Gaussian Energy Distribution Research Articles

Ultrafast laser micromachining the ultra-low expansion glass-ceramic: Optimization of processing parameters and physical mechanism

To fulfill the precise requirements of laser gyroscope for inertial navigation, using the mean surface roughness, taper angle and circularity degree as indicators, we optimize the processing parameters about ultrafast laser micromachining a commercial ultra-low expansion glass-ceramic (ULGC). Furthermore, through careful characterizations, we identify the sequential appearance of photo-darkening, crystalizing, melting, foaming and vaporizing regions during the interactions of ultrafast laser with ULGC. Especially, the foaming region is identified to effectively mediate the thermal stress at the interfaces between different regions. Originated from the Gaussian distribution of energy, poor processing quality by a Gaussian beam is mainly ascribed to the formation of various regions. By using a Bessel beam, higher surface quality could be obtained due to the possibility of the occurrence of only a foaming region in irradiated regions. This discovery gives us an important clue to optimize processing parameters to obtain high-quality ultrafast laser micromachining surface.

Physical Modeling on Effective Traps Density Near the Conduction Band Dependence of Electrical Characteristics of Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors

An (a-IGZO TFT) is modeled through experimental-based (a-IGZO TFTs) using (TCAD) simulator. A parametric study is performed on the numerical fit of the designed (a-IGZO TFT) current–voltage (I/V) characteristics, to obtain the near conduction band defects parameters optimal values, and to investigate the effect of the near band defects caused by oxygen vacancies on the (a-IGZO TFTs) output parameters. A new model approach is proposed for simulating (a-IGZO) electrical properties. The proposed model is known as a density of state models (DOS), and it is composed of two principal components, conduction band tail $$\left( {g_{ct}^{A} \left( E \right)} \right)$$ and Gaussian distributed donor-like $$\left( {g_{G}^{D} \left( E \right)} \right)$$ . The study of the presented (DOS) models is based on both conduction band tail elements that are known as tail acceptor density ( $$g_{ta}$$ ) as well as tail acceptor energy ( $$E_{a}$$ ), and Gaussian distributed donor-like elements which are donor gaussian energy ( $$E_{D}$$ ) and donor gaussian distribution ( $$g_{gd}$$ ). Results show that the tail acceptor states defects ( $$g_{ta}$$ , $$E_{a}$$ ) near the conduction band is the cause of the mobility and gaussian donor distribution degradation near the conduction band, and it has a major impact on changes that occur in the subthreshold region data [threshold voltage (Vth), subthreshold swing (SS), and on-state/off-states current ratio (Ion/Ioff)].

Optimizing thermo-mechanical processing and material coupling parameters in numerical modeling for additive manufacturing

Additive manufacturing (AM) is gaining increasing industrial interest. Initially conceived to facilitate the pre-production, to manufacture efficiently and cheaply unique parts such as prototypes, it is now able to deliver parts that meet industrial production needs. In addition, AM is an effective way to achieve parts designed using topological optimization. Laser beam melting is an AM technique able to produce specific parts with mechanical properties matching industrial expectations. However, efficient production remains complex because of distortion, cracking and other failures linked to the process and to the machine parameters. The prime material being generally expensive and in order to achieve the required manufacturing quality from the very first attempt while reducing the processing time to market necessary for low cost mass production, a high-quality digital simulation is mandatory. We thus study the relation between the process and the material parameters with the final mechanical state of the part using a numerical model, which is developed in parallel.This work focuses on the macroscopic scale. In order to carry out the thermo-mechanical study we use a finite element resolution method on the whole domain defined by the part, its supports and the baseplate. At this scale, one can neglect the packing of the powder as well as the hydrodynamic behavior of the melt pool in the laser beam melting process. We consider a Gaussian energy distribution for the heat source, imposed on several layers of powders below the deposited layer. Starting from a previous study [11], which considers the temperature dependence of the Young modulus, we improve, in this work, the model by considering the temperature dependency of other physical parameters pertaining to material properties or to elastoplastic and thermal laws coefficients. The aim is to bridge the macroscopic scale study of AM to the mesoscopic scale from results of this study.In a first step, simulations are carried out with simple models like walls, cubes, beams and the popular cantilever used for calibrations. The results show the gain in precision with the contribution of the temperature dependence of various parameters as well as by considering the phase-transition during the printing process. The computing time is compatible with laptops and can iterate the simulations easily. The accuracy of the model is validated by comparing the distortion to the experimental results

Using Geant4 Monte Carlo toolkit to evaluate a low power X-ray tube generator configuration

Monte Carlo technique has been widely used as an important tool to develop new irradiation equipment, prototype medical equipment parts, and test methodologies for dosimetry. In this manuscript, we present a methodology to design a low power X-ray tube generator using the Geant4 Monte Carlo toolkit. The simulations were performed considering a large number of variables, namely, the material composition of the target track, the window thickness, and the air pressure of the X-ray tube. The X-ray production was simulated considering monoenergetic electron beams impinging on targets of tungsten and copper with incident kinetic energies ranging from 20 keV to 60 keV and initial divergences from 5° to 30°. For the polyenergetic emission, a conservative approach with Gaussian energy distribution was adopted. The analysis indicates that among the evaluated parameters, the incident kinetic energy, and the target material produced the most notable changes in the spectra shape and conversion efficiency (CE), significantly impacting the X-ray tube design. The studies provide a reliable methodology to explore general configurations for X-ray tube generators, defining the best geometry, material compositions, and thicknesses to be used on spectroscopy applications.

Thermo-Fluid-Dynamic Modeling of the Melt Pool during Selective Laser Melting for AZ91D Magnesium Alloy.

A three dimensional finite element model (FEM) was established to simulate the temperature distribution, flow activity, and deformation of the melt pool of selective laser melting (SLM) AZ91D magnesium alloy powder. The latent heat in phase transition, Marangoni effect, and the movement of laser beam power with a Gaussian energy distribution were taken into account. The influence of the applied linear laser power on temperature distribution, flow field, and the melt-pool dimensions and shape, as well as resultant densification activity, was investigated and is discussed in this paper. Large temperature gradients and high cooling rates were observed during the process. A violent flow occurred in the melt pool, and the divergent flow makes the melt pool wider and longer but shallower. With the increase of laser power, the melt pool’s size increases, but the shape becomes longer and narrower. The width of the melt pool in single-scan experiment is acquired, which is in good agreement with the results predicted by the simulation (with error of 1.49%). This FE model provides an intuitive understanding of the complex physical phenomena that occur during SLM process of AZ91D magnesium alloy. It can help to select the optimal parameters to improve the quality of final parts and reduce the cost of experimental research.

Particle-scale numerical modeling of thermo-mechanical phenomena for additive manufacturing using the material point method

A fundamental numerical model at the powder particle scale based on the material point method (MPM) is developed for selective laser sintering (SLS). In order to describe the thermo-mechanical phenomena, a laser heat source model with a Gaussian energy distribution and the Perzyna viscoplastic model with a return mapping algorithm are employed. The principal process conditions, such as the laser power and radius, and the scanning speed are systematically varied. Based on the obtained temperature distribution generated by laser irradiation under these conditions, elastic–viscoplastic stresses were calculated to evaluate the deformation of powder particle pairs under the driving force of surface tension via a simple two-dimensional test case. The developed MPM model can capture minute changes of the deformation behavior and the temperature distribution history during melting and consolidation at the particle scale. Melting and consolidation of particle pairs during SLS are basic nature in determining the final product quality. The model can help to evaluate variations in the fusion of microscopic areas, melted by a laser, resulting from variations in the process conditions.

Beta Decay Rates Evaluated Within the Gross Theory Using Experimental Data for the Gamow-Teller Resonance Parameter

We improve the results for the β−-decay rates obtained within the context of the Gross Theory of Beta Decay (GTBD) by using new values of the parameter σN related to the standard deviation for the Gamow-Teller resonance: we include experimental data when they are available and, if not, we adopt the value of the nearest neighbor previous (that is, with less mass) that has experimental data. We evaluate the β−-decay rates using a Gaussian energy distribution function with the axial-vector weak coupling constant |gA| = 1, considering updated experimental mass defects and also an improved approximation for the Fermi function. Our sample consists of 94 nuclei with mass in the range 46 < A < 70, all of them decaying by means of allowed transitions, which are of interest in the pre-supernova phase and have experimental data in terrestrial conditions available in the Letter of Nuclides. We compare our result with those obtained within the same GTBD but using values of σN adjusted in Possidonio (Braz. J. Phys. 48:485, 2018) by minimizing the χ2-function, and also with systematic microscopic calculations. We have shown that the substitution of the adjusted parameters by experimental data in GTBD improves the results for β−-decay rates by 6.4%.

The impact Of impurity ion in deuterium-tritium fuel on the energy deposition pattern Of The Proton Ignitor Beam

The ignition stage of deuterium-tritium fuel in inertial confinement fusion is a challenging task affected by many undesirable processes especially material mixing processes in the hot-spot region. In this research, an alternative proposal of the enhanced energy deposition in the proton fast ignition has been suggested. It consists of two primary assumptions of the beam-plasma system. In the first place, we have adopted the proton beam generated by TNSA or RPA mechanisms, each described by a Maxwellian or Gaussian energy distributions. Next, a realistic, non-uniform fuel plasma was adopted. Then, the cumulative stopping power of a proton beam of 10 kJ energy, penetrating the low content metal-contaminated deuterium-tritium fuel has been examined. It has been shown that in the case of the very low impurity fractions, irregular spatial fluctuations in the cumulative stopping power relative to pure fuel plasma emerges. However, at the higher concentrations, a systematic pattern becomes visible such that the contribution of the deep layers in the stopping power reduces. We observe the enhanced energy deposition close to the corona/dense core interface. It has been shown that the corona/dense core energy deposition ratio differs by up to 2.5% between pure and contaminated DT plasma. In the contaminated fuel plasma, energy deposition in the TNSA regime will effectively heat the plasma corona. While in the RPA counterpart, at a similar level of contamination, most of the incident beam energy remains inside the core fuel region.

Diffusion of DNA-Binding Species in the Nucleus: A Transient Anomalous Subdiffusion Model

Single-particle tracking experiments have measured escape times of DNA-binding species diffusing in living cells: CRISPR-Cas9, TetR, and LacI. The observed distribution is a truncated power law. Working backward from the experimental results, the observed distribution appears inconsistent with a Gaussian distribution of binding energies. Working forward, the observed distribution leads to transient anomalous subdiffusion, in which diffusion is anomalous at short times and normal at long times, here only mildly anomalous. Monte Carlo simulations are used to characterize the time-dependent diffusion coefficient D(t) in terms of the anomalous exponent α, the crossover time tcross, and the limits D(0) and D(∞) and to relate these quantities to the escape time distribution. The simplest interpretations identify the escape time as the actual binding time to DNA or the period of one-dimensional diffusion on DNA in the standard model combining one-dimensional and three-dimensional search, but a more complicated interpretation may be required. The model has several implications for cell biophysics. 1) The initial anomalous regime represents the search of the DNA-binding species for its target DNA sequence. 2) Non-target DNA sites have a significant effect on search kinetics. False positives in bioinformatic searches of the genome are potentially rate-determining in vivo. For simple binding, the search would be speeded if false-positive sequences were eliminated from the genome. 3) Both binding and obstruction affect diffusion. Obstruction ought to be measured directly, using as the primary probe the DNA-binding species with the binding site inactivated and eGFP as a calibration standard among laboratories and cell types. 4) Overexpression of the DNA-binding species reduces anomalous subdiffusion because the deepest binding sites are occupied and unavailable. 5) The model provides a coarse-grained phenomenological description of diffusion of a DNA-binding species, useful in larger-scale modeling of kinetics, FCS, and FRAP.

Exploiting response surface methodology for experimental modeling and optimization of CO2 adsorption onto NaOH-modified nanoclay montmorillonite

In this work, operational conditions and adsorbent properties of modified montmorillonite nanoclay (MMT) with NaOH were investigated to improve CO2 adsorption capacity. To optimization the adsorption operational conditions, process factors e.g. reactor temperature and pressure, acid concentration for activating the surface and wt% NaOH for surface modification were evaluated through five level four factor central composite design (CCD) using RSM. According to the analysis of variance (ANOVA), wt% NaOH, pressure and temperature, respectively, were selected as the most important parameters affecting CO2 adsorption capacity in the outlet model. The optimum values are 65 °C, 1.00 bar, 5.99 M and 39.76 % for the input variables and the value of 105.55 mg/g for the response, respectively. The study of isotherm models shows the Toth isotherm model is well suited to experimental isotherm data and shows multi-layer adsorption on heterogeneous surfaces with Gaussian energy distribution. Also, the kinetic models showed that Elovich model provides the best fit to CO2 adsorption data. This suggests that the connection of CO2 in the modified montmorillonite appears to be due to the formation of chemical bonds.

DETERMINATION OF THE DENSITY VALUE SPECIFICALLY AT THE FOCAL POINT OF THE MIRROR CONCENTRATING SYSTEM

When designing mirror concentrating systems, it is necessary to determine in advance the optical-geometric and optical-energy characteristics of the installation. One is required to choose the mirrors with a reflection coefficient to satisfy the expected energy distribution in the focal area and to pay attention to the accuracy of the reflective surfaces of the mirrors, to the accuracy of the tracking system of the heliostats to the trajectory of the apparent motion of the Sun, to the partial shading to the reflective surfaces, etc. Based on these data, it is necessary to calculate the irradiance distribution in the focal zone of the installation. During installation and utilization of the equipment it is necessary to measure and monitor these parameters and, if necessary, to recalculate the energy distribution taking into account the new parameters.The methods for calculating the density distribution of the radiant flux in the focal zone of mirror-concentrating systems have been developed in parallel with the requirements of exploitation. They do not always correctly reflect the true picture formed in the focus of the heliostat. In this paper, the analysis presents the existing methods for calculating paraboloid concentrators based on the Gaussian distribution of energy in the focal plane. Developing the method of fallen and reflected elementary cone beam and on the basis of generated scattered optical images of the Sun and of the visible angular size (2γо = 32 angle of minutes) of the Sun, which shows non-Gaussian nature of the resulting distribution in the focal plane due to the influence of aberration of the optical paraboloidal surface depending on the change of the aperture angle 2U, we obtained an analytical calculation formula to determine the value of the concentrated radiant flux specifically at the focal point of a paraboloid mirror concentrating system.

Improved imaging quality of cluster LiDAR by optimizing laser energy distribution using an effective optical approach

The cluster LiDAR has been developed and applied for its superiority of high SNR, high resolution and long range. The laser energy distribution of optical antenna is the key component to improve the imaging quality of cluster LiDAR. Thus an effective optical approach is crucial for the design and optimization of the optical antenna. However, traditional approaches can hardly satisfy the requirement for cluster LiDAR technique. In this paper, an effective optical approach is proposed to optimize the imaging quality of cluster LiDAR. Double convex cone lenses and a cylindrical lens are mainly used to optimize the Gaussian laser energy distribution in the transmitting optical antenna. Then each APD can receive the same laser intensity from the targets. To verify the superiority of this method, mathematical model is established to analyze it in detail and an imaging experiment is conducted. The results indicate that the effective optical approach can increase the detectable area by about 30%. It is also worth mentioning that a special platform cylindrical lens is used to increase the energy utilization efficiency. The energy density is increased by 6 times than the original system, and the reflected laser intensity is greatly enhanced. Combining the above, the imaging quality of the cluster LiDAR is significantly improved.

Effects of Antineutrino mass on β−-Decay Rates Calculated Within the Gross Theory of Beta Decay

We analyze the effect of the antineutrino mass over the β−-decay rates calculated within the scheme of the Gross Theory of Beta Decay (GTBD). We give a non-null value to the mass of the antineutrino participating in β−-decay, $(A,Z)\rightarrow (A,Z+1)+e^{-}+\bar {\nu }_{e}$, which is usually neglected because we know it is small compared with electron mass. We have slightly modified the GTDB by inserting the antineutrino mass in the formalism. We have adopted a Gaussian energy distribution function with the axial-vector weak coupling constant gA = 1, as well as a new set of the adjustable parameter σN related to the standard deviation for the Gamow-Teller resonance, updated experimental mass defects, and also an improved approximation for the Fermi function. Our sample consists of a set of 94 nuclei of interest in the pre-supernova phase, which have experimental data in terrestrial conditions available in the Letter of Nuclide. We have compared the calculation without the inclusion of the antineutrino mass with that adopting a really overestimated value of 50 keV for it to illustrate the effect on the decay rates. We have shown that they are improved only by approximately one per thousand in this case. We conclude that the effect of the antineutrino mass on decay rates is not relevant.

Development and validation of a 1.5T MR-Linac full accelerator head and cryostat model for Monte Carlo dose simulations.

To develop, implement, and validate a full 1.5T/7MV magnetic resonance (MR)-Linac accelerator head and cryostat model in EGSnrc for high precision dose calculations accounting for magnetic field effects that are independent from the vendor treatment planning system. Primary electron beam parameters for the implemented model were adapted to be in accordance with measured dose profiles of the Elekta Unity (Elekta AB, Stockholm, Sweden). Parameters to be investigated were the mean electron energy as well as the Gaussian radial intensity and energy distributions. Energy tuning was done comparing depth dose profiles simulated with monoenergetic beams of varying energies to measurements. The optimum radial intensity distribution was found by varying the radial full width at half maximum (FWHM) and comparing simulated and measured lateral profiles. The influence of the energy distribution was investigated by comparing simulated lateral and depth dose profiles with varying energy spreads to measured data. Comparison of simulations and measurements was performed by calculating average and maximum local dose deviations. The model was validated recalculating a clinical intensity-modulated radiation therapy plan for the MR-Linac and comparing the resulting dose distribution with simulations from the commercial treatment planning system Monaco using the gamma criterion. Comparison of simulated and measured data showed that the optimum initial electron beam for MR-Linac simulations was monoenergetic with an electron energy of (7.4±0.2)MeV. The optimum Gaussian radial intensity distribution has a FWHM of (2.2±0.3)mm. The average relative deviations were smaller than 1% for all simulated profiles with optimum electron parameters, whereas the largest maximum deviation of 2.07% was found for the 22×22cm cross-plane profile. Profiles were insensitive to energy spread variations. The IMRT plan recalculated with the final MR-Linac model with optimized initial electron beam parameters showed a gamma pass rate of 99.83 % using a gamma criterion of 3%/3mm. The EGSnrc MR-Linac model developed in this study showed good accordance with measurements and was successfully used to recalculate a first full clinical IMRT treatment plan. Thus, it shows the general possibility for future secondary dose calculations of full IMRT plans with EGSnrc, which needs further detailed investigations before clinical use.

Charge carrier injection and transport in QLED layer with dynamic equilibrium of trapping/de-trapping carriers

A theoretical analysis on carrier injection and transport through layers of quantum dot light emitting display (QLED) device was attempted assuming dynamic equilibrium of trapping and detrapping charge carriers. Assuming traps in exponential or Gaussian energy distribution, the effect of parameters on the current-voltage relationship for the device was investigated. The energy level and distribution of charge traps, a Schottky barrier, and the ratio of detrapping rate constant to the trapping rate constant were found to affect the current-voltage relationship significantly in the charge transport layer. The results suggest that the parameters must be modulated simultaneously in order to achieve a charge balance in the quantum dot layer of the QLED device.

First-principles quantum corrections for carrier correlations in double-layer two-dimensional heterostructures

We present systematic ab initio calculations of the charge carrier correlations between adjacent layers of two-dimensional materials in the presence of both charged impurity and strain disorder potentials using the examples of monolayer and bilayer graphene. For the first time, our analysis yields unambiguous first-principles quantum corrections to the Thomas--Fermi densities for interacting two-dimensional systems described by orbital-free density functional theory. Specifically, using density-potential functional theory, we find that quantum corrections to the quasi-classical Thomas-Fermi approximation have to be taken into account even for heterostructures of mesoscopic size. In order for the disorder-induced puddles of electrons and holes to be anti-correlated at zero average carrier density for both layers, the strength of the strain potential has to exceed that of the impurity potential by at least a factor of ten, with this number increasing for smaller impurity densities. Furthermore, our results show that quantum corrections have a larger impact on puddle correlations than exchange does, and they are necessary for properly predicting the experimentally observed Gaussian energy distribution at charge neutrality.

Nanosecond Pulsed Laser Ablation on Stainless Steel − Combining Finite Element Modeling and Experimental Work

In the present work, finite element simulations to investigate nanosecond pulsed laser ablation of stainless steel under low laser fluence conditions is performed. The laser has a wavelength of 1064 nm as well as a Gaussian spatial and temporal energy distribution. The utilized model of heat transfer consists of thermal conduction, thermal convection, and thermal irradiation. Temperature‐dependent material's properties including absorptivity and the instantaneous material removal by evaporation are considered. Corresponding laser ablation experiments on stainless steel are also conducted, demonstrating good agreement in the widths of the evaporated area and the heat affected zone obtained by simulation results. The 2D simulation results of single pulse laser ablation demonstrate that low laser fluences ranging from 26.53 to 46.42 J cm−2 have a significant impact on both temperature distribution and material removal profile. Particularly for the width of the evaporated area, the maximum deviation of predicted values from experimental results is smaller than 10%. The 3D simulation results of groove texturing using multiple laser pulses also shows an excellent agreement with the experimental work in terms of the resulting groove morphology.

Polymeric adsorbents for oil removal from water

In this study, the application of four synthetic resins for the removal of emulsified oil from produced water was investigated. Key experimental parameters such as adsorbent dosage, contact time, initial oil concentration and pH were evaluated for Optipore L493, Amberlite IRA 958, Amberlite XAD 7 and Lewatit AF 5. Oil removal rates upwards of 98% were achieved using AF 5, XAD 7 and L493. IRA 958 recorded very modest removal rates of less than 25%. Isotherm data were further investigated and fitted using Langmuir, Freundlich, Toth, Flory Huggins and Dubinin-Radushkevich models. The results show that the adsorption onto XAD 7 and L 493 is a multilayer adsorption process over a heterogeneous surface that is best illustrated by the Freundlich and Toth models respectively. The Dubinin-Radushkevich best described the removal using AF 5 resin that assumes that the adsorption process occurs on a heterogenous surface with a gaussian energy distribution. Kinetic studies assessing the rate of removal for each resin were conducted. Experimental results were best fitted using pseudo second order kinetics. It is concluded that XAD 7 had the highest kinetics among all tested resins. Also, AF 5 exhibited the highest adsorption capacity. Overall, the study confirmed the applicability of the resins for the removal of oil from produced water.

Nanosecond pulsed laser ablation of silicon—finite element simulation and experimental validation

In the present work, we perform finite element simulations to investigate the ablated surface morphology of silicon by nanosecond pulsed laser ablation using low laser fluences ranging from 14.92 to 23.21 J cm−2. The utilized finite element model comprehensively considers the following aspects: (1) combined effects of thermal conduction, convection and radiation on heat conduction; (2) temperature-dependent material properties; (3) instantaneous update of the laser focus due to evaporation-induced surface recession for low laser fluences; and (4) spatial and temporal Gaussian energy distribution of the laser pulse. Experimental work using the same laser machining parameters compared to the conducted finite element simulations are carried out to validate the simulation results. Through the optimization of the laser machining parameters by 2D and 3D finite element simulations and the respective experimental validations for eliminating heat-affected zone and promoting forming accuracy, high accuracy aligned micro-grooves are fabricated on silicon with high anti-reflective properties in a wide range of wavelengths between 400 and 2000 nm. This is fairly comparable with the performance of similar silicon microstructures by femtosecond laser ablation. Consequently, the current work presents a way to fabricate precise surface microstructures with high anti-reflective properties on silicon at low cost by nanosecond pulsed laser ablation.

Solar Wind Implantation Into the Lunar Regolith: Monte Carlo Simulations of H Retention in a Surface With Defects and the H2 Exosphere

AbstractThe solar wind implants protons into the top 20–30 nm of lunar regolith grains, and the implanted hydrogen will diffuse out of the regolith but also interact with oxygen in the regolith oxides. We apply a statistical approach to estimate the diffusion of hydrogen in the regolith hindered by forming temporary bonds with regolith oxygen atoms. A Monte Carlo simulation was used to track the temporal evolution of bound OH surface content and the H2 exosphere. The model results are consistent with the interpretation of the Chandrayaan‐1 M3 observations of infrared absorption spectra by surface hydroxyls as discussed in Li and Milliken (2017, https://doi.org/10.1126/sciadv.1701471). The model reproduced the latitudinal concentration of OH by using a Gaussian energy distribution of f(U0 = 0.5 eV, UW = 0.078–0.1 eV) to characterize the activation energy barrier to the diffusion of hydrogen in space weathered regolith. In addition, the model results of the exospheric content of H2 are consistent with observations by the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter. Therefore, we provide support for hydroxyl formation by chemically trapped solar wind protons.