Simulated Radiation Research Articles

Toward Closing the Loop in Image-to-Image Conversion in Radiotherapy: A Quality Control Tool to Predict Synthetic Computed Tomography Hounsfield Unit Accuracy

In recent years, synthetic Computed Tomography (CT) images generated from Magnetic Resonance (MR) or Cone Beam Computed Tomography (CBCT) acquisitions have been shown to be comparable to real CT images in terms of dose computation for radiotherapy simulation. However, until now, there has been no independent strategy to assess the quality of each synthetic image in the absence of ground truth. In this work, we propose a Deep Learning (DL)-based framework to predict the accuracy of synthetic CT in terms of Mean Absolute Error (MAE) without the need for a ground truth (GT). The proposed algorithm generates a volumetric map as an output, informing clinicians of the predicted MAE slice-by-slice. A cascading multi-model architecture was used to deal with the complexity of the MAE prediction task. The workflow was trained and tested on two cohorts of head and neck cancer patients with different imaging modalities: 27 MR scans and 33 CBCT. The algorithm evaluation revealed an accurate HU prediction (a median absolute prediction deviation equal to 4 HU for CBCT-based synthetic CTs and 6 HU for MR-based synthetic CTs), with discrepancies that do not affect the clinical decisions made on the basis of the proposed estimation. The workflow exhibited no systematic error in MAE prediction. This work represents a proof of concept about the feasibility of synthetic CT evaluation in daily clinical practice, and it paves the way for future patient-specific quality assessment strategies.

All‐Sky Microwave Radiance Observation Operator Based on Deep Learning With Physical Constraints

AbstractSatellite data assimilation relies on the radiative transfer models (RTMs) to establish the relationships between model state variables and satellite radiances. However, atmospheric radiative transfer calculations are computationally expensive, especially when involving multiple‐scattering calculations in cloudy areas. In recent years, deep learning (DL) models have been increasingly applied to emulate and accelerate physical models. This study, for the first time, explores DL techniques to emulate all‐sky radiative transfer in microwave bands. The FengYun‐3E (FY‐3E) Microwave Humidity Sounder‐2 (MWHS‐2) was selected as the target instrument due to its comprehensive spectral coverage, with the radiative transfer for TOVS scattering module (RTTOV‐SCATT) serving as the reference model. Three DL architectures were trained and compared, including multilayer perceptron (MLP), Bidirectional Long Short‐Term Memory with Attention (BiLSTM‐Attention), and Transformer. The BiLSTM‐Attention architecture demonstrated superior performance in both clear‐sky and cloudy radiance simulations. This may be attributed to its bidirectional recurrent structure resembling physical radiative transfer processes and the attention mechanism's ability to link MWHS‐2 channels with corresponding vertical layers. Although DL models achieve high accuracy in forward prediction, they often struggle with instability in Jacobian calculations. To address this issue, the trained BiLSTM‐Attention model was fine‐tuned using the reference model Jacobians as physical constraints. The fine‐tuned BiLSTM‐Attention model accurately characterized radiance sensitivities to temperature, water vapor, and hydrometeors under different cloud conditions, indicating its potential to serve as a radiance observation operator in data assimilation and physical retrieval applications.

Peptide-Induced Hydrogelation with Ordered Metal-Organic Framework Nanoparticles Generating Reactive Oxygen Species for Integrated Wound Repair.

Hydrogels, with their high water content and flexible nature, are a promising class of medical dressings for combating bacterial wound infections. However, their development has been hindered by low sterilization efficiency. Here, this issue is addressed by designing a peptide hydrogel that assembles ordered metal-organic framework (MOF) nanoparticles with photocatalytic bactericidal activity. Specifically, a short peptide, Nap-Gly-Phe-Phe-His (Nap-GFFH), is used to induce the assembly of zinc-imidazolate MOF (ZIF-8) into a hydrogel (NHZ gel). This innovative structure integrates three key features: 1) ZIF-8 nanoparticles are encapsulated within the hydrogel, overcoming their inherent brittleness, insolubility, and limited moldability; 2) the ordered ZIF-8 structure enhances charge transfer, enabling efficient generation of reactive oxygen species (ROS); and 3) ZIF-8 simultaneously improves the photocatalytic bactericidal efficiency and mechanical properties of the hydrogel. The NHZ gel demonstrates remarkable antibacterial performance, achieving >99.9% and 99.99% inactivation of Escherichia coli and Staphylococcus aureus, respectively, within 15 min of simulated solar radiation. Additionally, the NHZ gel exhibits excellent biocompatibility, water retention, and exudate absorption, highlighting its broad potential for wound healing.

Enhancing pancreatic tumor delineation using dual-energy CT-derived extracellular volume fraction map

Precise identification of pancreatic tumors is challenging for radiotherapy planning due to the anatomical variability of the tumor and poor visualization of the tumor on 3D cross-sectional imaging. Low extracellular volume fraction (ECVf) correlates with poor vasculature uptake and possible necrosis or hypoxia in pancreatic tumors. This work investigates the feasibility of delineating pancreatic tumors using ECVf spatial distribution maps derived from contrast enhanced dual-energy CT (DECT). Data acquired from radiotherapy simulation of 12 pancreatic cancer patients, using a dual source DECT scanner, were analyzed. For each patient, an ECVf distribution of the pancreas was computed from the simultaneously acquired low and high energy DECT series during the late arterial contrast phase combined with the patient's hematocrit level. Volume of interest (VECVf) maps in ECVf distribution of pancreas were identified by applying an appropriate threshold condition and a connected components clustering algorithm. The obtained VECVf was compared with the clinical gross tumor volume (GTV) using the positive predictive value (PPV), Dice similarity coefficient (DSC), mean distance to agreement (MDA) and true positive rate (TPR). As a proof of concept, our hypothetical threshold condition based on the first quartile separation of the ECVf distribution to find VECVf of the pancreas elucidates the tumor volume within the pancreas. Notably, 7 out of 12 cases studied for VECVf matched well with the GTV and the mean PPV of 0.83±0.12. The mean MDA (2.83±1.0) of the cases confirms that VECVf lies within the tolerance for comparing to the pancreatic GTV. For the remaining 5 cases, the VECVf is substantially affected by other compounding factors, e.g., large cysts, dilate ducts, and thus did not align with the GTVs. This work demonstrated the promising application of the ECVf map, derived from contrast enhanced DECT, to help delineate tumor target for RT planning of pancreatic cancer.

Sex-specific effects on the heart from combined exposure to simulated galactic cosmic radiation and hindlimb unloading

Sex-specific effects on the heart from combined exposure to simulated galactic cosmic radiation and hindlimb unloading

Using Simulated Radiances to Understand the Limitations of Satellite‐Retrieved Volcanic Ash Data and the Implications for Volcanic Ash Cloud Forecasting

AbstractVolcanic Ash Advisory Centers (VAACs) have generated volcanic ash forecasts for the aviation industry since the mid‐1990s. The excellent spatial and temporal coverage of satellite data makes them critical to the validation of ash dispersion model forecasts. This study investigates the limitations of satellite‐retrieved volcanic ash data through the production of simulated radiances for a range of ash cloud properties encompassing the satellite retrieval's sensitivity. We run a detection and retrieval algorithm (Francis et al., 2012, https://doi.org/10.1029/2011JD016788) on these simulated ash clouds and assess the sensitivity and performance of the algorithms. Expected limitations are highlighted, including a lack of sensitivity to particles larger than ∼10 μm in radius and challenges in accurately retrieving heights in the stratosphere. However, other previously poorly defined limitations are also constrained, such as the reduction in sensitivity as ash column loading increases in optically thick ash clouds and increasingly underestimated column loading when column loadings are >∼7 g m−2. We consider the implications of the identified limitations when using satellite‐retrieved ash column loadings to verify dispersion model output. We show that, accounting for the limitations of the satellite retrieval, a significant proportion of mass in the model output can lie outside the sensitivity range of the satellite detection and retrieval. This demonstrates the importance of understanding observations' limitations when comparing to model output. This knowledge should be used when verifying operational volcanic ash cloud forecasts.

Addition of hydrogen peroxide to natural ferruginous water improves the efficacy of SODIS method against the waterborne pathogen Cryptosporidium

The enhancement of SODIS method against the waterborne pathogen Cryptosporidium by incorporating H2O2 in natural ferruginous water (NFW) was evaluated. Polyethylene terephthalate bottles containing distilled water or different NFW with added different concentrations of H2O2 (0–100 mg L−1) were spiked with Cryptosporidium parvum oocysts and exposed to simulated and natural solar radiation. Oocyst viability was evaluated by induced excystation and inclusion/exclusion of the vital dye propidium iodide (PI). The experiments performed under sunlight showed better C. parvum inactivation rates than those under simulated solar radiation. Oocyst viability rates of 2.26±1.91% and 16.52±3.83% were determined by induced excystation and inclusion/exclusion of PI, respectively, after exposure to natural sunlight during 6 h in NFW with 100 mg L−1 of H2O2. This study proves the enhancement in the effectiveness of conventional SODIS by the addition of H2O2 to natural ferruginous waters, speeding up the C. parvum oocyst inactivation. Since surface waters in countries where the SODIS method can be used often contain dissolved iron salts, the addition of small amounts of H2O2 will increase the microbiological quality of drinking waters and consequently would decrease the risk of diarrhoeal diseases in the population, having a positive impact in terms of development and poverty reduction.

DETERMINATION OF LOCAL DIAGNOSTIC REFERENCE LEVEL (DRL) ON CONVENTIONAL RADIOTHERAPY SIMULATOR WITH BRAIN METASTASIS CASES AT DR. ADHYATMA, MPH HOSPITAL

Conventional simulators in 2-dimensional (2D) radiotherapy procedures can be done with fluoroscopy and single exposure features. The most significant percentage of 2D patients in the radiotherapy installation of Dr. Adhyatma MPH Hospital, are patients with brain metastasis cases, with a percentage of 65% of all 2D patients. Therefore, this study focuses on brain metastasis cases. The feature used in the Radiotherapy Installation of Dr. Adhyatma MPH Hospital is the single exposure feature, which is identical to conventional diagnostic radiology examinations. Radiation in diagnostic radiology requires a local Diagnostic Reference Level (DRL) on a conventional radiotherapy simulator as a guideline for optimizing radiation protection for medical exposure. This study aims to determine the local DRL value of a conventional radiotherapy simulator in cases of brain metastasis and compare it with the national DRL in lateral head examinations. The local DRL value obtained is then used as a guideline in improving services to increase the quality of service to patients. The data collection method is carried out in 2 (two) ways, namely calculating the local DRL value from the ESAK value and interviews related to the quality of the resulting image. The exposure factors used in this study followed the same routine exposure factors with a tube voltage of 72 kV and a tube current of 25 mAs. The local DRL value obtained was 0.586 mGy, with a percentage difference of 51% lower than the national DRL. With this value, the quality of the resulting image is classified as optimal and easy to assess. Thus, the exposure factors in the conventional radiotherapy simulation process in cases of brain metastasis can be used as a guideline for clinical practice at RSUD dr. Adhyatma, MPH. Keywords: conventional radiotherapy simulator, 2-dimensional radiotherapy, local DRL, diagnostic patients, radiation dose.

Cross-Sectional National Survey of Practice Patterns in Radiotherapy for Rectal Cancer: A Snapshot of India.

The information on the practice of radiotherapy, including intensity-modulated radiotherapy (IMRT) use for rectal cancer in India, is lacking. This national survey was planned to understand the current status of knowledge, attitudes, and practice among radiation oncologists, specifically concerning the practice of IMRT for rectal cancers. A national survey was sent to radiation oncologists through e-mail or a WhatsApp message, where feasible, with a request letter containing the link to the survey questionnaire. The survey questionnaire was adapted from the UK IMRT survey with permission from the authors. It explored rectal cancer management, IMRT use, reasons for nonadoption, total neoadjuvant therapy (TNT), dose fractionation schedules and radiotherapy processes like radiotherapy simulation, target volume/organ at risk definition, and treatment planning, evaluation, and verification. Descriptive statistics is used to present the results. Over 300 radiation oncologists were approached, and 182 (60.6%) of the 153 institutes responded. Around 88% (160 of 182) indicated using IMRT or volumetric modulated arc therapy (VMAT) to treat rectal cancer, of whom 32% used exclusively IMRT/VMAT in all their patients. The reasons for not adopting IMRT were affordability/lack of insurance, resource constraints, and lack of guidelines. Long-course chemoradiation (capecitabine-based) followed by surgery was the most common neoadjuvant approach, with short course and TNT in less than a third of patients. Daily verification feasibility was reported by 60%. Seventy-three percent emphasized the need for a national IMRT guidance document. This national survey from India indicates a scope of routine implementation of IMRT in rectal cancer, highlighting the urgent need for a national IMRT guidance document, which could significantly enhance the quality of care for patients with rectal cancer in India.

Asymmetric Coplanar Strip Loaded With Meander Lines for Multiband Operations Using ANN Optimization

ABSTRACTA miniaturized asymmetric coplanar strip fed with meander lines is developed for hexaband wireless applications. Multiband with compact size of the antenna is developed by using meander lines. The designed antenna is enhanced by an increased number of meander lines. The invented antenna is composed of three meander lines, it yields the antenna to excite 1.13, 2.35, 2.91, 3.46, 3.96, and 4.5 GHz, respectively. The prototype antenna is fed by ACS, which is printed on a 14 24 1.6 mm3 FR‐4 substrate and dielectric constant of Ɛr = 4.4. MATLAB tool is utilized in the ANN computation to amend the physical values of the antenna. The calibrated and simulated radiation attributes are identical with each other. The designed antenna provides distinguishing characteristics such as good reflection coefficient, impedance matching, and size miniaturization. It imparts empirical peak gains of 0.028 dBi at 1.14 GHz, 1.305 dBi at 2.35 GHz, 1.54 dBi at 2.86 GHz, 1.79 dBi at 3.43 GHz, 2.43 dBi at 3.96 GHz, and 2.58 dBi at 4.5 GHz, which is suitable for GSM/WLAN/WiMAX and C‐band wireless applications.

A density functional theory study of a series of symmetric dibenzylideneacetone analogues as potential chemical UV-filters

The aim of this research was to provide valuable insights on symmetrical α,β-unsaturated ketones as potential chemical ultraviolet (UV) filters from experimental data and theoretical aspects. Towards this end, density functional theory (DFT/B3LYP) calculations on a series of symmetrical α,β-unsaturated ketones, (1E,4E)-1,5-bis[4-(R)phenyl]penta-1,4-diene-3-one (R = methylthio, 1; R = dimethylamino, 2; R = ethyl, 3), were performed to determine the effect of different electron-donating substituents on their stability when exposed to solar UV radiation. Their molecular structures, and UV–visible, infrared (IR) and NMR (1H and 13C) spectra were theoretically obtained from their optimized geometries with the B3LYP/6–311++ G (d, p) basis set and were compared with the experimental results. Conformational analysis was performed and the most stable conformer of each compound was identified as the trans-trans conformer, which was further supported by experimental NMR data. The UV spectra and effect of solvent polarity and proticity were studied by the time-dependent-DFT (TD-DFT) approach with the B3LYP/6–311++G (d, p) level of theory. Furthermore, various molecular parameters like dipole moment, frontier molecular orbital (FMO) energies, ΔEHOMO-LUMO gap, lifetime of the first excited state (τ), global chemical reactivity descriptors, and natural bond orbital analysis were predicted at the same level of theory and compared with the experimental data. Inspection of the active FMOs revealed the photoinstability trends of 1 and 3 under UV irradiation. However, introducing a -N(CH3)2 substituent to 2 at the para-position improves its photostability towards simulated solar UV radiation. Thus, compound 2 has the potential to provide efficient broad-spectrum protection against UV radiation. This work has shown that molecular modelling strategies can assist to rationalize experimental findings and also support the identification of photoproducts of 1 and 3.

Electrospun Nanofiber Dopped with TiO2 and Carbon Quantum Dots for the Photocatalytic Degradation of Antibiotics.

Novel photocatalysts were synthesized through the association of carbon quantum dots (CQDs) with commercial (P25) titanium dioxide (TiO2) by sonication. The resulting TiO2/CQDs composite was then incorporated into the polyamide 66 (PA66) biopolymer nanofibers using the electrospinning technique, considering a composite nanoparticles-to-polymer ratio of 1:2 in the electrospinning precursor solution. The produced nanofibers presented suitable morphology and were tested for the photocatalytic degradation under simulated solar radiation of 10 mg L-1 of amoxicillin (AMX) and sulfadiazine (SDZ), in phosphate buffer solution (pH 8.06) and river water, using 1.5 g L-1 of photocatalyst. The presence of the photocatalyst increased the removal of AMX in phosphate buffer solution by 30 times, reducing the AMX degradation half-life time from 62 ± 1 h (without catalyst) to 1.98 ± 0.06 h. Moreover, SDZ degradation half-life time in phosphate buffer solution was reduced from 5.4 ± 0.1 h (without catalyst) to 1.87 ± 0.05 h in the presence of the photocatalyst. Furthermore, the PA66/TiO2/CQDs were also efficient in river water samples and maintained their performance in at least three cycles of SDZ photodegradation in river water. The presented results evidence that the produced photocatalyst can be a promising and sustainable solution for antibiotics' efficient removal from water.

Rapid Destruction of Lipid Biomarkers Under Simulated Cosmic Radiation.

Understanding how organics degrade under galactic cosmic rays (GCRs) is critical as we search for traces of ancient life on Mars. Even if the planet harbored life early in its history, its surface rocks have been exposed to ionizing radiation for about four billion years, potentially destroying the vast majority of biosignatures. In this study, we investigated for the first time the impact of simulated GCRs (using gamma rays) on several types of lipid biosignatures (including hopane C30, sterane C27, alkanes, and fatty acids [FAs]) in both the presence and absence of salts (NaCl, KCl, and MgCl2). We measured that the lipids degraded 6-20 times faster than amino acids in similar conditions; moreover, when irradiated in the presence of a salt substrate, degradation was at least 4-6 times faster than without salt, which suggests that salty environments that are often preferred targets for astrobiology warrant caution. We detected radiolytic by-products only for FAs-in the form of alkanes and aldehydes. These results expand our understanding of the degradation of organic molecules in Mars analog environments and underscore the urgent need to direct rover missions to sampling sites protected from GCRs, for example, sites on Mars that have been recently exposed by a wind scarp retreat or meteoritic impact.

Intercomparison of aerosol optical depth retrievals from GAW-PFR and SKYNET sun photometer networks and the effect of calibration

Abstract. In this study, we assess the homogeneity of aerosol optical depth (AOD) between two sun photometer networks, the Global Atmosphere Watch-Precision Filter Radiometer (GAW-PFR) and the European SKYNET radiometers network (ESR), at the common wavelengths of their main instruments (500 and 870 nm). The main focus of this work is to evaluate the effect of the improved Langley plot calibration method (ILP) used by SKYNET and to investigate the factors affecting its performance. We used data from three intercomparison campaigns that took place during 2017–2021. Each campaign was organized at two locations (mountainous rural – Davos, Switzerland; urban – Rome, Italy). Our analysis shows that differences in AOD due to post-processing and instrument differences are minor. The main factor leading to AOD differences is the calibration method. We found a systematic underestimation of AOD in ESR compared to in GAW-PFR due to underestimation of the calibration constant calculated with the ILP method compared to the calibration transfers using the PFR as a reference. The calibration and AOD differences are smaller in Davos, where the traceability criteria are satisfied at 870 nm and where the median differences are below 0.01 at 500 nm. In Rome, the AOD median differences at 500 nm were in the 0.015–0.034 range. We conducted a sensitivity study, which shows that part of the difference can potentially be explained by errors in the assumed surface albedo and instrument solid-view angle provided as inputs to the ILP code (based on Skyrad pack 4.2). Our findings suggest that the ILP method is mainly sensitive to the measured sky radiance. The underestimation in calibration is probably caused by an error in the retrieved scattering AOD (sc-AOD) through the sky radiance inversion. Using an alternative retrieval method (Skyrad MRI pack version 2) to derive sc-AOD and to recalibrate the instruments with the ILP method, we found no significant differences between the retrieved sc-AOD and no systematic increase in the ILP-derived calibration constant when using the MRI pack for sc-AOD inversion instead of the Skyrad 4.2. The potential error may be a result of the model assumptions used for the sky radiance simulations. In conclusion, the on-site calibration of sun photometers has several advantages, including the fact that instrument shipments and data gaps can be avoided. However, it has also the disadvantages of a larger uncertainty and significant systematic differences compared to the traditional Langley calibration performed under low- and constant-AOD conditions at high-altitude sites. The larger uncertainty of the ILP method can be attributed to the required modelling and input parameters.

Design and Fabrication of a C-Band Patch Antenna with Low Loss BaM4Si5O17 Microwave Dielectric Ceramics.

Single-phase BaM4Si5O17 (M = Yb, Er, Y, Ho) ceramics have been investigated for their crystal structures, microwave dielectric properties, flexural strength, and potential applications in dielectric antennas. Rietveld refinement and TEM analysis revealed that the BaM4Si5O17 ceramics exhibit a monoclinic structure (space groups: P21/m). The εr of the BaM4Si5O17 ceramics was dominated by ionic polarizability and ρrel. The Q × f values were considerably larger at BaM4Si5O17 (M = Yb and Y) ceramics with the high Utotal and low intrinsic dielectric loss. The τf values were controlled by the MO6 octahedron distortion and -VBa. The flexural strength was mainly dominated by pores and average grain size and reached the maximum value (156 MPa) at BaY4Si5O17 ceramic with small average gain sizes and high relative density. Additionally, a patch antenna was fabricated using high-performance BaY4Si5O17 ceramic characterized by a εr value of 9.02, a Q × f value of 60620 at 12.30 GHz, and a τf value of -37.65 ppm/°C. This design achieved a high simulated radiation efficiency of 82.70% and a gain of 5.60 dBi at 6.97 GHz. indicating potential applications of BaY4Si5O17 ceramic because of its low dielectric loss and high flexural strength.

The Ice Cloud Imager: retrieval of frozen water column properties

Abstract. The Ice Cloud Imager (ICI) aboard the second generation of the EUMETSAT Polar System (EPS-SG) will provide novel measurements of ice hydrometeors. ICI is a passive conically scanning radiometer that will operate within a frequency range of 183 to 664 GHz, helping to cover the present wavelength gap between microwave and infrared observations. Reliable global data will be produced on a daily basis. This paper presents the retrieval database to be used operationally and performs a final pre-launch assessment of ICI retrievals. Simulations are performed within atmospheric states that are consistent with radar reflectivities and represent the three-dimensional (3D) variability of clouds. The radiative transfer calculations use empirically based hydrometeor models. Azimuthal orientation of particles is mimicked, allowing for the consideration of polarisation. The degrees of freedom (DoFs) of the ICI retrieval database are shown to vary according to cloud type. The simulations are considered to be the most detailed performed to this date. Simulated radiances are shown to be statistically consistent with real observations. Machine learning is applied to perform inversions of the simulated ICI observations. The method used allows for the estimation of non-Gaussian uncertainties for each retrieved case. Retrievals of ice water path (IWP), mean mass height (Zm), and mean mass diameter (Dm) are presented. Distributions and zonal means of both database and retrieved IWP show agreement with DARDAR. Retrieval tests indicate that ICI will be sensitive to IWP between 10−2 and 101 kg m−2. Retrieval performance is shown to vary with climatic region and surface type, with the best performance achieved over tropical regions and over ocean. As a consequence of this study, retrievals from real observations will be possible from day one of the ICI operational phase.

Improving the accuracy of SIF quantified from moderate spectral resolution airborne hyperspectral imager using SCOPE: assessment with sub-nanometer imagery

Hyperspectral imaging of solar-induced chlorophyll fluorescence (SIF) is required for plant phenotyping and stress detection. However, the most accurate instruments for SIF quantification, such as sub-nanometer (≤1-nm full-width at half-maximum, FWHM) airborne hyperspectral imagers, are expensive and uncommon. Previous studies have demonstrated that standard narrow-band hyperspectral imagers (i.e., 4–6-nm FWHM) are more cost-effective and can provide far-red SIF quantified at 760 nm (SIF760), which correlates strongly with precise sub-nanometer resolution measurements. Nevertheless, narrow-band SIF760 quantifications are subject to systematic overestimation owing to the influence of the spectral resolution (SR). In this study, we propose a modelling approach based on the Soil Canopy Observation, Photochemistry and Energy Fluxes (SCOPE) model with the objective of enhancing the accuracy of absolute SIF760 levels derived from standard airborne hyperspectral imagers in practical settings. The performance of the proposed method was evaluated using airborne imagery acquired from two airborne hyperspectral imagers (FWHM ≤ 0.2-nm and 5.8-nm) flown in tandem on board an aircraft that collected data from two different wheat and maize phenotyping trials. Leaf biophysical and biochemical traits were first estimated from airborne narrow-band reflectance imagery and subsequently used as SCOPE model inputs to simulate a range of top-of-canopy (TOC) radiance and SIF spectra at 1-nm FWHM. The SCOPE simulated radiance spectra were then convolved to match the spectral configuration of the narrow-band imager to compute the 5.8-nm FWHM SIF760. A site-specific model was constructed by employing the convolved 5.8-nm SR SIF760 as the independent variable and the 1-nm SR SIF760 directly simulated by SCOPE as the dependent variable. When applied to the airborne dataset, the estimated SIF760 at 1-nm SR from the standard narrow-band hyperspectral imager matched the reference sub-nanometer quantified SIF760 with root mean square error (RMSE) less than 0.5 mW/m2/nm/sr, yielding R2 = 0.93–0.95 from the two experiments. These results suggest that the proposed modelling approach enables the interpretation of SIF760 quantified using standard hyperspectral imagers of 4–6 nm FWHM for stress detection and plant physiological condition assessment.

Radiation image reconstruction and uncertainty quantification using a Gaussian process prior

We propose a complete framework for Bayesian image reconstruction and uncertainty quantification based on a Gaussian process prior (GPP) to overcome limitations of maximum likelihood expectation maximization (ML-EM) image reconstruction algorithm. The prior distribution is constructed with a zero-mean Gaussian process (GP) with a choice of a covariance function, and a link function is used to map the Gaussian process to an image. Unlike many other maximum a posteriori approaches, our method offers highly interpretable hyperparamters that are selected automatically with the empirical Bayes method. Furthermore, the GP covariance function can be modified to incorporate a priori structural priors, enabling multi-modality imaging or contextual data fusion. Lastly, we illustrate that our approach lends itself to Bayesian uncertainty quantification techniques, such as the preconditioned Crank–Nicolson method and the Laplace approximation. The proposed framework is general and can be employed in most radiation image reconstruction problems, and we demonstrate it with simulated free-moving single detector radiation source imaging scenarios. We compare the reconstruction results from GPP and ML-EM, and show that the proposed method can significantly improve the image quality over ML-EM, all the while providing greater understanding of the source distribution via the uncertainty quantification capability. Furthermore, significant improvement of the image quality by incorporating a structural prior is illustrated.

Kinetic Monte Carlo modelling of nano-oxide precipitation and its associated stability under neutron irradiation for the Fe-Ti-Y-O system

While developing nuclear materials, predicting their behavior under long-term irradiation regimes spanning decades poses a significant challenge. We developed a novel Kinetic Monte Carlo (KMC) model to explore the precipitation behavior of Y-Ti-O oxides along grain boundaries within nanostructured ferritic alloys (NFA). This model also assessed the response of the oxides to neutron irradiation, even up simulated radiation damage levels in the desired long dpa range for reactor components. Our simulations investigated how temperature and grain boundary sinks influenced the oxide characteristics of a 12YWT-like alloy during heat treatments at 1023, 1123, and 1223 K. The oxide characteristics observed in our simulations were in good agreement with existing literature. Furthermore, the impact of grain boundaries on precipitation was found to be minimal. The resulting oxide configurations and positions were used in subsequent simulations that exposed them to simulated neutron irradiation to a total accumulated dose of 8 dpa at three temperatures: 673, 773, and 873 K, and at dose rates of 10−3, 10−4, and 10−5 dpa/s. This demonstrated the expected inverse relationship between oxide size and dose rate. In a long-term irradiation simulation at 873 K and 10−3 dpa/s was taken out to 66 dpa and found the oxides in the vicinity of the grain boundary were more susceptible to dissolution. Additionally, we conducted irradiation simulations of a 14YWT-like alloy to reproduce findings from neutron irradiation experiments. The larger oxides in the 14YWT-like alloy did not dissolve and displayed stability similar to the experimental results.

Effect of Simulated Cosmic Radiation on Cytomegalovirus Reactivation and Lytic Replication.

Human exploration of the solar system will expose crew members to galactic cosmic radiation (GCR), with a potential for adverse health effects. GCR particles (protons and ions) move at nearly the speed of light and easily penetrate space station walls, as well as the human body. Previously, we have shown reactivation of latent herpesviruses, including herpes simplex virus, Varicella zoster virus, Epstein-Barr virus, and cytomegalovirus (CMV), during stays at the International Space Station. Given the prevalence of latent CMV and the known propensity of space radiation to cause alterations in many cellular processes, we undertook this study to understand the role of GCR in reactivating latent CMV. Latently infected Kasumi cells with CMV were irradiated with 137Cs gamma rays, 150 MeV protons, 600 MeV/n carbon ions, 600 MeV/n iron ions, proton ions, and simulated GCR. The CMV copy number increased significantly in the cells exposed to radiation as compared with the non-irradiated controls. Viral genome sequencing did not reveal significant nucleotide differences among the compared groups. However, transcriptome analysis showed the upregulation of transcription of the UL49 ORF, implicating it in the switch from latent to lytic replication. These findings support our hypothesis that GCR may be a strong contributor to the reactivation of CMV infection seen in ISS crew members.