Doorway States and Billiards

Whenever a distinct state is immersed in a sea of complicated and dense states, the strength of the distinct state, which we refer to as a doorway, is distributed in their neighboring states. We analyze this mechanism for 2-D billiards with different geometries. One of them is symmetric and integrable, another is symmetric but chaotic, and the third has a capricious form. The fact that the doorway-state mechanism is valid for such highly diverse cases, proves that it is robust.Comment: 7 pages, 6 figures, Accepted in Proceedings of "Symmetries in Nature", Symposium in Memoriam Marcos Moshinsk

The Present and Future of Planetary Nebula Research. A White Paper by the IAU Planetary Nebula Working Group

We present a summary of current research on planetary nebulae and their central stars, and related subjects such as atomic processes in ionized nebulae, AGB and post-AGB evolution. Future advances are discussed that will be essential to substantial improvements in our knowledge in the field.Comment: accepted for publication in RMxAA; 37 page

Charge exchange in collisions of 1-100-keV Sn3+ ions with H2 and D2

Absolute cross sections for single electron capture by Sn3+ colliding with H2 and D2 have been measured and calculated in the energy range of 1-100 keV. The cross sections are determined by measuring the change in ion beam current with varying target density and by measuring the yields of charged target fragments by means of a time-of-flight spectrometer. The results for D2 show good agreement with our seven-state semiclassical calculations, while for H2 the experimental results increase more strongly than the calculations toward lower energies. This discrepancy is attributed to vibrational effects, not included in the calculations, that lead to the breakdown of the Franck-Condon approximation

Chaotic scattering with direct processes: A generalization of Poisson's kernel for non-unitary scattering matrices

The problem of chaotic scattering in presence of direct processes or prompt responses is mapped via a transformation to the case of scattering in absence of such processes for non-unitary scattering matrices, \tilde S. In the absence of prompt responses, \tilde S is uniformly distributed according to its invariant measure in the space of \tilde S matrices with zero average, < \tilde S > =0. In the presence of direct processes, the distribution of \tilde S is non-uniform and it is characterized by the average (\neq 0). In contrast to the case of unitary matrices S, where the invariant measures of S for chaotic scattering with and without direct processes are related through the well known Poisson kernel, here we show that for non-unitary scattering matrices the invariant measures are related by the Poisson kernel squared. Our results are relevant to situations where flux conservation is not satisfied. For example, transport experiments in chaotic systems, where gains or losses are present, like microwave chaotic cavities or graphs, and acoustic or elastic resonators.Comment: Added two appendices and references. Corrected typo

Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives

Analysis of smokeless powders is of interest from forensics and security perspectives. This article reports the detection of smokeless powder organic additives (in their pre-detonation condition), namely the stabiliser diphenylamine and its derivatives 2-nitrodiphenylamine and 4-nitrodiphenylamine, and the additives (used both as stabilisers and plasticisers) methyl centralite and ethyl centralite, by means of swab sampling followed by thermal desorption and direct injection soft chemical ionisation-mass spectrometry. Investigations on the product ions resulting from the reactions of the reagent ions H3O+ and O2+ with additives as a function of reduced electric field are reported. The method was comprehensively evaluated in terms of linearity, sensitivity and precision. For H3O+, the limits of detection (LoD) are in the range of 41-88 pg of additive, for which the accuracy varied between 1.5 and 3.2%, precision varied between 3.7 and 7.3% and linearity showed R20.9991. For O2+, LoD are in the range of 72 to 1.4 ng, with an accuracy of between 2.8 and 4.9% and a precision between 4.5 and 8.6% and R20.9914. The validated methodology was applied to the analysis of commercial pre-blast gun powders from different manufacturers.(VLID)4826148Accepted versio

Quantum Theory of Noncommutative Fields

Generalizing the noncommutative harmonic oscillator construction, we propose a new extension of quantum field theory based on the concept of "noncommutative fields". Our description permits to break the usual particle-antiparticle degeneracy at the dispersion relation level and introduces naturally an ultraviolet and an infrared cutoff. Phenomenological bounds for these new energy scales are given.Comment: LaTeX file, JHEP3.cls, subequations.sty; 12 pages, no figures. Final version published in JHEP with some references adde

Evaluación sistématica de la degradación de materiales sometidos al intemperismo

La necesidad de actividades de restauración y conservación del patrimonio deriva de la acción agresiva que ejercen los agentes ambientales sobre los materiales de construcción. En la actualidad, existen numerosos proyectos destinados a evaluar el comportamiento de estos materiales en ambientes de elevada agresividad, tales como las atmósferas marinas e industriales. Sin embargo, no se conocen iniciativas similares que estén orientadas al estudio de los deterioros que se producen en climas menos severos, y que en nuestro país representan las condiciones de una extensa región. Por otra parte, para diseñar las medidas de reparación y conservación de las construcciones resulta indispensable contar con herramientas que permitan evaluar en forma sistemática el comportamiento de los materiales y la evolución de los deterioros que ellos sufren, a fin de determinar las causas de degradación. Posteriormente, estas mismas herramientas deben permitir monitorear la efectividad de los métodos de reparación aplicados. Los profesionales que desean conocer con certeza el comportamiento de los materiales ante el paso del tiempo y su respuesta ante las distintas condiciones de exposición deben recurrir a datos suministrados por el fabricante o antecedentes existentes en la bibliografía específica y provenientes de investigaciones realizadas al respecto. Muchas de estas fuentes se encuentran desactualizadas, no corresponden a las condiciones de exposición específicas o bien carecen de valor técnico. El CECOVI, dentro de las actividades de investigación y desarrollo de materiales de construcción y sistemas constructivos que lleva adelante, está desarrollando un proyecto que tiene por objetivo principal el abordaje sistemático de la problemática de la durabilidad de los materiales de construcción sometidos a la acción de la intemperie y su aptitud en servicio. Este proyecto se circunscribe, actualmente, al estudio de la durabilidad de hormigones convencionales y elaborados con agregados livianos, hormigones celulares, madera, suelocemento y materiales plásticos, mientras que el tipo de exposición se limita a las condiciones de intemperismo habituales en un clima templado húmedo, de acuerdo a la clasificación establecida por el Sistema Internacional de Koeppen. Paralelamente, se realizan contrastes con materiales mantenidos en condiciones de laboratorio que actúan como patrones de comparación. Los ejes fundamentales planteados están constituidos por el análisis teórico, el seguimiento sistemático del comportamiento de materiales ante condiciones reales de exposición y en condiciones de envejecimiento acelerado, tendientes al establecimiento de una metodología de evaluación de aplicabilidad general, correlaciones entre el deterioro de los materiales y variables ambientales típicas de la región y el desarrollo de técnicas que permitan predecir su vida útil

Electroactive tape extrusion : influence of processing conditions on the β-phase content of PVDF samples

Poly(vinylidene fluoride), PVDF, in its polar β-phase, is known to possess strong piezoelectric properties, among polymers. The α phase of PVDF is the most stable phase when the polymer crystallizes from the melt. In this way, the electroactive phase of the material is commonly obtained by inducing the α to β phase transformation through mechanical stretching at a given temperature, being the stretch ratio and temperature the most important parameters influencing the phase transformation [1]. Further, it has been demonstrated that the electroactive response of the material strongly depends on the β-phase and therefore on the processing conditions [2]. In the present work, the effect of processing variables in the content of β-phase PVDF extruded tape, namely the stretching ratio and process temperatures, was studied. For comparison purposes the produced samples were uniaxially stretched with ratios of up to 6, in the extrusion line (in-line) and in a tensile tester (off-line), at both 80ºC and 120ºC. The β-phase content was analysed by Fourier transform infrared spectroscopy (FTIR) and the electroactive phase content was correlated to the electroactive response of the material, obtained through the measurement of the d33 piezoelectric coefficient. The results obtained allowed to identify the most important parameters influencing the amount of the β-phase content and will be used as guidance for the development of a large scale production process for multilayer products with piezoelectric properties.FCT- Portuguese Foundation for Science and Technology through the project PTDC/CTM/108801/2008 and FEDER via FCT, Fundação para a Ciência e Tecnologia, under the POCI 2010 and Pluriannual program