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

Linear active disturbance rejection control of the hovercraft vessel model

A linearizing robust dynamic output feedback control scheme is proposed for earth coordinate position variables trajectory tracking tasks in a hovercraft vessel model. The controller design is carried out using only position and orientation measurements. A highly simplified model obtained from flatness considerations is proposed which vastly simplifies the controller design task. Only the order of integration of the input-to-flat output subsystems, along with the associated input matrix gain, is retained in the simplified model. All the unknown additive nonlinearities and exogenous perturbations are lumped into an absolutely bounded, unstructured, vector of time signals whose components may be locally on-line estimated by means of a high gain Generalized Proportional Integral (GPI) observer. GPI observers are the dual counterpart of GPI controllers providing accurate simultaneous estimation of each flat output associated phase variables and of the exogenous and endogenous perturbation inputs. These observers exhibit remarkably convenient self-updating internal models of the unknown disturbance input vector components. These two key pieces of on-line information are used in the proposed feedback controller to conform an active disturbance rejection, or disturbance accommodation, control scheme. Simulation results validate the effectiveness of the proposed design method

Control of a DC motor using algebraic derivative estimation with real time experiments

This paper presents an experimental control scheme for DC motors which combines an overlapping implementation of the algebraic derivative estimation method and a disturbance estimator based on the aforementioned algebraic derivative method. The methodology only requires the measurement of the angular position of the motor and the voltage input to the motor. The main advantages of the proposed approach are: it is independent of the motor’s initial conditions, the methodology is robust to Coulomb friction effects, it does not require any statistical knowledge of the noises that corrupt the data, the derivative estimation process does not require initial conditions or dependence between the system input and output, and the algorithm is computed on-line and in real time. The effectiveness of the proposed controller has been verified by means of computer simulations and it has also been experimentally implemented on a laboratory prototype with excellent results in both, stabilization and trajectory tracking tasks

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

First case of isolation of Nocardia wallacei reported in Mexico

AbstractNocardia species are aerobic, Gram-positive bacteria with branched filaments reported as opportunistic microorganisms associated with infectious diseases of the skin. We report the isolation of N. wallacei in Mexico from a 43-year-old man, an HIV-positive construction worker who sought care for difficulty breathing and abundant sputum

New Spectroscopy of U Gem

We present new optical spectroscopic observations of U Geminorum obtained during a quiescent stage. We performed a radial velocity analysis of three Balmer emission lines yielding inconsistent results. Assuming that the radial velocity semi amplitude accurately reflects the motion of the white dwarf, we arrive at masses for the primary which are in the range of M_wd= 1.21 - 1.37 M_Sun. Based on the internal radial velocity inconsistencies and results produced from the Doppler tomography -- wherein we do not detect emission from the hot spot, but rather an intense asymmetric emission overlaying the disc, reminiscent of spiral arms -- we discuss the possibility that the overestimation of the masses may be due to variations of gas opacities and a partial truncation of the disc.Comment: 16 pages, 10 figures, 3 tables, to be published on RevMexAA. arXiv admin note: text overlap with arXiv:2112.0343

Analysis of the Influence of the Molecular Volume to Predict Experimental Pressure-Temperature Behavior in the Isotropic-Nematic Phase Transition of PAP, 5CB, MBBA and EBBA

In this work, we have analyzed the experimental pressure-temperature behavior at the isotropic-nematic phase transition of the liquid crystals PAP, 5CB, MBBA, and EBBA at 1 atm by using the HERSW Convex Peg model in conjunction with the IPCM model. We have calculated the molecular volume values for the hard and attractive cores from theoretical quantum calculations at the PM3, PM6, B3LYP/6-311++G(d,p)//PM6, and M06/6-311++G(d,p)//PM6 levels of theory. The results suggest that the best theoretical prediction of the experimental pressure-temperature behavior is obtained when the molecular volume is evaluated at the DFT level.En este trabajo, nosotros analizamos el comportamiento experimental presión-temperatura pa la fase de transición Isotrópica-nemática de los cristales líquidos PAP, 5CB, MBBA, y EBBA a 1 atm usando el modelo HERSW Convex Peg en conjunto con el modelo IPCM. Nosotros calculamos el valor del volumen molecular y cálculos teóricos para los niveles PM3, PM6, B3LyP/6-311++G(d,p)//PM& y M06/6-311++(d,p)//PM6. Los resultados sugieren que la mejor predicción del comportamiento experimental presión-temperatura es obtenido cuando el volumen molecular es evaluado para el nivel DFT

El audiorae como estrategia para la visibilización de las comprensiones de los profesores de ciencias naturales

The purpose of the workshop is to recognize the AUDIORAE as a strategy to make students' comprehensions visible and as a means of evaluating the actions undertaken in the natural science classroom. The AUDIORAE involves in its production elements of information analysis through an academic summary of writings, and in its communication through a short audio recording that contains the central ideas and critical thinking. In this workshop, correlated actions are developed, such as the "Generate, Classify, Connect and Elaborate" (GCCE) thinking routine, designed for the construction of conceptual maps that demonstrate mental models (Ritchhart, 2015) from the capacity for synthesis and the relationship of ideas; and the production of an audio whose purpose is to make visible the comprehensions of a text, video or classroom exercise, in addition to the metacognitive process that accompanies the whole exercise. Together the two actions have been called AUDIORAE, concept proposed from the product that is obtained, a short audio and the medium that involves in relation to the analytical summary of writings (RAE).El propósito del taller es reconocer el AUDIORAE como estrategia de visibilización de las comprensiones de los estudiantes y como medio de evaluación de las acciones emprendidas en el aula de ciencias naturales. El AUDIORAE involucra en su producción elementos de análisis de información a través de un resumen académico de escritos, y en su comunicación a través de una grabación corta en audio que contenga las ideas centrales y pensamiento crítico. En este taller, se desarrollan acciones correlacionadas como la rutina de pensamiento “Generar, Clasificar, Conectar y Elaborar (GCCE)” pensada para la construcción de mapas conceptuales que evidencian modelos mentales (Ritchhart, 2015) desde la capacidad de síntesis y relación de ideas; y la producción de un audio cuyo fin es hacer visibles las comprensiones de un texto, video o ejercicio de aula, además del proceso metacognitivo que acompaña todo el ejercicio. En conjunto las dos acciones han sido denominadas AUDIORAE, concepto propuesto desde el producto que se obtiene, un audio de corta duración y el medio que involucra en relación con el resumen analítico de escritos (RAE)