Using Laboratory Experiments For Policy Making: An Example From The Georgia Irrigation Reduction Auction

In April 2000, the Georgia legislature passed a law requiring that the state use an unspecified "auction-like process" to pay some farmers to suspend irrigation in declared drought years. In response, we conducted a series of laboratory and field experiments to test a variety of auction procedures. This paper reports the results of these experiments, and how they were used by the policy makers who determined the auction procedures. Experimental results are compared with farmers' bidding behavior in the state-run irrigation auction conducted in March 2001. Working Paper # 2002-00

SLS Processing Studies of Nylon 11 Nanocomposites

Selective Laser Sintering (SLS) is widely used for rapid prototyping/manufacturing of nylon 11 and nylon 12 parts. This processing technique has not been explored for nylon nanocomposites. This study investigates the technicalities of processing nylon 11-clay and nylon-carbon nanofiber nanocomposites with SLS. Microstructural analyses of the SLS powders and parts were conducted under SEM. Results suggest that SLS processing is possible with the new nylon 11 nanocomposites. Yet the SLS parts built have inferior properties relative to those of injection molding, suggesting that more fine tuning for the processing is required.Mechanical Engineerin

Predicted effects of fluid loading on the vibration of elastic porous plates

International audienceThe effects of fluid loading on the vibration of rectangular, clamped, porous elastic plates and on their radiated sound power are considered. This requires the inclusion of an extra term in the equations for the plate vibration, corresponding to the additional external force acting on the plate. As is the case for vibrating non-porous plates, fluid-structure coupling is a very complex phenomenon since the plate modes are coupled by the fluid. The radiation impedance matrix, including direct terms and cross-coupling terms, has been defined and computed. A Gaussian quadrature scheme including twenty terms of the Legendre polynomial has been used to compute the fluid loaded plate deflection for four types of porous and elastic plate and compare the effects of the loading by water and air. The corresponding vibroacoustic indicators including mean square velocity, radiated sound power and radiation efficiency, have been calculated also. For some plate and fluid parameters, the predicted effects of fluid loading are considerable

High Flux Femtosecond X-ray Emission from the Electron-Hose Instability in Laser Wakefield Accelerators

Bright and ultrashort duration X-ray pulses can be produced by through betatron oscillations of electrons during Laser Wakefield Acceleration (LWFA). Our experimental measurements using the \textsc{Hercules} laser system demonstrate a dramatic increase in X-ray flux for interaction distances beyond the depletion/dephasing lengths, where the initial electron bunch injected into the first wake bucket catches up with the laser pulse front and the laser pulse depletes. A transition from an LWFA regime to a beam-driven plasma wakefield acceleration (PWFA) regime consequently occurs. The drive electron bunch is susceptible to the electron-hose instability and rapidly develops large amplitude oscillations in its tail, which leads to greatly enhanced X-ray radiation emission. We measure the X-ray flux as a function of acceleration length using a variable length gas cell. 3D particle-in-cell (PIC) simulations using a Monte Carlo synchrotron X-ray emission algorithm elucidate the time-dependent variations in the radiation emission processes.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev. Accel. Beam

Transmission loss predictions for dissipative silencers of arbitrary cross section in the presence of mean flow

A numerical technique is developed for the analysis of dissipative silencers of arbitrary, but axially uniform, cross section. Mean gas flow is included in a central airway which is separated from a bulk reacting porous material by a concentric perforate screen. The analysis begins by employing the finite element method to extract the eigenvalues and associated eigenvectors for a silencer of infinite length. Point collocation is then used to match the expanded acoustic pressure and velocity fields in the silencer chamber to those in the inlet and outlet pipes. Transmission loss predictions are compared with experimental measurements taken for two automotive dissipative silencers with elliptical cross sections. Good agreement between prediction and experiment is observed both without mean flow and for a mean flow Mach number of 0.15. It is demonstrated also that the technique presented offers a considerable reduction in computational expenditure when compared to a three dimensional finite element analysis

Spinal Progenitor-Laden Bridges Support Earlier Axon Regeneration Following Spinal Cord Injury.

Impact statementSpinal cord injury (SCI) results in loss of tissue innervation below the injury. Spinal progenitors have a greater ability to repair the damage and can be injected into the injury, but their regenerative potential is hampered by their poor survival after transplantation. Biomaterials can create a cell delivery platform and generate a more hospitable microenvironment for the progenitors within the injury. In this work, polymeric bridges are used to deliver embryonic spinal progenitors to the injury, resulting in increased progenitor survival and subsequent regeneration and functional recovery, thus demonstrating the importance of combined therapeutic approaches for SCI

Indestructibility of Vopenka's Principle

We show that Vopenka's Principle and Vopenka cardinals are indestructible under reverse Easton forcing iterations of increasingly directed-closed partial orders, without the need for any preparatory forcing. As a consequence, we are able to prove the relative consistency of these large cardinal axioms with a variety of statements known to be independent of ZFC, such as the generalised continuum hypothesis, the existence of a definable well-order of the universe, and the existence of morasses at many cardinals.Comment: 15 pages, submitted to Israel Journal of Mathematic

Innovative Selective Laser Sintering Rapid Manufacturing using Nanotechnology

The objective of this research is to develop an improved nylon 11 (polyamide 11) polymer with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering (SLS) rapid manufacturing (RM). A nanophase was introduced into nylon 11 via twin screw extrusion to provide improved material properties of the polymer blends. Atofina (now known as Arkema) RILSAN® nylon 11 injection molding polymer pellets was used with three types of nanoparticles: chemically modified montmorillonite (MMT) organoclays, nanosilica, and carbon nanofibers (CNF) to create nylon 11 nanocomposites. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of dispersion. Fifteen nylon 11 nanocomposites and control nylon 11 were fabricated by injection molding. Flammability properties (using a cone calorimeter with a radiant flux of 50 kW/m2 ) and mechanical properties such as tensile strength and modulus, flexural modulus, elongation at break were determined for the nylon 11 nanocomposites and compared with the baseline nylon 11. Based on flammability and mechanical material performance, five polymers including four nylon 11 nanocomposites and a control nylon 11 were cryogenically ground into fine powders for SLS RM. SLS specimens were fabricated for flammability, mechanical, and thermal properties characterization. Nylon 11-CNF nanocomposites exhibited the best overall properties for this study.Mechanical Engineerin