Trajectory and stability of Lagrangian point L2L_2 in the Sun-Earth system

This paper describes design of the trajectory and analysis of the stability of collinear point $L_2$ in the Sun-Earth system. The modified restricted three body problem with additional gravitational potential from the belt is used as the model for the Sun-Earth system. The effect of radiation pressure of the Sun and oblate shape of the Earth are considered. The point $L_2$ is asymptotically stable upto a specific value of time $t$ correspond to each set of values of parameters and initial conditions. The results obtained from this study would be applicable to locate a satellite, a telescope or a space station around the point $L_2$.Comment: Accepted for publication in Astrophysics & Space Scienc

Numerical and experimental analysis of the hydroelastic behavior of purse seine nets

The paper presents a general three dimensional hydro-elastic tool for the analysis of different types of fishing nets and aquaculture facilities. Flexible net strands are modeled by non-linear truss elements having two nodes. Hydrodynamic loads due to relative motion of the net with the surrounding fluid are computed using the Morison equation. The coupled hydrodynamic-elastodynamic equations are solved using finite element (FE) approximations. Furthermore, experimental data are presented for the drag resistance of a purse seine net, commonly used as fishing tool in the Mediterranean sea. The measurements were conducted in the towing tank of NTUA on a sample of a net. The net was tested in three configurations: vertical, horizontal and inclined at 451. The derived drag coefficients are compared to predictions of the FEM developed model. The vertical submergence behavior of the seine in calm water is also examined, both experimentally and theoretically. Moreover, the shooting phase of the purse-seine fishing is simulated with the aim to investigate the diving behavior of the net. The flow shading effect of neighboring strands is identified as a critical parameter for the consistent predictions of the diving behavior

Computation of a Sufficient Condition for System Input Redundancy

The calculation of an optimal subset of inputs from a set of candidate ones is known in the bibliography of system modeling as the input (or feature) selection problem. In this work we introduce a remarkable attribute of the FLR classifier: it's capacity to identify redundant system inputs, from a set of input/output data. The proposed approach is applicable beyond R N on any lattice ordered data set L N , which may include disparate types of data. Also, the proposed approach can deal with populations of data instead of crisp data vectors. Finally, it is highlighted that proposed approach can be employed for designing models with simple structure and significant performance. The method is successfully applied here on two well known real world classification problems, identifying redundant inputs and inducing FLR classifiers with simple structure and favorable classification performance

Static chamber methane flux measurements in volcanic/geothermal areas: preliminary data from Sousaki and Nisyros (Greece)

Methane plays an important role in the Earth’s atmospheric chemistry and radiative balance being the second most important greenhouse gas after carbon dioxide. Methane is released to the atmosphere by a wide number of sources, both natural and anthropogenic, with the latter being twice as large as the former (IPCC, 2007). It has recently been established that significant amounts of geological methane, produced within the Earth’s crust, are currently released naturally into the atmosphere (Etiope, 2004). Active or recent volcanic/geothermal areas represent one of these sources of geological methane. But due to the fact that methane flux measurements are laboratory intensive, very few data have been collected until now and the contribution of this source has been generally indirectly estimated (Etiope et al., 2007). The Greek territory is geodynamically very active and has many volcanic and geothermal areas. Here we report on methane flux measurements made at two volcanic/geothermal systems along the South Aegean volcanic arc: Sousaki and Nisyros. The former is an extinct volcanic area of Plio-Pleistocene age hosting nowadays a low enthalpy geothermal field. The latter is a currently quiescent active volcanic system with strong fumarolic activity due to the presence of a high enthalpy geothermal system. Both systems have gas manifestations that emit significant amounts of hydrothermal methane and display important diffuse carbon dioxide emissions from the soils. New data on methane isotopic composition and higher hydrocarbon contents point to an abiogenic origin of the hydrothermal methane in the studied systems. Measured methane flux values range from –48 to 29,000 (38 sites) and from –20 to 1100 mg/mˆ2/d (35 sites) at Sousaki and Nisyros respectively. At Sousaki measurement sites covered almost all the degassing area and the diffuse methane output can be estimated in about 20 t/a from a surface of about 10,000 mˆ2. At Nisyros measurements covered the Stephanos and Kaminakia areas, which represent only a part of the entire degassing area. The two areas show very different methane degassing pattern with latter showing much higher flux values. Methane output can be estimated in about 0.25 t/a from an area of about 30,000 mˆ2 at Stephanos and about 1 t/a from an area of about 20,000 mˆ2 at Kaminakia. The total output from the entire geothermal system of Nisyros probably should not exceed 2 t/a

Weak anisotropy and disorder dependence of the in-plane magnetoresistance in high mobility (100) Si-inversion layers

We report studies of the magnetoresistance (MR) in a two-dimensional electron system in (100) Si-inversion layers, for perpendicular and parallel orientations of the current with respect to the magnetic field in the 2D-plane. The magnetoresistance is almost isotropic; this result does not support the suggestion of the orbital origin of the MR in Si-inversion layer. In the hopping regime, however, the MR contains a weak anisotropic component that is non-monotonic in magnetic field. We found that the field, at which the MR saturates, for different samples varies by a factor of two, being lower or higher than the field of complete spin polarization of free carriers. Therefore, the saturation of the MR can not be identified with the spin polarization of free carriers.Comment: 4 pages, 4 figures; New data adde

Rice husk ash (RHA) effectiveness in cement and concrete as a function of reactive silica and fineness

Research on ash from burning of rice husks (RHA) has already demonstrated that it is one of the most promising supplementary cementing materials (SCM), given its high specific surface and great amount of silica soluble in alkaline conditions. Indeed, RHA could be a product of added value if it wasn't for its limited availability and periodically high residual carbon content, factors inhibiting its wider use in building materials. Most of the published work has exploited the effectiveness of RHA of very high specific surface and reactive silica, without really investigating the effect of these factors with respect to mechanical and durability characteristics of the derived cement and concrete. This is of crucial importance since someone could falsely rate RHA of moderate fineness and chemical reactivity as potentially reject, constituting thus a significant portion of this by-product unutilised. Reactive silica and fineness effect was assessed in this study by examining two different RHAs, both in blended cement and concrete level. It was found out that RHA is a material extremely "sensitive" to fineness changes; the higher being the fineness the more positive is the effect of RHA inclusion in the mix. Not surprisingly, active silica holds a key role especially for later-age strength gain, indicating that pozzolanic effect takes over from the "physical" effect of the pozzolan as hydration evolves. Pozzolanic potential, strength development of mortars and concrete, efficiency factors (k-values) estimation and resistance against chloride penetration are part of the testing performed and reveal the importance of the binary action of RHA in producing competitive blended cement and concrete

Diagnosis of Fanconi Anaemia (FA) in dizygotic twins

In this study we report on a case of FA in dizygotic twins with characteristic congenital abnormalities and the same deletions of the FANCA gene

Highly anisotropic g-factor of two-dimensional hole systems

Coupling the spin degree of freedom to the anisotropic orbital motion of two-dimensional (2D) hole systems gives rise to a highly anisotropic Zeeman splitting with respect to different orientations of an in-plane magnetic field B relative to the crystal axes. This mechanism has no analogue in the bulk band structure. We obtain good, qualitative agreement between theory and experimental data, taken in GaAs 2D hole systems grown on (113) substrates, showing the anisotropic depopulation of the upper spin subband as a function of in-plane B.Comment: 4 pages, 3 figure

DES vs RANS: The flatback airfoil case

Using flatback airfoils at the root of wind turbine (WT) blades is becoming more popular as the WTs increase in size. The reason is that they provide significant aerodynamic, aeroelastic and structural benefits. However, due to the blunt trailing edge (TE), the wake of such airfoils is highly unsteady and rich in three-dimensional vortical structures. This poses significant challenges on the numerical simulation of the flow around them, given the highly unsteady, three-dimensional turbulent character of their wake. In this work, computational predictions for a flatback airfoil employing both RANS and DES approaches on three successively refined grids up to 25 million cells are compared with available experimental data. Results suggest that even though URANS and DDES are in good agreement in terms of lift and drag, RANS simulations fail to accurately capture the turbulent wake unsteady characteristics