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151.
Abstract Phototropism is a common property of plants, but it is not known if different species use the same photoreceptor for their response. We have determined fluence-response relations for phototropism in response to brief, broad-band blue irradiation for four plant species grown under red light (Amaranthus paniculatus, Linum usitatissimum, Vigna radiata and Medicago sativa) and compared these to ones previously obtained for Pisum sativum and Zea mays, grown under similar conditions. Curves for all species showed a bell-shaped dependence on fluence, a characteristic of first positive curvature as originally defined for the Avena coleoptile, and had a similar optimal fluence, near 3 H.mol m?2. We have obtained an action spectrum in the blue and UV spectral regions for first positive phototropism of the hypocotyl of alfalfa grown under red light. Fluence-response curves at wavelengths between 300 and 500 nm were nearly identical in shape and magnitude; whereas below 300 nm, their slopes and maximum curvatures were reduced. The action spectrum showed that activity rose sharply at wavelengths below 500 nm, peaked at 450 nm with shoulders on either side of that peak, and had lesser peaks at 380 and, in the far ultraviolet, at 280 nm. This action spectrum was very similar to ones in the literature (obtained between 350 and 500 nm) for first and second positive phototropism of oat coleoptiles. We conclude that the same photoreceptor mediates phototropism in oat and alfalfa. 相似文献
152.
Patrick E. Cassidy C. Greg Johnson Charles J. Neef Isaac Jhingree Tejraj M. Aminabhavi 《Journal of polymer science. Part A, Polymer chemistry》1991,29(9):1313-1317
Pyromellitic dianhydride (PMDA) was condensed with different aromatic diacetic acids via a Perkin reaction to produce new polymers containing the benzylidenephthalide group in the backbone. Yields ranged from 50 to 90% with inherent viscosities ranging from 0.07 to 0.37 dL/g. Polymerizations at 275°C for 4 h using p-phenylenediacetic acid and PMDA gave the polymer with highest inherent viscosity. However, polymerization under identical conditions of p,p′-diphenyl ether diacetic acid, each with PMDA, yielded poor results. For these two monomers the best polymerization conditions were 250°C for 8 h. In general, the most thermally stable polymer was derived from the diphenyl ether diacetic acid monomer (308°C). This polymer was obtained in highest yields and gave the greatest amount of pyrolytic residue in argon (67%). 相似文献
153.
Alexandru D. Asandei Yanhui Chen Isaac W. Moran Gobinda Saha 《Journal of organometallic chemistry》2007,692(15):3174-3182
Cp2TiCl is the first example of a single electron transfer (SET) agent that both provides initiating radicals from three different types of functionalities (i.e. radical ring opening of epoxides and reduction of aldehydes and peroxides) and doubles as mediator for the living radical polymerization of styrene (St) by reversibly endcapping the growing polymer chains. An initiator (I) comparison was performed using 1,4-butanediol diglycidyl ether (BDE), benzaldehyde (BA) and benzoyl peroxide (BPO) as models. The investigation of the effect of reaction variables was carried out over a wide range of experimental conditions ([Cp2TiCl2]/[I] = 0.5/1-4/1; [Zn]/[Cp2TiCl2] = 0.5/1-3/1, [St]/[I] = 50/1-400/1 and T = 60-130 °C) to reveal living polymerization features such as a linear dependence of molecular weight on conversion and narrow molecular weight distribution (Mw/Mn) for each initiator class. However, progressively lower polydispersities and larger initiator efficiencies are obtained with increasing the [Cp2TiCl2]/[I] and [Zn]/[Cp2TiCl2] ratios and with decreasing temperature. Accordingly, optimum conditions correspond to [St]/[I]/[Cp2TiCl2]/[Zn] = [50-200]/[1]/[2-3]/[4-6] at 70-90 °C. By contrast to peroxides, aldehydes and the more reactive epoxides provide alcohol end groups useful in block or graft copolymers synthesis. 相似文献
154.
Magdassi S Grouchko M Toker D Kamyshny A Balberg I Millo O 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10264-10267
We demonstrate that metallic rings formed spontaneously at room temperature via evaporation of aqueous drops containing silver nanoparticles (20-30 nm in diameter) exhibit high electrical conductivity (up to 15% of that for bulk silver). The mechanism underlying this self-assembly phenomena is the "ring stain effect", where self-pinning is combined with capillary flow to form a ring consisting of close-packed metallic nanoparticles along the perimeter of a drying droplet. Our macroscopic and microscopic (applying conductive atomic force microscopy) transport measurements show that the conductivity of the ring, which has a metallic brightness, is orders of magnitude larger than that of corresponding aggregates developed without the ring formation, where high conductivity is known to appear only after annealing at high temperature. 相似文献
155.
We examine the integrability of two models used for the interaction of long and short waves in dispersive media. One is more classical but arguably cannot be derived from the underlying water wave equations, while the other one was recently derived. We use the method of Zakharov and Schulman to attempt to construct conserved quantities for these systems at different orders in the magnitude of the solutions. The coupled KdV–NLS model is shown to be nonintegrable, due to the presence of fourth-order resonances. A coupled real KdV–complex KdV system is shown to suffer the same fate, except for three special choices of the coefficients, where higher-order calculations or a different approach are necessary to conclude integrability or the absence thereof. 相似文献
156.
157.
A topological spaceX is called weakly first countable, if for every pointx there is a countable family {C
n
x
|n ∈ω} such thatx ∈C
n
+1x
⊆C
n
x
and such thatU ⊂X is open iff for eachx ∈U someC
n
x
is contained inU. This weakening of first countability is due to A. V. Arhangelskii from 1966, who asked whether compact weakly first countable
spaces are first countable. In 1976, N. N. Jakovlev gave a negative answer under the assumption of continuum hypothesis. His
result was strengthened by V. I. Malykhin in 1982, again under CH. In the present paper we construct various Jakovlev type
spaces under the weaker assumption b=c, and also by forcing.
The second author was supported by the Ben-Gurion University Center for Advanced Studies in Mathematics, Be’er Sheva.
The third author was supported by OTKA grant no. 37758 of Hungary. 相似文献
158.
Isaac Choi Zhigao Shen Dr. Emanuel Ronge Dr. Volker Karius Prof. Dr. Christian Jooss Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(50):12737-12741
Herein, we disclose a recyclable, hybrid manganese catalyst for site-selective azine C−H activation by weak amide assistance. The novel, reusable catalyst enabled C3–H arylation and C3–H alkylation with ample scope, and was characterized by detailed transmission electron microscopy analysis. 相似文献
159.
160.
The photodissociation dynamics of jet-cooled methylsulfinyl radicals, CH3SO, at 248?nm have been investigated using molecular beam photofragment translational spectroscopy. The primary channel is CH3S?+?O, which occurs via the initially prepared excited CH3SO state by rapid cleavage of the S-O bond to produce ground state products. The minor SO?+?CH3 channel has two components in comparable proportions: a fast feature corresponding to rapid C-S cleavage on the excited state to produce CH3 and electronically excited SO, and a slow feature due to internal conversion of CH3SO followed by statistical dissociation on the ground electronic state. Statistical ground state dissociation also produces small amounts of CH2SO, likely sulfine, and H-atoms. 相似文献