1,235 research outputs found
A conserved metalloprotease mediates ecdysis in Caenorhabditis elegans
Molting is required for progression between larval stages
in the life cycle of nematodes. We have identified four
mutant alleles of a <i>Caenorhabditis elegans</i> metalloprotease
gene, <i>nas-37</i>, that cause incomplete ecdysis. At each molt
the cuticle fails to open sufficiently at the anterior end and
the partially shed cuticle is dragged behind the animal. The
gene is expressed in hypodermal cells 4 hours before ecdysis
during all larval stages. The <i>NAS-37</i> protein accumulates
in the anterior cuticle and is shed in the cuticle after
ecdysis. This pattern of protein accumulation places NAS-
37 in the right place and at the right time to degrade the
cuticle to facilitate ecdysis. The nas-37 gene has orthologs
in other nematode species, including parasitic nematodes,
and they undergo a similar shedding process. For example,
<i>Haemonchus contortus</i> molts by digesting a ring of cuticle
at the tip of the nose. Incubating <i>Haemonchus</i> larvae in
extracted exsheathing fluids causes a refractile ring of
digested cuticle to form at the tip of the nose. When
<i>Haemonchus</i> cuticles are incubated with purified NAS-37,
a similar refractile ring forms. NAS-37 degradation of the
<i>Haemonchus</i> cuticle suggests that the metalloproteases and
the cuticle substrates involved in exsheathment of parasitic
nematodes are conserved in free-living nematodes
3D-Self-Assemblage and Self-Organization on Natural Colloidal Microinclusions in Mineral Sediments
The results of micro- and nanoscale research of fractal structure sediments from mineral water re-ceived by the drop method are given. Qualitative analysis of the underlying physical phenomena, allowed
us to establish the conditions of their 3D-fractalization that consider the size of colloidal nanoparticles, its
location and height from the drop center : rmin Rmax hmax and rmax Rmin hmin. It is shown that the main
contribution to 3D fractalization is due to surface tension forces and the Coulomb force interaction.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3625
Mechanisms of Fractal Formation in Colloidal Carbon-Bearing Natural System
By using the advanced nano-approach processes and phenomena in self-organizing colloidal systems are studied. The conditions of appearance of self-organized phenomena are determined and also ranges of operation of diffusion, capillary, and fractalization mechanisms are found.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3363
Synthesis of the Carbon Nanomaterials Based on Renewable Bioresources
The effectiveness and feasibility of producing nanoscale carbon materials from renewable bioresources
were shown as an example marsh mass. The mechanisms of synthesis of amorphous organic carbon from
sphagnum moss species modified by a liquid peat phase of humic nature are discussed. A fundamentally
new way of producing carbon nanotubes by mechanical activation of amorphous organic carbon is
described.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3627
Self-assembly and Self-organization Processes of Carbon Nanotubes in the Colloidal Systems
The features and patterns of self-organization processes in the diffusion-limited conditions (method of
drops) of carbon-containing compounds and carbon nanotubes have been studied. The results of the research
influence of the substrate temperature and solvent on the formation of nanoscale fractal structures
in sediments of colloidal solutions are provided
Self-assembly and Self-organization Processes of Carbon Nanotubes in the Colloidal Systems
The features and patterns of self-organization processes in the diffusion-limited conditions (method of
drops) of carbon-containing compounds and carbon nanotubes have been studied. The results of the research
influence of the substrate temperature and solvent on the formation of nanoscale fractal structures
in sediments of colloidal solutions are provided
Elastic moduli of model random three-dimensional closed-cell cellular solids
Most cellular solids are random materials, while practically all theoretical
results are for periodic models. To be able to generate theoretical results for
random models, the finite element method (FEM) was used to study the elastic
properties of solids with a closed-cell cellular structure. We have computed
the density () and microstructure dependence of the Young's modulus ()
and Poisson's ratio (PR) for several different isotropic random models based on
Voronoi tessellations and level-cut Gaussian random fields. The effect of
partially open cells is also considered. The results, which are best described
by a power law (), show the influence of randomness
and isotropy on the properties of closed-cell cellular materials, and are found
to be in good agreement with experimental data.Comment: 13 pages, 13 figure
Area Spectrum of Extremal Reissner-Nordstr\"om Black Holes from Quasi-normal Modes
Using the quasi-normal modes frequency of extremal Reissner-Nordstr\"om black
holes, we obtain area spectrum for these type of black holes. We show that the
area and entropy black hole horizon are equally spaced. Our results for the
spacing of the area spectrum differ from that of schwarzschild black holes.Comment: 6 pages, no figure, accepted for publication in Phys. Rev.
Spectral quark model and low-energy hadron phenomenology
We propose a spectral quark model which can be applied to low energy hadronic
physics. The approach is based on a generalization of the Lehmann
representation of the quark propagator. We work at the one-quark-loop level.
Electromagnetic and chiral invariance are ensured with help of the gauge
technique which provides particular solutions to the Ward-Takahashi identities.
General conditions on the quark spectral function follow from natural physical
requirements. In particular, the function is normalized, its all positive
moments must vanish, while the physical observables depend on negative moments
and the so-called log-moments. As a consequence, the model is made finite,
dispersion relations hold, chiral anomalies are preserved, and the twist
expansion is free from logarithmic scaling violations, as requested of a
low-energy model. We study a variety of processes and show that the framework
is very simple and practical. Finally, incorporating the idea of vector-meson
dominance, we present an explicit construction of the quark spectral function
which satisfies all the requirements. The corresponding momentum representation
of the resulting quark propagator exhibits only cuts on the physical axis, with
no poles present anywhere in the complex momentum space. The momentum-dependent
quark mass compares very well to recent lattice calculations. A large number of
predictions and relations can be deduced from our approach for such quantities
as the pion light-cone wave function, non-local quark condensate, pion
transition form factor, pion valence parton distribution function, etc.Comment: revtex, 24 pages, 3 figure
Structure Formation, Melting, and the Optical Properties of Gold/DNA Nanocomposites: Effects of Relaxation Time
We present a model for structure formation, melting, and optical properties
of gold/DNA nanocomposites. These composites consist of a collection of gold
nanoparticles (of radius 50 nm or less) which are bound together by links made
up of DNA strands. In our structural model, the nanocomposite forms from a
series of Monte Carlo steps, each involving reaction-limited cluster-cluster
aggregation (RLCA) followed by dehybridization of the DNA links. These links
form with a probability which depends on temperature and particle
radius . The final structure depends on the number of monomers (i. e. gold
nanoparticles) , , and the relaxation time. At low temperature, the
model results in an RLCA cluster. But after a long enough relaxation time, the
nanocomposite reduces to a compact, non-fractal cluster. We calculate the
optical properties of the resulting aggregates using the Discrete Dipole
Approximation. Despite the restructuring, the melting transition (as seen in
the extinction coefficient at wavelength 520 nm) remains sharp, and the melting
temperature increases with increasing as found in our previous
percolation model. However, restructuring increases the corresponding link
fraction at melting to a value well above the percolation threshold. Our
calculated extinction cross section agrees qualitatively with experiments on
gold/DNA composites. It also shows a characteristic ``rebound effect,''
resulting from incomplete relaxation, which has also been seen in some
experiments. We discuss briefly how our results relate to a possible sol-gel
transition in these aggregates.Comment: 12 pages, 10 figure
- …