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1

Fourier transform infrared spectroscopy used to evidence the prevention of beta-sheet formation of amyloid beta(1-40) peptide by a short amyloid fragment.  

PubMed

Reflectance Fourier transform infrared (FT-IR) microspectroscopy was applied to study the prevention of beta-sheet formation of amyloid beta (Abeta)(1-40) peptide by co-incubation with a hexapeptide containing a KLVFF sequence (Abeta(15-20) fragment). Second-derivative spectral analysis was used to locate the position of the overlapping components of the amide I band of Abeta peptide and assigned them to different secondary components. The result indicates that each intact sample of Abeta(15-20) fragment or Abeta(1-40) peptide previously incubated in distilled water at 37 degrees C transformed their secondary structure from 1649 (1651) or 1653cm(-1) to 1624cm(-1), suggesting the transformation from alpha-helix and/or random coil structures to beta-sheet structure. By co-incubating both samples with different molar ratio in distilled water at 37 degrees C, the structural transformation was not found for Abeta(1-40) peptide after 24h-incubation. But the beta-sheet formation of Abeta(1-40) peptide after 48h-incubation was evidenced from the appearance of the IR peak at 1626cm(-1) by adding a little amount of Abeta(15-20) fragment. There was no beta-sheet formation of Abeta(1-40) peptide after addition with much amount of Abeta(15-20) fragment, however, suggesting the higher amount of Abeta(15-20) fragment used might inhibit the beta-sheet formation of Abeta(1-40) peptide. The more Abeta(15-20) fragment used made the more stable structure of Abeta(1-40) peptide and the less beta-sheet formation of Abeta(1-40) peptide. The study indicates that the reflectance FT-IR microspectroscopy can easily evidence the prevention of beta-sheet formation of Abeta(1-40) peptide by a short amyloid fragment. PMID:12957314

Lin, Shan-Yang; Chu, Horng-Lun

2003-09-01

2

Conformational diversity in prion protein variants influences intermolecular [beta]-sheet formation  

SciTech Connect

A conformational transition of normal cellular prion protein (PrP{sup C}) to its pathogenic form (PrP{sup Sc}) is believed to be a central event in the transmission of the devastating neurological diseases known as spongiform encephalopathies. The common methionine/valine polymorphism at residue 129 in the PrP influences disease susceptibility and phenotype. We report here seven crystal structures of human PrP variants: three of wild-type (WT) PrP containing V129, and four of the familial variants D178N and F198S, containing either M129 or V129. Comparison of these structures with each other and with previously published WT PrP structures containing M129 revealed that only WT PrPs were found to crystallize as domain-swapped dimers or closed monomers; the four mutant PrPs crystallized as non-swapped dimers. Three of the four mutant PrPs aligned to form intermolecular {beta}-sheets. Several regions of structural variability were identified, and analysis of their conformations provides an explanation for the structural features, which can influence the formation and conformation of intermolecular {beta}-sheets involving the M/V129 polymorphic residue.

Lee, Seungjoo; Antony, Lizamma; Hartmann, Rune; Knaus, Karen J.; Surewicz, Krystyna; Surewicz, Witold K.; Yee, Vivien C. (Case Western); (Cleveland Clinic)

2010-04-19

3

Amyloid-beta-sheet formation at the air-water interface.  

PubMed Central

An amyloid(1-40) solution rich in coil, turn, and alpha-helix, but poor in beta-sheet, develops monolayers with a high beta-sheet content when spread at the air-water interface. These monolayers are resistant to repeated compression-dilatation cycles and interaction with trifluoroethanol. The secondary structure motifs were detected by circular dichroism (CD) in solution and with infrared reflection-absorption spectroscopy (IRRAS) at the interface. Hydrophobic influences are discussed for the structure conversion in an effort to understand the completely unknown reason for the natural change of the normal prion protein cellular (PrP(C)) into the abnormal prion protein scrapie (PrP(Sc)).

Schladitz, C; Vieira, E P; Hermel, H; Mohwald, H

1999-01-01

4

In situ Atomic Force Microscopy Study of Alzheimer's beta -amyloid Peptide on Different Substrates: New Insights into Mechanism of beta -sheet Formation  

Microsoft Academic Search

We have applied in situ atomic force microscopy to directly observe the aggregation of Alzheimer's beta -amiloid peptide (Abeta) in contact with two model solid surfaces: hydrophilic mica and hydrophobic graphite. The time course of aggregation was followed by continuous imaging of surfaces remaining in contact with 10-500 mu M solutions of Abeta in PBS (pH 7.4). Visualization of fragile

Tomasz Kowalewski; David M. Holtzman

1999-01-01

5

Leucine fastener formation mechanism between peptide beta-sheets in a monolayer studied by infrared multiple-angle incidence resolution spectroscopy.  

PubMed

A leucine zipper and a leucine fastener formed between peptide molecules have been hypothetical models of a molecular association via interdigitation. As a molecular interaction mechanism, a "leucine zipper" with the aid of an alpha-helix backbone in biological peptides is believed to play an important role in the molecular association, but no experimental evidence to prove the zipping has been reported thus far. In the same fashion, a "leucine fastener" built on the structure of peptide beta-sheets has never been experimentally captured either. In the present study, very fine changes of molecular stress and orientation in monolayers of a synthesized tetraleucine-containing amphiphile before and after the molecular interdigitation have readily been detected by infrared multiple-angle incidence resolution spectroscopy, which was recently developed for the analysis of structural anisotropy in thin materials. It has been suggested that the conventional molecular orientation model of the leucine fastener should be modified, and the backbone structure (parallel beta-sheet in the present study) plays a necessary role for the interlock of the leucine fastener. PMID:16851562

Hasegawa, Takeshi; Kakuda, Hiroyuki; Yamada, Norihiro

2005-03-17

6

Amyloid Beta Mediates Memory Formation  

ERIC Educational Resources Information Center

|The amyloid precursor protein (APP) undergoes sequential cleavages to generate various polypeptides, including the amyloid [beta] (1-42) peptide (A[beta][1-42]), which is believed to play a major role in amyloid plaque formation in Alzheimer's disease (AD). Here we provide evidence that, in contrast with its pathological role when accumulated,…

Garcia-Osta, Ana; Alberini, Cristina M.

2009-01-01

7

Mechanism of Enzymatic Degradation of Beta-sheet Crystals  

PubMed Central

The anti-parallel beta pleated sheet is a fundamental secondary structure in proteins and a major component in silk fibers generated by silkworms and spiders, with a key role to stabilize these proteins via physical cross-links. Importantly, these beta-sheets are fully degradable and nontoxic structures in biology, in contrast for example to beta-amyloid structures formed in disease states. Thus, insight into mechanism of enzymatic degradation would be instructive as a route to elucidating differences among these stable yet different structural features in biological systems. We report on the mechanism of enzymatic degradation of anti-parallel beta pleated sheets with Bombyx mori silk structures, leading to fibrils and subsequently to nanofilaments (2 nm thickness and 160 nm length). These nanofilaments play a role as nucleators of the crystalline regions, an important feature of the system that can be exploited to design silk-based biomaterials with predictable biodegradability and mechanical properties. The potential toxicity of degradation products from these proteolytic enzymes was also assessed in vitro and no cell toxicity found in vitro for the protease found in vivo in the human body. The degradation mechanism of beta-sheet silk crystals provides additional insight into the significant differences in biological impact between the anti-parallel beta-sheet silk biomaterials reported in this work vs. amyloid structures in disease states, adding to prior descriptions of chemical and structural differences that are more extensively documented.

Numata, Keiji; Cebe, Peggy; Kaplan, David L.

2009-01-01

8

Enhancement of beta-sheet assembly by cooperative hydrogen bonds potential  

PubMed Central

Motivation: The roughness of energy landscapes is a major obstacle to protein structure prediction, since it forces conformational searches to spend much time struggling to escape numerous traps. Specifically, beta-sheet formation is prone to stray, since many possible combinations of hydrogen bonds are dead ends in terms of beta-sheet assembly. It has been shown that cooperative terms for backbone hydrogen bonds ease this problem by augmenting hydrogen bond patterns that are consistent with beta sheets. Here, we present a novel cooperative hydrogen-bond term that is both effective in promoting beta sheets and computationally efficient. In addition, the new term is differentiable and operates on all-atom protein models. Results: Energy optimization of poly-alanine chains under the new term led to significantly more beta-sheet content than optimization under a non-cooperative term. Furthermore, the optimized structure included very few non-native patterns. Availability: The new term is implemented within the MESHI package and is freely available at http://cs.bgu.ac.il/?meshi. Contact: chen.keasar@gmail.com Supplementary information: Supplementary data are available at Bioinformatics online.

Levy-Moonshine, Ami; Amir, El-ad David; Keasar, Chen

2009-01-01

9

Relative orientation of close-packed beta-pleated sheets in proteins.  

PubMed

When beta-pleated sheets pack face to face in proteins, the angle between the strand directions of the two beta-sheets is observed to be near -30 degrees . We propose a simple model for beta-sheet-to-beta-sheet packing in concanavalin A, plastocyanin, gamma-crystallin, superoxide dismutase, prealbumin, and the immunoglobin fragment V(REI). This model shows how the observed relative orientation of two packed beta-sheets is a consequence of (i) the rows of side chains at the interface being approximately aligned and (ii) the beta-sheet having a right-handed twist. The special amino acid composition of residues at the beta-sheet-to-beta-sheet interfaces makes the contact surfaces essentially smooth and hydrophobic. PMID:16593054

Chothia, C; Janin, J

1981-07-01

10

Pressure-induced transformation of alpha-helix to beta-sheet in the secondary structures of amyloid beta (1-40) peptide exacerbated by temperature.  

PubMed

The effect of pressure on the conformational structure of amyloid beta (1-40) peptide (A beta(1-40)), exacerbated with or without temperature, was determined by Fourier transform infrared (FT-IR) microspectroscopy. The result indicates the shift of the maximum peak of amide I band of intact solid A beta(1-40) from 1655 cm(-1) (alpha-helix) to 1647-1643 cm(-1) (random coil) with the increase of the mechanical pressure. A new peak at 1634 cm(-1) assigned to beta-antiparallel sheet structure was also evident. Furthermore, the peak at 1540 cm(- 1) also shifted to 1527 (1529) cm(-1) in amide II band. The former was assigned to the combination of alpha-helix and random coil structures, and the latter was due to beta-sheet structure. Changes in the composition of each component in the deconvoluted and curve-fitted amide I band of the compressed A beta(1-40) samples were obtained from 33% to 22% for alpha-helix/random coil structures and from 47% to 57% for beta-sheet structure with the increase of pressure, respectively. This demonstrates that pressure might induce the conformational transition from alpha-helix to random coil and to beta- sheet structure. The structural transformation of the compressed A beta(1-40) samples was synergistically influenced by the combined effects of pressure and temperature. The thermal-induced formation of beta-sheet structure was significantly dependent on the pressures applied. The smaller the pressure applied the faster the beta-sheet structure transformed. The thermal-dependent transition temperatures of solid A beta(1-40) prepared by different pressures were near 55-60 degrees C. PMID:11843623

Lin, Shan-Yang; Chu, Horng-Lun; Wei, Yen-Shan

2002-02-01

11

Beta-sheet is the bioactive conformation of the anti-angiogenic anginex peptide.  

PubMed Central

Anginex is a designed peptide 33mer that functions as a cytokine-like agent to inhibit angiogenesis. Although this short linear peptide has been shown by NMR and CD to form a nascent beta-sheet conformation in solution, the actual bioactive structure formed upon binding to its receptor on the surface of endothelial cells could be quite different. By using a series of double-cysteine disulphide-bridged analogues, we provide evidence in the present study that the beta-sheet is in fact the bioactive conformation of anginex. CD and NMR spectral analysis of the analogues indicate formation of a beta-sheet conformation. Three functional assays, endothelial cell proliferation, apoptosis and in vitro angiogenesis, were performed on all analogues. As long as the placement of disulphide bonds preserved the beta-strand alignment, as in the proposed bioactive conformation, bioactivities were preserved. Knowledge of the bioactive conformation of anginex will aid in the design of smaller molecule mimetics of this potent anti-angiogenic peptide.

Dings, Ruud P M; Arroyo, Monica M; Lockwood, Nathan A; van Eijk, Loes I; Haseman, Judy R; Griffioen, Arjan W; Mayo, Kevin H

2003-01-01

12

Tape-casting technique can prepare beta-TCP sheets with uniform thickness and flexibility.  

PubMed

The objective of this study is to propose a new fabrication technology for bone substitutes. In this study, a tape-casting method was used to prepare flexible beta-tricalcium phosphate (beta-TCP) sheets. A beta-TCP slurry containing a binder and plasticizer was used in a doctor blade system. The beta-TCP sheet obtained by this tape-casting method was highly flexible, enabling twisting and free-form shaping. The beta-TCP sheet was approximately 0.21 mm thick. X-ray diffraction and Fourier transform infrared spectrometry revealed that the structure of the beta-TCP component in the sheet is the same as that of the original beta-TCP powder. Observation by field-emission scanning electron microscopy showed that the beta-TCP sheet had a flat, microgranular surface. During the early stages, the tensile stress-strain curves of the beta-TCP sheet showed a nonlinear behavior until reaching the point of final fracture. This result was derived from the ductile property of the prepared beta-TCP sheet. In conclusion, a flexible beta-TCP sheet was easily prepared using a tape-casting technique. Fabrication using tape casting offers the advantages of enabling the preparation of ceramic sheets with precise thickness and not requiring expensive fabrication facilities. PMID:15786445

Tanimoto, Yasuhiro; Hayakawa, Tohru; Nemoto, Kimiya

2005-04-01

13

Numerical simulation of current sheet formation in a quasiseparatrix layer using adaptive mesh refinement  

Microsoft Academic Search

The formation of a thin current sheet in a magnetic quasiseparatrix layer (QSL) is investigated by means of numerical simulation using a simplified ideal, low-beta, MHD model. The initial configuration and driving boundary conditions are relevant to phenomena observed in the solar corona and were studied earlier by Aulanier et al. [Astron. Astrophys. 444, 961 (2005)]. In extension to that

Frederic Effenberger; Kay Thust; Lukas Arnold; Rainer Grauer; Jürgen Dreher

2011-01-01

14

Folding of beta pep-4 beta-sheet sandwich dimers and tetramers is influenced by aliphatic hydrophobic residues at the intersubunit interface.  

PubMed Central

For the designed peptide 33mer, beta pep-4, formation of beta-sheet structure [Ilyina, Roongta and Mayo (1997) Biochemistry 36, 5245--5250] is thermodynamically linked to self-association. Dimers and tetramers are stabilized by interactions between hydrophobic residues lying on the hydrophobic faces of the amphipathic monomer subunits. The present study investigates the effects on folding and self-association of the substitution of two key hydrophobic residues (Ile(20) and Val(22)) at the beta-sheet sandwich interface of beta pep-4. Single-site (I20L, I20V, I20A, V22L, V22I and V22A; where I20L corresponds to the substitution of Ile(20) with leucine etc.) and double-site (I20L/V22L and I20V/V22I) variants have been investigated. Like parent beta pep-4, all variants can form dimers and tetramers. NOESY data indicate that the overall beta-sheet fold and intersubunit beta-strand alignments are the same in all variant tetramers. CD data for all variants indicate mostly beta-sheet character in dimers and random coil character in monomers. Only for the V22I variant is the beta-sheet fold stabilized in the monomer state. Pulse-field gradient NMR-derived diffusion coefficients, measured as a function of peptide concentration, provide a means for deriving the distribution of monomer, dimer and tetramer states and, therefore, equilibrium association constants. Relative thermodynamic stabilities, which vary no more than approx. 0.5 kcal/mol (where 1 kcal identical with 4.184 kJ) from peptide to peptide, are I20V/V22I>I20V>I20L/V22L=beta pep-4 (Delta G(D) of 7.5 kcal/mol)=I20L=I20A>V22I>V22L>V22A for dimer formation and I20V>I20L/V22L>I20L>beta pep-4 (Delta G(T) of 6 kcal/mol)>V22I>I20V/V22I>V22L>I20A>V22A for tetramer formation. For the most part, dimer and/or tetramer stabilities are enhanced by the presence of valine and leucine and are attenuated by the presence of isoleucine and alanine.

Cox, A; Arroyo, M M; Mayo, K H

2001-01-01

15

Evidence for a repeating cross-beta sheet structure in the adenovirus fibre.  

PubMed

The amino acid sequence of the adenovirus fibre protein reveals an approximately repeating motif of 15 residues. A diagonal comparison matrix established that these repeats extended from residue 43 to residue 400 of the 581 residue sequence. Assignment of secondary structure combined with model building showed that each 15-residue segment contained two short beta-strands and two beta-bends, one of which incorporated an extra residue in a beta-bulge of the Gx type. The 44 strands together gave a long (210 A) narrow, amphipathic beta-sheet, which could be stabilised by dimer formation to give the shaft of the fibre. The knob could arise from a dimer of the C-terminal 180 residue segment, predicted to be an 8-10 stranded beta-sandwich. This model is consistent with the electron micrographs of the fibre and it was supported by measurements of c.d. and of electron diffraction from microcrystals. The latter gave a pair of wide angle arcs, corresponding to a repeat of 4.7 A, oriented appropriately for a cross-beta structure. The relation of this structure to globular structures is discussed and a folding pathway is proposed. In its general features the structure resembles that proposed for the tail fibre of bacteriophage T4. PMID:10872331

Green, N M; Wrigley, N G; Russell, W C; Martin, S R; McLachlan, A D

1983-01-01

16

Low-frequency motions in protein molecules. Beta-sheet and beta-barrel.  

PubMed Central

Low-frequency internal motions in protein molecules play a key role in biological functions. Based on previous work with alpha-helical structure, the quasi-continuum model is extended to the beta-structure, another fundamental element in protein molecules. In terms of the equations derived here, one can easily calculate the low-frequency wave number of a beta-sheet in an accordionlike motion, and the low-frequency wave number of a beta-barrel in a breathing motion. The calculated results for immunoglobulin G and concanavalin A agree well with the observations. These findings further verify that the observed low-frequency motion (or the so-called dominant low-frequency mode) in a protein molecule is essentially governed by the collective fluctuations of its weak bonds, especially hydrogen bonds, and the internal displacement of the massive atoms therein, as described by the quasi-continuum model.

Chou, K C

1985-01-01

17

Cooperative deformation of hydrogen bonds in beta-strands and beta-sheet nanocrystals  

NASA Astrophysics Data System (ADS)

Beta-sheet protein domains are stabilized by weak hydrogen bonds, yet materials such as silk—whose ultimate tensile strength is controlled primarily by this secondary structure—can exceed the ultimate tensile strength of steel. Earlier work has suggested that this is because hydrogen bonds deform cooperatively within small protein domains to reach the maximum strength. Here we study the atomistic mechanism of this concerted deformation mechanism by applying an elastic structural model, used to solve the deformation field of the chemical bonds in beta-sheet nanostructures under stretching and thereby identify the number of hydrogen bonds that deform cooperatively. Through this analysis, we predict the optimal beta-strand and beta-sheet nanocrystal size associated with reaching the maximum usage of hydrogen bonds under loading applied per unit material volume. Our results, albeit based on a simple model and analytical equations, quantitatively agree with results based on experimental and molecular-dynamics studies and provide physical insight into the underlying molecular mechanisms of weak bond cooperativity. A comparison with the size of hydrogen bond clusters in biology reveals excellent agreement with the cluster sizes predicted by our analysis, suggesting that perhaps the confinement of hydrogen bonds into nanoscale elements is a universal biological design paradigm that turns weakness to strength. The parameters used in this study could be modified and applied to other protein and polymer structures, which imply potential applications of our model in understanding the physics of deformation and failure in a broader range of biological and polymer materials, as well as in de novo biomaterial design.

Qin, Zhao; Buehler, Markus J.

2010-12-01

18

Numerical simulation of current sheet formation in a quasiseparatrix layer using adaptive mesh refinement  

SciTech Connect

The formation of a thin current sheet in a magnetic quasiseparatrix layer (QSL) is investigated by means of numerical simulation using a simplified ideal, low-{beta}, MHD model. The initial configuration and driving boundary conditions are relevant to phenomena observed in the solar corona and were studied earlier by Aulanier et al. [Astron. Astrophys. 444, 961 (2005)]. In extension to that work, we use the technique of adaptive mesh refinement (AMR) to significantly enhance the local spatial resolution of the current sheet during its formation, which enables us to follow the evolution into a later stage. Our simulations are in good agreement with the results of Aulanier et al. up to the calculated time in that work. In a later phase, we observe a basically unarrested collapse of the sheet to length scales that are more than one order of magnitude smaller than those reported earlier. The current density attains correspondingly larger maximum values within the sheet. During this thinning process, which is finally limited by lack of resolution even in the AMR studies, the current sheet moves upward, following a global expansion of the magnetic structure during the quasistatic evolution. The sheet is locally one-dimensional and the plasma flow in its vicinity, when transformed into a comoving frame, qualitatively resembles a stagnation point flow. In conclusion, our simulations support the idea that extremely high current densities are generated in the vicinities of QSLs as a response to external perturbations, with no sign of saturation.

Effenberger, Frederic [Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Thust, Kay; Grauer, Rainer; Dreher, Juergen [Theoretische Physik I, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Arnold, Lukas [Institute for Advanced Simulation, Forschungszentrum Juelich, D-52425 Juelich (Germany)

2011-03-15

19

A nonlinear approximation for vortex sheet evolution and singularity formation  

NASA Astrophysics Data System (ADS)

The evolution of a vortex sheet in two-dimensional, incompressible, inviscid flow is governed by the integro-differential equation of Birkhoff-Rott. We derive a simple approximation for vortex sheet evolution, consisting of a system of four first-order differential equations. This approximate system has the advantage of involving only local operators. The errors in the approximation are shown to be relatively small even if the sheet has infinite curvature at a point. For the approximate equations, exact similarity solutions exhibiting singularity formation are constructed. Research supported by the National Science Foundation and the Alfred P. Sloan Foundation.

Caflisch, Russel E.; Semmes, Stephen

1990-03-01

20

Spangle formation in galvanized sheet steel coatings  

NASA Astrophysics Data System (ADS)

Very large grains, termed “spangles,” are produced on galvanized sheet steel coatings when lead is added to the zinc bath. The spangles have been attributed to melt undercooling prior to solidification. The present results indicate this is not the case, undercooling being less than 1 °C. The spangle diameter is shown to be dependent on the alloy addition to the bath, large spangles being obtained with Bi and Sb as well as Pb. The spangle size is related to the surface tension of the alloying addition, the size decreasing as the melt vapor surface tension of the alloying element increases. It is proposed that spangles form dendritically from a nucleus in the melt. Alloy additions with low interfacial energies and very limited solid solubility are highly concentrated ahead of the dendrite tip. This decreases the tip radius and increases the dendrite velocity, producing large grains. The basal plane orientation of the samples varies between 17 and 80 deg with respect to the steel sheet surface, which is inconsistent with basal plane dendritic growth in Zn along (1010) directions. It is proposed that solute additions to the melt and growth in a thin liquid layer can modify the dendrite growth direction, accounting for the spangle orientation.

Fasoyinu, F. A.; Weinberg, F.

1990-06-01

21

Folding mechanism of three structurally similar beta-sheet proteins.  

PubMed

The folding mechanism of cellular retinoic acid binding protein I (CRABP I), cellular retinol binding protein II (CRBP II), and intestinal fatty acid binding protein (IFABP) were investigated to determine if proteins with similar native structures have similar folding mechanisms. These mostly beta-sheet proteins have very similar structures, despite having as little as 33% sequence similarity. The reversible urea denaturation of these proteins was characterized at equilibrium by circular dichroism and fluorescence. The data were best fit by a two-state model for each of these proteins, suggesting that no significant population of folding intermediates were present at equilibrium. The native states were of similar stability with free energies (linearly extrapolated to 0 M urea, deltaGH2O) of 6.5, 8.3, and 5.5 kcal/mole for CRABP I, CRBP II, and IFABP, respectively. The kinetics of the folding and unfolding processes for these proteins was monitored by stopped-flow CD and fluorescence. Intermediates were observed during both the folding and unfolding of all of these proteins. However, the overall rates of folding and unfolding differed by nearly three orders of magnitude. Further, the spectroscopic properties of the intermediate states were different for each protein, suggesting that different amounts of secondary and/or tertiary structure were associated with each intermediate state for each protein. These data show that the folding path for proteins in the same structural family can be quite different, and provide evidence for different folding landscapes for these sequences. PMID:9741849

Burns, L L; Dalessio, P M; Ropson, I J

1998-10-01

22

On spontaneous formation of current sheets: Untwisted magnetic fields  

SciTech Connect

This is a study of the spontaneous formation of electric current sheets in an incompressible viscous fluid with perfect electrical conductivity, governed by the magnetohydrodynamic Navier-Stokes equations. Numerical solutions to two initial value problems are presented for a three-dimensional, periodic, untwisted magnetic field evolving, with no change in magnetic topology under the frozen-in condition and at characteristic fluid Reynolds numbers of the order of 500, from a nonequilibrium initial state with the fluid at rest. The evolution converts magnetic free energy into kinetic energy to be all dissipated away by viscosity so that the field settles into a minimum-energy, static equilibrium. The solutions demonstrate that, as a consequence of the frozen-in condition, current sheets must form during the evolution despite the geometric simplicity of the prescribed initial fields. In addition to the current sheets associated with magnetic neutral points and field reversal layers, other sheets not associated with such magnetic features are also in evidence. These current sheets form on magnetic flux surfaces. This property is used to achieve a high degree of the frozen-in condition in the simulations, by describing the magnetic field entirely in terms of the advection of its flux surfaces and integrating the resulting governing equations with a customized version of a general-purpose high-resolution (viz., nonoscillatory) hydrodynamical simulation code EULAG [J. M. Prusa et al., Comput. Fluids 37, 1193 (2008)]. Incompressibility imposes the additional global constraint that the flux surfaces must evolve with no change in the spatial volumes they enclose. In this approach, current sheet formation is demonstrated graphically by the progressive pressing together of suitably selected flux surfaces until their separation has diminished below the minimal resolved distance on a fixed grid. The frozen-in condition then fails in the simulation as the field reconnects through an effecting numerical resistivity. The principal results are related to the Parker theory of current-sheet formation and dissipation in the solar corona.

Bhattacharyya, R. [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur-313001 (India); National Center for Atmospheric Research, P.O. Box 3000, Boulder, Colorado 80307 (United States); Low, B. C.; Smolarkiewicz, P. K. [National Center for Atmospheric Research, P.O. Box 3000, Boulder, Colorado 80307 (United States)

2010-11-15

23

On spontaneous formation of current sheets: Untwisted magnetic fields  

NASA Astrophysics Data System (ADS)

This is a study of the spontaneous formation of electric current sheets in an incompressible viscous fluid with perfect electrical conductivity, governed by the magnetohydrodynamic Navier-Stokes equations. Numerical solutions to two initial value problems are presented for a three-dimensional, periodic, untwisted magnetic field evolving, with no change in magnetic topology under the frozen-in condition and at characteristic fluid Reynolds numbers of the order of 500, from a nonequilibrium initial state with the fluid at rest. The evolution converts magnetic free energy into kinetic energy to be all dissipated away by viscosity so that the field settles into a minimum-energy, static equilibrium. The solutions demonstrate that, as a consequence of the frozen-in condition, current sheets must form during the evolution despite the geometric simplicity of the prescribed initial fields. In addition to the current sheets associated with magnetic neutral points and field reversal layers, other sheets not associated with such magnetic features are also in evidence. These current sheets form on magnetic flux surfaces. This property is used to achieve a high degree of the frozen-in condition in the simulations, by describing the magnetic field entirely in terms of the advection of its flux surfaces and integrating the resulting governing equations with a customized version of a general-purpose high-resolution (viz., nonoscillatory) hydrodynamical simulation code EULAG [J. M. Prusa et al., Comput. Fluids 37, 1193 (2008)]. Incompressibility imposes the additional global constraint that the flux surfaces must evolve with no change in the spatial volumes they enclose. In this approach, current sheet formation is demonstrated graphically by the progressive pressing together of suitably selected flux surfaces until their separation has diminished below the minimal resolved distance on a fixed grid. The frozen-in condition then fails in the simulation as the field reconnects through an effecting numerical resistivity. The principal results are related to the Parker theory of current-sheet formation and dissipation in the solar corona.

Bhattacharyya, R.; Low, B. C.; Smolarkiewicz, P. K.

2010-11-01

24

Formation of Current Sheets in Two-dimensional Geometry  

NASA Astrophysics Data System (ADS)

We present two examples of current sheets that form in a magnetic configuration when it is subjected to quasi-static motions at the footpoints. The entire system is two-dimensional. There are no preexisting X-points and the footpoint motions are continuous. The calculations are motivated by the hypothesis of Parker that quasi-static deformations of MHD equilibria are generally accompanied by the formation of current sheets. The results demonstrate that three dimensions are not a necessary condition for current sheet formation. In addition, the calculation of Van Ballegooijen is not contradicted, because the initial magnetic field in our case is not dominantly collinear. Possible applications to the solar corona are discussed.

Scheper, R. A.; Hassam, A. B.

1998-11-01

25

Plasmoid Formation in Current Sheet with Finite Normal Magnetic Component  

NASA Astrophysics Data System (ADS)

Current sheet configurations in natural and laboratory plasmas are often accompanied by a finite normal magnetic component that is known to stabilize the two-dimensional resistive tearing instability in the high Lundquist number regime. Recent magnetohydrodynamic simulations indicate that the nonlinear development of ballooning instability is able to induce the formation of X lines and plasmoids in a generalized Harris sheet with a finite normal magnetic component in the high Lundquist number regime where the linear two-dimensional resistive tearing mode is stable.

Zhu, P.; Raeder, J.

2013-06-01

26

Hydrophobic interactions and hydrogen bonds in ?-sheet formation  

NASA Astrophysics Data System (ADS)

In this study, we investigate interactions of extended conformations of homodimeric peptides made of small (glycine or alanine) and large hydrophobic (valine or leucine) sidechains using all-atom molecular dynamics simulations to decipher driving forces for ?-sheet formation. We make use of a periodic boundary condition setup in which individual peptides are infinitely long and stretched. Dimers adopt ?-sheet conformations at short interpeptide distances (? ~ 0.5 nm) and at intermediate distances (~0.8 nm), valine and leucine homodimers assume cross-?-like conformations with side chains interpenetrating each other. These two states are identified as minima in the potential of mean force. While the number of interpeptide hydrogen bonds increases with decreasing interpeptide distance, the total hydrogen bond number in the system does not change significantly, suggesting that formation of ?-sheet structures from extended conformations is not driven by hydrogen bonds. This is supported by an increase in electrostatic energy at short interpeptide distances. A remarkable correlation between the volume of the system and the total electrostatic energy is observed, further reinforcing the idea that excluding water in proteins comes with an enthalpic penalty. We also discuss microscopic mechanisms accounting for ?-sheet formation based on computed enthalpy and entropy and we show that they are different for peptides with small and large side chains.

Narayanan, Chitra; Dias, Cristiano L.

2013-09-01

27

Structural patterns in alpha helices and beta sheets in globular proteins.  

PubMed

Secondary structural elements like alpha-helix and beta-sheet constitute the major components of proteins. Here we present a systematic position wise analysis of the structural and sequence characteristics of alpha-helices and beta-sheets. Helix and sheet are found to follow a complementary distribution pattern along the protein chain length. We have calculated the conformational parameters of the amino acids forming helices and sheets. Other properties like hydrophobicity, temperature-factor and relative entropy are found to be correlated with the distribution pattern of these secondary structures. This gives an insight about the conservation or variation of the secondary structure in proteins, which may have significant implications on de novo protein design. PMID:19689422

Bhattacharjee, Nicholus; Biswas, Parbati

2009-01-01

28

Kinetic studies of inhibition of the amyloid beta (1-42) aggregation using a ferrocene-tagged ?-sheet breaker peptide.  

PubMed

The aggregation of amyloidogenic proteins/peptides has been closely linked to the neuropathology of several important neurological disorders. In Alzheimer's disease, amyloid beta (A?) peptides and their aggregation are believed to be at least partially responsible for the etiology of Alzheimer's disease. The aggregate-inflicted cellular toxicity can be inhibited by short peptides whose sequences are homologous to segments of the A?(1-42) peptide responsible for ?-sheet stacking (referred to as the ?-sheet breaker peptides). Here, a water-soluble ferrocene (Fc)-tagged ?-sheet breaker peptide, Fc-KLVFFK(6), was used as an electrochemical probe for kinetic studies of the inhibition of the A?(1-42) fibrillation process and for determination of the optimal concentration of ?-sheet breaker peptide for efficient inhibition. Our results demonstrate that Fc-KLVFFK(6) interacts with the A? aggregates instantaneously in solution, and a sub-stoichiometric amount of Fc-KLVFFK(6) is sufficient to inhibit the formation of the A? oligomers and fibrils and to reduce the toxicity of A?(1-42). The interaction between Fc-KLVFFK(6) and A?(1-42) follows a pseudo-first-order reaction, with a rate constant of 1.89 ± 0.05 × 10(-4) s(-1). Tagging ?-sheet breaker peptides with a redox label facilitates design, screening, and rational use of peptidic inhibitors for impeding/altering A? aggregation. PMID:23232068

Zhang, Lin; Yagnik, Gargey; Peng, Yong; Wang, Jianxiu; Xu, H Howard; Hao, Yuanqiang; Liu, You-Nian; Zhou, Feimeng

2012-12-08

29

Osteogenic matrix sheet-cell transplantation using osteoblastic cell sheet resulted in bone formation without scaffold at an ectopic site.  

PubMed

We previously reported that in vivo bone formation could be observed in composites of porous hydroxyapatite (HA) scaffolds and cultured mesenchymal stem cells (MSCs). In the present study, we developed a new method for transplantation of cultured MSCs without the necessity of using a scaffold to form bone tissue. MSCs were culture-expanded and lifted as cell sheet structures. These cell sheets, designated osteogenic matrix sheets, showed positive alkaline phosphatase (ALP) staining, high ALP activities and high osteocalcin (OC) contents, indicating their osteogenic potential. We transplanted these sheets into subcutaneous sites in rats to assess whether they possessed in vivo bone-forming capability. The transplanted sheets showed mineralized matrix together with osteocytes and an active osteoblast lining, indicating new bone formation, at 6 weeks after transplantation. HA scaffolds were also wrapped with the sheets to make HA/sheet composites and implanted into subcutaneous sites in rats. Histological sections of the composites revealed bone formation in the HA pores at 4 weeks after implantation. Our present results indicate that MSCs can be cultured as sheet structures, and the resulting sheets themselves or HA-sheet composites represent osteogenic implants that can be used for hard tissue reconstruction. PMID:18493911

Akahane, Manabu; Nakamura, Akifumi; Ohgushi, Hajime; Shigematsu, Hideki; Dohi, Yoshiko; Takakura, Yoshinori

2008-06-01

30

Laminated Morphology of Nontwisting beta-Sheet Fibrilis Constructed via Peptide Self-Assembly  

SciTech Connect

A synthetic peptide has been de novo designed that self-assembles into {beta}-sheet fibrils exhibiting a nontwisted, stacked morphology. The stacked morphology is constituted by 2.5 nm wide filaments that laterally associate to form flat fibril laminates exceeding 50 nm in width and micrometers in length. The height of each fibril is limited to the length of exactly one peptide monomer in an extended {beta}-strand conformation, approximately 7 nm. Once assembled, these highly ordered, 2-D structures are stable over a wide range of pH and temperature and exhibit characteristics similar to those of amyloid fibrils. Furthermore, the rate of assembly and degree of fibril lamination can be controlled with kinetic parameters of pH and temperature. Finally, the presence of a diproline peptide between two {beta}-sheet-forming strands in the peptide sequence is demonstrated to be an important factor in promoting the nontwisting, laminated fibril morphology.

Lamm,M.; Rajagopal, K.; Schneider, J.; Pochan, D.

2005-01-01

31

High-beta plasma blobs in the morningside plasma sheet  

NASA Astrophysics Data System (ADS)

Equator-S frequently encountered, i.e. on 30% of the orbits between 1 March and 17 April 1998, strong variations of the magnetic field strength of typically 5-15-min duration outside about 9RE during the late-night/early-morning hours. Very high-plasma beta values were found, varying between 1 and 10 or more. Close conjunctions between Equator-S and Geotail revealed the spatial structure of these plasma blobs and their lifetime. They are typically 5-10° wide in longitude and have an antisymmetric plasma or magnetic pressure distribution with respect to the equator, while being altogether low-latitude phenomena (< 15°). They drift slowly sunward, exchange plasma across the equator and have a lifetime of at least 15-30 min. While their spatial structure may be due to some sort of mirror instability, little is known about the origin of the high-beta plasma. It is speculated that the morningside boundary layer somewhat further tailward may be the source of this plasma. This would be consistent with the preference of the plasma blobs to occur during quiet conditions, although they are also found during substorm periods. The relation to auroral phenomena in the morningside oval is uncertain. The energy deposition may be mostly too weak to generate a visible signature. However, patchy aurora remains a candidate for more disturbed periods.

Haerendel, G.; Baumjohann, W.; Georgescu, E.; Nakamura, R.; Kistler, L. M.; Klecker, B.; Kucharek, H.; Vaivads, A.; Mukai, T.; Kokubun, S.

1999-12-01

32

Vibrational coupling, isotopic editing, and beta-sheet structure in a membrane-bound polypeptide.  

PubMed

The N-acetylated hexapeptide WLLLLL (AcWL5) partitions into lipid membranes and is believed to assemble into an antiparallel beta-sheet. As a test of this structural assignment, the peptide bonds of residues 2-6 were labeled with (13)C and allowed to adsorb onto a supported lipid membrane. Peptides bound to the membrane were examined for evidence of coupling between the labeled vibrational modes in adjacent beta-strands with internal reflection infrared spectroscopy. Experimental results indicate that the amide I absorption band in D(2)O (i.e., amide I') attributable to (13)C is selectively enhanced when the label is at any one of several positions along the peptide backbone. Simulations employing an excitonic model with through-bond and through-space interactions were performed on AcWL5 models in parallel and antiparallel beta-sheet configurations. The simulations yield spectra in good agreement with the experimental results, accounting for the enhancement of both (13)C band intensities and band frequencies. They also yield insight into the physical origin and structure selectivity of the distinctive amide I' band shapes that arise in isotopically edited spectra. It is concluded that the beta-sheet formed by membrane-bound AcWL5 is indeed antiparallel, and the enhancement of (13)C bands in the infrared spectra of these peptides is caused by both interstrand and intrastrand coupling to (12)C modes. PMID:15125676

Paul, Cynthia; Wang, Jianping; Wimley, William C; Hochstrasser, Robin M; Axelsen, Paul H

2004-05-12

33

Assembly dynamics of two-beta sheets revealed by molecular dynamics simulations.  

PubMed

The assembly dynamics of two beta sheets with different initial separation distances are explored by multiple all-atom molecular dynamics simulations with the presence of explicit water solvent. The beta sheet is composed of seven identical peptides in an antiparallel fashion. The peptide sequence is the 20-29 segment of human Islet amyloid polypeptide. Our simulations show that the assembly occurs not only in the lateral direction but also along the longitudinal direction, which provides a new insight into the assembly pathway at the early stage of fibril elongation. Based on Poisson-Boltzmann free energy analysis and quasiharmonic configuration entropy estimation, the entropic contribution is found to play an important role in the longitudinal assembly. Moreover, a possible oligomeric state with cyclic form is suggested based on one assembly model found in the simulations, illustrating the polymorphic nature of aggregation of the amyloidogenic peptide. PMID:19405618

Xu, Weixin; Ping, Jiang; Li, Weifeng; Mu, Yuguang

2009-04-28

34

Conformational diversity in prion protein variants influences intermolecular ?-sheet formation  

PubMed Central

A conformational transition of normal cellular prion protein (PrPC) to its pathogenic form (PrPSc) is believed to be a central event in the transmission of the devastating neurological diseases known as spongiform encephalopathies. The common methionine/valine polymorphism at residue 129 in the PrP influences disease susceptibility and phenotype. We report here seven crystal structures of human PrP variants: three of wild-type (WT) PrP containing V129, and four of the familial variants D178N and F198S, containing either M129 or V129. Comparison of these structures with each other and with previously published WT PrP structures containing M129 revealed that only WT PrPs were found to crystallize as domain-swapped dimers or closed monomers; the four mutant PrPs crystallized as non-swapped dimers. Three of the four mutant PrPs aligned to form intermolecular ?-sheets. Several regions of structural variability were identified, and analysis of their conformations provides an explanation for the structural features, which can influence the formation and conformation of intermolecular ?-sheets involving the M/V129 polymorphic residue.

Lee, Seungjoo; Antony, Lizamma; Hartmann, Rune; Knaus, Karen J; Surewicz, Krystyna; Surewicz, Witold K; Yee, Vivien C

2010-01-01

35

Helix versus sheet formation in a small peptide  

NASA Astrophysics Data System (ADS)

Segments with the amino acid sequence EKAYLRT (glutamine-lysine-alanine-tyrosine-leucine-arginine-threonine) appear in naturally occurring proteins both in ?-helices and ?-sheets. For this reason, we have used this peptide to study how secondary structure formation in proteins depends on the local environment. Our data rely on multicanonical Monte Carlo simulations where the interactions among all atoms are taken into account. Results in gas phase are compared with that in an implicit solvent. We find that both the solvated molecule and EKAYLRT in gas phase form an ?-helix when not interacting with other molecules. However, in the vicinity of a ?-strand, the peptide forms a ?-strand. Because of this change in secondary structure our peptide may provide a simple model for the ??? transition that is supposedly related to the outbreak of prion diseases and similar illnesses.

Peng, Yong; Hansmann, Ulrich H.

2003-10-01

36

A new way of testing paper sheet formation  

Microsoft Academic Search

The mechanical properties of a paper sheet depend on the nature of the fibres, the bonding between the fibres and their distribution within the sheet. The information presented in this work is based on measurements made with a sensor that simultaneously measures basis-weight, anisotropy and dominant fibre orientation in paper sheets. This instrument uses a non-destructive process and works at

B Drouin; R Gagnon; Chamrong Cheam; Jacques Silvy

2001-01-01

37

Singularity formation and nonlinear evolution of a viscous vortex sheet model  

NASA Astrophysics Data System (ADS)

We study Dhanak's model [J. Fluid Mech. 269, 265 (1994)] of a viscous vortex sheet in the sharp limit, to investigate singularity formations and present nonlinear evolutions of the sheets. The finite-time singularity does not disappear by giving viscosity to the vortex sheet, but is delayed. The singularity in the sharp viscous vortex sheet is found to be different from that of the inviscid sheet in several features. A discontinuity in the curvature is formed in the viscous sheet, similarly as the inviscid sheet, but a cusp in the vortex sheet strength is less sharpened by viscosity. Exponential decay of the Fourier amplitudes is lost by the formation of the singularity, and the amplitudes of high wavenumbers exhibit an algebraic decay, while in the inviscid vortex sheet, the algebraic decay of the Fourier amplitudes is valid from fairly small wavenumbers. The algebraic decay rate of the viscous vortex sheet is approximately -2.5, independent of viscosity, which is the same rate as the asymptotic analysis of the inviscid sheet. Results for evolutions of the regularized vortex sheets show that the roll-up is weakened by viscosity, and the regularization parameter has more significant effects on the fine-structure of the core than does viscosity.

Sohn, Sung-Ik

2013-01-01

38

Investigation of genetically-engineered beta-sheet polypeptides for nanoelectronics  

NASA Astrophysics Data System (ADS)

Ongoing miniaturization in integrated circuit (IC) device fabrication via conventional lithography faces increasing technical challenges and imposes significant performance limitations on devices and interconnects stemming from the fundamental physics of electron transport. This drives the need to explore other nanofabrication approaches, such as self-assembly, and alternate device or interconnect structures with novel electron transport mechanisms, such as ballistic electron transport. Molecular self-assembly, ubiquitous in biology and bio-inspired materials, might have tremendous potential for nanoelectronic applications. Specifically, genetically-engineered beta-sheet polypeptides offer certain key attributes for nanoelectronic applications. These attributes include: controllable self-assembly, potential to form one dimensional quantum channels for ballistic electron transport, and substrate-specific interactions for interfacial engineering. This dissertation explores and evaluates the nanowire self-assembly characteristics of several de novo genetically-engineered beta-sheet polypeptides (synthesized by our group) on various substrates for applications in nanoelectronic interconnect schemes. In addition, substrate-attachment of the beta-sheet polypeptide nanowire structures is investigated and preliminary electrical testing of a polypeptide nanowire fibril is presented. Chapters 1 and 2 provide an overall introduction and discuss the characterization techniques utilized in the experimental work. Chapter 3 describes a detailed self-assembly study of various polypeptides and documents the formulation and deposition of controlled, linear self-assemblies of polypeptides. It was determined that control of the concentration and deposition-time enables the deposition of linear ordered polypeptide assemblies on substrates. A predominance of bilayer stacking of polypeptide sheets in the solution-formed linear assemblies has been observed. Template-directed self-assembly of linear polypeptide assemblies has also been documented on graphite surfaces. This has demonstrated the potential for epitaxial or template-directed ordering of polypeptides on substrates for potential nanoelectronic applications. Chapter 4 describes an adhesion study of polypeptide nanostructures on various substrates. A forced-scanning methodology based on atomic force microscopy was employed and used to identify specific (covalent) and non-specific (physisorbed) interactions of the polypeptide to a variety of substrates. This information is important for substrate and electrode attachment of polypeptides for nanoelectronic applications. Chapter 5 presents the results of scanning tunneling microscopy of polypeptide monolayers on graphite and theoretical charge density calculations. These results confirm that this polypeptide exhibits a beta-sheet conformation on the graphite substrate.

Rana, Narender

39

Factors contributing to decreased protein stability when aspartic acid residues are in {beta}-sheet regions.  

SciTech Connect

Asp residues are significantly under represented in {beta}-sheet regions of proteins, especially in the middle of {beta}-strands, as found by a number of studies using statistical, modeling, or experimental methods. To further understand the reasons for this under representation of Asp, we prepared and analyzed mutants of a {beta}-domain. Two Gln residues of the immunoglobulin light-chain variable domain (V{sub L}) of protein Len were replaced with Asp, and then the effects of these changes on protein stability and protein structure were studied. The replacement of Q38D, located at the end of a {beta}-strand, and that of Q89D, located in the middle of a {beta}-strand, reduced the stability of the parent immunoglobulin VL domain by 2.0 kcal/mol and 5.3 kcal/mol, respectively. Because the Q89D mutant of the wild-type V{sub L}-Len domain was too unstable to be expressed as a soluble protein, we prepared the Q89D mutant in a triple mutant background, V{sub L}-Len M4L/Y27dD/T94H, which was 4.2 kcal/mol more stable than the wild-type V{sub L}-Len domain. The structures of mutants V{sub L}-Len Q38D and V{sub L}-Len Q89D/M4L/Y27dD/T94H were determined by X-ray diffraction at 1.6 A resolution. We found no major perturbances in the structures of these QD mutant proteins relative to structures of the parent proteins. The observed stability changes have to be accounted for by cumulative effects of the following several factors: (1) by changes in main-chain dihedral angles and in side-chain rotomers, (2) by close contacts between some atoms, and, most significantly, (3) by the unfavorable electrostatic interactions between the Asp side chain and the carbonyls of the main chain. We show that the Asn side chain, which is of similar size but neutral, is less destabilizing. The detrimental effect of Asp within a {beta}-sheet of an immunoglobulin-type domain can have very serious consequences. A somatic mutation of a {beta}-strand residue to Asp could prevent the expression of the domain both in vitro and in vivo, or it could contribute to the pathogenic potential of the protein in vivo.

Pokkuluri, P. R.; Cai, X.; Raffen, R.; Gu, M.; Stevens, F. J.; Schiffer, M.

2002-07-01

40

Singularity formation for vortex sheets and hyperbolic equations  

NASA Astrophysics Data System (ADS)

Singularities are expected to occur in a variety of inviscid incompressible flows, the simplest being on a vortex sheet just preceding roll-up of the sheet. We present a new approach to the vortex sheet problem, in which the Birkhoff-Rott equation is approximated by a system of first order non-linear pde's. The system is solved in an analytic function setting, and singularities occur as branch points for the solution. In this paper, the general method is applied to Burger's equation and to the short time existence problem for a 2x2 system with initial singularities.

Caflisch, Russel E.

41

Strength limit of entropic elasticity in beta-sheet protein domains  

NASA Astrophysics Data System (ADS)

Elasticity and strength of individual beta-sheet protein domains govern key biological functions and the mechanical properties of biopolymers including spider silk, amyloids, and muscle fibers. The worm-like-chain (WLC) model is commonly used to describe the entropic elasticity of polypeptides and other biomolecules. However, force spectroscopy experiments have shown pronounced deviations from the ideal WLC behavior, leading to controversial views about the appropriate elastic description of proteins at nanoscale. Here we report a simple model that explains the physical mechanism that leads to the breakdown of the WLC idealization in experiments by using only two generic parameters of the protein domain, the H-bond energy and the protein backbone’s persistence length. We show that a rupture initiation condition characterized by the free energy release rate of H-bonds characterizes the limit of WLC entropic elasticity of beta-sheet protein domains and the onset of rupture. Our findings reveal that strength and elasticity are coupled and cannot be treated separately. The predictions of the model are compared with atomic force microscopy experiments of protein rupture.

Keten, Sinan; Buehler, Markus J.

2008-12-01

42

Joint cartilage formation induced by silastic sheet spacer.  

PubMed

In an experimental study in rabbits the effect on articular cartilage regeneration from subchondral bone induced by a temporary interposed silicone rubber sheet has been analyzed. The normal articular cartilage of the medial condyle of the femur was resected and the subchondral bone surface covered by a 2 mm thick Silastic sheet which was removed after 2 months. At that time cartilaginous tissue of a hyalin appearance was found to cover the resected surface. As early as one month after removal of the sheet this cartilage showed obvious signs of degeneration and a few months later no regenerating cartilage was left. It is concluded that in this study there is no experimental evidence supporting the idea that temporary interposition of a silicone rubber sheet is beneficial in the treatment of degenerative arthritis. PMID:7156903

Engkvist, O; af Ekenstam, F

1982-01-01

43

Collective behavior in two-dimensional biological systems: Receptor clustering and beta-sheet aggregation  

NASA Astrophysics Data System (ADS)

We studied two particular biomedical systems which exhibit collective molecular behavior. One is clustering of tumor necrosis factor receptor I (TNFR1), and another is ?-sheet folding and aggregation. Receptor clustering has been shown to be a crucial step in many signaling events but its biological meaning has not been adequately addressed. Here, via a simple lattice model, we show how cells use this clustering machinery to enhance sensitivity as well as robustness. On the other hand, intracellular deposition of aggregated protein rich in ?-sheet is a prominent cytopathological feature of most neurodegenerative diseases. How this aggregation occurs and how it responds to therapy is not completely understood. Here, we started from a reconstruction of the H-bond potential and carry out a full investigation of ?-sheet thermodynamics as well as kinetics. We show that ?-sheet aggregation is most likely due to molecular stacking and found that the minimal length of an aggregate mutant polymer corresponds well with the number observed in adult Huntington's disease. We have also shown that molecular agents such as dendrimers might fail at high-dose therapy; instead, a potential therapy strategy is to block ?-turn formation. Our predictions can be used for future experimental tests and clinical trials.

Guo, Chinlin

44

Occurrence, formation and function of organic sheets in the mineral tube structures of serpulidae (polychaeta, annelida).  

PubMed

A scanning electron microscopy study of organic sheets in serpulid tube mineral structures was carried out to discern their function, formation and evolution. The organic sheets may have some taxonomic value in distinguishing the two major clades of serpulids previously identified. The organic sheets in the mineral tube structure occur only in certain taxa belonging to clade A, but not all species in clade A have them. Organic sheets are best developed in genus Spirobranchus. One could speculate that organic sheets have evolved as an adaption to further strengthen the mechanical properties of the tubes in clade A, which contains serpulids with the most advanced mineral tube microstructures. The organic sheets are presumably secreted with at least some mineral phase. PMID:24116035

Vinn, Olev

2013-10-07

45

Occurrence, Formation and Function of Organic Sheets in the Mineral Tube Structures of Serpulidae (Polychaeta, Annelida)  

PubMed Central

A scanning electron microscopy study of organic sheets in serpulid tube mineral structures was carried out to discern their function, formation and evolution. The organic sheets may have some taxonomic value in distinguishing the two major clades of serpulids previously identified. The organic sheets in the mineral tube structure occur only in certain taxa belonging to clade A, but not all species in clade A have them. Organic sheets are best developed in genus Spirobranchus. One could speculate that organic sheets have evolved as an adaption to further strengthen the mechanical properties of the tubes in clade A, which contains serpulids with the most advanced mineral tube microstructures. The organic sheets are presumably secreted with at least some mineral phase.

Vinn, Olev

2013-01-01

46

Current Sheet Formation and Reconnection Dynamics in the Closed Corona Due to Intragranular Flow Lanes  

NASA Astrophysics Data System (ADS)

Current sheet formation and reconnection have been shown to be very important processes in coronal heating and dynamics. The formation of current discontinuities and therefore the reconnection dynamics in a low-beta, force-free system depend on two major influences: the structure of the driving flow fields, and the overall magnetic field geometry. Photospheric magnetograms show magnetic field footpoint elements moving along intragranular flow lanes. The magnetic field undergoes a major expansion as it passes from the photosphere, through the chromosphere, into the corona. We model this field expansion geometry and intragranular flow lanes with an initially analytic potential field. We simulate the closed corona using the Parker ansatz of line-tying the field at the upper and lower boundaries. The flows imposed at the photosphere are confined to two relatively thin lanes marking the footprints of the expanding field. We calculate the system evolution in fully 3D MHD, finding the current discontinuities forming along the topological separatricies of the magnetic field, as well as quasi-separatrix layers forming with the large velocity gradients - exactly as expected. Reconnection occurs across the current discontinuities, shifting flux between the different domains, reducing the free magnetic energy, while increasing the field complexity. The injected stresses do not accumulate significantly before reconnection, thus there are no major explosive energy release, only an average steady dissipation.

Edmondson, J. K.; Velli, M. M.; DeVore, C. R.

2010-12-01

47

Cold Dense Plasma Sheet Formation During Northward IMF  

NASA Astrophysics Data System (ADS)

A cold, dense plasma sheet (CDPS) is often observed when the IMF has been northward for an extended time period, usually several hours. One such period occurred October 22/23, 2003. During that period the IMF was strongly northward for approximately 36 hours, while Cluster II observed a cold dense plasma sheet. We present detailed global simulation results for this event that show how the CDPS develops due to lobe reconnection, which causes IMF flux tubes to be captured and subsequently convected into the tail, forming the CDPS.

Raeder, J.; Li, W.; Dorelli, J.; Oieroset, M.; Phan, T.

2004-12-01

48

Quantifying the fraction of glycine and alanine in beta-sheet and helical conformations in spider dragline silk using solid-state NMR.  

PubMed

Solid-state two-dimensional refocused INADEQUATE MAS NMR experiments resolve distinct helical and beta-sheet conformational environments for both alanine and glycine in Nephila clavipes dragline silk fibers; the fraction of alanine and glycine in beta-sheet structures is determined to be 82% +/- 4% and 28% +/- 5%, respectively. PMID:18997954

Holland, Gregory P; Jenkins, Janelle E; Creager, Melinda S; Lewis, Randolph V; Yarger, Jeffery L

2008-09-29

49

Shape measurement in sheet metal formation: requirements and solutions  

Microsoft Academic Search

Basically, optical profilometry has a wide spread application potential in sheet metal forming starting at the design stage when models have to be digitized, followed by needs for shape acquisition in tooling technology, and finally in on-line testing during mass production. In particular, deep-drawing of car body components and surface structures of aircrafts put high demands on metrology. In the

Roland Hoefling; Petra Aswendt; Reimund Neugebauer

1999-01-01

50

Current Sheets and Prominence Formation in the Solar Atmosphere  

Microsoft Academic Search

If magnetic field lines in opposite directions expand toward each other to squeeze out the field between them, they come into contact to form an abrupt field reversal (tangential discontinuity) which supports a current sheet. Field line expansion can be caused by the combined pressure gradient and gravity force, the magnetic field pressure gradient force, magnetic fields merging toward each

C. Z. Cheng; G. S. Choe

1998-01-01

51

Pancreatic beta-cell granule peptides form heteromolecular complexes which inhibit islet amyloid polypeptide fibril formation.  

PubMed Central

Islet amyloid polypeptide (IAPP), or 'amylin', is co-stored with insulin in secretory granules of pancreatic islet beta-cells. In Type 2 diabetes, IAPP converts into a beta-sheet conformation and oligomerizes to form amyloid fibrils and islet deposits. Granule components, including insulin, inhibit spontaneous IAPP fibril formation in vitro. To determine the mechanism of this inhibition, molecular interactions of insulin with human IAPP (hIAPP), rat IAPP (rIAPP) and other peptides were examined using surface plasmon resonance (BIAcore), CD and transmission electron microscopy (EM). hIAPP and rIAPP complexed with insulin, and this reaction was concentration-dependent. rIAPP and insulin, but not pro-insulin, bound to hIAPP. Insulin with a truncated B-chain, to prevent dimerization, also bound hIAPP. In the presence of insulin, hIAPP did not spontaneously develop beta-sheet secondary structure or form fibrils. Insulin interacted with pre-formed IAPP fibrils in a regular repeating pattern, as demonstrated by immunoEM, suggesting that the binding sites for insulin remain exposed in hIAPP fibrils. Since rIAPP and hIAPP form complexes with insulin (and each other), this could explain the lack of amyloid fibrils in transgenic mice expressing hIAPP. It is likely that IAPP fibrillogenesis is inhibited in secretory granules (where the hIAPP concentration is in the millimolar range) by heteromolecular complex formation with insulin. Alterations in the proportions of insulin and IAPP in granules could disrupt the stability of the peptide. The increase in the proportion of unprocessed pro-insulin produced in Type 2 diabetes could be a major factor in destabilization of hIAPP and induction of fibril formation.

Jaikaran, Emma T A S; Nilsson, Melanie R; Clark, Anne

2004-01-01

52

Beta toxin catalyzes formation of nucleoprotein matrix in staphylococcal biofilms  

PubMed Central

Biofilms are surface-associated communities of microbes encompassed by an extracellular matrix. It is estimated that 80% of all bacterial infections involve biofilm formation, but the structure and regulation of biofilms are incompletely understood. Extracellular DNA (eDNA) is a major structural component in many biofilms of the pathogenic bacterium Staphylococcus aureus, but its role is enigmatic. Here, we demonstrate that beta toxin, a neutral sphingomyelinase and a virulence factor of S. aureus, forms covalent cross-links to itself in the presence of DNA (we refer to this as biofilm ligase activity, independent of sphingomyelinase activity) producing an insoluble nucleoprotein matrix in vitro. Furthermore, we show that beta toxin strongly stimulates biofilm formation in vivo as demonstrated by a role in causation of infectious endocarditis in a rabbit model. Together, these results suggest that beta toxin cross-linking in the presence of eDNA assists in forming the skeletal framework upon which staphylococcal biofilms are established.

Huseby, Medora J.; Kruse, Andrew C.; Digre, Jeff; Kohler, Petra L.; Vocke, Jillian A.; Mann, Ethan E.; Bayles, Kenneth W.; Bohach, Gregory A.; Schlievert, Patrick M.; Ohlendorf, Douglas H.; Earhart, Cathleen A.

2010-01-01

53

Cooperative alpha-helix formation of beta-lactoglobulin induced by sodium n-alkyl sulfates.  

PubMed

It is generally assumed that folding intermediates contain partially formed native-like secondary structures. However, if we consider the fact that the conformational stability of the intermediate state is simpler than that of the native state, it would be expected that the secondary structures in a folding intermediate would not necessarily be similar to those of the native state. beta-Lactoglobulin is a predominantly beta-sheet protein, although it has a markedly high intrinsic preference for alpha-helical structure. The formation of non-native alpha-helical intermediate of beta-lactoglobulin was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; sodium dodecyl sulfate, SDS; and sodium tetradecyl sulfate, STS at special condition. The effect of n-alkyl sulfates on the structure of native beta-lactoglobulin at pH 2 was utilized to investigate the contribution of hydrophobic interactions to the stability of non-native alpha-helical intermediate. The addition of various concentrations of n-alkyl sulfates to the native state of beta-lactoglobulin (pH 2) appears to support the stabilized form of non-native alpha-helical intermediate at pH 2. The m values of the intermediate state of beta-lactoglobulin by SOS, SDeS, SDS and STS showed substantial variation. The enhancement of m values as the stability criterion of non-native alpha-helical intermediate state corresponded with increasing chain length of the cited n-alkyl sulfates. The present results suggest that the folding reaction of beta-lactoglobulin follows a non-hierarchical mechanism and hydrophobic interactions play important roles in stabilizing the non-native alpha-helical intermediate state. PMID:15996676

Chamani, J; Moosavi-Movahedi, A A; Rajabi, O; Gharanfoli, M; Momen-Heravi, M; Hakimelahi, G H; Neamati-Baghsiah, A; Varasteh, A R

2005-07-05

54

Complex formation between copper. beta. -diketonates and polyoxypropylene glycols  

SciTech Connect

The complex formation between copper (II) dipivaloylmethanate Cu(dpm)/sub 2/ and copper (II) hexafluoroacetylacetonate Cu(hfacac)/sub 2/ and polyoxypropylene glycols (PPG) with molecular masses of 200 and 1050 was studied by spectrophotometry in the visible region and by ESR. The compositions of the complexes (1:1) and the thermodynamic parameters of complex formation were determined. In complexing power Cu(dpm)/sub 2/ is inferior to Cu(hfacac)/sub 2/. Complex formation between Cu(hfacac)/sub 2/ and PPG is accompanied by structural changes in the ..beta..-diketonate.

Nizel'skii, Y.N.; Ishchenko, S.S.

1987-06-01

55

Shape measurement in sheet metal formation: requirements and solutions  

NASA Astrophysics Data System (ADS)

Basically, optical profilometry has a wide spread application potential in sheet metal forming starting at the design stage when models have to be digitized, followed by needs for shape acquisition in tooling technology, and finally in on-line testing during mass production. In particular, deep-drawing of car body components and surface structures of aircrafts put high demands on metrology. In the past, a number of restrictions caused application limits of optical 3D sensing in this field. The paper will show, that object size greater than 1 m, measuring time less than 1 s, vertical resolution less than 10-4 of object size and the capability to work on shining, oil-covered metallic surfaces are key criteria for industrial applications. New approaches are described addressing these practical needs. Based upon high brightness, high contrast pixel by pixel projection equipment (Digital Micromirror Device of Texas Instruments Inc.), algorithms have been developed and tested that meet the objectives named above. Multilevel adaption generates near-to- perfect sinusoidal fringes across the field of view and advanced phase analysis improves both, measuring accuracy and reliability of operation. Fast data acquisition has been obtained by development of sophisticated synchronization hardware. An application example will be given showing surface structures on a large sheet metal part at two different scales of height.

Hoefling, Roland; Aswendt, Petra; Neugebauer, Reimund

1999-09-01

56

Density functional calculations of backbone 15N shielding tensors in beta-sheet and turn residues of protein G  

PubMed Central

Summary We performed density functional calculations of backbone 15N shielding tensors in the regions of beta-sheet and turns of protein G. The calculations were carried out for all twenty-four beta-sheet residues and eight beta-turn residues in the protein GB3 and the results were compared with the available experimental data from solid-state and solution NMR measurements. Together with the alpha-helix data, our calculations cover 39 out of the 55 residues (or 71%) in GB3. The applicability of several computational models developed previously (Cai, Fushman, Kosov, J. Biomol NMR 2009, 45:245-253) to compute 15N shielding tensors of alpha-helical residues is assessed. We show that the proposed quantum chemical computational model is capable of predicting isotropic 15N chemical shifts for an entire protein that are in good correlation with experimental data. However, the individual components of the predicted 15N shielding tensor agree with experiment less well: the computed values show much larger spread than the experimental data, and there is a profound difference in the behavior of the tensor components for alpha-helix/turns and beta-sheet residues. We discuss possible reasons for this.

Cai, Ling; Kosov, Daniel S.; Fushman, David

2011-01-01

57

Numerical simulation of current sheet formation in a quasiseparatrix layer using adaptive mesh refinement  

NASA Astrophysics Data System (ADS)

The formation of a thin current sheet in a magnetic quasiseparatrix layer (QSL) is investigated by means of numerical simulation using a simplified ideal, low-?, MHD model. The initial configuration and driving boundary conditions are relevant to phenomena observed in the solar corona and were studied earlier by Aulanier et al. [Astron. Astrophys. 444, 961 (2005)]. In extension to that work, we use the technique of adaptive mesh refinement (AMR) to significantly enhance the local spatial resolution of the current sheet during its formation, which enables us to follow the evolution into a later stage. Our simulations are in good agreement with the results of Aulanier et al. up to the calculated time in that work. In a later phase, we observe a basically unarrested collapse of the sheet to length scales that are more than one order of magnitude smaller than those reported earlier. The current density attains correspondingly larger maximum values within the sheet. During this thinning process, which is finally limited by lack of resolution even in the AMR studies, the current sheet moves upward, following a global expansion of the magnetic structure during the quasistatic evolution. The sheet is locally one-dimensional and the plasma flow in its vicinity, when transformed into a comoving frame, qualitatively resembles a stagnation point flow. In conclusion, our simulations support the idea that extremely high current densities are generated in the vicinities of QSLs as a response to external perturbations, with no sign of saturation.

Effenberger, Frederic; Thust, Kay; Arnold, Lukas; Grauer, Rainer; Dreher, Jürgen

2011-03-01

58

Relating thin current sheet formation and tail reconnection to substorm development  

SciTech Connect

Observations and simulations have demonstrated the important role of thin current sheet formation and magnetic reconnection in the course of substorms. We discuss new results on the formation of thin current sheets, obtained both within MHD and kinetic theory. They demonstrate when kinetic effects become important and indicate the possibility of a catastrophic onset of substorm dynamics and the potential association with arc brightening. MHD simulations show the role of reconnection in the buildup of the substorm current wedge and the influence of the underlying configuration on the quasi-static and dynamic evolution.

Birn, J. (Joachim); Schindler, K.

2002-01-01

59

Thermal and pH-induced conformational changes of a beta-sheet protein monitored by infrared spectroscopy.  

PubMed

The stability of a lentil lectin, an all-beta protein, has been perturbed by changes in pH and temperature. In the pH interval 5.0 --> 10.0, the overall secondary structure does not undergo significant changes. However, if the individual components of the infrared amide I band are considered, changes in band components attributed to variations in beta-sheet and beta-turns cross-interactions are detected. The combined effects of pH and temperature reveal that the protein is more compact at pH 7.5 with lower denaturation temperatures at pH 5.0 or 10.0, indicating a less stable protein under those conditions. According to our results, the structural stability of the beta-sheet would depend not only on the intermolecular interactions among the strands but also on the conformation of the segments connecting these strands. The protein infrared band assignment has also been examined since the three-dimensional structure of the lentil lectin protein is known from X-ray diffraction studies. Two of the bands observed are attributed to beta-sheet. The one at 1620 cm-1, not affected if the medium is deuterated, is assigned to hairpins composed by two strands connected by a rigid turn whereas that located at 1633 cm-1 corresponds to strands associated by more flexible segments. The band appearing at 1645 cm-1 in H2O corresponds to the open, flexible loops that are connecting the beta-strands. The simplest assumption of the various secondary structure components having identical IR extinction coefficients is enough to provide IR-derived data that are in good agreement with the structure solved by X-ray diffraction. PMID:9931018

Chehín, R; Iloro, I; Marcos, M J; Villar, E; Shnyrov, V L; Arrondo, J L

1999-02-01

60

Development of the dual scintillator sheet and Phoswich detector for simultaneous Alpha and Beta-rays measurement  

Microsoft Academic Search

Thin sheet type of ZnS(Ag)\\/plastic dual scintillator for simultaneous counting of alpha- and beta-particles using a organic and inorganic scintillator widely used in the radiation measurement was manufactured, which could be applicable in the contamination monitoring systems. Counting materials were manufactured by solidification of the scintillator solution which mixed scintillator, solvent, and polymer. Prepared dual scintillator is a counting material

B. K. Seo; G. H. Kim; C. H. Park; Y. H. Jung; C. H. Jung; K. W. Lee; M. J. Han

2007-01-01

61

Effect of temperature on texture formation of 6061 aluminum sheet in equal-channel angular pressing  

Microsoft Academic Search

A novel equal-channel angular pressing (ECAP) procedure was conducted on 6061 aluminum sheet at temperature up to 513K to investigate temperature effect on microstructure and texture formation. The deformed microstructures were examined by transmission electron microscopy and the macrotexture evolution was investigated by orientation distribution functions (ODFs). The results shown that when ECAP at temperature below 433K the microstructures exhibit

Qin Jining; Zhang Di; Zhang Guoding; Jae-Chul Lee

2005-01-01

62

The search for local native-like nucleation centers in the unfolded state of beta -sheet proteins.  

PubMed

An approach involving the systematic computational conformational analysis of all overlapping hexapeptide segments in the protein sequence has found fragments with the higher than average propensity to adopt the native-like three-dimensional structure and other regular nonrandom structures in the unfolded states of four beta-sheet proteins, namely IFABP (intestinal fatty acid-binding protein), ILBP (ileal fatty acid-binding protein), CRABP I (cellular retinoic acid-binding protein), and CRBP II (cellular retinal binding protein). The native three-dimensional structures of these four proteins are very similar even though they possess as little as approximately 30% sequence similarity. The computational results were validated by comparison with the experimental data of the heteronuclear sequential quantum correlation NMR spectroscopy obtained earlier for IFABP at high urea concentrations. On this basis, a molecular model of the unfolded state of IFABP has been developed. The model presumes a dynamic equilibrium between various nonrandom structures (including the native-like structure) and random coil in the local segments of the protein sequence. The model explains experimental observations obtained earlier for folding of several mutants of IFABP, as well as the observed differences in molecular mechanisms of folding for the four beta-sheet proteins. Because the computational approach itself does not employ any experimentally derived information in advance, it is not necessarily limited to the beta-sheet proteins. PMID:12140369

Nikiforovich, Gregory V; Frieden, Carl

2002-07-24

63

A novel mode of DNA recognition by a beta-sheet revealed by the solution structure of the GCC-box binding domain in complex with DNA.  

PubMed Central

The 3D solution structure of the GCC-box binding domain of a protein from Arabidopsis thaliana in complex with its target DNA fragment has been determined by heteronuclear multidimensional NMR in combination with simulated annealing and restrained molecular dynamic calculation. The domain consists of a three-stranded anti-parallel beta-sheet and an alpha-helix packed approximately parallel to the beta-sheet. Arginine and tryptophan residues in the beta-sheet are identified to contact eight of the nine consecutive base pairs in the major groove, and at the same time bind to the sugar phosphate backbones. The target DNA bends slightly at the central CG step, thereby allowing the DNA to follow the curvature of the beta-sheet.

Allen, M D; Yamasaki, K; Ohme-Takagi, M; Tateno, M; Suzuki, M

1998-01-01

64

Formation of active monomers from tetrameric human beta-tryptase.  

PubMed Central

Tryptase is a serine protease that is stored at low pH in the mast cell secretory granules in complex with heparin proteoglycan. When mast cells are activated, e.g. during allergic responses, the tryptase/heparin complexes are released together with a variety of other preformed inflammatory mediators. Previous crystallization of human beta-tryptase revealed a unique tetrameric structure with all of the active sites facing a central pore that has a limited accessibility both for potential substrates as well as for protease inhibitors. In this study we examined whether human beta-tryptase, in addition, could form active monomers. Incubation of recombinant tetrameric human beta-tryptase at neutral pH and 37 degrees C, followed by gel-filtration analysis using a running buffer containing pig mucosal heparin, led to the formation of enzymically active compounds that were of a size compatible with tryptase monomers in complex with heparin. The monomers were, in contrast to tryptase in the tetrameric form, inhibited by bovine pancreatic trypsin inhibitor. Further, the monomers, but not the tetramers, degraded fibronectin. Formation of active monomers was more pronounced at pH 7.5 than at pH 6.0 and was not detected at room temperature or at high heparin/tryptase ratios. The present findings thus introduce the possibility that human beta-tryptase, after mast cell degranulation and exposure to neutral pH in the tissue, may dissociate into active monomers with properties that are distinct from the tetrameric counterpart. Possibly, some of the biological activities of human tryptase may be attributable to active tryptase in its monomeric rather than tetrameric form.

Fajardo, Ignacio; Pejler, Gunnar

2003-01-01

65

Development of the dual scintillator sheet and Phoswich detector for simultaneous Alpha- and Beta-rays measurement  

SciTech Connect

Thin sheet type of ZnS(Ag)/plastic dual scintillator for simultaneous counting of alpha- and beta-particles using a organic and inorganic scintillator widely used in the radiation measurement was manufactured, which could be applicable in the contamination monitoring systems. Counting materials were manufactured by solidification of the scintillator solution which mixed scintillator, solvent, and polymer. Prepared dual scintillator is a counting material which can simultaneously measure the alpha- and beta-particles. It was divided into two parts : an inorganic scintillator layer for alpha-particle detection and an organic one for beta-particle detection. The organic layer was composed of 2,5-diphenyloxazole [PPO] and 1,4,-bis[5-phenyl(oxazolyl)benzene] [POPOP] acting as the scintillator and polysulfone acting as the polymer. The inorganic layer was composed of ZnS(Ag) as scintillator and polysulfone as paste. The ZnS(Ag) scintillator layer was printed onto the organic layer using screen printing method. To estimate the detection ability of the prepared counting materials, alpha-particle emitting nuclide, Am-241, and beta emitting nuclide, Sr/Y-90, were used. The scintillations produced by interaction between radiation and scintillator were measured by photomultiplier tube. The overall counting results reveal that the developed detector is efficient for simultaneous counting of alpha- and beta-particles. For application test, the dual scintillator was fabricated with a Phoswich detector for monitoring the in-pipe alpha and beta contamination. To deploy inside a pipe, two types of Phoswich detectors, sheets and cylinders, were prepared. For in-pipe monitoring, it was found that the cylindrical type was excellent. In the study, polymer composite counting material and Phoswich detectors were prepared using organic and inorganic scintillator for detecting different radiations. In the future, it will be applied to the contamination monitoring system for nuclear decommissioning sites, waste treatment sites, and similar areas. (authors)

Seo, B.K.; Kim, G.H.; Park, C.H.; Jung, Y.H.; Jung, C.H.; Lee, K.W. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Han, M.J. [Kyungil Univ. (Korea, Republic of)

2007-07-01

66

Nature of axial tail instability and bubble-blob formation in near-Earth plasma sheet  

NASA Astrophysics Data System (ADS)

ABSTRACTPrevious global magnetohydrodynamic (MHD) simulations of substorm events have identified the dynamic presence of an axial tail instability that is uniform in the dawn-dusk direction in the near-Earth plasma sheet. The axial tail instability is found to be a major cause of the initial growing MHD force imbalance on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes. In this work, energy principle analysis indicates that a two-dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. However, linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Such resistive axial tail instability would by many researchers be considered as tearing instability in a two-dimensional tail configuration. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly a slippage process among neighboring flux tubes as facilitated by resistive dissipation. A natural consequence of the axial tail instability is shown to be the formation of bubble-blob pairs in the pressure and entropy profiles in the near-Earth plasma sheet.

Zhu, P.; Raeder, J.; Hegna, C. C.; Sovinec, C. R.

2013-02-01

67

Formation and recovery of a cell sheet by a particle monolayer with the surface roughness.  

PubMed

We studied the topographical effect of roughness displayed by a closely packed particle monolayer on formation of a cell monolayer (cell sheet). Particle monolayers were prepared by Langmuir-Blodgett deposition using particles, which were 527nm (SA053) and 1270nm (SA127) in diameter. Human umbilical vein endothelial cells (HUVECs) were seeded at a high density (2.0 x10(5)cells/cm(2)) onto particle monolayers. It was found that cells gradually became into contact with adjacent cells on the SA053 monolayer and the formed cell sheet could be readily detached from the particle monolayer by gentle pipetting. On the other hand, cells adhering onto the tissue culture polystyrene (TCPS) and the SA127 particle monolayer were difficult to peel off. At a low cell seeding density (5.0x10(4)cells/cm(2)), pre-coating with bovine plasma fibronectin (FN) allowed cell growth on an SA053 particle monolayer, and a confluent monolayer was able to be peeled as a cell sheet from the particle monolayer just by pipetting. By immunostaining of human fibronectin, we found that fibronectin was secreted and concentrated onto the substrate side of a cell sheet. The obtained cell sheet adhered and grew on the TCPS again within 20min. PMID:18619821

Miura, Manabu; Fujimoto, Keiji

2008-06-19

68

Delta98delta, a functional all-beta-sheet abridged form of intestinal fatty acid binding protein.  

PubMed

Intestinal fatty acid binding protein (IFABP) is a 15 kDa intracellular lipid-binding protein exhibiting a beta-barrel fold that resembles a clamshell. The beta-barrel, which encloses the ligand binding cavity, consists of two perpendicular five-stranded beta-sheets with an intervening helix-turn-helix motif between strands A and B. Delta98delta (fragment 29-126 of IFABP) was obtained either in its recombinant form or by limited proteolysis with clostripain. Despite lacking extensive stretches involved in the closure of the beta-barrel, delta98delta remains soluble and stable in solution. Spectroscopic analyses by circular dichroism, ultraviolet absorption, and intrinsic fluorescence indicate that the fragment retains substantial beta-sheet content and tertiary interactions. In particular, the environment around W82 is identical in both delta98delta and IFABP, a fact consistent with the conservation in the former of all the critical amino acid residues belonging to the hydrophobic core. In addition, the Stokes radius of delta98delta is similar to that of IFABP and 16% larger than that calculated from its molecular weight (11 kDa). The monomeric status of delta98delta was further confirmed by chemical cross-linking experiments. Although lacking 25% of the amino acids of the parent protein, in the presence of GdnHCl, delta98delta unfolds through a cooperative transition showing a midpoint at 0.90 M. Remarkably, it also preserves binding activity for fatty acids (Kd = 5.1 microM for oleic acid and Kd = 0.72 microM for trans-parinaric acid), a fact that exerts a stabilizing effect on its structure. These cumulative evidences show that delta98delta adopts a monomeric state with a compact core and a loose periphery, being so far the smallest structure of its kind preserving binding function. PMID:16229473

Curto, Lucrecia M; Caramelo, Julio J; Delfino, José M

2005-10-25

69

Reversal of temperature-induced conformational changes in the amyloid-beta peptide, A?40, by the ?-sheet breaker peptides 16-23 and 17-24  

PubMed Central

Background and purpose: Aggregates of the protein amyloid-beta (A?) play a crucial role in the pathogenesis of Alzheimer's disease (AD). Most therapeutic approaches to AD do not target A?, so determination of the factor(s) that facilitate aggregation and discovering agents that prevent aggregation have great potential therapeutic value. Experimental approach: We investigated ex vivo the temperature-sensitive regions of A?1–40 (A?40) and their interactions with octapeptides derived from sequences within A?40 –?-sheet breaker peptides (?SBP) – using enzyme-linked immunosorbent assay, and dot blot and far-UV circular dichroism (CD) spectroscopy. We measured changes within the physiological limits of temperature, using antibodies targeting epitopes 1–7, 5–10, 9–14 and 17–21 within A?40. Key results: Temperature-dependent conformational changes were observed in A?40 at epitopes 9–14 and 17–21 at 36–38 and 36–40°C respectively. The ?SBPs 16–23 and 17–24, but not 15–22 and 18–25, could inhibit the changes. Moreover, ?SBPs 16–23 and 17–24 increased digestion of A?40 by protease K, indicating a decreased aggregation of A?40, whereas ?SBPs 15–22 and 18–25 did not increase this digestion. CD spectra revealed that ?-sheet formation in A?40 at 38°C was reduced with ?SBPs 16–23 and 17–24. Conclusions and implications: The epitopes 9–14 and 17–21 are the temperature-sensitive regions within A?40. The ?SBPs, A?16–23 and 17–24 reversed temperature-induced ?-sheet formation, and decreased A?40 aggregation. The results suggest that the 17–23 epitope of A?40 is crucially involved in preventing A?40 aggregation and consequent deposition of A?40 in AD brain.

Hatip, Funda F Bolukbas?; Suenaga, Midori; Yamada, Tatsuo; Matsunaga, Yoichi

2009-01-01

70

Nature of Axial Tail Instability and Bubble-Blob Formation in Near-Earth Plasma Sheet*  

NASA Astrophysics Data System (ADS)

Previous global MHD simulations of substorm events have identified the dynamic presence of an axial tail instability with dawn-dusk symmetry in the near-Earth plasma sheet as a major cause of the initial loss of MHD equilibrium on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes [Raeder et al. 2010; Siscoe et al. 2009]. In this work, energy principle analysis indicates that a two-dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. Linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Mode growth and structure show both similarities and differences in comparison to the linear resistive tearing mode of a one-dimensional Harris sheet. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly an interchange or slippage process among neighboring flux tubes as facilitated by dissipations such as resistivity. The formation of bubble-blob pairs in pressure and entropy distributions in the near-Earth plasma sheet is shown to be a natural component as well as consequence of this axial instability process. *Supported by NSF grants AGS-0902360 and PHY-0821899. REFERENCES: Raeder, J., P. Zhu, Y. Ge, and G. Siscoe (2010), Open Geospace General Circulation Model simulation of a substorm: Axial tail instability and ballooning mode preceding substorm onset, J. Geophys. Res., 115, A00I16, doi:10.1029/2010JA015876. Siscoe, G. L., M. M. Kuznetsova, and J. Raeder (2009), Search for an onset mechanism that operates for both CMEs and substorms, Ann. Geophys., 27, 31413146.

Zhu, P.; Raeder, J.; Hegna, C. C.; Sovinec, C. R.

2011-12-01

71

Formation of the Harang reversal and its dependence on plasma sheet conditions: Rice convection model simulations  

NASA Astrophysics Data System (ADS)

The goal of this paper is to understand the formation of the Harang reversal and its association with the region 2 field-aligned current (FAC) system, which couples the plasma sheet transport to the ionosphere. We have run simulations with the Rice convection model (RCM) using the Tsyganenko 96 magnetic field model and realistic plasma sheet particle boundary conditions on the basis of Geotail observations. Our results show that the existence of an overlap in magnetic local time (MLT) of the region 2 upward and downward FAC is necessary for the formation of the Harang reversal. In the overlap region the downward FAC, which is located at lower latitudes, is associated with low-energy ions that penetrate closer to Earth toward the dawn side, while the upward FAC, which is located at higher latitudes, is associated with high-energy ions. Under the same enhanced convection we compare the Harang reversal resulting from a hotter and more tenuous plasma sheet with the one resulting from a colder and denser plasma sheet. For the former case the shielding of the convection electric field is less efficient than for the latter case, allowing low-energy protons to penetrate further earthward, resulting in a Harang reversal that extends to lower latitudes, expands wider in MLT, and is located further equatorward than the upward FAC peak and the conductivity peak. The return flows of the Harang reversal in the hot and tenuous case are located in a low conductivity region. This leads to an enhancement of these westward flows, resulting in subauroral polarization streams (SAPS).

Gkioulidou, Matina; Wang, Chih-Ping; Lyons, Larry R.; Wolf, Richard A.

2009-07-01

72

Vibrational self-trapping in beta-sheet structures observed with femtosecond nonlinear infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Self-trapping of NH-stretch vibrational excitations in synthetic ?-sheet helices is observed using femtosecond infrared pump-probe spectroscopy. In a dialanine-based ?-sheet helix, the transient-absorption change upon exciting the NH-stretch mode exhibits a negative absorption change at the fundamental frequency and two positive peaks at lower frequencies. These two induced-absorption peaks are characteristic for a state in which the vibrational excitation is self-trapped on essentially a single NH-group in the hydrogen-bonded NH...OC chain, forming a small (Holstein) vibrational polaron. By engineering the structure of the polymer we can disrupt the hydrogen-bonded NH...OC chain, allowing us to eliminate the self-trapping, as is confirmed from the NH-stretch pump-probe response. We also investigate a trialanine-based ?-sheet helix, where each side chain participates in two NH...OC chains with different hydrogen-bond lengths. The chain with short hydrogen bonds shows the same self-trapping behavior as the dialanine-based ?-sheet helix, whereas in the chain with long hydrogen bonds the self-trapping is too weak to be observable.

Bodis, Pavol; Schwartz, Erik; Koepf, Matthieu; Cornelissen, Jeroen J. L. M.; Rowan, Alan E.; Nolte, Roeland J. M.; Woutersen, Sander

2009-09-01

73

Plasma-beta dependence of the fast reconnection mechanism in an initially force-free current sheet  

NASA Astrophysics Data System (ADS)

The present paper systematically studies the spontaneous fast reconnection mechanism in an initially force-free current sheet in a wide range of plasma beta (?) in our previous work it was studied for a special case of ? = 0.15. In each case, the evolution as well as the resulting structure of the fast reconnection is qualitatively similar to the one that was already reported for the case of ? = 0.15. Quantitatively, the fast reconnection evolution becomes more rapid and drastic for the lower plasma beta. For the cases of very low plasma beta (? = 0.01 or 0.02), the plasma temperature is extremely enhanced to the value almost 1/? times larger than its initial value in the resulting fast reconnection jet and large-scale plasmoid regions. Once the fast reconnection mechanism is ignited in a local spot-like region, its basic structure eventually established is sustained almost steadily, giving rise to the plasmoid swelling with time and propagating outwards. Accordingly, the characteristic reconnection regions, where plasma thermodynamic quantities are remarkably enhanced, rapidly expand in all (x, y, and z) directions in Alfven time scales, which may be responsible for the explosive expansion of large flares as well as for the distinct plasma heating observed in the solar corona.

Ugai, M.

2011-10-01

74

Esker formation due to supraglacial lake drainage to the bed of the Cordilleran Ice Sheet  

NASA Astrophysics Data System (ADS)

A positive relation between increased surface melting and ice acceleration at land-terminating sections of the Greenland Ice Sheet (GrIS), particularly during supraglacial lake drainage, has been suggested as a mechanism for enhanced ice sheet decay. However, the paucity of direct measurements at the ice sheet bed restricts our understanding of subglacial drainage system evolution in response to transient meltwater inputs. On the Fraser Plateau, south-central British Columbia, a single thread ~40 km long and ~0.25-1 km wide erosional corridor, with upslope sections along its long profile, was generated subglacially in response to supraglacial lake drainage during late Cordilleran Ice Sheet (CIS) decay. Corridor fill includes gravel sheets and dunes (>9 m thick), as well as an esker system. In 2010, we collected >4.5 km of ground-penetrating radar (GPR) line and >0.7 km of electrical resistivity (ER) line on the corridor fill. Our data reveal that the esker, which is composed of ridge-wide macroforms that indicate high-magnitude deposition, is draped onto the broader corridor fill. Given the lack of late stage reworking of the corridor fill surrounding the esker, we suggest that waning stage floodwaters were constrained within the esker-forming conduit, following rapid collapse from the corridor-wide flow that eroded the tunnel channel and deposited the broad fill. However, our data reveal that whilst the esker formed subglacially and synchronously, up flow sections locally unroofed during the latest stages of esker formation, resulting in local deposition within subaerial ice-walled channels. This, combined with a lack of corridor fill deformation expected from ice-bed recoupling, indicate that the CIS was thin at the time of supraglacial lake drainage. Our data reveal a relatively simple event sequence that includes evolution from a large erosional channel that discharged rising stage floodwaters following initial supraglacial lake drainage, to a narrower R-channel that efficiently evacuated waning stage flow. Such rapid channelization suggests that thin ice conditions are not conducive to broad ice-bed decoupling and ice acceleration.

Burke, M. J.; Brennand, T.; Perkins, A. J.

2011-12-01

75

Racemic beta-sheets as templates of relevance to the origin of homochirality of peptides: lessons from crystal chemistry.  

PubMed

The origin of life is a historical event that has left no relevant fossils; therefore, it is unrealistic to reconstruct the chronology of its occurrence. Instead, by performing laboratory experiments under conditions that resemble the prebiotic world, one might validate feasible reaction pathways and reconstruct model systems of artificial life. Creating such life in a test tube should go a long way toward removing the shroud of mystery over how it began naturally. The riddle of the appearance of natural proteins and nucleic acids--that is, biopolymers wholly consisting of homochiral subunits (L-amino acids and D-sugars, respectively)--from the unanimated racemic prebiotic world is still unsolved. There are two hypotheses concerning the sequence of their emergence: one maintains that long homochiral (isotactic) peptides must have been formed after the appearance of the first living systems, whereas the other presumes that such biopolymers preceded the primeval enzymes. The latter scenario necessitates, however, the operation of nonlinear synthetic routes, because the polymerization of racemates in ideal solutions yields chains composed of residues of either handedness. In this Account, we suggest applying lessons learned from crystal chemistry, in which molecules from isotropic media are converted into crystals with three-dimensional (3D) periodic order, to understand how the generation of homochiral peptides from racemic alpha-amino acids might be achieved, despite its seemingly overwhelming complexity. We describe systems that include the self-assembly of activated alpha-amino acids either in two-dimensional (2D) or in 3D crystals, followed by a partial lattice-controlled polymerization at the crystal-aqueous solution interface. We also discuss the polymerization of mixtures of activated hydrophobic racemic alpha-amino acids in aqueous solutions, as initiated by primary amines or thiols. The distribution of the diastereomeric oligopeptides was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and MS/MS with monomers enantioselectively tagged with deuterium. The reaction performed in aqueous solutions encompasses the following sequential steps: (i) formation of a library of short racemic peptides enriched with isotactic diastereoisomers during the early stages of the polymerization, and (ii) self-assembly of oligopeptides into racemic beta-sheet colloidal-like aggregates that are delineated by enantiotopic sites or rims; these operate as templates (nuclei) for regio-enantioselective growth in the ensuing steps of chain elongation. Desymmetrization of the racemic mixtures of peptides was achieved with enantiopure alpha-amino acid esters as initiators. The enantiomeric excess of the isotactic peptides, not including the initiator, varies with chain length, the result of a cross-enantiomeric impeding mechanism. Our results suggest a feasible scenario in which primitive homochiral peptides might have emerged early in the prebiotic world. PMID:19480407

Weissbuch, Isabelle; Illos, Roni A; Bolbach, Gérard; Lahav, M

2009-08-18

76

Formation of Dipolarization Fronts as a Part of the Magnetic Reconnection Onset Process in Two-Dimensional Current Sheets  

NASA Astrophysics Data System (ADS)

Multiple puzzles surround the formation and behavior of dipolarization fronts (DFs). Although DFs can be successfully reproduced in MHD and hybrid codes using various models of localized resistivity to trigger reconnection, they are typically not seen in PIC simulations initialized with 1D Harris current sheets. Moreover, recent 3D PIC simulations suggest that DFs do even not arise from reconnection, but can instead be formed as a result of the ballooning-interchange instability. We consider PIC simulations starting from new classes of 2D current sheet equilibria, including multiscale magnetotail current sheets, and show that DF formation can play an integral part in reconnection onset due to the tearing instability. During DF formation, current sheets behave as metastable systems where the transition from slow to fast phases is not caused by topological changes. Rather, the fast phase resembles the formation of bubble-blob pairs, which then promote the formation of new X-lines and electron diffusion regions. The fast phase shares properties with the ion tearing instability. Distinctive features of particle acceleration and heating associated with this mechanism of DF formation are discussed and compared to THEMIS and Cluster observations.

Sitnov, M. I.; Swisdak, M. M.

2011-12-01

77

World Sheet Commuting beta-gamma CFT and Non-Relativistic StringTheories  

SciTech Connect

We construct a sigma model in two dimensions with Galilean symmetry in flat target space similar to the sigma model of the critical string theory with Lorentz symmetry in 10 flat spacetime dimensions. This is motivated by the works of Gomis and Ooguri[1] and Danielsson et. al.[2, 3]. Our theory is much simpler than their theory and does not assume a compact coordinate. This non-relativistic string theory has a bosonic matter {beta}{gamma} CFT with the conformal weight of {beta} as 1. It is natural to identify time as a linear combination of {gamma} and {bar {gamma}} through an explicit realization of the Galilean boost symmetry. The angle between {gamma} and {bar {gamma}} parametrizes one parameter family of selection sectors. These selection sectors are responsible for having a non-relativistic dispersion relation without a nontrivial topology in the non-relativistic setup, which is one of the major differences from the previous works[1, 2, 3]. This simple theory is the non-relativistic analogue of the critical string theory, and there are many different avenues ahead to be investigated. We mention a possible consistent generalization of this theory with different conformal weights for the {beta}{gamma} CFT. We also mention supersymmetric generalizations of these theories.

Kim, Bom Soo

2007-08-30

78

Formation of Beta-SiC in the Initial Growth Stage.  

National Technical Information Service (NTIS)

The formation of Beta-SiC at temperatures outside its thermally stable range of 1,400-1,600C was studied experimentally using the sublimation procedure and the synthetic method with molten silicon. From consideration of the molar surface energy of Beta- a...

S. Matsumoto Y. Inomata

1972-01-01

79

Enthalpies of Formation of Alpha and Beta Magnesium Sulfate and Magnesium Sulfate Monohydrate.  

National Technical Information Service (NTIS)

As part of the Federal Bureau of Mines effort to provide thermodynamic data for the advancement of minerals technology, energy conservation, and environmental preservation, the standard enthalpies of formation of alpha-magnesium sulfate, beta-magnesium su...

H. C. Ko G. E. Daut

1980-01-01

80

The digital geologic map of Colorado in ARC/INFO format, Part C. Explanation sheet database  

USGS Publications Warehouse

This geologic map was prepared as a part of a study of digital methods and techniques as applied to complex geologic maps. The geologic map was digitized from the original scribe sheets used to prepare the published Geologic Map of Colorado (Tweto 1979). Consequently the digital version is at 1:500,000 scale using the Lambert Conformal Conic map projection parameters of the state base map. Stable base contact prints of the scribe sheets were scanned on a Tektronix 4991 digital scanner. The scanner automatically converts the scanned image to an ASCII vector format. These vectors were transferred to a VAX minicomputer, where they were then loaded into ARC/INFO. Each vector and polygon was given attributes derived from the original 1979 geologic map. This database was developed on a MicroVAX computer system using VAX V 5.4 nd ARC/INFO 5.0 software. UPDATE: April 1995, The update was done solely for the purpose of adding the abilitly to plot to an HP650c plotter. Two new ARC/INFO plot AMLs along with a lineset and shadeset for the HP650C design jet printer have been included. These new files are COLORADO.650, INDEX.650, TWETOLIN.E00 and TWETOSHD.E00. These files were created on a UNIX platform with ARC/INFO 6.1.2. Updated versions of INDEX.E00, CONTACT.E00, LINE.E00, DECO.E00 and BORDER.E00 files that included the newly defined HP650c items are also included. * Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Descriptors: The Digital Geologic Map of Colorado in ARC/INFO Format Open-File Report 92-050

Green, Gregory N.

1992-01-01

81

Beta-sheet proteins with nearly identical structures have different folding intermediates.  

PubMed

The folding mechanisms of two proteins in the family of intracellular lipid binding proteins, ileal lipid binding protein (ILBP) and intestinal fatty acid binding protein (IFABP), were examined. The structures of these all-beta-proteins are very similar, with 123 of the 127 amino acids of ILBP having backbone and C(beta) conformations nearly identical to those of 123 of the 131 residues of IFABP. Despite this structural similarity, the sequences of these proteins have diverged, with 23% sequence identity and an additional 16% sequence similarity. The folding process was completely reversible, and no significant concentrations of intermediates were observed by circular dichroism or fluorescence at equilibrium for either protein. ILBP was less stable than IFABP with a midpoint of 2. 9 M urea compared to 4.0 M urea for IFABP. Stopped-flow kinetic studies showed that both the folding and unfolding of these proteins were not monophasic, suggesting that either multiple paths or intermediate states were present during these processes. Proline isomerization is unlikely to be the cause of the multiphasic kinetics. ILBP had an intermediate state with molten globule-like spectral properties, whereas IFABP had an intermediate state with little if any secondary structure during folding and unfolding. Double-jump experiments showed that these intermediates appear to be on the folding path for each protein. The folding mechanisms of these proteins were markedly different, suggesting that the different sequences of these two proteins dictate different paths through the folding landscape to the same final structure. PMID:10653629

Dalessio, P M; Ropson, I J

2000-02-01

82

Ballooning instability at the plasma sheet–lobe interface and its implications for polar arc formation  

Microsoft Academic Search

Huang et al. (1987, 1989) reported hot filaments of plasma sheet origin filling the magnetospheric lobes during northward interplanetary magnetic field (IMF). On the other hand, cold plasma transients of presumably lobe origin are often observed in the plasma sheet. These features can be interpreted in terms of plasma exchange at the plasma sheet–lobe interface (PSLI) proceeding in a filamentary

I. V. Golovchanskaya; A. Kullen; Y. P. Maltsev; H. Biernat

2006-01-01

83

Ballooning instability at the plasma sheet-lobe interface and its implications for polar arc formation  

Microsoft Academic Search

Huang et al. (1987, 1989) reported hot filaments of plasma sheet origin filling the magnetospheric lobes during northward interplanetary magnetic field (IMF). On the other hand, cold plasma transients of presumably lobe origin are often observed in the plasma sheet. These features can be interpreted in terms of plasma exchange at the plasma sheet-lobe interface (PSLI) proceeding in a filamentary

I. V. Golovchanskaya; A. Kullen; Y. P. Maltsev; H. Biernat

2006-01-01

84

Self-association process of a peptide in solution: from beta-sheet filaments to large embedded nanotubes.  

PubMed

Lanreotide is a synthetic octapeptide used in the therapy against acromegaly. When mixed with pure water at 10% (w/w), Lanreotide (acetate salt) forms liquid crystalline and monodisperse nanotubes with a radius of 120 A. The molecular and supramolecular organization of these structures has been determined in a previous work as relying on the lateral association of 26 beta-sheet filaments made of peptide noncovalent dimers, the basic building blocks. The work presented here has been devoted to the corresponding self-association mechanisms, through the characterization of the Lanreotide structures formed in water, as a function of peptide (acetate salt) concentration (from 2% to 70% (w/w)) and temperature (from 15 degrees C to 70 degrees C). The corresponding states of water were also identified and quantified from the thermal behavior of water in the Lanreotide mixtures. At room temperature and below 3% (w/w) Lanreotide acetate in water, soluble aggregates were detected. From 3% to 20% (w/w) long individual and monodisperse nanotubes crystallized in a hexagonal lattice were evidenced. Their molecular and supramolecular organizations are identical to the ones characterized for the 10% (w/w) sample. Heating induces the dissolution of the nanotubes into soluble aggregates of the same structural characteristics as the room temperature ones. The solubilization temperature increases from 20 degrees C to 70 degrees C with the peptide concentration and reaches a plateau between 15% and 25% (w/w) in peptide. These aggregates are proposed to be the beta-sheet filaments that self-associate to build the walls of the nanotubes. Above 20% (w/w) of Lanreotide acetate in water, polydisperse embedded nanotubes are formed and the hexagonal lattice is lost. These embedded nanotubes exhibit the same molecular and supramolecular organizations as the individual monodisperse nanotubes formed at lower peptide concentration. The embedded nanotubes do not melt in the range of temperature studied indicating a higher thermodynamic stability than individual nanotubes. In parallel, the thermal behaviors of water in mixtures containing 2-80% (w/w) in peptide have been studied by differential scanning calorimetry, and three different types of water were characterized: 1), bulk water melting at 0 degrees C, 2), nonfreezing water, and 3), interfacial water melting below 0 degrees C. The domains of existence and coexistence of these different water states are related to the different Lanreotide supramolecular structures. All these results were compiled into a binary Lanreotide-water phase diagram and allowed to propose a self-association mechanism of Lanreotide filaments into monodisperse individual nanotubes and embedded nanotubes. PMID:15041685

Valéry, C; Artzner, F; Robert, B; Gulick, T; Keller, G; Grabielle-Madelmont, C; Torres, M-L; Cherif-Cheikh, R; Paternostre, M

2004-04-01

85

Generation of Alzheimer beta Amyloid Protein in the Trans-Golgi Network in the Apparent Absence of Vesicle Formation  

Microsoft Academic Search

beta -amyloid protein (Abeta ) formation was reconstituted in permeabilized neuroblastoma cells expressing human Alzheimer beta -amyloid precursor protein (beta APP) harboring the Swedish double mutation associated with familial early-onset Alzheimer disease. Permeabilized cells were prepared following metabolic labeling and incubation at 20 degrees C, a temperature that allows beta APP to accumulate in the trans-Golgi network (TGN) without concomitant

Huaxi Xu; David Sweeney; Rong Wang; Gopal Thinakaran; Amy C. Y. Lo; Sangram S. Sisodia; Paul Greengard; Sam Gandy

1997-01-01

86

A Molecular Model of Alzheimer Amyloid beta Peptide Fibril Formation  

Microsoft Academic Search

Polymerization of the amyloid beta (Ab) peptide into protease-resistant fibrils is a significant step in the pathogenesis of Alzheimer's disease. It has not been pos- sible to obtain detailed structural information about this process with conventional techniques because the peptide has limited solubility and does not form crys- tals. In this work, we present experimental results lead- ing to a

Lars O. Tjernberg; David J. E. Callaway; Agneta Tjernbergi; Solveig Hahne; Christina Lilliehook; Lars Terenius; Johan Thyberg; Christer Nordstedt

1999-01-01

87

Zinc binding drives sheet formation by the SAM domain of diacylglycerol kinase ?  

PubMed Central

The Diacylglycerol Kinase (DGK) family of enzymes plays critical roles in lipid signaling pathways by converting diacylglycerol to phosphatidic acid, thereby downregulating signaling by the former and upregulating signaling by the latter second messenger. Ten DGK family isozymes have been identified to date, which possess different interaction motifs imparting distinct temporal and spatial control of DGK activity to each isozyme. Two DGK family members, ? and ?, contain a Sterile Alpha Motif (SAM) domain. The SAM domain of DGK?1 forms helical polymers that are important for retaining the enzyme in cytoplasmic puncta, thereby inhibiting activity at the plasma membrane until pathway activation. Because zinc was found to be important for stabilizing the similar SAM polymers of the scaffolding protein Shank-3, we investigated the potential role of zinc in DGK? SAM domain (DGK?SAM) assembly. We find that DGK?SAM binds zinc at multiple sites, driving the organization of the DGK?SAM into large sheets of polymers. Moreover, a mutant DGK? containing a SAM domain refractory to zinc binding diminishes the formation of cytoplasmic puncta, shows partially impaired regulation of transport to the plasma membrane, and lacks the ability to inhibit the formation of CopII coated vesicles. These results suggest that zinc may play an important role in the assembly and physiology of the DGK? isozyme.

Knight, Mary Jane; Joubert, Marisa K.; Plotkowski, Megan L.; Kropat, Janette; Gingery, Mari; Sakane, Fumio; Merchant, Sabeeha S.; Bowiel, James U.

2010-01-01

88

Vitamin C Treatment Promotes Mesenchymal Stem Cell Sheet Formation and Tissue Regeneration by Elevating Telomerase Activity  

PubMed Central

Cell sheet engineering has been developed as an alternative approach to improve mesenchymal stem cell-mediated tissue regeneration. In this study, we found that vitamin C (Vc) was capable of inducing telomerase activity in periodontal ligament stem cells (PDLSCs), leading to the up-regulated expression of extracellular matrix type I collagen, fibronectin, and integrin ?1, stem cell markers Oct4, Sox2, and Nanog as well as osteogenic markers RUNX2, ALP, OCN. Under Vc treatment, PDLSCs can form cell sheet structures because of increased cell matrix production. Interestingly, PDLSC sheets demonstrated a significant improvement in tissue regeneration compared with untreated control dissociated PDLSCs and offered an effective treatment for periodontal defects in a swine model. In addition, bone marrow mesenchymal stem cell sheets and umbilical cord mesenchymal stem cell sheets were also well constructed using this method. The development of Vc-mediated mesenchymal stem cell sheets may provide an easy and practical approach for cell-based tissue regeneration.

Wei, F.L.; Qu, C.Y.; Song, T.L.; Ding, G.; Fan, Z.P.; Liu, D.Y.; Liu, Y.; Zhang, C.M.; Shi, S.; Wang, S.L.

2011-01-01

89

Formation of extra centrosomal structures is dependent on beta-catenin.  

PubMed

beta-Catenin has important roles in cell-cell adhesion and in the regulation of gene transcription. Mutations that stabilize beta-catenin are common in cancer, but it remains unclear how these mutations contribute to cancer progression. beta-Catenin is also a centrosomal component involved in centrosome separation. Centrosomes nucleate interphase microtubules and the bipolar mitotic spindle in normal cells, but their organization and function in human cancers are abnormal. Here, we show that expression of stabilized mutant beta-catenin, which mimics mutations found in cancer, results in extra non-microtubule nucleating structures that contain a subset of centrosome proteins including gamma-tubulin and centrin, but not polo-like kinase 4 (Plk4), SAS-6 or pericentrin. A transcriptionally inactive form of beta-catenin also gives rise to abnormal structures of centrosome proteins. HCT116 human colon cancer cell lines, from which the mutant beta-catenin allele has been deleted, have reduced numbers of cells with abnormal centrosome structures and S-phase-arrested, amplified centrosomes. RNAi-mediated depletion of beta-catenin from centrosomes inhibits S-phase-arrested amplification of centrosomes. These results indicate that beta-catenin is required for centrosome amplification, and mutations in beta-catenin might contribute to the formation of abnormal centrosomes observed in cancers. PMID:20736306

Bahmanyar, Shirin; Guiney, Evan L; Hatch, Emily M; Nelson, W James; Barth, Angela I M

2010-08-24

90

Submarine push moraine formation during the early Fennoscandian Ice Sheet deglaciation  

NASA Astrophysics Data System (ADS)

The glacial history in the topographically confined paleo-ice stream drainage route of Vestfjorden, North Norway, was analysed based on multi-beam bathymetric data, high-resolution seismic records and 14C AMS-dated gravity cores. The inner part of the fjord is characterised by axial-parallel megascale lineations. In the central part of the fjord, a succession of transverse ridges form a zigzag like morphology. The ridges become wider and more prominent down-fjord and the largest, up to 40 m high forms the distal part of the Værøy morainal bank system. A second series of similar transverse, zigzag ridges occur in the Røst morainal bank system. They also increase in size down-fjord to terminate by a ~100 m high ridge. A mound, interpreted as a raft of sediment displaced from a similar-sized depression in the Røst morainal bank system, is located ca 8 km beyond the bank, indicating sediment drag and deformation. Seismic records show thrusted and folded sediment blocks within the ridges. The inner ridges of the Røst system terminate at the Værøy system, indicating that the latter is younger than the Røst system. The landforms are inferred to reflect basal processes and the transition from warm-based (inner fjord) to cold-based (outer fjord) conditions, i.e. fast flow followed by basal freeze-on, sediment deformation and morainal bank formation. The moraines formed during the final part of two paleo-ice sheet re-advances. 14C AMS dating indicates a maximum age of 13.7 14C ka BP (16.2 cal ka BP) for the Røst system whereas the Værøy system is inferred to be slightly older than 12.5 14C ka BP (14.5 cal ka BP). This demonstrates that the northern part of the Fennoscandian Ice Sheet behaved in a much more dynamic way during the early deglaciation than previously assumed. Acknowledgement This work is a contribution to the SPONCOM and GlaciPet (http://www.ngu.no/glacipet/) projects. Financial support from the Research Council of Norway and StatoilHydro is gratefully acknowledged. Further reading Laberg, J.S., Eilertsen, R.S., Salomonsen, G.R., Vorren, T.O. 2007. Submarine push moraine formation during the early Fennoscandian Ice Sheet deglaciation. Quaternary Research 67, 453-462. Laberg, J.S., Eilertsen, R.S., Vorren, T.O. in press. The paleo-ice stream in Vestfjorden, North Norway over the last 35ka: glacial erosion and sediment yield. Geological Society of America Bulletin. Fløistad, K.R., Laberg, J.S., Vorren, T.O. in press. Morphology of Younger Dryas ice-proximal submarine landforms, inner Vestfjorden, northern Norway. Boreas.

Laberg, J. S.; Eilertsen, R. S.; Salomonsen, G. R.; Vorren, T. O.

2009-04-01

91

Formation of High-Beta Plasma and Stable Confinement of Toroidal Electron Plasma in RT1  

Microsoft Academic Search

The Ring Trap 1 (RT-1) device is a laboratory magnetosphere generated by a levitated superconducting magnet. The goals of RT-1 are to realize stable formation of ultra high-beta plasma suitable for burning advanced fusion fuels, and confinement of toroidal non-neutral plasmas including antimatter particles. RT- 1 has produced high-beta plasma in the magnetospheric configuration. The effects of coil levitation and

Haruhiko Saitoh

2010-01-01

92

Inducing ?-sheets formation in synthetic spider silk fibers by aqueous post-spin stretching.  

PubMed

As a promising biomaterial with numerous potential applications, various types of synthetic spider silk fibers have been produced and studied in an effort to produce man-made fibers with mechanical and physical properties comparable to those of native spider silk. In this study, two recombinant proteins based on Nephila clavipes Major ampullate Spidroin 1 (MaSp1) consensus repeat sequence were expressed and spun into fibers. Mechanical test results showed that fiber spun from the higher molecular weight protein had better overall mechanical properties (70 KD versus 46 KD), whereas postspin stretch treatment in water helped increase fiber tensile strength significantly. Carbon-13 solid-state NMR studies of those fibers further revealed that the postspin stretch in water promoted protein molecule rearrangement and the formation of ?-sheets in the polyalanine region of the silk. The rearrangement correlated with improved fiber mechanical properties and indicated that postspin stretch is key to helping the spider silk proteins in the fiber form correct secondary structures, leading to better quality fibers. PMID:21574576

An, Bo; Hinman, Michael B; Holland, Gregory P; Yarger, Jeffery L; Lewis, Randolph V

2011-05-24

93

Spontaneous formation of stringlike clusters and smectic sheets for colloidal rods confined in thin wedgelike gaps.  

PubMed

Monodispersed colloidal rods of ?-FeOOH with sizes ranging from 270 to 580 nm in length and 50 to 80 nm in width were synthesized. Narrow wedgelike gaps (0 to 700 nm in height) were formed around the inner bottom edge of the suspension glass cells. Optical microscopic observations revealed the formation of stringlike clusters of the rods and smectic sheets (by spontaneous side-by-side clustering of the strings) in the isotropic phase of the rod suspensions confined in narrow gaps; the electrolyte (HCl) concentrations of the suspensions are 5-40 mM, at which inter-rod interactions are attractive. The strings exhibit different colors that were used to investigate the structures of the strings with the help of interference color theory for thin films. The results are as follows. (1) The rods, lying flat on the gap bottom, are connected side-by-side and stacked upward to form stringlike clusters with different thicknesses depending on the gap height. (2) The stacking numbers (Nsr) of the rods are estimated to be 1-5. With Nsr increasing from 2 to 5, the volume fractions (?) of the rods in the strings increased typically from 0.25-0.3 to 0.35-0.42 to reach limiting values (close to the ? values of the rods in the bulk smectic phase). (3) Unexpected low-? strings are found in regions with an intermediate height in the gaps. These behaviors of ? may be caused by thermal fluctuations of the strings. PMID:23876087

Maeda, Hideatsu; Maeda, Yoshiko

2013-08-05

94

Roles of double lobe reconnection and Kelvin-Helmholtz instability in the formation of the cold dense plasma sheet: A statistical study  

NASA Astrophysics Data System (ADS)

It is well known that the plasma sheet becomes cold and dense under prolonged northward IMF conditions [e.g., Terasawa et al., 1997]. Two major candidates, (1) high latitude reconnections in both hemispheres which capture magnetosheath plasmas on the newly closed field lines (double lobe reconnection) [e.g., Song and Russell, 1992] and (2) effective diffusive transport of magnetosheath plasma induced by the Kelvin-Helmholtz instability at the flank magnetopause [e.g., Hasegawa et al., 2004], have been discussed to account for the formation of the cold dense plasma sheet. The relative importance of the double lobe reconnection and the Kelvin-Helmholtz instability in the formation of the cold dense plasma sheet is so far an open question. We quantitatively examined the properties of the cold dense plasma sheet by fitting the observed ion and electron velocity distributions to a single/two-component Maxwellian. We statistically show that the cold dense plasma sheet in the dusk magnetosphere is characterized by ions consisting of separate cold and hot component and electrons consisting of a single cold component. Although the absence of a hot electron component in the cold dense plasma sheet can be explained naturally if we blame the formation of the cold dense plasma sheet on the double lobe reconnection scenario, it is hard to be explained by diffusion induced by the Kelvin-Helmholtz instability at the magnetopause. We also show that a sharp boundary exists between the cold dense plasma sheet and the hot tenuous plasma sheet. The observed velocity distributions of ions and electrons in the cold dense plasma sheet bordered by the hot tenuous plasma sheet indicate the supply of the hot ion component by diffusion and gradient/curvature B drift. The cold dense plasma sheet observed just inside the Kelvin-Helmholtz unstable magnetopause further suggests that the double lobe reconnection and the Kelvin-Helmholtz instability can occur simultaneously.

Hirai, M.; Hoshino, M.; Hashimoto, K.; Mukai, T.

2009-12-01

95

Modeling the ductile fracture process of void coalescence by void-sheet formation  

Microsoft Academic Search

Ductile fracture of engineering alloys frequently occurs by a mechanism of void coalescence in which void-sheets form between the primary voids. Based on the microstructural features that control failure of HY-100 steel, computational modeling has been performed to examine the deformation localization behavior between primary voids and to predict ductile fracture by the void-sheet coalescence mechanism. Elongated inclusion-initiated voids are

J. P Bandstra; D. A Koss

2001-01-01

96

Formation and maintenance of Alzheimer's disease beta-amyloid plaques in the absence of microglia.  

PubMed

In Alzheimer's disease, microglia cluster around beta-amyloid deposits, suggesting that these cells are important for amyloid plaque formation, maintenance and/or clearance. We crossed two distinct APP transgenic mouse strains with CD11b-HSVTK mice, in which nearly complete ablation of microglia was achieved for up to 4 weeks after ganciclovir application. Neither amyloid plaque formation and maintenance nor amyloid-associated neuritic dystrophy depended on the presence of microglia. PMID:19838177

Grathwohl, Stefan A; Kälin, Roland E; Bolmont, Tristan; Prokop, Stefan; Winkelmann, Georg; Kaeser, Stephan A; Odenthal, Jörg; Radde, Rebecca; Eldh, Therese; Gandy, Sam; Aguzzi, Adriano; Staufenbiel, Matthias; Mathews, Paul M; Wolburg, Hartwig; Heppner, Frank L; Jucker, Mathias

2009-10-18

97

Solution conformations and aggregational properties of synthetic amyloid beta-peptides of Alzheimer's disease. Analysis of circular dichroism spectra.  

PubMed

The A4 or beta-peptide (39 to 43 amino acid residues) is the principal proteinaceous component of amyloid deposits in Alzheimer's disease. Using circular dichroism (c.d.), we have studied the secondary structures and aggregational properties in solution of 4 synthetic amyloid beta-peptides: beta-(1-28), beta-(1-39), beta-(1-42) and beta-(29-42). The natural components of cerebrovascular deposits and extracellular amyloid plaques are beta-(1-39) and beta-(1-42), while beta-(1-28) and beta-(29-42) are unnatural fragments. The beta-(1-28), beta-(1-39) and beta-(1-42) peptides adopt mixtures of beta-sheet, alpha-helix and random coil structures, with the relative proportions of each secondary structure being strongly dependent upon the solution conditions. In aqueous solution, beta-sheet structure is favored for the beta-(1-39) and beta-(1-42) peptides, while in aqueous solution containing trifluoroethanol (TFE) or hexafluoroisopropanol (HFIP), alpha-helical structure is favored for all 3 peptides. The alpha-helical structure unfolds with increasing temperature and is favored at pH 1 to 4 and pH 7 to 10; the beta-sheet conformation is temperature insensitive and is favored at pH 4 to 7. Peptide concentration studies showed that the beta-sheet conformation is oligomeric (intermolecular), whereas the alpha-helical conformation is monomeric (intramolecular). The rate of aggregation to the oligomeric beta-sheet structure (alpha-helix----random coil----beta-sheet) is also dependent upon the solution conditions such as the pH and peptide concentration; maximum beta-sheet formation occurs at pH 5.4. These results suggest that beta-peptide is not an intrinsically insoluble peptide. Thus, solution abnormalities, together with localized high peptide concentrations, which may occur in Alzheimer's disease, may contribute to the formation of amyloid plaques. The hydrophobic beta-(29-42) peptide adopts exclusively an intermolecular beta-sheet conformation in aqueous solution despite changes in temperature or pH. Therefore, this segment may be the first region of the beta-peptide to aggregate and may direct the folding of the complete beta-peptide to produce the beta-pleated sheet structure found in amyloid deposits. Differences between the solution conformations of the beta-(1-39) and beta-(1-42) peptides suggests that the last 3 C-terminal amino acids are crucial to amyloid deposition. PMID:1613791

Barrow, C J; Yasuda, A; Kenny, P T; Zagorski, M G

1992-06-20

98

Synthesis of beta-functionalized porphyrins via palladium-catalyzed carbon-heteroatom bond formations: expedient entry into beta-chiral porphyrins.  

PubMed

A procedure was developed for the preparation of beta-monobromo-tetraphenylporphyrin (BrTPP) in a greatly improved yield from the selective bromination of tetraphenylporphyrin (TPP) by NBS. BrTPP was successfully employed as a versatile synthon for convenient synthesis of a wide range of beta-monofunctionalized porphyrins with various heteroatom functionalities via palladium-mediated carbon-heteroatom bond formations. Examples include beta-amino, -amido, -oxo, and -mercaptoporphyrins from reactions with amines, amides, alcohols, and thiols, respectively. Applying the synthetic approach to chiral amides, beta-chiral porphyrins were effectively constructed. PMID:17958370

Gao, Guang-Yao; Ruppel, Joshua V; Allen, D Brett; Chen, Ying; Zhang, X Peter

2007-10-24

99

Effects of salt concentration on formation and dissociation of beta-lactoglobulin/pectin complexes.  

PubMed

The formation and dissociation of beta-lactoglobulin/pectin complexes at various sodium chloride concentrations (CNaCl) have been studied by turbidimetric titration. An increase of CNaCl up to 0.1 M shifts the critical pHphi1, which designates the formation of beta-lactoglobulin/pectin coacervates, to higher pH values, whereas further increase of CNaCl from 0.1 to 0.8 M decreases pHphi1 values. These salt effects can be explained in terms of a salt-enhanced effect at lower salt concentrations or a salt-reduced effect at higher salt concentrations, respectively. On the other hand, the value of pHphi2, which corresponds to the dissociation of beta-lactoglobulin/pectin coacervates, tends to have smaller pH values when CNaCl increases from 0.1 to 0.3 M. No observable pHphi2 values are found at CNaCl higher than 0.3 M. The disappearance of pHphi2 is mainly attributed to the strong self-aggregation capability of beta-lactoglobulin at higher CNaCl. The aggregation of beta-lactoglobulin at high CNaCl is reversible, as suggested by the atomic force microscopy results. PMID:17979233

Wang, Xiaoyong; Wang, Yu-Wen; Ruengruglikit, Chada; Huang, Qingrong

2007-11-03

100

Influence of the hot rolling conditions on texture formation in Fe-Si sheets  

Microsoft Academic Search

The hypothesis that hot rolling conditions and the microstructure of the hot band produced thereby are the basic factors in developing distinct textures in sheet materials is confirmed by the results given. Starting from hot rolled plates of Fe-1% Si alloys with different carbon contents it was possible to obtain the three technically important textures ({110}, {100} and {111} fibre)

S. Mager; J. Wieting

1994-01-01

101

Current sheet formation in quasi-separatrix layers and hyperbolic ux tubes  

Microsoft Academic Search

In 3D magnetic eld congurations, quasi-separatrix layers (QSLs) are dened as volumes in which eld lines locally display strong gradients of connectivity. Considering QSLs both as the preferential locations for current sheet development and magnetic reconnection, in general, and as a natural model for solar ares and coronal heating, in particular, has been strongly debated issues over the past decade.

G. Aulanier; E. Pariat

102

Current sheet formation in quasi-separatrix layers and hyperbolic flux tubes  

Microsoft Academic Search

In 3D magnetic field configurations, quasi-separatrix layers (QSLs) are defined as volumes in which field lines locally display strong gradients of connectivity. Considering QSLs both as the preferential locations for current sheet development and magnetic reconnection, in general, and as a natural model for solar flares and coronal heating, in particular, has been strongly debated issues over the past decade.

G. Aulanier; E. Pariat; P. Démoulin

2005-01-01

103

Microwave study of the formation of brine layers on homogeneous saline ice sheets  

Microsoft Academic Search

When sea water freezes into sea ice, brine and pure ice are produced. Due to the effects of the expulsion of brine from the sea ice interior and the wicking action of snow and frost flowers deposited on the air-ice interface, brine may accumulate on the upper ice sheet surface. Brine is a concentrated solution of sea salts and water,

R. G. Onstott; M. P. Madden

1994-01-01

104

On the formation of the tunnel valleys of the southern Laurentide ice sheet  

Microsoft Academic Search

Catastrophic releases of meltwater, produced by basal melting and stored for decades in subglacial reservoirs at high pressure, may have been responsible for eroding the broad, deep tunnel valleys that are common along the margins of some lobes of the southern Laurentide ice sheet. We surmise that these releases began when the high water pressure was transmitted to the margin

Roger Le B. Hooke; Carrie E. Jennings

2006-01-01

105

Ethanol induced the formation of ?-sheet and amyloid-like fibrils by surfactant-like peptide A6K.  

PubMed

Self-assembly of natural or designed peptides into fibrillar structures based on ?-sheet conformation is a ubiquitous and important phenomenon. Recently, organic solvents have been reported to play inductive roles in the process of conformational change and fibrillization of some proteins and peptides. In this study, we report the change of secondary structure and self-assembling behavior of the surfactant-like peptide A6K at different ethanol concentrations in water. Circular dichroism indicated that ethanol could induce a gradual conformational change of A6K from unordered secondary structure to ?-sheet depending upon the ethanol concentration. Dynamic light scattering and atomic force microscopy revealed that with an increase of ethanol concentration the nanostructure formed by A6K was transformed from nanosphere/string-of-beads to long and smooth fibrils. Furthermore, Congo red staining/binding and thioflavin-T binding experiments showed that with increased ethanol concentration, the fibrils formed by A6K exhibited stronger amyloid fibril features. These results reveal the ability of ethanol to promote ?-sheet conformation and fibrillization of the surfactant-like peptide, a fact that may be useful for both designing self-assembling peptide nanomaterials and clarifying the molecular mechanism behind the formation of amyloid fibrils. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd. PMID:24105725

Chen, Yongzhu; Tang, Chengkang; Xing, Zhihua; Zhang, Jie; Qiu, Feng

2013-09-17

106

Formation and transport of sheet-electron beams and multibeam configurations for high-power microwave devices  

Microsoft Academic Search

Sheet electron beams and configurations with multiple electron beams have the potential to make possible higher power sources of microwave radiation due to their ability to transport high currents, at reduced current densities, through a single RF interaction circuit. Possible microwave device applications using sheet electron beams include sheet-beam klystrons, rectangular grating circuits, and planar FELs. Historically, implementation of sheet

Mark A. Basten; Jon H. Booske; Jim Anderson; John E. Scharer

1995-01-01

107

Formation of high-beta plasma and stable confinement of toroidal electron plasma in Ring Trap 1  

Microsoft Academic Search

Formation of high-beta electron cyclotron resonance heating plasma and stable confinement of pure electron plasma have been realized in the Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet. The effects of coil levitation resulted in drastic improvements of the confinement properties, and the maximum local beta value has exceeded 70%. Hot electrons are major

H. Saitoh; Z. Yoshida; J. Morikawa; M. Furukawa; Y. Yano; Y. Kawai; M. Kobayashi; G. Vogel; H. Mikami

2011-01-01

108

Role of glycogen synthase kinase 3 beta as a negative regulator of dorsoventral axis formation in Xenopus embryos.  

PubMed Central

The dorsoventral axis is established early in Xenopus development and may involve signaling by Wnts, a family of Wnt1-protooncogene-related proteins. The protein kinase shaggy functions in the wingless/Wnt signaling pathway, which operates during Drosophila development. To assess the role of a closely related kinase, glycogen synthase kinase 3 beta (GSK-3 beta), in vertebrate embryogenesis, we cloned a cDNA encoding a Xenopus homolog of GSK-3 beta (XGSK-3 beta). XGSK-3 beta-specific transcripts were detected by Northern analysis in Xenopus eggs and early embryos. Microinjection of the mRNA encoding a catalytically inactive form of rat GSK-3 beta into a ventrovegetal blastomere of eight-cell embryos caused ectopic formation of a secondary body axis containing a complete set of dorsal and anterior structures. Furthermore, in isolated ectodermal explants, the mutant GSK-3 beta mRNA activated the expression of neural tissue markers. Wild-type XGSK-3 beta mRNA suppressed the dorsalizing effects of both the mutated GSK-3 beta and Xenopus dishevelled, a proposed upstream signaling component of the same pathway. These results strongly suggest that XGSK-3 beta functions to inhibit dorsoventral axis formation in the embryo and provide evidence for conservation of the Wnt signaling pathway in Drosophila and vertebrates. Images Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6

Dominguez, I; Itoh, K; Sokol, S Y

1995-01-01

109

The evolution of electron current sheet and formation of secondary islands in guide field reconnection  

NASA Astrophysics Data System (ADS)

Two-dimensional particle-in-cell simulations are performed to investigate the evolution of the electron current sheet (ECS) in guide field reconnection. The ECS is formed by the electrons accelerated by the inductive electric field in the vicinity of the X line. The ECS is then extended along the direction due to of the imbalance between the electric field force and the Ampere force. The tearing instability is unstable when the ECS becomes sufficiently long, and several seed islands are formed. These tiny islands may coalesce and form a larger secondary island in the center of the ion diffusion region.

Huang, C.; Lu, Q.

2011-12-01

110

Reduced North Atlantic Central Water formation in response to early Holocene ice-sheet melting  

NASA Astrophysics Data System (ADS)

Central waters of the North Atlantic are fundamental for ventilation of the upper ocean and are also linked to the strength of the Atlantic Meridional Overturning Circulation (AMOC). Here, we show based on benthic foraminiferal Mg/Ca ratios, that during times of enhanced melting from the Laurentide Ice Sheet (LIS) between 9.0-8.5 thousand years before present (ka) the production of central waters weakened the upper AMOC resulting in a cooling over the Northern Hemisphere. Centered at 8.54 ± 0.2 ka and 8.24 ± 0.1 ka our dataset records two ˜150-year cooling events in response to the drainage of Lake Agassiz/Ojibway, indicating early slow-down of the upper AMOC in response to the initial freshwater flux into the subpolar gyre (SPG) followed by a more severe weakening of both the upper and lower branches of the AMOC at 8.2 ka. These results highlight the sensitivity of regional North Atlantic climate change to the strength of central-water overturning and exemplify the impact of both gradual and abrupt freshwater fluxes on eastern SPG surface water convection. In light of the possible future increase in Greenland Ice Sheet melting due to global warming these findings may help us to better constrain and possibly predict future North Atlantic climate change.

Bamberg, Audrey; Rosenthal, Yair; Paul, André; Heslop, David; Mulitza, Stefan; Rühlemann, Carsten; Schulz, Michael

2010-09-01

111

Low-temperature formation of beta-type silicon carbide by ion-beam mixing  

NASA Astrophysics Data System (ADS)

This paper reports on the ion mixing of a carbon-silicon system induced by the Ar-ion bombardment of carbon layers deposited by an arc-discharge on single-crystalline silicon substrates. A study using infrared absorption spectroscopy has shown that a disordered carbon-silicon mixture can be obtained immediately after bombardment and that subsequent annealing causes the formation of a crystalline beta-type silicon carbide phase at about 800 C. The formation temperature is lower by about 100 C than that for carbon-silicon mixed layers formed by the direct implantation of carbon ions into silicon substrates. Argon-ion bombardment, itself, is found to play an important role in a reduction of the formation temperature.

Kimura, T.; Tatebe, Y.; Kawamura, A.; Yugo, S.; Adachi, Y.

1985-12-01

112

Studies on the relationship between structure and electrophoretic mobility of alpha-helical and beta-sheet peptides using capillary zone electrophoresis.  

PubMed

The electrophoretic behaviour of a series of 33 different synthetic peptides has been investigated using free solution high-performance capillary zonal electrophoretic (HPCZE) methods. The dependency of the electrophoretic mobility, mu(em), on the peptide charge, q, and on the charge-to-size ratio parameter, zeta, determined according to several electromobility models, have been examined. Significant divergences from linearity in the mu(em) vs. q or the mu(em) vs. zeta plots were noted for several peptides, possibly due to the proclivity of specific arrangements of their amino acid sequences to assume preferred alpha-helical or beta-sheet conformational features rather than random coil structures under the HPCZE conditions. These results provide further demonstration of the facility of HPCZE procedures to probe the effects of compositional, sequential and conformational differences of closely-related peptides and their consequences on their physicochemical behaviour in solution. PMID:10536845

Sitaram, B R; Keah, H H; Hearn, M T

1999-10-01

113

Involvement of Streptococcus gordonii Beta-Glucoside Metabolism Systems in Adhesion, Biofilm Formation, and In Vivo Gene Expression  

PubMed Central

Streptococcus gordonii genes involved in beta-glucoside metabolism are induced in vivo on infected heart valves during experimental endocarditis and in vitro during biofilm formation on saliva-coated hydroxyapatite (sHA). To determine the roles of beta-glucoside metabolism systems in biofilm formation, the loci of these induced genes were analyzed. To confirm the function of genes in each locus, strains were constructed with gene inactivation, deletion, and/or reporter gene fusions. Four novel systems responsible for beta-glucoside metabolism were identified, including three phosphoenolpyruvate-dependent phosphotransferase systems (PTS) and a binding protein-dependent sugar uptake system for metabolizing multiple sugars, including beta-glucosides. Utilization of arbutin and esculin, aryl-beta-glucosides, was defective in some mutants. Esculin and oligochitosaccharides induced genes in one of the three beta-glucoside metabolism PTS and in four other genetic loci. Mutation of genes in any of the four systems affected in vitro adhesion to sHA, biofilm formation on plastic surfaces, and/or growth rate in liquid medium. Therefore, genes associated with beta-glucoside metabolism may regulate S. gordonii in vitro adhesion, biofilm formation, growth, and in vivo colonization.

Kilic, Ali O.; Tao, Lin; Zhang, Yongshu; Lei, Yu; Khammanivong, Ali; Herzberg, Mark C.

2004-01-01

114

Evidence of FCC titanium hydride formation in. beta. titanium alloy: An X-ray diffraction study  

SciTech Connect

Three types of titanium hydrides have been reported: delta, epsilon and ..gamma.. hydrides. The delta hydride forms in the composition range from TiH/sub 1.5/ to TiH/sub 1.99/ and has a CaF/sub 2/ structure with metal atoms on an fcc lattice and hydrogen atoms randomly occupying tetrahedral interstitial sites. At higher hydrogen concentrations, TiH/sub 2/, the fct (c/a < 1) epsilon hydride phase is formed below 310 K. The c/a ratio decreases with a decreasing temperature and it reaches and maintains a minimum value of 0.943 below 80 K. The fcc to tetragonal, delta ..-->.. epsilon transformation is apparently diffusionless, similar to that operating in the cubic/tetragonal transformation in zirconium hydride. The metastable fct ..gamma.. hydride having a c/a value of 1.09 or 1.12 forms from solid solutions of hydrogen in the hcp ..cap alpha.. matrix. While the titanium hydride precipitation in ..cap alpha..-Ti and its alloys has attracted extensive investigation, hydride formation in bcc ..beta..-Ti alloys has rarely been studied because they have not been thought to be liable to hydride formation. This paper shows conclusive evidence for the fcc delta hydride phase formation in the ..beta.. phase Ti-30 wt% Mo by x-ray diffraction study.

Shih, D.S.; Birnbaum, H.K.

1986-09-01

115

Delta98Delta, a minimalist model of antiparallel beta-sheet proteins based on intestinal fatty acid binding protein.  

PubMed

The design of beta-barrels has always been a formidable challenge for de novo protein design. For instance, a persistent problem is posed by the intrinsic tendency to associate given by free edges. From the opposite standpoint provided by the redesign of natural motifs, we believe that the intestinal fatty acid binding protein (IFABP) framework allows room for intervention, giving rise to abridged forms from which lessons on beta-barrel architecture and stability could be learned. In this context, Delta98Delta (encompassing residues 29-126 of IFABP) emerges as a monomeric variant that folds properly, retaining functional activity, despite lacking extensive stretches involved in the closure of the beta-barrel. Spectroscopic probes (fluorescence and circular dichroism) support the existence of a form preserving the essential determinants of the parent structure, albeit endowed with enhanced flexibility. Chemical and physical perturbants reveal cooperative unfolding transitions, with evidence of significant population of intermediate species in equilibrium, structurally akin to those transiently observed in IFABP. The recognition by the natural ligand oleic acid exerts a mild stabilizing effect, being of a greater magnitude than that found for IFABP. In summary, Delta98Delta adopts a monomeric state with a compact core and a loose periphery, thus pointing to the nonintuitive notion that the integrity of the beta-barrel can indeed be compromised with no consequence on the ability to attain a native-like and functional fold. PMID:19309727

Curto, Lucrecia María; Caramelo, Julio Javier; Franchini, Gisela Raquel; Delfino, José María

2009-04-01

116

Relationship between S100beta and GFAP expression in astrocytes during infarction and glial scar formation after mild transient ischemia.  

PubMed

The expression of astrocyte marker proteins (S100beta and GFAP) during infarction and glial scar formation after transient middle cerebral artery (MCA) occlusion was examined using double immunostaining. S100beta immunoreactivity markedly decreased in the core of the injured area when observed immediately after reperfusion and did not increase again. In the periphery, however, S100beta expression increased, showing that S100beta synthesis was up-regulated. S100beta+/iNOS+ astrocytes in the periphery were observed from day 1, when small infarct areas were detectable, up to day 5, when infarct expansion had almost ended. TUNEL+ cells in the periphery were present from days 1 to 5. S100beta+/TUNEL+ cells were observed centrally and around the periphery of the injured area, predicting that cell death contributes to the increase of S100beta concentration in the injured area. Our results suggest that (1) higher concentration of S100beta in the extracellular space due to S100beta leakage from damaged astrocytes leads to up-regulation of S100beta synthesis and induction of inducible nitric oxide synthase (iNOS) synthesis in astrocytes, contributing to infarct expansion that results in DNA damage or cell death via NO and ROS production, and (2) GFAP, but not S100beta, is a main contributor to glial scar formation. On day 1 postreperfusion, the microdiascopic images of the injured areas from the unstained thick sections or the areas detected by S100beta immunoreactivity were larger than those of the infarct areas detected by hematoxylin--eosin (HE)-staining. The difference between these sizes might be useful to predict infarct expansion. PMID:15328028

Yasuda, Yuko; Tateishi, Narito; Shimoda, Taiji; Satoh, Souichi; Ogitani, Eriko; Fujita, Setsuya

2004-09-17

117

AmrZ Beta-Sheet Residues Are Essential for DNA Binding and Transcriptional Control of Pseudomonas aeruginosa Virulence Genes ? †  

PubMed Central

AmrZ is a putative ribbon-helix-helix (RHH) transcriptional regulator. RHH proteins utilize residues within the ?-sheet for DNA binding, while the ?-helices promote oligomerization. AmrZ is of interest due to its dual roles as a transcriptional activator and as a repressor, regulating genes encoding virulence factors associated with both chronic and acute Pseudomonas aeruginosa infection. In this study, cross-linking revealed that AmrZ forms oligomers in solution but that the amino terminus, containing an unordered region and a ?-sheet, were not required for oligomerization. The first 12 unordered residues (extended amino terminus) contributed minimally to DNA binding. Mutagenesis of the AmrZ ?-sheet demonstrated that residues 18, 20, and 22 were essential for DNA binding at both activation and repressor sites, suggesting that AmrZ utilizes a similar mechanism for binding to these sites. Mice infected with amrZ mutants exhibited reduced bacterial burden, morbidity, and mortality. Direct in vivo competition assays showed a 5-fold competitive advantage for the wild type over an isogenic amrZ mutant. Finally, the reduced infection phenotype of the amrZ-null strain was similar to that of a strain expressing a DNA-binding-deficient AmrZ variant, indicating that DNA binding and transcriptional regulation by AmrZ is responsible for the in vivo virulence defect. These recent infection data, along with previously identified AmrZ-regulated virulence factors, suggest the necessity of AmrZ transcriptional regulation for optimal virulence during acute infection.

Waligora, Elizabeth A.; Ramsey, Deborah M.; Pryor, Edward E.; Lu, Haiping; Hollis, Thomas; Sloan, Gina P.; Deora, Rajendar; Wozniak, Daniel J.

2010-01-01

118

Kelvin-Helmholtz vortices around the magnetotail and cold plasma sheet formation: Insight as a multiscale phenomenon  

NASA Astrophysics Data System (ADS)

The magnetopause of the Earth's magnetosphere is a key region in magnetospheric physics, especially in the sense of multiscale coupling from global large-scale phenomena to microscale physics. The velocity shear across the magnetopause is believed to cause Kelvin-Helmholtz instability (KHI) on both the dawn and dusk sides when the interplanetary magnetic field (IMF) points northward; magnetic reconnection and some secondary instabilities are likely to occur in the vortical structure induced by KHI and to play a significant role in solar wind entry across the magnetopause as well as plasma mixing there. This is a manifestation of multiscale coupling; that is, large-scale KH instability may induce micro-scale phenomenon in the rolled-up vortices and resultant formation of the cold plasma sheet in a wide region of the near-Earth magnetotail. Here we show a nice simultaneous measurement of solar wind entry associated with KHI on both sides of the magnetosphere under prolonged northward IMF. In the event that we have found, Cluster on the dawnside and Geotail on the duskside had an opportunity to stay around the magnetopause simultaneously on the opposite side to each other for more than several hours. Proton distribution function on the magnetosphere side of the magnetopause presents dawn-dusk asymmetry, which means that different plasma mixing processes are actually taking place on both sides. Using the Grad-Shafranov reconstruction (GSR) technique that can visualize ambient plasma and field around spacecraft, we clarify that vortical structures due to KHI indeed developed on both sides. These observations and reconstruction analysis suggest that vortical structures induced by KHI result in dawn-dusk asymmetry of plasma mixing around the magnetopause and formation of the cold plasma sheet in a wide region of the near-Earth magnetotail.

Nishino, Masaki N.; Hasegawa, Hiroshi; Fujimoto, Masaki; Mukai, Toshifumi; Saito, Yoshifumi; Reme, Henri; Retino, Alessandro; Nakamura, Rumi; Lucek, Elizabeth

119

Alpha- and beta- aspartyl peptide ester formation via aspartimide ring opening.  

PubMed

The undesirable reaction of aspartimide formation has been proved to occur under both acid and base conditions in solid-phase peptide synthesis and is dependent on the beta-carboxyl protecting group, the acid or base used during the synthesis, as well as the peptide sequence. The hydrolysis of aspartimide-containing peptides, especially during HPLC purification, yields a mixture of alpha- and beta-aspartyl peptides that can not be purified easily. A previous study demonstrated that treatment of aspartimide-containing peptides with methanol in the presence of 2% diisopropylethylamine in solution leads to alpha- and beta-aspartyl peptide methyl esters. Taking advantage of these results and aiming at elucidating the optimal conditions for aspartimide ring opening, the effect of different types and concentrations of alcohols (primary and secondary) and bases (diisopropylethylamine, collidine, 4-pyrrolidinopyridine, 1-methyl-2-pyrrolidone, piperidine and KCN) was tested at various temperatures and reaction times. The best results were obtained with a combination of a primary alcohol and diisopropylethylamine, while aspartimide ring opening by secondary alcohols occurred only at high temperatures. The optimal conditions were also applied to solid-phase peptide synthesis. PMID:15884102

Stathopoulos, Panagiotis; Papas, Serafim; Kostidis, Sarantos; Tsikaris, Vassilios

2005-10-01

120

On the formation of the tunnel valleys of the southern Laurentide ice sheet  

USGS Publications Warehouse

Catastrophic releases of meltwater, produced by basal melting and stored for decades in subglacial reservoirs at high pressure, may have been responsible for eroding the broad, deep tunnel valleys that are common along the margins of some lobes of the southern Laurentide ice sheet. We surmise that these releases began when the high water pressure was transmitted to the margin through the substrate. The water pressure in the substrate at the margin would then have been significantly above the overburden pressure, leading to sapping failure. Headward erosion of a conduit in the substrate (piping) could then tap the stored water, resulting in the outburst. In some situations, development of a siphon may have lowered the reservoir below its overflow level, thus tapping additional water. Following the flood, the seal could have reformed and the reservoir refilled, setting up conditions for another outburst. Order of magnitude calculations suggest that once emptied, a subglacial reservoir could refill in a matter of decades. The amount of water released during several outbursts appears to be sufficient to erode a tunnel valley. We think that tunnel valleys are most likely to have formed in this way where and when the glacier margin was frozen to the bed and permafrost extended from the glacier forefield several kilometers back under the glacier, as reservoirs would then have been larger and more common, and the seal more robust and more likely to reform after an outburst. ?? 2006 Elsevier Ltd. All rights reserved.

Hooke, R. LeB.; Jennings, C. E.

2006-01-01

121

Formation of nanocrystalline surface layers by annealing and their role in filiform corrosion of aluminum sheet  

SciTech Connect

Annealing of specific rolled aluminum alloys at temperatures above 300 C causes a significant increase in the filiform corrosion susceptibility of the painted substrate. As demonstrated for a selected substrate (AA8006), the increased susceptibility is related to the formation of a thin, (electro-)chemically active nanocrystalline layer at the surface as a result of the annealing treatment. The corrosion resistance is significantly improved by removing the layer by etching during surface treatment. Possible causes of layer formation and its activity are discussed.

Leth-Olsen, H.; Nordlien, J.H.; Nisancioglu, K. [Norwegian Univ. of Science and Technology, Trondheim (Norway). Dept. of Electrochemistry

1997-07-01

122

Development of two immunoassay formats to detect beta-lactoglobulin: influence of heat treatment on beta-lactoglobulin immunoreactivity and assay applicability in processed food.  

PubMed

Milk proteins are commonly used as ingredients in the food industry because of their functional properties, but they can cause severe reactions in milk-allergic individuals. In this work, two enzyme-linked immunosorbent assay (ELISA) formats were developed to detect bovine beta-lactoglobulin. The indirect competitive ELISA involved the use of anti-beta-lactoglobulin antisera, and the sandwich ELISA involved the use of specific antibodies isolated using a beta-lactoglobulin immunosorbent material. The effect of heat treatment on immunoreactivity of the protein in buffer and in milk was determined with both assays. The amount of immunoreactive protein in buffer and in milk decreased as determined by the sandwich ELISA, whereas the amount increased when measuring with the competitive ELISA. Several food products, including meat, bakery products, sauces, and snacks, were analyzed. With both assays, 10 of 11 products in which the ingredient list included the terms "powdered milk" or "milk proteins" contained beta-lactoglobulin. However, the beta-lactoglobulin concentration in these products obtained with the competitive ELISA were much higher than those obtained with the sandwich ELISA. These differences could be explained by the fact that the determination of beta-lactoglobulin concentration by immunoassay is influenced by differences in antibody recognition of the protein present in highly processed foods. Therefore, the antigen-binding properties of antibodies used in a particular immunoassay are important for a correct interpretation of results obtained in food processed at high temperature. PMID:17685344

de Luis, R; Pérez, M D; Sánchez, L; Lavilla, M; Calvo, M

2007-07-01

123

Global MHD simulations of the relative effects of solar wind features on cold dense plasma sheet formation during the August 31 2005 storm  

Microsoft Academic Search

The solar wind data for the August 31 2005 storm incorporates a prolonged period of northward Bz followed by a sudden transition to an extended period of southward Bz. This northward to southward transition is one condition that leads to the formation of the cold dense plasma sheet. In addition to this evolution in Bz, the data also exhibits substantial

P. A. Damiano; W. Lotko; O. J. Brambles; M. J. Wiltberger; J. Lyon

2009-01-01

124

Formation of Ni–Cu–Platinum Group Element sulfide mineralization in the Sudbury Impact Melt Sheet  

Microsoft Academic Search

Summary The Ni–Cu–Platinum Group Element (PGE) sulfide deposits of the Sudbury Structure have provided a major portion of the world’s total nickel production and their host rocks have been the subject of numerous research studies, yet a number of perplexing problems remain to be solved. On the one hand, studies seeking to explain the formation of the Sudbury Structure have

R. R. Keays; P. C. Lightfoot

2004-01-01

125

The geologic mapping of Venus using C-1 format: Sheets 75N254, 60N263  

NASA Astrophysics Data System (ADS)

The results of geologic mapping of Venus, produced on the base of Magellan images, are presented. We submit two C-1 format geologic maps with the appropriate legend. The mapping territory was taken from Venera 15 and 16 missions and geologic maps were composed. Magellan images allow us to divide some types of the plains units to determine the lava flow direction and to map with better accuracy.

Shalimov, I. V.

1992-12-01

126

Models of beta-amyloid ion channels in the membrane suggest that channel formation in the bilayer is a dynamic process.  

PubMed

Here we model the Alzheimer beta-peptide ion channel with the goal of obtaining insight into the mechanism of amyloid toxicity. The models are built based on NMR data of the oligomers, with the universal U-shaped (strand-turn-strand) motif. After 30-ns simulations in the bilayer, the channel dimensions, shapes and subunit organization are in good agreement with atomic force microscopy (AFM). The models use the Abeta(17-42) pentamer NMR-based coordinates. Extension and bending of the straight oligomers lead to two channel topologies, depending on the direction of the curvature: 1), the polar/charged N-terminal beta-strand of Abeta(17-42) faces the water-filled pore, and the hydrophobic C-terminal beta-strand faces the bilayer (CNpNC; p for pore); and 2), the C-terminal beta-strand faces the solvated pore (NCpCN). In the atomistic simulations in a fully solvated DOPC lipid bilayer, the first (CNpNC) channel preserves the pore and conducts solvent; by contrast, hydrophobic collapse blocks the NCpCN channel. AFM demonstrated open pores and collapsed complexes. The final averaged CNpNC pore dimensions (outer diameter 8 nm; inner diameter approximately 2.5 nm) are in the AFM range (8-12 nm; approximately 2 nm, respectively). Further, in agreement with high-resolution AFM images, during the simulations, the channels spontaneously break into ordered subunits in the bilayer; however, we also observe that the subunits are loosely connected by partially disordered inner beta-sheet, suggesting subunit mobility in the bilayer. The cationic channel has strong selective affinity for Ca(2+), supporting experimental calcium-selective beta-amyloid channels. Membrane permeability and consequent disruption of calcium homeostasis were implicated in cellular degeneration. Consequently, the CNpNC channel topology can sign cell death, offering insight into amyloid toxicity via an ion "trap-release" transport mechanism. The observed loosely connected subunit organization suggests that amyloid channel formation in the bilayer is a dynamic, fluid process involving subunit association, dissociation, and channel rearrangements. PMID:17526580

Jang, Hyunbum; Zheng, Jie; Nussinov, Ruth

2007-05-25

127

Solvent effects on self-assembly of beta-amyloid peptide.  

PubMed Central

beta-amyloid peptide (A beta) is the primary protein component of senile plaques in Alzheimer's disease patients. Synthetic A beta spontaneously assembles into amyloid fibrils and is neurotoxic to cortical cultures. Neurotoxicity has been associated with the degree of peptide aggregation, yet the mechanism of assembly of A beta into amyloid fibrils is poorly understood. In this work, A beta was dissolved in several different solvents commonly used in neurotoxicity assays. In pure dimethylsulfoxide (DMSO), A beta had no detectable beta-sheet content; in 0.1% trifluoroacetate, the peptide contained one-third beta-sheet; and in 35% acetonitrile/0.1% trifluoroacetate, A beta was two-thirds beta-sheet, equivalent to the fibrillar peptide in physiological buffer. Stock solutions of peptide were diluted into phosphate-buffered saline, and fibril growth was followed by static and dynamic light scattering. The growth rate was substantially faster when the peptide was predissolved in 35% acetonitrile/0.1% trifluoroacetate than in 0.1% trifluoroacetate, 10% DMSO, or 100% DMSO. Differences in growth rate were attributed to changes in the secondary structure of the peptide in the stock solvent. These results suggest that formation of an intermediate with a high beta-sheet content is a controlling step in A beta self-assembly.

Shen, C L; Murphy, R M

1995-01-01

128

The effect of low levels of dopants upon the formation and properties of beta-phase molybdenum nitride  

SciTech Connect

The addition of 1 wt% Pd, Au, Ni and Cu dopants has been demonstrated to strongly alter the morphology of beta-phase molybdenum nitride prepared by treatment of MoO{sub 3} with a 3/1 H{sub 2}/N{sub 2} mixture at 750 deg. C. Furthermore, the addition of Pd significantly enhances the surface area and the formation of the nitride phase. It is proposed that the facile formation of molybdenum bronzes in this system is important in this respect. The dopants have also been observed to modify the denitridation characteristics of the beta-phase, with an overall reduction of the proportion of NH{sub 3} formed upon using a 3/1 H{sub 2}/Ar mixture with respect to the undoped sample. - Graphical abstract: Low levels of Pd, Au, Ni and Cu dopant have significant effects upon the morphology, formation and dentitridation characteristics of beta-phase molybdenum nitride.

Cairns, A.G.; Gallagher, J.G. [WestCHEM, Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Hargreaves, J.S.J., E-mail: justinh@chem.gla.ac.u [WestCHEM, Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Mckay, D. [WestCHEM, Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Rico, J.L., E-mail: jlrico@umich.m [Laboratorio de Catalisis, Facultad de Ingenieria Quimica, Universidad Michoacana, Edificio E, CU, Morelia Mich, C.P. 58060 (Mexico); Wilson, K. [WestCHEM, Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ (United Kingdom)

2010-03-15

129

Mutational analysis and membrane-interactions of the beta-sheet-like N-terminal domain of the pediocin-like antimicrobial peptide sakacin P.  

PubMed

To gain insight into how the N-terminal three-stranded beta-sheet-like domain in pediocin-like antimicrobial peptides positions itself on membranes, residues in the well-conserved (Y)YGNGV-motif in the domain were substituted and the effect of the substitutions on antimicrobial activity and binding of peptides to liposomes was determined. Peptide-liposome interactions were detected by measuring tryptophan-fluorescence upon exposing liposomes to peptides in which a tryptophan residue had been introduced in the N-terminal domain. The results revealed that the N-terminal domain associates readily with anionic liposomes, but not with neutral liposomes. The electrostatic interactions between peptides and liposomes facilitated the penetration of some of the peptide residues into the liposomes. Measuring the antimicrobial activity of the mutated peptides revealed that the Tyr2Leu and Tyr3Leu mutations resulted in about a 10-fold reduction in activity, whereas the Tyr2Trp, Tyr2Phe, Tyr3Trp and Tyr3Phe mutations were tolerated fairly well, especially the mutations in position 3. The Val7Ile mutation did not have a marked detrimental effect on the activity. The Gly6Ala mutation was highly detrimental, consistent with Gly6 being in one of the turns in the beta-sheet-like N-terminal domain, whereas the Gly4Ala mutation was tolerated fairly well. All mutations involving Asn5, including the conservative mutations Asn5Gln and Asn5Asp, were very deleterious. Thus, both the polar amide group on the side chain of Asn5 and its exact position in space were crucial for the peptides to be fully active. Taken together, the results are consistent with Val7 positioning itself in the hydrophobic core of target membranes, thus forcing most of the other residues in the N-terminal domain into the membrane interface region: Tyr3 and Asn5 in the lower half with their side chains pointing downward and approaching the hydrophobic core, Tyr2, Gly4 and His8 and 12 in the upper half, Lys1 near the middle of the interface region, and the side chain of Lys11 pointing out toward the membrane surface. PMID:16762606

Fimland, Gunnar; Pirneskoski, Jussi; Kaewsrichan, Jasadee; Jutila, Arimatti; Kristiansen, Per Eugen; Kinnunen, Paavo K J; Nissen-Meyer, Jon

2006-05-05

130

Characterization and bioactivity of tape-cast and sintered TCP sheets.  

PubMed

The purpose of this study was to investigate the influence of sintering temperature on in vivo and in vitro bioactivities of sintered tricalcium phosphate (TCP) sheets prepared by the tape casting technique. Green sheets of beta-TCP prepared by tape casting were sintered for 2 h in a furnace at atmospheric pressure, at five different sintering temperatures: 900, 1000, 1100, 1150, and 1200 degrees C. Measurement of X-ray diffraction and Fourier transform infrared spectrometry showed the presence of alpha-tricalcium phosphate phase in the TCP sheet sintered at 1200 degrees C, in addition to beta-TCP phase. As compared with the other sintered TCP sheet, the TCP sheet sintered at 1200 degrees C demonstrated a lower dissolution rate in phosphate buffered saline solution at 37 degrees C and pH 7.4 over 24 weeks, and more amount of apatite formation in Hanks' balanced salt solution with pH 7.4 was observed. After 4 weeks' implantation of sintered TCP sheets into tibial diaphyses of rabbits, the bone-sheet contact of the TCP sheet sintered at 1200 degrees C was significantly higher than that of the TCP sheet sintered at 900 degrees C. These results indicate that a flat sintered TCP sheet prepared by tape casting is a promising material for a bone substitute. PMID:16278874

Tanimoto, Yasuhiro; Hayakawa, Tohru; Sakae, Toshiro; Nemoto, Kimiya

2006-03-01

131

Glycogen synthase kinase 3beta modulates synphilin-1 ubiquitylation and cellular inclusion formation by SIAH: implications for proteasomal function and Lewy body formation.  

PubMed

alpha-Synuclein is known to play a major role in the pathogenesis of Parkinson disease. We previously identified synphilin-1 as an alpha-synuclein-interacting protein and more recently found that synphilin-1 also interacts with the E3 ubiquitin ligases SIAH-1 and SIAH-2. SIAH proteins ubiquitylate synphilin-1 and promote its degradation through the ubiquitin proteasome system. Inability of the proteasome to degrade synphilin-1 promotes the formation of ubiquitylated inclusion bodies. We now show that synphilin-1 is phosphorylated by GSK3beta within amino acids 550-659 and that this phosphorylation is significantly decreased by pharmacological inhibition of GSK3beta and suppression of GSK3beta expression by small interfering RNA duplex. Mutation analysis showed that Ser556 is a major GSK3beta phosphorylation site in synphilin-1. GSK3beta co-immunoprecipitated with synphilin-1, and protein 14-3-3, an activator of GSK3beta activity, increased synphilin-1 phosphorylation. GSK3beta decreased the in vitro and in vivo ubiquitylation of synphilin-1 as well as its degradation promoted by SIAH. Pharmacological inhibition and small interfering RNA suppression of GSK3beta greatly increased ubiquitylation and inclusion body formation by SIAH. Additionally, synphilin-1 S556A mutant, which is less phosphorylated by GSK3beta, formed more inclusion bodies than wild type synphilin-1. Inhibition of GSK3beta in primary neuronal cultures decreased the levels of endogenous synphilin-1, indicating that synphilin-1 is a physiologic substrate of GSK3beta. Using GFPu as a reporter to measure proteasome function in vivo, we found that synphilin-1 S556A is more efficient in inhibiting the proteasome than wild type synphilin-1, raising the possibility that the degree of synphilin-1 phosphorylation may regulate the proteasome function. Activation of GSK3beta during endoplasmic reticulum stress and the specific phosphorylation of synphilin-1 by GSK3beta place synphilin-1 as a possible mediator of endoplasmic reticulum stress and proteasomal dysfunction observed in Parkinson disease. PMID:16174773

Avraham, Eyal; Szargel, Raymonde; Eyal, Allon; Rott, Ruth; Engelender, Simone

2005-09-20

132

Dynamics of beta-amyloid peptide in cholesterol superlattice domain  

NASA Astrophysics Data System (ADS)

Presence of beta-amyloid peptide (beta-A) plagues in membranes of neuron cells is a clinical signature of Alzheimer disease. The onset of beta-A peptide aggregation occurs via a conformational transition from an alpha-helix state to a beta-sheet state. A gradual build-up of beta-A content in the neuronal extracellular space is another characteristic of the beta-A plague formation. Hypothetically, both the pathological conformation and the predominant localization of the beta-A can be a result of specific dynamic characteristics of the interphase between cellular membrane and extracellular milieu. In this study, the beta-A interphase problem has been investigated using a virtual membrane model implemented on the base of GROMACS molecular dynamics simulation package. The detailed folding pattern of beta-A has been examined using a novice interphase model comprised of a cholesterol supperlattice membrane and two water layers.

Smirnov, Anton; Zhu, Qing; Vaughn, Mark; Khare, Rajesh; Cheng, K.

2006-10-01

133

Formation kinetics and structural features of Beta-amyloid aggregates by sedimented solute NMR.  

PubMed

The accumulation of soluble toxic beta-amyloid (A?) aggregates is an attractive hypothesis for the role of this peptide in the pathology of Alzheimer's disease. We have introduced sedimentation through ultracentrifugation, either by magic angle spinning (in situ) or preparative ultracentrifuge (ex situ), to immobilize biomolecules and make them amenable for solid-state NMR studies (SedNMR). In situ SedNMR is used here to address the kinetics of formation of soluble A? assemblies by monitoring the disappearance of the monomer and the appearance of the oligomers simultaneously. Ex situ SedNMR allows us to select different oligomeric species and to reveal atomic-level structural features of soluble A? assemblies. PMID:23821412

Bertini, Ivano; Gallo, Gianluca; Korsak, Magdalena; Luchinat, Claudio; Mao, Jiafei; Ravera, Enrico

2013-07-02

134

Pulmonary surfactant-associated polypeptide C in a mixed organic solvent transforms from a monomeric alpha-helical state into insoluble beta-sheet aggregates.  

PubMed Central

In the 35-residue pulmonary surfactant-associated lipopolypeptide C (SP-C), the stability of the valyl-rich alpha-helix comprising residues 9-34 has been monitored by circular dichroism, nuclear magnetic resonance, and Fourier transform infrared spectroscopy in both a mixed organic solvent and in phospholipid micelles. The alpha-helical form of SP-C observed in freshly prepared solutions in a mixed solvent of CHCl3/CH3OH/0.1 M HCl 32:64:5 (v/v/v) at 10 degrees C undergoes within a few days an irreversible transformation to an insoluble aggregate that contains beta-sheet secondary structure. Hydrogen exchange experiments revealed that this conformational transition proceeds through a transition state with an Eyring free activation enthalpy of about 100 kJ mol(-1), in which the polypeptide segment 9-27 largely retains a helical conformation. In dodecylphosphocholine micelles, the helical form of SP-C was maintained after seven weeks at 50 degrees C. The alpha-helical form of SP-C thus seems to be the thermodynamically most stable state in this micellar environment, whereas its presence in freshly prepared samples in the aforementioned mixed solvent is due to a high kinetic barrier for unfolding. These observations support a previously proposed pathway for in vivo synthesis of SP-C through proteolytic processing from a 21-kDa precursor protein.

Szyperski, T.; Vandenbussche, G.; Curstedt, T.; Ruysschaert, J. M.; Wuthrich, K.; Johansson, J.

1998-01-01

135

Thermal conditions at the bed of the Laurentide ice sheet in Maine during deglaciation: implications for esker formation  

Microsoft Academic Search

The University of Maine Ice Sheet Model was used to study basal conditions during retreat of the Laurentide ice sheet in Maine. Within 150 km of the margin, basal melt rates average ˜5 mm a-1 during retreat. They decline over the next 100 km, so areas of frozen bed develop in northern Maine during retreat. By integrating the melt rate

Roger Leb. Hooke; James Fastook

2007-01-01

136

Influence of transforming growth factor-beta3 on fibrous capsule formation around microgrooved subcutaneous implants in vivo.  

PubMed

Previous studies have shown that addition of transforming growth factor-beta3 (TGF-beta3) is capable of reducing scar tissue formation in skin defects. Therefore, we examined whether TGF-beta3 can also influence the organization of a fibrous capsule around implants in vivo. For this reason, 24 silicone implants with microgrooves with a groove depth of 1.0 microm and a ridge and groove width of 10.0 microm were made and loaded with human recombinant TGF-beta3 (0, 5, 50, and 250 ng). An in vitro release enzyme-linked immunosorbent assay (ELISA) test was done with another 10 implants to estimate the amount of TGF released from the implants. The implants were inserted subcutaneously in the backs of 6 guinea pigs. Each animal received four implants, which were left in place for 10 weeks. At the end of the implantation time, the implants were retrieved, embedded, and processed for histology. Histomorphometrical measurements were done on the capsule formation and the implant-cell interface quality and quantity. The results showed a fibrous capsule of 15 microm up to 50 microm thickness around all implants. There were no significant differences between the TGF-beta3-loaded implants or the controls. Frequently, inflammatory cells were present in the capsule. The implant-tissue interface was on average between 5 and 15 microm thick and consisted mostly out of one or two layers of macrophages or foreign body giant cells. Statistical analysis again showed no significant differences between the various TGF-beta3-coated implants and controls. Finally, we concluded that a microtextured surface can indeed be used for the release of TGF-beta3. On the other hand, this did not result in major differences in wound healing between implants loaded with 5, 50, or 250 ng of TGF-beta3 and controls. PMID:11074937

Gehrke, T A; Walboomers, X F; Jansen, J A

2000-10-01

137

Esker formation and meltwater routing on and beneath the margins of the last Cordilleran Ice Sheet: implications for modelling ice sheet hydrology  

NASA Astrophysics Data System (ADS)

It has been suggested that ice sheet drainage system organization (i.e. channelized or distributed) may be predicted from variables such as substrate character (rigidity, permeability) and ice surface slope. Analysis of esker systems from paleoglacial environments is instructive in testing the validity of such model predictions. We combine data from grids of ground penetrating radar (GPR) and electrical resistivity (ER) with sedimentological observations, water well data and detailed geomorphic investigation to infer esker genesis and describe the character and context of three eskers at the margins of the last Cordilleran Ice Sheet (CIS) on British Columbia's (BC's) southern Fraser Plateau. This region is characterized by soft (deformation and deformed lodgement tills), low permeability diamictons (~50% clay and silt content) overlying basalt. Esker systems on the plateau include: 1) a 12 km long, relatively straight (sinuosity ratio, Sr, 1.061), single thread esker (Green Lake esker), with both undulatory and flat-topped sections, deposited in a 38 km long subglacial erosional corridor; 2) a 4.5 km long single thread, undulating, and moderately sinuous esker (Hooke Road esker, Sr 1.36) in the vicinity of ice marginal channels (useful in determining ice surface slope); and 3) a 6 km long esker-like ridge (Young Lake esker), that transitions from flat-topped upflow to undulating downflow and is bordered by closed depressions on the floor of a glacially-modified gorge. The individual eskers are respectively interpreted as: 1) a subglacial esker formed during supraglacial lake drainage, under low ice surface slopes; 2) a supraglacial esker formed by drainage across the ice marginal zone; and 3) an esker-like ridge formed in an ice-walled, unroofed channel within disintegrating ice blocks at a point beyond the intact ice margin. Together these landforms suggest that: 1) supraglacial water was a significant component of water flow at the base of the CIS; 2) CIS decay was, at times, facilitated by high magnitude water flows; and 3) organization of channelized drainage systems was probably not limited to rigid, impermeable beds or to locations of high ice surface slopes. Our data indicate that emerging models of ice sheet hydrology should incorporate sources of unsteady supraglacial drainage.

Perkins, A. J.; Brennand, T.; Burke, M. J.

2011-12-01

138

Proposal for ENDF formats that describe emission of post-fission beta-delayed photons  

SciTech Connect

Fission of heavy nuclides is accompanied by the birth of neutron rich fragment nuclei born in highly excited states. Following emission of prompt neutrons and {gamma}-rays, these fragments are typically left with atomic numbers that are 3-4 units smaller than stable nuclei with the same mass number. As these nuclides undergo {beta} decay to reach stability, a large number of {gamma}-rays are emitted. Figure 1 illustrates some of the processes leading to emission of {beta} delayed photons. A variety of applications (most notably those concerned with the detection and identification of clandestine fissile material) would benefit from a clear description of the spectral and temporal evolution of these {gamma}-rays. This proposal describes formats for representing emission of delayed photons and is based on the analysis presented in. At the present time, no single evaluated data set exists that directly provides for the temporal evolution of {gamma} rays from the decay of the fission products. However, evaluated data sets containing all of the physical parameters required for such calculations have been prepared. These include estimates of the independent and cumulative fission yields of all fission products, branching ratios in the decay of ground and isomeric states, lifetimes of these states, and the spectra of {gamma} rays emitted in their decay. Sizeable uncertainties and possibly significant errors are likely present concerning the shortest-lived fission products. However, the high-energy {gamma}-ray spectra generated from some of these data sets have been shown to be in reasonable agreement with initial experiments designed specifically to test them under conditions likely to be of interest to interrogation of sea-going cargo containers. For clarity we emphasize that the relationship between delayed neutron emission and delayed photon emission is tenuous. Only a small fraction of fission fragments - typically those characterized by large decay Q values - undergo {beta}{sup -}n emission. However, essentially all fission fragment decays result in the emission of a few photons. Also, it would be impractical to accurately specify and measure energies of delayed neutrons. By contrast, most fission fragments have decay spectra known to sub-keV accuracy that are readily resolved with inexpensive field HpGe detectors.

Brown, D; Pruet, J; Hedstrom, G; Hall, J; Descalle, M

2004-09-15

139

Palladium-catalyzed glycal imidate rearrangement: formation of alpha- and beta-N-glycosyl trichloroacetamides.  

PubMed

A novel palladium(II)-catalyzed stereoselective synthesis of alpha- and beta-N-glycosyl trichloroacetamides has been developed. The alpha- and beta-selectivity at the anomeric carbon depends on the nature of the palladium-ligand catalyst. While the cationic palladium(II) promotes the alpha-selectivity, the neutral palladium(II) favors the beta-selectivity. PMID:17880097

Yang, Jaemoon; Mercer, Gregory J; Nguyen, Hien M

2007-09-19

140

Effect of phosphorus on the formation of retained austenite and mechanical properties in Si-containing low-carbon steel sheet  

Microsoft Academic Search

The effect of phosphorus and silicon on the formation of retained austenite has been investigated in a low-carbon steel cold\\u000a rolled, intercritically annealed, and isothermally held in a temperature range of bainitic transformation followed by air\\u000a cooling. The steel sheet containing phosphorus after final heat-treatment consisted of ferrite, retained austenite, and bainite\\u000a or martensite. Phosphorus, especially in the presence of

H. C. Chen; H. Era; M. Shimizu

1989-01-01

141

Characterization of Sheet Fracture Patterns in Polygonal-Jointed Lavas at Kokostick Butte, OR, and Mazama Ridge, WA: Investigation and Interpretation of Their Formation and Significance  

NASA Astrophysics Data System (ADS)

Polygonal joints in lava flows ("columns") are commonly equant leading to a model of formation associated with cooling in an isotropic stress field. This model, however, does not explain rectangular columns, sheet-like fractures, fractures with crosscutting relationships, and fractures with orientations other than perpendicular to the cooling surface. These fracture patterns are often observed at glaciated volcanoes. The presence of preferential fracture orientations suggests an applied stress component likely due to environmental conditions such as the presence of glaciers or flow dynamics such as down-slope settling or flow margin inflation. During this study we investigated the formation and significance of these non-equant fracture patterns to propose a model for their formation. These `abnormal' fracture patterns have not been discussed in the literature and may be important to better understanding the cooling conditions of such lava flows. To test these possibilities we studied Kokostick Butte dacite flow, OR (near South Sister), and Mazama Ridge andesite flow at Mount Rainier, WA. Both of these flows have well developed sheet-like fractures and display evidence of ice-contact during eruption and emplacement. Sheet fractures are long and continuous fractures that have perpendicular connecting fractures forming rectangular columns. The sheet-like fractures are largely parallel to each other on the exposure surface and the connecting fractures vary locally from primary fractures (associated with cooling toward flow interior) to secondary fractures (associated with cooling by water infiltration). Detailed measurements of fracture orientations and spacing were collected at Kokostick Butte and Mazama Ridge to examine the relationship between the sheet fractures and flow geometry. Preliminary results support this relationship and suggest these patterns likely form due to shear associated with small amounts of flow advance by the rapidly cooling lava. Laboratory studies have been undertaken to complement the field observations and measurements. Starch- water experiments have been proven a useful analogue for lava column formation. Various experimental setups involving different mixture thicknesses and compression of the mixture were utilized to simulate the stresses acting during ponding of lava against glacial ice and to produce different fracture morphologies and patterns. Initial results show that compression of the starch slurry results in non-equant fracture patterns with some sheet-like fracturing present.

Lodge, R. W.; Lescinsky, D. T.

2006-12-01

142

Beta Sheet 2 - Alpha Helix C Loop of Cytochrome P450 Reductase Serves as a Docking Site for Redox Partners  

PubMed Central

As a promiscuous redox partner, the biological role of cytochrome P450 reductase (CPR) depends significantly on protein-protein interactions. We tested a hypothesized CPR docking site by mutating D113, E115, and E116 to alanine and assaying activity toward various electron acceptors as a function of ionic strength. Steady-state cytochrome c studies demonstrated the mutations improved catalytic efficiency and decreased the impact of ionic strength on catalytic parameters when compared to wild type. Based on activity toward 7-ethoxy-4-trifluoro-methylcoumarin, CYP2B1 and CPR favored formation of an active CYP2B1·CPR complex and inactive (CYP2B1)2·CPR complex until higher ionic strength whereby only the binary complex was observed. The mutations increased dissociation constants only for the binary complex and suppressed the ionic strength effect. Studies with a non-binding substrate, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) suggest changes in activity toward cytochrome c and CYP2B1 reflect alterations in the route of electron transfer caused by the mutations. Electrostatic modeling of catalytic and binding parameters confirmed the importance of D113 and especially the double mutant E115 and E116 as mediators in forming charge-charge interactions between CPR and complex partners.

Jang, Hyun-Hee; Jamakhandi, Arvind P.; Sullivan, Shane Z.; Yun, Chul-Ho; Hollenberg, Paul F.; Miller, Grover P.

2010-01-01

143

The Role of Plasma Sheet Conditions in Ring Current Formation and Energetic Neutral Atom Emissions: TWINS Results and CRCM Comparison  

NASA Astrophysics Data System (ADS)

The dynamics of the ring current is sensitive to plasma sheet density and temperature. The situation is further complicated by ionospheric feedback and the existence of electric shielding at low latitudes. Most of the ring current pressure is carried by ions with energies of ~5-50 keV. In this energy range, H-H+ charge exchange cross section falls sharply with increasing energy. As a result, the intensity of energetic neutral atoms (ENA) emitted from the ring current is very sensitive to the ion energy distribution, which, in turn, is controlled by the plasma sheet temperature. Using the Comprehensive Ring Current Model (CRCM) with different plasma sheet models, we calculate ENA emissions during several moderate storms in years 2008 and 2009. We compare the simulated images with those from the TWINS imagers and study the effects of plasma sheet conditions on the ring current and the associated ENA emissions.

Fok, M.; Buzulukova, N.; McComas, D.; Brandt, P.; Goldstein, J.; Valek, P.; Alquiza, J.

2009-05-01

144

Sedimentologic evidence for outburst floods from the Laurentide Ice Sheet margin in Wisconsin, USA: implications for tunnel-channel formation  

Microsoft Academic Search

Clast-supported boulder gravel in outwash-fans along the glacial-maximum margin of the Laurentide Ice Sheet in Wisconsin indicates the occurrence of outburst floods. These sediments, with clast intermediate axes of up to 2m, are located downstream of tunnel channels and were deposited shortly before cessation of glaciofluvial activity on each fan. Since tunnel channels with fans are widespread along the ice-sheet

Paul M. Cutler; Patrick M. Colgan; David M. Mickelson

2002-01-01

145

Mitochondrion-Derived Reactive Oxygen Species Lead to Enhanced Amyloid Beta Formation  

PubMed Central

Abstract Aims: Intracellular amyloid beta (A?) oligomers and extracellular A? plaques are key players in the progression of sporadic Alzheimer's disease (AD). Still, the molecular signals triggering A? production are largely unclear. We asked whether mitochondrion-derived reactive oxygen species (ROS) are sufficient to increase A? generation and thereby initiate a vicious cycle further impairing mitochondrial function. Results: Complex I and III dysfunction was induced in a cell model using the respiratory inhibitors rotenone and antimycin, resulting in mitochondrial dysfunction and enhanced ROS levels. Both treatments lead to elevated levels of A?. Presence of an antioxidant rescued mitochondrial function and reduced formation of A?, demonstrating that the observed effects depended on ROS. Conversely, cells overproducing A? showed impairment of mitochondrial function such as comprised mitochondrial respiration, strongly altered morphology, and reduced intracellular mobility of mitochondria. Again, the capability of these cells to generate A? was partly reduced by an antioxidant, indicating that A? formation was also ROS dependent. Moreover, mice with a genetic defect in complex I, or AD mice treated with a complex I inhibitor, showed enhanced A? levels in vivo. Innovation: We show for the first time that mitochondrion-derived ROS are sufficient to trigger A? production in vitro and in vivo. Conclusion: Several lines of evidence show that mitochondrion-derived ROS result in enhanced amyloidogenic amyloid precursor protein processing, and that A? itself leads to mitochondrial dysfunction and increased ROS levels. We propose that starting from mitochondrial dysfunction a vicious cycle is triggered that contributes to the pathogenesis of sporadic AD. Antioxid. Redox Signal. 16, 1421–1433.

Schutt, Tanja; Kurz, Christopher; Eckert, Schamim H.; Schiller, Carola; Occhipinti, Angelo; Mai, Soren; Jendrach, Marina; Eckert, Gunter P.; Kruse, Shane E.; Palmiter, Richard D.; Brandt, Ulrich; Drose, Stephan; Wittig, Ilka; Willem, Michael; Haass, Christian; Reichert, Andreas S.; Muller, Walter E.

2012-01-01

146

Facultative heterochromatin formation at the IL-1 beta promoter in LPS tolerance and sepsis.  

PubMed

The clinical phenotype in sepsis that is observed as LPS tolerance is determined by silencing of pro-inflammatory genes like IL-1 beta (IL-1?). This study shows that facultative heterochromatin (fHC) silences IL-1? expression during sepsis, where we find dephosphorylated histone H3 serine 10 and increased binding of heterochromatin protein-1 (HP-1) to the promoter. In both human sepsis blood leukocytes and an LPS tolerant human THP-1 cell model, we show that I?B? and v-rel reticuloendotheliosis viral oncogene homolog B (RelB) function as dominant labile mediators of fHC formation at the IL-1? promoter. Protein synthesis inhibition decreases levels of I?B? and RelB, converts silent fHC to euchromatin, and restores IL-1? transcription. We further show TLR dependent NF?B p65 and histone H3 serine 10 phosphorylation binding at the promoter. We conclude that the resolution phase of sepsis, which correlates with survival in humans, may depend on the plasticity of chromatin structure as found in fHC. PMID:21078560

Yoza, Barbara K; McCall, Charles E

2011-02-01

147

Facultative heterochromatin formation at the IL-1 beta promoter in LPS tolerance and sepsis  

PubMed Central

The clinical phenotype in sepsis that is observed as LPS tolerance is determined by silencing of proinflammatory genes like IL-1 beta (IL-1?). This study shows that facultative heterochromatin (fHC) silences IL-1? expression during sepsis, where we find dephosphorylated histone H3 serine 10 and increased binding of heterochromatin protein-1 (HP-1) to the promoter. In both human sepsis blood leukocytes and an LPS tolerant human THP-1 cell model, we show that I?B? and v-rel reticuloendotheliosis viral oncogene homolog B (RelB) function as dominant labile mediators of fHC formation at the IL-1? promoter. Protein synthesis inhibition decreases levels of I?B? and RelB, converts silent fHC to euchromatin, and restores IL-1? transcription. We further show TLR dependent NF?B p65 and histone H3 serine 10 phosphorylation binding at the promoter. We conclude that the resolution phase of sepsis, which correlates with survival in humans, may depend on the plasticity of chromatin structure as found in fHC.

Yoza, Barbara K.; McCall, Charles E.

2010-01-01

148

Formation of multiple complexes between beta-dystroglycan and dystrophin family products  

Microsoft Academic Search

Beta-dystroglycan is expressed in a wide variety of tissues and has generally been reported with an Mr of 43 kDa, sometimes\\u000a accompanied with a 31 kDa protein assumed to be a truncated product. This molecule was recently identified as the anomalous\\u000a beta-dystroglycan expressed in various carcinoma cell lines. We produced and characterized a G5 polyclonal antibody specific\\u000a to beta-dystroglycan that

M. Royuela; D. Chazalette; G. Hugon; R. Paniagua; V. Guerlavais; J. A. Fehrentz; J. Martinez; J.-P. Labbe; F. Rivier; D. Mornet

2003-01-01

149

Estradiol acts via estrogen receptors alpha and beta on pathways important for synaptic plasticity in the mouse hippocampal formation  

PubMed Central

Estradiol affects hippocampal-dependent spatial memory and underlying structural and electrical synaptic plasticity in female mice and rats. Using estrogen receptor (ER) alpha and beta knockout mice and wild-type littermates, we investigated the role of ERs in estradiol effects on multiple pathways important for hippocampal plasticity and learning. Six hours of estradiol administration increased immunoreactivity for phosphorylated Akt throughout the hippocampal formation, while 48 hours of estradiol increased immunoreactivity for phosphorylated TrkB receptor. Estradiol effects on phosphorylated Akt and TrkB immunoreactivities were abolished in ER alpha and ER beta knockout mice. Estradiol also had distinct effects on immunoreactivity for PSD-95 and BDNF mRNA in ER alpha and beta knockout mice. Thus, estradiol acts through both ERs alpha and beta in several subregions of the hippocampal formation. The different effects of estradiol at 6 and 48 hours indicate that several mechanisms of estrogen receptor signaling contribute to this female hormone’s influence on hippocampal synaptic plasticity. By further delineating these mechanisms, we will better understand and predict the effects of endogenous and exogenous ovarian steroids on mood, cognition, and other hippocampal-dependent behaviors.

Spencer-Segal, Joanna L.; Tsuda, Mumeko C.; Mattei, Larissa; Waters, Elizabeth M.; Romeo, Russell D.; Milner, Teresa A.; McEwen, Bruce S.; Ogawa, Sonoko

2012-01-01

150

Formation and bioactivity of porous and nanostructured TiO2/beta-TCP coating on titanium.  

PubMed

Titanium and its alloys have been widely used as hard tissue implants due to their excellent mechanical properties and biocompatibility. However, their near bio-inertness and metallic ion release are still the problems with clinical uses. In this paper, porous and nanostructured TiO2/beta-tricalcium phosphate (beta-TCP) composite coatings were prepared on titanium substrates by plasma electrolytic oxidation (PEO) in a Ca and P-containing electrolyte. The influence of PEO electric current density on phase composition and bioactivity of the coatings were studied. X-ray diffraction, scanning electron microscopy and Fourier transfer infrared spectroscopy were utilized to characterize the phase composition and microstructure of the coatings. Simulated body fluid immersion tests were employed on the coatings to evaluate their bioactivity. The results reveal that TiO2/beta-TCP composite coating with pores size less than 10 microm and grains of 50-100 nm in size was prepared. The electric current density of PEO is an important factor in the formation of the composite coating. The TiO2/beta-TCP composite coating shows good bioactivity, which are attributed to the incorporation of beta-TCP. PMID:22409024

Hu, Hongjie; Liu, Xuanyong; Meng, Fanhao; Ding, Chuanxian

2011-12-01

151

The effect of low levels of dopants upon the formation and properties of beta-phase molybdenum nitride  

NASA Astrophysics Data System (ADS)

The addition of 1 wt% Pd, Au, Ni and Cu dopants has been demonstrated to strongly alter the morphology of beta-phase molybdenum nitride prepared by treatment of MoO3 with a 3/1 H2/N2 mixture at 750 °C. Furthermore, the addition of Pd significantly enhances the surface area and the formation of the nitride phase. It is proposed that the facile formation of molybdenum bronzes in this system is important in this respect. The dopants have also been observed to modify the denitridation characteristics of the beta-phase, with an overall reduction of the proportion of NH3 formed upon using a 3/1 H2/Ar mixture with respect to the undoped sample.

Cairns, A. G.; Gallagher, J. G.; Hargreaves, J. S. J.; McKay, D.; Rico, J. L.; Wilson, K.

2010-03-01

152

The localization of LAP2 beta during pronuclear formation in bovine oocytes after fertilization or activation.  

PubMed

We have shown that the assembly of lamin-associated polypeptide (LAP) 2beta was detected surrounding the chromatin mass around the time of extrusion of the second polar body (PB) in some fertilized oocytes, but not in most activated oocytes, by using A23187 and cycloheximide (CaA + CH). Here, we immunohistologically analysed the correlation between LAP2beta assembly and chromatin condensation in fertilized and activated oocytes during the second meiosis. In bovine cumulus cells, the onset of LAP2beta assembly was observed around anaphase chromosomes with strongly phosphorylated histone H3. No LAP2beta assembled around the chromosomes in the first and second polar bodies and the alternative oocyte chromatin (oCh) if histone H3 was phosphorylated. Only histone H3 of oCh was completely dephosphorylated during the telophase II/G1 transition (Tel II/G1), and then LAP2beta assembled around only the oCh without phosphorylated histone H3. In the oocytes activated by CaA + CH, LAP2beta did not assemble around the condensed oCh during the Tel II/G1 transition, although their histone H3 dephosphorylation occurred rather rapidly compared with that of the fertilized oocytes. The patterns of histone H3 dephosphorylation and LAP2beta assembly in oocytes activated by CaA alone showed greater similarity to those in fertilized oocytes than to those in oocytes activated by CaA + CH. These results show that LAP2beta assembles around only oCh after complete dephosphorylation of histone H3 after fertilization and activation using CaA alone, and that the timing of histone H3 dephosphorylation and LAP2beta assembly in these oocytes is different from that of somatic cells. The results also indicate that CH treatment inhibits LAP2beta assembly around oCh but not histone H3 dephosphorylation. PMID:16719951

Isaji, Mamiko; Iwata, Hisataka; Harayama, Hiroshi; Miyake, Masashi

2006-05-01

153

Predicted alpha-helix/beta-sheet secondary structures for the zinc-binding motifs of human papillomavirus E7 and E6 proteins by consensus prediction averaging and spectroscopic studies of E7.  

PubMed Central

The E7 and E6 proteins are the main oncoproteins of human papillomavirus types 16 and 18 (HPV-16 and HPV-18), and possess unknown protein structures. E7 interacts with the cellular tumour-suppressor protein pRB and contains a zinc-binding site with two Cys-Xaa2-Cys motifs spaced 29 or 30 residues apart. E6 interacts with another cellular tumour-suppressor protein p53 and contains two zinc-binding sites, each with two Cys-Xaa2-Cys motifs at a similar spacing of 29 or 30 residues. By using the GOR I/III, Chou-Fasman, SAPIENS and PHD methods, the effectiveness of consensus secondary structure predictions on zinc-finger proteins was first tested with sequences for 160 transcription factors and 72 nuclear hormone receptors. These contain Cys2His2 and Cys2Cys2 zinc-binding regions respectively, and possess known atomic structures. Despite the zinc- and DNA-binding properties of these protein folds, the major alpha-helix structures in both zinc-binding regions were correctly identified. Thus validated, the use of these prediction methods with 47 E7 sequences indicated four well-defined alpha-helix (alpha) and beta-sheet (beta) secondary structure elements in the order beta beta alpha beta in the zinc-binding region of E7 at its C-terminus. The prediction was tested by Fourier transform infrared spectroscopy of recombinant HPV-16 E7 in H2O and 2H2O buffers. Quantitative integration showed that E7 contained similar amounts of alpha-helix and beta-sheet structures, in good agreement with the averaged prediction of alpha-helix and beta-sheet structures in E7 and also with previous circular dichroism studies. Protein fold recognition analyses predicted that the structure of the zinc-binding region in E7 was similar to a beta beta alpha beta motif found in the structure of Protein G. This is consistent with the E7 structure predictions, despite the low sequence similarities with E7. This predicted motif is able to position four Cys residues in proximity to a zinc atom. A model for the zinc-binding motif of E7 was constructed by combining the Protein G coordinates with those for the zinc-binding site in transcription factor TFIIS. Similar analyses for the two zinc-binding motifs in E6 showed that they have different alpha/beta secondary structures from that in E7. When compared with 12 other zinc-binding proteins, these results show that E7 and E6 are predicted to possess novel types of zinc-binding structure.

Ullman, C G; Haris, P I; Galloway, D A; Emery, V C; Perkins, S J

1996-01-01

154

beta-Endorphin: formation of alpha-helix in lipid solutions.  

PubMed Central

Human beta-endorphin adopts a partial helical conformation in aqueous solutions of cerebroside sulfate, ganglioside GM1, phosphatidylserine, and phosphatidic acid, but not of cerebroside and phosphatidylcholine, as evidenced by circular dichroic spectra. Addition of Ca2+ to the peptide in cerebroside sulfate solution can break up the helix; at 10 mM Ca2+ the peptide (12 microM) essentially exists in an unordered form. For comparison, sheep beta-lipotropin in acidic cerebroside sulfate solution (pH less than 4) also has a partial helical conformation of the complex between human beta-endorphin and lipids may be related to the opiatelike function of this peptide hormone.

Wu, C S; Lee, N M; Loh, H H; Yang, J T; Li, C H

1979-01-01

155

Formation and self-healing' of magnetic islands in finite-[beta] Helias equilibria  

SciTech Connect

The behavior of finite-pressure-induced magnetic islands is numerically analyzed for three-dimensional magnetohydrostatic equilibria of the Helias configuration by using a three- dimensional equilibrium code. It is found that an island chain is generated on the 5/6 rational surface, when such a surface appears in the plasma region of the finite-[beta] equilibrium. The island chain, however, is not so dangerous as to destroy the plasma confinement even if it appears in a vanishingly small shear region. Thus, a high [beta] equilibrium with clear magnetic surfaces can be realized. Moreover, it is definitely confirmed that the finite pressure effect sometimes exhibits an unexpectedly good aspect, namely, that the vacuum islands are removed as [beta] increases, which can be called self-healing' of islands. This property can be explained by the numerically discovered fact that the phases of islands induced by the finite-pressure effect are always locked in the same phase regardless of [beta].

Hayashi, T.; Sato, T. (National Institute for Fusion Science, Furocho, Nagoya 464-01 (Japan)); Merkel, P.; Nuehrenberg, J.; Schwenn, U. (Max-Planck-Institut fuer Plasmaphysik, IPP-EURATOM Association, D-8046 Garching bei Muenchen (Germany))

1994-10-01

156

High-beta plasma formation and observation of peaked density profile in RT1  

Microsoft Academic Search

High-beta ECH plasma is generated and stably sustained in a magnetospheric configuration, the Ring Trap 1 (RT-1) device, generated by a levitated dipole field magnet. Geomagnetic-field compensation and optimized operation have realized drastic improvements in plasma properties. The maximum local beta value has reached 70% and the pressure profiles have a rather steep gradient near the superconducting magnet. Electrons of

H. Saitoh; Z. Yoshida; J. Morikawa; Y. Yano; T. Mizushima; Y. Ogawa; M. Furukawa; Y. Kawai; K. Harima; Y. Kawazura; Y. Kaneko; K. Tadachi; S. Emoto; M. Kobayashi; T. Sugiura; G. Vogel

2011-01-01

157

Architectural variability of confined turbidite sheet-sands: facies, geometry and infill of associated elementary channels. Examples from the Trois Evêchés Basin, Annot Sandstone Formation, SE France  

NASA Astrophysics Data System (ADS)

The worldwide known Annot Sandstone Formation has been considered as a reference of confined siliciclastic turbidite system. This formation crops out in SE France and represents the Upper Eocene to Lower Oligocene gravitary infill of complex foreland basins, developed in front of the Alpine thrusts. This system can be assimilated as a sand-rich turbidite ramp, sourced by multiple fan deltas leading to topographically complex sub-basins. Highly bypassing channelized systems dominate in the most proximal and most confined areas. They distally evolve to relatively less confined areas, in which sedimentary bodies appear to be more continuous and homogenous on a regional scale. These last architectural elements, defined as sheet-sands or depositional lobes, have been the focus of this study in poorly documented areas. From an important dataset made of very high resolution outcrop correlations (gathered mainly in the Trois Evêchés and Lauzanier sub-basins), we have quantified the complex distribution of sedimentary facies and structures, grain-size and key surfaces in sand-rich sheets. This was done to understand their variability from depositional event to architectural element scales and to better characterize dimensions and characteristics of their components. Six main types of architectural elements were defined, composed of both channelized and unchannelized elements. Channelized units show a high variability in terms of facies, geometry and patterns of infill that are related to multiple erosional and depositional processes, which will be discussed. We notably relate some evidences of sinuous channels, represented by lateral accretion deposits in the channel complex axis and by low angle cross-bedded facies. We interpret this particular facies as the result of flow deconfinement and overbanks above channel margins. The stratigraphic analysis of elementary objects allows us to propose a genetic model and a spatial distribution model of sheet-sand architectural elements. The latter provides their longitudinal repartition, from proximal vertically stacked internal channels to distal compensating sheets. Those features have not been accurately described in relatively distal sand-rich turbidite deposits so far and this high internal variability necessarily implies heterogeneities both in terms of petrophysical characteristics and reservoir connection. Besides, it also implies reconsidering sedimentary processes involved in these environments. Key Words: Annot Sandstones, Confined Systems, Reservoir Heterogeneities, Turbidite Sheet-sands.

Etienne, S.; Mulder, T.; Pace, A.; Bez, M.; Desaubliaux, G.

2012-04-01

158

Plasmodium falciparum: effect of Solanum nudum steroids on thiol contents and beta-hematin formation in parasitized erythrocytes.  

PubMed

We studied the effects on total thiols glutathione (GSH) and cysteine contents in Plasmodium falciparum in vitro when treated with four steroid derivatives and a sapogenin (Diosgenone) extracted from Solanum nudum. We also determined their capacity to inhibit beta-hematin formation. We showed that SN-1 (16alpha-acetoxy-26-hydroxycholest-4-ene-3,22-dione) increased total glutathione and cysteine concentrations while SN-4 (26-O-beta-d-glucopyranosyloxy-16alpha-acetoxycholest-4-ene-3,22-dione) decreased the concentration of both thiols. Acetylation in C16 was crucial for the effect of SN-1 while type furostanol and terminal glucosidation were necessary for the inhibitory properties of SN-4. The combination of steroids and buthionine sulfoximine, a specific inhibitor of a step-limiting enzyme in GSH synthesis, did not modify the glutathione contents. Finally, we found that SN-1 inhibited more than 80% of beta-hematin formation at 5.0mM, while the other steroids did not show any effect. PMID:19442662

Pabón, Adriana; Deharo, Eric; Zuluaga, Lina; Maya, Juan D; Saez, Jairo; Blair, Silvia

2009-05-12

159

Tribological behaviour of thin organic coatings on 55%Al-Zn steel sheet — influence of transfer and tribo film formation  

Microsoft Academic Search

The tribological behaviour of 7 thin organic coatings deposited on hot-dip coated 55% Al-Zn steel sheets was evaluated by ball-on- disc testing. The results obtained show that the tribological performance, i.e. the possibility to inhibit a metal-metal contact at the sliding interface, of the organic coatings is strongly dependent on the amount and type of resins and additives which they

P. Carlsson; M. Olsson

160

Assessment sheets  

NSDL National Science Digital Library

This website offers assessment sheets on humans, plants, habitats, materials, light, earth and beyond, sound, forces, electricity, and science. The sheets tell you what the student should know from each objective.

2007-09-11

161

Global Simulations of Differentially Rotating Magnetized Disks: Formation of Low-beta Filaments and Structured Coronae.  

PubMed

We present the results of three-dimensional global magnetohydrodynamic simulations of the Parker-shearing instability in a differentially rotating torus initially threaded by toroidal magnetic fields. An equilibrium model of a magnetized torus is adopted as an initial condition. When beta0=Pgas&solm0;Pmag approximately 1 at the initial state, magnetic flux buoyantly escapes from the disk and creates looplike structures similar to those in the solar corona. Inside the torus, the growth of nonaxisymmetric magnetorotational (or Balbus & Hawley) instability generates magnetic turbulence. Magnetic field lines are tangled on a small scale, but on a large scale they show low azimuthal wavenumber spiral structure. After several rotation periods, the system oscillates around a state with beta approximately 5. We found that magnetic pressure-dominated (beta<1) filaments are created in the torus. The volume filling factor of the region in which betabeta regions may lead to violent flaring activities in accretion disks and in galactic gas disks. PMID:10702134

Machida; Hayashi; Matsumoto

2000-03-20

162

Formation, separation and characterization of three beta-1,3-glucanases from Sclerotium glucanicum.  

PubMed

The appearance of beta-1,3-glucanases in supernatants of Sclerotium glucanicum cultures was followed by SDS-PAGE and shown to be dependent on cultivation time. Three beta-1,3-glucanases were isolated and purified. Glucanase I and III appeared homogeneous on SDS-PAGE with molecular masses of 85 and 33.5 kDa, respectively. Enzyme I was an endo-splitting beta-1,3-glucanase. In hydrolyzing laminarin it released glucose, laminaritriose and laminaribiose as major endproducts and smaller amounts of higher oligosaccharides. Enzyme III was an exo-beta-1,3-glucanase removing glucose from laminarin and gentiobiose and glucose from scleroglucan. For laminarin as substrate the Km of enzyme I and III was 2.5 and 3.33 mg/ml, respectively. Enzyme II was only partially purified and found to be also an exo-beta-1,3-glucanase, releasing glucose as the only hydrolysis product from laminarin. It did not attack scleroglucan. Its molecular weight was determined to be 78 kDa. Optimum pH and temperature of the three enzymes were determined. The three activities were significantly inhibited by 1 mM Hg2+. PMID:1627595

Rapp, P

1992-07-21

163

Formation of a long-lived hot field reversed configuration by dynamically merging two colliding high-{beta} compact toroids  

SciTech Connect

A high temperature field reversed configuration (FRC) has been produced in the newly built, world's largest compact toroid (CT) facility, C-2, by colliding and merging two high-{beta} CTs produced using the advanced field-reversed {theta}-pinch technology. This long-lived, stable merged state exhibits the following key properties: (1) apparent increase in the poloidal flux from the first pass to the final merged state, (2) significantly improved confinement compared to conventional {theta}-pinch FRCs with flux decay rates approaching classical values in some cases, (3) strong conversion from kinetic energy into thermal energy with total temperature (T{sub e} + T{sub i}) exceeding 0.5 keV, predominantly into the ion channel. Detailed modeling using a new 2-D resistive magnetohydrodynamic (MHD) code, LamyRidge, has demonstrated, for the first time, the formation, translation, and merging/reconnection dynamics of such extremely high-{beta} plasmas.

Guo, H. Y.; Binderbauer, M. W.; Barnes, D.; Putvinski, S.; Rostoker, N.; Sevier, L.; Tuszewski, M.; Anderson, M. G.; Andow, R.; Bonelli, L.; Brown, R.; Bui, D. Q.; Bystritskii, V.; Clary, R.; Cheung, A. H.; Conroy, K. D.; Deng, B. H.; Dettrick, S. A.; Douglass, J. D.; Feng, P. [Tri Alpha Energy, Inc., P.O. Box 7010, Rancho Santa Margarita, California 92688 (United States)

2011-05-15

164

Wetlands Fact Sheets  

NSDL National Science Digital Library

The U.S. Environmental Protection Agency has provided an extensive list of over 40 fact sheets relating to various aspects of wetlands. Most are provided in a low resoluion format for viewing or a high resolution format for printing. A great deal of basic information regarding the definition, values, and functions of wetlands is provided.

2007-01-07

165

Ice Sheets  

NSDL National Science Digital Library

This educational brief describes the nature and properties of the Greenland and Antarctica ice sheets. Topics include the thickness and aereal extent of the ice sheets, volume of water contained in them, mass balance, and the mechanisms by which ice is lost from or accumulated by the ice sheets.

166

Induction of extracellular beta-galactosidase (Bga1) formation by D-galactose in Hypocrea jecorina is mediated by galactitol.  

PubMed

The ability of Hypocrea jecorina (Trichoderma reesei) to grow on lactose strongly depends on the formation of an extracellular glycoside hydrolase (GH) family 35 beta-galactosidase, encoded by the bga1 gene. Previous studies, using batch or transfer cultures of pregrown cells, had shown that bga1 is induced by lactose and d-galactose, but to a lesser extent by galactitol. To test whether the induction level is influenced by the different growth rates attainable on these carbon sources, bga1 expression was compared in carbon-limited chemostat cultivations at defined dilution (=specific growth) rates. The data showed that bga1 expression by lactose, d-galactose and galactitol positively correlated with the dilution rate, and that galactitol and d-galactose induced the highest activities of beta-galactosidase at comparable growth rates. To know more about the actual inducer for beta-galactosidase formation, its expression in H. jecorina strains impaired in the first steps of the two d-galactose-degrading pathways was compared. Induction by d-galactose and galactitol was still found in strains deleted in the galactokinase-encoding gene gal1, which is responsible for the first step of the Leloir pathway of d-galactose catabolism. However, in a strain deleted in the aldose/d-xylose reductase gene xyl1, which performs the reduction of d-galactose to galactitol in a recently identified second pathway, induction by d-galactose, but not by galactitol, was impaired. On the other hand, induction by d-galactose and galactitol was not affected in an l-arabinitol 4-dehydrogenase (lad1)-deleted strain which is impaired in the subsequent step of galactitol degradation. These results indicate that galactitol is the actual inducer of Bga1 formation during growth on d-galactose in H. jecorina. PMID:17259622

Fekete, Erzsébet; Karaffa, Levente; Kubicek, Christian P; Szentirmai, Attila; Seiboth, Bernhard

2007-02-01

167

Silicon nitride: Enthalpy of formation of the {alpha}- and {beta}-polymorphs and the effect of C and O impurities  

SciTech Connect

High-temperature oxidative drop solution calorimetry was used to measure the enthalpy of formation of {alpha}{endash} and {beta}{endash}Si{sub 3}N{sub 4}. Two different solvents, molten alkali borate (48&hthinsp;wt&hthinsp;{percent} LiBO{sub 2}{center_dot}52&hthinsp;wt&hthinsp;{percent} NaBO{sub 2}) at 1043 and 1073 K and potassium vanadate (K{sub 2}O{center_dot}3V{sub 2}O{sub 5}) at 973 K, were used, giving the same results. Pure {alpha}{endash} and {beta}{endash}Si{sub 3}N{sub 4} polymorphs have the same molar enthalpy of formation at 298 K of {minus}850.9{plus_minus}22.4 and {minus}852.0{plus_minus}8.7 kJ/mol, respectively. The unit cell dimensions of impure {alpha}{endash}Si{sub 3}N{sub 4} samples depend linearly on the O and C impurity contents, and so does the molar enthalpy of formation. The energetic stability of the {alpha}{endash}Si{sub 3}N{sub 4} phase decreases when the sample contains O and C impurities. The experimental evidence strongly suggests that the impurities dissolve into the {alpha}{endash}Si{sub 3}N{sub 4} structure to form a (limited) isostructural solid solution series but that this solid solution series is energetically less stable than a mechanical mixture of pure ({alpha} or {beta}) Si{sub 3}N{sub 4}, SiO{sub 2}, and SiC. Thus, the {alpha}-phase is not stabilized by impurities and is probably always metastable. {copyright} {ital 1999 Materials Research Society.}

Liang, J.; Topor, L.; Navrotsky, A. [Thermochemistry Facility, Chemistry Building, Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, California 95616 (United States); Mitomo, M. [National Institute of Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305 (Japan)

1999-05-01

168

Habit and Formation Mechanism of beta-BaB2O4 Crystal.  

National Technical Information Service (NTIS)

The relationship between the orientation of structure unit (B3O6)(3-) anion ring and the morphology of Beta-BaB2O4 crystal has been studied on the basis of crystallography. According to the results measured from the solution structure of Na2O-B2O3 system,...

W. Z. Zhong H. Hong Z. Lu T. Zhao S. Hua D. Tang Q. Zhao

1994-01-01

169

Formation of Ultra High Beta Spherical Tokamak by Use of Merging Spheromak Plasmas  

NASA Astrophysics Data System (ADS)

We formed ultra-high beta spherical tokamak plasmas using both of two spherical plasma merging and ramp-up of external toroidal field.footnotetextY. Ono et al. Nucl. Fusion 43, 789, (2003). The merging and reconnection heats ions significantly during magnetic reconnection in TS-3 experiments. The maximum ion temperature Ti˜ 250 eV is obtained in two merging spheromaks with counter-helicity and Ti˜ 120 eV in those with co-helicity. While the reconnection heating decreases with the external guide toroidal field Bt, the confinement time of toroidal plasma tends to increase with external Bt. In order to confine the maximum ion thermal energy, we applied external Bt to merging low-q plasmas such as spheromaks with co- and counter-helicity after completion of reconnection, transforming the high-beta low-q toroid to an ultra high-beta ST in TS-3^[1] and TS-4. This transformation increases the life times of low-q toroids by fact 2-3. It is noted that the high-beta ST has an absolute minimum B profile with deep magnetic well. With increasing the ramp-up speed of external Bt, the magnetic well increases, but stays longer in low-q state unstable to MHD modes.

Ito, Taichi; Toru, II; Inomoto, Michiaki; Ono, Yasushi

2012-10-01

170

Separation of drug stereoisomers by the formation of. beta. -cyclodextrin inclusion complexes  

SciTech Connect

For many drugs, only racemic mixtures are available for clinical use. Because different stereoisomers of drugs often cause different physiological responses, the use of pure isomers could elicit more exact therapeutic effects. Differential complexation of a variety of drug stereoisomers by immobilized ..beta..-cyclodextrin was investigated. Chiral recognition and racemic resolution were observed with a number of compounds from such clinically useful classes as ..beta..-blockers, calcium-channel blockers, sedative hypnotics, antihistamines, anticonvulsants, diuretics, and synthetic opiates. Separation of the diastereomers of the cardioactive and antimalarial cinchona alkaloids and of two antiestrogens was demonstrated as well. Three dimensional projections of ..beta..-cyclodextrin complexes of propanol, which is resolved by this technique, and warfarin, which is not, are compared. These studies have improved the understanding and application of the chiral interactions of ..beta..-cyclodextrin, and they have demonstrated a means to measure optical purity and to isolate or produce pure enantiomers of drugs. In addition, this highly specific technique could also be used in the pharmacological evaluation of enantiometric drugs. 27 references, 3 figures, 2 tables.

Armstrong, D.W.; Ward, T.J.; Armstrong, R.D.; Beesley, T.E.

1986-05-30

171

Separation of drug stereoisomers by the formation of. beta. -cyclodextrin inclusion complexes  

Microsoft Academic Search

For many drugs, only racemic mixtures are available for clinical use. Because different stereoisomers of drugs often cause different physiological responses, the use of pure isomers could elicit more exact therapeutic effects. Differential complexation of a variety of drug stereoisomers by immobilized ..beta..-cyclodextrin was investigated. Chiral recognition and racemic resolution were observed with a number of compounds from such clinically

D. W. Armstrong; T. J. Ward; R. D. Armstrong; T. E. Beesley

1986-01-01

172

Oxidative stress is induced by islet amyloid formation and time-dependently mediates amyloid-induced beta cell apoptosis  

Microsoft Academic Search

Aims\\/hypothesis  Islet amyloid in type 2 diabetes contributes to loss of beta cell mass and function. Since islets are susceptible to oxidative\\u000a stress-induced toxicity, we sought to determine whether islet amyloid formation is associated with induction of oxidative\\u000a stress.\\u000a \\u000a \\u000a \\u000a Methods  Human islet amyloid polypeptide transgenic and non-transgenic mouse islets were cultured for 48 or 144 h with or without the\\u000a antioxidant N-acetyl-l-cysteine (NAC)

S. Zraika; R. L. Hull; J. Udayasankar; K. Aston-Mourney; S. L. Subramanian; R. Kisilevsky; W. A. Szarek; S. E. Kahn

2009-01-01

173

Identification of the high affinity binding site in transforming growth factor-beta involved in complex formation with alpha 2-macroglobulin. Implications regarding the molecular mechanisms of complex formation between alpha 2-macroglobulin and growth factors, cytokines, and hormones.  

PubMed

The biological activities of transforming growth factor-beta isoforms (TGF-beta(1,2)) are known to be modulated by alpha(2)-macroglobulin (alpha(2)M). alpha(2)M forms complexes with numerous growth factors, cytokines, and hormones, including TGF-beta. Identification of the binding sites in TGF-beta isoforms responsible for high affinity interaction with alpha(2)M many unravel the molecular basis of the complex formation. Here we demonstrate that among nine synthetic pentacosapeptides with overlapping amino acid sequences spanning the entire TGF-beta(1) molecule, the peptide (residues 41-65) containing Trp-52 exhibited the most potent activity in inhibiting the formation of complexes between (125)I-TGF-beta(1) and activated alpha(2)M (alpha(2)M*) as determined by nondenaturing polyacrylamide gel electrophoresis and by plasma clearance in mice. TGF-beta(2) peptide containing the homologous sequence and Trp-52 was as active as the TGF-beta(1) peptide, whereas the corresponding TGF-beta(3) peptide lacking Trp-52, was inactive. The replacement of the Trp-52 with alanine abolished the inhibitory activities of these peptides. (125)I-TGF-beta(3), which lacks Trp-52, bound to alpha(2)M* with an affinity lower than that of (125)I-TGF-beta(1). Furthermore, unlabeled TGF-beta(3) and the mutant TGF-beta(1)W52A, in which Trp-52 was replaced with alanine, were less potent than unlabeled TGF-beta(1) in blocking I(125)-TGF-beta(1) binding to alpha(2)M*. TGF-beta(1) and TGF-beta(2) peptides containing Trp-52 were also effective in inhibiting I(125)-nerve growth factor binding to alpha(2)M*. Tauhese results suggest that Trp-52 is involved in high affinity binding of TGF-beta to alpha(2)M*. They also imply that TGF-beta and other growth factors/cytokines/hormones may form complexes with alpha(2)M* via a common mechanism involving the interactions between topologically exposed Trp and/or other hydrophobic residues and a hydrophobic region in alpha(2)M*. PMID:11583997

Liu, Q; Ling, T Y; Shieh, H S; Johnson, F E; Huang, J S; Huang, S S

2001-10-02

174

Study of the {alpha}{yields}{beta} phase transformation of a Ti-6Al-4V sheet by means of texture change  

SciTech Connect

Although a large number of studies on the {alpha}/{beta} phase transformation in titanium alloys have been reported, only a few works deal with the texture change observed during the {alpha}{yields}{beta} transformation during continuous heating. This is due to the difficulty to obtain information about the metallurgical state of the high temperature {beta} phase, which is not stable at room temperature. In pure titanium, the hcp {alpha} phase generally transforms into the bcc {beta} phase according to the Burgers relation with sometimes orientation variant selections. In the case of Ti-6Al-4V alloy, the transformation of the {alpha} phase is performed in the presence of a low volume fraction of {beta} phase which can influence the transformation mechanism. In the present paper, the {alpha}{yields}{beta} texture change of Ti-6Al-4V material is characterized using adapted methods. The resulting textures allows us to discuss the influence of the residual {beta} phase on the transition texture.

Gey, N.; Humbert, M.; Moustahfid, H.

2000-02-01

175

Determination of stoichiometric coefficients and apparent formation constants for beta-cyclodextrin complexes of trans-resveratrol using reversed-phase liquid chromatography.  

PubMed

The complexation of trans-resveratrol with beta-cyclodextrin (beta-CD) was investigated using reversed-phase liquid chromatography and mobile phases to which beta-CD was added. The decrease in the retention times with increasing concentrations of beta-CD (0-2.5 mM) showed that trans-resveratrol forms a 1:1 complex with beta-CD, while the apparent formation constants (K(F)) were strongly dependent of the water-methanol proportion of the mobile phase employed. A slight decrease in K(F) was observed at 50-55% water in the mobile phase but a large increase from 55 to 70% water. The values of K(F) for the trans-resveratrol-beta-CD interaction decreased when the temperature was raised from 20 to 37 degrees C. In order to gain information about the mechanism aspect of the trans-resveratrol affinity for beta-CD, the thermodynamic parameters of the complexation were obtained. Complex formation of trans-resveratrol with beta-CD (DeltaG degrees =-17.01 kJ/mol) is largely driven by enthalpy (DeltaH degrees = -30.62 kJ/mol) and slightly entropy changes (DeltaS degrees = -45.68 J/mol K). PMID:17083948

López-Nicolás, José Manuel; Núñez-Delicado, Estrella; Pérez-López, Antonio J; Barrachina, Angel Carbonell; Cuadra-Crespo, Paula

2006-11-02

176

{beta}-Ti(M) solid solution formation and its thermal stability in a NiAl-Cr(Mo)-(Hf,Ti) near eutectic alloy  

SciTech Connect

The effects of combined additions of Ti and Hf to NiAl-Cr(Mo) eutectics on the as-cast microstructure and its thermal stability are investigated through SEM, EDS and TEM, with focus on the formation mechanism of {beta}-Ti(M, M = Hf,Cr,Ni) solid solution phase and its thermal stability after short-term heat treatment. The results show that, due to the presence of large concentrations of {beta}-phase forming and stabilizing elements dissolved into the Ti solid solution phase during solidification, the thermodynamically metastable {beta}-phase was preserved at room temperature. With respect to its thermal stability, within the experimental range examined, the {beta}-Ti(M) solid solution phase, is not influenced. From the practical application point of view, this {beta}-Ti(M) solid solution phase may offer application as a strengthening phase for the design of NiAl-Cr(Mo)-Hf based alloys.

Li Hutian [Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110004 (China); Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)], E-mail: htli@imr.ac.cn; Wang Qiang; He Jicheng [Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110004 (China); Guo Jianting; Ye Hengqiang [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

2008-10-15

177

Fibril stability in solutions of twisted Format="TEX"/>-sheet peptides: a new kind of micellization in chiral systems  

NASA Astrophysics Data System (ADS)

The problem of fibril (fibre) formation in chiral systems is explored theoretically being supported by experiments on synthetic de novo 11-mer peptide forming self-assembled -sheet tapes. Experimental data unambiguously indicate that the tapes form fibrils of nearly monodisperse thickness ca. 8-10 nm. Fibril formation and stabilisation are attributed to inter-tape face-to-face attraction and their intrinsic twist, correspondingly. The proposed theory is capable of predicting the fibril aggregation number and its equilibrium twist in terms of molecular parameters of the primary tapes. The suggested novel mechanism of twist stabilisation of finite aggregates (fibrils) is different to the well-known stabilisation of micelles in amphiphilic systems, and it is likely to explain the formation and stability of fibrils in a wide variety of systems including proteinaceous amyloid fibres, sickle-cell hemoglobin fibres responsible for HbS anemia, corkscrew threads found in chromonics in the presence of chiral additives and native cellulose microfibrillar crystallites. The theory also makes it possible to extract the basic molecular parameters of primary tapes (inter-tape attraction energy, helical twist step, elastic moduli) from the experimental data.

Nyrkova, I. A.; Semenov, A. N.; Aggeli, A.; Boden, N.

2000-10-01

178

Polymorphic fibril formation by residues 10-40 of the Alzheimer's beta-amyloid peptide.  

PubMed

We report investigations of the morphology and molecular structure of amyloid fibrils comprised of residues 10-40 of the Alzheimer's beta-amyloid peptide (Abeta(10-40)), prepared under various solution conditions and degrees of agitation. Omission of residues 1-9 from the full-length Alzheimer's beta-amyloid peptide (Abeta(1-40)) did not prevent the peptide from forming amyloid fibrils or eliminate fibril polymorphism. These results are consistent with residues 1-9 being disordered in Abeta(1-40) fibrils, and show that fibril polymorphism is not a consequence of disorder in residues 1-9. Fibril morphology was analyzed by atomic force and electron microscopy, and secondary structure and inter-side-chain proximity were probed using solid-state NMR. Abeta(1-40) fibrils were found to be structurally compatible with Abeta(10-40): Abeta(1-40) fibril fragments were used to seed the growth of Abeta(10-40) fibrils, with propagation of fibril morphology and molecular structure. In addition, comparison of lyophilized and hydrated fibril samples revealed no effect of hydration on molecular structure, indicating that Abeta(10-40) fibrils are unlikely to contain bulk water. PMID:16565054

Paravastu, Anant K; Petkova, Aneta T; Tycko, Robert

2006-03-24

179

Beta-sheet secondary structure of the trimeric globular domain of C1q of complement and collagen types VIII and X by Fourier-transform infrared spectroscopy and averaged structure predictions.  

PubMed Central

C1q plays a key role in the recognition of immune complexes, thereby initiating the classical pathway of complement activation. Although the triple-helix conformation of its N-terminal segment is well established, the secondary structure of the trimeric globular C-terminal domain is as yet unknown. The secondary structures of human C1q and C1q stalks and pepsin-extracted human collagen types I, III and IV (with no significant non-collagen-like structure) were studied by Fourier-transform i.r. spectroscopy in 2H2O buffers. After second-derivative calculation to resolve the fine structure of the broad amide I band, the Fourier-transform i.r. spectrum of C1q showed two major bands, one at 1637 cm-1, which is a characteristic frequency for beta-sheets, and one at 1661 cm-1. Both major bands were also detected for Clq in H2O buffers. Only the second major band was observed at 1655 cm-1 in pepsin-digested C1q which contains primarily the N-terminal triple-helix region. The Fourier-transform i.r. spectra of collagen in 2H2O also showed a major band at 1659 cm-1 (and minor bands at 1632 cm-1 and 1682 cm-1). It is concluded that the C1q globular heads contain primarily beta-sheet structure. The C-terminal domains of C1q show approximately 25% sequence identity with the non-collagen-like C-terminal regions of the short-chain collagen types VIII and X. To complement the Fourier-transform-i.r. spectroscopic data, averaged Robson and Chou-Fasman structure predictions on 15 similar sequences for the globular domains of C1q and collagen types VIII and X were performed. These showed a clear pattern of ten beta-strands interspersed by beta-turns and /or loops. Residues thought to be important for C1q-immune complex interactions with IgG and IgM were predicted to be at a surface-exposed loop. Sequence insertions and deletions, glycosylation sites, the free cysteine residue and RGD recognition sequences were also predicted to be at surface-exposed positions. Images Figure 4

Smith, K F; Haris, P I; Chapman, D; Reid, K B; Perkins, S J

1994-01-01

180

Molecular basis of isozyme formation of beta-galactosidases in Bacillus stearothermophilus: isolation of two beta-galactosidase genes, bgaA and bgaB.  

PubMed Central

Bacillus stearothermophilus IAM11001 produced three beta-galactosidases, beta-galactosidase I, II, and III (beta-gal I, II, and III), which are detectable by polyacrylamide (nondenatured) gel electrophoresis. By connecting restriction fragments of the chromosomal DNA to plasmid vectors, followed by transformation of Escherichia coli, two beta-galactosidase genes (bgaA and bgaB) located close to each other on the chromosome were isolated. Identification of the gene products and Southern hybridization analyses with a 2.7-kilobase-pair EcoRI fragment containing the bgaA gene as probe revealed that a single bgaA gene exists on the genome and that beta-gal II and beta-gal III consist of a common subunit (the bgaA gene product; molecular weight, 120,000), but differ in their assembly (beta-gal II is a dimer, and beta-gal III is a tetramer). The bgaB gene product (molecular weight, 70,000) in Bacillus subtilis harboring pHG5 (a hybrid plasmid consisting of pUB110 and a 2.9-kilobase-pair EcoRI fragment) was estimated to be the beta-gal I protein from its heat stability. Southern hybridization and immunological testing indicated that the two genes have no homology. Images

Hirata, H; Negoro, S; Okada, H

1984-01-01

181

Disintegration of liquid sheets  

NASA Astrophysics Data System (ADS)

The development, stability, and disintegration of liquid sheets issuing from a two-dimensional air-assisted nozzle is studied. Detailed measurements of mean drop size and velocity are made using a phase Doppler particle analyzer. Without air flow the liquid sheet converges toward the axis as a result of surface tension forces. With airflow a quasi-two-dimensional expanding spray is formed. The air flow causes small variations in sheet thickness to develop into major disturbances with the result that disruption starts before the formation of the main break-up region. In the two-dimensional variable geometry air-blast atomizer, it is shown that the air flow is responsible for the formation of large, ordered, and small chaotic 'cell' structures.

Mansour, Adel; Chigier, Norman

1990-05-01

182

Large spectral change due to amide modes of a ?-sheet upon the formation of an early photointermediate of middle rhodopsin.  

PubMed

Rhodopsin contains retinal as the chromophore within seven transmembrane helices. Recently, we found a unique rhodopsin (middle rhodopsin, MR), which is evolutionarily located between the well-studied bacteriorhodopsin and sensory rhodopsin II, and which accommodates three retinal isomers in its ground state (the all-trans, the 13-cis, and, uniquely, the 11-cis isomers). In this study, we investigated structural changes of both the protein moiety and the retinal chromophore during photocycles of MR by time-resolved Fourier-transform infrared spectroscopy. Three photointermediates with decay time constants of 95 ?s, 0.9 ms, and >~10 ms were identified by the global exponential fitting analysis. The first and third intermediates were attributed to the all-trans photocycle, in accordance with recently published results, whereas the second intermediate was likely one that was spectroscopically silent in the visible region and that was formed between the first and third states or resulted from the activation of the 13-cis isomer. By comparing light-induced difference spectra with various isotope labels in either the retinal or the protein moiety, we concluded that a ?-sheet structure in the hydrophilic part was significantly altered during the all-trans photocycle of MR, which may involve an active state of the protein. This feature is characteristic of MR among microbial (type-1) rhodopsins. PMID:23477373

Furutani, Yuji; Okitsu, Takashi; Reissig, Louisa; Mizuno, Misao; Homma, Michio; Wada, Akimori; Mizutani, Yasuhisa; Sudo, Yuki

2013-03-26

183

Formation of high-{beta} plasma and stable confinement of toroidal electron plasma in Ring Trap 1  

SciTech Connect

Formation of high-{beta} electron cyclotron resonance heating plasma and stable confinement of pure electron plasma have been realized in the Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet. The effects of coil levitation resulted in drastic improvements of the confinement properties, and the maximum local {beta} value has exceeded 70%. Hot electrons are major component of electron populations, and its particle confinement time is 0.5 s. Plasma has a peaked density profile in strong field region [H. Saitoh et al., 23rd IAEA Fusion Energy Conference EXC/9-4Rb (2010)]. In pure electron plasma experiment, inward particle diffusion is realized, and electrons are stably trapped for more than 300 s. When the plasma is in turbulent state during beam injection, plasma flow has a shear, which activates the diocotron (Kelvin-Helmholtz) instability. The canonical angular momentum of the particle is not conserved in this phase, realizing the radial diffusion of charged particles across closed magnetic surfaces. [Z. Yoshida et al., Phys Rev. Lett. 104, 235004 (2010); H. Saitoh et al., Phys. Plasmas 17, 112111 (2010).].

Saitoh, H.; Yoshida, Z.; Morikawa, J.; Furukawa, M.; Yano, Y.; Kawai, Y.; Kobayashi, M.; Vogel, G.; Mikami, H. [Department of Advanced Energy, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan)

2011-05-15

184

The role of TGF beta signaling in the formation of the dorsal nervous system is conserved between Drosophila and chordates.  

PubMed

Transforming growth factor beta signaling mediated by Decapentaplegic and Screw is known to be involved in defining the border of the ventral neurogenic region in the fruitfly. A second phase of Decapentaplegic signaling occurs in a broad dorsal ectodermal region. Here, we show that the dorsolateral peripheral nervous system forms within the region where this second phase of signaling occurs. Decapentaplegic activity is required for development of many of the dorsal and lateral peripheral nervous system neurons. Double mutant analysis of the Decapentaplegic signaling mediator Schnurri and the inhibitor Brinker indicates that formation of these neurons requires Decapentaplegic signaling, and their absence in the mutant is mediated by a counteracting repression by Brinker. Interestingly, the ventral peripheral neurons that form outside the Decapentaplegic signaling domain depend on Brinker to develop. The role of Decapentaplegic signaling on dorsal and lateral peripheral neurons is strikingly similar to the known role of Transforming growth factor beta signaling in specifying dorsal cell fates of the lateral (later dorsal) nervous system in chordates (Halocythia, zebrafish, Xenopus, chicken and mouse). It points to an evolutionarily conserved mechanism specifying dorsal cell fates in the nervous system of both protostomes and deuterostomes. PMID:12117808

Rusten, Tor Erik; Cantera, Rafael; Kafatos, Fotis C; Barrio, Rosa

2002-08-01

185

Hydrogen- Facts Sheet  

NSDL National Science Digital Library

This fact sheet provides some basic information about hydrogen. Hydrogen's history, physical and chemical properties, the production of hydrogen, details on how it is stored, safety tips for working with hydrogen and reasons for using hydrogen are outlined. This document may be downloaded in PDF file format.

2011-12-26

186

South Circumpolar Ice Sheet on Mars: Regional Drainage of Meltwater Beneath the Hesperian-aged Dorsa Argentea Formation  

NASA Astrophysics Data System (ADS)

We examine the head regions of two of the five drainage channels that lead away from the Dorsa Argentea Formation. We find evidence for basal drainage of meltwater beneath the DAF, and drainage of this water away from the area along the external channels.

Ghatan, G. J.; Head, J. W.

2003-07-01

187

Matrix metalloproteinase inhibition delays wound healing and blocks the latent transforming growth factor-beta1-promoted myofibroblast formation and function.  

PubMed

The ability to regulate wound contraction is critical for wound healing as well as for pathological contractures. Matrix metalloproteinases (MMPs) have been demonstrated to be obligatory for normal wound healing. This study examined the effect that the broad-spectrum MMP inhibitor BB-94 has when applied topically to full-thickness skin excisional wounds in rats and its ability to inhibit the promotion of myofibroblast formation and function by the latent transforming-growth factor-beta1 (TGF-beta1). BB-94 delayed wound contraction, as well as all other associated aspects of wound healing examined, including myofibroblast formation, stromal cell proliferation, blood vessel formation, and epithelial wound coverage. Interestingly, BB-94 dramatically increased the level of latent and active MMP-9. The increased levels of active MMP-9 may eventually overcome the ability of BB-94 to inhibit this MMP and may explain why wound contraction and other associated events of wound healing were only delayed and not completely inhibited. BB-94 was also found to inhibit the ability of latent TGF-beta1 to promote the formation and function of myofibroblasts. These results suggest that BB-94 could delay wound closure through a twofold mechanism; by blocking keratinocyte migration and thereby blocking the necessary keratinocyte-fibroblast interactions needed for myofibroblast formation and by inhibiting the activation of latent TGF-beta1. PMID:20409148

Mirastschijski, Ursula; Schnabel, Reinhild; Claes, Juliane; Schneider, Wolfgang; Agren, Magnus S; Haaksma, Carol; Tomasek, James J

2010-03-12

188

Stability of single sheet GNNQQNY aggregates analyzed by replica exchange molecular dynamics: Antiparallel versus parallel association  

SciTech Connect

Protein and peptide aggregation into amyloid plaques is associated with a large variety of neurodegenerative diseases. The definition of the molecular bases of these pathologies is hampered by the transient nature of pre-fibrillar small-oligomers that are considered the toxic species. The ability of the peptide GNNQQNY to form amyloid-like structures makes it a good model to investigate the complex processes involved into amyloid fiber formation. By employing full atomistic replica exchange molecular dynamics simulations, we constructed the free energy surface of small assemblies of GNNQQNY to gain novel insights into the fiber formation process. The calculations suggest that the peptide exhibits a remarkable tendency to form both parallel and antiparallel {beta}-sheets. The data show that GNNQQNY preference for parallel or antiparallel {beta}-sheets is governed by a subtle balance of factors including assemblies' size, sidechain-sidechain interactions and pH. The samplings analysis provides a rationale to the observed trends.

Vitagliano, Luigi; Esposito, Luciana; Pedone, Carlo [Istituto di Biostrutture e Bioimmagini, CNR via Mezzocannone 16, I-80134 Napoli (Italy); De Simone, Alfonso [Department of Chemistry, University of Cambridge, Lensfield Road CB2 1EW, Cambridge (United Kingdom)], E-mail: ad491@cam.ac.uk

2008-12-26

189

Genetic analysis of microtubule structure: a beta-tubulin mutation causes the formation of aberrant microtubules in vivo and in vitro  

Microsoft Academic Search

A recessive male sterile mutation (B2t s) that encodes a stable variant of the testis-specific 132-tubulin of Drosophila causes the assembly of aber- rant microtubules both in vivo and in vitro. The B2t s mutation appears to cause defects in the formation of in- terprotofilament bonds. In testes from homozygous mutant males, the most commonly observed aberrant structures were sheets

Margaret T. Fuller; Joan H. Caulton; Jeffrey A. Hutchens; Thomas C. Kaufman; Elizabeth C. Raft

1987-01-01

190

Identification and characterization of diarylimidazoles as hybrid inhibitors of butyrylcholinesterase and amyloid beta fibril formation.  

PubMed

In this contribution, a chemical collection of aromatic compounds was screened for inhibition on butyrylcholinesterase (BChE)'s hydrolase activity using Ellman's reaction. A set of diarylimidazoles was identified as highly selective inhibitors of BChE hydrolase activity and amyloid ? (A?) fibril formation. New derivatives were synthesized resulting in several additional hits, from which the most active was 6c, 4-(3-ethylthiophenyl)-2-(3-thienyl)-1H-imidazole, an uncompetitive inhibitor of BChE hydrolase activity (IC?? BChE=0.10 ?M; K(i)=0.073 ± 0.011 ?M) acting also on A? fibril formation (IC??=5.8 ?M). With the aid of structure-activity relationship (SAR) studies, chemical motifs influencing the BChE inhibitory activity of these imidazoles were proposed. These bifunctional inhibitors represent good tools in basic studies of BChE and/or promising lead molecules for AD therapy. PMID:22108346

Karlsson, Daniela; Fallarero, Adyary; Brunhofer, Gerda; Guzik, Przemyslaw; Prinz, Michaela; Holzgrabe, Ulrike; Erker, Thomas; Vuorela, Pia

2011-11-16

191

Mitochondrial beta-cyanoalanine synthase is essential for root hair formation in Arabidopsis thaliana.  

PubMed

Cyanide is stoichiometrically produced as a coproduct of the ethylene biosynthesis pathway and is detoxified by ?-cyanoalanine synthase enzymes. The molecular and phenotypical analysis of T-DNA insertion mutants of the mitochondrial ?-cyanoalanine synthase CYS-C1 suggests that discrete accumulation of cyanide is not toxic for the plant and does not alter mitochondrial respiration rates but does act as a strong inhibitor of root hair development. The cys-c1 null allele is defective in root hair formation and accumulates cyanide in root tissues. The root hair defect is phenocopied in wild-type plants by the exogenous addition of cyanide to the growth medium and is reversed by the addition of hydroxocobalamin or by genetic complementation with the CYS-C1 gene. Hydroxocobalamin not only recovers the root phenotype of the mutant but also the formation of reactive oxygen species at the initial step of root hair tip growth. Transcriptional profiling of the cys-c1 mutant reveals that cyanide accumulation acts as a repressive signal for several genes encoding enzymes involved in cell wall rebuilding and the formation of the root hair tip as well as genes involved in ethylene signaling and metabolism. Our results demonstrate that mitochondrial ?-cyanoalanine synthase activity is essential to maintain a low level of cyanide for proper root hair development. PMID:20935247

García, Irene; Castellano, José María; Vioque, Blanca; Solano, Roberto; Gotor, Cecilia; Romero, Luis C

2010-10-08

192

Post-transcriptional contribution of a cAMP-dependent pathway to the formation of alpha- and beta/gamma-secretases-derived products of beta APP maturation in human cells expressing wild-type and Swedish mutated beta APP.  

PubMed Central

BACKGROUND: The physiopathological maturation of the beta-amyloid precursor protein can be modulated by effectors targeting a protein kinase C-dependent pathway. These agents increase the recovery of APP alpha, the physiological alpha-secretase-derived product of beta APP processing, and concomittantly lower the production of the pathogenic beta/gamma-secretase-derived A beta fragment. METHODS: We set up stably transfected HEK293 cells expressing wild-type or Swedish mutated beta APP. By combined metabolic labeling and/or immunoprecipitation procedures, we assessed the effect of various cAMP effectors on the production of the beta APP maturation products A beta 40, A beta 42, APP alpha, and its C-terminal counterpart. RESULTS: We show here that the cAMP-dependent protein kinase (PKA) effectors, dibutyryl-cAMP (dBut-cAMP) and forskolin, but not the inactive analog dideoxyforskolin, enhance the secretion of APP alpha and the intracellular production of its C-terminal counterpart (p10) in stably transfected HEK293 cells. The above agonists also drastically increase both A beta 40 and A beta 42 secretions and intracellular A beta recovery. The same influence was observed with HEK293 cells overexpressing the Swedish mutated beta APP. We attempted to delineate the relative contribution of transcriptional and post-transcriptional events in the cAMP-mediated response. We show here that the dBut-cAMP and forskolin-induced increase of APP alpha and A beta s secretions is not prevented by the transcription inhibitor actinomycin D. CONCLUSION: Our data suggest a major contribution of post-transcriptional events in the cAMP-dependent effect on beta APP maturation. It appears likely that cAMP triggers the PKA-dependent phosphorylation of a protein involved in beta APP maturation and occurring upstream to alpha- and beta/gamma-secretase cleavages. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Marambaud, P.; Chevallier, N.; Ancolio, K.; Checler, F.

1998-01-01

193

Fact Sheets  

Center for Food Safety and Applied Nutrition (CFSAN)

Quick Links: Skip to main page content Skip to Search Skip to Topics Menu Skip to ... Below is a list of available fact sheets and information by topic. ... More results from www.fda.gov/food/guidanceregulation/fsma

194

Natalizumab plus interferon beta-1a reduces lesion formation in relapsing multiple sclerosis.  

PubMed

The SENTINEL study showed that the addition of natalizumab improved outcomes for patients with relapsing multiple sclerosis (MS) who had experienced disease activity while receiving interferon beta-1a (IFNbeta-1a) alone. Previously unreported secondary and tertiary magnetic resonance imaging (MRI) measures are presented here. Patients received natalizumab 300 mg (n=589) or placebo (n=582) intravenously every 4 weeks plus IFNbeta-1a 30 microg intramuscularly once weekly. Annual MRI scans allowed comparison of a range of MRI end points versus baseline. Over 2 years, 67% of patients receiving natalizumab plus IFNbeta-1a remained free of new or enlarging T2-lesions compared with 30% of patients receiving IFNbeta-1a alone. The mean change from baseline in T2 lesion volume over 2 years decreased in patients receiving natalizumab plus IFNbeta-1a and increased in those receiving IFNbeta-1a alone (-277.5mm(3) versus 525.6mm(3); p<0.001). Compared with IFNbeta-1a alone, add-on natalizumab therapy resulted in a smaller increase in mean T1-hypointense lesion volume after 2 years (1821.3mm(3) versus 2210.5mm(3); p<0.001), a smaller mean number of new T1-hypointense lesions over 2 years (2.3 versus 4.1; p<0.001), and a slower rate of brain atrophy during the second year of therapy (-0.31% versus -0.40%; p=0.020). Natalizumab add-on therapy reduced gadolinium-enhancing, T1-hypointense, and T2 MRI lesion activity and slowed brain atrophy progression in patients with relapsing MS who experienced disease activity despite treatment with IFNbeta-1a alone. PMID:20236661

Radue, Ernst-Wilhelm; Stuart, William H; Calabresi, Peter A; Confavreux, Christian; Galetta, Steven L; Rudick, Richard A; Lublin, Fred D; Weinstock-Guttman, Bianca; Wynn, Daniel R; Fisher, Elizabeth; Papadopoulou, Athina; Lynn, Frances; Panzara, Michael A; Sandrock, Alfred W

2010-03-16

195

Inhibition of oxidative stress-induced amyloid beta formation in NT2 neurons by culture filtrate of a strain of Streptomyces antibioticus.  

PubMed

Actinomycetes isolated from Iran soil habitats were tested for the capacity to produce compounds which can protect neurons from cell death generated by oxidative stress in NT2 neurons. Confirmation of our initial hit was accomplished via the determination of amyloid beta level using the enzyme-linked immunosorbent assay test. The most interesting amyloid beta formation inhibitor discovered in our study was a secondary metabolite which was produced by strain HM45. This bioactive strain was identified as a strain of Streptomyces antibioticus DSM 40234 using polyphasic approach. The strain HM45 was deposited in Deutsche Sammlung von Mikroorganismen und Zellkulturen as S. antibioticus DSM 41955 and University of Tehran Microorganisms Sollection as S. antibioticus UTMC 00105. This work is the first report on efficiency of an actinomycete metabolite in prohibition of neurons death caused by amyloid beta formation. PMID:20180120

Eftekharzadeh, Bahareh; Hamedi, Javad; Mohammadipanah, Fatemeh; Khodagholi, Fariba; Maghsoudi, Nader; Klenk, Hans Peter

2010-02-24

196

An alternative pathway to beta -carotene formation in plant chromoplasts discovered by map-based cloning of beta and old-gold color mutations in tomato.  

PubMed

Carotenoid pigments in plants fulfill indispensable functions in photosynthesis. Carotenoids that accumulate as secondary metabolites in chromoplasts provide distinct coloration to flowers and fruits. In this work we investigated the genetic mechanisms that regulate accumulation of carotenoids as secondary metabolites during ripening of tomato fruits. We analyzed two mutations that affect fruit pigmentation in tomato (Lycopersicon esculentum): Beta (B), a single dominant gene that increases beta-carotene in the fruit, and old-gold (og), a recessive mutation that abolishes beta-carotene and increases lycopene. Using a map-based cloning approach we cloned the genes B and og. Molecular analysis revealed that B encodes a novel type of lycopene beta-cyclase, an enzyme that converts lycopene to beta-carotene. The amino acid sequence of B is similar to capsanthin-capsorubin synthase, an enzyme that produces red xanthophylls in fruits of pepper (Capsicum annum). Our results prove that beta-carotene is synthesized de novo during tomato fruit development by the B lycopene cyclase. In wild-type tomatoes B is expressed at low levels during the breaker stage of ripening, whereas in the Beta mutant its transcription is dramatically increased. Null mutations in the gene B are responsible for the phenotype in og, indicating that og is an allele of B. These results confirm that developmentally regulated transcription is the major mechanism that governs lycopene accumulation in ripening fruits. The cloned B genes can be used in various genetic manipulations toward altering pigmentation and enhancing nutritional value of plant foods. PMID:10995464

Ronen, G; Carmel-Goren, L; Zamir, D; Hirschberg, J

2000-09-26

197

Self-assembly and mineralization of genetically modifiable biological nanofibers driven by beta-structure formation  

PubMed Central

Bio-inspired mineralization is an innovative approach to the fabrication of bone biomaterials mimicking the natural bone. Bone mineral hydroxylapatite (HAP) is preferentially oriented with c-axis parallel to collagen fibers in natural bone. However, such orientation control is not easy to achieve in artificial bone biomaterials. To overcome the lack of such orientation control, we fabricated a phage-HAP composite by genetically engineering M13 phage, a non-toxic bio-nanofiber, with two HAP-nucleating peptides derived from one of the non-collagenous proteins, Dentin Matrix Protein-1 (DMP1). The phage is a biological nanofiber that can be mass produced by infecting bacteria and is non-toxic to human beings. The resultant HAP-nucleating phages are able to self-assemble into bundles by forming ?-structure between the peptides displayed on their side walls. The ?-structure further promotes the oriented nucleation and growth of HAP crystals within the nanofibrous phage bundles with their c-axis preferentially parallel to the bundles. We proposed that the preferred orientation resulted from the stereochemical matching between the negatively charged amino acid residues within the ?-structure and the positively charged calcium ions on the (001) plane of HAP crystals. The self-assembly and mineralization driven by the ?-structure formation represent a new route for fabricating mineralized fibers that can serve as building blocks in forming bone repair biomaterials and mimic the basic structure of natural bones.

Xu, Hong; Cao, Binrui; George, Anne; Mao, Chuanbin

2011-01-01

198

Electron beam cutting in amorphous alumina sheets  

SciTech Connect

We have found that nanometer diameter holes and slots can be cut in thin sheets of amorphous alumina using an intense electron beam. The holes, formed by a nonthermal process, are uniform in diameter, are surrounded by metallic aluminum, and can penetrate a 100-nm sheet in a few seconds. The amorphous alumina sheets are formed by anodization of electropolished high purity aluminum. The electron beam cutting seems very similar to the process reported in the metal ..beta..-aluminas. Since uniform, stable, and easily handled sheets of amorphous alumina can be fabricated and electron beam cut, this process is now practical for nanolithography as well as many other applications.

Mochel, M.E.; Eades, J.A.; Metzger, M.; Meyer, J.I.; Mochel, J.M.

1984-03-01

199

Removal of the N-terminal hexapeptide from human beta2-microglobulin facilitates protein aggregation and fibril formation.  

PubMed Central

The solution structure and stability of N-terminally truncated beta2-microglobulin (deltaN6beta2-m), the major modification in ex vivo fibrils, have been investigated by a variety of biophysical techniques. The results show that deltaN6beta2-m has a free energy of stabilization that is reduced by 2.5 kcal/mol compared to the intact protein. Hydrogen exchange of a mixture of the truncated and full-length proteins at microM concentrations at pH 6.5 monitored by electrospray mass spectrometry reveals that deltaN6beta2-m is significantly less protected than its wild-type counterpart. Analysis of deltaN6beta2-m by NMR shows that this loss of protection occurs in beta strands I, III, and part of II. At mM concentration gel filtration analysis shows that deltaN6beta2-m forms a series of oligomers, including trimers and tetramers, and NMR analysis indicates that strand V is involved in intermolecular interactions that stabilize this association. The truncated species of beta2-microglobulin was found to have a higher tendency to self-associate than the intact molecule, and unlike wild-type protein, is able to form amyloid fibrils at physiological pH. Limited proteolysis experiments and analysis by mass spectrometry support the conformational modifications identified by NMR and suggest that deltaN6beta2-m could be a key intermediate of a proteolytic pathway of beta2-microglobulin. Overall, the data suggest that removal of the six residues from the N-terminus of beta2-microglobulin has a major effect on the stability of the overall fold. Part of the tertiary structure is preserved substantially by the disulfide bridge between Cys25 and Cys80, but the pairing between beta-strands far removed from this constrain is greatly perturbed.

Esposito, G.; Michelutti, R.; Verdone, G.; Viglino, P.; Hernandez, H.; Robinson, C. V.; Amoresano, A.; Dal Piaz, F.; Monti, M.; Pucci, P.; Mangione, P.; Stoppini, M.; Merlini, G.; Ferri, G.; Bellotti, V.

2000-01-01

200

Sheet1  

Center for Drug Evaluation (CDER)

Text Version4Q2012. Sheet1. A, B, C, D, E, F. 1, 2Q2013EXCEL. 2, DMF#, STATUS, Type, SUBMIT DATE, HOLDER, SUBJECT. 3, 0, I, 2/8/1981, ... More results from www.fda.gov/downloads/drugs/developmentapprovalprocess

201

Sheet1  

Center for Drug Evaluation (CDER)

Text Version4Q2012. Sheet1. A, B, C, D, E, F. 1, 4Q2012EXCEL. 2, DMF#, STATUS, Type, SUBMIT DATE, HOLDER, SUBJECT. 3, 0, I, 2/8/1981, ... More results from www.fda.gov/downloads/drugs/developmentapprovalprocess

202

Sheet1  

Center for Drug Evaluation (CDER)

Text Version4Q2012. Sheet1. A, B, C, D, E, F. 1, 3Q2013EXCEL. 2, DMF#, STATUS, Type, SUBMIT DATE, HOLDER, SUBJECT. 3, 0, I, 2/8/1981, ... More results from www.fda.gov/downloads/drugs/developmentapprovalprocess

203

Influence of Blockade of beta-Adrenoreceptors and Acute Stress on Antibody Formation, Delayed Type of Hypersensitivity, Phagocytic Cell Activity in Local Immune Response.  

PubMed

In the experiments on male Wistar rats a study was made on the effect of acute 6-h immobilization stress on antibody formation, delayed type hypersensitivity (DTH), functional activity of phagocytes in the case of a local form of immune response to sheep red blood cells at the background of beta-adrenergic receptor blockade. It was established that immobilization stress resulted in substantial inhibition of the expressibility of immune inflammation in the case of DTH, cancellation of an increase of the phagocytic activity of macrophages of the regional lymph node and the level of antibodies. The blockade of the beta-adrenergic receptors with propranolol antagonized with these effects of stress. After termination of the immobilization, activation of neutrophil phagocytosis was detected, this being related to an increase of neutrophil immigration from the bone marrow. Eosinophilic phagocytosis at the early period of stress was inhibited, the blockade of beta-adrenergic receptors canceled this effect. PMID:12687230

Shilov, Juri I.; Gein, Sergei V.; Chereshnev, Valery A.

2001-10-01

204

Crystal structure of Src-like adaptor protein 2 reveals close association of SH3 and SH2 domains through ?-sheet formation.  

PubMed

The Src-like adaptor proteins (SLAP/SLAP2) are key components of Cbl-dependent downregulation of antigen receptor, cytokine receptor, and receptor tyrosine kinase signaling in hematopoietic cells. SLAP and SLAP2 consist of adjacent SH3 and SH2 domains that are most similar in sequence to Src family kinases (SFKs). Notably, the SH3-SH2 connector sequence is significantly shorter in SLAP/SLAP2 than in SFKs. To understand the structural implication of a short SH3-SH2 connector sequence, we solved the crystal structure of a protein encompassing the SH3 domain, SH3-SH2 connector, and SH2 domain of SLAP2 (SLAP2-32). While both domains adopt typical folds, the short SH3-SH2 connector places them in close association. Strand ?e of the SH3 domain interacts with strand ?A of the SH2 domain, resulting in the formation of a continuous ? sheet that spans the length of the protein. Disruption of the SH3/SH2 interface through mutagenesis decreases SLAP-32 stability in vitro, consistent with inter-domain binding being an important component of SLAP2 structure and function. The canonical peptide binding pockets of the SH3 and SH2 domains are fully accessible, in contrast to other protein structures that display direct interaction between SH3 and SH2 domains, in which either peptide binding surface is obstructed by the interaction. Our results reveal potential sites of novel interaction for SH3 and SH2 domains, and illustrate the adaptability of SH2 and SH3 domains in mediating interactions. As well, our results suggest that the SH3 and SH2 domains of SLAP2 function interdependently, with implications on their mode of substrate binding. PMID:24018043

Wybenga-Groot, Leanne E; McGlade, C Jane

2013-09-07

205

DNA sequences preceding the rabbit beta-globin gene are required for formation in mouse L cells of beta-globin RNA with the correct 5' terminus.  

PubMed Central

Mouse thymidine kinase-negative (TK-) L cells were transformed with concatenates of cloned herpes simplex virus 1 TK DNA and different rabbit beta-globin DNAs in which the globin genes were preceded by native flanking sequences of 14, 66, 76, 425, and 1500 nucleotides.l In all cases, selection for TK+ cell lines led to a high yield of lines producing 5-1500 mature rabbit beta-globin-specific RNA strands per cell. The 5' termini of the transcripts mapped to (i) the "cap" nucleotide, (ii) positions 42 to 48 nucleotides downstream from the cap site, or (iii) positions in the vector DNA preceding the gene. In the case of the gene with only 14 base pairs of 5' flanking sequence, a high level of rabbit beta-globin RNA was produced, but none of the transcripts had the correct 5' end; most of them originated in the vector moiety. With 66 base pairs of 5' flanking sequence, 5% of the 5' termini were correct, and with 76 or more base pairs, 30-85% were correct. The region between 14 and 66 base pairs preceding the cap site contains the Hogness box and appears to be essential for correct initiation of transcription. The region between 66 and 76 base pairs before the cap site contains a variant of the canonical sequence G-G-C-T-C-A-A-T-C-T found preceding many other genes at a similar location, and this region may modulate the efficiency of transcription. The sequence of 425 nucleotides preceding the rabbit beta-globin gene is reported. Images

Dierks, P; van Ooyen, A; Mantei, N; Weissmann, C

1981-01-01

206

Ectopic bone formation associated with recombinant human bone morphogenetic proteins-2 using absorbable collagen sponge and beta tricalcium phosphate as carriers  

Microsoft Academic Search

The ectopic bone formation of recombinant human bone morphogenetic protein-2(rhBMP-2) was evaluated using absorbable collagen sponges (ACS) and beta tricalcium phosphate (?-TCP) as carriers in a rat subcutaneous assay model. Subcutaneous pockets were created on the back of rats. The pockets were implanted with rhBMP-2\\/ACS, rhBMP-2\\/?-TCP, ACS alone, and ?-TCP alone. The rats were sacrificed at 2 or 8 weeks

Chang-Sung Kim; Joon-Il Kim; Jin Kim; Seong-Ho Choi; Jung-Kiu Chai; Chong-Kwan Kim; Kyoo-Sung Cho

2005-01-01

207

Effect of dietary. beta. -carotene, vitamin A and selenium on formation of preneoplastic lesions in rat liver  

SciTech Connect

The effect of dietary ..beta..-carotene (BC), retinyl acetate (RA) and sodium selenite on formation of ..gamma..-glutamyltranspeptidase-positive foci in rat liver was investigated. Male Sprague-Dawley rats, 50g, were fed for 16 wks semipurified diets supplemented with either BC (500 mg/kg diet), RA (6400 IU/kg diet for wks 1-7 and 10,000 IU/kg for wks 8-16), 1.8 ppm selenium (Se) or both 1.8 ppm Se and 500 mg/kg BC. The control diet contained 0.1 ppm Se and 3200 IU RA/kg diet. During wks 3-4 rats received 10 intragastric doses of aflatoxin B/sub 1/ (0.4 mg/kg body weight/dose). Preneoplastic foci were quantitated at wk 16. Diet had no significant effect on growth rate or food consumption. None of the treatments resulted in significant differences in the number of foci per cm/sup 2/ liver section, but differences in focal size occurred. RA increased total focal area (mm/sup 2//cm/sup 2/ liver), while Se decreased focal area 5-fold. BC slightly decreased focal area. The combination of BC and Se was not as effective as Se alone. BC, RA, and BC-Se diets yielded equivalent levels of total liver retinol, which exceeded levels in control and Se rats by 30-fold. Livers from BC fed rats contained 4-5 ..mu..g BC/g liver. The different effects of dietary RA and BC on focal development may indicate a role for BC other than as a retinol precursor. The influence of each nutrient on focal size, but not number, implies they act during the post-initiation stage of focal development.

Colford, J.; Parker, R.S.

1986-03-05

208

Polyalanine and Abeta Aggregation Kinetics: Probing Intermediate Oligomer Formation and Structure Using Computer Simulations  

NASA Astrophysics Data System (ADS)

The aggregation of proteins into stable, well-ordered structures known as amyloid fibrils has been associated with many neurodegenerative diseases. Amyloid fibrils are long straight, and un-branched structures containing several proto-filaments, each of which exhibits "cross beta structure," -- ribbon-like layers of large beta sheets whose strands run perpendicular to the fibril axis. It has been suggested in the literature that the pathway to fibril formation has the following steps: unfolded monomers associate into transient unstable oligomers, the oligomers undergo a rearrangement into the cross-beta structure and form into proto-filaments, these proto-filaments then associate and grow into fully formed fibrils. Recent experimental studies have determined that the unstable intermediate structures are toxic to cells and that their presence may play a key role in the pathogenesis of the amyloid diseases. Many efforts have been made to determine the structure of intermediate oligomer aggregates that form during the fibrillization process. The goal of this work is to provide details about the structure and formation kinetics of the unstable oligomers that appear in the fibril formation pathway. The specific aims of this work are to determine the steps in the fibril formation pathway and how the kinetics of fibrillization changes with variations in temperature and concentration. The method used is the application of discontinuous molecular dynamics to large systems of peptides represented with an intermediate resolution model, PRIME, that was previously developed in our group. Three different peptide sequences are simulated: polyalanine (KA14K), Abeta17-40, and Abeta17-42; the latter two are truncated sequences of the Alzheimer's peptide. We simulate the spontaneous assembly of these peptide chains from a random initial configuration of random coils. We investigate aggregation kinetics and oligomer formation of a system of 192 polyalanine (KA14K) chains over a variety of temperatures and concentrations. The fibril formation pathway has the following steps: free monomers associate into small amorphous aggregates, those small amorphous aggregates grow, the amorphous aggregates rearrange into beta-sheets, and finally the beta-sheets stack into small fibrillar structures. The rate of fibril formation increases as concentration increases and temperature decreases; this faster fibril formation is the combination of several effects, including increased amorphous aggregate formation from free monomers, increased amorphous aggregate rearrangement into beta-sheets, and increased stacking into small fibrils. There is a competition between enthalpy and entropy that determine the behavior of the final structure in the system. At low temperature, enthalpy is dominant and the system produces multiple large fibrils, while at high temperature entropy is dominant and the system produces one or no large fibrils. As temperature increases and concentration decreases the intermediate structures that form, such as beta-sheets and large independent amorphous aggregates, are more stabilized which leads to slower fibril formation and fewer chains in the large final fibrillar structure. We study the formation of beta-sheets and small fibrillar structures for both Abeta17-40 and Abeta17-42 to determine the difference between the two sequences in aggregation kinetics and oligomer structure as a function of temperature. We observe that at low temperatures, both Abeta17-40 and Abeta17-42 form large amorphous aggregates with a small amount of beta-sheet character, at intermediate temperatures the peptides form a mixture of beta-sheets and fibrils that are surrounded by amorphous aggregates, and at high temperatures the peptides form small amorphous aggregates or remain isolated as free monomers. Abeta 17-42 forms fibrils over a larger temperature range than Abeta 17-40. The structure of the beta-sheets changes as temperature increases through the range conducive to fibril formation. Abeta17-42 goes through the transition from predominantly intr

Phelps, Erin Melissa

209

Effect of ?-sheet propensity on peptide aggregation  

NASA Astrophysics Data System (ADS)

The effect of ?-sheet propensity on the structural features of peptide aggregates was investigated using an off-lattice coarse-grained peptide model. A phase diagram as a function of temperature and ?-sheet propensity reveals a diverse family of supramolecular assemblies. Highly rigid peptides (peptides with high ?-sheet propensity) are seen to assemble predominantly into fibrillar structures. Increasing the flexibility of the peptide (reducing ?-sheet propensity) leads to a variety of structures, including fibrils, ?-barrel structures, and amorphous aggregates. Nonfibrillar entities have been suggested as primary causative agents in amyloid diseases and our simulations indicate that mutations that decrease ?-sheet propensity will decrease fibril formation and favor the formation of such toxic oligomers. Parallels between ?-sheet aggregates and nematic liquid crystals are discussed.

Bellesia, Giovanni; Shea, Joan-Emma

2009-04-01

210

Eumelanin kinetics and sheet structure  

NASA Astrophysics Data System (ADS)

Melanins are common pigments with a non-repeating primary structure that is generally accepted to be composed of dihydroxyindoles. However, despite intensive research the secondary structure defining the minimum functional unit (protomolecule) remains elusive. We have revisited eumelanin formation in-situ during the non-enzymatic auto-oxidation of 3,4-dihydroxy-L-phenylalanine by using the fluorescence of thioflavin T; an extrinsic probe known to report on sheet structure. This approach obviates the complex intrinsic fluorescence and reveals a sigmoidal temporal dependence of assembly that is consistent with protomolecule formation and assembly into a stacked sheet structure rather than a randomized heteropolymer formed by monomer addition.

Sutter, J. U.; Bidláková, T.; Karolin, J.; Birch, D. J. S.

2012-03-01

211

Synthesis of guanosine and its derivatives from 5-amino-1-beta-D-ribofuranosyl-4-imidazolecarboxamide. III. Formation of a novel cycloimidazole nucleoside and its cleavage reactions.  

PubMed Central

A new cycloimidazole nucleoside, 5-(1 inch -benzamido-1 inch-hydroxymethylene) amino-2', 1 inch-anhydro-1-beta-D-ribofuranosyl-4-imidazolecarboxamide (III) was synthesized by reaction of 5-amino-1-beta-D-ribofuranosyl-4-imidazolecarboxamide (AICA-riboside) with benzoyl isothiocyanate followed by methylation with methyl iodide. The structure of III was elucidated on the basis of its nmr spectra and chemical reactions. Of special interest are reactions of III with various nucleophiles. For example, guanosine (IX) was obtained by amination of III wtih ammonia in 72% yield. Analogous reactions of III with methylamine and dimethylamine gave N2-methylguanosine (X) and N2-dimethylguanosine (XI), respectively. Refluxing of III in alkaline solution afforded xanthosine (VII). The probable mechanism of formation and facile ring-opening of III is also discussed.

Okutsu, M; Yamazaki, A

1976-01-01

212

Pinch sheets and reconnection in astrophysics  

Microsoft Academic Search

Magnetic reconnection processes involving the formation and destruction of pinch current sheets in plasma are a universal phenomenon typical of both laboratory and space plasmas. In current sheets a rapid dissipation of the magnetic field is possible in conditions of high conductivity and large scales of the plasma. This effect results from specific features of the flow near the null

S. I. Syrovatskii

1981-01-01

213

Fact Sheets about Farmworkers  

MedlinePLUS

... 26 27 28 29 30 31 Sep Nov Fact Sheets About Farmworkers NCFH has created a set of fact sheets that provide detailed information on specific aspects of farmworker health. These fact sheets are updated every couple of years in ...

214

Beta-synuclein inhibits formation of alpha-synuclein protofibrils: a possible therapeutic strategy against Parkinson's disease.  

PubMed

Parkinson's disease (PD) is an age-associated and progressive movement disorder that is characterized by dopaminergic neuronal loss in the substantia nigra and, at autopsy, by fibrillar alpha-synuclein inclusions, or Lewy bodies. Despite the qualitative correlation between alpha-synuclein fibrils and disease, in vitro biophysical studies strongly suggest that prefibrillar alpha-synuclein oligomers, or protofibrils, are pathogenic. Consistent with this proposal, transgenic mice that express human alpha-synuclein develop a Parkinsonian movement disorder concurrent with nonfibrillar alpha-synuclein inclusions and the loss of dopaminergic terminii. Double-transgenic progeny of these mice that also express human beta-synuclein, a homologue of alpha-synuclein, show significant amelioration of all three phenotypes. We demonstrate here that beta- and gamma-synuclein (a third homologue that is expressed primarily in peripheral neurons) are natively unfolded in monomeric form, but structured in protofibrillar form. Beta-synuclein protofibrils do not bind to or permeabilize synthetic vesicles, unlike protofibrils comprising alpha-synuclein or gamma-synuclein. Significantly, beta-synuclein inhibits the generation of A53T alpha-synuclein protofibrils and fibrils. This finding provides a rationale for the phenotype of the double-transgenic mice and suggests a therapeutic strategy for PD. PMID:12667059

Park, June-Young; Lansbury, Peter T

2003-04-01

215

?-Sheet PoreForming Peptides Selected from a Rational Combinatorial Library:  Mechanism of Pore Formation in Lipid Vesicles and Activity in Biological Membranes †  

Microsoft Academic Search

In a previous report we described the selection of potent, ‚-sheet pore-forming peptides from a combinatorial library designed to mimic membrane-spanning ‚-hairpins (Rausch, J. M., Marks, J. R., and Wimley, W. C. (2005) Proc. Natl. Acad. Sci. U.S.A. 102 , 10511-10515). Here, we characterize their mechanism of action and compare the structure-function relationships in lipid vesicles to their activity in

Joshua M. Rausch; Jessica R. Marks; Ramesh Rathinakumar; William C. Wimley

2007-01-01

216

Estradiol stimulates capillary formation by human endothelial progenitor cells: role of estrogen receptor-{alpha}/{beta}, heme oxygenase 1, and tyrosine kinase.  

PubMed

Endothelial progenitor cells (EPCs) repair damaged endothelium and promote capillary formation, processes involving receptor tyrosine kinases (RTKs) and heme oxygenase 1 (HO-1). Because estradiol augments vascular repair, we hypothesize that estradiol increases EPC proliferation and capillary formation via RTK activation and induction of HO-1. Physiological concentrations of estradiol (10 nmol/L) increased EPC-induced capillary sprout and lumen formation in matrigel/fibrin/collagen systems. Propyl-pyrazole-triol (PPT; 100 nmol/L; estrogen receptor [ER]-alpha agonist), but not diarylpropionitrile (ER-beta agonist), mimicked the stimulatory effects of estradiol on capillary formation, and methyl-piperidino-pyrazole (ER-alpha antagonist) abolished the effects of estradiol and PPT. Three different RTK activators (vascular endothelial growth factor, hepatocyte growth factor, and stromal derived growth factor 1) mimicked the capillary-stimulating effects of estradiol and PPT. SU5416 (RTK inhibitor) blocked the stimulatory effects of estradiol and PPT on capillary formation. Estradiol increased HO-1 expression by 2- to 3-fold, an effect blocked by SU5416, and PPT mimicked the effects of estradiol on HO-1. The ability of estradiol to enhance capillary formation, increase expression of HO-1, and augment phosphorylation of extracellular signal-regulated kinase 1/2, Akt, and vascular endothelial growth factor receptor 2 was mimicked by its cell-impermeable analog BSA estradiol. Actinomycin (transcription inhibitor) did not alter the effects of estradiol on RTK activity or vascular endothelial growth factor secretion. We conclude that estradiol via ER-alpha promotes EPC-mediated capillary formation by a mechanism that involves nongenomic activation of RTKs and HO-1 activation. Estradiol in particular and ER-alpha agonists in general may promote healing of injured vascular beds by promoting EPC activity leading to more rapid endothelial recovery and capillary formation after injury. PMID:20644008

Baruscotti, Isabella; Barchiesi, Federica; Jackson, Edwin K; Imthurn, Bruno; Stiller, Ruth; Kim, Jai-Hyun; Schaufelberger, Sara; Rosselli, Marinella; Hughes, Christopher C W; Dubey, Raghvendra K

2010-07-19

217

Activated extracellular signal-regulated kinase correlates with cyst formation and transforming growth factor-beta expression in fetal obstructive uropathy.  

PubMed

Human renal dysplasia is frequently associated with urinary tract obstruction and the abnormal expression of mitogen-activated protein kinase (MAPK). Here, we determined the renal responses and MAPK expression in developing kidneys that were obstructed in fetal lambs. Kidneys were harvested at various times after obstruction (gestation day 60) through normal term (day 145). Dilation of Bowman's capsule and proximal tubules was seen 2 days after obstruction and involved the whole cortex 18 days later, with numerous cysts present throughout the kidney at term. The proliferation marker Ki-67 and transforming growth factor-beta (TGF-beta) were detected 2 days after obstruction and progressively increased in tubules, cysts, and the interstitium. In control kidneys, p38 was expressed in tubules only during the fetal stage, whereas phosphorylated extracellular signal-regulated kinase (P-ERK) was limited to ureteric buds and collecting ducts at all stages examined. However, Jun-N-terminal kinase (JNK) was absent in the fetal kidney but present in tubules at term. In obstructed kidneys, cyst epithelia were positive for p38 and P-ERK but negative for JNK throughout all stages. These studies show that P-ERK correlated spatially and temporally with Ki-67 and TGF-beta expression, which suggests that ERK may contribute to cyst formation and fibrosis in the obstructed fetal kidney. PMID:18272960

Omori, S; Kitagawa, H; Koike, J; Fujita, H; Hida, M; Pringle, K C; Awazu, M

2008-02-13

218

TGF{beta}-mediated formation of pRb-E2F complexes in human myeloid leukemia cells  

SciTech Connect

TGF{beta} is well known for its inhibitory effect on cell cycle G1 checkpoint kinases. However, its role in the control of pRb-E2F complexes is not well established. TGF{beta} inhibits phosphorylation of pRb at several serine and threonine residues and regulates the association of E2F transcription factors with pRb family proteins. Recent studies found that predominantly E2F-4, p130, and histone deacetylase (HDAC) are found to bind to corresponding E2F-responsive promoters in G0/G1 phase. As cells progress through mid-G1, p130-E2F4 complex are replaced by p107-E2F4 followed by activators E2F1, 2, and 3. pRb was not detectable in the promoters containing the E2F-responsive site in cycling cells but was associated with E2F4-p130 complexes or E2F4-p107 complexes during G0/G1 phase. In human myeloid leukemia cell line, MV4-11, TGF{beta} upregulated pRb-E2F-4 and p130-E2F-4, and downregulated p107-E2F-4 complexes. However, pRB-E2F1 and pRb-E2F3 complexes were found in proliferating cells but not in TGF{beta} arrested G1 cells. In addition, electrophoretic gel mobility shift assay (EMSA) could not detect pRb-E2F DNA-binding activities either in S or G1 phase but exhibited the existence of p107-E2F4 in proliferating cells and p130-E2F4 complexes in TGF{beta}-arrested G1 cells, respectively. Our data suggest that p107 and p130, but not pRb, and the repressor E2F, but not activator E2Fs, play a critical role in regulating E2F-responsive gene expression in TGF{beta}-mediated cell cycle control in human myeloid leukemia cells.

Hu Xiaotang [School of Natural and Health Science, Barry University, 11300 Northeast Second Avenue, Miami Shores, FL 33161 (United States)], E-mail: xthu@mail.barry.edu

2008-05-02

219

Camera data sheet for pictorial electronic still cameras  

Microsoft Academic Search

A data sheet is presented outlining the performance and characteristics of a Kodak DCS 200mi camera. In addition to providing information on this camera, the format and content of the data sheet could serve as a guide in the organization and display of pertinent information on electronic still cameras in general. Such data sheets are already common in silver halide

Sabine Susstrunk; Jack M. Holm

1995-01-01

220

Deriving star-formation and extinction in normal galaxies from H(alpha) and Paschen(beta) imaging  

Microsoft Academic Search

We propose to derive spatial maps of extinction corrected ionizing radiation and dust columns using narrow-band imaging in H(alpha) and Paschen(beta) of normal, nearby galaxies. This is possible because the intrinsic line ratios are insensitive to temperature and densities in HII regions. Comparison of observed line ratios to the intrinsic ones, using the extinction law, will yield column densities of

Sangeeta Malhotra; Daniel Dale; James Rhoads; George Helou; Robert Kennicutt; Deidre Hunter

1999-01-01

221

Islet amyloid formation associated with hyperglycemia in transgenic mice with pancreatic beta cell expression of human islet amyloid polypeptide.  

PubMed Central

Pancreatic islet amyloid deposits are a characteristic pathologic feature of non-insulin-dependent diabetes mellitus and contain islet amyloid polypeptide (IAPP; amylin). We used transgenic mice that express human IAPP in pancreatic beta cells to explore the potential role of islet amyloid in the pathogenesis of non-insulin-dependent diabetes mellitus. Extensive amyloid deposits were observed in the pancreatic islets of approximately 80% of male transgenic mice > 13 months of age. Islet amyloid deposits were rarely observed in female transgenic mice (11%) and were never seen in nontransgenic animals. Ultrastructural analysis revealed that these deposits were composed of human IAPP-immunoreactive fibrils that accumulated between beta cells and islet capillaries. Strikingly, approximately half of the mice with islet amyloid deposits were hyperglycemic (plasma glucose > 11 mM). In younger (6- to 9-month-old) male transgenic mice, islet amyloid deposits were less commonly observed but were always associated with severe hyperglycemia (plasma glucose > 22 mM). These data indicate that expression of human IAPP in beta cells predisposes male mice to the development of islet amyloid and hyperglycemia. The frequent concordance of islet amyloid with hyperglycemia in these mice suggests an interdependence of these two conditions and supports the hypothesis that islet amyloid may play a role in the development of hyperglycemia. Images Fig. 1 Fig. 2

Verchere, C B; D'Alessio, D A; Palmiter, R D; Weir, G C; Bonner-Weir, S; Baskin, D G; Kahn, S E

1996-01-01

222

The fate of beta-D-mannopyranose after its formation by endoplasmic reticulum alpha-(1-->2)-mannosidase I catalysis.  

PubMed

The automated docking program AutoDock was used to dock all 38 characteristic beta-D-mannopyranose ring conformers into the active site of the yeast endoplasmic reticulum alpha-(1-->2)-mannosidase I, a Family 47 glycoside hydrolase that converts Man9GlcNAc2 to Man8GlcNAc2. The subject of this work is to establish the conformational pathway that allows the cleaved glycon product to leave the enzyme active site and eventually reach the ground-state conformation. Twelve of the 38 conformers optimally dock in the active site where the inhibitors 1-deoxymannonojirimycin and kifunensine are found in enzyme crystal structures. A further 23 optimally dock in a second site on the side of the active-site well, while three dock outside the active-site cavity. It appears, through analysis of the internal energies of different ring conformations, of intermolecular energies between the ligands and enzyme, and of forces exerted on the ligands by the enzyme, that beta-D-mannopyranose follows the path 3E-->1C4-->1H2-->B2,5 before being expelled by the enzyme. The highly conserved second site that strongly binds beta-D-mannopyranose-4C1 may exist to prevent competitive inhibition by the product, and is worthy of further investigation. PMID:17157281

Mulakala, Chandrika; Nerinckx, Wim; Reilly, Peter J

2006-11-16

223

[1-butanol synthesis by Escherichia coli cells through butyryl-CoA formation by heterologous enzymes of clostridia and native enzymes of fatty acid beta-oxidation].  

PubMed

Anaerobic biosynthesis of 1-butanol from glucose is investigated in recombinant Escherichia coli strains which form butyryl-CoA using the heterologous enzyme complex of clostridia or as a result of a reversal in the action of native enzymes of the fatty acid beta-oxidation pathway. It was revealed that when the basic pathways of acetic and lactic acid formation are inactivated due to deletions in the ackA, pta, poxB, and ldhA genes, the efficiency of butyryl-CoA biosynthesis and its reduced product, i.e., 1-butanol, by two types of recombinant stains is comparable. The limiting factor for 1-butanol production by the obtained strains is the low substrate specificity of the basic CoA-dependent alcohol/aldehyde AdhE dehydrogenase from E. coli to butyryl-CoA. It was concluded that, in order to construct an efficient 1-butanol producer based on a model strain synthesizing butyryl-CoA as a result of a reversal in fatty acid beta-oxidation enzymes, it is necessary to provide intensive formation of acetyl-CoA and enhanced activity of alternative alcohol and aldehyde dehydrogenases in the cells of a strain. PMID:23035570

Gulevich, A Iu; Skorokhodova, A Iu; Morzhakova, A A; Antonova, S V; Sukhozhenko, A V; Shakulov, R S; Debabov, V G

224

Comparison of hydrogels in the in vivo formation of tissue-engineered bone using mesenchymal stem cells and beta-tricalcium phosphate.  

PubMed

Availability of grafts and morbidity at the donor site limit autologous transplantation in patients requiring bone reconstruction. A tissue-engineering approach can overcome these limitations by producing bone-like tissue of custom shape and size from isolated cells. Several hydrogels facilitate osteogenesis on porous scaffolds; however, the relative suitability of various hydrogels has not been rigorously assessed. Fibrin glue, alginate, and collagen I hydrogels were mixed with swine bone marrow-derived differentiated mesenchymal stem cells (MSCs), applied to 3-dimensionally printed porous beta-tricalcium phosphate (beta-TCP) scaffolds and implanted subcutaneously in nude mice. Although noninvasive assessment of osteogenesis in 3 dimensions is desirable for monitoring new bone formation in vivo, correlations with traditional histological and mechanical testing need to be established. High-resolution volumetric computed tomography (VCT) scanning, histological examination, biomechanical compression testing, and osteonectin (ON) expression were performed on excised scaffolds after 1, 2, 4, and 6 weeks of subcutaneous implantation in mice. Statistical correlation analyses were performed between radiological density, stiffness, and ON expression. Use of collagen I as a hydrogel carrier produced superior bone formation at 6 weeks, as demonstrated using VCT scanning with densities similar to native bone and the highest compression values. Continued contribution of the seeded MSCs was demonstrated using swine-specific messenger ribonucleic acid probes. Radiological density values correlated closely with the results of histological and biomechanical testing and ON expression. High-resolution VCT is a promising method for monitoring osteogenesis. PMID:17223744

Weinand, Christian; Gupta, Rajiv; Huang, Albert Y; Weinberg, Eli; Madisch, Ijad; Qudsi, Rameez A; Neville, Craig M; Pomerantseva, Irina; Vacanti, Joseph P

2007-04-01

225

Interleukin-1beta and signaling of interleukin-1 in vascular wall and circulating cells modulates the extent of neointima formation in mice.  

PubMed

Interleukin (IL)-1 is an important mediator of inflammation and cardiovascular disease. Here, we examined the role of IL-1 in arterial neointima formation. Carotid artery neointima was induced by ligation, and arteries were harvested 4 weeks after injury. The neointima/media of mice deficient in the IL-1 signaling receptor (IL-1R1(-/-)) was significantly reduced compared to IL-1R1(+/+) controls (P < 0.01). IL-1R1(+/+) mice receiving subcutaneous IL-1ra also had significantly reduced neointima/media compared with placebo (P < 0.05). IL-1beta(-/-) mice had reduced neointima/media compared to wild-type (P < 0.05), whereas IL-1alpha(-/-) mice were no different from controls. Mice deficient in the P2X(7) receptor (involved in IL-1 release) or caspase-1 (involved in IL-1 activation) did not differ in their response to carotid ligation compared to controls. To examine the site of IL-1 signaling, we generated chimeric mice. IL-1R1(+/+) mice receiving IL-1R1(-/-) marrow and IL-1R1(-/-) mice receiving IL-1R1(+/+) marrow both had significantly reduced neointima/media compared with IL-1R1(+/+) to IL-1R1(+/+) (P < 0.05) but had significantly greater neointima/media than IL-1R1(-/-) to IL-1R1(-/-) controls (P < 0.05). These data confirm the importance of IL-1beta signaling in mediating arterial neointima formation and suggest the involvement of IL-1 signaling in both circulating and arterial wall cells. Furthermore, receptor antagonism may be a better therapeutic target than interruption of IL-1beta processing or release. PMID:16565512

Chamberlain, Janet; Evans, David; King, Andrea; Dewberry, Rachael; Dower, Steven; Crossman, David; Francis, Sheila

2006-04-01

226

S-Adenosylhomocysteine increases beta-amyloid formation in BV-2 microglial cells by increased expressions of beta-amyloid precursor protein and presenilin 1 and by hypomethylation of these gene promoters.  

PubMed

S-Adenosylhomocysteine (SAH) has been implicated as a risk factor for neurodegenerative diseases such as Alzheimer's disease. As SAH is a potent inhibitor of all cellular methyltransferases, we herein examined the hypothesis that SAH may increase the formation of amyloid beta-peptide (Abeta) in BV-2 mouse microglial cells through hypomethylation of presenilin 1 protein (PS1) and beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), both of which cleave Abeta precursor protein (APP) to form Abeta. The results showed that SAH increased Abeta protein formation in a concentration-dependent manner (10-500 nM), and this effect of SAH was accompanied by significantly increased expression of APP and PS1 proteins, although SAH only significantly increased the expression of BACE1 at the highest concentration used (500 nM). SAH (500 nM) markedly induced hypomethylation of APP and PS1 gene promoters. Incubation of cells with 5'-azc (20 microM), also an inhibitor of DNA methyltransferases enhanced Abeta protein expression and APP and PS1 gene promoters hypomethylation. By contrast, pre-incubation of cells with betaine (1.0 mM), 30 min followed by incubation with SAH (500 nM) or 5'-azc (20 microM) for 24h markedly prevented the expression of Abeta protein (by 50%, P<0.05) and the gene promoter hypomethylation of APP and PS1. Taken together, this study demonstrates that SAH increases the production of Abeta in BV-2 cells possibly by increased expression of APP and induction of hypomethylation of APP and PS1 gene promoters. PMID:19635394

Lin, Hung-Chi; Hsieh, Huei-Min; Chen, Yu-Hsuan; Hu, Miao-Lin

2009-04-08

227

Tracking fiber formation in human islet amyloid polypeptide with automated 2D-IR spectroscopy.  

PubMed

Amyloid forming proteins have been implicated in many human diseases. The kinetics of amyloid fiber formation are of particular interest because evidence points to intermediate folding structures as potential cytotoxic species. The standard methods for monitoring the kinetics are to use fluorescence or circular dichroism spectroscopy, which do not uniquely resolve secondary structures. In this work, we use a new technology for rapidly scanning 2D-IR spectra that allows us to follow the fiber formation kinetics of the human islet amyloid polypeptide (hIAPP) that is involved in type II diabetes. Spectroscopic markers are identified that uniquely monitor random coil versus beta-sheet secondary structures as well as probe beta-sheet elongation and stacking. Our measurements provide more rigorous kinetics for the secondary structure evolution of amyloid formation than is available with other techniques. PMID:18459774

Strasfeld, David B; Ling, Yun L; Shim, Sang-Hee; Zanni, Martin T

2008-05-07

228

Near-earth Thin Current Sheets and Birkeland Currents during Substorm Growth Phase  

SciTech Connect

Two important phenomena observed during the magnetospheric substorm growth phase are modeled: the formation of a near-Earth (|X| {approx} 9 R{sub E}) thin cross-tail current sheet, as well as the equatorward shift of the ionospheric Birkeland currents. Our study is performed by solving the 3-D force-balance equation with realistic boundary conditions and pressure distributions. The results show a cross-tail current sheet with large current (J{sub {phi}} {approx} 10 nA/m{sup 2}) and very high plasma {beta} ({beta} {approx} 40) between 7 and 10 R{sub E}. The obtained region-1 and region-2 Birkeland currents, formed on closed field lines due to pressure gradients, move equatorward and become more intense (J{sub {parallel}max} {approx} 3 {micro}A/m{sup 2}) compared to quiet times. Both results are in agreement with substorm growth phase observations. Our results also predict that the cross-tail current sheet maps into the ionosphere in the transition region between the region-1 and region-2 currents.

Sorin Zaharia; C.Z. Cheng

2003-04-30

229

Overexpression of protein kinase C. beta. 1 enhances phospholipase D activity and diacylglycerol formation in phorbol ester-stimulated rat fibroblasts  

SciTech Connect

The authors are using a Rat-6 fibroblast cell line that stably overexpresses the {beta}1 isozyme of protein kinase C (PKC) to study regulation of phospholipid hydrolysis by PKC. Stimulation of control (R6-C1) or overexpressing (R6-PKC3) cells with phorbol ester results in an increase in diacylglycerol (DAG) mass with no increase in inositol phosphates, indicating that DAG is not formed by inositol phospholipid breakdown. A more dramatic DAG increase occurs in R6-PKC3 cells compared to R6-C1 cells. To further define the source of DAG, phosphatidylcholine (PC) pools were labeled with ({sup 3}H)myristic acid or with ({sup 3}H)- or ({sup 32}P)alkyllyso-PC and formation of labeled phosphatidylethanol, an unambiguous marker of phospholipase D activation, was monitored. Phorbol ester-stimulated phosphatidylethanel formation is 5-fold greater in the R6-PKC3 cell line. Formation of radiolabeled phosphatidic acid (PA) is also enhanced by PKC overepression. In cells double-labeled with ({sup 3}H)- and ({sup 32}P)-alkyl-lysoPC, the {sup 3}H/{sup 32}P ratio of PA and PC are identical 15 min after stimulation, suggesting that a phospholipase D mechanism predominates. These results indicate that phospholipase D is regulated by the action of PKC. Enhanced phospholipase D activity may contribute to the growth abnormalities seen in PKC-overexpressing cells.

Pai, Jinkeon; Pachter, J.A.; Bishop, W.R. (Schering-Plough Research, Bloomfield, NJ (United States)); Weinstein, I.B. (Columbia Univ., New York, NY (United States))

1991-01-15

230

Nonlinear analysis for the evolution of vortex sheets  

NASA Astrophysics Data System (ADS)

Mathematical results on nonlinear vortex sheet evolution and singularity formation are presented. For sufficiently small analytic perturbations of a nearly flat vortex sheet, smooth solutions of the Birkhoff-Rott equation are shown to exist almost up to the expected time of singularity formation. A construction of exact solutions that develop singularities in finite time starting from analytic initial data is presented.

Caflisch, Russel E.

1988-09-01

231

Hydroxylated metabolites of beta- and delta-hexachlorocyclohexane: bacterial formation, stereochemical configuration, and occurrence in groundwater at a former production site.  

PubMed

Although the use of hexachlorocyclohexane (HCH), one of the most popular insecticides after the Second World War, has been discontinued in many countries, problems remain from former production and waste sites. Despite the widespread occurrence of HCHs, the environmental fate of these compounds is not fully understood. In particular, environmental metabolites of the more persistent beta-HCH and delta-HCH have not been fully identified. Such knowledge, however, is important to follow degradation and environmental fate of the HCHs. In the present study, several hydroxy metabolites that formed during incubation of beta- and delta-HCH with the common soil microorganism Sphingobium indicum B90A were isolated, characterized, and stereochemically identified by gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). The metabolites were identified as isomeric pentachlorocyclohexanols (B1, D1) and tetrachlorocyclohexane-1,4-diols (B2, D2); delta-HCH additionally formed a tetrachloro-2-cyclohexen-1-ol (D3) and a trichloro-2-cyclohexene-1,4-diol (D4), most likely by hydroxylation of delta-pentachlorocyclohexene (delta-PCCH), initially formed by dehydrochlorination. The dehydrochlorinase LinA was responsible for conversion of delta-HCH into delta-PCCH, and the haloalkane dehalogenase LinB was responsible for the transformation of beta-HCH and delta-HCH into B1 and D1, respectively, and subsequently into B2 and D2, respectively. LinB was also responsible for transforming delta-PCCH into D3 and subsequently into D4. These hydroxylations proceeded in accordance with SN2 type reactions with initial substitution of equatorial Cls and formation of axially hydroxylated stereoisomers. The apparently high reactivity of equatorial Cls in beta- and delta-HCH toward initial hydroxylation by LinB of Sphingobium indicum B90A is remarkable when considering the otherwise usually higher reactivity of axial Cls. Several of these metabolites were detected in groundwater from a former HCH production site in Switzerland. Their presence indicates that these reactions proceed under natural environmental conditions and that the metabolites are of environmental relevance. PMID:17626427

Raina, Vishakha; Hauser, Andrea; Buser, Hans Rudolf; Rentsch, Daniel; Sharma, Poonam; Lal, Rup; Holliger, Christof; Poiger, J Thomas; Müller, Markus D; Kohler, Hans-Peter E

2007-06-15

232

Beta amyloid and hyperphosphorylated tau deposits in the pancreas in type 2 diabetes  

SciTech Connect

Strong epidemiologic evidence suggests an association between Alzheimer disease (AD) and type 2 diabetes. To determine if amyloid beta (A{beta}) and hyperphosphorylated tau occurs in type 2 diabetes, pancreas tissues from 21 autopsy cases (10 type 2 diabetes and 11 controls) were analyzed. APP and tau mRNAs were identified in human pancreas and in cultured insulinoma beta cells (INS-1) by RT-PCR. Prominent APP and tau bands were detected by Western blotting in pancreatic extracts. Aggregated A{beta}, hyperphosphorylated tau, ubiquitin, apolipoprotein E, apolipoprotein(a), IB1/JIP-1 and JNK1 were detected in Langerhans islets in type 2 diabetic patients. A{beta} was co-localized with amylin in islet amyloid deposits. In situ beta sheet formation of islet amyloid deposits was shown by infrared microspectroscopy (SIRMS). LPS increased APP in non-neuronal cells as well. We conclude that A{beta} deposits and hyperphosphorylated tau are also associated with type 2 diabetes, highlighting common pathogenetic features in neurodegenerative disorders, including AD and type 2 diabetes and suggesting that A{beta} deposits and hyperphosphorylated tau may also occur in other organs than the brain.

Miklossy, J.; Miller, L.; Qing, H.; Radenovic, A.; Kis, A.; Vileno, B.; Laszlo, F.; Martins, R.N.; Waeber, G.; Mooser, V.; Bosman, F.; Khalili, K.; Darbinian, N.; McGeer, P.L.

2008-08-25

233

Pesticide Fact Sheets  

MedlinePLUS

... but they are written in more general terms. Technical Active Ingredient Fact Sheets are designed to provide ... such as physicians, veterinarians, regulators or research scientists. Technical fact sheets contain information on the pesticide's physical ...

234

Experimental Study of Lower-hybrid Drift Turbulence in a Reconnecting Current Sheet  

SciTech Connect

The role of turbulence in the process of magnetic reconnection has been the subject of a great deal of study and debate in the theoretical literature. At issue in this debate is whether turbulence is essential for fast magnetic reconnection to occur in collisionless current sheets. Some theories claim it is necessary in order to provide anomalous resistivity, while others present a laminar fast reconnection mechanism based on the Hall term in the generalized Ohm's law. In this work, a thorough study of electrostatic potential fluctuations in the current sheet of the Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)] was performed in order to ascertain the importance of turbulence in a laboratory reconnection experiment. Using amplified floating Langmuir probes, broadband fluctuations in the lower hybrid frequency range (fLH approximately 5-15 MHz) were measured which arise with the formation of the current sheet in MRX. The frequency spectrum, spatial amplitude profile, and spatial correlation characteristics of the measured turbulence were examined carefully, finding consistency with theories of the lower-hybrid drift instability (LHDI). The LHDI and its role in magnetic reconnection has been studied theoretically for decades, but this work represents the first detection and detailed study of the LHDI in a laboratory current sheet. The observation of the LHDI in MRX has provided the unique opportunity to uncover the role of this instability in collisionless reconnection. It was found that: (1) the LHDI fluctuations are confined to the low-beta edge of current sheets in MRX; (2) the LHDI amplitude does not correlate well in time or space with the reconnection electric field, which is directly related to the rate of reconnection; and (3) significant LHDI amplitude persists in high collisionality current sheets where the reconnection rate is classical. These findings suggest that the measured LHDI fluctuations do not play an essential role in determining the reconnection rate in MRX.

T.A. Carter, M. Yamada, H. Ji, R.M. Kulsrud, and F. Trintchouk

2002-06-18

235

Electrical interaction between cardiomyocyte sheets separated by non-cardiomyocyte sheets in heterogeneous tissues.  

PubMed

Electrical coupling between cardiomyocytes is important in synchronous beating and normal heart functions. Cardiomyocytes are also electrically coupled to non-cardiomyocytes. The electrical interactions between cardiomyocytes and non-cardiomyocytes, or those between separated cardiomyocytes, are important for normal heart function because abnormalities of the coupling and variation of the cell population induce pathological heart functions and arrhythmias. In this study the three-dimensional time course of the electrical interaction between two rat neonatal cardiomyocyte sheets separated by non-cardiomyocyte sheets was analysed by a multiple-electrode extracellular recording system. The two cardiomyocyte sheets separated by a single- or double-layered mouse fibroblast NIH3T3 cell sheet coupled electrically at 113 +/- 28 or 287 +/- 87 min after layering, respectively. The time course of the electrical coupling, when the single-layer NIH3T3 cell sheet was inserted, is similar to that of a layered cardiomyocyte sheet. Immunocytological analysis and dye transfer assay suggested the formation of gap junctions at heterocellular junctions of cardiomyocytes and NIH3T3 cells. On the other hand, when a double-layered NIH3T3 cell sheet was inserted, an incomplete electrical coupling of two cardiomyocyte sheets, including a conduction delay, was observed. The electrical coupling of cardiomyocyte sheets was completely blocked (conduction block) by insertion of a triple-layered NIH3T3 cell sheet, a communication-defective HeLa cell sheet or a Ca(2+)-antagonist LaCl(3)-treated cell sheet. These electrophysiological analyses of heterogeneously stacked cell sheets might provide insights into complex electrical conduction systems that resemble those of native or damaged heart and transplanted tissues. PMID:20014093

Haraguchi, Yuji; Shimizu, Tatsuya; Yamato, Masayuki; Okano, Teruo

2010-06-01

236

Application of a magnetized coaxial plasma gun for formation of a high-beta field-reversed configuration  

Microsoft Academic Search

We have tested a field-reversed configuration (FRC) formation with a spheromak injection for the first time. In this method, initial pre-ionized plasma is injected as a magnetized spheromak-like plasmoid into the discharge chamber prior to main field reversal. The FRC plasma with an electron density of 1.3×1021m?3, a separatrix radius of 0.04m and a plasma length of 0.8m was produced

T. Nishida; T. Kiguchi; T. Asai; T. Takahashi; Y. Matsuzawa; T. Okano; Y. Nogi

2006-01-01

237

A biased probe analysis of potential well formation in an electron only, low beta Polywell magnetic field  

NASA Astrophysics Data System (ADS)

Orbital limited motion theory has been applied to two biased probes in a low beta Polywell. The cases studied include electron injection, magnetic field scaling, Polywell bias scaling, and radial position profiles. Langmuir's original orbital limited motion results for a monoenergetic electron beam are shown to be in excellent agreement for electron injection into the Polywell. A distribution function is proposed for the electron plasma characteristics in the centre of the magnetic null and confirmed with experimental results. A translational stage was used to measure the radial plasma potential profile. In other experiments, two probes were used to simultaneously measure the profiles in both the null and a position halfway along a corner cusp. The results confirm a radial potential well created by electron trapping in the device. In addition, we present preliminary results of the potential well scaling with the magnetic field, Polywell bias voltage, and the injected beam current. The electron population was found to maintain non-equilibrium in all cases studied.

Carr, Matthew; Khachan, Joe

2013-05-01

238

Note Sheets: A Reliable Predictor of Success?  

NSDL National Science Digital Library

Students in a large introductory-level biology course brought one page of notes to their exams. The authors scored these note sheets for their format and content. Student performance on exams showed a very limited correlation with the format or content of

White, Brian; Puopolo, Denise; Ceglie, Robert

2001-11-01

239

Structural model of the amyloid fibril formed by beta(2)-microglobulin #21-31 fragment based on vibrational spectroscopy.  

PubMed

A structural model of amyloid fibril formed by the #21-31 fragment of beta2-microglobulin is proposed from microscope IR measurements on specifically 13C-labeled peptide fibrils and Raman spectra of the dispersed fibril solution. The 13C-shifted amide frequency indicated the secondary structure of the labeled residues. The IR spectra have demonstrated that the region between F22 and V27 forms the core part with the extended beta-sheet structure. Raman spectra indicated the formation of a dimer with a disulfide bridge between C25 residues. PMID:15926803

Hiramatsu, Hirotsugu; Goto, Yuji; Naiki, Hironobu; Kitagawa, Teizo

2005-06-01

240

Locating Current Sheets in the Solar Corona  

Microsoft Academic Search

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection.\\u000a Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an\\u000a unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even\\u000a topological properties of a force-free coronal magnetic field.

J. Büchner

2006-01-01

241

Explosive disruption of the current sheet  

NASA Astrophysics Data System (ADS)

This is a summary of the experimental study of nonlinear phenomena resulting from the formation of the current sheet and its subsequent disruption. The latter process begins with a local increase in the magnetic reconnection velocity and leads to significant changes in the magnetic configuration and a redistribution of the current density and plasma density. The current sheet disruption is connected with the rise of plasma turbulence and anomalous resistance.

Frank, A. G.

242

Network structure of polyfluorene sheets as a function of alkyl side chain length.  

PubMed

The formation of self-organized structures in poly(9,9-di-n-alkylfluorene)s ?1 vol % methylcyclohexane (MCH) and deuterated MCH (MCH-d(14)) solutions was studied at room temperature using neutron and x-ray scattering (with the overall q range of 0.00058-4.29 Å(-1)) and optical spectroscopy. The number of side chain carbons (N) ranged from 6 to 10. The phase behavior was rationalized in terms of polymer overlap, cross-link density, and blending rules. For N=6-9, the system contains isotropic areas and lyotropic areas where sheetlike assemblies (lateral size of >400 Å) and free polymer chains form ribbonlike agglomerates (characteristic dimension of >1500 Å) leading to a gel-like appearance of the solutions. The ribbons are largely packed together with surface fractal characteristics for N=6-7 but become open networklike structures with mass fractal characteristics for N=8-9, until the system goes through a transition to an isotropic phase of overlapping rodlike polymers for N=10. The polymer order within sheets varies allowing classification for loose membranes and ordered sheets, including the so-called ? phase. The polymers within the ordered sheets have restricted motion for N=6-7 but more freedom to vibrate for N=8-9. The nodes in the ribbon network are suggested to contain ordered sheets cross-linking the ribbons together, while the nodes in the isotropic phase appear as weak density fluctuations cross-linking individual chains together. The tendencies for macrophase separation and the formation of non beta sheets decrease while the proportion of free chains increases with increasing N. The fraction of ? phase varies nonlinearly, reaching its maximum at N = 8. PMID:21728563

Knaapila, M; Bright, D W; Stepanyan, R; Torkkeli, M; Almásy, L; Schweins, R; Vainio, U; Preis, E; Galbrecht, F; Scherf, U; Monkman, A P

2011-05-19

243

Semiflexible Chain Networks Formed via Self-Assembly of Beta-Hairpin Molecules  

NASA Astrophysics Data System (ADS)

We present experimental results from a de novo designed oligopeptide that intermolecularly self-assembles into rigid hydrogel networks after an intramolecular folding event. The effect of ionic strength and beta hairpin peptide strand length on beta-sheet formation, self-assembly and resultant rheological properties were studied. The peptide molecules are locally amphiphilic with two linear strands of alternating hydrophobic valine and hydrophilic lysine amino acids flanking a central turn sequence. The beta-sheet formation of 24, 20, 16 and 12 amino acid long beta-hairpin molecules were studied by CD spectroscopy. The network properties and the nanostructure of the hydrogels were studied by rheology, TEM and SANS. The hydrogel network is composed of semiflexible fibrillar assemblies with viscoelastic behavior that follows the theoretical prediction for heavily crosslinked,semi-flexible polymer networks. SANS results show that the cross-sectional diameter of the fibrils, and thus, the bending modulus of the chains can be varied by changing the number of amino acids of strands of the molecules. Rheological measurements reveal that rigidity, creep and relaxation behavior of the hydrogels vary with the magnitude of stimulus and with the cross-section diameter of the chains.

Ozbas, Bulent; Rajagopal, Karthikan

2005-03-01

244

Huperzine A attenuates amyloid beta-peptide fragment 25-35-induced apoptosis in rat cortical neurons via inhibiting reactive oxygen species formation and caspase-3 activation.  

PubMed

Huperzine A, a novel Lycopodium alkaloid originally discovered in the Chinese herb Qian Ceng Ta (Huperzia serrata), is a reversible, potent, and selective acetylcholinesterase (AChE) inhibitor and has been extensively used for the treatment of Alzheimer's disease (AD) in China. The present studies were designed to investigate effects of huperzine A on amyloid beta-peptide fragment 25-35 (Abeta25-35)-induced neuronal apoptosis and potential mechanisms in primary cultured rat cortical neurons. After exposure of the cells to Abeta25-35 (20 microM), apoptotic cell death was observed as evidenced by a significant decrease in cell viability, alteration of neuronal morphology, and DNA fragmentation. Pretreatment of the cells with huperzine A (0.01-10 microM) prior to Abeta25-35 exposure significantly elevated the cell survival and reduced Abeta25-35-induced nuclei fragmentation. Reactive oxygen species (ROS)-based fluorescence, caspase-3-like fluorogenic cleavage, and Western blot analysis demonstrated that huperzine A reduced Abeta25-35-induced ROS formation in a dose-dependent manner, and 1 microM of huperzine A attenuated Abeta25-35-induced caspase-3 activity at 6, 12, 24, and 48 hr posttreatment. Our results provide the first direct evidence that huperzine A protects neurons against Abeta25-35-induced apoptosis via the inhibition of ROS formation and caspase-3 activity. PMID:11754078

Xiao, Xiao Qiu; Zhang, Hai Yan; Tang, Xi Can

2002-01-01

245

Amyloid fibril formation is progressive and correlates with beta-cell secretion in transgenic mouse isolated islets  

Microsoft Academic Search

\\u000a \\u000a Abstract\\u000a \\u000a   \\u000a \\u000a Aims\\/hypothesis. Amyloid fibrils are formed in islets isolated from transgenic mice expressing the gene for human islet amyloid polypeptide\\u000a (IAPP) by an unknown mechanism. This model of islet amyloidosis in Type II (non-insulin-dependent) diabetes mellitus has been\\u000a used to investigate the temporal and glucose dependency of fibril formation. Methods. To determine the time course and nature of amyloid-like

D. L. A. MacArthur; E. J. P. de Koning; J. S. Verbeek; J. F. Morris; A. Clark

1999-01-01

246

Expression level and agonist-binding affect the turnover, ubiquitination and complex formation of peroxisome proliferator activated receptor beta.  

PubMed

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily that modulate target gene expression in response to fatty acid ligands. Their regulation by post-translational modifications has been reported but is poorly understood. In the present study, we investigated whether ligand binding affects the turnover and ubiquitination of the PPARbeta subtype (also known as PPARdelta). Our data show that the ubiquitination and degradation of PPARbeta is not significantly influenced by the synthetic agonist GW501516 under conditions of moderate PPARbeta expression. By contrast, the overexpression of PPARbeta dramatically enhanced its degradation concomitant with its polyubiquitination and the formation of high molecular mass complexes containing multiple, presumably oligomerized PPARbeta molecules that lacked stoichiometical amounts of the obligatory PPARbeta dimerization partner, retinoid X receptor. The formation of these apparently aberrant complexes, as well as the ubiquitination and destabilization of PPARbeta, were strongly inhibited by GW501516. Our findings suggest that PPARbeta is subject to complex post-translational regulatory mechanisms that partly may serve to safeguard the cell against deregulated PPARbeta expression. Furthermore, our data have important implications regarding the widespread use of overexpression systems to evaluate the function and regulation of PPARs. PMID:17803688

Rieck, Markus; Wedeken, Lena; Müller-Brüsselbach, Sabine; Meissner, Wolfgang; Müller, Rolf

2007-09-04

247

Oncoprotein E7 from Beta Human Papillomavirus 38 Induces Formation of an Inhibitory Complex for a Subset of p53-Regulated Promoters.  

PubMed

Our previous studies on cutaneous beta human papillomavirus 38 (HPV38) E6 and E7 oncoproteins highlighted a novel activity of I?B kinase beta (IKK?) in the nucleus of human keratinocytes, where it phosphorylates and stabilizes ?Np73?, an antagonist of p53/p73 functions. Here, we further characterize the role of the IKK? nuclear form. We show that IKK? nuclear translocation and ?Np73? accumulation are mediated mainly by HPV38 E7 oncoprotein. Chromatin immunoprecipitation (ChIP)/Re-ChIP experiments showed that ?Np73? and IKK? are part, together with two epigenetic enzymes DNA methyltransferase 1 (DNMT1) and the enhancer of zeste homolog 2 (EZH2), of a transcriptional regulatory complex that inhibits the expression of some p53-regulated genes, such as PIG3. Recruitment to the PIG3 promoter of EZH2 and DNMT1 resulted in trimethylation of histone 3 on lysine 27 and in DNA methylation, respectively, both events associated with gene expression silencing. Decreases in the intracellular levels of HPV38 E7 or ?Np73? strongly affected the recruitment of the inhibitory transcriptional complex to the PIG3 promoter, with consequent restoration of p53-regulated gene expression. Finally, the ?Np73?/IKK?/DNMT1/EZH2 complex appears to bind a subset of p53-regulated promoters. In fact, the complex is efficiently recruited to several promoters of genes encoding proteins involved in DNA repair and apoptosis, whereas it does not influence the expression of the prosurvival factor Survivin. In summary, our data show that HPV38 via E7 protein promotes the formation of a multiprotein complex that negatively regulates the expression of several p53-regulated genes. PMID:24006445

Saidj, Djamel; Cros, Marie-Pierre; Hernandez-Vargas, Hector; Guarino, Francesca; Sylla, Bakary S; Tommasino, Massimo; Accardi, Rosita

2013-09-04

248

Role of PDGF-B and PDGFR-beta in recruitment of vascular smooth muscle cells and pericytes during embryonic blood vessel formation in the mouse.  

PubMed

Development of a vascular system involves the assembly of two principal cell types - endothelial cells and vascular smooth muscle cells/pericytes (vSMC/PC) - into many different types of blood vessels. Most, if not all, vessels begin as endothelial tubes that subsequently acquire a vSMC/PC coating. We have previously shown that PDGF-B is critically involved in the recruitment of pericytes to brain capillaries and to the kidney glomerular capillary tuft. Here, we used desmin and alpha-smooth muscle actin (ASMA) as markers to analyze vSMC/PC development in PDGF-B-/- and PDGFR-beta-/- embryos. Both mutants showed a site-specific reduction of desmin-positive pericytes and ASMA-positive vSMC. We found that endothelial expression of PDGF-B was restricted to immature capillary endothelial cells and to the endothelium of growing arteries. BrdU labeling showed that PDGFR-beta-positive vSMC/PC progenitors normally proliferate at sites of endothelial PDGF-B expression. In PDGF-B-/- embryos, limb arterial vSMC showed a reduced BrdU-labeling index. This suggests a role of PDGF-B in vSMC/PC cell proliferation during vascular growth. Two modes of vSMC recruitment to newly formed vessels have previously been suggested: (1) de novo formation of vSMC by induction of undifferentiated perivascular mesenchymal cells, and (2) co-migration of vSMC from a preexisting pool of vSMC. Our data support both modes of vSMC/PC development and lead to a model in which PDGFR-beta-positive vSMC/PC progenitors initially form around certain vessels by PDGF-B-independent induction. Subsequent angiogenic sprouting and vessel enlargement involves PDGF-B-dependent vSMC/PC progenitor co-migration and proliferation, and/or PDGF-B-independent new induction of vSMC/PC, depending on tissue context. PMID:10375497

Hellström, M; Kalén, M; Lindahl, P; Abramsson, A; Betsholtz, C

1999-06-01

249

Synergistic Action of Fibroblast Growth Factor-2 and Transforming Growth Factor-beta1 Enhances Bioprinted Human Neocartilage Formation  

PubMed Central

Bioprinting as a promising but unexplored approach for cartilage tissue engineering has the advantages of high throughput, digital control, and highly accurate placement of cells and biomaterial scaffold to the targeted 3D locations with simultaneous polymerization. This study tested feasibility of using bioprinting for cartilage engineering and examined the influence of cell density, growth and differentiation factors. Human articular chondrocytes were printed at various densities, stimulated transiently with growth factors and subsequently with chondrogenic factors. Samples were cultured for up to 4 weeks to evaluate cell proliferation and viability, mechanical properties, mass swelling ratio, water content, gene expression, ECM production, DNA content, and histology. Bioprinted samples treated with FGF-2/TGF-?1 had the best chondrogenic properties among all groups apparently due to synergistic stimulation of cell proliferation and chondrogenic phenotype. ECM production per chondrocyte in low cell density was much higher than that in high cell seeding density. This finding was also verified by mechanical testing and histology. In conclusion, cell seeding density that is feasible for bioprinting also appears optimal for human neocartilage formation when combined with appropriate growth and differentiation factors.

Cui, Xiaofeng; Breitenkamp, Kurt; Lotz, Martin; D'Lima, Darryl

2012-01-01

250

MHD Ballooning Instability in the Plasma Sheet  

SciTech Connect

Based on the ideal-MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where beta (sub)eq is greater than or equal to 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial brightening location of the breakup arc in the ionosphere. However, the MHD beq threshold is too low in comparison with observations by AMPTE/CCE at X = -(8 - 9)R(sub)E, which show that a low-frequency instability is excited only when beq increases over 50. The difficulty is mitigated by considering the kinetic effects of ion gyrorad ii and trapped electron dynamics, which can greatly increase the stabilizing effects of field line tension and thus enhance the beta(sub)eq threshold [Cheng and Lui, 1998]. The consequence is to reduce the equatorial region of the unstable ballooning modes to the strong cross-tail current sheet region where the free energy associated with the plasma pressure gradient and magnetic field curvature is maximum.

C.Z. Cheng; S. Zaharia

2003-10-20

251

W-Band Sheet Beam Klystron Design  

SciTech Connect

Sheet beam devices provide important advantages for very high power, narrow bandwidth RF sources like accelerator klystrons [1]. Reduced current density and increased surface area result in increased power capabi1ity, reduced magnetic fields for focusing and reduced cathode loading. These advantages are offset by increased complexity, beam formation and transport issues and potential for mode competition in the ovennoded cavities and drift tube. This paper will describe the design issues encountered in developing a 100 kW peak and 2 kW average power sheet beam k1ystron at W-band including beam formation, beam transport, circuit design, circuit fabrication and mode competition.

Scheitrum, G.; Caryotakis, G.; Burke, A.; Jensen, A.; Jongewaard, E.a Krasnykh, A.; Neubauer, M.; Phillips, R.; Rauenbuehler, K.; /SLAC

2011-11-11

252

Detection and analysis of agonist-induced formation of the complex of the stimulatory guanine nucleotide-binding protein with adenylate cyclase in intact wild-type and beta 2-adrenoceptor-expressing NG108-15 cells.  

PubMed Central

Neuroblastoma x glioma hybrid, NG108-15, cells appear to express the alpha-subunit of the guanine nucleotide-binding protein Gs in a substantial molar excess over its effector adenylate cyclase [Kim, Adie and Milligan (1994) Eur. J. Biochem. 219, 135-143]. Addition of the IP prostanoid receptor agonist iloprost to intact NG108-15 cells resulted in a dose-dependent increase in formation of the complex between Gs alpha and adenylate cyclase (GSAC) as measured by specific high-affinity binding of [3H]forskolin. NG108-15 cells transfected to express either relatively high (clone beta N22) or low (clone beta N17) levels of beta 2-adrenoceptor both showed dose-dependent increases in specific [3H]forskolin binding in response to the beta-adrenoceptor agonist isoprenaline, and maximally effective concentrations of isoprenaline resulted in the generation of similar numbers of GSAC complexes in both clones. The dose-effect curve for clone beta N22, however, was some 15-fold to the left of that for clone beta N17, which is similar to that noted for isoprenaline-mediated stimulation of adenylate cyclase activity [Adie and Milligan (1994) Biochem. J. 303, 803-808]. In contrast, dose-effect curves for iloprost stimulation of [3H]forskolin binding were not different in clones beta N22 and beta N17. Basal specific [3H]forskolin binding in the absence of agonist was significantly greater in cells of clone beta N22 than clone beta N17. This was not a reflection of higher immunological levels of adenylate cyclase, indicating that the higher basal formation of GSAC probably reflects empty-receptor activation of Gs. This higher basal specific [3H]forskolin binding was partially reversed by propranolol. The addition of the opioid peptide D-Ala-D-Leu-enkephalin to NG108-15 cells did not reduce iloprost-stimulated [3H]forskolin binding even though this peptide inhibits stimulated adenylate cyclase activity by activation of a delta opioid receptor. Images Figure 6

Kim, G D; Carr, I C; Milligan, G

1995-01-01

253

Healthcare Professional Sheets  

Center for Drug Evaluation (CDER)

... Healthcare Professional Sheets. As of January 29, 2010, FDA has transitioned to using one safety communication to provide ... More results from www.fda.gov/drugs/drugsafety/postmarketdrugsafetyinformationforpatientsandproviders

254

Study on the binding of Thioflavin T to ?-sheet-rich and non-?-sheet cavities  

Microsoft Academic Search

Amyloid fibril formation plays a role in more than 20 diseases including Alzheimer’s disease. In vitro detection of these fibrils is often performed using Thioflavin T (ThT), though the ThT binding mode is largely unknown. In the present study, spectral properties of ThT in binding environments representing ?-sheet-rich and non-?-sheet cavities were examined. Acetylcholinesterase and ?-cyclodextrin induced a characteristic ThT

Minna Groenning; Lars Olsen; Marco van de Weert; James M. Flink; Sven Frokjaer; Flemming S. Jørgensen

2007-01-01

255

Impact of heat flux anomalies on hydrocarbon maturity around salt diapirs and salt sheets in Gulf Coast: models and observations  

Microsoft Academic Search

The authors investigated the characteristics of conductive heat flow and the associated temperature distributions around both a highly conductive salt diapir and a salt sheet embedded in a lower conductivity host rock. For the salt sheet, temperatures in the subsalt formations are emphasized. Even relatively thin sheets can cause a significant change in the subsalt temperature; a sheet 1000 m

J. J. OBrien; I. Lerche

1988-01-01

256

Superfund fact sheet: Community interviews. Fact sheet  

SciTech Connect

The fact sheet describes the interview program used by the EPA to develop the Community Relations Plan, a program designed to keep people informed about cleanup activities at the contaminated site in their community. In the interview program, questions, concerns, and additional information are collected from people in the community to determine the community already knows and/or wants to know about the cleanup site and what will be done at the site. The fact sheet is one in a series providing reference information about Superfund issues and is intended for readers with no formal scientific training.

Not Available

1992-09-01

257

Heliospheric current sheet structure  

NASA Astrophysics Data System (ADS)

Corona expansion and heliospheric current sheet creation have been investigated by numerical solution of 3D MHD equations, using the Peresvet code. Plasma compression, dissipation, thermal conductivity, and gravitation are taken into account. The dipole magnetic field corresponding to the solar activity minimum, and typical corona parameters are used as initial conditions. It is shown, that some critical value of the coronal plasma pressure should be achieved for stationary solar wind creation. At radial expansion of the solar corona polarization does not appear. As a result, E=0 in the sheet, and the current density becomes as j = B/c. The normal magnetic field component is an important feature of the heliospheric current sheet. The sheet can not be a neutral one. Current generation is similar to action of a short closed MHD generator. The solar wind temperature is determined by plasma cooling because of plasma expansion and heat conduction from the Sun. In the process of expansion the solar wind is accelerated and achieves the supersonic velocity at a distance of about 3 solar radii. The stationary plasma flow is very sensible to corona parameters. The current sheet is surrounding by a thick plasma sheet, but plasma velocity is drops inside the sheet. The plasma velocity inside the sheet prevents magnetic reconnection. Calculation without gravitation is also carried out for comparison our results with data obtained by other authors.

Podgorny, I. M.; Podgorny, A. I.

258

Quahog Fact Sheet  

NSDL National Science Digital Library

This Rhode Island Sea Grant Fact Sheet describes quahogs, a type of shellfish, and their role in commercial fishery. It includes information about quahog physical description, habitat preference, and the rise of quahog harvests in Rhode Island. The Fact Sheet concludes with a section describing how to dig up your own quahogs, shuck (open) them, and eat them.

Ely, Eleanor; Grant, Rhode I.

259

Plasma sheet boundary layer  

Microsoft Academic Search

The plasma sheet boundary layer is a temporally variable transition region located between the magnetotail lobes and the central plasma sheet. We have made a survey of these regions by using particle spectra and three-dimensional velocity-space distributions sampled by the ISEE 1 LEPEDEA. Ion composition measurements obtained by the Lockhead ion mass spectrometers indicate that ionospheric ions play a crucial

T. E. Eastman; L. A. Frank; W.K. Peterson; W. Lennartsson

1984-01-01

260

Greenland Ice Sheet  

NSDL National Science Digital Library

A study of the Greenland ice sheet has shown it is melting faster than expected. This radio broadcast describes how the ice sheet thickness is measured and how this factors into the fight over whether pollution is raising global temperatures. The broadcast from 1999 is 3 minutes and 46 seconds in length.

261

A Combination of Human alpha 1 and beta 1 Subunits is Required for Formation of Detectable GABA-Activated Chloride Channels in Sf9 Cells  

Microsoft Academic Search

The baculovirus expression system was used to produce alpha 1 and beta 1 subunits of the human GABAA receptor in Sf9 cells. In cells infected with both alpha 1 and beta 1 recombinent viruses, GABA elicited an outwardly rectifying chloride current that was blocked by bicuculline and potentiated by pentobarbitone. GABA did not produce detectable currents in cells infected with

B. Birnir; M. L. Tierney; S. M. Howitt; G. B. Cox; P. W. Gage

1992-01-01

262

A low-saturated-fat, low-cholesterol diet decreases plasma CETP activity and pre beta-HDL formation but does not affect cellular cholesterol efflux to plasma from type 1 diabetic patients.  

PubMed

The aim of this study was to evaluate the effect of a low-saturated-fat, low-cholesterol diet on plasma lipopoproteins, pre beta-high density lipoprotein (HDL) formation, lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) activities, as well as on the ability of plasma to stimulate cellular cholesterol efflux. Twelve male type 1 diabetic patients with plasma cholesterol >5.0 mmol/L were studied while consuming their usual diet and after 6 weeks of a low-fat, low-cholesterol diet. Pre beta-HDL formation was measured using crossed immuno-electrophoresis. Plasma LCAT, CETP and PLTP activities were assayed by exogenous substrate methods. The ability of plasma to promote cellular cholesterol efflux out of Fu5AH rat hepatoma cells and out of human skin fibroblasts was also determined. Saturated fat intake was lowered (p = 0.001) due to replacement with carbohydrates, while mono- and polyunsaturated fat intake remained unchanged. Cholesterol intake decreased as well (p = 0.003). The changes in plasma total cholesterol, very low and low-density lipoprotein (VLDL+LDL) cholesterol, HDL cholesterol, HDL phospholipids, apolipoprotein (apo) A-I, plasma LCAT activity and PLTP activity were not significant. Plasma CETP activity (p = 0.008) and pre beta-HDL formation (p = 0.008) decreased. The ability of plasma to promote cholesterol efflux out of fibroblasts and Fu5AH cells remained unchanged. Reduction in dietary saturated fat and cholesterol intake does not adversely affect cellular cholesterol efflux to plasma from type 1 diabetic patients, despite a drop in pre beta-HDL formation. PMID:16319046

De Vries, R; Beusekamp, B J; Kerstens, M N; Groen, A K; Van Tol, A; Dullaart, R P F

2005-01-01

263

An unusual feature revealed by the crystal structure at 2.2 A resolution of human transforming growth factor-beta 2.  

PubMed

Transforming growth factor type beta 2 (TGF-beta 2) is a member of an expanding family of growth factors that regulate proliferation and differentiation of many different cell types. TGF-beta 2 binds to various receptors, one of which was shown to be a serine/threonine kinase. TGF-beta 2 is involved in wound healing, bone formation and modulation of immune functions. We report here the crystal structure of TGF-beta 2 at 2.2 A resolution, which reveals a novel monomer fold and dimer association. The monomer consists of two antiparallel pairs of beta-strands forming a flat curved surface and a separate, long alpha-helix. The disulphide-rich core has one disulphide bone pointing through a ring formed by the sequence motifs Cys-Ala-Gly-Ala-Cys and Cys-Lys-Cys, which are themselves connected through the cysteines. Two monomers are connected through a single disulphide bridge and associate such that the helix of one subunit interacts with the concave beta-sheet surface of the other. Four exposed loop regions might determine receptor specificity. The structure provides a suitable model for the TGF-beta s and other members of the super-family and is the basis for the analysis of the TGF-beta 2 interactions with the receptor. PMID:1641027

Schlunegger, M P; Grütter, M G

1992-07-30

264

Locating Current Sheets in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection. Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even topological properties of a force-free coronal magnetic field. First, there are separatrices related to magnetic nulls. Through separatrices the magnetic connectivity changes discontinuously. Coronal magnetic nulls are, however, very rare. Second, inspired by the concept of generalized magnetic reconnection without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the magnetic connectivity changes continuously, though strongly. The strength of the connectivity change can be quantified by measuring the squashing of the flux tubes which connect the magnetically conjugated photospheres. We verify the QSL and separatrix concepts by comparing the sites of magnetic nulls and enhanced squashing with the location of current concentrations in the corona. Due to the known difficulties of their direct observation, we simulated coronal current sheets by numerically calculating the response of the corona to energy input from the photosphere, heating a simultaneously observed Extreme Ultraviolet Bright Point. We did not find coronal current sheets at separatrices but at several QSL locations. The reason is that, although the geometrical properties of force-free extrapolated magnetic fields can indeed hint at possible current concentrations, a necessary condition for current sheet formation is the local energy input into the corona.

Büchner, J.

2006-02-01

265

Beta Thalassemia  

MedlinePLUS

... South Asian (Indian, Pakistani, etc.), Southeast Asian and Chinese descent. ß Normal beta globin genes found on chromosomes 11 ß ..then there is a 25% chance with each pregnancy that their child will inherit two abnormal beta ...

266

Support vector machines for prediction and analysis of beta and gamma-turns in proteins.  

PubMed

Tight turns have long been recognized as one of the three important features of proteins, together with alpha-helix and beta-sheet. Tight turns play an important role in globular proteins from both the structural and functional points of view. More than 90% tight turns are beta-turns and most of the rest are gamma-turns. Analysis and prediction of beta-turns and gamma-turns is very useful for design of new molecules such as drugs, pesticides, and antigens. In this paper we investigated two aspects of applying support vector machine (SVM), a promising machine learning method for bioinformatics, to prediction and analysis of beta-turns and gamma-turns. First, we developed two SVM-based methods, called BTSVM and GTSVM, which predict beta-turns and gamma-turns in a protein from its sequence. When compared with other methods, BTSVM has a superior performance and GTSVM is competitive. Second, we used SVMs with a linear kernel to estimate the support of amino acids for the formation of beta-turns and gamma-turns depending on their position in a protein. Our analysis results are more comprehensive and easier to use than the previous results in designing turns in proteins. PMID:15852509

Pham, Tho Hoan; Satou, Kenji; Ho, Tu Bao

2005-04-01

267

Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum.  

PubMed

The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets. PMID:22144623

Weber, Michael E; Clark, Peter U; Ricken, Werner; Mitrovica, Jerry X; Hostetler, Steven W; Kuhn, Gerhard

2011-12-01

268

Interhemispheric ice-sheet synchronicity during the last glacial maximum  

USGS Publications Warehouse

The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets.

Weber, Michael E.; Clark, Peter U.; Ricken, Werner; Mitrovica, Jerry X.; Hostetler, Steven W.; Kuhn, Gerhard

2011-01-01

269

Statistical study of thin current sheet evolution around substorm onset  

NASA Astrophysics Data System (ADS)

The spatial distribution of current sheet thinning in the substorm growth phase is examined statistically using Geotail data. The current density is calculated from the ion and electron velocity moments. It is found that the current sheet becomes thin before the onset mainly on the Earthward side of the initial near-Earth neutral line (NENL) position and becomes less than 0.5 RE on average. However, on the tailward side of the NENL position, the current sheet becomes thin only after the onset. This result implies that the NENL forms at or near the tailward edge of the thin current sheet. An intense current sheet is formed in the center of the plasma sheet on average, but the largest current density is temporarily observed in the off-neutral sheet region, indicating the formation of a double-peaked current sheet. The current carriers becomes mainly electrons in the thin current sheet under the existence of the ambipolar electric field directed toward the neutral sheet.

Asano, Y.; Mukai, T.; Hoshino, M.; Saito, Y.; Hayakawa, H.; Nagai, T.

2004-05-01

270

Development of a macroscopic shear during sheet forming of an Al-Mg alloy  

Microsoft Academic Search

Strain localization during sheet forming leads to the formation of a trough of rapidly thinning material or local neck. Metal flow during the onset of necking is usually envisaged as nonuniform over the scale of the sheet, but microscopically homogeneous. Experimental observations made during flow of 5182-0 aluminum sheet do not support this assumption. Slip offsets seen during plane strain

K. E. Newman; J. E. Bird

2008-01-01

271

Properties of gluten-based sheet produced by twin-screw extruder  

Microsoft Academic Search

Wheat gluten sheet plasticized with glycerol was successfully produced using a twin-screw extruder and the formation of the translucent sheet was found to occur when temperature of the melt was around 137°C. Water sorption, thermal, mechanical and gas permeability properties of the extruded gluten sheet were studied at various relative humidities. The water sorption isotherms obtained were typical for a

Agnes Hochstetter; Riku A. Talja; Harry J. Helén; Lea Hyvönen; Kirsi Jouppila

2006-01-01

272

Modeling ice sheet permafrost interaction around the southern Laurentide Ice Sheet  

NASA Astrophysics Data System (ADS)

The existence of permanently frozen ground has a major influence on the dynamics of an advancing ice sheet and the formation of landforms. Cooling early in a glacial cycle produced extensive permafrost. The insulation effect of the ice sheet after advancing over areas of permafrost led to a slow degradation of permafrost under the ice. Finally, warming after the LGM casued the disappearence of subglacial premafrost. Subglacial permafrost affects directly the evolution of basal temperature and subglacial hydrology, both critical conditions for formation of landforms and fast flow instabilities. Surge-type flow instabilities may account for the relatively thin ice lobes, the dominant features around the southern margin of the Laurentide Ice Sheet (LIS). Numerical experiments of the last glacial cycle of the southern LIS were performed with a permafrost model of the earth's crust coupled with the three-dimensional thermomechanical UBC ice sheet model. This ice sheet model contains thickness evolution, ice flow, temperature evolution, and isostasy. The permafrost growth and decay is modeled solving the heat-transport equation for a mixture of sediment and bedrock with varying water and ice content. The transient permafrost condition beneath and peripheral to the ice sheet was analyzed for the last glacial maximum and the transition period to present climate.

Bauder, A.; Mickelson, D. M.; Marshall, S. J.

2003-04-01

273

The formation mechanism of a textured ceramic of thermoelectric [Ca2CoO3](0.62)[CoO2] on beta-Co(OH)2 templates through in situ topotactic conversion.  

PubMed

We investigated the formation mechanism of thermoelectric [Ca(2)CoO(3)](0.62)[CoO(2)] (CCO) on beta-Co(OH)(2) templates with maintained orientations by identifying the intermediate phases and specifying the relationship between their crystallographic orientations. We mixed beta-Co(OH)(2) templates with the complementary reactant CaCO(3) and prepared a compact by tape casting, with the developed (001) plane of the templates aligned along the casting plane. High-temperature XRD of the compact revealed that beta-Co(OH)(2) decomposed into Co(3)O(4) by 873 K, and Co(3)O(4) reacted with CaO to form CCO by 1193 K via the formation of the newly detected intermediate phase beta-Na(x)()CoO(2)-type Ca(x)()CoO(2) at 913-973 K. Pole figure measurements and SEM and TEM observations revealed that the relationship between the crystallographic planes was (001) beta-Co(OH)(2)//{111} Co(3)O(4)//(001) Ca(x)()CoO(2)//(001) CCO. The crystal structures of the four materials possess the common CoO(2) layer (or similar), which is composed of edge-sharing CoO(6) octahedra, parallel to the planes. The cross-sectional HRTEM analysis of an incompletely reacted specimen showed transient lattice images from Ca(x)()CoO(2) into CCO, in which every other CoO(2) layer of Ca(x)()CoO(2) was preserved. Thus, it was demonstrated that a textured CCO ceramic is produced through a series of in situ topotactic conversion reactions with a preserved CoO(2) layer of its template. PMID:15853344

Itahara, Hiroshi; Seo, Won-Seon; Lee, Sujeong; Nozaki, Hiroshi; Tani, Toshihiko; Koumoto, Kunihito

2005-05-01

274

Pesticide Fact Sheet: Flufenacet.  

National Technical Information Service (NTIS)

This document contains up-to-date chemical information, including a summary of the Agency's regulatory position and rationale, on a specific pesticide or group of pesticides. A Fact Sheet is issued after registration of a new chemical.

1998-01-01

275

Failure in Sheet Forming.  

National Technical Information Service (NTIS)

The role of inclusions in sheet steel for forming applications has received little serious consideration, it being generally considered that formability is limited by plastic instability. Several writers have explicitly rejected the notion that steel clea...

I. L. Dillamore R. A. Maynard

1975-01-01

276

Pesticide Fact Sheet: Azoxystrobin.  

National Technical Information Service (NTIS)

The document contains up-to-date chemical information, including a summary of the Agency's regulatory position and rationale, on a specific pesticide or group of pesticides. A Fact Sheet is issued after registration of a new chemical.

1997-01-01

277

Global ice sheet modeling  

SciTech Connect

The University of Maine conducted this study for Pacific Northwest Laboratory (PNL) as part of a global climate modeling task for site characterization of the potential nuclear waste respository site at Yucca Mountain, NV. The purpose of the study was to develop a global ice sheet dynamics model that will forecast the three-dimensional configuration of global ice sheets for specific climate change scenarios. The objective of the third (final) year of the work was to produce ice sheet data for glaciation scenarios covering the next 100,000 years. This was accomplished using both the map-plane and flowband solutions of our time-dependent, finite-element gridpoint model. The theory and equations used to develop the ice sheet models are presented. Three future scenarios were simulated by the model and results are discussed.

Hughes, T.J.; Fastook, J.L. [Univ. of Maine, Orono, ME (United States). Institute for Quaternary Studies

1994-05-01

278

Avian Fact Sheet  

SciTech Connect

OAK-B135 After conducting four national research meetings, producing a document guiding research: Metrics and Methods for Determining or Monitoring Potential Impacts on Birds at Existing and Proposed Wind Energy Sites, 1999, and another paper, Avian Collisions with Wind Turbines: A Summary of Existing Studies and Comparisons to Other Sources of Avian Collision Mortality in the United States, 2001, the subcommittee recognized a need to summarize in a short fact sheet what is known about avian-wind interaction and what questions remain. This fact sheet attempts to summarize in lay terms the result of extensive discussion about avian-wind interaction on land. This fact sheet does not address research conducted on offshore development. This fact sheet is not intended as a conclusion on the subject; rather, it is a summary as of Fall/Winter 2002.

NWCC Wildlife Work Group

2004-12-01

279

Pesticide Fact Sheet: Kaolin.  

National Technical Information Service (NTIS)

This document contains up-to-date chemical information, including a summary of the Agency's regulatory position and rationale, on a specific pesticide or group of pesticides. A Fact Sheet is issued after registration of a new chemical.

1998-01-01

280

Pesticide Fact Sheet: Cinnamaldehyde.  

National Technical Information Service (NTIS)

This document contains up-to-date chemical information, including a summary of the Agency's regulatory position and rationale, on a specific pesticide or group of pesticides. A Fact Sheet is issued after Registration of a significantly changed use pattern...

1995-01-01

281

Structural Studies of Copper(I) Complexes of Amyloid-Beta Peptide Fragments: Formation of Two-Coordinate Bis(Histidine) Complexes  

SciTech Connect

The beta bind: Copper(I) binds to amyloid {beta}-peptide fragments (see structure) as a stable bis(histidine), two-coordinate, near-linear complex, even in the presence of potential additional ligands. As has been proposed or assumed in other studies, the copper(I)-peptide complexes react with dioxygen to form the reactive oxygen species H{sub 2}O{sub 2}, without the need for a third histidine ligand to promote the chemistry.

Himes, R.A.; Park, G.Young.; Siluvai, G.Sutha.; Blackburn, N.J.; Karlin, K.D.

2009-05-18

282

Energy information sheets  

SciTech Connect

The National Energy Information Center (NEIC), as part of its mission, provides energy information and referral assistance to Federal, State, and local governments, the academic community, business and industrial organizations, and the public. The Energy Information Sheets was developed to provide general information on various aspects of fuel production, prices, consumption, and capability. Additional information on related subject matter can be found in other Energy Information Administration (EIA) publications as referenced at the end of each sheet.

NONE

1995-07-01

283

In-situ Pb isotope analysis of Fe-Ni-Cu sulphides by laser ablation multi-collector ICPMS: New insights into ore formation in the Sudbury impact melt sheet  

NASA Astrophysics Data System (ADS)

Laser-ablation (LA) multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) is ideally suited to in situ determination of isotope ratios in sulphide minerals. Using samples of magmatic sulphide ore from the Sudbury impact structure, we test LA-MC-ICPMS analytical protocols that aim to meet a range of analytical challenges in the analysis of Pb isotopes. These include: potential matrix sensitive isotopic fractionation; interferences on Pb isotopes; low melting points of many sulphide minerals; the availability of standards. Magmatic sulphides of wide ranging mineralogy (pyrrhotite, pentlandite, chalcopyrite, pyrite and sphalerite) were analysed for Pb isotopic composition, using the silicate glass NIST SRM 610 as an external standard to correct for instrumental mass-fractionation. Despite matrix sensitive melting and re-deposition around ablation pits, several lines of evidence indicate that all analyses are accurate, within typical analytical uncertainties of 0.003-2% (2?), and that the defined approach is insensitive to compositional diversity in sample matrix: (a) laser ablation and dissolution based measurements of sulphide powders are in agreement; (b) analyses from each sample define isochron ages within uncertainty of the known crystallization age (1850 Ma); (c) the results of sulphide measurements by laser ablation are consistent with age-corrected feldspar analyses from the same samples. The results have important implications for ore formation in Sudbury. The Pb isotope data regressions are consistent with age corrected feldspar analyses from each respective sample, which together with time integrated Th/U ratios that match whole rock values (3.1, 4.0 and 6.1 for the Worthington, Copper Cliff and Parkin Offset Dykes, respectively) indicate chemical equilibrium between the silicate and sulphide systems during ore formation. The sulphides within each respective sample have indistinguishable model initial Pb isotope ratios (207Pb/204Pbm), irrespective of mineralogy or texture, indicating a common origin for ores within each of three different Offset Dykes. Furthermore, variations between Offset Dykes (e.g., 207Pb/204Pbm = 15.514 ± 0.012, 15.399 ± 0.009 and 15.275 ± 0.003) show that the ores have differing crustal sources on previously unrecognized scales. Mass balance considerations, particularly for MgO, Ni and Cu, indicate that the spatial distribution of mafic target rocks played a significant role in controlling the mineralization potential in different parts of the melt sheet.

Darling, J. R.; Storey, C. D.; Hawkesworth, C. J.; Lightfoot, P. C.

2012-12-01

284

Thin Sheet Formation in Viscous Splash  

Microsoft Academic Search

Ambient air is crucial for creating a splash on smooth dry surfaces for both viscous and inviscid liquids.footnotetextL. Xu, Phys. Rev. E 75, 056316 (2007); L. Xu et al., Phys. Rev. Lett. 94, 184505 (2005). In a viscous splash, the drop initially spreads in the form of a thick lamella until tejt at which time it emits a thin fluid

Michelle Driscoll; Sidney Nagel

2009-01-01

285

Nuclear Data Sheets for A = 193  

SciTech Connect

The present revision of the properties for the nuclides belonging to the A = 193 mass chain contains many improvements, corrections and additions to the material presented in previous evaluations (1998Ar07, Nucl. Data Sheets 83, 921 (1998); 1990Sh30, Nucl, Data Sheets 61, 519 (1990)). Among these are measurement results for quadrupole moments, angular distribution coefficients, half-lives and g-factors, for both previously known and new transitions and levels. In addition, major changes to the previously known status of this mass chain consist in the inclusion of data for new superdeformed bands in {sup 193}Pb, and the creation of level schemes for {sup 193}Bi, {sup 193}Po and {sup 193}At. The latter were previously unavailable, except for a very limited attempt in the case of {sup 193}Po, which was not confirmed in later work. Furthermore, the {sup 193}Os beta decay was re-evaluated in order to account for new absolute intensity measurements.

Achterberg, E. [Laboratorio TANDAR, Departamento de Fisica, Comision Nacional de Energia Atomica, Buenos Aires (Argentina); Capurro, O.A. [Laboratorio TANDAR, Departamento de Fisica, Comision Nacional de Energia Atomica, Buenos Aires (Argentina); Marti, G.V. [Laboratorio TANDAR, Departamento de Fisica, Comision Nacional de Energia Atomica, Buenos Aires (Argentina); Vanin, V.R. [Lab. do Acelerador Linear, Universidade de San Paulo, Sao Paulo, SP (Brazil); Castro, R.M. [Lab. do Acelerador Linear, Universidade de San Paulo, Sao Paulo, SP (Brazil); Instituto de Estudos Avancados - IEAv, Centro Tecnico Aerospacial - CTA, Sao Jose dos Campos, SP (Brazil)

2006-01-15

286

The storm time central plasma sheet  

NASA Astrophysics Data System (ADS)

The plasma sheet plays a key role during magnetic storms because it is the bottleneck through which large amounts of magnetic flux that have been eroded from the dayside magnetopause have to be returned to the dayside magnetosphere. Using about five years of Geotail data we studied the average properties of the near- and midtail central plasma sheet (CPS) in the 10 30 RE range during magnetic storms. The earthward flux transport rate is greatly enhanced during the storm main phase, but shows a significant earthward decrease. Hence, since the magnetic flux cannot be circulated at a sufficient rate, this leads to an average dipolarization of the central plasma sheet. An increase of the specific entropy of the CPS ion population by a factor of about two during the storm main phase provides evidence for nonadiabatic heating processes. The direction of flux transport during the main phase is consistent with the possible formation of a near-Earth neutral line beyond ~20 RE.

Schödel, R.; Dierschke, K.; Baumjohann, W.; Nakamura, R.; Mukai, T.

2002-11-01

287

Maternal antioxidants prevent beta cell apoptosis and promote formation of dual hormone-expressing endocrine cells in male offspring following fetal and neonatal nicotine exposure  

PubMed Central

Aim Fetal and neonatal nicotine exposure causes beta cell oxidative stress and apoptosis in neonates, leading to adult-onset dysglycemia. The goal of this study was to determine whether an antioxidant intervention could prevent nicotine-induced beta cell loss. Methods Nulliparous female Wistar rats received daily subcutaneous injections of either saline or nicotine bitartrate (1.0 mg/kg/d) for 2 weeks prior to mating until weaning. Nicotine-exposed dams received either normal chow or diet containing antioxidants (1000 IU/kg vitamin E, 0.25% w/w coenzyme Q10 and 0.1% w/w alpha-lipoic acid) during mating, pregnancy and lactation; saline-exposed dams received normal chow. Pancreas tissue was collected from male offspring at 3 weeks of age to measure beta cell fraction, apoptosis, proliferation and the presence of cells co-expressing insulin and glucagon. Results The birth weight of the offspring born to nicotine-exposed dams receiving dietary antioxidants was significantly reduced. Most interestingly, the antioxidant intervention to nicotine-exposed dams prevented the beta cell loss and apoptosis observed in nicotine exposed male offspring whose mothers did not receive antioxidants. Male pups born to nicotine-treated mothers receiving antioxidants also had a trend towards increased beta cell proliferation and a significant increase in islets containing insulin/glucagon bi-hormonal cells relative to the other two treatment groups. Conclusion This study demonstrates that exposure to maternal antioxidants protects beta cells from the damaging effects of nicotine thus preserving beta cell mass.

BRUIN, Jennifer E; WOYNILLOWICZ, Amanda K; HETTINGA, Bart P; TARNOPOLSKY, Mark A; MORRISON, Katherine M; GERSTEIN, Hertzel C; HOLLOWAY, Alison C

2013-01-01

288

Cyclic Modular ?-Sheets  

PubMed Central

The development of peptide ?-hairpins is problematic, because folding depends on the amino acid sequence and changes to the sequence can significantly decrease folding. Robust ?-hairpins that can tolerate such changes are attractive tools for studying interactions involving protein ?-sheets and developing inhibitors of these interactions. This paper introduces a new class of peptide models of protein ?-sheets that addresses the problem of separating folding from sequence. These model ?-sheets are macrocyclic peptides that fold in water to present a pentapeptide ?-strand along one edge; the other edge contains the tripeptide ?-strand mimic Hao [JACS 2000, 122, 7654] and two additional amino acids. The pentapeptide and Hao-containing peptide strands are connected by two ?-linked ornithine (?Orn) turns [JACS 2003, 125, 876]. Each ?Orn turn contains a free ?-amino group that permits the linking of individual modules to form divalent ?-sheets. These “cyclic modular ?-sheets” are synthesized by standard solid-phase peptide synthesis of a linear precursor followed by solution-phase cyclization. Eight cyclic modular ?-sheets 1a–1h containing sequences based on ?-amyloid and macrophage inflammatory protein 2 were synthesized and characterized by 1H NMR. Linked cyclic modular ?-sheet 2, which contains two modules of 1b, was also synthesized and characterized. 1H NMR studies show downfield ?-proton chemical shifts, ?Orn ?-proton magnetic anisotropy, and NOE crosspeaks that establish all compounds but 1c and 1g to be moderately or well folded into a conformation that resembles a ?-sheet. Pulsed-field gradient NMR diffusion experiments show little or no self-association at low (? 2 mM) concentrations. Changes to the residues in the Hao-containing strands of 1c and 1g improve folding and show that folding of the structures can be enhanced without altering the sequence of the pentapeptide strand. Well-folded cyclic modular ?-sheets 1a, 1b, and 1f each have a phenylalanine directly across from Hao, suggesting that cyclic modular ?-sheets containing aromatic residues across from Hao are better folded.

Woods, R. Jeremy; Brower, Justin O.; Castellanos, Elena; Hashemzadeh, Mehrnoosh; Khakshoor, Omid; Russu, Wade A.

2008-01-01

289

Effects of oat bran, processed to different molecular weights of beta-glucan, on plasma lipids and caecal formation of SCFA in mice.  

PubMed

In the present study, we evaluated the cholesterol-lowering effects of different oat bran (OB) preparations, differing regarding their peak molecular weight (MWp) of beta-glucans (2348, 1311, 241, 56, 21 or < 10 kDa), in C57BL/6NCrl mice. The diets were designed to be atherogenic (0.8 % cholesterol and 0.1 % cholic acid), and they reflected the Western diet pattern (41 % energy fat). All OB preparations that were investigated significantly reduced plasma cholesterol when compared with a cellulose-containing control diet, regardless of the molecular weight of beta-glucan. Moreover, the difference in viscous properties between the processed OB (from 0.11 to 17.7 l/g) did not appear to play a major role in the cholesterol-lowering properties. In addition, there was no correlation between the molecular weight of beta-glucan and the amount of propionic acid formed in caecum. Interestingly, however, there was a significant correlation between the ratio of (propionic acid+butyric acid)/acetic acid and the MWp of beta-glucans: the ratio increased with increasing molecular weight. The results of the present study suggest that the molecular weights and viscous properties of beta-glucan in oat products may not be crucial parameters for their cholesterol-lowering effects. PMID:20334710

Immerstrand, Tina; Andersson, Kristina E; Wange, Caroline; Rascon, Ana; Hellstrand, Per; Nyman, Margareta; Cui, Steve W; Bergenståhl, Björn; Trägårdh, Christian; Oste, Rickard

2010-03-25

290

Interhemispheric Ice-Sheet Synchronicity During the Last Glacial Maximum  

NASA Astrophysics Data System (ADS)

The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood because only a few findings with robust chronologies exist for Antarctic ice sheets. We developed a chronology for the Weddell Sea sector of the East Antarctic ice sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates the advance to and retreat from their maximum extent was nearly synchronous with Northern Hemisphere ice sheets. As for the deglaciation, modeling studies suggest a late ice-sheet retreat starting around 14 ka BP and ending around 7 ka BP with a large impact of an unstable West Antarctic Ice Sheet (WAIS) and a small impact of a stable East Antarctic Ice Sheet (EAIS). However, the Weddell Sea sites studied here, as well as sites from the Scotia Sea, provide evidence that specifically the EAIS responded much earlier, possibly provided a significant contribution to the last sea-level rise, and was much more dynamic than previously thought. Deep-sea sediment sites from the central Scotia Sea "iceberg alley" show four phases of enhanced deposition of ice-rated detritus (IRD) occurred at 19.5, 16.5,14.5, and 12 ka. The first two relate to the two ice-sheet retreat signals documented for the Weddell Sea; the third phase indicates an Antarctic component to meltwater pulse 1a; the fourth phase falls roughly into period of the Younger Dryas. Our modeling studies show that surface climate forcing of Antarctic ice sheets would have likely increased ice mass balance during deglaciation, whereby a warming climate would increase accumulation but not surface melting. We propose that sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deepwater formation and attendant heat flux to Antarctic grounding lines provided the teleconnections to synchronize the hemispheric ice sheets.

Weber, M. E.; Clark, P. U.; Kuhn, G.; Ricken, W.; Sprenk, D.

2011-12-01

291

Fiber formation of a synthetic spider peptide derived from Nephila clavata.  

PubMed

Dragline silk is a high-performance biopolymer with exceptional mechanical properties. Artificial spider dragline silk is currently prepared by a recombinant technique or chemical synthesis. However, the recombinant process is costly and large-sized synthetic peptides are needed for fiber formation. In addition, the silk fibers that are produced are much weaker than a fiber derived from a native spider. In this study, a small peptide was chemically synthesized and examined for its ability to participate in fiber formation. A short synthetic peptide derived from Nephila clavata was prepared by a solid-phase peptide method, based on a prediction using the hydrophobic parameter of each individual amino acid residue. After purification of the spider peptide, fiber formation was examined under several conditions. Fiber formation proceeded in the acidic pH range, and larger fibers were produced when organic solvents such as trifluoroethanol and acetonitrile were used at an acidic pH. Circular dichroism measurements of the spider peptide indicate that the peptide has a beta-sheet structure and that the formation of a beta-sheet structure is required for the spider peptide to undergo fiber formation. PMID:20564008

Hidaka, Yuji; Kontani, Ko-Ichi; Taniguchi, Rina; Saiki, Masatoshi; Yokoi, Sayoko; Yukuhiro, Kenji; Yamaguchi, Hiroshi; Miyazawa, Mitsuhiro

2011-01-01

292

Nuclear data sheets for A = 192  

SciTech Connect

Experimental data for all nuclei with mass A = 192 have been evaluated. This evaluation, covering data received by August 1, 1998, supersedes the 1991 evaluation by V.S. Shirley (Nuclear Data Sheets 64, 205 (1991)). It also incorporates the evaluation of {sup 192}Ir (73.827 d) decay prepared by Edgardo Browne as part of an ongoing international collaboration engaged in the evaluation of T{sub 1/2} and radiation energy and intensity data for selected radionuclides (see comment with {sup 192}Ir (73.827 d) {epsilon} decay and {beta}{sup {minus}} decay data sets).

Baglin, C. M. [Lawrence Berkeley National Lab., CA (United States). Nuclear Science Div.

1998-08-01

293

Differences between the pressure- and temperature-induced denaturation and aggregation of beta-lactoglobulin A, B, and AB monitored by FT-IR spectroscopy and small-angle X-ray scattering.  

PubMed

We examined the temperature- and pressure-induced unfolding and aggregation of beta-lactoglobulin (beta-Lg) and its genetic variants A and B up to temperatures of 90 degrees C in the pressure range from 1 bar to 10 kbar. To achieve information simultaneously on the secondary, tertiary, and quaternary structures, we have applied Synchrotron small-angle X-ray diffraction and Fourier transform infrared spectroscopy. Upon heating a beta-Lg solution at pH 7.0, the radius of gyration Rg first decreases, indicating a partial dissociation of the dimer into the monomers, the secondary structures remaining essentially unchanged. Above 50 degrees C, the infrared spectroscopy data reveal a decrease in intramolecular beta-sheet and alpha-helical structures, whereas the contribution of disordered structures increases. Within the temperature range from 50 to 60 degrees C, the appearance of the pair distance distribution function is not altered significantly, whereas the amount of defined secondary structures declines approximately by 10%. Above 60 degrees C the aggregation process of 1% beta-Lg solutions is clearly detectable by the increase in Rg and intermolecular beta-sheet content. The irreversible aggregation is due to intermolecular S-H/S-S interchange reactions and hydrophobic interactions. Upon pressurization at room temperature, the equilibrium between monomers and dimers is also shifted and dissociation of dimers is induced. At pressures of approximately 1300 bar, the amount of beta-sheet and alpha-helical structures decreases and the content of disordered structures increases, indicating the beginning unfolding of the protein which enables aggregation. Contrary to the thermal denaturation process, intermolecular beta-sheet formation is of less importance in pressure-induced protein aggregation and gelation. The spatial extent of the resulting protein clusters is time- and concentration-dependent. The aggregation of a 1% (w/w) solution of A, B, and the mixture AB results in the formation of at least octameric units as can be deduced from the radius of gyration of about 36 A. No differences in the pressure stability of the different genetic variants of beta-Lg are detectable in our FT-IR and SAXS experiments. Even application of higher pressures (up to 10 kbar) does not result in complete unfolding of all beta-Lg variants. PMID:10350469

Panick, G; Malessa, R; Winter, R

1999-05-18

294

Identification, classification, and analysis of beta-bulges in proteins.  

PubMed Central

A beta-bulge is a region of irregularity in a beta-sheet involving two beta-strands. It usually involves two or more residues in the bulged strand opposite to a single residue on the adjacent strand. These irregularities in beta-sheets were identified and classified automatically, extending the definition of beta-bulges given by Richardson et al. (Richardson, J.S., Getzoff, E.D., & Richardson, D.C., 1978, Proc. Natl. Acad. Sci. USA 75, 2574-2578). A set of 182 protein chains (170 proteins) was used, and a total of 362 bulges were extracted. Five types of beta-bulges were found: classic, G1, wide, bent, and special. Their characteristic amino acid preferences were found for most classes of bulges. Basically, bulges occur frequently in proteins; on average there are more than two bulges per protein. In general, beta-bulges produce two main changes in the structure of a beta-sheet: (1) disrupt the normal alternation of side-chain direction; (2) accentuate the twist of the sheet, altering the direction of the surrounding strands.

Chan, A. W.; Hutchinson, E. G.; Harris, D.; Thornton, J. M.

1993-01-01

295

Peptide-directed microstructure formation of polymers in organic media.  

PubMed

Synthesis and peptide-guided self-assembly of an organo-soluble peptide-polymer conjugate, comprising a sequence-defined polypeptide and a poly(n-butyl acrylate), are described. The amino acid sequence of the peptide encodes a high tendency to adopt an antiparallel beta-sheet motif, and thus programs the formation of tapelike microstructures. Easy synthesis and controllable self-assembly is ensured by the incorporation of structure breaking switch defects into the peptide segment. This suppresses temporarily the aggregation tendency of the conjugate as shown by circular dichroism, infrared spectroscopy (FT-IR), and atomic force microscopy (AFM). A pH-controlled rearrangement in the switch segments restores the native peptide backbone, triggering the self-assembly process and leading to the formation of densely twisted tapelike microstructures as could be observed by AFM and transmission electron microscopy. The resulting helical superstructures, when deposited on a substrate, are 2.9 nm high, 10 nm wide, and up to 2.3 mum long. The helical pitch is about 37 nm, and the pitch angle is 48 degrees . The helical superstructures undergo defined entanglement to form superhelices, leading to the formation of soft, continuous organo-gels. A twisted two-dimensional core-shell tape is proposed as a structure model, in which the peptide segments form an antiparallel beta-sheet with a polymer shell. PMID:17061898

Hentschel, Jens; Börner, Hans G

2006-11-01

296

Thermal denaturation of beta-galactosidase and of two site-specific mutants.  

PubMed

The thermal denaturation of wild-type beta-galactosidase and two beta-galactosidases with substitutions at the active site was studied by kinetics, differential scanning calorimetry, electrophoresis, molecular exclusion chromatography, and circular dichroism. From the results, a model is developed for thermal denaturation of beta-galactosidase which includes the reversible dissociation of ligands, reversible formation of an inactive tetramer, irreversible dissociation of the inactive tetramer to inactive monomers, and subsequent aggregation of inactive monomers to dimers and larger aggregates. Under some conditions, partial reversibility of the activity loss could be demonstrated, and several intermediates in the thermal denaturation process were trapped by quenching and observed by electrophoresis and molecular exclusion chromatography. The ligands Mg2+ and phenylethyl thio-beta-D-galactoside increase the stability of beta-galactosidase to heat denaturation by shifting the ligand binding equilibrium according to Le Chatelier's principle, thus decreasing the concentration of the ligand-free tetramer which can proceed to subsequent steps. Circular dichroism results indicated that beta-galactosidase is dominated by beta-sheet with lower amounts of alpha-helix. Large changes in secondary structure begin to occur only after activity has been lost. Single amino acid changes at the active site can have significant effects on thermal stability of beta-galactosidases. Some of the effects result from increased thermal stability of the ligand-free enzyme itself. Other effects result from changes in ligand binding, but the magnitude of the resulting changes in stability is not related to the strength of ligand binding in a simple fashion. PMID:2125499

Edwards, R A; Jacobson, A L; Huber, R E

1990-12-11

297

Sheet Music Consortium  

NSDL National Science Digital Library

For those who love everything from Sousa to show tunes, the Sheet Music Consortium is a fabulous find. The Consortium is comprised of a number of member libraries (including UCLA) who are interested in building "an open collection of digitized sheet music." Their work has been supported by the Institute of Museum and Library Services and currently offers cross collection searching of 22 sheet music collections, with a total of 226,000 items. Visitors can click on the Virtual Collection to get started with offerings such as "Texas Cowboy Songs" and "The Titanic." The Browse feature is a great way to get a sense of the materials here. Finally, the Activity Stream provides an updated list of the most recently added items for general consumption. [KMG

2013-02-15

298

California Sheet Music Project  

NSDL National Science Digital Library

With oversight provided by Professor Mary Kay Duggan of the University of California at Berkeley, the California Sheet Music Project provides online access to some 2000 pieces of sheet music published in California between 1852 and 1900. The project was funded by the U.S. Institute of Museum and Library Services, and also contains interesting ephemera ranging from a music publisher's catalog from 1872, advertisements, and photographs. The entire database may be searched or browsed by image subject (from the frontispiece of each composition) or by the subject addressed by each piece of music. Some of the songs included in the archive deal with beggars ("Just One Penny to Buy Bread," babies ("Baby's Asleep"), and politicians ("Horace Greeley's Grand March"). Finally the site also has several musical performances of pieces from the collection for the listening pleasure of those compelled to visit this interesting tribute to the sheet music of the Golden State.

Duggan, Mary K.

299

Sheet material cutting system  

US Patent & Trademark Office Database

The sheet material cutting system includes a cutting board having a reference corner with its two edges at a right angle with respect to each other. Cutting grooves are formed in the cutting board through the top layer thereof to expose a different colored layer for groove visibility. The grooves are positioned at known distances from the reference corner. The reference corner carries stops so that, when a sheet of colored transparent material is placed against the stops, the grooves can be used to guide a knife for cutting a square piece of colored transparent material for use in color frames in stage and similar lighting systems.

Judge; Stephen J. (Pacific Grove, CA)

2001-06-05

300

Energy information sheets  

SciTech Connect

The National Energy Information Center (NEIC), as part of its mission, provides energy information and referral assistance to Federal, State, and local governments, the academic community, business and industrial organizations, and the general public. Written for the general public, the EIA publication Energy Information Sheets was developed to provide information on various aspects of fuel production, prices, consumption and capability. The information contained herein pertains to energy data as of December 1991. Additional information on related subject matter can be found in other EIA publications as referenced at the end of each sheet.

Not Available

1993-12-02

301

71. PALMDALE WATER COMPANY, EASTWOOD MULTIPLEARCHED DAM: STRESS SHEET, SHEET ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

71. PALMDALE WATER COMPANY, EASTWOOD MULTIPLE-ARCHED DAM: STRESS SHEET, SHEET 3; DECEMBER 20, 1918. Littlerock Water District files. - Little Rock Creek Dam, Little Rock Creek, Littlerock, Los Angeles County, CA

302

Formation of fast shocks by magnetic reconnection in the solar corona  

SciTech Connect

Reconnections of magnetic fields over the solar surface are expected to generate abundant magnetohydrodynamic (MHD) discontinuities and shocks, including slow shocks and rotational discontinuities. However, the generation of fast shocks by magnetic reconnection process is relatively not well studied. In this paper, magnetic reconnection in a current sheet is studied based on two-dimensional resistive MHD numerical simulations. Magnetic reconnections in the current sheet lead to the formation of plasma jets and plasma bulges. It is further found that the plasma bulges, the leading part of plasma jets, in turn lead to the generation of fast shocks on flanks of the bulges. The simulation results show that during the magnetic reconnection process, the plasma forms a series of structures: plasma jets, plasma bulges, and fast shocks. As time increases, the bulges spread out along the current sheet ({+-}z direction) and the fast shocks move just ahead of the bulges. The effects of initial parameters {rho}{sub s}/{rho}{sub m}, {beta}{sub {infinity}}, and t{sub rec} on the fast shock generation are also examined, where {rho}{sub s}/{rho}{sub m} is the ratio of plasma densities on two sides of the initial current sheet, {beta}{sub {infinity}}=P{sub {infinity}}/(B{sub {infinity}}{sup 2}/2{mu}{sub 0}), P{sub {infinity}} is the plasma pressure and B{sub {infinity}} is the magnetic field magnitude far from the current sheet, and t{sub rec} is the reconnection duration. In the asymmetric case with {rho}{sub s}/{rho}{sub m}=2, {beta}{sub {infinity}}=0.01 and t{sub rec}=1000, the maximum Alfven Mach number of fast shocks (M{sub A1max}) is M{sub A1max} congruent with 1.1, where M{sub A1}=V{sub n1}/V{sub A1}, and V{sub n1} and V{sub A1} are, respectively, the normal upstream fluid velocity and the upstream Alfven speed in the fast shocks frame. As the density ratio {rho}{sub s}/{rho}{sub m} (=1-8) and plasma beta {beta}{sub {infinity}} (=0.0001-1) increase, M{sub A1max} varies slightly. For the case with a large plasma beta {beta}{sub {infinity}} (=5), the fast shock is very weak. As the reconnection duration t{sub rec} increases, the bulges lead to generation of fast shocks with a higher M{sub A1max}. The present results can be applied to the mechanism of coronal heating by fast shocks.

Hsieh, M. H. [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Tsai, C. L. [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Earth Dynamic System Research Center, National Cheng Kung University, Tainan 701, Taiwan (China); Ma, Z. W. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Lee, L. C. [Institute of Space Science, National Central University, Jhongli 320, Taiwan (China)

2009-09-15

303

Wrinkling of a Stretched Thin Sheet  

Microsoft Academic Search

When a thin rectangular sheet is clamped along two opposing edges and stretched, its inability to accommodate the Poisson\\u000a contraction near the clamps may lead to the formation of wrinkles with crests and troughs parallel to the axis of stretch.\\u000a A variational model for this phenomenon is proposed. The relevant energy functional includes bending and membranal contributions,\\u000a the latter depending

Eric Puntel; Luca Deseri; Eliot Fried

2011-01-01

304

Polio - Fact Sheet for Parents  

MedlinePLUS

... Preventable Diseases Polio Vaccination Polio - Fact Sheet for Parents Diseases and the Vaccines that Prevent Them Español: ... FAQs Vaccines website for parents Fact Sheets for Parents Diseases and the Vaccines that Prevent Them Chickenpox ...

305

A three-dimensional kinetic-fluid numerical code to study the equilibrium structure of the magnetotail: The role of electrons in the formation of the bifurcated current sheet  

Microsoft Academic Search

In this work we present a new stationary three-dimensional kinetic-fluid code with ions represented by particles and electrons by a massless fluid. The magnetotail current sheet is modeled as a magnetic field reversal with a normal magnetic field component B n . A cross tail electric field E y is included. An ion test particle simulation is performed in these

A. Greco; R. De Bartolo; G. Zimbardo; P. Veltri

2007-01-01

306

Heliospheric current sheet structure  

Microsoft Academic Search

Corona expansion and heliospheric current sheet creation have been investigated by numerical solution of 3D MHD equations, using the Peresvet code. Plasma compression, dissipation, thermal conductivity, and gravitation are taken into account. The dipole magnetic field corresponding to the solar activity minimum, and typical corona parameters are used as initial conditions. It is shown, that some critical value of the

I. M. Podgorny; A. I. Podgorny

2004-01-01

307

GED Testing Fact Sheet  

ERIC Educational Resources Information Center

This GED Testing fact sheet provides information on: (1) GED[R] Tests; (2) Versions and Editions of the GED Tests; (3) Earning a Credential; (4) GED Testing Service[R]; (5) History of the GED Tests; (6) Who Accepts the GED Credential; (7) Public/Private Partnership of GEDTS; (8) Renowned GED Credential Recipients; (9) GED Testing Numbers for 2008;…

GED Testing Service, 2009

2009-01-01

308

Characteristics of liquid sheets formed by splash plate nozzles  

NASA Astrophysics Data System (ADS)

An experimental study was conducted to identify the effect of viscosity on the characteristics of liquid sheets formed by a splash plate nozzle. Various mixtures of corn syrup and water are used to obtain viscosities in the range 1-170 mPa.s. Four different splash plates with nozzle diameters of 0.5, 0.75, 1, and 2 mm, with a constant plate angle of 55° were tested. Liquid sheets formed under various operating conditions were directly visualized. The sheet atomization process for the range of parameters studied here is governed by two different mechanisms: Rayleigh-Plateau (R-P) and Rayleigh-Taylor (R-T) instabilities. R-P occurs at the rim and R-T occurs on the thin sheet. The rim instability can be laminar or turbulent, depending on the jet Reynolds number. The R-T instability of the sheet is observed at the outer edges of the radially spreading sheet, where the sheet is the thinnest. It can also occur inside the sheet, due to formation of holes and ruptures.

Ahmed, M.; Amighi, A.; Ashgriz, N.; Tran, H. N.

2008-01-01

309

In-situ time-of-flight neutron diffraction of ErD2 (beta phase) formation during D2 loading.  

SciTech Connect

In an effort to better understand the structural changes occurring during hydrogen loading of erbium target materials, we have performed D{sub 2} loading of erbium metal (powder) with simultaneous neutron diffraction analysis. This experiment tracked the conversion of Er metal to the {alpha} erbium deuteride (solid-solution) phase and then on to the {beta} (fluorite) phase. Complete conversion to ErD{sub 2.0} was accomplished at 10 Torr D{sub 2} pressure with deuterium fully occupying the tetrahedral sites in the fluorite lattice. Increased D{sub 2} pressure (up to 500 Torr at 450 C) revealed {approx}10 % deuterium occupation of the octahedral sites. Subsequent vacuum pumping of the sample at 450 C removed octahedral site occupancy while maintaining tetrahedral deuterium occupancy, thereby yielding stoichiometric ErD{sub 2.0} {beta} phase.

Browning, James Frederick (Oak Ridge National Laboratory, Oak Ridge, TN); Llobet, Anna (Los Alamos National Laboratory, Los Alamos, NM); Snow, Clark Sheldon; Rodriguez, Mark Andrew; Wixom, Ryan R.

2008-06-01

310

Minimalist design of water-soluble cross-[beta] architecture  

SciTech Connect

Demonstrated successes of protein design and engineering suggest significant potential to produce diverse protein architectures and assemblies beyond those found in nature. Here, we describe a new class of synthetic protein architecture through the successful design and atomic structures of water-soluble cross-{beta} proteins. The cross-{beta} motif is formed from the lamination of successive {beta}-sheet layers, and it is abundantly observed in the core of insoluble amyloid fibrils associated with protein-misfolding diseases. Despite its prominence, cross-{beta} has been designed only in the context of insoluble aggregates of peptides or proteins. Cross-{beta}'s recalcitrance to protein engineering and conspicuous absence among the known atomic structures of natural proteins thus makes it a challenging target for design in a water-soluble form. Through comparative analysis of the cross-{beta} structures of fibril-forming peptides, we identified rows of hydrophobic residues ('ladders') running across {beta}-strands of each {beta}-sheet layer as a minimal component of the cross-{beta} motif. Grafting a single ladder of hydrophobic residues designed from the Alzheimer's amyloid-{beta} peptide onto a large {beta}-sheet protein formed a dimeric protein with a cross-{beta} architecture that remained water-soluble, as revealed by solution analysis and x-ray crystal structures. These results demonstrate that the cross-{beta} motif is a stable architecture in water-soluble polypeptides and can be readily designed. Our results provide a new route for accessing the cross-{beta} structure and expanding the scope of protein design.

Biancalana, Matthew; Makabe, Koki; Koide, Shohei (UC)

2010-08-13

311

The Physics of Ice Sheets  

ERIC Educational Resources Information Center

|The great ice sheets in Antarctica and Greenland are vast deposits of frozen freshwater that contain enough to raise sea level by approximately 70 m if they were to completely melt. Because of the potentially catastrophic impact that ice sheets can have, it is important that we understand how ice sheets have responded to past climate changes and…

Bassis, J. N.

2008-01-01

312

Atomization of undulating liquid sheets  

Microsoft Academic Search

The fragmentation of a laminar undulating liquid sheet flowing in quiescent air is investigated. Combining various observations and measurements we propose a sequential atomization scenario describing the overall sheet-drop transition in this configuration. The undulation results from a controlled primary Kelvin-Helmholtz instability. As the liquid travels through the undulating pattern, it experiences transient accelerations perpendicular to the sheet. These accelerations

N. Bremond; C. Clanet; E. Villermaux

2007-01-01

313

Skill Sheets for Agricultural Mechanics.  

ERIC Educational Resources Information Center

|This set of 33 skill sheets for agricultural mechanics was developed for use in high school and vocational school agricultural mechanics programs. Some sheets teach operational procedures while others are for simple projects. Each skill sheet covers a single topic and includes: (1) a diagram, (2) a step-by-step construction or operational…

Iowa State Univ. of Science and Technology, Ames. Dept. of Agricultural Education.

314

Casimir forces and graphene sheets  

Microsoft Academic Search

The Casimir force between two infinitely thin parallel sheets in a setting of N such sheets is found. The finite two-dimensional conductivities, which describe the dispersive and absorptive properties of each sheet, are taken into account, whereupon the theory is applied to interacting graphenes. By exploring similarities with in-plane optical spectra for graphite, the conductivity of graphene is modeled as

D. Drosdoff; Lilia M. Woods

2010-01-01

315

Deletion of the p110beta isoform of phosphoinositide 3-kinase in platelets reveals its central role in Akt activation and thrombus formation in vitro and in vivo.  

PubMed

During platelet activation, phosphoinositide 3-kinases (PI3Ks) produce lipid second messengers participating in the regulation of functional responses. Here, we generated a megakaryocyte-restricted p110beta null mouse model and demonstrated a critical role of PI3Kbeta in platelet activation via an immunoreceptor tyrosine-based activation motif, the glyco-protein VI-Fc receptor gamma-chain complex, and its contribution in response to G-protein-coupled receptors. Interestingly, the production of phosphatidylinositol 3,4,5-trisphosphate and the activation of protein kinase B/Akt were strongly inhibited in p110beta null platelets stimulated either via immunoreceptor tyrosine-based activation motif or G-protein-coupled receptors. Functional studies showed an important delay in fibrin clot retraction and an almost complete inability of these platelets to adhere onto fibrinogen under flow condition, suggesting that PI3Kbeta is also acting downstream of alpha(IIb)beta(3). In vivo studies showed that these mice have a normal bleeding time and are not protected from acute pulmonary thromboembolism but are resistant to thrombosis after FeCl(3) injury of the carotid, suggesting that PI3Kbeta is a potential target for antithrombotic drugs. PMID:20065293

Martin, Valérie; Guillermet-Guibert, Julie; Chicanne, Gaétan; Cabou, Cendrine; Jandrot-Perrus, Martine; Plantavid, Monique; Vanhaesebroeck, Bart; Payrastre, Bernard; Gratacap, Marie-Pierre

2010-01-11

316

THE DEPENDENCE OF MAGNETIC RECONNECTION ON PLASMA {beta} AND MAGNETIC SHEAR: EVIDENCE FROM SOLAR WIND OBSERVATIONS  

SciTech Connect

We address the conditions for the onset of magnetic reconnection based on a survey of 197 reconnection events in solar wind current sheets observed by the Wind spacecraft. We report the first observational evidence for the dependence of the occurrence of reconnection on a combination of the magnetic field shear angle, {theta}, across the current sheet and the difference in the plasma {beta} values on the two sides of the current sheet, {Delta}{beta}. For low {Delta}{beta}, reconnection occurred for both low and high magnetic shears, whereas only large magnetic shear events were observed for large {Delta}{beta}: Events with shears as low as 11{sup 0} were observed for {Delta}{beta} < 0.1, but for {Delta}{beta} > 1.5 only events with {theta} > 100{sup 0} were detected. Our observations are in quantitative agreement with a theoretical prediction that reconnection is suppressed in high {beta} plasmas at low magnetic shears due to super-Alfvenic drift of the X-line caused by plasma pressure gradients across the current sheet. The magnetic shear-{Delta}{beta} dependence could account for the high occurrence rate of reconnection observed in current sheets embedded within interplanetary coronal mass ejections, compared to those in the ambient solar wind. It would also suggest that reconnection could occur at a substantially higher rate in solar wind current sheets closer to the Sun than at 1 AU and thus may play an important role in the generation and heating of the solar wind.

Phan, T. D.; Pasma, C.; Oeieroset, M.; Larson, D.; Lin, R. P.; Davis, M. S. [SSL, University of California, Berkeley, CA 94720 (United States); Gosling, J. T. [University of Colorado, Boulder, CO (United States); Paschmann, G. [MPE, Garching (Germany); Drake, J. F., E-mail: phan@ssl.berkeley.ed [University of Maryland, College Park, MD (United States)

2010-08-20

317

Peptide hybrids containing alpha - and beta-amino acids: structure of a decapeptide beta-hairpin with two facing beta-phenylalanine residues.  

PubMed

A beta-hairpin conformation has been characterized in crystals of the decapeptide t-butoxycarbonyl-Leu-Val-beta Phe-Val-(D)Pro-Gly-Leu-beta Phe-Val-Val-methyl ester [beta Phe; (S)-beta(3) homophenylalanine] by x-ray diffraction. The polypeptide chain reversal is nucleated by the centrally positioned (D)Pro-Gly segment, which adopts a type-I' beta-turn conformation. Four intramolecular cross-strand hydrogen bonds stabilize the peptide fold. The beta Phe(3) and beta Phe(8) residues occupy facing positions on the hairpin, with the side chains projecting on opposite faces of the beta-sheet. At the site of insertion of beta-residues, the polarity of the peptide units along each strand reverses, as compared with the alpha-peptide segments. In this analog, a small segment of a polar sheet is observed, where adjacent CO and NH groups line up in opposite directions in each strand. In the crystal, an extended beta-sheet is formed by hydrogen bonding between strands of antiparallel pairs of beta-hairpins. The crystallographic parameters for C(65)H(102)N(10)O(13) x 3H(2)O are: space group P2(1)2(1)2(1); a = 19.059(8) A, b = 19.470(2) A, c = 21.077(2) A; Z = 4; agreement factor R(1) = 9.12% for 3,984 data observed >4 sigma(F) and a resolution of 0.90 A. PMID:11259666

Karle, I L; Gopi, H N; Balaram, P

2001-03-20

318

Light Sheet Fluorescence Microscopy  

PubMed Central

Light sheet fluorescence microscopy (LSFM) functions as a non-destructive microtome and microscope that uses a plane of light to optically section and view tissues with subcellular resolution. This method is well suited for imaging deep within transparent tissues or within whole organisms, and because tissues are exposed to only a thin plane of light, specimen photobleaching and phototoxicity are minimized compared to wide-field fluorescence, confocal, or multiphoton microscopy. LSFMs produce well-registered serial sections that are suitable for three-dimensional reconstruction of tissue structures. Because of a lack of a commercial LSFM microscope, numerous versions of light sheet microscopes have been constructed by different investigators. This review describes development of the technology, reviews existing devices, provides details of one LSFM device, and shows examples of images and three-dimensional reconstructions of tissues that were produced by LSFM.

Santi, Peter A.

2011-01-01

319

SHEET PLASMA DEVICE  

DOEpatents

An ion-electron plasma heating apparatus of the pinch tube class was developed wherein a plasma is formed by an intense arc discharge through a gas and is radially constricted by the magnetic field of the discharge. To avoid kink and interchange instabilities which can disrupt a conventional arc shortiy after it is formed, the apparatus is a pinch tube with a flat configuration for forming a sheet of plasma between two conductive plates disposed parallel and adjacent to the plasma sheet. Kink instabilities are suppressed by image currents induced in the conductive plates while the interchange instabilities are neutrally stable because of the flat plasma configuration wherein such instabilities may occur but do not dynamically increase in amplitude. (AEC)

Henderson, O.A.

1962-07-17

320

Clean Cities Fact Sheet  

SciTech Connect

This fact sheet explains the Clean Cities Program and provides contact information for all coalitions and regional offices. It answers key questions such as: What is the Clean Cities Program? What are alternative fuels? How does the Clean Cities Program work? What sort of assistance does Clean Cities offer? What has Clean Cities accomplished? What is Clean Cities International? and Where can I find more information?

Not Available

2004-01-01

321

GMC Sierra fact sheet  

SciTech Connect

The U.S. Department of Energy (DOE) is promoting the use of alternative fuels and alternative fuel vehicles (AFVs). The National Renewable Energy Laboratory (NREL) has been directed to conduct projects to evaluate the performance and acceptability of light-duty AFVs. This fact sheet gives the results of tests performed on 1998 GM pickups (GMC Sierra): one bi-fuel CNG and a gasoline model as closely matched as possible.

NREL

1999-05-01

322

Honda Civic fact sheet  

SciTech Connect

The U.S. Department of Energy (DOE) is promoting the use of alternative fuels and alternative fuel vehicles (AFVs). The National Renewable Energy Laboratory (NREL) has been directed to conduct projects to evaluate the performance and acceptability of light-duty AFVs. This fact sheet describes the test results on 1998 Honda Civics: one dedicated CNG and a gasoline model as closely matched as possible.

NREL

1999-05-01

323

Biomolecular Science (Fact Sheet)  

SciTech Connect

A brief fact sheet about NREL Photobiology and Biomolecular Science. The research goal of NREL's Biomolecular Science is to enable cost-competitive advanced lignocellulosic biofuels production by understanding the science critical for overcoming biomass recalcitrance and developing new product and product intermediate pathways. NREL's Photobiology focuses on understanding the capture of solar energy in photosynthetic systems and its use in converting carbon dioxide and water directly into hydrogen and advanced biofuels.

Not Available

2012-04-01

324

Kepler Mission Fact Sheet  

NSDL National Science Digital Library

This 2-page color fact sheet briefly describes NASAâs Kepler mission, its instruments, and ground system. Also included are tables listing the instrument parameters and the major institutions involved. Kepler is a spaceborne telescope specifically designed to survey our region of the Milky Way galaxy to detect and characterize hundreds of Earth-size and smaller planets in or near the habitable zone. The habitable zone encompasses the distances from a star where liquid water can exist on a planet's surface.

2007-01-01

325

Silver ion high pressure liquid chromatography provides unprecedented separation of sterols: application to the enzymatic formation of cholesta-5,8-dien-3 beta-ol.  

PubMed Central

We report that silver ion HPLC provides remarkable separations of C27 sterols differing only in the number or location of olefinic double bonds. This technique has been extended to LC-MS, analysis of purified components by GC, GC-MS, and 1H NMR, and to its use on a semipreparative scale. The application of this methodology for the demonstration of the catalysis, by rat liver microsomes, of the conversion of 7-dehydrocholesterol to cholesta-5,8-dien-3 beta-ol is also presented.

Ruan, B; Shey, J; Gerst, N; Wilson, W K; Schroepfer, G J

1996-01-01

326

Bioactivation of Nephrotoxic Haloalkenes by Glutathione Conjugation: Formation of Toxic and Mutagenic Intermediates by Cysteine Conjugate Beta-Lyase. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

The concept that glutathione S-conjugate biosynthesis, which leads to mercapturic acid formation and excretion, is an important mechanism of drug and chemical detoxification is well established. Glutathione S-conjugates are synthesized by the hepatic cyto...

W. Dekant S. Vamvakas M. W. Anders

1989-01-01

327

Early stages of misfolding and association of beta2-microglobulin: insights from infrared spectroscopy and dynamic light scattering.  

PubMed

Conformational changes associated with the assembly of recombinant beta 2-microglobulin in vitro under acidic conditions were investigated using infrared spectroscopy and static and dynamic light scattering. In parallel, the morphology of the different aggregated species obtained under defined conditions was characterized by electron microscopy. The initial salt-induced aggregate form of beta 2-microglobulin, composed of small oligomers (dimers to tetramers), revealed the presence of beta-strands organized in an intramolecular-like fashion. Further particle growth was accompanied by the formation of intermolecular beta-sheet structure and led to short curved forms. An increase in temperature by only 25 degrees C was able to disaggregate these assemblies, followed by the formation of longer filamentous structures. In contrast, a rise in temperature up to 100 degrees C was associated with a reorganization of the short curved forms at the level of secondary structure and the state of assembly, leading to a species with a characteristic infrared spectrum different from those of all the other aggregates observed before, suggesting a unique overall structure. The infrared spectral features of this species were nearly identical to those of beta 2-microglobulin assemblies formed at low ionic strength with agitation, indicating the presence of fibrils, which was confirmed by electron microscopy. The observed spectroscopic changes suggest that the heat-triggered conversion of the short curved assemblies into fibrils involves a reorganization of the beta-strands from an antiparallel arrangement to a parallel arrangement, with the latter being characteristic of amyloid fibrils of beta 2-microglobulin. PMID:18540682

Fabian, Heinz; Gast, Klaus; Laue, Michael; Misselwitz, Rolf; Uchanska-Ziegler, Barbara; Ziegler, Andreas; Naumann, Dieter

2008-06-10

328

Inhibitory effects of 1,2,3,4,6-penta-O-galloyl-beta-D-glucopyranose on biofilm formation by Staphylococcus aureus.  

PubMed

1,2,3,4,6-Penta-O-galloyl-?-D-glucopyranose (PGG) is an active ingredient in plants that are commonly used in Chinese medicine to treat inflammation. We demonstrate here that PGG, at 6.25 ?M, does not inhibit the growth of Staphylococcus aureus, and yet it prevents biofilm formation on polystyrene and polycarbonate surfaces. At the same concentration, PGG is not toxic to human epithelial and fibroblast cells. PGG has an IB?? value, i.e., the PGG concentration that inhibits 50% biofilm formation, of 3.6 ?M. The value is substantially lower than that of N-acetylcysteine, iodoacetamide, and N-phenyl maleimide, which are known to inhibit biofilm formation by S. aureus. Biochemical and scanning electron microscopy results also reveal that PGG inhibits initial attachment of the bacteria to solid surface and the synthesis of polysaccharide intercellular adhesin, explaining how PGG inhibits biofilm formation. The results of this study demonstrate that coating PGG on polystyrene and silicon rubber surfaces with polyaniline prevents biofilm formation, indicating that PGG is highly promising for clinical use in preventing biofilm formation by S. aureus. PMID:21173176

Lin, Mei-Hui; Chang, Fang-Rong; Hua, Mu-Yi; Wu, Yang-Chang; Liu, Shih-Tung

2010-12-20

329

Receptors for transforming growth factor-beta (TGF-beta) on rat lung fibroblasts have higher affinity for TGF-beta 1 than for TGF-beta 2  

SciTech Connect

Most cell types have receptors for transforming growth factor-beta (TGF-beta) and respond similarly to TGF-beta 1 and TGF-beta 2. We have demonstrated the presence of a single class of high-affinity receptors (approximately 10,000 sites/cell) for TGF-beta 1 (Kd = 23 pM) and TGF-beta 2 (Kd = 41 pM) on early-passage rat lung fibroblasts (RLF). Incubation with unlabeled TGF-beta 1 and TGF-beta 2 resulted in concentration-dependent inhibition of binding of 15 pM ({sup 125}I)TGF-beta 1 (ED50, 20 and 28 pM, respectively) and ({sup 125}I)TGF-beta 2 (ED50, 36 and 56 pM, respectively). TGF-beta receptors affinity-cross-linked with 100 pM ({sup 125}I)TGF-beta 1 or ({sup 125}I)TGF-beta 2 were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis and exhibited labeled protein bands of 68, 88, and 286 kD. Densitometric analysis of the resulting autoradiograms showed that the different molecular weight TGF-beta binding proteins exhibited separate affinities for the two forms of TGF-beta. Both TGF-beta 1 and TGF-beta 2 altered the morphology and cytoskeleton of RLF in a similar manner, but TGF-beta 1 was more potent than TGF-beta 2 in the inhibition of RLF growth and colony formation, with 50% inhibition by 0.12 pM TGF-beta 1 and 4.4 pM TGF-beta 2. Different affinities for the TGF-beta s may indicate selectivity among the receptor subtypes with regard to the biologic responsiveness of RLF to TGF-beta s. We believe this to be the first demonstration of biologically responsive TGF-beta receptors with different affinities for TGF-beta 1 and TGF-beta 2 on cells derived from normal, nonimmortal RLF. In establishing the basic mechanisms of pulmonary fibrosis, it will be essential to understand the biology and biochemistry of the receptors that may control cell division and production of extracellular matrix components by fibroblasts.

Kalter, V.G.; Brody, A.R. (National Institute of Environmental Health Sciences, Research Triangle Park, NC (USA))

1991-05-01

330

Characterization of an antibody scFv that recognizes fibrillar insulin and beta-amyloid using Atomic Force Microscopy  

PubMed Central

Fibrillar amyloid is the hallmark feature of many protein aggregation diseases, such as Alzheimer’s and Parkinson’s Diseases. A monoclonal single chain variable fragment (scFv) targeting insulin fibrils was isolated using phage display technology and an atomic force microscopy (AFM) mica substrate. Specific targeting of the scFv to insulin fibrils but not monomers or other small oligomeric forms, under similar conditions, was demonstrated both by Enzyme linked immunosorbent assays (ELISA’s) and AFM recognition imaging. The scFv also recognizes beta-amyloid fibrils, a hallmark feature of Alzheimer’s disease. The results suggest that the isolated scFv possibly targets a shared fibrillar motif - likely the cross-beta sheet characteristic of amyloid fibrils. The techniques outlined here provide additional tools to further study the process of fibril formation. The scFvs isolated can have potential use as diagnostic or therapeutic reagents for protein aggregation diseases.

Marcus, W. D.; Wang, H.; Lindsay, S. M.; Sierks, M. R.

2008-01-01

331

Conformations of synthetic beta peptides in solid state and in aqueous solution: relation to toxicity in PC12 cells.  

PubMed

The secondary structures of peptides beta 25-35 (the active toxic fragment) and beta 35-25 (reverse sequence and non-toxic fragment), as well as of the amidated beta (25-35)-NH2 peptide were investigated in aqueous solution and in the solid state by means of Fourier-transformed infrared spectroscopy and circular dichroism spectroscopy. The conformations of the beta 25-35 and beta 35-25 in solid state were identical and contained mostly beta-sheet structures. In solid state the amidated beta (25-35)-NH2 peptide also contained mostly beta-sheet structures. Freshly prepared aqueous solutions of the beta 25-32 (0.5 - 3.8 mM) contained a mixture of beta-sheet and random coil structures. Within 30-60 min incubation at 37 degrees C in water or in phosphate-buffered saline solution (PBS), beta 25-35 was almost fully converted to a beta-sheet structure. Decreasing the temperature from 37 degrees C to 20 degrees C decreased the rate of conversion from random coil to beta-sheet structures, 1-2 h being required for complete conversion. In contrast beta 35-25 in water or in PBS buffer had mostly a random coil structure and remained so for 6 days. The amidated beta(25-35)-NH2 peptide in water (2.7 mM) was also mostly random coil. However, when this peptide (2-2.7 mM) was dissolved in PBS (pH 7.4) or in 140 mM NaCl, a gel was formed and its conformation was mostly beta-sheet. Decreasing the concentration of beta (25-35)-NH2 peptide in 140 mM NaCl aqueous solution from 2 mM to 1 mM or below favored the conversion from beta-sheet structures to random coil structures. The beta 25-35 was toxic to PC12 cells while beta 35-25 was not. The amidated peptide beta (25-35)-NH2 was at least 500-fold less toxic than beta 25-35. Structural differences between these beta peptides in aqueous solutions may explain the difference in their respective toxicities. PMID:8611645

Buchet, R; Tavitian, E; Ristig, D; Swoboda, R; Stauss, U; Gremlich, H U; de La Fournière, L; Staufenbiel, M; Frey, P; Lowe, D A

1996-01-17

332

Relevance of organic farming and effect of climatological conditions on the formation of alpha-acids, beta-acids, desmethylxanthohumol, and xanthohumol in hop (Humulus lupulus L.).  

PubMed

The concentrations of alpha-acids, beta-acids, desmethylxanthohumol, and xanthohumol were monitored in the hop varieties Admiral (A), Wye Challenger (WC), and First Gold (FG) during the harvest seasons of 2003 through 2005. Hops grown under an organic regimen were compared to plants grown conventionally in hop fields in close vicinity. The concentrations of the key compounds depended very much on climatological conditions showing, in general, highest levels in poorest weather conditions (2004). Of the three varieties studied, FG was the only one showing a clear trend for higher concentrations of secondary metabolites under organic growing conditions than under conventional farming conditions. Cultivation of A and WC seems to be very sensitive to climatic conditions and environmental stresses caused by pests and diseases, thereby leading to various results. WC proved to be a rich source of bioactive chalcones, particularly desmethylxanthohumol. PMID:17199314

Keukeleire, Jelle De; Janssens, Ina; Heyerick, Arne; Ghekiere, Greet; Cambie, Joris; Roldan-Ruiz, Isabel; Bockstaele, Erik Van; Keukeleire, Denis De

2007-01-10

333

In vivo formation of gene fusions encoding hybrid beta-galactosidase proteins in one step with a transposable Mu-lac transducing phage.  

PubMed Central

A Mu-lac bacteriophage transposon, MudII301 (Ap, lac), was constructed to form hybrid protein gene fusions. When it integrates into structural genes in the appropriate direction and reading phase, transcription and translation from outside gene controlling regions can proceed across 116 nucleotides from the right end of Mu into lacZ codons to form hybrid proteins that are enzymatically active for beta-galactosidase. Integration can be obtained either by infection to form lysogens or by transposition during growth of a lysogen. The size of the hybrid protein product either corresponds to or, in the cases of translation restart or protein degradation, is a minimal estimate of the distance of the Mu insertion from the translation initiation site of the gene. Hybrid proteins formed by insertions in randomly selected genes and in the araB and A genes were examined by polyacrylamide gel electrophoresis. Images

Casadaban, M J; Chou, J

1984-01-01

334

Formation of decarboxylated betacyanins in heated purified betacyanin fractions from red beet root (Beta vulgaris L.) monitored by LC-MS/MS.  

PubMed

Mixtures of mono-, bi-, and tridecarboxylated betacyanins together with their corresponding neobetacyanins obtained from Beta vulgaris L. root juice as heating degradation products of betacyanins were identified by high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) and diode-array (LC-DAD) detection. Two monodecarboxy-betacyanin pairs of diastereomers were detected after the decarboxylation in ethanolic and aqueous solutions. Generation of 17-decarboxy-betacyanins and 2-decarboxy-betacyanins was suggested, the latter so far never having been attributed to betacyanin thermal degradation products. Other main products of decarboxylation were 2,17-bidecarboxybetanin, its isoform, and 14,15-dehydrogenated (neobetacyanin) derivatives of all the decarboxylated betacyanins. The results of this research are crucial in determining betacyanin degradation mechanisms in juices or extracts of B. vulgaris L. roots and other products containing these pigments. PMID:15853391

Wybraniec, S?awomir

2005-05-01

335

Dynamic Formation of a Hot Field Reversed Configuration with Improved Confinement by Supersonic Merging of Two Colliding High-{beta} Compact Toroids  

SciTech Connect

A hot stable field-reversed configuration (FRC) has been produced in the C-2 experiment by colliding and merging two high-{beta} plasmoids preformed by the dynamic version of field-reversed {theta}-pinch technology. The merging process exhibits the highest poloidal flux amplification obtained in a magnetic confinement system (over tenfold increase). Most of the kinetic energy is converted into thermal energy with total temperature (T{sub i}+T{sub e}) exceeding 0.5 keV. The final FRC state exhibits a record FRC lifetime with flux confinement approaching classical values. These findings should have significant implications for fusion research and the physics of magnetic reconnection.

Binderbauer, M. W.; Guo, H. Y.; Tuszewski, M.; Putvinski, S.; Sevier, L.; Barnes, D.; Rostoker, N.; Anderson, M. G.; Andow, R.; Bonelli, L.; Brown, R.; Bui, D. Q.; Bystritskii, V.; Clary, R.; Cheung, A. H.; Conroy, K. D.; Deng, B. H.; Dettrick, S. A.; Douglass, J. D.; Feng, P. [Tri Alpha Energy, Inc., Post Office Box 7010, Rancho Santa Margarita, California 92688 (United States)

2010-07-23

336

Thinning of the plasma sheet during substorms. Technical report  

SciTech Connect

Concurrent measurements of plasma by the SCATHA satellite in near-synchronous orbit and by ISEE 2 in the near magnetotail are used to examine the phenomenon of plasma-sheet thinning associated with substorms. Results show that thinning occurs in two stages, thought to be attributable to two different processes. For 30-60 minutes before expansive phase offset, gradual thinning occurred over the region from geosynchronous orbit out to 20 RE in the tail. This was attributable to the tail-like configuration thought to lead to neutral line formation and the beginning of magnetic reconnection within the plasma sheet. At expansive phase onset, extreme thinning was seen and is thought to occur as a portion of the plasma sheet (a plasmoid), severed by magnetic connection at a near-earth neutral line, quickly departs tailward. Earthward of the neutral line, the plasma sheet expanded. Results generally support the neutral-line model of substorms.

Hones, E.W.; Bame, S.J.; Fennell, J.F.; Croley, D.R.

1987-03-17

337

Asymmetric Magnetic Reconnection in Coronal Mass Ejection Current Sheets  

NASA Astrophysics Data System (ADS)

Flux rope models of coronal mass ejections (CMEs) predict the formation ofan elongated current sheet in the wake behind the rising plasmoid. These current sheets have been seen to drift or tilt over time by instruments including SOHO/LASCO and Hinode/XRT. We measure this in multiple observations including the 2008 April 9 "Cartwheel CME" and find an average drift that is far more than can be accounted for via the effects of solar rotation. The observed drift could be due to different parts of the current sheet actively reconnecting at different times (e.g., Savage et al. 2010), macroscopic effects from the rising flux rope pulling the plasma sheet along with it, or asymmetry in the magnetic reconnection process itself. These drift rates are compared with resistive magnetohydrodynamic (MHD) simulations of line-tied reconnection between magnetic fields of different strengths. The observed drift rates are comparable to predictions made by the simulations.

Pope, Crystal; Miralles, M. P.; Murphy, N. A.

2012-01-01

338

In silico and in vitro studies to elucidate the role of Cu(2+) and galanthamine as the limiting step in the amyloid beta (1-42) fibrillation process.  

PubMed

The formation of fibrils and oligomers of amyloid beta (A?) with 42 amino acid residues (A?1-42 ) is the most important pathophysiological event associated with Alzheimer's disease (AD). The formation of A? fibrils and oligomers requires a conformational change from an ?-helix to a ?-sheet conformation, which is encouraged by the formation of a salt bridge between Asp 23 or Glu 22 and Lys 28. Recently, Cu(2+) and various drugs used for AD treatment, such as galanthamine (Reminyl(®) ), have been reported to inhibit the formation of A? fibrils. However, the mechanism of this inhibition remains unclear. Therefore, the aim of this work was to explore how Cu(2+) and galanthamine prevent the formation of A?1-42 fibrils using molecular dynamics (MD) simulations (20 ns) and in vitro studies using fluorescence and circular dichroism (CD) spectroscopies. The MD simulations revealed that A?1-42 acquires a characteristic U-shape before the ?-helix to ?-sheet conformational change. The formation of a salt bridge between Asp 23 and Lys 28 was also observed beginning at 5 ns. However, the MD simulations of A?1-42 in the presence of Cu(2+) or galanthamine demonstrated that both ligands prevent the formation of the salt bridge by either binding to Glu 22 and Asp 23 (Cu(2+) ) or to Lys 28 (galanthamine), which prevents A?1-42 from adopting the U-characteristic conformation that allows the amino acids to transition to a ?-sheet conformation. The docking results revealed that the conformation obtained by the MD simulation of a monomer from the 1Z0Q structure can form similar interactions to those obtained from the 2BGE structure in the oligomers. The in vitro studies demonstrated that A? remains in an unfolded conformation when Cu(2+) and galanthamine are used. Then, ligands that bind Asp 23 or Glu 22 and Lys 28 could therefore be used to prevent ? turn formation and, consequently, the formation of A? fibrils. PMID:23904252

Hernández-Rodríguez, Maricarmen; Correa-Basurto, José; Benitez-Cardoza, Claudia G; Resendiz-Albor, Aldo Arturo; Rosales-Hernández, Martha C

2013-08-19

339

Cellulose wet wiper sheets prepared with cationic polymer and carboxymethyl cellulose using a papermaking technique  

Microsoft Academic Search

Carboxymethyl cellulose (CMC)-rich cellulose sheets were prepared with a cationic retention aid, poly[N,N,N-trimethyl-N-(2-methacryloxyethyl)ammonium chloride] (PTMMAC), using a papermaking technique. When 5% PTMMAC and 5% CMC were added to\\u000a cellulose slurries, approximately 94% of the polymers were retained in the sheets by formation of polyion complexes between\\u000a the two polymers. When the PTMMAC\\/CMC\\/cellulose sheets were soaked in solutions consisting of ethanol,

Takehiko Uematsu; Yoshiaki Matsui; Shusuke Kakiuchi; Akira Isogai

2011-01-01

340

Planetary Fact Sheets  

NSDL National Science Digital Library

Offered by the National Space Science Data Center of NASA, the Planetary Fact Sheets Web site contains helpful information for students studying astronomy. The site lists links to all of the planets, their satellites, and their rings, as well as to tables comparing all the planets. The planet pages contain a photograph and a simple list of dozens of facts such as mass, volume, distance to the earth, temperature, and much more. Although not flashy, the information provided by this site can be very useful to anyone wanting to learn more about our solar system.

1969-12-31

341

Europa Fact Sheet  

NSDL National Science Digital Library

The Galileo spacecraft provided images of Europa, one of Jupiter's moons. The images showed signs of a possible ocean on the surface of the moon. NASA's Europa Fact Sheet provides information and images on this Jovian moon. This site covers one of the top ten scientific breakthroughs of 1997, compiled in the December 19, 1997 issue of Science. The top scientific breakthrough of 1997 was the cloning of a sheep, resulting in a lamb named Dolly. The nine runners up were: the Pathfinder mission to Mars, synchrotrons, biological clock genes, gamma ray bursts, Neandertal DNA, nanotubes, Europa's ocean, whole genome sequencing, and neurons.

342

Ice sheets and nitrogen.  

PubMed

Snow and ice play their most important role in the nitrogen cycle as a barrier to land-atmosphere and ocean-atmosphere exchanges that would otherwise occur. The inventory of nitrogen compounds in the polar ice sheets is approximately 260 Tg N, dominated by nitrate in the much larger Antarctic ice sheet. Ice cores help to inform us about the natural variability of the nitrogen cycle at global and regional scale, and about the extent of disturbance in recent decades. Nitrous oxide concentrations have risen about 20 per cent in the last 200 years and are now almost certainly higher than at any time in the last 800 000 years. Nitrate concentrations recorded in Greenland ice rose by a factor of 2-3, particularly between the 1950s and 1980s, reflecting a major change in NOx emissions reaching the background atmosphere. Increases in ice cores drilled at lower latitudes can be used to validate or constrain regional emission inventories. Background ammonium concentrations in Greenland ice show no significant recent trend, although the record is very noisy, being dominated by spikes of input from biomass burning events. Neither nitrate nor ammonium shows significant recent trends in Antarctica, although their natural variations are of biogeochemical and atmospheric chemical interest. Finally, it has been found that photolysis of nitrate in the snowpack leads to significant re-emissions of NOx that can strongly impact the regional atmosphere in snow-covered areas. PMID:23713125

Wolff, Eric W

2013-05-27

343

Preparation of creep data sheet: Material strength data sheet  

Microsoft Academic Search

Continuing from the first and the second term, creep rupture data sheet on metals for high temperatures was continued targeting for 100,000 hours. Creep strain data sheet for elastic analysis, conceived in the second term was carried out this term. Additionally, research was planned into the Cr group steel, which is increasingly in demand for high temperature equipment, and material

Chiaki Tanaka; Koichi Yagi; Sadao Ikeda; Hiroshi Ito; Eiji Baba; Masaru Shimizu; Hideo Tanaka; Kenji Yokokawa; Hideo Nagai; Osamu Kanamaru

1993-01-01

344

Internal hydrogen embrittlement of high-strength beta-alpha titanium alloys  

NASA Astrophysics Data System (ADS)

Potential problems and uncertainties are associated with the complex nature of fracture in solution treated and aged (STA) beta-titanium (beta-Ti) alloys, as well as the potential for long-term alloy degradation due to hydrogen embrittlement. This research characterizes the effects of predissolved hydrogen and microstructural conditions on the fracture resistance of two solution treated and aged (STA) high strength beta-titanium alloys, Low Cost Beta (LCB) and Ti-15-3, in sheet form. Rising-CMOD fracture test results demonstrate that STA beta-Ti alloys are severely embrittled at room temperature and a slow displacement rate above a relatively low threshold hydrogen concentration. Hydrogen concentrations of 400 and 500 wppm reduce the threshold stress intensity at the onset of hydrogen cracking to 50% of the air fracture toughness in STA LCB, and Ti-15-3, respectively. Significant embrittlement for both alloys is triggered at concentrations in excess of 750 wppm, with reductions in threshold stress intensity to an asymptotic value equal to 25% of the air fracture toughness. Reductions in crack growth resistance with increasing hydrogen concentrations are accompanied by significant increases in subcritical crack growth rates. Changes in fracture mode are concurrent with reduced in fracture resistance. With increasing hydrogen concentration, the fracture mode changes from microvoid coalescence to transgranular hydrogen-assisted alpha/beta interface cracking. Two mechanisms of internal hydrogen embrittlement in STA metastable beta-Ti alloys, bond decohesion and hydride formation are proposed to occur at alpha/beta interfaces. A critical isothermal aging time must be exceeded to render Ti-15-3 susceptible to internal hydrogen embrittlement. This is attributed to a critical alpha volume fraction and the associated stress and hydrogen concentration. The internal hydrogen embrittlement of STA Ti-15-3 is a time dependent phenomenon. Experimental results and crack tip strain rate calculations demonstrate that embrittlement will persist in STA Ti-15-3 to loading rates of approximately 0.5 MPa?m/s. As such, hydrogen redistribution to the crack tip is a critical component of internal hydrogen embrittlement. Local transport of hydrogen in intra-alpha beta to susceptible alpha/beta interfaces, and possibly growth kinetics of gamma-TiH2, in the fracture process zone are consistent with the observed kinetics and appear to govern the time dependence.

Hayes, Sean Paul

345

Dynamics of charged current sheets at high-latitude magnetopause  

NASA Astrophysics Data System (ADS)

E. Amata (2), L. Zelenyi (1), M. Dunlop (3), M. Andre (4), P. Song (5), J. Blecki (6), J. Buechner (7), J.L Rauch, J.G. Trotignon (8), G. Consolini, F. Marcucci (2), B. Nikutowski (7), A. Skalsky, S. Romanov, E. Panov (1) (2) IFSI, Roma, Italy, (3) RAL, UK, (4) IRFU, Uppsala, Sweden, (5) U. Mass. Lowell, USA, (6) SRC, Warsaw, Poland, (7) MPAe, Germany, (8) LPCE, Orleans, France; We study dynamics of thin current sheets over polar cusps from data of Interball-1 and Cluster. At the high-beta magnetopause current sheet width often reaches ion gyroradius scales, that leads to their Hall dynamics in the presence of local surface charges. Respective perpendicular electric fields provide the means for momentum coupling through the current sheets and are able to accelerate ions with gyroradius of the order or larger than the sheet width. At borders of large diamagnetic cavities this mechanism is able to support mass exchange and accelerate/ heat incoming magnetosheath particles. At larger scales the inhomogeneous electric fields at the current sheet borders can accelerate incident plasma downtail along magnetopause via inertial drift. It serves to move external plasma away for dynamic equilibrium supporting. Farther away from magnetopause similar nonlinear electric field wave trains, selfconsistently produced by interaction of reflected from the obstacle waves with magnetosheath fluctuations, destroy the incident flux into accelerated magnetosonic jets and decelerated Alfvenic flows and generate small-scale current sheets due to different sign of electron and ion inertial drift in the nonlinear electric field bursts. We suggest that this direct kinetic energy transformation creates current sheets with anomalous statistics of field rotation angles in the turbulent boundary layer in front of magnetopause, which have been attributed earlier to an intermittent turbulence. We compare measured spectra with a model of nonlinear system with intermittent chaotic behavior. Work was supported by INTAS grant 03-51-4872.

Savin, S.; Amata, E.; Zelenyi, L.; Dunlop, M.; Andre, M.; Song, P.; Blecki, J.; Buechner, J.; Rauch, J. L.; Skalsky, A.

346

Beta-helix core packing within the triple-stranded oligomerization domain of the P22 tailspike.  

PubMed Central

A right-handed parallel beta-helix of 400 residues in 13 tightly packed coils is a major motif of the chains forming the trimeric P22 tailspike adhesin. The beta-helix domains of three identical subunits are side-by-side in the trimer and make predominantly hydrophilic inter-subunit contacts (Steinbacher S et al., 1994, Science 265:383-386). After the 13th coil the three individual beta-helices terminate and the chains wrap around each other to form three interdigitated beta-sheets organized into the walls of a triangular prism. The beta-strands then separate and form antiparallel beta-sheets, but still defining a triangular prism in which each side is a beta-sheet from a different subunit (Seckler R, 1998, J Struct Biol 122:216-222). The subunit interfaces are buried in the triangular core of the prism, which is densely packed with hydrophobic side chains from the three beta-sheets. Examination of this structure reveals that its packed core maintains the same pattern of interior packing found in the left-handed beta-helix, a single-chain structure. This packing is maintained in both the interdigitated parallel region of the prism and the following antiparallel sheet section. This oligomerization motif for the tailspike beta-helices presumably contributes to the very high thermal and detergent stability that is a property of the native tailspike adhesin.

Kreisberg, J. F.; Betts, S. D.; King, J.

2000-01-01

347

Electron-microscopic investigation of the formation of colloidal beta FeOOH during slow hydrolysis of an aqueous ferric chloride solution at room temperature  

Microsoft Academic Search

Summary  The occurrence and the morphology of spindle-shaped particles of colloidal?-FeOOH, formed by slow hydrolysis of the aqueous solution of FeCl3 at the room temperature, have been examined by electron microscope.\\u000a \\u000a The region of the formation of spindle-shaped particles is limited by the concentration of FeCl3 solution and the age of the system (figs. 1 and 2). The increase of the

R. H. H. Wolf; M. Wrischer; J. Šipalo-Žuljevi?

1967-01-01

348

Synthesis of ductile titanium-titanium boride (Ti-TiB) composites with a beta-titanium matrix: The nature of TiB formation and composite properties  

Microsoft Academic Search

The study focused on the in-situ synthesis of titanium (Ti)-titanium boride (TiB) composites with ? phase in the matrix by reaction sintering of TiB2 with Ti and alloying element powders. The goal was to examine the nature of TiB whisker formation in three different kinds\\u000a of powder mixtures: (1) ?-Ti alloy powders and TiB2; (2) ?-Ti powder, a master alloy

K. B. Panda; K. S. Ravi Chandran

2003-01-01

349

Human Recombinant Butyrylcholinesterase Purified from the Milk of Transgenic Goats Interacts with Beta-Amyloid Fibrils and Suppresses Their Formation in vitro  

Microsoft Academic Search

Background: In Alzheimer’s disease (AD), brain butyrylcholinesterase (BChE) co-localizes with ?-amyloid (A?) fibrils. Aims: In vitro testing of the significance of this phenomenon to AD progress. Methods: A thioflavine T (ThT) fluorogenic assay, photo-induced cross-linking and quantifiable electron microscopy served to compare the effect on A? fibril formation induced by highly purified recombinant human BChE (rBChE) produced in the milk

E. Podoly; T. Bruck; S. Diamant; A. Weiss; Y. Huang; O. Livnah; S. Langermann; H. Wilgus; H. Soreq

2008-01-01

350

Signaling through the TGF Beta-Activin Receptors ALK4/5/7 Regulates Testis Formation and Male Germ Cell Development  

PubMed Central

The developing testis provides an environment that nurtures germ cell development, ultimately ensuring spermatogenesis and fertility. Impacts on this environment are considered to underlie aberrant germ cell development and formation of germ cell tumour precursors. The signaling events involved in testis formation and male fetal germ cell development remain largely unknown. Analysis of knockout mice lacking single Tgf? family members has indicated that Tgf?'s are not required for sex determination. However, due to functional redundancy, it is possible that additional functions for these ligands in gonad development remain to be discovered. Using FACS purified gonadal cells, in this study we show that the genes encoding Activin's, TGF?'s, Nodal and their respective receptors, are expressed in sex and cell type specific patterns suggesting particular roles in testis and germ cell development. Inhibition of signaling through the receptors ALK4, ALK5 and ALK7, and ALK5 alone, demonstrated that TGF? signaling is required for testis cord formation during the critical testis-determining period. We also show that signaling through the Activin/NODAL receptors, ALK4 and ALK7 is required for promoting differentiation of male germ cells and their entry into mitotic arrest. Finally, our data demonstrate that Nodal is specifically expressed in male germ cells and expression of the key pluripotency gene, Nanog was significantly reduced when signaling through ALK4/5/7 was blocked. Our strategy of inhibiting multiple Activin/NODAL/TGF? receptors reduces the functional redundancy between these signaling pathways, thereby revealing new and essential roles for TGF? and Activin signaling during testis formation and male germ cell development.

Stringer, Jessica M.; van den Bergen, Jocelyn A.; Wilhelm, Dagmar; Sinclair, Andrew H.; Western, Patrick S.

2013-01-01

351

Nuclear Data Sheets for A = 81  

SciTech Connect

Nuclear structure data pertaining to all nuclei with mass number A = 81 (Zn, Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb) have been compiled and evaluated and incorporated into the ENSDF data file. This publication for A = 81 supersedes the previous publication (Coral M. Baglin, Nuclear Data Sheets79, 447 (1996), literature cutoff 1 November 1996) and the subsequent updates by C. Baglin for {sup 81}Y (literature cutoff 8 October 1998) and {sup 81}Zr (literature cutoff 24 March 2000). All literature available prior to 15 August 2008 has been considered. Subsequent to previous A = 81 evaluations, excited states have been reported for the first time in {sup 81}Ga, and knowledge of excited state properties for {sup 81}Y and {sup 81}Zr has been significantly expanded. However, the expected {epsilon}+{beta}{sup +} decay of {sup 81}Zr has yet to be studied.

Baglin, Coral M. [Nuclear Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States)

2008-10-15

352

beta-Aminobutyric acid-induced resistance against downy mildew in grapevine acts through the potentiation of callose formation and jasmonic acid signaling.  

PubMed

beta-Aminobutyric acid (BABA) was used to induce resistance in grapevine (Vitis vinifera) against downy mildew (Plasmopara viticola). This led to a strong reduction of mycelial growth and sporulation in the susceptible cv. Chasselas. Comparing different inducers, the best protection was achieved with BABA followed by jasmonic acid (JA), whereas benzo (1,2,3)-thiadiazole-7-carbothionic acid-S-methyl ester (a salicylic acid [SA] analog) and abscisic acid (ABA) treatment did not increase the resistance significantly. Marker genes for the SA and JA pathways showed potentiated expression patterns in BABA-treated plants following infection. The callose synthesis inhibitor 2-deoxy-D-glucose partially suppressed BABA- and JA-induced resistance against P viticola in Chasselas. Application of the phenylalanine ammonia lyase inhibitor 2-aminoindan-2-phosphonic acid and the lipoxygenase (LOX) inhibitor 5, 8, 11, 14-eicosatetraynoic acid (ETYA) also led to a reduction of BABA-induced resistance (BABA-IR), suggesting that callose deposition as well as defense mechanisms depending on phenylpropanoids and the JA pathways all contribute to BABA-IR. The similar phenotype of BABA- and JA-induced resistance, the potentiated expression pattern of JA-regulated genes (LOX-9 and PR-4) following BABA treatment, and the suppression of BABA-IR with ETYA suggest an involvement of the JA pathway in BABA-IR of grapevine leading to a primed deposition of callose and lignin around the infection sites. PMID:16134894

Hamiduzzaman, Mollah Md; Jakab, Gabor; Barnavon, Laurent; Neuhaus, Jean-Marc; Mauch-Mani, Brigitte

2005-08-01

353

Complex formation of beta-cyclodextrin in aqueous media with poly(N,N-dimethylacrylamide)containing pendent perfluorooctanesulfonamido groups. Final Report, September 15, 1998 - September 14, 1999  

SciTech Connect

The effect of time on the viscosity of solutions of 0.50--1.0 weight % polyacrylamide copolymers containing 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate (FOSA) comonomer units was monitored at constant shear rates varying from 0.60 to 3.0 sec{sup {minus}1}. The viscosities decreased to a plateau over a period of about thirty minutes. The copolymer solutions sheared at much higher shear rates of 24 sec{sup {minus}1} showed pronounced shear thinning but regained most of their original viscosities after standing for 20 minutes. Heating the solutions less than one hour caused an increase in the low shear viscosity whereas longer heating times decreased solution viscosities presumably due to hydrolysis of the acrylate groups. Addition of beta-cyclodextrin to solutions of the hydrophobically modified polyacrylamide resulted in sharply decreased copolymer viscosities at cyclodextrin concentrations on the order of about 10{sup {minus}3} M. The above is consistent with competitive hydrophobic association of the perfluorocarbon groups of the copolymer with the cyclodextrin disrupting the mutual association of the perfluorocarbon groups.

Dr. Thieo Hogen-Esch

1999-11-01

354

[Clip Sheets from BOCES. Opportunities. Health. Careers. = Oportunidades. Salud. Una Camera En...  

ERIC Educational Resources Information Center

|This collection of 83 clip sheets, or classroom handouts, was created to help U.S. migrants learn more about health, careers, and general "opportunities" including education programs. They are written in both English and Spanish and are presented in an easily understandable format. Health clip-sheet topics include the following: Abuse; AIDS;…

State Univ. of New York, Geneseo. Coll. at Geneseo. Migrant Center.

355

Vertical motions of passive margins of Greenland: influence of ice sheet, glacial erosion, and sediment transport  

Microsoft Academic Search

The sub-ice topography of Greenland is characterized by a central depression below the sea level and by elevated (in some places significantly) margins. Whereas the central depression may be explained by significant load of the Greenland ice sheet, the origin of the peripheral relief remains unclear. We analyze the influence of formation of the ice sheet and carving by glacial

A. Souche; S. Medvedev; E. H. Hartz

2009-01-01

356

Modern processes of production of thin sheets and strips by continuous casting  

NASA Astrophysics Data System (ADS)

The history of the development of producing thin sheets and strips by continuous casting methods is considered. The mechanism of this sheet formation during casting of steel in a two-roll continuous caster is described. The advantages of this process over the corresponding traditional technologies are discussed.

Smirnov, A. N.

2012-06-01

357

Numerical modeling investigations of the subglacial conditions of the southern Laurentide ice sheet  

Microsoft Academic Search

Sub- and proglacial bed conditions influence advance and retreat of an ice sheet. The existence and distribution of frozen ground is of major importance for better understanding of ice-flow dynamics and landform formation. The southern margin of the Laurentide ice sheet (LIS) was dominated by the presence of relatively thin ice lobes that seem to have been very sensitive to

Andreas Bauder; David M. Mickelson; Shawn J. Marshall

2005-01-01

358

Structure of beta-crystallite assemblies formed by Alzheimer beta-amyloid protein analogues: analysis by x-ray diffraction.  

PubMed Central

To elucidate the relation between amyloid fibril formation in Alzheimer disease and the primary structure of the beta/A4 protein, which is the major component of the amyloid, we have been investigating the ability of peptides sharing sequences with beta/A4 to form fibrils in vitro. In previous studies we focused on the macroscopic morphology of the assemblies formed by synthetic peptides corresponding in sequence to different regions of this protein. In the present study we analyze the x-ray diffraction patterns obtained from these assemblies. All specimens showed wide angle reflections that could be indexed by an orthogonal lattice of beta-crystallites having unit cell dimensions a = 9.4 A, b = 7 A, and c = 10 A, where a refers to hydrogen bonding direction, b to polypeptide chain direction, and c to intersheet direction. Given the amino acid sequence of beta/A4 as NH2-DAEFRHDSGYEVHHQKLVFFAEDVGSNKGAIIGLMVGGVVIAT-COOH, we found that, based on their orientation and assembly, the analogues could be classified into three groups: Group A, residues 19-28, 13-28, 12-28, 11-28, 9-28, 1-28, 1-38, 1-40, 6-25, 11-25 and 34-42; Group B, residues 18-28, 17-28, and 15-28; and Group C, residues 22-35 and 26-33. For Groups A and C, the sharpest reflections were (h00), indicating that the assemblies were fibrillar, i.e., elongated in a single direction. Lateral alignment of the crystallites in Group A account for its cross-beta pattern, in which the hydrogen bonding (H-bonding) direction is the fiber (rotation) axis. By comparison, the beta-crystallites of Group C had no preferential orientation, thus giving circular scattering. For Group B, the sharpest reflections were (h0l) on the meridian, indicating that the assemblies were plate-like, i.e., extended in two directions. A series of equatorial Bragg reflections having a 40 A period indicated regular stacking of the plates, and the rotation axis was normal to the surface of the plates. Of the Group A peptides, the analogues 11-28 and 6-25 showed intensity maxima on the equator as well as on higher layer lines, indicating that the beta-crystallites are highly ordered relative to one another in the axial, H-bonding direction. This sampling of the layer lines by a larger period (60 A) suggests that the beta-crystallites are arrayed either in cylindrical or small restricted crystalline lattices. Consistent with its electron microscopic images, we modeled the structure as a tube with five or six f,-crystallites constituting the wall and with the individual crystallite, which either rotates freely or is restricted, made of five or fewer beta-pleated sheets. For the Group B peptides, the electron density projection along the b-axis was calculated from the observed intensities using phase combinations from fl-keratin.Amino acid side-chain positions were apparent and, when refined as 4-A-diameter spheres, led to a substantial decrease in the R-factors.For peptide 18-28 the electron density peaks, which are thought to correspond to side chains, were centered 3.3 A from the peptide backbone, whereas for peptides 17-28 and 15-28, these peaks were centered 1 A or more further from the backbone. Peaks having high electron density faced peaks having lower density, suggesting a favorable stereochemical arrangement of the residues. Thus, our analysis of the fiber x-ray patterns from beta/A4 peptides shows the organization of the beta-crystallites that form the wall of the amyloid fibrils as well as possible side-chain interactions. Images FIGURE 1

Inouye, H.; Fraser, P. E.; Kirschner, D. A.

1993-01-01

359

Active volcanism beneath the West Antarctic ice sheet and implications for ice-sheet stability  

USGS Publications Warehouse

IT is widely understood that the collapse of the West Antarctic ice sheet (WAIS) would cause a global sea level rise of 6 m, yet there continues to be considerable debate about the detailed response of this ice sheet to climate change1-3. Because its bed is grounded well below sea level, the stability of the WAIS may depend on geologically controlled conditions at the base which are independent of climate. In particular, heat supplied to the base of the ice sheet could increase basal melting and thereby trigger ice streaming, by providing the water for a lubricating basal layer of till on which ice streams are thought to slide4,5. Ice streams act to protect the reservoir of slowly moving inland ice from exposure to oceanic degradation, thus enhancing ice-sheet stability. Here we present aerogeophysical evidence for active volcanism and associated elevated heat flow beneath the WAIS near the critical region where ice streaming begins. If this heat flow is indeed controlling ice-stream formation, then penetration of ocean waters inland of the thin hot crust of the active portion of the West Antarctic rift system could lead to the disappearance of ice streams, and possibly trigger a collapse of the inland ice reservoir.

Blankenship, D. D.; Bell, R. E.; Hodge, S. M.; Brozena, J. M.; Behrendt, J. C.; Finn, C. A.

1993-01-01

360

The quantitative inspection of iron aluminide green sheet using transient thermography  

SciTech Connect

The recent development of manufacturing techniques for the fabrication of thin iron aluminide, FeAl, sheet requires advanced quantitative methods for on-line inspection. An understanding of the mechanisms responsible for flaws and the development of appropriate flaw detection methods are key elements in an effective quality management system. The first step in the fabrication of thin FeAl alloy sheet is the formation of a green sheet, either by cold rolling or tape casting FeAl powder mixed with organic binding agents. The finished sheet is obtained using a series of process steps involving binder elimination, densification, sintering, and annealing. Non-uniformities within the green sheet are the major contributor to material failure in subsequent sheet processing and the production of non-conforming finished sheet. Previous work has demonstrated the advantages of using active thermography to detect the flaws and heterogeneity within green powder composites (1)(2)(3). The production environment and physical characteristics of these composites provide for unique challenges in developing a rapid nondestructive inspection capability. Thermography is non-contact and minimizes the potential damage to the fragile green sheet. Limited access to the material also demands a one-sided inspection technique. In this paper, we will describe the application of thermography for 100% on-line inspection within an industrial process. This approach is cost competitive with alternative technologies, such as x-ray imaging systems, and provides the required sensitivity to the variations in material composition. The formation of green sheet flaws and their transformation into defects within intermediate and finished sheet products will be described. A green sheet conformance criterion will be presented which would significantly reduce the probability of processing poor quality green sheet which contributes to higher waste and inferior bulk alloy sheet.

Watkins, Michael L. [Philip Morris U.S.A., R, D and E, Richmond, Virginia (United States); Hinders, Mark K. [College of William and Mary, Williamsburg, Virginia (United States); Scorey, Clive [Ametek Specialty Metals Division, Wallingford, Connecticut (United States); Winfree, William [NASA Langley Research Center, Hampton, Virginia (United States)

1999-12-02

361

Ice Sheet And Satellite Altimetry  

Microsoft Academic Search

Since 1991, the altimeters of the ERS European Satellites allow the observation of 80% of the Antarctica ice sheet and the whole Greenland ice sheet: They thus offer for the first time a unique vision of polar ice caps. Indeed, surface topography is an essential data thanks to its capacity to highlight the physical processes which control the surface shape,

Frédérique Rémy; Benoît Legresy; Laurent Testut

2001-01-01

362

Electromechanical Resonators from Graphene Sheets  

Microsoft Academic Search

Nanoelectromechanical systems were fabricated from single- and multilayer graphene sheets by mechanically exfoliating thin sheets from graphite over trenches in silicon oxide. Vibrations with fundamental resonant frequencies in the megahertz range are actuated either optically or electrically and detected optically by interferometry. We demonstrate room-temperature charge sensitivities down to 8 × 10–4 electrons per root hertz. The thinnest resonator consists

J. Scott Bunch; Arend M. Van der Zande; Scott S. Verbridge; Ian W. Frank; David M. Tanenbaum; Jeevak M. Parpia; Harold G. Craighead; Paul L. McEuen

2007-01-01

363

Texture and sheet forming  

SciTech Connect

The classical Marciniak-Kuczynski (Defect) theory, which consists in calculating the behavior of an initial defect in the sheet, in the form of a thin groove, is applied together with a full-constraints or relaxed-constraints theory of polycrystal viscoplasticity. Purpose of this is to investigate the effect of the induced texture on the Forming Limit Diagram (FLD), and the effect of grain shape as well. An alternative fast way of deriving FLD's is also proposed using a perturbation method. Comparisons are made between the results obtained by both Defect and Perturbation theories, in the case of ideal fcc rolling texture components, and in the case of polycrystals. 13 refs., 7 figs.

Canova, G.R.; Kocks, U.F.; Fressengeas, C.; Dudzinski, D.; Lequeu, Ph.; Sornberger, G.

1987-01-01

364

TGF-Beta and Breast Cancer Induction.  

National Technical Information Service (NTIS)

The breast produces inhibitors of mammary tumor formation. We hypothesized increases in the amount of these compounds would delay cancer onset. We study the molecule TGF-beta, which blocks cell growth. TGF-beta is produced as latent complex consisting of ...

B. B. Dabovic

2001-01-01

365

Current Sheets and Collisionless Damping in Kinetic Plasma Turbulence  

NASA Astrophysics Data System (ADS)

We present the first study of the formation and dissipation of current sheets at electron scales in a wave-driven, weakly collisional, three-dimensional kinetic turbulence simulation. We investigate the relative importance of dissipation associated with collisionless damping via resonant wave-particle interactions versus dissipation in small-scale current sheets in weakly collisional plasma turbulence. Current sheets form self-consistently from the wave-driven turbulence, and their filling fraction is well correlated to the electron heating rate. However, the weakly collisional nature of the simulation necessarily implies that the current sheets are not significantly dissipated via Ohmic dissipation. Rather, collisionless damping via the Landau resonance with the electrons is sufficient to account for the measured heating as a function of scale in the simulation, without the need for significant Ohmic dissipation. This finding suggests the possibility that the dissipation of the current sheets is governed by resonant wave-particle interactions and that the locations of current sheets correspond spatially to regions of enhanced heating.

TenBarge, J. M.; Howes, G. G.

2013-07-01

366

An electron-microscope study of beta-glucuronidase crystals.  

PubMed Central

beta-Glucuronidase from rat preputial glands was crystallized as thin sheets having p6 symmetry in projection with a equal 20.2nm. A filtered image was produced by Fourier methods to a resolution of 2.2 nm by averaging information from six areas. This suggests an approximately triangular molecular outline in projection, and this is taken to indicate a probable tetrahedral arrangement of the four subunits of the beta-glucuronidase molecule. Images PLATE 1

Dickson, M R; Stewart, M; Hawley, D E; Marsh, C A

1979-01-01

367

Penguin Fact Sheet.  

ERIC Educational Resources Information Center

|Presents factual information on penguins using an outline format. Includes descriptions of physical characteristics, behavioral mechanisms, geographical distribution, and physiological processes. Provides separate bibliographies for teachers and students. (ML)|

Flotsam and Jetsam: A Newsletter for Massachusetts Marine Educators, 1985

1985-01-01

368

Current sheets from Ulysses observation  

NASA Astrophysics Data System (ADS)

Current sheet is a significant source of solar wind MHD turbulence intermittency. It has long been recognized that these structures can arise from non-linear interactions of MHD turbulence. Alternatively, they may also be relic structures in the solar wind that have a solar origin, e.g., magnetic walls of flux tubes that separate solar wind plasma into distinct parcels. Identifying these structures in the solar wind is crucial to understanding the properties of the solar wind MHD turbulence. Using Ulysses observations we examine 3-year worth of solar wind magnetic field data when the Ulysses is at low latitude during solar minimum. Extending the previous work of Li (2007, 2008), we develop an automatic data analysis method of current sheet identification. Using this method, we identify more than 28000 current sheets. Various properties of the current sheet are obtained. These include the distributions of the deflection angle across the current sheet, the thickness of the current sheet and the waiting time statistics between current sheets.

Miao, B.; Peng, B.; Li, G.

2011-02-01

369

The comparative effectiveness of demineralized bone matrix, beta-tricalcium phosphate, and bovine-derived anorganic bone matrix on inflammation and bone formation using a paired calvarial defect model in rats  

PubMed Central

Background In this study, the effectiveness of Iranian Tissue Bank–produced demineralized bone matrix (ITB-DBM), beta-tricalcium phosphate (?TCP), and Bio-Oss® (Geistlich Pharma AG, Wolhusen, Switzerland) were evaluated and compared with double controls. The main goal was to measure the amount of new bone formation in the center of defects created in rat calvaria. Another goal was to compare the controls and evaluate the effects of each treatment material on their adjacent untreated (control) defects. Methods In this study, 40 male Wistar rats were selected and divided into four groups, In each group, there were ten rats with two defects in their calvarias; one of them is considered as control and the other one was treated with ITB-DBM (group 1), BIO-OSS (group2), and ?TCP (group 3), respectively. But in group 4, both defects were considered as control. The amount of inflammation and new bone formation were evaluated at 4 and 10 weeks. In the first group, one defect was filled with ITB-DBM; in the second group, one defect was filled with Bio-Oss; in the third group, one defect was filled with ?TCP; and in the fourth group, both defects were left unfilled. Zeiss microscope (Carl Zeiss AG, Oberkochen, Germany) and Image Tool® (version 3.0; University of Texas Health Science Center at San Antonio, San Antonio, TX) software were used for evaluation. SPSS Statistics (IBM Corp, Somers, NY) was used for statistical analysis. Results Maximum bone formation at 4 and 10 weeks were observed in the ITB-DBM group (46.960% ± 4.366%, 94.970% ± 0.323%), which had significant difference compared with the other groups (P < 0.001). Ranking second was the Bio-Oss group and third, the ?TCP group. Bone formation in the group with two unfilled defects was much more significant than in the other controls beside the Bio-Oss and ?TCP after 10 weeks (29.1 ± 2.065, 29.05 ± 1.649), while this group had the least bone formation compared with the other controls at week 4 (2.100% ± 0.758%, 1.630% ± 0.668%, P < 0.001). Conclusion Overall, the ITB-DBM group showed the best results, although the results for other experimental groups were unfavorable. The authors conclude that human DBM (ITB-DBM) should be offered as an alternative for bone regeneration in animals, such as horses, as well as in humans, especially for jaw reconstruction. In relation to bone regeneration in control defects, the effect of experimental material on controls was apparent during the initial weeks.

Khoshzaban, Ahad; Mehrzad, Shahram; Tavakoli, Vida; Keshel, Saeed Heidari; Behrouzi, Gholam Reza; Bashtar, Maryam

2011-01-01

370

Global distribution, structure, and solar wind control of low altitude current sheets at Mars  

NASA Astrophysics Data System (ADS)

We present the results of the first systematic survey of current sheets encountered by Mars Global Surveyor in its ˜400 km mapping orbit. We utilize an automated procedure to identify over 10,000 current sheet crossings during the ˜8 year mapping mission. The majority of these lie on the nightside and in the polar regions, but we also observe over 1800 current sheets at solar zenith angle <60°. The distribution and orientation of current sheets and their dependence on solar wind drivers suggests that most magnetotail current sheets have a local induced magnetospheric origin caused by magnetic field draping. On the other hand, most current sheets observed on the day side likely result from solar wind discontinuities advected through the martian system. However, the clustering of low altitude dayside current sheet crossings around the perimeters of strongly magnetized crustal regions, and the smaller than expected rotations in the IMF draping direction, suggest that crustal magnetic fields may also play an indirect role in their formation. The apparent thicknesses of martian current sheets, and the characteristics of electrons observed in and around the current sheets, suggest one of two possibilities. Martian current sheets at low altitudes are either stationary, with thicknesses of a few hundred km and currents carried by low energy (<10 eV) electrons, or they move at tens of km/s, with thicknesses of a few thousand km and currents carried by ions.

Halekas, J. S.; Brain, D. A.

2010-03-01

371

Structural and Functional Properties of Peptides Based on the N-terminus of HIV-1 gp41 and the C-terminus of the Amyloid-Beta Protein  

PubMed Central

Given their high alanine and glycine levels, plaque formation, ?-helix to ?-sheet interconversion and fusogenicity, FP (i.e., the N-terminal fusion peptide of HIV-1 gp41; 23 residues) and amyloids were proposed as belonging to the same protein superfamily. Here, we further test whether FP may exhibit ‘amyloid-like’ characteristics, by contrasting its structural and functional properties with those of A?(26–42), a 17-residue peptide from the C-terminus of the amyloid-beta protein responsible for Alzheimer’s. FTIR spectroscopy, electron microscopy, light scattering and predicted amyloid structure aggregation (PASTA) indicated that aqueous FP and A?(26–42) formed similar networked ?-sheet fibrils, although the FP fibril interactions were weaker. FP and A?(26–42) both lysed and aggregated human erythrocytes, with the hemolysis-onsets correlated with the conversion of ?-helix to ?-sheet for each peptide in liposomes. Congo red (CR), a marker of amyloid plaques in situ, similarly inhibited either FP- or A?(26–42)-induced hemolysis, and surface plasmon resonance indicated that this may be due to direct CR-peptide binding. These findings suggest that membrane-bound ?-sheets of FP may contribute to the cytopathicity of HIV in vivo through an amyloid-type mechanism, and support the classification of HIV-1 FP as an ‘amyloid homolog’ (or ‘amylog’).

Gordon, Larry M.; Nisthal, Alex; Lee, Andy B.; Eskandari, Sepehr; Ruchala, Piotr; Jung, Chun-Ling; Waring, Alan J.; Mobley, Patrick W.

2008-01-01

372

Effects of au plating on small-scale resistance spot welding of thin-sheet nickel  

Microsoft Academic Search

The effects of Au plating on joint formation and joint strength in small-scale resistance spot welding (SSRSW) of Ni sheets\\u000a have been investigated using tensile-shear testing, optical microscopy, scanning electron microscopy (SEM), and energy-dispersive\\u000a X-ray spectroscopy (EDX). The results show that the mechanisms of the joint formation during the welding of Au-plated Ni sheets\\u000a involve solid-state bonding, brazing, and fusion

W. Tan; Y. Zhou; H. W. Kerr

2002-01-01

373

Development of measurement technique for carbon atoms employing vacuum ultraviolet absorption spectroscopy with a microdischarge hollow-cathode lamp and its application to diagnostics of nanographene sheet material formation plasmas  

SciTech Connect

This study describes the development of a compact measurement technique for absolute carbon (C) atom density in processing plasmas, using vacuum ultraviolet absorption spectroscopy (VUVAS) employing a high-pressure CO{sub 2} microdischarge hollow-cathode lamp (C-MHCL) as the light source. The characteristics of the C-MHCL as a resonance line source of C atoms at 165.7 nm for VUVAS measurements of the absolute C atom density are reported. The emission line profile of the C-MHCL under typical operating conditions was estimated to be the Voigt profile with a DELTAnu{sub L}/DELTAnu{sub D} value of 2.5, where DELTAnu{sub L} is the Lorentz width and DELTAnu{sub D} is the Doppler width. In order to investigate the behavior of C and H atoms in the processing plasma used for the fabrication of two-dimensional nanographene sheet material, measurements of the atom densities were carried out using the VUVAS technique. The H atom density increased with increasing pressure, while the C atom density was almost constant at 5x10{sup 12} cm{sup -3}. The density ratio of C to H atoms in the plasma was found to influence the morphology of carbon nanowalls (CNWs). With increasing H/C density ratio, the growth rate decreased and the space between the walls of the CNWs became wider.

Takeuchi, Wakana; Sasaki, Hajime; Takashima, Seigo [Department of Electric Engineering and Computer Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Kato, Satoru; Hiramatsu, Mineo [Department of Electrical and Electronic Engineering, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468-8502 (Japan); Hori, Masaru [Department of Electric Engineering and Computer Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); JST, CREST, 4-1-8 Hon-chou, Kawaguchi, Saitama 332-0012 (Japan)

2009-06-01

374

Development of measurement technique for carbon atoms employing vacuum ultraviolet absorption spectroscopy with a microdischarge hollow-cathode lamp and its application to diagnostics of nanographene sheet material formation plasmas  

NASA Astrophysics Data System (ADS)

This study describes the development of a compact measurement technique for absolute carbon (C) atom density in processing plasmas, using vacuum ultraviolet absorption spectroscopy (VUVAS) employing a high-pressure CO2 microdischarge hollow-cathode lamp (C-MHCL) as the light source. The characteristics of the C-MHCL as a resonance line source of C atoms at 165.7 nm for VUVAS measurements of the absolute C atom density are reported. The emission line profile of the C-MHCL under typical operating conditions was estimated to be the Voigt profile with a ??L/??D value of 2.5, where ??L is the Lorentz width and ??D is the Doppler width. In order to investigate the behavior of C and H atoms in the processing plasma used for the fabrication of two-dimensional nanographene sheet material, measurements of the atom densities were carried out using the VUVAS technique. The H atom density increased with increasing pressure, while the C atom density was almost constant at 5×1012 cm-3. The density ratio of C to H atoms in the plasma was found to influence the morphology of carbon nanowalls (CNWs). With increasing H/C density ratio, the growth rate decreased and the space between the walls of the CNWs became wider.

Takeuchi, Wakana; Sasaki, Hajime; Kato, Satoru; Takashima, Seigo; Hiramatsu, Mineo; Hori, Masaru

2009-06-01

375

Double beta decay  

SciTech Connect

The subjects of the two-neutrino (2{nu}{beta}{beta}) and neutrinoless double beta (0{nu}{beta}{beta}) decays are introduced. The main theoretical and experimental issues related to the double beta decay are discussed. It is stressed that the study of the 0{nu}{beta}{beta} decay is the most important source of information about the Majorana nature of neutrinos. In addition, the 0{nu}{beta}{beta}-decay half-life can constrain the absolute neutrino mass-scale and the neutrino mass pattern. Morever, the Majorana CP-violating phases, which might be responsible for the matter asymmetry of the Universe, could be deduced from the measured 0{nu}{beta}{beta}-decay rate, once this process will be observed. One can conclude that the double beta decay is an important process for the fields of nuclear physics, particle physics, astrophysics and cosmology.

Stekl, Ivan [Institute of Experimental and Applied Physics, CTU in Prague, Horska 3a, 128 00 Prague 2 (Czech Republic)

2007-11-26

376

The Hofmeister effect on amyloid formation using yeast prion protein.  

PubMed

A variety of proteins are capable of converting from their soluble forms into highly ordered fibrous cross-beta aggregates (amyloids). This conversion is associated with certain pathological conditions in mammals, such as Alzheimer disease, and provides a basis for the infectious or hereditary protein isoforms (prions), causing neurodegenerative disorders in mammals and controlling heritable phenotypes in yeast. The N-proximal region of the yeast prion protein Sup35 (Sup35NM) is frequently used as a model system for amyloid conversion studies in vitro. Traditionally, amyloids are recognized by their ability to bind Congo Red dye specific to beta-sheet rich structures. However, methods for quantifying amyloid fibril formation thus far were based on measurements linking Congo Red absorbance to concentration of insulin fibrils and may not be directly applicable to other amyloid-forming proteins. Here, we present a corrected formula for measuring amyloid formation of Sup35NM by Congo Red assay. By utilizing this corrected procedure, we explore the effect of different sodium salts on the lag time and maximum rate of amyloid formation by Sup35NM. We find that increased kosmotropicity promotes amyloid polymerization in accordance with the Hofmeister series. In contrast, chaotropes inhibit polymerization, with the strength of inhibition correlating with the B-viscosity coefficient of the Jones-Dole equation, an increasingly accepted measure for the quantification of the Hofmeister series. PMID:19890987

Yeh, Victor; Broering, James M; Romanyuk, Andrey; Chen, Buxin; Chernoff, Yury O; Bommarius, Andreas S

2010-01-01

377

Chickenpox - Fact Sheet for Parents  

MedlinePLUS

... Immunizations Vaccines Home Vaccines & Preventable Diseases Chickenpox (Varicella) Vaccination Chickenpox - Fact Sheet for Parents Diseases and the Vaccines that Prevent Them Español: Varicela Printer friendly version[403 KB, 2 pages] Benefits of chickenpox vaccine Saves lives. Protects against serious ...

378

Analysis of a Sheet Silicate.  

ERIC Educational Resources Information Center

|Describes a student project in analytical chemistry using sheet silicates. Provides specific information regarding the use of phlogopite in an experiment to analyze samples for silicon, aluminum, magnesium, iron, potassium, and fluoride. (CS)|

Adams, J. M.; Evans, S.

1980-01-01

379

Pesticide Fact Sheet: Fish Oil.  

National Technical Information Service (NTIS)

This document contains up-to-date chemical information, including a summary of the Agency's regulatory position and rationale, on a specific pesticide or group of pesticides. A Fact Sheet is issued after registration of a significantly changed use pattern...

1998-01-01

380

Measurements and Characterization (Fact Sheet)  

SciTech Connect

Capabilities fact sheet for the National Center for Photovoltaics: Measurements and Characterization that includes scope, core competencies and capabilities, and contact/web information for Analytical Microscopy, Electro-Optical Characterization, Surface Analysis, and Cell and Module Performance.

Not Available

2011-06-01

381

New Pesticide Face Sheet: Fipronil.  

National Technical Information Service (NTIS)

This document contains up-to-date chemical information, including a summary of the Agency's regulatory position and rationale, on a specific pesticide or group of pesticides. A Fact Sheet is issued after Registration of a new chemical.

1996-01-01

382

Secondary conformations and temperature effect on structural transformation of amyloid beta (1-28), (1-40) and (1-42) peptides.  

PubMed

Secondary structure of three amyloid b-peptides [A beta(1-28), A beta(1-40) and A beta(1-42)] in the solid state was respectively determined by Fourier transform infrared (FT-IR) microspectroscopy. Their thermal-dependent structural transformation were also investigated by FT-IR microspectroscopy equipped with a thermal analyzer. The present result demonstrates that the solid-state A beta(1-28), A beta(1-40) and A beta(1-42) peptides showed a significant IR spectral difference in the amide I and II bands. The secondary conformation of A beta(1-28) peptide was the combination of major beta-sheet and minor alpha-helix with little random coil structures, but A beta(1-40) peptide showed the co-existence of major beta-sheet and minor random coil with little alpha-helix structures. A beta(1-42) peptide mainly consisted of the predominant b-sheet structure. Although the intact A beta(1-28), A beta(1-40) or A beta(1-42) peptide exhibits a different secondary structure, a similar beta-conformation may form after thermal treatment. A thermal-dependent transition was found for solid A beta(1-28) and A beta(1-40) peptides near 40 degrees C and 45 degrees C, respectively. There was no transition temperature for solid A beta(1-42) peptide, however, due to only a very little level of alpha-helix and random coil structure containing in the solid A beta(1-42) peptide. The thermal denaturation plays an important role in the structural transformation from alpha-helix/random coil to beta-sheet. PMID:12529158

Lin, Shan-Yang; Chu, Horng-Lun; Wei, Yen-Shan

2003-02-01

383

A Logical OR Redundancy within the Asx-Pro-Asx-Gly Type 1 {Beta}-Turn Motif  

SciTech Connect

Turn secondary structure is essential to the formation of globular protein architecture. Turn structures are, however, much more complex than either {alpha}-helix or {beta}-sheet, and the thermodynamics and folding kinetics are poorly understood. Type I {beta}-turns are the most common type of reverse turn, and they exhibit a statistical consensus sequence of Asx-Pro-Asx-Gly (where Asx is Asp or Asn). A comprehensive series of individual and combined Asx mutations has been constructed within three separate type I 3:5 G1 bulge {beta}-turns in human fibroblast growth factor-1, and their effects on structure, stability, and folding have been determined. The results show a fundamental logical OR relationship between the Asx residues in the motif, involving H-bond interactions with main-chain amides within the turn. These interactions can be modulated by additional interactions with residues adjacent to the turn at positions i + 4 and i + 6. The results show that the Asx residues in the turn motif make a substantial contribution to the overall stability of the protein, and the Asx logical OR relationship defines a redundant system that can compensate for deleterious point mutations. The results also show that the stability of the turn is unlikely to be the prime determinant of formation of turn structure in the folding transition state.

Lee, Jihun; Dubey, Vikash Kumar; Longo, Lian M.; Blaber, Michael (FSU)

2008-04-19

384

Absorption of Beta Particles in Different Materials: An Undergraduate Experiment  

ERIC Educational Resources Information Center

|The absorption of beta rays from a radioactive source in different materials was investigated by the use of a simple setup based on a Geiger counter and a set of absorber sheets. The number of electrons traversing the material was measured as a function of its thickness. Detailed GEANT simulations were carried out to reproduce the obtained…

La Rocca, Paola; Riggi, Francesco

2009-01-01

385

Crib sheets or security blankets?  

PubMed

This article describes the sanctioned use of crib sheets as a nursing intervention to decrease test anxiety when the classroom is the practice setting for psychiatric/mental health nursing faculty. The products that the students created offered additional unsuspected benefits. The faculty were convinced that the use of crib sheets can be a sound intervention to reduce students' test-taking anxiety. PMID:9661379

Drake, V K; Freed, P; Hunter, J M

386

Energy information sheets, July 1998  

SciTech Connect

The National Energy Information Center (NEIC), as part of its mission, provides energy information and referral assistance to Federal, State, and local governments, the academic community, business and industrial organizations, and the public. The Energy Information Sheets was developed to provide general information on various aspects of fuel production, prices, consumption, and capability. Additional information on related subject matter can be found in other Energy Information Administration (EIA) publications as referenced at the end of each sheet.

NONE

1998-07-01

387

Energy information sheets, September 1996  

SciTech Connect

The National Energy Information Center (NEIC), as part of its mission, provides energy information and referral assistance to Federal, State, and local governments, the academic community, business and industrial organizations, and the public. The Energy Information Sheets was developed to provide general information on various aspects of fuel production, prices, consumption, and capability. Additional information on related subject matter can be found in other Energy Information Administration (EIA) publications as referenced at the end of each sheet.

NONE

1996-09-01

388

Electroslag remelting during production of sheet steel  

Microsoft Academic Search

Electroslag remelting is the most efficient method of obtaining sheet and slab ingots for further conversion to rolled sheet steel of especially high quality. The method can be used to produce rectangular sheet ingots with flat sides for rolling on slabbing mills and with convex narrow sides for conversion on blooming mills, and to obtain sheet ingots and also slab

B. Y. Paton; B. I. Medovar; G. E. Tsukanov

1974-01-01

389

Dynamic behavior of liquid sheets  

NASA Astrophysics Data System (ADS)

An experiment was conducted to study the aerodynamic instability of liquid sheets issuing from a two-dimensional air-assisted nozzle. Detailed measurements of the frequency of oscillation of the liquid sheet have been made. The measured vibrational frequencies were then correlated with the resulting spray angle. It was shown that the liquid sheet oscillations are dynamically similar to that of hard spring systems. For each air pressure, three distinct modes of breakup are distinguished. At low liquid flow rates, both the sinusoidal and the dilational modes are superimposed on the liquid sheet. With a further increase in liquid flow rate, the liquid sheet oscillations mainly become of the dilational type. It was also shown that the effect of introducing air in the nozzle is similar to the effect of inducing forced vibrations on the nozzle jaws. Thus, for each air flow rate, there is a specific vibration frequency for the nozzle. The frequency of these vibrations is proportional to the air velocity. As the liquid sheet natural frequency approaches that of the nozzle, resonance is established. At resonance, the maximum spray angle is achieved.

Mansour, Adel; Chigier, Norman

1991-12-01

390

Interrupted hydrogen/deuterium exchange reveals the stable core of the remarkably helical molten globule of alpha-beta parallel protein flavodoxin.  

PubMed

Kinetic intermediates that appear early during protein folding often resemble the relatively stable molten globule intermediates formed by several proteins under mildly denaturing conditions. Molten globules have a substantial amount of secondary structure but lack virtually all tertiary side-chain packing characteristics of natively folded proteins. Due to exposed hydrophobic groups, molten globules are prone to aggregation, which can have detrimental effects on organisms. The molten globule that is observed during folding of alpha-beta parallel flavodoxin from Azotobacter vinelandii is a remarkably non-native species. This folding intermediate is helical and contains no beta-sheet and is kinetically off-pathway to the native state. It can be trapped under native-like conditions by substituting residue Phe(44) for Tyr(44). To characterize this species at the residue level, in this study, use is made of interrupted hydrogen/deuterium exchange detected by NMR spectroscopy. In the molten globule of flavodoxin, the helical region comprising residues Leu(110)-Val(125) is shown to be better protected against exchange than the other ordered parts of the folding intermediate. This helical region is better buried than the other helices, causing its context-dependent stabilization against unfolding. Residues Leu(110)-Val(125) thus form the stable core of the helical molten globule of alpha-beta parallel flavodoxin, which is almost entirely structured. Non-native docking of helices in the molten globule of flavodoxin prevents formation of the parallel beta-sheet of native flavodoxin. Hence, to produce native alpha-beta parallel protein molecules, the off-pathway species needs to unfold. PMID:19959481

Nabuurs, Sanne M; van Mierlo, Carlo P M

2009-12-03

391

Global ice-sheet system interlocked by sea level  

SciTech Connect

Denton and Hughes postulated that sea level linked a global ice-sheet system with both terrestrial and grounded marine components during later Quaternary ice ages. Summer temperature changes near Northern Hemisphere melting margins initiated sea-level fluctuations that controlled marine components in both polar hemispheres. It was further proposed that variations of this ice-sheet system amplified and transmitted Milankovitch summer half-year insolation changes between 45 and 75/sup 0/N into global climatic changes. New tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the Antarctic Ice Sheet. But factors other than areal changes of the grounded Antarctic Ice Sheet may have strongly influenced Southern Hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres. Atmospheric carbon dioxide linked to high-latitude oceans is the most likely candidate, but another potential influence was high-frequency climatic oscillations. It is postulated that variations in atmospheric carbon dioxide acted through an Antarctic ice shelf linked to the grounded ice sheet to produce and terminate Southern Hemisphere ice-age climate. It is further postulated that Milankovitch summer insolation combined with a warm-high frequency oscillation caused marked recession of Northern Hemisphere ice-sheet melting margins and the North Atlantic polar front about 14,000 /sup 14/C yr B.P. This permitted renewed formation of North Atlantic Deep Water, which could well have controlled atmospheric carbon dioxide. Combined melting and consequent sea-level rise from the three warming factors initiated irreversible collapse of the interlocked global ice-sheet system, which was at its largest but most vulnerable configuration.

Denton, G.H.; Hughes, T.J.; Karlen, W.

1986-01-01

392

Quantum mechanical studies on model ?-pleated sheets  

PubMed Central

Pauling and Corey proposed a pleated-sheet configuration, now called ?-sheet, as one of the protein secondary structures in addition to ?-helix and ?-sheet. Recently, it has been suggested that ?-sheet is a common feature of amyloidogenic intermediates. We have investigated the stability of anti-parallel ?-sheet and two conformations of ?-sheet in solution phase using the density functional theoretical method. The peptides are modeled as two-strand Acetyl-(Ala)2-N-methylamine. Using stages of geometry optimization and single point energy calculation at B3LYP/cc-pVTZ//B3LYP/6-31G* level and including zero-point energies, thermal, and entropic contribution, we have found that ?-sheet is the most stable conformation, while the ?-sheet proposed by Pauling and Corey has 13.6 kcal/mol higher free energy than the ?-sheet. The ?-sheet that resembles the structure observed in molecular dynamics simulations of amyloidogenic proteins at low pH becomes distorted after stages of geometry optimization in solution. Whether the ?-sheets with longer chains would be increasingly favorable in water relative to the increase in internal energy of the chain needs further investigation. Different from the quantum mechanics results, AMBER parm94 force field gives small difference in solution phase energy between ?-sheet and ?-sheet. The predicted amide I IR spectra of ?-sheet shows the main band at higher frequency than ?-sheet.

Wu, Hao; Canfield, Alana; Adhikari, Jhashanath; Huo, Shuanghong

2009-01-01

393

Uncharged thioflavin-T derivatives bind to amyloid-beta protein with high affinity and readily enter the brain  

Microsoft Academic Search

In vivo assessment of the beta-sheet proteins deposited in amyloid plaques (A? peptide) or neurofibrillary tangles (tau protein) presents a target for the development of biological markers for Alzheimer's disease (AD). In an effort to develop in vivo beta-sheet imaging probes, derivatives of thioflavin-T (ThT) were synthesized and evaluated. These compounds lack the positively charged quaternary heterocyclic nitrogen of ThT

William E. Klunk; Yanming Wang; Guo-feng Huang; Manik L. Debnath; Daniel P. Holt; Chester A. Mathis

2001-01-01

394

Reversible Unfolding of ?-Sheets in Membranes: A Calorimetric Study  

PubMed Central

The hexapeptide acetyl-Trp-Leu5 (AcWL5) has the remarkable ability to assemble reversibly and spontaneously into ?-sheets on lipid membranes as a result of monomer partitioning followed by cooperative assembly This system provides a unique opportunity to study the thermodynamics of protein folding in membranes, which we have done using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). The results, which may represent the first example of reversible thermal unfolding of peptides in membranes, help to define the contribution of hydrogen bonding to the extreme thermal stability of membrane proteins. ITC revealed that the enthalpy change for partitioning of monomeric, unstructured AcWL5 from water into membranes was zero within experimental error over the temperature range of 5 °C to 75 °C. DSC showed that the ?-sheet aggregates underwent a reversible, endothermic, and very asymmetric thermal transition with a concentration-dependent transition temperature (Tm) in the range of 60 °C to 80 °C. A numerical model of nucleation and growth-dependent assembly of oligomeric ?-sheets, proposed earlier to describe ?-sheet formation in membranes, recreated remarkably well the unusual shape and concentration-dependence of the transition peaks. The enthalpy for thermal unfolding of AcWL5 ?-sheets in the membrane was found to be about 8(±1) kcal mol?1, or about 1.3(±0.2) kcal mol?1 per residue.

Wimley, William C.; White, Stephen H.

2010-01-01

395

Interaction between inclined current sheets and the heliospheric termination shock  

NASA Astrophysics Data System (ADS)

Using two-dimensional hybrid simulations we study the interaction between the Heliospheric Current Sheet (HCS) and the solar wind termination shock (TS). Hot flow anomalies (HFA) are regions of hot, deflected and disturbed plasma flow which may form at the intersection of a shock and current sheet. We study the role played by the inclination, $\\theta$Cn, of the current sheet relative to the shock normal. As previously found, low values of $\\theta$Cn are associated with HFA formation. We find that as $\\theta$Cn increases the HFA is modified, until at $\\theta$Cn = 60° it disappears completely. Thus, HFAs are unlikely to be formed near the TS since the HCS is highly inclined relative to the radial direction ($\\theta$Cn > 60°). We also find that some suprathermal particles, particularly interstellar pickup ions, are trapped near the intersection point of the shock and current sheet where they gain considerable energy, and subsequently drift along the current sheet upstream of the shock. This process is more effective for larger values of $\\theta$Cn. Thus, we expect that upstream of the TS there are likely to be high-energy particles (energized pickup ions) associated with crossings of the HCS, but only of the particular magnetic reversal polarity associated with HFAs. This may be relevant to recently reported Voyager observations.

Giacalone, Joe; Burgess, David

2010-10-01

396

Neoproterozoic ice sheets of the Siberian Platform: U-Pb-LA-ICP-MS ages of detrital zircons from the Bol'shoi Patom formation and the geotectonic position of its provenance  

NASA Astrophysics Data System (ADS)

The centers of many Neoproterozoic and Phanerozoic glaciations were located on cratons and crystalline shields not necessarily, as some researchers believe, associated with rifts. An example is the Vendian Bol'shoi Patom glacial formation (Lena River, Yakutia). The U-Pb ages of detrital zircons from this formation imply that it was deposited by glaciers located on the pre-Riphean crystalline shields of the Siberian Platform. Glaciation in this region occurred after cessation of rifting and could not be related to the latter. The Bol'shoi Patom Formation is an element of the Middle Siberian glacial horizon that was deposited during the Marino Glaciation and is traceable along the southern periphery of the Siberian Platform from the Aldan Shield to the Baikal and Sayany regions. This indicates that the Marinoan Glaciation in Siberia involved at least the entire southern part of the Siberian Platform. Rifting was not the single, or even a principal, factor responsible for glaciations, although it could accompany and enhance them simultaneously providing space for sedimentation and conditions for preserving glacial deposits from erosion.

Chumakov, N. M.; Linnemann, U.; Hofmann, M.; Pokrovskii, B. G.

2011-12-01

397

Mechanics of Sheeting Joints and Spheroidal Weathering (Invited)  

NASA Astrophysics Data System (ADS)

Physical weathering in low-porosity materials, like most crystalline rocks, commonly involves fracture, which increases the surface area that can be accessed by reactive chemicals. Chemical reactions on these surfaces can in turn affect the course of further fracturing. Physical and chemical weathering thus commonly go hand in hand, although one process can dominate the other. Two common products of physical weathering are sheeting joints and spheroidal weathering. Both involve fracturing parallel or subparallel to a nearby surface, but they are distinctly different in several ways. Sheeting joints can achieve dimensions of a couple of hundred meters, typically have radii of curvature of 100m - 1000m, and are bounded on one side by the topographic surface. As the distance from the topographic surface increases, the spacing between sheeting joints generally increases and they become less curved. Neither chemical weathering nor grain-scale effects appear to be consequential in the formation of sheeting joints. In contrast, for spheroidal weathering the individual fractures are roughly grain-sized, form in “shells” with radii of curvature of about 1m, and are bounded on all sides by pre-existing bedrock fractures. As the distance from the bounding surfaces increases, the spacing between fractures generally stays about the same but the “shells” defined by the fractures become more curved. Both chemical weathering and grain-scale cracking accompany spheroidal weathering. The processes of sheeting joint formation and spheroidal weathering have been approached from the perspective of a complete boundary value problem in continuum mechanics, where several factors generally are needed to predict the physical failure of a rock mass, including: (a) the shape of a rock body; (b) the stresses acting on its surface, (c) the body forces within it, and (d) the equations of equilibrium; and (e) the constitutive laws for the material. In the cases of sheeting joint formation and spheroidal weathering, a simpler approach that depends on only four factors can be used to provide insight into the fracture process: (a) the shape of a rock body; (b) the stress distribution parallel to its surface, (c) the body forces within it, and (d) a single equation of equilibrium. This approach indicates that in both cases high compressive stresses parallel to convex bounding surfaces contribute fundamentally to the formation of the fractures. In at least some cases involving sheeting joints, the origin of these stresses is likely to be tectonic. In the case of spheroidal weathering, the compressive stresses are likely to arise from chemical alteration of grains.

Martel, S. J.

2010-12-01

398

Greenland Ice Sheet’s response to global warming (Invited)  

NASA Astrophysics Data System (ADS)

Air temperatures along the west coast on the Greenland ice sheet have increased by 2 deg. C per decade since 1991, with largest warming during the winter months. The ice sheet melt area increased by 20% since 1979, and the increase in bare ice area is unmistakable at 13% per year. Warm summers and extended melt seasons are to blame for 3.5 m surface lowering at the long-term equilibrium line altitude, (1100 m elevation at 70 deg. N) between 2000 and 2007. The precipitation does not show a clear trend and varies between 30 cm and 200 cm annual snow accumulation at the equilibrium line altitude along the western slope of the ice sheet, 1979-2008. Increase in ice velocity in the ablation region and the concurrent increase in melt water suggests that water penetrates to great depth through moulins and cracks, lubricating the bottom of the ice sheet. The mass balance of the Greenland ice sheet has been negative for the past decade and the ice loss seems to be accelerating in recent years. Some of the ice loss can be explained by increase in surface melting (40%), however, ocean-ice interaction and ice dynamics play a major role. Several glaciers located north of Jakobshavn Isbrea (70 N) have increased flow velocities and loosing considerable ice volume to the ocean. New insight was gained of subsurface hydrologic channels and cavities using new instrumentation and a video system during the melt peak in August 2006-2009. Volume and geometry of a 100 m deep moulin were mapped with a rotating laser, and photographs with digital cameras. Sub-glacial hydrologic channels were investigated and filmed using a tethered, autonomous system, several hundred meters into the ice. These new results will be discussed in view of the rapid increase in melt area and mass loss of the Greenland ice sheet due to increasing air temperatures.

Steffen, K.

2009-12-01

399

Osteoblast-like cell proliferation on tape-cast and sintered tricalcium phosphate sheets.  

PubMed

The influence of sintering temperature on the in vitro proliferation of osteoblast-like cells to sintered tricalcium phosphate (TCP) sheets prepared by tape-casting was investigated. Green sheets of tape-cast beta-TCP were sintered for 2h in a furnace at atmospheric pressure at five different sintering temperatures: 900, 1000, 1100, 1150 and 1200 degrees C. The number of osteoblast-like (MC3T3-E1) cells deposited onto TCP sheets was counted after cell cultivation for 1week and was found to have increased with increasing sintering temperature. The TCP sheets sintered at 900 degrees C exhibited a significantly lower cell number than TCP sheets sintered at 1000, 1100, 1150 and 1200 degrees C. In the attenuated total reflection infrared spectra, the peaks around 900-1150cm(-1), corresponding to the P-O vibration mode of the phosphate group, gradually decreased and shifted to lower wavenumbers with increasing sintering temperature. Meanwhile, the zeta potential of TCP sintered at 900 degrees C showed a highly negative charge when compared with the other groups. This would suggest that the higher solubility of the TCP sheets sintered at 900 degrees C exerted the higher negative charge obtained from zeta potential measurement. Within the limitations of this study, it was indicated that osteoblast-like cell proliferation increased with increasing sintering temperature. The biological stability of the sintered TCP sheet surface was considered to have affected cell proliferation. PMID:18054299

Tanimoto, Yasuhiro; Shibata, Yo; Kataoka, Yu; Miyazaki, Takashi; Nishiyama, Norihiro

2007-10-13

400

Three-dimensional evolution of the fast reconnection mechanism in a force-free current sheet  

SciTech Connect

As a sequence of the recent paper on the fast reconnection evolution in a sheared current sheet [M. Ugai, Phys. Plasmas 17, 032313 (2010)], the present paper further studies the three-dimensional fast reconnection evolution in a force-free current sheet system. In general, for the larger sheared field magnitude, the fast reconnection evolution requires the larger spatial scales of the curr