11,864 research outputs found
Unchartered Territory for the Bluegrass State : Lessons to be learned from over a Quarter-century of State Charter School Legislation
Charter school success or failure is not simply a matter of chance. Both the existence and aggregate quality of charter schools in a state depend on the provisions of state charter school laws. These laws address a wide range of issues and vary from state to state. But the experiences of states with significant charter sectors, as well as those with innovative charter policies, provide important lessons for the charter school movement as a whole
Icing and De-Icing of a Propeller with Internal Electric Blade Heaters
An investigation has been made in the NACA Cleveland icing research tunnel to determine the de-icing effectiveness of an experimental configuration of an Internal electric propeller-blade heater. Two atmospheric Icing conditions and two propeller operating conditions were Investigated, In experiments with unheated blades and with heat applied to the blades both continuously and cyclically. Data are presented to show the effect of propeller speed., ambient air temperature and liquid-water concentration, and the duration of the heat-on and cycle times on the power requirements and de-Icing performance of the blade heaters. The extent of ice-covered area on the blades for various icing ax4 operating conditions has been determined. The largest iced area was obtained at the higher ambient-air temperatures and at low propeller speed. The ohord.wise extent of Icing In practically every case was greater than that covered by blade heaters. Adequate de-icing in the heated area with continuous application of heat was obtained with the power available but a maximum power, input of 1250 watts per blade was insufficient for cyclic de-Icing for the range of conditions investigated. Blade-surface temperature rates of rise of 0.2 to 0.7 F per second were obtained and the minimum cooling period for cyclic de-icing was found to be approximately 2-1/2 times the heating period
An investigation of fracture toughness, fatigue-crack growth, sustained-load flaw growth, and impact properties of three pressure vessel steels
The elastic fracture toughness of the three steels is shown to not decrease significantly with decreasing temperature from room temperature to about 244 K (-20 F.). The elastic fracture toughness of the three steels increased with increasing specimen width and thickness. The fatigue-crack-growth data for all three steels fall into relatively narrow scatter bands on plots of rate against stress-intensity range. An equation is shown to predict the upper bounds of the scatter bands reasonably well. Charpy impact energies decreased with decreasing temperature in the nominal temperature range from room temperature to 244 K (-20 F). The nil-ductility temperatures of the steels are discussed
Resistance and lifetime measurements of polymer solar cells using glycerol doped poly[3,4-ethylenedioxythiophene]: poly[styrenesulfonate] hole injection layers
We have performed resistivity measurements of
poly[3,4-ethylenedioxythiophene]: poly[styrenesulfonate] (PEDOT:PSS) films with
varying concentrations of glycerol. Resistivity is seen to decrease
exponentially from roughly 3 ohm-cm for pure PEDOT:PSS to 3x10-2 ohm-cm for 35
mg/cm3 glycerol in PEDOT:PSS. Beyond this concentration adding glycerol does
not significantly change resistivity. Bulk heterojunction polymer solar cells
using these variously doped PEDOT:PSS layers as electrodes were studied to
characterize the effects on efficiency and lifetime. Although our data display
significant scatter, lowering the resistance of the PEDOT:PSS layers results in
lower device resistance and higher efficiency as expected. We also note that
the lifetime of the devices tends to be reduced as the glycerol content of
PEDOT:PSS is increased. Many devices show an initial increase in efficiency
followed by a roughly exponential decay. This effect is explained based on
concomitant changes in the zero bias conductance of the samples under dark
conditions
One-Parameter Squeezed Gaussian States of Time-Dependent Harmonic Oscillator and Selection Rule for Vacuum States
By using the invariant method we find one-parameter squeezed Gaussian states
for both time-independent and time-dependent oscillators. The squeezing
parameter is expressed in terms of energy expectation value for
time-independent case and represents the degree of mixing positive and negative
frequency solutions for time-dependent case. A {\it minimum uncertainty
proposal} is advanced to select uniquely vacuum states at each moment of time.
We show that the Gaussian states with minimum uncertainty coincide with the
true vacuum state for time-independent oscillator and the Bunch-Davies vacuum
for a massive scalar field in a de Sitter spacetime.Comment: 13 Pages, ReVTeX, no figure
A Web application for creating and sharing visual bibliographies
The amount of information provided by peer-reviewed scientific literature citation indexes such as Scopus, Web of Science (WOS), CrossRef and OpenCitations is huge: it offers to the users a lot of metadata about publications, such as the list of papers written by a specific author, the editorial and content details of a paper, the list of references and citations. But, for a researcher could be interesting also to: extract in real-time these data in order to create bibliographies, for example, starting with a small set of significant papers or a restricted number of authors, and progressively enriching them by exploring cited/citing references; dispose of a graphical and aggregate representation for them; be able to easily share them with other interested researchers.
With these main intents, we modelled and realized VisualBib, a Web application prototype, which enables the user to select sets of papers and/or authors in order to create customized bibliographies, and in real-time visualize them, aggregating data from different sources, in a comprehensive, holistic graphical view.
The bibliographies are displayed using time-based visualizations, called narrative views, which contain explicit representations of the authorship and citing relations. These views may help users to: describe a research area; disseminate the research on a specific topic through the sharing of personal points of view; show in a fresh look the entire production of a researcher, or research groups, in order present or evaluate it
Mass spectrometric gas composition measurements associated with jet interaction tests in a high-enthalpy wind tunnel
Knowledge of test gas composition is important in wind-tunnel experiments measuring aerothermodynamic interactions. This paper describes measurements made by sampling the top of the test section during runs of the Langley 7-Inch High-Temperature Tunnel. The tests were conducted to determine the mixing of gas injected from a flat-plate model into a combustion-heated hypervelocity test stream and to monitor the CO2 produced in the combustion. The Mass Spectrometric (MS) measurements yield the mole fraction of N2 or He and CO2 reaching the sample inlets. The data obtained for several tunnel run conditions are related to the pressures measured in the tunnel test section and at the MS ionizer inlet. The apparent distributions of injected gas species and tunnel gas (CO2) are discussed relative to the sampling techniques. The measurements provided significant real-time data for the distribution of injected gases in the test section. The jet N2 diffused readily from the test stream, but the jet He was mostly entrained. The amounts of CO2 and Ar diffusing upward in the test section for several run conditions indicated the variability of the combustion-gas test-stream composition
The Born-Oppenheimer Approach to the Matter-Gravity System and Unitarity
The Born-Oppenheimer approach to the matter-gravity system is illustrated and
the unitary evolution for matter, in the absence of phenomena such as
tunnelling or other instabilities, verified. The Born-Oppenheimer approach to
the matter-gravity system is illustrated in a simple minisuperspace model and
the corrections to quantum field theory on a semiclassical background
exhibited. Within such a context the unitary evolution for matter, in the
absence of phenomena such as tunnelling or other instabilities, is verified and
compared with the results of other approaches. Lastly the simplifications
associated with the use of adiabatic invariants to obtain the solution of the
explicitly time dependent evolution equation for matter are evidenced.Comment: Latex, 12 pages. Revised version as accepted for publication by
Class. and Quant. Grav. Some points explained and misprints correcte
The Solar-System-Scale Disk Around AB Aurigae
The young star AB Aurigae is surrounded by a complex combination of gas-rich
and dust dominated structures. The inner disk which has not been studied
previously at sufficient resolution and imaging dynamic range seems to contain
very little gas inside a radius of least 130 astronomical units (AU) from the
star. Using adaptive-optics coronagraphy and polarimetry we have imaged the
dust in an annulus between 43 and 302 AU from the star, a region never seen
before. An azimuthal gap in an annulus of dust at a radius of 102 AU, along
with a clearing at closer radii inside this annulus, suggests the formation of
at least one small body at an orbital distance of about 100 AU. This structure
seems consistent with crude models of mean motion resonances, or accumulation
of material at two of the Lagrange points relative to the putative object and
the star. We also report a low significance detection of a point source in this
outer annulus of dust. This source may be an overdensity in the disk due to
dust accreting onto an unseen companion. An alternate interpretation suggests
that the object's mass is between 5 and 37 times the mass of Jupiter. The
results have implications for circumstellar disk dynamics and planet formation.Comment: 11 pages, 5 figures, accepted for publication in Astrophysical
Journal, V. 680, June 10, 200
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