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Microscopic Scale (microscopic + scale)
Selected AbstractsFiber tracking using magnetic resonance diffusion tensor imaging and its applications to human brain developmentDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 3 2003Richard Watts Abstract Diffusion tensor imaging is unique in its ability to noninvasively visualize white matter fiber tracts in the human brain in vivo. Diffusion is the incoherent motion of water molecules on a microscopic scale. This motion is itself dependent on the micro-structural environment that restricts the movement of the water molecules. In white matter fibers there is a pronounced directional dependence on diffusion. With white matter fiber tracking or tractography, projections among brain regions can be detected in the three-dimensional diffusion tensor dataset according to the directionality of the fibers. Examples of developmental changes in diffusion, tracking of major fiber tracts, and examples of how diffusion tensor tractography and functional magnetic resonance imaging can be combined are provided. These techniques are complimentary and allow both the identification of the eloquent areas of the brain involved in specific functional tasks, and the connections between them. The noninvasive nature of magnetic resonance imaging will allow these techniques to be used in both longitudinal developmental and diagnostic studies. An overview of the technique and preliminary applications are presented, along with its current limitations. MRDD Research Reviews 2003;9:168,177. © 2003 Wiley-Liss, Inc. [source] Photoinduced Shuttling Dynamics of Rotaxanes in Viscous Polymer SolutionsADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Dhiredj C. Jagesar Abstract The effect of external friction, caused by medium viscosity, on the photoinduced translational motion in a rotaxane-based molecular shuttle 1 is investigated. The shuttle is successfully operated in solutions of poly(methacrylonitrile) (PMAN) of different molecular weights in MeCN and PrCN. The viscosity of the medium is tuned by changing the PMAN concentration. The rheological behavior of the polymer solution gives insight into the structure of the polymer solution on the microscopic scale. In PrCN, the entanglement regime is reached at lower concentration than in MeCN. This is also reflected by the effect on the shuttling: in the PrCN/PMAN system, a larger viscosity effect is observed compared to MeCN/PMAN. The shuttle is found to be slowed down in the polymer solutions but is still active at high viscosities. The observed retardation effect on the kinetics of shuttling in MeCN/PMAN and PrCN/PMAN can be correlated to the PMAN concentration through the hydrodynamic scaling model. The Stokes,Einstein relationship proves inadequate to correlate the shuttling rates to macroscopic viscosity, but the dependence of the shuttling rate on the bulk viscosity fits well to a commonly observed power-law relationship. The viscosity effect on the shuttling is found to be weak in all cases. [source] Constraints on deformation mechanisms during folding provided by rock physical properties: a case study at Sheep Mountain anticline (Wyoming, USA)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010K. Amrouch SUMMARY The Sheep Mountain anticline (Wyoming, USA) is a well-exposed asymmetric, basement-cored anticline that formed during the Laramide orogeny in the early Tertiary. In order to unravel the history of strain during folding, we carried out combined anisotropy of magnetic susceptibility (AMS), anisotropy of P -wave velocity (APWV) and Fry strain analyses. The results are compared to previously published stress,strain data from calcite twins at the microscopic scale and from fracture sets at the mesoscopic scale, and are used to discuss the kinematics and mechanics of forced folding. The results obtained in sandstone and carbonate lithologies demonstrate a good agreement between (1) the principal axes of the AMS and APWV tensors, (2) stress,strain tensors derived from calcite twins, (3) Fry strain axes and mesoscopic fracture sets. Furthermore, these tensors are coaxial with the main structural trends of the anticline. The differences between AMS and APWV fabrics on one hand, and the differential stress values of the forelimb and the backlimb on the other hand, emphasize how the macroscopic asymmetry of Sheep Mountain anticline affects the strain pattern at the microscopic scale. The data set presented in this paper offers a consistent mechanical scenario for the development of Sheep Mountain anticline. [source] A micromechanical approach to the strength criterion of Drucker-Prager materials reinforced by rigid inclusionsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7-8 2004Jean-François Barthélémy Abstract At the microscopic scale, concrete can be considered as a frictional matrix (cement paste) surrounding rigid inclusions (aggregate or sand inclusions). The present paper proposes a theoretical approach to the strength criterion of such a composite material. It is shown that the macroscopic stress states on the yield surface can be obtained from the solution to non-linear viscous problems defined on a representative volume element. The practical determination of the yield surface implements a non-linear homogenization scheme based on the modified secant method. The role of the interface between the matrix and the inclusions is also investigated. Two extreme modellings are considered: perfect bonding and non-frictional interfaces. In both cases, the method yields a macroscopic strength criterion of the Drucker,Prager type. The macroscopic friction angle is a function of that of the matrix and of the volume fraction of the inclusions. In the case of perfect bonding, the inclusions have a reinforcing effect. In contrast, this may not be true for a non-frictional interface. Copyright © 2004 John Wiley & Sons, Ltd. [source] About Darcy's law in non-Galilean frameINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2004C. Geindreau Abstract This paper is aimed towards investigating the filtration law of an incompressible viscous Newtonian fluid through a rigid non-inertial porous medium (e.g. a porous medium placed in a centrifuge basket). The filtration law is obtained by upscaling the flow equations at the pore scale. The upscaling technique is the homogenization method of multiple scale expansions which rigorously gives the macroscopic behaviour and the effective properties without any prerequisite on the form of the macroscopic equations. The derived filtration law is similar to Darcy's law, but the tensor of permeability presents the following remarkable properties: it depends upon the angular velocity of the porous matrix, it verifies Hall,Onsager's relationship and it is a non-symmetric tensor. We thus deduce that, under rotation, an isotropic porous medium leads to a non-isotropic effective permeability. In this paper, we present the results of numerical simulations of the flow through rotating porous media. This allows us to highlight the deviations of the flow due to Coriolis effects at both the microscopic scale (i.e. the pore scale), and the macroscopic scale (i.e. the sample scale). The above results confirm that for an isotropic medium, phenomenological laws already proposed in the literature fails at reproducing three-dimensional Coriolis effects in all types of pores geometry. We show that Coriolis effects may lead to significant variations of the permeability measured during centrifuge tests when the inverse Ekman number Ek,1 is ,,(1). These variations are estimated to be less than 5% if Ek,1<0.2, which is the case of classical geotechnical centrifuge tests. We finally conclude by showing that available experimental data from tests carried out in centrifuges are not sufficient to determining the effective tensor of permeability of rotating porous media. Copyright © 2004 John Wiley & Sons, Ltd. [source] Elastic Indentation Response of Float Glass SurfacesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2010Andrea M. Muller Instrumented Hertzian indentation was used to evaluate the reduced elastic modulus and cone-crack initiation forces for the as-received surfaces of commercial float glasses. Custom-built indentation equipment with the capability of acoustic emission detection was used to monitor continuously the load and depth of penetration at the microscopic scale for forces up to 1 kN. Equipment verification was performed using a reference material, GE 124. The air and tin surfaces of commercial soda,lime,silica and borosilicate float glasses were tested to determine any difference in indentation response for the elastic and fracture behavior of as-received surfaces. Information obtained from the analysis of the load,displacement curves and from the visual inspection of the indentation sites was used to determine the elastic modulus, and the conditions for the onset of cone cracking as a function of surface roughness. The reduced modulus results were verified using additional equipment that allowed the in situ observation of the contact area during loading and unloading. The results showed that there was no difference in the reduced modulus data for the air and tin surfaces for the range of surface displacements studied. The same conclusions were found for cone-cracking loads on as-received surfaces but tests on abraded surfaces showed that the tin surfaces had slightly more resistance to cone cracking than the air surfaces. [source] Fluorescence staining of human ovarian cancer tissue following application of 5-aminolevulinic acid: Fluorescence microscopy studiesLASERS IN SURGERY AND MEDICINE, Issue 5 2006Martin C. Löning Abstract Background and Objectives Application of 5-aminolevulinic acid (ALA) for fluorescence-guided second-look laparoscopy has been shown to be a promising new procedure in the early diagnosis of ovarian carcinoma metastases. However, for assessing the reliability of this method, information on the microscopic distribution of protoporphyrin IX (PP IX) in the tissue is needed. Additionally, the selectivity of PP IX uptake is essential for a potential photodynamic therapy (PDT) of ovarian cancer metastases. Study Design/Materials and Methods Thirty-six patients with epithelial ovarian cancer and two patients suffering from fallopian tube carcinoma underwent a laparoscopic second-look procedure 5 hours after the application of ALA. In 17 patients 36 fluorescence-guided biopsies were taken from fluorescing and non-fluorescing tissues for further evaluation. Fluorescence microscopy and digital image processing were utilized to determine the presence of PP IX fluorescence. Results A specificity of 88% and a sensitivity of 100% with a negative predictive value of 100% and a positive predictive value of 91% were calculated for PP IX fluorescence on a microscopic level as marker for ovarian cancer metastases. Conclusions On a microscopic scale, ALA-induced PP IX fluorescence is confined to ovarian cancer tumor tissue sparing stromal tissues. Lasers Surg. Med. © 2006 Wiley-Liss, Inc. [source] Grafting of polyolefins with maleic anhydride: alchemy or technology?MACROMOLECULAR SYMPOSIA, Issue 1 2003Martin van Duin Abstract Nowadays, the process of maleic anhydride (MA) grafting and the application of MA-grafted polyolefins are viewed as mature technologies. The chemistry and technology of modifying apolar polyolefins with the polar and reactive MA either in solution or in the melt were already explored as far back as the 1950s. Commercial applications exploit the improved adhesion of polyolefins to polar materials, both at the macroscopic scale and on the microscopic scale. However, it is hardly recognised that, from a scientific point of view, grafting has still a strong resemblance to alchemy. Both process and application technologies have been developed in a trial and error fashion. Only in the last decade the structure of MA-grafted polyolefins has been elucidated and attempts to "look" inside the extruder during grafting were only recently successful. The first steps towards the development of sound chemical models are currently made. An overview will be given of the progress made in the various areas mentioned. [source] Some estimates for the torsional rigidity of composite rodsMATHEMATISCHE NACHRICHTEN, Issue 3 2007Graziano Crasta Abstract A well-known problem in elasticity consists in placing two linearly elastic materials (of different shear moduli) in a given plane domain ,, so as to maximize the torsional rigidity of the resulting rod; moreover, the proportion of these materials is prescribed. Such a problem may not have a classical solution as the optimal design may contain homogenization regions, where the two materials are mixed in a microscopic scale. Then, the optimal torsional rigidity becomes difficult to compute. In this paper we give some different theoretical upper and lower bounds for the optimal torsional rigidity, and we compare them on some significant domains. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Raman tensor analysis of baddeleyite single-crystal and its application to define crystallographic domains in polycrystalline zirconiaPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010Kyoju Fukatsu Abstract The angular dependence of polarized Raman intensity for the Ag and Bg modes was investigated and the full set of Raman tensor elements defined for a baddeleyite single-crystal, namely the monoclinic polymorph of zirconia (ZrO2). Based on the quantitative knowledge of the tensor elements, a method has been proposed for the determination of unknown crystallographic textures in monoclinic zirconia. An application of this method is also shown, which consists of a Raman analysis of crystal orientation on the microscopic scale in polycrystalline ZrO2 after its tetragonal-to-monoclinic (t,m) polymorphic transformation (i.e., occurred under an externally applied stress field). This working example not only confirms the well-known phenomenon of stress-induced phase transformation in polycrystalline zirconia, but also proves the existence of textured domain patterns in the monoclinic phase on a scale larger than that of individual grains. This finding might suggest that the structural and functional properties of polycrystalline zirconia after partial phase transformation should be reinterpreted with taking into account a crystallographic reorientation effect. [source] NMR properties of half-Heusler CoVSbPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006H. Nishihara Abstract The complex NMR properties of CoVSb are reported. On the basis of band structure calculations the compound is predicted to be a half metallic ferromagnet but magnetisation measurements suggest that the compound is a weak ferromagnet. In zero applied field at 4.2 K, three spin echo signals have been observed with peak frequencies of 30, 63 and 82 MHz, which are tentatively assigned as signals associated with antimony, vanadium and cobalt atoms. The cobalt atoms are suggested to have moments of about 0.8 ,B. In addition three spin echo signals have been observed in swept applied fields at 4.2 K which include signals from non magnetic cobalt and vanadium sites. Thus weak ferromagnetism in CoVSb is concluded to be complex on a microscopic scale with the moment of 0.18 ,B per formula unit, obtained from static magnetic measurements, being the average moment of magnetic and nonmagnetic sites of cobalt and vanadium atoms. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of ionic strength on lysozyme uptake rates in cation exchangers.BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2005I: Uptake in SP Sepharose FF Fluorescence scanning confocal microscopy was used in parallel with batch uptake and breakthrough measurements of transport rates to study the effect of ionic strength on the uptake of lysozyme into SP Sepharose FF. In all cases the adsorption isotherms were near-rectangular. As described previously, the intraparticle profiles changed from slow-moving self-sharpening fronts at low salt concentration, to fast-moving diffuse profiles at high salt concentration, and batch uptake rates correspondingly increased with increasing salt concentration. Shrinking core and homogeneous diffusion frameworks were used successfully to obtain effective diffusivities for the low salt and high salt conditions, respectively. The prediction of column breakthrough was generally good using these frameworks, except for low-salt uptake results. In those cases, the compressibility of the stationary phase coupled with the shrinking core behavior appears to reduce the mass transfer rates at particle-particle contacts, leading to shallower breakthrough curves. In contrast, the fast uptake rates at high ionic strength appear to reduce the importance of mass transfer limitations at the particle contacts, but the confocal results do show a flow rate dependence on the uptake profiles, suggesting that external mass transfer becomes more limiting at high ionic strength. These results show that the complexity of behavior observable at the microscopic scale is directly manifested at the column scale and provides a phenomenological basis to interpret and predict column breakthrough. In addition, the results provide heuristics for the optimization of chromatographic conditions. © 2005 Wiley Periodicals, Inc. [source] Integration of environmental and host-derived signals with quorum sensing during plant,microbe interactionsCELLULAR MICROBIOLOGY, Issue 3 2004J. A. Newton Summary Many plant-associated microbes use secreted autoinducer molecules, including N -acylhomoserine lactones (AHLs), to regulate diverse behaviours in association with their population density (quorum sensing). Often, these responses are affected by environmental conditions, including the presence of other AHL-producing bacterial species. In addition, plant-derived metabolites, including products that arise as a direct result of the bacterial infection, may profoundly influence AHL-regulated behaviours. These plant products can interact directly and indirectly with the quorum-sensing network and can profoundly affect the quorum-sensing behaviour. Local conditions on a microscopic scale may affect signal molecule longevity, stability and accumulation, and this could be used to give information in addition to cell density. Furthermore, in many Gram-negative bacteria, AHL signalling is subservient to an additional two-component signalling system dependent upon homologues of GacS and GacA. The signal(s) to which GacS responds are not known, but recent research suggests that a self-produced ligand may be being detected. This review will focus on two well-studied examples of AHL-regulated plant-associated behaviour, Erwinia carotovora and Agrobacterium tumefaciens, to illustrate the complexity of such signalling networks. [source] 2111: Adaptive optics imaging in hereditary macular diseasesACTA OPHTHALMOLOGICA, Issue 2010K NAKASHIMA Purpose This research aimed at exploring and characterizing differences in vivo between healthy and pathology retinas, hereditary macular diseases at the microscopic scale using a compact adaptive optics (AO) retinal camera and high resolution OCT. Methods Seven RP patients, Cone-rod dystrophies (3), Stargardt diseases (5), Occult macular dystrophies (4) and indeterminate macular dystrophies (4) had undergone en face retinal imaging by AO camera "rtx1" (Imagine Eyes, France). AO images were taken at the eccentricities from 0 deg to 6 deg temporal and nasal from fovea. Each patient was examined using high resolution spectral domain (SD)-OCT and infrared SLO (Spectralis OCT). Results Cellular-resolution images could be obtained in most cases. In inherited retinal dystrophies, AO helped to better evaluate losses of cone cells across the retina. Other microstructures, slightly larger in size than cones, were also visible in several pathological retinas. Hereditary macular disease cases showed loss of cone mosaics. Some of these cases, there were patchy areas of increased reflectance. In Cone rod dystrophy and some other cases, the RPE mosaic was visible where cone had disappeared. Conclusion Cellular-resolution images could be obtained in most cases. In inherited retinal dystrophies, AO helped to better evaluate losses of cone cells across the retina. Other microstructures, slightly larger in size than cones, were also visible in several pathological retinas. Hereditary macular disease cases showed loss of cone mosaics. Some of these cases, there were patchy areas of increased reflectance. In Cone rod dystrophy and some other cases, the RPE mosaic was visible where cone had disappeared. [source] | |||||||||||||||||||