The Green relations approach to congruences on completely regular semigroups

On the congruence lattice (2(5) of a completely regular semigroup S the following mappings are considered _p: P and _p: VP, whereP is any of the Green relationsH, L, R orD. The equivalence relationsP andP ^V induced by these maps represent the main object of study in the paper. The former is a complete -congruence whereas the latter is a complete congruence onC(S). In particularH ,H ^V,L ^V,R ^V coincide with the kernel, trace, left trace and right trace relations onC(S), respectively. All essential properties known for the latter relations carry over to the new relationsP andP ^V. In addition, some interesting interplays of these provide for more richness in the theory of congruences on completely regular than is the case for the kernel-trace approach to congruences on regular semigroups.     

Homogenization of the heat equation for a domain with a network of pipes with a well-mixed fluid

We consider the linear heat equation in a domain occupied by a solid material with a network of pipes in which a well-mixed fluid is circulating. The temperature of the fluid in the pipe is uniform and its time variation is determined by the thermal flux on the wall of the pipe, plus a given internal source; continuity of the temperature across the pipe is also assumed. We suppose that we deal with a periodic geometry, with cells of size with inclusions of size r_g; we study in detail in the case r, referring to a previous paper for the case r In the limit »0 we get a homogenized equation. The limit depends strongly on the ratio between the time variation of the temperature in the inclusions and the thermal flux through the interface. The homogenized equation has a new specific heat, which depends on the porosity and the constant of proportionality between the time variation of temperature and the flux on the boundary of the pipe. We also have a new thermal conductivity depending on the microstructure, and volume sources appear. The main tool is the energy method and we generalize the classical results for the more standard boundary conditions for parabolic equations. Finally, we consider the network of pipes forming a random ball structure. We prove convergence for this case. The homogenized equation is of the same form as in the periodic case but auxiliary problems are stochastic.     

Time behavior of stressed nonhierarchical networks

In this paper it is shown, by means of simulation, that interesting time behavior is observed for damaged and overloaded networks, and that adaptive, decentralized intelligence can have a dramatic influence on the overall network performance. The time behavior of nonhierarchical networks is modeled by a system of nonlinear difference equations among global variables, and bistability is shown to exist. Using a simple adaptive control mechanism, it is shown that, depending upon the value of a certain network variable, either limit cycle or steady state behavior results. A few ideas are discussed for applications of nonhierarchical communications to cellular automata and to decision-making systems.     

Solutions of the Strominger System via Stable Bundles on Calabi-Yau Threefolds

We prove that a given Calabi-Yau threefold with a stable holomorphic vector bundle can be perturbed to a solution of the Strominger system provided that the second Chern class of the vector bundle is equal to the second Chern class of the tangent bundle. If the Calabi-Yau threefold has strict SU(3) holonomy then the equations of motion derived from the heterotic string effective action are also satisfied by the solutions we obtain.     

The Suzuki homocoupling reaction under high-intensity ultrasound

The Pd-catalysed Suzuki homocoupling of boronic acids was successfully carried out in water under high-intensity ultrasound (HIU). Heterogeneous catalysis with Pd/C, facilitating work up and purification, could be used without adding phosphine ligands. Reaction rates and yields were strongly influenced by the oxidant employed; excellent results were obtained using either molecular oxygen or 3-bromo-4-hydroxycoumarin. 3-Arylation of the latter with the Suzuki procedure had failed, exclusively affording the homocoupling products, symmetric biaryls. Besides offering a number of operational advantages, the use of HIU broadens the field of application for the Suzuki reaction.     

13C direct detected experiments: optimization for paramagnetic signals

To optimize 13C direct detected experiments for the observation of signals close to a paramagnetic center, we have assessed the sensitivity of different sequences based on CO-Cali coherence transfer. Features of CACO experiments were tested for Calbindin D9k, in which one of the two native Ca2+ ions is replaced by the paramagnetic Ce3+ ion. We have studied the comparison of single vs multiple quantum coherence transfer evolution as well as the influence of in-phase vs anti-phase detection of 13CO signals and finally the comparison of a coherence transfer step based on a CyO in plane with respect to a Cy ali in plane. The acquisition of the anti-phase component of the signal, accomplished by the removal of the last refocusing steps, allowed the identification of some signals unobserved with other pathways. The structural dependency of paramagnetism-induced nuclear relaxation is such that the identification of the most suitable coherence transfer pathway is not known "a priori" but it is driven by the relative proximity of Cali and CO to the paramagnetic center.     

Investigation of a Fluorescence Signal Amplification Mechanism Used for the Direct Molecular Detection of Nucleic Acids

A fluorescence signal amplification mechanism allowing detection limits for DNA in the zeptomolar range was investigated. Photophysical properties of the molecular system were studied in order to better explain the signal amplification that is observed. We show that the confinement of a fluorescent DNA hybridization transducer in aggregates improves its quantum yield and photostability. Furthermore, we show that the combination of the resonance energy transfer occurring within the aggregates with the use of a conjugated polymer as the hybridization transducer and donor allows ultrafast and efficient energy coupling to the aggregates and can lead to the excitation of a large number of acceptors by only one donor.     

Modal-Hamiltonian Interpretation of Quantum Mechanics and Casimir Operators: The Road Toward Quantum Field Theory

The general aim of this paper is to extend the Modal-Hamiltonian interpretation of quantum mechanics to the case of relativistic quantum mechanics with gauge U(1) fields. In this case we propose that the actual-valued observables are the Casimir operators of the Poincaré group and of the group U(1) of the internal symmetry of the theory. Moreover, we also show that the magnitudes that acquire actual values in the relativistic and in the non-relativistic cases are correctly related through the adequate limit.