31 research outputs found
IMPACT OF FRESH AND SHEARED OIL VISCOSITY REQUIREMENTS ON THE FORMULATION OF HYDRAULIC FLUIDS
Već se godinama odabir hidrauličkih ulja obavlja na temelju ISO 3448 klasifikacije viskoznosti razvijene sredinom sedamdesetih godina, koja definira određeni broj diskontinuiranih gradacija viskoznosti na temelju minimalne i maksimalne kinematičke viskoznosti kod 40 °C. Aktivnošću ASTM-a 1997. godine uvedena je ASTM D 6080-97 klasifikacija koja uključuje nekoliko zahtjeva za viskoznošću svježeg ulja i ulja nakon smicanja. U posljednje vrijeme predložene su dvije nove postavke viskoznosti i ograničenje indeksa viskoznosti kod svježih ulja i ulja nakon smicanja kako bi se poboljšala učinkovitost opreme u usporedbi s konvencionalnim HM uljima. Definirana je maksimalna djelotvornost hidrauličke tekućine (MEHF) i National Fluid Power Association (NFPA) smjernice za odabir viskoznosti hidrauličkih tekućina. Svaki dodatni viskometrijski zahtjev za određivanje ISO gradacije viskoznosti uvodi nova ograničenja na kinematičku viskoznost i indeks viskoznosti kod formulacije. Korištenjem velikog broja mješavina temeljenih na poboljšivačima indeksa viskoznosti s različitom smičnom stabilnosti, ispitan je utjecaj ograničenja viskoznosti, uključen u MEHF i NFPA smjernice, na područje formulacije tri najčešće ISO gradacije viskoznosti. Utvrđeno je da stupanj preklapanja smjernica, takozvano "područje formulacije", ovisi o ISO gradaciji viskoznosti i smičnoj stabilnosti poboljšivača indeksa viskoznosti kojeg se razmatra. Ovaj rad pruža okvir za poboljšanu sposobnost odabira ciljeva formuliranja s obzirom na spomenute nove smjernice.For many years hydraulic oils were selected using the ISO 3448 viscosity classification. Developed in the mid-seventies, it defines a finite number of discontinuous grades based on a minimum and maximum viscosity at 40 °C. In 1997, efforts by ASTM resulted in the ASTM D 6080-97 classification that included several viscosity requirements on the fresh and sheared oil. More recently, two new sets of viscosity and VI limits on the fresh and sheared oil were proposed to provide improved equipment efficiency compared to conventional HM oils. These are the Maximum Efficiency Hydraulic Fluid definition (MEHF) and the National Fluid Power Association (NFPA) guidelines for hydraulic fluid viscosity selection.
Any additional viscometric requirement to the ISO grade definition introduces new constraints on both the kinematic viscosity and VI of the formulation. Using a large number of blends based on VI Improvers having a different shear stability level, we investigated the impact of the viscosity constraints included in the MEHF and NFPA guidelines on the formulation windows of the three most common ISO grades. The degree to which the guidelines overlap, the so-called “formulation window” was found to depend on the ISO grade and shear stability of the VI Improver considered. This work provides a framework for an improved ability to select formulation targets considering these new guidelines
IMPACT OF FRESH AND SHEARED OIL VISCOSITY REQUIREMENTS ON THE FORMULATION OF HYDRAULIC FLUIDS
Već se godinama odabir hidrauličkih ulja obavlja na temelju ISO 3448 klasifikacije viskoznosti razvijene sredinom sedamdesetih godina, koja definira određeni broj diskontinuiranih gradacija viskoznosti na temelju minimalne i maksimalne kinematičke viskoznosti kod 40 °C. Aktivnošću ASTM-a 1997. godine uvedena je ASTM D 6080-97 klasifikacija koja uključuje nekoliko zahtjeva za viskoznošću svježeg ulja i ulja nakon smicanja. U posljednje vrijeme predložene su dvije nove postavke viskoznosti i ograničenje indeksa viskoznosti kod svježih ulja i ulja nakon smicanja kako bi se poboljšala učinkovitost opreme u usporedbi s konvencionalnim HM uljima. Definirana je maksimalna djelotvornost hidrauličke tekućine (MEHF) i National Fluid Power Association (NFPA) smjernice za odabir viskoznosti hidrauličkih tekućina. Svaki dodatni viskometrijski zahtjev za određivanje ISO gradacije viskoznosti uvodi nova ograničenja na kinematičku viskoznost i indeks viskoznosti kod formulacije. Korištenjem velikog broja mješavina temeljenih na poboljšivačima indeksa viskoznosti s različitom smičnom stabilnosti, ispitan je utjecaj ograničenja viskoznosti, uključen u MEHF i NFPA smjernice, na područje formulacije tri najčešće ISO gradacije viskoznosti. Utvrđeno je da stupanj preklapanja smjernica, takozvano "područje formulacije", ovisi o ISO gradaciji viskoznosti i smičnoj stabilnosti poboljšivača indeksa viskoznosti kojeg se razmatra. Ovaj rad pruža okvir za poboljšanu sposobnost odabira ciljeva formuliranja s obzirom na spomenute nove smjernice.For many years hydraulic oils were selected using the ISO 3448 viscosity classification. Developed in the mid-seventies, it defines a finite number of discontinuous grades based on a minimum and maximum viscosity at 40 °C. In 1997, efforts by ASTM resulted in the ASTM D 6080-97 classification that included several viscosity requirements on the fresh and sheared oil. More recently, two new sets of viscosity and VI limits on the fresh and sheared oil were proposed to provide improved equipment efficiency compared to conventional HM oils. These are the Maximum Efficiency Hydraulic Fluid definition (MEHF) and the National Fluid Power Association (NFPA) guidelines for hydraulic fluid viscosity selection.
Any additional viscometric requirement to the ISO grade definition introduces new constraints on both the kinematic viscosity and VI of the formulation. Using a large number of blends based on VI Improvers having a different shear stability level, we investigated the impact of the viscosity constraints included in the MEHF and NFPA guidelines on the formulation windows of the three most common ISO grades. The degree to which the guidelines overlap, the so-called “formulation window” was found to depend on the ISO grade and shear stability of the VI Improver considered. This work provides a framework for an improved ability to select formulation targets considering these new guidelines
A water budget dichotomy of rocky protoplanets from Al-heating
In contrast to the water-poor inner solar system planets, stochasticity
during planetary formation and order of magnitude deviations in exoplanet
volatile contents suggest that rocky worlds engulfed in thick volatile ice
layers are the dominant family of terrestrial analogues among the extrasolar
planet population. However, the distribution of compositionally Earth-like
planets remains insufficiently constrained, and it is not clear whether the
solar system is a statistical outlier or can be explained by more general
planetary formation processes. Here we employ numerical models of planet
formation, evolution, and interior structure, to show that a planet's bulk
water fraction and radius are anti-correlated with initial Al levels in
the planetesimal-based accretion framework. The heat generated by this
short-lived radionuclide rapidly dehydrates planetesimals prior to accretion
onto larger protoplanets and yields a system-wide correlation of planet bulk
abundances, which, for instance, can explain the lack of a clear orbital trend
in the water budgets of the TRAPPIST-1 planets. Qualitatively, our models
suggest two main scenarios of planetary systems' formation: high-Al
systems, like our solar system, form small, water-depleted planets, whereas
those devoid of Al predominantly form ocean worlds, where the mean
planet radii between both scenarios deviate by up to about 10%.Comment: Preprint version; free-to-read journal version at
https://rdcu.be/bmdlw; blog article at https://t.co/p6SValG1i
Near-Infrared Spectroscopy of the Extrasolar Planet HR 8799 b
[Abridged] We present 2.12-2.23 um high contrast integral field spectroscopy
of the extrasolar planet HR 8799 b. Our observations were obtained with OSIRIS
on the Keck II telescope and sample the 2.2 um CH4 feature, which is useful for
spectral classification and as a temperature diagnostic for ultracool objects.
The spectrum of HR 8799 b is relatively featureless, with little or no methane
absorption, and does not exhibit the strong CH4 seen in T dwarfs of similar
absolute magnitudes. Overall, we find that HR 8799 b has a spectral type
consistent with L5-T2, although its SED is atypical compared to most field
objects. We fit the 2.2 um spectrum and the infrared SED using the Hubeny &
Burrows, Burrows et al., and Ames-Dusty model atmosphere grids, which
incorporate nonequilibrium chemistry, non-solar metallicities, and clear and
cloudy variants. No models agree with all of the data, but those with
intermediate clouds produce significantly better fits. The largest discrepancy
occurs in the J-band, which is highly suppressed in HR 8799 b. The best-fitting
effective temperatures range from 1300-1700 K with radii between ~0.3-0.5 RJup.
These values are inconsistent with evolutionary model-derived values of 800-900
K and 1.1-1.3 RJup based on the luminosity of HR 8799 b and the age of HR 8799,
a discrepancy that probably results from imperfect atmospheric models or the
limited range of physical parameters covered by the models. The low temperature
inferred from evolutionary models indicates that HR 8799 b is ~400 K cooler
than field L/T transition objects, providing further evidence that the L/T
transition is gravity-dependent. With an unusually dusty photosphere, an
exceptionally low luminosity for its spectral type, and hints of extreme
secondary physical parameters, HR 8799 b appears to be unlike any class of
field brown dwarf currently known.Comment: 21 pages, 23 figures; accepted by Ap
High precision astrometry mission for the detection and characterization of nearby habitable planetary systems with the Nearby Earth Astrometric Telescope (NEAT)
(abridged) A complete census of planetary systems around a volume-limited
sample of solar-type stars (FGK dwarfs) in the Solar neighborhood with uniform
sensitivity down to Earth-mass planets within their Habitable Zones out to
several AUs would be a major milestone in extrasolar planets astrophysics. This
fundamental goal can be achieved with a mission concept such as NEAT - the
Nearby Earth Astrometric Telescope. NEAT is designed to carry out space-borne
extremely-high-precision astrometric measurements sufficient to detect
dynamical effects due to orbiting planets of mass even lower than Earth's
around the nearest stars. Such a survey mission would provide the actual
planetary masses and the full orbital geometry for all the components of the
detected planetary systems down to the Earth-mass limit. The NEAT performance
limits can be achieved by carrying out differential astrometry between the
targets and a set of suitable reference stars in the field. The NEAT instrument
design consists of an off-axis parabola single-mirror telescope, a detector
with a large field of view made of small movable CCDs located around a fixed
central CCD, and an interferometric calibration system originating from
metrology fibers located at the primary mirror. The proposed mission
architecture relies on the use of two satellites operating at L2 for 5 years,
flying in formation and offering a capability of more than 20,000
reconfigurations (alternative option uses deployable boom). The NEAT primary
science program will encompass an astrometric survey of our 200 closest F-, G-
and K-type stellar neighbors, with an average of 50 visits. The remaining time
might be allocated to improve the characterization of the architecture of
selected planetary systems around nearby targets of specific interest (low-mass
stars, young stars, etc.) discovered by Gaia, ground-based high-precision
radial-velocity surveys.Comment: Accepted for publication in Experimental Astronomy. The full member
list of the NEAT proposal and the news about the project are available at
http://neat.obs.ujf-grenoble.fr. The final publication is available at
http://www.springerlink.co
A full transit of v 2 Lupi d and the search for an exomoon in its Hill sphere with CHEOPS
The planetary system around the naked-eye star v2 Lupi (HD 136352; TOI-2011) is composed of three exoplanets with masses of 4.7, 11.2, and 8.6 Earth masses (M⊕). The TESS and CHEOPS missions revealed that all three planets are transiting and have radii straddling the radius gap separating volatile-rich and volatile-poor super-earths. Only a partial transit of planet d had been covered so we re-observed an inferior conjunction of the long-period 8.6 M⊕ exoplanet v2 Lup d with the CHEOPS space telescope. We confirmed its transiting nature by covering its whole 9.1 h transit for the first time. We refined the planet transit ephemeris to P = 107.13610.0022+0.0019 days and Tc = 2459009.77590.0096+0.0101 BJDTDB, improving by ~40 times on the previously reported transit timing uncertainty. This refined ephemeris will enable further follow-up of this outstanding long-period transiting planet to search for atmospheric signatures or explore the planet s Hill sphere in search for an exomoon. In fact, the CHEOPS observations also cover the transit of a large fraction of the planet s Hill sphere, which is as large as the Earth s, opening the tantalising possibility of catching transiting exomoons. We conducted a search for exomoon signals in this single-epoch light curve but found no conclusive photometric signature of additional transiting bodies larger than Mars. Yet, only a sustained follow-up of v2 Lup d transits will warrant a comprehensive search for a moon around this outstanding exoplanet
Nightside condensation of iron in an ultra-hot giant exoplanet
Ultra-hot giant exoplanets receive thousands of times Earth's insolation.
Their high-temperature atmospheres (>2,000 K) are ideal laboratories for
studying extreme planetary climates and chemistry. Daysides are predicted to be
cloud-free, dominated by atomic species and substantially hotter than
nightsides. Atoms are expected to recombine into molecules over the nightside,
resulting in different day-night chemistry. While metallic elements and a large
temperature contrast have been observed, no chemical gradient has been measured
across the surface of such an exoplanet. Different atmospheric chemistry
between the day-to-night ("evening") and night-to-day ("morning") terminators
could, however, be revealed as an asymmetric absorption signature during
transit. Here, we report the detection of an asymmetric atmospheric signature
in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this
signature thanks to the combination of high-dispersion spectroscopy with a
large photon-collecting area. The absorption signal, attributed to neutral
iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be
explained by a combination of planetary rotation and wind blowing from the hot
dayside. In contrast, no signal arises from the nightside close to the morning
terminator, showing that atomic iron is not absorbing starlight there. Iron
must thus condense during its journey across the nightside.Comment: Published in Nature (Accepted on 24 January 2020.) 33 pages, 11
figures, 3 table
TOI-836 : a super-Earth and mini-Neptune transiting a nearby K-dwarf
Funding: TGW, ACC, and KH acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant ST/R003203/1.We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (T = 8.5 mag), high proper motion (∼200 mas yr−1), low metallicity ([Fe/H]≈−0.28) K-dwarf with a mass of 0.68 ± 0.05 M⊙ and a radius of 0.67 ± 0.01 R⊙. We obtain photometric follow-up observations with a variety of facilities, and we use these data-sets to determine that the inner planet, TOI-836 b, is a 1.70 ± 0.07 R⊕ super-Earth in a 3.82 day orbit, placing it directly within the so-called ‘radius valley’. The outer planet, TOI-836 c, is a 2.59 ± 0.09 R⊕ mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that TOI-836 b has a mass of 4.5 ± 0.9 M⊕, while TOI-836 c has a mass of 9.6 ± 2.6 M⊕. Photometric observations show Transit Timing Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet.Publisher PDFPeer reviewe
TOI-836: A super-Earth and mini-Neptune transiting a nearby K-dwarf
We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364)
using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (
mag), high proper motion ( mas yr), low metallicity
([Fe/H]) K-dwarf with a mass of M and a
radius of R. We obtain photometric follow-up
observations with a variety of facilities, and we use these data-sets to
determine that the inner planet, TOI-836 b, is a R
super-Earth in a 3.82 day orbit, placing it directly within the so-called
'radius valley'. The outer planet, TOI-836 c, is a R
mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that
TOI-836 b has a mass of M , while TOI-836 c has a mass
of M. Photometric observations show Transit Timing
Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are
no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by
an undetected exterior planet
Two warm Neptunes transiting HIP 9618 revealed by TESS and Cheops
peer reviewedHIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright (G = 9.0 mag) solar analogue. TESS photometry revealed the star to have two candidate planets with radii of 3.9 ± 0.044 R (HIP 9618 b) and 3.343 ± 0.039 R (HIP 9618 c). While the 20.77291 d period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-d gap in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d. High-resolution spectroscopy with HARPS-N, SOPHIE, and CAFE revealed a mass of 10.0 ± 3.1M for HIP 9618 b, which, according to our interior structure models, corresponds to a 6.8 ± 1.4 per cent gas fraction. HIP 9618 c appears to have a lower mass than HIP 9618 b, with a 3-sigma upper limit of 50 d, opening the door for the atmospheric characterization of warm (Teq < 750 K) sub-Neptunes