6,700 research outputs found
Brown dwarf disks with ALMA
We present ALMA continuum and spectral line data at 0.89 mm and 3.2 mm for
three disks surrounding young brown dwarfs and very low mass stars in the
Taurus star forming region. Dust thermal emission is detected and spatially
resolved for all the three disks, while CO(J=3-2) emission is seen in two
disks. We analyze the continuum visibilities and constrain the disks physical
structure in dust. The results of our analysis show that the disks are
relatively large, the smallest one with an outer radius of about 70 AU. The
inferred disk radii, radial profiles of the dust surface density and disk to
central object mass ratios lie within the ranges found for disks around more
massive young stars. We derive from our observations the wavelength dependence
of the millimeter dust opacity. In all the three disks data are consistent with
the presence of grains with at least millimeter sizes, as also found for disks
around young stars, and confirm that the early stages of the solid growth
toward planetesimals occur also around very low mass objects. We discuss the
implications of our findings on models of solids evolution in protoplanetary
disks, on the main mechanisms proposed for the formation of brown dwarfs and
very low mass stars, as well as on the potential of finding rocky and giant
planets around very low mass objects.Comment: 15 pages, 10 figures, accepted for publication in Ap
A quasi-static nonlinear analysis for assessing the fire resistance of 3d frames exploiting time-dependent yield surface
In this work an automatic procedure for evaluating the axial force-biaxial bending yield surface of reinforced concrete sections in fire is proposed. It provides an accurate time-dependent expression of the yield condition by a section analysis carried out once and for all, accounting for the strength reduction of the materials, which is a function of the fire duration. The equilibrium state of 3D frames with such yield conditions, once discretized using beam finite elements, is formulated as a nonlinear vectorial equation defining a curve in the hyperspace of the discrete variables and the fire duration. A generalized path-following strategy is proposed for tracing this curve and evaluating, if it exists, the limit fire duration, that is the time of exposure which leads to structural collapse. Compared to the previous proposals on the topic, which are limited to local sectional checks, this work is the first to present a global analysis for assessing the fire resistance of 3D frames, providing a time history of the fire event and taking account of the stress redistribution. Numerical examples are given to illustrate and validate the proposal
Three Li-rich K giants: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952
We report on spectroscopic analyses of three K giants previously suggested to
be Li-rich: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952.
High-resolution optical spectra and the LTE model atmospheres are used to
derive the stellar parameters: (, log , [Fe/H]), elemental
abundances, and the isotopic ratio C/C. IRAS 13539-4153 shows an
extremely high Li abundance of (Li) 4.2, a value ten
times more than the present Li abundance in the local interstellar medium. This
is the third highest Li abundance yet reported for a K giant. IRAS 12327-6523
shows a Li abundances of (Li) 1.4. IRAS 17596-3952 is a
rapidly rotating ( 35 km s) K giant with
(Li) 2.2. Infrared photometry which shows the presence
of an IR excess suggesting mass-loss. A comparison is made between these three
stars and previously recognized Li-rich giants.Comment: 17 pages, 6 figures, accepted for A
Harmonic damped oscillators with feedback. A Langevin study
We consider a system in direct contact with a thermal reservoir and which, if
left unperturbed, is well described by a memory-less equilibrium Langevin
equation of the second order in the time coordinate. In such conditions, the
strength of the noise fluctuations is set by the damping factor, in accordance
with the Fluctuation and Dissipation theorem. We study the system when it is
subject to a feedback mechanism, by modifying the Langevin equation
accordingly. Memory terms now arise in the time evolution, which we study in a
non-equilibrium steady state. Two types of feedback schemes are considered, one
focusing on time shifts and one on phase shifts, and for both cases we evaluate
the power spectrum of the system's fluctuations. Our analysis finds application
in feedback cooled oscillators, such as the Gravitational Wave detector AURIGA.Comment: 17 page
On random flights with non-uniformly distributed directions
This paper deals with a new class of random flights defined in the real space characterized
by non-uniform probability distributions on the multidimensional sphere. These
random motions differ from similar models appeared in literature which take
directions according to the uniform law. The family of angular probability
distributions introduced in this paper depends on a parameter which
gives the level of drift of the motion. Furthermore, we assume that the number
of changes of direction performed by the random flight is fixed. The time
lengths between two consecutive changes of orientation have joint probability
distribution given by a Dirichlet density function.
The analysis of is not an easy task, because it
involves the calculation of integrals which are not always solvable. Therefore,
we analyze the random flight obtained as
projection onto the lower spaces of the original random
motion in . Then we get the probability distribution of
Although, in its general framework, the analysis of is very complicated, for some values of , we can provide
some results on the process. Indeed, for , we obtain the characteristic
function of the random flight moving in . Furthermore, by
inverting the characteristic function, we are able to give the analytic form
(up to some constants) of the probability distribution of Comment: 28 pages, 3 figure
Education with a Heart
Gregorio Banaga explains how Catholic education in the Philippines created and became limited to the elite. He describes the history of Adamson University and what it is doing to increase poor persons’ access to education, raise students’ awareness of poverty, and create motivation for social change. Adamson fosters social responsibility and has made service part of all students’ learning. All of this is part of Banaga’s definition of Vincentian education, which he says is “of the poor, from the poor, with the poor, and for the poor.” In addition to the actions mentioned above, this philosophy requires the university to be attuned to the experience of persons who are poor and to construct curricula that will best use their gifts and promote their growth
Strategies to improve seedling quality in smallholder forestry in the Philippines: A synthesis of findings from a systems research program
Project ASEM/2006/091 and earlier forestry projects in the Philippines funded by the Australian Centre for International Agricultural Research (ACIAR) have identified the prevalence of low quality forestry seedlings. A research strategy involving systems modelling to identify intervention measures, and progress in applying these measures, are described. This has involved developing a seed centre, identifying superior mother trees, developing nursery best management practice guidelines, and assisting the national government to trial these guidelines. Recommendations are made to increase the extension and training effort in production of high quality seedlings, and to conduct further research into watershed restoration utilizing hiqh quality germplasm of indigenous tree species
Rationale and key research questions addressed by field trails established as part of the ACIAR Smallholder Tree Farmer Project
A series of field trials have been established as part of the ACIAR Smallholder Tree Farmer Project. These trials are designed to have both a research and demonstration function. A field trial was designed to investigate the potential interaction between four species providing a combination of native and exotic species and nitrogen-fixing vs non-nitrogen-fixing. Importantly, this design provides information about different mixture ratios using only one plot. This field trial will provide important information about the interactions of the four species when grown in varying mixture ratios. A clinal trial using the design of Vanclay (2006) was established in Leyte Leyte in December 2007 using four species. This trial will provide important information on ideal spacing at which trees should be established and how initial planting density affects site capture and early growth, especially in respect to indigenous species. Field trials have also been established to investigate the effect of fertiliser and shade on the establishment and early growth of mayapis and to demonstrate the positive impact that the use of high quality germplasm and good early age silviculture has on the growth of gmelina. The establishment of the field trials has been an important capacity building exercise within the project team. Filipino collaborators have been intimately involved in the design, establishment and monitoring of the field trials and are now capable of establishing similar rigorous field experiments
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