Threshold current reduction in InGaN MQW laser diode withλ/4 air/semiconductor Bragg reflectors

A 13% reduction in the threshold current density of InGaN laser diodes is demonstrated upon the introduction of two 5λ/4 air/nitride Bragg reflectors. These are defined at one end of the laser cavity by means of focused ion beam etching     

Characterization of the temperature sensitivity of gain and recombination mechanisms in 1.3-/spl mu/m AlGaInAs MQW lasers

The potential of 1.3-/spl mu/m AlGaInAs multiple quantum-well (MQW) laser diodes for uncooled operation in high-speed optical communication systems is experimentally evaluated by characterizing the temperature dependence of key parameters such as the threshold current, transparency current density, optical gain and carrier lifetime. Detailed measurements performed in the 20/spl deg/C-100/spl deg/C temperature range indicate a localized T/sub 0/ value of 68 K at 98/spl deg/C for a device with a 2.8 /spl mu/m ridge width and 700-/spl mu/m cavity length. The transparency current density is measured for temperatures from 20/spl deg/C to 60/spl deg/C and found to increase at a rate of 7.7 A/spl middot/cm/sup -2//spl middot/ /spl deg/C/sup -1/. Optical gain characterizations show that the peak modal gain at threshold is independent of temperature, whereas the differential gain decreases linearly with temperature at a rate of 3/spl times/10/sup -4/ A/sup -1//spl middot//spl deg/C/sup -1/. The differential carrier lifetime is determined from electrical impedance measurements and found to decrease with temperature. From the measured carrier lifetime we derive the monomolecular ( A), radiative (B), and nonradiative Auger (C) recombination coefficients and determine their temperature dependence in the 20/spl deg/C-80/spl deg/C range. Our study shows that A is temperature independent, B decreases with temperature, and C exhibits a less pronounced increase with temperature. The experimental observations are discussed and compared with theoretical predictions and measurements performed on other material systems.     

Stage 6 object concept in nonhuman primate cognition: A comparison between gorilla (Gorilla gorilla gorilla) and Japanese macaque (Macaca fuscata).

Several investigators have reported the achievement of Stage 6 object concept in a number of species of nonhuman primates. Because Stage 6 object concept implies a capacity for mental representation, such an achievement would demonstrate the presence of a crucial capacity in nonhuman primate cognition. There are, it is suggested, problems in the way nonhuman primates have been tested for Stage 6 object concept (i.e., that the tasks employed could be solved in nonrepresentational ways). The present study attempted to differentiate between representational and nonrepresentational responses in the typical task used for testing Stage 6 object concept (following the invisible displacements of an object). The performance of 2 22-mo-old Ss, a Japanese macaque and a gorilla, was compared. It was found that only the gorilla solved the task with the use of mental representation. The macaque consistently tried to solve the task by employing practical, nonrepresentational strategies. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An effective multipurpose building block for 3D electropolymerisation: 2,2′-Bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene

Novel thiophene-based oligomer, 2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene (TX), was designed and synthesized, and its electrochemical and spectral properties characterised. TX was readily polymerised electrochemically to form well organized conducting homopolymer films on various solid electrode substrates. Moreover, it was successfully used for deposition by electropolymerisation of electrochemically active thin films of co-polymers with three different monomers of functionalised bis(2,2′-bithienyl)methane derivatives. It appeared that TX was an effective crosslinker and 3D promoter in these electropolymerisations involving co-monomers intrinsically showing limited aptitude for the electropolymerisation or forming polymer films of low conductivity. This attractive TX ability stems from combination of its (i) high conjugation efficiency in each of the two planar moieties, (ii) intrinsic 3D structure on account of the presence of the central node, and (iii) intrinsic regioselectivity in electropolymerisation on account of the positions of the two available free α-thiophene sites.     

Microgel electrospinning: A novel tool for the fabrication of nanocomposite fibers

We demonstrate for the first time herein that electrospinning of soluble crosslinked polymer particles (microgels) is feasible and that it can be used to obtain micron-sized fibers from these macromolecules. Most notably, the electrospinning approach is found to be successful also in the case of microgels bearing metal nanoclusters, and allows to prepare composite fibers containing a homogeneous dispersion of metal nanoparticles without alterations in the nanoparticle size and size distribution. Given the broad applicability of microgels as exotemplates and stabilisers for inorganic nanoparticles, the proposed preparation method stands out as a novel, general approach for the synthesis of potentially useful composite fibers containing inorganic nanoparticles.