Showing papers by "Roma Tre University published in 2002"

Chandra Deep Field South: The 1 Ms Catalog

Abstract: In this paper we present the source catalog obtained from a 942 ks exposure of the Chandra Deep Field South (CDFS), using the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory. Eleven individual pointings made between 1999 October and 2000 December were combined to generate the final image used for object detection. Catalog generation proceeded simultaneously using two different methods; a method of our own design using a modified version of the SExtractor algorithm, and a wavelet transform technique developed specifically for Chandra observations. The detection threshold has been set in order to have less than 10 spurious sources, as assessed by extensive simulations. We subdivided the catalog into four sections. The primary list consists of objects common to the two detection methods. Two secondary lists contain sources which were detected by (1) the SExtractor algorithm alone and (2) the wavelet technique alone. The fourth list consists of possible diffuse or extended sources. The flux limits at the aimpoint for the soft (0.5-2 keV) and hard (2-10 keV) bands are 5.5 × 10-17 erg s-1 cm-2 and 4.5 × 10-16 erg s-1 cm-2, respectively. The total number of sources is 346; out of them, 307 were detected in the 0.5-2 keV band, and 251 in the 2-10 keV band. We also present optical identifications for the cataloged sources. Our primary optical data are R band imaging from VLT/FORS1 to a depth of R ~ 26.5 (Vega). In regions of the field not covered by the VLT/FORS1 deep imaging, we use R-band data obtained with the Wide Field Imager (WFI) on the ESO-MPI 2.2 m telescope, as part of the ESO Imaging Survey (EIS), which cover the entire X-ray survey. We found that the FORS1/Chandra offsets are small, ~1''. Coordinate cross-correlation finds 85% of the Chandra sources covered by FORS1 R to have counterparts within the 3 σ error box (15 depending on off-axis angle and X-ray signal-to-noise). The unidentified fraction of sources, approximately ~10%-15%, is close to the limit expected from the observed X-ray flux to R-band ratio distribution for the identified sample.

The Chandra Deep Field-South: The 1 Million Second Exposure*

Abstract: We present the main results from our 940 ks observation of the Chandra Deep Field-South using the source catalog described in an accompanying paper by Giacconi et al. We extend the measurement of source number counts to 5.5 × 10-17 ergs cm-2 s-1 in the soft 0.5-2 keV band and 4.5 × 10-16 ergs cm-2 s-1 in the hard 2-10 keV band. The hard-band log N-log S shows a significant flattening (slope 0.6) below ≈10-14 ergs cm-2 s-1, leaving at most 10%-15% of the X-ray background to be resolved, the main uncertainty lying in the measurement of the total flux of the X-ray background (XRB). On the other hand, the analysis in the very hard 5-10 keV band reveals a relatively steep log N-log S (slope 1.3) down to 10-15 ergs cm-2 s-1. Together with the evidence of a progressive flattening of the average X-ray spectrum near the flux limit, this indicates that there is still a nonnegligible population of faint hard sources to be discovered at energies not well probed by Chandra, which possibly contributes to the 30 keV bump in the spectrum of the XRB. We use optical redshifts and identifications, obtained with the Very Large Telescope, for one-quarter of the sample to characterize the combined optical and X-ray properties of the Chandra Deep Field-South sample. Different source types are well separated in a parameter space that includes X-ray luminosity, hardness ratio, and R-K color. Type II objects, while redder on average than the field population, have colors that are consistent with being hosted by a range of galaxy types. Type II active galactic nuclei are mostly found at z 1, in contrast with predictions based on active galactic nucleus population synthesis models, thus suggesting a revision of their evolutionary parameters.

Neuroglobin and cytoglobin. Fresh blood for the vertebrate globin family.

Abstract: Neuroglobin and cytoglobin are two recently discovered members of the vertebrate globin family. Both are intracellular proteins endowed with hexacoordinated heme-Fe atoms, in their ferrous and ferric forms, and display O2 affinities comparable with that of myoglobin. Neuroglobin, which is predominantly expressed in nerve cells, is thought to protect neurons from hypoxic–ischemic injury. It is of ancient evolutionary origin, and is homologous to nerve globins of invertebrates. Cytoglobin is expressed in many different tissues, although at varying levels. It shares common ancestry with myoglobin, and can be traced to early vertebrate evolution. The physiological roles of neuroglobin and cytoglobin are not completely understood. Although supplying cells with O2 is the likely function, it is also possible that both globins act as O2-consuming enzymes or as O2 sensors. Here, we review what is currently known about neuroglobin and cytoglobin in terms of their function, tissue distribution and relatedness to the well-known hemoglobin and myoglobin. Strikingly, the data reveal that O2 metabolism in cells is more complicated than was thought before, requiring unexpected O2-binding proteins with potentially novel functional features.

Iron transport and regulation, cell signalling and genomics: lessons from Escherichia coli and Pseudomonas.

Abstract: A variety of bacterial species secrete and take up chelating compounds that enable acquisition of iron (siderophores). It has become clear that a common feature in regulation of different iron acquisition systems is the involvement of alternative sigma factor proteins of the extracytoplasmic function (ECF) family. Two of these proteins, PvdS from Pseudomonas aeruginosa and FecI from Escherichia coli K-12, have been studied extensively. PvdS directs transcription of genes required for the biosynthesis of a siderophore, pyoverdine, and FecI causes expression of genes for uptake of ferric citrate. FecI forms part of a signalling system that responds to the presence of ferric citrate. Here, we review recent advances in understanding of PvdS and of the Fec signalling system. PvdS and FecI are part of a distinct subfamily of ECF sigma factors involved in iron acquisition and hence named the iron-starvation sigmas. Analysis of microbial genome sequences shows that Fec-like signalling systems are present in a wide range of species and many such systems may be present in a single species. The availability of tools for large-scale genome analysis is likely to lead to rapid advances in our understanding of this expanding family of proteins.

The tracking detector of the KLOE experiment

Abstract: The design and construction of the large Drift Chamber for the KLOE experiment at the Frascati φ-factory, DAΦNE, are described. The relevant aspects of the various elements of the detector are reviewed together with a description of the track reconstruction program and of the calibration procedures. The performance of the detector based on measurements with cosmic rays and with e+e− colliding beams during DAΦNE commissioning is presented.

Compton reflection and iron fluorescence in BeppoSAX observations of Seyfert type 1 galaxies

Abstract: A sample of nine bright Seyfert 1 and NELG type galaxies, observed with BeppoSAX, is analyzed to assess on a truly broad band basis (0.1{200 keV) the issue of the spectral contributions of Compton reflection and iron line fluorescence from circumnuclear gas. The empirical description adopted for the direct continuum is the commonly used power law with an exponential cut{o. The most direct test of the theoretical predictions, namely that the equivalent width of the line, W, and the strength R of the reflection relative to the direct continuum are closely related to each other, gives a substantially positive result, that is their mean ratio is very close to expectation, and only a modest spread in the iron abundance seems implied. The existence of a steep correlation between R and the slope of the power law is not conrmed. A weak evidence is found that the existence of a very shallow trend to increase on average with cannot be altogether excluded in both R and W, but needs to be tested with a larger sample. The energy Ef in the exponential cut{o spans a range from about 80 to more than 300 keV. A possible correlation is found, with Ef increasing on average with : if ignored, for instance by keeping Ef at a xed value in a sample study, it could be cause of articial steepening in a correlation between R and .

Chandra Discovery of a Tree in the X-Ray Forest toward PKS 2155–304: The Local Filament?

Abstract: We present the first X-ray detection of resonant absorption from warm/hot local gas either in our Galaxy, or in the intergalactic space surrounding our Galaxy, along the line of sight toward the blazar PKS 2155-304. The Chandra HRCS/LETG spectrum of this z = 0.116 source clearly shows, at ≥5 σ level, unresolved (FWHM ≤ 800 km s-1 at a 2 σ confidence level) O VII Kα and Ne IX Kα resonant absorption lines at 21.603 and 13.448 A (i.e., cz = 14 km s-1 in the rest frame, from the O VII Kα line). O VIII Kα and O VII Kβ from the same system are also detected at a lower significance level (i.e., ~3 σ), while upper limits are set on O VIII Kβ, Ne X Kα, and Ne IX Kβ. The Far Ultraviolet Spectroscopic Explorer spectrum of this source shows complex O VI 2s→2p absorption at the same redshift as the X-ray system, made by at least two components: one relatively narrow (FWHM = 106 ± 9 km s-1) and slightly redshifted (cz = 36 ± 6 km s-1), and one broader (FWHM = 158 ± 26 km s-1) and blueshifted (cz = -135 ± 14 km s-1). We demonstrate that the physical states of the UV and X-ray absorbers are hard to reconcile with a single, purely collisionally ionized, equilibrium plasma. We propose instead that the X-ray and at least the broader and blueshifted UV absorber are produced in a low-density intergalactic plasma, collapsing toward our Galaxy, consistent with the predictions of a warm-hot intergalactic medium from numerical simulations. We find that any reasonable solution requires overabundance of Ne compared to O by a factor of ~2, with respect to the solar value. We propose several scenarios to account for this observation.

XMM-Newton observation of the Lockman Hole - II. Spectral analysis

Abstract: We present the results of the X-ray spectral analysis of the first deep X-ray survey with the XMM-Newton observa- tory during Performance Verification. The X-ray data of the Lockman Hole field and the derived cumulative source counts were reported by Hasinger et al. (2001). We restrict the analysis to the sample of 98 sources with more than 70 net counts (flux limit in the (0.5-7) keV band of 1:6 10 15 erg cm 2 s 1 ) of which 61 have redshift identification. We find no correlation between the spectral index and the intrinsic absorption column density NH and, for both the Type-1 and Type-2 AGN populations, we obtainh i' 2. The progressive hardening of the mean X-ray source spectrum with decreasing flux is essentially due to an increase in intrinsic absorption. The marked separation between the two AGN populations in several diagnostics diagrams, involving X-ray colour, X-ray flux, optical/near IR colour and optical brightness, is also a consequence of dierent absorption column densities and enables the classification of optically faint obscured AGN. The Type-2 and obscured AGN have weaker soft X-ray and optical fluxes and redder R K 0 colours. They follow the evolutionary tracks of their host galaxies in a color- redshift diagram. About 27% of the subsample with R K 0 colour are EROs (R K 0 5) and most of these 18 X-ray selected EROs contain an obscured AGN as revealed by their high X-ray-to-optical/near IR flux ratios. There are six sources in our sample with LX(0:5 10)> 10 44 erg s 1 and log(NH)> 10 22 cm 2 : which are likely Type-2 QSOs and we thus derive a density of69 objects of this class per square degree.

All-optical switching and logic gating with spatial solitons in liquid crystals

Abstract: Using mW light beams to generate spatial solitons in nematic liquid crystals, all-optical switching/logic can be performed on a signal launched in the soliton-induced waveguides. Through the collisional behavior of solitons in a nonlocal medium, the signal can be steered in angle and output position. A power-dependent X junction, AND, and NOR gates are demonstrated.

Final results of magnetic monopole searches with the MACRO experiment

Abstract: We present the final results obtained by the MACRO experiment in the search for GUT magnetic monopoles in the penetrating cosmic radiation, for the range 4×10 −5 <β< 1. Several searches with all the MACRO sub-detectors (i.e. scintillation counters, limited streamer tubes and nuclear track detectors) were performed, both in stand alone and combined ways. No candidates were detected and a 90% Confidence Level (C.L.) upper limit to the local magnetic monopole flux was set at the level of 1.4 × 10 −16 cm −2 s −1 sr −1 . This result is the first experimental limit obtained in direct searches which is well below the Parker

The HELLAS2XMM Survey. II. Multiwavelength Observations of P3: An X-Ray-bright, Optically Inactive Galaxy*

Abstract: Recent X-ray surveys have clearly demonstrated that a population of optically dull, X-ray–bright galaxies is emerging at 2–10 keV fluxes of the order of 10 � 14 ergs cm � 2 s � 1 . Although they might constitute an important fraction of the sources responsible for the hard X-ray background, their nature is still unknown. With the aim of better understanding the physical mechanisms responsible for the observed properties, we have started an extensive program of multiwavelength follow-up observations of hard X-ray, optically quiet galaxies discovered with XMM-Newton. Here we report the results of what can be considered the first example of this class of objects: CXOU J031238.9� 765134, originally discovered by Chandra, and optically identified by Fiore et al. (2000) with an apparently normal early-type galaxy at z ¼ 0:159, usually known as FIORE P3. Analysis of the broadband energy distribution suggests the presence of a heavily obscured active nucleus. Subject headings: galaxies: active — galaxies: individual (P3) — galaxies: nuclei — X-rays: galaxies

Distinct nongenomic signal transduction pathways controlled by 17β-estradiol regulate DNA synthesis and cyclin D1 gene transcription in HepG2 cells

Abstract: Estrogens induce cell proliferation in target tissues by stimulating progression through the G1 phase of the cell cycle. Activation of cyclin D1 gene expression is a critical feature of this hormonal action. The existence of rapid/nongenomic estradiol-regulated protein kinase C (PKC-α) and extracellular signal-regulated kinase (ERK) signal transduction pathways, their cross talk, and role played in DNA synthesis and cyclin D1 gene transcription have been studied herein in human hepatoma HepG2 cells. 17β-Estradiol was found to rapidly activate PKC-α translocation and ERK-2/mitogen-activated protein kinase phosphorylation in this cell line. These actions were independent of each other, preceding the increase of thymidine incorporation into DNA and cyclin D1 expression, and did not involve DNA binding by estrogen receptor. The results obtained with specific inhibitors indicated that PKC-α pathway is necessary to mediate the estradiol-induced G1-S progression of HepG2 cells, but it does not exert any effect(s) on cyclin D1 gene expression. On the contrary, ERK-2 cascade was strongly involved in both G1-S progression and cyclin D1 gene transcription. Deletion of its activating protein-1 responsive element motif resulted in attenuation of cyclin D1 promoter responsiveness to estrogen. These results indicate that estrogen-induced cyclin D1 transcription can occur in HepG2 cells independently of the transcriptional activity of estrogen receptor, sustaining the pivotal role played by nongenomic pathways of estrogen action in hormone-induced proliferation.

Probabilistic Expert Systems for Forensic Inference from Genetic Markers

Abstract: We present a number of real and fictitious examples in illustration of a new approach to analysing complex cases of forensic identification inference. This is effected by careful restructuring of the relevant pedigrees as a Probabilistic Expert System. Existing software can then be used to perform the required inferential calculations. Specific complications which are readily handled by this approach include missing data on one or more relevant individuals, and genetic mutation. The method is particularly valuable for disputed paternity cases, but applies also to certain criminal cases.

Copper amine oxidase expression in defense responses to wounding and Ascochyta rabiei invasion.

Abstract: Wounding chickpea (Cicer arietinum) internodes or cotyledons resulted in an increase in the steady-state level of copper amine oxidase (CuAO) expression both locally and systemically. Dissection of the molecular mechanisms controlling CuAO expression indicated that jasmonic acid worked as a potent inducer of the basal and wound-inducible CuAO expression, whereas salicylic acid and abscisic acid caused a strong reduction of the wound-induced CuAO expression, without having any effect on the basal levels. Epicotyl treatment with the CuAO mechanism-based inhibitor 2-bromoethylamine decreased hydrogen peroxide (H2O2) levels in all the internodes, as evidenced in vivo by 3,3′-diaminobenzidine oxidation. Moreover, inhibitor pretreatment of wounded epicotyls resulted in a lower accumulation of H2O2 both at the wound site and in distal organs. In vivo CuAO inhibition by 2-bromoethylamine after inoculation of resistant chickpea cv Sultano with Ascochyta rabiei resulted in the development of extended necrotic lesions, with extensive cell damage occurring in sclerenchyma and cortical parenchyma tissues. These results, besides stressing the fine-tuning by key signaling molecules in wound-induced CuAO regulation, demonstrate that local and systemic CuAO induction is essential for H2O2 production in response to wounding and indicate the relevance of these enzymes in protection against pathogens.

The Miocene tectono‐sedimentary evolution of the southern Tyrrhenian Sea: stratigraphy, structural and palaeomagnetic data from the on‐shore Amantea basin (Calabrian Arc, Italy)

Abstract: We report on new stratigraphic, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) results from the Amantea basin, located on-shore along the Tyrrhenian coast of the Calabrian Arc (Italy). The Miocene Amantea Basin formed on the top of a brittlely extended upper plate, separated from a blueschist lower plate by a low-angle top-to-the-west extensional detachment fault. The stratigraphic architecture of the basin is mainly controlled by the geometry of the detachment fault and is organized in several depositional sequences, separated by major unconformities. The first sequence (OSI) directly overlaps the basement units, and is constituted by Serravallian coarse-grained conglomerates and sandstones. The upper boundary of this sequence is a major angular unconformity locally marked by a thick palaeosol (type 1 sequence boundary). The second depositional sequence OS2 (middle Tortonian-early Messinian) is mainly formed by conglomerates, passing upwards to calcarenites, sandstones, claystones and diatomites. Finally, Messinian limestones and evaporites form the third depositional sequence (OS3). Our new biostratigraphic data on the Neogene deposits of the Amantea basin indicate a hiatus of 3Ma separating sequences OSI and OS2. The structural architecture of the basin is characterized by faulted homoclines, generally westward dipping, dissected by eastward dipping normal faults. Strike-slip faults are also present along the margins of the intrabasinal structural highs. Several episodes of syn-depositional tectonic activity are marked by well-exposed progressive unconformities, folds and capped normal faults. Three main stages of extensional tectonics affected the area during Neogene-Quaternary times: (1) Serravallian low-angle normal faulting; (2) middle Tortonian high-angle syn-sedimentary normal faulting; (3) Messinian-Quaternary high-angle normal faulting. Extensional tectonics controlled the exhumation of high-P/low-T metamorphic rocks and later the foundering of the Amantea basin, with a constant WNW-ESE stretching direction (present-day coordinates), defined by means of structural analyses and by AMS data. Palaeomagnetic aoalyses performed mainly on the claystone deposits of OS1 show a post-Serravallian clockwise rotation of the Amantea basin. The data presented in this paper constrain better the overall timing, structure and kinematics of the early stages of extensional tectonics of the southern Tyrrhenian Sea. In particular, extensional basins in the southern Tyrrhenian Sea opened during Serravallian and evolved during late Miocene. These data confirm that, at that time, the Amantea basin represented the conjugate extensional margin of the Sardinian border, and that it later drifted south-eastward and rotated clockwise as a part of the Calabria-Peloritani terrane.

RoadRunner: automatic data extraction from data-intensive web sites

Abstract: Data extraction from HTML pages is performed by software modules, usually called wrappers. Roughly speaking, a wrapper identifies and extracts relevant pieces of text inside a web page, and reorganizes them in a more structured format. In the literature there is a number of systems to (semi-)automatically generate wrappers for HTML pages [1]. We have recently investigated for original approaches that aims at pushing further the level of automation of the wrapper generation process. Our main intuition is that, in a dataintensive web site, pages can be classified in a small number of classes, such that pages belonging to the same class share a rather tight structure. Based on this observation, we have studied an novel technique, we call the matching technique [2], that automatically generates a common wrapper by exploiting similarities and differences among pages of the same class. In addition, in order to deal with the complexity and the heterogeneities of real-life web sites, we have also studied several complementary techniques that greatly enhance the effectiveness of matching. Our demonstration presents RoadRunner, our prototype that implements matching and its companion techniques. We have conducted several experiments on pages from real life web sites; these experiences have shown the effectiveness of the approach, as well as the efficiency of the system [2]. The matching technique for wrapper inference [2] is based on an iterative process; at every step, matching works on two objects at a time: (i) an input page, which represented as a list of tokens (each token is either a tag or a text field), and (ii) a wrapper, expressed as a regular expression. The process starts by taking one input page as an initial version of the wrapper; then, the wrapper is matched against the sample and it is progressively refined trying to solve mismatches: a mismatch happens when some token in the sample does not comply to the grammar specified by the wrapper. Mismatches can be solved by generalizing the wrapper. The process succeeds if a common wrapper can be generated by solving all mismatches encountered.

Finite commutative rings and their applications

Abstract: Foreword by Dieter Jungnickel Finite Commutative Rings and their Applications answers a need for an introductory reference in finite commutative ring theory as applied to information and communication theory. This book will be of interest to both professional and academic researchers in the fields of communication and coding theory. The book is a concrete and self-contained introduction to finite commutative local rings, focusing in particular on Galois and Quasi-Galois rings. The reader is provided with an active and concrete approach to the study of the purely algebraic structure and properties of finite commutative rings (in particular, Galois rings) as well as to their applications to coding theory. Finite Commutative Rings and their Applications is the first to address both theoretical and practical aspects of finite ring theory. The authors provide a practical approach to finite rings through explanatory examples, thereby avoiding an abstract presentation of the subject. The section on Quasi-Galois rings presents new and unpublished results as well. The authors then introduce some applications of finite rings, in particular Galois rings, to coding theory, using a solid algebraic and geometric theoretical background.

An accurate model for capacitive micromachined ultrasonic transducers

Abstract: Modeling of capacitive micromachined ultrasonic transducers (cMUTs) is based on a two-port network with an electrical and a mechanical side. To obtain a distributed model, a solution of the differential equation of motion of the diaphragm for each element of the transducer has to be found. Previous works omit the mechanical load of the cavity behind the diaphragm, i.e., the effect of the gas inside. In this paper, we propose a distributed model for cMUTs that takes this effect into account. A closed-form solution of the mechanical impedance of the membranes has been obtained, including the effect of the restoring forces because of the stiffness of the membrane and because of the compression of the air in the cavity. Simulation results based on the presented model are compared with the experimental data for two types of cMUTs reported in the recent literature. It is demonstrated that the compression of the air has a significant effect on the fundamental frequency of the air transducer, with a deviation of about 22% from the prediction of a model that does not consider the interaction between the vibrating diaphragm and the air cushion.

Experimental study on reducing cogging torque and no-load power loss in axial-flux permanent-magnet machines with slotted winding

Abstract: The axial-flux permanent-magnet machine (AFPM) topology is suited for direct-drive applications and, due to their enhanced flux-weakening capability, AFPMs having slotted windings are the most promising candidates for use in wheel-motor drives. In consideration of this, this paper deals with an experimental study devoted to investigate a number of technical solutions to be used in AFPMs having slotted windings in order to achieve substantial reduction of both cogging torque and no-load power loss in the machine. To conduct such an experimental study, a laboratory machine was purposely built incorporating facilities that allow easy-to-achieve offline modifications of the overall magnetic arrangement at the machine air gaps, such as magnet skewing, angular shifting between rotor discs, and accommodation of either PVC or Somaloy wedges for closing the slot openings. The paper discusses experimental results and gives guidelines for the design of AFPMs with improved performance.

η Photoproduction on the Proton for Photon Energies from 0.75 to 1.95 GeV

Abstract: Differential cross sections for gammap-->etap have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W=1.75 GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass approximately 1.8 GeV couples to the etaN channel.

Control strategy for multiple input DC-DC power converters devoted to hybrid vehicle propulsion systems

Abstract: Customer demands for greater acceleration, performance, and vehicle range in pure EVs plus mandated requirements to further reduce emissions in HEVs increase the appeal for combined on-board energy storage systems and generators. This paper deals with the control system of an original HEV propulsion system that includes fuel cell generator and storage energy system combining ultracapacitor tank and battery. The three on-board power sources supply the vehicle traction drive through a multi-input DC-to-DC power converter which provides the desired management of the power flows. In particular, in the proposed arrangement the ultracapacitor tank is used for leveling the battery load current during transients resulting from either acceleration or braking operation of the vehicle. The paper outlines the features of the control unit of the DC-to-DC power converter being used in the proposed propulsion system and describes the main characteristics of a 35 kW prototype developed to conduct laboratory experiments and validate the control strategy.