9,657 research outputs found
Spatial Organization of the Cytoskeleton enhances Cargo Delivery to Specific Target Areas on the Plasma Membrane of Spherical Cells
Intracellular transport is vital for the proper functioning and survival of a
cell. Cargo (proteins, vesicles, organelles, etc.) is transferred from its
place of creation to its target locations via molecular motor assisted
transport along cytoskeletal filaments. The transport efficiency is strongly
affected by the spatial organization of the cytoskeleton, which constitutes an
inhomogeneous, complex network. In cells with a centrosome microtubules grow
radially from the central microtubule organizing center towards the cell
periphery whereas actin filaments form a dense meshwork, the actin cortex,
underneath the cell membrane with a broad range of orientations. The emerging
ballistic motion along filaments is frequently interrupted due to constricting
intersection nodes or cycles of detachment and reattachment processes in the
crowded cytoplasm. In order to investigate the efficiency of search strategies
established by the cell's specific spatial organization of the cytoskeleton we
formulate a random velocity model with intermittent arrest states. With
extensive computer simulations we analyze the dependence of the mean first
passage times for narrow escape problems on the structural characteristics of
the cytoskeleton, the motor properties and the fraction of time spent in each
state. We find that an inhomogeneous architecture with a small width of the
actin cortex constitutes an efficient intracellular search strategy.Comment: 14 pages, 9 figure
Crossovers in the Two Dimensional Ising Spin Glass with ferromagnetic next-nearest-neighbor interactions
By means of extensive computer simulations we analyze in detail the two
dimensional Ising spin glass with ferromagnetic next-nearest-neighbor
interactions. We found a crossover from ferromagnetic to ``spin glass'' like
order both from numerical simulations and analytical arguments. We also present
evidences of a second crossover from the ``spin glass'' behavior to a
paramagnetic phase for the largest volume studied.Comment: 19 pages with 9 postscript figures also available at
http://chimera.roma1.infn.it/index_papers_complex.html. Some changes in
captions of figures 1 and
Competitive Copolymerization: Access to Azridine Copolymers with Adjustable Gradient Strengths
Particle acceleration close to the supermassive black hole horizon: the case of M87
The radio galaxy M87 has recently been found to be a rapidly variable TeV
emitting source. We analyze the implications of the observed TeV
characteristics and show that it proves challenging to account for them within
conventional acceleration and emission models. We discuss a new pulsar-type
scenario for the origin of variable, very high energy (VHE) emission close to
the central supermassive black hole and show that magneto-centrifugally
accelerated electrons could efficiently Compton upscatter sub-mm ADAF disk
photons to the TeV regime, leading to VHE characteristics close to the observed
ones. This suggests, conversely, that VHE observations of highly under-luminous
AGNs could provide an important diagnostic tool for probing the conditions
prevalent in the inner accretion disk of these sources.Comment: 5 pages, one figure (typos corrected); based on presentation at "High
Energy Phenomena in Relativistic Outflows", Dublin, Sept. 2007; accepted for
publication in International Journal of Modern Physics
Nonequilibrium Dynamics and Aging in the Three--Dimensional Ising Spin Glass Model
The low temperature dynamics of the three dimensional Ising spin glass in
zero field with a discrete bond distribution is investigated via MC
simulations. The thermoremanent magnetization is found to decay algebraically
and the temperature dependent exponents agree very well with the experimentally
determined values. The nonequilibrium autocorrelation function shows
a crossover at the waiting (or {\em aging}) time from algebraic {\em
quasi-equilibrium} decay for times to another, faster algebraic
decay for with an exponent similar to one for the remanent
magnetization.Comment: Revtex, 11 pages + 4 figures (included as Latex-files
Maternal Interactive Behaviors and Developmental Outcomes in Preschoolers Born Very Low Birth Weight
Children born very low birth weight (VLBW) are at greater risk for cognitive and executive deficits than children born normal birth weight. One factor in development is parental wellbeing. Parents who report more depressive symptoms and lower perception of resources have poorer quality interactive behaviors. This study investigated the associations between maternal interactive behaviors during play and developmental outcomes in preschoolers born VLBW. A secondary goal was to understand the associations among maternal depressive symptoms, perception of resources, and interactive behaviors. A tertiary goal was to investigate racial and ethnic differences in maternal behaviors. Overall, one maternal behavior was negatively associated with a measure of executive functioning. Maternal depressive symptoms were negatively correlated with one maternal behavior and maternal perception of resources was negatively correlated with another maternal behavior. Additional analyses found a trend in racial and ethnic differences in attention directing behaviors between Caucasian and Native American mothers
Evaluation of a microbial muramidase supplementation on growth performance, apparent ileal digestibility, and intestinal histology of broiler chickens
The current study evaluated the effects of different inclusion levels of microbial muramidase (Muramidase 007, DSM Nutritional Products) on gastrointestinal functionality by determination of apparent ileal digestibility (AID) of nutrients, investigation of intestinal histomorphology, and quantification of resulting growth performance. Four maize-wheat-soybean experimental diets were produced without (C) and with different dosages of muramidase: low (L, 25,000 LSU(F)/kg), medium (M, 35,000 LSU(F)/kg), and high (H, 45,000 LSU(F)/kg); diets were fed to broilers for 35 d. At the end of the experiment, AID of ether extract (EE), crude protein (CP), Ca, and P were determined and samples of the mid-jejunum and -ileum were collected for histomorphological observations. Data were subjected to ANOVA analysis using the GLM procedure. Orthogonal polynomial contrasts were used to assess linear and quadratic effects of different levels of the muramidase. At the end of the trial, Muramidase 007 supplementation linearly increased body weight gain and decreased feed conversion ratio (FCR) (P ≤ 0.05). Adding the muramidase to broiler diets also linearly increased the European poultry efficiency factor (P ≤ 0.05). Inclusion of the muramidase in broiler diets linearly increased AID of CP, EE, and P (P ≤ 0.05), and the H group had a higher AID of EE and CP compared to C group (P ≤ 0.05). Microbial muramidase supplementation linearly increased ileal villus length to crypt depth ratio and decreased the number of ileal CD45 cells (P ≤ 0.05). Broilers fed M and H diets had fewer number of CD45 cells in the ileum compared to those in C group (P ≤ 0.05). In conclusion, the results of the present study demonstrated that inclusion of the microbial muramidase in broiler diets could increase AID of key nutrients and improve growth performance in broilers. Adding microbial muramidase to broiler diets can therefore be considered as an interesting prospect to improve gastrointestinal functionality. Biological mechanisms causing these improvements need to be studied further
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