High Order IMEX Stochastic Galerkin Schemes for Linear Transport Equation with Random Inputs and Diffusive Scalings

In this paper,we consider the high order method for solving the linear transport equations under diffusive scaling and with random inputs.To tackle the randomness in the problem,the stochastic Galerkin method of the generalized polynomial chaos approach has been employed.Besides,the high order implicit-explicit scheme under the micro-macro decomposition framework and the discontinuous Galerkin method have been employed.We provide several numerical experiments to validate the accuracy and the stochastic asymptotic-preserving property.

Heat Transport in Double-Bond Linear Chains of Fullerenes

Heat transport in one kind of double-bond linear chains of fullerenes （C60＇s） is investigated by the classical nonequilibrium molecular dynamics method. It is found that the negative differential thermal resistance （NDTR） is more likely to occur at larger temperature difference and shorter length. In addition, with the increase of the length, the thermal conductivity of the chains increases, and NDTR region shrinks and vanishes in the end. The temperature profiles reveal that a large temperature jump exists at a high-temperature boundary of the chains when NDTR occurs. These results may be helpful for designing thermal devices where low-dimensional C60 polymers can be used.

Field Observations of Near-Surface Wind Flow Across Expressway Embankment on the Qinghai–Tibet Plateau

Crushed rock layers(CRLs),ventilation ducts(VDs)and thermosyphons are air-cooling structures(ACSs)widely used for maintaining the long-term stability of engineered infrastructures in permafrost environments.These ACSs can effectively cool and maintain the permafrost subgrade’s frozen state under climate warming by facilitating heat exchange with ambient air in cold seasons.As convection is a crucial working mechanism of these ACSs,it is imperative to understand the near-surface wind flow(NSWF)across a constructed infrastructure,such as an embankment.This article describes a yearlong field observation of the NSWF across an experimental expressway embankment,the first of its kind on the Qinghai–Tibet Plateau(QTP).The wind speed and direction along a transect perpendicular to the embankment on both the windward and leeward sides and at four different heights above the ground surface were collected and analyzed.The results showed that the embankment has a considerable impact on the NSWF speed within a distance of up to ten times its height,and in the direction on the leeward side.A power law can well describe the speed profiles of NSWF across the embankment,with the power-law indices(PLIs)varying from 0.14 to 0.40.On an annual basis,the fitted NSWF PLI far away from the embankment was 0.19,which differs substantially from the values widely used in previous thermal performance evaluations of ACSs on the QTP.Finally,the significance of the NSWF to the thermal performance of the ACSs,particularly the CRLs and VDs,in linear transportation infrastructure is discussed.It is concluded that underestimating the PLI and neglecting wind direction variations may lead to unconservative designs of the ACSs.The results reported in this study can provide valuable guidance for infrastructure engineering on the QTP and other similar permafrost regions.

PGR5-PGRL1-Dependent Cyclic Electron Transport Modulates Linear Electron Transport Rate in Arabidopsis thaliana

Plants need tight regulation of photosynthetic electron transport for survival and growth under environ- mental and metabolic conditions. For this purpose, the linear electron transport （LET） pathway is supple- mented by a number of alternative electron transfer pathways and valves. In Arabidopsis, cyclic electron transport （CET） around photosystem I （PSI）, which recycles electrons from ferrodoxin to plastoquinone, is the most investigated alternative route. However, the interdependence of LET and CET and the relative importance of CET remain unclear, largely due to the difficulties in precise assessment of the contribution of CET in the presence of LET, which dominates electron flow under physiological conditions. We there- fore generated Arabidopsis mutants with a minimal water-splitting activity, and thus a low rate of LET, by combining knockout mutations in Psb01, PsbP2, PsbQ1, PsbQ2, and PsbR loci. The resulting 45 mutant is viable, although mature leaves contain only ~20% of wild-type naturally less abundant Psb02 protein. 45 plants compensate for the reduction in LET by increasing the rate of CET, and inducing a strong non-photochemical quenching （NPQ） response during dark-to-light transitions. To identify the molecular origin of such a high-capacity CET, we constructed three sextuple mutants lacking the qE component of NPQ （45 npq4-1）, NDH-mediated CET （45 crr4-3）, or PGR5-PGRLl-mediated CET （45 pgrS）. Their analysis revealed that PGR5-PGRLl-mediated CET plays a major role in ~pH formation and induction of NPQ in C3 plants. Moreover, while pgr5 dies at the seedling stage under fluctuating light conditions, 45 pgr5 plants are able to survive, which underlines the importance of PGR5 in modulating the intersystem electron transfer.

Second-Order Accurate Structure-Preserving Scheme for Solute Transport on Polygonal Meshes

We analyze mimetic properties of a conservative finite-volume (FV) scheme on polygonal meshes used for modeling solute transport on a surface with variable elevation. Polygonal meshes not only provide enormous mesh generation flexibility, but also tend to improve stability properties of numerical schemes and reduce bias towards any particular mesh direction. The mathematical model is given by a system of weakly coupled shallow water and linear transport equations. The equations are discretized using different explicit cell-centered FV schemes for flow and transport subsystems with different time steps. The discrete shallow water scheme is well balanced and preserves the positivity of the water depth. We provide a rigorous estimate of a stable time step for the shallow water and transport scheme and prove a bounds-preserving property of the solute concentration. The scheme is second-order accurate over fully wet regions and first-order accurate over partially wet or dry regions. Theoretical results are verified with numerical experiments on rectangular, triangular, and polygonal meshes.

STABLE BOUNDARY CONDITIONS AND DISCRETIZATION FOR P_(N) EQUATIONS

A solution to the linear Boltzmann equation satisfies an energy bound,which reflects a natural fact:The energy of particles in a finite volume is bounded in time by the energy of particles initially occupying the volume augmented by the energy transported into the volume by particles entering the volume over time.In this paper,we present boundary conditions(BCs)for the spherical harmonic(P_(N))approximation,which ensure that this fundamental energy bound is satisfied by the P_(N) approximation.Our BCs are compatible with the characteristic waves of P_(N) equations and determine the incoming waves uniquely.Both,energy bound and compatibility,are shown on abstract formulations of P_(N) equations and BCs to isolate the necessary structures and properties.The BCs are derived from a Marshak type formulation of BC and base on a non-classical even/odd-classification of spherical harmonic functions and a stabilization step,which is similar to the truncation of the series expansion in the P_(N) method.We show that summation by parts(SBP)finite differences on staggered grids in space and the method of simultaneous approximation terms(SAT)allows to maintain the energy bound also on the semi-discrete level.