26,283 research outputs found
Irradiation of Sperm Tails by Laser Microbeam
1. Sea-urchin and starfish sperm tails were irradiated at pre-selected points along the flagellum and at pre-selected phases of the beat cycle by means of a pulsed ruby laser microbeam. Multiple-exposure dark-field photomicrographs were taken immediately before and after irradiation. The flagellum usually appeared to be broken at the irradiated point.
2. The portion of a flagellum between the head and the irradiated point continued for at least a few beats if its length was at least 25% of the length of the tail, and stopped immediately if it was shorter.
3. Bends already established beyond the irradiated point continued to propagate to the tip of the flagellum. Their propagation velocity generally decreased, and there were usually changes in other bend parameters.
4. No new bends ever developed beyond the irradiated point.
5. Irradiation within a bent region often completely eliminated that region
Small flow rate can supply inwardly migrating shortest-period planets
The number of exoplanets found with periods as short as one day and less was
surprising given how fast these planets had been expected to migrate into the
star due to the tides raised on the star by planets at such close distances. It
has been seen as improbable that we would find planets in such a small final
fraction of their lives. The favored solution has been that the tidal
dissipation is much weaker than expected, which would mean that the final
infall would be a larger fraction of the planets' life. We find no reason to
exclude the explanation that a small number of planets are continuously sent
migrating inwards such that these planets indeed are in the last fraction of
their lives. Following the observation that the distribution of medium planets
disfavors tidal dissipation being significantly weaker than has been found from
observations of binary stars, we now show that the numbers of planets in such a
"flow" of excess planets migrating inwards is low enough that even depletion of
the three-day pileup is a plausible source. Then the shortest period occurrence
distribution would be shaped by planets continuously being sent into the star,
which may explain the depletion of the pileup in the Kepler field relative to
the solar neighborhood (Howard et al. 2012, hereafter H12). Because Kepler
observes above the galactic plane, H12 suggested the Kepler field may include
an older population of stars. The tidal dissipation strength in stars due to
giant planets may be not greatly weaker than it is in binary stars.Comment: Four pages, four figures, submitted to Hot Planets Cold Stars
conference (2012 November Garching, Germany
Identity and ethnicity in /t/ in Glasgow-Pakistani high-school girls
This paper presents an acoustic phonetic analysis
of Glasgow Asian syllable-initial /t/, in speech data
collected from Pakistani-Muslim girls in a
Glasgow high school after a long-term participant
observation into their shared and differing social
practices. The results show differences in spectral
energy and shape according to following phonetic
segment, and to membership in two contrasting
Communities of Practice, more conservative girls
maintaining traditional cultural practices, and more
rebellious girls whose behaviour challenges such
norms. The findings demonstrate that ethnicity is
integrally linked with locally-salient identity, and
hence that fine phonetic variation which indexes
ethnicity is in fact indexical of local ethnic identity
Gamma Limit for Transition Paths of Maximal Probability
Chemical reactions can be modelled via diffusion processes conditioned to
make a transition between specified molecular configurations representing the
state of the system before and after the chemical reaction. In particular the
model of Brownian dynamics - gradient flow subject to additive noise - is
frequently used. If the chemical reaction is specified to take place on a given
time interval, then the most likely path taken by the system is a minimizer of
the Onsager-Machlup functional. The Gamma limit of this functional is
determined in the case where the temperature is small and the transition time
scales as the inverse temperatur
Smooth matter and source size in microlensing simulations of gravitationally lensed quasars
Several gravitationally lensed quasars are observed with anomalous
magnifications in pairs of images that straddle a critical curve. Simple
theoretical arguments suggest that the magnification of these images should be
approximately equivalent, whereas one image is observed to be significantly
demagnified. Microlensing provides a possible explanation for this discrepancy.
There are two key parameters when modelling this effect. The first, the
fraction of smooth matter in the lens at the image positions, has been explored
by Schechter and Wambsganss (2002). They have shown that the anomalous flux
ratio observed in the lensed quasar MG 0414+0534 is a priori a factor of 5 more
likely if the assumed smooth matter content in the lens model is increased from
0% to 93%. The second parameter, the size of the emission region, is explored
in this paper, and shown to be more significant. We find that the broadening of
the magnification probability distributions due to smooth matter content is
washed out for source sizes that are predicted by standard models for quasars.
We apply our model to the anomalous lensed quasar MG 0414+0534, and find a 95%
upper limit of 2.62 x 10^(16) h^(-1/2) (M/Msun)^(1/2) cm on the radius of the
I-band emission region. The smooth matter percentage in the lens is
unconstrained.Comment: 6 pages, 6 figures. To be published in MNRA
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