1,135 research outputs found
Extension of a three-dimensional viscous wing flow analysis user's manual: VISTA 3-D code
Three-dimensional unsteady viscous effects can significantly influence the performance of fixed and rotary wing aircraft. These effects are important in both flows about helicopter rotors in forward flight and flows about three-dimensional (swept and tapered) supercritical wings. A computational procedure for calculating such flow field was developed. The procedure is based upon an alternating direction technique employing the Linearized Block Implicit method for solving three-dimensional viscous flow problems. In order to demonstrate the viability of this method, two- and three-dimensional problems are computed. These include the flow over a two-dimensional NACA 0012 airfoil under steady and oscillating conditions, and the steady, skewed, three-dimensional flow on a flat plate. Although actual three-dimensional flows over wings were not obtained, the ground work was laid for considering such flows. In this report a description of the computer code is given
Extension of a three-dimensional viscous wing flow analysis
Three-dimensional unsteady viscous effects can significantly influence the performance of fixed and rotary wing aircraft. These effects are important in both flows about helicopter rotors in forward flight and flows about 3-D (swept and tapered) supercritical wings. A computational procedure for calculating such flow field is developed, and therefore would be of great value in the design process as well as in understanding the corresponding flow phenomena. The procedure is based upon an alternating direction technique employing the Linearized Block Implicit method for solving 3-D viscous flow problems. In order to demonstrate the viability of this method, 2-D and 3-D problems are computed. These include the flow over a 2-D NACA 0012 airfoil under steady and oscillating conditions, and the steady, skewed, 3-D flow on a flat plate. Although actual 3-D flows over wings were not obtained, the ground work was laid for considering such flows. The description of the computational procedure and results are given
A generalized approach to model the spectra and radiation dose rate of solar particle events on the surface of Mars
For future human missions to Mars, it is important to study the surface
radiation environment during extreme and elevated conditions. In the long term,
it is mainly Galactic Cosmic Rays (GCRs) modulated by solar activity that
contributes to the radiation on the surface of Mars, but intense solar
energetic particle (SEP) events may induce acute health effects. Such events
may enhance the radiation level significantly and should be detected as
immediately as possible to prevent severe damage to humans and equipment.
However, the energetic particle environment on the Martian surface is
significantly different from that in deep space due to the influence of the
Martian atmosphere. Depending on the intensity and shape of the original solar
particle spectra as well as particle types, the surface spectra may induce
entirely different radiation effects. In order to give immediate and accurate
alerts while avoiding unnecessary ones, it is important to model and well
understand the atmospheric effect on the incoming SEPs including both protons
and helium ions. In this paper, we have developed a generalized approach to
quickly model the surface response of any given incoming proton/helium ion
spectra and have applied it to a set of historical large solar events thus
providing insights into the possible variety of surface radiation environments
that may be induced during SEP events. Based on the statistical study of more
than 30 significant solar events, we have obtained an empirical model for
estimating the surface dose rate directly from the intensities of a power-law
SEP spectra
Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
We present the first analysis of an optical to mid-infrared spectrum of the
T7.5 dwarf Gliese 570D with model atmospheres, synthetic spectra, and brown
dwarf evolution sequences. We obtain precise values for the basic parameters of
Gl 570D: Teff=800 - 820K, log g (cm/s^2)=5.09 - 5.23, and log L/Lsun= -5.525 to
-5.551. The Spitzer IRS spectrum shows prominent features of ammonia (NH3) that
can only be fitted by reducing the abundance of NH3 by about one order of
magnitude from the value obtained with chemical equilibrium models. We model
departures from chemical equilibrium in the atmosphere of Gl 570D by
considering the kinetics of nitrogen and carbon chemistry in the presence of
vertical mixing. The resulting model spectrum reproduces the data very well.Comment: Accepted for publication in the ApJ. 10 pages, including 3 figure
Symptomatic plate removal after treatment of facial fractures
Aims: To identify the rates and reasons for plate removal (PR) among patients treated for facial fractures. Materials and methods: A retrospective review of files of 238 patients. Results: Forty-eight patients (20.2%) had plates removed. The reason for removal was objective in 33.3% and subjective in 29.2%. The most common subjective reason was cold sensitivity, and the most common objective reason was wound dehiscence/infection. Women had PR for subjective reasons more often than men (p = 0.018). Removal was performed more often for subjective reasons after zygomatico-orbital fractures than after mandibular fractures (p = 0.002). Plates inserted in the mandible from an intraoral approach were removed more frequently than extraorally inserted mandibular plates, intraorally inserted maxillary plates, and extraorally inserted plates in other locations (p < 0.001). Orbital rim plates had a higher risk of being removed than maxillary or frontal bone plates (p = 0.02). Conclusions: Subjective discomfort is a notable reason for PR among Finnish patients, suggesting that the cold climate has an influence on the need for removal. Patients receiving mandibular osteosynthesis with miniplates from an intraoral approach are at risk of hardware removal because of wound dehiscence/infection and loose/broken hardware, reminding us that more rigid fixation devices should not be forgotten despite the widespread use of miniplates. (C) 2010 European Association for Cranio-Maxillo-Facial Surger
Philosophy of science for sustainability science
Sustainability science seeks to extend scientific investigation into domains characterized by a distinct problem-solving agenda, physical and social complexity, and complex moral and ethical landscapes. In this endeavor, it arguably pushes scientific investigation beyond its usual comfort zones, raising fundamental issues about how best to structure such investigation. Philosophers of science have long scrutinized the structure of science and scientific practices, and the conditions under which they operate effectively. We propose a critical engagement between sustainability scientists and philosophers of science with respect to how to engage in scientific activity in these complex domains. We identify specific issues philosophers of science raise concerning current sustainability science and the contributions philosophers can make to resolving them. In conclusion, we reflect on the steps philosophers of science could take to advance sustainability science.Peer reviewe
Chemical abundances of planet-host stars: Results for alpha and Fe-group elements
In this paper, we present a study of the abundances of Si, Ca, Sc, Ti, V, Cr,
Mn, Co, and Ni in a large set of stars known to harbor giant planets, as well
as in a comparison sample of stars not known to have any planet ary-mass
companions. We have checked for possible chemical differences between planet
hosts and field stars without known planets. Our results show that overall, and
for a given value of [Fe/H], the abundance trends for the planet hosts are
nearly indistinguishable from those of the field stars. In general, the trends
show no discontinuities,and the abundance distributions of stars with giant
planets are high [Fe/H] extensions to the curves traced by the field dwarfs
without planets. The only elements that might present slight differences
between the two groups of stars are V, Mn, and to a lesser extent Ti and Co. We
also use the available data to describe galactic chemical evolution trends for
the elements studied. When comparing the results with former studies, a few
differences emerge for the high [Fe/H] tail of the distribution, a region that
is sampled with unprecedented detail in our analysis.Comment: Accepted for publication in Astronomy & Astrophysic
Detailed Analysis of Nearby Bulgelike Dwarf Stars III. Alpha and Heavy-element abundances
The present sample of nearby bulgelike dwarf stars has kinematics and
metallicities characteristic of a probable inner disk or bulge origin. Ages
derived by using isochrones give 10-11 Gyr for these stars and metallicities
are in the range -0.80< [Fe/H]< +0.40. We calculate stellar parameters from
spectroscopic data, and chemical abundances of Mg, Si, Ca, Ti, La, Ba, Y, Zr
and Eu are derived by using spectrum synthesis.
We found that [alpha-elements/Fe] show different patterns depending on the
element. Si, Ca and Ti-to-iron ratios decline smoothly for increasing
metallicities, and follow essentially the disk pattern. O and Mg, products of
massive supernovae, and also the r-process element Eu, are overabundant
relative to disk stars, showing a steeper decline for metallicities [Fe/H] >
-0.3 dex. [s-elements/Fe] roughly track the solar values with no apparent trend
with metallicity for [Fe/H] < 0, showing subsolar values for the metal rich
stars. Both kinematical and chemical properties of the bulgelike stars indicate
a distinct identity of this population when compared to disk stars.Comment: 21 pages, 9 figures, to appear in Ap
Linear instability criteria for ideal fluid flows subject to two subclasses of perturbations
In this paper we examine the linear stability of equilibrium solutions to
incompressible Euler's equation in 2- and 3-dimensions. The space of
perturbations is split into two classes - those that preserve the topology of
vortex lines and those in the corresponding factor space. This classification
of perturbations arises naturally from the geometric structure of
hydrodynamics; our first class of perturbations is the tangent space to the
co-adjoint orbit. Instability criteria for equilibrium solutions are
established in the form of lower bounds for the essential spectral radius of
the linear evolution operator restricted to each class of perturbation.Comment: 29 page
Till death (or an intruder) do us part: intrasexual-competition in a monogamous Primate
Polygynous animals are often highly dimorphic, and show large sex-differences in the degree of intra-sexual competition and aggression, which is associated with biased operational sex ratios (OSR). For socially monogamous, sexually monomorphic species, this relationship is less clear. Among mammals, pair-living has sometimes been assumed to imply equal OSR and low frequency, low intensity intra-sexual competition; even when high rates of intra-sexual competition and selection, in both sexes, have been theoretically predicted and described for various taxa. Owl monkeys are one of a few socially monogamous primates. Using long-term demographic and morphological data from 18 groups, we show that male and female owl monkeys experience intense intra-sexual competition and aggression from solitary floaters. Pair-mates are regularly replaced by intruding floaters (27 female and 23 male replacements in 149 group-years), with negative effects on the reproductive success of both partners. Individuals with only one partner during their life produced 25% more offspring per decade of tenure than those with two or more partners. The termination of the pair-bond is initiated by the floater, and sometimes has fatal consequences for the expelled adult. The existence of floaters and the sporadic, but intense aggression between them and residents suggest that it can be misleading to assume an equal OSR in socially monogamous species based solely on group composition. Instead, we suggest that sexual selection models must assume not equal, but flexible, context-specific, OSR in monogamous species.Wenner-Gren Foundation, L.S.B. Leakey Foundation, the National Geographic Society, National
Science Foundation (BCS- 0621020), the University of Pennsylvania Research Foundation and the Zoological Society of San Diego, German
Science Foundation (HU 1746-2/1
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