Low-rank matrix decompositions for ab initio nuclear structure

The extension of ab initio quantum many-body theory to higher accuracy and larger systems is intrinsically limited by the handling of large data objects in form of wave-function expansions and/or many-body operators. In this work we present matrix factorization techniques as a systematically improvable and robust tool to significantly reduce the computational cost in many-body applications at the price of introducing a moderate decomposition error. We demonstrate the power of this approach for the nuclear two-body systems, for many-body perturbation theory calculations of symmetric nuclear matter, and for non-perturbative in-medium similarity renormalization group simulations of finite nuclei. Establishing low-rank expansions of chiral nuclear interactions offers possibilities to reformulate many-body methods in ways that take advantage of tensor factorization strategies

Least-square approach for singular value decompositions of scattering problems

It was recently observed that chiral two-body interactions can be efficientlyrepresented using matrix factorization techniques such as the singular valuedecomposition. However, the exploitation of these low-rank structures in a few-or many-body framework is nontrivial and requires reformulations thatexplicitly utilize the decomposition format. In this work, we present a generalleast-square approach that is applicable to different few- and many-bodyframeworks and allows for an efficient reduction to a low number of singularvalues in the least-square iteration. We verify the feasibility of theleast-square approach by solving the Lippmann-Schwinger equation in factorizedform. The resulting low-rank approximations of the $T$ matrix are found tofully capture scattering observables. Potential applications of theleast-square approach to other frameworks with the goal of employing tensorfactorization techniques are discussed.<br

Low-Rank Decompositions of Three-Nucleon Forces via Randomized Projections

Ab initio calculations for nuclei and nuclear matter are limited by the computational requirements of processing large data objects. In this work, we develop low-rank singular value decompositions for chiral three-nucleon interactions, which dominate these limitations. In order to handle the large dimensions in representing three-body operators, we use randomized decomposition techniques. We study in detail the sensitivity of different three-nucleon topologies to low-rank matrix factorizations. The developed low-rank three-nucleon interactions are benchmarked in Faddeev calculations of the triton and ab initio calculations of medium-mass nuclei. Exploiting low-rank properties of nuclear interactions will be particularly important for the extension of ab initio studies to heavier and deformed systems, where storage requirements will exceed the computational capacities of the most advanced high-performance-computing facilities.Comment: 7 pages, 4 figure

Prenatal diagnosis and outcome of fetuses with isolated agenesis of septum pellucidum: cohort study and meta-analysis

Objective: To evaluate the postnatal outcome of children with a prenatal diagnosis of apparently isolated agenesis of the septum pellucidum (ASP). Methods: A retrospective cohort study of cases of prenatally diagnosed ASP followed in two tertiary centers and a meta-analysis combining data from the cohort study with data from published studies identified in a systematic review were carried out. Only cases with apparently isolated ASP on antenatal ultrasound and/or magnetic resonance imaging and with available postnatal follow-up data were considered eligible for inclusion. The following outcomes were analyzed: incidence of chromosomal anomalies, agreement between antenatal and postnatal findings, overall incidence of septo-optic dysplasia (SOD) and incidence of major neurological disability (motor, language, coordination or behavioral disorder or epilepsy) in non-SOD children. The incidence of SOD in infants with apparently normal optic pathways on antenatal imaging was also evaluated. Results: Fifteen cases of isolated ASP, with median postnatal follow-up of 36 months (range, 12-60 months), were selected from the two centers. Six previously published studies met the inclusion criteria for the systematic review and a total of 78 cases were eligible for the analysis, including the 15 cases from our series. Genetic tests were carried out antenatally in 30 fetuses, of which two had an abnormal result (pooled proportion, 9.0% (95% CI, 1.8-20.7%); I2  = 0%). Additional or discordant imaging findings were noted postnatally in 9/70 (pooled proportion, 13.7% (95% CI, 3.5-29.0%); I2  = 63.9%) cases. Of all 78 neonates with available follow-up, SOD was diagnosed postnatally in 14 (pooled proportion, 19.4% (95% CI, 8.6-33.2%); I2  = 51.2%). In 60 cases, the optic pathways were considered to be normal on antenatal imaging, and six of these (pooled proportion, 9.1% (95% CI, 1.1-24.0%); I2  = 62.0%) were diagnosed postnatally with SOD. Of the 46 infants with available neurological follow-up who were not affected by SOD, a major neurological disability was diagnosed in three (pooled proportion, 6.5% (95% CI, 0.5-18.6%); I2  = 40.1%). Conclusions: In the vast majority of cases with a prenatal diagnosis of apparently isolated ASP, the prognosis is favorable. However, an additional anomaly is detected after birth in about 14% of cases and has a negative impact on clinical outcome. Detailed antenatal assessment of the brain and optic pathways is strongly recommended in order to identify the presence of associated anomalies. Antenatal visualization of apparently normal optic pathways does not rule out SOD. © 2021 International Society of Ultrasound in Obstetrics and Gynecology

Influence of wiring cost on the large-scale architecture of human cortical connectivity

In the past two decades some fundamental properties of cortical connectivity have been discovered: small-world structure, pronounced hierarchical and modular organisation, and strong core and rich-club structures. A common assumption when interpreting results of this kind is that the observed structural properties are present to enable the brain's function. However, the brain is also embedded into the limited space of the skull and its wiring has associated developmental and metabolic costs. These basic physical and economic aspects place separate, often conflicting, constraints on the brain's connectivity, which must be characterized in order to understand the true relationship between brain structure and function. To address this challenge, here we ask which, and to what extent, aspects of the structural organisation of the brain are conserved if we preserve specific spatial and topological properties of the brain but otherwise randomise its connectivity. We perform a comparative analysis of a connectivity map of the cortical connectome both on high- and low-resolutions utilising three different types of surrogate networks: spatially unconstrained (‘random’), connection length preserving (‘spatial’), and connection length optimised (‘reduced’) surrogates. We find that unconstrained randomisation markedly diminishes all investigated architectural properties of cortical connectivity. By contrast, spatial and reduced surrogates largely preserve most properties and, interestingly, often more so in the reduced surrogates. Specifically, our results suggest that the cortical network is less tightly integrated than its spatial constraints would allow, but more strongly segregated than its spatial constraints would necessitate. We additionally find that hierarchical organisation and rich-club structure of the cortical connectivity are largely preserved in spatial and reduced surrogates and hence may be partially attributable to cortical wiring constraints. In contrast, the high modularity and strong s-core of the high-resolution cortical network are significantly stronger than in the surrogates, underlining their potential functional relevance in the brain

Oxidative Coupling as a Biomimetic Approach to the Synthesis of Scytonemin

The first total synthesis of the dimeric alkaloid pigment scytonemin is described. The key transformations In Its synthesis from 3-indole acetic acid are a Heck carbocyclization and a Suzuki-Miyaura cross-coupling, orchestrated In a stereospecific tandem fashion, followed by a biosynthetically inspired oxidative dimerization. The tandem sequence generates a tetracyclic (E)-3-(arylidene)-3,4-dihydrocyclopenta[b]indol-2(1H)-one that is subsequently dimerized into the unique homodimeric core structure of scytonemin

Granger Causality Analysis of Steady-State Electroencephalographic Signals during Propofol-Induced Anaesthesia

Changes in conscious level have been associated with changes in dynamical integration and segregation among distributed brain regions. Recent theoretical developments emphasize changes in directed functional (i.e., causal) connectivity as reflected in quantities such as ‘integrated information’ and ‘causal density’. Here we develop and illustrate a rigorous methodology for assessing causal connectivity from electroencephalographic (EEG) signals using Granger causality (GC). Our method addresses the challenges of non-stationarity and bias by dividing data into short segments and applying permutation analysis. We apply the method to EEG data obtained from subjects undergoing propofol-induced anaesthesia, with signals source-localized to the anterior and posterior cingulate cortices. We found significant increases in bidirectional GC in most subjects during loss-of-consciousness, especially in the beta and gamma frequency ranges. Corroborating a previous analysis we also found increases in synchrony in these ranges; importantly, the Granger causality analysis showed higher inter-subject consistency than the synchrony analysis. Finally, we validate our method using simulated data generated from a model for which GC values can be analytically derived. In summary, our findings advance the methodology of Granger causality analysis of EEG data and carry implications for integrated information and causal density theories of consciousness

Positron emission tomography in patients with psychogenic non-epileptic seizures

Aileen McGonigal,1&ndash;3 Marie Arthuis,3 Jean-Arthur Micoulaud-Franchi,4,5 Fabrice Bartolomei,1&ndash;3 Eric Guedj6&ndash;8 1Institut de Neurosciences des Syst&egrave;mes, INSERM UMR 1106, Marseille, France; 2Aix Marseille University, Faculty of Medicine, Marseille, France; 3Clinical Neurophysiology Department, Timone Hospital, Marseille, France; 4Department of Functional Investigation of the Nervous System, Sleep Clinic, Bordeaux University Hospital, Bordeaux, France; 5USR CNRS 3413, University of Bordeaux, France; 6Biophysics and Nuclear Medicine Department, Timone Hospital, Marseille, France; 7Aix-Marseille University, CERIMED, Marseille, France; 8Aix-Marseille University, CNRS, UMR7289, INT, Marseille, FranceWe have read with interest the recent review entitled &ldquo;Uncovering the etiology of conversion disorder: insights from functional neuroimaging&rdquo; by Maryam Ejareh dar and Richard AA Kanaan,1 published in Neuropsychiatric Disease and Treatment. Our paper on resting state brain metabolism measured by positron emission tomography (PET) was included and discussed.2 We were most surprised to see that the authors of the review seem to have misunderstood the findings of our study, which concerned patients with psychogenic non-epileptic seizures (PNES). The authors state that the 16 patients included in our study &ldquo;were later found to have PNES with comorbid epilepsy&rdquo;. This is incorrect, since our study included only patients with PNES in whom comorbid epilepsy was excluded. This crucial point is indeed detailed in the Methods section of our article and clearly stated in the abstract: &ldquo;in all patients, the diagnosis was subsequently confirmed to be PNES with no coexisting epilepsy.&rdquo; It is thus on the basis of incorrect understanding of our results that Drs Ejareh dar and Kanaan discuss the possible significance of hypometabolism in the anterior cingulate region described in our paper, and erroneously suggest that interpretation of PET findings is complicated by coexistent epilepsy, which was not in fact the case.Read the original article.&nbsp

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La voie de Rome, entre Méditerranée et Atlantique, catalogue de l'exposition présentée à l'Archéopôle d'Aquitaine d'octobre 2008 à fin mars 2009, sous la direction de C. Sanchez et S. Vincent, Ausonius éditions, Bordeau