Effects of pore fluids on quasi‐static shear modulus caused by pore‐scale interfacial phenomena

It is evident from the laboratory experiments that shear moduli of different porous isotropic rocks may show softening behaviour upon saturation. The shear softening means that the shear modulus of dry samples is higher than of saturated samples. Shear softening was observed both at low (seismic) frequencies and high (ultrasonic) frequencies. Shear softening is stronger at seismic frequencies than at ultrasonic frequencies, where the softening is compensated by hardening due to unrelaxed squirt flow. It contradicts to Gassmann's theory suggesting that the relaxed shear modulus of isotropic rock should not depend upon fluid saturation, provided that no chemical reaction between the solid frame and the pore fluid. Several researchers demonstrated that the shear softening effect is reversible during re‐saturation of rock samples, suggesting no permanent chemical reaction between the solid frame and the pore fluid. Therefore, it is extremely difficult to explain this fluid‐rock interaction mechanism theoretically, because it does not contradict to the assumptions of Gassmann's theory, but contradicts to its conclusions. We argue that the observed shear softening of partially‐saturated rocks by different pore fluids is related to pore‐scale interfacial phenomena effects, typically neglected by the rock physics models. These interface phenomena effects are dependent on surface tension between immiscible fluids, rock wettability, aperture distribution of microcracks, compressibility of microcracks, porosity of microcracks, elastic properties of rock mineral, fluid saturation, effective stress and wave amplitude. Derived equations allow to estimate effects of pore fluids and saturation on the shear modulus and mechanical strength of rocks.publishedVersio

The Role of Digital Geography in the Development of Tourism and Tourist Activities

Geography and tourism are interconnected and mutually enriching areas. Tourism, as the most susceptible activity to innovations, responds to digital geography by increasing population flows, developing territories, organizing services and leads to an increase in the level of self-organization of activities. Digital technologies are actively penetrating the field of excursions and independent tourism. Mobile audio guides capture the infinite variety of urban space, help young people get involved in the process of developing audio guides, update knowledge of geography, history, culture and form the skill of digital presentation of the knowledge gained. Digital technologies contribute to the intensive development of independent tourism in places inside of the "Infrastructures oecumene ". High rates of inbound tourism are registered in Iceland. Tourism in the form of a family trip by car is largely due to the arrival of digital services for accommodation and meals, car rental. In connection with the development of digital geography in the sphere of tourism, new areas of research are taking shape. The main aim of the study is to investigate the role of digital geography in the development of tourism and tourist activities and attempt to draw some practical and innovative conclusion since the tourism industry has been one of the most lucrative industries over the last decades. In this study, methods of analysis and synthesis of scientific literature, data from a review of audio tours of Perm on the izi.TRAVEL platform, and official tourism statistics from Iceland were utilized to fulfil the aim of the study

Association between exposure to radioactive iodine after the Chernobyl accident and thyroid volume in Belarus 10-15 years later

Background: While there is a robust literature on environmental exposure to iodine-131 (131I) in childhood and adolescence and the risk of thyroid cancer and benign nodules, little is known about its effects on thyroid volume. Methods: To assess the effect of 131I dose to the thyroid on the volume of the thyroid gland, we examined the data from the baseline screening of the Belarusian-American Cohort Study of residents of Belarus who were exposed to the Chernobyl fallout at ages ≤18 years. Thyroid dose estimates were based on individual thyroid activity measurements made shortly after the accident and dosimetric data from questionnaires obtained 10-15 years later at baseline screening. During baseline screening, thyroid gland volume was assessed from thyroid ultrasound measurements. The association between radiation dose and thyroid volume was modeled using linear regression where radiation dose was expressed with power terms to address non-linearity. The model was adjusted for attained age, sex, and place of residence, and their modifying effects were examined. Results: The analysis was based on 10,703 subjects. We found a statistically significant positive association between radiation dose and thyroid volume (P \u3c 0.001). Heterogeneity of association was observed by attained age (P \u3c 0.001) with statistically significant association remaining only in the subgroup of ≥18 years at screening (P \u3c 0.001). For this group, increase in dose from 0.0005 to 0.15 Gy was associated with a 1.27 ml (95% CI: 0.46, 2.07) increase in thyroid volume. The estimated effect did not change with increasing doses above 0.15 Gy. Conclusions: This is the first study to examine the association between 131I dose to the thyroid gland and thyroid volume in a population of individuals exposed during childhood and systematically screened 10-15 years later. It provides evidence for a moderate statistically significant increase in thyroid volume among those who were ≥ 18 years at screening. Given that this effect was observed at very low doses and was restricted to a narrow dose range, further studies are necessary to better understand the effect

A New Method for Treating Burn Wounds Using Targeted Delivery of Medicinal Substances by Magnetic Nanocarrier (Experimental Part)

Проведено экспериментальное исследование на лабораторных животных по изучению эффективности адресной доставки мази левомеколь с помощью магнитных наночастиц и внешнего магнитного поля при термических ожогах. В исследовании принимало участие 20 крыс с двумя очагами ожога. Крысы были разделены на 4 группы: без лечения, терапия с использованием мази левомеколь, лечение с использованием наночастиц, мази левомеколь и внешнего магнитного поля и только магнитотерапии. При гистологическом исследовании на 14-е сутки во всех группах в зоне термического повреждения кожи были отмечены признаки глубокого ожога III и IV степени с распространением некроза на всю глубину дермы и на мышцы. В группе с наночастицами, мазью левомеколь и магнитным полем на фоне уменьшения воспаления отмечалось очаговое появление грануляционной ткани. Таким образом, гистологические исследования ожогового раневого процесса лабораторных животных показали, что использование инновационного биологически активного ранозаживляющего средства на основе наночастиц в сочетании с мазью левомеколь улучшает регенерацию тканей и приводит к ускорению эпителизации, что в целом повышает результаты лечения ожоговой раны. Использование внешнего магнитного поля способствует адресной доставке лечебного нанокомплекса и поддержанию оптимальной концентрации препарата в ранеExperimental studies have been carried out on laboratory animals to investigate the effectiveness of targeted delivery of levomekol ointment using magnetic nanoparticles and an external magnetic field for treatment of thermal burns. The study involved 20 rats, with two burns on each. The rats were divided into 4 groups: untreated; treated with levomekol ointment; treated with levomekol ointment associated with nanoparticles and an external magnetic field; and treated with magnetic field alone. Histological examination was conducted on Day 14, and in all groups, in the thermal burn zone of the skin there were signs of deep three- and four-degree burns with necrosis spread through the dermis, reaching the muscle. In the group with levomekol ointment associated with nanoparticles and magnetic field, inflammation was decreased, and focal granulation tissue formation was observed. Thus, histological studies of the burn wound process in laboratory animals showed that the use of an innovative biologically active wound healing agent based on nanoparticles in combination with the levomecol ointment improved tissue regeneration and accelerated epithelialization, which enhanced the effectiveness of burn wound treatment. The use of an external magnetic field facilitated targeted delivery of the therapeutic nanosystem and maintenance of the optimal concentration of the drug in the woun

Bulk moduli and seismic attenuation in partially saturated rocks: hysteresis of liquid bridges effect

This is the peer reviewed version of the following article: Rozhko, A.Y. (2019) Bulk moduli and seismic attenuation in partially saturated rocks: hysteresis of liquid bridges effect. Geophysical Prospecting, which has been published in final form at https://onlinelibrary.wiley.com/doi/abs/10.1111/1365-2478.12782. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.A key task of exploration geophysics is to find relationships between seismic attributes (velocities and attenuation) and fluid properties (saturation and pore pressure). Experimental data suggests that at least three different factors affect these relationships, which are not well‐explained by classical Gassmann, Biot, squirt‐flow, mesoscopic‐flow and gas dissolution/exsolution models. Some of these additional factors include: i) effect of wettability and surface tension between immiscible fluids; ii) saturation history effects (drainage vs imbibition); iii) effects of wave amplitude and effective stress. We apply a new rock physics model to explain the role of all these additional factors on seismic properties of partially saturated rock. The model is based on well‐known effect in surface chemistry: hysteresis of liquid bridges. This effect is taking place in cracks, which are partially‐saturated with two immiscible fluids. Using our model, we investigated: 1) physical factors affecting empirical Brie correlation for effective bulk modulus of fluid; 2) the role of liquids on seismic attenuation in the low frequency (static) limit; 3) water‐weakening effects and 4) saturation history effects. Our model is applicable in the low frequency limit (seismic frequencies) when capillary forces dominate over viscous forces during wave‐induced two‐phase fluid‐flow. The model is relevant for seismic characterization of immiscible fluids with high contrast in compressibilities, i.e. for shallow gas exploration and CO2 monitoring.acceptedVersio

Effective fluid bulk modulus in the partially saturated rock and the amplitude dispersion effects

Frequency dispersion is a well-known effect in geophysics, which means that waves of different wavelengths propagate at different velocities. Amplitude dispersion is a less-known effect, which means that waves of different amplitudes propagate at different velocities. Herewith, we consider the alteration of the interfacial energy during wave-induced two-phase fluid flow in a partially saturated rock and demonstrate that this leads to a nonlinear amplitude dispersion effect. When the wave amplitude is small, seismic waves cause bending of the interface menisci between immiscible fluids at the pore scale. However, when the wave amplitude is sufficiently large, the interface menisci will slip at the pore scale, causing attenuation of the elastic energy by the contact line friction mechanism. At the zero frequency limit, all viscous dissipation models predict zero attenuation of the elastic wave energy, while this approach predicts a nonzero attenuation due to a static contact angle hysteresis effect. Herein, we extend the Gassmann's theory with three extra terms, which can be obtained from standard laboratory tests: pore-size distribution and interfacial tension between immiscible fluids and rock wettability (advancing and receding contact angles). We derive closed-form analytical expressions predicting the effective fluid modulus in partially saturated rock, which falls between Voigt and Reuss averages. Next, we demonstrate that the nonlinear amplitude dispersion effect leads to energy transfer between different frequencies. This may explain the low-frequency microtremor anomalies, frequently observed above hydrocarbon reservoirs, when the low-frequency energy of ocean waves (0.1–1 Hz) is converted to higher frequencies (2–6 Hz) by partially saturated reservoirs.publishedVersio

Rôle des forces de succion sur la fracturation hydraulique

The mechanical role of seepage forces on hydraulic fracturing and failure patterns was studied both by the analytical methods of the continuum mechanics and by numerical simulations. Seepage forces are frictional forces caused by gradients of pore-fluid pressure. Formation of different failure patterns (localized shear bands or tensile fractures) driven by the localized fluid overpressure in the poro-elasto-plastic medium was studied using a numerical code specially developed for this purpose. The pre-failure condition for different failure patterns and fluid pressure at the failure onset was predicted using a new analytical solution. In the analytical solution the elliptical cavity filled with fluid in the non-hydrostatic far-field stress-state is considered. Since, the fluid pressure inside cavity differs from the far-field pore-fluid pressure; the poroelastic coupling is taking into account in the calculation of the deformation. Using Griffith's theory for failure and this analytical solution, the generalized equation for the effective stress law was obtained. This generalized effective stress law controls the failure in the fluid-saturated porous medium with a non-homogeneous fluid pressure distribution.L'effet mécanique des forces de succion, forces exercées par un fluide qui se déplace dans un milieu poreux, a été étudié dans le cadre de la fracturation hydraulique des roches de la croûte terrestre. Cet effet a été étudié par des méthodes analytiques issues de la mécanique des milieux continus, et par des simulations numériques. Ces forces de succion sont des forces de frottement causées par des gradients de pression fluide dans les milieux poreux. Différents modes de fracturation (bandes de cisaillement localisées, fractures en mode I) causés par une augmentation localisée de la pression fluide dans la croûte ont été reproduits dans un milieu poro-élastique grâce à plusieurs codes numériques spécialement développés à cet effet. La valeur de la pression fluide lors de la nucléation de la fracturation est aussi prédite à l'aide d'une nouvelle solution analytique. Dans la solution analytique, une cavité elliptique dans un solide poreux est remplie avec un fluide à une pression non-hydrostatique. On considère aussi que le milieu poreux est soumis à un champ de contrainte externe. Puisque la pression du fluide dans la cavité est différente de la pression de pore dans la roche; le couplage poro-élastique est pris en compte dans le calcul des déformations. A partir de la théorie de Griffith qui donne une condition pour la propagation d'une fracture, et en utilisant la solution analytique obtenue, une équation généralisée a été obtenue pour la contrainte effective dans le milieu. Cette nouvelle loi décrit la fracturation dans un milieu poreux saturé avec un fluide, et dans lequel la distribution de pression fluide n'est pas homogène

Comparison of Effects of Uranium and Americium on Bioluminescent Bacteria

Effect of UO2(NO3)2 on bioluminescent bacteria P.Phosphoreum was studied. It was compared with the effect of solutions of the more active radionuclide - 241Am(NO3)3 studied earlier (Rozhko et al., 2007). Bioluminescence inhibition was observed under uranyl concentrations exceeding 10-7 M (30 Bq/l); and bioluminescence activation was not observed under all radionuclide concentrations and exposure times in the experiment. Effect of uranyl was attributed to chemical component of its impact, not radiation one. It was shown that solutions of Americium were detoxified by humic substances (0.25 mg/ml), but solutions of uranyl – are not

Stimulating relative permeability changes by low-frequency elastic waves: Theory and lab experiments

A model is presented to describe how low-frequency vibrations can induce changes to relative permeabilities in dual-porosity dual-permeability rocks. We show that a combination of two physical processes may cause this effect: 1) the wave-induced two-phase fluid flow between soft pores (fractures or cracks) and stiff pores (matrix); and 2) the contact angle hysteresis effect. These two effects lead to redistribution of fluid saturation between fractures and matrix, which may explain alteration of relative permeabilities by small transient strains (∼10−6) in rocks where the fluid flow occurs primarily through the fracture network, and fluid storage occurs predominantly in the porous matrix. We assume that the frequency is low enough that viscous and inertial effects are negligible and that any stress-induced increments of pore pressure are uniform within wetting and nonwetting fluid phases. We demonstrate that pulse-like vibrations are much more efficient in changing relative permeabilities than sinusoidal-shaped vibrations. Furthermore, we show that two waveforms with the same amplitude and frequency but with different polarities could have opposite effects on the alteration of relative permeabilities. Specifically, extensional pulses increase oil relative permeability and decrease water relative permeability in the water-wet rock. Contrary, compressional pulses decrease oil relative permeability and increase water relative permeability in the water-wet rock. To validate theoretical results, we developed a unique low-frequency laboratory setup and experimental methods. We performed drainage and imbibition cycles on a sandstone sample using oil and water as pore fluids. During flooding, the sample was excited by small-strain seismic pulses of a specific shape, with varying polarization direction, frequency, and amplitude. The preliminary laboratory results validate the theoretical model qualitatively. The proposed model may contribute to environmentally friendly and low-cost methods for stimulating hydrocarbon production in conventional reservoirs without invasive chemicals or fracking. In unconventional reservoirs, however, this technology can be envisioned as supplementary to standard EOR/IOR techniques. Normally, the seismic wave energy is too low to increase absolute permeability or decrease oil viscosity; only relative permeabilities can be affected.publishedVersio

Breakdown of the quantum Hall effect in epitaxial graphene

We present the phase space defined by the quantum Hall effect breakdown in polymer gated epitaxial graphene on SiC (SiC/G) as a function of temperature, current, carrier density, and magnetic field. At 2 K, breakdown currents (Ic) almost 2 orders of magnitude greater than in GaAs devices are observed. We use this knowledge to explore the potential of using graphene as a high temperature (> 2 K) and low magnetic field (< 5 T) quantum resistance standard