Debris disks with extremely large infrared excesses (fractional luminosities \(> 10^{-2}\)) are rare. Those with ages between 30 and 130 Myr are of interest because their evolution has progressed ...well beyond that of protoplanetary disks (which dissipate with a timescale of order 3 Myr), yet they represent a period when dynamical models suggest that terrestrial planet building may still be progressing through large, violent collisions that could yield large amounts of debris and large infrared excesses. For example, our Moon was formed through a violent collision of two large proto-planets during this age range. We report two disks around the solar-like stars ID8 and HD 23514 in this age range where the 24 {\mu}m infrared excesses vary on timescales of a few years, even though the stars are not variable in the optical. Variations this rapid are difficult to understand if the debris is produced by collisional cascades, as it is for most debris disks. It is possible that the debris in these two systems arises in part from condensates from silicate-rich vapor produced in a series of violent collisions among relatively large bodies. If their evolution is rapid, the rate of detection of extreme excesses would indicate that major collisions may be relatively common in this age range.
Short-term accelerated life test activity on high brightness light emitting diodes is reported. Two families of 1-W light-emitting diodes (LEDs) from different manufacturers were submitted to ...distinct stress conditions: high temperature storage without bias and high dc current test. During aging, degradation mechanisms like light output decay and electrical property worsening were detected. In particular, the degradation in light efficiency induced by thermal storage was found to follow an exponential law, and the activation energy of the process was extrapolated. Aged devices exhibited a modification of the package epoxy color from white to brown. The instability of the package contributes to the overall degradation in terms of optical and spectral properties. In addition, an increase in thermal resistance was detected on one family of LEDs. This increase induces higher junction temperature levels during operative conditions. In order to correlate the degradation mechanisms and kinetics found during thermal stress, a high dc current stress was performed. Results from this comparative analysis showed similar behavior, implying that the degradation process of dc current aged devices is thermal activated due to high temperatures reached by the junction during stress. Finally, the different effects of the stress on two families of LEDs were taken into account in order to identify the impact of aging on device structure.
The experimental static current-voltage I-V characteristics of almost ideal silicon p-n junctions are not adequately described by the classic Sah-Noyce-Shockley theory. The I-V characteristics are ...accurately modeled by admitting the presence of a new class of defects in addition to Shockley-Read-Hall generation-recombination centers. The new center, modeled as a donor-acceptor twin, behaves as a pure generation center.
Phys.Rev. C74 (2006) 034609 A systematic investigation of the average multiplicities of light charged
particles and intermediate mass fragments emitted in peripheral and
semiperipheral collisions is ...presented as a function of the beam energy,
violence of the collision and mass of the system.
The data have been collected with the "Fiasco" setup in the reactions
93Nb+93Nb at 17, 23, 30, 38AMeV and 116Sn+116Sn at 30, 38AMeV.
The midvelocity emission has been separated from the emission of the
projectile-like fragment. This last component appears to be compatible with an
evaporation from an equilibrated source at normal density, as described by the
statistical code Gemini at the appropriate excitation energy.
On the contrary, the midvelocity emission presents remarkable differences for
what concerns both the dependence of the multiplicities on the energy deposited
in the midvelocity region and the isotopic composition of the emitted light
charged particles.
Phys.Rev.Lett. 93 (2004) 232701 Peripheral and semi-peripheral collisions have been studied in the system
93Nb+93Nb at 38 AMeV. The evaporative and midvelocity components of the light
charged ...particle and intermediate mass fragment emissions have been carefully
disentangled. In this way it was possible to obtain the average amount not only
of charge and mass, but also of energy, pertaining to the midvelocity emission,
as a function of an impact parameter estimator. This emission has a very
important role in the overall balance of the reaction, as it accounts for a
large fraction of the emitted mass and for more than half of the dissipated
energy. As such, it may give precious clues on the microscopic mechanism of
energy transport from the interaction zone toward the target and projectile
remnants.
A systematic investigation of the average multiplicities of light charged particles and intermediate mass fragments emitted in peripheral and semiperipheral collisions is presented as a function of ...the beam energy, violence of the collision and mass of the system. The data have been collected with the "Fiasco" setup in the reactions 93Nb+93Nb at 17, 23, 30, 38AMeV and 116Sn+116Sn at 30, 38AMeV. The midvelocity emission has been separated from the emission of the projectile-like fragment. This last component appears to be compatible with an evaporation from an equilibrated source at normal density, as described by the statistical code Gemini at the appropriate excitation energy. On the contrary, the midvelocity emission presents remarkable differences for what concerns both the dependence of the multiplicities on the energy deposited in the midvelocity region and the isotopic composition of the emitted light charged particles.
Peripheral and semi-peripheral collisions have been studied in the system 93Nb+93Nb at 38 AMeV. The evaporative and midvelocity components of the light charged particle and intermediate mass fragment ...emissions have been carefully disentangled. In this way it was possible to obtain the average amount not only of charge and mass, but also of energy, pertaining to the midvelocity emission, as a function of an impact parameter estimator. This emission has a very important role in the overall balance of the reaction, as it accounts for a large fraction of the emitted mass and for more than half of the dissipated energy. As such, it may give precious clues on the microscopic mechanism of energy transport from the interaction zone toward the target and projectile remnants.
