Temporally Causal Discovery Tests for Discrete Time Series and Neural Spike Trains

We consider the problem of detecting causal relationships between discrete time series, in the presence of potential confounders. A hypothesis test is introduced for identifying the temporally causal influence of $(x_n)$ on $(y_n)$, causally conditioned on a possibly confounding third time series $(z_n)$. Under natural Markovian modeling assumptions, it is shown that the null hypothesis, corresponding to the absence of temporally causal influence, is equivalent to the underlying `causal conditional directed information rate' being equal to zero. The plug-in estimator for this functional is identified with the log-likelihood ratio test statistic for the desired test. This statistic is shown to be asymptotically normal under the alternative hypothesis and asymptotically $\chi^2$ distributed under the null, facilitating the computation of $p$-values when used on empirical data. The effectiveness of the resulting hypothesis test is illustrated on simulated data, validating the underlying theory. The test is also employed in the analysis of spike train data recorded from neurons in the V4 and FEF brain regions of behaving animals during a visual attention task. There, the test results are seen to identify interesting and biologically relevant information.Comment: 31 pages, 4 figure

Summation characteristics of the detection of compound gratings

AbstractMany classical experiments have shown that two superimposed gratings are more easily detected than a single grating, in keeping with probability theory. Here we test the rules for the detection of 2-component compound gratings by extending the range of parameters used in previous experiments. Two complementary methods of deriving summation indices are described. Data are presented so that the conditions for the transition from probability to neural summation are easily identified. True probability summation occurs only when grating contrasts are carefully perceptually equalised and spatial frequency differs by more than a factor of 2. A wide range of contrast ratios of the component gratings were explored such that gratings were at different contrasts, relative to respective thresholds. We find clear evidence of suppressive interactions when the compound gratings are composed of a close to threshold low frequency component and a below-threshold higher spatial frequency component

Electron cloud buildup and impedance effects on beam dynamics in the future circular e+e− collider and experimental characterization of thin TiZrV vacuum chamber coatings

The Future Circular Collider FCC-ee is a study toward a high luminosity electron-positron collider with a centre-of-mass energy from 91 GeV to 365 GeV. Due to the beam parameters and pipe dimensions, collective effects and electron cloud can be very critical aspects for the machine and can represent the main limitations to its performance. An estimation of the electron cloud build up in the main machine components and an impedance model are required to analyze the induced instabilities and to find solutions for their mitigation. Special attention has been given to the resistive wall impedance associated with a layer of nonevaporable getter (NEG) coating on the vacuum chamber required for electron cloud mitigation. The studies presented in this paper will show that minimizing the thickness of this coating layer is mandatory to increase the single bunch instability thresholds in the proposed lepton collider at 45.6 GeV. For this reason, NEG thin films with thicknesses below 250 nm have been investigated by means of numerical simulations to minimize the resistive wall impedance. In parallel, an extensive measurement campaign was performed at CERN to characterize these thin films, with the purpose of finding the minimum effective thickness satisfying vacuum and electron cloud requirements

Χρήση του δείκτη QBR για την εκτίμηση των επιπτώσεων της κατασκευής φραγμάτων κατά μήκος της κοίτης ενός μεσογειακού χειμάρρου στην παρόχθια βλάστηση

Ο χείμαρρος «Γεραμπίνη» Ζαγοράς Πηλίου, ο οποίος αποτελεί την περιοχή μελέτης, είναι ένα υδατικό οικοσύστημα με έντονες διακυμάνσεις στο υδρολογικό του ισοζύγιο. Με κύριο στόχο την αποτροπή των πλημυρρικών φαινομένων, κατασκευάστηκαν κατά μήκος του, είκοσι ένα (21) φράγματα στερέωσης. Στην παρούσα εργασία προσδιορίζεται και αναλύεται ο δείκτης QBR «Qualitat del Bosc de Ribera», ο οποίος αποτελεί έναν αξιόπιστο ποιοτικό δείκτη της παρόχθιας βλάστησης για τα μεσογειακά υδατικά οικοσυστήματα. Από την συλλογή, επεξεργασία και ανάλυση των δεδομένων προκύπτει ότι η τεχνητή διευθέτηση του μεσογειακού χειμάρρου δεν αποτέλεσε τροχοπέδη στη διατήρηση και στην αναβάθμιση της δυναμικής των στοιχείων που συντελούν στη φυσική εξέλιξη της παρόχθιας βλάστησής του

Wolbachia Horizontal Transmission Events in Ants: What Do We Know and What Can We Learn?

While strict vertical transmission insures the durability of intracellular symbioses, phylogenetic incongruences between hosts and endosymbionts suggest horizontal transmission must also occur. These horizontal acquisitions can have important implications for the biology of the host. Wolbachia is one of the most ecologically successful prokaryotes in arthropods, infecting an estimated 50–70% of all insect species. Much of this success is likely due to the fact that, in arthropods, Wolbachia is notorious for manipulating host reproduction to favor transmission through the female germline. However, its natural potential for horizontal transmission remains poorly understood. Here we evaluate the fundamental prerequisites for successful horizontal transfer, including necessary environmental conditions, genetic potential of bacterial strains, and means of mediating transfers. Furthermore, we revisit the relatedness of Wolbachia strains infecting the Panamanian leaf-cutting ant, Acromyrmex echinatior, and its inquiline social parasite, Acromyrmex insinuator, and compare our results to a study published more than 15 years ago by Van Borm et al. (2003). The results of this pilot study prompt us to reevaluate previous notions that obligate social parasitism reliably facilitates horizontal transfer and suggest that not all Wolbachia strains associated with ants have the same genetic potential for horizontal transmission

The psychology of conspiracy theories

What psychological factors drive the popularity of conspiracy theories that explain important events as secret plots by powerful and malevolent groups? What are the psychological consequences of adopting these theories? We review the current research, and find that it answers the first of these questions more thoroughly than the second. Belief in conspiracy theories appears to be driven by motives that can be characterized as epistemic (understanding one’s environment), existential (being safe and in control of one’s environment) and social (maintaining a positive image of the self and the social group). However, little research has investigated the consequences of conspiracy belief, and to date, this research does not indicate that conspiracy belief fulfills people’s motivations. Instead, for many people conspiracy belief may be more appealing than satisfying. Further research is needed to determine for whom, and under what conditions, conspiracy theories may satisfy key psychological motives

Efficient construction of the kedarcidin chromophore ansamacrolide

The streamlined assembly of the ansamacrolide framework of the kedarcidin chromophore via an efficient atropselective Sonogashira coupling step is described. To this end, two newly improved practical syntheses of the cyclopentene and dine fragments have been developed, which feature 0.2 mol % catalytic loadings for an RCM step and i-PrMgCl/CH2I2 as a new entry to gem-disubstituted epoxides from ketones, both being applicable to 49-g scales