1,005 research outputs found
Differential growth of wrinkled biofilms
Biofilms are antibiotic-resistant bacterial aggregates that grow on moist
surfaces and can trigger hospital-acquired infections. They provide a classical
example in biology where the dynamics of cellular communities may be observed
and studied. Gene expression regulates cell division and differentiation, which
affect the biofilm architecture. Mechanical and chemical processes shape the
resulting structure. We gain insight into the interplay between cellular and
mechanical processes during biofilm development on air-agar interfaces by means
of a hybrid model. Cellular behavior is governed by stochastic rules informed
by a cascade of concentration fields for nutrients, waste and autoinducers.
Cellular differentiation and death alter the structure and the mechanical
properties of the biofilm, which is deformed according to Foppl-Von Karman
equations informed by cellular processes and the interaction with the
substratum. Stiffness gradients due to growth and swelling produce wrinkle
branching. We are able to reproduce wrinkled structures often formed by
biofilms on air-agar interfaces, as well as spatial distributions of
differentiated cells commonly observed with B. subtilis.Comment: 19 pages, 13 figure
Oscillatory wave fronts in chains of coupled nonlinear oscillators
Wave front pinning and propagation in damped chains of coupled oscillators
are studied. There are two important thresholds for an applied constant stress
: for (dynamic Peierls stress), wave fronts fail to propagate,
for stable static and moving wave fronts coexist, and
for (static Peierls stress) there are only stable moving wave
fronts. For piecewise linear models, extending an exact method of Atkinson and
Cabrera's to chains with damped dynamics corroborates this description. For
smooth nonlinearities, an approximate analytical description is found by means
of the active point theory. Generically for small or zero damping, stable wave
front profiles are non-monotone and become wavy (oscillatory) in one of their
tails.Comment: 18 pages, 21 figures, 2 column revtex. To appear in Phys. Rev.
Ripples in a string coupled to Glauber spins
Each oscillator in a linear chain (a string) interacts with a local Ising
spin in contact with a thermal bath. These spins evolve according to Glauber
dynamics. Below a critical temperature, a rippled state in the string is
accompanied by a nonzero spin polarization. The system is shown to form ripples
in the string which, for slow spin relaxation, vibrates rapidly about
quasi-stationary states described as snapshots of a coarse-grained stroboscopic
map. For moderate observation times, ripples are observed irrespective of the
final thermodynamically stable state (rippled or not).Comment: 5 pages, 2 figure
Nonlinear stability of oscillatory wave fronts in chains of coupled oscillators
We present a stability theory for kink propagation in chains of coupled
oscillators and a new algorithm for the numerical study of kink dynamics. The
numerical solutions are computed using an equivalent integral equation instead
of a system of differential equations. This avoids uncertainty about the impact
of artificial boundary conditions and discretization in time. Stability results
also follow from the integral version. Stable kinks have a monotone leading
edge and move with a velocity larger than a critical value which depends on the
damping strength.Comment: 11 figure
Modelling the Molecular Gas in NGC 6240
We present the first observations of HCN, HCO
and SiO in NGC\,6240, obtained with the IRAM PdBI. Combining a Markov
Chain Monte Carlo (MCMC) code with Large Velocity Gradient (LVG) modelling, and
with additional data from the literature, we simultaneously fit three gas
phases and six molecular species to constrain the physical condition of the
molecular gas, including massluminosity conversion factors. We find
of dense molecular gas in cold, dense clouds (\,K, \,cm) with a volume filling factor
, embedded in a shock heated molecular medium (\,K,
\,cm), both surrounded by an extended diffuse
phase (\,K, \,cm). We
derive a global with gas masses
, dominated by the
dense gas. We also find , which traces the
cold, dense gas. The [C]/[C] ratio is only slightly elevated
(), contrary to the very high [CO]/[CO] ratio (300-500)
reported in the literature. However, we find very high [HCN]/[HCN] and
[HCO]/[HCO] abundance ratios which we
attribute to isotope fractionation in the cold, dense clouds.Comment: 27 pages, 17 figures, 9 tables. Accepted in Ap
Contenido de beta-caroteno, hierro y zinc, efecto de almacenamiento y tipo de cocción en genotipos de camote (Ipomoea batatas L)
El camote (Ipomoea batatas L) es el principal componente en la dieta de millones de personas que viven en países tropicales, y un mejoramiento en el contenido de â-caroteno podría incrementar el suministro de vitamina A para satisfacer la mayor parte de las necesidades diarias de la gente. En el presente estudio, el contenido de â-caroteno (BC), hierro (Fe) y zinc (Zn) fueron determinados en 25 genotipos de camote provenientes de las localidades de La Molina y San Ramón (Perú). Así mismo, los cambios en el contenido de BC en siete genotipos de camote fueron investigados usando diferentes métodos de cocción y tiempos de almacenamiento. El contenido de BC fue medido vía absorbancia a 450 nm e identificado a través del HPLC y el contenido de Fe y Zn fueron determinados a través de técnicas de ICP-OES. Los resultados muestran variación significativa entre genotipo, ambiente y en la interacción genotipo-ambiente. La concentración de BC en las raíces de camote recién cosechado varió entre 7.62 y 18.93 mg/100 g en peso fresco (PF). El contenido de hierro presentó un rango de 0.40 – 0.96 mg/100 g PF y el contenido de zinc presentó un rango de 0.25 – 0.51 mg/100 mg PF. Los genotipos 440442 y 440518 presentaron los niveles más altos de BC en los dos ambientes. Diferencias en el contenido de BC fueron encontrados entre los métodos de cocción y los tiempos de almacenamiento. La concentración de BC de las raíces cocidas por ebullición (15.15 mg/100 g PF) fue mayor que las raíces cocidas por horneado (14.29 mg/100 g PF); sin embargo, no hubo diferencias entre los genotipos 440442 y 420081 por efecto del método de cocción. Asimismo, el contenido de BC se incrementó durante el tiempo de almacenamiento, donde el genotipo 440442 presentó los mayores niveles de BC durante el tiempo de almacenamiento, mientras que los genotipos 440413 y 440513 no presentaron cambios significativos
Use of resistivity measurements to detect urban caves in Mexico City and to assess the related hazard
International audienceIn the XIX century when Mexico City was much smaller than at present, there was non-regulated mining of building materials in a region of tuffs northwest of the city in an inhabited countryside. With the growth of the city during the XX century, this region was increasingly populated and in the 1970's many two-level bricks houses were built, without regard for underground caves created by the earlier extractions. Some ground sinkings in adjacent areas alarmed the residents who now are worried about this permanent hazard. An association of residents contracted a private company for a geophysical study in order to know the distribution of the caves. Resistivity measurements were taken in the area to detect the caves in order to alert city authorities. Resistivity data along most of the streets were collected with the array pole-dipole that consisted of three grounded electrodes. We performed 2-D dimensional inversions to the data in order to get a 2-D resistivity image of every street. This is similar to a resistivity cross-section of the ground but obtained from the inversion of pole-dipole and Schlumberger resistivity data simultaneously. Using the information of previous drills we modified our programming code in order to perform constrained inversion and to get more accurate resistivity models in agreement with the drills. From the resistivity models obtained for every street it was possible to produce a map which shows the horizontal distribution of the resistive bodies at a depth of 12m. These resistive bodies show coherent alignments that seem to correspond with a distributions of interconnected caves or tunnels used for extracting the sandy-tuffs. From these kind of interpretation method it was intended to get a more accurate horizontal distribution of the excavated areas in order to better know the urbanized area affected and lead the authorities to remedy the area with refill material
ANALYSIS OF PROTEIN ISOLATE FROM QUINOA (CHENOPODIUM QUINOA WILLD)
ABSTRACTObjective: The aim of this study was to obtain protein isolate from quinoa using alkaline pH at different pHs of precipitation and to analyze proteinisolate with electrophoresis.Methods: Quinoa protein isolates were obtained using isoelectric precipitation method at different pHs. Proteins were analyzed using electrophoresisnative-polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate - PAGE.Results: A yield of 6.29% of protein isolate of defatted quinoa at pH 4.0 was obtained. The content of protein isolate was higher than 64% in allpH assays. Globulins and albumins in protein isolate at different pHs were observed. One band near 130 kDa was found. A band with MW 60 kDacorresponding to 7S globulin was found. The bands, MW 33-36 kDa and MW 20-22 kDa, correspond to 11S globulin. Bands less to 15.4 kDa correspondto albumins.Conclusions: Quinoa is a good source of proteins. Globulins and albumins were identified in the quinoa protein isolate.Keywords: Quinoa, Globulins, Albumins, Polypeptides, Protein isolate
Scale free chaos in the confined Vicsek flocking model
The Vicsek model encompasses the paradigm of active dry matter. Motivated by
collective behavior of insects in swarms, we have studied finite size effects
and criticality in the three dimensional, harmonically confined Vicsek model.
We have discovered a phase transition that exists for appropriate noise and
small confinement strength. On the critical line of confinement versus noise,
swarms are in a state of scale-free chaos characterized by minimal correlation
time, correlation length proportional to swarm size and topological data
analysis. The critical line separates dispersed single clusters from confined
multicluster swarms. Scale-free chaotic swarms occupy a compact region of space
and comprise a recognizable `condensed' nucleus and particles leaving and
entering it. Susceptibility, correlation length, dynamic correlation function
and largest Lyapunov exponent obey power laws. The critical line and a narrow
criticality region close to it move simultaneously to zero confinement strength
for infinitely many particles. At the end of the first chaotic window of
confinement, there is another phase transition to infinitely dense clusters of
finite size that may be termed flocking black holes.Comment: 24 pages, 26 figures, revte
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