Knowledge of fracture orientation and density is significant for reservoir and aquifer characterization. In this study, field experiments are designed to estimate fracture parameters in situ from seismic and GPR (radar) data. The seismic experiment estimates parameters of orientation, density, and filling material. The GPR experiment estimates channel flow geometry and aperture. In the seismic study, lines of 2D data are acquired in a vertically fractured limestone at three different azimuths to look for differences in seismic velocities. A sledgehammer, vertical source and a multicomponent, Vibroseis source are used with multicomponent receivers. Acquisition parameters of frequency, receiver spacing and source-to-receiver offset are varied. The entire suite of seismic body waves and Rayleigh waves is analyzed to characterize the subsurface. Alford rotations are used to determine fracture orientation and demonstrate good results when geophone orientation is taken into account. Results indicate that seismic anisotropy is caused by regional faulting. Average fracture density of less than 5% and water table depth estimates are consistent with field observations. Groundwater flow direction has been observed by others to cross the fault trend and is subparallel to a secondary fracture set. In this study, seismic anisotropy appears unrelated to this secondary fracture set. Vp/Vs and Poisson's ratio values indicate a dolomite lithology. Sledgehammer and Vibroseis data provide consistent results. In the GPR experiment, reflection profiles are acquired through common-offset profiling perpendicular to the dominant flow direction. High frequency waves are used to delineate fluid flow paths through a subhorizontal fracture and observe tracer channeling. Channeling of flow is expected to control solute transport. Changes in radar signal are quantitatively associated with changes in fracture filling material from an innovative method using correlation coefficients. Mapping these changes throughout the survey area reveals the geometry of the flow path of each injected liquid. The tracer is found to be concentrated in the center of the survey area where fracture apertures are large. This demonstrates that spatial variations in concentration are controlled by fluid channel geometry.

Many hydrocarbon reservoirs have sufficient porosity but low permeability (for example, tight gas sands and coal beds). However, such reservoirs are often naturally fractured. The fracture patterns in these reservoirs can control flow and transport properties, and therefore, play an important role in drilling production wells. On the scale of seismic wavelengths, closely spaced parallel fractures behave like an anisotropic media, which precludes the response of individual fractures in the seismic data. There are a number of fracture parameters which are needed to fully characterize a fractured reservoir. However, seismic data may reveal only certain fracture parameters and those are fracture orientation, crack density and fracture infill. Most of the widely used fracture characterization methods such as Swave splitting analysis or amplitude vs. offset and azimuth (AVOA) analysis fail to render desired results in laterally varying media. I have conducted a systematic study of the response of fractured reservoirs with laterally varying elastic and fracture properties, and I have developed a scheme to invert for the fracture parameters. I have implemented a 3D finite-difference method to generate multicomponent synthetic seismic data in general anisotropic media. I applied the finite-difference algorithm in both Standard and Rotated Staggered grids. Standard Staggered grid is used for media having symmetry up to orthorhombic (isotropic, transversely isotropic, and orthorhombic), whereas Rotated Staggered grid is implemented for monoclinic and triclinic media. I have also developed an efficient and accurate ray-bending algorithm to compute seismic traveltimes in 3D anisotropic media. AVOA analysis is equivalent to the first-order Born approximation. However, AVOA analysis can be applied only in a laterally uniform medium, whereas the Born-approximation does not pose any restriction on the subsurface structure. I have developed an inversion scheme based on a ray-Born approximation to invert for the fracture parameters. Best results are achieved when both vertical and horizontal components of the seismic data are inverted simultaneously. I have also developed an efficient positivity constraint which forbids the inverted fracture parameters to be negative in value. I have implemented the inversion scheme in the frequency domain and I show, using various numerical examples, that all frequency samples up to the Nyquist are not required to achieve desired inversion results.

Spectroscopic second-harmonic generation (SHG) and reflectance-anisotropy spectroscopy (RAS) are used to probe molecular adsorption on clean reconstructed single-domain stepped Si(001) in ultra-high vacuum (UHV). We implement a simplified bond hyperpolarizability model (SBHM) as a common microscopic analysis for SHG and RAS. Three different scenarios are studied: (i) The dissociative adsorption of molecular hydrogen on dangling bonds of D[subscript B] step-edges. (ii) Structural changes to rebonded r-D[subscript B] steps induced by exposure to atomic hydrogen. (iii) The adsorption of cyclopentene on Si(001)(2x1) terrace dimers in a [2+2] cycloaddition pathway. Using the SBHM we develop a new optical fingerprinting method to isolate, identify and monitor individual types of bonds (e.g. dimers, rebonds, dangling bonds, backbonds) and their chemical activity on a single-domain stepped Si(001) surface using nonresonant, but rotationally-anisotropic, second-harmonic generation (RA-SHG). The methods presented here will be applicable to many material systems and allow to track, in-situ and in real-time, the chemical action of adsorbates on surfaces. / text

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A time-dependent two-dimensional (2D) modulation model including drifts, the solar wind tennination shock (TS) with diffusive shock acceleration and a heliosheath based on the Parker (1965) transport equation is used to study the modulation of galactic cosmic rays (GCRs) and the anomalous component of cosmic rays (ACRs) in the heliosphere. In particular, the latitude dependence of the TS compression ratio and injection efficiency of the ACRs (source strength) based on the hydrodynamic modeling results of Scherer et al. (2006) is used for the first time in a modulation model. The subsequent effects on differential intensities for both GCRs and ACRs are illustrated, comparing them to the values without a latitude dependence for these parameters. It is found that the latitude dependence of these parameters is important and that it enables an improved description of the modulation of ACRs beyond the TS. With this modeling approach (without fitting observations) to the latitude dependence of the two parameters, it is possible to obtain a TS spectrum for ACRs at a polar angle of B = 55" that qualitatively approximates the main features of the Voyager 1 observations. This positive result has to be investigated further. Additionally, it is shown that the enhancement of the cosmic ray intensity just below the cut-off energy found for the ACR at the TS in an A < 0 magnetic polarity cycle in the equatorial plane with the latitude independent scenario, disappears in this region when the latitude dependence of the compression ratio and injection efficiency is assumed. Subsequent effects of these scenarios are illustrated on the global anisotropy vector of both GCRs and ACRs as the main theme of this work. For this purpose the radial and latitudinal gradients for GCRs and ACRs were accurately computed. The radial and latitudinal anisotropy components were then computed as a function of energy, radial distance and polar angle. It is also the first time that the anisotropy vector is comprehensively calculated in such a global approach to cosmic ray modeling in the heliosphere, in particular for ACRs. It is shown that the anisotropy vector inside (up-stream) and outside (down-stream) the TS behaves in a complicated way, so care must be taken in interpreting it. It is found that the latitude dependence of the two mentioned parameters can alter the direction (sign) of the anisotropy vector. Its behaviour beyond the TS is markedly different from inside the TS, mainly because of the slower solar wind velocity, with less dependence on the magnetic polarity cycles. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2007.

The universe is filled with a thermal glow called the cosmic microwave background that comes from the hot plasma which filled it early on. Measurements of this background made by the NASA satellite WMAP have determined the age, geometry and composition of the universe with new precision, determining that the universe today is dominated by a dark energy that is causing it to expand ever more rapidly. The mission has also determined that baryonic matter--the atoms and molecules we see around us--only form a few percent of the total energy density of the universe today, and has determined the epoch at which the first stars formed. Recent results give a tantalizing picture of the first very small fraction of a second in the "big bang". Six years after its launch WMAP remains healthy and the data continue to pour in. This talk will explain to a general audience what this experiment tells us about how the universe began and what it is made out of.

The kinematics and white dwarf distribution have been studied for the Globular Cluster NGC 6397. The data was obtained from NASA’s Hubble Space Telescope in 2005. In particular, we used the images of a field 5’ Southeast of the core of NGC 6397 from Advanced Camera for Surveys to conduct our analyses. The first part of the study is about the kinematics of the globular cluster. Isotropy of velocity distribution and cluster rotation have been considered. As anticipated, this relaxed cluster exhibited no strong signs of anisotropy. However, there appears to be some level of rotation. The rotational motion turns out to be mu sub alpha cos(delta) = 3.88 ± 1.41 mas yr −1 and mu sub delta = −14.83 ± 0.58 mas yr −1. This result is not entirely expected and deserves further investigation in future studies. The second of the thesis is based on white dwarf populations in the globular cluster and the Galactic Bulge. As a first glance, there appears to be a lacking of white dwarfs at the age of approximately 0.6 Gyr. Further investigation reveals this to be statistically insignificant. Through this analysis, another pattern of white dwarf abundance is discovered. There appeared to be much more stars at the age between 0.9 − 2.0 Gyr. This could be a manifestation of modeling error. As the final consideration of this thesis, white dwarf candidates in the Galactic Bulge are illustrated. Approximately 10 candidates are found at the most probable location of stars in the Bulge. The analyses conducted in this thesis set stage for further development in understanding of globular clusters. In particular, the rotation analysis raises curiosity about the dynamics of NGC 6397 in the plane of the sky. Moreover, the velocity distribution analysis confirms properties and theories pertaining to globular clusters.

There has been a dramatic increase in both the amount and type of geophysical well log data acquired in gas hydrate saturated rocks. Data has been acquired in both offshore and Arctic environments; its availability has shed light on the applicability of current tools and the potential usefulness of recently developed and developing technologies. Some of the more interesting areas of interest are related to the usefulness of nuclear elemental spectroscopy data and the comparison of thermal and epithermal neutron porosity measurements, the measurement of in-situ permeability, the interpretation of electrical borehole image and borehole sonic data. A key parameter for reservoir characterization and simulation is formation permeability. A reasonable understanding of this property is key to the development of future gas hydrate production. Typical applications of borehole image data are an appreciation of a reservoir’s geological environment. In hydrate saturated reservoirs, borehole images can also be used to assist in the understanding of the gas migratory path to the hydrate bearing formation. This paper presents a review of some of the current state of the art geophysical log measurements and their application in hydrate saturated reservoirs..

Abbrevations t – fluorescence lifetime j – rotational correlational time ([Ru(bpy)2(phen-ITC)]2+) – Bis-(bipyridine)-5-(isotiocyanatophenantrolin)-Ru(PF6-)2 Ab – antibody AF – Alexa Fluor 660 AF-hGH – with Alexa Fluor 660 labelled human growth hormone FITC – fluorescein isothiocyanate FITC-Ab – FITC labelled antibody FP – fluorescence polarization FRET – fluorescence resonance energy transfer hGH – human growth hormone PMI – N-(3-pyrene)maleimide PMI-hGH – human growth hormone labelled N-(3-pyrene)maleimide PVPPB – poly(N-vinyl-2-pyrolidone) with phenylboronic acid copolymer r – anisotropy RITC – rodamine B isothiocyanate RITC-hGH – with RITC labeled human growth hormone SDS-PAGE – sodium dodecylsulfate-polyacrylamide gel electrophoresis INTRODUCTION Relevance of the study. Human growth hormone (hGH) is a heterogeneous protein with several molecular forms (isoforms). Human growth hormone measurements are complicated because of the heterogeneous nature of hGH. Specific assays for each isoform are currently unavailable. Because the different antibodies used in immunoassays bind to a different spectrum of hGH isoforms, hGH concentrations measured by immunoassay are likely to depend on the particular antibody used. Moreover, because the distribution of the different hGH isoforms varies among individuals, the results from different immunoassays cannot be interrelated easily by using a single conversion factor. Fluorescence is by far the most important optical... [to full text]

This numerical investigation of an advanced Gurson-Tvergaard-Needleman (GTN) model is an extension of the original work of Ben Bettaieb et al. (2011). The model has been implemented as a user-defined material model subroutine (VUMAT) in the Abaqus/explicit FE code. The current damage model extends the previous version by integrating the three damage mechanisms: nucleation, growth and coalescence of voids. Physically based void nucleation and growth laws are considered, including an effect of the kinematic hardening. These new contributions are based and validated on experimental results provided by high-resolution X-ray absorption tomography measurements. Also, the numerical implementation of the kinematic hardening in this damage extension has obliged to readapt the classical triaxiality definition. Besides, a secondary fracture initiation criterion based on the ultimate average inter-cavities distance has been integrated to localize and quantify with good accuracy the strain distribution just before the material fails apart. The current damage model is applied in industrial conditions to predict the damage evolution, the stress state and the fracture initiation in various tensile thin flat sheet geometries and the cross-die drawing tests.