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  • American Institute of Physics (AIP)  (8)
  • American Association for the Advancement of Science (AAAS)  (2)
  • 1985-1989  (10)
  • 1986  (10)
  • 1
    Electronic Resource
    Electronic Resource
    NMR pulse response and measurement of the quadrupole coupling constant of I=3/2 nuclei (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6923-6927 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rf pulse response of a system of I=3/2 nuclei which experience identical first-order quadrupole splitting is investigated using the density matrix method. A general expression is derived for the time evolution of the in-phase magnetization following a rectangular pulse applied at the center line frequency. The maximum amplitude of the magnetization associated with the center line, and the length of pulse that gives rise to it, are calculated as a function of the ratio of the quadrupole splitting to the amplitude of the rf field. Data obtained for 23Na in a single crystal of NaNO3 are in fairly good agreement with the theoretical form. The theory has been extended to the case where the nuclei are situated at equivalent sites in a polycrystalline sample. The length of pulse that maximizes the amplitude of the FID of 23Na in a powder sample of NaNO3 has been measured as a function of the amplitude of the rf field. The quadrupole coupling constant, found by fitting the data to the theoretical form, is in very good agreement with the accepted value. It is proposed that this method can be widely used to measure the quadrupole coupling constants of I=3/2 nuclei.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451378
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  • 2
    Electronic Resource
    Electronic Resource
    Filamentation instability of a self-pinched hollow electron beam (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 3074-3083 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Filamentation stability properties of a self-pinched hollow electron beam propagating through a collisional plasma channel are investigated within the framework of linearized Vlasov–Maxwell equations, assuming that the beam is thin and that the equilibrium and perturbed space-charge fields are neutralized by background plasma. It is further assumed that the perturbations are well tuned with kβbc+lωb and satisfy la(very-much-less-than)R0, where l and k are the azimuthal and axial wavenumbers, βbc and ωb are the axial velocity and the rotational frequency of the beam, and 2a and R0 are the thickness and mean radius of the beam. From the stability analysis, two distinctive unstable mechanisms are identified: the return-current driven instability and the resistively driven instability. It is also found that high-l-mode perturbations are easily stabilized by a spread in the canonical angular momentum. Making use of a linearized particle-in-cell code, numerical simulations are performed. The agreement between the analytical results and those of simulations is excellent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865468
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  • 3
    Electronic Resource
    Electronic Resource
    Electromagnetic instability in a quadrupole-focusing accelerator (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 1698-1703 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The addition of helical quadrupole focusing to a modified betatron configuration is shown to give rise to an electromagnetic instability under certain conditions. The instability arises from a three-wave coupling between the helical field, a transverse mode on the beam, and a transverse-electric waveguide mode. An analytic dispersion relation is derived. Several features of the instability are confirmed using three-dimensional computer simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865635
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  • 4
    Electronic Resource
    Electronic Resource
    Theory of response of radiation sensing field-effect transistors in zero-bias operation (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 1216-1217 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Radiation sensing field-effect transistors operated at zero bias show a low-dose response that is roughly linear in the thickness of the gate oxide. The same devices show a thickness squared dependence if a bias is applied during the irradiation. This effect can be explained by examining the effect of diffusion and electron trapping on the buildup of net positive charge in the gate oxide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337369
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  • 5
    Electronic Resource
    Electronic Resource
    Resistive filamentation of self-pinched electron beams (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 577-584 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for resistive filamentation of a self-pinched slab electron beam is presented. The lowest-order modes are found to consist of a body mode which leads to bunching of the beam, and a surface mode which leads to rigid rippling of the beam. The dispersion relations for these modes are compared to results from a linearized particle simulation code. The analytic model and simulation code are applied to the interpretation of a recent experiment in which filamentation was observed in a self-pinched annular electron beam propagating in low-pressure air.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337450
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  • 6
    Electronic Resource
    Electronic Resource
    Time-resolved optical emissions from high-current relativistic electron beams propagating in 150-mTorr air (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 1866-1871 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of a time-resolved study of optical emissions from high-current relativistic (6.5 MeV) electron beams propagating in air at a pressure of 150 mTorr are presented. The emissions included N+ lines at λλ4803, 4630, 4552, and 4530 A(ring). Data were obtained on a single-shot basis by simultaneously recording the temporal history of all four ion lines. For propagating electron beam pulses, each ion line exhibited peak intensity a few microseconds after the passage of the 80-ns-wide electron pulse. This behavior is explained on the basis of inductive (magnetic) energy storage in the return current plasma channel. Spatially integrated plasma temperatures are measured to be in the 20 000–30 000 K range, reaching a maximum when the inductive energy storage has gone to zero.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336414
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  • 7
    Electronic Resource
    Electronic Resource
    The elasticity of weakly flocculated suspensions (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 559-566 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monodisperse polystyrene lattices, at high electrolyte concentrations and with an adsorbed layer of nonionic surface active agent, produced weakly flocculated dispersions which sedimented rapidly to give a final sediment concentration of ∼30% by volume. Three lattices were used with particle sizes in the range 1–2 μm. The surface active agent used was C12E6. Optical microscopy of dilute systems showed that dense flocs were formed which were easily disrupted by small shear stresses. Shear wave propagation experiments were used to give the volume fraction dependence of the wave rigidity modulus, G˜, of these systems at high frequency. The high frequency limit to the shear modulus, G(∞), was calculated from the particle pair potential and the particle pair distribution function determined by using one of the current perturbation theories. The interparticle pair potential was calculated from a combination of van der Waals' attraction, and both steric and electrostatic repulsion. Good agreement was obtained between the value of G(∞) obtained from this statistical mechanical analysis and the experimental value of G˜ over the full range of volume fraction studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451580
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  • 8
    Electronic Resource
    Electronic Resource
    Multicomponent cluster ions. I. The proton solvated by CH3CN/H2O (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 4958-4969 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Experimental and ab initio dissociation energies of the (H2O)n(CH3CN)mH+ ions are reported. The experimental energies range from 10–35 kcal/mol. The proton is best stabilized by placing the maximum number of acetonitrile molecules close to the protonated center in such a way that the formation of a network of strong hydrogen bonds is still possible. Other results from this work are: (1) Distinct solvent shells can be distinguished in these complex ions. (2) Mixtures of several isomeric structures are unlikely for n≤4. (3) When a water or an acetonitrile molecule clusters with (H2O)(CH3CN)H+, the proton is transferred from the acetonitrile to the water. (4) Although electrostatic interactions make the dominant contribution to the bonding in these systems, polarization and charge-transfer effects contribute also. (5) There is a cooperativity effect among the hydrogen bonds that leads to extensive changes in geometry and charge distribution as successive hydrogen bonds are formed. (6) The relative complexation energies along a series of reactions correlate with many properties of the electron donor and with several properties of the proton donor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449982
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  • 9
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    Optical image quality and the cone mosaic (1986)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1986-01-31
    Description: Contrary to the orthodox view that optical image quality should "match" the photoreceptor grain, anatomical data from the eyes of various animals suggest that the image quality is significantly superior to the potential resolution of the cone mosaic in most retinal regions. A new theory is presented to explain the existence of this relation and to better appreciate eye design. It predicts that photoreceptors are potentially visible through the natural optics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Snyder, A W -- Bossomaier, T R -- Hughes, A -- New York, N.Y. -- Science. 1986 Jan 31;231(4737):499-501.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/3941914" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Cats ; Humans ; Models, Neurological ; Photoreceptor Cells/*anatomy & histology ; Rats ; Snakes ; Species Specificity ; *Vision, Ocular ; *Visual Perception
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    Structure of pressinoic acid: the cyclic moiety of vasopressin (1986)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1986-06-06
    Description: Arginine vasopressin consists of a 20-membered, disulfide-linked macrocyclic ring system called pressinoic acid to which is attached a COOH-terminal tripeptide. The molecular conformation of pressinoic acid has been determined from single crystal x-ray diffraction data. The 20-membered macrocyclic ring, stabilized by two intramolecular hydrogen bonds, has a type I beta-bend centered on Gln4 and Asn5 and a highly distorted type II' bend centered on Phe3 and Gln4. In vasopressin the Asn5 side chain extends away from the macrocyclic ring system and hydrogen bonds to the terminal tripeptide, but in pressinoic acid the Asn5 side chain lies over the molecule and forms a strong hydrogen bond to the nitrogen of Tyr2. The absence of pressor activity in pressinoic acid may be a result of both the loss of the COOH-terminal tripeptide and the incorrect orientation of the Asn5 side chain. Whether this class of hormones has pressor or oxytocic activity is determined by the orientation of the Tyr2 side chain, that is, whether it is extended away from or over the ring system, respectively. In pressinoic acid, the Tyr2 side chain is in the expected "pressor conformation," that is, extended away from the ring system, and is stabilized through a hydrophobic interaction with the Phe3 side chain. Thus, the conformation of the pressinoic acid molecule partly explains the activity of vasopressin-like hormones.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Langs, D A -- Smith, G D -- Stezowski, J J -- Hughes, R E -- GM32812/GM/NIGMS NIH HHS/ -- HL32303/HL/NHLBI NIH HHS/ -- New York, N.Y. -- Science. 1986 Jun 6;232(4755):1240-2.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/3704648" target="_blank"〉PubMed〈/a〉
    Keywords: *Arginine Vasopressin ; Models, Molecular ; Molecular Conformation ; *Vasopressins ; X-Ray Diffraction
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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