Absorbed Photon Energy Research Articles

Effects of precipitation on photosynthesis and water potential in Andropogon gerardii and Schizachyrium scoparium in a southern mixed grass prairie

In grassland ecosystems, spatial and temporal variability in precipitation is a key driver of species distributions and population dynamics. We experimentally manipulated precipitation to understand the physiological basis for differences in responses of species to water availability in a southern mixed grass prairie. We focused on the performance of two dominant C 4 grasses, Andropogon gerardii Vitman and Schizachyrium scoparium (Michx.) Nash, in treatments that received ambient rainfall, half of ambient rainfall (“drought” treatment), or approximately double ambient rainfall (“irrigated” treatment). Water potentials of S. scoparium were lower than A. gerardii, suggesting superior ability to adjust to water deficit in S. scoparium. Additionally, drought reduced photosynthesis to a greater extent in A. gerardii compared to S. scoparium. Leaf-level photosynthesis rates were similar in ambient and irrigated treatments, but were significantly lower in the drought treatment. Although stomatal conductance was reduced by drought, this was not limiting for photosynthesis. Leaf δ 13C values were decreased by drought, caused by an increase in C i / C a . Chlorophyll fluorescence measures indicated light-harvesting rates were highest in irrigated treatments, and were lower in ambient and drought treatments. Moreover, drought resulted in a greater proportion of absorbed photon energy being lost via thermal pathways. Reductions in photosynthesis came as a result of non-stomatal limitations in the C 4 cycle. Our results provide mechanistic support for the hypothesis that S. scoparium is more drought tolerant than A. gerardii.

Investigation of human teeth with respect to the photon interaction, energy absorption and buildup factor

The effective atomic numbers and electron densities of human teeth have been calculated for total photon interaction ( Z PI eff , Ne PI eff ) and photon energy absorption ( Z PEA eff , Z RW eff Ne PEA eff ) in the energy region 1 keV–20 MeV. Besides, the energy absorption ( EABF ) and exposure ( EBF ) buildup factors have been calculated for these samples by using the geometric progression fitting approximation in the energy region 0.015–15 MeV up to 40 mfp (mean free path). Wherever possible the results were compared with experiment. Effective atomic numbers ( Z PI eff ) of human teeth were calculated using different methods. Discrepancies were noted in Z PI eff between the direct and interpolation methods in the low and high energy regions where absorption processes dominate while good agreement was observed in intermediate energy region where Compton scattering dominates. Significant variations up to 22% were observed between Z PI eff and Z PEA eff in the energy region 30–150 keV which is the used energy range in dental cone beam computed tomography (CBCT) X-ray machines. The Z eff values of human teeth were found to relatively vary within 1% if different laser treatments are applied. In this variation, the Er:YAG laser treated samples were found to be less effected than Nd:YAG laser treated ones when compared with control group. Relative differences between EABF and EBF were found to be significantly high in the energy region 60 keV–1 MeV even though they have similar variations with respect to the different parameters viz. photon energy, penetration depth.

Preparation of Gold Nanoparticle Aggregates and Their Photothermal Heating Property

This report describes simple synthetic strategies to prepare partially aggregated gold nanoparticles (GNPs) and their ability to produce photothermally-induced heating of an aqueous medium upon exposure to broadband light. The formation of various GNPs and their aggregates were accomplished in the absence of surfactants at room temperature. The morphologies, structures, and absorption properties of these GNPs were carefully characterized. Given that the resulting GNPs possessing strong and wide absorption bands fall in the most intense solar radiation spectrum, the photothermally-induced heating of water was examined in the presence of the GNPs via irradiation with a solar simulator (i.e., 100 mW/cm2; 1-sun condition). Our GNPs exhibited a slightly greater increase in the water temperature (3-4 degrees C) than that of conventional citrate-stabilized GNPs. This superior photothermal heating property of our GNPs directly indicated that the intense and broad absorption band effectively improved the conversion of highly absorbed photon energy into heat.

Energy transfer from phosphorescent blue-emitting oxidized porous silicon to rhodamine 110

Nanocomposites consisting of oxidized porous Si (OPSi) impregnated with rhodamine 110 (Rh110) molecules are characterized in terms of luminescence properties. The photoluminescence and its polarization memory strongly indicates a trace of energy transfer from the fast blue luminescence band of OPSi to the green one of Rh110. Time-resolved experiments showed that energy transfer to Rh110 also takes place from the long-lived blue phosphorescence of OPSi. The transfer channel from nonradiative states of OPSi to Rh110 was also found. The ability of OPSi to harvest and transfer absorbed photon energy to a guest is promising for applications in optoelectronics and biology.

Photocatalytic Formation of I−I Bonds Using DNA Which Enables Detection of Single Nucleotide Polymorphisms

By decreasing the HOMO energy gap between the base-pairs to increase the charge conductivity of DNA, the positive charge photochemically generated in DNA can be made to migrate along the π-way of DNA over long distances to form a long-lived charge-separated state. By fine-tuning the kinetics of the charge-transfer reactions, we designed a functionalized DNA system in which absorbed photon energy is converted into chemical energy to form I-I covalent bonds, where more than 100 I(2) molecules were produced per functionalized DNA. Utilizing the fact that charge-transfer kinetics through DNA is sensitive to the presence of a single mismatch that causes the perturbation of the π-stacks, single nucleotide polymorphisms (SNPs) in genomic sequences were detected by measuring the photon energy conversion efficiency in DNA by a conventional starch iodine method.

Impact of the Peltier effect on concentrating photovoltaic cells

Photovoltaic cells convert most of the absorbed photon energy to heat. Removal of the heat by thermal conduction creates a heat flux that is significant in concentrating photovoltaic (CPV) cells subject to high incident radiation flux. The Peltier effect interaction of this heat flux and the electrical current in the cell can either increase or decrease the temperature gradient within the cell. Here we show that the Peltier effect contributes to a measurable change in the temperature gradient in Ge-based CPV cells and therefore this effect should be considered in cell modelling. The effect may also have an impact on the temperature gradient of other photovoltaic cells and of other high power optoelectronic devices.

DNA (6−4) Photolesion Repair Occurs in the Electronic Ground State of the TT Dinucleotide Dimer Radical Anion

(6−4) Photolyases are enzymes utilizing light to repair DNA pyrimidine−pyrimidone photolesions. The first step of enzyme function involves absorption of a photon and electron transfer from a flavin adenine dinucleotide anion (FADH−) to the (6−4) lesion-inducing repair, that is, splitting of the covalently bound nucleobase dimer. Here we demonstrate that the repair mechanism occurs in the electronic ground state of the lesion radical anion because the initially absorbed photon energy is not sufficient to initiate electron transfer and to excite electronically the radical anion of the (6−4) lesion simultaneously.

A Study of Photon Interaction and Photon Energy Absorption Effective Atomic Numbers for Some Amino Acids

Photon interaction (ZPIeff) and photon energy absorption (ZPEAeff) effective atomic numbers have been computed for some amino acids, namely, alanine (C3H7NO2), arginine (C6H14N4O2), aspartic acid (C4H7NO4), glycine (C2H5NO2), isoleucine (C6H13NO2), serine (C3H7NO3), and valine (C5H11NO2) in the energy range of 1 keV to 20 MeV. It has been observed that the effective atomic numbers (photon interaction and photon energy absorption) for the selected amino acid differ only in the lower-energy region (5 to 100 keV) and the maximum deviation is observed at ∼30 keV. Further, the maximum values of the effective atomic numbers for photon interaction and photon energy absorption were observed to be at different energies. For the photon interaction effective atomic number, the maximum for the selected amino acids appears at ∼5 keV, whereas the photon energy absorption effective atomic number has its maximum for the selected amino acids at ∼15 keV. Among the selected amino acids, aspartic acid shows the maximum effective atomic number, whereas the least effective atomic numbers were observed for isoleucine.

Spectral dependency of superconducting single photon detectors

We investigate the effect of varying both incoming optical wavelength and width of NbN nanowires on the superconducting single photon detectors (SSPD) detection efficiency. The SSPD are current biased close to critical value and temperature fixed at 4.2 K, far from transition. The experimental results are found to verify with a good accuracy predictions based on the “hot spot model,” whose size scales with the absorbed photon energy. With larger optical power inducing multiphoton detection regime, the same scaling law remains valid, up to the three-photon regime. We demonstrate the validity of applying a limited number of measurements and using such a simple model to reasonably predict any SSPD behavior among a collection of nanowire device widths at different photon wavelengths. These results set the basis for designing efficient single photon detectors operating in the infrared (2–5 μm range).

Standard photoacoustic spectrometer: Model and validation using O2 A-band spectra

We model and measure the absolute response of an intensity-modulated photoacoustic spectrometer comprising a 10 cm long resonator and having a Q-factor of approximately 30. We present a detailed theoretical analysis of the system and predict its response as a function of gas properties, resonance frequency, and sample energy transfer relaxation rates. We use a low-power continuous wave laser to probe O(2) A-band absorption transitions using atmospheric, humidified air as the sample gas to calibrate the system. This approach provides a convenient and well-characterized method for calibrating the absolute response of the system provided that water-vapor-mediated relaxation effects are properly taken into account. We show that for photoacoustic spectroscopy (PAS) of the O(2) A-band, the maximum conversion efficiency of absorbed photon energy to acoustic energy is approximately 40% and is limited by finite collision-induced relaxation rates between the two lowest-lying excited electronic states of O(2). PAS also shows great potential for high-resolution line shape measurements: calculated and experimental values for the PAS system response differ by about 1%.

Impact of the Thomson effect on concentrating photovoltaic cells

Photovoltaic cells convert most of the absorbed photon energy to heat. Removal of the heat by thermal conduction creates a temperature gradient that is significant in concentrating photovoltaic (CPV) cells subject to high incident radiation flux. The Thomson effect interaction between this temperature gradient and the electrical current in the cell can either increase or decrease the electrical power output of the cell. Here we show that the Thomson effect has a non-negligible impact on the conversion efficiency of Ge-based CPV cells, which is comparable to the impact of typical series resistance, and therefore this effect should be considered in cell modeling. The effect may also have a significant impact on the performance of other high power optoelectronic devices.

Light management in dye-sensitized solar cell

Dye-sensitized solar cell (DSSC) is composed of a nanocrystalline TiO2 film whose surface is covered with dye molecules, an iodide/tri-iodide electrolyte and a platinum counter electrode. Charge generation occurs when dye absorbs photon energy, which is separated by injection of photo-excited electrons into the conduction band of TiO2. The photo-injected electrons are transported through TiO2 network and collected at transparent conducting electrode. The oxidized dyes are regenerated by oxidation of iodide. Light-to-electricity conversion efficiency depends on photocurrent density, open-circuit voltage and fill factor. Photocurrent density is related to the incident photon-to-current conversion efficiency (IPCE) that is a collective measure of light harvesting, charge separation and charge collection efficiency. Since the higher IPCE, the higher photocurrent density becomes, light management in DSSC is one of most important issues. In this paper, effective methods to improve IPCE are described including size-dependent light scattering effect, bi-functionality design in material synthesis and panchromatic approach such as selective position of different dyes in a mesoporous TiO2 film.

First results of a cryogenic optical photon-counting imaging spectrometer using a DROID array

Context. In this paper we present the first system test in which we demonstrate the concept of using an array of Distributed Read Out Imaging Devices (DROIDs) for optical photon detection. Aims. After the successful S-Cam 3 detector the next step in the development of a cryogenic optical photon counting imaging spectrometer under the S-Cam project is to increase the field of view using DROIDs. With this modification the field of view of the camera has been increased by a factor of 5 in area, while keeping the number of readout channels the same. Methods. The test has been performed using the flexible S-Cam 3 system and exchanging the 10x12 Superconducting Tunnel Junction array for a 3x20 DROID array. The extra data reduction needed with DROIDs is performed offline. Results. We show that, although the responsivity (number of tunnelled quasiparticles per unit of absorbed photon energy, e- /eV) of the current array is too low for direct astronomical applications, the imaging quality is already good enough for pattern detection, and will improve further with increasing responsivity. Conclusions. The obtained knowledge can be used to optimise the system for the use of DROIDs.

Photon energy absorption parameters for some polymers

Some photon energy absorption parameters viz. mass energy absorption coefficient (μ/ρ)en, photon energy absorption effective atomic number (ZPEA), electron density (Ne) and KERMA relative to air has been computed in the energy range from 1 keV to 20 MeV for some polymers such as nylon, poly-acrylo-nitrile, poly-methyl-acrylate, poly-vinyl-chloride, poly-styrene, synthetic rubber and poly-tetra-fluro-ethylene. The dependence of different parameters on incident photon energy and chemical composition of the selected polymers has been studied .

Cyclic electron flow around photosystem I is required for adaptation to high temperature in a subtropical forest tree, Ficus concinna

Dissipation mechanisms of excess photon energy under high-temperature stress were studied in a subtropical forest tree seedling, Ficus concinna. Net CO(2) assimilation rate decreased to 16% of the control after 20 d high-temperature stress, and thus the absorption of photon energy exceeded the energy required for CO(2) assimilation. The efficiency of excitation energy capture by open photosystem II (PSII) reaction centres (F(v)'/F(m)') at moderate irradiance, photochemical quenching (q(P)), and the quantum yield of PSII electron transport (Phi(PSII)) were significantly lower after high-temperature stress. Nevertheless, non-photochemical quenching (q(NP)) and energy-dependent quenching (q(E)) were significantly higher under such conditions. The post-irradiation transient of chlorophyll (Chl) fluorescence significantly increased after the turnoff of the actinic light (AL), and this increase was considerably higher in the 39 degrees C-grown seedlings than in the 30 degrees C-grown ones. The increased post-irradiation fluorescence points to enhanced cyclic electron transport around PSI under high growth temperature conditions, thus helping to dissipate excess photon energy non-radiatively.

Photon interaction and energy absorption in glass: A transparent gamma ray shield

The effective atomic number, Z eff, the effective electron density, N e,eff, and the energy dependence, ED, have been calculated at photon energies from 1 keV to 1 GeV for CaO–SrO–B 2O 3, PbO–B 2O 3, Bi 2O 3–B 2O 3, and PbO–Bi 2O 3–B 2O 3 glasses with potential applications as gamma ray shielding materials. For medium- Z glasses, Z eff is about constant and equal to the mean atomic number in a wide energy range, typically 0.3 < E < 4 MeV, where Compton scattering is the main photon interaction process. In contrast, for high- Z glasses there is no energy region where Compton scattering is truly dominating. Heavy-metal oxide glasses containing PbO and/or Bi 2O 3 are promising gamma ray shielding materials due to their high effective atomic number and strong absorption of gamma rays. They compare well with concrete and other standard shielding materials and have the additional advantage of being transparent to visible light. The single-valued effective atomic number calculated by XMuDat is approximately valid at low energies where photoelectric absorption is dominating.

Mα and Mβ X-ray emission spectra of Au atoms upon photoionization of L subshells

The structure and relative intensity of the Mα and Mβ X-ray fluorescence spectra of Au atoms are studied experimentally at the energies of absorbed photons both below and above the ionization thresholds of L subshells (Kα1, 2 radiation of Cr, Cu, and Mo). The M5N and M4N high-energy satellites are separated from the total spectral profiles and their relative intensities are determined. A model of the M emission is proposed that allows one to take into account the main channels of vacancy transfer from L to M subshells, which are responsible for the generation of double vacancy (M4, 5N and M4, 5O) and triple vacancy (M4, 5N2, M4, 5NO, and M4, 5O2) states. Comparison of the experimental relative intensities of separated M5N and M4N satellites excited by the Mo Kα1, 2 radiation with the calculated results indicates the correctness of the model used. The partial and total M emission cross sections of Au in the absorbed photon energy range of 5–30 keV are calculated. It is found that, in the photon energy region above the ionization threshold of the L3 subshell, our results noticeably differ from the data calculated by other authors. Possible reasons for these discrepancies are discussed.

Impact of light variation on development of photoprotection, antioxidants, and nutritional value in Lactuca sativa L.

Lettuce plants were grown at low (LL), middle (ML), and high light (HL) conditions to examine the relationship between photoacclimatory plasticity, light energy utilization, and antioxidant capacity. With the increase in light intensity from LL to ML, the energy flux via DeltapH- and xanthophylls-regulated thermal dissipation, fluorescence and constitutive thermal dissipation, and electron transport for photorespiratory carbon oxidation all increased significantly. However, plants at HL exhibited reduced electron transport for photosynthetic carbon reduction and decreased maximal photochemical efficiency of photosytem II (PSII) as compared to that at ML. Increasing light level significantly increased the alternative electron transport, O(2)(*-) production rate, and H(2)O(2) and malondialdehyde (MDA) contents followed by increased ferric reducing antioxidant power (FRAP) and activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Moreover, plants exposed to HL showed higher nutritional value as indicated by the high contents of ascorbate, glutathione, carotenoids, and alpha-tocopherol. It was concluded that absorption of excess photon energy at high light was associated with increased antioxidant capacity and that produce quality could be improved by short-term exposure to suboptimum irradiance.

USING A NONANALYTICAL APPROACH TO MODEL NONLINEAR DYNAMICS IN PHOTOSYNTHESIS AT THE PHOTOSYSTEM LEVEL(1).

Nonlinear dynamics in photon capture and uptake at the photosystem level may have a strong effect on photosynthetic yield. However, the magnitude of such effects is difficult to estimate theoretically because nonlinear systems often cannot be represented accurately using equations. A nonanalytical simulation was developed that used a simple decision tree and Monte Carlo methods, instead of equations, to model how a population of photosystems absorbs and utilizes photons from an ambient light field. This simulation replicated realistic kinetics in the closure and variable fluorescence yield of PSII on the single-turnover timescale, as well as the saturating behavior in light-driven electron flow that is observed in nature with increasing irradiance. This simulation indicated that the transfer of absorbed photon energy among PSII units can introduce strong nonlinear enhancement in light-driven electron flow. However, this effect was seen only in populations with particular photosynthetic states as determined by physiological properties of PSII. Other populations with the same degree of energy transfer but with different photosynthetic states exhibited little enhancement in electron flow and, in some cases, a reduction. This nonanalytical approach provides a simple means to quantify theoretically how nonlinear dynamics in photosynthesis arise at the photosystem level and how these dynamics may act to enhance or constrain photosynthetic rates and yields. Such simulations can provide quantitative insight into different physiological bases of nonlinear light-harvesting dynamics and identify those that would have the strongest theoretical influence and thus warrant closer experimental examination.

Dependency of threshold switching on density of localized states of Ge2Sb2Te5 thin films for phase change random access memory

The threshold switching of Ge2Sb2Te5 (GST) films for phase change random access memory applications was investigated by measuring the variation in the threshold voltage (VT) with the crystallinity of the GST films and photon energy absorption spectra. As the GST film was amorphized, VT increased to approximately 1 V and its electrical resistance increased. The optical band gap and Urbach edge of the GST increased from 0.66 to 0.97 eV and from 12 to 65 meV, respectively, upon its amorphization. It was experimentally confirmed that the threshold switching is associated with the density of localized states of the GST.