1,426 research outputs found
Propagation speed of the maximum of the fundamental solution to the fractional diffusion-wave equation
No full textIn this paper, the one-dimensional time-fractional diffusion-wave equation with the fractional derivative of order 1≤α≤2 is revisited. This equation interpolates between the diffusion and the wave equations that behave quite differently regarding their response to a localized disturbance: whereas the diffusion equation describes a process, where a disturbance spreads infinitely fast, the propagation speed of the disturbance is a constant for the wave equation. For the time fractional diffusion-wave equation, the propagation speed of a disturbance is infinite, but its fundamental solution possesses a maximum that disperses with a finite speed. In this paper, the fundamental solution of the Cauchy problem for the time-fractional diffusion-wave equation, its maximum location, maximum value, and other important characteristics are investigated in detail. To illustrate analytical formulas, results of numerical calculations and plots are presented. Numerical algorithms and programs used to produce plots are discussed
Physical-chemical conditions and composition of ore-building fluids of Russian oroganic gold deposits
No full textThe detailed research of fluid inclusions and stable isotopes in minerals of industrial ore veins large-scale orogenic gold deposits of different regions of Russia was carried out. The deposits under investigation are Berezovsk and Kochkarskoye (Ural), Olympiada (the Yenisei Ridge), Mayskoye (Chukotka), Nezhdaninskoye (Yakutiya) and Sukhoy Log (Eastern Siberia). Temperatures of industrial ores formation for all investigated deposits are stacked in an interval 190-485 oС. Fluid pressure under ore formations changed from 1.0 up to 3.6 kbar. The hydrothermal fluid of all orogenic gold deposits under investigation is a low-mineralized water solution with the general concentration of salts 2-17 % in weight, and sodium and potassium chlorides are prevailed. For fluids from the majority of deposits the high concentrations of dissolved CO2 (3-7 mol/kg H2O) with a small impurity of other gases are characteristic. Variations of geochemical ratio volumes for K/Rb, Br/Cl and others which can serve as indicators of the ore-forming fluid natures are established. Au-bearing fluid from all deposits had the magmatic nature and had mixed up with formation solutions under ore sediments
Agricultural and non-agricultural outputs and energy consumption in Tunisia: empirical evidences from cointegration and causality
No full textThis short paper investigates the cointegration and causality link between energy consumption and agricultural, non-agricultural outputs (manufacturing sector and services sector) and overall gross domestic product in Tunisia for 1971-2003 period. Empirical results suggest that there is only unidirectional causality running from agricultural and non-agricultural sectors to energy consumption as well as from overall GDP growth to energy consumption. This unidirectional causality signifies a less energy dependent economy and suggests that it is sectoral growth that drives the energy consumption in Tunisia and not vice versa. Empirical results suggest also that Tunisian agricultural sector growth does not depend on energy, and high consumption of energy do not implies more productivity in the short run for this sector.energy consumption, output growth, causality, cointegration, Tunisia, Resource /Energy Economics and Policy,
On the changing ecology of Venice Lagoon.
No full text© 2002 Kluwer Academic Publishers. Printed in the Netherlands
MEP: a 3D PIC Code for the Simulation of the Dynamics of a Non-Neutral Plasma
No full textThe three-dimensional evolution of a pure electron plasma is studied by means of a newly developed particle-in-cell code which solves the drift-Poisson system where kinetic effects in the motion parallel to the magnetic field are taken into account. Different results relevant to the non-linear dynamics of trapped plasmas and low-energy electron beams are presented. [All rights reserved Elsevier]
Experimental investigation of coherent structures in a low-energy electron beam
No full textA sharp transition to a space-charge dominated regime is induced in a low-energy electron beam produced in a Malmberg–Penning trap by increasing the emission current of the source. The transition is characterized by the appearance of a region, around the axis of the beam, not accessible to beam electrons, and by the fast development of coherent structures in the remaining electron plasma, due to the sharp increase of local vorticity. The results are interpreted in the framework of a cold fluid drift–Poisson model, and using a three-dimensional particle-in-cell simulation code
New records of Iranian bark beetles (Coleoptera: Curculionidae, Scolytinae) and their host plants
No full textAmini, Sudabe, Nozari, Jamasb, Mandelshtam, Michail Yu., Knížek, Miloš, Etemad, Vahid, Faccoli, Massimo (2017): New records of Iranian bark beetles (Coleoptera: Curculionidae, Scolytinae) and their host plants. Zootaxa 4350 (2), DOI: 10.11646/zootaxa.4350.2.1
Systematic conformational search analysis of the SRR and RRR epimers of 7-hydroxymatairesinol
No full textAn extensive and systematic conformational search was performed on the two epimers of the natural lignan 7-hydroxymatairesinol (HMR), by means of a home-made Systematic Conformational Search Analysis (SCSA) code, designed to select more and more stable conformers through sequential geometry optimization of trial structures at increasing levels of calculation theory. In the present case, the starting molecular structures were selected by the semi-empirical AM1 method and filtered – i.e. decreased in number by choosing the more stable species – on the basis of their energy calculated by the HF method and the 6-31G(d) basis set. The geometries obtained were further refined by performing density functional theory (DFT) optimizations, using the B3LYP functional and the 6 31G(d,p) basis set, both in vacuo and in ethanol solution. This procedure allowed us to isolate, at a high level of theory, three groups of epimer conformers characterized by open, semi-folded, and folded conformations. Moreover, the SCSA allowed us to describe a conformational space made-up by about 20 species for each of the two epimers. The corresponding energy content of these species was within 27 kJ molS1 from the absolute minimum found, both in vacuo and in ethanol solution. The conformational analysis, followed by the inspection of the stereochemistry of the two most stable conformers of both epimers, provides support in rationalizing the proposed reaction mechanism of the catalytic hydrogenolysis of the HMR to matairesinol (MAT)
Platinum group metals as catalysts in enantioselective 1-phenyl-1,2-propandione hydrogenation
No full textDifferent γ-Al2O3 supported Ir, Pd, Ru, Rh and Pt catalysts were tested in enantioselective 1-phenylpropane-1,2-dione hydrogenation using cinchona alkaloid modifiers. Activity and enantioselectivity over Ir and Ru catalysts were low. Pd catalyst was active in the hydrogenation of 1-phenylpropane-1,2-dione, however, the enantioselectivity over this catalyst was almost negligible. Over Pd hydrogenation proceeded mainly via hydrogenation of the C1O1 carbonyl group, which is attached to the phenyl ring. Hydrogenation over Pd did not proceed in the second hydrogenation step via an enol form as found for ethyl pyruvate hydrogenation over Pd. The structure-selectivity relationship and solvent effects are similar over Pt and Rh in the first hydrogenation step. However, in the second hydrogenation step of hydroxyketones to diols large mechanistical differences between Pt and Rh were observed. Although the activity over Rh catalysts was lower than over Pt after optimization the best result obtained with Rh/γ-Al2O 3 (5754 Lancaster) was 60% ee in toluene at maximum yield of 28%, which makes Rh a promising metal for enantioselective hydrogenation
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