Mechanical properties and the evolution of matrix molecules in PTFE upon irradiation with MeV alpha particles

The morphology, chemical composition, and mechanical properties in the surface region of α-irradiated polytetrafluoroethylene (PTFE) have been examined and compared to unirradiated specimens. Samples were irradiated with 5.5 MeV 4He2+ ions from a tandem accelerator to doses between 1 × 106 and 5 × 1010 Rad. Static time-of-flight secondary ion mass spectrometry (ToF-SIMS), using a 20 keV C60+ source, was employed to probe chemical changes as a function of a dose. Chemical images and high resolution spectra were collected and analyzed to reveal the effects of a particle radiation on the chemical structure. Residual gas analysis (RGA) was utilized to monitor the evolution of volatile species during vacuum irradiation of the samples. Scanning electron microscopy (SEM) was used to observe the morphological variation of samples with increasing a particle dose, and nanoindentation was engaged to determine the hardness and elastic modulus as a function of a dose. The data show that PTFE nominally retains its innate chemical structure and morphology at a doses <109 Rad. At α doses ≥109 Rad the polymer matrix experiences increased chemical degradation and morphological roughening which are accompanied by increased hardness and declining elasticity. At  α doses >1010 Rad the polymer matrix suffers severe chemical degradation and material loss. Chemical degradation is observed in ToF-SIMS by detection of ions that are indicative of fragmentation, unsaturation, and functionalization of molecules in the PTFE matrix. The mass spectra also expose the subtle trends of crosslinking within the α-irradiated polymer matrix. ToF-SIMS images support the assertion that chemical degradation is the result of a particle irradiation and show morphological roughening of the sample with increased a dose. High resolution SEM images more clearly illustrate the morphological roughening and the mass loss that accompanies high doses of a particles. RGA confirms the supposition that the outcome of chemical degradation in the PTFE matrix with continuing irradiation is evolution of volatile species resulting in morphological roughening and mass loss. Finally, we reveal and discuss relationships between chemical structure and mechanical properties such as hardness and elastic modulus.

The evolution of learning systems:to Bayes or not to be

Bayesian algorithms pose a limit to the performance learning algorithms can achieve. Natural selection should guide the evolution of information processing systems towards those limits. What can we learn from this evolution and what properties do the intermediate stages have? While this question is too general to permit any answer, progress can be made by restricting the class of information processing systems under study. We present analytical and numerical results for the evolution of on-line algorithms for learning from examples for neural network classifiers, which might include or not a hidden layer. The analytical results are obtained by solving a variational problem to determine the learning algorithm that leads to maximum generalization ability. Simulations using evolutionary programming, for programs that implement learning algorithms, confirm and expand the results. The principal result is not just that the evolution is towards a Bayesian limit. Indeed it is essentially reached. In addition we find that evolution is driven by the discovery of useful structures or combinations of variables and operators. In different runs the temporal order of the discovery of such combinations is unique. The main result is that combinations that signal the surprise brought by an example arise always before combinations that serve to gauge the performance of the learning algorithm. This latter structures can be used to implement annealing schedules. The temporal ordering can be understood analytically as well by doing the functional optimization in restricted functional spaces. We also show that there is data suggesting that the appearance of these traits also follows the same temporal ordering in biological systems. © 2006 American Institute of Physics.

Impact of third-order dispersion on the evolution of parabolic pulses

We present a perturbation analysis that describes the effect of third-order dispersion on the similariton pulse solution of the nonlinear Schrödinger equation in a fibre gain medium. The theoretical model predicts with sufficient accuracy the pulse structural changes induced, which are observed through direct numerical simulations.

Tracing the evolution of physics on the backbone of citation networks

Many innovations are inspired by past ideas in a nontrivial way. Tracing these origins and identifying scientific branches is crucial for research inspirations. In this paper, we use citation relations to identify the descendant chart, i.e., the family tree of research papers. Unlike other spanning trees that focus on cost or distance minimization, we make use of the nature of citations and identify the most important parent for each publication, leading to a treelike backbone of the citation network. Measures are introduced to validate the backbone as the descendant chart. We show that citation backbones can well characterize the hierarchical and fractal structure of scientific development, and lead to an accurate classification of fields and subfields. © 2011 American Physical Society.

The evolution of the car-making industry

Mass-production, cars, pollution – they all have long become well known and well connected phenomena of the modern life. Nowadays the people can also add to the list such items like awareness, scientific approach, long-term thinking, and environmental responsibility. They are surrounded by a multitude of consumer goods, most of which are produced in a scientific manner, and all of which will more sooner than later end up in the garbage. Cars are the most noticeable – both by size and by numbers – and also the most expensive of all the mass products in people’s view. For many of them they are a clear target for reprimand and regulation, and, as a result, the automotive industry is being increasingly brought under bureaucratic control, together with its whole supplier and distributor network. The author started writing this article in an attempt to place the above process under scrutiny, because it is his firm belief that similar measures, similar tough governmental control will inevitably spill over to other industries, which at the moment are producing more inconspicuous, but still polluting products. The present paper shows the relationship between car-making, supply chain management and the efforts of public administration to protect the environment – a connection with clear practical implications.

Unravelling the evolution of autumn colours: an interdisciplinary approach.

Leaf colour change is commonly observed in temperate deciduous forests in autumn. This is not simply a side effect of leaf senescence, and, in the past decade, several hypotheses have emerged to explain the evolution of autumn colours. Yet a lack of crosstalk between plant physiologists and evolutionary ecologists has resulted in slow progress, and so the adaptive value of this colour change remains a mystery. Here we provide an interdisciplinary summary of the current body of knowledge on autumn colours, and discuss unresolved issues and future avenues of research that might help reveal the evolutionary meaning of this spectacle of nature.

Phylogenetic and ecological significance in the evolution of Cetacean tonal sounds

Cetaceans are aquatic mammals that rely primarily on sound for most daily tasks. A compendium of sounds is emitted for orientation, prey detection, and predator avoidance, and to communicate. Communicative sounds are among the most studied Cetacean signals, particularly those referred to as tonal sounds. Because tonal sounds have been studied especially well in social dolphins, it has been assumed these sounds evolved as a social adaptation. However, whistles have been reported in ‘solitary’ species and have been secondarily lost three times in social lineages. Clearly, therefore, it is necessary to examine closely the association, if any, between whistles and sociality instead of merely assuming it. Several hypotheses have been proposed to explain the evolutionary history of Cetacean tonal sounds. The main goal of this dissertation is to cast light on the evolutionary history of tonal sounds by testing these hypotheses by combining comparative phylogenetic and field methods. This dissertation provides the first species-level phylogeny of Cetacea and phylogenetic tests of evolutionary hypotheses of cetacean communicative signals. Tonal sounds evolution is complex in that has likely been shaped by a combination of factors that may influence different aspects of their acoustical structure. At the inter-specific level, these results suggest that only tonal sound minimum frequency is constrained by body size. Group size also influences tonal sound minimum frequency. Species that live in large groups tend to produce higher frequency tonal sounds. The evolutionary history of tonal sounds and sociality may be intertwined, but in a complex manner rejecting simplistic views such as the hypothesis that tonal sounds evolved ‘for’ social communication in dolphins. Levels of social and tonal sound complexity nevertheless correlate indicating the importance of tonal sounds in social communication. At the intraspecific level, tonal sound variation in frequency and temporal parameters may be product of genetic isolation and local levels of underwater noise. This dissertation provides one of the first insights into the evolution of Cetacean tonal sounds in a phylogenetic context, and points out key species where future studies would be valuable to enrich our understanding of other factors also playing a role in tonal sound evolution. ^

Toward A Better Understanding of the Evolution of Hotel Development: A Discussion of Product-specific Lodging Demand

In his essay - Toward a Better Understanding of the Evolution of Hotel Development: A Discussion of Product-Specific Lodging Demand - by John A. Carnella, Consultant, Laventhol & Horwath, cpas, New York, Carnella initially describes his piece by stating: “The diversified hotel product in the united states lodging market has Resulted in latent room-night demand, or supply-driven demand resulting from the introduction of a lodging product which caters to a specific set of hotel patrons. The subject has become significant as the lodging market has moved toward segmentation with regard to guest room offerings. The author proposes that latent demand is a tangible, measurable phenomenon best understood in light of the history of the guest room product from its infancy to its present state.” The article opens with an ephemeral depiction of hotel development in the United States, both pre’ and post World War II. To put it succinctly, the author wants you to know that the advent of the inter-state highway system changed the complexion of the hotel industry in the U.S. “Two essential ingredients were necessary for the next phase of hotel development in this country. First was the establishment of the magnificently intricate infrastructure which facilitated motor vehicle transportation in and around the then 48 states of the nation,” says Carnella. “The second event…was the introduction of affordable highway travel. Carnella goes on to say that the next – big thing – in hotel evolution was the introduction of affordable air travel. “With the airways filled with potential lodging guests, developers moved next to erect a new genre of hotel, the airport hotel,” Carnella advances his picture. Growth progressed with the arrival of the suburban hotel concept, which wasn’t fueled by developments in transportation, but by changes in people’s living habits, i.e. suburban affiliations as opposed to urban and city population aggregates. The author explores the distinctions between full-service and limited service lodging operations. “The market of interest with consideration to the extended-stay facility is one dominated by corporate office parks,” Carnella proceeds. These evolutional states speak to latent demand, and even further to segmentation of the market. “Latent demand… is a product-generated phenomenon in which the number of potential hotel guests increases as the direct result of the introduction of a new lodging facility,” Carnella brings his unique insight to the table with regard to the specialization process. The demand is already there; just waiting to be tapped. In closing, “…there must be a consideration of the unique attributes of a lodging facility relative to its ability to attract guests to a subject market, just as there must be an examination of the property's ability to draw guests from within the subject market,” Carnella proposes.

Phylogenetic and Ecological Significance in the Evolution of Cetacean Tonal Sounds

Cetaceans are aquatic mammals that rely primarily on sound for most daily tasks. A compendium of sounds is emitted for orientation, prey detection, and predator avoidance, and to communicate. Communicative sounds are among the most studied Cetacean signals, particularly those referred to as tonal sounds. Because tonal sounds have been studied especially well in social dolphins, it has been assumed these sounds evolved as a social adaptation. However, whistles have been reported in ‘solitary’ species and have been secondarily lost three times in social lineages. Clearly, therefore, it is necessary to examine closely the association, if any, between whistles and sociality instead of merely assuming it. Several hypotheses have been proposed to explain the evolutionary history of Cetacean tonal sounds. The main goal of this dissertation is to cast light on the evolutionary history of tonal sounds by testing these hypotheses by combining comparative phylogenetic and field methods. This dissertation provides the first species-level phylogeny of Cetacea and phylogenetic tests of evolutionary hypotheses of cetacean communicative signals. Tonal sounds evolution is complex in that has likely been shaped by a combination of factors that may influence different aspects of their acoustical structure. At the inter-specific level, these results suggest that only tonal sound minimum frequency is constrained by body size. Group size also influences tonal sound minimum frequency. Species that live in large groups tend to produce higher frequency tonal sounds. The evolutionary history of tonal sounds and sociality may be intertwined, but in a complex manner rejecting simplistic views such as the hypothesis that tonal sounds evolved ‘for’ social communication in dolphins. Levels of social and tonal sound complexity nevertheless correlate indicating the importance of tonal sounds in social communication. At the intraspecific level, tonal sound variation in frequency and temporal parameters may be product of genetic isolation and local levels of underwater noise. This dissertation provides one of the first insights into the evolution of Cetacean tonal sounds in a phylogenetic context, and points out key species where future studies would be valuable to enrich our understanding of other factors also playing a role in tonal sound evolution.

The evolution of immigration discourse in the Maltese press from 2005 to 2015: A case study of the Times of Malta

El drama migratorio del cual está siendo Europa testigo en estas últimas semanas es en parte el resultado de una falta de políticas comunitarias en relación a este tema, hecho del cual, en los últimos años, se han hecho eco multitud de medios. Europa, y en especial los países del Mediterráneo, ha experimentado un incremento sustancial en el número de inmigrantes que llegan a sus costas en condiciones cada vez más deplorables y arriesgando gravemente su integridad física. Este hecho está principalmente motivado por el aumento y la intensidad de los conflictos bélicos en países de África y Oriente próximo. En el caso de Malta, un diminuto archipiélago ubicado entre los territorios de Libia y Sicilia, el cambio en la tendencia migratoria que se produjo en 2002 le hizo pasar de ser un país de emigrantes a un país receptor de inmigrantes. Este cambio dio como resultado la aparición de grupos y partidos anti-inmigración, como Azzjoni Nazzjonali, y de un sentimiento de preocupación frente a la llegada de inmigrantes que crece de manera constante según se refleja en encuestas europeas (véase Eurobarometer 82-83). Desde el punto de vista lingüístico, el discurso discriminatorio empleado por los medios de comunicación, organismos y figuras políticas ha sido ampliamente estudiado dentro de la rama del Análisis Crítico del Discurso (Charteris-Black, 2006; Fairclough, 1989, Reisigl & Wodak, 2001; Santa Ana, 1999; Van Dijk, 1984, 1992, 1999, 2000, 2006, Van Leeuwen & Wodak, 1999). En los últimos años, se ha potenciado el uso de un enfoque cognitivo en el análisis de este tipo de discursos. Dicho enfoque utiliza elementos tomados de la lingüística cognitiva para explicar cómo la representación de eventos y participantes en el discurso atiende, o está motivada por la conceptualización mental de dichos eventos y participantes (Charteris-Black, 2006; Hart, 2011; Musolff, 2012; Núñez-Perucha, 2011; O’Brien, 2003; Santa Ana, 1999; Van Dijk, 1992, 1998, 1999, 2000, 2006; Wodak, 2006). El Análisis Crítico del Discurso es una disciplina cuyo principal objetivo es analizar cómo ciertos fenómenos sociales que se basan en relaciones de abuso de poder y dominación se representan en el discurso de las denominadas élites (Van Dijk, 2001). Muchos de estos discursos atienden a lo que en lingüística se ha denominado discurso de discriminación, en donde un grupo dominante ejerce poder sobre otro mediante el uso de diversas herramientas discursivas. Generalmente, estos estudios sobre discursos de discriminación se han centrado en fenómenos como el machismo o el racismo. Dentro de este último campo, cabe destacar el trabajo de Van Dijk en el análisis del discurso del racismo y del discurso de la inmigración (Van Dijk, 1992, 1999, 2000, 2001, 2006). El presente trabajo se centra en analizar cómo la prensa maltesa ha representado el fenómeno de la inmigración y a los inmigrantes desde 2005 hasta 2015. Dentro de esta línea temporal, se presta especial atención al día 2 de abril de 2013. Esta es la fecha en la que la Associated Press, una organización de prensa independiente con subscriptores alrededor del mundo, decidió incluir un importante cambio léxico en su manual de estilo. El motivo del mismo era modificar el uso del adjetivo “ilegal” recomendando su uso para referirse exclusivamente a acciones (ej. Inmigración ilegal) pero nunca para referirse a individuos (ej. Inmigrante ilegal). Nuestro estudio pretende identificar hasta qué punto esta medida se ha puesto en práctica en los periódicos malteses y qué repercusiones ha tenido su incorporación en la representación de los inmigrantes y la inmigración. Para ello, se ha seleccionado como caso de estudio uno de los periódicos en lengua inglesa más leídos en el archipiélago, Times of Malta. El estudio se ha centrado en el análisis de un total de treinta artículos de opinión repartidos de manera homogénea (quince y quince) en dos corpus. El primer corpus contiene artículos pertenecientes a un periodo de tiempo que va desde 2005 hasta la fecha en la cual el cambio léxico de la Associated Press fue publicado, es decir, el 2 de abril de 2013. Por otro lado, el segundo corpus contiene artículos desde el 2 de abril de 2013 hasta mediados de 2015. Para agilizar y facilitar el análisis de los artículos, se ha hecho uso del programa llamado WordSmith Tools, el cual está especializado en el trabajo con corpus. Este programa se utilizó principalmente para analizar la representación semántica de los distintos participantes y eventos. Los resultados del análisis demuestran que el periódico ha aplicado el cambio léxico sugerido por la Associated Press al no encontrarse ningún ejemplo de “inmigrante ilegal” o “migrante ilegal” a partir del 2 de abril de 2013. En estos mismos resultados también se aprecia una representación más positiva de la figura del inmigrante en el segundo corpus, dónde el inmigrante abandona la categoría léxica de “criminal” para comenzar a ser visto cada vez más como la víctima. También a nivel léxico, se puede observar cómo los autores tienden a usar cada vez más el término “migrante” en lugar de “inmigrante”. A pesar de que este último continúa siendo el término más utilizado para referirse a la persona que llega desde otro país, el significativo incremento del uso de la palabra “migrante” en el segundo corpus es llamativo y puede deberse a que la palabra “inmigrante” haya adquirido connotaciones negativas por su repetido uso junto al adjetivo “ilegal”. De entre las estrategias discursivas empleadas en la representación de la sociedad maltesa, cabe destacar dos. Por un lado, tenemos el uso de la victimización, mediante la cual la población maltesa aparece como una víctima frente a la inmigración, que es vista como una amenaza, al mismo tiempo que Malta es también víctima de la falta de apoyo internacional. En segundo lugar, es también común encontrar artículos en donde el autor destaca las cualidades positivas de la sociedad maltesa, especialmente su generosidad. Esta última estrategia es lo que Van Dijk denomina national self-glorifiation (2000:220; 2006:738). En cuanto al uso de las metáforas, el cambio es menos significativo. En general, ambos corpus muestran ejemplos de metáforas en las que el inmigrante aparece conceptualizado como parte de un fenómeno natural incontrolable, un invasor o un organismo dispuesto a infectar o dañar de algún modo el país. En el segundo corpus, sin embargo, desaparecen las metáforas en las que el inmigrante se percibe como un animal inferior, que sí aparecían en el primer corpus. Esto supone un cambio positivo. Hasta este punto hemos resumido los cambios en la representación de los inmigrantes. Respecto al modo en el cual el fenómeno de la inmigración aparece representado en los periódicos, también encontramos cambios importantes. A nivel léxico, el cambio que mencionábamos relativo a los términos “inmigrante” y “migrante” también se produce a la hora de nombrar este fenómeno social. De este modo, la palabra “migración” es más usada en el segundo corpus que en el primero, aunque sigue ocupando el segundo lugar por detrás de la palabra “inmigración”. En cuanto a los contenidos, se puede observar un cambio positivo hacia una mayor concienciación social. Por ejemplo, vemos cómo en el segundo corpus en ocasiones se pide una respuesta estatal a temas como la integración de los inmigrantes o el racismo entre la sociedad, mientras que en el primer corpus la integración era una labor del inmigrante y el racismo era un tema incómodo. En el segundo corpus también encontramos la queja más clara hacia el uso de centros de detención en la isla. En el primer corpus, aunque algunos autores manifestaban su disconformidad con las condiciones en las cuales los inmigrantes vivían dentro de los centros de detención, todos asumían que tener dichos centros era una medida necesaria. Esta especie de consenso social y político acerca del uso de centros de detención se consigue mediante el empleo de herramientas discursivas que representen la inmigración como una amenaza de la cual hay que protegerse (negative other-presentation Van Dijk, 2000:221; 2006:738). En resumen, podemos decir que este trabajo muestra una progresión en el discurso de inmigración en Malta hacia una representación más positiva y amable del inmigrante y de la inmigración. Aunque las limitaciones de este estudio hacen imposible establecer una relación única y directa entre los cambios experimentados por el periódico y el cambio léxico sugerido por la Associated Press, lo cierto es que la descriminalización de los inmigrantes a nivel léxico (mediante la supresión de términos como “ilegal” o “detenidos”) ha influido de manera positiva en el tono y la forma en que este periódico se refiere al fenómeno social de la inmigración

The evolution of IL-4 and IL-13 and their receptor subunits

Peer reviewed