The Progenitors of Recent Core-Collapse Supernovae

We present the results of our analysis of Hubble Space Telescope (HST) and deep ground-based images to isolate the massive progenitor stars of the two recent core-collapse supernovae 2008 bk and 2008 cn. The identification of the progenitors is facilitated in one of these two cases by high-precision astrometry based on our HST imaging of SNe at late times

The Brera Multi-scale Wavelet (BMW) ROSAT HRI source catalog. I: the algorithm

We present a new detection algorithm based on the wavelet transform for the analysis of high energy astronomical images. The wavelet transform, due to its multi-scale structure, is suited for the optimal detection of point-like as well as extended sources, regardless of any loss of resolution with the off-axis angle. Sources are detected as significant enhancements in the wavelet space, after the subtraction of the non-flat components of the background. Detection thresholds are computed through Monte Carlo simulations in order to establish the expected number of spurious sources per field. The source characterization is performed through a multi-source fitting in the wavelet space. The procedure is designed to correctly deal with very crowded fields, allowing for the simultaneous characterization of nearby sources. To obtain a fast and reliable estimate of the source parameters and related errors, we apply a novel decimation technique which, taking into account the correlation properties of the wavelet transform, extracts a subset of almost independent coefficients. We test the performance of this algorithm on synthetic fields, analyzing with particular care the characterization of sources in poor background situations, where the assumption of Gaussian statistics does not hold. For these cases, where standard wavelet algorithms generally provide underestimated errors, we infer errors through a procedure which relies on robust basic statistics. Our algorithm is well suited for the analysis of images taken with the new generation of X-ray instruments equipped with CCD technology which will produce images with very low background and/or high source density.Comment: 8 pages, 6 figures, ApJ in pres

HST's view of the youngest massive stars in the Magellanic Clouds

Accurate physical parameters of newborn massive stars are essential ingredients to shed light on their formation, which is still an unsolved problem. The rare class of compact H II regions in the Magellanic Clouds (MCs), termed ``high-excitation blobs'' (HEBs), presents a unique opportunity to acquire this information. These objects (~ 4" to 10", ~ 1 to 3 pc, in diameter) harbor the youngest massive stars of the OB association/molecular cloud complexes in the MCs accessible through high-resolution near-IR and optical techniques. We present a brief overview of the results obtained with HST mainly on two HEBs, one in the LMC (N159-5) and the other in the SMC (N81).Comment: 5 pages, to appear in the Proceedings of the 41st ESLAB Symposium "The Impact of HST on European Astronomy", 29 May to 1 June 2007, ESTEC, Noordwijk, Netherlands; eds. Guido De Marchi and Duccio Macchett

Repulsive Casimir Force: Sufficient Conditions

In this paper the Casimir energy of two parallel plates made by materials of different penetration depth and no medium in between is derived. We study the Casimir force density and derive analytical constraints on the two penetration depths which are sufficient conditions to ensure repulsion. Compared to other methods our approach needs no specific model for dielectric or magnetic material properties and constitutes a complementary analysis.Comment: 11 pages. 3 figures. Misprints corrected in Eq. (4

Digitalizing Circular Economy through Blockchains: The Blockchain Circular Economy Index

The integration of circular economy (CE) models into everyday contexts generates huge amount of data involved in goods tracking and tokenization procedures. The sector of blockchain platforms is extremely varied, and the choice of the proper technology is not easy. It is important that the selection is conducted consistently with respect to the CE models. With this study, we present a performance index named Blockchain Circular Economy Index (BCEI). BCEI, obtained through Multicriteria Decision Analysis and Analytic Hierarchy Process, aims to measure the suitability of blockchain platforms to the needs highlighted by a CE scenario. The present study is contextualized by comparing six blockchain platforms, for each of which, the related BCEI is calculated. The results of the analysis show that transaction fee and energy consumption are the two most critical parameters. In addition, the results show the lack of a leading blockchain technology in CE models. Thus, there is a market space that can be exploited given the growing interest in digital and sustainable issues

Permutation symmetry for the tomographic probability distribution of a system of identical particles

The symmetry properties under permutation of tomograms representing the states of a system of identical particles are studied. Starting from the action of the permutation group on the density matrix we define its action on the tomographic probability distribution. Explicit calculations are performed in the case of the two-dimensional harmonic oscillator.Comment: 13 pages, latex, no figure