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  • 1
    ISSN: 1573-904X
    Keywords: melanin binding ; physicochemical properties ; tissue distribution ; multiple linear regression approach ; molecular modeling ; quantitative whole-body autoradiography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The relationship between the physicochemical characteristics of 27 new drug candidates and their distribution into the melanin-containing structure of the rat eye, the uveal tract, was examined. Tissue distribution data were obtained from whole-body autoradiograms of pigmented Long–Evans rats sacrificed at 5 min and 96 hr after dosing. The physicochemical parameters considered include molecular weight, pK a, degree of ionization, octanol/water partition coefficient (log P o/w), drug-melanin binding energy, and acid/base status of the functional groups within the molecule. Multiple linear regression analysis was used to describe the best model correlating physicochemical and/or biological characteristics of these compounds to their initial distribution at 5 min and to the retention of residual radioactivity in ocular melanin at 96 hr post-injection. The early distribution was a function primarily of acid/base status, pK a, binding energy, and log P (o/W), whereas uveal tract retention in rats was a function of volume of distribution (V 1), log P (o/w), pK a, and binding energy. Further, there was a relationship between the initial distribution of a compound into the uveal tract and its retention 96 hr later. More specifically, the structures most likely to be distributed and ultimately retained at high concentrations were those containing strongly basic functionalities, such as piperidine or piperazine moieties and other amines. Further, the more lipophilic and, hence, widely distributed the basic compound, the greater the likelihood that it interacts with ocular melanin. In summary, the use of multiple linear regression analysis was useful in distinguishing which physicochemical characteristics of a compound or group of compounds contributed to melanin binding in pigmented rats in vivo.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Autonomous robots 2 (1995), S. 283-289 
    ISSN: 1573-7527
    Keywords: microrover ; rocker-bogie ; autonomous navigation ; hazard avoidance ; solid silica aerogel ; radio modem ; remotely operated vehicle ; mobility ; planetary rover ; planetary vehicle ; solar array/battery power system ; integrated power control electronics
    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 When the Mars Pathfinder (MPF) spacecraft lands on Mars, the Microrover Flight Experiment (MFEX) will be deployed and perform its mission to conduct technology experiments verifying the engineering design, to deploy an alpha proton x-ray spectrometer (APXS) to measure elemental properties of rocks and soil, and to image the MPF lander. In accomplishing this mission the MFEX rover must determine a safe path to goal locations traversing over a poorly known Martian surface. The rover does this mission with a capable mobile platform executing on-board autonomous functions of navigation and hazard avoidance. In this paper we describe the rover, its operational environment and the implementation of the on-board autonomous functions.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have measured the critical magnetic field for superconductivity in tungsten from 5.5 to 15 mK using a γ-ray anisotropy thermometer, and we have measured the heat capacity between 0.35 and 25 K. Analysis of the data givesH o =1.237 Oe for the 0 K critical field,T c =16.0 mK for the critical temperature, γ=1.008 mJ/mole · K 2 for the coefficient of the electronic heat capacity, and Θ o =383 K for the 0 K Debye temperature. The measured values of the critical fieldH c are consistently higher than those reported by Black, Johnson, and Wheatley (BJW) on the CMN temperature scale, but the temperature dependence is similar. This discrepancy and the temperature dependence ofH c suggest that both sets ofH c data are affected by magnetic impurities. Use of the calorimetric γ value permits an improved test of the CMN temperature scale with the very-low-temperatureH c data obtained by BJW.
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  • 4
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent theoretical work suggests that magnesium and lithium should be superconducting in the m°K temperature range. We have cooled samples of each of these metals to a temperature of 4 m°K, measured by a gamma-ray anisotropy thermometer. Although the magnetic field was less than 10−2 Oe, no superconducting transitions were observed. The use of a nuclear orientation thermometer employing60Co in single crystal (hcp) cobalt is described.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 6
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A PAC study of111Cd substiuted antiferromagnetic transition metal salts is reported. Supertransferred hyperfine fields at111Cd nuclei were used for the first time to observe three effects: zero-point spin deviations, temperature variation, and pressure shift of the hyperfine field. Comparison of KNiF3 and RbMnF3 with their corresponding quadraticlayer fluorides K2NiF4 and Rb2MnF4 yields an estimate for the magnitude of the zeropoint spin deviation in doped antiferromagnets. The temperature dependences of the Cd hyperfine fields in RbMnF3/Cd and MnF2/Cd have been determined. The shift in hyperfine field observed for α-MnS/Cd under external pressure further supports our model for the origin of the supertransferred hyperfine fields.
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  • 7
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Time-differential perturbed angular correlation was applied to measure the quadrupole coupling constants of111Cd (247 keV) at the In and Sn sites for rare-earth compounds of the series RIn3 and RSn3 that have the AuCu3 structure. Definitive evidence was found for Yb and Eu having lower valence states relative to the assumed value of +3 for the other rare earths. Measurements at liquid helium temperatures and pressures to 18.5 kbar indicate that the room temperature valencies of CeSn3, YbSn3, and YbIn3 have not changed.
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  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The HeI (584 A(ring)) high resolution photoelectron spectra of As+2, Sb+2, and Bi+2 have been obtained with a high temperature molecular beam source. A pure As2 beam was produced by evaporating Cu3As. Sb2 was generated as a mixture with the atoms and tetramers by evaporating the pure element, while Bi2 was generated as a mixture with only the atoms from the pure element. Vibrational structure was well resolved for the As+2 spectrum. Spectroscopic constants were derived and reported for the related ionic states. In addition, we have carried out relativistic complete active space self-consistent field followed by multireference single + double configuration interaction calculations on these dimers both for the neutral ground states and the related ionic states. The agreements between the calculated and experimentally derived spectroscopic constants were fairly good, although the calculations tended to underestimate consistently the strength of the bonding in these heavy homonuclear diatomics.
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  • 9
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Methods employing high resolution HeI (584 A(ring)) photoelectron spectroscopy have been applied to the tetrameric clusters of the group V elements, to resolve details of vibronic and spin–orbit structure in the first three electronic states of P+4, As+4, and Sb+4. Measured spacings of distinct vibrational progressions in the ν1 mode for the 2A1 states of P+4 and As+4, yield vibrational frequencies of 577 (5) cm−1 for P+4 and 350 (6) cm−1 for As+4. Franck–Condon factor calculations suggest bond length changes for the ions in the 2A1 states of 0.054 (3) A(ring) for P+4 and 0.060 (3) A(ring) for As+4. Strong Jahn–Teller distortions in the ν2(e) vibrational mode dominate the structure of the 2E ground states of the tetrameric ions. Both Jahn–Teller and spin–orbit effects appear in the spectra of the 2T2 states of the tetrameric ions, with the spin–orbit effect being dominant in Sb+4 and the Jahn–Teller effect dominant in P+4. Vibrational structure is resolved in the P+4 spectrum, and the ν3(t2) mode is found to be the one principally active in the Jahn–Teller coupling. A classical metal-droplet model is found to fit well with trends in the IPs of the clusters as a function of size.
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  • 10
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High resolution He i (584 A(ring)) photoelectron spectra of ZnCl2, MnCl2, and NiCl2 were measured using a high temperature supersonic molecular beam source. In ZnCl2, vibrational structures were resolved, and spectroscopic constants were derived for the observed molecular ion states. A single ν1 vibrational progression was observed for the C 2Σ+g state of ZnCl+2. A Franck–Condon factor calculation allowed us to obtain a Zn–Cl equilibrium bond length increase of 0.095(5) A(ring) and a ν1 vibrational frequency of 290(8) cm−1. For the open-shell molecules, MnCl2 and NiCl2, no vibrational structure could be resolved because of their very low bending frequencies. Transitions from the ligand orbital and metal d orbital ionizations were clearly resolved, with those of the d orbitals having considerably narrower band widths. Even though many final states are expected for ionization of the open-shell d orbitals, only a few states were observed. This was explained in MnCl2 by the one-electron spin selection rule: Sf=Si ±1/2. Besides the spin selection rule, a propensity toward high spin was proposed to account for the spectrum of NiCl2. From the metal d orbital and ligand orbital splittings, the degree of covalent bonding was inferred to be in the order of: MnCl2〉NiCl2〉ZnCl2.
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