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This paper describes some of the principles for building a freely available web-based university with open content. The "tutor-web" is an international project for web-assisted education, including such free and open access. This project was initiated by the University of Iceland in partnership with many universities around the world, among them the University of Craiova, Romania. The aim of this paper is to present this project, to point out its specificity and to arouse interest for collaboration in the project, which uses http://tutor-web.net as the home location. (Contains 3 figures.)

The classical bifurcations that occur in the SIR system were already studied in many papers. Our attention is focused on the singular bifurcations, when the system has in infinite number of periodic points at the bifurcation limit. The dynamics of the system is analyzed and the results are interpreted from a practical point of view.

The paper studies the bifurcations that occur in the T-system, a 3D dynamical system symmetric in respect to the Oz axis. Results concerning some local bifurcations (pitchfork and Hopf bifurcation) are presented and our attention is focused on a special bifurcation, when the system has infinitely many equilibrium points. It is shown that, at the bifurcation limit, the phase space is foliated by infinitely many invariant surfaces, each of them containing two equilibrium points (an attractor and a saddle). For values of the bifurcation parameter close to the bifurcation limit, the study of the system's dynamics is done according to the singular perturbation theory. The dynamics is characterized by mixed mode oscillations (also called fast-slow oscillations or oscillations-relaxations) and a finite number of equilibrium points. The specific features of the bifurcation are highlighted and explained. The influence of the pitchfork and Hopf bifurcations on the fast-slow dynamics is also pointed out. [ABSTRACT FROM AUTHOR]

In this paper we study the pitchfork and Hopf bifurcations in a 3D dynamical system that models some oscillations of plasma parameters in Tokamaks. The pitchfork bifurcation's parameter is the input power in the system and the Hopf bifurcation is analyzed with respect of the three parameters of the system. In each case necessary and sufficient conditions for the occurrence of the Hopf bifurcation are provided. A special attention is paid to the case when the input power is varied. A case study is performed. It is emphasized the stable periodic orbits collision occurred after Hopf bifurcation, and the appearance of the double-scroll attractor. It is also noticeable the coexistence of three attractors (two stable points and a double-scroll attractor) whose basins of attraction are analyzed. [ABSTRACT FROM AUTHOR]

In this paper we study the double Hopf bifurcation in a 4D dynamical system modelling the dynamics of two coupled oscillators: a primary body (PB) subjected to vibrations induced by aerodynamic forces and a tuned mass damper (TMD) aiming to reduce the ow-induced vibrations of (PS). The stability of the trivial equilibrium of this model is studied in a four parameters space and the equation of the co-dimension 2 critical manifold of the double Hopf bifurcation is derived. The normal form method is then used in order to study the dynamics of the system when the parameters are slightly varied from their bifurcation values. [ABSTRACT FROM AUTHOR]

The discrete models associated with Hamiltonian systems are obtained using the symmetric mapping techniques derived from Hamilton-Jacobi theorem. A local criterion for determining the optimal mapping step for the preservation of the dynamical characteristic (regular or chaotic) of an orbit is proposed. A global criterion is also derived. These criteria are applied for the study of a Hamiltonian system modeling the magnetic field configuration in tokamak. [ABSTRACT FROM AUTHOR]

Isothermal P-x vapor-liquid equilibrium and excess enthalpy (HE) data were experimentally determined for the 10 binary systems hexane, heptane, 1-octene, benzene, toluene, ethanol, methanol, ethyl acetate, dibutyl ether, and dichloromethane with N,N- dimethylacetamide using the static synthetic method and isothermal flow calorimetry, respectively. The experimental data from this work together with data taken from literature were used for the extension of the group contribution method Modified UNIFAC (Dortmund). [ABSTRACT FROM AUTHOR]

For process development and simulation, the group contribution concept can be successfully applied for the estimation of the missing pure component and mixture properties. This concept has the great advantage that only a limited number of group interaction parameters is required. With the support of a company consortium founded 1996 at the University of Oldenburg, the group contribution model modified UNIFAC (Dortmund) for the prediction of phase equilibria and excess properties has been continuously revised and extended. Within the consortium the number of available group interaction parameters has been doubled. At the same time, the reliability of the results was greatly improved, and the range of applicability was extended to ionic liquids, polyethers, and so forth, and systems for which no experimental data are available, e.g., reactive systems. In this paper the group interaction parameters for the sulfur groups sulfones, sulfides, and disulfides are given. Furthermore, the current status of the consortium developments is discussed. [ABSTRACT FROM AUTHOR]

The existence of transport barriers in 3/2 degrees of freedom degenerate Hamiltonian systems is studied using the associated stroboscopic maps. For small enough amplitudes of the perturbations, a transport barrier (formed by infinitely many invariant rotational circles) is proven to exist and to form in the degenerate annulus. These results are applied to Hamiltonian models which describe some magnetic configurations in tokamak plasmas. [ABSTRACT FROM AUTHOR]

Gyrotrons are microwave sources whose operation is based on the stimulated cyclotron radiation of electrons oscillating in a static magnetic field. This process is described by the system of two complex differential equations: nonlinear first order ordinary differential equation with parameter (averaged equation of electron motion) and second order partial differential equation for high frequency field (RF field) in resonator (Schrödinger type equation for the wave amplitude). The stationary problem of the single mode gyrotron equation in short time interval with real initial conditions was numerically examined in our earlier work. In this paper we consider the stationary and nonstationary problems in large time interval with complex oscillating initial conditions. We use the implicit finite difference schemes and the method of lines realized with MATLAB. Two versions of gyrotron equation are investigated. We consider different methods for modelling new and old versions of the gyrotron equations. The main physical result is the possibility to determine the maximal value of the wave amplitude and the electron efficiency coefficient. [ABSTRACT FROM AUTHOR]

Abstract: We present the case of a 53 years-old woman presenting with congestive heart failure and pleural and pericardial effusions, in whom transthoracic and transesophageal echocardiography revealed multilocular cardiac tumor involving the left atrium wall, extending into the pericardium. Tumor was excised surgically and proved to be a malignant fibrous histiocytoma, primarily confined to the heart. Despite surgery followed by chemotherapy, the patient died a few months later. This is the 47th case of primary cardiac fibrous malignant histiocytoma reported in the literature. The pericardial involvement has been only rarely reported. Echocardiography was the method of diagnosis before rapid referral to surgery. [Copyright &y& Elsevier]

Surgical replacement of the native aortic valve with either a biological or a mechanical valve has been the "gold standard" treatment for severe symptomatic aortic stenosis for a long time. However, during the last ten years transcutaneous aortic valve replacement (TAVR) has emerged as an alternative to classic surgery, especially for patients considered to be inoperable or at high surgical risk. TAVR, developed to avoid the high morbi-mortality and complications associated with classic surgical intervention, has its own complications which need to be known in order to prevent them properly. We present the case of a 63 year-old man with symptomatic severe aortic stenosis deemed to be inoperable because of severe depression of left and right ventricular systolic function, which benefited from TAVR with a "valve in valve" procedure because of significant paravalvular aortic regurgitation after the insertion of the first percutaneously implanted valve. [ABSTRACT FROM AUTHOR]

Carotid intima-media thickness (CIMT) can be reliably determined in vivo by carotidian ultrasound and is an accessible and reliable method to assess subclinical atherosclerosis. Available epidemiological data showed that CIMT is significantly correlated with future cardiovascular events. However it has limited value to help risk stratification on top of standard risk-derived functions such as Framingham risk score. It is particularly useful in individuals classified as being at intermediate or high risk by the presence of multiple conventional risk factors. CIMT has a class ha (LOE: B) reccommendation for cardiovascular risk assessment according to the practice guidelines published in 2010, emphasizing the presence of high risk off the common carotid artery intima-media thickness is above the 75th percentile. There is no indication to measure IMT in patients with full-blown atherosclerotic carotid disease, although carotidian ultrasound still remains a very useful tool to assess the severity of disease even in these subjects. Progression of CIMT (also associated with increasing age) can be delayed by some drugs (statins, colestipol and niacin) and by risk factors modification. However, there is no consistent data demonstrating a link between progression of CIMT and coronary and cerebral events. Subsequently, studies using CIMT progression as primary outcome to indicate the influence of a certain therapy on cardiovascular risk are inherently misleading as suggested in the recently published ACC/AHA Guidelines. [ABSTRACT FROM AUTHOR]

Atherosclerosis is a chronic inflammatory disease started by endothelial injury and defined by arterial wall load with free and esterified cholesterol, followed by subintimal focal recruitment of circulating monocytes and T-lymphocytes that heals by fibrosis and calcification. Inflammation plays a crucial role in atherogenesis either by local cellular mechanisms or humoral consequences easily measurable in plasma. In most cases inflammation and endothelial dysfunction are triggered by cardiovascular risk factors: hypercholesterolemia, hypertension, smoking or diabetes. In other cases inflammation precedes atherosclerotic changes that occur in autoimmune diseases, as systemic lupus erythematosus and rheumatoid arthritis. In these diseases atherogenesis is mostly independent from conventional risk factors. Irrespective of its cause systemic inflammation is correlated with cardiovascular events, but currently there are controversial results regarding inflammatory markers and early atherosclerotic process. We designed a study to identify if the amplitude of inflammation expressed by multiple serum markers is correlated with the severity of the atherosclerotic process measured by coronary atheroma volume and carotid intima-media thickness. The selected inflammatory markers are associated with different pathogenic steps in atherogenesis: acute phase reactants (C-reactive protein); pro-inflammatory cytokines (TNF-alpha, interleukin-6 and -18); endothelium activation markers (soluble VCAM-1, ICAM-1); and specific factors (anticardiolipinic antibodies). We aim to enrol the two different patient subsets with early atherosclerosis: one with conventional risk factors and one with autoimmune diseases without traditional risk factors, in whom inflammation is part of the systemic disease progression. [ABSTRACT FROM AUTHOR]

Aims - Baseline mechanical intraventricular dyssynchrony showed only a weak correlation with response to CRT in HF patients with wide QRS. We aimed to evaluate the effects of RV pacing on baseline intraventricular dyssynchrony in patients submitted to CRT. Methods - In 40 consecutive HF patients (LBBB, sinus rhythm, normal PR interval, 22 ischemic etiology, 65.5±10.7 years, 21 women, NYHA class 3.3 ± 0.5, LV ejection fraction 20.1±4.1%), speckle tracking radial strain was performed during sinus rhythm (ODO mode) and during RV pacing (DDD with optimum AV interval) one week after biventricular device implantation. RV lead was placed on interventricular septum (RVS, n=30) and RV apex (RVA, n=10). Patients had significant baseline intraventricular dyssynchrony, (i.e. =130 ms time difference in peak septal wall to infero-lateral wall strain). Maximum LV delay area (MDA) was defined as the segment with the latest systolic peak from the 6 regional color-coded time-strain curves. Midventricular global radial strain (mGRS) was determined averaging the segmental radial strain values. Results - Overall, RV pacing did not significantly increased intraventricular dyssynchrony (350±98 ms vs. 322±90 ms during SR, p=0.08). However, RVA pacing significantly increased LV dyssynchrony (367±58 ms vs. 312±60 ms during SR, p<0.001). mGRS was significantly reduced during RV pacing (13.3±8.5% vs. 18.3±7.4% during SR, p<0.001). The location of MDA shifted during RV pacing in 31 out of 40 patients (77%). Conclusions - In HF patients with wide QRS submitted to CRT, RV pacing alters the pattern of intraventricular dyssynchrony and impairs LV strain. [ABSTRACT FROM AUTHOR]

We analyze statistically the energization of particles in a large scale environment of strong turbulence that is fragmented into a large number of distributed current filaments. The turbulent environment is generated through strongly perturbed, 3D, resistive magnetohydrodynamics simulations, and it emerges naturally from the nonlinear evolution, without a specific reconnection geometry being set up. Based on test-particle simulations, we estimate the transport coefficients in energy space for use in the classical Fokker-Planck (FP) equation, and we show that the latter fails to reproduce the simulation results. The reason is that transport in energy space is highly anomalous (strange), the particles perform Levy flights, and the energy distributions show extended power-law tails. Newly then, we motivate the use and derive the specific form of a fractional transport equation (FTE), we determine its parameters and the order of the fractional derivatives from the simulation data, and we show that the FTE is able to reproduce the high energy part of the simulation data very well. The procedure for determining the FTE parameters also makes clear that it is the analysis of the simulation data that allows us to make the decision whether a classical FP equation or a FTE is appropriate. [ABSTRACT FROM AUTHOR]

Abstract: (Vapor+liquid) equilibrium (VLE) data for a ternary mixture, namely {methanol+propan-1-ol+dimethyl carbonate (DMC)}, and four binary mixtures, namely an {alcohol (C3 or C4)+DMC}, containing the binary constituent mixtures of the ternary mixture, were measured at p =(40.00 to 93.32)kPa using a modified Swietoslawski-type ebulliometer. The experimental data for the binary systems were correlated using the Wilson model. The Wilson model was also applied to the ternary system to predict the VLE behavior using parameters from the binary mixtures. The modified UNIFAC (Dortmund) model was also tested for the predictions of the VLE behavior of the binary and ternary mixtures. In addition, the experimental VLE data for the ternary and constituent binary mixtures were correlated using the extended Redlich–Kister (ERK) model, which can completely represent the azeotropic points. For the ternary system, a comparison of the experimental and the predicted or correlated boiling points obtained using the Wilson and ERK models showed that the ERK model is more accurate. The valley line, i.e., the curve which divides the patterns of vapor–liquid tie lines, was found in the (methanol+propan-1-ol+DMC) system. This valley line could be represented by the ERK model. Finally, the composition profile for simple distillation of this ternary mixture was obtained by analysis of the residue curves from the estimated Wilson parameters of the constituent binary mixtures. [Copyright &y& Elsevier]

Abstract: The objective of this study is the selection of a suitable entrainer for the separation of the binary azeotropic mixture, namely methanol+dimethyl carbonate (DMC) by extractive distillation. In this study, 2-ethoxyethanol and 4-methyl-2-pentanone were considered as entrainer candidates for the separation of methanol and DMC. Isobaric vapor–liquid equilibria (VLE) were measured for the ternary mixtures methanol+DMC+2-ethoxyethanol and methanol+DMC+4-methyl-2-pentanone, and for their constituent binary mixtures, under reduced pressures of 66.66kPa and 93.32kPa. Experimental VLE data for the constituent binary mixtures were represented by the Wilson and the NRTL model. The VLE predictions for two ternary mixtures were compared with the experimental VLE data on the basis of the Wilson or NRTL parameters obtained from the constituent binary VLE data. The modified UNIFAC (Dortmund) model was also used for the prediction of the binary and ternary mixtures. The solvent effects of the two entrainer candidates investigated are discussed using the predicted results for the ternary mixtures and both 2-ethoxyethanol and 4-methyl-2-pentanone were found to be suitable entrainers for the separation of methanol and DMC. When the selectivity of 2-ethoxyethanol and 4-methyl-2-pentanone are compared, it could be concluded from the separation factors that 4-methyl-2-pentanone shows a higher selectivity. [Copyright &y& Elsevier]

The coexistence of stable limit cycles and chaotic attractors has already been observed in some 3D dynamical systems. In this paper we show, using the T-system, that unstable limit cycles and chaotic attractors can also coexist. Moreover, by completing the characterization of the existence of invariant algebraic surfaces and their associated global dynamics, we give a better understanding on the disappearance of the strange attractor and the limit cycles of the studied system., Competing Interests: No competing interests were disclosed., (Copyright: © 2021 Constantinescu D et al.)