25,420 research outputs found
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
Quantum atomic delocalization vs. structural disorder in amorphous silicon
Quantum effects on the atom delocalization in amorphous silicon have been
studied by path-integral Monte Carlo simulations from 30 to 800 K. The quantum
delocalization is appreciable vs. topological disorder, as seen from structural
observables such as the radial distribution function (RDF). At low
temperatures, the width of the first peak in the RDF increases by a factor of
1.5 due to quantum effects. The overall anharmonicity of the solid vibrations
at finite temperatures in amorphous silicon is clearly larger than in the
crystalline material. Low-energy vibrational modes are mainly located on
coordination defects in the amorphous material.Comment: 5 pages, 5 PS figures, REVTE
A rapid perturbation procedure for determining nonlinear flow solutions: Application to transonic turbomachinery flows
Perturbation procedures and associated computational codes for determining nonlinear flow solutions were developed to establish a method for minimizing computational requirements associated with parametric studies of transonic flows in turbomachines. The procedure that was developed and evaluated was found to be capable of determining highly accurate approximations to families of strongly nonlinear solutions which are either continuous or discontinuous, and which represent variations in some arbitrary parameter. Coordinate straining is employed to account for the movement of discontinuities and maxima of high gradient regions due to the perturbation. The development and results reported are for the single parameter perturbation problem. Flows past both isolated airfoils and compressor cascades involving a wide variety of flow and geometry parameter changes are reported. Attention is focused in particular on transonic flows which are strongly supercritical and exhibit large surface shock movement over the parametric range studied; and on subsonic flows which display large pressure variations in the stagnation and peak suction pressure regions. Comparisons with the corresponding 'exact' nonlinear solutions indicate a remarkable accuracy and range of validity of such a procedure
Development of a multiple-parameter nonlinear perturbation procedure for transonic turbomachinery flows: Preliminary application to design/optimization problems
An investigation was conducted to continue the development of perturbation procedures and associated computational codes for rapidly determining approximations to nonlinear flow solutions, with the purpose of establishing a method for minimizing computational requirements associated with parametric design studies of transonic flows in turbomachines. The results reported here concern the extension of the previously developed successful method for single parameter perturbations to simultaneous multiple-parameter perturbations, and the preliminary application of the multiple-parameter procedure in combination with an optimization method to blade design/optimization problem. In order to provide as severe a test as possible of the method, attention is focused in particular on transonic flows which are highly supercritical. Flows past both isolated blades and compressor cascades, involving simultaneous changes in both flow and geometric parameters, are considered. Comparisons with the corresponding exact nonlinear solutions display remarkable accuracy and range of validity, in direct correspondence with previous results for single-parameter perturbations
Most Sub-Arcsecond Companions of Kepler Exoplanet Candidate Host Stars are Gravitationally Bound
Using the known detection limits for high-resolution imaging observations and
the statistical properties of true binary and line-of-sight companions, we
estimate the binary fraction of {\it Kepler} exoplanet host stars. Our speckle
imaging programs at the WIYN 3.5-m and Gemini North 8.1-m telescopes have
observed over 600 {\it Kepler} objects of interest (KOIs) and detected 49
stellar companions within 1 arcsecond. Assuming binary stars follow a
log-normal period distribution for an effective temperature range of 3,000 to
10,000 K, then the model predicts that the vast majority of detected
sub-arcsecond companions are long period ( years), gravitationally bound
companions. In comparing the model predictions to the number of real detections
in both observational programs, we conclude that the overall binary fraction of
host stars is similar to the 40-50\% rate observed for field stars
Understanding The Effects Of Stellar Multiplicity On The Derived Planet Radii From Transit Surveys: Implications for Kepler, K2, and TESS
We present a study on the effect of undetected stellar companions on the
derived planetary radii for the Kepler Objects of Interest (KOIs). The current
production of the KOI list assumes that the each KOI is a single star. Not
accounting for stellar multiplicity statistically biases the planets towards
smaller radii. The bias towards smaller radii depends on the properties of the
companion stars and whether the planets orbit the primary or the companion
stars. Defining a planetary radius correction factor , we find that if the
KOIs are assumed to be single, then, {\it on average}, the planetary radii may
be underestimated by a factor of . If typical
radial velocity and high resolution imaging observations are performed and no
companions are detected, this factor reduces to . The correction factor is dependent upon the primary
star properties and ranges from for A and F
stars to for K and M stars. For missions like
K2 and TESS where the stars may be closer than the stars in the Kepler target
sample, observational vetting (primary imaging) reduces the radius correction
factor to . Finally, we show that if the
stellar multiplicity rates are not accounted for correctly, occurrence rate
calculations for Earth-sized planets may overestimate the frequency of small
planets by as much as \%.Comment: 10 pages, 6 Figures, Accepted for publication in The Astrophysical
Journal (Fix typo in Equation 6 of original astroph submission; correction
also submitted to Journal
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