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result(s) for
"Efremov, A. P"
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Carbonate-Quartz Cement Composites
The technology of obtaining multicomponent high-quality concrete using limestone powders as fillers is considered. In order to select fillers for powder-activated concrete, a study was made of the water absorption of limestone gravel of various kinds. According to the water absorption index, eight categories of limestone species have been identified. It was revealed that organogenic limestone is one of the materials that is preferred as a filler for high-quality concrete. The experimental results were obtained and graphical dependences of changes in the tensile strength under bending and compression, the dynamic modulus of elasticity and water demand of organogenic cement composites filled with limestone from granulometric composition and filler content were constructed. It has been established that the best strength properties are manifested in materials with optimal indicators of the content and size of limestone and silica powder.
Journal Article
Analysis of the corrosion and inhibitive protection of the Lukoil Komi oil-fields equipment
Monitoring data on the contamination by sulfate-reducing bacteria (SRB) of the pay beds of the Usinsk, Vozei, and Khar’ yaga oil fields (OOO Lukoil Komi) and the corrosion state of oil-field equipment are presented. It was experimentally found that SRB affect the rate and character of the corrosion of carbon and low-allowed steels. The formulations Olazol T2P and T2PM were tested as corrosion inhibitors and bactericides in H2S-containing mineralized aqueous and two-phase media. The experience of their commercial application was generalized.
Journal Article
Corrosion Behavior of Aluminum Alloys in the Presence of Hydrogen Sulfide
The corrosion-electrochemical behavior of both carbon steel and aluminum alloys in hydrogen sulfide-bearing mineralized media is considered. An increase in the partial pressure of hydrogen sulfide aggravates the catastrophic breakdown of carbon steel, yet diminishes both the corrosion rate and the localization of corrosion attack on aluminum alloys. An investigation of the nature of the nonstoichiometry of surface oxide films on both carbon steel and aluminum alloys with the use of photoelectric-recombination method, revealed that the films fundamentally differ in semiconductive properties, according to which hydrogen sulfide can either promote or inhibit the corrosion. That is why hydrogen sulfide oppositely affects the corrosion-electrochemical behavior of aluminum alloys and carbon steels.[PUBLICATION ABSTRACT]
Journal Article
Further Development of Ideas of G.V. Akimov on the Surface Oxide Films and Their Effect on the Corrosion and Mechanical Behavior of Aluminum Alloys
The importance of oxide films and their perfection in extending the application of aluminum alloys are shown. The composition and structure of oxide films formed by microarc oxidation on aluminum alloys of different alloying systems and production methods are studied. The dependence of the oxide coating properties on the parameters of microarc oxidation are found. The results obtained are discussed in terms of the existing concepts of microarc oxidation.[PUBLICATION ABSTRACT]
Journal Article
Inhibition of constitutive and BCR-induced Syk activation downregulates Mcl-1 and induces apoptosis in chronic lymphocytic leukemia B cells
The protein kinase Syk is a key mediator of proximal B-cell receptor (BCR) signaling. Following antigen stimulation, Syk is recruited to the BCR and becomes activated by phosphorylation at Y352. Recently, Syk was found to be constitutively phosphorylated in several common B-cell lymphoma subtypes, indicating a role for antigen-independent Syk activation in the pathogenesis of these diseases. We now report that Syk is constitutively phosphorylated on the activating Y352 residue in chronic lymphocytic leukemia (CLL) B cells. To examine the effects of constitutive Syk activity on intracellular signaling and leukemic cell survival, we performed
in vitro
studies with the Syk inhibitor R406. Treatment with R406 induced leukemic cell apoptosis in the majority of investigated cases and affected the basal activity or expression of several pro-survival molecules regulated by Syk, including the Akt and extracellular signal-regulated (ERK) kinases, and the anti-apoptotic protein Mcl-1. In addition, R406 prevented the increase in leukemic cell viability induced by sustained BCR engagement and inhibited BCR-induced Akt activation and Mcl-1 upregulation. Collectively, these data identify Syk as a potential target for CLL treatment and suggest that inhibition of this kinase could provide a double therapeutic benefit by disrupting both antigen-dependent and antigen-independent signaling pathways that regulate leukemic cell survival.
Journal Article
Viscoelasticity in simple indentation-cycle experiments: a computational study
Instrumented indentation has become an indispensable tool for quantitative analysis of the mechanical properties of soft polymers and biological samples at different length scales. These types of samples are known for their prominent viscoelastic behavior, and attempts to calculate such properties from the indentation data are constantly made. The simplest indentation experiment presents a cycle of approach (deepening into the sample) and retraction of the indenter, with the output of the force and indentation depth as functions of time and a force versus indentation dependency (force curve). The linear viscoelastic theory based on the elastic–viscoelastic correspondence principle might predict the shape of force curves based on the experimental conditions and underlying relaxation function of the sample. Here, we conducted a computational analysis based on this theory and studied how the force curves were affected by the indenter geometry, type of indentation (triangular or sinusoidal ramp), and the relaxation functions. The relaxation functions of both traditional and fractional viscoelastic models were considered. The curves obtained from the analytical solutions, numerical algorithm and finite element simulations matched each other well. Common trends for the curve-related parameters (apparent Young’s modulus, normalized hysteresis area, and curve exponent) were revealed. Importantly, the apparent Young’s modulus, obtained by fitting the approach curve to the elastic model, demonstrated a direct relation to the relaxation function for all the tested cases. The study will help researchers to verify which model is more appropriate for the sample description without extensive calculations from the basic curve parameters and their dependency on the indentation rate.
Journal Article
Myosin IIA and formin dependent mechanosensitivity of filopodia adhesion
Filopodia, dynamic membrane protrusions driven by polymerization of an actin filament core, can adhere to the extracellular matrix and experience both external and cell-generated pulling forces. The role of such forces in filopodia adhesion is however insufficiently understood. Here, we study filopodia induced by overexpression of myosin X, typical for cancer cells. The lifetime of such filopodia positively correlates with the presence of myosin IIA filaments at the filopodia bases. Application of pulling forces to the filopodia tips through attached fibronectin-coated laser-trapped beads results in sustained growth of the filopodia. Pharmacological inhibition or knockdown of myosin IIA abolishes the filopodia adhesion to the beads. Formin inhibitor SMIFH2, which causes detachment of actin filaments from formin molecules, produces similar effect. Thus, centripetal force generated by myosin IIA filaments at the base of filopodium and transmitted to the tip through actin core in a formin-dependent fashion is required for filopodia adhesion.
Fiolopodia are involved in cell migration and their attachment to the ECM is mediated by integrin receptors. Here the authors show that myosin X induced filipodia adhesion to fibronectin requires activity of myosin IIA at the filopodium base and formin at the tip to support force transmission through the actin core.
Journal Article
Sufficient condition for a quantum state to be genuinely quantum non-Gaussian
We show that the expectation value of the operator ˆ exp ( − c x ˆ 2 ) + exp ( − c p ˆ 2 ) defined by the position and momentum operators x ˆ and p ˆ with a positive parameter c can serve as a tool to identify quantum non-Gaussian states, that is states that cannot be represented as a mixture of Gaussian states. Our condition can be readily tested employing a highly efficient homodyne detection which unlike quantum-state tomography requires the measurements of only two orthogonal quadratures. We demonstrate that our method is even able to detect quantum non-Gaussian states with positive-definite Wigner functions. This situation cannot be addressed in terms of the negativity of the phase-space distribution. Moreover, we demonstrate that our condition can characterize quantum non-Gaussianity for the class of superposition states consisting of a vacuum and integer multiples of four photons under more than 50 % signal attenuation.
Journal Article
Detection of HOCl-driven degradation of the pericardium scaffolds by label-free multiphoton fluorescence lifetime imaging
Artificial biomaterials can significantly increase the rate of tissue regeneration. However, implantation of scaffolds leads not only to accelerated tissue healing but also to an immune response of the organism, which results in the degradation of the biomaterial. The synergy of the immune response and scaffold degradation processes largely determines the efficiency of tissue regeneration. Still, methods suitable for fast, accurate and non-invasive characterization of the degradation degree of biomaterial are highly demandable. Here we show the possibility of monitoring the degradation of decellularized bovine pericardium scaffolds under conditions mimicking the immune response and oxidation processes using multiphoton tomography combined with fluorescence lifetime imaging (MPT-FLIM). We found that the fluorescence lifetimes of genipin-induced cross-links in collagen and oxidation products of collagen are prominent markers of oxidative degradation of scaffolds. This was verified in model experiments, where the oxidation was induced with hypochlorous acid or by exposure to activated neutrophils. The fluorescence decay parameters also correlated with the changes of micromechanical properties of the scaffolds as assessed using atomic force microscopy (AFM). Our results suggest that FLIM can be used for quantitative assessments of the properties and degradation of the scaffolds essential for the wound healing processes in vivo.
Journal Article