New Pteraspidiform Heterostracans (Vertebrata) from the lower Devonian of La Gileppe and Nonceveux, Belgium

Original material of vertebrates from two Lower Devonian localities of the Belgian Ardenne Massif is described. The material from La Gileppe includes Rhinopteraspis crouchi (Vertebrata, Heterostraci, Pteraspidiformes) and is the first confirmation of vertebrate for this late Lochkovian locality belonging to the Z Spore Zone, and correlated to the lower part of the Althaspis leachi Fish Zone. This confirms the overlapping range of R. crouchi and A. leachi in the siliciclastic Lower Devonian of Western Europe. An orbital plate and two other elements of an undetermined pteraspidiform from Nonceveux are added to the material already known from this locality. The Nonceveux locality is late Lochkovian in age and belongs to the G Spore Zone, which is correlated to the base of the A. leachi Fish Zone. The La Gileppe material is composed of small specimens which are interpreted as either of juvenile individuals or of small adults. It is consistent with previous results on French-Belgian localities among the Early Devonian siliciclastic deposits of Western Europe (Old Red Sandstones and allied facies) which have been interpreted as confined, restricted marine environments

Hyperconvex representations and exponential growth

Let $G$ be a real algebraic semi-simple Lie group and $\Gamma$ be the fundamental group of a compact negatively curved manifold. In this article we study the limit cone, introduced by Benoist, and the growth indicator function, introduced by Quint, for a class of representations $\rho:\Gamma\to G$ admitting a equivariant map from $\partial\Gamma$ to the Furstenberg boundary of $G$'s symmetric space together with a transversality condition. We then study how these objects vary with the representation

A group model for stable multi-subject ICA on fMRI datasets

Spatial Independent Component Analysis (ICA) is an increasingly used data-driven method to analyze functional Magnetic Resonance Imaging (fMRI) data. To date, it has been used to extract sets of mutually correlated brain regions without prior information on the time course of these regions. Some of these sets of regions, interpreted as functional networks, have recently been used to provide markers of brain diseases and open the road to paradigm-free population comparisons. Such group studies raise the question of modeling subject variability within ICA: how can the patterns representative of a group be modeled and estimated via ICA for reliable inter-group comparisons? In this paper, we propose a hierarchical model for patterns in multi-subject fMRI datasets, akin to mixed-effect group models used in linear-model-based analysis. We introduce an estimation procedure, CanICA (Canonical ICA), based on i) probabilistic dimension reduction of the individual data, ii) canonical correlation analysis to identify a data subspace common to the group iii) ICA-based pattern extraction. In addition, we introduce a procedure based on cross-validation to quantify the stability of ICA patterns at the level of the group. We compare our method with state-of-the-art multi-subject fMRI ICA methods and show that the features extracted using our procedure are more reproducible at the group level on two datasets of 12 healthy controls: a resting-state and a functional localizer study

Exploratory fMRI analysis without spatial normalization

Author Manuscript received 2010 March 11. 21st International Conference, IPMI 2009, Williamsburg, VA, USA, July 5-10, 2009. ProceedingsWe present an exploratory method for simultaneous parcellation of multisubject fMRI data into functionally coherent areas. The method is based on a solely functional representation of the fMRI data and a hierarchical probabilistic model that accounts for both inter-subject and intra-subject forms of variability in fMRI response. We employ a Variational Bayes approximation to fit the model to the data. The resulting algorithm finds a functional parcellation of the individual brains along with a set of population-level clusters, establishing correspondence between these two levels. The model eliminates the need for spatial normalization while still enabling us to fuse data from several subjects. We demonstrate the application of our method on a visual fMRI study.McGovern Institute for Brain Research at MIT. Neurotechnology ProgramNational Science Foundation (U.S.) (CAREER Grant 0642971)National Institutes of Health (U.S.) (NIBIB NAMIC U54-EB005149)National Institutes of Health (U.S.) (NCRR NAC P41-RR13218

Statistically Valid Variable Importance Assessment through Conditional Permutations

Variable importance assessment has become a crucial step in machine-learning applications when using complex learners, such as deep neural networks, on large-scale data. Removal-based importance assessment is currently the reference approach, particularly when statistical guarantees are sought to justify variable inclusion. It is often implemented with variable permutation schemes. On the flip side, these approaches risk misidentifying unimportant variables as important in the presence of correlations among covariates. Here we develop a systematic approach for studying Conditional Permutation Importance (CPI) that is model agnostic and computationally lean, as well as reusable benchmarks of state-of-the-art variable importance estimators. We show theoretically and empirically that $\textit{CPI}$ overcomes the limitations of standard permutation importance by providing accurate type-I error control. When used with a deep neural network, $\textit{CPI}$ consistently showed top accuracy across benchmarks. An empirical benchmark on real-world data analysis in a large-scale medical dataset showed that $\textit{CPI}$ provides a more parsimonious selection of statistically significant variables. Our results suggest that $\textit{CPI}$ can be readily used as drop-in replacement for permutation-based methods

Parametric oscillator based on non-linear vortex dynamics in low resistance magnetic tunnel junctions

Radiofrequency vortex spin-transfer oscillators based on magnetic tunnel junctions with very low resistance area product were investigated. A high power of excitations has been obtained characterized by a power spectral density containing a very sharp peak at the fundamental frequency and a series of harmonics. The observed behaviour is ascribed to the combined effect of spin transfer torque and Oersted-Amp\`ere field generated by the large applied dc-current. We furthermore show that the synchronization of a vortex oscillation by applying a ac bias current is mostly efficient when the external frequency is twice the oscillator fundamental frequency. This result is interpreted in terms of a parametric oscillator.Comment: 4 pages, 4 figure

Information Literacy in Students Entering Higher Education in the French Speaking Community of Belgium: lessons learned from an evaluation

Although universities are providing more and more information literacy training for their undergraduate students, the students’ real level of information literacy at the beginning of their studies has never been assessed. Hence EduDOC has decided to team up with the CIUF ‘Library’ Commission in order to organize a wide study aiming at objectively describing this initial level of information literacy, at identifying the students’ main weaknesses, as well as allowing instructors to adjust their training on this basis. The questionnaire was based on a similar study carried out in Québec and contains 20 questions grouped in five themes relating to information search steps. It was sent in September 2007 to a random sample of students entering a higher education institution in the French Speaking Community of Belgium for the first time. The students’ rather poor results confirm that organizing an information literacy program is imperative if students are to perform well in their studies.Peer reviewe

Multi-input CRISPR/Cas genetic circuits that interface host regulatory networks

Genetic circuits require many regulatory parts in order to implement signal processing or execute algorithms in cells. A potentially scalable approach is to use dCas9, which employs small guide RNAs (sgRNAs) to repress genetic loci via the programmability of RNA:DNA base pairing. To this end, we use dCas9 and designed sgRNAs to build transcriptional logic gates and connect them to perform computation in living cells. We constructed a set of NOT gates by designing five synthetic Escherichia coli σ[subscript 70] promoters that are repressed by corresponding sgRNAs, and these interactions do not exhibit crosstalk between each other. These sgRNAs exhibit high on‐target repression (56‐ to 440‐fold) and negligible off‐target interactions (< 1.3‐fold). These gates were connected to build larger circuits, including the Boolean‐complete NOR gate and a 3‐gate circuit consisting of four layered sgRNAs. The synthetic circuits were connected to the native E. coli regulatory network by designing output sgRNAs to target an E. coli transcription factor (malT). This converts the output of a synthetic circuit to a switch in cellular phenotype (sugar utilization, chemotaxis, phage resistance).United States. Defense Advanced Research Projects Agency (CLIO N66001‐12‐C‐4016)National Institutes of Health (U.S.) (GM095765)National Institute of General Medical Sciences (U.S.) (Grant P50 GMO98792)Synthetic Biology Engineering Research Center (EEC0540879)United States. Defense Advanced Research Projects Agency (Ginkgo BioWorks. CLIO N66001‐12‐C‐4018)United States. Office of Naval Research. Multidisciplinary University Research Initiative (Grant N00014‐13‐1‐0074)United States. Office of Naval Research. Multidisciplinary University Research Initiative (Boston University. Award 4500000552)United States. Air Force Office of Scientific Research (FA9550‐11‐C‐0028)American Society for Engineering Education. National Defense Science and Engineering Graduate Fellowship (32 CFR 168a

Micro-SQUID technique for studying the temperature dependence of switching fields of single nanoparticles

An improved micro-SQUID technique is presented allowing us to measure the temperature dependence of the magnetisation switching fields of single nanoparticles well above the critical superconducting temperature of the SQUID. Our first measurements on 3 nm cobalt nanoparticle embedded in a niobium matrix are compared to the Neel Brown model describing the magnetisation reversal by thermal activation over a single anisotropy barrier.Comment: 3 pages, 4 figures; conference proceeding: 1st Joint European Magnetic Symposia (JEMS'01), Grenoble (France), 28th August - 1st September, 200