Evolution of a Cold Non-neutral Electron-Positron Plasma Slab

Evolution of a non-neutral cold electron-positron plasma slab is investigated. Initially the slab consists of a quasineutral plasma core bounded on both sides by layers containing only positrons （or electrons）. Results from a nonperturbative, or mathematically exact, analysis of the governing fluid conservation equations and the Poisson equation show that despite their equal mass and charge magnitude, the electron and positron fronts can expand separately as well as a single fluid, and that nonlinear surface oscillations can be excited on the expansion fronts.

Loading Detection and Number Estimation of an Electron Plasma in a Penning Trap

A quadrupole Penning trap for spectroscopy and investigations of non-neutral plasmas was designed and built. In this work we provide details of the trap design and a discussion of a simple design and procedure for convenient electron loading from an aligned filament. Electrons from thermionic emission which form a low-energy diffuse beam are trapped in weak magnetic fields. They are detected through a non-destructive electronic detection scheme, the details of which are discussed. The detection signal is diminished when the electron beam energy is increased while the electron flux is kept constant. This is explained by considering the energy shift in the distribution function of electrons emitted from the filament and entering the trap. We present a calculation of the number of trapped electrons from the shape of the detection signal. This calculation, based on a model of a driven damped harmonic oscillator to describe the axial motion of the electrons, compares favourably with the numbers obtained by measurements of the space charge induced shift in the trap potential.

The effects of fertilization on the trait-abundance relationships in a Tibetan alpine meadow community

Aims Comparisons of the trait-abundance relationships from various habitat types are critical for community ecology,which can offer us insights about the mechanisms underlying the local community assembly,such as the relative role of neutral vs.niche processes in shaping community structure.Here,we explored the responses of trait-abundance relationships to nitrogen(N),phosphorus(P)and potassium(K)fertilization in an alpine meadow.Methods Five fertilization treatments(an unfertilized control and additions of N,P,K and NPK respectively)were implemented using randomized block design in an alpine Tibetan meadow.Species relative abundance(SRA),plant above-ground biomass and species richness were measured in each plot.For 24 common species,we measured species functional traits:saturated height,specific leaf area(SLA)and leaf dry matter content(LDMC)in each treatment but seed size only in the unfertilized control.Standard major axis(SMA)regression and phylogenetically independent contrasts(PICs)analysis were used to analyse species trait-abundance relationships in response to different fertilization treatments.Important Findings Positive correlations between SRA and saturated height were raised following N,P and NPK fertilizations,which indicated an increase in light competition in these plots.In P fertilized plots,SRA was also positively correlated with LDMC because tall grasses with a nutrients conservation strategy often have a relative competitive advantage in capturing limited light and soil nutrients.In K fertilized plots,neither the trait-abundance relationships nor above-ground biomass or species richness significantly differed from that in the control,which suggests that K was not a limiting resource in our study site.These significant correlations between species traits and relative abundance in fertilized treatment suggest that trait-based selection plays an important role in determining species abundance within local communities in alpine meadows.