Cost-effective technology advancement directions for electric propulsion transportation systems in earth-orbital missions

The directions that electric propulsion technology should take to meet the primary propulsion requirements for earth-orbital missions in the most cost effective manner are determined. The mission set requirements, state of the art electric propulsion technology and the baseline system characterized by it, adequacy of the baseline system to meet the mission set requirements, cost optimum electric propulsion system characteristics for the mission set, and sensitivities of mission costs and design points to system level electric propulsion parameters are discussed. The impact on overall costs than specific masses or costs of propulsion and power systems is evaluated

Commutative association schemes

Association schemes were originally introduced by Bose and his co-workers in the design of statistical experiments. Since that point of inception, the concept has proved useful in the study of group actions, in algebraic graph theory, in algebraic coding theory, and in areas as far afield as knot theory and numerical integration. This branch of the theory, viewed in this collection of surveys as the "commutative case," has seen significant activity in the last few decades. The goal of the present survey is to discuss the most important new developments in several directions, including Gelfand pairs, cometric association schemes, Delsarte Theory, spin models and the semidefinite programming technique. The narrative follows a thread through this list of topics, this being the contrast between combinatorial symmetry and group-theoretic symmetry, culminating in Schrijver's SDP bound for binary codes (based on group actions) and its connection to the Terwilliger algebra (based on combinatorial symmetry). We propose this new role of the Terwilliger algebra in Delsarte Theory as a central topic for future work.Comment: 36 page

Deviation Between δ13C and Leaf Intercellular Co2 in Salix Interior Cuttings Developing Under Low Light

This is the publisher's official version. It is also available electronically from: http://www.jstor.org/stable/10.1086/322892.Leaf δ13C values of perennial species are sometimes less negative than model‐predicted δ13C values derived from instantaneous measures of pi/pa. It has been hypothesized that the less negative δ13C values could be caused by 13C‐enriched stored carbon imported during the early stages of leaf growth. The δ13C values of newly emerging leaves could thus represent δ13C values of stem‐stored carbohydrates and may also provide integral measures of pi/pa at the end of the past growing season. We tested these hypotheses by sprouting cuttings of Salix interior under wet and dry soil‐moisture conditions in a controlled environmental chamber. Plants were defoliated after 56 d, and watering treatments were then reversed for half of the plants in each treatment. The δ13C values of newly emerging leaves did not correlate with pi/pa ratios of newly emerging leaves or of mature leaves prior to defoliation, thereby indicative that δ13C values of newly emerging leaves are not a simple reflection of prior pi/pa. Also, the δ13C values of newly emerging leaves were more enriched in 13C relative to the δ13C values of stem carbohydrates in the treatments where water regimes were reversed. Newly emerging leaves after defoliation had higher δ13C values despite the lower instantaneous water‐use efficiency and similar values of pi/pa to older photosynthetic leaves. Large differences between observed and model‐predicted pi/pa values also occurred in older, more mature leaves, and this may be because large proportions of their total mass were derived from carbon import

Improving experimental phases for strong reflections prior to density modification.

Experimental phasing of diffraction data from macromolecular crystals involves deriving phase probability distributions. These distributions are often bimodal, making their weighted average, the centroid phase, improbable, so that electron-density maps computed using centroid phases are often non-interpretable. Density modification brings in information about the characteristics of electron density in protein crystals. In successful cases, this allows a choice between the modes in the phase probability distributions, and the maps can cross the borderline between non-interpretable and interpretable. Based on the suggestions by Vekhter [Vekhter (2005), Acta Cryst. D61, 899-902], the impact of identifying optimized phases for a small number of strong reflections prior to the density-modification process was investigated while using the centroid phase as a starting point for the remaining reflections. A genetic algorithm was developed that optimizes the quality of such phases using the skewness of the density map as a target function. Phases optimized in this way are then used in density modification. In most of the tests, the resulting maps were of higher quality than maps generated from the original centroid phases. In one of the test cases, the new method sufficiently improved a marginal set of experimental SAD phases to enable successful map interpretation. A computer program, SISA, has been developed to apply this method for phase improvement in macromolecular crystallography

Structure of HrcQ(B)-C, a conserved component of the bacterial type III secretion systems

Type III secretion systems enable plant and animal bacterial pathogens to deliver virulence proteins into the cytosol of eukaryotic host cells, causing a broad spectrum of diseases including bacteremia, septicemia, typhoid fever, and bubonic plague in mammals, and localized lesions, systemic wilting, and blights in plants. In addition, type III secretion systems are also required for biogenesis of the bacterial flagellum. The HrcQ(B) protein, a component of the secretion apparatus of Pseudomonas syringae with homologues in all type III systems, has a variable N-terminal and a conserved C-terminal domain (HrcQ(B)-C). Here, we report the crystal structure of HrcQ(B)-C and show that this domain retains the ability of the full-length protein to interact with other type III components. A 3D analysis of sequence conservation patterns reveals two clusters of residues potentially involved in protein–protein interactions. Based on the analogies between HrcQ(B) and its flagellum homologues, we propose that HrcQ(B)-C participates in the formation of a C-ring-like assembly

A deformed analogue of Onsager's symmetry in the XXZ open spin chain

The XXZ open spin chain with general integrable boundary conditions is shown to possess a q-deformed analogue of the Onsager's algebra as fundamental non-abelian symmetry which ensures the integrability of the model. This symmetry implies the existence of a finite set of independent mutually commuting nonlocal operators which form an abelian subalgebra. The transfer matrix and local conserved quantities, for instance the Hamiltonian, are expressed in terms of these nonlocal operators. It follows that Onsager's original approach of the planar Ising model can be extended to the XXZ open spin chain.Comment: 12 pages; LaTeX file with amssymb; v2: typos corrected, clarifications in the text; v3: minor changes in references, version to appear in JSTA

X-ray structure determination using low-resolution electron microscopy maps for molecular replacement.

Structures of multisubunit macromolecular machines are primarily determined either by electron microscopy (EM) or by X-ray crystallography. In many cases, a structure for a complex can be obtained at low resolution (at a coarse level of detail) with EM and at a higher resolution (with finer detail) by X-ray crystallography. The integration of these two structural techniques is becoming increasingly important for the generation of atomic models of macromolecular complexes. A low-resolution EM image can be a powerful tool for obtaining the 'phase' information that is missing from an X-ray crystallography experiment; however, integration of EM and X-ray diffraction data has been technically challenging. Here we present a step-by-step protocol that explains how low-resolution EM maps can be placed in the crystallographic unit cell by molecular replacement, and how initial phases computed from the placed EM density are extended to high resolution by averaging maps over noncrystallographic symmetry. As the resolution gap between EM and X-ray crystallography continues to narrow, the use of EM maps to help with X-ray crystal structure determination, as described in this protocol, will become increasingly effective.R.N.J. is supported by the National Research Service Award postdoctoral fellowship (F32 GM108436) from the US National Institutes of Health (NIH). R.J.R. and T.C.T. are supported by a grant (GM063210) from the NIH. R.J.R. is supported by a Principal Research Fellowship from the Wellcome Trust (grant no. 082961/Z/07/Z). Research in the Wiedenheft lab is supported by the NIH IDeA Program COBRE (GM110732), an R01 to B.W. (GM108888), the National Science Foundation EPSCoR (EPS-110134), the M.J. Murdock Charitable Trust and the Montana State University Agricultural Experimental Station.This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/nprot.2015.06

SAGA: A project to automate the management of software production systems

The project to automate the management of software production systems is described. The SAGA system is a software environment that is designed to support most of the software development activities that occur in a software lifecycle. The system can be configured to support specific software development applications using given programming languages, tools, and methodologies. Meta-tools are provided to ease configuration. Several major components of the SAGA system are completed to prototype form. The construction methods are described