1,701,138 research outputs found
Structure and behaviour of the sperm terminal filament
Light- and electron-microscopic observations of Ciona and Lytechinus spermatozoa show a thin terminal filament at the distal end. The terminal filament is 5-6 microns long and contains the two central microtubules and a variable number of A-tubule extensions of the peripheral doublet microtubules. The transition from the 9 + 2 region to the terminal filament is tapered more gradually in Lytechinus than in Ciona. Photographs of the movement of beating spermatozoa do not show any obvious discontinuity in curvature at the transition region. Bends are propagated smoothly off the end of the flagellum with no decrease in curvature. However, spermatozoa in which the terminal filament has been removed show a clear 'end effect'. This end effect involves a rapid unbending of bends that have reached the distal end of the flagellum. Computer simulations of flagellar models lacking a terminal filament show a similar end effect. Addition of a terminal filament to the end of the computer model can eliminate the end effect. Realistic bending behaviour of the model is obtained by using a terminal filament with a tapered elastic bending resistance in the basal portion of the terminal filament and a value of 0.03 x 10^(9) pN nm^2 in the remainder of the terminal filament. This leads to estimates of 0.01 x 10^(9) pN nm^2 for the elastic bending resistance of an individual microtubule, and 0.2 x 10^(9) pN nm^2 for the elastic bending resistance of the 9 + 2 region of the flagellum. An improvement in propulsive effectiveness by addition of a terminal filament remains to be demonstrated
Spontaneous Symmetry Breaking for Driven Interacting Particles on Triangular Substrates
For collectively interacting repulsive particles driven on triangular
substrates, we show that for certain directions of drive a spontaneous symmetry
breaking phenomena occurs where the particles can flow in one of two directions
that are not aligned with the external drive, giving rise to a positive or
negative Hall current. Along these directions, the particle flow is highly
ordered, while in the direction of the drive the flow is disordered. We also
find a number of dynamical phase transitions and unusual hysteretic properties
that arise due to the symmetry breaking properties of the flows.Comment: 4 pages, 4 postscript figure
Are people really conformist-biased? An empirical test and a new mathematical model
According to an influential theory in cultural evolution, within-group similarity of culture is explained by a human 'conformist-bias', which is a hypothesized evolved predisposition to preferentially follow a member of the majority when acquiring ideas and behaviours. However, this notion has little support from social psychological research. In fact, a major theory in social psychology (LATANÉ and WOLF, 1981) argues for what is in effect a ‘nonconformist-bias’: by analogy to standard psychophysics they predict minority sources of influence to have relatively greater impact than majority sources. Here we present a new mathematical model and an experiment on social influence, both specifically designed to test these competing predictions. The results are in line with nonconformism. Finally, we discuss within-group similarity and suggest that it is not a general phenomenon but must be studied trait by trait
Counting Smooth Solutions to the Equation A+B=C
This paper studies integer solutions to the Diophantine equation A+B=C in
which none of A, B, C have a large prime factor. We set H(A, B,C) = max(|A|,
|B|, |C|), and consider primitive solutions (gcd}(A, B, C)=1) having no prime
factor p larger than (log H(A, B,C))^K, for a given finite K. On the assumption
that the Generalized Riemann hypothesis (GRH) holds, we show that for any K > 8
there are infinitely many such primitive solutions having no prime factor
larger than (log H(A, B, C))^K. We obtain in this range an asymptotic formula
for the number of such suitably weighted primitive solutions.Comment: 35 pages latex; v2 corrected misprint
The Radon Monitoring System in Daya Bay Reactor Neutrino Experiment
We developed a highly sensitive, reliable and portable automatic system
(H) to monitor the radon concentration of the underground experimental
halls of the Daya Bay Reactor Neutrino Experiment. H is able to measure
radon concentration with a statistical error less than 10\% in a 1-hour
measurement of dehumidified air (R.H. 5\% at 25C) with radon
concentration as low as 50 Bq/m. This is achieved by using a large radon
progeny collection chamber, semiconductor -particle detector with high
energy resolution, improved electronics and software. The integrated radon
monitoring system is highly customizable to operate in different run modes at
scheduled times and can be controlled remotely to sample radon in ambient air
or in water from the water pools where the antineutrino detectors are being
housed. The radon monitoring system has been running in the three experimental
halls of the Daya Bay Reactor Neutrino Experiment since November 2013
On solutions to the non-Abelian Hirota-Miwa equation and its continuum limits
In this paper, we construct grammian-like quasideterminant solutions of a
non-Abelian Hirota-Miwa equation. Through continuum limits of this non-Abelian
Hirota-Miwa equation and its quasideterminant solutions, we construct a cascade
of noncommutative differential-difference equations ending with the
noncommutative KP equation. For each of these systems the quasideterminant
solutions are constructed as well.Comment: 9 pages, 1 figur
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