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  • 1
    Electronic Resource
    Electronic Resource
    Probing the glass transition process of poly(ethyl methacrylate) by the mass diffusion of thymorquinone (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 3839-3841 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100346a092
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  • 2
    Electronic Resource
    Electronic Resource
    The holographic investigation of diffusion of methyl red in poly(caprolactone) diol (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5211-5214 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The translational diffusion process of methyl red dissolved in poly(caprolactone) diol has been investigated as a function of temperature, using the laser induced holographic grating relaxation technique. The tracer diffusion coefficients of methyl red in trans and cis forms are found to follow the WLF type of temperature dependence with the WLF coefficients identical to that associated with the shear modulus of the polymer host. The cis isomer of methyl red although about 8% smaller in size diffuses about three times slower than the trans isomer. This is interpreted as due to a stronger interaction between the cis isomer and the polymer host.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454756
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  • 3
    Electronic Resource
    Electronic Resource
    Holographic method for investigating the diffusion of dye molecules in the polymer host (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2603-2613 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser induced holographic grating relaxation studies of thymoquinone dissolved in amorphous poly(α-methyl styrene) have been carried out. The Onsager theory of mutual diffusion for binary and tertiary systems are utilized to analyze the shape of the diffraction intensity curve. Different line shapes that are associated with the relaxation of the diffraction intensity are interpreted in terms of the diffusion processes. Diffusion coefficients are obtained as a function of thymoquinone concentration from 0.3 to 20 wt. % at various temperatures. It is shown that at very low concentrations (less than 0.5%), the self-diffusion coefficients of the dye molecule and its photoproduct are obtained. Above 0.5% concentrations the diffusion coefficient rapidly increases with increasing dye concentration. The temperature dependence of the self-diffusion coefficient follows the Williams–Landel–Ferry equation, whereas the mutual diffusion coefficient at higher dye concentrations follows the Arrhenius equation. The self-diffusion coefficient rapidly decreases as the sample temperature is traversed across the glass transition temperature (Tg). However at finite dye concentrations there is no detectable effect owing to the onset of Tg on the mutual diffusion coefficient. The difference is attributed to the plasticizing effect of the dye molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457954
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of the mutual diffusion in poly(ethylene oxide)/poly(methyl methacrylate) blends by photon correlation spectroscopy (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3229-3234 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photon correlation spectroscopic studies of the mutual diffusion of poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blends are carried out. The experimental investigation deals with the measurement of the mutual diffusion coefficient of the PEO/PMMA blend by varying the molecular weight of PEO but keeping the molecular weight of PMMA fixed. At 20% volume fraction of PEO, and high PMMA molecular weight, the mutual diffusion coefficient linearly decreases with M−1PEO. The temperature dependence of the mutual diffusion coefficient is non-Arrhenius. The Onsager coefficient of mutual diffusion is obtained as a function of temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459792
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  • 5
    Electronic Resource
    Electronic Resource
    Orthogonal vibroseis sweeps (2005)
    PO Box 1354, 9600 Garsington Road , Oxford OX4 2XG , UK . : Blackwell Science Ltd
    Geophysical prospecting 53 (2005), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Vibroseis is a method that imparts coded seismic energy into the ground. The energy is recorded with geophones and then processed using the known (coded) input signal. The resulting time-domain representation of vibroseis data is an impulsive wavetrain with wavelet properties consistent with the coded input signal convolved with the earth's reflectivity series. Historically, vibratory seismic surveys collect data from one source location at a time, summing one or more sources at each location. We present a method of designing orthogonal sweeps using the concept of combisweeps. The orthogonal sweeps allow simultaneous recording and later separation of two or more unique source locations. Orthogonality of sweeps permits separation of the data into unique source-location field records by a conventional correlation procedure. The separation power of the orthogonal sweeps is demonstrated by a comparison between separated data and data acquired with one vibrator. Separation noise was at a negligible level for our demonstration data sets when two vibrators were located 50 m to 200 m apart. Coincident generation and recording of two vibroseis sweeps at different locations would allow almost double the amount of data to be recorded for a given occupation time and requires only half the storage medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.2005.00491.x
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  • 6
    Electronic Resource
    Electronic Resource
    Valence hole subbands and optical gain spectra of GaN/Ga1−xAlxN strained quantum wells (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3471-3478 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The valence hole subbands, TE and TM mode optical gains, transparency carrier density, and radiative current density of the zinc-blende GaN/Ga0.85Al0.15N strained quantum well (100 A(ring) well width) have been investigated using a 6×6 Hamiltonian model including the heavy hole, light hole, and spin-orbit split-off bands. At the k=0 point, it is found that the light hole strongly couples with the spin-orbit split-off hole, resulting in the so+lh hybrid states. The heavy hole does not couple with the light hole and the spin-orbit split-off hole. Optical transitions between the valence subbands and the conduction subbands obey the Δn=0 selection rule. At the k≠0 points, there is strong band mixing among the heavy hole, light hole, and spin-orbit split-off hole. The optical transitions do not obey the Δn=0 selection rule. The compressive strain in the GaN well region increases the energy separation between the so1+lh1 energy level and the hh1 energy level. Consequently, the compressive strain enhances the TE mode optical gain, and strongly depresses the TM mode optical gain. Even when the carrier density is as large as 1019 cm−3, there is no positive TM mode optical gain. The TE mode optical gain spectrum has a peak at around 3.26 eV. The transparency carrier density is 6.5×1018 cm−3, which is larger than that of GaAs quantum well. The compressive strain overall reduces the transparency carrier density. The Jrad is 0.53 kA/cm2 for the zero optical gain. The results obtained in this work will be useful in designing quantum well GaN laser diodes and detectors. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363217
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  • 7
    Electronic Resource
    Electronic Resource
    Electronic properties of zinc-blende GaN, AlN, and their alloys Ga1−xAlxN (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 188-194 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electronic properties of wide-energy gap zinc-blende structure GaN, AlN, and their alloys Ga1−xAlxN are investigated using the empirical pseudopotential method. Electron and hole effective mass parameters, hydrostatic and shear deformation potential constants of the valence band at Γ and those of the conduction band at Γ and X are obtained for GaN and AlN, respectively. The energies of Γ, X, L conduction valleys of Ga1−xAlxN alloy versus Al fraction x are also calculated. The information will be useful for the design of lattice mismatched heterostructure optoelectronic devices based on these materials in the blue light range application. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360930
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  • 8
    Electronic Resource
    Electronic Resource
    Doping effects of 3D metal on single-phase YBa2Cu3O7−δ (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3589-3592 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The measurements of x-ray diffraction, the temperature dependence of the dc resistance and the ac susceptibility have been performed for the single-phase 3D-metal doping systems YBa2 Cu3−x Mx Oy (M=Fe, Co, and Ni; x=0.025, 0.05, 0.075, 0.10, 0.25, and 0.50 for Ni and Co and 0.05, 0.075, 0.10, 0.15, and 0.20 for Fe). With an increase of impurity content, two structural transitions were observed for the Co and Fe dopants but only one for the Ni dopant. The resistivity in the normal state changes from metallic to semiconductinglike behavior and the depression of Tc is linear with the impurity concentration (x) when x〈0.10. A weak Curie–Weiss type paramagnetism, which is enhanced with impurity content, exists in the samples studied. Incorporating other work on oxygen defects, we suggest that a change of oxygen content induced by doping was the dominant effect on superconductivity in these samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341393
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  • 9
    Electronic Resource
    Electronic Resource
    Spin-wave resonance in FeNiBSi films (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3805-3807 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic resonance (FMR) measurements have been performed on thin films of Fe80−xNixB15 Si5 alloys (x=5, 40, and 60). The effective magnetization (4πMeff ), magnetic anisotropy field (HA), and g factor were measured. The values of g for all the films ranged between 1.90〈g〈2.11. Spin-wave resonance (SWR) excitations were observed for H, the magnetic field, applied perpendicular to the film plane. SWR fields were found to obey the n2 law and yielded exchange constants in the range of A=0.2–1.9×10−6 ergs/cm. The nearest-neighbor exchange parameter J was deduced from A and implies that J varies within a factor of 2 as the value of x changes. In one of the nickel-rich samples, the SWR fields appear to be linear with n implying nonuniform distribution of magnetization in the film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340620
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  • 10
    Electronic Resource
    Electronic Resource
    A voltage-controlled tunable two-color infrared photodetector using GaAs/AlAs/GaAlAs and GaAs/GaAlAs stacked multiquantum wells (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2114-2116 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A voltage-controlled tunable two-color infrared detector with photovoltaic (PV) and photoconductive (PC) dual-mode operation at 3–5 μm and 8–14 μm using GaAs/AlAs/AlGaAs double barrier quantum wells (DBQWs) and bound-to-continuum GaAs/AlGaAs quantum wells is demonstrated. The photoresponse peak of the photovoltaic GaAs/AlAs/GaAlAs DBQWs is at 5.3 μm, and that of the photoconductive GaAs/GaAlAs quantum wells is at 9.0 μm. When the two-color detector is under a zero bias, the spectral response at 5.3 μm is close to saturate and the peak detectivity at 80 K can reach 1.0×1011 cmHz1/2/W, while the spectral photoresponsivity at 9.0 μm is absolutely zero completely. When the external voltage of the two-color detector is changed to 2.0 V, the spectral photoresponsivity at 5.3 μm becomes zero while the spectral photoresponsivity at 9.0 μm increases comparable to that at 5.3 μm under zero bias, and the peak detectivity (9.0 μm) at 80 K can reach 1.5×1010 cmHz1/2/W. Strictly speaking, this is a real bias-controlled tunable two-color infrared photodetector. We have proposed a model based on the PV and PC dual-mode operation of stacked two-color QWIPs and the effects of tunneling resonance with narrow energy width of photoexcited electrons in DBQWs, which can explain qualitatively the voltage-controlled tunable behavior of the photoresponse of the two-color infrared photodetector. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115602
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