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Ulrich Ch . Fischer Paul Towner Dieter Oesterhelt 《Photochemistry and photobiology》1981,33(4):529-537
Abstract— Bacteriorhodopsin (BR) from the purple membrane of Haiobacterium halobium contains covalently bound retinal in the 13- cis and all- trans configurations. Several forms of bacteriorhodopsin are known, with different absorption maxima which are designated as BRλmax (nm). At acidic pH, BR605 is formed from BR560. The following sequence of reactions was found, which is initiated by irradiation of BR605 with red light:
An all- trans /13- cis to 9- cis isomerisation occurs in the light induced reaction BR605 ∼ BR500. BR500 seems to contain covalently bound retinal, whereas BR390 contains free retinal. By irradiation with light, BR500, BR450 and BR390 can be reconverted to BR560. 相似文献
An all- trans /13- cis to 9- cis isomerisation occurs in the light induced reaction BR605 ∼ BR500. BR500 seems to contain covalently bound retinal, whereas BR390 contains free retinal. By irradiation with light, BR500, BR450 and BR390 can be reconverted to BR560. 相似文献
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A new survey of all world data on superallowed beta decays provides demanding tests of, and tight constraints on, the weak interaction. In confirmation of the conserved vector current hypothesis, the vector coupling constant G(V) is demonstrated to be constant to better than three parts in 10(4), and any induced scalar current is limited to f(S)=0.0013 in electron rest-mass units. Any possible fundamental scalar current is similarly limited to /C(S)/C(V)/=0.0013. The superallowed data also determine the up-down element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix to be V(ud)=0.9738(4). With Particle Data Group values for V(us) and V(ub), the top-row test of CKM unitarity yields /V(ud)/(2)+/V(us)/(2)+/V(ub)/(2)=0.9966(14); if V(us) comes instead from two recent results on K(e3) decay, this sum becomes 0.9996(11). Either unitarity result can be used to constrain the possible existence of right-hand currents. 相似文献
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A BaTiO3 thin-film electro-optic waveguide modulator with a low half-wave voltage-length product has been demonstrated at near-infrared wavelengths of 1-1.6 microm. Half-wave voltage-length products as small as 0.25 and 0.5 V cm were measured for a 5-mm-long device at wavelengths of 973 and 1561 nm, respectively. The effective electro-optic coefficients were calculated as 420 pm/V at 973 nm and 360 pm/V at 1561 nm. Further improvements in device performance by optimizing the ferroelectric domain structure are anticipated. 相似文献
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Superallowed β-decay provides a sensitive means for probing the limitations of the Electroweak Standard Model. To date, the
strengths (ft-values) of superallowed 0+→0+ β-decay transitions have been determined with high precision from nine different short-lived nuclei, ranging from 10C to 54Co. Each result leads to an independent measure for the vector coupling constant G
V and collectively the nine values can be used to test the conservation of the weak vector current (CVC). Within current uncertainties,
the results support CVC to better than a few parts in 10,000 - a clear success for the Standard Model! However, when the average
value of G
V, as determined in this way, is combined with data from decays of the muon and kaon to test another prediction of the Standard
Model, the result is much more provocative. A test of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix fails by more
than two standard deviations. This result can be made more definitive by experiments that require extremely precise mass measurements,
in some cases on very short-lived (≤100 ms) nuclei. This talk presents the current status and future prospects for these Standard-Model
tests, emphasizing the role of precise mass, or mass-difference measurements. There remains a real challenge to mass-measurement
technique with the opportunity for significant new results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Qiu P Jensen C Charity N Towner R Mao C 《Journal of the American Chemical Society》2010,132(50):17724-17732
We report a general method for preparing nanoparticle clusters (NPCs) in an oil-in-water emulsion system mediated by cetyl trimethylammonium bromide (CTAB), where previously only individual nanoparticles were obtained. NPCs of magnetic, metallic, and semiconductor nanoparticles have been prepared to demonstrate the generality of the method. The NPCs were spherical and composed of densely packed individual nanoparticles. The number density of nanoparticles in the oil phase was found to be critical for the formation, morphology, and yield of NPCs. The method developed here is scalable and can produce NPCs in nearly 100% yield at a concentration of 5 mg/mL in water, which is approximately 5 times higher than the highest value reported in the literature. The surface chemistry of NPCs can also be controlled by replacing CTAB with polymers containing different functional groups via a similar procedure. The reproducible production of NPCs with well-defined shapes has allowed us to compare the properties of individual and clustered iron oxide nanoparticles, including magnetization, magnetic moments, and contrast enhancement in magnetic resonance imaging (MRI). We found that, due to their collective properties, NPCs are more responsive to an external magnetic field and can potentially serve as better contrast enhancement agents than individually dispersed magnetic NPs in MRI. 相似文献
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I. S. Towner 《Nuclear Physics A》1992,540(3-4):478-500
We give a shell-model calculation of the nuclear-structure-dependent axial-vector contribution of the Born graphs to the radiative correction in superallowed Fermi β-decay. The impact of the correction is to give a modest improvement in the test of the conserved-vector-current (CVC) hypothesis, and a slightly smaller value of the quark-mixing matrix element, Vud. The test of the unitary of the first row of the Kobayashi-Maskawa matrix gives: Vud2 + νus2 + Vub2 = 0.9962 ± 0.0016, violating the three-generation standard model. Hints from neutron-only data suggest that nuclear-structure corrections in superallowed Fermi β-decay are still not fully under control. 相似文献
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O. Häusser T.K. Alexander D.L. Disdier A.J. Ferguson A.B. McDonald I.S. Towner 《Nuclear Physics A》1973,216(3):617-628
The α-decay of several unbound levels in 20Ne has been studied by 16O(α, α) elastic and inelastic scattering. A narrow resonance, Γc.m. = 13±4 eV, with Jπ = 5? was found at and is associated with the lowest K = 2? quasirotational band. Several new, narrow resonances were found between Ex = 16.0?18.4 MeV. Reduced α-decay widths have been obtained for the lowest K = 0+, 2? and 0?bands. For states described predominantly by the (8, 2) representation of SU(3) we note a reduction of the reduced widths with increasing spin. Reduced widths of positive parity bands are reviewed. 相似文献