463 research outputs found
Weight Reduction in Electric Motors: Aluminum vs Copper Wires
Environmental concerns driven by climate change have resulted in increased market demand for lightweight and inexpensive electric vehicles. This study examines the feasibility of replacing copper conductors with aluminum conductors in automotive scale electric motors to address this demand. A comprehensive review of the literature contrasting aluminum and copper conductors is included to create a unified source for future research. This study also contains a two-part formability and windability analysis of square cross section electrical conductor aluminum and rectangular electrolytic tough pitch copper. The first part of the analysis applies standardized testing from ASTM D1676 to characterize the formability and windability of both conductors. Aluminum saw formability and windability advantages over copper, especially regarding springback, accommodation of elongation during high speed winding, and repeated absorption of bends and twists during winding; however, insulation adhesion and delamination issues occurred for elongation beyond 10% due to incompatibility of properties between the polymer coating and aluminum wire. The second part of the analysis compares forming behaviour of aluminum to known results for copper using a novel wire bending simulator machine. The effects of normal load, wire travel speed, and forming angle on coefficient of friction (COF) are analyzed to determine the feasibility of using aluminum for hairpin windings. The analysis finds that COF increases with both wire travel speed and forming angle. COF versus normal load shows a spike in COF followed by a sharp decrease indicative of a deformation mechanism that copper did not experience. Macroscopic analysis reveals aluminum to be more susceptible to damage from the forming equipment when compared to copper. Microscopic analysis reveals shingles and a suspected near-surface deformed layer at the aluminum/insulation interface. Detachment of these imperfections was found to occur at peak COF loads and higher from crack propagation and insulation flow into said cracks. Overall, this study shows aluminum is a viable conductor that provides significant cost and weight savings in electric machines with similar performance to copper; however, further improvement to aluminum surface quality and insulation properties is required to effectively replace copper
Near-infrared integral-field spectra of the planet/brown dwarf companion AB Pic b
Chauvin et al. 2005 imaged a co-moving companion at ~260 AU from the young
star AB Pic A. Evolutionary models predictions based on J H K photometry of AB
Pic b suggested a mass of ~13 - 14 MJup, placing the object at the
deuterium-burning boundary. We used the adaptive-optics-fed integral field
spectrograph SINFONI to obtain high quality medium-resolution spectra of AB Pic
b (R = 1500-2000) over the 1.1 - 2.5 microns range. Our analysis relies on the
comparison of our spectra to young standard templates and to the latest
libraries of synthetic spectra developed by the Lyon's Group. AB Pic b is
confirmed to be a young early-L dwarf companion. We derive a spectral type
L0-L1 and find several features indicative of intermediate gravity atmosphere.
A comparison to synthetic spectra yields Teff = 2000+100-300 K and log(g) = 4
+- 0.5 dex. The determination of the derived atmospheric parameters of AB Pic b
is limited by a non-perfect match of current atmosphere spectra with our
near-infrared observations of AB Pic b. The current treatment of dust settling
and missing molecular opacity lines in the atmosphere models could be
responsible. By combining the observed photometry, the surface fluxes from
atmosphere models and the known distance of the system, we derive new mass,
luminosity and radius estimates of AB Pic b. They confirm independently the
evolutionary model predictions. We finally review the current methods used to
characterize planetary mass companions and discuss them in the perspective of
future planet deep imaging surveys.Comment: 8 pages, 8 figure
Spectroscopy across the brown dwarf/planetary mass boundary - I. Near-infrared JHK spectra
With a uniform VLT SINFONI data set of nine targets, we have developed an
empirical grid of J,H,K spectra of the atmospheres of objects estimated to have
very low substellar masses of \sim5-20 MJup and young ages of \sim1-50 Myr.
Most of the targets are companions, objects which are especially valuable for
comparison with atmosphere and evolutionary models, as they present rare cases
in which the age is accurately known from the primary. Based on the sample
youth, all objects are expected to have low surface gravity, and this study
investigates the critical early phases of the evolution of substellar objects.
The spectra are compared with grids of five different theoretical atmosphere
models. This analysis represents the first systematic model comparison with
infrared spectra of young brown dwarfs. The fits to the full JHK spectra of
each object result in a range of best fit effective temperatures of +/-150-300K
whether or not the full model grid or a subset restricted to lower log(g)
values is used. This effective temperature range is significantly larger than
the uncertainty typically assigned when using a single model grid. Fits to a
single wavelength band can vary by up to 1000K using the different models.
Since the overall shape of these spectra is governed more by the temperature
than surface gravity, unconstrained model fits did not find matches with low
surface gravity or a trend in log(g) with age. This suggests that empirical
comparison with spectra of unambiguously young objects targets (such as these
SINFONI data) may be the most reliable method to search for indications of low
surface gravity and youth. For two targets, the SINFONI data are a second epoch
and the data show no variations in morphology over time. The analysis of two
other targets, AB Pic B and CT Cha B, suggests that these objects may have
lower temperatures, and consequently lower masses, than previously estimated.Comment: 15 pages, 13 figure
The substellar mass function in sigma Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects
We investigate the mass function in the substellar domain down to a few
Jupiter masses in the young sigma Orionis open cluster (3+/-2 Ma, d =
360^+70_-60 pc). We have performed a deep IJ-band search, covering an area of
790 arcmin^2 close to the cluster centre. This survey was complemented with an
infrared follow-up in the HKs- and Spitzer 3.6-8.0 mum-bands. Using
colour-magnitude diagrams, we have selected 49 candidate cluster members in the
magnitude interval 16.1 mag < I < 23.0 mag. Accounting for flux excesses at 8.0
mum and previously known spectral features of youth, 30 objects are bona fide
cluster members. Four are first identified from our optical-near infrared data.
Eleven have most probable masses below the deuterium burning limit and are
classified as planetary-mass object candidates. The slope of the substellar
mass spectrum (Delta N / Delta M = a M^-alpha) in the mass interval 0.11 Msol M
< 0.006 Msol is alpha = +0.6+/-0.2. Any opacity mass-limit, if these objects
form via fragmentation, may lie below 0.006 Msol. The frequency of sigma
Orionis brown dwarfs with circumsubstellar discs is 47+/-15 %. The continuity
in the mass function and in the frequency of discs suggests that very low-mass
stars and substellar objects, even below the deuterium-burning mass limit, may
share the same formation mechanism.Comment: Accepted for publication in A&A (12/04/2007). It has not been edited
for language ye
Prevalence and molecular epidemiology of mcr-mediated colistin-resistance Escherichia coli from healthy poultry in France after national plan to reduce exposure to colistin in farm
IntroductionWithin the 2007â2014 programme for the surveillance of antimicrobial resistance (AMR) in livestock in France, mcr-1 prevalence average in commensal Escherichia coli was found to be 5.9% in turkeys and 1.8% in broilers, indicating that mobile colistin resistance had spread in farm animals. In 2017, the French national Ecoantibio2 plan was established to tackle AMR in veterinary medicine, with the objective of a 50% reduction in exposure to colistin in farm animals within 5âyears (from 2014â2015 to 2020). Our objective was to update data concerning the prevalence and molecular epidemiology of colistin resistance, in consideration of colistin sales in poultry production in France.MethodsAntimicrobial susceptibility of commensal E. coli isolated from broilers and turkeys at slaughterhouse was determined by broth micro-dilution. The mcr genes were screened by polymerase chain reaction (PCR). Whole genome sequencing (WGS) was used to investigate the genetic diversity of colistin-resistant isolates. Transformation experiments enabled identification of the mcr-bearing plasmid replicon types. The correlation between prevalence of colistin resistance and colistin usage data was explored statistically.Results and discussionIn 2020, in France, the resistance prevalence to colistin in poultry production was 3% in turkeys and 1% in broilers, showing a significant highly positive correlation with a â68% decrease of poultry exposure to colistin since 2014. Only the mcr-1 gene was detected among the colistin-resistant E. coli. More than 80% of isolates are multi-drug resistant with 40% of isolates originating from turkeys and 44% originating from broilers co-resistant to the critically important antimicrobial ciprofloxacin. Most of the strains had no clonal relationship. The mcr gene was located in different plasmid types, carrying various other AMR genes. The decrease in colistin resistance among poultry in France can be considered a positive outcome of the national action plans for reduced colistin usage
Near-IR coronagraphic imaging of the companion to HR 7672
This article presents coronagraphic images of the low-mass companion to the
star HR 7672 observed at the Palomar 200 inch telescope and first detected at
Gemini and Keck in the K band by \citet{liu02}. We obtained additional
photometry in (), () and () bands to
cover the full near-IR domain and hence to further constrain the nature of the
companion. A mass estimate of 58-71 is derived from evolutionary
models of very low-mass objects.Comment: 6 pages, 9 figures, to be published in Astronomy and Astrophysic
Jasmonoyl isoleucine accumulation is needed for abscisic acid build-up in roots of Arabidopsis under water stress conditions
Phytohormones are central players in sensing and signallingnumerous environmental conditions like drought. In thiswork, hormone proïŹling together with gene expression ofkey enzymes involved in abscisic acid (ABA) and jasmonatebiosynthesis were studied in desiccating Arabidopsis roots.Jasmonic acid (JA) content transiently increased after stressimposition whereas progressive and concomitant ABA andJasmonoyl Isoleucine (JA-Ile) accumulations were detected.Molecular data suggest that, at least, part of the hormonalregulation takes place at the biosynthetic level. These obser-vations also point to a possible involvement of jasmonates onABA biosynthesis under stress. To test this hypothesis,mutants impaired in jasmonate biosynthesis (opr3, lox6 andjar1-1) and in JA-dependent signalling (coi1) wereemployed. Results showed that the early JA accumulationleading to JA-Ile build up was necessary for an ABA increasein roots under two different water stress conditions. Signaltransduction between water stress-induced JA-Ile accumula-tion and COI1 is necessary for a full induction of the ABAbiosynthesis pathway and subsequent hormone accumula-tion in roots of Arabidopsis plants. The present work adds alevel of interaction between jasmonates and ABA at thebiosynthetic levelThis work was supported by the Spanish Ministerio deEconomĂa y Competitividad (MINECO) through grantsAGL2010-22195-C03-01 and AGL2013-42038R to A.G.-C.Hormonal proïŹles were performed at Instrumental centralfacilities (SCIC) of Universitat Jaume I. The authors have noconïŹict of interest to declar
Are isolated planetary-mass objects really isolated? A brown dwarf-exoplanet system candidate in the sigma Orionis cluster
The recent detection by direct imaging of three giant planets at wide
separation (50-250 AU) from their primaries has raised the question about the
``true isolation'' of planetary-mass objects in clusters. Our goal was to test
the possibility that some free-floating planetary-mass object could in fact be
part of wide planetary systems. We searched in the literature for stellar and
brown-dwarf member candidates of the sigma Orionis cluster at small angular
separations from published candidate planetary-mass objects. We found one
candidate planetary system, SE 70, composed of an X-ray source and a
planetary-mass object, namely S Ori 68, separated by only 4.6 arcsec. In order
to assess the cluster membership of the X-ray source, we obtained
mid-resolution optical spectroscopy using ISIS on the William Herschel
Telescope. We also compiled additional data on the target from available
astronomical catalogues. We have found that SE 70 follows the
spectrophotometric sequence of the cluster and displays spectroscopic features
of youth, such as lithium in absorption and chromospheric Halpha emission. The
radial velocity is consistent with cluster membership. Hence, SE 70 is very
probably a sigma Orionis cluster member. The projected physical separation
between SE 70 and S Ori 68 is 1700+/-300 AU at the distance of the cluster. If
the common proper motion is confirmed in the near future, the system would be
composed of an M5-6 brown dwarf with an estimated mass of ~45 M_Jup and an
L5+/-2 giant planet with an estimated mass of ~5 M_Jup. It would be the widest
and one of the lowest-mass planetary systems known so far.Comment: Accepted for publication in A&A (7 pages, 4 figures). Abridged
abstract
New constraints on the membership of the T dwarf S Ori 70 in the sigma Orionis cluster
(Abridged) The nature of S Ori 70, a faint mid-T type object found towards
the direction of the young sigma Orionis cluster, is still under debate. We
intend to disentangle whether it is a field brown dwarf or a 3-Myr old
planetary-mass member of the cluster. We report on near-infrared JHK_s and
mid-infrared [3.6] and [4.5] IRAC/Spitzer photometry recently obtained for S
Ori 70. The new near-infrared images (taken 3.82 yr after the discovery data)
have allowed us to derive a very small proper motion (11.0 +/- 5.9 mas/yr) for
this object, which is consistent with the proper motion of the cluster within
1.5 sigma the astrometric uncertainty. The colors (H-K_s), (J-K_s) and
K_s-[3.6] appear discrepant when compared to T4-T7 dwarfs in the field. This
behavior could be ascribed to a low-gravity atmosphere or alternatively to an
atmosphere with a metallicity significantly different than solar. Taking into
account the small proper motion of S Ori 70 and its new near- and mid-infrared
colors, a low-gravity atmosphere remains as the most likely explanation to
account for our observations. This supports S Ori 70's membership in sigma
Orionis, with an estimated mass in the interval 2-7 Mjup, in agreement with our
previous derivation.Comment: Accepted for publication in A&
In-depth study of moderately young but extremely red, very dusty substellar companion HD206893B
Accepted for publication in Astronomy & Astrophysics. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.The substellar companion HD206893b has recently been discovered by direct imaging of its disc-bearing host star with the SPHERE instrument. We investigate the atypical properties of the companion, which has the reddest near-infrared colours among all known substellar objects, either orbiting a star or isolated, and we provide a comprehensive characterisation of the host star-disc-companion system. We conducted a follow-up of the companion with adaptive optics imaging and spectro-imaging with SPHERE, and a multiinstrument follow-up of its host star. We obtain a R=30 spectrum from 0.95 to 1.64 micron of the companion and additional photometry at 2.11 and 2.25 micron. We carried out extensive atmosphere model fitting for the companions and the host star in order to derive their age, mass, and metallicity. We found no additional companion in the system in spite of exquisite observing conditions resulting in sensitivity to 6MJup (2MJup) at 0.5" for an age of 300 Myr (50 Myr). We detect orbital motion over more than one year and characterise the possible Keplerian orbits. We constrain the age of the system to a minimum of 50 Myr and a maximum of 700 Myr, and determine that the host-star metallicity is nearly solar. The comparison of the companion spectrum and photometry to model atmospheres indicates that the companion is an extremely dusty late L dwarf, with an intermediate gravity (log g 4.5-5.0) which is compatible with the independent age estimate of the system. Though our best fit corresponds to a brown dwarf of 15-30 MJup aged 100-300 Myr, our analysis is also compatible with a range of masses and ages going from a 50 Myr 12MJup planetary-mass object to a 50 MJup Hyades-age brown dwarf...Peer reviewedFinal Accepted Versio
- âŠ