Entropy and irreversibility for a single isolated two level system: New individual quantum states and new nonlinear equation of motion

We propose a new nonlinear equation of motion for a single isolated two-level quantum system. The resulting generalized two-level quantum dynamical theory entails a new alternative resolution of the long-standing dilemma on the nature of entropy and irreversibility. Even for a single isolated degree of freedom, in addition to the individual mechanical states for which all the results of conventional quantum mechanics remain valid, our theory implies the existence of new nonmechanical individual quantum states. These states have nonzero individual entropy and, by virtue of a constant-energy, internal redistribution mechanism, relax irreversibly toward stable equilibrium. We discuss the possibility of an experimental verification of these conclusions by means of a high-resolution, essentially single-particle, magnetic-resonance experiment.     

Noether symmetry approach in matter-dominated cosmology with variable G and Λ

In the framework of renormalization-group improved cosmologies, we use the Noether symmetry approach to get exact and general integration of the matter-dominated cosmological equations. This is performed by using an expression of Λ = Λ (G) determined by the method itself. We also work out a comparison between such a model and the concordance ΛCDM model as to the magnitude–redshift relationship, hence showing that no appreciable differences occur.     

Smart panel with active damping units. Implementation of decentralized control

This paper contains the second part of a study on a smart panel with five decentralized velocity feedback control units using proof mass electrodynamic actuators [Gonzalez Diaz et al., J. Acoust. Soc. Am. 124, 886 (2008)]. The implementation of five decentralized control loops is analyzed, both theoretically and experimentally. The stability properties of the five decentralized control units have been assessed with the generalized Nyquist criterion by plotting the loci of the eigenvalues of the fully populated matrix of frequency response functions between the five error signals and five input signals to the amplifiers driving the actuators. The control performance properties have been assessed in terms of the spatially averaged response of the panel measured with a scanning laser vibrometer and the total sound power radiated measured in an anechoic room. The two analyses have shown that reductions of up to 10 dB in both vibration response and sound radiation are measured at low audio frequencies, below about 250 Hz.     

Diversity enabling equilibration: disorder and the ground state in artificial spin ice

We report a novel approach to the question of whether and how the ground state can be achieved in square artificial spin ices where frustration is incomplete. We identify two sources of randomness that affect the approach to ground state: quenched disorder in the island response to fields and randomness in the sequence of driving fields. Numerical simulations show that quenched disorder can lead to final states with lower energy, and randomness in the sequence of driving fields always lowers the final energy attained by the system. We use a network picture to understand these two effects: disorder in island responses creates new dynamical pathways, and a random sequence of driving fields allows more pathways to be followed.     

Radon levels in underground workplaces – results of a nationwide survey in Italy

In Italy an extensive survey has been carried out with the aim to evaluate annual average radon concentration in underground workplaces.The survey covered 933 underground rooms located in 311 bank workplaces spread throughout in all Italian regions; at this scope the sampling was stratified random in order to be representative on national scale. The annual radon concentration was estimated by using passive radon dosemeters (NRPB/SSI type holder and CR-39 as detector): the devices were exposed for a period of about 3 months and 4 cycles were performed to cover a solar year. The radon levels in underground workplaces ranged from 27 to 4851 Bq/m³ with an overall mean value of 153 Bq/m³. As expected, radon distribution is not uniform throughout Italy: in several regions high radon annual averages have been found, confirming previous surveys.The analysis of data shows a high variability among regions and intra-region but low spread among rooms belonging to the same workplace.About 5% of underground workplaces displayed radon concentration exceeding 400 Bq/m³, and the 4.4% exceeds 500 Bq/m³, the national action level for the exposure to natural radioactivity in workplaces.     

A variational method for the calculation of spin-rovibronic energy levels of triatomic molecules with three interacting electronic states

A general method is presented for the evaluation of the spin rovibronic energy levels of triatomic molecules with up to three interacting potential energy surfaces. The full theory is outlined in detail, both for singlet and for doublet electronic states and the method is then applied to the benchmark example of C₂H. High quality multireference configuration interaction calculations have been carried out to generate the 3-dimensional near-equilibrium adiabatic potential energy surfaces of the three lowest 1²A'(X²Σ⁺), 2²A'(A²Π), 1²A''(A²Π) electronic states of C₂H, and the pair of interacting states of A 0 symmetry have then been diabatized. Results are presented for J up to 7/2 and compared with gas-phase high resolution experimental results for energies up to 5600 cm¹.     

On a Volume‐Constrained Variational Problem

. Existence of minimizers for a volume-constrained energy $ E(u) := \int_{\Omega} W(\nabla u)\, dx Existence of minimizers for a volume-constrained energy E(u) : = ò_W W(?u) dx E(u) := \int_{\Omega} W(\nabla u)\, dx where L^N({u = z_i}) = a_i, i = 1, ?, P, {\cal L}^N(\{u = z_i\}) = \alpha_i, i = 1, \ldots, P, is proved for the case in which z_iz_i are extremal points of a compact, convex set in \Bbb R^d\Bbb R^d and under suitable assumptions on a class of quasiconvex energy densities W. Optimality properties are studied in the scalar-valued problem where d=1d=1, P=2P=2, W(x)=|x|²W(\xi)=|\xi|^2, and the &-limit as the sum of the measures of the 2 phases tends to \L(W)\L(\Omega) is identified. Minimizers are fully characterized when N=1N=1, and candidates for solutions are studied for the circle and the square in the plane.     

Enantioselective Organocatalytic Diels–Alder Trapping of Photochemically Generated Hydroxy‐o‐Quinodimethanes

The photoenolization/Diels–Alder strategy offers straightforward access to synthetically valuable benzannulated carbocyclic products. This historical light‐triggered process has never before succumbed to efforts to develop an enantioselective catalytic approach. Herein, we demonstrate how asymmetric organocatalysis provides simple yet effective catalytic tools to intercept photochemically generated hydroxy‐o‐quinodimethanes with high stereoselectivity. We used a chiral organic catalyst, derived from natural cinchona alkaloids, to activate maleimides toward highly stereoselective Diels–Alder reactions. An unconventional mechanism of stereocontrol is operative, wherein the organocatalyst is actively involved in both the photochemical pathway, by leveraging the formation of the reactive photoenol, and the stereoselectivity‐defining event.     

Five-coordinate low-spin cobalt(II) complexes with benzeneseleninato ions and ethylenediamine as ligands

Summary Five-coordinate bis(benzeneseleninato)tris(ethylenediamine) cobalt (II)complexes are obtained by reaction of Co(H₂O)₂ (XC₆ H4 SeO₂)2 complexes (X = H, p-Cl, m-CI, p-Br, ni-Br, p-Me,p-NO₂) with ethylenediamine. The diaquo complexes (one mole)react with ethylenediamine (three moles)to form O-seleninato derivatives. Spectral and magnetic properties show that the complexes are low-spin (s = 1/2) and,on the basis of the electronic spectra a distorted trigonal geometry,D _3h , is suggested. Assignments for the electronic spectra are proposed. Conductivity data indicate that these derivatives are nonelectrolytes. Both ethylenediamine and [RSeO₂ ]^– behave as monodentate ligands.