Inverse Flux Research Articles

Prediction of Flow and Temperature Distributions in a High Flux Research Reactor Using the Porous Media Approach

High thermal neutron fluxes are needed in some research reactors and for irradiation tests of materials. A High Flux Research Reactor (HFRR) with an inverse flux trap-converter target structure is being developed by the Reactor Engineering Analysis Lab (REAL) at Tsinghua University. This paper studies the safety of the HFRR core by full core flow and temperature calculations using the porous media approach. The thermal nonequilibrium model is used in the porous media energy equation to calculate coolant and fuel assembly temperatures separately. The calculation results show that the coolant temperature keeps increasing along the flow direction, while the fuel temperature increases first and decreases afterwards. As long as the inlet coolant mass flow rate is greater than 450 kg/s, the peak cladding temperatures in the fuel assemblies are lower than the local saturation temperatures and no boiling exists. The flow distribution in the core is homogeneous with a small flow rate variation less than 5% for different assemblies. A large recirculation zone is observed in the outlet region. Moreover, the porous media model is compared with the exact model and found to be much more efficient than a detailed simulation of all the core components.

Reconciling the differences between a bottom-up and inverse-estimated FFCO2 emissions estimate in a large US urban area

The INFLUX experiment has taken multiple approaches to estimate the carbon dioxide (CO2) flux in a domain centered on the city of Indianapolis, Indiana. One approach, Hestia, uses a bottom-up technique relying on a mixture of activity data, fuel statistics, direct flux measurement and modeling algorithms. A second uses a Bayesian atmospheric inverse approach constrained by atmospheric CO2 measurements and the Hestia emissions estimate as a prior CO2 flux. The difference in the central estimate of the two approaches comes to 0.94 MtC (an 18.7% difference) over the eight-month period between September 1, 2012 and April 30, 2013, a statistically significant difference at the 2-sigma level. Here we explore possible explanations for this apparent discrepancy in an attempt to reconcile the flux estimates. We focus on two broad categories: 1) biases in the largest of bottom-up flux contributions and 2) missing CO2 sources. Though there is some evidence for small biases in the Hestia fossil fuel carbon dioxide (FFCO2) flux estimate as an explanation for the calculated difference, we find more support for missing CO2 fluxes, with biological respiration the largest of these. Incorporation of these differences bring the Hestia bottom-up and the INFLUX inversion flux estimates into statistical agreement and are additionally consistent with wintertime measurements of atmospheric 14CO2. We conclude that comparison of bottom-up and top-down approaches must consider all flux contributions and highlight the important contribution to urban carbon budgets of animal and biotic respiration. Incorporation of missing CO2 fluxes reconciles the bottom-up and inverse-based approach in the INFLUX domain.

Post-harvest banana peel splitting as a function of relative humidity storage conditions

Peel splitting is a major physiological disorder affecting post-harvest banana quality. This phenomenon occurs only 3–6 days after ripening induction in specific cultivars such as cv. 925 when stored in saturating humidity conditions. In these conditions, Cavendish cultivars (Grande Naine, cv. GN) are not susceptible to splitting. Cvs. 925 and GN were thus investigated to detect possible determinants associated with splitting. Splitting intensity was tentatively found to be associated with an inverse water flux at high relative humidity (RH) through an osmotic peel to pulp water flux resulting from the higher sugar content in the pulp than in the peel. Rheological properties were measured, and although the peel resistance and elasticity in cv. 925 were surprisingly higher than in cv. GN, saturating humidity conditions (100 % RH) substantially reduced the peel resistance. However, the peel epicuticular wax in cv. 925 was clearly thinner than that in cv. GN, thus leading to limitation of peel hydration in cv. GN. Peel splitting in cv. 925 was also associated with a boost in respiration, an increase in oxidative stress markers (H2O2), resulting in an increase in cellular damage markers (MDA, PEL). Overall, our results suggest that peel splitting at high RH in cv. 925 is related to fast decrease peel water content and the induction of high oxidative stress damage.

Increasing summer net CO<sub>2</sub> uptake in high northern ecosystems inferred from atmospheric inversions and comparisons to remote-sensing NDVI

Abstract. Warmer temperatures and elevated atmospheric CO2 concentrations over the last several decades have been credited with increasing vegetation activity and photosynthetic uptake of CO2 from the atmosphere in the high northern latitude ecosystems: the boreal forest and arctic tundra. At the same time, soils in the region have been warming, permafrost is melting, fire frequency and severity are increasing, and some regions of the boreal forest are showing signs of stress due to drought or insect disturbance. The recent trends in net carbon balance of these ecosystems, across heterogeneous disturbance patterns, and the future implications of these changes are unclear. Here, we examine CO2 fluxes from northern boreal and tundra regions from 1985 to 2012, estimated from two atmospheric inversions (RIGC and Jena). Both used measured atmospheric CO2 concentrations and wind fields from interannually variable climate reanalysis. In the arctic zone, the latitude region above 60° N excluding Europe (10° W–63° E), neither inversion finds a significant long-term trend in annual CO2 balance. The boreal zone, the latitude region from approximately 50–60° N, again excluding Europe, showed a trend of 8–11 Tg C yr−2 over the common period of validity from 1986 to 2006, resulting in an annual CO2 sink in 2006 that was 170–230 Tg C yr−1 larger than in 1986. This trend appears to continue through 2012 in the Jena inversion as well. In both latitudinal zones, the seasonal amplitude of monthly CO2 fluxes increased due to increased uptake in summer, and in the arctic zone also due to increased fall CO2 release. These findings suggest that the boreal zone has been maintaining and likely increasing CO2 sink strength over this period, despite browning trends in some regions and changes in fire frequency and land use. Meanwhile, the arctic zone shows that increased summer CO2 uptake, consistent with strong greening trends, is offset by increased fall CO2 release, resulting in a net neutral trend in annual fluxes. The inversion fluxes from the arctic and boreal zones covering the permafrost regions showed no indication of a large-scale positive climate–carbon feedback caused by warming temperatures on high northern latitude terrestrial CO2 fluxes from 1985 to 2012.

Mapping the landscape of metabolic goals of a cell.

Genome-scale flux balance models of metabolism provide testable predictions of all metabolic rates in an organism, by assuming that the cell is optimizing a metabolic goal known as the objective function. We introduce an efficient inverse flux balance analysis (invFBA) approach, based on linear programming duality, to characterize the space of possible objective functions compatible with measured fluxes. After testing our algorithm on simulated E. coli data and time-dependent S. oneidensis fluxes inferred from gene expression, we apply our inverse approach to flux measurements in long-term evolved E. coli strains, revealing objective functions that provide insight into metabolic adaptation trajectories.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-016-0968-2) contains supplementary material, which is available to authorized users.

The heat flux identification problem for a nonlinear parabolic equation in 2D

We consider the heat flux identification problem (HFIP) based on the boundary measurements for a nonlinear parabolic equation in 2-dimensional space. The standard linearization algorithm is applied to the nonlinear direct problem. The method of Conjugate Gradient Algorithm, based on the gradient formula for the cost functional, is then proposed for numerical solution of the inverse heat flux problem. Numerical analysis of the algorithm applied to the inverse problem in typical classes of flux functions is presented. Computational results, obtained for random noisy output data, indicate how the iteration number of the Conjugate Gradient Algorithm can be estimated. Numerical results illustrate bounds of applicability of proposed algorithm, as well as its efficiency and accuracy.

Inverse heat flux in double layer thermal metamaterial

An approach to controlling heat flux based on electron emission in the double layer assembly of two materials with different work functions has been developed. It is shown that this two-electrode assembly promotes the inverse heat flux exhibiting a thermal metamaterial property in a wide range of temperatures. The proposed thermal metamaterial can be used as an active element of a thermal diode, ensuring heat flux in one direction regardless of temperature difference.

Fault Detection of Irreversible Demagnetization Based on Space Harmonics According to Equivalent Magnetizing Distribution

Efficiency, stability and reliability of interior permanent magnet (IPM) type brushless DC motor(BLDCM) are verified through a number of studies and experiment until today. In addition, IPM type BLDCM is widely used in many applications for high power and excellent control of the per unit volume. Especially, IPM type BLDCM is used as a core driving source in the factory automation and electric propulsion systems of electric vehicles due to their wide control range and high robustness. Although there is many merits, IPM type BLDC motors involve potentially risk about an irreversible magnetization. If these systems are continuously driving under the irreversible magnetization condition, the residual flux density of permanent magnet is more decreased because the demagnetizing regions are increased by overlap of inverse flux.

Formation of the bi-directional energy cascade in low-frequency damped wave-turbulent systems

We demonstrate that in wave-turbulent systems, an inverse energy flux can be formed in addition to the conventional direct energy flux if large-scale wave damping is present. Such a bi-directional energy cascade can be understood in terms of the wave energy transfer on the temperature wave background. The formation of the bi-directional cascade provides an effective mechanism for global coupling between the scales where the turbulent fluctuations at small scales are affected by the wave distribution at large scales due to the total energy conservation. We discuss physical systems where this scenario is realized.

Comparison of the data‐driven top‐down and bottom‐up global terrestrial CO2 exchanges: GOSAT CO2 inversion and empirical eddy flux upscaling

AbstractWe examined the consistency between terrestrial biosphere fluxes (terrestrial CO2 exchanges) from data‐driven top‐down (GOSAT CO2 inversion) and bottom‐up (empirical eddy flux upscaling based on a support vector regression (SVR) model) approaches over 42 global terrestrial regions from June 2009 to October 2011. Seasonal variations of the biosphere fluxes by the two approaches agreed well in boreal and temperate regions across the Northern Hemisphere. Both fluxes also exhibited strong anomalous signals in response to contrasting anomalous spring temperatures observed in North America and boreal Eurasia. This indicates that the CO2 concentration data integrated in the GOSAT inversion and the meteorological and vegetation data in the SVR models are equally effective in producing spatiotemporal variations of biosphere flux. Meanwhile, large differences in seasonality were found in subtropical and tropical South America, South Asia, and Africa. The GOSAT inversion showed seasonal variations that pivoted around CO2 neutral, while the SVR model showed seasonal variations that tended toward CO2 sink. Thus, a large difference in CO2 budget was identified between the two approaches in subtropical and tropical regions across the Southern Hemisphere. Examination of the integrated data revealed that the large tropical sink of CO2 by the SVR model was an artifact due to the underrepresented biosphere fluxes predicted by limited eddy flux data for tropical biomes. Because of the global coverage of CO2 concentration data, the GOSAT inversion provides better estimates of continental CO2 flux than the SVR model in the Southern Hemisphere.

Witnessing magnetic twist with high-resolution observation from the 1.6-m New Solar Telescope.

Magnetic flux ropes are highly twisted, current-carrying magnetic fields. They are crucial for the instability of plasma involved in solar eruptions, which may lead to adverse space weather effects. Here we present observations of a flaring using the highest resolution chromospheric images from the 1.6-m New Solar Telescope at Big Bear Solar Observatory, supplemented by a magnetic field extrapolation model. A set of loops initially appear to peel off from an overall inverse S-shaped flux bundle, and then develop into a multi-stranded twisted flux rope, producing a two-ribbon flare. We show evidence that the flux rope is embedded in sheared arcades and becomes unstable following the enhancement of its twists. The subsequent motion of the flux rope is confined due to the strong strapping effect of the overlying field. These results provide a first opportunity to witness the detailed structure and evolution of flux ropes in the low solar atmosphere.

Inverse analysis of a rectangular fin using the lattice Boltzmann method

Inverse methods have many applications in determining unknown variables in heat transfer problems when direct measurements are impossible. As most common inverse methods are iterative and time consuming especially for complex geometries, developing more efficient methods seems necessary. In this paper, a direct transient conduction–convection heat transfer problem (fin) under several boundary conditions was solved by using lattice Boltzmann method (LBM), and then the results were successfully validated against both the finite difference method and analytical solution. Then, in the inverse problem both unknown base temperatures and heat fluxes in the rectangular fin were estimated by combining the adjoint conjugate gradient method (ACGM) and LBM. A close agreement between the exact values and estimated results confirmed the validity and accuracy of the ACGM–LBM. To compare the calculation time of ACGM–LBM, the inverse problem was solved by implicit finite difference methods as well. This comparison proved that the ACGM–LBM was an accurate and fast method to determine unknown thermal boundary conditions in transient conduction–convection heat transfer problems. The findings can efficiently determine the unknown variables in fins when a desired temperature distribution is available.

Low frequency modulation of jets in quasigeostrophic turbulence

Quasigeostrophic turbulence on a β-plane with a finite deformation radius is studied numerically, with particular emphasis on frequency and combined wavenumber-frequency domain analyses. Under suitable conditions, simulations with small-scale random forcing and large-scale drag exhibit a spontaneous formation of multiple zonal jets. The first hint of wave-like features is seen in the distribution of kinetic energy as a function of frequency; specifically, for progressively larger deformation scales, there are systematic departures in the form of isolated peaks (at progressively higher frequencies) from a power-law scaling. Concomitantly, there is an inverse flux of kinetic energy in frequency space which extends to lower frequencies for smaller deformation scales. The identification of these peaks as Rossby waves is made possible by examining the energy spectrum in frequency-zonal wavenumber and frequency-meridional wavenumber diagrams. In fact, the modified Rhines scale turns out to be a useful measure of the dominant meridional wavenumber of the modulating Rossby waves; once this is fixed, apart from a spectral peak at the origin (the steady jet), almost all the energy is contained in westward propagating disturbances that follow the theoretical Rossby dispersion relation. Quite consistently, noting that the zonal scale of the modulating waves is restricted to the first few wavenumbers, the energy spectrum is almost entirely contained within the corresponding Rossby dispersion curves on a frequency-meridional wavenumber diagram. Cases when jets do not form are also considered; once again, there is a hint of Rossby wave activity, though the spectral peaks are quite muted. Further, the kinetic energy scaling in frequency domain follows a −5/3 power-law and is distributed much more broadly in frequency-wavenumber diagrams.

On the edge of an inverse cascade.

We demonstrate that systems with a parameter-controlled inverse cascade can exhibit critical behavior for which at the critical value of the control parameter the inverse cascade stops. In the vicinity of such a critical point, standard phenomenological estimates for the energy balance will fail since the energy flux towards large length scales becomes zero. We demonstrate this using the computationally tractable model of two-dimensional (2D) magnetohydrodynamics in a periodic box. In the absence of any external magnetic forcing, the system reduces to hydrodynamic fluid turbulence with an inverse energy cascade. In the presence of strong magnetic forcing, the system behaves as 2D magnetohydrodynamic turbulence with forward energy cascade. As the amplitude of the magnetic forcing is varied, a critical value is met for which the energy flux towards the large scales becomes zero. Close to this point, the energy flux scales as a power law with the departure from the critical point and the normalized amplitude of the fluctuations diverges. Similar behavior is observed for the flux of the square vector potential for which no inverse flux is observed for weak magnetic forcing, while a finite inverse flux is observed for magnetic forcing above the critical point. We conjecture that this behavior is generic for systems of variable inverse cascade.

UNRAVELLING THE REGULATION OF SOMATIC EMBRYOGENESIS BY EXTRACELLULAR CALCIUM AND AUXIN EFFLUX BLOCKERS IN HYPOCOTYL EXPLANTS OF ALBIZZIA LEBBECK L.: SIMILARITY IN ACTION

Somatic embryogenesis involves developmental reprogramming and de-differentiation of somatic cells towards embryo development that is crucial for cellular totipotency in higher plants. It is a prototype for comprehension of the physiological, biochemical and molecular biological events transpiring during plant embryo development. In this study, we analyzed the role of exogenous calcium and auxin during somatic embryogenesis in hypocotyl explants of Albizzia lebbeck L. Light microscopic studies revealed that anterior and posterior ends of hypocotyl explants had entirely different patterns of differentiation . Scanning electron microscopic analysis of cultured hypocotyl explants exhibited globular-, heart- and torpedo-shaped somatic embryos developing from the anterior cut surface and gradually proceeding towards the other end. Surface texture of these somatic embryos showed uni-or bi-celled trichomes. Presence of exogenous calcium (1-4mM) in hormone-free B5 medium is prerequisite for induction of somatic embryos in hypocotyl explants derived from 7-d-old, light grown seedlings of Albizzia lebbeck L. A two-fold increase in calcium concentration from 2mM (B 5 medium) to 4mM led to doubling of somatic embryogenic response whereas, embryogenic callus was induced in explants raised on medium containing 10 or 20mM calcium. Depletion or high dosage in the medium (20 mM) induce non-embryogenic callus in explants. A similar response induced on hypocotyl explants upon treatments with NPA and PCIB, (auxin transport blockers). Results indicate that polar auxin transport or basipetal movement of IAA triggers acropetal transport of calcium. This combination of inverse fluxes acts as the primary signal for embryogenic response at the cut ends proximal to shoot apex and callusing at the cut ends distal to shoot apex of explants. Moreover, a correlation exists between NPA and PCIB-induced disruption of basipetal IAA transport and the inhibitory effect of NPA and PCIB on calcium translocation in the induction of similar morphogenetic responses.

Model‐data comparison of MCI field campaign atmospheric CO2 mole fractions

AbstractAtmospheric transport model errors are a major contributor to uncertainty in CO2 inverse flux estimates. Our study compares CO2 mole fraction observations from the North American Carbon Program Mid‐Continental Intensive (MCI) field campaign and modeled mole fractions from two atmospheric transport models: the global Transport Model 5 from NOAA's CarbonTracker system and the mesoscale Weather Research and Forecasting model. Both models are coupled to identical CO2 fluxes and lateral boundary conditions from CarbonTracker (CT2009 release). Statistical analyses were performed for two periods of 2007 using observed daily daytime average mole fractions of CO2 to test the ability of these models to reproduce the observations and to infer possible causes of the discrepancies. TM5‐CT2009 overestimates midsummer planetary boundary layer CO2 for sites in the U.S. corn belt by 10 ppm. Weather Research and Forecasting (WRF)‐CT2009 estimates diverge from the observations with similar magnitudes, but the signs of the differences vary from site to site. The modeled mole fractions are highly correlated with the observed seasonal cycle (r ≥ 0.7) but less correlated in the growing season, where weather‐related changes in CO2 dominate the observed variability. Spatial correlations in residuals from TM5‐CT2009 are higher than WRF‐CT2009 perhaps due to TM5's coarse horizontal resolution and shallow vertical mixing. Vertical mixing appears to have influenced CO2 residuals from both models. TM5‐CT2009 has relatively weak vertical mixing near the surface limiting the connection between local CO2 surface fluxes and boundary layer. WRF‐CT2009 has stronger vertical mixing that may increase the connections between local surface fluxes and the boundary layer.

An investigation into the spectral properties of bright Fermi blazars

We investigate the spectral properties of blazars detected with the Fermi-Large Area Telescope (LAT) in the high energy regime 100 MeV - 100 GeV. We find that over long timescales a log-parabola provides an adequate description of the spectrum in almost all objects and in most cases is significantly better than a simple power law or broken power law description. Broken power law descriptions appear to arise from two causes: confusion with nearby sources and as an artifact of older LAT instrument response functions. We create a light curve for 2FGLJ2253.9+1609 (3C 454.3), the brightest of the objects investigated. During the quiescent state we find the spectrum to be fairly stable and well-described by a log-parabola. There is some evidence that, on average, the peak energy of the inverse Compton emission is lower in the quiescent state than in the time-averaged state, suggesting that increases in flux are due to changing parameters within the jet as opposed to changes in an external photon field. However, no correlation between inverse Compton peak energy and flux is apparent. During high flux states, deviation of the spectral shape from a simple power law continues. In some cases a log-parabola provides a significantly better fit than a broken power law but in others the reverse is true.

Geometry of scale-to-scale energy and enstrophy transport in two-dimensional flow

Using filter-space techniques, we analyze the transport of energy and enstrophy between scales in an experimental quasi-two-dimensional weakly turbulent flow. By decomposing the scale-to-scale energy and enstrophy fluxes into three components that consist of distinct types of triad interactions, we find that different triads are responsible for forward and inverse flux. To understand this behavior, we analyze the geometric alignment between the turbulent stresses that drive scale-to-scale transfer and the large-scale velocity and vorticity gradients, and show that different triad interactions have distinct alignment signatures. Our results shed light on the role played by geometric alignment in the net behavior of triad interactions in turbulence.

Identification of heat partition in grinding related to process parameters, using the inverse heat flux conduction model

Grinding is an abrasive machining process characterized by producing high quality components for high added-value industries. Thermal damage is an undesired phenomenon that may ruin nearly finished products. The study of thermal damage requires understanding the mechanisms of heat partition between wheel and workpiece. In this work and original methodology and experimental set-up for the study the influence of grinding variables on the heat partition to the workpiece, Rw, is presented. The new methodology avoids errors related to the steep thermal gradients typical of grinding operations. In addition, uncertainty related to the actual area of contact is suppressed thanks to a rigid and controlled experimental configuration. An inverse model based on Levenberg–Marquardt algorithm and a finite element model has been used for heat partition to the workpiece identification. Results have lead to a time-dependant Rw definition which had not been previously proposed in literature, and they have allowed as well relating variations in Rw values to physical removing mechanisms of grinding. Results have been validated by means of an indirect parameter: workpiece hardness variation during the tests, which strengthens the validity of the results.

Planetary boundary layer errors in mesoscale inversions of column‐integrated CO2 measurements

Observing platforms of greenhouse gas column mole fractions using remote sensing instruments have enhanced the capability of carbon data assimilation systems at large scales and helped improve our understanding of the underlying processes involved in the exchange of carbon at the surface of the globe. In this study, we quantify the additional information carried by these measurements at finer scales and consider the impact of vertical transport errors in current modeling systems, one of the main sources of uncertainties in regional inverse flux estimates. Surface‐based column‐integrated sensors are shown to be a significant source of information to constrain local surface fluxes at fine scales. Gain and error reduction are only about 20% lower than for in situ instruments. Column measurements show less dependence on near‐field surface fluxes compared to in situ, with the error reduction being more homogeneously distributed. However, vertical transport errors still impact the flux retrievals, as with in situ measurements but to a lesser extent. Inverse fluxes from both types of measurements were affected by errors in vertical mixing and mean horizontal winds, with a larger impact on the inverse carbon balance using in situ measurements. The use of remote sensing measurements also appeared to constrain significantly the boundary concentrations, a critical limitation in current regional inversions. We finally performed a pseudo‐data experiment combining both types of instruments, creating an optimal observing network with a lower impact of planetary boundary layer transport errors on the surface fluxes and the boundary concentrations, and a more widely distributed reduction of the errors over the boundaries.