The ROSAT X-ray Spectra of BL Lacertae Objects

We study the X-ray spectra of 85 BL Lacertae objects using the hardness ratios as given in the WGA catalogue of {\it ROSAT} sources. This sample includes all WGA BL Lacs with high-quality data and comprises about 50 per cent of presently known BL Lacs. We find that BL Lacs have energy power-law spectral indices between 0 and 3 with a mean value $\alpha_{\rm x}\sim 1.4$. Significant differences, however, are present between high-energy cutoff BL Lacs (HBLs), normally selected in the X-ray band, and low-energy cutoff BL Lacs (LBLs), generally found in radio surveys. HBLs have steeper X-ray spectral slopes ($\alpha_{\rm x}\sim 1.5$) well correlated with $\alpha_{\rm ox}$, and anti-correlated with the X-ray-to-radio flux ratio and cutoff frequency, with convex overall broad-band spectra. LBLs, on the other hand, have flatter X-ray spectra ($\alpha_{\rm x}\sim 1.1$) and concave optical-X-ray continuum. We interpret these results in terms of different mechanisms being responsible for the X-ray emission in the two classes, namely synchrotron and inverse Compton for HBLs and LBLs respectively. The observed differences are consistent with the hypothesis that HBLs and LBLs are powered by essentially the same non-thermal engines differing mainly in their synchrotron cutoff energy.Comment: Uuencoded compressed tar file containing 9 page TeX file and 8 postscript figures. Uses mn.tex and psfig.tex. To appear in MNRAS. TeX and postscript files also available at http://itovf2.roma2.infn.it/padovani/xray_spectra/bllacs.htm

Open book decompositions versus prime factorizations of closed, oriented 3-manifolds

Let $M$ be a closed, oriented, connected 3--manifold and $(B,\pi)$ an open book decomposition on $M$ with page $\Sigma$ and monodromy $\varphi$. It is easy to see that the first Betti number of $\Sigma$ is bounded below by the number of $S^2\times S^1$--factors in the prime factorization of $M$. Our main result is that equality is realized if and only if $\varphi$ is trivial and $M$ is a connected sum of $S^2\times S^1$'s. We also give some applications of our main result, such as a new proof of the result by Birman and Menasco that if the closure of a braid with $n$ strands is the unlink with $n$ components then the braid is trivial.Comment: 8 pages, 1 figure. Submitted to the proceedings of the conference "Interactions between low dimensional topology and mapping class groups", July 1-5, 2013, Max Planck Institute for Mathematics, Bon

Renewal, Modulation and Superstatistics

We consider two different proposals to generate a time series with the same non-Poisson distribution of waiting times, to which we refer to as renewal and modulation. We show that, in spite of the apparent statistical equivalence, the two time series generate different physical effects. Renewal generates aging and anomalous scaling, while modulation yields no aging and either ordinary or anomalous diffusion, according to the prescription used for its generation. We argue, in fact, that the physical realization of modulation involves critical events, responsible for scaling. In conclusion, modulation rather than ruling out the action of critical events, sets the challenge for their identification

Multi-scaling of moments in stochastic volatility models

We introduce a class of stochastic volatility models $(X_t)_{t \geq 0}$ for which the absolute moments of the increments exhibit anomalous scaling: \E\left(|X_{t+h} - X_t|^q \right) scales as $h^{q/2}$ for $q < q^*$, but as $h^{A(q)}$ with $A(q) q^*$, for some threshold $q^*$. This multi-scaling phenomenon is observed in time series of financial assets. If the dynamics of the volatility is given by a mean-reverting equation driven by a Levy subordinator and the characteristic measure of the Levy process has power law tails, then multi-scaling occurs if and only if the mean reversion is superlinear

Digital image correlation (DIC) analysis of the 3 December 2013 Montescaglioso landslide (Basilicata, Southern Italy). Results from a multi-dataset investigation

Image correlation remote sensing monitoring techniques are becoming key tools for providing effective qualitative and quantitative information suitable for natural hazard assessments, specifically for landslide investigation and monitoring. In recent years, these techniques have been successfully integrated and shown to be complementary and competitive with more standard remote sensing techniques, such as satellite or terrestrial Synthetic Aperture Radar interferometry. The objective of this article is to apply the proposed in-depth calibration and validation analysis, referred to as the Digital Image Correlation technique, to measure landslide displacement. The availability of a multi-dataset for the 3 December 2013 Montescaglioso landslide, characterized by different types of imagery, such as LANDSAT 8 OLI (Operational Land Imager) and TIRS (Thermal Infrared Sensor), high-resolution airborne optical orthophotos, Digital Terrain Models and COSMO-SkyMed Synthetic Aperture Radar, allows for the retrieval of the actual landslide displacement field at values ranging from a few meters (2–3 m in the north-eastern sector of the landslide) to 20–21 m (local peaks on the central body of the landslide). Furthermore, comprehensive sensitivity analyses and statistics-based processing approaches are used to identify the role of the background noise that affects the whole dataset. This noise has a directly proportional relationship to the different geometric and temporal resolutions of the processed imagery. Moreover, the accuracy of the environmental-instrumental background noise evaluation allowed the actual displacement measurements to be correctly calibrated and validated, thereby leading to a better definition of the threshold values of the maximum Digital Image Correlation sub-pixel accuracy and reliability (ranging from 1/10 to 8/10 pixel) for each processed dataset

Enabling Distributed Knowledge Management: Managerial and Technological Implications

In this paper we show that the typical architecture of current KM systems re.ects an objectivistic epistemology and a traditional managerial control paradigm. We argue that such an objectivistic epistemology is inconsistent with many theories on the nature of knowledge, in which subjectivity and sociality are taken as essential features of knowledge creation and sharing. We show that adopting such a new epistemological view has dramatic consequences at an architectural, managerial and technological level