8,952 research outputs found
Heavy Ion Physics at LHC
The study of heavy ion interactions constitutes an important part of the
experimental program outlined for the Large Hadron Collider under construction
at CERN and expected to be operational by 2006. ALICE is the single detector
having the capabilities to explore at the same time most of the characteristics
of high energy heavy ion interactions. Specific studies of jet quenching and
quarkonia production, essentially related to detection are also planned
by CMS.Comment: 5 pages, 1 figure (in eps) talk given at XXXI International Symposium
on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL
http://ismd31.ccnu.edu.cn
Dynamics of a FitzHugh-Nagumo system subjected to autocorrelated noise
We analyze the dynamics of the FitzHugh-Nagumo (FHN) model in the presence of
colored noise and a periodic signal. Two cases are considered: (i) the dynamics
of the membrane potential is affected by the noise, (ii) the slow dynamics of
the recovery variable is subject to noise. We investigate the role of the
colored noise on the neuron dynamics by the mean response time (MRT) of the
neuron. We find meaningful modifications of the resonant activation (RA) and
noise enhanced stability (NES) phenomena due to the correlation time of the
noise. For strongly correlated noise we observe suppression of NES effect and
persistence of RA phenomenon, with an efficiency enhancement of the neuronal
response. Finally we show that the self-correlation of the colored noise causes
a reduction of the effective noise intensity, which appears as a rescaling of
the fluctuations affecting the FHN system.Comment: 13 pages, 10 figure
IL SITO PREISTORICO DELLO ZUBBIO DI COZZO SAN PIETRO S.I.C. RUPI DI CATALFANO E CAPO ZAFFERANO
All’interno del S.I.C, “Rupi di Catalfano e Capo Zafferano”, alcune delle grotte presenti sono state frequentate dall’uomo fin dalla preistoria. Mettendo a confronto la genesi delle cavità e la loro ubicazione topografica, è evidente che la scelta dei siti consoni a essere usati dall’uomo è marcatamente strategica e ponderata. L’indagine è stata condotta dapprima individuando e raggiungendo i siti noti in bibliografia, dai quali si è cercato di elaborare un modello per individuare nuovi siti che potessero presentare evidenze di frequentazione umana risalenti alla preistoria, soprattutto recente. All’interno di una grotta, Zubbio di Cozzo San Pietro, ubicata ad una quota di 300 m s.l.m sul versante est di Cozzo San Pietro, ad una profondità di 15 m, è stato rinvenuto e fotografato un deposito contenente resti umani, ossa, denti, alcuni frammenti d’industria litica, fra cui una scheggia di ossidiana, e numerosi frammenti fittili, alcuni databili all’età del Bronzo Medio, facies di Thapsos. A breve, all’interno del sito verrà effettuato un saggio di scavo. Sulla base delle osservazioni precedenti, sono stati considerati tutti gli elementi noti sul popolamento umano del territorio indagato, con un approccio mirato alla comprensione delle dinamiche di utilizzo dell’ambiente secondo le economie del passato
A hyperbolic model for the effects of urbanization on air pollution
AbstractA hyperbolic model to study effects of industrialization and urbanization on air pollution propagation is proposed.The existence of smooth and discontinuous traveling wave-like solutions, related to the spread of both the pollution in the atmosphere and the level of urbanization, is discussed. Validation of the model in point is also accomplished by searching for numerical solutions of the system of PDEs
Hitting Time Distributions in Financial Markets
We analyze the hitting time distributions of stock price returns in different time windows, characterized by different levels of noise present in the market. The study has been performed on two sets of data from US markets. The first one is composed by daily price of 1071 stocks trade for the 12-year period 1987-1998, the second one is composed by high frequency data for 100 stocks for the 4-year period 1995-1998. We compare the probability distribution obtained by our empirical analysis with those obtained from different models for stock market evolution. Specifically by focusing on the statistical properties of the hitting times to reach a barrier or a given threshold, we compare the probability density function (PDF) of three models, namely the geometric Brownian motion, the GARCH model and the Heston model with that obtained from real market data. We will present also some results of a generalized Heston model
Hitting time distribution in financial markets
We analyze the hitting time distributions of stock price returns in different time windows, characterized by different levels of noise present in the market. The study has been performed on two sets of data from US markets. The first one is composed by daily price of 1071 stocks trade for the 12-year period 1987\u20131998, the second one is composed by high frequency data for 100 stocks for the 4-year period 1995\u20131998. We compare the probability distribution obtained by our empirical analysis with those obtained from different models for stock market evolution. Specifically by focusing on the statistical properties of the hitting times to reach a barrier or a given threshold, we compare the probability density function (PDF) of three models, namely the geometric Brownian motion, the GARCH model and the Heston model with that obtained from real market data. We will present also some results of a generalized Heston model
Experimental evidence of the thermal effect of lubricating oil sprayed in sliding-vane air compressors
A way to increase the efficiency of positive-displacement air compressor is spraying the lube oil to exploit it not only as lubricating and sealing agent but also as thermal ballast. This work seeks the experimental evidence in sliding-vane compressors by measuring the air standard volume flow rate and the electrical power input of three diverse configurations. The first configuration, taken as reference, employs a conventional injection system comprising calibrated straight orifices. The other two, referred to as advanced, adopt smaller orifices and pressure-swirl full-cone nozzles designed for the purpose; the third configuration utilizes a pump to boost the oil pressure. The laser imagining technique shows that the nozzles generate sprays that break-up within a short distance into spherical droplets, ligaments, ramifications and undefined structures. Tests on the packaged compressors reveal that the advanced configurations provide almost the same air flow rate while utilizing half of the oil because the sprays generate a good sealing. Moreover, the sprayed oil is acting as a thermal ballast because the electrical input is reduced by 3.0% and 3.5%, respectively, if the pump is not or is present, while the specific energy requirement, accounting for the slightly reduced air flow, by 2.4% and 2.9%, respectively
Mass accretion rates from multi-band photometry in the Carina Nebula: the case of Trumpler 14
We present a study of the mass accretion rates of pre-Main Sequence (PMS)
stars in the cluster Trumpler 14 (Tr14) in the Carina Nebula. Using optical
multi-band photometry we were able to identify 356 PMS stars showing H-alpha
excess emission with equivalent width EW(H-alpha)>20\AA. We interpret this
observational feature as indication that these objects are still actively
accreting gas from their circumstellar medium. From a comparison of the HR
diagram with PMS evolutionary models we derive ages and masses of the PMS
stars. We find that most of the PMS objects are younger than 10 Myr with a
median age of ~3 Myr. Surprisingly, we also find that ~20% of the mass
accreting objects are older than 10 Myr. For each PMS star in Trumpler 14 we
determine the mass accretion rate () and discuss its dependence
on mass and age. We finally combine the optical photometry with near-IR
observations to build the spectral energy distribution (SED) for each PMS star
in Tr14. The analysis of the SEDs suggests the presence of transitional discs
in which a large amount of gas is still present and sustains accretion onto the
PMS object at ages older than 10 Myr. Our results, discussed in light of recent
recent discoveries with Herschel of transitional discs containing a massive gas
component around the relatively old PSM stars TW Hydrae, 49 Ceti, and HD 95086,
support a new scenario in which old and evolved debris discs still host a
significant amount of gas.Comment: 12 pages, 13 figures, accepted for publication on A&
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