Correction Factor Research Articles

The response of radiation detectors in modulated fields for small targets

Intensity-modulated delivery techniques in radiotherapy are advanced methods that use the superposition of small fields to create complex dose distributions. These techniques result in intense gradients and inhomogeneous dose regions, making the dosimetry of composite fields challenging, especially when the sub-fields superposition does not restore charged particle equilibrium. This work aims to address the response of radiation detectors in non-equilibrium conditions. Two ionization chambers and a micro-diamond detector were irradiated using composite fields from VMAT plans with spherical targets with diameters ranging from 0.5 to 8 cm. The radiation detectors' response and the dose delivered by the VMAT plans were measured using a plastic scintillator detector and radiochromic film as reference detectors. It was observed that an under-response of the ionization chambers was up to 13% and an over-response of the micro-diamond detector was up to 2.5%. Additionally, output correction factors were derived and used to measure the absorbed dose in composite plans using the radiation detectors. The measured dose was compared with that measured with radiochromic film. A dose difference was found within radiochromic film uncertainties (<2.5%). The results of this work suggest that radiation detectors require output correction factors when non-equilibrium conditions persist in composite fields. However, a link between static and composite fields could not be established because the field size cannot be determined accurately.

Effect of bar diameter on bond performance of helically ribbed GFRP bar to UHPC

The bar diameter is one of the key factor affecting the bond performance between GFRP bar and ultra-high performance concrete (UHPC). However, there is no consensus regarding the effect of bar diameter on the corresponding bond strength in existing studies. An experimental study on centric pull-out test of helically ribbed GFRP bars with nine different diameters was conducted to investigate the effect of bar diameter on the bond strength between GFRP bars and UHPC. The parametric analysis regarding steel bars and UHPC was investigated in the comparative test. For GFRP bars with diameters ranging from 8 mm to 25 mm and an embedment length of 1–2 times the bar diameter, the bond strength between UHPC and GFRP bars varies between 26.5 MPa and 56.2 MPa. The bond strength initially increases with the bar diameter in the range from 8 mm to 18 mm, while it decreases in the range from 18 mm to 25 mm. The relative rib height Hrd is observed as the decisive factor among geometric parameters of the GFRP bar affecting the bond strength. In addition, a correction factor Kr obtained from the geometric parameters and experiments results was proposed to modify the existing prediction formula of bond strength. The prediction of the proposed formula shows a good agreement with the experimental results.

Mammalian and avian species quantification in homogenized foods: real time PCR and digital PCR as tools for label compliance controls

Currently food fraud and authenticity of products composition are topics of great concern; ingredients quantification could allow to identify small amounts of contaminats or voluntary addition of improper components. Many molecular methods are available for species identification in foodstuffs but, for a better application, they should not be affected by the interference of other ingredients. The main purpose of this work was to verify the Real Time PCR and the Digital PCR (dPCR) quantification performances on baby food samples, specifically selected for their high miscibility to limit variability; chicken was selected as target to verify the performance of quantification of methods after having spiked the same quantity in different baby foods. The other aims were: (1) to verify a constant genome copies ratio existence between mammalian and avian species (2) to verify the dPCR performance, set up on housekeeping, to quantify mammalian and avian species in commercial products. Digital PCR showed fewer differences respect to Real Time PCR, at the same 15% w/w chicken spiking level. Despite the constant difference between mammalian and avian genome copies, in samples with the same spiking weight, the confidence intervals increasing towards the extreme values, made impossible to use genome copies ratio as a sort of correction factor between species. Finally, the dPCR system using the myostatin housekeeping gene to determine the chicken content seemed reliable to verify the labelling compliance in meat-based commercial products.

Diagnostic and prognostic value of an ejection fraction adjusted for myocardial remodeling.

Ejection fraction (EF) is widely used to evaluate heart function during heart failure (HF) due to its simplicity compared but it may misrepresent cardiac function during ventricular hypertrophy, especially in heart failure with preserved EF (HFpEF). To resolve this shortcoming, we evaluate a correction factor to EF, which is equivalent to computing EF at the mid-wall layer (without the need for mid-layer identification) rather than at the endocardial surface, and thus better complements other complex metrics. The retrospective cohort data was studied, consisting of 2,752 individuals (56.5% male, age 69.3 ± 16.4 years) admitted with a request of a troponin test and undergoing echocardiography as part of their clinical assessment across three centres. Cox-proportional regression models were constructed to compare the adjusted EF (EFa) to EF in evaluating risk of heart failure admissions. Comparing HFpEF patients to non-HF cases, there was no significant difference in EF (62.3 ± 7.6% vs. 64.2 ± 6.2%, p = 0.79), but there was a significant difference in EFa (56.6 ± 6.4% vs. 61.8 ± 9.9%, p = 0.0007). Both low EF and low EFa were associated with a high HF readmission risk. However, in the cohort with a normal EF (EF ≥ 50%), models using EFa were significantly more associative with HF readmissions within 3 years, where the leave one out cross validation ROC analysis showed a 18.6% reduction in errors, and Net Classification Index (NRI) analysis showed that risk increment classification of events increased by 12.2%, while risk decrement classification of non-events decreased by 16.6%. EFa is associated with HF readmission in patients with a normal EF.

A Morphometric Study of the Pars Plana of the Ciliary Body in Human Cadaver Eyes.

This study aimed to determine the pars plana length in postmortem human eyes using advanced morphometric techniques and correlate demographics to ocular metrics such as age, sex, ethnicity, and axial length. Between February and July 2005, we conducted a cross-sectional observational study on 46 human cadaver eyes deemed unsuitable for transplant by the SBO Eye Bank. The morphometric analysis was performed on projected images using a surgical microscope and a video-microscopy system with a 20.5:1 correction factor. The pars plana length was measured three times per quadrant, with the final value being the mean of these measurements. Of the 46 eyes collected, 9 were unsuitable for the study due to technical constraints in conducting intraocular measurements. Overall, the average axial length was 25.20 mm. The average pars plana length was 3.8 mm in all quadrants, with no measurements below 2.8 mm or above 4.9 mm. There were no statistically significant variations across quadrants or with age, sex, axial length, or laterality. Accurately defining the pars plana dimensions is crucial for safely accessing the posterior segment of the eye and minimizing complications during intraocular procedures, such as intravitreal injections and vitreoretinal surgeries.

Estimating beluga whale abundance from space: using drones to ground‐validate VHR satellite imagery

AbstractRoutine monitoring of cetaceans is imperative for understanding their population trends and making informed management decisions. However, the inherent nature of cetaceans and the marine ecosystems they inhabit make annual population surveys logistically and economically challenging with current survey methods. One emerging solution is utilizing very high‐resolution (VHR) satellite imagery, which is a logistically efficient method for providing an instantaneous view of areas spanning hundreds of square kilometers. The objective of this study was to determine two factors required to reliably conduct beluga whale population abundance estimates with VHR satellite imagery: (1) depths that beluga whales are visible in VHR satellite images, which are used to define availability bias correction factors, and (2) a comparison of abundance estimates in VHR satellite imagery to current aerial methods. We submerged beluga whale models to different depths in two different water clarities and determined that beluga whales are distinguished only at the surface in turbid water (Secchi depth: 2.56 m) and at depths of 0–2 m in clear water (Secchi depth: 4.04 m). Based on the proportion of time beluga whales spend at these depths, an availability bias correction factor for Western Hudson Bay beluga whales was defined as 2.40 ± 0.16 for turbid water and 1.89 ± 0.05 for clear water. Synchronous ground‐validation surveys determined availability corrected beluga whale abundance estimates in 0.31 m VHR satellite imagery (n = 173 beluga whales) and imagery that was HD sharpened using a proprietary algorithm to approximate 0.15 m resolution (n = 170) to be comparable to drone imagery (n = 164). VHR satellite imagery has the potential to increase the frequency of beluga whale population surveys, which has become increasingly important as beluga whales face rapid ecosystem changes and increased anthropogenic disturbances.

Challenges in the measurement of cross-shore geotechnical characteristics of sandy beach surface sediments

Geotechnical properties of surficial beach sediments affect beach erosion and shoreline changes. This study sets out to measure relative density, moisture content, friction angle, and shear strength of sandy beach surface sediments from dune to swash zone towards the goal of assessing their importance in sandy beach morphodynamics. Methods of sediment sampling, a conductivity based moisture probe, field penetrometers, and a field vane shear were deployed to collect data at the sandy Atlantic-side beach in Duck, North Carolina. The tools used were assessed based on their operability in the beach environment and data quality, and results are discussed in the context of beach morphodynamics. A digital field vane shear provided an efficient and direct method of measuring shear strength, but the difficulty of computing stresses on the failure plane, which is necessary to validate the results, ultimately reduced the usability of this instrument. The results from three penetrometers were compared to a partially-saturated bearing capacity model, where a portable free-fall penetrometer yielded the best fit. However, a modified velocity-dependent strain rate correction factor (K=0.31vi) was required to convert dynamic sediment resistance to a quasi-static resistance for the partially saturated sands. A small-scale digital push in penetrometer also achieved a positive correlation when compared to moisture content, but the small tip diameter (5 mm) coupled with the grain size at the beach (0.35 mm) raised concerns about the ability to derive an accurate measure of strength. It was determined that estimating strength parameter using a partially saturated bearing capacity model was appropriate for water contents less than 25% by volume, or anywhere in the crosshore above the swash to the dune. Relative density and moisture content were found to be closely linked, with partial saturation resulting in samples that featured negative relative densities up to −40%.

Experimental comparison of cylindrical and plane parallel ionization chambers for reference dosimetry in continuous and pulsed scanned proton beams

Objective. In this experimental work we compared the determination of absorbed dose to water using four ionization chambers (ICs), a PTW-34045 Advanced Markus, a PTW-34001 Roos, an IBA-PPC05 and a PTW-30012 Farmer, irradiated under the same conditions in one continuous- and in two pulsed-scanned proton beams. Approach. The ICs were positioned at 2 cm depth in a water phantom in four square-field single-energy scanned-proton beams with nominal energies between 80 and 220 MeV and in the middle of 10 × 10 × 10 cm3 dose cubes centered at 10 cm or 12.5 cm depth in water. The water-equivalent thickness (WET) of the entrance window and the effective point of measurement was considered when positioning the plane parallel (PP) ICs and the cylindrical ICs, respectively. To reduce uncertainties, all ICs were calibrated at the same primary standards laboratory. We used the beam quality (k Q ) correction factors for the ICs under investigation from IAEA TRS-398, the newly calculated Monte Carlo (MC) values and the anticipated IAEA TRS-398 updated recommendations. Main results. Dose differences among the four ICs ranged between 1.5% and 3.7% using both the TRS-398 and the newly recommended k Q values. The spread among the chambers is reduced with the newly k Q values. The largest differences were observed between the rest of the ICs and the IBA-PPC05 IC, obtaining lower dose with the IBA-PPC05. Significance. We provide experimental data comparing different types of chambers in different proton beam qualities. The observed dose differences between the ICs appear to be related to inconsistencies in the determination of the k Q values. For PP ICs, MC studies account for the physical thickness of the entrance window rather than the WET. The additional energy loss that the wall material invokes is not negligible for the IBA-PPC05 and might partially explain the low k Q values determined for this IC. To resolve this inconsistency and to benchmark MC values, k Q values measured using calorimetry are needed.

Consideration of the Accuracy of Empirical and Indirect Laboratory Methods for the Characterisation of Tension Strength

AbstractThis research explores the results of the most common laboratory based indirect tension strength methods over the range of UCS strengths 0.1 MPa (cemented paste backfill) to 100 MPa (concrete). The accuracy of each of the methods is considered through a comparison with direct strength measurements completed on the same material. The results of 241 individual tests suggest that the use of indirect tension methods to determine tension strength for all geo-material strength ranges may provide misleading results unless a correction-factor is applied. Correction factors that relate splitting and flexure results to direct tension results are provided. The correction factors are based on the characteristic UCS of the material. A comparison of the traditional empirical relationship to derive tension from UCS is presented and an updated relationship is proposed that is relevant over the UCS strength range 0.1–100 MPa.

Cross-section induced uncertainties in neutron source mission rate calculations

Analysis presented in the paper is focused on the characterization of uncertainties induced by cross-section data, which contributing to the overall uncertainty of the correction factors. Advances in computational methods and computational power shifted the calculation of correction factors among the standard steps of the manganese bath method what decrease an interest about this part of the method. Anyway, with the development of computational tools, the cross-section data were also improved, and new evaluations of nuclear data libraries include more information about the cross-section data covariances. Therefore, the propagation of uncertainties induced by neutron cross-sections can be carried out within standard transport calculation of the manganese sulphate bath model. In this paper, the super-sequence SAMPLER module that implements stochastic techniques is used to assess the uncertainty in computed results. Reaction rates on all nuclides of the solution are computed in 400 cases with uncertain parameters and the results are evaluated by an auxiliary tool. Consideration of nuclear data uncertainty in calculations is a general trend that requires the attention of nuclear researchers and should draw attention in metrology. Additional 1.5 % (one-sigma) uncertainty is introduced to the overall uncertainty through correction factor.

The development of a cylindrical phantom for nanoDotTM calibration with multiple beam angles

Background: The nanoDotTM dosimeter, an optically stimulated luminescent dosimeter (OSLD), is compact and precise, ideal for various applications like radiation dosimetry. The nanoDotTM requires calibration before use with the detector alignment perpendicular to the central beam axis. It exhibits angular dependence that may impact the calibration factor, requiring the fabrication of a specific cylindrical phantom for the calibration procedure. Objective: This study aimed to develop a cylindrical phantom for nanoDotTM calibration to facilitate dose measurements in composite fields with various beam angles and to evaluate the nanoDotTM calibration factors for different plans. Materials and methods: The cylindrical phantom was constructed using cast nylon material to accommodate the nanoDotTM or a cylindrical ionization chamber (IC). The novel phantom underwent validation for physical characteristics, including dimensions, density, and uniformity. Validation for the calibration factor, using cylindrical phantom (CF cylin) under standard conditions with a 10x10 cm² field size at 10 cm depth was conducted with 6 MV X-rays, comparing it with calibration factor using slab solid water phantoms (CFsolid). The CFcylin for different numbers of beams were determined and validated against a reference IC in various planning conditions. Furthermore, angular correction factors were determined for their application in the single-beam calibration factor. Results: The cylindrical phantom had dimensions of 20 cm in diameter and 30 cm in length, a density of 1.145 g/cm³ and good uniformity. As a result of single beam, the CF cylin, agreed well with CFsolid, showing a difference of -0.069%. The CFcylin increased with the number of beams, ranging between 1.179 and 1.242. Additionally, the angular correction factor increased as the number of beams increased, peaking at 1.058 with 9 beams. When comparing the results to the IC, it was observed that with an increase in the number of beams to 4 beams, the single-beam calibration factor exhibited a variation of more than 2%. However, when applying the CF cylin specific to the number of beams or correcting for the angular correction factor, the dose differences between nanoDotTM and IC measurements were within 2%. Conclusion: The developed cylindrical phantom is suitable for nanoDotTM calibration under single beam angle and in composite fields with various beam angles. The new calibration factors for specific numbers of beams allow for accurate dose measurements using nanoDotTM, thus reducing the dose difference from the IC to acceptable levels. Further studies should investigate its application in clinical situations.

Investigation of the 106Ru ophthalmic plaque dose distribution in a pseudotumor-contained eye-equivalent phantom by silica glass beads

PurposeTo investigate the 106Ru dose distribution in an intraocular pseudotumor by micro silica glass beads thermo-luminescence dosimeters (TLD). Materials and methodsDosimetry was conducted using Monte Carlo (MC) simulation as well as an experimental setup by employing an in-house eye equivalent phantom. A BEBIG CCA model of 106Ru plaque was used. Bead TLDs were modeled using MCNPX code, choosing water and plexiglass as phantom mediums along with CCA plaque. The deposited energy and electron energy spectra were calculated using *f8 and f4 tallies, respectively. A dedicated eye-equivalent phantom was designed and fabricated by 3D-printing techniques to place glass beads. ResultsAbsorbed dose at the central axis of the CCA plaque by beads TLDs was compared to manufacturer-reported data and simulation results. Maximum, minimum, and mean relative differences of 23%, 7%, and 15% with the manufacturer and 14%, 0%, and 1.6% with the simulation were obtained, respectively. Replacing glass bead material with water resulted in an average relative difference of 33.9% in absorbed energy per mass unit, corresponding to 21% and 44.8% at the first (0.5 mm depth) and last dosimetry points (9.5 mm depth), respectively. It has also been shown that glass beads can shadow each other, leading to a dose reduction of 15%. ConclusionA specific eye equivalent phantom with a pseudotumor was constructed, and silica glass beads were used for dosimetry. The results of the experiment and the MC simulation are in good accord. In the case of 106Ru ophthalmic brachytherapy plaque dosimetry, replacing glass beads material with water led to a mean difference of about 34% as well as shadowing effects. This emphasizes how crucial it is to employ a reliable correction factor in clinical applications.

The IAEA remote audit of small field dosimetry for testing the implementation of the TRS-483 code of practice.

The TRS‑483, an IAEA/AAPM International Code of Practice on dosimetry of small static photon fields, underwent testing via an IAEA coordinated research project (CRP). Alongside small field output factors (OFs) measurements using active dosimeters by CRP participants, the IAEA Dosimetry Laboratory received a mandate to formulate a remote small field dosimetry audit method using its passive dosimetry systems. This work aimed to develop a small field dosimetry audit methodology employing radiophotoluminescent dosimeters (RPLDs) and radiochromic films. The methodology was subsequently evaluated through a multicenter pilot study with CRP participants. The developments included designing and manufacturing a dosimeter holder set and the characterization of an RPLD system for measurements in small photon fields using the new holder. The audit included verification of small field OFs and lateral beam profiles for small fields. At first, treatment planning system (TPS) calculated OFs were checked against a reference data set that was available for conventional linacs. Second, calculated OFs were verified through the RPLD measurement of point doses in a machine-specific reference field, 4cm × 4cm, 2cm × 2cm, and 1cm × 1cm, corresponding size circularfields or nearest achievable field sizes. Lastly, profile checks in in-plane and cross-plane directions were done for the two smallest fields by comparing film measurements with TPS calculations at 20%, 50%, and 80% isodose levels. RPLD correction factors for small field measurements were approximately unity. However, they influenced the dose determination's overall uncertainty in small fields, estimated at 2.30% (k=1 level). Considering the previous experience in auditing reference beam output following the TRS-398 Code of Practice, the acceptance limit of 5% for the ratio of the dose determined by RPLD to the dose calculated by TPS, DRPLD/DTPS, was considered adequate. The multicenter pilot study included 15 participants from 14 countries (39 beams). Consistent with the previous findings, the results of the OF check against the reference data confirmed that TPSs tend to overestimate OFs for the smallest fields included in this exercise. All except three RPLD measurement results were within the acceptance limit, and the spread of results increased for smaller field sizes. The differences between the film measured and TPS calculated dose profiles were within 3mm for most of the beams checked; deviated results revealed problems with TPS commissioning and calibration of the treatment unit collimation systems. The newly developed small field dosimetry audit methodology proved effective and successfully complemented the CRP OF measurements by participants with RPLD audit results.

Step 3 for the treatment of periodontal diseases: non-regenerative periodontal surgery

This article outlines the key aspects of considering non-regenerative periodontal surgery in step 3 of the UK version of the EFP S3-level clinical practice guidelines for the treatment of periodontitis. The third step of periodontal treatment is aimed at treating those sites that have not responded adequately, targeting non-responding or residual deep pockets. The purpose of non-regenerative surgery is to achieve access to root surfaces associated with residual pockets for further subgingival instrumentation, aiming to eliminate those lesions that add complexity to the management of periodontitis (such as infrabony defects, root concavities and furcations). At these localized sites, the main objective of periodontal surgery is to improve direct vision and access for professional instrumentation, to reduce or correct anatomical factors, partially regenerate lost periodontal tissue where possible, and ultimately create an environment that is easy and comfortable for the patient and the dental professional to maintain. CPD/Clinical Relevance: Knowledge of the non-regenerative surgical treatment of Stage III and IV periodontitis patients is valuable for dental clinicians.

Abstract PO1-02-05: An exploratory comparison of MINDACT and TAILORx genomic risk proportions and outcomes in patients with HR+/HER2-, node-negative early-stage breast cancer, stratified by clinical risk

Abstract Introduction: Genomic tests provide physicians with critical information to evaluate the risk of distant metastasis and inform treatment plans by identifying those patients who may safely avoid chemotherapy (CT). The 70-gene signature (MammaPrint, MP) through the MINDACT trial and the 21-gene signature (Oncotype DX, ODx) through the TAILORx trial are the only tests validated with level 1A evidence that can be used for CT de-escalation decisions. Differences in trial design have made direct comparison of results difficult. We provide a comparison of MammaPrint and ODx genomic risk distributions and associated survival in patients with HR+/HER2-, node-negative (N0) early-stage breast cancer (EBC), stratified by clinical risk. Methods: Data from the MINDACT 2021 publication in The Lancet Oncology and landmark TAILORx 2019 publication in The New England Journal of Medicine were reviewed, in addition to publicly available data submitted to the Dutch Health Technology Assessment (HTA) authorities regarding survival data in patients with clinical High Risk in TAILORx. In MINDACT, patients were randomized based on both clinical (as per MINDACT definition) and genomic risk (clinical high/MP low, randomized to treatment according to clinical risk [i.e. CT] vs treatment according to MammaPrint risk [i.e. no CT]), while in TAILORx randomization was based on genomic risk alone. In TAILORx, enrollment for the population in the RS 11–25 group was enriched by 73% to account for the larger than expected non-adherence to randomized treatment plan based on the ODx results, as described in the original publication. This enrichment was only done for the RS 11–25 group. In this analysis, this enrollment enrichment was removed by applying the same proportional 73% corrective factor to the RS 11–25 group. Outcome data are reported for Overall Survival (OS), the only comparable endpoint used in both trials. Results: This explorative comparison focuses on patients with HR+/HER2- and N0 EBC in MINDACT (n=4,225) and TAILORx (n=6,686, without population enrichment). Similar proportions of patients identified as candidates for CT de-escalation (MP Low Risk or ODx RS≤25) were observed in this population of MINDACT (75%) and TAILORx (80%) when removing the RS 11–25 population enrichment in TAILORx (Table). In clinical high risk patients, the proportion with genomic low risk of distant metastasis were also comparable between MINDACT (55%) and TAILORx (63%) (Table). In the original clinical high risk but MammaPrint Low Risk population treated without CT in MINDACT the reported 8-year OS was 93.9%. In TAILORx, the comparable population of patients (ie. clinical high risk, low genomic risk, not treated with CT) had a 9-year OS of 89.2% in the RS 0–10 group and 91.6% in the RS 11–25 group (Table). Conclusions: Accounting for differences in trial design and population, comparable proportions of patients with genomic low risk results were observed between MP and ODx, justifying similar rates of CT de-escalation. Patients with clinical high risk tumors who are MammaPrint Low Risk had an excellent survival at 8 years. Genomic risk distributions and associated OS in HR+HER2- N0 patients in MINDACT and TAILORx MP, MammaPrint; OS, Overall Survival; RS, Recurrence Score. Number of patients in the TAILORx RS 11 – 25 group are adjusted to remove the proportional enrichment in the trial. OS data presented per original MINDACT and TAILORx populations. Citation Format: Patrick Neven, Josephine Lopes-Cardozo, Fatima Cardoso, Laura Van ’t Veer. An exploratory comparison of MINDACT and TAILORx genomic risk proportions and outcomes in patients with HR+/HER2-, node-negative early-stage breast cancer, stratified by clinical risk [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-02-05.

Development of additively manufactured cryogenic heat exchangers for hydrogen-electric aircraft propulsion

Storage of liquid hydrogen at low pressures and temperatures is advantageous in terms of overall system weight compared to high-pressure gas storage at room temperature [1]. The weight penalty for insulation of cryogenic media is typically outperforming the combined weight and volume penalty of high-pressure storage [2] [3]. For aviation applications, where light-weight and compact design is key, it is, therefore, preferred to store the propellant as liquid. In the context of hydrogen, this implies storage of the liquid between 20K and 30K, depending on tank pressure. As the fuel cell, which converts chemical energy to electrical energy, requires the hydrogen to be provided at temperatures well above the freezing level of water, hydrogen extracted from the tank must be thermally conditioned, to comply with applicable requirements [4] [5].In the presented work, a liquid hydrogen and fuel cell based electrical propulsion system for aircraft is developed, which incorporates several novel technologies and non-trivial operating conditions [6]. One major focus is the utilization of additive manufacturing enabling advanced geometric designs to enhance performance and reduce weight. However, the influence of hydrogen and cryogenic operating conditions on thermal and mechanical properties of additively manufactured materials must be assessed and accounted for in the design process.The underlying architecture of the investigated hydrogen-electric aircraft powertrain incorporates several heat exchangers with different purposes. One of the heat exchangers is tasked with transfer of heat from a liquid coolant cycle to the gaseous hydrogen in order to rise its temperature to the working level of the fuel cell (>300K). The design of the heat exchanger is based on empirical formulae for cylindrical tube bundles (pins), which enhance heat transfer on the gas side. Alternating flow planes of gaseous hydrogen and liquid coolant media are stacked to reach a number of units, which generate the desired heat transfer rates and keep the pressure loss due to friction below the defined limit. The particular arrangement of rows, columns, pin diameter or distances between individual pins is optimized to arrive at the minimum structural mass, while satisfying heat transfer and pressure drop requirements. Boundaries for this parameter optimization may originate from manufacturing limitations, like the minimum thickness of fine structures impacting the reliability of the manufacturing process. Therefore, accompanying manufacturing tests are required, to feed the optimizer with meaningful limits.After the initial optimization, computational fluid dynamics (CFD) analysis confirms the performance of the entire heat exchanger, including the intake and outflow manifold. Lastly, the lower limits of wall thicknesses may be defined by either the manufacturability in the 3d-printer or the differential pressure across the wall causing material stress. Therefore, mechanical analysis is performed, to confirm that the manufacturing limit is the actual driving limit for the minimum wall thickness.Comparison of results of the analytical method with CFD show very good agreement with deviations of average media temperature at the heat exchanger exit of less than 3% for relevant conditions. The pressure drop results deviate predictably in the order of 50%, which can be accounted for with a correction factor. CFD analysis of the entire heat exchanger shows good agreement of the flow properties in the heat exchanger core, but also demonstrate that the intake (from pipe flow into heat exchanger core) and outflow plena can contribute significantly to the overall pressure drop, depending on flow conditions and geometry.This presentation summarizes the entire development process of a heat exchanger starting with the requirements derivation based on a system analysis, via the initial design optimization based on empirical coupled thermal and fluid mechanical formulae to CFD and mechanical strength analysis of the detailed design. Close attention is paid on the additional degrees of freedom and restrictions in design gained by additive manufacturing as well as the impact of the manufacturing method on material properties especially in the context of cryogenic hydrogen.

Mean force emission theory for classical bremsstrahlung in strongly coupled plasmas

This work presents mean force emission theory, which extends the classical theory of bremsstrahlung emission to strongly coupled plasmas. In the high-frequency limit, the theory reduces to solving for the electron trajectory during a binary collision, but where the electron–ion interactions occur through the potential of mean force. In the low-frequency limit, it uses an autocorrelation formalism that captures effects of multiple collisions and strongly correlated motion. The predictions are benchmarked by comparison with first-principles classical molecular dynamics simulations of a fully ionized hydrogen plasma in which all interactions are repulsive. The comparison shows good agreement up to Coulomb coupling strengths of Γ∼30. The theory improves upon traditional models by including strong coupling effects and systematically including the effect of multiple collisions. Furthermore, mean force emission theory provides evidence that the Drude correction factor commonly used in quantum calculations of optical quantities may not be adequate at strong coupling.

Development of a plastic scintillating optical fibers array dosimeter for radiobiology

In this work a detector prototype built as an array of Scintillating Plastic Optical fibers (SPOFs) is presented. The primary aim of this detector is to improve spatial resolution, provide real-time dose mapping and a tissue equivalent detector in radiobiology experiments. Details on the design and construction are provided along with the initial tests carried out using low-energy X-ray and electrons from a 90Sr source. Regarding the design and construction of the detector, the mechanical design of the irradiation box is presented and the Quality Assurance (QA) the optical fiber arrays were subjected to is discussed. The QA measurements show that the alignment of the optical fibers is within acceptable tolerances for dose readout. After the detector assembly, correction factors for each fiber were extracted from tests using a collimated X-ray beam. Special care was taken to ensure that each fiber is submitted to the same dose. Broad field tests show that the measurements are reproducible to within 3 %. Potential innovative features of this system for radiobiological experiments are discussed as well as the future follow-up of the prototype.

Monte Carlo simulation for photon energy response from the RADOS dosemeter.

Ionizing radiation interaction models are commonly included in Monte Carlo codes. However, as there are different models and different output quantities available, it is important to understand the physical phenomena used. So, the aim of this study is to analyze the photon interaction model called Simple Physical Treatment of the Monte Carlo code MCNPX to estimate the energy dependence of photons from the RADOS dosemeter and to validate this calculation method by comparing it with experimental results found in the literature. The energy deposition in the MTS-N detector and the air kerma were obtained accompanied by their uncertainties, which varied between 1.5% and 3.0%. The RADOS dosemeter simulation and the calculation methodology applied in this study have been validated. Therefore, when using the Simple Physical Treatment model, the effective dose can be corrected by a correction factor calculated from the simulated results.

Analysis of nonlinear wave propagation within architected materials consisting of nonlinear Timoshenko beam structural elements

In the present work, a full nonlinear Timoshenko beam employing nonlinear shape functions is developed. The extended Hamilton principle is employed for deriving the differential equations of motion and the associated boundary conditions. The general form of the boundary conditions is then utilized to determine the static solution of the beam motion. Using this solution for the deformation and rotation of the beam, the nonlinear shape functions of the beam are identified, which leads to the linear and nonlinear mass and stiffness matrices of the Timoshenko beam element. The nonlinear dispersion diagram incorporating the non-linear corrections is obtained using the Linstedt–Poincaré perturbation method. An analysis of the effect of internal transverse shear and bending on the nonlinear dispersion characteristics of wave propagation in two-dimensional periodic network materials made of nonlinear Timoshenko beams is done. The formulated theory shows that the percentage of correction factor of the nonlinear kinematics versus the linear dynamical behavior is inversely proportional to the frequency amplitude. The shear and extension modes are shown to have the higher effect in the non-linear correction term in comparison to the flexural mode.