Noise measurements on a tunnel junction d.c. SQUID for a gravitational radiation detector at ultralow temperature

Summary We present noise measurements made at temperatures down to 200 mK on a tunnel junction d.c. SQUID, to be used as amplifier for the gravitational-wave experiment Nautilus of the Rome group. We find that the flux noise decreases with temperature, as expected, with a best measured value of at 0.2 K. The presence of an excess noise term independent of temperature is discussed.     

Regularity of the value function and viscosity solutions in optimal stopping problems for general Markov processes

We consider optimal stopping problems for Markov processes with a semicontinuous reward function g , and we show that under suitable conditions the value function w = w [ g ] is itself semicontinuous and is a viscosity solution of the associated variational inequality.     

Optimal stopping problems with discontinous reward: Regularity of the value function and viscosity solutions

In this paper we show that the solution of a stochastic boundary value problem with additive noise and with a completely nonlinear drift is a Markov field if only if the boundary condition is an initial or a final type condition     

Mechanism of dioxygen activation in 2-oxoglutarate-dependent enzymes: a hybrid DFT study

The reaction mechanism for dioxygen activation in 2-oxoglutarate-dependent enzymes has been studied by means of hybrid density functional theory. The results reported here support a mechanism in which all chemical transformations take place on a quintet potential-energy surface. More specifically, the activated dioxygen species attacks the carbonyl group of the co-substrate producing the Fe(II)-persuccinate-CO(2) complex, which readily releases the carbon dioxide molecule. The step in which the Fe(II)-peracid-CO(2) complex is formed is found to be rate-limiting and irreversible. Subsequent heterolysis of the Obond;O bond in the Fe(II)-persuccinate complex proceeds in two one-electron steps and produces the high-valent iron-oxo species Fe(IV)dbond;O, which is most likely to be responsible for oxidative reactions catalyzed by 2-oxoglutarate-dependent enzymes. The concerted pathway for simultaneous Obond;O and Cbond;C bond cleavage on the septet potential-energy surface is found to be less favorable. The relative stability of different forms of the active iron-oxo species is assessed, and the quintet five-coordinate complex is found to be most stable.     

Positive dependence orderings and stopping times

We study the positive dependence of pairs of stochastic processes and examine its relation with the properties of certain stopping times. Some special cases, such as dependent random walks, Gaussian processes and exchangeable sequences of elliptically contoured random variables, are taken into account.     

Experimental study of the dynamic Newtonian field with a cryogenic gravitational wave antenna

We present an experiment performed to study the behaviour of the dynamic gravitational interaction at laboratory scale. We used as field generator a mass quadrupole rotating in the range of 460 Hz and we detected the acceleration field with the cryogenic gravitational wave antenna Explorer of the Rome group. We report the measurements of this interaction as a function of the distance between the field source and the detector. An upper limit on the parameters of a Yukawa-like potential, modeling an hypotetic deviation from the Newtonian law of gravity, is derived. Received: 14 June 1998 / Published online: 16 September 1998     

Sensitivity analysis of a two-mode resonant gravitational-wave detector with arbitrary tuning

Summary We present a very general characterization of a resonant gravity wave detector and an explicit algorithm to evaluate its noise temperature when a passive transducer is used. This procedure also provides quantitative results for the sensitivity of such a detector in applications yet to be analysed, like insufficient or excessive tuning of the second resonator and use in detection of monochromatic radiation, both on and off resonance.

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Riassunto Si presenta una caratterizzazione del tutto generale di un'antenna gravitazionale risonante, ed un algoritmo esplicito per calcolarne la temperature di rumore nel caso in cui venga usato un trasduttore di vibrazioni passivo. Questo metodo fornisce risultati quantitativi per la sensibilità di un tale apparato anche in applicazioni non ancora analizzate completamente, quali un'imperfetta accordatura del secondo oscillatore e la rivelazione di radiazione monocromatica di frequenza coincidente o prossima alla risonanza dell'antenna.

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Резюме Приводятся характеристики общего типа резонансного детектора гравитационных волн. Предлагается явный алгоритм оценки температуры шума этого детектора в случае, когда используется пассивный преобразователь. Эта процедура также дает количественные результаты для чувствительности такого детектора при несовершенной настройке второго резонатора и при детектировании монохроматического излучения в резонансе и вне резонанса.

     

Some results about stochastic flows with and without jumps

Work supported by M. P. I.