89 research outputs found
The Circumstellar Disk of HD 141569 Imaged with NICMOS
Coronagraphic imaging with the Near Infrared Camera and Multi Object
Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4'')
radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected
light image at 1.1 micron shows the disk oriented at a position angle of 356
+/- 5 deg and inclined to our line of sight by 51 +/- 3 deg; the intrinsic
scattering function of the dust in the disk makes the side inclined toward us,
the eastern side, brighter. The disk flux density peaks 185 AU (1.''85) from
the star and falls off to both larger and smaller radii. A region of depleted
material, or a gap, in the disk is centered 250 AU from the star. The dynamical
effect of one or more planets may be necessary to explain this morphology.Comment: 4 pages, LaTeX with emulateapj.sty and epsfig.sty, 4 postscript
figures, Accepted to ApJ Letter
A Candidate Substellar Companion to HR 7329
We present the discovery of a candidate substellar companion from a survey of
nearby, young stars with the NICMOS coronagraph on the Hubble Space Telescope.
The H ~ 12 mag object was discovered approximately 4" from the young A0V star
HR 7329. Using follow-up spectroscopy from STIS, we derive a spectral type
between M7V and M8V with an effective temperature of ~ 2600 K. We estimate that
the probability of a chance alignment with a foreground dwarf star of this
nature is ~ 10^(-8) and therefore suggest the object (HR 7329B) is physically
associated with HR 7329 with a projected separation of 200 AU. Current brown
dwarf cooling models indicate a mass of less than 50 Jupiter masses for HR
7329B based on age estimates of < 30 Myr for HR7329A.Comment: 8 pages LATEX, 5 ps figures, accepted for Ap
Urban food waste for soil amendment? Analysis and characterisation of waste-based compost for soil fertility management in agroecological horticultural production systems in the city of Rosario, Argentina
Urban and peri-urban lands can be an important source of food production for localised and sustainable food systems, however, their soils can be of poor quality, degraded or damaged by anthropic activities, and little is known about their suitability or safety. This paper aims to contribute to this knowledge gap by assessing the soil remediation capacity and qualities of different types of compost made from urban and peri-urban organic wastes for agroecological food production. Prepared over the course of 2021, and used in 2022 for food growing, five different composts were observed and analysed, in two different farms in the city of Rosario, Argentina. Four raw materials generated largely by local industries were used to make the composts: chicken manure, rumen (cowâs stomachs), brewerâs bagasse (byproducts of the beer industry) and urban leaves collected from the municipality waste collection. These were mixed in different proportions (all reaching the 20â30 C/N ratio, typical of quality compost) to produce viable growing substrates where radishes and lettuces were grown. The aim of the study was to assess the possibility, quality and limitations to use locally available organic inputs for soil fertility management in agroecological farming, in the context of urbanisation and to assess pathways to develop closed-cycle agroecological agriculture at metropolitan level. Natural manure substrates (raw and composted) were analysed, as well as crops grown and fertilised with each of the substrates. The attributes and limiting factors of each substrate and their response to local soil conditions were compared and physicochemical, biochemical, and microbiological analyses were performed, including among others, the study of microbial biomass, biological activity, biophytotoxicity, pH, aerobic heterotrophs, nitrogen fixation, and the presence of antibiotics, agrochemicals and heavy metals. The results of the analyses show that all the composted materials improved the physical, chemical and biological properties. However, in some cases, pollutants were present even after composting. Analysis carried out on the vegetables generally indicate undetectable levels or levels below the admissible limits, demonstrating the filtering capacity of the different composts and the soil
Chitosan as Source for Pesticide Formulations
Late blight and wilt caused by the oomycete, Phytophthora infestans, and the fungus, Fusarium solani f. sp. eumartii, respectively, are severe diseases in Solanaceae crops worldwide. Although traditional approaches to control plant diseases have mainly relied on toxic chemical compounds, current studies are focused to identify more sustainable options. Finding alternatives, a low molecular weight chitosan (LMWCh) obtained from biomass of Argentine Seaâs crustaceans was assayed. In an attempt to characterize the action of LMWCh alone or in combination with the synthetic fungicide Mancozeb, the antimicrobial properties of LMWCh were assayed. In a side-by-side comparison with the SYTOX Green nucleic acid stain and the nitric oxideâspecific probe, diaminofluorescein-FM diacetate (DAF-FM DA), yielded a similar tendency, revealing LMWCh-mediated cell death. The efficacy of LMWCh, Mancozeb, and the mixture LMWChâMancozeb was in turn tested. A synergistic effect in the reduction of F. eumartii spore germination was measured in the presence of subinhibitory dosis of 0.025 mg mlâ1 LMWCh and 0.008 mg mlâ1 Mancozeb. This mixture was efficient to increase the effectiveness of the single treatments in protecting against biotic stress judged by a drastic reduction of lesion area in P. infestansâinoculated tissues and activation of the potato defense responses
An Infrared Coronagraphic Survey for Substellar Companions
We have used the F160W filter (1.4-1.8 um) and the coronagraph on the
Near-InfraRed Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space
Telescope (HST) to survey 45 single stars with a median age of 0.15 Gyr, an
average distance of 30 pc, and an average H-magnitude of 7 mag. For the median
age we were capable of detecting a 30 M_Jup companion at separations between 15
and 200 AU. A 5 M_Jup object could have been detected at 30 AU around 36% of
our primaries. For several of our targets that were less than 30 Myr old, the
lower mass limit was as low as a Jupiter mass, well into the high mass planet
region. Results of the entire survey include the proper motion verification of
five low-mass stellar companions, two brown dwarfs (HR7329B and TWA5B) and one
possible brown dwarf binary (Gl 577B/C).Comment: 11 figures, accepted by A
Magnetic field effects on the fluorescence of Cr3+ in GdAlO3
The fluorescence spectrum of Cr3+ in GdAlO3 has been examined at 4.2 K as a function of magnetic field up to 60 kG. The resulting splitting of the 2E 4A2 emission lines are explained in terms of a modified molecular field approximation, which incorporates the effect of the spin fluctuations. The exchange constant in the relaxed excited state is found to be 1.2 cm-1, which differs from that reported from absorption data. It is suggested that the difference may be related to the Frank-Condon effect
Teste de aceitabilidade de brotos de soja da cultivar BRS 216.
bitstream/item/71823/1/ID-30964.pd
An approach to numerical simulation of the gas distribution in the atmosphere of Enceladus
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94942/1/jgra20509.pd
- âŠ