The role of singular spinor fields in a torsional gravity,Lorentz-violating,framework

In this work, we consider a generalization of quantum electrodynamics including Lorentz violation and torsional-gravity, in the context of general spinor fields as classified in the Lounesto scheme. Singular spinor fields will be shown to be less sensitive to the Lorentz violation, as far as couplings between the spinor bilinear covariants and torsion are regarded. In addition, we prove that flagpole spinor fields do not admit minimal coupling to the torsion. In general, mass dimension four couplings are deeply affected when singular—flagpoles—spinors are considered, instead of the usual Dirac spinors. We also construct a mapping between spinors in the covariant framework and spinors in Lorentz symmetry breaking scenarios, showing how one may transliterate spinors of different classes between the two cases. Specific examples concerning the mapping of Dirac spinor fields in Lorentz violating scenarios into flagpole and flag-dipole spinors with full Lorentz invariance (including the cases of Weyl and Majorana spinors) are worked out.     

Double-resonance decoupling for resolution enhancement of 31P solid-state MAS and 27Al --> 31P MQHETCOR NMR

27Al decoupling has been used to remove residual J-coupling interactions between 31P and 27Al in microporous aluminophosphates AlPO4-14 and AlPO4-40. In combination with 1H high-power decoupling, 27Al adapted decoupling yields 31P spectra with optimal sensitivity and resolution. The importance of double-resonance decoupling is further demonstrated by incorporating this technique in the MQHETCOR sequence. Unambiguous assignment of all the AlPO4-14 nuclear magnetic resonances is achieved by combining multiple-quantum evolution in the 27Al dimension and double-resonance decoupling in the 31P acquisition domain.     

Jordan algebra field theory

It is shown that the set of observable functionals associated with a constrained field theory satisfying two given assumptions is a Jordan algebra under the symmetric Dirac bracket composition law.     

Relativistic and interchannel coupling effects in photoionization angular distributions by synchrotron spectrocopy of laser cooled atoms

We investigate the angular distribution of photoionization fragments at low photon energies (12-40 eV) in an open shell atom, by synchrotron radiation recoil ion momentum spectroscopy in a laser cooled and trapped sample. For cesium atoms, for which relativistic effects play an important role and the ion recoil is relatively small, we could determine large and rapid changes of the asymmetry parameter beta from two, observed for s electrons outside resonances and far from the Cooper minimum. They can be explained by relativistic effects and interchannel coupling arising from final state configuration mixing.     

Indication of unusual pentagonal structures in atomic-size Cu nanowires

We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of approximately 0.45 nm and approximately 4.5 conductance quanta.     

Conductance oscillations in zigzag platinum chains

Using first principles simulations we perform a detailed study of the structural, electronic, and transport properties of monatomic platinum chains, sandwiched between platinum electrodes. First, we demonstrate that the most stable atomic configuration corresponds to a zigzag arrangement that gradually straightens as the chains are stretched. Second, we find that the averaged conductance shows slight parity oscillations with the number of atoms in the chain. Additionally, the conductance of chains of fixed oscillates as the end atoms are pulled apart, due to the gradual closing and opening of conductance channels as the chain straightens.     

Lissoclinotoxins E and F, novel cytotoxic alkaloids from a Philippine didemnid ascidian

Bioassay-guided fractionation of the MeOH extract from a Philippine didemnid ascidian resulted in the isolation of two new dimeric alkaloids, lissoclinotoxins E (1) and F (2). The polysulfide structures for compounds 1 and 2 were determined by interpretation of spectroscopic data and chemical degradation. Computational chemistry studies suggested that the N-alkyl chains about the tricyclic systems of lissoclinotoxins E and F had trans and cis orientations, respectively. Alkaloids 1 and 2 displayed IC₅₀ values of 2.3 and 1.5 μg/mL, respectively, towards the PTEN-deficient human breast carcinoma cell line, MDA-MB-468.     

Naturalness of nonlinear \sigma, \omega self-couplings in relativistic mean-field models for neutron stars

We investigate dense hadronic matter in a relativistic mean-field approach. For a generalized baryon-meson Lagrangian effective field theory, we confront expansions from naive dimensional analysis for the nonlinear self-couplings of the , fields with estimates from microscopic pair creation models from Quantum Chromodynamics. Upon adjusting the model parameters to ordinary nuclear matter, we discuss implications of the approach to dense hadronic matter and in particular to neutron stars.Received: 30 September 2002, Published online: 22 October 2003PACS: 11.10.-z Field theory - 21.65. + f Nuclear matter - 26.60. + c Nuclear matter aspects of neutron stars     

Cellulose TETPA: a chelating collector designed for multielement preconcentration in flow systems

Summary A cellulose collector with immobilized triethylenetetraminepentaacetic acid (TETPA) groups has been developed for multielement preconcentration (e.g., Al, Be, Bi, Cd, Co, Cu, Fe(III), In, Mn, Ni, Pb, Tl(III), U(VI), V(IV), Zn) using a low-pressure flow system. Analyte distribution coefficients K_d of the order of 10⁴–10⁵ ml/g (0.5 mol/l NaCl, pH 3–8) and fast exchange kinetics enable effective trace/matrix separations by means of small TETPA-filled (75 mg) columns even at high flow rates (contact time<1 s). Accordingly, recovery rates ranging from 88 (Tl(III)) to 99.5% (Ni), relative standard deviations s_r mostly between 1.5 and 4.0% (off-line determined by flame AAS) and blank levels (e.g., Cu, Fe, Zn) in the lower ng range (quantified by ETAAS) can be achieved. Metal-complexing dissolved organic substances (e.g. humic substances), however, considerably lower the recovery rates of some analytes (e.g., Cu, Fe, Ni). A series of water analyses (e.g., river, sea, bog water) prove the reliability of the developed flow-preconcentration system.Dedicated to Prof. Dr. V. Krivan on the occasion of his 60th birthday