3,112 research outputs found
Dynamical decay of a massive multiple system in Orion KL?
We present absolute astrometry of 35 radio sources in the Orion Trapezium and
Becklin-Neugebauer/Kleinman-Low regions, obtained from Very Large Array
archival observations collected over a period of 15 years. By averaging the
results for all the sources, we estimate the mean absolute proper motion of
Orion to be --in Galactic coordinates-- = +2.1 0.2 mas
yr; = 0.1 0.2 mas yr. These values agree
remarkably well with those expected from the differential rotation of the Milky
Way. Subtraction of this mean motion from the individual measurements allows us
to register all proper motions to the rest frame of the Orion nebula, and
identify radio sources with large residual velocities. In the KL region, we
find three sources in this situation: the BN object, the radio source I, and
the radio counterpart of the infrared source n. All three objects appear to be
moving away from a common point where they must all have been located about 500
years ago. This suggests that all three sources were originally part of a
multiple massive stellar system that recently disintegrated as a result of a
close dynamicalComment: Accepted for publication in the Ap
Route to turbulence in a trapped Bose-Einstein condensate
We have studied a Bose-Einstein condensate of atoms under an
oscillatory excitation. For a fixed frequency of excitation, we have explored
how the values of amplitude and time of excitation must be combined in order to
produce quantum turbulence in the condensate. Depending on the combination of
these parameters different behaviors are observed in the sample. For the lowest
values of time and amplitude of excitation, we observe a bending of the main
axis of the cloud. Increasing the amplitude of excitation we observe an
increasing number of vortices. The vortex state can evolve into the turbulent
regime if the parameters of excitation are driven up to a certain set of
combinations. If the value of the parameters of these combinations is exceeded,
all vorticity disappears and the condensate enters into a different regime
which we have identified as the granular phase. Our results are summarized in a
diagram of amplitude versus time of excitation in which the different
structures can be identified. We also present numerical simulations of the
Gross-Pitaevskii equation which support our observations.Comment: 6 pages, 3 figure
Three-vortex configurations in trapped Bose-Einstein condensates
We report on the creation of three-vortex clusters in a
Bose-Einstein condensate by oscillatory excitation of the condensate. This
procedure can create vortices of both circulation, so that we are able to
create several types of vortex clusters using the same mechanism. The
three-vortex configurations are dominated by two types, namely, an
equilateral-triangle arrangement and a linear arrangement. We interpret these
most stable configurations respectively as three vortices with the same
circulation, and as a vortex-antivortex-vortex cluster. The linear
configurations are very likely the first experimental signatures of predicted
stationary vortex clusters.Comment: 4 pages, 4 figure
Molecular Mechanism and Potential Targets for Blocking HPV-Induced Lesion Development
Persistent infection with high-risk HPV is the etiologic agent associated with the development of cervical cancer (CC) development. However, environmental, social, epidemiological, genetic, and host factors may have a joint influence on the risk of disease progression. Cervical lesions caused by HPV infection can be removed naturally by the host immune response and only a small percentage may progress to cancer; thus, the immune response is essential for the control of precursor lesions and CC. We present a review of recent research on the molecular mechanisms that allow HPV-infected cells to evade immune surveillance and potential targets of molecular therapy to inhibit tumor immune escape
A functional role of the SNP -592 of human IL10 gene regulatory region is associated with an increased IL-10 expression and risk for human papillomavirus cervical lesion and cervical cancer development
Modelling entomological-climatic interactions of Plasmodium falciparum malaria transmission in two Colombian endemic-regions: contributions to a National Malaria Early Warning System
BACKGROUND: Malaria has recently re-emerged as a public health burden in Colombia. Although the problem seems to be climate-driven, there remain significant gaps of knowledge in the understanding of the complexity of malaria transmission, which have motivated attempts to develop a comprehensive model. METHODS: The mathematical tool was applied to represent Plasmodium falciparum malaria transmission in two endemic-areas. Entomological exogenous variables were estimated through field campaigns and laboratory experiments. Availability of breeding places was included towards representing fluctuations in vector densities. Diverse scenarios, sensitivity analyses and instabilities cases were considered during experimentation-validation process. RESULTS: Correlation coefficients and mean square errors between observed and modelled incidences reached 0.897–0.668 (P > 0.95) and 0.0002–0.0005, respectively. Temperature became the most relevant climatic parameter driving the final incidence. Accordingly, malaria outbreaks are possible during the favourable epochs following the onset of El Niño warm events. Sporogonic and gonotrophic cycles showed to be the entomological key-variables controlling the transmission potential of mosquitoes' population. Simulation results also showed that seasonality of vector density becomes an important factor towards understanding disease transmission. CONCLUSION: The model constitutes a promising tool to deepen the understanding of the multiple interactions related to malaria transmission conducive to outbreaks. In the foreseeable future it could be implemented as a tool to diagnose possible dynamical patterns of malaria incidence under several scenarios, as well as a decision-making tool for the early detection and control of outbreaks. The model will be also able to be merged with forecasts of El Niño events to provide a National Malaria Early Warning System
A Spectroscopic Study of Field and Runaway OB Stars
Identifying binaries among runaway O- and B-type stars offers valuable
insight into the evolution of open clusters and close binary stars. Here we
present a spectroscopic investigation of 12 known or suspected binaries among
field and runaway OB stars. We find new orbital solutions for five single-lined
spectroscopic binaries (HD 1976, HD 14633, HD 15137, HD 37737, and HD 52533),
and we classify two stars thought to be binaries (HD 30614 and HD 188001) as
single stars. In addition, we reinvestigate their runaway status using our new
radial velocity data with the UCAC2 proper motion catalogs. Seven stars in our
study appear to have been ejected from their birthplaces, and at least three of
these runaways are spectroscopic binaries and are of great interest for future
study.Comment: 21 pages, 1 figure, 7 tables; Accepted to Ap
Tunable Interferometers Driven by Coherent Surface Acoustic Phonons
[EN] We demonstrate a compact tunable photonic modulator driven by surface acoustic waves (SAWs) in the low GHz frequency range. The device follows a well-known Mach-Zehnder interferometer (MZI) structure with three output channels, built upon multi-mode interference (MMI) couplers. The light continuously switches paths between the central and the side channels, avoiding losses and granting a 180¿-dephasing synchronization between them. The modulator was monolithically fabricated on (Al,Ga)As, and can be used as a building block for more complex photonic functionalities. It can also be implemented in other material platforms such as Silicon or (In,Ga)P. Light modulated at multiples of the fundamental acoustic frequency can be accomplished by adjusting the applied acoustic power. An excellent agreement between theory and experiment is achievedCrespo-Poveda, A.; Hernández-Mínguez, A.; Biermann, K.; Tahraoui, A.; Gargallo-Jaquotot, B.; Muñoz, P.; Santos, P.... (2016). Tunable Interferometers Driven by Coherent Surface Acoustic Phonons. MRS Advances. 1651-1656. doi:10.1557/adv.2016.234S16511656Beck, M., de Lima, M. M., Wiebicke, E., Seidel, W., Hey, R., & Santos, P. V. (2007). Acousto-optical multiple interference switches. Applied Physics Letters, 91(6), 061118. doi:10.1063/1.2768889Soldano, L. B., & Pennings, E. C. M. (1995). Optical multi-mode interference devices based on self-imaging: principles and applications. Journal of Lightwave Technology, 13(4), 615-627. doi:10.1109/50.372474De Lima, M. M., Beck, M., Hey, R., & Santos, P. V. (2006). Compact Mach-Zehnder acousto-optic modulator. Applied Physics Letters, 89(12), 121104. doi:10.1063/1.2354411Crespo-Poveda, A., Hey, R., Biermann, K., Tahraoui, A., Santos, P. V., Gargallo, B., … de Lima, M. M. (2013). Synchronized photonic modulators driven by surface acoustic waves. Optics Express, 21(18), 21669. doi:10.1364/oe.21.021669Crespo-Poveda, A., Hernández-Mínguez, A., Gargallo, B., Biermann, K., Tahraoui, A., Santos, P. V., … de Lima, M. M. (2015). Acoustically driven arrayed waveguide grating. Optics Express, 23(16), 21213. doi:10.1364/oe.23.021213Sun, J., Timurdogan, E., Yaacobi, A., Hosseini, E. S., & Watts, M. R. (2013). Large-scale nanophotonic phased array. Nature, 493(7431), 195-199. doi:10.1038/nature1172
Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI and Direct Adaptive Optics Imaging Surveys: Giant Planets are Rare at Large Separations
We examine the implications for the distribution of extrasolar planets based
on the null results from two of the largest direct imaging surveys published to
date. Combining the measured contrast curves from 22 of the stars observed with
the VLT NACO adaptive optics system by Masciadri et al. (2005), and 48 of the
stars observed with the VLT NACO SDI and MMT SDI devices by Biller et al.
(2007) (for a total of 60 unique stars; the median star for our survey is a 30
Myr K2 star at 25 pc), we consider what distributions of planet masses and
semi-major axes can be ruled out by these data, based on Monte Carlo
simulations of planet populations. We can set this upper limit with 95%
confidence: the fraction of stars with planets with semi-major axis from 20 to
100 AU, and mass >4 M_Jup, is 20% or less. Also, with a distribution of planet
mass of dN/dM ~ M^-1.16 between 0.5-13 M_Jup, we can rule out a power-law
distribution for semi-major axis (dN/da ~ a^alpha) with index 0 and upper
cut-off of 18 AU, and index -0.5 with an upper cut-off of 48 AU. For the
distribution suggested by Cumming et al. (2007), a power-law of index -0.61, we
can place an upper limit of 75 AU on the semi-major axis distribution. At the
68% confidence level, these upper limits state that fewer than 8% of stars have
a planet of mass >4 M_Jup between 20 and 100 AU, and a power-law distribution
for semi-major axis with index 0, -0.5, and -0.61 cannot have giant planets
beyond 12, 23, and 29 AU, respectively. In general, we find that even null
results from direct imaging surveys are very powerful in constraining the
distributions of giant planets (0.5-13 M_Jup) at large separations, but more
work needs to be done to close the gap between planets that can be detected by
direct imaging, and those to which the radial velocity method is sensitive.Comment: 46 pages, 17 figures, accepted to Ap
Chromomagnetic Dipole Moment of the Top Quark Revisited
We study the complete one-loop contributions to the chromagnetic dipole
moment of the top quark in the Standard Model, two Higgs doublet
models, topcolor assited technicolor models (TC2), 331 models and extended
models with a single extra dimension. We find that the SM predicts
and that the predictions of the other models are also
consitent with the constraints imposed on by low-energy
precision measurements.Comment: 20 pages, 5 figures, Updat
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