The Wiring of Developing Sensory Circuits—From Patterned Spontaneous Activity to Synaptic Plasticity Mechanisms

In order to accurately process incoming sensory stimuli, neurons must be organized into functional networks, with both genetic and environmental factors influencing the precise arrangement of connections between cells. Teasing apart the relative contributions of molecular guidance cues, spontaneous activity and visual experience during this maturation is on-going. During development of the sensory system, the first, rough organization of connections is created by molecular factors. These connections are then modulated by the intrinsically generated activity of neurons, even before the senses have become operational. Spontaneous waves of depolarizations sweep across the nervous system, placing them in a prime position to strengthen correct connections and weaken others, shaping synapses into a useful network. A large body of work now support the idea that, rather than being a mere side-effect of the system, spontaneous activity actually contains information which readies the nervous system so that, as soon as the senses become active, sensory information can be utilized by the animal. An example is the neonatal mouse. As soon as the eyelids first open, neurons in the cortex respond to visual information without the animal having previously encountered structured sensory input (Cang et al., 2005b; Rochefort et al., 2011; Zhang et al., 2012; Ko et al., 2013). In vivo imaging techniques have advanced considerably, allowing observation of the natural activity in the brain of living animals down to the level of the individual synapse. New (opto)genetic methods make it possible to subtly modulate the spatio-temporal properties of activity, aiding our understanding of how these characteristics relate to the function of spontaneous activity. Such experiments have had a huge impact on our knowledge by permitting direct testing of ideas about the plasticity mechanisms at play in the intact system, opening up a provocative range of fresh questions. Here, we intend to outline the most recent descriptions of spontaneous activity patterns in rodent developing sensory areas, as well as the inferences we can make about the information content of those activity patterns and ideas about the plasticity rules that allow this activity to shape the young brain

Orographic cirrus in a future climate

A cloud resolving model (CRM) is used to investigate the formation of orographic cirrus clouds in the current and future climate. The formation of cirrus clouds depends on a variety of dynamical and thermodynamical processes, which act on different scales. First, the capability of the CRM in realistically simulating orographic cirrus clouds has been tested by comparing the simulated results to aircraft measurements of an orographic cirrus cloud. The influence of a warmer climate on the microphysical and optical properties of cirrus clouds has been investigated by initializing the CRM with vertical profiles of horizontal wind, potential temperature and equivalent potential temperature, respectively. The vertical profiles are extracted from IPCC A1B simulations for the current climate and for the period 2090–2099 for two regions representative for North and South America. The influence of additional moisture in a future climate on the propagation of gravity waves and the formation of orographic cirrus could be estimated. In a future climate, the increase in moisture dampens the vertical propagation of gravity waves and the occurring vertical velocities in the moist simulations. Together with higher temperatures fewer ice crystals nucleate homogeneously. Assuming that the relative humidity does not change in a warmer climate the specific humidity in the model is increased. This increase in specific humidity in a warmer climate results in a higher ice water content. The net effect of a reduced ice crystal number concentration and a higher ice water content is an increased optical depth. However, in some moist simulations dynamical changes contribute to changes in the ice water content, ice crystal number concentration and optical depth. For the corresponding dry simulations dynamical changes are more pronounced leading to a decreased optical depth in a future climate in some cases

On the recombination in high-order harmonic generation in molecules

We show that the dependence of high-order harmonic generation (HHG) on the molecular orientation can be understood within a theoretical treatment that does not involve the strong field of the laser. The results for H_2 show excellent agreement with time-dependent strong field calculations for model molecules, and this motivates a prediction for the orientation dependence of HHG from the N_2 3s_g valence orbital. For both molecules, we find that the polarization of recombination photons is influenced by the molecular orientation. The variations are particularly pronounced for the N_2 valence orbital, which can be explained by the presence of atomic p-orbitals.Comment: 6 pages 7 figure

Electrical Transport in High Quality Graphene pnp Junctions

We fabricate and investigate high quality graphene devices with contactless, suspended top gates, and demonstrate formation of graphene pnp junctions with tunable polarity and doping levels. The device resistance displays distinct oscillations in the npn regime, arising from the Fabry-Perot interference of holes between the two pn interfaces. At high magnetic fields, we observe well-defined quantum Hall plateaus, which can be satisfactorily fit to theoretical calculations based on the aspect ratio of the device.Comment: to appear in a special focus issue in New Journal of Physic

3114 Optical zone centration of excimer laser photo-refractive keratectomy for myopia relative to the pupil with and without the use of an active eye tracking system

Explosive volcanic eruptions can eject large quantities of particulate matter that, along with other aerosol droplets and trace gases, are carried upwards into the atmosphere by the buoyant eruption column and then dispersed by winds aloft. The presence in the atmosphere of volcanic ash is a sporadic yet important factor that can threaten human health, affect the urban built environment, disrupt aerial navigation and, for very large eruptions, alter both atmospheric composition and chemistry. Once volcanic ash is injected into the atmosphere, it can be transported over great distances, even circumnavigating the entire planet. Volcanic ash modeling systems are used to simulate the atmospheric dispersion of volcanic ash and to generate operational short-term forecasts to support civil aviation and emergency management. The efficiency of response and mitigation actions is directly associated to the accuracy of the volcanic ash cloud detection. Volcanic ash modeling systems normally require an emission or source term model to characterize the eruption column; a dispersal model to simulate the atmospheric transport, dispersion and ground deposition of ash particles; and a meteorological model for the description of the atmospheric conditions. Traditional forecasts for volcanic ash build on off-line coupled modeling systems, where meteorological variables are only updated at the specified coupling intervals. Although this approach is computationally advantageous is some cases, there is a concern that it can lead to a number of accuracy issues and limitations that can be corrected by on-line modeling strategies. Despite these concerns, to date, no on-line coupled model is available for operational forecast of volcanic ash. In addition, the quantification of the limitations associated to the off-line systems has received no attention. This Ph.D. thesis describes and evaluates NMMB-MONARCH-ASH, a novel fully coupled on-line multiscale meteorological and atmospheric transport model designed to predict ash cloud trajectories, concentration of ash at relevant flight levels, and the expected deposit thickness for both regional and global domains in research and operational set-ups. The first activity targeted a model validation against several well-characterized events including, the Mt. Etna 2001, Eyjafjallajökull 2010, and Cordón Caulle 2011 eruptions. The model has shown to be robust, scalable, and capable to reproduce the spatial and temporal dispersal variability of the ash cloud and tephra deposits, showing promising results and improving the performance from well-known off-line operational models. The second activity quantified the model shortcomings and systematic errors associated to traditional off-line forecasts employed in operational set-ups. NMMB-MONARCH-ASH demonstrated that off-line forecasts could fail to reproduce up to 45-70% of the ash cloud of an on-line forecast, considered to be the best estimate of the true outcome. The uncertainty associated to off-line systems was found to be as relevant (same order of magnitude) as those uncertainties attributed to the source term. The third activity focused on a global application of NMMB-MONARCH-ASH to analyze the potential impacts of ash dispersal from Antarctic volcanoes. Numerical simulations suggested that volcanic ash emitted from Antarctic volcanoes could potentially encircle the globe, leading to significant consequences for global aviation safety. The last activity included a novel computational inversion method to account, for the first time, for the Plinian and co-ignimbrite phases of the 39 ka Campanian Ignimbrite super-eruption. This particular application employed the off-line coupled FALL3D model, found to be more suitable from a computational point of view. The outcome of this Ph.D. thesis encourages operational groups responsible for real-time advisories for aviation to consider using computationally efficient on-line coupled ash dispersal models.Las erupciones volcánicas explosivas pueden emitir una gran cantidad de material que, junto con otros aerosoles y gases traza, son inyectados en la atmósfera por la columna eruptiva para luego ser dispersados por los vientos en altura. La presencia en la atmósfera de cenizas volcánicas es un factor esporádico aunque importante, que puede llegar a amenazar la salud humana, afectar las infraestructuras urbanas, interrumpir la navegación aérea y, en el caso de grandes erupciones, alterar la composición atmosférica y química. Una vez en la atmósfera, la ceniza puede ser transportada a grandes distancias, llegando incluso a circunnavegar todo el planeta. Los sistemas de modelado de cenizas volcánicas se utilizan para simular la dispersión atmosférica de estas partículas, y para generar pronósticos operacionales a corto plazo empleados para dar soporte a la aviación civil y a la gestión de emergencias. La eficacia para responder a estos eventos está directamente asociada a la precisión de los modelos de transporte de cenizas volcánicas. Los sistemas de modelado de cenizas volcánicas requieren de un modelo de emisión de partículas para la caracterización de la columna eruptiva; un modelo de dispersión para la simulación del transporte atmosférico y la deposición de cenizas; y de un modelo meteorológico para la descripción de las condiciones atmosféricas. Los pronósticos tradicionales se basan en sistemas de modelado desacoplados (off-line), donde las variables meteorológicas sólo se actualizan a intervalos de tiempo especificados. Aunque este enfoque presenta ventajas desde el punto de vista computacional, existe la preocupación de que puede estar asociado a limitaciones y problemas de precisión que, por el contrario, pueden ser corregidos mediante estrategias de modelado acoplado (on-line). A pesar de estas preocupaciones, hasta la fecha no hay un modelo acoplado on-line disponible para el pronóstico operativo de la cenizas volcánicas. Además, tampoco existe una cuantificación de las limitaciones asociadas a los sistemas off-line. Este doctorado describe y evalúa NMMB-MONARCH-ASH, un modelo de transporte meteorológico y atmosférico multiescalar (regional/global) completamente acoplado on-line, para su uso en investigación y predicción operacional. El modelo está diseñado para predecir trayectorias de cenizas volcánicas, concentración de ceniza en niveles de vuelo (flight levels), y el correspondiente espesor de depósito. La primera actividad de esta tesis se centra en la validación de modelo mediante erupciones bien caracterizadas (Mt. Etna 2001, Eyjafjallajökull 2010, y del Cordón Caulle 2011). El modelo ha demostrado ser robusto, escalable y capaz de reproducir la variabilidad de la dispersión espacial y temporal de los depósitos y de las nubes de ceniza, ostrando resultados prometedores y mejorando el rendimiento de modelos operacionales. La segunda actividad cuantifica los errores sistemáticos asociados a los pronósticos off-line. NMMB-MONARCH-ASH demuestra que estps pronósticos podrían no reproducir hasta un 45-70% de la nube de cenizas de un pronóstico on-line, considerado éste último como la mejor estimación de la realidad. Esta actividad concluye que la incertidumbre asociada a los sistemas off-line puede llegar a ser tan relevante como aquellas incertidumbres atribuidas al término fuente. La tercera actividad se centra en una aplicación global de NMMB-MONARCH-ASH para analizar los posibles impactos asociados a la dispersión de ceniza de volcanes antárticos. Los resultados alertan de las posibles consequencias de estas erupciones en la aviación a nivel mundial . La última actividad incluye un nuevo método de inversión computacional para identificar, por primera vez, las fases Pliniana y coignimbrita de la super-erupción de la Ignimbrita Campaniana (39 ka) con FALL3D. Los resultados de este Ph.D. alientan a considerar el uso de modelos acoplados on-line para generar pronósticos operacionales de ceniza volcánica

Interpretation Of The Space Bandwidth Product As The Entropy Of Distinctconnection Patterns In Multifacet Optical Interconnection Architectures

Cataloged from PDF version of article.We show that the entropy of the distinct connection patterns that are possible with multifacet optical interconnection architectures is approximately equal to the space-bandwidth product of the optical system

Investigation of a direction sensitive sapphire detector stack at the 5 GeV electron beam at DESY-II

Extremely radiation hard sensors are needed in particle physics experiments to instrument the region near the beam pipe. Examples are beam halo and beam loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial diamond sensors are widely used. In this paper single crystal sapphire sensors are considered as a promising alternative. Industrially grown sapphire wafers are available in large sizes, are of low cost and, like diamond sensors, can be operated without cooling. Here we present results of an irradiation study done with sapphire sensors in a high intensity low energy electron beam. Then, a multichannel direction-sensitive sapphire detector stack is described. It comprises 8 sapphire plates of 1 cm^2 size and 525 micro m thickness, metallized on both sides, and apposed to form a stack. Each second metal layer is supplied with a bias voltage, and the layers in between are connected to charge-sensitive preamplifiers. The performance of the detector was studied in a 5 GeV electron beam. The charge collection efficiency measured as a function of the bias voltage rises with the voltage, reaching about 10 % at 950 V. The signal size obtained from electrons crossing the stack at this voltage is about 22000 e, where e is the unit charge. The signal size is measured as a function of the hit position, showing variations of up to 20 % in the direction perpendicular to the beam and to the electric field. The measurement of the signal size as a function of the coordinate parallel to the electric field confirms the prediction that mainly electrons contribute to the signal. Also evidence for the presence of a polarisation field was observed.Comment: 13 pages, 7 figures, 3 table