89 research outputs found
Analysis of hybrid separation schemes for levulinic acid separation by process intensification and assessment of thermophysical properties impact
From the time levulinic acid was listed as one of the top-12 building blocks for the sugars-high value compounds conversion, the interest in this compound increased. As part of its possible production route, the definition of viable separation schemes appears of paramount importance in the overall development of levulinic acid exploitation. Hybrid sequences where liquid-liquid extraction is followed by distillation were considered proving how the direct and direct-indirect separation schemes appeared to be the best alternatives in terms of total annual cost and environmental impact. These alternatives were further analyzed to improve their design by complementing the process simulator database with thermophysical experimental values. After obtaining a reliable design for the hybrid direct and direct-indirect configurations used as benchmarks, two intensified al-ternatives were generated. The first intensified configuration is classified as thermodynamically equivalent sequence, while the second one includes a divided wall column. For both, it was achieved a reduction of the total annual cost of 11% without any penalty for the environmental impact compared to the reference case
Love: a guide for amateurs
This eBook has been produced by the Freud Museum London to explore our collective capacity for love. It is part of a series of events on the theme of Freud and Love. Freud & Eros: Love, Lust and Longing is a new exhibition at the Freud Museum London, running from 22 October 2014 – 8 March 2015. The exhibition looks at Sigmund Freud's revolutionary ideas on love and the libidinal drive through Freud's own art collection and his passionate courtship of his wife Martha Bernays. The exhibition is accompanied by an exciting programme of talks, performance, classes and events, including this ebook, event and conference. From January 2015 we will be asking you what you know about love - from how to get on with your family to how to turn your office into a love grotto. You are cordially invited to join us on this journey which we are calling #LoveAmateurs on @survivingwk and www.survivingwork.org
Mode identification in the high-amplitude {\delta} Scuti star V2367 Cyg
We report on a multi-site photometric campaign on the high-amplitude
Scuti star V2367 Cyg in order to determine the pulsation modes. We also used
high-dispersion spectroscopy to estimate the stellar parameters and projected
rotational velocity. Time series multicolour photometry was obtained during a
98-d interval from five different sites. These data were used together with
model atmospheres and non-adiabatic pulsation models to identify the spherical
harmonic degree of the three independent frequencies of highest amplitude as
well as the first two harmonics of the dominant mode. This was accomplished by
matching the observed relative light amplitudes and phases in different
wavebands with those computed by the models. In general, our results support
the assumed mode identifications in a previous analysis of Kepler data.Comment: 9 pages, 5 figures, 4 tables. Accepted for publication in MNRA
The magnetic Bp star 36 Lyncis, I. Magnetic and photospheric properties
This paper reports the photospheric, magnetic and circumstellar gas
characteristics of the magnetic B8p star 36 Lyncis (HD 79158). Using archival
data and new polarised and unpolarised high-resolution spectra, we redetermine
the basic physical properties, the rotational period and the geometry of the
magnetic field, and the photospheric abundances of various elements.}{Based on
magnetic and spectroscopic measurements, we infer an improved rotational period
of d. We determine a current epoch of the longitudinal
magnetic field positive extremum (HJD 2452246.033), and provide constraints on
the geometry of the dipole magnetic field (i\geq 56\degr, G, unconstrained). We redetermine the effective
temperature and surface gravity using the optical and UV energy distributions,
optical photometry and Balmer line profiles ( K,
), and based on the Hipparcos parallax we redetermine the
luminosity, mass, radius and true rotational speed ( \kms). We
measure photospheric abundances for 21 elements using optical and UV spectra,
and constrain the presence of vertical stratification of these elements. We
perform preliminary Doppler Imaging of the surface distribution of Fe, finding
that Fe is distributed in a patchy belt near the rotational equator. Most
remarkably, we confirm strong variations of the H line core which we
interpret as due to occultations of the star by magnetically-confined
circumstellar gas.Comment: Accepted by Astronomy and Astrophysic
A multisite photometric study of two unusual Beta Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph
We report a multisite photometric campaign for the Beta Cep stars V2052 Oph
and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren,
Johnson and Geneva time-series photometry were obtained with eight telescopes
on five continents during 182 nights. Frequency analyses of the V2052 Oph data
enabled the detection of three pulsation frequencies, the first harmonic of the
strongest signal, and the rotation frequency with its first harmonic.
Pulsational mode identification from analysing the colour amplitude ratios
confirms the dominant mode as being radial, whereas the other two oscillations
are most likely l=4. Combining seismic constraints on the inclination of the
rotation axis with published magnetic field analyses we conclude that the
radial mode must be the fundamental. The rotational light modulation is in
phase with published spectroscopic variability, and consistent with an oblique
rotator for which both magnetic poles pass through the line of sight. The
inclination of the rotation axis is 54o <i< 58o and the magnetic obliquity 58o
<beta< 66o. The possibility that V2052 Oph has a magnetically confined wind is
discussed. The photometric amplitudes of the single oscillation of V986 Oph are
most consistent with an l=3 mode, but this identification is uncertain.
Additional intrinsic, apparently temporally incoherent, light variations of
V986 Oph are reported. Different interpretations thereof cannot be
distinguished at this point, but this kind of variability appears to be present
in many OB stars. The prospects of obtaining asteroseismic information for more
rapidly rotating Beta Cep stars, which appear to prefer modes of higher l, are
briefly discussed.Comment: 12 pages, 8 figures, MNRAS, in pres
An eccentric wave in the circumstellar disc of the Be/X-ray binary X Persei
We present spectroscopic observations of the Be/X-ray binary X Per obtained during the period 2017 December-2020 January (MJD 58095-58865). In 2017 December, the H α, H β, and He I 6678 emission lines were symmetric with violet-to-red peak ratio V/R ≈ 1. During the first part of the period (2017 December-2018 August), the V/R ratio decreased to 0.5 and the asymmetry developed simultaneously in all three lines. In 2018 September, a third component with velocity ≈250 km s−1 appeared on the red side of the He I line profile. Later, this component emerged in H β, accompanied by the appearance of a red shoulder in H α. Assuming that it is due to an eccentric wave in the circumstellar disc, we find that the eccentric wave appeared first in the innermost part of the disc, it spreads out with outflowing velocity vwave ≈ 1.1 ± 0.2 km s−1, and the eccentricity of the eccentric wave is ewave ≈ 0.29 ± 0.07. A detailed understanding of the origin of such eccentricities would have applications to a wide range of systems from planetary rings to AGNs
TESS Cycle 2 observations of roAp stars with 2-min cadence data
We present the results of a systematic search of the Transiting Exoplanet
Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap
(roAp) stars observed during the Cycle 2 phase of its mission. We find seven
new roAp stars previously unreported as such and present the analysis of a
further 25 roAp stars that are already known. Three of the new stars show
multiperiodic pulsations, while all new members are rotationally variable
stars, leading to almost 70 per cent (22) of the roAp stars presented being
CVn-type variable stars. We show that targeted observations of known
chemically peculiar stars are likely to overlook many new roAp stars, and
demonstrate that multi-epoch observations are necessary to see pulsational
behaviour changes. We find a lack of roAp stars close to the blue edge of the
theoretical roAp instability strip, and reaffirm that mode instability is
observed more frequently with precise, space-based observations. In addition to
the Cycle 2 observations, we analyse TESS data for all known roAp stars. This
amounts to 18 further roAp stars observed by TESS. Finally, we list six known
roAp stars that TESS is yet to observe. We deduce that the incidence of roAp
stars amongst the Ap star population is just 5.5 per cent, raising fundamental
questions about the conditions required to excite pulsations in Ap stars. This
work, coupled with our previous work on roAp stars in Cycle 1 observations,
presents the most comprehensive, homogeneous study of the roAp stars in the
TESS nominal mission, with a collection of 112 confirmed roAp stars in total.Comment: Accepted for publication in MNRAS. 32 Pages, 2 Tables, 77 Figure
<em>TESS</em> Cycle 2 observations of roAp stars with 2-min cadence data
\ua9 The Author(s) 2023.We present the results of a systematic search of the Transiting Exoplanet Survey Satellite (TESS) 2-min cadence data for new rapidly oscillating Ap (roAp) stars observed during the Cycle 2 phase of its mission. We find seven new roAp stars previously unreported as such and present the analysis of a further 25 roAp stars that are already known. Three of the new stars show multiperiodic pulsations, while all new members are rotationally variable stars, leading to almost 70 per cent (22) of the roAp stars presented being α2 CVn-type variable stars. We show that targeted observations of known chemically peculiar stars are likely to overlook many new roAp stars, and demonstrate that multiepoch observations are necessary to see pulsational behaviour changes. We find a lack of roAp stars close to the blue edge of the theoretical roAp instability strip, and reaffirm that mode instability is observed more frequently with precise, space-based observations. In addition to the Cycle 2 observations, we analyse TESS data for all-known roAp stars. This amounts to 18 further roAp stars observed by TESS. Finally, we list six known roAp stars that TESS is yet to observe. We deduce that the incidence of roAp stars amongst the Ap star population is just 5.5 per cent, raising fundamental questions about the conditions required to excite pulsations in Ap stars. This work, coupled with our previous work on roAp stars in Cycle 1 observations, presents the most comprehensive, homogeneous study of the roAp stars in the TESS nominal mission, with a collection of 112 confirmed roAp stars in total
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