481 research outputs found
Thermodynamics of nano-cluster phases: a unifying theory
We propose a unifying, analytical theory accounting for the self-organization
of colloidal systems in nano- or micro-cluster phases. We predict the
distribution of cluter sizes with respect to interaction parameters and colloid
concentration. In particular, we anticipate a proportionality regime where the
mean cluster size grows proportionally to the concentration, as observed in
several experiments. We emphasize the interest of a predictive theory in soft
matter, nano-technologies and biophysics.Comment: 4 pages, 1 figur
Scaling the Temperature-dependent Boson Peak of Vitreous Silica with the high-frequency Bulk Modulus derived from Brillouin Scattering Data
The position and strength of the boson peak in silica glass vary considerably
with temperature . Such variations cannot be explained solely with changes
in the Debye energy. New Brillouin scattering measurements are presented which
allow determining the -dependence of unrelaxed acoustic velocities. Using a
velocity based on the bulk modulus, scaling exponents are found which agree
with the soft-potential model. The unrelaxed bulk modulus thus appears to be a
good measure for the structural evolution of silica with and to set the
energy scale for the soft potentials.Comment: Accepted for publication in Physical Review Letter
A study of the effects of certain potting media and fertilizers on the growth and flowering of azaleas
Typescript (photocopy) Thesis (M.S.)--Iowa State College, 1947. Includes bibliography
Epigenetic regulation of the honey bee transcriptome: unravelling the nature of methylated genes
Background: Epigenetic modification of DNA via methylation is one of the key inventions in eukaryotic evolution. It provides a source for the switching of gene activities, the maintenance of stable phenotypes and the integration of environmental and genomic signals. Although this process\ud
is widespread among eukaryotes, both the patterns of methylation and their relevant biological roles not only vary noticeably in different lineages, but often are poorly understood. In addition, the evolutionary origins of DNA methylation in multicellular organisms remain enigmatic. Here we used a new 'epigenetic' model, the social honey bee Apis mellifera, to gain insights into the significance of methylated genes.\ud
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Results: We combined microarray profiling of several tissues with genome-scale bioinformatics and bisulfite sequencing of selected genes to study the honey bee methylome. We find that around 35% of the annotated honey bee genes are expected to be methylated at the CpG dinucleotides by a highly conserved DNA methylation system. We show that one unifying feature of the methylated genes in this species is their broad pattern of expression and the associated 'housekeeping' roles. In contrast, genes involved in more stringently regulated spatial or temporal functions are predicted to be un-methylated.\ud
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Conclusion: Our data suggest that honey bees use CpG methylation of intragenic regions as an epigenetic mechanism to control the levels of activity of the genes that are broadly expressed and might be needed for conserved core biological processes in virtually every type of cell. We discuss the implications of our findings for genome-scale regulatory network structures and the evolution\ud
of the role(s) of DNA methylation in eukaryotes. Our findings are particularly important in the context of the emerging evidence that environmental factors can influence the epigenetic settings of some genes and lead to serious metabolic and behavioural disorders
Observation of the onset of strong scattering on high frequency acoustic phonons in densified silica glass
The linewidth of longitudinal acoustic waves in densified silica glass is
obtained by inelastic x-ray scattering. It increases with a high power alpha of
the frequency up to a crossover where the waves experience strong scattering.
We find that \alpha is at least 4, and probably larger. Resonance and
hybridization of acoustic waves with the boson-peak modes seems to be a more
likely explanation for these findings than Rayleigh scattering from disorder.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Letter
The nature of the short wavelength excitations in vitreous silica: X-Rays Brillouin scattering study
The dynamical structure factor (S(Q,E)) of vitreous silica has been measured
by Inelastic X-ray Scattering varying the exchanged wavevector (Q) at fixed
exchanged energy (E) - an experimental procedure that, contrary to the usual
one at constant Q, provides spectra with much better identified inelastic
features. This allows the first direct evidence of Brillouin peaks in the
S(Q,E) of SiO_2 at energies above the Boson Peak (BP) energy, a finding that
excludes the possibility that the BP marks the transition from propagating to
localised dynamics in glasses.Comment: 4 pages, 3 Postscript figures. To appear in Physical Review Letter
Charged inclusion in nematic liquid crystals
We present a general theory of liquid crystals under inhomogeneous electric
field in a Ginzburg-Landau scheme. The molecular orientation can be deformed by
electric field when the dielectric tensor is orientation-dependent. We then
investigate the influence of a charged particle on the orientation order in a
nematic state. The director is aligned either along or perpendicular to the
local electric field around the charge, depending on the sign of the dielectric
anisotropy. The deformation becomes stronger with increasing the ratio ,
where is the charge and is the radius of the particle. Numerical
analysis shows the presence of defects around the particle for large .
They are nanometer-scale defects for microscopic ions. If the dielectric
anisotropy is positive, a Saturn ring defect appears. If it is negative, a pair
of point defects appear apart from the particle surface, each being connected
to the surface by a disclination line segment.Comment: 12 figure
Correction: Ocean acidification at a coastal CO2 vent induces expression of stress-related transcripts and transposable elements in the sea anemone Anemonia viridis.
[This corrects the article DOI: 10.1371/journal.pone.0210358.]
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