Coherent States and Duality

We formulate a relation between quantum-mechanical coherent states and complex-differentiable structures on the classical phase space ${\cal C}$ of a finite number of degrees of freedom. Locally-defined coherent states parametrised by the points of ${\cal C}$ exist when there is an almost complex structure on ${\cal C}$. When ${\cal C}$ admits a complex structure, such coherent states are globally defined on ${\cal C}$. The picture of quantum mechanics that emerges allows to implement duality transformations.Comment: 7 pages, LaTe

Note on Scalar Fields Non-Minimally Coupled to (2+1)-Gravity

Scalar fields non--minimally coupled to (2+1)-gravity, in the presence of cosmological constant term, are considered. Non-minimal couplings are described by the term $\zeta R \Psi^2$ in the Lagrangian. Within a class of static circularly symmetric space-times, it is shown that the only existing physically relevant solutions are the anti-de Sitter space-time for $\zeta=0$, and the Martinez-Zanelli black hole for $\zeta=1/8$. We obtain also two new solutions with non-trivial scalar field, for $\zeta=1/6$ and $\zeta=1/8$ respectively, nevertheless, the corresponding space-times can be reduced, via coordinate transformations, to the standard anti-de Sitter space.Comment: 5 pages, RevTe

Zigzag equilibrium structure in monatomic wires

We have applied first-principles density-functional calculations to the study of the energetics, and the elastic and electronic properties of monatomic wires of Au, Cu, K, and Ca in linear and a planar-zigzag geometries. For Cu and Au wires, the zigzag distortion is favorable even when the linear wire is stretched, but this is not observed for K and Ca wires. In all the cases, the equilibrium structure is an equilateral zigzag (bond angle of 60$^{\rm o}$). Only in the case of Au, the zigzag geometry can also be stabilized for an intermediate bond angle of 131$^{\rm o}$. The relationship between the bond and wire lengths is qualitatively different for the metallic (Au, Cu and, K) and semiconducting (Ca) wires.Comment: 4 pages with 3 postscript figures. To appear in Surf. Science (proceedings of the European Conference on Surface Science, ECOSS-19, Madrid Sept. 2000

Complex dynamics in a simple model of pulsations for Super-Asymptotic Giant Branch Stars

When intermediate mass stars reach their last stages of evolution they show pronounced oscillations. This phenomenon happens when these stars reach the so-called Asymptotic Giant Branch (AGB), which is a region of the Hertzsprung-Russell diagram located at about the same region of effective temperatures but at larger luminosities than those of regular giant stars. The period of these oscillations depends on the mass of the star. There is growing evidence that these oscillations are highly correlated with mass loss and that, as the mass loss increases, the pulsations become more chaotic. In this paper we study a simple oscillator which accounts for the observed properties of this kind of stars. This oscillator was first proposed and studied by Icke et al. [Astron.Astrophys. 258, 341 (1992)] and we extend their study to the region of more massive and luminous stars - the region of Super-AGB stars. The oscillator consists of a periodic nonlinear perturbation of a linear Hamiltonian system. The formalism of dynamical systems theory has been used to explore the associated Poincare map for the range of parameters typical of those stars. We have studied and characterized the dynamical behaviour of the oscillator as the parameters of the model are varied, leading us to explore a sequence of local and global bifurcations. Among these, a tripling bifurcation is remarkable, which allows us to show that the Poincare map is a nontwist area preserving map. Meandering curves, hierarchical-islands traps and sticky orbits also show up. We discuss the implications of the stickiness phenomenon in the evolution and stability of the Super-AGB stars.Comment: 13 pages, 9 figure

The African swine fever virus dynein-binding protein p54 induces infected cell apoptosis

AbstractA specific interaction of ASFV p54 protein with 8 kDa light chain cytoplasmic dynein (DLC8) has been previously characterized and this interaction is critical during virus internalization and transport to factory sites. During early phases of infection, the virus induces the initiation of apoptosis triggering activation of caspase-9 and -3. To analyze the role of the structural protein p54 in apoptosis, transient expression experiments of p54 in Vero cells were carried out which resulted in effector caspase-3 activation and apoptosis. Interestingly, p54 mutants, lacking the 13 aa dynein-binding motif lose caspase activation ability and pro-death function of p54. This is the first reported ASFV protein which induces apoptosis

Tautomeric state of α-sarcin histidines. Nδ tautomers are a common feature in the active site of extracellular microbial ribonucleases

Extracellular fungal RNases, including ribotoxins such as α-sarcin, constitute a family of structurally related proteins represented by RNase T1. The tautomeric preferences of the α-sarcin imidazole side chains have been determined by nuclear magnetic resonance and electrostatic calculations. Histidine residues at the active site, H50 and H137, adopt the Nδ tautomer, which is less common in short peptides, as has been found for RNase T1. Comparison with tautomers predicted from crystal structures of other ribonucleases suggests that two active site histidine residues with the Nδ tautomer are a conserved feature of microbial ribonucleases and that this is related to their ribonucleolytic function.This work was supported by Grants PB98-0677 and BMC2000-0551 from the Ministerio de Educación y Cultura (MEC) (Spain)

Deletion of the NH2-terminal β-Hairpin of the Ribotoxin α-Sarcin Produces a Nontoxic but Active Ribonuclease

Ribotoxins are a family of highly specific fungal ribonucleases that inactivate the ribosomes by hydrolysis of a single phosphodiester bond of the 28 S rRNA. α-Sarcin, the best characterized member of this family, is a potent cytotoxin that promotes apoptosis of human tumor cells after internalization via endocytosis. This latter ability is related to its interaction with phospholipid bilayers. These proteins share a common structural core with nontoxic ribonucleases of the RNase T1 family. However, significant structural differences between these two groups of proteins are related to the presence of a long amino-terminal β-hairpin in ribotoxins and to the different length of their unstructured loops. The amino-terminal deletion mutant Δ(7–22) of α-sarcin has been produced in Escherichia coli and purified to homogeneity. It retains the same conformation as the wild-type protein as ascertained by complete spectroscopic characterization based on circular dichroism, fluorescence, and NMR techniques. This mutant exhibits ribonuclease activity against naked rRNA and synthetic substrates but lacks the specific ability of the wild-type protein to degrade rRNA in intact ribosomes. The results indicate that α-sarcin interacts with the ribosome at two regions, i.e. the well known sarcin-ricin loop of the rRNA and a different region recognized by the β-hairpin of the protein. In addition, this latter protein portion is involved in interaction with cell membranes. The mutant displays decreased interaction with lipid vesicles and shows behavior compatible with the absence of one vesicle-interacting region. In agreement with this conclusion, the deletion mutant exhibits a very low cytotoxicity on human rhabdomyosarcoma cells.This work was supported by Grant BMC2000-0551 from the Ministerio de Ciencia y Tecnología and Grants PB98–0083 and PB98–0677 from the Ministerio de Educación y Cultura