Crystal structure of Schmallenberg orthobunyavirus nucleoprotein-RNA complex reveals a novel RNA sequestration mechanism

Schmallenberg virus (SBV) is a newly emerged orthobunyavirus (family Bunyaviridae) that has caused severe disease in the offspring of farm animals across Europe. Like all orthobunyaviruses, SBV contains a tripartite negative-sense RNA genome that is encapsidated by the viral nucleocapsid (N) protein in the form of a ribonucleoprotein complex (RNP). We recently reported the three-dimensional structure of SBV N that revealed a novel fold. Here we report the crystal structure of the SBV N protein in complex with a 42-nt-long RNA to 2.16 Å resolution. The complex comprises a tetramer of N that encapsidates the RNA as a cross-shape inside the protein ring structure, with each protomer bound to 11 ribonucleotides. Eight bases are bound in the positively charged cleft between the N- and C-terminal domains of N, and three bases are shielded by the extended N-terminal arm. SBV N appears to sequester RNA using a different mechanism compared with the nucleoproteins of other negative-sense RNA viruses. Furthermore, the structure suggests that RNA binding results in conformational changes of some residues in the RNA-binding cleft and the N- and C-terminal arms. Our results provide new insights into the novel mechanism of RNA encapsidation by orthobunyaviruses

Spherical magnetic nanoparticles: magnetic structure and interparticle interaction

The interaction between spherical magnetic nanoparticles is investigated from micromagnetic simulations and ananlysed in terms of the leading dipolar interaction energy between magnetic dipoles. We focus mainly on the case where the particles present a vortex structure. In a first step the local magnetic structure in the isolated particle is revisited. For particles bearing a uniaxial magnetocrystaline anisotropy, it is shown that the vortex core orientation relative to the easy axis depends on both the particle size and the anisotropy constant. When the particles magnetization present a vortex structure, it is shown that the polarization of the particles by the dipolar field of the other one must be taken into account in the interaction. An analytic form is deduced for the interaction which involves the vortex core magnetization and the magnetic susceptibility which are obtained from the magnetic properties of the isolated particle.Comment: 20 pages, 10 figures Published in Journal of Applied Physics. To be found at: http://link.aip.org/link/?jap/105/07391

Field-induced structure transformation in electrorheological solids

We have computed the local electric field in a body-centered tetragonal (BCT) lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to examine the effects of a structure transformation on the local field strength. For the ground state of an electrorheological solid of hard spheres, we identified a novel structure transformation from the BCT to the face-centered cubic (FCC) lattices by changing the uniaxial lattice constant c under the hard sphere constraint. In contrast to the previous results, the local field exhibits a non-monotonic transition from BCT to FCC. As c increases from the BCT ground state, the local field initially decreases rapidly towards the isotropic value at the body-centered cubic lattice, decreases further, reaching a minimum value and increases, passing through the isotropic value again at an intermediate lattice, reaches a maximum value and finally decreases to the FCC value. An experimental realization of the structure transformation is suggested. Moreover, the change in the local field can lead to a generalized Clausius-Mossotti equation for the BCT lattices.Comment: Submitted to Phys. Rev.

Spectral Energy Distributions of Gamma Ray Bursts Energized by External Shocks

Sari, Piran, and Narayan have derived analytic formulas to model the spectra from gamma-ray burst blast waves that are energized by sweeping up material from the surrounding medium. We extend these expressions to apply to general radiative regimes and to include the effects of synchrotron self-absorption. Electron energy losses due to the synchrotron self-Compton process are also treated in a very approximate way. The calculated spectra are compared with detailed numerical simulation results. We find that the spectral and temporal breaks from the detailed numerical simulation are much smoother than the analytic formulas imply, and that the discrepancies between the analytic and numerical results are greatest near the breaks and endpoints of the synchrotron spectra. The expressions are most accurate (within a factor of ~ 3) in the optical/X-ray regime during the afterglow phase, and are more accurate when epsilon_e, the fraction of swept-up particle energy that is transferred to the electrons, is <~ 0.1. The analytic results provide at best order-of-magnitude accuracy in the self-absorbed radio/infrared regime, and give poor fits to the self-Compton spectra due to complications from Klein-Nishina effects and photon-photon opacity.Comment: 16 pages, 7 figures, ApJ, in press, 537, July 1, 2000. Minor changes in response to referee report, corrected figure

Multiwavelength Observations of GX 339-4 in 1996. II. Rapid X-ray Variability

As part of our multiwavelength campaign of GX 339-4 observations in 1996 we present the rapid X-ray variability observed July 26 using the RXTE when the source was in a hard state (= soft X-ray low state). We found that the source was extremely variable, with many bright flares. The flares have relatively symmetric time profiles. There are a few time intervals where the flux rises steadily and then drops suddenly, sometimes to a level lower than the average before the increase. Hardness ratios showed that the source was slightly softer when the flux was brighter. The power density spectra (PDS) were also complicated and we found that broken power laws do not provide adequate fits to any of them. Instead a pair of zero-centered Lorentzians gives a good general description of the shape of the PDS. We found several quasi-periodic oscillations (QPO), including some that are harmonically spaced with the most stable frequency at 0.35 Hz. While the overall rms variability of the source was close to being constant throughout the observation (29% integrating between 0.01 and 50 Hz), there is a small but significant change in the PDS shape with time. More importantly, we show that the soft 2-5 keV band is more variable than the harder 5-10 and 10-40 keV bands, which is unusual for this source and for other black hole candidates. Cross correlation functions (CCF) between these bands show that the light curve for the 10-40 keV band lags that of the 2-5 keV band by 5 msec.Comment: Submitted to Astrophysical Journal. 20 pages. 8 figure

Correlated Two-Electron Wave Functions of Any Symmetry

Using a procedure originally due to Hylleraas, a convenient expansion in coupled spherical harmonics which terminates in a very small number of terms is applied to the treatment of fully correlated two-electron wave functions of any symmetry (total angular momentum, parity, and spin). Coupled equations satisfied by these wave functions are derived which are well adapted to computation and which we discretize on a numerical lattice utilizing the basis-spline collocation method. Use of this method which relies on very flexible basis functions is intended to facilitate subsequently the consideration of time-dependent rearrangments such as autoionization, photoionization, and electron-impact excitation and ionization. Here, we describe the underlying theoretical and computational methods concerning our treatment of the two-electron problem, the lattice discretization, and partial eigensolution by damped relaxation. Results of explicit calculations are given regarding the ground state and two low-lying singly excited states of helium

Radiation from collision-dominated relativistic pair fireballs

It is generally accepted that gamma-ray bursts (GRBs) are initiated by a relativistic pair fireball, converting its internal energy into kinetic energy of a relativistically moving plasmoid and subsequently into radiation. Here, we investigate the early stages of this evolution, after the pair fireball has become optically thin to gamma-gamma pair production. We show that for a short period of time, ~ 0.1 - a few seconds after the initial explosion, the pair plasmoid evolution might be dominated by collisional processes prior to the formation of a collisionless shock. We simulate these processes during the early pair plasmoid evolution and calculate the expected radiative signatures. We show that the radiation from the collision-dominated pair plasmoid phase results in a short (~ a few ms) flash of thermal soft X-ray emission, followed by a transition phase of < 1 s during which the fireball turns Thomson thin, but its radiation remains dominated by thermal Comptonization, peaking at around E_pk ~ 100 MeV - a few GeV. While the very early thermal emission could be associated with the quasi-thermal radiation signatures found in the very early phases of several bright BATSE GRBs, the predicted subsequent flash of high-energy emission should be easily detectable with the GLAST satellite.Comment: AASTeX, 25 pages, including 7 figures. Accepted for publication in Ap

Broadband Spectral Analysis of PKS 0528+134: A Report on Six Years of EGRET Observations

The multiwavelength spectra of PKS 0528+134 during six years of observations by EGRET have been analyzed using synchrotron self-Compton (SSC) and external radiation Compton (ERC) models. We find that a two-component model, in which the target photons are produced externally to the gamma-ray emitting region, but also including an SSC component, is required to suitably reproduce the spectral energy distributions of the source. Our analysis indicates that there is a trend in the observed properties of PKS 0528+134, as the source goes from a gamma-ray low state to a flaring state. We observe that during the higher gamma-ray states, the bulk Lorentz factor of the jet increases and the ERC component dominates the high-energy emission. Our model calculations indicate the trend that the energies of the electrons giving rise to the synchrotron peak decreases, and the power-ratio of the gamma-ray and low energy spectral components increases, as the source goes from a low to a high gamma-ray state.Comment: 36 pages, 13 figures, final version accepted for publication in ApJ; includes minor modification

Lamination And Microstructuring Technology for a Bio-Cell Multiwell array

Microtechnology becomes a versatile tool for biological and biomedical applications. Microwells have been established long but remained non-intelligent up to now. Merging new fabrication techniques and handling concepts with microelectronics enables to realize intelligent microwells suitable for future improved cancer treatment. The described technology depicts the basis for the fabrication of a elecronically enhanced microwell. Thin aluminium sheets are structured by laser micro machining and laminated successively to obtain registration tolerances of the respective layers of 5..10\^A$\mu$m. The microwells lasermachined into the laminate are with 50..80\^A$\mu$m diameter, allowing to hold individual cells within the well. The individual process steps are described and results on the microstructuring are given.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/EDA-Publishing

Identifying Gamma-Ray Burst Remnants in Nearby Galaxies

We study the spectral signatures arising from cooling and recombination of an interstellar medium whose equilibrium state has been altered over \sim 100 pc by the radiation of a Gamma-Ray Burst (GRB) and its afterglow. We identify signatures in the line diagnostics which are indicative of a photo-ionized GRB remnant which is \la 5 x 10^4 years old . We estimate that at least a few such remnants should be detectable in the Virgo cluster of galaxies. If the gamma-ray emission from GRBs is beamed to a fraction f_b of their sky, then the expected number of Virgo remnants is larger by a factor of f_b^{-1}. Virgo remnants can be resolved with arcsecond imaging, and are likely to be center-filled using narrow-band filters of high ionization lines (such as [O III] \lambda5007 or He II \lambda4686), and limb-brightened for low-ionization lines (such as [S II] \lambda6717). The non-relativistic blast wave might be visible separately, since it does not reach the outer edge of these young photo-ionized remnants. The remnants should show evidence for ionization cones if the prompt or afterglow UV emission from GRBs is beamed.Comment: 21 pages, 10 figures, submitted to Ap