7,725 research outputs found
Evidence for dust accumulation just outside the orbit of Venus
To contribute to the knowledge of dynamics of interplanetary dust we are
searching for structures in the spatial distribution of interplanetary dust
near the orbit of Venus. To this end we study the radial gradient of zodiacal
light brightness, as observed by the zodiacal light photometer on board the
Helios space probes on several orbits from 1975 to 1979. The cleanest data
result from Helios B (= Helios 2) launched in January 1976. With respect to the
general increase of zodiacal light brightness towards the Sun, the data show an
excess brightness of a few percent for positions of the Helios space probe just
outside the orbit of Venus. We consider this as evidence for a dust ring
associated with the orbit of Venus, somewhat similar to that found earlier
along the Earth's orbit.Comment: 7 pages, 8 figures, Astronomy&Astrophysics, accepte
Some energy conservative schemes for vibro-impacts of a beam on rigid obstacles
Caused by the problem of unilateral contact during vibrations of satellite solar arrays, the aim of this paper is to better understand such a phenomenon. Therefore, it is studied here a simplified model composed by a beam moving between rigid obstacles. Our purpose is to describe and compare some families of fully discretized approximations and their properties, in the case of non-penetration Signorini’s conditions. For this, starting from the works of Dumont and Paoli, we adapt to our beam model the singular dynamic method introduced by Renard. A particular emphasis is given in the use of a restitution coefficient in the impact law. Finally, various numerical results are presented and energy conservation capabilities of the schemes are investigated
Stress Concentration Around an Open Circular Hole in a Plate Subjected to Bending Normal to the Plane of the Plate
An aluminum-alloy plate containing an open circular hole of diameter large compared with the thickness of the plate was subjected to bending forces normal to the plane of the plate. Deflection and strain measurements were taken for two different loads. Stress concentrations occurred at the edge of the hole and the maximum stresses were tangential to the hole at the ends of the transverse diameter. The maximum stress at the edge of the hole was 1.59 times the computed stress on the net section and 1.85 times the computed stress in a solid plate of the same dimensions subjected to the same bending forces. The maximum deflections were about 20 percent greater than the corresponding deflection for a solid plate of the same size subjected to the same bending forces. The smallest edge distance was equal to 2-1/2 times the diameter of the hole and the stress concentration on this side of the hole was the same as on the side where the edge distance was about 4-1/2 diameters. A theoretical analysis of the problem shows that, for an aluminum plate of infinite width, the stress concentration at the edge of the hole would be 1.87 times the stress in a solid plate, which is substantially the same relation obtained for the plate tested
Corals at risk: effectiveness of the removal of a keystone coral-predator Acanthaster planci in a marine park of Malaysia
Mini‐symposium 22: Management and Conservation of Coral Reef EcosystemspostprintThe 2nd Asia Pacific Coral Reef Symposium (APCRS 2010), Phuket, Thailand, 20-24 June 2010
Double-Peaked Broad Emission Lines in NGC 4450 and Other LINERs
Spectra taken with HST reveal that NGC 4450 emits Balmer emission lines with
displaced double peaks and extremely high-velocity wings. This characteristic
line profile, previously seen in a few nearby LINERs and in a small fraction of
broad-line radio galaxies, can be interpreted as a kinematic signature of a
relativistic accretion disk. We can reproduce the observed profile with a model
for a disk with a radial range of 1000-2000 gravitational radii and inclined by
27 degrees along the line of sight. The small-aperture HST data also allow us
to detect, for the first time, the featureless continuum at optical wavelengths
in NGC 4450; the nonstellar nucleus is intrinsically very faint, with M_B =
-11.2 mag for D = 16.8 Mpc. We have examined the multiwavelength properties of
NGC 4450 collectively with those of other low-luminosity active nuclei which
possess double-peaked broad lines and find a number of common features. These
objects are all classified spectroscopically as "type 1" LINERs or closely
related objects. The nuclear luminosities are low, both in absolute terms and
relative to the Eddington rates. All of them have compact radio cores, whose
strength relative to the optical nuclear emission places them in the league of
radio-loud active nuclei. The broad-band spectral energy distributions of these
sources are most notable for their deficit of ultraviolet emission compared to
those observed in luminous Seyfert 1 nuclei and quasars. The double-peaked
broad-line radio galaxies Arp 102B and Pictor A have very similar attributes.
We discuss how these characteristics can be understood in the context of
advection-dominated accretion onto massive black holes.Comment: To appear in The Astrophysical Journal. Latex, 15 pages, embedded
figures and tabl
Is the Broad-Line Region Clumped or Smooth? Constraints from the H alpha Profile in NGC 4395, the Least Luminous Seyfert 1 Galaxy
The origin and configuration of the gas which emits broad lines in Type I
active galactic nuclei is not established yet. The lack of small-scale
structure in the broad emission-line profiles is consistent with a smooth gas
flow, or a clumped flow with many small clouds. An attractive possibility for
the origin of many small clouds is the atmospheres of bloated stars, an origin
which also provides a natural mechanism for the cloud confinement. Earlier
studies of the broad-line profiles have already put strong lower limits on the
minimum number of such stars, but these limits are sensitive to the assumed
width of the lines produced by each cloud. Here we revisit this problem using
high-resolution Keck spectra of the H alpha line in NGC 4395, which has the
smallest known broad-line region (~10^14 cm). Only a handful of the required
bloated stars (each having r~10^14 cm) could fit into the broad-line region of
NGC 4395, yet the observed smoothness of the H alpha line implies a lower limit
of ~10^4-10^5 on the number of discrete clouds. This rules out conclusively the
bloated-stars scenario, regardless of any plausible line-broadening mechanisms.
The upper limit on the size of the clouds is ~10^12 cm, which is comparable to
the size implied by photoionization models. This strongly suggests that gas in
the broad-line region is structured as a smooth rather than a clumped flow,
most likely in a rotationally dominated thick disk-like configuration. However,
it remains to be clarified why such a smooth, gravity-dominated flow generates
double-peaked emission lines only in a small fraction of active galactic
nuclei.Comment: 12 pages, including 3 figures, accepted for publication in The
Astrophysical Journa
A novel programmable lysozyme-based lysis system in Pseudomonas putida for biopolymer production
Indexación: Scopus; Web of Science.Cell lysis is crucial for the microbial production of industrial fatty acids, proteins, biofuels, and biopolymers. In this work, we developed a novel programmable lysis system based on the heterologous expression of lysozyme. The inducible lytic system was tested in two Gram-negative bacterial strains, namely Escherichia coli and Pseudomonas putida KT2440. Before induction, the lytic system did not significantly arrest essential physiological parameters in the recombinant E. coli (ECPi) and P. putida (JBOi) strain such as specific growth rate and biomass yield under standard growth conditions. A different scenario was observed in the recombinant JBOi strain when subjected to PHA-producing conditions, where biomass production was reduced by 25% but the mcl-PHA content was maintained at about 30% of the cell dry weight. Importantly, the genetic construct worked well under PHA-producing conditions (nitrogen-limiting phase), where more than 95% of the cell population presented membrane disruption 16 h post induction, with 75% of the total synthesized biopolymer recovered at the end of the fermentation period. In conclusion, this new lysis system circumvents traditional, costly mechanical and enzymatic cell-disrupting procedures.https://www.nature.com/articles/s41598-017-04741-2.pd
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