Electron Energy Distributions at Relativistic Shock Sites: Observational Constraints from the Cygnus A Hotspots

We report new detections of the hotspots in Cygnus A at 4.5 and 8.0 microns with the Spitzer Space Telescope. Together with detailed published radio observations and synchrotron self-Compton modeling of previous X-ray detections, we reconstruct the underlying electron energy spectra of the two brightest hotspots (A and D). The low-energy portion of the electron distributions have flat power-law slopes (s~1.5) up to the break energy which corresponds almost exactly to the mass ratio between protons and electrons; we argue that these features are most likely intrinsic rather than due to absorption effects. Beyond the break, the electron spectra continue to higher energies with very steep slopes s>3. Thus, there is no evidence for the `canonical' s=2 slope expected in 1st order Fermi-type shocks within the whole observable electron energy range. We discuss the significance of these observations and the insight offered into high-energy particle acceleration processes in mildly relativistic shocks.Comment: 5 pages, 3 figures, in Extragalactic Jets: Theory and Observation from Radio to Gamma Ray, Eds. T. A. Rector and D. S. De Youn

A cosmic ray cocoon along the X-ray jet of M87?

Relativistic jets propagating through an ambient medium must produce some observational effects along their side boundaries because of interactions across the large velocity gradient. One possible effect of such an interaction would be a sheared magnetic field structure at the jet boundaries, leading to a characteristic radio polarization pattern. As proposed by Ostrowski, another effect can come from the generation of a high energy cosmic ray component at the boundary, producing dynamic effects on the medium surrounding the jet and forming a cocoon dominated by cosmic rays with a decreased thermal gas emissivity. We selected this process for our first attempt to look for the effects of this type of interaction. We analyzed the Chandra X-ray data for the radio galaxy M87 in order to verify if the expected regions of diminished emissivity may be present near the spectacular X-ray jet in this source. The detailed analysis of the data, merged from 42 separate observations, shows signatures of lower emissivity surrounding the jet. In particular we detect an intensity dip along the part of the jet, which would be approximately 150 pc x 2 kpc in size, if situated along the jet which is inclined toward us. Due to a highly non-uniform X-ray background in the central region we are not able to claim the discovery of a cosmic ray cocoon around the M87 jet: we only have demonstrated that the data show morphological structures which could be accounted for if a cosmic ray cocoon exists.Comment: 8 pages, 8 pictures accepted for publication in MNRA

A Novel Approach in Constraining Electron Spectra in Blazar Jets: The Case of Markarian 421

We report results from the observations of the well studied TeV blazar Mrk 421 with the Swift and the Suzaku satellites in December 2008. During the observation, Mrk 421 was found in a relatively low activity state, with the corresponding 2-10 keV flux of $3 \times 10^{-10}$ erg/s/cm^2. For the purpose of robust constraining the UV-to-X-ray emission continuum we selected only the data corresponding to truly simultaneous time intervals between Swift and Suzaku, allowing us to obtain a good-quality, broad-band spectrum despite a modest length (0.6 ksec) exposure. We analyzed the spectrum with the parametric forward-fitting SYNCHROTRON model implemented in XSPEC assuming two different representations of the underlying electron energy distribution, both well motivated by the current particle acceleration models: a power-law distribution above the minimum energy $\gamma_{\rm min}$ with an exponential cutoff at the maximum energy $\gamma_{\rm max}$, and a modified ultra-relativistic Maxwellian with an equilibrium energy $\gamma_{\rm eq}$. We found that the latter implies unlikely physical conditions within the blazar zone of Mrk 421. On the other hand, the exponentially moderated power-law electron distribution gives two possible sets of the model parameters: (i) flat spectrum $dN'_e/d\gamma \propto \gamma^{-1.91}$ with low minimum electron energy $\gamma_{\rm min}<10^3$, and (ii) steep spectrum $\propto \gamma^{-2.77}$ with high minimum electron energy $\gamma_{\rm min}\simeq 2\times10^4$. We discuss different interpretations of both possibilities in the context of a diffusive acceleration of electrons at relativistic, sub- or superluminal shocks. We also comment on how exactly the gamma-ray data can be used to discriminate between the proposed different scenarios.Comment: 18 pages, 2 figures; accepted for publication in the Astrophysical Journa

Operational issues involving use of supplementary cooling towers to meet stream temperature standards with application to the Browns Ferry Nuclear Plant

A mixed mode cooling system is one which operates in either the open, closed, or helper (once-through but with the use of the cooling towers) modes. Such systems may be particularly economical where the need for supplementary cooling to meet environmental constraints on induced water temperature changes is seasonal or dependent upon other transient factors such as stream- flow. The issues involved in the use of mixed mode systems include the design of the open cycle and closed cycle portions of the cooling system, the specification of the environmental standard to be met, and the monitoring system and associated decision rules used to determine when mode changes are necessary. These issues have been examined in the context of a case study of TVA's Browns Ferry Nuclear Plant which utilizes the large quantity of site specific data reflecting conditions both with and without plant operation. The most important findings of this study are: (1) The natural temperature differences in the Tennessee River are of the same order of magnitude (50F) as the maximum allowed induced temperature increase. (2) Predictive estimates based on local hydrological and meteorological data are capable of accounting for 40% of the observed natural variability. (3) Available algorithms for plant induced temperature increases provide estimates within 1F of observed values except during periods of strong stratification. (4) A mixed mode system experiences only 10% of the capacity losses experienced by a totally closed system, (5) The capacity loss is relatively more sensitive to the environmental standard than to changes in cooling system design. (6) About one third of the capacity loss incurred using the mixed mode system is the result of natural temperature variations. This unnecessary loss may be halved by the use of predictive estimates for natural temperature differences

Trends in added sugars from packaged beverages available and purchased by US households, 2007–2012

Background: The US Food and Drug Administration's updated nutrition labeling requirements will include added sugars starting in July 2018, but no measure currently exists to identify the added sugar content of products and what it represents among purchases. Beverages are one of the first targets for reducing added sugar consumption, and hence are the focus here. Objective: Our goal was to estimate trends in added sugars in nonalcoholic packaged beverage products available in the United States and to estimate amounts of added sugars obtained from these beverages given the purchases of US households overall and by subpopulations. Design: On the basis of nutrition label data from multiple sources, we used a stepwise approach to derive the added sugar content of 160,713 beverage products recorded as purchased by US households in 2007-2012 (345,193 observations from 110,539 unique households). We estimated the amounts of added sugars obtained from packaged beverages US households reported buying in 2007-2008, 2009-2010, and 2011-2012, overall and by subpopulations based on household composition, race/ethnicity, and income. The key outcomes are added sugars in terms of per capita grams per day and the percentage of calories from packaged beverages. Results: Packaged beverages alone account for per capita consumption of 12 g/d of added sugars purchased by US households in 2007-2012, representing 32-48% of calories from packaged beverages. Whereas the absolute amount of added sugars from beverages has not changed meaningfully over time, the relative contribution of added sugars to calories from beverages has increased. Non-Hispanic black households and low-income households obtain both higher absolute and relative amounts of added sugars from beverages than non-Hispanic white households and high-income households (all P < 0.01). Conclusions: These results provide measures of added sugars from packaged beverages at both the product level and the population level in the United States and can be used for comparisons after the revised nutrition labels are implemented and for future monitoring

The mechanics of undulatory locomotion: the mixed kinematic and dynamic case

This paper studies the mechanics of undulatory locomotion. This type of locomotion is generated by a coupling of internal shape changes to external non-holonomic constraints. Employing methods from geometric mechanics, the authors use the dynamic symmetries and kinematic constraints to develop a specialized form of the dynamic equations which govern undulatory systems. These equations are written in terms of physically meaningful and intuitively appealing variables that show the role of internal shape changes in driving locomotion

On the Interaction of the PKS B1358-113 Radio Galaxy with the Abell 1836 Cluster

[abridged] Here we present the analysis of multifrequency data gathered for the FRII radio galaxy PKS B1358-113, hosted in the brightest cluster galaxy of Abell 1836. The galaxy harbors one of the most massive black holes known to date and our analysis of the optical data reveals that this black hole is only weakly active. Based on new Chandra and XMM-Newton X-ray observations and archival radio data we derive the preferred range for the jet kinetic luminosity $\sim (0.5-3) \times 10^{45}$ erg s$^{-1}$. This is above the values implied by various scaling relations proposed for radio sources in galaxy clusters, being instead very close to the maximum jet power allowed for the given accretion rate. We constrain the radio source lifetime as $\sim 40-70$ Myrs, and the total amount of deposited jet energy $\sim (2-8) \times 10^{60}$\,ergs. The detailed analysis of the X-ray data provides indication for the presence of a bow-shock driven by the expanding radio lobes into the Abell 1836 cluster environment, with the corresponding Mach number $\sim 2-4$. This, together with the recently growing evidence that powerful FRII radio galaxies may not be uncommon in the centers of clusters at higher redshifts, supports the idea that jet-induced shock heating may indeed play an important role in shaping the properties of clusters, galaxy groups, and galaxies in formation. We speculate on a possible bias against detecting jet-driven shocks in poorer environments, resulting from an inefficient electron heating at the shock front, combined with a relatively long electron-ion equilibration timescale.Comment: Version accepted to Ap