A complete Lagrangian formulation of superconductivity

We present here a complete Lagrangian formulation of superconductivity. Only the boson degrees of freedom are explicitly introduced. The BCS solution is obtained as classical approximation. The physical interpretation of the Goldstone boson comes up naturally from this theory.     

Simple microscopic model for the scalar-isoscalar component of the Landau-Migdal amplitude

A simple microscopic model is proposed that describes the coordinate dependence of the zeroth harmonic f ₀(r) of the scalar-isoscalar component of the Landau-Migdal amplitude. In the theory of finite Fermi systems due to Migdal, such a dependence was introduced phenomenologically. The model presented in this study is based on a previous analysis of the Brueckner G matrix for a planar slab of nuclear matter; it expresses the function f ₀(r) in terms of the off-mass-shell T matrix for free nucleon-nucleon scattering. The result involves the T matrix taken at the negative energy value equal to the doubled chemical potential μ of the nucleus being considered. The amplitude f ₀(r) found in this way is substituted into the condition that, in the theory of finite Fermi systems, ensures consistency of the self-energy operator, effective quasiparticle interaction, and the density distribution. The calculated isoscalar component of the mean nuclear field V(r) agrees fairly well with a phenomenological nuclear potential. Owing to a strong E dependence of the T matrix at low energies, the potential-well depth V(0) depends sharply on μ, increasing as |μ| is reduced. This effect must additionally stabilize nuclei near the nucleon drip line, where μ vanishes.     

Air-stable,long-length,solution-based graphene nanoribbons

Within the context of nanoelectronics, general strategies for the development of electronically tunable and air stable graphene nanoribbons are crucial. Previous studies towards the goal of processable nanoribbons have been complicated by ambient condition instability, insolubility arising from aggregation, or poor cyclization yield due to electron deficiency. Herein, we present a general strategy for the elongation of smaller graphene nanoribbon fragments into air-stable, easily processed, and electronically tunable nanoribbons. This strategy is facilitated by the incorporation of electron-rich donor units between electron-poor acceptor perylene diimide oligomeric units. The ribbons are processed in solution via a visible-light flow photocyclization using LEDs. The resulting long nanoribbons can be solution-cast and imaged, which are necessary characteristics for device fabrication. The ribbons become conductive after thermolysis of the pendent side-chains. The electron-accepting character of these nanoribbons in solution is reversible, and the conductivity of the thermolyzed species as a solid remains stable. This work highlights our general strategy for the mild and reliable fabrication of tunable and ambient-stable graphene nanoribbons, and charts a straightforward route for facile device incorporation.

A strategy is shown for the elongation of graphene nanoribbon (GNR) fragments into air-stable, solution processable and electronically tunable GNRs, aided by incorporating electron-rich donor units between electron-poor oligomeric acceptor units.     

On limits of ab initio calculations of pairing gap in nuclei

A brief review of recent microscopic calculations of nuclear pairing gap is given. A semi-microscopic model is suggested in which the ab initio effective pairing interaction is supplemented with a small phenomenological addendum. It involves a parameter which is universal for all medium and heavy nuclei. Calculations for several isotopic and isotonic chains of semi-magic nuclei confirm the relevance of the model.     

Plasmons in strong superconductors

We present a study of the possible plasmon excitations that can occur in systems where strong superconductivity is present. In these systems the plasmon energy is comparable to or smaller than the pairing gap. As a prototype of these systems we consider the proton component of Neutron Star matter just below the crust when electron screening is not taken into account. For the realistic case we consider in detail the different aspects of the elementary excitations when the proton, electron components are considered within the Random-Phase Approximation generalized to the superfluid case, while the influence of the neutron component is considered only at qualitative level. Electron screening plays a major role in modifying the proton spectrum and spectral function. At the same time the electron plasmon is strongly modified and damped by the indirect coupling with the superfluid proton component, even at moderately low values of the gap. The excitation spectrum shows the interplay of the different components and their relevance for each excitation modes. The results are relevant for neutrino physics and thermodynamical processes in neutron stars. If electron screening is neglected, the spectral properties of the proton component show some resemblance with the physical situation in high-T _c superconductors, and we briefly discuss similarities and differences in this connection. In a general prospect, the results of the study emphasize the role of Coulomb interaction in strong superconductors.     

Effective pairing interaction for the Argonne nucleon-nucleon potential v<Subscript>18</Subscript>

The effective pairing interaction corresponding to the Argonne nucleon-nucleon potential v₁₈ is found within the local potential approximation for several values of the boundary energy E ₀ that specifies the model subspace S ₀. A detailed comparison with the analogous effective interaction calculated previously for the Paris nucleon-nucleon potential is performed. It is shown that the effective interactions obtained for the two different nucleon-nucleon potentials at the same value of E ₀ are very close to each other. In the case of the Paris potential, a very wide subspace S′ complementary to S ₀ was required in calculating the effective interaction (the corresponding cutoff momentum being k _max = 160?180 fm^?1), whereas a much narrower subspace S′ corresponding to k _max = 10?12 fm^?1 could be used in the case of the Argonne potential.     

Electrophotocatalysis with a Trisaminocyclopropenium Radical Dication

Visible‐light photocatalysis and electrocatalysis are two powerful strategies for the promotion of chemical reactions. Here, these two modalities are combined in an electrophotocatalytic oxidation platform. This chemistry employs a trisaminocyclopropenium (TAC) ion catalyst, which is electrochemically oxidized to form a cyclopropenium radical dication intermediate. The radical dication undergoes photoexcitation with visible light to produce an excited‐state species with oxidizing power (3.33 V vs. SCE) sufficient to oxidize benzene and halogenated benzenes via single‐electron transfer (SET), resulting in C?H/N?H coupling with azoles. A rationale for the strongly oxidizing behavior of the photoexcited species is provided, while the stability of the catalyst is rationalized by a particular conformation of the cis‐2,6‐dimethylpiperidine moieties.     

The effects of ultrasound on starch grains

Ultrasound has been applied to an aqueous starch suspension and the erosion of starch grains that are free to move and whose dimensions approximate those of cavitational bubbles has been examined. The examination was carried out with a scanning electron microscope. The type of erosion (state of the surface and position and form of the pits) is analysed as a function of the experimental conditions — chiefly the type of surrounding gas: air, hydrogen, oxygen and carbon dioxide.     

Effects of the mercury ion concentration on the preparation of mercury deposits on platinum micro-disk electrodes

In this paper, the effect of mercury ion concentration on the preparation of mercury microelectrodes fabricated on a platinum microdisk of 10 microns radius was studied. The preparation of the mercury microelectrodes was followed by chronoamperometry, and the measurements were performed in Hg2(NO3)2 solutions with concentrations over the range 0.1-12.5 mM. The mercury microelectrode size was referred to as h/a, where h is the height of the mercury deposit and a is the radius of the inlaid microdisk. The mercury microelectrodes investigated had h/a values over the range 0-2. The results obtained indicated that from concentrated mercury ion solutions (> 0.5 mM) the mercury growth was somehow erratic due to the coalescence of small mercury droplets. On the other hand, from dilute solutions (< 0.5 mM), the mercury deposits grew smoothly. Under the latter conditions the geometric coefficient k, which characterises the steady state diffusion limiting current expression at a mercury microelectrode, was determined with good accuracy (within 5% error) from the chronoamperometric curves recorded during the mercury microelectrode preparation. In general, the coefficient k was calculated from theoretical expressions derived for a sphere cap and spheroidal geometry, which may model the shape of the mercury deposits. The comparison between theoretical and experimental k values suggested that both geometries equally modelled the experimental mercury deposit obtained. Finally, for the sphere cap geometry an algebraic expression relating k and h/a was derived for an easier k evaluation from experimental h/a values.