62,422 research outputs found
Heat capacity mapping mission
There are no author-identified significant results in this report
Heat Capacity Mapping Mission (HCMM)
Tapes for day and night passes on May 16 and May 20, 1978 and a day pass on May 3, 1980 were processed. Results indicate that it is extremely difficult to locate a field of 9 pixel size and temperature data from the HCMM are consistently lower than temperatures measured with a scanner flown at low altitudes. The temperature differences between the satellite and aircraft data appear to be temperature dependent, being smaller at lower temperatures. Three data points are in the format (airc, HCMM) (12,9), (30,23), and (39,30). The linear equation for these three points is T sub HCMM = 0.778 T sub airc -0.33
Soil moisture inferences from thermal infrared measurements of vegetation temperatures
Thermal infrared measurements of wheat (Triticum durum) canopy temperatures were used in a crop water stress index to infer root zone soil moisture. Results indicated that one time plant temperature measurement cannot produce precise estimates of root zone soil moisture due to complicating plant factors. Plant temperature measurements do yield useful qualitative information concerning soil moisture and plant condition
The effect of starspots on the radii of low-mass pre-main sequence stars
A polytropic model is used to investigate the effects of dark photospheric
spots on the evolution and radii of magnetically active, low-mass (M<0.5Msun),
pre-main sequence (PMS) stars. Spots slow the contraction along Hayashi tracks
and inflate the radii of PMS stars by a factor of (1-beta)^{-N} compared to
unspotted stars of the same luminosity, where beta is the equivalent covering
fraction of dark starspots and N \simeq 0.45+/-0.05. This is a much stronger
inflation than predicted by the models of Spruit & Weiss (1986) for main
sequence stars with the same beta, where N \sim 0.2 to 0.3. These models have
been compared to radii determined for very magnetically active K- and M-dwarfs
in the young Pleiades and NGC 2516 clusters, and the radii of tidally-locked,
low-mass eclipsing binary components. The binary components and ZAMS K-dwarfs
have radii inflated by \sim 10 per cent compared to an empirical
radius-luminosity relation that is defined by magnetically inactive field
dwarfs with interferometrically measured radii; low-mass M-type PMS stars, that
are still on their Hayashi tracks, are inflated by up to \sim 40 per cent. If
this were attributable to starspots alone, we estimate that an effective spot
coverage of 0.35 < beta < 0.51 is required. Alternatively, global inhibition of
convective flux transport by dynamo-generated fields may play a role. However,
we find greater consistency with the starspot models when comparing the loci of
active young stars and inactive field stars in colour-magnitude diagrams,
particularly for the highly inflated PMS stars, where the large, uniform
temperature reduction required in globally inhibited convection models would
cause the stars to be much redder than observed.Comment: MNRAS in press, 13 page
Swept-wavelength mid-infrared fiber laser for real-time ammonia gas sensing
The mid-infrared (mid-IR) spectral region holds great promise for new
laser-based sensing technologies, based on measuring strong mid-IR molecular
absorption features. Practical applications have been limited to date, however,
by current low-brightness broadband mid-IR light sources and slow
acquisition-time detection systems. Here, we report a new approach by
developing a swept-wavelength mid-infrared fiber laser, exploiting the broad
emission of dysprosium and using an acousto-optic tunable filter to achieve
electronically controlled swept-wavelength operation from 2.89 to 3.25 {\mu}m
(3070-3460 cm^-1). Ammonia (NH3) absorption spectroscopy is demonstrated using
this swept source with a simple room-temperature single-pixel detector, with
0.3 nm resolution and 40 ms acquisition time. This creates new opportunities
for real-time high-sensitivity remote sensing using simple, compact mid-IR
fiber-based technologies.Comment: Invited article for APL Photonic
Mode-locked dysprosium fiber laser: picosecond pulse generation from 2.97 to 3.30 {\mu}m
Mode-locked fiber laser technology to date has been limited to sub-3 {\mu}m
wavelengths, despite significant application-driven demand for compact
picosecond and femtosecond pulse sources at longer wavelengths. Erbium- and
holmium-doped fluoride fiber lasers incorporating a saturable absorber are
emerging as promising pulse sources for 2.7--2.9 {\mu}m, yet it remains a major
challenge to extend this coverage. Here, we propose a new approach using
dysprosium-doped fiber with frequency shifted feedback (FSF). Using a simple
linear cavity with an acousto-optic tunable filter, we generate 33 ps pulses
with up to 2.7 nJ energy and 330 nm tunability from 2.97 to 3.30 {\mu}m
(3000--3400 cm^-1)---the first mode-locked fiber laser to cover this spectral
region and the most broadly tunable pulsed fiber laser to date. Numerical
simulations show excellent agreement with experiments and also offer new
insights into the underlying dynamics of FSF pulse generation. This highlights
the remarkable potential of both dysprosium as a gain material and FSF for
versatile pulse generation, opening new opportunities for mid-IR laser
development and practical applications outside the laboratory.Comment: Accepted for APL Photonics, 22nd August 201
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