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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 m 2 , 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 CO 2 concentration of 400 or 600 μmol CO 2 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 m 2 ), 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 CO 2 , NO 2 , O 2 , and O 3 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 CO 2 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.

The investigation of integral elastic cross-section (ICS), momentum transfer cross-section (MTCS), viscosity cross-section (VCS), absorption cross-section (ABSCS), and total cross-section (TCS) of atoms by electron (e−) and positron (e+) impact is very crucial and essential for understanding fundamental atomic processes and their applications in various fields such as plasma physics, molecular physics, and astrophysics. This study investigates and analyses the ICS, MTCS, VCS, ABSCS, and TCS of the atoms, Li, Be, B, Ti, and W, over a wide energy range. By employing the computational Optical Potential Method (OPM) and quantum scattering integrated in a computational package, ELSEPA (Elastic scattering of electrons and positrons by atoms, positive ions and molecules), the cross-sections of atoms by electron and positron impact are calculated. The present results shows good agreement with all the experimental and theoretical data available in the literature. The obtained cross-sections may facilitate the development of accurate models for plasma simulations and fusion research.

The article describes a new practical model for the infrared absorption of chlorofluorocarbons and other gases with dense spectra, based on high-resolution transmission molecular absorption database (HITRAN) absorption cross-sections. The model is very simple, consisting of frequency-dependent polynomial coefficients describing the pressure and temperature dependence of absorption. Currently it is implemented for the halocarbon species required by the Radiative Forcing Model Intercomparison Project. In cases where cross-section data is available at a range of different temperatures and pressures, this approach offers practical advantages compared to previously available options, and is traceable, since the polynomial coefficients follow directly from the laboratory spectra. The new model is freely available and has several important applications, notably in remote sensing and in developing advanced radiation schemes for global circulation models that include halocarbon absorption. For demonstration, the model is applied to the problem of computing instantaneous clear-sky halocarbon radiative efficiencies and present day radiative forcing. Results are in reasonable agreement with earlier assessments that were carried out with the less explicit Pinnock method, and thus broadly validate that method.

This study provides a thorough investigation of the trends of organic carbon (OC) and elemental carbon (EC) in particulate matter (PM) 10 and PM 2.5 samples collected at the Monte Curcio Observatory (1780 m a.s.l.), a station of the Global Atmosphere Watch (GAW) program and Global Mercury Observation System (GMOS) network. Although the drawn attention toward these pollutants, there is still a lack of data for southern Italy, and this work is a contribution toward the filling of this gap. PM was sampled daily in 2016 and analyzed by thermo-optical transmittance method, while equivalent black carbon (eBC) concentrations in PM 10 were simultaneously measured using a multiangle absorption photometer. The results showed that in PM 10 , the average values of OC and EC were 1.43 μgC/m 3 and 0.12 μgC/m 3 , whereas in PM 2.5 , these concentrations were 1.09 μgC/m 3 and 0.12 μgC/m 3 , respectively. We detected a clear seasonal variability in OC and EC with higher concentrations during the warm period. Moreover, the analysis of the OC/EC ratio revealed that most of the carbonaceous aerosol was transported by long-range air masses, as further confirmed by the use of the concentration-weighed trajectory (CWT) model. The mass absorption cross-section at 632 nm of EC (MAC EC ) over the entire period was 9.67 ± 4.86 m 2 /g and 8.70 ± 3.18 m 2 /g in PM 2.5 and PM 10 , respectively, and did not exhibit a clear seasonal variation. The concentrations for OC and EC were also used for the computation of the secondary organic carbon (SOC) content, whose outcomes resulted in a seasonal trend similar to those obtained for OC and EC. As regards the eBC, its weekly pattern showed a slight increase during the weekend in the warm period, consistent with the anthropic activities in the touristic area surrounding the observatory.

Based on the ideas used by Kiselev, we study three black holes surrounded by quintessence and the effects of quintessence on the classical and semiclassical scattering cross-sections. In contrast, the absorption section is studied with the sinc approximation in the eikonal limit. For Schwarzschild, Reissner–Nordström and Bardeen black holes surrounded by quintessence, the critical values of charges, and the normalization factor are obtained. We also described the horizons and the extremal condition of the black holes surrounded by quintessence, by setting the quintessence state parameter in the two particular cases ω = - 2 / 3 and ω = - 1 / 2 .

Mass absorption cross-section of black carbon (MACBC) describes the absorptive cross-section per unit mass of black carbon, and is, thus, an essential parameter to estimate the radiative forcing of black carbon. Many studies have sought to estimate MACBC from a theoretical perspective, but these studies require the knowledge of a set of aerosol properties, which are difficult and/or labor-intensive to measure. We therefore investigate the ability of seven data analytical approaches (including different multivariate regressions, support vector machine, and neural networks) in predicting MACBC for both ambient and biomass burning measurements. Our model utilizes multi-wavelength light absorption and scattering as well as the aerosol size distributions as input variables to predict MACBC across different wavelengths. We assessed the applicability of the proposed approaches in estimating MACBC using different statistical metrics (such as coefficient of determination (R2), mean square error (MSE), fractional error, and fractional bias). Overall, the approaches used in this study can estimate MACBC appropriately, but the prediction performance varies across approaches and atmospheric environments. Based on an uncertainty evaluation of our models and the empirical and theoretical approaches to predict MACBC, we preliminarily put forth support vector machine (SVM) as a recommended data analytical technique for use. We provide an operational tool built with the approaches presented in this paper to facilitate this procedure for future users.

Chlorophyll (Chl) fluorescence induction (FI) upon a dark–light transition has been widely analyzed to derive information on initial events of energy conversion and electron transfer in photosystem II (PSII). However, currently, there is no analytical solution to the differential equation of QA reduction kinetics, raising a doubt about the fitting of FI by numerical iteration solution. We derived an analytical solution to fit the OJ phase of FI, thereby yielding estimates of three parameters: the functional absorption cross-section of PSII (σPSII), a probability parameter that describes the connectivity among PSII complexes (p), and the rate coefficient for QA− oxidation (kox). We found that σPSII, p, and kox exhibited dynamic changes during the transition from O to J. We postulated that in high excitation light, some other energy dissipation pathways may vastly outcompete against excitation energy transfer from a closed PSII trap to an open PSII, thereby giving the impression that connectivity seemingly does not exist. We also conducted a case study on the urban heat island effect on the heat stability of PSII using our method and showed that higher-temperature-acclimated leaves had a greater σPSII, lower kox, and a tendency of lower p towards more shade-type characteristics.

In the present study, the heat generation in gold nanodimer when irradiated at their localized surface plasmon resonances is investigated numerically. The theoretical calculations are performed employing the first principal approach to obtain the absorption cross-section of gold nanodimer for different parameter ranges. The heating mechanism is enumerated in terms of its temperature by solving the steady-state heat transfer equation which depends on the absorption cross-section and surface plasmon resonance wavelength. These surface plasmon resonances are quite sensitive to the distance between the dimer and have been tuned from visible to IR range by managing the distance between spheres from 0 to 6 nm. The computation of normalized electric field distribution of gold nanodimer under the plasmon resonance has been mapped using boundary element method(BEM) which enables visualization of the local hot spot that plays a significant role in optical heating applications. The work furnishes the basic understanding of the heating mechanism of gold nanodimer which can find application as plasmonic nanoheaters in several branches of science in visible and near-infrared regions of the electromagnetic spectrum.

We present the evolution of multispectral optical properties through urban aerosols that have aged and interacted with biogenic emissions, resulting in stronger short wavelength absorption and the formation of moderately brown secondary organic aerosols. Ground-based aerosol measurements were made in June 2010 within the Sacramento urban area (site T0) and at a 40-km downwind location (site T1) in the forested Sierra Nevada foothills area. Data on black carbon (BC) and non-refractory aerosol mass and composition were collected at both sites. In addition, photoacoustic (PA) instruments with integrating nephelometers were used to measure spectral absorption and scattering coefficients for wavelengths ranging from 355 to 870 nm. The daytime absorption Ångström exponent (AAE) indicated a modest wavelength-dependent enhancement of absorption at both sites throughout the study. From 22 to 28 June 2010, secondary organic aerosol mass increased significantly at both sites, which was due to increased biogenic emissions coupled with intense photochemical activity and air mass recirculation in the area. During this period, the median BC mass-normalized absorption cross-section (MAC) values for 405 nm and 532 nm at T1 increased by ~23% and ~35%, respectively, compared with the relatively less aged urban emissions at the T0 site. In contrast, the average MAC values for the 870 nm wavelength were similar for both sites. These results suggest the formation of moderately brown secondary organic aerosols in biogenically-influenced urban air.

In this paper, we present the revision of the cross-section database used for the retrieval of aerosol and gas species from remote sensing measurements by the GOMOS instrument onboard ENVISAT. The absorption cross-section spectra concern ozone, nitrogen dioxide and nitrogen trioxide, for which improved datasets have been published since the implementation of the original GOMOS cross-section database in preparation of the ENVISAT mission. We evaluate the molecular absorption cross-section spectra currently available for O3, NO2 and NO3, and we present and discuss our selection of datasets and the set-up of the revised absorption cross-section database, with the focus on these three gases. The objective is to provide an optimal characterization of their absorption spectrum over the UV-visible-near IR range used by AerGOM, a retrieval algorithm that was designed to optimize the retrieval of aerosol species from GOMOS measurements. Despite its application to the specific case of GOMOS, it is the aim of this work to cover a more general scope than this particular mission, and to provide an evaluation applicable to any other case of remote sensing experiment covering the UV to near IR range, possibly with a high spectral resolution.