4,278 research outputs found
BioinformĂĄtica: formação acadĂȘmica e plataformas com softwares e ferramentas.
bitstream/item/31228/1/doc-109.pd
Reflectance measurement of two-dimensional photonic crystal nanocavities with embedded quantum dots
The spectra of two-dimensional photonic crystal slab nanocavities with
embedded InAs quantum dots are measured by photoluminescence and reflectance.
In comparing the spectra taken by these two different methods, consistency with
the nanocavities' resonant wavelengths is found. Furthermore, it is shown that
the reflectance method can measure both active and passive cavities. Q-factors
of nanocavities, whose resonant wavelengths range from 1280 to 1620 nm, are
measured by the reflectance method in cross polarization. Experimentally,
Q-factors decrease for longer wavelengths and the intensity, reflected by the
nanocavities on resonance, becomes minimal around 1370 nm. The trend of the
Q-factors is explained by the change of the slab thickness relative to the
resonant wavelength, showing a good agreement between theory and experiment.
The trend of reflected intensity by the nanocavities on resonance can be
understood as effects that originate from the PC slab and the underlying air
cladding thickness. In addition to three dimensional finite-difference
time-domain calculations, an analytical model is introduced that is able to
reproduce the wavelength dependence of the reflected intensity observed in the
experiment.Comment: 24 pages, 7 figures, corrected+full versio
Direct evaporative cooling of 41K into a Bose-Einstein condensate
We have investigated the collisional properties of 41K atoms at ultracold
temperature. To show the possibility to use 41K as a coolant, a Bose-Einstein
condensate of 41K atoms in the stretched state (F=2, m_F=2) was created for the
first time by direct evaporation in a magnetic trap. An upper bound of three
body loss coefficient for atoms in the condensate was determined to be 4(2)
10^{-29} cm -6 s-1. A Feshbach resonance in the F=1, m_F=-1 state was observed
at 51.42(5) G, which is in good agreement with theoretical prediction.Comment: 4 pages, 4 figure
The method of fundamental solutions for problems in static thermo-elasticity with incomplete boundary data
An inverse problem in static thermo-elasticity is investigated. The aim is to reconstruct the unspecified boundary data, as well as the temperature and displacement inside a body from over-specified boundary data measured on an accessible portion of its boundary. The problem is linear but ill-posed. The uniqueness of the solution is established but the continuous dependence on the input data is violated. In order to reconstruct a stable and accurate solution, the method of fundamental solutions is combined with Tikhonov regularization where the regularization parameter is selected based on the L-curve criterion. Numerical results are presented in both two and three dimensions showing the feasibility and ease of implementation of the proposed technique
Inelastic Neutron Scattering Study of Ferroelectric Phase Transition in Lithium Heptagermanate (Li(2)Ge(7)O(15))
Phonon dispersions in ferroelectric lithium heptagermanate Li(2)Ge(7)O(15) (LGO) were measured by inelastic neutron scattering in the vicinity of the transition temperature T(C) = 283.5 K. The (300) reflections show more pronounced temperature dependence than the (500) reflections. The energy of a peak corresponding to the Brillouin zone-center phonon, around 0.5 meV at 297.0 K, decreases as the temperature decreases. Then, this inelastic component disappears into the central component at 288.0 K, just above T(C). The present phonon shows the typical soft mode feature and shows good accordance with the B(1u) mode observed by hyper-Raman and FTIR measurements. It is confirmed that the ferroelectric phase transition in LGO is associated with the soft optical phonon at the zone center. Moreover, elastic diffuse scattering is observed below 0.1 meV. This implies that there exists a critical phenomenon at energies below than 0.1 meV.ArticleFERROELECTRICS. 412(0):45-51 (2011)journal articl
A single point mutation confers tetrodotoxin and saxitoxin insensitivity on the sodium channel II.
A single point mutation of the rat sodium channel II reduces its sensitivity to tetrodotoxin and saxitoxin by more than three orders of magnitude. The mutation replaces glutamic acid 387 with a glutamine and has only slight effects on the macroscopic current properties, as measured under voltage-clamp in Xenopus oocytes injected with the corresponding cDNA-derived mRNA
Role of the conduction electrons in mediating exchange interactions in Heusler alloys
Because of large spatial separation of the Mn atoms in Heusler alloys the Mn
3d states belonging to different atoms do not overlap considerably. Therefore
an indirect exchange interaction between Mn atoms should play a crucial role in
the ferromagnetism of the systems. To study the nature of the ferromagnetism of
various Mn-based semi- and full-Heusler alloys we perform a systematic
first-principles calculation of the exchange interactions in these materials.
The calculation of the exchange parameters is based on the frozen-magnon
approach. The calculations show that the magnetism of the Mn-based Heusler
alloys depends strongly on the number of conduction electrons, their spin
polarization and the position of the unoccupied Mn 3d states with respect to
the Fermi level. Various magnetic phases are obtained depending on the
combination of these characteristics. The Anderson's s-d model is used to
perform a qualitative analysis of the obtained results. The conditions leading
to diverse magnetic behavior are identified. If the spin polarization of the
conduction electrons at the Fermi energy is large and the unoccupied Mn 3d
states lie well above the Fermi level, an RKKY-type ferromagnetic interaction
is dominating. On the other hand, the contribution of the antiferromagnetic
superexchange becomes important if unoccupied Mn 3d states lie close to the
Fermi energy. The resulting magnetic behavior depends on the competition of
these two exchange mechanisms. The calculational results are in good
correlation with the conclusions made on the basis of the Anderson s-d model
which provides useful framework for the analysis of the results of
first-principles calculations and helps to formulate the conditions for high
Curie temperature.Comment: 16 pages, 9 figures, 2 table
Pressure-induced polarization reversal in multiferroic
The low-temperature ferroelectric polarization of multiferroic is
completely reversed at a critical pressure of 10 kbar and the phase transition
from the incommensurate to the commensurate magnetic phase is induced by
pressures above 14 kbar. The high-pressure data correlate with thermal
expansion measurements indicating a significant lattice strain at the
low-temperature transition into the incommensurate phase. The results support
the exchange striction model for the ferroelectricity in multiferroic
compounds and they show the importance of magnetic frustration as
well as the spin-lattice coupling
Aerodynamic performance of a free-flying dragonflyâA span-resolved investigation
We present a quantitative characterization of the unsteady aerodynamic features of a live, free-flying dragonfly under a well-established flight condition. In particular, our investigations cover the span-wise features of vortex interactions between the fore- and hind-pairs of wings that could be a distinctive feature of a high aspect ratio tandem flapping wing pair. Flapping kinematics and dynamic wing-shape deformation of a dragonfly were measured by tracking painted landmarks on the wings. Using it as the input, computational fluid dynamics analyses were conducted, complemented with time-resolved particle image velocimetry flow measurements to better understand the aerodynamics associated with a dragonfly. The results show that the flow structures around hindwingâs inner region are influenced by forewingâs leading edge vortex, while those around hindwingâs outer region are more influenced by forewingâs shed trailing edge vortex. Using a span-resolved approach, we found that the forewingâhindwing interactions affect the horizontal force (thrust) generation of the hindwing most prominently and the modulation of the force generation is distributed evenly around the midspan. Compared to operating in isolation, the thrust of the hindwing is largely increased during upstroke, albeit the drag is also slightly increased during the downstroke. The vertical force generation is moderately affected by the forewingâhindwing interactions and the modulation takes place in the outer 40% of the hindwing span during the downstroke and in the inner 60% of the span during the upstroke
O papel das mutaçÔes na compreensão da genética do milho.
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