Fluence Rate Research Articles

Preparation and characterization of solid lipid nanoparticles incorporating bioactive coumarin analogues as photosensitizing agents

Daphnetin (7,8-dihydroxy-coumarin, DAPH) is a naturally occurring coumarin presenting a wide array of biological activities. In the present study, daphnetin and its novel synthetic analogue 7,8-dihydroxy-4-methyl-3-(4-hydroxyphenyl)-coumarin (DHC) were encapsulated in solid lipid nanoparticles (SLNs) with Encapsulation Efficiency values of 80% and 40%, respectively. Nanoparticles of an average hydrodynamic diameter of approximately 250 nm were formed, showing a good stability in aqueous dispersion (polydispersity index 0.3–0.4), as determined by Dynamic Light Scattering (DLS). The SLNs were also characterized using Fourier Transform-Infrared (FT-IR) spectroscopy and Thermogravimetric Analysis (TGA). TEM images of the blank-SLNs indicated a spherical morphology and a size of 20–50 nm. The release studies of the coumarin analogues indicated a non-Fickian diffusion mechanism, while the release profiles better fitted on the Higuchi kinetic model. Moreover, the coumarin analogues and their SLNs were examined for their antioxidant activity using DPPH and anti-lipid peroxidation assays, exhibiting stronger antioxidant activity when encapsulated than in their free form. The coumarin derivatives and their SLNs were examined for their photodynamic therapy (PDT) efficacy against the human squamous carcinoma A431 cell line, with DHC coumarin both in its free and encapsulated form exhibiting significant PDT activity, reducing the cell viability to 11% after irradiation with a fluence rate of 2.16 J/cm2. Finally, the intracellular localization studies indicated the enhanced cellular uptake of the coumarin analogues when loaded in the SLNs.

MLEM Neutron Spectra Unfolding in a Radiotherapy Bunker Using Bonner Sphere Spectrometer

High-energy radiotherapy treatments of a medical Linear Accelerator (LinAc) generate secondary neutrons that can produce health damage on the human body as the induction of secondary cancers. The energy spectrum of these neutrons must be determined to estimate the extra dose received by patients inside a radiotherapy room during radiotherapy treatment. To quantify the neutron production, a Ludlum Bonner sphere spectrometer (BSS) is used for measurement at different points of a LinAc bunker at the Hospital Universitari i Politècnic La Fe de València. With the neutron measured data and a set of response detector curves obtained by Monte Carlo simulations with MCNP6.1.1, the Maximum Likelihood Expectation Maximization unfolding method is used to unfold the energy neutron spectrum. Unfolded neutron spectra at different locations were compared to those obtained by Monte Carlo simulation of the same setup, showing the same energetic behavior. The fluence rate decreases with source distance, and the shape changes from a fast neutron peak in the nearest LinAc head location to a prominent thermal neutron peak in the bunker maze region. Moreover, the neutron ambient equivalent dose was obtained from the unfolded spectra and compared to Berthold detector measurements, being consistent.

Estimation of scattered radiation influence on neutron beams at a calibration laboratory using Monte Carlo simulation of a long counter

At the Neutron Calibration Laboratory (LCN) of IPEN/CNEN, a 241AmBe source was used to test and calibrate neutron detectors. The neutrons emitted by the source reach the detector as intended, but they also scatter undesirably from the building's floor, ceiling, and walls, leading to indirect detection. A Long Counter (LC) detector was modeled using the MCNPX Monte Carlo code. The objective of this study was to measure the contribution of scattered radiation at the LCN / IPEN, and to determine the fluence rate, at different points in the calibration room at source-to-detector distances of 100 cm and 150 cm; subsequently, the results were compared with those of the Brazilian Laboratory of Metrology of Ionizing Radiation (LNMRI). The results show that the fluence rates of LCN / IPEN are comparable to those of this neutron laboratory for the 100 and 150 cm source-to-detector distances using a 241AmBe source (37 GBq). The results show that the calibration of neutron detectors should be performed at distances less than 100 cm, where the contribution of scattered radiation is within the 40% limit recommended by ISO 8529-1.

Radiation Modeling and the Simulation of the Microorganism Disinfection in Ultraviolet Reactors

Ultraviolet disinfection can effectively destroy waterborne microorganisms. Modeling ultraviolet disinfection includes the solution of the flow field, the radiation field, and the concentration field. Radiation plays an important role in the inactivation kinetics of microorganisms. The present study presents the irradiance method to determine the irradiation flux at the lamp surface, which satisfies the energy conservation law. A careful analysis shows that the fluence rate method may overestimate the emitted energy of the lamp nearly 30–40% and violates the energy conservation law. The simulation of ultraviolet reactors shows that the fluence rate is overestimated by the fluence rate method. The concentration of microorganisms in ultraviolet reactors is also overestimated nearly 32% by the fluence rate method than by the irradiance method. The LOG reduction predicted using the fluence rate method is nearly 50% more than that using the irradiance method. The present irradiance method can ensure energy conservation and predict the correct disinfection performance in ultraviolet reactors.

Thermal neutron reference radiation facility with high thermalization and large uniformity area

A new thermal neutron facility based on 12 241Am–Be neutron sources has been established at the National Institute of Metrology, China. It has two independent irradiation fields, the inner field and outer field, constructed with high-purity graphite and heavy water as moderators, respectively. Three innovative designs, including the reflection cavity, reflection layer, and homogenizing lens, were introduced to improve the performance of the facility. The reflection layer can increase the thermal neutron fluence rate by about 3–4 times, the reflection cavity also enhances thermal fluence by 3–4 times by taking advantage of multiple scattering of neutrons, and the homogenizing lens mounted on the neutron exit surface of the moderator improve the distribution of thermal neutron. The characteristics of the two fields were investigated by Monte Carlo simulations and experimental measurements. The results show that the new facility has high thermalization and large uniformity area with these innovative designs. For the inner field, the thermal neutron fluence rate at the reference position is (21 433.3 ± 407.2) cm−2 s−1, the cadmium ratio is 20.6, the non-uniformity is 0.1% over the 40 cm × 40 cm region. For the outer field, the thermal fluence rate at the reference position is (2046.0 ± 49.1) cm−2 s−1, the cadmium ratio is 1433, and the non-uniformity is 0.7% in the 70 cm × 70 cm region. The facility is expected to be suitable for the large-size detector, and its excellent performance is attractive for various thermal neutron experiments.

Light-driven transitions in quantum paraelectrics

Motivated by recent experiments on pump-induced polar ordering in the quantum paraelectric SrTiO$_3$, we study a driven phonon system close to a second order phase transition. Analyzing its classical dynamics, we find that sufficiently strong driving leads to transitions into polar phases whose structures, determined by the light polarization, are not all accessible in equilibrium. In addition, for certain intensity profiles we demonstrate the possibility of two-step transitions as a function of fluence. For even stronger field intensities, the possibility of period-doubling and chaotic behavior is demonstrated. Finally we develop a generalized formalism that allows us to consider quantum corrections to the classical dynamics in a systematic fashion. We predict a shift in the critical pump fluence due to quantum fluctuations with a characteristic dependence on the fluence increase rate, which can be observed in experiments.

Multiple roles of UV/KMnO4 in cyanobacteria containing water treatment: Cell inactivation & removal, and microcystin degradation

Cyanobacterial blooms present great challenges to drinking water treatment and human health. The novel combination of potassium permanganate (KMnO4) and ultraviolet (UV) radiation is engaged as a promising advanced oxidation process in water purification. This study investigated the treatment of a typical cyanobacteria, Microcystis aeruginosa by UV/KMnO4. Cell inactivation was significantly improved by UV/KMnO4 treatment, compared to UV alone or KMnO4 alone, and cells were completely inactivated within 35 min by UV/KMnO4 in natural water. Moreover, effective degradation of associated microcystins was simultaneously achieved at UV fluence rate of 0.88 mW cm-2 and KMnO4 dosages of 3–5 mg L-1. The significant synergistic effect is possibly attributable to the highly oxidative species produced during UV photolysis of KMnO4. In addition, the cell removal efficiency via self-settling reached 87.9 % after UV/KMnO4 treatment, without additional coagulants. The fast in situ generated manganese dioxide was responsible for the enhancement of M. aeruginosa cell removal. This study firstly reports multiple roles of UV/KMnO4 process in cyanobacterial cell inactivation and removal, as well as simultaneous microcystin degradation under practical conditions.

Metronomic Photodynamic Therapy with Conjugated Polymer Nanoparticles in Glioblastoma Tumor Microenvironment.

Alternative therapies such as photodynamic therapy (PDT) that combine light, oxygen and photosensitizers (PSs) have been proposed for glioblastoma (GBM) management to overcome conventional treatment issues. An important disadvantage of PDT using a high light irradiance (fluence rate) (cPDT) is the abrupt oxygen consumption that leads to resistance to the treatment. PDT metronomic regimens (mPDT) involving administering light at a low irradiation intensity over a relatively long period of time could be an alternative to circumvent the limitations of conventional PDT protocols. The main objective of the present work was to compare the effectiveness of PDT with an advanced PS based on conjugated polymer nanoparticles (CPN) developed by our group in two irradiation modalities: cPDT and mPDT. The in vitro evaluation was carried out based on cell viability, the impact on the macrophage population of the tumor microenvironment in co-culture conditions and the modulation of HIF-1α as an indirect indicator of oxygen consumption. mPDT regimens with CPNs resulted in more effective cell death, a lower activation of molecular pathways of therapeutic resistance and macrophage polarization towards an antitumoral phenotype. Additionally, mPDT was tested in a GBM heterotopic mouse model, confirming its good performance with promising tumor growth inhibition and apoptotic cell death induction.

The photosensory function of Zmphot1 differs from that of Atphot1 due to the C-terminus of Zmphot1 during phototropic response

The role of phot1 in triggering hypocotyl phototropism and optimizing growth orientation has been well-characterized in Arabidopsis, whereas the role of Zmphot1 in maize remains largely unclear. Here, we show that Zmphot1 is involved in blue light-induced phototropism. Compared with Atphot1, Zmphot1 exhibited a weaker phototropic response to very low-fluence rates of blue light (< 0.01 μmol m−2 s−1), but stronger phototropic response to high-fluence rates of blue light (> 10 μmol m−2 s−1) than Atphot1. Notably, blue light exposure induced Zmphot1-green fluorescent protein (GFP), but not Atphot1-GFP, to form the aggregates in the cytoplasm of Nicotiana benthamiana cells. Furthermore, by generating the chimeric phot1 proteins, we found that the serine-threonine kinase (STK) domain at the C-terminus is responsible for a more volatile membrane association of Zmphot1. Consistently, the chimeric phot1 protein fusing the STK domain of Zmphot1 with other domains of Atphot1 responded similarly as Zmphot1 to both low and high fluence rates of blue light. Interestingly, although both Zmphot1 and Atphot1 interact with AtNPH3, Zmphot1 induced weaker dephosphorylation of NON-PHOTOTROPIC HYPOCOTYL 3 (NPH3) than Atphot1. Together, our findings indicate that Zmphot1 and Atphot1 exhibit different photosensory function during phototropic response and that the STK domain may play a key role in determining their properties.

Numerical study of light scattering and propagation in soymilk: Effects of particle size distributions, concentrations, and medium sizes

Understanding light scattering and propagation in soymilk is crucial for the nondestructive evaluation of food qualities of soymilk and its products by near-infrared spectroscopy. We aim to numerically examine light scattering and propagation in soymilk samples with different solid-content properties (particle size distributions and concentrations) and medium sizes. Using the dependent scattering theory, we calculated the light-scattering properties of the samples on the sub-nanometer scale. In contrast, we calculated light propagation on the millimeter scale using the radiative transfer theory. Our numerical results show that the scattering properties of soymilk strongly depend on the solid-content properties, implying a high correlation between the solid-content and scattering properties. The sample with the largest mean diameter and broadest size distribution has the smallest reduced scattering coefficient among the samples, although it has the largest scattering coefficient. We compared the reflected fluence rates in a cylinder and semi-infinite medium. The comparative study shows the finite size effect on light propagation can be negligible at the cylinder radius of more than 2.0 cm. In that case, the light propagation model for a semi-infinite medium is a better choice to provide fast calculations in inverse analysis on the scattering properties. Our findings are essential for further developing near-infrared spectroscopy using scattered light and the physics of light scattering in dense polydisperse media.

Cosmic neutrons at ground: new spectral measurements at 3480 m a.s.l. and benchmarking of the cascade component as a function of the elevation at around 45° geomagnetic latitude

Within the INFN-based project SAMADHA, environment neutron spectrum measurements were performed at 3480 m a.s.l. on the Italian western Alps. An extended range Bonner Sphere Spectrometer was used, that was especially designed to operate unattended and to discriminate genuine neutron events from spurious ones. In addition to the measurements of neutron fluence rate, its energy distribution and the related ambient dose equivalent, as well as the arrival time distribution of the events were also studied. The high-energy component of the neutron fluence rate was compared to literature data measured with the same technique at similar latitudes as a function of the elevation, in turn being fitted with an exponential curve and compared to the results from EXPACS code. As the cascade component is not influenced by the materials surrounding the measurement site, this curve can be regarded as “universal” at the studied latitudes.

Radiation modeling of microplasma UV lamps for design analysis and optimization

Microplasma UV lamps have recently emerged as viable excimer-based sources of UV radiation, garnering significant attention during the recent COVID-19 pandemic for their use in disinfection applications because of their ability to emit human-safe far-UVC (200–240 nm) spectrums. An accurate model to simulate the radiation profile of microplasma UV lamps is of paramount importance to develop efficient microplasma lamp-implemented systems. We developed a 3D numerical model of microplasma UV lamps using the ray optics method. The simulation results for lamp irradiance and fluence rate were experimentally validated with standard optical radiometry and actinometry measurements, respectively. To improve the optical efficiency of microplasma lamps, an in-depth analysis of radiation behavior inside the standard commercially available lamp was performed using the geometrical optics method, and several potential scenarios were explored. A 2D modeling of an individual microcavity indicated that the current common lamp design can be significantly improved by preventing radiation loss, and small modifications in optical design can greatly increase the energy performance of the system. Based on the findings of this study, several virtual design concepts were proposed, and their performances were numerically compared with that of the original design of commercial microplasma lamps. The developed model can potentially be integrated with hydrodynamic and kinetic models for the virtual prototyping of complex photoreactors operating with UV microplasma lamps.

KrF excimer laser for Pt–NPs synthesis by PLAL in isopropanol solution and their use in a SERS application

Pulsed laser ablation in aqueous isopropanol (IPA) solution (PLAL) using KrF excimer laser was employed for the first time to produce platinum nanoparticles (Pt–NPs). The dependence of their optical and morphological properties on the IPA concentration and ablation time at certain values of the laser fluence (LF) and repetition rates (RR), was investigated. The UV/Vis transmission (T) spectra of the Pt–NPs were measured to assess indirectly their type, relative mean size (MS) and standard deviation (SD). Peculiarities of this spectra, related to the presence of a volatile component in the solution are discussed. Morphological properties as shape, MS, SD, and microstructure were studied via High-Resolution Scanning Transmission Electron Microscopy (HR-STEM). The created Pt–NPs show spherical shape with smallest MS value of 1.7 nm using 2.3 Jcm−2 LF, 10 Hz RR and 10 min ablation time in 80% aqueous IPA solution and the narrowest SD of ±0.7 nm with the same technological parameters but using 30% IPA concentration. The Pt nature of the NPs was confirmed by Energy Dispersive X-Ray technique. The crystallographic structure was determined by HR-STEM and X-ray diffraction measurements. An application of the synthesized Pt–NPs is presented using their role as substrate in methylene blue through surface-enhanced Raman spectroscopy method.

Optimization of energy parameters for laser-induced PDT of cervical tissues using numerical simulation and fluorescent monitoring

The main problem in the photodynamic therapy (PDT) of tumors is insufficient light exposure to tissue or the appearance of undesirable surface effects. The reason is the irregular distribution of the absorbed light dose by depth. The influence of the spot diameter on the relative fluence rate in the near-surface layer of the cervical tissue was studied by Monte Carlo simulation. Photodynamic exposure with chlorine-type photosensitizer (PS) was carried out on the tissue model with laser 660 nm at the same power density with a change in spot diameter from 5 to 15 mm and radiation energy density from 100 to 300 J cm−2. The distributions of the fluorescence indices of the PS and the hemoglobin oxygenation degree by depth were obtained. The dependence of PS photobleaching on the energy density was established at the same power density and different spot diameters. The developed method increased the efficiency of PDT by delivering a sufficient energy density of laser radiation to the entire tumor tissue by depth without thermal damage, that allowed minimizing side effects and prevent possible growth and recurrence of the disease.

The Influence Mechanism of Neutron Kinetics of the Accelerator-Driven Subcritical Reactor Based on the Fast/Thermal Neutron Spectra by Monte Carlo Homogenization Method

For the sake of understanding the mechanism of deep subcriticality and high heterogeneity of neutron fluence rate in time–space on the neutron kinetics of the Accelerator-driven Subcritical Reactor Subcritical Reactor (ADSR) under varied beam transients and neutron spectra. A Monte Carlo homogenization approach for the neutron time–space kinetics of the ADSR is proposed in this study, and the influence mechanism on the kinetic parameters of the ADSR under varied neutron spectra, subcriticality, and beam transients is examined. The results show that the Monte Carlo homogenization for the α eigenvalue mode is more adaptable to the subcriticality characteristics under varied subcriticality; under beam transients, the relative differences in the kinetic parameters of the different modes of the ADSR with fast/thermal spectra increase with the depth of subcriticality, and the differences in neutron generation time for varied modes are larger than those of effective fraction of delayed neutron. Thus, it is recommended to use a more adaptable Monte Carlo homogenization method for the time–space kinetics of ADSR, and the effects of the high heterogeneity of neutron fluence rate and deep subcriticality in time–space on the neutron generation time should be considered.

Optimizing UVC-disinfection using LEDs as an energy efficient pre-treatment for biofouling control in spiral-wound membrane systems

Biofouling remains a major challenge for reverse osmosis (RO) systems. Pulsed ultraviolet (UV) pre-treatment has been proposed as a mitigation strategy for biofouling control of RO membranes. This study investigated whether increasing fluence rate during pulsed UV disinfection leads to enhanced inactivation. Further, UV irradiation from 1.5 to 61.3 mJ cm−2 was tested for optimal biofouling control. Therefore, an UVC-LED reactor was characterized by successfully adapting an actinometry method for flow-through mode. The inactivation of microorganisms was compared in flow-through biodosimetry experiments in pulsed and continuous irradiation. Finally, several settings were applied as pre-treatment in lab-scale biofouling experiments and membrane performance and biofilm removability elucidated. Whereas no enhanced inactivation was observed during biodosimetry experiments, pulsed UV disinfection resulted in an average of 20.6 % increased delay of biofilm formation. On the contrary, for pulsed UV disinfection, the biofilm hydraulic resistance seemed higher than continuous equivalents, but not significantly. Overall, savings of operational expenditures per fluence applied was highest around 4 mJ cm−2. UV pre-treated biofilms showed no enhanced removability, but delay in biofilm formation was noticeable in two of three experiments. In case the effects translate to up-scaled applications over several cleanings, UV pre-treatment for biofouling control is an interesting option.

Shade-Induced Leaf Senescence in Plants.

Leaf senescence is a vital developmental process that involves the orderly breakdown of macromolecules to transfer nutrients from mature leaves to emerging and reproductive organs. This process is essential for a plant's overall fitness. Multiple internal and external factors, such as leaf age, plant hormones, stresses, and light environment, regulate the onset and progression of leaf senescence. When plants grow close to each other or are shaded, it results in significant alterations in light quantity and quality, such as a decrease in photosynthetically active radiation (PAR), a drop in red/far-red light ratios, and a reduction in blue light fluence rate, which triggers premature leaf senescence. Recently, studies have identified various components involved in light, phytohormone, and other signaling pathways that regulate the leaf senescence process in response to shade. This review summarizes the current knowledge on the molecular mechanisms that control leaf senescence induced by shade.

Modeling optical fluence and diffuse reflectance distribution in normal and cancerous breast tissues exposed to planar and Gaussian NIR beam shapes using Monte Carlo simulation

Precise knowledge about light propagation in biological tissues is necessary for accurate diagnostics and effective therapies utilizing optical technologies. In the current paper, the Monte Carlo simulation is applied to study light dispersion in normal and cancerous breast after irradiating to different laser beam shapes. Two distinct laser wavelengths (800-1100nm) with planar and Gaussian shapes were employed. The spatially resolved steady-state diffuse reflectance of normal tissue and tumor was investigated using Monte Carlo simulation method via MCML and MCXLAB computations. The diffusion equation was solved to simulate the fluence rate at the tissue surface based on the optical parameter values (i.e., scattering and absorption coefficients). The results confirm differences in diffuse reflectance and optical fluence distribution between the normal and tumor tissues at each wavelength. Tissue optical parameters and the utilized laser beam shape control the distribution of the fluence rate within tissues. Therefore, offering visual representations of these distributions can provide a secure visual route for biological diagnostics.

Response Function of Active Thermal Neutron Detector for Boron Neutron Capture Therapy Using Back-Illuminated Thin Si PIN Diode

A lithium fluoride-silicon-based neutron detector was developed for real-time measurement of neutron beams for boron neutron capture therapy (BNCT). Detection efficiencies for thermal neutrons were measured at the national standard neutron field in Japan and simulated using a Monte Carlo simulation code to evaluate the absolute BNCT neutron fluence rates. The simulation neutron detection efficiencies agreed excellently with the experimental results, within an experimental error of 3%. The simulation results reproduced well the peaks of tritons and alpha particles emitted from the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li(n,t) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> He reaction, peak of the protons produced by the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> N(n,p) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> C reaction in air, and distribution of alpha particles produced by the neutron capture reactions of dopant boron. The active BNCT neutron detector was characterized based on the experimental and simulation results.

A Monte Carlo simulation for Moving Light Source in Intracavity PDT.

We developed a simulation method for modeling the light fluence delivery in intracavity Photodynamic Therapy (icav-PDT) for pleural lung cancer using a moving light source. Due to the large surface area of the pleural lung cavity, the light source needs to be moved to deliver a uniform dose around the entire cavity. While multiple fixed detectors are used for dosimetry at a few locations, an accurate simulation of light fluence and fluence rate is still needed for the rest of the cavity. We extended an existing Monte Carlo (MC) based light propagation solver to support moving light sources by densely sampling the continuous light source trajectory and assigning the proper number of photon packages launched along the way. The performance of Simphotek GPU CUDA-based implementation of the method - PEDSy-MC - has been demonstrated on a life-size lung-shaped phantom, custom printed for testing icav-PDT navigation system at the Perlman School of Medicine (PSM) - calculations completed under a minute (for some cases) and within minutes have been achieved. We demonstrate results within a 5% error of the analytic solution for multiple detectors in the phantom. PEDSy-MC is accompanied by a dose-cavity visualization tool that allows real-time inspection of dose values of the treated cavity in 2D and 3D, which will be expanded to ongoing clinical trials at PSM. PSM has developed a technology to measure 8-detectors in a pleural cavity phantom using Photofrin-mediated PDT that has been used during validation.