18,667 research outputs found
The young massive stellar cluster associated to RCW121
We report NIR broad and narrow band photometric observations in the direction
of the IRAS17149-3916 source that reveal the presence of a young cluster of
massive stars embedded in an HII region coincident with RCW121. These
observations, together with published radio data, MSX and Spitzer images were
used to determine some of the physical parameters of the region. We found 96
cluster member candidates in an area of about 1.5 x 2.0 square arcmin, 30% of
them showing excess emission in the NIR. IRS 1, the strongest source in the
cluster with an estimated spectral type of O5V-O6V ZAMS based on the
color-magnitude diagram, is probably the main ionizing source of the HII region
detected at radio wavelengths. Using the integrated Brgamma and the 5 GHz flux
densities, we derived a mean visual extinction AV=5.49 magnitudes. From the
observed size of the Brgamma extended emission, we calculated the emission
measure E and the electron density ne, characteristic of compact HII regions.Comment: 18 pages, 8 figures, accepted for publication on AJ (February/2006
Nambu monopoles interacting with lattice defects in two-dimensional artificial square spin ice
The interactions between an excitation (similar to a pair of Nambu monopoles)
and a lattice defect are studied in an artificial two-dimensional square spin
ice. This is done by considering a square array of islands containing only one
island different from all others. This difference is incorporated in the
magnetic moment (spin) of the "imperfect" island and several cases are studied,
including the special situation in which this distinct spin is zero (vacancy).
We have shown that the two extreme points of a malformed island behave like two
opposite magnetic charges. Then, the effective interaction between a pair of
Nambu monopoles with the deformed island is a problem involving four magnetic
charges (two pairs of opposite poles) and a string. We also sketch the
configuration of the field lines of these four charges to confirm this picture.
The influence of the string on this interaction decays rapidly with the string
distance from the defect.Comment: 7 pages, 13 figure
Event-Driven Network Programming
Software-defined networking (SDN) programs must simultaneously describe
static forwarding behavior and dynamic updates in response to events.
Event-driven updates are critical to get right, but difficult to implement
correctly due to the high degree of concurrency in networks. Existing SDN
platforms offer weak guarantees that can break application invariants, leading
to problems such as dropped packets, degraded performance, security violations,
etc. This paper introduces EVENT-DRIVEN CONSISTENT UPDATES that are guaranteed
to preserve well-defined behaviors when transitioning between configurations in
response to events. We propose NETWORK EVENT STRUCTURES (NESs) to model
constraints on updates, such as which events can be enabled simultaneously and
causal dependencies between events. We define an extension of the NetKAT
language with mutable state, give semantics to stateful programs using NESs,
and discuss provably-correct strategies for implementing NESs in SDNs. Finally,
we evaluate our approach empirically, demonstrating that it gives well-defined
consistency guarantees while avoiding expensive synchronization and packet
buffering
Non-parametric comparison of histogrammed two-dimensional data distributions using the Energy Test
When monitoring complex experiments, comparison is often made between regularly acquired histograms of data and reference histograms which represent the ideal state of the equipment. With the larger HEP experiments now ramping up, there is a need for automation of this task since the volume of comparisons could overwhelm human operators. However, the two-dimensional histogram comparison tools available in ROOT have been noted in the past to exhibit shortcomings. We discuss a newer comparison test for two-dimensional histograms, based on the Energy Test of Aslan and Zech, which provides more conclusive
discrimination between histograms of data coming from different distributions than methods provided in a recent ROOT release.The Science and Technology Facilities Council, U
Estudo dos elementos mínimos para projeto de sistemas embarcados compatíveis para máquinas e implementos agrícolas.
The true nature of the alleged planetary nebula W16-185
We report the discovery of a small cluster of massive stars embedded in a NIR
nebula in the direction of the IRAS15411-5352 point source, which is related to
the alleged planetary nebula W16-185. The majority of the stars present large
NIR excess characteristic of young stellar objects and have bright counterparts
in the Spitzer IRAC images; the most luminous star (IRS1) is the NIR
counterpart of the IRAS source. We found very strong unresolved Brgamma
emission at the IRS1 position and more diluted and extended emission across the
continuum nebula. From the sizes and electron volume densities we concluded
that they represent ultra-compact and compact HII regions, respectively.
Comparing the Brgamma emission with the 7 mm free-free emission, we estimated
that the visual extinction ranges between 14 and 20 mag. We found that only one
star (IRS1) can provide the number of UV photons necessary to ionize the
nebula.Comment: 30 pages, 15 figures, 2 tables V3: minor grammatical changes. Figure
4 is available in pdf file. Accepted for publication in AJ, April / 200
Traditional vegetables: preliminary studies on seeds of vinegar (Hibiscus sabdariffae L.).
Abstract 96
Germinação de sementes do híbrido interespecífico do caiaué com dendezeiro: cultivar BRS Manicoré.
O objetivo desse estudo foi aperfeiçoar a metodologia utilizada, adequando o período de superação de dormência e o teor de água ideal para germinação das sementes
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