937 research outputs found
Representability Conditions by Grassmann Integration
No full textRepresentability conditions on the one- and two-particle density matrix for fermion systems are formulated by means of Grassmann integrals. A positivity condition for a certain kind of Grassmann integral is established which, in turn, induces the well-known G-, P- and Q-Conditions of quantum chemistry by an appropriate choice of the integrand. Similarly, the T1- and T2-Conditions are derived. Furthermore, quasifree Grassmann states are introduced and, for every operator γ ̃ ∈ H⊕H with 0 ≤ γ ̃ ≤ 1, the existence of a unique quasifree Grassmann state whose one-particle density matrix is γ ̃ is shown
Grassmann and flag manifolds
No full textTitle: Grassmann and flag manifolds Author: Jakub Eliáš Department: Matematický ústav Univerzity Karlovy Supervisor: Mgr. Lukáš Krump, Ph.D., Matematický ústav Univerzity Karlovy Abstract: This bachelor thesis deals with describing Grassmann and flag man- ifolds as smooth manifolds with their properties. In order to do so we use Lie group theory to introduce a way to construct a smooth atlas on a general quo- tient of a Lie group and its closed Lie subgroup. The thesis consists of two parts. In the first part we summarize needed basics of Lie group theory, we introduce the quotient of a Lie group and its closed Lie subgroup and describe a means how to express it as a homogeneous space. In the second part we introduce the Grassmann manifolds and flag manifolds (which we break up to complete and partial ones) and express both types of them as homogeneous spaces. Keywords: Grassmann manifold, flag manifold, homogeneous space, isotropy group
La fisica per l’innovazione tecnologica nell’ambito della sostenibilit`a.
No full textAd oggi, le tecnologie tradizionali per lo sfruttamento delle energie rinnovabili non sostitu- iscono completamente i carburanti fossili. La fisica puo` dare pero` un contributo importante per sviluppare tecnologie fondamentalmente nuove, in grado di spianare la strada a questa sostituzione. Si discutono qui tre esempi: 1) Lo Specchio Lineare, capace di fornire energia solare termica anche ad alte temperature e d’inverno in modo facile ed economico. 2) Un nuovo assorbitore sole-aria basato su un criterio di selettivita` spaziale, diverso dagli assor- bitori tradizionali che lavorano sul principio della selettivita` delle lunghezza d’onda. 3) Un gassificatore per biomasse povere che usa una grande quantit`a di ossigeno (mentre i gassi- ficatori tradizionali si basano sull’assunzione di una presenza limitata di ossigeno, il che ne limita fortemente le performance) ed `e capace di raggiunge una densita` di potenza pari a 10 MWatt/m3, paragonabile a quella di un reattore nucleare
Simple ternary complex Grassmann algebras
No full textThis work introduces a new class of simple comtrans algebras obtained in the tangent space of a complex Grassmann manifold. It is shown that some of the simple algebras of this new, Grassmann type do not appear as simple algebras of any of the previously known types. In chapter one, comtrans algebras are defined and examples given for the four broad types of simple comtrans algebras currently known. Some of the prerequisite details of the general algebraic theory of comtrans algebras, particularly concerning the universal enveloping algebra of a comtrans algebra, are summarized. In chapter two we define a new class of comtrans algebras. The algebras are said to be of complex Grassmann type. We discuss their simplicity and show that each algebra in this class is an internal Thomas sum of its subalgebras E and F defined in the chapter. Chapter three is devoted to the problem of showing that the complex Grassmann comtrans algebras are not isomorphic to other types of simple comtrans algebras, and in conclusion we outline a few conjectures as open problems for further research.</p
A characterization of the Grassmann embedding of H(q), with q even
No full textIn this note, we characterize the Grassmann embedding of H(q), q even, as the unique full embedding of H(q) in PG(12, q) for which each ideal line of H(q) is contained in a plane. In particular, we show that no such embedding exists for H(q), with q odd. As a corollary, we can classify all full polarized embeddings of H(q) in PG(12, q) with the property that the lines through any point are contained in a solid; they necessarily are Grassmann embeddings of H(q), with q even
Comments on the CDF 88-89 di-lepton top candidate event
No full textCDF reported a possible top candidate event from their 988/89 run. The event was interpreted and reconstructed as pp→tt→ W + W + jet(b) + + jet(B) + Μ.(B) by some authors. We study the structure of the event to see whether this interpretation is likely. © 1994 Società Italiana di Fisica
Open Questions regarding the Desertec Project
No full textRecently, the construction of a large system of concentrating mirrors in the African Desert (Desertec Project) has been proposed at a cost of more than 400 billion €, in order to produce electricity and send it to Europe. In spite of the huge amount of public money to be spent, it has never been shown, that Desertec is of advantage from an economic point of view. Nor has the impact of Desertec on the world climate ever been discussed. In this note we want to arrive at some first results on the economic and ecologic consequences of Desertec
A Characterization of Grassmann Spaces of Index h of a Projective Space
No full textAbstractIn 1982/83 Bichara and Tallini characterized Grassmann spaces Gr(h,P ) of a projective space P involving intersection properties of the two disjoint families of maximal subspaces of Gr(h, P). In 1984 Melone and Olanda characterized Gr(1,P ) using only one family of maximal subspaces. In this paper the generalization of the result of Melone and Olanda to general index is given. More precisely, I prove that the natural extension of the axiom of Melone and Olanda is not sufficient to characterize Gr(h, P) when h> 1, since the affine Grassmann spaceGr (1, A) of the lines of an affine space A satisfies the axioms, too. Thus, an additional axiom is given and the characterization follows
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