ABSTRACT
We processed images taken with the Hubble Space Telescope(HST) to investigate any morphological features in the inner coma suggestive of a peculiar activity on the nucleus of the ...interstellar comet 2I/Borisov. The coma shows an evident elongation, in the position angle (PA) ∼0−180○ direction, which appears related to the presence of a jet originating from a single active source on the nucleus. A counterpart of this jet directed towards PA ∼10○ was detected through analysis of the changes of the inner coma morphology on HST images taken on different dates and processed with different filters. These findings indicate that the nucleus is probably rotating with a spin axis projected near the plane of the sky and oriented at PA ∼100−280○ , and that the active source is lying in a near-equatorial position. Subsequent observations of HST allowed us to determine the direction of the spin axis at right ascension (RA) = 17h20m ± 15○ and declination (Dec.) = $-35^\circ \, \pm 10^\circ$. Photometry of the nucleus on HST images of 2019 October 12 only spans ∼7 h, insufficient to reveal a rotational period. The morphology exhibited by the interstellar comet 2I/Borisov is very similar to that of comet C/2014 B1 suggesting that the activation processes are the same as those observed in the Solar system native comets.
ABSTRACT
The recent close approach of comet C/2020 F3 (NEOWISE) allowed us to study the morphology of its inner coma. From the measurement of the dust ejection velocity on spiral structures expanding ...around the nucleus, we estimated a mean deprojected expansion velocity Vd = 1.11 ± 0.08 km s−1. Assuming that a new shell formed after every rotation of the comet, a period of 7.8 ± 0.2 h was derived. The spin axis orientation was estimated at RA 210° ± 10°, Dec. +35° ± 10°. The coma morphology appears related to two strong, diametrically opposite emissions located at mid-latitudes on the nucleus. A qualitative modelling of the coma produced consistent results with a wide range of dust sizes (0.80–800 μm), with inversely correlated densities (0.003–3.0 g cm−3). Images taken with Vj and r-Sloan filters showed a greater concentration of dust in the first two shells, and an increasing density of radicals emitting in the B and V band passes from the third shell outwards. Striae-like structures in the tail suggest that dust particles have different sizes.
This paper presents the case study of two wind turbines installed in Mexico which are analyzed using the life cycle assessment (LCA) methodology. Environmental impacts of different fabrication ...materials and electricity consumption were studied for the main turbine components. The designs of both turbines were examined through the phases of manufacture, construction, and final disposal. Both turbines (turbine A and turbine B) were of 2.0 megawatts (MW). Results ascertain that the most intensive environmental impacts come from the nacelle and tower components of both turbines; and that within life cycle phases, turbine A influences the environment less than turbine B, specifically during manufacture and final disposal. This study is valuable for decision makers in the domain of technological product design and marketing; in order to determine which features of the wind turbines can be modified to mitigate environmental impacts, contributing to technological innovation in the domains of sustainability and renewable energies in Mexico.
•Two wind turbines were compared by LCA methodology in Mexican conditions.•The overall assessment of the environmental impacts in all phases was achieved.•LCA technique revealed that the nacelle and tower have most environmental impacts.•Environmental impacts reduction in LC of turbines will enrich Mexican wind industry.
Context. The available set of spin and shape modelled asteroids is strongly biased against slowly rotating targets and those with low lightcurve amplitudes. This is due to the observing selection ...effects. As a consequence, the current picture of asteroid spin axis distribution, rotation rates, radiometric properties, or aspects related to the object’s internal structure might be affected too. Aims. To counteract these selection effects, we are running a photometric campaign of a large sample of main belt asteroids omitted in most previous studies. Using least chi-squared fitting we determined synodic rotation periods and verified previous determinations. When a dataset for a given target was sufficiently large and varied, we performed spin and shape modelling with two different methods to compare their performance. Methods. We used the convex inversion method and the non-convex SAGE algorithm, applied on the same datasets of dense lightcurves. Both methods search for the lowest deviations between observed and modelled lightcurves, though using different approaches. Unlike convex inversion, the SAGE method allows for the existence of valleys and indentations on the shapes based only on lightcurves. Results. We obtain detailed spin and shape models for the first five targets of our sample: (159) Aemilia, (227) Philosophia, (329) Svea, (478) Tergeste, and (487) Venetia. When compared to stellar occultation chords, our models obtained an absolute size scale and major topographic features of the shape models were also confirmed. When applied to thermophysical modelling (TPM), they provided a very good fit to the infrared data and allowed their size, albedo, and thermal inertia to be determined. Conclusions. Convex and non-convex shape models provide comparable fits to lightcurves. However, some non-convex models fit notably better to stellar occultation chords and to infrared data in sophisticated thermophysical modelling (TPM). In some cases TPM showed strong preference for one of the spin and shape solutions. Also, we confirmed that slowly rotating asteroids tend to have higher-than-average values of thermal inertia, which might be caused by properties of the surface layers underlying the skin depth.
An experimental and numerical research, aimed at evaluating the in-plane seismic performance of an innovative external steel modular system for the strengthening of load-bearing masonry walls, is ...currently underway at the EUCENTRE Foundation in Pavia. This paper presents, in particular, the results of the experimental part of this research campaign. Solid clay brick and hollow clay "doppio UNI" masonry typologies, representing common solutions in Italian existing buildings, were considered. After the mechanical characterization of the masonry and of the components of the reinforcement system, cyclic in-plane pseudo-static tests on full-scale specimens were performed in order to investigate the influence of the proposed system on the in-plane response of the walls, compared to the unreinforced conditions. The main seismic parameters of the masonry walls (i.e. elastic stiffness, lateral resistance, displacement capacity and energy dissipation) were assessed depending on the achieved damage mechanism. The proposed reinforcement system provided very promising results, improving the in-plane seismic performance of masonry walls at serviceability and especially at ultimate conditions, with a significant increase of deformation capacity above all in the case of shear mechanisms.
Within the European FP7 Project "INSYSME", the research unit of the University of Pavia has developed a seismic-resistant masonry infill system with original details, which subdivides the masonry ...panel into horizontal stripes through the insertion of "sliding joints" and deformable joints at the infill-frame interface. The out-of-plane stability is governed by the flexural/arching resistance of the masonry stripes and adequate supports at the RC columns. An extensive experimental campaign has been performed. In this paper, the results of the out-of-plane dynamic tests on shaking-table conducted on the specimens with and without opening are discussed. These types of tests, never applied before on innovative masonry infill typologies, have involved a very demanding testing protocol, constituted of artificial input motions at increasing intensity. To interpret the test results and provide first indications for safety checks, simplified numerical and analytical simulations of the tests have been conducted. According to the out-of-plane experimental performance of this innovative infill system and to the satisfactory in-plane response, the solution appears to be very promising for real applications.
We report the detection of transits by the $3.1~M_{\rm Jup}$ companion to the $V=8.17$ G0V star HD 17156. The transit was observed by three independant observers on Sep. 9/10, 2007 (two in central ...Italy and one in the Canary Islands), who obtained detections at confidence levels of 3.0σ, 5.3σ, and 7.9σ, respectively. The observations were carried out under the auspices of the Transitsearch.org network, which organizes follow-up photometric transit searches of known planet-bearing stars during the time intervals when transits might be expected to occur. Analyses of the 7.9σ data set indicates a transit depth $d=0.0062$ ± 0.0004 and a transit duration $t=186$ ± 5 min. These values are consistent with the transit of a Jupiter-sized planet with an impact parameter $b=a \cos{i}/R_{\star} \sim 0.8$. This planet occupies a unique regime among known transiting extrasolar planets, both as a result of its large orbital eccentricity ($e=0.67$) and long orbital period ($P=21.2~{\rm d}$). The planet receives a 26-fold variation in insolation during the course of its orbit, which will make it a useful object for characterizing exoplanetary atmospheric dynamics.
Several architectural configurations of unreinforced masonry residential buildings are designed according to the different methods proposed in the Italian code: rules for the so-called simple masonry ...buildings, linear and nonlinear static analyses. Always complying with code requirements, for each building-site combination, the design was made, as much as possible, without an excessive margin of safety. The different design methods provided buildings with very different levels of safety, being linear static analysis largely overconservative with respect to the nonlinear static approach. These buildings were then analyzed in the companion paper.
Three Mexican power sector scenarios for the period 1996–2025 are subjected to a cost-benefit analysis. The three scenarios are: base (using fuel oil), official (introducing natural gas) and ...transition (incorporating renewable energy). Also technical, economic and energy resources databases are constructed to supply information for the analysis. Benefit/cost ratios (B/C) are obtained by varying the following economic parameters: fossil fuel average prices, discount rates and capital costs evolution as an expression of technological change. For present technical and economic conditions, the B/C ratio of the official scenario is more economically favorable than that of the transition and the transition is more favorable than the base scenario. Also, the viability of the transition scenario increases rapidly when technological change is taken into consideration.
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