19,178 research outputs found
Experimental Determination of Thermal Entanglement in Spin Clusters using Magnetic Susceptibility Measurements
The present work reports an experimental observation of thermal entanglement
in a clusterized spin chain formed in the compound NaCuSiO.
The presence of entanglement was investigated through two measured quantities,
an Entanglement Witness and the Entanglement of Formation, both derived from
the magnetic susceptibility. It was found that pairwise entanglement exists
below K. Tripartite entanglement was also observed below K. A theoretical study of entanglement evolution as a function of applied
field and temperature is also presented.Comment: Submited to Phys. Rev.
On the choice of parameters in solar structure inversion
The observed solar p-mode frequencies provide a powerful diagnostic of the
internal structure of the Sun and permit us to test in considerable detail the
physics used in the theory of stellar structure. Amongst the most commonly used
techniques for inverting such helioseismic data are two implementations of the
optimally localized averages (OLA) method, namely the Subtractive Optimally
Localized Averages (SOLA) and Multiplicative Optimally Localized Averages
(MOLA). Both are controlled by a number of parameters, the proper choice of
which is very important for a reliable inference of the solar internal
structure. Here we make a detailed analysis of the influence of each parameter
on the solution and indicate how to arrive at an optimal set of parameters for
a given data set.Comment: 14 pages, 15 figures. Accepted for publication on MNRA
Teor de açúcar da água residuária do processamento do café.
A fermentação dos açúcares contidos na mucilagem da água residuária do café (ARC) possibilita obter álcool. Para se obter bom rendimento de álcool é necessário ajustar o teor de açúcar da ARC para 16° Brix. O trabalho teve como objetivo quantificar os teores de açúcar da ARC, após sucessivas reciclagens no processo de desmucilamento. Colocou-se água de torneira em amostras de café cereja descascado, das variedades Bourbon Vermelho e Bourbon Amarelo, e a mucilagem foi extraída, girando-se um bastão de vidro, por 3 minutos. Foram feitas até seis extrações, em seqüência, reciclando-se a ARC obtida. Os teores de açúcar da ARC aumentaram linearmente com o aumento do número de extrações realizadas. O teor de açúcar da ARC elevou-se de 3,1 para 9,3° Brix, após cinco extrações, e de 2,6 para 10,3° Brix, após seis extrações da mucilagem do cereja descascado, das variedades Bourbon Vermelho e Bourbon Amarelo, respectivamente
Group theory for structural analysis and lattice vibrations in phosphorene systems
Group theory analysis for two-dimensional elemental systems related to
phosphorene is presented, including (i) graphene, silicene, germanene and
stanene, (ii) dependence on the number of layers and (iii) two stacking
arrangements. Departing from the most symmetric graphene space
group, the structures are found to have a group-subgroup relation, and analysis
of the irreducible representations of their lattice vibrations makes it
possible to distinguish between the different allotropes. The analysis can be
used to study the effect of strain, to understand structural phase transitions,
to characterize the number of layers, crystallographic orientation and
nonlinear phenomena.Comment: 24 pages, 3 figure
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