A necessary extension of the surface flux transport model

Customary two-dimensional flux transport models for the evolution of the magnetic field at the solar surface do not account for the radial structure and the volume diffusion of the magnetic field. When considering the long-term evolution of magnetic flux, this omission can lead to an unrealistic long-term memory of the system and to the suppression of polar field reversals. In order to avoid such effects, we propose an extension of the flux transport model by a linear decay term derived consistently on the basis of the eigenmodes of the diffusion operator in a spherical shell. A decay rate for each eigenmode of the system is determined and applied to the corresponding surface part of the mode evolved in the flux transport model. The value of the volume diffusivity associated with this decay term can be estimated to be in the range 50--100 km^2/s by considering the reversals of the polar fields in comparison of flux transport simulations with observations. We show that the decay term prohibits a secular drift of the polar field in the case of cycles of varying strength, like those exhibited by the historical sunspot record.Comment: for further information visit: http://solweb.oma.be/users/baumann

The ground state in a spin-one color superconductor

Color superconductors in which quarks of the same flavor form Cooper pairs are investigated. These Cooper pairs carry total spin one. A systematic group-theoretical classification of possible phases in a spin-one color superconductor is presented, revealing parallels and differences to the theory of superfluid $^3$He. General expressions for the gap parameter, the critical temperature, and the pressure are derived and evaluated for several spin-one phases, with special emphasis on the angular structure of the gap equation. It is shown that the (transverse) color-spin-locked phase is expected to be the ground state.Comment: 36 pages, 3 figures, error corrected in App. C, conclusion change

Canonical Transformation Approach to the Ultrafast Non-linear Optical Dynamics of Semiconductors

We develop a theory describing the effects of many-particle Coulomb correlations on the coherent ultrafast nonlinear optical response of semiconductors and metals. Our approach is based on a mapping of the nonlinear optical response of the ``bare'' system onto the linear response of a ``dressed'' system. The latter is characterized by effective time-dependent optical transition matrix elements, electron/hole dispersions, and interaction potentials, which in undoped semiconductors are determined by the single-exciton and two-exciton Green functions in the absence of optical fields. This mapping is achieved by eliminating the optically-induced charge fluctuations from the Hamiltonian using a Van Vleck canonical transformation. It takes into account all many-body contributions up to a given order in the optical fields as well as important Coulomb-induced quantum dynamics to all orders in the optical field. Our approach allows us to distinguish between optical nonlinearities of different origins and provides a physically-intuitive interpretation of their manifestations in ultrafast coherent nonlinear optical spectroscopy.Comment: 24 page

Stability conditions and Fermi surface topologies in a superconductor

Candidate homogeneous, isotropic superfluid or superconducting states of paired fermion species with different chemical potentials, can lead to quasiparticle excitation energies that vanish at either zero, one, or two spheres in momentum space. With no zeroes, we have a conventional BCS superconductor. The other two cases, ``gapless'' superconductors, appear in mean field theory for sufficiently large mismatches and/or sufficiently large coupling strengths. Here we examine several stability criteria for those candidate phases. Positivity of number susceptibility appears to provide the most powerful constraint, and renders all the two-zero states that we have examined mechanically unstable. Our results should apply directly to ultracold fermionic atom systems.Comment: 18 pages, 7 figures; v2: some clarifications in Sec. IIC; references added; version accepted for publication in Phys. Rev.

Electron momentum distribution of a single mobile hole in the t-J model

We investigate the electron momentum distribution function (EMDF) for the two-dimensional t-J model. The results are based on the self-consistent Born approximation (SCBA) for the self-energy and the wave function. In the Ising limit of the model we give the results in a closed form, in the Heisenberg limit the results are obtained numerically. An anomalous momentum dependence of EMDF is found and the anomaly is in the lowest order in number of magnons expressed analitycally. We interpret the anomaly as a fingerprint of an emerging large Fermi surface coexisting with hole pockets.Comment: M2S - submitted to Physica

Till death do us part? : Kirchnerism, neodevelopmentalism and the struggle for hegemony in Argentina, 2003-2015

The extended Kirchnerist decade in Argentina (2003-15) is reaching its closure, and the political transition towards a new phase of the neodevelopmentalist era has begun. This new phase will be earmarked by the heritage of Kirchnerism as a hegemonic political project and will reflect both the new policies introduced by it and the profound continuities with the neoliberal era, whose main traits were consolidated and perfected during this period (Féliz, 2012a). This transition occurs in a global and regional framework that has violently mutated in recent years since the beginning of the 2008 capitalist crisis in the centre, and the unexpected death of Venezuela’s President Hugo Chávez. This chapter analyzes how the era politically dominated by Kirchnerism carne to mould the constitution and crisis of neodevelopmentalism in Argentina after the downfall of neoliberal rule. In this process, popular organizations struggled to push forward the organizational momentum that was built through clashes with neoliberalism in the late 1990s. But the limits of Kirchnerism as a progressive, ‘social-democratic’ movement became evident as it could not surpass the boundaries of dependent capitalism, thus becoming a farce of its own discourse of change.Facultad de Humanidades y Ciencias de la Educació

Till death do us part? : Kirchnerism, neodevelopmentalism and the struggle for hegemony in Argentina, 2003-2015

The extended Kirchnerist decade in Argentina (2003-15) is reaching its closure, and the political transition towards a new phase of the neodevelopmentalist era has begun. This new phase will be earmarked by the heritage of Kirchnerism as a hegemonic political project and will reflect both the new policies introduced by it and the profound continuities with the neoliberal era, whose main traits were consolidated and perfected during this period (Féliz, 2012a). This transition occurs in a global and regional framework that has violently mutated in recent years since the beginning of the 2008 capitalist crisis in the centre, and the unexpected death of Venezuela’s President Hugo Chávez. This chapter analyzes how the era politically dominated by Kirchnerism carne to mould the constitution and crisis of neodevelopmentalism in Argentina after the downfall of neoliberal rule. In this process, popular organizations struggled to push forward the organizational momentum that was built through clashes with neoliberalism in the late 1990s. But the limits of Kirchnerism as a progressive, ‘social-democratic’ movement became evident as it could not surpass the boundaries of dependent capitalism, thus becoming a farce of its own discourse of change.Facultad de Humanidades y Ciencias de la Educació

Discovery of Escherichia coli methionyl-tRNA synthetase mutants for efficient labeling of proteins with azidonorleucine in vivo

Incorporation of noncanonical amino acids into cellular proteins often requires engineering new aminoacyl-tRNA synthetase activity into the cell. A screening strategy that relies on cell-surface display of reactive amino acid side-chains was used to identify a diverse set of methionyl-tRNA synthetase (MetRS) mutants that allow efficient incorporation of the methionine (Met) analog azidonorleucine (Anl). We demonstrate that the extent of cell-surface labeling in vivo is a good indicator of the rate of Anl activation by the MetRS variant harbored by the cell. By screening at low Anl concentrations in Met-supplemented media, MetRS variants with improved activities toward Anl and better discrimination against Met were identified

Till death do us part? : Kirchnerism, neodevelopmentalism and the struggle for hegemony in Argentina, 2003-2015

The extended Kirchnerist decade in Argentina (2003-15) is reaching its closure, and the political transition towards a new phase of the neodevelopmentalist era has begun. This new phase will be earmarked by the heritage of Kirchnerism as a hegemonic political project and will reflect both the new policies introduced by it and the profound continuities with the neoliberal era, whose main traits were consolidated and perfected during this period (Féliz, 2012a). This transition occurs in a global and regional framework that has violently mutated in recent years since the beginning of the 2008 capitalist crisis in the centre, and the unexpected death of Venezuela’s President Hugo Chávez. This chapter analyzes how the era politically dominated by Kirchnerism carne to mould the constitution and crisis of neodevelopmentalism in Argentina after the downfall of neoliberal rule. In this process, popular organizations struggled to push forward the organizational momentum that was built through clashes with neoliberalism in the late 1990s. But the limits of Kirchnerism as a progressive, ‘social-democratic’ movement became evident as it could not surpass the boundaries of dependent capitalism, thus becoming a farce of its own discourse of change.Facultad de Humanidades y Ciencias de la Educació

The Effects of Additives on the Physical Properties of Electroformed Nickel and on the Stretch of Photoelectroformed Nickel Components

The process of nickel electroforming is becoming increasingly important in the manufacture of MST products, as it has the potential to replicate complex geometries with extremely high fidelity. Electroforming of nickel uses multi-component electrolyte formulations in order to maximise desirable product properties. In addition to nickel sulphamate (the major electrolyte component), formulation additives can also comprise nickel chloride (to increase nickel anode dissolution), sulphamic acid (to control pH), boric acid (to act as a pH buffer), hardening/levelling agents (to increase deposit hardness and lustre) and wetting agents (to aid surface wetting and thus prevent gas bubbles and void formation). This paper investigates the effects of some of these variables on internal stress and stretch as a function of applied current density.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions