6,525 research outputs found
Preliminary assessment of power-generating tethers in space and of propulsion for their orbit maintenance
The concept of generating power in space by means of a conducting tether deployed from a spacecraft was studied. Using hydrogen and oxygen as the rocket propellant to overcome the drag of such a power-generating tether would yield more benefit than if used in a fuel cell. The mass consumption would be 25 percent less than the reactant consumption of fuel cells. Residual hydrogen and oxygen in the external tank and in the orbiter could be used very effectively for this purpose. Many other materials (such as waste from life support) could be used as the propellant. Electrical propulsion using tether generated power can compensate for the drag of a power-generating tether, half the power going to the useful load and the rest for electric propulsion. In addition, the spacecraft's orbital energy is a large energy reservoir that permits load leveling and a ratio of peak to average power equal to 2. Critical technologies to be explored before a power-generating tether can be used in space are delineated
Driven Intrinsic Localized Modes in a Coupled Pendulum Array
Intrinsic localized modes (ILMs), also called discrete breathers, are
directly generated via modulational instability in an array of coupled
pendulums. These ILMs can be stabilized over a range of driver frequencies and
amplitudes. They are characterized by a pi-phase difference between their
center and wings. At higher driver frequencies, these ILMs are observed to
disintegrate via a pulsating instability, and the mechanism of this breather
instability is investigated.Comment: 5 pages, 6 figure
CONSUMER PREFERENCES FOR ELECTRICITY FROM BIOENERGY AND OTHER RENEWABLES
This study ascertains residential electricity consumers' support and willingness to pay for electricity from renewable sources. Then, willingness to pay for specified renewable energy sources (solar, wind, landfill wastes, bioenergy from fast growing crops, and bioenergy from forest products wastes). Effects of demographics and environmental behaviors are estimated.Institutional and Behavioral Economics,
Polarization dependent photoionization cross-sections and radiative lifetimes of atomic states in Ba
The photoionization cross-sections of two even-parity excited states, and , of atomic Ba at the ionization-laser wavelength of
556.6 nm were measured. We found that the total cross-section depends on the
relative polarization of the atoms and the ionization-laser light. With
density-matrix algebra, we show that, in general, there are at most three
parameters in the photoionization cross-section. Some of these parameters are
determined in this work. We also present the measurement of the radiative
lifetime of five even-parity excited states of barium.Comment: 11 pages, 7 figure
Geographical Analysis of US Green Sector Industry Concentration
This paper analyzes the geographic distribution of “green energy” sector clustering in the lower 48 United States using recent developments in industry concentration analysis. Evidence suggests that the ten green energy subsectors and the aggregate of the firms comprising the green energy sector are regionally concentrated. Positive changes in industry concentration from 2002 to 2006 tended to be greatest in non-metropolitan counties, suggesting comparative advantage with respect to site location for the composite of firms making up these sectors.Agglomeration, Location Quotient, Renewable Energy, Community/Rural/Urban Development, Industrial Organization, Research and Development/Tech Change/Emerging Technologies,
Forecast of Future Aviation Fuels. Part 1: Scenarios
A preliminary set of scenarios is described for depicting the air transport industry as it grows and changes, up to the year 2025. This provides the background for predicting the needs for future aviation fuels to meet the requirements of the industry as new basic sources, such as oil shale and coal, which are utilized to supplement petroleum. Five scenarios are written to encompass a range of futures from a serious resource-constrained economy to a continuous and optimistic economic growth. A unique feature is the choice of one immediate range scenario which is based on a serious interruption of economic growth occasioned by an energy shortfall. This is presumed to occur due to lags in starting a synfuels program
Discrete breathers in a nonlinear electric line: Modeling, Computation and Experiment
We study experimentally and numerically the existence and stability
properties of discrete breathers in a periodic nonlinear electric line. The
electric line is composed of single cell nodes, containing a varactor diode and
an inductor, coupled together in a periodic ring configuration through
inductors and driven uniformly by a harmonic external voltage source. A simple
model for each cell is proposed by using a nonlinear form for the varactor
characteristics through the current and capacitance dependence on the voltage.
For an electrical line composed of 32 elements, we find the regions, in driver
voltage and frequency, where -peaked breather solutions exist and
characterize their stability. The results are compared to experimental
measurements with good quantitative agreement. We also examine the spontaneous
formation of -peaked breathers through modulational instability of the
homogeneous steady state. The competition between different discrete breathers
seeded by the modulational instability eventually leads to stationary
-peaked solutions whose precise locations is seen to sensitively depend on
the initial conditions
The interaction of phylloxera infection, rootstock, and irrigation on young Concord grapevine growth
Concord roots are moderately resistant to phylloxera, which form nodosities on the fine roots and weaken the root system. Rootstocks and vineyard floor management both have the potential to eliminate or reduce the effect of phylloxera in New York Concord vineyards. Young, container-grown Concord grapevines were used to evaluate the interaction between rootstock (own-rooted, Couderc 3309), irrigation, and phylloxera infection on vine growth. Phylloxera inoculation alone caused a 21 % decrease in vine dry mass and lack of irrigation (mid-day stem water potential: -0.9 to -1.0 M Pa) alone caused a 34 % decrease in vine dry mass. The combination of phylloxera stress and water stress was additive and caused a 54 % decrease in vine dry mass. Because C3309 rootstock is resistant to phylloxera, the grafted vines showed a response to irrigation but not phylloxera inoculation. This container study shows the potential benefits of irrigating own-rooted Concord grapevines or the use of rootstocks without irrigation to withstand phylloxera infection.
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