Threshold Irradiance Research Articles

Sintering of copper nanoparticles using intense pulsed light for screen-printed films on flexible substrate

Abstract Rapid growth in applications involving large area flexible electronics has led to wide adoption of the technique of sintering printed films using intense pulsed light due to its pulse mode operation and ability to reach high sintering temperatures without affecting the underlying substrate significantly. We study the sintering mechanisms of screen-printed thin films of copper nanoparticles on polyethylene terephthalate plastic substrates by varying the irradiance energy over a wide range to monitor conductivity and associated microstructure changes. We obtain optimized parameters which indicate the existence of a sharp threshold irradiance energy to kickstart sintering, and two distinct regimes beyond that. The low temperature regime has a high energy barrier while the high temperature regime has a substantially reduced energy barrier with a change of phase due to local melting.

Effects of specular reflectance in laser-induced breakdown of metals

We investigate the effects of specular reflection on the laser-induced breakdown (LIB) of copper, iron, and tungsten using fast photography and optical emission spectroscopy. The laser parameters include spot diameter ranging from 30.89 to 1589.33 μm, irradiance from 467.10 to 0.17 GW/cm2, with a single pulse of 6 ns duration and 21 mJ energy. As the laser spot defocuses, the plasma morphology changes from a single plasma near the target surface to a separated, independently evolving two-component plasma, and then to a single plasma suspended above. The defocusing distance for this transition is significantly influenced by specular reflectance. The separate plasma, comprising of a metallic component and an air component, occurs only under high specular reflectance conditions: ≥66.7% for copper, ≥51.4% for iron, and ≥44.9% for tungsten. The spectral emission of the metallic component initially increases and then decreases with reducing specular reflectance, due to a trade-off between enhanced surface absorption and reduced irradiance caused by surface roughening. LIB threshold irradiance increases with specular reflectance, rising from 0.31 to 1.22 GW/cm2 for copper, 0.24 to 0.70 GW/cm2 for iron, and 0.38 to 0.87 GW/cm2 for tungsten. These findings show the impact of sample pretreatment on LIB ignition and subsequent plasma evolution, offering insights into potential sources of inaccuracy in LIB applications.

Highly efficient and thermally conductive phosphor in glass based on two-component regulatory and h-BN addition

Achieving laser-driven solid-state lighting with higher brightness and laser power density engenders new requirements for higher-performance phosphor conversion materials. In this study, a highly efficient and thermally conductive tellurite phosphor-in-glass (PIG) added with hexagonal boron nitride (h-BN) was prepared for high-power laser driving. Reduction in the thermal expansion coefficient and refractive index matching with phosphor were realized by two-component regulation of the tellurite glass, which contributed to an enhanced laser irradiation threshold and luminous efficiency of the PIG. Furthermore, the micron h-BN powder, which served as a heat dissipation material and light scattering center, was uniformly dispersed within the PIG by stirring, which increased the thermal conductivity of the composite by 42 %. Microstructural characterization and XRD analysis indicated the ideal compound effect of h-BN and the integrity of the phosphor crystal phase. Notably, under irradiation with a high-power laser, the thermal stability of the composite material was significantly improved, and the luminous efficiency increased to 183.2 lm/W. Therefore, through component regulation and process optimization, the h-BN-added tellurite PIG acquired a high laser irradiation threshold and superior luminous efficiency, making it promising for applications in laser-driven white lighting.

Light Polymerization through Glass-ceramics: Influence of Light-polymerizing Unit's Emitted Power and Restoration Parameters (Shade, Translucency, and Thickness) on Transmitted Radiant Power.

This in vitro study assessed light transmission through ceramic discs varying in shade, translucency, and thickness using light-polymerizing units with different radiant power/flux (RP) outputs. Disc-shaped specimens (0.5 mm, 1.0 mm, and 2.0 mm) were made from high and low-translucency glass-ceramic ingots (IPS e.max Press) in shades A1 and A4, totaling 60 discs. Two light-polymerizing units with different power outputs were used, and their emission spectra were verified. The transmitted RP values for each ceramic specimen were measured and irradiance and radiant energy influx were calculated. Differences between the light-polymerizing units and the influence of the three ceramic parameters were evaluated using an independent-samples t-test and three-way analysis of variance (ANOVA) tests (α = 0.05). A statistically significant difference was observed in the mean transmitted RP values between the two light-polymerizing units. Furthermore, the three-way ANOVA test showed a significant effect of shade, translucency, and thickness, as well as a significant interaction between each pair of variables and all three variables on the transmitted RP (P < 0.05). Despite the significant attenuation in the transmitted RP, especially in ceramics with higher shade chromaticity and thickness and lower translucency, the calculated minimal irradiance values for both light-polymerizing units (their emitted power ≥ 500 mW) were greater than the minimum recommended irradiance threshold (100 mW/cm2). However, the exposure duration needs to be increased to provide the resin with sufficient radiant exposure for adequate polymerization.

Picosecond laser-induced evolution of processing properties of 4H–SiC

The irradiation threshold of 4H–SiC under picosecond laser action was calculated, and the influence of laser parameters on the size of 4H–SiC was studied. According to the model, the evolution rule of the microgroove size was predicted. The effect of laser parameters on the mechanical properties of 4H–SiC was studied by nanoindentation. The results show that the ablation threshold energy density of the picosecond laser on 4H–SiC is 2.67 J/cm2. The effect regular of laser parameters on the size of 4H–SiC microgrooves: energy density > scanning speed > scanning interval. The error of the microgroove which is between the predicted value and measurements is within 10 %. By doing nanoindentation detection, proving that Pop-in is the elastic-plastic transition point. It shows that laser irradiation has a significant modification effect on the mechanical properties of 4H–SiC. According to the difference range of elastic modulus and hardness, showing that the influence of laser energy density on mechanical properties is dominant. The consequences of the study provide a theoretical foundation for subsequent CMP processing.

Comparing different approaches to define shading control threshold via a new automatic building simulation platform

Active shading systems are essential to prevent heat gains in buildings and reduce the risk of overheating phenomena. The control logic must avoid overheating while allowing solar gains during heating hours. In general, smart control is based on a temperature and/or solar irradiation threshold; however, innovative informatics tools now allow optimising these thresholds based on specific building and climate characteristics. The paper presents a new building energy dynamic simulation platform used here to define optimal shading control thresholds for free-running and mechanically cooled spaces. Several shading control approaches are applied and compared, considering fixed hourly schedules, controls based on standard thresholds, and optimised thresholds with the tool. The analysis is performed considering the sole summer. The approach shows how the developed platform and the proposed methodology can optimise shading control thresholds, considering the specific building characteristics and the local climate conditions, consequently reducing energy needs or thermal discomfort conditions.

Probabilistic Solar Forecasts as a Binary Event Using a Sky Camera

With the fast increase of solar energy plants, a high-quality short-term forecast is required to smoothly integrate their production in the electricity grids. Usually, forecasting systems predict the future solar energy as a continuous variable. But for particular applications, such as concentrated solar plants with tracking devices, the operator needs to anticipate the achievement of a solar irradiance threshold to start or stop their system. In this case, binary forecasts are more relevant. Moreover, while most forecasting systems are deterministic, the probabilistic approach provides additional information about their inherent uncertainty that is essential for decision-making. The objective of this work is to propose a methodology to generate probabilistic solar forecasts as a binary event for very short-term horizons between 1 and 30 min. Among the various techniques developed to predict the solar potential for the next few minutes, sky imagery is one of the most promising. Therefore, we propose in this work to combine a state-of-the-art model based on a sky camera and a discrete choice model to predict the probability of an irradiance threshold suitable for plant operators. Two well-known parametric discrete choice models, logit and probit models, and a machine learning technique, random forest, were tested to post-process the deterministic forecast derived from sky images. All three models significantly improve the quality of the original deterministic forecast. However, random forest gives the best results and especially provides reliable probability predictions.

Assessment of automated shading systems’ utilization and environmental performance: An experimental study

This paper presents an experimental study conducted in a full-scale test cell “btga-box” from July until September 2020 at Wuppertal University, Germany. This study focused on evaluating occupant interaction and satisfaction with automated shading systems in office environments, and the underlying thermal and visual conditions under different scenarios to optimize automated shading design and operation for improving occupant comfort and energy efficiency. Six different scenarios were evaluated using several performance metrics. Twenty-eight participants of varying ages, gender, and ethnicity took part in the experiments. After each scenario, the participants were asked to complete a web-based questionnaire to report their behaviour, their perceived thermal and visual comfort, satisfaction, and preferences concerning the performance of automated shading controls. Concurrently, indoor environmental parameters, weather data, and system and user-triggered actions were recorded. The key findings of this study suggest that a robust shading system (i.e., few override actions) can be achieved by: deploying a multi-objective control strategy with an intermediate position, an acceptable range of irradiance thresholds, and a decent level of other adaptive behavioural control options (i.e., window opening, fan usage, and light control). Providing active cooling or ventilation systems (i.e., operable windows, exhaust ventilation, and ceiling fan) can improve user satisfaction with the indoor environment, including shade operation. Using a small window size combined with a high irradiance shade-lowering threshold decreased the user-raising actions by 49% compared to the low threshold. However, energy implications should be considered for further studies since user satisfaction with blind control should be balanced with energy efficiency.

Quantitative analysis of the optogenetic excitability of CA1 neurons.

Optogenetics has emerged as a promising technique for modulating neuronal activity and holds potential for the treatment of neurological disorders such as temporal lobe epilepsy (TLE). However, clinical translation still faces many challenges. This in-silico study aims to enhance the understanding of optogenetic excitability in CA1 cells and to identify strategies for improving stimulation protocols. Employing state-of-the-art computational models coupled with Monte Carlo simulated light propagation, the optogenetic excitability of four CA1 cells, two pyramidal and two interneurons, expressing ChR2(H134R) is investigated. The results demonstrate that confining the opsin to specific neuronal membrane compartments significantly improves excitability. An improvement is also achieved by focusing the light beam on the most excitable cell region. Moreover, the perpendicular orientation of the optical fiber relative to the somato-dendritic axis yields superior results. Inter-cell variability is observed, highlighting the importance of considering neuron degeneracy when designing optogenetic tools. Opsin confinement to the basal dendrites of the pyramidal cells renders the neuron the most excitable. A global sensitivity analysis identified opsin location and expression level as having the greatest impact on simulation outcomes. The error reduction of simulation outcome due to coupling of neuron modeling with light propagation is shown. The results promote spatial confinement and increased opsin expression levels as important improvement strategies. On the other hand, uncertainties in these parameters limit precise determination of the irradiance thresholds. This study provides valuable insights on optogenetic excitability of CA1 cells useful for the development of improved optogenetic stimulation protocols for, for instance, TLE treatment.

Observation of the two-photon transition enhanced first hyperpolarizability spectra in cinnamaldehyde derivatives: A femtosecond regime study.

The application of nonlinear optical effects in optoelectronic devices is still scarce because the irradiance threshold necessary to induce a specific effect is very high. In this context, knowing the frequency-resolved first order molecular hyperpolarizability (β) is essential to identifying regions where this response is intense enough to allow for applications in commercial devices. Thus, herein, we have determined the β spectral dependence of five new push-pull cinnamylidene acetophenone derivatives using femtosecond laser-induced Hyper-Rayleigh Scattering (HRS). A considerable increase in β values was observed in molecules. We found remarkable β values in regions near the two-photon resonance, which are mediated by electron withdrawing and donating groups. This effect was mapped using wavelength-tunable femtosecond Z-scan technique. Furthermore, it was modeled in light of the sum-over-states approach for the second- and third-order nonlinearities. Finally, our outcomes suggest a strategy to obtain large β values mediated by the 2PA transition.

Bioluminescence potential during polar night: impact of behavioral light sensitivity and water mass pathways

During polar nights of 2012 and 2017, bioluminescence (BL) potential surveys demonstrated high emissions at depths around and below 100 m at offshore stations to the north of a Svalbard fjord (Rijpfjorden). We demonstrated that the highest bioluminescent emissions for offshore stations are located at depths below depths of modelled/ambient light intensities corresponding to the reported irradiance thresholds for the behavioral light sensitivity of krill and copepods, and suggest that behavioral light sensitivity is one of the reasons for high values of BL potential observed below 100 m at offshore stations. In order to understand sources of bioluminescent taxa responsible for the observed high values of BL potential in offshore waters, we have investigated the origin and pathways of water masses circulating to the north, offshore of the fjord Rijpfjorden by using a hydrodynamic model. For both 2012 and 2017, the model water masses mostly originate from the west, where the Atlantic water is flowing northward, then along the shelf and shelf slope of northern Svalbard, and to the offshore of the fjord. This indicates that the advection of zooplankton by North Atlantic Water is one possible source of bioluminescent organisms offshore of northern Svalbard. In 2012, water masses also originated from the inflow through Hinlopen trench and strait, while, in 2017, the offshore water was advected and upwelled into the fjord on time scales less than 10 days, and after that there was a recirculation back from the fjord to offshore on time scales larger than 10 days. This recirculation from the fjord might be another source of bioluminescent organisms in the offshore waters.

The discovery of three hot Jupiters, NGTS-23b, 24b, and 25b, and updated parameters for HATS-54b from the Next Generation Transit Survey

ABSTRACT We report the discovery of three new hot Jupiters with the Next Generation Transit Survey (NGTS) as well as updated parameters for HATS-54b, which was independently discovered by NGTS. NGTS-23b, NGTS-24b, and NGTS-25b have orbital periods of 4.076, 3.468, and 2.823 d and orbit G-, F-, and K-type stars, respectively. NGTS-24 and HATS-54 appear close to transitioning off the main-sequence (if they are not already doing so), and therefore are interesting targets given the observed lack of hot Jupiters around sub-giant stars. By considering the host star luminosities and the planets’ small orbital separations (0.037–0.050 au), we find that all four hot Jupiters are above the minimum irradiance threshold for inflation mechanisms to be effective. NGTS-23b has a mass of 0.61 MJ and radius of 1.27 RJ and is likely inflated. With a radius of 1.21 RJ and mass of 0.52 MJ, NGTS-24b has a radius larger than expected from non-inflated models but its radius is smaller than the predicted radius from current Bayesian inflationary models. Finally, NGTS-25b is intermediate between the inflated and non-inflated cases, having a mass of 0.64 MJ and a radius of 1.02 RJ. The physical processes driving radius inflation remain poorly understood, and by building the sample of hot Jupiters we can aim to identify the additional controlling parameters, such as metallicity and stellar age.

A novel approach to account for shape-morphing and kinetic shading systems in building energy performance simulations

This paper proposes an innovative approach to analyse the energy behaviour of complex kinetic shading systems. Although several studies have analysed this topic, many are focused only on certain aspects or on simple shading systems due to a lack of tools for running reliable energy simulations on complex systems. This study aims to develop and validate a tool based on Python and EnergyPlus that can consider the continuous nature of the energy simulation and analyse complex kinetic systems. Simply providing an EnergyPlus model and a model of the shading configurations, the algorithm provides as output a comparison sheet to evaluate the performance of the system. The paper provides a description of the tools and studies focused on this topic; subsequently, a methodological insight is presented to explain the workflow, its validation, and the algorithm developed. Finally, the algorithm is tested on a case study to analyse a kinetic shading system. Abbreviations: DSF: Dynamic Shading File; EDSM: Equivalent Dynamic Shading Model; EMS: Energy Management System; ESSM: Equivalent Static Shading Model; Gf: Incident irradiance; Gf max: Incident irradiance threshold; PV: Photovoltaic; ST1/2/3: State 1/2/3; SSM: Static Shading Model; SF: Sunlit Fraction; SSF: Static Shading File; To: Outdoor temperature; To max 1/2: Outdoor temperature threshold 1/2; Tsol: Solar transmittance

Glare Potential Evaluation of Structured PV Glass Based on Gonioreflectometry

Potential glare through reflected sunlight can be a significant hindrance factor for photovoltaic (PV) installations, especially for building-integrated PVs with atypical orientations and tilt angles present. Structured glass surfaces or antireflective (AR) coatings are often used as a solution, however, there is currently no universally recognized method or metric to estimate their impact on glare. This article presents an evaluation of the glare potential of different surface glasses for use in PV modules based on their bidirectional reflectance distribution functions (BRDF). BRDF threshold values for retinal burn damage, flash blindness, and discomfort glare are calculated based on retinal irradiance thresholds from literature. Subsequently, gonioreflectometric measurements on PV minimodules are used to characterize the reflectance profiles of eight different glass surfaces. Results for all measured structured glasses, both satinated and macrotextured, show significant reductions in BRDF compared with smooth glass, largely eliminating the potential for flash blindness as well as discomfort glare at low incidence angles. At high incidence angles, increased potential for discomfort glare as well as forward scattering along the glass surface can be observed. AR coatings, however, are shown to be insufficient to eliminate glare causing flash blindness.

Inactivation of Fluorescent Lipid Bilayers by Irradiation With 300 keV Electrons Using Liquid Cell Transmission Electron Microscopy

Liquid cell transmission electron microscopy allows for imaging of samples in a fully hydrated state at high resolution and has the potential for visualizing static or dynamic biological structures. However, the ionizing nature of the electron beam makes it difficult to discern real physiological dynamics from radiation induced artifacts within liquid cell samples. Electron flux thresholds for achieving high resolution structures from biological samples frozen in ice have been described extensively by the cryo-electron microscopy field, while electron flux thresholds which do not result in a functional change for biological samples within the hydrated environment of a transmission electron microscope liquid cell is less clear. Establishing these functional thresholds for biologically relevant samples is important for accurate interpretation of results from liquid cell experiments. Here we demonstrate the electron damage threshold of fluorescently tagged lipid bilayers by quantifying the change in fluorescence before and after electron exposure. We observe the reduction of fluorescent signal in bilayers by 25% after only 0.0005 e−/Å2 and a reduction of over 90% after 0.01 e−/Å2. These results indicate that the loss of function occurs at irradiation thresholds far below a typical single high resolution (scanning) transmission electron microscopy image and orders of magnitude below fluxes used for preserving structural features with cryo-electron microscopy.

Development of thermo–electrical loss model for photovoltaic module with inhomogeneous temperature

Accurate, efficient, and reliable measurements of solar photovoltaic (PV) modules are essential for the evaluation and diagnosis of the actual operating status of PV plants. However, current online measurements and extraction models are limited because they do not account for power losses caused by inhomogeneous thermal performance of photovoltaic modules. Accordingly, this paper develops a coupled thermo–electrical loss model to access the power generation, energy losses, and degradation rate of photovoltaic modules with inhomogeneous temperature under actual operating conditions. The experiments indicate that the temperature coefficient of power dissipation and efficiency for solar cells with uneven temperature distribution PV modules are within −0.68W/oC to −0.83 W/°C and −0.46%/oC to −5.81%/oC, respectively. Additionally, the relative error values for the maximum power range from −2.54% to 4.09%, demonstrating the feasibility of the proposed model for predicting the power output behavior of operating PV modules with inhomogeneous temperature distributions. Furthermore, the daily performances of the modules indicate heat and electricity losses ranging from 0.245 kWh to 0.337 kWh, while the ratios of electrical energy dissipation to daily losses vary from 36% to 50%. To ensure the reliability of measuring degradation rates, the solar irradiance thresholds of PV module performance tests are nearly 632W/m2, 781W/m2, 875W/m2, and 875W/m2, respectively. Finally, for the long-term performance valuation, the levelized costs of electricity increase by approximately 0.011 CNY/kWh for every 5% reduction in annual power generation, and the PBP is extended by 4.81yr, 4.22yr, 3.62yr, and 7.10yr, respectively.

Selective Large-Area Retinal Pigment Epithelial Removal by Microsecond Laser in Preparation for Cell Therapy.

PurposeCell therapy is a promising treatment for retinal pigment epithelium (RPE)-associated eye diseases such as age-related macular degeneration. Herein, selective microsecond laser irradiation targeting RPE cells was used for minimally invasive, large-area RPE removal in preparation for delivery of retinal cell therapeutics.MethodsTen rabbit eyes were exposed to laser pulses 8, 12, 16, and 20 µs in duration (wavelength, 532 nm; top-hat beam profile, 223 × 223 µm²). Post-irradiation retinal changes were assessed with fluorescein angiography (FA), indocyanine green angiography (ICGA), and optical coherence tomography (OCT). RPE viability was evaluated with an angiographic probit model. Following vitrectomy, a subretinal injection of balanced salt solution was performed over a lasered (maximum 13.6 mm2) and untreated control area. Bleb retinal detachment (bRD) morphology was then evaluated by intraoperative OCT.ResultsWithin 1 hour after irradiation, laser lesions showed FA and ICGA leakage. OCT revealed that large-area laser damage was limited to the RPE. The angiographic median effective dose irradiation thresholds (ED50) were 45 µJ (90 mJ/cm2) at 8 µs, 52 µJ (104 mJ/cm2) at 12 µs, 59 µJ (118 mJ/cm2) at 16 µs, and 71 µJ (142 mJ/cm2) at 20 µs. Subretinal injection over the lasered area resulted in a controlled, shallow bRD rise, whereas control blebs were convex in shape, with less predictable spread.ConclusionsLarge-area, laser-based removal of host RPE without visible photoreceptor damage is possible and facilitates surgical retinal detachment.Translational RelevanceSelective microsecond laser-based, large-area RPE removal prior to retinal cell therapy may reduce iatrogenic trauma.

Threshold Ocular Exposure to Near Infrared Radiation for Causing Acute Opacification in the Rabbit Lens.

Surveys and epidemiological studies have reported an increased prevalence of cataracts in the glass and steel industries, which are associated with exposure to intense infrared radiation (IR). Indeed, animal studies have demonstrated that IR exposure can produce acute changes in the crystalline lens that are likely to lead to cataract formation. However, little is known about threshold IR exposure for causing acute cataractous changes, which is important in the prevention of IR-induced cataract, especially as a basis for short-term IR exposure limits. Previously, we exposed rabbit eyes to 808 nm wavelength IR at different irradiances for 6 min to determine the threshold irradiance to cause acute lens opacification. Presently, we similarly determined the threshold irradiance for exposure durations of 3 min, 1 min, 30 s, 10 s and 4 s. The threshold irradiance increased steadily with decreasing exposure duration, from 1.1 W cm-2 at 6 min to 4.1 W·cm-2 at 4 s. These threshold values are consistent with ICNIRP exposure limits to avoid IR-induced cataract formation in the tested range of exposure duration, but suggest that it may be necessary to lower the exposure limits for shorter exposure durations.

Comparative evaluation of two photovoltaic multi-pump parallel system configurations for optimal distribution of the generated power

The suitability of a strategy for distributing the power generated by a photovoltaic pumping system equipped with two equal pumps working in parallel is proven. This strategy aims to improve energy management and consists of feeding a single pump with all the power generated until it exceeds a threshold value from which the power distribution must be at 50% between the two pumps. This pumping method was compared with the operation mode usually applied in parallel PV pumping facilities (50% of the power always assigned to each pump). A system equipped with two 0.75 kW pumps was employed. The assessment of the facility’s performance under the two alternative working conditions and several pumping heads was conducted using simulation techniques. Both the pumped annual volume and the annual efficiency of the motor-pump group increased when the strategy was applied compared to operation with power distribution at 50%. This increase was greater the higher the head (6.21% at H = 18 m vs. 57.60% at H = 48 m for pumped annual volume and 6.42% at H = 18 m vs. 57.51% at H = 48 m for annual efficiency). The halving of the irradiance threshold and the improved efficiency (36.4% vs. 34.8%) may explain this increase.

Ignition Thresholds and Flame Propagation of Methane/Air Mixtures Ignited via Radiatively Heated Inert Particles

The prevention and evaluation of explosions requires suitable standards of measurement. As such, for this study two ignition thresholds, the ignition temperature and the minimum ignition irradiance were selected as the assessment criteria. These ignition threshold values were experimentally determined by heating stationary inert silicon carbide particles via thermal radiation with a large spot size in order to ignite quiescent methane-air fuel mixtures. A high-speed Schlieren camera was used to capture the progression of the formation and propagation of the flames throughout the experiments. The results of the experiments show that the irradiance and temperature threshold are directly and inversely proportional to the particle size, respectively. Furthermore, the irradiance and temperature thresholds have similar tendencies within the flammability limits; wherein, the minimum value corresponds to fuel mixtures at a stoichiometric ratio, and increases as the equivalence ratio shifts toward the flammability limits. Irradiance thresholds, though, are more sensitive to changes in equivalence ratio than temperature. The temperature histories of the heated particle determined that when the irradiance is lower than its ignition threshold value, the heated particle-fuel mixture system will arrive at a thermal equilibrium, rather than ignition, due to the inability of the particle to reach the ignition temperature. This study also found that longer ignition times will result in a more drastic deformation of the flame fronts caused by natural convection.