X-ray standing wave and reflectometric characterization of multilayer structures

Microstructural characterization of synthetic periodic multilayers by x-ray standing waves have been presented. It has been shown that the analysis of multilayers by combined x-ray reflectometry (XRR) and x-ray standing wave (XSW) techniques can overcome the deficiencies of the individual techniques in microstructural analysis. While interface roughnesses are more accurately determined by the XRR technique, layer composition is more accurately determined by the XSW technique where an element is directly identified by its characteristic emission. These aspects have been explained with an example of a 20 period Pt/C multilayer. The composition of the C-layers due to Pt dissolution in the C-layers, Pt$_{x}$C$_{1-x}$, has been determined by the XSW technique. In the XSW analysis when the whole amount of Pt present in the C-layers is assumed to be within the broadened interface, it l eads to larger interface roughness values, inconsistent with those determined by the XRR technique. Constraining the interface roughness values to those determined by the XRR technique, requires an additional amount of dissolved Pt in the C-layers to expl ain the Pt fluorescence yield excited by the standing wave field. This analysis provides the average composition Pt$_{x}$C$_{1-x}$ of the C-layers .Comment: 12 pages RevTex, 10 eps figures embedde

Growth of epitaxially oriented Ag nanoislands on air-oxidized Si(111)-(7x7) surfaces: Influence of short range order on the substrate

Clean Si(111)-(7{x7) surfaces, followed by air-exposure, have been investigated by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Fourier transforms (FTs) of STM images show the presence of short range (7x7) order on the air-oxidized surface. Comparison with FTs of STM images from a clean Si(111)-(7x7) surface shows that only the 1/7th order spots are present on the air-oxidized surface. The oxide layer is ~ 2-3 nm thick, as revealed by cross-sectional transmission electron microscopy (XTEM). Growth of Ag islands on these air-oxidized Si(111)-(7x7) surfaces has been investigated by in-situ RHEED and STM and ex-situ XTEM and scanning electron microscopy. Ag deposition at room temperature leads to the growth of randomly oriented Ag islands while preferred orientation evolves when Ag is deposited at higher substrate temperatures. For deposition at 550{\deg}C face centered cubic Ag nanoislands grow with a predominant epitaxial orientation [1 -1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si along with its twin [-1 1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si, as observed for epitaxial growth of Ag on Si(111) surfaces. The twins are thus rotated by a 180{\deg} rotation of the Ag unit cell about the Si [111] axis. It is intriguing that Ag nanoislands follow an epitaxial relationship with the Si(111) substrate in spite of the presence of a 2-3 nm thick oxide layer between Ag and Si. Apparently the short range order on the oxide surface influences the crystallographic orientation of the Ag nanoislands.Comment: 10 figure

Lipoprotein-apheresis reduces circulating microparticles in individuals with familial hypercholesterolemia

Lipoprotein-apheresis (apheresis) removes LDL-cholesterol in patients with severe dyslipidemia. However, reduction is transient, indicating that the long-term cardiovascular benefits of apheresis may not solely be due to LDL removal. Microparticles (MPs) are submicron vesicles released from the plasma membrane of cells. MPs, particularly platelet-derived MPs, are increasingly being linked to the pathogenesis of many diseases. We aimed to characterize the effect of apheresis on MP size, concentration, cellular origin, and fatty acid concentration in individuals with familial hypercholesterolemia (FH). Plasma and MP samples were collected from 12 individuals with FH undergoing routine apheresis. Tunable resistive pulse sensing (np200) and nanoparticle tracking analysis measured a fall in MP concentration (33 and 15%, respectively; P < 0.05) pre- to post-apheresis. Flow cytometry showed MPs were predominantly annexin V positive and of platelet (CD41) origin both pre- (88.9%) and post-apheresis (88.4%). Fatty acid composition of MPs differed from that of plasma, though apheresis affected a similar profile of fatty acids in both compartments, as measured by GC-flame ionization detection. MP concentration was also shown to positively correlate with thrombin generation potential. In conclusion, we show apheresis nonselectively removes annexin V-positive platelet-derived MPs in individuals with FH. These MPs are potent inducers of coagulation and are elevated in CVD; this reduction in pathological MPs could relate to the long-term benefits of apheresis

X-ray standing waves in noncentrosymmetric crystals and the phase problem in crystallography

The effect of the variation of f' and f'' on the phase of the X-ray standing wave field is discussed with the example of a semiforbidden GaAs(200) reflection and incident X-ray energies around Ga and As K edges. In noncentrosymmetric crystals the phases of the structure factors contribute to the phase of the standing wave field relative to lattice atoms in the unit cell. Generation of standing waves with (006) and (00 anti 6) reflections in a (00 anti 1)-cut LiNbO_3 crystal and detecting Nb fluorescence yield demonstrates how the phases of the structure factors F(006) and F(00 anti 6) with respect to the origin at an Nb atom can be determined. The phase determination does not require the incident energy to be tuned very close to an absorption edge. (orig.)Also published in: Materlik, G.; Sparks, C.J.; Fischer, D. (eds.): Resonant anomalous X-ray scattering. Theory and applications. Elsevier Science B.V., 1994, p. 119-143Available from TIB Hannover: RN 5581(94-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Submonolayers of lead on silicon (111) surfaces: an X-ray standing wave analysis

Published in the proceedings of ICOSS-II, Amsterdam, June 1987, Springer Series in Surface ScienceSIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

High-temperature X-ray standing wave study: Application to melting of monolayers of Pb on Ge(111) surfaces

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Not Available

Not AvailableThe ravine areas are most fragile ecosystem and subjected to various kinds of natural resource losses and threat to biodiversity. Due to unregulated and over exploitation, the forest area under ravines are facing severe threats of losing biodiversity. In this context, a study was conducted to assess the tree diversity of ravine areas in different parts of Bundelkhand viz., Orai, Banda and Datia. In each study site, quadrats of 20 m × 20 m were randomly laid out and the tree diversity were documented. The species diversity, richness and evenness were studied using different indices like Shannon, Simpson, Margalef and Berger-Parker. The relative density and relative frequency were also calculated. In the present study, the Shannon diversity was highest in ravines of Datia (1.887) followed by Banda (1.871) and Orai (1.259). Whereas the Shannon equitability index was found higher in Banda (0.899) followed by Datia (0.859) and Orai (0.782). The lowest value of Simpson diversity was reported in Banda (0.183) followed by Datia (0.194) and Orai (0.333). In Datia (9 species) maximum number of species were recorded, followed by Banda (8 species) and Orai (5 species). The Inverted Berger-Parker dominance was highest in Banda (3.296) followed by Datia (2.804) and Orai (2.500). Hence it indicates that, ravine areas of Banda and Datia are more diverse and healthier than Orai. Further analysis revealed that, the relative density of Anogeissus pendula was highest in Orai (40.16%) and Datia (38.18%), whereas Holoptelea integrifolia (27.72%) and Balanites aegyptiaca (21.85%) population was higher in Banda. The overall diversity of all the three sites was found low. The survey also reported high biotic interferences, which escalates ravine degradation. However, crop cultivation in these lands is not desirable as it leads to accelerated erosion, thus adding to their fast degradation. The best scientific land use of these lands is to place them under permanent vegetation through agroforestry interventions involving forest and fruit trees along with the grasses. The planting and management of indigenous tree species like Anogeissus pendula, Acacia leucophloea, A. nilotica, Ziziphus spp., Carissa carandas and Capparis decidua will pave the way towards sustaining ravine ecosystem and livelihood of the people.Not Availabl