2,092 research outputs found
N′-[(E)-4-ChloroÂbenzylÂidene]-2-(4-isobutylÂphenÂyl)propanohydrazide
The asymmetric unit of title compound, C20H23ClN2O, consists of two crystallographically independent molÂecules (A and B) in which the orientations of the 4-isobutylÂphenyl units are different. The isobutyl group of molÂecule B is disordered over two positions with occupancies of 0.850 (5) and 0.150 (5). The dihedral angle between the two benzene rings is 88.70 (9)° in molÂecule A and 89.38 (9)° in molÂecule B. The independent molÂecules are linked together into chains along [100] by N—H⋯O and C—H⋯O hydrogen bonds, and by C—H⋯π interÂactions. In the chain, N—H⋯O and C—H⋯O hydrogen bonds generate R
2
1(6) ring motifs. In addition, C—H⋯N hydrogen bonds are observed. The presence of pseudosymmetry in the structure suggests the higher symmetry space group Pbca but attempts to refine the structure in this space group resulted in high R (0.119) and wR (0.296) values
Influence of Anisotropy on Creep in a Whisker Reinforced MMC Rotating Disc
Whisker reinforced MMC may be employed in rotating disc , a common component in friction drives , turbines and a number of other machine components, often exposed to elevated temperatures . Creep characteristics of these composites have been studied analytically using von Mises flow rule and Norton 's steady state creep equations
. The results for isotropic A16061 alloy and for isotropic composite containing 20 vol% SiCµ in a matrix of A16061 alloy have been compared with those obtained for anisotropic composites with characteristic parameters a = 0.7 and 1. 31, indicating respectively relative strengthening and weakening in the tangential direction presumably introduced by either processing or inhomogeneous distribution of reinforcement.The creep strain rates resulting in the isotropic rotating disc made of composite as well as the aluminum alloy, are tensile in the tangential direction but compressive in the axial and radial directions, also conforming to the condition of volume constancy.The creep rates in the composite are significantly reduced (by about three orders of
magnitude) in all the directions compared to those observed in the base alloy. In case of anisotropy lowering the strength in the tangential direction (a> 1.0), the radial stresses in the region near inner periphery of the disc, increase while those near the outer periphery decrease in comparison to those for the isotropic composite . But the tangential stresses reduce in the middle region of the disc and enhances near the inner and the outer periphery, when compared to those for the isotropic composite . The magnitude of stress distribution , however, changes by a small extent due to ani sotropy in the disc introduced through processing or reinforcement distribution . The radial strain rate
which always remained compressive for the isotropic composite and for a = 1.3,becomes tensile in the middle region of the disc when a = 0.7. If a is reduced from
1.3 to 0 . 7, the variation of tensile strain rate in the tangential direction remains similar but the magnitude reduces by five orders of magnitude . Anisotropy therefore, introduces significant change in the strain rates although its effect on the resulting stress
distribution may be relatively small
Discovery of a bright eclipsing cataclysmic variable
We report on the discovery of J0644+3344, a bright deeply eclipsing
cataclysmic variable (CV) binary. Spectral signatures of both binary components
and an accretion disk can be seen at optical wavelengths. The optical spectrum
shows broad H I, He I, and He II accretion disk emission lines with deep narrow
absorption components from H I, He I, Mg II and Ca II. The absorption lines are
seen throughout the orbital period, disappearing only during primary eclipse.
These absorption lines are either the the result of an optically-thick inner
accretion disk or from the photosphere of the primary star. Radial velocity
measurements show that the H I, He I, and Mg II absorption lines phase with the
the primary star, while weak absorption features in the continuum phase with
the secondary star. Radial velocity solutions give a 150+/-4 km/s
semi-amplitude for the primary star and 192.8+/-5.6 km/s for the secondary. The
individual stellar masses are 0.63-0.69 Mdot for the primary and 0.49-0.54 Mdot
for the secondary. The bright eclipsing nature of this binary has helped
provide masses for both components with an accuracy rarely achieved for CVs.
This binary most closely resembles a nova-like UX UMa or SW Sex type of CV.
J0644+3344, however, has a longer orbital period than most UX UMa or SW Sex
stars. Assuming an evolution toward shorter orbital periods, J0644+3344 is
therefore likely to be a young interacting binary. The secondary star is
consistent with the size and spectral type of a K8 star, but has an M0 mass.Comment: 10 pages, 13 figure, accepted for publication in A&
The Very Low Albedo of WASP-12b From Spectral Eclipse Observations with
We present an optical eclipse observation of the hot Jupiter WASP-12b using
the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope.
These spectra allow us to place an upper limit of (97.5%
confidence level) on the planet's white light geometric albedo across 290--570
nm. Using six wavelength bins across the same wavelength range also produces
stringent limits on the geometric albedo for all bins. However, our
uncertainties in eclipse depth are 40% greater than the Poisson limit and
may be limited by the intrinsic variability of the Sun-like host star --- the
solar luminosity is known to vary at the level on a timescale of
minutes. We use our eclipse depth limits to test two previously suggested
atmospheric models for this planet: Mie scattering from an aluminum-oxide haze
or cloud-free Rayleigh scattering. Our stringent nondetection rules out both
models and is consistent with thermal emission plus weak Rayleigh scattering
from atomic hydrogen and helium. Our results are in stark contrast with those
for the much cooler HD 189733b, the only other hot Jupiter with spectrally
resolved reflected light observations; those data showed an increase in albedo
with decreasing wavelength. The fact that the first two exoplanets with optical
albedo spectra exhibit significant differences demonstrates the importance of
spectrally resolved reflected light observations and highlights the great
diversity among hot Jupiters.Comment: 8 pages, 4 figures, 1 table, published in ApJL, in pres
Laser ablation loading of a radiofrequency ion trap
The production of ions via laser ablation for the loading of radiofrequency
(RF) ion traps is investigated using a nitrogen laser with a maximum pulse
energy of 0.17 mJ and a peak intensity of about 250 MW/cm^2. A time-of-flight
mass spectrometer is used to measure the ion yield and the distribution of the
charge states. Singly charged ions of elements that are presently considered
for the use in optical clocks or quantum logic applications could be produced
from metallic samples at a rate of the order of magnitude 10^5 ions per pulse.
A linear Paul trap was loaded with Th+ ions produced by laser ablation. An
overall ion production and trapping efficiency of 10^-7 to 10^-6 was attained.
For ions injected individually, a dependence of the capture probability on the
phase of the RF field has been predicted. In the experiment this was not
observed, presumably because of collective effects within the ablation plume.Comment: submitted to Appl. Phys. B., special issue on ion trappin
Spectroscopic and Photometric Analysis of HS 1136+6646: A Hot Young DAO+K7 V Post-Common-Envelope, Pre-Cataclysmic Variable Binary
Extensive photometric and spectroscopic observations have been obtained for HS 1136+6646. The observations reveal a newly formed post–common-envelope binary system containing a hot ~DAO.5 primary and a highly irradiated secondary. HS 1136+6646 is the most extreme example yet of a class of short-period hot H-rich white dwarfs with K–M companion systems such as V471 Tau and Feige 24. HS 1136+6646 is a double-line spectroscopic binary showing emission lines of H i, He ii, C ii, Ca ii, and Mg ii, due in part to irradiation of the K7 V secondary by the hot white dwarf. Echelle spectra reveal the hydrogen emission lines to be double-peaked with widths of ~200 km s-1, raising the possibility that emission from an optically thin disk may also contribute. The emission lines are observed to disappear near the inferior conjunction. An orbital period of 0:83607 ± 0:00003 days has been determined through the phasing of radial velocities, emission-line equivalent widths, and photometric measurements spanning a range of 24 months. Radial velocity measurements yield an amplitude of KWD ¼ 69 ± 2 km s-1 for the white dwarf and KK7V = 115 ± 1 km s-1 for the secondary star. In addition to orbital variations, photometric measurements have also revealed a low-amplitude modulation with a period of 113.13 minutes and a semiamplitude of 0.0093 mag. These short-period modulations are possibly associated with the rotation of the white dwarf. From fits of the Balmer line profiles, the white dwarf is estimated to have an effective temperature and gravity of ~70,000 K and log g ~ 7:75, respectively. However, this optically derived temperature is difficult to reconcile with the far-UV spectrum of the Lyman line region. Far Ultraviolet Spectroscopic Explorer spectra show the presence of O vi absorption lines and a spectral energy distribution whose slope persists nearly to the Lyman limit. The extremely high temperature of the white dwarf, from both optical and UV measurements, indicates that the binary system is one of the earliest post–common-envelope objects known, having an age around 7:7 x 105 yr. Although the spectrum of the secondary star is best represented by a K7 V star, indications are that the star may be overly luminous for its mass
Overcast on Osiris: 3D radiative-hydrodynamical simulations of a cloudy hot Jupiter using the parametrized, phase-equilibrium cloud formation code EDDYSED (article)
This is the final version. Available from OUP via the DOI in this recordThe dataset associated with this article is available in ORE: https://doi.org/10.24378/exe.1483We present results from 3D radiative-hydrodynamical simulations of HD 209458b with a fully coupled treatment of clouds using the EDDYSED code, critically, including cloud radiative feedback via absorption and scattering. We demonstrate that the thermal and optical structure of the simulated atmosphere is markedly different, for the majority of our simulations, when including cloud radiative effects, suggesting this important mechanism cannot be neglected. Additionally, we further demonstrate that the cloud structure is sensitive to not only the cloud sedimentation efficiency (termed fsed in EDDYSED), but also the temperature–pressure profile of the deeper atmosphere. We briefly discuss the large difference between the resolved cloud structures of this work, adopting a phase-equilibrium and parametrized cloud model, and our previous work incorporating a cloud microphysical model, although a fairer comparison where, for example, the same list of constituent condensates is included in both treatments is reserved for a future work. Our results underline the importance of further study into the potential condensate size distributions and vertical structures, as both strongly influence the radiative impact of clouds on the atmosphere. Finally, we present synthetic observations from our simulations reporting an improved match, over our previous cloud-free simulations, to the observed transmission, HST WFC3 emission, and 4.5 μm Spitzer phase curve of HD 209458b. Additionally, we find all our cloudy simulations have an apparent albedo consistent with observations.Leverhulme TrustScience and Technology Facilities Council (STFC
Spectroscopic signatures of spin-charge separation in the quasi-one-dimensional organic conductor TTF-TCNQ
The electronic structure of the quasi-one-dimensional organic conductor
TTF-TCNQ is studied by angle-resolved photoelectron spectroscopy (ARPES). The
experimental spectra reveal significant discrepancies to band theory. We
demonstrate that the measured dispersions can be consistently mapped onto the
one-dimensional Hubbard model at finite doping. This interpretation is further
supported by a remarkable transfer of spectral weight as function of
temperature. The ARPES data thus show spectroscopic signatures of spin-charge
separation on an energy scale of the conduction band width.Comment: 4 pages, 4 figures; to appear in PR
- …