Random Sampling with Interspike-Intervals of the Exponential Integrate and Fire Neuron: A Computational Interpretation of UP-States

Oscillations between high and low values of the membrane potential (UP and DOWN states respectively) are an ubiquitous feature of cortical neurons during slow wave sleep and anesthesia. Nevertheless, a surprisingly small number of quantitative studies have been conducted only that deal with this phenomenon’s implications for computation. Here we present a novel theory that explains on a detailed mathematical level the computational benefits of UP states. The theory is based on random sampling by means of interspike intervals (ISIs) of the exponential integrate and fire (EIF) model neuron, such that each spike is considered a sample, whose analog value corresponds to the spike’s preceding ISI. As we show, the EIF’s exponential sodium current, that kicks in when balancing a noisy membrane potential around values close to the firing threshold, leads to a particularly simple, approximative relationship between the neuron’s ISI distribution and input current. Approximation quality depends on the frequency spectrum of the current and is improved upon increasing the voltage baseline towards threshold. Thus, the conceptually simpler leaky integrate and fire neuron that is missing such an additional current boost performs consistently worse than the EIF and does not improve when voltage baseline is increased. For the EIF in contrast, the presented mechanism is particularly effective in the high-conductance regime, which is a hallmark feature of UP-states. Our theoretical results are confirmed by accompanying simulations, which were conducted for input currents of varying spectral composition. Moreover, we provide analytical estimations of the range of ISI distributions the EIF neuron can sample from at a given approximation level. Such samples may be considered by any algorithmic procedure that is based on random sampling, such as Markov Chain Monte Carlo or message-passing methods. Finally, we explain how spike-based random sampling relates to existing computational theories about UP states during slow wave sleep and present possible extensions of the model in the context of spike-frequency adaptation.

Fraxinus excelsior in Europe: distribution, habitat, usage and threats

Common ash (Fraxinus excelsior L.) is a medium-sized deciduous tree with large compound leaves that develop relatively late in spring. It flowers before leaf-buds burst and trees can carry male, female, or hermaphrodite flowers, or different combinations of the flower types. It grows throughout the European temperate zone, but is absent from the driest Mediterranean areas because it does not tolerate extended summer drought, and from the northern boreal regions, with its seedlings in particular being vulnerable to late spring frost. Soils exert a strong control on common ash distribution locally. The species grows best on fertile soils where soil pH exceeds 5.5. It rarely forms pure stands, more often it is found in small groups in mixed stands. Ash trees produce high quality timber that combines light weight, strength, and flexibility. Before the mass use of steel, it was used for a wide range of purposes, from agricultural implements to construction of boat and car frames. Today

Optimal Test for Parameter Instability When the Unstable Process and the Error Distribution are Unknown

This paper proposes asymptotically optimal tests for unstable parameter process under the feasible circumstance that the researcher has little information about the unstable parameter process and the error distribution, and suggests conditions under which the knowledge of those processes does not provide asymptotic power gains. I first derive a test under known error distribution, which is asymptotically equivalent to LR tests for correctly identified unstable parameter processes under suitable conditions. The conditions are weak enough to cover a wide range of unstable processes such as various types of structural breaks and time varying parameter processes. The test is then extended to semiparametric models in which the underlying distribution in unknown but treated as unknown infinite dimensional nuisance parameter. The semiparametric test is adaptive in the sense that its asymptotic power function is equivalent to the power envelope under known error distribution.

Facies distribution in CRP sediment cores from the Ross Sea, Antarctica

Clasts from the Cape Roberts Project cores CRP-2/2A and CRP-3 provide indications of glacially influenced depositional environments in Oligocene and Miocene strata in the western Victoria Land Basin, Antarctica. CRP-2/2A is interpreted to represent strongly glacially influenced, unconformity bound depositional sequences produced by repeated advance and retreat of floating and grounded ice across the shelf. A similar interpretation is extended to the upper 330 meters of the CRP-3 core, but the lower part of the core records shallow marine deposition with significantly less glacial influence. Clast shape analysis from selected coarse-grained facies throughout the cored interval indicates that most clasts are glacially sourced, with little distinction between diamictite and conglomeratic facies. Three dimensional clast fabric analysis from units immediately above sequence boundaries generally display weak or random fabrics and do not suggest that grounded ice actually reached the drillsite at these intervals. Striated and outsized clasts present in fine-grained lithofacies throughout the cores provide further evidence of sub-glacially transported sediment and iceberg rafting. The distribution of these striated and out-sized clasts indicate that a significant glacial influence persisted through most of the time represented by the cores with glaciers actively calving at sea-level introducing ice-berg rafted glacial debris even in the earliest Oligocene.

Grain size distribution in surface sediments samples of the continental shelf and slope of southeast Greenland

During "Meteor" Cruise 6/1966 in the northwest Atlantic a systematic survey of the bottom topography of the southeast Greenland continental margin was undertaken. Eighty-seven profiles transverse to the shelf edge at distances of 3-4 nautical miles and two longitudinal profiles parallel to the coast were carried out with the ELAC Narrow Beam Echo-Sounder giving a reliable record of even steep slopes. On the basis of the echo soundings the topography and morphology of the continental shelf and slope are evaluated. A detailed bathymetric chart and a serial profile chart were designed as working material for the morphological research. These maps along with the original echograms are morphometrically evaluated. The analysis of the sea bottom features is the basis of a subsequent morphogenetical interpretation, verified and extended by means of interpretation of magnetic data and sediment analysis (grain size, roundness, lithology). The results of the research are expressed in a geomorphological map. The primary findings can be summarized as follows: 1) The southeast Greenland shelf by its bottom topography can be clearly designated as a glacially formed area. The glacial features of the shelf can be classified into two zones nearly parallel to the coast: glacial erosion forms on the inner shelf and glacial accumulation forms on the outer shelf. The inner shelf is characterized by the rugged and hummocky topography of ice scoured plains with clear west/east slope asymmetry. On the outer shelf three types of glacial accumulation forms can be recognized: ice margin deposits with clearly expressed terminal moraines, glacial till plains and glaciomarine outwash fans. Both zones of the shelf can be subdivided into two levels of relief. The ice scoured plains, with average depths of 240 meters (m), are dissected to a maximum depth of 1060 m (Gyldenloves Trough) by trough valleys, which are the prolongations of the Greenland fjords. The banks of the outer shelf, with an average depth of 180 m, surround glacial basins with a maximum depth of 670 meters. 2) The sediments of the continental shelf can be classified as glacial due to their grain size distribution and the degree of roundness of the gravel particles. The ice margin deposits on the outer shelf can be recognized by their high percentage of gravels. On the inner shelf a rock surface is suggested, intermittently covered by glacial deposits. In the shelf troughs fine-grained sediments occur mixed with gravels. 3) Topography and sediments show that the southeast Greenland shelf was covered by an ice sheet resting on the sea floor during the Pleistocene ice-age. The large end moraines along the shelf edge probably indicate the maximum extent of the Wurm shelf ice resting on the sea floor. The breakthroughs of the end moraines in front of the glacial basins suggest that the shelf ice has floated further seaward over the increasing depths. 4) Petrographically the shelf sediments consist of gneisses, granites and basalts. While gneisses and granites occire on the nearby coast, basalt is not known to exist here. Either this material has been drifted by icebergs from the basalt province to the north or exists on the southeast Greenland shelf itself. The last interpretation is supported bythe high portion of basalt contained in the sediment samples taken and the strong magnetic anomalies probably caused by basaltic intrusions. 5) A magnetic profile allows the recognition of two magnetically differing areas which approximately coincide with the glacial erosion and accumulation zones. The inner shelf shows a strong and variable magnetic field because the glacially eroded basement forms the sea floor. The outer shelf is characterized by a weak and homogenous magnetic field, as the magnetized basement lies at greater depthy, buried by a thick cover of glacial sediments. The strong magnetic anomalies of the inner shelf are probably caused by dike swarms, similar to those observed further to the north in the Kangerdlugssuaq Fjord region. This interpretation is supported by the high basalt content of the sediment samples and the rough topography of the ice scoured plains which correlates in general with the magnetic fluctuations. The dike structures of the basement have been differentially eroded by the shelf ice. 6) The continental slope, extending from the shelf break at 313 m to a depth of 1270 m with an average slope of 11°, is characterized by delta-shaped projections in front of the shelf basins, by marginal plateaus, ridges and hills, by canyons and slumping features. The projections could be identified as glaciomarine sediment fans. This conclusion is supported by the strong decrease of magnetic field intensity. The deep sea hills and ridges with their greater magnetic intensities have to be regarded as basement outcrops projecting through the glaciomarine sediment cover. The upper continental rise, sloping seaward at about 2°, is composed of wide sediment fans and slump material. A marginal depression on the continental rise running parallel to the shelf edge has been identified. In this depression bottom currents capable of erosion have been recorded. South of Cape Farvel the depression extends to the accumulation zone of the "Eirik" sedimentary ridge. 7) By means of a study of the recent marine processes, postglacial modification of the ice-formed relief can be postulated. The retention effect of the fjord troughs and the high velocity of the East Greenland stream prevents the glacial features from being buried by sediments. Bottom currents capable of active erosion have only been found in the marginal depression on the continental rise. In addition, at the time of the lowest glacio-eustatic sea level, the shelf bottom was not situated in the zone of wave erosion. Only on the continental slope and rise bottom currents, sediment slumps and turbidity currents have led to significant recent modifications. Considering these results, the geomorphological development of the southeast Greenland continental terrace can be suggested as follows: 1. initial formation of a "peneplain", 2. fluvial incision, 3. submergence, and finally 4. glacial modification.

Distribution of Cretaceous redeposited benthic foraminifers at DSDP Site 89-585

Cretaceous benthic foraminifers from Site 585 in the East Mariana Basin, western Pacific Ocean, provide an environmental and tectonic history of the Basin and the surrounding seamounts. Age diagnostic species (from a fauna of 155 benthic species identified) range from late Aptian to Maestrichtian in age. Displaced species in sediments derived from the tops and flanks of nearby seamounts were deposited sporadically on the Basin floor well below the carbonate compensation depth (CCD) at abyssal depths of 5000 to 6000 m. These depths, characterized by an indigenous assemblage of benthic foraminifers, recrystallized radiolarians, fish debris, and sponge spicules, existed in the Mariana Basin from late Aptian to the present. Early Albian and older edifice-building volcanism had reached the photic zone with associated shallow-water bank or reef environments. By middle Albian, the dominant source areas subsided to outer-neritic to upper-bathyal depths. Major volcanic activity ceased and fine-grained sediments were deposited by distal turbidites, although intermittent volcanism and the influx of rare neritic material continued until the late Albian. By the Cenomanian to Turonian, upper- to middle-bathyal depths were reached by the dominant source areas, and the sediments recovered from this interval include organic carbon-rich layers. Rare benthic foraminifers from the Coniacian-Santonian interval indicate a continuation of dominantly middle-bathyal source areas. A change in sedimentation during the Campanian-Maestrichtian from older zeolitic claystone to abundant chert in the Campanian, and nannofossil chalk and claystone in the Maestrichtian resulted from migration of the site beneath the equatorial productive zone due to northwestward plate motion. The appearance of rare middle-neritic and upper-bathyal species in the Maestrichtian interval associated with volcanogenic debris gives evidence of the remobilization and downslope transport of pelagic deposits due to thermally induced uplift. Episodic redeposition of shallow-water material during the Aptian-Albian was produced by edifice-building volcanism perhaps combined with eustatic lowering of sea level. The Cenomanian-Turonian pulse coincided with a low global sea-level stand as does the transported material during the Coniacian-Santonian. The Maestrichtian pulse was caused by renewed midplate volcanism that extended over a large area of the central Pacific.

Heavy minerals, grain size distribution, and ice-rafted debris in the Greenland Sea during 44 to 30 Ma

The widely accepted age estimate for the onset of glaciation in the Northern Hemisphere ranges between 2 and 15 million years ago (Ma). However, recent studies indicate the date for glacial onset may be significantly older. We report the presence of ice-rafted debris (IRD) in ~44 to 30 Ma sediments from the Greenland Sea, evidence for glaciation in the North Atlantic during the Middle Eocene to Early Oligocene. Detailed sedimentological evidence indicates that glaciers extended to sea level in the region, allowing icebergs to be produced. IRD may have been sourced from tidewater glaciers, small ice caps, and/or a continental ice sheet.

Distribution of Florisphaera profunda and Helicosphaera carteri in down core and surface sediments

A detailed assessment of the respective roles of production, export, and subsequent preservation of organic carbon (Corg) in the eastern Mediterranean (EMED) sediments during the formation of sapropels remains elusive. Here we present new micropaleontological results for both surface samples taken at several locations in the EMED and last interglacial sapropel S5 from core LC21 in the southeastern Aegean Sea. A strong exponential anticorrelation between relative abundances of the lower photic zone coccolithophore Florisphaera profundain the surface sediments and modern concentrations of chlorophyll a (Chl-a) at the sea surface suggests thatF. profunda percentages can be used to track past productivity changes in the EMED. Prior to S5 deposition, an abrupt and large increase of F. profunda percentages in LC21 coincided (within the multidecadal resolution of the records) with the marked freshening of EMED surface waters. This suggests a strong coupling between freshwater-bound surface to intermediate water (density) stratification and enhanced upward advection of nutrients to the base of the photic zone, fuelling a productive deep chlorophyll maximum (DCM) underneath a nutrient-starved surface layer. Our findings imply that (at least) at the onset of sapropel formation physical and biogeochemical processes likely operated in tandem, enabling high Corg accumulation at the seafloor.

Distribution of benthic foraminifera in surface sediments on the continental margin off North-West Africa

The benthic foraminiferal populations along three traverses across the Northwest African continental margin were analyzed on the base of ca. 60 surface sediment samples. Depth ranges of 213 species were established and the main trends of vertical distribution are compared with those known from adjacent regions. Main faunal breaks occure at 100/200 m and 1000/1500 m depth of water. Some species show latitudinal distribution boundaries and the same applies to population density (standing stock), reflecting the regional distribution of nutrients supply by river discharge and upwelling processes. - High proportions of Bolivina test at the lower slope indicate extended downslope transport.

How are global value chains fragmented and extended in China's domestic production networks?

Global value chains are supported not only directly by domestic regions that export goods and services to the world market, but also indirectly by other domestic regions that provide parts, components, and intermediate services to final exporting regions. In order to better understand the nature of a country’s position and degree of participation in global value chains, we need to more fully examine the role of individual domestic regions. Understanding the domestic components of global supply chains is especially important for large developing countries like China and India, where there may be large variations in economic scale and development between domestic regions. This paper proposes a new framework for measuring domestic linkages to global value chains. This framework measures domestic linkages by endogenously embedding a country’s domestic interregional input-output (IO) table in an international IO model. Using this framework, we can more clearly describe how global production is fragmented and extended through linkages across a country’s domestic regions. This framework will also enable us to estimate how value added is created and distributed in both domestic and international segments of global value chains. For examining the validity and usefulness of this new approach, some numerical results are presented and discussed based on the 2007 Chinese interregional IO table, China customs statistics at the provincial level, and World Input-Output Tables (WIOTs).

Extended Triple-Junction Solar Cell 3D Distributed Model: Application to Chromatic Aberration-Related Losses

An extended 3D distributed model based on distributed circuit units for the simulation of triple‐junction solar cells under realistic conditions for the light distribution has been developed. A special emphasis has been put in the capability of the model to accurately account for current mismatch and chromatic aberration effects. This model has been validated, as shown by the good agreement between experimental and simulation results, for different light spot characteristics including spectral mismatch and irradiance non‐uniformities. This model is then used for the prediction of the performance of a triple‐junction solar cell for a light spot corresponding to a real optical architecture in order to illustrate its suitability in assisting concentrator system analysis and design process.

Study of the temperature distribution in Si nanowires under microscopic laser beam excitation

The use of laser beams as excitation sources for the characterization of semiconductor nanowires (NWs) is largely extended. Raman spectroscopy and photoluminescence (PL) are currently applied to the study of NWs. However, NWs are systems with poor thermal conductivity and poor heat dissipation, which result in unintentional heating under the excitation with a focused laser beam with microscopic size, as those usually used in microRaman and microPL experiments. On the other hand, the NWs have subwavelength diameter, which changes the optical absorption with respect to the absorption in bulk materials. Furthermore, the NW diameter is smaller than the laser beam spot, which means that the optical power absorbed by the NW depends on its position inside the laser beam spot. A detailed analysis of the interaction between a microscopic focused laser beam and semiconductor NWs is necessary for the understanding of the experiments involving laser beam excitation of NWs. We present in this work a numerical analysis of the thermal transport in Si NWs, where the heat source is the laser energy locally absorbed by the NW. This analysis takes account of the optical absorption, the thermal conductivity, the dimensions, diameter and length of the NWs, and the immersion medium. Both free standing and heat-sunk NWs are considered. Also, the temperature distribution in ensembles of NWs is discussed. This analysis intends to constitute a tool for the understanding of the thermal phenomena induced by laser beams in semiconductor NWs.

Architectures for Video-on-Demand content distribution in managed networks

La demanda de contenidos de vídeo ha aumentado rápidamente en los últimos años como resultado del gran despliegue de la TV sobre IP (IPTV) y la variedad de servicios ofrecidos por los operadores de red. Uno de los servicios que se ha vuelto especialmente atractivo para los clientes es el vídeo bajo demanda (VoD) en tiempo real, ya que ofrece una transmisión (streaming) inmediata de gran variedad de contenidos de vídeo. El precio que los operadores tienen que pagar por este servicio es el aumento del tráfico en las redes, que están cada vez más congestionadas debido a la mayor demanda de contenidos de VoD y al aumento de la calidad de los propios contenidos de vídeo. Así, uno de los principales objetivos de esta tesis es encontrar soluciones que reduzcan el tráfico en el núcleo de la red, manteniendo la calidad del servicio en el nivel adecuado y reduciendo el coste del tráfico. La tesis propone un sistema jerárquico de servidores de streaming en el que se ejecuta un algoritmo para la ubicación óptima de los contenidos de acuerdo con el comportamiento de los usuarios y el estado de la red. Debido a que cualquier algoritmo óptimo de distribución de contenidos alcanza un límite en el que no se puede llegar a nuevas mejoras, la inclusión de los propios clientes del servicio (los peers) en el proceso de streaming puede reducir aún más el tráfico de red. Este proceso se logra aprovechando el control que el operador tiene en las redes de gestión privada sobre los equipos receptores (Set-Top Box) ubicados en las instalaciones de los clientes. El operador se reserva cierta capacidad de almacenamiento y streaming de los peers para almacenar los contenidos de vídeo y para transmitirlos a otros clientes con el fin de aliviar a los servidores de streaming. Debido a la incapacidad de los peers para sustituir completamente a los servidores de streaming, la tesis propone un sistema de streaming asistido por peers. Algunas de las cuestiones importantes que se abordan en la tesis son saber cómo los parámetros del sistema y las distintas distribuciones de los contenidos de vídeo en los peers afectan al rendimiento general del sistema. Para dar respuesta a estas preguntas, la tesis propone un modelo estocástico preciso y flexible que tiene en cuenta parámetros como las capacidades de enlace de subida y de almacenamiento de los peers, el número de peers, el tamaño de la biblioteca de contenidos de vídeo, el tamaño de los contenidos y el esquema de distribución de contenidos para estimar los beneficios del streaming asistido por los peers. El trabajo también propone una versión extendida del modelo matemático mediante la inclusión de la probabilidad de fallo de los peers y su tiempo de recuperación en el conjunto de parámetros del modelo. Estos modelos se utilizan como una herramienta para la realización de exhaustivos análisis del sistema de streaming de VoD asistido por los peers para la amplia gama de parámetros definidos en los modelos. Abstract The demand of video contents has rapidly increased in the past years as a result of the wide deployment of IPTV and the variety of services offered by the network operators. One of the services that has especially become attractive to the customers is real-time Video on Demand (VoD) because it offers an immediate streaming of a large variety of video contents. The price that the operators have to pay for this convenience is the increased traffic in the networks, which are becoming more congested due to the higher demand for VoD contents and the increased quality of the videos. Therefore, one of the main objectives of this thesis is finding solutions that would reduce the traffic in the core of the network, keeping the quality of service on satisfactory level and reducing the traffic cost. The thesis proposes a system of hierarchical structure of streaming servers that runs an algorithm for optimal placement of the contents according to the users’ behavior and the state of the network. Since any algorithm for optimal content distribution reaches a limit upon which no further improvements can be made, including service customers themselves (the peers) in the streaming process can further reduce the network traffic. This process is achieved by taking advantage of the control that the operator has in the privately managed networks over the Set-Top Boxes placed at the clients’ premises. The operator reserves certain storage and streaming capacity on the peers to store the video contents and to stream them to the other clients in order to alleviate the streaming servers. Because of the inability of the peers to completely substitute the streaming servers, the thesis proposes a system for peer-assisted streaming. Some of the important questions addressed in the thesis are how the system parameters and the various distributions of the video contents on the peers would impact the overall system performance. In order to give answers to these questions, the thesis proposes a precise and flexible stochastic model that takes into consideration parameters like uplink and storage capacity of the peers, number of peers, size of the video content library, size of contents and content distribution scheme to estimate the benefits of the peer-assisted streaming. The work also proposes an extended version of the mathematical model by including the failure probability of the peers and their recovery time in the set of parameters. These models are used as tools for conducting thorough analyses of the peer-assisted system for VoD streaming for the wide range of defined parameters.

An extension of Mohring’s model for land rent distribution

In an early paper Herbert Mohring (J. Poi Et on , 49 (1961)) presented a model for land rent distribution yielding the well-known result that the price of land must fall with the distance from the city center to offset transportation costs. Our paper is an extension of Mohring's model in which we relax some of his drastic simplifying assumptions. This extended model has been incorporated in a method for economic evaluation of city master plans which has been applied to a Swedish city. In this method the interdependence among housing, heating, and transportation, the dura-bility of urban structures, and the uncertainty of future demand are explicitly considered within a cost-benefit approach. Some empirical results from this pilot study concerning land rent distributions are also presented here.