Cluster PEACE observations of electron pressure tensor divergence in the magnetotail

Cluster crossed the magnetotail neutral sheet on four occasions between 16: 38 and 16: 43 UT on 08/17/2003. The four-spacecraft capabilities of Cluster are used to determine spatial gradients from the magnetic field vectors and, for the first time, full electron pressure tensors. We find that the contribution to the electric field from the Hall term (max of similar to 6 mV/m) pointed towards the neutral sheet, whereas that from the electron pressure divergence ( max of similar to 1 mV/m) pointed away from the neutral sheet. The electric field contributions in this direction were closely anti-correlated. During this period Clusters 1 and 4 were sometimes above and below the neutral sheet respectively. This allowed the simultaneous observation of magnetic fields that are interpreted as two quadrants of the Hall magnetic field system. An associated field-aligned current system was detected using the curlometer and moments of the particle distributions

Voting models and semilinear parabolic equations

We present probabilistic interpretations of solutions to semi-linear parabolic equations with polynomial nonlinearities in terms of the voting models on the genealogical trees of branching Brownian motion (BBM). These extend the connection between the Fisher-KPP equation and BBM discovered by McKean in~\cite{McK}. In particular, we present ``random outcome'' and ``random threshold'' voting models that yield any polynomial nonlinearity $f$ satisfying $f(0)=f(1)=0$ and a ``recursive up the tree'' model that allows to go beyond this restriction on $f$. We compute a few examples of particular interest; for example, we obtain a curious interpretation of the heat equation in terms of a nontrivial voting model and a ``group-based'' voting rule that leads to a probabilistic view of the pushmi-pullyu transition for a class of nonlinearities introduced by Ebert and van Saarloos.Comment: 20 page

Metastable states of a driven flux lattice in a superconductor with strong pins

The flux lattice driven by a uniform driving force in a superconductor with hot, strong, sharp and randomly distributed pinning centers, with applied magnetic field half the matching field is simulated. At low temperature both a non activated regime, where flux motion occurs within a robust percolative flux flow channel, and an activated regime are obtained depending on the sample preparation. These two regimes exhibit distinct resistivity and magnetic induction. In the non activated regime, a clear fingerprint is observed in the autocorrelation function of the longitudinal resitivity, which oscillates at a frequency close to the inverse lattice diffusion time.Comment: 6 figure

Topological dissection of the membrane transport protein Mhp1 derived from cysteine accessibility and mass spectrometry

Cys accessibility and quantitative intact mass spectrometry (MS) analyses have been devised to study the topological transitions of Mhp1, the membrane protein for sodium-linked transport of hydantoins from Microbacterium liquefaciens. Mhp1 has been crystallised in three forms (outward-facing open, outward-facing occluded with substrate bound, and inward-facing open). We show that one natural cysteine residue, Cys327, out of three, has an enhanced solvent accessibility in the inward-facing (relative to the outward-facing) form. Reaction of the purified protein, in detergent, with the thiol-reactive N-ethylmalemide (NEM), results in modification of Cys327, suggesting that Mhp1 adopts predominantly inward-facing conformations. Addition of either sodium ions or the substrate 5-benzyl-L-hydantoin (L-BH) does not shift this conformational equilibrium, but, systematic co-addition of the two results in an attenuation of labelling, indicating a shift toward outward-facing conformations that can be interpreted using conventional enzyme kinetic analyses. Such measurements can afford the Km for each ligand as well as the stoichiometry of ion-substrate coupled conformational changes. Mutations that perturb the substrate binding site either result in the protein being unable to adopt outward-facing conformations or in a global destabilisation of structure. The methodology combines covalent labeling, mass spectrometry and kinetic analyses in a straightforward workflow applicable to a range of systems, enabling the interrogation of changes in a protein’s conformation required for function at varied concentrations of substrates, and the consequences of mutations on these conformational transitions

The archaeometry and archaeology of ancient Chinese glass: a review

This paper provides a new review of archaeometric research carried out on glass found in China, set in an archaeological context, from its earliest occurrence, to the Song dynasty. It is set within a broad geographical context taking the terrestrial and maritime Silk Road contacts into account. We discuss chemical and isotopic compositional contrasts in glasses from different periods found in different parts of China, the glasses that were almost certainly made in China and those that were imported. A theme that runs through the paper is the problem of provenancing glass found in China. We discuss the glass artefacts that are of typical Chines types and contrast these with imports. The structure reflects the contrast between imported and Chinese made with glasses. We discuss potential new scientific and archaeological approaches to Chinese glass

Estimation and inference under economic restrictions

Estimation of economic relationships often requires imposition of constraints such as positivity or monotonicity on each observation. Methods to impose such constraints, however, vary depending upon the estimation technique employed. We describe a general methodology to impose (observation-specific) constraints for the class of linear regression estimators using a method known as constraint weighted bootstrapping. While this method has received attention in the nonparametric regression literature, we show how it can be applied for both parametric and nonparametric estimators. A benefit of this method is that imposing numerous constraints simultaneously can be performed seamlessly. We apply this method to Norwegian dairy farm data to estimate both unconstrained and constrained parametric and nonparametric models

Effects of Grassland Management Practices on Ant Functional Groups in Central North America

Tallgrass prairies of central North America have experienced disturbances including fire and grazing for millennia. Little is known about the effects of these disturbances on prairie ants, even though ants are thought to play major roles in ecosystem maintenance. We implemented three management treatments on remnant and restored grassland tracts in the central U.S., and compared the effects of treatment on abundance of ant functional groups. Management treatments were: (1) patch-burn graze—rotational burning of three spatially distinct patches within a fenced tract, and growing-season cattle grazing; (2) graze-and-burn—burning entire tract every 3 years, and growing-season cattle grazing, and (3) burn-only—burning entire tract every 3 years, but no cattle grazing. Ant species were classified into one of four functional groups. Opportunist ants and the dominant ant species, Formica montana, were more abundant in burn-only tracts than tracts managed with either of the grazing treatments. Generalists were more abundant in graze-and-burn tracts than in burn-only tracts. Abundance of F. montana was negatively associated with pre-treatment time since fire, whereas generalist ant abundance was positively associated. F. montanawere more abundant in restored tracts than remnants, whereas the opposite was true for subdominants and opportunists. In summary, abundance of the dominant F. montana increased in response to intense disturbances that were followed by quick recovery of plant biomass. Generalist ant abundance decreased in response to those disturbances, which we attribute to the effects of competitive dominance of F. montana upon the generalists

Expression, purification and characterization of the Lily symptomless virus coat protein from Lanzhou Isolate

Background: Lily symptomless virus (LSV) is widespread in many countries where lily are grown or planted, and causes severe economic losses in terms of quantity and quality of flower and bulb production. To study the structure-function relationship of coat protein (CP) of LSV, to investigate antigenic relationships between coat protein subunits or intact virons, and to prepare specific antibodies against LSV, substantial amounts of CP protein are needed. Results: Thus, full-length cDNA of LSV coat protein was synthesized and amplified by RT-PCR from RNA isolated from LSV Lanzhou isolate. The extended 33.6 kDa CP was cloned and expressed prokaryoticly and then purified by Ni-ion affinity chromatography. Its identity and antigenicity of recombinant CP were identified on Western-blotting by using the prepared anti-LSV antibodies. Conclusions: The results indicate that fusion CP maintains its native antigenicity and specificity, providing a good source of antigen in preparation of LSV related antibodies. Detailed structural analysis of a pure recombinant CP should allow a better understanding of its role in cell attachment and LSV tropism. This investigation to LSV should provide some specific antibodies and aid to development a detection system for LSV diagnostics and epidemiologic surveys

Conserved presence of G-quadruplex forming sequences in the Long Terminal Repeat Promoter of Lentiviruses

G-quadruplexes (G4s) are secondary structures of nucleic acids that epigenetically regulate cellular processes. In the human immunodeficiency lentivirus 1 (HIV-1), dynamic G4s are located in the unique viral LTR promoter. Folding of HIV-1 LTR G4s inhibits viral transcription; stabilization by G4 ligands intensifies this effect. Cellular proteins modulate viral transcription by inducing/unfolding LTR G4s. We here expanded our investigation on the presence of LTR G4s to all lentiviruses. G4s in the 5'-LTR U3 region were completely conserved in primate lentiviruses. A G4 was also present in a cattle-infecting lentivirus. All other non-primate lentiviruses displayed hints of less stable G4s. In primate lentiviruses, the possibility to fold into G4s was highly conserved among strains. LTR G4 sequences were very similar among phylogenetically related primate viruses, while they increasingly differed in viruses that diverged early from a common ancestor. A strong correlation between primate lentivirus LTR G4s and Sp1/NF\u3baB binding sites was found. All LTR G4s folded: their complexity was assessed by polymerase stop assay. Our data support a role of the lentiviruses 5'-LTR G4 region as control centre of viral transcription, where folding/unfolding of G4s and multiple recruitment of factors based on both sequence and structure may take place