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  • 1
    Electronic Resource
    Electronic Resource
    Effect of quench depth on grain structure in quiescently ordered block copolymers (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 10196-10211 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Grain growth in a polystyrene–polyisoprene block copolymer melt is studied by time-resolved depolarized light scattering after a quiescent quench from the disordered to the ordered state. At shallow quench depths, classical nucleation and growth kinetics are observed. Grains comprising the equilibrated ordered phase nucleate and grow by consuming the surrounding disordered phase. In contrast, deep quenches result in the formation of disorganized grains with an average order parameter that is well below the equilibrium value. Small angle neutron scattering and rheological experiments were conducted to facilitate the interpretation of the light scattering data. We show that the nonequilibrium grain structure formed during deep quenches is due to extremely high nucleation density. Under these circumstances, the space required for the formation of equilibrated grains is unavailable. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357796
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  • 2
    Electronic Resource
    Electronic Resource
    Crystal structure and magnetic properties of the compound Nd5Co21B4 (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1931-1933 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A compound Nd5Co21B4 belonging to the series Rm+nCo5m+3nB2n with m=3, n=2 has been synthesized by melt spinning. The crystal structure and magnetic properties of the compound have been studied by means of x-ray diffraction and magnetic measurements. The compound crystallizes in a hexagonal structure with space group P6/mmm. The Curie temperature, the saturation moment, and the planar anisotropy field of the compound are 570 K, 31.1 μB/f.u., and 861 kOe, respectively. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1389082
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  • 3
    Electronic Resource
    Electronic Resource
    Boundary layer flow on a long thin cylinder (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 14 (2002), S. 628-637 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The development of the boundary layer along a long thin cylinder aligned with the flow is considered. Numerical solutions are presented and compared with previous asymptotic results. Very near the leading edge the flow is given by the Blasius solution for a flat plate. However, there is soon a significant deviation from Blasius flow, with a thinner boundary layer and higher wall shear stress. Linear normal mode stability of the flow is investigated. It is found that for Reynolds numbers less than a critical value of 1060 the flow is unconditionally stable. Also, axisymmetric modes are only the fourth least stable modes for this problem, with the first three three-dimensional modes all having a lower critical Reynolds number. Further, for Reynolds numbers above the critical value, the flow is unstable only for a finite distance, and returns to stability sufficiently far downstream. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1427921
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  • 4
    Electronic Resource
    Electronic Resource
    The development and study of a fiber delivery system for beam shaping (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2185-2189 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high power fiber delivery system has been developed for a Q-switched Nd:YAG laser. Multimode fibers with a core diameter of 400 μm were tested with a view to transmitting the maximum possible amount of optical energy. The importance of surface finish was investigated by employing a number of different polishing procedures. Atomic force microscopy and laser-induced damage threshold measurements were used to identify a clear correlation between surface finish and transmission capability. Surface roughness measurements as low as 3 nm were made and the transmission of up to 30 J/cm2 achieved. The front face of the fibers would be improved during laser testing due to plasma formation which acts to anneal the surface. The various damage mechanisms that limit the performance of the fiber have been studied and attributed to different optical and physical effects. The nature of the light spot emerging from the fiber was analyzed and quantified by beam profilometry. A number of different methods for altering the beam profile were tried but changing the length of the fiber was found to be the most effective. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1468682
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  • 5
    Electronic Resource
    Electronic Resource
    H− ion source test and development capabilities at ISIS : Papers from the Ninth International Conference on Ion Sources (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 896-898 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The ISIS ion source is a surface plasma ion source of the Penning type, and routinely produces 35 mA of H− ions during a 200 μs pulse at 50 Hz for uninterrupted periods of up to 50 days. However, because of the constant demands on ISIS from the neutron user community, very little ion source development has ever been possible. It is now necessary to produce sources with enhanced performances for next generation projects such as the European spallation source. Hence a dedicated ion source development rig (ISDR) has been constructed at Rutherford Appleton Laboratory to fully characterize the ISIS ion source and then facilitate appropriate development work. The ISDR has been designed to replicate the beam transport configurations on both the present ISIS preinjector and the proposed ISIS radio frequency quadrupole, while providing additional beam diagnostics equipment. The commissioning of the ISDR will be described, and initial results presented, along with future development plans. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1430879
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  • 6
    Electronic Resource
    Electronic Resource
    Electro-optic characteristics of 4-domain vertical alignment nematic liquid crystal display with interdigital electrode (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 8259-8263 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated a vertically aligned 4-domain nematic liquid crystal display cell with thin film transistor. Unlike the conventional method constructing 4-domain, i.e., protrusion and surrounding electrode which needs additional processes, in this study the pixel design forming 4-domain with interdigital electrodes is suggested. In the device, one pixel is divided into two parts. One part has a horizontal electric field in the vertical direction and the other part has a horizontal one in the horizontal direction. Such fields in the horizontal and vertical direction drive the liquid crystal director to tilt down in four directions. In this article, the electro-optic characteristics of cells with 2 and 4 domain have been studied. The device with 4 domain shows faster response time than normal twisted-nematic and in-plane switching cells, wide viewing angle with optical compensation film, and more stable color characteristics than 2-domain vertical alignment cell with similar structure. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373535
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison of two methods of measuring the rapid temperature rises in split Hopkinson bar specimens (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1766-1771 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The temperature rise produced in iron and copper specimens by high strain deformation in a compression split Hopkinson pressure bar was measured simultaneously using two independent techniques: (i) small thermocouples (0.2 mm junction size) and (ii) an infrared (IR) camera system based on mercury cadmium telluride (spectral response between 8 and 12 μm). The response time of the thermocouple system was limited by the time taken for heat to diffuse into the junction. In order to obtain useful data with the IR camera system, the emissivity of the specimen surface needed to be modified by depositing a layer of soot. Even so, the measured emissivity was low (0.4), suggesting that the soot layer was semitransparent to IR radiation. The thermocouples, however, yielded temperature measurements that were consistent with all the mechanical work performed on the specimens being converted to heat. The main positive result obtained with the IR camera system is that heating of the iron specimens was spatially nonuniform. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150534
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  • 8
    Electronic Resource
    Electronic Resource
    InxGa1−xAs/AlyGa1−yAs/AlzGa1−zAs asymmetric step quantum-well middle wavelength infrared detectors (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3437-3441 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InxGa1−xAs/AlyGa1−yAs/AlzGa1−zAs asymmetric step quantum-well middle wavelength (3–5 μm) infrared detectors are fabricated. The components display photovoltaic-type photocurrent response as well as the bias-controlled modulation of the peak wavelength of the main response, which is ascribed to the Stark shifts of the intersubband transitions from the local ground states to the extended first excited states in the quantum wells, at the 3–5.3 μm infrared atmospheric transmission window. The blackbody detectivity (Dbb*) of the detectors reaches to about 1.0×1010 cm Hz1/2/W at 77 K under bias of ±7 V. By expanding the electron wave function in terms of normalized plane wave basis within the framework of the effective-mass envelope-function theory, the linear Stark effects of the intersubband transitions between the ground and first excited states in the asymmetric step well are calculated. The obtained results agree well with the corresponding experimental measurements. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1391414
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  • 9
    Electronic Resource
    Electronic Resource
    Vacuum ultraviolet emission dynamics of a coplanar electrode microdischarge: dependence on voltage and Xe concentration (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 682-689 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report nanosecond time-resolved measurements of the vacuum ultraviolet (VUV) emission and current waveforms for a planar, surface-discharge plasma display electrode in Xe/Ne mixtures. The 173 nm excimer emission is separately resolved from the overall VUV emission by a removable fused silica filter. The time difference between the maximum of excimer emission and that of resonant atomic emission is measured at high Xe concentration. The decay time of the overall VUV emission decreases strongly as the Xe concentration increases due to three-body collisions leading to Xe2 formation. The decay time constants versus Xe concentration and pressure are measured and compared with published rate constants. The efficiency of VUV emission increases rapidly from 4% to 10% Xe, but only marginally with further increase to 30% Xe. For fixed Xe ratio, the VUV emission efficiency drops with increasing driving voltage. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1486041
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  • 10
    Electronic Resource
    Electronic Resource
    Growth kinetics and mechanisms of aluminum-oxide films formed by thermal oxidation of aluminum (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 1649-1656 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth kinetics and mechanisms of thin aluminum-oxide films formed by the dry, thermal oxidation of a bare Al(431) substrate at a partial oxygen pressure of 1.33×10−4 Pa in the temperature range of 373–773 K were studied using x-ray photoelectron spectroscopy. The initial oxidation of the bare Al substrate proceeds by an island-by-layer growth mechanism, involving the lateral diffusion over the bare Al substrate surface of mobile oxygen species. At low temperatures (T≤573 K), an amorphous oxide film develops that attains a limiting (uniform) thickness. At high temperatures (T〉573 K), growth is not impeded at a limiting thickness. Kinetic analysis established the occurrences of two different oxide-film growth regimes: an initial regime of very fast oxide-film growth and a second, much slower oxidation stage that is observed only at T〉573 K. These results could be discussed in terms of electric-field controlled, interstitial, outward transport of Al cations through a close packing of O anions in the amorphous films, and inward diffusion of O along grain boundaries in the crystalline films, respectively. For the electric-field controlled Al cation motion, a value of 2.6 eV was determined for the rate-limiting energy barrier, which is located at the metal/oxide interface. This corresponds with a Mott potential of −1.6 V. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1491591
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