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1

Hydrophobic interactions and hydrogen bonds in \\beta-sheet formation  

E-print Network

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 \\beta-sheet formation. We make use of a periodic boundary condition setup in which individual peptides are infinitely long and stretched. Dimers adopt \\beta-sheet conformations at short interpeptide distances (\\xi ~ 0.5 nm) and at intermediate distances (~ 0.8 nm), valine and leucine homodimers assume cross-\\beta-like conformations with side chains interpenetrating each other. These two states are identified as minima in the Potential of Mean Force (PMF). 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 \\beta-sheet structures from extended conformations is not driven by hydrogen bonds. This is supported by...

Narayanan, Chitra

2013-01-01

2

Non-native beta-sheet formation: insights into protein amyloidosis  

E-print Network

Protein amyloidosis is a cytopathological process characterized by the formation of highly beta-sheet-rich fibrils. How this process occurs and how to prevent/treat the associated diseases are not completely understood. Here, we carry out a theoretical investigation of sequence-independent beta-sheet formation, based on recent findings regarding the cooperativity of hydrogen-bond network formation. Our results strongly suggest that in vivo beta-sheet aggregation is induced by inter-sheet stacking dynamics. This leads to a prediction for the minimal length of susceptible polymer needed to form such an aggregate. Remarkably, the prediction corresponds quite well with the critical lengths detected in poly-glutamine-related diseases. Our work therefore provides a theoretical framework capable of understanding the underlying mechanism and shedding light on therapy strategies of protein amyloidosis.

Chinlin Guo; Herbert Levine; David A. Kessler

2002-03-08

3

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

4

Sequence specificity, statistical potentials, and three-dimensional structure prediction with self-correcting distance geometry calculations of beta-sheet formation in proteins.  

PubMed Central

A statistical analysis of a representative data set of 169 known protein structures was used to analyze the specificity of residue interactions between spatial neighboring strands in beta-sheets. Pairwise potentials were derived from the frequency of residue pairs in nearest contact, second nearest and third nearest contacts across neighboring beta-strands compared to the expected frequency of residue pairs in a random model. A pseudo-energy function based on these statistical pairwise potentials recognized native beta-sheets among possible alternative pairings. The native pairing was found within the three lowest energies in 73% of the cases in the training data set and in 63% of beta-sheets in a test data set of 67 proteins, which were not part of the training set. The energy function was also used to detect tripeptides, which occur frequently in beta-sheets of native proteins. The majority of native partners of tripeptides were distributed in a low energy range. Self-correcting distance geometry (SECODG) calculations using distance constraints sets derived from possible low energy pairing of beta-strands uniquely identified the native pairing of the beta-sheet in pancreatic trypsin inhibitor (BPTI). These results will be useful for predicting the structure of proteins from their amino acid sequence as well as for the design of proteins containing beta-sheets. PMID:10048326

Zhu, H.; Braun, W.

1999-01-01

5

The Promiscuity of [beta]-Strand Pairing Allows for Rational Design of [beta]-Sheet Face Inversion  

SciTech Connect

Recent studies suggest the dominant role of main-chain H-bond formation in specifying {beta}-sheet topology. Its essentially sequence-independent nature implies a large degree of freedom in designing {beta}-sheet-based nanomaterials. Here we show rational design of {beta}-sheet face inversions by incremental deletions of {beta}-strands from the single-layer {beta}-sheet of Borrelia outer surface protein A. We show that a {beta}-sheet structure can be maintained when a large number of native contacts are removed and that one can design large-scale conformational transitions of a {beta}-sheet such as face inversion by exploiting the promiscuity of strand-strand interactions. High-resolution X-ray crystal structures confirmed the success of the design and supported the importance of main-chain H-bonds in determining {beta}-sheet topology. This work suggests a simple but effective strategy for designing and controlling nanomaterials based on {beta}-rich peptide self-assemblies.

Makabe, Koki; Koide, Shohei (UC)

2009-06-17

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

Bayesian Models and Algorithms for Protein Beta-Sheet Prediction  

E-print Network

0 Bayesian Models and Algorithms for Protein Beta-Sheet Prediction Zafer Aydin, Student Member of -sheet prediction defined as the prediction of -strand pairings, interaction types (parallel or anti acid pairing potentials with a priori knowledge of -strand organizations. To select the optimum -sheet

Erdogan, Hakan

8

Hydrophobic interactions and hydrogen bonds in ?-sheet formation  

E-print Network

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 \\beta-sheet formation. We make use of a periodic boundary condition setup in which individual peptides are infinitely long and stretched. Dimers adopt \\beta-sheet conformations at short interpeptide distances (\\xi ~ 0.5 nm) and at intermediate distances (~ 0.8 nm), valine and leucine homodimers assume cross-\\beta-like conformations with side chains interpenetrating each other. These two states are identified as minima in the Potential of Mean Force (PMF). 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 \\beta-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 \\beta-sheet formation based on computed enthalpy and entropy and we show that they are different for peptides with small and large side chains.

Chitra Narayanan; Cristiano L. Dias

2013-08-22

9

Beating the Heat - Fast Scanning Melts Silk Beta Sheet Crystals  

NASA Astrophysics Data System (ADS)

Beta-pleated-sheet crystals are among the most stable of protein secondary structures, and are responsible for the remarkable physical properties of many fibrous proteins, such as silk, or proteins forming plaques as in Alzheimer's disease. Previous thinking, and the accepted paradigm, was that beta-pleated-sheet crystals in the dry solid state were so stable they would not melt upon input of heat energy alone. Here we overturn that assumption and demonstrate that beta-pleated-sheet crystals melt directly from the solid state to become random coils, helices, and turns. We use fast scanning chip calorimetry at 2,000 K/s and report the first reversible thermal melting of protein beta-pleated-sheet crystals, exemplified by silk fibroin. The similarity between thermal melting behavior of lamellar crystals of synthetic polymers and beta-pleated-sheet crystals is confirmed. Significance for controlling beta-pleated-sheet content during thermal processing of biomaterials, as well as towards disease therapies, is envisioned based on these new findings.

Cebe, Peggy; Hu, Xiao; Kaplan, David L.; Zhuravlev, Evgeny; Wurm, Andreas; Arbeiter, Daniela; Schick, Christoph

2013-01-01

10

Beating the Heat - Fast Scanning Melts Silk Beta Sheet Crystals  

PubMed Central

Beta-pleated-sheet crystals are among the most stable of protein secondary structures, and are responsible for the remarkable physical properties of many fibrous proteins, such as silk, or proteins forming plaques as in Alzheimer's disease. Previous thinking, and the accepted paradigm, was that beta-pleated-sheet crystals in the dry solid state were so stable they would not melt upon input of heat energy alone. Here we overturn that assumption and demonstrate that beta-pleated-sheet crystals melt directly from the solid state to become random coils, helices, and turns. We use fast scanning chip calorimetry at 2,000?K/s and report the first reversible thermal melting of protein beta-pleated-sheet crystals, exemplified by silk fibroin. The similarity between thermal melting behavior of lamellar crystals of synthetic polymers and beta-pleated-sheet crystals is confirmed. Significance for controlling beta-pleated-sheet content during thermal processing of biomaterials, as well as towards disease therapies, is envisioned based on these new findings. PMID:23350037

Cebe, Peggy; Hu, Xiao; Kaplan, David L.; Zhuravlev, Evgeny; Wurm, Andreas; Arbeiter, Daniela; Schick, Christoph

2013-01-01

11

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

E-print Network

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 ...

Qin, Zhao

12

Protein Beta-Sheets Predicted in 1951 by Pauling et Al. using standard bond length and  

E-print Network

-Sheets #12;Beta-Bulge #12;Beta-Helix PDB code 1QCX #12;Beta-Propeller PDB code 1HXN #12;Beta-Sandwich PDB code 2RHE #12;Beta-Barrel BetaBarrel (1TIM) #12;Beta-Barrel PDB code 1TIM #12;"The fact that natural

Guermeur, Yann

13

Current Sheet Formation and Reconnection Dynamics in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current sheet formation is a necessary consequence of the evolution of the multi-polar magnetic field topologies that are ubiquitous throughout the solar corona. We present a very high-resolution study of 3D MHD current sheet formation and the resulting reconnection dynamics in an environment appropriate for the corona. The initial field consists of a translationally invariant, potential field with a null-point topology (i.e., 4-flux systems) and a low-beta plasma. A finite-extent, 3D Syrovatskii-type current sheet forms as a result of stressing of this system by a uniform, incompressible flow applied at the line-tied photospheric boundary. The system is assumed to be ideal, except for the presence of numerical resistivity. The fully 3-D evolution is calculated with very high resolution (9x and 10x refinement across the full extent of the current sheet) using the Adaptively Refined MHD Solver (ARMS). The initial evolution of this computationally-intensive simulation results in a current sheet with a nearly 30-to-1 aspect ratio, a significant fraction of the system characteristic length, that unexpectedly appears to be stable. In addition, up to this point in the evolution any magnetic reconnection that we observe is of the slow Sweet-Parker type. We expect, however, that as we continue stressing the field, the current sheet will become unstable and develop explosive dynamics. We discuss the implications of our results on coronal structure and activity, such as heating and eruptions. This work has been supported, in part, by the NASA HTP and SR&T programs.

Edmondson, Justin K.; Antiochos, S. K.; DeVore, C.; Zurbuchen, T. H.

2009-05-01

14

Role of Polyalanine Domains in -Sheet Formation in Spider Silk Block Copolymers  

SciTech Connect

Genetically engineered spider silk-like block copolymers were studied to determine the influence of polyalanine domain size on secondary structure. The role of polyalanine block distribution on {beta}-sheet formation was explored using FT-IR and WAXS. The number of polyalanine blocks had a direct effect on the formation of crystalline {beta}-sheets, reflected in the change in crystallinity index as the blocks of polyalanines increased. WAXS analysis confirmed the crystalline nature of the sample with the largest number of polyalanine blocks. This approach provides a platform for further exploration of the role of specific amino acid chemistries in regulating the assembly of {beta}-sheet secondary structures, leading to options to regulate material properties through manipulation of this key component in spider silks.

Rabotyagova, O.; Cebe, P; Kaplan, D

2010-01-01

15

Events in the kinetic folding pathway of a small, all beta-sheet protein.  

PubMed

The folding of cardiotoxin analogue III (CTX III), a small (60 amino acids), all beta-sheet protein from the venom of the Taiwan Cobra (Naja naja atra) is here investigated. The folding kinetics is monitored by using a variety of techniques such as NMR, fluorescence, and circular dichroism spectroscopy. The folding of the protein is complete within a time scale of 200 ms. The earliest detectable event in the folding pathway of CTX III is the formation of a hydrophobic cluster, which possess strong affinity to bind to nonpolar dye such as 1-anilino-8-napthalene-sulfonic acid. Quenched-flow deuterium-hydrogen exchange experiments indicate that the segment spanning residues 51-55 along with Lys23, Ile39, Val49, Tyr51 and Val52 could constitute the "hydrophobic cluster." Folding kinetics of CTX III based on the amide-protection data reveals that the triple-stranded, antiparallel beta-sheet segment, which is located in the central core of the molecule, appears to fold faster than the double-stranded beta-sheet segment. PMID:9553067

Sivaraman, T; Kumar, T K; Chang, D K; Lin, W Y; Yu, C

1998-04-24

16

Stability and folding properties of a model beta-sheet protein, Escherichia coli CspA.  

PubMed Central

Although beta-sheets represent a sizable fraction of the secondary structure found in proteins, the forces guiding the formation of beta-sheets are still not well understood. Here we examine the folding of a small, all beta-sheet protein, the E. coli major cold shock protein CspA, using both equilibrium and kinetic methods. The equilibrium denaturation of CspA is reversible and displays a single transition between folded and unfolded states. The kinetic traces of the unfolding and refolding of CspA studied by stopped-flow fluorescence spectroscopy are monoexponential and thus also consistent with a two-state model. In the absence of denaturant, CspA refolds very fast with a time constant of 5 ms. The unfolding of CspA is also rapid, and at urea concentrations above the denaturation midpoint, the rate of unfolding is largely independent of urea concentration. This suggests that the transition state ensemble more closely resembles the native state in terms of solvent accessibility than the denatured state. Based on the model of a compact transition state and on an unusual structural feature of CspA, a solvent-exposed cluster of aromatic side chains, we propose a novel folding mechanism for CspA. We have also investigated the possible complications that may arise from attaching polyhistidine affinity tags to the carboxy and amino termini of CspA. PMID:9521124

Reid, K. L.; Rodriguez, H. M.; Hillier, B. J.; Gregoret, L. M.

1998-01-01

17

Folding dynamics of a family of beta-sheet proteins  

NASA Astrophysics Data System (ADS)

Fatty acid binding proteins (FABP) consist of ten anti-parallel beta strands and two small alpha helices. The beta strands are arranged into two nearly orthogonal five-strand beta sheets that surround the interior cavity, which binds unsaturated long-chain fatty acids. In the brain isoform (BFABP), these are very important for the development of the central nervous system and neuron differentiation. Furthermore, BFABP is implicated in the pathogenesis of a variety of human diseases including cancer and neuronal degenerative disorders. In this work, site-directed spin labeling combined with EPR techniques have been used to study the folding mechanism of BFABP. In the first series of studies, we labeled the two Cys residues at position 5 and 80 in the wild type protein with an EPR spin marker; in addition, two singly labeled mutants at positions 5 and 80 in the C80A and C5A mutants, respectively, were also produced and used as controls. The changes in the distances between the two residues were examined by a pulsed EPR method, DEER (Double Electron Electron Resonance), as a function of guanidinium hydrochloride concentration. The results were compared with those from CW EPR, circular dichroism and fluorescence measurements, which provide the information regarding sidechain mobility, secondary structure and tertiary structure, respectively. The results will be discussed in the context of the folding mechanism of the family of fatty acid binding proteins.

Rousseau, Denis

2008-03-01

18

Diffraction from the beta-sheet crystallites in spider silk  

E-print Network

We analyze the wide angle x-ray scattering from oriented spider silk fibers in terms of a quantitative scattering model, including both structural and statistical parameters of the $\\beta$-sheet crystallites of spider silk in the amorphous matrix. The model is based on kinematic scattering theory and allows for rather general correlations of the positional and orientational degrees of freedom, including the crystallite's size, composition and dimension of the unit cell. The model is evaluated numerically and compared to experimental scattering intensities allowing us to extract the geometric and statistical parameters. We show explicitly that for the experimentally found mosaicity (width of the orientational distribution) inter-crystallite effects are negligible and the data can be analyzed in terms of single crystallite scattering, as is usually assumed in the literature.

Stephan Ulrich; Anja Glišovi?; Tim Salditt; Annette Zippelius

2008-11-25

19

Structural characterization of adsorbed helical and beta-sheet peptides  

NASA Astrophysics Data System (ADS)

Adsorbed peptides on surfaces have potential applications in the fields of biomaterials, tissue engineering, peptide microarrays and nanobiotechnology. The surface region, the "biomolecular interface" between a material and the biological environment, plays a crucial role in these applications. As a result, characterization of adsorbed peptide structure, especially with respect to identity, concentration, spatial distribution, conformation and orientation, is important. The present research employs NEXAFS (near-edge X-ray absorption fine structure spectroscopy) and SFG (sum frequency generation spectroscopy) to provide information about the adsorbed peptide structure. Soft X-ray NEXAFS is a synchrotron-based technique which typically utilizes polarized X-rays to interrogate surfaces under ultra-high vacuum conditions. SFG is a non-linear optical technique which utilizes a combination of a fixed visible and a tunable infrared laser beams to generate a surface-vibrational spectrum of surface species. SFG has the added advantage of being able to directly analyze the surface-structure at the solid-liquid interface. The main goals of the present research were twofold: characterize the structure of adsorbed peptides (1) ex situ using soft X-ray NEXAFS, and (2) in situ using non-linear laser spectroscopy (SFG). Achieving the former goal involved first developing a comprehensive characterization of the carbon, nitrogen and oxygen k-edge NEXAFS spectra for amino acids, and then using a series of helical and beta-sheet peptides to demonstrate the sensitivity of polarization-dependent NEXAFS to secondary structure of adsorbed peptides. Characterizing the structure of adsorbed peptides in situ using SFG involved developing a model system to probe the solid-liquid interface in situ; demonstrating the ability to probe the molecular interactions and adsorbed secondary structure; following the time-dependent ordering of the adsorbed peptides; and establishing the ability to obtain high-resolution peptide-surface interactions in situ. The results from the present research establish SFG and NEXAFS as powerful techniques for chemical and structural characterization of surfaces and biomolecules immobilized onto those surfaces.

Samuel, Newton Thangadurai

20

Characteristics of Amyloid-Related Oligomers Revealed by Crystal Structures of Macrocyclic [beta]-Sheet Mimics  

SciTech Connect

Protein amyloid oligomers have been strongly linked to amyloid diseases and can be intermediates to amyloid fibers. {beta}-Sheets have been identified in amyloid oligomers. However, because of their transient and highly polymorphic properties, the details of their self-association remain elusive. Here we explore oligomer structure using a model system: macrocyclic peptides. Key amyloidogenic sequences from A{beta} and tau were incorporated into macrocycles, thereby restraining them to {beta}-strands, but limiting the growth of the oligomers so they may crystallize and cannot fibrillate. We determined the atomic structures for four such oligomers, and all four reveal tetrameric interfaces in which {beta}-sheet dimers pair together by highly complementary, dry interfaces, analogous to steric zippers found in fibers, suggesting a common structure for amyloid oligomers and fibers. In amyloid fibers, the axes of the paired sheets are either parallel or antiparallel, whereas the oligomeric interfaces display a variety of sheet-to-sheet pairing angles, offering a structural explanation for the heterogeneity of amyloid oligomers.

Liu, Cong; Sawaya, Michael R.; Cheng, Pin-Nan; Zheng, Jing; Nowick, James S.; Eisenberg, David (UCI); (UCLA)

2011-09-20

21

Formation of current sheets in magnetic reconnection  

SciTech Connect

An ideal evolution of magnetic fields in three spatial dimensions tends to cause neighboring field lines to increase their separation exponentially with distance ? along the lines, ?(?)=?(0)e{sup ?(?)}. The non-ideal effects required to break magnetic field line connections scale as e{sup ??}, so the breaking of connections is inevitable for ? sufficiently large—even though the current density need nowhere be large. When the changes in field line connections occur rapidly compared to an Alfvén transit time, the constancy of j{sub ||}/B along the magnetic field required for a force-free equilibrium is broken in the region where the change occurs, and an Alfvénic relaxation of j{sub ||}/B occurs. Independent of the original spatial distribution of j{sub ||}/B, the evolution is into a sheet current, which is stretched by a factor e{sup ?} in width and contracted by a factor e{sup ?} in thickness with the current density j{sub ||} increasing as e{sup ?}. The dissipation of these sheet currents and their associated vorticity sheets appears to be the mechanism for transferring energy from a reconnecting magnetic field to a plasma. Harris sheets, which are used in models of magnetic reconnection, are shown to break up in the direction of current flow when they have a finite width and are in a plasma in force equilibrium. The dependence of the longterm nature of magnetic reconnection in systems driven by footpoint motion can be studied in a model that allows qualitative variation in the nature of that motion: slow or fast motion compared to the Alfvén transit time and the neighboring footpoints either exponentially separating in time or not.

Boozer, Allen H., E-mail: ahb17@columbia.edu [Department of Applied Physics and Applied Mathematics Columbia University, New York, New York 10027 (United States)

2014-07-15

22

Flanking Polyproline Sequences Inhibit [beta]-Sheet Structure in Polyglutamine Segments by Inducing PPII-like Helix Structure  

SciTech Connect

Polyglutamine (poly(Q)) expansion is associated with protein aggregation into {beta}-sheet amyloid fibrils and neuronal cytotoxicity. In the mutant poly(Q) protein huntingtin, associated with Huntington's disease, both aggregation and cytotoxicity may be abrogated by a polyproline (poly(P)) domain flanking the C terminus of the poly(Q) region. To understand structural changes that may occur with the addition of the poly(P) sequence, we synthesized poly(Q) peptides with 3-15 glutamine residues and a corresponding set of poly(Q) peptides flanked on the C terminus by 11 proline residues (poly(Q)-poly(P)), as occurs in the huntingtin sequence. The shorter soluble poly(Q) peptides (three or six glutamine residues) showed polyproline type II-like (PPII)-like helix conformation when examined by circular dichroism spectroscopy and were monomers as judged by size-exclusion chromatography (SEC), while the longer poly(Q) peptides (nine or 15 glutamine residues) showed a {beta}-sheet conformation by CD and defined oligomers by SEC. Soluble poly(Q)-poly(P) peptides showed PPII-like content but SEC showed poorly defined, overlapping oligomeric peaks, and as judged by CD these peptides retained significant PPII-like structure with increasing poly(Q) length. More importantly, addition of the poly(P) domain increased the threshold for fibril formation to {approx} 15 glutamine residues. X-ray diffraction, electron microscopy, and film CD showed that, while poly(Q) peptides with {ge} 6 glutamine residues formed {beta}-sheet-rich fibrils, only the longest poly(Q)-poly(P) peptide (15 glutamine residues) did so. From these and other observations, we propose that poly(Q) domains exist in a 'tug-of-war' between two conformations, a PPII-like helix and a {beta}-sheet, while the poly(P) domain is conformationally constrained into a proline type II helix (PPII). Addition of poly(P) to the C terminus of a poly(Q) domain induces a PPII-like structure, which opposes the aggregation-prone {beta}-sheet. These structural observations may shed light on the threshold phenomenon of poly(Q) aggregation, and support the hypothesized evolution of 'protective' poly(P) tracts adjacent to poly(Q) aggregation domains.

Darnell, Gregory; Orgel, Joseph P.R.O.; Pahl, Reinhard; Meredith, Stephen C. (IIT); (UC)

2008-06-24

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

Amyloid Peptide Pores and the Beta Sheet Conformation  

Microsoft Academic Search

\\u000a \\u000a Over 20 clinical syndromes have been described as amyloid diseases. Pathologically, these illnesses are characterized by the\\u000a deposition in various tissues of amorphous, Congo red staining deposits, referred to as amyloid. Under polarizing light microscopy,\\u000a these deposits exhibit characteristic green birefringence. X-ray diffraction reveals cross-beta structure of extended amyloid\\u000a fibrils. Although there is always a major protein in amyloid deposits,

Bruce L. Kagan; Jyothi Thundimadathil

25

Possible participation of transient sheets of 1. -->. 4-. beta. -glucans in the biosynthesis of cellulose I. [Acetobacter xylinum  

SciTech Connect

It is suggested that a primary, essential stage in the biologic formation of a microfibril of cellulose I is an extracellular, lateral association of presynthesized (1..-->..4)-..beta..-D-glucans, by hydrogen bonding, to form long, thin sheets. These sheets then superimpose themselves nonenzymatically by London forces to form the nascent microfibril. The ends of the constituent glucans of the nascent microfibril may undergo extension or rearrangement of the type indicated by Maclachlan and colleagues. The formation of the metastable, native structure (cellulose I) may be deduced from the above suggestion as a natural consequence of closest packing of the sheets. The irreversibility of the change from cellulose I to cellulose II, either by mercerization or regeneration, also follows from the postulate. The suggestion also explains why cellulose microfibrils and chitin microfibrils may be formed contiguously in cell walls without interfering with each other. High-resolution electron micrographs of the tips of newly formed microfibrils of bacterial cellulose which had been very lightly negatively stained with sodium phosphotungstate are consistent with the suggestion. 33 references, 3 figures.

Colvin, J.R.

1983-01-01

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

Captides: rigid junctions between beta sheets and small molecules.  

PubMed

An extensive series of covalently linked small molecule-peptide adducts based on a terminally capped-beta hairpin motif is reported. The constructs can be prepared by standard solid-phase Fmoc chemistry with one to four peptide chains linked to small molecule hubs bearing carboxylic acid moieties. The key feature of interest is the precise, buried environment of the small molecule, and its rigid orientation relative to one or more short but fully structured peptide chain(s). Most of this study employs a minimalist nine residue 'captide', a capped ?-turn, but we illustrate general applicability to peptides which can terminate in a beta strand. The non-peptide portion of these adducts can include nearly any molecule bearing one or more carboxylic acid groups. Fold-dependent rigidity sets this strategy apart from the currently available bioconjugation methods, which typically engender significant flexibility between peptide and tag. Applications to catalyst enhancement, drug design, higher-order assembly, and FRET calibration rulers are discussed. PMID:24909552

Kier, Brandon L; Andersen, Niels H

2014-09-01

28

Designed ?-sheet peptides inhibit amyloid formation by targeting toxic oligomers  

PubMed Central

Previous studies suggest that the toxic soluble-oligomeric form of different amyloid proteins share a common backbone conformation, but the amorphous nature of this oligomer prevents its structural characterization by experiment. Based on molecular dynamics simulations we proposed that toxic intermediates of different amyloid proteins adopt a common, nonstandard secondary structure, called ?-sheet. Here we report the experimental characterization of peptides designed to be complementary to the ?-sheet conformation observed in the simulations. We demonstrate inhibition of aggregation in two different amyloid systems, ?-amyloid peptide (A?) and transthyretin, by these designed ?-sheet peptides. When immobilized the ?-sheet designs preferentially bind species from solutions enriched in the toxic conformer compared with non-aggregated, nontoxic species or mature fibrils. The designs display characteristic spectroscopic signatures distinguishing them from conventional secondary structures, supporting ?-sheet as a structure involved in the toxic oligomer stage of amyloid formation and paving the way for novel therapeutics and diagnostics. DOI: http://dx.doi.org/10.7554/eLife.01681.001 PMID:25027691

Hopping, Gene; Kellock, Jackson; Barnwal, Ravi Pratap; Law, Peter; Bryers, James; Varani, Gabriele; Caughey, Byron; Daggett, Valerie

2014-01-01

29

Blue color formation of cyanobacteria with beta-cyclocitral.  

PubMed

Volatile compounds, such as beta-cyclocitral, geosmin, and 2-methylisoborneol, from cyanobacteria showed a lytic activity against cyanobacteria. Particularly, beta-cyclocitral caused an interesting color change in the culture broth from green to blue during the lysis process. In the present study, the lytic behavior of various cyanobacteria with beta-cyclocitral was investigated, and a mechanism for the blue color formation was developed. beta-Cyclocitral lysed both the laboratory strains of any genera and bloom samples including many species of cyanobacteria, and caused the characteristic color change from green to blue. beta-Cyclocitral provided a characteristic behavior, such that the absorption maxima of chlorophyll-a and beta-carotene disappeared, but that of phycocyanin still remained after 12 h, which indicated that beta-cyclocitral decomposed chlorophyll-a and beta-carotene rapidly, so that the inherent colors from the tolerant water-soluble pigments became observable in the cultured broth. This phenomenon was confirmed by another experiment using Phormidium (NIES-611), which showed a pink color derived from phycoerythrin. beta-Cyclocitral was more easily oxidized when compared with similar aldehyde compounds, so that the pH of the solution quickly decreased to 4.5. An oxidation product of beta-cyclocitral in water solution was isolated and identified as 2,6,6-trimethylcyclohexene-1-carboxylic acid. This study provides support that beta-cyclocitral derived from cyanobacteria plays an important role in the lysis of cyanobacteria and participates in the blue color formation under natural conditions. PMID:19936836

Harada, Ken-Ichi; Ozaki, Keiko; Tsuzuki, Sayaka; Kato, Hajime; Hasegawa, Masateru; Kuroda, Emilia K; Arii, Suzue; Tsuji, Kiyomi

2009-11-01

30

Thermally Induced Alpha-Helix to Beta-Sheet Transition in Regenerated Silk Fibers and Films  

SciTech Connect

The structure of thin films cast from regenerated solutions of Bombyx mori cocoon silk in hexafluoroisopropyl alcohol (HFIP) was studied by synchrotron X-ray diffraction during heating. A solid-state conformational transition from an alpha-helical structure to the well-known beta-sheet silk II structure occurred at a temperature of approximately 140 degrees C. The transition appeared to be homogeneous, as both phases do not coexist within the resolution of the current study. Modulated differential scanning calorimetry (DSC) of the films showed an endothermic melting peak followed by an exothermic crystallization peak, both occurring near 140 degrees C. Oriented fibers were also produced that displayed this helical molecular conformation. Subsequent heating above the structural transition temperature produced oriented beta-sheet fibers very similar in structure to B. mori cocoon fibers. Heat treatment of silk films at temperatures well below their degradation temperature offers a controllable route to materials with well-defined structures and mechanical behavior.

Drummy,L.; Phillips, D.; Stone, M.; Farmer, B.; Naik, R.

2005-01-01

31

Formation and dynamical history of the beta Pictoris system  

NASA Astrophysics Data System (ADS)

The structure of the beta Pic disk holds many clues to its formation and dynamical history. In particular there is strong evidence for sculpting by the beta Pic-b planet. For example, a warp in the disk at 80au is thought to be driven by the secular perturbations of that planet, and scattering of comets by beta Pic-b is thought to be the origin of the Falling Evaporating Bodies. A clump in the disk coincident with the warp, also at ~80au, provides clues to the outer planetary system which for now is poorly constrained. One possible origin for the clump is in trapping of comets into resonance with an outer planet currently at ~60au, with an alternative scenario being a giant impact between planetary embryos. This talk will consider the various disk structures and what they tell us about the formation and dynamical history of the beta Pictoris system.

Wyatt, M.

2014-09-01

32

Identification of 'molten globule'-like state in all beta-sheet protein.  

PubMed

The cardiotoxin analogue III (CTX III), isolated from the Taiwan Cobra venom (Naja naja atra), is a sixty amino acid, all beta-sheet protein. The 2,2,2-trifluoro ethanol (TFE) induced unfolding of CTX III is studied under acidic conditions (pH 2.5). Using circular dichroism, 1-anilino-8-napthalene sulphonic acid binding and NMR experiments, it is shown that stable, partially structured state(s) ['molten globule'-like state] is formed between 50 and 80% TFE concentrations. The protein was found to exist in an unfolded state in 80% TFE containing 2M urea. The TFE induced unfolding process is shown to be completely reversible. In the 'molten globule' state of CTX III in 80% TFE, though portion(s) of the backbone of the protein assume helical conformation, most of the original beta-sheet secondary structural elements in the protein are intact. In our opinion, this is the first report of the identification of a 'molten globule'-like state in the unfolding pathway of an all beta-sheet monomeric protein. PMID:7864840

Kumar, T K; Jayaraman, G; Lee, C S; Sivaraman, T; Lin, W Y; Yu, C

1995-02-15

33

CURRENT SHEETS FORMATION IN TANGLED CORONAL MAGNETIC FIELDS  

SciTech Connect

We investigate the dynamical evolution of magnetic fields in closed regions of solar and stellar coronae. To understand under which conditions current sheets form, we examine dissipative and ideal reduced magnetohydrodynamic models in Cartesian geometry, where two magnetic field components are present: the strong guide field B{sub 0}, extended along the axial direction, and the dynamical orthogonal field b. Magnetic field lines thread the system along the axial direction that spans the length L and are line-tied at the top and bottom plates. The magnetic field b initially has only large scales, with its gradient (current) length scale of the order of l{sub b}. We identify the magnetic intensity threshold b/B{sub 0} {approx} l{sub b}/L. For values of b below this threshold, field-line tension inhibits the formation of current sheets, while above the threshold they form quickly on fast ideal timescales. In the ideal case, above the magnetic threshold, we show that current sheets thickness decreases in time until it becomes smaller than the grid resolution, with the analyticity strip width {delta} decreasing at least exponentially, after which the simulations become underresolved.

Rappazzo, A. F. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Parker, E. N., E-mail: franco.rappazzo@gmail.com, E-mail: parker@oddjob.uchicago.edu [Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 (United States)

2013-08-10

34

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

35

Amyloid-like fibril formation in an all beta-barrel protein. Partially structured intermediate state(s) is a precursor for fibril formation.  

PubMed

Acidic fibroblast growth factor from newt (Notopthalmus viridescens) is a approximately 15-kDa, all beta-sheet protein devoid of disulfide bonds. In the present study, we investigate the effects of 2,2,2-trifluoroethanol (TFE) on the structure of newt acidic fibroblast growth factor (nFGF-1). The protein aggregates maximally in 10% (v/v) TFE. Congo red and thioflavin T binding experiments suggest that the aggregates induced by TFE have properties resembling the amyloid fibrils. Transmission electron microscopy and x-ray fiber diffraction data show that the fibrils (induced by TFE) are straight, unbranched, and have a cross-beta structure with an average diameter of 10-15 A. Preformed fibrils (induced by TFE) of nFGF-1 are observed to seed amyloid-like fibril formation in solutions containing the protein (nFGF-1) in the native beta-barrel conformation. Fluorescence, far-UV CD, anilino-8-napthalene sulfonate binding, multidimensional NMR, and Fourier transformed infrared spectroscopy data reveal that formation of a partially structured intermediate state(s) precedes the onset of the fibrillation process. The native beta-barrel structure of nFGF-1 appears to be disrupted in the partially structured intermediate state(s). The protein in the partially structured intermediate state(s) is found to be "sticky" with a solvent-exposed non-polar surface(s). Amyloid fibril formation appears to occur due to coalescence of the protein in the partially structured intermediate state(s) through solvent-exposed non-polar surfaces and intermolecular beta-sheet formation among the extended, linear beta-strands in the protein. PMID:12584201

Srisailam, Sampath; Kumar, Thallampuranam Krishnaswamy S; Rajalingam, Dakshinamurthy; Kathir, Karuppanan Muthusamy; Sheu, Hwo-Shuenn; Jan, Fuh-Jyh; Chao, Pei-Chi; Yu, Chin

2003-05-16

36

Microphase Separation Controlled beta-Sheet Crystallization Kinetics in Fibrous Proteins  

SciTech Connect

Silk is a naturally occurring fibrous protein with a multiblock chain architecture. As such, it has many similarities with synthetic block copolymers, including the possibility for e-sheet crystallization restricted within the crystallizable blocks. The mechanism of isothermal crystallization kinetics of e-sheet crystals in silk multiblock fibrous proteins is reported in this study. Kinetics theories, such as Avrami analysis which was established for studies of synthetic polymer crystal growth, are for the first time extended to investigate protein self-assembly in e-sheet rich Bombyx mori silk fibroin samples, using time-resolved Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and synchrotron real-time wide-angle X-ray scattering (WAXS). The Avrami exponent, n, was close to 2 for all methods and crystallization temperatures, indicating formation of e-sheet crystals in silk proteins is different from the 3-D spherulitic crystal growth found in synthetic polymers. Observations by scanning electron microscopy support the view that the protein structures vary during the different stages of crystal growth, and show a microphase separation pattern after chymotrypsin enzyme biodegradation. We present a model to explain the crystallization of the multiblock silk fibroin protein, by analogy to block copolymers: crystallization of e-sheets occurs under conditions of geometrical restriction caused by phase separation of the crystallizable and uncrystallizable blocks. This crystallization model could be widely applicable in other proteins with multiblock (i.e., crystallizable and noncrystallizable) domains.

Hu, X.; Lu, Q; Kaplan, D; Cebe, P

2009-01-01

37

Designing biomaterials exploiting beta-sheet forming peptides self-assembly  

NASA Astrophysics Data System (ADS)

The use of non-covalent self-assembly to construct materials has become a prominent strategy in material science offering practical routes for the construction of increasingly functional materials for a variety of applications ranging from electronic to biotechnology. A variety of molecular building blocks can be used for this purpose, one such block that has attracted considerable attention are de-novo designed peptides. The library of 20 natural amino acids offers the ability to play with the intrinsic properties of the peptide such as structure, hydrophobicity, charge and functionality allowing the design of materials with a wide range of properties. The beta-sheet motif is of particular interest as short peptides can be designed to form beta-sheet rich fibres that entangle and consequently form hydrogels. These hydrogels can be further functionalised using specific biological signals or drugs by synthesising functionalised peptides that are incorporated into the hydrogel network during the self-assembling process. This functionalisation approach is very attractive has it does not require any chemistry avoiding therefore the use of additional potentially toxic chemicals. It also offers the possibility to introduce multiple functionalities in a straightforward fashion. The hydrogels can also be made responsive through the use of enzymatic catalysis and/or conjugation with responsive polymers. In this presentation we will discuss the design opportunities offered by these peptides to create new functional biomaterials.

Saiani, Alberto

2013-03-01

38

Countermeasures against Pattern Formation Phenomena of Thin Sheet Winder by Using Dynamic Absorbers  

NASA Astrophysics Data System (ADS)

This paper deals with a countermeasure against pattern formation phenomena generated on thin sheet winder using dynamic absorbers. The thin sheet is widely used as paper, aluminum, etc. Pattern formation phenomena of the wound sheet sometimes occur in operation because of the viscoelastic characteristics of the sheet. The pattern formation phenomena lead to a fatal damage on the thin sheet. This problem is similar to the other pattern formation phenomena, for instance, polygonal deformations of the smoother roll of paper making machines and pattern formation of the elastic yarn of textile winding machines. The authors conducted experiment to generate the pattern formation using experimental apparatus, and theoretically analyzed to clarify the mechanism of the pattern formation phenomena considering the elastic deformation of the rolls. They also theoretically examined the countermeasure to suppress the phenomena by attaching some dynamic absorbers. The effectiveness of the tunable dynamic absorbers was confirmed by the theoretical analysis, and an example of the tunable dynamic absorber was introduced.

Ryu, Takahiro; Matsuzaki, Kenichiro; Sueoka, Atsuo; Morita, Hidetoshi

39

Hamiltonian Dynamics of the Protein Chain and Normal Modes of Alpha-Helix and Beta-Sheet  

E-print Network

We use the torsional angles of the protein chain as generalized coordinates in the canonical formalism, derive canonical equations of motion, and investigate the coordinate dependence of the kinetic energy expressed in terms of the canonical momenta. We use the formalism to compute the normal-frequency distributions of the alpha-helix and the beta-sheet, under the assumption that they are stabilized purely through hydrogen bonding. Comparison of their free energies show the existence of a phase transition between the alpha-helix and the beta-sheet at a critical temperature.

Hon-Wai Leong; Lock-Yue Chew; Kerson Huang

2008-09-11

40

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. PMID:19927125

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

2010-01-01

41

A method to predict edge strands in beta-sheets from protein sequences.  

PubMed

There is a need for rules allowing three-dimensional structure information to be derived from protein sequences. In this work, consideration of an elementary protein folding step allows protein sub-sequences which optimize folding to be derived for any given protein sequence. Classical mechanics applied to this system and the energy conservation law during the elementary folding step yields an equation whose solutions are taken over the field of rational numbers. This formalism is applied to beta-sheets containing two edge strands and at least two central strands. The number of protein sub-sequences optimized for folding per amino acid in beta-strands is shown in particular to predict edge strands from protein sequences. Topological information on beta-strands and loops connecting them is derived for protein sequences with a prediction accuracy of 75%. The statistical significance of the finding is given. Applications in protein structure prediction are envisioned such as for the quality assessment of protein structure models. PMID:24688737

Guilloux, Antonin; Caudron, Bernard; Jestin, Jean-Luc

2013-01-01

42

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

43

Interaction between A beta(1-42) and A beta(1-40) in Alzheimer's beta-amyloid fibril formation in vitro.  

PubMed

We analyzed the interaction of two kinds of amyloid beta-peptides (A beta), i.e., A beta(1-42) and A beta(1-40), in the kinetics of beta-amyloid fibril (fA beta) formation in vitro, based on a nucleation-dependent polymerization model using fluorescence spectroscopy with thioflavin T. When 25 microM A beta(1-42) was incubated with increasing concentrations of amyloidogenic A beta(1-40), the time to proceed to equilibrium was extended dose-dependently. A similar inhibitory effect was observed when 45 microM A beta(1-40) was incubated with increasing concentrations of A beta(1-42). On the other hand, when 50 microM of nonamyloidogenic A beta(1-40) was incubated with A beta(1-42) at a molar ratio of 10:1 or 5:1, A beta(1-42) initiated fA beta formation from A beta(1-40). The lag time of the reaction shortened in a concentration-dependent manner, with A beta(1-42). We next examined the seeding effect of fA beta formed from A beta(1-42) (fA beta(1-42)) on nonamyloidogenic A beta(1-40). When 50 microM of nonamyloidogenic A beta(1-40) was incubated with 10 or 20 microg/mL (2.2 or 4.4 microM) of fA beta(1-42), the fluorescence showed a sigmoidal increase. The lag time of the reaction was shortened by fA beta(1-42) in a concentration-dependent manner. However, the time to proceed to equilibrium was much longer than when an equal concentration of fA beta formed from A beta(1-40) (fA beta(1-40)) was added to A beta(1-40). The fluorescence increased hyperbolically without a lag phase when 25 microM A beta(1-42) was incubated with 10 or 20 microg/mL (2.3 or 4.6 microM) of fA beta(1-40), and proceeded to equilibrium more rapidly than without fA beta(1-40). An electron microscopic study indicated that the morphology of fA beta formed is governed by the major component of fresh A beta peptides in the reaction mixture, not by the morphology of preexisting fibrils. These results may indicate the central role of A beta(1-42) for fA beta deposition in vivo, among the different coexisting A beta species. PMID:10569934

Hasegawa, K; Yamaguchi, I; Omata, S; Gejyo, F; Naiki, H

1999-11-23

44

Hybrid modeling of the formation and structure of thin current sheets in the magnetotail  

SciTech Connect

Hybrid simulations are used to investigate the formation of a thin current sheet inside the plasma sheet of a magnetotail-like configuration. The initial equilibrium is subjected to a driving electric field qualitatively similar to what would be expected from solar wind driving. As a result, we find the formation of a raw current sheet, with a thickness of approximately the ion inertial length. The current density inside the current sheet region is supplied largely by the electrons. Ion acceleration in the cross-tail direction is absent due since the driving electric field fails to penetrate into the equatorial region.

Hesse, M.; Winske, D.; Birn, J.

1996-07-01

45

A novel beta-catenin-binding protein inhibits beta-catenin-dependent Tcf activation and axis formation.  

PubMed

beta-Catenin is efficiently phosphorylated by glycogen synthase kinase-3beta in the Axin complex in the cytoplasm, resulting in the down-regulation. In response to Wnt, beta-catenin is stabilized and translocated into the nucleus where it stimulates gene expression through Tcf/Lef. Here we report a novel protein, designated Duplin (for axis duplication inhibitor), which negatively regulates the function of beta-catenin in the nucleus. Duplin was located in the nucleus. Duplin bound directly to the Armadillo repeats of beta-catenin, thereby inhibiting the binding of Tcf to beta-catenin. It did not affect the stability of beta-catenin but inhibited Wnt- or beta-catenin-dependent Tcf activation. Furthermore, expression of Duplin in Xenopus embryos inhibited the axis formation and beta-catenin-dependent axis duplication, and prevented the beta-catenin's ability to rescue ventralizing phenotypes induced by ultraviolet light irradiation. Thus, Duplin is a nuclear protein that inhibits beta-catenin signaling. PMID:10921920

Sakamoto, I; Kishida, S; Fukui, A; Kishida, M; Yamamoto, H; Hino, S; Michiue, T; Takada, S; Asashima, M; Kikuchi, A

2000-10-20

46

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. PMID:21305337

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

2011-01-01

47

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. PMID:24116035

Vinn, Olev

2013-01-01

48

Molecular Dynamics Simulation of the alpha-Helix to beta-Sheet Transition in Coiled Protein Filaments: Evidence for a Critical Filament Length Scale  

E-print Network

The alpha-helix to beta-sheet transition (?-? transition) is a universal deformation mechanism in alpha-helix rich protein materials such as wool, hair, hoof, and cellular proteins. Through a combination of molecular and ...

Buehler, Markus J.

49

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. PMID:9736626

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

1998-01-01

50

Current Sheet Formation in a Conical Theta Pinch Faraday Accelerator with Radio-frequency Assisted Discharge  

NASA Technical Reports Server (NTRS)

Data from an inductive conical theta pinch accelerator are presented to gain insight into the process of inductive current sheet formation in the presence of a preionized background gas produced by a steady-state RF-discharge. The presence of a preionized plasma has been previously shown to allow for current sheet formation at lower discharge voltages and energies than those found in other pulsed inductive accelerator concepts, leading to greater accelerator efficiencies at lower power levels. Time-resolved magnetic probe measurements are obtained for different background pressures and pulse energies to characterize the effects of these parameters on current sheet formation. Indices are defined that describe time-resolved current sheet characteristics, such as the total current owing in the current sheet, the time-integrated total current ('strength'), and current sheet velocity. It is found that for a given electric field strength, maximums in total current, strength, and velocity occur for one particular background pressure. At other pressures, these current sheet indices are considerably smaller. The trends observed in these indices are explained in terms of the principles behind Townsend breakdown that lead to a dependence on the ratio of the electric field to the background pressure. Time-integrated photographic data are also obtained at the same experimental conditions, and qualitatively they compare quite favorably with the time-resolved magnetic field data.

Polzin, Kurt A.; Hallock, Ashley K.; Choueiri, Edgar Y.

2008-01-01

51

Instability of current sheets and formation of plasmoid chains  

SciTech Connect

Current sheets formed in magnetic reconnection events are found to be unstable to high-wavenumber perturbations. The instability is very fast: its maximum growth rate scales as S{sup 1/4}v{sub A}/L{sub CS}, where L{sub CS} is the length of the sheet, v{sub A} the Alfven speed, and S the Lundquist number. As a result, a chain of plasmoids (secondary islands) is formed, whose number scales as S{sup 3/8}.

Loureiro, N. F.; Schekochihin, A. A.; Cowley, S. C. [Center for Multiscale Plasma Dynamics, University of Maryland, College Park, Maryland 20742-3511 (United States) and Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Blackett Laboratory, Imperial College, London SW7 2BW, United Kingdom and King's College, University of Cambridge, Cambridge CB2 1ST (United Kingdom); Blackett Laboratory, Imperial College, London SW7 2BW (United Kingdom) and Department of Physics and Astronomy, UCLA, Los Angeles, California 90095-1547 (United States)

2007-10-15

52

The formation of cavity clusters at sheet cavity \\/ re-entrant jet contact  

Microsoft Academic Search

The fast flow of water past a hydrofoil often results in the formation of a sheet cavity on the suction side of the foil, and from its trailing edge a re-entrant jet develops and moves upstream into the cavity. Eventually this jet gets into contact with the cavity surface and causes the formation of small clouds of cavities at the

K. A. Mørch; G. Bark; P. L. Nielsen; M. Grekula; P. Stendys

53

Plasma sheet and (nonstorm) ring current formation from solar and polar wind sources  

Microsoft Academic Search

We consider the formation of the plasma sheet and geosynchronous region (nonstorm) ring current in the framework of collisionless test particle motions in three-dimensional magnetospheric fields obtained from self-consistent MHD simulations. Simulation results are compared with observations of the near-Earth plasma sheet from the Polar spacecraft during 2001 and 2002. Many particles were initiated in two regions representative of the

T. E. Moore; M.-C. Fok; M. O. Chandler; C. R. Chappell; S. P. Christon; D. C. Delcourt; J. Fedder; M. Huddleston; M. Liemohn; W. K. Peterson; S. Slinker

2005-01-01

54

Plasma Sheet and (non-storm) Ring Current Formation from Solar and Polar Wind Sources  

Microsoft Academic Search

We consider the formation of the plasma sheet and geosynchronous region (non-storm) ring current in the framework of collisionless test particle motions in 3D magnetospheric fields obtained from self-consistent MHD simulations. Simulation results are compared with observations of the near-Earth plasma sheet from the Polar spacecraft, during 2001 and 2002. Many particles were initiated in two regions representative of the

T. E. Moore; M. C. Fok; M. O. Chandler; C. R. Chappell; S. P. Christon; D. C. Delcourt; J. Fedder; M. Huddleston; M. Liemohn; W. K. Peterson; S. Slinker

2004-01-01

55

Plasma Sheet and Ring Current Formation from Solar and Polar Wind Sources  

Microsoft Academic Search

We consider the formation of the plasma sheet and quiet ring current in the framework of collisionless test particle motions in 3D magnetospheric fields obtained from self-consistent MHD simulations. Simulation results are compared with observations of the near-Earth plasma sheet from the Polar spacecraft, during 2001 and 2002. Many particles were initiated in two regions representative of the solar wind

T. E. Moore; M. C. Fok; M. O. Chandler; C. R. Chappell; S. P. Christon; D. C. Delcourt; J. Fedder; M. Huddleston; M. Liemohn; W. K. Peterson; S. Slinker

2004-01-01

56

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

57

Beta-D-Allose inhibits fruiting body formation and sporulation in Myxococcus xanthus.  

PubMed

Myxococcus xanthus, a gram-negative soil bacterium, responds to amino acid starvation by entering a process of multicellular development which culminates in the assembly of spore-filled fruiting bodies. Previous studies utilizing developmental inhibitors (such as methionine, lysine, or threonine) have revealed important clues about the mechanisms involved in fruiting body formation. We used Biolog phenotype microarrays to screen 384 chemicals for complete inhibition of fruiting body development in M. xanthus. Here, we report the identification of a novel inhibitor of fruiting body formation and sporulation, beta-d-allose. beta-d-Allose, a rare sugar, is a member of the aldohexose family and a C3 epimer of glucose. Our studies show that beta-d-allose does not affect cell growth, viability, agglutination, or motility. However, beta-galactosidase reporters demonstrate that genes activated between 4 and 14 h of development show significantly lower expression levels in the presence of beta-d-allose. Furthermore, inhibition of fruiting body formation occurs only when beta-d-allose is added to submerged cultures before 12 h of development. In competition studies, high concentrations of galactose and xylose antagonize the nonfruiting response to beta-d-allose, while glucose is capable of partial antagonism. Finally, a magellan-4 transposon mutagenesis screen identified glcK, a putative glucokinase gene, required for beta-d-allose-mediated inhibition of fruiting body formation. Subsequent glucokinase activity assays of the glcK mutant further supported the role of this protein in glucose phosphorylation. PMID:17056749

Chavira, Marielena; Cao, Nga; Le, Karen; Riar, Tanveer; Moradshahi, Navid; McBride, Melinda; Lux, Renate; Shi, Wenyuan

2007-01-01

58

Engineering of betabellin-15D: a 64 residue beta sheet protein that forms long narrow multimeric fibrils.  

PubMed Central

The betabellin target structure is a beta-sandwich protein consisting of two 32 residue beta-sheets packed against one another by interaction of their hydrophobic faces. The 32 residue chain of betabellin-15S (HSLTAKIpkLTFSIAphTYTCAV pkYTAKVSH, where p=DPro, k=DLys, and h=DHis) did not fold in water at pH 6.5. Air oxidation of betabellin-15S provided betabellin-15D, the 64 residue disulfide bridged two-chain molecule, which also remained unfolded in water at pH 6.5. By circular dichroic spectropolarimetry, the extent of beta structure observed for betabellin-15D increased with the pH and ionic strength of the solution and the betabellin-15D concentration. By electron microscopy, in 5.0 mM MOPS and 0.25 M NaCl at pH 6.9, betabellin-15D formed long narrow multimeric fibrils. A molecular model was constructed to show that the dimensions of these betabellin-15D fibrils are consistent with a single row of beta-sandwich molecules joined by multiple intersheet H-bonds. PMID:9684887

Lim, A.; Saderholm, M. J.; Makhov, A. M.; Kroll, M.; Yan, Y.; Perera, L.; Griffith, J. D.; Erickson, B. W.

1998-01-01

59

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

60

Contributions of Residue Pairing to bbb-sheet Formation: Conservation and Covariation of Amino  

E-print Network

Contributions of Residue Pairing to bbb-sheet Formation: Conservation and Covariation of Amino Acid Residue Pairs on Antiparallel bbb-strands Yael Mandel-Gutfreund1 , Sydney M. Zaremba2 and Lydia M is weak. Moreover, in spite of the preference of certain amino acid pairs to occupy neighboring positions

Mandel-Gutfreund, Yael

61

The Wnt\\/beta-catenin pathway regulates cardiac valve formation  

Microsoft Academic Search

Truncation of the tumour suppressor adenomatous polyposis coli (Apc) constitutively activates the Wnt\\/beta-catenin signalling pathway. Apc has a role in development: for example, embryos of mice with truncated Apc do not complete gastrulation. To understand this role more fully, we examined the effect of truncated Apc on zebrafish development. Here we show that, in contrast to mice, zebrafish do complete

Adam F. L. Hurlstone; Anna-Pavlina G. Haramis; Erno Wienholds; Harry Begthel; Jeroen Korving; Fredericus van Eeden; Edwin Cuppen; Danica Zivkovic; Ronald H. A. Plasterk; Hans Clevers

2003-01-01

62

Research of vacancy defect formation on the surface of two-dimensional boron sheets  

NASA Astrophysics Data System (ADS)

Mechanism of vacancy defect formation on the surface of two types of BS: triangular BS (TBS), ?-sheet (?BS) have been calculated within the model of molecular cluster with the use of quantum chemical MNDO scheme. The process of atomic vacancy formation of BS has been modeled by step-by-step abstraction of one central boron atom. Incremental method allowed us to build energy curves for vacancy formation process. The process of vacancy migration on the BS surface has also have been investigated, and more probable paths of migration have been found.

Boroznina, E. V.; Zhiganova, T. A.; Boroznin, S. V.

2015-01-01

63

Characteristics of Amyloid-Related Oligomers Revealed by Crystal Structures of Macrocyclic [beta]Sheet Mimics  

Microsoft Academic Search

Protein amyloid oligomers have been strongly linked to amyloid diseases and can be intermediates to amyloid fibers. -Sheets have been identified in amyloid oligomers. However, because of their transient and highly polymorphic properties, the details of their self-association remain elusive. Here we explore oligomer structure using a model system: macrocyclic peptides. Key amyloidogenic sequences from A and tau were incorporated

Cong Liu; Michael R. Sawaya; Pin-Nan Cheng; Jing Zheng; James S. Nowick; David Eisenberg

2011-01-01

64

Formation and Reconnection of Three-Dimensional Current Sheets in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as interchange reconnection at the boundaries between coronal holes and helmet streamers in the Sun's corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional magnetohydrodynamic (3D MHD) simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to apply directly the vast body of knowledge gained from the many studies of 2D reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet-Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona.

Edmondson, Justin K.; Antiochos, S. K.; DeVore, C.; Velli, M.; Zurbuchen, T. H.

2010-05-01

65

Formation and Reconnection of Three-dimensional Current Sheets in the Solar Corona  

NASA Astrophysics Data System (ADS)

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun's corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional (3D) magnetohydrodynamic simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to directly apply the vast body of knowledge gained from the many studies of two-dimensional (2D) reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet-Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona.

Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.

2010-07-01

66

Formation and Reconnection of Three-Dimensional Current Sheets in the Solar Corona  

NASA Technical Reports Server (NTRS)

Current-sheet formation and magnetic reconnection are believed to be the basic physical processes responsible for much of the activity observed in astrophysical plasmas, such as the Sun s corona. We investigate these processes for a magnetic configuration consisting of a uniform background field and an embedded line dipole, a topology that is expected to be ubiquitous in the corona. This magnetic system is driven by a uniform horizontal flow applied at the line-tied photosphere. Although both the initial field and the driver are translationally symmetric, the resulting evolution is calculated using a fully three-dimensional magnetohydrodynamic (3D MHD) simulation with adaptive mesh refinement that resolves the current sheet and reconnection dynamics in detail. The advantage of our approach is that it allows us to apply directly the vast body of knowledge gained from the many studies of 2D reconnection to the fully 3D case. We find that a current sheet forms in close analogy to the classic Syrovatskii 2D mechanism, but the resulting evolution is different than expected. The current sheet is globally stable, showing no evidence for a disruption or a secondary instability even for aspect ratios as high as 80:1. The global evolution generally follows the standard Sweet- Parker 2D reconnection model except for an accelerated reconnection rate at a very thin current sheet, due to the tearing instability and the formation of magnetic islands. An interesting conclusion is that despite the formation of fully 3D structures at small scales, the system remains close to 2D at global scales. We discuss the implications of our results for observations of the solar corona. Subject Headings: Sun: corona Sun: magnetic fields Sun: reconnection

Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Zurbuchen, T. H.

2010-01-01

67

Effect of aluminum raw materials on the formation of potassium-beta-aluminas  

Microsoft Academic Search

Depending on the alumina precursor used during beta-alumina synthesis, phase-pure and relatively stable ??-alumina can be prepared both in the binary and the ternary compositional range. In addition, higher-indexed beta-alumina species ?? and ?IV, which show a relation to ?- and ??'-alumina respectively, can also be prepared. Alumina precursors exhibiting a cubic-close-packed (?) oxygen sublattice, lead to the direct formation

Günter W. Schaefer; Arnoud P. De Kroon; Fritz Aldinger

1995-01-01

68

Multinuclear NMR studies of the flavodoxin from Anabaena 7120:. beta. -sheet structure and the flavin mononucleotide binding site  

SciTech Connect

A concerted approach to primary {sup 1}H, {sup 13}C, and {sup 15}N nuclear magnetic resonance assignments in proteins was developed. The method requires enrichment of the protein with {sup 13}C and {sup 15}N. The technique relies on the comparison of data sets from NMR experiments that correlate various nuclei: {sup 13}C({sup 13}C) double quantum correlations, {sup 1}H({sup 13}C) and {sup 1}H({sup 15}N) single bond correlations, and {sup 1}H({sup 13}C) and {sup 1}H({sup 15}N) multiple bond correlations. Comparison of data sets increases the number of resonances that can be assigned and improves assignment confidence. By combined use of these and conventional NMR techniques, sequential assignments were made for the {beta}-sheet and flavin mononucleotide (FMN) binding site residues in flavodoxin from Anabaena 7120. The {beta}-sheet structure was found to be similar to that seen in the crystal structure of Anacystis nidulans flavodoxin. In the FMN binding site, a total of 69 NOEs were identified: eight between protons of FMN, 36 between protons of binding site residues, and 25 between protons of FMN and protein. These constraints were used to determine the localized solution structure of the flavin binding site. The electronic environment and conformation of the protein-bound isoalloxazine ring were investigated by determining chemical shifts and coupling constants for the ring atoms. The carbonyl edge of the flavin ring was found to be slightly polarized by hydrogen bonding to the protein. The xylene ring was found to be nonplanar. The C{sup 6}-N{sup 5} region of the flavin appears to be solvent accessible.

Stockman, B.J.

1989-01-01

69

Association thermodynamics and conformational stability of beta-sheet amyloid beta(17-42) oligomers: effects of E22Q (Dutch) mutation and charge neutralization.  

PubMed

Amyloid fibrils are associated with many neurodegenerative diseases. It was found that amyloidogenic oligomers, not mature fibrils, are neurotoxic agents related to these diseases. Molecular mechanisms of infectivity, pathways of aggregation, and molecular structure of these oligomers remain elusive. Here, we use all-atom molecular dynamics, molecular mechanics combined with solvation analysis by statistical-mechanical, three-dimensional molecular theory of solvation (also known as 3D-RISM-KH) in a new MM-3D-RISM-KH method to study conformational stability, and association thermodynamics of small wild-type Abeta(17-42) oligomers with different protonation states of Glu(22), as well the E22Q (Dutch) mutants. The association free energy of small beta-sheet oligomers shows near-linear trend with the dimers being thermodynamically more stable relative to the larger constructs. The linear (within statistical uncertainty) dependence of the association free energy on complex size is a consequence of the unilateral stacking of monomers in the beta-sheet oligomers. The charge reduction of the wild-type Abeta(17-42) oligomers upon protonation of the solvent-exposed Glu(22) at acidic conditions results in lowering the association free energy compared to the wild-type oligomers at neutral pH and the E22Q mutants. The neutralization of the peptides because of the E22Q mutation only marginally affects the association free energy, with the reduction of the direct electrostatic interactions mostly compensated by the unfavorable electrostatic solvation effects. For the wild-type oligomers at acidic conditions such compensation is not complete, and the electrostatic interactions, along with the gas-phase nonpolar energetic and the overall entropic effects, contribute to the lowering of the association free energy. The differences in the association thermodynamics between the wild-type Abeta(17-42) oligomers at neutral pH and the Dutch mutants, on the one hand, and the Abeta(17-42) oligomers with protonated Glu(22), on the other, may be explained by destabilization of the inter- and intrapeptide salt bridges between Asp(23) and Lys(28). Peculiarities in the conformational stability and the association thermodynamics for the different models of the Abeta(17-42) oligomers are rationalized based on the analysis of the local physical interactions and the microscopic solvation structure. PMID:20338850

Blinov, Nikolay; Dorosh, Lyudmyla; Wishart, David; Kovalenko, Andriy

2010-01-20

70

Six new candidate members of the alpha/beta twisted open-sheet family detected by sequence similarity to flavodoxin.  

PubMed Central

Strong sequence similarity has been reported among WrbA (the Trp repressor-binding protein of Escherichia coli); Ycp4, a protein of unknown function from the budding yeast Saccharomyces cerevisiae; P25, the pap1-dependent protein of the fission yeast Schizosaccharomyces pombe; and the translation product of a partial cDNA sequence from rice seedling root (Oryza sativa, locus Ricr02421a; here referred to as RicR). Further homology search with the profile method indicates that all the above sequences are related to the flavodoxin family and, in turn, allows detection of the recently proposed flavodoxin-like proteins from E. coli, MioC and the hypothetical protein YihB. We discuss sequence conservation with reference to the known 3-dimensional structures of flavodoxins. Conserved sequence and hydrophobicity patterns, as well as residue-pair interaction potentials, strongly support the hypothesis that these proteins share the alpha/beta twisted open-sheet fold typical of flavodoxins, with an additional alpha/beta unit in the WrbA family. On the basis of the proposed structural homology, we discuss the details of the putative FMN-binding sites. Our analysis also suggests that the helix-turn-helix motif we identified previously in the C-terminal region of the WrbA family is unlikely to reflect a DNA-binding function of this new protein family. PMID:7756978

Grandori, R.; Carey, J.

1994-01-01

71

Mechanism of IAPP amyloid fibril formation involves an intermediate with a transient ?-sheet  

PubMed Central

Amyloid formation is implicated in more than 20 human diseases, yet the mechanism by which fibrils form is not well understood. We use 2D infrared spectroscopy and isotope labeling to monitor the kinetics of fibril formation by human islet amyloid polypeptide (hIAPP or amylin) that is associated with type 2 diabetes. We find that an oligomeric intermediate forms during the lag phase with parallel ?-sheet structure in a region that is ultimately a partially disordered loop in the fibril. We confirm the presence of this intermediate, using a set of homologous macrocyclic peptides designed to recognize ?-sheets. Mutations and molecular dynamics simulations indicate that the intermediate is on pathway. Disrupting the oligomeric ?-sheet to form the partially disordered loop of the fibrils creates a free energy barrier that is the origin of the lag phase during aggregation. These results help rationalize a wide range of previous fragment and mutation studies including mutations in other species that prevent the formation of amyloid plaques. PMID:24218609

Buchanan, Lauren E.; Dunkelberger, Emily B.; Tran, Huong Q.; Cheng, Pin-Nan; Chiu, Chi-Cheng; Cao, Ping; Raleigh, Daniel P.; de Pablo, Juan J.; Nowick, James S.; Zanni, Martin T.

2013-01-01

72

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

73

Swelling and folding as mechanisms of 3D shape formation in thin elastic sheets  

NASA Astrophysics Data System (ADS)

We work with two different mechanisms to generate geometric frustration on thin elastic sheets; isotropic differential growth and folding. We describe how controlled growth and prescribing folding patterns are useful tools for designing three-dimensional objects from information printed in two dimensions. The first mechanism is inspired by the possibility to control shapes by swelling polymer films, where we propose a solution for the problem of shape formation by asking the question, “what 2D metric should be prescribed to achieve a given 3D shape?”', namely the reverse problem. We choose two different types of initial configurations of sheets, disk-like with one boundary and annular with two boundaries. We demonstrate our technique by choosing four examples of 3D axisymmetric shapes and finding the respective swelling factors to achieve the desired shape. Second, we present a mechanical model for a single curved fold that explains both the buckled shape of a closed fold and its mechanical stiffness. The buckling arises from the geometrical frustration between the prescribed crease angle and the bending energy of the sheet away from the crease. This frustration increases as the sheet's area increases. Stiff folds result in creases with constant space curvature while softer folds inherit the broken symmetry of the buckled shape. We extend the application of our numerical model to show the potential to study multiple fold structures.

Dias, Marcelo A.

74

World sheet commuting {beta}{gamma} conformal field theory and nonrelativistic string theories  

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 [J. Math. Phys. (N.Y.) 42, 3127 (2001)] and Danielsson et al. [J. High Energy Phys. 10 (2000) 020; J. High Energy Phys. 03 (2001) 041.]. Our theory is much simpler than their theory and does not assume a compact coordinate. This nonrelativistic string theory has a bosonic matter {beta}{gamma} conformal field theory with the conformal weight of {beta} as 1. It is natural to identify time as a linear combination of {gamma} and {gamma} through an explicit realization of the Galilean boost symmetry. The angle between {gamma} and {gamma} parametrizes one parameter family of selection sectors. These selection sectors are responsible for having a nonrelativistic dispersion relation without a nontrivial topology in the nonrelativistic setup, which is one of the major differences from the previous works of Gomis and Ooguri and of Danielsson and co-workers. This simple theory is the nonrelativistic 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} conformal field theory. We also mention supersymmetric generalizations of these theories.

Kim, Bom Soo [Department of Physics, University of California, Berkeley, California 94720 (United States) and Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2007-11-15

75

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

76

Landscape formation by past continental ice sheets: insights into the subglacial environment  

NASA Astrophysics Data System (ADS)

Glaciers and ice sheets are known as most powerful, climatically driven agents of large-scale sediment redistribution and landscape formation in the Earth system. During the Quaternary, repeated waxing and waning of continental ice sheets contributed to profound reshaping of the Earth surface and set the scene for the development of ecosystems in the post-glacial time. Despite the well-established impact of glaciers on the upper lithosphere the specific processes of glacial erosion, transport and deposition and the formation landforms at the ice-bed interface are contentious. In particular, the relative importance of direct ice impact versus the impact of glacial meltwater is highly controversial. Here, we focus on the southern peripheral area of the Scandinavian Ice Sheet hosting thick successions of soft, deformable sediments and examine some spectacular sediment/landform assemblages found nowadays in both terrestrial and marine settings to illustrate the nature of the subglacial processes. In order to decipher the past ice sheet behavior field, experimental and numerical approaches are combined. It is shown that the strength of the coupling between the ice and the bed that controls the response of the substratum to ice overriding and stress propagation depends primarily on the ability of the glacial system to evacuate meltwater from ice-bed interface. Strong coupling, locally enhanced by subglacial permafrost resulted in deeply rooted (100's of meters) glaciotectonic deformation reflected on the surface as ice-shoved hills whereas weak coupling promoted by water accumulating under the ice triggered the formation of deep (100's of meters) tunnel valley networks. Under the arteries of fast-flowing ice known as palaeo-ice streams, remoulding of soft sediments generated mega-scale glacial lineations and drumlins that hold the key to understanding glacier dynamics. The subglacial environment is envisaged as a four-dimensional mosaic of stable and deforming spots transient in time and space whose impact is embedded in the properties of sediment/landform systems.

Piotrowski, Jan A.

2014-05-01

77

Current sheet Formation in a Conical Theta Pinch Faraday Accelerator with Radio-Frequency Assisted Discharge  

NASA Technical Reports Server (NTRS)

The inductive formation of current sheets in a conical theta pinch FARAD (Faraday Accelerator with Radio-frequency Assisted Discharge) thruster is investigated experimentally with time-integrated photography. The goal is to help in understanding the mechanisms and conditions controlling the strength and extent of the current sheet, which are two indices important for FARAD as a propulsion concept. The profiles of these two indices along the inside walls of the conical acceleration coil are assumed to be related to the profiles of the strength and extent of the luminosity pattern derived from photographs of the discharge. The variations of these profiles as a function of uniform back-fill neutral pressure (with no background magnetic field and all parameters held constant) provided the first clues on the nature and qualitative dependencies of current sheet formation. It was found that there is an optimal pressure for which both indices reach a maximum and that the rate of change in these indices with pressure differs on either side of this optimal pressure. This allowed the inference that current sheet formation follows a Townsend-like breakdown mechanism modified by the existence of a finite pressure-dependent radio-frequency-generated electron density background. The observation that the effective location of the luminosity pattern favors the exit-half of the conical coil is explained as the result of the tendency of the inductive discharge circuit to operate near its minimal self-inductance. Movement of the peak in the luminosity pattern towards the upstream side of the cone with increasing pressure is believed to result from the need of the circuit to compensate for the increase in background plasma resistivity due to increasing pressure.

Hallock, Ashley K.; Choueiri, Edgar Y.; Polzin, Kurt A.

2007-01-01

78

Alzheimer's beta-peptide oligomer formation at physiologic concentrations.  

PubMed

When diluted from dimethyl sulfoxide or 1,1,1,3,3,3-hexafluoro-2-propanol, synthetic human Abeta(1-42) readily forms oligomeric structures at near physiologic concentrations (1-20 nM). Oligomers 40 kDa are detected in a sandwich enzyme-linked immunosorbant assay where the capture and detection antibodies recognize the same primary sequence epitope. Monomeric peptide with a single epitope does not react in this format. Abeta(1-40) peptide does not oligomerize readily under these conditions. The rate of oligomer formation has a steep linear temperature dependence but is weakly affected by ionic strength up to 0.5M NaCl or KCl. Oligomer formation is inhibited by concentrations of Tween 20 and several other detergents well below their critical micelle concentrations. Once formed, high-molecular-weight oligomers are stabilized by Tween 20. Gel permeation chromatography of an oligomer preparation formed at nanomolar concentrations indicates that the majority of the Abeta(1-42) peptide chromatographs as monomers/dimers of apparent mw approximately 10 kDa. The most abundant oligomers have apparent mobilities corresponding to 220 kDa (48-mer) and higher multiples of this without detectable concentrations of intermediate low-molecular-weight species. Very little immunoreactive peptide appears in the void volume (>1.5 MDa) of a Superose 12 column. The oligomers are stable, rechromatographing at their original position. Abeta(1-42) oligomer formation at physiologic concentrations is a reproducible process that is amenable to kinetic analysis and inhibition. PMID:15519574

LeVine, Harry

2004-12-01

79

Calcofluor fluorescence assay for wort beta-glucan in a microplate format  

Technology Transfer Automated Retrieval System (TEKTRAN)

The widely-used fluorescent (Calcofluor) flow injection analysis method for determining the concentrations of beta-glucans in Congress worts from barley malts is adapted to microplate format. Adaptation of the Calcofluor assay to use widely available fluorescent microplate readers makes the assay m...

80

Low cost fabrication of sheet structure using a new beta titanium alloy, Ti-15V-3Cr-3Al-3Sn  

NASA Technical Reports Server (NTRS)

Development efforts have been undertaken to improve the processing and structural efficiencies of advanced cold-formable beta Ti alloys, using the standard, hot-formed and rivetted construction of Ti-6Al-4V sheet structures as a basis for comparison. Ti-15V-3Cr-3Al-3Sn (Ti-15-3) beta alloy is formable, brazable and weldable in the solution-treated condition, and after aging displays mechanical properties suitable for postulated service in the -65 to 600 F temperature range. A novel methodology using cold-formed Ti-15-3 stringers and Ti-6Al-4V face sheets that are joined by means of an out-of-furnace isothermal brazing process, followed by low temperature aging, can reduce production costs by as much as 28 per cent. Structural efficiency has been demonstrated in room and elevated temperature crippling tests of small skin-stringer assemblies.

Kaneko, R. S.; Davis, G. W.; Woods, C. A.; Royster, D. M.

1982-01-01

81

Molecular cloud evolution. I. Molecular cloud and thin CNM sheet formation  

E-print Network

We discuss molecular cloud formation by large-scale supersonic compressions in the diffuse warm neutral medium (WNM). Initially, a shocked layer forms, and within it, a thin cold layer. An analytical model and high-resolution 1D simulations predict the thermodynamic conditions in the cold layer. After $\\sim 1$ Myr of evolution, the layer has column density $\\sim 2.5 \\times 10^{19} \\psc$, thickness $\\sim 0.03$ pc, temperature $\\sim 25$ K and pressure $\\sim 6650$ K $\\pcc$. These conditions are strongly reminiscent of those recently reported by Heiles and coworkers for cold neutral medium sheets. In the 1D simulations, the inflows into the sheets produce line profiles with a central line of width $\\sim 0.5 \\kms$ and broad wings of width $\\sim 1 \\kms$. 3D numerical simulations show that the cold layer develops turbulent motions and increases its thickness, until it becomes a fully three-dimensional turbulent cloud. Fully developed turbulence arises on times ranging from $\\sim 7.5$ Myr for inflow Mach number $\\Mr = 2.4$ to $> 80$ Myr for $\\Mr = 1.03$. These numbers should be considered upper limits. The highest-density turbulent gas (HDG, $n > 100 \\pcc$) is always overpressured with respect to the mean WNM pressure by factors 1.5--4, even though we do not include self-gravity. The intermediate-density gas (IDG, $10 sheets may be formed transiently by this mechanism, when the compressions are only weakly supersonic.

Enrique Vazquez-Semadeni; Dongsu Ryu; Thierry Passot; Ricardo F. Gonzalez; Adriana Gazol

2006-02-06

82

Interepithelial signaling with nephric duct is required for the formation of overlying coelomic epithelial cell sheet.  

PubMed

In most organs of the body, epithelial tissues are supported by their own basement membrane and underlying stroma, the latter being regarded as a complex of amorphous cells, extracellular matrices, and soluble factors. We demonstrate here that an epithelial tube can serve as a component of stroma that supports the formation of epithelial cell sheet derived from a different origin. During development of the mesonephros in chicken embryos, the intermediate mesoderm (IMM), which contains the Wolffian duct (WD) and its associated tubules, is overlain by a sheet of epithelial cells derived from lateral plate (coelomic) mesoderm. We describe that in normal embryos, epitheliogenesis of IMM tubes and the adjacent coelomic cell sheet proceed in a coordinated manner. When the WD was surgically ablated, the overlying coelomic epithelium exhibited aberrant morphology accompanied by a punctated basement membrane. Furthermore, the WD-ablated coelomic epithelium became susceptible to latent external stress; electroporation of Rac1 resulted in epithelial-to-mesenchymal transitions (EMTs) within the coelomic epithelium. The distorted coelomic epithelium was rescued by implanting fibronectin-producing cells in place of the WD, suggesting that fibronectin provided by WD has an important role acting interepithelially. This notion was corroborated further by directly visualizing a translocation of EGFP-tagged fibronectin from fibronectin-producing to -receiving epithelia in vivo. Our findings provide a novel insight into interepithelial signaling that also might occur in adult tissues to protect against EMT and suggest a possible new target for anticancer therapeutic strategy. PMID:24753584

Yoshino, Takashi; Saito, Daisuke; Atsuta, Yuji; Uchiyama, Chihiro; Ueda, Shinya; Sekiguchi, Kiyotoshi; Takahashi, Yoshiko

2014-05-01

83

Caldera faults capture and deflect inclined sheets: an alternative mechanism of ring dike formation  

NASA Astrophysics Data System (ADS)

The subsurface structures of caldera ring faults are often inferred from numerical and analog models as well as from geophysical studies. All of these inferred structures need to be compared with actual ring faults so as to test the model implications. Here, we present field evidence of magma channeling into a caldera ring fault as exhibited at Hafnarfjall, a deeply eroded and well-exposed 5-Ma extinct volcano in western Iceland. At the time of collapse caldera formation, over 200 m of vertical displacement was accommodated along a ring fault, which is exceptionally well exposed at a depth of approximately 1.2 km below the original surface of the volcano. There are abrupt changes in the ring fault attitude with depth, but its overall dip is steeply inward. Several inclined sheets within the caldera became arrested at the ring fault; other sheets became deflected up along the fault to form a multiple ring dike. We present numerical models showing stress fields that encourage sheet deflection into the subvertical ring fault. Our findings provide an alternative mechanical explanation for magma channeling along caldera ring faults, which is a process likely to be fundamental in controlling the location of post-caldera volcanism.

Browning, John; Gudmundsson, Agust

2015-01-01

84

Factors of paleosol formation in a Late Cretaceous eolian sand sheet paleoenvironment, Marlia Formation, Southeastern Brazil  

E-print Network

Formation, Southeastern Brazil Patrick Francisco Führ Dal' Bó a, , Giorgio Basilici a , Rômulo Simões), Brazil b IG ­ Universidade Federal do Pará, 66075-110, Belém (PA), Brazil a b s t r a c ta r t i c l e i Late Cretaceous The Marília Formation, which crops out in southeastern Brazil, is interpreted as a Late

Ahmad, Sajjad

85

Aluminium and iron, but neither copper nor zinc, are key to the precipitation of beta-sheets of Abeta_{42} in senile plaque cores in Alzheimer's disease.  

PubMed

A number of metals including Fe(II)/Fe(III), Al(III), Zn(II) and Cu(II) are found co-localised with beta-sheets of Abeta_{42} in senile plaque cores in AD brain. We know neither why nor how the co-localisation takes place or, indeed, if it is entirely aberrant or partly protective. There are data from in vitro studies which may begin to explain some of these unanswered questions and in considering these I have summised that Al(III) and Fe(III)/Fe(II) are directly involved in the precipitation of beta-sheets of Abeta_{42} in senile plaque cores whereas the presence of Cu(II) and Zn(II) is adventitious. The co-deposition of Al(III), Fe(III) and beta-sheets of Abeta_{42} could act as a source of reactive oxygen species and begin to explain some of the oxidative damage found in the immediate vicinity of senile plaques. Whether such metal-Abeta_{42} synergisms are an integral part of the aetiology of AD remains to be confirmed. PMID:17119286

Exley, Christopher

2006-11-01

86

Effect of secondary structure on the potential of mean force for poly-L-lysine in the alpha-Helix and beta-sheet conformations  

SciTech Connect

Because poly-L-lysine (PLL) can exist in the {alpha}-helix or {beta}-sheet conformation depending on solution preparation and solution conditions, PLL is a suitable candidate to probe the dependence of protein interactions on secondary structure. The osmotic second virial coefficient and weight-average molecular weight are reported from low-angle laser-light scattering measurements for PLL as a function of NaCl concentration, pH, and {alpha}-helix or {beta}-sheet content. Interactions between PLL molecules become more attractive as salt concentration increases due to screening of PLL charge by salt ions and at low salt concentration become more attractive as pH increases due to decreased net charge on PLL. The experimental results show that interactions are stronger for the {beta}-sheet conformation than for the {alpha}-helix conformation. A spherically-symmetric model for the potential of mean force is used to account for specific interactions not described by DLVO theory and to show how differences in secondary structure affect PLL interactions.

Grigsby, J.J.; Blanch, H.W.; Prausnitz, J.M.

2001-10-30

87

Biosynthesis of streptothricin F. 5. Formation of. beta. -lysine by Streptomyces L-1689-23  

SciTech Connect

The formation of the ..beta..-lysine moiety of streptothricin F has been studied by feeding to Streptomyces L-1689-23 ..cap alpha..-(3-/sup 13/C,/sup 15/N)-, ..cap alpha..-((3RS)-/sup 2/H/sub 2/)-, ..cap alpha..-((3R)-/sup 2/H)-, and ..cap alpha..-((3S)-/sup 2/H)lysine and ..beta..-((2S)-/sup 2/H)lysine. From the analysis of either the /sup 13/C NMR or /sup 2/H NMR spectrum of the derived antibiotics, it has been determined that the ..cap alpha..-nitrogen migrates to C-3 with inversion of configuration by an intramolecular process, and the 3-pro-R hydrogen migrates to C-2 with inversion of configuration by a process that is substantially or completely intermolecular. The very high degree of incorporation of labeled ..beta..-lysine indicates it is probably an intermediate in the biosynthesis of streptothricin F.

Thiruvengadam, T.K. (Univ. of Connecticut, Storrs); Gould, S.J.; Aberhart, D.J.; Lin, H.J.

1983-08-10

88

Amyloid formation and inhibition of an all-beta protein: A study on fungal polygalacturonase  

NASA Astrophysics Data System (ADS)

Theoretically, all proteins can adopt the nanofibrillar structures known as amyloid, which contain cross-beta structures. The all-beta folded proteins are particularly interesting in this regard, since they appear to be naturally more predisposed toward this structural arrangement. In this study, methanol has been used to drive the beta-helix protein polygalacturonase (PG), toward amyloid fibril formation. Congo red absorbance, thioflavin T fluorescence, circular dichroism (CD) and transmission electron microscopy have been used to characterize this process. Similar to other all-beta proteins, PG shows a non-cooperative fibrillation mechanism, but the structural changes that are monitored by CD indicate a different pattern. Furthermore, several compounds containing aromatic components were tested as potential inhibitors of amyloid formation. Another protein predominantly composed of alpha-helices (human serum albumin) was also targeted by these ligands, in order to get an insight into their potential anti-aggregation property toward structurally different proteins. Among tested compounds, silibinin and chlorpropamide were able to considerably affect both proteins fibrillation process.

Chinisaz, Maryam; Ghasemi, Atiyeh; Larijani, Bagher; Ebrahim-Habibi, Azadeh

2014-02-01

89

Concentration-dependency of beta-lactam-induced filament formation in Gram-negative bacteria  

Microsoft Academic Search

Ceftazidime and cefotaxime are beta-lactam antibiotics with dose-related affinities for penicillin-binding protein (PBP)-3 and PBP-1. At low concentrations, these antibiotics inhibit PBP-3, leading to filament formation. Filaments are long strands of non-dividing bacteria that contain enhanced quantities of endotoxin molecules. Higher concentrations of ceftazidime or cefotaxime cause inhibition of PBP-1, resulting in rapid bacterial lysis, which is associated with low

J. Buijs; A. S. M. Dofferhoff; J. W. Mouton; J. H. T. Wagenvoort

2008-01-01

90

Involvement of transforming growth factor-beta in the formation of fibrotic lesions in carcinoid heart disease.  

PubMed Central

Carcinoid heart disease is a complication of a neuroendocrine carcinoid tumor. Morphologically, it is characterized by the formation of fibrotic plaques with deposition of extracellular matrix in the subendocardium, frequently causing heart valve dysfunction and cardiac failure. Because members of the transforming growth factor-beta (TGF-beta) family are known to stimulate fibroblasts in their production of extracellular matrix, we investigated the expression of the three isoforms of TGF-beta and the binding protein for latent TGF-beta 1 (LTBP) in carcinoid plaques of the right side of the heart, as well as from control tissue, using immunohistochemistry. Tissue specimens were obtained intraoperatively from nine consecutive patients undergoing valve replacement surgery. TGF-beta 1 and TGF-beta 3 were detected in the fibroblasts of all plaques analyzed, whereas TGF-beta 2 was only rarely expressed. The localization of LTBP was partly concordant with that of TGF-beta 1, but the positive staining for LTBP was extracellular. Sections from unaffected heart tissue contained few fibroblasts in the subendocardium, showing only weak or no immunostaining for TGF-beta 1, -beta 2, and -beta 3 and no staining for LTBP. These results suggest that TGF-beta may play a role in the proliferation of fibroblasts and their matrix production in carcinoid heart lesions. Images Figure 1 p75-a Figure 2 PMID:8424467

Waltenberger, J.; Lundin, L.; Oberg, K.; Wilander, E.; Miyazono, K.; Heldin, C. H.; Funa, K.

1993-01-01

91

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 PMID:7667318

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

1995-01-01

92

Locally injection of cell sheet fragments enhances new bone formation in mandibular distraction osteogenesis: a rabbit model.  

PubMed

Effective methods to shorten the treatment period of distraction osteogenesis (DO) are needed. To investigate whether injections of osteogenic bone marrow stromal cell (BMSC) sheet fragments could be used to facilitate new bone formation during DO, 30 rabbits underwent bilateral mandibular osteotomy and their mandibles were lengthened at a rate of 0.75?mm/12?h for 6 days after a 5-day latency period. There were three treatment groups (n?=?10 for each group): Serum-free medium, dissociated BMSCs, and BMSC sheet fragments. A local injection was conducted with a needle directly into the distracted areas immediately after distraction. Rabbits were sacrificed for examination at 3 and 6 weeks after injection. Gross examination, radiographic evaluation, and micro-CT scanning indicated a significant increase in bony union in the BMSC sheet fragment group, compared with the medium group and the dissociated cell group. The histomorphometric analysis showed more intensive bone formation in the sheet fragment group than the other two groups at each time point. Additionally, the peak load was significantly higher in the fragment group than those in the others. The results show that injection of BMSC sheet fragments promotes bone formation in DO and indicate a promising approach to shorten the treatment period of osteodistraction. PMID:23494761

Ma, Dongyang; Ren, Liling; Yao, Hong; Tian, Wenyan; Chen, Fulin; Zhang, Junrui; Liu, Yanpu; Mao, Tianqiu

2013-07-01

93

2D 1H and 3D 1H-15N NMR of zinc-rubredoxins: contributions of the beta-sheet to thermostability.  

PubMed Central

Based on 2D 1H-1H and 2D and 3D 1H-15N NMR spectroscopies, complete 1H NMR assignments are reported for zinc-containing Clostridium pasteurianum rubredoxin (Cp ZnRd). Complete 1H NMR assignments are also reported for a mutated Cp ZnRd, in which residues near the N-terminus, namely, Met 1, Lys 2, and Pro 15, have been changed to their counterparts, (-), Ala and Glu, respectively, in rubredoxin from the hyperthermophilic archaeon, Pyrococcus furiosus (Pf Rd). The secondary structure of both wild-type and mutated Cp ZnRds, as determined by NMR methods, is essentially the same. However, the NMR data indicate an extension of the three-stranded beta-sheet in the mutated Cp ZnRd to include the N-terminal Ala residue and Glu 15, as occurs in Pf Rd. The mutated Cp Rd also shows more intense NOE cross peaks, indicating stronger interactions between the strands of the beta-sheet and, in fact, throughout the mutated Rd. However, these stronger interactions do not lead to any significant increase in thermostability, and both the mutated and wild-type Cp Rds are much less thermostable than Pf Rd. These correlations strongly suggest that, contrary to a previous proposal [Blake PR et al., 1992, Protein Sci 1:1508-1521], the thermostabilization mechanism of Pf Rd is not dominated by a unique set of hydrogen bonds or electrostatic interactions involving the N-terminal strand of the beta-sheet. The NMR results also suggest that an overall tighter protein structure does not necessarily lead to increased thermostability. PMID:8732760

Richie, K. A.; Teng, Q.; Elkin, C. J.; Kurtz, D. M.

1996-01-01

94

Nonlinear evolution of three-dimensional instabilities of thin and thick electron scale current sheets: Plasmoid formation and current filamentation  

SciTech Connect

Nonlinear evolution of three dimensional electron shear flow instabilities of an electron current sheet (ECS) is studied using electron-magnetohydrodynamic simulations. The dependence of the evolution on current sheet thickness is examined. For thin current sheets (half thickness =d{sub e}=c/?{sub pe}), tearing mode instability dominates. In its nonlinear evolution, it leads to the formation of oblique current channels. Magnetic field lines form 3-D magnetic spirals. Even in the absence of initial guide field, the out-of-reconnection-plane magnetic field generated by the tearing instability itself may play the role of guide field in the growth of secondary finite-guide-field instabilities. For thicker current sheets (half thickness ?5?d{sub e}), both tearing and non-tearing modes grow. Due to the non-tearing mode, current sheet becomes corrugated in the beginning of the evolution. In this case, tearing mode lets the magnetic field reconnect in the corrugated ECS. Later thick ECS develops filamentary structures and turbulence in which reconnection occurs. This evolution of thick ECS provides an example of reconnection in self-generated turbulence. The power spectra for both the thin and thick current sheets are anisotropic with respect to the electron flow direction. The cascade towards shorter scales occurs preferentially in the direction perpendicular to the electron flow.

Jain, Neeraj; Büchner, Jörg [Max Planck/Princeton Center for Plasma Physics, Göttingen (Germany); Max Planck Institute for Solar System Research, Justus-Von-Liebig-Weg-3, Göttingen (Germany)

2014-07-15

95

Carbon Nanotube Inhibits the Formation of ?-Sheet-Rich Oligomers of the Alzheimer's Amyloid-?(16-22) Peptide  

PubMed Central

Alzheimer's disease is associated with the abnormal self-assembly of the amyloid-? (A?) peptide into toxic ?-rich aggregates. Experimental studies have shown that hydrophobic nanoparticles retard A? fibrillation by slowing down the nucleation process; however, the effects of nanoparticles on A? oligomeric structures remain elusive. In this study, we investigate the conformations of A?(16-22) octamers in the absence and presence of a single-walled carbon nanotube (SWCNT) by performing extensive all-atom replica exchange molecular-dynamics simulations in explicit solvent. Our simulations starting from eight random chains demonstrate that the addition of SWCNT into A?(16-22) solution prevents ?-sheet formation. Simulation starting from a prefibrillar ?-sheet octamer shows that SWCNT destabilizes the ?-sheet structure. A detailed analysis of the A?(16-22)/SWCNT/water interactions reveals that both the inhibition of ?-sheet formation and the destabilization of prefibrillar ?-sheets by SWCNT result from the same physical forces: hydrophobic and ?-stacking interactions (with the latter playing a more important role). By analyzing the stacking patterns between the Phe aromatic rings and the SWCNT carbon rings, we find that short ring–centroid distances mostly favor parallel orientation, whereas large distances allow all other orientations to be populated. Overall, our computational study provides evidence that SWCNT is likely to inhibit A?(16-22) and full-length A? fibrillation. PMID:22067167

Li, Huiyu; Luo, Yin; Derreumaux, Philippe; Wei, Guanghong

2011-01-01

96

Activity of enzymes catalyzing formation of beta-L-fucosyl phosphate and GDP-beta-L-fucose in amphibian tissues and their application in chemo-enzymic synthesis of GDP-beta-L-fucose.  

PubMed

Amphibian oviduct and liver were shown to contain enzymes that catalyze the formation of GDP-beta-L-fucose from GDP-alpha-D-mannose or L-fucose. The conversion of L-fucose into beta-L-fucopyranosyl phosphate was achieved on a preparative scale using high-activity fucokinase in toad liver extracts. For chemo-enzymic preparation of GDP-beta-L-fucose, a convenient modification for pyrophosphate synthesis through phosphomorpholidate which does not require anhydrous conditions is suggested. PMID:10424902

Druzhinina, T N; Utkina, N S; Chan, K; Strecker, G; Shibaev, V N

1999-07-01

97

Concentration-dependent reversible self-oligomerization of serum albumins through intermolecular ?-sheet formation.  

PubMed

Proteins inside a cell remain in highly crowded environments, and this often affects their structure and activity. However, most of the earlier studies involving serum albumins were performed under dilute conditions, which lack biological relevance. The effect of protein-protein interactions on the structure and properties of serum albumins at physiological conditions have not yet been explored. Here, we report for the first time the effect of protein-protein and protein-crowder interactions on the structure and stability of two homologous serum albumins, namely, human serum albumin (HSA) and bovine serum albumin (BSA), at physiological conditions by using spectroscopic techniques and scanning electron microscopy (SEM). Concentration-dependent self-oligomerization and subsequent structural alteration of serum albumins have been explored by means of fluorescence and circular dichroism spectroscopy at pH 7.4. The excitation wavelength (?ex) dependence of the intrinsic fluorescence and the corresponding excitation spectra at each emission wavelength indicate the presence of various ground state oligomers of serum albumins in the concentration range 10-150 ?M. Circular dichroism and thioflavin T binding assay revealed formation of intermolecular ?-sheet rich interfaces at high protein concentration. Excellent correlations have been observed between ?-sheet content of both the albumins and fluorescence enhancement of ThT with protein concentrations. SEM images at a concentration of 150 ?M revealed large dispersed self-oligomeric states with sizes vary from 330 to 924 nm and 260 to 520 nm for BSA and HSA, respectively. The self-oligomerization of serum albumins is found to be a reversible process; upon dilution, these oligomers dissociate into a native monomeric state. It has also been observed that synthetic macromolecular crowder polyethylene glycol (PEG 200) stabilizes the self-associated state of both the albumins which is contrary to expectations that the macromolecular crowding favors compact native state of proteins. PMID:25409497

Bhattacharya, Arpan; Prajapati, Roopali; Chatterjee, Surajit; Mukherjee, Tushar Kanti

2014-12-16

98

Different roles of protein kinase C-beta and -delta in arachidonic acid cascade, superoxide formation and phosphoinositide hydrolysis.  

PubMed Central

In contrast with protein kinase C (PKC)-beta, PKC-delta is exclusively detectable in the membrane fraction of liver macrophages. After long-term treatment with phorbol 12-myristate 13-acetate (PMA) PKC-beta is depleted faster (within 3 h) than PKC-delta (> 7h). Simultaneously, pretreatment with PMA for 3 h inhibits the PMA- and zymosan-induced generation of superoxide and the PMA-induced formation of prostaglandin (PG) E2, whereas a preincubation of more than 7 h is required to affect the zymosan-induced release of PGE2 and inositol phosphates. These results support an involvement of PKC-beta in the PMA-induced activation of the arachidonic acid cascade and in superoxide formation and imply an involvement of PKC-delta in zymosan-induced phosphoinositide hydrolysis and PGE2 formation. Two phorbol ester derivates, sapintoxin A (SAPA) and 12-deoxyphorbol 13-phenylacetate 20-acetate (DOPPA), which have been previously reported to activate preferentially PLC-beta but not PKC-delta in vitro [Ryves, Evans, Olivier, Parker and Evans (1992) FEBS Lett. 288, 5-9], induce the formation of PGE2 and superoxide, down-regulate PKC-delta and potentiate inositol phosphate formation in parallel SAPA, but not DOPPA, down-regulates PKC-beta and inhibits the PMA-induced formation of eicosanoids and superoxide. Images Figure 1 Figure 2 Figure 5 PMID:8389125

Duyster, J; Schwende, H; Fitzke, E; Hidaka, H; Dieter, P

1993-01-01

99

Analysis of Nugget Formation During Resistance Spot Welding on Dissimilar Metal Sheets of Aluminum and Magnesium Alloys  

NASA Astrophysics Data System (ADS)

The nugget formation of resistance spot welding (RSW) on dissimilar material sheets of aluminum and magnesium alloys was studied, and the element distribution, microstructure, and microhardness distribution near the joint interface were analyzed. It was found that the staggered high regions at the contact interface of aluminum and magnesium alloy sheets, where the dissimilar metal melted together, tended to be the preferred nucleation regions of nugget. The main technical problem of RSW on dissimilar metal sheets of aluminum and magnesium alloys was the brittle-hard Al12Mg17 intermetallic compounds distributed in the nugget, with hardness much higher than either side of the base materials. Microcracks tended to generate at the interface of the nugget and base materials, which affected weld quality and strength.

Luo, Yi; Li, Jinglong

2014-10-01

100

Formation of a very thin current sheet in the near-earth magnetotail and the explosive growth phase of substorms  

NASA Technical Reports Server (NTRS)

A magnetofricional method is used to construct two-dimensional MHD equilibria of the Earth's magnetosphere for a given distribution of entropy functions(S = pV(exp gamma), where p is the plasma pressure and V is the tube volume per unit magnetic flux. It is found that a very thin current sheet with B (sub zeta) is less than 0.5 nu T and thickness less than 1000 km can be formed in the near-earth magnetotail (x is approximately -8 to -20R(sub e) during the growth phase of substorm. The tail current sheets are found to become thinner as the entropy or the entropy gradient increases. It is suggested that the new entropy anti-diffusion instability associated with plasma transport across field lines leads to magnetic field dipolarization and accelerates the formation of thin current sheet, which may explain the observed explosive growth phase of substorms.

Lee, L. C.; Zhang, L.; Choe, G. S.; Cai, H. J.

1995-01-01

101

Protein Secondary Structures (alpha-helix and beta-sheet) at a Cellular Levle and Protein Fractions in Relation to Rumen Degradation Behaviours of Protein: A New Approach  

SciTech Connect

Studying the secondary structure of proteins leads to an understanding of the components that make up a whole protein, and such an understanding of the structure of the whole protein is often vital to understanding its digestive behaviour and nutritive value in animals. The main protein secondary structures are the {alpha}-helix and {beta}-sheet. The percentage of these two structures in protein secondary structures influences protein nutritive value, quality and digestive behaviour. A high percentage of {beta}-sheet structure may partly cause a low access to gastrointestinal digestive enzymes, which results in a low protein value. The objectives of the present study were to use advanced synchrotron-based Fourier transform IR (S-FTIR) microspectroscopy as a new approach to reveal the molecular chemistry of the protein secondary structures of feed tissues affected by heat-processing within intact tissue at a cellular level, and to quantify protein secondary structures using multicomponent peak modelling Gaussian and Lorentzian methods, in relation to protein digestive behaviours and nutritive value in the rumen, which was determined using the Cornell Net Carbohydrate Protein System. The synchrotron-based molecular chemistry research experiment was performed at the National Synchrotron Light Source at Brookhaven National Laboratory, US Department of Energy. The results showed that, with S-FTIR microspectroscopy, the molecular chemistry, ultrastructural chemical make-up and nutritive characteristics could be revealed at a high ultraspatial resolution ({approx}10 {mu}m). S-FTIR microspectroscopy revealed that the secondary structure of protein differed between raw and roasted golden flaxseeds in terms of the percentages and ratio of {alpha}-helixes and {beta}-sheets in the mid-IR range at the cellular level. By using multicomponent peak modelling, the results show that the roasting reduced (P <0.05) the percentage of {alpha}-helixes (from 47.1% to 36.1%: S-FTIR absorption intensity), increased the percentage of {beta}-sheets (from 37.2% to 49.8%: S-FTIR absorption intensity) and reduced the {alpha}-helix to {beta}-sheet ratio (from 0.3 to 0.7) in the golden flaxseeds, which indicated a negative effect of the roasting on protein values, utilisation and bioavailability. These results were proved by the Cornell Net Carbohydrate Protein System in situ animal trial, which also revealed that roasting increased the amount of protein bound to lignin, and well as of the Maillard reaction protein (both of which are poorly used by ruminants), and increased the level of indigestible and undegradable protein in ruminants. The present results demonstrate the potential of highly spatially resolved synchrotron-based infrared microspectroscopy to locate 'pure' protein in feed tissues, and reveal protein secondary structures and digestive behaviour, making a significant step forward in and an important contribution to protein nutritional research. Further study is needed to determine the sensitivities of protein secondary structures to various heat-processing conditions, and to quantify the relationship between protein secondary structures and the nutrient availability and digestive behaviour of various protein sources. Information from the present study arising from the synchrotron-based IR probing of the protein secondary structures of protein sources at the cellular level will be valuable as a guide to maintaining protein quality and predicting digestive behaviours.

Yu,P.

2007-01-01

102

Inducing ?-Sheets Formation in Synthetic Spider Silk Fibers by Aqueous Post-Spin Stretching  

PubMed Central

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 manmade 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

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

2012-01-01

103

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

104

Formation of High-Beta Plasma and Stable Confinement of Toroidal Electron Plasma in RT-1  

NASA Astrophysics Data System (ADS)

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 geomagnetic field compensation [Y. Yano et al., Plasma Fusion Res. 4, 039] resulted drastic improvements of the plasma properties, and a maximum local beta value exceeded 70%. Because plasma is generated by electron cyclotron resonance heating (ECH) in the present experiment, the plasma pressure is mainly due to hot electrons, whose bremsstrahlung was observed with an x-ray CCD camera. The pressure profiles have rather steep gradient near the superconducting coil in the strong field region. The decay rates of magnetic probe and interferometer signals have different time constants, suggesting multiple temperature components. The energy confinement time estimated from the input RF power and stored magnetic energy is on the order of 1s, which is comparable to the decay time constant of the density of hot electron component. Pure electron plasma experiments are also conducted in RT-1. Radial profiles of electrostatic potential and electron density showed that the plasma rigidly rotates in the toroidal direction in the stable confinement phase. Long time confinement of toroidal non- neutral plasma for more than 300s and inward particle diffusion to strong field regions, caused by the activation of the diocotron (Kelvin-Helmholtz) instability, have been realized [Z. Yoshida et al., Phys. Rev. Lett. 104, 235004].

Saitoh, Haruhiko

2010-11-01

105

Doubling the cross-linking interface of a rationally designed beta roll peptide for calcium-dependent proteinaceous hydrogel formation.  

PubMed

We have rationally engineered a stimulus-responsive cross-linking domain based on a repeats-in-toxin (RTX) peptide to enable calcium-dependent formation of supramolecular hydrogel networks. The peptide isolated from the RTX domain is intrinsically disordered in the absence of calcium. In calcium rich environments, the peptide binds Ca(2+) ions and folds into a beta roll (?-roll) secondary structure composed to two parallel ?-sheet faces. Previously, we mutated one of the faces to contain solvent exposed leucine side chains which are localized only in the calcium-bound ?-roll conformation. We demonstrated the ability of this mutant peptide to self-assemble into hydrogels in the presence of calcium with the aid of additional peptide-based cross-linking moieties. Here, we have expanded this approach by engineering both ?-roll faces to contain leucine residues, thereby doubling the cross-linking interface for each monomeric building block. These leucine rich surfaces impart a hydrophobic driving force for self-assembly. Extensive characterization was performed on this double-faced mutant to ensure the retention of calcium affinity and subsequent structural rearrangement similar to that of the wild type domain. We genetically fused an ?-helical leucine zipper capable of forming tetrameric coiled-coil bundles to the peptide and the resulting chimeric protein self-assembles into a hydrogel only in calcium rich environments. Since this new mutant peptide enables cross-linking on both surfaces simultaneously, a higher oligomerization state was achieved. To further investigate the cross-linking capability, we constructed concatemers of the ?-roll with maltose binding protein (MBP), a monomeric globular protein, without the leucine zipper domains. These concatemers show a similar sol-gel transition in response to calcium. Several biophysical techniques were used to probe the structural and mechanical properties of the mutant ?-roll domain and the resulting supramolecular networks including circular dichroism, fluorescence resonance energy transfer, bis-ANS binding, and microrheology. These results demonstrate that the engineered ?-roll peptides can mediate calcium-dependent cross-linking for protein hydrogel formation without the need for any other cross-linking moieties. PMID:25226243

Dooley, Kevin; Bulutoglu, Beyza; Banta, Scott

2014-10-13

106

Study of Benzyl Salicylate\\/beta-Cyclodextrin Inclusion Complex Formation by Positron Annihilation  

Microsoft Academic Search

Results of positron annihilation lifetime spectra of beta-cyclodextrin and beta-cyclodextrin complexed with benzyl salicylate,benzyl acetate, or ethyl salicylate in air and vacuum were used to determine the fraction of beta-cyclodextrin which remains uncomplexed in the benzyl salicylate\\/beta-cyclodextrin 1:2 molar ratio inclusion complex. The intensity of the longest-lived component in vacuum was shown to decrease when the beta-cyclodextrin cavity was filled

V. J. Bellitto; F. H. Hsu Hadley Jr.; T. Trinh

1996-01-01

107

Alpha2-macroglobulin associates with beta-amyloid peptide and prevents fibril formation.  

PubMed

We have used the yeast two-hybrid system to isolate cDNAs encoding proteins that specifically interact with the 42-aa beta-amyloid peptide (Abeta), a major constituent of senile plaques in Alzheimer's disease. The carboxy terminus of alpha2-macroglobulin (alpha2M), a proteinase inhibitor released in response to inflammatory stimuli, was identified as a strong and specific interactor of Abeta, utilizing this system. Direct evidence for this interaction was obtained by co-immunoprecipitation of alpha2M with Abeta from the yeast cell, and by formation of SDS-resistant Abeta complexes in polyacrylamide gels by using synthetic Abeta and purified alpha2M. The association of Abeta with alpha2M and various purified amyloid binding proteins was assessed by employing a method measuring protein-protein interactions in liquid phase. The dissociation constant by this technique for the alpha2M-Abeta association using labeled purified proteins was measured (Kd = 350 nM). Electron microscopy showed that a 1:8 ratio of alpha2M to Abeta prevented fibril formation in solution; the same ratio to Abeta of another acute phase protein, alpha1-antichymotrypsin, was not active in preventing fibril formation in vitro. These results were corroborated by data obtained from an in vitro aggregation assay employing Thioflavine T. The interaction of alpha2M with Abeta suggests new pathway(s) for the clearance of the soluble amyloid peptide. PMID:9501253

Hughes, S R; Khorkova, O; Goyal, S; Knaeblein, J; Heroux, J; Riedel, N G; Sahasrabudhe, S

1998-03-17

108

Amyloid-like fibril formation in an all beta-barrel protein involves the formation of partially structured intermediate(s).  

PubMed

In the present study, we demonstrate the thermal induced amyloid formation in a beta-barrel protein, such as the acidic fibroblast growth factor from Notopthalmus viridescens (nFGF-1). Fibril formation in nFGF-1 is observed to occur maximally at 65 degrees C. Electron microscope analysis of the thermal induced fibrils of nFGF-1 shows that they are filamentous with an average diameter of about 20 nm. X-ray diffraction analysis reveals that the thermal induced fibrils of nFGF-1 have a typical "cross-beta" structure with the beta-strands perpendicular to the fibril axis. By using a variety of biophysical techniques including multidimensional NMR, we demonstrate that fibril formation involves the formation of a partially structured intermediate(s) in the thermal unfolding pathway of the protein (nFGF-1). Results of the anilino-8-napthalene sulfonate binding experiments indicate that fibril formation occurs due to the coalescence of the protein (in the intermediate state(s)) through the solvent-exposed non-polar surface(s). In this study, we also demonstrate that organic osmolytes, such as proline, can efficiently prevent the thermal induced amyloid formation in nFGF-1. Proline is found to stabilize the native conformation of the protein. The addition, proline is observed to increase the cooperativity of the unfolding (native <--> denatured) reaction and consequently decrease the population of the "sticky" thermal equilibrium intermediate(s) responsible for the fibril formation. PMID:11877422

Srisailam, Sampath; Wang, Han-Min; Kumar, Thallampuranam Krishnaswamy S; Rajalingam, Dakshinamurthy; Sivaraja, Vaithiyalingam; Sheu, Hwo-Shuenn; Chang, Yen-Chung; Yu, Chin

2002-05-24

109

Mechanistic studies on the stereoselective formation of beta-mannosides from mannosyl iodides using alpha-deuterium kinetic isotope effects.  

PubMed

Stereoselective synthesis of beta-mannosides is one of the most challenging linkages to achieve in carbohydrate chemistry. Both the anomeric effect and the C2 axial substituent favor the formation of the axial glycoside (alpha-product). Herein, we describe mechanistic studies on the beta-selective glycosidation of trimethylene oxide (TMO) using mannosyl iodides. Density functional calculations (at the B3LYP/6-31+G(d,p):LANL2DZ level) suggest that formation of both alpha- and beta-mannosides involve loose S(N)2-like transition-state structures with significant oxacarbenium character, although the transition structure for formation of the alpha-mannoside is significantly looser. alpha-Deuterium kinetic isotope effects (alpha-DKIEs) based upon these computed transition state geometries match reasonably well with the experimentally measured values: 1.16 +/- 0.02 for the beta-linkage (computed to be 1.15) and 1.19 +/- 0.05, see table 2 for the alpha-analogue (computed to be 1.26). Since it was unclear if beta-selectivity resulted from a conformational constraint induced by the anomeric iodide, a 4,6-O-benzylidine acetal was used to lock the iodide into a chairlike conformation. Both experiments and calculations on this analogue suggest that it does not mirror the behavior of mannosyl iodides lacking bridging acetal protecting groups. PMID:17539683

El-Badri, Mohamed H; Willenbring, Dan; Tantillo, Dean J; Gervay-Hague, Jacquelyn

2007-06-22

110

Reduced Reelin expression accelerates amyloid-beta plaque formation and tau pathology in transgenic Alzheimer's disease mice.  

PubMed

In addition to the fundamental role of the extracellular glycoprotein Reelin in neuronal development and adult synaptic plasticity, alterations in Reelin-mediated signaling have been suggested to contribute to neuronal dysfunction associated with Alzheimer's disease (AD). In vitro data revealed a biochemical link between Reelin-mediated signaling, Tau phosphorylation, and amyloid precursor protein (APP) processing. To directly address the role of Reelin in amyloid-beta plaque and Tau pathology in vivo, we crossed heterozygous Reelin knock-out mice (reeler) with transgenic AD mice to investigate the temporal and spatial AD-like neuropathology. We demonstrate that a reduction in Reelin expression results in enhanced amyloidogenic APP processing, as indicated by the precocious production of amyloid-beta peptides, the significant increase in number and size of amyloid-beta plaques, as well as age-related aggravation of plaque pathology in double mutant compared with single AD mutant mice of both sexes. Numerous amyloid-beta plaques accumulate in the hippocampal formation and neocortex of double mutants, precisely in layers with strongest Reelin expression and highest accumulation of Reelin plaques in aged wild-type mice. Moreover, concentric accumulations of phosphorylated Tau-positive neurons around amyloid-beta plaques were evident in 15-month-old double versus single mutant mice. Silver stainings indicated the presence of neurofibrillary tangles, selectively associated with amyloid-beta plaques and dystrophic neurites in the entorhinal cortex and hippocampus. Our findings suggest that age-related Reelin aggregation and concomitant reduction in Reelin-mediated signaling play a proximal role in synaptic dysfunction associated with amyloid-beta deposition, sufficient to enhance Tau phosphorylation and tangle formation in the hippocampal formation in aged Reelin-deficient transgenic AD mice. PMID:20610758

Kocherhans, Samira; Madhusudan, Amrita; Doehner, Jana; Breu, Karin S; Nitsch, Roger M; Fritschy, Jean-Marc; Knuesel, Irene

2010-07-01

111

Magnetic relaxation, current sheets, and structure formation in an extremely tenuous fluid medium  

E-print Network

—. 1987, Revista Brasiliera de Ciencias Mecanicas, IX, 93 – 23 – Parker, E. N. 1994, Spontaneous Current Sheets in Magnetic Fields (Oxford University Press) Pfrommer, C. & Dursi, J. 2010, Nat. Phys., 6, 520 Priest, E. & Forbes, T. 2007, Magnetic...

Bajer, K.; Moffatt, H. K.

2013-12-03

112

Molecular analysis of cell surface $\\\\beta$1,4-galactosyltransferase function during lamellipodal formation, cell polarization, and cell migration  

Microsoft Academic Search

The rate and direction of fibroblast locomotion is regulated by the formation of lamellipodia. In turn, lamellipodal formation is modulated in part by adhesion of that region of the cell from which the lamellipodia will extend or orginate. Cell surface $\\\\beta$1,4-galactosyltransferase (GalTase) is one molecule that has been demonstrated to mediate cellular interactions with extracellular matrices. In the case of

Paul Andrew Appeddu

1993-01-01

113

Alpha-helix formation in melittin and beta-lactoglobulin A induced by fluorinated dialcohols.  

PubMed

Extensive study of the effect of fluorinated alcohols on protein conformations, notably the induction of alpha-helix formation, is important because of its wide range of applications. Circular dichroism (CD) was used to show that the enhancement of helix induction in beta-lactoglobulin A and melittin by the fluorinated diols 2,2,3,3-tetrafluoro-1,4-butanediol (TFBD), 2,2,3,3,4,4-hexafluoro-1,6-pentanediol (HFPD), and 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol (OFHD) increases in the order TFBD < HFPD < OFHD. For fluorinated diols and monoalcohols the effectiveness of helix induction was found to increase exponentially with increasing number of fluorine atoms per alcohol molecule, and OFHD was found to be more effective than any previously reported fluorinated alcohol. Formation of standard micelles was ruled out as the cause of the enhanced helix induction by the fluorinated diols. The negligible red-edge excitation shift in the fluorescence of melittin indicated that the fluorinated diol/water solvent shell surrounding the tryptophan chromophore is less immobilized than are molecules in a lamellar vesicle. PMID:16771343

Schuh, Merlyn D; Baldwin, Melinda C

2006-06-01

114

Engineering of betabellin-15d: A 64 residue beta sheet protein that forms long narrow multimeric fibrils  

Microsoft Academic Search

The betabellin target structure is a P-sandwich protein consisting of two 32 residue P-sheets packed against one another by interaction of their hydrophobic faces. The 32 residue chain of betabellin-15s (HSLTAKIpkLTFSIAphTYTCAV pkYTAKVSH, where p = DPrO, k = DLYS, and h = DHis) did not fold in water at pH 6.5. Air oxidation of betabellin-15s provided betabellin- 15D, the 64

Amareth Lim; Matthew J. Saderholm; Mathias Kroll; Yibing Yan; Lalith Perera; Bruce W. Erickson; Alexander M. Makhov; Jack D. Griffith

1998-01-01

115

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

116

Phosphorylation of amyloid beta (A?) peptides – A trigger for formation of toxic aggregates in Alzheimer's disease  

PubMed Central

Alzheimer's disease (AD) is the most common form of dementia and associated with the progressive accumulation of amyloid ?-peptides (A?) in form of extracellular amyloid plaques in the human brain. A critical role of A? in the pathogenesis of AD is strongly supported by gene mutations that cause early-onset familial forms of the disease. Such mutations have been identified in the APP gene itself and in presenilin 1 and 2. Importantly, all the identified mutations commonly lead to early deposition of extracellular plaques likely by increasing the generation and/or aggregation of A?. However, such mutations are very rare and molecular mechanisms that might trigger aggregation and deposition of A?, in the most common late onset AD are largely unknown. We recently demonstrated that extracellular A? undergoes phosphorylation by a cell surface-localized or secreted form of protein kinase A. The phosphorylation of serine residue 8 promotes aggregation by stabilization of ?-sheet conformation of A? and increased formation of oligomeric A? aggregates that represent nuclei for fibrillization. Phosphorylated A? was detected in the brains of transgenic mice and human AD brains and showed increased toxicity in Drosophila models as compared with non-phosphorylated A?. Together, these findings demonstrate a novel molecular mechanism that triggers aggregation and toxicity of A?. Thus, phosphorylation of A? could be relevant in the pathogenesis of late onset AD. The identification of extracellular protein kinase A should also stimulate pharmacological approaches to decrease A? phosphorylation in the therapy and/or prevention of AD. PMID:21869458

Kumar, Sathish; Walter, Jochen

2011-01-01

117

Semaphorin 3A blocks the formation of pathologic choroidal neovascularization induced by transforming growth factor beta  

PubMed Central

Objective Choroidal neovascularization (CNV) is a major cause of vision loss in retinal diseases such as age-related macular degeneration (AMD). Previously, we demonstrated that semaphorin3A (Sema3A), which is a chemorepellent guidance molecule, inhibited the formation of retina neovascularization. In the present study, we investigated the antiangiogenic effects of Sema3A on transforming growth factor beta (TGF-?) in vitro and in vivo. Methods Enzyme-linked immunosorbent assays (ELISAs) were used to measure the TGF-? levels in the vitreous humor of patients with AMD and controls. Human umbilical vein endothelial cells (HUVECs) were used for the in vitro study, and a laser-induced CNV mouse model was prepared for the in vivo study. The HUVECs were incubated with TGF-? and Sema3A. The proliferation, migration, apoptosis, and tube formation of the cells were then measured using BrdU, Transwell, flow cytometry, and Matrigel assays, respectively, and the SMAD2/3 signaling pathways were analyzed using western blot analysis. The C57BL/6J mouse retina was exposed to a laser to induce choroidal neovascularization (CNV), and Sema3A was injected intravitreously. After 14 days, fundus fluorescein angiography was performed to evaluate the leakage area of the CNV. The vascular endothelial growth factor (VEGF) and TGF-? concentrations in the retina-choroid complex were measured with ELISA. Components of the p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase-1/2 (ERK1/2), c-Jun NH2-terminal kinase (JNK), and SMAD2/3 signaling pathways in the Sema3A-treated groups were analyzed using western blotting. Results In this study, we first verified that the vitreous TGF-? level was higher in patients with neovascular AMD than in the controls. We also showed that Sema3A inhibited TGF-?-induced HUVEC proliferation, migration, and tube formation and inhibited the downstream SMAD2/3 signaling pathway. Sema3A also induced TGF-?-stimulated HUVEC apoptosis and inhibited the response of TGF-? in vitro. In vivo, the TGF-? level was increased in the CNV mouse model. Sema3A not only inhibited laser-induced CNV formation but also inhibited the uptake of VEGF and TGF-?. In the western blot analysis, Sema3A was shown to inhibit the phosphorylation of p38 MAPK, ERK1/2, and JNK and to inhibit the SMAD2/3 signaling pathway after Sema3A treatment in CNV mice. Conclusions Sema3A can be applied as a useful, adjunctive therapeutic strategy for preventing CNV formation. PMID:25352735

Bai, Yujing; Liang, Shuting; Zhao, Min; Huang, Lvzhen; Zhao, Mingwei; Li, Xiaoxin

2014-01-01

118

Current sheet formation in a sheared force-free-magnetic field. [in sun  

NASA Technical Reports Server (NTRS)

This paper presents the results of a study showing how continuous shearing motion of magnetic footpoints in a tenuous, infinitely conducting plasma can lead to the development of current sheets, despite the absence of such sheets or even of neutral points in the initial state. The calculations discussed here verify the earlier suggestion by Low and Wolfson (1988) that extended current sheets should form due to the shearing of a force-free quadrupolar magnetic field. More generally, this work augments earlier studies suggesting that the appearance of discontinuities - current sheets - may be a necessary consequence of the topological invariance imposed on the magnetic field geometry of an ideal MHD system by virtue of its infinite conductivity. In the context of solar physics, the work shows how the gradual and continuous motion of magnetic footpoints at the solar photosphere may lead to the buildup of magnetic energy that can then be released explosively when finite conductivity effects become important and lead to the rapid dissipation of current sheets. Such energy release may be important in solar flares, coronal mass ejections, and other eruptive events.

Wolfson, Richard

1989-01-01

119

Efficiently engineered cell sheet using a complex of polyethylenimine-alginate nanocomposites plus bone morphogenetic protein 2 gene to promote new bone formation.  

PubMed

Regeneration of large bone defects is a common clinical problem. Recently, stem cell sheet has been an emerging strategy in bone tissue engineering. To enhance the osteogenic potential of stem cell sheet, we fabricated bone morphogenetic protein 2 (BMP-2) gene-engineered cell sheet using a complex of polyethylenimine-alginate (PEI-al) nanocomposites plus human BMP-2 complementary(c)DNA plasmid, and studied its osteogenesis in vitro and in vivo. PEI-al nanocomposites carrying BMP-2 gene could efficiently transfect bone marrow mesenchymal stem cells. The cell sheet was made by culturing the cells in medium containing vitamin C for 10 days. Assays on the cell culture showed that the genetically engineered cells released the BMP-2 for at least 14 days. The expression of osteogenesis-related gene was increased, which demonstrated that released BMP-2 could effectively induce the cell sheet osteogenic differentiation in vitro. To further test the osteogenic potential of the cell sheet in vivo, enhanced green fluorescent protein or BMP-2-producing cell sheets were treated on the cranial bone defects. The results indicated that the BMP-2-producing cell sheet group was more efficient than other groups in promoting bone formation in the defect area. Our results suggested that PEI-al nanocomposites efficiently deliver the BMP-2 gene to bone marrow mesenchymal stem cells and that BMP-2 gene-engineered cell sheet is an effective way for promoting bone regeneration. PMID:24855355

Jin, Han; Zhang, Kai; Qiao, Chunyan; Yuan, Anliang; Li, Daowei; Zhao, Liang; Shi, Ce; Xu, Xiaowei; Ni, Shilei; Zheng, Changyu; Liu, Xiaohua; Yang, Bai; Sun, Hongchen

2014-01-01

120

Efficiently engineered cell sheet using a complex of polyethylenimine–alginate nanocomposites plus bone morphogenetic protein 2 gene to promote new bone formation  

PubMed Central

Regeneration of large bone defects is a common clinical problem. Recently, stem cell sheet has been an emerging strategy in bone tissue engineering. To enhance the osteogenic potential of stem cell sheet, we fabricated bone morphogenetic protein 2 (BMP-2) gene-engineered cell sheet using a complex of polyethylenimine–alginate (PEI–al) nanocomposites plus human BMP-2 complementary(c)DNA plasmid, and studied its osteogenesis in vitro and in vivo. PEI–al nanocomposites carrying BMP-2 gene could efficiently transfect bone marrow mesenchymal stem cells. The cell sheet was made by culturing the cells in medium containing vitamin C for 10 days. Assays on the cell culture showed that the genetically engineered cells released the BMP-2 for at least 14 days. The expression of osteogenesis-related gene was increased, which demonstrated that released BMP-2 could effectively induce the cell sheet osteogenic differentiation in vitro. To further test the osteogenic potential of the cell sheet in vivo, enhanced green fluorescent protein or BMP-2-producing cell sheets were treated on the cranial bone defects. The results indicated that the BMP-2-producing cell sheet group was more efficient than other groups in promoting bone formation in the defect area. Our results suggested that PEI–al nanocomposites efficiently deliver the BMP-2 gene to bone marrow mesenchymal stem cells and that BMP-2 gene-engineered cell sheet is an effective way for promoting bone regeneration. PMID:24855355

Jin, Han; Zhang, Kai; Qiao, Chunyan; Yuan, Anliang; Li, Daowei; Zhao, Liang; Shi, Ce; Xu, Xiaowei; Ni, Shilei; Zheng, Changyu; Liu, Xiaohua; Yang, Bai; Sun, Hongchen

2014-01-01

121

Molecular cloning and characterization of beta-expansin gene related to root hair formation in barley.  

PubMed

Root hairs are specialized epidermal cells that play a role in the uptake of water and nutrients from the rhizosphere and serve as a site of interaction with soil microorganisms. The process of root hair formation is well characterized in Arabidopsis (Arabidopsis thaliana); however, there is a very little information about the genetic and molecular basis of root hair development in monocots. Here, we report on isolation and cloning of the beta-expansin (EXPB) gene HvEXPB1, tightly related to root hair initiation in barley (Hordeum vulgare). Using root transcriptome differentiation in the wild-type/root-hairless mutant system, a cDNA fragment present in roots of wild-type plants only was identified. After cloning of full-length cDNA and genomic sequences flanking the identified fragment, the subsequent bioinformatics analyses revealed homology of the protein coded by the identified gene to the EXPB family. Reverse transcription-PCR showed that expression of HvEXPB1 cosegregated with the root hair phenotype in F2 progeny of the cross between the hairless mutant rhl1.a and the wild-type Karat parent variety. Expression of the HvEXPB1 gene was root specific; it was expressed in roots of wild-type forms, but not in coleoptiles, leaves, tillers, and spikes. The identified gene was active in roots of two other analyzed root hair mutants: rhp1.a developing root hair primordia only and rhs1.a with very short root hairs. Contrary to this, a complete lack of HvEXPB1 expression was observed in roots of the spontaneous root-hairless mutant bald root barley. All these observations suggest a role of the HvEXPB1 gene in the process of root hair formation in barley. PMID:16679418

Kwasniewski, Miroslaw; Szarejko, Iwona

2006-07-01

122

A High-Beta, Supersonic Plasma Flow and Shock Formation in Magnetic Channels  

NASA Astrophysics Data System (ADS)

Plasma acceleration and shock wave formation are investigated in the HITOP device of Tohoku University. A high-beta(>50%), and highly-ionized(>50%), flowing He-plasma is produced quasi-steadily(1ms) by an MPD arc jet and is injected into a cylindrical vacuum chamber (diameter: 0.8m, length: 3.3m) along various axial magnetic channels. Axial profiles of an ion acoustic Mach number Mi are measured by a Mach probe and a spectroscopic method. It is found that Mi is almost unity in a uniform magnetic field and Mi increases up to 3 in a diverging magnetic field. When a magnetic bump is added in the diverging field, a shock wave with a sudden decrease in Mi and increase in density is observed near the inlet of the bump region. The subsonic plasma flow is re-accelerated in the converging field. Mi attains to unity near the magnetic throat and increases up to 3 in the diverging region. The bump field works as a magnetic Laval nozzle. These phenomena are quite similar to those in a compressible gas flow through a conventional Laval nozzle.

Inutake, Masaaki; Ando, Akira; Hattori, Kunihiko; Yoshinuma, Mikirou; Imasaki, Atsushi; Yagai, Tsuyoshi; Tobari, Hiroyuki; Murakami, Fumitake; Ashino, Masashi

2000-10-01

123

Current Sheet Formation in a Conical Theta Pinch Faraday Accelerator with Radio-frequency Assisted  

E-print Network

, Propulsion Research and Technology Branch, Propulsion Systems Dept., kurt.a.polzin@nasa.gov. 1 The 30th Discharge IEPC-2007-165 Presented at the 30th International Electric Propulsion Conference, Florence, Italy sheet, which are two in- dices important for FARAD as a propulsion concept. The profiles of these two

Choueiri, Edgar

124

Conformational Stability of Fibrillar Amyloid-Beta Oligomers via Protofilament Pair Formation – A Systematic Computational Study  

PubMed Central

Amyloid- (A) oligomers play a crucial role in Alzheimer’s disease due to their neurotoxic aggregation properties. Fibrillar A oligomerization can lead to protofilaments and protofilament pairs via oligomer elongation and oligomer association, respectively. Small fibrillar oligomers adopt the protofilament topology, whereas fibrils contain at least protofilament pairs. To date, the underlying growth mechanism from oligomers to the mature fibril still remains to be elucidated. Here, we performed all-atom molecular dynamics simulations in explicit solvent on single layer-like protofilaments and fibril-like protofilament pairs of different size ranging from the tetramer to the 48-mer. We found that the initial U-shaped topology per monomer is maintained over time in all oligomers. The observed deviations of protofilaments from the starting structure increase significantly with size due to the twisting of the in-register parallel -sheets. This twist causes long protofilaments to be unstable and leads to a breakage. Protofilament pairs, which are stabilized by a hydrophobic interface, exhibit more fibril-like properties such as the overall structure and the twist angle. Thus, they can act as stable conformational templates for further fibril growth. Key properties like the twist angle, shape complementarity, and energetics show a size-dependent behavior so that small oligomers favor the protofilament topology, whereas large oligomers favor the protofilament pair topology. The region for this conformational transition is at the size of approximately twelve A monomers. From that, we propose the following growth mechanism from A oligomers to fibrils: (1) elongation of short protofilaments; (2) breakage of large protofilaments; (3) formation of short protofilament pairs; and (4) elongation of protofilament pairs. PMID:23936224

Kahler, Anna; Sticht, Heinrich; Horn, Anselm H. C.

2013-01-01

125

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

126

Correlation and emplacement of a large, zoned, discontinuously exposed ash flow sheet: The 40 Ar\\/ 39 Ar chronology, paleomagnetism, and petrology of the Pahranagat Formation, Nevada  

Microsoft Academic Search

Many single-cryslal 4oAr\\/3gAr ages and thermoremanent magnetization directions have resolved the problematic stratigraphic correlation of the laterally and vertically zoned rhyolite ash flow sheet of the Pahranagat Formation in the southern Great Basin. This outflow sheet was previously designated by four different stratigraphic names in different locations over its highly discontinuous exposure area of 33,000 kmz. We show that it

Myron G. Best; Eric H. Christiansen; Alan L. Deino; C. Sherman Grommé; David G. Tingeyl

1995-01-01

127

Beta4 integrin-dependent formation of polarized three-dimensionalarchitecture confers resistance to apoptosis in normal and malignantmammary epithelium  

SciTech Connect

Tumor cells can evade chemotherapy by acquiring resistanceto apoptosis. We investigated the molecular mechanism whereby malignantand nonmalignant mammary epithelial cells become insensitive toapoptosis. We show that regardless of growth status formation ofpolarized, three-dimensional structures driven by basement membraneconfers protection to apoptosis in both nonmalignant and malignantmammary epithelial cells. By contrast, irrespective of their malignantstatus, nonpolarized structures are sensitive to induction of apoptosis.Resistance to apoptosis requires ligation of beta4 integrins, whichregulates tissue polarity, hemidesmosome formation and NFkB activation.Expression of beta4 integrin that lacks the hemidesmosome targetingdomain interferes with tissue polarity and NFkB activation and permitsapoptosis. These results indicate that integrin-induced polarity maydrive tumor cell resistance to apoptosis-inducing agents via effects onNFkB.

Weaver, Valerie M.; Lelievre, Sophie; Lakins, Johnathon N.; Chrenek, Micah A.; Jones, Jonathan C.R.; Giancotti, Filippo; Werb, Zena; Bissell, Mina J.

2002-08-27

128

Lactate adversely affects the in vitro formation of endothelial cell tubular structures through the action of TGF-{beta}1  

SciTech Connect

When lactate accumulation in a tumor microenvironment reaches an average concentration of 10-20 mM, it tends to reflect a high degree of malignancy. However, the hypothesis that tumor-derived lactate has a number of partially adverse biological effects on malignant and tumor-associated host cells requires further evidence. The present study attempted to evaluate the impact of lactate on the process of angiogenesis, in particular on the formation of tubular structures. The endothelial cell (EC) network in desmoplastic breast tumors is primarily located in areas of reactive fibroblastic stroma. We employed a fibroblast-endothelial cell co-culture model as in vitro angiogenesis system normally producing florid in vitro tubule formation to analyze this situation. In contrast to previous studies, we found that lactate significantly reduces EC network formation in a dose-dependent manner as quantified by semi-automated morphometric analyses following immunohistochemical staining. The decrease in CD31-positive tubular structures and the number of intersections was independent of VEGF supplementation and became more pronounced in the presence of protons. The number of cells, primarily of the fibroblast population, was reduced but cell loss could not be attributed to a decrease in proliferative activity or pronounced apoptotic cell death. Treatment with 10 mM lactate was accompanied by enhanced mRNA expression and release of TGF-{beta}1, which also shows anti-angiogenic activity in the model. Both TGF-{beta}1 and lactate induced myofibroblastic differentiation adjacent to the EC tubular structures. The lactate response on the EC network was diminished by TGF-{beta}1 neutralization, indicating a causal relationship between lactate and TGF-{beta}1 in the finely tuned processes of vessel formation and maturation which may also occur in vivo within tumor tissue.

Schmid, Stephan A. [Institute of Pathology, University of Regensburg, 93042 Regensburg (Germany)]. E-mail: leoni.kunz-schughart@oncoray.de; Gaumann, Andreas [Institute of Pathology, University of Regensburg, 93042 Regensburg (Germany); Wondrak, Marit [Institute of Pathology, University of Regensburg, 93042 Regensburg (Germany); OncoRay-Center for Radiation Research in Oncology, Faculty of Medicine Carl Gustav Carus, TU Dresden, 01307 Dresden (Germany); Eckermann, Christoph [Institute of Pathology, University of Regensburg, 93042 Regensburg (Germany); Schulte, Stephanie [Institute of Pathology, Brigham and Women's Hospital, Boston, MA 02115 (United States); Mueller-Klieser, Wolfgang [Institute of Physiology and Pathophysiology, University of Mainz, 55128 Mainz (Germany); Wheatley, Denys N. [BioMedES, Leggat House, Keithhall, Inverrurie, Aberdeen, AB51 0LX (United Kingdom); Kunz-Schughart, Leoni A. [Institute of Pathology, University of Regensburg, 93042 Regensburg (Germany); OncoRay-Center for Radiation Research in Oncology, Faculty of Medicine Carl Gustav Carus, TU Dresden, 01307 Dresden (Germany)

2007-07-15

129

Design study of the geometry of the blanking tool to predict the burr formation of Zircaloy-4 sheet  

SciTech Connect

In this work, we investigated factors that influence burr formation for zircaloy-4 sheet used for spacer grids of nuclear fuel roads. Factors we considered are geometric factors of punch. We changed clearance and velocity in order to consider the failure parameters, and we changed shearing angle and corner radius of L-shaped punch in order to consider geometric factors of punch. First, we carried out blanking test with failure parameter of GTN model using L-shaped punch. The tendency of failure parameters and geometric factors that affect burr formation by analyzing sheared edges is investigated. Consequently, geometric factor's influencing on the burr formation is also high as failure parameters. Then, the sheared edges and burr formation with failure parameters and geometric factors is investigated using FE analysis model. As a result of analyzing sheared edges with the variables, we checked geometric factors more affect burr formation than failure parameters. To check the reliability of the FE model, the blanking force and the sheared edges obtained from experiments are compared with the computations considering heat transfer.

Ha, Jisun, E-mail: nskim@sogang.ac.kr; Lee, Hyungyil, E-mail: nskim@sogang.ac.kr; Kim, Dongchul, E-mail: nskim@sogang.ac.kr; Kim, Naksoo, E-mail: nskim@sogang.ac.kr [Sogang University, Department of Mechanical Engineering, Seoul, 121-742 (Korea, Republic of)

2013-12-16

130

Beta4 integrin is required for hemidesmosome formation, cell adhesion and cell survival  

PubMed Central

The integrin heterodimer alpha 6 beta 4 is expressed in many epithelia and in Schwann cells. In stratified epithelia, alpha 6 beta 4 couple with BPAG1-e and BPAG2 to form hemidesmosomes, attaching externally to laminin and internally to the keratin cytoskeleton. To explore the function of this atypical integrin, and its relation to conventional actin-associated integrins, we targeted the removal of the beta 4 gene in mice. Tissues that express alpha 6 beta 4 are grossly affected. Stratified tissues are devoid of hemidesmosomes, display only a very fragile attachment to the basal lamina, and exhibit signs of degeneration and tissue disorganization. Simple epithelia which express alpha 6 beta 4 are also defective in adherence, even though they do not form hemidesmosomes. In the absence of beta 4, alpha 6 is dramatically downregulated, and other integrins do not appear to compensate for the loss of this heterodimer. These data have important implications for understanding integrin function in cell-substratum adhesion, cell survival and differentiation, and for understanding the role of alpha 6 beta 4 in junctional epidermolysis bullosa, an often lethal human disorder with pathology similar to our mice. PMID:8707838

1996-01-01

131

One-dimensional barrier-preserving free-energy projections of a beta-sheet miniprotein: new insights into the folding process.  

PubMed

The conformational space of a 20-residue three-stranded antiparallel beta-sheet peptide (double hairpin) was sampled by equilibrium folding/unfolding molecular dynamics simulations for a total of 20 micros. The resulting one-dimensional free-energy profiles (FEPs) provide a detailed description of the free-energy basins and barriers for the folding reaction. The similarity of the FEPs obtained using the probability of folding before unfolding (pfold) or the mean first passage time supports the robustness of the procedure. The folded state and the most populated free-energy basins in the denatured state are described by the one-dimensional FEPs, which avoid the overlap of states present in the usual one- or two-dimensional projections. Within the denatured state, a basin with fluctuating helical conformations and a heterogeneous entropic state are populated near the melting temperature at about 11% and 33%, respectively. Folding pathways from the helical basin or enthalpic traps (with only one of the two hairpins formed) reach the native state through the entropic state, which is on-pathway and is separated by a low barrier from the folded state. A simplified equilibrium kinetic network based on the FEPs shows the complexity of the folding reaction and indicates, as augmented by additional analyses, that the basins in the denatured state are connected primarily by the native state. The overall folding kinetics shows single-exponential behavior because barriers between the non-native basins and the folded state have similar heights. PMID:18590307

Krivov, Sergei V; Muff, Stefanie; Caflisch, Amedeo; Karplus, Martin

2008-07-24

132

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. PMID:9865947

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

1998-01-01

133

Proton-conducting beta  

Microsoft Academic Search

Proton Conducting beta-alumina via Microwave Assisted Synthesis. The microwave assisted synthesis of proton conducting Mg- and Li-stabilized NH4+\\/H3O+ beta-alumina from a solution based gel precursor is reported. beta-alumina is a ceramic fast ion conductor containing two-dimensional sheets of mobile cations. Na +-beta-alumina is the most stable at the sintering temperatures (1740°C) reached in a modified microwave oven, and can be

Brent William Kirby

2008-01-01

134

Formation of a quasi-one-dimensional current sheet in the laboratory experiment and in the Earth's magnetotail  

NASA Astrophysics Data System (ADS)

Two-dimensional current sheets (CSs) generated in the CS-3D laboratory device are considered. Results obtained in the laboratory experiment are compared with spacecraft observations of CSs in the Earth's magnetotail. The longitudinal and transverse CS structures, as well as CS evolution during the thinning process are studied. It is demonstrated that the CSs obtained in the laboratory experiments and those observed by spacecraft possess common properties: they have the same dimensionless spatial scales, similar distributions of the normal component of the magnetic field along the sheet, and similar ratios between the current density and the normal component of the magnetic field. The results of comparison allow one to guess some details of the structure and dynamics of the Earth's magnetotail CS. In particular, on the basis of the laboratory experiment, it is concluded that the formation of a quasi-one-dimensional CS in the magnetotail at distances of x ˜ -15 R E from the Earth (where R E is the Earth' radius) is accompanied by the growth of the amplitude B 0 of the tangential component of the magnetic field and that the field B 0 in the quasi-stationary state increases tailward. The critical value of the current density is likely equal to , where N e is the electron density and is the ion thermal velocity. The current density cannot substantially exceed this value. Moreover, the CS thickness cannot be substantially smaller then the ion Larmor radius or the ion inertial length.

Yushkov, E. V.; Frank, A. G.; Artemyev, A. V.; Petrukovich, A. A.; Vasko, I. Y.

2015-01-01

135

Physics Resource Reference Sheet  

NSDL National Science Digital Library

This reference sheet, presented by the National Nanotechnology Infrastructure Network provides a valuable physics reference sheet for high school students. Definition of terms, diagrams, abbreviations, mathematical notations, force diagrams, and other useful information is provided in an easy to use format. Included in this lesson are the front and back sides of this reference sheet.

136

Physical Science Reference Sheets  

NSDL National Science Digital Library

This reference sheet, presented by the National Nanotechnology Infrastructure Network provides a valuable physical science reference sheet for high school students. Definition of terms, diagrams, abbreviations, mathematical notations, the periodic table, and other useful information is provided in an easy to use format. Included in this lesson are the front and back sides of this reference sheet.

137

Chemistry Reference Sheets  

NSDL National Science Digital Library

This reference sheet, presented by the National Nanotechnology Infrastructure Network provides a valuable chemistry reference sheet for high school students. Definition of terms, diagrams, abbreviations, mathematical notations, the periodic table, and other useful information is provided in an easy to use format. Included in this lesson are the front and back sides of this reference sheet.

138

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

139

One-step synthesis of hierarchical zeolite beta via network formation of uniform nanocrystals.  

PubMed

A hierarchical mesoporous network of zeolite beta with very high micropore as well as mesopore volume was synthesized without the need of a porogen at near 100% yield in the form of easily retrievable micrometer-sized particles. This was achieved by a dense-gel synthesis utilizing steam-assisted conversion (SAC) to induce a burst of nucleation. During the first phase of the synthesis, individual, evenly sized zeolite beta nanoparticles are formed that subsequently condense into a porous network displaying uniform mesopores. The final product consists of hierarchical self-sustaining macroscopic zeolite aggregates assembled from 20 nm crystalline domains of zeolite beta. The small size of the zeolite crystals in the resulting materials gives rise to mesopores with dominant pore sizes of about 13 nm. Large surface areas between 630 and 750 m(2)/g and total pore volumes up to 0.9 mL/g were obtained without sacrificing the microporosity (usually larger than 0.20 mL/g). Crystallization conditions were optimized for different Si/Al ratios between 10 and 33. A complete conversion into hierarchical zeolite beta was achieved in only a few hours at 170-180 °C if the amount of water present during the steam-assisted conversion was adequately adjusted. This dense gel steam conversion process proves to be a highly efficient strategy for fabricating hierarchical zeolite beta networks in a single step. PMID:21410255

Möller, Karin; Yilmaz, Bilge; Jacubinas, Richard M; Müller, Ulrich; Bein, Thomas

2011-04-13

140

Does Long-Term Administration of a Beta-Blocker (Timolol) Induce Fibril-Based Cataract Formation In-vivo?  

PubMed Central

Timolol is a non-selective beta-adrenergic receptor antagonist administered for treating glaucoma, heart attacks and hypertension. In the present study, we set out to determine whether or not timolol can provoke cataract formation, thus the influence of timolol on the amyloid-type aggregation of crystallin was investigated. We then provided experimental evidence of crystallin aggregation and its induction by timolol using different spectroscopic measurements. Turbidimetric measurements as well as ThT fluorescence data indicated that timolol induce extent of crystallin amyloid formation. The kinetic of protein aggregation was also changed in presence of increasing concentrations of the drug suggesting that long-term drug administration may contribute to the development of cataract. Since the consequence of timolol-crystallin interaction has yet to be identified, additional data on it may help us to postpone amyloid cataract formation. PMID:25237356

Nikbakht, Mohammad Reza; Ashrafi-Kooshk, Mohammad Reza; Jaafari, Morteza; Ghasemi, Moosa; Khodarahmi, Reza

2014-01-01

141

Kinetics of formation and physicochemical characterization of thermally-induced beta-lactoglobulin aggregates.  

PubMed

The kinetics of heat denaturation and aggregation for beta-lactoglobulin dispersions (5% w/v) were studied at 3 pHs (6, 6.4, and 6.8) and at a heating temperature of 80 degrees C. Protein aggregates were characterized for hydrodynamic diameter, microstructure, and molecular weight by means of dynamic light scattering, transmission electron microscopy, and polyacrylamide gel electrophoresis, respectively. Concentration of native beta-lactoglobulin decreased with holding time and with a decrease in the pH. Apparent rate constants were calculated for beta-lactoglobulin denaturation applying the general kinetic equation solved for a reaction order of 1.5. Values of the apparent reaction rate constant k = 7.5, 6.3 and 5.6 x 10(-3) s(-1) were found for pH 6, 6.4, and 6.8, respectively. Decreasing the pH of the dispersions produced higher aggregate sizes. After a holding time of 900 s, average hydrodynamic diameters for beta-lactoglobulin aggregates at pH 6, 6.4, and 6.8 were 96, 49, and 42 nm, respectively. These results were confirmed by transmission electron microscopy images, where a shift in the size and morphology of aggregates was found, from large and spherical at pH 6 to smaller and linear aggregates at pH 6.8. beta-Lactoglobulin formed disulfide-linked intermediates (dimers, trimers, tetramers) and so on) which then formed high molecular weight aggregates. From the results obtained by DLS, TEM, and SDS-PAGE a mechanism for beta-lactoglobulin aggregation was proposed. This study shows that heat treatment can be used to produce protein aggregates with different sizes and morphologies to be utilized as ingredients in foods. PMID:20629872

Zúñiga, R N; Tolkach, A; Kulozik, U; Aguilera, J M

2010-06-01

142

Heliospheric plasma sheets N. U. Crooker,1  

E-print Network

sheet (HPS) encasing the heliospheric current sheet shows a high degree of variability. A study of 52 that only half concur with both high-beta plasma and current sheets, as required for an HPS. The remaining et al. [1990a] designated the heliospheric plasma sheet (HPS) as the equatorial solar wind sandwiched

California at Berkeley, University of

143

Cyclic Acetal Formation Between 2-Pyridinecarboxaldehyde and gamma-Hydroxy-alpha,beta-Acetylenic Esters.  

PubMed

A new transformation between 2-pyridinecarboxyaldehyde and gamma-hydroxy-alpha,beta-acetylenic esters to form highly functionalized cyclic acetals was discovered. This transformation proceeds under very mild conditions without any additives and is promoted by the basic nature of the pyridine ring. PMID:19907635

Osman, Sami; Koide, Kazunori

2008-11-10

144

Magnetic neutral sheets in evolving fields. I - General theory. II - Formation of the solar corona  

NASA Technical Reports Server (NTRS)

The problem of the hydrostatic equilibrium of a large-scale magnetic field embedded in a fluid with infinite electrical conductivity is considered. It is pointed out that a necessary condition for static equilibrium is the invariance of the small-scale pattern in the field along the large-scale direction. A varying topological pattern implies that no fluid pressure distribution exists for which the field is everywhere static. Magnetic neutral sheets form, and dynamical reconnection of the field takes place. It is shown here that the invariance is also a sufficient condition for the existence of a fluid pressure distribution producing static equilibrium. Even in the simplest cases, however, the requirements on the fluid pressure are extreme and, a priori, are unlikely. It is concluded that almost all twisted flux tubes packed together produce dynamical nonequilibrium and dissipation of their twisting. This is the basic effect underlying the long-standing conjecture that the shuffling of the footpoints of the bipolar magnetic fields in the sun is responsible for heating the active corona. Attention is then given to the consequences of this general dynamical dissipation in the magnetic fields that produce the active corona of the sun. The footpoints of the field are continually manipulated by the subphotospheric convection in such a way that the lines of force are continually wrapped and rotated about one another.

Parker, E. N.

1983-01-01

145

Inhibition of beta-amyloid aggregation by fluorescent dye labels  

SciTech Connect

The fluorescence decay of beta-amyloid's (A?) intrinsic fluorophore tyrosine has been used for sensing the oligomer formation of dye-labelled A? monomers and the results compared with previously studied oligomerization of the non-labelled A? peptides. It has been demonstrated that two different sized, covalently bound probes 7-diethylaminocoumarin-3-carbonyl and Hilyte Fluor 488 (HLF), alter the rate and character of oligomerization to different extents. The ability of HLF to inhibit formation of highly ordered structures containing beta-sheets was also shown. The implications of our findings for using fluorescence methods in amyloidosis research are discussed and the advantages of this auto-fluorescence approach highlighted.

Amaro, Mariana; Wellbrock, Thorben; Birch, David J. S.; Rolinski, Olaf J., E-mail: o.j.rolinski@strath.ac.uk [Photophysics group, Centre for Molecular Nanometrology, Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG (United Kingdom)

2014-02-10

146

Inhibition of beta-amyloid aggregation by fluorescent dye labels  

NASA Astrophysics Data System (ADS)

The fluorescence decay of beta-amyloid's (A?) intrinsic fluorophore tyrosine has been used for sensing the oligomer formation of dye-labelled A? monomers and the results compared with previously studied oligomerization of the non-labelled A? peptides. It has been demonstrated that two different sized, covalently bound probes 7-diethylaminocoumarin-3-carbonyl and Hilyte Fluor 488 (HLF), alter the rate and character of oligomerization to different extents. The ability of HLF to inhibit formation of highly ordered structures containing beta-sheets was also shown. The implications of our findings for using fluorescence methods in amyloidosis research are discussed and the advantages of this auto-fluorescence approach highlighted.

Amaro, Mariana; Wellbrock, Thorben; Birch, David J. S.; Rolinski, Olaf J.

2014-02-01

147

Suppression of established experimental autoimmune encephalomyelitis and formation of meningeal lymphoid follicles by lymphotoxin beta receptor-Ig fusion protein.  

PubMed

We have recently shown that de novo formation of lymphoid structures resembling B-cell follicles occurs in the inflamed central nervous system (CNS) meninges in a subset of patients with secondary progressive multiple sclerosis and in SJL mice with relapsing-remitting experimental autoimmune encephalomyelitis (EAE). Because lymphotoxin (LT) alpha(1)beta(2) is essential for lymphoid tissue organization, we used real-time PCR to examine LTbeta and LTbeta receptor (LTbetaR) gene expression in the CNS of SJL mice immunized with PLP 139-151 peptide. Moreover, we used the decoy receptor LTbetaR-immunoglobulin fusion protein to block the interaction of lymphotoxin (LT) alpha(1)beta(2) with the LTbeta receptor (LTbetaR) in mice with established EAE and evaluate the effect of systemic and local treatments with the fusion protein on disease progression, CNS lymphocytic infiltration and formation of meningeal B-cell follicles. The present findings indicate that both LTbeta and LTbetaR are upregulated at EAE onset and during subsequent relapses and that systemic and local blockade of the LT pathway with LTbetaR-Ig results in protracted and transient inhibition of EAE clinical signs, respectively. LTbetaR-Ig treatment also reduces T- and B-cell infiltration and prevents the induction of the chemokines CXCL10 and CXCL13 and the formation of organized ectopic follicles in the EAE-affected CNS. Targeting of molecules involved in lymphoid organogenesis could represent a valid strategy to inhibit CNS inflammation and formation of ectopic follicles, which may play a role in maintaining an abnormal, intrathecal humoral immune response in CNS autoimmune disease. PMID:16870269

Columba-Cabezas, Sandra; Griguoli, Marilena; Rosicarelli, Barbara; Magliozzi, Roberta; Ria, Francesco; Serafini, Barbara; Aloisi, Francesca

2006-10-01

148

Spontaneous Formation of Oligomers and Fibrils in Large-Scale Molecular Dynamics Simulations of A-beta Peptides  

NASA Astrophysics Data System (ADS)

Protein aggregation is associated with serious and eventually-fatal neurodegenerative diseases including Alzheimer's and Parkinson's. While atomic resolution molecular dynamics simulations have been useful in this regard, they are limited to examination of either oligomer formation by a small number of peptides or analysis of the stability of a moderate number of peptides placed in trial or known experimental structures. We describe large scale intermediate-resolution molecular dynamics simulations of the spontaneous formation of fibrils by systems containing large numbers ( 48) of peptides including A-beta (16-22), and A-beta ( 17-42) peptides. We trace out the aggregation process from an initial configuration of random coils to proto-filaments with cross-? structures and demonstrate how kinetics dictates the structural details of the fully formed fibril. Fibrillization kinetics depends strongly on the temperature. Nucleation and templated growth via monomer addition occur at and near a transition temperature above which fibrils are unlikely to form. Oligomeric merging and structural rearrangement are observed at lower temperatures.

Hall, Carol

2013-03-01

149

The role of proline-containing peptide triads in ?-sheet formation: A kinetic study.  

PubMed

The design of biomimetic materials through molecular self-assembly is a growing area of modern nanotechnology. With problems of protein folding, self-assembly, and sequence-structure relationships as essential in nanotechnology as in biology, the effect of the nucleation of ?-hairpin formation by proline on the folding process has been investigated in model studies. Previously such studies were limited to investigations of the influence of proline on the formation of turns in short peptide sequences. The effect of proline-based triads on the folding of an 11-kDa amyloidogenic peptide GH6 [(GA)3 GY(GA)3 GE]8 GAH6 (YE8) was investigated by selective substitution of the proline-substituted triads at the ?-turn sites. The folding and fibrillation of the singly proline-substituted polypeptides, e.g., GH6?[(GA)3GY(GA)3GE]7(GA)3GY(GA)3PD?GAH6 (8PD), and doubly proline-substituted polypeptides, e.g., GH6?[(GA)3GY(GA)3GE]3(GA)3GY(GA)3PD[(GA)3GY(GA)3GE]3(GA)3GY(GA)3PD?GAH6 (4,8PD), were directly monitored by circular dichroism and deep UV resonance Raman and fluorescence spectroscopies. These findings were used to identify the essential folding domains, i.e., the minimum number of ?-strands necessary for stable folding. These experimental findings may be especially useful in the design and construction of peptidic materials for a wide range of applications as well as in understanding the mechanisms of folding critical to fibril formation. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 339-350, 2015. PMID:25656820

Takor, Gaius A; Higashiya, Seiichiro; Sikirzhytski, Vitali K; Seeley, Jason P; Lednev, Igor K; Welch, John T

2015-06-01

150

Astrocyte transforming growth factor beta 1 promotes inhibitory synapse formation via CaM kinase II signaling.  

PubMed

The balance between excitatory and inhibitory synaptic inputs is critical for the control of brain function. Astrocytes play important role in the development and maintenance of neuronal circuitry. Whereas astrocytes-derived molecules involved in excitatory synapses are recognized, molecules and molecular mechanisms underlying astrocyte-induced inhibitory synapses remain unknown. Here, we identified transforming growth factor beta 1 (TGF-?1), derived from human and murine astrocytes, as regulator of inhibitory synapse in vitro and in vivo. Conditioned media derived from human and murine astrocytes induce inhibitory synapse formation in cerebral cortex neurons, an event inhibited by pharmacologic and genetic manipulation of the TGF-? pathway. TGF-?1-induction of inhibitory synapse depends on glutamatergic activity and activation of CaM kinase II, which thus induces localization and cluster formation of the synaptic adhesion protein, Neuroligin 2, in inhibitory postsynaptic terminals. Additionally, intraventricular injection of TGF-?1 enhanced inhibitory synapse number in the cerebral cortex. Our results identify TGF-?1/CaMKII pathway as a novel molecular mechanism underlying astrocyte control of inhibitory synapse formation. We propose here that the balance between excitatory and inhibitory inputs might be provided by astrocyte signals, at least partly achieved via TGF-?1 downstream pathways. Our work contributes to the understanding of the GABAergic synapse formation and may be of relevance to further the current knowledge on the mechanisms underlying the development of various neurological disorders, which commonly involve impairment of inhibitory synapse transmission. PMID:25042347

Diniz, Luan Pereira; Tortelli, Vanessa; Garcia, Matheus Nunes; Araújo, Ana Paula Bérgamo; Melo, Helen M; Silva, Gisele S Seixas da; Felice, Fernanda G De; Alves-Leon, Soniza Vieira; Souza, Jorge Marcondes de; Romão, Luciana Ferreira; Castro, Newton Gonçalves; Gomes, Flávia Carvalho Alcantara

2014-12-01

151

High frequency Agrobacterium -mediated transformation and plant regeneration via direct shoot formation from leaf explants in Beta vulgaris and Beta maritima  

Microsoft Academic Search

We have developed a new procedure for Agrobacterium-mediated transformation of plants in the genus Beta using shoot-base as the material for Agrobacterium infection. The frequency of regeneration from shoot bases was analyzed in seven accessions of sugarbeet ( Beta vulgaris) and two accessions of B. maritima to select materials suitable for obtaining transformed plants. The frequency of transformation of the

H. Hisano; Y. Kimoto; H. Hayakawa; J. Takeichi; T. Domae; R. Hashimoto; J. Abe; S. Asano; A. Kanazawa; Y. Shimamoto

2004-01-01

152

Formation of deglycosylated alpha-L-fucosidase by endo-beta-N-acetylglucosaminidase in Fusarium oxysporum.  

PubMed Central

Two forms of alpha-L-fucosidase, deglycosylated and glycosylated, were found in the fucose-inducing culture broth of Fusarium oxysporum. Endo-beta-N-acetylglucosaminidase was also found in the same culture broth. The deglycosylated alpha-L-fucosidase was purified from the culture broth to homogeneity on polyacrylamide disc gel electrophoresis and analytical ultracentrifugation. Purified deglycosylated alpha-L-fucosidase was compared in chemical composition and immunological homology with glycosylated alpha-L-fucosidase which had been reported previously (K. Yamamoto, Y. Tsuji, H. Kumagai, and T. Tochikura, Agric. Biol. Chem. 50: 1689, 1986). Both enzymes had nearly the same amino acid compositions and were immunologically identical. Glycosylated alpha-L-fucosidase had mannose, galactose, and N-acetylglucosamine residues. In contrast, the deglycosylated enzyme had only N-acetylglucosamine residues. These results suggest that the deglycosylated alpha-L-fucosidase is formed by the release of sugar chains from the glycosylated form by Fusarium endo-beta-N-acetylglucosaminidase. Furthermore, various enzymatic properties were compared: the two alpha-L-fucosidases were found to exhibit similar catalytic activities and thermal stability profiles. The deglycosylated enzyme, however, was slightly unstable in the acidic pH range compared with the glycosylated enzyme. Images PMID:2111117

Tsuji, Y; Yamamoto, K; Tochikura, T

1990-01-01

153

Beta- Lactam Antibiotics Stimulate Biofilm Formation in Non-Typeable Haemophilus influenzae by Up-Regulating Carbohydrate Metabolism  

PubMed Central

Non-typeable Haemophilus influenzae (NTHi) is a common acute otitis media pathogen, with an incidence that is increased by previous antibiotic treatment. NTHi is also an emerging causative agent of other chronic infections in humans, some linked to morbidity, and all of which impose substantial treatment costs. In this study we explore the possibility that antibiotic exposure may stimulate biofilm formation by NTHi bacteria. We discovered that sub-inhibitory concentrations of beta-lactam antibiotic (i.e., amounts that partially inhibit bacterial growth) stimulated the biofilm-forming ability of NTHi strains, an effect that was strain and antibiotic dependent. When exposed to sub-inhibitory concentrations of beta-lactam antibiotics NTHi strains produced tightly packed biofilms with decreased numbers of culturable bacteria but increased biomass. The ratio of protein per unit weight of biofilm decreased as a result of antibiotic exposure. Antibiotic-stimulated biofilms had altered ultrastructure, and genes involved in glycogen production and transporter function were up regulated in response to antibiotic exposure. Down-regulated genes were linked to multiple metabolic processes but not those involved in stress response. Antibiotic-stimulated biofilm bacteria were more resistant to a lethal dose (10 µg/mL) of cefuroxime. Our results suggest that beta-lactam antibiotic exposure may act as a signaling molecule that promotes transformation into the biofilm phenotype. Loss of viable bacteria, increase in biofilm biomass and decreased protein production coupled with a concomitant up-regulation of genes involved with glycogen production might result in a biofilm of sessile, metabolically inactive bacteria sustained by stored glycogen. These biofilms may protect surviving bacteria from subsequent antibiotic challenges, and act as a reservoir of viable bacteria once antibiotic exposure has ended. PMID:25007395

Wu, Siva; Li, Xiaojin; Gunawardana, Manjula; Maguire, Kathleen; Guerrero-Given, Debbie; Schaudinn, Christoph; Wang, Charles; Baum, Marc M.; Webster, Paul

2014-01-01

154

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 PMID:9932109

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

1998-01-01

155

Evidence that a beta-1,4-endoglucanase secreted by Acetobacter xylinum plays an essential role for the formation of cellulose fiber.  

PubMed

Cellulose-producing Acetobacter xylinum has been known to secrete a cellulose-hydrolyzing beta-1,4-endoglucanase (CMCax). When antibodies to recombinant CMCax were added to the culture medium, the formation of cellulose fiber was severely inhibited. Western blot analysis using the antibody showed that this enzyme was secreted into the medium even by a cellulose non-producing strain (Cel-). These results indicate that beta-1,4-endoglucanase in the medium plays a critical role in the formation of cellulose fiber by the microorganism. PMID:9972249

Koo, H M; Song, S H; Pyun, Y R; Kim, Y S

1998-11-01

156

Impaired alpha(IIb)beta(3) integrin activation and shear-dependent thrombus formation in mice lacking phospholipase D1.  

PubMed

Platelet aggregation is essential for hemostasis but can also cause myocardial infarction and stroke. A key but poorly understood step in platelet activation is the shift of the principal adhesive receptor, alpha(IIb)beta(3) integrin, from a low- to high-affinity state for its ligands, a process that enables adhesion and aggregation. In response to stimulation of heterotrimeric guanosine triphosphate-binding protein or immunoreceptor tyrosine-based activation motif-coupled receptors, phospholipases cleave membrane phospholipids to generate lipid and soluble second messengers. An essential role in platelet activation has been established for phospholipase C (PLC) but not for PLD and its product phosphatidic acid. Here, we report that platelets from Pld1(-/-) mice displayed impaired alpha(IIb)beta(3) integrin activation in response to major agonists and defective glycoprotein Ib-dependent aggregate formation under high shear conditions. These defects resulted in protection from thrombosis and ischemic brain infarction without affecting tail bleeding times. These results indicate that PLD1 may be a critical regulator of platelet activity in the setting of ischemic cardiovascular and cerebrovascular events. PMID:20051593

Elvers, Margitta; Stegner, David; Hagedorn, Ina; Kleinschnitz, Christoph; Braun, Attila; Kuijpers, Marijke E J; Boesl, Michael; Chen, Qin; Heemskerk, Johan W M; Stoll, Guido; Frohman, Michael A; Nieswandt, Bernhard

2010-01-01

157

Lipid-specific ?-sheet formation in a mussel byssus protein domain.  

PubMed

Intrinsically disordered proteins (IDP) or regions (IDR) can adopt multiple conformational states, depending on the interaction partners they encounter. This enables proteins or individual domains to fulfill multiple functions. Here, we analyzed the flank sequences of preCol-NG, one of three collagenous proteins of a mussel byssus thread governing its mechanical performance. preCol-NG comprises a collagen domain and nonrepetitive termini enclosing specific flank regions characterized by tandem repeats known from silk proteins, protein elastomers, and plant cell wall-associated proteins. We recombinantly produced a protein mimicking the M. galloprovincialis preCol-NG C-terminal flank region. The protein was intrinsically unfolded in solution, even at elevated temperatures. However, upon contact with small unilamellar vesicles (SUVs) reversible ?-structure formation occurred, reminiscent of partitioning-folding coupling. This behavior of preCol-NG flank domains likely impacts byssogenesis and sheds new light on a distinct mechanism of how fibrous protein materials might be achieved by lipid-induced self-assembly in nature. PMID:23947342

Heim, Markus; Elsner, Martina B; Scheibel, Thomas

2013-09-01

158

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

159

Hydrogen-1, carbon-13, and nitrogen-15 NMR spectroscopy of Anabaena 7120 flavodoxin: Assignment of. beta. -sheet and flavin binding site resonances and analysis of protein-flavin interactions  

SciTech Connect

Sequence-specific {sup 1}H and {sup 13}C NMR assignments have been made for residues that form the five-stranded parallel {beta}-sheet and the flavin mononucleotide (FMN) binding site of oxidized Anabaena 7120 flavodoxin. Interstrand nuclear Overhauser enhancements (NOEs) indicate that the {beta}-sheet arrangement is similar to that observed in the crystal structure of the 70% homologous long-chain flavodoxin from Anacystis nidulans. A total of 62 NOEs were identified: 8 between protons of bound FMN, 29 between protons of the protein in the flavin binding site, and 25 between protons of bound FMN and protons of the protein. These constraints were used to determine the localized solution structure of the FMN binding site. The electronic environment and conformation of the protein-bound flavin isoalloxazine ring were investigated by determining {sup 13}C-{sup 1}H coupling constants. The carbonyl edge of the flavin ring was found to be slightly polarized. The xylene ring was found to be nonplanar. Tyrosine 94, located adjacent to the flavin isoalloxazine ring, was shown to have a hindered aromatic ring flip rate.

Stockman, B.J.; Krezel, A.M.; Markley, J.L. (Univ. of Wisconsin, Madison (USA)); Leonhardt, K.G.; Straus, N.A. (Univ. of Toronto, Ontario (Canada))

1990-10-01

160

A novel mechanism for cyclic adenosine monophosphate-mediated memory formation: Role of amyloid beta.  

PubMed

Cyclic adenosine monophosphate (cAMP) regulates long-term potentiation (LTP) and ameliorates memory in healthy and diseased brain. Increasing evidence shows that, under physiological conditions, low concentrations of amyloid ? (A?) are necessary for LTP expression and memory formation. Here, we report that cAMP controls amyloid precursor protein (APP) translation and A? levels, and that the modulatory effects of cAMP on LTP occur through the stimulation of APP synthesis and A? production. PMID:24591104

Ricciarelli, Roberta; Puzzo, Daniela; Bruno, Olga; Canepa, Elisa; Gardella, Elena; Rivera, Daniela; Privitera, Lucia; Domenicotti, Cinzia; Marengo, Barbara; Marinari, Umberto Maria; Palmeri, Agostino; Pronzato, Maria Adelaide; Arancio, Ottavio; Fedele, Ernesto

2014-04-01

161

Formation of stable, high-beta, relativistic-electron plasmas using electron cyclotron heating  

Microsoft Academic Search

A one-dimensional, steady-state, relativistic Fokker-Planck model of electron cyclotron heating (ECH) is used to analyse the heating kinetics underlying the formation of the two-component hot-electron plasmas characteristic of ECH in magnetic mirror configurations. The model is first applied to the well diagnosed plasmas obtained in SM-1 and is then used to simulate the effective generation of relativistic electrons by upper

G. E. Guest; R. L. Miller

1988-01-01

162

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

163

Biology Reference Sheets  

NSDL National Science Digital Library

This reference sheet, presented by the National Nanotechnology Infrastructure Network provides a valuable list biology reference material for high school students in the life sciences. Definition of terms, diagrams, abbreviations, mathematical notations, and other useful information is provided in an easy to use format. Included in this lesson are the front and back sides of this reference sheet.

164

Structural basis for the impaired channeling and allosteric inter-subunit communication in the beta A169L/beta C170W mutant of tryptophan synthase.  

PubMed

We determined the 2.25 A resolution crystal structure of the betaA169L/betaC170W mutant form of the tryptophan synthase alpha(2)beta(2) complex from Salmonella typhimurium complexed with the alpha-active site substrate analogue 5-fluoro-indole-propanol-phosphate to identify the structural basis for the changed kinetic properties of the mutant (Anderson, K. S., Kim, A. Y., Quillen, J. M., Sayers, E., Yang, X. J., and Miles, E. W. (1995) J. Biol. Chem. 270, 29936-29944). Comparison with the wild-type enzyme showed that the betaTrp(170) side chain occludes the tunnel connecting the alpha- and beta-active sites, explaining the accumulation of the intermediate indole during a single enzyme turnover. To prevent a steric clash between betaLeu(169) and betaGly(135), located in the beta-sheet of the COMM (communication) domain (betaGly(102)-betaGly(189)), the latter reorganizes. The changed COMM domain conformation results in a loss of the hydrogen bonding networks between the alpha- and beta-active sites, explaining the poor activation of the alpha-reaction upon formation of the aminoacrylate complex at the beta-active site. The 100-fold reduced affinity for serine seems to result from a movement of betaAsp(305) away from the beta-active site so that it cannot interact with the hydroxyl group of a pyridoxal phosphate-bound serine. The proposed structural dissection of the effects of each single mutation in the betaA169L/betaC170W mutant would explain the very different kinetics of this mutant and betaC170F. PMID:11034989

Weyand, M; Schlichting, I

2000-12-29

165

Molecular basis of transmembrane beta-barrel formation of staphylococcal pore-forming toxins.  

PubMed

Pathogenic bacteria secrete pore-forming toxins (PFTs) to attack target cells. PFTs are expressed as water-soluble monomeric proteins, which oligomerize into nonlytic prepore intermediates on the target cell membrane before forming membrane-spanning pores. Despite a wealth of biochemical data, the lack of high-resolution prepore structural information has hampered understanding of the ?-barrel formation process. Here, we report crystal structures of staphylococcal ?-haemolysin and leucocidin prepores. The structures reveal a disordered bottom half of the ?-barrel corresponding to the transmembrane region, and a rigid upper extramembrane half. Spectroscopic analysis of fluorescently labelled mutants confirmed that the prepore is distinct from the pore within the transmembrane region. Mutational analysis also indicates a pivotal role for the glycine residue located at the lipid-solvent interface as a 'joint' between the two halves of the ?-barrel. These observations suggest a two-step transmembrane ?-barrel pore formation mechanism in which the upper extramembrane and bottom transmembrane regions are formed independently. PMID:25263813

Yamashita, Daichi; Sugawara, Takaki; Takeshita, Miyu; Kaneko, Jun; Kamio, Yoshiyuki; Tanaka, Isao; Tanaka, Yoshikazu; Yao, Min

2014-01-01

166

Controllable formation of graphene and graphene oxide sheets using photo-catalytic reduction and oxygen plasma treatment  

NASA Astrophysics Data System (ADS)

Au/SiO2/Si interdigital electrodes with thickness of 1 ?m were created on silicon substrate. Graphene oxide (GO) sheets hanging from these electrodes were obtained by spin coating of chemically synthesized GO dispersed in water. We used UV-light-induced photo-catalytic activity of titanium oxide nanoparticles to reduce the GO layer. Effects of the photo-induced chemical reduction on the conductivity of the GO were investigated. Also, low power DC plasma was used for oxidation of the sheets. Oxygen bombardment leads to sheets with low electrical conductivity. Measurements show that graphene and GO sheets with the controlled electrical conductivity were obtained by these processes. Scanning electron and atomic force microscopy were used to study the morphology of the TiO2/GO and graphene structures. X-ray diffraction and Raman scattering analysis were used to verify the structural characteristics of the prepared sheets. Analysis showed a gradual increase in the number of C-O bonds on the surface of the graphene layer as a result of increasing the time of plasma bombardment. Based on the Raman spectroscopy, the photo-catalytic activity of TiO2 nanoparticles resulted in a decrease in the number of C-O bonds.

Ostovari, Fatemeh; Abdi, Yaser; Ghasemi, Foad

2012-12-01

167

Beta-hexosaminidase activity of the oral pathogen Tannerella forsythia influences biofilm formation on glycoprotein substrates  

PubMed Central

Tannerella forsythia is an important pathogen in periodontal disease. Previously, we showed that sialidase activity is key to its utilisation of sialic acid from a range of human glycoproteins for biofilm growth and initial adhesion. Removal of terminal sialic acid residues often exposes ?-linked glucosamine or galactosamine which may also be important adhesive molecules. In turn, these residues are often removed by a group of enzymes known as ?-hexosaminidases. We show here that T. forsythia has the ability to cleave glucosamine and galactosamine from model substrates and that this activity can be inhibited by the hexosaminidase inhibitor PugNAc (O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino N-phenyl carbamate). We now demonstrate for the first time that ?-hexosaminidase activity plays a role in biofilm growth on glycoprotein coated surfaces since biofilm growth and initial cell adhesion is inhibited by PugNAc. In contrast, adhesion to siallo-protein coated surfaces is unaltered by PugNAc in the absence of sialidase activity (using a sialidase deficient mutant) or surprisingly on the clinically relevant substrates saliva or serum. These data indicate that ?-hexosaminidase activity has a significant role in biofilm formation in combination with sialidase activity in the biofilm lifestyle of T. forsythia. PMID:22276920

Roy, Sumita; Phansopa, Chatchawal; Stafford, Prachi; Honma, Kiyonobu; Douglas, C. W. Ian; Sharma, Ashu; Stafford, Graham P.

2014-01-01

168

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. PMID:21520924

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

2011-01-01

169

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. PMID:10850793

Esposito, G.; Michelutti, R.; Verdone, G.; Viglino, P.; Hernández, 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

170

Intrastriatal injection of interleukin-1 beta triggers the formation of neuromyelitis optica-like lesions in NMO-IgG seropositive rats  

PubMed Central

Background Neuromyelitis optica (NMO) is a severe, disabling disease of the central nervous system (CNS) characterized by the formation of astrocyte-destructive, neutrophil-dominated inflammatory lesions in the spinal cord and optic nerves. These lesions are initiated by the binding of pathogenic aquaporin 4 (AQP4)-specific autoantibodies to astrocytes and subsequent complement-mediated lysis of these cells. Typically, these lesions form in a setting of CNS inflammation, where the blood–brain barrier is open for the entry of antibodies and complement. However, it remained unclear to which extent pro-inflammatory cytokines and chemokines contribute to the formation of NMO lesions. To specifically address this question, we injected the cytokines interleukin-1 beta, tumor necrosis factor alpha, interleukin-6, interferon gamma and the chemokine CXCL2 into the striatum of NMO-IgG seropositive rats and analyzed the tissue 24 hours later by immunohistochemistry. Results All injected cytokines and chemokines led to profound leakage of immunoglobulins into the injected hemisphere, but only interleukin-1 beta induced the formation of perivascular, neutrophil-infiltrated lesions with AQP4 loss and complement-mediated astrocyte destruction distant from the needle tract. Treatment of rat brain endothelial cells with interleukin-1 beta, but not with any other cytokine or chemokine applied at the same concentration and over the same period of time, caused profound upregulation of granulocyte-recruiting and supporting molecules. Injection of interleukin-1 beta caused higher numbers of blood vessels with perivascular, cellular C1q reactivity than any other cytokine tested. Finally, the screening of a large sample of CNS lesions from NMO and multiple sclerosis patients revealed large numbers of interleukin-1 beta-reactive macrophages/activated microglial cells in active NMO lesions but not in MS lesions with comparable lesion activity and location. Conclusions Our data strongly suggest that interleukin-1 beta released in NMO lesions and interleukin-1 beta-induced production/accumulation of complement factors (like C1q) facilitate neutrophil entry and BBB breakdown in the vicinity of NMO lesions, and might thus be an important secondary factor for lesion formation, possibly by paving the ground for rapid lesion growth and amplified immune cell recruitment to this site. PMID:24252536

2013-01-01

171

Anatomy and controlling factors of a Late Cretaceous Aeolian sand sheet: The Marília and the Adamantina formations, NW Bauru Basin, Brazil  

NASA Astrophysics Data System (ADS)

Few previous studies have given significant consideration to the palaeosols in aeolian sand sheet sedimentary successions and, mainly, to their palaeoenvironmental and stratigraphic meaning in interaction with the deposits. These themes are considered in this study that deals with the depositional architecture and the factors controlling the construction, accumulation and preservation of an ancient aeolian sand sheet, that forms part of the Adamantina and Marília formations, in the Bauru Basin (Late Cretaceous, Brazil). In the NW portion of the Bauru Basin, these two units, ca 220 m thick, consist of sandstone, and secondarily of sandy conglomerate and mudstone, and are characterised by vertically alternated palaeosols and deposits. Facies analyses of the deposits and macroscopic characterisation of the palaeosols in 45 outcrops were integrated with laboratory analyses that consisted in descriptions of slabs of rock samples, petrographic analyses, clay mineralogy determination, geochemical analyses of the major oxides, and micromorphological characterisation of the palaeosols. Three architectural elements were recognised: palaeosols, wind-ripple-dominated aeolian sand sheet deposits, and ephemeral river deposits. The palaeosols constitute 66% of the entire sedimentary succession, and consist principally of Aridisols and, subordinately, of Alfisols, Vertisols, and Entisols. The wind-ripple-dominated aeolian sand sheet deposits (25%) are composed of sandstone, organised in translatent climbing wind-ripple strata, and secondarily of sandstone and mudstone deposited by infrequent floods. The ephemeral river deposits (9%) consist of sandy conglomerates 4 m thick and ca 2 km wide. Wind-ripple-dominated aeolian sand sheet deposits formed during relatively dry climate period on an unstable topographic surface of an aeolian sand sheet, where aeolian deposition or erosion prevailed. Palaeosols and ephemeral river deposits formed in a more humid climate period on a stable topographic surface of the aeolian sand sheet. Six bounding surfaces permitted the subdivision of the study formations into genetic geological bodies, revealing different spatial and temporal orders. Two first order surfaces separate mature palaeosol profiles (Aridisols, Alfisols, and Vertisols) from overlying aeolian deposits or other mature palaeosol profiles. A second order surface separates immature palaeosols (Entisols) from overlying aeolian deposits. A third order surface constitutes the channel bottom. A fourth order surface is located at the bottom of flood deposits. A fifth order surface divides translatent wind-ripple. The constructional phase of the aeolian sand sheet occurred during the relatively dry climate period, when the available sediment was supplied from the material originally deposited by rivers and stored during a more humid period (primary supply), and by soil erosion during a drier climate (secondary supply). The accumulation surface was controlled during the drier climate by cemented Bk horizons over Aridisols and by the force of the wind blowing over the other soils or deposits. Otherwise, during the more humid climate, the accumulation surface was a stabilised surface represented by the soil. Preservation was dominated by tectonically induced subsidence and burial.

Basilici, Giorgio; Führ Dal'Bó, Patrick Francisco

2010-04-01

172

Processing of 3D sheet metal components in STEP AP203 format. Part II: feature reasoning system  

Microsoft Academic Search

Both feature recognition and reasoning are needed for automating manufacturing planning activities for 3D sheet metal components. The feature reasoning system proposed here generates manufacturing information (e.g. flat pattern, locations of various features, internal cuts and blank profiles, type of tools required, operation sequence, bending sequence, etc.) for the features recognized in Part I of this paper. The issues related

T. R. Kannan; M. S. Shunmugam

2009-01-01

173

Double Mantle Plume Upwelling—A Possible Formation Mechanism of Beta Plateau and Devana Chasma,Venus  

NASA Astrophysics Data System (ADS)

Ning Ding,Zuoxun Zeng,China University of Geosciences,Wuhan,430074,China NingDing.eagle@gmail.com Introduction:Venus represents a‘one plate planet’[1],and the uplift,fractures and volcanism in Beta Regio on Venus are considered to be formed by lithosphere uplift driven by a hot plume[2]. Based on the double peaking saddle landform,we suggest the tectonic pattern of double mantle plume upwelling to interpret the formation mechanism of Beta Plateau and Devana Chasma.We take a physical modeling to validate this possibility. Model:There is no ductile shear in Venus[3],so we use quartz sands to simulate the crust of Venus.We use two wood stickes 1.5cm in diameter rising from the rubber canvas slowly and straight till about half of the model,then falling down slowly and straight.The base is a hard rubber plate,in the center of which,there are two holes 3cm in diameter,and the distance between them is 5cm.The holes are covered by rubber canvas.We use the quartz sands in colours of white, red and black with particle size of 70 mess as the model materials. Result:Fig.1:At the beginning of the wood stickes upwelling,only fine radial cracks are formed above the upwelling from central to outside.With the upwelling continue,surface energy of the fine radial cracks increase and make the cracks unstable,finally,the fine radial cracks connect each other and form a fracture zone.And then the two mantle plume downwelling,the fracture zone is developed to form a chasma at the end. Fig.2:The four profiles all form reverse faults outside and normal faults inside.But the difference is the faults in the middle of the chasma goes deeper than others.It is the pattern of Beta Plateau where the tectonic rising is cut by Devana Chasma zone in the topographic features. Fig.3:From the tow fig., we can see two points similar:a.the elevation is high and distribution area is large around the area of two upwelling and it is high around the area of chasma,but the distribution area is small;b.both of them shows saddle shape and two highland connectting bya chasma. Discussion:Based on the‘Geology Map of V-17’,two highlands of Northern part of Devana Chasma,but the material Unit of North and South highland are different.The material Units of North highland are the oldest unit tt and t,the material Unit of South highland is pl and the material Unit of rift is r are both the youngest unit.From the Magellan SAR mosaic[5],we can clearly see Devana Chasma cut the material Unit of tt and pl.So the two highlands of Northern part of Devana Chasma are simultaneous formed.The younger material Unit of South highland of Northern part of Devana Chasma is because of the volcanic eruption of Theia Mons. Conclusion:The physical modeling validates the model of the double plume upwelling is a possible explanation. Acknowledgements:This research was supported by the National Teaching Bases For Geology(CUG)foundation funded. References:[1]I.López,Icarus2008[2]A.T.Basilevsky,Icarus2007[3]J.C.Aubele,2009,LPSC[4]A.V.Vezolainen,2003,Journalofgeophysicalres5earch[5]http://planetarynames.wr.usgs.gov/images/v17_comp&v29_comp.pdf Fig.1 Fig.2 Fig.3a,3b

Ding, N.

2009-12-01

174

Nickel-catalyzed formation of a carbon-nitrogen bond at the beta position of saturated ketones.  

PubMed

Gone fishing: When propiophenone and related ethyl ketones are treated with morpholine in the presence of K(3)PO(4), chlorobenzene, and [Ni(cod)(2)]/PMe(3) catalyst, a carbon-nitrogen bond is formed selectively at the beta position (see scheme; cod = cycloocta-1,5-diene). Secondary amines were employed as substrates to give the corresponding beta-enaminones. PMID:19444844

Ueno, Satoshi; Shimizu, Ryosuke; Kuwano, Ryoichi

2009-01-01

175

[Beta]-Adrenergic Receptors in the Insular Cortex are Differentially Involved in Aversive vs. Incidental Context Memory Formation  

ERIC Educational Resources Information Center

The goal of this research was to determine the effects of [beta]-adrenergic antagonism in the IC before or after inhibitory avoidance (IA) training or context pre-exposure in a latent inhibition protocol. Pretraining intra-IC infusion of the [beta]-adrenergic antagonist propranolol disrupted subsequent IA retention and impaired latent inhibition…

Miranda, Maria Isabel; Sabath, Elizabeth; Nunez-Jaramillo, Luis; Puron-Sierra, Liliana

2011-01-01

176

Copper induces increased beta-sheet content in the scrapie-susceptible ovine prion protein PrPVRQ compared with the resistant allelic variant PrPARR.  

PubMed Central

Prion diseases are characterized by conformational change in the copper-binding protein PrP (prion protein). Polymorphisms in ovine PrP at amino acid residues 136, 154 and 171 are associated with variation in susceptibility to scrapie. PrPVRQ [PrP(Val136/Arg154/Gln171)] or PrPARQ [PrP(Ala136/Arg154/Gln171)] animals show susceptibility to scrapie, whereas those that express Ala136/Arg154/Arg171 (PrPARR) show resistance. Results are presented here that show PrPVRQ and PrPARR display different conformational responses to metal-ion interaction. At 37 degrees C copper induced different levels of b-sheet content in the allelic variants of ovine full-length prion protein (amino acid 25-232). PrPVRQ showed a significant increase in b-sheet content when exposed to copper at 37 degrees C, whereas PrPARR remained relatively unchanged. The conversion of a-helical PrPVRQ to b-sheet form was shown by CD spectroscopy and the decreased binding of C-terminal specific monoclonal anti-PrP antibodies. This conversion to an increased b-sheet form did not occur with truncated PrPVRQ (amino acids 89-233), which demonstrates that additional metal-binding sites outside of the N-terminus may not overtly influence the overall structure of ovine PrP. Despite the difference in b-sheet content, both the scrapie-susceptible and -resistant allelic forms of ovine PrP acquired resistance to proteinase K digestion following exposure to copper at 37 degrees C, suggesting the potential for disease-associated PrPARR to accumulate in vivo. Our present study demonstrates that allelic variants of ovine PrP differ in their structure and response to the interaction with copper. These observations will contribute to a better understanding of the mechanism of susceptibility and resistance to prion disease. PMID:14969585

Wong, Edmond; Thackray, Alana M; Bujdoso, Raymond

2004-01-01

177

Betaxanthin formation and free amino acids in hairy roots of Beta vulgaris var. lutea depending on nutrient medium and glutamate or glutamine feeding  

Microsoft Academic Search

Feeding of amino acids to hairy roots of the yellow beet (Beta vulgaris var. lutea) usually results in the formation of the respective betaxanthins. One exception is (S)-glutamate whose feeding leads to an increase in the betaxanthin vulgaxanthin I (glutamine as amino-acid moiety) instead of vulgaxanthin II (glutamate as amino-acid moiety). To elucidate this phenomenon, hairy roots were cultivated in

Hartmut Böhm; Gisela Mäck

2004-01-01

178

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

179

Processing of 3D sheet metal components in STEP AP203 format. Part I: feature recognition system  

Microsoft Academic Search

To automate planning activities in a computer integrated manufacturing environment, an integrated system of feature recognition and reasoning is essential. An attempt is made in the present work to develop such a system for 3D sheet metal components. Though certain part-modellers use feature-based methodology, they lack the information required for manufacturing and entire feature information is lost when converted to

T. R. Kannan; M. S. Shunmugam

2009-01-01

180

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

181

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.

182

24 CFR 1710.117 - Cost sheet, signature of Senior Executive Officer.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 false Cost sheet, signature of Senior Executive Officer...Reporting Requirements § 1710.117 Cost sheet, signature of Senior Executive Officer. (a) Cost sheet—Format. (1) The cost sheet...

2013-04-01

183

12 CFR 1010.117 - Cost sheet, signature of Senior Executive Officer.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 2012-01-01 false Cost sheet, signature of Senior Executive Officer...Reporting Requirements § 1010.117 Cost sheet, signature of Senior Executive Officer. (a) Cost sheet—Format. (1) The cost sheet...

2012-01-01

184

24 CFR 1710.117 - Cost sheet, signature of Senior Executive Officer.  

Code of Federal Regulations, 2014 CFR

...2014-04-01 2014-04-01 false Cost sheet, signature of Senior Executive Officer...Reporting Requirements § 1710.117 Cost sheet, signature of Senior Executive Officer. (a) Cost sheet—Format. (1) The cost sheet...

2014-04-01

185

24 CFR 1710.117 - Cost sheet, signature of Senior Executive Officer.  

Code of Federal Regulations, 2012 CFR

...2012-04-01 2012-04-01 false Cost sheet, signature of Senior Executive Officer...Reporting Requirements § 1710.117 Cost sheet, signature of Senior Executive Officer. (a) Cost sheet—Format. (1) The cost sheet...

2012-04-01

186

24 CFR 1710.117 - Cost sheet, signature of Senior Executive Officer.  

Code of Federal Regulations, 2011 CFR

...2011-04-01 2011-04-01 false Cost sheet, signature of Senior Executive Officer...Reporting Requirements § 1710.117 Cost sheet, signature of Senior Executive Officer. (a) Cost sheet—Format. (1) The cost sheet...

2011-04-01

187

12 CFR 1010.117 - Cost sheet, signature of Senior Executive Officer.  

Code of Federal Regulations, 2014 CFR

...2014-01-01 2014-01-01 false Cost sheet, signature of Senior Executive Officer...Reporting Requirements § 1010.117 Cost sheet, signature of Senior Executive Officer. (a) Cost sheet—Format. (1) The cost sheet...

2014-01-01

188

12 CFR 1010.117 - Cost sheet, signature of Senior Executive Officer.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 2013-01-01 false Cost sheet, signature of Senior Executive Officer...Reporting Requirements § 1010.117 Cost sheet, signature of Senior Executive Officer. (a) Cost sheet—Format. (1) The cost sheet...

2013-01-01

189

24 CFR 1710.117 - Cost sheet, signature of Senior Executive Officer.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Cost sheet, signature of Senior Executive Officer...Reporting Requirements § 1710.117 Cost sheet, signature of Senior Executive Officer. (a) Cost sheet—Format. (1) The cost sheet...

2010-04-01

190

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.

191

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

192

Induction of multinucleation by beta-glucosyl Yariv reagent in regenerated cells from Marchantia polymorpha protoplasts and involvement of arabinogalactan proteins in cell plate formation.  

PubMed

Arabinogalactan proteins (AGPs) are abundant plant cell surface proteoglycans widely distributed in plant species. Since high concentrations of beta-glucosyl Yariv reagent (betaglcY), which binds selectively to AGPs, inhibited cell division of protoplast-regenerated cells of the liverwort Marchantia polymorpha L. (Shibaya and Sugawara in Physiol Plant 130:271-279, 2007), we investigated the mechanism underlying the inability of the cells to divide normally by staining nuclei, cell walls and beta-1,3-glucan. Microscopic observation showed that the diameter of regenerated cells cultured with betaglcY was about 2.8-fold larger than that of cells cultured without betaglcY. The cells cultured with betaglcY were remarkably multinucleated. These results indicated that betaglcY did not inhibit mitosis but induced multinucleation. In the regenerated cells cultured with low concentrations of betaglcY (5 and 1 microg ml(-1)), the cell plate was stained strongly by betaglcY, suggesting abundant AGPs in the forming cell plate. In these cell plates, beta-1,3-glucan was barely detectable or not detected. In multinucleated cells, cell plate-like fragments, which could not reach the cell wall, were frequently observed and they were also stained strongly by betaglcY. Our results indicated that AGPs might have an important role in cell plate formation, and perturbation of AGPs with betaglcY might result in remarkable multinucleation in protoplast-regenerated cells of M. polymorpha. PMID:19475420

Shibaya, Taeko; Sugawara, Yasutake

2009-08-01

193

Designing a patient-care 24-hour flow sheet.  

PubMed

Flow sheets provide a clear understanding of the patient in a timely manner, but designing the new charting format can be complex. This guide defines a patient-care document's purpose, flow sheet strengths, and the evaluation format. PMID:10640040

Chelewski, P K

1999-01-01

194

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

195

Light scattering analysis of fibril growth from the amino-terminal fragment beta(1-28) of beta-amyloid peptide.  

PubMed Central

beta-Amyloid protein (beta-A/4) is the major protein component of Alzheimer disease-related senile plaques and has been postulated to be a significant contributing factor in the onset and/or progression of the disease. In the senile plaque, beta-A/4 appears as bundles of amyloid fibrils. The biological activity of beta-A/4 may be related to its state of aggregation. In this work, self-assembly, fibril formation, and interfibrillary aggregation of beta(1-28), a synthetic peptide homologous with the amino-terminal fragment of beta-A/4, were investigated. The predominant form of beta(1-28) detected by size-exclusion chromatography and polyacrylamide gel electrophoresis was apparently a tetramer which does not bind Congo red. Aggregates containing cross-beta sheet structures which bind Congo red and thioflavin T were observed at concentrations of approximately 0.3 mg/ml or greater. Concentrations of 0.5-1 mg/ml were necessary for aggregation into fibrils to be detectable by classical or quasielastic light scattering. Both fibril elongation and fibril-fibril aggregation occur over the time scale investigated. The kinetics of aggregation were much faster at physiological salt concentrations than at lower ionic strength. Ionic strength also appeared to influence the morphology of the fibril aggregates. The data indicate that sample preparation method and sample history influence fibril size and number density. Images FIGURE 3 FIGURE 10 PMID:8312477

Shen, C L; Scott, G L; Merchant, F; Murphy, R M

1993-01-01

196

A calorimetric determination of the enthalpy of formation and a description of the defect structure of the ordered beta-phase /Ni, Cu/ /1-x/ Al/x/  

NASA Technical Reports Server (NTRS)

In order to describe thermodynamically the defect structure of an ordered B-Hume-Rothery phase, the heat of formation of (Ni,Cu)(1-x)Al(x) was measured at 1100 K as a function of concentration in the range x (sub Al) = 0.4 and 0.55 for three substitution rations x (sub Ni)/x (sub Cu) = infinity; 11; 5. The heat of formation of the NiAl beta-phase is strongly negative. For the stoichiometric composition it is -72.2 kJ/g-atom. On both the nickel-rich side and the aluminum-rich side the magnitude of the enthalpy of formation decreases linearly with concentration. Substitution of nickel for copper decreases the magnitude of the enthalpy of formation over the entire homogeneity range for the phase (Ni,Cu)(1-x)Al(x). The curve for the enthalpy of formation as well as the literature values for the chemical potential of aluminum are described with great accuracy by the disorder model of Wagner-Schottky.

Henig, E. T.; Lukas, H. L.

1988-01-01

197

Development of a novel composite material with carbon nanotubes assisted by self-assembled peptides designed in conjunction with ?-sheet formation.  

PubMed

A novel composite material is developed with single-walled carbon nanotubes (SWCNTs) and artificially designed peptides, and its chemical and physicochemical characteristics are evaluated with an aim toward biomedical application. The peptides were designed to form a ?-sheet structure that would be suitable for wrapping SWCNTs. The complex of SWCNTs and peptide (SWCNT-peptide) showed good dispersibility in aqueous media and was considerably stable even in the absence of an excess amount of peptide in the media. The formation of SWCNT-peptide was confirmed by its performance in water, atomic force microscopy and transmission electron microscopy observation, and molecular modeling. The possibility of introducing various functions to SWCNT-peptide was also demonstrated by several methods, such as introduction of special amino acids, chemical modification, and additional complex formation based on electrostatic interaction. These results suggest the potential of the SWCNT-peptide complex as a molecular platform on which a desirable structure and/or function can be constructed for biomedical and industrial application. PMID:22488097

Hashida, Yasuhiko; Umeyama, Tomokazu; Mihara, Junya; Imahori, Hiroshi; Tsujimoto, Masahiko; Isoda, Seiji; Takano, Mikio; Hashida, Mitsuru

2012-09-01

198

Estrogen treatment improves spatial learning in APP + PS1 mice but does not affect beta amyloid accumulation and plaque formation  

Microsoft Academic Search

We investigated the effects of ovariectomy (OVX) and 17?-estradiol (0.18 mg per pellet) treatment on spatial learning and memory, hippocampal beta amyloid (A?) levels, and amyloid plaque counts in double transgenic mice (A\\/P) carrying mutated amyloid precursor protein (APPswe) and presenilin-1 (PS1-A246E). After OVX at 3 months of age, the mice received estrogen treatment for the last 3 months of

T. Heikkinen; G. Kalesnykas; A. Rissanen; T. Tapiola; S. Iivonen; J. Wang; J. Chaudhuri; H. Tanila; R. Miettinen; J. Puoliväli

2004-01-01

199

The unexpected formation of the stable beta phase of L-glutamic acid during pH-shift precipitation  

NASA Astrophysics Data System (ADS)

Rapid pre-mixing of solutions of sodium L-glutamate and of sulphuric acid enabled the creation of a high supersaturation ratio 4-22 for pH-shift precipitation of L-glutamic acid. In post-mixed samples the prismatic crystals of the metastable alpha polymorph formed in accordance with Ostwald's rule. However, from non-post-mixed samples spherulite-like crystals of the stable beta polymorph were obtained. Without agitation, crystals were observed later than in agitated samples. The mechanism proposed to explain these results assumes that both polymorphs nucleate concomitantly. Both forms nucleate slowly but the beta form nucleates at the highest rate. Without post-mixing the large number of beta crystals depletes most of the supersaturation although the few alpha crystals grow faster. With post-mixing, the fast-growing alpha crystals first reach the critical size for attrition. From that moment attrition generates a large number of secondary alpha nuclei that rapidly deplete the solution.

Roelands, C. P. M.; ter Horst, Joop H.; Kramer, Herman J. M.; Jansens, Peter J.

2005-02-01

200

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.

201

The effect of glutamic acid side chain on acidity constant of lysine in beta-sheet: A density functional theory study  

NASA Astrophysics Data System (ADS)

In this work, the possibility of proton transfer between side chain of lysine and glutamic acid in peptide of Glu--Ala-Lys+ was demonstrated using density functional theory (DFT). We have shown that the proton transfer takes place between side chain of glutamic and lysine residues through the hydrogen bond formation. The structures of transition state for proton transfer reaction were detected in gas and solution phases. Our kinetic studies show that the proton transfer reaction rate in gas phase is higher than solution phase. The ionization constant (p K a) value of lysine residue in peptide was estimated 1.039 which is lower than intrinsic p K a of lysine amino acid.

Sargolzaei, M.; Afshar, M.; Sadeghi, M. S.; Kavee, M.

2014-07-01

202

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

203

Fibers of tau fragments, but not full length tau, exhibit a cross beta-structure: implications for the formation of paired helical filaments.  

PubMed

We have used X-ray fiber diffraction to probe the structure of fibers of tau and tau fragments. Fibers of fragments from the microtubule binding domain had a cross beta-structure that closely resembles that reported both for neurofibrillary tangles found in Alzheimer's disease brain and for fibrous lesions from other protein folding diseases. In contrast, fibers of full-length tau had a different, more complex structure. Despite major differences at the molecular level, all fiber types exhibited very similar morphology by electron microscopy. These results have a number of implications for understanding the etiology of Alzheimer's and other tauopathic diseases. The morphology of the peptide fibers suggests that the region in tau corresponding to the peptides plays a critical role in the nucleation of fiber assembly. The dramatically different structure of the full length tau fibers suggests that some region in tau has enough inherent structure to interfere with the formation of cross beta-fibers. Additionally, the similar appearance by electron microscopy of fibrils with varying molecular structure suggests that different molecular arrangements may exist in other samples of fibers formed from tau. PMID:11206064

Giannetti, A M; Lindwall, G; Chau, M F; Radeke, M J; Feinstein, S C; Kohlstaedt, L A

2000-12-01

204

Fibers of tau fragments, but not full length tau, exhibit a cross beta-structure: implications for the formation of paired helical filaments.  

PubMed Central

We have used X-ray fiber diffraction to probe the structure of fibers of tau and tau fragments. Fibers of fragments from the microtubule binding domain had a cross beta-structure that closely resembles that reported both for neurofibrillary tangles found in Alzheimer's disease brain and for fibrous lesions from other protein folding diseases. In contrast, fibers of full-length tau had a different, more complex structure. Despite major differences at the molecular level, all fiber types exhibited very similar morphology by electron microscopy. These results have a number of implications for understanding the etiology of Alzheimer's and other tauopathic diseases. The morphology of the peptide fibers suggests that the region in tau corresponding to the peptides plays a critical role in the nucleation of fiber assembly. The dramatically different structure of the full length tau fibers suggests that some region in tau has enough inherent structure to interfere with the formation of cross beta-fibers. Additionally, the similar appearance by electron microscopy of fibrils with varying molecular structure suggests that different molecular arrangements may exist in other samples of fibers formed from tau. PMID:11206064

Giannetti, A. M.; Lindwall, G.; Chau, M. F.; Radeke, M. J.; Feinstein, S. C.; Kohlstaedt, L. A.

2000-01-01

205

Transforming Growth Factor Beta Signaling Is Essential for the Autonomous Formation of Cartilage-Like Tissue by Expanded Chondrocytes  

PubMed Central

Cartilage is a tissue with limited self-healing potential. Hence, cartilage defects require surgical attention to prevent or postpone the development of osteoarthritis. For cell-based cartilage repair strategies, in particular autologous chondrocyte implantation, articular chondrocytes are isolated from cartilage and expanded in vitro to increase the number of cells required for therapy. During expansion, the cells lose the competence to autonomously form a cartilage-like tissue, that is in the absence of exogenously added chondrogenic growth factors, such as TGF-?s. We hypothesized that signaling elicited by autocrine and/or paracrine TGF-? is essential for the formation of cartilage-like tissue and that alterations within the TGF-? signaling pathway during expansion interfere with this process. Primary bovine articular chondrocytes were harvested and expanded in monolayer culture up to passage six and the formation of cartilage tissue was investigated in high density pellet cultures grown for three weeks. Chondrocytes expanded for up to three passages maintained the potential for autonomous cartilage-like tissue formation. After three passages, however, exogenous TGF-?1 was required to induce the formation of cartilage-like tissue. When TGF-? signaling was blocked by inhibiting the TGF-? receptor 1 kinase, the autonomous formation of cartilage-like tissue was abrogated. At the initiation of pellet culture, chondrocytes from passage three and later showed levels of transcripts coding for TGF-? receptors 1 and 2 and TGF-?2 to be three-, five- and five-fold decreased, respectively, as compared to primary chondrocytes. In conclusion, the autonomous formation of cartilage-like tissue by expanded chondrocytes is dependent on signaling induced by autocrine and/or paracrine TGF-?. We propose that a decrease in the expression of the chondrogenic growth factor TGF-?2 and of the TGF-? receptors in expanded chondrocytes accounts for a decrease in the activity of the TGF-? signaling pathway and hence for the loss of the potential for autonomous cartilage-like tissue formation. PMID:25775021

Tekari, Adel; Luginbuehl, Reto; Hofstetter, Willy; Egli, Rainer J.

2015-01-01

206

Structural modifications of human beta 2 microglobulin treated with oxygen-derived radicals.  

PubMed Central

Treatment of human beta 2 microglobulin (beta 2m) with defined oxygen-derived species generated by treatment with gamma-radiation was studied. As assessed by SDS/PAGE, the hydroxyl radicals (.OH) caused the disappearance of the protein band at 12 kDa that represents beta 2m, and cross-linked the protein into protein bands stable to both SDS and reducing conditions. However, when .OH was generated under oxygen in equimolar combination with the superoxide anion radical (O2.-), the high-molecular-mass protein products were less represented, and fragmented derivatives were not obviously detectable. Exposure to .OH alone, or to .OH + O2.- in the presence of O2, induced the formation of beta 2m protein derivatives with a more acidic net electrical charge than the parent molecule. In contrast, O2.- alone had virtually no effect on molecular mass or pI. Changes in u.v. fluorescence during .OH attack indicated changes in conformation, as confirmed by c.d. spectrometry. A high concentration of radicals caused the disappearance of the beta-pleated sheet structure and the formation of a random coil structure. Loss of tryptophan and significant production of dityrosine (2,2'-biphenol type) were noted, exhibiting a clear dose-dependence with .OH alone or with .OH + O2.-. The combination of .OH + O2.- induced a pattern of changes similar to that with .OH alone, but more extensive for c.d. and tryptophan oxidation (2 Trp/beta 2m molecule), and more limited for dityrosine formation. Lower levels of these oxidative agents caused the reproducible formation of species at 18 and 25 kDa which were recognized by antibodies against native beta 2m. These findings provide a model for the protein pattern observed in beta 2m amyloidosis described in the literature. Images Fig. 4. Fig. 5. PMID:1649598

Capeillere-Blandin, C; Delaveau, T; Descamps-Latscha, B

1991-01-01

207

Influence of Nanoparticle Size and Shape on Oligomer Formation of an Amyloidogenic Peptide  

E-print Network

Understanding the influence of macromolecular crowding and nanoparticles on the formation of in-register $\\beta$-sheets, the primary structural component of amyloid fibrils, is a first step towards describing \\emph{in vivo} protein aggregation and interactions between synthetic materials and proteins. Using all atom molecular simulations in implicit solvent we illustrate the effects of nanoparticle size, shape, and volume fraction on oligomer formation of an amyloidogenic peptide from the transthyretin protein. Surprisingly, we find that inert spherical crowding particles destabilize in-register $\\beta$-sheets formed by dimers while stabilizing $\\beta$-sheets comprised of trimers and tetramers. As the radius of the nanoparticle increases crowding effects decrease, implying smaller crowding particles have the largest influence on the earliest amyloid species. We explain these results using a theory based on the depletion effect. Finally, we show that spherocylindrical crowders destabilize the ordered $\\beta$-sheet dimer to a greater extent than spherical crowders, which underscores the influence of nanoparticle shape on protein aggregation.

Edward P. O'Brien; John E. Straub; Bernard R. Brooks; D. Thirumalai

2011-05-05

208

Domain formation induced by lipid-ion and lipid-peptide interactions.  

PubMed

High sensitivity titration calorimetry was performed for metal ions such as calcium and lanthanum and for different types of Alzheimer peptides. Ca2+ adsorbs to mixed phosphatidylcholine (PC)/phosphatidylglycerol (PG) membranes with an endothermic reaction enthalpy of delta H approximately +0.1 kcal/mol. La3+ binds to sonified PC vesicles with a reaction enthalpy of delta H approximately + 1.8 kcal/mol. The binding constants are of the order of 10 M-1 for Ca2+ and 4 x 10(3) M-1 for La3+. The role of lipids in the random coil<-->beta-sheet equilibrium of different types of Alzheimer model peptides was investigated with circular dichroism (CD) and high sensitivity titration calorimetry. Alzheimer peptide beta AP(1-40)OH and several fragments of this peptide undergo a concentration-dependent, co-operative random coil<-->beta-sheet transition in solution which can be described by a linear association model with a nucleation parameter sigma approximately 0.2-0.01 and a growth parameter s approximately 10(4) M-1. Addition of sonified lipid vesicles containing negatively charged lipids shifts the equilibrium towards the beta-sheet conformation. This can be explained by an aggregation phenomenon at the lipid/water interphase. The cationic peptides are attracted to the negatively charged membrane surface causing a local increase in peptide concentration. The high peptide concentration, together with the ordering of the peptide molecules on the membrane surface, facilitates beta-sheet formation, constituting the first experimental evidence for the induction of beta-sheet formation via the membrane surface. The binding of Alzheimer peptide fragments to the lipid membrane is accompanied by an exothermic heat of reaction with delta H in the range -2 - -8 kcal/mol. PMID:7767383

Seelig, J; Lehrmann, R; Terzi, E

1995-01-01

209

Interaction of the Molecular Chaperone DNAJB6 with Growing Amyloid-beta 42 (A?42) Aggregates Leads to Sub-stoichiometric Inhibition of Amyloid Formation*  

PubMed Central

The human molecular chaperone protein DNAJB6 was recently found to inhibit the formation of amyloid fibrils from polyglutamine peptides associated with neurodegenerative disorders such as Huntington disease. We show in the present study that DNAJB6 also inhibits amyloid formation by an even more aggregation-prone peptide (the amyloid-beta peptide, A?42, implicated in Alzheimer disease) in a highly efficient manner. By monitoring fibril formation using Thioflavin T fluorescence and far-UV CD spectroscopy, we have found that the aggregation of A?42 is retarded by DNAJB6 in a concentration-dependent manner, extending to very low sub-stoichiometric molar ratios of chaperone to peptide. Quantitative kinetic analysis and immunochemistry studies suggest that the high inhibitory efficiency is due to the interactions of the chaperone with aggregated forms of A?42 rather than the monomeric form of the peptide. This interaction prevents the growth of such species to longer fibrils and inhibits the formation of new amyloid fibrils through both primary and secondary nucleation. A low dissociation rate of DNAJB6 from A?42 aggregates leads to its incorporation into growing fibrils and hence to its gradual depletion from solution with time. When DNAJB6 is eventually depleted, fibril proliferation takes place, but the inhibitory activity can be prolonged by introducing DNAJB6 at regular intervals during the aggregation reaction. These results reveal the highly efficacious mode of action of this molecular chaperone against protein aggregation, and demonstrate that the role of molecular chaperones can involve interactions with multiple aggregated species leading to the inhibition of both principal nucleation pathways through which aggregates are able to form. PMID:25217638

Månsson, Cecilia; Arosio, Paolo; Hussein, Rasha; Kampinga, Harm H.; Hashem, Reem M.; Boelens, Wilbert C.; Dobson, Christopher M.; Knowles, Tuomas P. J.; Linse, Sara; Emanuelsson, Cecilia

2014-01-01

210

Interaction of the molecular chaperone DNAJB6 with growing amyloid-beta 42 (A?42) aggregates leads to sub-stoichiometric inhibition of amyloid formation.  

PubMed

The human molecular chaperone protein DNAJB6 was recently found to inhibit the formation of amyloid fibrils from polyglutamine peptides associated with neurodegenerative disorders such as Huntington disease. We show in the present study that DNAJB6 also inhibits amyloid formation by an even more aggregation-prone peptide (the amyloid-beta peptide, A?42, implicated in Alzheimer disease) in a highly efficient manner. By monitoring fibril formation using Thioflavin T fluorescence and far-UV CD spectroscopy, we have found that the aggregation of A?42 is retarded by DNAJB6 in a concentration-dependent manner, extending to very low sub-stoichiometric molar ratios of chaperone to peptide. Quantitative kinetic analysis and immunochemistry studies suggest that the high inhibitory efficiency is due to the interactions of the chaperone with aggregated forms of A?42 rather than the monomeric form of the peptide. This interaction prevents the growth of such species to longer fibrils and inhibits the formation of new amyloid fibrils through both primary and secondary nucleation. A low dissociation rate of DNAJB6 from A?42 aggregates leads to its incorporation into growing fibrils and hence to its gradual depletion from solution with time. When DNAJB6 is eventually depleted, fibril proliferation takes place, but the inhibitory activity can be prolonged by introducing DNAJB6 at regular intervals during the aggregation reaction. These results reveal the highly efficacious mode of action of this molecular chaperone against protein aggregation, and demonstrate that the role of molecular chaperones can involve interactions with multiple aggregated species leading to the inhibition of both principal nucleation pathways through which aggregates are able to form. PMID:25217638

Månsson, Cecilia; Arosio, Paolo; Hussein, Rasha; Kampinga, Harm H; Hashem, Reem M; Boelens, Wilbert C; Dobson, Christopher M; Knowles, Tuomas P J; Linse, Sara; Emanuelsson, Cecilia

2014-11-01

211

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

SciTech Connect

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 [Department of Plasma Physics, School of Physics A28, University of Sydney NSW 2006 (Australia)] [Department of Plasma Physics, School of Physics A28, University of Sydney NSW 2006 (Australia)

2013-05-15

212

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

213

Study on the Formation and Characterization of the Intermetallics in Friction Stir Welding of Aluminum Alloy to Coated Steel Sheet Lap Joint  

NASA Astrophysics Data System (ADS)

Multimaterial fabrication such as joining of steel and aluminum is currently prominent in a variety of industries. Friction stir welding is a novel solid-state welding process that causes good joint strength between steel and aluminum. However, the phenomenon contributing significant strength at the interface is not yet clear. In the present study, the interface of the friction stir lap-welded aluminum and coated steel sheet having joint strength maximum (71.4 pct of steel base metal) and minimum, respectively, under two parameter combinations, i.e., 1000 rpm 50 mm min-1 and 500 rpm 100 mm min-1, was exclusively characterized by X-ray diffraction, transmission electron microscopy (TEM), concentration profile, and elemental mapping by electron-probe microanalysis. A TEM-assisted EDS study identifies the morphologies of large size Al13Fe4 and small size Fe3Al-type intermetallic compounds at the interface. The diffusion-induced intermetallic growth (thickness) measured from a backscattered image and concentration profile agreed well with the numerically calculated one. The growth of these two phases at 1000 rpm 50 mm min-1 is attributed to the slower cooling rate (~3.5 K/s) with higher diffusion time (44 seconds) along the interface in comparison to the same for 500 rpm 100 mm min-1 with faster cooling rate (~10 K/s) and less diffusion time (13.6 seconds). The formation of thermodynamically stable and hard intermetallic phase Al13Fe4 at 1000 rpm and travel speed 50 mm min-1 in amounts higher than 500 rpm and a travel speed of 100 mm min-1 results in better joint strength, i.e., 71.4 pct, of the steel base metal.

Das, H.; Ghosh, R. N.; Pal, T. K.

2014-10-01

214

Ensemble modeling of [beta]-sheet proteins  

E-print Network

Our ability to characterize protein structure and dynamics is vastly outpaced by the speed of modern genetic sequencing, creating a growing divide between our knowledge of biological sequence and structure. Structural ...

O'Donnell, Charles William

2011-01-01

215

Practical asymmetric synthesis of beta-hydroxy-beta-trifluoromethylated ketones via the first example of the in situ generation of trifluoro-acetaldehyde and its successive asymmetric carbon-carbon bond formation reaction with chiral imines.  

PubMed

Not only trifluoroactaldehyde ethyl hemiacetal or hydrate but also other polyfluoroalkylaldehydes acetals or hydrates react with an equimolar amount of various chiral imines, followed by hydrolysis to produce the corresponding (S)-beta-hydroxy-beta-polyfluoroalkyl ketones in good yields with good enantioselectivities; furthermore, the ee of the products can be improved by simple recrystallization. PMID:15367972

Funabiki, Kazumasa; Hashimoto, Wataru; Matsui, Masaki

2004-09-21

216

Free Cholesterol Induces Higher ?-Sheet Content in A? Peptide Oligomers by Aromatic Interaction with Phe19  

PubMed Central

Accumulating experimental evidence support an enhancing effect of free cholesterol on amyloid-beta (A?) aggregation. To probe the mechanisms of cholesterol-mediated A? aggregation, we applied all-atom molecular dynamic simulations on A?42 peptides in presence of free cholesterol. Several control systems were also designed to examine the specificity of cholesterol-residue interactions, including mutation on aromatic residue, substitution of cholesterol with sphingomyelin (SM) and DPPC bilayer, and a mixing SM and cholesterol. Each system was performed 4 independent simulations, with a total time of 560 ns. It was found that cholesterol increased ?-sheet formation by 4 folds, but the Phe19?Ser mutation on A?42 peptide totally eliminated cholesterol’s effect. A stable contact was recognized between the steroid group of cholesterol and the Benzyl group of Phe19. Interestingly, our simulation revealed a regular 1 ns time interval between the establishment of cholesterol-phenylalanine contact and consequent ?-sheet formation, suggesting an important role of steroid-benzyl interaction in cholesterol-mediated aggregation. The presence of SM slightly increased ?-sheet formation, but the mixture of cholesterol and SM had a strong induction effect. Also, the measurement of Phe19-lipid distance indicates that aromatic side chains of peptides prone to bind to cholesterol on the surface of the mixed micelle. In the DPPC system, polar chains were attracted to the surface of membrane, yielding moderate increase of ?-sheet formation. These results shed light on the mechanism of cholesterol-mediated fibrillogenesis, and help to differentiate the effects of cholesterol and other lipids on ?-sheet formation process. PMID:23049991

2012-01-01

217

Apolipoprotein E structural requirements for the formation of SDS-stable complexes with beta-amyloid-(1-40): the role of salt bridges.  

PubMed Central

Of the three major isoforms of human apolipoprotein E (apoE), apoE4 is a risk factor for the development of Alzheimer's disease. Among possible neurologically relevant differences in the properties of apoE3 and apoE4 is the fact that apoE3 forms an SDS-stable complex with beta-amyloid-(1-40) (Abeta40) with greater avidity than does apoE4. This interaction may sequester potentially toxic species of Abeta or facilitate clearance. To understand more about this difference, we examined whether differences in salt bridges between apoE domains influence the capacity of apoE isoforms to form complexes with Abeta. In apoE3 there is a salt bridge between Arg-61 and Asp-65, while in apoE4 there are salt bridges between Arg-61 and Glu-255, and Arg-112 and Glu-109. Mutation of position 112, which is Cys in apoE3 and Arg in apoE4, to Ala or Lys abolished complex formation, while mutant apoE with Ser at this position retained the capacity to form complex. Substituting Ala for Glu-109 had no effect on the ability of either apoE4 or apoE3 to form complexes. On the other hand, substitution of Thr for Arg-61 in apoE3 abolished, and truncation of apoE3 at position 201 substantially lowered, but did not abolish, complex formation. Neither of these mutations within apoE4 had any affect on its complex formation with Abeta. These results suggest that the nature of the cysteine residue in apoE3 and interactions between the N-terminal and C-terminal domains of human apoE are important for the ability of apoE3 to form an SDS-stable complex with Abeta40. PMID:12015813

Bentley, Nicholas M; Ladu, Mary Jo; Rajan, Chandrika; Getz, Godfrey S; Reardon, Catherine A

2002-01-01

218

The motion of thrust sheets  

Microsoft Academic Search

The regional average basal shear stress tau of a thrust sheet of thickness H is equal to the down-surface slope stress pgHalpha. Thrusts always move in the direction of surface slope alpha, even if they are moving up the dip beta of the base. The sole thrust beneath the Canadian Rockies had tau of the order of 5×106 Pa (50

David Elliott

1976-01-01

219

Facilitation by procaterol, a beta-adrenoceptor agonist, of noradrenaline release in the pithed rat independently of angiotensin II formation.  

PubMed

1. The effects of the beta 2-adrenoceptor agonist, procaterol, on sympathetic neuroeffector transmission were studied in the pithed adrenal demedullated rat to determine if generation of angiotensin II was involved in its effect. Pressor responses were elicited by either electrical stimulation (20 V, 2 Hz) of the entire spinal sympathetic outflow or methoxamine (0.1 mg kg-1, i.v.). 2. Sodium nitroprusside (3 and 5 micrograms kg-1 min-1, i.v.) produced hypotension and the pressor responses to both sympathetic nerve stimulation and methoxamine were reduced. This indicates that decreasing blood pressure in pithed rats reduces pressor responses. Procaterol (10 and 30 ng kg-1 min-1, i.v.) also produced hypotension but did not alter pressor responses to sympathetic nerve stimulation. Nevertheless, procaterol (10 and 30 ng kg-1 min-1, i.v.) did reduce pressor responses to to methoxamine. Together these results suggest that procaterol may have enhanced sympathetic neurotransmitter release. This was confirmed in another series of experiments where procaterol (30 ng kg-1 min-1, i.v.) increased plasma noradrenaline levels during sympathetic nerve stimulation. 3. Captopril (5 mg kg-1, i.v.) produced hypotension and as expected reduced pressor responses to sympathetic nerve stimulation. When the hypotensive effect of captopril was abolished by concomitant vasopressin infusion (1.5-4.5 i mu kg-1 min-1, i.v.), pressor responses to sympathetic nerve stimulation were restored to pre-captopril levels. In this situation procaterol (10 and 30 ng kg-' min', i.v.) reduced basal blood pressure and did not alter pressor responses to sympathetic nerve stimulation whereas the pressor responses were reduced by an equihypotensive infusion of sodium nitroprusside (3 and 5 jig kg-' min' , i.v.). The lack of reduction of pressor responses after procaterol in the presence of captopril is indirect evidence that procaterol may have enhanced noradrenaline release independently of angiotensin II.4. In another series of experiments, plasma noradrenaline levels elicited by sympathetic nerve stimulation were not altered by captopril (5 mg kg', i.v.). In the presence of captopril (5 mg kg-', i.v.),procaterol (30 ng kg- min-1, i.v.) no longer enhanced plasma noradrenaline levels during sympathetic nerve stimulation. However, since the dose of captopril is well above that required to block angiotens in converting enzyme (ACE) the effect may be non-specific. Therefore, the selective AT, receptor antagonist, losartan (10mgkg'1, i.v.), was also used. Losartan (10mgkg'1, i.v.) did not alter plasma noradrenaline levels during sympathetic nerve stimulation, and in the presence of losartan procaterol(30 ng kg-I min-', i.v.) enhanced plasma noradrenaline levels during sympathetic nerve stimulation. This result further suggests that 1-adrenoceptor facilitation of noradrenaline release from sympathetic nerves in the pithed rat occurs by a mechanism independent of angiotensin II generation. PMID:7858867

Kotsonis, P; Majewski, H

1994-11-01

220

STATE AUTHORITIES SUPERANNUATION SCHEME (SASS) FACT SHEET FACT SHEET FACT SHEET FACT SHEET FACT SH  

E-print Network

STATE AUTHORITIES SUPERANNUATION SCHEME (SASS) FACT SHEET FACT SHEET FACT SHEET FACT SHEET FACT SH superannuation and tax legislation. STC has published this Fact Sheet. STC is not licensed to provide financial in this Fact Sheet and nothing in it is intended to be or should be regarded as personal advice

University of Technology, Sydney

221

Acceleration of enzymatic reaction of trypsin through the formation of water-soluble complexes with poly(ethylene glycol)-block-poly(alpha,beta-aspartic acid).  

PubMed

The amidase activity of bovine pancreas trypsin in water-soluble complexes with poly(ethylene glycol)-block-poly(alpha,beta-aspartic acid) (PEG-PAA) was evaluated by a colorimetric assay using L-lysine p-nitroanilide as a substrate. The enzymatic reaction of trypsin was accelerated through the complexation with PEG-PAA. By determining the kinetic parameters of the enzymatic reaction of trypsin, it was confirmed that the catalytic rate constant of the complexed trypsin was 15 times higher than that of the native trypsin. From the evaluation of pH dependence of initial reaction rate, it was indicated that this acceleration was induced by a stabilization of the imidazolium ion of the His residue in the catalytic site, the Asp-His-Ser triad, of trypsin due to the Asp units of PEG-PAA. The hydrogen bonded Asp-His pairs are critical constituents in several key enzymatic reactions including serine protease and apurinic endonucleases, and it was expected that the acceleration of the catalytic reaction might occur for other enzymes by the formation of water-soluble complexes with PEG-PAA. PMID:15762622

Kawamura, Akifumi; Yoshioka, Yuriko; Harada, Atsushi; Kono, Kenji

2005-01-01

222

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

223

Beta experiment  

NASA Technical Reports Server (NTRS)

A focused laser doppler velocimeter (LDV) system was developed for the measurement of atmospheric backscatter (beta) from aerosols at infrared wavelengths. A Doppler signal generator was used in mapping the coherent sensitive focal volume of a focused LDV system. System calibration data was analyzed during the flight test activity scheduled for the Beta system. These analyses were performed to determine the acceptability of the Beta measurement system's performance.

1982-01-01

224

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

225

Beta Thalassemia  

MedlinePLUS

... globin gene, the condition is almost identical to sickle cell disease. When some beta globin is produced by the ... trait (the abnormal hemoglobin found in people with sickle cell disease) ß ß S ? ß S 25% sickle-beta thalassemia normal ...

226

Effect of formation and state of interface on joint strength in friction stir spot welding for advanced high strength steel sheets  

NASA Astrophysics Data System (ADS)

The tensile shear strength and cross tension strength of friction stir spot welded joints were evaluated in the cases of lap joints of 270 N/mm2 grade and 980 N/mm2 grade cold rolled steel sheets with respect to the stir zone area, hardness distribution, and interface condition between the sheets. The results suggested that both the tensile shear strength and cross tension strength were based on the stir zone area and its hardness in both grades of steel. The "hook" shape of the interface also affected the joint strength. However, the joining that occurred across the interfaces had a significant influence on the value of the joint strength in the case of the 270 N/mm2 grade steel.

Taniguchi, Koichi; Matsushita, Muneo; Ikeda, Rinsei; Oi, Kenji

2014-08-01

227

Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines  

USGS Publications Warehouse

The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (

Todd, Brian J.; Valentine, Page C.; Longva, Oddvar; Shaw, John

2007-01-01

228

Secondary structure formation in peptide amphiphile micelles  

NASA Astrophysics Data System (ADS)

Peptide amphiphiles (PAs) are capable of self-assembly into micelles for use in the targeted delivery of peptide therapeutics and diagnostics. PA micelles exhibit a structural resemblance to proteins by having folded bioactive peptides displayed on the exterior of a hydrophobic core. We have studied two factors that influence PA secondary structure in micellar assemblies: the length of the peptide headgroup and amino acids closest to the micelle core. Peptide length was systematically varied using a heptad repeat PA. For all PAs the addition of a C12 tail induced micellization and secondary structure. PAs with 9 amino acids formed beta-sheet interactions upon aggregation, whereas the 23 and 30 residue peptides were displayed in an apha-helical conformation. The 16 amino acid PA experienced a structural transition from helix to sheet, indicating that kinetics play a role in secondary structure formation. A p53 peptide was conjugated to a C16 tail via various linkers to study the effect of linker chemistry on PA headgroup conformation. With no linker the p53 headgroup was predominantly alpha helix and a four alanine linker drastically changed the structure of the peptide headgroup to beta-sheet, highlighting the importance of hydrogen boding potential near the micelle core.

Tirrell, Matthew

2012-02-01

229

Rh-catalyzed formation of dioxolanes from alpha-alkyl diazoesters: diastereoselective cycloadditions of carbonyl ylides with selectivity over beta-hydride elimination.  

PubMed

Described here is a diastereoselective Rh-catalyzed method for the preparation of dioxolanes from alpha-alkyl-alpha-diazoesters. This represents the first general method for generating carbonyl ylides from alpha-diazoesters that possess beta-hydrogens, as such diazo compounds typically give rise to alkenes via beta-hydride elimination. Subsequent cycloaddition with aromatic aldehydes gives tetrasubstituted dioxolanes with unusually high diastereoselectivity. A model is set forth to explain the diastereoselectivity of the cycloaddition. PMID:18189412

DeAngelis, Andrew; Panne, Patricia; Yap, Glenn P A; Fox, Joseph M

2008-02-15

230

Liquid sheet radiator apparatus  

NASA Technical Reports Server (NTRS)

An external flow, liquid sheet radiator apparatus adapted for space applications has as its radiating surface a thin stable liquid sheet formed by fluid flow through a very narrow slit affixed to the sheet generator. As a result of surface tension forces, the sheet has a triangular shape and is collected into a simply designed collector positioned at the apex of the triangle. The specific power for the liquid sheet is virtually the same as the droplet sheet specific power.

Chubb, Donald L. (inventor)

1990-01-01

231

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

232

SILO Proposal Cover Sheet  

E-print Network

SILO Proposal Cover Sheet Student ID# ______________ Funding Cycle: October 15 (for Spring semester items such as travel, lodging, supplies, and printing. Attach an additional sheet as needed. Proposer

Gering, Jon C.

233

Planning Sheet NAME ____________________________ _______________________ ___________________  

E-print Network

Planning Sheet NAME ____________________________ _______________________ ___________________ Last to your advisor, then return the signed sheet to 600 Fairchild. Courses Completed in Freshman Year Towards

Tong, Liang

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.

Carter, T. A.; Yamada, M.; Ji, H.; Kulsrud, R. M.; Trintchouck, F.

2002-06-18

235

Wounding in lizards results in the release of beta-defensins at the wound site and formation of an antimicrobial barrier.  

PubMed

After tail loss in lizards no infections occur indicating the presence of an effective anti-microbial barrier in the exposed tissues of the tail stump. Previous molecular studies on the lizard Anolis carolinensis have identified some beta-defensin-like genes and the deduced peptides that may be involved in anti-infective protection. The present study has analyzed the tissues of wounded and normal tails in lizards in order to immune-localize one of the beta-defensins previously found (AcBD15) and to detect variation in its gene expression during wounding. No immunoreactivity for this beta-defensin is present in normal tissues or in the epidermis of lizards, except for some sparse granulocytes. The latter are seen during the first 1-6 days after tail amputation and AcBD15 immunoreactivity is present in their granules. Degenerating granulocytes are incorporated, together with dead erythrocytes, platelets and keratinocytes into the scab. Real time RT-PCR and western blotting analysis indicates up-regulation of AcBD15 expression during wounding with respect to normal tissues, indicating that production, storage and release of this beta-defensin from granulocytes are active following wounding. The production of beta-defensins from granulocytes would allow protection of exposed tissues from microbial invasion avoiding a persistent inflammation, a process that leads to tissue regeneration. PMID:22001772

Alibardi, Lorenzo; Celeghin, Andrea; Dalla Valle, Luisa

2012-03-01

236

Formation in Rhizobium and Agrobacterium spp. of a 235-kilodalton protein intermediate in beta-D(1-2) glucan synthesis.  

PubMed

beta-D(1-2) Glucan was synthesized by Agrobacterium and Rhizobium spp. in vitro with enzymes from the internal membranes upon the addition of UDF glucose and Mg2+ or Mn2+. An intermediate containing protein and beta-D(1-2) glucan was formed during the reaction. It could be precipitated with trichloroacetic acid or separated by polyacrylamide gel electrophoresis under denaturing conditions. After detection with Coomassie blue or a radioactive substrate, the intermediate appeared as a 235-kilodalton protein. The radioactivity could be chased with a nonradioactive substrate. All strains that formed beta-D(1-2) glucan in vitro formed the 235-kilodalton protein, whereas avirulent, beta-D(1-2) glucan-negative mutants did not synthesize it. Transposon insertions in the chvB locus of strains ME2 and ME116 did not alter the virulence of the strains. These strains were able to form beta-D(1-2) glucan in vitro and synthesize the 235-kilodalton protein. PMID:3745125

Zorreguieta, A; Ugalde, R A

1986-09-01

237

Biosynthesis of the sesquiterpene botrydial in Botrytis cinerea. Mechanism and stereochemistry of the enzymatic formation of presilphiperfolan-8beta-ol.  

PubMed

Presilphiperfolan-8beta-ol synthase, encoded by the BcBOT2 gene from the necrotrophic plant pathogen Botrytis cinerea, catalyzes the multistep cyclization of farnesyl diphosphate (2) to the tricyclic sesquiterpene alcohol presilphiperfolan-8beta-ol (3), the preursor of the phytotoxin botrydial, a strain-dependent fungal virulence factor. Incubation of (1R)-[1-(2)H]farnesyl diphosphate (2b) with recombinant presilphiperfolan-8beta-ol synthase gave exclusively (5R)-[5alpha-(2)H]-3b, while complementary incubation of (1S)-[1-(2)H]FPP (2c) gave (5S)-[5beta-(2)H]-3c. These results established that cyclization of farnesyl diphosphate involves displacement of the diphosphate group from C-1 with net inversion of configuration and ruled out the proposed intermediacy of the cisoid conformer of nerolidyl diphosphate (9) in the cyclization. While not a mandatory intermediate, (3R)-nerolidyl diphosphate was shown to act as a substrate surrogate. Cyclization of [13,13,13-(2)H(3)] farnesyl diphosphate (2d) gave [14,14,14-(2)H(3)]-3d, thereby establishing that electrophilic attack takes place exclusively on the si face of the 12,13-double bond of 2. The combined results provide a detailed picture of the conformation of enzyme-bound farnesyl diphosphate at the active site of presilphiperfolan-8beta-ol synthase. PMID:19476353

Wang, Chieh-Mei; Hopson, Russell; Lin, Xin; Cane, David E

2009-06-24

238

MESSENGER and Venus Express Observations of the Near-tail of Venus: Magnetic Flux Transport, Current Sheet Structure, and Flux Rope Formation  

NASA Technical Reports Server (NTRS)

At 23:08 UT on 5 June 2007 the MESSENGER spacecraft reached its closest approach altitude (338 km) during its second flyby of Venus en route to its 2011 orbit insertion at Mercury. Whereas no measurements were collected during MESSENGER'S first Venus flyby in October 2006, the Magnetometer (MAG) and the Energetic Particle and Plasma Spectrometer (EPPS) operated successfully throughout this second encounter. Venus provides the solar system's best example to date of a solar wind - ionosphere planetary interaction. We present MESSENGER observations of the near-tail of Venus with emphasis on determining the time scales for magnetic flux transport, the structure of the cross-tail current sheet at very low altitudes (approx. 300 to 1000 km), and the nature and origin of a magnetic flux rope observed in the current sheet. The availability of the simultaneous Venus Express upstream measurements provides a unique opportunity to examine the influence of solar wind plasma and interplanetary magnetic field conditions on this planet's solar wind interaction at solar minimum.

Slavin, James A.; Boardsen, S. A.; Sarantos, M.; Acuna, M. H.; Anderson, B. J.; Barabash, S.; Benna, M.; Fraenz, M.; Gloeckler, G.; Gold, R. E.; Ho, G. C.; Korth, H.; Krimigis, S. M.; McNutt, R. L., Jr.; Raines, J. M.; Solomon, S. C.; Zhang, T.-L.; Zurbuchen, T. H.

2008-01-01

239

The magnetohydrodynamics of current sheets  

NASA Technical Reports Server (NTRS)

Examples of current sheets are summarized and their formation is described. A universal phenomenon in cosmic plasmas is the creation of sheets off intense current near X-type neutral points (where the magnetic field vanishes). These sheets are important as sites where the magnetic-field energy is converted efficiently into heat and bulk kinetic energy and where particles can be accelerated to high energies. Examples include disruptions in laboratory tokamaks, substorms in the earth's magnetosphere, and flares on the sun. The basic behavior of a one-dimensional sheet is presented, together with an account of the linear tearing-mode instability that can cause the field lines in such a sheet to reconnect. Such reconnection may develop in different ways: it may arise from a spontaneous instability or it may be driven, either from outside by motions or locally by a resistivity enhancement. Various processes are described that may occur during the nonlinear development of tearing, along with the many numerical and laboratory experiments that are aiding our understanding of this intriguing cosmical process.

Priest, E. R.

1985-01-01

240

Gender-related effects of 17-{beta}-estradiol and B-hexachlorocyclohexane on liver tumor formation in medaka (Oryzias latipes)  

SciTech Connect

When medaka were acutely exposed to diethylnitrosamine (DEN), greater incidence of hepatocarcinoma was seen in female versus male fish. This is possibly related to elevated female endogenous estrogens, which increase liver weight and production of vitellogenin. To examine roles of estrogens in tumor modulation, 21-day old medaka were exposed to DEN (200 ppm for 24 hr.), then fed purified diets containing the estrogenic compound {beta}-hexachlorocyclohexane ({beta}-HCH) or 17-{beta}estradiol (E2) for 6 months. Incidences of basophilic preneoplastic foci of cellular alteration in females receiving DEN and 0.01, 0.1, or 1.0 ppm E2 were three times the incidences in similarly-treated males. Also, incidences of basophilic foci in DEN + 0.1 ppm E2 males were significantly increased over DEN-only males and were equal to incidences in DEN-only females. Liver weights and hepatosomatic indices of males given 0.1 ppm E2 were not significantly different than females fed control diet. Females fed 0.01-10.0 ppm {beta}-HCH after DEN had 4--5 times greater incidences of basophilic foci as males. Gender-related effects on kinetics of growth rates and volumes of foci are being examined.

Cooke, J.B.; Hinton, D.E. [Univ. of California, Davis, CA (United States)

1994-12-31

241

Restoration of epithelial cell polarity in a colorectal cancer cell line by suppression of beta-catenin/T-cell factor 4-mediated gene transactivation.  

PubMed

Beta-catenin acts as a transcriptional coactivator by forming a complex with T-cell factor/lymphoid enhancer factor (TCF/LEF) DNA-binding proteins. Aberrant transactivation of a certain set of target genes by beta-catenin and TCF4 complexes has been implicated in familial and sporadic colorectal tumorigenesis. A colorectal cancer cell line, DLD-1, becomes irregularly multilayered, when maintained confluent for 2-3 weeks, and forms numerous dome-like polypoid foci piled-up over the surface of cell sheets. By the use of a strict tetracycline-regulation system, we found that the continuous suppression of beta-catenin/TCF4-mediated gene transactivation by dominant-negative TCF4B (deltaN30) reduced these piled-up foci and restored a simple monolayer of polarized columnar cells resembling normal intestinal epithelium. The restoration of epithelial cell polarity was evident in two ways: (a) the formation of microvilli over the apical surface; and (b) the distribution of a tight junction protein, ZO-1, to the lateral plasma membrane. Retroviral expression of stabilized beta-catenin (deltaN89) induced the formation of similar piled-up foci in untransformed IEC6 intestinal epithelial cells. Sulindac, a nonsteroidal antiinflammatory drug effective against colorectal tumorigenesis in familial adenomatous polyposis syndrome, suppressed the formation of foci. The loss of epithelial cell polarity may be a critical cellular event driving beta-catenin/TCF4-mediated intestinal tumorigenesis. PMID:11289158

Naishiro, Y; Yamada, T; Takaoka, A S; Hayashi, R; Hasegawa, F; Imai, K; Hirohashi, S

2001-03-15

242

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

243

Peptide LSARLAF activates alpha(IIb)beta3 on resting platelets and causes resting platelet aggregate formation without platelet shape change.  

PubMed

Adhesion of resting platelets to fibrinogen was enhanced by a peptide which was designed to bind near the presumptive fibrinogen gamma-chain binding site of the alpha subunit of the integrin alpha(IIb)beta3. This peptide, but not a scrambled control peptide, induced adhesion of resting platelets to fibronectin, vitronectin, von Willebrand factor, and monovalent (lacks one functional gamma-chain) fibrinogen. Resting platelets not treated with the agonist peptide did not adhere to these ligands. Agonist peptide induced adhesion of resting platelets to Fg was not secretion dependent and was inhibited by the monoclonal antibody 7E3. The agonist peptide caused aggregation of resting platelets on resting platelets adherent to immobilized Fg without causing platelet shape change. Therefore, the agonist peptide may activate alpha(IIb)beta3 by directly inducing a conformation change in the receptor on resting platelets. PMID:9610758

Derrick, J M; Loudon, R G; Gartner, T K

1998-01-01

244

Formation of gamma(sup prime)-Ni3Al via the Peritectoid Reaction: gamma + beta (+ Al2O3)=gamma(sup prime)(+ Al2O3)  

NASA Technical Reports Server (NTRS)

The activities of Al and Ni were measured using multi-cell Knudsen effusion-cell mass spectrometry (multi-cell KEMS), over the composition range 8-32 at.%Al and temperature range T=1400-1750 K in the Ni-Al-O system. These measurements establish that equilibrium solidification of gamma(sup prime)-Ni3Al-containing alloys occurs by the eutectic reaction, L (+ Al2O3)=gamma + Beta(+ Al2O3), at 1640 +/- 1 K and a liquid composition of 24.8 +/- 0.2 at.%al (at an unknown oxygen content). The {gamma + Beta (+Al2O3} phase field is stable over the temperature range 1633-1640 K, and gamma(sup prime)-Ni3Al forms via the peritectoid, gamma + Beta (+ Al2O3)=gamma(sup prime) (+ Al2O3), at 1633 +/- 1 K. This behavior is consistent with the current Ni-Al phase diagram and a new diagram is proposed. This new Ni-Al phase diagram explains a number of unusual steady-state solidification structures reported previously and provides a much simpler reaction scheme in the vicinity of the gamma(sup prime)-Ni2Al phase field.

Copeland, Evan

2008-01-01

245

Formation of gamma'-Ni3Al via the Peritectoid Reaction: gamma plus beta (+Al2O3) equals gamma'(+Al2O3)  

NASA Technical Reports Server (NTRS)

The activities of Al and Ni were measured using multi-cell Knudsen effusion-cell mass spectrometry (multi-cell KEMS), over the composition range 8 - 32 at.%Al and temperature range T = 1400 - 1750 K in the Ni-Al-O system. These measurements establish that equilibrium solidification of gamma'-Ni3Al-containing alloys occurs by the eutectic reaction, L (+ Al2O3) = gamma + beta (+ Al2O3), at 1640 plus or minus 1 K and a liquid composition of 24.8 plus or minus 0.2 at.%Al (at an unknown oxygen content). The {gamma + beta + Al2O3} phase field is stable over the temperature range 1633 - 1640 K, and gamma'-Ni3Al forms via the peritectiod, gamma + beta (+ Al2O3) = gamma'(+ Al2O3), at 1633 plus or minus 1 K. This behavior is inconsistent with the current Ni-Al phase diagram and a new diagram is proposed. This new Ni-Al phase diagram explains a number of unusual steady state solidification structures reported previously and provides a much simpler reaction scheme in the vicinity of the gamma'-Ni3Al phase field.

Copland, Evan

2008-01-01

246

Protein purification with novel porous sheets containing derivatized cellulose.  

PubMed

Novel porous sheets containing commercially available cellulosic ion exchange media of several different functionalities in a PVC matrix have been prepared and evaluated. The advantages of these materials are resistance to alkali, clean in place procedures and low nonspecific binding. These sheets thus provide well-known and well-characterized particulate chromatographic media in a porous sheet format. The porous sheet format permits use of short, squat geometries (stacked sheets) as well as tolerance of high pressure gradients. The net result is the ability to handle much higher flow rates (10-fold or greater) than achievable by comparable cellulosic packed columns of the neat particulate media. Chromatographic separation of natural egg white proteins by a linear salt gradient on a single sheet of 1.3-mm thickness was demonstrated. In addition, a very significant advantage of the porous sheet format is that it permits the fabrication of devices which are not possible with particulate media. An example of such a device is the Acti-Mod Spiral Module. In the spiral module a spiral flow channel is formed by wrapping the porous sheet material around a mandrel. Embossed ribbing in the porous sheet provides channel spacing. The small open channel accommodates high flow rates of biological suspensions while the porous sheet walls selectively remove components of the suspension. PMID:7763697

Manganaro, J L; Goldberg, B S

1993-01-01

247

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

248

Beta measurements  

NASA Technical Reports Server (NTRS)

The second year's results of the BETA project research are presented. The program is divided into two areas, aerosol modification and climatology in the trade wind region and the climatology of BETA (CO2) on remote mountain top locations. Limited data is available on the aerosol climatology of the marine free troposphere (MFT) in the trade wind region. In order to study the effects of cumulus convection on the MFT values of BETA, a cloud model was developed to simulate the evolution of a typical Pacific trade wind cumulus cloud. The stages involved in this development are outlined. The assembly of the major optical components of the lidar was made. Tests were run of the spectral bandwidth of the Synrad laser when a portion of the beam is mixed with a component which has traveled 450 meters corresponding to a delay of 1.5 microsecs. The bandwidth of the beat signal was measured to be 3 KHz. The data processing system based on a parallel processing filter bank analyzer using true time squaring detectors at each filter was completed.

Schotland, R. M.; Warren, A. J.; Funariu, O. M.

1991-01-01

249

Effect of Strand Symmetry on the Nanostructure and Material Properties in Beta-Hairpin Peptide Hydrogels  

NASA Astrophysics Data System (ADS)

Hydrogels have been established as promising biomaterials for applications such as scaffolds for tissue engineering, controlled drug delivery and cell encapsulation. De novo designed beta hairpin peptides, capable of undergoing self assembly and hydrogel formation, were investigated that contain asymmetric beta strand arms surrounding a turn sequence. The stimuli responsive self assembly of the hydrogels occurs via an intramolecular folding and strand interdigitation mechanism. CD and FTIR indicate a beta sheet secondary structure. WAXS shows a fibril structure reminiscent of the cross beta spine. SANS has been employed to globally quantify the local structure as being rod-like. Modification of the strand registry results in fibrils with non-twisting, laminated vs. twisted nanostructure. Fibril dimensions as measured by TEM and AFM corroborate the interdigitated assembly. Bulk material properties of these hydrogels studied using oscillatory rheology vary significantly for the different morphologies. Differences in the peptide registry that drive hydrogel nanostructure and the consequent material properties can be potentially utilized for usage in specific biomaterial applications.

Hule, Rohan; Pochan, Darrin; Nagarkar, Radhika; Schneider, Joel

2007-03-01

250

Cosuppression of the alpha subunits of beta-conglycinin in transgenic soybean seeds induces the formation of endoplasmic reticulum-derived protein bodies.  

PubMed

The expression of the alpha and alpha' subunits of beta-conglycinin was suppressed by sequence-mediated gene silencing in transgenic soybean seed. The resulting seeds had similar total oil and protein content and ratio compared with the parent line. The decrease in beta-conglycinin protein was apparently compensated by an increased accumulation of glycinin. In addition, proglycinin, the precursor of glycinin, was detected as a prominent polypeptide band in the protein profile of the transgenic seed extract. Electron microscopic analysis and immunocytochemistry of maturing transgenic soybean seeds indicated that the process of storage protein accumulation was altered in the transgenic line. In normal soybeans, the storage proteins are deposited in pre-existing vacuoles by Golgi-derived vesicles. In contrast, in transgenic seed with reduced beta-conglycinin levels, endoplasmic reticulum (ER)-derived vesicles were observed that resembled precursor accumulating-vesicles of pumpkin seeds and the protein bodies accumulated by cereal seeds. Their ER-derived membrane of the novel vesicles did not contain the protein storage vacuole tonoplast-specific protein alpha-TIP, and the sequestered polypeptides did not contain complex glycans, indicating a preGolgi and nonvacuolar nature. Glycinin was identified as a major component of these novel protein bodies and its diversion from normal storage protein trafficking appears to be related to the proglycinin buildup in the transgenic seed. The stable accumulation of proteins in a protein body compartment instead of vacuolar accumulation of proteins may provide an alternative intracellular site to sequester proteins when soybeans are used as protein factories. PMID:11340189

Kinney, A J; Jung, R; Herman, E M

2001-05-01

251

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

252

Beta Blockers  

PubMed Central

Infantile hemangiomas are benign vascular tumors seen in 4.5 percent of neonates and infants. While most infantile hemangiomas can be managed with active nonintervention, a subset of patients will require more aggressive management. Here the authors review the use of beta-blockers in the treatment of infantile hemangiomas, including oral, topical, and multimodal treatment options. They discuss the latest data on propranolol, including criteria for patient selection, dosing recommendations, and appropriate monitoring for side effects and efficacy. Lastly, they review indications for topical timolol treatment and the potential benefits of concomitant laser therapy. PMID:25053982

Admani, Shehla; Feldstein, Stephanie; Gonzalez, Ernesto M.

2014-01-01

253

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

254

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

2011-03-01

255

Inhibition of the electrostatic interaction between beta-amyloid peptide and membranes prevents beta-amyloid-induced toxicity.  

PubMed

The accumulation of beta-amyloid peptides (Abeta) into senile plaques is one of the hallmarks of Alzheimer disease. Aggregated Abeta is toxic to cells in culture and this has been considered to be the cause of neurodegeneration that occurs in the Alzheimer disease brain. The discovery of compounds that prevent Abeta toxicity may lead to a better understanding of the processes involved and ultimately to possible therapeutic drugs. Low nanomolar concentrations of Abeta1-42 and the toxic fragment Abeta25-35 have been demonstrated to render cells more sensitive to subsequent insults as manifested by an increased sensitivity to formazan crystals following MTT (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide) reduction. Formation of the toxic beta-sheet conformation by Abeta peptides is increased by negatively charged membranes. Here we demonstrate that phloretin and exifone, dipolar compounds that decrease the effective negative charge of membranes, prevent association of Abeta1-40 and Abeta25-35 to negatively charged lipid vesicles and Abeta induced cell toxicity. These results suggest that Abeta toxicity is mediated through a nonspecific physicochemical interaction with cell membranes. PMID:9256496

Hertel, C; Terzi, E; Hauser, N; Jakob-Rotne, R; Seelig, J; Kemp, J A

1997-08-19

256

The Heck reaction for porphyrin functionalisation: synthesis of meso-alkenyl monoporphyrins and palladium-catalysed formation of unprecedented meso-beta ethene-linked diporphyrins.  

PubMed

Palladium-catalysed coupling of the vinyl derivatives methyl acrylate, styrene and acrylonitrile with 5-bromo-10,15,20-triphenylporphyrin (MTriPPBr; M = 2H, Ni, Zn) and 5,15-dibromo-10,20-bis(3,5-di-tert-butylphenyl)porphyrin (MDAPBr(2)) produced a series of mono- and disubstituted alkenylporphyrins, thus demonstrating the applicability of meso-haloporphyrins in Heck-type reactions. The same technique was also applied to meso-ethenylporphyrins and simple aryl halides, with mixed results. Only meso-vinyl nickel(ii) porphyrins showed any reactivity under our conditions. A mixture of 1,1- and 1,2-disubstitution across the alkene was observed for 5-vinyl-10,15,20-triphenylporphyrinatonickel(ii) (meso-vinylNiTriPP), whereas 5-vinyl-10,20-bis(3,5-di-t-butylphenyl)porphyrinatonickel(ii) (meso-vinylNiDAP) produced a mixture of meso-1,1-, meso-1,2- and, surprisingly, beta-1,2-disubstituted Heck products. Coupling meso-vinylNiDAP with MTriPPBr under similar Heck conditions led unexpectedly to transbeta-meso-NiDAP-ethene-MTriPP dyads, affording the first members of a new class of alkenyl-linked diporphyrins. A mechanism for the unusual meso to beta rearrangement is discussed. The electronic absorption spectra of the dyads have a red-shifted shoulder on the Soret (B) band, which is evidence of a moderate degree of electronic interaction between the porphyrins via the ethenyl bridge. PMID:16493475

Locos, Oliver B; Arnold, Dennis P

2006-03-01

257

Intersheet rearrangement of polypeptides during nucleation of -sheet aggregates  

Microsoft Academic Search

Many neurodegenerative diseases are characterized by the accumulation of amyloid fibers in the brain, which can occur when a protein misfolds into an extended -sheet conformation. The nucleation of these -sheet aggregates is of particular interest, not only because it is the rate-determining step toward fiber formation but also because early, soluble aggregate species may be the cytotoxic entities in

Sarah A. Petty; Sean M. Decatur

2005-01-01

258

Neutrinoless. beta beta. -decay in gauge theories  

SciTech Connect

The lepton violating neutrinoless ..beta beta..-decay is investigated in the context of fashionable gauge theories. Various mechanisms are examined e.g. light or heavy neutrinos, with or without right-handed currents, intermediate doubly charged Higgs Particles, majoron emission etc. Numerical results have been obtained for the transitions /sup 48/Ca ..-->.. /sup 8/Ti(..beta../sup -/..beta../sup -/) and /sup 58/Ni ..-->.. /sup 58/Fe (..beta../sup +/..beta../sup +/, electron capture, double electron capture) employing realistic nuclear models.

Vergados, J.D.

1983-01-01

259

Formability of type 304 stainless steel sheet  

SciTech Connect

Punch-stretch tests to determine formability of type 304 stainless steel sheet were conducted using a hemispherical dome test. Sheets of 19.1 mm width and 177.8 mm width were stretched on a 101.6 mm diameter punch at punch rates between 0.042 to 2.12 mm/s with three lubricant systems: a mineral seal oil, thin polytetrafluoroethelyne sheet with mineral seal oil, and silicone rubber with mineral seal oil. The resulting strain distributions were measured and the amount of martensite was determined by magnetic means. Increasing lubricity resulted in more uniform strain distributions while increased punch rates tended to decrease both strain and transformation distributions. High forming limit values were related to the formation of high and uniformly distributed martensite volume fractions during deformation. The results of this study are interpreted with an analysis of the effects of strain and temperature on strain induced martensite formation in metastable austenitic stainless steels.

Coubrough, G.J. [EG and G Rocky Flats, Inc., Golden, CO (United States). Rocky Flats Plant; Matlock, D.K.; VanTyne, C.J. [Colorado School of Mines, Golden, CO (United States)

1992-09-01

260

In silico and in vitro studies to elucidate the role of Cu2+ and galanthamine as the limiting step in the amyloid beta (1–42) fibrillation process  

PubMed Central

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, Cu2+ 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 Cu2+ 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 Cu2+ or galanthamine demonstrated that both ligands prevent the formation of the salt bridge by either binding to Glu 22 and Asp 23 (Cu2+) 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 Cu2+ 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

2013-01-01

261

Laboratory Investigations of Current Sheets at the Electron Skin Depth Scale  

Microsoft Academic Search

Laboratory Investigations of Current Sheets at the Electron Skin Depth Scale. Theoretical investigations, in situ spacecraft and rocket missions, and laboratory studies form an essential triad for understanding the variety of current sheet phenomena found in space plasmas. In the Large Plasma Device (LAPD) at UCLA, the formation dynamics, equilibrium state, and wave-mediated disruptions of current sheets can be studied

S. Vincena; W. Gekelman

2005-01-01

262

Graphene sheets fabricated from disposable paper cups as a catalyst support material for fuel cells  

E-print Network

Graphene sheets fabricated from disposable paper cups as a catalyst support material for fuel cells Hong Zhao and T. S. Zhao* Disposable paper-cups are used for the formation of graphene sheets with Fe2+ as a catalyst. The proposed synthesis strategy not only enables graphene sheets to be produced in high yield

Zhao, Tianshou

263

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

264

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, M.E.; Clark, P.U.; Ricken, W.; Mitrovica, J.X.; Hostetler, S.W.; Kuhn, G.

2011-01-01

265

Student Data Sheet Crystal Experiment: _______________________________  

E-print Network

Student Data Sheet Name: Date: Crystal Experiment: _______________________________ Observations;Student Data Sheet Name: Date: Observations of Crystals Name of Crystal Observation Bismuth Pyrite in Matrix Pyrite Cube Ulexite #12;Iceland Spar (calcite) Quartz Fluorite #12;Student Data Sheet Name: Date

Pike, Robert D.

266

Cereal beta-glucans  

Technology Transfer Automated Retrieval System (TEKTRAN)

Cereal beta-glucans occur predominantly in oats and barley, but can be found in other cereals. Beta-glucan structure is a mixture of single beta-1,3-linkages and consecutive beta-1,4-linkages, and cellotriosyl and cellotetraosyl units typically make up 90-95% of entire molecule. Lichenase can hydr...

267

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

268

COED BASKETBALL Information Sheet  

E-print Network

COED BASKETBALL Information Sheet Fall 2013 This information sheet is intended to provide basic. Team rosters are limited to eighteen players. Each participant may play for only one Coed Basketball The participants must provide basketballs. A limited supply of basketballs is available in the locker rooms. A 28

Seamons, Kent E.

269

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.

Eleanor Ely

270

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. PMID:23674917

Khoshzaban, Ahad; Mehrzad, Shahram; Tavakoli, Vida; Keshel, Saeed Heidari; Behrouzi, Gholam Reza; Bashtar, Maryam

2011-01-01

271

State Climate Change Impacts Information Sheets  

NSDL National Science Digital Library

The Environmental Protection Agency's (EPA) Global Warming site (discussed in the February 21, 1997 Scout Report) has placed all 50 state-specific global warming sheets online in HTML and .pdf format. Browseable via a clickable map or alphabetically, the sheets summarize expected climate change in each state and explain the projected consequences on factors such as health, agriculture, water resources, ecosystems, forests, and coastal areas. Brief countrywide overviews of these factors are also available, as well as short discussions of climate change and fisheries, birds, and national parks. Additional resources include a bibliography, glossary, and internal search engine.

1997-01-01

272

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

273

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

274

Effects of mutations in the {beta} subunit hinge domain on ATP synthase F{sub 1} sector rotation: Interaction between Ser 174 and Ile 163  

SciTech Connect

A complex of {gamma}, {epsilon}, and c subunits rotates in ATP synthase (F{sub o}F{sub 1}) coupling with proton transport. Replacement of {beta}Ser174 by Phe in {beta}-sheet4 of the {beta} subunit ({beta}S174F) caused slow {gamma} subunit revolution of the F{sub 1} sector, consistent with the decreased ATPase activity [M. Nakanishi-Matsui, S. Kashiwagi, T. Ubukata, A. Iwamoto-Kihara, Y. Wada, M. Futai, Rotational catalysis of Escherichia coli ATP synthase F1 sector. Stochastic fluctuation and a key domain of the {beta} subunit, J. Biol. Chem. 282 (2007) 20698-20704]. Modeling of the domain including {beta}-sheet4 and {alpha}-helixB predicted that the mutant {beta}Phe174 residue undergoes strong and weak hydrophobic interactions with {beta}Ile163 and {beta}Ile166, respectively. Supporting this prediction, the replacement of {beta}Ile163 in {alpha}-helixB by Ala partially suppressed the {beta}S174F mutation: in the double mutant, the revolution speed and ATPase activity recovered to about half of the levels in the wild-type. Replacement of {beta}Ile166 by Ala lowered the revolution speed and ATPase activity to the same levels as in {beta}S174F. Consistent with the weak hydrophobic interaction, {beta}Ile166 to Ala mutation did not suppress {beta}S174F. Importance of the hinge domain [phosphate-binding loop (P-loop)/{alpha}-helixB/loop/{beta}-sheet4, {beta}Phe148-{beta}Gly186] as to driving rotational catalysis is discussed.

Kashiwagi, Sachiko [Department of Biochemistry, Faculty of Pharmaceutical Sciences, Iwate Medical University, Iwate 028-3694 (Japan); Futai Special Laboratory, Microbial Chemistry Research Center, Shinagawa-ku, Tokyo 141-002 (Japan); Iwamoto-Kihara, Atsuko [Department of Bioscience, Nagahama Institute of Bioscience and Technology, Nagahama, Shiga 526-0829 (Japan); Kojima, Masaki; Nonaka, Takamasa [Department of Biochemistry, Faculty of Pharmaceutical Sciences, Iwate Medical University, Iwate 028-3694 (Japan); Futai, Masamitsu [Department of Biochemistry, Faculty of Pharmaceutical Sciences, Iwate Medical University, Iwate 028-3694 (Japan); Futai Special Laboratory, Microbial Chemistry Research Center, Shinagawa-ku, Tokyo 141-002 (Japan)], E-mail: futaim@iwate-med.ac.jp; Nakanishi-Matsui, Mayumi [Department of Biochemistry, Faculty of Pharmaceutical Sciences, Iwate Medical University, Iwate 028-3694 (Japan); Futai Special Laboratory, Microbial Chemistry Research Center, Shinagawa-ku, Tokyo 141-002 (Japan)

2008-01-11

275

Mechanism of inactivation of alanine racemase by beta, beta, beta-trifluoroalanine  

SciTech Connect

The alanine racemases are a group of PLP-dependent bacterial enzymes that catalyze the racemization of alanine, providing D-alanine for cell wall synthesis. Inactivation of the alanine racemases from the Gram-negative organism Salmonella typhimurium and Gram-positive organism Bacillus stearothermophilus with beta, beta, beta-trifluoroalanine has been studied. The inactivation occurs with the same rate constant as that for formation of a broad 460-490-nm chromophore. Loss of two fluoride ions per mole of inactivated enzyme and retention of (1-/sup 14/C)trifluoroalanine label accompany inhibition, suggesting a monofluoro enzyme adduct. Partial denaturation (1 M guanidine) leads to rapid return of the initial 420-nm chromophore, followed by a slower (t1/2 approximately 30 min-1 h) loss of the fluoride ion and /sup 14/CO/sub 2/ release. At this point, reduction by NaB/sub 3/H/sub 4/ and tryptic digestion yield a single radiolabeled peptide. Purification and sequencing of the peptide reveals that lysine-38 is covalently attached to the PLP cofactor. A mechanism for enzyme inactivation by trifluoroalanine is proposed and contrasted with earlier results on monohaloalanines, in which nucleophilic attack of released aminoacrylate on the PLP aldimine leads to enzyme inactivation. For trifluoroalanine inactivation, nucleophilic attack of lysine-38 on the electrophilic beta-difluoro-alpha, beta-unsaturated imine provides an alternative mode of inhibition for these enzymes.

Faraci, W.S.; Walsh, C.T.

1989-01-24

276

The ripple's enhancement in graphene sheets by spark plasma sintering  

NASA Astrophysics Data System (ADS)

This paper introduces a simple and effective process of directly enhancing the ripple formation of graphene sheets by using spark plasma sintering (SPS) system. The morphology, microstructure and surface property of the pristine and SPS treated graphene sheets were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and contact angle meter. The results reveal that: 1) A large amount of ripples can be induced in graphene sheets after SPS treatment at 1300 °C, and the pristine graphene surfaces change from smoothness into roughness with the patterns; 2) There are three kinds of graphene ripples with different structures after SPS treatment; (3) After the formation of ripples, the SPS-treated graphene sheets become hydrophobicity. In addition, the formation mechanism of the graphene ripples was also discussed in this paper.

Cao, Bing; Yu, Guannan; Pan, Chunxu

2011-09-01

277

Divergent effects of 17-{beta}-estradiol on human vascular smooth muscle and endothelial cell function diminishes TNF-{alpha}-induced neointima formation  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer TNF-{alpha} augments neointimal hyperplasia in human saphenous vein. Black-Right-Pointing-Pointer TNF-{alpha} induces detrimental effects on endothelial and smooth muscle cell function. Black-Right-Pointing-Pointer Estradiol exerts modulatory effects on TNF-induced vascular cell functions. Black-Right-Pointing-Pointer The modulatory effects of estradiol are discriminatory and cell-type specific. -- Abstract: Coronary heart disease (CHD) is a condition characterized by increased levels of proinflammatory cytokines, including tumor necrosis factor-{alpha} (TNF-{alpha}). TNF-{alpha} can induce vascular endothelial cell (EC) and smooth muscle cell (SMC) dysfunction, central events in development of neointimal lesions. The reduced incidence of CHD in young women is believed to be due to the protective effects of estradiol (E2). We therefore investigated the effects of TNF-{alpha} on human neointima formation and SMC/EC functions and any modulatory effects of E2. Saphenous vein (SV) segments were cultured in the presence of TNF-{alpha} (10 ng/ml), E2 (2.5 nM) or both in combination. Neointimal thickening was augmented by incubation with TNF-{alpha}, an effect that was abolished by co-culture with E2. TNF-{alpha} increased SV-SMC proliferation in a concentration-dependent manner that was optimal at 10 ng/ml (1.5-fold increase), and abolished by E2 at all concentrations studied (1-50 nM). Surprisingly, E2 itself at low concentrations (1 and 5 nM) stimulated SV-SMC proliferation to a level comparable to that of TNF-{alpha} alone. SV-EC migration was significantly impaired by TNF-{alpha} (42% of control), and co-culture with E2 partially restored the ability of SV-EC to migrate and repair the wound. In contrast, TNF-{alpha} increased SV-SMC migration by 1.7-fold, an effect that was completely reversed by co-incubation with E2. Finally, TNF-{alpha} potently induced ICAM-1 and VCAM-1 expression in both SV-EC and SV-SMC. However there was no modulation by E2 in either cell-type. In conclusion, TNF-{alpha} induced SV neointima formation, increased SMC proliferation and migration, impaired SV-EC migration and increased expression of adhesion molecules. E2 exerted distinct cell-type and function-specific modulation, the mechanisms underlying which are worthy of further detailed study.

Nintasen, Rungrat [Division of Cardiovascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT (United Kingdom) [Division of Cardiovascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT (United Kingdom); Multidisciplinary Cardiovascular Research Center (MCRC), University of Leeds, Leeds LS2 9JT (United Kingdom); Department of Tropical Pathology, Faculty of Tropical Medicine, Mahidol University (Thailand); Riches, Kirsten; Mughal, Romana S. [Division of Cardiovascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT (United Kingdom) [Division of Cardiovascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT (United Kingdom); Multidisciplinary Cardiovascular Research Center (MCRC), University of Leeds, Leeds LS2 9JT (United Kingdom); Viriyavejakul, Parnpen; Chaisri, Urai; Maneerat, Yaowapa [Department of Tropical Pathology, Faculty of Tropical Medicine, Mahidol University (Thailand)] [Department of Tropical Pathology, Faculty of Tropical Medicine, Mahidol University (Thailand); Turner, Neil A. [Division of Cardiovascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT (United Kingdom) [Division of Cardiovascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT (United Kingdom); Multidisciplinary Cardiovascular Research Center (MCRC), University of Leeds, Leeds LS2 9JT (United Kingdom); Porter, Karen E., E-mail: medkep@leeds.ac.uk [Division of Cardiovascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT (United Kingdom); Multidisciplinary Cardiovascular Research Center (MCRC), University of Leeds, Leeds LS2 9JT (United Kingdom)

2012-04-20

278

Ferulic acid destabilizes preformed {beta}-amyloid fibrils in vitro  

SciTech Connect

Inhibition of the formation of {beta}-amyloid fibrils (fA{beta}), as well as the destabilization of preformed fA{beta} in the CNS, would be attractive therapeutic targets for the treatment of Alzheimer's disease (AD). We reported previously that curcumin (Cur) inhibits fA{beta} formation from A{beta} and destabilizes preformed fA{beta} in vitro. Using fluorescence spectroscopic analysis with thioflavin T and electron microscopic studies, we examined the effects of ferulic acid (FA) on the formation, extension, and destabilization of fA{beta} at pH 7.5 at 37 deg C in vitro. We next compared the anti-amyloidogenic activities of FA with Cur, rifampicin, and tetracycline. Ferulic acid dose-dependently inhibited fA{beta} formation from amyloid {beta}-peptide, as well as their extension. Moreover, it destabilized preformed fA{beta}s. The overall activity of the molecules examined was in the order of: Cur > FA > rifampicin = tetracycline. FA could be a key molecule for the development of therapeutics for AD.

Ono, Kenjiro [Department of Neurology and Neurobiology of Aging, Kanazawa University Graduate School of Medical Science, Kanazawa 920-8640 (Japan); Hirohata, Mie [Department of Neurology and Neurobiology of Aging, Kanazawa University Graduate School of Medical Science, Kanazawa 920-8640 (Japan); Yamada, Masahito [Department of Neurology and Neurobiology of Aging, Kanazawa University Graduate School of Medical Science, Kanazawa 920-8640 (Japan)]. E-mail: m-yamada@med.kanazawa-u.ac.jp

2005-10-21

279

Hypertrophic scar model in the rabbit ear: a reproducible model for studying scar tissue behavior with new observations on silicone gel sheeting for scar reduction.  

PubMed

Hypertrophic scarring poses a clinically relevant problem as it can be cosmetically disfiguring and functionally debilitating. A lack of animal models has hindered an understanding of the pathogenesis and development of new treatment strategies therefore has largely been empiric. Our group has developed a unique hypertrophic scar (HS) model in the rabbit ear. The model has been reproducible, quantifiable, and measurable over a time period of 1 month. We describe the development as well as the reliability and responsiveness of this model to different therapeutic agents, such as TGF-beta blockade, silicone occlusion, and application of collagen-synthesis inhibitors. Moreover, it has given insights into the mechanism of action of silicone sheeting occlusive treatment and ultimately suggests that the epidermis plays a critical role in the development of HS. Additionally, we will present new data supporting the importance of the epidermis and further clarify the mechanism of action of silicone sheeting. When a semi-occlusive polyurethane film was left in place for an additional time period, scar formation was reduced. HSs of this model covered with silicone sheets and five layers of Tegaderm showed a significant scar reduction by 80% compared with wounds with only one layer of Tegaderm. The HS model in the rabbit ear is a highly reliable, responsive, and practical model for studying scar tissue behavior. Furthermore, our data suggest that the degree and the duration of occlusion are most important for reducing scar tissue formation. PMID:17727466

Kloeters, Oliver; Tandara, Andrea; Mustoe, Thomas A

2007-01-01

280

Microcomponent sheet architecture  

DOEpatents

The invention is a microcomponent sheet architecture wherein macroscale unit processes are performed by microscale components. The sheet architecture may be a single laminate with a plurality of separate microcomponent sections or the sheet architecture may be a plurality of laminates with one or more microcomponent sections on each laminate. Each microcomponent or plurality of like microcomponents perform at least one unit operation. A first laminate having a plurality of like first microcomponents is combined with at least a second laminate having a plurality of like second microcomponents thereby combining at least two unit operations to achieve a system operation.

Wegeng, Robert S. (Richland, WA); Drost, M. Kevin (Richland, WA); McDonald, Carolyn E. (Richland, WA)

1997-01-01

281

Microcomponent sheet architecture  

DOEpatents

The invention is a microcomponent sheet architecture wherein macroscale unit processes are performed by microscale components. The sheet architecture may be a single laminate with a plurality of separate microcomponent sections or the sheet architecture may be a plurality of laminates with one or more microcomponent sections on each laminate. Each microcomponent or plurality of like microcomponents perform at least one unit operation. A first laminate having a plurality of like first microcomponents is combined with at least a second laminate having a plurality of like second microcomponents thereby combining at least two unit operations to achieve a system operation. 14 figs.

Wegeng, R.S.; Drost, M.K..; McDonald, C.E.

1997-03-18

282

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’). PMID:18515070

Gordon, Larry M.; Nisthal, Alex; Lee, Andy B.; Eskandari, Sepehr; Ruchala, Piotr; Jung, Chun-Ling; Waring, Alan J.; Mobley, Patrick W.

2008-01-01

283

Low-Temperature Forming of Beta Titanium Alloys  

NASA Technical Reports Server (NTRS)

Low cost methods for titanium structural fabrication using advanced cold-formable beta alloys were investigated for application in a Mach 2.7 supersonic cruise vehicle. This work focuses on improving processing and structural efficiencies as compared with standard hot formed and riveted construction of alpha-beta alloy sheet structure. Mechanical property data and manufacturing parameters were developed for cold forming, brazing, welding, and processing Ti-15V-3Cr-3Sn-3Al sheet, and Ti-3Al-8V-6Cr-4Zr on a more limited basis. Cost and structural benefits were assessed through the fabrication and evaluation of large structural panels. The feasibility of increasing structural efficiency of beta titanium structure by selective reinforcement with metal matrix composite was also explored.

Kaneko, R. S.; Woods, C. A.

1983-01-01

284

Spectroscopic investigations of synthetic beta amyloid peptides of Alzheimer's disease  

NASA Astrophysics Data System (ADS)

The chemical mechanism of binding between Congo red dye and amyloid proteins was investigated using infrared spectroscopy. Synthetic amyloid corresponding to the amino-acid residues 1 to 28 of Alzheimer's beta amyloid and insulin fibers prepared with the Burke and Rougvie method were used as substrates. Both peptides clearly demonstrate beta-pleated sheet conformations. The analysis shows that Congo red binds to amyloid proteins via interactions between the two negatively-charged sulfonic acid groups of Congo red and two positively charged amino acid residues of amyloid protein molecules. Evidence leads to the conclusion that the beta-pleated sheet conformation of the protein aids in orienting the dye molecules, thus favoring stabilisation and bonding.

Elhaddaoui, A.; Pigorsch, E.; Delacourte, A.; Turrell, S.

1995-03-01

285

Singular Solutions and Pattern Formation in Aggregation Equations  

E-print Network

singularity formation in vortex-sheet motion by a spectrallypreviously, the motion of the vortex sheet is governed byvortex patches in incompressible inviscid fluids and swarm patches, which both exhibit rotational motion

Sun, Hui

2013-01-01

286

Monolithic graphene oxide sheets with controllable composition.  

PubMed

Graphene oxide potentially has multiple applications and is typically prepared by solution-based chemical means. To date, the synthesis of a monolithic form of graphene oxide that is crucial to the precision assembly of graphene-based devices has not been achieved. Here we report the physical approach to produce monolithic graphene oxide sheets on copper foil using solid carbon, with tunable oxygen-to-carbon composition. Experimental and theoretical studies show that the copper foil provides an effective pathway for carbon diffusion, trapping the oxygen species dissolved in copper and enabling the formation of monolithic graphene oxide sheets. Unlike chemically derived graphene oxide, the as-synthesized graphene oxide sheets are electrically active, and the oxygen-to-carbon composition can be tuned during the synthesis process. As a result, the resulting graphene oxide sheets exhibit tunable bandgap energy and electronic properties. Our solution-free, physical approach may provide a path to a new class of monolithic, two-dimensional chemically modified carbon sheets. PMID:24577159

Chu, Jae Hwan; Kwak, Jinsung; Kim, Sung-Dae; Lee, Mi Jin; Kim, Jong Jin; Park, Soon-Dong; Choi, Jae-Kyung; Ryu, Gyeong Hee; Park, Kibog; Kim, Sung Youb; Kim, Ji Hyun; Lee, Zonghoon; Kim, Young-Woon; Kwon, Soon-Yong

2014-01-01

287

Rutin-induced beta-glucosidase activity in Streptococcus faecium VGH-1 and Streptococcus sp. strain FRP-17 isolated from human feces: formation of the mutagen, quercetin, from rutin.  

PubMed Central

A fecal isolate, Streptococcus sp. strain FRP-17, and strain VGH-1 of Streptococcus faecium were shown to contain beta-glucosidases which converted rutin (quercetin-3-O-beta-D-glucose-alpha-L-rhamnose) to quercetin and were active against o-nitrophenyl-beta-D-glucose. The activity against rutin could be measured by increased mutagenicity in the Ames assay or visualized on thin-layer chromatography plates. In both organisms, the beta-glucosidase activities were inducible by the addition of rutin to the growth media. Several closely related strains of Streptococcus spp. lacked any beta-glucosidase activity. In cell preparations of the active organisms, activities with rutin and o-nitrophenyl-beta-D-glucose were optimal at pH 6.8 and could be enhanced by increasing the ionic strength of the assay system. At low ionic strengths, both quercetin and a new product (intermediate between the polarities of rutin and quercetin) were formed by the incubation of rutin with cell preparations of either active organism. This product disappeared with increased ionic strength, suggesting that it may be a reaction intermediate, quercetin-3-O-beta-D-glucose. These results suggest that the beta-glucosidase active against rutin and that active against o-nitrophenyl-beta-D-glucose are the same. PMID:6424566

MacDonald, I A; Bussard, R G; Hutchison, D M; Holdeman, L V

1984-01-01

288

Viscous Sheet Retraction  

E-print Network

We present the results of a combined theoretical and numerical investigation of the rim-driven retraction of flat fluid sheets in both planar and circular geometries. Particular attention is given to the influence of the ...

Savva, Nikos

289

Sheet electron beam tester  

NASA Astrophysics Data System (ADS)

The DARPA HiFIVE project uses a pulsed electron sheet beam gun to power a traveling wave tube amplifier operating at 220 GHz. Presented is a method for characterizing the high current density 0.1 mm by 1 mm sheet electron beam. A tungsten tipped probe was scanned through the cross section of the sheet electron beam inside of a vacuum vessel. The probe was controlled with sub-micron precision using stepper motors and LabView computer control while boxcar averaging hardware sampled the pulsed beam. Matlab algorithms were used to interpret the data, calculate beam dimensions and current density, and create 2-dimensional cross section images. Full characterization of two separate HiFIVE sheet electron guns was accomplished and is also presented.

Spear, Alexander Grenbeaux

290

Monoatomically thin polarizable sheets  

E-print Network

We consider a flat lattice of dipoles modeled by harmonic oscillators interacting with the electromagnetic field in dipole approximation. Eliminating the variables from the coupled equations of motion, we come to effective Maxwell equations. These allow for taking the lattice spacing $a$ to zero. As a result, we obtain reflection coefficients for the scattering of electromagnetic waves off the sheet. These are a generalization of that known from the hydrodynamic model. For instance, we get a non trivial scattering for polarizability perpendicular to the sheet. Also we show that the case of a sheet polarizable parallel to the sheet can be obtained in a natural way from a plasma layer of finite thickness. As an alternative approach we discuss the elimination of the electromagnetic fields resulting in effective equations for the oscillators. These show, for $a\\to 0$, divergent behavior, resulting from the electrostatic interaction of the dipoles.

M. Bordag

2014-04-18

291

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

292

Fact Sheet HEALTH SCIENCE  

E-print Network

Fact Sheet HEALTH SCIENCE Highlights · Health Science is the multidisciplinary study of the factors that influence health across the life course to health for all. · Health Science majors learn in the classroom

Su, Xiao

293

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

294

Seat Belt Fact Sheet  

MedlinePLUS

Travel & Motor Vehicle Safety Seat Belt Fact Sheet Safety belts are the most effective means of reducing deaths and serious injuries ... than 90 people die every day in motor vehicle crashes When lap and shoulder belts are used ...

295

AgentSheets  

NSDL National Science Digital Library

From personal and information Agents to interactive demos, modifiable simulations to virtual game worlds, AgentSheets' unique user interface captivates people and draws them into a new relationship with technology.

Alex Reppening

296

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

297

Biodiesel Basics (Fact Sheet)  

SciTech Connect

This fact sheet provides a brief introduction to biodiesel, including a discussion of biodiesel blends, which blends are best for which vehicles, where to buy biodiesel, how biodiesel compares to diesel fuel in terms of performance, how biodiesel performs in cold weather, whether biodiesel use will plug vehicle filters, how long-term biodiesel use may affect engines, biodiesel fuel standards, and whether biodiesel burns cleaner than diesel fuel. The fact sheet also dismisses the use of vegetable oil as a motor fuel.

Not Available

2014-06-01

298

Domoic Acid Fact Sheet  

NSDL National Science Digital Library

This online fact sheet illustrates the transfer of domoic acid through the food web. Domoic acid is a nerve toxin produced by a naturally occurring Harmful Algal Bloom (HAB) usually (but not always) of the genus Pseudonitzchia. The sheet explains what to do if you find a sick or dead animal and includes contact information for injured/sick/entangled animal rescue networks in California.

Channel Islands National Marine Sanctuary

299

Simulating Thin Sheets: Buckling, Wrinkling, Folding and Growth  

NASA Astrophysics Data System (ADS)

Numerical simulations of thin sheets undergoing large deformations are computationally challenging. Depending on the scenario, they may spontaneously buckle, wrinkle, fold, or crumple. Nature's thin tissues often experience significant anisotropic growth, which can act as the driving force for such instabilities. We use a recently developed finite element model to simulate the rich variety of nonlinear responses of Kirchhoff-Love sheets. The model uses subdivision surface shape functions in order to guarantee convergence of the method, and to allow a finite element description of anisotropically growing sheets in the classical Rayleigh-Ritz formalism. We illustrate the great potential in this approach by simulating the inflation of airbags, the buckling of a stretched cylinder, as well as the formation and scaling of wrinkles at free boundaries of growing sheets. Finally, we compare the folding of spatially confined sheets subject to growth and shrinking confinement to find that the two processes are equivalent.

Vetter, Roman; Stoop, Norbert; Wittel, Falk K.; Herrmann, Hans J.

2014-03-01

300

Beta-carotene  

MedlinePLUS

... carotene is one of a group of red, orange, and yellow pigments called carotenoids. Beta-carotene and ... of beta-carotene can turn skin yellow or orange. There is growing concern that taking high doses ...

301

Gamma, Beta, Erf  

NSDL National Science Digital Library

This page includes the encyclopedia entries for gamma, beta and erf functions including factorials, binomials, gamma functions and inverses, differentiated gamma functions, beta functions and inverses, probability integrals and inverses, Frensnel integrals and exponential integrals.

302

Beta Thalassemia (For Parents)  

MedlinePLUS

Thalassemias Thalassemias are a group of blood disorders that affect the way the body makes hemoglobin, a ... results in that type of thalassemia. About Beta Thalassemia Beta thalassemia occurs when the gene that controls ...

303

Magnetic configurations of the tilted current sheets in magnetotail  

NASA Astrophysics Data System (ADS)

In this research, the geometrical structures of tilted current sheet and tail flapping waves have been analysed based on multiple spacecraft measurements and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1) The magnetic field lines (MFLs) in the tilted current sheet are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the equatorial plane, while the normal of the tilted current sheet leans severely to the dawn or dusk side. (2) The tilted current sheet may become very thin, the half thickness of its neutral sheet is generally much less than the minimum radius of the curvature of the MFLs. (3) In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4) In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1 RE, while the neutral sheet may be very thin, with its half thickness being several tenths of RE. During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45°. The phase velocities of these flapping waves are several tens km/s, while their periods and wavelengths are several tens of minutes, and several earth radii, respectively. These tail flapping events generally last several hours and occur during quiet periods or periods of weak magnetospheric activity.

Shen, C.; Rong, Z. J.; Li, X.; Dunlop, M.; Liu, Z. X.; Malova, H. V.; Lucek, E.; Carr, C.

2008-11-01

304

Sulfated polysaccharides promote the assembly of amyloid beta(1-42) peptide into stable fibrils of reduced cytotoxicity.  

PubMed

The histopathological hallmarks of Alzheimer disease are the self-aggregation of the amyloid beta peptide (Abeta) in extracellular amyloid fibrils and the formation of intraneuronal Tau filaments, but a convincing mechanism connecting both processes has yet to be provided. Here we show that the endogenous polysaccharide chondroitin sulfate B (CSB) promotes the formation of fibrillar structures of the 42-residue fragment, Abeta(1-42). Atomic force microscopy visualization, thioflavin T fluorescence, CD measurements, and cell viability assays indicate that CSB-induced fibrils are highly stable entities with abundant beta-sheet structure that have little toxicity for neuroblastoma cells. We propose a wedged cylinder model for Abeta(1-42) fibrils that is consistent with the majority of available data, it is an energetically favorable assembly that minimizes the exposure of hydrophobic areas, and it explains why fibrils do not grow in thickness. Fluorescence measurements of the effect of different Abeta(1-42) species on Ca(2+) homeostasis show that weakly structured nodular fibrils, but not CSB-induced smooth fibrils, trigger a rise in cytosolic Ca(2+) that depends on the presence of both extracellular and intracellular stocks. In vitro assays indicate that such transient, local Ca(2+) increases can have a direct effect in promoting the formation of Tau filaments similar to those isolated from Alzheimer disease brains. PMID:18819917

Bravo, Ramona; Arimon, Muriel; Valle-Delgado, Juan José; García, Raquel; Durany, Núria; Castel, Susanna; Cruz, Montserrat; Ventura, Salvador; Fernàndez-Busquets, Xavier

2008-11-21

305

Current status of solar cell performance of unconventional silicon sheets  

NASA Technical Reports Server (NTRS)

It is pointed out that activities in recent years directed towards reduction in the cost of silicon solar cells for terrestrial photovoltaic applications have resulted in impressive advancements in the area of silicon sheet formation from melt. The techniques used in the process of sheet formation can be divided into two general categories. All approaches in one category require subsequent ingot wavering. The various procedures of the second category produce silicon in sheet form. The performance of baseline solar cells is discussed. The baseline process included identification marking, slicing to size, and surface treatment (etch-polishing) when needed. Attention is also given to the performance of cells with process variations, and the effects of sheet quality on performance and processing.

Yoo, H. I.; Liu, J. K.

1981-01-01

306

Cross-talk between integrins {alpha}1{beta}1 and {alpha}2{beta}1 in renal epithelial cells  

SciTech Connect

The collagen-binding integrins {alpha}1{beta}1 and {alpha}2{beta}1 have profoundly different functions, yet they are often co-expressed in epithelial cells. When both integrins are expressed in the same cell, it has been suggested that {alpha}1{beta}1 negatively regulates integrin {alpha}2{beta}1-dependent functions. In this study we utilized murine ureteric bud (UB) epithelial cells, which express no functionally detectable levels of endogenous integrins {alpha}1{beta}1 and {alpha}2{beta}1, to determine the mechanism whereby this regulation occurs. We demonstrate that UB cells expressing integrin {alpha}2{beta}1, but not {alpha}1{beta}1 adhere, migrate and proliferate on collagen I as well as form cellular cords in 3D collagen I gels. Substitution of the transmembrane domain of the integrin {alpha}2 subunit with that of {alpha}1 results in decreased cell adhesion, migration and cord formation. In contrast, substitution of the integrin {alpha}2 cytoplasmic tail with that of {alpha}1, decreases cell migration and cord formation, but increases proliferation. When integrin {alpha}1 and {alpha}2 subunits are co-expressed in UB cells, the {alpha}1 subunit negatively regulates integrin {alpha}2{beta}1-dependent cord formation, adhesion and migration and this inhibition requires expression of both {alpha}1 and {alpha}2 tails. Thus, we provide evidence that the transmembrane and cytoplasmic domains of the {alpha}2 integrin subunit, as well as the {alpha}1 integrin subunit, regulate integrin {alpha}2{beta}1 cell function.

Abair, Tristin D. [Department of Medicine, Division of Nephrology, Vanderbilt University, Nashville, TN 37232 (United States); Department of Cancer Biology, Vanderbilt University, Nashville, TN 37232 (United States); Sundaramoorthy, Munirathinam; Chen, Dong [Department of Medicine, Division of Nephrology, Vanderbilt University, Nashville, TN 37232 (United States); Heino, Jyrki [Department of Biochemistry and Food Chemistry, University of Turku, Turku (Finland); Ivaska, Johanna [VTT Technical Research Centre of Finland, Medical Biotechnology, Turku (Finland); Hudson, Billy G. [Department of Medicine, Division of Nephrology, Vanderbilt University, Nashville, TN 37232 (United States); Department of Biochemistry, Vanderbilt University, Nashville, TN 37232 (United States); Sanders, Charles R. [Department of Biochemistry, Vanderbilt University, Nashville, TN 37232 (United States); Pozzi, Ambra [Department of Medicine, Veterans Affairs Hospital, Nashville, TN 37232 (United States); Department of Medicine, Division of Nephrology, Vanderbilt University, Nashville, TN 37232 (United States); Department of Cancer Biology, Vanderbilt University, Nashville, TN 37232 (United States); Zent, Roy [Department of Medicine, Veterans Affairs Hospital, Nashville, TN 37232 (United States); Department of Medicine, Division of Nephrology, Vanderbilt University, Nashville, TN 37232 (United States); Department of Cancer Biology, Vanderbilt University, Nashville, TN 37232 (United States); Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN 37232 (United States)], E-mail: roy.zent@vanderbilt.edu

2008-11-15

307

Development of skeletal muscles in transforming growth factor-beta 1 (TGF-beta1) null-mutant mice.  

PubMed

Fetal transforming growth factor-beta 1 (TGF-beta1) has been postulated to regulate the onset of myotube formation and/or pattern formation in developing skeletal muscles. In apparent contradiction of these hypotheses, the development of the extensor digitorum longus and soleus in TGF-beta1 null-mutant muscle was normal. The onset of secondary myotube formation, the numbers of myotubes formed, the proportion of fast and slow fibers, and the patterns of fiber types and connective tissues were essentially identical in TGF-beta1(+/+) and TGF-beta1(-/-) mice. A portion of the TGFbeta1 in skeletal muscles is derived from the mother, via the placenta. This maternal-derived TGF-beta1 was also not essential for the development of skeletal muscles, as the characteristics of pups born to a TGF-beta1(-/-) mother were normal TGF-beta1(-/-) mice die at weaning due to a generalized autoimmune attack. This postnatal death was circumvented by breeding the TGF-beta1 null mutation into nude mice (Whn(-/-)). Like many other strains of TGF-beta1(-/-) mice, extensive loss of Whn(-/-), TGF-beta1(-/-) embryos occurred in utero. However, a portion of the Whn(-/-), TGF-beta1(-/-) mice survived past weaning, remained healthy, and were fertile. The TGF-beta1(-/-) x Whn(-/-) mouse thus represents a valuable tool for the study of the function of TGF-beta1 in the adult, including its putative role as a pregnancy-related hormone. PMID:10741419

McLennan, I S; Poussart, Y; Koishi, K

2000-03-01

308

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 their maximum extent at 29 -28 ka, and retreat from their maximum extent at 19 ka was nearly synchronous with Northern Hemisphere ice sheets (Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J. X., Hostetler, S. W., and Kuhn, G. (2011): Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum. - Science, 334, 1265-1269, doi: 10.1126:science.1209299). 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. Using the results of an atmospheric general circulation we conclude that surface climate forcing of Antarctic ice mass balance would likely cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Furthermore, our new data support teleconnections involving a sea-level fingerprint forced from Northern Hemisphere ice sheets as indicated by gravitational modeling. Also, changes in North Atlantic Deepwater formation and attendant heat flux to Antarctic grounding lines may have contributed to synchronizing the hemispheric ice sheets.

Weber, M. E.; Clark, P. U.; Ricken, W.; Mitrovica, J. X.; Hostetler, S. W.; Kuhn, G.

2012-04-01

309

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 of an elongated current sheet in the wake behind the rising plasmoid. Magnetic reconnection in these current sheets is highly asymmetric. Sunward outflow impacts the post-flare loops and regions of high plasma and magnetic pressure, whereas antisunward outflow impacts the rising flux rope. There are strong gradients along the outflow direction for upstream density, pressure, and magnetic field strength. Resistive magnetohydrodynamic simulations of X-line retreat predict that the majority of the outflow energy is directed upward because the principal X-line is located near the lower base of the current sheet. We derive an exact expression showing that the rate of X-line retreat is given by a combination of advection and diffusion. During line-tied reconnection with asymmetric upstream magnetic field strengths, the structure of the post-flare loops is skewed and the current sheet drifts along the inflow direction. We compare the drift rate to observations of CME current sheets that characteristically drift or tilt with time, including the 2008 April 9 "Cartwheel CME." We will present simulations of plasmoid formation in high Lundquist number current sheets, and report our progress using time-dependent ionization to predict observational signatures from simulations of CME current sheets.

Murphy, N. A.; Miralles, M. P.; Pope, C. L.; Raymond, J. C.; Young, A. K.; Shen, C.; Lin, J.; Reeves, K. K.; Seaton, D. B.; Webb, D. F.

2011-12-01

310

Raman and AFM study of gamma irradiated plastic bottle sheets  

SciTech Connect

In this investigation, the effects of gamma irradiation on the structural properties of plastic bottle sheet are studied. The Plastic sheets were exposed with 1.25MeV {sup 60}Co gamma rays source at various dose levels within the range from 0-670 kGy. The induced modifications were followed by micro-Raman and atomic force microscopy (AFM). The Raman spectrum shows the decrease in Raman intensity and formation of unsaturated bonds with an increase in the gamma dose. AFM image displays rough surface morphology after irradiation. The detailed Raman analysis of plastic bottle sheets is presented here, and the results are correlated with the AFM observations.

Ali, Yasir; Kumar, Vijay; Dhaliwal, A. S. [Department of Physics, Sant Longowal Institute of Engineering and Technology Longowal, Punjab-148106 (India); Sonkawade, R. G. [School of Physical Sciences, Babasaheb Bhimrao Ambedkar University, Lucknow-226025 (India)

2013-02-05

311

Numerical simulation and fabrication of silicon sheet via spin casting.  

PubMed

A spin-casting process for fabricating polycrystalline silicon sheets for use as solar cell wafers is proposed, and the parameters that control the sheet thickness are investigated. A numerical study of the fluidity of molten silicon indicates that the formation of thin silicon sheets without a mold and via spin casting is feasible. The faster the rotation speed of graphite mold, the thinner the thickness of sheet. After the spread of the molten silicon to cover the graphite mold with rotation speed of above 500 rpm, the solidification has to start. Silicon sheets can be produced by using the centrifugal force under appropriate experimental conditions. The spin-cast sheet had a vertical columnar microstructure due to the normal heat extraction to the substrate, and the sheet lifetime varied from 0.1 microS to 0.3 microS measured by using the microwave photoconductance decay (MW-PCD) to confirm that the spin-cast silicon sheet is applicable to photovoltaics. PMID:23858887

Lee, Jaewoo; Kim, Hyunhui; Lee, Changbum; Kim, Joonsoo; Jang, Bo-Yun; Lee, Jinseok; Ahn, Youngsoo; Yoon, Wooyoung

2013-05-01

312

Bioengineered cardiac cell sheet grafts have intrinsic angiogenic potential  

Microsoft Academic Search

Previously, we have demonstrated the long-term survival of myocardial cell sheet constructs in vivo, with microvascular network formation throughout the engineered tissues. The understanding and control of these vascularization processes are a key factor for creating thicker functional tissues. Here, we show that cardiac cell sheets express angiogenesis-related genes and form endothelial cell networks in culture. After non-invasive harvest and

Sachiko Sekiya; Tatsuya Shimizu; Masayuki Yamato; Akihiko Kikuchi; Teruo Okano

2006-01-01

313

Mechanism-based inactivation of dopamine beta-monooxygenase by beta-chlorophenethylamine.  

PubMed

Functionalization of the beta-carbon of phenethylamines has been shown to produce a new class of substrate/inhibitor of dopamine beta-monooxygenase. Whereas both beta-hydroxy- and beta- chlorophenethylamine are converted to alpha-aminoacetophenone at comparable rates, only the latter conversion is accompanied by concomitant enzyme inactivation ( Klinman , J. P., and Krueger , M. (1982) Biochemistry 21, 67-75). In the present study, the nature of the reactive intermediates leading to dopamine beta-monooxygenase inactivation by beta- chlorophenethylamine has been investigated employing kinetic deuterium isotope effects and oxygen- 18 labeling as tools. Mechanistically significant findings presented herein include: 1) an analysis of primary deuterium isotope effects on turnover, indicating major differences in rate-determining steps for beta-chloro- and beta- hydroxyphenethylamine hydroxylation, Dkcat = 6.1 and 1.0, respectively; 2) evidence that dehydration of the gem-diol derived from oxygen- 18-labeled beta- hydroxyphenethylamine hydroxylation occurs in a random manner, attributed to dissociation of enzyme-bound gem-diol prior to alpha-aminoacetophenone formation; 3) the observation of a deuterium isotope effect for beta- chlorophenethylamine inactivation, Dkinact = 3.7, implicating C--H bond cleavage in the inactivation process; and 4) the demonstration that alpha-aminoacetophenone can replace ascorbic acid as exogenous reductant in the hydroxylation of tyramine. As discussed, these findings support the intermediacy of enzyme-bound alpha-aminoacetophenone in beta- chlorophenethylamine inactivation, and lead us to propose an intramolecular redox reaction to generate a ketone-derived radical cation as the dopamine beta-monooxygenase-inactivating species. PMID:6547439

Mangold, J B; Klinman, J P

1984-06-25

314

Quantitative analysis of simvastatin and its beta-hydroxy acid in human plasma using automated liquid-liquid extraction based on 96-well plate format and liquid chromatography-tandem mass spectrometry.  

PubMed

An assay based on automated liquid-liquid extraction (LLE) and liquid chromatography-tandem mass spectrometry (LC/MS/MS) has been developed and validated for the quantitative analysis of simvastatin (SV) and its beta-hydroxy acid (SVA) in human plasma. A Packard MultiProbe II workstation was used to convert human plasma samples collected following administration of simvastatin and quality control (QC) samples from individual tubes into 96-well plate format. The workstation was also used to prepare calibration standards and spike internal standards. A Tomtec Quadra 96-channel liquid handling workstation was used to perform LLE based on 96-well plates including adding solvents, separating organic from aqueous layer and reconstitution. SV and SVA were separated through a Kromasil C18 column (50 mm x 2 mm i.d., 5 microm) and detected by tandem mass spectrometry with a TurboIonspray interface. Stable isotope-labeled SV and SVA, 13CD(3)-SV and 13 CD(3)-SVA, were used as the internal standards for SV and SVA, respectively. The automated procedures reduced the overall analytical time (96 samples) to 1/3 of that of manual LLE. Most importantly, an analyst spent only a fraction of time on the 96-well LLE. A limit of quantitation of 50 pg/ml was achieved for both SV and SVA. The interconversion between SV and SVA during the 96-well LLE was found to be negligible. The assay showed very good reproducibility, with intra- and inter-assay precision (%R.S.D.) of less than 7.5%, and accuracy of 98.7-102.3% of nominal values for both analytes. By using this method, sample throughput should be enhanced at least three-fold compared to that of the manual procedure. PMID:14738932

Zhang, Nanyan; Yang, Amy; Rogers, John Douglas; Zhao, Jamie J

2004-01-27

315

73. PALMDALE WATER COMPANY, EASTWOOD MULTIPLEARCHED DAM: REINFORCEMENT SHEET, SHEET ...  

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

73. PALMDALE WATER COMPANY, EASTWOOD MULTIPLE-ARCHED DAM: REINFORCEMENT SHEET, SHEET 4; DECEMBER 30, 1918. Littlerock Water District files. - Little Rock Creek Dam, Little Rock Creek, Littlerock, Los Angeles County, CA

316

5. Historic American Buildings Survey Taken from drawing sheet, SHEET ...  

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

5. Historic American Buildings Survey Taken from drawing sheet, SHEET #21, Showing the house as restored since Survey. (Dormer windows omitted as not authentic) - Samuel des Marest House, River Road, New Milford, Bergen County, NJ

317

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

318

Slow Mode Waves in the Heliospheric Plasma Sheet  

NASA Technical Reports Server (NTRS)

We report the results of a search for waves/turbulence in the Heliospheric Plasma Sheet (HPS) surrounding the Heliospheric Current Sheet (HCS). The HPS is treated as a distinctive heliospheric structure distinguished by relatively high Beta, slow speed plasma. The data used in the investigation are from a previously published study of the thicknesses of the HPS and HCS that were obtained in January to May 2004 when Ulysses was near aphelion at 5 AU. The advantage of using these data is that the HPS is thicker at large radial distances and the spacecraft spends longer intervals inside the plasma sheet. From the study of the magnetic field and solar wind velocity components, we conclude that, if Alfven waves are present, they are weak and are dominated by variations in the field magnitude, B, and solar wind density, NP, that are anti-correlated.

Smith, Edward. J.; Zhou, Xiaoyan

2007-01-01

319

Latent TGF-[beta] structure and activation  

SciTech Connect

Transforming growth factor (TGF)-{beta} is stored in the extracellular matrix as a latent complex with its prodomain. Activation of TGF-{beta}1 requires the binding of {alpha}v integrin to an RGD sequence in the prodomain and exertion of force on this domain, which is held in the extracellular matrix by latent TGF-{beta} binding proteins. Crystals of dimeric porcine proTGF-{beta}1 reveal a ring-shaped complex, a novel fold for the prodomain, and show how the prodomain shields the growth factor from recognition by receptors and alters its conformation. Complex formation between {alpha}v{beta}6 integrin and the prodomain is insufficient for TGF-{beta}1 release. Force-dependent activation requires unfastening of a 'straitjacket' that encircles each growth-factor monomer at a position that can be locked by a disulphide bond. Sequences of all 33 TGF-{beta} family members indicate a similar prodomain fold. The structure provides insights into the regulation of a family of growth and differentiation factors of fundamental importance in morphogenesis and homeostasis.

Shi, Minlong; Zhu, Jianghai; Wang, Rui; Chen, Xing; Mi, Lizhi; Walz, Thomas; Springer, Timothy A. (Harvard-Med)

2011-09-16

320

Characterization of Hydrogels Formed via Intramolecular Folding and Consequent Self-Assembly of Beta-HAIRPIN Peptides  

NASA Astrophysics Data System (ADS)

Stimuli-responsive and biocompatible networks formed via self-assembly serve great opportunities in tissue engineering and drug delivery applications. In this work we present the formation of hydrogels via the intramolecular folding and consequent self-assembly of 20 aminoacid long beta-Hairpin peptide molecules. These hairpin molecules are amphiphilic in nature with an alternating sequence of hydrophobic valine and hydrophilic lysine amino acids. These molecules are found to form hydrogels with a unique microstructure and nanostructure at different physical condition at low peptide concentrations ( ˜ 1 wt %). However, gelation is observed at high pH values ( ˜9) and at high salt concentrations ( ˜150 mM) where beta-sheet secondary structure due to hairpin folding is observed. The intimate relationship between beta-Hairpin molecule turn sequence and the consequent materials properties will be discussed. LSCM data reveals that hydrogel structure is heterogeneous at the microscale with water channels in the order of 10 ?m. Cryo-TEM technique shows that the network is consists of interconnected fibrillar/tubular networks. The viscoelastic properties of the hydrogels, as measured by rheology. Importantly, the gel is also reversible with pH, returning to a viscosity of water with a drop in pH that unfolds, and disassembles, the hairpin molecules.

Ozbas, Bulent; Pakstis, Lisa; Pochan, Darrin J.; Rajagopal, Karthikan; Gill, Juliana; Schneider, Joel P.

2003-03-01

321

Historic Sheet Music  

NSDL National Science Digital Library

If you're looking for compelling sheet music from decades gone by, this website from the University of Oregon Libraries is just the ticket. Initially created to showcase sheet music from the Oregon Music Collection, their digitization work continues apace, and there are already over 650 pieces of sheet music available here. Visitors to the site can browse the collection by title, composer, or topic. Perhaps the most unique items here are those pieces composed by Oregonian women, such as Amy Beach, Marion Bauer, and Liza Lehmann. Not surprisingly, the collection is also strong in the area of Western Americana, as attested to by songs like "Broncho Buster", "Oh you round up, let 'er buck", and "The Gray Haired Pioneer".

322

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 Kay

323

Historic American Sheet Music  

NSDL National Science Digital Library

Duke University's Historic American Sheet Music Project (HASM) presents digital images of 3,042 pieces of sheet music from Duke's collections, published between 1850 and 1920. Highlights of the collection include "antebellum Southern music, Confederate imprints, and Civil war songs." The search capabilities at the site are sophisticated, allowing users to look for music by publisher name, composer, title, performer, and many other terms. There is online help for searching and a glossary of subject headings. Much of the sheet music is illustrated, and it is possible to search for pictures by "illustration type" (theme), allowing access to the subjects of the illustrations as well as the music itself. It is also possible to browse all the cover illustrations. HASM was originally funded by Ameritech as part of the ongoing Library of Congress/Ameritech Digital Library Competition; it will soon be part of the American Memory Collections at the Library of Congress (described in the November 6, 1998 Scout Report).

324

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

325

Kepler Mission Fact Sheet  

NSDL National Science Digital Library

This 2-page color fact sheet briefly describes NASA's 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. Note: The fact sheets states that the Kepler Telescope was launched in 2007 but did not launch until 2009.

326

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

327

Radiation Therapy Side Effects Sheets  

Cancer.gov

Radiation therapy fact sheets that help patients understand their treatment and manage side effects. The fact sheets (also available in audio) have tips from patients and healthcare providers, and questions to ask providers.

328

Rubella - Fact Sheet for Parents  

MedlinePLUS

... and 4 through 6 years Fact Sheet for Parents Printer friendly version[2 pages] Español: Rubéola The ... according to the recommended schedule. Fact Sheets for Parents Diseases and the Vaccines that Prevent Them Chickenpox ...

329

Measles - Fact Sheet for Parents  

MedlinePLUS

... MMR shot before traveling abroad. Fact Sheet for Parents Printer friendly version[2 pages] Español: Sarampión The ... according to the recommended schedule. Fact Sheets for Parents Diseases and the Vaccines that Prevent Them Chickenpox ...

330

Polio - Fact Sheet for Parents  

MedlinePLUS

... months 4 through 6 years Fact Sheet for Parents Printer friendly version[2 pages] Español: Polio The ... according to the recommended schedule. Fact Sheets for Parents Diseases and the Vaccines that Prevent Them Chickenpox ...

331

Immunolocalization of alpha-keratins and feather beta-proteins in feather cells and comparison with the general process of cornification in the skin of mammals.  

PubMed

The maturation of the corneous material of feathers is a special case of cornification in vertebrate epidermis and is believed to occur mainly by the accumulation of small proteins of about 100 amino acids and a central beta-pleated sheet region known as feather keratins. The present immunocytochemical study carried out using double-labeling immunogold shows that a small amount of alpha-keratins of intermediate filament type form the early keratin clumps in barb and barbule cells. These initial nuclei of formation of corneous material are rapidly coated by the deposition of large amounts of small feather keratin-associated beta-proteins (feather keratins). The latter proteins turn the keratin bundles of barb and barbule cells into a compact and apparently amorphous mass of corneous material where no sign of intermediate filaments are seen. Feather beta-proteins however form an irregular filamentous network of 2-3nm thick electron-pale filaments and produce the characteristic feather X-ray pattern due to their prevalent amount over any other protein present in feather cells. The modality of cornification in feathers is discussed in relation to the process of formation of corneous material in the skin of vertebrates in general that occurs by the association of intermediate filament proteins and keratin-associated proteins. PMID:23228339

Alibardi, L

2013-03-01

332

Functional polymer sheet patterning using microfluidics.  

PubMed

Poly(dimethylsiloxane) (PDMS)-based microfluidics provide a novel approach to advanced material synthesis. While PDMS has been successfully used in a wide range of industrial applications, due to the weak mechanical property channels generally possess low aspect ratios (AR) and thus produce microparticles with similarly low ARs. By increasing the channel width to nearly 1 cm, AR to 267, and implementing flow lithography, we were able to establish the slit-channel lithography. Not only does this allow us to synthesize sheet materials bearing multiscale features and tunable chemical anisotropy but it also allows us to fabricate functional layered sheet structures in a one-step, high-throughput fashion. We showcased the technique's potential role in various applications, such as the synthesis of planar material with micro- and nanoscale features, surface morphologies, construction of tubular and 3D layered hydrogel tissue scaffolds, and one-step formation of radio frequency identification (RFID) tags. The method introduced offers a novel route to functional sheet material synthesis and sheet system fabrication. PMID:24967616

Li, Minggan; Humayun, Mouhita; Kozinski, Janusz A; Hwang, Dae Kun

2014-07-22

333

Fast Light-Sheet Scanner  

NASA Technical Reports Server (NTRS)

Optomechanical apparatus maintains sheet of pulsed laser light perpendicular to reference axis while causing sheet of light to translate in oscillatory fashion along reference axis. Produces illumination for laser velocimeter in which submicrometer particles entrained in flow illuminated and imaged in parallel planes displaced from each other in rapid succession. Selected frequency of oscillation range upward from tens of hertz. Rotating window continuously shifts sheet of light laterally while maintaining sheet parallel to same plane.

Hunter, William W., Jr.; Humphreys, William M., Jr.; Bartram, Scott M.

1995-01-01

334

Polymer Injection Forming (PIF) Of Thin-Walled Sheet Metal Parts — Preliminary Experimental Results  

NASA Astrophysics Data System (ADS)

Polymer Injection Forming (PIF) is a new technology to manufacture sheet metal/polymer macro-composite components in a one-operation production process. During the process, a metal blank is shaped inside an injection mould by using the injection pressure of the molten polymer. In the same step the polymer is permanently bonded to the metal sheet creating a fully finished product in only one production step. Thus, the PIF technology is a combination of the injection moulding and sheet metal forming processes. In this paper, the influence of the main injection moulding process parameters on the sheet metal formability has been experimentally investigated. The results show that melt temperature and clamp force have a great effect on the sheet deformation since they affect respectively the ductility of the sheet metal and the degree of pure drawing. In order to maximize sheet metal formability avoiding the flash formation, the main process parameters have been optimized.

Lucchetta, Giovanni; Baesso, Ruggero

2007-04-01

335

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.

336

US Geological Survey Fact Sheets  

NSDL National Science Digital Library

The US Geological Survey (USGS) Fact Sheets Web site summarizes research and investigations done by the agency and provides details about particular activities. The sheets are organized by theme, including resources, hazards, environment, information management, by individual state, and by scientific discipline. The fact sheets give basic summations of the research and provide links to more detailed pages for those seeking further information.

337

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

338

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

339

STATE SupErAnnuATion SchEmE (SSS) FACT SHEET FACT SHEET FACT SHEET FACT SHEET FACT SH  

E-print Network

STATE SupErAnnuATion SchEmE (SSS) FACT SHEET FACT SHEET FACT SHEET FACT SHEET FACT SH www Sheet. STC is not licensed to provide financial product advice in relation to SSS. Reasonable care has been taken in producing the information in this Fact Sheet and nothing in it is intended

University of Technology, Sydney

340

Partially reflecting sheet arrays  

Microsoft Academic Search

Multiple reflections of electromagnetic waves between two planes are studied, and the increase in directivity that results by placing a partially reflecting sheet in front of an antenna with a reflecting screen is investigated at a wavelength of 3.2 cm. The construction and performance of various models of such arrays is discussed. Thus, for example, a \\

G. V. Trentini

1956-01-01

341

Software Fact Sheet Description  

E-print Network

Software Fact Sheet Description Display & Analysis Software Data Access Software www.unidata.ucar.edu/software, and multidisciplinary integration, Unidata provides a rich set of software tools to access and visualize Earth with the aid of three tools: the LDM, RAMADDA and the TDS. Data Management Software Unidata facilitates

342

Risk Assessment Fact Sheet  

E-print Network

Risk Assessment ® Fact Sheet U.S. Army Corps of Engineers Building Strong ® Buffalo District June 2012 Risk Assessment A risk assessment is performed for hazardous, toxic, and radioactive waste sites to estimate the potential risks to human health and the environment posed by radioactive substances

US Army Corps of Engineers

343

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

344

Mineral Properties Sheets  

NSDL National Science Digital Library

These sheets are designed to give students a framework for making observations of minerals in hand specimen and (for selected minerals) in thin section. I place most of the emphasis on the distinguishing properties, rather than requiring an exhaustive list. Students use hand specimen observation, thin section observation (for selected minerals) and references to complete the forms.

Dave Hirsch

345

Cascading Style Sheets  

NSDL National Science Digital Library

Cascading style sheets allow for greater control over how a web document is presented, and this site can help interested users learn about them. W3C's CSS page offers even more information regarding CSS, it's history, and what's new. It also provides a listing of other related guides and tools.

346

Youth Demographics. Fact Sheet  

ERIC Educational Resources Information Center

This fact sheet compares the numbers of 18-25 year-old residents and citizens by gender, race, ethnicity, geographic distribution, marital status, military status, unemployment, educational attainment, and assesses population trends from 1968-2006. It explores such demographic characteristics of young people using data from the March Annual…

Lopez, Mark Hugo; Marcelo, Karlo Barrios

2006-01-01

347

Ethanol Basics (Fact Sheet)  

SciTech Connect

Ethanol is a widely-used, domestically-produced renewable fuel made from corn and other plant materials. More than 96% of gasoline sold in the United States contains ethanol. Learn more about this alternative fuel in the Ethanol Basics Fact Sheet, produced by the U.S. Department of Energy's Clean Cities program.

Not Available

2015-01-01

348

Imperfect World of $\\beta\\beta$-decay Nuclear Data Sets  

E-print Network

The precision of double-beta ($\\beta\\beta$) decay experimental half lives and their uncertainties is reanalyzed. The method of Benford's distributions has been applied to nuclear reaction, structure and decay data sets. First-digit distribution trend for $\\beta\\beta$-decay T$_{1/2}^{2\

Pritychenko, B

2015-01-01

349

Amino acid distribution rules predict protein fold: protein grammar for beta-strand sandwich-like structures.  

PubMed

We present an alternative approach to protein 3D folding prediction based on determination of rules that specify distribution of "favorable" residues, that are mainly responsible for a given fold formation, and "unfavorable" residues, that are incompatible with that fold, in polypeptide sequences. The process of determining favorable and unfavorable residues is iterative. The starting assumptions are based on the general principles of protein structure formation as well as structural features peculiar to a protein fold under investigation. The initial assumptions are tested one-by-one for a set of all known proteins with a given structure. The assumption is accepted as a "rule of amino acid distribution" for the protein fold if it holds true for all, or near all, structures. If the assumption is not accepted as a rule, it can be modified to better fit the data and then tested again in the next step of the iterative search algorithm, or rejected. We determined the set of amino acid distribution rules for a large group of beta sandwich-like proteins characterized by a specific arrangement of strands in two beta sheets. It was shown that this set of rules is highly sensitive (~90%) and very specific (~99%) for identifying sequences of proteins with specified beta sandwich fold structure. The advantage of the proposed approach is that it does not require that query proteins have a high degree of homology to proteins with known structure. So long as the query protein satisfies residue distribution rules, it can be confidently assigned to its respective protein fold. Another advantage of our approach is that it allows for a better understanding of which residues play an essential role in protein fold formation. It may, therefore, facilitate rational protein engineering design. PMID:25625198

Kister, Alexander

2015-01-01

350

Trisaccharide synthesis by glycosyl transfer from p-nitrophenyl beta-D-N-acetylgalactosaminide on to disaccharide acceptors catalysed by the beta-N-acetylhexosaminidase from Aspergillus oryzae.  

PubMed

The beta-N-acetylhexosaminidase from Aspergillus oryzae catalysed the transfer of beta-D-N-acetylgalactosaminyl residues from p-nitrophenyl beta-D-N-acetylglucosaminide on to disaccharide acceptors consisting of thioethyl glycosides of alpha-D-Glc-(1-->4)-beta-D-Glc, beta-D-Glc-(1-->4)-beta-D-Glc and beta-D-Glc-(1-->6)-beta-D-Glc. The principle of 'anomeric control' was exemplified by the results which showed that an alpha-linkage between the units of the acceptor favoured exclusively the formation of a new (1-->4)-linkage, whereas the beta-configuration in the acceptor led to a mixture of (1-->4)- and (1-->3)-linked products, as observed for simple glycosides of monosaccharide acceptors. With the thioethyl beta-lactoside as acceptor, beta-D-Gal-(1-->6)-beta-D-Gal-(1-->4)-beta-D-GlcSEt was formed, owing to the action of residual beta-D-galactosidase activity in the N-acetylhexosaminidase on the thioethyl beta-lactoside acting as both donor and acceptor. PMID:9648256

Singh, S; Scigelova, M; Critchley, P; Crout, D H

1997-12-01

351

Eruptive Current Sheets Trailing SOHO/LASCO CMEs  

NASA Astrophysics Data System (ADS)

Current sheets are important signatures of magnetic reconnection during the eruption of solar magnetic structures. Many models of eruptive flare/Coronal Mass Ejections (CMEs) involve formation of a current sheet connecting the ejecting CME flux rope with the post-eruption magnetic loop arcade. Current sheets have been interpreted in white light images as narrow rays trailing the outward-moving CME, in ultraviolet spectra as narrow, bright hot features, and with different manifestations in other wavebands. This study continues that of Webb et al. (2003), who analyzed SMM white light CMEs having candidate magnetic disconnection features at the base of the CME. About half of those were followed by coaxial, bright rays suggestive of newly formed current sheets, and Webb et al. (2003) presented detailed results of analysis of those structures. In this work we extend the study of white light eruptive current sheets to the more sensitive and extensive SOHO/LASCO coronagraph data on CMEs. We comprehensively examined all LASCO CMEs during two periods that we identify with the minimum and maximum activity of solar cycle 23. We identified ~130 ray/current sheets during these periods, nearly all of which trailed CMEs with concave-outward backs. The occurrence rate of the ray/current sheets is 6-7% of all CMEs, irrespective of the solar cycle. We analyze the rays for durations, speeds, alignments, and motions and compare the observational results with some model predictions.

Webb, David F.

2015-04-01

352

Sheet Music from Canada's Past  

NSDL National Science Digital Library

The National Library of Canada has recently updated their collection of historical Canadian sheet music. Sheet Music from Canada's Past (see the November 17, 2000 Scout Report for an earlier mention) has updated their collection of sheet music from the World War I era with sheet music published before the Confederation in 1867. One can search the entire collection or search the World War I and pre-Confederation collections separately. The site also features articles devoted to describing each collection, and the posted music may be printed out from the site. Future plans include digitizing sheet music published between 1867 and 1913.

353

One-way transparent sheets  

E-print Network

In this paper we introduce the concept of metasurfaces which are fully transparent when looking from one of the two sides of the sheet and have controllable functionalities for waves hitting the opposite side (one-way transparent sheets). We address the question on what functionalities are allowed, considering limitations due to reciprocity and passivity. In particular, we have found that it is possible to realize one-way transparent sheets which have the properties of a twist-polarizer in reflection or transmission when illuminated from the other side. Also one-way transparent sheets with controllable co-polarized reflection and transmission from the opposite side are feasible. We show that particular non-reciprocal magneto-electric coupling inside the sheet is necessary to realize lossless non-active transparent sheets. Furthermore, we derive the required polarizabilities of constituent dipole particles such that the layers composed of them form one-way transparent sheets. We conclude with design and simula...

Ra'di, Younes; Tretyakov, Sergei

2013-01-01

354

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

355

A Single Mutation at the Sheet Switch Region Results in Conformational Changes Favoring 6 Light-Chain Fibrillogenesis  

SciTech Connect

Systemic amyloid light-chain (LC) amyloidosis is a disease process characterized by the pathological deposition of monoclonal LCs in tissue. All LC subtypes are capable of fibril formation although {lambda} chains, particularly those belonging to the {lambda}6 type, are overrepresented. Here, we report the thermodynamic and in vitro fibrillogenic properties of several mutants of the {lambda}6 protein 6aJL2 in which Pro7 and/or His8 was substituted by Ser or Pro. The H8P and H8S mutants were almost as stable as the wild-type protein and were poorly fibrillogenic. In contrast, the P7S mutation decreased the thermodynamic stability of 6aJL2 and greatly enhanced its capacity to form amyloid-like fibrils in vitro. The crystal structure of the P7S mutant showed that the substitution induced both local and long-distance effects, such as the rearrangement of the VL (variable region of the light chain)-VL interface. This mutant crystallized in two orthorhombic polymorphs, P2{sub 1}2{sub 1}2{sub 1} and C222{sub 1}. In the latter, a monomer that was not arranged in the typical Bence-Jones dimer was observed for the first time. Crystal-packing analysis of the C222{sub 1} lattice showed the establishment of intermolecular {beta}-{beta} interactions that involved the N-terminus and {beta}-strand B and that these could be relevant in the mechanism of LC fibril formation. Our results strongly suggest that Pro7 is a key residue in the conformation of the N-terminal sheet switch motif and, through long-distance interactions, is also critically involved in the contacts that stabilized the VL interface in {lambda}6 LCs.

Hernández-Santoyo, A.; Del Pozo Yauner, L; Fuentes-Silva, D; Ortiz, E; Rudiño-Piñera, E; Sánchez-López, R; Horjales, E; Becerril, B; Rodríguez-Romero, A

2010-01-01

356

Application Cover Sheet Please clearly enter all the information on this application cover sheet.  

E-print Network

Application Cover Sheet Please clearly enter all the information on this application cover sheet Application Includes: · Applicant information sheet (application and complete details available at www

Snider, Barry B.

357

Beta Coin Experiment  

NSDL National Science Digital Library

This resource consists of a Java applet and expository text. The applet illustrates Bayesian estimation of the probability of heads for a coin. The prior beta distribution, true probability of heads, and the sample size can be specified. The applet shows the posterior beta distribution.

Kyle Siegrist

358

Beta-Carotene  

Technology Transfer Automated Retrieval System (TEKTRAN)

Beta-carotene is a pigment that occurs naturally in many photosynthetic plants and organisms and one of the most abundant carotenoids found in human blood. The richest dietary sources of beta-carotene are yellow, orange, and leafy green fruits and vegetables, such as carrots, spinach, sweet potatoes...

359

BETA GAUGE OPERATION MANUAL  

EPA Science Inventory

This manual provides description and operating instructions for a redesigned Beta Gauge for measuring particles from vehicle exhaust. The improvements and a new control system including a control unit which is radically different from the prior unit, are described. Complete Beta ...

360

MOON for neutrino-less {beta}{beta} decays and {beta}{beta} nuclear matrix elements  

SciTech Connect

The MOON project aims at spectroscopic 0v{beta}{beta} studies with the v-mass sensitivity of 100-30 meV by measuring two beta rays from {sup 100}Mo and/or {sup 82}Se. The detector is a compact super-module of multi-layer PL scintillator plates. R and D works made by the pro to-type MOON-1 and the small PL plate show the possible energy resolution of around {sigma}{approx}2.2%, as required for the mass sensitivity. Nuclear matrix elements M{sup 2v} for 2v{beta}{beta} are shown to be given by the sum {sigma}{sub L}M{sub k} of the 2v{beta}{beta} matrix elements M{sub k} through intermediate quasi-particle states in the Fermi-surface, where Mi is obtained experimentally by using the GT(J{sup {pi}} = 1{sup +}) matrix elements of M{sub i}(k) and M{sub f}(k) for the successive single-{beta} transitions through the k-th intermediate state.

Ejiri, H. [Research Center for Nuclear Physics, Osaka University, Osaka 567-0047 (Japan)

2009-11-09

361

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

362

[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.

363

Conversion of rice husk ash to zeolite beta.  

PubMed

White rice husk ash (RHA), an agriculture waste containing crystalline tridymite and alpha-cristobalite, was used as a silica source for zeolite Beta synthesis. The crystallization of zeolite Beta from RHA at 150 degrees C in the presence of tetraethylammonium hydroxide was monitored by XRD, FTIR and (29)Si MAS NMR techniques. It was found that zeolite Beta started to form after 12h and the complete crystallization of zeolite Beta phase was achieved after 2d. XRD, (29)Si MAS NMR and solid yield studies indicate that the transformation mechanism of silica present in RHA to zeolite Beta involves dissolution of the ash, formation of an amorphous aluminosilicate after 6h of crystallization, followed by dissolution in the mother liquor and final transformation to pure zeolite Beta crystals. PMID:16274981

Prasetyoko, Didik; Ramli, Zainab; Endud, Salasiah; Hamdan, Halimaton; Sulikowski, Bogdan

2006-01-01

364

Irish Sheet Music Archives  

NSDL National Science Digital Library

Based out of Milwaukee, the Ward Irish Music Archives were established in 1992 and is dedicated to the preservation of Irish and Irish-American music in all of its forms. Visitors to this remarkable site can browse over 5,000 pieces of Irish and Irish-American sheet music. While some of these ditties are not in the public domain, the collection can be narrowed down by filtering for only publicly available items. The History section contains a topical history of sheet music from the days of the broadside to the more challenging days of the early 21st century when digital versions became dominant. The Galleries are another great feature, containing additional information about cover artists, composers, and themes. It's an amazing collection and one that will inspire a few sing-a-longs from Dublin to Boston.

365

Temple Sheet Music Collections  

NSDL National Science Digital Library

Over the past few years, more and more university libraries have worked diligently to digitize some of their vast sheet music holdings. Old chestnuts are being revived by vocal groups on campus and farther afield, which is certainly a good thing. This sheet music collection from the Temple University Libraries brings together 850 pieces of music for consideration by the general public. Visitors can search the collection as they see fit. They will find that most of the music here is from the Gilded Age and earlier. There are a number of melodic tunes in here; visitors might do well to consider "Drifting Leaves" from 1905 or 1852's "Dreams of Home" as a way to get started on their journey. The site will be of great interest to musicologists and to anyone with an interest in the history of American popular song and musical heritage.

2012-08-24

366

Genetics Home Reference: Beta thalassemia  

MedlinePLUS

... Recent literature OMIM Genetic disorder catalog Conditions > Beta thalassemia On this page: Description Genetic changes Inheritance Diagnosis ... Glossary definitions Reviewed July 2009 What is beta thalassemia? Beta thalassemia is a blood disorder that reduces ...

367

Dynamics of dikes versus cone sheets in volcanic systems  

NASA Astrophysics Data System (ADS)

Igneous sheet intrusions of various shapes, such as dikes and cone sheets, coexist as parts of complex volcanic plumbing systems likely fed by common sources. How they form is fundamental regarding volcanic hazards, yet no dynamic model simulates and predicts satisfactorily their diversity. Here we present scaled laboratory experiments that reproduced dikes and cone sheets under controlled conditions. Our models show that their formation is governed by a dimensionless ratio (?1), which describes the geometry of the magma source, and a dynamic dimensionless ratio (?2), which compares the viscous stresses in the flowing magma to the host rock strength. Plotting our experiments against these two numbers results in a phase diagram evidencing a dike and a cone sheet field, separated by a sharp transition that fits a power law. This result shows that dikes and cone sheets correspond to distinct physical regimes of magma emplacement in the crust. For a given host rock strength, cone sheets preferentially form when the source is shallow, relative to its lateral extent, or when the magma influx velocity (or viscosity) is high. Conversely, dikes form when the source is deep compared to its size, or when magma influx rate (or viscosity) is low. Both dikes and cone sheets may form from the same source, the shift from one regime to the other being then controlled by magma dynamics, i.e., different values of ?2. The extrapolated empirical dike-to-cone sheet transition is in good agreement with the occurrence of dikes and cone sheets in various natural volcanic settings.

Galland, Olivier; Burchardt, Steffi; Hallot, Erwan; Mourgues, Régis; Bulois, Cédric

2014-08-01

368

Sheets by Patchy Particles  

NSDL National Science Digital Library

Simulation Software: Glotzer Group Code Simulation Method: Brownian Dynamics A system of 80 spherical particles with four patches in the equator of the sphere at a concentration of 0.20, was run starting at an effectively infinite temperature then instantaneously quenched to a temperature of 1.0. The final equillibrium structure is sheets with spheres packing in square lattices. Simulation Model: United Atom Rigid Body with Lennard-Jones

Zhang, Zhenli

2005-01-31

369

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

370

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

371

Kepler Mission Fact Sheet  

NSDL National Science Digital Library

This 2-page color fact sheet briefly describes NASA’s 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

372

Between the Sheets: Accounting  

NSDL National Science Digital Library

This guide from the British Website BizEd helps users understand the ways to use spreadsheets in accounting. The tutorial starts with general information: introductions for both students and teachers, a guide to downloadable spreadsheets, a guide to using spreadsheets, and a glossary of important terms. The guide offers a collection of spreadsheets that require Microsoft Excel 97. Also featured is an introduction to balance sheets and income statements, budgeting, and cost volume profit analysis.

373

MAGNETIC RECONNECTION IN THE SOLAR WIND AT CURRENT SHEETS ASSOCIATED WITH EXTREMELY SMALL FIELD SHEAR ANGLES  

SciTech Connect

Using Wind 3 s plasma and magnetic field data, we have identified nine reconnection exhausts within a solar wind disturbance on 1998 October 18-20 driven by a moderately fast interplanetary coronal mass ejection (ICME). Three of the exhausts within the ICME were associated with current sheets having local field shear angles, {theta}, ranging from 4 Degree-Sign to 9 Degree-Sign , the smallest reported values of {theta} yet associated with reconnection exhausts in a space plasma. They were observed in plasma characterized by extremely low (0.02-0.04) plasma {beta}, and very high (281-383 km s{sup -1}) Alfven speed, V{sub A}. Low {beta} allows reconnection to occur at small {theta} and high V{sub A} leads to exhaust jets that are fast enough relative to the surrounding solar wind to be readily identified. Very small-{theta} current sheets are common in the solar wind at 1 AU, but typically are not associated with particularly low plasma {beta} or high V{sub A}. On the other hand, small-{theta} current sheets should be common in the lower solar corona, a plasma regime of extremely low {beta} and extremely high V{sub A}. Our observations lend credence to models that predict that reconnection at small-{theta} current sheets is primarily responsible for coronal heating.

Gosling, J. T. [Laboratory for Atmospheric and Space Physics, University of Colorado, 3665 Discovery Drive, Boulder, CO 80303 (United States); Phan, T. D., E-mail: jack.gosling@lasp.colorado.edu [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)

2013-02-01

374

Organic polymeric materials for nonlinear optics: oligopeptide-bound chromophores in ?-sheets  

NASA Astrophysics Data System (ADS)

The synthesis and preliminary characterization of new polypeptide-bound chromophores are reported. These polymers were made for the purpose of assembling (beta) -sheets at an air- water surface, and processing them into nonlinear optical films by Langmuir-Blodgett (LB) deposition. These films should be amenable to integration on semiconductor wafers, e.g., as active optical waveguides for phase shifting.

Lindsay, Geoffrey A.; Hoover, James M.; Nadler, Melvin P.; Nissan, R.; Stenger-Smith, John D.; Schram, A.

1993-04-01

375

A novel intersubunit repair mechanism in the tryptophan synthase alpha 2 beta 2 complex. Critical role of the beta subunit lysine 167 in intersubunit communication.  

PubMed

This study explores intersubunit communication in the tryptophan synthase alpha 2 beta 2 complex from Salmonella typhimurium. We find that an engineered mutation in the contact region between the alpha and beta subunits remarkably alters the catalytic and spectroscopic properties of the beta subunit in the alpha 2 beta 2 complex. Ligands that bind to the alpha subunit largely repair the deleterious effects of the beta subunit mutation in the alpha 2 beta 2 complex. The conserved residue chosen for mutation, beta subunit lysine 167, appears to form an ion pair with alpha subunit aspartate 56 in the crystal structure of the wild type alpha 2 beta 2 complex. Although replacement of beta subunit lysine 167 by threonine does not prevent formation of the alpha 2 beta 2 complex, this mutation reduces the rate of synthesis of L-tryptophan from L-serine and indole (beta reaction) 25-fold. Ligands that bind to the alpha subunit (indole-3-glycerol phosphate, indole-3-propanol phosphate, alpha-glycerol 3-phosphate, or potassium phosphate) largely restore the activity of the mutant alpha 2 beta 2 complex in the beta reaction. We conclude that beta subunit lysine 167 plays an important role in intersubunit communication in the alpha 2 beta 2 complex. The striking allosteric effects of alpha subunit ligands on the mutant beta subunit in the alpha 2 beta 2 complex may result from ligand-induced conformational changes in the alpha subunit that are transmitted to the beta subunit and repair the mutational defect in the beta subunit. PMID:8226734

Yang, X J; Miles, E W

1993-10-25

376

Synthesis and spectral investigation of Al(III) catechin/beta-cyclodextrin and Al(III) quercetin/beta-cyclodextrin inclusion compounds.  

PubMed

Al-catechin/beta-cyclodextrin and Al-quercetin/beta-cyclodextrin (beta-CD) inclusion compounds were synthesized and characterized by IR, UV-vis, 1H and 13C NMR and TG and DTA analyses. Because quercetin is sparingly soluble in water, the stability constants of the Al-quercetin/beta-CD and Al-catechin/beta-CD compounds were determined by phase solubility studies. The AL-type diagrams indicated the formation of 1:1 inclusion compounds and allowed calculation of the stability constants. The thermodynamic parameters were obtained from the dependence of the stability constants on temperature and results indicated that the formation of the inclusion compounds is an enthalpically driven process. The thermal decomposition of the solid Al-quercetin/beta-CD and Al-catechin/beta-CD inclusion compounds took place at different stages, compared with the respective precursors, proving that an inclusion complexation process really occurred. PMID:18054838

Dias, Karina; Nikolaou, Sofia; De Giovani, Wagner F

2008-06-01

377

Mammalian ciliary-body epithelial cells in culture produce transforming growth factor-beta  

Microsoft Academic Search

Transforming growth factor-beta (TGF-beta) has recently been found in the aqueous humor. The present study was initiated to test whether the ciliary-body epithelium, the site of aqueous humor formation, is capable of producing TGF-beta. Human, rat and bovine ciliary epithelial cells were grown in tissue culture and their supernatants were tested for TGF-beta using a bioassay. After acid activation of

Horst Helbig; Karen L. Kittredge; Miguel Coca-Prados; Janet Davis; Alan G. Palestine; Robert B. Nussenblatt

1991-01-01

378

Evolution of the H$\\beta$+[OIII] and [OII] luminosity functions and the [OII] star-formation history of the Universe up to $z$ ~ 5 from HiZELS  

E-print Network

We investigate the evolution of the H$\\beta$+[OIII] and [OII] luminosity functions from $z$ ~ 0.8 to ~ 5 in multiple redshift slices using data from the High-$z$ Emission Line Survey (HiZELS). This is the first time that the H$\\beta$+[OIII] and [OII] luminosity functions have been studied at these redshifts in a self-consistent analysis. This is also the largest sample of [OII] and H$\\beta$+[OIII] emitters (3484 and 3301 emitters, respectively) in this redshift range, with large co-moving volumes ~ $1 \\times 10^6$ Mpc$^{3}$ in two independent volumes (COSMOS and UDS), greatly reducing the effects of cosmic variance. The emitters were selected by a combination of photometric redshift and color-color selections, as well as spectroscopic follow-up, including recent spectroscopic observations using DEIMOS and MOSFIRE on the Keck Telescopes and FMOS on Subaru. We find a strong increase in $L_\\star$ and a decrease in $\\phi_\\star$ with increasing redshift up to $z \\sim 2$ and $z \\sim 5$ for H$\\beta$+[OIII] and [OII]...

Khostovan, Ali Ahmad; Mobasher, Bahram; Best, Philip N; Smail, Ian; Stott, John P; Hemmati, Shoubaneh; Nayyeri, Hooshang

2015-01-01

379

Amyloid beta 1-42 deposits do not lead to Alzheimer's neuritic plaques in aged dogs.  

PubMed Central

In alzheimer's disease, amyloid beta (A beta) is deposited in senile plaques and amyloid angiopathy. Longer A beta peptides, which extend to residue 42 (A beta 42), have been suggested to be critical for the seeding of amyloid. Aged dogs develop cerebral vessel amyloid and parenchymal preamyloid lesions. Preamyloid in humans is related to senile plaques, whereas in dogs such progression is rare. We evaluated the composition of aged canine vessel amyloid and preamyloid both biochemically and immunohistochemically. The vessel amyloid extended mainly to residue 40 (A beta 40), while preamyloid contained a mixture of A beta 17-42 and A beta 42, with minimal A beta 40. Our results suggest other factors besides A beta 42 are important for neuritic plaque formation. PMID:8573095

Wisniewski, T; Lalowski, M; Bobik, M; Russell, M; Strosznajder, J; Frangione, B

1996-01-01

380

Magnetic Configurations of the Tilted Current Sheets and Dynamics of Their Flapping in Magnetotail  

NASA Astrophysics Data System (ADS)

Based on multiple spacecraft measurements, the geometrical structures of tilted current sheet and tail flapping waves have been analyzed and some features of the tilted current sheets have been made clear for the first time. The geometrical features of the tilted current sheet revealed in this investigation are as follows: (1) The magnetic field lines (MFLs) are generally plane curves and the osculating planes in which the MFLs lie are about vertical to the magnetic equatorial plane, while the tilted current sheet may lean severely to the dawn or dusk side. (2) The tilted current sheet may become very thin, its half thickness is generally much less than the minimum radius of the curvature of the MFLs. (3) In the neutral sheet, the field-aligned current density becomes very large and has a maximum value at the center of the current sheet. (4) In some cases, the current density is a bifurcated one, and the two humps of the current density often superpose two peaks in the gradient of magnetic strength, indicating that the magnetic gradient drift current is possibly responsible for the formation of the two humps of the current density in some tilted current sheets. Tilted current sheets often appear along with tail thick current sheet flapping waves. It is found that, in the tail flapping current sheets, the minimum curvature radius of the MFLs in the current sheet is rather large with values around 1RE, while the neutral sheet may be very thin, with its half thickness being several tenths ofRE. During the flapping waves, the current sheet is tilted substantially, and the maximum tilt angle is generally larger than 45

Shen, C.; Rong, Z. J.; Li, X.; Dunlop, M.; Liu, Z. X.; Malova, H. V.; Lucek, E.; Carr, C.

2009-04-01

381

Method for heating a glass sheet  

DOEpatents

A method for heating a glass sheet includes the steps of heating a glass sheet to a first predetermined temperature and applying microwave energy to the glass sheet to heat the glass sheet to at least a second predetermined temperature to allow the glass sheet to be formed. 5 figs.

Boaz, P.T.

1998-07-21

382

Method for heating a glass sheet  

DOEpatents

A method for heating a glass sheet includes the steps of heating a glass sheet to a first predetermined temperature and applying microwave energy to the glass sheet to heat the glass sheet to at least a second predetermined temperature to allow the glass sheet to be formed.

Boaz, Premakaran Tucker (Livonia, MI)

1998-01-01

383

Cartilage engineering using chondrocyte cell sheets and its application in reconstruction of microtia  

PubMed Central

The imperfections of scaffold materials have hindered the clinical application of cartilage tissue engineering. The recently developed cell-sheet technique is adopted to engineer tissues without scaffold materials, thus is considered being potentially able to overcome the problems concerning the scaffold imperfections. This study constructed monolayer and bilayer chondrocyte cell sheets and harvested the sheets with cell scraper instead of temperature-responsive culture dishes. The properties of the cultured chondrocyte cell sheets and the feasibility of cartilage engineering using the chondrocyte cell sheets was further investigated via in vitro and in vivo study. Primary extracellular matrix (ECM) formation and type II collagen expression was detected in the cell sheets during in vitro culture. After implanted into nude mice for 8 weeks, mature cartilage discs were harvested. The morphology of newly formed cartilage was similar in the constructs originated from monolayer and bilayer chondrocyte cell sheet. The chondrocytes were located within evenly distributed ovoid lacunae. Robust ECM formation and intense expression of type II collagen was observed surrounding the evenly distributed chondrocytes in the neocartilages. Biochemical analysis showed that the DNA contents of the neocartilages were higher than native human costal cartilage; while the contents of the main component of ECM, glycosaminoglycan and hydroxyproline, were similar to native human costal cartilage. In conclusion, the chondrocyte cell sheet constructed using the simple and low-cost technique is basically the same with the cell sheet cultured and harvested in temperature-responsive culture dishes, and can be used for cartilage tissue engineering. PMID:25755694

Zhou, Libin; Ding, Ruiying; Li, Baowei; Han, Haolun; Wang, Hongnan; Wang, Gang; Xu, Bingxin; Zhai, Suoqiang; Wu, Wei

2015-01-01

384

Cartilage engineering using chondrocyte cell sheets and its application in reconstruction of microtia.  

PubMed

The imperfections of scaffold materials have hindered the clinical application of cartilage tissue engineering. The recently developed cell-sheet technique is adopted to engineer tissues without scaffold materials, thus is considered being potentially able to overcome the problems concerning the scaffold imperfections. This study constructed monolayer and bilayer chondrocyte cell sheets and harvested the sheets with cell scraper instead of temperature-responsive culture dishes. The properties of the cultured chondrocyte cell sheets and the feasibility of cartilage engineering using the chondrocyte cell sheets was further investigated via in vitro and in vivo study. Primary extracellular matrix (ECM) formation and type II collagen expression was detected in the cell sheets during in vitro culture. After implanted into nude mice for 8 weeks, mature cartilage discs were harvested. The morphology of newly formed cartilage was similar in the constructs originated from monolayer and bilayer chondrocyte cell sheet. The chondrocytes were located within evenly distributed ovoid lacunae. Robust ECM formation and intense expression of type II collagen was observed surrounding the evenly distributed chondrocytes in the neocartilages. Biochemical analysis showed that the DNA contents of the neocartilages were higher than native human costal cartilage; while the contents of the main component of ECM, glycosaminoglycan and hydroxyproline, were similar to native human costal cartilage. In conclusion, the chondrocyte cell sheet constructed using the simple and low-cost technique is basically the same with the cell sheet cultured and harvested in temperature-responsive culture dishes, and can be used for cartilage tissue engineering. PMID:25755694

Zhou, Libin; Ding, Ruiying; Li, Baowei; Han, Haolun; Wang, Hongnan; Wang, Gang; Xu, Bingxin; Zhai, Suoqiang; Wu, Wei

2015-01-01

385

Chemical chaperones interfere with the formation of scrapie prion protein.  

PubMed Central

The fundamental event in prion diseases involves a conformational change in one or more of the alpha-helices of the cellular prion protein (PrP(C)) as they are converted into beta-sheets during the formation of the pathogenic isoform (PrP(Sc)). Here, we show that exposure of scrapie-infected mouse neuroblastoma (ScN2a) cells to reagents known to stabilize proteins in their native conformation reduced the rate and extent of PrP(Sc) formation. Such reagents include the cellular osmolytes glycerol and trimethylamine N-oxide (TMAO) and the organic solvent dimethylsulfoxide (DMSO), which we refer to as 'chemical chaperones' because of their influence on protein folding. Although the chemical chaperones did not appear to affect the existing population of PrP(Sc) molecules in ScN2a cells, they did interfere with the formation of PrP(Sc) from newly synthesized PrP(C). We suggest that the chemical chaperones act to stabilize the alpha-helical conformation of PrP(C) and thereby prevent the protein from undergoing a conformational change to produce PrP(Sc). These observations provide further support for the idea that prions arise due to a change in protein conformation and reveal potential strategies for preventing PrP(Sc) formation. Images PMID:8978663

Tatzelt, J; Prusiner, S B; Welch, W J

1996-01-01

386

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, John C.; Finn, C.A.

1993-01-01

387

Inhibition of Alzheimer's Amyloidosis by Peptides That Prevent ?-Sheet Conformation  

Microsoft Academic Search

Amyloid ?-peptide (A?) is a major fibrillar component of neuritic plaques in Alzheimer's disease (AD) brains and is related to the pathogenesis of the disease. We hypothesized that amyloid formation could be inhibited by peptides homologous to A? (position 17-21) with a similar degree of hydrophobicity, but with a very low propensity to adopt a ?-sheet conformation by incorporating proline

Claudio Soto; Mark S. Kindy; Marc Baumann; Blas Frangione

1996-01-01

388

Growth and Structure of Crystalline Silica Sheet on Ru(0001)  

Microsoft Academic Search

Thin SiO2 films were grown on a Ru(0001) single crystal and studied by photoelectron spectroscopy, infrared spectroscopy and scanning probe microscopy. The experimental results in combination with density functional theory calculations provide compelling evidence for the formation of crystalline, double-layer sheet silica weakly bound to a metal substrate.

D. Löffler; J. J. Uhlrich; M. Baron; B. Yang; X. Yu; L. Lichtenstein; L. Heinke; C. Büchner; M. Heyde; S. Shaikhutdinov; H.-J. Freund; R. Wlodarczyk; M. Sierka; J. Sauer

2010-01-01

389

Transforming growth factors beta 1 and beta 2 are differentially expressed in fibrotic liver disease.  

PubMed Central

Transforming growth factor (TGF) beta 1 has been implicated in the control of hepatocyte growth and stimulation of extracellular matrix synthesis in acute and chronic liver disease. The cellular localization of transforming growth factor (TGF) beta 1 and beta 2 RNA transcripts was determined in normal and fibrotic liver by in situ hybridization with [35S]-labeled RNA probes in combination with immunostaining for cell type characteristic markers. Fibrotic specimens were from patients with hepatitis B virus infection or alcohol abuse and rats with fibrosis secondary to bile duct ligation and scission. In normal liver, low levels of TGF beta 1 transcripts were found in some portal tract stromal cells, and TGF beta 2 RNA was not detectable. In fibrotic liver, high TGF beta 1 RNA levels were present in most mesenchymal liver cells, in most inflammatory cells, and in few bile duct epithelial cells. Hepatocytes did not express this cytokine with the exception of few limiting plate hepatocytes in cases of human cirrhosis with high activity. TGF beta 2 transcripts were detected at high levels in proliferating bile ducts of fibrotic livers, but were absent in all other cell types. TGF beta 1 expression in the liver is thus a function predominantly of mononuclear and mesenchymal cells as well as of some hepatocytes, whereas TGF beta 2 expression is a specific property of bile duct epithelial cells that may be related to the formation of specialized periductular connective tissue during bile duct proliferation. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 PMID:1750499

Milani, S.; Herbst, H.; Schuppan, D.; Stein, H.; Surrenti, C.

1991-01-01

390

CURRENT SHEETS AND COLLISIONLESS DAMPING IN KINETIC PLASMA TURBULENCE  

SciTech Connect

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., E-mail: jason-tenbarge@uiowa.edu [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States)

2013-07-10

391

Neutrinoless double beta decay  

E-print Network

The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations are presented as well as the current status of experiments. Finally an outlook towards the future, work on nuclear matrix elements and alternative processes is given.

K. Zuber

2012-01-23

392

Beta Estimate Experiment  

NSDL National Science Digital Library

This resource consists of a Java applet and expository text. The applet simulates a random sample from a beta distribution, and computes standard point estimates of the left and right parameters. The bias and mean square error are also computed.

Kyle Siegrist

393

ICQ 2000b Beta  

NSDL National Science Digital Library

The latest beta release of the universally popular instant messaging program ICQ ("I seek you") contains a number of new features, including ICQphone, which makes it possible for users to initiate and participate in PC-to-PC and PC-to-Phone calls, support for SMS technology, integration with Outlook, and email address import, among others. Users can download ICQ 2000b Beta for free at the ICQ site.

394

Beta-thalassemia  

Microsoft Academic Search

Beta-thalassemias are a group of hereditary blood disorders characterized by anomalies in the synthesis of the beta chains of hemoglobin resulting in variable phenotypes ranging from severe anemia to clinically asymptomatic individuals. The total annual incidence of symptomatic individuals is estimated at 1 in 100,000 throughout the world and 1 in 10,000 people in the European Union. Three main forms

Renzo Galanello; Raffaella Origa

2010-01-01

395

Engineering Research Center Fact Sheets  

NSDL National Science Digital Library

Curious about the latest developments in bioengineering, microelectronics, or earthquake hazard reduction? Wondering what type of research your tax dollars support? Then have a look at this recent posting from the National Science Foundation's (NSF's) Engineering Research Centers (ERC) Program which supports university research in partnership with industry. Here, users can access project descriptions from a variety of laboratories associated with the ERC. Examples of centers featured include Georgia Tech/ Emory Center for the Engineering of Living Tissues, Pacific Earthquake Engineering Research Center, Center for Neuromorphic Systems Engineering, and Center for Advanced Engineering Fibers and Films, to name a few. The research pages, available in either HTML or .pdf formats, present research goals, collaborating institutions, facility overviews, technology transfer initiatives, educational outreach projects, and links to contacts. At many of the pages, color photographs and illustrations accompany text. So the next time you are taking a break from work, peruse the NSF's Engineering Research Centers Fact Sheets and get the latest news about federally funded research and technology.

2001-01-01

396

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.

397

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

398

Kinetic Alfven instabilities and anomalous resistivity in inhomogenous current sheets  

NASA Astrophysics Data System (ADS)

As it has been shown recently, the current-driven instability (CDI) of kinetic Alfven waves (KAWs) has a lower threshold current density than other known instabilities in low-beta uni-form plasmas. The currents flowing between interacting magnetic fluxes are concentrated in thin current sheets and are thus very inhomogeneous, which makes waves and instabilities in such sheets much different from those in uniform plasmas. We show that the current inhomo-geneity has a profound influence on KAWs and their CDI. The KAW phase velocity spans a wide velocity range decreasing from super-Alfvenic velocities to zero with increasing current shear. In this velocity range KAWs undergo a kinetic instability that depends on both desta-bilizing factors: current strength and current shear. The kinetic instability has a low threshold and can attain a high growth rate with moderate current shears. For stronger current shears, the KAW phase velocity becomes imaginary and the KAW transforms into a purely growing mode (aperiodic instability). Both instabilities can develop in the same current sheet simulta-neously but in different regions: aperiodic instability at the flanks of the current sheet where the current shear maximizes, and the kinetic instability shifted towards current sheet center, where the current density is higher. The anomalous resistivity generated by the near-threshold regime of the inhomogeneous CDI of KAWs is capable of supporting a fast (Petschek) magnetic reconnection. The corresponding current sheet width is about 20 gyroradii, which is 3 times thicker then in the case of homogenous CDI. It seems that the interplay of kinetic and purely growing KAW instabilities can make magnetic reconnection intrinsically intermittent. Possible implications of our results are discussed in the context of magnetic reconnection at the Earth's magnetopause and in the solar corona.

Voitenko, Yuriy; de Keyser, Johan

399

Beta-Lactamasen und Beta-Lactamase- Inhibitoren  

Microsoft Academic Search

Die Bildung von Beta-Lactamasen ist der häufigste Resistenzmechanismus gegenüber Beta-Lactam-Antibiotika. Die Enzyme hydrolysieren mit unterschiedlicher Effizienz die Substanzen dieser Gruppe.Als Antwort auf den hohen Selektionsdruck führte folglich die vermehrte Anwendung der Beta-Lactam-Antibiotika im Krankenhaus zu einer entspre- chenden Vielfalt an unterschiedlichen Enzymen. Trotz neuer Beta-Lactam-Antibiotika mit verbesserter Lactamase-Stabilität ist das Reservoir an möglichen bakteriellen Gegen- strategien unerschöpflich. Beta-Lactamasen, die durch

Ursula Theuretzbacher

400

9. Photograph of sheet 1 (index and title sheet) of ...  

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

9. Photograph of sheet 1 (index and title sheet) of the State Highway Department of Indiana repair plans of 1957 for the Cicott Street Bridge. Photograph of a 24' by 36' print made from microfilm in the archives of the Indiana Department of Transportation in Indianapolis. - Cicott Street Bridge, Spanning Wabash River at State Road 25, Logansport, Cass County, IN

401

Laminated sheet composites reinforced with modular filament sheet  

NASA Technical Reports Server (NTRS)

Aluminum and magnesium composite sheet laminates reinforced with low density, high strength modular filament sheets are produced by diffusion bonding and explosive bonding. Both processes are accomplished in normal atmosphere and require no special tooling or cleaning other than wire brushing the metal surfaces just prior to laminating.

Reece, O. Y.

1968-01-01

402

13. Photograph of sheet 1 (index and title sheet) of ...  

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

13. Photograph of sheet 1 (index and title sheet) of the Indiana State Highway Commission repair plans of 1969 for the Cicott Street Bridge. Photograph of a 24' by 36' print made from microfilm in the archives of the Indiana Department of Transportation in Indianapolis. - Cicott Street Bridge, Spanning Wabash River at State Road 25, Logansport, Cass County, IN

403

17. INTAKE PIER, BRIDGE STRESS SHEET, SHEET 8 OF 117, ...  

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

17. INTAKE PIER, BRIDGE STRESS SHEET, SHEET 8 OF 117, 1920. - Sacramento River Water Treatment Plant Intake Pier & Access Bridge, Spanning Sacramento River approximately 175 feet west of eastern levee on river; roughly .5 mile downstream from confluence of Sacramento & American Rivers, Sacramento, Sacramento County, CA

404

Current Sheet Properties and Dynamics During Sympathetic Breakout Eruptions  

NASA Astrophysics Data System (ADS)

We present the continued analysis of the high-resolution 2.5D MHD simulations of sympathetic magnetic breakout eruptions from a pseudostreamer source region. We examine the generation of X- and O-type null points during the current sheet tearing and track the magnetic island formation and evolution during periods of reconnection. The magnetic breakout eruption scenario forms an overlying 'breakout' current sheet that evolves slowly and removes restraining flux from above the sheared field core that will eventually become the center of the erupting flux rope-like structure. The runaway expansion from the expansion-breakout reconnection positive feedback enables the formation of the second, vertical/radial current sheet underneath the rising sheared field core as in the standard CHSKP eruptive flare scenario. We will examine the flux transfer rates through the breakout and flare current sheets and compare the properties of the field and plasma inflows into the current sheets and the reconnection jet outflows into the flare loops and flux rope ejecta.

Lynch, B. J.; Edmondson, J. K.

2013-12-01

405

Beta-cardiotoxin: a new three-finger toxin from Ophiophagus hannah (king cobra) venom with beta-blocker activity.  

PubMed

Snake venoms have provided a number of novel ligands with therapeutic potential. We have constructed a partial cDNA library from the mRNA of Ophiophagus hannah (king cobra) venom gland tissue and identified five new genes encoding proteins belonging to the three-finger toxin family of snake venom proteins. We have isolated and characterized one of these beta-sheet containing proteins with a mass of 7012.43 +/- 0.91 Da from the venom. The protein was nonlethal up to a dose of 10 mg/kg when injected intraperitoneally into Swiss albino mice. However, it induces labored breathing and death at a dose of 100 mg/kg. It does not show any hemolytic or anticoagulant activity. It caused a dose-dependent decrease of heart rate in vivo (anesthetized Sprague-Dawley rats) and also ex vivo (Langendorff isolated rat heart). This is in contrast to classical cardiotoxins from snake venom that increase the heart rate in animals. Radioligand displacement studies showed that this protein targets beta-adrenergic receptors with a binding affinity (Ki) of 5.3 and 2.3 microM toward beta1 and beta2 subtypes, respectively, to bring about its effect, and hence, it was named as beta-cardiotoxin. This is the first report of a natural exogenous beta-blocker. PMID:17616557

Rajagopalan, Nandhakishore; Pung, Yuh Fen; Zhu, Yi Zhun; Wong, Peter Tsun Hon; Kumar, Prakash P; Kini, R Manjunatha

2007-11-01

406

Stacked sets of parallel, in-register beta-strands of beta2-microglobulin in amyloid fibrils revealed by site-directed spin labeling and chemical labeling.  

PubMed

beta(2)-microglobulin (beta(2)m) is a 99-residue protein with an immunoglobulin fold that forms beta-sheet-rich amyloid fibrils in dialysis-related amyloidosis. Here the environment and accessibility of side chains within amyloid fibrils formed in vitro from beta(2)m with a long straight morphology are probed by site-directed spin labeling and accessibility to modification with N-ethyl maleimide using 19 site-specific cysteine variants. Continuous wave electron paramagnetic resonance spectroscopy of these fibrils reveals a core predominantly organized in a parallel, in-register arrangement, by contrast with other beta(2)m aggregates. A continuous array of parallel, in-register beta-strands involving most of the polypeptide sequence is inconsistent with the cryoelectron microscopy structure, which reveals an architecture based on subunit repeats. To reconcile these data, the number of spins in close proximity required to give rise to spin exchange was determined. Systematic studies of a model protein system indicated that juxtaposition of four spin labels is sufficient to generate exchange narrowing. Combined with information about side-chain mobility and accessibility, we propose that the amyloid fibrils of beta(2)m consist of about six beta(2)m monomers organized in stacks with a parallel, in-register array. The results suggest an organization more complex than the accordion-like beta-sandwich structure commonly proposed for amyloid fibrils. PMID:20335170

Ladner, Carol L; Chen, Min; Smith, David P; Platt, Geoffrey W; Radford, Sheena E; Langen, Ralf

2010-05-28

407

48 CFR 53.110 - Continuation sheets.  

Code of Federal Regulations, 2011 CFR

... 2011-10-01 false Continuation sheets. 53.110 Section 53.110 Federal...FORMS General 53.110 Continuation sheets. Except as may be otherwise indicated...b) specially constructed continuation sheets (e.g., OF 336)....

2011-10-01

408

48 CFR 53.110 - Continuation sheets.  

Code of Federal Regulations, 2012 CFR

... 2012-10-01 false Continuation sheets. 53.110 Section 53.110 Federal...FORMS General 53.110 Continuation sheets. Except as may be otherwise indicated...b) specially constructed continuation sheets (e.g., OF 336)....

2012-10-01

409

48 CFR 53.110 - Continuation sheets.  

Code of Federal Regulations, 2014 CFR

... 2014-10-01 false Continuation sheets. 53.110 Section 53.110 Federal...FORMS General 53.110 Continuation sheets. Except as may be otherwise indicated...b) specially constructed continuation sheets (e.g., OF 336)....

2014-10-01

410

48 CFR 53.110 - Continuation sheets.  

Code of Federal Regulations, 2013 CFR

... 2013-10-01 false Continuation sheets. 53.110 Section 53.110 Federal...FORMS General 53.110 Continuation sheets. Except as may be otherwise indicated...b) specially constructed continuation sheets (e.g., OF 336)....

2013-10-01

411

Environment and Women's Health Fact Sheet  

MedlinePLUS

... women's health fact sheet ePublications The environment and women's health fact sheet Print this fact sheet The environment ... Return to top How can the environment affect women's health? Chemicals and other substances in the environment can ...

412

Vitamin and Mineral Supplement Fact Sheets  

MedlinePLUS

... view as pdf | share Create PDF Vitamin and Mineral Supplement Fact Sheets A - E | F - L | M - S | ... Information Botanical Dietary Supplements: Background Information Vitamin and Mineral Fact Sheets Botanical Supplement Fact Sheets Frequently Asked ...

413

48 CFR 53.110 - Continuation sheets.  

Code of Federal Regulations, 2010 CFR

... 2010-10-01 false Continuation sheets. 53.110 Section 53.110 Federal...FORMS General 53.110 Continuation sheets. Except as may be otherwise indicated...b) specially constructed continuation sheets (e.g., OF 336)....

2010-10-01

414

Creation of prompt and thin-sheet splashing by varying surface roughness or increasing air pressure.  

PubMed

A liquid drop impacting a solid surface may splash either by emitting a thin liquid sheet that subsequently breaks apart or by promptly ejecting droplets from the advancing liquid-solid contact line. Using high-speed imaging, we show that surface roughness and air pressure influence both mechanisms. Roughness inhibits thin-sheet formation even though it also increases prompt splashing at the advancing contact line. If the air pressure is lowered, droplet ejection is suppressed not only during thin-sheet formation but also for prompt splashing. PMID:23006177

Latka, Andrzej; Strandburg-Peshkin, Ariana; Driscoll, Michelle M; Stevens, Cacey S; Nagel, Sidney R

2012-08-01

415

Creation of Prompt and Thin-Sheet Splashing by Varying Surface Roughness or Increasing Air Pressure  

NASA Astrophysics Data System (ADS)

A liquid drop impacting a solid surface may splash either by emitting a thin liquid sheet that subsequently breaks apart or by promptly ejecting droplets from the advancing liquid-solid contact line. Using high-speed imaging, we show that surface roughness and air pressure influence both mechanisms. Roughness inhibits thin-sheet formation even though it also increases prompt splashing at the advancing contact line. If the air pressure is lowered, droplet ejection is suppressed not only during thin-sheet formation but also for prompt splashing.

Latka, Andrzej; Strandburg-Peshkin, Ariana; Driscoll, Michelle M.; Stevens, Cacey S.; Nagel, Sidney R.

2012-08-01

416

Formation of current coils in geodynamo simulations  

NSDL National Science Digital Library

This Nature article describes experiments used to simulate the formation of a geodynamo. Included figures show convection vorticity, simulated sheet plumes, magnetic field structure near the inner core, and modeled current coils with magnetic field lines.

Akira Kageyama1

417

Twisting of sheet metals  

NASA Astrophysics Data System (ADS)

Twisting of metallic sheets is one particular mode of springback that occurs after drawing of elongated parts, i.e. with one dimension much larger than the two others. In this study, a dedicated device for drawing of elongated part with a U-shaped section has been designed on purpose, in order to obtain reproducible data. Very thin metallic sheet, of thickness 0.15 mm, has been used, so that the maximum length of the part is 100 mm. Two different orientations of the part with respect to the tools have been chosen: either aligned with the tools, or purposefully misaligned by 2°. Several samples were drawn for each configuration, leading to the conclusion that almost no twisting occurs in the first case whereas a significant one can be measured for the second one. In a second step, 2D and 3D numerical simulations within the implicit framework for drawing and springback were carried out. A mixed hardening law associated to von Mises yield criterion represents accurately the mechanical behavior of the material. This paper highlights a comparison of numerical predictions with experiments, e.g. the final shape of the part and the twisting parameter.

Pham, C. H.; Thuillier, S.; Manach, P. Y.

2013-12-01

418

Ice sheets and nitrogen  

PubMed Central

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.

2013-01-01

419

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

420

MIXED DOUBLES TENNIS Information Sheet  

E-print Network

MIXED DOUBLES TENNIS Information Sheet Fall 2013 This information sheet is intended to provide will be played at the SFH Indoor Tennis Courts. CHECK-IN It is recommended that participants check for the intramural activity fee at their first match. EQUIPMENT Each team must provide tennis balls (preferably new

Seamons, Kent E.

421

MIXED DOUBLES TENNIS Information Sheet  

E-print Network

MIXED DOUBLES TENNIS Information Sheet Winter 2014 This information sheet is intended to provide:00-10:00 PM and Saturday from 12:00-6:00 PM in the SFH Indoor Tennis Courts. CHECK-IN It is recommended their rackets and a can of tennis balls. It is strongly recommended that the tennis balls are new. Equipment may

Seamons, Kent E.

422

FACT SHEETS HIV and Pregnancy  

E-print Network

FACT SHEETS HIV and Pregnancy HIV Testing and Pregnancy Mother-to-Child Transmission of HIV Anti-HIV Medications for Use in Pregnancy Safety of Anti-HIV Medications During Pregnancy Preventing Transmission and Pregnancy These fact sheets on HIV and pregnancy are intended for women infected with HIV who are pregnant

Levin, Judith G.

423

Communication Fact Sheets for Parents.  

ERIC Educational Resources Information Center

This booklet contains 28 fact sheets on communication written primarily for parents and families with a child who is deaf-blind. They attempt to address fundamental but complex issues related to the communication needs of children with vision and hearing impairments. Each fact sheet targets a specific area, including: (1) communication; (2)…

Stremel, Kathleen; Bixler, Betsy; Morgan, Susanne; Layton, Kristen

424

Amyloid Beta as a Modulator of Synaptic Plasticity  

PubMed Central

Alzheimer’s disease is associated with synapse loss, memory dysfunction and pathological accumulation of amyloid beta in plaques. However, an exclusively pathological role for amyloid beta is being challenged by new evidence for an essential function of amyloid beta at the synapse. Amyloid beta protein exists in different assembly states in the central nervous system and plays distinct roles ranging from synapse and memory formation to memory loss and neuronal cell death. Amyloid beta is present in the brain of symptom-free people where it likely performs important physiological roles. New evidence indicates that synaptic activity directly evokes the release of amyloid beta at the synapse. At physiological levels, amyloid beta is a normal, soluble product of neuronal metabolism that regulates synaptic function beginning early in life. Monomeric amyloid beta 40 and 42 are the predominant forms required for synaptic plasticity and neuronal survival. With age, some assemblies of amyloid beta are associated with synaptic failure and Alzheimer’s disease pathology, possibly targeting the N-methyl-D-aspartic acid (NMDA) receptor through the ?7-nicotinic acetylcholine receptor (?7-nAChR), mitochondrial amyloid-? alcohol dehydrogenase (ABAD) and cyclophilin D. But emerging data suggests a distinction between age effects on the target response in contrast to the assembly state or the accumulation of the peptide. Both aging and beta amyloid independently decrease neuronal plasticity. Our laboratory has reported that amyloid beta, glutamate and lactic acid are each increasingly toxic with neuron age. The basis of the age-related toxicity partly resides in age-related mitochondrial dysfunction and an oxidative shift in mitochondrial and cytoplasmic redox potential. In turn, signaling through phosphorylated extracellular signal-regulated protein kinases (pERK) is affected along with an age-independent increase in phosphorylated cAMP response element-binding protein (pCREB) This review examines the long-awaited functional impact of amyloid beta on synaptic plasticity. PMID:20847424

Parihar, Mordhwaj S; Brewer, Gregory J

2011-01-01

425

Windows Media Player 6.2 Beta  

NSDL National Science Digital Library

With the Windows Media Player 6.2 Beta, Microsoft enters the high quality, compressed digital music fray. Not only does Microsoft's new media player support numerous media formats, but it also has several novel features. It supports the new MS Audio 4.0 format, which claims to provide MP3-quality sound at half the size of MP3 files, and it offers "intelligent streaming," which increases the probability of a smooth streamed media experience. Somewhat less wonderful for the end-user may be its support for the Windows Media Rights Manager, which provides piracy protection and license control. Though similar to RealPlayer, the Windows Media Player 6.2 Beta's interesting and unique features make it worth checking out. The player runs on Win95/98/NT and is free to download and use.

426

Distinguished Research Professorship Nomination Cover Sheet  

E-print Network

Distinguished Research Professorship Nomination Cover Sheet Date: _______________ NOMINEE Qualifications Sheet describing how he/she is qualified to evaluate the nominee Has evidence that the nomination

Arnold, Jonathan

427

Synthesis and thermal stability of polycrystalline new divalent [beta][double prime]- and [beta]-ferrites prepared by ion exchange  

SciTech Connect

Using ion-exchange chemistry the divalent cations Ba[sup 2+], Sr[sup 2+], Ca[sup 2+], Mg[sup 2+], Cd[sup 2+], Pb[sup 2+], Co[sup 2+], Zn[sup 2+], Mn[sup 2+], Fe[sup 2+], and Sn[sup 2+] have been substituted for K[sup +] in polycrystalline CdO-stabilized K-[beta][double prime]-ferrite samples. Ba, Sr, Ca, Mg, Pb, and Cd ion exchange led to the synthesis of new materials, the divalent M[sup 2+]-[beta][double prime]-ferrites (M = Ba, Sr, Ca, Mg) and M[sup 2+]-[beta]-ferrites (M = Cd, Pb), respectively. Co[sup 2+]-diffusion resulted in the formation of a spinel-type Co-ferrite. In the case of Zn, Mn, Fe, and Sn the samples decomposed to [alpha]-Fe[sub 2]O[sub 3]. The thermal stability of the new divalent [beta][double prime]- and [beta]-ferrites was studied either by high-temperature exchange reactions or by air annealing of the exchanged products. Ba- and Sr-[beta][double prime]-ferrites and Pb-[beta]-ferrite converted to M-type hexagonal ferrites with the magnetoplumbite structure, Mg-[beta][double prime]-ferrite decomposed to a spinel-type Mg-ferrite, and Ca-[beta][double prime]-ferrite and Cd-[beta]-ferrite decomposed to [alpha]-Fe[sub 2]O[sub 3]. Composition, lattice parameters, SEM photographs, and magnetic properties of the ferrites formed are given. The magnetic susceptibilities of the divalent [beta][double prime]- or [beta]-ferrites have values between 0.63 and 1.14 [times] 10[sup [minus]4] emu/g[center dot]Oe at room temperature. 41 refs., 1 fig., 4 tabs.

Kalogirou, O. (Univ. of Hamburg (Germany) Aristotle Univ., Thessaloniki (Greece))

1993-02-01

428

Boosted Beta Regression  

PubMed Central

Regression analysis with a bounded outcome is a common problem in applied statistics. Typical examples include regression models for percentage outcomes and the analysis of ratings that are measured on a bounded scale. In this paper, we consider beta regression, which is a generalization of logit models to situations where the response is continuous on the interval (0,1). Consequently, beta regression is a convenient tool for analyzing percentage responses. The classical approach to fit a beta regression model is to use maximum likelihood estimation with subsequent AIC-based variable selection. As an alternative to this established - yet unstable - approach, we propose a new estimation technique called boosted beta regression. With boosted beta regression estimation and variable selection can be carried out simultaneously in a highly efficient way. Additionally, both the mean and the variance of a percentage response can be modeled using flexible nonlinear covariate effects. As a consequence, the new method accounts for common problems such as overdispersion and non-binomial variance structures. PMID:23626706

Schmid, Matthias; Wickler, Florian; Maloney, Kelly O.; Mitchell, Richard; Fenske, Nora; Mayr, Andreas