The 2-10 keV emission properties of PSR B1937+21

We present the results of a BeppoSAX observation of the fastest pulsar known: PSR B1937+21. The ~ 200 ks observation (78.5 (34) ks MECS (LECS) exposure times) allowed us to investigate with high statistical significance both the spectral properties and the pulse profile shape. The absorbed power law spectral model gave a photon index of ~ 1.7 and N_H ~ 2.3 x 10^22 cm^-2. These values explain both a) the ROSAT non-detection and b) the deviant estimate of a photon index of ~ 0.8 obtained by ASCA. The pulse profile appears, for the first time, clearly double peaked with the main component much stronger than the other. The statistical significance is 10 sigma (main peak) and 5 sigma (secondary peak). The 1.6-10 keV pulsed fraction is consistent with 100%; only in the 1.6-4 keV band there is a ~ 2 sigma indication for a DC component. The secondary peak is detected significantly only for energies above 3 / 4 keV. The unabsorbed (2-10 keV) flux is F_2-10 = 3.7 x 10^-13 erg cm^-2 s^-1, implying a luminosity of L_X = 4.6 x 10^31 Theta (d/3.6 kpc)^2 erg s^-1 and an X-ray efficiency of eta = 4 x 10^-5 Theta, where Theta is the solid angle spanned by the emission beam. These results are in agreement with those obtained by ASCA.Comment: 4 pages, 4 figures, 2 tables. To appear in the Proceedings of the 270. WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan. 21-25, 2002, Physikzentrum Bad Honnef, eds W. Becker, H. Lesch & J. Truemper. Proceedings are available as MPE-Report 27

Escaping the evolutionary trap: Can size-related contest advantage compensate for juvenile mortality disadvantage when parasitoids develop in unnatural invasive hosts?

The quality of hosts for a parasitoid wasp may be influenced by attributes such as host size or species, with high quality for successful development usually coincident with high quality for larger offspring. This is not always the case: for the Scelionid wasp Trissolcus basalis, oviposition in eggs of the Brown Marmorated Stink Bug, Halyomorpha halys, rather than of the normal host, the Southern Green Stink Bug, Nezara viridula, leads to lower offspring survival, but survivors can be unusually large. Adult female T. basalis engage in contests for host access. As larger contestants are typically favoured in contests between parasitoids, the larger size of surviving offspring may compensate for the mortality of others. We construct a general game-theoretic model to explore whether size advantage can sustain a maternal preference to utilize a more deadly host species. We find that size advantage alone is unlikely to sustain a shift in host preference, yet such an outcome is possible when size asymmetries act simultaneously with advantages in host possession (ownership effect). Halyomorpha halys is an invasive pest of major agro-economic importance in Europe and the Americas, and use of its eggs as hosts by native parasitoids such as T. basalis has been seen as an evolutionary trap due to their high developmental mortality. Our model suggests that the recently discovered effect of host choice on offspring size may provide an escape from the trap via effects on contest biology of T. basalis which could foster a more stable association with H. halys. An evolutionary shift in the reproductive value of H. halys could increase the efficiency of T. basalis as a biological control agent of this invasive stink bug pest

Responsabilità e merito nel mondo antico. Retorica, Giustizia, Società. Atti del Convegno di Palermo, 10-11 febbraio 2016

"Merit and Responsability. A Study in Greek Values" è il titolo di un volume pubblicato ormai cinquant’anni or sono da W.H. Adkins. L’autore metteva in evidenza il mancato sviluppo, nel mondo greco, del concetto di responsabilità morale a vantaggio della nozione di arete, postulando la distanza irriducibile tra l’etica greca e quella contemporanea. Quelle di responsabilità e merito sono in effetti categorie su cui la cultura contemporanea si è notevolmente esercitata e continua a interrogarsi, soprattutto in questi anni caratterizzati da un sentimento di incertezza in tutti gli aspetti della nostra esistenza e in particolare nell’agire quotidiano e nelle relazioni sociali. E tuttavia si tratta di un insieme di riflessioni su cui il pensiero antico molto ha ancora da dirci, spesso con una complessità e una sensibilità sorprendenti

Responsabilit\ue0 e merito nel mondo antico. Retorica, Giustizia, Societ\ue0. Atti del Convegno di Palermo, 10-11 febbraio 2016

"Merit and Responsability. A Study in Greek Values" \ue8 il titolo di un volume pubblicato ormai cinquant\u2019anni or sono da W.H. Adkins. L\u2019autore metteva in evidenza il mancato sviluppo, nel mondo greco, del concetto di responsabilit\ue0 morale a vantaggio della nozione di arete, postulando la distanza irriducibile tra l\u2019etica greca e quella contemporanea. Quelle di responsabilit\ue0 e merito sono in effetti categorie su cui la cultura contemporanea si \ue8 notevolmente esercitata e continua a interrogarsi, soprattutto in questi anni caratterizzati da un sentimento di incertezza in tutti gli aspetti della nostra esistenza e in particolare nell\u2019agire quotidiano e nelle relazioni sociali. E tuttavia si tratta di un insieme di riflessioni su cui il pensiero antico molto ha ancora da dirci, spesso con una complessit\ue0 e una sensibilit\ue0 sorprendenti

BeppoSAX observation of the X-ray binary pulsar Vela X-1

We report on the spectral (pulse averaged) and timing analysis of the ~ 20 ksec observation of the X-ray binary pulsar Vela X-1 performed during the BeppoSAX Science Verification Phase. The source was observed in two different intensity states: the low state is probably due to an erratic intensity dip and shows a decrease of a factor ~ 2 in intensity, and a factor 10 in Nh. We have not been able to fit the 2-100 keV continuum spectrum with the standard (for an X--ray pulsar) power law modified by a high energy cutoff because of the flattening of the spectrum in ~ 10-30 keV. The timing analysis confirms previous results: the pulse profile changes from a five-peak structure for energies less than 15 keV, to a simpler two-peak shape at higher energies. The Fourier analysis shows a very complex harmonic component: up to 23 harmonics are clearly visible in the power spectrum, with a dominant first harmonic for low energy data, and a second one as the more prominent for energies greater than 15 keV. The aperiodic component in the Vela X-1 power spectrum presents a knee at about 1 Hz. The pulse period, corrected for binary motion, is 283.206 +/- 0.001 sec.Comment: 5 pages, 4 PostScript figure, uses aipproc.sty, to appear in Proceedings of Fourth Compton Symposiu