8,470 research outputs found
Tri-county pilot study
The author has identified the following significant results. An area inventory was performed for three southeast Texas counties (Montgomery, Walker, and San Jacinto) totaling 0.65 million hectares. The inventory was performed using a two level hierarchy. Level 1 was divided into forestland, rangeland, and other land. Forestland was separated into Level 2 categories: pine, hardwood, and mixed; rangeland was not separated further. Results consisted of area statistics for each county and for the entire study site for pine, hardwood, mixed, rangeland, and other land. Color coded county classification maps were produced for the May data set, and procedures were developed and tested
An extreme, blueshifted iron line profile in the Narrow Line Seyfert 1 PG 1402+261; an edge-on accretion disk or highly ionized absorption?
We report on a short XMM-Newton observation of the radio-quiet Narrow Line
Seyfert 1 PG 1402+261. The EPIC X-ray spectrum of PG 1402+261 shows a strong
excess of counts between 6-9 keV in the rest frame. This feature can be modeled
by an unusually strong (equivalent width 2 keV) and very broad (FWHM velocity
of 110000 km/s) iron K-shell emission line. The line centroid energy at 7.3 keV
appears blue-shifted with respect to the iron Kalpha emission band between
6.4-6.97 keV, while the blue-wing of the line extends to 9 keV in the quasar
rest frame. The line profile can be fitted by reflection from the inner
accretion disk, but an inclination angle of >60 deg is required to model the
extreme blue-wing of the line. Furthermore the extreme strength of the line
requires a geometry whereby the hard X-ray emission from PG 1402+261 above 2
keV is dominated by the pure-reflection component from the disk, while little
or none of the direct hard power-law is observed. Alternatively the spectrum
above 2 keV may instead be explained by an ionized absorber, if the column
density is sufficiently high (N_H > 3 x 10^23 cm^-2) and if the matter is
ionized enough to produce a deep (tau~1) iron K-shell absorption edge at 9 keV.
This absorber could originate in a large column density, high velocity outflow,
perhaps similar to those which appear to be observed in several other high
accretion rate AGN. Further observations, especially at higher spectral
resolution, are required to distinguish between the accretion disk reflection
or outflow scenarios.Comment: Accepted for publication in ApJ (18 pages, 5 figures, 1 table
The connection between the 15 GHz radio and gamma-ray emission in blazars
Since mid-2007 we have carried out a dedicated long-term monitoring programme
at 15 GHz using the Owens Valley Radio Observatory 40 meter telescope. One of
the main goals of this programme is to study the relation between the radio and
gamma-ray emission in blazars and to use it as a tool to locate the site of
high energy emission. Using this large sample of objects we are able to
characterize the radio variability, and study the significance of correlations
between the radio and gamma-ray bands. We find that the radio variability of
many sources can be described using a simple power law power spectral density,
and that when taking into account the red-noise characteristics of the light
curves, cases with significant correlation are rare. We note that while
significant correlations are found in few individual objects, radio variations
are most often delayed with respect to the gamma-ray variations. This suggests
that the gamma-ray emission originates upstream of the radio emission. Because
strong flares in most known gamma-ray-loud blazars are infrequent, longer light
curves are required to settle the issue of the strength of radio-gamma
cross-correlations and establish confidently possible delays between the two.
For this reason continuous multiwavelength monitoring over a longer time period
is essential for statistical tests of jet emission models.Comment: To appear in the Proceedings of the IAU Symposium No. 313:
"Extragalactic jets from every angle," Galapagos, Ecuador, 15-19 September
2014, F. Massaro, C. C. Cheung, E. Lopez, and A. Siemiginowska (Eds.),
Cambridge University Pres
A quasi-periodic oscillation in the blazar J1359+4011
The OVRO 40-m telescope has been monitoring the 15 GHz radio flux density of
over 1200 blazars since 2008. The 15 GHz light curve of the flat spectrum radio
quasar J1359+4011 shows a strong and persistent quasi-periodic oscillation. The
time-scale of the oscillation varies between 120 and 150 days over a
year time span. We interpret this as the active galactic nucleus mass-scaled
analog of low-frequency quasi-periodic oscillations from Galactic microquasars,
or as evidence of modulation of the accretion flow by thermal instabilites in
the "inner" accretion disc.Comment: 4 pages, 2 figures, 1 table. Accepted for publication in MNRAS
Letter
Quantitative acoustic models for superfluid circuits
We experimentally realize a highly tunable superfluid oscillator circuit in a
quantum gas of ultracold atoms and develop and verify a simple lumped-element
description of this circuit. At low oscillator currents, we demonstrate that
the circuit is accurately described as a Helmholtz resonator, a fundamental
element of acoustic circuits. At larger currents, the breakdown of the
Helmholtz regime is heralded by a turbulent shedding of vortices and density
waves. Although a simple phase-slip model offers qualitative insights into the
circuit's resistive behavior, our results indicate deviations from the
phase-slip model. A full understanding of the dissipation in superfluid
circuits will thus require the development of empirical models of the turbulent
dynamics in this system, as have been developed for classical acoustic systems.Comment: 12 pages, 9 figure
Southern hemispheric halon trends and global halon emissions, 1978–2011
The atmospheric records of four halons, H-1211 (CBrClF2), H-1301 (CBrF3), H-2402 (CBrF2CBrF2) and H-1202 (CBr2F2), measured from air collected at Cape Grim, Tasmania, between 1978 and 2011, are reported. Mixing ratios of H-1211, H-2402 and H-1202 began to decline in the early to mid-2000s, but those of H-1301 continue to increase up to mid-2011. These trends are compared to those reported by NOAA (National Oceanic and Atmospheric Administration) and AGAGE (Advanced Global Atmospheric Experiment). The observations suggest that the contribution of the halons to total tropospheric bromine at Cape Grim has begun to decline from a peak in 2008 of about 8.1 ppt. An extrapolation of halon mixing ratios to 2060, based on reported banks and predicted release factors, shows this decline becoming more rapid in the coming decades, with a contribution to total tropospheric bromine of about 3 ppt in 2060. Top-down global annual emissions of the halons were derived using a two-dimensional atmospheric model. The emissions of all four have decreased since peaking in the late 1980s–mid-1990s, but this decline has slowed recently, particularly for H-1301 and H-2402 which have shown no decrease in emissions over the past five years. The UEA (University of East Anglia) top-down model-derived emissions are compared to those reported using a top-down approach by NOAA and AGAGE and the bottom-up estimates of HTOC (Halons Technical Options Committee). The implications of an alternative set of steady-state atmospheric lifetimes are discussed. Using a lifetime of 14 yr or less for H-1211 to calculate top-down emissions estimates would lead to small, or even negative, estimated banks given reported production data. Finally emissions of H-1202, a product of over-bromination during the production process of H-1211, have continued despite reported production of H-1211 ceasing in 2010. This raises questions as to the source of these H-1202 emissions
Reciprocal and dynamic polarization of planar cell polarity core components and myosin
Citation: Newman-Smith, E., Kourakis, M. J., Reeves, W., Veeman, M., & Smith, W. C. (2015). Reciprocal and dynamic polarization of planar cell polarity core components and myosin. eLife, 2015(4). doi:10.7554/eLife.05361The Ciona notochord displays PCP-dependent polarity, with anterior localization of Prickle (Pk) and Strabismus (Stbm). We report that a myosin is polarized anteriorly in these cells and strongly colocalize with Stbm. Disruption of the actin/myosin machinery with cytochalasin or blebbistatin disrupts polarization of Pk and Stbm, but not of myosin complexes, suggesting a PCP-independent aspect of myosin localization. Washout of cytochalasin restored Pk polarization, but not if done in the presence of blebbistatin, suggesting an active role for myosin in core PCP protein localization. On the other hand, in the pk mutant line aimless myosin polarization in approximately one third of the cells, indicating a reciprocal action of core PCP signaling on myosin localization. Our results indicate a complex relationship between the actomyosin cytoskeleton and core PCP components in which myosin is not simply a downstream target of PCP signaling, but also required for PCP protein localization. © 2015, eLife. All rights reserved
Previous attentional set can induce an attentional blink with task-irrelevant initial targets
Identification of a second target is often impaired by the requirement to process a prior target in a rapid serial visual presentation (RSVP). This is termed the attentional blink. Even when the first target is task-irrelevant an attentional blink may occur providing this first target shares similar features with the second target (contingent capture). An RSVP experiment was undertaken to assess whether this first target can still cause an attentional blink when it did not require a response and did not share any features with the following target. The results revealed that such task-irrelevant targets can induce an attentional blink providing that they were task-relevant on a previous block of trials. This suggests that irrelevant focal stimuli can distract attention on the basis of a previous attentional set
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