Publications (8)1.44 Total impact
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Article: HERschel Observations of Edge-on Spirals (HEROES). I: Far-infrared morphology and dust mass determination
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ABSTRACT: Context. Edge-on spiral galaxies with prominent dust lanes provide us with an excellent opportunity to study the distribution and properties of the dust within them. The HEROES project was set up to observe a sample of seven large edge-on galaxies across various wavelengths for this investigation. Aims. Within this first paper, we present the Herschel observations and perform a qualitative and quantitative analysis on them, and we derive some global properties of the far infrared and submillimetre emission. Methods. We determine horizontal and vertical profiles from the Herschel observations of the galaxies in the sample and describe the morphology. Modified black-body fits to the global fluxes, measured using aperture photometry, result in dust temperatures and dust masses. The latter values are compared to those that are derived from radiative transfer models taken from the literature. Results. On the whole, our Herschel flux measurements agree well with archival values. We find that the exponential horizontal dust distribution model often used in the literature generally provides a good description of the observed horizontal profiles. Three out of the seven galaxies show signatures of extended vertical emission at 100 and 160 {\mu}m at the 5{\sigma} level, but in two of these it is probably due to deviations from an exactly edge-on orientation. Only for NGC 4013, a galaxy in which vertically extended dust has already been detected in optical images, we can detect vertically extended dust, and the derived scaleheight agrees with the value estimated through radiative transfer modelling. Our analysis hints at a correlation between the dust scaleheight and its degree of clumpiness, which we infer from the difference between the dust masses as calculated from modelling of optical data and from fitting the spectral energy distribution of Herschel datapoints.05/2013; -
Article: Herschel and JCMT observations of the early-type dwarf galaxy NGC 205
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ABSTRACT: We present Herschel dust continuum, James Clerk Maxwell Telescope CO(3-2) observations and a search for [CII] 158 micron and [OI] 63 micron spectral line emission for the brightest early-type dwarf satellite of Andromeda, NGC 205. While direct gas measurements (Mgas ~ 1.5e+6 Msun, HI + CO(1-0)) have proven to be inconsistent with theoretical predictions of the current gas reservoir in NGC 205 (> 1e+7 Msun), we revise the missing interstellar medium mass problem based on new gas mass estimates (CO(3-2), [CII], [OI]) and indirect measurements of the interstellar medium content through dust continuum emission. Based on Herschel observations, covering a wide wavelength range from 70 to 500 micron, we are able to probe the entire dust content in NGC 205 (Mdust ~ 1.1-1.8e+4 Msun at Tdust ~ 18-22 K) and rule out the presence of a massive cold dust component (Mdust ~ 5e+5 Msun, Tdust ~ 12 K), which was suggested based on millimeter observations from the inner 18.4 arcsec. Assuming a reasonable gas-to-dust ratio of ~ 400, the dust mass in NGC 205 translates into a gas mass Mgas ~ 4-7e+6 Msun. The non-detection of [OI] and the low L_[CII]-to-L_CO(1-0) line intensity ratio (~ 1850) imply that the molecular gas phase is well traced by CO molecules in NGC 205. We estimate an atomic gas mass of 1.5e+4 Msun associated with the [CII] emitting PDR regions in NGC 205. From the partial CO(3-2) map of the northern region in NGC 205, we derive a molecular gas mass of M_H2 ~ 1.3e+5 Msun. [abridged]04/2012; -
Article: The Herschel Exploitation of Local Galaxy Andromeda (HELGA) II: Dust and Gas in Andromeda
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ABSTRACT: We present an analysis of the dust and gas in Andromeda, using Herschel images sampling the entire far-infrared peak. We fit a modified-blackbody model to ~4000 quasi-independent pixels with spatial resolution of ~140pc and find that a variable dust-emissivity index (beta) is required to fit the data. We find no significant long-wavelength excess above this model suggesting there is no cold dust component. We show that the gas-to-dust ratio varies radially, increasing from ~20 in the center to ~70 in the star-forming ring at 10kpc, consistent with the metallicity gradient. In the 10kpc ring the average beta is ~1.9, in good agreement with values determined for the Milky Way (MW). However, in contrast to the MW, we find significant radial variations in beta, which increases from 1.9 at 10kpc to ~2.5 at a radius of 3.1kpc and then decreases to 1.7 in the center. The dust temperature is fairly constant in the 10kpc ring (ranging from 17-20K), but increases strongly in the bulge to ~30K. Within 3.1kpc we find the dust temperature is highly correlated with the 3.6 micron flux, suggesting the general stellar population in the bulge is the dominant source of dust heating there. At larger radii, there is a weak correlation between the star formation rate and dust temperature. We find no evidence for 'dark gas' in M31 in contrast to recent results for the MW. Finally, we obtained an estimate of the CO X-factor by minimising the dispersion in the gas-to-dust ratio, obtaining a value of (1.9+/-0.4)x10^20 cm^-2 [K kms^-1]^-1.04/2012; -
Article: Diagnostic accuracy of second-generation dual-source computed tomography coronary angiography with iterative reconstructions: a real-world experience.
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ABSTRACT: The authors evaluated the diagnostic accuracy of second-generation dual-source (DSCT) computed tomography coronary angiography (CTCA) with iterative reconstructions for detecting obstructive coronary artery disease (CAD). Between June 2010 and February 2011, we enrolled 160 patients (85 men; mean age 61.2±11.6 years) with suspected CAD. All patients underwent CTCA and conventional coronary angiography (CCA). For the CTCA scan (Definition Flash, Siemens), we use prospective tube current modulation and 70-100 ml of iodinated contrast material (Iomeprol 400 mgI/ ml, Bracco). Data sets were reconstructed with iterative reconstruction algorithm (IRIS, Siemens). CTCA and CCA reports were used to evaluate accuracy using the threshold for significant stenosis at ≥50% and ≥70%, respectively. No patient was excluded from the analysis. Heart rate was 64.3±11.9 bpm and radiation dose was 7.2±2.1 mSv. Disease prevalence was 30% (48/160). Sensitivity, specificity and positive and negative predictive values of CTCA in detecting significant stenosis were 90.1%, 93.3%, 53.2% and 99.1% (per segment), 97.5%, 91.2%, 61.4% and 99.6% (per vessel) and 100%, 83%, 71.6% and 100% (per patient), respectively. Positive and negative likelihood ratios at the per-patient level were 5.89 and 0.0, respectively. CTCA with second-generation DSCT in the real clinical world shows a diagnostic performance comparable with previously reported validation studies. The excellent negative predictive value and likelihood ratio make CTCA a first-line noninvasive method for diagnosing obstructive CAD.La radiologia medica 11/2011; 117(5):725-38. · 1.44 Impact Factor -
Article: Global attraction to the origin in a parametrically driven nonlinear oscillator
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ABSTRACT: We consider a parametrically driven nonlinear ODE, which encompasses a simple model of an electronic circuit known as a parametric amplifier, whose linearisation has a zero eigenvalue. By adopting two different approaches, we obtain conditions for the origin to be a global attractor which is approached (a) non-monotonically and (b) monotonically. In case (b), we obtain an asymptotic expression for the convergence to the origin. Some further numerical results are reported.Applied Mathematics and Computation. -
Article: KAM theorem revisited
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ABSTRACT: A combinatorial proof of the KAM theorem for the Thirring model is presented, by using renormalization group techniques usual in the formalism of quantum field theory.Physica D: Nonlinear Phenomena. -
Article: Design of switches for self-reconfiguring VLSI array structures
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ABSTRACT: VLSI implementation is particularly suited to array architectures of identical processing cells; fault-tolerance becomes then an important requirement for enhancing both production yield and device lifetime. Architectures allowing to achieve reconfiguration and survival to a number of faults via limited redundancy and simple reconfiguration algorithms have been presented previously; with VLSI implementation, in fact, a compromise between reconfiguration capacity and added complexity (thence, ultimately, added chip area) has to be reached.In the present paper, we suggest implementation of a reconfigurable architecture making use of a switch organization that allows relevant reduction of added interconnection area. The complete structure, down to reconfiguration circuitry layout, is detailed; since switches could constitute a bottleneck for system reliability, both a self-testing design and a fault-tolerant ones are presented.Microprocessing and Microprogramming. -
Article: On homoclinic splitting problems
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ABSTRACT: Counterexamples to the homoclinic splitting claimed in the paper “Existence of exponentially small separatrix settings and homoclinic connections between whiskered tori in weakly hyperbolic near-integrable Hamiltonian systems” by Rudnev and Wiggins [Physica D 114 (1998) 3–80] are given. These counterexamples invalidate the proofs of the main results of that paper.Physica D: Nonlinear Phenomena.
