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The observability of isolated neutron stars and black holes.
No full textThe detection of old neuron stars and black holes in isolation is one of the cornerstones of compact object astrophysics. However, forty years after the first pioneering studies, no succesful candidates have been found to confirm the early predictions, making the search for old isolated compact objects a still open and intriguing subject. The scope of this thesis is thus to investigate the observability of isolated neutron stars and black holes with the final objective of defining new possible strategies for the long sought detection of these elusive objects.
The thesis is organized as follows. In Chapter 1, after a short discussion on the origin of neuron stars and stellar mass black holes in isolation, I summarize the results of past efforts made to constrain their observational properties.
In Chapter 2 I tackle with the dynamics of isolated neutron stars. I describe the set up of a numerical Monte Carlo code, named Population Synthesis of Compact Objects (PSYCO in brief), developed as part of the PhD project. I then present the results of the simulation with particular emphasis for statistical properties of neutron stars in the Galactic disk and in the solar neighbourhood. These first results will be used as base to explore alternative methods to detect old neutron stars and black holes. It should be noted that, following the standard practice, these first results are obtained considering only neutron stars born in the disk of the Milky Way. As it will be shown in Chapter 3, the contribution of neutron stars, and black holes, born in the Galactic bulge cannot be neglected since they could represent the majority of detectable objects.
In Chapter 3 the feasibility of microlensing as a technique to detect isolated neutron stars and black holes is explored, making use of the results illustrated in the previous Chapter. After an overview of results obtained so far by the several surveys, I describe the basic microlensing quantities and expressions. I then describe the models adopted in my work for the distribution of bulge and disk stars, to which the contribution of neutron stars and black oles is then compared to. I compare the optical depth and event rate due to neutron stars and black holes with that of normal stars. Also, I study the distribution of event time scales in both cases.
After the results reported in Chapter 3, in Chapter 4 I present a systematic cross correlation analysis of microlensing events with the catalogues of X-rays sources of the XMM-Newton and Chandra satellites, which appeared recently. I report the results of the cross correlation and the properties of a source resulting from the cross correlation procedure.
Finally, in Chapter 5 I review the results of my PhD project and draw the final conclusion. I also discuss possible future developments
Prosystemin coordinates multiple responses in tomato.
No full textIn Solanaceae, a family of peptide hormones called Systemins are involved in the activation of defense genes in response to wounding and herbivory. In tomato, Systemin (Sys) is an 18-aa oligopeptide released from a cytosolic precursor protein of 200 aa called prosystemin (ProSys). ProSys involvement in tomato response to chewing insects has long been described, but little is known about its role in modulating defense responses to phloem-feeding insects or other biotic agents such as pathogenic fungi. The aim of this research activity is to shed more light on ProSys involvement in tomato responses against several stress conditions and to evaluate a possible use of this plant hormone as a broad-spectrum defence instrument. For this reason, tomato cv. “Red Setter” was chosen to over-express ProSys gene since this tomato cultivar lacks the dominant allel at Mi locus, a gene involved in resistance against aphids, nematodes and white flies (Rossi et al., 1998). Solanum lycopersicum cv. “Red Setter” was genetically transformed via A. tumefaciens containing the pMZ vector carrying 35S2:prosystemin, already described by Rocco and collaborators (2008). ProSys conferred-resistance to aphids and fungi was underlined by bioassays. Tomato responses were further investigated by time-course transcriptional analysis of untransformed “Red Setter” plants challenged by aphids or fungi. The comparison with the expression profiles of the same genes in ProSys over-expressing plants underlined that ProSys induces most of the genes associated to tomato responses against these pests. In order to get a global vision of ProSys impact on tomato transcriptome, a microarray analysis was carried out underlining many defence-related differentially expressed genes, most of them supporting these biological evidences. The functional analyses of differentially espressed genes indicated that prosystemin affects genes involved in JA-, SA-, ET and auxin pathways. Molecular data were further investigated in silico to predict networks that highlight protein-protein interactions active in the signaling cascade activated by ProSys gene. This work was carried out at the Bioinformatic Department of “Centro de Investigation Principe Felipe” (CIPF, Valencia). The resulted network contained 195 proteins and highlighted some possible novel interactions such as between the ProSys-regulated ERD4 (early responsive to dehydration) and FPS (pharnesyl pyrophosphate synthase), a promising molecular link between abiotic and biotic response
Advanced manufacturing techniques for X-ray and VHE gamma-ray astronomical mirrors.
No full textThe main theme of this thesis is on the development of the technologies for the future X-ray astronomy telescopes and specifically for the New Hard X-ray Mission and eROSITA (Spectrum-RG) missions. Other important next future X-ray missions, currently under advanced study and/or manufacturing are NuSTAR (USA), ASTRO-H (Japan) and GEMS (USA).
The New Hard X-ray Mission (NHXM) is being developed in Italy as an evolution of the original HEXIT-SAT project and is now the hard x-ray project of reference for the Italian high energy community. NHXM is meant to provide a real breakthrough on a number of hot astrophysical issues, by exploiting the most advanced technology in broad-band (0.2 – 80 keV) high angular resolution (<20 arc seconds HEW) grazing incidence mirrors and spectroscopic detectors, together with the use of a high efficiency imaging polarimeter. Such issues can be summarized in two main headings:
● making the census of the population of black holes in the Universe and probing the physics of accretion in the most diverse conditions;
● investigating the particle acceleration mechanisms at work in different contexts, and the effects of radiative transfer in highly magnetized plasmas and strong gravitational fields.
These topics were identified as top priority in the study commissioned by the Italian Space Agency (ASI) in 2004 to the Italian scientific community with contracts involving Thales-Alenia Space Italy (TAS-I, Turin), the Media Lario Technologies (MLT, Lecco) company and the INAF institution. NHXM benefits from the phase A study of the canceled French-Italian-German SIMBOL-X mission (2007-2008) and has been recently subjected to a scientific phase B study financed by ASI. Media Lario Technologies company received a contract from ASI in 2009 for a Technology Development Program (ASI-TDP) aiming at improving the technology readiness level with also in-house adoption of hardware for the metrology/manufacturing of the multilayer x-ray optics.
Spectrum-RG is a Russian - German x-ray astrophysical observatory scheduled for lunch in 2013. German Space Agency (DLR) is responsible for the development of the key mission instrument - the x-ray grazing incident mirror telescope eROSITA. The second experiment is ART-XC - an x-ray mirror telescope with a harder response than eROSITA, which is being developed by Russia (IKI, Moscow and VNIIEF, Sarov). The name eROSITA stands for extended Roentgen Survey with an Imaging Telescope Array. The general design of the eROSITA x-ray telescope is derived from that of ABRIXAS: a bundle of 7 mirror modules with short focal lengths make up a compact telescope which is ideal for survey observations. Similar designs had been proposed for the missions DUO and ROSITA but were not realized. Compared to those, however, the effective area in the soft x-ray band has now much increased by adding 27 additional outer mirror shells to the original 27 ones of each mirror module. The requirement on the on-axis resolution has also been confined, namely to 15 arc seconds HEW. For these reasons the prefix “extended” to the original name “ROSITA” had been added. The scientific motivation for this extension is founded in the ambitious goal to detect about 100000 clusters of galaxies which trace the large scale structure of the Universe in space and time.
The main scientific goals are:
● to detect the hot intergalactic medium of 50-100 thousand galaxy clusters and groups and hot gas in filaments between clusters to map out the large scale structure in the Universe for the study of cosmic structure evolution;
● to detect systematically all obscured accreting Black Holes in nearby galaxies and many (up to 3 Million) new, distant active galactic nuclei;
● to study in detail the physics of galactic x-ray source populations, like pre-main sequence stars, supernova remnants and x-ray binaries.
Max-Planck-Institute für extraterrestrische Physik (MPE) is the scientific institute responsible for the eROSITA Payload. Media Lario Technologies (MLT) is the industrial enabler for the manufacturing of the Optical Payload for eROSITA - including the flight quality mandrels, and it is currently in the C/D Phase of the project.
The research activity described in this thesis has been carried out at Media Lario Technologies company and at the Brera Astronomical Observatory under the supervision of INAF-OAB researchers Dott. Giovanni Pareschi and Dott. Gianpiero Tagliaferri. The research activity of the author of this thesis is focused on the development of an advance polishing technique for the mandrels to be used as masters in the mirrors replication by electroforming. The goal is to implement a process where the mandrels can be manufactured with a high accuracy (< 6 arc seconds HEW) and low roughness (< 0.2 nm rms) within a consistent short time. In the contest of the eROSITA and NHXM (projects currently running in MLT) the author participated as technical/scientific responsible, investigating innovative mandrels manufacturing technologies (e.g. Single Point Diamond Turning, shape corrective polishing) representing an evolution of the standard approach used so far. In this frame the author has also contributed to the adoption of a customized deterministic polishing machine and a customized 3D metrology device for the mandrel geometrical characterization.
An additional research activity, performed by the author at Media Lario Technologies company and at the Brera Astronomical Observatory, is focused on the development of lightweight glass mirrors manufactured via cold-slumping technique for Imaging Atmospheric Cherenkov Telescopes (IACT). Very High Energy (VHE) gamma rays, with photon energies in the TeV range, can be detected by ground based experiments. In fact, such high energy photons interact high in the upper atmosphere and generate an air shower of secondary particles. These particles emit the so-called Cherenkov light, a faint blue light. The mirror elements here developed have a sandwich-like structure where the reflecting and backing facets are composed by glass sheets with an interposed honeycomb aluminum core. This effort found application at the world’s largest IACT, the 17m MAGIC II telescope (currently operating in Roque de los Muchachos - La Palma, Canary Islands), where 112 mirrors (~ 1 squared meter each), manufactured with the newly developed cold-slumping technique here described, are installed
CDKL5 regulates neuronal polarization of hippocampal neurons through interaction with shootin1.
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Il capello come matrice per il monitoraggio della esposizione ad antiparassitari.
No full textThis Thesis is based mainly on the results of the timing analysis applied to the gamma-ray pulsars observed principally by the AGILE satellite and also extended, in some cases, to observations with the Fermi-LAT satellite and the MAGIC Cherenkov telescope. Aim of this extended study of pulsars at the high energies was to characterize their properties based, now, on a more statistically relevant sample, and be able to disentangle useful informations that can be key to explain the emission mechanisms in pulsars.
THE SCIENTIFIC CONTEXT Pulsars are highly-magnetized, rapidly-rotating neutron stars. As explained in Chapter 1, they have been observed in the radio band over the past forty years, due to their highly anisotropic emission, which, when combined with the misalignment between the rotation and the magnetic axis, produces the pulsed emission we observed, also called the ”lighthouse effect”. Pulsars have been observed as gamma-ray emitters as well, but it is only in the past three years that their number hit the double digits and they started to yield their potential as keys to explain the neutron stars mechanisms.
In Chapter 1, the basics of pulsar theory are given. While the phenomenological aspects have been widely studied thanks to extensive radio observations through the years, their electrodynamics represents an articulated field that is difficult to probe. The ”classical” models of magnetosphere predict the presence of regions of particles’ under-density (a ”gap”), inside an overall force-free magnetized area that surrounds the pulsar, where the particles can be accelerated and can produce the observed radiation, after a number of cascade processes. More ”modern” models of magnetosphere, with their roots in old predictions, discuss the hypothesis of a totally force-free magnetosphere. The discussed theories search for a confirmation in our gamma-ray observations, as the gamma-rays are the ones carrying away a good fraction of the rotational energy loss.
THE NEW PERSPECTIVES OPENED BY THE MULTI-BAND OBSERVATIONS
In April 2007 the Italian Space Agency launched the AGILE satellite for gamma-ray astronomy. About one year later, AGILE was joined in the observation of gammarays by the 16 times bigger Fermi-LAT satellite launched by NASA. AGILE and Fermi-LAT, with their wide field of view and large collective area, are particularly suited for the study of pulsars at high energies. Most recently, the window of veryhigh energy observations has opened up to pulsar studies and, in particular, by the MAGIC telescope, with the lowest up to now threshold for ground-based telescopes, at 25 GeV. Its observations are briefly described, together with AGILE and Fermi-LAT’s, in Chapter 2.
The techniques for studying pulsars in the gamma-rays are also explained in Chapter 2, with the fundamental premise about the radio observations which were part of my analysis work, as they constitute the primary basis for the gammaray observations. The advances with respect to the observations of the previous generation gamma-ray instruments are highlighted. In particular, AGILE was able to take into account, for the first time in gamma-ray observations, the timing noise that affects young pulsars. In this way, the observations can be carried out for longer time spans without being affected by sensible light curve smearing. Thus, we could take advantage of the long time span, up to now the longest for gamma-ray observations, to increase the resolution of our light curves and see structures at the sub-millisecond level.
GAMMA-RAY PULSARS AGILE and Fermi-LAT pulsar observations first concentrated on the known gamma-ray pulsars. As shown in Chapter 3, the apparently ”familiar” pulsars actually hid thriving new prospects for pulsar studies, as well as the new pulsars subsequently detected, described in Chapter 4.
In these two Chapters, the properties of the gamma-ray emission ars analyzed for a number of pulsars, mainly using AGILE data, but also with Fermi-LAT and MAGIC observations. The light curves are investigated with increased resolution from previous observations and the spectral properties are addressed. The availability of a statistically significant sample of gamma-ray pulsars led us to draw some lines on the models. The classical polar cap model seems to be failing the test of gamma-ray observations for most of the present sample, and a simple explanation of which can be found in conservation laws arguments discussed in Chapter 4. At the same time it starts getting clear that a model that contemplates a single gap zone does not seem to be feasible to explain the observed pulse profiles. And, possibly, the entire gap theory should be combined with the more physical force-free models.
Episodes of variability in pulsars have been observed and studied in this context. The Vela glitch of August 2007 was observed by AGILE in search for gamma-ray emission. The Crab pulsar could have a contribution to the emission from a newly observed third pulsar peak, that is less significant and much weaker than the canonical two, and could be due to giant pulses. AGILE observed the first gamma-ray millisecond pulsar but its emission only appeared in a restricted time interval, leading to the interesting possibility that pulsar emission might have some intrinsic variability.
HIGH MAGNETIC FIELD PULSARS After the advent of Fermi-LAT, AGILE found its collocation in the gamma-ray astronomy in the characterization of the low-energy gamma-rays (from 30 to 100 MeV), where the collective areas of the two instruments is equivalent, but AGILE deals with much lower background. For this reason, we concentrated on those pulsars that show a low-energy cutoff, which were theorized to emit gamma-ray radiation through the exotic QED process of photon splitting.
A detailed analysis of the two most significant cases is given in Chapter 5. We have found that the concurrence of a high magnetic field and an aligned geometry, could overcome the objections from Chapter 4 against inner magnetosphere emission and be, indeed, dominated by polar cap emission. Interestingly, this phenomenology, that is observed in pulsars that are similar to magnetars, may be observed in objects that are transitioning from pulsar to magnetar.
THE ENVIRONMENT OF PULSARS Young pulsars are known to power a relativistic wind of particles that surrounds the pulsar and is best known as its Pulsar Wind Nebula (PWN). Important phenomena take place in the PWN and they are powered by the pulsar inside it. As discussed in Chapter 6, very high energy emission was already observed from PWN, but high energy emission was missing, in a spectral region where important constraints on the emission processes could be given.
AGILE was the first satellite to detect GeV emission from a PWN apart from Crab, Vela X, and it was also the first to claim the unexpected flux variation in the Crab Nebula which underwent two intense flares in 2010 and 2011. In Chapter 6 we give a description of the events and a possible trail for an interpretation, although no clear picture can yet emerge from the observed events.
CONCLUSIONS AND FUTURE PROSPECTS The multi-band approach that has been used for the observations described in this Thesis has proven valid for the exploitation of new science and the most useful approach for the comprehensive analysis of pulsar phenomena across the electromagnetic spectrum. As a completion to this work, the more comprehensive AGILE Pulsar Catalog is in preparation. It will comprise all the pulsars observed by AGILE and particularly focus on the low-energy tail of them, which present interesting properties that bridge pulsars and magnetars
Mechanics and fluid-dynamics of the initial lymphatic system.
No full textThe diaphragmatic lymphatic system drains fluid and solutes from the pleural and peritoneal cavities by exploiting pressure gradients (ΔPTM = Plymph-Pint ) between the vessel lumen and the interstitium; while lymph progression is sustained by pressure gradients (ΔPl = Plymph2–Plymph1) between adjacent lymphatic segments. The aim of the study is to examine the pattern of fluid fluxes in the lymphatics, determining the role of tissue and vessel wall in the transmission of tissue forces to the lymphatic lumen and clarifying whether the organization of the diaphragmatic network might be a tool to optimize lymphatic absorption and/or progression. Experiments were performed in anesthetized, paralysed and mechanically ventilated rats. Lymph hydraulic pressure and flux were recorded by the micropuncture technique combined with fluorescent dextrans injection to visualise lymph flow. Flow velocity and direction were calculated by measuring the fluorescence progression and vessel diameter on acquired videos. Mechanical compliance of the vessel wall was measured by sequential injections of saline solution into the vessel, while recording Plymph. The presence of muscular fibers around the lymphatic vessel wall was investigated by immunofluorescence assay.
Two populations of vessels were identified with different mechanical properties: compliant vessels work as reservoirs of drained lymph, stiffer vessels propel fluid along the network. Flow direction and amplitude vary with time and, with respect to the Plymph pressure gradient, flow direction in some vessels reverts multiple times independently from both cardiac and ventilatory action
Advanced languages and techniques for trust negotiation.
No full textThe Web is quickly shifting from a document browsing and delivery system to a hugely complex ecosystem of interconnected online applications. A relevant portion of these applications dramatically increase the number of users required to dynamically authenticate themselves and to, on the other hand, to identify the service they want to use. In order to manage interactions among such users/services is required a flexible but powerful mechanism.
Trust management, and in particular trust negotiation techniques, is a reasonable solution.
In this work we present the formalization of the well known trust negotiation framework Trust-X, of a rule-based policy definition language, called X-RNL.
Moreover, we present the extension of both the framework and of the language to provide advanced trust negotiation architectures, namely negotiations among groups.
We also provide protocols to adapt trust negotiations to mobile environments, specifically, we present protocols allowing a trust negotiation to be executed among several, distinct, sessions while still preserving its security properties. Such protocols have also been extended to provides the capability to migrate a ongoing trust negotiation among a set of known, reliable, subjects.
Finally, we present the application of the previously introduced trust negotiation techniques into real world scenarios: online social networks, critical infrastructures and cognitive radio networks