Effective Absorption Cross Section Research Articles

Investigation on absorption cross-section of photosynthetic pigment molecules based on a mechanistic model of the photosynthetic electron flow-light response in C3, C4 species and cyanobacteria grown under various conditions.

Investigation on intrinsic properties of photosynthetic pigment molecules participating in solar energy absorption and excitation, especially their eigen-absorption cross-section (σ ik) and effective absorption cross-section (σ ' ik), is important to understand photosynthesis. Here, we present the development and application of a new method to determine these parameters, based on a mechanistic model of the photosynthetic electron flow-light response. The analysis with our method of a series of previously collected chlorophyll a fluorescence data shows that the absorption cross-section of photosynthetic pigment molecules has different values of approximately 10-21 m2, for several photosynthetic organisms grown under various conditions: (1) the conifer Abies alba Mill., grown under high light or low light; (2) Taxus baccata L., grown under fertilization or non-fertilization conditions; (3) Glycine max L. (Merr.), grown under a CO2 concentration of 400 or 600 μmol CO2 mol-1 in a leaf chamber under shaded conditions; (4) Zea mays L., at temperatures of 30°C or 35°C in a leaf chamber; (5) Osmanthus fragrans Loureiro, with shaded-leaf or sun-leaf; and (6) the cyanobacterium Microcystis aeruginosa FACHB905, grown under two different nitrogen supplies. Our results show that σ ik has the same order of magnitude (approximately 10-21 m2), and σ ' ik for these species decreases with increasing light intensity, demonstrating the operation of a key regulatory mechanism to reduce solar absorption and avoid high light damage. Moreover, compared with other approaches, both σ ik and σ ' ik can be more easily estimated by our method, even under various growth conditions (e.g., different light environment; different CO2, NO2, O2, and O3 concentrations; air temperatures; or water stress), regardless of the type of the sample (e.g., dilute or concentrated cell suspensions or leaves). Our results also show that CO2 concentration and temperature have little effect on σ ik values for G. max and Z. mays. Consequently, our approach provides a powerful tool to investigate light energy absorption of photosynthetic pigment molecules and gives us new information on how plants and cyanobacteria modify their light-harvesting properties under different stress conditions.

Testing the ϕ-nuclear potential in pion-induced ϕ meson production on nuclei near threshold

The near-threshold pion-induced ϕ production off nuclei has been studied in the kinematical conditions of the HADES experiment using a collision model based on the nuclear spectral function. Starting from the elementary reaction π−p→ϕn, absolute differential and integral cross sections for the production of ϕ mesons off a light carbon and a heavy tungsten target have been calculated and compared to the recently reported experimental cross sections. The absolute cross section values are shown to be sensitive to the effective nuclear scalar ϕ and neutron potentials while the transparency ratio is governed by the ϕN absorption cross section. The experimental data are found to be consistent with an attractive ϕ-nucleus potential of ≈ -(50–100) MeV at normal nuclear matter density ρ0 and an effective ϕN absorption cross section of ≈ 12–25 mb. The extracted ϕ-nucleus potential is deeper than previous theoretical and experimental findings as well as those obtained in the present work within the (tρ) approximation with accounting for Pauli correlations from the spin-averaged ϕ-p scattering length reported in a recent ALICE experiment.

Intercomparison of NO3 under Humid Conditions with Open-Path and Extractive IBBCEAS in an Atmospheric Reaction Chamber

We report an open-path incoherent broadband cavity-enhanced absorption spectroscopy (OP-IBBCEAS) technique for in situ simultaneous optical monitoring of NO2, NO3, and H2O in a reaction chamber. The measurement precision values (1σ) are 2.9 ppbv and 2.9 pptv for NO2 and NO3 in 2 s, respectively, and the measurement uncertainties are 6% for NO2 and 14% for NO3. Intercomparison of measured concentrations of NO2 and NO3 by open-path and extractive IBBCEAS was carried out in the SAES-ARC reaction chamber during the reaction of NO2 with O3. The measurement accuracy of OP-IBBCEAS is verified by an NO2 intercomparison and the NO3 transmission efficiency of the extractive IBBCEAS is determined by comparison against the in situ NO3 measurement. The relationship between H2O absorption cross section and its mixing ratio at 295 K and 1 atm was analysed. Due to the spectral resolution of IBBCEAS system, the strong and narrow absorption lines of H2O are unresolved and exhibit non-Beer–Lambert Law behaviour. Therefore, a correction method is used to obtain the effective absorption cross section for fitting the H2O structure. An inappropriate H2O absorption cross section can cause an overestimation of NO3 concentration of about 28% in a humid atmosphere (H2O = 1.8%). This spectroscopic correction provides an approach to obtain accurate NO3 concentrations for open-path optical configurations, for example in chamber experiments or field campaigns. The measurement precision values are improved by a factor of 3 to 4 after applying Kalam filtering, achieving sub-ppbv (0.8 ppbv) and sub-pptv (0.9 pptv) performance in 2 s for NO2 and NO3, respectively.

Compact, Fast Cavity Ring-Down Spectroscopy Monitor for Simultaneous Measurement of Ozone and Nitrogen Dioxide in the Atmosphere

A sensitive, compact detector for the simultaneous measurement of O3 and NO2 is presented in this work. There are two channels in the detector, namely the Ox channel and the NO2 channel. In the presence of excess NO, ambient O3 is converted to NO2 in the Ox measurement channel. In both channels, NO2 is directly detected via cavity ring-down spectroscopy (CRDS) at 409 nm. At a 10 s integration time, the Ox and NO2 channels have a 1σ precision of 14.5 and 13.5 pptv, respectively. The Allan deviation plot shows that the optimal sensitivity of O3 and NO2 occurs at an integration time of ~60 s, with values of 10.2 and 8.5 pptv, respectively. The accuracy is 6% for the O3 channel and 5% for the NO2 channel, and the largest uncertainty comes from the effective NO2 absorption cross-section. Intercomparison of the NO2 detection between the NO2 and Ox channels shows good agreement within their uncertainties, with an absolute shift of 0.31 ppbv, a correlation coefficient of R2 = 0.99 and a slope of 0.98. Further intercomparison for ambient O3 measurement between the O3/NO2-CRDS developed in this work and a commercial UV O3 monitor also shows excellent agreement, with linear regression slopes close to unity and an R2 value of 0.99 for 1 min averaged data. The system was deployed to measure O3 and NO2 concentrations in Hefei, China, and the observation results show obvious diurnal variation characteristics. The successful deployment of the system has demonstrated that the instrument can provide a new method for retrieving fast variations in ambient O3 and NO2.

Linear and nonlinear absorption properties of hemicyanine dyes containing 5-(4H)-oxazolone as heterocyclic ring

A series of dyes containing electron-donating (D) and electron-accepting (A) groups connected through a π-conjugated linker were designed and their linear and nonlinear absorption properties were studied. The dyes combined 1,3-oxazol-5(4H)-one core with methoxy, methyl, phenyl, cyano, and nitro group in the para-position of a phenyl ring. Spectrally resolved two-photon absorption cross-section measurements carried out by the femtosecond Z-scan technique showed wide wavelength regions of nonlinear optical absorption. The studied compound containing the phenyl ring exhibits relatively high effective two-photon absorption cross-section equal to 772 ± 100 GM at 600 nm. The experimental optical characterization is supported by the results of electronic-structure calculations.

Two quinoline-based two-photon fluorescent probes for imaging of viscosity in subcellular organelles of living HeLa cells

Two viscosity-sensitive two-photon fluorescent probes (QL and QLS) were designed and synthesized, which can be localized in lysosome and mitochondria in living HeLa cells, respectively. As the increases of viscosity from 2.55 to 1150 cP, the fluorescence quantum yield (Φ) of QL and QLS was increased by 28-fold and 37-fold, respectively. At the same time, its effective two-photon absorption cross section (ΦδTPA) was enhanced by 15-fold and 16-fold, respectively. Fluorescence lifetime imaging (FLIM) of living HeLa cells stained with QL and QLS, revealed that lysosomal viscosity ranged from 100.76 to 254.74 cP and mitochondrial viscosity ranged from 92.21 to 286.79 cP. This type of fluorescent probe is helpful in the design and application of materials for monitoring diseases associated with abnormal viscosity.

Radiation shielding properties of modified concrete mixes and their suitability in dry storage cask

Radiation shielding properties of 8 concrete mixes were studied in detail. The concrete mixes included 4 coarse aggregate types; dolomite, barite, ilmenite, and celestite, and 2 cementing material content. Important parameters accounted for in this study include: Mass attenuation coefficient that was calculated using WinXCom program then linear attenuation coefficient, half value layer, tenth value layer, and mean free path were deduced; Effective atomic number was calculated using Auto-Zeff software; Exposure build-up factor was calculated using the Geometric Progression approximation method up to 40 mean free path using Phy-X/PSD Software; Fast neutrons macroscopic effective removal cross-section and thermal neutron macroscopic absorption cross-section were calculated using MRCsC and JANIS-4 programs, respectively. Subsequently, the mixes were assessed for use in a dry storage cask using OpenMC code. The results showed that concrete mixes containing barite and celestite were the best in attenuating gamma rays emitted in narrow and broad beam situations.

Гибридный металлополимер на основе полиметилметакрилата с внедренными металлическими наночастицами как активная среда оптоакустического генератора ультразвука

A study was made of a hybrid metal-polymer material consisting of polymethyl methacrylate (PMMA) and nanoparticles distributed throughout its volume, silver, gold, copper or aluminum. The effective permittivity and absorption cross section are calculated, and the processes of temperature relaxation are modeled. It has been shown that mixtures of PMMA with silver, copper, aluminum, or gold nanoparticles can be used as an active medium in optoacoustic ultrasound generators.

A hybrid metal polymer based on polymethyl methacrylate with embedded metal nanoparticles

A study was made of a hybrid metal-polymer material consisting of polymethyl methacrylate (PMMA) and nanoparticles distributed throughout its volume, silver, gold, copper or aluminum. The effective permittivity and absorption cross section are calculated, and the processes of temperature relaxation are modeled. It has been shown that mixtures of PMMA with silver, copper, aluminum, or gold nanoparticles can be used as an active medium in optoacoustic ultrasound generators. Keywords: hybrid material, ultrasound generator, nanoparticle, polymethyl methacrylat.

Evaluation of the irradiation-averaged fission yield for burnup determination in spent fuel assays

In order to derive the burnup of spent nuclear fuel from the concentration of selected fission products (typically the Nd isotopes and 137Cs), their irradiation-averaged fission yields need to be known with sufficient accuracy, as they evolve with the changes in the actinide vector over the irradiation history. To obtain irradiation-averaged values, radiochemists often resort to robust generic methods – i.e., based on simple mathematical relations – that weight the fission yields according to the actinides contributing to fission, without performing core physics calculations. In order to assess the performance of those generic methods, a database of about 30 000 spent nuclear fuel inventories has been constructed from neutron transport and depletion simulations, covering a representative range of fuel enrichment, burnup, assembly designs and reactor types. When testing several existing methods for effective fission yield calculation, some inaccuracies were identified, originating from improper one-group cross-section parameters that do not accurately reflect resonance and self-shielding effects, and too crude approximations in the estimation of the actinide concentration evolution. Revised effective fission and absorption cross-section parameters are then proposed here, as a first improvement to the earlier burnup determination methods. As a second step, a novel method is proposed that reduces the error on their radiation-averaged fission yield values, and hence on burnup, while retaining a straightforward calculation scheme.

State of the phycobilisome determines effective absorption cross-section of Photosystem II in Synechocystis sp. PCC 6803

Quenching of excess excitation energy is necessary for the photoprotection of light-harvesting complexes. In cyanobacteria, quenching of phycobilisome (PBS) excitation energy is induced by the Orange Carotenoid Protein (OCP), which becomes photoactivated under high light conditions. A decrease in energy transfer efficiency from the PBSs to the reaction centers decreases photosystem II (PS II) activity. However, quantitative analysis of OCP-induced photoprotection in vivo is complicated by similar effects of both photochemical and non-photochemical quenching on the quantum yield of the PBS fluorescence overlapping with the emission of chlorophyll. In the present study, we have analyzed chlorophyll a fluorescence induction to estimate the effective cross-section of PS II and compared the effects of reversible OCP-dependent quenching of PBS fluorescence with reduction of PBS content upon nitrogen starvation or mutations of key PBS components. This approach allowed us to estimate the dependency of the rate constant of PS II primary electron acceptor reduction on the amount of PBSs in the cell. We found that OCP-dependent quenching triggered by blue light affects approximately half of PBSs coupled to PS II, indicating that under normal conditions, the concentration of OCP is not sufficient for quenching of all PBSs coupled to PS II.

The study of neutron capture processes in AlN nanoparticles

The neutron capture processes in the AlN nanoparticles were investigated by computer modeling. Neutrons absorption were separately investigated for aluminum (Al) and nitrogen (N) atoms in the AlN nanoparticles. The modeling was performed separately for each stable Al and N isotopes, because the effective absorption cross-section of different types of isotopes of Al and N atoms is different. Moreover, effective cross-section spectra of neutron capture for aluminum and nitrogen atoms were comparatively investigated.

Phytoplankton community and the fluorescence-derived photo-physiological parameters in the South Atlantic Ocean

Assessing the composition and photo-physiology of phytoplankton communities are fundamental pieces of information to understand their role in global biogeochemical cycles mediated by primary production rates in the oceans. Photo-physiological parameters, namely the maximal photochemical efficiency (Fv/Fm) and the effective absorption cross-section of Photosystem II (σPSII), are currently used to estimate primary production rates in the laboratory and nature, and although variable fluorescence techniques substantially expand opportunities for new measurements in both time and space, their results reflect synergies among phytoplankton composition, cell size, limiting nutrients, and light history that need to be accounted for. The current work compared the variability of Fv/Fm and σPSII, as well as phytoplankton groups derived by pigment-CHEMTAX analyses, at the surface and deep chlorophyll maximum (DCM) of two sections of oceanographic stations over in the productive South Atlantic Subtropical Front (STF) at 35°S of latitude, and crossing the adjacent oligotrophic waters of the South Atlantic Gyre. High chlorophyll-a concentrations were found in the STF, where the presence of cyclonic eddies displaced the pycnocline upwards, and Fv/Fm varied according to specific photo-protective mechanisms of the phytoplankton groups in the surface. In the DCM, higher Fv/Fm were related to the Chl-a synthesis, suggesting a more favorable growing condition at this layer. In the Gyre transect, Fv/Fm showed significant linear relationships with the taxonomical composition, with larger values related to the presence of Prochlorococcus and Chl b-containing green flagellates. Overall, σPSII varied independently from Fv/Fm but were related to the presence of diatoms and the relative proportion between Synechococcus and Prochlorococcus in the STF and Gyre, respectively. Our results encourage the development of more complex models for primary production that should include instantaneous and high-resolution fluorescence-derived parameters as proxies for phytoplankton community and physiological acclimation state.

Strong increase in the effective two-photon absorption cross-section of excitons in quantum dots due to the nonlinear interaction with localized plasmons in gold nanorods.

Excitons in semiconductor quantum dots (QDs) feature high values of the two-photon absorption cross-sections (TPACSs), enabling applications of two-photon-excited photoluminescence (TPE PL) of QDs in biosensing and nonlinear optoelectronics. However, efficient TPE PL of QDs requires high-intensity laser fields, which limits these applications. There are two possible ways to increase the TPE PL of QDs: by increasing their photoluminescence quantum yield (PLQY) or by further increasing the TPACS. Plasmonic nanoparticles (PNPs) may act as open nanocavities for increasing the PLQY via the Purcell effect, but this enhancement is strictly limited by the maximum possible PLQY value of 100%. Here we directly investigated the effect of PNPs on the effective TPACS of excitons in QDs. We have found that effective TPACS of excitons in a QD-PMMA thin film can be increased by a factor of up to 12 near the linearly excited gold nanorods (GNRs). Using gold nanospheres (GNSs), in which plasmons cannot be excited in the infrared range, as a control system, we have shown that, although both GNSs and GNRs increase the recombination rate of excitons, the TPACS is increased only in the case of GNRs. We believe that the observed effect of TPACS enhancement is a result of the nonlinear interaction of the plasmons in GNRs with excitons in QDs, which we have supported by numerical simulations. The results show the way to the rational design of the spectral features of plasmon-exciton hybrids for using them in biosensing and nonlinear optoelectronics.

Absorption, quenching, and enhancement by tracer in acetone/toluene laser-induced fluorescence* *Project supported by the National Natural Science Foundation of China (Grant Nos. 51536002, 61405048, and 91441130).

To measure the equivalent ratio distribution of the two-stage lean premixed (DLP) flame, we propose using acetone/toluene planar laser-induced fluorescence (PLIF) technology to simultaneously measure the concentrations of the two components. Appropriate excitation laser wavelength and filters are used to assess the influence of acetone and toluene on each other’s fluorescence signal at room temperature. Experimental results show that acetone has a strong absorption effect on toluene’s fluorescence signal, the effective absorption cross-section is 5.77 × 10−20 cm−2. Acetone has an obvious quenching effect on the toluene fluorescence signal, and the Stern–Volmer coefficient is 0.50 kPa−1. The collisions between the molecules of toluene and acetone will lead to the enhancement of the fluorescence signal of acetone, and the enhancement coefficient is exponential with the acetone’s concentration. The quantitative relationship between the fluorescence intensity and the concentrations of the two tracers is obtained by establishing the photophysical model of toluene and acetone’s fluorescence signals.

Cavity ring-down spectroscopy measurements of ambient NO3 and N2O5

NO3 and N2O5 are important participants in nocturnal atmospheric chemical processes, and their concentrations are of great significance in the study of the mechanism of nocturnal atmospheric chemical reactions. A two-channel diode laser based cavity ring-down spectroscopy (CRDS) instrument was developed to monitor the concentrations of NO3 and N2O5 in the atmosphere. The effective absorption length ratio and the total loss coefficient of the instrument were calibrated using laboratory standard samples. The effective absorption cross section of NO3 at 662 nm was derived. A detection sensitivity of 1.1 pptv NO3 in air was obtained at a time resolution of 1 s. N2O5was converted to NO3 and detected online in the second CRDS channel. The instrument was used to monitor the concentrations of NO3 and N2O5 in the atmosphere of winter in Hefei in real time. By comparing the concentration changes of pollutants such as nitrogen oxides, ozone, PM2.5 in a rapid air cleaning process, the factors affecting the concentrations of NO3 and N2O5 in the atmosphere were discussed.

Photobleaching of Phthalocyanine Molecules within a Complex with Colloidal Quantum Dots

Fluorescent nanoparticles are currently considered as promising enhancers of photodynamic activity of traditional photosensitizers in procedures for photodynamic therapy of cancer and inactivation of pathogens. On the one hand, such nanoparticles act as a nanoplatform for target delivery of dye molecules to cells; on the other hand, they act as light-harvesting antennas that increase the effective absorption cross-section of the dye. This paper investigates the effect of semiconductor CdSe/ZnS quantum dots coated with a polymer shell on the photostability of zinc or aluminum polycationic phthalocyanines. It was shown that the rate of photobleaching of phthalocyanines increases significantly in the presence of quantum dots both under direct illumination of phthalocyanine by red light and under the quantum dot-mediated illumination by blue light. This effect can be explained by the fact that phthalocyanine inside the polymer shell of the quantum dot is the primary target for the attack by reactive oxygen species. The rate of bleaching of the chemical trap of reactive oxygen species, 4-nitroso-N,N-dimethylaniline, in a phthalocyanine solution increases in the presence of the quantum dot under red light illumination. We believe that the chemical trap is concentrated in the polymer shell of the quantum dot, which increases the probability of its damage by active oxygen species generated by phthalocyanine. Since the diffusion of reactive oxygen species from the polymer shell of the nanoparticle into the surrounding solution is slow, the use of quantum dots as an enhancer of the photodynamic action of phthalocyanines can be effective only in the absence of significant steric obstacles to the diffusion of reactive oxygen species to the target molecules of photodynamic inactivation.

Optimizing performance of metamaterial wormhole superabsorbers.

Transmission line-based metamaterials are used to realize and model the conjugate-impedance matched superabsorbers. Here, we formulate an analytical-numerical approach for maximizing the effective absorption cross section of the metamaterial wormhole superabsorber, under the goal of minimizing the complexity of the structure. Analytical expressions for the gradient of the absorption cross section as a function of the structural parameters are derived. Numerical results showing enhanced absorption are obtained under three different optimization strategies: a ring-by-ring approach, a gradient-based optimization, and a mixed algorithm. The best results are achieved with the mixed algorithm, with which it is demonstrated that the optimal wormhole superabsorber significantly outperforms a black body-type absorber of a similar size. This study is of a particular interest for applications of the conjugate-impedance-matched superabsorbers as efficient harvesters of electromagnetic radiation.

Nanoplasma properties in metallic clusters driven by a Gaussian laser beam in the presence of helical magnetic undulator

The motivation of present paper is the investigation of effective permittivity and absorption cross section of cluster nanoplasmas in the interaction of a Gaussian laser beam with a cluster of metallic nanoparticles, in the presence of a helical magnetic undulator. The static magnetic field of the undulator couples with the field of the laser wave, and forms a nonlinear force in the interaction region. As a result, the nonlinear force varies the plasmonic oscillations of the electron of nanoplasmas that leads to electron density modulation, which modifies absorption cross section and effective permittivity of nanoparticles. Using a perturbative method, we analytically derived the nonlinear dispersion waves and dielectric constant of metallic nanoparticles lattice (gold, silver, and copper) in the presence of a helical magnetic undulator. Numerical results indicate that with increasing the undulator magnetic field strength, absorption cross section of cluster nanoplasmas increases and absorption phenomenon occurs at frequencies close to the effective plasma frequency. Besides, with decreasing distance of nanoparticles in the cluster (and with increasing the nanoparticles radius), absorption cross section increases. We also found that the dielectric constant of the cluster nanoplasma medium increases with enhancing undulator magnetic field strength only near the effective plasmonic frequency. This concept opens a path toward new properties of cluster nanoplasmas as quantum dots, diagnostics, and sensors based on magnetic undulator structures.

Optimal chlorophyll fluorescence parameter selection for rapid and sensitive detection of lead toxicity to marine microalgae Nitzschia closterium based on chlorophyll fluorescence technology

Heavy metal pollution as one of the most serious pollution problems of marine environment, seriously threatens the safety of marine organism and human health, and will lead to potential risks for the marine ecological environment. In order to develop a rapid and sensitive toxicity detection method for marine heavy metals, in this study, marine diatom Nitzschia closterium was used as the test organism, and the effects of different concentrations of lead (Pb) on the five chlorophyll fluorescence parameters of N. closterium including the maximum photochemical quantum yield of PSII (Fv/Fm), the effective quantum yield of PSII photochemical energy conversion (ΦPSII), the effective absorption cross section of PSII photochemistry (σPSII′), the relative electron transfer rate of PSII (rP), and the PSII electron flux per unit volume (JVPII) at different exposure times were investigated based on chlorophyll fluorescence technology. By comparing with the photosynthetic activity fluorescence parameter Fv/Fm which is commonly used for toxicity analysis of pollutants using algae as test organisms, the optimal chlorophyll fluorescence parameter that could rapidly and sensitively determine Pb toxicity to N. closterium was selected. The results indicate that all the five chlorophyll fluorescence parameters of Fv/Fm, ΦPSII, σPSII′, rP and JVPII showed good dose-response relationships with Pb within 8 h exposure time, and they all could be used as endpoints to rapidly determine Pb toxicity to N. closterium. Among the five chlorophyll fluorescence parameters, JVPII was the most sensitive fluorescence parameter for detecting the toxicity of Pb to N. closterium within 6 h exposure. And for JVPII, the median effective concentration (EC50) values of Pb at 2, 4 and 6 h were 0.329, 0.068 and 0.040 mmol L−1, respectively. However, when the exposure time was 8 h, ΦPSII was the most sensitive fluorescence parameter for the toxicity detection of Pb, and the EC50 value of Pb at 8 h was 0.038 mmol L−1. This study will provide an important basis for the development of a rapid and sensitive detection method for the biological toxicity of marine heavy metals, and those results will be helpful for ecological risk assessment in marine environment.