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  • 1
    Electronic Resource
    Electronic Resource
    The pachytene chromosomes of maize as revealed by fluorescence in situ hybridization with repetitive DNA sequences (2000)
    Springer
    Theoretical and applied genetics 101 (2000), S. 30-36 
    Details
    ISSN: 1432-2242
    Keywords: Key words Zea mays ; Pachytene chromosome ; Karyotype ; Repetitive DNA sequence ; Fluorescence in situ hybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A repetitive DNA sequence, ZmCR2.6c, was isolated from maize based on centromeric sequence CCS1 of the wild grass Brachypodium sylvaticum. ZmCR2.6c is 309 bp in length and shares 65% homology to bases 421–721 of the sorghum centromeric sequence pSau3A9. Fluorescence in situ hybridization (FISH) localized ZmCR2.6c to the primary constrictions of pachytene bivalents and to the stretched regions of MI/AI chromosomes, indicating that ZmCR2.6c is an important part of the centromere. Based on measurements of chromosome lengths and the positions of FISH signals of several cells, a pachytene karyotype was constructed for maize inbred line KYS. The karyotype agrees well with those derived from traditional analyses. Four classes of tandemly repeated sequences were mapped to the karyotype by FISH. Repeats 180 bp long are present in cytologically detectable knobs on 5L, 6S, 6L, 7L, and 9S, as well as at the termini and in the interstitial regions of many chromosomes not reported previously. A most interesting finding is the presence of 180-bp repeats in the NOR-secondary constriction. TR-1 elements co-exist with 180-bp repeats in the knob on 6S and form alone a small cluster in 4L. 26S and 5S rRNA genes are located in the NOR and at 2L.88, respectively. The combination of chromosome length, centromere position, and distribution of the tandem repeats allows all chromosomes to be identified unambiguously. The results presented form an important basis for using FISH for physical mapping and for investigating genome organization in maize.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220051445
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  • 2
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    Design of Polymer Processes Using the Coupling of Commercial Simulation Packages Polymers Plus and PREDICI (2001)
    Details
    Publication Date: 2020-03-20
    Language: English
    Type: article , doc-type:article
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    OPUS
  • 3
    Electronic Resource
    Electronic Resource
    Polarization effects in the valence and inner-shell spectra of poly(di-n-hexylsilane) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5925-5933 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The polarized absorption spectra of oriented films of phase-I and phase-II poly(di-n-hexylsilane), PDHS, have been determined in the visible/UV and in the near-edge regions of the C 1s and Si 1s x-ray ionization potentials. The phase-I absorption band at 360 nm is strongly polarized parallel to the direction of the Si chain, whereas the analog of this band in phase II (317 nm) is only weakly polarized in the same direction; this is consistent with partial trans→gauche isomerization of the Si chain in phase II and delocalization of the excitation in part onto disordered n-hexyl groups. Polarized absorption in the vicinity of the Si 1s ionization limit reveals strong polarization of the discrete and continuum transitions in both phase I and phase II, whereas the equivalent spectra taken in the vicinity of the C 1s limit show strong polarization in phase I but little or no polarization in phase II. The x-ray spectra are interpreted as showing that the Si chain and the n-hexyl groups of the polymer are ordered in phase I and are essentially perpendicular to one another, whereas in phase II the n-hexyl chains are disordered while the Si backbone remains relatively fixed in space. The Si 1s electron-yield spectra also display EXAFS interferences which have been transformed to yield Si–Si and Si–C distances in the polymer of 2.37±0.02 and 1.81±0.03 A(ring), respectively. The various discrete and continuum transitions are assigned according to an orbital model, and the visible/UV thermochromism earlier reported for PDHS is now observed in the Si 1s x-ray near-edge spectrum as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454752
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  • 4
    Electronic Resource
    Electronic Resource
    Measurements of two-photon absorption cross sections for liquid benzene and methyl benzenes (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4671-4677 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-photon cross sections of neat benzene and methyl substituted benzenes at various wavelengths for selective excitation were measured by two-photon induced fluorescence spectra for the first time. The results show that the two-photon rate increases rapidly with the frequency of the photon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453781
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  • 5
    Electronic Resource
    Electronic Resource
    Ionization and temperature dependent attachment cross section measurements in C3F8 and C2H3Cl (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2585-2592 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Total ionization and attachment cross sections have been measured in C3F8 at 330 K using an electron beam and a total ion collection technique, calibrated by similar measurements on N2O and Xe. Our total ionization cross section is similar in general shape to a previous measurement of this type, but with typically half the magnitude. The ionization threshold cannot be accurately derived from these measurements, due to severe upward curvature immediately above threshold. The positive-ion signal rises above the background at 13.0±0.1 eV, to be regarded as a lower limit to the true threshold. An overall ionization cross section with a threshold at 13.3 eV is recommended, based on threshold data from photoelectron spectroscopy and the present data between 14 and 80 eV. The room temperature total attachment cross section peaks at 2.8 eV with a value of 1.75×10−17 cm2. This is 14 times smaller than the only other measurement of this type we are aware of. There is much better agreement with two more recently reported values unfolded from swarm experiments. The temperature dependence of the predominant dissociative attachment process, involving F− production, was studied in a different apparatus using a mass filter and ion pulse counting. At 730 K the peak cross section has increased by ∼60% and the threshold is lower by 1.1 eV. This second type of measurement was used to study the predominant dissociative attachment process in C2H3Cl, involving Cl− production. At 290 K this has a threshold at 0.85 eV and a peak at 1.35 eV of 3.2×10−17 cm2, in good agreement with recent work elsewhere. At 850 K the cross section at the peak is 2.6 larger, and lower in energy by 0.33 eV, while at 0 eV it has reached 6×10−18 cm2. At higher temperatures effects ascribed to thermal dissociation of the C2H3Cl were observed. The implications of the present results regarding the use of these gases in diffuse discharge switches are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455956
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  • 6
    Electronic Resource
    Electronic Resource
    Performance and application of a superlattice infrared photodetector with a blocking barrier (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 943-948 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An infrared photodetector that contains a superlattice structure and a blocking barrier was investigated. The photodetector shows advantages including a low operating voltage (〈0.7 V), wide detection bandwidth, flexible miniband engineering, and in particular, voltage-tunable spectral responsivity. The blocking barrier not only prohibits the dark current but also acts as a high-pass energy filter to tune the spectral responsivity. The zero background peak detectivity of our detector is 3.7×109 cm Hz0.5/W (9.7 μm) at −0.5 V and 2.2×1010 cm Hz0.5/W (6.7 μm) at −0.1 V. Since the spectral responsivity at different biases is independent, temperature sensing is feasible by taking the ratio of the measured photocurrent at different biases. A demonstration of temperature sensing by using our superlattice infrared photodetector with a blocking barrier is also shown in this article. Those results show the superlattice is a simple and efficient structure for the design of a multicolor infrared photodetector. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1430887
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  • 7
    Electronic Resource
    Electronic Resource
    Photothermal ionization spectroscopy of shallow nitrogen donor states in 4H–SiC (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3800-3805 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photothermal ionization spectroscopy (PTIS) measurements were carried out on a free-standing, high purity and high quality 4H–SiC epitaxial layer at various temperatures. The two step photothermal ionization process is clearly reflected in the temperature dependence of the photoconductivity. The PTI spectrum at a temperature of 25.6 K exhibits one order of magnitude higher energy resolution than the infrared absorption spectra of 4H–SiC bulk material. It reveals five strong, well resolved electronic transition lines associated with the shallow nitrogen donor. The ionization energy of the shallow nitrogen donor is deduced to be 60.2±0.5 meV based on experimental results. Furthermore, PTI magnetospectroscopy measurements were performed to investigate the symmetry properties of these transitions in Faraday configuration. No linear Zeeman splitting is observed, however, these lines show a diamagnetic shift. It indicates that the excited states of the shallow nitrogen donor are nondegenerate at zero magnetic field, which is consistent with the fact that the effective mass tensor of 4H–SiC has three different diagonal components. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372417
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  • 8
    Electronic Resource
    Electronic Resource
    Two-photon (vacuum ultraviolet + visible) spectroscopy of argon, krypton, xenon, and molecular hydrogen (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5429-5441 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-photon transitions have been examined in argon, krypton, xenon, and molecular hydrogen using a coherent vacuum ultraviolet (VUV) photon at a fixed wavelength of 118 nm and a tunable photon from a dye laser. The 118 nm VUV photon is produced by third harmonic generation in xenon using UV light at 355 nm from a frequency tripled Nd:YAG laser. Though the VUV intensity is very weak, (∼100 nJ per pulse) it was utilized very efficiently since most of VUV photons in the ionization region were absorbed. Spectra were obtained in the region of 12.5 to 13.5 eV and the corresponding two-photon rate constants were calculated. This is the first time that coherent VUV light has been employed with tunable visible light for the production of two-photon spectra and the measurement of two-photon rates. The two-photon ionization rate of xenon was measured using photons at fixed wavelengths of 118 and 355 nm. A new parameter is proposed for direct comparison of the data from various two-photon experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455595
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  • 9
    Electronic Resource
    Electronic Resource
    Mechanisms and control of beam halo formation in intense microwave sources and accelerators : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2203-2214 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Halo formation and control in space-charge-dominated electron and ion beams are investigated in parameter regimes relevant to the development of high-power microwave (HPM) sources and high-intensity electron and ion linear accelerators. In particular, a mechanism for electron beam halo formation is identified in high-power periodic permanent magnet (PPM) focusing klystron amplifiers. It is found in self-consistent simulations that large-amplitude current oscillations induce mismatched beam envelope oscillations and electron beam halo formation. Qualitative agreement is found between simulations and the 50 MW 11.4 GHz PPM focusing klystron experiment at Stanford Linear Accelerator Center (SLAC) (D. Sprehn, G. Caryotakis, E. Jongewaard, and R. M. Phillips, "Periodic permanent magnetic development for linear collider X-band klystrons," Proceedings of the XIXth International Linac Conference, Argonne National Laboratory Report ANL-98/28, 1998, p. 689). Moreover, a new class of cold-fluid corkscrewing elliptic beam equilibria is discovered for ultrahigh-brightness, space-charge dominated electron or ion beam propagation through a linear focusing channel consisting of uniform solenoidal magnetic focusing fields, periodic solenoidal magnetic focusing fields, and/or alternating-gradient quadrupole magnetic focusing fields in an arbitrary arrangement including field tapering. As an important application of such new cold-fluid corkscrewing elliptic beam equilibria, a technique is developed and demonstrated for controlling of halo formation and beam hollowing in a rms-matched ultrahigh-brightness ion beam as it is injected from an axisymmetric Pierce diode into an alternating-gradient magnetic quadrupole focusing channel. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874042
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  • 10
    Electronic Resource
    Electronic Resource
    Equilibrium and stability properties of self-organized electron spiral toroids (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4441-4449 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A cold-fluid model for a self-organized electron spiral toroid (EST) is presented. In the present model, the electrons are assumed to undergo energetic spiral motion along a hollow torus with a fixed ion background, the electron mean free path is assumed to be long compared with the torus size, and the minor radius of the EST is assumed to be small compared with the major radius. Using this model, the equilibrium and stability properties of the electron flow in the self-organized EST are analyzed. It is found that a class of self-organized EST equilibria exists with or without an externally applied toroidal magnetic field. It is shown that in the absence of any applied toroidal magnetic field, the EST equilibria are stable at high electron densities (i.e., at high toroidal self-magnetic fields), although they are unstable at low electron densities (i.e., at low toroidal self-magnetic fields). © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1400792
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