Algebraic description of spacetime foam

A mathematical formalism for treating spacetime topology as a quantum observable is provided. We describe spacetime foam entirely in algebraic terms. To implement the correspondence principle we express the classical spacetime manifold of general relativity and the commutative coordinates of its events by means of appropriate limit constructions.Comment: 34 pages, LaTeX2e, the section concerning classical spacetimes in the limit essentially correcte

Spacetime topology from the tomographic histories approach: Part II

As an inverse problem, we recover the topology of the effective spacetime that a system lies in, in an operational way. This means that from a series of experiments we get a set of points corresponding to events. This continues the previous work done by the authors. Here we use the existence of upper bound in the speed of transfer of matter and information to induce a partial order on the set of events. While the actual partial order is not known in our operational set up, the grouping of events to (unordered) subsets corresponding to possible histories, is given. From this we recover the partial order up to certain ambiguities that are then classified. Finally two different ways to recover the topology are sketched and their interpretation is discussed.Comment: 21 pages, slight change in title and certain minor corrections in this second version. To apear in IJT

`Iconoclastic', Categorical Quantum Gravity

This is a two-part, `2-in-1' paper. In Part I, the introductory talk at `Glafka--2004: Iconoclastic Approaches to Quantum Gravity' international theoretical physics conference is presented in paper form (without references). In Part II, the more technical talk, originally titled ``Abstract Differential Geometric Excursion to Classical and Quantum Gravity'', is presented in paper form (with citations). The two parts are closely entwined, as Part I makes general motivating remarks for Part II.Comment: 34 pages, in paper form 2 talks given at ``Glafka--2004: Iconoclastic Approaches to Quantum Gravity'' international theoretical physics conference, Athens, Greece (summer 2004

Studio della quota di volo mediante GNSS, altimetro radar e barometro per rilievi di spettroscopia gamma da velivolo

Lo studio della distribuzione dei radionuclidi terrestri (238U, 232Th e 40K) realizzato mediante tecniche di spettroscopia gamma da velivolo è influenzato dalla quota a cui il rivelatore si trova rispetto al suolo. Un'incertezza del 10% a 100 m di altezza origina un errore nella stima del segnale gamma del 208Tl, appartenente alla catena di decadimenti del 232Th, dell’ordine del 7%. L'impiego di una nuova classe di spettrometri montati a bordo di UAV (Unmanned Aerial Vehicle) per raffinate misure in contesti ostili o remoti rende necessaria un'accurata stima in real time della quota di volo. Il Radgyro è un velivolo dedicato a survey multiparametrici, capace di trasportare strumentazione pari ad un payload massimo di 120 kg, tra cui quattro spettrometri gamma NaI(Tl). Una stazione inerziale con ricevitore integrato GNSS (Global Navigation Satellite System) restituisce l'assetto del velivolo con una frequenza massima di 400 Hz. Il velivolo è dotato di un network di tre ricevitori GNSS posizionati alle estremità della carena del velivolo. Un altimetro radar a 24 GHz rileva la quota con una frequenza di 60 Hz. La misura di pressione e temperatura consente di ricavare la quota barometrica a 2 Hz. Con l'obiettivo di studiare le incertezze associate alle misure della quota di volo acquisite dagli altimetri in relazione ai dati GNSS, sono stati realizzati tre voli sul mare in un range di altezze comprese tra 31 m e 249 m, per un totale di 4702 secondi di volo effettivo. Al termine dello studio è possibile concludere che l'errore complessivo delle abbondanze di K, U e Th aumenta di 7.7%, 0.5% e 2.7% rispettivamente, a causa delle incertezze della quota di volo

Reversible Pressure-Induced Amorphization in Solid C70 : Raman and Photoluminescence Study

We have studied single crystals of $C_{70}$ by Raman scattering and photoluminescence in the pressure range from 0 to 31.1 GPa. The Raman spectrum at 31.1 GPa shows only a broad band similar to that of the amorphous carbon without any trace of the Raman lines of $C_{70}$. After releasing the pressure from 31.1 GPa, the Raman and the photoluminescence spectra of the recovered sample are that of the starting $C_{70}$ crystal. These results indicate that the $C_{70}$ molecules are stable upto 31.1 GPa and the amorphous carbon high pressure phase is reversible, in sharp contrast to the results on solid $C_{60}$. A qualitative explaination is suggested in terms of inter- versus intra-molecular interactions.Comment: To appear in Phys. Rev. Lett., 12 pages, RevTeX (preprint format), 3 figures available upon reques

Comparison of the Electronic Structures and Energetics of Ferroelectric LiNbO3 and LiTaO3

This paper explains the origin of the ferroelectric instability in LiNbO3 and LiTaO3 and compares the electronic structures and energetics of the two materials.Comment: 31 pages, 11 Postscript figure

`Third' Quantization of Vacuum Einstein Gravity and Free Yang-Mills Theories

Based on the algebraico-categorical (:sheaf-theoretic and sheaf cohomological) conceptual and technical machinery of Abstract Differential Geometry, a new, genuinely background spacetime manifold independent, field quantization scenario for vacuum Einstein gravity and free Yang-Mills theories is introduced. The scheme is coined `third quantization' and, although it formally appears to follow a canonical route, it is fully covariant, because it is an expressly functorial `procedure'. Various current and future Quantum Gravity research issues are discussed under the light of 3rd-quantization. A postscript gives a brief account of this author's personal encounters with Rafael Sorkin and his work.Comment: 43 pages; latest version contributed to a fest-volume celebrating Rafael Sorkin's 60th birthday (Erratum: in earlier versions I had wrongly written that the Editor for this volume is Daniele Oriti, with CUP as publisher. I apologize for the mistake.

Исследование характеристик ядерных трековых мембран для создания дренажной системы в лечении глаукомы

In this article has been researched possibility of using nuclear track membrane for fluid transport in the implementation and maintenance of the cornea weaklydehydrated state