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71.
Phytochromes constitute a superfamily of photoreceptor proteins existing in two forms that absorb red (Pr) and far‐red (Pfr) light. Although it is well‐known that the conversion of Pr into Pfr (the biologically active form) is triggered by a Z→E photoisomerization of the linear tetrapyrrole chromophore, direct evidence is scarce as to why this reaction always occurs at the methine bridge between pyrrole rings C and D. Here, we present hybrid quantum mechanics/molecular mechanics calculations based on a high‐resolution Pr crystal structure of Deinococcus radiodurans bacteriophytochrome to investigate the competition between all possible photoisomerizations at the three different (AB, BC and CD) methine bridges. The results demonstrate that steric interactions with the protein are a key discriminator between the different reaction channels. In particular, it is found that such interactions render photoisomerizations at the AB and BC bridges much less probable than photoisomerization at the CD bridge. 相似文献
72.
Farshad?Merrikh-BayatEmail author Meysam?Parvizi 《Applied Physics A: Materials Science & Processing》2016,122(6):602
A new method to realize a discrete memristor is proposed. The device under study consists of a tube filled of aqueous saturated solution of copper sulfate which can be electrolyzed by using two asymmetric copper electrodes, one of which has a considerably smaller cross-sectional area than to the other one. It is shown both theoretically and experimentally that this device has exactly the properties of a memristor if it is designed such that the electrical field and the current density on the thinner electrode when it acts as anode are sufficiently large. Different aspects of the proposed discrete memristor, including pinched hysteresis loop, on-off resistance ratio and memory volatilization, are studied and experimental results are presented. 相似文献
73.
Suberythemal Sun Exposures at Swedish Schools Depend on Sky Views of the Outdoor Environments – Possible Implications for Pupils’ Health
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Peter Pagels Ulf Wester Margareta Söderström Bernt Lindelöf Cecilia Boldemann 《Photochemistry and photobiology》2016,92(1):201-207
More scheduled outdoor stay is increasingly advocated for school children. This study measured 2nd, 5th and 8th graders’ erythemal UV‐exposure in September, March and May at four Swedish schools. We related those exposures, as fractions of total available ambient radiation, to the schools outdoor environments differing in amount of shade, vegetation, and peripheral city‐scape quantified as percentage of free sky view calculated from fish‐eye photographs. Exposures correlated with the sky views (with exceptions in May) and were suberythemal. The exposures were also below the threshold limit of the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) for hazard evaluation of UVR but were potentially enough for adequate vitamin D formation according to a cited model calculation – as illustrated in the results and discussed. The school environments, typical in southern and middle Sweden, offer enough shade to protect children from overexposure during seasons with potentially harmful solar UV radiation. Pupils’ outdoor stay may be extended during September and March. In May extended outdoor stay of the youngest pupils requires a more UVR‐protective environment. 相似文献
74.
A novel method is proposed to estimate the primary tonal frequency of speech. The method is based on singular spectrum analysis. A singular model of a vocalized segment of a speech signal is presented that considers the direct and inverse problems. A study is conducted of the process of singular estimation of the primary tonal frequency of speech. Experimental research is carried out using a model that yields adequacy and reliability estimates. The concept of singular estimation of the primary tonal frequency of speech is introduced. 相似文献
75.
76.
White KN Sen I Szundi I Landaverry YR Bria LE Konopelski JP Olmstead MM Einarsdóttir O 《Chemical communications (Cambridge, England)》2007,(31):3252-3254
Tridentate cross-linked histidine-phenol Cu(ii) ether and ester complexes, chemical analogs of the active site of several heme-copper oxidases, have been synthesized and crystallized. 相似文献
77.
The commensurate superstructures of a NiAs/Ni2In type parent structure, Ni3.32InTe2 and Ni3.12In0.86Te2.14 (q=γ[0 0 1]*, γ=2/3) as well as one dimensionally incommensurate structure of Ni3InTe2 (γ=0.71) were refined from neutron powder diffraction data (Rwp=4.77%, 4.53% and 4.91% for the three structures, respectively, at 298 K). The commensurate structures were refined in the P63/mmc space group (c=3cNiAs). The stacking sequence at the hcp array is -In/Te/Te/- and the trigonal bipyramidal site within the In layer, Ni(2), is partially occupied while it is empty in the Te layers. The octahedral position in between the In and Te layers, Ni(1a), is fully occupied while the octahedral position in between two adjacent Te layers, Ni(1b), is partially occupied. With decreasing In and Ni content, the modulation wave vector, γ, was found to increase continuously until γ=1. From this, crenel functions to describe the whole homogeneity range of the solid solution were constructed with the length of the atomic domains ΔTe=γ (and hence ΔIn=ΔNi=1−γ) and ΔNi(1b)=γ/2 (and hence ΔNi(1a)=1−γ/2) which were then used for the refinement of the incommensurate structure of Ni3InTe2. The corresponding effect in real space is that the single In layers separating double layers of Te occur less frequent when γ in increasing until at γ=1 the CdI2 type structure of Ni1+xTe2 is reached. 相似文献
78.
Natural clays were characterized by XRD, TGA and SEM/EDX, then pressed to pellets and analyzed by impedance measurements under
various defined gas compositions and temperatures. From the Nyquist plot, conductivity values were calculated for the different
clay samples. A strong dependence of the conductivity on the water vapour concentration at low temperatures was found for
all investigated clay samples. Partial substitution of water by methanol led to a decrease in conductivity at low temperatures,
confirming the essential role water plays in the conductivity mechanism at these temperatures. Increasing the temperature
resulted in a decrease in conductivity, until a turn-over point was reached. Beyond this temperature an Arrhenius behaviour
was observed, suggesting a change in the conductivity mechanism.
Paper presented at the 5th Euroconference on Solid State Ionics, Benamádena, Spain, Sept. 13–20, 1998. 相似文献
79.
Lszl Ktai KalyanK. Banerji Istvn Saj Jnos Kristf B. Sreedhar Sndor Holly Gbor Keresztury Antal Rockenbauer 《Helvetica chimica acta》2002,85(8):2316-2327
Tetraamminecopper(2+) bis(permanganate) ([Cu(NH3)4](MnO4)2; 1 ) was prepared, and its properties were studied in both aqueous solution and the solid phase. The presence of H‐bond interactions between the ammonia ligand of the complex cation and an O‐atom of the permanganate ion was detected by IR and Raman methods. The solid‐phase thermal deammoniation of 1 led to an unusual intramolecular redox reaction between the Mn O⋅⋅⋅H N linkage with formation of NH4NO3 and CuMn2O4‐type mixed oxides instead of stepwise deammoniation, even below 100°. The thermal deammoniation of 1 in aqueous solution led, instead of to hydrated copper(2+) bis(permanganate), to the formation of NH4MnO4 ( 2 ). Since the temperature of the thermal deammoniation of 1 is lower than the decomposition temperature of the permanganate ion, the regulated solid‐phase decomposition of 1 allowed preparation of CuMn2O4‐type oxides with mixing of copper and manganese at the atomic level. 相似文献
80.
The synthesis, characterization and voltammetric and spectroelectrochemical properties of newly synthesized metal-free and
metallo phthalocyanines (M = Co, Cu, Zn) containing four dialkylaminophenoxy or trialkylammoniumphenoxy substituents on peripheral
positions have been presented in this work. The new compounds have been characterized by using elemental analysis, UV–Vis,
FT-IR, 1H NMR and MS spectroscopic data. Phthalocyanines with trialkylammoniumphenoxy substituents are soluble in aqueous solution
over a wide pH range, and these compounds are present as aggregated species in solution as confirmed by the blue shift of
Q-bands in their electronic spectra. The electrochemical behavior of the phthalocyanines was investigated by cyclic voltammetry
and differential pulse voltammetry on a platinum-working electrode in DCM and DMSO. The voltammetric and spectroelectrochemical
measurements of the complexes show that while cobalt phthalocyanine gives both ligand- and metal-based redox processes, metal-free,
zinc and copper phthalocyanine complexes give only ligand-based processes in harmony with common phthalocyanine complexes. 相似文献