1,433 research outputs found
Turbulent mixing film cooling correlation
Film cooling effectiveness correlation predicts air flow requirement for cooling gas turbine combustors. Turbulent mixing model accounts for mixing rate between cooling film and hot gas stream. Resulting equation correlates data within plus or minus 20 percent
Examining Different Patterns of Children’s Early Dual Language Development and Nonverbal Executive Functioning
Children from non-English-speaking homes often lag behind their English speaking peers academically. However, people who speak two languages often have better executive functioning skills than people who speak only one language. Executive functions are neurologically-based skills related to managing oneself to achieve a goal. The relation between bilingualism and executive function may be due to how two languages are processed in the brain. However, it is unclear if more balanced bilinguals experience larger gains in executive function than people who are less balanced.
Children from low-income homes are at a disadvantage as compared to children from homes with higher incomes. A quarter of children in the Head Start program, which serves children from low-income homes, come from homes that speak a language other than English which puts them at a double disadvantage. Longitudinal data from 3-year-old children enrolled in Head Start who were from Spanish-speaking households were used to investigate whether there were different patterns of dual language development and if those patterns related differently to executive function.
Results revealed three groups of dual language development. Groups were compared in terms of children’s performance on a nonverbal executive functioning task. Results showed that children in the group that had the most similar proficiency between English and Spanish had the highest average executive functioning scores, even after controlling for child age and gender. This indicates balanced bilingualism may enjoy additional benefits to executive functioning development as compared to individuals with relative imbalance between languages
Scattered light images of spiral arms in marginally gravitationally unstable discs with an embedded planet
Scattered light images of transition discs in the near-infrared often show
non-axisymmetric structures in the form of wide-open spiral arms in addition to
their characteristic low-opacity inner gap region. We study self-gravitating
discs and investigate the influence of gravitational instability on the shape
and contrast of spiral arms induced by planet-disc interactions.
Two-dimensional non-isothermal hydrodynamical simulations including viscous
heating and a cooling prescription are combined with three-dimensional dust
continuum radiative transfer models for direct comparison to observations. We
find that the resulting contrast between the spirals and the surrounding disc
in scattered light is by far higher for pressure scale height variations, i.e.
thermal perturbations, than for pure surface density variations. Self-gravity
effects suppress any vortex modes and tend to reduce the opening angle of
planet-induced spirals, making them more tightly wound. If the disc is only
marginally gravitationally stable with a Toomre parameter around unity, an
embedded massive planet (planet-to-star mass ratio of ) can trigger
gravitational instability in the outer disc. The spirals created by this
instability and the density waves launched by the planet can overlap resulting
in large-scale, more open spiral arms in the outer disc. The contrast of these
spirals is well above the detection limit of current telescopes.Comment: Accepted for publication in MNRAS; 13 pages, 8 figure
High-Temperature Superconductive Cabling Investigated for Space Solar Power Satellites
NASA has been directed by Congress to take a fresh look at the Space Solar Power (SSP) concept that was studied by the Department of Energy and NASA about 20 years ago. To summarize, the concept involves (1) collecting solar energy and converting it to electrical energy via photovoltaic arrays on satellites in Earth orbit, (2) conducting the electricity to the microwave transmitting portion of the satellite, and (3) transmitting the power via microwave transmitters (or possibly via lasers) to ground power station antennas located on the surface of the Earth. One Sun Tower SSP satellite concept is illustrated here. This figure shows many photovoltaic arrays attached to a "backbone" that conducts electricity down to a wireless transmitter, which is pointed toward the Earth. Other variations on this concept use multiple backbones to reduce the overall length of the satellite structure. In addition, non-Sun-Tower concepts are being considered. The objective of the work reported here was to determine the benefits to the SSP concept of using high-temperature superconductors (HTS) to conduct the electricity from the photovoltaic arrays to the wireless power transmitters. Possible benefits are, for example, reduced mass, improved efficiency, and improved reliability. Dr. James Powell of Plus Ultra Technologies, Inc., of Stony Brook, New York, is conducting the study, and it is being managed by the NASA Glenn Research Center at Lewis Field via a task-order contract through Scientific Applications International Corp. (SAIC)
Random elastic networks : strong disorder renormalization approach
For arbitrary networks of random masses connected by random springs, we
define a general strong disorder real-space renormalization (RG) approach that
generalizes the procedures introduced previously by Hastings [Phys. Rev. Lett.
90, 148702 (2003)] and by Amir, Oreg and Imry [Phys. Rev. Lett. 105, 070601
(2010)] respectively. The principle is to eliminate iteratively the elementary
oscillating mode of highest frequency associated with either a mass or a spring
constant. To explain the accuracy of the strong disorder RG rules, we compare
with the Aoki RG rules that are exact at fixed frequency.Comment: 8 pages, v2=final versio
High-Temperature Optical Constants of Dust Analogues for the Solar Nebula
The dust in protoplanetary disks is influenced by a lot of different
processes. Besides others, heating processes are the most important ones: they
change not only the physical and chemical properties of dust particles, but
also their emission spectra. In order to compare observed infrared spectra of
young stellar systems with laboratory data of hot (up to 700{\deg}C)
circumstellar dust analogues, we investigate materials, which are important
constituents of dust in protoplanetary disks. We calculated the optical
constants by means of a simple Lorentzian oscillator fit and apply them to
simulations of small-particle emission spectra in order to compare our results
with real astronomical spectra of AGB-stars and protoplanetary disks.Comment: 4 pages, 3 figures, Contribution for the ECLA proceedings (European
Conference on Laboratory Astrophysics
Measurement of the hyperfine structure of antihydrogen in a beam
A measurement of the hyperfine structure of antihydrogen promises one of the
best tests of CPT symmetry. We describe an experiment planned at the Antiproton
Decelerator of CERN to measure this quantity in a beam of slow antihydrogen
atoms.Comment: 5th International Symposium on Symmetries in Subatomic Physics
(SSP2012), Groningen (The Netherlands), June 18 to 22, 201
Particle interactions and lattice dynamics: Scenarios for efficient bidirectional stochastic transport?
Intracellular transport processes driven by molecular motors can be described
by stochastic lattice models of self-driven particles. Here we focus on
bidirectional transport models excluding the exchange of particles on the same
track. We explore the possibility to have efficient transport in these systems.
One possibility would be to have appropriate interactions between the various
motors' species, so as to form lanes. However, we show that the lane formation
mechanism based on modified attachment/detachment rates as it was proposed
previously is not necessarily connected to an efficient transport state and is
suppressed when the diffusivity of unbound particles is finite. We propose
another interaction mechanism based on obstacle avoidance that allows to have
lane formation for limited diffusion. Besides, we had shown in a separate paper
that the dynamics of the lattice itself could be a key ingredient for the
efficiency of bidirectional transport. Here we show that lattice dynamics and
interactions can both contribute in a cooperative way to the efficiency of
transport. In particular, lattice dynamics can decrease the interaction
threshold beyond which lanes form. Lattice dynamics may also enhance the
transport capacity of the system even when lane formation is suppressed.Comment: 25 pages, 17 figures, 2 table
Sulphur monoxide exposes a potential molecular disk wind from the planet-hosting disk around HD100546
Sulphur-bearing volatiles are observed to be significantly depleted in interstellar and circumstellar regions. This missing sulphur is postulated to be mostly locked up in refractory form. With ALMA we have detected sulphur monoxide (SO), a known shock tracer, in the HD 100546 protoplanetary disk. Two rotational transitions: J=7₇-6₆ (301.286 GHz) and J=7₈-6₇ (304.078 GHz) are detected in their respective integrated intensity maps. The stacking of these transitions results in a clear 5σ detection in the stacked line profile. The emission is compact but is spectrally resolved and the line profile has two components. One component peaks at the source velocity and the other is blue-shifted by 5 km s‾¹. The kinematics and spatial distribution of the SO emission are not consistent with that expected from a purely Keplerian disk. We detect additional blue-shifted emission that we attribute to a disk wind. The disk component was simulated using LIME and a physical disk structure. The disk emission is asymmetric and best fit by a wedge of emission in the north east region of the disk coincident with a `hot-spot' observed in the CO J=3-2 line. The favoured hypothesis is that a possible inner disk warp (seen in CO emission) directly exposes the north-east side of the disk to heating by the central star, creating locally the conditions to launch a disk wind. Chemical models of a disk wind will help to elucidate why the wind is particularly highlighted in SO emission and whether a refractory source of sulphur is needed. An alternative explanation is that the SO is tracing an accretion shock from a circumplanetary disk associated with the proposed protoplanet embedded in the disk at 50 au. We also report a non-detection of SO in the protoplanetary disk around HD 97048
Dust evolution in protoplanetary disks around Herbig Ae/Be stars - The Spitzer view
In this paper we present mid-infrared spectra of a comprehensive set of
Herbig Ae/Be stars observed with the Spitzer Space Telescope. The
signal-to-noise ratio of these spectra is very high, ranging between about a
hundred and several hundreds. During the analysis of these data we tested the
validity of standard protoplanetary dust models and studied grain growth and
crystal formation. On the basis of the analyzed spectra, the major constituents
of protoplanetary dust around Herbig Ae/Be stars are amorphous silicates with
olivine and pyroxene stoichiometry, crystalline forsterite and enstatite and
silica. No other solid state features, indicating other abundant dust species,
are present in the Spitzer spectra. Deviations of the synthetic spectra from
the observations are most likely related to grain shape effects and
uncertainties in the iron content of the dust grains. Our analysis revealed
that larger grains are more abundant in the disk atmosphere of flatter disks
than in that of flared disks, indicating that grain growth and sedimentation
decrease the disk flaring. We did not find, however, correlations between the
value of crystallinity and any of the investigated system parameters. Our
analysis shows that enstatite is more concentrated toward the warm inner disk
than forsterite, in contrast to predictions of equilibrium condensation models.
None of the three crystal formation mechanisms proposed so far can alone
explain all our findings. It is very likely that all three play at least some
role in the formation of crystalline silicates.Comment: 56 pages, 21 figures, accepted for publication in Ap
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