1,531 research outputs found
Dynamics of closed ecosystems described by operators
We adopt the so--called \emph{occupation number representation}, originally
used in quantum mechanics and recently adopted in the description of several
classical systems, in the analysis of the dynamics of some models of closed
ecosystems. In particular, we discuss two linear models, for which the solution
can be found analytically, and a nonlinear system, for which we produce
numerical results. We also discuss how a damping effect could be {\em
effectively} implemented in the model
Evolutionary plasticity of developmental gene regulatory network architecture
Sea stars and sea urchins evolved from a last common ancestor that lived at the end of the Cambrian, approximately half a billion years ago. In a previous comparative study of the gene regulatory networks (GRNs) that embody the genomic program for embryogenesis in these animals, we discovered an almost perfectly conserved five-gene network subcircuit required for endoderm specification. We show here that the GRN structure upstream and downstream of the conserved network kernel has, by contrast, diverged extensively. Mesoderm specification is accomplished quite differently; the Delta–Notch signaling system is used in radically distinct ways; and various regulatory genes have been coopted to different functions. The conservation of the conserved kernel is thus the more remarkable. The results indicate types of network linkage subject to evolutionary change. An emergent theme is that subcircuit design may be preserved even while the identity of genes performing given roles changes because of alteration in their cis-regulatory control systems
Transfer of a large gene regulatory apparatus to a new developmental address in echinoid evolution
Of the five echinoderm classes, only the modern sea urchins (euechinoids) generate a precociously specified embryonic micromere lineage that ingresses before gastrulation and then secretes the biomineral embryonic skeleton. The gene regulatory network (GRN) underlying the specification and differentiation of this lineage is now known. Many of the same differentiation genes as are used in the biomineralization of the embryo skeleton are also used to make the similar biomineral of the spines and test plates of the adult body. Here, we determine the components of the regulatory state upstream of these differentiation genes that are shared between embryonic and adult skeletogenesis. An abrupt “break point” in the micromere GRN is thus revealed, on one side of which most of the regulatory genes are used in both, and on the other side of which the regulatory apparatus is entirely micromere-specific. This reveals the specific linkages of the micromere GRN forged in the evolutionary process by which the skeletogenic gene batteries were caused to be activated in the embryonic micromere lineage. We also show, by comparison with adult skeletogenesis in the sea star, a distant echinoderm outgroup, that the regulatory apparatus responsible for driving the skeletogenic differentiation gene batteries is an ancient pleisiomorphic aspect of the echinoderm-specific regulatory heritage
Spreading of information on a network: a quantum view
This paper concerns with the modeling of the spreading of information through
a complex, multi-layered network, where the information is transferred from an
initial transmitter to a final receiver. The mathematical model is deduced
within the framework of operatorial methods, according to the formal
mathematical apparatus typical of quantum mechanics. Two different approaches
are considered: one based on the ()-induced dynamics, and one on the
Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) equation. For each method,
numerical results are presented.Comment: 31 pages, 35 image
Spreading of Information on a Network: A Quantum View
This paper concerns the modeling of the spread of information through a complex, multilayered
network, where the information is transferred from an initial transmitter to a final receiver.
The mathematical model is deduced within the framework of operatorial methods, according to the
formal mathematical apparatus typical of quantum mechanics. Two different approaches are considered:
one based on the (H, \rho)-induced dynamics and one on the Gorini–Kossakowski–Sudarshan–
Lindblad (GKSL) equation. For each method, numerical results are presented
L’agricoltura biologica e lo sviluppo del territorio di qualità: un caso studio siciliano
Farming grows into an intense relationship with the territory; local products are the expression of local culture and environment. Territory itself is an attribute of the goods; at the same time, the consumer becomes a user of the same territory. It is possible to turn on a strategy that considers the territory a source of competitive advantage. Organic farming is paradigmatic of the relationship between agricultural production and the territory that is based on the pursuit of harmonious interaction between human activities and the environmen
A nonlocal phase-field model of Ginzburg-Landau-Korteweg fluids
A thermodynamic model of Korteweg fluids undergoing phase transition and/or phase separation
is developed within the framework of weakly nonlocal thermodynamics. Compatibility with second law of
thermodynamics is investigated by applying a generalized Liu procedure recently introduced in the literature.
Possible forms of the free energy and of the stress tensor, which generalize some earlier ones proposed by
several authors in the last decades, are carried out. Owing to the new procedure applied for exploiting the
entropy principle, the thermodynamic potentials are allowed to depend on the whole set of variables spanning
the state space, including the gradients of the unknown fields, without postulating neither the presence of an
energy or entropy extra-flux, nor an additional balance law for microforce
Breaking the silence around academic harassment
It is time to hold every member of the scientific community responsible and 'response able' in addressing/reporting academic harassment. Stop applauding academic stars on the podium prior to checking what is happening underneath!</p
Moving away from the Near-Horizon Attractor of the Extreme Kerr Force-Free Magnetosphere
We consider force-free magnetospheres around the extreme Kerr black hole. In
this case there is no known exact analytic solution to force free
electrodynamics which is stationary, axisymmetric and magnetically-dominated.
However, any stationary, axisymmetric and regular force-free magnetosphere in
extreme Kerr black hole approaches the same attractor solution in the
near-horizon extreme Kerr (NHEK) limit with null electromagnetic field. We show
that by moving away from the attractor solution in the NHEK region, one finds
magnetically-dominated solutions in the extreme Kerr black hole with finite
angular momentum outflow. This result is achieved using a perturbative analysis
up to the second order.Comment: 33 pages, 2 figures; v2: matches published version in JCA
Force-free magnetosphere attractors for near-horizon extreme and near-extreme limits of Kerr black hole
We propose a new approach to find magnetically-dominated force-free
magnetospheres around highly spinning black holes, relevant for models of
astrophysical jets. Employing the near-horizon extreme Kerr (NHEK) limit of the
Kerr black hole, any stationary, axisymmetric and regular force-free
magnetosphere reduces to the same attractor solution in the NHEK limit with
null electromagnetic field strength. We use this attractor solution as the
universal starting point for perturbing away from the NHEK region in the
extreme Kerr spacetime. We demonstrate that by going to second order in
perturbation theory, it is possible to find magnetically dominated
magnetospheres around the extreme Kerr black hole. Furthermore, we consider the
near-horizon near-extreme Kerr (near-NHEK) limit that provides access to a
different regime of highly spinning black holes. Also in this case we find a
novel force-free attractor, which can be used as the universal starting point
for a perturbative construction of force-free magnetospheres. Finally, we
discuss the relation between the NHEK and near-NHEK attractors.Comment: 5 pages, 1 figur
- …