Effectiveness Of Energy Transfer Research Articles

Elucidation of the timescales and origins of quantum electronic coherence in LHCII

Photosynthetic organisms harvest sunlight with near unity quantum efficiency. The complexity of the electronic structure and energy transfer pathways within networks of photosynthetic pigment-protein complexes often obscures the mechanisms behind the efficient light-absorption-to-charge conversion process. Recent experiments, particularly using two-dimensional spectroscopy, have detected long-lived quantum coherence, which theory suggests may contribute to the effectiveness of photosynthetic energy transfer. Here, we present a new, direct method to access coherence signals: a coherence-specific polarization sequence, which isolates the excitonic coherence features from the population signals that usually dominate two-dimensional spectra. With this polarization sequence, we elucidate coherent dynamics and determine the overall measurable lifetime of excitonic coherence in the major light-harvesting complex of photosystem II. Coherence decays on two distinct timescales of 47fs and ~800fs. We present theoretical calculations to show that these two timescales are from weakly and moderately strongly coupled pigments, respectively.

Detrimental Effect of Fast Neutrons on Cultured Immature Rat Hippocampal Cells: Relative Biological Effectiveness ofIn VitroCell Death Indices

This in vitro study compared the detrimental effect and relative biological effectiveness (RBE) of high-linear energy transfer (LET) fast neutrons on rat immature hippocampal cultured cells with those of low-LET γ rays. Immature hippocampal cells were exposed to fast neutrons or γ rays. Cytotoxicity and cell viability were analyzed using a lactate dehydrogenase (LDH)-release assay and a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay, respectively. The cytotoxicity and cell viability with fast neutrons or γ rays varied in a dose-dependent pattern. In the LDH release and MTT assay indices, the RBEs of fast neutrons were approximately 2.35 and 2.42, respectively. Fast neutrons markedly induced apoptotic changes in immature hippocampal cells with increased expression of active caspase-3 and cleaved poly(ADP-ribose) polymerase. Increased cytotoxicity and decreased cell viability in immature hippocampal cells were seen in a dose-dependent pattern after fast-neutron and γ irradiation. Fast neutrons have a higher RBE for cell death indices than γ rays.

Analysis of segmental kinetic energy in cricket bowling

Fast bowling in cricket is an athletic motion requiring the coordination of multiple body segments in order to release a ball at high speed. The application of the kinetic link principle to bowling proposes that the optimal coordination of movement actuation follows a proximal to distal sequence, allowing the systematic and progressive transfer of angular momentum from the larger, heavier body segments to the smaller distal segments. An analysis of segmental kinetic energy potentially provides information on the order of segmental sequencing and the effectiveness of energy transfer between the segments throughout the kinetic link chain. However, there has been no calculation of segmental kinetic energy in cricket fast bowling. In this study, 34 fast bowlers (22.2±3.9 years) of premier grade level and above were tested using a three-dimensional motion analysis system (240Hz). Based on the range of measured balls (27.0 m s-1 to 35.6 m s-1), the sample was divided into four speed group categories: slow-medium, medium, medium-fast and fast. With exception of the fast group relative to medium-fast group, each faster group tended to have higher segmental kinetic energies. Although there were no clearly discernible sequencing differences between bowling speed groups, the temporal occurrences of peak segment kinetic energies showed that bowlers exhibited a general order of proximal to distal sequencing with the larger heavier proximal segments having the highest energy and activated first. In general, there is an approximate proximal to distal sequence in cricket bowling, which indicates that bowlers of varying speed levels first produce high kinetic energies in their trunk segments before circumducting the bowling arm during the acceleration phase.

Linking principles of soil formation and flow regimes

Summary Preferential flow (PF) is a fundamentally important soil hydrologic process that controls a variety of soil physical, chemical, and biological functions. However, the lack of theory in this field and the existence of conceptual and technological bottlenecks continue to hinder the advancement of PF modeling and prediction. This paper explores three theoretical perspectives on the relationships between pedogenesis and flow regimes in field soils. First, we examine non-equilibrium thermodynamics as applied to open dissipative field soils with continuous energy inputs and mass exchanges with the surrounding environment. The dual-partitioning of pedogenesis (dissipating and organizing processes) is consistent with the theory of dissipative structure, which explains the genesis and evolution of soil architecture (structure + matrix) and organized heterogeneity found in various soils. Such organized heterogeneity leads to widespread potential for PF occurrence. Second, we investigate constructal theory to explain the tendency for dual-flow regimes in soils – one with high resistivity (Darcy flow) and the other with low resistivity (PF) – together, they form PF configuration that provides the least global flow resistance. This theory is applied to explain some general characteristics of weathering processes and related flow regime changes, which are supported by limited chronologic data from the literature on subsoil’s saturated hydraulic conductivity decrease after a soil reaches a certain age. Third, the theory of evolving networks sheds light on a variety of PF networks observed in field soils, which increase the effectiveness of energy and mass transfer in the subsurface. This is because networks are a part of the organization resulting from the minimum energy dissipation principle and far-from-equilibrium thermodynamics. All the three theories discussed support the notion that the potential for PF occurrence in field soils is likely universal. However, controversies and challenges associated with these theories require further efforts to rigorously test their applicability in natural soils and to formulate explicit quantitative relationships between PF occurrence and its controls. The principle of soil formation and evolution provides a useful guide to this endeavor.

High Relative Biologic Effectiveness of Carbon Ion Radiation on Induction of Rat Mammary Carcinoma and its Lack of H- ras and Tp53 Mutations

The high relative biologic effectiveness (RBE) of high-linear energy transfer (LET) heavy-ion radiation has enabled powerful radiotherapy. The potential risk of later onset of secondary cancers, however, has not been adequately studied. We undertook the present study to clarify the RBE of therapeutic carbon ion radiation and molecular changes that occur in the rat mammary cancer model. We observed 7-8-week-old rats (ACI, F344, Wistar, and Sprague-Dawley) until 1 year of age after irradiation (0.05-2 Gy) with either 290 MeV/u carbon ions with a spread out Bragg peak (LET 40-90 keV/mum) generated from the Heavy-Ion Medical Accelerator in Chiba or (137)Cs gamma-rays. Carbon ions significantly induced mammary carcinomas in Sprague-Dawley rats but less so in other strains. The dose-effect relationship for carcinoma incidence in the Sprague-Dawley rats was concave downward, providing an RBE of 2 at a typical therapeutic dose per fraction. In contrast, approximately 10 should be considered for radiation protection at low doses. Immunohistochemically, 14 of 18 carcinomas were positive for estrogen receptor alpha. All carcinomas examined were free of common H-ras and Tp53 mutations. Importantly, lung metastasis (7%) was characteristic of carbon ion-irradiated rats. We found clear genetic variability in the susceptibility to carbon ion-induced mammary carcinomas. The high RBE for carbon ion radiation further supports the importance of precise dose localization in radiotherapy. Common point mutations in H-ras and Tp53 were not involved in carbon ion induction of rat mammary carcinomas.

Large-scale flows and convection at the base of solar convection zone

AbstractDevelopment of convection in sun's outer shell is caused by reduction of effectiveness of energy transfer by radiation. Traditionally, models of solar convection are considered to be axisymmetric on the scale of solar radius. Such models provide basic understanding of convection under solar conditions. However, interpretation of a number of observable large-scale long-lived solar phenomena requires developing a non-axisymmetric approach. We present such a model in which large-scale non-axisymmetry is caused by large-scale flows such as Rossby waves and vortices. We model flows near the base of the solar convection zone. Anelastic approximation is used, which is valid for flow velocities much smaller than local sound speed. Our three-dimensional numerical simulations show that interaction of convection with large-scale flows leads to the establishment of non-axisymmetric large-scale temperature distribution. The interaction also gives rise to large-scale variations of penetration depth of convective plumes. Generation of the magnetic field by large-scale non-axisymmetric flows can explain such solar phenomena as complexes of activity, active longitudes, drifts of large-scale magnetic fields from equator to the poles, and appearance of distinct rotation periods of magnetic fields at some latitudes. We discuss a possibility of detection of large-scale non-axisymmetric flows and temperature distributions associated with them by the methods of helioseismology.

Characterization of a mutant strain of Rhodovulum sulfidophilum lacking the pufA and pufB genes encoding the polypeptides for the light-harvesting complex 1 (B 870)

Contradictory results on the effectiveness of energy transfer from the light harvesting complex 2 (LH2) directly to the reaction center (RC) in mutant strains lacking the core light-harvesting complex 1 (LH1) have been obtained with cells of Rhodobacter capsulatus and Rhodobacter sphaeroides. A LH1(-) mutant of Rhodovulum sulfidophilum, named rsLRI, was constructed by deletion of the pufBA genes, resulting in a kanamycin resistant photosynthetically positive clone. To restore the wild type phenotype, a complemented strain C2 was constructed by inserting in trans a DNA segment containing the pufBA genes. Light-induced FTIR difference spectra indicate that the RC in the rsLRI mutant and in the C2 complemented strains are functionally and structurally identical with those in the wild type strain, demonstrating that the assembly and the function of the RC is not impaired by the LH1 deletion. The photosynthetic growth rate of the rsLRI strain increased with decreasing light intensity. At 50 W m(-2 )no photosynthetic growth was observed. These results indicate that the light energy harvested by the LH2 complex was not or inefficiently transferred to the RC; thus most of the energy necessary for photosynthetic growth is in the LH1(-) strain directly absorbed by the RC. It is supposed that in the mutant strain, RC and LH2 cannot interact in an efficient way.

Electroluminescence from two fluorinated organic emitters embedded in polyvinylcarbazole

Electroluminescence and photoluminescence of two fluorinated dyes emitting in the blue and in the green, blended with polyvinylcarbazole and an oxadiazole compound, are reported. Organic light-emitting diodes realized with about 0.1wt% dye concentration show interesting performances. Excited state complexes reduce the effectiveness of energy transfer in the blue-emitting device while, for the green-emitting device, the main mechanism of exciton generation is based on charge trapping at the emissive dye.

Photoluminescence of Er3+ ions in layers of quasi-ordered silicon nanocrystals in a silicon dioxide matrix

The spectra and kinetics of photoluminescence from multilayered structures of quasi-ordered silicon nanocrystals in a silica matrix were studied for undoped samples and samples doped with erbium. It was shown that the optical excitation energy of silicon nanocrystals could be effectively transferred to Er3+ ions, which was followed by luminescence at a wavelength of 1.5 µm. The effectiveness of energy transfer increased as the size of silicon nanocrystals decreased and the energy of exciting light quanta increased. The excitation of erbium luminescence in the structures was explained based on dipole-dipole interaction (the Forster mechanism) between excitons in silicon nanocrystals and Er3+ ions in silica surrounding them.

Fluorogenic substrates for proteases based on intramolecular fluorescence energy transfer (IFETS)

A prospective class of intramolecular fluorescence energy transfer substrates (IFETS) is described. In contrast to the known chromogenic and fluorogenic substrates that are used widely in the scientific and medical research, IFETS allow to control the enzymatic cleavage at any point of the peptide chain and thus permit simultaneous studies of enzymes of different specificity. We discuss the main types of donor and acceptor, their advantages and drawbacks and the effectiveness of exited-state energy transfer between them. High sensitivity and selectivity of IFETS in the assay of proteinases was demonstrated. They prove to be a very useful and very promising instrument for enzymology and medicine.

Non equilibrium gas-liquid flows in variable cross section ducts

The behaviour of two-phase high velocity flows in variable cross section ducts was investigated using a one-dimensional numerical model developed for the study of the annular flow configuration. Heat, mass, and momentum transfer between the phases during the flow were considered. The validation of the calculation procedure was made with some experimental data for the air-water couple, while the main application concerned the evaluation of momentum transfer from an expanding gas to an entrained liquid stream in droplet form. A liquid metal-gas flow was considered to simulate the process taking place in a plant where electrical power is generated by a liquid metal flowing in a magnetic field (MHD). The effectiveness of energy and momentum transfer between the liquid and the gas phase during the expansion was evaluated and the influence of nozzles with different convergence angles was investigated.

Correlation of steady-state and time-dependent studies of a two-phase isotactic polystyrene gel

Time-resolved fluorescence emission spectra of isotactic polystyrene/benzyl alcohol (iPS/BA) gel annealed at 318K are reported. Time-resolved spectra and analysis of the fluorescence decay parameters on fresh gel, crystalline isotactic polystyrene together with data from the gel allow identification of two excimer components. Good agreement between the steady-state fluorescence emission spectrum with a theoretically predicted excimer emission spectrum, constructed on the basis of a mechanism that assumes the existence of separate domains, was observed. The dependence of the emission intensity of components is discussed in terms of the effectiveness of photo energy transfer and energy migration.

RBE Vs. Dose for Low Doses of High-let Radiations

According to track theory, the relative biological effectiveness (RBE) of high linear energy transfer (LET) radiations varies with cellular radiosensitivity parameters and the radiation environment. Of special interest is that the RBE varies as the dose of high-LET radiation to the power (1/m - 1) where m is the "target number" parameter, which varies from 2-4 in different cell lines. This applies to neutrons as well as to heavy ions at sufficiently low doses such that cells are not activated in the gamma-kill mode; that is, the tracks of single heavy ions are sufficiently far apart so that there are few cases of inter-track inactivation.

STUDY OF LUMINESCENT FORMS OF THE URANYL ION

Abstract—Luminescence spectra and luminescence decay kinetics of uranyl sulphate water and uranyl nitrate acetone solutions of different concentrations have been studied. Similar experiments have been done with uranyl sulphate powder under vacuum. It has been experimentally shown that the hydrolysis of uranyl sulphate in water takes place, and under low salt concentrations (0.1‐4.0 times 10‐4M) a luminescence of a basic form of the photoexcited ion with a tentative structure of UO2OH+* has been observed. The luminescence of the acidic form UO+* has been observed under higher salt concentrations (1–4 times 10‐2M) in water and under any salt concentration in acetone. The acidic form has the characteristic emission spectrum possessing vibrational structure. The luminescence concentrational quenching of both photoexcited uranyl forms and exciplex emission have not been observed. The effect of a number of organic quenchers and molecular oxygen on uranyl luminescence has been studied. There is no luminescence quenching by O2 up to 2 times 106 Pa (20 atm) pressure. The low effectiveness of energy transfer from the photoexcited uranyl forms has been explained in terms of strong steric screening of 5f‐uranium (VI) orbital by oxygen atoms and by external filled up uranium electronic shells.

Fly photoreceptors and temperature: Relative UV-sensitivity is increased by cooling

Intracellular responses from blowfly photoreceptor cells were recorded at various temperatures in order to study the behaviour of the transduction system, with particular reference to spectral sensitivity. with decreased temperature the V-log I functions showed a reduction in amplitude and the responses showed a slowed time course. For double peaked spectral sensitivity function the UV or 350 nm peak was much less dependent on temperature than the peak in the visible region. The higher UV-sensitivity is interpreted in terms of the sensitizing pigment theory to indicate changes in the effectiveness of energy transfer between the two chromophores.

Collision dominated relaxation of electrons in a weakly ionized nitrogen plasma after abrupt change of the electric field

Abstract The investigations are related to the relaxation of the electron component to new stationary states and start from different stationary states, caused by an abrupt change of the electric field in a molecular nitrogen plasma. By numerically solving the time-dependent Boltzmann equation for the electron the temporal evolution of the energy distribution and of resulting macroscopic quantities is obtained. A relaxation time of = 10 9 cm −3 s has been obtained in all cases considered, independent of the eventual presence of vibrationally excited molecules. The results are discussed on the basis of the effectiveness of energy transfer in the collisional processes.

Luminescence yield of ruby with electron excitation

The emission spectra of ruby on electron excitation are investigated for various temperatures and current densities. The luminescence yield of ruby on excitation by an electron beam is determined. The effectiveness of excitation energy transfer from the lattice to the chromium ions is evaluated. The possibility of generation at the depth of electron beam penetration into the crystal is discussed.