612 research outputs found
Enhacement in the dymanic response of a viscoelastic fluid flowing through a longitudinally vibrating tube
We analyzed effects of elasticity on the dynamics of fluids in porous media
by studying a flow of a Maxwell fluid in a tube, which oscillates
longitudinally and is subject to oscillatory pressure gradient. The present
study investigates novelties brought about into the classic Biot's theory of
propagation of elastic waves in a fluid-saturated porous solid by inclusion of
non-Newtonian effects that are important, for example, for hydrocarbons. Using
the time Fourier transform and transforming the problem into the frequency
domain, we calculated: (A) the dynamic permeability and (B) the function
that measures the deviation from Poiseuille flow friction as a
function of frequency parameter . This provides a more complete theory
of flow of Maxwell fluid through the longitudinally oscillating cylindrical
tube with the oscillating pressure gradient, which has important practical
applications. This study has clearly shown transition from dissipative to
elastic regime in which sharp enhancements (resonances) of the flow are found
La temporalidad de la pensión compensatoria en la jurisprudencia del tribunal supremo
En el presente trabajo se estudian los criterios jurisprudenciales en orden a determinar si una pensión compensatoria debe tener carácter indefinido o temporal
Los alimentos debidos a los hijos menores de edad: un estudio jurisprudencial
This study analyzes the case law interpretation of Article 93.I of the Spanish Civil Code with regard to maintenance owed to minor children
Coherent and Incoherent Scattering Mechanisms in Air-Filled Permeable Materials
Ultrasonic evaluation of porous materials can take advantage of some very specific acoustic phenomena that occur only in fluid-saturated consolidated solids of continuously connected pore structure. The most interesting feature of acoustic wave propagation in such media is the appearance of a second compressional wave, the so-called slow wave [1,2]. The slow compressional wave represents a relative motion between the fluid and the solid frame. This motion is very sensitive to the kinematic viscosity of the fluid and the dynamic permeability of the porous formation. Certain material properties such as tortuosity, permeability, porosity, and pore size, shape and surface quality are inherently connected to the porous nature of the material and can be evaluated best from the propagation properties of the slow compressional wave.</p
Freeform Fresnel RXI-RR Köhler design with spectrum-splitting for photovoltaics
The development of a novel optical design for the high concentration photovoltaics (HPCV) nonimaging concentrator (>500x) that utilizes a built-in spectrum splitting concept is presented. The primary optical element (POE) is a flat Fresnel lens and the secondary optical element (SOE) is a free-form RXI-type concentrator with a band-pass filter embedded in it. The POE and SOE perform Köhler integration to produce light homogenization on the receiver. The system uses a combination of a commercial concentration GaInP/GaInAs/Ge 3J cell and a concentration Back-PointContact (BPC) silicon cell for efficient spectral utilization, and an external confinement technique for recovering the 3J cell’s reflection. A design target of an “equivalent” cell efficiency ~46% is predicted using commercial 39% 3J and 26% Si cells. A projected CPV module efficiency of greater than 38% is achievable at a concentration level greater than 500X with a wide acceptance angle of ±1º. A first proof-of concept receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ~100x and lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using a 3J cell with a peak efficiency of 36.9
Free-form Fresnel RXI-RR Köhler design for high-concentration photovoltaics with spectrum-splitting
Development of a novel HCPV nonimaging concentrator with high concentration (>500x) and built-in spectrum splitting concept is presented. It uses the combination of a commercial concentration GaInP/GaInAs/Ge 3J cell and a concentration Back-Point-Contact (BPC) silicon cell for efficient spectral utilization, and external confinement techniques for recovering the 3J cell's reflection. The primary optical element (POE) is a flat Fresnel lens and the secondary optical element (SOE) is a free-form RXI-type concentrator with a band-pass filter embedded in it - Both the POE and SOE performing Köhler integration to produce light homogenization on the receiver. The band-pass filter transmits the IR photons in the 900-1200 nm band to the silicon cell. A design target of an "equivalent" cell efficiency ~46% is predicted using commercial 39% 3J and 26% Si cells. A projected CPV module efficiency of greater than 38% is achievable at a concentration level larger than 500X with a wide acceptance angle of ±1°. A first proof-of concept receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ~100x and lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using a 3J cell with a peak efficiency of 36.9%
Ultra-High Efficiency, High-Concentration PV System Based On Spectral Division Between GaInP/GaInAs/Ge And BPC Silicon Cells
A novel HCPV nonimaging concentrator concept with high concentration (>500×) is presented. It uses the combination of a commercial concentration GaInP∕GaInAs∕Ge 3J cell and a concentration Back‐Point‐Contact (BPC) concentration silicon cell for efficient spectral utilization, and external confinement techniques for recovering the 3J cell′s reflection. The primary optical element (POE) is a flat Fresnel lens and the secondary optical element (SOE) is a free‐form RXI‐type concentrator with a band‐pass filter embedded it, both POE and SOE performing Köhler integration to produce light homogenization. The band‐pass filter sends the IR photons in the 900–1200 nm band to the silicon cell. Computer simulations predict that four‐terminal terminal designs could achieve ∼46% added cell efficiencies using commercial 39% 3J and 26% Si cells. A first proof‐of concept receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ∼ 100× and lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using a 3J with peak efficiency of 36.9
Evidence for Anthropogenic Surface Loading as Trigger Mechanism of the 2008 Wenchuan Earthquake
Two and a half years prior to China's M7.9 Wenchuan earthquake of May 2008,
at least 300 million metric tons of water accumulated with additional seasonal
water level changes in the Minjiang River Valley at the eastern margin of the
Longmen Shan. This article shows that static surface loading in the Zipingpu
water reservoir induced Coulomb failure stresses on the nearby Beichuan thrust
fault system at <17km depth. Triggering stresses exceeded levels of daily lunar
and solar tides and perturbed a fault area measuring 416+/-96km^2. These stress
perturbations, in turn, likely advanced the clock of the mainshock and directed
the initial rupture propagation upward towards the reservoir on the
"Coulomb-like" Beichuan fault with rate-and-state dependent frictional
behavior. Static triggering perturbations produced up to 60 years (0.6%) of
equivalent tectonic loading, and show strong correlations to the coseismic
slip. Moreover, correlations between clock advancement and coseismic slip,
observed during the mainshock beneath the reservoir, are strongest for a longer
seismic cycle (10kyr) of M>7 earthquakes. Finally, the daily event rate of the
micro-seismicity (M>0.5) correlates well with the static stress perturbations,
indicating destabilization.Comment: 22 pages, 4 figures, 3 table
Thermoelastic Damping in Micro- and Nano-Mechanical Systems
The importance of thermoelastic damping as a fundamental dissipation
mechanism for small-scale mechanical resonators is evaluated in light of recent
efforts to design high-Q micrometer- and nanometer-scale electro-mechanical
systems (MEMS and NEMS). The equations of linear thermoelasticity are used to
give a simple derivation for thermoelastic damping of small flexural vibrations
in thin beams. It is shown that Zener's well-known approximation by a
Lorentzian with a single thermal relaxation time slightly deviates from the
exact expression.Comment: 10 pages. Submitted to Phys. Rev.
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