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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Analysis of the Defect Structure of B2 Feal Alloys

The Bozzolo, Ferrante and Smith (BFS) method for alloys is applied to the study of the defect structure of B2 FeAI alloys. First-principles Linear Muffin Tin Orbital calculations are used to determine the input parameters to the BFS method used in this work. The calculations successfully determine the phase field of the B2 structure, as well as the dependence with composition of the lattice parameter. Finally, the method is used to perform 'static' simulations where instead of determining the ground state configuration of the alloy with a certain concentration of vacancies, a large number of candidate ordered structures are studied and compared, in order to determine not only the lowest energy configurations but other possible metastable states as well. The results provide a description of the defect structure consistent with available experimental data. The simplicity of the BFS method also allows for a simple explanation of some of the essential features found in the concentration dependence of the heat of formation, lattice parameter and the defect structure.

Bozzolo, Guillermo↗
NASA NTRS1998

Are clouds collapsing at the 2' north position of Sagittarius B2?

The 3 mm lines of HCO2+ and HNCO have been observed toward Sgr B2. Besides the well-known "principal cloud" and an extended envelope, we find another gas cloud 2' north of Sgr B2(M). This 2' north (2' N) cloud which may be located behind the principal cloud, has a total mass of approximately 10(5) Msolar and a diameter of approximately 7 pc. HCO2+ and HNCO exist mainly at 2' north, and their column densities are about 2.2 x 10(14) and 2.3 x 10(15) cm-2, respectively. The fractional abundances of these species relative to molecular hydrogen appear to be enhanced by at least a factor of 10 compared to the principal cloud. We have also identified redshifted and blueshifted high-velocity components which move toward the 2' N position with projected velocities of +/- 30 km s-1. These components are located symmetrically around 2' N, along the Galactic plane, and have diameters of about 4-5 pc and masses of approximately 1 x 10(4) Msolar. The flow energies are large enough to initiate new star formation in the 2' N region on the free-fall timescale of 10(5) yr. This large-scale collapsing motion may cause a strong shock in the 2' N cloud and result in the enhancement of HCO2+ and HNCO.

NASA Discipline Exobiology↗
NASA NTRS1996

Detection of abundant ethane and methane, along with carbon monoxide and water, in comet C/1996 B2 Hyakutake: evidence for interstellar origin

The saturated hydrocarbons ethane (C2H6) and methane (CH4) along with carbon monoxide (CO) and water (H2O) were detected in comet C/1996 B2 Hyakutake with the use of high-resolution infrared spectroscopy at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. The inferred production rates of molecular gases from the icy, cometary nucleus (in molecules per second) are 6.4 X 10(26) for C2H6, 1.2 X 10(27) for CH4, 9.8 X 10(27) for CO, and 1.7 X 10(29) for H2O. An abundance of C2H6 comparable to that of CH4 implies that ices in C/1996 B2 Hyakutake did not originate in a thermochemically equilibrated region of the solar nebula. The abundances are consistent with a kinetically controlled production process, but production of C2H6 by gas-phase ion molecule reactions in the natal cloud core is energetically forbidden. The high C2H6/CH4 ratio is consistent with production of C2H6 in icy grain mantles in the natal cloud, either by photolysis of CH4-rich ice or by hydrogen-addition reactions to acetylene condensed from the gas phase.

Non-programmatic↗
NASA NTRS2018

Performing a Large-Scale Modal Test on the B2 Stand Crane at NASA's Stennis Space Center

A modal test of NASA's Space Launch System (SLS) Core Stage is scheduled to occur at the Stennis Space Center B2 test stand. A derrick crane with a 150-ft long boom, located at the top of the stand, will be used to suspend the Core Stage in order to achieve defined boundary conditions. During this suspended modal test, it is expected that dynamic coupling will occur between the crane and the Core Stage. Therefore, a separate modal test was performed on the B2 crane itself, in order to evaluate the varying dynamic characteristics and correlate math models of the crane. Performing a modal test on such a massive structure was challenging and required creative test setup and procedures, including implementing both AC and DC accelerometers, and performing both classical hammer and operational modal analysis. This paper describes the logistics required to perform this large-scale test, as well as details of the test setup, the modal test methods used, and an overview and application of the results.

Stasiunas, Eric C.↗
NASA NTRS2018

Performing a Large-Scale Modal Test on the B2 Stand Crane at NASA's Stennis Space Center

A modal test of NASA’s Space Launch System (SLS) Core Stage is scheduled to occur prior to propulsion system verification testing at the Stennis Space Center B2 test stand. A derrick crane with a 180-ft long boom, located at the top of the stand, will be used to suspend the Core Stage in order to achieve defined boundary conditions. During this suspended modal test, it is expected that dynamic coupling will occur between the crane and the Core Stage. Therefore, a separate modal test was performed on the B2 crane itself, in order to evaluate the varying dynamic characteristics and correlate math models of the crane. Performing a modal test on such a massive structure was challenging and required creative test setup and procedures, including implementing both AC and DC accelerometers, and performing both classical hammer and operational modal analysis. This paper describes the logistics required to perform this large-scale test, as well as details of the test setup, the modal test methods used, and an overview of the results.

Stasiunas, Eric C.↗
DOE OSTI2020

Materials Data on B2(CN2)3 by Materials Project

B2(CN2)3 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three N3- atoms. There are a spread of B–N bond distances ranging from 1.44–1.49 Å. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three N3- atoms. There are a spread of B–N bond distances ranging from 1.40–1.45 Å. There are three inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a distorted see-saw-like geometry to four N3- atoms. There are a spread of C–N bond distances ranging from 1.46–1.54 Å. In the second C4+ site, C4+ is bonded to four N3- atoms to form corner-sharing CN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.45–1.61 Å. In the third C4+ site, C4+ is bonded to four N3- atoms to form corner-sharing CN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.45–1.62 Å. There are six inequivalent N3- sites. In the first N3- site, N3- is bonded in a trigonal planar geometry to one B3+ and two C4+ atoms. In the second N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one B3+ and two C4+ atoms. In the third N3- site, N3- is bonded in a distorted trigonal planar geometry to one B3+ and two C4+ atoms. In the fourth N3- site, N3- is bonded in a distorted trigonal planar geometry to one B3+ and two equivalent C4+ atoms. In the fifth N3- site, N3- is bonded in a distorted trigonal planar geometry to one B3+ and two C4+ atoms. In the sixth N3- site, N3- is bonded in a distorted trigonal planar geometry to one B3+ and two equivalent C4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on B2(CN2)3 by Materials Project

B2(CN2)3 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four inequivalent B3+ sites. In the first B3+ site, B3+ is bonded to four N3- atoms to form BN4 tetrahedra that share corners with eight CN4 tetrahedra. There are a spread of B–N bond distances ranging from 1.46–1.71 Å. In the second B3+ site, B3+ is bonded to four N3- atoms to form BN4 tetrahedra that share a cornercorner with one BN4 tetrahedra, corners with eight CN4 tetrahedra, and an edgeedge with one BN4 tetrahedra. There are a spread of B–N bond distances ranging from 1.47–1.63 Å. In the third B3+ site, B3+ is bonded to four N3- atoms to form BN4 tetrahedra that share a cornercorner with one BN4 tetrahedra, corners with six CN4 tetrahedra, and an edgeedge with one CN4 tetrahedra. There are a spread of B–N bond distances ranging from 1.47–1.63 Å. In the fourth B3+ site, B3+ is bonded in a trigonal planar geometry to three N3- atoms. There are a spread of B–N bond distances ranging from 1.43–1.50 Å. There are six inequivalent C4+ sites. In the first C4+ site, C4+ is bonded to four N3- atoms to form CN4 tetrahedra that share corners with four CN4 tetrahedra and corners with five BN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.41–1.59 Å. In the second C4+ site, C4+ is bonded to four N3- atoms to form CN4 tetrahedra that share corners with two BN4 tetrahedra, corners with four CN4 tetrahedra, and an edgeedge with one BN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.44–1.62 Å. In the third C4+ site, C4+ is bonded to four N3- atoms to form CN4 tetrahedra that share corners with four BN4 tetrahedra and corners with four CN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.44–1.55 Å. In the fourth C4+ site, C4+ is bonded to four N3- atoms to form CN4 tetrahedra that share corners with three BN4 tetrahedra and corners with four CN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.42–1.55 Å. In the fifth C4+ site, C4+ is bonded to four N3- atoms to form CN4 tetrahedra that share corners with four BN4 tetrahedra and corners with four CN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.46–1.55 Å. In the sixth C4+ site, C4+ is bonded to four N3- atoms to form CN4 tetrahedra that share corners with four BN4 tetrahedra and corners with four CN4 tetrahedra. There are a spread of C–N bond distances ranging from 1.46–1.61 Å. There are twelve inequivalent N3- sites. In the first N3- site, N3- is bonded in a trigonal non-coplanar geometry to one B3+ and two C4+ atoms. In the second N3- site, N3- is bonded in a trigonal non-coplanar geometry to one B3+ and two C4+ atoms. In the third N3- site, N3- is bonded in a tetrahedral geometry to two B3+ and two C4+ atoms. In the fourth N3- site, N3- is bonded in a trigonal non-coplanar geometry to one B3+ and two C4+ atoms. In the fifth N3- site, N3- is bonded in a trigonal planar geometry to one B3+ and two C4+ atoms. In the sixth N3- site, N3- is bonded in a trigonal planar geometry to one B3+ and two C4+ atoms. In the seventh N3- site, N3- is bonded in a distorted trigonal non-coplanar geometry to one B3+ and two C4+ atoms. In the eighth N3- site, N3- is bonded in a trigonal non-coplanar geometry to one B3+ and two C4+ atoms. In the ninth N3- site, N3- is bonded in a trigonal non-coplanar geometry to one B3+ and two C4+ atoms. In the tenth N3- site, N3- is bonded to two equivalent B3+ and two C4+ atoms to form a mixture of edge and corner-sharing NB2C2 tetrahedra. In the eleventh N3- site, N3- is bonded to two B3+ and two C4+ atoms to form corner-sharing NB2C2 tetrahedra. In the twelfth N3- site, N3- is bonded in a trigonal planar geometry to one B3+ and two C4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electronic and Magnetic Properties of Ru{sub 2}FeSi{sub 1−x}Ge{sub x} Alloys in B2 Structure: a First-Principle Study

In this letter, structural, electronic structure, and magnetic properties of Ru{sub 2}FeSi{sub 1−x}Ge{sub x} were analyzed for the first time in the stable B2 phase by using the first-principle calculation. The exchange and correlation potentials are described by using generalized gradient approximations (GGA) The B{sub 2} structure is found to be energetically more favorable than the L2{sub 1} structure. It was found that the lattice parameters increase linearly with increasing x. For all the range studied, the Ru{sub 2}FeSi{sub 1−x}Ge{sub x} alloys exhibit a metallic character. The origin of magnetic moment is due to the exchange splitting of Fe-d states, and the atomic magnetic moment of the present material originates mainly from Fe atom.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Regulation of membrane raft recruitment of the bradykinin B2 receptor by close association with the ATP/UTP receptor P2Y2

Highlights: • P2Y{sub 2}R recruits bradykinin B2R to lipid rafts. • B2R does not affect lipid raft distribution of P2Y{sub 2}R. • Signal crosstalk between P2Y{sub 2}R and B2R occurs in lipid rafts. • Association of P2Y{sub 2}R with both lipid rafts and B2R occurs in the ER. Several G protein-coupled receptors are present in lipid rafts. We have shown that most of the P2Y{sub 2} receptor (P2Y{sub 2}R) protein is fractionated into lipid rafts in COS 7 cells. In the same cells, about 25–30% of the bradykinin B2 receptor (B2R) protein is also fractionated into lipid rafts. When both P2Y{sub 2}R and B2R are co-expressed, the distribution of P2Y{sub 2}R remained unchanged, but more B2R shifted into the raft fraction. This indicates that the interaction between both receptors recruited B2R into the lipid rafts. After 15 min of UTP stimulation, both receptors almost completely disappeared from the cell surface by endocytosis as observed with a confocal fluorescence microscope. Furthermore, with bradykinin stimulation for 15 min, portions of both receptors disappeared from the cell surface and were endocytosed. As we reported previously with both CHO-K1 cells and HEK 293 cells, continuous stimulation of COS7 cells with GT1b and CSC resulted in the disappearance of both P2Y{sub 2}R and B2R from the cell membrane surface. Thus, both P2Y{sub 2}R and B2R migrate into membrane rafts and are endocytosed in parallel with signal crosstalk, clearly indicating that both closely interact on membrane rafts. The P2Y{sub 2}R N-glycosylation deficient mutant does not migrate to the cell surface. It remains predominantly in the endoplasmic reticulum and is fractionated into raft fractions. In the presence of this glycosylation mutant, most of B2R remains in the endoplasmic reticulum, and is fractionated into the raft fraction. These findings demonstrate that in the membrane rafts of the endoplasmic reticulum, both receptors are already closely associated, and B2R shifts into the rafts by affinity with P2Y{sub 2}R.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Ligand Binding Enhances Millisecond Conformational Exchange in Xylanase B2 from Streptomyces lividans

Xylanases catalyze the hydrolysis of xylan, an abundant carbon and energy source with important commercial ramifications. Despite tremendous efforts devoted to the catalytic improvement of xylanases, success remains limited because of our relatively poor understanding of their molecular properties. Previous reports suggested the potential role of atomic-scale residue dynamics in modulating the catalytic activity of GH11 xylanases; however, dynamics in these studies was probed on time scales orders of magnitude faster than the catalytic time frame. Here, we used nuclear magnetic resonance titration and relaxation dispersion experiments ( 15 N-CPMG) in combination with X-ray crystallography and computational simulations to probe conformational motions occurring on the catalytically relevant millisecond time frame in xylanase B2 (XlnB2) and its catalytically impaired mutant E87A from Streptomyces lividans 66. Our results show distinct dynamical properties for the apo and ligand-bound states of the enzymes. The apo form of XlnB2 experiences conformational exchange for residues in the fingers and palm regions of the catalytic cleft, while the catalytically impaired E87A variant displays millisecond dynamics only in the fingers, demonstrating the long-range effect of the mutation on flexibility. Ligand binding induces enhanced conformational exchange of residues interacting with the ligand in the fingers and thumb loop regions, emphasizing the potential role of residue motions in the fingers and thumb loop regions for recognition, positioning, processivity, and/or stabilization of ligands in XlnB2. To the best of our knowledge, this work represents the first experimental characterization of millisecond dynamics in a GH11 xylanase family member. Furthermore, these results offer new insights into the potential role of conformational exchange in GH11 enzymes, providing essential dynamic information to help improve protein engineering and design applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Computational ranking identifies Plexin-B2 in circulating tumor cell clustering with monocytes in breast cancer metastasis

Abstract Multicellular circulating tumor cell (CTC) clusters can be up to 50 times more efficient than single CTCs in mediating viable metastasis. Here, combining computational ranking and functional determination, we identify the transmembrane protein Plexin-B2 (PLXNB2) as one of the top molecular targets associated with unfavorable distant metastasis-free survival, showing enriched expression in CTC clusters versus single CTCs from patients with advanced breast cancer (mostly female). Loss of PLXNB2 (Plxnb2) reduces the formation of homotypic tumor cell clusters and heterotypic tumor-myeloid cell clusters, reducing spontaneous metastases in female mice bearing human (mouse) breast cancer. Interactions of PLXNB2 with its ligands SEMA4C on tumor cells and SEMA4A on myeloid cells (monocytes) promote homotypic and heterotypic CTC cluster formation, respectively, thereby driving lung metastasis. Global proteomic analysis reveals downstream effectors of the PLXNB2 pathway associated with tumor cell clustering. Thus, PLXNB2 is a therapeutic target for preventing new metastasis in breast cancer.

Science & Technology - Other Topics↗
DOE OSTI2013

Origin of thickness dependent spin reorientation transition of B2 type FeCo alloy films

We have investigated the origin of thickness dependent spin reorientation transition (SRT) of B2 type FeCo alloy using the full potential linearized augmented plane wave method. It has been reported that FeCo alloy films on various substrates show a SRT from perpendicular to in-plane magnetization at an approximate thickness of 15 monolayers (MLs). The enhanced perpendicular magnetic anisotropy in bulk FeCo is attributed to a tetragonal distortion. However, we have found that the tetragonal distortion tends to suppress the magnetocrystalline anisotropy (MCA) energy at increasing film thickness in two-dimensional structure. In contrast, the magnitude of the shape anisotropy energy increases at increasing FeCo film thickness. Interestingly, the shape anisotropy overcomes the MCA and the SRT, from perpendicular anisotropy to in-plane magnetization, which occurs at a thickness of 15 ML. Consequently, we are able to clearly understand the physical mechanism of the thickness dependent SRT in terms of the competing reactions of these two counteracting contributions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

TEM investigation of the surface layer structure [111]{sub B2} of the single NiTi crystal modified by the Si-ion beam implantation

The study was carried on for the single NiTi crystals subjected to the Si-ion beam implantation. Using the transmission electron microscopy technique (TEM), the surface layer structure [111]{sub B2} was examined for the treated material. The modified near-surface sublayers were found to have different composition. Thus the uppermost sublayer contained mostly oxides; the lower-lying modified sublayer material was in an amorphous state and the thin underlying sublayer had a defect structure.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Crystallographic analysis of the implanted TiNi monocrystal containing misoriented localized shear mesobands in its near-surface layer [001]{sub B2}

The study was carried on for the implanted single TiNi crystal containing misoriented localized shear mesobands in its near-surface layer [001] B2. Due to the response of material to the Si ion implantation treatment of the single TiNi crystal, deformation mesobands would form in its near-surface layer. Specially designed software tools were employed for the treatment of experimental data obtained from X-ray and electron diffraction patterns. The 3D crystallographic orientations were calculated for the localized shear regions, which were displaced relative to one another and with respect to the original monocrystal orientation.

36 MATERIALS SCIENCE↗
DOE OSTI2012

A COUPLED CHEMISTRY-EMISSION MODEL FOR ATOMIC OXYGEN GREEN AND RED-DOUBLET EMISSIONS IN THE COMET C/1996 B2 HYAKUTAKE

The green (5577 Angstrom-Sign ) and red-doublet (6300, 6364 Angstrom-Sign ) lines are prompt emissions of metastable oxygen atoms in the {sup 1}S and {sup 1}D states, respectively, that have been observed in several comets. The value of the intensity ratio of green to red-doublet (G/R ratio) of 0.1 has been used as a benchmark to identify the parent molecule of oxygen lines as H{sub 2}O. A coupled chemistry-emission model is developed to study the production and loss mechanisms of the O({sup 1}S) and O({sup 1}D) atoms and the generation of red and green lines in the coma of C/1996 B2 Hyakutake. The G/R ratio depends not only on photochemistry, but also on the projected area observed for cometary coma, which is a function of the dimension of the slit used and the geocentric distance of the comet. Calculations show that the contribution of photodissociation of H{sub 2}O to the green (red) line emission is 30%-70% (60%-90%), while CO{sub 2} and CO are the next potential sources contributing 25%-50% (<5%). The ratio of the photoproduction rate of O({sup 1} S) to O({sup 1} D) would be around 0.03 ({+-}0.01) if H{sub 2}O is the main source of oxygen lines, whereas it is {approx}0.6 if the parent is CO{sub 2}. Our calculations suggest that the yield of O({sup 1} S) production in the photodissociation of H{sub 2}O cannot be larger than 1%. The model-calculated radial brightness profiles of the red and green lines and G/R ratios are in good agreement with the observations made on the comet Hyakutake in 1996 March.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Orbital hybridisation effects in B2 phase Cr doped Co 2 MnAl

Here we investigate here the magnetic, transport, local structural and electronic properties of Co 2 Mn 1−x Cr x Al (x = 0, 0.05, 0.1 and 0.2). Our results show that all the compounds stabilise in B2 phase and are ferromagnets. The results reveal disorder at the structural and magnetic levels. X-ray absorption near edge structure (XANES) analysis reveal signature of antisite disorder between Mn and Al atoms with equal ratio. The electronic structure calculations suggest enhancement in the half metallicity, localisation of electrons at the Fermi level and an increment in density of states with doping. The combined results of electronic structure calculations and XANES studies suggest transfer of electrons to the Co site. The results of high temperature resistivity measurements suggest the conduction electrons are undergoing transition from delocalisation to weak localisation to activated behaviour with Cr doping. The extended x-ray absorption spectroscopic analysis shows that the local structure around Mn atom is different from the global structure as obtained from the x-ray diffraction results. The behaviour of the edge region is in line with the trend as obtained from the compositional analysis. We observe link between the hybridisation of 3d like states at the Mn, Cr sites with that at the Co site and the transport properties. This could help in understanding the unusual decrement in the lattice parameter with doping. These results reveal the role of local structure in understanding the physical properties of such systems.

36 MATERIALS SCIENCE↗
DOE OSTI2013

DETECTION OF E-CYANOMETHANIMINE TOWARD SAGITTARIUS B2(N) IN THE GREEN BANK TELESCOPE PRIMOS SURVEY

The detection of E-cyanomethanimine (E-HNCHCN) toward Sagittarius B2(N) is made by comparing the publicly available Green Bank Telescope (GBT) PRIMOS survey spectra to laboratory rotational spectra from a reaction product screening experiment. The experiment uses broadband molecular rotational spectroscopy to monitor the reaction products produced in an electric discharge source using a gas mixture of NH{sub 3} and CH{sub 3}CN. Several transition frequency coincidences between the reaction product screening spectra and previously unassigned interstellar rotational transitions in the PRIMOS survey have been assigned to E-cyanomethanimine. A total of eight molecular rotational transitions of this molecule between 9 and 50 GHz are observed with the GBT. E-cyanomethanimine, often called the HCN dimer, is an important molecule in prebiotic chemistry because it is a chemical intermediate in proposed synthetic routes of adenine, one of the two purine nucleobases found in DNA and RNA. New analyses of the rotational spectra of both E-cyanomethanimine and Z-cyanomethanimine that incorporate previous millimeter-wave measurements are also reported.

79 ASTRONOMY AND ASTROPHYSICS↗