Trophic Transfer of Arsenic from an Aquatic Insect to Terrestrial Insect Predators.

The movement of energy and nutrients from aquatic to terrestrial ecosystems can be substantial, and emergent aquatic insects can serve as biovectors not only for nutrients, but also for contaminants present in the aquatic environment. The terrestrial predators Tenodera aridifolia sinensis (Mantodea: Mantidae) and Tidarren haemorrhoidale (Araneae: Theridiidae) and the aquatic predator Buenoa scimitra (Hemiptera: Notonectidae) were chosen to evaluate the efficacy of arsenic transfer between aquatic and terrestrial environments. Culex tarsalis larvae were reared in either control water or water containing 1000 µg l(-1) arsenic. Adults that emerged from the control and arsenic treatments were fed to the terrestrial predators, and fourth instar larvae were fed to the aquatic predator reared in control or arsenic contaminated water. Tenodera a. sinensis fed arsenic-treated Cx. tarsalis accumulated 658±130 ng g(-1) of arsenic. There was no significant difference between control and arsenic-fed T. haemorrhoidale (range 142-290 ng g(-1)). Buenoa scimitra accumulated 5120±406 ng g(-1) of arsenic when exposed to arsenic-fed Cx. tarsalis and reared in water containing 1000 µg l(-1) arsenic. There was no significant difference between controls or arsenic-fed B. scimitra that were not exposed to water-borne arsenic, indicating that for this species environmental exposure was more important in accumulation than strictly dietary arsenic. These results indicate that transfer to terrestrial predators may play an important role in arsenic cycling, which would be particularly true during periods of mass emergence of potential insect biovectors. Trophic transfer within the aquatic environment may still occur with secondary predation, or in predators with different feeding strategies

Guidelines for Signing and Marking of Low-Volume Rural Roads

Existing standards and guidelines for the application of signs and markings are unsuited and inefficient for use on low-volume rural roads (less than 400 A D T ) . T o alleviate this inadequacy, several potentially hazardous situations were evaluated to ascertain actual needs for signs and markings as they relate to economy and safety. These evaluations were based on recent research and on probability of conflict analyses regarding the needs for signing and marking of intersections, horizontal curves, and sections of inadequate passing sight distance.The research revealed that more efficient intersection control can be attained from the careful application of S T O P signs and CROSS R O A D warning signs based on approach speed, sight distance, and combined intersecting volumes. It was found that the treatment of horizontal curves can be made more efficient through the application of more stringent guidelines without adversely affecting safety. Striping of no-passing zones was found to be very inefficient in most instances, as the probability of conflict in these situations is virtually n il; guidelines for alternative treatments are presented. Overall, it was the opinion of the authors that application of guidelines suited to the rural con­text would result in savings in time, money, and frustration on the part of responsible agencies

NuSTAR Discovery of a Cyclotron Line in the Be/X-ray Binary RX J0520.5-6932 During Outburst

We present spectral and timing analysis of NuSTAR observations of RX J0520.5$-$6932 in the 3-79 keV band collected during its outburst in January 2014. The target was observed on two epochs and we report the detection of a cyclotron resonant scattering feature with central energies of $E_\mathrm{CRSF} = 31.3_{-0.7}^{+0.8}$ keV and $31.5_{-0.6}^{+0.7}$ keV during the two observations, respectively, corresponding to a magnetic field of $B \approx 2 \times10^{12}$ G. The 3-79 keV luminosity of the system during the two epochs assuming a nominal distance of 50 kpc was $3.667\pm0.007\times 10^{38}\,\mathrm{erg\,s^{-1}}$ and $3.983\pm0.007\times10^{38}\,\mathrm{erg\,s^{-1}}$. Both values are much higher than the critical luminosity of $\approx1.5\times10^{37}\,\mathrm{erg\,s^{-1}}$ above which a radiation dominated shock front may be expected. This adds a new object to the sparse set of three systems that have a cyclotron line observed at luminosities in excess of $10^{38}\,\mathrm{erg\,s^{-1}}$. A broad ($\sigma\approx0.45$ keV) Fe emission line is observed in the spectrum at a central energy of $6.58_{-0.05}^{+0.05}$ keV in both epochs. The pulse profile of the pulsar was observed to be highly asymmetric with a sharply rising and slowly falling profile of the primary peak. We also observed minor variations in the cyclotron line energy and width as a function of the rotation phase.% As in observations of other cyclotron absorption line sources, there is a small ($\Delta\phi\lesssim0.1$) phase difference between the peak of the cyclotron energy variation and the peak of the flux variation.Comment: 9 pages, 4 figures, 6 tables. Accepted to Ap

A NuSTAR observation of the reflection spectrum of the low mass X-ray binary 4U 1728-34

We report on a simultaneous NuSTAR and Swift observation of the neutron star low-mass X-ray binary 4U 1728-34. We identified and removed four Type I X-ray bursts during the observation in order to study the persistent emission. The continuum spectrum is hard and well described by a black body with $kT=$ 1.5 keV and a cutoff power law with $\Gamma=$ 1.5 and a cutoff temperature of 25 keV. Residuals between 6 and 8 keV provide strong evidence of a broad Fe K$\alpha$ line. By modeling the spectrum with a relativistically blurred reflection model, we find an upper limit for the inner disk radius of $R_{\rm in}\leq2 R_{\rm ISCO}$. Consequently we find that $R_{\rm NS}\leq23$ km, assuming M=1.4{\mbox{\rm\,M_{\mathord\odot}}} and $a=0.15$. We also find an upper limit on the magnetic field of $B\leq2\times10^8$ G.Comment: 9 pages, 8 figure

NuSTAR and Swift observations of the black hole candidate XTE J1908+094 during its 2013 outburst

The black hole candidate XTE J1908+094 went into outburst for the first time since 2003 in October 2013. We report on an observation with the Nuclear Spectroscopic Telescope Array (NuSTAR) and monitoring observations with Swift during the outburst. NuSTAR caught the source in the soft state: the spectra show a broad relativistic iron line, and the light curves reveal a ~40 ks flare with the count rate peaking about 40% above the non-flare level and with significant spectral variation. A model combining a multi-temperature thermal component, a power-law, and a reflection component with an iron line provides a good description of the NuSTAR spectrum. Although relativistic broadening of the iron line is observed, it is not possible to constrain the black hole spin with these data. The variability of the power-law component, which can also be modeled as a Comptonization component, is responsible for the flux and spectral change during the flare, suggesting that changes in the corona (or possibly continued jet activity) are the likely cause of the flare.Comment: 9 pages, 6 figures, 3 tables, accepted for publication in Ap

The smooth cyclotron line in Her X-1 as seen with NuSTAR

Her X-1, one of the brightest and best studied X-ray binaries, shows a cyclotron resonant scattering feature (CRSF) near 37 keV. This makes it an ideal target for detailed study with the Nuclear Spectroscopic Telescope Array (NuSTAR), taking advantage of its excellent hard X-ray spectral resolution. We observed Her X-1 three times, coordinated with Suzaku, during one of the high flux intervals of its 35d super-orbital period. This paper focuses on the shape and evolution of the hard X-ray spectrum. The broad-band spectra can be fitted with a powerlaw with a high-energy cutoff, an iron line, and a CRSF. We find that the CRSF has a very smooth and symmetric shape, in all observations and at all pulse-phases. We compare the residuals of a line with a Gaussian optical depth profile to a Lorentzian optical depth profile and find no significant differences, strongly constraining the very smooth shape of the line. Even though the line energy changes dramatically with pulse phase, we find that its smooth shape does not. Additionally, our data show that the continuum is only changing marginally between the three observations. These changes can be explained with varying amounts of Thomson scattering in the hot corona of the accretion disk. The average, luminosity-corrected CRSF energy is lower than in past observations and follows a secular decline. The excellent data quality of NuSTAR provides the best constraint on the CRSF energy to date.Comment: 13 pages, 13 figures, accepted for publication in Ap

Developmental succession of the microbiome of Culex mosquitoes

Background: The native microflora associated with mosquitoes have important roles in mosquito development and vector competence. Sequencing of bacterial V3 region from 16S rRNA genes across the developmental stages of Culex mosquitoes (early and late larval instars, pupae and adults) was used to test the hypothesis that bacteria found in the larval stage of Culex are transstadially transmitted to the adult stage, and to compare the microbiomes of field-collected versus laboratory-reared mosquitoes.Results: Beta diversity analysis revealed that bacterial community structure differed among three life stages (larvae, pupae and adults) of Culex tarsalis. Although only similar to 2 % of the total number of bacterial OTUs were found in all stages, sequences from these OTUs accounted for nearly 82 % of the total bacterial sequences recovered from all stages. Thorsellia (Gammaproteobacteria) was the most abundant bacterial taxon found across all developmental stages of field-collected Culex mosquitoes, but was rare in mosquitoes from laboratory-reared colonies. The proportion of Thorsellia sequences in the microbiomes of mosquito life stages varied ontogenetically with the greatest proportions recovered from the pupae of C. tarsalis and the lowest from newly emerged adults. The microbiome of field-collected late instar larvae was not influenced significantly by differences in the microbiota of the habitat due to habitat age or biopesticide treatments. The microbiome diversity was the greatest in the early instar larvae and the lowest in laboratory-reared mosquitoes.Conclusions: Bacterial communities in early instar C. tarsalis larvae were significantly more diverse when compared to late instar larvae, pupae and newly emerged adults. Some of the bacterial OTUs found in the early instar larvae were also found across developmental stages. Thorsellia dominated the bacterial communities in field-collected immature stages but occurred at much lower relative abundance in adults. Differences in microbiota observed in larval habitats did not influence bacterial community profiles of late instar larvae or adults. However, bacterial communities in laboratory-reared C. tarsalis larvae differed significantly from the field. Determining the role of Thorsellia in mosquitoes and its distribution across different species of mosquitoes warrants further investigation

NuSTAR observations of the powerful radio-galaxy Cygnus A

We present NuSTAR observations of the powerful radio galaxy Cygnus A, focusing on the central absorbed active galactic nucleus (AGN). Cygnus A is embedded in a cool-core galaxy cluster, and hence we also examine archival XMM-Newton data to facilitate the decomposition of the spectrum into the AGN and intracluster medium (ICM) components. NuSTAR gives a source-dominated spectrum of the AGN out to >70keV. In gross terms, the NuSTAR spectrum of the AGN has the form of a power law (Gamma~1.6-1.7) absorbed by a neutral column density of N_H~1.6x10^23 cm^-2. However, we also detect curvature in the hard (>10keV) spectrum resulting from reflection by Compton-thick matter out of our line-of-sight to the X-ray source. Compton reflection, possibly from the outer accretion disk or obscuring torus, is required even permitting a high-energy cutoff in the continuum source; the limit on the cutoff energy is E_cut>111keV (90% confidence). Interestingly, the absorbed power-law plus reflection model leaves residuals suggesting the absorption/emission from a fast (15,000-26,000km/s), high column-density (N_W>3x10^23 cm^-2), highly ionized (xi~2,500 erg cm/s) wind. A second, even faster ionized wind component is also suggested by these data. We show that the ionized wind likely carries a significant mass and momentum flux, and may carry sufficient kinetic energy to exercise feedback on the host galaxy. If confirmed, the simultaneous presence of a strong wind and powerful jets in Cygnus A demonstrates that feedback from radio-jets and sub-relativistic winds are not mutually exclusive phases of AGN activity but can occur simultaneously.Comment: 13 pages; accepted for publication in The Astrophysical Journa