11,820 research outputs found
Markov chain approach to the distribution of ancestors in species of biparental reproduction
We studied how to obtain a distribution for the number of ancestors in
species of sexual reproduction. Present models concentrate on the estimation of
distributions repetitions of ancestors in genealogical trees. It has been shown
that is not possible to reconstruct the genealogical history of each species
along all its generations by means of a geometric progression. This analysis
demonstrates that it is possible to rebuild the tree of progenitors by modeling
the problem with a Markov chain. For each generation, the maximum number of
possible ancestors is different. This brings huge problems for the resolution.
We found a solution through a dilation of the sample space, although the
distribution defined there takes smaller values respect to the initial problem.
In order to correct the distribution for each generation, we introduced the
invariance under gauge (local) group of dilations. These ideas can used to
study the interaction of several processes and provide a new approach on the
problem of the common ancestor. In the same direction, this model also provide
some elements that can be used to improve models of animal reproduction.Comment: English version with change
Noise-robust quantum sensing via optimal multi-probe spectroscopy
The dynamics of quantum systems are unavoidably influenced by their
environment and in turn observing a quantum system (probe) can allow one to
measure its environment: Measurements and controlled manipulation of the probe
such as dynamical decoupling sequences as an extension of the Ramsey
interference measurement allow to spectrally resolve a noise field coupled to
the probe. Here, we introduce fast and robust estimation strategies for the
characterization of the spectral properties of classical and quantum dephasing
environments. These strategies are based on filter function orthogonalization,
optimal control filters maximizing the relevant Fisher Information and
multi-qubit entanglement. We investigate and quantify the robustness of the
schemes under different types of noise such as finite-precision measurements,
dephasing of the probe, spectral leakage and slow temporal fluctuations of the
spectrum.Comment: 13 pages, 14 figure
Off-diagonal helicity density matrix elements for vector mesons produced in polarized e+e- processes
Final state quark-antiquark interactions give origin to non zero values of
the off-diagonal element rho_{1,-1} of the helicity density matrix of vector
mesons produced in e+e- annihilations, as confirmed by recent OPAL data on Phi,
D^* and K^*'s. New predictions are given for rho_{1,-1} of several mesons
produced at large x_E and small p_T -- i.e. collinear with the parent jet -- in
the annihilation of polarized e+ and e-; the results depend strongly on the
elementary dynamics and allow further non trivial tests of the Standard Model.Comment: LaTeX, 20 pages, 6 ps figures, uses epsfig.st
Quark fragmentation into vector and pseudoscalar mesons at LEP
Some data on the ratio of vector to vector + pseudoscalar mesons, V/(V+P),
and the probability of helicity zero vector states, rho_00, are now available
from LEP. A possible relation between these two quantities and their
interpretation in terms of polarized fragmentation functions are discussed;
numerical estimates are given for the relative occupancies of K and K*, D and
D*, B and B* states.Comment: 5 pages, no figure
Noise-enhanced classical and quantum capacities in communication networks
The unavoidable presence of noise is thought to be one of the major problems
to solve in order to pave the way for implementing quantum information
technologies in realistic physical platforms. However, here we show a clear
example in which noise, in terms of dephasing, may enhance the capability of
transmitting not only classical but also quantum information, encoded in
quantum systems, through communication networks. In particular, we find
analytically and numerically the quantum and classical capacities for a large
family of quantum channels and show that these information transmission rates
can be strongly enhanced by introducing dephasing noise in the complex network
dynamics.Comment: 4 pages, 4 figures; See Video Abstract at
http://www.quantiki.org/video_abstracts/1003587
Pool temperature stratification analysis in CIRCE-ICE facility with RELAP5-3D© model and comparison with experimental tests
In the frame of heavy liquid metal (HLM) technology development, CIRCE pool facility at ENEA/Brasimone Research Center was updated by installing ICE (Integral Circulation Experiments) test section which simulates the thermal behavior of a primary system in a HLM cooled pool reactor. The experimental campaign led to the characterization of mixed convection and thermal stratification in a HLM pool in safety relevant conditions and to the distribution of experimental data for the validation of CFD and system codes. For this purpose, several thermocouples were installed into the pool using 4 vertical supports in different circumferential position for a total of 119 thermocouples [1][2]. The aim of this work is to investigate the capability of the system code RELAP5-3D (c) to simulate mixed convection and thermal stratification phenomena in a HLM pool in steady state conditions by comparing code results with experimental data. The pool has been simulated by a 3D component divided into 1728 volumes, 119 of which are centered in the exact position of the thermocouples. Three dimensional model of the pool is completed with a mono-dimensional nodalization of the primary main flow path. The results obtained by code simulations are compared with a steady state condition carried out in the experimental campaign. Results of axial, radial and azimuthal temperature profile into the pool are in agreement with the available experimental data Furthermore the code is able to well simulate operating conditions into the main flow path of the test section
Equivalent quantum systems
We have studied quantum systems on finite-dimensional Hilbert spaces and
found that all these systems are connected through local transformations.
Actually, we have shown that these transformations give rise to a gauge group
that connects the Hamiltonian operators associated with each quantum system.
This bridge allows us to connect different quantum systems, in such a way that
studying one of them allows to understand the other through a gauge
transformation. Furthermore, we included the case where the Hamiltonian
operator can be time-dependent. An application for this construction will be
achieved in the theory of control quantum systems
Development of a high brightness ultrafast Transmission Electron Microscope based on a laser-driven cold field emission source
We report on the development of an ultrafast Transmission Electron Microscope
based on a cold field emission source which can operate in either DC or
ultrafast mode. Electron emission from a tungsten nanotip is triggered by
femtosecond laser pulses which are tightly focused by optical components
integrated inside a cold field emission source close to the cathode. The
properties of the electron probe (brightness, angular current density,
stability) are quantitatively determined. The measured brightness is the
largest reported so far for UTEMs. Examples of imaging, diffraction and
spectroscopy using ultrashort electron pulses are given. Finally, the potential
of this instrument is illustrated by performing electron holography in the
off-axis configuration using ultrashort electron pulses.Comment: 23 pages, 9 figure
Pre-test analysis of protected loss of primary pump transients in CIRCE-HERO facility
In the frame of LEADER project (Lead-cooled European Advanced Demonstration Reactor), a new configuration of the steam generator for ALFRED (Advanced Lead Fast Reactor European Demonstrator) was proposed. The new concept is a super-heated steam generator, double wall bayonet tube type with leakage monitoring [1]. In order to support the new steam generator concept, in the framework of Horizon 2020 SESAME project (thermal hydraulics Simulations and Experiments for the Safety Assessment of MEtal cooled reactors), the ENEA CIRCE pool facility will be refurbished to host the HERO (Heavy liquid mEtal pRessurized water cOoled tubes) test section to investigate a bundle of seven full scale bayonet tubes in ALFRED-like thermal hydraulics conditions. The aim of this work is to verify thermofluid dynamic performance of HERO during the transition from nominal to natural circulation condition. The simulations have been performed with RELAP5-3D© by using the validated geometrical model of the previous CIRCE-ICE test section [2], in which the preceding heat exchanger has been replaced by the new bayonet bundle model. Several calculations have been carried out to identify thermal hydraulics performance in different steady state conditions. The previous calculations represent the starting points of transient tests aimed at investigating the operation in natural circulation. The transient tests consist of the protected loss of primary pump, obtained by reducing feed-water mass flow to simulate the activation of DHR (Decay
Heat Removal) system, and of the loss of DHR function in hot conditions, where feed-water mass flow rate is absent. According to simulations, in nominal conditions, HERO bayonet bundle offers excellent thermal hydraulic behavior and, moreover, it allows the operation in natural circulation
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