3,724 research outputs found
Environmental exposure effects on composite materials for commercial aircraft
A study was conducted to determine the effects of long term flight and ground exposure on three commercially available graphite-epoxy material systems: T300/5208, T300/5209, and T300/934. Sets of specimens were exposed on commercial aircraft and ground racks for 1, 2, 3, 5, and 10 years. Inflight specimen sites included both the interior and exterior of aircraft based in Hawaii, Texas, and New Zealand. Ground racks were located at NASA-Dryden and the above mentioned states. Similar specimens were exposed to controlled lab conditions for up to 2 years. After each exposure, specimens were tested for residual strength and a dryout procedure was used to measure moisture content. Both room and high temperature residual strengths were measured and expressed as a pct. of the unexposed strength. Lab exposures included the effects of time alone, moisture, time on moist specimens, weatherometer, and simulated ground-air-ground cycling. Residual strengths of the long term specimens were compared with residual strengths of the lab specimens. Strength retention depended on the exposure condition and the material system. Results showed that composite materials can be successfully used on commercial aircraft if environmental effects are considered
Pyrolysis of Wastewater Biosolids Significantly Reduces Estrogenicity
Most wastewater treatment processes are not specifically designed to remove micropollutants. Many micropollutants are hydrophobic so they remain in the biosolids and are discharged to the environment through land-application of biosolids. Micropollutants encompass a broad range of organic chemicals, including estrogenic compounds (natural and synthetic) that reside in the environment, a.k.a. environmental estrogens. Public concern over land application of biosolids stemming from the occurrence of micropollutants hampers the value of biosolids which are important to wastewater treatment plants as a valuable by-product. This research evaluated pyrolysis, the partial decomposition of organic material in an oxygen-deprived system under high temperatures, as a biosolids treatment process that could remove estrogenic compounds from solids while producing a less hormonally active biochar for soil amendment. The estrogenicity, measured in estradiol equivalents (EEQ) by the yeast estrogen screen (YES) assay, of pyrolyzed biosolids was compared to primary and anaerobically digested biosolids. The estrogenic responses from primary solids and anaerobically digested solids were not statistically significantly different, but pyrolysis of anaerobically digested solids resulted in a significant reduction in EEQ; increasing pyrolysis temperature from 100 °C to 500 °C increased the removal of EEQ with greater than 95% removal occurring at or above 400 °C. This research demonstrates that biosolids treatment with pyrolysis would substantially decrease (removal \u3e 95%) the estrogens associated with this biosolids product. Thus, pyrolysis of biosolids can be used to produce a valuable soil amendment product, biochar, that minimizes discharge of estrogens to the environment
Quantum Dynamics of Skyrmions in Chiral Magnets
We study the quantum propagation of a Skyrmion in chiral magnetic insulators
by generalizing the micromagnetic equations of motion to a finite-temperature
path integral formalism, using field theoretic tools. Promoting the center of
the Skyrmion to a dynamic quantity, the fluctuations around the Skyrmionic
configuration give rise to a time-dependent damping of the Skyrmion motion.
From the frequency dependence of the damping kernel, we are able to identify
the Skyrmion mass, thus providing a microscopic description of the kinematic
properties of Skyrmions. When defects are present or a magnetic trap is
applied, the Skyrmion mass acquires a finite value proportional to the
effective spin, even at vanishingly small temperature. We demonstrate that a
Skyrmion in a confined geometry provided by a magnetic trap behaves as a
massive particle owing to its quasi-one-dimensional confinement. An additional
quantum mass term is predicted, independent of the effective spin, with an
explicit temperature dependence which remains finite even at zero temperature.Comment: 14 pages, 10 figure
Impurity Induced Quantum Phase Transitions and Magnetic Order in Conventional Superconductors: Competition between Bound and Quasiparticle states
We theoretically study bound states generated by magnetic impurities within
conventional -wave superconductors, both analytically and numerically. In
determining the effect of the hybridization of two such bound states on the
energy spectrum as a function of magnetic exchange coupling, relative angle of
magnetization, and distance between impurities, we find that quantum phase
transitions can be modulated by each of these parameters. Accompanying such
transitions, there is a change in the preferred spin configuration of the
impurities. Although the interaction between the impurity spins is
overwhelmingly dominated by the quasiparticle contribution, the ground state of
the system is determined by the bound state energies. Self-consistently
calculating the superconducting order parameter, we find a discontinuity when
the system undergoes a quantum phase transition as indicated by the bound state
energies.Comment: 8 pages, 7 figure
Spin-dependent coupling between quantum dots and topological quantum wires
Considering Rashba quantum wires with a proximity-induced superconducting gap
as physical realizations of Majorana fermions and quantum dots, we calculate
the overlap of the Majorana wave functions with the local wave functions on the
dot. We determine the spin-dependent tunneling amplitudes between these two
localized states and show that we can tune into a fully spin polarized
tunneling regime by changing the distance between dot and Majorana fermion.
Upon directly applying this to the tunneling model Hamiltonian, we calculate
the effective magnetic field on the quantum dot flanked by two Majorana
fermions. The direction of the induced magnetic field on the dot depends on the
occupation of the nonlocal fermion formed from the two Majorana end states
which can be used as a readout for such a Majorana qubit.Comment: 18 pages, 11 figure
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