148 research outputs found
Discovery of Quasi-Periodic Oscillations in the Recurrent Burst Emission from SGR 1806-20
We present evidence for Quasi-Periodic Oscillations (QPOs) in the recurrent
outburst emission from the soft gamma repeater SGR 1806-20 using NASA's Rossi
X-ray Timing Explorer (RXTE) observations. By searching a sample of 30 bursts
for timing signals at the frequencies of the QPOs discovered in the 2004
December 27 giant flare from the source, we find three QPOs at 84, 103, and 648
Hz in three different bursts. The first two QPOs lie within 1
from the 92 Hz QPO detected in the giant flare. The third QPO lie within
9 from the 625 Hz QPO also detected in the same flare. The detected
QPOs are found in bursts with different durations, morphologies, and
brightness, and are vindicated by Monte Carlo simulations, which set a lower
limit confidence interval . We also find evidence for
candidate QPOs at higher frequencies in other bursts with lower statistical
significance. The fact that we can find evidence for QPOs in the recurrent
bursts at frequencies relatively close to those found in the giant flare is
intriguing and can offer insight about the origin of the oscillations. We
confront our finding against the available theoretical models and discuss the
connection between the QPOs we report and those detected in the giant flares.
The implications to the neutron star properties are also discussed.Comment: 5 pages, 2 figures, Accepted for publication in the Astrophysical
Journal Letters (ApJL
A Magnetic Flux Tube Oscillation Model for QPOs in SGR Giant Flares
Giant flares from soft gamma-ray repeaters (SGRs) are one of the most violent
phenomena in neutron stars. Quasi-periodic oscillations (QPOs) with frequencies
ranging from 18 to 1840 Hz have been discovered in the tails of giant flares
from two SGRs, and were ascribed to be seismic vibrations or torsional
oscillations of magnetars. Here we propose an alternative explanation for the
QPOs in terms of standing sausage mode oscillations of flux tubes in the
magnetar coronae. We show that most of the QPOs observed in SGR giant flares
could be well accounted for except for those with very high frequencies (625
and 1840 Hz).Comment: 15 pages,1 figures,1 table, accepted for publication in The
Astrophysical Journa
Von Bezold assimilation effect reverses in stereoscopic conditions
Lightness contrast and lightness assimilation are opposite phenomena: in contrast,
grey targets appear darker when bordering bright surfaces (inducers) rather than dark ones; in
assimilation, the opposite occurs. The question is: which visual process favours the occurrence
of one phenomenon over the other? Researchers provided three answers to this question. The
first asserts that both phenomena are caused by peripheral processes; the second attributes their
occurrence to central processes; and the third claims that contrast involves central processes,
whilst assimilation involves peripheral ones. To test these hypotheses, an experiment on an IT
system equipped with goggles for stereo vision was run. Observers were asked to evaluate the
lightness of a grey target, and two variables were systematically manipulated: (i) the apparent
distance of the inducers; and (ii) brightness of the inducers. The retinal stimulation was kept
constant throughout, so that the peripheral processes remained the same. The results show that
the lightness of the target depends on both variables. As the retinal stimulation was kept constant, we
conclude that central mechanisms are involved in both lightness contrast and lightness assimilation
Detecção de riquĂ©tsias em carrapatos do gĂȘnero Amblyomma (Acari: Ixodidae) coletados em parque urbano do municĂpio de Campinas, SP
Breaking Functional Connectivity into Components: A Novel Approach Using an Individual-Based Model, and First Outcomes
Landscape connectivity is a key factor determining the viability of populations in fragmented landscapes. Predicting âfunctional connectivityâ, namely whether a patch or a landscape functions as connected from the perspective of a focal species, poses various challenges. First, empirical data on the movement behaviour of species is often scarce. Second, animal-landscape interactions are bound to yield complex patterns. Lastly, functional connectivity involves various components that are rarely assessed separately. We introduce the spatially explicit, individual-based model FunCon as means to distinguish between components of functional connectivity and to assess how each of them affects the sensitivity of species and communities to landscape structures. We then present the results of exploratory simulations over six landscapes of different fragmentation levels and across a range of hypothetical bird species that differ in their response to habitat edges. i) Our results demonstrate that estimations of functional connectivity depend not only on the response of species to edges (avoidance versus penetration into the matrix), the movement mode investigated (home range movements versus dispersal), and the way in which the matrix is being crossed (random walk versus gap crossing), but also on the choice of connectivity measure (in this case, the model output examined). ii) We further show a strong effect of the mortality scenario applied, indicating that movement decisions that do not fully match the mortality risks are likely to reduce connectivity and enhance sensitivity to fragmentation. iii) Despite these complexities, some consistent patterns emerged. For instance, the ranking order of landscapes in terms of functional connectivity was mostly consistent across the entire range of hypothetical species, indicating that simple landscape indices can potentially serve as valuable surrogates for functional connectivity. Yet such simplifications must be carefully evaluated in terms of the components of functional connectivity they actually predict
Search for invisible modes of nucleon decay in water with the SNO+ detector
This paper reports results from a search for nucleon decay through invisible modes, where no visible energy is directly deposited during the decay itself, during the initial water phase of SNO+. However, such decays within the oxygen nucleus would produce an excited daughter that would subsequently deexcite, often emitting detectable gamma rays. A search for such gamma rays yields limits of 2.5Ă1029âây at 90% Bayesian credibility level (with a prior uniform in rate) for the partial lifetime of the neutron, and 3.6Ă1029âây for the partial lifetime of the proton, the latter a 70% improvement on the previous limit from SNO. We also present partial lifetime limits for invisible dinucleon modes of 1.3Ă1028âây for nn, 2.6Ă1028âây for pn and 4.7Ă1028âây for pp, an improvement over existing limits by close to 3 orders of magnitude for the latter two
Effect of NaCl on leaf H+-ATPase and the relevance to salt tolerance in two contrasting poplar species
Improving PBL in Empowering Meta cognitive Skill of Students
Abstract
Objective: Problem-Based Learning (PBL) is a potential constructivist learning strategy that empowers studentsâ Meta cognitive skill. PBL focuses on problem, involves thinking activity to solve problems, and correlates to cognitive function of students. Methods: The implementation of PBL reveals various benefits, but there are also some weaknesses in this learning strategy. Thus, it is necessary to implement a certain learning strategy that can cover the PBL weaknesses, such as Reading, Questioning, and Answering (RQA) learning strategy. RQA is a new learning strategy developed based on a fact that almost all students do not read the next lecture materials, causing failure of learning strategy planned and finally the studentsâ comprehension becomes low. RQA is also potential to empower studentsâ Meta cognitive skill. Findings: The integration of RQA and PBL learning strategy is called PBL-RQA learning strategy. This study was a quasi-experimental
study designed to compare the effect of PBL, RQA, and PBL-RQA learning strategies on the studentsâ Meta cognitive skill of Faculty of Mathematics and Science, State University of Makassar. Application: The results of the study showed that the potency of PBL learning strategy in empowering the studentsâ Meta cognitive skill has been increased by integrating it to RQA learning strategy. The meta cognitive skill mean score of the students taught by PBL-RQA learning strategy was 21% higher than that of the students taught by PBL and 26.9% higher than that of the students taught by RQA learning strategy.
Keywords: Answering, Meta Cognitive Skill, Problem-Based Learning, Questioning, Reading, PBL-RQ
An atlas of over 90.000 conserved noncoding sequences provides insight into crucifer regulatory regions
Despite the central importance of noncoding DNA to gene regulation and evolution, understanding of the extent of selection on plant noncoding DNA remains limited compared to that of other organisms. Here we report sequencing of genomes from three Brassicaceae species (Leavenworthia alabamica, Sisymbrium irio and Aethionema arabicum) and their joint analysis with six previously sequenced crucifer genomes. Conservation across orthologous bases suggests that at least 17% of the Arabidopsis thaliana genome is under selection, with nearly one-quarter of the sequence under selection lying outside of coding regions. Much of this sequence can be localized to approximately 90,000 conserved noncoding sequences (CNSs) that show evidence of transcriptional and post-transcriptional regulation. Population genomics analyses of two crucifer species, A. thaliana and Capsella grandiflora, confirm that most of the identified CNSs are evolving under medium to strong purifying selection. Overall, these CNSs highlight both similarities and several key differences between the regulatory DNA of plants and other species
Development, characterisation, and deployment of the SNO+ liquid scintillator
A liquid scintillator consisting of linear alkylbenzene as the solvent and 2,5-diphenyloxazole as the fluor was developed for the SNO+ experiment. This mixture was chosen as it is compatible with acrylic and has a competitive light yield to pre-existing liquid scintillators while conferring other advantages including longer attenuation lengths, superior safety characteristics, chemical simplicity, ease of handling, and logistical availability. Its properties have been extensively characterized and are presented here. This liquid scintillator is now used in several neutrino physics experiments in addition to SNO+
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