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  • 1
    ISSN: 1573-5117
    Keywords: Organic pollution ; clams ; seawaters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A preliminary survey on the contamination of clams and sea-waters in various towns in Tolo Harbour was carried out using bacteriological tests. The ‘percentage clean’ method and the ‘most probably number’ method were employed. The pH, salinity and temperature of the seawater were also tested in the field. It was discovered that the number of coliform bacteria obtained by the ‘percentage clean’ was zero in both seawater and clams from all sites including the control. The ‘most probable number’ indicated that the water and the clam tissue collected in the three sites in Tolo Harbour ranged from 15–1,100/100 ml in the water and 825–11,000/g in the clams compared with 0/100 ml and 115/g of the control site. Due to the high level of organic pollution in Tolo Harbour, improvement of the sanitary situation is urged. Cultivation of clams collected in this area in clean and sterilized water for a few days before consumption is recommended.
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 773-775 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Si phototransistors with a punchthrough base were fabricated with regular planar technology. Optical conversion gains larger than 15 000 were observed. In addition to very high gain, the unique structure of the device also resulted in a fast transient response as well as low output noise. The measured full width at half maximum of the device transient response is 1.6 ns and a −3 dB bandwidth of 300 MHz. The measured output noises at different currents can be well fitted by the relation in2=2qIC. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1416-1418 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmittance difference spectroscopy has been applied to study the optical properties of spin-cast rigid-rod polymer films. Significant in-plane optical anisotropy is observed for both the real and the imaginary parts of the transmittance of the poly(2,5-pyridine diyl) films. This in-plane optical anisotropy is a result of the partial alignment of the polymer chains, oriented radially outward from the center of the film, during the spin casting process. This observation has important implications for emissive polymer devices, particularly for devices sensitive to polarization direction and those using waveguide confinement where relatively long propagation distance within the films are required. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3321-3323 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the measurement of third-order optical nonlinearity (χ(3)) of ZnO microcrystallite thin films near the excitonic resonance at various temperatures using the femtosecond degenerate four-wave-mixing technique. The measured χ(3) response times are 270, 240, and 160 fs at 4.2 K, 77 K, and room temperature, respectively. The values of χ(3) range from 10−7 to 10−4 esu. The maximum values of χ(3) always correspond to the absorption peaks at different temperatures. Room-temperature excitonic enhancement of χ(3) is also observed. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3663-3665 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-resolved reflectance difference spectroscopy (TRDS) has been applied to study the dynamics and relaxation processes of the 2.7 eV ZnSe/GaAs interface state associated with Zn–As bonds. The instantaneous screening due to the photoexcited carriers and ∼18 ps recovery time of the 2.7 eV interface state is observed in the TRDS spectra. The rapid cooling of the hot carrier in the spectral region above the ZnSe band edge is also observed. © 1999 American Institute of Physics.
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  • 6
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The wavelength dependence of the third-order nonlinear optical susceptibilities, χ(3), of the Au:TiO2 composite films with Au concentration varying from 15% to 60% (volume fraction), was measured by a degenerate four-wave mixing (DFWM) technique using a probe laser with a pulse width of 200 fs. It was found that, with the wavelength of the probe laser close to the surface plasmon resonance (∼680 nm), both the χ(3) and the figure of merit, χ(3)/α (α is optical absorption coefficient) were significantly enhanced. The maximum value of the χ(3) was 6×10−7 esu and occurred at an Au concentration of about 38%. Femtosecond time-resolved DFWM measurements revealed that the response time of the optical nonlinearity in the Au:TiO2 films is extremely fast. The time-resolved DFWM results suggest that the main physical mechanism involved in the optical nonlinearity in Au:TiO2 films on the femtoseconds time scale is the interband electric–dipole transition, and the hot electron excitation only partially contributes to the χ(3) on the femtosecond time scale and it becomes dominant only in the picosecond region. © 1998 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 16-18 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The frequency response and quantum efficiency (QE) of silicon-on-insulator (SOI) metal-semiconductor-metal photodetectors in the near-infrared (∼800 nm) are greatly enhanced with a simple reactive ion etching to form electrodes inside the interdigitated trenches. Detectors with 1.25 μm trench spacing were fabricated on a SOI substrate with a 6-μm-thick silicon top layer. The unique device structure isolates carriers generated deep inside the semiconductor substrate and at the same time provides a highly uniform electric field throughout the active region of the detector, resulting in an instrumentation limited response time of 23 ps at 5 V bias and a −3 dB bandwidth of 2.3 GHz as measured at 790 nm. The dc responsivity is 0.12 A/W, corresponding to an external QE of 18.7% and an internal QE of 88.5%. The large bandwidth and good responsivity at the wavelength of interest, combined with their low operating voltages, make these detectors attractive for use in short-distance optical communication systems. © 1996 American Institute of Physics.
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  • 8
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the femtosecond dynamics of the nonlinear optical response χ(3) in polydiethynylsilane (C4H2SiBu2)x, a novel class of π-conjugated polymers incorporating Si, using degenerate four-wave mixing and photoinduced absorption techniques. In resonance conditions at 620 nm we found χ(3)=3×10−9 esu, which decays in a record time of 135 fs, followed by a slower decay component of 750 fs, without a long tail even at high laser intensities. This material is an excellent candidate for nonlinear optical devices in the sub-THz frequency range.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of femtosecond time-resolved one- and two-photon-excited photoluminescence of bulk ZnSe enable us to distinguish the surface and bulk contributions to recombination dynamics. A photoluminescence lifetime of several nanoseconds or longer is measured for the bulk. A fast relaxation component with a decay time constant τT of a few tens of picoseconds observed in one-photon-pumped time-resolved spectra is identified as the result of diffusion and rapid surface recombination. A one-dimensional model taking into account surface nonradiative recombination and carrier diffusion is able to describe the observed behavior. The temperature dependence of τT shows good agreement with the theory. At room temperature, a surface recombination velocity S=5.8×105 cm s−1 and a diffusion constant D=10 cm2 s−1 are found using this model. © 1998 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1811-1813 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial growth of Zn1−xMgxS alloy thin films on GaP(100) substrates was carried out using the molecular-beam-epitaxy technique. In situ reflection high-energy electron diffraction studies show that the alloys can be grown with a stable zinc-blende structure up to x around 30%. For x〉30%, a structural transition will occur at a critical thickness which is sensitively dependent on the x composition. A near-band-edge peak with a full width at half maximum of about 10 nm was observed in room-temperature photoluminescence measurements made on as-grown alloy thin films. Several Zn1−xMgxS-based Schottky barrier photodetectors were fabricated. Room-temperature photoresponse measurements were performed on these detectors and abrupt long-wavelength cutoffs covering 325, 305, 295, and 270 nm were achieved for devices with Mg composition of 16%, 44%, 57%, and 75%, respectively. The response curve of the Zn0.43Mg0.57S device offers a close match to the erythemal action spectrum that describes human skin sensitivity to UV radiation. © 2001 American Institute of Physics.
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