2,970 research outputs found
Quantifying stretching and rearrangement in epithelial sheet migration
Although understanding the collective migration of cells, such as that seen
in epithelial sheets, is essential for understanding diseases such as
metastatic cancer, this motion is not yet as well characterized as individual
cell migration. Here we adapt quantitative metrics used to characterize the
flow and deformation of soft matter to contrast different types of motion
within a migrating sheet of cells. Using a Finite-Time Lyapunov Exponent (FTLE)
analysis, we find that - in spite of large fluctuations - the flow field of an
epithelial cell sheet is not chaotic. Stretching of a sheet of cells (i.e.,
positive FTLE) is localized at the leading edge of migration. By decomposing
the motion of the cells into affine and non-affine components using the metric
D, we quantify local plastic rearrangements and describe the motion
of a group of cells in a novel way. We find an increase in plastic
rearrangements with increasing cell densities, whereas inanimate systems tend
to exhibit less non-affine rearrangements with increasing density.Comment: 21 pages, 7 figures This is an author-created, un-copyedited version
of an article accepted for publication in the New Journal of Physics. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The Version of Record is
available online at doi:10.1088/1367-2630/15/2/02503
Lagrangian Structure Functions in Turbulence: A Quantitative Comparison between Experiment and Direct Numerical Simulation
A detailed comparison between data from experimental measurements and
numerical simulations of Lagrangian velocity structure functions in turbulence
is presented. By integrating information from experiments and numerics, a
quantitative understanding of the velocity scaling properties over a wide range
of time scales and Reynolds numbers is achieved. The local scaling properties
of the Lagrangian velocity increments for the experimental and numerical data
are in good quantitative agreement for all time lags. The degree of
intermittency changes when measured close to the Kolmogorov time scales or at
larger time lags. This study resolves apparent disagreements between experiment
and numerics.Comment: 13 RevTeX pages (2 columns) + 8 figures include
Path lengths in turbulence
By tracking tracer particles at high speeds and for long times, we study the
geometric statistics of Lagrangian trajectories in an intensely turbulent
laboratory flow. In particular, we consider the distinction between the
displacement of particles from their initial positions and the total distance
they travel. The difference of these two quantities shows power-law scaling in
the inertial range. By comparing them with simulations of a chaotic but
non-turbulent flow and a Lagrangian Stochastic model, we suggest that our
results are a signature of turbulence.Comment: accepted for publication in Journal of Statistical Physic
Ultraestructura de la red alveolar y su relación con el recubrimiento de las paredes vasculares en olmos infectados con Ophiostoma novo-ulmi y en otras plantas infectadas con enfermedades similares de marchitamiento
In elms infected with Dutch elm disease, alveolar networks, demarcated by filamentous-like bands and confluent with similar matter (the coating) accumulating on vessel walls, occurred regularly in vessel elements. Similar material lined vessel walls in inoculated, sterilized, thin elm wood sections fixed by high pressure freezing. The coating was observed to connect with fungal cells and occasionally contained small opaque particles, the size of ribosomes, membranous and vesicular structures, and, following incubation of wood chips taken from diseased samples incubated on an agar medium, it still displayed similar matter. Coating and alveolar bands increased in thickness by confluence of other bands or membranous structures. Similar matter and structures also occurred in other plants affected by similar fungal wilt diseases. In all systems, the compact coating did not label for chitin, cellulose and pectin. In staghorn sumac, the probe for DNA attached to the coating. Altogether, in the light of these data, it appears that the coating and alveolar networks are not inert components, a fact which indicates their primordial probable pathogen origin. It is proposed that these elements might be important not only in the initial infection stages but also in older or recurrent infections at a time when host resistance mechanisms are ineffective.En olmos afectados por la grafiosis, la red alveolar, demarcada por bandas filamentosas, y confluente con acumulaciones de la misma sustancia (cubrición) presentes en las paredes de los vasos, aparece regularmente en los elementos conductores. Sustancias similares tapizan las paredes de los vasos en secciones de madera delgada de olmo inoculada y esterilizada, y posteriormente criofijadas a altas presiones. Se observó que la cubrición se conecta con las células del micelio y que ocasionalmente contenía pequeñas partículas opacas del tamaño de los ribosomas, estructuras membranosas y vesiculares, así como que, tras la incubación de astillas leñosas cogidas de muestras enfermas incubadas en agar, aún se presentaba una sustancia similar. La cubrición y las bandas alveolares aumentaron su espesor en la confluencia con otras bandas o estructuras membranosas. Estructuras y sustancias similares aparecieron también en otras plantas afectadas por enfermedades similares originadas por hongos que producen marchitamiento. En todos los sistemas, la cubrición compacta no pudo ser marcada como quitina, celulosa ni pectina. En zumaque (Rhus typhina), la sonda de ADN se pegó a la cubrición. En resumen, a la vista de estos datos, parece ser que la cubrición y la red alveolar no están formados por componentes inertes, un hecho que indica su probable origen patogénico. Se sugiere que esos elementos podrían ser importantes no sólo en las fases iniciales de la infección, sino también, en infecciones más desarrolladas o recurrentes, en el momento en que los mecanismos de resistencia del hospedante no son efectivos
The Evolution of Blue Stragglers Formed Via Stellar Collisions
We have used the results of recent smoothed particle hydrodynamic simulations
of colliding stars to create models appropriate for input into a stellar
evolution code. In evolving these models, we find that little or no surface
convection occurs, precluding angular momentum loss via a magnetically-driven
stellar wind as a viable mechanism for slowing rapidly rotating blue stragglers
which have been formed by collisions. Angular momentum transfer to either a
circumstellar disk (possibly collisional ejecta) or a nearby companion are
plausible mechanisms for explaining the observed low rotation velocities of
blue stragglers. Under the assumption that the blue stragglers seen in NGC 6397
and 47 Tuc have been created solely by collisions, we find that the majority of
these blue stragglers cannot have been highly mixed by convection or meridional
circulation currents at anytime during their evolution. Also, on the basis of
the agreement between the predictions of our non-rotating models and the
observed blue straggler distribution, the evolution of blue stragglers is
apparently not dominated by the effects of rotation.Comment: 36 pages, including 1 table and 7 postscript figures (LaTeX2e). Also
avaliable at http://astrowww.phys.uvic.ca/~ouellet/ . Accepted for
publication in A
Does the Supreme Court Follow the Economic Returns? A Response to A Macrotheory of the Court
Today, there is a widespread idea that parents need to learn how to carry out their roles as parents. Practices of parental learning operate throughout society. This article deals with one particular practice of parental learning, namely nanny TV, and the way in which ideal parents are constructed through such programmes. The point of departure is SOS family, a series broadcast on Swedish television in 2008. Proceeding from the theorising of governmentality developed in the wake of the work of Michel Foucault, we analyse the parental ideals conveyed in the series, as an example of the way parents are constituted as subjects in the ‘advanced liberal society’ of today. The ideal parent is a subject who, guided by the coach, is constantly endeavouring to achieve a makeover. The objective of this endeavour, however, is self-control, whereby the parents will in the end become their own coaches.
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The sins of the child: Public opinion about parental responsibility for juvenile crime
Previous research indicates that people ascribe less responsibility to juvenile offenders than adult offenders for the crimes they have committed. Although assignment of responsibility to parents varies depending upon the youth’s age, we know little about the role of other factors. The current study used randomized factorial vignettes to examine whether the seriousness of the offense, peer involvement, and the offender's race, age, sex, and prior record influence support for parental responsibility. We found that participants in our study placed substantial responsibility on parents for dealing with juvenile offenders; however, support for punishing the parents was low, while the importance attached to enrolling parents in training was high. Views on parental responsibility were influenced by the age of the juvenile and the seriousness of the offense. The implications of these findings and how they fit in with previous work are discussed
Half Life of the Doubly-magic r-Process Nucleus 78Ni
Nuclei with magic numbers serve as important benchmarks in nuclear theory. In
addition, neutron-rich nuclei play an important role in the astrophysical rapid
neutron-capture process (r-process). 78Ni is the only doubly-magic nucleus that
is also an important waiting point in the r-process, and serves as a major
bottleneck in the synthesis of heavier elements. The half-life of 78Ni has been
experimentally deduced for the first time at the Coupled Cyclotron Facility of
the National Superconducting Cyclotron Laboratory at Michigan State University,
and was found to be 110 (+100 -60) ms. In the same experiment, a first
half-life was deduced for 77Ni of 128 (+27 -33) ms, and more precise half-lives
were deduced for 75Ni and 76Ni of 344 (+20 -24) ms and 238 (+15 -18) ms
respectively.Comment: 4 pages, 3 figure
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