496 research outputs found
Measurements of entanglement over a kilometric distance to test superluminal models of Quantum Mechanics: preliminary results
As shown in the \emph{EPR} paper (Einstein, Podolsky e Rosen, 1935), Quantum
Mechanics is a non-local Theory. The Bell theorem and the successive
experiments ruled out the possibility of explaining quantum correlations using
only local hidden variables models. Some authors suggested that quantum
correlations could be due to superluminal communications that propagate
isotropically with velocity \emph{} in a preferred reference frame.
For finite values of \emph{} and in some special cases, Quantum
Mechanics and superluminal models lead to different predictions. So far, no
deviations from the predictions of Quantum Mechanics have been detected and
only lower bounds for the superluminal velocities \emph{} have been
established. Here we describe a new experiment that increases the maximum
detectable superluminal velocities and we give some preliminary results.Comment: 16 pages, 10 figures, Eighth International Workshop DICE2016,
Castiglioncello (IT), September 12-16, 201
S 2p photoabsorption of the SF5CF3 molecule: Experiment, theory and comparison with SF6
The S 2p core excitation spectrum of the SF5CF3 molecule has been measured in the total ion yield mode. It resembles a lot the analogous spectrum of SF6, also recorded in this study, displaying intense transitions to the empty molecular orbitals both below and above the S 2p ionization potential (IP) and weak transitions to the Rydberg orbitals. The S 2p photoabsorption spectra of SF6 and SF5CF3 have been calculated using time-dependent density functional theory, whereby the spin–orbit coupling was included for the transitions below the S 2p IP. The agreement between experiment and theory is good for both molecules, which allows us to assign the main S 2p absorption features in SF5CF3
Perturbative and Numerical Methods for Stochastic Nonlinear Oscillators
Interferometric gravitational wave detectors are devoted to pick up the
effect induced on masses by gravitational waves. The variations of the length
dividing two mirrors is measured through a laser interferometric technique. The
Brownian motion of the masses related to the interferometer room temperature is
a limit to the observation of astrophysical signals. It is referred to as
thermal noise and it affects the sensitivity of both the projected and the
future generation interferometers. In this paper we investigate the relevance
of small non-linear effects and point out their impact on the sensitivity curve
of interferometric gravitational wave detectors (e.g. VIRGO, LIGO, GEO, ...)
through perturbative methods and numerical simulations. We find that in the
first order approximation the constants characterizing the power spectrum
density (PSD) are renormalized but it retains its typical shape. This is due to
the fact that the involved Feynman diagrams are of tadpole type. Higher order
approximations are required to give rise to up-conversion effects. This result
is predicted by the perturbative approach and is in agreement with the
numerical results obtained by studying the system's non-linear response by
numerically simulating its dynamics.Comment: 12 pages, REVTeX + 7 PostScript figure
Optimization of density fitting auxiliary Slater-type basis functions for time-dependent density functional theory
A new set of auxiliary basis function suitable to fit the induced electron density is presented. Such set has been optimized in order to furnish accurate absorption spectra using the complex polarizability algorithm of time-dependent density functional theory (TDDFT). An automatic procedure has been set up, able, thanks to the definition of suitable descriptors, to evaluate the resemblance of the auxiliary basis-dependent calculated spectra with respect to a reference. In this way, it has been possible to reduce the size of the basis set maximizing the basis set accuracy. Thanks to the choice to employ a collection of molecules for each element, such basis has proven transferable to molecules outside the collection. The final sets are therefore much more accurate and smaller than the previously optimized ones and have been already included in the database of the last release of the AMS suite of programs. The availability of the present new set will allow to improve drastically the applicability range of the polTDDFT method with higher accuracy and less computational effort
A new time dependent density functional algorithm for large systems and plasmons in metal clusters
A new algorithm to solve the Time Dependent Density Functional Theory (TDDFT) equations in the
space of the density fitting auxiliary basis set has been developed and implemented. The method
extracts the spectrum from the imaginary part of the polarizability at any given photon energy,
avoiding the bottleneck of Davidson diagonalization. The original idea which made the present
scheme very efficient consists in the simplification of the double sum over occupied-virtual pairs
in the definition of the dielectric susceptibility, allowing an easy calculation of such matrix as a linear
combination of constant matrices with photon energy dependent coefficients. The method has been
applied to very different systems in nature and size (from H2 to [Au147] 12). In all cases, the maximum
deviations found for the excitation energies with respect to the Amsterdam density functional code are
below 0.2 eV. The new algorithm has the merit not only to calculate the spectrum at whichever photon
energy but also to allow a deep analysis of the results, in terms of transition contribution maps, Jacob
plasmon scaling factor, and induced density analysis, which have been all implemente
In the search for the low-complexity sequences in prokaryotic and eukaryotic genomes: how to derive a coherent picture from global and local entropy measures
We investigate on a possible way to connect the presence of Low-Complexity
Sequences (LCS) in DNA genomes and the nonstationary properties of base
correlations. Under the hypothesis that these variations signal a change in the
DNA function, we use a new technique, called Non-Stationarity Entropic Index
(NSEI) method, and we prove that this technique is an efficient way to detect
functional changes with respect to a random baseline. The remarkable aspect is
that NSEI does not imply any training data or fitting parameter, the only
arbitrarity being the choice of a marker in the sequence. We make this choice
on the basis of biological information about LCS distributions in genomes. We
show that there exists a correlation between changing the amount in LCS and the
ratio of long- to short-range correlation
Il bitcoin è halal? Una visione islamicamente orientata sulle valute virtuali
The essay investigates bitcoins and virtual currencies, which have had a great diffusion in international markets over the last decade, in the light of Islamic law. Starting therefore from the rules established by the Shari'a for Islamic finance, in particular the prohibition of gharar and gambling, tha study analyzes the debate arised between Muslim scholars and economists about the lawfulness of crytpocurrencies according to Islam. Finally, after translating a recent fatwa issued by the Grand Mufti of Egypt, and after explaining the importance of such kind of pronouncements in the Sunni world, the most important passages of the judgment are highlighted to demonstrate thath bitcoin is not shari’a complian
Accurate Vertical Excitation Energies of BODIPY/Aza-BODIPY Derivatives from Excited-State Mean-Field Calculations
We report a benchmark study of vertical excitation energies and oscillator strengths for the HOMO -> LUMO transitions of 17 boron-dipyrromethene (BODIPY) structures, showing a large variety of ring sizes and substituents. Results obtained at the time-dependent density functional theory (TDDFT) and at the delta-self-consistent-field (Delta SCF) by using 13 different exchange correlation kernels (within LDA, GGA, hybrid, and range-separated approximations) are benchmarked against the experimental excitation energies when available. It is found that the time-independent Delta SCF DFT method, when used in combination with hybrid PBE0 and B3LYP functionals, largely outperforms TDDFT and can be quite competitive, in terms of accuracy, with computationally more costly wave function based methods such as CC2 and CASPT2
A new time-dependent density-functional method for molecular plasmonics: Formalism, implementation, and the Au144(SH)60 case study
We describe the implementation and application of a recently developed time-dependent density-functional theory (TDDFT) algorithm based on the complex dynamical polarizability to calculate the photoabsorption spectrum of large metal clusters, with specific attention to the field of molecular plasmonics. The linear response TDDFT equations are solved in the space of the density fitting functions, so the problem is recast as an inhomogeneous system of linear equations whose resolution needs a numerical effort comparable to that of a SCF procedure. The construction of the matrix representation of the dielectric susceptibility is very efficient and is based on the discretization of the excitation energy, so such matrix is easily obtained at each photon energy value as a linear combination of constant matrix and energy-dependent coefficients. The code is interfaced to the Amsterdam Density Functional (ADF) program and is fully parallelized with standard message passing interface. Finally, an illustrative application of the method to the photoabsorption of the Au144(SH)60 cluster is presented
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