6,333 research outputs found
New distinguished classes of spectral spaces: a survey
In the present survey paper, we present several new classes of Hochster's
spectral spaces "occurring in nature", actually in multiplicative ideal theory,
and not linked to or realized in an explicit way by prime spectra of rings. The
general setting is the space of the semistar operations (of finite type),
endowed with a Zariski-like topology, which turns out to be a natural
topological extension of the space of the overrings of an integral domain,
endowed with a topology introduced by Zariski. One of the key tool is a recent
characterization of spectral spaces, based on the ultrafilter topology, given
in a paper by C. Finocchiaro in Comm. Algebra 2014. Several applications are
also discussed
Phonon Properties of Knbo3 and Ktao3 from First-Principles Calculations
The frequencies of transverse-optical phonons in KNbO and
KTaO are calculated in the frozen-phonon scheme making use of the
full-potential linearized muffin-tin orbital method. The calculated frequencies
in the cubic phase of KNbO and in the tetragonal ferroelectric phase are in
good agreement with experimental data. For KTaO, the effect of lattice
volume was found to be substantial on the frequency of the soft mode, but
rather small on the relative displacement patterns of atoms in all three modes
of the symmetry. The TO frequencies in KTaO are found to be of the
order of, but somehow higher than, the corresponding frequencies in cubic
KNbO.Comment: 8 pages + 1 LaTeX figure, Revtex 3.0, SISSA-CM-94-00
Some closure operations in Zariski-Riemann spaces of valuation domains: a survey
In this survey we present several results concerning various topologies that
were introduced in recent years on spaces of valuation domains
Non-equilibrium phase transitions in biomolecular signal transduction
We study a mechanism for reliable switching in biomolecular
signal-transduction cascades. Steady bistable states are created by system-size
cooperative effects in populations of proteins, in spite of the fact that the
phosphorylation-state transitions of any molecule, by means of which the switch
is implemented, are highly stochastic. The emergence of switching is a
nonequilibrium phase transition in an energetically driven, dissipative system
described by a master equation. We use operator and functional integral methods
from reaction-diffusion theory to solve for the phase structure, noise
spectrum, and escape trajectories and first-passage times of a class of minimal
models of switches, showing how all critical properties for switch behavior can
be computed within a unified framework
Uso de marcadores moleculares para a solução de questões de identidade de cultivares de videira.
O objetivo deste trabalho é demonstrar como a análise genético-molecular pode contribuir para resolver questões de identidade
Uso de marcadores moleculares SSR na identificação de cultivares de videira.
A ocorrência de sinonímias e/ou homonímias, muitas vezes consequência da mistura de material propagativo de cultivares diferentes, é uma barreira para o setor vitivinícola. As caracterizações morfológica e molecular têm sido usadas pelo Laboratório do Banco Ativo de Germoplasma de Uva para a identificação correta de cultivares. O objetivo deste trabalho foi demonstrar como a análise genético-molecular pode contribuir para resolver questões de identidade
Hunting for planets in the HL Tau disk
Recent ALMA images of HL Tau show gaps in the dusty disk that may be caused
by planetary bodies. Given the young age of this system, if confirmed, this
finding would imply very short timescales for planet formation, probably in a
gravitationally unstable disk. To test this scenario, we searched for young
planets by means of direct imaging in the L'-band using the Large Binocular
Telescope Interferometer mid-infrared camera. At the location of two prominent
dips in the dust distribution at ~70AU (~0.5") from the central star we reach a
contrast level of ~7.5mag. We did not detect any point source at the location
of the rings. Using evolutionary models we derive upper limits of ~10-15MJup at
<=0.5-1Ma for the possible planets. With these sensitivity limits we should
have been able to detect companions sufficiently massive to open full gaps in
the disk. The structures detected at mm-wavelengths could be gaps in the
distributions of large grains on the disk midplane, caused by planets not
massive enough to fully open gaps. Future ALMA observations of the molecular
gas density profile and kinematics as well as higher contrast infrared
observations may be able to provide a definitive answer.Comment: Accepted for publication on ApJ Letter
Large phenotype jumps in biomolecular evolution
By defining the phenotype of a biopolymer by its active three-dimensional
shape, and its genotype by its primary sequence, we propose a model that
predicts and characterizes the statistical distribution of a population of
biopolymers with a specific phenotype, that originated from a given genotypic
sequence by a single mutational event. Depending on the ratio g0 that
characterizes the spread of potential energies of the mutated population with
respect to temperature, three different statistical regimes have been
identified. We suggest that biopolymers found in nature are in a critical
regime with g0 in the range 1-6, corresponding to a broad, but not too broad,
phenotypic distribution resembling a truncated Levy flight. Thus the biopolymer
phenotype can be considerably modified in just a few mutations. The proposed
model is in good agreement with the experimental distribution of activities
determined for a population of single mutants of a group I ribozyme.Comment: to appear in Phys. Rev. E; 7 pages, 6 figures; longer discussion in
VII, new fig.
Peeling fingers in an elastic Hele-Shaw channel
Using experiments and a depth-averaged numerical model, we study
instabilities of two-phase flows in a Hele-Shaw channel with an elastic upper
boundary and a non-uniform cross-section prescribed by initial collapse.
Experimentally, we find increasingly complex and unsteady modes of air-finger
propagation as the dimensionless bubble speed, Ca, and level of collapse are
increased, including pointed fingers, indented fingers and the feathered modes
first identified by Cuttle et al.(J. Fluid Mech., vol. 886, 2020, A20).
By introducing a measure of the viscous contribution to finger propagation,
we identify a Ca threshold beyond which viscous forces are superseded by
elastic effects. Quantitative prediction of this transition between 'viscous'
and 'elastic' reopening regimes across levels of collapse establishes the
fidelity of the numerical model. In the viscous regime, we recover the
non-monotonic dependence on Ca of the finger pressure, which is characteristic
of benchtop models of airway reopening. To explore the elastic regime
numerically, we extend the depth-averaged model introduced by Fontana et al.
(J. Fluid Mech., vol. 916, 2021, A27) to include an artificial disjoining
pressure which prevents the unphysical self-intersection of the interface.
Using time simulations, we capture for the first time the majority of
experimental finger dynamics, including feathered modes. We show that these
disordered states continually evolve, with no evidence of convergence to steady
or periodic states. We find that the steady bifurcation structure
satisfactorily predicts the bubble pressure as a function of Ca, but that it
does not provide sufficient information to predict the transition to unsteady
dynamics which appears strongly nonlinear.Comment: 28 pages, 15 figure
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