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  • 1
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: We have synthesized a series of non-macrocyclic ligands to FKBP12 that are comparable in binding potency and peptidyl prolyl isomerase (PPIase) inhibition to FK506 itself. We have also solved the structure of one of these ligands in complex with FKBP12, and have compared that structure to the FK506–FKBP12 complex. Consistent with the observed inhibitory equipotency of these compounds, we observe a strong similarity in the conformation of the two ligands in the region of the protein that mediates PPIase activity. Our compounds, however, are not immunosuppressive. In the FKBP12–FK506 complex, a significant portion of the FK506 ligand, its `effector domain', projects beyond the envelope of the binding protein in a manner that is suggestive of a potential interaction with a second protein, the calcium-dependent phosphatase, calcineurin, whose inhibition by the FKBP 12–FK506 complex interrupts the T-cell activation events leading to immunosuppression. In contrast, our compounds bind within the surface envelope of FKBP12, and induce significant changes in the structure of the FKBP12 protein which may also affect calcineurin binding indirectly.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of comparative physiology 176 (1995), S. 727-735 
    ISSN: 1432-1351
    Keywords: Chicks ; Auditory threshold shift ; Basilar papilla ; Water jet ; Hair cell micromechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract 1. The in vitro effect of intense stimulation on the micromechanical stiffness of hair cell sensory hair bundles was studied at three locations on the chick basilar papilla. Threshold levels of hair bundle motion, produced by a water jet stimulus, were examined before and after exposure to a 300 Hz water jet stimulus set at 25 dB above the pre-exposure threshold level. 2. Threshold levels of motion were systematically examined in 8 unexposed control cells. The level of water jet stimulus needed to achieve the detection threshold of motion remained constant in these cells when periodically tested over a 36.5-min interval. 3. Post-exposure changes in the motion detection threshold of hair bundles were examined in 82 hair bundles, and a number of effects were identified: 2.4% of the hair bundles showed no threshold change; 31.7% of the hair bundles had threshold shifts which indicated an increase in stiffness; 18.3% exhibited a threshold shift that indicated a decrease in hair bundle stiffness, but with no recovery; and 47.6% had thresholds that indicated a decrease in hair bundle stiffness with recovery to pre-exposure levels within 16–18 min. 4. The results suggest that chick hair bundles exhibit complex and varied responses to overstimulation which are very different from that seen in the mammal.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of intelligent and robotic systems 12 (1995), S. 145-153 
    ISSN: 1573-0409
    Keywords: Redundant robot ; critical manipulation ; backbone curve ; end-point deflection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The redundant robots analyzed here have large numbers of degrees of freedom. Such robots are analogous to snake or tentacles and are useful for operation in highly constrained environments and novel forms of locomotion — here it has been defined as critical manipulation. In this paper the end-point deflection of hyper-redundant robots have been studied by parameterization of the flexible links of the robot manipulator. A number of planar configurations of the redundant manipulator were taken into consideration for the present study and the configuration which gives minimum end-point deflection has been recommended for the critical manipulation. This work is significant for some of the research activities recently going on in NASA's Kennedy Space Center towards the application of hyper-redundant robots for manipulation inside the space Shuttle Cargo Bay.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Mineralium deposita 30 (1995), S. 199-210 
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A deep “parent” composition for bonanza oreforming fluids at the Sleeper deposit was calculated by the computer program SOLVEQ using fluid-inclusion microthermometric and gas data, and by assuming equilibrium with the following minerals present in vein samples below the bonanza zones: gold, chalcedony, adularia, pyrite, chalcopyrite, and acanthite. The calculated dissolved gold content of 295 ppb is approximately 2 orders of magnitude higher than that assumed for typical geothermal systems. Thus, a gold-enriched fluid appears to have been a principal factor in the genesis of bonanza Au-Ag ores at the Sleeper deposit. Geochemical modelling of possible ore-forming processes using the computer program CHILLER, with the reconstructed ore-forming solution as a starting composition, indicates that boiling most closely reproduces observed minerals and their relative abundances in bonanza ores. The constraint imposed by the association of amorphous silica with gold precludes all of the mixing scenarios modelled, such as mixing with cold and steam-heated groundwaters (acid-sulfate, CO2-rich). Modelling indicates that boiling of a gold-rich deep solution leads to rapid gold precipitation, and that the amount of gold precipitated initially is large relative to other minerals. These factors apparently led to nucleation of colloidal gold particles instead of in-situ gold deposition or coprecipitation with other phases. Gold colloids apparently were entrained in the upward-flowing hydrothermal solutions and grew as they travelled. Upon reaching a critical size (10–100 nm?), they were deposited due to orthokinetic aggregation at an elevation and temperature at which amorphous silica was nucleating and aggregating.
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  • 5
    ISSN: 1432-2242
    Keywords: Key words Electrofusion ; AFLP DNA analysis ; Somatic fusion ; Phytoremediation ; Metal toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Somatic hybrids between the zinc hyperaccumulator Thlaspi caerulescens and Brassica napus were produced by electrofusion of protoplasts isolated from each species. Optimization of electrofusion parameters yielded interspecies heteroplasmic fusion rates of up to 13%. Hybrids were selected by screening the growing calli for Zn tolerance. In addition, a second novel selection technique was developed based on the observation that a high proportion of hybrid microcalli grown in liquid media did not adhere to the wall of the culture vessel, while microcalli derived from parental cells did. Seventeen from a total of 64 regenerated plants were conclusively verified as hybrids by AFLP DNA analysis. The hybrid plants were grown in soil for up to 4 months, and at least five flowered. Several of these hybrids survived when grown on high-zinc media.These hybridsaccumulated levels of zinc and cadmium that would have been toxic for B. napus. The data indicate that transfer of the trait for metal hyperaccumulation in plants is possible through somatic hybridization.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 101 (1995), S. 713-719 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements are reported of the magnetic susceptibility of pure3He films, at coverages for which the nuclear exchange interaction is antiferromagnetic. A comparison is made with earlier results obtained on preplated graphite. The data suggest that all the spins participate in the exchange.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 110 (1998), S. 399-404 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 3 He droplets embedded in a solid 4 He matrix have been studied by NMR and pressure measurements. One feature of the experiment is that the mixture crystals, of 3 He concentration 1%, are grown under constant pressure conditions to minimise the formation of defects. A number of sample pressures below 34 bar have been studied. Isotopic phase separation and the melting of the bubbles are clearly observed. Measurements of T1 , T2 and magnetisation give detailed information on the structure of the droplets. At an initial sample pressure of 28.3 bar preliminary measurements of the T1 of the liquid bubbles show a temperature dependence of the form (A+ B/T2)−1. This indicates that the expected relaxation in the liquid is augmented by a constant contribution, probably from the surface of the droplets.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 110 (1998), S. 627-633 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report preliminary results of the first heat capacity measurements on atomically layered 3 He – 4 He mixture films adsorbed on the surface of graphite. The 4 He film consists of two solid and two superfluid atomic layers. The heat capacity has been investigated over the range 1 – 70mK as a function of the surface density of 3 He atoms added to the film. At coveragesn3 〈 4nm −2 , the 3He forms a uniform two dimensional Fermi system. The coverage dependence of the linear coefficient of the heat capacity, γ, allows a determination of the hydrodynamic effective mass and $$F_1^s $$ . At higher coverages a step-like increase in γ is observed, interpreted as the formation of a second two dimensional Fermi system.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 110 (1998), S. 261-267 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report experiments in which we have used DC SQUIDs in pulsed NMR spectrometers to observe directly the free precession of nuclear spins. A broadband spectrometer, which operates in flux-locked loop mode with a bandwidth of 3.4 MHz using a SQUID with additional positive feedback and an untuned superconducting input circuit, has been used to observe NMR signals from platinum powder at frequencies of 38, 65, 85, 240 and 513 kHz. The performance is compared with a second system in which a DC SQUID is operated open loop as a small signal rf amplifier with a series tank input circuit tuned at 1 MHz.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 113 (1998), S. 265-270 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Nuclear spin exchange in the low density two dimensional quantum solid formed by 3 He adsorbed on graphite plated by a bilayer of HD has been studied by heat capacity and magnetization measurements. The low densities result in a frustrated magnet with significantly larger effective exchange constants than observed in the antiferromagnetic second layer of 3 He on bare graphite. Promotion to a fluid overlayer occurs at 6.8 nm −2. A ferromagnetic anomaly is observed in magnetization measurements at 10 nm −2 with an effective exchange constant of 1.0 mK, about half the value observed at the corresponding anomaly on bare graphite.
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