investigation of coefficient of thermal expansion of silver thin film on different substrates using X-ray diffraction  

Microsoft Academic Search

Silver thin films (200nm) were deposited on two different substrates, SiO2 and polyethylene naphthalate (PEN) by e-beam evaporation. The thickness of the Ag thin film on both substrates was determined to be 200nm by Rutherford backscattering spectrometry. X-ray diffraction analysis showed that the coefficient of thermal expansion (CTE) of Ag on PEN (1.9×10?5\\/°C) was the same as that of bulk

Yeongseok Zoo; Daniel Adams; J. W. Mayer; T. L. Alford

2006-01-01

343

Effects of soil and canopy characteristics on microwave backscattering of vegetation  

NASA Technical Reports Server (NTRS)

A frequency modulated continuous wave C-band (4.8 GHz) scatterometer was mounted on an aerial lift truck and backscatter coefficients of corn were acquired as functions of polarizations, view angles, and row directions. As phytomass and green leaf area index increased, the backscatter also increased. Near anthesis when the canopies were fully developed, the major scattering elements were located in the upper 1 m of the 2.8 m tall canopy and little backscatter was measured below that level. C-band backscatter data could provide information to monitor vegetation at large view zenith angles.

Daughtry, C. S. T.; Ranson, K. J.

1991-01-01

344

The depolarization-attenuated backscatter relationship for dust plumes.  

PubMed

This study identified the relationship between the layer-integrated attenuated backscatter coefficient and layer-integrated depolarization ratio of dust plumes and compared it with that of cloud, using CALIPSO LIDAR measurements. The histogram distribution of the integrated color ratio for dust and cloud was also examined. On the basis of the layer-integrated attenuated backscatter coefficient and layer-integrated depolarization ratio relation, a simple method of detecting dust plumes was developed. A case study of dust identification over the Taklimakan Desert was conducted and compared with the current CALIPSO products. The result shows that the proposed method can significantly improve the classification of cloud and dust plumes and can supplement the current space-borne LIDAR discrimination approach, especially over dust source regions. In addition, The zonal and meridional mean occurrence derived by the proposed method and the CALIPSO's method were compared for Asian dust over East Asia region (30°N -45°N, 80°E -180°E) using the night measurements of CALIPSO from March to May, 2007. The comparison showed that the dust occurrence obtained from the proposed method is larger than that of CALIPSO's method. The dust could be found up to around 6-8 km (Above Sea Level, ASL) near the Taklimakan desert region, and maximum occurrence is over 80%. The transport altitude remained at 3 km-7 km (ASL) as the dust was transported across the Pacific Ocean. PMID:23842305

Zhou, Tian; Huang, Jianping; Huang, Zhongwei; Liu, Jingjing; Wang, Wencai; Lin, Lei

2013-07-01

345

Nimbus 7 solar backscatter ultraviolet (SBUV) ozone products user's guide  

NASA Technical Reports Server (NTRS)

Three ozone tape products from the Solar Backscatter Ultraviolet (SBUV) experiment aboard Nimbus 7 were archived at the National Space Science Data Center. The experiment measures the fraction of incoming radiation backscattered by the Earth's atmosphere at 12 wavelengths. In-flight measurements were used to monitor changes in the instrument sensitivity. Total column ozone is derived by comparing the measurements with calculations of what would be measured for different total ozone amounts. The altitude distribution is retrieved using an optimum statistical technique for the inversion. The estimated initial error in the absolute scale for total ozone is 2 percent, with a 3 percent drift over 8 years. The profile error depends on latitude and height, smallest at 3 to 10 mbar; the drift increases with increasing altitude. Three tape products are described. The High Density SBUV (HDSBUV) tape contains the final derived products - the total ozone and the vertical ozone profile - as well as much detailed diagnostic information generated during the retrieval process. The Compressed Ozone (CPOZ) tape contains only that subset of HDSBUV information, including total ozone and ozone profiles, considered most useful for scientific studies. The Zonal Means Tape (ZMT) contains daily, weekly, monthly and quarterly averages of the derived quantities over 10 deg latitude zones.

Fleig, Albert J.; Mcpeters, R. D.; Bhartia, P. K.; Schlesinger, Barry M.; Cebula, Richard P.; Klenk, K. F.; Taylor, Steven L.; Heath, Donald F.

1990-01-01

346

Lidar backscatter signal recovery from phototransistor systematic effect by deconvolution.  

PubMed

Backscatter lidar detection systems have been designed and integrated at NASA Langley Research Center using IR heterojunction phototransistors. The design focused on maximizing the system signal-to-noise ratio rather than noise minimization. The detection systems have been validated using the Raman-shifted eye-safe aerosol lidar (REAL) at the National Center for Atmospheric Research. Incorporating such devices introduces some systematic effects in the form of blurring to the backscattered signals. Characterization of the detection system transfer function aided in recovering such effects by deconvolution. The transfer function was obtained by measuring and fitting the system impulse response using single-pole approximation. An iterative deconvolution algorithm was implemented in order to recover the system resolution, while maintaining high signal-to-noise ratio. Results indicated a full recovery of the lidar signal, with resolution matching avalanche photodiodes. Application of such a technique to atmospheric boundary and cloud layers data restores the range resolution, up to 60 m, and overcomes the blurring effects. PMID:18846166

Refaat, Tamer F; Ismail, Syed; Abedin, M Nurul; Spuler, Scott M; Mayor, Shane D; Singh, Upendra N

2008-10-10

347

Backscatter Mossbauer Spectrometer (BaMS) for extraterrestrial applications  

NASA Technical Reports Server (NTRS)

Mossbauer spectroscopy is a nuclear gamma resonance technique particularly well suited to the study of materials that contain iron (Fe-57). It can provide information on the oxidation state of iron as well as the type and proportion of iron-containing mineral species in a sample of interest. Iron Mossbauer spectroscopy (FeMS) has been applied to samples believed to have come from Mars (SNC meteorites) and has been helpful in refining the choice among putative Martian surface materials by suggesting a likely nanophase component of the Martian regolity. FeMS spectrum of a Martial analogue material (Hawaiian palagonite) is shown; it is dominated by ferric-bearing phases and shows evidence of a nanophase component. FeMS has also been applied to lunar materials. It can be used to measure the maturity of lunar surface material and has been proposed as a prospector for lunar ilmenite, an oxygen resource mineral. Several years ago we suggested a backscatter Mossbauer spectrometer (BaMS) for a Mars rover mission. Backscatter design was selected as most appropriate for in-situ application because no sample preparation is required. Since that time, we have continued to develop the BaMS instrument in anticipation that it would eventually find a home on a NASA planetary mission. Gooding proposed BaMS as a geochemistry instrument on MESUR. More recently, an LPI workshop has recommended that BaMS be included in a three-instrument payload on the next (1996?) lunar lander.

Agresti, D. G.; Shelfer, T. D.; Pimperl, M. M.; Wills, E. L.; Shen, M. H.; Morris, R. V.

1993-01-01

348

Rutherford backscattering analysis of the failure of chlorine anodes  

SciTech Connect

Rutherford Backscattering Spectrometry, carried out at the ORNL Surface Modification And Characterization Collaborative Research Center (SMAC) facility, has been applied to the nondestructive analysis of RuO[sub 2]-TiO[sub 2] electrodes of 5000 Angstroms, which mimic the DSA anodes in composition and the method of preparation. Occidental Chemical Corporation provided electrodes, which had been subjected to life time testing in H[sub 2]S04 solution, for analysis by ORNL. The results were used to test the hypothesis of degradation of theses, and similar electrodes, from a process involving a decrease in the RuO[sub 2]:TiO[sub 2] ratio at and near the electrode surface and the related decrease in the electrode electrical conductivity. The drop in electrode activity is closely linked to a decrease in Ru content, and the measured profiles show that the loss takes place across the thin RuO[sub 2]-TiO[sub 2] coating. No build up of a pure TiO[sub 2] layer is apparent. The data agree quantitatively with the critical concentration previously reported by ORNL for materials produced by ion implantation and characterized by Rutherford Backscattering Spectrometry and Photoacoustic Spectrometry. The study has brought a better understanding of the degradation process in electrodes of great technological importance, and has given a more solid background in designing new fabrication procedures for improved electrodes.

Vallet, C.E. [Oak Ridge National Lab., TN (United States); Tilak, B.V. [Occidental Chemical Corp., Niagara Falls, NY (United States)

1996-06-01

349

Rutherford backscattering analysis of the failure of chlorine anodes  

SciTech Connect

Rutherford Backscattering Spectrometry, carried out at the ORNL Surface Modification And Characterization Collaborative Research Center (SMAC) facility, has been applied to the nondestructive analysis of Ru02-Ti02 electrodes of 5000A, which mimic the DSA anodes in composition and the method of preparation. Occidental Chemical Corporation provided electrodes, which had been subjected to lifetime testing in H2S04 solution, for analysis by ORNL. The results were used to test the hypothesis of degradation of these, and similar electrodes, from a process involving a decrease in the Ru02:Ti02 ratio at and near the electrode surface and the related decrease in the electrode electrical conductivity. The drop in electrode activity is closely linked to a decrease in Ru content, and the measured profiles show that the loss takes place across the thin Ru02-Ti02 coating. No buildup of a pure Ti02 layer is apparent. The data agree quantitatively with the critical concentration previously reported by ORNL for materials produced by ion implantation and characterized by Rutherford Backscattering Spectrometry and Photoacoustic Spectrometry. The study has brought a better understanding of the degradation process in electrodes of great technological importance, and has given a more solid background in designing new fabrication procedures for improved electrodes.

Tilak, B.V.; Vallet, C.E.

1996-06-01

350

Investigation of microwave backscatter from the air-sea interface  

NASA Technical Reports Server (NTRS)

Monitoring the ocean surface winds and mean ocean surface level is essential for improving our knowledge of the climate. Two instruments that may provide us with this information are satellite-based scatterometers and altimeters. However, these instruments measure the backscatter characteristics of the ocean surface from which other physical parameters, such as the wind speed or ocean surface height, are derived. To improve the algorithms or models that relate the electromagnetic backscatter to the desired physical parameters, the University of Massachusetts (UMass) Microwave Remote Sensing Laboratory (MIRSL) designed and fabricated three airborne scatterometers: a C-band scatterometer (CSCAT), Ku-band scatterometer (KUSCAT) and C/Ku-band scatterometer (EMBR). One or more of these instruments participated in the Electromagnetic Bias experiment (EM Bias), Shelf Edge Exchange Processes experiment (SEEP), Surface Wave Dynamics Experiment (SWADE), Southern Ocean Wave Experiment (SOWEX), Hurricane Tina research flights, Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE), and Ladir In-space Technology Experiment (LITE). This document describes the three scatterometers, summarizes our measurement campaigns and major contributions to the scientific and engineering communities, lists the publications that resulted, and presents the degrees earned under the support of this NASA grant.

Mcintosh, Robert E.; Carswell, James R.

1995-01-01

351

Particle characterisation in highly concentrated dispersions using ultrasonic backscattering method.  

PubMed

Determining particle size and concentration in highly concentrated suspensions and emulsions is challenging, especially under process conditions. In general, ultrasound therefore can be used for particle characterisation due to the ability of sound waves to pass opaque dispersions, whereas optical detection principles mostly are limited to low particulate contents. An established acoustic method, the ultrasonic attenuation spectroscopy, uses a transmission setup for measuring the attenuation of a dispersion. A major drawback of this measurement method is caused by the fact, that the measuring gap tends to plug, which again limits the inline capability. To overcome this limitation, an ultrasonic reflection setup is used for gathering the sound waves, which are reflected, respectively backscattered by the dispersion. Statistically analysing the corresponding backscattering signal yields the sound attenuation as well as a scattering intensity equivalent. Both measurement parameters can be shown to be sensitive against particle size and concentration. Based on a single scattering theory, a semi-empirical approach is presented for interpretation of measurement results with respect to particle size and concentration. Measurements, performed on a glass beads in water dispersion, show good agreement with theory for dimensionless wave number 0.1

Weser, Robert; Wöckel, Sebastian; Wessely, Benno; Hempel, Ulrike

2013-03-01

352

Control of collective FSBS and backscatter SRS through plasma composition  

NASA Astrophysics Data System (ADS)

Nominal NIF parameters are near the collective forward SBS (FSBS) threshold (P. M. Lushnikov and H. A. Rose, Phys. Rev. Lett. 92, 255003 (2004), ``L&R''). It will be shown that being on this instability edge can be used as a control lever: a small amount of high Z dopant may lead to qualitative change in FSBS regime at fixed laser intensity, possibly reducing backscatter instability losses (Such results have already been observed, but absent SSD, a key aspect of our theory: R. M. Stevenson et al., Phys. Plasmas 11, 2709 (2004); L. J. Suter et al., 2738, ib.). Ponderomotive FSBS regimes are determined by the parameter I=F^2( vosc / vosc ve . - ve )^2( ne / ne nc . - nc ) / ( ne / ne nc . - nc ) ? . - ?, with ? the dimensionless ion acoustic damping coefficient and F the optic f/#. Analytical results will be presented which show a decrease of I1pt's threshold value through the addition of high Z dopant to low Z plasma, owing to increased thermal contribution to FSBS. Alternatively, one may raise the threshold by managing the value of ?by, e.g., adding He to SiO2. For nominal NIF parameters, a range of He fraction in SiO2 plasma is predicted to suppress backscatter SRS while maintaining control of forward SBS.

Rose, Harvey; Lushnikov, Pavel

2005-10-01

353

X-band microwave backscattering from ocean waves  

SciTech Connect

Backscattering experiments at microwave frequencies were conducted off the west coast of Scotland in the summer of 1991. Using a dual-polarization, 8-frequency X-band coherent scatterometer mounted on the bow of a boat, we measured time-resolved backscattering from ocean waves at a range of grazing angles from 10{degrees} to 70{degrees}. From the grazing-angle-dependent signals and their Doppler spectra, we differentiate Bragg scattering from non-Bragg scattering and resolve ``peak separation`` between the vertical and horizontal polarizations. We observe instances of ``super`` events, i.e., instances when the horizontal polarization return power equals or exceeds the vertical polarization power. We find that ``super`` events occur not only at low grazing angles but at any grazing angle for against-wind viewing directions. Statistics for such occurrences as a function of grazing angle are obtained. We study the coherence properties of scatterers and find strong evidence that at low grazing angles, lifetime-dominated, non-Bragg scattering contributes noticeably to returns of both polarizations, but is dominant in providing returns for the horizontal polarization. We examine ``spiking`` events and find that they can be related to, but need not be limited to, breaking wave events. By comparing the data of against-wind runs with cross-wind and circle runs, we obtain wind-direction dependence of Doppler spectra which further assists in the identification of scattering mechanisms.

Lee, P.H.Y.; Barter, J.D.; Beach, K.L. [TRW Space and Electronics Group, Redondo Beach, CA (United States)] [and others

1994-01-04

354

Backscattering measuring system for optimization of intravenous laser irradiation dose  

NASA Astrophysics Data System (ADS)

Intravenous laser blood irradiation as an effective method of biostimulation and physiotherapy becomes a more popular procedure. Optimal irradiation conditions for each patient are needed to be established individually. A fiber optics feedback system combined with conventional intravenous laser irradiation system was developed to control of irradiation process. The system consists of He-Ne laser, fiber optics probe and signal analyzer. Intravenous blood irradiation was performed in 7 healthy volunteers and 19 patients with different diseases. Measurements in vivo were related to in vitro blood irradiation which was performed in the same conditions with force-circulated venous blood. Comparison of temporal variations of backscattered light during all irradiation procedures has shown a strong discrepancy on optical properties of blood in patients with various health disorders since second procedure. The best cure effect was achieved when intensity of backscattered light was constant during at least five minutes. As a result, the optical irradiation does was considered to be equal 20 minutes' exposure of 3 mW He-Ne laser light at the end of fourth procedure.

Rusina, Tatyana V.; Popov, V. D.; Melnik, Ivan S.; Dets, Sergiy M.

1996-11-01

355

Discriminant classification of different fish-species backscattering  

NASA Astrophysics Data System (ADS)

The complex structure of fish and multispecies composition complicate the analysis of acoustic data. Consequently, it is difficult to obtain a highly accurate rate of classification by using current approaches. This paper introduces two discriminating methods: the adaptive segmentation temporal centroid method and the wavelet packet multi-scale information entropy method. To verify and compare these two methods, an ex situ experiment has been performed with three kinds of fish: Crucian carp (Carassius auratus), Yellow-headed catfish (Pelteobagrus fulvidraco) and Bluntnose black bream (Megalobrama amblycephale). The backscattering signals of these fishes are obtained. Then the temporal centroid in the divided sub-segmentation of the backscattering envelope is calculated, and the multi-scale information entropy of the wavelet packet decomposition in different frequency bands is extracted. Finally, three kinds of fish are successfully classified by using a BP neural network. The result shows that the adaptive segmentation temporal centroid method is 4% more accurate than the wavelet packet multi-scale information entropy method.

Zhang, Qiao; Xu, Feng; Liu, Yin; Zhang, Chun

2012-11-01

356

Microstructure Characterization in Cement Paste Using Backscattered Diffuse Ultrasound  

NASA Astrophysics Data System (ADS)

In this paper, the quantitative ultrasound technique (QUS) technique is applied to characterize voids in cement paste. Experiments are conducted on two series of cement paste specimens: a pair of regular samples with two levels of capillary porosity and a pair of air entrained samples with two concentrations of bubbles. The specimens are placed in a water tank and scanned at 5 MHz in pulse-echo mode. Velocity, attenuation, transmission coefficient and backscattering cross section are measured. Then, several models are used to estimate the parameters of the microstructure from the backscattered energy. Finally, the microstructure is analyzed from digital images. In the air-entrained samples, the mean scatterer size is correctly estimated and a clear difference in the acoustic concentration is observed in both samples, although this difference is higher than expected. In regular cement paste, the ultrasonically estimated scatterer size is too high to correspond to capillary pores. In this case, the scattered energy may originate from clumps of flocculated cement paste.

Goueygou, M.; Popovics, J.; Hall, K.; Oelze, M.; Lafhaj, Z.

2009-03-01

357

Generation of Attosecond pulse train by Self - Thomson Backscattering  

NASA Astrophysics Data System (ADS)

A scheme is investigated to generate the attosecond pulse train by nonlinear Thomson backscattering of a ultra-intense laser from counter propagating electron sheets. The process is termed as Self- Thomson Backscattering since the counter propagating electron sheets are generated by the laser itself. The radiation pressure acceleration model is considered for the interaction of a super-intense linearly polarized laser pulse with a thin foil in one-dimensional (1D) PIC simulations. At extremely high laser intensities radiation reaction (RR) effects become increasingly important as RR can be the dominant force acting on electrons [1]. The RR force is included in PIC simulation via the Landau-Lifshitz approach [2]. It is found that the reflected attosecond pulse train is intensified twice by inclusion of RR effects.[4pt] [1] L. D. Landau and E. M. Lifshitz, The Classsical Theory of Fields 2^nd edn (Oxford: Elsevier, 1975). [0pt] [2] M. Tamburini, F. Pegoraro, A. Di Piazza, C. H. Keitel and A. Macchi, New J. Phys. 12, 123005 (2010).

Sharma, Ashutosh; Keitel, C. H.; di Piazza, Antonino

2011-11-01

358

Extinction and backscatter cross sections of biological materials  

NASA Astrophysics Data System (ADS)

Aerosol backscatter and extinction cross-sections are required to model and evaluate the performance of both active and passive detection systems. A method has been developed that begins with laboratory measurements of thin films and suspensions of biological material to obtain the complex index refraction of the biological material from the UV to the LWIR. Using that result with particle size distribution and shape information as inputs to T-matrix or discrete dipole approximation (DDA) calculations yields the extinction cross-section and backscatter cross section as a function of wavelength. These are important inputs to the lidar equation. In a continuing effort to provide validated optical cross-sections, measurements have been made on a number of high purity biological species in the laboratory as well as measurements of material released at recent field tests. The resulting observed differences between laboratory and field measurements aid in distinguishing between intrinsic and extrinsic effects, which can affect the characteristic signatures of important biological aerosols. A variety of biological and test aerosols are examined, including Bacillus atrophaeus (BG), and Erwina, ovalbumin, silica and polystyrene.

Thomas, M. E.; Hahn, D. V.; Carr, A. K.; Limsui, D.; Carter, C. C.; Boggs, N. T.; Jackman, J.

2008-04-01

359

Radar Backscatter Saturation with Forest Biomass: Facts and Myths  

NASA Astrophysics Data System (ADS)

In recent years, climate change policies and scientific research created a widespread interest in quantify the carbon stock and changes of global forests extending from forest patches to national and regional scales. However, because of the large spatial extent of forests, their heterogeneity from structural and species diversity causing meters to kilometer scales variations, their complex dynamics causing landscape scale differences in changes of biomass, and their continues degradation from human activities, the quantification of forest biomass from conventional inventory data alone has become a major challenge. Remote sensing techniques with Lidar and Radar are considered to be the most efficient way of estimating forest biomass at large scales and with uncertainty comparable to estimation from inventory plots. Radar backscatter and interferometric based estimation of forest biomass has been studied extensively and considered as dedicated spaceborne options of monitoring and quantifying forest biomass. However, the literature on the radar-based estimation techniques of biomass has been misleading in defining the sensitivity and lack of sensitivity, so called saturation effect of radar measurements. In this paper, I provide results from a combination of observations and model simulations to demonstrate the physical nature of the loss of sensitivity of radar backscatter to biomass, examine the biophysical that impact the sensitivity, extend the results to other radar measurements including polarimetric and interferometric modes.

Saatchi, S. S.

2012-12-01

360

Combinatorial investigation of structural quality of Au\\/Ni contacts on GaN  

Microsoft Academic Search

A combinatorial library of Au\\/Ni metallizations on GaN was microstructurally characterized by X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The array of single- and bi-layered metal elements of systematically varying thicknesses was deposited by electron-beam evaporation on a GaN\\/c-sapphire wafer. The elements with a single layer of Au on GaN had a fiber texture with

A. V. Davydov; L. A. Bendersky; W. J. Boettinger; D. Josell; M. D. Vaudin; K.-S. Chang; I. Takeuchi

2004-01-01

361

Analysis of Electromagnetic Backscattering from Rotational Flat Blades  

E-print Network

to employ physical theory of diffraction (PTD)-equivalent currents method (ECM) to estimate RCS of three, Sun [3] proposed ECM. In 2002, Pouliguen [4] used PO/PTD and ECM to calculate scattered fields

Myung, Noh-Hoon

362

Computer Simulation of Diffraction Patterns.  

ERIC Educational Resources Information Center

Describes an Apple computer program (listing available from author) which simulates Fraunhofer and Fresnel diffraction using vector addition techniques (vector chaining) and allows user to experiment with different shaped multiple apertures. Graphics output include vector resultants, phase difference, diffraction patterns, and the Cornu spiral…

Dodd, N. A.

1983-01-01

363

Color Perception with Diffraction Gratings.  

ERIC Educational Resources Information Center

Describes an experiment enabling students to apply concept of diffraction, determine limits of their color perception, learn how to measure wavelength with a simple apparatus, observe continuous and line spectra, and associate colors with corresponding wavelengths. The homemade diffraction-grating spectrometer used is easily constructed. (JN)

Kruglak, Haym; Campbell, Don

1983-01-01

364

Diffraction: the first recorded observation  

Microsoft Academic Search

The discovery of diffraction by Francesco Maria Grimaldi is described. He described the experiments that led to its discovery in the book De Lumine, first published in 1665, two years after Grimaldi's death. Grimaldi's life and his experimental observations are described. Newton's disregard of Grimaldi's work and substitution of the word inflexion for diffraction are discussed

R. Cecchini; G. Pelosi

1990-01-01

365

Multiresolution of quasicrystal diffraction spectra.  

PubMed

A method for analyzing and classifying two-dimensional pure point diffraction spectra (i.e. a set of Bragg peaks) of certain self-similar structures with scaling factor beta > 1, such as quasicrystals, is presented. The two-dimensional pure point diffraction spectrum Pi is viewed as a point set in the complex plane in which each point is assigned a positive number, its Bragg intensity. Then, by using a nested sequence of self-similar subsets called beta-lattices, we implement a multiresolution analysis of the spectrum Pi. This analysis yields a partition of Pi simultaneously in geometry, in scale and in intensity (the 'fingerprint' of the spectrum, not of the diffracting structure itself). The method is tested through numerical explorations of pure point diffraction spectra of various mathematical structures and also with the diffraction pattern of a realistic model of a quasicrystal. PMID:19844031

Elkharrat, Avi; Gazeau, Jean Pierre; Dénoyer, Françoise

2009-11-01

366

University of Salford Tutorials: Diffraction  

NSDL National Science Digital Library

This multimedia tutorial provides explanations and models of wave diffraction. It contains multiple images, animations, and interactive simulations designed to represent what happens when a wave encounters an obstacle. The tutorial begins by explaining how the amount of diffraction depends on the wavelength and the size of the object being encountered. It progresses to discussions of various diffraction effects, Huygen's Principle, and concludes with diffraction through two slits (a simulation of Young's classic experiment). This resource is part of a larger collection of multimedia tutorials on waves and acoustics. It was developed specifically to help learners visualize how waves of varying wavelength will diffract in predictable ways, and how this behavior is related to practical applications, like radio/TV broadcasting and acoustics.

367

Lidar aerosol backscatter cross sections in the 2-{mu}m near-infrared wavelength region  

SciTech Connect

Lidar backscatter cross-sectional measurements at 1.064, 0.532, and 1.54 {mu}m were acquired during November 1989 and May{endash}June 1990 around the Pacific region by the NASA DC-8 aircraft as part of the Global Backscatter Experiment. The primary motivation for the Global Backscatter Experiment was the study of lidar backscatter cross sections for the development of a spaceborne wind-sensing lidar. Direct backscatter measurements obtained by the NASA Goddard Space Flight Center visible and infrared lidar are compared with backscatter cross sections calculated from aerosol size distributions obtained by particle counters. Results for one flight with pronounced aerosol layers in the upper troposphere southeast of Japan are presented. Because 2-{mu}m region wavelengths are possible candidates for a spaceborne wind-sensing lidar, the visible and infrared lidar backscatter cross sections at 1.064, 0.532, and 1.54 {mu}m are extrapolated to the 2-{mu}m region. The extrapolated 2-{mu}m cross sections are compared with lidar measurements at 9 {mu}m. A significant range in the ratio of 2{endash}9-{mu}m backscatter cross sections is found, but a large number of points concentrate near ratios of three to ten. A large number of 1.064- and 1.54-{mu}m cross sections were binned to provide an estimate of backscatter for various percentiles for the flight. The ratio of the 50-percentile backscatter values at 1.064 and 1.54 {mu}m suggest a {lambda}{sup {minus}1.9} to {lambda}{sup {minus}3.0} wavelength dependence of aerosol backscatter cross section in the near infrared for the observational case. {copyright} {ital 1996 Optical Society of America.}

Chudamani, S. [Science Systems Applications, Inc., Lanham, Maryland 20706 (United States); Spinhirne, J.D. [Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Clarke, A.D. [Department of Oceanography, University of Hawaii, Honolulu, Hawaii 96822 (United States)

1996-08-01

368

Lidar aerosol backscatter cross sections in the 2-?m near-infrared wavelength region.  

PubMed

Lidar backscatter cross-sectional measurements at 1.064, 0.532, and 1.54 ?m were acquired during November 1989 and May-June 1990 around the Pacific region by the NASA DC-8 aircraft as part of the Global Backscatter Experiment. The primary motivation for the Global Backscatter Experiment was the study of lidar backscatter cross sections for the development of a spaceborne wind-sensing lidar. Direct backscatter measurements obtained by the NASA Goddard Space Flight Center visible and infrared lidar are compared with backscatter cross sections calculated from aerosol size distributions obtained by particle counters. Results for one flight with pronounced aerosol layers in the upper troposphere southeast of Japan are presented. Because 2-?m region wavelengths are possible candidates for a spaceborne wind-sensing lidar, the visible and infrared lidar backscatter cross sections at 1.064, 0.532, and 1.54 ?m are extrapolated to the 2-?m region. The extrapolated 2-?m cross sections are compared with lidar measurements at 9 ?m. A significant range in the ratio of 2-9-?m backscatter cross sections is found, but a large number of points concentrate near ratios of three to ten. A large number of 1.064- and 1.54-?m cross sections were binned to provide an estimate of backscatter for various percentiles for the flight. The ratio of the 50-percentile backscatter values at 1.064 and 1.54 ?m suggest a ?(-1.9) to ?(-3.0) wavelength dependence of aerosol backscatter cross section in the near infrared for the observational case. PMID:21102906

Chudamani, S; Spinhirne, J D; Clarke, A D

1996-08-20

369

Anisotropic and Heterogeneous Development of Microstructures. Combining Laboratory/Synchrotron X-rays and EBSD on a few SPD Metallic Systems  

NASA Astrophysics Data System (ADS)

The onset of Severe Plastic Deformation (SPD) regime is quite instructive on the possible origins of the nano-microstructures developed in metals and alloys. It is known that grain fragmentation and dislocation accumulation, among other defects, proceed at different paces depending fundamentally on grain orientations and active deformation mechanisms. There have been many attempts to characterize nano-microstructure anisotropy, leading all of them to sometimes contradictory conclusions. Moreover, the characterizations rely on different measurements techniques and pos-processing approaches, which can be observing different manifestations of the same phenomena. On the current presentation we show a few experimental and computer pos-processing and simulation approaches, applied to some SPD/alloy systems. Williamson-Hall and Convolutional Multiple Whole Profile (CMWP) techniques will be applied to peak broadening analysis on experimental results stemming from laboratory Cu Ka X-rays, and synchrotron radiation from LNLS (Laboratório Nacional de Luz Síncrotron, Campinas, Brazil) and Petra III line (HEMS station, at DESY, Hamburg, Germany). Taking advantage of the EBSD capability of giving information on orientational and topological characteristics of grain boundaries, microstructures, grain sizes, etc., we also performed investigations on dislocation density and Geometrically Necessary Dislocation Boundaries (GNDB) and their correlation with texture components. Orientation dependent nano-microstructures and domain sizes are shown on the scheme of generalized pole figures and discussions provide some hints on nano-microstructure anisotropy.

Bolmaro, Raúl E.; De Vincentis, Natalia S.; Benatti, Emanuel; Kliauga, Andrea M.; Avalos, Martina C.; Schell, Norbert; Brokmeier, Heinz-Günter

2014-08-01

370

Kinematics of Compton backscattering x-ray source for angiography  

SciTech Connect

Calculations of X-Ray production rates, energy spread, and spectrum of Compton-backscattered photons from a Free Electron Laser on an electron beam in a low energy (136-MeV) compact (8.5-m circumference) storage ring indicate that an X-Ray intensity of 34.6 10{sup 7} X-Ray photons per 0.5-mm {times} 0.5-mm pixel for Coronary Angiography near the 33.169-keV iodine K-absorption edge can be achieved in a 4-msec pulse within a scattering cone of 1-mrad half angle. This intensity, at 10-m from the photon-electron interaction point to the patient is about a factor of 10 larger than presently achieved from a 4.5-T superconducting wiggler source in the NSLS 2.5-GeV storage ring and over an area about 5 times larger. The 2.2-keV energy spread of the Compton-backscattered beam is, however, much larger than the 70-eV spread presently attained form the wiggler source and use of a monochromator. The beam spot at the 10-m interaction point-to-patient distance is 20-mm diameter; larger spots are attainable at larger distances but with a corresponding reduction in X-Ray flux. Such a facility could be an inexpensive clinical alternative to present methods of non-invasive Digital Subtraction Angiography (DSA), small enough to be deployed in an urban medical center, and could have other medical, industrial and aerospace applications. Problems with the Compton backscattering source include laser beam heating of the mirror in the FEL oscillator optical cavity, achieving a large enough X-Ray beam spot at the patient, and obtaining radiation damping of the transverse oscillations and longitudinal emittance dilution of the storage ring electron beam resulting from photon-electron collisions without going to higher electron energy where the X-Ray energy spread becomes excessive for DSA. 38 refs.

Blumberg, L.N.

1992-05-01

371

A WIND AND RAIN BACKSCATTER MODEL DERIVED FROM AMSR AND SEAWINDS DATA  

E-print Network

. In this thesis, a new wind and rain radar backscatter model is developed for the SWR algorithm using a global co weather prediction winds. The new SWR algorithm produces accurate rain estimates and detects rainA WIND AND RAIN BACKSCATTER MODEL DERIVED FROM AMSR AND SEAWINDS DATA by Seth N. Nielsen A thesis

Long, David G.

372

Estimation of Specific Differential Phase and Differential Backscatter Phase From Polarimetric Weather Radar Measurements of Rain  

Microsoft Academic Search

The estimation of the specific differential phase par- ticularly in the presence of the differential backscatter phase and nonuniform propagation paths is a long-standing goal in weather radar polarimetry. Furthermore, a reliable estimator of the differential backscatter phase for precipitation measure- ments has not been proposed yet, although it contains valuable information about the presence of non-Rayleigh scattering and the

Tobias Otto; Herman W. J. Russchenberg

2011-01-01

373

Influence of particle size and concentration on the diffuse backscattering of polarized light from  

E-print Network

Influence of particle size and concentration on the diffuse backscattering of polarized light from-backscattered intensity when linearly polarized light is incident upon highly scattering media. Experiments on polystyrene for cell characterization. © 1997 Optical Society of America Key words: Polarization, multiple scattering

Bigio, Irving J.

374

Modelling the Backscatter Response of Different Zones Within a Polar Glacier  

Microsoft Academic Search

In order to better quantify the causes of backscatter in glaciers, we model the backscatter response of a polar glacier to C-band GPR imaging. The motivation for such modeling is the need to develop improved algorithms for glacier parameter retrieval from SAR data, including snow facies type, accumulation rate, etc.. These efforts require a better understanding of C-band scattering mechanisms

K. Langley; K. Meuller; O. Brandt; E. Hamran

2005-01-01

375

Toward Hyperspectral Lidar: Measurement of Spectral Backscatter Intensity With a Supercontinuum Laser Source  

Microsoft Academic Search

We have tested the use of a supercontinuum laser source in laser-based spectral backscatter measurement. The calibration and first results with the prototype instrument are presented with a discussion of improvements and applications in laser-based hyperspectral remote sensing and laboratory measurements. This technique enables the spectral study of the backscatter effects and the calibration and test measurements for the purpose

Sanna Kaasalainen; Tomi Lindroos; Juha Hyyppa

2007-01-01

376

Coherent light backscattering by refractive turbulence in lidar sounding of the atmosphere and the ocean  

Microsoft Academic Search

Theoretical analysis of light waves backscattering by a layer of random medium with weak refractive index fluctuations is presented, and some estimates for the effect contribution to lidar signals in atmospheric and ocean remote sounding are given. It is shown that coherent light backscattering by a thin turbulent layer may be strong enough compared with incoherent component caused by dispersed

Yurij I. Kopilevich

1995-01-01

377

An Agroecological Modeling Approach to Explain ERS SAR Radar Backscatter of Agricultural Crops  

Microsoft Academic Search

An agroecological approach is presented to simulate time series of ERS SAR radar backscatter of agricultural crops from integrated crop growth (SUCROS), water balance (SAHEL), and radar backscatter (Cloud) modeling. SUCROS is used to calculate the amount of water in canopies and SAHEL the amount of water in the top soil, which serve both as driving variables for the Cloud

B. A. M. Bouman; D. W. G. van Kraalingen; W. Stol; H. J. C. van Leeuwen

1999-01-01

378

Identification of major backscattering sources in trees and shrubs at 10 GHz  

NASA Technical Reports Server (NTRS)

A short-range very-fine-resolution FM-CW radar scatterometer has been used to identify the primary contributors to 10-GHz radar backscatter from pine, pin oak, American sycamore and sugar maple trees, and from creeping juniper shrubs. This system provided a range resolution of 11 cm and gave a 16-cm diameter illumination area at the target range of about 4 m. For a pine tree, the needles caused the strongest backscatter as well as the strongest attenuation in the radar signal. Cones, although insignificant contributors to the total backscatter, were more important for backscattering than for attenuation. For the rest of the trees, leaves were the strongest cause of backscattering and attenuation. However, in the absence of leaves, the petioles, small twigs, and branches gave relatively strong backscatter. For American sycamore and sugar maple trees, the fruits did not affect the total backscatter unless they were packed in clusters. For creeping juniper the backscattered energy and attenuation in the radar signal were mainly due to the top two layers of the evergreen scales. The contribution of the tree trunks was not determined.

Zoughi, R.; Wu, L. K.; Moore, R. K.

1986-01-01

379

Multiple Backscattering and Depolarization from Water Clouds for a Pulsed Lidar System  

Microsoft Academic Search

A computational approach for the multiple backscattering from spherical cloud droplets for a collimated pulsed radar system has been developed, based on the geometry of the system. The radiative transfer relationships include a complete set of Stokes' parameters. The depolarization ratio of the multiple backscattering from a volume of spherically symmetrical and uniformly distributed water drops is obtained.Calculations are performed

Kuo-Nan Liou; Richard M. Schotland

1971-01-01

380

Measurement of intrinsic optical backscattering characteristics of cells using fiber-guided near infrared light  

Microsoft Academic Search

BACKGROUND: Intrinsic optical signals (IOS), which reflect changes in transmittance and scattering light, have been applied to characterize the physiological conditions of target biological tissues. Backscattering approaches allow mounting of the source and detector on the same side of a sample which creates a more compact physical layout of device. This study presents a compact backscattering design using fiber-optic guided

Ching-Huang Hsu; Gwo-Ching Chang; En-Ting Li; Yu-Jing Lin; Jia-Jin Jason Chen

2010-01-01

381

Experimental results and Monte Carlo simulations of a landmine localization device using the neutron backscattering method  

Microsoft Academic Search

Experiments were carried out to investigate the possible use of neutron backscattering for the detection of landmines buried in the soil. Several landmines, buried in a sand-pit, were positively identified. A series of Monte Carlo simulations were performed to study the complexity of the neutron backscattering process and to optimize the geometry of a future prototype. The results of these

C. P. Datema; V. R. Bom; C. W. E. van Eijk

2002-01-01

382

Low-coherence enhanced backscattering: review of principles and applications for colon cancer screening  

E-print Network

Low-coherence enhanced backscattering: review of principles and applications for colon cancer the risk of colon carcinogenesis and colonoscopy-free screening for colorectal cancer CRC . © 2006 Society; enhanced backscattering; low coherence; elas- tic light scattering; spectroscopy; colorectal cancer. Paper

Ottino, Julio M.

383

Combining angular response classification and backscatter imagery segmentation for benthic biological habitat mapping  

NASA Astrophysics Data System (ADS)

Backscatter information from multibeam echosounders (MBES) have been shown to contain useful information for the characterisation of benthic habitats. Compared to backscatter imagery, angular response of backscatter has shown advantages for feature discrimination. However its low spatial resolution inhibits the generation of fine scale habitat maps. In this study, angular backscatter response was combined with image segmentation of backscatter imagery to characterise benthic biological habitats in Discovery Bay Marine National Park, Victoria, Australia. Angular response of backscatter data from a Reson Seabat 8101 MBES (240 kHz) was integrated with georeferenced underwater video observations for constructing training data. To produce benthic habitat maps, decision tree supervised classification results were combined with mean shift image segmentation for class assignment. The results from mean angular response characteristics show effects of incidence angle at the outer angle for invertebrates (INV) and mixed red and invertebrates (MRI) classes, whilst mixed brown algae (MB) and mixed brown algae and invertebrates (MBI) showed similar responses independent from incidence angle. Automatic segmentation processing produce over segmented results but showed good discrimination between heterogeneous regions. Accuracy assessment from habitat maps produced overall accuracies of 79.6% (Kappa coefficient = 0.66) and 80.2% (Kappa coefficient = 0.67) for biota and substratum classifications respectively. MRI and MBI produced the lowest average accuracy while INV the highest. The ability to combine angular response and backscatter imagery provides an alternative approach for investigating biological information from acoustic backscatter data.

Che Hasan, Rozaimi; Ierodiaconou, Daniel; Laurenson, Laurie

2012-01-01

384

Hard diffraction -- 20 years later  

E-print Network

The idea of diffractive processes with a hard scale involved, to resolve the underlying parton dynamics, was published 1985 and experimentally verified 1988. Today hard diffraction is an active research field with high-quality data and new theoretical models. The trend from Regge-based pomeron models to QCD-based parton level models has given insights on QCD dynamics involving perturbative gluon exchange mechanisms, including the predicted BFKL-dynamics, as well as novel ideas on non-perturbative colour fields and their interactions. Extrapolations to the LHC include the interesting possibility of diffractive Higgs production.

Gunnar Ingelman

2005-12-12

385

Compton backscattering for the calibration of KEDR tagging system  

NASA Astrophysics Data System (ADS)

KEDR detector has the tagging system (TS) to study the gamma-gamma processes. To determine the two-photon invariant mass, the energies of the scattered at small angles electrons and positrons are measured by the magnetic spectrometer embedded into the lattice of the VEPP-4M collider. The energy resolution (scattered electron/positron energy resolution divided by the beam energy) of this spectrometer varies from 0.6% to 0.03% depending on the electron/positron energy. The Compton backscattering of laser radiation on the electron/positron beam is used for the accurate energy scale and resolution calibration of the tagging system. The report covers the design, recent results and current status of the KEDR TS calibration system.

Kaminskiy, V. V.; Muchnoi, N. Yu; Zhilich, V. N.

2014-08-01

386

Unusual Radar Backscatter along the Northern Rim of Imbrium Basin  

NASA Technical Reports Server (NTRS)

A viewgraph presentation of the unusual radar backscatter properties along the Northern Rim of Imbrium Basin is shown. The contents include: 1) Visual and Infrared Observations of Moon; 2) Radar Observations of Moon; 3) Lunar Orbiter Photographs Geologic Setting; 4) 70-cm Radar Data; 5) .70-cm Radar Dark Halo Craters; 6) 3.8-cm Radar Data; 7) 7.5-m Radar Data; 8) 70cm, 3.8 cm and 7.5-m Radar Data; 9) Optical and Infrared Data; 10) Plato Rilles; 11) Isopachs of Crater Ejecta; 12) Plato-like Craters; 13) Observation Summary; 14) Interpretation Matrix; 15) Dark Halo Diameters vs. Crater Size; and 16) Radar Geologic Column.

Thompson, Thomas W.; Campbell, Bruce A.; Ghent, Rebecca R.; Hawke, B. Ray; Leverington, David W.

2006-01-01

387

Electromagnetic backscattering from a random distribution of lossy dielectric scatterers  

NASA Technical Reports Server (NTRS)

Electromagnetic backscattering from a sparse distribution of discrete lossy dielectric scatterers occupying a region 5 was studied. The scatterers are assumed to have random position and orientation. Scattered fields are calculated by first finding the mean field and then by using it to define an equivalent medium within the volume 5. The scatterers are then viewed as being embedded in the equivalent medium; the distorted Born approximation is then used to find the scattered fields. This technique represents an improvement over the standard Born approximation since it takes into account the attenuation of the incident and scattered waves in the equivalent medium. The method is used to model a leaf canopy when the leaves are modeled by lossy dielectric discs.

Lang, R. H.

1980-01-01

388

Results from the Daresbury Compton backscattering X-ray source  

NASA Astrophysics Data System (ADS)

The Daresbury Compton Backscattering X-ray Source uses a high power Ti Sapphire laser interacting in head on geometry with electron bunches in the ALICE energy recovery linear accelerator. X-ray photons with peak energy of 21 keV were generated with the accelerator operating at an energy of 29.6 MeV. The spatial profile of the X-rays emitted near the electron beam axis was measured. The characteristics of the X-ray yield measured as a function of relative timing between the laser pulse and the interacting electron bunch was found to be consistent with the modelled intensity behaviour using measured electron and laser beam parameters.

Laundy, D.; Priebe, G.; Jamison, S. P.; Graham, D. M.; Phillips, P. J.; Smith, S. L.; Saveliev, Y.; Vassilev, S.; Seddon, E. A.

2012-10-01

389

Post-image acquisition processing approaches for coherent backscatter validation  

NASA Astrophysics Data System (ADS)

Utilizing a retro-reflector from a target point, the reflected irradiance of a laser beam traveling back toward the transmitting point contains a peak point of intensity known as the enhanced backscatter (EBS) phenomenon. EBS is dependent on the strength regime of turbulence currently occurring within the atmosphere as the beam propagates across and back. In order to capture and analyze this phenomenon so that it may be compared to theory, an imaging system is integrated into the optical set up. With proper imaging established, we are able to implement various post-image acquisition techniques to help determine detection and positioning of EBS which can then be validated with theory by inspection of certain dependent meteorological parameters such as the refractive index structure parameter, Cn2 and wind speed.

Smith, Christopher A.; Belichki, Sara B.; Coffaro, Joseph T.; Panich, Michael G.; Andrews, Larry C.; Phillips, Ronald L.

2014-10-01

390

Snow backscatter in the 1-8 GHz region  

NASA Technical Reports Server (NTRS)

The 1-8 GHz microwave active spectrometer system was used to measure the backscatter response of snow covered ground. The scattering coefficient was measured for all linear polarization combinations at angles of incidence between nadir and 70 deg. Ground truth data consisted of soil moisture, soil temperature profile, snow depth, snow temperature profile, and snow water equivalent. The radar sensitivity to snow water equivalent increased in magnitude with increasing frequency and was almost angle independent for angles of incidence higher than 30 deg, particularly at the higher frequencies. In the 50 deg to 70 deg angular range and in the 6 to 8 GHz frequency range, the sensitivity was typically between -0.4 dB/.1 g/sq cm and -0.5 dB/,1 g/sq cm, and the associated linear correlation coefficient had a magnitude of about 0.8.

Ulaby, F. T.

1976-01-01

391

Ocean Raman Scattering in Satellite Backscatter UV Measurements  

NASA Technical Reports Server (NTRS)

Ocean Raman scattering significantly contributes to the filling-in of solar Fraunhofer lines measured by satellite backscatter ultraviolet (buy) instruments in the cloudless atmosphere over clear ocean waters. A model accounting for this effect in buy measurements is developed and compared with observations from the Global Ozone Monitoring Experiment (GONE). The model extends existing models for ocean Raman scattering to the UV spectral range. Ocean Raman scattering radiance is propagated through the atmosphere using a concept of the Lambert equivalent reflectively and an accurate radiative transfer model for Rayleigh scattering. The model and observations can be used to evaluate laboratory measurements of pure water absorption in the UV. The good agreement between model and observations suggests that buy instruments may be useful for estimating chlorophyll content.

Vasilkov, Alexander P.; Joiner, Joanna; Gleason, James; Bhartia, Pawan; Bhartia, P. K. (Technical Monitor)

2002-01-01

392

Direct wavefront sensing in adaptive optical microscopy using backscattered light.  

PubMed

Adaptive optics has been used to compensate the detrimental effects of aberrations in a range of high-resolution microscopes. We investigate how backscattered laser illumination can be used as the source for direct wavefront sensing using a pinhole-filtered Shack-Hartmann wavefront sensor. It is found that the sensor produces linear response to input aberrations for a given specimen. The gradient of this response is dependent upon experimental configuration and specimen structure. Cross sensitivity between modes is also observed. The double pass nature of the microscope system leads in general to lower sensitivity to odd-symmetry aberration modes. The results show that there is potential for use of this type of wavefront sensing in microscopes. PMID:23913074

Rahman, Saad A; Booth, Martin J

2013-08-01

393

Enhanced backscatter of optical beams reflected in atmospheric turbulence  

NASA Astrophysics Data System (ADS)

Optical beams propagating through the atmosphere acquire phase distortions from turbulent fluctuations in the refractive index. While these distortions are usually deleterious to propagation, beams reflected in a turbulent medium can undergo a local recovery of spatial coherence and intensity enhancement referred to as enhanced backscatter (EBS). Using simulations, we investigate the EBS of optical beams reflected from mirrors, corner cubes, and rough surfaces, and identify the regimes in which EBS is most distinctly observed. Standard EBS detection requires averaging the reflected intensity over many passes through uncorrelated turbulence. Here we present an algorithm called the "tilt-shift method" which allows detection of EBS in static turbulence, improving its suitability for potential applications.

Nelson, W.; Palastro, J. P.; Wu, C.; Davis, C. C.

2014-10-01

394

Diffraction of short pulses with boundary diffraction wave theory.  

PubMed

The diffraction of short pulses is studied on the basis of the Miyamoto-Wolf theory of the boundary diffraction wave, which is a mathematical formulation of Young's idea about the nature of diffraction. It is pointed out that the diffracted field is given by the superposition of the boundary wave pulse (formed by interference of the elementary boundary diffraction waves) and the geometric (direct) pulse (governed by the laws of geometrical optics). The case of a circular aperture is treated in details. The diffracted field on the optical axis is calculated analytically (without any approximation) for an arbitrary temporal pulse shape. Because of the short pulse duration and the path difference the geometric and the boundary wave pulses appear separately, i.e., the boundary waves are manifested in themselves in the illuminated region (in the sense of geometrical optics). The properties of the boundary wave pulse is discussed. Its radial intensity distribution can be approximated by the Bessel function of zero order if the observation points are in the illuminated region and far from the plane of the aperture and close to the optical axis. Although the boundary wave pulse propagates on the optical axis at a speed exceeding c, it does not contradict the theory of relativity. PMID:11308595

Horváth, Z L; Bor, Z

2001-02-01

395

Backscattering and Nonparaxiality Arrest Collapse of Damped Nonlinear Waves  

NASA Technical Reports Server (NTRS)

The critical nonlinear Schrodinger equation (NLS) models the propagation of intense laser light in Kerr media. This equation is derived from the more comprehensive nonlinear Helmholtz equation (NLH) by employing the paraxial approximation and neglecting the backscattered waves. It is known that if the input power of the laser beam (i.e., L(sub 2) norm of the initial solution) is sufficiently high, then the NLS model predicts that the beam will self-focus to a point (i.e.. collapse) at a finite propagation distance. Mathematically, this behavior corresponds to the formation of a singularity in the solution of the NLS. A key question which has been open for many years is whether the solution to the NLH, i.e., the 'parent' equation, may nonetheless exist and remain regular everywhere, in particular for those initial conditions (input powers) that lead to blowup in the NLS. In the current study, we address this question by introducing linear damping into both models and subsequently comparing the numerical solutions of the damped NLH (boundary-value problem) with the corresponding solutions of the damped NLS (initial-value problem). Linear damping is introduced in much the same way as done when analyzing the classical constant-coefficient Helmholtz equation using the limiting absorption principle. Numerically, we have found that it provides a very efficient tool for controlling the solutions of both the NLH and NHS. In particular, we have been able to identify initial conditions for which the NLS solution does become singular. whereas the NLH solution still remains regular everywhere. We believe that our finding of a larger domain of existence for the NLH than that for the NLS is accounted for by precisely those mechanisms, that have been neglected when deriving the NLS from the NLH, i.e., nonparaxiality and backscattering.

Fibich, G.; Ilan, B.; Tsynkov, S.

2002-01-01

396

The Low Backscattering Targets Classification in Urban Areas  

NASA Astrophysics Data System (ADS)

The Polarimetric and Interferometric Synthetic Aperture Radar (POLINSAR) is widely used in urban area nowadays. Because of the physical and geometric sensitivity, the POLINSAR is suitable for the city classification, power-lines detection, building extraction, etc. As the new X-band POLINSAR radar, the china prototype airborne system, XSAR works with high spatial resolution in azimuth (0.1 m) and slant range (0.4 m). In land applications, SAR image classification is a useful tool to distinguish the interesting area and obtain the target information. The bare soil, the cement road, the water and the building shadow are common scenes in the urban area. As it always exists low backscattering sign objects (LBO) with the similar scattering mechanism (all odd bounce except for shadow) in the XSAR images, classes are usually confused in Wishart-H-Alpha and Freeman-Durden methods. It is very hard to distinguish those targets only using the general information. To overcome the shortage, this paper explores an improved algorithm for LBO refined classification based on the Pre-Classification in urban areas. Firstly, the Pre-Classification is applied in the polarimetric datum and the mixture class is marked which contains LBO. Then, the polarimetric covariance matrix C3 is re-estimated on the Pre-Classification results to get more reliable results. Finally, the occurrence space which combining the entropy and the phase-diff standard deviation between HH and VV channel is used to refine the Pre-Classification results. The XSAR airborne experiments show the improved method is potential to distinguish the mixture classes in the low backscattering objects.

Shi, L.

2012-07-01

397

Relating multifrequency radar backscattering to forest biomass: Modeling and AIRSAR measurement  

NASA Technical Reports Server (NTRS)

During the last several years, significant efforts in microwave remote sensing were devoted to relating forest parameters to radar backscattering coefficients. These and other studies showed that in most cases, the longer wavelength (i.e. P band) and cross-polarization (HV) backscattering had higher sensitivity and better correlation to forest biomass. This research examines this relationship in a northern forest area through both backscatter modeling and synthetic aperture radar (SAR) data analysis. The field measurements were used to estimate stand biomass from forest weight tables. The backscatter model described by Sun et al. was modified to simulate the backscattering coefficients with respect to stand biomass. The average number of trees per square meter or radar resolution cell, and the average tree height or diameter breast height (dbh) in the forest stand are the driving parameters of the model. The rest of the soil surface, orientation, and size distributions of leaves and branches, remain unchanged in the simulations.

Sun, Guo-Qing; Ranson, K. Jon

1992-01-01

398

Electrically-programmable diffraction grating  

DOEpatents

An electrically-programmable diffraction grating is disclosed. The programmable grating includes a substrate having a plurality of electrodes formed thereon and a moveable grating element above each of the electrodes. The grating elements are electrostatically programmable to form a diffraction grating for diffracting an incident beam of light as it is reflected from the upper surfaces of the grating elements. The programmable diffraction grating, formed by a micromachining process, has applications for optical information processing (e.g. optical correlators and computers), for multiplexing and demultiplexing a plurality of light beams of different wavelengths (e.g. for optical fiber communications), and for forming spectrometers (e.g. correlation and scanning spectrometers). 14 figs.

Ricco, A.J.; Butler, M.A.; Sinclair, M.B.; Senturia, S.D.

1998-05-26

399

X-Ray Diffraction Apparatus  

NASA Technical Reports Server (NTRS)

An x-ray diffraction apparatus for use in analyzing the x-ray diffraction pattern of a sample is introduced. The apparatus includes a beam source for generating a collimated x-ray beam having one or more discrete x-ray energies, a holder for holding the sample to be analyzed in the path of the beam, and a charge-coupled device having an array of pixels for detecting, in one or more selected photon energy ranges, x-ray diffraction photons produced by irradiating such a sample with said beam. The CCD is coupled to an output unit which receives input information relating to the energies of photons striking each pixel in the CCD, and constructs the diffraction pattern of photons within a selected energy range striking the CCD.

Blake, David F. (Inventor); Bryson, Charles (Inventor); Freund, Friedmann (Inventor)

1996-01-01

400

Quasi-diffraction-free beams.  

PubMed

A diffraction-free beam is obtained by the superposing of plane waves whose wave vectors make an angle with the propagation axis. These plane waves are realized with point sources that are distributed uniformly around a circle and an infinitely large aperture lens. After the field passes through the lens it has nondiffracting properties and is described by the zero-order Bessel function. Relaxing these conditions makes the beam diffraction free within only a limited region. The beam generated from such a geometry is referred to as a quasi-diffraction-free beam. The effects of the width of the annular source on the beam spread are discussed and compared with those for a Gaussian beam. Approximate expressions for quasi-diffraction-free beams are also obtained. PMID:11444556

Tanaka, K; Taguchi, M; Tanaka, T

2001-07-01

401

Diffractive dijet production in CDF  

SciTech Connect

We have studied events with a high-x{sub F} antiproton and two central jets in CDF, with p{anti p} collisions at {radical}s = 630 and 1800 GeV. These events are expected to be dominated by diffraction (pomeron exchange). The jet E{sub T} spectra are very similar to those of non-diffractively produced jets but slightly steeper; their azimuthal difference {Delta}{phi} is more peaked at 180{degree}.

Albrow, M.G.; CDF Collaboration

1998-04-17

402

Diffraction efficiency analysis for multi-level diffractive optical elements  

SciTech Connect

Passive optical components can be broken down into two main groups: Refractive elements and diffractive elements. With recent advances in manufacturing technologies, diffractive optical elements are becoming increasingly more prevalent in optical systems. It is therefore important to be able to understand and model the behavior of these elements. In this report, we present a thorough analysis of a completely general diffractive optical element (DOE). The main goal of the analysis is to understand the diffraction efficiency and power distribution of the various modes affected by the DOE. This is critical to understanding cross talk and power issues when these elements are used in actual systems. As mentioned, the model is based on a completely general scenario for a DOE. This allows the user to specify the details to model a wide variety of diffractive elements. The analysis is implemented straightforwardly in Mathematica. This report includes the development of the analysis, the Mathematica implementation of the model and several examples using the Mathematical analysis tool. It is intended that this tool be a building block for more specialized analyses.

Erteza, I.A.

1995-11-01

403

Detonation Diffraction into a Confined Volume  

E-print Network

little attention. Experimental work needs to be conducted on detonation diffraction into a confined volume to better understand how the interaction of the diffracted shock wave with a confining wall impacts the detonation diffraction process. Therefore, a...

Polley, Nolan Lee

2012-02-14

404

Spectral characteristics of High Frequency (HF) backscatter for high latitude ionospheric irregularities: Preliminary analysis of statistical properties  

Microsoft Academic Search

OTH-B radar signals backscattered from ionospheric irregularities can be very intense, and any effort to mitigate against their influence requires knowledge of at least the Doppler shift and spread that they introduce in the backscattered signals. This report presents the Doppler spectral characteristics of HF signals backscattered from F-region ionospheric irregularities at high latitudes. The report will show that the

K. B. Baker; R. A. Greenwald; J. P. Villian; S. Wing

1988-01-01

405

Impact of diurnal variation in vegetation water content on radar backscatter of maize during water stress  

NASA Astrophysics Data System (ADS)

Microwave emission and backscatter of vegetated surfaces are influenced by vegetation water content (VWC), which varies in response to availability of soil moisture in the root zone. Understanding the influence of diurnal VWC dynamics on radar backscatter will improve soil moisture retrievals using microwave remote sensing, and will provide insight into the potential use for radar to directly monitor vegetation water status. The goal of this research is to investigate the effect of diurnal variation in VWC of an agricultural canopy on backscatter for different radar configurations. Water stress was induced in a corn (Zea mays) canopy near Citra, Florida, between September 1 and October 20, 2013. Diurnal destructive samples from the canopy were collected to determine leaf, stalk and total VWC. Water stress was quantified by calculating the evaporation deficit and measuring the soil water tension. The water-cloud model was used to model the influence of VWC and soil moisture variations on backscatter for a range of frequencies, polarizations and incidence angles. Furthermore, radar backscatter time series was simulated to show the effect of water stress on the diurnal variation in backscatter due to VWC. Results of this study show the very significant effects that VWC dynamics have on radar backscatter. We also highlight the potential for vegetation and soil water status monitoring using microwave remote sensing.

van Emmerik, Tim; Steele-Dunne, Susan; Judge, Jasmeet; van de Giesen, Nick

2014-05-01

406

100 keV electron backscattered range and coefficient for silicon.  

SciTech Connect

The authors have measured the range and intensity of backscattered electrons in silicon from a 100 keV source using a process independent method. Backscattered electrons contributed to the total dose of features written in a negative tone electron beam resist. Instead of measuring the height of the resist and using a contrast curve to convert the resist height to dose, the heights of the features were made equal by adjusting the backscattered contribution through dose assignments. Creating features of equal height eliminated the need to use a contrast curve to convert from resist height to total dose. Also, it allowed for measurements of the backscattered contribution from larger distances. Using a circularly symmetric torus pattern, the three-dimensional backscatter problem was reduced to a 1-dimensional Gaussian form. The authors measured the range of the backscattered electrons, {beta}, to be 31.08 {+-} 0.06 {micro}m. By varying the writing dose of the pattern, we determined the backscatter coefficient, {eta}, to be 0.63 {+-} 0.03.

Czaplewski, D.A.; Ocola, L.E. (Center for Nanoscale Materials)

2012-01-01

407

Pharmaceutical Powder Diffraction: Structure Solution from PXRD  

E-print Network

Pharmaceutical Powder Diffraction: Structure Solution from PXRD How reliable are our structures? Pharmaceutical Powder Diffraction: Structure Solution from PXRD How reliable are our structures? Maryjane

408

Secondary diffraction of diffracted Gaussian beam of laser radiation  

NASA Astrophysics Data System (ADS)

The diffraction of a narrow Gaussian beam of laser radiation on mutually perpendicular edges of crossed, superimposed sharp wedge-shaped blades (safety razors) has been studied. The diffraction pattern observed on a flat screen behind the blades comprises a very bright central spot, which exhibits the structure of a "light network" with rectangular cells, and four groups of narrow bright bands that expand from the central spot toward the periphery and form a rectangular cross. The spatial frequency of light-field modulation on the screen can be controlled by varying the distance from the blades to screen.

Vasil'Ev, Yu. V.; Kozar', A. V.; Matyunin, A. V.

2011-10-01

409

Electromagnetic diffraction efficiencies for plane reflection diffraction gratings  

NASA Technical Reports Server (NTRS)

The theory and computer programs, based on electromagnetic theory, for the analysis and design of echelle gratings were developed. The gratings are designed for instruments that operate in the ultraviolet portion of the spectrum. The theory was developed so that the resulting computer programs will be able to analyze deep (up to 30 wavelengths) gratings by including as many as 100 real or homogeneous diffraction orders. The program calculates the complex amplitude coefficient for each of the diffracted orders. A check on the numerical method used to solve the integral equations is provided by a conservation of energy calculation.

Marathay, A. S.; Shrode, T. E.

1974-01-01

410

Distributed Optical Fiber Vibration Sensor Based on Rayleigh Backscattering  

NASA Astrophysics Data System (ADS)

This thesis includes studies of developing distributed optical fiber vibration sensor based on Rayleigh backscattering with broad frequency response range and high spatial resolution. Distributed vibration sensor based on all-polarization-maintaining configurations of the phase-sensitive optical time domain reflectometry (OTDR) is developed to achieve high frequency response and spatial resolution. Signal fading and noise induced by polarization change can be mitigated via polarization-maintaining components. Pencil-break event is tested as a vibration source and the layout of the sensing fiber part is designed for real applications. The spatial resolution is 1m and the maximum distance between sensing fiber and vibration event is 18cm. Wavelet denoising method is introduced to improve the performance of the distributed vibration sensor based on phase-sensitive OTDR in standard single-mode fiber. Noise can be reduced more effectively by thresholding the wavelet coefficient. Sub-meter spatial resolution is obtained with a detectable frequency up to 8 kHz. A new distributed vibration sensor based on time-division multiplexing (TDM) scheme is also studied. A special probe waveform including a narrow pules and a quasi-continuous wave can combine the conventional phase-sensitive OTDR system and polarization diversity scheme together in one single-mode fiber without crosstalk. Position and frequency of the vibration can be determined by these two detection systems consecutively in different time slots. Vibration event up to 0.6 MHz is detected with 1m spatial resolution along a 680m single-mode sensing fiber. Continuous wavelet transform (CWT) is investigated to study the non-stationary vibration events measured by our phase OTDR system. The CWT approach can access both frequency and time information of the vibration event simultaneously. Distributed vibration measurements of 500Hz and 500Hz to 1 kHz sweep events over 20 cm fiber length are demonstrated using a single-mode fiber. Optical frequency-domain reflectometry (OFDR) for vibration sensing is proposed for the first time. The local Rayleigh backscatter spectrum shift in time sequence could be used to determine dynamic strain information at a specific position of the vibrated state with respect to that of the non-vibrated state. Measurable frequency range of 0-32 Hz with the spatial resolution of 10 cm is demonstrated along a 17 m fiber.

Qin, Zengguang

411

Synchrotron X-ray diffraction study of texture evolution in 904L stainless steel under dynamic shock compression  

SciTech Connect

The influence of strain rate on development of deformation texture under a dynamic shock compression of a 904L stainless steel was quantitatively investigated using synchrotron X-ray diffraction and crystallographic orientation distribution function (ODF) analysis. Split-Hopkinson Pressure Bar technique was used to generate a high strain rate of > 103 s-1 for preparing the deformed samples. Starting with an almost random texture in a solution treatment condition, the deformed material developed several typical texture components, such as ‘Goss’ texture and ‘Brass’ texture. Compared to the texture components displayed in the state of quasi-static compression deformation, it was found that the high-speed deformation generated much weaker texture components. In combination with the change in microstructures observed by EBSD and TEM technique, the high-energy X-ray diffraction provides a powerful tool for characterizing the strain-rate dependence of grain rotation at each stage of deformation. The deformation heterogeneity evident in our experiment can be explained by a transition of deformation mechanism from the dislocation/twin-dominated mode to shear-band-dominated one with increasing strain rate.

Li, Nanan; Wang, Y. D.; Peng, R. Lin; Sun, Xin; Ren, Yang; Wang, L.; Cai, H. N.

2011-01-01

412

A time-of-flight backscattering spectrometer at the Spallation Neutron Source, BASIS  

SciTech Connect

We describe the design and current performance of the backscattering silicon spectrometer (BASIS), a time-of-flight backscattering spectrometer built at the spallation neutron source (SNS) of the Oak Ridge National Laboratory (ORNL). BASIS is the first silicon-based backscattering spectrometer installed at a spallation neutron source. In addition to high intensity, it offers a high-energy resolution of about 3.5 {mu}eV and a large and variable energy transfer range. These ensure an excellent overlap with the dynamic ranges accessible at other inelastic spectrometers at the SNS.

Mamontov, E.; Herwig, K. W. [Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2011-08-15

413

A laboratory experiment on EM backscatter from Farley-Buneman and gradient drift waves  

NASA Technical Reports Server (NTRS)

Results of laboratory experiment on Bragg backscatter of 3-cm microwaves by turbulent waves driven by the Farley-Buneman and gradient drift instabilities are reported. It is noted that the study is the third in a series of laboratory experiments performed to test, under controlled conditions, prevalent ideas on EM scattering by equatorial and high-latitude ionospheric waves and irregularities. It is shown through separate backscattering from fast and slow ion beam modes that a beam of EM radiation actually provides, in backscatter, information on the spectral content of the scattering medium.

Alport, M. J.; Dangelo, N.; Pecseli, H. L.

1981-01-01

414

Computer model study of pseudorandom noise modulation continuous-wave (PRN-cw) backscatter lidar  

NASA Astrophysics Data System (ADS)

We present a computer model for simulation of PRN-cw atmospheric backscatter lidar performances. The program for calculation operates on a PC type computer. The model covers a variety of cases for the lidar platforms: satellite borne (nadir-looking), airborne (both nadir- and zenith-looking) and ground based. The estimation of the lidar response function includes the following inputs: A) ESA/ATLID cloud and aerosol backscatter/extinction model and molecular atmosphere backscatter and extinction model, based on US standard atmosphere. B) Terrain surface function model. C) Different M-sequences modulation formats, sub-system parameters and solar background.

Matthey, Renaud; Mitev, Valentin

1995-09-01

415

Observations of Enhanced Radar Backscatter (ERB) from Millstone Hill  

NASA Technical Reports Server (NTRS)

Intense enhancements of the incoherent radar backscatter spectrum from the topside ionosphere were observed with the Millstone Hill UHF radar. Enhancements occurring at the local ion acoustic frequency causing large asymmetries in the measured ion line may be produced by current driven instabilities. These enhancements pose a practical problem for space surveillance systems because their cross section and spectral width are characteristic of satellites. Conversely, their hard target signature complicates the study of naturally occurring ERB events; it is nearly impossible to distinguish them from satellites based on a single measurement. Statistical comparisons of observed coherent echo distributions with predictions from a satellite catalog were used to broadly identify periods of ERB activity. A series of experiments using multiple diagnostics, including satellite instruments, for simultaneous observations have established the association of ERB with large fluxes of soft suprathermal electrons carrying field aligned currents. Zenith data are also presented which show the asymmetric growth of ion acoustic waves directly above Millstone Hill. Details of these results are presented.

Lee, M. C.

1991-01-01

416

Vacuum birefringence by Compton backscattering through a strong field  

NASA Astrophysics Data System (ADS)

We propose a novel scheme to measure nonlinear effects in electrodynamics arising from QED corrections. Our theoretical starting point is the Heisenberg-Euler-Schwinger effective Lagrangian which predicts that a vacuum with a strong static electromagnetic field turns birefringent. We propose to employ a pulsed laser to create Compton backscattered photons off a high energy electron beam. These photons will pass through a strong static magnetic field, which according to the QED prediction changes the state of polarization of the radiation—an effect proportional to the photon energy. This change will be measured by using an aligned single crystal, since a large difference in the pair production cross sections at high energies can be achieved with proper orientation of the crystal. As an example we will consider the machine, LHeC, under consideration at CERN as the source of these electrons, and an LHC dipole magnet as the source of the strong static magnetic field. In the proposed experimental setup the birefringence effect will be manifested in a difference in the number of pairs created in the polarizer crystal as the initial laser light has a varying state of polarization, achieved with a rotating quarter wave plate. This will be seen as a clear peak in the Fourier transform spectrum of the pair-production rate signal, which can be obtained with 3 hours of measurement. We also comment on the sensitivity of the experiment, to the existence of an axion, a hypothetical spin-0 particle that couples to two photons.

Wistisen, Tobias N.; Uggerhøj, Ulrik I.

2013-09-01

417

A compact double-pass Raman backscattering amplifier/compressor  

SciTech Connect

The enhancement of stimulated Raman backscattering (SRBS) amplification was demonstrated by introducing a plasma density gradient along the pump and the seed interaction path and by a novel double-pass design. The energy transfer efficiency was significantly improved to a level of 6.4%. The seed pulse was amplified by a factor of more than 20 000 from the input in a 2 mm long plasma, which also exceeded the intensity of the pump pulse by 2 orders of magnitude. This was accompanied by very effective pulse compression, from 500 fs to 90 fs in the first pass measurements and in the second pass down to approximately 50 fs, as it is indicated by the energy-pulse duration relation. Further improvements to the energy transfer efficiency and the SRBS performance by extending the region of resonance is also discussed where a uniform {approx}4 mm long plasma channel for SRBS was generated by using two subsequent laser pulses in an ethane gas jet.

Ren, J.; Li, S.; Morozov, A.; Suckewer, S. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Yampolsky, N. A.; Malkin, V. M.; Fisch, N. J. [Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States)

2008-05-15

418

Coherent backscattering cone shape depends on the beam size.  

PubMed

Coherent backscattering (CBS) is a beautiful physical phenomenon that takes place in a highly scattering medium, which has potential application in noninvasive optical property measurement. The current model that explains the CBS cone shape, however, assumes the incoming beam diameter is infinitely large compared to the transport length. In this paper, we evaluate the effect of a finite scalar light illumination area on the CBS cone, both theoretically and experimentally. The quantitative relationship between laser beam size and the CBS cone shape is established by using two different finite beam models (uniform top hat and Gaussian distribution). A series of experimental data with varying beam diameters is obtained for comparison with the theory. Our study shows the CBS cone shape begins to show distortion when beam size becomes submillimeter, and this effect should not be ignored in general. In biological tissue where a normal large beam CBS cone is too narrow for detection, this small beam CBS may be more advantageous for more accurate and higher resolution tissue characterization. PMID:22968267

Bi, Renzhe; Dong, Jing; Lee, Kijoon

2012-09-10

419

Ray-Based Calculations of Backscatter in Laser Fusion Targets  

SciTech Connect

A steady-state model for Brillouin and Raman backscatter along a laser ray path is presented. The daughter plasma waves are treated in the strong damping limit, and have amplitudes given by the (linear) kinetic response to the ponderomotive drive. Pump depletion, inverse-bremsstrahlung damping, bremsstrahlung emission, Thomson scattering off density fluctuations, and whole-beam focusing are included. The numerical code deplete, which implements this model, is described. The model is compared with traditional linear gain calculations, as well as 'plane-wave' simulations with the paraxial propagation code pf3d. Comparisons with Brillouin-scattering experiments at the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, p. 495 (1997)] show that laser speckles greatly enhance the reflectivity over the deplete results. An approximate upper bound on this enhancement, motivated by phase conjugation, is given by doubling the deplete coupling coefficient. Analysis with deplete of an ignition design for the National Ignition Facility (NIF) [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technol. 26, p. 755 (1994)], with a peak radiation temperature of 285 eV, shows encouragingly low reflectivity. Doubling the coupling to bound the speckle enhancement suggests a less optimistic picture. Re-absorption of Raman light is seen to be significant in this design.

Strozzi, D J; Williams, E A; Hinkel, D E; Froula, D H; London, R A; Callahan, D A

2008-02-26

420

Microwave backscattering and emission model for grass canopies  

NASA Technical Reports Server (NTRS)

Microwave radar and radiometer measurements of grasslands indicate a substantial reduction in sensor sensitivity to soil moisture in the presence of a thatch layer. When this layer is wet it masks changes in the underlying soil, making the canopy appear warm in the case of passive sensors (radiometer) and decreasing backscatter in the active case (scatterometer). A model for a grass canopy with thatch will be presented in this paper to explain this behavior and to compare with observations. The canopy model consists of three layers: grass, thatch, and the underlying soil. The grass blades are modeled by elongated elliptical discs and the thatch is modeled as a collection of disk shaped water droplets (i.e., the dry matter is neglected). The ground is homogeneous and flat. The distorted Born approximation is used to compute the radar cross section of this three layer canopy and the emissivity is computed from the radar cross section using the Peake formulation for the passive problem. Results are computed at L-band (1.4 GHz) and C-band (4.75 GHz) using canopy parameters (i.e., plant geometry, soil moisture, plant moisture, etc.) representative of Konza Prairie grasslands. The results are compared to C-band scatterometer measurements and L-band radiometer measurements at these grasslands.

Saatchi, Sasan S.; Levine, David M.; Lang, Roger H.

1994-01-01

421

Resolving gravity waves from mesospheric radar backscatter using MAARSY  

NASA Astrophysics Data System (ADS)

The Middle Atmosphere Alomar Radar System (MAARSY) at the northern Norwegian Island of Andøya is is a monostatic radar with an active phased array antenna operating at a frequency of 53.5 MHz. The radar is capable to perform rapid scanning experiments using advanced beam steering on a pulse-to-pulse basis. The antenna array is divided into 61 subgroups and each receiving signal of a antenna sub-structure can be selected as an input of a 16 channel receiver system, which provides a high flexibility for interferometric applications. Here we present first results to estimate gravity wave parameters by applying an extended velocity azimuth display analysis (EVAD) using polar mesospheric summer echoes as radar backscatter. The high power and fast beam steering ensures a high spatial and temporal resolution. The radial velocities are corrected for angle of arrival effects making use of the interferometric capabilities of the radar. The gravity wave properties are obtained by computing images of the radial velocity fluctuations using the complete scanning volume. The images are computed by comparing the EVAD theoretical radial velocities with the measurements.

Stober, G.; Sommer, S.; Latteck, R.; Zecha, M.; Rapp, M.

2012-12-01

422

Modeling the backscattering and transmission properties of vegetation canopies  

NASA Technical Reports Server (NTRS)

Experimental measurements of canopy attenuation at 10.2 GHz (X-band) for canopies of wheat and soybeans, experimental observations of the effect upon the microwave backscattering coefficient (sigma) of free water in a vegetation canopy, and experimental measurements of sigma (10.2 GHz, 50 deg, VV and VH polarization) of 30 agricultural fields over the growing season of each crop are discussed. The measurements of the canopy attenuation through wheat independently determined the attenuation resulting from the wheat heads and that from the stalks. An experiment conducted to simulate the effects of rain or dew on sigma showed that sigma increases by about 3 dB as a result of spraying a vegetation canopy with water. The temporal observations of sigma for the 30 agricultural fields (10 each of wheat, corn, and soybeans) indicated fields of the same crop type exhibits similar temporal patterns. Models previously reported were tested using these multitemporal sigma data, and a new model for each crop type was developed and tested. The new models proved to be superior to the previous ones.

Allen, C. T.; Ulaby, F. T.

1984-01-01

423

Detonation diffraction through different geometries  

NASA Astrophysics Data System (ADS)

We performed the study of the diffraction of a self-sustained detonation from a cylindrical tube (of inner diameter d) through different geometric configurations in order to characterise the transmission processes and to quantify the transmission criteria to the reception chamber. For the diffraction from a tube to the open space the transmission criteria is expressed by d c = k c · ? (with ? the detonation cell size and k c depending on the mixture and on the operture configuration, classically 13 for alkane mixtures with oxygen). The studied geometries are: (a) a sharp increase of diameter ( D/ d > 1) with and without a central obstacle in the diffracting section, (b) a conical divergent with a central obstacle in the diffracting section and (c) an inversed intermediate one end closed tube insuring a double reflection before a final diffraction between the initiator tube and the reception chamber. The results for case A show that the reinitiation process depends on the ratio d/ ?. For ratios below k c the re-ignition takes place at the receptor tube wall and at a fixed distance from the step, i.e. closely after the diffracted shock reflection shows a Mach stem configuration. For ratios below a limit ratio k lim (which depends on D/ d) the re-ignition distance increases with the decrease of d/?. For both case A and B the introduction of a central obstacle (of blockage ratio BR = 0.5) at the exit of the initiator tube decreases the critical transmission ratio k c by 50%. The results in configuration C show that the re-ignition process depends both on d/ ? and the geometric conditions. Optimal configuration is found that provides the transmission through the two successive reflections (from d = 26 mm to D ch = 200 mm) at as small d/ ? as 2.2 whatever the intermediate diameter D is. This configuration provides a significant improvement in the detonation transmission conditions.

Sorin, Rémy; Zitoun, Ratiba; Khasainov, Boris; Desbordes, Daniel

2009-04-01

424

Boundary diffraction wave integrals for diffraction modeling of external occulters.  

PubMed

An occulter is a large diffracting screen which may be flown in conjunction with a telescope to image extrasolar planets. The edge is shaped to minimize the diffracted light in a region beyond the occulter, and a telescope may be placed in this dark shadow to view an extrasolar system with the starlight removed. Errors in position, orientation, and shape of the occulter will diffract additional light into this region, and a challenge of modeling an occulter system is to accurately and quickly model these effects. We present a fast method for the calculation of electric fields following an occulter, based on the concept of the boundary diffraction wave: the 2D structure of the occulter is reduced to a 1D edge integral which directly incorporates the occulter shape, and which can be easily adjusted to include changes in occulter position and shape, as well as the effects of sources-such as exoplanets-which arrive off-axis to the occulter. The structure of a typical implementation of the algorithm is included. PMID:22772218

Cady, Eric

2012-07-01

425

Acoustooptic Diffraction in Borate Crystals  

E-print Network

The efficiency of acoustooptic (AO) diffraction in a-BaB2O4 and Li2B4O7 crystals is studied experimentally. The crystals are shown to be quite good AO materials. The efficiency of AO diffraction in a-BaB2O4 reaches h=30% at the electric signal power of P=0.7W for the transverse acoustic wave and 15% at the power of P=0.56W for the longitudinal wave. The same parameter for Li2B4O7 reaches h=21% at P=0,81W for the longitudinal acoustic wave.

I. Martynyuk-Lototska; T. Dudok; O. Krupych; V. Adamiv; Ye. Smirnov; R. Vlokh

2007-08-15

426

Characterization of nuclear physics targets using Rutherford backscattering and particle induced x-ray emission  

E-print Network

Rutherford backscattering and particle induced x-ray emission have been utilized to precisely characterize targets used in nuclear fission experiments. The method allows for a fast and non destructive determination of target thickness, homogeneity and element composition.

Th. Rubehn; G. J. Wozniak; L. Phair; L. G. Moretto; Kin M. Yu

1996-09-23

427

Frequency and concentration dependence of the ultrasonic backscatter coefficient in a soft tissue  

E-print Network

gives the backscattering coefficient. The sample is insonified by a sine-wave burst from a narrow- band of mimick- ing humain tissues with respect to these characteristics. The speed of sound in the tissue

Boyer, Edmond

428

Interior view, looking northeast in computer room OvertheHorizon Backscatter ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Interior view, looking northeast in computer room - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Five Receiver Building, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

429

Interior view, looking south in computer room OvertheHorizon Backscatter ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Interior view, looking south in computer room - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Six Receiver Building, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

430

General view of array, looking northeast OvertheHorizon Backscatter Radar ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

General view of array, looking northeast - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Four Antenna Array, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

431

Oblique view to south OvertheHorizon Backscatter Radar Network, Mountain ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Oblique view to south - Over-the-Horizon Backscatter Radar Network, Mountain Home Air Force Operations Building, On Desert Street at 9th Avenue Mountain Home Air Force Base, Mountain Home, Elmore County, ID

432

Exterior view, looking west OvertheHorizon Backscatter Radar Network, Tulelake ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Exterior view, looking west - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Four Receiver Building, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

433

Exterior view, looking southwest OvertheHorizon Backscatter Radar Network, Tulelake ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Exterior view, looking southwest - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Four Receiver Building, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

434

Interior view, looking northwest OvertheHorizon Backscatter Radar Network, Tulelake ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Interior view, looking northwest - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Four Receiver Building, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

435

General view of Antenna Array, looking west OvertheHorizon Backscatter ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

General view of Antenna Array, looking west - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Six Antenna Array, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

436

General view, looking southeast OvertheHorizon Backscatter Radar Network, Tulelake ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

General view, looking southeast - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Four Communications Antenna, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

437

Detail of antenna array, looking northnorthwest OvertheHorizon Backscatter Radar ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Detail of antenna array, looking north-northwest - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Five Antenna Array, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

438

Interior view, looking north in generator room OvertheHorizon Backscatter ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Interior view, looking north in generator room - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Five Receiver Building, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

439

Detail of antenna tower structure, looking northnorthwest OvertheHorizon Backscatter ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Detail of antenna tower structure, looking north-northwest - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Five Antenna Array, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

440

Oblique view, looking northeast OvertheHorizon Backscatter Radar Network, Tulelake ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Oblique view, looking northeast - Over-the-Horizon Backscatter Radar Network, Tulelake Radar Site Receive Sector Five Antenna Array, Unnamed Road West of Double Head Road, Tulelake, Siskiyou County, CA

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