25,686 research outputs found
The importance of planetary rotation period for ocean heat transport
The climate, and hence potential habitability, of a planet crucially depends on how its atmospheric and oceanic circulation transports heat from warmer to cooler regions. However, previous studies of planetary climate have concentrated on modelling the dynamics of their atmospheres whilst dramatically simplifying the treatment of the oceans, which neglects or misrepresents the effect of the ocean in the total heat transport. Even the majority of studies with a dynamic ocean have used a simple so-called aquaplanet having no continental barriers, which is a configuration which dramatically changes the oceanic dynamics. Here the significance of the response of poleward ocean heat transport to planetary rotation period is shown with a simple meridional barrier â the simplest representation of any continental configuration. The poleward ocean heat transport increases significantly as the planetary rotation period is increased. The peak heat transport more than doubles when the rotation period is increased by a factor of ten. There are also significant changes to ocean temperature at depth, with implications for the carbon cycle. There is strong agreement between the model results and a scale analysis of the governing equations. This result highlights the importance of both planetary rotation period and the ocean circulation when considering planetary habitability
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Trace gas transport in the subsurface of Mars
The ExoMars Trace Gas Orbiter (TGO) will have the capability of detecting and characterizing a broad suite of trace gases in the atmosphere of Mars. Interpreting the results of this mission will require an understanding of how these trace gases are transported from their sources, which may be deep underground, to the atmosphere. Here we present results of modeling designed to measure the timescales of release from putative subsurface methane sources. These transport timescales are far longer than mixing times in the atmosphere and could be up to 10 million years
GaAs-based Self-Aligned Stripe Superluminescent Diodes Processed Normal to the Cleaved Facet
We demonstrate GaAs-based superluminescent diodes (SLDs) incorporating a window-like back facet in a self-aligned stripe. SLDs are realised with low spectral modulation depth (SMD) at high power spectral density, without application of anti-reflection coatings. Such application of a window-like facet reduces effective facet reflectivity in a broadband manner. We demonstrate 30mW output power in a narrow bandwidth with only 5% SMD, outline the design criteria for high power and low SMD, and describe the deviation from a linear dependence of SMD on output power as a result of Joule heating in SLDs under continuous wave current injection. Furthermore, SLDs processed normal to the facet demonstrate output powers as high as 20mW, offering improvements in beam quality, ease of packaging and use of real estate. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
Non-abelian dynamics in first-order cosmological phase transitions
Bubble collisions in cosmological phase transitions are explored, taking the
non-abelian character of the gauge fields into account. Both the QCD and
electroweak phase transitions are considered. Numerical solutions of the field
equations in several limits are presented.Comment: 8 pages, 2 figures. Contribution to the CosPA 2003 Cosmology and
Particle Astrophysics Symposium. Typos correcte
XMM-Newton Spectroscopy of the Starburst Dominated Ultra Luminous Infrared Galaxy NGC 6240
We present new XMM-Newton observation of the Ultra Luminous Infrared Galaxy
(ULIRG) NGC 6240. We analyze the reflecting grating spectrometer (RGS) data,
and data from the other instruments, and find a starburst dominated 0.5-3 keV
spectrum with global properties resembling those observed in M82 but with a
much higher luminosity. We show that the starburst region can be divided into
an outer zone, beyond a radius of about 2.1 kpc, with a gas temperature of
about 10^7 K and a central region with temperatures in the range (2-6) x 10^7
K. The gas in the outer region emits most of the observed Oviii Lyman-alpha
line and the gas in the inner region the emission lines of higher ionization
ions, including a strong Fexxv line. We also identify a small inner part, very
close to the active nuclei, with typical Seyfert 2 properties including a large
amount of photoionized gas producing a strong Fe K-alpha 6.4 keV line. The
combined abundance, temperature and emission measure analysis indicates super
solar Ne/O, Mg/O, Si/O, S/O and possibly also Fe/O. The analysis suggests
densities in the range of (0.07-0.28) x epsilon^(-1/2) cm^(-3) and a total
thermal gas mass of about 4 x 10^8 x epsilon^(1/2) solar masses, where epsilon
is the volume filling factor. We used a simple model to argue that a massive
starburst with an age of about 2 x 10^7 years can explain most of the observed
properties of the source. NGC 6240 is perhaps the clearest case of an X-ray
bright luminous AGN, in a merger, whose soft X-ray spectrum is dominated by a
powerful starburst.Comment: 10 pages, 6 diagrams, accepted by ApJ, added a few minor change
Worker heterogeneity, new monopsony, and training
A worker's output depends not only on his/her own ability but also on that of colleagues, who can facilitate the performance of tasks that each individual cannot accomplish on his/her own. We show that this common-sense observation generates monopsony power and is sufficient to explain why employers might expend resources on training employees even when the training is of use to other firms. We show that training will take place in better-than-average or âgoodâ firms enjoying greater monopsony power, whereas âbadâ firms will have low-ability workers unlikely to receive much training
Human subjective response to steering wheel vibration caused by diesel engine idle
This study investigated the human subjective response to steering wheel vibration of the type caused by a four-cylinder diesel engine idle in passenger cars. Vibrotactile perception was assessed using sinusoidal amplitude-modulated vibratory stimuli of constant energy level (r.m.s. acceleration, 0.41 m/s(2)) having a carrier frequency of 26 Hz (i.e. engine firing frequency) and modulation frequency of 6.5 Hz (half-order engine harmonic). Evaluations of seven levels of modulation depth parameter m (0.0, 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0) were performed in order to define the growth function of human perceived disturbance as a function of amplitude modulation depth. Two semantic descriptors were used (unpleasantness and roughness) and two test methods (the Thurstone paired-comparison method and the Borg CR-10 direct evaluation scale) for a total of four tests. Each test was performed using an independent group of 25 individuals. The results suggest that there is a critical value of modulation depth m = 0.2 below which human subjects do not perceive differences in amplitude modulation and above which the stimulus-response relationship increases monotonically with a power function. The Stevens power exponents suggest that the perceived unpleasantness is non-linearly dependent on modulation depth m with an exponent greater than 1 and that the perceived roughness is dependent with an exponent close to unity
The cool wake around 4C 34.16 as seen by XMM-Newton
We present XMM-Newton observations of the wake-radiogalaxy system 4C34.16,
which shows a cool and dense wake trailing behind 4C34.16's host galaxy. A
comparison with numerical simulations is enlightening, as they demonstrate that
the wake is produced mainly by ram pressure stripping during the galactic
motion though the surrounding cluster. The mass of the wake is a substantial
fraction of the mass of an elliptical galaxy's X-ray halo. This observational
fact supports a wake formation scenario similar to the one demonstrated
numerically by Acreman et al (2003): the host galaxy of 4C34.16 has fallen into
its cluster, and is currently crossing its central regions. A substantial
fraction of its X-ray halo has been stripped by ram pressure, and remains
behind to form the galaxy wake.Comment: 9 pages, 6 figures, accepted for publication in MNRA
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