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

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

Hydrogen and muonium in diamond: A path-integral molecular dynamics simulation

Isolated hydrogen, deuterium, and muonium in diamond have been studied by path-integral molecular dynamics simulations in the canonical ensemble. Finite-temperature properties of these point defects were analyzed in the range from 100 to 800 K. Interatomic interactions were modeled by a tight-binding potential fitted to density-functional calculations. The most stable position for these hydrogenic impurities is found at the C-C bond center. Vibrational frequencies have been obtained from a linear-response approach, based on correlations of atom displacements at finite temperatures. The results show a large anharmonic effect in impurity vibrations at the bond center site, which hardens the vibrational modes with respect to a harmonic approximation. Zero-point motion causes an appreciable shift of the defect level in the electronic gap, as a consequence of electron-phonon interaction. This defect level goes down by 70 meV when replacing hydrogen by muonium.Comment: 11 pages, 8 figure

Branchiosyllis salazari sp. n. (Polychaeta, Syllidae) del Caribe noroccidental y comentarios sobre el material tipo de B. exilis (Gravier, 1900)

Basándonos en el estudio de 195 ejemplares procedentes del Caribe Noroccidental, se describe una nueva especie de Branchiosyllis Ehlers, 1887. Branchiosyllis salazari sp. n. tiene tres pares de ojos (dos pares pequeños en el margen anterior del prostomio, el tercer par está en una línea transversal), sin branquias, sedas con artejo en forma de ganchos grandes ya en los setígeros medios, y proventrículo sin línea mediodorsal. El material tipo de B. exilis (Gravier, 1900), una especie aparentemente circuntropical, fue revisado para clarificar su presencia en el Mar Caribe. Sus características diagnósticas son: dos pares de ojos en una línea transversa, sin branquias, sedas con artejo en forma de gancho grande restringidas a los setígeros posteriores y proventrículo con una línea mediadorsal de células en forma de diamante. Se anexa una clave para las siete especies de Branchiosyllis en el Gran Caribe. Palabras clave: Branchiosyllis salazari sp. n., Taxonomía, Gran Caribe, Syllidae, Polychaeta.On the basis of 195 specimens from the Northwestern Caribbean Sea, a new species of Branchiosyllis Ehlers, 1887 is described. Branchiosyllis salazari n. sp. has three pairs of eyes (two small pairs above the anterior margin of the prostomium, the third pair in a transverse line), without branchia, setae with large hooked blades in median setigers, and proventricle without middorsal line. The type material of B. exilis (Gravier, 1900), an apparently circumtropical species, was revised to clarify its presence in the Caribbean Sea. Its diagnostic features are: two pairs of eyes in a transverse line, no branchia, setae with large hooked blades in posterior setigers only, and proventricle with a middorsal line of Diamond-shaped cells. A key for the seven species of Branchiosyllis in the Grand Caribbean is included. Key words: Branchiosyllis salazari n. sp., Taxonomy, Grand Caribbean, Syllidae, Polychaeta.Basándonos en el estudio de 195 ejemplares procedentes del Caribe Noroccidental, se describe una nueva especie de Branchiosyllis Ehlers, 1887. Branchiosyllis salazari sp. n. tiene tres pares de ojos (dos pares pequeños en el margen anterior del prostomio, el tercer par está en una línea transversal), sin branquias, sedas con artejo en forma de ganchos grandes ya en los setígeros medios, y proventrículo sin línea mediodorsal. El material tipo de B. exilis (Gravier, 1900), una especie aparentemente circuntropical, fue revisado para clarificar su presencia en el Mar Caribe. Sus características diagnósticas son: dos pares de ojos en una línea transversa, sin branquias, sedas con artejo en forma de gancho grande restringidas a los setígeros posteriores y proventrículo con una línea mediadorsal de células en forma de diamante. Se anexa una clave para las siete especies de Branchiosyllis en el Gran Caribe. Palabras clave: Branchiosyllis salazari sp. n., Taxonomía, Gran Caribe, Syllidae, Polychaeta

Aprovechamiento de residuos industriales para la síntesis de clínker belítico

The synthesis of belite clinker was studied using industrial wastes: paper sludge, cement kiln dust and rice husk ashes, as substitutes for natural raw materials. Wastes were characterized by XRF, XRD and TG analysis. Different formulations were prepared to produce clinker at 1300, 1350 and 1400 °C. The clinker obtained was characterized using optical microscopy, XRD and f-CaO content determined by ethylene glycol method. Finally, the hydration of prepared cements with the clinkers was evaluated by isothermal microcalo­rimetry. It was found that by mixing paper sludge, cement kiln dust and rice husk ashes, it is possible to obtain belite clinker with f-CaO content below 0.5%, in clinkering temperatures between 1350 °C and 1400 °C without the use of natural raw materials. It was found that these cements have a high hydration kinetic, far above the rate of Ordinary Portland Cement, due mainly by the amorphous phase content in clinkers obtained.En el presente trabajo se estudió la síntesis de clínker belítico usando residuos industriales: lodo papelero, polvo de horno de cemento y ceniza de cascarilla de arroz, como sustitutos de las materias primas naturales. Los residuos se caracterizaron mediante FRX, DRX y TGA. Se prepararon formulaciones para producir clínker a 1300, 1350 y 1400 °C. El clínker se caracterizó usando microscopía óptica, DRX y f-CaO. Finalmente, se evaluó la hidratación de cementos preparados a partir de los clínkeres obtenidos. Se encontró que, con lodo papelero, polvo de horno de cemento y ceniza de cascarilla de arroz, es posible obtener clínker belítico con contenidos de f-CaO ≤ 0,5%, a temperaturas entre 1350 y 1400 °C sin el uso de materias primas de origen natural. Se encontró una alta cinética de hidratación, muy por encima de la velocidad de hidratación de un cemento Portland convencional, principal­mente debido al contenido de fase amorfa en los clínkeres obtenidos

Scaling properties of granular materials

Given an assembly of viscoelastic spheres with certain material properties, we raise the question how the macroscopic properties of the assembly will change if all lengths of the system, i.e. radii, container size etc., are scaled by a constant. The result leads to a method to scale down experiments to lab-size.Comment: 4 pages, 2 figure

General Non-equilibrium Theory of Colloid Dynamics

A non-equilibrium extension of Onsager's canonical theory of thermal fluctuations is employed to derive a self-consistent theory for the description of the statistical properties of the instantaneous local concentration profile n(r,t) of a colloidal liquid in terms of the coupled time evolution equations of its mean value n(r,t) and of the covariance {\sigma}(r,r';t) \equiv of its fluctuations {\delta}n(r, t) = n(r, t) - n(r, t). These two coarse-grained equations involve a local mobility function b(r, t) which, in its turn, is written in terms of the memory function of the two-time correlation function C(r, r' ; t, t') \equiv <{\delta}n(r, t){\delta}n(r',t')>. For given effective interactions between colloidal particles and applied external fields, the resulting self-consistent theory is aimed at describing the evolution of a strongly correlated colloidal liquid from an initial state with arbitrary mean and covariance n^0(r) and {\sigma}^0(r,r') towards its equilibrium state characterized by the equilibrium local concentration profile n^(eq)(r) and equilibrium covariance {\sigma}^(eq)(r,r'). This theory also provides a general theoretical framework to describe irreversible processes associated with dynamic arrest transitions, such as aging, and the effects of spatial heterogeneities