Daniel Varela Magalhães

Hardness evaluation of a dental composite polymerized with experimental LED-based devices.

OBJECTIVE The main goal of this study was the hardness evaluation of a composite resin cured by five LED (Light Emitting Diodes) based devices and a comparison with a conventional curing unit. The hardness test was used to compare the efficacy of both types of light source. METHODS The LED-based devices were made employing an array of LEDs (Nichia Chem. Ind., Japan) emitting light peaked at 470nm. Composite resin (Z100, shade A3) was cured for 20, 40, 60, 120 and 180s with each LED-based device and for 40s with the halogen lamp. The composite samples were prepared with 0.35, 1.25 and 1.8mm of thickness. Five samples of each set of parameters were done. The hardness evaluation was performed at the non-illuminate surface with three indentations for each sample. RESULTS All the samples cured by the LED-based devices showed inferior hardness values when compared with the halogen lamp at the typical curing time (40s). The L6 (device composed of six LEDs) was the most efficient one of the LED-based devices. Its obtained irradiance was 79mW/cm(2), whereas the halogen lamp irradiance was of 475mW/cm(2). For the L6 device here presented, longer exposure times or a thinner resin layer are required to achieve reasonable hardness values. SIGNIFICANCE Besides the difference of irradiance when compared with halogen lamps, LED-based devices show to be a promising alternative curing instrument. Further development in instrumentation may result in devices even more efficient than conventional lamps.

Ultrastable lasers based on vibration insensitive cavities

We present two ultrastable lasers based on two vibration insensitive cavity designs, one with vertical optical axis geometry, the other horizontal. Ultrastable cavities are constructed with fused silica mirror substrates, shown to decrease the thermal noise limit, in order to improve the frequency stability over previous designs. Vibration sensitivity components measured are equal to or better than

Doppler-free spectroscopy of the 1S0-3P0 optical clock transition in laser-cooled fermionic isotopes of neutral mercury.

1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}/\text{m}\text{ }{\text{s}}^{\ensuremath{-}2}

Observation of vortex formation in an oscillating trapped Bose-Einstein condensate

for each spatial direction, which shows significant improvement over previous studies. We have tested the very low dependence on the position of the cavity support points, in order to establish that our designs eliminate the need for fine tuning to achieve extremely low vibration sensitivity. Relative frequency measurements show that at least one of the stabilized lasers has a stability better than

Battery state estimation for applications in intelligent warehouses

5.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}

Laser locking to the 199 Hg 1 S 0 − 3 P 0 clock transition with 5.4 × 10 −15 /✓τ fractional frequency instability

at 1 s, which is the best result obtained for this length of cavity.

Laser locking to the 199Hg clock transition with 5.4x10^(-15)/sqrt(tau) fractional frequency instability

We report direct laser spectroscopy of the 1S0-3P0 transition at 265.6 nm in fermionic isotopes of neutral mercury in a magneto-optical trap. Measurements of the frequency against the LNE-SYRTE primary reference using an optical frequency comb yield 1 128 575 290 808.4+/-5.6 kHz in 199Hg and 1 128 569 561 139.6+/-5.3 kHz in 201Hg. The uncertainty, allowed by the observation of the Doppler-free recoil doublet, is 4 orders of magnitude lower than previous indirect determinations. Mercury is a promising candidate for future optical lattice clocks due to its low sensitivity to blackbody radiation.

Bose-Einstein condensation in 87Rb: characterization of the Brazilian experiment

We report on the observation of vortex formation in a Bose-Einstein condensate of

Construction and evaluation of the first Brazilian atomic clock

^{87}\text{R}\text{b}

Magneto-optical trap of neutral mercury for an optical lattice clock

atoms. Vortices are generated by superimposing an oscillating excitation to the trapping potential introduced by an external magnetic field. For small amplitudes of the external excitation field we observe a bending of the cloud axis. Increasing the amplitude we observe formation of a growing number of vortices in the sample. Shot-to-shot variations in both vortex number and position within the condensed cloud are observed, probably due to the intrinsic vortex nucleation dynamics. We discuss the possible formation of vortices and antivortices in the sample as well as possible mechanisms for vortex nucleation.