Search results for "Clos"

Closeness to Parents and Experiencing Threats with COVID-19 Mediates the Link between Personality and Stress among Adolescents

2021

Purpose: many researchers have already established that the 2019 COVID-19 pandemic poses a threat to adolescent psychological health. Studies on the COVID-19 pandemic mainly focus on individual psychological consequences, such as anxiety, depression or stress. The presented study added a family context to psychological analyses of the COVID-19 pandemic in adolescence. We examined the mediational effects of closeness to parents and perceived pandemic-related threats to relationships between personality (emotional stability and agreeableness) and stress in adolescents. Methods: in total, 413 students from secondary schools in southern Poland completed questionnaires measuring stress, personal…

Technology for plant food support in Antarctica

2011

TWO-DIMENSIONAL FINITE STATE RECOGNIZABILITY

1996

The purpose of this paper is to investigate about a new notion of finite state recognizability for two-dimensional (picture) languages. This notion takes as starting point the characterization of one-dimensional recognizable languages in terms of local languages and projections. Such notion can be extended in a natural way to the two-dimensional case. We first introduce a notion of local picture language and then we define,a recognizable picture language as a projection of a local picture language. The family of recognizable picture languages is denoted by REC. We study some combinatorial and language-theoretic properties of family REC. In particular we prove some closure properties with re…

On the group of the automorphisms of some algebraic systems

1968

Within a framework of general algebra we firstly formulate a proposition on the group of the automorphisms of some irreducible algebrae (id est algebrae without proper non trivial subalgebrae). This proposition includes as particular cases the uniqueness of the automorphisms of the rational field and the Burnside theorem on the commutant of an irreducible set of operators of a finite dimensional vector space over an algebraically closed field. Afterwards we apply the general proposition to modules with irreducible sets of semilinear operators and we obtain a theorem which generalises from several points of view the Burnside theorem. Finally we derive as an application a proposition which sp…

Birkhoff-Frink representations as functors

2010

In an earlier article we characterized, from the viewpoint of set theory, those closure operators for which the classical result of Birkhoff and Frink, stating the equivalence between algebraic closure spaces, subalgebra lattices and algebraic lattices, holds in a many-sorted setting. In the present article we investigate, from the standpoint of category theory, the form these equivalences take when the adequate morphisms of the several different species of structures implicated in them are also taken into account. Specifically, our main aim is to provide a functorial rendering of the Birkhoff-Frink representation theorems for both single-sorted algebras and many-sorted algebras, by definin…

Closure operations for Schunck classes and formations of finite solvable groups

1979

The purpose of the present note is to investigate the closure operations common to both the operations of forming classes and formations. Furthermore, new descriptions of formations and saturated formations in terms of closure operations are given.

On many-sorted algebraic closure operators

2004

A theorem of Birkhoff-Frink asserts that every algebraic closure operator on an ordinary set arises, from some algebraic structure on the set, as the corresponding generated subalgebra operator. However, for many-sorted sets, i.e., indexed families of sets, such a theorem is not longer true without qualification. We characterize the corresponding many-sorted closure operators as precisely the uniform algebraic operators. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Stereoselective synthesis of the naturally occurring 2-pyranone dodoneine

2008

The first total synthesis of the naturally occurring dihydropyranone dodoneine is reported. Asymmetric allylation reactions were used for the stereoselective generation of the two stereogenic centers. The pyranone ring was created by ring-closing metathesis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

New approaches to the synthesis of organofluorine nitrogenated derivatives

2004

Fluorinated carboxylic acids are valuable building blocks for several types of organofluorine nitrogenated derivatives. In this review paper, several strategies that use these compounds as starting materials are described. First, fluorinated seven-membered cyclic β-amino esters can be diastereoselectively synthesized from these compounds with a ring-closing metathesis (RCM) reaction as the key step. The use of the RCM reaction in a different approach enables the preparation of fluorinated cyclic α-amino acid derivatives. Fluorinated carboxylic acids also constitute the starting material for the asymmetric synthesis of fluorinated allylic amines. Finally, a solution and solid-phase synthesis…

On the mechanism of the interaction between oxygen and close-packed single-crystal aluminum surfaces

2003

Abstract Using periodic first principles simulations we investigate the interaction of oxygen molecules with both regular Al(111) and Al(001) surfaces as well as a stepped Al(111) substrate. The limitation of this approach is the use of thin metallic slabs with a limited range for their coverage by adsorbed oxygen. The advantage is the detailed modeling that is possible at an atomic level. On the regular Al(111) surface, we have been able to follow the oxidation process from the approach of O 2 molecules to the surface, through the chemisorption and absorption of O atoms, up to the formation of first Al 2 O 3 formula units. An energetically feasible mechanism for the formation of these Al 2…