1,356 research outputs found
Rotation-stimulated structures in the CN and C3 comae of comet 103P/Hartley 2 around the EPOXI encounter
In late 2010 a Jupiter Family comet 103P/Hartley 2 was a subject of an
intensive world-wide investigation. On UT October 20.7 the comet approached the
Earth within only 0.12 AU, and on UT November 4.6 it was visited by NASA's
EPOXI spacecraft. We joined this international effort and organized an
observing campaign. The images of the comet were obtained through narrowband
filters using the 2-m telescope of the Rozhen National Astronomical
Observatory. They were taken during 4 nights around the moment of the EPOXI
encounter. Image processing methods and periodicity analysis techniques were
used to reveal transient coma structures and investigate their repeatability
and kinematics. We observe shells, arc-, jet- and spiral-like patterns, very
similar for the CN and C3 comae. The CN features expanded outwards with the
sky-plane projected velocities between 0.1 to 0.3 km/s. A corkscrew structure,
observed on November 6, evolved with a much higher velocity of 0.66 km/s.
Photometry of the inner coma of CN shows variability with a period of
18.32+/-0.30 h (valid for the middle moment of our run, UT 2010 Nov. 5.0835),
which we attribute to the nucleus rotation. This result is fully consistent
with independent determinations around the same time by other teams. The
pattern of repeatability is, however, not perfect, which is understendable
given the suggested excitation of the rotation state, and the variability
detected in CN correlates well with the cyclic changes in HCN, but only in the
active phases. The revealed coma structures, along with the snapshot of the
nucleus orientation obtained by EPOXI, let us estimate the spin axis
orientation. We obtained RA=122 deg, Dec=+16 deg (epoch J2000.0), neglecting at
this point the rotational excitation.Comment: 9 pages, 10 figures, submitted to Astron. Astrophy
Biological Bodies: Defining Sex in the Modern Era
Biological sex is largely accepted at face value, unquestioned by scientists or the public. It is so ingrained into our culture that it has been used to do everything from cornering the children’s toy market to justifying the exclusion of women in STEM fields . After all, who would question what we can clearly see? Boys have penises, testes, seminiferous tubules, testosterone, and rampant body hair while girls have vaginas, clitorises, ovaries, uteruses, estrogen, fallopian tubes, and breasts– plain and simple. But, what about the times when it isn’t plain and simple? What about the times when babies are born with empty scrota, or genitals too little to be a penis but too big to be a clitoris, or when a child grows up with a vagina but discovers upon puberty that they have XY chromosomes, or when a father of four wakes up from surgery to be told that he has a uterus? What becomes of these people under the definition of biological sex? More importantly, what becomes of biological sex when its parameters fail to be as unquestionable as we claim them to be
Quantum Feynman-Kac perturbations
We develop fully noncommutative Feynman-Kac formulae by employing quantum
stochastic processes. To this end we establish some theory for perturbing
quantum stochastic flows on von Neumann algebras by multiplier cocycles.
Multiplier cocycles are constructed via quantum stochastic differential
equations whose coefficients are driven by the flow. The resulting class of
cocycles is characterised under alternative assumptions of separability or
Markov regularity. Our results generalise those obtained using classical
Brownian motion on the one hand, and results for unitarily implemented flows on
the other.Comment: 27 pages. Minor corrections to version 2. To appear in the Journal of
the London Mathematical Societ
The Increasing Rotation Period of Comet 10P/Tempel 2
We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March.
R-band lightcurves were obtained on 11 of these nights from 1999 April through
1999 June, prior to both the onset of significant coma activity and perihelion.
Phasing of the data yields a double-peaked lightcurve and indicates a nucleus
rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75
mag. Our data are sufficient to rule out all other possible double-peaked
solutions as well as the single- and triple- peaked solutions. This rotation
period agrees with one of five possible solutions found in post-perihelion data
from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously
eliminates their remaining four solutions. We applied our same techniques to
published lightcurves from 1988 which were obtained at an equivalent orbital
position and viewing geometry as in 1999. We found a rotation period of 8.932
+/- 0.001 hr in 1988, consistent with the findings of previous authors and
incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by
~32 s between 1988 and 1999 (two intervening perihelion passages). If the
spin-down is due to a systematic torque, then the rotation period prior to
perihelion during the 2010 apparition is expected to be an additional 32 s
longer than in 1999.Comment: Accepted by The Astronomical Journal; 22 pages of text, 3 tables, 6
figure
AssessingOpportunities and Barriers to Reducing the Environmental Footprint of Natural GasDevelopment in Utah’s Uintah Basin
Development of natural gas resources in the United States has increased dramatically over the past two decades, a boom driven by favorable prices, new technological developments, and growing interest in domestic sources of energy with a smaller carbon footprint than coal or oil. Most of the expansion in U.S. natural gas production has been from so-called ‘unconventional’ reserves in which extensive natural gas resources trapped in continuous sandstone and shale formations can now be extracted using modern directional drilling and hydraulic fracturing technologies. The Uintah Basin in northeastern Utah has been one of several areas in the U.S. where major tight sands and shale gas plays have been the focus of recent natural gas exploration and development
Resilience: Protective Factors for Depression and Post Traumatic Stress Disorder among African American Women?
There is a great need to carefully examine issues that may elevate one’s risk for mental illness and develop strategies to mitigate risk and cultivate resilience. African Americans, specifically African American women (AAW), are disproportionately affected by mental illness, including depression and post-traumatic stress disorder (PTSD). Higher rates of PTSD among AAW may be explained by significant rates of trauma exposure. Higher resiliency in individuals with mental illnesses is associated with better treatment response/outcomes. An examination of two (2) promising psycho-educational curricula for AAW at risk for depression and PTSD supports consideration of resilience as a protective factor among this population. Strengthening psychological resilience among diverse AAW at risk for depression and/or PTSD may serve as a protective factor for symptom severity. Multidimensional prevention and intervention strategies should incorporate culturally-centered, gender-specific, and strengths-based (resilience) models of care to help encourage mental health help-seeking and promotion of wellness for AAW
The Cratering History of Asteroid (2867) Steins
The cratering history of main belt asteroid (2867) Steins has been
investigated using OSIRIS imagery acquired during the Rosetta flyby that took
place on the 5th of September 2008. For this purpose, we applied current models
describing the formation and evolution of main belt asteroids, that provide the
rate and velocity distributions of impactors. These models coupled with
appropriate crater scaling laws, allow the cratering history to be estimated.
Hence, we derive Steins' cratering retention age, namely the time lapsed since
its formation or global surface reset. We also investigate the influence of
various factors -like bulk structure and crater erasing- on the estimated age,
which spans from a few hundred Myrs to more than 1Gyr, depending on the adopted
scaling law and asteroid physical parameters. Moreover, a marked lack of
craters smaller than about 0.6km has been found and interpreted as a result of
a peculiar evolution of Steins cratering record, possibly related either to the
formation of the 2.1km wide impact crater near the south pole or to YORP
reshaping.Comment: Accepted by Planetary and Space Scienc
Improving transferability of introduced species' distribution models: new tools to forecast the spread of a highly invasive seaweed
Extent: 13 p.The utility of species distribution models for applications in invasion and global change biology is critically dependent on their transferability between regions or points in time, respectively. We introduce two methods that aim to improve the transferability of presence-only models: density-based occurrence thinning and performance-based predictor selection. We evaluate the effect of these methods along with the impact of the choice of model complexity and geographic background on the transferability of a species distribution model between geographic regions. Our multifactorial experiment focuses on the notorious invasive seaweed Caulerpa cylindracea (previously Caulerpa racemosa var. cylindracea) and uses Maxent, a commonly used presence-only modeling technique. We show that model transferability is markedly improved by appropriate predictor selection, with occurrence thinning, model complexity and background choice having relatively minor effects. The data shows that, if available, occurrence records from the native and invaded regions should be combined as this leads to models with high predictive power while reducing the sensitivity to choices made in the modeling process. The inferred distribution model of Caulerpa cylindracea shows the potential for this species to further spread along the coasts of Western Europe, western Africa and the south coast of Australia.Heroen Verbruggen, Lennert Tyberghein, Gareth S. Belton, Frederic Mineur, Alexander Jueterbock, Galice Hoarau, C. Frederico D. Gurgel, Olivier De Clerc
The impact of main belt asteroids on infrared--submillimetre photometry and source counts
> Among the components of the infrared and submillimetre sky background,
the closest layer is the thermal emission of dust particles and minor bodies in
the Solar System. This contribution is especially important for current and
future infrared and submillimetre space instruments --like those of Spitzer,
Akari and Herschel -- and must be characterised by a reliable statistical
model. > We describe the impact of the thermal emission of main belt
asteroids on the 5...1000um photometry and source counts, for the current and
future spaceborne and ground-based instruments, in general, as well as for
specific dates and sky positions. > We used the statistical asteroid model
(SAM) to calculate the positions of main belt asteroids down to a size of 1km,
and calculated their infrared and submillimetre brightness using the standard
thermal model. Fluctuation powers, confusion noise values and number counts
were derived from the fluxes of individual asteroids. > We have constructed
a large database of infrared and submillimetre fluxes for SAM asteroids with a
temporal resolution of 5 days, covering the time span January 1, 2000 --
December 31, 2012. Asteroid fluctuation powers and number counts derived from
this database can be obtained for a specific observation setup via our public
web-interface. > Current space instruments working in the mid-infrared
regime (Akari and Spitzer Space Telescopes) are affected by asteroid confusion
noise in some specific areas of the sky, while the photometry of space infrared
and submillimetre instruments in the near future (e.g. Herschel and Planck
Space Observatories) will not be affected by asteroids. Faint main belt
asteroids might also be responsible for most of the zodiacal emission
fluctuations near the ecliptic.Comment: accepted for publication in Astronomy & Astrophysics; Additional
material (appendices) and the related web-interface can be found at:
"http://kisag.konkoly.hu/solarsystem/irsam.html
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