Search results for "Toni"
showing 10 items of 8001 documents
Trace detection of plutonium by three-step photoionization with a laser system pumped by a copper vapor laser
1985
Laser photoionization has been used to detect trace amounts of plutonium. A high sensitivity and selectivity has been achieved by applying three-step excitation and ionization of the plutonium atoms with high pulse-repetition rates and additional mass determination by time-of-flight measurements. A laser system was developed which consists of a copper vapor laser pumping three dye lasers simultaneously. Samples containing between 1010 and 1012 atoms of239Pu on Re filaments were measured yielding strong resonance signals with maximum ion count rates of several kHz at a vanishingly low background. A detection efficiency of 10−7 was determined allowing the detection of about 108 plutonium atom…
Supercontinuum generation with 532 nm quasi-continuum pulses in photonic crystal fibre tapers
2007
We report experimental results on supercontinuum generation in PCF tapers using quasi-continuous pump pulses of 7 ns duration at 532 nm. SC generation in normal and anomalous dispersion regimes are presented. Introduction Supercontinuum generation (SC) in photonic crystal fibres (PCF), fibre tapers, and PCF tapers has been demonstrated in the past with pump pulses of fs, ps, and tenths of ns duration [1-2]. Here, we present experimental results on SC generation in PCF tapers using quasi-continuous pump pulses of 7 ns duration at 532 nm. Fabrication of the PCF tapers The PCF from which the tapers were made, was a large-air-hole PCF ("cobweb" PCF) with two rings of air holes around a solid si…
A strike-slip core complex from the Najd fault system, Arabian shield
2014
Metamorphic core complexes are usually thought to be associated with regional crustal extension and crustal thinning, where deep crustal material is exhumed along gently dipping normal shear zones oblique to the regional extension direction. We present a new mechanism whereby metamorphic core complexes can be exhumed along crustal-scale strike-slip fault systems that accommodated crustal shortening. The Qazaz metamorphic dome in Saudi Arabia was exhumed along a gently dipping jog in a crustal-scale vertical strike-slip fault zone that caused more than 25 km of exhumation of lower crustal rocks by 30 km of lateral motion. Subsequently, the complex was transected by a branch of the strike-sli…
Deficiencias epistemológicas en la enseñanza habitual de los conceptos de campo y potencial eléctrico
1997
This article intends to analyse up to what extent the scarce learning produced when introducing the basic concepts on electrostatics is due to deficiencies and inadequacies in its routine teaching. So, on the one hand, we analyse what have been the principal epistemological leaps forward in the making of electricity as a science. On the other hand, we analyse Physics books and the teachers’ opinions.
Gli spazi di relazione nell’interno quotidiano
2016
Nel campo disciplinare del progetto, e per una corretta esecuzione dell’architettura, è necessario che tutti gli attori sociali, che possono rinnovare le risorse attraverso il dialogo, comprendano la visione d’insieme di uno spazio fisico organizzato da completare. In questo saggio si riflette, attraverso degli esempi puntuali, sul grado di connettività degli abitanti in rapporto con lo spazio preesistente come possibile ipotesi di ricerca per la definizione di un metodo scientifico. Questo approccio, che valuta le potenzialità degli spazi di relazione di un sito fino alla definizione delle soluzioni di modificazione del ‘costruire nel costruito’ (Vittorio Gregotti, ‘Casabella’ dal 1982 al …
La ri-composizione del territorio / The ricomposition of territory
2017
Il saggio, inserito nel volume di sintesi della ricerca PRIN 2009 (“Dalla campagna urbanizzata alla : le norme compositive dell’architettura nel territorio dei centri minori”) presenta alcune aspetti fondamentali del lavoro svolto dall’unità di ricerca locale dell’Università degli Studi di Palermo (responsabile prof.. A. Margagliotta) che ha studiato l’attraverso interno Palermo-Agrigento e il ruolo dell’infrastruttura stradale in rapporto alla questione dei centri minori e della campagna. In particolare il saggio mette approfondisce il tema dei luoghi dell’attraversamento e il ruolo delle infrastrutture; la questione della la campagna e della sua capacità rigenerante nei confronti della re…
Coupled cluster calculations of the vertical excitation energies of tetracyanoethylene
2003
The vertical spectrum of tetracyanoethylene was studied using coupled cluster theory. It was found that the lowest singlet-singlet transition, which corresponds to the excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) excitation, occurs at 5.16 eV in the gas phase and is lowered approximately 0.1 eV due to solvent effects in acetonitrile. A parallel study on the ethene spectrum showed the quality of the basis sets and methods used, by placing the V state 7.92 eV above the ground state and giving an energy for the 0-0 transition of 5.42 eV to be compared with the experimental value of 5.50 eV.
The tensor of interaction of a two-level system with an arbitrary strain field
2007
The interaction between two-level systems (TLS) and strain fields in a solid is contained in the diagonal matrix element of the interaction hamiltonian, $\delta$, which, in general, has the expression $\delta=2[\gamma]:[S]$, with the tensor $[\gamma]$ describing the TLS ``deformability'' and $[S]$ being the symmetric strain tensor. We construct $[\gamma]$ on very general grounds, by associating to the TLS two objects: a direction, $\hat\bt$, and a forth rank tensor of coupling constants, $[[R]]$. Based on the method of construction and on the invariance of the expression of $\delta$ with respect to the symmetry transformation of the solid, we conclude that $[[R]]$ has the same structure as …
Systematic approach toβand2νββdecays of massA=100–136nuclei
2015
In this work we perform a systematic study of pairs of single-$\ensuremath{\beta}$-decaying nuclei in the mass region $A=100--136$ to extract information on the effective value of the axial-vector coupling constant ${g}_{\mathrm{A}}$. As the many-body framework we use the quasiparticle random-phase approximation (QRPA) and its proton-neutron variant (pnQRPA) in single-particle valence bases with Woods-Saxon-calculated single-particle energies. It is found that, to a reasonable approximation, ${g}_{\mathrm{A}}$ is a linear function of the mass number $A$, with a slightly different parametrization below and above the mass $A=121$. Using the values of ${g}_{\mathrm{A}}$ extracted from the line…
Effective hamiltonian approach to the non-Markovian dynamics in a spin-bath
2010
We investigate the dynamics of a central spin that is coupled to a bath of spins through a non-uniform distribution of coupling constants. Simple analytical arguments based on master equation techniques as well as numerical simulations of the full von Neumann equation of the total system show that the short-time damping and decoherence behaviour of the central spin can be modelled accurately through an effective Hamiltonian involving a single effective coupling constant. The reduced short-time dynamics of the central spin is thus reproduced by an analytically solvable effective Hamiltonian model.