86,883 research outputs found
A GEOSITE TO BE SAVED: THE TYRRHENIAN FOSSIL DEPOSIT ON THE ISLAND OF USTICA
No full textDuring the 1960s, fossil beds characterized by a tropical-sea malacofauna were discovered by G.
Ruggieri and G. Buccheri in the Island of Ustica, on the southern slope of Falconiera hill, 32 m asl.
Thanks to the presence of Strombus bubonius and other Senegalese guests, the authors estimated that
the molluscan fauna had lived around 125,000 years ago, during the Tyrrhenian stage. Recently on
the initiative of the “Centro Studi e Documentazione Isola di Ustica”, a research has been initiated to
verify the persistence of sand-layers mixed up with Tyrrhenian fossils, even though, in the last 50
years, that area has undergone great changes, because of earthworks which have sealed the deposit.
The new research led to the discovery of a fossil assemblage formed by 22 taxa (16 species of gastropods
and 6 of bivalves), characterized by the presence of some Senegalese guests and other accompanying
species that can be associated with the Eutyrrhenian subunit (MIS 5.5). This is the main subject
of this note, along with the suggestion to preserve what remains of the Ustica Tyrrhenian deposit
Relative phase and Josephson dynamics between weakly coupled Richardson models
No full textWe consider two weakly coupled Richardson models to study the formation of a relative phase and the Josephson dynamics between two mesoscopic attractively interacting fermionic systems. Our results apply to superconducting properties of coupled ultrasmall metallic grains and to Cooper-pairing superfluidity in neutral systems with a finite number of fermions. We discuss how a definite relative phase between the two systems emerges and how it can be conveniently extracted from the many-body wave function, finding that a definite relative phase difference emerges even for very small numbers of pairs (∼10). The Josephson dynamics and the current-phase characteristics are then investigated, showing that the critical current has a maximum at the BCS-BEC crossover. For the considered initial conditions a two-state model gives a good description of the dynamics and of the current-phase characteristics
Finite temperature one-point functions in non-diagonal integrable field theories: the sine-Gordon model
No full textWe study the finite-temperature expectation values of exponential fields in the sine-Gordon model. Using finite-volume regularization, we give a low-temperature expansion of such quantities in terms of the connected diagonal matrix elements, for which we provide explicit formulas. For special values of the exponent, computations by other methods are available and used to validate our findings. Our results can also be interpreted as a further support for a previous conjecture about the connection between finite- and infinite-volume form factors valid up to terms exponentially decaying in the volume
HARK the SHARK: Realized Volatility Modeling with Measurement Errors and Nonlinear Dependencies
No full textDespite their effectiveness, linear models for realized variance neglect measurement errors on integrated variance and exhibit several forms of misspecification due to the inherent nonlinear dynamics of volatility. We propose new extensions of the popular approximate long-memory heterogeneous autoregressive (HAR) model apt to disentangle these effects and quantify their separate impact on volatility forecasts. By combining the asymptotic theory of the realized variance estimator with the Kalman filter and by introducing time-varying HAR parameters, we build new models that account for: (i) measurement errors (HARK), (ii) nonlinear dependencies (SHAR) and (iii) both measurement errors and nonlinearities (SHARK). The proposed models are simply estimated through standard maximum likelihood methods and are shown, both on simulated and real data, to provide better out-of-sample forecasts compared to standard HAR specifications and other competing approaches
A DCC-type approach for realized covariance modeling with score-driven dynamics
No full textWe propose a class of score-driven realized covariance models where volatilities and correlations are separately estimated. We can thus combine univariate realized volatility models with a recently introduced class of score-driven realized covariance models based on Wishart and matrix-F distributions. Compared to the latter, the proposed models remain computationally simple at high dimensions and allow for higher flexibility in parameter estimation. Through a Monte-Carlo study, we show that the two-step maximum likelihood procedure provides accurate parameter estimates in small samples. Empirically, we find that the proposed models outperform those based on joint estimation, with forecasting gains that become more significant as the cross-section dimension increases
Electroweak radiative corrections to Higgs production via vector boson fusion using soft-collinear effective theory: Numerical results
No full textElectroweak radiative corrections are computed for Higgs production through vector boson fusion, qq→qqH, which is one of the most promising channels for detecting and studying the Higgs boson at the LHC. Using soft-collinear effective theory, we obtain numerical results for the resummed logarithmic contributions to the hadronic cross section at next-to-leading logarithmic order. We compare our results to HAWK and find good agreement below 2 TeV where the logarithms do not dominate. The soft-collinear effective theory method is at its best in the high LHC energy domain where the corrections are found to be slightly larger than predicted by HAWK and by other one-loop fixed order approximations. This is one of the first tests of this formalism at the level of a hadronic cross section, and demonstrates the viability of obtaining electroweak corrections for generic processes without the need for difficult electroweak loop calculations
A DCC-type approach for realized covariance modeling with score-driven dynamics
No full textWe propose a class of score-driven realized covariance models where volatilities and correlations are separately estimated. We can thus combine univariate realized volatility models with a recently introduced class of score-driven realized covariance models based on Wishart and matrix-F distributions. Compared to the latter, the proposed models remain computationally simple at high dimensions and allow for higher flexibility in parameter estimation. Through a Monte-Carlo study, we show that the two-step maximum likelihood procedure provides accurate parameter estimates in small samples. Empirically, we find that the proposed models outperform those based on joint estimation, with forecasting gains that become more significant as the cross-section dimension increases
Topological Kondo Effect
No full textWe review recent theoretical progress in the understanding of the topological Kondo effect in Coulomb-blockaded Majorana devices and generalizations thereof. The central ingredient in Majorana devices is the so-called Majorana box which encodes a spin-1/2 degree of freedom in the Majorana subspace that can be addressed by electron cotunneling processes. In particular, after explaining the basic physics of the topological Kondo effect in a Majorana box connected to a set of normal-conducting leads, we discuss the Josephson current-phase relation in a superconducting multi-terminal setup where the central junction is again formed by a Majorana box but the leads are phase-biased superconductors. For large Kondo temperature, one finds that the competition between two-channel Kondo physics and the gap opening in the leads results in a 6π periodicity of the current-phase relation. This periodicity is due to the fractionalized charge excitations characterizing the non-Fermi liquid two-channel Kondo fixed point. We also explore generalizations of this Majorana-based topological Kondo setup to platforms hosting parafermionic excitations
Sign-changing solutions for elliptic problems with singular gradient terms and L1 data
No full textIn this paper we deal with singular boundary value problems of the type
−div(a(x,u)∇u)+b(x)|∇u|2|u|θ sign (u)=f(x),u=0, in Ω, (0.1) on ∂Ω,
where Ω is a open bounded set of RN with N>2 , a(x, t) is a Carathéodory function with polynomial growth with respect to t, b(x) is bounded and measurable, θ∈(0,1) and f(x) belongs to L1(Ω) . The main concern is to consider sign-changing solutions outside the energy space W1,20(Ω)
Sign-changing solutions for elliptic problems with singular gradient terms and L1 data
No full textIn this paper we deal with singular boundary value problems of the type
−div(a(x,u)∇u)+b(x)|∇u|2|u|θ sign (u)=f(x),u=0, in Ω, (0.1) on ∂Ω,
where Ω is a open bounded set of RN with N>2 , a(x, t) is a Carathéodory function with polynomial growth with respect to t, b(x) is bounded and measurable, θ∈(0,1) and f(x) belongs to L1(Ω) . The main concern is to consider sign-changing solutions outside the energy space W1,20(Ω)
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