The Two-Dimensional Stringy Black-Hole: A New Approach and a Pathology

The string propagation in the two-dimensional stringy black-hole is investigated from a new approach. We completely solve the classical and quantum string dynamics in the lorentzian and euclidean regimes. In the lorentzian case all the physics reduces to a massless scalar particle described by a Klein-Gordon type equation with a singular effective potential. The scattering matrix is found and it reproduces the results obtained by coset CFT techniques. It factorizes into two pieces : an elastic coulombian amplitude and an absorption part. In both parts, an infinite sequence of imaginary poles in the energy appear. The generic features of string propagation in curved D-dimensional backgrounds (string stretching, fall into spacetime singularities) are analyzed in the present case. A new physical phenomenon specific to the present black-hole is found : the quantum renormalization of the speed of light. We find c_{quantum} = \sqrt{{k\o{k-2}}}~c_{classical}, where $k$ is the integer in front of the WZW action. This feature is, however, a pathology. Only for $k \to \infty$ the pathology disappears (although the conformal anomaly is present). We analyze all the classical euclidean string solutions and exactly compute the quantum partition function. No critical Hagedorn temperature appears here.Comment: 32 pages, uses phyzz

Massive pre-main sequence stars in M17

The formation process of massive stars is still poorly understood. Massive young stellar objects (mYSOs) are deeply embedded in their parental clouds, they are rare and thus typically distant, and their reddened spectra usually preclude the determination of their photospheric parameters. M17 is one of the best studied HII regions in the sky, is relatively nearby, and hosts a young stellar population. With X-shooter on the ESO Very Large Telescope we have obtained optical to near-infrared spectra of candidate mYSOs, identified by Hanson et al. (1997), and a few OB stars in this region. The large wavelength coverage enables a detailed spectroscopic analysis of their photospheres and circumstellar disks. We confirm the pre-main sequence (PMS) nature of six of the stars and characterise the O stars. The PMS stars have radii consistent with being contracting towards the main sequence and are surrounded by a remnant accretion disk. The observed infrared excess and the (double-peaked) emission lines provide the opportunity to measure structured velocity profiles in the disks. We compare the observed properties of this unique sample of young massive stars with evolutionary tracks of massive protostars by Hosokawa & Omukai (2009), and propose that these mYSOs near the western edge of the HII region are on their way to become main-sequence stars ($\sim 6 - 20$ $M_{\odot}$) after having undergone high mass-accretion rates (${\dot{M}_{\rm acc}} \sim 10^{-4} - 10^{-3}$ $M_{\odot}$ $\rm yr^{-1}$). Their spin distribution upon arrival at the zero age main sequence (ZAMS) is consistent with that observed for young B stars, assuming conservation of angular momentum and homologous contraction.Comment: Accepted for publication in A&A. Appendixes A and B have been truncated due to size limitations, the full version will be available on A&

La transición política: una revisión crítica

La situación económica, social y política del país, con la que se inicia el sexenio de Miguel de la Madrid, ha generado un proceso de transformaciones, tanto en el comportamiento y estructura del gobierno como en las relaciones de éste con los diversos sectores de la sociedad. El denominador común de dichos cambios es el abandono paulatino de los rasgos característicos del Estado populista y de los compromisos sociales derivados de la Revolución Mexicana. Mientras en el plano económico, el llamado proyecto de transformaciones estructurales es aplicado, en el nivel de la política, la pretendida modernización no ha significado aún un cambio sustantivo en las reglas del juego político

The Success Story of Gold-Based Catalysts for Gas- and Liquid-Phase Reactions: A Brief Perspective and Beyond

Gold has long held the fascination of mankind. For millennia it has found use in art, cosmetic metallurgy and architecture; this element is seen as the ultimate statement of prosperity and beauty. This myriad of uses is made possible by the characteristic inertness of bulk gold; allowing it to appear long lasting and above the tarnishing experienced by other metals, in part providing its status as the most noble meta

CLASSICAL SPLITTING OF FUNDAMENTAL STRINGS

We find exact solutions of the string equations of motion and constraints describing the {\em classical}\ splitting of a string into two. We show that for the same Cauchy data, the strings that split have {\bf smaller} action than the string without splitting. This phenomenon is already present in flat space-time. The mass, energy and momentum carried out by the strings are computed. We show that the splitting solution describes a natural decay process of one string of mass $M$ into two strings with a smaller total mass and some kinetic energy. The standard non-splitting solution is contained as a particular case. We also describe the splitting of a closed string in the background of a singular gravitational plane wave, and show how the presence of the strong gravitational field increases (and amplifies by an overall factor) the negative difference between the action of the splitting and non-splitting solutions.Comment: 27 pages, revtex

Genome-wide DNA-(de)methylation is associated with Noninfectious Bud-failure exhibition in Almond (Prunus dulcis [Mill.] D.A.Webb).

Noninfectious bud-failure (BF) remains a major threat to almond production in California, particularly with the recent rapid expansion of acreage and as more intensive cultural practices and modern cultivars are adopted. BF has been shown to be inherited in both vegetative and sexual progeny, with exhibition related to the age and propagation history of scion clonal sources. These characteristics suggest an epigenetic influence, such as the loss of juvenility mediated by DNA-(de)methylation. Various degrees of BF have been reported among cultivars as well as within sources of clonal propagation of the same cultivar. Genome-wide methylation profiles for different clones within almond genotypes were developed to examine their association with BF levels and association with the chronological time from initial propagation. The degree of BF exhibition was found to be associated with DNA-(de)methylation and clonal age, which suggests that epigenetic changes associated with ageing may be involved in the differential exhibition of BF within and among almond clones. Research is needed to investigate the potential of DNA-(de)methylation status as a predictor for BF as well as for effective strategies to improve clonal selection against age related deterioration. This is the first report of an epigenetic-related disorder threatening a major tree crop

The frequency map for billiards inside ellipsoids

The billiard motion inside an ellipsoid Q \subset \Rset^{n+1} is completely integrable. Its phase space is a symplectic manifold of dimension $2n$, which is mostly foliated with Liouville tori of dimension $n$. The motion on each Liouville torus becomes just a parallel translation with some frequency $\omega$ that varies with the torus. Besides, any billiard trajectory inside $Q$ is tangent to $n$ caustics $Q_{\lambda_1},...,Q_{\lambda_n}$, so the caustic parameters $\lambda=(\lambda_1,...,\lambda_n)$ are integrals of the billiard map. The frequency map $\lambda \mapsto \omega$ is a key tool to understand the structure of periodic billiard trajectories. In principle, it is well-defined only for nonsingular values of the caustic parameters. We present four conjectures, fully supported by numerical experiments. The last one gives rise to some lower bounds on the periods. These bounds only depend on the type of the caustics. We describe the geometric meaning, domain, and range of $\omega$. The map $\omega$ can be continuously extended to singular values of the caustic parameters, although it becomes "exponentially sharp" at some of them. Finally, we study triaxial ellipsoids of \Rset^3. We compute numerically the bifurcation curves in the parameter space on which the Liouville tori with a fixed frequency disappear. We determine which ellipsoids have more periodic trajectories. We check that the previous lower bounds on the periods are optimal, by displaying periodic trajectories with periods four, five, and six whose caustics have the right types. We also give some new insights for ellipses of \Rset^2.Comment: 50 pages, 13 figure

Phase and Charge reentrant phase transitions in two capacitively coupled Josephson arrays with ultra-small junction

We have studied the phase diagram of two capacitively coupled Josephson junction arrays with charging energy, $E_c$, and Josephson coupling energy, $E_J$. Our results are obtained using a path integral Quantum Monte Carlo algorithm. The parameter that quantifies the quantum fluctuations in the i-th array is defined by $\alpha_i\equiv \frac{E_{{c}_i}}{E_{J_i}}$. Depending on the value of $\alpha_i$, each independent array may be in the semiclassical or in the quantum regime: We find that thermal fluctuations are important when $\alpha \lesssim 1.5$ and the quantum fluctuations dominate when $2.0 \lesssim \alpha$. We have extensively studied the interplay between vortex and charge dominated individual array phases. The two arrays are coupled via the capacitance $C_{{\rm inter}}$ at each site of the lattices. We find a {\it reentrant transition} in $\Upsilon(T,\alpha)$, at low temperatures, when one of the arrays is in the semiclassical limit (i.e. $\alpha_{1}=0.5$) and the quantum array has $2.0 \leq\alpha_{2} \leq 2.5$, for the values considered for the interlayer capacitance. In addition, when $3.0 \leq \alpha_{2} < 4.0$, and for all the inter-layer couplings considered above, a {\it novel} reentrant phase transition occurs in the charge degrees of freedom, i.e. there is a reentrant insulating-conducting transition at low temperatures. We obtain the corresponding phase diagrams and found some features that resemble those seen in experiments with 2D JJA.Comment: 25 Latex pages including 8 encapsulated poscript figures. Accepted for publication in Phys. Rev B (Nov. 2004 Issue