Plasma effects on relativistic pair beams from TeV blazars: PIC simulations and analytical predictions

Pair beams produced by very high-energy radiation from TeV blazars emit gamma rays in the GeV band by inverse-Compton scattering of soft photons. The observed GeV-band signal is smaller than that expected from the full electromagnetic cascade. This means that the pair beams must be affected by other physical processes reducing their energy flux. One possible loss mechanism involves beam-plasma instabilities that we consider in the present work. For realistic parameters the pair beams can not be simulated by modern computers. Instead, we use a simple analytical model to find a range of the beam parameters that (i) provides a physical picture similar to that of realistic pair beams and (ii) at the same time can be handled by available computational resources. Afterwards, we performed corresponding 2D PIC simulations. We confirm that the beams experience only small changes in the relevant parameter regime, and other processes such as deflection in magnetic field must be at play.Comment: 11 pages, 19 figures, 1table, accepted for publication in A&

Non-relativistic perpendicular shocks modeling young supernova remnants: nonstationary dynamics and particle acceleration at forward and reverse shocks

For parameters that are applicable to the conditions at young supernova remnants, we present results of 2D3V particle-in-cell simulations of a non-relativistic plasma shock with a large-scale perpendicular magnetic field inclined at 45-deg angle to the simulation plane to approximate 3D physics. We developed an improved clean setup that uses the collision of two plasma slabs with different density and velocity, leading to the development of two distinctive shocks and a contact discontinuity. The shock formation is mediated by Weibel-type filamentation instabilities that generate magnetic turbulence. Cyclic reformation is observed in both shocks with similar period, for which we note global variations on account of shock rippling and local variations arising from turbulent current filaments. The shock rippling occurs on spatial and temporal scales given by gyro-motions of shock-reflected ions. The drift motion of electrons and ions is not a gradient drift, but commensurates with E x B drift. We observe a stable suprathermal tail in the ion spectra, but no electron acceleration because the amplitude of Buneman modes in the shock foot is insufficient for trapping relativistic electrons. We see no evidence of turbulent reconnection. A comparison with other 2D simulation results suggests that the plasma beta and the ion-to-electron mass ratio are not decisive for efficient electron acceleration, but pre-acceleration efficacy might be reduced with respect to the 2D results once three-dimensional effects are fully accounted for. Other microphysical factors may also be at play to limit the amplitude of Buneman waves or prevent return of electrons to the foot region.Comment: Astrophysical Journal, in press, some figures with low resolutio

Design optimisation for cold rolled steel beam sections with complex stiffeners considering cold working effects

This paper presents the analysis and design optimization of the cold rolled steel sections for flexural strength considering the effect of cold working exerted on the section during the roll forming process. The sections included channel and zed shapes with complex longitudinal web and flange stiffeners. Nonlinear Finite Element (FE) modelling was developed to model the flexural strength of the channel and zed beams and validated against the four-point bending experiments for these sections. The material properties of steel at the section’s flat parts, corners, and stiffener bends were obtained from tensile tests and were incorporated into the FE simulations to account for the true material properties at these regions. The section strength was then optimized using FE modelling results based on the Design of Experiments (DOE) and response surface methodology. Optimal designs for the channel and zed sections with maximum strength in distortional buckling could be obtained while changing the stiffeners’ position, shape, sizes, and considering material properties at section corners and stiffener bends. It revealed that, the optimal designs provided up to 13% and 17% increase in flexural strength for the channel and zed sections, respectively; however, when the true material properties at the section corner and the stiffener’s bend regions was included, the increase in flexural strength increased up to 20% and 23%, respectively

Characterization of the blue emission of Tm/Er co-implanted GaN

Comparative studies have been carried out on the cathodoluminescence (CL) and photoluminescence (PL) properties of GaN implanted with Tin and GaN co-implanted with Tin and a low concentration of Er. Room temperature CL spectra were acquired in an electron probe microanalyser to investigate the rare earth emission. The room temperature CL intensity exhibits a strong dependence on the annealing temperature of the implanted samples. The results of CL temperature dependence are reported for blue emission (similar to 477 nm) which is due to intra 4f-shell electron transitions ((1)G(4)-> H-3(6)) associated with Tm3+ ions. The 477 nm blue CL emission is enhanced strongly as the annealing temperature increases up to 1200 degrees C. Blue PL emission has also been observed from the sample annealed at 1200 degrees C. To our knowledge, this is the first observation of blue PL emission from Tin implanted GaN samples. Intra-4f transitions from the D-1(2) level (similar to 465 nm emission lines) of Tm3+ ions in GaN have been observed in GaN:Tm films at temperatures between 20-200 K. We will discuss the temperature dependent Tm3+ emission in both GaN:Tm,Er and GaN:Tm samples

Benchmarking study of 10 MW TLB floating offshore wind turbine

This paper presents a benchmarking study of four floating wind platform’ motion and dynamic tension responses to verify an innovative design with the intention of overall cost reduction of a durable, reliable, safe design. An aero-hydro-servo-elastic code is applied to benchmark a 10 MW tension leg buoy (TLB) floating wind turbine to the current leading technology types for floating offshore wind platforms, specifically spar buoy, Semi-submersible and tension leg platform (TLP) floating wind turbines. This study assumes that the platforms will deploy in the northern region of the North Sea, with a water depth of 110 m under various environmental conditions, including wind field descriptions covering uniform wind to fluctuating turbulent wind. The obtained dynamic response results showed low motion responses for the TLB platform for all design load cases. More specifically, the TLB surge and pitch motion responses are insignificant under both operational and survival conditions, allowing decreased spacing between individual wind turbines and increasing wind farms' total energy generation capacity. An additional benefit is that the wind turbine systems can be installed without significant pitch modification to the control system. The TLB platform is less complex which simplifies the construction process and has the potential for significant cost reductions

Coupled numberical analysis of a concept TLB type floating offshore wind turbine

The main drivers for the continued decarbonisation of the global energy market are renewable energy sources. Moreover, the leading technological solutions to achieve this are offshore wind turbines. As installed capacity has been increasing rapidly and shallow water near shore sites are exhausted, projects will need to be developed further from shore and often in deeper waters, which will pose greater technical challenges and constrain efforts to reduce costs. Current floating platform solutions such as the spar and semi submersible rely on large amounts of ballast and complex structural designs with active stabilization systems for stability of the floating offshore wind turbine platform (FOWT). The primary focus of this study is to present a design concept and mooring arrangement for an alternative floating platform solution that places emphasis on the mooring system to achieve stability for a FOWT. The tension leg buoy (TLB) is designed to support future 10MW offshore wind turbine generators. This paper presents the numerical methodology used for a coupled hydro-elastic analysis of the floater and mooring system under combined wind, wave and current effects. A concept TLB design is presented and its platform motion and mooring line tension characteristics are analysed for a three-hour time domain simulation representing operating and survival conditions in the northern North Sea with water depths of 110 meters. The importance of wave drift forces and the other non-linear excitation forces in the concept design stage are evaluated by comparing the motion and tension responses of three different numerical simulation cases with increasing numerical complexity. The preliminary TLB system design demonstrated satisfactory motion response for the operation of a FOWT and survival in a 100-year storm condition. The results show that accounting for second-order effect is vital in terms of having a clear understanding of the full behavior of the system and the detailed response characteristics in operational and survival conditions. Extreme loads are significantly reduced when accounting for the second-order effects. This can be a key aspect to not over-design the system and consequently achieve significant cost savings

Modelling and performance evaluation of sustainable arresting gear energy recovery system for commercial aircraft

A significant amount of kinetic energy is dissipated during each commercial aircraft landing. To improve energy efficiency and environmental sustainability, the kinetic energy can instead be converted to electricity by utilizing the arresting gear systems. This paper presents a novel design that couples an arresting gear system to electrical generators. The results show that the system can successfully recover aircraft kinetic energy and is applicable to different aircraft sizes ranging from Airbus A319 up to A380. Beyond system performance, wider context technical aspects including system integration into grid with multiple energy storage possibilities, safety and passenger comfort are discussed.Engineering and Physical Sciences Research Council (EPSRC): 2517982. Airbus Operations Ltd

Coupled aero-hydro-servo-elastic analysis of 10MW TLB floating offshore wind turbine

This paper presents a fully coupled aero-hydro-servo elastic analysis of a 10MW offshore wind turbine supported by a tension leg buoy (TLB) platform, with a taut mooring system. The study investigates the TLB's dynamic response characteristics under the northern North Sea environmental conditions with water depths of 110 metres, comparing the performance of steel, polyester, and nylon mooring line configurations. Innovating floating wind turbines requires a cost-effective system that achieves reliable performance in operational and survival conditions. The innovative system should compete with other existing FOWT types and fixed-bottom offshore wind turbines in terms of LCOE. The dynamic responses of the relatively less complex TLB platform in terms of construction and installation showed small motion and accelerations for all available mooring materials from the current supply chain, enabling the wind turbine to be installed without significant modifications to their control systems. The mooring materials' elasticity is essential in the system achieving motion response