Presence Of Microstructures Research Articles

Combined Cathodoluminescence and Micro-Raman Study of Helium-Ion-Implanted Albite

ABSTRACT Cathodoluminescence (CL) spectra of experimentally radiated albite at 4.0 MeV energy of He+ ion implantation have red emissions at 700−750 nm, of which the intensities increase with an increase in the radiation dose. These emissions are assigned to a radiation-induced defect center. Pseudocolor CL images of the implanted samples show red CL halo on the implanted surface, of which thickness is approximately 14 µm corresponding to a theoretical range of He+ ion implantation of 4.0 MeV. 2D Raman mapping of the peak at 508 cm−1 for CL halo area indicates minimum intensity and maximum full width at half maximum at ∼14 µm from the implanted surface, suggesting production of radiation-induced defect center due to a partial breaking of the framework structure. CL spectral deconvolution of the red emission reveals a Gaussian component at 1.861 eV attributed to the defect center. The integral intensity of this component closely correlates with the radiation dose as a function of radiation-induced defect center, but does not depend on the density and distribution of other emission centers related to CL of albite, the presence of microstructures or texture, and crystallographic orientation. CL spectral deconvolution is expected to be used for quantitative estimation of alpha radiation dose from natural radionuclides on Na-rich feldspar as an indicator for geodosimetry.

An integrated experimental and analytical approach to the chemical state imaging of iron in brain gliomas using X-ray absorption near edge structure spectroscopy

X-ray absorption near-edge structure spectroscopy is used for human neoplastic tissues in order to investigate distributions and chemical states of iron. The specimens used in this study were obtained intraoperatively from brain gliomas of different types and various grades of malignancy and from a control subject. An integrated experimental and analytical approach toward topographic and quantitative analysis in thin freeze-dried cryo-sections is presented. The full XANES spectra at the Fe absorption K edge show the presence of both chemical forms of Fe in the analyzed points of the tissues. The main goal of the work is the chemical state imaging of Fe in tissue areas. Topographic analysis of Fe speciation in the tissues investigated with the use of the XANES technique indicates the presence of microstructures where Fe 2+ is dominant as well as those with a high abundance of the oxidized form of Fe. The quantitative analysis shows that for all cases the content of the oxidized form of Fe is significantly higher in comparison with Fe 2+. The highest level of Fe 3+ is found in the control sample, and the lowest one for the glioma of the highest grade of malignancy. The content of either Fe 2+ or Fe 3+ is increased in low grade gliomas in comparison to high-grade malignant tumors.

On the effects of characteristic lengths in bending and torsion on Mode III crack in couple stress elasticity

The problem of a stationary semi-infinite crack in an elastic solid with microstructures subject to remote classical K III field is investigated in the present work. The material behavior is described by the indeterminate theory of couple stress elasticity developed by Koiter. This constitutive model includes the characteristic lengths in bending and torsion and thus it is able to account for the underlying microstructure of the material as well as for the strong size effects arising at small scales. The stress and displacement fields turn out to be strongly influenced by the ratio between the characteristic lengths. Moreover, the symmetric stress field turns out to be finite at the crack tip, whereas the skew-symmetric stress field displays a strong singularity. Ahead of the crack tip within a zone smaller than the characteristic length in torsion, the total shear stress and reduced tractions occur with the opposite sign with respect to the classical LEFM solution, due to the relative rotation of the microstructural particles currently at the crack tip. The asymptotic fields dominate within this zone, which however has limited physical relevance and becomes vanishing small for a characteristic length in torsion of zero. In this limiting case the full-field solution recovers the classical K III field with square-root stress singularity. Outside the zone where the total shear stress is negative, the full-field solution exhibits a bounded maximum for the total shear stress ahead of the crack tip, whose magnitude can be adopted as a measure of the critical stress level for crack advancing. The corresponding fracture criterion defines a critical stress intensity factor, which increases with the characteristic length in torsion. Moreover, the occurrence of a sharp crack profile denotes that the crack becomes stiffer with respect to the classical elastic response, thus revealing that the presence of microstructures may shield the crack tip from fracture.

Optimal design and optimal damping set for a hyperbolic problem (Poster Presentation)

AbstractIn this work we analyze a 2D optimal design problem governed by a linear damped 1D wave equation. In this we would like to find simultaneously the spatio‐temporal layout of two isotropic materials of constants α and β (0 < α < β) and the static position of a damping set in order to minimize certain functional ([5]). By means of the gradient Young measures, we compute a full relaxation of the problem which is justified by the presence of microstructures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Permeability evolution in quartz fault gouges under hydrothermal conditions

The permeability (k) of fine‐grained quartz aggregates were measured in situ during hot pressing (HPing) experiments to explore the evolution of fluid transport properties of fault zones during the interseismic period. Experiments were conducted at temperatures of 150°C and between 700 and 850°C, with confining and pore water pressures of 250 and 150 MPa, respectively. Significant permeability reduction was observed between 700 and 850°C, with permeability reduction rates (r = (1/t) ln (kto/kt)), ranging from approximately 6 × 10−5 s−1 at 700°C to a maximum of approximately 7.4 × 10−4 s−1 at 850°C. Permeability decreased exponentially with time, and the permeability reduction rate increased with increasing temperature, increasing differential stress, and decreasing grain size. Analysis of the permeability‐porosity relationships indicates that permeability in the simulated gouge at high temperature shuts off at a critical porosity of 0.045 ± 0.004. The presence of microstructures, such as grain interpenetration, grain shape truncation, arrays of fluid inclusions, and development of quartz overgrowths on grains, indicate that k reduction was controlled by dissolution‐precipitation creep processes. Extrapolation of the permeability reduction rates, measured in this study, to temperatures typical of the continental seismogenic regime highlights the strongly time‐dependent nature of permeability in natural fault wear products at depths of nucleation of major earthquakes. Within the recurrence time of large earthquakes, quartz‐rich fault zones in the fluid‐active midcrustal to lower continental crustal regimes can evolve from high‐permeability conduits to low‐permeability seals. Episodic changes in the fluid transport properties of faults during the interseismic period are likely to impact on the pore pressure evolution of fault wear products.

Effect of reactive end groups on the rheology of disk lubricant systems

We systematically investigate the properties of perfluoropolyethers with different weights and chain-end functionalities, which are used as lubricants in hard disk drive systems. The temperature dependence of the viscosity yields an Arrhenius form; the activation energy and hydrodynamic volume are determined for different molecular weights. The activation energy depends on both end group functionality and molecular weight. Also, modified Cole-Cole plots for storage modulus vs. loss modulus reveal the presence of microstructures due to the interaction of polymer chain-end groups in the bulk. The viscosity-molecular weight relationship exhibits a remarkable crossover behaviour at a critical molecular weight (M/sub c/) for ZdolTX (Zdol with C/O end group ratio of 1.7). Fly stiction (tribology) data also exhibit an M/sub c/ and an excellent correlation with viscosity (rheology) is obtained.

Aqueous and nonaqueous microemulsions with high molecular weight alkanes

This study extends the existing phenomenological thermodynamic model of aqueous microemulsions to nonaqueous microemulsions and examines the phase patterns when the melting temperature of the alkane oil is in the range of other liquid-liquid transition temperatures. The liquid paraffins studied are the alkane oils of greater than 17 carbons and are solid at room temperature. Water, water and ethylene glycol (4∶1 by wt.), propylene glycol and water (4∶1 by wt.), and propylene glycol are the four non-oleic components examined. Homogeneous polyoxyethylene nonionic surfactants and the commercial surfactants of the Brij series, Neodol series, and the LP series were used. Small-angle x-ray scattering gives evidence for the presence of microstructures in these solutions and, thus these systems are true microemulsions at temperatures above the melting point of the alkane. Systematic paths to move from aqueous to nonaqueous microemulsions are outlined. These results are utilized in optimizing the performance requirements of an inkjet printing application.

Evidence for widespread sperm displacement ability among Zygoptera (Odonata) and the means for predicting its presence

Males of the coenagrionid damselflies Argia moesta, A. sedula and hchnura ramburii use similar penis morphology to remove and/or reposition sperm of previous males from the storage organs of females prior to inseminating them. Although the species vary in the degree to which sperm is removed from or packed into the spermatheca, in all three species, sperm is removed from the bursa copulatrix. Since sperm in the bursa probably has priority in fertilizing eggs in at least the first oviposition after mating, sperm precedence can be estimated as the percentage of sperm (by volume) in the bursa belonging to the last male to mate. Estimated sperm precedence for these species is approximately 71% for Argia sedula, 82% for I. ramburii and 93% for A. moesta. These results, combined with similar ones for other damselflies clearly indicate that the ability to displace sperm may be widespread among temperate-zone Zygoptera. Species with each of the four major variations in damselfly penis structure have now been shown to displace sperm using this morphology. The systematic distribution of these major variants suggests several origins of sperm displacement ability within the Zygoptera. Whether or not all damselflies are capable of sperm displacement depends on both the presence of micro-structures used in sperm removal or repositioning and on the presence of sperm of previous males in mating females. It is possible, therefore, to predict that sperm displacement occurs in a damselfly if (1) females mate more than once, (2) mating females store sperm in organs accessible to penis morphology, (3) the distal segment of the male penis has structures similar to those known to be involved in sperm removal or repositioning, and (4) oviposition occurs in tandem or with the male non-contact guarding his mate.

Theoretical study of the effects of solid particles in the lubricant of externally pressurized porous thrust bearings

Abstract The effects of suspended particles (microstructures) in the lubricant of an externally pressurized porous thrust bearing are studied. The expressions determining the pressure distribution and the load capacity are found to be functions of the parameter h k , i.e. the reciprocal of the ratio of the average radius of gyration k of the microstructures to the film gap h of the bearing, and the parameters characterizing the porous matrix. The presence of microstructures in the lubricant increases the pressure level in the bearing, and consequently the load-carrying capacity of a bearing lubricated with a micropolar fluid is greater than that of a similar bearing under similar conditions lubricated with a non-micropolar fluid. The load capacity also increases as the parameters characterizing the porous matrix increase.

Electromagnetically-Induced Surface Microstructures and Enhanced Field Effects in Laser Processing

ABSTRACTThe presence of microstructures on surfaces undergoing laser processing modifies the electromagnetic boundary conditions and can lead to dramatic changes in the intensity of the local electromagnetic fields and hence in the reaction rates and final morphologies resulting from the laser reaction. Examples are presented for periodic structures on planar surfaces — the rippling of Ag surfaces during laser oxidation; and for isolated dielectric structures — enhanced scattering (∼ 100x) due to dipolar resonances in Si particles.

Low-Temperature Heat Conduction in Pure, Monocrystalline Ice

The heat conduction of ice single crystals is measured by a steady-state heat-flux method between 1.7 K and 100 K. For temperatures higher than 16 K all experimental points are found to be on the same curve. For temperatures lower than 16 K the heat conduction curves depend on the material of the crystallization vessel, the ageing of the sample and the cooling rate between the temperature of the mount (≈ 260 K) and liquid-nitrogen temperature. No anisotropy can be found for temperatures higher than 9 K. Computer fits are made, based on Callaway’s model of heat conduction in dielectric crystals. An attempt is made to explain the observed extrinsic heat conduction by the presence of microstructures in ice. It is shown that heat-conduction measurements can be used to establish a “quality-list” of samples studied in laboratories.

Low-Temperature Heat Conduction in Pure, Monocrystalline Ice

The heat conduction of ice single crystals is measured by a steady-state heat-flux method between 1.7 K and 100 K. For temperatures higher than 16 K all experimental points are found to be on the same curve. For temperatures lower than 16 K the heat conduction curves depend on the material of the crystallization vessel, the ageing of the sample and the cooling rate between the temperature of the mount (≈ 260 K) and liquid-nitrogen temperature. No anisotropy can be found for temperatures higher than 9 K. Computer fits are made, based on Callaway’s model of heat conduction in dielectric crystals. An attempt is made to explain the observed extrinsic heat conduction by the presence of microstructures in ice. It is shown that heat-conduction measurements can be used to establish a “quality-list” of samples studied in laboratories.