Compact Configuration Research Articles

The Southern-sky MWA Rapid Two-metre (SMART) pulsar survey—II. Survey status, pulsar census, and first pulsar discoveries

Abstract In Paper I, we presented an overview of the Southern-sky MWA Rapid Two-metre (SMART) survey, including the survey design and search pipeline. While the combination of MWA’s large field-of-view and the voltage capture system brings a survey speed of ${\sim} 450\, {\textrm{deg}}^{2}\,\textrm{h}^{-1}$ , the progression of the survey relies on the availability of compact configuration of the Phase II array. Over the past few years, by taking advantage of multiple windows of opportunity when the compact configuration was available, we have advanced the survey to 75% of the planned sky coverage. To date, about 10% of the data collected thus far have been processed for a first-pass search, where 10 min of observation is processed for dispersion measures out to 250 ${\textrm{pc cm}}^{-3}$ , to realise a shallow survey that is largely sensitive to long-period pulsars. The ongoing analysis has led to two new pulsar discoveries, as well as an independent discovery and a rediscovery of a previously incorrectly characterised pulsar, all from ${\sim} 3\% $ of the data for which candidate scrutiny is completed. In this sequel to Paper I, we describe the strategies for further detailed follow-up including improved sky localisation and convergence to timing solution, and illustrate them using example pulsar discoveries. The processing has also led to re-detection of 120 pulsars in the SMART observing band, bringing the total number of pulsars detected to date with the MWA to 180, and these are used to assess the search sensitivity of current processing pipelines. The planned second-pass (deep survey) processing is expected to yield a three-fold increase in sensitivity for long-period pulsars, and a substantial improvement to millisecond pulsars by adopting optimal de-dispersion plans. The SMART survey will complement the highly successful Parkes High Time Resolution Universe survey at 1.2–1.5 GHz, and inform future large survey efforts such as those planned with the low-frequency Square Kilometre Array (SKA-Low).

The Southern-sky MWA Rapid Two-metre (SMART) pulsar survey—I. Survey design and processing pipeline

Abstract We present an overview of the Southern-sky MWA Rapid Two-metre (SMART) pulsar survey that exploits the Murchison Widefield Array’s large field of view and voltage-capture system to survey the sky south of 30 $^{\circ}$ in declination for pulsars and fast transients in the 140–170 MHz band. The survey is enabled by the advent of the Phase II MWA’s compact configuration, which offers an enormous efficiency in beam-forming and processing costs, thereby making an all-sky survey of this magnitude tractable with the MWA. Even with the long dwell times employed for the survey (4800 s), data collection can be completed in $<$ 100 h of telescope time, while still retaining the ability to reach a limiting sensitivity of $\sim$ 2–3 mJy (at 150 MHz, near zenith), which is effectively 3–5 times deeper than the previous-generation low-frequency southern-sky pulsar survey, completed in the 1990s. Each observation is processed to generate $\sim$ 5000–8000 tied-array beams that tessellate the full $\sim 610\, {\textrm{deg}^{2}}$ field of view (at 155 MHz), which are then processed to search for pulsars. The voltage-capture recording of the survey also allows a multitude of post hoc processing options including the reprocessing of data for higher time resolution and even exploring image-based techniques for pulsar candidate identification. Due to the substantial computational cost in pulsar searches at low frequencies, the survey data processing is undertaken in multiple passes: in the first pass, a shallow survey is performed, where 10 min of each observation is processed, reaching about one-third of the full-search sensitivity. Here we present the system overview including details of ongoing processing and initial results. Further details including first pulsar discoveries and a census of low-frequency detections are presented in a companion paper. Future plans include deeper searches to reach the full sensitivity and acceleration searches to target binary and millisecond pulsars. Our simulation analysis forecasts $\sim$ 300 new pulsars upon the completion of full processing. The SMART survey will also generate a complete digital record of the low-frequency sky, which will serve as a valuable reference for future pulsar searches planned with the low-frequency Square Kilometre Array.

The application of in situ liquid cell TEM in advanced battery research

The fast development of modern battery research highly relies on advanced characterisation methods to unveil the fundamental mechanisms of their electrochemical processes. The continued development of in situ characterisation techniques allows the study of dynamic changes during battery cycling rather than just the initial and the final phase. Among these, in situ transmission electron microscopy (TEM) is able to provide direct observation of the structural and morphological evolution in batteries at the nanoscale. Using a compact liquid cell configuration, which allows a fluid to be safely imaged in the high vacuum of the TEM, permits the study of a wide range of candidate liquid electrolytes. In this review, the experimental setup is outlined and the important points for reliable operation are summarised, which are critical to the safety and reproducibility of experiments. Furthermore, the application of in situ liquid cell TEM in understanding various aspects, including dendrite growth, the solid electrolyte interface (SEI) formation, and the electrode structural evolution in different battery systems, is systematically presented. Finally, challenges in the current application and perspectives of the future development of the in situ liquid cell TEM technique are briefly addressed.

On a mechanistic impact of transmembrane tetramerization in the pathological activation of RTKs

Constitutive activation of receptor tyrosine kinases (RTKs) via different mutations has a strong impact on the development of severe human disorders, including cancer. Here we propose a putative activation scenario of RTKs, whereby transmembrane (TM) mutations can also promote higher-order oligomerization of the receptors that leads to the subsequent ligand-free activation. We illustrate this scenario using a computational modelling framework comprising sequence-based structure prediction and all-atom 1 µs molecular dynamics (MD) simulations in a lipid membrane for a previously characterised oncogenic TM mutation V536E in platelet-derived growth factor receptor alpha (PDGFRA). We show that in the course of MD simulations the mutant TM tetramer retains stable and compact configuration strengthened by tight protein-protein interactions, while the wild type TM tetramer demonstrates looser packing and a tendency to dissociate. Moreover, the mutation affects the characteristic motions of mutated TM helical segments by introducing additional non-covalent crosslinks in the middle of the TM tetramer, which operate as mechanical hinges. This leads to dynamic decoupling of the C-termini from the rigidified N-terminal parts and facilitates more pronounced possible displacement between the C-termini of the mutant TM helical regions that can provide more freedom for mutual rearrangement of the kinase domains located downstream. Our results for the V536E mutation in the context of PDGFRA TM tetramer allow for the possibility that the effect of oncogenic TM mutations can go beyond alternating the structure and dynamics of TM dimeric states and might also promote the formation of higher-order oligomers directly contributing to ligand-independent signalling effectuated by PDGFRA and other RTKs.

On the Thermal Environmental Quality of Typical Urban Settlement Configurations

Urban overheating and energy imbalances are severe environmental concerns. The role of urban sprawl patterns in the formation of Heat Island has recently absorbed the researchers’ interest. The research focuses on metropolitan areas with a range of urban typologies. However, there still is a knowledge gap in how UHI responds to different urban typologies. The interaction between urban configurations and heat island characteristics is explored in Sydney. A combination of terrestrial surveys and modelling techniques was implemented, and results were extracted based on simulation results. The Urban Taskforce Australia suggested the applied categorization methods that follow Stewart and Oke’s Local Climate Zones (LCZs) scheme. We assessed eleven urban designs on ambient air temperature, wind characteristics, heat intensity, and outdoor thermal comfort over three summer days. We correlated results to density and the built-up ratio in all configurations and found that the maximum configurational impact on the heat island reached 2.33 °C. Configurations with a built-up ratio between 0.37 to 0.5 present a sharp downward trend in the average wind speed value and indicate a minimum with a built-up ratio of 0.63. Wind maps present an increase in layouts with built-up ratios of 0.23 to 0.37, whereas they decreased with built-up ratios of higher than 0.43. The average temperature decrease in high-rise compact configurations was 1.12 °C per hour. This record is substantially higher than its open counterparts. The study showed the importance of urban configuration on thermal environmental quality. In addition, implementing appropriate urban design parameters is vital to mitigate heat islands and improve environmental thermal comfort in urban areas.

SIT 45: An interacting, compact, and star-forming isolated galaxy triplet

Context. The underlying scenario of the formation and evolution of galaxy triplets is still uncertain. Mergers of galaxies in isolated triplets give us the opportunity to study the already complex merging process, with minimal contamination of other environmental effects that potentially allow and accelerate galaxy transitions from active star-forming to passive galaxies. Aims. The merging system SIT 45 (UGC 12589) is one of 315 systems in the SDSS-based catalogue of Isolated Triplets (SIT); it is an unusual isolated galaxy triplet, consisting of three merging late-type galaxies. The main aims of this work are to study the dynamical evolution and star formation history (SFH) of SIT 45, as well as its dependence on its local and large-scale environment. Methods. To study its dynamics, parameters such as the velocity dispersion (σv), the harmonic radius (RH), the crossing time (H0tc), and the virial mass (Mvir), along with the compactness of the triplet (S) were considered. To investigate the possible dependence of these dynamical parameters on the environment, the tidal force Q parameters (both local and large-scale) and the projected local density (ηk) were used. To constrain the SFH, we used CIGALE to fit its observed spectral energy distribution using multiwavelength data from the ultraviolet to the infrared. Results. SIT 45 is one of the most compact triplets in the SIT, and it is also more compact than triplets in other samples. According to its SFH, SIT 45 presents star formation, where the galaxies also present recent (∼200 Myr) star formation increase, indicating that this activity may have been triggered by the interaction. Its dynamical configuration suggests that the system is highly evolved in comparison to the SIT. However, this is not expected for systems composed of star-forming late-type galaxies, based on observations in compact groups. Conclusions. We conclude that SIT 45 is a system of three interacting galaxies that are evolving within the same dark matter halo; its compact configuration is a consequence of the ongoing interaction rather than being due to a long-term evolution (as suggested from its H0tc value). We consider two scenarios for the present configuration of the triplet, one where one of the members is a tidal galaxy, and another where this galaxy arrives to the system after the interaction. Both scenarios need further exploration. The isolated triplet SIT 45 is therefore an ideal system to study short timescale mechanisms (∼108 yr), such as starbursts triggered by interactions which are more frequent at higher redshift.

Implications of [formula omitted] gravity on the complexity factor of a physically consistent charged anisotropic stellar model

The present manuscript throws light on the existence of an electrically charged compact stellar model and explores the behavior of complexity factor, proposed by Herrera (2018), against the selected model in the background of f(R,T) gravity (R is the Ricci scalar, while T is the trace of energy–momentum tensor). The set of f(R,T) field equations has been solved by choosing Adler Finch–Skea solution, where the presence of electromagnetic radiations have also been considered in the stellar interior. For the space–time continuity, the boundary conditions have been described by taking Reissner–Nordström solution as exterior space–time. The physical analysis has been made by choosing the radii of PSR J 1614-2230 and SAX J 1808.4-3658, which shows that the model is physically consistent in the realm of f(R,T) gravity, and we obtain more compact stellar configurations for negative values of coupling constant λ. The implications of λ on the total mass and complexity factor of the stellar model have been explored in details. The total mass has been found maximum for λ=−0.4 and minimum for λ=0.4. The complexity factor is increased for negative values of λ as compared to the other scenarios (i.e., λ≥0). The comparison of anisotropy factor and complexity factor has been made, which indicates the presence of less anisotropy in pressure distribution and more inhomogeneity in energy density of the fluid configuration for negative values of λ.

A numerical analysis of a highly sensitive hexagonal plasmonic refractive index sensor

The article proposes and quantitatively investigates the performance characteristics of a surface plasmon polariton based refractive index sensor with metal–insulator–metal arrangement, which demonstrates higher sensitivity than many recent studies. The Finite Element Method (FEM) has been used to quantitatively analyze the refractive index sensor’s transmission properties and sensitivity in various configurations. The structure consists of two symmetrical triangular stubs coupled to a ring-type hexagonal resonator with two slits in opposing arms. The highest sensitivity and FOM observed is 4571.7 nm/RIU and 63.3, respectively. It has a sensing resolution of 2.18×10−7 RIU. Mode 1 has a maximum figure of merit and quality factor of 197.6 and 204.15, respectively. The high quality factor of mode 1 indicates that this sensor is suitable for use as a notch filter. The sensor has been evaluated for temperature sensing, and the temperature sensitivity is significantly higher than that of recent studies. Some sensors claim to be highly sensitive, but they often use a high refractive index region to evaluate the sensor, which is misleading because the sensitivity would be higher in the region with a high refractive index. The effect of adding the two slits in opposing arms is that the figure of merit can be increased by increasing the width of the two slits. Refractive index sensors are useful in medical diagnostics and have a wide variety of applications. The combination of very high sensitivity and FOM in a tiny and compact configuration is ideal for on-chip plasmonic nanosensors.

Unconventional energetics of small vacancy clusters in BCC high-entropy alloy Nb0.75ZrTiV0.5

The stability of small vacancy clusters including divacancy, trivacancy and tetravacancy has been studied in body-centered cubic high-entropy alloy Nb0.75ZrTiV0.5 in structures of random solid solution and short-range order by first-principles calculations and molecular dynamics simulations. Different from conventional body-centered cubic metals, the tightly bound configurations have a lower structural stability and are not preferred energetically in the studied high-entropy alloy. Instability of vacancy configurations leads to vacancy-atom exchanges that favor less compact configurations. The formation energy of small vacancy clusters is much smaller than its constituent elements of Nb and V due to the large structural adjustment induced by severe local lattice distortion. The difference in local lattice distortion and elemental arrangement in the vacancy neighborhood leads to significant site-to-site variation in vacancy cluster energy and configuration. The formation energy has a strong correlation with the local energy state of the vacancy configuration and the extent of structural relaxation. Compared to random solid solution, the structure of short-range order has a higher stability for the most compact cluster configurations and tends to have higher vacancy cluster formation energy. According to classical molecular dynamics simulations of cluster diffusion at high temperature, the studied high-entropy alloy has a higher probability of cluster dissociation compared to Nb and V. The unconventional energetics of small vacancy clusters is expected to have a profound impact on their generation, diffusion, dissociation, coalescence, as well as the defect microstructure evolution during irradiation.

Towards the design and optimisation of future compact aero-engines: intake/fancowl trade-off investigation

PurposeRelative to in-service aero-engines, the bypass ratio of future civil architectures may increase further. If traditional design rules are applied to these new configurations and the housing components are scaled, then it is expected that the overall weight, nacelle drag and the effects of aircraft integration will increase. For this reason, the next generation of civil turbofan engines may use compact nacelles to maximise the benefits from the new engine cycles. The purpose of this paper is to present a multi-level design and optimisation process for future civil aero-engines.Design/methodology/approachAn initial set of multi-point, multi-objective optimisations for axisymmetric configurations are carried out to identify the trade-off between intake and fancowl bulk parameters of highlight radius and nacelle length on nacelle drag. Having identified the likely optimal part of the design space, a set of computationally expensive optimisations for three-dimensional non-axisymmetric configurations is performed. The process includes cruise- and windmilling-type operating conditions to ensure aerodynamic robustness of the downselected configurations.FindingsRelative to a conventional aero-engine nacelle, the developed process yielded a compact aero-engine configuration with mid-cruise drag reduction of approximately 1.6% of the nominal standard net thrust.Originality/valueThe multi-point, multi-objective optimisation is carried out with a mixture of regression and classification functions to ensure aerodynamic robustness of the downselected configurations. The developed computational approach enables the optimisation of future civil aero-engine nacelles that target a reduction of the overall fuel consumption.

Experimental study on a two-stage large cooling capacity stirling cryocooler working below 30 K

Developing superconducting technology and hydrogen energy system requires large cooling capacity devices working below 30 K. Two-stage Stirling cryocooler has the advantages of large cooling capacity, high efficiency, fast cool-down process, and compact configuration, etc. A two-stage Stirling cryocooler driven by crank-rod mechanism was developed and studied experimentally. The operating characteristics, including the cooling down processes, the pressure characteristics, the heat transfer characteristics of the ambient heat exchanger, and the cooling performances, are analyzed. Under 2.2 MPa charging pressure, a no-load refrigeration temperature of 15.84 K was obtained. With no heat load on the first stage, the cryocooler was capable of providing a cooling power of 138.1 W@30 K with a relative Carnot efficiency of 12.87 %, which is one of the best results of Stirling-type cryocoolers at present. Additionally, a cooling capacity of 47.4 W at 20 K with the relative Carnot efficiency of 6.44 % was achieved. During the cooling down process, an acceleration of cooling down rate of the second stage was observed, leading to a distinct acceleration phase of the declining rate of compression space’s mean pressure. It was found that the influence of the heat load on the first stage on the second stage’s cooling performance was not remarkable, and the cryocooler can provide around 131 W@30 K or 40 W@20 K cooling power on the second stage while the first stage can provide 100 W of cooling power at 75.01 K or 78.42 K, respectively. These experimental results have laid a solid foundation for a deeper understanding of the cryocooler’s operating mechanism and practical application.

Process analysis of the novel Flash-ME desalination process driven by low-grade thermal energy

Low-grade thermal desalination can contribute to reduce the energy and carbon footprint of the water sector since it can be coupled to both waste heat and renewable energy sources. In this work we present a new process, named FlashME, that integrates MSF and MED architectures in an innovative and compact configuration able to obtain desalinated water from non-conventional sources with the highest energy and exergy efficiency. The paper presents the overall process scheme and the related simulation campaign carried in the Aspen Plus environment. The sensitive analysis is implemented to highlight the effect of main independent variables and operative parameters. The results point out the role of the first flashing temperature that should be reduced as much as possible (in relation to the allowable temperature differences between stages) to increase the thermodynamic performances. FlashME simulations are compared with the data available from recent work on low-temperature MED and different “boosted-MED” configurations showing better performances, in particular at very low top brine temperatures where it shows the highest II-law efficiencies among the available thermal processes. In comparison with MED-based and boosted-MED configurations, this system has the advantage to avoid additional flashing stages and vapor injections with the advantage of less complexity as well as improved performance along with reduced energy consumption. In the lowest temperature range (65–70 °C) the results show that the FlashME production rate is increased by 20–28% compared to FB-MED and up to 100% relative to conventional MED.

Decoupled 2-DOF Magnetic Levitation Actuator for Single-Body High-Throughput Pick-and-Place Module

This article presents the design, control methods, and experiments of a novel two degree-of-freedom (DOF) magnetic levitation actuator, which is capable of decoupling the levitational- and lateral-direction control in a compact single-body configuration. Our single-body 2-DOF actuator is composed of an U-shaped iron-core with its legs wrapped by two actuating coils and an internal permanent magnet (PM) inserted to the core, levitating a target of 1-inch steel ball at a nominal airgap of 10 mm. We present the decoupled 2-DOF stabilization control method using a combination of common and differential current excitation modes on top of the biased flux generated from the internal PM, with the target position feedback measured by dual fiber optic sensors. For the rapid target lifting, we use a hybrid method of open- and closed-loop controls to have a robust and long-range lifting operation up to the sensing limit of −18 mm below the nominal levitation position, also achieving more than 30 % faster operation compared to a common method of lifting by a predetermined trajectory. Our decoupled lateral-position control also significantly improves both the stiffness and damping in that direction, thereby achieving approximately 82 % reduction of the lateral deviation and 99 % reduction of the target settling time during high-acceleration transportation.

High-Performance Compact Pre-Lens Retarding Field Energy Analyzer for Energy Distribution Measurements of an Electron Gun.

The energy distribution of an electron gun is one of the most important characteristics determining the performance of electron beam-based instruments, such as electron microscopes and electron energy loss spectroscopes. For accurate measurements of the energy distribution, this study presents a novel retarding field energy analyzer (RFEA) with the feature of an additional integrated pre-lens, which enables an adjustment of beam trajectory into the analyzer. The advantages of this analyzer are its compact size and simple electrode configuration. According to trajectory simulation theories, the optimum condition arises when the incident electron beam inside the RFEA is focused on the center of a retarding electrode. Comparing I–V curves depending on whether the pre-lens working or not, it is confirmed that the use of the pre-lens dramatically improves the energy resolution and efficiency of the signal acquisition process. The pre-lens RFEA was applied to characterize a Schottky electron gun under various temperatures and extraction voltages as operational conditions. When the tip temperature was increased by 50 K, we were able to measure an energy distribution broadening of 13.8 meV with the proposed pre-lens RFEA. The relative standard deviation of energy distribution was 0.7% for each working condition.

Performance assessment of planar and non-planar cryogenic pulsating heat pipe with novel condenser

Pulsating heat pipe (PHP) is gaining popularity as a viable solution for thermal conductive links associated with a cryogenic cooling system. A competitive commercial environment requires PHP with a more compact configuration, high heat load removal capacity, and free of orientation dependency. Making orientation-free PHP, a planar PHP (2D layout), requires a large number of turns, increasing the overall size of the PHP device. A PHP with a non-planar (3D layout) layout is capable of accommodating a large number of turns in a short area to tackle both compactness and orientation-dependent issues. The present paper focuses on a comparative thermal performance assessment of planar and non-planar configurations of cryogenic PHP by developing a novel cylindrical shell-type condenser (CSTC). Liquid nitrogen is used as a working fluid. Two separate test setups are developed with 2D Four-Turn PHP (2D FT-PHP) and 3D Four-Turn PHP (3D FT-PHP) with a novel CSTC. The condenser, adiabatic, and evaporator lengths of PHP are kept as 60 mm, 120 mm, and 50 mm, respectively. The thermal performance is assessed by varying Filling Ratio (FR) (38−95 %) and heat load (1 W–130 W) with an evaporator at the bottom position. It is observed that, for a particular heat load, a 3D FT-PHP performed better than a 2D FT-PHP, irrespective of FR. The anti-dry-out ability of 3D FT-PHP is observed to be superior to 2D FT-PHP at a low FR. The frequency analysis results with Wavelet transform show that the working fluid oscillates with a more dominant frequency in 3D FT-PHP than in 2D FT-PHP configuration.

Single-shot complex field imaging through a diffuser by in-line holography with polarization multiplexing

The imaging of complex-amplitude objects that are hidden behind scattering media by single frame detection has faced challenges. Here, we propose, and experimentally demonstrate, a novel complex-field imaging technique through a scattering medium by utilizing the in-line holography scheme in combination with polarization multiplexing. The imaging is achieved by using a polarization multiplexing assisted four-step phase shifting scheme and by designing a compact in-line holographic configuration. Moreover, the randomness associated with the speckle pattern generation of the object transmission through the diffuser is removed after an imaging system in accordance with the shower-curtain effect is employed. We experimentally demonstrate the potential of the technique by single-shot measurement of multiple phase-shifting holograms acquired with a polarization camera and illustrate the dominance of the approach over traditional phase-shifting holography-based imaging through diffusers. Finally, the efficacy of the approach is demonstrated with complex field imaging of nervures in the honeybee wing.

Orientation Workspace Analysis and Parameter Optimization of 3-RRPS Parallel Robot for Pelvic Fracture Reduction

Abstract For parallel robots with general configuration, it is difficult to achieve the large rotation range requirement for pelvic fracture reduction. Application-based workspace optimization is important. In this paper, a 3-revolute-revolute-prismatic-spherical (3-RRPS) parallel robot with optimized parameters is studied, which can offer a large orientation workspace and relatively compact configuration. The inverse kinematics of the robot is analyzed by the closed-loop vector method. The cylindrical coordinate searching algorithm and boundary extraction method are adopted to calculate the orientation workspace. Defining the comprehensive branch length (CBL) to express robot’s compactness under the premise of satisfying the required orientation workspace. The genetic algorithm (GA) is adopted to optimize structural parameters of the robot with CBL as the objective function. The optimization results show that when the orientation angles of the moving platform are limited to not less than 28 deg, the CBL of the robot is 291 mm. Finally, the virtual prototype simulation verification shows that the orientation angles of the moving platform around x-axis and y-axis can reach ±28 deg, the orientation angle around z-axis can reach ±40 deg, which meets the requirements of the rotational range for pelvic fracture reduction surgery.

Mechanism of curaxin-dependent nucleosome unfolding by FACT.

Human FACT (FACT) is a multifunctional histone chaperone involved in transcription, replication and DNA repair. Curaxins are anticancer compounds that induce FACT-dependent nucleosome unfolding and trapping of FACT in the chromatin of cancer cells (c-trapping) through an unknown molecular mechanism. Here, we analyzed the effects of curaxin CBL0137 on nucleosome unfolding by FACT using spFRET and electron microscopy. By itself, FACT adopted multiple conformations, including a novel, compact, four-domain state in which the previously unresolved NTD of the SPT16 subunit of FACT was localized, apparently stabilizing a compact configuration. Multiple, primarily open conformations of FACT-nucleosome complexes were observed during curaxin-supported nucleosome unfolding. The obtained models of intermediates suggest "decision points" in the unfolding/folding pathway where FACT can either promote disassembly or assembly of nucleosomes, with the outcome possibly being influenced by additional factors. The data suggest novel mechanisms of nucleosome unfolding by FACT and c-trapping by curaxins.

Preliminary investigation of neutron shielding compounds for ARC-class tokamaks

Radiation shielding design is a crucial step in the development of a nuclear fusion reactor. Superconducting magnets are indeed a highly engineered component whose properties are particularly sensitive to irradiation damage. In addition, novel magnet technologies, such as High Temperature Superconductors (HTS), and the attractiveness of compact tokamak designs (like Affordable Robust Compact - ARC - reactor), require an even higher precision in the shielding design. In this work most promising radiation shielding solutions for compact tokamaks are explored. The study applies a Monte Carlo particles transport technique assisted by the OpenMC code. A D-shaped model is built and ARC reactor core is considered as main case study. A detailed analysis of the radiation environment is carried out. The study then assesses the most promising compounds on the basis of most suitable cross sections, material shielding properties and space constraints. In addition, the work addresses the problem of energy deposition on the shield providing an analytical model for active cooling necessities. Results highlighted the necessity of heavy elements and high density compounds as a considerable photon flux is generated in neutron-material interactions. Tungsten borides (WxBy) ceramics seem to be particularly promising for shielding radiation in a compact configuration.

Structural growth, stability and electronic characteristics of Al-Sc clusters

Al-Sc alloys that are important and interesting industry materials have recently attracted attention, largely owing to their high-strength properties. In comparison, there are only two reports of the Al-Sc clusters currently available through the Google Scholar. Here, structure characteristics, stability and electronic properties of (AlSc)n (n = 1–9) and (Al3Sc)m (m = 1–5) clusters are investigated using the GA-DFT method. It is found that the Al-Sc clusters prefer compact configurations, involving singlet and triplet states, where Al atoms grow together more easily Sc atoms. Among them, the highly symmetric C2v structure is the very stable for the (AlSc)3 cluster. The AIMD simulations show that the (AlSc)3 cluster still has a good thermal stability at 700 K. The molecular orbitals reveal that the 18 valence electrons of the (AlSc)3 cluster fill shell orbitals resulting in an electron configuration of 1S21P61D82S2. The total density of states of the (AlSc)3 cluster comes from joint contributions of Al and Sc atoms. The NPA charge analysis shows that the charge transfer occurs from the Sc to Al atoms in the cluster. Moreover, the IR and Raman spectroscopy are obtained to manifest structure details of the cluster. It is hoped that our work can further provide beneficial inferences for the study of larger sized Al-Sc clusters in the future.