Buoyancy-driven inflow to a relic cold core: the gas belt in radio galaxy 3C 386

We report measurements from an XMM-Newton observation of the low-excitation radio galaxy 3C 386. The study focusses on an X-ray-emitting gas belt, which lies between and orthogonal to the radio lobes of 3C 386 and has a mean temperature of $0.94\pm0.05$ keV, cooler than the extended group atmosphere. The gas in the belt shows temperature structure with material closer to the surrounding medium being hotter than gas closer to the host galaxy. We suggest that this gas belt involves a `buoyancy-driven inflow' of part of the group-gas atmosphere where the buoyant rise of the radio lobes through the ambient medium has directed an inflow towards the relic cold core of the group. Inverse-Compton emission from the radio lobes is detected at a level consistent with a slight suppression of the magnetic field below the equipartition value.Comment: 11 pages, 10 figures, accepted for publication in MNRA

Strain-Modified RKKY Interaction in Carbon Nanotubes

For low-dimensional metallic structures, such as nanotubes, the exchange coupling between localized magnetic dopants is predicted to decay slowly with separation. The long-range character of this interaction plays a significant role in determining the magnetic order of the system. It has previously been shown that the interaction range depends on the conformation of the magnetic dopants in both graphene and nanotubes. Here we examine the RKKY interaction in carbon nanotubes in the presence of uniaxial strain for a range of different impurity configurations. We show that strain is capable of amplifying or attenuating the RKKY interaction, significantly increasing certain interaction ranges, and acting as a switch: effectively turning on or off the interaction. We argue that uniaxial strain can be employed to significantly manipulate magnetic interactions in carbon nanotubes, allowing an interplay between mechanical and magnetic properties in future spintronic devices. We also examine the dimensional relationship between graphene and nanotubes with regards to the decay rate of the RKKY interaction.Comment: 7 pages, 6 figures, submitte

How to estimate a cumulative process’s rate-function

Consider two sequences of bounded random variables, a value and a timing process, that satisfy the large deviation principle (LDP) with rate-function J(·,·) and whose cumulative process satisfies the LDP with rate-function I(·). Under mixing conditions, an LDP for estimates of I constructed by transforming an estimate of J is proved. For the case of cumulative renewal processes it is demonstrated that this approach is favorable to a more direct method as it ensures the laws of the estimates converge weakly to a Dirac measure at I

How to estimate a cumulative process’s rate-function

Consider two sequences of bounded random variables, a value and a timing process, that satisfy the large deviation principle (LDP) with rate-function J(·,·) and whose cumulative process satisfies the LDP with rate-function I(·). Under mixing conditions, an LDP for estimates of I constructed by transforming an estimate of J is proved. For the case of cumulative renewal processes it is demonstrated that this approach is favorable to a more direct method as it ensures the laws of the estimates converge weakly to a Dirac measure at I

Tail asymptotics for busy periods

The busy period for a queue is cast as the area swept under the random walk until it first returns to zero, $B$. Encompassing non-i.i.d. increments, the large-deviations asymptotics of $B$ is addressed, under the assumption that the increments satisfy standard conditions, including a negative drift. The main conclusions provide insight on the probability of a large busy period, and the manner in which this occurs: I) The scaled probability of a large busy period has the asymptote, for any $b>0$, \lim_{n\to\infty} \frac{1}{\sqrt{n}} \log P(B\geq bn) = -K\sqrt{b}, \hbox{where} \quad K = 2 \sqrt{-\int_0^{\lambda^*} \Lambda(\theta) d\theta}, \quad \hbox{with $\lambda^*=\sup\{\theta:\Lambda(\theta)\leq0\}$,} and with $\Lambda$ denoting the scaled cumulant generating function of the increments process. II) The most likely path to a large swept area is found to be a simple rescaling of the path on $[0,1]$ given by, [\psi^*(t) = -\Lambda(\lambda^*(1-t))/\lambda^*.] In contrast to the piecewise linear most likely path leading the random walk to hit a high level, this is strictly concave in general. While these two most likely paths have very different forms, their derivatives coincide at the start of their trajectories, and at their first return to zero. These results partially answer an open problem of Kulick and Palmowski regarding the tail of the work done during a busy period at a single server queue. The paper concludes with applications of these results to the estimation of the busy period statistics $(\lambda^*, K)$ based on observations of the increments, offering the possibility of estimating the likelihood of a large busy period in advance of observing one.Comment: 15 pages, 5 figure

Detection, attribution, and sensitivity of trends toward earlier streamflow in the Sierra Nevada

Observed changes in the timing of snowmelt dominated streamflow in the western United States are often linked to anthropogenic or other external causes. We assess whether observed streamflow timing changes can be statistically attributed to external forcing, or whether they still lie within the bounds of natural (internal) variability for four large Sierra Nevada (CA) basins, at inflow points to major reservoirs. Streamflow timing is measured by “center timing” (CT), the day when half the annual flow has passed a given point. We use a physically based hydrology model driven by meteorological input from a global climate model to quantify the natural variability in CT trends. Estimated 50-year trends in CT due to natural climate variability often exceed estimated actual CT trends from 1950 to 1999. Thus, although observed trends in CT to date may be statistically significant, they cannot yet be statistically attributed to external influences on climate. We estimate that projected CT changes at the four major reservoir inflows will, with 90% confidence, exceed those from natural variability within 1–4 decades or 4–8 decades, depending on rates of future greenhouse gas emissions. To identify areas most likely to exhibit CT changes in response to rising temperatures, we calculate changes in CT under temperature increases from 1 to 5°. We find that areas with average winter temperatures between −2°C and −4°C are most likely to respond with significant CT shifts. Correspondingly, elevations from 2000 to 2800 m are most sensitive to temperature increases, with CT changes exceeding 45 days (earlier) relative to 1961–1990

Yukawa Scalar Self-Mass on a Conformally Flat Background

We compute the one loop self-mass-squared of a massless, minimally coupled scalar which is Yukawa-coupled to a massless Dirac fermion in a general conformally flat background. Dimensional regularization is employed and a fully renormalized result is obtained. For the special case of a locally de Sitter background our result is manifestly de Sitter invariant. By solving the effective field equations we show that the scalar mode functions acquire no significant one loop corrections. In particular, the phenomenon of super-adiabatic amplification is not affected. One consequence is that the scalar-catalyzed production of fermions during inflation should not be reduced by changes in the scalar sector before it has time to go to completion.Comment: 23 pages, LaTeX 2epsilon, 3 figures (uses axodraw

Locating mesolithic hunter-gatherer camps in the Carpathian Basin

The Mesolithic in Eastern Europe was the last time that hunter-gatherer economies thrived there before the spread of agriculture in the second half of the seventh millennium BC. But the period, and the interactions between foragers and the first farmers, are poorly understood in the Carpathian Basin and surrounding areas because few sites are known, and even fewer have been excavated and published. How did site location differ between Mesolithic and Early Neolithic settlers? And where should we look for rare Mesolithic sites? Proximity analysis is seldom used for predictive modeling for hunter-gatherer sites at large scales, but in this paper, we argue that it can serve as an important starting point for prospection for rare and poorly understood sites. This study uses proximity analysis to provide quantitative landscape associations of known Mesolithic and Early Neolithic sites in the Carpathian Basin to show how Mesolithic people chose attributes of the landscape for camps, and how they differed from the farmers who later settled. We use elevation and slope, rivers, wetlands prior to the twentieth century, and the distribution of lithic raw materials foragers and farmers used for toolmaking to identify key proxies for preferred locations. We then build predictive models for the Mesolithic and Early Neolithic in the Pannonian region to highlight parts of the landscape that have relatively higher probabilities of having Mesolithic sites still undiscovered and contrast them with the settlement patterns of the first farmers in the area. We find that large parts of Pannonia conform to landforms preferred by Mesolithic foragers, but these areas have not been subject to investigation