7,182 research outputs found
Magnification Ratio of the Fluctuating Light in Gravitational Lens 0957+561
Radio observations establish the B/A magnification ratio of gravitational
lens 0957+561 at about 0.75. Yet, for more than 15 years, the optical
magnfication ratio has been between 0.9 and 1.12. The accepted explanation is
microlensing of the optical source. However, this explanation is mildly
discordant with (i) the relative constancy of the optical ratio, and (ii)
recent data indicating possible non-achromaticity in the ratio. To study these
issues, we develop a statistical formalism for separately measuring, in a
unified manner, the magnification ratio of the fluctuating and constant parts
of the light curve. Applying the formalism to the published data of Kundi\'c et
al. (1997), we find that the magnification ratios of fluctuating parts in both
the g and r colors agrees with the magnification ratio of the constant part in
g-band, and tends to disagree with the r-band value. One explanation could be
about 0.1 mag of consistently unsubtracted r light from the lensing galaxy G1,
which seems unlikely. Another could be that 0957+561 is approaching a caustic
in the microlensing pattern.Comment: 12 pages including 1 PostScript figur
The brain's temporal dynamics from a collective decision to individual action
Social animals constantly make decisions together. What determines if individuals will subsequently adjust their behavior to align with collective choices? Here, using functional magnetic resonance imaging in humans, we characterize a novel temporal model of brain response from the time a collective decision is made to the time an individual action is required. We reveal that whether a behavioral modification will occur is determined not necessarily by the brain’s response to the initial social influence, but by how that response(specifically in the orbitofrontal cortex; OFC) is mirrored at a later time when the individual selects their own action. This result suggests that the OFC may reconstitute an initial state of collective influence when individual action is subsequently needed. Importantly, these dynamics vary across individuals as a function of trait conformity and mediate the relationship between this personality characteristic and behavioral adjustment toward the group
Human Frontal–Subcortical Circuit and Asymmetric Belief Updating
How humans integrate information to form beliefs about reality is a question that has engaged scientists for centuries, yet the biological system supporting this process is not well understood. One of the most salient attributes of information is valence. Whether a piece of news is good or bad is critical in determining whether it will alter our beliefs. Here, we reveal a frontal–subcortical circuit in the left hemisphere that is simultaneously associated with enhanced integration of favorable information into beliefs and impaired integration of unfavorable information. Specifically, for favorable information, stronger white matter connectivity within this system, particularly between the left inferior frontal gyrus (IFG) and left subcortical regions (including the amygdala, hippocampus, thalamus, putamen, and pallidum), as well as insular cortex, is associated with greater change in belief. However, for unfavorable information, stronger connectivity within this system, particularly between the left IFG and left pallidum, putamen, and insular cortex, is associated with reduced change in beliefs. These novel results are consistent with models suggesting that partially separable processes govern learning from favorable and unfavorable information
A controlled experiment for the empirical evaluation of safety analysis techniques for safety-critical software
Context: Today's safety critical systems are increasingly reliant on
software. Software becomes responsible for most of the critical functions of
systems. Many different safety analysis techniques have been developed to
identify hazards of systems. FTA and FMEA are most commonly used by safety
analysts. Recently, STPA has been proposed with the goal to better cope with
complex systems including software. Objective: This research aimed at comparing
quantitatively these three safety analysis techniques with regard to their
effectiveness, applicability, understandability, ease of use and efficiency in
identifying software safety requirements at the system level. Method: We
conducted a controlled experiment with 21 master and bachelor students applying
these three techniques to three safety-critical systems: train door control,
anti-lock braking and traffic collision and avoidance. Results: The results
showed that there is no statistically significant difference between these
techniques in terms of applicability, understandability and ease of use, but a
significant difference in terms of effectiveness and efficiency is obtained.
Conclusion: We conclude that STPA seems to be an effective method to identify
software safety requirements at the system level. In particular, STPA addresses
more different software safety requirements than the traditional techniques FTA
and FMEA, but STPA needs more time to carry out by safety analysts with little
or no prior experience.Comment: 10 pages, 1 figure in Proceedings of the 19th International
Conference on Evaluation and Assessment in Software Engineering (EASE '15).
ACM, 201
The Athletic Profile of Fast Bowling in Cricket : A Review
Cricket is a global sport played in over 100 countries with elite performers attracting multimillion dollar contracts. Therefore, performers maintaining optimum physical fitness and remaining injury free is important. Fast bowlers have a vital position in a cricket team, and there is an increasing body of scientific literature that has reviewed this role over the past decade. Previous research on fast bowlers has tended to focus on biomechanical analysis and injury prevention in performers. However, this review aims to critically analyze the emerging contribution of physiological-based literature linked to fast bowling in cricket, highlight the current evidence related to simulated and competitive in-match performance, and relate this practically to the conditioning coach. Furthermore, the review considers limitations with past research and possible avenues for future investigation. It is clear with the advent of new applied mobile monitoring technology that there is scope for more ecologically valid and longitudinal exploration capturing in-match data, providing quantification of physiological workloads, and analysis of the physical demands across the differing formats of the game. Currently, strength and conditioning specialists do not have a critical academic resource with which to shape professional practice, and this review aims to provide a starting point for evidence in the specific areaPeer reviewedFinal Accepted Versio
Values of H_0 from Models of the Gravitational Lens 0957+561
The lensed double QSO 0957+561 has a well-measured time delay and hence is
useful for a global determination of H0. Uncertainty in the mass distribution
of the lens is the largest source of uncertainty in the derived H0. We
investigate the range of \hn produced by a set of lens models intended to mimic
the full range of astrophysically plausible mass distributions, using as
constraints the numerous multiply-imaged sources which have been detected. We
obtain the first adequate fit to all the observations, but only if we include
effects from the galaxy cluster beyond a constant local magnification and
shear. Both the lens galaxy and the surrounding cluster must depart from
circular symmetry as well.
Lens models which are consistent with observations to 95% CL indicate
H0=104^{+31}_{-23}(1-\kthirty) km/s/Mpc. Previous weak lensing measurements
constrain the mean mass density within 30" of G1 to be kthirty=0.26+/-0.16 (95%
CL), implying H0=77^{+29}_{-24}km/s/Mpc (95% CL). The best-fitting models span
the range 65--80 km/s/Mpc. Further observations will shrink the confidence
interval for both the mass model and \kthirty.
The range of H0 allowed by the full gamut of our lens models is substantially
larger than that implied by limiting consideration to simple power law density
profiles. We therefore caution against use of simple isothermal or power-law
mass models in the derivation of H0 from other time-delay systems. High-S/N
imaging of multiple or extended lensed features will greatly reduce the H0
uncertainties when fitting complex models to time-delay lenses.Comment: AASTEX, 48 pages 4 figures, 2 tables. Also available at:
http://www.astro.lsa.umich.edu:80/users/philf/www/papers/list.htm
Fall speed measurement and high-resolution multi-angle photography of hydrometeors in free fall
We describe here a new instrument for imaging hydrometeors in free fall. The Multi-Angle Snowflake Camera (MASC) captures high-resolution photographs of hydrometeors from three angles while simultaneously measuring their fall speed. Based on the stereoscopic photographs captured over the two months of continuous measurements obtained at a high altitude location within the Wasatch Front in Utah, we derive statistics for fall speed, hydrometeor size, shape, orientation and aspect ratio. From a selection of the photographed hydrometeors, an illustration is provided for how the instrument might be used for making improved microwave scattering calculations. Complex, aggregated snowflake shapes appear to be more strongly forward scattering, at the expense of reduced back-scatter, than heavily rimed graupel particles of similar size
Boosting jet power in black hole spacetimes
The extraction of rotational energy from a spinning black hole via the
Blandford-Znajek mechanism has long been understood as an important component
in models to explain energetic jets from compact astrophysical sources. Here we
show more generally that the kinetic energy of the black hole, both rotational
and translational, can be tapped, thereby producing even more luminous jets
powered by the interaction of the black hole with its surrounding plasma. We
study the resulting Poynting jet that arises from single boosted black holes
and binary black hole systems. In the latter case, we find that increasing the
orbital angular momenta of the system and/or the spins of the individual black
holes results in an enhanced Poynting flux.Comment: 7 pages, 5 figure
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