Reviewing the effect of aggregates in Rhodamine 6G aqueous solution on fluorescence quantum efficiency.

Rhodamines constitute a class of dyes extensively investigated and applied in various contexts, primarily attributed to their high luminescence quantum yield. This study delves into the impact of aggregation on the thermal and optical properties of Rhodamine 6G (R-6G) solutions in distilled water. Examined properties encompass thermal diffusivity (D), temperature coefficient of the refractive index (dn/dT), fluorescence quantum efficiency (η), and energy transfer (ET). These parameters were assessed through thermal lens (TL) and conventional absorption and emission spectroscopic techniques. The dimerization of R-6G solutions was revisited, revealing that an increase in R-6G concentration alters the features of absorption and emission spectra due to dimer formation, resulting in unexpected behavior of η. Consequently, we introduce a novel model for the fraction of absorbed energy converted into heat (φ), which accounts for emissions from both monomers and dimers. Employing this model, we investigate and discuss the concentration-dependent behaviors of η for monomers (ηm) and dimers (ηd). Notably, our findings demonstrate that ηm values necessitate ηd = 0.2, a relatively substantial value that cannot be disregarded. Additionally, applying the Förster theory for dipole-dipole electric ET, we calculate microparameters for ET between monomers (CDD) and monomer-dimer (CDA). Critical ranges for ET in each case are quantified. Microparameter analysis indicates that ET between monomer-monomer and monomer-dimer species of R-6G dissolved in distilled water holds significance, particularly in determining ηm. These results bear significance, especially in scenarios involving high dye concentrations. While applicable to R-6G in water, similar assessments in other media featuring aggregates are encouraged.

Role of bundle sheath conductance in sustaining photosynthesis competence in sugarcane plants under nitrogen deficiency.

The role of bundle sheath conductance (gbs) in sustaining sugarcane photosynthesis under nitrogen deficiency was investigated. Sugarcane was grown under different levels of nitrogen supply and gbs was estimated using simultaneous measurements of leaf gas exchange and chlorophyll fluorescence at 21% or 2% [O2] and varying air [CO2] and light intensity. Maximum rates of PEPC carboxylation, Rubisco carboxylation, and ATP production increased with an increase in leaf nitrogen concentration (LNC) from 1 to 3 g m-2. Low nitrogen supply reduced Rubisco and PEPC abundancies, the quantum efficiency of CO2 assimilation and gbs. Because of reduced gbs, low photosynthetic rates were not associated with increased leakiness under nitrogen deficiency. In fact, low nitrogen supply increased bundle sheath cell wall thickness, probably accounting for low gbs and increased estimates of [CO2] at Rubisco sites. Effects of nitrogen on expression of ShPIP2;1 and ShPIP1;2 aquaporins did not explain changes in gbs. Our data revealed that reduced Rubisco carboxylation was the main factor causing low sugarcane photosynthesis at low nitrogen supply, in contrast to the previous report on the importance of an impaired CO2 concentration mechanism under N deficiency. Our findings suggest higher investment of nitrogen into Rubisco protein would favour photosynthesis and plant performance under low nitrogen availability.

Coarse-Grained Quantum Theory of Organic Photovoltaic Devices.

Understanding the exciton dissociation process in organic solar cells is a fundamental issue for the design of high-performance photovoltaic devices. In this article, a parameterized quantum theory based on a coarse-grained tight-binding model plus non-local electron-hole interactions is presented, while the diffusion and recombination of excitons are studied in a square lattice of excitonic states, where a real-space renormalization method on effective chains has been used. The Hamiltonian parameters are determined by fitting the measured quantum efficiency spectra and the theoretical short-circuit currents without adjustable parameters show a good agreement with the experimental ones obtained from several polymer:fullerene and polymer:polymer heterojunctions. Moreover, the present study reveals the degree of polymerization and the true driving force at donor-acceptor interface in each analyzed organic photovoltaic device.

Photochemical activity modulated by water, nitrogen, and phosphorus status in cactus pear

This study aimed to evaluate the effects of nitrogen (N) and phosphorus (P) associated with dry and rainy seasons on the photochemical activity of Opuntia ficus-indica (L.) Mill. cv. Gigante. Combinations of N (10.0, 70.0, 100.0, 130.0, and 190.0 kg ha−1 yr−1) and P2 O5 (10.0, 70.0, 100.0, 130.0, and 190.0 kg ha−1 yr−1) were evaluated in the dry and rainy seasons in semi-arid regions. A completely randomized block design with split-plot arrangement was adopted with four replications. In Quixadá, the maximum potential quantum efficiency of photosystem II (Fv/Fm) was 0.82, observed in third-order cladodes (rainy season and N/P 75.6/10.0 kg ha−1 yr−1), while in Tejuçuoca, the maximum Fv/Fm was 0.81, found in 2nd/3rd order cladodes (rainy season and N/P 10.0/190.0 kg ha−1 yr−1). In Quixadá, the maximum electron transport rate (ETR) was 31.6 µmol m−2 s−1 in 2nd/3rd order cladodes (rainy season and N/P 10.0/190.0 kg ha−1 yr−1), and in Tejuçuoca, the maximum ETR was 24.1 µmol m−2 s−1, in second-order cladodes (rainy season and N/P 110.1/10.0 kg ha−1 yr−1). In Quixadá and Tejuçuoca, higher values of Fv/Fm and ETR were observed in the rainy season. In Quixadá, the maximum fluorescence decrease ratio (FDR) was 4.04 in third-order cladodes (rainy season and N/P 10.0/114.8 kg ha−1 yr−1), while in Tejuçuoca, the maximum FDR was 6.93, found in 2nd/3rd order cladodes (rainy season and N/P 190.0/10.0 kg ha−1 yr−1). In Quixadá and Tejuçuoca, there was predominance of higher FDR values in the rainy season. Nitrogen, phosphorus, and water status modulate the photochemical efficiency of cladodes of cactus pear cv. Gigante in semi-arid regions.

Efficiencies Evaluation of Photocatalytic Paints Under Indoor and Outdoor Air Conditions.

The removal of indoor and outdoor air pollutants is crucial to prevent environmental and health issues. Photocatalytic building materials are an energy-sustainable technology that can completely oxidize pollutants, improving in situ the air quality of contaminated sites. In this work, different photoactive TiO2 catalysts (anatase or modified anatase) and amounts were used to formulate photocatalytic paints in replacement of the normally used TiO2 (rutile) pigment. These paints were tested in two different experimental systems simulating indoor and outdoor environments. In one, indoor illumination conditions were used in the photoreactor for the oxidation of acetaldehyde achieving conversions between 37 and 55%. The other sets of experiments were performed under simulated outdoor radiation for the degradation of nitric oxide, resulting in conversions between 13 and 35%. This wide range of conversions made it difficult to directly compare the paints. Thus, absorption, photonic, and quantum efficiencies were calculated to account for the paints photocatalytic performance. It was found that the formulations containing carbon-doped TiO2 presented the best efficiencies. The paint with the maximum amount of this photocatalyst showed the highest absorption and photonic efficiencies. On the other hand, the paint with the lowest amount of carbon-doped TiO2 presented the highest value of quantum efficiency, thus becoming the optimal formulation in terms of energy use.

Chlorophyll a fluorescence and leaf temperature are early indicators of oil palm diseases

Bud rot (BR) caused by Phytophthora palmivora and lethal wilt (LW) whose causal agent is unknown, are two diseases currently posing a threat to the oil palm ( Elaeis guineensis . Jacq) industry. BR, first reported in 1964, has destroyed more than 85,000 ha. LW, first reported in 1994 in the Llanos Orientales in Colombia, has destroyed more than 5,000 ha. Chlorophyll a fluorescence is useful as a provider of information about the efficiency of the photosynthetic process when plants are subjected to biotic or abiotic stresses. Oil palms affected by BR and LW showed anomalies in the photosynthetic system, manifested by reductions in Fv / F M and PSII. Changes in PSII, variable fluorescence yield ( Fv ) and maximum fluorescence in light-adapted leaves ( F M ) were observed from the start of BR infection. The most sensitive and early indicators of LW disease were leaf temperature and basal fluorescence ( F 0 ). Fv/F 0 significantly changed in diseased palms, indicating problems with movement of electrons through the electron transport chain. Leaf temperature changed in response to both diseases, but variation was greater in LW. We concluded that damage to the photochemical system caused by the diseases affected the processes by which the plant captures and transports energy, causing a physiological imbalance in the plant reflected in the observed variations in chlorophyll a fluorescence and leaf temperature. The two parameters began to change early in the onset of BR and before visual symptoms appeared in LW, which is very important to the management of both diseases, the foundation of which is early detection.

Chlorophyll a fluorescence and leaf temperature are early indicators of oil palm diseases

Bud rot (BR) caused by Phytophthora palmivora and lethal wilt (LW) whose causal agent is unknown, are two diseases currently posing a threat to the oil palm ( Elaeis guineensis . Jacq) industry. BR, first reported in 1964, has destroyed more than 85,000 ha. LW, first reported in 1994 in the Llanos Orientales in Colombia, has destroyed more than 5,000 ha. Chlorophyll a fluorescence is useful as a provider of information about the efficiency of the photosynthetic process when plants are subjected to biotic or abiotic stresses. Oil palms affected by BR and LW showed anomalies in the photosynthetic system, manifested by reductions in Fv / F M and PSII. Changes in PSII, variable fluorescence yield ( Fv ) and maximum fluorescence in light-adapted leaves ( F M ) were observed from the start of BR infection. The most sensitive and early indicators of LW disease were leaf temperature and basal fluorescence ( F 0 ). Fv/F 0 significantly changed in diseased palms, indicating problems with movement of electrons through the electron transport chain. Leaf temperature changed in response to both diseases, but variation was greater in LW. We concluded that damage to the photochemical system caused by the diseases affected the processes by which the plant captures and transports energy, causing a physiological imbalance in the plant reflected in the observed variations in chlorophyll a fluorescence and leaf temperature. The two parameters began to change early in the onset of BR and before visual symptoms appeared in LW, which is very important to the management of both diseases, the foundation of which is early detection.(AU)

Heterogeneous photo-Fenton process using iron-modified regional clays as catalysts: photonic and quantum efficiencies.

A regional raw clay was used as the starting material to prepare iron-pillared clays with different iron contents. The catalytic activity of these materials was tested in the heterogeneous photo-Fenton process, applied to the degradation of 2-chlorophenol chosen as the model pollutant. Different catalyst loads between 0.2 and 1.0 g L-1 and pH values between 3.0 and 7.0 were studied. The local volumetric rate of photon absorption (LVRPA) in the reactor was evaluated solving the radiative transfer equation applying the discrete ordinate method and using the optical properties of the catalyst suspensions. The photonic and quantum efficiencies of the 2-chlorophenol degradation depend on both the catalyst load and the iron content of the catalyst. The higher values for these parameters, 0.080 mol Einstein-1 and 0.152 mol Einstein-1, respectively, were obtained with 1.0 g L-1 of the catalyst with the higher iron content (17.6%). For the mineralization process, photonic and quantum efficiencies depend mainly on the catalyst load. Therefore, it was possible to employ a natural and cheap resource from the region to obtain pillared clay-based catalysts to degrade organic pollutants in water.

Water stress effects on chlorophyll fluorescence and chlorophyll content in sugarcane cultivars with contrasting tolerance / Efeitos do estresse hídrico na fluorescência e conteúdo de clorofila em cultivares de cana-de-açúcar com tolerância contrastante

One way to minimize the impacts caused by water deficit (WD) in agriculture is the use of tolerant cultivars. The physiological evaluation of plants through the potential quantum efficiency of photosystem II (Fv/Fm) and estimated chlorophyll content (SPAD index) can be an effective tool in the selection and recommendation of water deficit-tolerant cultivars. Within this context, the aim of this study was to evaluate the physiological responses of sugarcane cultivars classified as tolerant or susceptible to water deficit. The experiment was carried out near the city of Jaú, SP, Brazil in a greenhouse, between July and December 2013. The experimental design was completely randomized in a 4 x 2 factorial arrangement, with four replications. We studied four sugarcane cultivars: RB72454, RB855453 (prone to WD), SP81-3250 and SP83-2847 (WD-tolerant) in two water management regimes (with and without deficit). WD reduced stems dry mass of all cultivars, however, the greatest decreases were observed in susceptible cultivars to WD, where the decrease was 58.3 and 74.5% for cultivars RB855443 and RB72454, respectively. As for the SP81-3250 and SP83-2847 cultivars (tolerant), the reduction was 44.1 and 47.7%, respectively. For water deficit-tolerant cultivars, there was lower reduction in potential quantum efficiency of photosystem II and SPAD index; therefore, the physiological characteristics (Fv/Fm and SPAD index) are features that can aid the identification and selection of water deficit tolerant cultivars, and also help the recommendation of these cultivars for harsh environments, minimizing the effects of water deficit on stem yield on the sugarcane crop.

Uma forma de minimizar os impactos causados pelo déficit hídrico (DH) na agricultura é o uso de cultivares tolerantes. A avaliação fisiológica das plantas através da eficiência quântica potencial do fotossistema II (Fv/Fm) e do índice SPAD pode se tornar uma ferramenta eficiente na seleção e recomendação de cultivares tolerantes ao déficit hídrico. Com base nesse contexto, o objetivo deste trabalho foi avaliar as respostas fisiológicas de cultivares de cana-de-açúcar classificadas como tolerantes e susceptíveis ao déficit hídrico. O experimento foi realizado na região do município de Jaú/SP/Brasil em casa de vegetação, entre os meses de julho e dezembro de 2013. O delineamento experimental foi inteiramente casualizado no esquema fatorial 4 x 2, com quatro repetições. Foram estudadas quatro cultivares de cana-de-açúcar: RB72454, RB855453 (susceptíveis ao DH), SP81-3250 e SP83-2847 (tolerantes ao DH) em dois regimes hídricos (com e sem déficit). O DH reduziu a massa seca dos colmos de todas cultivares, porém, as maiores quedas foram observadas nas cultivares susceptíveis ao DH, em que nas cultivares RB855443 e RB72454 a queda foi de 58,3 e 74,5%, respectivamente. Já para as cultivares SP81-3250 e SP83-2847 (tolerantes), a redução foi de 44,1 e 47,7%, respectivamente. As cultivares tolerantes ao déficit hídrico tiveram menor redução na eficiência quântica potencial do fotossistema II e no índice SPAD, demonstrando, portanto, que os parâmetros fisiológicos (Fv/Fm e índice SPAD) são características que podem auxiliar a identificação e seleção de cultivares tolerantes ao déficit hídrico, e ainda, auxiliar a recomendação dessas cultivares para ambientes desfavoráveis, minimizando os efeitos do déficit hídrico sobre o rendimento de colmos na cultura da cana-de-açúcar.

Detective quantum efficiency for photon-counting hybrid pixel detectors in the tender X-ray domain: application to Medipix3RX.

Synchrotron-radiation-based X-ray imaging techniques using tender X-rays are facing a growing demand, in particular to probe the K absorption edges of low-Z elements. Here, a mathematical model has been developed for estimating the detective quantum efficiency (DQE) at zero spatial frequency in the tender X-ray energy range for photon-counting detectors by taking into account the influence of electronic noise. The experiments were carried out with a Medipix3RX ASIC bump-bonded to a 300 µm silicon sensor at the Soft X-ray Spectroscopy beamline (D04A-SXS) of the Brazilian Synchrotron Light Laboratory (LNLS, Campinas, Brazil). The results show that Medipix3RX can be used to develop new imaging modalities in the tender X-ray range for energies down to 2 keV. The efficiency and optimal DQE depend on the energy and flux of the photons. The optimal DQE values were found in the 7.9-8.6 keV photon energy range. The DQE deterioration for higher energies due to the lower absorption efficiency of the sensor and for lower energies due to the electronic noise has been quantified. The DQE for 3 keV photons and 1 × 10(4) photons pixel(-1) s(-1) is similar to that obtained with 19 keV photons. Based on our model, the use of Medipix3RX could be extended down to 2 keV which is crucial for coming applications in imaging techniques at modern synchrotron sources.

Optical characterization of core-shell quantum dots embedded in synthetic saliva: Temporal dynamics.

The present work reports the spectroscopic and thermo-optical properties of CdSe/ZnS and CdSe/CdS core-shell quantum dots (QDs) embedded in synthetic saliva. Spectroscopy studies were performed applying nonfunctionalized CdSe/ZnS QDs (3.4, 3.9 and 5.1 nm cores) and hydroxyl group-functionalized ultrasmall CdSe/CdS core-shell quantum dots (1.6 nm core) suspended in artificial saliva at different potential of hydrogen (pH) values. Saliva was chosen because it is important in a variety of functions such as protecting teeth through the buffering capacity of the formed biofilm, hydration, and dental remineralization. Thermo-optical characterizations using the thermal lens (TL) technique were performed in QD-biofluids for different QD sizes and pH values (3.9-8.3) of the synthetic oral fluids. Transient TL measurements were applied to determine the fluorescence quantum efficiency (η) in QD-biomaterial systems. High η value was obtained for ultrasmall CdSe/CdS QDs. Fluorescence spectral measurements of the biomaterials support the TL results. In addition, for nonfunctionalized (3.4 and 5.1 nm) and hydroxyl group-functionalized QDs, the temporal behavior of the fluorescence spectra was accomplished about approximately 1200 h at two different biofluid pH values (3.9 and 8.3). The temporal fluorescence intensity result is dependent on the pH of the saliva in which the QDs were embedded, QD functionalization and QD sizes. The time for an approximately 50% decrease in the peak intensity fluorescence of CdSe/ZnS QDs (3.4 nm core) and ultrasmall CdSe/CdS QDs is respectively 25 h and 312 h at pH 3.9 and 48 h and 360 h at pH 8.3.

Estudio de la eficiencia cuántica de un detector de microbandas de silicio mediante la modelación matemática / Study of silicon microstrips detector quantum efficiency using mathematical simulation

RESUMEN Se presentan los resultados en la aplicación de la simulación matemática para el estudio de la eficiencia cuántica de un detector de silicio cristalino del tipo microbandas, destinado a imagenología médica y al desarrollo de otras aplicaciones como la autenticación y fechado de obras de arte. Se evaluó el efecto de la geometría fuente-detector, de la energía de los rayos X y del grosor de la zona muerta del detector en la eficiencia cuántica de este dispositivo. Los resultados de la simulación se compararon con el pronóstico teórico y con los datos experimentales disponibles, verificándose una adecuada correspondencia. Se concluyó que la configuración frontal es más eficiente para energías incidentes menores a los 17 keV, y que la configuración de borde es la recomendada para aplicaciones que requieran la detección de energías superiores a este valor. También se determinó que la disminución de la zona muerta del detector conduce a un considerable aumento de la eficiencia para cualquier valor de energía en el intervalo de 5 a 100 keV.

ABSTRACT The paper shows the results from the application of mathematical simulation to study the quantum efficiency of a microstrips crystalline silicon detector, intended for medical imaging and the development of other applications such as authentication and dating of cultural heritage. The effects on the quantum efficiency of some parameters of the system, such as the detector-source geometry, X rays energy and detector dead zone thickness, were evaluated. The simulation results were compared with the theoretical prediction and experimental available data, resulting in a proper correspondence. It was concluded that the use of frontal configuration for incident energies lower than 17 keV is more efficient, however the use of the edge-on configuration for applications requiring the detection of energy above this value is recommended. It was also found that the reduction of the detector dead zone led to a considerable increase in quantum efficiency for any energy value in the interval from 5 to 100 keV.

Efeito da inundação de longa duração sob o crescimento de Pouteria glomerata (Sapotaceae), uma arbórea da várzea da Amazônia Central

To understand the occurrence of P. glomerata in the Amazonian várzea we investigated the morpho-physiological responses to long-term flooding. Seedlings of P. glomerata were subjected to two flooding treatments (partial and total) for six months. Following flooding treatments, we examined light-saturated photosynthesis (A), the potential quantum yield of photosystem II (inferred as the Fv/Fm ratio), height, number of leaves (NF), stem diameter at the base of the plant (DCC), leaf area and plant biomass. We found a decrease in gas exchange parameters and growth rates, whereas leaf damage increased with flooding. After six months of flooding, leaf area, and the total plant biomass as well as the biomass of the vegetative organs (leaf, stem and root) were lower in flooded seedlings than in control, non-flooded plants. As flooding level increased assimilated carbon was mainly allocated to stems. However, flooding treatments had no significant effect on specific leaf area, the root/shoot ratio and dry mass of roots. Totally submerged roots of flooded seedlings were strongly affected, showing to be the most critical condition for maintenance of physiological metabolism. P. glomerata was affected by long-term flooding. Thus, P. glomerata exhibited adjusts morpho-fisiological which makes it possible for this species to occur in the Amazon floodplain forest.

Para entender a ocorrência de P. glomerata na várzea amazônica, investigamos as respostas morfo-fisiológicas a longo período de inundação. Durante seis meses, plântulas de P. glomerata foram submetidas a dois tratamentos de inundação (parcial e total) para análise da assimilação fotossintética líquida (A), eficiência quântica do fotosistema II (referido como Fv/Fm), altura, número de folhas, diâmetro do colo do caule (DCC), área foliar e biomassa da planta. Encontramos um decréscimo da atividade de trocas gasosas, das taxas de crescimento e danos foliares com o aumento do nível de inundação. Após seis meses de experimento, a área foliar, a biomassa dos órgãos vegetativos (raiz, caule e folha) e a biomassa total das plântulas inundadas foram menores que das plântulas controle, plântulas não-inundadas. De acordo com o aumento do nível de inundação, a biomassa fotoassimilada foi alocada principalmente para o caule. Somente área foliar específica, razão raiz / parte aérea e massa seca de raiz não apresentaram diferenças entre os tratamentos. As plântulas totalmente inundadas foram fortemente comprometidas, demonstrando ser esta à condição mais crítica para a manutenção do metabolismo fisiológico. P. glomerata foi afetada pelo longo período de inundação, no entanto a espécie revela adaptações morfo-fisiologica que justifica a sua ocorrência em florestas de várzea.

Efeito da inundação de longa duração sob o crescimento de Pouteria glomerata (Sapotaceae), uma arbórea da várzea da Amazônia Central

To understand the occurrence of P. glomerata in the Amazonian várzea we investigated the morpho-physiological responses to long-term flooding. Seedlings of P. glomerata were subjected to two flooding treatments (partial and total) for six months. Following flooding treatments, we examined light-saturated photosynthesis (A), the potential quantum yield of photosystem II (inferred as the Fv/Fm ratio), height, number of leaves (NF), stem diameter at the base of the plant (DCC), leaf area and plant biomass. We found a decrease in gas exchange parameters and growth rates, whereas leaf damage increased with flooding. After six months of flooding, leaf area, and the total plant biomass as well as the biomass of the vegetative organs (leaf, stem and root) were lower in flooded seedlings than in control, non-flooded plants. As flooding level increased assimilated carbon was mainly allocated to stems. However, flooding treatments had no significant effect on specific leaf area, the root/shoot ratio and dry mass of roots. Totally submerged roots of flooded seedlings were strongly affected, showing to be the most critical condition for maintenance of physiological metabolism. P. glomerata was affected by long-term flooding. Thus, P. glomerata exhibited adjusts morpho-fisiological which makes it possible for this species to occur in the Amazon floodplain forest.

Para entender a ocorrência de P. glomerata na várzea amazônica, investigamos as respostas morfo-fisiológicas a longo período de inundação. Durante seis meses, plântulas de P. glomerata foram submetidas a dois tratamentos de inundação (parcial e total) para análise da assimilação fotossintética líquida (A), eficiência quântica do fotosistema II (referido como Fv/Fm), altura, número de folhas, diâmetro do colo do caule (DCC), área foliar e biomassa da planta. Encontramos um decréscimo da atividade de trocas gasosas, das taxas de crescimento e danos foliares com o aumento do nível de inundação. Após seis meses de experimento, a área foliar, a biomassa dos órgãos vegetativos (raiz, caule e folha) e a biomassa total das plântulas inundadas foram menores que das plântulas controle, plântulas não-inundadas. De acordo com o aumento do nível de inundação, a biomassa fotoassimilada foi alocada principalmente para o caule. Somente área foliar específica, razão raiz / parte aérea e massa seca de raiz não apresentaram diferenças entre os tratamentos. As plântulas totalmente inundadas foram fortemente comprometidas, demonstrando ser esta à condição mais crítica para a manutenção do metabolismo fisiológico. P. glomerata foi afetada pelo longo período de inundação, no entanto a espécie revela adaptações morfo-fisiologica que justifica a sua ocorrência em florestas de várzea.