1,504 research outputs found
Advanced single permanent magnet axipolar ironless stator ac motor for electric passenger vehicles
A program was conducted to design and develop an advanced-concept motor specifically created for propulsion of electric vehicles with increased range, reduced energy consumption, and reduced life-cycle costs in comparison with conventional systems. The motor developed is a brushless, dc, rare-earth cobalt, permanent magnet, axial air gap inductor machine that uses an ironless stator. Air cooling is inherent provided by the centrifugal-fan action of the rotor poles. An extensive design phase was conducted, which included analysis of the system performance versus the SAE J227a(D) driving cycle. A proof-of-principle model was developed and tested, and a functional model was developed and tested. Full generator-level testing was conducted on the functional model, recording electromagnetic, thermal, aerodynamic, and acoustic noise data. The machine demonstrated 20.3 kW output at 1466 rad/s and 160 dc. The novel ironless stator demonstated the capability to continuously operate at peak current. The projected system performance based on the use of a transistor inverter is 23.6 kW output power at 1466 rad/s and 83.3 percent efficiency. Design areas of concern regarding electric vehicle applications include the inherently high windage loss and rotor inertia
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The Wolf-Rayet population of Westerlund 1
New NTT/SOFI near-IR narrow-band imaging and spectroscopy reveals an additional four Wolf-Rayet (WR) stars in the massive cluster Westerlund 1, bringing the total WR population to 24. Sixteen of the WR stars in Wd1 have been classified WN5–11, while eight are WC8–9. An observed WR to RSG/YHG ratio of ∼3 suggests an age of 4.5–5.0 Myr, with WR stars descended from 40–55MSolar progenitors. On the basis of dust and hard X-ray emission, we estimate that 40–65% are probable members of massive star binary systems
Novel Josephson Junction Geometries in NbCu bilayers fabricated by Focused Ion Beam Microscope
We explore novel junction configurations as an extension of our established
Focused Ion Beam-based low TC SNS Junction fabrication technique. By milling a
circular trench (diameter 1 micron, width 50 nm) in a 125 nm Nb 75 nm Cu
bilayer we define a superconducting island connected to the bulk of the film by
a normal metal barrier and entirely enclosed in-plane by the superconducting
film. The circular junction properties can be probed by depositing an
insulating layer over the device and drilling a 0.3 micron diameter hole down
to the island to allow a Nb via to be deposited. Device behavior has been
studied at 4.2 K. An SNS-like current voltage characteristic and Shapiro steps
are observed. It is in terms of magnetic field behavior that the device
exhibits novel characteristics: as the device is entirely enclosed in type II
superconductor, when a magnetic field is applied perpendicular to the plane of
the film, only quantized flux can enter the junction. Hence as applied magnetic
field is increased the junction critical current is unchanged, then abruptly
suppressed as soon as a flux quantum enters (close to the expected value of
lower critical field for the film).Comment: 10 pages including 6 figures Minor Corrections inlight of referees'
comment
RNA interference pathways display high rates of adaptive protein evolution in multiple invertebrates
The influence of nonrandom extra-pair paternity on heritability estimates derived from wild pedigrees
Quantitative genetic analysis is often fundamental for understanding evolutionary processes in wild populations. Avian populations provide a model system due to the relative ease of inferring relatedness among individuals through observation. However, extra-pair paternity (EPP) creates erroneous links within the social pedigree. Previous work has suggested this causes minor underestimation of heritability if paternal misassignment is random and hence not influenced by the trait being studied. Nevertheless, much literature suggests numerous traits are associated with EPP and the accuracy of heritability estimates for such traits remains unexplored. We show analytically how nonrandom pedigree errors can influence heritability estimates. Then, combining empirical data from a large great tit (Parus major) pedigree with simulations, we assess how heritability estimates derived from social pedigrees change depending on the mode of the relationship between EPP and the focal trait. We show that the magnitude of the underestimation is typically small (<15%). Hence, our analyses suggest that quantitative genetic inference from pedigrees derived from observations of social relationships is relatively robust; our approach also provides a widely applicable method for assessing the consequences of nonrandom EPP
A census of the Wolf-Rayet content in Westerlund 1 from near-infrared imaging and spectroscopy
New NTT/SOFI imaging and spectroscopy of the Wolf-Rayet population in
Westerlund 1 are presented. Narrow-band near-IR imaging together with follow up
spectroscopy reveals four new WR stars, of which three were independently
identified recently by Groh et al., bringing the confirmed WR content to 24 (23
excluding source S) [..] A quantitative near-IR spectral classification scheme
for WR stars is presented and applied to members of Westerlund 1. Late subtypes
are dominant, with no subtypes earlier than WN5 or WC8 for the nitrogen and
carbon sequences, respectively. A qualitative inspection of the WN stars
suggests that most (75%) are highly H-deficient. The WR binary fraction is high
(>62%), on the basis of dust emission from WC stars, in addition to a
significant WN binary fraction from hard X-ray detections according to Clark et
al. We exploit the large WN population of Westerlund 1 to reassess its distance
(~5.0kpc) and extinction (A_Ks ~ 0.96 mag), such that it is located at the edge
of the Galactic bar, [..]. The observed ratio of WR stars to red and yellow
hypergiants, N(WR)/N(RSG+YHG)~3, favours an age of 4.5-5.0 Myr, with individual
WR stars descended from progenitors of initial mass ~ 40-55 Msun. Qualitative
estimates of current masses for non-dusty, H-free WR stars are presented,
revealing 10-18 Msun, such that ~75% of the initial stellar mass has been
removed via stellar winds or close binary evolution. We present a revision to
the cluster turn-off mass for other Milky Way clusters in which WR stars are
known, based upon the latest temperature calibration for OB stars. Finally,
comparisons between the observed WR population and subtype distribution in
Westerlund 1 and instantaneous burst evolutionary synthesis models are
presented.Comment: 20 pages, 11 figures, accepted for MNRA
Practical long-distance quantum key distribution system using decoy levels
Quantum key distribution (QKD) has the potential for widespread real-world
applications. To date no secure long-distance experiment has demonstrated the
truly practical operation needed to move QKD from the laboratory to the real
world due largely to limitations in synchronization and poor detector
performance. Here we report results obtained using a fully automated, robust
QKD system based on the Bennett Brassard 1984 protocol (BB84) with low-noise
superconducting nanowire single-photon detectors (SNSPDs) and decoy levels.
Secret key is produced with unconditional security over a record 144.3 km of
optical fibre, an increase of more than a factor of five compared to the
previous record for unconditionally secure key generation in a practical QKD
system.Comment: 9 page
Heritability of female extra-pair paternity rate in song sparrows (Melospiza melodia)
The forces driving the evolution of extra-pair reproduction in socially monogamous animals remain widely debated and unresolved. One key hypothesis is that female extra-pair reproduction evolves through indirect genetic benefits, reflecting increased additive genetic value of extra-pair offspring. Such evolution requires that a female's propensity to produce offspring that are sired by an extra-pair male is heritable. However, additive genetic variance and heritability in female extra-pair paternity (EPP) rate have not been quantified, precluding accurate estimation of the force of indirect selection. Sixteen years of comprehensive paternity and pedigree data from socially monogamous but genetically polygynandrous song sparrows (Melospiza melodia) showed significant additive genetic variance and heritability in the proportion of a female's offspring that was sired by an extra-pair male, constituting major components of the genetic architecture required for extra-pair reproduction to evolve through indirect additive genetic benefits. However, estimated heritabilities were moderately small (0.12 and 0.18 on the observed and underlying latent scales, respectively). The force of selection on extra-pair reproduction through indirect additive genetic benefits may consequently be relatively weak. However, the additive genetic variance and non-zero heritability observed in female EPP rate allow for multiple further genetic mechanisms to drive and constrain mating system evolution
Correlated photon-pair generation in a periodically poled MgO doped stoichiometric lithium tantalate reverse proton exchanged waveguide
We demonstrate photon-pair generation in a reverse proton exchanged waveguide
fabricated on a periodically poled magnesium doped stoichiometric lithium
tantalate substrate. Detected pairs are generated via a cascaded second order
nonlinear process where a pump laser at wavelength of 1.55 m is first
doubled in frequency by second harmonic generation and subsequently
downconverted around the same spectral region. Pairs are detected at a rate of
42 per second with a coincidence to accidental ratio of 0.7. This cascaded pair
generation process is similar to four-wave-mixing where two pump photons
annihilate and create a correlated photon pair
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