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  • 1
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    A specialized metabolic network selectively modulates Arabidopsis root microbiota (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2019
    Description: 〈p〉Plant specialized metabolites have ecological functions, yet the presence of numerous uncharacterized biosynthetic genes in plant genomes suggests that many molecules remain unknown. We discovered a triterpene biosynthetic network in the roots of the small mustard plant 〈i〉Arabidopsis thaliana.〈/i〉 Collectively, we have elucidated and reconstituted three divergent pathways for the biosynthesis of root triterpenes, namely thalianin (seven steps), thalianyl medium-chain fatty acid esters (three steps), and arabidin (five steps). 〈i〉A. thaliana〈/i〉 mutants disrupted in the biosynthesis of these compounds have altered root microbiota. In vitro bioassays with purified compounds reveal selective growth modulation activities of pathway metabolites toward root microbiota members and their biochemical transformation and utilization by bacteria, supporting a role for this biosynthetic network in shaping an 〈i〉Arabidopsis-〈/i〉specific root microbial community.〈/p〉
    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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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio calculations of dissociative electronic states of ClCN: Implications to the photodissociation dynamics of the cyanogen halides (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 331-340 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio configuration interaction calculations with full geometric optimization along the Cl–CN dissociation coordinate have been carried out for several electronic states of ClCN. The calculations treat all low-lying singlet and triplet states and yield the vertical transition probabilities and oscillator strengths, as well as angular dependences near the Franck–Condon (FC) region and least energy paths for several electronic states as a function of rCCl. We find that the low-lying excited states derive from three electronic configurations: π3σ*, π3π*, and σπ4σ*. The lowest excited triplet and singlet states derive from the π3σ* configuration and give rise to bent 1,3A' and 1,3A‘ states. States arising from the π3π* configuration are linear (Σ and Δ states). There is evidence of surface crossings along the reaction coordinate between triplet states arising from the π3π* configuration and those arising from the π3σ* and σπ4σ* configurations. These crossings can be induced by slight bending of ClCN causing lowering of the symmetry. The calculated vertical excitation energies are in good agreement with features of the absorption spectrum, and suggest that the A continuum of ClCN involves transitions to the 2 1A' and 1 1A‘ states. The implications to the photodissociation dynamics of the cyanogen halides are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460347
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  • 3
    Electronic Resource
    Electronic Resource
    Two-level systems and low-temperature glass dynamics: Spectral diffusion and thermal reversibility of hole-burning linewidths (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4145-4158 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Intermediate time-scale time-dependent hole-burning measurements are reported on three glassy organic systems which undergo spectral diffusion: cresyl violet in ethanol at 1.30 and 2.13 K, resorufin in ethanol at 2.13 K, and resorufin in glycerol at 2.13 K. The hole width is observed to broaden on a log time scale from 0.1 to 5000 s for each ethanol system while no broadening is observed in the system of resorufin in glycerol. A detailed theoretical treatment is introduced which allows the raw data to be converted to the fluctuation rate distribution of the underlying modes responsible for dephasing. Using this theory, the broadening in ethanol is found to be the result of a distribution of glassy modes which is Gaussian on a log R scale with a center rate at ∼0.02 s−1. In addition, temperature cycling hole-burning results are reported on the system cresyl violet in ethanol. A hole is burned at 1.30 K and detected before, during, and after a temperature cycle to 2.13 K and back. The hole width is observed to broaden at the high temperature and then narrow again in a completely reversible manner when the temperature is again lowered. Theoretical calculations show this behavior to be entirely consistent with the tunneling two-level-system (TLS) model of glass dynamics but incompatible with other models such as particle or defect diffusion. The cycling data is shown to fall exactly on the theoretical curve calculated from the TLS model using no adjustable parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457773
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  • 4
    Electronic Resource
    Electronic Resource
    The electronic spectrum of NOCl: Photofragment spectroscopy, vector correlations, and ab initio calculations (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3903-3914 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic absorption spectrum of NOCl in the region 620–180 nm is assigned by using vector properties of the NO photofragment and the results of ab initio calculations at the CI level. In assigning the electronic spectrum, we take into account the recoil anisotropy, rotational alignment, and Λ-doublet populations of NO, as well as the calculated vertical excitation energies, oscillator strengths, and the nature of the orbitals involved in the transitions. In the experiments, we use expansion-cooled samples and measure the recoil anisotropy parameters from the Doppler profiles of selected NO A 2Σ+←X 2Π rotational lines. The alignment parameters and Λ-doublet populations are derived from the rotational spectra using different laser polarizations and excitation–detection geometries. The theoretical calculations treat all low-lying singlet and triplet states. The calculations yield least energy paths for the excited states, with optimized rNO and ClNO angle as a function of rClN, as well as the angular dependences of the potentials and oscillator strengths of the singlet–singlet transitions. The following assignments are proposed for the main absorption bands: (1) E band—T1(1 3A‘)←S0(1 1A'); the transition borrows intensity by mixing with remote singlet states, predominantly the 4 1A' state; (2) D and C bands—S1(1 1A‘)←S0(1 1A'); the C band corresponds to excitation of ν'1 in S1; (3) B band—S3(2 1A')←S0(1 1A'); (4) A band—S5(4 1A')→S0(1 1A'). The assignments proposed here are in full agreement with all the experimental observations and the results of the calculations. Despite the shallow minima calculated for the T1 and S1 surfaces, dissociation on all the surfaces is fast, and the implications of the results to the dissociation dynamics are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455801
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  • 5
    Electronic Resource
    Electronic Resource
    Elimination of loading reverberation in the split Hopkinson torsional bar (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 5298-5304 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The loading reverberation is a multiple wave effect on the specimen in the split Hopkinson torsional bar (SHTB). Its existence intensively destroys the microstructure pattern in the tested material, and therefore, interferes with the study correlating the deformed microstructure to the macroscopic stress–strain response. This paper discusses the problem of the loading reverberation and its effects on the post-mortem observations in the SHTB experiment. The cause of the loading reverberation is illustrated by a stress wave analysis. The modification of the standard SHTB is introduced, which involves attaching two unloading bars at the two ends of the original main bar system and adopting a new loading head and a couple of specially designed clutches. The clutches are placed between the main bar system and the unloading bars in order to lead the secondary loading wave out of the main bar system and to cut off the connection in a timely manner. The loading head of the standard torsional bar was redesigned by using a tube-type loading device associated with a ratchet system to ensure the exclusion of the reflected wave. Thus, the secondary loading waves were wholly trapped in the two unloading bars. The wave recording results and the contrasting experiments for examining the post-mortem microstructure during shear banding both before and after the modification highly support the effectiveness of the modified version. The modified SHTB realizes a single wave pulse loading process and will become a useful tool for investigating the relation between the deformed microstructure and the macroscopic stress–strain response. It will play an important role especially in the study of the evolution of the microstructure during the shear banding process. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146102
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  • 6
    Electronic Resource
    Electronic Resource
    Simple and convenient nonoptical shear force sensor for shear force and near-field optical microscopes (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2731-2733 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple, compact, and inexpensive method for shear force distance regulation is presented. A single piezoelectric cantilever is employed to both dither a fiber probe and to detect the decrease in piezotension-induced voltage as it approaches the sample surface. On resonance, the large piezotension-induced voltage (∼0.2 mV/nm) allows for simple electronics to be used. It is expected to find application both in shear force microscopy and for shear force distance regulation in near-field optical microscopy. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125131
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  • 7
    Electronic Resource
    Electronic Resource
    High-dielectric-constant ceramic-powder polymer composites (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3804-3806 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A ceramic-powder polymer composite, making use of a relaxor ferroelectric polymer that has a high room-temperature dielectric constant as the matrix, is developed. The experimental data show that the dielectric constant of the composites with Pb(Mg1/3Nb2/3)O3–PbTiO3 powders can reach more than 250 with weak temperature dependence. In addition, the composites under a proper preparation procedure exhibit a high breakdown field strength (〉120 MV/m), leading to a maximum energy storage density of more than 15 J/cm3. Experimental results also indicate that the high electron irradiation does not have much effect on the dielectric behavior of Pb(Mg1/3Nb2/3)O3–PbTiO3 powders, possibly due to the relaxor nature of the ceramic. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126787
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  • 8
    Electronic Resource
    Electronic Resource
    Spectroscopy and dynamics of fast evolving states (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 6763-6774 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100171a007
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  • 9
    Electronic Resource
    Electronic Resource
    Factors influencing tissue culture responses of mature seeds and immature embryos in turf-type tall fescue (2001)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 120 (2001), S. 0 
    Details
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In an effort to optimize tissue culture responses of turf-type tall fescue for genetic transformation, the effects of five culture medium supplements on tissue culture responses were investigated with immature embryos and mature seeds of an elite cultivar, ‘Coronado’, as explant tissues. For both explants, calli induced on 6-benzylaminopurine (BAP)-containing medium had significantly improved regeneration ability. The optimal concentration of BAP for the induction of regenerable callus from mature seeds was 0.1 mg/l. Thidiazuron also improved callus regeneration frequency of mature seeds. Casein hydrolysate, L-proline and myo-inositol improved callus induction of immature embryos but not mature seeds. They did not improve callus regeneration frequencies with either explant tissue. By simply slicing the mature seeds into two halves longitudinally, the callus induction frequencies, as well as the corresponding overall plant regeneration frequencies, were increased approximately three- to six-fold in all three combinations of 2,4-dichlorophenoxyacetic acid and BAP in callus induction media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1439-0523.2001.00594.x
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  • 10
    Electronic Resource
    Electronic Resource
    Probing organic glasses at low temperature with variable time scale optical dephasing measurements (1990)
    s.l. : American Chemical Society
    Chemical reviews 90 (1990), S. 439-457 
    Details
    ISSN: 1520-6890
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cr00101a001
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