129 research outputs found
Temperature Dependence Of Dipolar Modes In Ferroelectric Batio3 By Infrared Studies
Temperature dependence of A1 modes in tetragonal phase and F1u modes in cubic phase of BaTiO3 has been studied by ir (infrared) reflectivity measurements. The spectra have been analyzed using Kramers-Kronig analysis and the coupled-mode classical oscillator fit. The results are in excellent agreement with each other and are compatible with the earlier Raman measurements. Such a compatibility indeed favors the conclusion of Pinczuk et al. with regard to the interpretation of the broad peaks at 270 and 520 cm-1 in the Raman spectrum to be of first order. A critical analysis of the earlier work in BaTiO3 is presented. © 1980 The American Physical Society.2252396240
Optical properties of tungsten thin films perforated with a bidimensional array of subwavelength holes
We present a theorical investigation of the optical transmission of a
dielectric grating carved in a tungsten layer. For appropriate wavelengths
tungsten shows indeed a dielectric behaviour. Our numerical simulations leads
to theoretical results similar to those found with metallic systems studied in
earlier works. The interpretation of our results rests on the idea that the
transmission is correlated with the resonant response of eigenmodes coupled to
evanescent diffraction orders.Comment: 4 pages, 3 figure
Strong Discontinuities in the Complex Photonic Band Structure of Transmission Metallic Gratings
Complex photonic band structures (CPBS) of transmission metallic gratings
with rectangular slits are shown to exhibit strong discontinuities that are not
evidenced in the usual energetic band structures. These discontinuities are
located on Wood's anomalies and reveal unambiguously two different types of
resonances, which are identified as horizontal and vertical surface-plasmon
resonances. Spectral position and width of peaks in the transmission spectrum
can be directly extracted from CPBS for both kinds of resonances.Comment: 4 pages, 4 figures, REVTeX version
The evolutionary implications of hemipenial morphology of rattlesnake crotalus durissus terrificus (Laurent, 1768) (Serpentes: Viperidae: Crotalinae)
FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ â CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOMost amniotes vertebrates have an intromittent organ to deliver semen. The reptile Sphenodon and most birds lost the ancestral penis and developed a cloaca-cloaca mating. Known as hemipenises, the copulatory organ of Squamata shows unique features between the amniotes intromittent organ. They are the only paired intromittent organs across amniotes and are fully inverted and encapsulated in the tail when not in use. The histology and ultrastructure of the hemipenes of Crotalus durissus rattlesnake is described as the evolutionary implications of the main features discussed. The organization of hemipenis of Crotalus durissus terrificus in two concentric corpora cavernosa is similar to other Squamata but differ markedly from the organization of the penis found in crocodilians, testudinata, birds and mammals. Based on the available data, the penis of the ancestral amniotes was made of connective tissue and the incorporation of smooth muscle in the framework of the sinusoids occurred independently in mammals and Crotalus durissus. The propulsor action of the muscle retractor penis basalis was confirmed and therefore the named should be changed to musculus hemipenis propulsor. The retractor penis magnus found in Squamata has no homology to the retractor penis of mammals, although both are responsible for the retraction of the copulatory organ86FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ â CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOFAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOCNPQ â CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICOFAPESP [2011/11828-4]sem informaçãosem informaçã
Transmission properties of a single metallic slit: From the subwavelength regime to the geometrical-optics limit
In this work we explore the transmission properties of a single slit in a
metallic screen. We analyze the dependence of these properties on both slit
width and angle of incident radiation. We study in detail the crossover between
the subwavelength regime and the geometrical-optics limit. In the subwavelength
regime, resonant transmission linked to the excitation of waveguide resonances
is analyzed. Linewidth of these resonances and their associated electric field
intensities are controlled by just the width of the slit. More complex
transmission spectra appear when the wavelength of light is comparable to the
slit width. Rapid oscillations associated to the emergence of different
propagating modes inside the slit are the main features appearing in this
regime.Comment: Accepted for publication in Phys. Rev.
Same-sign dileptons as a signature for heavy Majorana neutrinos in hadron-hadron collisions
We discuss the possibility of same-sign dileptons as a signature for Majorana
neutrinos. The production mechanism is given by a single heavy neutrino
production and decay proton-proton -> l^{\pm} N X -> l^{\pm} l^{\pm} X'. Cross
section and distributions are presented for the LHC energies.Comment: 07 pages, LaTeX; to be published in Physics Letters
Light scattering from disordered overlayers of metallic nanoparticles
We develop a theory for light scattering from a disordered layer of metal
nanoparticles resting on a sample. Averaging over different disorder
realizations is done by a coherent potential approximation. The calculational
scheme takes into account effects of retardation, multipole excitations, and
interactions with the sample. We apply the theory to a system similar to the
one studied experimentally by Stuart and Hall [Phys. Rev. Lett. {\bf 80}, 5663
(1998)] who used a layered Si/SiO/Si sample. The calculated results agree
rather well with the experimental ones. In particular we find conspicuous
maxima in the scattering intensity at long wavelengths (much longer than those
corresponding to plasmon resonances in the particles). We show that these
maxima have their origin in interference phenomena in the layered sample.Comment: 19 pages, 12 figure
Cosmic String in the Supersymmetric CSKR Theory
We study a cosmic string solution of an N=1-supersymmetric version of the
Cremmer-Scherk-Kalb-Ramond (CSKR) Lagrangian coupled to a vector superfield by
means of a topological mass term. The 2-form gauge potential is proposed to
couple non-minimally to matter, here described by a chiral scalar superfield.
The important outcome is that supersymmetry is kept exact both in the core and
in the exterior region of the string. We contemplate the bosonic configurations
and it can be checked that the solutions saturate the Bogomolnyi bound. A
glimpse on the fermionic zero modes is also given.Comment: 14 pages, LaTeX, presented at the XXI "Encontro Nacional de Fisica de
Particulas e Campos", Sao Lourenco, MG, Brazil, with zero modes adde
Confirmation of the presence of Janicea antiguensis (Chace, 1972) (Decapoda: Barbouriidae) in northeastern and eastern Brazil
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