Fokker-Planck and Langevin Equations from Forward--Backward Path Integral

Starting from a forward--backward path integral of a point particle in a bath of harmonic oscillators, we derive the Fokker-Planck and Langevin equations with and without inertia. Special emphasis is placed upon the correct operator order in the time evolution operator. The crucial step is the evaluation of a Jacobian with a retarded time derivative by analytic regularization.Comment: Author Information under http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of paper (including all PS fonts) at http://www.physik.fu-berlin.de/~kleinert/31

Dismembered and non-dismembered retroperitoneoscopic pyeloplasty for the treatment of ureteropelvic junction obstruction in children

Purpose: Open dismembered pyeloplasty according to Anderson-Hynes (AHP) is the gold standard treatment for ureteropelvic junction obstruction in children. However, during the last decade, the management has been revolutionized with introduction of laparoscopy and endourology yielding comparable results and less morbid outcomes. Methods: Between 1997 and 2010, dismembered and non-dismembered retroperitoneoscopic pyeloplasty was performed in 41 children with a median age of 130month (range 5-192). 20 children underwent a dismembered pyeloplasty (Anderson-Hynes) and 21 children were operated by a non-dismembered pyeloplasty (Y-V-Plasty). Results: The mean operation time was 120min (range 52-257). Intraoperative findings revealed in 29 cases a significant crossing vessel. Based on a furosemide nephrogram and subjective complaints, the success rate was 88% with a median follow-up of 69month (range 14-142). The 5 failures (2 Y-V-Plasty, 3 AHP) have been treated by open AHP (n=2), Laser endopyelotomy (n=2) and Lap-AHP (n=1) without further problems. Conclusion: With increasing improvement of the suture techniques, the laparoscopic pyeloplasty represents in experienced hands an alternative method with comparable success rates to the open technique. In our opinion, retroperitoneoscopic pyeloplasty is technically possible and feasible even in infants. We found in our series no statistically significant difference between dismembered and non-dismembered pyeloplast

Condensation of Ideal Bose Gas Confined in a Box Within a Canonical Ensemble

We set up recursion relations for the partition function and the ground-state occupancy for a fixed number of non-interacting bosons confined in a square box potential and determine the temperature dependence of the specific heat and the particle number in the ground state. A proper semiclassical treatment is set up which yields the correct small-T-behavior in contrast to an earlier theory in Feynman's textbook on Statistical Mechanics, in which the special role of the ground state was ignored. The results are compared with an exact quantum mechanical treatment. Furthermore, we derive the finite-size effect of the system.Comment: 18 pages, 8 figure

The non-linear Schr\"odinger equation and the conformal properties of non-relativistic space-time

The cubic non-linear Schr\"odinger equation where the coefficient of the nonlinear term is a function $F(t,x)$ only passes the Painlev\'e test of Weiss, Tabor, and Carnevale only for $F=(a+bt)^{-1}$, where $a$ and $b$ are constants. This is explained by transforming the time-dependent system into the constant-coefficient NLS by means of a time-dependent non-linear transformation, related to the conformal properties of non-relativistic space-time. A similar argument explains the integrability of the NLS in a uniform force field or in an oscillator background.Comment: Thoroughly revised version, in the light of new interest in non-relativistic conformal tranformation, with a new reference list. 8 pages, LaTex, no figures. To be published in Int. J. Theor. Phy

Real-time distance measurement immune from atmospheric parameters using optical frequency combs

We propose a direct and real-time ranging scheme using an optical frequency combs, able to compensate optically for index of refraction variations due to atmospheric parameters. This scheme could be useful for applications requiring stringent precision over a long distance in air, a situation where dispersion becomes the main limitation. The key ingredient is the use of a mode-locked laser as a precise source for multi-wavelength interferometry in a homodyne detection scheme. By shaping temporally the local oscillator, one can directly access the desired parameter (distance) while being insensitive to fluctuations induced by parameters of the environment such as pressure, temperature, humidity and CO$_2$ content

SEMANTIC MAPPING THOUGH NEURAL NETWORKS: THE SELF-ORGANIZING MAPS (SOM) AS REPRESENTATION OF PATTERNS AND FIELDS

[EN] The Science of Artificial Intelligence provides us with techniques to improve our understanding and characterization of the coherences and patterns which constitute reality. Among these, artificial neural networks and more specifically Self Organizing Maps (SOM) stand out because of their ability to map reality in such a way that their objectives are represented distributed and structured two-dimensionally, with their properties as a single starting point. In this way an entire series of topological relations is generated, which in their turn enable the grouping and characterization of reality. In this research these representations are explored as a valid method to obtain information and to interpret reality. By means of experimentation this kind of methods are implemented to further understanding of diverse exemplary residential fabrics, while obtaining a typological grouping which enables the characterization of urban forms starting from their defining variables[ES] Las ciencias de la Inteligencia Artificial proporcionan técnicas para la comprensión y caracterización de las coherencias y de los patrones que constituyen la realidad. Entre ellas destacan las redes neuronales artificiales y concretamente los Mapas Auto-organizados (SOM) por su capacidad de cartografiar la realidad, representando sus objetivos distribuidos estructurados bidimensionalmente, a partir únicamente de sus propiedades. Se generan así toda una serie de relaciones topológicas que permiten a su vez la agrupación y caracterización de la realidad. En la investigación se exploran estas representaciones como método válido de obtención de información e interpretación de la realidad. Como experimentación se implementan tales técnicas para la comprensión de diversos tejidos residenciales ejemplares, obteniéndose un agrupamiento tipológico que permite caracterizar las formas urbanas a partir de sus variables definidoras.Abarca-Alvarez, FJ.; Osuna Pérez, F. (2013). Cartografías semánticas mediante redes neuronales: los mapas auto-organizados (SOM) como representación de patrones y campos. EGA. Revista de Expresión Gráfica Arquitectónica. 18(22):154-163. doi:10.4995/ega.2013.1692.SWORD154163182

Strengthening the Case for Asteroidal Accrection: Evidence for Subtle and Diverse Disks at White Dwarfs

Spitzer Space Telescope IRAC 3-8 micron and AKARI IRC 2-4 micron photometry are reported for ten white dwarfs with photospheric heavy elements; nine relatively cool stars with photospheric calcium, and one hotter star with a peculiar high carbon abundance. A substantial infrared excess is detected at HE 2221-1630, while modest excess emissions are identified at HE 0106-3253 and HE 0307+0746, implying these latter two stars have relatively narrow (Delta r < 0.1 Rsol) rings of circumstellar dust. A likely 7.9 micron excess is found at PG 1225-079 and may represent, together with G166-58, a sub-class of dust ring with a large inner hole. The existence of attenuated disks at white dwarfs substantiates the connection between their photospheric heavy elements and the accretion of disrupted minor planets, indicating many polluted white dwarfs may harbor orbiting dust, even those lacking an obvious infrared excess.Comment: 13 pages, emulateapj, accepted to Ap

Smearing Formula for Higher-Order Effective Classical Potentials

In the variational approach to quantum statistics, a smearing formula describes efficiently the consequences of quantum fluctuations upon an interaction potential. The result is an effective classical potential from which the partition function can be obtained by a simple integral. In this work, the smearing formula is extended to higher orders in the variational perturbation theory. An application to the singular Coulomb potential exhibits the same fast convergence with increasing orders that has been observed in previous variational perturbation expansions of the anharmonic oscillator with quartic potential.Comment: Author Information under http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of paper also at http://www.physik.fu-berlin.de/~kleinert/kleiner_re267/preprint.htm

Scattering From a Two Dimensional Array of Flux Tubes: A Study of The Validity of Mean Field Theory

Mean Field Theory has been extensively used in the study of systems of anyons in two spatial dimensions. In this paper we study the physical grounds for the validity of this approximation by considering the Quantum Mechanical scattering of a charged particle from a two dimensional array of magnetic flux tubes. The flux tubes are arranged on a regular lattice which is infinitely long in the ``$y$'' direction but which has a (small) finite number of columns in the ``$x$'' direction. Their physical size is assumed to be infinitesimally small. We develop a method for computing the scattering angle as well as the reflection and transmission coefficients to lowest order in the Aharonov--Bohm interaction. The results of our calculation are compared to the scattering of the same particle from a region of constant magnetic field whose magnitude is equal to the mean field of all the flux tubes. For an incident plane wave, the Mean Field approximation is shown to be valid provided the flux in each tube is much less than a single flux quantum. This is precisely the regime in which Mean Field Theory for anyons is expected to be valid. When the flux per tube becomes of order 1, Mean Field Theory is no longer valid.Comment: 23 pages, University of British Columbia Preprint UBCTP93-01