2,389,873 research outputs found
Nascent bipolar outflows associated with the first hydrostatic core candidates Barnard 1b-N and 1b-S
In the theory of star formation, the first hydrostatic core (FHSC) phase is a
critical step in which a condensed object emerges from a prestellar core. This
step lasts about one thousand years, a very short time compared with the
lifetime of prestellar cores, and therefore is hard to detect unambiguously.
We present IRAM Plateau de Bure observations of the Barnard 1b dense
molecular core, combining detections of H2CO and CH3OH spectral lines and dust
continuum at 2.3" resolution (~ 500 AU). The two compact cores B1b-N and B1b-S
are detected in the dust continuum at 2mm, with fluxes that agree with their
spectral energy distribution. Molecular outflows associated with both cores are
detected. They are inclined relative to the direction of the magnetic field, in
agreement with predictions of collapse in turbulent and magnetized gas with a
ratio of mass to magnetic flux somewhat higher than the critical value, \mu ~ 2
- 7. The outflow associated with B1b-S presents sharp spatial structures, with
ejection velocities of up to ~ 7 kms from the mean velocity. Its dynamical age
is estimated to be ~2000 yrs. The B1b-N outflow is smaller and slower, with a
short dynamical age of ~1000 yrs. The B1b-N outflow mass, mass-loss rate, and
mechanical luminosity agree well with theoretical predictions of FHSC. These
observations confirm the early evolutionary stage of B1b-N and the slightly
more evolved stage of B1b-S.Comment: 6 pages, 3 figure
From Traditional DB to Notional DC Systems
This paper provides a critical review of the pension reform strategy which turns defined benefits (DB) public pay-as-you-go systems into notional defined contribution (NDC) systems. We show that properly designed NDC public pension systems contain powerful economic and political mechanisms that may facilitate pension reform, but that the distinction between public NDC and DB systems is more ambiguous than usually claimed.
Rupture process of the recent large Sumatra earthquakes: 26/12/2004 (Mw=9.3) and 28/03/2005 (Mw=8.6)
The Sumatra mega-earthquake with magnitude 9.3 of 26 December 2004 was the strongest earthquake in the world since the 1964 Alaska earthquake and the fourth since 1900. The earthquake occurred on the interface of the India and Burma plates and triggered a massive tsunami that affected several countries throughout South and Southeast Asia. The rupture, estimated by the aftershock distribution, start from central Sumatra northward for about 1200 kilometres (Borges et al., 2004). Three months latter in 28 March 2005, about 200 km south of this event, but at a greater depth (28 km) occurred a magnitude 8.6 earthquake. This event was probably triggered by stress variations caused by the December Sumatra mega-earthquake (McCloskey et al., 2005). In this work we describe the rupture process of the both earthquakes estimated from teleseismic broad-band waveform data
Machines must be wrong
Making mistakes is an intrinsic human feature. But far to be an unwelcome feature, it is useful. For instance it bears us to learn, to review our beliefs and to support our decisions among others. This capability of using mistakes in our reasonings is already represented by Logic by means of the inference rule of “reduction ad absurdum”, which can be seen as a “supervised kind of mistake”. However in Computer Sciences, apart from the theoretical tools of “reductio ad absurdum” and methods obtained from it (as SLD resolution [1]), contradictions and mistakes are considered features that must be avoided. In some situations this behavior is understandable (e.g. the control of a train or a medical device) but in others, it represents a considerable limitation (e.g. in learning or optimization). Thus, considering knowledge systems involved in wrong information is not only an option for the scientific community, but a necessity.
In this talk we explain how wrongness can be represented as a fuzzy notion and why con- tradictory information must be considered as an important piece of information nowadays. Moreover, the consideration of inconsistent knowledge systems is motivated to show how we can retrieve informations from wrongness. We refer to readers interested in more information to [2, 3].Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
FDTD Calculations of the Diffraction Coefficient of Vibrating Wedges
The full-vector Maxwell\u27s equations Unite-difference time-domain (FDTD) method is employed to calculate diffraction coefficients of vibrating conducting and dielectric wedges. Two-dimensional FDTD models of right-angle wedges are constructed to include total-field scattered-field incident plane-wave source conditions as well as convolutional perfectly matched-layer boundary conditions. These models are first validated by calculating the diffraction coefficient of a stationary perfect electrical conducting (PEC) right-angle wedge for comparison to uniform geometrical theory of diffraction (UTD) analytical solutions. Next, a brute-force FDTD technique for modeling wedge vibrations is utilized to calculate the Doppler diffraction coefficients of vibrating lossless and loss
Variance changes detection in multivariate time series
This paper studies the detection of step changes in the variances and in the correlation structure of the components of a vector of time series. Two procedures are considered. The first is based on the likelihood ratio test and the second on cusum statistics. These two procedures are compared in a simulation study and we conclude that the cusum procedure is more powerful. The procedures are illustrated in two examples.
La movilización como comunicación: Una contribución latinoamericana al estudio de los movimientos sociales
Many scholars have noted the lack of interdisciplinary dialogue and research between the areas of
social movements studies and that of media and
communications. While social movement studies fail
to fully analyse media practices and communicative
processes in relation to mobilization, in media and
communication the social and political aspects of
mobilization are seldom taken into account when
analysing communication in social movements. This
apparent lack of dialogue is presented in the paper
as a consequence of north-centred theorization in
the fields of social movement studies and media and
communication, which is addressed by spelling out
the contribution of Latin American communication
scholarship and a view of mobilization as anchored in
communication.Muchos académicos han observado la ausencia
de diálogo interdisciplinario entre los estudios
de los movimientos sociales y de los medios y la
comunicación. Mientras que los estudios de los
movimientos sociales no analizan de manera integral
las prácticas mediáticas y los procesos comunicacionales en relación con la movilización, los estudios
de medios y comunicación raras veces toman en
cuenta los aspectos socio-políticos cuando analizan
la comunicación en los movimientos sociales. Este
artículo plantea esa aparente falta de diálogo como una
consecuencia de una teorización eurocéntrica, explica
en detalle la contribución de los estudios latinoamericanos de la comunicación, y propone una visión de la
movilización centrada en la comunicación
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