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  • 1
    Electronic Resource
    Electronic Resource
    Lg Coda Q and its Relation to the Geology and Tectonics of the Middle East (1998)
    Springer
    Pure and applied geophysics 153 (1998), S. 563-585 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Lg, Lg coda, Q, Middle East, tectonics.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Regional seismograms were collected to image the lateral variations of Lg coda Q at 1 Hz (Q 0 ) and its frequency dependence 〈(eta)〉 in the Middle East using a back-projection method. The data include 124 vertical-component traces recorded at 10 stations during the period 1986–1996. The resulting images reveal lateral variations in both Q 0 and 〈eta〉. In the Turkish and Iranian Plateaus, a highly deformed and tectonically active region, Q 0 ranges between about 150 and 300, with the lowest values occurring in western Anatolia where extremely high heat flow has been measured. The low Q 0 values found in this region agree with those found in other tectonically active regions of the world. Throughout most of the Arabian Peninsula, a relatively stable region, Q 0 varies between 350 and 450, being highest in the shield area and lowest in the eastern basins. All values are considerably lower than those found in most other stable regions. Low Q values throughout the Middle East may be caused by interstitial fluids that have migrated to the crust from the upper mantle, where they were probably generated by hydrothermal reactions at elevated temperatures known to occur there. Low Q 0 values (about 250) are also found in the Oman folded zone, a region with thick sedimentary deposits. 〈eta〉 varies inversely with Q 0 throughout most of the Middle East, with lower values (0.4–0.5) in the Arabian Peninsula and higher values (0.6–0.8) in Iran and Turkey. Q 0 and 〈eta〉 are both low in the Oman folded zone and western Anatolia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050208
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  • 2
    Electronic Resource
    Electronic Resource
    Seismic Velocity and Q Structure of the Middle Eastern Crust and Upper Mantle from Surface-wave Dispersion and Attenuation (1998)
    Springer
    Pure and applied geophysics 153 (1998), S. 503-538 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Attenuation, Q, surface waves, Middle East.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Observed velocities and attenuation of fundamental-mode Rayleigh waves in the period range 7–82 sec were inverted for shear-wave velocity and shear-wave Q structure in the Middle East using a two-station method. Additional information on Q structure variation within each region was obtained by studying amplitude spectra of fundamental-mode and higher-mode Rayleigh waves. We obtained models for the Turkish and Iranian Plateaus (Region 1), areas surrounding and including the Black and Caspian Seas (Region 2), and the Arabian Peninsula (Region 3). The effect of continent-ocean boundaries and mixed paths in Region 2 may lead to unrealistic features in the models obtained there. At lower crustal and upper-mantle depths, shear velocities are similar in all three regions. Shear velocities vary significantly in the uppermost 10 km of the crust, being 3.21, 2.85, and 3.39 km/s for Regions 1, 2, and 3, respectively. Q models obtained from an inversion of interstation attenuation data show that crustal shear-wave Q is highest in Region 3 and lowest in Region 1. Q’s for the upper 10 km of the crust are 63, 71, and 201 for Regions 1, 2, and 3, respectively. Crustal Q’s at 30 km depth for the three regions are about 51, 71, and 134. The lower crustal Q values contrast sharply with results from stable continental regions where shear-wave Q may reach one thousand or more. These low values may indicate that fluids reside in faults, cracks, and permeable rock at lower crustal, as well as upper crustal depths due to convergence and intense deformation at all depths in the Middle Eastern crust.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050206
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  • 3
    Electronic Resource
    Electronic Resource
    LgCoda Q in Australia and its Relation to Crustal Structure and Evolution (1998)
    Springer
    Pure and applied geophysics 153 (1998), S. 639-653 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Lg, coda, Q, crust, Australia, attenuation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstrac —We have determined Lg Coda Q (Q c Lg) from ground motion recorded at seven broadband stations in Australia, using a stacked spectral ratio method. In spite of the relatively small number of events and less than optimum station coverage, we were able to use those data to obtain a tomographic map Q c Lg and its frequency dependence, at 1 Hz for almost the entire island continent. Q c Lg at 1 Hz in Australia varies between about 330 and 600. The lowest values (330–400) characterize the Tasman Fold Belt in eastern Australia; these may be associated with fluids produced by orogenic activity that occurred during the Devonian and Carboniferous periods or by sedimentation that occurred in Jurassic and Triassic times. Smaller reductions of Q c Lg, relative to maximum values, in central and western Australia, may be associated with sedimentation that occurred over a long-time interval between late Precambrian time and the Carboniferous period or with deformation that occurred in the Central Australian Mobile Belts during the Carboniferous.¶Q c Lg throughout most of Australia is 30 to 60% lower than it is in most other stable continental regions. Assuming that Q c Lg varies in the same proportion as Q Lg , ground motion computations for one-dimensional models of the Australian crust and upper mantle indicate that up to 20% reductions in Q c Lg can be produced if a velocity gradient, rather than a sharp boundary, resides at the crust-mantle transition. The remaining portion of the Q c Lg reduction may be caused by lateral variability in the thickness, depth, and severity of the velocity gradient which causes additional Lg energy to leak into the mantle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050211
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  • 4
    Electronic Resource
    Electronic Resource
    Piezoelectric effect in (001)- and (111)-oriented double-barrier resonant tunneling devices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7770-7774 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show experimentally that current–voltage characteristics of double-barrier resonant tunneling devices (DBRTDs) can be modified by internal polarization fields due to the piezoelectric effect induced by external uniaxial stresses. Electric polarization fields, perpendicular to the interfaces, arise in DBRTDs grown on (001)-oriented substrates under uniaxial, compressive stresses parallel to the (110) or (11¯0) crystal orientations, and in DBRTDs grown on (111)B-oriented substrates under stress parallel to (111) crystal orientation. The voltages at which the resonant tunneling current peaks occur (peak voltages) are sensitive to the polarization fields induced by external stresses. The peak voltages can shift to more positive voltages or more negative voltages depending on the directions of applied stresses. We measured current–voltage characteristics of AlAs/GaAs/AlAs double-barrier resonant tunneling structures as a function of external stresses at 77 K. Uniaxial stress was applied parallel to the (110) and the (11¯0) crystal orientations for (001)-oriented DBRTDs, as well as to the (111) orientation for (111)B-oriented DBRTDs. With the substrates grounded in all the measurements, we found that the peak voltages shift to more positive voltages for (001)-oriented DBRTDs under stress along the (110) orientation and for (111)-oriented DBRTDs under the stress along (111) orientation, and to more negative voltages for (001)-oriented devices under stress along the (11¯0) orientation. The results are in agreement with our calculations published in the preceding article, which take into account the piezoelectric effect and band alignment under stress. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362382
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  • 5
    Electronic Resource
    Electronic Resource
    Resonant tunneling in (001)- and (111)-oriented III–V double-barrier heterostructures under transverse and longitudinal stresses (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7763-7769 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Calculations of the effects of external stress on the current–voltage characteristics of double-barrier (001)- and (111)-oriented resonant tunneling devices are presented. Crystal strains arising from the application of external pressure and, in pseudomorphic structures, lattice mismatch cause shifts in the conduction and valence bands of the well and barrier layers with respect to the unstrained alignment. For certain stress orientations piezoelectric effects give rise to internal electric fields parallel to the current direction. The combined piezoelectric and band-structure effects modulate the transmission resonances which control the shape of the current versus voltage characteristics of the structures. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362381
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  • 6
    Electronic Resource
    Electronic Resource
    Linear in-plane uniaxial stress effects on the device characteristics of AlGaAs/GaAs modulation doped field effect transistors (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 502-505 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The current voltage relationships of AlGaAs/GaAs modulation doped field effect transistors (MODFETs) were measured as a function of applied uniaxial stress. Stresses in the [110] and [11¯0] directions on MODFETs that were grown on a (001) substrate produced threshold shifts of opposite sign. Stresses in [110] and [11¯0] directions resulted in threshold voltage pressure coefficients of −15 and 64 mV/Kbar, respectively. The asymmetric shifts in the threshold voltages are attributed to piezoelectric effects. In addition, stress induced changes in the slopes of the transconductance versus gate-to-source voltage relationships were also measured. For stresses in the [110] and [11¯0] directions, the dependencies were 0.4 and −0.7 mS/(VKbar), respectively.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364126
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  • 7
    Electronic Resource
    Electronic Resource
    Electrical and physical characterization of deuterium sinter on submicron devices (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1721-1723 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The impact of a deuterium (D2) sinter under two different annealing conditions, 450 °C/60 min and 450 °C/90 min, was studied and compared to the traditional forming gas (FG) sinter. Channel hot carrier (CHC) measurements indicated that while the D2 sinter for 60 min improves the lifetime of the devices by 10× over the FG sinter, an additional increase in the D2 anneal time actually has a negative impact on lifetime. DC current–voltage measurements also showed that samples sintered in D2 ambient for 60 min were the least prone to degradation under stress. Gated diode results showed no appreciable amount of difference in the initial interface state density among the different samples. Secondary ion mass spectroscopy indicated that neither poly nor salicide appears to be a complete barrier to D2 diffusion. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121163
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  • 8
    Electronic Resource
    Electronic Resource
    Far-field and beam characteristics of vertical-cavity surface-emitting lasers (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1829-1831 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have determined the far-field patterns and beam parameters of vertical-cavity surface-emitting lasers (VCSELs) with different structures. The results show that the window diameter and the active-layer aperture of VCSELs strongly influence laser far-field distributions and beam characteristics; for VCSELs with small window ω=5 μm, only one dominant lobe has been observed in the far-field profiles, even though injected current was increased up to 2 Ith; and the smaller the ratio of the window diameter to the active-layer aperture, the larger is the far-field divergence. The laser structure dependence of the K factor has also been studied. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117447
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  • 9
    Electronic Resource
    Electronic Resource
    Piezoelectric effects in (001)-oriented double barrier resonant tunneling structures (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1358-1360 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that piezoelectric effects can give rise to internal electric fields that modify the current–voltage characteristics of double barrier resonant tunneling devices, if suitable stresses are applied. Electric polarization fields in the direction perpendicular to the interfaces arise in heterostructures on (001)-oriented substrates under uniaxial stress parallel to the (110) or (11¯0) orientations. We measured current–voltage characteristics of (001)-oriented AlAs/GaAs/AlAs double barrier structures as a function of uniaxial external stress applied parallel to the (110) and the (11¯0) orientations. The substrate contact was grounded in all measurements. Under (110) stress, the resonance peaks shift to more positive voltages for both positive and negative bias. For (11¯0) stress, the peaks shift toward more negative voltages. We also calculated the current–voltage characteristics of resonant tunneling structures under uniaxial stress, taking into account stress effects on the band alignment and piezoelectric effects. We obtain satisfactory agreement between our calculations which contain no adjusted parameters and the measured data. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113200
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  • 10
    Electronic Resource
    Electronic Resource
    The intense microwave burst associated with a white light flare on 1991 June 6
    Amsterdam : Elsevier
    Chinese Astronomy and Astrophysics 18 (1994), S. 450-454 
    Details
    ISSN: 0275-1062
    Keywords: solar microwave burst-white light flare-polarization measurement
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0275-1062(94)90013-2
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