Fracture properties of GGBS-dolomite geopolymer concrete

Purpose This study aims to predict the fracture properties of geopolymer concrete, which is necessary for studying failure behaviour of concrete. Design/methodology/approach Geopolymers are new alternative binders for cement in which polymerization gives strength to concrete rather than through hydration. Geopolymer concrete was developed from industrial byproducts such as GGBS and dolomite. Present study estimates the fracture energy of GGBS geopolymer concrete using three point bending test (RILEM TC50-FMC) with different percentages of dolomite and compare with cement concrete having same strength. Findings The fracture properties such as peak load, critical stress intensity factor, fracture energy and characteristic length are found to be higher for GGBS-dolomite geopolymer concrete, when their proportion becomes 70:30. Originality/value To the best of the authors’ knowledge, this is an original experimental work.

Temperature Profiles During Cryolipolysis

Cryolipolysis is a noninvasive clinical procedure for the local reduction of adipose tissue. Paddles as cold as ~10 °C are placed in good thermal contact the epidermis. The goal is to cool the subcutaneous adipose tissue to ~10 °C, which induces apoptosis and an inflammatory response in the adipocytes. The dermis is, of course, cooler than the adipocytes, but the triglyceride in the adipocytes are thought to crystalize, causing apoptosis. The clinical procedure have been developed empirically. A mathematical model could aid in understanding the mechanisms of response and improving the design of the procedure. Here, the Pennes equation is used to model the temperature of the tissue during cooling. The two parameters identified are the thermal diffusivity of the tissue and a blood perfusion parameter, which also gives the characteristic length. Green's functions are used to solve the Pennes equation, which simplifies to a transient fin equation.

Self-Diffusion in Simple Liquids as a Random Walk Process

It is demonstrated that self-diffusion in dense liquids can be considered a random walk process; its characteristic length and time scales are identified. This represents an alternative to the often assumed hopping mechanism of diffusion in the liquid state. The approach is illustrated using the one-component plasma model.

Study of Momentum Diffusion with the Effect of Adiabatic Focusing

The momentum diffusion of charged energetic particles is an important mechanism of the transport process in astrophysics, the physics of fusion devices, and laboratory plasmas. In addition to the momentum diffusion term for a uniform field, we obtain an additional momentum diffusion term due to the focusing effect of the large-scale magnetic field. After evaluating the coefficient of the additional momentum diffusion term, we find that it is determined by the sign of the focusing characteristic length and the cross helicity of the turbulent magnetic field. Furthermore, by deriving the mean momentum change rate contributed from the additional momentum diffusion term, we identify that the focused field provides an additional momentum loss or gain process.

Cavity Expansion in Cohesive-Frictional Soils with Limited Dilation

The problem of cavity expansion from zero radius has no characteristic length and therefore possesses a similarity solution, in which the cavity pressure remains constant and the continuing deformation is geometrically self-similar. In this case, the incremental velocity approach first used by Hill (1950) to analyze cavity expansion in Tresca materials can be extended to derive a solution for limiting pressure of cavity expansion in other types of material. In this article, a rigorous semi-analytical solution is derived, following Hill's incremental velocity method, for the expansion of cavities from zero initial radius in cohesive-frictional soils with limited dilation. In particular, the radius of the elastic-plastic interface c is used in this article as the time scale and the solution for the limit pressure has been presented. Solutions are evaluated for a number of cases representative of a range of cohesive-frictional and dilatant soils. A comparison is also made between the solutions presented here and previous solutions for cohesive-frictional soils that have unlimited (on-going) plastic dilation. In particular, the influence of limited plastic dilation on the cavity limit pressure is identified and discussed.

On the limits of quasi-static theory in plasmonic nanostructures

The approximated analytical approach of Quasi-Static Theory (QST) is widely used in modelling the optical response of plasmonic nanoparticles. It is well known that its accuracy is remarkable provided that the particle is much smaller than the wavelength of the interacting radiation and that the field induced inside the structure is approximately uniform. Here, we investigate the limits of QST range of validity for gold nanostructures freestanding in air. First, we compare QST predictions of scattering spectra of nanospheres and cylindrical nanowires of various sizes with the exact results provided by Mie scattering theory. We observe a non-monotonic behaviour of the error of QST as a function of the characteristic length of the nanostructures, revealing a non-trivial scaling of its accuracy with the scatterer size. Second, we study nanowires with elliptical section upon different excitation conditions by performing finite element numerical analysis. Comparing simulation results with QST estimates of the extinction cross-section, we find that QST accuracy is strongly dependent on the excitation conditions, yielding good results even if the field is highly inhomogeneous inside the structure.

On mesoscale strain fluctuations in tensile tests on additively manufactured 17-4PH stainless steel

Additively manufactured materials usually exhibit mesoscale heterogeneities. Mesoscale fluctuations of strain fields in notched samples made of 17-4PH Stainless steel and loaded in tension are investigated. Regularized digital image correlation enables for the analysis of strain fluctuations at different length scales. Five tests on specimen fabricated with different printing parameters are studied. It is shown that the strain fluctuations have no characteristic length scale and are essentially independent of the probed processing parameters.

Multi-Dimensional Nuclear Magnetic Resonance Methods in the Inhomogeneous Magnetic Field

<p>This thesis introduces new NMR techniques which use the inhomogeneous internal magnetic fields present in the pore space of a porous medium exposed to an external magnetic field to obtain information about the pore size and heterogeneities of the the sample. Typically internal field inhomogeneities are regarded as unwanted due to their effect on various material properties such as relaxation and diffusion. However, in the experiments presented here, we choose samples specifically for their inhomogeneous internal fields and use multi-dimensional NMR methods and simulations to obtain our pore space and heterogeneity information. We first describe software developed to specifically simulate the internal magnetic field and diffusion through the pore space of a simple sphere pack system. This software generates a sphere pack and calculates the internal magnetic field generated by z-aligned magnetic dipoles placed at the center of each sphere. The internal magnetic field gradient is also calculated in the pore space. From there, a random walk method is developed and a realistic reflection off a sphere is introduced. We work through the development of this software and the mathematics behind the algorithms used. This simulation is used in all subsequent experimental chapters. We then use a two-dimensional exchange experiment to separate the susceptibility induced line broadening with the broadening caused by diffusion through the inhomogeneous field. We observe off-diagonal line broadening as the mixing time increases. We attempt to quantify this off-diagonal growth by selecting points on either side of the off-diagonal maximum and plotting their average as a function of mixing time. A biexponential fit to the average intensities with respect to mixing time results in a characteristic time and from that a characteristic length as a fraction of bead diameter. This experiment is simulated and a biexponential growth is also observed in the simulated off-diagonal with characteristic lengths comparable to experiment. To obtain a correlation length directly from experiment and not deduce one from a characteristic time, we add a spatial dimension to our exchange experiment in the form of a propagator dimension. This dimension allows us to select 2D spectra based on their Z-displacement. We observe off-diagonal growth due to both an increase in Z-displacement and an increase in mixing time. We move away from the biexponential fit and move to a relationship based on mixing time, effective diffusion, and Z-displacement to directly calculate a characteristic length. We see these same traits in the simulated data which agrees well with experiment. Lastly, we move away from exchange experiments and move to correlating the transverse relaxation time with the internal field offset. We find that there is correlation at large magnetic field offsets and small T2 times which appear to be indicative of sample heterogeneities. To confirm this we use a highly heterogeneous rock core sample which increases the correlations seen at the previous offsets and times. This experiment is more qualitative than the previous two as we do not have a concrete value for the heterogeneity of our samples. The simulation used throughout the thesis, while showing a definite correlation between field offset and T2 relaxation, is unable to accurately simulate the experiment and requires more development.</p>