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  • 1
    Electronic Resource
    Electronic Resource
    Effects of isolation by distance and geographical discontinuity on genetic subdivision of Littoraria cingulata (1998)
    Springer
    Marine biology 132 (1998), S. 295-303 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Littoraria cingulata (Philippi, 1846) is a Western Australian, mangrove littorine snail, represented by two morphologically distinct subspecies, whose distributions are separated by 〉300 km. The southern subspecies, L. cingulata pristissini, is distinguished from the northern subspecies, L. cingulata cingulata, by having a thinner, keelless shell with more primary grooves, and lower and much more numerous ribs. In contrast with these striking differences, L. cingulata cingulata is morphologically very similar to another species, L. sulculosa, with which it also shares a nearly coincident geographic range. Allozyme comparisons at 22 presumptive loci confirmed a large genetic distance between L. cingulata and L. sulculosa, and the apparent conspecificity of the morphologically divergent subspecies of L. cingulata. Based on geological evidence, the geographical separation of the morphologically divergent forms of L. cingulata has developed within the past 5000 to 10 000 yr. The extensive continuous distribution of the northern subspecies, L. cingulatacingulata, and the large geographic disjunction between the northern and Shark Bay subspecies, L. cingulata pristissini, allowed a test of the genetic importance of this relatively recent disjunction. Within the continuous distribution of the two subspecies, a pattern of isolation by distance was visible up to distances of 300 km. Beyond 300 km, genetic subdivision, measured by pairwise G ST (the proportion of genetic diversity due to differences between populations), averaged 0.028, whereas subdivision between Shark Bay and northern populations averaged 0.055 over the same range of distances. Although the relative paucity of barriers to gene flow tends to limit genetic subdivision in marine species with planktotrophic larvae, the results for L. cingulata suggest that subdivision can occur within a continuous distribution, but that special events leading to major disjunctions can substantially increase divergence, even over a relatively short period of time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050395
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  • 2
    Electronic Resource
    Electronic Resource
    Microwave electric-field imaging using a high-Tc scanning superconducting quantum interference device (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 984-986 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used a 77 K thin-film YBa2Cu3O7 superconducting quantum interference device (SQUID) in a scanning SQUID microscope to image room-temperature sources of high-frequency electric field. We find that time-varying electric fields capacitively induce currents in the SQUID, which in turn are rectified by the nonlinearity of the SQUID current–voltage characteristics, leading to changes in the quasistatic voltage across the SQUID. By observing changes in the voltage modulation depth ΔV of the SQUID as a sample is scanned past the SQUID, we obtain electric-field images in the 1–15 GHz frequency range with a SQUID-to-sample separation of about 80 μm. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122060
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  • 3
    Electronic Resource
    Electronic Resource
    Near-field scanning microwave microscope with 100 μm resolution (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3272-3274 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe the operation of a simple near-field scanning microwave microscope with a spatial resolution of about 100 μm. The probe is constructed from an open-ended resonant coaxial line which is excited by an applied microwave voltage in the frequency range of 7.5–12.4 GHz. We present images of conducting structures with the system configured in either receiving or reflection mode. The images demonstrate that the smallest resolvable feature is determined by the diameter of the inner wire of the coaxial line and the separation between the sample and probe. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118033
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  • 4
    Electronic Resource
    Electronic Resource
    Imaging radio-frequency fields using a scanning SQUID microscope (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1267-1269 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a liquid-nitrogen-cooled scanning SQUID magnetic microscope, we have developed a technique for broadband imaging of radio-frequency (rf) and microwave fields with a spatial resolution of about 15 μm. We have produced images of the amplitude of 50 MHz fields with an rms noise of 2.6 nT and a 300 μm/s scan rate. Detection is accomplished by using the nonlinearity of the voltage-flux characteristic of the SQUID to rectify the rf fields. Our present technique is limited by cavity mode resonances in the SrTiO3 substrate of our SQUID sensor. Using a small excitation probe, we have directly imaged these resonances at frequencies up to about 12.5 GHz. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113258
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  • 5
    Electronic Resource
    Electronic Resource
    Microwave microscopy using a superconducting quantum interference device (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 99-101 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results on a near-field scanning probe microwave microscope which is based on the nonlinear behavior of a YBa2Cu3O7 direct-current superconducting quantum interference device (SQUID). Our system has a spatial resolution of about 30 μm and derives its probing field from circulating currents in the SQUID loop. The frequency is set by the Josephson relation and is continuously tunable up to about 200 GHz. By imaging small patterned normal metal thin-film samples of Cu and Nb at 77 K, we have confirmed the operating bandwidth of the system and investigated the nature of the imaging process. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114159
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  • 6
    Electronic Resource
    Electronic Resource
    Activation status of platelet aggregates and platelet microparticles shed in sheared whole blood (1997)
    Springer
    Journal of materials science 8 (1997), S. 747-751 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The role of temperature and shear rate in the activation status of aggregating platelets and platelet microparticles (MPs) was investigated in a modified concentric-cylinder rotational viscometer. Whole blood anticoagulated with citrate was exposed to a range of shear rates typical of cardiopulmonary bypass circuits (0, 1000, 2000 and 4000 s-1) over four temperatures spanning hypothermic to mildly hyperthermic conditions (24, 30, 37 and 42°C) for short durations (100 s). Aliquots of blood were double-stained for CD41 (platelet GPIIb/IIIa) and CD62 (P-selectin). Platelets, platelet aggregates, MPs and red blood cell-platelet and -MP aggregates were identified by flow cytometry by acquiring only CD41-positive particles and differentiating on a plot of CD41 versus forward light scatter. The activation status of each particle was quantified by measuring CD62 expression (α-granule release). A degree of correlation between the shedding of MPs and the formation of platelet–platelet aggregates was observed for the data as a whole (r=0.85 for p〈0.01), although this trend was not observed for a shear rate of 4000 s-1. The mean expression of CD62 on both platelets and MPs was maintained at a very low level for all temperature and shear rate combinations. There was, however, a number of very highly activated MPs associated with red blood cells at high shear rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018556427716
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of temperature and shear rate on platelet aggregation (1997)
    Springer
    Journal of materials science 8 (1997), S. 887-890 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Samples of whole blood were obtained from male volunteers and exposed to combinations of shear rates and temperatures representative of cardiopulmonary bypass (CPB) in a modified computer-controlled concentric cylinder rotational viscometer for a period of 100 s. Blood sampled from the chamber was fixed in paraformaldehyde, stained with CD41 and analysed by flow cytometry. Only platelet-positive particles were acquired, each individual cell, or aggregate of cells, identified by analysis of its fluorescence and forward light scatter characteristics. Little platelet aggregation was observed at shear rates of less than 4000 s-1 for temperatures of greater than 24°C, but large numbers of aggregates were formed at all temperatures at 4000 s-1 (p〈0.05), with more aggregates forming at 24 and 30°C than at 37 and 42°C (p〈0.05). We conclude that the process of aggregation is dependent on both temperature and shear rate. We note that a large number of platelets become involved in aggregates under conditions of temperature and shear-rate typical of CPB.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018510006760
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  • 8
    Electronic Resource
    Electronic Resource
    Experimental determination of the symmetry of the order parameter in YBCO (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 491-494 
    Details
    ISSN: 1572-9605
    Keywords: Superconductivity ; pairing symmetry ; YBCO ; SQUID
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract At present, the symmetry of the order parameter in the high temperature superconductor YBCO is quite controversial. Recent experiments using SQUIDs and Josephson junctions appear to support competing theories, with some experiments supporting a dx2−y2 pairing symmetry for the order parameter and others a s-wave pairing symmetry. We note that a number of factors such as trapped flux, magnetic field gradients and SQUID asymmetries could lead such measurements astray. We use a Scanning SQUID Microscope and a time-reversal invariance test to resolve these experimental problems. We find the order parameter in YBCO has a time-reversal invariant dx2−y2 symmetric component. We estimate the amplitude of anyimaginary s-wave symmetric component to be less than 4% and anyreal s-wave component to be less than 82%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00722838
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  • 9
    Electronic Resource
    Electronic Resource
    The Toroidal Imaging Mass-Angle Spectrograph (TIMAS) for the polar mission (1995)
    Springer
    Space science reviews 71 (1995), S. 497-530 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The science objectives of the Toroidal Imaging Mass-Angle Spectrograph (TIMAS) are to investigate the transfer of solar wind energy and momentum to the magnetosphere, the interaction between the magnetosphere and the ionosphere, the transport processes that distribute plasma and energy throughout the magnetosphere, and the interactions that occur as plasma of different origins and histories mix and interact. In order to meet these objectives the TIMAS instrument measures virtually the full three-dimensional velocity distribution functions of all major magnetospheric ion species with one-half spin period time resolution. The TIMAS is a first-order double focusing (angle and energy), imaging spectrograph that simultaneously measures all mass per charge components from 1 AMU e−1 to greater than 32 AMU e−1 over a nearly 360° by 10° instantaneous field-of-view. Mass per charge is dispersed radially on an annular microchannel plate detector and the azimuthal position on the detector is a map of the instantaneous 360° field of view. With the rotation of the spacecraft, the TIMAS sweeps out very nearly a 4π solid angle image in a half spin period. The energy per charge range from 15 eV e−1 to 32 keV e−1 is covered in 28 non-contiguous steps spaced approximately logarithmically with adjacent steps separated by about 30%. Each energy step is sampled for approximately 20 ms;14 step (odd or even) energy sweeps are completed 16 times per spin. In order to handle the large volume of data within the telemetry limitations the distributions are compressed to varying degrees in angle and energy, log-count compressed and then further compressed by a lossless technique. This data processing task is supported by two SA3300 microprocessors. The voltages (up to 5 kV) for the tandem toroidal electrostatic analyzers and preacceleration sections are supplied from fixed high voltage supplies using optically controlled series-shunt regulators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00751339
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  • 10
    Electronic Resource
    Electronic Resource
    Development of a Simulator for Endovascular Repair of Abdominal Aortic Aneurysms (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 798-802 
    Details
    ISSN: 1573-9686
    Keywords: Training simulator ; Endoluminal repair ; Stent-grafts ; Simulating fluoroscopic imaging ; Endovascular repair ; Aortic aneurysms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The design and development of a simulator for endovascular repair of abdominal aortic aneurysm (AAA) is described. The simulator consists of an interchangeable model of a human AAA based on computed tomography data and is produced by means of computer-aided design and manufacture (CAD/CAM) techniques. The model has renal, iliac, and femoral arteries, and is perfused with a temperature controlled blood–analog fluid under simulated physiological flow conditions. “Fluoroscopic imaging” is simulated by a computerized imaging system that uses visible light. A movable video camera relays images in the antero–posterior and lateral planes of the AAA to a monitor. The imaging system allows “arteriography” and “road-mapping” to be performed so as to facilitate accurate deployment of endovascular stent-grafts. The system has been used for teaching and demonstrating endovascular techniques to clinicians, as well as the evaluation of new stent-graft devices. Its successful incorporation into endovascular workshops has demonstrated its role in the training of clinicians in endovascular repair of AAA. © 1998 Biomedical Engineering Society. PAC98: 0150-i, 8745Hw, 8759Fm
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.66
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