Taxonomy of lice and their endosymbiotic bacteria in the post-genomic era

AbstractRecent studies of molecular and genomic data from the parasitic lice of birds and mammals, as well as their mutualistic endosymbiotic bacteria, are changing the phylogenetic relationships and taxonomy of these organisms. Phylogenetic studies of lice suggest that vertebrate parasitism arose multiple times from free-living book and bark lice. Molecular clocks show that the major families of lice arose in the late Mesozoic and radiated in the early Cenozoic, following the radiation of mammals and birds. The recent release of the human louse genome has provided new opportunities for research. The genome is being used to find new genetic markers for phylogenetics and population genetics, to understand the complex evolutionary relationships of mitochondrial genes, and to study genome evolution. Genomes are informing us not only about lice, but also about their obligate endosymbiotic bacteria. In contrast to lice and their hosts, lice and their endosymbionts do not share common evolutionary histories, suggesting that endosymbionts are either replaced over time or that there are multiple independent origins of symbiosis in lice. Molecular phylogenetics and whole genome sequencing have recently provided the first insights into the phylogenetic placement and metabolic characteristics of these distantly related bacteria. Comparative genomics between distantly related louse symbionts can provide insights into conserved metabolic functions and can help to explain how distantly related species are fulfilling their role as mutualistic symbionts. In lice and their endosymbionts, molecular data and genome sequencing are driving our understanding of evolutionary relationships and classification, and will for the foreseeable future

A U-235 confirmation method with a discriminating view

Reprocessed spent nuclear fuel that has gone through various stages of chemical processing is currently stored at the INEEL. The material consists of three categories: clean U-235 with radiation readings in the mR/h range, U-235 and fission products up to 900 mR/h, and U-235 with U-232 from 100--200 mR/h. The material is contained in plastic bottles and stored in steel structures consisting of seven vertically arranged individual compartments. A total of forty stacks reside in individual concrete wells. This material is considered hard to measure due to excessive radiation exposure to personnel involved with handling the material during mass and NaI U-235 confirmation measurements for Safeguards inventory purposes. A U-235 confirmation method was developed to assay the individual items in place with the ability to discriminate one item from the other items in the stack. Equipment used with this method includes a portable high-resolution gamma-ray detection system, an appropriate tungsten shield and collimator, and a laser-positioning device. A discrimination control test was incorporated to compare the gamma-ray signal of an item in place to the background signal when the item is removed. Total discrimination of the 186-keV gamma ray signal was achieved

On the Two Spectra Inverse Problem for Semi-Infinite Jacobi Matrices

We present results on the unique reconstruction of a semi-infinite Jacobi operator from the spectra of the operator with two different boundary conditions. This is the discrete analogue of the Borg-Marchenko theorem for Schr{\"o}dinger operators in the half-line. Furthermore, we give necessary and sufficient conditions for two real sequences to be the spectra of a Jacobi operator with different boundary conditions.Comment: In this slightly revised version we have reworded some of the theorems, and we updated two reference

Technical guidelines for the management of field and in vitro germplasm collections

Plant species that are vegetatively propagated, that have long life cycles and/or produce nonorthodox seeds are traditionally maintained in field collections. Maintaining plants in the field is costly and carries high risks of loss; therefore, the strategies and procedures employed to establish and maintain field collections need to be practical, rational and economic, in addition to being scientifically sound. Experience in cost-effective management of field collections lies with individual curators and is not readily available to guide others. Further, there are increasing opportunities for using in vitro methods for the conservation of crops normally conserved in the field, and there is a need to develop strategies and procedures for managing in vitro collections as routine and integral part of the overall conservation strategy of a crop or collection

The 3D Structure of N132D in the LMC: A Late-Stage Young Supernova Remnant

We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the resultant data cube, we have been able to reconstruct the full 3D structure of the system of [O III] filaments. The majority of the ejecta form a ring of ~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We conclude that SNR N132D is approaching the end of the reverse shock phase before entering the fully thermalized Sedov phase of evolution. We speculate that the ring of oxygen-rich material comes from ejecta in the equatorial plane of a bipolar explosion, and that the overall shape of the SNR is strongly influenced by the pre-supernova mass loss from the progenitor star. We find tantalizing evidence of a polar jet associated with a very fast oxygen-rich knot, and clear evidence that the central star has interacted with one or more dense clouds in the surrounding ISM.Comment: Accepted for Publication in Astrophysics & Space Science, 18pp, 8 figure

Schrödinger operators with δ and δ′-potentials supported on hypersurfaces

Self-adjoint Schrödinger operators with δ and δ′-potentials supported on a smooth compact hypersurface are defined explicitly via boundary conditions. The spectral properties of these operators are investigated, regularity results on the functions in their domains are obtained, and analogues of the Birman–Schwinger principle and a variant of Krein’s formula are shown. Furthermore, Schatten–von Neumann type estimates for the differences of the powers of the resolvents of the Schrödinger operators with δ and δ′-potentials, and the Schrödinger operator without a singular interaction are proved. An immediate consequence of these estimates is the existence and completeness of the wave operators of the corresponding scattering systems, as well as the unitary equivalence of the absolutely continuous parts of the singularly perturbed and unperturbed Schrödinger operators. In the proofs of our main theorems we make use of abstract methods from extension theory of symmetric operators, some algebraic considerations and results on elliptic regularity

Three-body non-additive forces between spin-polarized alkali atoms

Three-body non-additive forces in systems of three spin-polarized alkali atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio calculations. The non-additive forces are found to be large, especially near the equilateral equilibrium geometries. For Li, they increase the three-atom potential well depth by a factor of 4 and reduce the equilibrium interatomic distance by 0.9 A. The non-additive forces originate principally from chemical bonding arising from sp mixing effects.Comment: 4 pages, 3 figures (in 5 files

Transport by molecular motors in the presence of static defects

The transport by molecular motors along cytoskeletal filaments is studied theoretically in the presence of static defects. The movements of single motors are described as biased random walks along the filament as well as binding to and unbinding from the filament. Three basic types of defects are distinguished, which differ from normal filament sites only in one of the motors' transition probabilities. Both stepping defects with a reduced probability for forward steps and unbinding defects with an increased probability for motor unbinding strongly reduce the velocities and the run lengths of the motors with increasing defect density. For transport by single motors, binding defects with a reduced probability for motor binding have a relatively small effect on the transport properties. For cargo transport by motors teams, binding defects also change the effective unbinding rate of the cargo particles and are expected to have a stronger effect.Comment: 20 pages, latex, 7 figures, 1 tabl

Fixed-Parameter Algorithms in Analysis of Heuristics for Extracting Networks in Linear Programs

We consider the problem of extracting a maximum-size reflected network in a linear program. This problem has been studied before and a state-of-the-art SGA heuristic with two variations have been proposed. In this paper we apply a new approach to evaluate the quality of SGA\@. In particular, we solve majority of the instances in the testbed to optimality using a new fixed-parameter algorithm, i.e., an algorithm whose runtime is polynomial in the input size but exponential in terms of an additional parameter associated with the given problem. This analysis allows us to conclude that the the existing SGA heuristic, in fact, produces solutions of a very high quality and often reaches the optimal objective values. However, SGA contain two components which leave some space for improvement: building of a spanning tree and searching for an independent set in a graph. In the hope of obtaining even better heuristic, we tried to replace both of these components with some equivalent algorithms. We tried to use a fixed-parameter algorithm instead of a greedy one for searching of an independent set. But even the exact solution of this subproblem improved the whole heuristic insignificantly. Hence, the crucial part of SGA is building of a spanning tree. We tried three different algorithms, and it appears that the Depth-First search is clearly superior to the other ones in building of the spanning tree for SGA. Thereby, by application of fixed-parameter algorithms, we managed to check that the existing SGA heuristic is of a high quality and selected the component which required an improvement. This allowed us to intensify the research in a proper direction which yielded a superior variation of SGA