Study Of Various Mechanisms Research Articles

Computer Simulation of Charge Transfer In a DNA Molecule within a Simple Model of an Open Quantum System

The quantum-statistical model proposed earlier by Skourtis and Nitzan to describe a charge (hole) propagation in a fragment of artificial DNA molecule has been generalized and further investigated. A numerical simulation of a charge transport was carried out taking into account two different dissipative processes, including the capture of the charged carrier by the environment and the decoherence of its quantum wave properties due to the influence of stochastic fields of the environment. The interaction of the carrier with the environment is regulated by a small set of phenomenological parameters whose values vary in the process of simulation. Within this model, the propagation of a hole carrier in DNA is described by solving the quantum Franke-Kossakovski–Lindblad–Glauber–Sudarshan equation (hereinafter referred to as the Lindblad equation) for the carrier density matrix using the Lindblad MPO Solver program. Results of numerical analysis of the model are in a good agreement with experimental observations and demonstrate two different types of the charged carrier motion, presumably tunneling and incoherent hopping. The model is put in more general context and non-unitary dynamics of the hole carrier is treated within the framework of a theory of continuous quantum measurements by the environment in an open quantum system. The main concepts of the theory of decoherence and superselection for open quantum systems and the prospects for their application for further study of various mechanisms of motion of a charged carrier in DNA are briefly discussed.

Recurrent genital endometriosis: risk factors and possible prevention strategy

Endometriosis is one of the most common gynecological diseases in women of reproductive age, which is characterized by a relapsing course. The recurrence rate varies greatly among literary sources. This review covers symptoms and types of endometriosis, laboratory tests, options for hormonal therapy, as well as features of surgical approaches that may be associated with the disease recurrence risk. The aim of this article was to analyze and summarize current literature on the definition of endometriosis recurrence, risk factors and prevention strategy. Despite advances in the study of various mechanisms for the development of endometriosis and the use of combined treatment, a high recurrence rate remains an unsolved problem for this disease. All of this underscores the need to develop new methods for early diagnosis and treatment, taking into account the risk group and a personalized approach.

Electrochemical Characterization of the Antioxidant Properties of Medicinal Plants and Products: A Review

Medicinal plants are an important source of bioactive compounds with a wide spectrum of practically useful properties. Various types of antioxidants synthesized in plants are the reasons for their application in medicine, phytotherapy, and aromatherapy. Therefore, reliable, simple, cost-effective, eco-friendly, and rapid methods for the evaluation of antioxidant properties of medicinal plants and products on their basis are required. Electrochemical methods based on electron transfer reactions are promising tools to solve this problem. Total antioxidant parameters and individual antioxidant quantification can be achieved using suitable electrochemical techniques. The analytical capabilities of constant-current coulometry, potentiometry, various types of voltammetry, and chrono methods in the evaluation of total antioxidant parameters of medicinal plants and plant-derived products are presented. The advantages and limitations of methods in comparison to each other and traditional spectroscopic methods are discussed. The possibility to use electrochemical detection of the antioxidants via reactions with oxidants or radicals (N- and O-centered) in solution, with stable radicals immobilized on the electrode surface, via oxidation of antioxidants on a suitable electrode, allows the study of various mechanisms of antioxidant actions occurring in living systems. Attention is also paid to the individual or simultaneous electrochemical determination of antioxidants in medicinal plants using chemically modified electrodes.

The investigation of a physical pendulum motion, which move along a horizontal axis

The article presents a study of the physical pendulum, taking into account the force of friction in the kinematic pair, as a result of which oscillations are damped. Graphs of the dependence of the pendulum deflection angle α and the angular velocity on time for different values of the velocity v have been given. It has been established that the speed of the sleeve significantly reduces the amplitude and angular velocity of the pendulum, and the frequency of its oscillations does not depend on the presence of dry friction in the system. The dependences of the change in the amplitude of pendulum oscillations have been given and the results of numerical integration of the differential equation of pendulum motion have been obtained. The graphical dependences of the pendulum deflection angle and the movement of the sleeve x along the horizontal axis from time to time have been obtained at different values of the coefficient of friction. It has been found that during the first five seconds of the system movement, the axial speed of the sleeve is practically independent of the coefficient of friction (at f = 0.3… 0.5). To verify the obtained results, an experimental laboratory installation has been designed and manufactured. Theoretical studies are satisfactorily consistent with experimental data, with an error not exceeding 16%. The obtained dependencies can be used in the design and study of various mechanisms, the motion of which is described by similar differential equations. Such mechanisms include inertial conveyors, the gutter of which performs in addition to longitudinal and transverse oscillations. In addition, the proposed technique can be used in the study of the motion of bulk materials in an inclined cylinder, which performs torsional oscillations around the axis of symmetry.

The investigation of a physical pendulum motion, which move along a horizontal axis

The article presents a study of the physical pendulum, taking into account the force of friction in the kinematic pair, as a result of which oscillations are damped. Graphs of the dependence of the pendulum deflection angle α and the angular velocity on time for different values of the velocity v have been given. It has been established that the speed of the sleeve significantly reduces the amplitude and angular velocity of the pendulum, and the frequency of its oscillations does not depend on the presence of dry friction in the system. The dependences of the change in the amplitude of pendulum oscillations have been given and the results of numerical integration of the differential equation of pendulum motion have been obtained. The graphical dependences of the pendulum deflection angle and the movement of the sleeve x along the horizontal axis from time to time have been obtained at different values of the coefficient of friction. It has been found that during the first five seconds of the system movement, the axial speed of the sleeve is practically independent of the coefficient of friction (at f = 0.3… 0.5). To verify the obtained results, an experimental laboratory installation has been designed and manufactured. Theoretical studies are satisfactorily consistent with experimental data, with an error not exceeding 16%. The obtained dependencies can be used in the design and study of various mechanisms, the motion of which is described by similar differential equations. Such mechanisms include inertial conveyors, the gutter of which performs in addition to longitudinal and transverse oscillations. In addition, the proposed technique can be used in the study of the motion of bulk materials in an inclined cylinder, which performs torsional oscillations around the axis of symmetry.

Hypolimnion behavior of technetium in freshwater at various stages of eutrophication

The article presents a study of various mechanisms of hypolimnion technetium behavior which occur at different stages of waterbodies eutrophication. Eutrophication stage was found to be positively correlated with the rate of 99Tc removal from water phase. The study identified a complex biogeochemical mechanism of technetium behavior. Planktonic phototrophic community plays a pivotal role in such a mechanism by ensuring fast oxygen consumption in hypolimnion. This creates favorable conditions for the active development of anaerobic bottom bacteria of sulfur and iron cycles given nutrients inflow. Sulfates and nitrates were discovered to have inhibitory effect on 99Tc biosorption by bottom sediments due to oxidizing conditions. Apart from the shift of redox potential of the medium to reducing values, the 99Tc removal and partial immobilization are also promoted by the presence of inorganic mineral phases of reduced sulfur and iron. These phases form a reducing barrier in the silt, thus preventing the oxidation and migration of technetium. We suggest the ways of stimulating in situ waterbody remediation by means of various additives, which will allow irreversible immobilization of technetium in silt once several growth periods have passed.

Перенос заряда в молекуле ДНК в рамках простой модели открытой квантовой системы

The quantum-mechanical model proposed earlier by Skourtis and Nitzan (J. of Chem. Phys. 119, (2003) 6271) to describe a charge transfer in a fragment of artificial DNA molecule has been numerically investigated. The current rationale for the model is carried out and values of its parameters are indicated. Within this model, the description of the transport of a hole carrier in DNA is based on solutions to the time-dependent Schrödinger equation including damping effects. The non-unitary dynamics of the hole carrier is treated by us within the framework of a theory of continuous quantum measurements by the environment in an open quantum system. Results of numerical analysis of the model are in a good agreement with experimental observations and demonstrate two different types of the charged carrier motion, presumably tunneling and incoherent hopping. The main concepts of the theory of decoherence and superselection for open quantum systems and the prospects for their application for further study of various mechanisms of motion of a charged carrier in DNA are briefly discussed.

Modeling of heat and mass transfer in the process of drying of colloid capillary - porous materials

The process of drying is an energy-consuming process, therefore, in order to optimize these energy costs during drying and to choose the rational structural and regime parameters of the equipment intended for this process, it is necessary to carry out a calculation analysis of heat and mass transfer on the basis of adequate mathematical models. The study of various mechanisms of diffusion in capillary - porous materials has become the basis for the creation of a mathematical model of heat - mass transfer and for the formulation of a corresponding system of nonlinear differential equations. Using mathematical model of heat-mass transfer A.V. Lykova constructed an appropriate numerical algorithm for modeling this process, numerical studies of the convection drying process of colloidal capillary - porous materials (KKPM) have been performed. The boundary conditions on the contact surface of the material in the drying chamber with the heat carrier flow are formulated. Based on the numerical solution of the system of one-dimensional heat and mass transfer equations in the material, depending on the time of its specific moisture content and temperature, as well as other characteristics of the convection drying process, the dependence was obtained. The estimated results are compared with the results of experimental studies. From the results of the comparison, it follows that the calculated model on the basis of the proposed system of equations satisfactorily describes the process of mass transfer in colloidal capillary - porous materials and can be used to approximate the characteristics of the drying process of colloidal capillary - porous materials, in particular the time required for drying the material. Numerical modeling of heat and mass transfer processes in colloid capillary and porous materials helps to solve an important scientific and technical problem, which is connected with the creation of software and hardware complexes, automated systems of scientific researches of energy-saving heat-technological processes of drying of materials with the provision of necessary quality indicators. Having analyzed the literature data concerning the existing developed mathematical modeling of colloidal capillary-porous materials, it has been established that this direction has a limited amount of information and therefore requires in-depth study and is an actual direction of research.

IMPORTANCE OF INSULIN-LIKE AND VASCULAR AND ENDOTHELIAL GROWTH FACTORS IN THE PATHOGENESIS OF POLYCYSTIC OVARY SYNDROME (REVIEW OF LITERATURE)

The study of various mechanisms of the pathogenesis of polycystic ovary syndrome (PCOS) shows the multifactorial nature of its development with the involvement of many organs and systems, as well as growth factors that are actively involved in the growth and proliferation processes of both normal and pathologically altered biological tissues, including the ovaries, not only with PCOS, but also with endometriosis and tumor formations. The article discusses new data on the involvement of insulin-like and vascular endothelial growth factors in the pathogenesis of PCOS. The study of their role is relevant and promising task.

IMMUNOPATHOGENESIS OF MYASTHENIA GRAVIS (REVIEW)

Myasthenia gravis is a progressive autoimmune disease, which characterized by the production of antibodies to the structures of the neuromuscular junction. High clinical heterogeneity of autoimmune myasthenia, initiating the flow, increases the urgency of studying its pathogenesis, searching for specific methods of marker diagnostics, developing algorithms for predicting the features of the development of the disease. At the present time, there are different approaches to the study of the etiology and pathogenesis of the disease, which include both serological, biochemical, genetic, etc. theory of the development of the disease. For decades, research has been carried out to find new pathogenetic links in myasthenia gravis. Today was described a number of antibodies such as for muscarin (MuSK), ryanodine receptors, to titin, lipoprotein bound receptor 4, cortactin, etc.). The serological diagnosis of myasthenia gravis has been used as a «gold standard» in clinical practice. The prognostic criteria describing the course of myasthenia gravis and the type of antibodies isolated in the blood serum of the patient. Also, already have been developed mechanisms of failure of autotolerance, triggering the production of antibodies to their own structures, and their genetic bases are also described. Thanks to the development of biotechnological methods, the researchers were able to identify the subtype of lymphocytes involved in the development of myasthenia gravis. Isolation of individual subpopulations of lymphocytes also became available. Researchers continue to search for new targets, allowing to improve diagnostics, to develop new directions in the therapy of the disease. However, despite the active study of various mechanisms for the development of myasthenia gravis, many unresolved problems still remain. The article describes briefly the main mechanisms studied in the development of myasthenia gravis, which in turn facilitates understanding of complex mechanisms of pathogenesis.

Lyα Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions

Abstract To shed more light on the nature of the observed Lyα absorption during transits of HD 209458b and to quantify the major mechanisms responsible for the production of fast hydrogen atoms (the so-called energetic neutral atoms, ENAs) around the planet, 2D hydrodynamic multifluid modeling of the expanding planetary upper atmosphere, which is driven by stellar XUV, and its interaction with the stellar wind has been performed. The model self-consistently describes the escaping planetary wind, taking into account the generation of ENAs due to particle acceleration by the radiation pressure and by the charge exchange between the stellar wind protons and planetary atoms. The calculations in a wide range of stellar wind parameters and XUV flux values showed that under typical Sun-like star conditions, the amount of generated ENAs is too small, and the observed absorption at the level of 6%–8% can be attributed only to the non-resonant natural line broadening. For lower XUV fluxes, e.g., during the activity minima, the number of planetary atoms that survive photoionization and give rise to ENAs increases, resulting in up to 10%–15% absorption at the blue wing of the Lyα line, caused by resonant thermal line broadening. A similar asymmetric absorption can be seen under the conditions realized during coronal mass ejections, when sufficiently high stellar wind pressure confines the escaping planetary material within a kind of bowshock around the planet. It was found that the radiation pressure in all considered cases has a negligible contribution to the production of ENAs and the corresponding absorption.

Performance study of the dual‐stack mobile IP protocols in the evolving mobile internet

The transition from IPv4 to IPv6 is an inexorable trend in the development of Internet. However, since IPv4 has been widely deployed for many years, it is mandatory that the existing IPv4 and the newly deployed IPv6 coexist and interoperate seamlessly. With the study of various mechanisms proposed for the interoperability between IPv4 and IPv6, some mobility management protocols are also extended to work in the mixed mobile Internet. In this study, the authors carry out an in-depth analysis of three types of standardised mobility management protocols with dual-stack support. Owing to the difference of underlying basic protocols, their individual dual-stack extensions have different features and thus are suited for deployment in different scenarios and stages in the evolution of the mobile Internet.

Comparative Study of Various Mechanisms for Metallocene-Catalyzed α-Olefin Polymerization

In this paper we try to give answers to some unexplained flaws in the widely accepted Cossée−Arlman mechanism (CAM) for the propagation step of the polymerization of α-olefins. We first take the bare cationic catalyst and make a comparison of the CAM with the so-called Trigger mechanism (TM) proposed by Ystenes, and not only see whether the latter model can predict, qualitatively, some reaction behaviors not explained by the former one but also theoretically calculate both reaction paths and make a quantitative comparison, in terms of reaction free energy. It turns out that, while in terms of electronic energy the TM is favored, inclusion of free energy corrections gives a lower energy profile for the CAM reaction path. We then make use of a model for an experimentally used catalyst counterion and study how it affects the reactivity of the metallocenic cation fragment toward the monomer.

Effect of optical nonreciprocity in crystals

The property of a material medium to provide different conditions for light propagation in the opposite directions is usually called optical nonreciprocity. This nonreciprocity can be related to the phase (propagation velocity), amplitude, and polarization of an electromagnetic wave. This work is focused on the optical nonreciprocity in phase, which is caused by different propagation velocities of the electromagnetic wave in the opposite directions. The optical nonreciprocity of a substance is usually manifested only when it is exposed to various external fields. However, from the general theoretical standpoint, the natural optical nonreciprocity in certain crystals may exist in the absence of any external fields. In my opinion, the existence of an intracrystalline electromagnetic field is one of the causes responsible for the natural optical nonreciprocity of a crystal. In this case, the preferential direction along which the optical nonreciprocity is maximal is determined by the vector product of intracrystalline electric and magnetic fields averaged over physically infinitesimal volumes. If the average value of this product in a crystal is nonzero, then the optical nonreciprocity can arise due to the nonlinearity of vacuum electrodynamics. As is well known [1], recent experiments at the Stanford accelerator confirmed that vacuum electrodynamics is nonlinear theory. Therefore, the propagation of electromagnetic waves in external electromagnetic fields differs from that in vacuum. In particular, as was shown in [2, 3], the propagation velocity of electromagnetic waves in the direction of the vector product of the external electric and magnetic fields differs from that in the opposite direction. It is worth noting that, in addition to the intracrystalline electromagnetic field, other causes can be responsible for the natural optical nonreciprocity in crystals. Therefore, one of the urgent problems of crystal optics is the theoretical study of various mechanisms responsible for the optical nonreciprocity and investigation of laws governing the propagation of electromagnetic waves in nonreciprocal crystals. The search for experimental methods for studying this phenomenon and experimental verification of its various possible mechanisms are also very important. Below, ignoring the details of various mechanisms that provide the natural optical nonreciprocity in crystals, we analyze basic laws governing the propagation of electromagnetic waves in them. In order to solve the posed problem, it is convenient to write the coupling equations in the form D = D ( B , E ), H = H ( B , E ) . This study is focused on the analysis of phenomena in anisotropic media in the presence of relatively weak electromagnetic fields, when nonlinear effects can be neglected. In this case, the coupling equations can be written as

Editorial Objectives Supply Chain Management

It is tempting to say that, for a very long time, supply chain management has been a central topic in the field of management science and operations management. In fact, however, it has evolved from the seminal work done in the 1960s on multiechelon inventory models to recent studies of various mechanisms for coordinating supply chain decisions. In this evolution, one sees a clear shift from studying centralized planning models, in which a central planner makes all the decisions to optimize a systemwide objective, to focusing on decentralized systems with independent decision makers. This is no trival change, for it is one step closer to many real life situations, it has brought about another layer of complexity, and it often requires the use of new analytical tools. The department of supply chain management was created to recognize, emphasize, and encourage this change, and it will continue to do so. Organizing supply chain activities is about determining who does what (in the case of managers, who decides what), who knows what, and the economic incentives motivating supply chain members. This suggests that the management of supply chains can be addressed along three dimensions: allocation of decision rights, information elicitation and sharing, and incentive alignment. This framework matches what we observe in practice: vendor-managed inventory is a supply chain partnership to reallocate stocking decision rights; the creation of corporate communication networks is an example of information sharing; and the myriad of contracts signed among supply chain partners are attempts to align incentives. Moreover, the above three dimensions are likely to characterize the research frontier in supply chain management for the years to come. The Department of Supply Chain Management welcomes papers that are motivated by real-world operations problems and contribute to the understanding of supply chain management issues. The contributions can be methodological, conceptual, empirical, application-oriented, etc. The department especially welcomes papers that present novel models that may open up new directions of research. Needless to say, all submitted manuscripts must follow the guidelines of Management Science, and they will be rigorously refereed according to the normal standards of the journal. Please send four copies of the paper to the departmental editor of supply chain management at the address printed above. The associate editors for the department are: Sven Axsater, Lund University Gerard P. Cachon, University of Pennsylvania Gary Eppen, University of Chicago Stephen C. Graves, MIT Albert Y. Ha, Yale University Martin A. Lariviere, Northwestern University Evan L. Porteus, Stanford University Ananth Raman, Harvard University Kaj Rosling, Lund University Jeannette Song, University of California, Irvine Sridhar Tayur, Carnegie Mellon University Seungjin Whang, Stanford University

Studies of various mechanisms of nuclear polarisation due to a resonant high-frequency field in radical reactions

Two different mechanisms of creation of nuclear polarisation in radical reaction products are studied by means of the high-frequency field influence on intermediate radical pairs (stimulated nuclear polarisation, SNP) and on intermediate short-lived radicals (dynamic nuclear polarisation, DNP). Criteria are formulated for distinguishing the contributions of DNP and SNP effects, and experimental demonstration of this possibility is presented for photoinduced reactions of quinones.

Catalysis in ?-elimination reactions. 6. Quantum-chemical calculations on intermediate compounds with correction for solvation in slightly polar solvents

1. Quantum-chemical calculations by the CNDO/BW and MINDO/2 methods have been carried out on certain modelβ-elimination reactions. 2. Study of various mechanisms involving ion solvation has shown that heterolytic C-H bond rupture is energetically favored over C-OR bond heterolysis, in solution but not in the gaseous phase. 3. In solutions with low dielectric constant (benzene, CH3COOH), ionic mechanisms can be realized only under the action of bases with PA's comparable to that of KOH. 4. Forβ-elimination reactions catalyzed by compounds such as CH3COOH and pyridine, we have proposed nonionic mechanisms based on proton transfer from theβ-carbon atom to the oxygen of the departing alcohol group. 5. It is proposed that the proton solvation energy in low-polarity solvents be calculated by making use of the electrostatic expression for the energy of solvation of the protonated solvent molecule.

The study of various mechanisms of in-cloud scavenging of large, moderately large, and small aerosol particles

The scavenging of aerosol particles is usually defined by such processes as condensation, Brownian diffusive capture by cloud droplets caused by the random motion of aerosol particles relative to the cloud droplets (for particles of radius 10-~-10 -7 cm) and the motion of aerosol particles to the drops as a result of pressure gradient. There has been recent interest in the role of thermoand diffusiophoresis in in-cloud scavenging. Thermoand diffusiophoresis may be expected to be important ill the scavenging problem since heat and water vapor fluxes are usually associated with the evaporation or condensation of the growth of precipitation elements. The role of diffusiophoresis in the scavenging of submicron radioactive particles (0.010.1 ~m) from the atmosphere has been studied by Goldsmith (1). Waldmanrt and Schmitt's theory of diffusiophoresis (2) of small particles moving in a diffusing binary gas mixture was applied. As a matter of record the authors have come to the conclusion that the role of diffusiophoresis in the scavenging of fallout particles from the atmosphere was not essential. This conclusion seems to be questionable. Diffusiophoresis was discussed by Facy (3) and by Vittori and Prodi (4). Facy has observed the dust-free space in the vicinity of evaporating surfaces during a number of laboratory investigations. Facy has explained this phenomenon by the sweeping away of particles by diffusiophoresis. Later Facy's effect was incorporated into a composite model of in-cloud scavenging by Vittori and Prodi. I t was shown that the formation of dust-free space around the droplets would serve to concentrate the aerosol elsewhere where there was opportunity for its capture by growing drops. I t was suggested by these authors that the particulate matter near growing droplets may be scavenged from the atmosphere. These researchers have concluded that thermophoresis should play only a minor role as a process of in-cloud scavenging. This conclusion was derived largely from the fact that the temperature gradient in the vicinity of atmospheric water droplets and crystals was small and thus thermophoretic forces are insufficient to cause appreciable capture. Derjaguin and Dukhin (5) investigating the significance of thermophoresis in the coagulation growing of cloud droplets, concluded that thermophoresis should be significant in promoting the coagulation of cloud droplets. However, these authors did not extend their analysis to the related problem of aerosol capture. I t was shown that at the surface of a drop the temperature gradient must be significant, hence, the thermophoretic forces should be more important than diffusiophoresis in the vicinity of cloud droplets. In the works by Slinn and Hales (6, 7) a comparison was made of the roles played by thermophoresis, Brownian diffusion, and

A Study of Various Mechanisms of Attrition of Fibres as a Result of Abrasion

A Study of Various Mechanisms of Attrition of Fibres as a Result of Abrasion