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  • 1
    ISSN: 1741-0444
    Keywords: Autozeroing ; Barometric method ; Electronic circuit ; Instrumentation ; Plethysmography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract An electronic circuit is described which automatically rezeroes a physiologic signal whenever it reaches the limit of a display. This modified signal can be used for polygraph monitoring while the raw signal is processed by a wide-range high-resolution a.d. convertor. The device is currently used in conjunction with the barometric method for measuring tidal volume, but should find general use in plethysmography.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-1405
    Keywords: Singular Value Decomposition ; photometric stereo ; illumination models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We describe a method of learning generative models of objects from a set of images of the object under different, and unknown, illumination. Such a model allows us to approximate the objects' appearance under a range of lighting conditions. This work is closely related to photometric stereo with unknown light sources and, in particular, to the use of Singular Value Decomposition (SVD) to estimate shape and albedo from multiple images up to a linear transformation (Hayakawa, 1994). Firstly we analyze and extend the SVD approach to this problem. We demonstrate that it applies to objects for which the dominant imaging effects are Lambertian reflectance with a distant light source and a background ambient term. To determine that this is a reasonable approximation we calculate the eigenvectors of the SVD on a set of real objects, under varying lighting conditions, and demonstrate that the first few eigenvectors account for most of the data in agreement with our predictions. We then analyze the linear ambiguities in the SVD approach and demonstrate that previous methods proposed to resolve them (Hayakawa, 1994) are only valid under certain conditions. We discuss alternative possibilities and, in particular, demonstrate that knowledge of the object class is sufficient to resolve this problem. Secondly, we describe the use of surface consistency for putting constraints on the possible solutions. We prove that this constraint reduces the ambiguities to a subspace called the generalized bas relief ambiguity (GBR) which is inherent in the Lambertian reflectance function (and which can be shown to exist even if attached and cast shadows are present (Belhumeur et al., 1997)). We demonstrate the use of surface consistency to solve for the shape and albedo up to a GBR and describe, and implement, a variety of additional assumptions to resolve the GBR. Thirdly, we demonstrate an iterative algorithm that can detect and remove some attached shadows from the objects thereby increasing the accuracy of the reconstructed shape and albedo.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1110-1112 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present prism coupling measurements on AlxGa1−xAs native oxides showing the dependence of refractive index on composition (0.3≤x≤0.97), oxidation temperature (400≤T≤500), and carrier gas purity. Index values range from n=1.490 (x=0.9, 400 °C) to 1.707 (x=0.3, 500 °C). The oxides are shown to adsorb moisture, increasing their index by up to 0.10 (7%). Native oxides of AlxGa1−xAs (x≤0.5) have index values up to 0.27 higher and are less hygroscopic when prepared with a small amount of O2 in the N2+H2O process gas. The higher index values are attributed to a transition from a hydroxide to a denser (AlxGa1−x)2O3 oxide phase. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transverse spin lifetimes of spin-polarized photogenerated carriers in InAs self-assembled quantum dots are extracted from the depolarization of their photoluminescence in a magnetic field perpendicular to the spin (the Hanle effect). Hanle measurements on a series of samples reveal that the dot dimensions influence the spin lifetime and its dependence on temperature. The spin lifetime as a function of excitation intensity is qualitatively distinct for carrier spins created in the GaAs host as compared to in the InAs wetting layer. © 2001 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1458-1460 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser cooling of a solid can occur when it emits photons of higher mean energy than those it absorbs. Photothermal deflection spectra of a fluorozirconate glass (ZBLANP) doped with 1 wt% Yb3+ show cooling in an internal volume of the sample at temperatures between 100 and 300 K. A cooling efficiency of ∼1% relative to the absorbed laser power at 1015 nm is maintained at all temperatures. The results show promise for solid-state cooling of bulk materials at temperatures below 150 K.© 1997 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 2123-2139 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In inertial confinement fusion (ICF) experiments, irradiation uniformity is improved by passing laser beams through distributed phase plates (DPPs), which produce focused intensity profiles with well-controlled, reproducible envelopes modulated by fine random speckle. [C. B. Burckhardt, Appl. Opt. 9, 695 (1970); Y. Kato and K. Mima, Appl. Phys. B 29, 186 (1982); Y. Kato et al., Phys. Rev. Lett. 53, 1057 (1984); Laboratory for Laser Energetics LLE Review 33, NTIS Document No. DOE/DP/40200-65, 1987 (unpublished), p. 1; Laboratory for Laser Energetics LLE Review 63, NTIS Document No. DOE/SF/19460-91, 1995 (unpublished), p. 1.] A uniformly ablating plasma atmosphere acts to reduce the contribution of the speckle to the time-averaged irradiation nonuniformity by causing the intensity distribution to move relative to the absorption layer of the plasma. This occurs most directly as the absorption layer in the plasma moves with the ablation-driven flow, but it is shown that the effect of the accumulating ablated plasma on the phase of the laser light also makes a quantitatively significant contribution. Analytical results are obtained using the paraxial approximation applied to the beam propagation, and a simple statistical model is assumed for the properties of DPPs. The reduction in the time-averaged spatial spectrum of the speckle due to these effects is shown to be quantitatively significant within time intervals characteristic of atmospheric hydrodynamics under typical ICF irradiation intensities. © 1997 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 924-931 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The uniformity of focused laser beams, that has been modified with randomly phased distributed phase plates [C. B. Burckhardt, Appl. Opt. 9, 695 (1970); Kato and Mima, Appl. Phys. B 29, 186 (1982); Kato et al., Phys. Rev. Lett. 53, 1057 (1984); LLE Rev. 33, 1 (1987)], can be improved further by constructing patterns of phase elements which minimize phase correlations over small separations. Long-wavelength nonuniformities in the intensity distribution, which are relatively difficult to overcome in the target by thermal smoothing and in the laser by, e.g., spectral dispersion [Skupsky et al., J. Appl. Phys. 66, 3456 (1989); LLE Rev. 36, 158 (1989); 37, 29 (1989); 37, 40 (1989)], result largely from short-range phase correlations between phase plate elements. To reduce the long-wavelength structure, we have constructed phase patterns with smaller short-range correlations than would occur randomly. Calculations show that long-wavelength nonuniformities in single-beam intensity patterns can be reduced with these masks when the intrinsic phase error of the beam falls below certain limits. We show the effect of this improvement on uniformity for spherical irradiation by a multibeam system.
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  • 8
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental data and hydrodynamic simulation results are presented for long-scale-length plasmas produced by the multibeam OMEGA fusion laser, with (approximately-less-than)1.5 kJ on target at wavelength 351 nm. The appropriately time-delayed beams from this system allow the production of millimeter-sized plasmas with (approximately-greater-than)1 keV electron temperatures maintained over extended periods of time ((approximately-greater-than)1 nsec). The two-dimensional plasma expansion and the temporal evolution of the electron temperature and density are found to be in very good agreement with simulations. The plasma thus produced forms an excellent tool for investigating laser–plasma interaction processes under conditions relevant to future laser-fusion reactor targets.
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  • 9
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct-drive-implosion core conditions have been characterized on the 60-beam OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser system with time-resolved Ar K-shell spectroscopy. Plastic shells with an Ar-doped deuterium fill gas were driven with a 23 kJ, 1 ns square laser pulse smoothed with 1 THz smoothing by spectral dispersion (SSD) and polarization smoothing (PS) using birefringent wedges. The targets are predicted to have a convergence ratio of ∼15. The emissivity-averaged core electron temperature (Te) and density (ne) were inferred from the measured time-dependent Ar K-shell spectral line shapes. As the imploding shell decelerates the observed Te and ne increase to 2.0 (±0.2) keV and 2.5 (±0.5)×1024 cm−3 at peak neutron production, which is assumed to occur at the time of the peak emissivity-averaged Te. At peak compression the ne increases to 3.1 (±0.6)×1024 cm−3 and the Te decreases to 1.7 (±0.17) keV. The observed core conditions are close to those predicted by a one-dimensional hydrodynamics code. © 2002 American Institute of Physics.
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  • 10
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct-drive implosions on the OMEGA laser [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] have been diagnosed using a wide range of techniques based on neutrons, charged particles, and x rays. These implosions use full single-beam smoothing (distributed phase plates, 1-THz-bandwidth smoothing by spectral dispersion and polarization smoothing). The beam-to-beam power imbalance is ≤5%. Fuel areal densities close to those in one-dimensional (1-D) simulations are inferred for implosions with calculated convergence ratios ∼15. The experimental neutron yields are ∼35% of 1-D yields. The complementary nature of the experimental observables is exploited to infer fuel shell mix in these implosions. Data suggest that this mix occurs at relatively small scales. Analysis of the experimental observables results in a picture of the core and mix region indicating that nearly 70% of the compressed fuel areal density is unmixed, and about 20% of the compressed shell areal density is in the mixed region. Comparisons of this model with inferred core conditions from argon-doped implosions are also presented. © 2002 American Institute of Physics.
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