3,192 research outputs found
An analysis of pilot error-related aircraft accidents
A multidisciplinary team approach to pilot error-related U.S. air carrier jet aircraft accident investigation records successfully reclaimed hidden human error information not shown in statistical studies. New analytic techniques were developed and applied to the data to discover and identify multiple elements of commonality and shared characteristics within this group of accidents. Three techniques of analysis were used: Critical element analysis, which demonstrated the importance of a subjective qualitative approach to raw accident data and surfaced information heretofore unavailable. Cluster analysis, which was an exploratory research tool that will lead to increased understanding and improved organization of facts, the discovery of new meaning in large data sets, and the generation of explanatory hypotheses. Pattern recognition, by which accidents can be categorized by pattern conformity after critical element identification by cluster analysis
Advanced engine study program
A design and analysis study was conducted to provide advanced engine descriptions and parametric data for space transfer vehicles. The study was based on an advanced oxygen/hydrogen engine in the 7,500 to 50,000 lbf thrust range. Emphasis was placed on defining requirements for high-performance engines capable of achieving reliable and versatile operation in a space environment. Four variations on the expander cycle were compared, and the advantages and disadvantages of each were assessed. Parametric weight, envelope, and performance data were generated over a range of 7,500 to 50,000 lb thrust and a wide range of chamber pressure and nozzle expansion ratio
Targeted disruption of metallothionein I and II genes increases sensitivity to cadmium.
Internal Extinction in Spiral Galaxies in the Near Infrared
In order to study the effects of internal extinction in spiral galaxies we
search for correlations of near infrared (NIR) photometric parameters with
inclination. We use data from the 2 Micron All-Sky Survey (2MASS) Extended
Source Catalog (XSC) on 15,224 spiral galaxies for which we also have
redshifts. For 3035 of the galaxies, I-band photometry is available which is
included in the analysis. From the simple dependence of reddening on
inclination we derive a lower limit to the difference in magnitude between the
face-on and edge-on aspect of 0.9, 0.3 and 0.1 magnitudes in I (0.81 um), J
(1.25 um) and H (1.65 um) bands. We find that the faintest isophotal radius
reported in the XSC (at the 21st mag/arc sq level) is closer to the centers of
the galaxies than other common isophotal measures (e.g. the 23.5 mag/arc sq
radius in I-band), and argue that it should not be assumed to represent an
outer isophote at which galaxies are transparent at all viewing angles. A
simple linear extinction law (i.e. Delta M = gamma log(a/b)) is not adequate
for the full range of disk inclinations and we adopt both a bi-linear and a
quadratic law. A simple photometric model is used to explain the observed
behavior. Internal extinction depends on galaxy luminosity. We show that for
galaxies with a K total magnitude dimmer than -20, -20.7 and -20.9 the data
indicates zero extinction in J, H and K respectively, while disk opacity
increases monotonically with increasing disk luminosity.Comment: Accepted for publication in AJ (July 2003). 28 pages, 13 figures.
Revised version corrects some typos including an error in the reported
luminosity dependence of the extinction correctio
Galaxy Zoo: star formation versus spiral arm number
Spiral arms are common features in low-redshift disc galaxies, and are prominent sites of star formation and dust obscuration. However, spiral structure can take many forms: from galaxies displaying two strong ‘grand design’ arms to those with many ‘flocculent’ arms. We investigate how these different arm types are related to a galaxy's star formation and gas properties by making use of visual spiral arm number measurements from Galaxy Zoo 2. We combine ultraviolet and mid-infrared (MIR) photometry from GALEX and WISE to measure the rates and relative fractions of obscured and unobscured star formation in a sample of low-redshift SDSS spirals. Total star formation rate has little dependence on spiral arm multiplicity, but two-armed spirals convert their gas to stars more efficiently. We find significant differences in the fraction of obscured star formation: an additional ∼10 per cent of star formation in two-armed galaxies is identified via MIR dust emission, compared to that in many-armed galaxies. The latter are also significantly offset below the IRX–β relation for low-redshift star-forming galaxies. We present several explanations for these differences versus arm number: variations in the spatial distribution, sizes or clearing time-scales of star-forming regions (i.e. molecular clouds), or contrasting recent star formation histories
Galaxy And Mass Assembly: Galaxy Zoo spiral arms and star formation rates
Understanding the effect spiral structure has on star formation properties of galaxies is important to complete our picture of spiral structure evolution. Previous studies have investigated connections between spiral arm properties and star formation, but the effect that the number of spiral arms has on this process is unclear. Here, we use the Galaxy And Mass Assembly (GAMA) survey paired with the citizen science visual classifications from the Galaxy Zoo project to explore galaxies’ spiral arm number and how it connects to the star formation process. We use the votes from the GAMA-Kilo Degree Survey Galaxy Zoo classification to investigate the link between spiral arm number and stellar mass, star formation rate, and specific star formation rate (sSFR). We find that galaxies with fewer spiral arms have lower stellar masses and higher sSFRs, while those with more spiral arms tend towards higher stellar masses and lower sSFRs, and conclude that galaxies are less efficient at forming stars if they have more spiral arms. We note how previous studies’ findings may indicate a cause for this connection in spiral arm strength or opacity
Microscopic Derivation of Non-Markovian Thermalization of a Brownian Particle
In this paper, the first microscopic approach to the Brownian motion is
developed in the case where the mass density of the suspending bath is of the
same order of magnitude as that of the Brownian (B) particle. Starting from an
extended Boltzmann equation, which describes correctly the interaction with the
fluid, we derive systematicaly via the multiple time-scale analysis a reduced
equation controlling the thermalization of the B particle, i.e. the relaxation
towards the Maxwell distribution in velocity space. In contradistinction to the
Fokker-Planck equation, the derived new evolution equation is non-local both in
time and in velocity space, owing to correlated recollision events between the
fluid and particle B. In the long-time limit, it describes a non-markovian
generalized Ornstein-Uhlenbeck process. However, in spite of this complex
dynamical behaviour, the Stokes-Einstein law relating the friction and
diffusion coefficients is shown to remain valid. A microscopic expression for
the friction coefficient is derived, which acquires the form of the Stokes law
in the limit where the mean-free in the gas is small compared to the radius of
particle B.Comment: 28 pages, no figure, submitted to Journal of Statistical Physic
The ALFA Zone of Avoidance Survey: Results from the Precursor Observations
The Arecibo L-band Feed Array Zone of Avoidance Survey (ALFA ZOA) will map
1350-1800 square degrees at low Galactic latitude, providing HI spectra for
galaxies in regions of the sky where our knowledge of local large scale
structure remains incomplete, owing to obscuration from dust and high stellar
confusion near the Galactic plane. Because of these effects, a substantial
fraction of the galaxies detected in the survey will have no optical or
infrared counterparts. However, near infrared follow up observations of ALFA
ZOA sources found in regions of lowest obscuration could reveal whether some of
these sources could be objects in which little or no star formation has taken
place ("dark galaxies"). We present here the results of ALFA ZOA precursor
observations on two patches of sky totaling 140 square degrees (near l=40
degrees, and l=192 degrees). We have measured HI parameters for detections from
these observations, and cross-correlated with the NASA/IPAC Extragalactic
Database (NED). A significant fraction of the objects have never been detected
at any wavelength. For those galaxies that have been previously detected, a
significant fraction have no previously known redshift, and no previous HI
detection.Comment: To appear in Proceedings of IAU Symp #244, "Dark Galaxies and Lost
Baryons", June 2007, 2 pages, including 1 figur
Learning deficit in cognitively normal apoe ε4 carriers with low β-amyloid
Introduction: In cognitively normal (CN) adults, increased rates of amyloid beta (Aβ) accumulation can be detected in low Aβ (Aβ–) apolipoprotein E (APOE) ε4 carriers. We aimed to determine the effect of ε4 on the ability to benefit from experience (ie, learn) in Aβ–CNs. Methods: Aβ– CNs(n= 333) underwent episodic memory assessments every 18 months for 108 months. A subset (n = 48) completed the Online Repeatable Cognitive Assessment-Language Learning Test (ORCA-LLT) over 6 days. Results: Aβ– ε4 carriers showed significantly lower rates of improvement on episodic memory over 108 months compared to non-carriers (d = 0.3). Rates of learning on the ORCA-LLT were significantly slower in Aβ– ε4 carriers compared to non-carriers (d = 1.2). Discussion: In Aβ– CNs,ε4 is associated with a reduced ability to benefit from experience. This manifested as reduced practice effects (small to moderate in magnitude) over 108 months on the episodic memory composite, and a learning deficit (large in magnitude) over 6 days on the ORCA-LLT. Alzheimer’s disease (AD)–related cognitive abnormalities can manifest before preclinical AD thresholds
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