37 research outputs found
Study of the factors affecting the karst volume assessment in the Dead Sea sinkhole problem using microgravity field analysis and 3-D modeling
Thousands of sinkholes have appeared in the Dead Sea (DS) coastal area in Israel and Jordan during two last decades. The sinkhole development is recently associated with the buried evaporation karst at the depth of 25–50 m from earth's surface caused by the drop of the DS level at the rate of 0.8–1.0 m/yr. Drop in the Dead Sea level has changed hydrogeological conditions in the subsurface and caused surface to collapse. The pre-existing cavern was detected using microgravity mapping in the Nahal Hever South site where seven sinkholes of 1–2 m diameter had been opened. About 5000 gravity stations were observed in the area of 200&times;200 m<sup>2</sup> by the use of Scintrex CG-3M AutoGrav gravimeter. Besides the conventional set of corrections applied in microgravity investigations, a correction for a strong gravity horizontal gradient (DS Transform Zone negative gravity anomaly influence) was inserted. As a result, residual gravity anomaly of –(0.08÷0.14) mGal was revealed. The gravity field analysis was supported by resistivity measurements. We applied the Emigma 7.8 gravity software to create the 3-D physical-geological models of the sinkholes development area. The modeling was confirmed by application of the <i>GSFC</i> program developed especially for 3-D combined gravity-magnetic modeling in complicated environments. Computed numerous gravity models verified an effective applicability of the microgravity technology for detection of karst cavities and estimation of their physical-geological parameters. A volume of the karst was approximately estimated as 35 000 m<sup>3</sup>. The visual analysis of large sinkhole clusters have been forming at the microgravity anomaly site, confirmed the results of microgravity mapping and 3-D modeling
Secondary Instabilities of Surface Waves on Viscous Fluids in the Faraday Instability
Secondary instabilities of Faraday waves show three regimes: (1) As seen
previously, low-viscosity (nu) fluids destabilize first into squares. At higher
driving accelerations a, squares show low-frequency modulations corresponding
to the motion of phase defects, while theory predicts a stationary transverse
amplitude modulation (TAM). (2) High-nu fluids destabilize first to stripes.
Stripes then show an oscillatory TAM whose frequency is incommensurate with the
driving frequency. At higher a, the TAM undergoes a phase instability. At still
higher a, edge dislocations form and fluid droplets are ejected. (3)
Intermediate-nu fluids show a complex coexistence of squares and stripes, as
well as stationary and oscillatory TAM instabilities of the stripes.Comment: REVTEX, with 3 separate uuencoded figures, to appear in Europhys.
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Localized and Cellular Patterns in a Vibrated Granular Layer
We propose a phenomenological model for pattern formation in a vertically
vibrated layer of granular material. This model exhibits a variety of stable
cellular patterns including standing rolls and squares as well as localized
objects (oscillons and worms), similar to recent experimental
observations(Umbanhowar et al., 1996). The model is an amplitude equation for
the parametrical instability coupled to the mass conservation law. The
structure and dynamics of the solutions resemble closely the properties of
localized and cellular patterns observed in the experiments.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Identification of a new hexagonal phase in the Al–Cu–Re system
Particles of an unknown intermetallic phase with the approximate composition Al65Cu25Re10 were observed in a ternary Al-Cu-Re alloy. The structure of this phase was investigated in a transmission electron microscope using the precession electron diffraction (PED) technique. This phase has a hexagonal unit cell with lattice parameters a = 11.029(6) and c = 12.746(1)angstrom; its crystal symmetry can be described by the P6(3) (173) space group. (C) 2009 Elsevier B.V. All rights reserved
Convective structures in a thin layer of an evaporating liquid under an airflow
International audienceEvolution of convective structures in a thin layer of an evaporating liquid (ethanol) located under a turbulent boundary layer of an airflow is studied experimentally and theoretically. Evolution of the structures is examined under conditions of an increased flow velocity. A transition is found from convective cells formed in the absence of the flow to convective rolls elongated in the streamwise direction. The theoretical analysis is performed within a two-dimensional model of the flow in the liquid layer. The boundary conditions on the liquid surface are obtained with the use of self-similar solutions for mean fields in the airflow. The onset and evolution of a periodic system of rolls are simulated numerically. Theoretical conclusions are compared with experimental data
Microstructure and morphology evolution in chemically deposited semiconductor films: 4. From isolated nanoparticles to monocrystalline PbS thin films on GaAs(100) substrates
Thin lead sulfide films were grown on single crystal GaAs(100) substrates by
chemical deposition using Pb(NO3)2 and CS(NH2)2 with
excess of NaOH in aqueous solution at a range of deposition temperatures
0–50 °C. The microstructure and morphology evolution were studied
as a function of the deposition conditions, resulting in a wide range of
microstructures. Ultrahigh resolution scanning electron microscopy and
atomic force microscopy indicated a systematic change in particle shape and
surface morphology as a function of deposition temperature and deposition
time. X-ray diffraction of 200–500 nm thick films indicated a dominant
texture throughout the deposition temperature range. At deposition
temperatures above 40 °C, single crystal films were obtained.
Cross-sectional transmission electron microscopy analyses showed a unique
(011)PbS||(100)GaAs and [100]PbS||[011]GaAs orientation relationship
Rotation motion of particles in sound field
It is known that sound field produces longitudinal oscillation motion of medium. If there are floating particles in a medium those particles oscillate together with liquid. In this paper we consider dynamics of floating particles, which have rotational oscillations in acoustic field. This novel phenomena produces additional sound attenuation due to viscous damping. In the present paper this effect is analytically described. The expression for sound attenuation in suspensions of such particles and estimations of the value of the effect are obtained, and possible applications are discussed