Monitoring of groundwater levels for real‑time conjunctive water management

Water users in the Arkansas Grand Prairie wish to maintain sufficient groundwater levels to: insure adequate groundwater reserves for time of drought, protect themselves from litigation caused by wells going dry, and insure a sustained yield. Achievement of these goals requires regular measurement of groundwater levels. Review of monitoring practice and technology indicates that spring and fall measurements taken over the entire area using steel tape and acoustic device is preferred for most long range planning. Continuous monitoring is indicated for critical parts of the region where saturated thicknesses are small. Desirable attributes of a data collection/transmission system for such areas are as follow: Data should be stored in digital format on machine readable medium. Collection device should be installable in existing wells and not require special well construction. Device should be able to monitor pump status, and time and water level at programmable intervals. Device should be upgradable to be able to transmit data as it is collected. A system which has these capabilities was built. It consists of an acoustic probe, interface, computer and cassette recorder

Controlling the Buckling Behavior of Bilayered Systems

A bilayered system is an assembly of two different materials and has the form of flat and thin layers. The two materials are attached to each other at the surface. The attachment method varies depending on the materials properties. Bilayered systems made of materials with different dimensions and stiffness have been widely studied and used for different applications. The characteristic scale of this kind of system can go from hundreds of km in the case of geological layers on the Earth surface to some µm in the case of very small electronic systems or microlenses. The behavior of a bilayered system, when submitted to a stimulus, is characterized by the conflict between the preferred response of each material and the constraint that one imposes on the other. As a result, the deformation of the bilayered system will be different from that which could be obtained when the materials are taken separately. Of particular interest is the buckling of such systems: when submitted to a particular stress distribution, one material will expand significantly more than the other, but as the two materials are attached at the interface surface, the material displacements must be continuous through this interface. The conflict between the continuity of displacement and the need to expand differently may result in nonlinear patterns at this interface. Those unstable situations can be used to define a limit of constraint for the materials or can be used as actuators for a desired surface pattern. Many studies have focused on characterizing homogeneous buckling within an entire surface due to homogeneous strain distribution within the top surface. This characterization was performed theoretically, numerically, and experimentally. But, some studies have shown different possibilities of evolution of the buckling patterns known today. As a consequence, we can pose two questions: 1) Is there a possibility to modify non-linear patterns regardless of what is imposed by mechanical properties and dimensions? 2) What happens in the case of a non-uniform state of constraints within the bilayered system? This thesis explores those questions for the case of a thin stiff film attached to a compliant thick substrate. The first part of this thesis serves to describe the initial buckling theory in the case of uniform strain and explains how to define the loading threshold resulting in uniform buckling at the surface characterized by a finite number of spatial frequencies. The second part of the thesis studies the consequences of a non-uniform loading within the surface. A numerical method based on the theory of the first part is implemented to show the emergence of new frequencies due to the discontinuous loading distribution. The third part focuses on the possibility of tuning a uniform buckling by including an electromechanical coupling into the bilayered system. This coupling makes the materials sensitive to electric fields, thus creating a new energy term to interfere with the mechanical energy of deformation, thereby modifying the resulting spatial frequency of the buckling. This study is done theoretically and numerically by finite element modeling.</p

Phylogeographic patterns of steppe species in Eastern Central Europe: a review and the implications for conservation

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Charged anisotropic matter with linear equation of state

We consider the general situation of a compact relativistic body with anisotropic pressures in the presence of the electromagnetic field. The equation of state for the matter distribution is linear and may be applied to strange stars with quark matter. Three classes of new exact solutions are found to the Einstein-Maxwell system. This is achieved by specifying a particular form for one of the gravitational potentials and the electric field intensity. We can regain anisotropic and isotropic models from our general class of solution. A physical analysis indicates that the charged solutions describe realistic compact spheres with anisotropic matter distribution. The equation of state is consistent with dark energy stars and charged quark matter distributions. The masses and central densities correspond to realistic stellar objects in the general case when anisotropy and charge are present.Comment: 17 pages, To appear in Class. Quantum Gra

Targeted and comprehensive space-environment sensors: description and recommendations

We discuss the roles of the two classes of space-environment sensors on operational space systems: (1) Targeted sensors capable of measuring the environment and effects at a level sufficient for providing situational awareness for the host spacecraft and (2) Comprehensive sensors capable of providing detailed environment measurements that can be mapped to a broad region of near-Earth space, providing global situational awareness and quantitative characterization of the environment. Our purpose is to show the usefulness of a heterogeneous architecture with both classes of sensors for the near-term and long-term needs of National Security Spac

Screening of Hydrodynamic Interactions in Semidilute Polymer Solutions: A Computer Simulation Study

We study single-chain motion in semidilute solutions of polymers of length N = 1000 with excluded-volume and hydrodynamic interactions by a novel algorithm. The crossover length of the transition from Zimm (short lengths and times) to Rouse dynamics (larger scales) is proportional to the static screening length. The crossover time is the corresponding Zimm time. Our data indicate Zimm behavior at large lengths but short times. There is no hydrodynamic screening until the chains feel constraints, after which they resist the flow: "Incomplete screening" occurs in the time domain.Comment: 3 figure

Telecommunication wavelength GaAsBi light emitting diodes

GaAsBi light emitting diodes containing ∼6% Bi are grown on GaAs substrates. Good room-temperature electroluminescence spectra are obtained at current densities as low as 8 Acm − 2. Measurements of the integrated emitted luminescence suggest that there is a continuum of localised Bi states extending up to 75 meV into the bandgap, which is in good agreement with previous photoluminescence studies. X-ray diffraction analysis shows that strain relaxation has probably occurred in the thicker samples grown in this study