Dirac-Hestenes spinor fields in Riemann-Cartan spacetime

In this paper we study Dirac-Hestenes spinor fields (DHSF) on a four-dimensional Riemann-Cartan spacetime (RCST). We prove that these fields must be defined as certain equivalence classes of even sections of the Clifford bundle (over the RCST), thereby being certain particular sections of a new bundle named Spin-Clifford bundle (SCB). The conditions for the existence of the SCB are studied and are shown to be equivalent to the famous Geroch's theorem concerning to the existence of spinor structures in a Lorentzian spacetime. We introduce also the covariant and algebraic Dirac spinor fields and compare these with DHSF, showing that all the three kinds of spinor fields contain the same mathematical and physical information. We clarify also the notion of (Crumeyrolle's) amorphous spinors (Dirac-K\"ahler spinor fields are of this type), showing that they cannot be used to describe fermionic fields. We develop a rigorous theory for the covariant derivatives of Clifford fields (sections of the Clifford bundle (CB)) and of Dirac-Hestenes spinor fields. We show how to generalize the original Dirac-Hestenes equation in Minkowski spacetime for the case of a RCST. Our results are obtained from a variational principle formulated through the multiform derivative approach to Lagrangian field theory in the Clifford bundle.Comment: 45 pages, special macros kapproc.sty and makro822.te

Construction of gateway binary vector for selection with bialaphos or carboxin and GFP expression in fungi.

Genomic data has created a growing demand for tools and methodologies for studying the genes function, which can be realized through loss of function experiments (gene knockout) or by RNA silencing (knockdown). The develop-ment of binary vectors for Agrobacterium tumefaciens mediated transformation (ATMT) has the advantage of being independent of protoplast formation and can be used directly on a wide variety of fungal species and tissue types. The selection of transformants using bialaphos and carboxin has the advantages of low cost in the transformation and availability of different selectable markers, also allowing the analysis of several genes and combination of study by knockout or knockdown, using selectable markers in the same transformant. Thus, this study aimed to build two binary vectors containing reporter gene and selectable markers that confer resistance to carboxin and bialaphos. The cassettes were constructed using the Gateway system to two fragments. The gene encoding the GFP protein and PtoxA and PtrpCpromoters were cloned into pDONR P1-P5R plasmid. Genes that confer bialaphos and carboxin resistance, bar and cbxr respectively, were cloned into pDONR P5-P2 plasmid. The pPGW plasmid was used as des-tination vector. The gfp gene transcription is controlled by PtoxA promoter and the bar and cbxr genes transcriptions are controlled by PtrpC promoter. These binary vectors were named pGWGFP-BAR and pGWGFP-CBXR. The assembly of cassettes was confi rmed by sequencing, and the validation of vectors is being accomplished through transformation (ATMT) with the plant pathogens Mycosphaerella fi jiensis and Fusarium oxysporum f. sp. cubense

Inverting Time-Dependent Harmonic Oscillator Potential by a Unitary Transformation and a New Class of Exactly Solvable Oscillators

A time-dependent unitary (canonical) transformation is found which maps the Hamiltonian for a harmonic oscillator with time-dependent real mass and real frequency to that of a generalized harmonic oscillator with time-dependent real mass and imaginary frequency. The latter may be reduced to an ordinary harmonic oscillator by means of another unitary (canonical) transformation. A simple analysis of the resulting system leads to the identification of a previously unknown class of exactly solvable time-dependent oscillators. Furthermore, it is shown how one can apply these results to establish a canonical equivalence between some real and imaginary frequency oscillators. In particular it is shown that a harmonic oscillator whose frequency is constant and whose mass grows linearly in time is canonically equivalent with an oscillator whose frequency changes from being real to imaginary and vice versa repeatedly.Comment: 7 pages, 1 figure include

Tuning the crystalline electric field and magnetic anisotropy along the CeCuBi2−x_{2-x}Sbx_{x} series

We have performed X-ray powder diffraction, magnetization, electrical resistivity, heat capacity and inelastic neutron scattering (INS) to investigate the physical properties of the intermetallic series of compounds CeCuBi$_{2-x}$Sb$_{x}$. These compounds crystallize in a tetragonal structure with space group $P4/nmm$ and present antiferromagnetic transition temperatures ranging from 3.6 K to 16 K. Remarkably, the magnetization easy axis changes along the series, which is closely related to the variations of the tetragonal crystalline electric field (CEF) parameters. This evolution was analyzed using a mean field model, which included anisotropic nearest-neighbor interactions and the tetragonal CEF Hamiltonian. The CEF parameters were obtained by fitting the magnetic susceptibility data with the constraints given by the INS measurements. Finally, we discuss how this CEF evolution can affect the Kondo physics and the search for a superconducting state in this family.Comment: 7 pages, 6 figures. To be published in Physical Review