1,076 research outputs found
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters: The Internal Kinematics of the Multiple Stellar Populations in NGC 2808
No full textSupport for this work comes from STScI grants for HST programs AR-12845 and GO-13297. E.V. acknowledges support by grant NASA-NNX13AF45G. G.P., S.C., F.D’A. and A.R. acknowledge support from PRIN-INAF 2014 (PI: S. Cassisi).Numerous observational studies have revealed the ubiquitous presence of multiple stellar populations in globular clusters and cast many difficult challenges for the study of the formation and dynamical history of these stellar systems. In this Letter we present the results of a study of the kinematic properties of multiple populations in NGC 2808 based on high-precision Hubble Space Telescope proper-motion measurements. In a recent study, Milone et al. identified five distinct populations (A-E) in NGC 2808. Populations D and E coincide with the helium-enhanced populations in the middle and the blue main sequences (mMS and bMS) previously discovered by Piotto et al.; populations A-C correspond to the redder main sequence that, in Piotto et al., was associated with the primordial stellar population. Our analysis shows that, in the outermost regions probed (between about 1.5 and 2 times the cluster half-light radius), the velocity distribution of populations D and E is radially anisotropic (the deviation from an isotropic distribution is significant at the ̃3.5σ level). Stars of populations D and E have a smaller tangential velocity dispersion than those of populations A-C, while no significant differences are found in the radial velocity dispersion. We present the results of a numerical simulation showing that the observed differences between the kinematics of these stellar populations are consistent with the expected kinematic fingerprint of the diffusion toward the cluster outer regions of stellar populations initially more centrally concentrated. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555
Third-Order Nonlinear Optical Properties of In-Backbone Substituted Oligo(triacetylene) Chromophores
No full textA new approach to tuning the nonlinear optical properties of hybrid oligo(triacetylene) compounds is studied.
The method is based on the insertion of a central heterospacer group between two (E)-hex-3-ene-1,5-diyne moieties. A significant increase in the second hyperpolarizability g is expected if the central spacer fragment is an extended conjugated chromophore. We present a series of molecules with enhanced second hyperpolarizability
caused by the presence of highly conjugated spacer groups, which increase the overall p-electron delocalization.
Some metal complexes obtained from the coordination of these hybrid oligomers to transitionmetal centers have also been investigated and revealed substantial differences in the capacities of the metal centers to act as electronic bridges. Finally, we show that theoretical predictions of the relative differences in the second hyperpolarizabilities of the new spacer compounds are in good agreement with the experimental results
Duckwort–Lewis run out?
No full textIn one-day cricket matches the two competing teams have the same number of overs, typically 50, and the highest scoring team wins, with ties possible but unusual. If the match is interrupted, then the Duckworth–Lewis method is accepted by the International Cricket Council as the algorithm for deciding the result. In 2007, John Turner suggested an alternative method, named the Player Specific Method, that models the performance of batters against different types of bowlers and the remaining time in an innings, and then uses computer simulation to generate an ensemble of possible scores. Then, either the mean value of these scores is used to determine the winning team, or a probability is assigned to one of the teams winning. This method is illustrated for the one-day match between Australia and Sri Lanka at the MCG on 22nd February 2008, and its feasibility as an alternative to the Duckworth–Lewis method is discussed.
References F. Duckworth and T. Lewis. Duckworth Lewis: the method and the men behind it. SportsBooks Ltd, 2011. S. E. Stern. The Duckworth–Lewis–Stern method: extending the Duckworth–Lewis methodology to deal with modern scoring rates. J. Oper. Res. Soc. 67(12):1469–1480, 2016. doi:10.1057/jors.2016.30 J. Piotto Duckworth Lewis, Run Out? Honours thesis, University of Adelaide, 2008. Sambit Bai. ESPN Cricinfo. http://www.espncricinfo.com/ The R Project for Statistical Computing. Vienna, Austria, 2013. http://www.R-project.org/ T. W. Yee. The VGAM package for categorical data analysis. J. Stat. Softw. 32:1–34, 2010. doi:10.18637/jss.v032.i1
The Hubble Space Telescope UV legacy survey of galactic globular clusters - X. The radial distribution of stellar populations in NGC2808
No full textEnvironmental effects on the globular cluster blue straggler population: a statistical approach
No full textContext: Blue stragglers stars (BSS) constitute an ubiquitous population of objects whose origin involves both dynamical and stellar evolution.
Aims: In this paper we study the properties of a catalogue of BSS extracted from an homogeneous sample of 56 Galactic globular clusters (GC) observed with Wide-Field Planetary Camera 2 on board of Hubble Space Telescope (WFPC2/HST).
Methods: With the purpose of investigating the environmental dependence of the BSS formation mechanisms, we explore possible monovariate relations between the frequency of BSS (divided in different subsamples according to their location with respect to the parent cluster core radius and half-mass radius) and the main parameters of their host GC. We also performed a principal component analysis (PCA) to extract the main parent cluster parameters, which characterise the BSS family.
Results: We find that any subpopulation of BSS strongly depends on the luminosity of the cluster, on the extension of the cluster horizontal branch, and on the central velocity dispersion: more luminous clusters and clusters with a smaller central velocity dispersion have a higher BSS frequency. Moreover, we find that clusters having higher mass, higher central densities, and smaller core relaxation timescales have, on average, more luminous BSS. Finally, different dependencies seem to hold for clusters with different integrated luminosity: brighter clusters show a BSS population that depends on the collisional parameter, while BSS in fainter clusters are mostly influenced by the cluster luminosity and the dynamical timescales.
The tables with the BSS catalogues, similar to Table [see full text], are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/483/18
DESIGN OF SMART SENSORS FOR DETECTION OF PHYSICAL QUANTITIES
No full textMicrosystems and integrated smart sensors represent a flourishing business thanks to the manifold benefits of these devices with respect to their respective macroscopic counterparts. Miniaturization to micrometric scale is a turning point to obtain high sensitive and reliable devices with enhanced spatial and temporal
resolution. Power consumption compatible with battery operated systems, and reduced cost per device are also pivotal for their success. All these characteristics make investigation on this filed very active nowadays.
This thesis work is focused on two main themes: (i) design and development of a single chip smart flow-meter; (ii) design and development of readout interfaces for capacitive micro-electro-mechanical-systems (MEMS) based on capacitance to pulse width modulation conversion.
High sensitivity integrated smart sensors for detecting very small flow rates of both gases and liquids aiming to fulfil emerging demands for this kind of devices in the industrial to environmental and medical applications. On the other hand, the prototyping of such sensor is a multidisciplinary activity involving the study of
thermal and fluid dynamic phenomenon that have to be considered to obtain a correct design. Design, assisted by finite elements CAD tools, and fabrication of the sensing structures using features of a standard CMOS process is discussed in the first chapter. The packaging of fluidic sensors issue is also illustrated as it has a
great importance on the overall sensor performances. The package is charged to allow optimal interaction between fluids and the sensors and protecting the latter from the external environment. As miniaturized structures allows a great spatial resolution, it is extremely challenging to fabricate low cost packages for multiple flow rate measurements on the same chip. As a final point, a compact anemometer prototype, usable for wireless sensor network nodes, is described.
The design of the full custom circuitry for signal extraction and conditioning is coped in the second chapter, where insights into the design methods are given for analog basic building blocks such as amplifiers, transconductors, filters, multipliers,
current drivers. A big effort has been put to find reusable design guidelines and
trade-offs applicable to different design cases. This kind of rational design enabled the implementation of complex and flexible functionalities making the interface circuits able to interact both with on chip sensors and external sensors.
In the third chapter, the chip floor-plan designed in the STMicroelectronics BCD6s
process of the entire smart flow sensor formed by the sensing structures and the readout electronics is presented. Some preliminary tests are also covered here.
Finally design and implementation of very low power interfaces for typical MEMS
capacitive sensors (accelerometers, gyroscopes, pressure sensors, angular displacement and chemical species sensors) is discussed. Very original circuital topologies, based on chopper modulation technique, will be illustrated. A prototype, designed within a joint research activity is presented. Measured performances
spurred the investigation of new techniques to enhance precision and accuracy capabilities of the interface.
A brief introduction to the design of active pixel sensors interface for hybrid CMOS
imagers is sketched in the appendix as a preliminary study done during an internship in the CNM-IMB institute of Barcelona
Absolute proper motion of the Galactic open cluster M 67
No full textWe derived the absolute proper motion (PM) of the old, solar-metallicity Galactic open cluster M 67 using observations collected with CFHT (1997) and with LBT (2007). About 50 galaxies with relatively sharp nuclei allow us to determine the absolute PM of the cluster. We find (μ_α cos δ, μ_δ)_J2000.0 = (-9.6 ± 1.1, -3.7 ± 0.8) mas yr-1. By adopting a line-of-sight velocity of 33.78 ± 0.18 km s-1, and assuming a distance of 815 ± 50 pc, we explore the influence of the Galactic potential, with and without the bar and/or spiral arms, on the galactic orbit of the cluster.
Based on data acquired with the Large Binocular Telescope (LBT) at Mt. Graham, Arizona, under the Commissioning of the Large Binocular Blue Camera. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; the Ohio State University, and the Research Corporation, on behalf of the University of Notre Dame, University of Minnesota and University of Virginia; and on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.Visiting PhD Student at STScI under the “2008 graduate research assistantship” program
The blue sky of GJ3470b: the atmosphere of a low-mass planet unveiled by ground-based photometry
No full textGJ3470b is a rare example of a "hot Uranus" transiting exoplanet orbiting a nearby M1.5 dwarf. It is crucial for atmospheric studies because it is one of the most inflated low-mass planets known, bridging the boundary between "super-Earths" and Neptunian planets. We present two new ground-based light curves of GJ3470b gathered by the LBC camera at the Large Binocular Telescope. Simultaneous photometry in the ultraviolet (lambdac = 357.5 nm) and optical infrared (lambdac = 963.5 nm) allowed us to detect a significant change in the effective radius of GJ3470b as a function of wavelength. This can be interpreted as a signature of scattering processes occurring in the planetary atmosphere, which should be cloud-free and with a low mean molecular weight. The unprecedented accuracy of our measurements demonstrates that the photometric detection of Earth-sized planets around M dwarfs is achievable using 8-10 m size ground-based telescopes. We provide updated planetary parameters and a greatly improved orbital ephemeris for any forthcoming study of this planet.
Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; the Ohio State University; and the Research Corporation, on behalf of the University of Notre Dame, University of Minnesota, and University of Virginia.Photometric data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/559/A3
Hs-CRP is associated with weight, BMI, and female sex but not with endothelial function in children with type 1 diabetes
No full text© 2009 John Wiley & Sons A/SBackground: Atherosclerosis is an inflammatory process, and high-sensitivity C-reactive protein (Hs-CRP), a marker of inflammation, predicts cardiovascular events in adults. Vascular endothelial and smooth muscle dysfunction, measurable precursors of atherosclerosis, begin in childhood. Therefore, we sought to determine if Hs-CRP is associated with vascular endothelial and smooth muscle dysfunction in children with type 1 diabetes mellitus (T1DM) and healthy control subjects. Methods: Hs-CRP and endothelial function assessed by flow-mediated dilatation (FMD) and smooth muscle function assessed by glyceryl-trinitrate (GTN)-induced dilatation were measured in 121 subjects with T1DM aged 14.1 (2.9) yr, of whom 31 were also studied at 4 and 8 wk, and in 33 healthy controls aged 14.2 (3.6) yr. Results: Hs-CRP did not differ between subjects with T1DM and healthy, age-matched controls. In both controls and subjects with T1DM, Hs-CRP did not relate to FMD or GTN at baseline or at intervals over 8 wk in T1DM. Hs-CRP did not change over time. In T1DM, but not healthy controls, Hs-CRP related to body mass index (BMI) z-score (r = 0.47, p < 0.001), weight z-score (r = 0.41, p < 0.001), and female sex (p = 0.008). Conclusions: Hs-CRP is not associated with early vascular dysfunction in children with T1DM. However, in children and adolescents with T1DM, Hs-CRP was associated with female sex and children with higher BMI, suggesting that these groups may be at greater cardiovascular risk. Maintenance of a healthy BMI may be important in the prevention of vascular disease of T1DM.Karen E MacKenzie, Esko J Wiltshire, Alexia S Peña, Roger Gent, Craig Hirte, Lino Piotto and Jennifer J Coupe
Novel Extended Tetrathiafulvalenes Based on Acetylenic Spacers: Synthesis and Electronic Properties
No full textA selection of mono- and diacetylenic dithiafulvalenes was synthesized and employed for the construction of extended tetrathiafulvalenes (TTFs) with hexa-2,4-diyne-1,6-diylidene or deca-2,4,6,8-tetrayne-1,10-diylidene spacers between the two 1,3-dithiole rings. By stepwise acetylenic scaffolding using (E)-1,2-diethynylethene (DEE) building blocks, an extended TTF containing a total of 18 C(sp) and C(sp2) atoms in the spacer was prepared. The versatility of the acetylenic dithiafulvene modules was also established by the efficient synthesis of a thiophenespaced TTF, employing a palladiumcatalyzed cross-coupling reaction. The developed synthetic protocols allow functionalization of the extended TTFs in three general ways: with 1) peripheral substituents on the fulvalene cores, 2) alkynyl moieties laterally appended to the spacer, and 3) cobalt clusters involving acetylenic moieties. Strong chromophoric properties of the extended TTFs were revealed by linear and nonlinear optical spectroscopies. Extensive electrochemical studies and calculations on these compounds are also reported, as well as X-ray crystallographic analyses
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