Fracturing of rocks and other geomaterials involves multi-scale processes, from the nucleation of small cracks, their propagation into a complex heterogeneous solid, to their final arrest. In the past 10 years, advances in X-ray tomography imaging techniques, either three dimensional or four dimensional when time-lapse acquisitions are performed, allow detecting fractures at small scale and the growth and coalescence of tiny cracks into well-developed fractures. Some of these fracturing processes involve the coupling between fluids, chemical reactions and fracturing. In the present study I illustrate some of these processes, how they can be imaged using high-resolution X-ray computed tomography; and how conceptual models can make the link between microscopic processes and macroscopic fracturing. This concerns a wide range of applications in geophysics, from fundamental understanding of the rheology of rocks in the Earth’s crust, to salt damage of cultural heritage monuments, hydraulic fracturing of underground reservoirs or emerging technologies of non-conventional hydrocarbon recovery and the underground geological storage of carbon dioxide.

Fast linear transformer driver (FLTD) has some advantages in repetitive operation compared with traditional pulsed power generators. However, different types of gas switches applied in the field of pulsed power technology in recent years cannot reach the requirements of repetitive operation of FLTD. Therefore, the capability of repetitive operation of a multigap gas switch has been investigated in a circuit similar to the basic discharge loop named as brick in this paper. The switch has been triggered more than 2000 times and the distribution of delay time and switch jitter are analyzed and reported. Also, the self-breakdown voltages of the switch during different segments of the triggered breakdown experiment have been tested. The experimental results indicate that the delay time obeys the Gauss distribution and the jitter of 2000 times of discharge is about 2.3 ns.

It is well known that space charge accumulation in insulating materials constitutes the principal cause of dielectric breakdown. Though space charge measurements in polymeric materials have been extensively developed over the last two decades, modeling and simulation works have progressed slowly in this respect. In the present study, a model for bipolar charge transport, as a basis for studying breakdown phenomenon in low density polyethylene (LDPE), is presented. Indeed, we are especially interested in external current dynamic which is the witness of the sample post breakdown. Our results show the effect of the high dc applied voltage and the generation of the space charge packets on the apparition of the post breakdown of the insulator. In order for this effect to be revealed, the external current evolutions under low and high dc applied voltages before and at the breakdown are determined. Indeed, these evolutions show an abrupt increase that is observed when the charge packet aspect occurred in the sample under high dc applied voltage. This observed abrupt increase of the external current is attributed to post breakdown phenomenon. These results are obtained for the first time in modeling and show some aspects similar to those observed in some experimental works.

Measurement of displacement time and length scale dependent dynamics by pulsed gradient spin echo nuclear magnetic resonance in porous media directly provides the preasymptotic hydrodynamic dispersion coefficient. This allows for comparison with nonequilibrium statistical mechanics models of hydrodynamics dispersion in porous media. Preasymptotic dispersion data and models provide characterization of porous media structure length scales relevant to transport and are related to the permeability and sample heterogeneity.

The split Hopkinson pressure bar (SHPB) was used to study the compressibility of shear thickening fluid (STF) at high deformation rate. In this study, a steel bulk was introduced into the SHPB system to confine and load the STF. A series of STFs with different particle types (SiO2 and PSt-EA) and volume fractions (63 vol.% and 65 vol.%) were tested and the results were compared. The reliability of the results was proved by repeating the tests and the force balance in suspension. The bulk modulus was used to evaluate the compressibility of STF, which indicated that the SiO2-based STF exhibited a larger compressibility than the PSt-EA-based STF. It was found that the bulk modulus increases with increasing of the strain rate and the volume fraction shows little effect on the bulk modulus. The structure-dependent mechanical property was analyzed and the loading effect of bulk modulus was considered to be originated from the interparticle clustering.

The Monte Carlo (MC) simulation of electron and hole impact ionization rates for 4H- and 6H-SiC in high electric field is presented. This work focuses on the study of impact ionization rates and impact ionization coefficients since these parameters play a very important role in determining the device performance. In our simulation, the impact ionization rates are obtained by using modified Keldysh equation with a softness factor fitted to the experimental data described by other researchers. The electron and hole impact ionization coefficients in 4H- and 6H-SiC are parameterized at high electric field. The electron and hole impact ionization coefficients for a wide range of electric fields have been successfully derived in our model.

We present multiscale experiments assessing the impact of the recrystallization dynamics of sodium sulfate and sodium chloride on damage observed in sandstone during humidity cycling. The deliquescence of both salts leads to the formation of homogeneous salt solutions which, upon drying, can reach high concentrations before (re)crystallization. For sodium chloride that has only a single crystalline phase, precipitation manifests itself as the fast growth of a small number of nuclei which grow to larger sizes in time. For sodium sulfate, with different crystalline phases, we observe that kinetically the precipitation of the thenardite (the anhydrous phase with the higher solubility) appears to be favored. The comparison of these results with those obtained when rewetting of crystals is done with liquid leads to the conclusion that the size of crystals that precipitate upon recrystallization is an important ingredient for explaining the damage observed in stones, besides the crystallization pressure that is usually invoked.

Permeability of reservoir rocks can be strongly altered by salt precipitation induced by drying. Indeed, gas injection in deep saline aquifers leads first to the brine displacement. The liquid saturation decreases near the injection point and reaches a residual water saturation. But at longer time, the water mass transfer to the gas phase by evaporation can become significant and the dissolved salt can precipitate in the porous structure. The solid salts fill the pores and the permeability decreases. Permeability alteration by salting out is a risk of injectivity decline in the context of CO2 geological storage in saline aquifers where high level of gas injection has to be maintained over decades. However, this problem has been poorly investigated. It implies physical processes that are strongly coupled: drying, water and gas flows in the porous structure and precipitation. This work is an experimental investigation aiming at measuring on natural rock samples the permeability alteration induced by convective drying where dry gas is injected through the sample. We show that alteration of permeability is strong and total blockage of the flow is even possible. We also show that the change in porosity due to the solid salt is heterogeneous along the rock samples. A local permeability-porosity relationship has been estimated from the measurements and we could deduce the permeability alteration function of time by modeling the drying dynamic. We show that it starts very early because capillary backflows are extremely efficient in this process to accumulate solid salt near the injection surfaces.

An all-electron scalar relativistic (AER) calculation on AunPtCO (n = 1–12) clusters had been performed using density functional theory (DFT) with the generalized gradient approximation (GGA) at Perdew-Wang 91 (PW91) exchange-correlation functional level. The CO molecule prefers to be adsorbed on Pt in AunPt (n = 1–12) clusters. The introduction of impurity Pt strengthens the adsorption toward CO molecule and then promotes the reactivity enhancement of CO molecule. The CO molecule is also more favorable to be adsorbed by the even-numbered AunPt clusters with closed-shell electronic structure.

This contribution deals with the state of the art of studies concerning the fabrication of electric double-layer capacitors (EDLCs) also called super- or ultracapacitors and obtained using carbon nanotubes (CNTs) without exploiting Faradic reactions. From the first work published in 1997, EDLCs fabricated using carbon nanotubes as constitutive material for electrodes showed very interesting characteristics. It appeared that they could potentially outperform traditional technologies based on activated carbon. Different methods to fabricate the CNT-based electrodes have been proposed in order to improve the performances (mainly energy densities and power densities), for example filtration, direct growth on metal collector or deposition using an air-brush technique. In this contribution we will introduce the main works in the field. Finally, we will point out an emerging interest for supercapacitors fabricated on flexible substrates, exploiting the outstanding mechanical performances of CNTs, for new kinds of applications such as portable electronics.

Thanks to atomic force microscope observation of swift heavy ion-induced structural modifications of SiO2-Si layer, we show that for a given linear energy transfer value the radial atomic modification along the ion track depends on the ion velocity regime.

An oligothiophene having a donor-acceptor-donor chromophore with hydrogen bonding groups is used as electron donor in planar heterojunction organic photovoltaic cells. We focus on the contact between the anode and the oligothiophene. Different anode buffer layers (ABLs) have been used, MoO3 and CuI, alone or coupled with MoO3. The thicknesses were 4 nm and 3 nm for MoO3 and CuI respectively. It is shown that the ABL improves the cells performances. The best results are achieved with the couple MoO3/CuI through an increase of the open circuit voltage and short circuit current. The optical absorption, the surface roughness and the organic film conductivity depend on the ABL. The conductivity of the oligothiophene film is one order of magnitude higher when the ABL is a CuI film. The influence of the ABL can be explained partly by the fact that it raises the anode work function. Nevertheless, the study of the structures ITO/ABL/oligothiophene shows that each ABL exhibits specific advantages and disadvantages. Therefore the couple MoO3/CuI allows summing up the advantages of both ABLs, MoO3 allows a very good band matching and avoids too high leakage current, while CuI allows achieving high Jsc thanks to its effect on the TTB conductivity.

This paper presents a preliminary experimental investigation of the damping effect of bubble levels on the rotation of pendulous systems. The damping efficiency of such a level is directly correlated to the energy dissipated by the bubble motion. This energy depends on the physical characteristics of the bubble level such as the radius of curvature of the tube, the liquid properties and the bubble length. This study demonstrates that a bubble level can be used to damp the oscillations of dynamic mechanical systems. In particular, commercially available bubble levels might prove suitable for applications where one needs to damp efficiently oscillating systems for which the initial potential energy is less than a hundred times the energy dissipated by the bubble displacement for the first oscillation.

Sliding friction at nanometer scale has become an important factor in the miniaturization of moving components in which the empirical laws of friction do not always hold. This paper carries out large-scale parallel molecular dynamics simulation on sliding friction at atomic scale to uncover the special physical essence. The simulation result shows that both of the elastic deformation normal to the sliding direction at the local area and the edge dislocation are generated in the bulk materials. The successive generation and fracture of the molecular junction between a friction pair ought to be the key reason for the variation of friction force. Furthermore, end failure is observed under both larger or smaller sliding velocity although it does not increase linearly by increasing velocity, that is to say, the end failure decreased if the velocity was larger than some critical value. Different kinds of materials transfer mode is observed in the friction process under different sliding velocity because of the different cross-section of the interaction surfaces. The stick-slip feature of this nanoscale sliding friction with zero separation is different from what was observed at a microscale and should be the integral effect of different control mechanism and the corresponding dynamic behavior.