61,201 research outputs found
Programming of Finite Element Methods in MATLAB
We discuss how to implement the linear finite element method for solving the
Poisson equation. We begin with the data structure to represent the
triangulation and boundary conditions, introduce the sparse matrix, and then
discuss the assembling process. We pay special attention to an efficient
programming style using sparse matrices in MATLAB
A prescription for projectors to compute helicity amplitudes in D dimensions
This article discusses a prescription to compute polarized dimensionally
regularized amplitudes, providing a recipe for constructing simple and general
polarized amplitude projectors in D dimensions that avoids conventional Lorentz
tensor decomposition and avoids also dimensional splitting. Because of the
latter, commutation between Lorentz index contraction and loop integration is
preserved within this prescription, which entails certain technical advantages.
The usage of these D-dimensional polarized amplitude projectors results in
helicity amplitudes that can be expressed solely in terms of external momenta,
but different from those defined in the existing dimensional regularization
schemes. Furthermore, we argue that despite being different from the
conventional dimensional regularization scheme (CDR), owing to the
amplitude-level factorization of ultraviolet and infrared singularities, our
prescription can be used, within an infrared subtraction framework, in a hybrid
way without re-calculating the (process-independent) integrated subtraction
coefficients, many of which are available in CDR. This hybrid CDR-compatible
prescription is shown to be unitary. We include two examples to demonstrate
this explicitly and also to illustrate its usage in practice.Comment: Matched to the version to be published in Eur. Phys. J.
Obsessive-compulsive disorder : novel insights on executive functions, gut microbiome, and genetics
Background: Obsessive-compulsive disorder (OCD) is characterized by intrusive
thoughts and images, and repetitive, time-consuming compulsions. It causes
disability and impaired quality of life. The neurobiological model of OCD revolves
around dysfunctional brain circuits, referred to as the cortico-striato-thalamocortical
(CSTC) loop.
Aim: This thesis sought to elucidate neurobiological factors associated with OCD.
Methods: In study I, we compared executive functions of patients with OCD
(n=29), body dysmorphic disorder (BDD) (n=27), and healthy controls (n=28), using
computerized and standardized neuropsychological tasks (CANTAB) for response
inhibition (stop-signal task, SST), cognitive flexibility (intra-extra dimensional shift
task, IED), and working memory (spatial working memory task, SWM). Correlation
between task performance and symptom severity was assessed using linear
regression models and effect sizes were measured with Pearson’s r. In study II, we
systematically reviewed gut microbiota studies of participants with psychiatric
disorders, published up to February 2020, following the PRISMA guidelines and the
pre-registered study-protocol at PROSPERO. In study III, we compared gut
microbiome of patients with OCD (n=32) with healthy controls (n=32) using whole
genome sequencing of stool samples. Moreover, we followed a subset of participants
longitudinally to compare changes in gut microbiome within patients with OCD
before and after exposure- and response prevention (ERP) therapy (n=15). In study
IV, we used whole exome sequencing to explore presence of gene-disruptive rare
variants (GDRVs) in patients with severe and treatment-resistant OCD (n=5) who
have received deep brain stimulation (DBS).
Results: In study I we found no significant differences in test performance
between individuals with OCD, BDD, and healthy controls. In study II, 69 studies
were included in the systematic review. The majority of studies did not report any
significant differences in gut microbiota -diversity indices (44%), but different
composition measured by -diversity indices (67%) between patients with
psychiatric disorders and healthy controls. However, the results were inconsistent
regarding which genera are differentially abundant, except for some studies that
reporter lower abundance of butyrate-producing microbes Faecalibacterium
prausnitzii and Roseburia species. In study III we found no significant differences
in -diversity, -diversity, or taxonomic dissimilarity at the species-level between
patients with OCD and healthy controls, or within patients with OCD before and
after ERP. Furthermore, functional analysis, based on gut-brain modules that are
relevant for metabolizing neuroactive compounds, did not reveal any significant
differences between patients with OCD and healthy controls, or within patients with
OCD before and after ERP. In study IV, we found three GDRVs, one of which was a
missense variant in the ion transporter domain of KCNB1 (hg19 20-47991077-C-T).
The patient with that missense variant was a responder to DBS treatment.
Conclusions:
Study I. Performance on neuropsychological tests suggest that patients with OCD
have comparable executive functions with a related group of patients and healthy
controls.
Study II and III. Despite the suggested importance of the microbiome-gut-brain
axis in psychiatric disorders, evidence for altered gut microbiome in psychiatric
disorders including OCD is inconclusive. Improved and consistent study design and
methodology are crucial for future studies in this research field.
Study IV. Patients with severe and treatment-resistant OCD is a cohort fit for whole
exome sequencing studies. Despite the small sample size, we found three GDRVs.
More samples are required to evaluate if the frequency of GDRVs is higher in this
cohort and if GDRVs could predict treatment outcome from DBS.
Patients with OCD represent a heterogeneous group, and individual biological
factors cannot explain the pathophysiological underpinning of this disorder.
Nevertheless, next-generation sequencing opens new opportunities to study complex
psychiatric conditions. Genomic analysis of severe and treatment-resistant patients
with OCD could increase our understanding of this complex disorder
Real-time Correlators and Hidden Conformal Symmetry in Kerr/CFT Correspondence
In this paper, we study the real-time correlators in Kerr/CFT, in the low
frequency limit of generic non-extremal Kerr(-Newman) black holes. From the low
frequency scattering of Kerr-Newman black holes, we show that for the uncharged
scalar scattering, there exists hidden conformal symmetry on the solution
space. Similar to Kerr case, this suggests that the Kerr-Newman black hole is
dual to a two-dimensional CFT with central charges and
temperatures .
Using the Minkowski prescription, we compute the real-time correlators of
charged scalar and find perfect match with CFT prediction. We further discuss
the low-frequency scattering of photons and gravitons by Kerr black hole and
find that their retarded Green's functions are in good agreement with CFT
prediction. Our study supports the idea that the hidden conformal symmetry in
the solution space is essential to Kerr/CFT correspondence.Comment: 15 pages, Latex; typos corrected, references updated; minor
correction, published versio
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