35,158 research outputs found
Oxidative Heck desymmetrisation of 2,2-disubstituted cyclopentene-1,3-diones
Oxidative Heck couplings have been successfully developed for 2,2-disubstituted cyclopentene-1,3-diones. The direct coupling onto the 2,2-disubstituted cyclopentene-1,3-dione core provides a novel expedient way of enantioselectively desymmetrising all-carbon quaternary centres
Hot Jupiters and Hot Spots: The Short- and Long-term Chromospheric Activity on Stars with Giant Planets
We monitored the chromospheric activity in the Ca II H & K lines of 13
solar-type stars (including the Sun); 8 of them over three years at the CFHT
and 5 in a single run at the VLT. Ten of the 13 targets have close planetary
companions. All of the stars observed at the CFHT show long-term (months to
years) changes in H & K intensity levels. Four stars display short-term (days)
cyclical activity. For two, HD 73256 and kappa^1 Ceti, the activity is likely
associated with an active region rotating with the star, however, the flaring
in excess of the rotational modulation may be associated with a hot jupiter. A
planetary companion remains a possibility for kappa^1 Ceti. For the other two,
HD 179949 and upsilon And, the cyclic variation is synchronized to the hot
jupiter's orbit. For both stars this synchronicity with the orbit is clearly
seen in two out of three epochs. The effect is only marginal in the third epoch
at which the seasonal level of chromospheric activity had changed for both
stars. Short-term chromospheric activity appears weakly dependent on the mean
K-line reversal intensities for the sample of 13 stars. Also, a suggestive
correlation exists between this activity and the M_p sin(i) of the star's hot
jupiter. Because of their small separation (<= 0.1 AU), many of the hot
jupiters lie within the Alfv\'en radius of their host stars which allows a
direct magnetic interaction with the stellar surface. We discuss the conditions
under which a planet's magnetic field might induce activity on the stellar
surface and why no such effect was seen for the prime candidate, tau Boo. This
work opens up the possibility of characterizing planet-star interactions, with
implications for extrasolar planet magnetic fields and the energy contribution
to stellar atmospheres.Comment: Accepted to the Astrophysical Journal; 39 pages including 17 figure
Off-line optimization based active control of torsional oscillation for electric vehicle drivetrain
© 2017 by the authors. As there is no clutch or hydraulic torque converter in electric vehicles to buffer and absorb torsional vibrations. Oscillation will occur in electric vehicle drivetrains when drivers tip in/out or are shifting. In order to improve vehicle response to transients, reduce vehicle jerk and reduce wear of drivetrain parts, torque step changes should be avoided. This article mainly focuses on drivetrain oscillations caused by torque interruption for shifting in a Motor-Transmission Integrated System. It takes advantage of the motor responsiveness, an optimal active control method is presented to reduce oscillations by adjusting motor torque output dynamically. A rear-wheel-drive electric vehicle with a two gear automated manual transmission is considered to set up dynamic differential equations based on Newton's law of motion. By linearization of the affine system, a joint genetic algorithm and linear quadratic regulator method is applied to calculate the real optimal motor torque. In order to improve immediacy of the control system, time consuming optimization process of parameters is completed off-line. The active control system is tested in AMEsim® and limitation of motor external characteristics are considered. The results demonstrate that, compared with the open-loop system, the proposed algorithm can reduce motion oscillation to a satisfied extent when unloading torque for shifting
Quantum Calculation of Inelastic CO Collisions with H. II. Pure Rotational Quenching of High Rotational Levels
Carbon monoxide is a simple molecule present in many astrophysical
environments, and collisional excitation rate coefficients due to the dominant
collision partners are necessary to accurately predict spectral line
intensities and extract astrophysical parameters. We report new quantum
scattering calculations for rotational deexcitation transitions of CO induced
by H using the three-dimensional potential energy surface~(PES) of Song et al.
(2015). State-to-state cross sections for collision energies from 10 to
15,000~cm and rate coefficients for temperatures ranging from 1 to
3000~K are obtained for CO(, ) deexcitation from to all lower
levels, where is the rotational quantum number. Close-coupling and
coupled-states calculations were performed in full-dimension for =1-5, 10,
15, 20, 25, 30, 35, 40, and 45 while scaling approaches were used to estimate
rate coefficients for all other intermediate rotational states. The current
rate coefficients are compared with previous scattering results using earlier
PESs. Astrophysical applications of the current results are briefly discussed.Comment: 8 figures, 1 tabl
Large-Scale CO Maps of the Lupus Molecular Cloud Complex
Fully sampled degree-scale maps of the 13CO 2-1 and CO 4-3 transitions toward
three members of the Lupus Molecular Cloud Complex - Lupus I, III, and IV -
trace the column density and temperature of the molecular gas. Comparison with
IR extinction maps from the c2d project requires most of the gas to have a
temperature of 8-10 K. Estimates of the cloud mass from 13CO emission are
roughly consistent with most previous estimates, while the line widths are
higher, around 2 km/s. CO 4-3 emission is found throughout Lupus I, indicating
widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the
NW end and along the edge of the B228 ridge in Lupus I, and a coherent velocity
gradient across the ridge, are consistent with interaction between the
molecular cloud and an expanding HI shell from the Upper-Scorpius subgroup of
the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be
stars, and shows no sign of external influence. Slightly warmer gas around the
core of Lupus IV and a low line width suggest heating by the
Upper-Centaurus-Lupus subgroup of Sco-Cen, without the effects of an HI shell.Comment: 54 pages, 27 figures, 5 tables. To appear in ApJS. Preprint also
available (with full-size figures) from
http://www.astro.ex.ac.uk/people/nfht/publications.html Datacubes available
from http://www.astro.ex.ac.uk/people/nfht/resources.htm
Efficient Classical Simulation of Optical Quantum Circuits
We identify a broad class of physical processes in an optical quantum circuit
that can be efficiently simulated on a classical computer: this class includes
unitary transformations, amplification, noise, and measurements. This
simulatability result places powerful constraints on the capability to realize
exponential quantum speedups as well as on inducing an optical nonlinear
transformation via linear optics, photodetection-based measurement and
classical feedforward of measurement results, optimal cloning, and a wide range
of other processes.Comment: 4 pages, published versio
Large parallel and perpendicular electric fields on electron spatial scales in the terrestrial bow shock
Large parallel ( 100 mV/m) and perpendicular ( 600 mV/m) electric
fields were measured in the Earth's bow shock by the vector electric field
experiment on the Polar satellite. These are the first reported direct
measurements of parallel electric fields in a collisionless shock. These fields
exist on spatial scales comparable to or less than the electron skin depth (a
few kilometers) and correspond to magnetic field-aligned potentials of tens of
volts and perpendicular potentials up to a kilovolt. The perpendicular fields
are amongst the largest ever measured in space, with energy densities of
of order 10%. The measured parallel electric field
implies that the electrons can be demagnetized, which may result in stochastic
(rather than coherent) electron heating
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