2,146 research outputs found
Lightning and charge processes in brown dwarf and exoplanet atmospheres
The study of the composition of brown dwarf atmospheres helped to understand
their formation and evolution. Similarly, the study of exoplanet atmospheres is
expected to constrain their formation and evolutionary states. We use results
from 3D simulations, kinetic cloud formation and kinetic ion-neutral chemistry
to investigate ionisation processes which will affect their atmosphere
chemistry: The dayside of super-hot Jupiters is dominated by atomic hydrogen,
and not HO. Such planetary atmospheres exhibit a substantial degree of
thermal ionisation and clouds only form on the nightside where lightning leaves
chemical tracers (e.g. HCN) for possibly long enough to be detectable. External
radiation may cause exoplanets to be enshrouded in a shell of highly ionised,
H-forming gas and a weather-driven aurora may emerge. Brown dwarfs enable
us to study the role of electron beams for the emergence of an extrasolar,
weather-system driven aurora-like chemistry, and the effect of strong magnetic
fields on cold atmospheric gases. Electron beams trigger the formation of
H in the upper atmosphere of a brown dwarf (e.g. LSR-J1835) which may
react with it to form hydronium, HO, as a longer lived chemical tracer.
Brown dwarfs and super-hot gas giants may be excellent candidates to search for
HO as an H product.Comment: 16 pages, accepted for publication in the Philosophical Transactions
A of the Royal Society, (some typos corrected
Exo-lightning radio emission: the case study of HAT-P-11b
Lightning induced radio emission has been observed on solar system planets.
Lecavelier des Etangs et al. [2013] carried out radio transit observations of
the exoplanet HAT-P-11b, and suggested a tentative detection of a radio signal.
Here, we explore the possibility of the radio emission having been produced by
lightning activity on the exoplanet, following and expanding the work of
Hodos\'an et al. [2016a]. After a summary of our previous work [Hodos\'an et
al. 2016a], we extend it with a parameter study. The lightning activity of the
hypothetical storm is largely dependent on the radio spectral roll-off, ,
and the flash duration, . The best-case scenario would
require a flash density of the same order of magnitude as can be found during
volcanic eruptions on Earth. On average, times larger flash
densities than the Earth-storms with the largest lightning activity is needed
to produce the observed signal from HAT-P-11b. Combined with the results of
Hodos\'an et al. [2016a] regarding the chemical effects of planet-wide
thunderstorms, we conclude that future radio and infrared observations may lead
to lightning detection on planets outside the solar system.Comment: Accepted to the Conference Proceedings of the 8th International
Workshop on Planetary, Solar and Heliospheric Radio Emissions (PRE 8), held
in Seggauberg near Leibnitz/Graz, Austria, October 25-27, 2016. 12 pages, 2
figure
Hybrid propulsion system with a gyro component for economic and dynamic operation
The design of a hybrid drive with gyro components is described and its drive components for a medium class private car are discussed. The gyro component affects the short-period output of the drive by accelerating and slowing down and -- because of the mechanical transfer of kinetic energy between the gyro and the vehicle -- it affects also the energy balance in the case of intermittent operation. Energy can be taken in as desired either in the form of fuel or as fuel and current. A high energy recovery efficiency as well as the favorable operating range of the interval combustion engine makes it possible to reduce the fuel consumption per unit distance travelled to almost half that for a private car with a traditional engine
Jupiter as a Giant Cosmic Ray Detector
We explore the feasibility of using the atmosphere of Jupiter to detect
Ultra-High-Energy Cosmic Rays (UHECR's). The large surface area of Jupiter
allows us to probe cosmic rays of higher energies than previously accessible.
Cosmic ray extensive air showers in Jupiter's atmosphere could in principle be
detected by the Large Area Telescope (LAT) on the Fermi observatory. In order
to be observed, these air showers would need to be oriented toward the Earth,
and would need to occur sufficiently high in the atmosphere that the gamma rays
can penetrate. We demonstrate that, under these assumptions, Jupiter provides
an effective cosmic ray "detector" area of km. We predict
that Fermi-LAT should be able to detect events of energy eV with
fluence erg cm at a rate of about one per month. The observed
number of air showers may provide an indirect measure of the flux of cosmic
rays eV. Extensive air showers also produce a synchrotron
signature that may be measurable by ALMA. Simultaneous observations of Jupiter
with ALMA and Fermi-LAT could be used to provide broad constraints on the
energies of the initiating cosmic rays.Comment: 8 pages, 5 figures. Accepted for publication in the Astrophysical
Journal Letter
The Influence of Galactic Cosmic Rays on Ion-Neutral Hydrocarbon Chemistry in the Upper Atmospheres of Free-Floating Exoplanets
Cosmic rays may be linked to the formation of volatiles necessary for
prebiotic chemistry. We explore the effect of cosmic rays in a
hydrogen-dominated atmosphere, as a proof-of-concept that ion-neutral chemistry
may be important for modelling hydrogen-dominated atmospheres. In order to
accomplish this, we utilize Monte Carlo cosmic ray transport models with
particle energies of eV eV in order to investigate the
cosmic ray enhancement of free electrons in substellar atmospheres. Ion-neutral
chemistry is then applied to a Drift-Phoenix model of a free-floating giant gas
planet. Our results suggest that the activation of ion-neutral chemistry in the
upper atmosphere significantly enhances formation rates for various species,
and we find that CH, CH, NH, CH and possibly
CH are enhanced in the upper atmospheres because of cosmic rays. Our
results suggest a potential connection between cosmic ray chemistry and the
hazes observed in the upper atmospheres of various extrasolar planets.
Chemi-ionization reactions are briefly discussed, as they may enhance the
degree of ionization in the cloud layer.Comment: 22 pages, 4 figures. Accepted to the International Journal of
Astrobiolog
Patents and royalties
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62916/1/387546a0.pd
Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets
Brown dwarfs and giant gas extrasolar planets have cold atmospheres with rich chemical compositions from which mineral cloud particles form. Their properties, like particle sizes and material composition, vary with height, and the mineral cloud particles are charged due to triboelectric processes in such dynamic atmospheres. The dynamics of the atmospheric gas is driven by the irradiating host star and/or by the rotation of the objects that changes during its lifetime. Thermal gas ionisation in these ultra-cool but dense atmospheres allows electrostatic interactions and magnetic coupling of a substantial atmosphere volume. Combined with a strong magnetic field , a chromosphere and aurorae might form as suggested by radio and x-ray observations of brown dwarfs. Non-equilibrium processes like cosmic ray ionisation and discharge processes in clouds will increase the local pool of free electrons in the gas. Cosmic rays and lighting discharges also alter the composition of the local atmospheric gas such that tracer molecules might be identified. Cosmic rays affect the atmosphere through air showers in a certain volume which was modelled with a 3D Monte Carlo radiative transfer code to be able to visualise their spacial extent. Given a certain degree of thermal ionisation of the atmospheric gas, we suggest that electron attachment to charge mineral cloud particles is too inefficient to cause an electrostatic disruption of the cloud particles. Cloud particles will therefore not be destroyed by Coulomb explosion for the local temperature in the collisional dominated brown dwarf and giant gas planet atmospheres. However, the cloud particles are destroyed electrostatically in regions with strong gas ionisation. The potential size of such cloud holes would, however, be too small and might occur too far inside the cloud to mimic the effect of, e.g. magnetic field induced star spots
Robust detection of quasi-periodic variability: A HAWK-I mini survey of late-T dwarfs
We present HAWK-I J-band light curves of five late-type T dwarfs (T6.5-T7.5) with a typical duration of four hours, and investigate the evidence for quasi-periodic photometric variability on intra-night timescales. Our photometry reaches precisions in the range 7-20 mmag, after removing instrumental systematics that correlate with sky background, seeing and airmass. Based upon a Lomb-Scargle periodogram analysis, the latest object in the sample - ULAS J2321 (T7.5) - appears to show quasi-periodic variability with a period of 1.64 hours and an amplitude of 3 mmag. Given the low amplitude of variability and presence of systematics in our lightcurves, we discuss a Bayesian approach to robustly determine if quasi-periodic variability is present in a lightcurve affected by red noise. Using this approach, we conclude that the evidence for quasi-periodic variability in ULAS J2321 is not significant. As a result, we suggest that studies which identify quasi-periodic variables using the false alarm probability from a Lomb-Scargle periodogram are likely to over-estimate the number of variable objects, even if field stars are used to set a higher false alarm probability threshold. Instead we argue that a hybrid approach combining a false alarm probability cut, followed by Bayesian model selection, is necessary for robust identification of quasi-periodic variability in lightcurves with red noise
Ultraviolet light-induced recombination
Stimulation of transduction in by ultraviolet irradiation of the transducing phage P1 requires the nuclease but not the product or DNA polymerase I. It is hypothesized that the first step in "normal" recombination can be bypassed by any procedure generating single-stranded ends of DNA (as, for example, by nuclease activity).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33755/1/0000007.pd
The glutamate dehydrogenase structural gene of Escherichin coli
The glutamate dehydrogenase structural gene, gdhA , was mapped at 38.6 min on the genetic map and at 1860 kb on the physical map. A detailed map of this region is presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47574/1/438_2004_Article_BF00264460.pd
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