The yeast spindle pole body component Spc72p interacts with Stu2p and is required for proper microtubule assembly

We have previously shown that Stu2p is a microtubule-binding protein and a component of the Saccharomyces cerevisiae spindle pole body (SPB). Here we report the identification of Spc72p, a protein that interacts with Stu2p. Stu2p and Spc72p associate in the two-hybrid system and can be coimmunoprecipitated from yeast extracts. Stu2p and Spc72p also interact with themselves, suggesting the possibility of a multimeric Stu2p-Spc72p complex. Spc72p is an essential component of the SPB and is able to associate with a preexisting SPB, indicating that there is a dynamic exchange between soluble and SPB forms of Spc72p. Unlike Stu2p, Spc72p does not bind microtubules in vitro, and was not observed to localize along microtubules in vivo. A temperature-sensitive spc72 mutation causes defects in SPB morphology. In addition, most spc72 mutant cells lack cytoplasmic microtubules; the few cytoplasmic microtubules that are observed are excessively long, and some of these are unattached to the SPB. spc72 cells are able to duplicate and separate their SPBs to form a bipolar spindle, but spindle elongation and chromosome segregation rarely occur. The chromosome segregation block does not arrest the cell cycle; instead, spc72 cells undergo cytokinesis, producing aploid cells and polyploid cells that contain multiple SPBs.     

Low-threshold vertical-cavity surface-emitting lasers based onoxide-confinement and high contrast distributed Bragg reflectors

The interest in low-threshold vertical-cavity surface-emitting lasers (VCSEL's) is increased by the demonstration of the small size, low loss optical mode due to oxide-confinement in the Fabry-Perot microcavity laser. Intense recent work in this area has resulted in numerous record breaking demonstrations of low-threshold current, high wall-plug efficiency, and high speed. In this paper, we discuss the impact of the dielectric cavity design to enhance control of the optical mode. We argue that high contrast dielectric mirrors can become an important design approach, especially for small apertures limited by diffraction loss. Experimental results are compared for different types of mirror and aperture designs     

1.54 lm GaSb/AlGaSb multi-quantum-well monolithic laser at 77 K grown on miscut Si substrate using interfacial misfit arrays

A GaSb quantum-well (QW) laser diode grown monolithically on a 5deg miscut Si (001) substrate is presented. The III-Sb epi-structure is grown monolithically on the miscut Si substrate via a thin (50 nm) AlSb nucleation layer. The 13% lattice mismatch between AlSb and Si is accommodated by a self-assembled 2D array of interfacial misfit dislocations (IMF). The 5deg miscut geometry enables simultaneous IMF formation and anti-phase domain suppression. The 1 mm times 100 mum GaSb QW laser diode operates under pulsed conditions at 77 K with a threshold current density of 2 kA/cm² and a maximum peak power of ~20 mW. Furthermore, the device is characterised by a 9.1 Omega forward resistance and a leakage current density of 0.7 A/cm² at -5 V.     

Structural Analysis of Highly Relaxed GaSb Grown on GaAs Substrates with Periodic Interfacial Array of 90° Misfit Dislocations

We report structural analysis of completely relaxed GaSb epitaxial layers deposited monolithically on GaAs substrates using interfacial misfit (IMF) array growth mode. Unlike the traditional tetragonal distortion approach, strain due to the lattice mismatch is spontaneously relieved at the heterointerface in this growth. The complete and instantaneous strain relief at the GaSb/GaAs interface is achieved by the formation of a two-dimensional Lomer dislocation network comprising of pure-edge (90°) dislocations along both [110] and [1-10]. In the present analysis, structural properties of GaSb deposited using both IMF and non-IMF growths are compared. Moiré fringe patterns along with X-ray diffraction measure the long-range uniformity and strain relaxation of the IMF samples. The proof for the existence of the IMF array and low threading dislocation density is provided with the help of transmission electron micrographs for the GaSb epitaxial layer. Our results indicate that the IMF-grown GaSb is completely (98.5%) relaxed with very low density of threading dislocations (10⁵ cm⁻²), while GaSb deposited using non-IMF growth is compressively strained and has a higher average density of threading dislocations (>10⁹ cm⁻²).     

Optical memory using a vertical-cavity surface emitting laser

Data are presented demonstrating optical switching and memory in a bistable vertical-cavity surface-emitting laser (VCSEL). Optical switching from lasing to nonlasing or from nonlasing to lasing in the vertical-cavity laser was demonstrated using an AlGaAs probe laser at ~0.78 μm     

Effects of spontaneous emission rates on lasing characteristics of long-wavelength (1.3 µm) GaAs-based quantum dot lasers

Data are presented characterizing the spectral emission and electroluminescence efficiency dependence on temperature of InGaAs/GaAs quantum dots that result in 1.3 μm lasing at room temperature. Efficient ground state emission is achieved at 80K, but the spontaneous efficiency decreases with increasing temperatures. The ground state spectral width is 26 meV at 80K and 31 meV at 300K. Ground state lasing is obtained over a wide range of temperatures, with an ultralow threshold current density of 14 A/cm² obtained at 80K.     

A quantum leap in laser emission

Medium- and long-haul, high-speed fiber communication systems are dominated by the need for low optical loss and low dispersion, and these systems require laser diodes and photodiodes that emit and detect at 1.33 and 1.55 μm. InGaAs/GaAs quantum dots enable 1.3 μm wavelengths in GaAs-based lasers for fiber-optic communication     

Enhanced spontaneous emission using quantum dots and an aperturedmicrocavity

Spontaneous emission characteristics from apertured microcavities are studied using quantum-dot light emitters. Spatial averaging over the emitter positions within the apertures significantly impacts the measured lifetime changes, but lifetime changes due to the aperture modes are still readily observed. A maximum increase of a factor of ~2.5 over the cavity-free emission rate is measured. We argue that, for a narrow bandwidth emitter, the microcavity enhancement can lead to nearly-single-mode and high-speed operation even in the spontaneous regime     

The Role of Prior Appropriation in Allocating Water Resources into the 21st Century

This article demonstrates how widespread technological changes in agriculture have weakened the security of traditional appropriative water rights. Since legal protection of these rights has severely restricted the use of transfer mechanisms to reallocate water to emerging social needs, this demonstration provides a powerful and novel argument for increasing the flexibility of the prior appropriation system and operating it in conjunction with other legitimate water-allocation doctrines protecting public interests in water.