116,843 research outputs found
The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs
Using SofI on the 3.5m New Technology Telescope, we have conducted an
extensive near-infrared monitoring survey of an unbiased sample of 69 brown
dwarfs spanning the L0 and T8 spectral range, with at least one example of each
spectral type. Each target was observed for a 2-4 hour period in the Js-band,
and the median photometric precision of the data is ~0.7%. A total of 14 brown
dwarfs were identified as variables with min-to-max amplitudes ranging from
1.7% to 10.8% over the observed duration. All variables satisfy a statistical
significance threshold with a p-value <5% based on comparison with the median
reference star light curve. Approximately half of the variables show sinusoidal
amplitude variations similar to 2M2139, and the remainder shows short timescale
evolving light curves similar to SIMP0136. The L/T transition has been
suggested to be a region of a higher degree of variability if patchy clouds are
present and this survey was designed to test the patchy cloud model with
photometric monitoring of both the L/T transition and non-transition brown
dwarfs. Considering the targets identified as variable with the same
statistical threshold, the measured variability frequency of 13^{+10}_{-4}% for
the L7 -- T4 transition region is indistinguishable from that of the earlier
spectral types (32^{+11}_{-8}%), the later spectral types (13^{+10}_{-4}%), or
the combination of all non-transition region brown dwarfs (21^{+7}_{-5}%). The
variables are not concentrated at the transition, in a specific colour, or with
binaries. We note that of the systems previously monitored for variability only
~60% maintained the state of variability (variable or constant), with the
remaining switching states. The 14 variables include nine newly identified
variables that will provide important systems for follow-up multi-wavelength
monitoring to further investigate brown dwarf atmosphere physics.Comment: Accepted for publication in the Astronomy & Astrophysics. 15 pages,
13 figure
Fabrication process of a high temperature polymer matrix engine duct
The process that was used in the molding of an advanced composite outer by-pass duct planned for the F404 engine is discussed. This duct was developed as a potential replacement for the existing titanium duct in order to reduce both the weight and cost of the duct. The composite duct is now going into the manufacturing technology portion of the program. The duct is fabricated using graphite cloth impregnated with the PMR-15 matrix system
Biological Individuals
The impressive variation amongst biological individuals generates many complexities in addressing the simple-sounding question what is a biological individual? A distinction between evolutionary and physiological individuals is useful in thinking about biological individuals, as is attention to the kinds of groups, such as superorganisms and species, that have sometimes been thought of as biological individuals. More fully understanding the conceptual space that biological individuals occupy also involves considering a range of other concepts, such as life, reproduction, and agency. There has been a focus in some recent discussions by both philosophers and biologists on how evolutionary individuals are created and regulated, as well as continuing work on the evolution of individuality
Industrial districts as organizational environments: resources, networks and structures
The paper combines economic and sociological perspectives on organizations in order to gain a better understanding of the forces shaping the structures of industrial districts (IDs) and the organizations of which they are constituted. To effect the combination , the resource based view (RBV) and resource dependency theory are combined to explain the evolution of different industry structures. The paper thus extends work by Toms and Filatotchev by spatializing consideration of resource distribution and resource dependence. The paper has important implications for conventional interpretations in the fields of business and organizational history and for the main areas of theory hitherto considered separately, particularly the Chandlerian model of corporate hierarchy as contrasted with the alternative of clusters of small firms coordinated by networks
Features controlling the early stages of creep deformation of Waspaloy
A model has been presented for describing primary and second stage creep. General equations were derived for the amount and time of primary creep. It was shown how the model can be used to extrapolate creep data. Applicability of the model was demonstrated for Waspaloy with gamma prime particle sizes from 75 - 1000 A creep tested in the temperature range 1000 - 1400 F (538 - 760 C). Equations were developed showing the dependence of creep parameters on dislocation mechanism, gamma prime volume fraction and size
Survey of projected growth and problems facing air transportation, 1975 - 1985
Results are presented of a survey conducted to determine the current opinion of people working in air transportation demand forecasting on the future of air transportation over the next ten years. In particular, the survey included questions on future demand growth, load factor, fuel prices, introduction date for the next new aircraft, the priorities of problems facing air transportation, and the probability of a substantial change in air transportation regulation. The survey participants included: airlines, manufacturers, universities, government agencies, and other organizations (financial institutions, private research companies, etc.). The results are shown for the average responses within the organization represented as well as the overall averages
The effect of stirring on the heterogeneous nucleation of water and of clathrates of tetrahydrofuran/water mixtures
The statistics of liquid-to-crystal nucleation are measured for both water
and for clathrate-forming mixtures of tetrahydrofuran (THF) and water using an
automatic lag time apparatus (ALTA). We measure the nucleation temperature
using this apparatus in which a single sample is repeatedly cooled, nucleated
and thawed. The effect of stirring on nucleation has been evaluated numerically
and is discussed. We find that stirring of the solution makes no difference to
the nucleation temperature of a given solution in a given tube.Comment: 4 pages, 4 figure
Measurements of the free-bound and free-free continua of nitrogen, oxygen and air
Photometric measurement of radiation in high temperature ai
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