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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of the reaction He++He+He→He+2+He. III. Effects of resonant quasibound states (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1015-1037 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two previous theoretical investigations of the three body association reaction He++He+He→He+2+He, both of them concerned with molecule formation by a mechanism largely classical in nature, are extended to take into account two hitherto neglected quantum effects, each involving resonant quasibound states (RQS) of the He+2 molecular ion and each involving tunneling through the rotational barrier. One of the quantum effects is the effect that the discrete nature of RQS has on outward tunneling after quasibound states are formed by the classical mechanism; and the other, which was proposed originally by Dickinson, Roberts, and Bernstein, is collisional deexcitation ofRQS formed by inward tunneling. While it is found that taking into account the discrete nature of RQS in determining the effect of outward tunneling re− sults in only minimal changes in the rate coefficient, it is also found that the formation of such states by inward tunneling can account for the 10% to 20%discrepancy between our previous calculations and the experimental results of Johnsen, Chen, and Biondi. As in previous work, computations were performedusing four assumed forms of the He+3 interaction; and while statistical accuracy now permits some of these interactions to be distinguished from one another, each gives a rate coefficient with magnitude and temperature dependence in agreement with experiment. A considerable amount of discussion is devoted to some of the approximations that have been made, principally our use of the JWKB approximation in identifying RQS and our neglect of collisional breakup of newly formed He+2 ions. It is argued that the inaccuracies introduced by these two approximations are likely to be of opposite sign and to have magnitudes not much greater than the experimental error. The uncertainties in our calculation notwithstanding, it is concluded that the inward tunneling mechanism surely plays a significant, though not dominant, role in He+ recombination. Our calculations of the rate coefficient due to inward tunneling are several times smaller than the very rough estimates accompanying the original suggestion of this mechanism, and it is noted that this difference may be due largely to our estimates of cross sections for collisional deexcitation of RQS, which are obtained using the Monte Carlo trajectory method and which have the appearance of being several times smaller than the simple gas kinetic estimates employed by Dickinson et al. Some other possible explanations of this difference are noted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457226
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  • 2
    Electronic Resource
    Electronic Resource
    Clemmensen reduction of 2-acetonaphthone (1972)
    s.l. : American Chemical Society
    The @journal of organic chemistry 37 (1972), S. 142-145 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00966a042
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of the reaction He++He+He→He+2+He. II. Improved sampling (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 4394-4400 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate coefficient for He+ ions recombining in helium gas is computed using the Wigner–Keck Monte Carlo trajectory method. The present calculation is a refinement of a previous one, the principal difference between the two being that simpler, more reliable, and much less time consuming procedures are now employed to select the trajectories. The results of the new calculation are consistent with, and statistically more accurate than, those of the previous one. The improved sampling procedures, unlike those employed in the previous calculation, have the appearance of being easily applicable to other, similar three body association reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450010
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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of the reaction He++He+He→He+2+He (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 3363-3389 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Wigner–Keck Monte Carlo trajectory method is employed to calculate the rate coefficient k for He+ ions recombining in gaseous helium at temperatures in the range 80〈T〈320 K. The attractive (repulsive) He+2 interaction is approximated by the sum of a Morse (anti-Morse) potential and a term taking into account the long range ion–induced dipole interaction. The relevant three body interaction is represented by an expression that is, in effect, an approximation to a simple variational calculation. This expression depends on the same parameters that specify the He+2 interactions. A method is devised for sampling points on the Wigner–Keck surface that permits the determination of a value of k to within a statistical error of about 10% by computing less than 1600 trajectories, of which less than 500 represent actual formation of a He+2 molecule. The computed values of k are found to be in fair agreement with experimental results obtained by Biondi and his collaborators. The temperature dependence is reproduced rather satisfactorily, but the magnitude is 10% to 20% too low. The computed values of k are found to be fairly insensitive to reasonable variations in the behavior of the two andthree body potentials. In particular, the results are found to be totally insensitive to the behavior of the three body potential if more than one of the internuclear separations are relatively small. It is also found that long range ion–induced dipole forces, while playing a very important role, do not appear to dominate the recombination process to quite the extent that had apparently been assumed in some previous investigations. The results generally support a model proposed by Mahan, who had suggested that charge transfer is the mechanism primarily responsible for the reaction. It is suggested that the remaining discrepancy with experiment might be largely due to the formation of highly excited quasibound states by inward tunneling through the rotational barrier, which is a mechanism that had originally been proposed by Dickinson et al. as the dominant one in He+ recombination. Some qualitative arguments are presented that indicate that this mechanism, which is not taken into account by classical trajectory calculations, might be less important than had originally been thought.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449197
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  • 5
    Electronic Resource
    Electronic Resource
    Universal personal communications: Emergence of a paradigm shift in the communications industry (1994)
    Springer
    International journal of wireless information networks 1 (1994), S. 149-163 
    Details
    ISSN: 1572-8129
    Keywords: Telecommunications ; personal communications ; wireless communications ; cellular communications
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract It is postulated that today we are in the midst of a major paradigm shift in the communications industry. The essence of this paradigm shift is a transition from today's universal telephone service which has been perfected over the past 100 years, to a future communication service environment, referred to as universal personal communication. Under this new paradigm, communications will be person based in contrast to the predominantly location-based communication environment of today. Societal trends, evolving global standards for communication, regulatory policies, and emergent technologies are seen as the forces driving such a transition. Universal personal communications will be characterized by flexible access to universal services permittingmore enduser control which will result in personalization and customization of such services. Furthermore, the centralized intelligence focus of today's communication networks needs to evolve toward a focus where network intelligence can be migrated to the periphery of the core transport network. The viability of universal personal communication will be critically dependent upon how well it addresses the end customer value proposition. Two key elements of this proposition are transparency of mobility and personalization of service environments. A zonal service environment model which classifies and characterizes these various service environments in terms of common communication parameters is proposed. This model is built around hierarchical structures for both cellular and digital wireless transmission, and can be viewed as critical towards the realization of transparent mobility management and personalization of services.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02107415
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  • 6
    Electronic Resource
    Electronic Resource
    Dissociation of renal cyclic AMP and phosphate responses to parathyroid hormone in uremia (1979)
    Springer
    Calcified tissue international 29 (1979), S. 147-154 
    Details
    ISSN: 1432-0827
    Keywords: Vitamin D ; Chronic uremia ; Rats ; Renal responsivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Various investigators have shown that chronic uremia is associated with a normal or exaggerated phosphaturic response to parathyroid hormone (PTH). To explore the relationship between progressive uremia, renal tubular cyclic AMP (cAMP), and inorganic phosphate (Pi) response to PTH and acidosis, in vivo and in vitro experiments were designed in rats with experimental uremia of 4–6 weeks’ duration. Both uremic and pair-fed control rats were treated with 1,25-dihydroxycholecalciferol (1,25(OH)2D3) and/or chronic NH4Cl feeding. Urinary Pi and cAMP and plasma immunoreactive PTH (iPTH) were measured as well as PTH- and NaF-stimulated cAMP from isolated renal tubules. Excretion of cAMP decreased by 30% in uremic as compared to control rats despite a 3-fold rise in Pi excretion. Acidosis superimposed on uremia did not further decrease cAMP excretion, nor did it significantly alter the elevated Pi excretion. 1,25(OH)2D3 treatment of uremic rats further lowered cAMP excretion although Pi excretion rose, hypercalcemia occurred, and plasma iPTH fell. In nonuremic control rats, 1,25(OH)2D3 treatment led to hypercalcemia, a progressive decrease in cAMP, and increase in Pi excretion. Isolated renal tubules from uremic or acidotic uremic rats revealed a 50% reduction in both PTH- and NaF-stimulated cAMP generation compared to control rat renal tubules. This observation was unchanged by 1,25(OH)2D3 treatment. Renal tubules of 1,25(OH)2D3-treated control rats demonstrated a decreased cAMP production in response to both PTH and NaF which was inversely related to the calcium content of the renal tubules. Renal tubular calcium levels of uremic rats, initially 3-fold elevated, also increased during 1,25(OH)2D3 treatment. These results are consistent with the hypothesis that progressive uremia results in a dissociation between PTH, urinary cAMP, and Pi excretion which cannot be explained by either metabolic acidosis or 1,25(OH)2D3 deficiency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02408070
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  • 7
    Electronic Resource
    Electronic Resource
    Bone maturation in the vitamin D, phosphate deficient rat and the response to acid loading (1979)
    Springer
    Calcified tissue international 27 (1979), S. 233-237 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Vitamin D ; Acidosis ; Phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Vitamin D and phosphate deficiency were produced in rats in order (a) to evaluate the degree of bone mineral and matrix maturation using a bromoform/toluene density gradient technique; and (b) to compare the aforementioned bone maturational changes due to vitamin D and phosphate deprivation to those produced with superimposed severe acidosis. Rats were fed a diet deficient in vitamin D and phosphorus (0.2%) from 3 weeks through 7 weeks of age. To examine the additional contribution of dietary calcium, we gave one-half of the animals either a low (0.06%) or high (1.3%) calcium diet. Following the 4 weeks of vitamin D deficiency, one-half of each group was given 1.8% NH4Cl in the drinking water for 4 succeeding days to induce an acute, severe acidosis. The degree of bone maturation was quantitated via bromoformtoulene density gradient fractionation; total mineral and hydroxyproline (collagen) levels were quantitated as well. The vitamin D-deficient rats deprived of adequate dietary phosphate responded by conserving phosphorus, and as a consequence total bone phosphorus levels were maintained within that level for control rats. This conservation was independent of calcium intake but was extremely sensitive to acute acid loading, where a significant reduction in total bone phosphorus was noted. The bone maturational profile obtained from the vitamin D-phosphate deficient rats, however, revealed a significant accumulation of less mature or dense bone collagen and mineral with a corresponding decrease in the most mature or dense moieties. In contrast to the reduction of the total bone phosphorus content by acute acidosis, the skeletal collagen-mineral maturational profile was not significantly affected by the short-term systemic acidosis. The observed retardations in the bone collagen and mineral maturation of the vitamin D-deficient, phosphate-deprived state provide an additional observation which may well relate to the progressive osteopenia documented in states of chronic, mild acidosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441191
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of vibrating-wire stress gage in soft rock (1977)
    Springer
    Experimental mechanics 17 (1977), S. 261-264 
    Details
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An analysis for the in situ elastic response of a vibrating-wire stress gage in soft rock (E〈105 Mpa) has been accomplished with the use of the finite-element method and approximate analytical procedures. The vibrating-wire stress gage is not a true stressmeter in that it is somewhat dependent on rock-modulus changes. Conventional procedures for calibration include the assumption that this dependency is linear with respect to rock modulus. In this analysis, a nonlinear relationship is demonstrated and an approximate mathematical expression is derived for it. Good agreement is obtained between theoretical calibration factors and test results on laboratory-scale samples with the stressmeter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02324840
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  • 9
    Electronic Resource
    Electronic Resource
    Bone cell populations and histomorphometric correlates to function (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 222 (1988), S. 228-236 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A circadian context has been used to develop information about the proliferative and functional behavior of the cell populations that function to model the long bones of growing rats. We asked: Are the proliferating cells in the growth cartilages and diaphyseal bone of young adult growing rats distributed within single or multiple populations? Can cytomorphometry (TEM-C) be used to determine ultrastructural correlates to the well-defined circadian rhythm of matrix formation displayed by functionally synchronous populations of metaphyseal osteoblasts? Can TEM-C reveal changes in osteoclast ultrastructure that could index a biological rhythm for osteoclastic bone mineralysis/resorption? Kinetic results derived from multiple radiothymidine labeling (DNA synthesis) support the single population model for chondrocytes and disphyseal osteoprogenitor cells. TEM-C studies at the midpoints of the daily light and dark spans show that osteoblast RER-membrane development and cysternal volumes are maximal at the recorded daytime peak of net collagen synthesis. The extent of metaphyseal osteoclast surface ruffling (mineralysis) is also twofold greater during the day than the night - an observation supporting the concept that bone formation and resorption activities are coupled.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1092220303
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