Extraction of radiative and nonradiative rates in Sb based midwave infrared lasers using a novel approach.

We developed a technique using nonlinear correlation of photoluminescence (PL) to characterize midwave infrared lasers by extracting the density and temperature dependence of the carrier lifetime and its exact branching into radiative and nonradiative processes. This was accomplished, without time resolving the PL recovery, through mathematical optimization. We extracted this information by using a laser source that can be operated in both continuous-wave and short pulse modes. Through fitting of the PL signal and its nonlinear correlation for both laser modes of operation, the carrier lifetime as a function of density is extracted. As a proof of principle, we investigated a midinfrared Sb based laser and showed that the radiative branching ratio drops from approximately 54% at 80 K to about 3% at room temperature, resulting from an order of magnitude increase in the nonradiative rate coupled with a factor of 2 reduction in the radiative rate. We believe that this is a very generic approach and can be extended to various luminescing material systems.

Time-resolved photoluminescence of type-II Ga(As)Sb/GaAs quantum dots embedded in an InGaAs quantum well.

Optical properties and carrier dynamics in type-II Ga(As)Sb/GaAs quantum dots (QDs) embedded in an InGaAs quantum well (QW) are reported. A large blueshift of the photoluminescence (PL) peak is observed with increased excitation densities. This blueshift is due to the Coulomb interaction between physically separated electrons and holes characteristic of the type-II band alignment, along with a band-filling effect of electrons in the QW. Low-temperature (4 K) time-resolved PL measurements show a decay time of [Formula: see text] ns from the transition between Ga(As)Sb QDs and InGaAs QW which is longer than that of the transition between Ga(As)Sb QDs and GaAs two-dimensional electron gas ([Formula: see text] ns).

Use of amalgam and stainless steel restorations for primary molars.

The findings of this study agree with those of Braft, namely, stainless steel crowns for primary molars are superior to multisurface amalgams. This is viewed in terms of the number of teeth requiring retreatment. Because of the eventual loss of primary molars, the actual longevity of restorations may be difficult to establish. Based on the information found in this study it is concluded that: In primary first molars, 75 percent of one-surface and 70 percent of two-surface amalgams will need replacement before the age of eight. In primary second molars, 32 percent of one-surface and 71.4 percent of two-surface amalgams will need replacement before the age of eight. Stainless steel crowns will need further treatment in 12.8 percent of primary first molars and in 11 percent of second molars. Before the first permanent molars erupt into occlusion (before the age of eight) stainless steel crowns are the treatment of choice, for the primary molars, particularly for multisurface lesions in the primary first molar.

A tetracycline study of cyclic longitudinal bone growth in the female rat.

This study shows that bone growth in the young female rat is cyclic. Using tetracycline labeling, measurements were taken for every possible 2-day growth interval during the 4-day estrous cycle. The slow phase of bone growth occurs when estrogen and glucocorticoid serum levels are elevated, whereas the rapid phase of growth occurs when estrogen serum levels are minimal. Parathyroidectomy or 1-microgram injections of exogeneous 17 beta-estradiol retard the rapid phase of growth. Adrenalectomy alters the rate of growth in that the slow phase no longer occurs but rather increases to a rate equal to the rapid phase. The results show that parathyroid hormone is an essential component of the cyclic growth pattern in the young adult female rat and that estrogen, which reduces the rate of longitudinal bone growth, has its effect primarily through its stimulation of glucocorticoid production. These findings are discussed in relation to other recent studies which show that there are no estrogen receptors in bone and that high levels of estrogen stimulate 1,25-dihydroxyvitamin D3 production in the kidney. A hypothetical model, interrelating these hormones to the cyclic longitudinal bone growth pattern found in the female rat, is proposed.