Nonlinear interfaces: intrinsically nonparaxial regimes and effects

The behaviour of optical solitons at planar nonlinear boundaries is a problem rich in intrinsically nonparaxial regimes that cannot be fully addressed by theories based on the nonlinear Schrödinger equation. For instance, large propagation angles are typically involved in external refraction at interfaces. Using a recently proposed generalized Snell's law for Helmholtz solitons, we analyse two such effects: nonlinear external refraction and total internal reflection at interfaces where internal and external refraction, respectively, would be found in the absence of nonlinearity. The solutions obtained from the full numerical integration of the nonlinear Helmholtz equation show excellent agreement with the theoretical predictions

Universal quantum computation with the Orbital Angular Momentum of a single photon

We prove that a single photon with quantum data encoded in its orbital angular momentum can be manipulated with simple optical elements to provide any desired quantum computation. We will show how to build any quantum unitary operator using beamsplitters, phase shifters, holograms and an extraction gate based on quantum interrogation. The advantages and challenges of these approach are then discussed, in particular the problem of the readout of the results.Comment: First version. Comments welcom

Helmholtz bright and boundary solitons

We report, for the first time, exact analytical boundary solitons of a generalized cubic-quintic Non-Linear Helmholtz (NLH) equation. These solutions have a linked-plateau topology that is distinct from conventional dark soliton solutions; their amplitude and intensity distributions are spatially delocalized and connect regions of finite and zero wave-field disturbances (suggesting also the classification as 'edge solitons'). Extensive numerical simulations compare the stability properties of recently-reported Helmholtz bright solitons, for this type of polynomial non-linearity, to those of the new boundary solitons. The latter are found to possess a remarkable stability characteristic, exhibiting robustness against perturbations that would otherwise lead to the destabilizing of their bright-soliton counterpart

Aplicación fraccionada de nitrógeno en colza (<i>Brassica napus L.</i> spp oleifera forma annua): efectos sobre el rendimiento y la calidad de la semilla

The higher nitrogen demand by rapeseed crop needs an adequate supply to maintain a sustainable production, which is highly dependent on the moment of N availability for the crop. The effect of splitting N application was evaluated during two years 1994, and 1995 in a field experiment in La Plata on two spring rapeseed cultivars (Iciola 41 and Global). Fertilisation treatments were: N0: (control) and the application of 90Kg de N.ha-1 (as urea) in N1: all at sowing, N2: half at sowing and half at the end of rosette stage and N3: 1/3 at sowing, 1/3 at the end of rosette stage and 1/3 at flowering onset. Biomass production, seed yield and its components were evaluated at ripeness and seed N and oil seed content were also measured. During 1995 biomass production and N accumulation at different phenological stages of crop development were also evaluated. Leaf area index was evaluated during different phenological stages on Global cultivar. No interactions were found between cultivars and fertilisation treatments for seed yield and its components. In 1994, N application, mainly as split dose, increased seed yield and biomass production. Significative differences were found between treatments N0 vs. N2 and N3 (94, 196 y 212 g.m-2 respectively). The higher seed production in this year was related to more number of seeds and siliques.m-2 but not to a higher seed weight. Seed N and oil content were influenced mainly by year. A significative fertilisation x cultivar interaction was observed. During 1995 no significative differences were observed between fertiliser treatments for all the variables evaluated probably due to a severe water deficit observed during the most sensitive crop period. Our results suggest that fertilisation response is highly dependent on year characteristics, specially on water availability during critic stages of crop development. When weather conditions are favourables for N response, application as split form results a more effective way to improve N agronomic efficiency for seed yield due to its effect on those components associated to seed number formation.El cultivo de colza requiere un suministro eficiente de nitrógeno para mantener una producción sostenible, lo que está relacionado con el momento en que esté disponible para el cultivo. Para evaluar el comportamiento del cultivo de colza-canola ante la aplicación fraccionada del fertilizante nitrogenado se realizaron 2 ensayos a campo en La Plata durante los años 1994 y 1995. Se sembraron 2 cultivares de primavera (Iciola 41 y Global) sometidos a los siguientes tratamientos: N0: testigo sin fertilizar y la aplicación de 90Kg de N.ha-1 en los siguientes momentos: N1: todo a la siembra; N2: en partes iguales en dos momentos (siembra y fin de roseta) y N3: en partes iguales en tres momentos (siembra, fin de roseta e inicios de floración). En madurez se evaluó la biomasa, el rendimiento y sus componentes y se determinó el contenido de nitrógeno y de materia grasa de la semilla. En 1995 se determinó además biomasa y nitrógeno acumulado en planta en los estados fin de roseta, inicios de floración y madurez. Sobre el cultivar Global se determinó el índice de área foliar en distintos momentos del desarrollo. No se encontró interacción entre cultivares y tratamientos para el rendimiento y sus componentes. En 1994 con la fertilización, sobre todo en dosis fraccionada, aumentó el rendimiento y la biomasa, encontrándose diferencias significativas en rendimiento entre N0 vs. N2 y N3 (94, 196 y 212 g.m-2 respectivamente). Este aumento se relacionó con un mayor número de semillas.m-2 y silícuas.m-2 y no con el peso de mil semillas. El contenido de N y de aceite en las semillas estuvo influenciado principalmente por las condiciones del año, aunque se observó una interacción significativa entre cultivares y tratamientos de fertilización. En 1995 no se encontraron diferencias significativas entre los tratamientos para ninguna de las variables analizadas, debido posiblemente a las condiciones hídricas del año. Nuestros resultados indican que las características hídricas del año condicionan el aprovechamiento del nitrógeno disponible y, por lo tanto, la respuesta del cultivo a la fertilización. Cuando las condiciones del año permiten una respuesta al agregado de N, la aplicación en dosis fraccionada resulta más eficiente en el uso del nitrógeno que la aplicación en una única dosis, debido a un aumento en los componentes que determinan un mayor número de granos

Assisted inflation in Friedmann-Robertson-Walker and Bianchi spacetimes

We use exact general solutions for the spatially flat FRW and the anisotropic Bianchi I cosmologies to show that generically uncoupled scalar fields cooperate to make inflation more probable, while the presence of several interacting fields hinders the occurrence of the phenomenon, in accordance with previous results based on particular power-law solutions. Similar conclusions are reached in the case of Bianchi VI$_0$ spacetimes, for power-law solutions which are proved to be attractors

Using social networks sites in the purchasing decision process

The rise of Web 2.0 tools and mobile devices means that the image of the traditional consumer has to be replaced with an active, permanently connected, consumer who uses the Internet to find information about brands and to share opinions and shopping experiences with other consumers – a consumer who can be classified as a prosumer (producer + consumer). In this context it is important for marketers to know how consumers use social networks within their purchasing decision process. The present work describes an online survey of more than 500 Facebook users in Spain and Portugal, aimed at identifying which aspects most influence their intention to use this social network in their purchasing decisions. A structural equation model was constructed based on the Technology Acceptance Model (TAM), in which the intended use of Facebook in purchasing decisions depends on two variables: perceived usefulness and perceived ease of use, with attitude being a mediating variable. The background variables considered were aptitude, network externalities, perceived privacy protection, and social influence. The results show that the intended use of Facebook in purchasing decisions is influenced by its perceived usefulness, by social influence, and by the attitude to Facebook. In contrast, the perceived ease of use does not have such direct influence

What motivates academic dishonesty in students? A reinforcement sensitivity theory explanation

BACKGROUND: Academic dishonesty (AD) is an increasing challenge for universities worldwide. The rise of the Internet has further increased opportunities for students to cheat. AIMS: In this study, we investigate the role of personality traits defined within Reinforcement Sensitivity Theory (RST) as potential determinants of AD. RST defines behaviour as resulting from approach (Reward Interest/reactivity, goal-drive, and Impulsivity) and avoidance (behavioural inhibition and Fight-Flight-Freeze) motivations. We further consider the role of deep, surface, or achieving study motivations in mediating/moderating the relationship between personality and AD. SAMPLE: A sample of UK undergraduates (N = 240). METHOD: All participants completed the RST Personality Questionnaire, a short-form version of the study process questionnaire and a measure of engagement in AD, its perceived prevalence, and seriousness. RESULTS: Results showed that RST traits account for additional variance in AD. Mediation analysis suggested that GDP predicted dishonesty indirectly via a surface study approach while the indirect effect via deep study processes suggested dishonesty was not likely. Likelihood of engagement in AD was positively associated with personality traits reflecting Impulsivity and Fight-Flight-Freeze behaviours. Surface study motivation moderated the Impulsivity effect and achieving motivation the FFFS effect such that cheating was even more likely when high levels of these processes were used. CONCLUSIONS: The findings suggest that motivational personality traits defined within RST can explain variance in the likelihood of engaging in dishonest academic behaviours