These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

CRYSTALLOGRAPHIC POINT AND SPACE  

E-print Network

CRYSTALLOGRAPHIC POINT AND SPACE GROUPS Andy Elvin June 10, 2013 #12;Contents Point and Space no reflection axes #12;Cube and Octahedron are dual Symmetries under Oh #12;Space Groups Subgroups of E(3) Point Group + Translation { R | 0 }{ E | t }a = { R | t }a = Ra + t 230 Space Groups 73 symmorphic space

California at Santa Cruz, University of

2

Fibered orbifolds and crystallographic groups, II  

E-print Network

Let G be an n-dimensional crystallographic group (n-space group). If G is a Z-reducible, then the flat n-orbifold E^n/G has a nontrivial fibered orbifold structure. We prove that this structure can be described by a generalized Calabi construction, that is, E^n/G is represented as the quotient of the Cartesian product of two flat orbifolds under the diagonal action of a structure group of isometries. We determine the structure group and prove that it is finite if and only if the fibered orbifold structure has an orthogonally dual fibered orbifold structure. A geometric fibration of E^n/G corresponds to a space group extension 1 -> N -> G -> G/N -> 1. We give a criterion for the splitting of a space group extension in terms of the structure group action that is strong enough to detect the splitting of all the space group extensions corresponding to the standard Seifert fibrations of a compact, connected, flat 3-orbifold. If G is an arbitrary n-space group, we prove that the group Isom(E^n/G) of isometries of E...

Ratcliffe, John G

2011-01-01

3

Fibered orbifolds and crystallographic groups  

E-print Network

In this paper, we prove that a normal subgroup N of an n-dimensional crystallographic group G determines a geometric fibered orbifold structure on the flat orbifold E^n/G, and conversely every geometric fibered orbifold structure on E^n/G is determined by a normal subgroup N of G, which is maximal in its commensurability class of normal subgroups of G. In particular, we prove that E^n/G is a fiber bundle, with totally geodesic fibers, over a b-dimensional torus, where b is the first Betti number of G. Let N be a normal subgroup of G which is maximal in its commensurability class. We study the relationship between the exact sequence 1 -> N -> G -> G/N -> 1 splitting and the corresponding fibration projection having an affine section. If N is torsion-free, we prove that the exact sequence splits if and only if the fibration projection has an affine section. If the generic fiber F = Span(N)/N has an ordinary point that is fixed by every isometry of F, we prove that the exact sequence always splits. Finally, we d...

Ratcliffe, John G

2008-01-01

4

Bilbao Crystallographic Server  

NSDL National Science Digital Library

The Bilbao Crystallographic Server provides access to crystallographic programs, tools, and databases. The tools are grouped according to type: space groups retrieval; group-subgroup relations of space groups; representation theory applications; solid state theory applications; structure utilities; and subperiodic groups (layer, rod, and frieze groups retrieval tools). The Incommensurate Crystal Structure Database (ICSDB) provides access to four categories of data: general (chemical information and publication data); average structure (cell, symmetry, atom sites, and experimental data for the average structure); modulated structure (cell, symmetry, atom sites, and experimental data for the modulated structure); and modulation parameters (descriptions of the modulation, wave vectors, and atom sites modulations).

5

Abelianization of space groups  

NASA Astrophysics Data System (ADS)

Tables of the abelianizations of all the n-dimensional space groups for n = 1, 2, 3 are provided. The exponent of the torsion subgroup of the abelianization of an arbitrary n-dimensional space group is shown to divide the order of its point group.

Ratcliffe, J. G.; Tschantz, S. T.

2009-01-01

6

The analysis of crystallographic symmetry types in finite groups  

NASA Astrophysics Data System (ADS)

Undeniably, it is human nature to prefer objects which are considered beautiful. Most consider beautiful as perfection, hence they try to create objects which are perfectly balance in shape and patterns. This creates a whole different kind of art, the kind that requires an object to be symmetrical. This leads to the study of symmetrical objects and pattern. Even mathematicians and ethnomathematicians are very interested with the essence of symmetry. One of these studies were conducted on the Malay traditional triaxial weaving culture. The patterns derived from this technique are symmetrical and this allows for further research. In this paper, the 17 symmetry types in a plane, known as the wallpaper groups, are studied and discussed. The wallpaper groups will then be applied to the triaxial patterns of food cover in Malaysia.

Sani, Atikah Mohd; Sarmin, Nor Haniza; Adam, Nooraishikin; Zamri, Siti Norziahidayu Amzee

2014-06-01

7

Novel Kac-Moody-type affine extensions of non-crystallographic Coxeter groups  

NASA Astrophysics Data System (ADS)

Motivated by recent results in mathematical virology, we present novel asymmetric {Z}[\\tau ]-integer-valued affine extensions of the non-crystallographic Coxeter groups H2, H3 and H4 derived in a Kac-Moody-type formalism. In particular, we show that the affine reflection planes which extend the Coxeter group H3 generate (twist) translations along two-, three- and five-fold axes of icosahedral symmetry, and we classify these translations in terms of the Fibonacci recursion relation applied to different start values. We thus provide an explanation of previous results concerning affine extensions of icosahedral symmetry in a Coxeter group context, and extend this analysis to the case of the non-crystallographic Coxeter groups H2 and H4. These results will enable new applications of group theory in physics (quasicrystals), biology (viruses) and chemistry (fullerenes).

Dechant, Pierre-Philippe; Bœhm, Céline; Twarock, Reidun

2012-07-01

8

Complete derivation of space groups of magnetic symmetry of crystals by numerical construction  

SciTech Connect

The solution is given to the problem regarding the derivation of the so-called space groups of magnetic symmetry with crystallographic angles of rotation of the spin vector, which was formulated as far back as the early 1970s. The crystallographic P-symmetries that should be used in the generalization with the three-dimensional space Fedorov groups G{sub 3} are revealed. The space groups G{sub 3} are generalized with each of these P-symmetries.

Palistrant, A. F. [State University of Moldova (Moldova, Republic of)], E-mail: mepalistrant@yandex.ru

2007-11-15

9

International Space Exploration Coordination Group  

E-print Network

on Earth. This document presents the status of the space agency exploration road mapping activityInternational Space Exploration Coordination Group The Global Exploration Roadmap August 2013 #12 ankles. The water seems inviting. The ocean calls." --Dr. Carl Sagan #12;The Global Exploration Roadmap

Rathbun, Julie A.

10

UCL DEPARTMENT OF SPACE & CLIMATE PHYSICS SPACE PLASMA PHYSICS GROUP  

E-print Network

UCL DEPARTMENT OF SPACE & CLIMATE PHYSICS SPACE PLASMA PHYSICS GROUP 18th September 2012 STFC 2012 #12;UCL DEPARTMENT OF SPACE & CLIMATE PHYSICS SPACE PLASMA PHYSICS GROUP 18th September 2012 STFC · Conclusion #12;UCL DEPARTMENT OF SPACE & CLIMATE PHYSICS SPACE PLASMA PHYSICS GROUP 18th September 2012 STFC

11

Platinum Group Thiophenoxyimine Complexes: Syntheses,Crystallographic and Computational Studies of Structural Properties  

SciTech Connect

Monomeric thiosalicylaldiminate complexes of rhodium(I) and iridium(I) were prepared by ligand transfer from the homoleptic zinc(II) species. In the presence of strongly donating ligands, the iridium complexes undergo insertion of the metal into the imine carbon-hydrogen bond. Thiophenoxyketimines were prepared by non-templated reaction of o-mercaptoacetophenone with anilines, and were complexed with rhodium(I), iridium(I), nickel(II) and platinum(II). X-ray crystallographic studies showed that while the thiosalicylaldiminate complexes display planar ligand conformations, those of the thiophenoxyketiminates are strongly distorted. Results of a computational study were consistent with a steric-strain interpretation of the difference in preferred ligand geometries.

Krinsky, Jamin L.; Arnold, John; Bergman, Robert G.

2006-10-03

12

Interactive PDF files with embedded 3D designs as support material to study the 32 crystallographic point groups  

NASA Astrophysics Data System (ADS)

Crystallography and X-ray diffraction techniques are essential topics in geosciences and other solid-state sciences. Their fundamentals, which include point symmetry groups, are taught in the corresponding university courses. In-depth meaningful learning of symmetry concepts is difficult and requires capacity for abstraction and spatial vision. Traditionally, wooden crystallographic models are used as support material. In this paper, we describe a new interactive tool, freely available, inspired in such models. Thirty-two PDF files containing embedded 3D models have been created. Each file illustrates a point symmetry group and can be used to teach/learn essential symmetry concepts and the International Hermann-Mauguin notation of point symmetry groups. Most interactive computer-aided tools devoted to symmetry deal with molecular symmetry and disregard crystal symmetry so we have developed a tool that fills the existing gap.

Arribas, Victor; Casas, Lluís; Estop, Eugènia; Labrador, Manuel

2014-01-01

13

Renormalization group in internal space  

NASA Astrophysics Data System (ADS)

Renormalization group in the internal space consists of the gradual change of the coupling constants. Functional evolution equations corresponding to the change of the mass or the coupling constant are presented in the framework of a scalar model. The evolution in the mass which yields the functional generalization of the Callan-Symanzik equation for the one-particle irreducible effective action is given in its renormalized, cutoff-independent form. The evolution of the coupling constant generates an evolution equation for the two-particle irreducible effective action.

Polonyi, J.; Sailer, K.

2005-01-01

14

UCL DEPARTMENT OF SPACE & CLIMATE PHYSICS SPACE PLASMA PHYSICS GROUP  

E-print Network

UCL DEPARTMENT OF SPACE & CLIMATE PHYSICS SPACE PLASMA PHYSICS GROUP ESA Lunar Lander ­ L-DEPP C.J. Owen and D.O. Kataria UCL/MSSL #12;UCL DEPARTMENT OF SPACE & CLIMATE PHYSICS SPACE PLASMA PHYSICS GROUP PLASMA PHYSICS GROUP What is L-DEPP? · L-DEPP = Lunar Dust Environment and Plasma Package; · Investigate

Anand, Mahesh

15

Position and Orientation Distributions for Non-Reversal Random Walks using Space-Group Fourier Transforms.  

PubMed

This paper presents an efficient group-theoretic approach for computing the statistics of non-reversal random walks (NRRW) on lattices. These framed walks evolve on proper crystallographic space groups. In a previous paper we introduced a convolution method for computing the statistics of NRRWs in which the convolution product is defined relative to the space-group operation. Here we use the corresponding concept of the fast Fourier transform for functions on crystallographic space groups together with a non-Abelian version of the convolution theorem. We develop the theory behind this technique and present numerical results for two-dimensional and three-dimensional lattices (square, cubic and diamond). In order to verify our results, the statistics of the end-to-end distance and the probability of ring closure are calculated and compared with results obtained in the literature for the random walks for which closed-form expressions exist. PMID:21037950

Skliros, Aris; Park, Wooram; Chirikjian, Gregory S

2010-01-01

16

Friendship, Group Size and Boundary Size: Small Group Spaces.  

ERIC Educational Resources Information Center

The results suggested group space boundaries increased with group size (from groups of one to two to four) if group members were strangers, but not if group members were friends. The only nonspatial variable found to correlate with boundary size was personal identity. (Author)

Edney, Julian J.; Grundmann, Michael J.

1979-01-01

17

Constructions of E_{vc} and E_{fbc} for groups acting on CAT(0) spaces  

E-print Network

If G is a group acting properly by semisimple isometries on a proper CAT(0) space X, then we build models for the classifying spaces E_{vc} and E_{fbc} under the additional assumption that the action of G has a well-behaved collection of axes in X. (This hypothesis is described in the paper.) We conjecture that the latter hypothesis is satisfied in a large range of cases. Our classifying spaces resemble those created by Connolly, Fehrman, and Hartglass for crystallographic groups G.

Farley, Daniel

2009-01-01

18

FUNDAMENTAL GROUPS AND COVERING SPACES ETHAN JERZAK  

E-print Network

FUNDAMENTAL GROUPS AND COVERING SPACES ETHAN JERZAK Abstract. In this paper, I will briefly develop) Date: August 22, 2008. 1 #12;2 ETHAN JERZAK the structure of a group; the constant loop is the identity

May, J. Peter

19

Crystallographic oxide phase identification of char deposits obtained from space shuttle Columbia window debris  

NASA Astrophysics Data System (ADS)

Char deposits on recovered fragments of space shuttle Columbia windowpanes were analyzed to further understand the events that occurred during orbiter reentry and breakup. The TEM analysis demonstrated that oxides of aluminum and titanium mixed with silicon oxides to preserve a history of thermal conditions to which portions of the vehicle were exposed. The presence of Ti during the beginning of the deposition process, along with the thermodynamic phase precipitation upon cool down, indicated that temperatures well above the Ti melt point were experienced. The stratified observations implied that additional exothermic reactions, expectedly metal combustion of a Ti-6Al-4V structure, had to occur for oxide formation. Results are significant for aerospace vehicles, where thermal protection system (TPS) breaches could cause material originally designed for substructural applications to be in direct path with reentry plasma.

Olivas, J. D.; Wright, M. C.; Christoffersen, R.; Cone, D. M.; McDanels, S. J.

2010-09-01

20

Space Station concept development group studies  

NASA Technical Reports Server (NTRS)

The NASA study activities in preparation for a Space Station began in the early 1970's. The early studies included many in-house NASA and contracted studies. A group of representatives from all the NASA Centers, titled the Space Station Concept Development Group (CDG) was involved in the studies which led to the initiation of the Space Station Program. The CDG studies were performed over a period of approximately one year and consisted of four phases. The initial phase had the objective to determine the functions required of the station as opposed to a configuration. The activities of the second phase were primarily concerned with a sizing of the facilities required for payloads and the resources necessary to support these mission payloads. The third phase of studies was designed to develop a philosophical approach to a number of areas related to autonomy, maintainability, operations and logistics, and verification. The fourth phase of the study was to be concerned with configuration assessment activities.

Powell, L. E.

1984-01-01

21

Guide to Space groups There are only 230 ways (space groups) to describe how identical objects can be  

E-print Network

Guide to Space groups There are only 230 ways (space groups) to describe how identical objects can but it gets better than that! If your structure contains a chrial center then any space group that has a mirror or an inversion operation can be rejected. Of the 230 space groups only 74 space groups

Meagher, Mary

22

GroupSpace 0.2.0  

NSDL National Science Digital Library

The Internet can serve as a communal gathering place, where like-minded community members can come together to discuss various pressing issues, share documents, take polls, and engage in the decision-making process as well. A recent project, GroupSpace, started at Stanford University as part of a research partnership with a local community organization, allows groups of individuals to do all of the above. As their mission statement suggests, the creation of the program is âÂÂto support the type of deliberation critical to the functioning of smaller, informal organizations in civil societyâÂÂ. It should be noted that this version of GroupSpace is a beta version.

23

Crystallographic Topology 2: Overview and Work in Progress  

SciTech Connect

This overview describes an application of contemporary geometric topology and stochastic process concepts to structural crystallography. In this application, crystallographic groups become orbifolds, crystal structures become Morse functions on orbifolds, and vibrating atoms in a crystal become vector valued Gaussian measures with the Radon-Nikodym property. Intended crystallographic benefits include new methods for visualization of space groups and crystal structures, analysis of the thermal motion patterns seen in ORTEP drawings, and a classification scheme for crystal structures based on their Heegaard splitting properties.

Johnson, C.K.

1999-08-01

24

UCLA IGPP Space Plasma Simulation Group  

NASA Technical Reports Server (NTRS)

During the past 10 years the UCLA IGPP Space Plasma Simulation Group has pursued its theoretical effort to develop a Mission Oriented Theory (MOT) for the International Solar Terrestrial Physics (ISTP) program. This effort has been based on a combination of approaches: analytical theory, large scale kinetic (LSK) calculations, global magnetohydrodynamic (MHD) simulations and self-consistent plasma kinetic (SCK) simulations. These models have been used to formulate a global interpretation of local measurements made by the ISTP spacecraft. The regions of applications of the MOT cover most of the magnetosphere: the solar wind, the low- and high-latitude magnetospheric boundary, the near-Earth and distant magnetotail, and the auroral region. Most recent investigations include: plasma processes in the electron foreshock, response of the magnetospheric cusp, particle entry in the magnetosphere, sources of observed distribution functions in the magnetotail, transport of oxygen ions, self-consistent evolution of the magnetotail, substorm studies, effects of explosive reconnection, and auroral acceleration simulations.

1998-01-01

25

Actuator grouping optimization on flexible space reflectors  

NASA Astrophysics Data System (ADS)

With the rapid advances in deployable membrane and mesh antenna technologies, the feasibility of developing large, lightweight reflectors has greatly improved. In order to achieve the required accuracy, precision surface control is needed on these lightweight reflectors. While studies have shown that domain control of space reflectors via Polyvinylidene Fluoride (PVDF) actuators is promising, the challenge is to realistically control a large number of distributed actuators with limited number of power supplies. In this research, a new En Mass Elimination method is synthesized to determine the optimal grouping of actuators when the actuator number exceeds the number of power supplies available. An analytical model is developed and the methodology is demonstrated numerically through system simulation on the derived model.

Hill, Jeffrey R.; Wang, K. W.; Fang, Houfei; Quijano, Ubaldo

2011-03-01

26

EXISTENTIALLY EQUIVALENT CYCLIC ULTRAMETRIC SPACES AND CYCLICALLY VALUED GROUPS.  

E-print Network

EXISTENTIALLY EQUIVALENT CYCLIC ULTRAMETRIC SPACES AND CYCLICALLY VALUED GROUPS. G. LELOUP Abstract we characterize existentially equivalence between cyclically ultrametric spaces, as well as existentially equivalence between generalized ultrametric spaces. We also describe classes of existentially

27

Group-to-Group Distance Collaboration: Examining the "Space Between"  

E-print Network

the constraints that exist when people communicate over media channels that limit social information. Access Grid technologies use interactive multi-media technologies with multicasting, showing multiple the challenges that group-to-group collaboration designers face in meeting requirements for supporting these new

Mark, Gloria

28

Space station group activities habitability module study  

NASA Technical Reports Server (NTRS)

This study explores and analyzes architectural design approaches for the interior of the Space Station Habitability Module (originally defined as Habitability Module 1 in Space Station Reference Configuration Decription, JSC-19989, August 1984). In the Research Phase, architectural program and habitability design guidelines are specified. In the Schematic Design Phase, a range of alternative concepts is described and illustrated with drawings, scale-model photographs and design analysis evaluations. Recommendations are presented on the internal architectural, configuration of the Space Station Habitability Module for such functions as the wardroom, galley, exercise facility, library and station control work station. The models show full design configurations for on-orbit performance.

Nixon, David

1986-01-01

29

Actuator grouping optimization on flexible space reflectors  

Microsoft Academic Search

With the rapid advances in deployable membrane and mesh antenna technologies, the feasibility of developing large, lightweight reflectors has greatly improved. In order to achieve the required accuracy, precision surface control is needed on these lightweight reflectors. While studies have shown that domain control of space reflectors via Polyvinylidene Fluoride (PVDF) actuators is promising, the challenge is to realistically control

Jeffrey R. Hill; K. W. Wang; Houfei Fang; Ubaldo Quijano

2011-01-01

30

SYMMETRIC SPACES OF THE NON-COMPACT TYPE : LIE GROUPS  

E-print Network

SYMMETRIC SPACES OF THE NON-COMPACT TYPE : LIE GROUPS by Paul-Emile PARADAN Abstract. -- In these notes, we give first a brief account to the theory of Lie groups. Then we consider the case of a smooth manifold with a Lie group of symmetries. When the Lie group acts transitively (e.g. the manifold

Paris-Sud XI, Université de

31

Actuator Grouping Optimization on Flexible Space Reflectors  

NASA Technical Reports Server (NTRS)

With the rapid advances in deployable membrane and mesh antenna technologies, the feasibility of developing large, lightweight reflectors has greatly improved. In order to achieve the required surface accuracy, precision surface control is needed on these lightweight reflectors. For this study, an analytical model is shown which combines a flexible Kapton reflector with Polyvinylidene fluoride (PVDF) actuators for surface control. Surface errors are introduced that are similar to real world scenarios, and a least squares control algorithm is developed for surface control. Experimental results on a 2.4 meter reflector show that while the analytical reflector model is generally correct, due to idiosyncrasies in the reflector it cannot be used for online control. A new method called the En Mass Elimination algorithm is used to determine the optimal grouping of actuators when the number of actuators in the system exceeds the number of power supplies available.

Hill, Jeffrey R.; Wang, K. W.; Fang, Houfei; Quijano, Ubaldo

2011-01-01

32

The space shuttle payload planning working groups. Volume 2: Atmospheric and space physics  

NASA Technical Reports Server (NTRS)

The findings of the Atmospheric and Space Physics working group of the space shuttle mission planning activity are presented. The principal objectives defined by the group are: (1) to investigate the detailed mechanisms which control the near-space environment of the earth, (2) to perform plasma physics investigations not feasible in ground-based laboratories, and (3) to conduct investigations which are important in understanding planetary and cometary phenomena. The core instrumentation and laboratory configurations for conducting the investigations are defined.

1973-01-01

33

The space shuttle payload planning working groups. Volume 10: Space technology  

NASA Technical Reports Server (NTRS)

The findings and recommendations of the Space Technology group of the space shuttle payload planning activity are presented. The elements of the space technology program are: (1) long duration exposure facility, (2) advanced technology laboratory, (3) physics and chemistry laboratory, (4) contamination experiments, and (5) laser information/data transmission technology. The space technology mission model is presented in tabular form. The proposed experiments to be conducted by each test facility are described. Recommended approaches for user community interfacing are included.

1973-01-01

34

Environmental interactions in space exploration: Environmental interactions working group  

NASA Technical Reports Server (NTRS)

With the advent of the Space Exploration Initiative, the possibility of designing and using systems on scales heretofore unattempted presents exciting new challenges in systems design and space science. The environments addressed by the Space Exploration Initiative include the surfaces of the Moon and Mars, as well as the varied plasma and field environments which will be encountered by humans and cargo enroute to these destinations. Systems designers will need to understand environmental interactions and be able to model these mechanisms from the earliest conceptual design stages through design completion. To the end of understanding environmental interactions and establishing robotic precursor mission requirements, an Environmental Interactions Working Group was established as part of the Robotic Missions Working Group. The working group is described, and its current activities are updated.

Kolecki, Joseph C.; Hillard, G. Barry

1992-01-01

35

Entanglement renormalization in free bosonic systems: real-space versus momentum-space renormalization group transforms  

E-print Network

The ability of entanglement renormalization (ER) to generate a proper real-space renormalization group (RG) flow in extended quantum systems is analysed in the setting of harmonic lattice systems in D=1 and D=2 spatial dimensions. A conceptual overview of the steps involved in momentum-space RG is provided and contrasted against the equivalent steps in the real-space setting. The real-space RG flow, as generated by ER, is compared against the exact results from momentum-space RG, including an investigation of a critical fixed point and the effect of relevant and irrelevant perturbations.

G. Evenbly; G. Vidal

2008-01-16

36

Group Fourier transform and the phase space path integral for finite dimensional Lie groups  

E-print Network

We formulate a notion of group Fourier transform for a finite dimensional Lie group. The transform provides a unitary map from square integrable functions on the group to square integrable functions on a non-commutative dual space. We then derive the first order phase space path integral for quantum mechanics on the group by using a non-commutative dual space representation obtained through the transform. Possible advantages of the formalism include: (1) The transform provides an alternative to the spectral decomposition via representation theory of Lie groups and the use of special functions. (2) The non-commutative dual variables are physically more intuitive, since despite the non-commutativity they are analogous to the corresponding classical variables. The work is expected, among other possible applications, to allow for the metric representation of Lorentzian spin foam models in the context of quantum gravity.

Matti Raasakka

2011-11-28

37

Crystallographic CourseWare  

NASA Astrophysics Data System (ADS)

Literature Cited

  1. International Tables for Crystallography: Volume A: Space Group Symmetry; Hanh, T., Ed.; D. Reidel: Boston, 1983.
  2. International Tables for Crystallography, Brief Teaching Edition of Volume A, Space-Group Symmetry, 3rd ed.; Hanh, T., Ed.; Dordrecht: Boston, 1993.
  3. Kastner, M. E. J. Appl. Crystallogr. 1999, 32, 327-331.
  4. Macromedia Director, version 6.5; Macromedia, Inc., San Francisco, CA; 1998.
  5. QuickTime, version 3.0; Apple Computer: Cupertino, CA, 1998.
  6. ToolBook II, Instructor, version 6.0; Asymetrix: Bellevue, WA, 1998.
  7. HyperCard 2.3.5; Apple Computer: Cupertino, CA, 1998.

Kastner, Margaret E.; Vasbinder, Eric; Kowalcyzk, Deborah; Jackson, Sean; Giammalvo, Joseph; Braun, James; Dimarco, Keith

2000-09-01

38

Metrics for comparison of crystallographic maps.  

PubMed

Numerical comparison of crystallographic contour maps is used extensively in structure solution and model refinement, analysis and validation. However, traditional metrics such as the map correlation coefficient (map CC, real-space CC or RSCC) sometimes contradict the results of visual assessment of the corresponding maps. This article explains such apparent contradictions and suggests new metrics and tools to compare crystallographic contour maps. The key to the new methods is rank scaling of the Fourier syntheses. The new metrics are complementary to the usual map CC and can be more helpful in map comparison, in particular when only some of their aspects, such as regions of high density, are of interest. PMID:25286844

Urzhumtsev, Alexandre; Afonine, Pavel V; Lunin, Vladimir Y; Terwilliger, Thomas C; Adams, Paul D

2014-10-01

39

Metrics for comparison of crystallographic maps  

PubMed Central

Numerical comparison of crystallographic contour maps is used extensively in structure solution and model refinement, analysis and validation. However, traditional metrics such as the map correlation coefficient (map CC, real-space CC or RSCC) sometimes contradict the results of visual assessment of the corresponding maps. This article explains such apparent contradictions and suggests new metrics and tools to compare crystallographic contour maps. The key to the new methods is rank scaling of the Fourier syntheses. The new metrics are complementary to the usual map CC and can be more helpful in map comparison, in particular when only some of their aspects, such as regions of high density, are of interest. PMID:25286844

Urzhumtsev, Alexandre; Afonine, Pavel V.; Lunin, Vladimir Y.; Terwilliger, Thomas C.; Adams, Paul D.

2014-01-01

40

Contractor renormalization group technology and exact Hamiltonian real-space renormalization group transformations  

Microsoft Academic Search

The contractor renormalization group method, a new approach to solving Hamiltonian lattice systems, is presented. The method defines a systematic and nonperturbative means of implementing Kadanoff-Wilson real-space renormalization group transformations using cluster expansion and contraction techniques. We illustrate the approach and demonstrate its effectiveness using scalar field theory, the Heisenberg antiferromagnetic chain, and the anisotropic Ising chain. Future applications to

Colin J. Morningstar; M. Weinstein

1996-01-01

41

CONFIGURATION SPACES AND BRAID GROUPS ON GRAPHS IN ROBOTICS  

E-print Network

CONFIGURATION SPACES AND BRAID GROUPS ON GRAPHS IN ROBOTICS ROBERT GHRIST School of Mathematics control schemes for Automated Guided Vehicles (robots) in industrial settings. In this announcement, we filtered through the robotics community [Lat91, KR90]. Surprisingly, topologists have been generally

Ghrist, Robert W.

42

The space shuttle payload planning working groups: Volume 9: Materials processing and space manufacturing  

NASA Technical Reports Server (NTRS)

The findings and recommendations of the Materials Processing and Space Manufacturing group of the space shuttle payload planning activity are presented. The effects of weightlessness on the levitation processes, mixture stability, and control over heat and mass transport in fluids are considered for investigation. The research and development projects include: (1) metallurgical processes, (2) electronic materials, (3) biological applications, and (4)nonmetallic materials and processes. Additional recommendations are provided concerning the allocation of payload space, acceptance of experiments for flight, flight qualification, and private use of the space shuttle.

1973-01-01

43

Structure of Escherichia coli ribonucleotide reductase R2 in space group P6[subscript 1]22  

SciTech Connect

A new crystal form of wild-type ribonucleotide reductase R2 from Escherichia coli was obtained. Crystals grow in space group P6{sub 1}22 with one R2 monomer in the asymmetric unit. A twofold crystallographic symmetry axis generates the physiological dimeric form of R2. Co-crystallization with CoCl{sub 2} or MnCl{sub 2} results in full occupancy of the dinuclear metal site. The structure of the Mn{sup II}-loaded form was determined to 2.6 {angstrom} resolution by molecular replacement. The crystallization conditions, backbone conformation, crystal-packing interactions and metal centers are compared with those of previously determined crystal forms.

Sommerhalter, Monika; Saleh, Lana; Bollinger Jr., J. Martin; Rosenzweig, Amy C. (NWU); (Penn)

2010-07-20

44

Topological classification of crystalline insulators with space group symmetry  

SciTech Connect

We show that in crystalline insulators, space group symmetry alone gives rise to a topological classification based on the discretization of electric polarization. Using C3 rotational symmetry as an example, we first prove that the polarization is discretized into three distinct classes, i.e., it can only take three inequivalent values. We then prove that these classes are topologically distinct. Therefore, a Z3 topological classification exists, with polarization as a topological class index. A concrete tight-binding model is derived to demonstrate the Z3 topological phase transition. Using first-principles calculations, we identify graphene on a BN substrate as a possible candidate to realize these Z3 topological states. To complete our analysis, we extend the classification of band structures to all 17 two-dimensional space groups. This work will contribute to a complete theory of symmetry-conserved topological phases and also elucidate topological properties of graphenelike systems.

Jadaun, Priyamvada [University of Texas at Austin; Xiao, Di [Carnegie Mellon University (CMU); Niu, Q. [University of Texas at Austin; Banerjee, Sanjay K. [University of Texas at Austin

2013-01-01

45

Differential calculus on quantum spaces and quantum groups  

SciTech Connect

A review of recent developments in the quantum differential calculus. The quantum group GL{sub q}(n) is treated by considering it as a particular quantum space. Functions on SL{sub q} (n) are defined as a subclass of functions on GL{sub q}(n). The case of SO{sub q}(n) is also briefly considered. These notes cover part of a lecture given at the XIX International Conference on Group Theoretic Methods in Physics, Salamanca, Spain 1992.

Zumino, B.

1992-12-10

46

Differential calculus on quantum spaces and quantum groups  

SciTech Connect

A review of recent developments in the quantum differential calculus. The quantum group GL[sub q](n) is treated by considering it as a particular quantum space. Functions on SL[sub q] (n) are defined as a subclass of functions on GL[sub q](n). The case of SO[sub q](n) is also briefly considered. These notes cover part of a lecture given at the XIX International Conference on Group Theoretic Methods in Physics, Salamanca, Spain 1992.

Zumino, B.

1992-12-10

47

Testing the Accuracy of Redshift Space Group Finding Algorithms  

E-print Network

Using simulated redshift surveys generated from a high resolution N-body cosmological structure simulation, we study algorithms used to identify groups of galaxies in redshift space. Two algorithms are investigated; both are friends-of-friends schemes with variable linking lengths in the radial and transverse dimensions. The chief difference between the algorithms is in the redshift linking length. The algorithm proposed by Huchra \\& Geller (1982) uses a generous linking length designed to find ``fingers of god'' while that of Nolthenius \\& White (1987) uses a smaller linking length to minimize contamination by projection. We find that neither of the algorithms studied is intrinsically superior to the other; rather, the ideal algorithm as well as the ideal algorithm parameters depend on the purpose for which groups are to be studied. The Huchra/Geller algorithm misses few real groups, at the cost of including some spurious groups and members, while the Nolthenius/White algorithm misses high velocity dispersion groups and members but is less likely to include interlopers in its group assignments. In a companion paper we investigate the accuracy of virial mass estimates and clustering properties of groups identified using these algorithms.

James J. Frederic

1994-09-07

48

Space station group activities habitability module study: A synopsis  

NASA Technical Reports Server (NTRS)

Space station habitability was studied by investigating crew activity routines, proximities, ergonomic envelopes, and group volumes. Ten alternative schematic interior designs were proposed. Preliminary conclusions include: (1) in-service interior modifications may be necessary and should be planned for; (2) design complexity will be increased if the module cluster is reduced from five to three; (3) the increased crew circulation attendant upon enhancement of space station activity may produce human traffic bottlenecks and should be planned for; (4) a single- or two-person quiet area may be desirable to provide crew members with needed solitude during waking hours; and (5) the decision to choose a two-shift or three-shift daily cycle will have a significant impact on the design configuration and operational efficiency of the human habitat.

Nixon, David; Glassman, Terry

1987-01-01

49

Hardy spaces on Lie groups of polynomial growth A.F.M. ter Elst1  

E-print Network

Hardy spaces on Lie groups of polynomial growth A.F.M. ter Elst1 , Derek W. Robinson2 and Yueping-order, subelliptic operators on Lie groups with polynomial growth. August 2004 Keywords: Lie groups, Hardy spaces of Hardy spaces on Lie groups of polynomial growth. Let G be a connected Lie group with Lie algebra g. One

Eindhoven, Technische Universiteit

50

Contractor renormalization group technology and exact Hamiltonian real-space renormalization group transformations  

SciTech Connect

The contractor renormalization group method, a new approach to solving Hamiltonian lattice systems, is presented. The method defines a systematic and nonperturbative means of implementing Kadanoff-Wilson real-space renormalization group transformations using cluster expansion and contraction techniques. We illustrate the approach and demonstrate its effectiveness using scalar field theory, the Heisenberg antiferromagnetic chain, and the anisotropic Ising chain. Future applications to the Hubbard and {ital t}-{ital J} models and lattice gauge theory are discussed. {copyright} {ital 1996 The American Physical Society.}

Morningstar, C.J. [Department of Physics, University of California at San Diego, La Jolla, California 92093-0319 (United States)] [Department of Physics, University of California at San Diego, La Jolla, California 92093-0319 (United States); Weinstein, M. [Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 (United States)] [Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309 (United States)

1996-09-01

51

Various cross-reactivity of the grass pollen group 4 allergens: crystallographic study of the Bermuda grass isoallergen Cyn d 4.  

PubMed

The structure of Cyn d 4, the group 4 allergen from Bermuda grass, is reported at 2.15 Å resolution and is the first crystal structure of a naturally isolated pollen allergen. A conserved N-terminal segment that is only present in the large isoallergens forms extensive interactions with surrounding residues and hence greatly enhances the structural stability of the protein. Cyn d 4 contains an FAD cofactor that is covalently linked to His88 and Cys152. To date, all identified bicovalent flavoproteins are oxidases and their substrates are either sugars or secondary metabolites. A deep large hydrophobic substrate-binding cleft is present. Thus, Cyn d 4 may be an oxidase that is involved in the biosynthesis of a pollen-specific metabolite. Cyn d 4 shares ~70% sequence identity with the Pooideae group 4 allergens. Various cross-reactivities between grass pollen group 4 allergens have previously been demonstrated using sera from allergic patients. The protein surface displays an unusually large number of positively charged clusters, reflecting the high pI of ~10. 38 decapeptides that cover the solvent-accessible sequences did not show any significant IgE-binding activity using sera with high Cyn d 4 reactivity from four patients, suggesting that the IgE epitopes of Cyn d 4 are predominantly conformational in nature. Several group 4 structures were then modelled and their potential cross-reactive and species-specific IgE epitopes were proposed. PMID:22993084

Huang, Tse-Hao; Peng, Ho-Jen; Su, Song-Nan; Liaw, Shwu-Huey

2012-10-01

52

Mineralogical, chemical, and crystallographic properties of supergene jarosite-group minerals from the Xitieshan Pb-Zn sulfide deposit, northern Tibetan Plateau, China  

USGS Publications Warehouse

Supergene jarosite-group minerals are widespread in weathering profiles overlying Pb-Zn sulfide ores at Xitieshan, northern Tibetan Plateau, China. They consist predominantly of K-deficient natrojarosite, with lesser amounts of K-rich natrojarosite and plumbojarosite. Electron microprobe (EMP) analyses, scanning electron microcopy (SEM) investigation, and X-ray mapping reveal that the jarosite-group minerals are characterized by spectacular oscillatory zoning composed of alternating growth bands of K-deficient and K-bearing natrojarosite (K2O >1 wt.%). Plumbojarosite, whenever present, occurs as an overgrowth in the outermost bands, and its composition can be best represented by K0.29Na0.19Pb0.31Fe2.66Al0.22(SO4)1.65(PO4)0.31(AsO4)0.04(OH)7.37. The substitution of monovalent for divalent cations at the A site of plumbojarosite is charge balanced by the substitution of five-valent for six-valent anions in XO,4/sub> at the X site. Thermogravimetric analysis (TGA) of representative samples reveal mass losses of 11.46 wt.% at 446.6 °C and 21.42 wt.% at 683.4 °C due to dehydroxylation and desulfidation, respectively. TGA data also indicate that the natrojarosite structure collapses at 446.6 °C, resulting in the formation of NaFe(SO4)2 and minor hematite. The decomposition products of NaFe(SO4) are hematite and Na,2SO4. Powder X-ray diffraction (XRD) analyses show that the jarosite-group minerals have mean unit-cell parameters of a=7.315 ä and c=016.598 ä. XRD and EMP data support the view that substitutions of Na for K in the A site and full Fe occupancy in the B site can considerably decrease the unit-cell parameter c, but only slightly increase a. The results from this study suggest that the observed oscillatory zoning of jarosite-group minerals at Xitieshan resulted mainly from substitutions of K for Na at the A site and P for S at the X site.

Chen, Lei; Li, Jian-Wei; Rye, Robert O.; Benzel, William H.; Lowers, H.A.; He, Ming-Zhong

2013-01-01

53

Phaser crystallographic software  

PubMed Central

Phaser is a program for phasing macromolecular crystal structures by both molecular replacement and experimental phasing methods. The novel phasing algorithms implemented in Phaser have been developed using maximum likelihood and multivariate statistics. For molecular replacement, the new algorithms have proved to be significantly better than traditional methods in discriminating correct solutions from noise, and for single-wavelength anomalous dispersion experimental phasing, the new algorithms, which account for correlations between F + and F ?, give better phases (lower mean phase error with respect to the phases given by the refined structure) than those that use mean F and anomalous differences ?F. One of the design concepts of Phaser was that it be capable of a high degree of automation. To this end, Phaser (written in C++) can be called directly from Python, although it can also be called using traditional CCP4 keyword-style input. Phaser is a platform for future development of improved phasing methods and their release, including source code, to the crystallographic community. PMID:19461840

McCoy, Airlie J.; Grosse-Kunstleve, Ralf W.; Adams, Paul D.; Winn, Martyn D.; Storoni, Laurent C.; Read, Randy J.

2007-01-01

54

Distributed interactive communication in simulated space-dwelling groups.  

PubMed

This report describes the development and preliminary application of an experimental test bed for modeling human behavior in the context of a computer generated environment to analyze the effects of variations in communication modalities, incentives and stressful conditions. In addition to detailing the methodological development of a simulated task environment that provides for electronic monitoring and recording of individual and group behavior, the initial substantive findings from an experimental analysis of distributed interactive communication in simulated space dwelling groups are described. Crews of three members each (male and female) participated in simulated "planetary missions" based upon a synthetic scenario task that required identification, collection, and analysis of geologic specimens with a range of grade values. The results of these preliminary studies showed clearly that cooperative and productive interactions were maintained between individually isolated and distributed individuals communicating and problem-solving effectively in a computer-generated "planetary" environment over extended time intervals without benefit of one another's physical presence. Studies on communication channel constraints confirmed the functional interchangeability between available modalities with the highest degree of interchangeability occurring between Audio and Text modes of communication. The effects of task-related incentives were determined by the conditions under which they were available with Positive Incentives effectively attenuating decrements in performance under stressful time pressure. PMID:14983895

Brady, Joseph V; Hienz, Robert D; Hursh, Steven R; Ragusa, Leonard C; Rouse, Charles O; Gasior, Eric D

2004-03-01

55

MOVING A MEDIA SPACE INTO THE REAL WORLD THROUGH GROUP-ROBOT INTERACTION  

E-print Network

MOVING A MEDIA SPACE INTO THE REAL WORLD THROUGH GROUP-ROBOT INTERACTION James E. Young, Gregor McEwan, Saul Greenberg, Ehud Sharlin1 Abstract New generation media spaces let group members see each other propose the AIBO Surrogate--a robotic interface for a media space group, allowing members to extend

56

MOVING A MEDIA SPACE INTO THE REAL WORLD THROUGH GROUP-ROBOT INTERACTION  

E-print Network

social entity, a surrogate of the media space group within the physical world, representing selectedMOVING A MEDIA SPACE INTO THE REAL WORLD THROUGH GROUP-ROBOT INTERACTION James E. Young, Gregor McEwan, Saul Greenberg, Ehud Sharlin1 Abstract New generation media spaces let group members see each other

Greenberg, Saul

57

Crystallographic and magnetic properties of UPdSn  

SciTech Connect

A single crystal of the intermetallic compound UPdSn has been studied by means of neutron diffraction using the white-beam Laue diffractometer (single-crystal diffractometer) at the Los Alamos spallation neutron source. Data were taken in the paramagnetic phase at 55 K and just below the Neel point at 37 K. The crystallographic data refine well within the space group [ital P]6[sub 3][ital mc] and confirm the results obtained previously on powders, namely that the Pd and Sn atoms are ordered. At low temperature, UPdSn undergoes two phase transitions at 40 and 25 K to complicated noncollinear antiferromagnetic structures. All three pairs of magnetic domains are observed, in roughly equal populations, in the intermediate-temperature orthorhombic magnetic structure (phase I). A uranium moment of 0.863[mu][sub [ital B

Johnson, S.W.; Robinson, R.A. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Nakotte, H.; Brueck, E.; de Boer, F.R. (Van der Waals-Zeeman Laboratorium, University of Amsterdam, 1018 XE, Amsterdam (Netherlands)); Larson, A.C. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))

1993-05-15

58

On space-time code design with a conditional PIC group decoding  

Microsoft Academic Search

Space-time code designs based on a partial interference cancellation (PIC) group decoding has been recently proposed. The PIC group decoding complexity depends on the group size and is between the lowest linear receiver complexity and the highest ML decoding complexity. The symbol rate for a space-time code achieving full diversity with the PIC group decoding is also between those for

Tianyi Xu; Xiang-Gen Xia

2010-01-01

59

The space shuttle payload planning working groups. Volume 1: Astronomy  

NASA Technical Reports Server (NTRS)

The space astronomy missions to be accomplished by the space shuttle are discussed. The principal instrument is the Large Space Telescope optimized for the ultraviolet and visible regions of the spectrum, but usable also in the infrared. Two infrared telescopes are also proposed and their characteristics are described. Other instruments considered for the astronomical observations are: (1) a very wide angle ultraviolet camera, (2) a grazing incidence telescope, (3) Explorer-class free flyers to measure the cosmic microwave background, and (4) rocket-class instruments which can fly frequently on a variety of missions. The stability requirements of the space shuttle for accomplishing the astronomy mission are defined.

1973-01-01

60

Scanning of magnetic space groups and the analysis of non-magnetic domain walls.  

PubMed

Similarly to atomic positions in a crystal being fixed, or at least constrained by the space group of that crystal, the displacements of atoms in a domain wall are determined or constrained by the symmetry of the wall given by the sectional layer group of the corresponding domain pair. The sectional layer group can be interpreted as comprised of operations that leave invariant a plane transecting two overlapping structures, the domain states of the two domains adhering to the domain wall. The procedure of determining the sectional layer groups for all orientations and positions of a transecting plane is called scanning of the space group. Scanning of non-magnetic space groups has been described and tabulated. It is shown here that the scanning of magnetic groups can be determined from that of non-magnetic groups. The information provided by scanning of magnetic space groups can be utilized in the symmetry analysis of domain walls in non-magnetic crystals since, for any dichromatic space group, which expresses the symmetry of overlapped structures of two non-magnetic domains, there exists an isomorphic magnetic space group. Consequently, a sectional layer group of a magnetic space group expresses the symmetry of a non-magnetic domain wall. Examples of this are given in the symmetry analysis of ferroelectric domain walls in non-magnetic perovskites. PMID:17703074

Janovec, V; Litvin, D B

2007-09-01

61

The NASA EEE parts assurance group (NEPAG) - An evolving approach to maximizing space parts assurance resources  

Microsoft Academic Search

This paper describes the activities of the National Aeronautics and Space Administration's (NASA's) Electrical, Electronic and Electromechanical (EEE) Parts Assurance Group (NEPAG) in its role as a resource sharing and coordinating force in EEE Parts assurance for space flight missions. NEPAG is a new organization, barely two years old. The EEE parts world for space applications faces a number of

M. J. Sampson

2002-01-01

62

The birth of an infant decreases group spacing in a zoo-housed lowland gorilla group (Gorilla gorilla gorilla).  

PubMed

Changes in group composition can alter the behavior of social animals such as gorillas. Although gorilla births are presumed to affect group spacing patterns, there is relatively little data about how these events affect gorilla group cohesion. We investigated how members of a western lowland gorilla group (n?=?6) at Lincoln Park Zoo (Chicago, IL, USA) spaced themselves prior to and after the birth of an infant, to investigate changes in group cohesion. Gorillas were housed in an indoor-outdoor enclosure in which access to the outdoors was permitted when temperatures exceeded 5°C. We recorded spatial locations of each group member using 30-min group scans on tablet computers with an electronic map interface, as well as noting their access to outdoor areas. Data from the 4 months following the birth was compared to a control period corresponding to early pregnancy. We measured distances between all possible group dyads for each scan and subsequently calculated a mean distance between all group members. An ANOVA revealed that access to the outdoors had no effect on group spacing (F(1,56)?=?0.066, P?=?0.799). However, the presence of an infant resulted in a significant reduction in inter-individual distance (F(1,56)?=?23.988, P?=?0.000), decreasing inter-individual spacing by 12.5%. This information helps characterize the behavioral impact of a new birth on captive gorilla social structure and could potentially inform future management of breeding gorilla groups. Zoo Biol. 33:471-474, 2014. © 2014 Wiley Periodicals Inc. PMID:25130595

Kurtycz, Laura M; Shender, Marisa A; Ross, Stephen R

2014-09-01

63

Iterative Spatial Sequence Estimator for Multi-Group Space Time Trellis Coded Systems  

E-print Network

Iterative Spatial Sequence Estimator for Multi-Group Space Time Trellis Coded Systems Samir Al fewer than what V-BLAST algorithm requires. By applying reduced state sequence estimation, complexity for decoding multi-group space time trellis coded systems. These systems consider a single user who transmits

Al-Ghadhban, Samir

64

Invariant-theoretic method for calculating Clebsch-Gordan coefficients for space groups  

SciTech Connect

A new invariant-theoretic method to directly calculate Clebsch-Gordan coefficients for space and point groups representations is proposed. The method is exemplified with the space groups O{sub h}{sup 5} and D{sub 6h}{sup 1}. 34 refs.

Aizenberg, A.Ya.; Gufan, Yu.M. [North Caucasus Research Center, Rostov-na-Donu (Russian Federation)

1995-03-01

65

Characterization of Shift-Invariant Spaces on a Class of Nilpotent Lie Groups with Applications  

E-print Network

Characterization of Shift-Invariant Spaces on a Class of Nilpotent Lie Groups with Applications Bradley Currey, Azita Mayeli , Vignon Oussa March 2, 2013 Abstract Given a simply connected nilpotent Lie-invariant spaces. Keywords: Nilpotent Lie groups; shift-invariant subspaces; frame and Reisz bases. 1 Introduction

Currey, Brad

66

On Full Diversity Space-Time Block Codes with Partial Interference Cancellation Group Decoding  

Microsoft Academic Search

In this paper, we propose a partial interference cancellati on (PIC) group decoding for linear disper- sive space-time block codes (STBC) and a design criterion for the codes to achieve full diversity when the PIC group decoding is used at the receiver. A PIC group decoding decodes the symbols embedded in an STBC by dividing them into several groups and

Xiaoyong Guo; Xiang-Gen Xia

2008-01-01

67

On full diversity space-time block codes with partial interference cancellation group decoding  

Microsoft Academic Search

In this paper, we propose a partial interference cancellation (PIC) group decoding strategy\\/scheme for linear dispersive space-time block codes (STBC) and a design criterion for the codes to achieve full diversity when the PIC group decoding is used at the receiver. A PIC group decoding decodes the symbols embedded in an STBC by dividing them into several groups and decoding

Xiaoyong Guo; Xiang-Gen Xia

2009-01-01

68

Polyimides Containing Pendent Phosphine Oxide Groups for Space Applications  

NASA Technical Reports Server (NTRS)

As part of an ongoing materials development activity to produce high performance polymers that are durable to the space environment, phosphine oxide containing polyimides have been under investigation. A novel dianhydride was prepared from 2,5-dihydroxyphenyldiphenylphosphine oxide in good yield. The dianhydride was reacted with commercially available diamines, and a previously reported diamine was reacted with commercially available dianhydrides to prepare isomeric polyimides. The physical and mechanical properties, particularly thermal and optical properties, of the polymers were determined. One material exhibited a high glass transition temperature, high tensile properties, and low solar absorptivity. The chemistry, physical, and mechanical properties of these resins will be discussed.

Thompson, C. M.; Smith, J. G., Jr.; Watson, K. A.; Connell, J. W.

2002-01-01

69

The space shuttle payload planning working groups. Volume 6: Communications and navigation  

NASA Technical Reports Server (NTRS)

The findings of the Communications and Navigation working group of the space shuttle payload planning activity are presented. The basic goals to be accomplished are to increase the use of space systems and to develop new space capabilities for providing communication and navigation services to the user community in the 1980 time period. Specific experiments to be conducted for improving space communication and navigation capabilities are defined. The characteristics of the experimental equipment required to accomplish the mission are discussed.

1973-01-01

70

Marathons versus Spaced Groups: Skin Conductance and the Effects of Time Distribution on Encounter Group Learning.  

ERIC Educational Resources Information Center

Randomly assigned 41 students to 2 twice-weekly groups, which met for 3 hours eight times; 2 marathons, which met continuously for 24 hours; and nontreatment control group. Treatment groups had significant positive changes on 14 of 15 measured personality variables between pre- and post-test, and positive change on all dependent measures between…

Loomis, Thomas P.

1988-01-01

71

Exploration of the Chemical Space of Group 4 Polymer Dielectrics  

NASA Astrophysics Data System (ADS)

The current standards for capacitive energy storage applications are polypropylene (PP) and polyethylene (PE) which have large band gap and high breakdown strength, but a small dielectric constant. The envisaged next generation dielectric should provide high dielectric constant, while still preserving the insulating characteristics of PP and PE. To meet these growing needs, we use high throughput density functional theory (DFT) calculations in combination with machine learning (ML) methods to identify classes of polymers with large dielectric constant and band gap. In our work, we consider various possible local chemical modifications to polyethylene (PE). To be specific, we allow the -CH2- unit in the PE backbone segment to be replaced by -SiF2-, -SiCl2-, -GeF2-, -GeCl2-, -SnF2-, or -SnCl2- units in a systematic manner. High throughput methods were used first to accurately determine the dielectric constant and band gap of the chemically modified PE chains for a set of limited compositions and configurations. ML methods were then used to predict the properties of systems spanning a much larger part of the configurational and compositional space. A set of most promising PE modifications (with simultaneously large dielectric constant and band gap) is identified using this strategy.

Wang, Chenchen; Pilania, Ghanshyam; Ramprasad, Rampi

2013-03-01

72

MCMC-Particle-based group tracking of space objects within Bayesian framework  

NASA Astrophysics Data System (ADS)

With the intense increase in space objects, especially space debris, it is necessary to efficiently track and catalog the extensive dense clusters of space objects. As the main instrument for low earth orbit (LEO) space surveillance, ground-based radar system is usually limited by its resolution while tracking small space debris with high density. Thus, the obtained measurement information could have been seriously missed, which makes the traditional tracking method inefficient. To address this issue, we conceived the concept of group tracking. For group tracking, the overall tendency of the group objects is expected to be revealed, and the trajectories of individual objects are simultaneously reconstructed explicitly. According to model the interaction between the group center and individual trajectories using the Markov random field (MRF) within Bayesian framework, the objects' number and individual trajectory can be estimated more accurately in the condition of high miss alarm probability. The Markov chain Monte Carlo (MCMC)-Particle algorithm was utilized for solving the Bayesian integral problem. Furthermore, we introduced the mechanism for describing the behaviors of groups merging and splitting, which can expand the single group tracking algorithm to track variable multiple groups. Finally, simulation of the group tracking of space objects was carried out to validate the efficiency of the proposed method.

Huang, Jian; Hu, Weidong

2014-01-01

73

Compound Poisson Processes and Lévy Processes in Groups and Symmetric Spaces  

Microsoft Academic Search

A sample path description of compound Poisson processes on groups is given and applied to represent Lévy processes on connected Lie groups as almost sure limits of sequences of Brownian motions with drift interlaced with random jumps. We obtain spherically symmetric Lévy processes in Riemannian symmetric spaces of the form M=G\\\\K, where G is a semisimple Lie group and K

David Applebaum

2000-01-01

74

Acyclicity of the groups of homeomorphisms of the Menger compact spaces  

Microsoft Academic Search

Let k be the k-dimensional Menger compact space. We show that the group Homeo ( k) of homeomorphisms of k is acyclic. Introduction. The homology of groups of homeomorphisms, which has been studied by many authors, is strongly related to characteristic classes for various structures. A theorem of Mather (13) says that the group Homeoc (R n ) of homeomor-

VLAD SERGIESCU; TAKASHI TSUBOI

1996-01-01

75

Space group revsion of the triclinic polymorph of salicyl-aldehyde azine  

PubMed Central

The structure of the title compound, C14H12N2O2 {systematic name: 2,2?-[hydrazinediylidenebis(methanylyl­idene)]diphen­ol}, has already been determined in the triclinic space group P with Z = 4 [El-Medani, Aboaly, Abdalla & Ramadan (2004 ?). Spectrosc. Lett. 37, 619–632]. However, the correct space group should be P21/c with Z = 4. This structure is a new polymorph of the already known monoclinic polymorph of salicyladehyde azine, which crystallizes in space group P21/n with Z = 2. The benzene rings form a dihedral angle of 46.12?(9)°. Two intramolucular O—H?N hydrogen bonds occur. PMID:22346901

Saeed, Aamer; Bolte, Michael; Arshad, Muhammad

2012-01-01

76

Iterative Spatial Sequence Estimator for Multi-Group Space Time Trellis  

E-print Network

1 Iterative Spatial Sequence Estimator for Multi-Group Space Time Trellis Coded Systems Samir N. Al GK Multi-Group Space Time Trellis Decoder1x iNx 1x KNx B1 BK y1 y2 yM-1 yM 1B% KB% MIMO Fading STTE GK Multi-Group Space Time Trellis Decoder1x iNx 1x KNx B1 BK y1 y2 yM-1 yM 1B% KB% MIMO Fading

Al-Ghadhban, Samir

77

Unusual space-group pseudo symmetry in crystals of human phosphopantothenoylcysteine decarboxylase  

SciTech Connect

Phosphopantothenoylcysteine (PPC) decarboxylase is an essential enzyme in the biosynthesis of coenzyme A and catalyzes the decarboxylation of PPC to phosphopantetheine. Human PPC decarboxylase has been expressed in Escherichia coli, purified and crystallized. The Laue class of the diffraction data appears to be {bar 3}m, suggesting space group R32 with two monomers per asymmetric unit. However, the crystals belong to the space group R3 and the asymmetric unit contains four monomers. The structure has been solved using molecular replacement and refined to a current R factor of 29%. The crystal packing can be considered as two interlaced lattices, each consistent with space group R32 and with the corresponding twofold axes parallel to each other but separated along the threefold axis. Thus, the true space group is R3 with four monomers per asymmetric unit.

Manoj, N.; Ealick, S.E. (Cornell)

2010-12-01

78

Stable splittings, spaces of representations and almost commuting elements in Lie groups  

NASA Astrophysics Data System (ADS)

In this paper the space of almost commuting elements in a Lie group is studied through a homotopical point of view. In particular a stable splitting after one suspension is derived for these spaces and their quotients under conjugation. A complete description for the stable factors appearing in this splitting is provided for compact connected Lie groups of rank one.By using symmetric products, the colimits $\\Rep(\\Z^n, SU)$, $\\Rep(\\Z^n,U)$ and $\\Rep(\\Z^n, Sp)$ are explicitly described as finite products of Eilenberg-MacLane spaces.

Adem, Alejandro; Cohen, Frederick R.; Gómez, José Manuel

2010-06-01

79

Crystallographic and magnetic properties of UPdSn  

SciTech Connect

A single crystal of the intermetallic compound UPdSn has been studied by means of neutron diffraction using the white-beam Laue diffractometer SCD at the Los Alamos spallation neutron source. Data were taken in the paramagnetic phase at 55K and just below the Neel point at 37K. The crystallographic data refine well within the space group P6{sub 3}mc and confirm the results obtained previously on powders, namely that the Pd and Sn atoms are ordered. At low temperature, UPdSn undergoes two phase transitions at 40K and 25K to complicated non-collinear antiferromagnetic structures. All three pairs of magnetic domains are observed, in roughly equal populations, in the intermediate-temperature orthorhombic magnetic structure (Phase 1). We obtain a uranium moment of 0.863 {mu}{sub B} and canting angles {phi} = 57.52{degrees} and {phi} = 18.63{degree}, in reasonable agreement with previous powder neutron data for this temperature. The observed form factor is characteristic of the tetravalent f{sup 2} configuration.

Johnson, S.W.; Robinson, R.A.; Larson, A.C. [Los Alamos National Lab., NM (United States); Nakotte, H.; Brueck, E.; de Boer, F.R. [Amsterdam Univ. (Netherlands). Zeeman Lab.

1992-09-01

80

Crystallographic and magnetic properties of UPdSn  

SciTech Connect

A single crystal of the intermetallic compound UPdSn has been studied by means of neutron diffraction using the white-beam Laue diffractometer SCD at the Los Alamos spallation neutron source. Data were taken in the paramagnetic phase at 55K and just below the Neel point at 37K. The crystallographic data refine well within the space group P6{sub 3}mc and confirm the results obtained previously on powders, namely that the Pd and Sn atoms are ordered. At low temperature, UPdSn undergoes two phase transitions at 40K and 25K to complicated non-collinear antiferromagnetic structures. All three pairs of magnetic domains are observed, in roughly equal populations, in the intermediate-temperature orthorhombic magnetic structure (Phase 1). We obtain a uranium moment of 0.863 {mu}{sub B} and canting angles {phi} = 57.52{degrees} and {phi} = 18.63{degree}, in reasonable agreement with previous powder neutron data for this temperature. The observed form factor is characteristic of the tetravalent f{sup 2} configuration.

Johnson, S.W.; Robinson, R.A.; Larson, A.C. (Los Alamos National Lab., NM (United States)); Nakotte, H.; Brueck, E.; de Boer, F.R. (Amsterdam Univ. (Netherlands). Zeeman Lab.)

1992-01-01

81

Functional gene groups are concentrated within chromosomes, among chromosomes and in the nuclear space  

E-print Network

1 Functional gene groups are concentrated within chromosomes, among chromosomes and in the nuclear:+972-3-6405384 Keywords: chromosomes organization, gene function, chromosome conformation, spatial;2 Functional gene groups are concentrated within chromosomes, among chromosomes and in the nuclear space

Shamir, Ron

82

Challenges in Teaching Space Physics to Different Target Groups From Space Weather Forecasters to Heavy-weight Theorists  

NASA Astrophysics Data System (ADS)

Plasma physics as the backbone of space physics is difficult and thus the space physics students need to have strong foundations in general physics, in particular in classical electrodynamics and thermodynamics, and master the basic mathematical tools for physicists. In many universities the number of students specializing in space physics at Master's and Doctoral levels is rather small and the students may have quite different preferences ranging from experimental approach to hard-core space plasma theory. This poses challenges in building up a study program that has both the variety and depth needed to motivate the best students to choose this field. At the University of Helsinki we require all beginning space physics students, regardless whether they enter the field as Master's or Doctoral degree students, to take a one-semester package consisting of plasma physics and its space applications. However, some compromises are necessary. For example, it is not at all clear, how thoroughly Landau damping should be taught at the first run or how deeply should the intricacies of collisionless reconnection be discussed. In both cases we have left the details to an optional course in advanced space physics, even with the risk that the student's appreciation of, e.g., reconnection may remain at the level of a magic wand. For learning experimental work, data analysis or computer simulations we have actively pursued arrangements for the Master's degree students to get a summer employments in active research groups, which usually lead to the Master's theses. All doctoral students are members of research groups and participate in experimental work, data analysis, simulation studies or theory development, or any combination of these. We emphasize strongly "learning by doing" all the way from the weekly home exercises during the lecture courses to the PhD theses which in Finland consist typically of 4-6 peer-reviewed articles with a comprehensive introductory part.

Koskinen, H. E.

2008-12-01

83

The quaternionic affine group and related continuous wavelet transforms on complex and quaternionic Hilbert spaces  

NASA Astrophysics Data System (ADS)

By analogy with the real and complex affine groups, whose unitary irreducible representations are used to define the one- and two-dimensional continuous wavelet transforms, we study here the quaternionic affine group and construct its unitary irreducible representations. These representations are constructed both on a complex and on a quaternionic Hilbert space. As in the real and complex cases, the representations for the quaternionic group also turn out to be square-integrable. Using these representations we construct quaternionic wavelets and continuous wavelet transforms on both the complex and quaternionic Hilbert spaces.

Ali, S. Twareque; Thirulogasanthar, K.

2014-06-01

84

National facilities study. Volume 5: Space research and development facilities task group  

NASA Technical Reports Server (NTRS)

With the beginnings of the U.S. space program, there was a pressing need to develop facilities that could support the technology research and development, testing, and operations of evolving space systems. Redundancy in facilities that was once and advantage in providing flexibility and schedule accommodation is instead fast becoming a burden on scarce resources. As a result, there is a clear perception in many sectors that the U.S. has many space R&D facilities that are under-utilized and which are no longer cost-effective to maintain. At the same time, it is clear that the U.S. continues to possess many space R&D facilities which are the best -- or among the best -- in the world. In order to remain world class in key areas, careful assessment of current capabilities and planning for new facilities is needed. The National Facility Study (NFS) was initiated in 1992 to develop a comprehensive and integrated long-term plan for future aerospace facilities that meets current and projected government and commercial needs. In order to assess the nation's capability to support space research and development (R&D), a Space R&D Task Group was formed. The Task Group was co-chaired by NASA and DOD. The Task Group formed four major, technologically- and functionally- oriented working groups: Human and Machine Operations; Information and Communications; Propulsion and Power; and Materials, Structures, and Flight Dynamics. In addition to these groups, three supporting working groups were formed: Systems Engineering and Requirements; Strategy and Policy; and Costing Analysis. The Space R&D Task Group examined several hundred facilities against the template of a baseline mission and requirements model (developed in common with the Space Operations Task Group) and a set of excursions from the baseline. The model and excursions are described in Volume 3 of the NFS final report. In addition, as a part of the effort, the group examined key strategic issues associated with space R&D facilities planning for the U.S., and these are discussed in Section 4 of this volume.

1994-01-01

85

Crystallization and preliminary X-ray crystallographic studies of dipeptidyl aminopeptidase BII from Pseudoxanthomonas mexicana WO24.  

PubMed

Dipeptidyl aminopeptidase BII from Pseudoxanthomonas mexicana WO24 (DAP BII) is able to cleave a variety of dipeptides from the amino-terminus of substrate peptides. For crystallographic studies, DAP BII was overproduced in Escherichia coli, purified and crystallized using the hanging-drop vapour-diffusion method. X-ray diffraction data to 2.3 Å resolution were collected using an orthorhombic crystal form belonging to space group P2(1)2(1)2(1), with unit-cell parameters a = 76.55, b = 130.86, c = 170.87 Å. Structural analysis by the multi-wavelength anomalous diffraction method is in progress. PMID:24637761

Sakamoto, Yasumitsu; Suzuki, Yoshiyuki; Iizuka, Ippei; Tateoka, Chika; Roppongi, Saori; Okada, Hirofumi; Nonaka, Takamasa; Morikawa, Yasushi; Nakamura, Kazuo T; Ogasawara, Wataru; Tanaka, Nobutada

2014-02-01

86

Constructions of E_{vc} and E_{fbc} for groups acting on CAT(0) spaces  

Microsoft Academic Search

If G is a group acting properly by semisimple isometries on a proper CAT(0) space X, then we build models for the classifying spaces E_{vc} and E_{fbc} under the additional assumption that the action of G has a well-behaved collection of axes in X. (This hypothesis is described in the paper.) We conjecture that the latter hypothesis is satisfied in

Daniel Farley

2009-01-01

87

Space group revsion of the triclinic polymorph of salicyl-aldehyde azine.  

PubMed

The structure of the title compound, C(14)H(12)N(2)O(2) {systematic name: 2,2'-[hydrazinediylidenebis(methanylyl-idene)]diphen-ol}, has already been determined in the triclinic space group P[Formula: see text] with Z = 4 [El-Medani, Aboaly, Abdalla & Ramadan (2004 ?). Spectrosc. Lett.37, 619-632]. However, the correct space group should be P2(1)/c with Z = 4. This structure is a new polymorph of the already known monoclinic polymorph of salicyladehyde azine, which crystallizes in space group P2(1)/n with Z = 2. The benzene rings form a dihedral angle of 46.12?(9)°. Two intramolucular O-H?N hydrogen bonds occur. PMID:22346901

Saeed, Aamer; Bolte, Michael; Arshad, Muhammad

2012-02-01

88

Normal subgroups of even index in an NEC group  

Microsoft Academic Search

1. Introduction. By a non-euclidean crystallographic group (NEC group) we mean a discrete subgroup F of the isometries group of the non-euclidean plane U (including the orientation reversing isometries, namely reflections and glide-reflections), with compact quotient space. The first results on subgroups of an NEC group are due to Hoare f5], and Hoare, Karras and Solitar [6]. These were developed

J. A. Bujalance

1987-01-01

89

Active space decomposition with multiple sites: Density matrix renormalization group algorithm  

E-print Network

We extend the active space decomposition method, recently developed by us, to more than two active sites using the density matrix renormalization group algorithm. The fragment wave functions are described by complete or restricted active-space wave functions. Numerical results are shown on a benzene pentamer and a perylene diimide trimer. It is found that the truncation errors in our method decrease almost exponentially with respect to the number of renormalization states M, allowing for numerically exact calculations (to a few {\\mu}Eh or less) with M = 128 in both cases, which is in contrast to conventional ab initio density matrix renormalization group.

Parker, Shane M

2014-01-01

90

Status of the IAA study group on traffic management rules for space operations  

NASA Astrophysics Data System (ADS)

The investigation of space traffic and its management has only recently become a point of wider discussion. In particular, the series of workshops organized by the American Institute of Aeronautics and Astronautics (AIAA) and other international organizations on international cooperation highlighted the issue. It was discussed thoroughly at the workshops, which took place in 1999 and 2001, respectively. It was at the 2001 workshop, when the suggestion was made that an International Academy of Astronautics (IAA) Study on the subject of space traffic management should be prepared. This suggestion was taken up and a proposal was presented to the Board of Trustees of IAA, which, in late 2001, accepted this proposal. Following this, an interdisciplinary study group of around 20 persons was composed. One early milestone in the process of work was the conduct of an International Institute of Space Law (IISL)/European Center of Space Law (ECSL) Symposium alongside the 2002 session of the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS) Legal Subcommittee. This symposium consisted of presentations of members of the IAA study group. Also, close coordination with other study projects of IAA, in particular with the one on space debris, is sought. This paper presents the status of work of the study group, in particular, the approach and the scope of the study as well as its preliminary findings. The study group intends to finalize its work in early 2004, in order to be able to put the study before IAA and launch its review process before the 2004 International Astronautical Congress. Following this review, the study will be published and may be expected to make an impact in fora like the UNCOPUOS. The authors of this paper act as the coordinators/the rapporteur to this study. The paper will be presented in the IAA—as well as the IISL—session dealing with space traffic, by that bridging the two areas and seeking input from various sources.

Contant, Corinne; Lala, Petr; Schrogl, Kai-Uwe

2007-10-01

91

Internet Based Open Access Crystallographic Databases  

NASA Astrophysics Data System (ADS)

Two freely accessible crystallographic databases are discussed: the Crystallographic Open Database (COD, http://crystallography.net) which contains over 37,000 crystal structures, and the Nano-Crystallography Database (NCD, http://nanocrystallography.research.pdx.edu) which we recently started to support image-based nanocrystallography and (nano) materials science education. Both databases collect crystallographic relevant information in a standardized format; the Crystallographic Information File (CIF). CIF is the standard file format adopted by the International Union of Crystallography (http://iucr.org) for the archiving and distribution of crystallographic information. A subset of the COD, the Predicted Crystallographic Online Database, allows for 3D structural displays of structural polyhedra and wireframes of approximately 2,600 entries. Since electron microscopist are interested in simple, yet technologically important materials, the crystallographic information for those materials will be included in our database. At our NCD site, entries in the COD and the NCD can be visualized in three dimensions (3D) along with (2D) lattice fringe fingerprints plots. The latter supports the identification of unknown nanocrystal phases from high-resolution transmission electron microscopy (HRTEM) images. Morphological crystal information from the database ``Bestimmungstabellen f"ur Kristalle/ ???????????? ??????????,'' (A.K. Boldyrew and W.W. Doliwo-Dobrowolsky, Zentrales Wissenschaftlichers Institute der Geologie und Sch"urfung, Leningrad/ Moscow, 1937/1939) will also be included in the NCD to support image-based nanocrystallography in 3D.

Upreti, Girish; Seipel, Bjoern; Harvey, Morgan; Garrick, Will; Moeck, Peter

2006-05-01

92

On Decoding and Performance Optimizing of Four-Group Decodable Space-Time Block Codes  

Microsoft Academic Search

A class of rate-one space-time block codes (STBC) allowing the decoding of transmitted symbols into four groups is recently proposed by Yuen, Guan and Tjhung. This code is called four-group decodable STBC (4Gp-STBC). In this paper, the equivalent channel of 4Gp-STBC is derived and a new method to decode 4Gp-STBC based on sphere decoders is proposed. Furthermore, the performance of

Dung Ngoc Dao; Chintha Tellambura; Chau Yuen; Tjeng Thiang Tjhung; Yong Liang Guan

93

On the Decoding and Optimizing Performance of Four-Group Decodable Space-Time Block Codes  

Microsoft Academic Search

A class of rate-one space-time block codes (STBC) allowing the decoding of transmitted symbols into four groups is recently proposed by Yuen, Guan and Tjhung. This code is called four-group decodable STBC (4Gp-STBC). In this paper, the equivalent channel of 4Gp-STBC is derived and a new method to decode 4Gp-STBC based on sphere decoders is presented. Furthermore, the performance of

Dung Ngoc Dao; C. Tellambura; Chau Yuen; Tjeng Thiang Tjhung; Yong Liang Guan

2006-01-01

94

Experiences of Young Bisexual Women in Lesbian\\/Bisexual Groups on MySpace  

Microsoft Academic Search

This exploratory study examined Topic threads in Lesbian\\/Bisexual Groups on MySpace to examine how young biwomen self-identify in online exchanges with other bisexuals and lesbians, as well as what attitudes and beliefs about bisexuality emerge from those exchanges. Four Topic threads from three Groups suggested that young biwomen use social networking sites to connect with others and create inclusive communities

M. Sue Crowley

2010-01-01

95

Groups of generalized flux transformations in the space of generalized connections  

E-print Network

We present a group of transformations in the space of generalized connections that contains the set of transformations generated by the flux variables of loop quantum gravity. This group is labelled by certain SU(2)-valued functions on the bundle of directions in the spatial manifold. A further generalization is obtained by considering functions that depend on germs of analytic curves, rather than just on directions.

J. M. Velhinho

2008-04-23

96

INFLUENCE OF SPAWNING GROUP SIZE AND SPACE ON REPRODUCTION BY SHEEPSHEAD MINNOWS, CYPRINODON VARIEGATUS  

EPA Science Inventory

Cripe, G.M., R.L. Hemmer and L.R. Goodman. In press. Influence of Spawning Group Size and Space on Reproduction Variability of Sheepshead Minnows, Cyprinodon variegatus (Abstract). To be presented at the SETAC Fourth World Congress, 14-18 November 2004, Portland, OR. 1 p. (ERL,GB...

97

Definition of spacecraft standard interfaces by the NASA Space Assembly and Servicing Working Group (SASWG)  

NASA Technical Reports Server (NTRS)

The purpose of the NASA Space Assembly and Servicing Working Group (SASWG) is to study enabling technologies for on-orbit spacecraft maintenance and servicing. One key technology required for effective space logistics activity is the development of standard spacecraft interfaces, including the 'Basic Set' defined by NASA, the U.S. Space Command, and industry panelists to be the following: (1) navigation aids; (2) grasping, berthing, and docking; and (3) utility connections for power, data, and fluids. Draft standards have been prepared and referred to professional standards organizations, including the AIAA, EIA, and SAE space standards committee. The objective of the SASWG is to support these committees with the technical expertise required to prepare standards, guidelines, and recommended practices which will be accepted by the ANSI and international standards organizations, including the ISO, IEC, and PASC.

Radtke, Robert; Woolley, Charles; Arnold, Lana

1993-01-01

98

Environmental interactions in Space Exploration: Announcement of the formation of an Environmental Interactions Working Group  

NASA Technical Reports Server (NTRS)

With the advent of the Space Exploration Initiative, the possibility of designing and using systems on scales not heretofore attempted presents exciting new challenges in systems design and space science. The environments addressed by the Space Exploration Initiative include the surfaces of the Moon and Mars, as well as the varied plasma and field environments which will be encountered by humans and cargo enroute to these destinations. Systems designers will need to understand environmental interactions and be able to model these mechanisms from the earliest conceptual design stages through design completion. To the end of understanding environmental interactions and establishing robotic precursor mission requirements, an Environmental Interactions Working Group has been established as part of the Robotic Missions Working Group. The current paper describes the working group and gives an update of its current activities. Working group charter and operation are reviewed, background information on the environmental interactions and their characteristics is offered, and the current status of the group's activities is presented along with anticipations for the future.

Kolecki, Joseph C.; Hillard, G. Barry

1991-01-01

99

Crystallographic and magnetic structure of UCu{sub 1.5}Sn{sub 2}  

SciTech Connect

We report on the crystallographic and magnetic structures of the antiferromagnet UCu{sub 1.5}Sn{sub 2}, as determined by x-ray and neutron powder diffraction. It forms in the tetragonal CaBe{sub 2}Ge{sub 2} structure type, with space group P/4nmm, and we find no site disorder between two different Sn 2c sites, in contrast with a previous report. UCu{sub 1.5}Sn{sub 2} orders antiferromagnetically with a Neel temperature of about 110 K. This is unusually high amongst uranium intermetallics. The uranium moments align along the c-axis in a collinear arrangement but alternating along the c-axis. The low-temperature uranium moment is 1.95{mu}{sub B}.

Purwanto, A.; Robinson, R.A.; Nakotte, H. [Los Alamos National Lab., NM (United States); Swainson, I. [Atomic Energy of Canada Limited, Chalk River, Ontario (Canada). Chalk River Lab.; Torikachvili, M. [San Diego State Univ., CA (United States). Dept. of Physics

1995-09-01

100

Extracellular overproduction and preliminary crystallographic analysis of a family I.3 lipase  

PubMed Central

A family I.3 lipase from Pseudomonas sp. MIS38 was secreted from Escherichia coli cells to the external medium, purified and crystallized and preliminary crystallographic studies were performed. The crystal was grown at 277?K by the hanging-drop vapour-diffusion method. Native X-ray diffraction data were collected to 1.7?Å resolution using synchrotron radiation at station BL38B1, SPring-8. The crystal belongs to space group P21, with unit-cell parameters a = 48.79, b = 84.06, c = 87.04?Å. Assuming the presence of one molecule per asymmetric unit, the Matthews coefficient V M was calculated to be 2.73?Å3?Da?1 and the solvent content was 55%. PMID:17329810

Angkawidjaja, Clement; You, Dong-Ju; Matsumura, Hiroyoshi; Koga, Yuichi; Takano, Kazufumi; Kanaya, Shigenori

2007-01-01

101

Kepler problem in deformed (quantum) four-dimensional space in non relativistic limit with Galilei group of motion  

E-print Network

It is shown that Kepler problem in deformed (quantum) four-dimensional space in non relativistic limit is integrable in quadratures. In non relativistic limit group of motion of quantum space coincide with Galilei one.

A. N. Leznov

2007-08-04

102

Information theory and crystallographic phase determination  

E-print Network

INFORMATION THEORY AND CRYSTALLOGRAPHIC PHASE DETERMINATION A Thesis by PATRICIA LOUISE BRITTEN Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE August... 1981 Major Subject: Chemistry INFORMATION THEORY AND CRYSTALLOGRAPHIC PHASE DETERMINAT ION A Thesis by PATRICIA LOUISE BRITTEN Approved as to style and content by: (Chairman of Committee) (Member ) (Member) (Head of Depar ent) August 1981...

Britten, Patricia Louise

2012-06-07

103

Phase-space shapes of clusters and rich groups of galaxies  

NASA Astrophysics Data System (ADS)

Context. Clusters and groups of galaxies are highly aspherical, with shapes approximated by nearly prolate ellipsoids of revolution. An equally fundamental property is the shape of these objects in velocity space which is the anisotropy of the global velocity dispersion tensor. Although many studies address the problem of the shape in position space, there has been no attempt to measure shapes in velocity space. Aims: Here we make use of kinematical data comprising ~600 nearby clusters and rich groups of galaxies from the Sloan Digital Sky Survey to place constraints on the phase-space shapes of these objects, i.e. their shapes in both position and velocity space. Methods: We show that the line of sight velocity dispersion normalised by a mass-dependent velocity scale correlates with the apparent elongation, with circular (elongated) clusters exhibiting an excessive (decremental) normalised velocity dispersion. This correlation holds for dynamically young or old clusters and, therefore, it originates from projecting their intrinsic phase-space shapes rather than from dynamical evolution. It signifies that clusters are preferentially prolate not only in position space, but also in velocity space. This property allows us to break the degeneracy between oblate and prolate models and thus to deproject the apparent elongations and the line of sight velocity dispersions obtaining constraints on the axial ratios of the ellipsoids approximating cluster shapes in 3D position or velocity space. Results: The distribution of the axial ratios in position space is found to be well approximated by a Gaussian with a mean, ? = 0.66 ± 0.01, and a dispersion, ? = 0.07 ± 0.008. The velocity ellipsoids representing the shapes in velocity space are more spherical, with a mean axial ratio of 0.78 ± 0.03. Conclusions: The mean axial ratio of the velocity ellipsoids points to a highly anisotropic velocity distribution and, therefore, to a strong dependance of the observed velocity dispersions on the angle between the line of sight and the semi-principle axes of the clusters. This finding has important implications for mass measurements based on the line of sight velocity dispersion profiles in individual clusters. For typical axial ratios of the velocity ellipsoids in the analysed cluster sample, systematic errors on the mass estimates inferred from the line of sight velocity dispersions become comparable to statistical uncertainties for galaxy clusters with as few as 40 spectroscopic redshifts.

Wojtak, Rados?aw

2013-11-01

104

Crystallization and preliminary X-ray crystallographic analysis of two dimeric hyperthermostable thioredoxins isolated from Sulfolobus solfataricus  

PubMed Central

The thioredoxin system of the archaeon Sulfolobus solfataricus involves a number of different proteins: two thioredoxin reductases (SsTrxRB2 and SsTrxRB3), two distinct thioredoxins (SsTrxA1 and SsTrxA2) and a disulfide oxidoreductase (SsPDO). Here, the crystallization and preliminary crystallo­graphic analyses of SsTrxA1 and SsTrxA2, two dimeric proteins endowed with extraordinary thermal stability, are reported. In addition to the functional thioredoxin domain, both SsTrxA1 and SsTrxA2 present an extra N-terminal fragment of approximately 30 residues. Although crystallization trials have been conducted on both forms of the proteins, crystals that were suitable for X-ray crystallographic analyses have only been obtained for their truncated variants. The crystals of SsTrxA2 belonged to space group P2, with unit-cell parameters a = 28.27, b = 27.88, c = 62.06?Å, ? = 92.34°, and diffracted to 1.83?Å resolution, whereas the crystals of SsTrxA1 belonged to space group P21, with unit-cell parameters a = 51.76, b = 75.09, c = 55.35?Å, ? = 112.64°, and diffracted to 1.90?Å resolution. The structures of the two proteins have been solved by molecular replacement. PMID:19478442

Ruggiero, Alessia; Lanzotti, Maria Angela; Ruocco, Maria Rosaria; Grimaldi, Pasquale; Marasco, Daniela; Arcari, Paolo; Masullo, Mariorosario; Zagari, Adriana; Vitagliano, Luigi

2009-01-01

105

Crystallization and preliminary X-ray crystallographic analysis of two dimeric hyperthermostable thioredoxins isolated from Sulfolobus solfataricus.  

PubMed

The thioredoxin system of the archaeon Sulfolobus solfataricus involves a number of different proteins: two thioredoxin reductases (SsTrxRB2 and SsTrxRB3), two distinct thioredoxins (SsTrxA1 and SsTrxA2) and a disulfide oxidoreductase (SsPDO). Here, the crystallization and preliminary crystallographic analyses of SsTrxA1 and SsTrxA2, two dimeric proteins endowed with extraordinary thermal stability, are reported. In addition to the functional thioredoxin domain, both SsTrxA1 and SsTrxA2 present an extra N-terminal fragment of approximately 30 residues. Although crystallization trials have been conducted on both forms of the proteins, crystals that were suitable for X-ray crystallographic analyses have only been obtained for their truncated variants. The crystals of SsTrxA2 belonged to space group P2, with unit-cell parameters a = 28.27, b = 27.88, c = 62.06 A, beta = 92.34 degrees , and diffracted to 1.83 A resolution, whereas the crystals of SsTrxA1 belonged to space group P2(1), with unit-cell parameters a = 51.76, b = 75.09, c = 55.35 A, beta = 112.64 degrees , and diffracted to 1.90 A resolution. The structures of the two proteins have been solved by molecular replacement. PMID:19478442

Ruggiero, Alessia; Lanzotti, Maria Angela; Ruocco, Maria Rosaria; Grimaldi, Pasquale; Marasco, Daniela; Arcari, Paolo; Masullo, Mariorosario; Zagari, Adriana; Vitagliano, Luigi

2009-06-01

106

The NASA EEE parts assurance group (NEPAG) - An evolving approach to maximizing space parts assurance resources  

NASA Astrophysics Data System (ADS)

This paper describes the activities of the National Aeronautics and Space Administration's (NASA's) Electrical, Electronic and Electromechanical (EEE) Parts Assurance Group (NEPAG) in its role as a resource sharing and coordinating force in EEE Parts assurance for space flight missions. NEPAG is a new organization, barely two years old. The EEE parts world for space applications faces a number of challenges as we enter the 21st Century but the most significant is clearly the economic incorporation of Commercial Off The Shelf (COTS) parts without sacrificing reliability. NEPAG has collaborated in designing a NASA-funded evaluation plan to take a comprehensive look at COTS. A cost/benefit study has been performed to compare the cost of ownership of the US MIL parts NASA has traditionally used with COTS parts screened to an equivalent reliability level.

Sampson, M. J.

2002-12-01

107

Planning and managing future space facility projects. [management by objectives and group dynamics  

NASA Technical Reports Server (NTRS)

To learn how ground-based personnel of a space project plan and organize their work and how such planning and organizing relate to work outcomes, longitudinal study of the management and execution of the Space Lab Mission Development Test 3 (SMD 3) was performed at NASA Ames Research Center. A view of the problems likely to arise in organizations and some methods of coping with these problems are presented as well as the conclusions and recommendations that pertain strictly to SMD 3 management. Emphasis is placed on the broader context of future space facility projects and additional problems that may be anticipated. A model of management that may be used to facilitate problem solving and communication - management by objectives (MBO) is presented. Some problems of communication and emotion management that MBO does not address directly are considered. Models for promoting mature, constructive and satisfying emotional relationships among group members are discussed.

Sieber, J. E.; Wilhelm, J. A.; Tanner, T. A.; Helmreich, R. L.; Burgenbauch, S. F.

1979-01-01

108

Exploiting space-group symmetry in fragment-based molecular crystal calculations.  

PubMed

Recent developments in fragment-based methods make it increasingly feasible to use high-level ab initio electronic structure techniques to molecular crystals. Such studies remain computationally demanding, however. Here, we describe a straightforward algorithm for exploiting space-group symmetry in fragment-based methods which often provides computational speed-ups of several fold or more. This algorithm does not require a priori specification of the space group or symmetry operators. Rather, the symmetrically equivalent fragments are identified automatically by aligning the individual fragments along their principle axes of inertia and testing for equivalence with other fragments. The symmetry operators relating equivalent fragments can then be worked out easily. Implementation of this algorithm for computing energies, nuclear gradients with respect to both atomic coordinates and lattice parameters, and the nuclear hessian is described. © 2014 Wiley Periodicals, Inc. PMID:25270380

Heit, Yonaton; Beran, Gregory J O

2014-11-15

109

Real-space dynamic renormalization group. III. Calculation of correlation functions  

SciTech Connect

The real-space dynamic renormalization group method developed in previous papers is applied to the kinetic Ising model defined on a square lattice. In particular we extend the formalism to the calculation of space- and time-dependent equilibrium averaged correlation functions. We find that conventional methods for implementing the real-space renormalization group via cumulant expansions in terms of the intercell coupling lead to correlation functions which decay algebraically in space at large distances in the disordered phase in qualitative disagreement with the known exponential decay. We indicate how one can develop new perturbation theory expansion methods which lead to the proper exponential decay at large distances and also lead to good quantitative results for other observable quantities like the magnetization, susceptibility, and single spin time autocorrelation function. As the result of a first-order calculation we obtain excellent results for the static critical exponents and a value of z=1.79 for the dynamic critical exponent. The critical exponents obtained from the correlation functions calculated using this method satisfy the proper static and dynamic scaling relations.

Mazenko, G.F.; Hirsch, J.E.; Nolan, M.J.; Valls, O.T.

1981-02-01

110

Realization of vector fields for quantum groups as pseudodifferential operators on quantum spaces  

SciTech Connect

The vector fields of the quantum Lie algebra are described for the quantum groups GL{sub q}(n), SL{sub q}(N) and SO{sub q}(N) as pseudodifferential operators on the linear quantum spaces covariant under the corresponding quantum group. Their expressions are simple and compact. It is pointed out that these vector fields satisfy certain characteristic polynomial identities. The real forms SU{sub q}(N) and SO{sub q}(N,R) are discussed in detail.

Chu, Chong-Sun; Zumino, B.

1995-01-24

111

Localization of the Einstein group and a nonsingular cosmological model of space-time with torsion  

NASA Astrophysics Data System (ADS)

We consider an Einstein-invariant gauge theory of gravitation (EGT), obtained by localizing the group of motions of a homogeneous static Einstein Universe. Taking into account the cosmological term, we find exact solutions of EGT are as nonsingular homogeneous Isotropic cosmological models with both the metric and the torsion regular. It is shown that EGT satisfies the principle of correspondence with Newton's theory of gravity and with the tetrad theory of gravity in the space of absolute parallelism.

Tunyak, V. N.

1986-10-01

112

A nice group structure on the orbit space of unimodular rows-II.  

E-print Network

We establish an Excision type theorem for niceness of group structure on the orbit space of unimodular rows of length $n$ modulo elementary action. This permits us to establish niceness for relative versions of results for the cases when $n = d+1$, $d$ being the dimension of the base algebra. We then study and establish niceness for the case when $n = d$, and also establish a relative version, when the base ring is a smooth affine algebra over an algebraically closed field.

Anjan Gupta; Anuradha Garge; Ravi A. Rao

113

Cohomologies of Configuration Spaces and Higher-Dimensional Polylogarithms in Renormalization Group Problems  

SciTech Connect

The deviation from commutativity of the renormalization and the action of all linear partial differential operators is the main source of the anomalies in quantum field theory, including the renormalization group action. This deviation is characterized by certain 'renormalization cocycles' that are related to cohomologies of the so called (ordered) configuration spaces. Cohomological differential equations that determine the renormalization cocycles up to the renormalization freedom are obtained. The solution of these equations requires introducing transcendental extensions related to higher-dimensional polylogarithms.

Nikolov, Nikolay M. [Institute for Nuclear Research and Nuclear Energy, Tsarigradsko Chaussee 72, BG-1784 Sofia (Bulgaria)

2010-06-17

114

Report from the MPP Working Group to the NASA Associate Administrator for Space Science and Applications  

NASA Technical Reports Server (NTRS)

NASA's Office of Space Science and Applications (OSSA) gave a select group of scientists the opportunity to test and implement their computational algorithms on the Massively Parallel Processor (MPP) located at Goddard Space Flight Center, beginning in late 1985. One year later, the Working Group presented its report, which addressed the following: algorithms, programming languages, architecture, programming environments, the way theory relates, and performance measured. The findings point to a number of demonstrated computational techniques for which the MPP architecture is ideally suited. For example, besides executing much faster on the MPP than on conventional computers, systolic VLSI simulation (where distances are short), lattice simulation, neural network simulation, and image problems were found to be easier to program on the MPP's architecture than on a CYBER 205 or even a VAX. The report also makes technical recommendations covering all aspects of MPP use, and recommendations concerning the future of the MPP and machines based on similar architectures, expansion of the Working Group, and study of the role of future parallel processors for space station, EOS, and the Great Observatories era.

Fischer, James R.; Grosch, Chester; Mcanulty, Michael; Odonnell, John; Storey, Owen

1987-01-01

115

One dimensional zone center phonons in $O_{h}$ space group  

E-print Network

Motivated by experiments, we performed a systematic study on the one dimensional zone center phonons in $O_{h}$ space groups. All the one dimensional phonon modes for different Wyckoff positions are tabulated. We show that at least four (inequivalent) atoms (in one set of Wyckoff positions) are needed to carry a single one dimensional phonon. A general restriction rule on the number of atoms and the number of one dimensional phonons is obtained. The same restriction applies to phonons of all cubic crystal systems ($T$, $T_{h}$, $T_{d}$, $O$, $O_{h}$) and to magnons for crystals whose unitary symmetry elements are in ($T$, $T_{h}$, $T_{d}$, $O$, $O_{h}$). Crystals with $A15$ structure are found to satisfy experimental requirements (to have a $\\Gamma_{2}^{+}$ phonon) while most crystals of $O_{h}$ space groups do not. $A15$ is also used to demonstrate the rules we found regarding the phonon structure in $O_{h}$ space groups.

Jian Li; Jiufeng J. Tu; Joseph L. Birman

2014-03-04

116

Iterative Joint and Interference Nulling/ Cancellation Decoding Algorithms for Multi-Group Space Time Trellis Coded Systems  

E-print Network

for multi-group space time trellis coded (MGSTTC) systems. By considering a single user who transmits simultaneously through K parallel space time trellis encoders, the system can provide high spectral efficiencies is transmitting a space time trellis code. The transmitter will divide the information stream and transmits from

Al-Ghadhban, Samir

117

Nexus, crystallographic computing all around the world.  

PubMed

Crystallographic Nexus CD-ROMs, containing a range of free crystallographic software for single-crystal and powder diffraction available on the Internet, have been distributed on request since 1996. The free CD is made in the form of a ;virtual Internet' with the main intent of benefiting crystallographers with inadequate Internet access. The IUCr funds an annual/biennial update which is distributed to known previous recipients. Feedback from current recipients indicates the CD is still useful. The most current IUCr-funded CD is being produced by the CCP14 project at University College London and The Royal Institution UK for distribution to the ECM 2007 and AsCA 2007 conferences. PMID:18156686

Cranswick, Lachlan Michael David; Bisson, William; Cockcroft, Jeremy Karl

2008-01-01

118

Confessions of an icosahedral virus crystallographer  

PubMed Central

This is a personal history of my structural studies of icosahedral viruses that evolved from crystallographic studies, to hybrid methods with electron cryo-microscopy and image reconstruction (cryoEM) and then developed further by incorporating a variety of physical methods to augment the high resolution crystallographic studies. It is not meant to be comprehensive, even for my own work, but hopefully provides some perspective on the growth of our understanding of these remarkable biologic assemblies. The goal is to provide a historical perspective for those new to the field and to emphasize the limitations of any one method, even those that provide atomic resolution information about viruses. PMID:23291268

Johnson, John E.

2013-01-01

119

Higher-order calculations in the real space dynamic renormalization group: One dimension  

NASA Astrophysics Data System (ADS)

The application of real space dynamic renormalization group methods to the one-dimensional kinetic Ising model, discussed in an earlier paper, is extended to one order higher in perturbation theory than was done previously. It is shown that the treatment of short-range, local quantities is improved in going to higher order in the perturbation expansion, while that of the long-range properties remains largely unaffected. Arbitrariness in the real space mapping function and how it may be exploited to our advantage is duscussed. It is shown that the renormalized Hamiltonian continues to be characterized by one coupling through second order. We find that the single spin-flip kinetic Ising model generates at second-order new spin-flip mechanisms in the renormalized dynamical operator but that their effects are small (at most 2%) over the entire temperature range.

Luscombe, J.; Mazenko, Gene F.

1983-03-01

120

P-SPACE: a program for simulating spatial behavior in small groups.  

PubMed

P-SPACE is a computer program that simulates spatial behavior in a small group of individuals. The program describes how interpersonal distances change through time as a result of changes in microlevel features, such as the minimization of local dissatisfaction. Agents are located in a two-dimensional lattice and can move some discrete space units at each discrete time unit within their neighborhood. A nonsymmetrical matrix of ideal distances between agents must be specified. Agents move in order to minimize their dissatisfaction, defined as a function of the discrepancy between possible future distances and ideal distances between agents. At each iteration, agents will move to those cells in their neighborhoods for which the function is minimized. Depending on the specific values in the ideal-distance matrix, different kinds of social dynamics can be simulated. PMID:10758677

Quera, V; Solanas, A; Salafranca, L; Beltran, F S; Herrando, S

2000-02-01

121

A Fun and Effective Exercise for Understanding Lattices and Space Groups  

NSDL National Science Digital Library

This activity uses figures from Francois Brisse as Esher drawings to teach students about 2-dimensional symmetry, especially involving translation. This exercise is based on discovery learning. Students need little introduction to lattices and space groups. They can figure things out for themselves. For example, they will figure out what a glide plane is, and if you tell them ahead of time it takes away from the learning experience. The last question, which asks them to make their own symmetrical drawings, is difficult but often leads to some spectacular results.

Perkins, Dexter

122

Real-space renormalization-group study of the Z(5) model  

NASA Astrophysics Data System (ADS)

The phase diagram of the nearest-neighbor Z(5) model on the square and triangular lattices is investigated using techniques of the real-space renormalization group. We use the recently introduced technique of Nienhuis, Berker, Riedel, and Schick, which yields the expected first-order transition on the Potts subspace of the Z(5) model on the triangular lattice. For the general Z(5) model we obtain a line of first-order transitions which crosses over into a line of second-order transitions. The same technique when applied to the square lattice is found to show this crossover behavior only in combination with a Migdal procedure.

Mizrahi, Victor; Domany, Eytan

1981-10-01

123

Real-space renormalization group study of the anisotropic antiferromagnetic Heisenberg model on a square lattice  

NASA Astrophysics Data System (ADS)

In this work we apply two different real-space renormalization-group (RSRG) approaches to the anisotropic antiferromagnetic spin-1/2 Heisenberg model on the square lattice. Our calculations allow for an approximate evaluation of the T vs ? phase diagram: the results suggest the existence of a critical value of ?>0, at which the critical temperature goes to zero, and the presence of reentrant behavior on the critical line between the ordered and disordered phases. This whole critical line is found to belong to the same universality class as the Ising model. Our results are in accordance with previous RSRG approaches but not with numerical simulations and spin-wave calculations.

Branco, N. S.; Ricardo de Sousa, J.

2000-09-01

124

Hardy spaces on Lie groups of polynomial growth A.F.M. ter Elst 1 , Derek W. Robinson 2 and Yueping Zhu 3  

E-print Network

Hardy spaces on Lie groups of polynomial growth A.F.M. ter Elst 1 , Derek W. Robinson 2 and Yueping­order, subelliptic operators on Lie groups with polynomial growth. August 2004 Keywords: Lie groups, Hardy spaces of Hardy spaces on Lie groups of polynomial growth. Let G be a connected Lie group with Lie algebra g. One

Eindhoven, Technische Universiteit

125

Crystallographic Texture of StressAffected Bainite  

E-print Network

transformation has been demonstrated for austenitic stainless steel deformed in tension (Kundu and Bhadeshia the macroscopic strains and crystallographic bias which develop when a polycrystalline sample of austenitic steel is transformed into bainite or martensite under the influence of an applied stress or a system of stresses. Any

Cambridge, University of

126

Hubble Space Telescope Images of Stephan's Quintet: Star Cluster Formation in a Compact Group Environment  

E-print Network

Analysis of Hubble Space Telescope/Wide Field Planetary Camera 2 images of Stephan's Quintet, Hickson Compact Group 92, yielded 115 candidate star clusters (with V-I < 1.5). Unlike in merger remants, the cluster candidates in Stephan's Quintet are not clustered in the inner regions of the galaxies; they are spread over the debris and surrounding area. Specifically, these sources are located in the long sweeping tail and spiral arms of NGC 7319, in the tidal debris of NGC 7318B/A, and in the intragroup starburst region north of these galaxies. Analysis of the colors of the clusters indicates several distinct epochs of star formation that appear to trace the complex history of dynamical interactions in this compact group.

S. C. Gallagher; J. C. Charlton; S. D. Hunsberger; D. Zaritsky; B. C. Whitmore

2001-03-31

127

Electron precession microdiffraction as a useful tool for the identification of the space group.  

PubMed

The possible space groups of a crystal can be identified from a few zone axis microdiffraction patterns provided the position (and not the intensity) of the reflections on the patterns is taken into account. The method is based on the observation of the shifts and the periodicity differences between the reflections located in the first-order Laue zone (FOLZ) with respect to the ones located in the zero-order Laue zone (ZOLZ). Electron precession microdiffraction patterns display more reflections in the ZOLZ and in the FOLZ than in the conventional microdiffraction patterns and this number increases with the precession angle. It is shown, from the TiAl example given in the present study, that this interesting feature brings a strong beneficial effect for the identification of the possible space groups since it becomes very easy to identify unambiguously the FOLZ/ZOLZ shifts and periodicity differences. In addition, the diffracted intensity on the precession patterns is the integrated intensity and this intensity can also be used to identify the Laue class. PMID:17845710

Morniroli, J-P; Redjaimia, A

2007-08-01

128

Space group symmetry applied to SCF calculations with periodic boundary conditions and Gaussian orbitals  

NASA Astrophysics Data System (ADS)

Space group symmetry is exploited and implemented in density functional calculations of extended systems with periodic boundary conditions. Our scheme for reducing the number of two-electron integrals employs the entire set of operations of the space group, including glide plains and screw axes. Speedups observed for the Fock matrix formation in simple 3D systems range from 2X to 9X for the near field Coulomb part and from 3X to 8X for the Hartree-Fock-type exchange, the slowest steps of the procedure, thus leading to a substantial reduction of the computational time. The relatively small speedup factors in special cases are attributed to the highly symmetric positions atoms occupy in crystals, including the ones tested here, as well as to the choice of the smallest possible unit cells. For quasi-1D systems with most atoms staying invariant only under identity, the speedup factors often exceed one order of magnitude reaching almost 70X (near-field Coulomb) and 57X (HFx) for the largest tested (16,7) single-walled nanotube with 278 symmetry operations.

Rusakov, Alexander A.; Frisch, Michael J.; Scuseria, Gustavo E.

2013-09-01

129

Intraspecific variation in space use, group size, and mating systems of caviomorph rodents  

PubMed Central

Intraspecific variation in social systems is widely recognized across many taxa, and specific models, including polygamy potential, resource defense, and resource dispersion, have been developed to explain the relationship between ecological variation and social organization. Although mammals from temperate North America and Eurasia have provided many insights into this relationship, rodents from the Neotropics and temperate South America have largely been ignored. In this review we focus on reports documenting intraspecific variation in spacing systems, group size, and mating systems of caviomorphs. This large group of New World hystricognath rodents occupies a diverse array of habitats; thus, members of the same species potentially exhibit different social systems in response to different ecological conditions. Spatial patterns vary in response to a diverse array of factors, including predation, food availability, population density, and soil characteristics. Changes in group size typically correlate with changes in resource availability, particularly food. Mating systems generally reflect the ability of males to control access to females, which may depend on population density or food distribution. In general, social organization in caviomorphs fits predictions of resource-based models; however, most studies have been purely observational, involving small numbers of animals over short time periods and reporting qualitative rather than quantitative levels of ecological correlates. In future studies the use of molecular techniques and controlled, experimental manipulations can increase our understanding of intraspecific variation in caviomorph social systems. This understudied group of rodents offers excellent opportunities to provide insights into the influence of ecological conditions on behavior such as social systems. PMID:22328790

Maher, Christine R.; Burger, Joseph Robert

2012-01-01

130

Real-space renormalization group method for quantum 1/2 spins on the pyrochlore lattice.  

PubMed

A simple phenomenological real-space renormalization group method for quantum Heisenberg spins with nearest and next nearest neighbour interactions on a pyrochlore lattice is presented. Assuming a scaling law for the order parameter of two clusters of different sizes, a set of coupled equations that gives the fixed points of the renormalization group transformation and, thus, the critical temperatures and ordered phases of the system is found. The particular case of spins 1/2 is studied in detail. Furthermore, to simplify the mathematical details, from all the possible phases arising from the renormalization group transformation, only those phases in which the magnetic lattice is commensurate with a subdivision of the crystal lattice into four interlocked face-centred cubic sublattices are considered. These correspond to a quantum spin liquid, ferromagnetic order, or non-collinear order in which the total magnetic moment of a tetrahedral unit is zero. The corresponding phase diagram is constructed and the differences with respect to the classical model are analysed. It is found that this method reproduces fairly well the phase diagram of the pyrochlore lattice under the aforementioned constraints. PMID:24625859

Garcia-Adeva, Angel J

2014-04-01

131

Systematic prediction of new ferroelectrics in space group R3. I.  

PubMed

Release 2005/1 of the Inorganic Crystal Structure Database contains 158 entries under the space group R3. The first 81 together with 15 related entries include 52 different structure types, 10 of which represent families that have two or more isostructural members. There are 18 types that satisfy the structural criteria for ferroelectricity with a confidence level that necessarily depends upon the reliability of each structural determination. Among them, (LiTaO3)9.Ta2O5 and the CsCd(NO2) family are known ferroelectrics. The remaining 16 include the high-intensity higher-order harmonic generator II-BaB2O4, not previously recognized as ferroelectric. The other predicted ferroelectrics are Te(OH)6.NaF, the MgSO3.6H2O family, Li3P3O9.3H2O, SeNbF9, Al2(H2PO4)3PO4.6H2O, [Cr(OCN2H4)6].[(Co(NH3)2(NO2)4]3.(H2O)(1.5)], NaZnBr3.5H2O, III-Ag3SI, Tl2S, the Ba3Yb4O9 family, the Fe(10.7)Ru(1.3)As5 family, Sr17Ta10S42, Pb8Sb3 and the Sc7I12C family. Six structures reported in the space group R3 most likely exhibit mirror symmetry, with three experimental confirmations. The other 19 structures are most likely nonpolar, with six experimental confirmations. The capacity for physical property prediction by the remaining ten structures is shown to be in doubt. Thus, 46% of the present 52 inorganic structure types initially determined in the space group R3 and 35% of those currently assigned to R3 more likely exhibit an additional inversion center, mirror or glide plane, strongly exceeding the recently reported error rate of approximately 11% in organic structures. PMID:16434790

Abrahams, S C

2006-02-01

132

Nuclear safety policy working group recommendations on nuclear propulsion safety for the space exploration initiative  

NASA Technical Reports Server (NTRS)

An interagency Nuclear Safety Working Group (NSPWG) was chartered to recommend nuclear safety policy, requirements, and guidelines for the Space Exploration Initiative (SEI) nuclear propulsion program. These recommendations, which are contained in this report, should facilitate the implementation of mission planning and conceptual design studies. The NSPWG has recommended a top-level policy to provide the guiding principles for the development and implementation of the SEI nuclear propulsion safety program. In addition, the NSPWG has reviewed safety issues for nuclear propulsion and recommended top-level safety requirements and guidelines to address these issues. These recommendations should be useful for the development of the program's top-level requirements for safety functions (referred to as Safety Functional Requirements). The safety requirements and guidelines address the following topics: reactor start-up, inadvertent criticality, radiological release and exposure, disposal, entry, safeguards, risk/reliability, operational safety, ground testing, and other considerations.

Marshall, Albert C.; Lee, James H.; Mcculloch, William H.; Sawyer, J. Charles, Jr.; Bari, Robert A.; Cullingford, Hatice S.; Hardy, Alva C.; Niederauer, George F.; Remp, Kerry; Rice, John W.

1993-01-01

133

International Space Station Air Quality Assessed According to Toxicologically-Grouped Compounds  

NASA Technical Reports Server (NTRS)

Scores of compounds are found in the International Space Station (ISS) atmospheric samples that are returned to the Johnson Space Center Toxicology Laboratory for analysis. Spacecraft Maximum Allowable Concentrations (SMACs) are set with the view that each compound is present as if there were no other compounds present. In order to apply SMACs to the interpretation of the analytical data, the toxicologist must employ some method of combining the potential effects of the aggregate of compounds found in the atmospheric samples. The simplest approach is to assume that each quantifiable compound has the potential for some effect in proportion to the applicable SMAC, and then add all the proportions. This simple paradigm disregards the fact that most compounds have potential to adversely affect only a few physiological systems, and their effects would be independent rather than additive. An improved approach to dealing with exposure to mixtures is to add the proportions only for compounds that adversely affect the same physiological system. For example, toxicants that cause respiratory irritation are separated from those that cause neurotoxicity or cardio-toxicity. Herein we analyze ISS air quality data according to toxicological groups with a view that this could be used for understanding any crew symptoms occurring at the time of the sample acquisition. In addition, this approach could be useful in post-flight longitudinal surveys where the flight surgeon may need to identify post-flight, follow-up medical studies because of on-orbit exposures that target specific physiological systems.

James, John T.; Limero, Thomas F.; Beck, Steve; Cheng, Patti F.; deVera, Vanessa J.; Hand, Jennifer; Macatangay, Ariel

2010-01-01

134

Outreach of Astronomy with emphasis to the Solar System by the Space group in Greece  

NASA Astrophysics Data System (ADS)

We have a long tradition in Space and Solar System outreach at the University of Athens (Space Group). We have contributed with many popular science articles in encyclopaedias (a total of some 200000 words), magazines and newspapers, public lectures around Greece and radio and TV programmes. We contribute in exhibitions for the public on many occasions (e.g. The British Exploration of the Planets, an exhibition organized by the British Council, at Eugenides Foundation and The Planetarium, where I prepared some 15 posters). We are preparing an outreach site of Astrophysics with sections for the planets, the exploration of the solar system and solar terrestrial relations. I am preparing several posters for the planets. We organize with the Hellenic Physical Union a series of Astrophysics Lectures at the University of Athens. Together with the Hellenic Physical Union we are planning to produce a theatrical play and CD or DVD concerning the planets. We have excellent collaboration with the amateur astronomers allover Greece and Cyprus. We organize, together with Physics or mathematics teachers in high schools several events related to astronomical observations (e.g. Venus transit, solar eclipe, astronomy nights). 1 We also organize popular science programmes in TV channels. I brief we consider Astronomy and especially the planetary system as a "Great Attractor" of pupil and the general public to science and we use it on every occasion for the benefit of the pupil and science. 2

Moussas, X.; Dialynas, K.; Babasides, G.; Fasoulopoulos, G.; Dimitropoulou, V.; Prassopoulos, D.; Kouphos, S.; Spandagos, E.; Strikis, J.

135

Fractal space-times under the microscope: A Renormalization Group view on Monte Carlo data  

E-print Network

The emergence of fractal features in the microscopic structure of space-time is a common theme in many approaches to quantum gravity. In this work we carry out a detailed renormalization group study of the spectral dimension $d_s$ and walk dimension $d_w$ associated with the effective space-times of asymptotically safe Quantum Einstein Gravity (QEG). We discover three scaling regimes where these generalized dimensions are approximately constant for an extended range of length scales: a classical regime where $d_s = d, d_w = 2$, a semi-classical regime where $d_s = 2d/(2+d), d_w = 2+d$, and the UV-fixed point regime where $d_s = d/2, d_w = 4$. On the length scales covered by three-dimensional Monte Carlo simulations, the resulting spectral dimension is shown to be in very good agreement with the data. This comparison also provides a natural explanation for the apparent puzzle between the short distance behavior of the spectral dimension reported from Causal Dynamical Triangulations (CDT), Euclidean Dynamical Triangulations (EDT), and Asymptotic Safety.

Martin Reuter; Frank Saueressig

2011-10-24

136

Quantum groups, roots of unity and particles on quantized Anti-de Sitter space  

SciTech Connect

Quantum groups in general and the quantum Anti-de Sitter group U{sub q}(so(2,3)) in particular are studied from the point of view of quantum field theory. The author shows that if q is a suitable root of unity, there exist finite-dimensional, unitary representations corresponding to essentially all the classical one-particle representations with (half) integer spin, with the same structure at low energies as in the classical case. In the massless case for spin {ge} 1, {open_quotes}naive{close_quotes} representations are unitarizable only after factoring out a subspace of {open_quotes}pure gauges{close_quotes}, as classically. Unitary many-particle representations are defined, with the correct classical limit. Furthermore, the author identifies a remarkable element Q in the center of U{sub q}(g), which plays the role of a BRST operator in the case of U{sub q}(so(2,3)) at roots of unity, for any spin {ge} 1. The associated ghosts are an intrinsic part of the indecomposable representations. The author shows how to define an involution on algebras of creation and anihilation operators at roots of unity, in an example corresponding to non-identical particles. It is shown how nonabelian gauge fields appear naturally in this framework, without having to define connections on fiber bundles. Integration on Quantum Euclidean space and sphere and on Anti-de Sitter space is studied as well. The author gives a conjecture how Q can be used in general to analyze the structure of indecomposable representations, and to define a new, completely reducible associative (tensor) product of representations at roots of unity, which generalizes the standard {open_quotes}truncated{close_quotes} tensor product as well as many-particle representations.

Steinacker, H. [Univ. of California, Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley National Lab., CA (United States)

1997-05-23

137

Analysis of the structural continuity in twinned crystals in terms of pseudo-eigensymmetry of crystallographic orbits.  

PubMed

The reticular theory of twinning gives the necessary conditions on the lattice level for the formation of twins. The latter are based on the continuation, more or less approximate, of a substructure through the composition surface. The analysis of this structural continuity can be performed in terms of the eigensymmetry of the crystallographic orbits corresponding to occupied Wyckoff positions in the structure. If [Formula: see text] is the space group of the individual and [Formula: see text] a space group which fixes the twin lattice obtained as an intersection of the space groups of the individuals in their respective orientations, then a structural continuity is obtained if (1) the eigensymmetry of an orbit under [Formula: see text] contains the twin operation; (2) the eigensymmetry of a union of orbits under [Formula: see text] contains the twin operation; (3) the eigensymmetry of a split orbit under [Formula: see text] contains the twin operation; or (4) the eigensymmetry of a union of split orbits under [Formula: see text] contains the twin operation. The case of the twins in melilite is analysed: the (approximate) restoration of some of the orbits explains the formation of these twins. PMID:25075318

Marzouki, Mohamed Amine; Souvignier, Bernd; Nespolo, Massimo

2014-01-01

138

Crystallographic and magnetic properties of Pb2?xBixIr2O7?? (0 ? x ? 2)  

NASA Astrophysics Data System (ADS)

The title series of compounds have been synthesized by solid state reaction and characterized by x-ray diffraction (PXD), neutron powder diffraction (PND), second harmonic generation (SHG), x-ray absorption spectroscopy (XAS) and magnetization measurements. The crystal structures have been refined from PND data in the centrosymmetric space group Fd\\bar{3}m with pyrochlore structure. No sign of a break of the centrosymmetry has been observed by SHG and no change of the structure to a polar space group in any component of the series, as it was previously reported for Pb2Ir2O7?? with non-centrosymmetric F\\bar{4}3m space group. We have determined by PND that the oxidation state of Ir is slightly decreasing from 5+-to-4+ in the Pb-rich to almost 4+ in the Bi-rich samples. This evolution is confirmed by XAS and also it explains the progression of the crystallographic parameters. All the samples are paramagnetic in the temperature range measured and the magnitude of the effective magnetic moment is enhanced with Bi content, correlated with the enhancement of Ir4+ compared to Ir5+; suggesting Ir5+ to be present in a trigonal antiprism crystal field splitting and therefore Ir4+ as the only magnetic cation.

Retuerto, M.; Sarkar, T.; Li, M.-R.; Ignatov, A.; Croft, M.; Hodges, J. P.; Thao Tran, T.; Shiv Halasyamani, P.; Greenblatt, M.

2014-12-01

139

Space station needs, attributes and architectural options study commercialization working group briefing  

NASA Technical Reports Server (NTRS)

The benefits for each of the following commercial areas was investigated: communications, remote sensing, materials processing in space, low Earth orbit (LEO) satellite assembly, testing, and servicing, and space tourism. In each case, where economic benefits are derived, the costs for accomplishing tasks with the Space Station are compared with the cost with the Space Transportation System only.

1983-01-01

140

Preliminary crystallographic analysis of the oxidized form of a two mono-nuclear iron centres protein from Desulfovibrio desulfuricans ATCC 27774.  

PubMed Central

Crystals of the fully oxidized form of desulfoferrodoxin were obtained by vapor diffusion from a solution containing 20% PEG 4000, 0.1 M HEPES buffer, pH 7.5, and 0.2 M CaCl2. Trigonal and/or rectangular prisms could be obtained, depending on the temperature used for the crystal growth. Trigonal prisms belong to the rhombohedral space group R32, with a = 112.5 A and c = 63.2 A; rectangular prisms belong to the monoclinic space group C2, with a = 77.7 A, b = 80.9 A, c = 53.9 A, and beta = 98.1 degrees. The crystallographic asymmetric unit of the rhombohedral crystal form contains one molecule. There are two molecules in the asymmetric unit of the monoclinic form, in agreement with the self-rotation function. PMID:8762151

Coelho, A. V.; Matias, P. M.; Carrondo, M. A.; Tavares, P.; Moura, J. J.; Moura, I.; Fulop, V.; Hajdu, J.; Le Gall, J.

1996-01-01

141

On the reflection type decomposition of the adjoint reduced phase space of a compact semisimple Lie group  

SciTech Connect

We consider a system with symmetries whose configuration space is a compact Lie group, acted upon by inner automorphisms. The classical reduced phase space of this system decomposes into connected components of orbit type subsets. To investigate hypothetical quantum effects of this decomposition one has to construct the associated costratification of the Hilbert space of the quantum system in the sense of Huebschmann. In the present paper, instead of the decomposition by orbit types, we consider the related decomposition by reflection types (conjugacy classes of reflection subgroups). These two decompositions turn out to coincide, e.g., for the classical groups SU(n) and Sp(n). We derive defining relations for reflection type subsets in terms of irreducible characters and discuss how to obtain from that the corresponding costratification of the Hilbert space of the system. To illustrate the method, we give explicit results for some low rank classical groups.

Hofmann, M. [Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Str. 3, 57068 Siegen (Germany)] [Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Str. 3, 57068 Siegen (Germany); Rudolph, G.; Schmidt, M. [Institut für Theoretische Physik, Universität Leipzig, Augustusplatz 10/11, 04109 Leipzig (Germany)] [Institut für Theoretische Physik, Universität Leipzig, Augustusplatz 10/11, 04109 Leipzig (Germany)

2013-08-15

142

Purification, crystallization and preliminary crystallographic studies of a Kunitz-type proteinase inhibitor from tamarind (Tamarindus indica) seeds  

PubMed Central

A Kunitz-type proteinase inhibitor has been purified from tamarind (Tamarindus indica) seeds. SDS–PAGE analysis of a purified sample showed a homogeneous band corresponding to a molecular weight of 21?kDa. The protein was identified as a Kunitz-type proteinase inhibitor based on N-terminal amino-acid sequence analysis. It was crystallized by the vapour-diffusion method using PEG 6000. The crystals belonged to the orthorhombic space group C2221, with unit-cell parameters a = 37.2, b = 77.1, c = 129.1?Å. Diffraction data were collected to a resolution of 2.7?Å. Preliminary crystallographic analysis indicated the presence of one proteinase inhibitor molecule in the asymmetric unit, with a solvent content of 44%. PMID:19574654

Patil, Dipak N.; Preeti; Chaudhry, Anshul; Sharma, Ashwani K.; Tomar, -Shailly; Kumar, Pravindra

2009-01-01

143

Crystallization and preliminary crystallographic studies of a phospholipase A2 from the venom of the Brazilian snake Bothrops moojeni.  

PubMed

A phospholipase A(2) purified from the venom of the snake Bothrops moojeni has been crystallized by vapour-diffusion techniques in hanging drops at 291 K. The crystals, which were grown in the absence of Ca(2+), belong to the cubic system, space group P432, with unit-cell parameters a = b = c = 91.86 A, and contain one molecule in the asymmetric unit (V(M) = 2.71 A(3) Da(-1)). X-ray diffraction experiments provide data to 2.35 A resolution collected on a rotating-anode home source at cryogenic temperatures. The structure has been solved via molecular-replacement techniques using a single monomer of the crystallographic structure of the phospholipase from the Western diamondback rattlesnake (Crotalus atrox) as a search model. PMID:11264594

Nonato, M C; Garratt, R C; Mascarenhas, Y P; Jesus, W D; Assakura, M T; Serrano, S M; Oliva, G

2001-04-01

144

Tangent spaces to motivic cohomology groups-on $CH^{\\bullet}(X,1)$ and $CH^{\\bullet}(X,2)$.  

E-print Network

Using higher K-theory and tensor triangular geometry, we propose K-theoretic higher Chow groups, at position 1 and 2, of derived categories of noetherian schemes and their Milnoe variants for regular schemes and infinitesimal thickenings. We discuss fuctoriality ans show that these new higher Chow groups agree with the classical ones for regular schemes. As an application, we define tangent spaces to these new higher Chow groups as usually and identify them with cohomology groups of absolute differentials. Moreover, combing our results with Green-Griffiths' work on tangent spaces to algebraic cycles, we put a geometric meaning to the tangent space to $CH^{2}(X,1)$, where X is a smooth projective surface over a field k, chark=0.

Sen Yang

145

Crystal growth and first crystallographic characterization of mixed uranium(IV)-plutonium(III) oxalates.  

PubMed

The mixed-actinide uranium(IV)-plutonium(III) oxalate single crystals (NH4)0.5[Pu(III)0.5U(IV)0.5(C2O4)2·H2O]·nH2O (1) and (NH4)2.7Pu(III)0.7U(IV)1.3(C2O4)5·nH2O (2) have been prepared by the diffusion of different ions through membranes separating compartments of a triple cell. UV-vis, Raman, and thermal ionization mass spectrometry analyses demonstrate the presence of both uranium and plutonium metal cations with conservation of the initial oxidation state, U(IV) and Pu(III), and the formation of mixed-valence, mixed-actinide oxalate compounds. The structure of 1 and an average structure of 2 were determined by single-crystal X-ray diffraction and were solved by direct methods and Fourier difference techniques. Compounds 1 and 2 are the first mixed uranium(IV)-plutonium(III) compounds to be structurally characterized by single-crystal X-ray diffraction. The structure of 1, space group P4/n, a = 8.8558(3) Å, b = 7.8963(2) Å, Z = 2, consists of layers formed by four-membered rings of the two actinide metals occupying the same crystallographic site connected through oxalate ions. The actinide atoms are nine-coordinated by oxygen atoms from four bidentate oxalate ligands and one water molecule, which alternates up and down the layer. The single-charged cations and nonbonded water molecules are disordered in the same crystallographic site. For compound 2, an average structure has been determined in space group P6/mmm with a = 11.158(2) Å and c = 6.400(1) Å. The honeycomb-like framework [Pu(III)0.7U(IV)1.3(C2O4)5](2.7-) results from a three-dimensional arrangement of mixed (U0.65Pu0.35)O10 polyhedra connected by five bis-bidentate ?(2)-oxalate ions in a trigonal-bipyramidal configuration. PMID:23577593

Tamain, Christelle; Arab Chapelet, Bénédicte; Rivenet, Murielle; Abraham, Francis; Caraballo, Richard; Grandjean, Stéphane

2013-05-01

146

Gas and dust in the beta Pictoris moving group as seen by the Herschel Space Observatory  

NASA Astrophysics Data System (ADS)

Context. Debris discs are thought to be formed through the collisional grinding of planetesimals, and then can be considered as the outcome of planet formation. Understanding the properties of gas and dust in debris discs can help us comprehend the architecture of extrasolar planetary systems. Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have provided a valuable dataset for the study of debris discs gas and dust composition. This paper is part of a series of papers devoted to the study of Herschel-PACS observations of young stellar associations. Aims: This work aims at studying the properties of discs in the beta Pictoris moving group (BPMG) through far-IR PACS observations of dust and gas. Methods: We obtained Herschel-PACS far-IR photometric observations at 70, 100, and 160 ?m of 19 BPMG members, together with spectroscopic observations for four of them. These observations were centred at 63.18 ?m and 157 ?m, aiming to detect [OI] and [CII] emission. We incorporated the new far-IR observations in the SED of BPMG members and fitted modified blackbody models to better characterise the dust content. Results: We have detected far-IR excess emission towards nine BPMG members, including the first detection of an IR excess towards HD 29391.The star HD 172555, shows [OI] emission, while HD 181296 shows [CII] emission, expanding the short list of debris discs with a gas detection. No debris disc in BPMG is detected in both [OI] and [CII]. The discs show dust temperatures in the range 55-264 K, with low dust masses (<6.6 × 10-5 M? to 0.2 M?) and radii from blackbody models in the range 3 to ~82 AU. All the objects with a gas detection are early spectral type stars with a hot dust component. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Riviere-Marichalar, P.; Barrado, D.; Montesinos, B.; Duchêne, G.; Bouy, H.; Pinte, C.; Menard, F.; Donaldson, J.; Eiroa, C.; Krivov, A. V.; Kamp, I.; Mendigutía, I.; Dent, W. R. F.; Lillo-Box, J.

2014-05-01

147

Gas and dust in the Beta Pictoris Moving Group as seen by the Herschel Space Observatory  

E-print Network

Context. Debris discs are thought to be formed through the collisional grinding of planetesimals, and can be considered as the outcome of planet formation. Understanding the properties of gas and dust in debris discs can help us to comprehend the architecture of extrasolar planetary systems. Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have provided a valuable dataset for the study of debris discs gas and dust composition. This paper is part of a series of papers devoted to the study of Herschel PACS observations of young stellar associations. Aims. This work aims at studying the properties of discs in the Beta Pictoris Moving Group (BPMG) through far-IR PACS observations of dust and gas. Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100 and 160 microns of 19 BPMG members, together with spectroscopic observations of four of them. Spectroscopic observations were centred at 63.18 microns and 157 microns, aiming to detect [OI] and [CII] emission. We incorpo...

Riviere-Marichalar, P; Montesinos, B; Duchêne, G; Bouy, H; Pinte, C; Menard, F; Donaldson, J; Eiroa, C; Krivov, A V; Kamp, I; Mendigutía, I; Dent, W R F; Lillo-Box, J

2014-01-01

148

LDEF meteoroid and debris special investigation group investigations and activities at the Johnson Space Center  

NASA Technical Reports Server (NTRS)

Since the return of the Long Duration Exposure Facility (LDEF) in January, 1990, members of the Meteoroid and Debris Special Investigation Group (M&D SIG) at the Johnson Space Center (JSC) in Houston, Texas have been examining LDEF hardware in an effort to expand the knowledge base regarding the low-Earth orbit (LEO) particulate environment. In addition to the various investigative activities, JSC is also the location of the general Meteoroid & Debris database. This publicly accessible database contains information obtained from the various M&D SIG investigations, as well as limited data obtained by individual LDEF Principal Investigators. LDEF exposed approximately 130 m(exp 2) of surface area to the LEO particulate environment, approximately 15.4 m(exp 2) of which was occupied by structural frame components (i.e., longerons and intercoastals) of the spacecraft. The data reported here was obtained as a result of detailed scans of LDEF intercoastals, 68 of which reside at JSC. The limited amount of data presently available on the A0178 thermal control blankets was reported last year and will not be reiterated here. The data presented here are limited to measurements of crater diameters and their frequency of occurrence (i.e., flux).

See, Thomas H.; Warren, Jack L.; Zolensky, Michael E.; Sapp, Clyde A.; Bernhard, Ronald P.; Dardano, Claire B.

1995-01-01

149

Effects of incentives on psychosocial performances in simulated space-dwelling groups  

NASA Astrophysics Data System (ADS)

Prior research with individually isolated 3-person crews in a distributed, interactive, planetary exploration simulation examined the effects of communication constraints and crew configuration changes on crew performance and psychosocial self-report measures. The present report extends these findings to a model of performance maintenance that operationalizes conditions under which disruptive affective responses by crew participants might be anticipated to emerge. Experiments evaluated the effects of changes in incentive conditions on crew performance and self-report measures in simulated space-dwelling groups. Crews participated in a simulated planetary exploration mission that required identification, collection, and analysis of geologic samples. Results showed that crew performance effectiveness was unaffected by either positive or negative incentive conditions, while self-report measures were differentially affected—negative incentive conditions produced pronounced increases in negative self-report ratings and decreases in positive self-report ratings, while positive incentive conditions produced increased positive self-report ratings only. Thus, incentive conditions associated with simulated spaceflight missions can significantly affect psychosocial adaptation without compromising task performance effectiveness in trained and experienced crews.

Hienz, Robert D.; Brady, Joseph V.; Hursh, Steven R.; Gasior, Eric D.; Spence, Kevin R.; Emurian, Henry H.

150

Overview of the Space Propulsion Synergy Group (SPSG) strategic planning support efforts for earth to orbit transportation  

NASA Astrophysics Data System (ADS)

An essential requirement of a successful space program is the assurance of a safe affordable routine access to space. In view of this, a national organization known as the Space Propulsion Synergy Group (SPSG) has been directed for the past two years toward supporting strategic planning for earth-to-orbit space transportation and propulsion systems. This paper presents a short description of the approach the SPSG followed in their space transportation and propulsion systems strategic planning support activities. The SPSG study emphasized the identification of the transportation systems users/customers and the characteristics of attributes most valued by them in earth-to-LEO payload transportation services. The study initiated the process known as Quality Function Deployment to ensure that the customer/user real requirements and needs are properly addressed and that the transportation system concepts advocated had the greatest probability of satisfying the custosmer's requirements and desired attributes.

Dankhoff, Walter F.; Hope, William P., Jr.

1993-06-01

151

Real-Space Renormalization-Group Approach to the Integer Quantum Hall Effect  

NASA Astrophysics Data System (ADS)

We review recent results based on an application of the real-space renormalization group (RG) approach to a network model for the integer quantum Hall (QH) transition. We demonstrate that this RG approach reproduces the critical distribution of the power transmission coefficients, i.e., two-terminal conductances, Pc(G), with very high accuracy. The RG flow of P(G) at energies away from the transition yields a value of the critical exponent ? that agrees with most accurate large-size lattice simulations. A description of how to obtain other relevant transport coefficients such as RL and RH is given. From the non-trivial fixed point of the RG flow we extract the critical level-spacing distribution (LSD). This distribution is close, but distinctively different from the earlier large-scale simulations. We find that the LSD obeys scaling behavior around the QH transition with ? = 2.37±0.02. Away from the transition it crosses over towards the Poisson distribution. We next investigate the plateau-to-insulator transition at strong magnetic fields. For a fully quantum coherent situation, we find a quantized Hall insulator with RH?h/e2 up to RL 20h/e2 when interpreting the results in terms of most probable value of the distribution function P(RH). Upon further increasing RL??, the Hall insulator with diverging Hall resistance R H? R L? is seen. The crossover between these two regimes depends on the precise nature of the averaging procedure for the distributions P(RL) and P(RH). We also study the effect of long-ranged inhomogeneities on the critical properties of the QH transition. Inhomogeneities are modeled by a smooth random potential with a correlator which falls off with distance as a power law r-?. Similar to the classical percolation, we observe an enhancement of ? with decreasing ?. These results exemplify the surprising fact that a small RG unit, containing only five nodes, accurately captures most of the correlations responsible for the localization-delocalization transition.

Cain, Philipp; Römer, Rudolf A.

152

Synthesis and Crystallographic Analysis of 5-Se-Thymidine DNAs  

SciTech Connect

We investigated the possibility of the interaction of 5-CH3 of thymidine and its 5?-phosphate backbone (C-H O-PO3 interaction) in DNA via the insertion of the atomic probe (a selenium atom) into the exo-5-position of thymidine (5-Se-T). 5-Se-T was synthesized for the first time, via Mn(OAc)3 assisted electrophilic addition of CH3SeSeCH3 to 3?,5?-di-O-benzoyl-2?-deoxyuridine. The 5-Se-T phosphoramidite was subsequently synthesized and incorporated into DNA in over 99% coupling yield. Biophysical and structural investigations of the 5-Se-T DNAs revealed that the Se-modified and nonmodified DNAs are virtually identical. In addition, the crystallographic analysis of a 5-Se-T DNA strongly suggests a hydrogen-bond formation between the 5-CH3 and 5?-phosphate groups (CH3 PO4- interaction).

Hassan, A.; Sheng, J; Jiang, J; Zhanbg, W; Huang, Z

2009-01-01

153

Group Dynamics as a Critical Component of Successful Space Exploration: Conceptual Theory and Insights from the Biosphere 2 Closure Experiment  

NASA Astrophysics Data System (ADS)

As space exploration and eventually habitation achieves longer durations, successfully managing group dynamics of small, physically isolated groups will become vital. The paper summarizes important underlying research and conceptual theory and how these manifested in a well-documented example: the closure experiments of Biosphere 2. Key research breakthroughs in discerning the operation of small human groups comes from the pioneering work of W.R. Bion. He discovered two competing modalities of behavior. The first is the “task-oriented” or work group governed by shared acceptance of goals, reality-thinking in relation to time, resources and rational, and intelligent management of challenges presented. The opposing, usually unconscious, modality is what Bion called the “basic-assumption” group and alternates between three “group animal” groups: dependency/kill the leader; fight/flight and pairing. If not dealt with, these dynamics work to undermine and defeat the conscious task group’s goal achievement. The paper discusses crew training and selection, various approaches to structuring the work and hierarchy of the group, the importance of contact with a larger population through electronic communication and dealing with the “us-them” syndrome frequently observed between crew and Mission Control. The experience of the first two year closure of Biosphere 2 is drawn on in new ways to illustrate vicissitudes and management of group dynamics especially as both the inside team of biospherians and key members of Mission Control had training in working with group dynamics. Insights from that experience may help mission planning so that future groups in space cope successfully with inherent group dynamics challenges that arise.

Nelson, Mark; Allen, John P.

154

Origin and evolution of moving groups I. Characterization in the observational kinematic-age-metallicity space  

E-print Network

Context. Recent studies have suggested that moving groups have a dynamic or "resonant" origin. Under this hypothesis, these kinematic structures become a powerful tool for studying the large-scale structure and dynamics of the Milky Way. Aims. We aim to characterize these structures in the U-V-age-[Fe/H] space and establish observational constraints that will allow us to study their origin and evolution. Methods. We apply multiscale techniques -wavelet denoising (WD)- to an extensive compendium of more than 24000 stars in the solar neighbourhood with the best available astrometric, photometric and spectroscopic data. Results. We confirm that the dominant structures in the U-V plane are the branches of Sirius, Coma Berenices, Hyades-Pleiades and Hercules, which are nearly equidistant in this kinematic plane and show a negative slope. The abrupt drops in the velocity distribution are characterized. We find a certain dependence of these kinematic structures on Galactic position with a significant change of contrast among substructures inside the branches. A large spread of ages is observed for all branches. The Hercules branch is detected in all subsamples with ages older than ~ 2 Gyr and the set of the other three branches is well established for stars > 400 Myr. The age-metallicity relation of each branch is examined and the relation between kinematics and metallicity is studied. Conclusions. Not all of these observational constraints are successfully explained by the recent models proposed for the formation of such kinematic structures. Simulations incorporating stellar ages and metallicities are essential for future studies. The comparison of the observed and simulated distributions obtained by WD will provide a physical interpretation of the existence of the branches in terms of local or large-scale dynamics. [Abridged

T. Antoja; F. Figueras; D. Fernandez; J. Torra

2008-09-02

155

Creating Social Spaces to Tackle AIDS-Related Stigma: Reviewing the Role of Church Groups in Sub-Saharan Africa  

Microsoft Academic Search

An expanding body of literature explores the role of African church groups in facilitating or hindering the support of people\\u000a living with AIDS and challenging or contributing to HIV\\/AIDS-related stigma. Treating church groups as social spaces in which\\u000a HIV\\/AIDS-related stigma may potentially be challenged, we systematically review this literature, identifying five themes that\\u000a highlight the complex and contradictory role of

C. Campbell; M. Skovdal; A. Gibbs

2011-01-01

156

Expression, purification, crystallization and preliminary crystallographic analysis of human myotubularin-related protein 3.  

PubMed

Myotubularin-related proteins are a large family of phosphatases that have the catalytic activity of dephosphorylating the phospholipid molecules phosphatidylinositol 3-phosphate and phosphatidylinositol 3,5-bisphosphate. Each of the 14 family members contains a phosphatase catalytic domain, which is inactive in six family members owing to amino-acid changes in a key motif for the activity. All of the members also bear PH-GRAM domains, which have low homologies between them and have roles that are not yet clear. Here, the cloning, expression, purification and crystallization of human myotubularin-related protein 3 encompassing the PH-GRAM and the phosphatase catalytic domain are reported. Preliminary X-ray crystallographic analysis shows that the crystals diffracted to 3.30?Å resolution at a synchrotron X-ray source. The crystals belonged to space group C2, with unit-cell parameters a = 323.3, b = 263.3, c = 149.4?Å, ? = 109.7°. PMID:25195900

Son, Ji Young; Lee, Jee Un; Yoo, Ki-Young; Shin, Woori; Im, Dong-Won; Kim, Seung Jun; Ryu, Seong Eon; Heo, Yong-Seok

2014-09-01

157

Purification, characterization and preliminary X-ray crystallographic studies on Neisseria gonorrhoeae Gly1ORF1.  

PubMed

Gly1ORF1 is a protein produced by the two pathogenic Neisseria species, N. gonorrhoeae and N. meningitidis, but not by commensal Neisseria, suggesting that it may be involved in pathogenesis. The protein has a signal sequence that is cleaved, is associated with outer membrane fractions of N. gonorrhoeae (GC) and is found in spent media and in outer-membrane fractions when expressed in Escherichia coli. GC strains with null mutations of the gly1 locus have increased toxicity to human fallopian tubes in organ culture, suggesting that Gly1ORF1 may alter the amount or properties of toxic moieties produced by GC [Arvidson et al. (1999), infect. Immun. 67, 643-652]. In an effort to understand the function of Gly1ORF1 and its role in pathogenesis, structural biology studies have been initiated. Here, the purification, characterization by dynamic light scattering, crystallization and preliminary X-ray crystallographic studies of recombinant Gly1ORF1 are reported. Dynamic light scattering indicated the protein to be a dimer in solution. The crystals belonged to space group P6(3), with unit-cell parameters a = 95.2, b = 95.2, c = 83.7 A and two molecules per asymmetric unit. The crystals diffracted to 2.4 A using a conventional X-ray source. PMID:12657800

Arvidson, Dennis N; Pearson, Robert F; Arvidson, Cindy Grove

2003-04-01

158

Purification, crystallization and preliminary crystallographic investigation of FrnE, a disulfide oxidoreductase from Deinococcus radiodurans.  

PubMed

In prokaryotes, Dsb proteins catalyze the formation of native disulfide bonds through an oxidative folding pathway and are part of the cell machinery that protects proteins from oxidative stress. Deinococcus radiodurans is an extremophile which shows unparalleled resistance to ionizing radiation and oxidative stress. It has a strong mechanism to protect its proteome from oxidative damage. The genome of Deinococcus shows the presence of FrnE, a Dsb protein homologue that potentially provides the bacterium with oxidative stress tolerance. Here, crystallization and preliminary X-ray crystallographic analysis of FrnE from D. radiodurans are reported. Diffraction-quality single crystals were obtained using the hanging-drop vapour-diffusion method with reservoir solution consisting of 100?mM sodium acetate pH 5.0, 10% PEG 8000, 15-20% glycerol. Diffraction data were collected on an Agilent SuperNova system using a microfocus sealed-tube X-ray source. The crystal diffracted to 1.8?Å resolution at 100?K. The space group of the crystal was found to be P21221, with unit-cell parameters a = 47.91, b = 62.94, c = 86.75?Å, ? = ? = ? = 90°. Based on Matthews coefficient analysis, one monomer per asymmetric unit is present in the crystal, with a solvent content of approximately 45%. PMID:25372826

Panicker, Lata; Misra, Hari Sharan; Bihani, Subhash Chandra

2014-11-01

159

The effect of crystallographic textures on the formability of high-strength steel sheets  

Microsoft Academic Search

The effect of crystallographic textures on the formability of high-strength steel sheets was investigated by using the elastic\\/crystalline viscoplastic finite element (FE) analysis. First, the preferred orientations, which correlate with the plastic anisotropy, were revealed by orientation fibers, skeleton lines and selected orientations in Euler angle space. Secondly, the mechanical properties such as R-values, yield loci and stress–strain relationships, and

C. L. Xie; E. Nakamachi

2002-01-01

160

Grouping  

NSDL National Science Digital Library

This interactive Flash applet models the measurement interpretation of division. A child or teacher chooses a total number of objects and a divisor representing the size of equal groups. The applet allows the user to move the objects into equal groups and links the process to jumps on a number line. The applet can be used to introduce children to remainders and to reinforce the language and notation of division. It works well on an interactive white board or projector. A teacher's guide to this collection of applets is cataloged separately.

2006-01-01

161

Effects of row spacing, seed rate and maturity group on late planted soybean under irrigated and dryland  

E-print Network

Effects of row spacing, seed rate and maturity group on late planted soybean under irrigated Oklahoma State University SUMMARY POINTS: For Irrigated Soybean a plant population of 180,000 resulted at the dryland location. Introduction Soybean Production has increased significantly in Oklahoma the past few

Balasundaram, Balabhaskar "Baski"

162

PRE AND POST BREAKUP MOVEMENTS AND SPACE USE OF BLACK BEAR FAMILY GROUPS IN CHEROKEE NATIONAL FOREST, TENNESSEE  

Microsoft Academic Search

The movements and space use of 7 yearling black bears (Ursus americanus) (3 males, 4 females) from 3 family groups were intensively monitored concurrently with 13 adults (6 males, 7 females) in the Cherokee National Forest, Tennessee from February 1983 until December 1983. The timing of family breakup occurred in 2 families between 29 May-5 June, and 22-25 June, respectively.

ANTHONY P. CLEVENGER; MICHAEL R. PELTON

163

Preliminary neutron crystallographic study of human transthyretin  

PubMed Central

Preliminary studies of perdeuterated crystals of human transthyretin (TTR) have been carried out using the LADI-III and D19 diffractometers at the Institut Laue–Langevin in Grenoble. The results demonstrate the feasibility of a full crystallographic analysis to a resolution of 2.0?Å using Laue diffraction and also illustrate the potential of using monochromatic instruments such as D19 for higher resolution studies where larger crystals having smaller unit cells are available. This study will yield important information on hydrogen bonding, amino-acid protonation states and hydration in the protein. Such information will be of general interest for an understanding of the factors that stabilize/destabilize TTR and for the design of ligands that may be used to counter TTR amyloid fibrillogenesis. PMID:22102249

Haupt, Melina; Blakeley, Matthew P.; Teixeira, Susana C. M.; Mason, Sax A.; Mitchell, Edward P.; Cooper, Jonathan B.; Forsyth, V. Trevor

2011-01-01

164

Tcl\\/Tk-based programs. IV. CALCRYS: crystallographic calculator  

Microsoft Academic Search

1. The crystallographic problem Crystallographers need to make a number of simple algebraic calculations in order to obtain lengths, angles, define relations between molecules, transformations of the coordinates, etc. These calculations can be performed by general means, e.g. either with a pocket calculator or with a computer using standard mathematical packages. Another possibility is to have a specialized tool, tuned

L. M. Urzhumtseva; A. G. Urzhumtsev

2000-01-01

165

Structure of delta-Bi{sub 2}O{sub 3} from density functional theory: A systematic crystallographic analysis  

SciTech Connect

A systematic crystallographic analysis of the <110> and <111> vacancy-ordered structure of cubic delta-Bi{sub 2}O{sub 3} obtained from electronic-structure calculations is presented. The ordering of vacancies leads to a doubling of the unit-cell that results in a 2x2x2 fluorite super-structure, with an associated reduction in its space group symmetry from Fm3-barm to Fm3-bar. The Bi atoms present inside the <111> vacancy-ordered oxygen sublattice have equal Bi-O bond lengths, whereas, those present inside the <110> vacancy-ordered oxygen sublattice have three different pairs of Bi-O bond lengths. The specific ionic displacements and electronic charge configurations also depend on the nature of vacancy ordering in the oxygen sub-lattice. - Graphical abstract: 1/8 of a 2x2x2 delta-Bi{sub 2}O{sub 3} superstructure having Fm3-bar space group. Every oxygen (black) has three possible positions, only one of which is filled either by O1 (red) or O{sub 2} (blue).

Aidhy, Dilpuneet S.; Sinnott, Susan B.; Wachsman, Eric D.; Phillpot, Simon R. [Department of Materials Science and Engineering, Rhines Hall, Gainesville, FL 32611 (United States); Nino, Juan C., E-mail: jnino@mse.ufl.ed [Department of Materials Science and Engineering, Rhines Hall, Gainesville, FL 32611 (United States)

2009-05-15

166

A summary of activities of the US/Soviet-Russian joint working group on space biology and medicine  

NASA Astrophysics Data System (ADS)

The very foundation of cooperation between the United States (US) and Russia (former Soviet Union) in space exploration is a direct result of the mutual desire for scientific understanding and the creation of a collaborative mechanism—the Joint Working Group (JWG) on Space Biology and Medicine. From the dawn of the space age, it has been the quest of humankind to understand its place in the universe. While nations can and do solve problems independently, it takes nations, working together, to accomplish great things. The formation of the JWG provided an opportunity for the opening of a series of productive relationships between the superpowers, the US and the Union of Soviet Socialist Republics (USSR); and served as a justification for continued relationship for medical assistance in spaceflight, and to showcase Earth benefits from space medicine research. This relationship has been played out on an international scale with the construction and operation of the International Space Station. The fundamental reason for this successful endeavor is a direct result of the spirit and perseverance of the men and women who have worked diligently side-by-side to promote science and move our understanding of space forward. This manuscript provides a historical perspective of the JWG; how it came about; its evolution; what it accomplished; and what impact it has had and continues to have in the 21st century with regard to human spaceflight and space life sciences research. It captures the spirit of this group, which has been in continuous existence for over 40 years, and provides a never before reported summary of its activities.

Doarn, Charles R.; Nicogossian, Arnauld E.; Grigoriev, Anatoly I.; Tverskaya, Galina; Orlov, Oleg I.; Ilyin, Eugene A.; Souza, Kenneth A.

2010-10-01

167

Space station needs attributes and architectural options study costing working group briefing  

NASA Technical Reports Server (NTRS)

Individuals in the United States who understand the promise of materials processing in space and who also are senior technical personnel associated with commercial firms that process materials: (1) endorsed the concept of a space station as a desirable national asset; (2) stated that a commercial MPS research program is mandatory to extend commericalization of space for materials processing; and (3) described in general terms a national research laboratory and free flying facilities that are needed. Participants agreed that industry R&D is motivated largely by market pull rather than by technology push, that initial interest is low-g materials research; and that to farther, commercial market assurance (a salable product) is a must.

1983-01-01

168

Japanese projects development under activity of working group 4 (space environment natural and artificial)  

NASA Astrophysics Data System (ADS)

Since the beginning of 90's, space environment international standards have been developed within the scope of ISO/TC20/SC14/WG 4(space environment natural and artificial) activities. Japanese WG4 members have developed and proposed 5 projects under WG4 activity. These 5 projects are (1) Observed proton fluences over long duration at GEO and guideline for selection of confidence level in statistical model of solar proton fluences (TS12208), (2) Process-Based Implementation of Meteoroid and Debris Environmental Models ( Orbital Altitudes Below GEO+2000km)(FDIS14200), (3)Methods for estimation of future geomagnetic activity(DIS16698), (4) Realtime solar activity and space environment information for spacecraft operation(CD16709), (5) Procedure for obtaining worst case and confidence level of fluence using the quasi-dynamic radiation belts model(NWIP). This report presents the first published TS12208 (2011-09-15) in the above 5 projects in detail.

Goka, Tateo; Kitazawa, Yukihito

2012-07-01

169

Evaluating a Safe Space Training for School Counselors and Trainees Using a Randomized Control Group Design  

ERIC Educational Resources Information Center

School counselors need to advocate and act as an ally for all students. Safe Space, a training designed to facilitate competency for working with and serving LGBTQ youth (i.e., LGBTQ competency), has received increased attention in the field of school counseling. However, limited empirical support exists for training interventions such as Safe…

Byrd, Rebekah; Hays, Danica G.

2014-01-01

170

Group therapy for women problem gamblers: A space of their own  

Microsoft Academic Search

This report presents the results of a grounded theory analysis produced from in-depth interviews with 14 women participating in group counselling for problem gambling. Themes emerged from this analysis that provided insights into effective counselling practices for women problem gamblers. The results explore the impact of a group therapy approach in addressing the needs of these women. Participants indicated that

Noëlla Piquette-Tomei; Erika Norman; Sonya Corbin Dwyer; Evelyn McCaslin

2008-01-01

171

ON THE CLASSIFYING SPACE FOR THE FAMILY OF VIRTUALLY CYCLIC SUBGROUPS FOR ELEMENTARY AMENABLE GROUPS  

E-print Network

that has a bound on the orders of its finite subgroups admits a finite dimensional model for EG with finite isotropy [19­21]. Finiteness conditions for EG for elementary amenable groups are very well under] it was conjectured that the only groups admitting a finite type model for EG are virtually cyclic

Sheldon, Nathan D.

172

INTRINSIC FINE-SCALE STRUCTURE IN COMPLEX MATERIALS: BEYOND GLOBAL CRYSTALLOGRAPHIC ANALYSIS  

SciTech Connect

Many important classes of materials owe their interesting properties to structures and patterns produced by local atomic deviations from ideal crystallographic positions. The pattern scale may vary from a few atomic spacings to many microns. In a macroscopic sample these deviations may still average to an ideal lattice while retaining the intrinsic fine-scale structures, or a phase transition may create a pattern of variants of a new crystallographic structure. We have carried out experiments on the formation of fine-scale structures in a range of materials, particularly those produced by phase transitions. We have used Resonant Ultrasound Spectroscopy for elastic properties and dissipation, neutron pair-distribution function, and electronic transport measurements to characterize samples. We have carried out extensive dynamical modeling based on Ginzberg-Landau formalisms to simulate the development and appearance of the structures. Our results highlight the importance of long-range strain fields and the intrinsic unstable equilibrium features of the materials studied.

A. MIGLIORI; ET AL

2000-12-01

173

D-side: A facility and workforce planning group multi-criteria decision support system for Johnson Space Center  

Microsoft Academic Search

Abstract “To understand and protect our home planet, to explore the universe and search for life, and to inspire the next generation of explorers” is NASA’s mission. The Systems Management,Office at Johnson Space Center (JSC) is searching for methods,to effectively manage,the Center’s resources to meet NASA’s mission. D-Side is a group multi-criteria decision support system (GMDSS) developed to support facility

Madjid Tavana; James W. Smither; Ralph V. Anderson

2007-01-01

174

Improved Crystallographic Structures using Extensive Combinatorial Refinement  

PubMed Central

Summary Identifying errors and alternate conformers, and modeling multiple main-chain conformers in poorly ordered regions are overarching problems in crystallographic structure determination that have limited automation efforts and structure quality. Here, we show that implementation of a full factorial designed set of standard refinement approaches, which we call ExCoR (Extensive Combinatorial Refinement), significantly improves structural models compared to the traditional linear tree approach, in which individual algorithms are tested linearly, and only incorporated if the model improves. ExCoR markedly improved maps and models, and reveals building errors and alternate conformations that were masked by traditional refinement approaches. Surprisingly, an individual algorithm that renders a model worse in isolation could still be necessary to produce the best overall model, suggesting that model distortion allows escape from local minima of optimization target function, here shown to be a hallmark limitation of the traditional approach. ExCoR thus provides a simple approach to improving structure determination. PMID:24076406

Nwachukwu, Jerome C.; Southern, Mark R.; Kiefer, James R.; Afonine, Pavel V.; Adams, Paul D.; Terwilliger, Thomas C.; Nettles, Kendall W.

2013-01-01

175

Crystallographic model quality at a glance  

PubMed Central

A crystallographic macromolecular model is typically characterized by a list of quality criteria, such as R factors, deviations from ideal stereochemistry and average B factors, which are usually provided as tables in publications or in structural databases. In order to facilitate a quick model-quality evaluation, a graphical representation is proposed. Each key parameter such as R factor or bond-length deviation from ‘ideal values’ is shown graphically as a point on a ‘ruler’. These rulers are plotted as a set of lines with the same origin, forming a hub and spokes. Different parts of the rulers are coloured differently to reflect the frequency (red for a low frequency, blue for a high frequency) with which the corresponding values are observed in a reference set of structures determined previously. The points for a given model marked on these lines are connected to form a polygon. A polygon that is strongly compressed or dilated along some axes reveals unusually low or high values of the corresponding characteristics. Polygon vertices in ‘red zones’ indicate parameters which lie outside typical values. PMID:19237753

Urzhumtseva, Ludmila; Afonine, Pavel V.; Adams, Paul D.; Urzhumtsev, Alexandre

2009-01-01

176

Creating Social Spaces to Tackle AIDS-Related Stigma: Reviewing the Role of Church Groups in Sub-Saharan Africa  

PubMed Central

An expanding body of literature explores the role of African church groups in facilitating or hindering the support of people living with AIDS and challenging or contributing to HIV/AIDS-related stigma. Treating church groups as social spaces in which HIV/AIDS-related stigma may potentially be challenged, we systematically review this literature, identifying five themes that highlight the complex and contradictory role of the church as a potential agent of health-enhancing social change. In many ways the church perpetuates HIV/AIDS-related stigma through (i) moralistic attitudes and (ii) its reinforcement of conservative gender ideologies. However some churches have managed move towards action that makes a more positive contribution to HIV/AIDS management through (iii) promoting various forms of social control for HIV prevention, (iv) contributing to the care and support of the AIDS-affected and (v) providing social spaces for challenging stigmatising ideas and practices. We conclude that church groups, including church leadership, can play a key role in facilitating or hindering the creation of supportive social spaces to challenge stigma. Much work remains to be done in developing deeper understandings of the multi-layered factors that enable some churches, but not others, to respond effectively to HIV/AIDS. PMID:20668927

Skovdal, M.; Gibbs, A.

2012-01-01

177

Crystallographic and magnetic structure of the perovskite-type compound BaFeO2.5: unrivaled complexity in oxygen vacancy ordering.  

PubMed

We report here on the characterization of the vacancy-ordered perovskite-type structure of BaFeO2.5 by means of combined Rietveld analysis of powder X-ray and neutron diffraction data. The compound crystallizes in the monoclinic space group P2(1)/c [a = 6.9753(1) Å, b = 11.7281(2) Å, c = 23.4507(4) Å, ? = 98.813(1)°, and Z = 28] containing seven crystallographically different iron atoms. The coordination scheme is determined to be Ba7(FeO4/2)1(FeO3/2O1/1)3(FeO5/2)2(FeO6/2)1 = Ba7Fe([6])1Fe([5])2Fe([4])4O17.5 and is in agreement with the (57)Fe Mössbauer spectra and density functional theory based calculations. To our knowledge, the structure of BaFeO2.5 is the most complicated perovskite-type superstructure reported so far (largest primitive cell, number of ABX2.5 units per unit cell, and number of different crystallographic sites). The magnetic structure was determined from the powder neutron diffraction data and can be understood in terms of "G-type" antiferromagnetic ordering between connected iron-containing polyhedra, in agreement with field-sweep and zero-field-cooled/field-cooled measurements. PMID:24901981

Clemens, Oliver; Gröting, Melanie; Witte, Ralf; Perez-Mato, J Manuel; Loho, Christoph; Berry, Frank J; Kruk, Robert; Knight, Kevin S; Wright, Adrian J; Hahn, Horst; Slater, Peter R

2014-06-16

178

Creating Spaces for Critical Transformative Dialogues: Legitimising Discussion Groups as Professional Practice  

ERIC Educational Resources Information Center

Focussed dialogue (as lived and living practices) can have a powerful role in renewing professional practice, advancing its sustainability and development as administrative and political systems colonise the practices of teachers and teacher educators. However, participating in discussion groups for many teachers, including those in academia, is…

Edwards-Groves, Christine J.

2013-01-01

179

Tribenzotriquinacenes bearing three peripheral or bridgehead urea groups stretched into the 3-D space  

PubMed Central

Summary The syntheses of tribenzotriquinacenes (TBTQ) bearing three phenylurea groupings at either the arene periphery or at the benzhydrylic bridgeheads of the rigid, convex–concave, C 3 v-symmetrical molecular framework are reported. 1H NMR data point to supramolecular aggregation of these TBTQ derivatives in low-polarity solvents. PMID:21512595

Tellenbroker, Jorg

2011-01-01

180

Deep neck space abscesses of dental origin: the impact of Streptococcus group Milleri.  

PubMed

In recent years, there has been rising interest in Streptococcus group Milleri (SM) because high mortality rates have been related to it. In case of deep neck infections (DNI), whatever the origin, mortality rates as high as 26% were reported. But there are no data available for DNI with SM of purely dental origin. The aim of our article was to describe and analyse DNI of purely dental origin involving on one hand SM and on the other hand infections without presence of SM. We compared these two groups and statistically investigated if there were differences in clinical presentation (age, mouth opening, length of hospital stay, laboratory parameters) or clinical behaviour (re-operation, re-hospitalisation, secondary osteomyelitis, stay at intensive care, length of antibiotic treatment, presence of resistances against antibiotics, incapacity to work). For this, we retrospectively searched medical records of our institution for all purulent DNI treated from 2004 till 2012. We found 81 patients meeting all inclusion criteria. Thirty-four patients had involvement of SM, 47 did not. The only statistically significant difference between the SM group and the non-SM group was the length of incapacity to work. All other parameters were non-significant. Furthermore, there were no fatalities. In conclusion, the clinical importance of this article is that patients with deep neck abscesses of purely dental origin involving SM do not need more or different care when compared to all other DNI of dental origin. PMID:24241360

Terzic, Andrej; Scolozzi, Paolo

2014-10-01

181

Assessment of various natural orbitals as the basis of large active space density-matrix renormalization group calculations  

NASA Astrophysics Data System (ADS)

It is well-known that not only the orbital ordering but also the choice of the orbitals itself as the basis may significantly influence the computational efficiency of density-matrix renormalization group (DMRG) calculations. In this study, for assessing the efficiency of using various natural orbitals (NOs) as the DMRG basis, we performed benchmark DMRG calculations with different bases, which included the NOs obtained by various traditional electron correlation methods, as well as NOs acquired from preliminary moderate DMRG calculations (e.g., preserved states less than 500). The tested systems included N2, transition metal Cr2 systems, as well as 1D hydrogen polyradical chain systems under equilibrium and dissociation conditions and 2D hydrogen aggregates. The results indicate that a good compromise between the requirement for low computational costs of acquiring NOs and the demand for high efficiency of NOs as the basis of DMRG calculations may be very dependent on the studied systems' diverse electron correlation characteristics and the size of the active space. It is also shown that a DMRG-complete active space configuration interaction (DMRG-CASCI) calculation in a basis of carefully chosen NOs can provide a less expensive alternative to the standard DMRG-complete active space self-consistent field (DMRG-CASSCF) calculation and avoid the convergence difficulties of orbital optimization for large active spaces. The effect of different NO ordering schemes on DMRG-CASCI calculations is also discussed.

Ma, Yingjin; Ma, Haibo

2013-06-01

182

High-level Expression Purification Crystallization and Preliminary X-ray Crystallographic Studies of the Receptor Binding Domain of botulinum neurotoxin Serotype D  

SciTech Connect

Botulinum neurotoxins (BoNTs) are highly toxic proteins for humans and animals that are responsible for the deadly neuroparalytic disease botulism. Here, details of the expression and purification of the receptor-binding domain (HCR) of BoNT/D in Escherichia coli are presented. Using a codon-optimized cDNA, BoNT/D{_}HCR was expressed at a high level (150-200 mg per litre of culture) in the soluble fraction. Following a three-step purification protocol, very pure (>98%) BoNT/D{_}HCR was obtained. The recombinant BoNT/D{_}HCR was crystallized and the crystals diffracted to 1.65 {angstrom} resolution. The crystals belonged to space group P2{sub 1}2{sub 1}2{sub 1}, with unit-cell parameters a = 60.8, b = 89.7, c = 93.9 {angstrom}. Preliminary crystallographic data analysis revealed the presence of one molecule in the asymmetric unit.

Y Zhang; X Gao; G Buchko; H Robinson; S Varnum

2011-12-31

183

High-level expression, purification, crystallization and preliminary X-ray crystallographic studies of the receptor-binding domain of botulinum neurotoxin serotype D  

PubMed Central

Botulinum neurotoxins (BoNTs) are highly toxic proteins for humans and animals that are responsible for the deadly neuroparalytic disease botulism. Here, details of the expression and purification of the receptor-binding domain (HCR) of BoNT/D in Escherichia coli are presented. Using a codon-optimized cDNA, BoNT/D_HCR was expressed at a high level (150–200 mg per litre of culture) in the soluble fraction. Following a three-step purification protocol, very pure (>98%) BoNT/D_HCR was obtained. The recombinant BoNT/D_HCR was crystallized and the crystals diffracted to 1.65?Å resolution. The crystals belonged to space group P212121, with unit-cell parameters a = 60.8, b = 89.7, c = 93.9?Å. Preliminary crystallographic data analysis revealed the presence of one molecule in the asymmetric unit. PMID:21139207

Zhang, Yanfeng; Gao, Xiaoli; Qin, Ling; Buchko, Garry W.; Robinson, Howard; Varnum, Susan M.

2010-01-01

184

Production, crystallization and preliminary crystallographic analysis of Allochromatium vinosum thiosulfate dehydrogenase TsdA, an unusual acidophilic c-type cytochrome.  

PubMed

The ability to perform the very simple oxidation of two molecules of thiosulfate to tetrathionate is widespread among prokaryotes. Despite the prevalent occurrence of tetrathionate formation and its well documented significance within the sulfur cycle, little is known about the enzymes that catalyze the oxidative condensation of two thiosulfate anions. To fill this gap, the thiosulfate dehydrogenase (TsdA) enzyme from the purple sulfur bacterium Allochromatium vinosum was recombinantly expressed in Escherichia coli, purified and crystallized, and a crystallographic data set was collected. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 79.2, b = 69.9, c = 57.9?Å, ? = 129.3°, contained one monomer per asymmetric unit and diffracted to a resolution of 1.98?Å. PMID:25286955

Brito, José A; Gutierres, André; Denkmann, Kevin; Dahl, Christiane; Archer, Margarida

2014-10-01

185

Crystallization and preliminary X-ray crystallographic studies of the outer membrane cytochrome OmcA from Shewanella oneidensis MR-1  

SciTech Connect

The outer membrane cytochrome OmcA functions as a terminal metal reductase in the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. The ten-heme centers shuttle electrons from the transmembrane donor complex to extracellular electron acceptors. Here, the crystallization and preliminary crystallographic analysis of OmcA are reported. Crystals of OmcA were grown by the sitting-drop vapor-diffusion method using PEG 20 000 as a precipitant. The OmcA crystals belonged to space group P21, with unit-cell parameters a = 93.0, b = 246.0, c = 136.6 A ° , * = 90, * = 97.8, * = 90*. X-ray diffraction data were collected to a maximum resolution of 3.25 A ° .

Tomanicek, S. J.; Johs, Alexander; Sawhney, M. S.; Shi, Liang; Liang, L.

2012-01-01

186

Crystallization and preliminary X-ray crystallographic studies of the outer membrane cytochrome OmcA from Shewanella oneidensis MR-1  

SciTech Connect

The outer membrane cytochrome OmcA functions as a terminal metal reductase in the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. The ten-heme centers shuttle electrons from the transmembrane donor complex to extracellular electron acceptors. Here, the crystallization and preliminary crystallographic analysis of OmcA are reported. Crystals of OmcA were grown by the sitting-drop vapor-diffusion method using PEG 20 000 as a precipitant. The OmcA crystals belonged to space group P2{sub 1}, with unit-cell parameters a = 93.0, b = 246.0, c = 136.6 {angstrom}, = 90, {beta} = 97.8, {gamma} = 90{sup o}. X-ray diffraction data were collected to a maximum resolution of 3.25 {angstrom}.

Tomanicek, S.J.; Johs, A.; Sawhney, M.S.; Shi, L.; Liang, L. (PNNL); (ORNL)

2012-05-24

187

Space  

NSDL National Science Digital Library

This unit begins by introducing students to the historical motivation for space exploration. They learn about the International Space Station, including current and futuristic ideas that engineers are designing to propel space research. Then they learn about the physical properties of the Moon, and think about what types of products engineers would need to design in order for humans to live on the Moon. Lastly, students learn some descriptive facts about asteroids, such as their sizes and how that relates to the potential danger of an asteroid colliding with the Earth.

Integrated Teaching And Learning Program

188

Application of the real space dynamic renormalization group method to the one-dimensional kinetic ising model  

NASA Astrophysics Data System (ADS)

We apply the recently developed real space dynamic renormalization group method to the one-dimensional kinetic Ising model. We show how one can develop block spin methods that lead to recursion relations for the space and time dependent correlation functions that correspond to the observables for this system. We point out the importance of carefully choosing the appropriate parameters governing the behavior of individual blocks of spins and the necessity of worrying about the high temperature properties of the temperature recursion relations if one is to obtain the proper exponential decay of correlation functions at large distances away from the critical point at zero temperature. We systematically investigate the accuracy of our approximate recursion relations for various correlation functions by checking them against the known exact results. Our simple methods work surprisingly well over a wide range of temperatures, wavenumbers and frequencies.

Mazenko, Gene F.; Luscombe, J.

1981-03-01

189

Using space-time visual analytic methods for exploring the dynamics of ethnic groups' residential patterns  

Microsoft Academic Search

In this article, we present a methodological framework, based on georeferenced house-level socio-demographic and infrastructure data, for investigating minority (or ethnic) group residential pattern dynamics in cities. This methodology, which uses visual analytical tools, is meant to help researchers examine how local land-use configurations shape minorities' residential dynamics and, thereby, affect the level of minority–majority segregation. This methodology responds to

Itzhak Omer; Peter Bak; Tobias Schreck

2010-01-01

190

Crystallization and preliminary X-ray crystallographic analysis of ?-glucosidase HaG from Halomonas sp. strain H11.  

PubMed

The ?-glucosidase HaG from the halophilic bacterium Halomonas sp. strain H11 catalyzes the hydrolysis of the glucosidic linkage at the nonreducing end of ?-glucosides, such as maltose and sucrose, to release ?-glucose. Based on its amino-acid sequence, this enzyme is classified as a member of glycoside hydrolase family 13. HaG has three unique characteristics: (i) a very narrow substrate specificity, almost exclusively hydrolyzing disaccharides; (ii) activation by monovalent cations, such as K(+), Rb(+), Cs(+) and NH4(+); and (iii) high transfer activity of the glucose moiety to the OH group of low-molecular-weight compounds, including glycerol and 6-gingerol. Crystallographic studies have been performed in order to understand these special features. An expression vector was constructed and recombinant HaG protein was overexpressed, purified and crystallized. A data set to 2.15?Å resolution was collected and processed. The crystal belonged to space group P212121, with unit-cell parameters a = 60.2, b = 119.2, c = 177.2?Å. The structure has been determined by molecular replacement using the isomaltulose synthase PalI as the search model (PDB entry 1m53). PMID:24699739

Shen, Xing; Saburi, Wataru; Gai, Zuo-Qi; Komoda, Keisuke; Yu, Jian; Ojima-Kato, Teruyo; Kido, Yusuke; Matsui, Hirokazu; Mori, Haruhide; Yao, Min

2014-04-01

191

An HI survey of the Centaurus and Sculptor Groups - Constraints on the space density of low mass galaxies  

E-print Network

We present results of two 21-cm HI surveys performed with the Australia Telescope Compact Array in the nearby Centaurus A and Sculptor galaxy groups. These surveys are sensitive to compact HI clouds and galaxies with HI masses as low as 3E+06 Msun, and are therefore among the most sensitive extragalactic HI surveys to date. The surveys consist of sparsely spaced pointings that sample approximately 2% of the groups' area on the sky. We detected previously known group members, but we found no new HI clouds or galaxies down to the sensitivity limit of the surveys. If the HI mass function had a faint end slope of alpha = 1.5 below M_{HI} = 10^{7.5} Msun in these groups, we would have expected ~3 new objects. Cold dark matter theories of galaxy formation predict the existence of a large number low mass DM sub-halos that might appear as tiny satellites in galaxy groups. Our results support and extend similar conclusions derived from previous HI surveys that a HI rich population of these satellites does not exist.

W. J. G. de Blok; M. A. Zwaan; M. Dijkstra; F. H. Briggs; K. C. Freeman

2001-11-13

192

Identification of succinic semialdehyde reductases from Geobacter: expression, purification, crystallization, preliminary functional, and crystallographic analysis  

SciTech Connect

Succinic semialdehyde reductase (SSAR) is an important enzyme involved in {gamma}-aminobutyrate (GABA) metabolism. By converting succinic semialdehyde (SSA) to {gamma}-hydroxybutyrate (GHB), the SSAR facilitates an alternative pathway for GABA degradation. In this study, we identified SSARs from Geobacter sulfurreducens and Geobacter metallireducens (GsSSAR and GmSSAR, respectively). The enzymes were over-expressed in Escherichia coli and purified to near homogeneity. Both GsSSAR and GmSSAR showed the activity of reducing SSA using nicotinamide adenine dinucleotide phosphate as a co-factor. The oligomeric sizes of GsSSAR and GmSSAR, as determined by analytical size exclusion chromatography, suggest that the enzymes presumably exist as tetramers in solution. The recombinant GsSSAR and GmSSAR crystallized in the presence of NADP{sup +}, and the resulting crystals diffracted to 1.89 {angstrom} (GsSSAR) and 2.25 {angstrom} (GmSSAR) resolution. The GsSSAR and GmSSAR crystals belong to the space groups P2{sub 1}22{sub 1} (a = 99.61 {angstrom}, b = 147.49 {angstrom}, c = 182.47 {angstrom}) and P1 (a = 75.97 {angstrom}, b = 79.14 {angstrom}, c = 95.47 {angstrom}, {alpha} = 82.15{sup o}, {beta} = 88.80{sup o}, {gamma} = 87.66{sup o}), respectively. Preliminary crystallographic data analysis suggests the presence of eight protein monomers in the asymmetric units for both GsSSAR and GmSSAR.

Zhang, Yanfeng; Gao, Xiaoli; Zheng, Yi; Garavito, R. Michael (MSU)

2012-04-30

193

On the renormalisation group for the boundary truncated conformal space approach  

NASA Astrophysics Data System (ADS)

In this paper we continue the study of the truncated conformal space approach to perturbed boundary conformal field theories. This approach to perturbation theory suffers from a renormalisation of the coupling constant and a multiplicative renormalisation of the Hamiltonian. We show how these two effects can be predicted by both physical and mathematical arguments and prove that they are correct to leading order for all states in the TCSA system. We check these results using the TCSA applied to the tri-critical Ising model and the Yang-Lee model. We also study the TCSA of an irrelevant (non-renormalisable) perturbation and find that, while the convergence of the coupling constant and energy scales are problematic, the renormalised and rescaled spectrum remain a very good fit to the exact result, and we find a numerical relationship between the IR and UV couplings describing a particular flow. Finally we study the large coupling behaviour of TCSA and show that it accurately encompasses several different fixed points.

Watts, Gérard M. T.

2012-06-01

194

The Exploration Atmospheres Working Group's Report on Space Radiation Shielding Materials  

NASA Technical Reports Server (NTRS)

This part of Exploration Atmospheres Working Group analyses focuses on the potential use of nonmetallic composites as the interior walls and structural elements exposed to the atmosphere of the spacecraft or habitat. The primary drive to consider nonmetallic, polymer-based composites as an alternative to aluminum structure is due to their superior radiation shielding properties. But as is shown in this analysis, these composites can also be made to combine superior mechanical properties with superior shielding properties. In addition, these composites can be made safe; i.e., with regard to flammability and toxicity, as well as "smart"; i.e., embedded with sensors for the continuous monitoring of material health and conditions. The analysis main conclusions are that (1) smart polymer-based composites are an enabling technology for safe and reliable exploration missions, and (2) an adaptive, synergetic systems approach is required to meet the missions requirements from structure, properties, and processes to crew health and protection for exploration missions.

Barghouty, A. F.; Thibeault, S. A.

2006-01-01

195

Communication constraints, indexical countermeasures, and crew configuration effects in simulated space-dwelling groups  

NASA Astrophysics Data System (ADS)

Previous research with groups of individually isolated crews communicating and problem-solving in a distributed interactive simulation environment has shown that the functional interchangeability of available communication channels can serve as an effective countermeasure to communication constraints. The present report extends these findings by investigating crew performance effects and psychosocial adaptation following: (1) the loss of all communication channels, and (2) changes in crew configuration. Three-person crews participated in a simulated planetary exploration mission that required identification, collection, and analysis of geologic samples. Results showed that crews developed and employed discrete navigation system operations that served as functionally effective communication signals (i.e., “indexical” or “deictic” cues) in generating appropriate crewmember responses and maintaining performance effectiveness in the absence of normal communication channels. Additionally, changes in crew configuration impacted both performance effectiveness and psychosocial adaptation.

Hienz, Robert D.; Brady, Joseph V.; Hursh, Steven R.; Banner, Michele J.; Gasior, Eric D.; Spence, Kevin R.

2007-02-01

196

Behavioral and biological effects of autonomous versus scheduled mission management in simulated space-dwelling groups  

NASA Astrophysics Data System (ADS)

Logistical constraints during long-duration space expeditions will limit the ability of Earth-based mission control personnel to manage their astronaut crews and will thus increase the prevalence of autonomous operations. Despite this inevitability, little research exists regarding crew performance and psychosocial adaptation under such autonomous conditions. To this end, a newly-initiated study on crew management systems was conducted to assess crew performance effectiveness under rigid schedule-based management of crew activities by Mission Control versus more flexible, autonomous management of activities by the crews themselves. Nine volunteers formed three long-term crews and were extensively trained in a simulated planetary geological exploration task over the course of several months. Each crew then embarked on two separate 3-4 h missions in a counterbalanced sequence: Scheduled, in which the crews were directed by Mission Control according to a strict topographic and temporal region-searching sequence, and Autonomous, in which the well-trained crews received equivalent baseline support from Mission Control but were free to explore the planetary surface as they saw fit. Under the autonomous missions, performance in all three crews improved (more high-valued geologic samples were retrieved), subjective self-reports of negative emotional states decreased, unstructured debriefing logs contained fewer references to negative emotions and greater use of socially-referent language, and salivary cortisol output across the missions was attenuated. The present study provides evidence that crew autonomy may improve performance and help sustain if not enhance psychosocial adaptation and biobehavioral health. These controlled experimental data contribute to an emerging empirical database on crew autonomy which the international astronautics community may build upon for future research and ultimately draw upon when designing and managing missions.

Roma, Peter G.; Hursh, Steven R.; Hienz, Robert D.; Emurian, Henry H.; Gasior, Eric D.; Brinson, Zabecca S.; Brady, Joseph V.

2011-05-01

197

Variations in Reactivity on Different Crystallographic Orientations of Cerium Oxide  

SciTech Connect

Cerium oxide is a principal component in many heterogeneous catalytic processes. One of its key characteristics is the ability to provide or remove oxygen in chemical reactions. The different crystallographic faces of ceria present significantly different surface structures and compositions that may alter the catalytic reactivity. The structure and composition determine the number of coordination vacancies surrounding surface atoms, the availability of adsorption sites, the spacing between adsorption sites and the ability to remove O from the surface. To investigate the role of surface orientation on reactivity, CeO2 films were grown with two different orientations. CeO2(100) films were grown ex situ by pulsed laser deposition on Nb-doped SrTiO3(100). CeO2(111) films were grown in situ by thermal deposition of Ce metal onto Ru(0001) in an oxygen atmosphere. The chemical reactivity was characterized by the adsorption and decomposition of various molecules such as alcohols, aldehydes and organic acids. In general the CeO2(100) surface was found to be more active, i.e. molecules adsorbed more readily and reacted to form new products, especially on a fully oxidized substrate. However the CeO2(100) surface was less selective with a greater propensity to produce CO, CO2 and water as products. The differences in chemical reactivity are discussed in light of possible structural terminations of the two surfaces. Recently nanocubes and nano-octahedra have been synthesized that display CeO2(100) and CeO2(111) faces, respectively. These nanoparticles enable us to correlate reactions on high surface area model catalysts at atmospheric pressure with model single crystal films in a UHV environment.

Mullins, David R [ORNL] [ORNL; Albrecht, Peter M [ORNL] [ORNL; Calaza, Florencia C [ORNL] [ORNL

2013-01-01

198

Incorporating Space Science Content Into the Undergraduate Curriculum by the NASA Education Forums' Higher Education Working Group  

NASA Astrophysics Data System (ADS)

As part of the NASA Education Forums, the Higher Education Working Group (HEWG) strives to support undergraduate science education through a variety of activities. These activities include: providing resource that incorporate space science topics into the existing undergraduate curriculum, understanding the role that community colleges play in STEM education and preparing STEM teachers, and identifying issues in diversity related to STEM education. To assess the best way of including space science into the undergraduate curriculum, the HEWG held a series of workshops and conducted surveys of undergraduate faculty who are conducting research in space science. During this engagement, the faculty expressed a need for a centralized repository of materials that can be used as part of already existing undergraduate courses in astronomy, physics, and earth science. Such a repository has since been developed, the 'EarthSpace Higher Education Clearing House (http://www.lpi.usra.edu/earthspace/) and it is still growing. Additional community tools, such as a newsletter, are provided through this website. To better understand the role and needs of community colleges, the HEWG undertook and extensive survey of community college STEM faculty. 187 faculty responded to the survey and the results show the extensive teaching load these faculty have, as well as the diverse demographics and the extent to which STEM teachers begin their preparation at 2 year institutions. Finally, the HEWG has begun to work on understanding the issues faced in increasing the diversity of the STEM work force. Progress and results of all this work will be summarized in this presentation.

Gross, N. A.; Buxner, S.; Cobabe-Ammann, E. A.; Fraknoi, A.; Moldwin, M.; Peticolas, L. M.; Low, R.; Schultz, G. R.

2013-12-01

199

Crystallographic evolution of microstructure in thin film processing: Part II. Grain boundary structure  

NASA Astrophysics Data System (ADS)

The technique of electron backscattered diffraction is used to charactcrize the microtexture and mesotexture of grain neighborhoods in an annealed thin film of Al97Ge3 on thermally oxidized silicon. Of the microstructural features present in this material, a “sunken” (or “collapsed”) grain neighborhood is examined in terms of its mesotexture. The representation of crystallographic orientation between a “sunken” grain and its surrounding neighbors is assessed using inverse pole figures and Rodrigues-Frank (R-F) space orientation mapping. The two types of mappings are compared and detailed calculations of R-F space are shown. The advantages of the R-F space representation are illustrated. The total number of grains examined is 78 while the number of axis-angle pairs is 72. The microtexture is a strongly preferred < 111> parallel to the substrate normal while the mesotexture is comprised of low angle boundaries and fiber mesotexture as indicated by a R-F map.

Petkie, Ronald R.; Tu, K. N.; Rajan, Krishna

1994-09-01

200

An application of the renormalization group to the calculation of the vacuum decay rate in flat and curved space-time  

E-print Network

I show that an application of renormalization group arguments may lead to significant corrections to the vacuum decay rate for phase transitions in flat and curved space-time. It can also give some information regarding its dependence on the parameters of the theory, including the cosmological constant in the case of decay in curved space-time.

D. Metaxas

2004-12-14

201

Overexpression, purification, crystallization and preliminary crystallographic studies of a hyperthermophilic adenylosuccinate synthetase from Pyrococcus horikoshii OT3.  

PubMed

Adenylosuccinate synthetase (AdSS) is a ubiquitous enzyme that catalyzes the first committed step in the conversion of inosine monophosphate (IMP) to adenosine monophosphate (AMP) in the purine-biosynthetic pathway. Although AdSS from the vast majority of organisms is 430-457 amino acids in length, AdSS sequences isolated from thermophilic archaea are 90-120 amino acids shorter. In this study, crystallographic studies of a short AdSS sequence from Pyrococcus horikoshii OT3 (PhAdSS) were performed in order to reveal the unusual structure of AdSS from thermophilic archaea. Crystals of PhAdSS were obtained by the microbatch-under-oil method and X-ray diffraction data were collected to 2.50 Å resolution. The crystal belonged to the trigonal space group P3(2)12, with unit-cell parameters a = b = 57.2, c = 107.9 Å. There was one molecule per asymmetric unit, giving a Matthews coefficient of 2.17 Å(3) Da(-1) and an approximate solvent content of 43%. In contrast, the results of native polyacrylamide gel electrophoresis and analytical ultracentrifugation showed that the recombinant PhAdSS formed a dimer in solution. PMID:22139164

Wang, Xiaoying; Akasaka, Ryogo; Takemoto, Chie; Morita, Satoshi; Yamaguchi, Machiko; Terada, Takaho; Shirozu, Mikako; Yokoyama, Shigeyuki; Chen, Shilin; Si, Shuyi; Xie, Yong

2011-12-01

202

Purification, crystallization and preliminary crystallographic analysis of the 16S rRNA methyltransferase RsmI from Escherichia coli.  

PubMed

RsmI and RsmH are AdoMet-dependent methyltransferases that are responsible for the 2'-O-methylation and N(4)-methylation of C1402 of Escherichia coli 16S rRNA, respectively. Modification of this site has been found to play a role in fine-tuning the shape and function of the P-site to increase the decoding fidelity. It is interesting to study the mechanism by which C1402 can be methylated by both RsmI and RsmH. The crystal structure of RsmH in complex with AdoMet and cytidine has recently been determined and provided some implications for N(4)-methylation of this site. Here, the purification and crystallization of RsmI as well as its preliminary crystallographic analysis are reported. Co-crystallization of RsmI with AdoMet was carried out by the sitting-drop vapour-diffusion method and X-ray diffraction data were collected to 2.60?Å resolution on beamline 1W2B at BSRF. The crystal contained three molecules per asymmetric unit and belonged to space group C2, with unit-cell parameters a = 121.9, b = 152.5, c = 54.2?Å, ? = 93.4°. PMID:25195904

Zhao, Mohan; Wang, Li; Zhang, Heng; Dong, Yuhui; Gong, Yong; Zhang, Linbo; Wang, Jian

2014-09-01

203

Crystallographic variant selection in {alpha}-{beta} brass  

SciTech Connect

The transformation texture of {alpha}/{beta} brass with a diffusional Widmanstaetten {alpha} growth morphology has been investigated. Electron micrographs and electron backscattered diffraction was used to determine that the orientation relationship between the {beta} phase and the {alpha} associated with nucleation at {beta} grain boundaries was 44.3 deg <1 1 6>. Crystallographic variant selection was observed across those prior {beta}/{beta} grain boundaries, but this has little effect on the transformation texture due to the crystal symmetry. The effect of the crystallographic variant selection on texture is further weakened by nucleation of diffusional transformed {alpha} in the grain interior.

Stanford, N. [Manchester Materials Science Centre, University of Manchester, Grosvenor Street, Manchester M1 7HS (United Kingdom); Bate, P.S. [Manchester Materials Science Centre, University of Manchester, Grosvenor Street, Manchester M1 7HS (United Kingdom)]. E-mail: pete.bate@man.ac.uk

2005-02-01

204

Crystallographic wet chemical etching of GaN  

NASA Astrophysics Data System (ADS)

We demonstrate well-controlled crystallographic etching of wurtzite GaN grown on c-plane sapphire using H3PO4, molten KOH, KOH dissolved in ethylene glycol, and NaOH dissolved in ethylene glycol between 90 and 180 °C, with etch rates as high as 3.2 ?m/min. The crystallographic GaN etch planes are {0001}, {101¯0}, {101¯ 1¯}, {101¯ 2¯}, and {101¯3}. The vertical {101¯0} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope. The activation energy is 21 kcal/mol, indicative of reaction-rate limited etching.

Stocker, D. A.; Schubert, E. F.; Redwing, J. M.

1998-11-01

205

Structure of N-acetylglucosamine-1-phosphate uridyltransferase (GlmU) from Mycobacterium tuberculosis in a cubic space group.  

PubMed

GlmU is a bifunctional enzyme that catalyzes the final two steps in the biosynthesis of UDP-GlcNAc. Crystals of GlmU from Mycobacterium tuberculosis obtained using ammonium sulfate as a precipitant diffracted poorly (to 3.4 A resolution) and displayed an unusually high solvent content (>80%) with sparse crystal packing that resulted in large solvent channels. With one molecule per asymmetric unit, the monomers from three neighbouring asymmetric units related by the crystal threefold formed a biological trimer. Although this is the first report of the structure of GlmU determined in a cubic crystal form, the trimeric arrangement here is similar to that observed for other GlmU structures determined in hexagonal (H3, H32, P6(3)22) space groups. PMID:19407371

Verma, Sunil Kumar; Jaiswal, Mamta; Kumar, Neeraj; Parikh, Amit; Nandicoori, Vinay Kumar; Prakash, Balaji

2009-05-01

206

Calculating field emission currents in nanodiodes - a multi-group formalism with space charge and exchange-correlation effects  

E-print Network

Inclusion of electron-electron interaction is essential in nano-diodes to understand the underlying physical phenomenon and tailor devices accordingly. However, both space charge and exchange-correlation interactions involve electrons at different energies and hence a self-consistent multi-energy-group solution of the Schr\\{o}dinger-Poisson system is required. It is shown here that the existence of a limiting density-dependent potential at low applied voltages allows calculation of the field emission current. Despite additional interactions, a Fowler-Nordheim behaviour is observed. It is also found that the exchange-correlation potential dominates at these voltages in nanogaps and possibly leads to a higher turn-on voltage.

Debabrata Biswas; Raghwendra Kumar

2013-10-10

207

Requirements for space-based observations in fire management: a report by the Wildland Fire Hazard Team, Committee on Earth Observation Satellites (CEOS) Disaster Management Support Group (DMSG)  

Microsoft Academic Search

The Wildland Fire Hazard Team reviewed potential requirements for space-based observations in fire management. The team produced a report, developed under the auspices of the Disaster Management Support Group (DMSG) of the G-7 Committee on Earth Observation Satellites (CEOS). The document was prepared by an international working group, with experience in the field of remote sensing as applied to wildland

T. J. Lynham; C. W. Dull; A. Singh

2002-01-01

208

Coordination of Advanced Solar Observatory (ASO) Science Working Group (SWG) for the study of instrument accommodation and operational requirements on space station  

NASA Technical Reports Server (NTRS)

The objectives are to coordinate the activities of the Science Working Group (SWG) of the Advanced Solar Observatory (ASO) for the study of instruments accommodation and operation requirements on board space station. In order to facilitate the progress of the objective, two conferences were organized, together with two small group discussions.

Wu, S. T.

1989-01-01

209

Detailed insights from microarray and crystallographic studies into carbohydrate  

E-print Network

Detailed insights from microarray and crystallographic studies into carbohydrate recognition of the parasite can be explained by carbohydrate microarray screening analyses that have demonstrated the ability of TgMIC1 to 2-3- and 2-6-linked sialyl carbohydrates. Interestingly, two novel synthetic fluorinated

Davis, Ben G.

210

Nanoscale lithography of graphene with crystallographic orientation control  

Microsoft Academic Search

The two scanning probe microscope based methods for the production of graphene nanoarchitectures with crystallographically oriented edges: scanning tunneling lithography (STL) and carbothermal etching (CTE) are compared. STL offers higher freedom in choosing the orientation, it makes possible sophisticated manipulation of the etched nanoarchitectures and immediate atomic resolution of the etched structure, but it suffers from the need of a

G. Dobrik; P. Nemes-Incze; L. Tapasztó; Ph. Lambin; L. P. Biró

211

Scripta Materialia 57 (2007) 869872 Crystallographic Texture and  

E-print Network

and martensite. Keywords: Transformation texture, martensite, stainless steel, stress­affected transforma- tion that in deformed austenitic stainless steels, the trans- formation texture should be calculated in two­stages [1 In a recent study the crystallographic texture of an austenitic stainless steel which trans- formed into body

Cambridge, University of

212

Crystallographic studies on hexaphenyl thin films — a review  

Microsoft Academic Search

Thin films of hexaphenyl show interesting crystallographic features, which are of great importance for technological applications. The textures and the sizes of the crystallites have large influence on the electronic and optical properties of the thin films. Hexaphenyl thin films are prepared by physical vapour deposition on various types of substrates: isotropic and mechanical pre-treated substrates or single crystalline surfaces.

Roland Resel

2003-01-01

213

X-ray Crystallographic Computations Using a Programmable Calculator.  

ERIC Educational Resources Information Center

Describes six crystallographic programs which have been developed to illustrate the range of usefulness of programmable calculators in providing computational assistance in chemical analysis. These programs are suitable for the analysis of x-ray diffraction data in the laboratory by students. (HM)

Attard, Alfred E.; Lee, Henry C.

1979-01-01

214

Crystallization and preliminary X-ray crystallographic studies of the oxidative-stress sensor SoxR and its complex with DNA.  

PubMed

SoxR, a member of the MerR family of transcriptional activators, functions as a sensor of oxidative stress. The redox states of the 2Fe-2S cluster of SoxR regulate the activity of SoxR. Here, the crystallization and preliminary crystallographic analysis of SoxR and its complex with DNA are reported. Crystals of SoxR were obtained using PEG 10,000 and glycerol as precipitants. The crystals of SoxR belong to space group P6(2) or P6(4), with unit-cell parameters a = b = 80.0, c = 88.1 A. Crystals of the SoxR-DNA complex were obtained using a 20 bp DNA fragment from a condition containing PEG 10,000 and sodium/potassium tartrate. The crystals of the SoxR-DNA complex belong to space group P6(1)22 or P6(5)22, with unit-cell parameters a = b = 53.5, c = 355.6 A. Diffraction data were collected to a maximum resolution of 3.2 and 2.7 A for SoxR and the SoxR-DNA complex, respectively. PMID:17142916

Watanabe, Satoshi; Kita, Akiko; Kobayashi, Kazuo; Takahashi, Yasuhiro; Miki, Kunio

2006-12-01

215

Recovery of Crystallographic Texture in Remineralized Dental Enamel  

PubMed Central

Dental caries is the most prevalent disease encountered by people of all ages around the world. Chemical changes occurring in the oral environment during the caries process alter the crystallography and microstructure of dental enamel resulting in loss of mechanical function. Little is known about the crystallographic effects of demineralization and remineralization. The motivation for this study was to develop understanding of the caries process at the crystallographic level in order to contribute towards a long term solution. In this study synchrotron X-ray diffraction combined with scanning electron microscopy and scanning microradiography have been used to correlate enamel crystallography, microstructure and mineral concentration respectively in enamel affected by natural caries and following artificial demineralization and remineralization regimes. In particular, the extent of destruction and re-formation of this complex structure has been measured. 2D diffraction patterns collected at the European Synchrotron Radiation Facility were used to quantify changes in the preferred orientation (crystallographic texture) and position of the (002) Bragg reflection within selected regions of interest in each tooth slice, and then correlated with the microstructure and local mineral mass. The results revealed that caries and artificial demineralization cause a large reduction in crystallographic texture which is coupled with the loss of mineral mass. Remineralization restores the texture to the original level seen in healthy enamel and restores mineral density. The results also showed that remineralization promotes ordered formation of new crystallites and growth of pre-existing crystallites which match the preferred orientation of healthy enamel. Combining microstructural and crystallographic characterization aids the understanding of caries and erosion processes and assists in the progress towards developing therapeutic treatments to allow affected enamel to regain structural integrity. PMID:25360532

Siddiqui, Samera; Anderson, Paul; Al-Jawad, Maisoon

2014-01-01

216

Atomic structure of defects in anion-deficient perovskite-based ferrites with a crystallographic shear structure.  

PubMed

Crystallographic shear (CS) planes provide a new structure-generation mechanism in the anion-deficient perovskites containing lone-pair cations. Pb2Sr2Bi2Fe6O16, a new n = 6 representative of the A(n)B(n)O(3n-2) homologous series of the perovskite-based ferrites with the CS structure, has been synthesized using the solid-state technique. The structure is built of perovskite blocks with a thickness of four FeO6 octahedra spaced by double columns of FeO5 edge-sharing distorted tetragonal pyramids, forming 1/2[110](101)p CS planes (space group Pnma, a = 5.6690(2) Å, b = 3.9108(1) Å, c = 32.643(1) Å). Pb2Sr2Bi2Fe6O16 features a wealth of microstructural phenomena caused by the flexibility of the CS planes due to the variable ratio and length of the constituting fragments with {101}p and {001}p orientation. This leads to the formation of "waves", "hairpins", "?-shaped" defects, and inclusions of the hitherto unknown layered anion-deficient perovskites Bi2(Sr,Pb)Fe3O8.5 and Bi3(Sr,Pb)Fe4O11.5. Using a combination of diffraction, imaging, and spectroscopic transmission electron microscopy techniques this complex microstructure was fully characterized, including direct determination of positions, chemical composition, and coordination number of individual atomic species. The complex defect structure makes these perovskites particularly similar to the CS structures in ReO3-type oxides. The flexibility of the CS planes appears to be a specific feature of the Sr-based system, related to the geometric match between the SrO perovskite layers and the {100}p segments of the CS planes. PMID:24479580

Batuk, Maria; Turner, Stuart; Abakumov, Artem M; Batuk, Dmitry; Hadermann, Joke; Van Tendeloo, Gustaaf

2014-02-17

217

The Star Formation Histories of Local Group Dwarf Galaxies I. Hubble Space Telescope / Wide Field Planetary Camera 2 Observations  

E-print Network

We present uniformly measured star formation histories (SFHs) of 40 Local Group dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with $\\tau$ $\\sim$ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs (dTrans), and dwarf ellipticals (dEs) can be approximated by the combination of an exponentially declining SFH ($\\tau$ $\\sim$ 3-4 Gyr) for lookback ages $>$ 10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z=2 ranges considerably (80\\%...

Weisz, Daniel R; Skillman, Evan D; Holtzman, Jon; Gilbert, Karoline M; Dalcanton, Julianne J; Williams, Benjamin F

2014-01-01

218

Expression, purification, crystallization and X-ray crystallographic studies of different redox states of the active site of thioredoxin 1 from the whiteleg shrimp Litopenaeus vannamei  

PubMed Central

Thioredoxin (Trx) is a 12?kDa cellular redox protein that belongs to a family of small redox proteins which undergo reversible oxidation to produce a cystine disulfide bond through the transfer of reducing equivalents from the catalytic site cysteine residues (Cys32 and Cys35) to a disulfide substrate. In this study, crystals of thioredoxin 1 from the Pacific whiteleg shrimp Litopenaeus vannamei (LvTrx) were successfully obtained. One data set was collected from each of four crystals at 100?K and the three-dimensional structures of the catalytic cysteines in different redox states were determined: reduced and oxidized forms at 2.00?Å resolution using data collected at a synchrotron-radiation source and two partially reduced structures at 1.54 and 1.88?Å resolution using data collected using an in-house source. All of the crystals belonged to space group P3212, with unit-cell parameters a = 57.5?(4), b = 57.5?(4), c = 118.1?(8)?Å. The asymmetric unit contains two subunits of LvTrx, with a Matthews coefficient (V M) of 2.31?Å3?Da?1 and a solvent content of 46%. Initial phases were determined by molecular replacement using the crystallographic model of Trx from Drosophila melanogaster as a template. In the present work, LvTrx was overexpressed in Escherichia coli, purified and crystallized. Structural analysis of the different redox states at the Trx active site highlights its reactivity and corroborates the existence of a dimer in the crystal. In the crystallographic structures the dimer is stabilized by several interactions, including a disulfide bridge between Cys73 of each LvTrx monomer, a hydrogen bond between the side chain of Asp60 of each monomer and several hydrophobic interactions, with a noncrystallographic twofold axis. PMID:23695560

Campos-Acevedo, Adam A.; Garcia-Orozco, Karina D.; Sotelo-Mundo, Rogerio R.; Rudino-Pinera, Enrique

2013-01-01

219

Geometrical and crystallographic constraints determine the self-organization of shell microstructures in Unionidae (Bivalvia: Mollusca).  

PubMed

Unionid shells are characterized by an outer aragonitic prismatic layer and an inner nacreous layer. The prisms of the outer shell layer are composed of single-crystal fibres radiating from spheruliths. During prism development, fibres progressively recline to the growth front. There is competition between prisms, leading to the selection of bigger, evenly sized prisms. A new model explains this competition process between prisms, using fibres as elementary units of competition. Scanning electron microscopy and X-ray texture analysis show that, during prism growth, fibres become progressively orientated with their three crystallographic axes aligned, which results from geometric constraints and space limitations. Interestingly transition to the nacreous layer does not occur until a high degree of orientation of fibres is attained. There is no selection of crystal orientation in the nacreous layer and, as a result, the preferential orientation of crystals deteriorates. Deterioration of crystal orientation is most probably due to accumulation of errors as the epitaxial growth is suppressed by thick or continuous organic coats on some nacre crystals. In conclusion, the microstructural arrangement of the unionid shell is, to a large extent, self-organized with the main constraints being crystallographic and geometrical laws. PMID:11321067

Checa, A G; Rodríguez-Navarro, A

2001-04-01

220

A crystallographic perspective on sharing data and knowledge.  

PubMed

The crystallographic community is in many ways an exemplar of the benefits and practices of sharing data. Since the inception of the technique, virtually every published crystal structure has been made available to others. This has been achieved through the establishment of several specialist data centres, including the Cambridge Crystallographic Data Centre, which produces the Cambridge Structural Database. Containing curated structures of small organic molecules, some containing a metal, the database has been produced for almost 50 years. This has required the development of complex informatics tools and an environment allowing expert human curation. As importantly, a financial model has evolved which has, to date, ensured the sustainability of the resource. However, the opportunities afforded by technological changes and changing attitudes to sharing data make it an opportune moment to review current practices. PMID:25091065

Bruno, Ian J; Groom, Colin R

2014-10-01

221

Crystallographic Transitions in Perovskite Crystals Observed with Raman Spectroscopy  

NASA Astrophysics Data System (ADS)

We have studied the interaction of carbon dioxide with the surface of ferroelectric oxides such as barium titanate and potassium niobate. The surface chemistry of KNbO3 towards CO2 changes when the oxide particles become smaller than 100 microns. We have used Micro-Raman spectroscopy to determine if the structure of the grains change depending on their size and temperature. We have been able of observing crystallographic transition in small grains of the Perovskite with Raman spectroscopy. Small grains of 50 microns BaTiO3 undergo a transition at 133 degree C and small grains of 50 microns KNbO3 undergo a transition around 224 and 408 degrees C. A correlation between CO2 desorption and crystallographic changes can be observed. References: [1] A. L. Cabrera, F. Vargas and R. Zarate J. Phys. Chem. Sol. 55 (1994) 1303. [2] A. L. Cabrera, F. Vargas and J. J. Albers, Surf. Sci. 336 (1995) 280.

Castillo-Andaeta, F.; Mura-Mardones, J.; Cabrera, G. B.; Cabrera, A. L.; Altamirano-Busschots, L. A.

2001-03-01

222

Equilibrium between point defects and crystallographic shear planes  

Microsoft Academic Search

Thermodynamic data and electron microscopy observations concerning WO3-x can be understood if it is assumed that point defects and C.S.P. can coexist within a single phase. A very simple model is proposed. An interesting feature is that the variation of the partial molar-free energy is only slightly affected by the presence of crystallographic shear planes (C.S.P.) in opposition with partial

G. Boureau; J. F. Marucco

1983-01-01

223

The behavioural and physiological reactions of farmed red deer to transport: effects of sex, group size, space allowance and vehicular motion  

Microsoft Academic Search

Sixty yearling red deer (30 males, 30 females), comprising eight single-sex groups of either 5 or 10 animals, were loaded onto a livestock transporter for 3 h, during which they were either transported or remained stationary, at one of two space allowances (males: 0.5 m2 or 1 m2\\/deer, females: 0.4 m2 or 0.8 m2\\/deer). One group was tested each day,

P. N Grigor; P. J Goddard; C. A Littlewood

1998-01-01

224

Patterns of space use common to widely different types of social groupings of a coral reef fish  

Microsoft Academic Search

Synopsis The protogynous, Indo-Pacific serranid fish Anthias squamipinnis forms three types of social groupings, often within the same population: discrete groups, continuous masses, and intermediate groupings. In an intermediate grouping on Aldabra Island, Indian Ocean, females had larger home ranges than males and moved over the home range of several males. The movement rate of females into and out of

Douglas Y. Shapiro

1987-01-01

225

36 CFR 1280.85 - What space in the National Archives at College Park is available for use by non-NARA groups and...  

Code of Federal Regulations, 2010 CFR

36 ? Parks, Forests, and Public Property ? 3 ? 2010-07-01 ? 2010-07-01 ? false ? What space in the National Archives at College Park is available for use by non-NARA groups and organizations? ? 1280.85 ? Section 1280.85 ? Parks, Forests, and Public Property ? NATIONAL ARCHIVES AND...

2010-07-01

226

High resolution neutron crystallographic studies of the hydration of coenzyme cob(II)alamin  

SciTech Connect

The hydration of coenzyme cob(II)alamin has been studied using high resolution monochromatic neutron crystallographic data collected at room temperature to a resolution of surrounded by flexible side chains with terminal functional groups may be significant for 0.92 on the original diffractometer D19 with a prototype 4o x 64o detector at the high-flux reactor neutron source run by the Institute Laue Langevin. The resulting structure provides H bonding parameters for the hydration of biomacromolecules to unprecedented accuracy. These experimental parameters will be used to define more accurate force-fields for biomacromolecular structure refinement. The presence of a hydrophobic bowl motif efficient scavenging of ligands. The feasibility of extending the resolution of this structure to ultra high resolution was investigated by collecting time-of-flight neutron crystallographic data on diffractometer TOPAZ with a prototype array of 14 modular 21o x 21o detectors at the Spallation Neutron Source run by Oak Ridge National Laboratory.

Jogl, Gerwald [Brown University; Wang, Xiaoping [ORNL; Mason, Sax [Institut Laue-Langevin (ILL); Kovalevsky, Andrey [Los Alamos National Laboratory (LANL); Mustyakimov, Marat [Los Alamos National Laboratory (LANL); Fisher, Zoe [Los Alamos National Laboratory (LANL); Hoffmann, Christina [ORNL; Kratky, Christoph [Institute of Biosciences, University of Graz; Langan, Paul [ORNL

2011-01-01

227

High-resolution neutron crystallographic studies of the hydration of the coenzyme cob(II)alamin.  

PubMed

The hydration of the coenzyme cob(II)alamin has been studied using high-resolution monochromatic neutron crystallographic data collected at room temperature to a resolution of 0.92 Å on the original D19 diffractometer with a prototype 4° × 64° detector at the high-flux reactor neutron source run by the Institute Laue-Langevin. The resulting structure provides hydrogen-bonding parameters for the hydration of biomacromolecules to unprecedented accuracy. These experimental parameters will be used to define more accurate force fields for biomacromolecular structure refinement. The presence of a hydrophobic bowl motif surrounded by flexible side chains with terminal functional groups may be significant for the efficient scavenging of ligands. The feasibility of extending the resolution of this structure to ultrahigh resolution was investigated by collecting time-of-flight neutron crystallographic data during commissioning of the TOPAZ diffractometer with a prototype array of 14 modular 2° × 21° detectors at the Spallation Neutron Source run by Oak Ridge National Laboratory. PMID:21636899

Jogl, Gerwald; Wang, Xiaoping; Mason, Sax A; Kovalevsky, Andrey; Mustyakimov, Marat; Fisher, Zöe; Hoffman, Christina; Kratky, Christoph; Langan, Paul

2011-06-01

228

Crystallographic Structure of the Human Leukocyte Antigen DRA, DRB3*0101: Models of a Directional Alloimmune Respone and Autoimmunity  

SciTech Connect

We describe structural studies of the human leukocyte antigen DR52a, HLA-DRA/DRB3*0101, in complex with an N-terminal human platelet integrin {alpha}II{sub B}{beta}III glycoprotein peptide which contains a Leu/Pro dimorphism. The 33:Leu dimorphism is the epitope for the T cell directed response in neonatal alloimmune thrombocytopenia and post-transfusion purpura in individuals with the {alpha}II{sub B}{beta}III 33:Pro allele, and defines the unidirectional alloimmune response. This condition is always associated with DR52a. The crystallographic structure has been refined to 2.25 {angstrom}. There are two {alpha}{beta} heterodimers to the asymmetric unit in space group P4{sub 1}2{sub 1}2. The molecule is characterized by two prominent hydrophobic pockets at either end of the peptide binding cleft and a deep, narrower and highly charged P4 opening underneath the beta 1 chain. Further, the peptide in the second molecule displays a sharp upward turn after pocket P9. The structure reveals the role of pockets and the distinctive basic P4 pocket, shared by DR52a and DR3, in selecting their respective binding peptide repertoire. We observe an interesting switch in a residue from the canonically assigned pocket 6 seen in prior class II structures to pocket 4. This occludes the P6 pocket helping to explain the distinctive '1-4-9' peptide binding motif. A {beta}57 Asp {yields} Val substitution abrogates the salt-bridge to {alpha}76 Arg and along with a hydrophobic {beta}37 is important in shaping the P9 pocket. DRB3*0101 and DRB1*0301 belong to an ancestral haplotype and are associated with many autoimmune diseases linked to antigen presentation, but whereas DR3 is susceptible to type 1 diabetes DR52a is not. This dichotomy is explored for clues to the disease.

Parry,C.; Gorski, J.; Stern, L.

2007-01-01

229

The moduli space and monodromies of the N=2 supersymmetric Yang-Mills theory with any Lie gauge groups  

E-print Network

We propose a unified scheme for finding the hyperelliptic curve of N=2 SUSY YM theory with any Lie gauge groups. Our general scheme gives the well known results for classical gauge groups and exceptional G_2 group. In particular, we present the curve for the exceptional gauge groups F_4, E_{6,7,8} and check consistency condition for them. The exact monodromies and the dyon spectrum of these theories are determined. We note that for any Lie gauge groups, the exact monodromies could be obtained only from the Cartan matrix.

Abolhasani, M R; Ghezelbash, A M; Abolhasani, Mohammad Reza; Alishahiha, Mohsen; Ghezelbash, Amir Masoud

1996-01-01

230

Activity budget, diet, and use of space by two groups of squirrel monkeys (Saimiri sciureus) in eastern Amazonia.  

PubMed

Squirrel monkeys (Saimiri spp.) are widely distributed in the Amazon basin. This study describes the ecological and behavioral patterns of two social groups of S. sciureus in forests adjacent to the Tucuruí hydroelectric reservoir in eastern Amazonia, including range size, activity budgets, and composition of the diet. The groups were monitored at Base 4 (group B4) and Germoplasma Island (group GI). Quantitative behavioral data were collected using instantaneous scan sampling to record behavior, substrate use, and height. Home ranges were delimited using a GPS to determine group position after each 50 m of movement. Home ranges were 75.0 ha for group B4 (39 members) and 77.5 ha for group GI (32 members). The use of vertical strata was well defined, with a marked preference for the middle and lower levels of the canopy. The activity budgets of both groups were typical of those of other squirrel monkeys and were dominated by foraging (B4 = 48.7 %; GI = 49.6 %), moving (both groups 28.9 %), and feeding (B4 = 14.6 %; GI = 12.4 %). Resting was rare (B4 = 3.5 %; GI = 2.6 %) and less common than social behavior (B4 = 4.3 %; GI = 6.4 %). The diet of both groups was dominated by plant material (B4 = 70.7 % of feeding records; GI = 71.4 %), which is in contrast with the more insectivorous diets recorded for Saimiri at other sites. Group GI spent more time foraging during the dry season, whereas group B4 spent more time in the rainy season when the consumption of fruit increased (significantly, in the case of group GI). The less insectivorous diet of these groups may be due to a number of factors, including the unique habitat configuration at the site and reduced hydrological stress due to the proximity of the reservoir. PMID:23546826

Pinheiro, Tatyana; Ferrari, Stephen F; Lopes, Maria Aparecida

2013-07-01

231

International summer school on macromolecular crystallographic computing. Final report  

SciTech Connect

The School was the seventh in a series of International Union of Crystallography (IUCr) Crystallographic Symposia. The format of the School was formal lectures in the morning, tutorials in the afternoon, and software demonstrations and more lectures in the evening. The full program which left both the organizers and attendees exhausted, reflects the current state of excitement in the field of macromolecular structure determination using the technique of X-ray crystallography. The new and improved technologies and techniques described in these Proceedings are contributing to that growth and at the same time, as pointed out in the paper given by Sussman, creating challenges for the Protein Data Bank (PDB). As the School progressed, the authors were struck by the similarities to events which took place in small molecule crystallography beginning some 20 to 25 years ago. Growth then was fueled by the advent of new algorithms, affordable computer hardware, and good software. So it is today for macromolecular crystallography, but with the added bonus of the Internet which is changing how scientist conduct their research. Flack presented this view as part of his on-going contribution to how crystallographers use the Internet. After presentations discussing structures en masse they returned to the more traditional mode of presentation which parallels the determination of a single macromolecular structure: data collection -- phasing -- model building and visualization -- refinement.

NONE

1998-08-01

232

High-resolution structure prediction and the crystallographic phase problem.  

PubMed

The energy-based refinement of low-resolution protein structure models to atomic-level accuracy is a major challenge for computational structural biology. Here we describe a new approach to refining protein structure models that focuses sampling in regions most likely to contain errors while allowing the whole structure to relax in a physically realistic all-atom force field. In applications to models produced using nuclear magnetic resonance data and to comparative models based on distant structural homologues, the method can significantly improve the accuracy of the structures in terms of both the backbone conformations and the placement of core side chains. Furthermore, the resulting models satisfy a particularly stringent test: they provide significantly better solutions to the X-ray crystallographic phase problem in molecular replacement trials. Finally, we show that all-atom refinement can produce de novo protein structure predictions that reach the high accuracy required for molecular replacement without any experimental phase information and in the absence of templates suitable for molecular replacement from the Protein Data Bank. These results suggest that the combination of high-resolution structure prediction with state-of-the-art phasing tools may be unexpectedly powerful in phasing crystallographic data for which molecular replacement is hindered by the absence of sufficiently accurate previous models. PMID:17934447

Qian, Bin; Raman, Srivatsan; Das, Rhiju; Bradley, Philip; McCoy, Airlie J; Read, Randy J; Baker, David

2007-11-01

233

Crystallographic alignment of high-density gallium nitride nanowire arrays  

NASA Astrophysics Data System (ADS)

Single-crystalline, one-dimensional semiconductor nanostructures are considered to be one of the critical building blocks for nanoscale optoelectronics. Elucidation of the vapour-liquid-solid growth mechanism has already enabled precise control over nanowire position and size, yet to date, no reports have demonstrated the ability to choose from different crystallographic growth directions of a nanowire array. Control over the nanowire growth direction is extremely desirable, in that anisotropic parameters such as thermal and electrical conductivity, index of refraction, piezoelectric polarization, and bandgap may be used to tune the physical properties of nanowires made from a given material. Here we demonstrate the use of metal-organic chemical vapour deposition (MOCVD) and appropriate substrate selection to control the crystallographic growth directions of high-density arrays of gallium nitride nanowires with distinct geometric and physical properties. Epitaxial growth of wurtzite gallium nitride on (100) ?-LiAlO2 and (111) MgO single-crystal substrates resulted in the selective growth of nanowires in the orthogonal [1 macr1 0] and [001] directions, exhibiting triangular and hexagonal cross-sections and drastically different optical emission. The MOCVD process is entirely compatible with the current GaN thin-film technology, which would lead to easy scale-up and device integration.

Kuykendall, Tevye; Pauzauskie, Peter J.; Zhang, Yanfeng; Goldberger, Joshua; Sirbuly, Donald; Denlinger, Jonathan; Yang, Peidong

2004-08-01

234

Crystallographic Evidence for Noncoplanar Catalytic Aspartic Acids in plasmepsin II Resides in the Protein Data Bank  

SciTech Connect

The carboxylate atoms of the two catalytic aspartic acid residues in aspartic proteases are nearly coplanar and in the uncomplexed form share an in-plane nucleophilic water molecule that is central to the mechanism of these enzymes. This note reports that while reviewing the electron-density maps derived from the deposited data for uncomplexed plasmepsin II from Plasmodium falciparum (Asojo et al. (2003), J. Mol. Biol. 327, 173-181; PDB code 1lf4), it was discovered that the aspartic acid residues in this structure should in fact be distinctly noncoplanar. The crystallographic model from the deposited coordinates has been re-refined against the 1.9 {angstrom} resolution published diffraction data to an R{sub cryst} of 21.2% and an R{sub free} of 22.2%. The catalytic water molecule is present, but the plane of the carboxylate group of Asp214 is rotated by 66 degrees from its original position.

Robbins, A.; Dunn, B; Agbandje-McKenna, M; McKenna, R

2009-01-01

235

Space, time and the pattern of individual associations in a group-living species: Sanderlings have no friends  

Microsoft Academic Search

The persistence of flock membership through time and space was examined for wintering sanderlings Calidris alba at Bodega Bay, California from October 1978 to March 1981. Observed patterns of association were then compared with those expected from a null model: that the set of birds within a given flock represent a random sample from the local population.

J. P. Myers

1983-01-01

236

Talk in Blended-Space Speech Communities: An Exploration of Discursive Practices of a Professional Development Group  

ERIC Educational Resources Information Center

This study is an exploration of alternative teacher professional development. While using symbolic interactionism for a research lens, it characterizes the discursive practices commonly found in formal, informal, and blended-space speech communities based on the talk within a leadership-development program comprised of five female, church-based…

Garvin, Tabitha Ann

2011-01-01

237

Effects of group reflection variations in project-based learning integrated in a Web 2.0 learning space  

Microsoft Academic Search

A Web 2.0 environment that is coupled with emerging multimodal interaction tools can have considerable influence on team learning outcomes. Today, technologies supporting social networking, collective intelligence, emotional interaction, and virtual communication are introducing new forms of collaboration that are profoundly impacting education. In this study, an empirical analysis was conducted on a Web 2.0 learning space designed to promote

Paul Kim; Ji-Seong Hong; Curtis Bonk; Gloria Lim

2011-01-01

238

Enveloping algebra-valued gauge transformations for non-abelian gauge groups on non-commutative spaces  

Microsoft Academic Search

.   An enveloping algebra-valued gauge field is constructed, its components are functions of the Lie algebra-valued gauge field\\u000a and can be constructed with the Seiberg-Witten map. This allows the formulation of a dynamics for a finite number of gauge\\u000a field components on non-commutative spaces.

B. Jurco; Stefan Schraml; Peter Schupp; Julius Wess

2000-01-01

239

The Space Density of Primordial Gas Clouds near Galaxies and Groups and their Relation to Galactic High-Velocity Clouds.  

PubMed

The Arecibo H i Strip Survey probed the halos of approximately 300 cataloged galaxies and the environments of approximately 14 groups with sensitivity to neutral hydrogen masses >/=107 M middle dot in circle. The survey detected no objects with properties resembling the high-velocity clouds (HVCs) associated with the Milky Way or Local Group. If the HVCs were typically MHi=107.5 M middle dot in circle objects distributed throughout groups and galaxy halos at distances of approximately 1 Mpc, the survey should have made approximately 70 HVC detections in groups and approximately 250 detections around galaxies. The null detection implies that HVCs are deployed at typical distances of group barycenters. If the clouds are in virial equilibrium, their average dark matter fraction must be 98% or higher. PMID:10655165

Zwaan; Briggs

2000-02-20

240

What is the real crystallographic structure of the L photointermediate of bacteriorhodopsin?  

PubMed

In the last few years, three laboratories have reported three entirely different crystallographic models for the L photointermediate of bacteriorhodopsin. All are from X-ray diffraction of illuminated crystals that contain L in photostationary states created at similar cryogenic temperatures. This article compares the models and their implications, the crystallographic statistics and the methods used to derive them, as well as their agreement with non-crystallographic information. PMID:15282169

Lanyi, Janos K

2004-07-23

241

Arginine Kinase. Joint Crystallographic & NMR RDC Analyses link Substrate-Associated Motions to Intrinsic Flexibility  

PubMed Central

The phosphagen kinase family, including creatine and arginine kinases, catalyze the reversible transfer of a “high energy” phosphate between ATP and a phospho-guanidino substrate. They have become a model for the study of both substrate-induced conformational change and intrinsic protein dynamics. Prior crystallographic studies indicated large substrate-induced domain rotations, but differences among a recent set of arginine kinase structures was interpreted as a plastic deformation. Here, the structure of Limulus substrate-free arginine kinase is refined against high resolution crystallographic data and compared quantitatively with NMR chemical shifts and residual dipolar couplings (RDCs). This demonstrates the feasibility of this type of RDC analysis of proteins that are large by NMR standards (42 kDa), and illuminates the solution structure, free from crystal-packing constraints. Detailed comparison of the 1.7 Å resolution substrate-free crystal structure against the 1.2 Å transition state analog complex shows large substrate-induced domain motions which can be broken down into movements of smaller quasi-rigid bodies. The solution state structure of substrate-free arginine kinase is most consistent with an equilibrium of substrate-free and –bound structures, with the substrate-free form dominating, but with varying displacements of the quasi-rigid groups. Rigid-group rotations evident from the crystal structures are about axes previously associated with intrinsic millisecond dynamics using NMR relaxation dispersion. Thus, “substrate-induced” motions are along modes that are intrinsically flexible in the substrate-free enzyme, and likely involve some degree of conformational selection. PMID:21075117

Niu, Xiaogang; Bruschweiler-Li, Lei; Davulcu, Omar; Skalicky, Jack J.; Bruschweiler, Rafael; Chapman, Michael S.

2010-01-01

242

Themed Space  

ERIC Educational Resources Information Center

This article presents a classroom activity that introduces students to the concept of themed space. Students learn to think critically about the spaces they encounter on a regular basis by analyzing existing spaces and by working in groups to create their own themed space. This exercise gives students the chance to see the relevance of critical…

Lynch, Christopher O.

2010-01-01

243

Report from the MPP Working Group to the NASA Associate Administrator for Space Science and Applications. Technical memorandum report, 1 October 1985-30 September 1986  

SciTech Connect

NASA's Office of Space Science and Applications (OSSA) gave a select group of scientists the opportunity to test and implement their computational algorithms on the Massively Parallel Processor (MPP) located at Goddard Space Flight Center, beginning in late 1985. One year later, the Working Group presented its report, which addressed the following: algorithms, programming languages, architecture, programming environments, the way theory relates, and performance measured. The findings point to a number of demonstrated computational techniques for which the MPP architecture is ideally suited. For example, besides executing much faster on the MPP than on conventional computers, systolic VLSI simulation (where distances are short), lattice simulation, neural network simulation, and image problems were found to be easier to program on the MPP's architecture than on a CYBER 205 or even a VAX. The report also makes technical recommendations covering all aspects of MPP use, and recommendations concerning the future of the MPP and machines based on similar architectures, expansion of the Working Group, and study of the role of future parallel processors for space station, EOS, and the Great Observatories era.

Fischer, J.R.; Grosch, C.; Mcanulty, M.; Odonnell, J.; Storey, O.

1987-11-01

244

Preliminary crystallographic examination of a novel fungal lysozyme from Chalaropsis  

NASA Technical Reports Server (NTRS)

The lysozyme from the fungus of the Chalaropsis species has been crystallized. This lysozyme displays no sequence homology with avian, phage, or mammalian lysozymes, however, preliminary studies indicate significant sequence homology with the bacterial lysozyme from Streptomyces. Both enzymes are unusual in possessing beta-1,4-N-acetylmuramidase and beta-1,4-N,6-O-diacetylmuramidase activity. The crystals grow from solutions of ammonium sulfate during growth periods from several months to a year. The space group is P2(1)2(1)2(1) with a = 34.0 A, b = 42.6 A, c = 122.1 A. Preliminary data indicate that there is 1 molecule/asymmetric unit.

Carter, Daniel C.; He, Xiao-Min; Lyne, James E.; Stubbs, Gerald; Hash, John H.

1990-01-01

245

Preliminary electron crystallographic analysis of ice-embedded tropomyosin crystals.  

PubMed

Electron images and diffraction patterns of ice-embedded tropomyosin crystalline sheets have been recorded at 100 and 400 kV. Optical diffractograms from the images indicated an elongated, centered unit cell with a = 799.2 +/- 10.6 A, b = 55.1 +/- 3.5 A. Evaluation of the phases in the computed Fourier transforms up to 7 A resolution revealed the presence of symmetry axes consistent with two-dimensional space group cmm. Electron diffraction patterns show diffuse arcs and discrete sampling at a resolution of 5.1 A, arising from the alpha-helical coiled-coil features of the molecule. These results demonstrate that tropomyosin thin sheets are highly ordered and suggest that retrieval of its high-resolution three-dimensional structure may be feasible by electron crystallography. PMID:8494673

Avila-Sakar, A J; Schmid, M F; Li, L S; Whitby, F G; Phillips, G N; Chiu, W

1993-01-01

246

X-ray crystallographic and tungsten-183 nuclear magnetic resonance structural studies of the [M4(H2O)2(XW9O34) 2]10- heteropolyanions (M = COII or Zn, X = P or As)  

USGS Publications Warehouse

The crystal structures of K10[Co4(H2O)2(PW9O 34)2]??22H2O (1) and isomorphous K10[Zn4(H2O)2(AsW9O 34)2]??23H2O (2) have been determined {Mo-K?? radiation, space group P21/n, Z = 2; (1) a = 15.794(2), b = 21.360(2), c = 12.312(1) A??, ?? = 91.96??, R = 0.084 for 3 242 observed reflections [I ??? 3??(I)]; (2) a = 15.842(4), b = 21.327(5), c = 12.308(4) A??, ?? = 92.42(4)??, R = 0.066 for 4 675 observed reflections [F ??? 3??(F)]}. The anions have crystallographic symmetry 1 and non-crystallographic symmetry very close to 2/m (C2h). Each consists of two [XW9O34]9- moieties [??-B isomers; X = P (1) or As (2)] linked via four CoIIO6 or ZnO6 groups. Two Co or Zn atoms each carry a water ligand. The 183W n.m.r. spectra of the anions [Zn4(H2O)2(XW9O34) 2]10- (X = P or As) confirm that the anions retain 2/m symmetry in aqueous solution. Homonuclear coupling constants between 183W atoms are 5.8-9.0 Hz for adjacent WO6 octahedra sharing edges, and 19.6-25.0 Hz for octahedra sharing corners.

Evans, H.T.; Tourne, C.M.; Tourne, G.F.; Weakley, T.J.R.

1986-01-01

247

Twinning-like lattice reorientation without a crystallographic twinning plane  

NASA Astrophysics Data System (ADS)

Twinning on the plane is a common mode of plastic deformation for hexagonal-close-packed metals. Here we report, by monitoring the deformation of submicron-sized single-crystal magnesium compressed normal to its prismatic plane with transmission electron microscopy, the reorientation of the parent lattice to a ‘twin’ lattice, producing an orientational relationship akin to that of the conventional twinning, but without a crystallographic mirror plane, and giving plastic strain that is not simple shear. Aberration-corrected transmission electron microscopy observations reveal that the boundary between the parent lattice and the ‘twin’ lattice is composed predominantly of semicoherent basal/prismatic interfaces instead of the twinning plane. The migration of this boundary is dominated by the movement of these interfaces undergoing basal/prismatic transformation via local rearrangements of atoms. This newly discovered deformation mode by boundary motion mimics conventional deformation twinning but is distinct from the latter and, as such, broadens the known mechanisms of plasticity.

Liu, Bo-Yu; Wang, Jian; Li, Bin; Lu, Lu; Zhang, Xi-Yan; Shan, Zhi-Wei; Li, Ju; Jia, Chun-Lin; Sun, Jun; Ma, Evan

2014-02-01

248

Nanoscale lithography of graphene with crystallographic orientation control  

NASA Astrophysics Data System (ADS)

The two scanning probe microscope based methods for the production of graphene nanoarchitectures with crystallographically oriented edges: scanning tunneling lithography (STL) and carbothermal etching (CTE) are compared. STL offers higher freedom in choosing the orientation, it makes possible sophisticated manipulation of the etched nanoarchitectures and immediate atomic resolution of the etched structure, but it suffers from the need of a conductive substrate. CTE at present can produce only zigzag edges, but these edges by the very nature of the process producing them are more regular than the edges produced by STL. CTE has the clear advantage that the produced nanoarchitectures are on an insulating substrate, no further transfer steps are needed. To date STL can produce graphene nanoribbons (GNRs) of a few nanometers in width, while the width of the GNRs produced by CTE is in the range of 20 nm.

Dobrik, G.; Nemes-Incze, P.; Tapasztó, L.; Lambin, Ph.; Biró, L. P.

2012-03-01

249

A prototype chopper for synchrotron time-resolved crystallographic measurements  

SciTech Connect

A mechanical x-ray chopper has been designed to perform microsecond time-resolved crystallographic studies at the DIAMOND synchrotron I19 beamline. It consists of two asymmetric absorbers rotating synchronously at frequencies from 0 to 50 Hz in the same direction around a rotation axis that is parallel to the x-ray beam. The duration of the x-ray pulses produced by the chopper is determined by the relative phase between the two blades, which can be adjusted. The chopper system presented in this paper offers a time resolution suitable for conducting in situ experiments that afford the crystal structure of materials while in their transient (>10 {mu}s) photoactivated excited states.

Husheer, S. L. G. [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom); Synchrotron Radiation Source, Daresbury Laboratory, Warrington WA4 4AD (United Kingdom); Cole, J. M. [Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom); Department of Physics, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Department of Chemistry, University of New Brunswick, P.O. Box 4400, Fredericton, New Brunswick E3B 5A3 (Canada); Department of Physics, University of New Brunswick, P.O. Box 4400, Fredericton, New Brunswick E3B 5A3 (Canada); D'Almeida, T. [Department of Physics, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Teat, S. J. [Synchrotron Radiation Source, Daresbury Laboratory, Warrington WA4 4AD (United Kingdom)

2010-04-15

250

Crystallographic data processing for free-electron laser sources.  

PubMed

A processing pipeline for diffraction data acquired using the `serial crystallography' methodology with a free-electron laser source is described with reference to the crystallographic analysis suite CrystFEL and the pre-processing program Cheetah. A detailed analysis of the nature and impact of indexing ambiguities is presented. Simulations of the Monte Carlo integration scheme, which accounts for the partially recorded nature of the diffraction intensities, are presented and show that the integration of partial reflections could be made to converge more quickly if the bandwidth of the X-rays were to be increased by a small amount or if a slight convergence angle were introduced into the incident beam. PMID:23793149

White, Thomas A; Barty, Anton; Stellato, Francesco; Holton, James M; Kirian, Richard A; Zatsepin, Nadia A; Chapman, Henry N

2013-07-01

251

Crystallographic data processing for free-electron laser sources  

PubMed Central

A processing pipeline for diffraction data acquired using the ‘serial crystallography’ methodology with a free-electron laser source is described with reference to the crystallographic analysis suite CrystFEL and the pre-processing program Cheetah. A detailed analysis of the nature and impact of indexing ambiguities is presented. Simulations of the Monte Carlo integration scheme, which accounts for the partially recorded nature of the diffraction intensities, are presented and show that the integration of partial reflections could be made to converge more quickly if the bandwidth of the X-rays were to be increased by a small amount or if a slight convergence angle were introduced into the incident beam. PMID:23793149

White, Thomas A.; Barty, Anton; Stellato, Francesco; Holton, James M.; Kirian, Richard A.; Zatsepin, Nadia A.; Chapman, Henry N.

2013-01-01

252

Twinning-like lattice reorientation without a crystallographic twinning plane  

PubMed Central

Twinning on the plane is a common mode of plastic deformation for hexagonal-close-packed metals. Here we report, by monitoring the deformation of submicron-sized single-crystal magnesium compressed normal to its prismatic plane with transmission electron microscopy, the reorientation of the parent lattice to a ‘twin’ lattice, producing an orientational relationship akin to that of the conventional twinning, but without a crystallographic mirror plane, and giving plastic strain that is not simple shear. Aberration-corrected transmission electron microscopy observations reveal that the boundary between the parent lattice and the ‘twin’ lattice is composed predominantly of semicoherent basal/prismatic interfaces instead of the twinning plane. The migration of this boundary is dominated by the movement of these interfaces undergoing basal/prismatic transformation via local rearrangements of atoms. This newly discovered deformation mode by boundary motion mimics conventional deformation twinning but is distinct from the latter and, as such, broadens the known mechanisms of plasticity. PMID:24522756

Liu, Bo-Yu; Wang, Jian; Li, Bin; Lu, Lu; Zhang, Xi-Yan; Shan, Zhi-Wei; Li, Ju; Jia, Chun-Lin; Sun, Jun; Ma, Evan

2014-01-01

253

Ocean acidification reduces the crystallographic control in juvenile mussel shells.  

PubMed

Global climate change threatens the oceans as anthropogenic carbon dioxide causes ocean acidification and reduced carbonate saturation. Future projections indicate under saturation of aragonite, and potentially calcite, in the oceans by 2100. Calcifying organisms are those most at risk from such ocean acidification, as carbonate is vital in the biomineralisation of their calcium carbonate protective shells. This study highlights the importance of multi-generational studies to investigate how marine organisms can potentially adapt to future projected global climate change. Mytilus edulis is an economically important marine calcifier vulnerable to decreasing carbonate saturation as their shells comprise two calcium carbonate polymorphs: aragonite and calcite. M. edulis specimens were cultured under current and projected pCO2 (380, 550, 750 and 1000?atm), following 6months of experimental culture, adults produced second generation juvenile mussels. Juvenile mussel shells were examined for structural and crystallographic orientation of aragonite and calcite. At 1000?atm pCO2, juvenile mussels spawned and grown under this high pCO2 do not produce aragonite which is more vulnerable to carbonate under-saturation than calcite. Calcite and aragonite were produced at 380, 550 and 750?atm pCO2. Electron back scatter diffraction analyses reveal less constraint in crystallographic orientation with increased pCO2. Shell formation is maintained, although the nacre crystals appear corroded and crystals are not so closely layered together. The differences in ultrastructure and crystallography in shells formed by juveniles spawned from adults in high pCO2 conditions may prove instrumental in their ability to survive ocean acidification. PMID:25180664

Fitzer, Susan C; Cusack, Maggie; Phoenix, Vernon R; Kamenos, Nicholas A

2014-10-01

254

Sharing electronic structure and crystallographic data with ETSF_IO  

NASA Astrophysics Data System (ADS)

We present a library of routines whose main goal is to read and write exchangeable files (NetCDF file format) storing electronic structure and crystallographic information. It is based on the specification agreed inside the European Theoretical Spectroscopy Facility (ETSF). Accordingly, this library is nicknamed ETSF_IO. The purpose of this article is to give both an overview of the ETSF_IO library and a closer look at its usage. ETSF_IO is designed to be robust and easy to use, close to Fortran read and write routines. To facilitate its adoption, a complete documentation of the input and output arguments of the routines is available in the package, as well as six tutorials explaining in detail various possible uses of the library routines. Catalogue identifier: AEBG_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBG_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Gnu Lesser General Public License No. of lines in distributed program, including test data, etc.: 63?156 No. of bytes in distributed program, including test data, etc.: 363?390 Distribution format: tar.gz Programming language: Fortran 95 Computer: All systems with a Fortran95 compiler Operating system: All systems with a Fortran95 compiler Classification: 7.3, 8 External routines: NetCDF, http://www.unidata.ucar.edu/software/netcdf Nature of problem: Store and exchange electronic structure data and crystallographic data independently of the computational platform, language and generating software Solution method: Implement a library based both on NetCDF file format and an open specification (http://etsf.eu/index.php?page=standardization)

Caliste, D.; Pouillon, Y.; Verstraete, M. J.; Olevano, V.; Gonze, X.

2008-11-01

255

Crystallographic site swapping of La3+ ion in BaA'LaTeO6 (A' = Na, K, Rb) double perovskite type compounds: diffraction and photoluminescence evidence for the site swapping.  

PubMed

Double perovskite type compounds of the formula BaA'LaTeO6 (A' = Na, K, Rb) were synthesized by solid state route and their crystal structures were determined by Rietveld analysis using powder X-ray diffraction and neutron diffraction data. Na compound crystallizes in the monoclinic system with P2?/n space group whereas, K and Rb compounds crystallize in Fm3m space group. All the three compounds show rock salt type ordering at B site. Crystal structure analysis shows that La ion occupies A site in Na compound whereas, it occupies B site in K and Rb compounds according to the general formula of AA'BB'O6 for a double perovskite type compound. Effect of this crystallographic site swapping of the La ion was also observed in the photoluminescence study by doping Eu(3+) in La(3+) site. The large decrease in the intensity of the electric dipole ((5)D0-(7)F2) transition in the Rb compound compared to the Na compound indicates that Eu(3+) ion resides in the centrosymmetric octahedral environment in the Rb compound. PMID:24363108

Phatak, R; Gupta, S K; Krishnan, K; Sali, S K; Godbole, S V; Das, A

2014-02-28

256

Theory of electronic and structural properties of materials: Novel group-IV materials and real space methods  

NASA Astrophysics Data System (ADS)

This dissertation consists of two parts. The first part employs existing computational techniques to study the electronic, and structural properties of novel group-IV and related materials, namely, carbon nanotubes, boron nitride nanotubes, and crystalline group-IV alloys. In the second part, we develop a new electronic structure calculation technique based on finite element methods with multigrid acceleration. The computation time of our new technique scales quadratically with the number of atoms in the system i.e., O( N2), as opposed to the unfavorable cubic scaling ( O(N3)) for most existing ab initio methods. Chapter 1 gives an overview of theoretical methods involved in this dissertation. Chapter 2 focuses on the structural properties of carbon and boron nitride nanotubes. First, a new nucleation model for carbon nanotubes is proposed. Second, plastic deformation of carbon nanotube under high tensile stress is studied using a tight-binding total energy model. The elastic limits of carbon nanotubes are found to be higher than any other known materials and very sensitive to the so-called wrapping angle of nanotubes. Chapter 3 is devoted to the electronic and structural properties of novel group-IV alloys formed from CVD precursor. Group-IV alloys have attracted considerable research interest recently. Using the newly developed UltraHigh Vacuum Chemical Vapor Deposition (UHV CVD) technique, group-IV alloys such as Si4C and Ge4C, which contain 20 atomic % carbon, have been realized. The computational time of traditional ab initio techniques such as pseudopotential planewave methods scales at least as O( N3), where N is the number of atoms in the system. This unfavorable scaling limits the number of atoms one can study using these methods to several hundreds, even with the most powerful supercomputers available today. In chapter 4, we develop an O( N2) ab initio electronic structure calculation technique based on the finite element methods with multigrid acceleration. O(N2) scaling is achieved by avoiding explicit re-orthogonalization between eigenvectors, which is made possible by a multigrid algorithm. With these new techniques, we can perform ab initio calculations for systems containing more than 32 atoms on a single workstation (Compaq alpha DS10). (Abstract shortened by UMI.)

Zhang, Peihong

257

Direct solution of renormalization group equations of QCD in x-space: NLO implementations at leading twist  

NASA Astrophysics Data System (ADS)

We illustrate the implementation of a method based on the use of recursion relations in (Bjorken) x-space for the solution of the evolution equations of QCD for all the leading twist distributions. The algorithm has the advantage of being very fast. The implementation that we release is written in C and is performed to next-to-leading order in ?s. Program summaryTitle of program:evolution.c Catalogue identifier: ADUB Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADUB Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: Athlon 1800 plus Operating system under which the program has been tested: Linux Programming language used: C Peripherals used: Laser printer No. of bytes in distributed program, including test data, etc.: 4559 No. of lines in distributed program, including test data, etc.: 1048 Distribution format: gzip file Nature of physical problem: The program provided here solves the DGLAP evolution equations to next-to-leading order ?s, for unpolarized, longitudinally polarized and transversely polarized parton distributions. Method of solution: We use a recursive method based on an expansion of the solution in powers of log( ?s( Q)/ ?s( Q0)). Typical running time: About 1 minute and 30 seconds for the unpolarized and longitudinally polarized cases and 1 minute for the transversely polarized case.

Cafarella, Alessandro; Corianò, Claudio

2004-07-01

258

Microfocus/Polycapillary-Optic Crystallographic X-Ray System  

NASA Technical Reports Server (NTRS)

A system that generates an intense, nearly collimated, nearly monochromatic, small-diameter x-ray beam has been developed for use in macromolecular crystallography. A conventional x-ray system for macromolecular crystallography includes a rotating-anode x-ray source, which is massive (.500 kg), large (approximately 2 by 2 by 1 m), and power-hungry (between 2 and 18 kW). In contrast, the present system generates a beam of the required brightness from a microfocus source, which is small and light enough to be mounted on a laboratory bench, and operates at a power level of only tens of watts. The figure schematically depicts the system as configured for observing x-ray diffraction from a macromolecular crystal. In addition to the microfocus x-ray source, the system includes a polycapillary optic . a monolithic block (typically a bundle of fused glass tubes) that contains thousands of straight or gently curved capillary channels, along which x-rays propagate with multiple reflections. This particular polycapillary optic is configured to act as a collimator; the x-ray beam that emerges from its output face consists of quasi-parallel subbeams with a small angular divergence and a diameter comparable to the size of a crystal to be studied. The gap between the microfocus x-ray source and the input face of the polycapillary optic is chosen consistently with the focal length of the polycapillary optic and the need to maximize the solid angle subtended by the optic in order to maximize the collimated x-ray flux. The spectrum from the source contains a significant component of Cu K (photon energy is 8.08 keV) radiation. The beam is monochromatized (for Cu K ) by a nickel filter 10 m thick. In a test, this system was operated at a power of 40 W (current of 897 A at an accelerating potential of 45 kV), with an anode x-ray spot size of 41+/-2 microns. Also tested, in order to provide a standard for comparison, was a commercial rotating-anode x-ray crystallographic system with a pyrolytic graphite monochromator and a 250-micron pinhole collimator, operating at a power of 3.15 kW (current of 70 mA at an accelerating potential of 45 kV). The flux of collimated Cu K radiation in this system was found to be approximately 16 times that in the rotatinganode system. Data on x-ray diffraction from crystals of tetragonal form of lysozyme (protein) in this system were found to be of high quality and to be reducible by use of standard crystallographic software.

Joy, Marshall; Gubarev, Mikhail; Ciszak, Ewa

2005-01-01

259

Ongoing Analyses of Rocket Based Combined Cycle Engines by the Applied Fluid Dynamics Analysis Group at Marshall Space Flight Center  

NASA Technical Reports Server (NTRS)

This paper presents the status of analyses on three Rocket Based Combined Cycle (RBCC) configurations underway in the Applied Fluid Dynamics Analysis Group (TD64). TD64 is performing computational fluid dynamics (CFD) analysis on a Penn State RBCC test rig, the proposed Draco axisymmetric RBCC engine and the Trailblazer engine. The intent of the analysis on the Penn State test rig is to benchmark the Finite Difference Navier Stokes (FDNS) code for ejector mode fluid dynamics. The Draco analysis was a trade study to determine the ejector mode performance as a function of three engine design variables. The Trailblazer analysis is to evaluate the nozzle performance in scramjet mode. Results to date of each analysis are presented.

Ruf, Joseph H.; Holt, James B.; Canabal, Francisco

2001-01-01

260

Ongoing Analysis of Rocket Based Combined Cycle Engines by the Applied Fluid Dynamics Analysis Group at Marshall Space Flight Center  

NASA Technical Reports Server (NTRS)

This paper presents the status of analyses on three Rocket Based Combined Cycle configurations underway in the Applied Fluid Dynamics Analysis Group (TD64). TD64 is performing computational fluid dynamics analysis on a Penn State RBCC test rig, the proposed Draco axisymmetric RBCC engine and the Trailblazer engine. The intent of the analysis on the Penn State test rig is to benchmark the Finite Difference Navier Stokes code for ejector mode fluid dynamics. The Draco engine analysis is a trade study to determine the ejector mode performance as a function of three engine design variables. The Trailblazer analysis is to evaluate the nozzle performance in scramjet mode. Results to date of each analysis are presented.

Ruf, Joseph; Holt, James B.; Canabal, Francisco

1999-01-01

261

Preferential crystallographic alignment in polycrystalline MnP  

NASA Astrophysics Data System (ADS)

The existence of preferential crystallographic alignment in hot pressed and die upset manganese phosphide (MnP) was investigated using magnetic measurements and electron backscatter diffraction (EBSD). Pole figures calculated from the EBSD data show that die upsetting causes the <1 1 0> directions to align preferentially along the die upset (DU) direction with the <0 0 1> direction preferentially perpendicular to the DU direction. Magnetic measurements show that the die upsetting can reduce the saturation field relative to that of a similar sample with randomly oriented grains. Since the low-field magnetocaloric effect in single crystals of MnP has been shown to be greatest along the <0 1 0> direction and smallest along the <1 0 0> direction, this technique offers a means to achieve the advantages of single crystal alignment with the economy of using bulk processing techniques on polycrystalline material. The peak magnetic entropy change measured with the field applied along the DU direction in the DU sample was 3%, 5%, and 8% greater than the peak entropy change of a randomly oriented powder at fields of 2.0, 1.0, and 0.5 T, respectively.

Booth, Ryan A.; Marinescu, Melania; Liu, JinFang; Majetich, Sara A.

2010-09-01

262

Towards automated crystallographic structure refinement with phenix.refine  

PubMed Central

phenix.refine is a program within the PHENIX package that supports crystallographic structure refinement against experimental data with a wide range of upper resolution limits using a large repertoire of model parameterizations. It has several automation features and is also highly flexible. Several hundred parameters enable extensive customizations for complex use cases. Multiple user-defined refinement strategies can be applied to specific parts of the model in a single refinement run. An intuitive graphical user interface is available to guide novice users and to assist advanced users in managing refinement projects. X-ray or neutron diffraction data can be used separately or jointly in refinement. phenix.refine is tightly integrated into the PHENIX suite, where it serves as a critical component in automated model building, final structure refinement, structure validation and deposition to the wwPDB. This paper presents an overview of the major phenix.refine features, with extensive literature references for readers interested in more detailed discussions of the methods. PMID:22505256

Afonine, Pavel V.; Grosse-Kunstleve, Ralf W.; Echols, Nathaniel; Headd, Jeffrey J.; Moriarty, Nigel W.; Mustyakimov, Marat; Terwilliger, Thomas C.; Urzhumtsev, Alexandre; Zwart, Peter H.; Adams, Paul D.

2012-01-01

263

Crystallographic studies of the Anthrax lethal toxin. Annual report  

SciTech Connect

The lethal form of Anthrax results from the inhalation of anthrax spores. Death is primarily due to the effects of the lethal toxin (Protective Antigen (PA) + Lethal Factor) from the causative agent, Bacillus anthracis. All the Anthrax vaccines currently in use or under development contain or produce PA, the major antigenic component of anthrax toxin, and there is a clear need for an improved vaccine for human use. In the previous report we described the first atomic resolution structure of PA, revealing that the molecule is composed largely of beta-sheets organized into four domains. This information can be used in the design. of recombinant PA vaccines. In this report we describe additional features of the full-length PA molecule derived from further crystallographic refinement and careful examination of the structure. We compare two crystal forms of PA grown at different pH values and discuss the functional implications. A complete definition of the function of each domain must await the crystal structure of the PA63 heptamer. We have grown crystals of the heptamer under both detergent and detergent-free conditions, and made substantial progress towards the crystal structure. The mechanism of anthrax intoxication in the light of our results is reviewed.

Frederick, C.A.

1996-07-01

264

Crystallographic orientation engineering in silicon-on-insulator substrates  

NASA Astrophysics Data System (ADS)

A bilayer silicon-on-insulator film was engineered to locally convert the crystallographic orientation from (100) to (110). The initial bilayer film is composed of a first 50 nm thick (110) oriented Si surface layer, above a second 20 nm thick (100) oriented Si underlayer. The bilayer film was elaborated using hydrophobic bonding to ensure an atomic contact between the two layers without any intermediate oxide. A local and deep-amorphization was developed by ion implantation to amorphize the (100) oriented Si underlayer, conserving also a partially crystalline (110) oriented surface layer. After such a deep amorphization, a solid phase epitaxy regrowth was performed at 900 °C. Transmission electron microscopy observations confirm that the partially crystalline surface layer acts as a seed for the epitaxial regrowth of the amorphized areas through the hydrophobic bonding interface. Thus, the orientation is locally converted from (100) to (110) in the underlayer, which could lead to the elaboration of hybrid films over a continuous insulating oxide that are mandatory for high performance electronic devices.

Signamarcheix, T.; Biasse, B.; Papon, A.-M.; Nolot, E.; Mazen, F.; Leveneur, J.; Faynot, O.; Clavelier, L.; Ghyselen, B.

2010-06-01

265

Using OLCI/Sentinel-3 and Sentinel-5-P data synergistically for retrieving different phytoplankton groups from space  

NASA Astrophysics Data System (ADS)

We are proposing the development of an algorithm, using the combination of data from OCLI (Sentinel-3) and Sentinel-5P sensors, which derives globally pyhtoplankton groups (phytoplankton functional types) biomass. The information of the total biomass will be achieved by standard processing of the Chlorophyll-a (chl-a) concentration using satellite data from multispectral imaging instruments (firstly SeaWiFS, MODIS and MERIS merged within the GlobColour data set, later OLCI data). The percentage of the main phytoplankton types on the total biomass will be retrieved by the analysis of characteristic absorption features in hyperspectral satellite measurements (firstly SCIAMACHY, later Sentinel-5-P) using the PhytoDOAS method by Bracher et al. (2009) and improved by Sadeghi et al. (2011). Thus, a synergistic product from information of multi- and hyperspectral satellite instruments which complements one another will be developed. The two instruments of the Sentinel mission will enable a data product of weekly to monthly temporal and 7 km by 7 km spatial resolution. On the the SCIAMACHY/Globcolour product (starting in 2002 until today) will be limited to a monthly and 0.5° degree resolution. The application of the algorithm is for assessing the spatial and temporal variability of specific phytoplankton types' biomass on longer time scale (10 to 20 and more years) with global coverage. This will engross the understanding of the role of different phytoplankton types in the world ocean's ecosystem and improve estimates on the contribution of different phytoplankton types to the global carbon cycle. The concept of the algorithm development, including its uncertainity determined via validaton with in-situ phytoplankton data and sensitivity studies using the coupled atmospheric-oceanic radiative transfer model SCIATRAN (Rozanov et al. 2002, Blum et al. in press) and examples for its application are given in the presentation.

Bracher, A.; Dinter, T.; Altenburg Soppa, M.; Taylor, B.; Rozanov, V.

2012-04-01

266

M8, Abstracts of the American CrystallographicAssociation Meeting,New Orleans, La., 1970.  

E-print Network

8087 M8, Abstracts of the American CrystallographicAssociation Meeting,New Orleans, La., 1970. (10 the Department of Chemistry, University of Colorado, Boulder, Colorado 80309. Received January 19, 1976 Abstract

Showalter, Kenneth

267

Crystallographic flat origami with three flat foldability types of the generating unit  

NASA Astrophysics Data System (ADS)

In this paper, we determine crystallographic flat origami from a crease pattern having three flat foldability types of its generating unit. In particular, we consider crease patterns arising from Archimedean tilings via the hinged tiling method.

Taganap, Eduard C.; De Las Peñas, Ma. Louise Antonette N.; Rapanut, Teofina A.

2014-06-01

268

Visualization of Time-Reversal Symmetry in Magnetic Point Groups  

NASA Astrophysics Data System (ADS)

The direct visualization of crystallographic and magnetic point group symmetry by means of computer graphics simplifies the teaching of point group symmetry at the undergraduate and graduate levels. Still images and animated movies for all 32 crystallographic point groups, and for the 122 magnetic point groups, are presented. For each point group, the action of the symmetry operators on scalar and pseudo-scalar objects, as well as on polar and axial vectors, is represented as a three-dimensional rendered image. All images and movies are made available as supplementary educational material via a dedicated web site.

de Graef, Marc

2010-05-01

269

On the preferential crystallographic orientation of Au nanoparticles: Effect of electrodeposition time  

Microsoft Academic Search

The crystallographic orientation of Au nanoparticles electrodeposited at glassy carbon (nano-Au\\/GC) electrodes (prepared by potential step electrolysis) is markedly influenced by the width of the potential step. The oxygen reduction reaction (ORR) and the reductive desorption of cysteine have been studied on nano-Au\\/GC electrodes. Furthermore, electron backscatter diffraction (EBSD) technique has been used to probe the crystallographic orientation of the

Mohamed S. El-Deab

2009-01-01

270

CRYSTALLOGRAPHICALLY ANISOTROPIC SHAPE OF FORSTERITE: NEW PROBE FOR EVALUATING DUST FORMATION HISTORY FROM INFRARED SPECTROSCOPY  

SciTech Connect

Crystalline dust has been observed by infrared spectroscopy around dust-enshrouded asymptotic giant branch stars, in protoplanetary disks, and from some comets. Crystalline materials often have a specific shape related to a specific crystallographic orientation (crystallographically anisotropic shape), which reflects the anisotropic nature of crystals, and their infrared spectral features depend on crystallographically anisotropic shapes. The crystallographically anisotropic shape is thus a potentially powerful probe to evaluate circumstellar dust-forming conditions quantitatively. In order to assess the possibility to determine the crystallographically anisotropic shape from infrared spectra, we calculated mass absorption coefficients for ellipsoidal forsterite particles, the most abundant circumstellar crystalline silicate, elongated and flattened along the crystallographic a-, b-, and c-axes with various aspect ratios in the wavelength range of 9-70 {mu}m. It was found that differences in infrared features caused by various crystallographicaly anisotropic shapes are distinguishable from each other irrespective of the effects of temperature, size, chemical composition, and grain edges of forsterite in the range of 9-12 {mu}m and 15-20 {mu}m. We thus concluded that the crystallographically anisotropic shape of forsterite can be deduced from peak features in infrared spectra. We also showed that the crystallographically anisotropic shapes formed by evaporation and condensation of forsterite can be distinguished from each other and the temperature condition for evaporation can be evaluated from the peak features. We applied the present results to the infrared spectrum of a protoplanetary disk HD100546 and found that a certain fraction ({approx}25%) of forsterite dust may have experienced high-temperature evaporation (>1600 K).

Takigawa, Aki; Tachibana, Shogo, E-mail: takigawa@eps.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo Tokyo 113-0033 (Japan)

2012-05-10

271

International Space Exploration Coordination Group  

E-print Network

surface of the Earth is the shore of the cosmic ocean. From it we have learned most of what we know will strengthen and enrich humanity's future, bringing nations together in a common cause, revealing new knowledge in strong partnerships that have brought discoveries, innovations, and inspiration to all mankind

272

An International Strategy for Human Exploration of the Moon: The International Space Exploration Coordination Group (ISECG) Reference Architecture for Human Lunar Exploration  

NASA Technical Reports Server (NTRS)

The International Space Exploration Coordination Group (ISECG) was established in response to The Global Exploration Strategy: The Framework for Coordination developed by fourteen space agencies and released in May 2007. Several ISECG participating space agencies have been studying concepts for human exploration of the moon that allow individual and collective goals and objectives to be met. This 18 month study activity culminated with the development of the ISECG Reference Architecture for Human Lunar Exploration. The reference architecture is a series of elements delivered over time in a flexible and evolvable campaign. This paper will describe the reference architecture and how it will inform near-term and long-term programmatic planning within interested agencies. The reference architecture is intended to serve as a global point of departure conceptual architecture that enables individual agency investments in technology development and demonstration, International Space Station research and technology demonstration, terrestrial analog studies, and robotic precursor missions to contribute towards the eventual implementation of a human lunar exploration scenario which reflects the concepts and priorities established to date. It also serves to create opportunities for partnerships that will support evolution of this concept and its eventual realization. The ISECG Reference Architecture for Human Lunar Exploration (commonly referred to as the lunar gPoD) reflects the agency commitments to finding an effective balance between conducting important scientific investigations of and from the moon, as well as demonstrating and mastering the technologies and capabilities to send humans farther into the Solar System. The lunar gPoD begins with a robust robotic precursor phase that demonstrates technologies and capabilities considered important for the success of the campaign. Robotic missions will inform the human missions and buy down risks. Human exploration will start with a thorough scientific investigation of the polar region while allowing the ability to demonstrate and validate the systems needed to take humans on more ambitious lunar exploration excursions. The ISECG Reference Architecture for Human Lunar Exploration serves as a model for future cooperation and is documented in a summary report and a comprehensive document that also describes the collaborative international process that led to its development. ISECG plans to continue with architecture studies such as this to examine an open transportation architecture and other destinations, with expanded participation from ISECG agencies, as it works to inform international partnerships and advance the Global Exploration Strategy.

Laurini, Kathleen C.; Hufenbach, Bernhard; Junichiro, Kawaguchi; Piedboeuf, Jean-Claude; Schade, Britta; Lorenzoni, Andrea; Curtis, Jeremy; Hae-Dong, Kim

2010-01-01

273

Significance of Dauphiné twins in crystallographic fabrics of quartz tectonites  

NASA Astrophysics Data System (ADS)

Dauphine twins are commonly found in quartz tectonites, however their role in deformation processes are not completely understood. This study represents a new attempt to understand the interaction between slip systems and Dauphine twins in deforming quartz-rich rocks at different temperatures. There is no doubt that Dauphine twins are mobilized under stress as this has been shown by experiments for single crystals and in polycrystalline aggregates where distinct crystallographic fabrics develop in previously randomly oriented aggregates related to minimization of elastic energy (Tullis 1972). However in quartz tectonites the Dauphine twin process is a part of interplay between plastic deformation and recovery processes which depends on PT, strain-rate and fluid composition and availability. In quartz tectonites with Y-girdle C-axis (GBM-regime) fabrics Dauphiné twins are abundant, relating different parts of r- and z rhomb "comet" distributions. This is interpreted as completion between prism slip and Dauphiné twinning. Slip rotates grains such that CRSS is low on the prism planes, but then Dauphiné twin boundaries sweeps through the grain back to the orientation giving lower stored elastic energy. The faster recovery at higher temperatures gives subgrain walls slowing down twin movement across the mm-sized grain of the GBM regime. At lower temperatures in the SGR-regime grain-size is reduced and different rotations of the grains are happening due to the domination of rhomb and basal slip. Because recrystallization is effective relative to grain-size the grains are commonly free of internal strain and subgrain walls, allowing the favorably oriented Dauphiné twin member to sweep across the whole grain overwhelming the unfavorably oriented Dauphiné twin member. As a consequence high strain reduces the number of Dauphiné twins and quartz rhomb fabrics appear trigonal, missing the "comet" shape of the GBM regime rhomb fabrics. Since Dauphiné twinning is also efficient at low temperatures rocks deformed in the brittle regime may also display stress-induced movement of Dauphiné twins. Though still highly debated Dauphiné twins and quartz rhombs fabrics may evolve as critical tools for determining paleostress orientation. Tullis, J. and Tullis, T. E., 1972, Preferred orientation of quartz produced by mechanical Dauphine twinning: thermodynamics and axial experiments in H. Heard et al., eds., Flow and Fracture of Rocks, Am. Geophys. Union Monograph 16, 67-82.

Eske Sørensen, Bjørn

2014-05-01

274

Synthesis and study of the crystallographic and magnetic structure of DyFeMnO{sub 5}: A new ferrimagnetic oxide  

SciTech Connect

The title oxide has been obtained by replacing Mn{sup 3+} by Fe{sup 3+} in the parent oxide DyMn{sub 2}O{sub 5}. The crystallographic and magnetic structures have been analysed from neutron powder diffraction (NPD) data, in complement with susceptibility and magnetic measurements. DyFeMnO{sub 5} is orthorhombic, belonging to the Pbam space group as the parent compound. The crystal structure contains infinite chains of edge-sharing Mn{sup 4+}O{sub 6} octahedra, interconnected by dimer units of Fe{sup 3+}O{sub 5} square pyramids. There is a certain antisite disorder in the crystal structure, with 8.0% of the Mn{sup 4+} sites occupied by Fe cations, and 8.2% of the Fe{sup 3+} positions occupied by Mn{sup 3+} cations. The magnetization measurements show that DyFeMnO{sub 5} presents magnetic order below T{sub C}{approx}178 K; a study of the magnetic structure from the low-temperature NPD patterns indicates an antiferromagnetic coupling of the Mn{sup 4+} and Fe{sup 3+} spins, with the polarization of the Dy{sup 3+} magnetic moments parallel to the those of the Fe sublattice. - Graphical abstract: DyFeMnO{sub 5} is orthorhombic (Pbam) as the parent DyMn{sub 2}O{sub 5} oxide. The crystal structure contains infinite chains of edge-sharing Mn{sup 4+}O{sub 6} octahedra, interconnected by dimer units of Fe{sup 3+}O{sub 5} square pyramids. It is ferrimagnetic below T{sub C}{approx}178 K; a NPD study indicated an antiferromagnetic coupling of the Mn{sup 4+} and Fe{sup 3+} spins, with Dy{sup 3+} magnetic moments parallel to those of Fe.

Martinez-Lope, M.J.; Retuerto, M. [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid (Spain); Alonso, J.A. [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid (Spain)], E-mail: ja.alonso@icmm.csic.es; Pomjakushin, V. [Laboratory for Neutron Scattering, ETHZ and PSI, CH-5232 Villigen PSI (Switzerland)

2008-09-15

275

Space Research Centre Space Research Centre  

E-print Network

Space Research Centre Space Research Centre www.src.le.ac.uk #12;2 University of Leicester � DeLivering over five DecaDes of space science anD instrUmentation expertise... Welcome to the SRC The Space Research Centre's (SRC) programme has two main foci: the Space Science and Instrumentation (SSI) Group

Hinton, Jim

276

OMEGA-GROUPS Group Theory For Wild Topology  

E-print Network

OMEGA-GROUPS Group Theory For Wild Topology Allan J. Sieradski The algebraic topology of locally. But for wild spaces, by which we mean metric spaces with arbitrarily small essential fea- tures, new group

277

Identifying unknown nanocrystals by fringe fingerprinting in two dimensions and free-access crystallographic databases  

NASA Astrophysics Data System (ADS)

New needs to determine the crystallography of nanocrystals arise with the advent of science and engineering on the nanometer scale. Direct space high-resolution phase-contrast transmission electron microscopy (HRTEM) and atomic resolution Z-contrast scanning TEM (Z-STEM), when combined with tools for image-based nanocrystallography possess the capacity to meet these needs. This paper introduces such a tool, i.e. fringe fingerprinting in two dimensions (2D), for the identification of unknown nanocrystal phases and compares this method briefly to qualitative standard powder X-ray diffractometry (i.e. spatial frequency fingerprinting). Free-access crystallographic databases are also discussed because the whole fingerprinting concept is only viable if there are comprehensive databases to support the identification of an unknown nanocrystal phase. This discussion provides the rationale for our ongoing development of a dedicated free-access Nano-Crystallography Database (NCD) that contains comprehensive information on both nanocrystal structures and morphologies. The current status of the NCD project and plans for its future developments are briefly outlined. Although feasible in contemporary HRTEMs and Z-STEMs, fringe fingerprinting in 2D (and image-based nanocrystallography in general) will become much more viable with the increased availability of aberration-corrected transmission electron microscopes. When the image acquisition and interpretation are, in addition, automated in such microscopes, fringe fingerprinting in 2D will be able to compete with powder X-ray diffraction for the identification of unknown nanocrystal phases on a routine basis. Since it possesses a range of advantages over powder X-ray diffractometry, e.g., fringe fingerprint plots contain much more information for the identification of an unknown crystal phase, fringe fingerprinting in 2D may then capture a significant part of the nanocrystal metrology market.

Moeck, Peter; ?ertik, Ond?ej; Seipel, Bjoern; Groebner, Rebecca; Noice, Lori; Upreti, Girish; Fraundorf, Philip; Erni, Rolf; Browning, Nigel D.; Kiesow, Andreas; Jolivet, Jean-Pierre

2005-11-01

278

Local dynamics of proteins and DNA evaluated from crystallographic B factors  

PubMed Central

The dynamics of protein and nucleic acid structures is as important as their average static picture. The local molecular dynamics concealed in diffraction images is expressed as so-called B factors. To find out how the crystal-derived B factors represent the dynamic behaviour of atoms and residues of proteins and DNA in their complexes, the distributions of scaled B factors from a carefully curated data set of over 700 protein–DNA crystal structures were analyzed [Schneider et al. (2014 ?), Nucleic Acids Res. 42, 3381–3394]. Amino acids and nucleotides were categorized based on their molecular neighbourhood as solvent-accessible, solvent-inaccessible (i.e. forming the protein core) or lying at protein–protein or protein–DNA interfaces; the backbone and side-chain atoms were analyzed separately. The B factors of two types of crystal-ordered water molecules were also analyzed. The analysis confirmed several expected features of protein and DNA dynamics, but also revealed surprising facts. Solvent-accessible amino acids have B factors that are larger than those of residues at the biomolecular interfaces, and core-forming amino acids are the most restricted in their movement. A unique feature of the latter group is that their side-chain and backbone atoms are restricted in their movement to the same extent; in all other amino-acid groups the side chains are more floppy than the backbone. The low values of the B factors of water molecules bridging proteins with DNA and the very large fluctuations of DNA phosphates are surprising. The features discriminating different types of residues are less pronounced in structures with lower crystallographic resolution. Some of the observed trends are likely to be the consequence of improper refinement protocols that may need to be rectified. PMID:25195754

Schneider, Bohdan; Gelly, Jean-Christophe; de Brevern, Alexandre G.; Cerny, Jiri

2014-01-01

279

A Practical Method of Solving Cutoff Coulomb Problems in Momentum Space --- Application to the Lippmann-Schwinger Resonating-Group Method and the pd Elastic Scattering ---  

NASA Astrophysics Data System (ADS)

A practical method of solving cutoff Coulomb problems of two-cluster systems in momentum space is given. When a sharply cut-off Coulomb force with a cutoff radius ? is introduced at the level of constituent particles, the two-cluster direct potential of the Coulomb force becomes in general a local screened Coulomb potential. The asymptotic Hamiltonian yields two types of asymptotic waves; one is an approximate Coulomb wave with ? in the middle-range region, and the other a free (no-Coulomb) wave in the longest-range region. The constant Wronskians of this Hamiltonian can be calculated in either region. We can evaluate the Coulomb-modified nuclear phase shifts for the screened Coulomb problem using the matching condition proposed by Vincent and Phatak for the sharply cut-off Coulomb problem. We apply this method first to an exactly solvable model of the ? ? scattering with the Ali-Bodmer potential and confirm that a complete solution is obtained with a finite ?. The stability of nuclear phase shifts with respect to the change in ? within some appropriate range is demonstrated in the ? ? resonating-group method (RGM) calculation using the Minnesota three-range force. An application to the pd elastic scattering is also discussed.

Fujiwara, Y.; Fukukawa, K.

2012-08-01

280

Crystallographic Image Processing with Unambiguous 2D Bravais Lattice Identification on the Basis of a Geometric Akaike Information Criterion  

NASA Astrophysics Data System (ADS)

Crystallographic image processing (CIP) is a technique first used to aid in the structure determination of periodic organic complexes imaged with a high-resolution transmission electron microscope (TEM). The technique has subsequently been utilized for TEM images of inorganic crystals, scanning TEM images, and even scanning probe microscope (SPM) images of two-dimensional periodic arrays. We have written software specialized for use on such SPM images. A key step in the CIP process requires that an experimental image be classified as one of only 17 possible mathematical plane symmetry groups. The current methods used for making this symmetry determination are not entirely objective, and there is no generally accepted method for measuring or quantifying deviations from ideal symmetry. Here, we discuss the crystallographic symmetries present in real images and the general techniques of CIP, with emphasis on the current methods for symmetry determination in an experimental 2D periodic image. The geometric Akaike information criterion (AIC) is introduced as a viable statistical criterion for both quantifying deviations from ideal symmetry and determining which 2D Bravais lattice best fits the experimental data from an image being processed with CIP. By objectively determining the statistically favored 2D Bravais lattice, the determination of plane symmetry in the CIP procedure can be greatly improved. As examples, we examine scanning tunneling microscope images of 2D molecular arrays of the following compounds: cobalt phthalocyanine on Au (111) substrate; nominal cobalt phthalocyanine on Ag (111); tetraphenoxyphthalocyanine on highly oriented pyrolitic graphite; hexaazatriphenylene-hexacarbonitrile on Ag (111). We show that the geometric AIC procedure can unambiguously determine which 2D Bravais lattice fits the experimental data for a variety of different lattice types. In some cases, the geometric AIC procedure can be used to determine which plane symmetry group best fits the experimental data, when traditional CIP methods fail to do so.

Bilyeu, Taylor Thomas

281

Allowed mesoscopic point group symmetries in domain average engineering of perovskite ferroelectric crystals  

E-print Network

Allowed mesoscopic point group symmetries in domain average engineering of perovskite ferroelectric the microscopic single domain crystal symmetry. Such engineered domain structures in certain ferroelectric the domain wall, since it usually appears as a planar structure along particular crystallographic orienta

Cao, Wenwu

282

Preliminary joint neutron and X-ray crystallographic study of human carbonic anhydrase II  

PubMed Central

Carbonic anhydrases catalyze the interconversion of CO2 to HCO3 ?, with a subsequent proton-transfer (PT) step. PT proceeds via a proposed hydrogen-bonded water network in the active-site cavity that is stabilized by several hydrophilic residues. A joint X-ray and neutron crystallographic study has been initiated to determine the specific water network and the protonation states of the hydrophilic residues that coordinate it in human carbonic anhydrase II. Time-of-flight neutron crystallographic data have been collected from a large (?1.2?mm3) hydrogen/deuterium-exchanged crystal to 2.4?Å resolution and X-­ray crystallographic data have been collected from a similar but smaller crystal to 1.5?Å resolution. Obtaining good-quality neutron data will contribute to the understanding of the catalytic mechanisms that utilize water networks for PT in protein environments. PMID:19407386

Fisher, S. Z.; Kovalevsky, A. Y.; Domsic, J. F.; Mustyakimov, M.; Silverman, D. N.; McKenna, R.; Langan, Paul

2009-01-01

283

Crystallization and preliminary crystallographic analysis of molybdenum-cofactor biosynthesis protein C from Thermus thermophilus  

SciTech Connect

The Gram-negative aerobic eubacterium Thermus thermophilus is an extremely important thermophilic microorganism that was originally isolated from a thermal vent environment in Japan. The molybdenum cofactor in this organism is considered to be an essential component required by enzymes that catalyze diverse key reactions in the global metabolism of carbon, nitrogen and sulfur. The molybdenum-cofactor biosynthesis protein C derived from T. thermophilus was crystallized in two different space groups. Crystals obtained using the first crystallization condition belong to the monoclinic space group P2{sub 1}, with unit-cell parameters a = 64.81, b = 109.84, c = 115.19 {angstrom}, {beta} = 104.9{sup o}; the crystal diffracted to a resolution of 1.9 {angstrom}. The other crystal form belonged to space group R32, with unit-cell parameters a = b = 106.57, c = 59.25 {angstrom}, and diffracted to 1.75 {angstrom} resolution. Preliminary calculations reveal that the asymmetric unit contains 12 monomers and one monomer for the crystals belonging to space group P2{sub 1} and R32, respectively.

Kanaujia, Shankar Prasad; Ranjani, Chellamuthu Vasuki; Jeyakanthan, Jeyaraman; Baba, Seiki; Chen, Lirong; Liu, Zhi-Jie; Wang, Bi-Cheng; Nishida, Masami; Ebihara, Akio; Shinkai, Akeo; Kuramitsu, Seiki; Shiro, Yoshitsugu; Sekar, Kanagaraj; Yokoyama, Shigeyuki (IIS); (SP8); (Georgia)

2010-12-03

284

Correlation between Crystallographic and Magnetic Domains at Co/NiO(001) Interfaces  

SciTech Connect

Using soft x-ray spectromicroscopy we show that NiO(001) exhibits a crystallographic and magnetic domain structure near the surface identical to that of the bulk. Upon Co deposition a perpendicular coupling between the Ni and Co moments is observed that persists even after formation of uncompensated Ni spins at the interface through annealing. The chemical composition at the interface alters its crystallographic structure and leads to a reorientation of the Ni moments from the <112> to the <110> direction. We show that this reorientation is driven by changes in the magnetocrystalline anisotropy rather than exchange coupling mediated by residual uncompensated spins.

Ohldag, H.; van der Laan, G.; Arenholz, E.

2008-12-18

285

Evolution of the crystallographic planes of cone-shaped patterned sapphire substrate treated by wet etching  

NASA Astrophysics Data System (ADS)

A series of wet etching experiments were performed to investigate the evolution of crystallographic planes of cone-shaped patterned sapphire substrate. During the etching process, three kinds of etching zones were found. Two etching zones appeared first and vanished with increasing etching time. The other one exposed later and expanded gradually. Finally, the cone-shaped pattern with an arcuate slope transformed to a hexagonal pyramid. The calculated orientation of the crystallographic planes in the two etching zones was {1 1¯ 0 3} and {4 3¯1¯ 27}, which were different from the previous reports.

Yang, Dechao; Liang, Hongwei; Qiu, Yu; Shen, Rensheng; Liu, Yang; Xia, Xiaochuan; Song, Shiwei; Zhang, Kexiong; Yu, Zhennan; Zhang, Yuantao; Du, Guotong

2014-03-01

286

High resolution neutron diffraction crystallographic investigation of Oxide Dispersion Strengthened steels of interest for fusion technology  

NASA Astrophysics Data System (ADS)

High resolution neutron diffraction measurements have been carried out to characterize the crystallographic phases present in different Oxide Dispersion Strengthened (ODS) steels of interest for fusion technology. The different lattice structures, Im3m for the ferritic ODS and Fm3m for the austenitic ODS, are resolved showing line anisotropy effects possibly correlated with differences in dislocation densities and texture. Many contributions from minority phases are detected well above the background noise; none of the expected crystallographic phases, such as M23C6 and including Y2O3, fits them, but the TiN phase is identified in accordance with results of other microstructural techniques.

Coppola, R.; Rodriguez-Carvajal, J.; Wang, M.; Zhang, G.; Zhou, Z.

2014-12-01

287

Petrographic and crystallographic study of silicate minerals in lunar rocks  

NASA Technical Reports Server (NTRS)

Optical U-stage measurements, chemical microprobe data, and X-ray procession photographs of a bytownite twin group from rock 12032,44 are compared. Sharp but weak b and no c-reflections were observed for this An89 bytownite indicating a partly disordered structure. Euler angles, used to characterize the orientation of the optical indicatrix, compare better with values for plutonic than for volcanic plagioclase. This indicates that structural and optical properties cannot be directly correlated.

Carmichael, I. S. E.; Turner, F. J.; Wenk, H. R.

1974-01-01

288

Wyartite: Crystallographic evidence for the first pentavalent-uranium mineral  

SciTech Connect

Determination of the structure of wyartite provides the first evidence for a pentavalent-U mineral. The structure of wyartite, CaU{sup 5+}(UO{sub 2}){sub 2}(CO{sub 3})O{sub 4}(OH)(H{sub 2}O), was solved by direct methods and refined to an agreement index (R) of 4.9% for 2309 unique reflections collected using MoK{alpha}X-radiation and a CCD-based detector. The structure contains three unique U positions; two contain U{sup 6+} and involve uranyl ions with typical pentagonal-bipyramidal coordination. Seven anions coordinate the other U position, but there is no uranyl ion present. The polyhedral geometry, the bond-valence sum incident at this U site, and electroneutrality requirements, all indicate that this site contains U{sup 5+}. The U{phi}{sub 7} ({phi}: O, OH, H{sub 2}O) polyhedra share edges and corners to form a unique sheet in which a CO{sub 3} group shares an edge with the U{sup 5+}{phi}{sub 7} polyhedron. The structure contains one Ca site coordinated by seven anions. The Ca atom and its associated H{sub 2}O groups occupy interlayer sites, along with two H{sub 2}O groups that are held in the structure by H bonds only. The Ca{phi}{sub 7} polyhedron is linked to one adjacent sheet by sharing an edge with the CO{sub 3} group and an O atom with a U{sup 6+}{phi}{sub 7} polyhedron. Structural units are linked together through hydrogen bonds only.

Burns, P.C. [Univ. of Notre Dame, IN (United States). Dept. of Civil Engineering and Geological Sciences; Finch, R.J. [Argonne National Lab., IL (United States). Chemical Technology Div.

1999-09-01

289

36 CFR 1280.74 - What spaces in the National Archives Building are available for use by non-NARA groups and...  

...Property 3 2014-07-01 2014-07-01 false What spaces in the National Archives Building are available for use by...National Archives Building, Washington, Dc § 1280.74 What spaces in the National Archives Building are available for use...

2014-07-01

290

36 CFR 1280.85 - What space in the National Archives at College Park is available for use by non-NARA groups and...  

...Property 3 2014-07-01 2014-07-01 false What space in the National Archives at College Park is available for use... National Archives at College Park, Md § 1280.85 What space in the National Archives at College Park is available for...

2014-07-01

291

Getting Crystals Your Crystallographer Will Treasure Richard J. Staples 03/09/2005 1 X-Ray Crystallography Laboratory  

E-print Network

Getting Crystals Your Crystallographer Will Treasure Richard J. Staples 03/09/2005 1 X-Ray Crystallography Laboratory Department of Chemistry And Chemical Biology Harvard University Getting Crystals Your Crystallographer Will Treasure Richard J. Staples Table of Contents · What is Crystal Structure and why do we want

Meagher, Mary

292

Ligand migration pathway and protein dynamics in myoglobin: A time-resolved crystallographic  

E-print Network

Ligand migration pathway and protein dynamics in myoglobin: A time-resolved crystallographic study-resolved x-ray crystallography at room temperature, structural relaxations and ligand migration were examined nanoseconds. They influence the concomitant migration of photodissociated CO to the Xe1 site, where it appears

Schmidt, Marius

293

Induction welding and heat treatment of steel pipes: evolution of crystallographic texture  

E-print Network

Induction welding and heat treatment of steel pipes: evolution of crystallographic texture detrimental to toughness P. Yan*1 , O¨. E. Gu¨ngo¨r2 , P. Thibaux2 and H. K. D. H. Bhadeshia1 Steel welding using induction heating to produce pipelines is found to have lower toughness at the weld junction than

Cambridge, University of

294

Crystallographic texture for tube and plate of the superelastic/shape-memory alloy Nitinol used for  

E-print Network

a study on how geometry and heat treatment can affect the texture of Nitinol, with specific quantificationCrystallographic texture for tube and plate of the superelastic/shape-memory alloy Nitinol used and Engineering, University of California, Berkeley, California 94720 2 SRI International, Menlo Park, California

Ritchie, Robert

295

Crystallographic and biochemical studies revealing the structural basis for antizyme inhibitor function  

E-print Network

Crystallographic and biochemical studies revealing the structural basis for antizyme inhibitor. In addition, the absence of residues and interactions required for pyridoxal 59-phosphate (PLP) binding suggests that AzI does not bind PLP. Biochemical studies confirmed the lack of PLP binding and revealed

Kahana, Chaim

296

Effects of substrate crystallographic orientations on crystal growth and microstructure development in laser  

E-print Network

Effects of substrate crystallographic orientations on crystal growth and microstructure development in laser surface-melted superalloy single crystals. Mathematical modeling of single-crystal growth that the substrate orientation has a predominant effect on crystal growth pattern, and simultaneously influences

DuPont, John N.

297

Crystallographic factors affecting the structure of polymeric spherulites. I. Morphology of directionally solidified polyamides  

Microsoft Academic Search

The morphology of even-even nylons has been reexamined in order to determine whether crystallographic factors can exert a dominant influence on the morphology and growth behavior of polymeric spherulites. Directional solidification of these polyamides produces long oriented spherulites at zone velocities below ~5 mum\\/min, while at higher rates unusual patterns are obtained by interaction with small positive spherulites. In most

Andrew J. Lovinger

1978-01-01

298

Crystallographic factors affecting the structure of polymeric spherulites. I. Morphology of directionally solidified polyamides  

Microsoft Academic Search

The morphology of even-even nylons has been reexamined in order to determine whether crystallographic factors can exert a dominant influence on the morphology and growth behavior of polymeric spherulites. Directional solidification of these polyamides produces long oriented spherulites at zone velocities below ?5 ?m\\/min, while at higher rates unusual patterns are obtained by interaction with small positive spherulites. In most

Andrew J. Lovinger

1978-01-01

299

Magnetic-field-induced crystallographic texture enhancement in cold-deformed FePt nanostructured magnets  

E-print Network

Magnetic-field-induced crystallographic texture enhancement in cold-deformed FePt nanostructured magnets B. Z. Cuia and K. Han National High Magnetic Field Laboratory, Florida State University Grenoble, France H. J. Schneider-Muntau National High Magnetic Field Laboratory, Florida State University

Garmestani, Hamid

300

Development of a metrology instrument for mapping the crystallographic axis in large optics  

Microsoft Academic Search

A metrology instrument has been developed to scan crystals and map the peak tuning angles for frequency conversion from the infrared to the ultra violet over large apertures. The need for such a device emerged from the National Ignition Facility (NIF) program where frequency conversion crystals have been found to have significant crystallographic axis wander at the large NIF aperture

R L Hibbard; L W Liou; R B Michie; M D Summers

1998-01-01

301

Inhibition of Staphyloxanthin Virulence Factor Biosynthesis in Staphylococcus aureus: In Vitro, in Vivo, and Crystallographic Results  

E-print Network

School of Pharmacy and Pharmaceutical Sciences, UniVersity of California, San Diego, 9500 Gilman Dri compounds are phosphonoacetamides that have low nanomolar Ki values for CrtM inhibition and are active the X-ray crystallographic structure of the most active compound, N-3-(3-phenoxyphenyl

Nizet, Victor

302

See ACA Newsletter, SPRING 2008 The 10 "must" read book list for X-ray Crystallographers.  

E-print Network

gota-have book for people interested in the bigger picture." 6. Structure Determination by XSee ACA Newsletter, SPRING 2008 The 10 "must" read book list for X-ray Crystallographers. As I books on any given subject. What ten books on X-ray crystallography would you recommend?" Unfortunately

Meagher, Mary

303

Abelian groups  

E-print Network

of G . Therefore x is the sum of elements in the G 's, pi p To finish our proof we wish to show this expression is unique. Suppose x ~ yl + y 2 + ~ ~ ~ + yg and m zl + s2 + ~ ~ ~ + s~o Then yl + y 2 + ~ ~ ~ + yy sl + $2 + ~ ~ ~ + zygo so that s... groups. In order to d. o this, we will need the aid. of some vector space theorys D~ef ~tp 4s10 A vector ~sac 7 over the field. P is an abelian group which admits mult1plicatlon by elements of t' he field. such that, for a, b e P and. x, y s V& (l) a...

Bolen, James Cordell

2012-06-07

304

Crystallographic texture in pulsed laser deposited hydroxyapatite bioceramic coatings  

PubMed Central

The orientation texture of pulsed laser deposited hydroxyapatite coatings was studied by X-ray diffraction techniques. Increasing the laser energy density of the KrF excimer laser used in the deposition process from 5 to 7 J/cm2 increases the tendency for the c-axes of the hydroxyapatite grains to be aligned perpendicular to the substrate. This preferred orientation is most pronounced when the incidence direction of the plume is normal to the substrate. Orientation texture of the hydroxyapatite grains in the coatings is associated with the highly directional and energetic nature of the ablation plume. Anisotropic stresses, transport of hydroxyl groups and dehydroxylation effects during deposition all seem to play important roles in the texture development. PMID:18563207

Kim, Hyunbin; Camata, Renato P.; Lee, Sukbin; Rohrer, Gregory S.; Rollett, Anthony D.; Vohra, Yogesh K.

2008-01-01

305

Sporulation Phosporelay Proteins And Their Complexes: Crystallographic Characterization  

SciTech Connect

Bacteria use two-component systems to adapt to changes in environmental conditions. In response to deteriorating conditions of growth, certain types of bacteria form spores instead of proceeding with cell division. The formation of spores is controlled by an expanded version of two-component systems called the phosphorelay. The phosphorelay comprises a primary kinase that receives the signal/stimulus and undergoes autophosphorylation, followed by two intermediate messengers that regulate the flow of the phosphoryl group to the ultimate response regulator/transcription factor. Sporulation is initiated when the level of phosphorylation of the transcription factor reaches a critical point. This chapter describes efforts to understand the mechanism of initiation of sporulation at the molecular level using X-ray crystallography as a tool. Structural analyses of individual members, as well as their complexes, provide insight into the mechanism of phosphoryl transfer and the origin of specificity in signal transduction.

Varughese, K.I.; Zhao, H.; Veldore, V.H.; Zapf, J.

2009-06-04

306

An evaluation of adhesive sample holders for advanced crystallographic experiments  

PubMed Central

The hydration state of macromolecular crystals often affects their overall order and, ultimately, the quality of the X-ray diffraction pattern that they produce. Post-crystallization techniques that alter the solvent content of a crystal may induce rearrangement within the three-dimensional array making up the crystal, possibly resulting in more ordered packing. The hydration state of a crystal can be manipulated by exposing it to a stream of air at controlled relative humidity in which the crystal can equilibrate. This approach provides a way of exploring crystal hydration space to assess the diffraction capabilities of existing crystals. A key requirement of these experiments is to expose the crystal directly to the dehydrating environment by having the minimum amount of residual mother liquor around it. This is usually achieved by placing the crystal on a flat porous support (Kapton mesh) and removing excess liquid by wicking. Here, an alternative approach is considered whereby crystals are harvested using adhesives that capture naked crystals directly from their crystallization drop, reducing the process to a one-step procedure. The impact of using adhesives to ease the harvesting of different types of crystals is presented together with their contribution to background scattering and their usefulness in dehydration experiments. It is concluded that adhesive supports represent a valuable tool for mounting macromolecular crystals to be used in humidity-controlled experiments and to improve signal-to-noise ratios in diffraction experiments, and how they can protect crystals from modifications in the sample environment is discussed. PMID:25195752

Mazzorana, Marco; Sanchez-Weatherby, Juan; Sandy, James; Lobley, Carina M. C.; Sorensen, Thomas

2014-01-01

307

A knowledge-driven approach for crystallographic protein model completion.  

PubMed

One of the most cumbersome and time-demanding tasks in completing a protein model is building short missing regions or ;loops'. A method is presented that uses structural and electron-density information to build the most likely conformations of such loops. Using the distribution of angles and dihedral angles in pentapeptides as the driving parameters, a set of possible conformations for the C(alpha) backbone of loops was generated. The most likely candidate is then selected in a hierarchical manner: new and stronger restraints are added while the loop is built. The weight of the electron-density correlation relative to geometrical considerations is gradually increased until the most likely loop is selected on map correlation alone. To conclude, the loop is refined against the electron density in real space. This is started by using structural information to trace a set of models for the C(alpha) backbone of the loop. Only in later steps of the algorithm is the electron-density correlation used as a criterion to select the loop(s). Thus, this method is more robust in low-density regions than an approach using density as a primary criterion. The algorithm is implemented in a loop-building program, Loopy, which can be used either alone or as part of an automatic building cycle. Loopy can build loops of up to 14 residues in length within a couple of minutes. The average root-mean-square deviation of the C(alpha) atoms in the loops built during validation was less than 0.4 A. When implemented in the context of automated model building in ARP/wARP, Loopy can increase the completeness of the built models. PMID:18391408

Joosten, Krista; Cohen, Serge X; Emsley, Paul; Mooij, Wijnand; Lamzin, Victor S; Perrakis, Anastassis

2008-04-01

308

Synthesis, growth, spectral, thermal and crystallographic studies of 5?,6?-epoxycholestane single crystals  

NASA Astrophysics Data System (ADS)

?-Selective epoxidation of 3?-chlorocholest-5-ene and 3?-acetoxycholest-5-ene has been performed with m-CPBA to synthesize 3?-chloro-5?,6?-epoxycholestane (1) and 3?-acetoxy-5?,6?-epoxycholestane (2). We provided an analysis of these compounds by means of FT-IR, FT-Raman, 1H NMR, 13C NMR, 2D cosy, NOESY, UV-visible and X-ray crystallography. The compound 1 crystallizes in the orthorhombic space group P212121 while compound 2 crystallizes in the monoclinic space group P21. We compared the conformations of both compounds in solid state and in solution by calculation of dihedral angles and coupling constant values. The powder X-ray diffraction (PXRD) of the compound was recorded to ascertain the purity of the grown crystals. Thermogravimetric analysis showed stability of the compounds up to 250 °C. Moreover, the ICH rule has been applied to test the stability of two crystals, which showed significant stability.

Shamsuzzaman; Khanam, Hena; Mashrai, Ashraf; Ahmad, Musheer; Mabkhot, Yahia Nasser; Frey, Wolfgang; Siddiqui, Nazish

2013-12-01

309

Purification, crystallization and preliminary X-ray crystallographic studies of Rv3705c from Mycobacterium tuberculosis  

PubMed Central

The conserved protein Rv3705c from Mycobacterium tuberculosis has been cloned, expressed, purified and crystallized by the sitting-drop vapour-diffusion method using PEG 3350 as a precipitant. The Rv3705c crystals exhibited space group P6122 or P6522, with unit-cell parameters a = b = 198.0, c = 364.1?Å, ? = ? = 90, ? = 120°, and diffracted to a resolution of 3.3?Å. PMID:25084389

Lu, Feifei; Gao, Feng; Li, Honglin; Gong, Weimin; Zhou, Lin; Bi, Lijun

2014-01-01

310

OAST Space Theme Workshop. Volume 3: Working group summary. 2: Data handling, communications (E-2). A. Statement. B. Technology needs (form 1). C. Priority assessment (form 2)  

NASA Technical Reports Server (NTRS)

Technologies required to support the stated OAST thrust to increase information return by X1000, while reducing costs by a factor of 10 are identified. The most significant driver is the need for an overall end-to-end data system management technology. Maximum use of LSI component technology and trade-offs between hardware and software are manifest in most all considerations of technology needs. By far, the greatest need for data handling technology was identified for the space Exploration and Global Services themes. Major advances are needed in NASA's ability to provide cost effective mass reduction of space data, and automated assessment of earth looking imagery, with a concomitant reduction in cost per useful bit. A combined approach embodying end-to-end system analysis, with onboard data set selection, onboard data processing, highly parallel image processing (both ground and space), low cost, high capacity memories, and low cost user data distribution systems would be necessary.

1976-01-01

311

Local Group(s)  

E-print Network

The properties of the galaxies of the Local Group are reviewed, followed by a brief discussion of nearby groups. The galaxy groups in our vicinity - the M81 group, the Cen A group, and the IC 342/Maffei group - are in many respects Local Group analogs: Their luminosity functions, galaxy content, fractional galaxy type distribution, crossing times, masses, and zero-velocity surface radii are similar to those of the Local Group. Also, the nearby groups usually consist of two subgroups, some of which approach each other and may ultimately merge to form a fossil group. These poor groups contrast with the less evolved, loose and extended galaxy ``clouds'' such as the Scl group and the CVn I cloud. These are characterized by long crossing times, are dominated by gas-rich, late-type galaxies, and lack gas-deficient, low luminosity early-type dwarfs. These clouds may be groups still in formation. The local Hubble flow derived from the clouds and groups is very cold.

Eva K. Grebel

2006-05-22

312

OAST Space Theme Workshop. Volume 3: Working group summary. 7: Material (M-1). A. Statement. B. Technology needs (form 1). C. Priority assessment (form 2)  

NASA Technical Reports Server (NTRS)

The approach of matching technology areas with various themes needs was not effective for the materials and thermal control discipline because of the diversity of requirements for each. Top priorities were evolved from the advanced space transportation system and the space power platform because these are essential building blocks in fulfilling some of the other themes. Important needs identified include life long-life cryogenic cooling systems for sensors, masers, and other devices and the needs for lightweight nuclear shielding materials for nuclear electric propulsion.

1976-01-01

313

Crystallographic Texture and Orientation Variants in Al2O3-Y3Al5O12 Directionally Solidified Eutectic Crystals  

NASA Technical Reports Server (NTRS)

Eutectic rods of Al2O3 and Y3Al5O12 were grown by a laser-heated float zone method, and their microstructure and crystallographic texture were studied by scanning electron microscopy, electron backscattered diffraction and x-ray diffraction. The composites were found to be highly textured with two twin-related crystallographic orientation relationships between the phases. Electron backscattered diffraction was employed to determine the spatial distribution of the orientational variants within the samples and to define the crystallographic orientation of various microstructural features.

Frazer, Colleen S.; Dickey, Elizabeth C.; Sayir, Ali; Farmer, Serene (Technical Monitor)

2001-01-01

314

Crystallographic and Microstructural Studies of Lath Martensitic Steel During Tensile Deformation  

NASA Astrophysics Data System (ADS)

Significant crystallographic refinement was observed in the as-quenched lath martensitic steel during tensile deformation up to a strain of 20 pct. Crystallographic investigation by electron backscattering diffraction analysis coupled with the use of crystal plasticity model confirmed that the activation behavior of slip systems is inhomogeneous even within each martensite block. In particular, the activation behavior of slip systems is initially affected by the initial crystal orientation; however, the effect becomes negligible with increasing deformation. In addition, slip systems parallel to the lath plane are preferentially activated during elongation. Our results indicate that the nonuniform crystal rotation within individual blocks is induced not only by grain interaction phenomena but also by the anisotropic activity of slip systems. These are key factor that determines the grain refinement behavior in the as-quenched lath martensitic steel during deformation.

Na, Hyuntaek; Nambu, Shoichi; Ojima, Mayumi; Inoue, Junya; Koseki, Toshihiko

2014-10-01

315

Crystallographic anisotropy of the resistivity size effect in single crystal tungsten nanowires  

PubMed Central

This work demonstrates an anisotropic increase in resistivity with decreasing width in single crystal tungsten (W) nanowires having a height of 21?nm. Nanowire-widths were in the range of 15–451?nm, with the anisotropy observed for widths below 50?nm. The longitudinal directions of the nanowires coincided with the <100>, <110> and <111> orientations of the body centered cubic phase of W. The resistivity increase was observed to be minimized for the <111>-oriented single crystal nanowires, exhibiting a factor of two lower increase in resistivity at a width of ~15?nm, relative to the thin film resistivity (i.e., an infinitely wide wire). The observed anisotropy is attributed to crystallographic anisotropy of the Fermi velocity and the resultant anisotropy of the electron mean free path in W, and underscores the critical role of crystallographic orientation in nanoscale metallic conduction. PMID:24005230

Choi, Dooho; Moneck, Matthew; Liu, Xuan; Oh, Soong Ju; Kagan, Cherie R.; Coffey, Kevin R.; Barmak, Katayun

2013-01-01

316

A preliminary neutron crystallographic study of proteinase K at pD 6.5  

SciTech Connect

AbstractA preliminary neutron crystallographic study of the proteolytic enzyme proteinase K is presented. Large hydrogenated crystals were prepared in deuterated crystallization buffer using the vapour-diffusion method. Data were collected to a resolution of 2.3 on the LADI-III diffractometer at the Institut Laue Langevin (ILL) in 2.5 days. The results demonstrate the feasibility of a full neutron crystallographic analysis of this structure aimed at providing relevant information on the location of H atoms, particularly at the active site. This information will contribute to further understanding of the molecular mechanisms underlying proteinase K's catalytic activity and to an enriched understanding of the subtilisin clan of serine proteases.

Gardberg, Anna S [ORNL; Blakeley, Matthew P. [Institut Laue-Langevin (ILL); Myles, Dean A A [ORNL

2009-01-01

317

Application of electron backscatter diffraction for crystallographic characterization of tin whiskers.  

PubMed

Understanding the growth of whiskers or high aspect ratio features on substrates can be aided when the crystallography of the feature is known. This study has evaluated three methods that utilize electron backscatter diffraction (EBSD) for the determination of the crystallographic growth direction of an individual whisker. EBSD has traditionally been a technique applied to planar, polished samples, and thus the use of EBSD for out-of-surface features is somewhat more difficult and requires additional steps. One of the methods requires the whiskers to be removed from the substrate resulting in the loss of valuable physical growth relationships between the whisker and the substrate. The other two techniques do not suffer this disadvantage and provide the physical growth information as well as the crystallographic growth directions. The final choice of method depends on the information required. The accuracy and the advantages and disadvantages of each method are discussed. PMID:22832083

Michael, Joseph R; McKenzie, Bonnie B; Susan, Donald F

2012-08-01

318

Preferred crystallographic orientation in the ice I ??? II transformation and the flow of ice II  

USGS Publications Warehouse

The preferred crystallographic orientation developed during the ice I ??? II transformation and during the plastic flow of ice II was measured in polycrystalline deuterium oxide (D2O) specimens using low-temperature neutron diffraction. Samples partially transformed from ice I to II under a non-hydrostatic stress developed a preferred crystallographic orientation in the ice II. Samples of pure ice II transformed from ice I under a hydrostatic stress and then when compressed axially, developed a strong preferred orientation of compression axes parallel to (101??0). A match to the observed preferred orientation using the viscoplastic self-consistent theory was obtained only when (101??0) [0001] was taken as the predominant slip system in ice II.

Bennett, K.; Wenk, H.-R.; Durham, W.B.; Stern, L.A.; Kirby, S.H.

1997-01-01

319

Mineralogical, crystallographic and morphological characteristics of natural kaolins from the Ivory Coast (West Africa)  

NASA Astrophysics Data System (ADS)

Thirteen clay samples from four deposits in the Ivory Coast (West Africa) were studied using X-ray diffraction, thermogravimetric analysis and chemical analysis. Mineralogical, crystallographic and morphological characteristics of these samples are given. Kaolinite is the principal mineral but other minerals are present in small quantities: illite, quartz, anatase and iron oxides (oxides and oxyhydroxides). The crystallographic, morphological and surface characteristics are influenced by the presence of these impurities. In particular, the presence of iron oxides was associated with reduced structural ordering and thermal stability of kaolinite and increased specific surface area. These clays could be used in the ceramics industry to make tiles and bricks, and also in agronomy as supports for chemical fertilizers or for environmental protection by immobilising potentially toxic waste products.

Sei, J.; Morato, F.; Kra, G.; Staunton, S.; Quiquampoix, H.; Jumas, J. C.; Olivier-Fourcade, J.

2006-10-01

320

Growth and crystallographic feature-dependent characterization of spinel zinc ferrite thin films by RF sputtering  

NASA Astrophysics Data System (ADS)

ZnFe2O4 (ZFO) thin films exhibiting varying crystallographic features ((222)-epitaxially, (400)-epitaxially, and randomly oriented films) were grown on various substrates by radio-frequency magnetron sputtering. The type of substrate used profoundly affected the surface topography of the resulting ZFO films. The surface of the ZFO (222) epilayer was dense and exhibited small rectangular surface grains; however, the ZFO (400) epilayer exhibited small grooves. The surface of the randomly oriented ZFO thin film exhibited distinct three-dimensional island-like grains that demonstrated considerable surface roughness. Magnetization-temperature curves revealed that the ZFO thin films exhibited a spin-glass transition temperature of approximately 40 K. The crystallographic orientation of the ZFO thin films strongly affected magnetic anisotropy. The ZFO (222) epitaxy exhibited the strongest magnetic anisotropy, whereas the randomly oriented ZFO thin film exhibited no clear magnetic anisotropy.

Liang, Yuan-Chang; Hsia, Hao-Yuan

2013-12-01

321

Model-building strategies for low-resolution X-ray crystallographic data  

PubMed Central

The interpretation of low-resolution X-ray crystallographic data proves to be challenging even for the most experienced crystallographer. Ambiguity in the electron-density map makes main-chain tracing and side-chain assignment difficult. However, the number of structures solved at resolutions poorer than 3.5?Å is growing rapidly and the structures are often of high biological interest and importance. Here, the challenges faced in electron-density interpretation, the strategies that have been employed to overcome them and developments to automate the process are reviewed. The methods employed in model generation from electron microscopy, which share many of the same challenges in providing high-confidence models of macromolecular structures and assemblies, are also considered. PMID:19171966

Karmali, Anjum M.; Blundell, Tom L.; Furnham, Nicholas

2009-01-01

322

In the space provided below, work with your group members to develop support strategies/tips for supporting traditional and non-traditional first generation college students.  

E-print Network

for supporting traditional and non-traditional first generation college students. Traditional first generation generation students · Place to study/meet with group Focusing on the First Year Conference, 2014 Group OSU to high-income first generation college students. Low-income first generation students · FAFSA completion

323

Finite group symmetry breaking  

E-print Network

Finite group symmetry is commonplace in Physics, in particular through crystallographic groups occurring in condensed matter physics -- but also through the inversions (C,P,T and their combinations) occurring in high energy physics and field theory. The breaking of finite groups symmetry has thus been thoroughly studied, and general approaches exist to investigate it. In Landau theory, the state of a system is described by a finite dimensional variable (the {\\it order parameter}), and physical states correspond to minima of a potential, invariant under a group. In this article we describe the basics of symmetry breaking analysis for systems described by a symmetric polynomial; in particular we discuss generic symmetry breakings, i.e. those determined by the symmetry properties themselves and independent on the details of the polynomial describing a concrete system. We also discuss how the plethora of invariant polynomials can be to some extent reduced by means of changes of coordinates, i.e. how one can reduce to consider certain types of polynomials with no loss of generality. Finally, we will give some indications on extension of this theory, i.e. on how one deals with symmetry breakings for more general groups and/or more general physical systems.

G. Gaeta

2005-10-02

324

Magnetic and Crystallographic Properties of Some Rare Earth Cobalt Compounds with CaZn5 Structure  

Microsoft Academic Search

The magnetic and crystallographic properties of CaZn5-type intermetallic compounds of cobalt and rare-earth elements (including Th) have been investigated. Strong deviations from 1:5 stoichiometry are observed when the rare-earth radius becomes relatively small. Both the saturation magnetizations (4?Is=2360–12 300 G) and the crystalline anisotropies (HA=25–210 kOe) depend on the rare-earth component. The coercive forces have been studied as a function

W. A. J. J. Velge; K. H. J. Buschow

1968-01-01

325

Microstructure, crystallographic texture and mechanical properties of friction stir welded AA2017A  

SciTech Connect

In this study a thick section (20 mm) friction stir welded AA2017A-T451 has been characterized in terms of microstructure, crystallographic texture and mechanical properties. For microstructural analysis both optical and scanning electron microscopes have been used. A detailed crystallographic texture analysis has been carried out using the electron back scattering diffraction technique. Crystallographic texture has been examined in both shoulder and probe affected regions of the weld NG. An entirely weak texture is observed at the shoulder affected region which is mainly explained by the effect of the sequential multi pass deformation experienced by both tool probe and tool shoulder. The texture in the probe dominated region at the AS side of the weld is relatively weak but still assembles the simple shear texture of FCC metals with B/B{sup Macron} and C components existing across the whole map. However, the texture is stronger at the RS than at the AS of the weld, mainly dominated byB/B{sup Macron} components and with C component almost absent across the map. An alternating bands between (B) components and (B{sup Macron }) component are observed only at the AS side of the weld. - Highlights: Black-Right-Pointing-Pointer Detailed investigation of microstructure and crystallographic texture. Black-Right-Pointing-Pointer The grain size is varied from the top to the bottom of the NG. Black-Right-Pointing-Pointer An entirely weak texture is observed at the shoulder affected region. Black-Right-Pointing-Pointer The texture in the probe affected region is dominated by simple shear texture.

Ahmed, M.M.Z., E-mail: mohamed_ahmed4@s-petrol.suez.edu.eg [Institute for Microstructural and Mechanical Processing Engineering, University of Sheffield (IMMPETUS), Mappin Street, Sheffield S1 3JD (United Kingdom); Department of Metallurgical and Materials Engineering, Suez Canal University, Suez 43721 (Egypt); Wynne, B.P.; Rainforth, W.M. [Institute for Microstructural and Mechanical Processing Engineering, University of Sheffield (IMMPETUS), Mappin Street, Sheffield S1 3JD (United Kingdom); Threadgill, P.L. [TWI LTD, Granta Park, Great Abington, Cambridge CB21 6AL (United Kingdom)

2012-02-15

326

3D mapping of crystallographic phase distribution using energy-selective neutron tomography.  

PubMed

Nondestructive 3D mapping of crystallographic phases is introduced providing distribution of phase fractions within the bulk (centimeter range) of samples with micrometer-scale resolution. The novel neutron tomography based technique overcomes critical limitations of existing techniques and offers a wide range of potential applications. It is demonstrated for steel samples exhibiting phase transformation after being subjected to tensile and torsional deformation. PMID:24692200

Woracek, Robin; Penumadu, Dayakar; Kardjilov, Nikolay; Hilger, Andre; Boin, Mirko; Banhart, John; Manke, Ingo

2014-06-25

327

Crystallographic study on CdS\\/CdTe heterostructure for 15% efficiency thin film solar cells  

Microsoft Academic Search

Crystallographic properties of CdS as well as their influence on the subsequent growth of CdTe and on the formation of the CdTe1-xSx interlayer have been investigated for fabricating high efficiency thin film solar cells, employing X-ray diffraction measurements. In hexagonal CdS films, the first preferentially oriented [002] grains are grown having a lattice match with the second preferentially oriented (103)

Kengo Matsune; Hiroyuki Oda; Morihisa Ohta; Toshihiko Toyama; Hiroaki Okamoto

2005-01-01

328

Annealing effects on optical and crystallographic properties of CBD grown CdS films  

Microsoft Academic Search

CdS films were prepared by chemical bath deposition (CBD) at 60 °C without stirring. The crystallographic structure of the films and the size of the crystallites in the films were studied by x-ray diffraction. The energy gap of the films was found to decrease by annealing. The best annealing temperature for CBD grown CdS films was found to be 350

H. Metin; R. Esen

2003-01-01

329

Crystallographic finite element modeling for dislocation generation in semiconductor crystals grown by VGF process  

NASA Astrophysics Data System (ADS)

The generation and multiplication of dislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals grown by the Vertical Gradient Freeze (VGF) process is predicted using a transient crystallographic finite element model. This transient model is developed by coupling microscopic dislocation motion and multiplication to macroscopic plastic deformation in the slip system of the grown crystals during their growth process. During the growth of InP and GaAs crystals, dislocations are generated in plastically deformed crystal as a result of crystallographic glide caused by excessive thermal stresses. The temperature fields are determined by solving the partial differential equation of heat conduction in a VGF crystal growth system. The effects of growth orientations and growth parameters (i.e., imposed temperature gradients, crystal radius and growth rate) on dislocation generation and multiplication in GaAs and InP crystals are investigated using the developed transient crystallographic finite element model. Dislocation density patterns on the cross section of GaAs and InP crystals are numerically calculated and compared with experimental observations. For crystals grown along [001] and [111] orientations, the results show that more dislocations are generated as the temperature gradient, the crystal growth rate and the crystal radius increase. For the same growth process, it shows that the crystal grown along [111] orientation is a favorable growth direction to grow lower dislocation density crystals. All the results show a famous "W" shape and four fold symmetry dislocation density pattern in GaAs and InP crystals grown from both orientations regardless of crystal growth parameters, which agree well with the patterns observed in actual grown crystals. Therefore, this developed crystallographic model can be employed by crystal grower to design an optimal growth parameters and orientations for growing low dislocation density in advanced semiconductor and optical crystals.

Sheu, Gary

330

Space languages  

NASA Technical Reports Server (NTRS)

Applications of linguistic principles to potential problems of human and machine communication in space settings are discussed. Variations in language among speakers of different backgrounds and change in language forms resulting from new experiences or reduced contact with other groups need to be considered in the design of intelligent machine systems.

Hays, Dan

1987-01-01

331

Crystallinity and Crystallographic Texture in Isotactic Polypropylene during Deformation and Heating  

E-print Network

The development of the crystallinity and of the crystallographic orientation of isotactic polypropylene (iPP) during rolling deformation and subsequent heat treatment is studied. The experiments are conducted by using X-ray diffraction with an area detector. The evolution of crystallographic orientation is tracked by calculating the pole figures and by applying a quantitative 3D texture component fit method. The rolling orientation after a true strain of -1.5 mainly consists of the (010)[001], (130)[001], and [001]//RD fiber components (RD: rolling direction). The results reveal that the crystallinity drastically decreases during rolling. We suggest that decrystallization (disaggregation) is a deformation mechanism which takes place as a microscopic alternative to crystallographic intralamellar shear depending on the orientation of the lamellae relative to the imposed deformation tensor. Heat treatment after rolling leads to the recrystallization of amorphous material and to a strong enhancement of the fiber orientation component. The recrystallization orientation is explained in terms of an oriented nucleation mechanism where amorphous material aligns along existing crystalline lamellae blocks which prevailed during the preceding deformation.

J. Jia; D. Raabe

2008-11-14

332

On the importance of crystallographic texture in the biocompatibility of titanium based substrate.  

PubMed

The role of grain size and crystallographic orientation on the biocompatibility of commercially pure titanium was investigated. Samples, with significant differences in crystallographic texture and average grain size (from 0.4 to 40 µm) were produced by equal channel angular pressing (ECAP) and post deformation annealing. X-ray diffraction and electron back scattered diffraction (EBSD) were used to evaluate differences in texture and microstructural characteristics. The titanium oxide film present on the surface of the samples was analyzed to determine the oxidation state of titanium and the chemical bonds between oxygen and titanium using X-ray photoelectron spectroscopy (XPS). Biocompatibility experiments were conducted using MC3T3 preosteoblast cells. Cell attachment was found to be texture-sensitive, where the number of attached cells was higher on the samples with higher number of (0002) planes exposed to the surface, regardless of the grain size. A relationship was also found between the titanium oxide species formed on the surface and the crystallographic texture underneath. The surface texture consisting of more densely packed basal planes promote the formation of Ti-OH on the surface, which in turn, enhances the cell-substrate interactions. These surface characteristics are deemed responsible for the observed difference in cell attachment behaviour of surfaces with different textures. Finally, it is inferred that texture, rather than the grain size, plays the major role in controlling the surface biocompatibility of biomedical devices fabricated from pure metallic titanium. PMID:24254817

Hoseini, Majid; Bocher, Philippe; Shahryari, Arash; Azari, Fereshteh; Szpunar, Jerzy A; Vali, Hojatollah

2014-10-01

333

Validation of crystallographic models containing TLS or other descriptions of anisotropy  

PubMed Central

The use of TLS (translation/libration/screw) models to describe anisotropic displacement of atoms within a protein crystal structure has become increasingly common. These models may be used purely as an improved methodology for crystallographic refinement or as the basis for analyzing inter-domain and other large-scale motions implied by the crystal structure. In either case it is desirable to validate that the crystallographic model, including the TLS description of anisotropy, conforms to our best understanding of protein structures and their modes of flexibility. A set of validation tests has been implemented that can be integrated into ongoing crystallographic refinement or run afterwards to evaluate a previously refined structure. In either case validation can serve to increase confidence that the model is correct, to highlight aspects of the model that may be improved or to strengthen the evidence supporting specific modes of flexibility inferred from the refined TLS model. Automated validation checks have been added to the PARVATI and TLSMD web servers and incorporated into the CCP4i user interface. PMID:20693688

Zucker, Frank; Champ, P. Christoph; Merritt, Ethan A.

2010-01-01

334

Protracted fabric evolution in olivine: Implications for the relationship among strain, crystallographic fabric, and seismic anisotropy  

NASA Astrophysics Data System (ADS)

Crystallographic fabrics in olivine-rich rocks provide critical information on conditions and mechanisms of deformation as well as seismic properties of Earth's upper mantle. Previous interpretations of fabrics produced in laboratory experiments were complicated by uncertainty as to whether the steady-state fabric was attained. To examine the systematics of the evolution of olivine crystallographic fabrics at high strain, we conducted torsion experiments on olivine aggregates to shear strains of up to ?20. Our results demonstrate that a steady-state fabric is not reached until a shear strain >10, a much higher value than previously thought necessary. Fabrics characterized by girdles of [010] and [001] axes or by clusters of [010] and [001] axes are both observed. Until now, these fabrics were associated with either two different deformation mechanisms or two different sets of deformation conditions. Here we establish that both fabrics are, in fact, part of the same evolutionary process. An eigenvalue analysis allows the fabric shape to be quantitatively correlated with the magnitude of shear strain. Misorientation analysis suggests that the observed fabric evolution results from the competition of the two easiest slip systems in olivine, (010)[100] and (001)[100]. Our results open up the possibility of using olivine crystallographic fabrics or seismic anisotropy to quantitatively evaluate strain histories in both field studies and geophysical investigations of upper-mantle rocks.

Hansen, Lars N.; Zhao, Yong-Hong; Zimmerman, Mark E.; Kohlstedt, David L.

2014-02-01

335

Protracted fabric evolution in olivine: Implications for the relationship among strain, crystallographic fabric, and seismic anisotropy  

NASA Astrophysics Data System (ADS)

Crystallographic fabrics in olivine-rich rocks provide critical information on conditions and mechanisms of deformation as well as seismic properties of Earth's upper mantle. Previous interpretations of fabrics produced in laboratory experiments were complicated by uncertainty as to whether the steady-state fabric was attained. To examine the systematics of the evolution of olivine crystallographic fabrics at high strain, we conducted torsion experiments on olivine aggregates to shear strains of up to ~20. Our results demonstrate that a steady-state fabric is not reached until a shear strain >10, a much higher value than previously thought necessary. Fabrics characterized by girdles of [010] and [001] axes or by clusters of [010] and [001] axes are both observed. Until now, these fabrics were associated with either two different deformation mechanisms or two different sets of deformation conditions. Here we establish that both fabrics are, in fact, part of the same evolutionary process. An eigenvalue analysis allows the fabric shape to be quantitatively correlated with the magnitude of shear strain. Misorientation analysis suggests that the observed fabric evolution results from the competition of the two easiest slip systems in olivine, (010)[100] and (001)[100]. Our results open up the possibility of using olivine crystallographic fabrics or seismic anisotropy to quantitatively evaluate strain histories in both field studies and geophysical investigations of upper-mantle rocks.

Hansen, Lars; Zhao, Yong-Hong; Zimmerman, Mark; Kohlstedt, David

2014-05-01

336

Expression, crystallization and preliminary X-ray crystallographic analyses of two N-terminal acetyltransferase-related proteins from Thermoplasma acidophilum.  

PubMed

N-terminal acetylation is one of the most common protein modifications in eukaryotes, occurring in approximately 80-90% of cytosolic mammalian proteins and about 50% of yeast proteins. ARD1 (arrest-defective protein 1), together with NAT1 (N-acetyltransferase protein 1) and possibly NAT5, is responsible for the NatA activity in Saccharomyces cerevisiae. In mammals, ARD1 is involved in cell proliferation, neuronal development and cancer. Interestingly, it has been reported that mouse ARD1 (mARD1(225)) mediates epsilon-acetylation of hypoxia-inducible factor 1alpha (HIF-1alpha) and thereby enhances HIF-1alpha ubiquitination and degradation. Here, the preliminary X-ray crystallographic analyses of two N-terminal acetyltransferase-related proteins encoded by the Ta0058 and Ta1140 genes of Thermoplasma acidophilum are reported. The Ta0058 protein is related to an N-terminal acetyltransferase complex ARD1 subunit, while Ta1140 is a putative N-terminal acetyltransferase-related protein. Ta0058 shows 26% amino-acid sequence identity to both mARD1(225) and human ARD1(235). The sequence identity between Ta0058 and Ta1140 is 28%. Ta0058 and Ta1140 were overexpressed in Escherichia coli fused with an N-terminal purification tag. Ta0058 was crystallized at 297 K using a reservoir solution consisting of 0.1 M sodium acetate pH 4.6, 8%(w/v) polyethylene glycol 4000 and 35%(v/v) glycerol. X-ray diffraction data were collected to 2.17 A. The Ta0058 crystals belong to space group P4(1) (or P4(3)), with unit-cell parameters a = b = 49.334, c = 70.384 A, alpha = beta = gamma = 90 degrees. The asymmetric unit contains a monomer, giving a calculated crystal volume per protein weight (V(M)) of 2.13 A(3) Da(-1) and a solvent content of 42.1%. Ta1140 was also crystallized at 297 K using a reservoir solution consisting of 0.1 M trisodium citrate pH 5.6, 20%(v/v) 2-propanol, 20%(w/v) polyethylene glycol 4000 and 0.2 M sodium chloride. X-ray diffraction data were collected to 2.40 A. The Ta1140 crystals belong to space group R3, with hexagonal unit-cell parameters a = b = 75.174, c = 179.607 A, alpha = beta = 90, gamma = 120 degrees. Two monomers are likely to be present in the asymmetric unit, with a V(M) of 2.51 A(3) Da(-1) and a solvent content of 51.0%. PMID:17077495

Han, Sang Hee; Ha, Jun Yong; Kim, Kyoung Hoon; Oh, Sung Jin; Kim, Do Jin; Kang, Ji Yong; Yoon, Hye Jin; Kim, Se-Hee; Seo, Ji Hae; Kim, Kyu-Won; Suh, Se Won

2006-11-01

337

Dependence of crystallographic tilt and defect distribution on mask material in epitaxial lateral overgrown GaN layers  

Microsoft Academic Search

We have investigated the dependence of crystallographic tilt and defect distribution on mask material in metalorganic chemical vapor deposition grown GaN layers formed utilizing an epitaxial lateral overgrowth (ELO) technique using x-ray diffraction and transmission electron microscopy. Crystallographic tilt in the ELO GaN layer was suppressed by changing the mask material from electron beam (EB)-evaporated SiO2 to plasma enhanced chemical

S. Tomiya; K. Funato; T. Asatsuma; T. Hino; S. Kijima; T. Asano; M. Ikeda

2000-01-01

338

Anisotropic crystallographic properties, strain, and their effects on band structure of m-plane GaN on LiAlO2(100)  

NASA Astrophysics Data System (ADS)

The m-plane GaN films grown on LiAlO2(100) by metal-organic chemical vapor deposition exhibit anisotropic crystallographic properties. The Williamson-Hall plots point out they are due to the different tilts and lateral correlation lengths of mosaic blocks parallel and perpendicular to GaN[0001] in the growth plane. The symmetric and asymmetric reciprocal space maps reveal the strain of m-plane GaN to be biaxial in-plane compress ?xx=-0.79% and ?zz=-0.14% with an out-of-plane dilatation ?yy=0.38%. This anisotropic strain further separates the energy levels of top valence band at ? point. The energy splitting as 37meV as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room temperature.

Liu, B.; Zhang, R.; Xie, Z. L.; Kong, J. Y.; Yao, J.; Liu, Q. J.; Zhang, Z.; Fu, D. Y.; Xiu, X. Q.; Chen, P.; Han, P.; Shi, Y.; Zheng, Y. D.; Zhou, S. M.; Edwards, G.

2008-06-01

339

On the subgroup structure of the hyperoctahedral group in six dimensions  

PubMed Central

The subgroup structure of the hyperoctahedral group in six dimensions is investigated. In particular, the subgroups isomorphic to the icosahedral group are studied. The orthogonal crystallographic representations of the icosahedral group are classified and their intersections and subgroups analysed, using results from graph theory and their spectra. PMID:25176990

Zappa, Emilio; Dykeman, Eric C.; Twarock, Reidun

2014-01-01

340

Expression, purification and preliminary crystallographic analysis of N-acetylglucosamine-1-phosphate uridylyltransferase from Mycobacterium tuberculosis.  

PubMed

The gene product of open reading frame Rv1018c from Mycobacterium tuberculosis is annotated as encoding a probable N-acetylglucosamine 1-phosphate uridylyltransferase (MtbGlmU), an enzyme that catalyzes the biosynthesis of UDP-N-acetylglucosamine, a precursor common to lipopolysaccharide and peptidoglycan biosynthesis. Following overexpression in Escherichia coli, the enzyme was purified and crystallized using the hanging-drop vapour-diffusion method. Native diffraction data were collected from crystals belonging to space group R32 and processed to a resolution of 2.2 A. PMID:18765909

Yin, Jiang; Garen, Craig R; Cherney, Maia M; Cherney, Leonid T; James, Michael N G

2008-09-01

341

Isolation, purification, crystallization and preliminary crystallographic studies of chitinase from tamarind (Tamarindus indica) seeds  

PubMed Central

A protein with chitinase activity has been isolated and purified from tamarind (Tamarindus indica) seeds. N-terminal amino-acid sequence analysis of this protein confirmed it to be an ?34?kDa endochitinase which belongs to the acidic class III chitinase family. The protein was crystallized by the vapour-diffusion method using PEG 4000. The crystals belonged to the tetragonal space group P41, with two molecules per asymmetric unit. Diffraction data were collected to a resolution of 2.6?Å. PMID:19342775

Patil, Dipak N.; Datta, Manali; Chaudhary, Anshul; Tomar, Shailly; Kumar Sharma, Ashwani; Kumar, Pravindra

2009-01-01

342

Crystallization and preliminary X-ray crystallographic analysis of recombinant ?-mannosidase from Aspergillus niger.  

PubMed

?-Mannosidase (EC 3.2.1.25) is an important exoglycosidase specific for the hydrolysis of terminal ?-linked mannoside in various oligomeric saccharide structures. ?-Mannosidase from Aspergillus niger was expressed in Pichia pastoris and purified to clear homogeneity. ?-Mannosidase was crystallized in the presence of D-mannose and the crystal diffracted to 2.41?Å resolution. The crystal belonged to space group P1, with unit-cell parameters a=62.37, b=69.73, c=69.90?Å, ?=108.20, ?=101.51, ?=103.20°. The parameters derived from the data collection indicate the presence of one molecule in the asymmetric unit. PMID:23519806

Demo, Gabriel; Fliedrová, Barbora; Weignerová, Lenka; Wimmerová, Michaela

2013-03-01

343

Crystallization and preliminary X-ray crystallographic analysis of Sulfolobus solfataricus thioredoxin reductase  

PubMed Central

A thermostable thioredoxin reductase isolated from Sulfolobus solfataricus (SsTrxR) has been successfully crystallized in the absence and in the presence of NADP. Two different crystal forms have been obtained. Crystals of the form that yields higher resolution data (1.8?Å) belong to space group P212121, with unit-cell parameters a = 76.77, b = 120.68, c = 126.85?Å. The structure of the enzyme has been solved by MAD methods using the anomalous signal from the Se atoms of selenomethionine-labelled SsTrxR. PMID:16511192

Ruggiero, Alessia; Ruocco, Maria Rosaria; Grimaldi, Pasquale; Arcari, Paolo; Masullo, Mariorosario; Zagari, Adriana; Vitagliano, Luigi

2005-01-01

344

Crystallization and preliminary X-ray crystallographic analysis of Sulfolobus solfataricus thioredoxin reductase.  

PubMed

A thermostable thioredoxin reductase isolated from Sulfolobus solfataricus (SsTrxR) has been successfully crystallized in the absence and in the presence of NADP. Two different crystal forms have been obtained. Crystals of the form that yields higher resolution data (1.8 A) belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 76.77, b = 120.68, c = 126.85 A. The structure of the enzyme has been solved by MAD methods using the anomalous signal from the Se atoms of selenomethionine-labelled SsTrxR. PMID:16511192

Ruggiero, Alessia; Ruocco, Maria Rosaria; Grimaldi, Pasquale; Arcari, Paolo; Masullo, Mariorosario; Zagari, Adriana; Vitagliano, Luigi

2005-10-01

345

Crystallization and preliminary X-ray crystallographic studies on Type III antifreeze protein.  

PubMed

Type III antifreeze protein, more specifically the recombinant QAE-Sephadex-binding isoform, has been crystallized in 50-55% saturated ammonium sulfate, 0.1 M sodium acetate, pH 4.0-4.5. The resultant crystals belong to the orthorhombic space group P212121 with a = 32.60 A, b = 39.00 A, and c = 46.57 A and diffract to at least 1.7 A. A set of 1.7-A native data has been collected, with completeness 93.4% and Rsym of 0.069. Initial screening for heavy-atom derivatives has yielded a Pt-bound derivative. PMID:7549887

Jia, Z; DeLuca, C I; Davies, P L

1995-06-01

346

Design of a back-illuminated, crystallographically etched, silicon-on-sapphire avalanche photodiode with monolithically integrated microlens, for dual-mode passive & active imaging arrays  

NASA Astrophysics Data System (ADS)

There is a growing need in space and environmental research applications for dual-mode, passive and active 2D and 3D ladar imaging methods. To fill this need, an advanced back-illuminated avalanche photodiode (APD) design is presented based on crystallographically etched (100) epitaxial silicon on R-plane sapphire (SOS), enabling single photon sensitive, solid-state focal plane arrays (FPAs) with wide dynamic range, supporting passive and active imaging capability in a single FPA. When (100) silicon is properly etched with KOH:IPA:H2O solution through a thermally grown oxide mask, square based pyramidal frustum or mesa arrays result with the four mesa sidewalls of the APD formed by (111) silicon planes that intersect the (100) planes at a crystallographic angle, ?c = 54.7°. The APD device is fabricated in the mesa using conventional silicon processing technology. Detectors are back-illuminated through light focusing microlenses fabricated in the thinned, AR-coated sapphire substrate. The APDs share a common, front-side anode contact, made locally at the base of each device mesa. A low resistance (Al) or (Cu) metal anode grid fills the space between pixels and also inhibits optical cross-talk. SOS-APD arrays are indium bump-bonded to CMOS readout ICs to produce hybrid FPAs. The quantum efficiency for the square 27 µm pixels exceeds 50% for 250 nm < ? < 400 nm and exceeds 80% for 400 nm < ? < 700 nm. The sapphire microlenses compensate detector quantum efficiency loss resulting from the mesa geometry and yield 100% sensitive-area-fill-factor arrays, limited in size only by the wafer diameter.

Stern, Alvin G.; Cole, Daniel C.

2008-12-01

347

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION  

E-print Network

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 1 NASA Earth Science Data Systems Software Reuse #12;NATIONAL AERONAUTICS AND SPACE ADMINISTRATION ESDS Reuse Working Group 2 Award Background: http://www.esdswg.com/softwarereuse/Resources/awards/ #12;NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Christian, Eric

348

Conformal Carroll groups  

NASA Astrophysics Data System (ADS)

Conformal extensions of Lévy-Leblond's Carroll group, based on geometric properties analogous to those of Newton-Cartan space-time are proposed. The extensions are labeled by an integer k. This framework includes and extends our recent study of the Bondi-Metzner-Sachs (BMS) and Newman-Unti (NU) groups. The relation to conformal Galilei groups is clarified. Conformal Carroll symmetry is illustrated by ‘Carrollian photons’. Motion both in the Newton-Cartan and Carroll spaces may be related to that of strings in the Bargmann space.

Duval, C.; Gibbons, G. W.; Horvathy, P. A.

2014-08-01

349

Crystallization and preliminary crystallographic analysis of two eukaryotic fructosyl peptide oxidases.  

PubMed

Fructosyl peptide oxidase (FPOX) catalyses the oxidation of ?-glycated dipeptides such as N(?)-(1-deoxy-D-fructos-1-yl)-L-valyl-L-histidine (Fru-ValHis) and is used in the diagnosis of diabetes mellitus. Here, two thermostable mutants of FPOX, CFP-T7 and EFP-T5M, were crystallized by the sitting-drop vapour-diffusion method. The crystal of CFP-T7 belonged to the tetragonal space group P4(1)2(1)2, with unit-cell parameters a = b = 110.09, c = 220.48 Å, and that of EFP-T5M belonged to the monoclinic space group P2(1), with unit-cell parameters a = 43.00, b = 230.05, c = 47.27 Å, ? = 116.99°. The crystals of CFP-T7 and EFP-T5M diffracted to 1.8 and 1.6 Å resolution, respectively. PMID:23385752

Ichiyanagi, Atsushi; Hirokawa, Kozo; Gomi, Keiko; Nakatsu, Toru; Kato, Hiroaki; Kajiyama, Naoki

2013-02-01

350

A new motif in the formation of peptide nanotubes: the crystallographic signature.  

PubMed

Terminally protected acyclic tripeptides Boc-Tyr(1)-Val(2)-Tyr(3)-OMe 1 and Boc-Tyr(1)-Ile(2)-Tyr(3)-OMe 2 self-assemble into nanotubes in crystals through various noncovalent interactions with an average internal diameter of 5 A (0.5 nm), and the tubular ensemble is developed through the hydrogen-bonded side chains of tyrosine residues. The inside of the hollow nanotubular structures is hydrophilic; however, no solvent molecules have been crystallographically detected. [structure: see text] PMID:15548051

Ray, Sudipta; Haldar, Debasish; Drew, Michael G B; Banerjee, Arindam

2004-11-25

351

Application of combined EBSD and 3D-SEM technique on crystallographic facet analysis of steel at low temperature.  

PubMed

Electron backscatter diffraction has been increasingly used to identify the crystallographic planes and orientation of cleavage facets with respect to the rolling direction in fracture surfaces. The crystallographic indices of cleavage planes can be determined either directly from the fracture surface or indirectly from metallographic sections perpendicular to the plane of the fracture surface. A combination of electron backscatter diffraction and 3D scanning electron microscopy imaging technique has been modified to determine crystallographic facet orientations. The main purpose of this work has been to identify the macroscopic crystallographic orientations of cleavage facets in the fracture surfaces of weld heat affected zones in a well-known steel fractured at low temperatures. The material used for the work was an American Petroleum Institute (API) X80 grade steel developed for applications at low temperatures, and typical heat affected zone microstructures were obtained by carrying out weld thermal simulation. The fracture toughness was measured at different temperatures (0°C, -30°C, -60°C and -90°C) by using Crack Tip Opening Displacement testing. Fracture surfaces and changes in microstructure were analyzed by scanning electron microscopy and light microscopy. Crystallographic orientations were identified by electron backscatter diffraction, indirectly from a polished section perpendicular to the major fracture surface of the samples. Computer assisted 3D imaging was used to measure the angles between the cleavage facets and the adjacent polished surface, and then these angles were combined with electron backscatter diffraction measurements to determine the macroscopic crystallographic planes of the facets. The crystallographic indices of the macroscopic cleavage facet planes were identified to be {100}, {110}, {211} and {310} at all temperatures. PMID:23692572

Mohseni, P; Solberg, J K; Karlsen, M; Akselsen, O M; Ostby, E

2013-07-01

352

Crystallization and preliminary crystallographic studies of the HA3 subcomponent of the type B botulinum neurotoxin complex  

PubMed Central

The haemagglutinin subcomponent HA3 of the type B botulinum neurotoxin complex, which is important in toxin absorption from the gastrointestinal tract, has been expressed, purified and subsequently crystallized in two crystal forms at different pH values. Form I belonged to space group R32, with unit-cell parameters a = b = 357.4, c = 249.5?Å, ? = ? = 90, ? = 120°. Form II belonged to space group I4132, with unit-cell parameters a = b = c = 259.0?Å, ? = ? = ? = 90°. Diffraction data were collected from these crystals to a resolution of 3.0?Å for both form I and form II. PMID:22102038

Nishimura, Kohsuke; Kitadokoro, Kengo; Takegahara, Yuki; Sugawara, Yo; Matsumura, Takuhiro; Karatani, Hajime; Fujinaga, Yukako

2011-01-01

353

Space Resources  

NASA Technical Reports Server (NTRS)

Space resources must be used to support life on the Moon and exploration of Mars. Just as the pioneers applied the tools they brought with them to resources they found along the way rather than trying to haul all their needs over a long supply line, so too must space travelers apply their high technology tools to local resources. The pioneers refilled their water barrels at each river they forded; moonbase inhabitants may use chemical reactors to combine hydrogen brought from Earth with oxygen found in lunar soil to make their water. The pioneers sought temporary shelter under trees or in the lee of a cliff and built sod houses as their first homes on the new land; settlers of the Moon may seek out lava tubes for their shelter or cover space station modules with lunar regolith for radiation protection. The pioneers moved further west from their first settlements, using wagons they had built from local wood and pack animals they had raised; space explorers may use propellant made at a lunar base to take them on to Mars. The concept for this report was developed at a NASA-sponsored summer study in 1984. The program was held on the Scripps campus of the University of California at San Diego (UCSD), under the auspices of the American Society for Engineering Education (ASEE). It was jointly managed under the California Space Inst. and the NASA Johnson Space Center, under the direction of the Office of Aeronautics and Space Technology (OAST) at NASA Headquarters. The study participants (listed in the addendum) included a group of 18 university teachers and researchers (faculty fellows) who were present for the entire 10-week period and a larger group of attendees from universities, Government, and industry who came for a series of four 1-week workshops. The organization of this report follows that of the summer study. Space Resources consists of a brief overview and four detailed technical volumes: (1) Scenarios; (2) Energy, Power, and Transport; (3) Materials; (4) Social Concerns. Although many of the included papers got their impetus from workshop discussions, most have been written since then, thus allowing the authors to base new applications on established information and tested technology. All these papers have been updated to include the authors' current work. This overview, drafted by faculty fellow Jim Burke, describes the findings of the summer study, as participants explored the use of space resources in the development of future space activities and defined the necessary research and development that must precede the practical utilization of these resources. Space resources considered included lunar soil, oxygen derived from lunar soil, material retrieved from near-Earth asteroids, abundant sunlight, low gravity, and high vacuum. The study participants analyzed the direct use of these resources, the potential demand for products from them, the techniques for retrieving and processing space resources, the necessary infrastructure, and the economic tradeoffs. This is certainly not the first report to urge the utilization of space resources in the development of space activities. In fact, Space Resources may be seen as the third of a trilogy of NASA Special Publications reporting such ideas arising from similar studies. It has been preceded by Space Settlements: A Design Study (NASA SP-413) and Space Resources and Space Settlements (NASA SP-428). And other, contemporaneous reports have responded to the same themes. The National Commission on Space, led by Thomas Paine, in Pioneering the Space Frontier, and the NASA task force led by astronaut Sally Ride, in Leadership and America's Future in Space, also emphasize expansion of the space Infrastructure; more detailed exploration of the Moon, Mars, and asteroids; an early start on the development of the technology necessary for using space resources; and systematic development of the skills necessary for long-term human presence in space. Our report does not represent any Government-authorized view or official NASA policy. NASA's official response to these challenging op

McKay, Mary Fae (Editor); McKay, David S. (Editor); Duke, Michael S. (Editor)

1992-01-01

354

Space Weather Now  

NSDL National Science Digital Library

The Space Weather Now page is intended to give the non-technical user a "plain language" look at space weather. It includes information about relevant events and announcements, data from and about different instruments and satellites watching various aspects of space weather, alerts and advisories, daily themes of products and services, and links appropriate for the various groups of users.

Center, Space E.; Service, National O.

355

Group Assignment-1 Group A Group B Group C  

E-print Network

Group Assignment-1 Group A Group B Group C Shirkhodai, Arta ( artashir ) Kurozumi, Dean ( kurozumi ) Trang, Derrick ( trangd ) Yim, Gilbert ( gyim ) Marchant, Richard ( rmarchan) Young, Garrett ( garrettz

Zhang, Rui

356

Group Assignment-2 Group A Group B Group C  

E-print Network

Group Assignment-2 Group A Group B Group C Shirkhodai, Arta ( artashir ) Kurozumi, Dean ( kurozumi ( cobatake ) Shultz, Allen ( shultzam ) Yamakawa, Kelsie ( kayama ) Young, Garrett ( garrettz ) Walser, Ryan

Zhang, Rui

357

Lie Groups, Physics, and Geometry  

NASA Astrophysics Data System (ADS)

1. Introduction; 2. Lie groups; 2. Matrix groups; 4. Lie algebras; 5. Matrix algebras; 6. Operator algebras; 7. Exponentiation; 8. Structure theory for Lie algebras; 9. Structure theory for simple Lie algebras; 10. Root spaces and Dykin diagrams; 11. Real forms; 12. Riemannian symmetric spaces; 13. Contraction; 14. Hydrogenic atoms; 15. Maxwell's equations; 16. Lie groups and differential equations; References; Index.

Gilmore, Robert

2008-01-01

358

The Structural Biology Center 19ID undulator beamline: facility specifications and protein crystallographic results.  

PubMed

The 19ID undulator beamline of the Structure Biology Center has been designed and built to take full advantage of the high flux, brilliance and quality of X-ray beams delivered by the Advanced Photon Source. The beamline optics are capable of delivering monochromatic X-rays with photon energies from 3.5 to 20 keV (3.5-0.6 A wavelength) with fluxes up to 8-18 x 10(12) photons s(-1) (depending on photon energy) onto cryogenically cooled crystal samples. The size of the beam (full width at half-maximum) at the sample position can be varied from 2.2 mm x 1.0 mm (horizontal x vertical, unfocused) to 0.083 mm x 0.020 mm in its fully focused configuration. Specimen-to-detector distances of between 100 mm and 1500 mm can be used. The high flexibility, inherent in the design of the optics, coupled with a kappa-geometry goniometer and beamline control software allows optimal strategies to be adopted in protein crystallographic experiments, thus maximizing the chances of their success. A large-area mosaic 3 x 3 CCD detector allows high-quality diffraction data to be measured rapidly to the crystal diffraction limits. The beamline layout and the X-ray optical and endstation components are described in detail, and the results of representative crystallographic experiments are presented. PMID:16371706

Rosenbaum, Gerd; Alkire, Randy W; Evans, Gwyndaf; Rotella, Frank J; Lazarski, Krzystof; Zhang, Rong Guang; Ginell, Stephan L; Duke, Norma; Naday, Istvan; Lazarz, Jack; Molitsky, Michael J; Keefe, Lisa; Gonczy, John; Rock, Larry; Sanishvili, Ruslan; Walsh, Martin A; Westbrook, Edwin; Joachimiak, Andrzej

2006-01-01

359

Differential Stability of the Crystallographic Interfaces of Mu- and Kappa-Opioid Receptors  

PubMed Central

The recent mu-opioid receptor (MOPr) and kappa-opioid receptor (KOPr) crystal structures have inspired hypotheses of physiologically relevant dimerization contacts, specifically: a closely packed interface involving transmembrane (TM) helices TM5 and TM6, and a less compact interface, involving TM1, TM2, and helix 8 (H8). While the former was only found in MOPr crystals, similar arrangements of the latter were identified for both KOPr and MOPr. The relevance of these interfaces outside of a crystal lattice is called into question by the possibility that they might be influenced by the specific crystallization conditions. In this study, we have employed umbrella sampling molecular dynamics simulations of coarse-grained representations of the interacting MOPr or KOPr crystallographic structures, in the absence of the T4 lysozyme, and in an explicit lipid-water environment, to determine the strength of receptor dimerization at the different crystallographic interfaces. We note that the shape of the interface plays a dominant role in the strength of the interaction, and the pattern of contacting residues defines the shape of the potential of mean force. This information can be used to guide experiments aimed at exploring the role of dimerization in opioid receptor function. PMID:24651466

Johnston, Jennifer M.; Filizola, Marta

2014-01-01

360

The Structural Biology Center 19ID undulator beamline: facility specifications and protein crystallographic results  

PubMed Central

The 19ID undulator beamline of the Structure Biology Center has been designed and built to take full advantage of the high flux, brilliance and quality of X-ray beams delivered by the Advanced Photon Source. The beamline optics are capable of delivering monochromatic X-rays with photon energies from 3.5 to 20 keV (3.5–0.6 Å wavelength) with fluxes up to 8–18 × 1012 photons s?1 (depending on photon energy) onto cryogenically cooled crystal samples. The size of the beam (full width at half-maximum) at the sample position can be varied from 2.2 mm × 1.0 mm (horizontal × vertical, unfocused) to 0.083 mm × 0.020 mm in its fully focused configuration. Specimen-to-detector distances of between 100 mm and 1500 mm can be used. The high flexibility, inherent in the design of the optics, coupled with a ?-geometry goniometer and beamline control software allows optimal strategies to be adopted in protein crystallographic experiments, thus maximizing the chances of their success. A large-area mosaic 3 × 3 CCD detector allows high-quality diffraction data to be measured rapidly to the crystal diffraction limits. The beamline layout and the X-ray optical and endstation components are described in detail, and the results of representative crystallographic experiments are presented. PMID:16371706

Rosenbaum, Gerd; Alkire, Randy W.; Evans, Gwyndaf; Rotella, Frank J.; Lazarski, Krzystof; Zhang, Rong-Guang; Ginell, Stephan L.; Duke, Norma; Naday, Istvan; Lazarz, Jack; Molitsky, Michael J.; Keefe, Lisa; Gonczy, John; Rock, Larry; Sanishvili, Ruslan; Walsh, Martin A.; Westbrook, Edwin; Joachimiak, Andrzej

2008-01-01

361

Integration of first-principles methods and crystallographic database searches for new ferroelectrics: Strategies and explorations  

SciTech Connect

In this concept paper, the development of strategies for the integration of first-principles methods with crystallographic database mining for the discovery and design of novel ferroelectric materials is discussed, drawing on the results and experience derived from exploratory investigations on three different systems: (1) the double perovskite Sr(Sb{sub 1/2}Mn{sub 1/2})O{sub 3} as a candidate semiconducting ferroelectric; (2) polar derivatives of schafarzikite MSb{sub 2}O{sub 4}; and (3) ferroelectric semiconductors with formula M{sub 2}P{sub 2}(S,Se){sub 6}. A variety of avenues for further research and investigation are suggested, including automated structure type classification, low-symmetry improper ferroelectrics, and high-throughput first-principles searches for additional representatives of structural families with desirable functional properties. - Graphical abstract: Integration of first-principles methods with crystallographic database mining, for the discovery and design of novel ferroelectric materials, could potentially lead to new classes of multifunctional materials. Highlights: Black-Right-Pointing-Pointer Integration of first-principles methods and database mining. Black-Right-Pointing-Pointer Minor structural families with desirable functional properties. Black-Right-Pointing-Pointer Survey of polar entries in the Inorganic Crystal Structural Database.

Bennett, Joseph W. [Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States)] [Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States); Rabe, Karin M., E-mail: rabe@physics.rutgers.edu [Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States)

2012-11-15

362

Nucleation and growth of single crystals with uniform crystallographic orientation inside alumina nanopores  

NASA Astrophysics Data System (ADS)

Single crystal rods, having nanometer-size diameter, were grown with uniform crystallographic orientation inside a matrix of alumina nanopores. The fabrication process of this nanocomposite structure consists of several stages. First, a highly dense array of alumina pores (about 1011cm-2 and an average diameter of about 35nm) is prepared by an electrochemical anodization process of pure Al substrate. Then, the pores are filled with a liquid solution aided by the pores' capillary forces. Finally, the temperature of the liquid solution is slightly decreased to a supersaturated state where precipitation starts only at the pore bottom. The nucleation preference at the pore bottom is explained thermodynamically based on the contact angle, geometrical parameters of the nucleus, surface curvature, and pore diameter. In each pore the nucleus is grown to a single crystal that completely fills its volume. The crystallographic orientation of the single crystals inside the pores can be controlled by temperature and composition during growth. The nucleation and growth processes in the alumina nanopores are demonstrated with Rochelle salt (NaKC4H4O6•4H2O) and potassium nitrate (KNO3).

Yadlovker, D.; Berger, S.

2007-02-01

363

Human ornithine transcarbamylase: crystallographic insights into substrate recognition and conformational changes.  

PubMed Central

Two crystal structures of human ornithine transcarbamylase (OTCase) complexed with the substrate carbamoyl phosphate (CP) have been solved. One structure, whose crystals were prepared by substituting N-phosphonacetyl-L-ornithine (PALO) liganded crystals with CP, has been refined at 2.4 A (1 A=0.1 nm) resolution to a crystallographic R factor of 18.4%. The second structure, whose crystals were prepared by co-crystallization with CP, has been refined at 2.6 A resolution to a crystallographic R factor of 20.2%. These structures provide important new insights into substrate recognition and ligand-induced conformational changes. Comparison of these structures with the structures of OTCase complexed with the bisubstrate analogue PALO or CP and L-norvaline reveals that binding of the first substrate, CP, induces a global conformational change involving relative domain movement, whereas the binding of the second substrate brings the flexible SMG loop, which is equivalent to the 240s loop in aspartate transcarbamylase, into the active site. The model reveals structural features that define the substrate specificity of the enzyme and that regulate the order of binding and release of products. PMID:11237854

Shi, D; Morizono, H; Yu, X; Tong, L; Allewell, N M; Tuchman, M

2001-01-01

364

Influence of crystallographic orientation and anisotropy on Kapitza conductance via classical molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

We investigate the influence of crystallographic orientation and anisotropy on local phonon density of states, phonon transmissivity, and Kapitza conductance at interfaces between Lennard-Jones solids via classical molecular dynamics simulations. In agreement with prior works, we find that the Kapitza conductance at an interface between two face-centered cubic materials is independent of crystallographic orientation. On the other hand, at an interface between a face-centered cubic material and a tetragonal material, the Kapitza conductance is strongly dependent on the relative orientation of the tetragonal material, albeit this dependence is subject to the overlap in vibrational spectra of the cubic and tetragonal materials. Furthermore, we show that interactions between acoustic phonons in the cubic material and optical phonons in the tetragonal material can lead to the interface exhibiting greater "thermal anisotropy" as compared to that of the constituent materials. Finally, it is noted that the relative match or mismatch between the Debye temperatures of two materials comprising an interface does not serve an accurate gauge of the efficiency of interfacial thermal transport when those materials have different crystal structures.

Duda, J. C.; Kimmer, C. J.; Soffa, W. A.; Zhou, X. W.; Jones, R. E.; Hopkins, P. E.

2012-11-01

365

Purpose and Features of Web-Based Open-Access Crystallographic Databases  

NASA Astrophysics Data System (ADS)

Roughly 5,000 new crystal structures are added to the (approximately 104,000 entry) Inorganic Crystal Structure Database each year (see http://icsdweb.fiz-karlsruhe.de/index.php for an approximately 4,000 entry demonstration version). Other commercial crystallographic databases specialize in organics, metals and alloys, and ``non-organics'' including minerals. This presentation gives an overview over these databases and evaluates the potential of open-access databases such as the (approximately 68,000 entry) Crystallography Open Database (http://crystallography.net/) and Portland State University's (PSU's) Wiki Crystallography Database, Crystal Morphology Database, and Nano-Crystallography Database (http://nanocrystallography.research.pdx.edu/CIF-searchable). Key features of open-access crystallographic databases are: a universal data exchange format, unrestricted internet access to the actual data (including downloads), search capabilities, and crystal structure identification functionalities. Interactive three-dimensional structure or morphology visualizations are also available at PSU's site. Most recently, we implemented at PSU community-based, Wikipedia-inspired data upload and database content management provisions. A selection of all of these features will be demonstrated (online) during the presentation.

Sondergeld, Peter; Moeck, Peter; Dusek, Boris; Hanke, Hynek

2008-05-01

366

Crystallographic superstructure in R2PdSi3 (R = heavy rare earth) compounds  

SciTech Connect

The R2PdSi3 intermetallic compounds have been reported to crystallize in a hexagonal AlB2- derived structure, with the rare earth atoms on the Al sites and Pd and Si atoms randomly distributed on the B sites. However, the intricate magnetic properties observed in the series of compounds have always suggested complications to the assumed structure. To clarify the situation, x-ray and neutron diffraction measurements were performed on the heavy rare earth compounds with R = Gd, Tb, Dy, Ho, Er, Tm, which revealed the existence of a crystallographic superstructure. The superstructure features a doubled unit cell in the hexagonal basal plane and an octuplication along the perpendicular c direction with respect to the primitive cell. No structural transition was observed between 300 K and 1.5 K. Extended x-ray absorption fine structure (EXAFS) analysis as well as density functional theory (DFT) calculations were utilized to investigate the local environments of the respective atoms. In this article the various experimental results will be presented and it will be shown that the superstructure is mainly due to the Pd-Si order on the B sites. A structure model will be proposed to fully describe the superstructure of Pd-Si order in R2PdSi3. The connection between the crystallographic superstructure and the magnetic properties will be discussed in the framework of the presented model.

Tang, Fei [TU Dresden; Frontzek, Matthias D [ORNL; Dshemuchadse, Julia [ETH Zurich, Switzerland; Leisegang, Tilmann [Technische Universitat Dresden; Zschornak, Matthias [Technische Universitat Dresden; Mietrach, Robert [Technische Universitat Dresden; Hoffman, Jens-Uwe [Helmholtz-Zentrum Berlin; Loeser, W [IFW Dresden; Gemming, Sibylle [Forschungszentrum Rossendorf, Dresden, Germany; Meyer, Dirk [Technische Universitat Dresden; Loewenhaupt, Michael [TU Dresden

2011-01-01

367

Effect of tungsten crystallographic orientation on He-ion-induced surface morphology changes  

SciTech Connect

In order to study the early stages of nanofuzz growth in fusion-plasma-facing tungsten, mirror-polished high-purity tungsten was exposed to 80 eV helium at 1130 C to a fluence of 4 1024 He/m2. The previously smooth surface shows morphology changes, and grains form one of four qualitatively different morphologies: smooth, wavy, pyramidal, or terraced/wide waves. Combining high-resolution scanning electron microscopy (SEM) observations to determine the morphology of each grain with quantitative measurement of the grain's orientation via electron backscatter diffraction (EBSD) in SEM shows that the normal-direction crystallographic orientation of the underlying grain controls the growth morphology. Specifically, near-<001> || normal direction (ND) grains formed pyramids, near-<114> to <112> || ND grains formed wavy and stepped structures, and near-<103> || ND grains remained smooth. Comparisons to control specimens indicate no changes to underlying bulk crystallographic texture, and the effects are attributed to surface energy anisotropy, although, surprisingly, the expected {101} low-energy planes were not the most stable. Future developments to control tungsten texture via thermomechanical processing, ideally obtaining a sharp near- <103> || ND processing texture, may delay the formation of nanofuzz.

Parish, Chad M [ORNL; Hijazi, Hussein Dib [ORNL; Meyer III, Harry M [ORNL; Meyer, Fred W [ORNL

2014-01-01

368

A Three-Dimensional Cellular Automata Model for Dendrite Growth with Various Crystallographic Orientations During Solidification  

NASA Astrophysics Data System (ADS)

A three-dimensional (3-D) cellular automata (CA) model coupled with the finite-element (FE) method has been proposed to simulate dendrite growth with various crystallographic orientations during solidification. The model introduces a new tracking neighborhood method to resolve the mesh dependency caused by the cubic lattice in the CA model for simulating 3-D dendrite growth. The migration of the solid-liquid (SL) interface is associated with the dendritic preferential orientation and the driving force for the phase transition. The latter is obtained from a thermodynamics database. The local curvature and anisotropy of the surface energy are also incorporated to describe the growth kinetics of the SL interface. The solute transfer is calculated using the FE method. A numerical simulation has been performed on a Fe-1.5 wt pct C alloy. The grain morphologies with various crystallographic orientations and the solute distribution during isothermal solidification are studied and discussed. The simulation results are compared with analytical solutions and experimental results, which are in good agreement.

Zhao, Yan; Chen, Dengfu; Long, Mujun; Arif, Tansel T.; Qin, Rongshan

2014-04-01

369

Substituent effects in nitro derivatives of carbazoles investigated by comparison of low-temperature crystallographic studies with density functional theory (DFT) calculations.  

PubMed

The crystal structure of 9H-carbazole, C12H9N, (I), has been redetermined at low temperature for use as a reference structure in a comparative study with the structures of 1-nitro-9H-carbazole, C12H8N2O2, (II), and 9-nitrocarbazole, C12H8N2O2, (III). The molecule of (I) has crystallographically imposed mirror symmetry (Z' = 0.5). All three solid-state structures are slightly nonplanar, the dihedral angles between the planes of the arene and pyrrole rings ranging from 0.40?(7)° in (III) to 1.82?(18)° in (II). Nevertheless, a density functional theory (DFT) study predicts completely planar conformations for the isolated molecules. To estimate the influence of nitro-group substitution on aromaticity, the HOMA (harmonic oscillator model of aromaticity) descriptor of ?-electron delocalization has been calculated in each case. The HOMA indices for the isolated and solid-state molecules are relatively consistent and decrease in value for aromatic rings that are substituted with a ?-electron-withdrawing nitro group. Substitution of the arene ring influences the ?-electron delocalization in the ring only weakly, showing strong resistance to a perturbation of its geometry, contrary to what is observed for nitro substitution of the five-membered heterocyclic pyrrole ring. In (II), the molecules are arranged in near-planar dimers connected to each other by strong N-H...O hydrogen bonds that stack parallel to the crystallographic b axis. A similar stacking arrangement is observed in (III), although here the stacked structure is formed by stand-alone molecules. PMID:25279602

Gajda, Katarzyna; Zarychta, Bartosz; Kopka, Katarzyna; Daszkiewicz, Zdzis?aw; Ejsmont, Krzysztof

2014-10-15

370

Ice in Space  

NSDL National Science Digital Library

This is a detailed lesson about space and how Earth fits in it. Learners will consider the essential question, "What is space?" Activities include small group miming, speaking, drawing, and/or writing about space and the evidence for ice in space. Included are detailed games and dialogue. Native stories are shared. This is lesson 9 of 12 in the unit, Exploring Ice in the Solar System.

371

The Tensor Theory Space  

E-print Network

The tensor track is a background-independent discretization of quantum gravity which includes a sum over all topologies. We discuss how to define a functional renormalization group flow and the Wetterich equation in the corresponding theory space. This space is different from the Einsteinian theory space of asymptotic safety. It includes all fixed-rank tensor-invariant interactions, hence generalizes matrix models and the (Moyal) non-commutative field theory space.

Vincent Rivasseau

2014-07-01

372

Crystallization and preliminary X-ray crystallographic analysis of chorismate synthase from Mycobacterium tuberculosis.  

PubMed

The enzymes of the shikimate pathway are potential targets for the development of new therapies because they are essential for bacteria but absent from mammals. The last step in this pathway is performed by chorismate synthase (CS), which catalyzes the conversion of 5-enolpyruvylshikimate-3-phosphate to chorismate. Optimization of crystallization trials allowed the crystallization of homogeneous recombinant CS from Mycobacterium tuberculosis (MtCS). The crystals of MtCS belong to space group P6(4)22 (or P6(2)22) and diffract to 2.8 A resolution, with unit-cell parameters a = b = 129.7, c = 156.8 A. There are two molecules in the asymmetric unit. Molecular-replacement trials were not successful. Heavy-atom derivative screening is in progress. PMID:15502309

Dias, Marcio Viniciusbertacine; Ely, Fernanda; Canduri, Fernanda; Pereira, José Henrique; Frazzon, Jeverson; Basso, Luiz Augusto; Palma, Mário Sérgio; de Azevedo, Walter Filgueira; Santos, Diógenes Santiago

2004-11-01

373

Preliminary crystallographic studies of yeast mitochondrial peripheral membrane protein Tim44p  

PubMed Central

Protein translocations across mitochondrial membranes play critical roles in mitochondrion biogenesis. Protein transport from the cell cytosol to the mitochondrial matrix is carried out by the translocase of the outer membrane (TOM) complex and the translocase of the inner membrane (TIM) complexes. Tim44p is an essential mitochondrial peripheral membrane protein and a major component of the TIM23 translocon. To investigate the mechanism by which Tim44p functions in the TIM23 translocon to deliver the mitochondrial protein precursors, the yeast Tim44p was crystallized. The crystals diffract to 3.2?Å using a synchrotron X-ray source and belong to space group P6322, with unit-cell parameters a = 124.25, c = 77.83?Å. There is one Tim44p molecule in one asymmetric unit, which corresponds to a solvent content of approximately 43%. Structure determination by MAD methods is under way. PMID:16511294

Josyula, Ratnakar; Jin, Zhongmin; McCombs, Deborah; DeLucas, Lawrence; Sha, Bingdong

2006-01-01

374

Crystallization and preliminary crystallographic analysis of recombinant human P38 MAP kinase.  

PubMed Central

The recombinant human p38 MAP kinase has been expressed and purified from both Escherichia coli and SF9 cells, and has been crystallized in two forms by the hanging drop vapor diffusion method using PEG as precipitant. Both crystal forms belong to space group P2(1)2(1)2(1). The cell parameters for crystal form 1 are a = 65.2 A, b = 74.6 A and c = 78.1 A. Those for crystal form 2 are a = 58.3 A, b = 68.3 A and c = 87.9 A. Diffraction data to 2.0 A resolution have been collected on both forms. PMID:9007996

Pav, S.; White, D. M.; Rogers, S.; Crane, K. M.; Cywin, C. L.; Davidson, W.; Hopkins, J.; Brown, M. L.; Pargellis, C. A.; Tong, L.

1997-01-01

375

Overexpression, crystallization and preliminary X-ray crystallographic analysis of the phosphotriesterase from Mycobacterium tuberculosis.  

PubMed

Organophosphates (OPs) are extremely toxic compounds that are used as insecticides or even as chemical warfare agents. Phosphotriesterases (PHPs) are responsible for the detoxification of OPs by catalysing their degradation. Almost 100 PHP structures have been solved to date, yet the crystal structure of the phosphotriesterase from Mycobacterium tuberculosis (mPHP) remains unavailable. This study reports the first crystallization of mPHP. The crystal belonged to space group C222(1), with unit-cell parameters a = 68.03, b = 149.60, c = 74.23?Å, ? = ? = ? = 90°. An analytical ultracentrifugation experiment suggested that mPHP exists as a dimer in solution, even though one molecule is calculated to be present in the asymmetric unit according to the structural data. PMID:23295488

Zhang, Liang; Chen, Ruyi; Dong, Zhe; Li, Xin

2013-01-01

376

Crystallization and preliminary X-ray crystallographic analysis of phosphoribulokinase from Rhodobacter sphaeroides.  

PubMed Central

A recombinant form of Rhodobacter sphaeroides phosphoribulokinase (PRK), expressed in Escherichia coli and isolated by affinity chromatography, was crystallized by the sitting drop vapor diffusion technique using NH4H2PO4 (pH 5.6) as the precipitating agent. PRK crystallizes in the cubic space group P432, with unit cell parameters a = b = c = 129.55 A. Based on the assumption of one 32-kDa monomer per asymmetric unit, the Vm value is 2.83 A3/Da. The octameric molecular symmetry is consistent with two planar tetramers stacked in a nearly eclipsed arrangement. A native data set has been collected to 2.6 A resolution. PMID:8563645

Roberts, D. L.; Runquist, J. A.; Miziorko, H. M.; Kim, J. J.

1995-01-01

377

Crystallization and preliminary X-ray crystallographic analysis of acetohydroxy acid isomeroreductase from Pseudomonas aeruginosa.  

PubMed

Acetohydroxy acid isomeroreductase (AHIR) is involved in the biosynthetic pathway of branched-chain amino acids in microorganisms and plants. AHIR from Pseudomonas aeruginosa has been overexpressed in Escherichia coli and crystallized at 297 K using potassium/sodium tartrate as a precipitant. X-ray diffraction data have been collected to 2.0 A resolution at 100 K using synchrotron radiation. The crystals belong to the cubic space group P2(1)3, with unit-cell parameters a = b = c = 184.38 A, alpha = beta = gamma = 90 degrees. Six monomers are present in the asymmetric unit, giving a V(M) of 2.34 A(3) Da(-1) and a solvent content of 47.4%. PMID:12454481

Eom, Su Jeong; Ahn, Hyung Jun; Yoon, Hye Jin; Lee, Byung Il; Bae, Seung Hee; Baek, Seung Hun; Suh, Se Won

2002-12-01

378

Cloning, purification, crystallization and preliminary crystallographic analysis of acylphosphatase from Pyrococcus horikoshii OT3.  

PubMed

Acylphosphatase is one of the smallest enzymes and catalyzes the hydrolysis of the carboxy-phosphate bond. An extremely thermostable acylphosphatase from a hyperthermophilic archaea, Pyrococcus horikoshii OT3, has been cloned, expressed in Escherichia coli, purified and crystallized using the sitting-drop vapour-diffusion method with potassium/sodium tartrate as the precipitant at pH 5.5. X-ray diffraction data have been collected to a highest resolution of 1.72 angstroms on a synchrotron-radiation source. The crystals belong to space group P3(2)21, with approximate unit-cell parameters a = b = 86.6, c = 75.4 angstroms and two monomers in the asymmetric unit. PMID:15159579

Miyazono, Ken Ichi; Kudo, Norio; Tanokura, Masaru

2004-06-01

379

Crystallization and preliminary X-ray crystallographic analysis of PBPD2 from Listeria monocytogenes.  

PubMed

Penicillin-binding proteins (PBPs), which mediate the peptidoglycan biosynthetic pathway in the bacterial cell wall, have been intensively investigated as a target for the design of antibiotics. In this study, PBPD2, a low-molecular-weight PBP encoded by lmo2812 from Listeria monocytogenes, was overexpressed in Escherichia coli, purified and crystallized at 295?K using the sitting-drop vapour-diffusion method. The crystal belonged to the primitive orthorhombic space group P212121, with unit-cell parameters a = 37.7, b = 74.7, c = 75.1?Å, and diffracted to 1.55?Å resolution. There was one molecule in the asymmetric unit. The preliminary structure was determined by the molecular-replacement method. PMID:24699757

Cha, Hyung Jin; Jeong, Jae-Hee; Kim, Yeon-Gil

2014-04-01

380

Purification, crystallization and preliminary X-ray crystallographic studies of S. cerevisiae Hsp40 Sis1.  

PubMed

Heat-shock protein 70 (Hsp70), one of the major molecular chaperones, has been shown to play a central role in many cellular processes. Heat-shock protein 40 (Hsp40) works as a co-chaperone for Hsp70. Hsp40, bound by unfolded polypeptide, can interact directly with Hsp70 to stimulate the ATPase activity of Hsp70. Hsp40 can also bind to unfolded polypeptides and prevent them from aggregating in vitro, thus acting as an independent molecular chaperone. The S. cerevisiae Hsp40 Sis1 C-terminal peptide-binding domain has been crystallized. The crystals diffract to 2.7 A and belong to space group P41212 or P43212 with a = 73.63, c = 80.16 A. The structure determination by the MAD method is under way. PMID:10329795

Sha, B; Cyr, D

1999-06-01

381

Preliminary crystallographic studies of human mitochondrial NAD(P)(+)-dependent malic enzyme.  

PubMed

Human mitochondrial NAD(P)(+)-dependent malic enzyme was overexpressed in Escherichia coli and purified by anion-exchange, ATP affinity, and gel filtration chromatography. The protein was crystallized with the hanging-drop vapor diffusion method. Many different crystal forms were observed, five of which were characterized in some detail. A 2.5-A multiple-wavelength anomalous diffraction data set and a 2.1-A native data set were collected using synchrotron radiation on crystals containing selenomethionyl residues. These crystals belong to space group B2, with a = 204.4 A, b = 107.0 A, c = 59.2 A, and gamma = 101.9 degrees. Self-rotation functions demonstrated that the tetramer of this enzyme obeys 222 symmetry. PMID:10479619

Bhargava, G; Mui, S; Pav, S; Wu, H; Loeber, G; Tong, L

1999-08-01

382

Crystallization and initial crystallographic characterization of a vicilin-type seed storage protein from Pinus koraiensis.  

PubMed

The cupin superfamily of proteins includes the 7S and 11S seed storage proteins. Many members of this family of proteins are known allergens. In this study, the Korean pine (Pinus koraiensis) vicilin-type 7S seed storage protein was isolated from defatted pine-nut extract and purified by sequential gel-filtration and anion-exchange chromatography. Well diffracting single crystals were obtained by the vapor-diffusion method in hanging drops. The crystals belong to the primitive cubic space group P2(1)3, with unit-cell parameters a = b = c = 148.174 A. Two vicilin molecules were present in the asymmetric unit and the Matthews coefficient was determined to be 2.90 A(3) Da(-1), with a corresponding solvent content of approximately 58%. A molecular-replacement structural solution has been obtained using the program Phaser. Refinement of the structure is currently under way. PMID:18084088

Jin, Tengchuan; Fu, Tong Jen; Kothary, Mahendra H; Howard, Andrew; Zhang, Yu Zhu

2007-12-01

383

Purification, identification and preliminary crystallographic studies of Pru du amandin, an allergenic protein from Prunus dulcis.  

PubMed

Food allergies appear to be one of the foremost causes of hypersensitivity reactions. Nut allergies account for most food allergies and are often permanent. The 360 kDa hexameric protein Pru du amandin, a known allergen, was purified from almonds (Prunus dulcis) by ammonium sulfate fractionation and ion-exchange chromatography. The protein was identified by a BLAST homology search against the nonredundant sequence database. Pru du amandin belongs to the 11S legumin family of seed storage proteins characterized by the presence of a cupin motif. Crystals were obtained by the hanging-drop vapour-diffusion method. The crystals belong to space group P4(1) (or P4(3)), with unit-cell parameters a = b = 150.7, c = 164.9 A. PMID:18097098

Gaur, Vineet; Sethi, Dhruv K; Salunke, Dinakar M

2008-01-01

384

National Aeronautics and Space Administration International Space  

E-print Network

: Enabling Exploration · International Activities ­ Global Exploration Strategy (GES) ­ International Space Exploration Coordination Group (ISECG) · 14 Int'l Space Agencies ­ Developing the Global Exploration Roadmap-traditional ­ Strong NASA interest in enabling commercial opportunities that contribute to exploration program success

Waliser, Duane E.

385

Comparative X-Ray crystallographic studies of systemic fungicides hexaconazole and tricyclazole  

NASA Astrophysics Data System (ADS)

Chemical structure of a chemical is useful for the synthesis of new compounds with more specific actions and fewer adverse reactions, to increase/decrease the duration of action of the original drug or to get a more potent compound, to restrict the action to a specific system of the body and to reduce the adverse reactions, toxicity and other disadvantages associated. Recently it has been observed that some of the fungicides are loosing their effects. So analogous compounds can be designed as substitute, if their structures are known. A rational approach to test these fungicides is to know the three dimensional structure of these compounds and macromolecular receptor sites as well as their molecular complex. The structures of these compounds can be obtained by X-ray diffraction method in crystalline form and they will invariably be similar to their structure in solutions. The composition of crystal (RS)-2-(2,4-dichlorophenyl)-1-(1H-1, 2,4-trizole-1-y1) hexane-2-ol or hexaconazole and Tricyclazole are confirmed by comparing the infra-red spectra of two components. The unit cell parameters of Hexaconozole are a=10. 9068(7) Å, b=10.9895(7) Å c=13.6124(8) Å, ?=90o, ?=106.554(2)o, ?=90.000(5)o. The Crystal system is Monoclinic, and space group P21/c . The unit cell parameters of Tricyclazole are a=14.896(5) Å, b=7.410(5)Å, c=7.556(5) Å, ?=90(5)o, ?=90.000(5)o, ?=90.000(5)o.The Crystal system is Orthorhombic and space group is Pca21.

Chauhan, Jyotsna; Sharma, Ashish Kumar; Bhattacharya, Gargi

2012-05-01

386

Effect of crystallographic orientation on hillock formation in thermally cycled large grain tin films  

NASA Astrophysics Data System (ADS)

Tin whiskers and hillocks grow spontaneously from the surfaces of polycrystalline Sn films at room temperature. Whiskers can grow long enough to cause short circuits in electronic devices. We hypothesized that the anisotropies of the crystal structure lead to locally high strain energies that are relieved by the growth of whiskers and hillocks. This research studies hillock formations on large grain Sn-alloy films relative to the crystallographic orientations of the adjacent grains. Large grain films were produced by solidifying 96.5wt% Sn - 3wt% Ag - 0.5wt% Cu solder alloy on a Cu substrate. These surface defects (hillocks) grew predominately at grain boundaries during thermal cycling. The formation of the surface defects between two grains created a pseudo-bi-crystal sample geometry, making it ideal for studying surface defects relative to the local crystallographic orientations and the grains' corresponding anisotropic properties. The crystallographic orientations of the grains were studied with Electron Backscatter Diffraction (EBSD) and Laue micro-diffraction at the Lawrence Berkeley National Laboratory Advanced Light Source. Local orientation studies of the surface defects and the surrounding grains indicated that the surface defects nucleated and grew with low dislocation densities. In addition, the linear surface defect densities along the grain boundaries were measured and observed to change as a function of orientation. The change in linear defect density with respect to orientation was due, in part, to the anisotropy of the coefficient of thermal expansion of ?-Sn. In addition, it was important to account for elastic anisotropies. The elastic stresses, strains, and strain energy densities of the microstructures were determined with Object Oriented Finite element analysis. The simulations indicated that during thermal cycling the local stresses exceeded the yield strength. As a result, the highest linear defect densities did not occur at orientations with the highest local strain energies. Instead, the highest local strain energies were accommodated by other plastic deformation mechanisms, indicating that surface defect formation is not only affected by local strain energy densities but also the local dominant deformation mechanism. Therefore, the propensity of specific grain orientations to form surface defects will change as a function of the thermal cycling process.

Koppes, John Patrick

387

Chapter: Reflection groups  

Microsoft Academic Search

This chapter is concerned with the theory of finite reflection groups, that is, finite groups generated by reflections in a real or complex vector space. This is a rich theory, both for intrinsic reasons and as far as applications in other mathematical areas or mathematical physics are concerned. The origin of the theory can be traced back to the ancient

MEINOLF GECK; GUNTER MALLE

388

Crystallization and preliminary X-ray crystallographic analysis of the amylomaltase from Corynebacterium glutamicum.  

PubMed

Amylomaltase (AM; EC 2.4.1.25) belongs to the 4-?-glucanotransferase group of the ?-amylase family. The enzyme can produce cycloamylose or large-ring cyclodextrin through intramolecular transglycosylation or cyclization reactions of ?-1,4-glucan. Amylomaltase from the mesophilic bacterium Corynebacterium glutamicum (CgAM) contains extra residues at the N-terminus for which the three-dimensional structure is not yet known. In this study, CgAM was overexpressed and purified to homogeneity using DEAE FF and Phenyl FF columns. The purified CgAM was crystallized by the vapour-diffusion method. Preliminary X-ray data showed that the CgAM crystal diffracted to 1.7?Å resolution and belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 73.28, b = 82.61, c = 118.64?Å. To obtain the initial phases, crystals of selenomethionyl-substituted amylomaltase were produced, and multiple-wavelength anomalous dispersion phasing and structure refinement are now in progress. PMID:23989149

Srisimarat, Wiraya; Murakami, Shuichiro; Pongsawasdi, Piamsook; Krusong, Kuakarun

2013-09-01

389

Causality Implies the Lorentz Group  

Microsoft Academic Search

Causality is represented by a partial ordering on Minkowski space, and the group of all automorphisms that preserve this partial ordering is shown to be generated by the inhomogeneous Lorentz group and dilatations.

E. C. Zeeman

1964-01-01

390

Communication spaces  

PubMed Central

Background and objective Annotations to physical workspaces such as signs and notes are ubiquitous. When densely annotated, work areas become communication spaces. This study aims to characterize the types and purpose of such annotations. Methods A qualitative observational study was undertaken in two wards and the radiology department of a 440-bed metropolitan teaching hospital. Images were purposefully sampled; 39 were analyzed after excluding inferior images. Results Annotation functions included signaling identity, location, capability, status, availability, and operation. They encoded data, rules or procedural descriptions. Most aggregated into groups that either created a workflow by referencing each other, supported a common workflow without reference to each other, or were heterogeneous, referring to many workflows. Higher-level assemblies of such groupings were also observed. Discussion Annotations make visible the gap between work done and the capability of a space to support work. Annotations are repairs of an environment, improving fitness for purpose, fixing inadequacy in design, or meeting emergent needs. Annotations thus record the missing information needed to undertake tasks, typically added post-implemented. Measuring annotation levels post-implementation could help assess the fit of technology to task. Physical and digital spaces could meet broader user needs by formally supporting user customization, ‘programming through annotation’. Augmented reality systems could also directly support annotation, addressing existing information gaps, and enhancing work with context sensitive annotation. Conclusions Communication spaces offer a model of how work unfolds. Annotations make visible local adaptation that makes technology fit for purpose post-implementation and suggest an important role for annotatable information systems and digital augmentation of the physical environment. PMID:24005797

Coiera, Enrico

2014-01-01

391

Morphological and Crystallographic Properties of Rare Earth Oxides Coatings Deposited by Double Dual Beam-Pld  

NASA Astrophysics Data System (ADS)

Various rare earth oxide nanostructures were synthesized for the first time by dual-double pulsed gas feeding/pulsed laser deposition. The optically transparent and insulating nanostructures do not exhibit the standard columnar configuration of rare earth oxide thin films but rather dense structures and a significant chemical stoichiometry. More precisely, they exhibit single crystallographic low temperature phases with preferential textures, generally similar to that of the bulk used powder targets. For the cubic fluorine type CeO2 and Ho2O3 films, an epitaxial growth is observed with a special feature noticed in the case of the Eu2O3 nanostructure. For this latter, localized and very large oriented crystallites embedded in disordered packed pyramidal crystallites are observed.

Khamlich, S.; Ngom, B. D.; Kotsedi, C. K.; Bouziane, K.; Manikandan, E.; Maaza, M.

2014-11-01

392

Crystallographic and spectroscopic studies of 5-arylidene-2-amino-imidazol-4-ones  

NASA Astrophysics Data System (ADS)

The series of 5-arylidene-2-anilino/benzylamino/isoniazid-imidazol-4-ones was studied. The X-ray structure analysis, performed for four representatives, confirmed Z configuration of an exocyclic double bond for all structures and showed that the hydrogen bond pattern in studied structures strongly depends on tautomeric form of 2-amino-imodazolone moiety as well as on properties of solvent molecules in the crystals. Stacking details and various motifs of multiple hydrogen bonded network, formed in the crystals by all possible tautomers, were discussed. Crystallographic investigations of selected objects have been supported by 1H and 13C NMR data, obtained for the extended set of 5-arylidene-2-amino-imidazol-4-ones. Comparison of all data allowed to analyze the tautomeric equilibrium of the investigated compounds, both in solution and in a solid state.

Karolak-Wojciechowska, Janina; Szyma?ska, Ewa; Mrozek, Agnieszka; Kie?-Kononowicz, Katarzyna

2009-07-01

393

The effect of the cracking plane crystallographic orientation on the stress corrosion cracking process  

NASA Astrophysics Data System (ADS)

We have chosen from the literature a model which describes the SCC evolution considering three stages of the crack propagation: intergranular, transgranular and ductile rupture. We have verified the applicability of this model to describe the SCC failure of the CANDU type nuclear fuel and adapted it by considering the particular mechanical properties of the cladding, the actual value of the area of interest for SCC and by calculating the local concentration using the values of the iodine activities in the gap as predicted by an adequate fuel element computer code. We improved this overall model expressing the transgranular cracking threshold stress in terms of surface energy, crystallographic orientation of the fracture plane and of the fractional coverage with ZrI 4. The results of the calculations performed using this improved model confirmed the applicability of the model to describe the SCC failure of the CANDU type nuclear fuel.

Ciocan, Eugenia; Ignat, Margareta; Gheorghiu, Elena

1998-05-01

394

Reintroducing Electrostatics into Macromolecular Crystallographic Refinement: Application to Neutron Crystallography and DNA Hydration  

PubMed Central

Summary Most current crystallographic structure refinements augment the diffraction data with a priori information consisting of bond, angle, dihedral, planarity restraints and atomic repulsion based on the Pauli exclusion principle. Yet, electrostatics and van der Waals attraction are physical forces that provide additional a priori information. Here we assess the inclusion of electrostatics for the force field used for all-atom (including hydrogen) joint neutron/X-ray refinement. Two DNA and a protein crystal structure were refined against joint neutron/X-ray diffraction data sets using force fields without electrostatics or with electrostatics. Hydrogen bond orientation/geometry favors the inclusion of electrostatics. Refinement of Z-DNA with electrostatics leads to a hypothesis for the entropic stabilization of Z-DNA that may partly explain the thermodynamics of converting the B form of DNA to its Z form. Thus, inclusion of electrostatics assists joint neutron/X-ray refinements, especially for placing and orienting hydrogen atoms. PMID:21481775

Fenn, Timothy D.; Schnieders, Michael J.; Mustyakimov, Marat; Wu, Chuanjie; Langan, Paul; Pande, Vijay S.; Brunger, Axel T.

2011-01-01

395

Crystallographic Orientation of the ? ? ?' Martensitic (Athermal) Transformation in a FeMnAlSi Steel  

NASA Astrophysics Data System (ADS)

The presence of athermal ?- and ?-martensite ( ?') in the as-cast structure of a Fe-0.08C-1.95Si-15.1Mn-1.4Al-0.017N alloy has been revealed by electron backscattered diffraction analysis. The alloy exhibited two athermal martensitic transformations described by ? ? ?' and ? ? ? ? ?'. The Shoji-Nishiyama orientation relationship was observed between ?-austenite and ?-martensite, while ?-martensite nucleated from ?-austenite exhibited a Kurdjumov-Sachs orientation relationship. Six crystallographic variants of ?-martensite consisting of three twin-related variant pairs were observed in ?-bands. A planar parallelism of {0001} ? || {110} ?' and a directional relation of lying within 1 deg of existed for these variants.

Pisarik, S. T.; Van Aken, D. C.

2014-07-01

396

Crystallographic analysis of the amorphization caused by ion irradiation: Self-irradiation  

NASA Astrophysics Data System (ADS)

We have examined a mechanism of Si amorphization, by a classical molecular-dynamics, paying attention to whether or not the self-interstitial atom (SIA) clusters were a precursor to amorphization, when a crystalline Si was self-irradiated by several keV ions at a low temperature of 100 K. The pixel mapping (PM) analyzed crystallographically a crystalline to amorphous (CA) transition caused by ion irradiation by means of a set of long-range-order parameters. The spatial distribution of SIAs were also counted by PM. Throughout the sequential self-irradiation, the fraction of isolated SIAs was dominant. Although the fractions were small, we found the significant increase of small SIA clusters, e.g. I2-I4, as the crystalline state was being collapsed. We conclude that those small SIA clusters can be the trigger to enhance the production of more SIAs, and results in CA transition.

Nakagawa, S. T.

2003-05-01

397

Crystallographic considerations of the delta in equilibrium. cap alpha. displacive transformation in plutonium alloys  

SciTech Connect

Determination of invariant-plane strain crystallographic solutions for martensitic transformation between the FCC delta and monoclinic ..cap alpha.. phases in plutonium alloys, using three possible lattice correspondences and 53 possible lattice-invariant shear systems, identifies the most probable delta-..cap alpha.. lattice correspondence. The operative lattice-invariant shear systems are predicted by comparison of both shape strain magnitudes and computed interfacial energies. For delta ..-->.. ..cap alpha.. transformation twinning on (001) (100)/sub ..cap alpha../ is favored, giving a (.817, .538, .208)/sub delta/ habit and a (.947, .269, .174)/sub delta/ shape strain of magnitude m/sub 1/ = .324. The ..cap alpha.. ..-->.. delta transformation favors slip on (111) (101)/sub delta/, giving a (.255, .844, .471)/sub ..cap alpha../ habit and (.822, .466, .355)/sub ..cap alpha../ shape strain of magnitude m/sub 1/ = .417.

Adler, P.H.; Olson, G.B.

1986-06-10

398

Shock-induced breaking of the nanowire with the dependence of crystallographic orientation and strain rate  

PubMed Central

The failure of the metallic nanowire has raised concerns due to its applied reliability in nanoelectromechanical system. In this article, the breaking failure is studied for the [100], [110], and [111] single-crystal copper nanowires at different strain rates. The statistical breaking position distributions of the nanowires have been investigated to give the effects of strain rate and crystallographic orientation on micro-atomic fluctuation in the symmetric stretching of the nanowires. When the strain rate is less than 0.26% ps-1, macro-breaking position distributions exhibit the anisotropy of micro-atomic fluctuation. However, when the strain rate is larger than 3.54% ps-1, the anisotropy is not obvious because of strong symmetric shocks. PMID:21711854

2011-01-01

399

Crystallographic dependence of loss in domain engineered relaxor-PT single crystals  

PubMed Central

Domain engineered ?001? oriented relaxor-PbTiO3 ferroelectric crystals exhibit high electromechanical properties and low mechanical Q values, analogous to “soft” piezoelectric ceramics. However, their characteristic low dielectric loss (?0.5%) and strain-electric field hysteresis are reflective of “hard” piezoelectric materials. In this work, the electromechanical behavior of relaxor-PT crystals was investigated as a function of crystallographic orientations. It was found that the electrical and mechanical losses in crystals depends on the specific engineered domain configuration, with high Q observed for the ?110? orientation. The high Q, together with high electromechanical coupling (?0.9) for ?110? oriented relaxor-PT crystals, make them promising candidates for resonant based high power transducer applications. PMID:19654880

Zhang, Shujun; Sherlock, Nevin P.; Meyer, Richard J.; Shrout, Thomas R.

2009-01-01

400

Magnetoresistance in granular CrO2: Effects of variation in crystallographic and magnetic microstructure  

NASA Astrophysics Data System (ADS)

We report magnetotransport measurements up to 5 Tesla on high purity sintered samples of granular CrO2 with a significantly enhanced grain size. The negative magnetoresistance (MR) as derived from RH isotherms is observed to be unhysteretic up to temperatures as high as 200 K. RH isotherms exhibit some unusual features between 240 and 290 K, including a positive MR and strong pinning effects. These features disappear above 290 K and are apparently related with the magnetic state of the insulating grain boundary. Qualitatively similar features with significantly enhanced MR are also observed when CrO2 is diluted with two antiferromagnetic oxides, Cr2O3 or Cr2O5. These results bring out the role played by the magnetic and crystallographic microstructure on the magnitude, sign, and hysteresis of the magnetoresistance in this technologically important material.

Bajpai, A.; Nigam, A. K.

2007-05-01

401

Using a conformation-dependent stereochemical library improves crystallographic refinement of proteins  

SciTech Connect

The major macromolecular crystallographic refinement packages restrain models to ideal geometry targets defined as single values that are independent of molecular conformation. However, ultrahigh-resolution X-ray models of proteins are not consistent with this concept of ideality and have been used to develop a library of ideal main-chain bond lengths and angles that are parameterized by the {phi}/{psi} angle of the residue [Berkholz et al. (2009), Structure, 17, 1316-1325]. Here, it is first shown that the new conformation-dependent library does not suffer from poor agreement with ultrahigh-resolution structures, whereas current libraries have this problem. Using the TNT refinement package, it is then shown that protein structure refinement using this conformation-dependent library results in models that have much better agreement with library values of bond angles with little change in the R values. These tests support the value of revising refinement software to account for this new paradigm.

Tronrud, Dale E.; Berkholz, Donald S.; Karplus, P. Andrew (Oregon State U.)

2010-07-02

402

Conformational analysis of environmental agents: use of X-ray crystallographic data to determine molecular reactivity.  

PubMed Central

This paper explores the use of crystallographic techniques as an aid in understanding the molecular reactivities of a number of agents that are of concern to pharmacologists and toxicologists. The selected examples demonstrate the role of structural data in the determination of absolute configuration, configurational flexibility and active-site topology for a reactive species. For example, the role of absolute stereochemistry in understanding synthetic pyrethroid structure-activity relationships is shown from analysis of their crystal structures; conformational flexibility among DDT analogues, and the importance of conformational and electronic properties in phenylalkanoic acid herbicides are shown from systematic analysis of their crystal structures; and interpretation of active-site stereochemistry is made by study of computer modeling of enzyme inhibitors in the active sites of related protein crystal structures. Thus, the observed patterns in conformational flexibility and their resultant effects on substrate pharmacological profile can be interpreted in understanding the molecular level events that influence biological reactivity. PMID:3905372

Cody, V

1985-01-01

403

Nanoscale crystal imperfection-induced characterization changes of manganite nanolayers with various crystallographic textures  

PubMed Central

(La,Sr)MnO3 (LSMO) nanolayers with various crystallographic textures were grown on the sapphire substrate with and without In2O3 epitaxial buffering. The LSMO nanolayer with In2O3 epitaxial buffering has a (110) preferred orientation. However, the nanolayer without buffering shows a highly (100)-oriented texture. Detailed microstructure analyses show that the LSMO nanolayer with In2O3 epitaxial buffering has a high degree of nanoscale disordered regions (such as subgrain boundaries and incoherent heterointerfaces) in the film. These structural inhomogeneities caused a low degree of ferromagnetic ordering in LSMO with In2O3 epitaxial buffering, which leads to a lower saturation magnetization value and Curie temperature, and higher coercivity and resistivity. PMID:23919442

2013-01-01

404

Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (?) Silicon Carbide  

SciTech Connect

Along with other desirable properties, the ability of silicon carbide (SiC) to retain high strength after elevated temperature exposures to neutron irradiation renders it potentially applicable in fusion and advanced fission reactors. However, properties of the material such as room temperature fracture toughness must be thoroughly characterized prior to such practical applications. The objective of this work is to investigate the dependence of fracture toughness on crystallographic orientation for single-crystalline ?-SiC. X-ray diffraction was first performed on the samples to determine the orientation of the crystal. Nanoindentation was used to determine a hardness of 39.1 and 35.2 GPa and elastic modulus of 474 and 446 GPa for the single-crystalline and polycrystalline samples, respectively. Additionally, crack lengths and indentation diagonals were measured via a Vickers micro-hardness indenter under a load of 100 gf for different crystallographic orientations with indentation diagonals aligned along fundamental cleavage planes. Upon examination of propagation direction of cracks, the cracks usually did not initiate and propagate from the corners of the indentation where the stresses are concentrated but instead from the indentation sides. Such cracks clearly moved along the {1 1 0} family of planes (previously determined to be preferred cleavage plane), demonstrating that the fracture toughness of SiC is comparatively so much lower along this set of planes that the lower energy required to cleave along this plane overpowers the stress-concentration at indentation corners. Additionally, fracture toughness in the <1 1 0> direction was 1.84 MPa·m1/2, lower than the 3.46 MPa·m1/2 measured for polycrystalline SiC (which can serve as an average of a spectrum of orientations), further demonstrating that single-crystalline ?-SiC has a strong fracture toughness anisotropy.

Pharr, M.; Katoh, Y.; Bei, H.

2006-01-01

405

A reciprocal space approach for locating symmetry elements in Patterson superposition maps  

SciTech Connect

A method for determining the location and possible existence of symmetry elements in Patterson superposition maps has been developed. A comparison of the original superposition map and a superposition map operated on by the symmetry element gives possible translations to the location of the symmetry element. A reciprocal space approach using structure factor-like quantities obtained from the Fourier transform of the superposition function is then used to determine the best'' location of the symmetry element. Constraints based upon the space group requirements are also used as a check on the locations. The locations of the symmetry elements are used to modify the Fourier transform coefficients of the superposition function to give an approximation of the structure factors, which are then refined using the EG relation. The analysis of several compounds using this method is presented. Reciprocal space techniques for locating multiple images in the superposition function are also presented, along with methods to remove the effect of multiple images in the Fourier transform coefficients of the superposition map. In addition, crystallographic studies of the extended chain structure of (NHC{sub 5}H{sub 5})SbI{sub 4} and of the twinning method of the orthorhombic form of the high-{Tc} superconductor YBa{sub 2}Cu{sub 3}O{sub 7-x} are presented. 54 refs.

Hendrixson, T.

1990-09-21

406

Space Station Human Factors Research Review. Volume 3: Space Station Habitability and Function: Architectural Research  

NASA Technical Reports Server (NTRS)

Articles are presented on a space station architectural elements model study, space station group activities habitability module study, full-scale architectural simulation techniques for space stations, and social factors in space station interiors.

Cohen, Marc M. (editor); Eichold, Alice (editor); Heers, Susan (editor)

1987-01-01

407

Asymmetric cold/warm rolling simulation by crystal plasticity multi-scale finite element analysis based on crystallographic homogenization  

SciTech Connect

The purpose of this study is forming a high formability aluminum alloy sheet metal by controlling the microcrystal structure and the texture. So asymmetric rolling is applied to the material process. Analysis method is crystal plasticity multi-scale finite element analysis based on crystallographic homogenization.

Onishi, Koshiro; Sakamoto, Hidetoshi [Kumamoto University, 2-39-1 Kurokami, 860-8555 Kumamoto (Japan); Kuramae, Hiroyuki [Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, 535-8585 Osaka (Japan); Morimoto, Hideo [The Furukawa Electric Co. Ltd., 2-4-3 Okano, Nishi-ku, 220-0073 Yokohama (Japan); Nakamachi, Eiji [Doshisha University, 1-3 Tatara-Miyakodani, Kyotanabe, 610-0394 Kyoto (Japan)

2010-06-15

408

New Crystallographic Shear Families Derived from the Rutile Structure, and the Possibility of Continuous Ordered Solid Solution.  

National Technical Information Service (NTIS)

A number of new families of titanium and mixed titanium plus chromium oxides has been discovered, their structures all being derived from the rutile type by crystallographic shear. Different families have different CS plans (hkl), and the members of a fam...

B. G. Hyde, D. K. Philp, L. A. Bursill

1970-01-01

409

Overview of International Space Standards  

NASA Technical Reports Server (NTRS)

This presentation reviews space standards as put forth by the International Organization for Standardization, additionally the organizational structure for both the international and US groups are presented. A new technical committee for space is proposed, areas of technical coverage are highlighted and models of space communications protocol and space link access service are presented.

Hooke, Adrian J.

2005-01-01

410

Space Station habitability research  

NASA Technical Reports Server (NTRS)

The purpose and scope of the Habitability Research Group within the Space Human Factors Office at the NASA/Ames Research Cente is described. Both near-term and long-term research objectives in the space human factors program pertaining to the U.S. manned Space Station are introduced. The concept of habitability and its relevancy to the U.S. space program is defined within a historical context. The relationship of habitability research to the optimization of environmental and operational determinants of productivity is discussed. Ongoing habitability research efforts pertaining to living and working on the Space Station are described.

Clearwater, Y. A.

1986-01-01

411

Space Station Habitability Research  

NASA Technical Reports Server (NTRS)

The purpose and scope of the Habitability Research Group within the Space Human Factors Office at the NASA/Ames Research Center is described. Both near-term and long-term research objectives in the space human factors program pertaining to the U.S. manned Space Station are introduced. The concept of habitability and its relevancy to the U.S. space program is defined within a historical context. The relationship of habitability research to the optimization of environmental and operational determinants of productivity is discussed. Ongoing habitability research efforts pertaining to living and working on the Space Station are described.

Clearwater, Yvonne A.

1988-01-01

412

Nanowire-templated lateral epitaxial growth of non-polar group III nitrides  

DOEpatents

A method for growing high quality, nonpolar Group III nitrides using lateral growth from Group III nitride nanowires. The method of nanowire-templated lateral epitaxial growth (NTLEG) employs crystallographically aligned, substantially vertical Group III nitride nanowire arrays grown by metal-catalyzed metal-organic chemical vapor deposition (MOCVD) as templates for the lateral growth and coalescence of virtually crack-free Group III nitride films. This method requires no patterning or separate nitride growth step.

Wang, George T. (Albuquerque, NM); Li, Qiming (Albuquerque, NM); Creighton, J. Randall (Albuquerque, NM)

2010-03-02

413

Expression, purification and preliminary crystallographic analysis of human thyroid hormone responsive protein  

PubMed Central

Thyroid hormone responsive protein (Thrsp, also known as Spot 14 and S14) is a carbohydrate-inducible and thyroid-hormone-inducible nuclear protein specific to liver, adipose and lactating mammary tissues. Thrsp functions to activate genes encoding fatty-acid synthesis enzymes. Recent studies have shown that in some cancers human Thrsp (hS14) localizes to the nucleus and is amplified, suggesting that it plays a role in the regulation of lipogenic enzymes during tumourigenesis. Thrsp, a member of the Spot 14 superfamily, is an acidic homodimeric protein with no sequence similarity to other mammalian gene products and its biochemical function is elusive. To shed light on the structure–function relationship of this protein, human Thrsp was crystallized. Recombinant human Thrsp (hThrsp), the N-terminally truncated human Thrsp10–146 (hThrsp9) and their selenomethionyl (SeMet) derivatives were expressed in Escherichia coli, purified and crystallized using the hanging-drop vapour-diffusion method. Diffraction-quality crystals were grown at 293?K using Li2SO4 as a precipitant. Using synchrotron radiation, data for the hThrsp SeMet derivative, hThrsp9 and its SeMet derivative were collected to 4.0, 3.0 and 3.6?Å resolution, respectively, at 100?K. The crystals of full-length hThrsp and its SeMet derivative belonged to space group P41212, with approximate unit-cell parameters a = b = 123.9, c = 242.1?Å, ? = ? = ? = 90.0°. In contrast, the crystals of the truncated hThrsp9 and its SeMet derivative belonged to space group P212121, with approximate unit-cell parameters a = 91.6, b = 100.8, c = 193.7?Å, ? = ? = ? = 90.0°. A molecular-replacement solution calculated using a murine Spot 14 structure as a search model indicated the presence of six molecules per asymmetric unit, comprising three hThrsp homodimers. PMID:21821901

Zhang, Wenzheng; Peng, Wei; Zhao, Mingzhuo; Lin, Dejun; Zeng, Zonghao; Zhou, Weihong; Bartlam, Mark

2011-01-01

414

ON ALMOST REPRESENTATIONS OF GROUPS  

Microsoft Academic Search

We say that a group G belongs to the class K if every nonunit quotient group of G has an element of order two. Let H be a Hilbert space and let U(H) be its group of unitary operators. Suppose that groups A and B belong to the class K and the order of B is more than two. Then

415

DYNAMICS OF PLANETCROSSING ASTEROIDS Space Mechanics Group,  

E-print Network

in a main belt between the orbits of Mars and Jupiter (Fig­ ure 1). A significant number of objects is also with up to date orbits L4 Trojans L5 Trojans Hildas Jupiter Mars Figure 1. The asteroid complex projected the orbits of Jupiter (whose current position is the cross at the left) and the orbit of Mars (the line near

Milani, Andrea

416

Space Elevator: Path to Space  

NASA Astrophysics Data System (ADS)

The Space Elevator is the most promising Space Transportation system on the drawing boards today, combining scalability, qualify of ride, and safety to deliver truly commercial-grade space access-practically comparable to a train ride to space.

Kaushal, A. K.

2012-05-01

417

Groups32  

NSDL National Science Digital Library

A group theory calculator. Groups32 computes information about groups of orders 1-32; has a permutation group package; and provides a search for groups with given generators and relations. Site includes documentation as well as course handouts in PDF format.

2007-11-08

418

Expression, purification, crystallization and preliminary X-ray crystallographic studies of Mycobacterium tuberculosis thioredoxin reductase.  

PubMed

Mycobacterium tuberculosis (H37Rv), the causative agent of the dreaded disease tuberculosis, contains three thioredoxins and a single thioredoxin reductase. Thioredoxin reductase is a member of the pyridine-nucleotide disulfide oxidoreductase family of flavoenzymes. The thioredoxin reductase gene with a His tag at the C-terminus was expressed in Escherichia coli and purified. The dimeric (70 kDa) protein was incubated with 10 mM DTT for 30 min and then crystallized using the hanging-drop vapour-diffusion method in the presence of 15% PEG 3350 and phosphate-citrate buffer pH 5 at room temperature (298 K). A diffraction data set complete to 3 A resolution has been collected under cryoconditions and the space group was determined to be P4(1)2(1)2, with unit-cell parameters a = 107.4, c = 118.2 A. Matthews coefficient calculations revealed the presence of two monomers in the asymmetric unit. PMID:15039584

Akif, Mohd; Chauhan, Radha; Mande, Shekhar C

2004-04-01

419

Crystallization and preliminary crystallographic analysis of poly(3-hydroxybutyrate) depolymerase from Bacillus thuringiensis.  

PubMed

Poly[(R)-3-hydroxybutyrate] (PHB) is a microbial biopolymer that has been commercialized as biodegradable plastics. The key enzyme for the degradation is PHB depolymerase (PhaZ). A new intracellular PhaZ from Bacillus thuringiensis (BtPhaZ) has been screened for potential applications in polymer biodegradation. Recombinant BtPhaZ was crystallized using 25% polyethylene glycol 3350, 0.2?M ammonium acetate, 0.1?M bis-tris pH 6.5 at 288?K. The crystals belonged to space group P1, with unit-cell parameters a = 42.97, b = 83.23, c = 85.50?Å, ? = 73.45, ? = 82.83, ? = 83.49°. An X-ray diffraction data set was collected to 1.42?Å resolution with an Rmerge of 6.4%. Unexpectedly, a molecular-replacement solution was obtained using the crystal structure of Streptomyces lividans chloroperoxidase as a template, which shares 24% sequence identity to BtPhaZ. This is the first crystal structure of an intracellular poly(3-hydroxybutyrate) depolymerase. PMID:25286954

Wang, Yung Lin; Lin, Yi Ting; Chen, Chia Lin; Shaw, Gwo Chyuan; Liaw, Shwu Huey

2014-10-01

420

Crystallization and preliminary X-ray crystallographic analysis of a blue-light-absorbing proteorhodopsin.  

PubMed

Proteorhodopsins (PRs), seven-transmembrane chromoproteins with retinal as a chromophore, are light-driven proton pumps. To elucidate the light-driven proton-pumping mechanism of PRs, a pET28a vector containing the blue-light-absorbing proteorhodopsin (BPR) gene was constructed and the protein was overexpressed in Escherichia coli. The protein was purified by immobilized metal-ion affinity chromatography (IMAC). The purified BPR D97N mutant protein (BPR_D97N) was crystallized using the vapour-diffusion method. Preliminary X-ray diffraction data analysis showed that the crystal belonged to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 161.6, b = 168.6, c = 64.7 Å. A complete data set was collected to 3.3 Å resolution using synchrotron radiation on beamline X06 of the Swiss Light Source (SLS). Molecular replacement was unsuccessful. To solve the structure of BPR_D97N by experimental phasing, selenomethionine-substituted protein crystals were prepared. These crystals diffracted to 3.0 Å resolution and a complete data set was collected on beamline BL17U of the Shanghai Synchrotron Radiation Facility (SSRF). Heavy-atom substructure determination and phasing by SAD clearly showed that the crystal contained five molecules in the asymmetric unit, with a V(M) of 3.26 Å(3)?Da(-1) and a solvent content of 62.3%. PMID:22442222

Wang, Ning; Wang, Meitian; Gao, Yanyan; Ran, Tingting; Lan, Yanli; Wang, Jian; Xu, Langlai; Wang, Weiwu

2012-03-01

421

Cloning, purification and preliminary crystallographic analysis of the Bacillus subtilis GTPase YphC-GDP complex  

PubMed Central

The Bacillus subtilis YphC gene encodes an essential GTPase thought to be involved in ribosome binding and whose protein product may represent a target for the development of a novel antibacterial agent. Sequence analysis reveals that YphC belongs to the EngA family of GTPases, which uniquely contain two adjacent GTP-binding domains. Crystals of a selenomethionine-incorporated YphC–GDP complex have been grown using the hanging-drop vapour-diffusion method and polyethylene glycol as a precipitating agent. The crystals belong to space group P212121, with unit-cell parameters a = 62.71, b = 65.05, c = 110.61?Å, and have one molecule in the asymmetric unit. Data sets at three different wavelengths were collected on a single crystal to 2.5?Å resolution at the Daresbury SRS in order to solve the structure by MAD. Ultimately, analysis of YphC in complex with GDP may allow a greater understanding of the EngA family of essential GTPases. PMID:16682769

Xu, Ling; Muench, Stephen P.; Roujeinikova, Anna; Sedelnikova, Svetlana E.; Rice, David W.

2006-01-01

422

Crystallographic structure of the turbine C-ring from spinach chloroplast F-ATP synthase  

PubMed Central

In eukaryotic and prokaryotic cells, F-ATP synthases provide energy through the synthesis of ATP. The chloroplast F-ATP synthase (CF1FO-ATP synthase) of plants is integrated into the thylakoid membrane via its FO-domain subunits a, b, b’ and c. Subunit c with a stoichiometry of 14 and subunit a form the gate for H+-pumping, enabling the coupling of electrochemical energy with ATP synthesis in the F1 sector. Here we report the crystallization and structure determination of the c14-ring of subunit c of the CF1FO-ATP synthase from spinach chloroplasts. The crystals belonged to space group C2, with unit-cell parameters a=144.420, b=99.295, c=123.51 Å, and ?=104.34° and diffracted to 4.5 Å resolution. Each c-ring contains 14 monomers in the asymmetric unit. The length of the c-ring is 60.32 Å, with an outer ring diameter 52.30 Å and an inner ring width of 40 Å. PMID:24521269

Balakrishna, Asha Manikkoth; Seelert, Holger; Marx, Sven-Hendric; Dencher, Norbert A.; Gruber, Gerhard

2014-01-01

423

Crystallization and preliminary crystallographic analysis of histamine dehydrogenase from Natrinema gari BCC 24369.  

PubMed

Histamine dehydrogenase (HADH) catalyzes the oxidative deamination of histamine, resulting in the production of imidazole acetaldehyde and an ammonium ion. The enzyme isolated from the newly identified halophilic archaeon Natrinema gari BCC 24369 is significantly different from the previously described protein from Nocardioides simplex. This newly identified HADH comprises three subunits with molecular weights of 49.0, 24.7 and 23.9?kDa, respectively, and is optimally active under high-salt conditions (3.5-5?M NaCl). As a step in the exploration of the unique properties of the protein, the HADH heterotrimer was purified and crystallized. Crystals were obtained using the sitting-drop vapor-diffusion method from a solution composed of 0.2?M calcium chloride dihydrate, 0.1?M HEPES pH 7.5, 28% PEG 400. Diffraction data were collected at -173°C to a resolution limit of 2.4?Å on the Southeast Regional Collaborative Access Team (SER-CAT) beamline 22-ID at the Advanced Photon Source, Argonne National Laboratory. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a=211.9, b=58.6, c=135.4?Å, ?=103.0°. The estimated Matthews coefficient is 3.21?Å3?Da(-1), corresponding to 61.7% solvent content. PMID:25005094

Zhou, Dongwen; Visessanguan, Wonnop; Chaikaew, Siriporn; Benjakul, Soottawat; Oda, Kohei; Wlodawer, Alexander

2014-07-01

424

Purification, crystallization and preliminary X-ray crystallographic analysis of glycosyltransferase-1 from Bacillus cereus.  

PubMed

Glycosyltransferases (GTs), which are distributed widely in various organisms, including bacteria, fungi, plants and animals, play a role in synthesizing biological compounds. Glycosyltransferase-1 from Bacillus cereus (BcGT-1), which is capable of transferring glucose to small molecules such as kaempferol and quercetin, has been identified as a member of the family 1 glycosyltransferases which utilize uridine diphosphate glucose (UDP-glucose) as the sugar donor. BcGT-1 (molecular mass 45.5?kDa) has been overexpressed, purified and crystallized using the hanging-drop vapour-diffusion method. According to X-ray diffraction of BcGT-1 crystals to 2.10?Å resolution, the crystal belonged to space group P1, with unit-cell parameters a = 54.56, b = 84.81, c = 100.12?Å, ? = 78.36, ? = 84.66, ? = 84.84°. Preliminary analysis indicates the presence of four BcGT-1 molecules in the asymmetric unit with a solvent content of 50.27%. PMID:25195897

Hsieh, Yin-Cheng; Chiu, Hsi-Ho; Huang, Yen-Chieh; Fun, Hoong-Kun; Lu, Chia-Yu; Li, Yaw-Kuen; Chen, Chun-Jung

2014-09-01

425

Crystallization and preliminary crystallographic analysis of cyanide-insensitive alternative oxidase from Trypanosoma brucei brucei.  

PubMed

Cyanide-insensitive alternative oxidase (AOX) is a mitochondrial membrane protein and a non-proton-pumping ubiquinol oxidase that catalyzes the four-electron reduction of dioxygen to water. In the African trypanosomes, trypanosome alternative oxidase (TAO) functions as a cytochrome-independent terminal oxidase that is essential for survival in the mammalian host; hence, the enzyme is considered to be a promising drug target for the treatment of trypanosomiasis. In the present study, recombinant TAO (rTAO) overexpressed in haem-deficient Escherichia coli was purified and crystallized at 293 K by the hanging-drop vapour-diffusion method using polyethylene glycol 400 as a precipitant. X-ray diffraction data were collected at 100 K and were processed to 2.9 A resolution with 93.1% completeness and an overall R(merge) of 9.5%. The TAO crystals belonged to the orthorhombic space group I222 or I2(1)2(1)2(1), with unit-cell parameters a = 63.11, b = 136.44, c = 223.06 A. Assuming the presence of two rTAO molecules in the asymmetric unit (2 x 38 kDa), the calculated Matthews coefficient (V(M)) was 3.2 A(3) Da(-1), which corresponds to a solvent content of 61.0%. This is the first report of a crystal of the membrane-bound diiron proteins, which include AOXs. PMID:20208159

Kido, Yasutoshi; Shiba, Tomoo; Inaoka, Daniel Ken; Sakamoto, Kimitoshi; Nara, Takeshi; Aoki, Takashi; Honma, Teruki; Tanaka, Akiko; Inoue, Masayuki; Matsuoka, Shigeru; Moore, Anthony; Harada, Shigeharu; Kita, Kiyoshi

2010-03-01

426

Crystallization and preliminary crystallographic analysis of cyanide-insensitive alternative oxidase from Trypanosoma brucei brucei  

PubMed Central

Cyanide-insensitive alternative oxidase (AOX) is a mitochondrial membrane protein and a non-proton-pumping ubiquinol oxidase that catalyzes the four-electron reduction of dioxygen to water. In the African trypanosomes, tryp­anosome alternative oxidase (TAO) functions as a cytochrome-independent terminal oxidase that is essential for survival in the mammalian host; hence, the enzyme is considered to be a promising drug target for the treatment of trypanosomiasis. In the present study, recombinant TAO (rTAO) overexpressed in haem-deficient Escherichia coli was purified and crystallized at 293?K by the hanging-drop vapour-diffusion method using polyethylene glycol 400 as a precipitant. X-ray diffraction data were collected at 100?K and were processed to 2.9?Å resolution with 93.1% completeness and an overall R merge of 9.5%. The TAO crystals belonged to the orthorhombic space group I222 or I212121, with unit-cell parameters a = 63.11, b = 136.44, c = 223.06?Å. Assuming the presence of two rTAO molecules in the asymmetric unit (2 × 38?kDa), the calculated Matthews coefficient (V M) was 3.2?Å3?Da?1, which corresponds to a solvent content of 61.0%. This is the first report of a crystal of the membrane-bound diiron proteins, which include AOXs. PMID:20208159

Kido, Yasutoshi; Shiba, Tomoo; Inaoka, Daniel Ken; Sakamoto, Kimitoshi; Nara, Takeshi; Aoki, Takashi; Honma, Teruki; Tanaka, Akiko; Inoue, Masayuki; Matsuoka, Shigeru; Moore, Anthony; Harada, Shigeharu; Kita, Kiyoshi

2010-01-01

427

Crystallographic and electronic structure of the Ca2TiMnO6 double perovskite  

NASA Astrophysics Data System (ADS)

In this work, we report synthesis and crystalline structure study of the Ca2TiMnO6 complex perovskite, by X-ray diffraction experiments and through the application of the Rietveld refinement using the GSAS code. Results revealed the crystallization of the system in a tetragonal perovskite with the characteristic structure given by I4/m (#87) space group and lattice parameters a=5.339(4) Å and c=7.736(6) Å. Ab initio calculations of density of states (DOS) and electronic structure were carried out for this perovskite-like system, by the Density Functional Theory (DFT) and using the Full-potential Linearized Augmented Plane Waves (FP-LAPW) method. The exchange-correlation potential was treated using the Generalized Gradient Approximation (GGA). All calculations were carried-out using spin polarization. For the up spin orientation the compound has a semiconducting behavior and for down spin polarization it behaves like a conductor. The calculated effective magnetic moment in cell was 4.02 ?B, which is close to the expected value calculated from Hund's rules.

López, J. P. Garzón; Cardona, R.; Santos, A. Sarmiento; Téllez, D. A. Landínez; Roa-Rojas, J.

2014-12-01

428

Crystallization and Preliminary X-ray Crystallographic Studies of the Alkanesulfonate FMN Reductase from Escherichia coli  

SciTech Connect

The alkanesulfonate FMN reductase (SsuE) from Escherichia coli catalyzes the reduction of FMN by NADPH to provide reduced flavin for the monooxygenase (SsuD) enzyme. The vapor-diffusion technique yielded single crystals that grow as hexagonal rods and diffract to 2.9 Angstrom resolution using synchrotron X-ray radiation. The protein crystallizes in the primitive hexagonal space group P622. The SsuE protein lacks any cysteine or methionine residues owing to the role of the SsuE enzyme in the acquisition of sulfur during sulfate starvation. Therefore, substitution of two leucine residues (Leu114 and Leu165) to methionine was performed to obtain selenomethionine-containing SsuE for MAD phasing. The selenomethionine derivative of SsuE has been expressed and purified and crystals of the protein have been obtained with and without bound FMN. These preliminary studies should lead to the structure solution of SsuE. It is anticipated that this new protein structure will provide detailed structural information on specific active-site regions of the protein and insight into the mechanism of flavin reduction and transfer of reduced flavin.

Gao,B.; Bertrand, A.; Boles, W.; Ellis, H.; Mallett, T.

2005-01-01

429

Overexpression, crystallization and preliminary X-ray crystallographic analysis of shikimate dehydrogenase from Archaeoglobus fulgidus.  

PubMed

Shikimate dehydrogenase (SDH), which catalyses the NADPH-dependent reduction of 3-dehydroshikimate to shikimate in the shikimate pathway, is an attractive target for the development of herbicides and antimicrobial agents. Previous structural studies have shown that SDH exists in two conformations, an open and a closed form, and it is believed that the conformational state is crucial to understanding its catalytic mechanism. In order to facilitate further structural comparisons among SDHs, including the conformational state, structural analysis of an SDH from Archaeoglobus fulgidus encoded by the Af2327 gene has been initiated. SeMet-labelled SDH from A. fulgidus was overexpressed in Escherichia coli and crystallized at 296 K using ammonium sulfate as a precipitant in order to use the MAD method for structure determination. Crystals of A. fulgidus SDH grown in the presence of NADP(+) diffracted to 2.8 Å resolution and belonged to the trigonal space group P3(2)21 (or P3(2)21), with unit-cell parameters a = 111.3, b = 111.3, c = 76.2 Å. Three diffraction data sets were collected. The asymmetric unit contains two monomers, with a corresponding V(M) of 2.34 Å(3) Da(-1) and a solvent content of 47% by volume. PMID:22139165

Lee, Hyung Ho

2011-12-01

430

Overexpression, crystallization, and preliminary X-ray crystallographic analysis of shikimate dehydrogenase from Thermotoga maritima.  

PubMed

Shikimate dehydrogenase (SDH), which catalyses the NADPH-dependent reduction of 3-dehydroshikimate to shikimate in the shikimate pathway, is an attractive target for the development of herbicides and antimicrobial agents. Previous structural studies showed that SDH exists in two conformations, an open form and a closed form, and it is believed that the conformational state is crucial to understanding a catalytic mechanism. To facilitate further structural comparisons among SDHs, structural analysis of an SDH from Thermotoga maritima encoded by the Tm0346 gene has been initiated. SDH from T. maritima has been overexpressed in Escherichia coli and crystallized at 296?K using ammonium sulfate as a precipitant. Crystals of T. maritima SDH diffracted to 1.45?Å resolution and belonged to orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a=54.21, b=62.45 and c=68.68?Å. The asymmetric unit contains a monomer, with a corresponding VM of 2.01?Å3?Da(-1) and a solvent content of 38.9% by volume. PMID:21795804

Lee, Hyung Ho

2011-07-01

431

Statistical crystallography of surface micelle spacing  

NASA Technical Reports Server (NTRS)

The aggregation of the recently reported surface micelles of block polyelectrolytes is analyzed using techniques of statistical crystallography. A polygonal lattice (Voronoi mosaic) connects center-to-center points, yielding statistical agreement with crystallographic predictions; Aboav-Weaire's law and Lewis's law are verified. This protocol supplements the standard analysis of surface micelles leading to aggregation number determination and, when compared to numerical simulations, allows further insight into the random partitioning of surface films. In particular, agreement with Lewis's law has been linked to the geometric packing requirements of filling two-dimensional space which compete with (or balance) physical forces such as interfacial tension, electrostatic repulsion, and van der Waals attraction.

Noever, David A.

1992-01-01

432

A High-strain Flow Law for Olivine: Grain-size Sensitivity and Crystallographic Fabric  

NASA Astrophysics Data System (ADS)

The dislocation-accommodated grain-boundary sliding regime, which has recently been recognized in deformation experiments on olivine aggregates, has important implications for the rheological characteristics of the upper mantle and for the interpretation of microstructures in naturally deformed rocks. However, previous experimental studies suffer from both the difficulty in synthesizing samples with a desired mean grain size and the limitation that crystallographic fabrics have not fully developed at low strains. We alleviate these difficulties in a series of innovative deformation experiments. Aggregates of iron-bearing olivine, hot pressed as hollow cylinders, were deformed in torsion at 1200°C in a gas-medium apparatus at constant strain rate until a steady-state shear stress was reached, which occurred by a shear strain of ~5. Since recrystallized grain size is a function of shear stress, we were able to systematically vary the mean grain size among samples by changing the controlling shear-strain rate. Above a shear strain of ~5, strain rate stepping tests were performed to determine the stress exponent. Between each strain-rate step, the strain rate was returned to the original strain rate to reset the microstructure. Experiments were stopped when the total shear strain reached ~11. Our results yield a stress exponent of ~4 and a grain size exponent of ~1, both of which agree with previous small-strain compression experiments on olivine in the dislocation-accommodated grain-boundary sliding regime. If the dependence of strain rate on grain size in the power-law flow law is removed by inserting the grain-size piezometer, the apparent stress exponent in the resulting grain size independent flow law increases to 5.2. Microstructural analyses indicate that very strong crystallographic-preferred orientation (CPO) fabrics are developed with M-indices of ~0.6. The CPO fabrics have [100] maxima sub-parallel to the shear direction and [010] maxima sub-perpendicular to the shear plane, consistent with activation of the (010)[100] slip system. These results confirm the validity of grain-size exponents previously determined in compression experiments and demonstrate that grain-boundary sliding can form very strong CPO fabrics at high strain. Thus, the observation of a pronounced CPO in naturally deformed rocks may indicate the activation of grain-boundary sliding rather than simply dislocation creep, and both the grain-size and the deformation conditions need to be compared to newly derived flow laws to determine the dominant deformation mechanism.

Hansen, L. N.; Zimmerman, M. E.; Kohlstedt, D. L.

2011-12-01

433

Aging and space travel  

NASA Technical Reports Server (NTRS)

The matter of aging and its relation to space vehicle crewmembers undertaking prolonged space missions is addressed. The capabilities of the older space traveler to recover from bone demineralization and muscle atrophy are discussed. Certain advantages of the older person are noted, for example, a greater tolerance of monotony and repetitious activities. Additional parameters are delineated including the cardiovascular system, the reproductive system, ionizing radiation, performance, and group dynamics.

Mohler, S. R.

1982-01-01

434

Space Tools! Space Tools!  

E-print Network

of the Universe. Radio telescopes are also used to search for signs of intelligent life on other planets. 13 #12 and planets they saw. The only tools they had to study space were their eyes and their imaginations. They had no other tools to help them learn what these lights in the sky really were. As people studied the night sky

435

Space Communication  

Microsoft Academic Search

As the space era approaches, the importance of including space science in the general curriculum and communicating space science to the general public is becoming extremely important. The paper, points out that the inclusion of more space education in the school curriculum and to the general public will increase awareness and interest in the new developments of space exploration. The

Bhavini Patel

2002-01-01

436

Space Travel  

NSDL National Science Digital Library

Students are introduced to the historical motivation for space exploration. They learn about the International Space Station as an example of space travel innovation and are introduced to new and futuristic ideas that space engineers are currently working on to propel space research far into the future!

Integrated Teaching And Learning Program

437

Space Discovery.  

ERIC Educational Resources Information Center

Describes one teacher's experience taking Space Discovery courses that were sponsored by the United States Space Foundation (USSF). These courses examine the history of space science, theory of orbits and rocketry, the effects of living in outer space on humans, and space weather. (DDR)

Blackman, Joan

1998-01-01

438

Surface energy-mediated construction of anisotropic semiconductor wires with selective crystallographic polarity  

NASA Astrophysics Data System (ADS)

ZnO is a wide band-gap semiconductor with piezoelectric properties suitable for opto-electronics, sensors, and as an electrode material. Controlling the shape and crystallography of any semiconducting nanomaterial is a key step towards extending their use in applications. Whilst anisotropic ZnO wires have been routinely fabricated, precise control over the specific surface facets and tailoring of polar and non-polar growth directions still requires significant refinement. Manipulating the surface energy of crystal facets is a generic approach for the rational design and growth of one-dimensional (1D) building blocks. Although the surface energy is one basic factor for governing crystal nucleation and growth of anisotropic 1D structures, structural control based on surface energy minimization has not been yet demonstrated. Here, we report an electronic configuration scheme to rationally modulate surface electrostatic energies for crystallographic-selective growth of ZnO wires. The facets and orientations of ZnO wires are transformed between hexagonal and rectangular/diamond cross-sections with polar and non-polar growth directions, exhibiting different optical and piezoelectrical properties. Our novel synthetic route for ZnO wire fabrication provides new opportunities for future opto-electronics, piezoelectronics, and electronics, with new topological properties.

Sohn, Jung Inn; Hong, Woong-Ki; Lee, Sunghoon; Lee, Sanghyo; Ku, Jiyeon; Park, Young Jun; Hong, Jinpyo; Hwang, Sungwoo; Park, Kyung Ho; Warner, Jamie H.; Cha, Seungnam; Kim, Jong Min

2014-07-01

439

The role of elastic anisotropy, length scale and crystallographic slip in fatigue crack nucleation  

NASA Astrophysics Data System (ADS)

Fatigue crack nucleation in polycrystal ferritic steel is investigated through experimental observation of multiple large-grained, notched, four-point bend tests combined with explicit microstructural representation of the same samples using crystal plasticity finite element techniques in order to assess fatigue indicator parameters, together with the roles of elastic anisotropy and length scale effects in slip development, and hence in crack nucleation. Elastic anisotropy has been demonstrated to play a pivotal role in the distribution and magnitude of polycrystal slip relative to observed crack nucleation sites in the context of constrained cyclic microplasticity. Length scale effects were found not to alter substantively the distributions or magnitudes of slip relative to the observed crack nucleation site, but in detailed analyses of an experimental sample, the location of highest magnitude of geometrically necessary dislocations was found to coincide precisely with the position of predicted peak plasticity and the experimentally observed crack nucleation site. The distributions of microplasticity within polycrystal samples were found to change quite significantly between the first yield and after multiple cycles. As a result, the effective plastic strain per cycle was found to be a better indicator of fatigue crack nucleation than peak effective plastic strain. In nine independently tested and analysed polycrystal samples, the cyclic effective plastic strain and crystallographic system peak accumulated slip were found to be good indicators of a fatigue crack nucleation site.

Sweeney, C. A.; Vorster, W.; Leen, S. B.; Sakurada, E.; McHugh, P. E.; Dunne, F. P. E.

2013-05-01

440

Spectroscopic study of graphene nanoribbons formed by crystallographic etching of highly oriented pyrolytic graphite  

NASA Astrophysics Data System (ADS)

We report a scanning tunneling spectroscopy study systematically performed on graphene nanoribbons (GNRs) with various widths and layer numbers. The GNRs are formed on highly oriented pyrolytic graphite (HOPG) by crystallographic etching, as reported by Datta and co-workers [Nano Lett. 8, 1912 (2008)]. Regardless of the width and layer numbers, GNRs having zigzag edges exhibit a peak at the Fermi energy in their local density of states (LDOS) when measured near the edges, whereas no peak appears away from the edges. On the other hand, a depression of the LDOS emerges at the Fermi energy in the case of a GNR having armchair edges with no relation to the measured position in an identical GNR. The energy gap of the LDOS depression monotonically decreases with increasing GNR width, whereas there is no apparent dependence on the layer numbers. By comparison with the band structure calculated by a nearest-neighbor tight-binding method, it is suggested that the overlap of wave functions between the topmost layer and the underlayers is negligible, resulting in an LDOS similar to that on an isolated monolayer GNR even on an HOPG substrate. From the quantitative scaling of energy gaps (Egap) of LDOS depression with respect to GNR widths (W), the relation between the two is obtained as Egap = 1.9 [eV nm]/W.

Sugiyama, Yoshihiro; Kubo, Osamu; Omura, Ryosuke; Shigehara, Masaaki; Tabata, Hiroshi; Mori, Nobuya; Katayama, Mitsuhiro

2014-09-01