Showing papers by "Roma Tre University published in 1999"
TL;DR: It is shown that, for a generic polarization state of the incident field, such a grating gives rise to first-order diffracted beams with counterrotating circular polarizations and can be used for measuring the Stokes parameters of a light beam in an achromatic manner.
Abstract: Ordinary gratings act on the amplitude and (or) the phase of a wave front. Polarization gratings produce instead a periodic modulation of the state of polarization. A simple grating of the latter type is constituted by a linear polarizer whose orientation varies periodically along a line. It is shown that, for a generic polarization state of the incident field, such a grating gives rise to first-order diffracted beams with counterrotating circular polarizations. It is also shown that such a grating can be used for measuring the Stokes parameters of a light beam in an achromatic manner. Several extensions are briefly discussed.
294 citations
TL;DR: The monochromator is a variable angle spherical grating instrument (plane mirror and grating between entrance and exit slits), with an undulator as the source as mentioned in this paper.
165 citations
TL;DR: In this paper, the authors reported the possible detection of redshifted iron line emission in the X-ray afterglow of gamma-ray burst GRB 970508 observed by BeppoSAX.
Abstract: We report the possible detection (99.3% of statistical significance) of redshifted iron line emission in the X-ray afterglow of gamma-ray burst GRB 970508 observed by BeppoSAX. Its energy is consistent with the redshift of the putative host galaxy determined from optical spectroscopy. The line disappeared ~1 day after the burst. We have also analyzed the spectral variability during the outburst event that characterizes the X-ray afterglow of this gamma-ray burst. The spectrum gets harder during the flare, then becoming steep when the flux decreases. The variability, intensity, and width of the line indicate that the emitting region should have a mass 0.5 M☉ (assuming that the iron abundance is similar to its solar value), should have a size of ~3×1015 cm, is distributed anisotropically, and is moving with subrelativistic speed. In contrast to the fairly clean environment expected in the merging of two neutron stars, the observed line properties would imply that the site of the burst is embedded in a large mass of material, consistent with preexplosion ejecta of a very massive star. This material could be related with the outburst observed in the afterglow 1 day after the GRB and with the spectral variations measured during this phase.
162 citations
TL;DR: The first crystal structure of a polyamine oxidase has been determined to a resolution of 1.9 A. The structure of PAO in complex with the inhibitor MDL72527 reveals the residues forming the catalytic machinery and unusual enzyme-inhibitor CH···O H bonds as discussed by the authors.
158 citations
TL;DR: In this article, a model for the development of the Mattinata Fault is proposed in which the cleavage surfaces are interpreted as fault-propagation deformations, and two distinct, time-sequential processes are shown to operate during the fault propagation: (1) typical millimetre-to centimetre sparsified solution surfaces form in the distal tip zone of the advancing fault plane; (2) as the tip advances, the fault plane breaks through the surface as minor shear displacements reactivate some of these nascent surfaces.
158 citations
TL;DR: In this article, the absorption, emission and decay kinetics characteristics of Cs 4 PbBr 6 bulk and thin film samples were measured in the UV-visible spectral range over 4.2-250 K.
144 citations
TL;DR: In this paper, metal-semiconductor-metal photodetectors based on epitaxial pure-Ge grown on silicon by chemical vapor deposition were designed and tested.
Abstract: We review our recent results on Ge-based near-infrared photodetectors grown on silicon. We fabricated metal-semiconductor-metal photodetectors based on epitaxial pure-Ge grown on silicon by chemical vapor deposition. Material characterization and device performances are illustrated and discussed. Exploiting a novel approach based on evaporation of polycrystalline-Ge on silicon, we also realized efficient near-infrared photodiodes with good speed and sensitivity. Finally, multiple-element devices were designed, fabricated, and tested, such as a voltage-tunable wavelength-selective photodetector based on a SiGe superlattice and a linear array of 16 photodetectors in poly-Ge on Si.
131 citations
TL;DR: The volcanic island of Ischia is located on the Tyrrhenian margin of Central Italy, characterized by Plio-Quaternary NW-SE- and NE-SW-trending extensional fractures as discussed by the authors.
129 citations
TL;DR: Proof nets and sequent calculus for the multiplicative fragment of non-commutative logic, which is an extension of both linear logic and cyclic linear logic, are introduced.
117 citations
TL;DR: In this paper, an AFM-assisted mask patterning is applied to the nanodevices to achieve the smallest possible separation between electrode pairs in order to achieve conformal growth and surface roughness comparable to that of the substrate.
Abstract: Nanoscale science and technology is today mainly focused on the fabrication of nanodevices. Our approach makes use of lithography processes to build the desired nanostructures directly. The fabrication process involves an electron-beam lithography technique to define metallic microstructures onto which nanometre scale patterning is performed using an atomic force microscope (AFM) as a mechanical modification tool. Both direct material removal and AFM-assisted mask patterning are applied in order to achieve the smallest possible separation between electrode pairs. The sample preparation involves a polymer deposition process that results in conformal growth and in surface roughness comparable to that of the substrate. The results of the application of this technique show that the process is reproducible and exhibits a good operation control during the lithographic steps, both ensured by the imaging facilities of the AFM. The nanolithography technique has been used to fabricate nanogap electrodes to be used for molecular devices. The study reported here can be considered as a reliable starting point for the development of more complex nanodevices, such as single-electron transistors.
107 citations
TL;DR: In this article, the D- and B-meson decay constants were obtained in the quenched approximation, by using the nonperturbatively improved clover lattice action at 6.2, with a sample of $100$ configurations.
Abstract: We present a study of the heavy-light spectrum and of the D- and B-meson decay constants. The results were obtained in the quenched approximation, by using the nonperturbatively improved clover lattice action at $\ensuremath{\beta}=6.2,$ with a sample of $100$ configurations, on a ${24}^{3}\ifmmode\times\else\texttimes\fi{}64$ lattice. After a careful analysis of the systematic errors present in the extraction of the physical results, by assuming quite conservative discretization errors, we find ${f}_{{D}_{s}}=231\ifmmode\pm\else\textpm\fi{}{12}_{\ensuremath{-}1}^{+8} \mathrm{MeV},$ ${f}_{D}=211\ifmmode\pm\else\textpm\fi{}{14}_{\ensuremath{-}12}^{+2} \mathrm{MeV},$ ${f}_{{D}_{s}}{/f}_{D}=1.10(2),$ ${f}_{{B}_{s}}=204\ifmmode\pm\else\textpm\fi{}{16}_{\ensuremath{-}0}^{+36} \mathrm{MeV},$ ${f}_{B}=179\ifmmode\pm\else\textpm\fi{}{18}_{\ensuremath{-}9}^{+34} \mathrm{MeV},$ ${f}_{{B}_{s}}{/f}_{B}{=1.14(3)}_{\ensuremath{-}1}^{+1}.$ Our results, which have smaller discretization errors than many previous estimates at fixed value of the lattice spacing a, support a large value of ${f}_{B}$ in the quenched approximation.
TL;DR: In this article, the authors carried out the BeppoSAX High Energy Large Area Survey (HELLAS) in the largely unexplored 5-10 keV band, finding 180 sources in ∼50 deg2 of sky with flux≳5×10−14 erg cm−2 s−1.
Abstract: Hard X-ray selection is the most efficient way to discriminate between accretion-powered sources, such as active galactic nuclei (AGN), and sources dominated by starlight. Hard X-rays are also less affected than other bands by obscuration. We have therefore carried out the BeppoSAX High Energy Large Area Survey (HELLAS) in the largely unexplored 5–10 keV band, finding 180 sources in ∼50 deg2 of sky with flux≳5×10−14 erg cm−2 s−1. After correction for the non-uniform sky coverage this corresponds to resolving about 30 per cent of the hard cosmic X-ray background (XRB). Here we report on a first optical spectroscopic identification campaign, finding 12 AGN out of 14 X-ray error boxes studied. Seven AGN show evidence for obscuration in X-ray and optical bands, a fraction higher than in previous ROSAT or ASCA–ROSAT surveys (at 95–99 and 90 per cent confidence levels respectively), thus supporting the scenario in which a significant fraction of the XRB is created by obscured AGN.
TL;DR: In this article, the authors explore collisional ionization and time-evolving photoionization in the X-ray-discovered, ionized absorbers in Seyfert galaxies.
Abstract: In this paper we explore collisional ionization and time-evolving photoionization in the X-ray-discovered, ionized absorbers in Seyfert galaxies. These absorbers show temporal changes inconsistent with simple equilibrium models. We develop a simple code to follow the temporal evolution of nonequilibrium photoionized gas. As a result several effects appear that are easily observable and that, in fact, may explain otherwise paradoxical behavior. Specifically, we find the following: 1. In many important astrophysical conditions (O VII, O VIII dominant and high [1022.5 cm-2] column density) pure collisional and photoionization equilibria can be distinguished with moderate spectral resolution observations, because of a strong absorption structure between 1 and 3 keV. This feature is due mainly to iron L XVII-XIX and neon K IX-X absorption, which is much stronger in collisional models. This absorption structure may be misinterpreted as a flattening of the intrinsic emission spectrum above ~1 keV in low-resolution data. 2. In time-evolving nonequilibrium photoionization models the response of the ionization state of the gas to sudden changes of the ionizing continuum is smoothed and delayed at low gas densities (usually up to 108 cm-3), even when the luminosity increases. The recombination time can be much longer (up to orders of magnitude) than the photoionization timescale. Hence, a photoionized absorber subject to frequent, quick, and consistent changes of ionizing luminosity is likely to be overionized with respect to the equilibrium ionization state. 3. If the changes of the ionizing luminosity are not instantaneous, and the electron density is low enough (the limit depends on the average ionization state of the gas but is usually ~107 to ~108 cm-3), the ionization state of the gas can continue to increase while the source luminosity decreases, so a maximum in the ionization state of a given element may occur during a minimum of the ionizing intensity (the opposite of the prediction of equilibrium models). 4. Different ions of different elements reach their equilibrium configuration on different timescales, so models in which all ions of all elements are in photoionization equilibrium so often fail to describe active galactic nucleus (AGN) spectral evolution. These properties are similar to those seen in several ionized absorbers in AGNs, properties that had hitherto been puzzling. We applied these models to a high signal-to-noise ratio ROSAT PSPC observation of the Seyfert 1 galaxy NGC 4051. The compressed dynamical range of variation of the ionization parameter U and the ionization delays seen in the ROSAT observations of NGC 4051 may be simply explained by a nonequilibrium photoionization model, giving well-constrained parameters: n=(1.0)×108 cm-3 and R=(0.74)×1016 cm (~3 light-days).
TL;DR: Investigation of D-AAO distribution in rat brain by immunocytochemistry with an affinity-purified polyclonal antibody found immunopositivity was virtually ubiquitous, and was especially strong in the reticular formation, pontine, ventral and dorsal cochlear, vestibular, cranial motor nuclei, and the cerebellar cortex.
Abstract: d-amino acid oxidase (d-AAO) is a peroxisomal flavoenzyme, the physiological substrate and the precise function of which are still unclear. We have investigated D-AAO distribution in rat brain, by immunocytochemistry, with an affinity-purified polyclonal antibody. Immunoreactivity occurred in both neuronal and glial cells, albeit at different densities. Glial immunostaning was strongest in the caudal brainstem and cerebellar cortex, particularly in astrocytes, Golgi-Bergmann glia, and tanycytes. Hindbrain neurons were generally more immunoreactive than those in the forebrain. Immunopositive forebrain cell populations included mitral cells in the olfactory bulb, cortical and hippocampal neurons, ventral pallidum, and septal, reticular thalamic, and paraventricular hypothalamic nuclei. Within the positive regions, not all the neuronal populations were equally immunoreactive; for example, in the thalamus, only the reticular and anterodorsal nuclei showed intense labelling. In the hindbrain, immunopositivity was virtually ubiquitous, and was especially strong in the reticular formation, pontine, ventral and dorsal cochlear, vestibular, cranial motor nuclei, deep cerebellar nuclei, and the cerebellar cortex, especially in Golgi and Purkinje cells.
TL;DR: In this paper, structural, petrographic and fluid inclusion data from Giglio Island (Northern Tyrrhenian Sea, Italy) are used to constrain kinematics, timing and thermal regimes associated with the post-thickening tectonic evolution of the innermost sector of the Northern Apennine belt.
TL;DR: The linewidths of a series of core excited atoms and small molecules have been measured in photo-absorption with ultra high resolution as discussed by the authors, and the lifetime widths of this range of chemical states and neutral excited states are compared critically with values derived from x-ray absorption and other spectroscopies.
TL;DR: In this paper, photoionization models accounting for both photoelectric and resonant absorption lines between 0.1 and 10 keV are presented, and profiles, intensities, and equivalent widths of each line, considering both Doppler and natural broadening mechanisms.
Abstract: We present photoionization models accounting for both photoelectric and resonant absorption. Resonance absorption lines from C, O, Ne, Mg, Si, S, and Fe between 0.1 and 10 keV are treated. In particular we consider the complex of almost 60 strong Fe L absorption lines around 1 keV. We calculate profiles, intensities, and equivalent widths of each line, considering both Doppler and natural broadening mechanisms. Doppler broadening includes a term accounting for turbulence of the gas along the line of sight. We computed spectra transmitted by gas illuminated by drastically different ionizing continua and compared them to spectra observed in flat X-ray spectrum, broad optical emission-line type 1 active galactic nuclei (AGNs), and steep X-ray spectrum, narrow optical emission-line type 1 AGNs. We show that the ~1 keV absorption feature observed in moderate-resolution X-ray spectra of several narrow-line Seyfert 1 galaxies can be explained by photoionization models, taking into account resonance absorption, without requiring relativistic outflowing velocities of the gas, if the physical properties of these absorbers are close to those found in flat X-ray spectrum Seyfert 1 galaxies. We finally present simulations of the spectra emerging from gas illuminated by both steep and flat ionizing continua, as seen by the AXAF high-energy transmission gratings and the baseline Constellation-X calorimeter. We discuss briefly the relevant physics that can be investigated with these instruments.
TL;DR: In this paper, the authors carried out the BeppoSAX High Energy Large Area Survey (HELLAS) in the largely unexplored 5-10 keV band, finding 180 sources in ~50 deg^2 of sky with flux >5E-14 erg cm-2 s-1.
Abstract: Hard X-ray selection is the most efficient way to discriminate between accretion-powered sources, such as AGN, from sources dominated by starlight. Hard X-rays are also less affected than other bands by obscuration. We have then carried out the BeppoSAX High Energy Large Area Survey (HELLAS) in the largely unexplored 5-10 keV band, finding 180 sources in ~50 deg^2 of sky with flux >5E-14 erg cm-2 s-1. After correction for the non uniform sky coverage this corresponds to resolving about 30 % of the hard Cosmic X-ray Background (XRB). Here we report on a first optical spectroscopic identification campaign, finding 12 AGN out of 14 X-ray error-boxes studied. Seven AGN show evidence for obscuration in X-ray and optical bands, a fraction higher than in previous ROSAT or ASCA-ROSAT surveys (at a 95-99 % and 90 % confidence level respectively), thus supporting the scenario in which a significant fraction of the XRB is made by obscured AGN.
TL;DR: In this paper, the authors examined the sources of errors with specific reference to crosstalk and electronic circuitry used to scan the array, and derived some guidelines for the use of scanning circuits.
Abstract: Arrays of piezoresistive sensors (PRS), which are often used for tactile sensing, suffer from crosstalk between adjacent elements that can alter the readings of the force applied. In this paper, the sources of errors, with specific reference to crosstalk and electronic circuitry used to scan the array, are examined. The solutions presented in the literature are discussed, evaluating their performance and errors. From this analysis, some guidelines can be derived for the use of scanning circuits.
TL;DR: In this paper, the near-edge x-ray absorption spectra of dinitrogen oxide and carbon dioxide have been measured with ultra high resolution and high statistical accuracy at the N 1s and O 1s edges, and at the C 1s, O 1 s and O 2 s edges in N2O and CO2, respectively.
Abstract: The near-edge x-ray absorption spectra of dinitrogen oxide and carbon dioxide have been measured with ultra high resolution and high statistical accuracy at the N 1s and O 1s edges, and at the C 1s and O 1s edges in N2O and CO2, respectively. The assignment of the peaks in the spectra is achieved via the analysis of the quantum defects of the Rydberg states, the use of the core-equivalent model and a comparison with previous photoabsorption and fragment ion spectra. New high-resolution spectra are provided for the O 1s excitations of CO2, and several new states are observed at the oxygen edge of N2O.
TL;DR: The NO‐mediated S‐nitrosylation of viral and host (macro)molecules appears to be an intriguing general mechanism for the control of the virus life cycle.
Abstract: Nitric oxide (NO) is considered an important signaling molecule implied in various different physiological processes, including nervous transmission, vascular regulation, and immune defence, as well as the pathogenesis of several diseases NO reportedly also has an antiviral effect on several DNA and RNA virus families The NO-mediated S-nitrosylation of viral and host (macro)molecules appears to be an intriguing general mechanism for the control of the virus life cycle In this respect, NO is able to nitrosylate cysteine-containing enzymes (eg, proteases, reverse transcriptase, and ribonucleotide reductase) Moreover, zinc-fingers and related domains present in enzymes (eg, HIV-1-encoded integrase or herpes simplex virus type-1 heterotrimeric helicase-primase complex) or nucleocapsid proteins may be considered as NO targets Also, NO may regulate both host (eg, nuclear factor-kappaB) and viral-encoded (eg, HIV-1 tat protein or Epstein-Barr virus Zta) transcriptional factors that are involved in virus replication Finally, NO-mediated S-nitrosylation of cysteine-containing glycoproteins and hemagglutinin may also occur Here, NO targets are summarised, and the molecular bases for the antiviral effect of NO are discussed
TL;DR: In this paper, the role of transverse structures on volcanic activity along the Tyrrhenian margin of Central Italy has been investigated with both analogue and mechanical models, and the results suggest that the Campi Flegrei Volcanic District (CFVD) is located along a NE-SW transfer zone connecting NW-SE regional normal faults.
15 Sep 1999
TL;DR: For both types of drawings, algorithms based on network flow techniques and the results of an experimentation conducted on the algorithms that are proposed for orthogonal drawings show the effectiveness of the approach.
Abstract: We consider the problem of computing orthogonal drawings and quasi-upward drawings with vertices of prescribed size For both types of drawings we present algorithms based on network flow techniques and show that the produced drawings are optimal within a wide class Further, we present the results of an experimentation conducted on the algorithms that we propose for orthogonal drawings The experiments show the effectiveness of the approach
TL;DR: In this paper, structural and anisotropy of magnetic susceptibility (AMS) results from the Upper Miocene sediments of the Amantea basin, located on the Tyrrhenian coast of the Calabrian Arc (Southern Italy), are reported.
TL;DR: In this paper, the use of porous silicon (PS) as an antireflection coating (ARC) in simplified processing for multicrystalline silicon solar cells is presented.
Abstract: The latest results on the use of porous silicon (PS) as an antireflection coating (ARC) in simplified processing for multicrystalline silicon solar cells are presented. The optimization of a PS selective emitter formation results in a 14.1% efficiency multicrystalline (5/spl times/5 cm/sup 2/) Si cell with evaporated contacts processed without texturization, surface passivation, or additional ARC deposition. Specific attention is given to the implementation of a PS ARC into an industrially compatible screen-printed solar cell process. Both the chemical and electrochemical PS ARC formation method are used in different solar cell processes, as well as on different multicrystalline silicon materials. Efficiencies between 12.1 and 13.2% are achieved on large-area (up to 164 cm/sup 2/) commercial Si solar cells.
TL;DR: In this paper, a general law for the M2 factor of any beam generated by a partially coherent Schell-model source was derived, where the fourth power of M differs from its minimum value by a term proportional to the second derivative of the modulus of the spectral degree of coherence evaluated for zero argument.
Abstract: We derive a general law for the M2 factor of any beam generated by a partially coherent Schell-model source. The fourth power of M differs from its minimum value, attained in the coherent limit, by a term proportional to the second derivative of the modulus of the spectral degree of coherence evaluated for zero argument. Examples are given for cases of practical interest.
TL;DR: The results show that the wavelet procedure performs better than the other methods both in information preservation and in time-detection, and the features of user-independence and adaptivity to the noise level suggest a wider range of applications of the proposed algorithm.
University of Basilicata1, Sapienza University of Rome2, University of Bari3, University of Michigan4, University of Pisa5, University of Bologna6, Roma Tre University7, University of Trieste8, California Institute of Technology9, Swarthmore College10, Pakistan Institute of Nuclear Science and Technology11
TL;DR: In this article, an indirect search for weakly interacting massive particles (WIMPs) using the MACRO detector was performed to look for neutrino-induced upward-going muons resulting from the annihilation of WIMPs trapped in the Sun and Earth.
Abstract: We perform an indirect search for weakly interacting massive particles (WIMPs) using the MACRO detector to look for neutrino-induced upward-going muons resulting from the annihilation of WIMPs trapped in the Sun and Earth. The search is conducted in various angular cones centered on the Sun and Earth to accommodate a range of WIMP masses. No significant excess over the background from atmospheric neutrinos is seen. We set experimental flux limits on the upward-going muon fluxes from the Sun and the Earth. These limits are used to constrain neutralino particle parameters from supersymmetric theory, including those suggested by recent results from DAMA-NaI. {copyright} {ital 1999} {ital The American Physical Society}
TL;DR: In this paper, Monte Carlo simulations are applied to the BeppoSAX data of the Seyfert 2 galaxy in Circinus and to the spectral modeling of the Cosmic X-ray Background.
TL;DR: In this paper, the selective catalytic reduction of NO with propene or ammonia in the presence of excess oxygen, was studied in a flow apparatus with reactant mixtures of various composition.
Abstract: Samples CuO x /ZrO 2 (0.1–8.4 Cu atoms nm −2 ) were prepared by adsorption or impregnation methods. The characterisation of samples by means of XPS, XRD, DRS, ESR, IR and volumetric adsorption of CO, showed copper dispersion up to 2.5 atoms nm −2 , and the presence of CuO in samples with higher Cu content. The selective catalytic reduction of NO with propene or ammonia in the presence of excess oxygen, was studied in a flow apparatus with reactant mixtures of various composition (NO : C 3 H 6 : O 2 = 0–4000 ppm : 100–2000 ppm : 0–3.5%; and NO : NH 3 : O 2 = 0–700 ppm : 700 ppm : 3.6%). With both propene and ammonia, CuO x /ZrO 2 catalysts containing up to 2.5 Cu atoms nm −2 were active, selective and stable as a function of the time on stream. On all catalysts, with ammonia as reducing agents, up to 523 K, NO conversion equalled NH 3 conversion leading to 100% selectivity. With both propene and ammonia, NO molecules that were converted to N 2 per Cu atom and per second were nearly independent of the Cu content up to 2.5 Cu atoms nm −2 .