Event-specific chorus wave and electron seed population models in DREAM3D using the Van Allen Probes

Abstract The DREAM3D diffusion model is applied to Van Allen Probes observations of the fast dropout and strong enhancement of MeV electrons during the October 2012 double-dip storm. We show that in order to explain the very different behavior in the two dips, diffusion in all three dimensions (energy, pitch angle, and Lo) coupled with data-driven, event-specific inputs, and boundary conditions is required. Specifically, we find that outward radial diffusion to the solar wind-driven magnetopause, an event-specific chorus wave model, and a dynamic lower-energy seed population are critical for modeling the dynamics. In contrast, models that include only a subset of processes, use statistical wave amplitudes, or rely on inward radial diffusion of a seed population, perform poorly. The results illustrate the utility of the high resolution, comprehensive set of Van Allen Probes\u27 measurements in studying the balance between source and loss in the radiation belt, a principal goal of the mission. Key Points DREAM3D uses event-specific driving conditions measured by Van Allen Probes Electron dropout is due to outward radial diffusion to compressed magnetopause Event-specific chorus and seed electrons are necessary for the enhancement

Diatom Vacuolar 1,6-β-Transglycosylases can Functionally Complement the Respective Yeast Mutants

Diatoms are unicellular photoautotrophic algae, which can be found in any aquatic habitat. The main storage carbohydrate of diatoms is chrysolaminarin, a nonlinear β-glucan, consisting of a linear 1,3-β-chain with 1,6-β-branches, which is stored in cytoplasmic vacuoles. The metabolic pathways of chrysolaminarin synthesis in diatoms are poorly investigated, therefore we studied two potential 1,6-β-transglycosylases (TGS) of the diatom Phaeodactylum tricornutum which are similar to yeast Kre6 proteins and which potentially are involved in the branching of 1,3-β-glucan chains by adding d-glucose as 1,6-side chains. We genetically fused the full-length diatom TGS proteins to GFP and expressed these constructs in P. tricornutum, demonstrating that the enzymes are apparently located in the vacuoles, which indicates that branching of chrysolaminarin may occur in these organelles. Furthermore, we demonstrated the functionality of the diatom enzymes by expressing TGS1 and 2 proteins in yeast, which resulted in a partial complementation of growth deficiencies of a transglycosylase-deficient ∆kre6 yeast strain.publishe

The influence of friction on elasto-plastic material in nanoindentation

A comprehensive computational study is undertaken to identify the influence of friction in nanoindentation of elasto-plastic materials, the impacts of friction on calculation results with conical and spherical indenters are shown in this paper. The results clearly demonstrate that, for some elasto-plastic materials, the P h curves obtained either by spherical or conical indenters with different friction coefficients cannot be distinguished. However, if utilizing the parameter (see text for details), to quantify the deformation of piling-up or sinking-in, it is easy to find that the influence of friction on piling-up or sinking-in in nanoindentation is significant. Therefore, the material parameters derived from the projected area will have a large error caused by the influence of friction. In this paper, the maximum error on hardness can reach 14% for some elastic materials. These results do not agree with those from researchers who stated that instrumented indentation experiments are not significantly affected by friction. Moreover, in conical indentation, friction can effectively restrain the slip on the interface between indenter and specimen, which leads to a decrease in the amount of piling-up or increase in the amount of sinking-in. However, when the half apex angle is large enough, the influence of friction becomes a minor factor in indentation. In spherical indentation, the amount of piling-up decreases or of sinking-in increases with an increasing friction coefficient. But the friction is independent of the radius of spherical indenter, the piling-up or sinking-in obtained by two different spherical indenters with varying friction coefficients are nearly identical

Study of the influence of friction in imperfect conical indentation for elasto-plastic material

peer reviewe

Magnetic field power spectra and magnetic radial diffusion coefficients using CRRES magnetometer data

We used the fluxgate magnetometer data from Combined Release and Radiation Effects Satellite (CRRES) to estimate the power spectral density (PSD) of the compressional component of the geomagnetic field in the ∼1 mHz to ∼8 mHz range. We conclude that magnetic wave power is generally higher in the noon sector for quiet times with no significant difference between the dawn, dusk, and the midnight sectors. However, during high Kp activity, the noon sector is not necessarily dominant anymore. The magnetic PSDs have a very distinct dependence on Kp. In addition, the PSDs appear to have a weak dependence on McIlwain parameter L with power slightly increasing as L increases. The magnetic wave PSDs are used along with the Fei et al. (2006) formulation to compute DBLL[CRRES] as a function of L and Kp. The L dependence of DBLL[CRRES] is systematically studied and is shown to depend on Kp. More significantly, we conclude that DELL is the dominant term driving radial diffusion, typically exceeding DBLL by 1–2 orders of magnitude

Reduced vacuolar β-1,3-glucan synthesis affects carbohydrate metabolism as well as plastid homeostasis and structure in Phaeodactylum tricornutum

The β-1,3-glucan chrysolaminarin is the main storage polysaccharide of diatoms. In contrast to plants and green algae, diatoms and most other algal groups do not accumulate storage polysaccharides in their plastids. The diatom Phaeodactylum tricornutum possesses only a single gene encoding a putative β-1,3-glucan synthase (PtBGS). Here, we characterize this enzyme by expressing GFP fusion proteins in P. tricornutum and by creating and investigating corresponding gene silencing mutants. We demonstrate that PtBGS is a vacuolar protein located in the tonoplast. Metabolite analyses of two mutant strains with reduced amounts of PtBGS reveal a reduction in their chrysolaminarin content and an increase of soluble sugars and lipids. This indicates that carbohydrates are shunted into alternative pathways when chrysolaminarin production is impaired. The mutant strains show reduced growth and lower photosynthetic capacities, while possessing higher photoprotective abilities than WT cells. Interestingly, a strong reduction in PtBGS expression also results in aberrations of the usually very regular thylakoid membrane patterns, including increased thylakoid thickness, reduced numbers of thylakoids per plastid, and increased numbers of lamellae per thylakoid stack. Our data demonstrate the complex intertwinement of carbohydrate storage in the vacuoles with carbohydrate metabolism, photosynthetic homeostasis, and plastid morphology.publishe

Synthetic strategy for preparing chiral double-semicrystalline polyether block copolymers

We report an effective strategy for the synthesis of semi-crystalline block copolyethers with well-defined architecture and stereochemistry. As an exemplary system, triblock copolymers containing either atactic (racemic) or isotactic (R or S) poly(propylene oxide) end blocks with a central poly(ethylene oxide) mid-block were prepared by anionic ring-opening procedures. Stereochemical control was achieved by an initial hydrolytic kinetic resolution of racemic terminal epoxides followed by anionic ring-opening polymerization of the enantiopure monomer feedstock. The resultant triblock copolymers were highly isotactic (meso triads [mm]% ~ 90%) with optical microscopy, differential scanning calorimetry, wide angle x-ray scattering and small angle x-ray scattering being used to probe the impact of the isotacticity on the resultant polymer and hydrogel properties