Facultad de Ciencias Exactas

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Conserved Charges for Gravity with Locally Anti–de Sitter Asymptotics
(American Physical Society, 2000-02) Aros, R; Contreras, M.; Olea, R.; Troncoso, R.; Zanelli, J.
A new formula for the conserved charges in 3+1 gravity for spacetimes with local anti-de Sitter asymptotic geometry is proposed. It is shown that requiring the action to have an extremum for this class of asymptotia sets the boundary term that must be added to the Lagrangian as the Euler density with a fixed weight factor. The resulting action gives rise to the mass and angular momentum as Noether charges associated to the asymptotic Killing vectors without requiring specification of a reference background in order to have a convergent expression. A consequence of this definition is that any negative constant curvature spacetime has vanishing Noether charges. These results remain valid in the Λ = 0 limit.
Conserved charges for even dimensional asymptotically AdS gravity theories
(American Physical Society, 2000-08) Aros, R.; Contreras, M.; Olea, R.; Troncoso, R.; Zanelli, J.
Mass and other conserved Noether charges are discussed for solutions of gravity theories with locally anti-de Sitter (AdS) asymptotics in 2n dimensions. The action is supplemented with a boundary term whose purpose is to guarantee that it reaches an extremum on the classical solutions, provided the space-time is locally AdS space-time at the boundary. It is also shown that if space-time is locally AdS at spatial infinity, the conserved charges are finite and properly normalized without requiring subtraction of a reference background. In this approach, Noether charges associated with Lorentz and diffeomorphism invariance vanish identically for constant curvature space-times. The case of a zero cosmological constant is obtained as a limit of AdS space-time, where Λ plays the role of a regulator. ©2000 The American Physical Society.
Environmental reprogramming of the expression of protein kinase CK2β subunit in fish
(Springer, 2001) Alvarez, M.; Kausel, G.; Figueroa, J.; Vera, M.
The dramatic segregation of the nucleolar components in winter-acclimatized carp is the most striking cellular-phenotypical feature observed during the seasonal adaptation of this fish toward the circannual changes in its habitat. Our studies also show that the carp habitat temperature and photoperiod winter conditions provoke a remarkable reduction of both rRNA transcription and the processing of their precursors. To gain knowledge on the mechanisms involved in the regulation of nucleolar activity during the seasonal adaptation process, we studied the behavior of some genes, specifically snoRNA U3 and protein kinase CK2. Consistent with the reduction in the synthesis and processing of pre-rRNA observed during the cold season, the level of CK2β expression decreases in winter when compared to that attained in summer. Similarly, in winter, liver and kidney cells contain lower levels of CK2β subunit protein compared to summer. CK2 is associated with or modifies different factors and enzymes involved in the nucleolar activity; therefore, its higher or lower content could be part of the molecular mechanisms underlying the nucleolar seasonal changes that occur during the compensatory acclimatization process.
Isolation and characterization of homokaryotic strains from the ligninolytic basidiomycete Ceriporiopsis subvermispora
(Federation of European Microbiological Societies, 2001-05) Tello, M.; Seelenfreund, D.; Lobos, S.; Gaskell, J.; Cullen, D.; Vicuña, R.
Genetic analyses of the lignin-degrading fungus Ceriporiopsis subvermispora is complicated by a dikaryotic nuclear condition and the absence of spore forms. Previous investigations had identified a family of closely related sequences encoding manganese peroxidase (MnP), but the relationship between genes and allelic variants could not be experimentally established. Addressing this issue, homokaryotic derivatives of C. subvermipora strain FP105752 were isolated from regenerated protoplasts. Designated CsA and CsB, their homokaryotic nature was established by polymerase chain reaction amplification and sequence analysis of the allelic variants of three MnP genes. Isoelectrofocusing revealed fewer MnP isoenzymes in filtrates of homokaryon cultures relative to the parental strain. The homokaryotic strains will simplify genetic analyses, particularly the identification of new genes.
In vitro biocontrol activity of Trichoderma harzianum on Alternaria alternata in the presence of growth regulators
(Electronic Journal of Biotechnology, 2001-08) Roco, A.; Pérez, L.
The in vitro biocontrol ability of Trichoderma harzianum on the phytopathogen Alternaria alternata improved in the presence of the growth regulators gibberellic acid (GA3), or indolacetic acid (IAA) or benzylaminopurine (BAP) or foliar nutrient at concentrations similar or higher than those used at the field level. These plant hormones decreased the secretion of endopolygalacturonase (endo-PG) of A. alternata by approximately 20%, did not modify endochitinase (endo-CH) secretion of T. harzianum and did not alter germination of conidia or mycelia growth of any of these fungi. The presence of T. harzianum decreased endo-PGase secretion of A. alternata by about 50%. This inhibitory effect was independent of the presence of growth regulators. The level of secreted endo-PG of T. harzianum was not modified by the presence of A. alternata, but the presence of this phytopathogen in cultures of T. harzianum, increased both the growth of the biocontroller and its secretion of endo-CH.
Analysing charges in even dimensions
(IOP Publishing, 2001-12-21) Aros, R
Lanczos-Lovelock theories of gravity, in its first-order version, are studied on asymptotically locally anti-de Sitter spaces. It is shown that thermodynamics satisfies the standard behaviour and an expression for entropy is found for this formalism. Finally, a short analysis of the algebra of conserved charges is presented.
Supersymmetry of gravitational ground states
(Institute of Physics Publishing, 2002-05) Aros, Rodrigo; Martínez, Cristian; Troncoso, Ricardo; Zanelli, Jorge
A class of black objects which are solutions of pure gravity with negative cosmological constant are classified through the mapping between the Killing spinors of the ground state and those of the transverse section. It is shown that these geometries must have transverse sections of constant curvature for spacetime dimensions d below seven. For d ≥ 7, the transverse sections can also be euclidean Einstein manifolds. In even dimensions, spacetimes with transverse section of non-constant curvature exist only in d = 8 and 10. This classification goes beyond standard supergravity and the eleven-dimensional case is analyzed. It is shown that if the transverse section has negative scalar curvature, only extended objects can have a supersymmetric ground state. In that case, some solutions are explicitly found whose ground state resembles a wormhole
A complementary view to the bonding pattern in the N5 +cation an electron localization function and local temperature analysis
(Sociedad Chilena de Química, 2003) Chamorro, E. (UNAB)
The electron localization function (ELF), a local measure of the Pauli repulsion effect, and the local Kohn-Sham temperature analysis, which is defined within the framework of a local thermodynamics description of density functional theory, have been used to explore the bonding characteristics in the open chain N5+ cation. It is found that both the ELF and local temperature maps depict uniquely the regions of pair localizations, yielding a description of bonding which agrees and complements previous techniques of analysis. Particularly, the three-center four-electron interaction in the NNN terminal atoms of N5+ and the contribution of terminal triple bonds to the bonding nature of the cation have been characterized in detail from the electron fluctuation among ELF basins populations. The features of bonding in terms of the local kinetic energy analysis have been visualized directly from the analysis of local temperature map.
The horizon and its charges in the first order gravity
(Institute of Physics Publishing, 2003-04) Aros, R.
In this work the algebra of charges of diffeomorphisms at the horizon of generic black holes is analyzed within first order gravity. This algebra reproduces the algebra of diffeomorphisms at the horizon, (Diff (S 1)), without a central extension.
Path integral measure for first-order and metric gravities
(IOP Publishing, 2003-07-07) Aros, R; Contreras, M; Zanelli, J
The equivalence between the path integrals for first-order gravity and the standard torsion-free, metric gravity in 3 + 1 dimensions is analysed. Starting with the path integral for first-order gravity, the correct measure for the path integral of the metric theory is obtained.
About the difference in the quadrupole splitting of water between cationic and anionic nematic lyotropic liquid crystals. H-2-NMR and molecular dynamics study
(SOCIEDAD CHILENA DE QUIMICA, 2004) Ahumada, H.; Montecino, R.; Martínez, R.; Araya Maturana, R.; Weiss López, B. E.
Deuterium quadrupole splittings, of deuterated water, Deltav, in anionic discotic nematic lyomesophases are always much larger than in cationic mesophases. To explore the possible origins of this difference, Deltav and T-1 relaxation times of HDO (H2O 0.2% D2O) and decanol (DeOH 14% alpha-d(2)), in solutions of cationic and anionic discotic lyotropic nernatic liquid crystals, were measured using H-2-NMR. The four component mesophases were prepared based on tetradecyltrimethylammonium bromide, (TTAB/DeOH/NaBr/H2O), and cesium N-dodecanoyl-L-alaninate, (CsDAla/DeOH/KCI/H2O), amphiphiles with cationic and anionic head-groups, respectively. For a better understanding of the experimental results, 15 ns molecular dynamics (MD) trajectories of both systems were calculated. The results suggest that the large difference observed in the quadrupole splittings of the solvent can be mainly attributed to a preferential orientation of the water molecules, induced by the strong electric field generated by the electrical bilayer formed at the interface of the anionic mesophase. Restrictions to solvent reorientational dynamics or differences in the thickness of the interface do not seem to play a significant role to explain the observed difference.
Spin-orbit effects metal-metal-multiple bonded m2x2 halide complexes
(Sociedad Chilena de Química, 2004) Henández Acevedo, Lucía; Arratia Pérez, Ramiro
Dirac molecular spinor calculations on the Re2Cl82-, Re2Br82-, Os2Cl82- (both staggered and eclipsed isomers), Os2Br82- and Os2I82- cluster ions are reported. Here we report the calculations of the spin-orbit splitting affecting the metal and ligand core-like states and also affecting the p and d metal-metal bonds. We also compare the calculated molecular spin-orbit splitting against the calculated atomic spin-orbit splitting, and, against available experimental data.
On the reduction of 4-oxo-4h-benzopyran-3-carbaldehydes : global and local electrophilicity patterns
(Sociedad Chilena de Química, 2004) Araya Maturana, Ramiro; Heredia Moya, Jorge; Escobar, Carlos A.; Pérez, Patricia
The theoretical global and local electrophilicity patterns of substituted and chelated 4-oxo-4H-benzopyran-3-carbaldehydes (formylchromones) have been evaluated using the electrophilicity index proposed by Parr et al [J. Am. Chem. Soc. 1999, 121, 1922]. The complexation of formylchromones with aluminum predicts a strong electrophilic character of these compounds against nucleophiles. Local response at the active sites may also be assessed in terms of a global contribution described by the global electrophilicity, and a local contribution described by the variations in electrophilic Fukui function at those sites. The highest local electrophilicity is found at the formyl group of the chelated formylchromones, in spite of that, the highest positive charge is located on the pyrone carbonyl group. This result is consistent with the experimental observed reactivity displayed by 4-oxo-4H-benzopyran-3-carbaldehydes in the presence of 2-propanol and alumina.
Quantitative representation of reactivity, selectivity and site activation concepts in organic chemistry
(Sociedad Chilena de Química, 2004) Pérez, Patricia; Parra-Mouche, Julia; Contreras, Renato R.
Reactivity, selectivity and site activation are classical concepts in chemistry which are amenable to quantitative representation, in terms of static global, local and non local density response functions. The use of these electronic indexes describing chemical interconversion is developed in this work along the perspective of the pioneering work conducted in Chile by the late Professor Fernando Zuloaga, to whom this article is dedicated in memoriam. While global responses, represented as derivatives of the electronic energy with respect to the total number of electrons quantitatively describe the propensity of a system to interconvert into another chemical species (chemical reactivity), the local counterparts assesses well those regions in the molecule where the reactivity pattern dictated by the global quantities is developed (selectivity). Site activation /deactivation may in turn be described by the variations in the local or regional patterns of reactivity, that may be induced by solvent effects or chemical substitution. These concepts are illustrated for a series of chemical reactions in Organic Chemistry, including electrocyclic processes, cycloadditions and electrophilic addition reactions. Some relationships between quantitative scales of reactivity and reaction mechanisms are discussed.
Local reactivity index as descriptor of benzene adsorption in cluster models of exchanged zeolite-Y
(Elsevier, 2004-01) Santos, J.; Chamorro, E.; Contreras, R.; Fuentealba, P.
The adsorption of benzene over sites I, II and III of Cu- and Na-exchanged zeolite-Y, has been studied using the energy profiles for the host-guess interaction, and electronic descriptors of reactivity such as the electronic chemical potential and a local σk index recently defined. Both, the energy and the reactivity index based models consistently complement each other to give a correct interpretation of the reactivity and selectivity patterns experimentally established for these systems.
A Lux-like quorum sensing system in the extreme acidophile Acidithiobacillus ferrooxidans
(BMC, 2005) Rivas, M.; Seeger, M.; Holmes, D.; Jedlicki, E.
The genome of the acidophilic, proteobacterium Acidithiobacillus ferrooxidans, contains linked but divergently oriented genes, termed afeI and afeR, whose predicted protein products are significantly similar to the LuxI and LuxR families of proteins. A possible promoter and Lux box are predicted upstream of afeI. A cloned copy of afeI, expressed in E. coli, encodes an enzyme that catalyzes the production of a diffusible compound identified by gas chromatography and mass spectrometry as an unsubstituted N-acyl homoserine lactone (AHL) of chain length C14. This AHL can be detected by a reporter strain of Sinorhizobium meliloti Rm4l suggesting that it is biologically active. The reporter strain also responds to extracts of the supernatant of A. ferrooxidans grown to early stationary phase in sulfur medium indicating that a diffusible AHL is produced by this microorganism. Semi-quantitative RT-PCR experiments indicate that afeI and afeR are expressed maximally in early stationary phase and are more expressed when A. ferrooxidans is grown in sulfur- rather than iron-containing medium. Given the predicted amino acid sequence and functional properties of AfeI and AfeR it is proposed that A. ferrooxidans has a quorum sensing system similar to the LuxI-LuxR paradigm.
Closed inflationary universe models in Brane World Cosmology
(World Scientific Publishing, 2005-05-01) Del Campo, S; Herrera, R; Saavedra, J
In this article we study closed inflationary universe models proposed by Linde in a brane world cosmological context. In this scenario we determine and characterize the existence of a closed universe, in presence of one self-interacting scalar field with an inflationary stage. We have found that our model, which takes into account a Brane World Cosmology, is less restrictive than the one that uses standard Einstein's General Relativity cosmology.
ℵ=1 supergravity Noether charges -: art. no. 127701
(AMER PHYSICAL SOC, 2005-06-01) Aros, R
In this work a generic set of boundary conditions for N = 1 supergravity is proposed. These conditions define that Hamiltonian charges equal Noether ones, including supercharge.
Extended closed inflationary universes
(IOP Publishing Ltd, 2005-07-07) del Campo, S; Herrera, R
In this paper, we study a type of model for a closed inflationary universe using the Jordan-Brans-Dicke theory. Herein we determine and characterize the existence of Omega > 1, together with the period of inflation. We have found that our model, which takes into account a Jordan-Brans-Dicke type of theory, is less restrictive than that used in Einstein's theory of general relativity. Our results are compared to those found in Einstein's theory of relativity.
(2+1)-dimensional charged black hole in topologically massive electrodynamics -: art. no. 021102
(American Physical Society, 2005-07-08) Andrade, T; Bañados, M; Benguria, RD; Gomberoff, A
The 2+1 black hole coupled to a Maxwell field can be charged in two different ways. Besides a Coulomb field, whose potential grows logarithmically in the radial coordinate, there also exists a topological charge due to the existence of a noncontractible cycle. The topological charge does not gravitate and is somehow decoupled from the black hole. This situation changes if one turns on the Chem-Simons term for the Maxwell field. First, the flux integral at infinity becomes equal to the topological charge. Second, demanding regularity of the black hole horizon, the Coulomb charge must vanish identically. Hence, in 2+1 topologically massive electrodynamics coupled to gravity, the black hole can support holonomies only for the Maxwell field. This means that the charged black hole is constructed from the vacuum by means of spacetime identifications.

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