Local Shielding Research Articles

Droplet–droplet vapor-mediated interactions in confined environments

The evaporation of multiple droplets ensues ubiquitously in nature and industry. Vapor mediation caused by evaporating neighboring droplets is a demonstrated phenomenon that shows that droplets can interact with each other via the vapor in both open and confined configurations, i.e., the “shielding effect.” However, interactions between paired droplets in confined environments, more common in industrial processes, remain unexplored. In this Letter, we experimentally investigate the evaporation of water based paired sessile droplets on hydrophilic glass slides at different spacings in the absence and presence of an enclosed chamber. The results demonstrate that a confined environment significantly attenuates droplet evaporation, which intensifies with decreasing spacing between droplets. A 30%–82% increase in the droplet lifetime is found for the shortest distance studied in a confined environment, while results in an open environment are provided as a control. Both the local shielding effect and the global vapor accumulation due to confinement collaboratively induce such strong evaporation suppression. In addition, two well differentiated evaporation regimes ensue in a confined environment where the shielding effect initially dominates the evaporation suppression, whereas confinement governs the later evaporation stage. The later stage accounts for over 60% of the droplet lifetime. Such transition and further evaporation suppression, when compared to the classical shielding effect, highlights the importance of a confined environment in multiple droplet evaporation.

Engineering design status of IFMIF-DONES High Energy Beam Transport line and Beam Dump system inside the TIR and RIZ

IFMIF-DONES (International Fusion Materials Irradiation Facility – DEMO Oriented Neutron Source) is a fusion materials testing facility that is currently being designed under the framework of a work package of the EUROfusion Consortium. It will use a 125mA at 40MeV deuteron beam to generate a high neutron flux through Li(d,xn) stripping nuclear reactions in a liquid lithium target. The High Energy Beam Transport line (HEBT), the most upstream system of the IFMIF-DONES accelerator, is responsible for the guidance and shaping of the beam towards the target. Additionally, during commissioning periods, the HEBT is also responsible for diverting the beam, through the Beam Dump Transport Line, to the Beam Dump for testing purposes. The HEBT is spread along different rooms and zones: the Accelerator Vault, the Radiation Interface Zone (RIZ), and Target Interface Room (TIR). The engineering design of the HEBT components situated within the TIR and RIZ has been updated to satisfy new requirements, with a focus on ensuring the protecting of the Fast Isolation Valve (FIV) from the backscattered radiation from the target. These modifications include relocating the FIV from the TIR to the RIZ, adjusting the building layout to accommodate the new FIV module, configuring an enclosure cabinet for the RIZ, and adding local shielding to extend the lifetime of the FIV seal actuators. This work describes the current status of these TIR and RIZ engineering design, including radioprotection, commissioning and maintenance plan, beam diagnostics devices, beam dynamics and new remote handling approaches, as well as the layout and integration of the required components along the beamline. The TIR and RIZ are critical areas for IFMIF-DONES, and their design and operation must be compliant with functional, reliability and safety requirements. The updated design addresses potential issues and enhances the facility’s overall functionality.

Rule-based shields embedded safe reinforcement learning approach for electric vehicle charging control

The optimal and secure electric vehicles charging control can be formulated as a large-scale partially-observable constrained Markov decision process (PO-CMDP) problem with high levels of security risks and uncertainties. Such a problem is very difficult to be handled by optimization-theory-based methods. Data-driven methods, especially reinforcement learning (RL), are suitable for handling uncertainties but are poor in ensuring safety, which is unacceptable in power systems. Motivated by the fact that humans could be supervised by an expert when learning a new skill involving risk, this paper proposes a safe RL framework that embeds rule-based local and global shields in the loop of RL for supervising the actions of agents. The proposed framework not only strictly guarantees local and global security in the training and execution phases, but also helps the agent to find a more near-optimal policy. The effectiveness and efficiency are demonstrated by comparison with multiple baseline methods in the IEEE-33 node system.

Additive Manufacturing of Ti-6Al-4V with laser-wire DED and local shielding gas protection

Additive Manufacturing of titanium has the need of protecting the hot metal from atmospheric gases like oxygen using a shielding gas. The paper shows a possibility to realize this during laser-wire-DED with a local shielding gas stream and without the need of a chamber. A simple nozzle design together with a welding strategy of using short seams in the range of the nozzle diameter exhibits only minor discolorations. Tensile stress tests have been performed showing a significant deviation of the mechanical properties regarding the direction. The vertical results, which are perpendicular to the layer, are much better compared to the horizontal results in the layer plane. The vertical tests show an average of the tensile strength of 1215.8 N/mm² and an average elongation of 3.97%.

From Wire to Component: Aluminium Lithium Alloy Development for Wire and Arc Additive Manufacturing

The Innovative Aluminium filler Wires for Aircraft Structures (IAWAS) project aimed to demonstrate the potential of Wire Arc Additive Manufacture (WAAM) for the production of aluminium lithium components. Preliminary testing demonstrated the possibility of depositing an 2395 aluminium lithium filler wire using a plasma arc heat source and a local shielding device. The deposit had a low porosity level but also low ductility caused by long, vertical, segregated grain boundaries. Both chemical composition and deposition conditions are known to impact the deposit microstructure. In-situ alloying, an efficient technique to develop new material, was implemented using plasma arc as a heat source on aluminium lithium alloys. The results aligned with the literature review on the impact of copper on crack sensitivity and led to the design of a new alloy. Unfortunately, the composition selected yielded challenges during the drawing process, and the filler material quality was poor, leading to a low WAAM deposit quality. Machine hammer peening was implemented on the AA2395 alloy, resulting in a drastic increase in ductility and yield strength of 480 MPa after solution treatment and ageing. This alloy was used to manufacture an aluminium lithium demonstrator to showcase the potential of WAAM to produce real-life components.

Numerical investigate of the effects of surface roughness on local scour around pipeline under steady current condition

A two-dimensional numerical model was developed to investigate the effects of the surface roughness on local scour around pipeline based on Naiver-Stokes equations. Both suspended load and bedload transport are considered for the sand motion equation. Present numerical model is verified accurately for simulating local scour around pipeline. The numerical results show that the surface roughness has a significant effect on the process of local scour, i.e. forces, Shields parameter and scour depth. For rough pipeline, the average value of the drag force coefficient on the pipeline, the RMS value of the lift coefficient, the scour depth and the scour width all decrease rapidly with increasing roughness and then change slowly.

Effect of oxygen shielding on the tensile and fatigue performance of 300M repaired through laser-directed energy deposition

AbstractLaser-directed energy deposition (L-DED) is a key enabling technology for the repair of high-value aerospace components, as damaged regions can be removed and replaced with additively deposited material. While L-DED repair improves strength and fatigue performance compared to conventional subtractive techniques, mechanical performance can be limited by process-related defects. To assess the role of oxygen on defect formation, local and chamber-based shielding methods were applied in the repair of 300M high strength steel. Oxidation between layers for locally shielded specimens is confirmed to cause large gas pores which have deleterious effects on fatigue life. Such pores are eliminated for chamber shielded specimens, resulting in an increased ductility of ∼15%, compared to ∼11% with chamber shielding. Despite this, unmelted powder defects are not affected by oxygen content and are found in both chamber- and locally shielded samples, which still have negative consequences for fatigue.

Spatial Oxygen Distribution of the Direct Metal Deposition Process for Different Powder Nozzles

Additive manufacturing processes are among the most innovative manufacturing processes of this century. Powder-based direct metal deposition (DMD) is one of these processes. In the DMD process, local shielding takes place via the powder nozzle. The process is therefore critical for oxidation, especially for materials with an affinity for oxidation such as titanium, aluminum and their alloys. In order to study the oxidation behavior in more detail, the present gas dynamics must be further understood. Wirth and Wegener have made a first approach with their gas flow simulation. In this study, a measurement method for spatial oxygen concentration determination is presented. It can be shown that the spatial oxygen concentration follows the nozzle geometry. Furthermore, the coaxial nozzle is superior to the three-jet nozzle with respect to a low oxygen concentration from a carrier gas to shielding gas volume flow ratio of equal to or greater than 0.4. Finally, it can be shown that the use of a shielding gas chamber eliminates the optimization of the gas flow settings.

Design and Investigation of a Novel Local Shielding Gas Concept for Laser Metal Deposition with Coaxial Wire Feeding

Laser metal deposition with coaxial wire feeding is a directed energy deposition process in which a metal wire is fed to a laser-induced melt pool. Oxidation occurring during the process is a major challenge as it significantly influences the mechanical properties of the produced part. Therefore, an inert gas atmosphere is required in the high temperature process zone, whereby local shielding offers significant cost advantages over an inert gas chamber. In this work, a novel local shielding gas nozzle was developed based on basic methods of fluid mechanics. A gas flow-optimized prototype incorporating internal cooling channels was additively manufactured by laser-powder bed fusion and tested for its effectiveness via deposition experiments. Using the developed local shielding gas concept, an unwanted mixing with the atmosphere due to turbulence was avoided and an oxide-free deposition was achieved when processing a stainless steel ER316LSi wire. Furthermore, the effects of the shielding gas flow rate were investigated, where a negative correlation with the melt pool temperature as well as the weld bead width was demonstrated. Finally, a solid cuboid was successfully built up without oxide inclusions. Overheating of the nozzle due to reflected laser radiation could be avoided by the internal cooling system. The concept, which can be applied to most commercially available coaxial wire deposition heads, represents an important step for the economical application of laser metal deposition.

Particle‐induced degradation of III–V multi‐junction solar cells under different configurations of displacement damage dose

AbstractThe solar arrays of spacecrafts are subjected to a severe radiative environment. Associated degradation rates are dependent on operational orbit configuration. The current approach used in models and tools to determine power degradation shall thus be validated to ensure good prediction accuracy. This paper reports on extensive irradiation test campaigns realized on triple‐junction solar cells to compare degradation induced by different configurations of irradiation reproducing nominally the same displacement damage dose (DDD) in the active layer. These test campaigns data are used to support the validation of a new tool developed to optimize prediction accuracy of solar cell degradation. The DDD equivalence between front/rear irradiation on solar cell assemblies and on bare solar cells, between different electron and proton energies, as well as the verification of the superposition principle are addressed. Results are conclusive regarding the equivalence of degradation obtained with electrons, protons and/or combined electrons and protons, accounting for local shielding.

Establishing local manufacture of PPE for healthcare workers in the time of a global pandemic

A face shield is a secondary personal protective equipment (PPE) for healthcare workers (HCW). Worn with the appropriate face masks/respirators, it provides short term barrier protection against potentially infectious droplet particles. Coronavirus disease 2019 (COVID-19) caused a spike in demand for PPE, leading to a shortage and risking the safety of HCW. Transport restrictions further challenged the existing PPE supply chain which has been reliant on overseas-based manufacturers. Despite the urgency in demand, PPE must be properly tested for functionality and quality. We describe the establishment of local face shields manufacture in Western Australia to ensure adequate PPE for HCW. Ten thousand face shields for general use (standard) and for ear, nose and throat (ENT) specialist use were produced. Materials and design considerations are described, and the face shields were vigorously tested to the relevant Standards to ensure their effectiveness as a protective barrier, including splash and impact resistance. Comparative testing with traditional and other novel face shields was also undertaken. Therapeutic Goods Administration (TGA) licence was obtained to manufacture and supply the face shields as a Class I medical device. The swiftness of process is a credit to collaboration from industry, academia and healthcare.

Results from the Radiation Assessment Detector on the International Space Station: Part 1, the Charged Particle Detector

We report the results of the first six years of measurements of the energetic particle radiation environment on the International Space Station (ISS) with the Radiation Assessment Detector (ISS-RAD), spanning the period from February 2016 to February 2022. The first RAD was designed and built for MSL, the Mars Science Laboratory rover, also known as Curiosity; it has been operating on Mars since 2012 and is referred to here as MSL-RAD. ISS-RAD combines two sensor heads, one nearly identical to the single MSL-RAD sensor head, the other with greatly enhanced sensitivity to fast neutrons. These two sensor heads are referred to as the Charged Particle Detector (CPD) and Fast Neutron Detector (FND), respectively. Despite its name, the CPD is also capable of measuring high-energy neutrons and γ-rays, as is MSL-RAD. ISS-RAD was flown to the ISS in December 2015 and was deployed in February 2016, initially in the USLab module. RAD was used as a survey instrument from January 2017 through May 2020, when the instrument was positioned in the USLab and set to a zenith-pointing orientation. The energetic particle environment on the ISS is complex and varies on short time scales owing to the orbit, which has a 51.6∘ inclination with respect to the equator and has had an altitude in the 400–440 km range in this time period. The ISS moves continuously through the geomagnetic field, the strength of which varies with latitude, longitude, and altitude. The orbit passes through the South Atlantic Anomaly (SAA) several times a day, where magnetically trapped protons and electrons produce large but transient increases in observed fluxes and absorbed dose rates. The environment inside the ISS is affected by the solar cycle, altitude, and the local shielding, which varies between different ISS modules. We report results for charged particle absorbed dose and dose equivalent rates in various positions in the ISS. In an accompanying paper, we report similar results for neutron dose equivalent rates obtained with the ISS-RAD Fast Neutron Detector.

Surface morphology and carbon structure effects on sputtering: Bridging scales between molecular dynamics simulations and experiments

Experiments report large scatter in the sputtering yield of carbon materials under the bombardment of low-energy noble gas ions. Here, we conduct scale-bridging molecular dynamics (MD) simulations on the xenon bombardment of carbon substrates across ion energies of 75 eV to 2 keV, and at ion incidence angles of 0°–75°, to resolve uncertainties in the sputtering data. Results show rapid amorphization of the carbon subsurface with ion bombardment, but the structural characteristics (sp/sp2/sp3 bond proportion, atomic density) eventually plateau once steady-state sputtering is achieved. In addition, we obtain virtually indistinguishable “steady-state” amorphous structures across the range of ion energies and ion incidence angles, as well as for several different carbon structures, which suggests that the steady-state sputtering yield data is independent of the initial carbon structure and prior sputtering history. By accounting for changes in the local incidence angle, surface shielding, and redeposition of the sputterants associated with surface morphology effects, we demonstrate that the sputtering predictions from MD are in perfect agreement with prior experiments across the range of ion energies and incidence angles. Using a Bayesian approach based on the MD data, we calibrate the parameters of a semi-empirical sputtering model for different surface morphologies.

Dense Local Triplet States and Steric Shielding of a Multi‐Resonance TADF Emitter Enable High‐Performance Deep‐Blue OLEDs (Adv. Mater. 50/2022)

Dense Local Triplet States and Steric Shielding of a Multi‐Resonance TADF Emitter Enable High‐Performance Deep‐Blue OLEDs (Adv. Mater. 50/2022)

Influence of oxygen content in the shielding gas chamber on mechanical properties and macroscopic structure of Ti-6Al-4V during wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) of titanium parts shows promising potential for aerospace application due to its high deposition rates allowing a fast and economical production of large components. The cost savings are high, especially for expensive alloys like Ti-6Al-4V. However, due to high oxygen affinity of Ti-6Al-4V at elevated temperatures an excellent shielding gas coverage seems necessary to prevent embrittlement of the material during the welding process. Regarding the future development of local shielding gas coverage set-ups for gas metal arc welding (GMAW) based WAAM, this study investigates the influence of the oxygen content in the shielding gas chamber on mechanical properties of Ti-6Al-4V during the welding process. Samples are welded at different oxygen contents in the shielding gas chamber and stress-relief heat treated afterwards. Inert gas milling and hot gas extraction are used to determine the material oxygen content at different deposition heights. Metallographic methods are used to show macroscopic grain structure, evaluate possible α-case thickness and its dissolution by the subsequent layer. Hardness testing is used to investigate possible material inhomogeneities in the deposit and tensile properties of the material welded at different chamber oxygen contents are displayed. It is concluded, that even at high chamber oxygen levels of 6000 ppm the welding process is stable, the forming α-case at top of the layer dissolves in the melt pool of the subsequent layer and that the aerospace requirements on tensile properties can be reached.

Dense Local Triplet States and Steric Shielding of a Multi-Resonance TADF Emitter Enable High-Performance Deep-Blue OLEDs.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules based on boron and nitrogen atoms are emerging as next-generation blue emitters for organic light-emitting diodes (OLEDs) due to their narrow emission spectra and triplet harvesting properties. However, intermolecular aggregation stemming from the planar structure of typical MR-TADF molecules that leads to concentration quenching and broadened spectra limits the utilization of the full potential of MR-TADF emitters. Herein, a deep-blue MR-TADF emitter, pBP-DABNA-Me, is developed to suppress intermolecular interactions effectively. Furthermore, photophysical investigation and theoretical calculations reveal that adding biphenyl moieties to the core body creates dense local triplet states in the vicinity of S1 and T1 energetically, letting the emitter harvest excitons efficiently. OLEDs based on pBP-DABNA-Me show a high external quantum efficiency (EQE) of 23.4% and a pure-blue emission with a Commission Internationale de L'Eclairage (CIE) coordinate of (0.132, 0.092), which are maintained even at a high doping concentration of 100wt%. Furthermore, by incorporating a conventional TADF sensitizer, deep-blue OLEDs with a CIE value of (0.133, 0.109) and an extremely high EQE of 30.1% are realized. These findings provide insight into design strategies for developing efficient deep-blue MR-TADF emitters with fast triplet upconversion and suppressed self-aggregation.

Two-Phase Flow Modeling for Bed Erosion by a Plane Jet Impingement

This paper presents experimental and numerical studies on the erosion of a horizontal granular bed by a two-dimensional plane vertical impinging jet to predict the eroded craters’ size scaling (depth and width). The simulations help understand the microscopic processes that govern erosion in this complex flow. A modified jet-bed distance, accounting for the plane jet virtual origin, is successfully used to obtain a unique relationship between the crater size and a local Shields parameter. This work develops a two-phase flow numerical model to reproduce the experimental results. The numerical techniques are based on a finite volume formulation to approximate spatial derivatives, a projection technique to calculate the pressure and velocity for each phase, and a staggered grid to avoid spurious oscillations. Different options for the sediment’s solid-to-liquid transition during erosion are proposed, tested, and discussed. One model is based on unified equations of continuum mechanics, others on modified closure equations for viscosity or momentum transfer. A good agreement between the numerical solutions and the experimental measurements is obtained.

EMI Mitigation of GaN Power Inverter Leg by Local Shielding Techniques

This paper presents local shielding techniques applied to a half-bridge inverter leg with the aim to reduce the common mode (CM) current noise at converter's DC input. The research study is conducted for 650V Enhancement mode Gallium Nitride (GaN) power transistor switches. Main contributors of parasitic capacitances referred to the inverter-leg middle point node are identified. Then, shielding solutions are proposed to reduce CM current emission by these capacitances. Respecting the precautions concerning the isolation of CM currents of the half-bridge inverter leg, the electromagnetic compatibility measurement setup is developed. Experimental step-by-step addition of local shielding copper layers to different contributors of middle point capacitance shows progressive attenuation of CM noise spectra.

Mitigation of the Magnetic Field Susceptibility of Transition-Edge Sensors Using a Superconducting Groundplane

Transition edge sensor (TES) microcalorimeters and bolometers are used for a variety of applications. The sensors are based on the steep temperature-dependent resistance of the normal-to-superconducting transition, and are thus intrinsically sensitive to magnetic fields. Conventionally the detectors are shielded from stray magnetic fields using external magnetic shields. However, in particular for applications with strict limits on the available space and mass of an instrument, external magnetic shields might not be enough to obtain the required shielding factors or field homogeneity. Additionally, these shields are only effective for magnetic fields generated external to the TES array, and are ineffective to mitigate the impact of internally generated magnetic fields. Here we present an alternative shielding method based on a superconducting groundplane deposited directly on the backside of the silicon nitride membrane on which the TESs are located. We demonstrate that this local shielding for external magnetic fields has a shielding factor of at the least ~ 75, and is also effective at reducing internal self-induced magnetic fields, as demonstrated by measurements and simulation of the eddy current losses in our AC biased detectors. Measurements of 5.9 keV X-ray photons show that our shielded detectors have a high resilience to external magnetic fields, showing no degradation of the energy resolution or shifts of the energy scale calibration for fields of several microTesla, values higher than expected in typical real-world applications.

Evaluation of the effectiveness of testicular shielding in rectal cancer radiotherapy

This study aimed to investigate the effect of local shielding on the reduction of the dose received by the male sexual organs in pelvic radiation therapy. For this purpose, a clinical case, and its corresponding simulation with the Monte Carlo Geant4 toolkit were studied. Here, the 15 MV photon mode of a medical LINAC was used to irradiate the pelvic region of three patients with rectal cancer. Using thermoluminescent dosimeter (TLD) 100, the doses received by the testes, seated out of the field, were measured in two situations, i.e., with and without a testicular shield. After benchmarking the simulation setup by comparing the simulated and experimental PDDs (Percentage Depth Dose) and lateral profiles in a water phantom, the simulation corresponding to the clinical case has been done. Afterward, the desired quantities such as absorbed dose, total equivalent dose, and neutron equivalent dose have been calculated. The results indicate that the local placement of a spherical lead shield leads to a decrease in the absorbed dose received by the testes with a coefficient greater than 2. It was also observed that shielding had a minimal contribution to the production of secondary neutrons and was not seen any sensible change in neutron equivalent dose, whereas a decrease in the total equivalent dose by a factor of 2.2 for the testes was observed. These observations imply that the risk of secondary cancers decreased proportionately, as well as a reduction in the risk of permanent infertility for young men.