6,437 research outputs found
An asymptotically normal test for the selective neutrality hypothesis
An important parameter in the study of population evolution is
, where is the effective population size and is the
rate of mutation per locus per generation. Therefore, represents the
mean number of mutations per site per generation. There are many estimators of
, one of them being the mean number of pairwise nucleotide differences,
which we call . Other estimators are , based on
the number of segregating sites and , based on the number of
singletons. The concept of selective neutrality can be interpreted as a
differentiated nucleotide distribution for mutant sites when compared to the
overall nucleotide distribution. Tajima (1989) has proposed the so-called
Tajima's test of selective neutrality based on .
Its complex empirical behavior (Kiihl, 2005) motivates us to propose a test
statistic solely based on . We are thus able to prove asymptotic
normality under different assumptions on the number of sequences and number of
sites via -statistics theory.Comment: Published in at http://dx.doi.org/10.1214/193940307000000293 the IMS
Collections (http://www.imstat.org/publications/imscollections.htm) by the
Institute of Mathematical Statistics (http://www.imstat.org
Can a 1-D mantle electrical conductivity model generate magnetic jerk differential time delays?
Worldwide jerks occurring in 1969, 1978 and 1991 are not simultaneous at the earth's surface, showing differential delays of about 2 yr. One way to explain this intriguing temporal pattern is to consider the earth's mantle as a conductor. Consequently the geomagnetic field observed at the earth's surface will correspond to a filtered version of the original field generated at the core-mantle boundary (CMB). We developed the forward approach to this problem assuming the temporal part of the jerk as a simultaneous impulse in the third time-derivative of the magnetic field at the CMB. Two synthetic spherical harmonic models of the jerk amplitudes are built by using two different power spectra. The effect of the mantle is illustrated by a 1-D radial electrical conductivity model that acts as linear, causal and time-invariant filter. The key point is that the mantle filter is different for each harmonic degree. Therefore, because the mixing of harmonics varies with location, distinct time delays will exist at the earth's surface. By using Backus' mantle filter theory, we demonstrate that a simple 1-D mantle electrical conductivity model is able to generate differential jerk time delays that depend strongly on the jerk morphology input model. We also illustrate that the time delays will vary for each component of the magnetic fiel
Dementia in low-income and middle-income countries: Different realities mandate tailored solutions
CNPq (a Brazilian public agency)Univ Fed Sao Paulo, Dept Psychobiol, Sao Paulo, BrazilChristian Med Coll & Hosp, Dept Psychiat, Vellore, Tamil Nadu, IndiaUniv Fed Sao Paulo, Dept Psychobiol, Sao Paulo, BrazilCNPq: 311031/2016-1Web of Scienc
On the applicability of Backus' mantle filter theory
Geomagnetic jerks are sudden changes of trend in the geomagnetic secular variation. The Earth's mantle behaves as a filter for the jerks, causing a delayed and a smoothed signal at the Earth's surface. Backus' mantle filter theory relies on approximating the impulse response function (IRF) of the mantle by a Gaussian. The advantage of this theory is the linear relation between jerks' delay times and the mantle electrical conductivity, as expressed by kernels. However, the limitations of this theory arise when negative delay and/or smoothing times occur. The applicability of the mantle filter theory is examined by analysing the validity of the Gaussian as an approximation for the composite IRF (CIRF) at a given location. We show that the electrical conductivity of the lower mantle is mostly responsible for the jerk delay time. Alternating sign CIRFs might cause negative delay and/or smoothing times which prevents the use of the mantle filter theory. Adequate/inadequate Gaussian approximations to the CIRFs give small/large differences in the convolved jerk occurrence times. Most observatories yield positive time constants, but in most cases the difference in the jerk occurrence times exceeds 0.5y
Lattice fence and hedge barriers around an apiary increase honey bee flight height and decrease stings to people nearby
Urban beekeeping is becoming more popular in the UK. One of the challenges faced by urban beekeepers is finding a suitable apiary location. Honey bees are often perceived as a nuisance, mainly due to their stinging behaviour. Here, we experimentally test the assumption that barriers around an apiary such as walls or fences, force the bees to fly above human height, thereby reducing collisions with people and, consequently, stinging. The experiment was conducted in two apiaries using two common types of barrier: a lattice fence (trellis) and hedge. Barriers were 2 m high, which is taller than > 99% of humans and is also the maximum height allowed by UK planning regulations for garden fences or walls. We found that barriers were effective at both raising the mean honey bee flight height and reducing stinging. However, the effects were only seen when the barrier had been in place for a few days, not immediately after the barrier was put in place. Although this raises interesting questions regarding honey bee navigation and memory, it is not a problem for beekeepers, as any barrier placed around an apiary will be permanent. The effect of the barriers on raising bee flight height to a mean of c. 2.2-2.5 m was somewhat weak and inconsistent, probably because the bees flew high, mean of c. 1.6-2.0 m, even in the absence of a barrier. As barriers can also reduce wind exposure, improve security and are inexpensive, we recommend their use around urban apiaries in places such as private gardens or allotments, where nuisance to humans is likely to be a problem
Towards Multi-class Object Detection in Unconstrained Remote Sensing Imagery
Automatic multi-class object detection in remote sensing images in
unconstrained scenarios is of high interest for several applications including
traffic monitoring and disaster management. The huge variation in object scale,
orientation, category, and complex backgrounds, as well as the different camera
sensors pose great challenges for current algorithms. In this work, we propose
a new method consisting of a novel joint image cascade and feature pyramid
network with multi-size convolution kernels to extract multi-scale strong and
weak semantic features. These features are fed into rotation-based region
proposal and region of interest networks to produce object detections. Finally,
rotational non-maximum suppression is applied to remove redundant detections.
During training, we minimize joint horizontal and oriented bounding box loss
functions, as well as a novel loss that enforces oriented boxes to be
rectangular. Our method achieves 68.16% mAP on horizontal and 72.45% mAP on
oriented bounding box detection tasks on the challenging DOTA dataset,
outperforming all published methods by a large margin (+6% and +12% absolute
improvement, respectively). Furthermore, it generalizes to two other datasets,
NWPU VHR-10 and UCAS-AOD, and achieves competitive results with the baselines
even when trained on DOTA. Our method can be deployed in multi-class object
detection applications, regardless of the image and object scales and
orientations, making it a great choice for unconstrained aerial and satellite
imagery.Comment: ACCV 201
GHIGLS: HI mapping at intermediate Galactic latitude using the Green Bank Telescope
This paper introduces the data cubes from GHIGLS, deep Green Bank Telescope
surveys of the 21-cm line emission of HI in 37 targeted fields at intermediate
Galactic latitude. The GHIGLS fields together cover over 1000 square degrees at
9.55' spatial resolution. The HI spectra have an effective velocity resolution
about 1.0 km/s and cover at least -450 < v < +250 km/s. GHIGLS highlights that
even at intermediate Galactic latitude the interstellar medium is very complex.
Spatial structure of the HI is quantified through power spectra of maps of the
column density, NHI. For our featured representative field, centered on the
North Ecliptic Pole, the scaling exponents in power-law representations of the
power spectra of NHI maps for low, intermediate, and high velocity gas
components (LVC, IVC, and HVC) are -2.86 +/- 0.04, -2.69 +/- 0.04, and -2.59
+/- 0.07, respectively. After Gaussian decomposition of the line profiles, NHI
maps were also made corresponding to the narrow-line and broad-line components
in the LVC range; for the narrow-line map the exponent is -1.9 +/- 0.1,
reflecting more small scale structure in the cold neutral medium (CNM). There
is evidence that filamentary structure in the HI CNM is oriented parallel to
the Galactic magnetic field. The power spectrum analysis also offers insight
into the various contributions to uncertainty in the data. The effect of 21-cm
line opacity on the GHIGLS NHI maps is estimated.Comment: Accepted for publication in The Astrophysical Journal, 2015 July 16.
32 pages, 21 figures (Fig. 10 new). Minor revisions from review, particularly
Section 8 and Appendix C; results unchanged. Additional surveys added and
made available; new Appendix B. Added descriptions of available FITS files
and links to four illustrative movies on enhanced GHIGLS archive
(www.cita.utoronto.ca/GHIGLS/
Quantum entanglement of bound particles under free center of mass dispersion
On the basis of the full analytical solution of the overall unitary dynamics,
the time evolution of entanglement is studied in a simple bipartite model
system evolving unitarily from a pure initial state. The system consists of two
particles in one spacial dimension bound by harmonic forces and having its free
center of mass initially localized in space in a minimum uncertainty wave
packet. The existence of such initial states in which the bound particles are
not entangled is pointed out. The entanglement of the two particles is shown to
be independent of the wavepacket mean momentum, and to increase monotonically
in a time scale distinct from that of the spreading of the center of mass
wavepacket.Comment: 17 pages, 5 figure
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