99 research outputs found
Wavefront spacing and Gouy phase in presence of primary spherical aberration
No full textWe study the Gouy phase of a scalar wavefield that is focused by a lens suffering from primary spherical aberration. It is found that the Gouy phase has different behaviors at the two sides of the intensity maximum. This results in a systematic increase of the successive wavefront spacings around the diffraction focus. Since all lenses have some amount of spherical aberration, this observation has implications for optical calibration and metrology.Electrical Engineering, Mathematics and Computer Scienc
The Gouy phase of Airy beams
No full textThe phase behavior of Airy beams is studied, and their Gouy phase is defined. Analytic expressions for the idealized, infinite-energy type beam are derived. They are shown to be excellent approximations for finite-energy beams generated under typical experimental conditions.TelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Direct observation of Gouy phase shift in a propagating optical vortex
No full textDirect observation of Gouy phase shift on an optical vortex was presented through investigating the intensity profiles of a modified LG_p^m beam with an asymmetric defect, around at the focal point. It was quantitatively found that the rotation profile of a modified LG_p^m beam manifests the Gouy phase effect where the rotation direction depends on only the sign of topological charge m. This profile measurement method by introducing an asymmetric defect is a simple and useful technique for obtaining the information of the Gouy phase shift, without need of a conventional interference method. In addition, the 3-dimernsional trajectory of the defect was found to describe a uniform straight line
Generalized Gouy phase for focused partially coherent light and its implications for interferometry
No full textThe Gouy phase, sometimes called the phase anomaly, is the remarkable effect that in the region of focus a converging wave field undergoes a rapid phase change by an amount of ?, compared to the phase of a plane wave of the same frequency. This phenomenon plays a crucial role in any application where fields are focused, such as optical coherence tomography, mode selection in laser resonators, and interference microscopy. However, when the field is spatially partially coherent, as is often the case, its phase is a random quantity. When such a field is focused, the Gouy phase is therefore undefined. The correlation properties of partially coherent fields are described by their so-called spectral degree of coherence. We demonstrate that this coherence function does exhibit a generalized Gouy phase. Its precise behavior in the focal region depends on the transverse coherence length. We show that this effect influences the fringe spacing in interference experiments in a nontrivial manner.TelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Manifestation of the Gouy phase in strongly focused, radially polarized beams
No full textThe Gouy phase, sometimes called the focal phase anomaly, is the curious effect that in the vicinity of its focus a diffracted field, compared to a non-diffracted, converging spherical wave of the same frequency, undergoes a rapid phase change by an amount of ?. We theoretically investigate the phase behavior and the polarization ellipse of a strongly focused, radially polarized beam. We find that the significant variation of the state of polarization in the focal region, is a manifestation of the different Gouy phases that the two electric field components undergo.Electrical Engineering, Mathematics and Computer Scienc
STRAF-A convenient online tool for STR data evaluation in forensic genetics.
No full textPopulation data in forensic genetics has to be checked for a variety of statistical parameters before it can be employed for case work. A lot of very powerful statistical tools are available for this task, most of them developed by labs having their research focus on population genetics or evolution. However, most of these programs require a substantial amount of experience. In addition, to our knowledge, none of the freely available programs calculates all the common parameters for a population study in forensic genetics at once, based on a single input file. We present here a convenient online tool that fills this gap. STRAF (STR Analysis for Forensics) provides an intuitive interface and input file format and computes all the relevant parameters for a classical population study based on autosomal STR data at once and in a convenient way. In addition, STRAF includes a PCA module that can be used for population substructure detection or quality control. The results generated by the program were verified by recalculating parameters from an already published population study
Polygenic Patterns of Adaptive Introgression in Modern Humans Are Mainly Shaped by Response to Pathogens
No full textAnatomically modern humans carry many introgressed variants from other hominins in their genomes. Some of them affect their phenotype and can thus be negatively or positively selected. Several individual genes have been proposed to be the subject of adaptive introgression, but the possibility of polygenic adaptive introgression has not been extensively investigated yet. In this study, we analyze archaic introgressionmaps with refined functional enrichmentmethods to find signals of polygenic adaptation of introgressed variants. We first apply a method to detect sets of connected genes (subnetworks) within biological pathways that present higher-than-expected levels of archaic introgression. We then introduce and apply a new statistical test to distinguish between epistatic and independent selection in gene sets of present-day humans.We identify several known targets of adaptive introgression, and we show that they belong to larger networks of introgressed genes. After correction for genetic linkage, we find that signals of polygenic adaptation are mostly explained by independent and potentially sequential selection episodes. However, we also find some gene sets where introgressed variants present significant signals of epistatic selection. Our results confirm that archaic introgression has facilitated local adaptation, especially in immunity related and metabolic functions and highlight its involvement in a coordinated response to pathogens out of Africa.
Key words: adaptive introgression, polygenic selection, Neandertal, Denisova, immunity
A holistic approach for the selection of forensic DNA swabs
No full textIn the present study, we compared the performance of five different ISO 18385 certified forensic swabs for DNA sampling in practice over a time period of five months. Comparisons were made for DNA profiling success rates, measured as the percentage of CODIS (Combined DNA Index System) suitable profiles as well as for practical suitability during sampling at the scene, measured through a survey among collaborators. More than forty members of our crime scene investigation (CSI) unit took part in the test series and provided structured feedback concerning different aspects of swab handling. A total number of 1094 "touch" DNA samples have been subjected to DNA analysis. Swabs performed significantly different in terms of DNA profiling success rates. We also observed significant differences in DNA extraction efficiency between swabs. The evaluation by the collaborators of various aspects of handling differed significantly between swabs. We can assume that a more convenient handling decreases the risk of contamination or sample mislabelling and increases sampling efficiency and staff satisfaction. Our results demonstrate that the selection of disposable sampling devices such as forensic swabs for DNA sampling should be made based on a holistic approach. To be able to select the best performing swab for a given combination of CSI and DNA laboratory procedures, it might not be sufficient to only perform DNA extraction comparisons and trace sampling under controlled laboratory conditions
Suite de la discussion sur la liquidation de la dette publique, lors de la séance du 18 septembre 1790
No full textGouy-d'Arsy Louis Marthe, marquis de, Vernier Théodore, Démeunier Jean Nicolas, Bureaux de Pusy Jean-Xavier, Talleyrand Périgord Charles Maurice de, Harambure Louis François Alexandre, baron d'. Suite de la discussion sur la liquidation de la dette publique, lors de la séance du 18 septembre 1790. In: Archives Parlementaires de 1787 à 1860 - Première série (1787-1799) Tome XIX - Du 16 septembre au 23 octobre 1790. Paris : Librairie Administrative P. Dupont, 1884. pp. 48-61
Detecting gene subnetworks under selection in biological pathways
No full textSupplementary materials files: supplementary material; replication data.Advances in high throughput sequencing technologies have created a gap between data production and functional data analysis. Indeed, phenotypes result from interactions between numerous genes, but traditional methods treat loci independently, missing important knowledge brought by network-level emerging properties. Therefore, detecting selection acting on multiple genes affecting the evolution of complex traits remains challenging. In this context, gene network analysis provides a powerful framework to study the evolution of adaptive traits and facilitates the interpretation of genome-wide data. We developed a method to analyse gene networks that is suitable to evidence polygenic selection. The general idea is to search biological pathways for subnetworks of genes that directly interact with each other and that present unusual evolutionary features. Subnetwork search is a typical combinatorial optimization problem that we solve using a simulated annealing approach. We have applied our methodology to find signals of adaptation to high-altitude in human populations. We show that this adaptation has a clear polygenic basis and is influenced by many genetic components. Our approach, implemented in the R package signet, improves on gene-level classical tests for selection by identifying both new candidate genes and new biological processes involved in adaptation to altitude
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