A new class of symbolic abstract neural nets

Starting from the way the inter-cellular communication takes place by means of protein channels and also from the standard knowledge about neuron functioning, we propose a computing model called a tissue P system, which processes symbols in a multiset rewriting sense, in a net of cells similar to a neural net. Each cell has a finite state memory, processes multisets of symbol-impulses, and can send impulses (?excitations?) to the neighboring cells. Such cell nets are shown to be rather powerful: they can simulate a Turing machine even when using a small number of cells, each of them having a small number of states. Moreover, in the case when each cell works in the maximal manner and it can excite all the cells to which it can send impulses, then one can easily solve the Hamiltonian Path Problem in linear time. A new characterization of the Parikh images of ET0L languages are also obtained in this framework.

Solving SAT in linear time with a neural-like membrane system

We present in this paper a neural-like membrane system solving the SAT problem in linear time. These neural Psystems are nets of cells working with multisets. Each cell has a finite state memory, processes multisets of symbol-impulses, and can send impulses (?excitations?) to the neighboring cells. The maximal mode of rules application and the replicative mode of communication between cells are at the core of the eficiency of these systems.

Measurements and Prediction of Pedestrian Walking Loads on an Aluminium Catwalk

During the last two decades the topic of human induced vibration has attracted a lot of attention among civil engineering practitioners and academics alike. Usually this type of problem may be encountered in pedestrian footbridges or floors of paperless offices. Slender designs are becoming increasingly popular, and as a consequence, the importance of paying attention to vibration serviceability also increases. This paper resumes the results obtained from measurements taken at different points of an aluminium catwalk which is 6 m in length by 0.6 m in width. Measurements were carried out when subjecting the structure to different actions:1)Static test: a steel cylinder of 35 kg was placed in the middle of the catwalk; 2)Dynamic test: this test consists of exciting the structure with singles impulses; 3)Dynamic test: people walking on the catwalk. Identification of the mechanical properties of the structure is an achievement of the paper. Indirect methods were used to estimate properties including the support stiffness, the beam bending stiffness, the mass of the structure (using Rayleigh method and iterative matrix method), the natural frequency (using the time domain and frequency domain analysis) and the damping ratio (by calculating the logarithmic decrement). Experimental results and numerical predictions for the response of an aluminium catwalk subjected to walking loads have been compared. The damping of this light weight structure depends on the amplitude of vibration which complicates the tuning of a structural model. In the light of the results obtained it seems that the used walking load model is not appropriate as the predicted transient vibration values (TTVs) are much higher than the measured ones.

Habitar lo irreal. aproximaciones a una arquitectónica de los mundos virtuales

Lo virtual es el lugar donde todo empieza, el germen de la imaginación productiva, un ámbito de pulsiones inaugurales y preexistencias sin forma donde todo convive, a la espera de ser diferenciado. Lo virtual es el sitio donde nacen las primeras exploraciones de cualquier acto de concepción, incluida la creación artística o el proyectar arquitectónico. Sin embargo, en las últimas tres décadas de revolución digital, el término ha sido utilizado de forma abusiva para referirse a todo tipo de entornos simulados informáticamente, es decir, a ficciones cerradas, programadas, controladas por el software y sus rutinas, radicalmente actualizadas, acabadas, completas, formalizadas. Paradójicamente, lo virtual ha servido para nombrar construcciones profundamente anti-virtuales. La telemática está propiciando el acceso del ser humano a un nuevo tipo de irrealidad cotidiana sustentada en prácticas espaciales cada vez menos vinculadas con la física y la biología. Esta condición fantasmagórica del habitar digital exige nuevos espacios de diálogo entre arquitectura y tecnología que se centren en el hecho imaginario. Para ello esta tesis propone —a partir de la recuperación del término griego arquitectónica— llevar el alcance de la disciplina hasta el hecho global del habitar. Y, al mismo tiempo, devolver al adjetivo virtual su auténtico significado preliminar, entendiendo que los verdaderos mundos virtuales no pueden simular nada, representar nada, formalizar nada, porque ellos son el origen infinito y amorfo de todo mundo. ABSTRACT The virtual is where it all starts, the seed of productive imagination, an area of inaugural impulses and formless preexistences that beat together, waiting to be differentiated. The virtual is the birthplace of any creative exploration, including those of the architectural project. However, in the last three decades of digital revolution, the term has been mostly misused to refer to all types of computer simulated environments; shut, finished, complete, formalized, radically actualized fictions controlled by software routines. Paradoxically, the virtual has been giving name to profoundly anti-virtual constructions. Telematics is allowing humans to access to a new kind of unreality, based on everyday spatial practices that are increasingly detached from physics and biology. This spectral condition of the digital living demands new dialectics between architecture and technology, focused on the imaginary. This thesis proposes — beginning by recovering the Greek word architectonics— to extend the scope of the discipline beyond edification to the overall fact of inhabiting. And, at the same time, to return to the adjective virtual its authentic preliminary meaning, realizing that the true virtual worlds cannot simulate, represent or formalize anything because they are the amorphous and endless source of every world.

Acoustic characterization of open cavities with the image source model

El objetivo de esta tesis es investigar las resonancias acústicas de una cavidad abierta tridimensional, de paredes rectas o inclinadas, mediante un método rápido y eficiente en el dominio del tiempo. Este método modela la respuesta temporal en cualquier punto como la convolución de la forma de onda de la fuente con la respuesta impulsiva de la cavidad, la cual se obtiene como una secuencia de impulsos retardados y atenuados procedentes de la fuente real, el primero, y de las fuentes imágenes especulares, los siguientes (Modelo Fuente Imagen, ISM). Además de las componentes directa y reflejadas en las paredes, la respuesta impulsiva también incluye las contribuciones difractadas en los bordes, obtenidas mediante la generación de las componentes difractadas de cada fuente imagen. Las frecuencias de resonancia acústica de la cavidad abierta son extraídas de los picos de la Función de Respuesta en Frecuencia (FRF), obtenida como la transformada de Fourier de la respuesta temporal correspondiente entre una fuente puntual y un punto cualquiera de la cavidad. Las frecuencias de resonancia acústicas estimadas mediante este Método de Fuentes Imagen + difracción en bordes son validadas por comparación con las que proporciona un Modelo de Elementos Finitos (FEM) y con las medidas experimentalmente, con diferencias menores que el 1.6 % y el 2.7 %, respectivamente. A modo de comparación, las frecuencias de resonancia estimadas para la misma cavidad por el método ISM, cuando no se incluye la difracción en los bordes, difieren en un 5.7 % de las obtenidas experimentalmente. ABSTRACT The goal of this thesis is to investigate the acoustic resonances of a three-dimensional open cavity, with parallel and non-parallel walls, by a fast and efficient method in the time domain. This method models the time response in any point as the convolution of the source waveform with the impulse response of the cavity, which, in turn, is obtained as a sequence of attenuated and delayed impulses coming, the first from the real, and the subsequent from the mirror imaged sources (Image Source Model). Besides direct and wall-reflected components, the impulse response includes also edge-diffracted contributions by generating first order diffraction components for each image source. The acoustic resonance frequencies of the open cavity are extracted from the peaks of the Frequency Response Function (FRF), obtained as the Fourier transform of the corresponding time response between a point source and any point in the cavity. The acoustic resonance frequencies estimated by the Image Source Model + edge diffraction are validated by comparison with those provided by a Finite Element Model (FEM) and the ones measured experimentally, differing less than 1.6 % and 2.7 %, respectively. As a comparison, resonance frequencies estimated with the pure Image Source Model differ by 5.7 % from the measured ones.