2,098 research outputs found
Development of 2 underseat energy absorbers for application to crashworthy passenger seats for general aviation aircraft
This report presents the methodology and results of a program conducted to develop two underseat energy absorber (E/A) concepts for application to nonadjustable crashworthy passenger seats for general aviation aircraft. One concept utilizes an inflated air bag, and the other, a convoluted sheet metal bellows. Prototypes of both were designed, built, and tested. Both concepts demonstrated the necessary features of an energy absorber (load-limiter); however, the air bag concept is particularly encouraging because of its light weight. Several seat frame concepts also were investigated as a means of resisting longitudinal and lateral loads and of guiding the primary vertical stroke of the underseat energy absorber. Further development of a seat system design using the underseat energy absorbers is recommended because they provide greatly enhanced crash survivability as compared with existing general aviation aircraft seats
The GEMPAK Barnes objective analysis scheme
GEMPAK, an interactive computer software system developed for the purpose of assimilating, analyzing, and displaying various conventional and satellite meteorological data types is discussed. The objective map analysis scheme possesses certain characteristics that allowed it to be adapted to meet the analysis needs GEMPAK. Those characteristics and the specific adaptation of the scheme to GEMPAK are described. A step-by-step guide for using the GEMPAK Barnes scheme on an interactive computer (in real time) to analyze various types of meteorological datasets is also presented
Multi-scale analysis of compressible viscous and rotating fluids
We study a singular limit for the compressible Navier-Stokes system when the
Mach and Rossby numbers are proportional to certain powers of a small parameter
\ep. If the Rossby number dominates the Mach number, the limit problem is
represented by the 2-D incompressible Navier-Stokes system describing the
horizontal motion of vertical averages of the velocity field. If they are of
the same order then the limit problem turns out to be a linear, 2-D equation
with a unique radially symmetric solution. The effect of the centrifugal force
is taken into account
The origin of the E+ transition in GaAsN alloys
Optical properties of GaAsN system with nitrogen concentrations in the range
of 0.9-3.7% are studied by full-potential LAPW method in a supercell approach.
The E+ transition is identified by calculating the imaginary part of the
dielectric function. The evolution of the energy of this transition with
nitrogen concentration is studied and the origin of this transition is
identified by analyzing the contributions to the dielectric function from
different band combinations. The L_1c-derived states are shown to play an
important role in the formation of the E+ transition, which was also suggested
by recent experiments. At the same time the nitrogen-induced modification of
the first conduction band of the host compound are also found to contribute
significantly to the E+ transition. Further, the study of several model
supercells demonstrated the significant influence of the nitrogen potential on
the optical properties of the GaAsN system.Comment: 5 pages, 3 figure
Field spectrometer to measure percent ground coverage and leaf area index of agriculture crops
Measurement of percent ground cover (PGC) and leaf area index (LAI) are required for crop modelling, yield estimation and for ground truth data in remote sensing studies.
An instrument which traverses on a track above a crop and continuously measures the ratio of incident and reflected radiation at various wavelengths was developed and tested.
Spectral irradiance and reflectance measurements were made at four wavelengths (647.8, 675.5, 739.9, 790.4 nm) at eight stages of growth of wheat and barley for three crop densities. Data provided information on the relations between spectral properties at selected wavelength and leaf area expansion at different growth stages. The spectral data were highly correlated with leaf area index measurements
Exploring X-ray Binary Populations in Compact Group Galaxies with
We obtain total galaxy X-ray luminosities, , originating from
individually detected point sources in a sample of 47 galaxies in 15 compact
groups of galaxies (CGs). For the great majority of our galaxies, we find that
the detected point sources most likely are local to their associated galaxy,
and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic
nuclei (AGNs). For spiral and irregular galaxies, we find that, after
accounting for AGNs and nuclear sources, most CG galaxies are either within the
scatter of the Mineo et al. (2012) - star formation rate
(SFR) correlation or have higher than predicted by this correlation for
their SFR. We discuss how these "excesses" may be due to low metallicities and
high interaction levels. For elliptical and S0 galaxies, after accounting for
AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et
al. (2011) - stellar mass correlation for low-mass XRBs, with larger
scatter, likely due to residual effects such as AGN activity or hot gas.
Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB
luminosity functions to estimate the probability that stochastic effects can
lead to such extreme values. We find that, although stochastic effects do
not in general appear to be important, for some galaxies there is a significant
probability that high values can be observed due to strong XRB
variability.Comment: Accepted by Ap
Variations of crop canopy spectral reflectance measurements under changing sky conditions
The possibility of using reflectance data collected under both cloudy and sunny conditions is studied. Extrenle values of red and far-red reflectances measured directly over bare soil and crop canopies during intermittently cloudy conditions can differ by more than 100 percent and 60 percent, respectively. Eliminating the irradiance variations by using only data collected under sunny conditions reduced such variation to within 1 percent for bare soil and to within 8 percent and 20 percent for crop canopy red and far-red reflectances, respectively. In general, the reflectances measured under cloudy conditions with relatively constant irradiance values are constant and approximately 10 percent larger than the ones measured at similar sun angles during sunny conditions. This result is independent of the species and the spectral regions under study
Existence of global strong solutions to a beam-fluid interaction system
We study an unsteady non linear fluid-structure interaction problem which is
a simplified model to describe blood flow through viscoleastic arteries. We
consider a Newtonian incompressible two-dimensional flow described by the
Navier-Stokes equations set in an unknown domain depending on the displacement
of a structure, which itself satisfies a linear viscoelastic beam equation. The
fluid and the structure are fully coupled via interface conditions prescribing
the continuity of the velocities at the fluid-structure interface and the
action-reaction principle. We prove that strong solutions to this problem are
global-in-time. We obtain in particular that contact between the viscoleastic
wall and the bottom of the fluid cavity does not occur in finite time. To our
knowledge, this is the first occurrence of a no-contact result, but also of
existence of strong solutions globally in time, in the frame of interactions
between a viscous fluid and a deformable structure
Stellar Populations in Compact Galaxy Groups: a Multi-Wavelength Study of HCGs 16, 22, and 42, their Star Clusters and Dwarf Galaxies
We present a multi-wavelength analysis of three compact galaxy groups, HCGs
16, 22, and 42, which describe a sequence in terms of gas richness, from space-
(Swift, HST, Spitzer) and ground-based (LCO, CTIO) imaging and spectroscopy. We
study various signs of past interactions including a faint, dusty tidal feature
about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the
possible detection of a tidal feature at the end of its phase of optical
observability. Our HST images also resolve what were thought to be double
nuclei in HCG 16C and D into multiple, distinct sources, likely to be star
clusters. Beyond our phenomenological treatment, we focus primarily on
contrasting the stellar populations across these three groups. The star
clusters show a remarkable intermediate-age population in HCG 22, and identify
the time at which star formation was quenched in HCG 42. We also search for
dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27
'associates' (possible members) radically changes group dynamical masses, which
in turn may affect previous evolutionary classifications. The extended
membership paints a picture of relative isolation in HCGs 16 and 22, but shows
HCG 42 to be part of a larger structure, following a dichotomy expected from
recent studies. We conclude that (a) star cluster populations provide an
excellent metric of evolutionary state, as they can age-date the past epochs of
star formation; and (b) the extended dwarf galaxy population must be considered
in assessing the dynamical state of a compact group.Comment: 29 pages, 13 figures. Accepted for publication in The Astrophysical
Journa
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