3,021 research outputs found
Superposed epoch study of ICME sub-structures near Earth and their effects on galactic cosmic rays
Interplanetary coronal mass ejections (ICMEs) are the interplanetary
manifestations of solar eruptions. The overtaken solar wind forms a sheath of
compressed plasma at the front of ICMEs. Magnetic clouds (MCs) are a subset of
ICMEs with specific properties (e.g. the presence of a flux rope). When ICMEs
pass near Earth, ground observations indicate that the flux of galactic cosmic
rays (GCRs) decreases. The main aims of this paper are to find: common plasma
and magnetic properties of different ICME sub-structures, and which ICME
properties affect the flux of GCRs near Earth. We use a superposed epoch method
applied to a large set of ICMEs observed \insitu\ by the spacecraft ACE,
between 1998 and 2006. We also apply a superposed epoch analysis on GCRs time
series observed with the McMurdo neutron monitors. We find that slow MCs at 1
AU have on average more massive sheaths. We conclude that it is because they
are more effectively slowed down by drag during their travel from the Sun. Slow
MCs also have a more symmetric magnetic field and sheaths expanding similarly
as their following MC, while in contrast, fast MCs have an asymmetric magnetic
profile and a compressing sheath in compression. In all types of MCs, we find
that the proton density and the temperature, as well as the magnetic
fluctuations can diffuse within the front of the MC due to 3D reconnection.
Finally, we derive a quantitative model which describes the decrease of cosmic
rays as a function of the amount of magnetic fluctuations and field strength.
The obtained typical profiles of sheath/MC/GCR properties corresponding to
slow, mid, and fast ICMEs, can be used for forecasting/modelling these events,
and to better understand the transport of energetic particles in ICMEs. They
are also useful for improving future operative space weather activities.Comment: 13 pages, 6 figures, paper accepted in A&
Using a Gridded Global Dataset to Characterize Regional Hydroclimate in Central Chile
Central Chile is facing dramatic projections of climate change, with a consensus for declining precipitation, negatively affecting hydropower generation and irrigated agriculture. Rising from sea level to 6000 m within a distance of 200 km, precipitation characterization is difficult because of a lack of long-term observations, especially at higher elevations. For understanding current mean and extreme conditions and recent hydroclimatological change, as well as to provide a baseline for downscaling climate model projections, a temporally and spatially complete dataset of daily meteorology is essential. The authors use a gridded global daily meteorological dataset at 0.25° resolution for the period 1948–2008, adjusted by monthly precipitation observations interpolated to the same grid using a cokriging method with elevation as a covariate. For validation, daily statistics of the adjusted gridded precipitation are compared to station observations. For further validation, a hydrology model is driven with the gridded 0.25° meteorology and streamflow statistics are compared with observed flow. The high elevation precipitation is validated by comparing the simulated snow extent to Moderate Resolution Imaging Spectroradiometer (MODIS) images. Results show that the daily meteorology with the adjusted precipitation can accurately capture the statistical properties of extreme events as well as the sequence of wet and dry events, with hydrological model results displaying reasonable agreement with observed streamflow and snow extent. This demonstrates the successful use of a global gridded data product in a relatively data-sparse region to capture hydroclimatological characteristics and extremes
Multi-filter transit observations of WASP-39b and WASP-43b with three San Pedro M\'artir telescopes
Three optical telescopes located at the San Pedro M\'artir National
Observatory were used for the first time to obtain multi-filter defocused
photometry of the transiting extrasolar planets WASP-39b and WASP-43b. We
observed WASP-39b with the 2.12m telescope in the U filter for the first time,
and additional observations were carried out in the R and I filters using the
0.84m telescope. WASP-43b was observed in VRI with the same instrument, and in
the i filter with the robotic 1.50m telescope. We reduced the data using
different pipelines and performed aperture photometry with the help of custom
routines, in order to obtain the light curves. The fit of the light curves
(1.5--2.5mmag rms), and of the period analysis, allowed a revision of the
orbital and physical parameters, revealing for WASP-39b a period ( days) which is seconds larger than
previously reported. Moreover, we find for WASP-43b a planet/star radius
() which is larger in the i filter
with respect to previous works, and that should be confirmed with additional
observations. Finally, we confirm no evidence of constant period variations in
WASP-43b.Comment: 13 pages, 7 figures, accepted in PASP, scheduled for the February 1,
2015 issu
Probing Yukawian gravitational potential by numerical simulations. I. Changing N-body codes
In the weak field limit general relativity reduces, as is well known, to the
Newtonian gravitation. Alternative theories of gravity, however, do not
necessarily reduce to Newtonian gravitation; some of them, for example, reduce
to Yukawa-like potentials instead of the Newtonian potential. Since the
Newtonian gravitation is largely used to model with success the structures of
the universe, such as for example galaxies and clusters of galaxies, a way to
probe and constrain alternative theories, in the weak field limit, is to apply
them to model the structures of the universe. In the present study, we consider
how to probe Yukawa-like potentials using N-body numerical simulations.Comment: 17 pages, 11 figures. To appear in General Relativity and Gravitatio
Evolution of the Mass-Metallicity relations in passive and star-forming galaxies from SPH-cosmological simulations
We present results from SPH-cosmological simulations, including
self-consistent modelling of SN feedback and chemical evolution, of galaxies
belonging to two clusters and twelve groups. We reproduce the mass-metallicity
(ZM) relation of galaxies classified in two samples according to their
star-forming activity, as parametrized by their sSFR, across a redshift range
up to z=2.
Its slope shows irrelevant evolution in the passive sample, being steeper in
groups than in clusters. However, the sub-sample of high-mass passive galaxies
only is characterized by a steep increase of the slope with redshift, from
which it can be inferred that the bulk of the slope evolution of the ZM
relation is driven by the more massive passive objects. (...ABRIDGED...)
The ZM relation for the star-forming sample reveals an increasing scatter
with redshift, indicating that it is still being built at early epochs. The
star-forming galaxies make up a tight sequence in the SFR-M_* plane at high
redshift, whose scatter increases with time alongside with the consolidation of
the passive sequence. We also confirm the anti-correlation between sSFR and
stellar mass, pointing at a key role of the former in determining the galaxy
downsizing, as the most significant means of diagnostics of the star formation
efficiency. Likewise, an anti-correlation between sSFR and metallicity can be
established for the star-forming galaxies, while on the contrary more active
galaxies in terms of simple SFR are also metal-richer.
We discuss these results in terms of the mechanisms driving the evolution
within the high- and low-mass regimes at different epochs: mergers,
feedback-driven outflows and the intrinsic variation of the star formation
efficiency.Comment: Emended list of author
Semi-field assessment of the BG-Malaria trap for monitoring the African malaria vector, Anopheles arabiensis
Odour-baited technologies are increasingly considered for effective monitoring of mosquito populations and for the evaluation of vector control interventions. The BG-Malaria trap (BGM), which is an upside-down variant of the widely used BG-Sentinel trap (BGS), has been demonstrated to be effective to sample the Brazilian malaria vector, Anopheles darlingi. We evaluated the BGM as an improved method for sampling the African malaria vectors, Anopheles arabiensis. Experiments were conducted inside a large semi-field cage to compare trapping efficiencies of BGM and BGS traps, both baited with the synthetic attractant, Ifakara blend, supplemented with CO2. We then compared BGMs baited with either of four synthetic mosquito lures, Ifakara blend, Mbita blend, BG-lure or CO2, and an unbaited BGM. Lastly, we compared BGMs baited with the Ifakara blend dispensed via either nylon strips, BG cartridges (attractant-infused microcapsules encased in cylindrical plastic cartridge) or BG sachets (attractant-infused microcapsules encased in plastic sachets). All tests were conducted between 6P.M. and 7A.M., with 200–600 laboratory-reared An. arabiensis released nightly in the test chamber. The median number of An. arabiensis caught by the BGM per night was 83, IQR:(73.5–97.75), demonstrating clear superiority over BGS (median catch = 32.5 (25.25–37.5)). Compared to unbaited controls, BGMs baited with Mbita blend caught most mosquitoes (45 (29.5–70.25)), followed by BGMs baited with CO2 (42.5 (27.5–64)), Ifakara blend (31 (9.25–41.25)) and BG lure (16 (4–22)). BGM caught 51 (29.5–72.25) mosquitoes/night, when the attractants were dispensed using BG-Cartridges, compared to BG-Sachet (29.5 (24.75–40.5)), and nylon strips (27 (19.25–38.25)), in all cases being significantly superior to unbaited controls (p < 000.1). The findings demonstrate potential of the BGM as a sampling tool for African malaria vectors over the standard BGS trap. Its efficacy can be optimized by selecting appropriate odour baits and odour-dispensing systems
Firearms and Community Supervision Officers
Should CSOs (CSO) carry firearms? The 33rd/424th Judicial District allows all of its CSOs to carry firearms. This has been an eye-opening research topic as I did not realize how controversial this topic would be. This paper is not to influence Community Supervision and Corrections Departments one way or another but to simply show the data so that Directors and Judges can make an educated decision. CSCDs across the State should be aware that their decision impact their CSOs
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