scholarly journals Layer groups: Brillouin-zone and crystallographic databases on the Bilbao Crystallographic Server

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Gemma de la Flor ◽  
Bernd Souvignier ◽  
Gotzon Madariaga ◽  
Mois I. Aroyo
Keyword(s):  
New York ◽  
Brillouin Zone ◽  
Maximal Subgroups ◽  
Group Representations ◽  
Crystallographic Databases ◽  
Character Tables ◽  
Symmetry Properties ◽  
Parameter Ranges ◽  
Layer Groups

The section of the Bilbao Crystallographic Server (https://www.cryst.ehu.es/) dedicated to subperiodic groups contains crystallographic and Brillouin-zone databases for the layer groups. The crystallographic databases include the generators/general positions (GENPOS), Wyckoff positions (WYCKPOS) and maximal subgroups (MAXSUB). The Brillouin-zone database (LKVEC) offers k-vector tables and Brillouin-zone figures of all 80 layer groups which form the background of the classification of their irreducible representations. The symmetry properties of the wavevectors are described applying the so-called reciprocal-space-group approach and this classification scheme is compared with that of Litvin & Wike [(1991), Character Tables and Compatibility Relations of the Eighty Layer Groups and Seventeen Plane Groups. New York: Plenum Press]. The specification of independent parameter ranges of k vectors in the representation domains of the Brillouin zones provides a solution to the problems of uniqueness and completeness of layer-group representations. The Brillouin-zone figures and k-vector tables are described in detail and illustrated by several examples.

Brillouin-zone database on theBilbao Crystallographic Server

2014 ◽  
Vol 70 (2) ◽  
pp. 126-137 ◽  
Author(s):  
Mois I. Aroyo ◽  
Danel Orobengoa ◽  
Gemma de la Flor ◽  
Emre S. Tasci ◽  
J. Manuel Perez-Mato ◽  
...  
Keyword(s):  
New York ◽  
Brillouin Zone ◽  
Irreducible Representations ◽  
Group Representations ◽  
General Introduction ◽  
Space Groups ◽  
Symmetry Properties ◽  
Parameter Ranges ◽  
Representations Of Space

The Brillouin-zone database of theBilbao Crystallographic Server(http://www.cryst.ehu.es) offersk-vector tables and figures which form the background of a classification of the irreducible representations of all 230 space groups. The symmetry properties of the wavevectors are described by the so-called reciprocal-space groups and this classification scheme is compared with the classification of Cracknellet al.[Kronecker Product Tables, Vol. 1,General Introduction and Tables of Irreducible Representations of Space Groups(1979). New York: IFI/Plenum]. The compilation provides a solution to the problems of uniqueness and completeness of space-group representations by specifying the independent parameter ranges of general and specialkvectors. Guides to thek-vector tables and figures explain the content and arrangement of the data. Recent improvements and modifications of the Brillouin-zone database, including new tables and figures for the trigonal, hexagonal and monoclinic space groups, are discussed in detail and illustrated by several examples.

scholarly journals Performance of Various Deep-Learning Networks in the Seed Classification Problem

Symmetry ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1892
Author(s):  
Recep Eryigit ◽  
Bulent Tugrul
Keyword(s):  
Performance Metrics ◽  
Classification Problem ◽  
Grass Species ◽  
Test Accuracy ◽  
Learning Networks ◽  
Symmetry Properties ◽  
Depth Study ◽  
Image Set ◽  
Accuracy Performance

We report the results of an in-depth study of 15 variants of five different Convolutional Neural Network (CNN) architectures for the classification of seeds of seven different grass species that possess symmetry properties. The performance metrics of the nets are investigated in relation to the computational load and the number of parameters. The results indicate that the relation between the accuracy performance and operation count or number of parameters is linear in the same family of nets but that there is no relation between the two when comparing different CNN architectures. Using default pre-trained weights of the CNNs was found to increase the classification accuracy by ≈3% compared with training from scratch. The best performing CNN was found to be DenseNet201 with a 99.42% test accuracy for the highest resolution image set.

Elements of Group Theory

2021 ◽  
pp. 51-110
Author(s):  
J. Iliopoulos ◽  
T.N. Tomaras
Keyword(s):  
Group Theory ◽  
Lie Groups ◽  
Lorentz Group ◽  
Unitary Representations ◽  
Compact Groups ◽  
Mathematical Language ◽  
Group Representations ◽  
Infinite Groups ◽  
Infinite Dimensional ◽  
Symmetry Properties

The mathematical language which encodes the symmetry properties in physics is group theory. In this chapter we recall the main results. We introduce the concepts of finite and infinite groups, that of group representations and the Clebsch–Gordan decomposition. We study, in particular, Lie groups and Lie algebras and give the Cartan classification. Some simple examples include the groups U(1), SU(2) – and its connection to O(3) – and SU(3). We use the method of Young tableaux in order to find the properties of products of irreducible representations. Among the non-compact groups we focus on the Lorentz group, its relation with O(4) and SL(2,C), and its representations. We construct the space of physical states using the infinite-dimensional unitary representations of the Poincaré group.

VI.—New Classifications of the Brachiopoda

1893 ◽  
Vol 10 (7) ◽  
pp. 318-323
Author(s):  
Agnes Crane
Keyword(s):  
New York ◽  
History Of ◽  
The Individual

Mr. Charles Schuchert of Newhaven, Conn., U.S.A., has recently published in the “American Geologist” (Vol. xi.No. 3) an important and highly suggestive “Classification of the Brachiopoda,” based on the history of the class (Chronogenesis) and the ontogeny of the individual. It embodies the latest results of the remarkable investigations on the Palaeozoic forms of Prof. James Hall and Mr. J. M. Clarke, who have thrown so much light on the evolution of genera among the Brachiopoda in the eighth volume of “The Palæontology of New York” (Part I. Brachiopoda, 1892).

Automated Text Classification of News Articles: A Practical Guide

2020 ◽  
Vol 29 (1) ◽  
pp. 19-42 ◽  
Author(s):  
Pablo Barberá ◽  
Amber E. Boydstun ◽  
Suzanna Linn ◽  
Ryan McMahon ◽  
Jonathan Nagler
Keyword(s):  
New York ◽  
New York Times ◽  
Fixed Number ◽  
Machine Learning Algorithms ◽  
Supervised Machine Learning ◽  
Methodological Choices ◽  
Units Of Analysis ◽  
Human Validation ◽  
Corpus Selection

Automated text analysis methods have made possible the classification of large corpora of text by measures such as topic and tone. Here, we provide a guide to help researchers navigate the consequential decisions they need to make before any measure can be produced from the text. We consider, both theoretically and empirically, the effects of such choices using as a running example efforts to measure the tone of New York Times coverage of the economy. We show that two reasonable approaches to corpus selection yield radically different corpora and we advocate for the use of keyword searches rather than predefined subject categories provided by news archives. We demonstrate the benefits of coding using article segments instead of sentences as units of analysis. We show that, given a fixed number of codings, it is better to increase the number of unique documents coded rather than the number of coders for each document. Finally, we find that supervised machine learning algorithms outperform dictionaries on a number of criteria. Overall, we intend this guide to serve as a reminder to analysts that thoughtfulness and human validation are key to text-as-data methods, particularly in an age when it is all too easy to computationally classify texts without attending to the methodological choices therein.

scholarly journals Considering context and dynamics: A classification of transit-orientated development for New York City

2020 ◽  
Vol 85 ◽  
pp. 102711
Author(s):  
Yunzhe Liu ◽  
Alex Singleton ◽  
Daniel Arribas-Bel
Keyword(s):  
New York ◽  
New York City ◽  
York City

Symmetrized Kronecker Products of Group Representations

1974 ◽  
Vol 26 (02) ◽  
pp. 328-339 ◽  
Author(s):  
P. H. Butler ◽  
R. C. King
Keyword(s):  
Irreducible Representation ◽  
Simple Groups ◽  
Kronecker Products ◽  
Group Representations ◽  
Symmetry Properties ◽  
Image Position

Certain phases are associated with the Kronecker squares and cubes of representations of the finite and of the compact semi-simple groups. These phases are important in giving the symmetry properties of the 1 — jm and 3 — jm symbols of the groups [4; 9]. It is our primary purpose to evaluate these phases. The Frobenius-Schur invariant [12, p. 142] for an irreducible representation of group G (1.1)

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