Topographic electrophysiological signatures of FMRI Resting State Networks

Background: fMRI Resting State Networks (RSNs) have gained importance in the present fMRI literature. Although their functional role is unquestioned and their physiological origin is nowadays widely accepted, little is known about their relationship to neuronal activity. The combined recording of EEG and fMRI allows the temporal correlation between fluctuations of the RSNs and the dynamics of EEG spectral amplitudes. So far, only relationships between several EEG frequency bands and some RSNs could be demonstrated, but no study accounted for the spatial distribution of frequency domain EEG. Methodology/Principal Findings: In the present study we report on the topographic association of EEG spectral fluctuations and RSN dynamics using EEG covariance mapping. All RSNs displayed significant covariance maps across a broad EEG frequency range. Cluster analysis of the found covariance maps revealed the common standard EEG frequency bands. We found significant differences between covariance maps of the different RSNs and these differences depended on the frequency band. Conclusions/Significance: Our data supports the physiological and neuronal origin of the RSNs and substantiates the assumption that the standard EEG frequency bands and their topographies can be seen as electrophysiological signatures of underlying distributed neuronal networks.

Statistics of the received power for free space optical channels

Free space optical (FSO) communication links can experience extreme signal degradation due to atmospheric turbulence induced spatial and temporal irradiance fuctuations (scintillation) in the laser wavefront. In addition, turbulence can cause the laser beam centroid to wander resulting in power fading, and sometimes complete loss of the signal. Spreading of the laser beam and jitter are also artifacts of atmospheric turbulence. To accurately predict the signal fading that occurs in a laser communication system and to get a true picture of how this affects crucial performance parameters like bit error rate (BER) it is important to analyze the probability density function (PDF) of the integrated irradiance fuctuations at the receiver. In addition, it is desirable to find a theoretical distribution that accurately models these ?uctuations under all propagation conditions. The PDF of integrated irradiance fuctuations is calculated from numerical wave-optic simulations of a laser after propagating through atmospheric turbulence to investigate the evolution of the distribution as the aperture diameter is increased. The simulation data distribution is compared to theoretical gamma-gamma and lognormal PDF models under a variety of scintillation regimes from weak to very strong. Our results show that the gamma-gamma PDF provides a good fit to the simulated data distribution for all aperture sizes studied from weak through moderate scintillation. In strong scintillation, the gamma-gamma PDF is a better fit to the distribution for point-like apertures and the lognormal PDF is a better fit for apertures the size of the atmospheric spatial coherence radius ρ0 or larger. In addition, the PDF of received power from a Gaussian laser beam, which has been adaptively compensated at the transmitter before propagation to the receiver of a FSO link in the moderate scintillation regime is investigated. The complexity of the adaptive optics (AO) system is increased in order to investigate the changes in the distribution of the received power and how this affects the BER. For the 10 km link, due to the non-reciprocal nature of the propagation path the optimal beam to transmit is unknown. These results show that a low-order level of complexity in the AO provides a better estimate for the optimal beam to transmit than a higher order for non-reciprocal paths. For the 20 km link distance it was found that, although minimal, all AO complexity levels provided an equivalent improvement in BER and that no AO complexity provided the correction needed for the optimal beam to transmit. Finally, the temporal power spectral density of received power from a FSO communication link is investigated. Simulated and experimental results for the coherence time calculated from the temporal correlation function are presented. Results for both simulation and experimental data show that the coherence time increases as the receiving aperture diameter increases. For finite apertures the coherence time increases as the communication link distance is increased. We conjecture that this is due to the increasing speckle size within the pupil plane of the receiving aperture for an increasing link distance.

Effects of amygdala-hippocampal stimulation on synchronization.

Changes in EEG synchronization, i.e., spatio-temporal correlation, with amygdala-hippocampal stimulation were studied in patients with temporal lobe epilepsy. Synchronization was evaluated for high frequency, 130Hz, pseudo-monophasic or biphasic charge-balanced pulses. Desynchronization was most frequently induced by stimulation. There was no correlation between the changes in synchronization and the changes in interictal epileptiform discharge rates. Changes in synchronization do not appear yet to be a marker of stimulation efficiency in reducing seizures.

STUDIES OF DISULFOTON TOLERANCE IN RATS

Disulfoton (O,O, diethyl S-2-(ethylthio)ethyl phosphorodithioate) and other organophosphorus ester compounds are insecticides which inhibit acetylcholinesterase. Chemicals of this class cause signs of toxicity in mammals which are referable to acculmulation of acetylcholine at neuroeffector sites. A tolerance to this toxic action can be induced in experimental animals by giving multiple, sublethal doses of the compounds. There is strong evidence that disulfoton tolerance occurs because of a reduction in the sensitivity of tissues in the affected animals to acetylcholine.^ Experiments were designed to test the possibility that a decrease in the number of muscarinic cholinergic receptors could be downmodulating the sensitivity of tissues to acetylcholine. It was found that, concomitant with the onset of disulfoton tolerance, there was a decrease relative to control values in the specific binding of {('3)H} quinuclidinyl benzilate ({('3)H}QNB, a compound which selectively labels muscarinic cholinergic receptors) to homogenates of rat brain and ileal muscle. The decrease in {('3)H}QNB binding was due to a reduction in the density of muscarinic receptors. There was, however, no alteration in the binding of {('3)H} QNB, or the muscarinic agonists {('3)H} oxotremorine-M and oxotremorine to atria from disulfoton-tolerant rats. The possibility that cardiac tissue was not subsensitive to cholinergic agonists was ruled out in experiments testing the effect of the muscarinic agonist carbachol on heart rate in vivo, and the negative chronotropic effect of oxotremorine on atria from disulfoton-tolerant rats: a clear reduction in the sensitivity to cholinergic agonists was seen in each case. It was, therefore concluded that the specificity and temporal correlation of {('3)H}QNB binding decreases suggested that the loss of muscarinic receptors might play a role in modulating the sensitivity of several tissues to acetylcholine, but that other mechanisms also contribute to the tolerance phenomenon.^ Other experiments revealed that disulfoton tolerance, as measured by resistance to the lethal effects of carbachol, could be induced by feeding rats low levels of the organophosphorus ester in the diet. The concentration of disulfoton used inhibited acetylcholinesterase, but not to the extent that overt signs of toxicity were observed. These results suggested that tolerance to organophosphorus ester insecticides could be induced in rodents with a dosing scheme which more closely modeled the sort of low level exposures which would be expected in humans environmentally or occupationally in contact with these compounds. ^

Correlación de medidas de diversos sistemas de sensores inalámbricos a través del uso de smartphone

Este Proyecto Fin de Grado se centra en la definición de unos interfaces y el desarrollo de unos módulos que los ofrezcan y que permitan desarrollar un sistema para Smartphone mediante el que se puedan obtener medidas tanto de dispositivos biométricos como de una red inalámbrica de sensores (WSN – Wireless Sensor Network). Estos dos tipos de medidas deben poder ser mostradas de manera que se observe gráficamente su correlación espacio-temporal. Por tanto, estos interfaces ofrecen, principalmente, la posibilidad de gestionar un número indeterminado de dispositivos biométricos y tomar medidas de ellos, además de mecanismos de almacenamiento para dichas medidas. También existe la posibilidad de crear una representación gráfica de dichas medidas. Por último, se desarrolla un interfaz para obtener información proveniente de una red de sensores inalámbricos instalada en un determinado entorno en el cual el usuario estará realizando sus propias medidas. Además, se lleva a cabo la creación de la aplicación comentada, que hace uso de las interfaces especificadas, para realizar la correlación de las medidas. La aplicación permite al usuario mantener una lista de dispositivos, pudiendo consultar los parámetros de configuración de los mismos y tomar las medidas de aquellos que desee. Podrá visualizar en todo momento las medidas que se van realizando, y, por último, podrá representarlas gráficamente en pantalla. Los interfaces están creados de forma que sean flexibles de modo que puedan añadirse nuevas funciones en un futuro y permitan ser utilizados para diferentes aplicaciones. Los módulos que ofrecen estos interfaces están desarrollados para cumplir todas las funcionalidades que esperamos llevar a cabo en la aplicación creada. ABSTRACT. This Final Degree Project is focused on the definition of a set of interfaces, together with the implementation of the modules that comply with them, with the aim of creating a smartphone-based system to obtain measurements from both biometric devices and a wireless sensor network (WSN). These two types of measurements have to be graphically shown in order to observe their spatial and temporal correlation. Thus, the main purpose of the aforementioned interfaces is to manage an indeterminate number of biometric devices in order to obtain and store the measurements provided by them. There is also the possibility of creating a graphical representation of the data. In addition to all this, an interface has been developed for obtaining the information coming from a wireless sensor network deployed in the area where the user is taking his/her measurements. Also as part of the work performed, the smartphone application that utilizes the specified interfaces has been implemented, in order to actually perform the measurements correlation. This application allows the user to maintain the biometric devices list and control their configuration, including the activation of the measurements taking process. These data can be visualized anytime and, moreover, they can be represented graphically in the smartphone screen. The design of the interfaces is flexible in the sense that new functionality may be easily added to them in the future and new applications with different purposes may make use of them. The modules implemented as part of this Final Degree Project have been developed in order to comply with all the requirements of the smartphone system described above.

Hardware timestamping for image acquisition system based on FlexRIO and IEEE 1588 v2 Standard

Current fusion devices consist of multiple diagnostics and hundreds or even thousands of signals. This situation forces on multiple occasions to use distributed data acquisition systems as the best approach. In this type of distributed systems, one of the most important issues is the synchronization between signals, so that it is possible to have a temporal correlation as accurate as possible between the acquired samples of all channels. In last decades, many fusion devices use different types of video cameras to provide inside views of the vessel during operations and to monitor plasma behavior. The synchronization between each video frame and the rest of the different signals acquired from any other diagnostics is essential in order to know correctly the plasma evolution, since it is possible to analyze jointly all the information having accurate knowledge of their temporal correlation. The developed system described in this paper allows timestamping image frames in a real-time acquisition and processing system using 1588 clock distribution. The system has been implemented using FPGA based devices together with a 1588 synchronized timing card (see Fig.1). The solution is based on a previous system [1] that allows image acquisition and real-time image processing based on PXIe technology. This architecture is fully compatible with the ITER Fast Controllers [2] and offers integration with EPICS to control and monitor the entire system. However, this set-up is not able to timestamp the frames acquired since the frame grabber module does not present any type of timing input (IRIG-B, GPS, PTP). To solve this lack, an IEEE1588 PXI timing device its used to provide an accurate way to synchronize distributed data acquisition systems using the Precision Time Protocol (PTP) IEEE 1588 2008 standard. This local timing device can be connected to a master clock device for global synchronization. The timing device has a buffer timestamp for each PXI trigger line and requires tha- a software application assigns each frame the corresponding timestamp. The previous action is critical and cannot be achieved if the frame rate is high. To solve this problem, it has been designed a solution that distributes the clock from the IEEE 1588 timing card to all FlexRIO devices [3]. This solution uses two PXI trigger lines that provide the capacity to assign timestamps to every frame acquired and register events by hardware in a deterministic way. The system provides a solution for timestamping frames to synchronize them with the rest of the different signals.

Scale dependence in earthquake phenomena and its relevance to earthquake prediction.

The recent discovery of a low-velocity, low-Q zone with a width of 50-200 m reaching to the top of the ductile part of the crust, by observations on seismic guided waves trapped in the fault zone of the Landers earthquake of 1992, and its identification with the shear zone inferred from the distribution of tension cracks observed on the surface support the existence of a characteristic scale length of the order of 100 m affecting various earthquake phenomena in southern California, as evidenced earlier by the kink in the magnitude-frequency relation at about M3, the constant corner frequency for earthquakes with M below about 3, and the sourcecontrolled fmax of 5-10 Hz for major earthquakes. The temporal correlation between coda Q-1 and the fractional rate of occurrence of earthquakes in the magnitude range 3-3.5, the geographical similarity of coda Q-1 and seismic velocity at a depth of 20 km, and the simultaneous change of coda Q-1 and conductivity at the lower crust support the hypotheses that coda Q-1 may represent the activity of creep fracture in the ductile part of the lithosphere occurring over cracks with a characteristic size of the order of 100 m. The existence of such a characteristic scale length cannot be consistent with the overall self-similarity of earthquakes unless we postulate a discrete hierarchy of such characteristic scale lengths. The discrete hierarchy of characteristic scale lengths is consistent with recently observed logarithmic periodicity in precursory seismicity.

Strand specificity in the transcriptional targeting of recombination at immunoglobulin switch sequences.

B-lymphocyte-specific class switch recombination is known to occur between pairs of 2- to 10-kb switch regions located immediately upstream of the immunoglobulin constant heavy-chain genes. Others have shown that the recombination is temporally correlated with the induction of transcription at the targeted switch regions. To determine whether this temporal correlation is due to a mechanistic linkage, we have developed an extrachromosomal recombination assay that closely recapitulates DNA deletional class switch recombination. In this assay, the rate of recombination is measured between 24 and 48 hr posttransfection. We find that recombinants are generated in a switch sequence-dependent manner. Recombination occurs with a predominance within B-cell lines representative of the mature B-cell stage and within a subset of pre-B-cell lines. Transcription stimulates the switch sequence-dependent recombination. Importantly, transcription activates recombination only when directed in the physiologic orientation but has no effect when directed in the nonphysiologic orientation.

Hierarchical indexing structure for efficient similarity search in video retrieval

With the rapid increase in both centralized video archives and distributed WWW video resources, content-based video retrieval is gaining its importance. To support such applications efficiently, content-based video indexing must be addressed. Typically, each video is represented by a sequence of frames. Due to the high dimensionality of frame representation and the large number of frames, video indexing introduces an additional degree of complexity. In this paper, we address the problem of content-based video indexing and propose an efficient solution, called the Ordered VA-File (OVA-File) based on the VA-file. OVA-File is a hierarchical structure and has two novel features: 1) partitioning the whole file into slices such that only a small number of slices are accessed and checked during k Nearest Neighbor (kNN) search and 2) efficient handling of insertions of new vectors into the OVA-File, such that the average distance between the new vectors and those approximations near that position is minimized. To facilitate a search, we present an efficient approximate kNN algorithm named Ordered VA-LOW (OVA-LOW) based on the proposed OVA-File. OVA-LOW first chooses possible OVA-Slices by ranking the distances between their corresponding centers and the query vector, and then visits all approximations in the selected OVA-Slices to work out approximate kNN. The number of possible OVA-Slices is controlled by a user-defined parameter delta. By adjusting delta, OVA-LOW provides a trade-off between the query cost and the result quality. Query by video clip consisting of multiple frames is also discussed. Extensive experimental studies using real video data sets were conducted and the results showed that our methods can yield a significant speed-up over an existing VA-file-based method and iDistance with high query result quality. Furthermore, by incorporating temporal correlation of video content, our methods achieved much more efficient performance.

Mechanisms for triggering high-voltage breakdown in vacuum

The electrical and optical characteristics of a cylindrical alumina insulator (94% Al203) have been measured under ultra-high vacuum (P < 10-8 mBar) conditions. A high-resolution CCD camera was used to make real-time optical recordings of DC prebreakdown luminescence from the ceramic, under conditions where DC current magnitudes were limited to less than 50μA. Two concentric metallized rings formed a pair of co-axial electrodes, on the end-face of the alumina tube; a third 'transparent' electrode was employed to study the effect of an orthogonal electric field upon the radial conduction processes within the metallized alumina specimen. The wavelength-spectra of the emitted light was quantified using a high-speed scanning monochromator and photo-multiplier tube detector. Concurrent electrical measurements were made alongside the recording of optical-emission images. An observed time-dependence of the photon-emission is correlated with a time-variation observed in the DC current-voltage characteristics of the alumina. Optical images were also recorded of pulsed-field surface-flashover events on the alumina ceramic. An intensified high-speed video technique provided 1ms frames of surface-flashover events, whilst 100ns frames were achieved using an ultra high-speed fast-framing camera. By coupling this fast-frame camera to a digital storage oscilloscope, it was possible to establish a temporal correlation between the application of a voltage-pulse to the ceramic and the evolution of photonic emissions from the subsequent surface-flashover event. The electro-optical DC prebreakdown characteristics of the alumina are discussed in terms of solid-state photon-emission processes, that are believed to arise from radiative electron-recombination at vacancy-defects and substitutional impurity centres within the surface-layers of the ceramic. The physical nature of vacancy-defects within an alumina dielectric is extensively explored, with a particular focus placed upon the trapped electron energy-levels that may be present at these defect centres. Finally, consideration is given to the practical application of alumina in the trigger-ceramic of a sealed triggered vacuum gap (TVG) switch. For this purpose, a physical model describing the initiation of electrical breakdown within the TVG regime is proposed, and is based upon the explosive destabilisation of trapped charge within the alumina ceramic, triggering the onset of surface-flashover along the insulator. In the main-gap prebreakdown phase, it is suggested that the electrical-breakdown of the TVG is initiated by the low-field 'stripping' of prebreakdown electrons from vacancy-defects in the ceramic under the influence of an orthogonal main-gap electric field.

Fluctuations and correlations in sandpiles and interfaces with boundary pinning

Interfaces are studied in an inhomogeneous critical state where boundary pinning is compensated with a ramped force. Sandpiles driven off the self-organized critical point provide an example of this ensemble in the Edwards-Wilkinson (EW) model of kinetic roughening. A crossover from quenched to thermal noise violates spatial and temporal translational invariances. The bulk temporal correlation functions have the effective exponents β1D∼0.88±0.03 and β2D∼0.52±0.05, while at the boundaries βb,1D/2D∼0.47±0.05. The bulk β1D is shown to be reproduced in a randomly kicked thermal EW model.

Fluctuations and correlations in sandpiles and interfaces with boundary pinning

Interfaces are studied in an inhomogeneous critical state where boundary pinning is compensated with a ramped force. Sandpiles driven off the self-organized critical point provide an example of this ensemble in the Edwards-Wilkinson (EW) model of kinetic roughening. A crossover from quenched to thermal noise violates spatial and temporal translational invariances. The bulk temporal correlation functions have the effective exponents β1D∼0.88±0.03 and β2D∼0.52±0.05, while at the boundaries βb,1D/2D∼0.47±0.05. The bulk β1D is shown to be reproduced in a randomly kicked thermal EW model.

Manometry-Based Cough Identification Algorithm

Gastroesophageal reflux disease (GERD) is a common cause of chronic cough. For the diagnosis and treatment of GERD, it is desirable to quantify the temporal correlation between cough and reflux events. Cough episodes can be identified on esophageal manometric recordings as short-duration, rapid pressure rises. The present study aims at facilitating the detection of coughs by proposing an algorithm for the classification of cough events using manometric recordings. The algorithm detects cough episodes based on digital filtering, slope and amplitude analysis, and duration of the event. The algorithm has been tested on in vivo data acquired using a single-channel intra-esophageal manometric probe that comprises a miniature white-light interferometric fiber optic pressure sensor. Experimental results demonstrate the feasibility of using the proposed algorithm for identifying cough episodes based on real-time recordings using a single channel pressure catheter. The presented work can be integrated with commercial reflux pH/impedance probes to facilitate simultaneous 24-hour ambulatory monitoring of cough and reflux events, with the ultimate goal of quantifying the temporal correlation between the two types of events.

O paradoxo da superdifusão de uma caminhada aleatória com memória exponencial

The random walk models with temporal correlation (i.e. memory) are of interest in the study of anomalous diffusion phenomena. The random walk and its generalizations are of prominent place in the characterization of various physical, chemical and biological phenomena. The temporal correlation is an essential feature in anomalous diffusion models. These temporal long-range correlation models can be called non-Markovian models, otherwise, the short-range time correlation counterparts are Markovian ones. Within this context, we reviewed the existing models with temporal correlation, i.e. entire memory, the elephant walk model, or partial memory, alzheimer walk model and walk model with a gaussian memory with profile. It is noticed that these models shows superdiffusion with a Hurst exponent H > 1/2. We study in this work a superdiffusive random walk model with exponentially decaying memory. This seems to be a self-contradictory statement, since it is well known that random walks with exponentially decaying temporal correlations can be approximated arbitrarily well by Markov processes and that central limit theorems prohibit superdiffusion for Markovian walks with finite variance of step sizes. The solution to the apparent paradox is that the model is genuinely non-Markovian, due to a time-dependent decay constant associated with the exponential behavior. In the end, we discuss ideas for future investigations.

Statistical Analysis of Wind Power Generation in Europe

Studies have shown that large geographical spreading can reduce the wind power variability and smooth production. It is frequently assumed that storage and interconnection can manage wind power variability and are totally flexible. However, constraints do exist. In the future more and more electricity will be provided by renewable energy sources and more electricity interconnectors will be built between European Union (EU) countries, as outlines in many of the Projects of Common Interests. It is essential to understand the correlation of wind generation throughout Europe considering power system constraints. In this study the spatial and temporal correlation of wind power production across several countries is examined in order to understand how “the wind ‘travels’ across Europe”. Three years of historical hourly wind power generation from ten EU countries is analysed to investigate the geographic diversity and time scales influence on correlation of wind power variations. Results are then compared with two other studies and show similar general characteristics of correlation between EU country pairs to identify opportunities for storage optimisation, power system operations, and trading.