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  • 1
    Electronic Resource
    Electronic Resource
    Temperature dependence of the lasing wavelength of InGaAs quantum dot lasers (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4859-4861 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We observe that the emission wavelength of edge-emitting InGaAs quantum dot lasers has a much weaker temperature dependence (0.6 Å K−1) than equivalent quantum well devices (3 Å K−1). Measured gain and absorption spectra show that the gain peak wavelength due to dot states is almost independent of temperature for a given value of peak gain whereas the absorption edge shifts at a rate of about 2 Å K−1. Above 100 K the occupancy of dot states can be described by Fermi functions and on this basis we find that the measured gain and absorption spectra are in excellent quantitative agreement. Although the band edge energy reduces with increasing temperature, this analysis shows that the energy distribution of dot states matches the evolution of the Fermi functions such as to leave the quasi Fermi level separation and the wavelength of the gain peak unchanged as a function of temperature for a given value of peak gain. This energy distribution is a consequence of the dot size distribution so the match to the Fermi functions is probably fortuitous. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1402666
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  • 2
    Electronic Resource
    Electronic Resource
    Determination of single-pass optical gain and internal loss using a multisection device (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2527-2529 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a technique for the measurement of optical gain and loss in semiconductor lasers using a single, multisection device. The method provides a complete description of the gain spectrum in absolute units and over a wide current range. Comparison of the transverse electric and transverse magnetic polarized spectra also provides the quasi-Fermi-level energy separation. Measurements on AlGaInP quantum well laser structures with emission wavelengths close to 670 nm show an internal loss of 10 cm−1 and peak gain values up to 4000 cm−1 for current densities up to 4 kA cm−2. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125066
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  • 3
    Electronic Resource
    Electronic Resource
    Measurement of true spontaneous emission spectra from the facet of diode laser structures (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1-3 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurement of the spontaneous emission and gain spectra provides a complete characterization of a semiconductor gain medium, however, this requires the observation of emission in two directions to avoid amplification of the spontaneous emission spectrum. We show that both the gain spectrum and the true spontaneous emission spectrum can be obtained from amplified spontaneous emission (ASE) spectra measured from the end of a segmented-contact device. The spontaneous emission spectra agree with spectra measured through a top contact window. If the carrier populations are fully inverted at low photon energy, it is possible to convert the ASE-derived spontaneous emission into real units. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1428774
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  • 4
    Electronic Resource
    Electronic Resource
    Modal gain and internal optical mode loss of a quantum dot laser (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 163-165 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The modal gain spectra and internal optical mode loss of a semiconductor laser structure containing a single layer of InGaAs quantum dots have been measured independently and directly as a function of current density. The quantum dot gain exhibits no obvious polarization dependence. The maximum modal gain of (11±4) cm−1 obtained from the ground state of a single layer of quantum dots is in this case insufficient for lasing operation since the internal optical mode loss measured on the same sample is (11±4) cm−1. As expected laser emission is not observed from the dot ground state, but from the excited dot state or from the wetting layer depending on device length. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126911
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  • 5
    Electronic Resource
    Electronic Resource
    Seed dispersal in Erythronium grandiflorum (Liliaceae) (1995)
    Springer
    Oecologia 102 (1995), S. 211-219 
    Details
    ISSN: 1432-1939
    Keywords: Gene flow ; Neighborhood size ; Seed dispersal ; Seed predation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Primary and secondary seed dispersal was investigated for the glacier lily Erythronium grandiflorum in the Colorado Rocky Mountains. These heavy seeds have no obvious adaptations for biotic or abiotic dispersal, but can be thrown short distances when the dehiscent fruits are shaken by wind. We used sticky traps to measure primary transport of seeds up to 1 m away from individual plants. A seed cafeteria experiment examined the role of ants and rodents in secondary seed transport. Primary dispersal by wind was positively skewed and median transport distances were influenced by variation in plant height. Secondary dispersal was negligible compared to Viola nuttallii, an elaiosome-bearing species. Thus, seed dispersal was highly restricted in E. grandiflorum, and a 1 m radius encompassed the modal section of the seed dispersal curve. The seed dispersal component of gene flow was quantified and combined with previous measurements of pollen flow to yield a more complete estimate of Wright's neighborhood size, N e, for E. grandiflorum. The lack of a special seed dispersal mechanism in E. grandiflorum is discussed in terms of a source-sink model for seedling establishment with respect to distance from the parental plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333253
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  • 6
    Electronic Resource
    Electronic Resource
    Response of traplining bumble bees to competition experiments: shifts in feeding location and efficiency (1987)
    Springer
    Oecologia 71 (1987), S. 295-300 
    Details
    ISSN: 1432-1939
    Keywords: Aralia ; Bombus ; Competition ; Energy budget foraging ; Niche shift ; Trapline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In field experiments, we mapped the regular foraging routes (traplines) of marked bumble bees visiting Aralia hispida. When other bees were removed to create localized “competitive vacuums”, the marked bees shifted their feeding activity toward the removal areas. Bees foraging in these competitive vacuums probed more flowers per inflorescence than control bees. One bee's foraging was studied intensively before and after its local competitors were removed. Compared to four nestmates foraging elsewhere, the focal bee's trip times were shorter (p〈0.005) and its food collection rate was marginally higher (P=0.064) during the removal, although all the bees foraged similarly before the removal. These observations indicate that traplining bumble bees opportunistically modify their use of space in response to the activities of other bees in a highly competitive environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377298
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  • 7
    Electronic Resource
    Electronic Resource
    Metal concentration changes in growing Pacific oysters, Crassostrea gigas, cultivated in Tasmania, Australia (1982)
    Springer
    Marine biology 67 (1982), S. 135-142 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pacific oyster spat (Crassostrea gigas Thunberg) transferred from the Tamar Estuary to two growing areas in southern Tasmania were monitored for their metal contents over one growing season (1974–1975). Oysters at Pipeclay Lagoon were grown with stick and tray culture while those at Dart Island were cultured with the longline technique. Metal content of the oysters increased with time and the trend was similar to the weight growth curves. Mean dry weights of oysters increased from 0.07 to 1.19 g at Pipeclay Lagoon and from 0.25 to 1.47 g at Dart Island. Metal contents (μg) increased at each site, respectively: Fe 57 to 326; 91 to 446; Zn 259 to 6 555; 755 to 5 335; Cd 1.5 to 13.3; 1.9 to 16.3; Cu 26 to 142; 9 to 116; Pb 1.9 to 11.9; 0.6 to 3.8. Concentration curves generally showed a downward trend with time. The relationships of metal concentrations with weight did not differ from sample to sample at a site nor did they differ at one site compared with the other. The only exception was lead, which showed no relationship of concentration with weight at Pipeclay Lagoon and a negative one at Dart Island. It is postulated that higher winter concentrations of metals in the oysters were linked with greater solubility of metal ions in lower salinity water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00401279
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