We observed short-period comet 252P/LINEAR post-perihelion during its 2016 passage, which presented a favorable opportunity to survey its chemical composition at a close Earth approach (∼0.14 au). We ...characterized the comet's chemical composition on four dates (UT 2016 April 12, 19, 26, and 29) using spectroscopic measurements with the Near-infrared Spectrograph (NIRSPEC) at the Keck Observatory on Maunakea, HI. Our high-resolution infrared spectra yielded production rates for four species (H2O, CH3OH, C2H6, and HCN) and upper limits for five species (NH3, H2CO, C2H2, CO, and CH4). We measured water at an average production rate of 4.9 0.1 × 1027 molec s−1. The chemical properties of 252P suggest a rather typical composition, yet somewhat enriched in methanol and ethane but low in formaldehyde (upper limit) compared to other short-period comets surveyed at infrared wavelengths. Analysis of the ortho/para ratio in water indicates a nuclear spin temperature larger than ∼38 K, consistent with statistical equilibrium (2 ). Spatial distributions of gases, which are representative of possible heterogeneity in the nucleus and/or gas dynamics upon sublimation, showed rather symmetric profiles, with subtle enhancements of the more volatile species C2H6 and HCN toward the sunward hemisphere, while water showed spatial distributions that were extended toward the anti-sunward hemisphere. The continuum was characterized by a narrow distribution. We place our infrared results in the context of observations with the Discovery Channel Telescope, the James Clerk Maxwell submillimeter Telescope, and the Hubble Space Telescope.
The electric resistivity of a clean multi-walled carbon nanotube (MWNT) mat sample was studied at temperatures
T between 300 and 1900
K. We found that the resistivity
ρ decreases monotonously with ...increasing temperature without showing any sign of turn up. Our results can be well fitted with a power law of
T
−
α
within the framework of one dimensional Luttinger liquid theory with
α
=
0.13 or with a simple thermally activated inter shell hopping model.
In this paper we present an experimental strategy to measure the micro power dissipation due to Foucault "eddy" currents in a copper cylinder rolling on two parallel conductive rails in the presence ...of a magnetic field. Foucault power dissipation is obtained from kinematical measurements carried out by using a common PC webcam and video analysis done by means of software tools freely available within Windows operating system ("Paint" and "Movie Maker"). The proposed method allows us to experimentally discern the contribution to dissipation due to the velocity-independent rolling friction from that owed to the viscous-like friction emerging from complex electrodynamic interactions among eddy currents and the external magnetic field. In this way a microdissipation of some tens of muW is measured. The easily reproducible experimental setup, the simple implementation of data analysis and the discussion on various experimental approaches and strategies make the proposed activity highly significant for university undergraduates, since involved crucial skills can be efficiently strengthened. (Contains 1 footnote, 1 table, and 7 figures.)
Under some conditions, the method of images (well known in electrostatics) may be implemented in magnetostatic problems too, giving an excellent example of the usefulness of formal analogies in the ...description of physical systems. In this paper, we develop a quantitative model for the magnetic interactions underlying the so-called GeomagTM paradox and describe a quantitative experimental investigation to validate the model. The validity ranges of some approximations involved in this problem are quantitatively discussed and the advantages of a dimensionless formulation of the interaction are pointed out. This work offers many educational suggestions suitable for university students. (Contains 3 footnotes and 13 figures.)
In this article we describe an experimental learning path about electromagnetic induction which uses an Atwood machine where one of the two hanging bodies is a cylindrical magnet falling through a ...plexiglass guide, surrounded either by a coil or by a copper pipe. The first configuration (magnet falling across a coil) allows students to quantitatively study the Faraday-Neumann-Lenz law, while the second configuration (falling through a copper pipe) permits learners to investigate the complex phenomena of induction by quantifying the amount of electric power dissipated through the pipe as a result of Foucault eddy currents, when the magnet travels through the pipe. The magnet's fall acceleration can be set by adjusting the counterweight of the Atwood machine so that both the kinematic quantities associated with it and the electromotive force induced within the coil are continuously and quantitatively monitored (respectively, by a common personal computer (PC) equipped with a webcam and by freely available software that makes it possible to use the audio card to convert the PC into an oscilloscope). Measurements carried out when the various experimental parameters are changed provide a useful framework for a thorough understanding and clarification of the conceptual nodes related to electromagnetic induction. The proposed learning path is under evaluation in various high schools participating in the project "Lauree Scientifiche" promoted by the Italian Department of Education. (Contains 15 figures and 2 footnotes.)
We report an electron spectroscopy study on Na
+ ion implantation and Na atom deposition on carbon structures. Our results show that, for implanted Na at the same ion dose, the Na surface ...concentration decreases with the structure order, while deposited Na particles readily diffuse in the bulk.
Thermo- and iono-luminescence on MWCNT bundles Barberio, M.; Barone, P.; Bonanno, A. ...
Radiation physics and chemistry (Oxford, England : 1993),
03/2007, Letnik:
76, Številka:
3
Journal Article
Recenzirano
In this paper, we report preliminary studies on luminescence emission from bundles of multiwalled carbon nanotube (MWCNT) induced either by heating (thermo-luminescence, TL) or by ion bombardment of ...(iono-luminescence, IL) the sample. For N
2 exposure we do not observe any evidence of N
2 absorption on the sample. For 2
keV
N
2
+
ion bombardment or Na vapour deposition or Na
+ ion implantation, IL spectra show a continuous decrease of luminescence intensity. These results are interpreted as due to an increasing sample doping.
The two rings of (50000) Quaoar Pereira, C. L.; Sicardy, B.; Morgado, B. E. ...
Astronomy & astrophysics,
05/2023, Letnik:
673
Journal Article
Recenzirano
Odprti dostop
Context.
Quaoar is a classical trans-Neptunian object (TNO) with an area-equivalent diameter of 1100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations ...observed between 2018 and 2021, an inhomogeneous ring (Q1R, i.e., Quaoar’s first ring) has been detected around this body.
Aims.
A new stellar occultation by Quaoar was observed on August 9, 2022, with the aim of improving Quaoar’s shape models and the physical parameters of Q1R, while searching for additional material around the body.
Methods.
The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements).
Results.
Quaoar’s elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of 579.5 ± 4.0 km, apparent oblateness of 0.12 ± 0.01, and area-equivalent radius of 543 ± 2 km. Quaoar’s limb orientation is consistent with Q1R and Weywot orbiting in Quaoar’s equatorial plane. The orbital radius of Q1R is refined to a value of 4057 ± 6 km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of ∼5 km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of 2520 ± 20 km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10 km and a normal optical depth of ∼0.004. Just as Q1R, it also lies outside Quaoar’s classical Roche limit.
