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  • 1990-1994  (113)
  • 1975-1979  (42)
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  • 1
    Electronic Resource
    Electronic Resource
    Tetracyclopropylethylene glycol (1979)
    s.l. : American Chemical Society
    The @journal of organic chemistry 44 (1979), S. 4729-4731 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00393a064
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of 2-, 4-, and 7-methylthio-substituted cephalosporins (1979)
    s.l. : American Chemical Society
    The @journal of organic chemistry 44 (1979), S. 811-818 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo01319a033
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  • 3
    Electronic Resource
    Electronic Resource
    Nonlinear spectroscopy near half-gap in bulk and quantum well GaAs/AlGaAs waveguides (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1927-1935 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the nonlinear properties of bulk AlGaAs and GaAs/AlGaAs multiple quantum wells (MQW) below the half-band-gap energy using subpicosecond pulses between 1.65 and 1.7 μm. In the bulk material we find a value for the nonlinear index n2 = +3.6× 10−14 cm2/W and a two-photon absorption coefficient β = 0.26 × 10−4 cm/MW. In the MQW we measure an n2 up to 2.4 times larger, and we attribute this enhancement to a stronger 1S-exciton intermediate state. The β value is up to 25 times larger in the MQW. This larger value may result from midgap states that resonantly enhance the virtual intermediate state in two-photon absorption and act as a real transition in a two-step absorption process. The resulting figure of merit (2n2/βλ) for the bulk (MQW) material is 17 (1.6), which means that these semiconductors below half band gap are appropriate for all-optical switching and quantum optics applications. We confirm that n2 is instantaneous on the 300 fs time scale of our pulses from self-phase-modulation spectra as well as time-resolved pump-probe measurements. However, we find an intriguing exchange of energy between the two orthogonal axes as evidenced by the signal along the probe axis following the negative derivative of the pump intensity. This result may be explained by self-phase modulation of the pump combined with a low-frequency Raman process that couples the modes along orthogonal axes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351182
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  • 4
    Electronic Resource
    Electronic Resource
    Electrical inhomogeneity in Ga-rich undoped GaAs crystals: Dependence on melt stoichiometry and dislocation distribution (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4140-4148 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Studies have been made of the macroscopic and microscopic electrical inhomogeneity in undoped bulk GaAs single crystals grown from As/As+Ga melt ratios of 0.48–0.45. Microscopic inhomogeneity was characterized by contact resistance line scans and whole wafer anodization, which gives high-resolution two-dimensional images of the low-resistivity p-type regions within the wafers. The resistivity was nonuniform in wafers from 0.48 As/As+Ga crystals, having a W-shaped radial dependence with minima in the 〈110〉 directions and varying by six orders of magnitude across a wafer, whereas it was uniform in low-resistivity wafers from 0.45 As/As+Ga crystals at fractions of melt solidified, g〉0.4. Precise correlation of microscopic inhomogeneity with grown-in linear and cellular arrays of dislocations was obtained in nonuniform wafers, but no correlation with slip dislocations was observed. Anodization images show that the carrier concentration is quantitatively in agreement with a uniform acceptor background compensated by EL2 concentration fluctuations of factors of 2–3 at the dislocation networks. Inhomogeneity variation with g and As/As+Ga ratio is consistent with macroscopic and microscopic decrease in EL2 with melt stoichiometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344975
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  • 5
    Electronic Resource
    Electronic Resource
    Room-temperature stability of the electrical properties of metalorganic vapor phase epitaxial Hg1−xCdxTe on GaAs (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7173-7177 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Significant changes have been observed in the electrical properties after prolonged storage at room temperature of undoped metalorganic vapor phase epitaxial layers of Hg1−xCdxTe grown on (100) GaAs. These changes occur in uniform n-type and nonuniform n-p layer structures and are due to the out-diffusion of donors from the bulk of the layers. In situ growth of a surface passivation layer of CdTe prevents these effects and produces stable electrical properties. Uniform n-type layers grown simultaneously on (111) GaAs do not show changes in electrical properties even when not in situ passivated with CdTe. The time dependent properties do not appear to be associated with impurities and are attributed to the diffusion of a combination of native donor defects and Hg acceptor vacancies, which are estimated to have diffusion coefficients, respectively, of 7×10−14 and 2–3 ×10−16 cm2 s−1 at room temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347609
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  • 6
    Electronic Resource
    Electronic Resource
    A high precision ultrasonic system for vibration measurements (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5435-5441 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A microcomputer-aided ultrasonic system that can be used to measure the vibratory displacements of an object is presented. A pair of low cost 40-kHz ultrasonic transducers is used to transmit ultrasound toward an object and receive the ultrasound reflected from the object. The relative motion of the object modulates the phase angle difference between the transmitted and received ultrasound signals. A single-chip microcomputer-based phase detector was designed to record and analyze the phase shift information which is then sent to a PC-AT microcomputer for processing. We have developed an ingenious method to reconstruct the relative motion of an object from the acquired data of the phase difference changes. A digital plotter based experiment was also designed for testing the performance of the whole system. The measured accuracy of the system in the reported experiments is within ±0.4 mm and the theoretical maximal measurable speed of the object is 89.6 cm/s. The main advantages of this ultrasonic vibration measurement system are high resolution, low cost, noncontact measurement and it is easily installed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143415
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  • 7
    Electronic Resource
    Electronic Resource
    Nutrient fluxes in runoff on reseeded blanket bog, limed and fertilized with urea, phosphorus and potassium (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 10 (1994), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Studies have been made of the effects of 15 g N/m2 as urea in two dressings during April and June on annual nutrient fluxes in runoff from reseeded blanket bog also receiving annually 6 g P/m2 as granular superphosphate and 6 kg K/m2 as potassium chloride. Urea applications increased significantly (P 〈 0.05) the mean annual ammonium-N flux from 17 mg/m2 for the P + K plots to 245 mg/m2 for the N + P + K plots. Annual fluxes of total P, K and Ca were also increased (P 〈 0.05) by the addition of urea. This was attributed to the effects of increased acidity around grass roots following N uptake as ammonium-N. In contrast, nitrate-N was removed from rainwater throughout the year and concentrations in runoff were at the limit of detection (〈 0.01 mg/1) on many occasions. Concentrations of organic-N in runoff exceeded those of ammonium-N, but were not significantly changed by fertilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.1994.tb00482.x
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  • 8
    Electronic Resource
    Electronic Resource
    Strained-layer multiple quantum well distributed Bragg reflector lasers with a fast monitoring photodiode (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1239-1240 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a photonic integrated circuit composed of a distributed Bragg reflector laser and a fast monitoring photodiode operating at 1.54 μm wavelength. The integrated waveguide photodiode has a 3 dB bandwidth of 2 GHz with 1.2 mA/mW responsivity. We demonstrate "on chip'' monitoring of a digitally modulated laser signal at 2 Gbit/s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104322
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  • 9
    Electronic Resource
    Electronic Resource
    Substituent effects on reductive cleavage of N-methylarenesulfonanilides. Cleavage by sodium anthracene and electrochemically at the vitreous carbon electrode (1978)
    s.l. : American Chemical Society
    The @journal of organic chemistry 43 (1978), S. 1311-1316 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00401a005
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  • 10
    Electronic Resource
    Electronic Resource
    Bulk semiconductor saturable absorber for a NaCl color center laser (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2177-2179 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using bulk InGaAsP as a saturable absorber we have passively mode locked a NaCl color center laser to produce transform-limited, pedestal-free pulses near 1.6 μm as short as 197 fs with up to 4.2 kW peak power. Our results simplify the saturable absorber material requirements and prove that excitons are not required for generating subpicosecond pulses. By comparing a dozen samples we find that a minimum band-edge absorbance of 40% is required to generate subpicosecond pulses, although details of the band edge are not critical. In addition, we find stable mode locking always occurs on the long-wavelength side of the laser gain peak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102960
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