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11.
Self-optical parametric oscillation is demonstrated for the first time to our knowledge in a periodically poled neodymium-doped lithium niobate (Nd:PPLN) crystal. The crystal is pumped by a cw Ti:sapphire laser at 813.5 nm. The Nd(3+) ions absorb the 813.5-nm radiation to generate 1084-nm laser oscillation. The internally Q switched 1084-nm radiation pumps the periodically poled lithium niobate host matrix to generate optical parametric oscillation at 1.55 and 3.6 microm . Up to 24% conversion efficiency from laser to signal is observed. 相似文献
12.
Earlier geometrical theories of gravitation with short-range forces are analyzed, in view of a more general approach, to compare some of the properties of such theories with general relativity (GR). It is found that neither the scalar-tensor nor the fourth-order theories of gravity share with GR the interesting property that the binding energy of a gravitating system may be attributed to the loss of energy in packing the matter under its own gravitational field. This general approach, in the form of a GR field equation with an effective energy-momentum tensor is used to construct a constant-density, spherically-symmetric star model, via a heuristic argument, as a perturbation of the corresponding model in GR to study the modifications to the limiting gravitational mass. The application of the present study to other problems of physical interest is briefly mentioned. 相似文献
13.
We consider a class of fourth order theories of gravity with arbitrary matter fields arising from a diffeomorphism invariant Lagrangian density
, with
and
the phenomenological representation of the nongravitational fields. We derive first the generalization of the Einstein pseudotensor and the von Freud superpotential. We then show, using the arbitrariness that is always present in the choice of pseudotensor and superpotential, that we can choose these superpotentials to have the same form as those for the Hilbert Lagrangian of general relativity (GR). In particular we may introduce the Moller superpotential of GR as associated with a double-index differential conservation law. Similarly, using the Moller superpotential we prove that we can choose the Komar vector of GR to construct a conserved quantity for isolated asymptotically flat systems. For the example R + R2theory we prove then, that the active mass is equal to the total energy (or inertial mass) of the system. 相似文献
14.
The first order formalism is applied to study the field equations of a general Lagrangian density for gravity of the form
. These field equations correspond to theories which are a subclass of conformally metric theories in which the derivative of the metric is proportional to the metric by a Weyl vector field. The resulting geometrical structure is unique, except whenf(R)=aR
2, in the sense that the Weyl field is identifiable in terms of the trace of the energy-momentum tensor and its derivatives. In the casef(R)=aR
2 the metric is only defined up to a conformai factor. We discuss the matter conservation equations which are implied by the invariance of the theories under diffeomorphisms. We apply the results to the case of dust and obtain that in general the dust particles will not follow geodesic Unes. We consider the linearized field equations and apply them to obtain the weak field slow motion limit. It is found that the gravitational potential acquires a new term which depends linearly on the mass density. The importance of these new equations is briefly discussed. 相似文献
15.
We study the properties of the solution space of local surface-forming null sub-congruences in the neighbourhood of a given null geodesic in a pseudo-Riemannian space-time. This solution space is a three-dimensional manifold, naturally endowed with a conformai Minkowski metric. 相似文献
16.
O. A. Oviedo D. Barraco E. P. M. Leiva 《Journal of Solid State Electrochemistry》2014,18(10):2837-2839
The present article comments on the article of Stephen Fletcher (Journal of Solid State Electrochemistry Volume 18, Issue 5, pp 1231–1238). The analysis deals with the validity of equation (31 or 40) of the latter for an ideally polarisable interface. 相似文献
17.
Sacha Smrekar Martin E. Zoloff Michoff Jorge E. Thomas Cecilia A. Calderón Lucas M. Farigliano Arnaldo Visintin Ezequiel P. M. Leiva Daniel E. Barraco 《Journal of Solid State Electrochemistry》2018,22(6):1721-1733
The nucleation of Sn nanoparticles by chemical reduction was studied using three different carbonaceous substrates, to obtain Sn/C composites. When used as active materials in anodes for lithium-ion batteries, these composites displayed higher capacities than commercially used graphite, and showed a good cyclability. The differences in morphology, capacity, cyclability, and diffusion between the resulting materials are highlighted. The resulting materials were characterized by charge-discharge cycling, voltammetry, EIS, SEM, and TEM microscopy. It was found that the substrate has a determinant effect on the deposition of Sn. This effect is interpreted in terms of the relative adsorption energies of a single Sn atom obtained from DFT calculations. 相似文献
18.
Victor Hugo Hamity M. A. Cécere D. E. Barraco 《General Relativity and Gravitation》2009,41(11):2657-2676
Although infinite cylinders are not astrophysical entities, it is possible to learn a great deal about the basic qualitative
features of generation of gravitational waves and the behavior of the matter conforming such shells in the limits of very
small radius. We study an analytical model of a relativistic cylindrical shell of counter-rotating particles using kinetic
theory for the matter and the junction conditions through the shell to obtain its equation of motion. The nature of the static
solutions are analyzed, both for a single shell as well as for two coaxial shells. In the latter case, we integrate numerically
the time dependent equation of motion of the external shell, when we neglect the wave components of the gravitational field
at the shells locations. We obtain solutions that correspond to shells that perform damped oscillations, collapse, or are
locally expanding. The collapse ends (numerically) when the external shell hits the interior shell. The numerically work also
shows that the radiation becomes important after the bounce of the external shell. 相似文献
19.
Within a fourth-order theory of gravity we give,for a static asymptotically flat spacetime, anexpression of the active mass (gravitational mass), infirst order in the coupling constant, , of the curvature squared term in the Lagrangiandensity, a generalization of the Tolman expression forthe energy, which establishes a relationship between theactive mass and the source structure in a static spacetime. Within this approximation, we canprove that the fourth-order theory shares with Generalrelativity (GR) the property that, for sources ofcompact support, the active mass is independent of any two-dimensional surface which encloses thesupport of the matter distribution. Finally, we provethat only for conformally invariant sources thefourth-order theory and GR share the same static andasymptotically flat solutions. 相似文献
20.
Dr. E. Maximiliano Gavilán-Arriazu Prof. Daniel E. Barraco Prof. Yair Ein-Eli Prof. Ezequiel P. M. Leiva 《Chemphyschem》2023,24(6):e202200665
In this work, we develop a new tool to provide a diagnostic map for alkali-ion intercalation materials under galvanostatic conditions. These representations, stated in the form of capacity level diagrams, are built from hundreds of numerical simulations representing different experimental conditions, summarized in two dimensionless parameters: a kinetic parameter denominated Ξ and a finite diffusion parameter l. To lay the theoretical and methodological foundations, a general model is used here. This model can be adapted to the thermodynamic and kinetic framework of specific systems. We provide two representative examples. 相似文献