The initial electron transfer rate and protein dynamics in wild type and five mutant reaction centers from Rhodobacter sphaeroides have been studied as a function of temperature (10−295 K). Detailed kinetic measurements of initial electron transfer in Rhodobacter sphaeroides reaction centers can be quantitatively described by a reaction diffusion formalism at all temperatures from 10 to 295 K. In this model, the time course of electron transfer is determined by the ability of the protein to interconvert between conformations until one is found where the activation energy for electron transfer is near zero. In reaction centers with a free energy for electron transfer similar to wild type, the reaction proceeds at least as fast at cryogenic temperatures as at room temperature. This may be because interconversion between conformations at low temperature is restricted to conformations with near zero activation energy (it is not possible to diffuse away from this region of conformational space). In contrast, mutants with a decreased free energy initially find themselves in conformations unfavorable for electron transfer and require more extensive conformational diffusion to achieve a low activation energy conformation. They therefore undergo electron transfer more slowly at 10 K vs 295 K.
The search for a simple, affordable, and rapidly separation method for oil-water mixtures is one of the most serious challenges that the world is facing today. Superhydrophobic, or superoleophilic, materials and surfaces are promising choices for these types of separations. In the present work, pre-wetting of river sand, sea sand and desert sand have been used in a gravity-driven separation of an oil–water mixture. The superoleophobicity properties of these pre-wetted sand materials were found to be good, with a maximum and minimum oil contact angle of about 141.1° for desert sand and 113.8° for sea sand. Also, the relationship between the porosity of the respective sand layer and the water phase separation rate was constructed. As a result of a simple particle size screening, the highest separation rate of sea sand (24.3±2.4 mm/s) was obtained. And this is the highest oil-water separation rate that has ever been achieved for a sand material. In addition to the particle size of sand, the effect by the number of separation cycles, thickness of sand layer, temperature, pH value, salt concentration, and different oil-water mixtures, have also been investigated.
Nitrous oxide (N2O) as a by-product of soil nitrogen (N) cylces, its production may be affected by soil salinity which have been proved to have significant negative effect on soil N transformation processes. The response of N2O production across a range of different soil salinities is poorly documented; accordingly, we conducted a laboratory incubation experiment using an array of soils bearing six different salinity levels ranging from 0.25 to 6.17 dS m−1. With ammonium-rich organic fertilizer as their N source, the soils were incubated at three soil moisture ( θ ) levels—50%, 75% and 100% of field capacity ( θ fc )—for six weeks. Both N2O fluxes and concentrations of ammonium, nitrite and nitrate (NH4+-N, NO2−-N and NO3−-N) were measured throughout the incubation period. The rates of NH4+-N consumption and NO3−-N accumulation increased with increasing soil moisture and decreased with increasing soil salinity, while the accumulation of NO2−-N increased first then decreased with increasing soil salinity. N2O emissions were significantly promoted by greater soil moisture. As soil salinity increased from 0.25 to 6.17 dS m−1, N2O emissions from soil first increased then decreased at all three soil moisture levels, with N2O emissions peaking at electric conductivity (EC) values of 1.01 and 2.02 dS m−1. N2O emissions form saline soil were found significantly positively correlated to soil NO2−-N accumulation. The present results suggest that greater soil salinity inhibits both steps of nitrification, but that its inhibition of nitrite oxidation is stronger than that on ammonia oxidation, which leads to higher NO2−-N accumulation and enhanced N2O emissions in soil with a specific salinity range.
We first report measurement of air laser impulse coupling coefficients as large as 15 dyn/W, obtain with ns-duration 0.53 micrometers (double frequency) laser pulses incident on Al-targets, and compare with that of 1.06 micrometers laser.
The photon-gated intensity effect upon holographic storage for thin layers of polyvinyl alcohol matrices doped methyl orange dyes is investigated. The dynamic curves for grating growing and decay are given for different gating intensity. The time that grating gets to saturation becomes short. The maximum diffraction efficiency of the grating gets little with the rise of gating light intensity. The proper intensity Ar-ion laser can erase grating. The erasing velocity is proportional to erasing light intensity. The modulation transfer function is measured for writing beams having different polarization states.
Abstract It is generally accepted that the absence of recombination reduces the efficacy of natural selection for, or against, mutations. A special case is Muller’s Ratchet (MR) whereby non-recombining genomes experience irreversible fitness decline due to the accumulation of deleterious mutations. MR has been a main hypothesis for sexual reproduction as well as many other biological phenomena. We now ask whether the fitness decline can indeed be stopped if an asexual population turns sexual to become recombining. The possible fitness decline under recombination is referred to as Ohta’s Ratchet (OR). In comparison, MR is more effective in driving fitness reduction than OR, but only in a restricted parameter space of mutation rate, population size and selection. Outside of this space, the two ratchets are equally effective or, alternatively, neither is sufficiently powerful. Furthermore, beneficial mutations can affect the population fitness, which may diverge between the two ratchets, but only in a small parameter space. Since recombination plays a limited role in driving fitness decline, the operation of MR could be far less common in nature than believed. A companion report (see Supplement) surveying the biological phenomena attributed to MR indeed suggests the alternative explanations to be generally more compelling.
A synthesized blue fluorescent protein (BFP) chromophore analogue 2-BFP ((4Z)-4-[(1H-imidazol-2-yl)methylene]-1-methyl-2-phenyl-1H-imidazol-5(4H)-one) displays dual fluorescent emission that arises from the same Z-isomer. The larger Stokes shift emission is a result of excited-state intramolecular proton transfer (ESIPT) mediated by an N-H···N type of hydrogen bond. Compared to other green fluorescent protein (GFP) analogues with ESIPT such as o-HBDI, 2-BFP possesses greatly enhanced quantum yields and much slower proton-transfer rates. In addition, fluorescence up-conversion experiments revealed two rising components of lifetime for the tautomer formation of 2-BFP. The results imply that the relaxation of the N* state in 2-BFP triggers the proton transfer of the molecule. The weaker photoacidity of N-H is proposed to be crucial for these photophysical and photochemical properties. Finally, the ESIPT process in 2-BFP is inhibited in protic solvents (MeOH) or by the formation of metal-chelate complexes, providing insights for further developments and applications of ESIPT molecules.
Using the random telegraph model, we investigate optical dephasing processes arising from Poisson stochastic modulation, we obtain the analytic expression for free-induced decay (FID) and photon-echo decay in the whole range of the stochastic parameters. In the small modulation range, FID or echo-intensity decay varies from single exponential to multiexponential with the increase of frequency modulation. In the large modulation range, FID is a damping oscillation, and the echo intensity decays exponentially with periodical fluctuations. When the modulation is very large the echo-intensity decay tends to go back to an exponential. The ${\mathit{R}}_{1}$(-3/2) echo-intensity decay in ruby at high magnetic fields is calculated based on the analytic expression; the result is compared with experiments and computer simulations. \textcopyright{} 1996 The American Physical Society.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)