Studies on water transport in quasi two-dimensional porous systems using neutron radiography

The spontaneous wetting and drying of flat porous samples of linen, cotton and synthetic textiles were studied using dynamic neutron radiography (DNR). The progress of the wetting process of the media was delineated from the obtained neutron dynamical radiography images. The results of the investigation reveal a non-classical behaviour of kinetics of wicking of these materials. The character of the wetting kinetics is discussed in terms of the fractal character of the tortuosity of fabric capillaries.

Pore Structure and Fractal Character of Lacustrine Oil-Bearing Shale from the Dongying Sag, Bohai Bay Basin, China

To better understand the pore structure and fractal character of lacustrine shales and their influence on liquid hydrocarbon occurrences, in this study, a total of 29 lacustrine oil-bearing shale samples collected from the Shahejie Formation in the Dongying Sag, Bohai Bay Basin, were investigated based on nitrogen adsorption (NGA) analysis combined with TOC, Rock-Eval pyrolysis, X-ray diffraction (XRD), and field emission-scanning electron microscopy (FE-SEM) experiments. The relationships among the compositions (TOC, minerals, and oil content), pore structures, and fractal dimensions of the lacustrine shale samples were discussed. The results showed that the adsorption and fractal characteristics of lacustrine oil-bearing shales differ at relative pressures of 0-0.1 and 0.5-1. Two corresponding fractal dimensions D 1 and D 2 were determined by the FHH model according to the nitrogen adsorption branches. Specifically, D 1 varies from 2.4292 to 2.6109 (mean 2.5245), and D 2 varies between 2.4680 and 2.8535 (mean 2.6889). The specific surface area (SSA) ranges from 1.512 m2/g to 34.002 m2/g, with an average of 13.656 m2/g, the total pore volume is between 6.0 × 10-3 cm3/g and 48.4 × 10-3 cm3/g (mean 24.5 × 10-3 cm3/g), and the average pore diameter is in the range of 4.22 nm to 19.57 nm (mean 9.35 nm). Both D 1 and D 2 increase with increasing SSA and increase with decreasing average pore diameters but have no correlation with pore volume. Moreover, D 1 and D 2 exhibit positive relationships with clay minerals and negative correlations with carbonate minerals (calcite and dolomite). The relationship between fractal dimensions ( D 1 and D 2 ) and TOC contents is expressed as a U-shaped curve, characterized by the minimum D values at approximately 3% TOC. The shale oil content is controlled by the pore structures and fractal dimensions, and lacustrine shales with lower SSAs and smaller fractal dimensions would have more free oil. Therefore, lacustrine shales in the oil window with TOC contents ranging from 2% to 4% are probably the preferred shale oil exploration target in the Shahejie Formation, Dongying Sag, Bohai Bay Basin. The results indicate that fractal analysis can provide insight into the pore structure characteristics and oil storage capacity of lacustrine shales.

Nonlinear excitation of hypersound vibrations in ferrite plate in conditions of combine influence in two frequencies. Part 2. Variation of constant field

The task about nonlinear excitation of hypersound vibrations in ferrite plate in conditions of combine influence in two frequencies is investigated. The thickness of plate is chosen so as the frequency of its elastic resonance was equal to difference of two components of alternating field. The most attention is given to properties of excited elastic vibrations by changing the value of applied constant field. The system of nonlinear motion equations of magnetization and elastic displacement is described. For solving of this system, the numerical method Runge-Cutta is applied. The results of this calculation are the time-evolvent of vibrations, dependencies magnetic end elastic vibrations amplitudes and also the spectra of vibrations in permanent conditions after end of relaxation processes. The influence of constant field value on character of vibrations is investigated. The comparison of amplitude-frequency characteristics of magnetic and elastic vibrations in linear and nonlinear regimes by the thickness of plate correspond to resonance on central and different frequencies is carried out. It is shown that by thickness which correspond to resonance on different frequency the characteristic has large indented skirting. It is found the large variety of dependencies of elastic vibrations character from field. In condition of stabilization so as after the completion of relaxation establishment processes it is found five more character regimes of vibrations: regime №1 – small-amplitude chaos; regime №2 – regular vibrations; regime №3 – non-symmetrical doubling of period; regime №4 – symmetrical doubling of period; regime №5 – irregular beating. For each of regimes the evolution of vibrations along time are obtained and the corresponding frequency spectra are found. The localization of regimes along the value of constant field by difference excitation level is investigated. It is found that the region of large-amplitude regimes (№2–№5) is limited in both sides by regions of small-amplitude regime №1. It is found that inside of region where large-amplitude regimes take place the most extended regime is generalized regime with doubling of period which is the sum of regimes №3 and №4 which occupies about 79%. The next on prevalence it the regime №5 – irregular beating which occupies 13% of whole region. The most exceptional is the regime №2 – regular vibrations which occupies only 8% from whole interval. It is found the extremely large critical intending of dependence of elastic vibrations amplitude from constant field. It is found that the structure of amplitude-field characteristic is very sensual to excitation level and plate thickness and the degree of sensitivity reach part of percent. From the comparison of localization on field by magnetic and elastic characteristics it is found that elastic characteristics as a whole are displaced down along field relatively magnetic characteristics. In this case the low-field falling of elastic characteristics is localized on the same falling of magnetic characteristics but the high-field falling of elastic characteristics is localized slightly lower of the field value which correspond to ferromagnetic resonance on central frequency. It is found that the reason of this displacement in this case is elastic resonance of plate on difference frequency. The card of regimes on the plane "alternating field – constant field” along broad interval of varying of both fields is constructed. It is found that by the constant field the large-amplitude regimes on the card occupy the “curved-linear trapezium” which axis lies along the coordinate “alternating field” and transverse width along coordinate “constant field” by increasing of alternating field is increased. It is found that outside of both sides by constant field of this “trapezium” the low-amplitude regime №1 – “small-amplitude chaos” is exited. The middle of “trapezium” occupies the strip directed along coordinate “alternating field” which is filled by regime №5 – “irregular beating”. Along both sides from this strip also right until the boundaries of “trapezium” the regimes №3 and №4 – “doubling of period” are excided. The reasons and necessary conditions of chaotic character of elastic vibrations are investigated. It is found that the necessary condition of chaos is excitation simultaneous in two frequencies. It is found that the large indented jumping character of dependence elastic vibrations amplitude from constant field has as first-reason the chaotic character magnetic vibrations. The character of jumps in dependence elastic vibrations amplitude from constant field is investigated. It is shown that by two-frequencies excitation the increasing of step along field causes large increasing of indenting of characteristics. It is found that the same behavior of amplitude-field dependencies of vibrations reveals its fractal character. The some comments about nature of jumps are proposed. It is found that jumps are determined by non-permanent character exactly magnetic vibrations which are shown only by two-frequency excitation on enough large level and have fractal character. As an analogy is mentioned that the line (skirting) of elastic vibrations field dependence on the plane “amplitude-field” is similar to chaotic trajectory of time-evolvent of vibrations on the plane “amplitude-time” for different oscillators which show chaotic vibrations. It is mentioned that the same behavior of trajectories on the plane “coordinate-potential” take place in cases when potential has dynamic character. The supposition is proposed that in investigated here task about two-frequency excitation of magnetostriction transducer may by constructed the function which can play the role of dynamic potential.

Friction of sea ice

Static and kinetic friction play a fundamental role in sea-ice mechanics. The coefficient of static friction increases with hold time under normal load and is modelled in terms of creep and fracture of asperities in contact. The coefficient of kinetic friction exhibits velocity strengthening at lower speeds and velocity weakening at intermediate speeds. Strengthening is modelled in terms of asperity creep and hardness; weakening is modelled in terms of a progressive increase in the true area of contact wetted by meltwater produced through frictional heating. The concept is introduced of contact size distribution in which the smallest contacts melt first, leading to the onset of weakening; the largest melt last, leading to a third regime of kinetic friction and again to strengthening where hydrodynamics governs. Neither the static nor the kinetic coefficient is significantly affected by the presence of sea water. The paper closes with a few implications for sea-ice mechanics. The paper is based largely upon a critical review of the literature, but includes a more quantitative, physics-based analysis of velocity strengthening and a new analysis of velocity weakening that incorporates parameters that describe the (proposed) fractal character of the sliding interface. This article is part of the theme issue ‘Modelling of sea-ice phenomena’.

IUPAC Large or Small? Some Fractal Character?

Some of you will have come across delightful pictures of those weird beasts called fractals, whether they be mathematically generated, or those that abound in nature (such as ferns). If you haven’t, then I think you should spend a little time hunting some down on the web. Apart from the almost magical self-similarity at different scales (which means that even if you zoom in you get a picture that looks very similar to that you started with), the other notable feature of fractals is that they have non-integer dimensions. A piece of paper is two-dimensional when laid out flat; a ball is a three-dimensional. A crumpled up piece of paper, an object with some two-dimensional character due to its origin (and the fact that it is still really only a surface) and some three-dimensional character (as it does fill space in some way), is somewhere in the middle. A coastline is more than one-dimensional but less than two dimensional—it too is a fractal. One of the interesting features of fractals, like a coastline, is that the length that you measure depends on the size of ruler you use.

CHARACTERIZATION OF THE IRREGULARITY OF A TERRAIN USING FRACTAL DIMENSION OF LAKES' BOUNDARIES

Even though many objects and phenomena of importance in geophysics have been shown to have fractal character, there are still many of them which show self-similar character and yet to be studied. The objective of the present work is to demonstrate that the fractal dimension of the boundary of a natural water body can be used to shed light on irregularity as well as other properties of a region. Owing to easy availability of satellite images and image processing softwares, this turns out to be a handy tool. In this study, we have analyzed several lakes in India mostly around the Western Ghats region. We find that the fractal dimension of their boundaries for the length scales between around 40 m to 2 km, in general, has broad variation from 1.2 to 1.6. But when they are grouped into three categories, viz., lakes along the ridge of Western Ghats, lakes in the planes and lakes in the mountain region, we find the first two groups to have a narrower distribution of dimensions.