Simulating the Effects of Lower-Energy (<30 keV) Electrons on the Inner Magnetosphere Satellite Surface Charging Environment

&lt;p&gt;Satellite surface charging often occurs in the inner magnetosphere from the pre-midnight to the dawn sector when electron fluxes of&amp;#160; hundreds of eV to tens of keV are largely enhanced. Inner magnetosphere ring current models can be used to simulate/predict the satellite surface charging environment, with their flux outer boundary conditions specified either based on observations or provided by other models, such as MHD models. In the latter approach, the flux spectrum at the outer boundary is usually assumed to follow a Kappa or Maxwellian distribution, which however often departs greatly from, or underestimates, the realistic distribution below tens of keV, the energy range that is crucial in the spacecraft surface charging anomaly. This study aims to optimize the electron flux boundary condition of the inner magnetosphere ring current model to achieve a better representation of the surface charging environment. The MHD-parameterized flux spectrum is combined with an empirical electron flux model that specifies the &lt; 40 keV electron flux spectrum. New simulation results indicate that the surface charging environment, monitored by an integrated electron flux between 10&lt;E&lt;50 keV, is significantly enhanced by 1-2 orders of magnitude as opposed to the case in which Kappa/Maxwellian distribution is used at the outer boundary. The new results therefore show better agreement with Van Allen Probes measurements. The improved boundary condition also impacts the auroral precipitation, which may change the conductivity and circulated dynamics.&amp;#160;&lt;/p&gt;

Effects of light intensity on mating of the black soldier fly (Hermetia illucens, Diptera: Stratiomyidae)

The irradiance (W/m2) of light to which groups of black soldier fly adults were exposed in screen cages was manipulated by varying the distance between the cages and a 100 W, white light-emitting diode (LED) chip on a 14L:10D photoperiod. After combining the sexes at the beginning of a light period (photophase), the mating status of all individuals was noted every 10 min for two consecutive photophases. Of all matings, 92% occurred during the first photophase. Mating pairs were nearly motionless and the duration of 93% of couplings was ≥20 min, so essentially all matings were observed. Cumulative probability of mating increased from an estimated 23% at an irradiance of 0.92 W/m2 to 70% at 431 W/m2. Over the same range of irradiances, average time of mating initiation decreased from an estimated 6.4 h to 3.4 h post photophase initiation so that the percentage of matings initiated 15:00 or later decreased from 50 to 0%. Consequently, the occurrence of matings more than 7 hours after photophase initiation was associated with reduced lifetime probability of mating. Peaks in the flux spectrum of the LED at 440 (indigo/blue) and 540 nm (green) coincided with published measurements of the wavelengths at which two of the classes of photoreceptors in the retina of the black soldier fly are maximally sensitive. This study suggests that mating success of reared black soldier fly can be dramatically increased by exposing the adults to light that is particularly rich in wavelengths near 440 and/or 540 nm and has an irradiance that is an appreciable fraction of the intensity of full sunlight.

The energy flux spectrum of internal waves generated by turbulent convection

We present three-dimensional direct numerical simulations of internal waves excited by turbulent convection in a self-consistent, Boussinesq and Cartesian model of mixed convective and stably stratified fluids. We demonstrate that in the limit of large Rayleigh number ($Ra\in [4\times 10^{7},10^{9}]$) and large stratification (Brunt–Väisälä frequencies$f_{N}\gg f_{c}$, where$f_{c}$is the convective frequency), simulations are in good agreement with a theory that assumes waves are generated by Reynolds stresses due to eddies in the turbulent region as described in Lecoanet & Quataert (Mon. Not. R. Astron. Soc., vol. 430 (3), 2013, pp. 2363–2376). Specifically, we demonstrate that the wave energy flux spectrum scales like$k_{\bot }^{4}\,f^{-13/2}$for weakly damped waves (with$k_{\bot }$and$f$the waves’ horizontal wavenumbers and frequencies, respectively), and that the total wave energy flux decays with$z$, the distance from the convective region, like$z^{-13/8}$.

Variable Reactivity Control in Small Modular High Temperature Reactors Using Moderation Manipulation Techniques

With extensive research being undertaken into small modular reactor design concepts, this has brought new challenges to the industry. One key challenge is to be able to compete with large scale nuclear power plants economically. In this article, a novel approach is applied to reduce the overall dependence on fixed burnable poisons during high reactivity periods within a high temperature graphite moderated reactor. To reduce the excess activity, we aim to harden the flux spectrum across the core by removing part of the central moderation column, thus breeding more plutonium, in a later period the flux spectrum is softened again to utilise this plutonium again. This provides a neutron storage effect within the 238U and the resulting breeding of Plutonium. Due to the small size and the annular design of the high temperature reactor, the central reflector is key to the thermalization process. By removing a large proportion of the central reflector, the fuel within the proximity of the central reflector are less likely to receive neutrons within the thermal energy range. In addition to this, the fuel at the extremities of the core have a higher chance of fission due to the higher number of neutrons reaching them. This works as a method of balancing the power distribution between the central and outside fuel pins. During points of low reactivity, such as the end of the fuel cycle, the central reflector can be reinserted and the additionally bred plutonium and U235 at the centre of the core will encounter a higher probability of fission due to more thermal neutrons within this region. By removing the central reflector, this provided a 320 pcm reactivity drop for the duration of the fuel cycle. The plutonium buildup provided additional fissile material up until the central reflector was reinserted. The described method created a two-fold benefit. The overall full power days within the core was increased by ~31 days due to the additional fissile material within the core and secondly the highest loaded power pins saw a 30% power reduction during the removal of the central reflector column.

SwissFEL Aramis beamline photon diagnostics

The SwissFEL Aramis beamline, covering the photon energies between 1.77 keV and 12.7 keV, features a suite of online photon diagnostics tools to help both users and FEL operators in analysing data and optimizing experimental and beamline performance. Scientists will be able to obtain information about the flux, spectrum, position, pulse length, and arrival time jitterversusthe experimental laser for every photon pulse, with further information about beam shape and size available through the use of destructive screens. This manuscript is an overview of the diagnostics tools available at SwissFEL and presents their design, working principles and capabilities. It also features new developments like the first implementation of a THz-streaking based temporal diagnostics for a hard X-ray FEL, capable of measuring pulse lengths to 5 fs r.m.s. or better.

Calculations to Support On-line Neutron Spectrum Adjustment by Measurements with Miniature Fission Chambers in the JSI TRIGA Reactor

Preliminary calculations were performed with the aim to establish optimal experimental conditions for the measurement campaign within the collaboration between the Jožef Stefan Institute (JSI) and Commissariat à l’Énergie Atomique et aux Énergies Alternatives (CEA Cadarache). The goal of the project is to additionally characterize the neutron spectruminside the JSI TRIGA reactor core with focus on the measurement epi-thermal and fast part of the spectrum. Measurements will be performed with fission chambers containing different fissile materials (235U, 237Np and 242Pu) covered with thermal neutron filters (Cd and Gd). The changes in the detected signal and neutron flux spectrum with and without transmission filter were studied. Additional effort was put into evaluation of the effect of the filter geometry (e.g. opening on the top end of the filter) on the detector signal. After the analysis of the scoping calculations it was concluded to position the experiment in the outside core ring inside one of the empty fuel element positions.

Indium Tin Oxide-Based Selective Emitter for Nano-Gap Thermophotovoltaic Applications

This paper seeks to use numerical simulation to study the effect of indium tin oxide-based emitters on the optical response and performance of nanogap thermophotovoltaic systems using a one-dimensional multi-layered model that incorporates fluctuational electrodynamics to solve the heat transfer problem. It is proposed that ITO be used as a selective emitter whose surface plasmon-polariton-enhanced heat flux spectrum is tuned by changing its processing method. In order to study the optical response of this system, an ITO layer is paired with three types of substrate materials to form three different two-layered emitters at 1000 K. It is discovered that an Ag/ITO emitter produces relatively high heat flux within a narrow spectrum as compared to the other two. It is shown that a substrate material possessing a dielectric function with low ε’ and ε” values (low absorption) contributes the least amount of heat flux and maximizes the contribution of the ITO layer at the resonant frequency producing a narrower spectral heat flux profile. Furthermore the substrate thickness has a significant effect on the heat flux spectrum especially at lower thicknesses. Finally, it is shown that by tuning ITO properties to better match the TPV cell’s band gap, higher power output and conversion efficiencies can be obtained.

Self-similarity of passive scalar flow in grid turbulence with a mean cross-stream gradient

Scaling of grid turbulence with a constant mean cross-stream temperature gradient is investigated using a combination of theoretical predictions and experimental data. A novel nanoscale temperature probe (T-NSTAP) was used to acquire temperature data. Conditions for self-similarity of the governing equations and the scalar spectrum are investigated, which reveals necessary conditions for the existence of a self-similar solution. These conditions provide a theoretical framework for scaling of the temperature spectrum as well as the temperature flux spectrum. One necessary condition, predicted by the theory, is that the characteristic length scale describing the scalar spectrum must vary as $\sqrt{t}$ in the case of a zero virtual origin for a self-similar solution to exist. As predicted by the similarity analysis, the data show the variance growing as a power law with streamwise position. When scaled with the similarity variable, as found through the theoretical analysis, the temperature spectra show a good collapse over all wavenumbers. A new method to determine the quality of the scaling was developed, comparing the coefficient of variation. The minimum coefficient of variation, and thus the best scaling, for the measured spectra agrees well with the similarity requirements. The theoretical work also reveals an additional requirement related to the scaling of the scalar flux spectrum.