Determining the helicity structure of third generation resonances

International Nuclear Information System (INIS)

Papaefstathiou, Andreas

2011-11-01

We examine methods that have been proposed for determining the helicity structure of decays of new resonances to third generation quarks and/or leptons. We present analytical and semi-analytical predictions and assess the applicability of the relevant variables in realistic reconstruction scenarios using Monte Carlo-generated events, including the effects of QCD radiation and multiple parton interactions, combinatoric ambiguities and fast detector simulation. (orig.)

Numerical modeling of formation of helical structures in reversed-field-pinch plasma

International Nuclear Information System (INIS)

Mizuguchi, N.; Ichiguchi, K.; Todo, Y.; Sanpei, A.; Oki, K.; Masamune, S.; Himura, H.

2012-11-01

Nonlinear three-dimensional magnetohydrodynamic(MHD) simulations have been executed for the low-aspect-ratio reversed-field-pinch (RFP) plasma to reveal the physical mechanism of the formation processes of helical structures. The simulation results show a clear formation of n=4 structure as a result of dominant growth of resistive modes, where n represents the toroidal mode number. The resultant relaxed helical state consists of a unique bean-shaped and hollow pressure profile in the poloidal cross section for both cases of resonant and non-resonant triggering instability modes. The results are partially comparable to the experimental observations. The physical mechanisms of those processes are examined. (author)

Particle-in-cell simulation of helical structure onset in plasma fiber with dust grains

International Nuclear Information System (INIS)

Kulhanek, Petr; Bren, David; Kaizr, Vaclav; Pasek, Jan

2002-01-01

Fully three dimensional PIC program package for the helical pinch numerical simulation was developed in our department. Both electromagnetic and gravitational interactions are incorporated into the model. Collisions are treated via Monte Carlo methods. The program package enabled to prove the conditions of onset of spiral and helical structures in the pinch

Zn(II) coordination polymers with flexible V-shaped dicarboxylate ligand: Syntheses, helical structures and properties

Energy Technology Data Exchange (ETDEWEB)

Li, Lin [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Liu, Chong-Bo, E-mail: cbliu@nchu.edu.cn [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Yang, Gao-Shan [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Xiong, Zhi-Qiang [Center for Analysis and Testing, Nanchang Hangkong University, Nanchang 330063 (China); Liu, Hong [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Wen, Hui-Liang [State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047 (China)

2015-11-15

Hydrothermal reactions of 2,2′-[hexafluoroisopropylidenebis(p-phenyleneoxy)]diacetic acid (H{sub 2}L) and zinc ions in the presence of N-donor ancillary ligands afford four novel coordination polymers, namely, [Zn{sub 2}(μ{sub 2}-OH)(μ{sub 4}-O){sub 0.5}(L)]·0.5H{sub 2}O (1), [Zn(L)(2,2′-bipy)(H{sub 2}O)] (2), [Zn{sub 3}(L){sub 3}(phen){sub 2}]·H{sub 2}O (3) and [Zn{sub 2}(L){sub 2}(4,4′-bipy)] (4) (2,2′-bipy=2,2′-bipyridine; 4,4′-bipy=4,4′-bipyridine; phen=1,10-phenanthroline). Their structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Complex 1 shows a 3-D clover framework consisting of [Zn{sub 4}(µ{sub 4}-O)(µ{sub 2}-OH){sub 2}]{sup 4+} clusters, and exhibits a novel (3,8)-connected topological net with the Schläfli symbol of {3·4·5}{sub 2}{3"4·4"4·5"2·6"6·7"1"0·8"2}, and contains double-stranded and two kinds of meso-helices. 2 displays a helical chain structure, which is further extended via hydrogen bonds into a 3-D supramolecular structure with meso-helix chains. 3 displays a 2-D {4"4·6"2} parallelogram structure, which is further extended via hydrogen bonds into a 3-D supramolecular structure with single-stranded helical chains. 4 shows a 2-D {4"4·6"2} square structure with left- and right-handed helical chains. Moreover, the luminescent properties of 1–4 have been investigated. - Graphical abstract: Four new Zn(II) coordination polymers with helical structures based on flexible V-shaped dicarboxylate ligand have been synthesized and structurally characterized. Photoluminescent properties have been investigated. - Highlights: • Four novel Zn(II) coordination polymers with V-shaped ligand were characterized. • Complexes 1–4 show diverse intriguing helical characters. • Fluorescence properties of complexes 1–4 were investigated.

Variation in the Helical Structure of Native Collagen

Science.gov (United States)

2014-02-24

notochord were obtained in previous studies [4,10,20–22]. The scaled amplitudes of the central, meridional section of each data set were used to...including helical, structure) from rat tail tendon (collagen type I) and lamprey notochord (collagen type II) show several common features (Figure 5). Of...also a possible consequence of the type II collagen notochord samples being stretched, perhaps to a greater extant then the type I tendon samples to aid

Observation of helical structure in a low energy plasma focus pinch

International Nuclear Information System (INIS)

Rout, R.K.; Shyam, A.

1989-01-01

Helical structure and hot spots were observed in a Mather-type plasma focus operated at 3 KJ of bank energy. The experiments were carried out with the help of a fast optical framing camera and two X-ray pin-hole cameras with different filters. It was observed that initially a conical pinch (with base diameter of 6 mm and length of 14 mm) with temperature of ≅ 10 2 eV was formed. This pinch disintegrated after ≅ 50 ns by a single lobe sausage instability into a central high temperature (≅ 10 3 eV) filament of 1 mm diameter and 8 mm length containing a high emissivity helical structure. This helix is probably responsible for generation of axial magnetic field and relaxation of the focus pinch. Hot spots of high X-ray intensity and temperature (≅ 10 3 eV) were also observed much beyond the filament region. (author)

Salt-bridging effects on short amphiphilic helical structure and introducing sequence-based short beta-turn motifs.

Science.gov (United States)

Guarracino, Danielle A; Gentile, Kayla; Grossman, Alec; Li, Evan; Refai, Nader; Mohnot, Joy; King, Daniel

2018-02-01

Determining the minimal sequence necessary to induce protein folding is beneficial in understanding the role of protein-protein interactions in biological systems, as their three-dimensional structures often dictate their activity. Proteins are generally comprised of discrete secondary structures, from α-helices to β-turns and larger β-sheets, each of which is influenced by its primary structure. Manipulating the sequence of short, moderately helical peptides can help elucidate the influences on folding. We created two new scaffolds based on a modestly helical eight-residue peptide, PT3, we previously published. Using circular dichroism (CD) spectroscopy and changing the possible salt-bridging residues to new combinations of Lys, Arg, Glu, and Asp, we found that our most helical improvements came from the Arg-Glu combination, whereas the Lys-Asp was not significantly different from the Lys-Glu of the parent scaffold, PT3. The marked 3 10 -helical contributions in PT3 were lessened in the Arg-Glu-containing peptide with the beginning of cooperative unfolding seen through a thermal denaturation. However, a unique and unexpected signature was seen for the denaturation of the Lys-Asp peptide which could help elucidate the stages of folding between the 3 10 and α-helix. In addition, we developed a short six-residue peptide with β-turn/sheet CD signature, again to help study minimal sequences needed for folding. Overall, the results indicate that improvements made to short peptide scaffolds by fine-tuning the salt-bridging residues can enhance scaffold structure. Likewise, with the results from the new, short β-turn motif, these can help impact future peptidomimetic designs in creating biologically useful, short, structured β-sheet-forming peptides.

High-resolution crystal structures of protein helices reconciled with three-centered hydrogen bonds and multipole electrostatics.

Science.gov (United States)

Kuster, Daniel J; Liu, Chengyu; Fang, Zheng; Ponder, Jay W; Marshall, Garland R

2015-01-01

Theoretical and experimental evidence for non-linear hydrogen bonds in protein helices is ubiquitous. In particular, amide three-centered hydrogen bonds are common features of helices in high-resolution crystal structures of proteins. These high-resolution structures (1.0 to 1.5 Å nominal crystallographic resolution) position backbone atoms without significant bias from modeling constraints and identify Φ = -62°, ψ = -43 as the consensus backbone torsional angles of protein helices. These torsional angles preserve the atomic positions of α-β carbons of the classic Pauling α-helix while allowing the amide carbonyls to form bifurcated hydrogen bonds as first suggested by Némethy et al. in 1967. Molecular dynamics simulations of a capped 12-residue oligoalanine in water with AMOEBA (Atomic Multipole Optimized Energetics for Biomolecular Applications), a second-generation force field that includes multipole electrostatics and polarizability, reproduces the experimentally observed high-resolution helical conformation and correctly reorients the amide-bond carbonyls into bifurcated hydrogen bonds. This simple modification of backbone torsional angles reconciles experimental and theoretical views to provide a unified view of amide three-centered hydrogen bonds as crucial components of protein helices. The reason why they have been overlooked by structural biologists depends on the small crankshaft-like changes in orientation of the amide bond that allows maintenance of the overall helical parameters (helix pitch (p) and residues per turn (n)). The Pauling 3.6(13) α-helix fits the high-resolution experimental data with the minor exception of the amide-carbonyl electron density, but the previously associated backbone torsional angles (Φ, Ψ) needed slight modification to be reconciled with three-atom centered H-bonds and multipole electrostatics. Thus, a new standard helix, the 3.6(13/10)-, Némethy- or N-helix, is proposed. Due to the use of constraints from

Self-assembly of a double-helical complex of sodium.

Science.gov (United States)

Bell, T W; Jousselin, H

1994-02-03

Spontaneous self-organization of helical and multiple-helical molecular structures occurs on several levels in living organisms. Key examples are alpha-helical polypeptides, double-helical nucleic acids and helical protein structures, including F-actin, microtubules and the protein sheath of the tobacco mosaic virus. Although the self-assembly of double-helical transition-metal complexes bears some resemblance to the molecular organization of double-stranded DNA, selection between monohelical, double-helical and triple-helical structures is determined largely by the size and geometrical preference of the tightly bound metal. Here we present an example of double-helical assembly induced by the weaker and non-directional interactions of an alkali-metal ion with an organic ligand that is pre-organized into a coil. We have characterized the resulting complex by two-dimensional NMR and fast-atom-bombardment mass spectrometry. These results provide a step toward the creation of molecular tubes or ion channels consisting of intertwined coils.

Dynamics and deformability of α-, 310- and π-helices

Directory of Open Access Journals (Sweden)

Narwani Tarun Jairaj

2018-01-01

Full Text Available Protein structures are often represented as seen in crystals as (i rigid macromolecules (ii with helices, sheets and coils. However, both definitions are partial because (i proteins are highly dynamic macromolecules and (ii the description of protein structures could be more precise. With regard to these two points, we analyzed and quantified the stability of helices by considering α-helices as well as 310- and π-helices. Molecular dynamic (MD simulations were performed on a large set of 169 representative protein domains. The local protein conformations were followed during each simulation and analyzed. The classical flexibility index (B-factor was confronted with the MD root mean square flexibility (RMSF index. Helical regions were classified according to their level of helicity from high to none. For the first time, a precise quantification showed the percentage of rigid and flexible helices that underlie unexpected behaviors. Only 76.4% of the residues associated with α-helices retain the conformation, while this tendency drops to 40.5% for 310-helices and is never observed for π-helices. α-helix residues that do not remain as an α-helix have a higher tendency to assume β-turn conformations than 310- or π-helices. The 310-helices that switch to the α-helix conformation have a higher B-factor and RMSF values than the average 310-helix but are associated with a lower accessibility. Rare π-helices assume a β-turn, bend and coil conformations, but not α- or 310-helices. The view on π-helices drastically changes with the new DSSP (Dictionary of Secondary Structure of Proteins assignment approach, leading to behavior similar to 310-helices, thus underlining the importance of secondary structure assignment methods.

Magnetohydrodynamic helical structures in nominally axisymmetric low-shear tokamak plasmas

International Nuclear Information System (INIS)

Graves, J P; Brunetti, D; Cooper, W A; Reimerdes, H; Halpern, F; Pochelon, A; Sauter, O; Chapman, I T

2013-01-01

The primary goal of hybrid scenarios in tokamaks is to enable high performance operation with large plasma currents whilst avoiding MHD instabilities. However, if a local minimum in the safety factor is allowed to approach unity, the energy required to overcome stabilizing magnetic field line bending is very small, and as a consequence, large MHD structures can be created, with typically dominant m = n = 1 helical component. If there is no exact q = 1 rational surface the essential character of these modes can be modelled assuming ideal nested magnetic flux surfaces. The methods used to characterize these structures include linear and non-linear ideal MHD stability calculations which evaluate the departure from an axisymmetric plasma state, and also equilibrium calculations using a 3D equilibrium code. While these approaches agree favourably for simulations of ITER relevant hybrid regimes in this paper, the relevance of the ideal MHD model itself is tested through empirical examination of helical states in MAST and TCV. While long lived modes in MAST do not have island structures, some of the continuous mode oscillations exhibited in high elongation experiments in TCV indicate that resistivity may play a role in further weakening the ability of the tokamak core to remain axisymmetric. The simulations and experiments consistently highlight the need to control the safety factor in hybrid scenarios planned for future fusion grade tokamaks such as ITER. (paper)

Structural details (kinks and non-alpha conformations) in transmembrane helices are intrahelically determined and can be predicted by sequence pattern descriptors.

Science.gov (United States)

Rigoutsos, Isidore; Riek, Peter; Graham, Robert M; Novotny, Jiri

2003-08-01

One of the promising methods of protein structure prediction involves the use of amino acid sequence-derived patterns. Here we report on the creation of non-degenerate motif descriptors derived through data mining of training sets of residues taken from the transmembrane-spanning segments of polytopic proteins. These residues correspond to short regions in which there is a deviation from the regular alpha-helical character (i.e. pi-helices, 3(10)-helices and kinks). A 'search engine' derived from these motif descriptors correctly identifies, and discriminates amongst instances of the above 'non-canonical' helical motifs contained in the SwissProt/TrEMBL database of protein primary structures. Our results suggest that deviations from alpha-helicity are encoded locally in sequence patterns only about 7-9 residues long and can be determined in silico directly from the amino acid sequence. Delineation of such variations in helical habit is critical to understanding the complex structure-function relationships of polytopic proteins and for drug discovery. The success of our current methodology foretells development of similar prediction tools capable of identifying other structural motifs from sequence alone. The method described here has been implemented and is available on the World Wide Web at http://cbcsrv.watson.ibm.com/Ttkw.html.

Electronic Band Structure of Helical Polyisocyanides.

Science.gov (United States)

Champagne, Benoît; Liégeois, Vincent; Fripiat, Joseph G; Harris, Frank E

2017-10-19

Restricted Hartree-Fock computations are reported for a methyl isocyanide polymer (repeating unit -C═N-CH 3 ), whose most stable conformation is expected to be a helical chain. The computations used a standard contracted Gaussian orbital set at the computational levels STO-3G, 3-21G, 6-31G, and 6-31G**, and studies were made for two line-group configurations motivated by earlier work and by studies of space-filling molecular models: (1) A structure of line-group symmetry L9 5 , containing a 9-fold screw axis with atoms displaced in the axial direction by 5/9 times the lattice constant, and (2) a structure of symmetry L4 1 that had been proposed, containing a 4-fold screw axis with translation by 1/4 of the lattice constant. Full use of the line-group symmetry was employed to cause most of the computational complexity to depend only on the size of the asymmetric repeating unit. Data reported include computed bond properties, atomic charge distribution, longitudinal polarizability, band structure, and the convoluted density of states. Most features of the description were found to be insensitive to the level of computational approximation. The work also illustrates the importance of exploiting line-group symmetry to extend the range of polymer structural problems that can be treated computationally.

Helical structures in vertically aligned dust particle chains in a complex plasma

Science.gov (United States)

Hyde, Truell W.; Kong, Jie; Matthews, Lorin S.

2013-05-01

Self-assembly of structures from vertically aligned, charged dust particle bundles within a glass box placed on the lower, powered electrode of a Gaseous Electronics Conference rf reference cell were produced and examined experimentally. Self-organized formation of one-dimensional vertical chains, two-dimensional zigzag structures, and three-dimensional helical structures of triangular, quadrangular, pentagonal, hexagonal, and heptagonal symmetries are shown to occur. System evolution is shown to progress from a one-dimensional chain structure, through a zigzag transition to a two-dimensional, spindlelike structure, and then to various three-dimensional, helical structures exhibiting multiple symmetries. Stable configurations are found to be dependent upon the system confinement, γ2=ω0h/ω0v2 (where ω0h,v are the horizontal and vertical dust resonance frequencies), the total number of particles within a bundle, and the rf power. For clusters having fixed numbers of particles, the rf power at which structural phase transitions occur is repeatable and exhibits no observable hysteresis. The critical conditions for these structural phase transitions as well as the basic symmetry exhibited by the one-, two-, and three-dimensional structures that subsequently develop are in good agreement with the theoretically predicted configurations of minimum energy determined employing molecular dynamics simulations for charged dust particles confined in a prolate, spheroidal potential as presented theoretically by Kamimura and Ishihara [Kamimura and Ishihara, Phys. Rev. EPLEEE81063-651X10.1103/PhysRevE.85.016406 85, 016406 (2012)].

Self-Assembling Peptide Surfactants A6K and A6D Adopt a-Helical Structures Useful for Membrane Protein Stabilization

Directory of Open Access Journals (Sweden)

Furen Zhuang

2011-10-01

Full Text Available Elucidation of membrane protein structures have been greatly hampered by difficulties in producing adequately large quantities of the functional protein and stabilizing them. A6D and A6K are promising solutions to the problem and have recently been used for the rapid production of membrane-bound G protein-coupled receptors (GPCRs. We propose that despite their short lengths, these peptides can adopt α-helical structures through interactions with micelles formed by the peptides themselves. These α-helices are then able to stabilize α-helical motifs which many membrane proteins contain. We also show that A6D and A6K can form β-sheets and appear as weak hydrogels at sufficiently high concentrations. Furthermore, A6D and A6K together in sodium dodecyl sulfate (SDS can form expected β-sheet structures via a surprising α-helical intermediate.

Stiffness versus architecture of single helical polyisocyanopeptides

NARCIS (Netherlands)

Buul, van A.M.; Schwartz, E.; Brocorens, P.; Koepf, M.; Beljonne, D.; Maan, J.C.; Christianen, P.C.M.; Kouwer, P.H.J.; Nolte, R.J.M.; Engelkamp, H.; Blank, K.; Rowan, A.E.

2013-01-01

Helical structures play a vital role in nature, offering mechanical rigidity, chirality and structural definition to biological systems. Little is known about the influence of the helical architecture on the intrinsic properties of polymers. Here, we offer an insight into the nano architecture of

Stochastic field line structures appearing in field line tracing calculations for a helical magnetic limiter on TORE SUPRA

International Nuclear Information System (INIS)

Fuchs, G.; Steffen, B.; Blenski, T.; Grosman, A.; Samain, A.

1985-05-01

The influence on the structure of the magnetic field of a tokamak produced by small helical currents flowing near the plasma in TORE SUPRA was investigated numerically by drawing Poincare plots. The current in the helical conductors, the pitch of the windings, the rotational transform and the plasma pressure have been varied. The topology of the magnetic field line structure is discussed in some detail and simple examples are given for illustration. (orig.)

Helicity in proton–proton elastic scattering and the spin structure of the pomeron

Directory of Open Access Journals (Sweden)

Carlo Ewerz

2016-12-01

Full Text Available We discuss different models for the spin structure of the nonperturbative pomeron: scalar, vector, and rank-2 symmetric tensor. The ratio of single-helicity-flip to helicity-conserving amplitudes in polarised high-energy proton–proton elastic scattering, known as the complex r5 parameter, is calculated for these models. We compare our results to experimental data from the STAR experiment. We show that the spin-0 (scalar pomeron model is clearly excluded by the data, while the vector pomeron is inconsistent with the rules of quantum field theory. The tensor pomeron is found to be perfectly consistent with the STAR data.

Beta-helical polymers from isocyanopeptides

NARCIS (Netherlands)

Cornelissen, J.J.L.M.; Donners, J.J.J.M.; Gelder, de R.; Graswinckel, W.S.; Metselaar, G.A.; Rowan, A.E.; Sommerdijk, N.A.J.M.; Nolte, R.J.M.

2001-01-01

Polymerization of isocyanopeptides results in the formation of high molecular mass polymers that fold in a proteinlike fashion to give helical strands in which the peptide chains are arranged in ß-sheets. The ß-helical polymers retain their structure in water and unfold in a cooperative process at

Assembly of alginate microfibers to form a helical structure using micromanipulation with a magnetic field

International Nuclear Information System (INIS)

Sun, Tao; Huang, Qiang; Shi, Qing; Wang, Huaping; Li, Pengyun; Fukuda, Toshio; Hu, Chengzhi; Nakajima, Masahiro

2016-01-01

Helical structures assembled using alginate microfibers have a promising spatial architecture mimicking in vivo vessels for culturing vascular cells. However, the helical structure can only be assembled at the macroscale, since a microassembly-based approach has not yet been developed. In this paper, we propose a magnetic-field-based micromanipulation method to fabricate a helical microstructure. By microfluidic spinning, alginate microfibers encapsulating magnetic nanoparticles are synthesized to enable the control of an electromagnetic needle (EMN). We developed a microrobotic system to actuate a micropipette to fix a free end of the microfiber, and then move the EMN to reel the microfiber around a micropillar. The motion of the EMN is guided using an upright microscope and a side-view camera. Because of the limitation of operation space, a spacer sleeve was designed to keep the tip of the EMN attracted to the microfiber, and simultaneously to keep the other part of the EMN isolated from the microfiber. To ensure the availability of the microfiber for continuously coiling, we enable the EMN tip to slide on the surface of the microfiber without changing the tensioning of the microfiber for positioning control. Furthermore, stable and repeatable micromanipulation was achieved to form multi-turn microfiber coils based on the motion planning of the EMN. Finally, we successfully fabricated a helical microstructure that can be applied in vascular tissue engineering in the future. (paper)

General architecture of the alpha-helical globule.

Science.gov (United States)

Murzin, A G; Finkelstein, A V

1988-12-05

A model is presented for the arrangement of alpha-helices in globular proteins. In the model, helices are placed on certain ribs of "quasi-spherical" polyhedra. The polyhedra are chosen so as to allow the close packing of helices around a hydrophobic core and to stress the collective interactions of the individual helices. The model predicts a small set of stable architectures for alpha-helices in globular proteins and describes the geometries of the helix packings. Some of the predicted helix arrangements have already been observed in known protein structures; others are new. An analysis of the three-dimensional structures of all proteins for which co-ordinates are available shows that the model closely approximates the arrangements and packing of helices actually observed. The average deviations of the real helix axes from those in the model polyhedra is +/- 20 degrees in orientation and +/- 2 A in position (1 A = 0.1 nm). We also show that for proteins that are not homologous, but whose helix arrangements are described by the same polyhedron, the root-mean-square difference in the position of the C alpha atoms in the helices is 1.6 to 3.0 A.

Structural details (kinks and non-α conformations) in transmembrane helices are intrahelically determined and can be predicted by sequence pattern descriptors

Science.gov (United States)

Rigoutsos, Isidore; Riek, Peter; Graham, Robert M.; Novotny, Jiri

2003-01-01

One of the promising methods of protein structure prediction involves the use of amino acid sequence-derived patterns. Here we report on the creation of non-degenerate motif descriptors derived through data mining of training sets of residues taken from the transmembrane-spanning segments of polytopic proteins. These residues correspond to short regions in which there is a deviation from the regular α-helical character (i.e. π-helices, 310-helices and kinks). A ‘search engine’ derived from these motif descriptors correctly identifies, and discriminates amongst instances of the above ‘non-canonical’ helical motifs contained in the SwissProt/TrEMBL database of protein primary structures. Our results suggest that deviations from α-helicity are encoded locally in sequence patterns only about 7–9 residues long and can be determined in silico directly from the amino acid sequence. Delineation of such variations in helical habit is critical to understanding the complex structure–function relationships of polytopic proteins and for drug discovery. The success of our current methodology foretells development of similar prediction tools capable of identifying other structural motifs from sequence alone. The method described here has been implemented and is available on the World Wide Web at http://cbcsrv.watson.ibm.com/Ttkw.html. PMID:12888523

New helical-shape magnetic pole design for Magnetic Lead Screw enabling structure simplification

DEFF Research Database (Denmark)

Lu, Kaiyuan; Xia, Yongming; Wu, Weimin

2015-01-01

Magnetic lead screw (MLS) is a new type of high performance linear actuator that is attractive for many potential applications. The main difficulty of the MLS technology lies in the manufacturing of its complicated helical-shape magnetic poles. Structure simplification is, therefore, quite...

Cryogenic structural material and design of support structures for the Large Helical Device

International Nuclear Information System (INIS)

Nishimura, Arata; Imagawa, Shinsaku; Tamura, Hitoshi

1997-01-01

This paper describes a short history of material selection for the cryogenic support structures for the Large Helical Device (LHD) which has superconducting coils. Since the support structures are cooled down to 4.4 K together with the coils, SUS 316 was chosen because of its stable austenitic phase, sufficient mechanical properties at cryogenic temperature and good weldability. Also, outlines of the design and fabrication processes of the support structures are summarized. On the design of the support structures, a deformation analysis was carried out to maintain the proper magnetic field during operation. Afterwards, a stress analysis was performed. During machining and assembling, tolerance was noticed to keep coil positions accurate. Special welding grooves and fabrication processes were considered and achieved successfully. Finally, a cryogenic supporting post which sustains the cryogenic structures and superconducting coils is presented. CFRP was used in this specially developed supporting post to reduce the heat conduction from ambient 300 K structures. (author)

Light scattering measurements supporting helical structures for chromatin in solution.

Science.gov (United States)

Campbell, A M; Cotter, R I; Pardon, J F

1978-05-01

Laser light scattering measurements have been made on a series of polynucleosomes containing from 50 to 150 nucleosomes. Radii of gyration have been determined as a function of polynucleosome length for different ionic strength solutions. The results suggest that at low ionic strength the chromatin adopts a loosely helical structure rather than a random coil. The helix becomes more regular on increasing the ionic strength, the dimension resembling those proposed by Finch and Klug for their solenoid model.

Helicity-flip in particle production on nuclei

International Nuclear Information System (INIS)

Faeldt, G.

1977-01-01

Coherent nuclear production processes are generally analyzed assuming helicity conserving production amplitudes. In view of the uncertainties of the actual helicity structure this could be a dangerous assumption. It is shown that helicity-flip contributions might be part of the explanation of the small effective (pππ)-nucleon cross sections observed in coherent production. (Auth.)

Fifty years of coiled-coils and alpha-helical bundles: a close relationship between sequence and structure.

Science.gov (United States)

Parry, David A D; Fraser, R D Bruce; Squire, John M

2008-09-01

alpha-Helical coiled coils are remarkable for the diversity of related conformations that they adopt in both fibrous and globular proteins, and for the range of functions that they exhibit. The coiled coils are based on a heptad (7-residue), hendecad (11-residue) or a related quasi-repeat of apolar residues in the sequences of the alpha-helical regions involved. Most of these, however, display one or more sequence discontinuities known as stutters or stammers. The resulting coiled coils vary in length, in the number of chains participating, in the relative polarity of the contributing alpha-helical regions (parallel or antiparallel), and in the pitch length and handedness of the supercoil (left- or right-handed). Functionally, the concept that a coiled coil can act only as a static rod is no longer valid, and the range of roles that these structures have now been shown to exhibit has expanded rapidly in recent years. An important development has been the recognition that the delightful simplicity that exists between sequence and structure, and between structure and function, allows coiled coils with specialized features to be designed de novo.

Polarization Selectivity of Artificial Anisotropic Structures Based on DNA-Like Helices

International Nuclear Information System (INIS)

Semchenko, I. V.; Khakhomov, S. A.; Balmakov, A. P.

2010-01-01

Currently, 2D and 3D structures of different symmetries can be formed from DNA molecules. The electromagnetic properties of this new natural chiral material can be changed by metalizing DNA. Spatial structures of this type can be used in nanotechnology to prepare metamaterials for the far-UV region. It is shown by the example of an octahedron and a cube composed of DNA-like helices that these structures may exhibit polarization selectivity to electromagnetic radiation. In addition, it is suggested that the effect of the polarization selectivity of DNA-like artificial structures may also occur in the soft X-ray region for all living organisms in nature due to the universal DNA form.

ICRF heating on helical devices

International Nuclear Information System (INIS)

Rasmussen, D.A.; Lyon, J.F.; Hoffman, D.J.; Murakami, M.; England, A.C.; Wilgen, J.B.; Jaeger, E.F.; Wang, C.; Batchelor, D.B.

1995-01-01

Ion cyclotron range of frequency (ICRF) heating is currently in use on CHS and W7-AS and is a major element of the heating planned for steady state helical devices. In helical devices, the lack of a toroidal current eliminates both disruptions and the need for ICRF current drive, simplifying the design of antenna structures as compared to tokamak applications. However the survivability of plasma facing components and steady state cooling issues are directly applicable to tokamak devices. Results from LHD steady state experiments should be available on a time scale to strongly influence the next generation of steady state tokamak experiments. The helical plasma geometry provides challenges not faced with tokamak ICRF heating, including the potential for enhanced fast ion losses, impurity accumulation, limited access for antenna structures, and open magnetic field lines in the plasma edge. The present results and near term plans provide the basis for steady state ICRF heating of larger helical devices. An approach which includes direct electron, mode conversion, ion minority and ion Bernstein wave heating addresses these issues

ICRF heating on helical devices

International Nuclear Information System (INIS)

Rasmussen, D.A.; Lyon, J.F.; Hoffman, D.J.

1995-01-01

Ion cyclotron range of frequency (ICRF) heating is currently in use on CHS and W7AS and is a major element of the heating planned for steady state helical devices. In helical devices, the lack of a toroidal current eliminates both disruptions and the need for ICRF current drive, simplifying the design of antenna structures as compared to tokamak applications. However the survivability of plasma facing components and steady state cooling issues are directly applicable to tokamak devices. Results from LHD steady state experiments should be available on a time scale to strongly influence the next generation of steady state tokamak experiments. The helical plasma geometry provides challenges not faced with tokamak ICRF heating, including the potential for enhanced fast ion losses, impurity accumulation, limited access for antenna structures, and open magnetic field lines in the plasma edge. The present results and near term plans provide the basis for steady state ICRF heating of larger helical devices. An approach which includes direct electron, mode conversion, ion minority and ion Bernstein wave heating addresses these issues

Stimuli-Directed Helical Chirality Inversion and Bio-Applications

Directory of Open Access Journals (Sweden)

Ziyu Lv

2016-08-01

Full Text Available Helical structure is a sophisticated ubiquitous motif found in nature, in artificial polymers, and in supramolecular assemblies from microscopic to macroscopic points of view. Significant progress has been made in the synthesis and structural elucidation of helical polymers, nevertheless, a new direction for helical polymeric materials, is how to design smart systems with controllable helical chirality, and further use them to develop chiral functional materials and promote their applications in biology, biochemistry, medicine, and nanotechnology fields. This review summarizes the recent progress in the development of high-performance systems with tunable helical chirality on receiving external stimuli and discusses advances in their applications as drug delivery vesicles, sensors, molecular switches, and liquid crystals. Challenges and opportunities in this emerging area are also presented in the conclusion.

Helical Antimicrobial Sulfono- {gamma} -AApeptides

Energy Technology Data Exchange (ETDEWEB)

Li, Yaqiong; Wu, Haifan; Teng, Peng; Bai, Ge; Lin, Xiaoyang; Zuo, Xiaobing; Cao, Chuanhai; Cai, Jianfeng

2015-06-11

Host-defense peptides (HDPs) such as magainin 2 have emerged as potential therapeutic agents combating antibiotic resistance. Inspired by their structures and mechanism of action, herein we report the fi rst example of antimicrobial helical sulfono- γ - AApeptide foldamers. The lead molecule displays broad-spectrum and potent antimicrobial activity against multi-drug-resistant Gram- positive and Gram-negative bacterial pathogens. Time-kill studies and fl uorescence microscopy suggest that sulfono- γ -AApeptides eradicate bacteria by taking a mode of action analogous to that of HDPs. Clear structure - function relationships exist in the studied sequences. Longer sequences, presumably adopting more-de fi ned helical structures, are more potent than shorter ones. Interestingly, the sequence with less helical propensity in solution could be more selective than the stronger helix-forming sequences. Moreover, this class of antimicrobial agents are resistant to proteolytic degradation. These results may lead to the development of a new class of antimicrobial foldamers combating emerging antibiotic-resistant pathogens.

Helical Confinement Concepts

Energy Technology Data Exchange (ETDEWEB)

Beidler, C; Brakel, R; Burhenn, R; Dinklage, A; Erckmann, V; Feng, Y; Geiger, J; Hartmann, D; Hirsch, M; Jaenicke, R; Koenig, R; Laqua, H P; Maassberg, H; Wagner, F; Weller, A; Wobig, H [Max-Planck Institut fuer Plasmaphysik, EURATOM Association, Greifswald (Germany)

2012-09-15

Stellarators, conceived 1951 by Lyman Spitzer in Princeton, are toroidal devices that confine a plasma in a magnetic field which originates from currents in coils outside the plasma. A plasma current driven by external means, for example by an ohmic transformer, is not required for confinement. Supplying the desired poloidal field component by external coils leads to a helically structured plasma topology. Thus stellarators - or helical confinement devices - are fully three-dimensional in contrast to the toroidal (rotational) symmetry of tokamaks. As stellarators can be free of an inductive current, whose radial distribution depends on the plasma parameters, their equilibrium must not be established via the evolving plasma itself, but to a first order already given by the vacuum magnetic field. They do not need an active control (like positional feedback) and therefore cannot suffer from its failure. The outstanding conceptual advantage of stellarators is the potential of steady state plasma operation without current drive. As there is no need for current drive, the recirculating power is expected to be smaller than in equivalent tokamaks. The lack of a net current avoids current driven instabilities; specifically, no disruptions, no resistive wall modes and no conventional or neoclassical tearing modes appear. Second order pressure-driven currents (Pfirsch-Schlueter, bootstrap) exist but they can be modified and even minimized by the magnetic design. The magnetic configuration of helical devices naturally possesses a separatrix, which allows the implementation of a helically structured divertor for exhaust and impurity control. (author)

Integrated Structural Biology for α-Helical Membrane Protein Structure Determination.

Science.gov (United States)

Xia, Yan; Fischer, Axel W; Teixeira, Pedro; Weiner, Brian; Meiler, Jens

2018-04-03

While great progress has been made, only 10% of the nearly 1,000 integral, α-helical, multi-span membrane protein families are represented by at least one experimentally determined structure in the PDB. Previously, we developed the algorithm BCL::MP-Fold, which samples the large conformational space of membrane proteins de novo by assembling predicted secondary structure elements guided by knowledge-based potentials. Here, we present a case study of rhodopsin fold determination by integrating sparse and/or low-resolution restraints from multiple experimental techniques including electron microscopy, electron paramagnetic resonance spectroscopy, and nuclear magnetic resonance spectroscopy. Simultaneous incorporation of orthogonal experimental restraints not only significantly improved the sampling accuracy but also allowed identification of the correct fold, which is demonstrated by a protein size-normalized transmembrane root-mean-square deviation as low as 1.2 Å. The protocol developed in this case study can be used for the determination of unknown membrane protein folds when limited experimental restraints are available. Copyright © 2018 Elsevier Ltd. All rights reserved.

Energy landscape, structure and rate effects on strength properties of alpha-helical proteins

International Nuclear Information System (INIS)

Bertaud, Jeremie; Hester, Joshua; Jimenez, Daniel D; Buehler, Markus J

2010-01-01

The strength of protein domains is crucial to identify the mechanical role of protein domains in biological processes such as mechanotransduction, tissue mechanics and tissue remodeling. Whereas the concept of strength has been widely investigated for engineered materials, the strength of fundamental protein material building blocks and how it depends on structural parameters such as the chemical bonding, the protein filament length and the timescale of observation or deformation velocity remains poorly understood. Here we report a systematic analysis of the influence of key parameters that define the energy landscape of the strength properties of alpha-helical protein domains, including energy barriers, unfolding and refolding distances, the locations of folded and unfolded states, as well as variations of the length and pulling velocity of alpha-helical protein filaments. The analysis is facilitated by the development of a double-well mesoscale potential formulation, utilized here to carry out a systematic numerical analysis of the behavior of alpha-helices. We compare the results against widely used protein strength models based on the Bell model, one of the simplest models used to characterize the strength of protein filaments. We find that, whereas Bell-type models are a reasonable approximation to describe the rupture of alpha-helical protein domains for a certain range of pulling speeds and values of energy barriers, the model ceases to hold for very large energy barriers and for very small pulling speeds, in agreement with earlier findings. We conclude with an application of our mesoscale model to investigate the effect of the length of alpha-helices on their mechanical strength. We find a weakening effect as the length of alpha-helical proteins increases, followed by an asymptotic regime in which the strength remains constant. We compare strand lengths found in biological proteins with the scaling law of strength versus alpha-helix filament length. The

Phase diagram of structure of radial electric field in helical plasmas

International Nuclear Information System (INIS)

Toda, S.; Itoh, K.

2002-01-01

A set of transport equations in toroidal helical plasmas is analyzed, including the bifurcation of the radial electric field. Multiple solutions of E r for the ambipolar condition induces domains of different electric polarities. A structure of the domain interface is analyzed and a phase diagram is obtained in the space of the external control parameters. The region of the reduction of the anomalous transport is identified. (author)

Helicity and Filament Channels? The Straight Twist!

Science.gov (United States)

Antiochos, Spiro K.

2010-01-01

One of the most important and most puzzling features of the coronal magnetic field is that it appears to have smooth magnetic structure with little evidence for non-potentiality except at special locations, photospheric polarity inversions lines where the non-potentiality is observed as a filament channel. This characteristic feature of the closed-field corona is highly unexpected given that photospheric motions continuously tangle its magnetic field. Although reconnection can eliminate some of the injected structure, it cannot destroy the helicity, which should build up to produce observable complexity. We propose that an inverse cascade process transports the injected helicity from the interior of closed flux regions to their boundaries, polarity inversion lines, creating filament channels. We describe how the helicity is injected and transported and calculate the relevant rates. We argue that one process, helicity transport, can explain both the observed lack and presence of structure in the coronal magnetic field.

Stable single helical C- and I-chains inside single-walled carbon nanotubes

International Nuclear Information System (INIS)

Yao Z; Li Y; Jing X D; Meng F S; Zhao X; Li J H; Qiu Z Y; Yuan Q; Wang W X; Bi L; Liu H; Zhang Y P; Liu C J; Zheng S P; Liu B B

2016-01-01

The helicity of stable single helical carbon chains and iodine chains inside single-walled carbon nanotubes (SWCNTs) is studied by calculating the systematic van der Waals interaction energy. The results show that the optimal helical radius increases linearly with increasing tube radius, which produces a constant separation between the chain structure and the tube wall. The helical angle exhibits a ladder-like decrease with increasing tube radius, indicating that a large tube can produce a small helicity in the helical structures. (paper)

Structural analysis of compression helical spring used in suspension system

Science.gov (United States)

Jain, Akshat; Misra, Sheelam; Jindal, Arun; Lakhian, Prateek

2017-07-01

The main aim of this work has to develop a helical spring for shock absorber used in suspension system which is designed to reduce shock impulse and liberate kinetic energy. In a vehicle, it increases comfort by decreasing amplitude of disturbances and it improves ride quality by absorbing and dissipating energy. When a vehicle is in motion on a road and strikes a bump, spring comes into action quickly. After compression, spring will attempt to come to its equilibrium state which is on level road. Helical springs can be made lighter with more strength by reducing number of coils and increasing the area. In this research work, a helical spring is modeled and analyzed to substitute the existing steel spring which is used in suspension. By using different materials, stress and deflection of helical spring can be varied. Comparability between existing spring and newly replaced spring is used to verify the results. For finding detailed stress distribution, finite element analysis is used to find stresses and deflection in both the helical springs. Finite element analysis is a method which is used to find proximate solutions of a physical problem defined in a finite domain. In this research work, modeling of spring is accomplished using Solid Works and analysis on Ansys.

Synthesis, structure, and magnetic properties of two 1-D helical coordination polymeric Cu(II) complexes

Science.gov (United States)

Bian, He-Dong; Yang, Xiao-E.; Yu, Qing; Chen, Zi-Lu; Liang, Hong; Yan, Shi-Ping; Liao, Dai-Zheng

2008-01-01

Two helical coordination polymeric copper(II) complexes bearing amino acid Schiff bases HL or HL', which are condensed from 2-hydroxy-1-naphthaldehyde with 2-aminobenzoic acid or L-valine, respectively, have been prepared and characterised by X-ray crystallography. In [CuL] n ( 1) the copper(II) atoms are bridged by syn- anti carboxylate groups giving infinite 1-D right-handed helical chains which are further connected by weak C-H⋯Cu interactions to build a 2-D network. While in [CuL'] n ( 2) the carboxylate group acts as a rare monatomic bridge to connect the adjacent copper(II) atoms leading to the formation of a left-handed helical chain. Magnetic susceptibility measurements indicate that 1 exhibits weak ferromagnetic interactions whereas an antiferromagnetic coupling is established for 2. The magnetic behavior can be satisfactorily explained on the basis of the structural data.

Helical filaments

Energy Technology Data Exchange (ETDEWEB)

Barbieri, Nicholas; Lim, Khan; Durand, Magali; Baudelet, Matthieu; Richardson, Martin [Townes Laser Institute, CREOL—The College of Optics and Photonics, University of Central Florida, Orlando, Florida 32816 (United States); Hosseinimakarem, Zahra; Johnson, Eric [Micro-Photonics Laboratory – Center for Optical Material Science, Clemson, Anderson, South Carolina 29634 (United States)

2014-06-30

The shaping of laser-induced filamenting plasma channels into helical structures by guiding the process with a non-diffracting beam is demonstrated. This was achieved using a Bessel beam superposition to control the phase of an ultrafast laser beam possessing intensities sufficient to induce Kerr effect driven non-linear self-focusing. Several experimental methods were used to characterize the resulting beams and confirm the observed structures are laser air filaments.

Three-dimensional structure of a schistosome serpin revealing an unusual configuration of the helical subdomain

Energy Technology Data Exchange (ETDEWEB)

Granzin, Joachim [Institute of Complex Systems, ICS-6: Structural Biochemistry, Forschungszentrum Jülich, 52425 Jülich (Germany); Huang, Ying; Topbas, Celalettin [Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195 (United States); Huang, Wenying [Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195 (United States); Wu, Zhiping [Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195 (United States); Misra, Saurav [Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195 (United States); Hazen, Stanley L. [Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195 (United States); Blanton, Ronald E. [Department of Infectious Diseases, Case Western Reserve University, Cleveland, OH 44190 (United States); Lee, Xavier [Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195 (United States); Weiergräber, Oliver H., E-mail: o.h.weiergraeber@fz-juelich.de [Institute of Complex Systems, ICS-6: Structural Biochemistry, Forschungszentrum Jülich, 52425 Jülich (Germany)

2012-06-01

The crystal structure of ShSPI, a serpin from the blood fluke S. haematobium, reveals some peculiar features of the helical subdomain which have not been observed previously in the serpin superfamily. Parasitic organisms are constantly challenged by the defence mechanisms of their respective hosts, which often depend on serine protease activities. Consequently, protease inhibitors such as those belonging to the serpin superfamily have emerged as protective elements that support the survival of the parasites. This report describes the crystal structure of ShSPI, a serpin from the trematode Schistosoma haematobium. The protein is exposed on the surface of invading cercaria as well as of adult worms, suggesting its involvement in the parasite–host interaction. While generally conforming to the well established serpin fold, the structure reveals several distinctive features, mostly concerning the helical subdomain of the protein. It is proposed that these peculiarities are related to the unique biological properties of a small serpin subfamily which is conserved among pathogenic schistosomes.

Two unique ligand-binding clamps of Rhizopus oryzae starch binding domain for helical structure disruption of amylose.

Directory of Open Access Journals (Sweden)

Ting-Ying Jiang

Full Text Available The N-terminal starch binding domain of Rhizopus oryzae glucoamylase (RoSBD has a high binding affinity for raw starch. RoSBD has two ligand-binding sites, each containing a ligand-binding clamp: a polyN clamp residing near binding site I is unique in that it is expressed in only three members of carbohydrate binding module family 21 (CBM21 members, and a Y32/F58 clamp located at binding site II is conserved in several CBMs. Here we characterized different roles of these sites in the binding of insoluble and soluble starches using an amylose-iodine complex assay, atomic force microscopy, isothermal titration calorimetry, site-directed mutagenesis, and structural bioinformatics. RoSBD induced the release of iodine from the amylose helical cavity and disrupted the helical structure of amylose type III, thereby significantly diminishing the thickness and length of the amylose type III fibrils. A point mutation in the critical ligand-binding residues of sites I and II, however, reduced both the binding affinity and amylose helix disruption. This is the first molecular model for structure disruption of the amylose helix by a non-hydrolytic CBM21 member. RoSBD apparently twists the helical amylose strands apart to expose more ligand surface for further SBD binding. Repeating the process triggers the relaxation and unwinding of amylose helices to generate thinner and shorter amylose fibrils, which are more susceptible to hydrolysis by glucoamylase. This model aids in understanding the natural roles of CBMs in protein-glycan interactions and contributes to potential molecular engineering of CBMs.

In situ structure solution of helical sulphur at 3 GPa and 400 C

International Nuclear Information System (INIS)

Crichton, W.A.; Vaughan, G.B.M.; Mezouar, M.

2001-01-01

The structure of a 2-chain helical form of sulphur with 9 atoms per unit-cell has been determined from powder synchrotron X-ray diffraction data obtained at 3 GPa and 400 C, using a combination of global optimization, simulated annealing and Rietveld refinement techniques. Final refinement of the structure in trigonal space group P3 2 21 (no. 154) results in a = 7.0897(2) A, c = 4.30238(9) A and V = 187.282(10) A 3 . There are two unique S sites per unit cell, the general S1 6c position with x = 0.7727(9), y = 0.3067(11) and z = 0.6105(12) and the S2 3b with x = 0.8755(8) A. Bond length and angle analysis shows S1-S1 = 2.070(4) A and S2-S2 = 2.096(7) A with an helical S1-S1-S1 divalent angle of 102.7(2) and 101.7(3) for S2-S2-S2. The 2 helices formed, contrary to other polymeric sulphur phases (principally, ψ-S), are non-chiral and evidently have repeats along the (001) translation; that is one turn includes each of the 3 equivalent atoms about the 3 2 -screw axis (S1 helix) and vertex (S2) of the cell. This phase, although temperature quenchable, is observed to back transform to a 4.04 A phase at pressures less than 0.5 GPa. It is likely that this phase represents the true form of the phase XII of Vezzoli and Walsh. (orig.)

Helicity content and tokamak applications of helicity

International Nuclear Information System (INIS)

Boozer, A.H.

1986-05-01

Magnetic helicity is approximately conserved by the turbulence associated with resistive instabilities of plasmas. To generalize the application of the concept of helicity, the helicity content of an arbitrary bounded region of space will be defined. The definition has the virtues that both the helicity content and its time derivative have simple expressions in terms of the poloidal and toroidal magnetic fluxes, the average toroidal loop voltage and the electric potential on the bounding surface, and the volume integral of E-B. The application of the helicity concept to tokamak plasmas is illustrated by a discussion of so-called MHD current drive, an example of a stable tokamak q profile with q less than one in the center, and a discussion of the possibility of a natural steady-state tokamak due to the bootstrap current coupling to tearing instabilities

Signs of helicity in solar prominences and related features

Science.gov (United States)

Martin, S.

This review illustrates several ways to identify the chirality (handedness) of solar prominences (filaments) from their structure and the structure of their surrounding magnetic fields in the chromosphere and corona. For prominences, these structural elements include the axial magnetic field direction, orientation of barbs, and direction of the prominence fine structure. The surrounding structures include the pattern of fibrils beneath the prominences and the pattern of coronal loops above the prominences. These ways of identifying chirality are then interpreted in terms of the formal definitions of helicity to yield a consistent set of one-to-one helicity relationships for all features. The helicity of some prominences can also be independently determined during their eruption by their fine structure, apparent crossings in the line-of-sight of different parts of the same prominence, and by large- scale twist of the prominence structure. Unlike observations of prominences (filaments) observed prior to eruption, in some cases evidence of both signs of helicity are found within the same erupting prominence. This indicates the continued application of forces on the prominences during the eruption process or the possible introduction of force(s) not present during earlier stages of their evolution.

Syntheses, structures and luminescence properties of lanthanide coordination polymers with helical character

International Nuclear Information System (INIS)

Zhou Ruisha; Cui Xiaobing; Song Jiangfeng; Xu Xiaoyu; Xu Jiqing; Wang Tiegang

2008-01-01

A series of lanthanide coordination polymers, (Him) n [Ln(ip) 2 (H 2 O)] n [Ln=La(1), Pr(2), Nd(3) and Dy(4), H 2 ip=isophthalic acid, im=imidazole] and [Y 2 (ip) 3 (H 2 O) 2 ] n .nH 2 O (5), have been synthesized and characterized by elemental analyses, infrared (IR), ultraviolet-visible-near infrared (UV-Vis-NIR) and single-crystal X-ray diffraction analyses. The isostructural compounds 1-4 possess 3-D structures with three different kinds of channels. Compound 5 features a 2-D network making of two different kinds of quadruple-helical chains. Compounds 2 and 3 present the characteristic emissions of Pr(III) and Nd(III) ions in NIR region, respectively. Compound 4 shows sensitized luminescence of Dy(III) ions in visible region. - Graphical abstract: A series of lanthanide coodination polymers, (Him) n [Ln(ip) 2 (H 2 O)] n [Ln=La(1), Pr(2), Nd(3) and Dy(4)] and [Y 2 (ip) 3 (H 2 O) 2 ] n .nH 2 O (5), have been reported. The isostructural compounds 1-4 possess 3-D structures with three different kinds of channels. Compound 5 displays a 2-D network making of two kinds of quadruple-helical chains. Display Omitted

Circularly-polarized, semitransparent and double-sided holograms based on helical photonic structures.

Science.gov (United States)

Kobashi, Junji; Yoshida, Hiroyuki; Ozaki, Masanori

2017-11-28

Recent advances in nanofabrication techniques are opening new frontiers in holographic devices, with the capability to integrate various optical functions in a single device. However, while most efficient holograms are achieved in reflection-mode configurations, they are in general opaque because of the reflective substrate that must be used, and therefore, have limited applicability. Here, we present a semi-transparent, reflective computer-generated hologram that is circularly-polarization dependent, and reconstructs different wavefronts when viewed from different sides. The integrated functionality is realized using a single thin-film of liquid crystal with a self-organized helical structure that Bragg reflects circularly-polarized light over a certain band of wavelengths. Asymmetry depending on the viewing side is achieved by exploiting the limited penetration depth of light in the helical structure as well as the nature of liquid crystals to conform to different orientational patterns imprinted on the two substrates sandwiching the material. Also, because the operation wavelength is determined by the reflection band position, pseudo-color holograms can be made by simply stacking layers with different designs. The unique characteristics of this hologram may find applications in polarization-encoded security holograms and see-through holographic signage where different information need to be displayed depending on the viewing direction.

Crystal structures and thermodynamics/kinetics of Zn(II) coordination polymers with helical chains

Energy Technology Data Exchange (ETDEWEB)

He, Tian [Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710069 (China); Yue, Ke-Fen, E-mail: ykflyy@nwu.edu.cn [Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710069 (China); Zhao, Yi-xing; Chen, San-Ping [Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710069 (China); Zhou, Chun-sheng, E-mail: slzhoucs@126.com.cn [Shaanxi Key Laboratory of Comprehensive Utilization of Tailings Resources, College of Chemical Engineering and Modern Materials, Shangluo University, Shangluo 726000 (China); Yan, Ni [Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710069 (China)

2016-07-15

Solvothermal reactions of Zn(II) acetates and four V-shaped carboxylates ligands in the presence of 1,4-Bis(2-methyl-imidazol-1-yl)butane afforded four interesting Zn(II) coordination polymers with helical chains, namely, {[Zn(bib)(atibdc)]·2H_2O}{sub n} (1), {[Zn(bib)(atbip)]·H_2O}{sub n} (2), {[Zn(bib)(2,2′-tda)]}{sub n} (3) and {[Zn(bib)(5-tbipa)]·EtOH}{sub n} (4), (H{sub 2}atibdc=5-amino-2,4,6-triiodoisophthalic acid, H{sub 2}atbip=5-amino-2,4,6-tribromoisophthalic acid, 2,2′-H{sub 2}tad=2,2′-thiodiacetic acid, 5-H{sub 2}tbipa=5-tert-butyl-isophthalic acid). 1 reveals a 3D chiral framework with three kinds of helical chains along a, b and c axis. 2 shows a 2D step-type chiral framework with right-handed helical chains. 3 displays a wavelike 2D layer network possessing alternate left- and right-handed helical chains. 4 presents a four-connected 3D framework with zigzag and meso-helical chains. The different spacers and substituent group of carboxylic acid ligands may lead to the diverse network structures of 1–4. The fluorescent properties of complexes 1−4 were studied. In addition, the thermal decompositions properties of 1–4 were investigated by simultaneous TG/DTG–DSC technique. The apparent activation energy E and the pre-exponential factor (A) of skeleton collapse for the complexes 1–4 are calculated by the integral Kissinger's method and Ozawa–Doyle's method. The activation energy E (E{sub 1}=209.658 kJ·mol{sup −1}, E{sub 2}=250.037 kJ mol{sup −1}, E{sub 3}=225.300 kJ mol{sup −1}, E{sub 4}=186.529 kJ·mol{sup −1}) demonstrates that the reaction rate of the melting decomposition is slow. The thermodynamic parameters (ΔH{sup ‡}, ΔG{sup ‡} and ΔS{sup ‡}) at the peak temperatures of the DTG curves were also calculated. ΔG{sup ‡}>0 indicates that the skeleton collapse is not spontaneous. ΔH{sub d}>0 suggests that the skeleton collapse is endothermic, corresponding to the intense endothermic peak of the DSC

In situ structure solution of helical sulphur at 3 GPa and 400 C

Energy Technology Data Exchange (ETDEWEB)

Crichton, W.A.; Vaughan, G.B.M.; Mezouar, M. [European Synchrotron Radiation Facility (ESRF), 38 - Grenoble (France)

2001-07-01

The structure of a 2-chain helical form of sulphur with 9 atoms per unit-cell has been determined from powder synchrotron X-ray diffraction data obtained at 3 GPa and 400 C, using a combination of global optimization, simulated annealing and Rietveld refinement techniques. Final refinement of the structure in trigonal space group P3{sub 2}21 (no. 154) results in a = 7.0897(2) A, c = 4.30238(9) A and V = 187.282(10) A{sup 3}. There are two unique S sites per unit cell, the general S1 6c position with x = 0.7727(9), y = 0.3067(11) and z = 0.6105(12) and the S2 3b with x = 0.8755(8) A. Bond length and angle analysis shows S1-S1 = 2.070(4) A and S2-S2 = 2.096(7) A with an helical S1-S1-S1 divalent angle of 102.7(2) and 101.7(3) for S2-S2-S2. The 2 helices formed, contrary to other polymeric sulphur phases (principally, {psi}-S), are non-chiral and evidently have repeats along the (001) translation; that is one turn includes each of the 3 equivalent atoms about the 3{sub 2}-screw axis (S1 helix) and vertex (S2) of the cell. This phase, although temperature quenchable, is observed to back transform to a 4.04 A phase at pressures less than 0.5 GPa. It is likely that this phase represents the true form of the phase XII of Vezzoli and Walsh. (orig.)

Structure-activity relationship study of Aib-containing amphipathic helical peptide-cyclic RGD conjugates as carriers for siRNA delivery.

Science.gov (United States)

Wada, Shun-Ichi; Takesada, Anna; Nagamura, Yurie; Sogabe, Eri; Ohki, Rieko; Hayashi, Junsuke; Urata, Hidehito

2017-12-15

The conjugation of Aib-containing amphipathic helical peptide with cyclo(-Arg-Gly-Asp-d-Phe-Cys-) (cRGDfC) at the C-terminus of the helix peptide (PI) has been reported to be useful for constructing a carrier for targeted siRNA delivery into cells. In order to explore structure-activity relationships for the development of potential carriers for siRNA delivery, we synthesized conjugates of Aib-containing amphipathic helical peptide with cRGDfC at the N-terminus (PII) and both the N- and C-termini (PIII) of the helical peptide. Furthermore, to examine the influence of PI helical chain length on siRNA delivery, truncated peptides containing 16 (PIV), 12 (PV), and 8 (PVI) amino acid residues at the N-terminus of the helical chain were synthesized. PII and PIII, as well as PI, could deliver anti-luciferase siRNA into cells to induce the knockdown of luciferase stably expressed in cells. In contrast, all of the truncated peptides were unlikely to transport siRNA into cells. Copyright © 2017 Elsevier Ltd. All rights reserved.

TRANSAT-- method for detecting the conserved helices of functional RNA structures, including transient, pseudo-knotted and alternative structures.

Science.gov (United States)

Wiebe, Nicholas J P; Meyer, Irmtraud M

2010-06-24

The prediction of functional RNA structures has attracted increased interest, as it allows us to study the potential functional roles of many genes. RNA structure prediction methods, however, assume that there is a unique functional RNA structure and also do not predict functional features required for in vivo folding. In order to understand how functional RNA structures form in vivo, we require sophisticated experiments or reliable prediction methods. So far, there exist only a few, experimentally validated transient RNA structures. On the computational side, there exist several computer programs which aim to predict the co-transcriptional folding pathway in vivo, but these make a range of simplifying assumptions and do not capture all features known to influence RNA folding in vivo. We want to investigate if evolutionarily related RNA genes fold in a similar way in vivo. To this end, we have developed a new computational method, Transat, which detects conserved helices of high statistical significance. We introduce the method, present a comprehensive performance evaluation and show that Transat is able to predict the structural features of known reference structures including pseudo-knotted ones as well as those of known alternative structural configurations. Transat can also identify unstructured sub-sequences bound by other molecules and provides evidence for new helices which may define folding pathways, supporting the notion that homologous RNA sequence not only assume a similar reference RNA structure, but also fold similarly. Finally, we show that the structural features predicted by Transat differ from those assuming thermodynamic equilibrium. Unlike the existing methods for predicting folding pathways, our method works in a comparative way. This has the disadvantage of not being able to predict features as function of time, but has the considerable advantage of highlighting conserved features and of not requiring a detailed knowledge of the cellular

Helicity conservation under quantum reconnection of vortex rings.

Science.gov (United States)

Zuccher, Simone; Ricca, Renzo L

2015-12-01

Here we show that under quantum reconnection, simulated by using the three-dimensional Gross-Pitaevskii equation, self-helicity of a system of two interacting vortex rings remains conserved. By resolving the fine structure of the vortex cores, we demonstrate that the total length of the vortex system reaches a maximum at the reconnection time, while both writhe helicity and twist helicity remain separately unchanged throughout the process. Self-helicity is computed by two independent methods, and topological information is based on the extraction and analysis of geometric quantities such as writhe, total torsion, and intrinsic twist of the reconnecting vortex rings.

Continuous liquid level detection based on two parallel plastic optical fibers in a helical structure

Science.gov (United States)

Zhang, Yingzi; Hou, Yulong; Zhang, Yanjun; Hu, Yanjun; Zhang, Liang; Gao, Xiaolong; Zhang, Huixin; Liu, Wenyi

2018-02-01

A simple and low-cost continuous liquid-level sensor based on two parallel plastic optical fibers (POFs) in a helical structure is presented. The change in the liquid level is determined by measuring the side-coupling power in the passive fiber. The side-coupling ratio is increased by just filling the gap between the two POFs with ultraviolet-curable optical cement, making the proposed sensor competitive. The experimental results show that the side-coupling power declines as the liquid level rises. The sensitivity and the measurement range are flexible and affected by the geometric parameters of the helical structure. A higher sensitivity of 0.0208 μW/mm is acquired for a smaller curvature radius of 5 mm, and the measurement range can be expanded to 120 mm by enlarging the screw pitch to 40 mm. In addition, the reversibility and temperature dependence are studied. The proposed sensor is a cost-effective solution offering the advantages of a simple fabrication process, good reversibility, and compensable temperature dependence.

Godbillon Vey Helicity and Magnetic Helicity in Magnetohydrodynamics

Science.gov (United States)

Webb, G. M.; Hu, Q.; Anco, S.; Zank, G. P.

2017-12-01

The Godbillon-Vey invariant arises in homology theory, and algebraic topology, where conditions for a layered family of 2D surfaces forms a 3D manifold were elucidated. The magnetic Godbillon-Vey helicity invariant in magnetohydrodynamics (MHD) is a helicity invariant that occurs for flows, in which the magnetic helicity density hm= A\\cdotB=0 where A is the magnetic vector potential and B is the magnetic induction. Our purpose is to elucidate the evolution of the magnetic Godbillon-Vey field η =A×B/|A|2 and the Godbillon-Vey helicity hgv}= η \\cdot∇ × η in general MHD flows in which the magnetic helicity hm≠q 0. It is shown that hm acts as a source term in the Godbillon-Vey helicity transport equation, in which hm is coupled to hgv via the shear tensor of the background flow. The transport equation for hgv depends on the electric field potential ψ , which is related to the gauge for A, which takes its simplest form for the advected A gauge in which ψ =A\\cdot u where u is the fluid velocity.

Pressure effect on the amide I frequency of the solvated α-helical structure in water

International Nuclear Information System (INIS)

Takekiyo, T; Yoshimura, Y; Shimizu, A; Koizumi, T; Kato, M; Taniguchi, Y

2007-01-01

As a model system of the pressure dependence of the amide I mode of the solvated α-helical structure in a helical peptide, we have calculated the frequency shifts of the amide I modes as a function of the distance between trans-N-methylacetamide (t-NMA) dimer and a water molecule (d C=O···H-O ) by the density-functional theory (DFT) method at the B3LYP/6-31G++(d,p) level. Two amide I frequencies at 1652 and 1700 cm -1 were observed under this calculation. The former is ascribed to the amide I mode forming the intermolecular hydrogen bond (H-bond) between t-NMA and H 2 O in addition to the intermolecular H-bond in the t-NMA dimer. The latter is due to the amide I mode forming only the intermolecular H-bond in the t-NMA dimer. We have found that the amide I frequency at 1652 cm -1 shifts to a lower frequency with decreasing d C=O···H-O ) (i.e., increasing pressure), whereas that at 1700 cm -1 shifts to a higher frequency. The amide I frequency shift of 1652 cm -1 is larger than that of 1700 cm -1 by the intermolecular H-bond. Thus, our results clearly indicate that the pressure-induced amide I frequency shift of the solvated α-helical structure correlates with the change in d C=O···H-O )

Double-helical - ladder structural transition in the B-DNA is induced by a loss of dispersion energy

Czech Academy of Sciences Publication Activity Database

Černý, Jiří; Kabeláč, Martin; Hobza, Pavel

2008-01-01

Roč. 130, č. 47 (2008), s. 16055-16059 ISSN 0002-7863 R&D Projects: GA MŠk LC512; GA AV ČR IAA400550808 Institutional research plan: CEZ:AV0Z40550506 Keywords : B-DNA * double-helical structure * ladder-like structure Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 8.091, year: 2008

Buckwheat trypsin inhibitor with helical hairpin structure belongs to a new family of plant defence peptides.

Science.gov (United States)

Oparin, Peter B; Mineev, Konstantin S; Dunaevsky, Yakov E; Arseniev, Alexander S; Belozersky, Mikhail A; Grishin, Eugene V; Egorov, Tsezi A; Vassilevski, Alexander A

2012-08-15

A new peptide trypsin inhibitor named BWI-2c was obtained from buckwheat (Fagopyrum esculentum) seeds by sequential affinity, ion exchange and reversed-phase chromatography. The peptide was sequenced and found to contain 41 amino acid residues, with four cysteine residues involved in two intramolecular disulfide bonds. Recombinant BWI-2c identical to the natural peptide was produced in Escherichia coli in a form of a cleavable fusion with thioredoxin. The 3D (three-dimensional) structure of the peptide in solution was determined by NMR spectroscopy, revealing two antiparallel α-helices stapled by disulfide bonds. Together with VhTI, a trypsin inhibitor from veronica (Veronica hederifolia), BWI-2c represents a new family of protease inhibitors with an unusual α-helical hairpin fold. The linker sequence between the helices represents the so-called trypsin inhibitory loop responsible for direct binding to the active site of the enzyme that cleaves BWI-2c at the functionally important residue Arg(19). The inhibition constant was determined for BWI-2c against trypsin (1.7×10(-1)0 M), and the peptide was tested on other enzymes, including those from various insect digestive systems, revealing high selectivity to trypsin-like proteases. Structural similarity shared by BWI-2c, VhTI and several other plant defence peptides leads to the acknowledgement of a new widespread family of plant peptides termed α-hairpinins.

Polymorphic transformation of helical flagella of bacteria

Science.gov (United States)

Lim, Sookkyung; Howard Berg Collaboration; William Ko Collaboration; Yongsam Kim Collaboration; Wanho Lee Collaboration; Charles Peskin Collaboration

2016-11-01

Bacteria such as E. coli swim in an aqueous environment by utilizing the rotation of flagellar motors and alternate two modes of motility, runs and tumbles. Runs are steady forward swimming driven by bundles of flagellar filaments whose motors are turning CCW; tumbles involve a reorientation of the direction of swimming triggered by motor reversals. During tumbling, the helical flagellum undergoes polymorphic transformations, which is a local change in helical pitch, helical radius, and handedness. In this work, we investigate the underlying mechanism of structural conformation and how this polymorphic transition plays a role in bacterial swimming. National Science Foundation.

Influence of 63Ser phosphorylation and dephosphorylation on the structure of the stathmin helical nucleation sequence: a molecular dynamics study.

Science.gov (United States)

Missimer, John H; Steinmetz, Michel O; van Gunsteren, Wilfred F; Dolenc, Jožica

2012-10-23

Phosphorylation is an important mechanism regulating protein-protein interactions involving intrinsically disordered protein regions. Stathmin, an archetypical example of an intrinsically disordered protein, is a key regulator of microtubule dynamics in which phosphorylation of 63Ser within the helical nucleation sequence strongly down-regulates the tubulin binding and microtubule destabilizing activities of the protein. Experimental studies on a peptide encompassing the 19-residue helical nucleation sequence of stathmin (residues 55-73) indicate that phosphorylation of 63Ser destabilizes the peptide's secondary structure by disrupting the salt bridges supporting its helical conformation. In order to investigate this hypothesis at atomic resolution, we performed molecular dynamics simulations of nonphosphorylated and phosphorylated stathmin-[55-73] at room temperature and pressure, neutral pH, and explicit solvation using the recently released GROMOS force field 54A7. In the simulations of nonphosphorylated stathmin-[55-73] emerged salt bridges associated with helical configurations. In the simulations of 63Ser phosphorylated stathmin-[55-73] these configurations dispersed and were replaced by a proliferation of salt bridges yielding disordered configurations. The transformation of the salt bridges was accompanied by emergence of numerous interactions between main and side chains, involving notably the oxygen atoms of the phosphorylated 63Ser. The loss of helical structure induced by phosphorylation is reversible, however, as a final simulation showed. The results extend the hypothesis of salt bridge derangement suggested by experimental observations of the stathmin nucleation sequence, providing new insights into regulation of intrinsically disordered protein systems mediated by phosphorylation.

High-n helicity-induced shear Alfven eigenmodes

International Nuclear Information System (INIS)

Nakajima, N.; Cheng, C.Z.; Okamoto, M.

1992-05-01

The high-n Helicity-induced shear Alfven Eigenmodes (HAE) are considered both analytically and numerically for the straight helical magnetic system, where n is the toroidal mode number. The eigenmode equation for the high-n HAE modes is derived along the field line and with the aid of the averaging method is shown to reduce to the Mathieu equation asymptotically. The discrete HAE modes are shown to exist inside the continuum spectrum gaps. The continuous spectrum gaps appear around ω 2 = ω A 2 [N(lι-m)/2] 2 for N = 1,2,.., where ω A is the toroidal Alfven transit frequency, and l, m, and ι are the polarity of helical coils, the toroidal pitch number of helical coils, and the rotational transform, respectively. For the same ω A and ι, the frequency of the helical continuum gap is larger than that of the continuum gap in tokamak plasmas by |l-ι -1 m|. The polarity of helical coils l plays a crucial role in determining the spectrum gaps and the properties of the high-n HAE modes. The spectrum gaps near the magnetic axis are created by the helical ripple with circular flux surfaces for l = 1, and ≥ 3 helicals. For l = 2 helical systems, the spectrum gaps are created by the ellipticity of the flux surfaces. These analytical results for the continuum gaps and the existence of the high-n HAE modes in the continuum gaps are confirmed numerically for the l = 2 case, and we find that the HAE modes exist for mode structures with the even and the odd parities. (author)

A Lennard-Jones-like perspective on first order transitions in biological helices

DEFF Research Database (Denmark)

Oskolkov, Nikolay N.; Bohr, Jakob

2013-01-01

Helical structures with Lennard-Jones self-interactions are studied for optimal conformations. For this purpose, their self-energy is analyzed for extrema with respect to the geometric parameters of the helices. It is found that Lennard-Jones helices exhibit a first order phase transition from...

CHSalign: A Web Server That Builds upon Junction-Explorer and RNAJAG for Pairwise Alignment of RNA Secondary Structures with Coaxial Helical Stacking.

Directory of Open Access Journals (Sweden)

Lei Hua

Full Text Available RNA junctions are important structural elements of RNA molecules. They are formed when three or more helices come together in three-dimensional space. Recent studies have focused on the annotation and prediction of coaxial helical stacking (CHS motifs within junctions. Here we exploit such predictions to develop an efficient alignment tool to handle RNA secondary structures with CHS motifs. Specifically, we build upon our Junction-Explorer software for predicting coaxial stacking and RNAJAG for modelling junction topologies as tree graphs to incorporate constrained tree matching and dynamic programming algorithms into a new method, called CHSalign, for aligning the secondary structures of RNA molecules containing CHS motifs. Thus, CHSalign is intended to be an efficient alignment tool for RNAs containing similar junctions. Experimental results based on thousands of alignments demonstrate that CHSalign can align two RNA secondary structures containing CHS motifs more accurately than other RNA secondary structure alignment tools. CHSalign yields a high score when aligning two RNA secondary structures with similar CHS motifs or helical arrangement patterns, and a low score otherwise. This new method has been implemented in a web server, and the program is also made freely available, at http://bioinformatics.njit.edu/CHSalign/.

Design study of a normal conducting helical snake for AGS

CERN Document Server

Takano, Junpei; Okamura, Masahiro; Roser, Thomas; MacKay, William W; Luccio, Alfredo U; Takano, Koji

2004-01-01

A new normal conducting snake magnet is being fabricated for the Alternate Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL). In the Relativistic Heavy Ion Collider (RHIC) project, a superconducting type helical dipole magnets had been developed and it performed successfully in high-energy polarized proton acceleration. The new AGS helical snake has the same basic magnetic structure but is more complicated. To achieve no beam shift and no beam deflection in one magnetic device, helical pitches and rotating angles were carefully calculated. Compared to a superconducting magnet, a normal warm magnet must have a large cross- sectional area of conductors which make it difficult to design a magnet with large helical pitch. We developed a modified window frame structure to accommodate the large number of conductors. Its three dimensional magnetic field was simulated by using OPERA3D/TOSCA. 3 Refs.

Helicity, Reconnection, and Dynamo Effects

International Nuclear Information System (INIS)

Ji, Hantao

1998-01-01

The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo effects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly affects the reconnection rate, as well as the shape of the diffusion region. Conversely, magnetic reconnection events also strongly affect the global helicity, resulting in efficient helicity cancellation (but not dissipation) during counter-helicity reconnection and a finite helicity increase or decrease (but less efficiently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo effects. The turbulent electromotive force along the mean magnetic field (alpha-effect), due to either electrostatic turbulence or the electron diamagnetic effect, transports mean-field helicity across space without dissipation. This has been supported by direct measurements of helicity flux in a laboratory plasma. When the dynamo effect is driven by electromagnetic turbulence, helicity in the turbulent field is converted to mean-field helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery effect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation

Probing alpha-helical and beta-sheet structures of peptides at solid/liquid interfaces with SFG.

Science.gov (United States)

Chen, Xiaoyun; Wang, Jie; Sniadecki, Jason J; Even, Mark A; Chen, Zhan

2005-03-29

We demonstrated that sum frequency generation (SFG) vibrational spectroscopy can distinguish different secondary structures of proteins or peptides adsorbed at solid/liquid interfaces. The SFG spectrum for tachyplesin I at the polystyrene (PS)/solution interface has a fingerprint peak corresponding to the B1/B3 mode of the antiparallel beta-sheet. This peak disappeared upon the addition of dithiothreitol, which can disrupt the beta-sheet structure. The SFG spectrum indicative of the MSI594 alpha-helical structure was observed at the PS/MSI594 solution interface. This research validates SFG as a powerful technique for revealing detailed secondary structures of interfacial proteins and peptides.

Exploring biological effects of MoS2 nanosheets on native structures of α-helical peptides

International Nuclear Information System (INIS)

Gu, Zonglin; Li, Weifeng; Hong, Linbi; Zhou, Ruhong

2016-01-01

Recent reports of mono- and few-layer molybdenum disulfide (MoS 2 ), a representative transition metal dichacogenide (TMD), as antibacterial and anticancer agents have shed light on their potential in biomedical applications. To better facilitate these promising applications, one needs to understand the biological effects of these TMDs as well, such as their potential adverse effects on protein structure and function. Here, we sought to understand the interaction of MoS 2 nanosheets with peptides using molecular dynamics simulations and a simple model polyalanine with various lengths (PA n , n = 10, 20, 30, and 40; mainly α − helices). Our results demonstrated that MoS 2 monolayer has an exceptional capability to bind all peptides in a fast and strong manner. The strong attraction from the MoS 2 nanosheet is more than enough to compensate the energy needed to unfold the peptide, regardless of the length, which induces drastic disruptions to the intra-peptide hydrogen bonds and subsequent secondary structures of α − helices. This universal phenomenon may point to the potential nanotoxicity of MoS 2 when used in biological systems. Moreover, these results aligned well with previous findings on the potential cytotoxicity of TMD nanomaterials.

Helical modes generate antimagnetic rotational spectra in nuclei

Science.gov (United States)

Malik, Sham S.

2018-03-01

A systematic analysis of the antimagnetic rotation band using r -helicity formalism is carried out for the first time. The observed octupole correlation in a nucleus is likely to play a role in establishing the antimagnetic spectrum. Such octupole correlations are explained within the helical orbits. In a rotating field, two identical fermions (generally protons) with paired spins generate these helical orbits in such a way that its positive (i.e., up) spin along the axis of quantization refers to one helicity (right-handedness) while negative (down) spin along the same quantization-axis decides another helicity (left-handedness). Since the helicity remains invariant under rotation, therefore, the quantum state of a fermion is represented by definite angular momentum and helicity. These helicity represented states support a pear-shaped structure of a rotating system having z axis as the symmetry axis. A combined operation of parity, time-reversal, and signature symmetries ensures an absence of one of the signature partner band from the observed antimagnetic spectrum. This formalism has also been tested for the recently observed negative parity Δ I =2 antimagnetic spectrum in odd-A 101Pd nucleus and explains nicely its energy spectrum as well as the B (E 2 ) values. Further, this formalism is found to be fully consistent with twin-shears mechanism popularly known for such type of rotational bands. It also provides significant clue for extending these experiments in various mass regions spread over the nuclear chart.

Helical magnetized wiggler for synchrotron radiation laser

International Nuclear Information System (INIS)

Wang Mei; Park, S.Y.; Hirshfield, J.L.

1999-01-01

A helical magnetized iron wiggler has been built for a novel infrared synchrotron radiation laser (SRL) experiment. The wiggler consists of four periods of helical iron structure immersed in a solenoid field. This wiggler is to impart transverse velocity to a prebunched 6 MeV electron beam, and thus to obtain a desired high orbit pitch ratio for the SRL. Field tapering at beam entrance is considered and tested on a similar wiggler. Analytic and simulated characteristics of wigglers of this type are discussed and the performance of the fabricated wigglers is demonstrated experimentally. A 4.7 kG peak field was measured for a 6.4 mm air gap and a 5.4 cm wiggler period at a 20 kG solenoid field. The measured helical fields compare favorably with the analytical solution. This type of helical iron wigglers has the potential to be scaled to small periods with strong field amplitude

Helical magnetized wiggler for synchrotron radiation laser

CERN Document Server

Wang Mei; Hirshfield, J L

1999-01-01

A helical magnetized iron wiggler has been built for a novel infrared synchrotron radiation laser (SRL) experiment. The wiggler consists of four periods of helical iron structure immersed in a solenoid field. This wiggler is to impart transverse velocity to a prebunched 6 MeV electron beam, and thus to obtain a desired high orbit pitch ratio for the SRL. Field tapering at beam entrance is considered and tested on a similar wiggler. Analytic and simulated characteristics of wigglers of this type are discussed and the performance of the fabricated wigglers is demonstrated experimentally. A 4.7 kG peak field was measured for a 6.4 mm air gap and a 5.4 cm wiggler period at a 20 kG solenoid field. The measured helical fields compare favorably with the analytical solution. This type of helical iron wigglers has the potential to be scaled to small periods with strong field amplitude.

Examining the Conservation of Kinks in Alpha Helices.

Directory of Open Access Journals (Sweden)

Eleanor C Law

Full Text Available Kinks are a structural feature of alpha-helices and many are known to have functional roles. Kinks have previously tended to be defined in a binary fashion. In this paper we have deliberately moved towards defining them on a continuum, which given the unimodal distribution of kink angles is a better description. From this perspective, we examine the conservation of kinks in proteins. We find that kink angles are not generally a conserved property of homologs, pointing either to their not being functionally critical or to their function being related to conformational flexibility. In the latter case, the different structures of homologs are providing snapshots of different conformations. Sequence identity between homologous helices is informative in terms of kink conservation, but almost equally so is the sequence identity of residues in spatial proximity to the kink. In the specific case of proline, which is known to be prevalent in kinked helices, loss of a proline from a kinked helix often also results in the loss of a kink or reduction in its kink angle. We carried out a study of the seven transmembrane helices in the GPCR family and found that changes in kinks could be related both to subfamilies of GPCRs and also, in a particular subfamily, to the binding of agonists or antagonists. These results suggest conformational change upon receptor activation within the GPCR family. We also found correlation between kink angles in different helices, and the possibility of concerted motion could be investigated further by applying our method to molecular dynamics simulations. These observations reinforce the belief that helix kinks are key, functional, flexible points in structures.

Ruby-Helix: an implementation of helical image processing based on object-oriented scripting language.

Science.gov (United States)

Metlagel, Zoltan; Kikkawa, Yayoi S; Kikkawa, Masahide

2007-01-01

Helical image analysis in combination with electron microscopy has been used to study three-dimensional structures of various biological filaments or tubes, such as microtubules, actin filaments, and bacterial flagella. A number of packages have been developed to carry out helical image analysis. Some biological specimens, however, have a symmetry break (seam) in their three-dimensional structure, even though their subunits are mostly arranged in a helical manner. We refer to these objects as "asymmetric helices". All the existing packages are designed for helically symmetric specimens, and do not allow analysis of asymmetric helical objects, such as microtubules with seams. Here, we describe Ruby-Helix, a new set of programs for the analysis of "helical" objects with or without a seam. Ruby-Helix is built on top of the Ruby programming language and is the first implementation of asymmetric helical reconstruction for practical image analysis. It also allows easier and semi-automated analysis, performing iterative unbending and accurate determination of the repeat length. As a result, Ruby-Helix enables us to analyze motor-microtubule complexes with higher throughput to higher resolution.

Generation of uniform magnetic field using a spheroidal helical coil structure

International Nuclear Information System (INIS)

Öztürk, Yavuz; Aktaş, Bekir

2016-01-01

Uniformity of magnetic fields are of great importance especially in magnetic resonance studies, namely in magnetic resonance spectroscopy applications (NMR, FMR, ESR, EPR etc.) and magnetic resonance imaging applications (MRI, FMRI). Field uniformity is also required in some other applications such as eddy current probes, magnetometers, magnetic traps, particle counters etc. Here we proposed a coil winding regime, which follows the surface of a spheroid (an ellipsoid of rotation); in light of previous theoretical studies suggesting perfect uniformity for a constant ampere per turn in the axial direction thereof. We demonstrated our theoretical results from finite element calculations suggesting 0.15% of field uniformity for the proposed structure, which we called a Spheroidal Helical Coil. (paper)

Seismic analysis of a helical coil type heat exchanger

International Nuclear Information System (INIS)

Nishiguchi, I.; Baba, O.; Yatabe, H.

1984-01-01

The intermediate heat exchanger (IHX) which forms the reactor coolant pressure boundary is one of the most important components of the Multi-purpose Experimental Very High Temperature Gas-cooled Reactor (ex. VHTR) under development at Japan Atomic Energy Research Institute. This paper presents the results of the finite element modeling, eigenvalue analysis and dynamic response analysis of the IHX. For the modeling, the structure of the IHX was separated into a helical tube bundle, inner and outer vessels, and a center pipe. The eigenvalue analysis was made for each structure with a detailed three-dimensional finite element model. Then the simplified model of the whole structure of the IHX was constructed using the result of the eigenvalue analysis. A dynamic response analysis was made for the simplified model with and without stoppers of the helical tube bundle supports and the center pipe. The effect of stoppers on the behavior of the center pipe, the helical tube, and the connecting tube is discussed. (author)

Right-Handed Helical Foldamers Consisting of De Novo d -AApeptides

Energy Technology Data Exchange (ETDEWEB)

Teng, Peng; Ma, Ning; Cerrato, Darrell Cole; She, Fengyu; Odom, Timothy; Wang, Xiang; Ming, Li-June; van der Vaart, Arjan; Wojtas, Lukasz; Xu, Hai; Cai, Jianfeng

2017-05-16

New types of foldamer scaffolds are formidably challenging to design and synthesize, yet highly desirable as structural mimics of peptides/proteins with a wide repertoire of functions. In particular, the development of peptidomimetic helical foldamers holds promise for new biomaterials, catalysts, and drug molecules. Unnatural l-sulfono-γ-AApeptides were recently developed and shown to have potential applications in both biomedical and material sciences. However, d-sulfono-γ-AApeptides, the enantiomers of l-sulfono-γ-AApeptides, have never been studied due to the lack of high-resolution three-dimensional structures to guide structure-based design. Herein, we report the first synthesis and X-ray crystal structures of a series of 2:1 l-amino acid/d-sulfono-γ-AApeptide hybrid foldamers, and elucidate their folded conformation at the atomic level. Single-crystal X-ray crystallography indicates that this class of oligomers folds into well-defined right-handed helices with unique helical parameters. The helical structures were consistent with data obtained from solution 2D NMR, CD studies, and molecular dynamics simulations. Our findings are expected to inspire the structure-based design of this type of unique folding biopolymers for biomaterials and biomedical applications.

Helical type vacuum container

International Nuclear Information System (INIS)

Owada, Kimio.

1989-01-01

Helical type vacuum containers in the prior art lack in considerations for thermal expansion stresses to helical coils, and there is a possibility of coil ruptures. The object of the present invention is to avoid the rupture of helical coils wound around the outer surface of a vacuum container against heat expansion if any. That is, bellows or heat expansion absorbing means are disposed to a cross section of a helical type vacuum container. With such a constitution, thermal expansion of helical coils per se due to temperature elevation of the coils during electric supply can be absorbed by expansion of the bellows or absorption of the heat expansion absorbing means. Further, this can be attained by arranging shear pins in the direction perpendicular to the bellows axis so that the bellows are not distorted when the helical coils are wound around the helical type vacuum container. (I.S.)

Escherichia coli DnaA forms helical structures along the longitudinal cell axis distinct from MreB filaments.

Science.gov (United States)

Boeneman, Kelly; Fossum, Solveig; Yang, Yanhua; Fingland, Nicholas; Skarstad, Kirsten; Crooke, Elliott

2009-05-01

DnaA initiates chromosomal replication in Escherichia coli at a well-regulated time in the cell cycle. To determine how the spatial distribution of DnaA is related to the location of chromosomal replication and other cell cycle events, the localization of DnaA in living cells was visualized by confocal fluorescence microscopy. The gfp gene was randomly inserted into a dnaA-bearing plasmid via in vitro transposition to create a library that included internally GFP-tagged DnaA proteins. The library was screened for the ability to rescue dnaA(ts) mutants, and a candidate gfp-dnaA was used to replace the dnaA gene of wild-type cells. The resulting cells produce close to physiological levels of GFP-DnaA from the endogenous promoter as their only source of DnaA and somewhat under-initiate replication with moderate asynchrony. Visualization of GFP-tagged DnaA in living cells revealed that DnaA adopts a helical pattern that spirals along the long axis of the cell, a pattern also seen in wild-type cells by immunofluorescence with affinity purified anti-DnaA antibody. Although the DnaA helices closely resemble the helices of the actin analogue MreB, co-visualization of GFP-tagged DnaA and RFP-tagged MreB demonstrates that DnaA and MreB adopt discrete helical structures along the length of the longitudinal cell axis.

Improved particle confinement in transition from multiple-helicity to quasi-single-helicity regimes of a reversed-field pinch.

Science.gov (United States)

Frassinetti, L; Predebon, I; Koguchi, H; Yagi, Y; Hirano, Y; Sakakita, H; Spizzo, G; White, R B

2006-10-27

The quasi-single-helicity (QSH) state of a reversed-field pinch (RFP) plasma is a regime in which the RFP configuration can be sustained by a dynamo produced mainly by a single tearing mode and in which a helical structure with well-defined magnetic flux surfaces arises. In this Letter, we show that spontaneous transitions to the QSH regime enhance the particle confinement. This improvement is originated by the simultaneous and cooperative action of the increase of the magnetic island and the reduction of the magnetic stochasticity.

Conformal avoidance helical tomotherapy for dogs with nasopharyngeal tumors

International Nuclear Information System (INIS)

Welsh, J.S.; Turek, M.; Mackie, T.R.; Miller, P.; Mehta, M.P.; Forrest, L.J.

2003-01-01

Helical tomotherapy provides a unique means of delivering intensity-modulated radiation therapy (IMRT) using a novel treatment unit, which merges features of a linear accelerator with a helical CT scanner. Thanks to the CT imaging capacity, targeted regions can be visualized prior to, during, or immediately after each treatment. Such image-guidance through megavoltage CT will allow the realization and refinement of the concept of adaptive radiotherapy - the reconstruction of the actually delivered daily dose (as opposed to planned dose) accompanied by prescription adjustments when appropriate. In addition to this unique feature, helical tomotherapy promises further improvements in the specific avoidance of critical normal structures, i.e. conformal avoidance, the counterpart of conformal therapy. The first definitive treatment protocol using helical tomotherapy is presently underway for dogs with nasopharyngeal tumors. In general, such tumors can be treated with conventional external beam radiation therapy but at the cost of severe ocular toxicity due to the anatomy of the canine head. These are readily measurable toxicities and are almost universal in incidence; therefore, the canine nasopharyngeal tumor presents an ideal model to assess the ability to conformally avoid critical structures. It is hoped that conformal avoidance helical tomotherapy will improve tumor control via dose-escalation while reducing ocular toxicity in these veterinary patients. A total of 10 fractions are scheduled for these patients; the first 3 dogs have all received at least 7 fractions delivered via helical tomotherapy. Although preliminary, the first 3 dogs treated have not shown any evidence of ocular toxicity in this ongoing study

Designing self-standing silicon-copper composite helices as anodes for lithium ion batteries

International Nuclear Information System (INIS)

Polat, B.D.; Keles, O.

2016-01-01

In this study, we have fabricated helical thin films to be used as an anode material in lithium ion batteries (LIB). The thin films having various Cu−Si atomic ratios (30–70%, 20–80%, and 10–90%) are prepared by using ion-assisted glancing angle co-deposition. Cu plays a crucial role in holding the electrode together, minimizing overall capacity loss and enabling faster electron transfer thus, improving the electrochemical performances of the electrodes. Increasing the Cu/Si atomic ratio affects the structure of the helices and their alignment. Implementing ion assisted deposition at the beginning of the film deposition helps to improve film adhesion. The Si-20 at.% Cu anode delivers 1885 mAh g"−"1 initially with 98% coulombic efficiency and retains 77% of the capacity after 100 cycles at 100 mA g"−"1. - Highlights: • Highly adherent SiCu helices are deposited by ion assisted glancing angle deposition. • Cu content in the SiCu helices affects the helice' morphology and structure. • SiCu helices with different Cu contents have been used as anodes for LIB. • Helices being like microsprings, improve the mechanical resistance of the anode.

Manipulation of wavefront using helical metamaterials.

Science.gov (United States)

Yang, Zhenyu; Wang, Zhaokun; Tao, Huan; Zhao, Ming

2016-08-08

Helical metamaterials, a kind of 3-dimensional structure, has relatively strong coupling effect among the helical nano-wires. Therefore, it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. In this paper, using the finite-difference time-domain (FDTD) method, we studied the phase shift properties in the helical metamaterials. It is found that the phase shift occurs for both transmitted and reflected light waves. And the maximum of reflection coefficients can reach over 60%. In addition, the phase shift (φ) is dispersionless in the range of 600 nm to 860 nm, that is, it is only dominated by the initial angle (θ) of the helix. The relationship between them is φ = ± 2θ. Using Jones calculus we give a further explanation for these properties. Finally, by arranging the helixes in an array with a constant phase gradient, the phenomenon of anomalous refraction was also observed in a broad wavelength range.

Biot-Savart helicity versus physical helicity: A topological description of ideal flows

Science.gov (United States)

Sahihi, Taliya; Eshraghi, Homayoon

2014-08-01

For an isentropic (thus compressible) flow, fluid trajectories are considered as orbits of a family of one parameter, smooth, orientation-preserving, and nonsingular diffeomorphisms on a compact and smooth-boundary domain in the Euclidian 3-space which necessarily preserve a finite measure, later interpreted as the fluid mass. Under such diffeomorphisms the Biot-Savart helicity of the pushforward of a divergence-free and tangent to the boundary vector field is proved to be conserved and since these circumstances present an isentropic flow, the conservation of the "Biot-Savart helicity" is established for such flows. On the other hand, the well known helicity conservation in ideal flows which here we call it "physical helicity" is found to be an independent constant with respect to the Biot-Savart helicity. The difference between these two helicities reflects some topological features of the domain as well as the velocity and vorticity fields which is discussed and is shown for simply connected domains the two helicities coincide. The energy variation of the vorticity field is shown to be formally the same as for the incompressible flow obtained before. For fluid domains consisting of several disjoint solid tori, at each time, the harmonic knot subspace of smooth vector fields on the fluid domain is found to have two independent base sets with a special type of orthogonality between these two bases by which a topological description of the vortex and velocity fields depending on the helicity difference is achieved since this difference is shown to depend only on the harmonic knot parts of velocity, vorticity, and its Biot-Savart vector field. For an ideal magnetohydrodynamics (MHD) flow three independent constant helicities are reviewed while the helicity of magnetic potential is generalized for non-simply connected domains by inserting a special harmonic knot field in the dynamics of the magnetic potential. It is proved that the harmonic knot part of the vorticity

EVOLUTION OF MAGNETIC HELICITY AND ENERGY SPECTRA OF SOLAR ACTIVE REGIONS

International Nuclear Information System (INIS)

Zhang, Hongqi; Brandenburg, Axel; Sokoloff, D. D.

2016-01-01

We adopt an isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field to estimate the magnetic energy and helicity spectra as well as current helicity spectra of two individual active regions (NOAA 11158 and NOAA 11515) and the change of the spectral indices during their development as well as during the solar cycle. The departure of the spectral indices of magnetic energy and current helicity from 5/3 are analyzed, and it is found that it is lower than the spectral index of the magnetic energy spectrum. Furthermore, the fractional magnetic helicity tends to increase when the scale of the energy-carrying magnetic structures increases. The magnetic helicity of NOAA 11515 violates the expected hemispheric sign rule, which is interpreted as an effect of enhanced field strengths at scales larger than 30–60 Mm with opposite signs of helicity. This is consistent with the general cycle dependence, which shows that around the solar maximum the magnetic energy and helicity spectra are steeper, emphasizing the large-scale field

EVOLUTION OF MAGNETIC HELICITY AND ENERGY SPECTRA OF SOLAR ACTIVE REGIONS

Energy Technology Data Exchange (ETDEWEB)

Zhang, Hongqi [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Brandenburg, Axel [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden); Sokoloff, D. D., E-mail: hzhang@bao.ac.cn [Department of Physics, Moscow University, 119992 Moscow (Russian Federation)

2016-03-10

We adopt an isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field to estimate the magnetic energy and helicity spectra as well as current helicity spectra of two individual active regions (NOAA 11158 and NOAA 11515) and the change of the spectral indices during their development as well as during the solar cycle. The departure of the spectral indices of magnetic energy and current helicity from 5/3 are analyzed, and it is found that it is lower than the spectral index of the magnetic energy spectrum. Furthermore, the fractional magnetic helicity tends to increase when the scale of the energy-carrying magnetic structures increases. The magnetic helicity of NOAA 11515 violates the expected hemispheric sign rule, which is interpreted as an effect of enhanced field strengths at scales larger than 30–60 Mm with opposite signs of helicity. This is consistent with the general cycle dependence, which shows that around the solar maximum the magnetic energy and helicity spectra are steeper, emphasizing the large-scale field.

Turbulent Helicity in the Atmospheric Boundary Layer

Science.gov (United States)

Chkhetiani, Otto G.; Kurgansky, Michael V.; Vazaeva, Natalia V.

2018-05-01

We consider the assumption postulated by Deusebio and Lindborg (J Fluid Mech 755:654-671, 2014) that the helicity injected into the Ekman boundary layer undergoes a cascade, with preservation of its sign (right- or alternatively left-handedness), which is a signature of the system rotation, from large to small scales, down to the Kolmogorov microscale of turbulence. At the same time, recent direct field measurements of turbulent helicity in the steppe region of southern Russia near Tsimlyansk Reservoir show the opposite sign of helicity from that expected. A possible explanation for this phenomenon may be the joint action of different scales of atmospheric flows within the boundary layer, including the sea-breeze circulation over the test site. In this regard, we consider a superposition of the classic Ekman spiral solution and Prandtl's jet-like slope-wind profile to describe the planetary boundary-layer wind structure. The latter solution mimics a hydrostatic shallow breeze circulation over a non-uniformly heated surface. A 180°-wide sector on the hodograph plane exists, within which the relative orientation of the Ekman and Prandtl velocity profiles favours the left rotation with height of the resulting wind velocity vector in the lowermost part of the boundary layer. This explains the negative (left-handed) helicity cascade toward small-scale turbulent motions, which agrees with the direct field measurements of turbulent helicity in Tsimlyansk. A simple turbulent relaxation model is proposed that explains the measured positive values of the relatively minor contribution to turbulent helicity from the vertical components of velocity and vorticity.

Experimental measurement of fluid force coefficients for helical tube arrays in air cross flow

International Nuclear Information System (INIS)

Shen Shifang; Liu Reilan

1993-01-01

A helical coil steam generator is extensively used in the High Temperature Gas Cooled Reactor (HTGCR) and Sodium Cooled Reactor (SCR) nuclear power stations because of its compact structure, good heat-exchange, and small volume. The experimental model is established by the structure parameter of 200MW HTGCR. The fluid elastic instability of helical tube arrays in air cross flow is studied in this experiment, and the fluid force coefficients of helical tube arrays having the same notational direction of two adjacent layers in air cross flow are obtained. As compared to the fluid force coefficients of cylinder tube arrays, the fluid force coefficients of helical tube arrays are smaller in the low velocity area, and greater in the high velocity area. The experimental results help the study of the dynamic characteristics of helical tube arrays in air cross flow

Effect of Anisotropy Structure on Plume Entropy and Reactive Mixing in Helical Flows

DEFF Research Database (Denmark)

Ye, Yu; Chiogna, Gabriele; Lu, Chunhui

2018-01-01

Plume dilution and reactive mixing can be considerably enhanced by helical flows occurring in three-dimensional anisotropic porous media. In this study, we perform conservative and reactive transport simulations considering different anisotropy structures of a single inclusion with the objective...... of exploring the effect of the inclusion’s geometry and orientation on the patterns of twisted streamlines and on the overall dilution and reaction of solute plumes. We analyzed 100 different scenarios by varying key parameters such as the angle of the anisotropic structures with respect to the average flow...... velocity, the spacing between alternated heterogeneous zones of coarse and fine materials, the permeability contrast between such matrices, and the magnitude of the seepage velocity. Entropy conservation equations and entropy-based metrics for both conservative and reactive species were adopted to quantify...

Neutronics investigation of advanced self-cooled liquid blanket systems in helical reactor

International Nuclear Information System (INIS)

Tanaka, T.; Sagara, A.; Muroga, T.; Youssef, M.Z.

2006-10-01

Neutronics performances of advanced self-cooled liquid blanket systems have been investigated in design activity of the helical-type reactor FFHR2. In the present study, a new three-dimensional (3-D) neutronics calculation system has been developed for the helical-type reactor to enhance quick feedback between neutronics evaluation and design modification. Using this new calculation system, advanced Flibe-cooled and Li-cooled liquid blanket systems proposed for FFHR2 have been evaluated to make clear design issues to enhance neutronics performance. Based on calculated results, modification of the blanket dimensions and configuration have been attempted to achieve the adequate tritium breeding ability and neutron shielding performance in the helical reactor. The total tritium breeding ratios (TBRs) obtained after modifying the blanket dimensions indicated that all the advanced blanket systems proposed for FFHR2 would achieve adequate tritium self-sufficiency by dimension adjustment and optimization of structures in the breeder layers. Issues in neutron shielding performance have been investigated quantitatively using 3-D geometry of the helical blanket system, support structures, poloidal coils etc. Shielding performance of the helical coils against direct neutrons from core plasma would achieve design target by further optimization of shielding materials. However, suppression of the neutron streaming and reflection through the divertor pumping areas in the original design is important issue to protect the poloidal coils and helical coils, respectively. Investigation of the neutron wall loading indicated that the peaking factor of the neutron wall load distribution would be moderated by the toroidal and helical effect of the plasma distribution in the helical reactor. (author)

Design windows and cost analysis on helical reactors

International Nuclear Information System (INIS)

Kozaki, Y.; Imagawa, S.; Sagara, A.

2007-01-01

The LHD type helical reactors are characterized by a large major radius but slender helical coil, which give us different approaches for power plants from tokamak reactors. For searching design windows of helical reactors and discussing their potential as power plants, we have developed a mass-cost estimating model linked with system design code (HeliCos), thorough studying the relationships between major plasma parameters and reactor parameters, and weight of major components. In regard to cost data we have much experience through preparing ITER construction. To compare the weight and cost of magnet systems between tokamak and helical reactors, we broke down magnet systems and cost factors, such as weights of super conducting strands, conduits, support structures, and winding unit costs, through estimating ITER cost data basis. Based on FFHR2m1 deign we considered a typical 3 GWth helical plant (LHD type) with the same magnet size, coil major radius Rc 14 m, magnetic energy 120 GJ, but increasing plasma densities. We evaluated the weight and cost of magnet systems of 3 GWth helical plant, the total magnet weights of 16,000ton and costs of 210 BYen, which are similar values of tokamak reactors (10,200 ton, 110 BYen in ITER 2002 report, and 21,900 ton, 275 BYen in ITER FDR1999). The costs of strands and winding occupy 70% of total magnet costs, and influence entire power plants economics. The design windows analysis and comparative economics studies to optimize the main reactor parameters have been carried out. Economics studies show that it is misunderstanding to consider helical coils are too large and too expensive to achieve power plants. But we should notice that the helical reactor design windows and economics are very sensitive to allowable blanket space (depend on ergodic layer conditions) and diverter configuration for decreasing heat loads. (orig.)

Bearing capacity of helical pile foundation in peat soil from different, diameter and spacing of helical plates

Science.gov (United States)

Fatnanta, F.; Satibi, S.; Muhardi

2018-03-01

In an area dominated by thick peat soil layers, driven piles foundation is often used. These piles are generally skin friction piles where the pile tips do not reach hard stratum. Since the bearing capacity of the piles rely on the resistance of their smooth skin, the bearing capacity of the piles are generally low. One way to increase the bearing capacity of the piles is by installing helical plates around the pile tips. Many research has been performed on helical pile foundation. However, literature on the use of helical pile foundation on peat soil is still hardly found. This research focus on the study of axial bearing capacity of helical pile foundation in peat soil, especially in Riau Province. These full-scale tests on helical pile foundation were performed in a rectangular box partially embedded into the ground. The box is filled with peat soil, which was taken from Rimbo Panjang area in the district of Kampar, Riau Province. Several helical piles with different number, diameter and spacing of the helical plates have been tested and analysed. The tests result show that helical pile with three helical plates of uniform diameter has better bearing capacity compared to other helical piles with varying diameter and different number of helical plates. The bearing capacity of helical pile foundation is affected by the spacing between helical plates. It is found that the effective helical plates spacing for helical pile foundation with diameter of 15cm to 35cm is between 20cm to 30cm. This behaviour may be considered to apply to other type of helical pile foundations in peat soil.

Plasmodium vivax antigen discovery based on alpha-helical coiled coil protein motif

DEFF Research Database (Denmark)

Céspedes, Nora; Habel, Catherine; Lopez-Perez, Mary

2014-01-01

Protein α-helical coiled coil structures that elicit antibody responses, which block critical functions of medically important microorganisms, represent a means for vaccine development. By using bioinformatics algorithms, a total of 50 antigens with α-helical coiled coil motifs orthologous to Pla...

Energy and helicity of magnetic torus knots and braids

Science.gov (United States)

Oberti, Chiara; Ricca, Renzo L.

2018-02-01

By considering steady magnetic fields in the shape of torus knots and unknots in ideal magnetohydrodynamics, we compute some fundamental geometric and physical properties to provide estimates for magnetic energy and helicity. By making use of an appropriate parametrization, we show that knots with dominant toroidal coils that are a good model for solar coronal loops have negligible total torsion contribution to magnetic helicity while writhing number provides a good proxy. Hence, by the algebraic definition of writhe based on crossing numbers, we show that the estimated values of writhe based on image analysis provide reliable information for the exact values of helicity. We also show that magnetic energy is linearly related to helicity, and the effect of the confinement of magnetic field can be expressed in terms of geometric information. These results can find useful application in solar and plasma physics, where braided structures are often present.

Exploring biological effects of MoS{sub 2} nanosheets on native structures of α-helical peptides

Energy Technology Data Exchange (ETDEWEB)

Gu, Zonglin; Li, Weifeng, E-mail: wfli@suda.edu.cn, E-mail: ruhong@us.ibm.com [School for Radiological and Interdisciplinary Sciences (RAD-X) and Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123 (China); Hong, Linbi [Computational Biological Center, IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (United States); Zhou, Ruhong, E-mail: wfli@suda.edu.cn, E-mail: ruhong@us.ibm.com [School for Radiological and Interdisciplinary Sciences (RAD-X) and Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123 (China); Computational Biological Center, IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (United States); Department of Chemistry, Columbia University, New York, New York 10027 (United States)

2016-05-07

Recent reports of mono- and few-layer molybdenum disulfide (MoS{sub 2}), a representative transition metal dichacogenide (TMD), as antibacterial and anticancer agents have shed light on their potential in biomedical applications. To better facilitate these promising applications, one needs to understand the biological effects of these TMDs as well, such as their potential adverse effects on protein structure and function. Here, we sought to understand the interaction of MoS{sub 2} nanosheets with peptides using molecular dynamics simulations and a simple model polyalanine with various lengths (PA{sub n}, n = 10, 20, 30, and 40; mainly α − helices). Our results demonstrated that MoS{sub 2} monolayer has an exceptional capability to bind all peptides in a fast and strong manner. The strong attraction from the MoS{sub 2} nanosheet is more than enough to compensate the energy needed to unfold the peptide, regardless of the length, which induces drastic disruptions to the intra-peptide hydrogen bonds and subsequent secondary structures of α − helices. This universal phenomenon may point to the potential nanotoxicity of MoS{sub 2} when used in biological systems. Moreover, these results aligned well with previous findings on the potential cytotoxicity of TMD nanomaterials.

Topological characteristics of helical repeat proteins

NARCIS (Netherlands)

Groves, M R; Barford, D

The recent elucidation of protein structures based upon repeating amino acid motifs, including the armadillo motif, the HEAT motif and tetratricopeptide repeats, reveals that they belong to the class of helical repeat proteins. These proteins share the common property of being assembled from tandem

Helical CT defecography

International Nuclear Information System (INIS)

Ferrando, R.; Fiorini, G.; Beghello, A.; Cicio, G.R.; Derchi, L.E.; Consigliere, M.; Resasco, M.; Tornago, S.

1999-01-01

The purpose of this work is to investigate the possible role of Helical CT defecography in pelvic floor disorders by comparing the results of the investigations with those of conventional defecography. The series analyzed consisted of 90 patients, namely 62 women and 28 men, ranging in age 24-82 years. They were all submitted to conventional defecography, and 18 questionable cases were also studied with Helical CT defecography. The conventional examination was performed during the 4 standard phases of resting, squeezing, Valsalva and straining; it is used a remote-control unit. The parameters for Helical CT defecography were: 5 mm beam collimation, pitch 2, 120 KV, 250 m As and 18-20 degrees gantry inclination to acquire coronal images of the pelvic floor. The rectal ampulla was distended with a bolus of 300 mL nonionic iodinated contrast agent (dilution: 3g/cc). The patient wore a napkin and was seated on the table, except for those who could not hold the position and were thus examined supine. Twenty-second helical scans were performed at rest and during evacuation; multiplanar reconstructions were obtained especially on the sagittal plane for comparison with conventional defecographic images. Coronal Helical CT defecography images permitted to map the perineal floor muscles, while sagittal reconstructions provided information on the ampulla and the levator ani. To conclude, Helical CT defecography performed well in study of pelvic floor disorders and can follow conventional defecography especially in questionable cases [it

HELICAL MOTIONS OF FINE-STRUCTURE PROMINENCE THREADS OBSERVED BY HINODE AND IRIS

Energy Technology Data Exchange (ETDEWEB)

Okamoto, Takenori J. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Liu, Wei [Bay Area Environmental Research Institute, 625 2nd Street, Suite 209, Petaluma, CA 94952 (United States); Tsuneta, Saku, E-mail: joten.okamoto@nao.ac.jp [ISAS/JAXA, Sagamihara, Kanagawa 252-5210 (Japan)

2016-11-10

Fine-structure dynamics in solar prominences holds critical clues to understanding their physical nature of significant space-weather implications. We report evidence of rotational motions of horizontal helical threads in two active-region prominences observed by the Hinode and/or Interface Region Imaging Spectrograph satellites at high resolution. In the first event, we found transverse motions of brightening threads at speeds up to 55 km s{sup -1} seen in the plane of the sky. Such motions appeared as sinusoidal space–time trajectories with a typical period of ∼390 s, which is consistent with plane-of-sky projections of rotational motions. Phase delays at different locations suggest the propagation of twists along the threads at phase speeds of 90–270 km s{sup -1}. At least 15 episodes of such motions occurred in two days, none associated with an eruption. For these episodes, the plane-of-sky speed is linearly correlated with the vertical travel distance, suggestive of a constant angular speed. In the second event, we found Doppler velocities of 30–40 km s{sup -1} in opposite directions in the top and bottom portions of the prominence, comparable to the plane-of-sky speed. The moving threads have about twice broader line widths than stationary threads. These observations, when taken together, provide strong evidence for rotations of helical prominence threads, which were likely driven by unwinding twists triggered by magnetic reconnection between twisted prominence magnetic fields and ambient coronal fields.

Silica biomineralization via the self-assembly of helical biomolecules.

Science.gov (United States)

Liu, Ben; Cao, Yuanyuan; Huang, Zhehao; Duan, Yingying; Che, Shunai

2015-01-21

The biomimetic synthesis of relevant silica materials using biological macromolecules as templates via silica biomineralization processes attract rapidly rising attention toward natural and artificial materials. Biomimetic synthesis studies are useful for improving the understanding of the formation mechanism of the hierarchical structures found in living organisms (such as diatoms and sponges) and for promoting significant developments in the biotechnology, nanotechnology and materials chemistry fields. Chirality is a ubiquitous phenomenon in nature and is an inherent feature of biomolecular components in organisms. Helical biomolecules, one of the most important types of chiral macromolecules, can self-assemble into multiple liquid-crystal structures and be used as biotemplates for silica biomineralization, which renders them particularly useful for fabricating complex silica materials under ambient conditions. Over the past two decades, many new silica materials with hierarchical structures and complex morphologies have been created using helical biomolecules. In this review, the developments in this field are described and the recent progress in silica biomineralization templating using several classes of helical biomolecules, including DNA, polypeptides, cellulose and rod-like viruses is summarized. Particular focus is placed on the formation mechanism of biomolecule-silica materials (BSMs) with hierarchical structures. Finally, current research challenges and future developments are discussed in the conclusion. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Robust integer and fractional helical modes in the quantum Hall effect

Science.gov (United States)

Ronen, Yuval; Cohen, Yonatan; Banitt, Daniel; Heiblum, Moty; Umansky, Vladimir

2018-04-01

Electronic systems harboring one-dimensional helical modes, where spin and momentum are locked, have lately become an important field of their own. When coupled to a conventional superconductor, such systems are expected to manifest topological superconductivity; a unique phase hosting exotic Majorana zero modes. Even more interesting are fractional helical modes, yet to be observed, which open the route for realizing generalized parafermions. Possessing non-Abelian exchange statistics, these quasiparticles may serve as building blocks in topological quantum computing. Here, we present a new approach to form protected one-dimensional helical edge modes in the quantum Hall regime. The novel platform is based on a carefully designed double-quantum-well structure in a GaAs-based system hosting two electronic sub-bands; each tuned to the quantum Hall effect regime. By electrostatic gating of different areas of the structure, counter-propagating integer, as well as fractional, edge modes with opposite spins are formed. We demonstrate that, due to spin protection, these helical modes remain ballistic over large distances. In addition to the formation of helical modes, this platform can serve as a rich playground for artificial induction of compounded fractional edge modes, and for construction of edge-mode-based interferometers.

Concept and development of measurement method of time sensitivity profile (TSP) in X-ray CT. Comparison of non-helical, single-slice helical, and multi-slice helical scans

International Nuclear Information System (INIS)

Tsujioka, Katsumi; Ida, Yoshihiro; Ohtsubo, Hironori; Takahashi, Yasukata; Niwa, Masayoshi

2000-01-01

We focused on the time element contained in a single CT image, and devised the concept of a time-sensitivity profile (TSP) describing how the time element is translated into an image. We calculated the data collection time range when the helical pitch is changed in non helical scans, single slice helical scans, and multi slice helical scans. We then calculated the time sensitivity profile (TSP) from the weighting applied when the data collection time range is translated into an image. TSP was also measured for each scanning method using our self-made moving phantom. TSPs obtained from the calculation and the experiments were very close. TSP showed interesting characteristics with each scanning method, especially in the case of multi slice helical scanning, in which TSP became shorter as helical pitch increased. We referred to the TSP's FWHM as the effective scanning time. When we conducted multi slice helical scanning at helical pitch 3, the effective scanning time increased to about 24% longer than that of a non helical scan. When we conducted multi slice helical scanning at helical pitch 5 or 6, the effective scanning time was about half that of a non helical scan. The time sensitivity profile (TSP) is a totally new concept that we consider an important element in discussing the time resolution of a CT scanner. The results of this review will provide significant data in determining the scanning parameters when scanning a moving object. (author)

Rational assembly of Pb(II)/Cd(II)/Mn(II) coordination polymers based on flexible V-shaped dicarboxylate ligand: Syntheses, helical structures and properties

Energy Technology Data Exchange (ETDEWEB)

Yang, Gao-Shan [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Liu, Chong-Bo, E-mail: cbliu@nchu.edu.cn [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China); School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Liu, Hong [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Robbins, Julianne; Zhang, Z. John [School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Yin, Hong-Shan [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China); Wen, Hui-Liang [State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047 (China); Wang, Yu-Hua [School of Environment and Chemical Engineering, Nanchang Hangkong University, Nanchang 330063 (China)

2015-05-15

Six new coordination polymers, namely, [Pb(L)(H{sub 2}O)] (1), [Pb(L)(phen)] (2), [Pb{sub 2}(L){sub 2}(4,4′-bipy){sub 0.5}] (3), [Cd(L)(phen)] (4), [Cd(L)(4,4′-bipy)]·H{sub 2}O (5) and [Mn(L)(4,4′-bipy)]·H{sub 2}O (6) have been synthesized by the hydrothermal reaction of 2,2′-[hexafluoroisopropylidenebis(p-phenyleneoxy)]diacetic acid (H{sub 2}L) with Pb(II)/Cd(II)/Mn(II) in the presence of ancillary ligands 4,4′-bipyridine (4,4′-bipy) or 1,10-phenanthroline (phen). Complexes 1 and 4–6 exhibit 2-D structures, and complexes 2–3 display 3-D frameworks, of which L{sup 2−} ligands join metal ions to single-stranded helical chains of 1, 3–6 and double-stranded helical chains of 2. Complexes 2 and 3 also contain double-stranded Metal–O helices. Topology analysis reveals that complexes 1 and 4 both represent 4-connected sql net, 2 represents 6-connected pcu net, 3 exhibits a novel (3,12)-connected net, while 5 and 6 display (3,5)-connected gek1 net. The six complexes exhibit two kinds of inorganic–organic connectivities: I{sup 0}O{sup 2} for 1, 4–6, and I{sup 1}O{sup 2} for 2–3. The photoluminescent properties of 4–5 and the magnetic properties of 6 have been investigated. - Graphical abstract: Six new Pb(II)/Cd(II)/Mn(II) coordination polymers with helical structures based on flexible V-shaped dicarboxylate ligand have been synthesized and structurally characterized. Photoluminescent and magnetic properties have been investigated. - Highlights: • Six novel M(II) coordination polymers with 2,2′-[hexafluoroisopropylidenebis(p-phenyleneoxy)]diacetic acid and N-donor ligands. • Complexes 1–6 show diverse intriguing helical characters. • The luminescent properties of complexes 1–5 were investigated. • Complex 6 shows antiferromagnetic coupling.

Hexagonally Ordered Arrays of α-Helical Bundles Formed from Peptide-Dendron Hybrids

Energy Technology Data Exchange (ETDEWEB)

Barkley, Deborah A. [Department; Rokhlenko, Yekaterina [Department; Marine, Jeannette E. [Department; David, Rachelle [Department; Sahoo, Dipankar [Department; Watson, Matthew D. [Department; Koga, Tadanori [Department; Department; Osuji, Chinedum O. [Department; Rudick, Jonathan G. [Department

2017-10-24

Combining monodisperse building blocks that have distinct folding properties serves as a modular strategy for controlling structural complexity in hierarchically organized materials. We combine an α-helical bundle-forming peptide with self-assembling dendrons to better control the arrangement of functional groups within cylindrical nanostructures. Site-specific grafting of dendrons to amino acid residues on the exterior of the α-helical bundle yields monodisperse macromolecules with programmable folding and self-assembly properties. The resulting hybrid biomaterials form thermotropic columnar hexagonal mesophases in which the peptides adopt an α-helical conformation. Bundling of the α-helical peptides accompanies self-assembly of the peptide-dendron hybrids into cylindrical nanostructures. The bundle stoichiometry in the mesophase agrees well with the size found in solution for α-helical bundles of peptides with a similar amino acid sequence.

Helical polyurethane-attapulgite nanocomposite: Preparation, characterization and study of optical activity

International Nuclear Information System (INIS)

Wang Zhiqiang; Zhou Yuming; Sun Yanqing; Fan Kai; Guo Xingxing; Jiang Xiaolei

2009-01-01

Helical polyurethane-attapulgite (BM-ATT) based on R-1,1'-binaphthyl-2',2-diol (R-BINOL) composite was prepared after the surface modification of attapulgite (ATT). BM-ATT was characterized by Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HTEM) and vibrational circular dichroism (VCD) spectroscopy. FT-IR and XRD analyses indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified ATT without destroying the original crystalline structure of ATT. BM-ATT exhibits the rod-like structure by SEM, TEM, and HTEM photographs. BM-ATT displays obvious Cotton effect for some absorbance in VCD spectrum, and its optical activity results from the singlehanded conformation of helical polyurethane. - Graphical Abstract: Helical polyurethane-attapulgite (BM-ATT) based on R-1,1'-binaphthyl-2',2-diol (R-BINOL) nanocomposite was prepared after surface modification of attapulgite (ATT). This rod-like composite is coated by the optically active polyurethane shell on the surfaces.

Temperature-dependent structural changes in intrinsically disordered proteins: formation of alpha-helices or loss of polyproline II?

DEFF Research Database (Denmark)

Kjærgaard, Magnus; Nørholm, Ann-Beth; Hendus-Altenburger, Ruth

2010-01-01

temperature, which most likely reflects formation of transient alpha-helices or loss of polyproline II (PPII) content. Using three IDPs, ACTR, NHE1, and Spd1, we show that the temperature-induced structural change is common among IDPs and is accompanied by a contraction of the conformational ensemble...... with increasing temperature, and accordingly these were not responsible for the change in the CD spectra. In contrast, the nonhelical regions exhibited a general temperature-dependent structural change that was independent of long-range interactions. The temperature-dependent CD spectroscopic signature of IDPs...

Pulling Helices inside Bacteria: Imperfect Helices and Rings

Science.gov (United States)

Allard, Jun F.; Rutenberg, Andrew D.

2009-04-01

We study steady-state configurations of intrinsically-straight elastic filaments constrained within rod-shaped bacteria that have applied forces distributed along their length. Perfect steady-state helices result from axial or azimuthal forces applied at filament ends, however azimuthal forces are required for the small pitches observed for MreB filaments within bacteria. Helix-like configurations can result from distributed forces, including coexistence between rings and imperfect helices. Levels of expression and/or bundling of the polymeric protein could mediate this coexistence.

Sequence and conformational preferences at termini of α-helices in membrane proteins: role of the helix environment.

Science.gov (United States)

Shelar, Ashish; Bansal, Manju

2014-12-01

α-Helices are amongst the most common secondary structural elements seen in membrane proteins and are packed in the form of helix bundles. These α-helices encounter varying external environments (hydrophobic, hydrophilic) that may influence the sequence preferences at their N and C-termini. The role of the external environment in stabilization of the helix termini in membrane proteins is still unknown. Here we analyze α-helices in a high-resolution dataset of integral α-helical membrane proteins and establish that their sequence and conformational preferences differ from those in globular proteins. We specifically examine these preferences at the N and C-termini in helices initiating/terminating inside the membrane core as well as in linkers connecting these transmembrane helices. We find that the sequence preferences and structural motifs at capping (Ncap and Ccap) and near-helical (N' and C') positions are influenced by a combination of features including the membrane environment and the innate helix initiation and termination property of residues forming structural motifs. We also find that a large number of helix termini which do not form any particular capping motif are stabilized by formation of hydrogen bonds and hydrophobic interactions contributed from the neighboring helices in the membrane protein. We further validate the sequence preferences obtained from our analysis with data from an ultradeep sequencing study that identifies evolutionarily conserved amino acids in the rat neurotensin receptor. The results from our analysis provide insights for the secondary structure prediction, modeling and design of membrane proteins. © 2014 Wiley Periodicals, Inc.

Self-assembly of hard helices: a rich and unconventional polymorphism.

Science.gov (United States)

Kolli, Hima Bindu; Frezza, Elisa; Cinacchi, Giorgio; Ferrarini, Alberta; Giacometti, Achille; Hudson, Toby S; De Michele, Cristiano; Sciortino, Francesco

2014-11-07

Hard helices can be regarded as a paradigmatic elementary model for a number of natural and synthetic soft matter systems, all featuring the helix as their basic structural unit, from natural polynucleotides and polypeptides to synthetic helical polymers, and from bacterial flagella to colloidal helices. Here we present an extensive investigation of the phase diagram of hard helices using a variety of methods. Isobaric Monte Carlo numerical simulations are used to trace the phase diagram; on going from the low-density isotropic to the high-density compact phases a rich polymorphism is observed, exhibiting a special chiral screw-like nematic phase and a number of chiral and/or polar smectic phases. We present full characterization of the latter, showing that they have unconventional features, ascribable to the helical shape of the constituent particles. Equal area construction is used to locate the isotropic-to-nematic phase transition, and the results are compared with those stemming from an Onsager-like theory. Density functional theory is also used to study the nematic-to-screw-nematic phase transition; within the simplifying assumption of perfectly parallel helices, we compare different levels of approximation, that is second- and third-virial expansions and a Parsons-Lee correction.

Passive base isolation with superelastic nitinol SMA helical springs

International Nuclear Information System (INIS)

Huang, Bin; Zhang, Haiyang; Wang, Han; Song, Gangbing

2014-01-01

Seismic isolation of structures such as multi-story buildings, nuclear reactors, bridges, and liquid storage tanks should be designed to preserve structural integrity. By implementing seismic isolation technology, the deformation of superstructures can be dramatically reduced, consequently helping to protect their safety as well. In this paper, an innovative type of passive base isolation system, which is mainly composed of superelastic nitinol SMA helical springs, is developed. In order to verify the effectiveness of the proposed system, a two-story experimental steel frame model is constructed, and two superelastic SMA helical springs are thermo-mechanically built in the laboratory. To describe the nonlinear mechanical properties of the superelastic SMA helical springs under reciprocating load, a phenomenological model is presented in terms of a series of tensile tests. Afterwards, a numerical model of the two-story frame with the suggested isolation system is set up to simulate the response of the isolated frame subjected to an earthquake. Both the experimental and the numerical simulation results indicate that the proposed base isolation system can remarkably suppress structural vibrations and has improved isolation effects when compared with a steel spring isolation system. Due to the capabilities of energy dissipation as well as fully re-centering, it is very applicable to utilize the suggested isolation system in base isolated structures to resist earthquakes. (paper)

Helical system. History and current state of helical research

International Nuclear Information System (INIS)

Yokoyama, Masayuki

2017-01-01

This paper described the following: (1) history of nuclear fusion research of Japan's original heliotron method, (2) worldwide development of nuclear fusion research based on helical system such as stellarator, and (3) worldwide meaning of large helical device (LHD) aiming to demonstrate the steady-state performance of heliotron type in the parameter area extrapolable to the core plasma, and research results of LHD. LHD demonstrated that the helical system is excellent in steady operation performance at the world's most advanced level. In an experiment using deuterium gas in 2017, LHD achieved to reach 120 million degrees of ion temperature, which is one index of nuclear fusion condition, demonstrated the realization of high-performance plasma capable of extrapolating to future nuclear fusion reactors, and established the foundation for full-scale research toward the realization of nuclear fusion reactor. Besides experimental research, this paper also described the helical-type stationary nuclear fusion prototype reactor, FFHR-d1, which was based on progress of large-scale simulation at the world's most advanced level. A large-scale superconducting stellarator experimental device, W7-X, with the same scale as LHD, started experiment in December 2015, whose current state is also touched on here. (A.O.)

Review of the helicity formalism

International Nuclear Information System (INIS)

Barreiro, F.; Cerrada, M.; Fernandez, E.

1972-01-01

Our purpose in these notes has been to present a brief and general review of the helicity formalism. We begin by discussing Lorentz invariance, spin and helicity ideas, in section 1 . In section 2 we deal with the construction of relativistic states and scattering amplitudes in the helicity basis and we study their transformation properties under discrete symmetries. Finally we present some more sophisticated topics like kinematical singularities of helicity amplitudes, kinematical constraints and crossing relations 3, 4, 5 respectively. (Author) 8 refs

Electron image reconstruction of helical protein assemblies

International Nuclear Information System (INIS)

Cremers, A.F.M.

1980-01-01

The analysis of projections of large ordered biological systems obtained by electron microscopy of negatively stained specimens is described. The biological structures amenable to this approach are constructed from a large number of identical protein molecules, which are arranged according to helical symmetry. Electron images of these structures generally contain sufficient information in order to calculate a three-dimensional density map. (Auth.)

Hamiltonian theory of vacuum helical torus lines of magnetic force

International Nuclear Information System (INIS)

Gnudi, Giovanni; Hatori, Tadatsugu

1994-01-01

For making plasma into equilibrium state, the lines of magnetic force must have magnetic surfaces. However in a helical system, space is divided into the region having magnetic surface structure and the region that does not have it. Accordingly, it is an important basic research for the plasma confinement in a helical system to examine where is the boundary of both regions and how is the large area structure of the lines of magnetic force in the boundary region. The lines of magnetic force can be treated as a Hamilton mechanics system, and it has been proved that the Hamiltonian for the lines of magnetic force can be expressed by a set of canonical variables and the function of time. In this research, the Hamiltonian that describes the lines of magnetic force of helical system torus coordination in vacuum was successfully determined concretely. Next, the development of new linear symplectic integration method was carried out. The important supports for the theory of determining Hamiltonian are Lie transformation and paraxial expansion. The procedure is explained. In Appendix, Lie transformation, Hamiltonian for the lines of magnetic force, magnetic potential, Taylor expansion of the potential, cylindrical limit approximation, helical toroidal potential and integrable model are described. (K.I.)

A note on helicity

International Nuclear Information System (INIS)

Bialynicki-Birula, I.; Newmann, E.T.; Porter, J.; Winicour, J.; Lukacs, B.; Perjes, Z.; Sebestyen, A.

1981-03-01

The authors give a formal definition of the helicity operator for integral spin fields, which does not involve their momentum-space decomposition. The discussion is based upon a representation of the Pauli-Lubanski operator in terms of the action on tensor fields by the Killing vectors associated with the generators of the Poincare group. This leads to an identification of the helicity operator with the duality operator defined by the space-time alternating tensor. Helicity eigenstates then correspond to self-dual or anti-self-dual fields, in agreement with usage implicit in the literature. In addiition, the relationship between helicity eigenstates which are intrinsically non-classical, and states of right or left circular polarization in classical electrodynamics are discussed. (author)

Kinetic assembly of block copolymers in solution helical cylindrical micelles and patchy nanoparticles

Science.gov (United States)

Zhong, Sheng

There is always an interest to understand how molecules behave under different conditions. One application of this knowledge is to self-assemble molecules into increasingly complex structures in a simple fashion. Self-assembly of amphiphilic block copolymer in solution has produced a large variety of nanostructures through the manipulation in polymer chemistry, assembly environment, and additives. Moreover, some reports suggest the formation of many polymeric assemblies is driven by kinetic process. The goal of this dissertation is to study the influence of kinetics on the assembly of block copolymer. The study shows kinetic control can be a very effective way to make novel polymeric nanostructures. Two examples discussed here are helical cylindrical micelles and patchy nanoparticles. Helical cylindrical micelles are made from the co-assembly of amphiphilic triblock copolymer poly(acrylic acid)-block-poly(methyl acrylate)- block-polystyrene and organoamine molecules in a mixture of tetrahydrofuran (THF) and water (H2O). This system has already shown promise of achieving many assembled structures. The unique aspects about this system are the use of amine molecules to complex with acid groups and the existence of cosolvent system. Application of amine molecules offers a convenient control over assembled morphology and the introduction of PMA-PS selective solvent, THF, promotes the mobility of the polymer chains. In this study, multivalent organoamine molecules, such as diethylenetriamine and triethylenetetramine, are used to interact with block copolymer in THF/water mixture. As expected, the assembled morphologies are dependent on the polymer architecture, selection and quantity of the organoamine molecules, and solution composition. Under the right conditions, unprecedented, multimicrometer-long, supramolecular helical cylindrical micelles are formed. Both single-stranded and double-stranded helices are found in the same system. These helical structures share

l=1 helical axis heliotron device in Kyoto university

International Nuclear Information System (INIS)

Nagasaki, K.; Sano, F.; Mizuuchi, T.; Hanatani, K.; Okada, H.; Obiki, T.

1999-01-01

Helical systems are an attractive candidate for magnetic fusion reactor. Recently, there has been great progress in theoretical research of three dimensional magnetic field structures, resulting in several kinds of confinement optimization being proposed for toroidal magnetic confinement system. For example, some sophisticated ideas have appeared on stage such as quasi-helical symmetry and quasi-isodynamic system. To find experimentally which way is the best Optimisation, a new helical axis heliotron device, so called 'Heliotron J', is under construction in the Institute of Advanced Energy, Kyoto University, Japan. In this conference, the basic concept and the present status will be presented. In the conventional plane axis helical system, it was difficult to have both good particle confinement and good MHD stability simultaneously. The goal of Heliotron J project is to clarify their compatibility in the spatial axis toroidal device. The best way for Optimising the helical magnetic field configuration will be explored by investigating the plasma response to the change in the field components. The main subjects for plasma experiment are: demonstration of the existence of good magnetic flux surfaces, reduction of neoclassical transport in collisionless regime, MHD Stabilisation in high β plasma, controllability of bootstrap current, good confinement of high energy particles

Diagnostic value of triphasic incremental helical CT in early and progressive gastric carcinoma

International Nuclear Information System (INIS)

Gao Jianbo; Yan Xuehua; Li Mengtai; Guo Hua; Chen Xuejun; Guan Sheng; Zhang Xiefu; Li Shuxin; Yang Xiaopeng

2001-01-01

Objective: To investigate helical CT enhancement characteristics of gastric carcinoma, and the diagnostic value and preoperative staging of gastric carcinoma with triphasic incremental helical CT of the stomach with water-filling method. Methods: Both double-contrast barium examination and triphasic incremental helical CT of the stomach with water-filling method were performed in 46 patients with gastric carcinoma. Results: (1) Among these patients, normal gastric wall exhibited one layered structure in 18 patients, two or three layered structure in 28 patients in the arterial and portal venous phase. (2) Two cases of early stomach cancer showed marked enhancement in the arterial and portal venous phase and obvious attenuation of enhancement in the equilibrium phase. On the contrary, 32 of the 44 advanced gastric carcinoma was showed marked enhancement in the venous phase compared with the arterial phase ( t = 4.226, P < 0.05). (3) The total accuracy of triphasic incremental helical CT in determining TNM-staging was 81.0%. Conclusion: Different types of gastric carcinoma have different enhancement features. Triphases incremental helical CT is more accurate than conventional CT in the preoperative staging of gastric carcinoma

TIME EVOLUTION OF CORONAL MAGNETIC HELICITY IN THE FLARING ACTIVE REGION NOAA 10930

International Nuclear Information System (INIS)

Park, Sung-Hong; Jing, Ju; Wang Haimin; Chae, Jongchul; Tan, Changyi

2010-01-01

To study the three-dimensional (3D) magnetic field topology and its long-term evolution associated with the X3.4 flare of 2006 December 13, we investigate the coronal relative magnetic helicity in the flaring active region (AR) NOAA 10930 during the time period of December 8-14. The coronal helicity is calculated based on the 3D nonlinear force-free magnetic fields reconstructed by the weighted optimization method of Wiegelmann, and is compared with the amount of helicity injected through the photospheric surface of the AR. The helicity injection is determined from the magnetic helicity flux density proposed by Pariat et al. using Solar and Heliospheric Observatory/Michelson Doppler Imager magnetograms. The major findings of this study are the following. (1) The time profile of the coronal helicity shows a good correlation with that of the helicity accumulation by injection through the surface. (2) The coronal helicity of the AR is estimated to be -4.3 x 10 43 Mx 2 just before the X3.4 flare. (3) This flare is preceded not only by a large increase of negative helicity, -3.2 x 10 43 Mx 2 , in the corona over ∼1.5 days but also by noticeable injections of positive helicity through the photospheric surface around the flaring magnetic polarity inversion line during the time period of the channel structure development. We conjecture that the occurrence of the X3.4 flare is involved with the positive helicity injection into an existing system of negative helicity.

Three-dimensional printing of freeform helical microstructures: a review.

Science.gov (United States)

Farahani, R D; Chizari, K; Therriault, D

2014-09-21

Three-dimensional (3D) printing is a fabrication method that enables creation of structures from digital models. Among the different structures fabricated by 3D printing methods, helical microstructures attracted the attention of the researchers due to their potential in different fields such as MEMS, lab-on-a-chip systems, microelectronics and telecommunications. Here we review different types of 3D printing methods capable of fabricating 3D freeform helical microstructures. The techniques including two more common microfabrication methods (i.e., focused ion beam chemical vapour deposition and microstereolithography) and also five methods based on computer-controlled robotic direct deposition of ink filament (i.e., fused deposition modeling, meniscus-confined electrodeposition, conformal printing on a rotating mandrel, UV-assisted and solvent-cast 3D printings) and their advantages and disadvantages regarding their utilization for the fabrication of helical microstructures are discussed. Focused ion beam chemical vapour deposition and microstereolithography techniques enable the fabrication of very precise shapes with a resolution down to ∼100 nm. However, these techniques may have material constraints (e.g., low viscosity) and/or may need special process conditions (e.g., vacuum chamber) and expensive equipment. The five other techniques based on robotic extrusion of materials through a nozzle are relatively cost-effective, however show lower resolution and less precise features. The popular fused deposition modeling method offers a wide variety of printable materials but the helical microstructures manufactured featured a less precise geometry compared to the other printing methods discussed in this review. The UV-assisted and the solvent-cast 3D printing methods both demonstrated high performance for the printing of 3D freeform structures such as the helix shape. However, the compatible materials used in these methods were limited to UV-curable polymers and

LHD helical divertor

International Nuclear Information System (INIS)

Ohyabu, N.; Watanabe, T.; Ji Hantao

1993-07-01

The Large Helical Device (LHD) now under construction is a heliotron/torsatron device with a closed divertor system. The edge LHD magnetic structure has been studied in detail. A peculiar feature of the configuration is existence of edge surface layers, a complicated three dimensional magnetic structure which does not, however, seem to hamper the expected divertor functions. Two divertor operational modes are being considered for the LHD experiment, high density, cold radiative divertor operation as a safe heat removal scheme and high temperature divertor plasma operation. In the latter operation, a divertor plasma with temperature of a few kev, generated by efficient pumping, expects to lead to significant improvement in core plasma confinement. Conceptual designs of the LHD divertor components are under way. (author)

Generalized helicity and its time derivative

International Nuclear Information System (INIS)

Jarboe, T.R.; Marklin, G.J.

1985-01-01

Spheromaks can be sustained against resistive decay by helicity injection because they tend to obey the minimum energy principle. This principle states that a plasma-laden magnetic configuration will relax to a state of minimum energy subject to the constraint that the magnetic helicity is conserved. Use of helicity as a constraint on the minimization of energy was first proposed by Woltjer in connection with astrophysical phenomena. Helicity does decay on the resistive diffusion time. However, if helicity is created and made to flow continuoiusly into a confinement geometry, these additional linked fluxes can relax and sustain the configuration indefinitely against the resistive decay. In this paper we will present an extension of the definition of helicity to include systems where B vector can penetrate the boundary and the penetration can be varying in time. We then discuss the sustainment of RFPs and spheromaks in terms of helicity injection

Synthesis, model and stability of helically coiled carbon nanotubes

DEFF Research Database (Denmark)

Fejes, Dora; Raffai, Manuella; Hernadi, Klara

2013-01-01

. Our experiments focused on the production and development of catalysts for the synthesis of helically coiled CNTs (carbon nanotubes). The catalysts were tested in the decomposition of acetylene by CCVD (Catalytic Chemical Vapor Deposition) method. The carbon deposit was imaged by TEM (Transmission......Structural model of helically coiled carbon nanotubes is proposed. It is constructed by means of topological coordinate method. Relaxation and cohesive energy calculation are performed by molecular mechanics, using second-generation bond order potential for hydrocarbons introduced by D. W. Brenner...

Structural fragment clustering reveals novel structural and functional motifs in α-helical transmembrane proteins

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Vassilev Boris

2010-04-01

Full Text Available Abstract Background A large proportion of an organism's genome encodes for membrane proteins. Membrane proteins are important for many cellular processes, and several diseases can be linked to mutations in them. With the tremendous growth of sequence data, there is an increasing need to reliably identify membrane proteins from sequence, to functionally annotate them, and to correctly predict their topology. Results We introduce a technique called structural fragment clustering, which learns sequential motifs from 3D structural fragments. From over 500,000 fragments, we obtain 213 statistically significant, non-redundant, and novel motifs that are highly specific to α-helical transmembrane proteins. From these 213 motifs, 58 of them were assigned to function and checked in the scientific literature for a biological assessment. Seventy percent of the motifs are found in co-factor, ligand, and ion binding sites, 30% at protein interaction interfaces, and 12% bind specific lipids such as glycerol or cardiolipins. The vast majority of motifs (94% appear across evolutionarily unrelated families, highlighting the modularity of functional design in membrane proteins. We describe three novel motifs in detail: (1 a dimer interface motif found in voltage-gated chloride channels, (2 a proton transfer motif found in heme-copper oxidases, and (3 a convergently evolved interface helix motif found in an aspartate symporter, a serine protease, and cytochrome b. Conclusions Our findings suggest that functional modules exist in membrane proteins, and that they occur in completely different evolutionary contexts and cover different binding sites. Structural fragment clustering allows us to link sequence motifs to function through clusters of structural fragments. The sequence motifs can be applied to identify and characterize membrane proteins in novel genomes.

Meso-Helical Ag(I) Coordination Polymer Based on a Pyridylimidazole Ligand

International Nuclear Information System (INIS)

Kang, Youngjin; Kim, Jinho; Lee, Eunji; Park, Ki-Min; Moon, Suk-Hee

2016-01-01

In the fields of material science and metallosupramolecular chemistry, coordination polymers with various helical types have been extensively explored because of their charming structures, and their potential applications in material chemistry. Among them, meso-helical coordination polymers consisting of achiral 1D strands, which are generally constructed by a crystallographic inversion symmetry, are relatively rare. The coordination polymer 1 exhibits a rare one-dimensional meso-helical chain topology constructed by its internal inversion symmetry. The skeleton of this meso-helical chain is preserved up to 300°C. The complexation of silver(I) ion to the free pyim ligand give rise to the enhanced photoluminescence intensity and slightly blue-shifted emission maximum, originated from intraligand (IL) π[BOND]π* transition and rigidochromic effect. Further exploration of complexation of this ligand with other transition metal ions is currently in progress

MH2c: Characterization of major histocompatibility α-helices - an information criterion approach.

Science.gov (United States)

Hischenhuber, B; Frommlet, F; Schreiner, W; Knapp, B

2012-07-01

Major histocompatibility proteins share a common overall structure or peptide binding groove. Two binding groove domains, on the same chain for major histocompatibility class I or on two different chains for major histocompatibility class II, contribute to that structure that consists of two α -helices ("wall") and a sheet of eight anti-parallel beta strands ("floor"). Apart from the peptide presented in the groove, the major histocompatibility α -helices play a central role for the interaction with the T cell receptor. This study presents a generalized mathematical approach for the characterization of these helices. We employed polynomials of degree 1 to 7 and splines with 1 to 2 nodes based on polynomials of degree 1 to 7 on the α -helices projected on their principal components. We evaluated all models with a corrected Akaike Information Criterion to determine which model represents the α -helices in the best way without overfitting the data. This method is applicable for both the stationary and the dynamic characterization of α -helices. By deriving differential geometric parameters from these models one obtains a reliable method to characterize and compare α -helices for a broad range of applications. Program title: MH 2 c (MH helix curves) Catalogue identifier: AELX_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AELX_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 327 565 No. of bytes in distributed program, including test data, etc.: 17 433 656 Distribution format: tar.gz Programming language: Matlab Computer: Personal computer architectures Operating system: Windows, Linux, Mac (all systems on which Matlab can be installed) RAM: Depends on the trajectory size, min. 1 GB (Matlab) Classification: 2.1, 4.9, 4.14 External routines: Curve

Plasmodium vivax antigen discovery based on alpha-helical coiled coil protein motif.

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Nora Céspedes

Full Text Available Protein α-helical coiled coil structures that elicit antibody responses, which block critical functions of medically important microorganisms, represent a means for vaccine development. By using bioinformatics algorithms, a total of 50 antigens with α-helical coiled coil motifs orthologous to Plasmodium falciparum were identified in the P. vivax genome. The peptides identified in silico were chemically synthesized; circular dichroism studies indicated partial or high α-helical content. Antigenicity was evaluated using human sera samples from malaria-endemic areas of Colombia and Papua New Guinea. Eight of these fragments were selected and used to assess immunogenicity in BALB/c mice. ELISA assays indicated strong reactivity of serum samples from individuals residing in malaria-endemic regions and sera of immunized mice, with the α-helical coiled coil structures. In addition, ex vivo production of IFN-γ by murine mononuclear cells confirmed the immunogenicity of these structures and the presence of T-cell epitopes in the peptide sequences. Moreover, sera of mice immunized with four of the eight antigens recognized native proteins on blood-stage P. vivax parasites, and antigenic cross-reactivity with three of the peptides was observed when reacted with both the P. falciparum orthologous fragments and whole parasites. Results here point to the α-helical coiled coil peptides as possible P. vivax malaria vaccine candidates as were observed for P. falciparum. Fragments selected here warrant further study in humans and non-human primate models to assess their protective efficacy as single components or assembled as hybrid linear epitopes.

Numerical simulation of helical-vortex effects in Rayleigh-Bénard convection

Directory of Open Access Journals (Sweden)

G. V. Levina

2006-01-01

Full Text Available A numerical approach is substantiated for searching for the large-scale alpha-like instability in thermoconvective turbulence. The main idea of the search strategy is the application of a forcing function which can have a physical interpretation. The forcing simulates the influence of small-scale helical turbulence generated in a rotating fluid with internal heat sources and is applied to naturally induced fully developed convective flows. The strategy is tested using the Rayleigh-Bénard convection in an extended horizontal layer of incompressible fluid heated from below. The most important finding is an enlargement of the typical horizontal scale of the forming helical convective structures accompanied by a cells merging, an essential increase in the kinetic energy of flows and intensification of heat transfer. The results of modeling allow explaining how the helical feedback can work providing the non-zero mean helicity generation and the mutual intensification of horizontal and vertical circulation, and demonstrate how the energy of the additional helical source can be effectively converted into the energy of intensive large-scale vortex flow.

The management of helical rim keloids with excision, split thickness skin graft and intralesional triamcinolone acetonide

Directory of Open Access Journals (Sweden)

Ibrahim Abdul Rasheed

2014-01-01

Full Text Available Keloids of the helical rim are disfiguring. A cosmetically acceptable reconstruction is difficult especially in moderate to large sized lesions because the helical rim is a 3-dimensional structure with curved and thin cartilage. We report our experience in the management of moderate (4-10 cm and large (>10 cm helical rim keloids in five patients. Six helical rim keloids were reconstructed. There were four moderate (4-10 cm and two large (>10 cm helical rim keloids. Four were on the right helix and two on the left helix. One patient had bilateral helical rim keloids. The follow-up period ranged from 6 months to 4 years. No secondary surgical revision was required to improve the contour of the reconstructed helical rim. The aesthetic results were satisfactory in all the patients.

Magnetic helicity and active filament configuration

Science.gov (United States)

Romano, P.; Zuccarello, F.; Poedts, S.; Soenen, A.; Zuccarello, F. P.

2009-11-01

Context: The role of magnetic helicity in active filament formation and destabilization is still under debate. Aims: Although active filaments usually show a sigmoid shape and a twisted configuration before and during their eruption, it is unclear which mechanism leads to these topologies. In order to provide an observational contribution to clarify these issues, we describe a filament evolution whose characteristics seem to be directly linked to the magnetic helicity transport in corona. Methods: We applied different methods to determine the helicity sign and the chirality of the filament magnetic field. We also computed the magnetic helicity transport rate at the filament footpoints. Results: All the observational signatures provided information on the positive helicity and sinistral chirality of the flux rope containing the filament material: its forward S shape, the orientation of its barbs, the bright and dark threads at 195 Å. Moreover, the magnetic helicity transport rate at the filament footpoints showed a clear accumulation of positive helicity. Conclusions: The study of this event showed a correspondence between several signatures of the sinistral chirality of the filament and several evidences of the positive magnetic helicity of the filament magnetic field. We also found that the magnetic helicity transported along the filament footpoints showed an increase just before the change of the filament shape observed in Hα images. We argued that the photospheric regions where the filament was rooted might be the preferential ways where the magnetic helicity was injected along the filament itself and where the conditions to trigger the eruption were yielded.

Experimental investigation on enhanced heat transfer of vertical condensers with trisection helical baffles

International Nuclear Information System (INIS)

Wu, Jiafeng; Zhou, Jiahao; Chen, Yaping; Wang, Mingchao; Dong, Cong; Guo, Ya

2016-01-01

Highlights: • Trisection helical baffles are introduced for vertical condenser enhancement. • Condensation in short-section and intermediate drainage is applied in new schemes. • Helical baffles with liquid dam and drainage gaps can promote condenser performance. • Dual-thread baffle scheme is superior to that of single-thread one by about 19%. • Condensation enhancement ratio of helical schemes is 1.5–2.5 over segment one. - Abstract: The vertical condensers have advantages of small occupation area, convenient in assemble or dismantle tube bundle and simple structure etc. However, the low heat transfer performance limits their applications. To enhance the heat transfer, a novel type of vertical condensers was designed by introducing trisection helical baffles with liquid dams and gaps for facilitating condensate drainage. Four configurations of vertical condensers with trisection helical baffle are experimentally studied and compared to a traditional segment baffle condenser. The enhancement ratio of trisection helical baffle schemes is about 1.5–2.5 and the heat transfer coefficient of the dual-thread trisection helical baffle scheme is superior to that of the single-thread one by about 19%. Assistant by the theoretical study, the experimental data is simulated and the condensation enhancement mechanisms by applying trisection helical baffle in vertical condenser are summarized as condensate drainage, short tube construct and reduce steam dead zone functions of the helical baffles.

Structures and related properties of helical, disulfide-stabilized peptides

Energy Technology Data Exchange (ETDEWEB)

Pagel, Mark D. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

1993-11-01

The three dimensional structure of several peptides were determined by NMR spectroscopy and distance geometry calculations. Each peptide formed a predictable, rigid structure, consisting of an α-helix, a "scaffold" region which packed along one face of the helix, and two disulfide bridges which covalently connect the helix and scaffold regions. The peptide Apa-M5 was designed to constrain the M5 peptide from MLCK in a helical geometry using the apamin disulfide scaffold. This scaffold constrains the N- terminal end of the helix with two disulfide bridges and a reverse turn. Like the M5 peptide, Apa-M5 was found to bind calmodulin in a Ca²⁺-dependent 1:1 stoichiometry. However, the dissociation constant of the (Apa-M5)-calmodulin complex, 107 nM, was 100-fold higher than the dissociation constant of the M5-calmodulin complex. This difference was due to a putative steric overlap between the Apa-M5 scaffold and calmodulin. The peptide Apa-Cro was designed to replace the large structural protein matrix of λ Cro with the apamin disulfide scaffold. However, Apa-Cro did not bind the consensus DNA operator half-site of λ Cro, probably due to a steric overlap between the Apa-Cro disulfide framework and the DNA. The amino acid sequence of the scaffold-disulfide bridge arrangement of the peptide Max was derived from the core sequence of scyllatoxin, which contains an α-helix constrained at the C-terminal end by two disulfide bridges and a two-stranded βsheet scaffold. Max was shown to fold with >84% yield to form a predictable, stable structure that is similar to scyllatoxin. The folding and stability properties of Max make this scaffold and disulfide bridge arrangement an ideal candidate for the development of hybrid sequence peptides. The dynamics of a fraying C-terminal end of the helix of the peptide Apa-AlaN was determined by analysis of ¹⁵N NMR relaxation properties.

Helical Phase Inflation and Monodromy in Supergravity Theory

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Tianjun Li

2015-01-01

Full Text Available We study helical phase inflation which realizes “monodromy inflation” in supergravity theory. In the model, inflation is driven by the phase component of a complex field whose potential possesses helicoid structure. We construct phase monodromy based on explicitly breaking global U(1 symmetry in the superpotential. By integrating out heavy fields, the phase monodromy from single complex scalar field is realized and the model fulfills natural inflation. The phase-axion alignment is achieved from explicitly symmetry breaking and gives super-Planckian phase decay constant. The F-term scalar potential provides strong field stabilization for all the scalars except inflaton, which is protected by the approximate global U(1 symmetry. Besides, we show that helical phase inflation can be naturally realized in no-scale supergravity with SU(2,1/SU(2×U(1 symmetry since the supergravity setup needed for phase monodromy is automatically provided in the no-scale Kähler potential. We also demonstrate that helical phase inflation can be reduced to another well-known supergravity inflation model with shift symmetry. Helical phase inflation is free from the UV-sensitivity problem although there is super-Planckian field excursion, and it suggests that inflation can be effectively studied based on supersymmetric field theory while a UV-completed framework is not prerequisite.

Numerical simulation of an excited round jet under helical disturbances by three-dimensional discrete vortex method; Helical kakuran ni yoru reiki enkei funryu no uzuho simulation

Energy Technology Data Exchange (ETDEWEB)

Izawa, S.; Kiya, M.; Mochizuki, O. [Hokkaido University, Sapporo (Japan)

1998-09-25

The evolution of vortical structure in an impulsively started round jet has been studied numerically by means of a three-dimensional vortex blob method. The viscous diffusion of vorticity is approximated by a core spreading model originally proposed by Leonard (1980). The jet is forced by axisymmetric, helical and multiple disturbances. The multiple disturbances are combinations of two helical disturbances of the same mode rotating in the opposite directions. The multiple disturbances are found to enhance both the generation of small-scale structures and the growth rate of the jet. The small-scale structures have highly organized spatial distributions. The core spreading method is effective in aquiring the core overlapping in regions of high extensional rate of strain. 21 refs., 12 figs.

Hydrogen bonds and heat diffusion in α-helices: a computational study.

Science.gov (United States)

Miño, German; Barriga, Raul; Gutierrez, Gonzalo

2014-08-28

Recent evidence has shown a correlation between the heat diffusion pathways and the known allosteric communication pathways in proteins. Allosteric communication in proteins is a central, yet unsolved, problem in biochemistry, and the study and characterization of the structural determinants that mediate energy transfer among different parts of proteins is of major importance. In this work, we characterized the role of hydrogen bonds in diffusivity of thermal energy for two sets of α-helices with different abilities to form hydrogen bonds. These hydrogen bonds can be a constitutive part of the α-helices or can arise from the lateral chains. In our in vacuo simulations, it was observed that α-helices with a higher possibility of forming hydrogen bonds also had higher rates of thermalization. Our simulations also revealed that heat readily flowed through atoms involved in hydrogen bonds. As a general conclusion, according to our simulations, hydrogen bonds fulfilled an important role in heat diffusion in structural patters of proteins.

Diffraction by DNA, carbon nanotubes and other helical nanostructures

International Nuclear Information System (INIS)

Lucas, Amand A; Lambin, Philippe

2005-01-01

This review discusses the diffraction patterns of x-rays or electrons scattered by fibres of helical biological molecules and by carbon nanotubes (CNTs) from the unified point of view of the Fourier-Bessel transform of an atomic helix. This paper is intended for scientists who are not professional crystallographers. X-ray fibre diffraction patterns of Pauling's protein α-helix and of Crick and Pauling's protein coiled-coil are revisited. This is followed by a non-technical comparison between the historic x-ray diffraction patterns of the A and B conformations of DNA, which were crucial for the discovery of the double helix. The qualitative analysis of the diffraction images is supported by novel optical simulation experiments designed to pinpoint the gross structural informational content of the patterns. The spectacular helical structure of the tobacco mosaic virus determined by Rosalind Franklin and co-workers will then be described as an early example of the great power of x-ray crystallography in determining the structure of a large biomolecular edifice. After these mostly historical and didactic case studies, this paper will consider electron diffraction and transmission electron microscopy of CNTs of great current interest, focusing particularly on recent data obtained for single-wall, double-wall and scrolled nanotubes. Several points of convergence between the interpretations of the diffraction patterns of biological helices and CNTs will be emphasized

Amphipathic alpha-helices and putative cholesterol binding domains of the influenza virus matrix M1 protein are crucial for virion structure organisation.

Science.gov (United States)

Tsfasman, Tatyana; Kost, Vladimir; Markushin, Stanislav; Lotte, Vera; Koptiaeva, Irina; Bogacheva, Elena; Baratova, Ludmila; Radyukhin, Victor

2015-12-02

The influenza virus matrix M1 protein is an amphitropic membrane-associated protein, forming the matrix layer immediately beneath the virus raft membrane, thereby ensuring the proper structure of the influenza virion. The objective of this study was to elucidate M1 fine structural characteristics, which determine amphitropic properties and raft membrane activities of the protein, via 3D in silico modelling with subsequent mutational analysis. Computer simulations suggest the amphipathic nature of the M1 α-helices and the existence of putative cholesterol binding (CRAC) motifs on six amphipathic α-helices. Our finding explains for the first time many features of this protein, particularly the amphitropic properties and raft/cholesterol binding potential. To verify these results, we generated mutants of the A/WSN/33 strain via reverse genetics. The M1 mutations included F32Y in the CRAC of α-helix 2, W45Y and W45F in the CRAC of α-helix 3, Y100S in the CRAC of α-helix 6, M128A and M128S in the CRAC of α-helix 8 and a double L103I/L130I mutation in both a putative cholesterol consensus motif and the nuclear localisation signal. All mutations resulted in viruses with unusual filamentous morphology. Previous experimental data regarding the morphology of M1-gene mutant influenza viruses can now be explained in structural terms and are consistent with the pivotal role of the CRAC-domains and amphipathic α-helices in M1-lipid interactions. Copyright © 2015 Elsevier B.V. All rights reserved.

Helical waves in easy-plane antiferromagnets

Science.gov (United States)

Semenov, Yuriy G.; Li, Xi-Lai; Xu, Xinyi; Kim, Ki Wook

2017-12-01

Effective spin torques can generate the Néel vector oscillations in antiferromagnets (AFMs). Here, it is theoretically shown that these torques applied at one end of a normal AFM strip can excite a helical type of spin wave in the strip whose properties are drastically different from characteristic spin waves. An analysis based on both a Néel vector dynamical equation and the micromagnetic simulation identifies the direction of magnetic anisotropy and the damping factor as the two key parameters determining the dynamics. Helical wave propagation requires the hard axis of the easy-plane AFM to be aligned with the traveling direction, while the damping limits its spatial extent. If the damping is neglected, the calculation leads to a uniform periodic domain wall structure. On the other hand, finite damping decelerates the helical wave rotation around the hard axis, ultimately causing stoppage of its propagation along the strip. With the group velocity staying close to spin-wave velocity at the wave front, the wavelength becomes correspondingly longer away from the excitation point. In a sufficiently short strip, a steady-state oscillation can be established whose frequency is controlled by the waveguide length as well as the excitation energy or torque.

Study on reinforced concrete beams with helical transverse reinforcement

Science.gov (United States)

Kaarthik Krishna, N.; Sandeep, S.; Mini, K. M.

2018-02-01

In a Reinforced Concrete (R.C) structure, major reinforcement is used for taking up tensile stresses acting on the structure due to applied loading. The present paper reports the behavior of reinforced concrete beams with helical reinforcement (transverse reinforcement) subjected to monotonous loading by 3-point flexure test. The results were compared with identically similar reinforced concrete beams with rectangular stirrups. During the test crack evolution, load carrying capacity and deflection of the beams were monitored, analyzed and compared. Test results indicate that the use of helical reinforcement provides enhanced load carrying capacity and a lower deflection proving to be more ductile, clearly indicating the advantage in carrying horizontal loads. An analysis was also carried out using ANSYS software in order to compare the test results of both the beams.

Pyrolysis of Helical Coordination Polymers for Metal-Sulfide-Based Helices with Broadband Chiroptical Activity.

Science.gov (United States)

Hirai, Kenji; Yeom, Bongjun; Sada, Kazuki

2017-06-27

Fabrication of chiroptical materials with broadband response in the visible light region is vital to fully realize their potential applications. One way to achieve broadband chiroptical activity is to fabricate chiral nanostructures from materials that exhibit broadband absorption in the visible light region. However, the compounds used for chiroptical materials have predominantly been limited to materials with narrowband spectral response. Here, we synthesize Ag 2 S-based nanohelices derived from helical coordination polymers. The right- and left-handed coordination helices used as precursors are prepared from l- and d-glutathione with Ag + and a small amount of Cu 2+ . The pyrolysis of the coordination helices yields right- and left-handed helices of Cu 0.12 Ag 1.94 S/C, which exhibit chiroptical activity spanning the entire visible light region. Finite element method simulations substantiate that the broadband chiroptical activity is attributed to synergistic broadband light absorption and light scattering. Furthermore, another series of Cu 0.10 Ag 1.90 S/C nanohelices are synthesized by choosing the l- or d-Glu-Cys as starting materials. The pitch length of nanohelicies is controlled by changing the peptides, which alters their chiroptical properties. The pyrolysis of coordination helices enables one to fabricate helical Ag 2 S-based materials that enable broadband chiroptical activity but have not been explored owing to the lack of synthetic routes.

Measurements of the Canonical Helicity Evolution of a Gyrating Kinked Flux Rope

Science.gov (United States)

von der Linden, J.; Sears, J.; Intrator, T.; You, S.

2017-12-01

Magnetic structures in the solar corona and planetary magnetospheres are often modelled as magnetic flux ropes governed by magnetohydrodynamics (MHD); however, inside these structures, as exhibited in reconnection, conversions between magnetic and kinetic energies occur over a wide range of scales. Flux ropes based on the flux of canonical momentum circulation extend the flux rope concept to include effects of finite particle momentum and present the distinct advantage of reconciling all plasma regimes - e.g. kinetic, two-fluid, and MHD - with the topological concept of helicity: twists, writhes, and linkages. This presentation shows the first visualization and analysis of the 3D dynamics of canonical flux ropes and their relative helicity evolution from laboratory measurements. Ion and electron canonical flux ropes are visualized from a dataset of Mach, triple, and Ḃ probe measurements at over 10,000 spatial locations of a gyrating kinked flux rope. The flux ropes co-gyrate with the peak density and electron temperature in and out of a measurement volume. The electron and ion canonical flux ropes twist with opposite handedness and the ion flux ropes writhe around the electron flux ropes. The relative cross helicity between the magnetic and ion flow vorticity flux ropes dominates the relative ion canonical helicity and is anti-correlated with the relative magnetic helicity. The 3D nature of the kink and a reverse eddy current affect the helicity evolution. This work is supported by DOE Grant DE-SC0010340 and the DOE Office of Science Graduate Student Research Program and prepared in part by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-735426

Swimming Characteristics of Bioinspired Helical Microswimmers Based on Soft Lotus-Root Fibers

Directory of Open Access Journals (Sweden)

Jia Liu

2017-11-01

Full Text Available Various kinds of helical swimmers inspired by E. coli bacteria have been developed continually in many types of researches, but most of them are proposed by the rigid bodies. For the targeted drug delivery, the rigid body may hurt soft tissues of the working region with organs. Due to this problem, the biomedical applications of helical swimmers may be restricted. However, the helical microswimmers with the soft and deformable body are appropriate and highly adaptive in a confined environment. Thus, this paper presents a lotus-root-based helical microswimmer, which is fabricated by the fibers of lotus-root coated with magnetic nanoparticles to active under the magnetic fields. The helical microstructures are derived from the intrinsic biological structures of the fibers of the lotus-root. This paper aims to study the swimming characteristic of lotus-root-based microswimmers with deformable helical bodies. In the initial step under the uniform magnetic actuation, the helical microswimmers are bent lightly due to the heterogeneous distribution of the internal stress, and then they undergo a swimming motion which is a spindle-like rotation locomotion. Our experiments report that the microswimmers with soft bodies can locomote faster than those with rigid bodies. Moreover, we also find that the curvature of the shape decreases as a function of actuating field frequency which is related to the deformability of lotus-root fibers.

Employing helicity amplitudes for resummation

International Nuclear Information System (INIS)

Moult, Ian; Stewart, Iain W.; Tackmann, Frank J.; Waalewijn, Wouter J.; Amsterdam Univ.

2015-08-01

Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are directly given in terms of color-ordered helicity amplitudes. Using this basis allows one to seamlessly combine fixed-order helicity amplitudes at any order they are known with a resummation of higher-order logarithmic corrections. In particular, the virtual loop amplitudes can be employed in factorization theorems to make predictions for exclusive jet cross sections without the use of numerical subtraction schemes to handle real-virtual infrared cancellations. We also discuss matching onto SCET in renormalization schemes with helicities in 4- and d-dimensions. To demonstrate that our helicity operator basis is easy to use, we provide an explicit construction of the operator basis, as well as results for the hard matching coefficients, for pp → H+0,1,2 jets, pp → W/Z/γ+0,1,2 jets, and pp → 2,3 jets. These operator bases are completely crossing symmetric, so the results can easily be applied to processes with e + e - and e - p collisions.

Helical bifurcation and tearing mode in a plasma—a description based on Casimir foliation

International Nuclear Information System (INIS)

Yoshida, Z; Dewar, R L

2012-01-01

The relation between the helical bifurcation of a Taylor relaxed state (a Beltrami equilibrium) and a tearing mode is analyzed in a Hamiltonian framework. Invoking an Eulerian representation of the Hamiltonian, the symplectic operator (defining a Poisson bracket) becomes non-canonical, i.e. the symplectic operator has a nontrivial cokernel (dual to its nullspace), foliating the phase space into level sets of Casimir invariants. A Taylor relaxed state is an equilibrium point on a Casimir (helicity) leaf. Changing the helicity, equilibrium points may bifurcate to produce helical relaxed states; a necessary and sufficient condition for bifurcation is derived. Tearing yields a helical perturbation on an unstable equilibrium, producing a helical structure approximately similar to a helical relaxed state. A slight discrepancy found between the helically bifurcated relaxed state and the linear tearing mode viewed as a perturbed, singular equilibrium state is attributed to a Casimir element (named ‘helical flux’) pertinent to a ‘resonance singularity’ of the non-canonical symplectic operator. While the helical bifurcation can occur at discrete eigenvalues of the Beltrami parameter, the tearing mode, being a singular eigenfunction, exists for an arbitrary Beltrami parameter. Bifurcated Beltrami equilibria appearing on the same helicity leaf are isolated by the helical-flux Casimir foliation. The obstacle preventing the tearing mode to develop in the ideal limit turns out to be the shielding current sheet on the resonant surface, preventing the release of the ‘potential energy’. When this current is dissipated by resistivity, reconnection is allowed and tearing instability occurs. The Δ′ criterion for linear tearing instability of Beltrami equilibria is shown to be directly related to the spectrum of the curl operator. (paper)

Water-stable helical structure of tertiary amides of bicyclic β-amino acid bearing 7-azabicyclo[2.2.1]heptane. Full control of amide cis-trans equilibrium by bridgehead substitution.

Science.gov (United States)

Hosoya, Masahiro; Otani, Yuko; Kawahata, Masatoshi; Yamaguchi, Kentaro; Ohwada, Tomohiko

2010-10-27

Helical structures of oligomers of non-natural β-amino acids are significantly stabilized by intramolecular hydrogen bonding between main-chain amide moieties in many cases, but the structures are generally susceptible to the environment; that is, helices may unfold in protic solvents such as water. For the generation of non-hydrogen-bonded ordered structures of amides (tertiary amides in most cases), control of cis-trans isomerization is crucial, even though there is only a small sterical difference with respect to cis and trans orientations. We have established methods for synthesis of conformationally constrained β-proline mimics, that is, bridgehead-substituted 7-azabicyclo[2.2.1]heptane-2-endo-carboxylic acids. Our crystallographic, 1D- and 2D-NMR, and CD spectroscopic studies in solution revealed that a bridgehead methoxymethyl substituent completely biased the cis-trans equilibrium to the cis-amide structure along the main chain, and helical structures based on the cis-amide linkage were generated independently of the number of residues, from the minimalist dimer through the tetramer, hexamer, and up to the octamer, and irrespective of the solvent (e.g., water, alcohol, halogenated solvents, and cyclohexane). Generality of the control of the amide equilibrium by bridgehead substitution was also examined.

RosettaTMH: a method for membrane protein structure elucidation combining EPR distance restraints with assembly of transmembrane helices

Directory of Open Access Journals (Sweden)

Andrew Leaver-Fay

2015-12-01

Full Text Available Membrane proteins make up approximately one third of all proteins, and they play key roles in a plethora of physiological processes. However, membrane proteins make up less than 2% of experimentally determined structures, despite significant advances in structure determination methods, such as X-ray crystallography, nuclear magnetic resonance spectroscopy, and cryo-electron microscopy. One potential alternative means of structure elucidation is to combine computational methods with experimental EPR data. In 2011, Hirst and others introduced RosettaEPR and demonstrated that this approach could be successfully applied to fold soluble proteins. Furthermore, few computational methods for de novo folding of integral membrane proteins have been presented. In this work, we present RosettaTMH, a novel algorithm for structure prediction of helical membrane proteins. A benchmark set of 34 proteins, in which the proteins ranged in size from 91 to 565 residues, was used to compare RosettaTMH to Rosetta’s two existing membrane protein folding protocols: the published RosettaMembrane folding protocol (“MembraneAbinitio” and folding from an extended chain (“ExtendedChain”. When EPR distance restraints are used, RosettaTMH+EPR outperforms ExtendedChain+EPR for 11 proteins, including the largest six proteins tested. RosettaTMH+EPR is capable of achieving native-like folds for 30 of 34 proteins tested, including receptors and transporters. For example, the average RMSD100SSE relative to the crystal structure for rhodopsin was 6.1 ± 0.4 Å and 6.5 ± 0.6 Å for the 449-residue nitric oxide reductase subunit B, where the standard deviation reflects variance in RMSD100SSE values across ten different EPR distance restraint sets. The addition of RosettaTMH and RosettaTMH+EPR to the Rosetta family of de novo folding methods broadens the scope of helical membrane proteins that can be accurately modeled with this software suite.

Optimization of the Magnetic Field Structure for Sustained Plasma Gun Helicity Injection for Magnetic Turbulence Studies at the Bryn Mawr Plasma Laboratory

Science.gov (United States)

Cartagena-Sanchez, C. A.; Schaffner, D. A.; Johnson, H. K.; Fahim, L. E.

2017-10-01

A long-pulsed magnetic coaxial plasma gun is being implemented and characterized at the Bryn Mawr Plasma Laboratory (BMPL). A cold cathode discharged between the cylindrical electrodes generates and launches plasma into a 24cm diameter, 2m long chamber. Three separately pulsed magnetic coils are carefully positioned to generate radial magnetic field between the electrodes at the gun edge in order to provide stuffing field. Magnetic helicity is continuously injected into the flux-conserving vacuum chamber in a process akin to sustained slow-formation of spheromaks. The aim of this source, however, is to supply long pulses of turbulent magnetized plasma for measurement rather than for sustained spheromak production. The work shown here details the optimization of the magnetic field structure for this sustained helicity injection.

Is gadolinium a helical antiferromagnet or a collinear ferromagnet?

Indian Academy of Sciences (India)

that a helical spin structure similar to that prevalent in other heavy rare-earth .... magnetocrystalline anisotropy factor, HK is the uniaxial anisotropy field and MS is .... lends firm support to the observation that the asymptotic critical behaviour of ...

Chirality induction and protonation-induced molecular motions in helical molecular strands.

Science.gov (United States)

Kolomiets, Elena; Berl, Volker; Lehn, Jean-Marie

2007-01-01

The long oligopyridinedicarboxamide strand 9, containing 15 heterocyclic rings has been synthesized and its helical structure determined by X-ray crystallography. It was shown that the shorter analogue 6 displays induced circular dichroism and amplification of induced chirality upon dissolution in an optically active solvent, diethyl-L-tartrate. A novel class of helical foldamers was prepared, strands 14-16, based on two oligopyridine carboxamide segments linked through a L-tartaric acid derived spacer. These tartro strands display internal chirality induction as well as chirality amplification. NMR spectroscopy (on 8 and 9) and circular dichroism (on 16) studies show that the oligopyridine carboxamide strands undergo reversible unfolding/folding upon protonation. The protonation-induced unfolding has been confirmed by X-ray crystallographic determination of the molecular structure of the extended protonated heptameric form 8(+). The molecular-scale mechano-chemical motions of the protonation-induced structural switching consist of a change of the length of the molecule, from 6 angstroms (6, coiled form) to 29 angstroms (8(+), uncoiled form) for the heptamer and from 12.5 angstroms (9, coiled form, X-ray structure) to 57 angstroms (9(+), uncoiled form, from modeling) for the pentadecamer. Similar unfolding/folding motional processes take place in the L-tartro strands 15 and 16 upon protonation/deprotonation, with loss of helicity-induced circular dichroism on unfolding as shown for the protonated form 16(+).

Magnetic helicity balance in the Sustained Spheromak Plasma Experiment

International Nuclear Information System (INIS)

Stallard, B.W.; Hooper, E.B.; Woodruff, S.; Bulmer, R.H.; Hill, D.N.; McLean, H.S.; Wood, R.D.

2003-01-01

The magnetic helicity balance between the helicity input injected by a magnetized coaxial gun, the rate-of-change in plasma helicity content, and helicity dissipation in electrode sheaths and Ohmic losses have been examined in the Sustained Spheromak Plasma Experiment (SSPX) [E. B. Hooper, L. D. Pearlstein, and R. H. Bulmer, Nucl. Fusion 39, 863 (1999)]. Helicity is treated as a flux function in the mean-field approximation, allowing separation of helicity drive and losses between closed and open field volumes. For nearly sustained spheromak plasmas with low fluctuations, helicity balance analysis implies a decreasing transport of helicity from the gun input into the spheromak core at higher spheromak electron temperature. Long pulse discharges with continuously increasing helicity and larger fluctuations show higher helicity coupling from the edge to the spheromak core. The magnitude of the sheath voltage drop, inferred from cathode heating and a current threshold dependence of the gun voltage, shows that sheath losses are important and reduce the helicity injection efficiency in SSPX

On the inverse transfer of (non-)helical magnetic energy in a decaying magnetohydrodynamic turbulence

Science.gov (United States)

Park, Kiwan

2017-12-01

In our conventional understanding, large-scale magnetic fields are thought to originate from an inverse cascade in the presence of magnetic helicity, differential rotation or a magneto-rotational instability. However, as recent simulations have given strong indications that an inverse cascade (transfer) may occur even in the absence of magnetic helicity, the physical origin of this inverse cascade is still not fully understood. We here present two simulations of freely decaying helical and non-helical magnetohydrodynamic (MHD) turbulence. We verified the inverse transfer of helical and non-helical magnetic fields in both cases, but we found the underlying physical principles to be fundamentally different. In the former case, the helical magnetic component leads to an inverse cascade of magnetic energy. We derived a semi-analytic formula for the evolution of large-scale magnetic field using α coefficient and compared it with the simulation data. But in the latter case, the α effect, including other conventional dynamo theories, is not suitable to describe the inverse transfer of non-helical magnetic energy. To obtain a better understanding of the physics at work here, we introduced a 'field structure model' based on the magnetic induction equation in the presence of inhomogeneities. This model illustrates how the curl of the electromotive force leads to the build up of a large-scale magnetic field without the requirement of magnetic helicity. And we applied a quasi-normal approximation to the inverse transfer of magnetic energy.

The α-Helical Structure of Prodomains Promotes Translocation of Intrinsically Disordered Neuropeptide Hormones into the Endoplasmic Reticulum*

Science.gov (United States)

Dirndorfer, Daniela; Seidel, Ralf P.; Nimrod, Guy; Miesbauer, Margit; Ben-Tal, Nir; Engelhard, Martin; Zimmermann, Richard; Winklhofer, Konstanze F.; Tatzelt, Jörg

2013-01-01

Different neuropeptide hormones, which are either too small to adopt a stable conformation or are predicted to be intrinsically disordered, are synthesized as larger precursors containing a prodomain in addition to an N-terminal signal peptide. We analyzed the biogenesis of three unstructured neuropeptide hormones and observed that translocation of these precursors into the lumen of the endoplasmic reticulum (ER) is critically dependent on the presence of the prodomain. The hormone domains could be deleted from the precursors without interfering with ER import and secretion, whereas constructs lacking the prodomain remained in the cytosol. Domain-swapping experiments revealed that the activity of the prodomains to promote productive ER import resides in their ability to adopt an α-helical structure. Removal of the prodomain from the precursor did not interfere with co-translational targeting of the nascent chain to the Sec61 translocon but with its subsequent productive translocation into the ER lumen. Our study reveals a novel function of prodomains to enable import of small or intrinsically disordered secretory proteins into the ER based on their ability to adopt an α-helical conformation. PMID:23532840

Diffusion in a tokamak with helical magnetic cells

International Nuclear Information System (INIS)

Wakatani, Masahiro

1975-05-01

In a tokamak with helical magnetic cells produced by a resonant helical magnetic field, diffusion in the collisional regime is studied. The diffusion coefficient is greatly enhanced near the resonant surface even for a weak helical magnetic field. A theoretical model for disruptive instabilities based on the enhanced transport due to helical magnetic cells is discussed. This may explain experiments of the tokamak with resonant helical fields qualitatively. (author)

Nano-structure and optical properties (plasmonic) of graded helical square tower-like (terraced) Mn sculptured thin films

Energy Technology Data Exchange (ETDEWEB)

Savaloni, Hadi, E-mail: savaloni@khayam.ut.ac.ir [Department of Physics, University of Tehran, North-Kargar Street, Tehran (Iran, Islamic Republic of); Fakharpour, Mahsa [Department of Physics, Islamic Azad University, Science and Research Branch, Tehran (Iran, Islamic Republic of); Siabi-Garjan, Araz [Department of Advanced Technologies, University of Mohaghegh Ardabili, Namin, Ardabil (Iran, Islamic Republic of); Department of Materials Engineering and Nanotechnology, Sabalan University of Advanced Technologies (SUAT), Namin (Iran, Islamic Republic of); Placido, Frank [SUPA and Institute of Thin Films, Sensors and Imaging, University of The West of Scotland, High Street, Paisley (United Kingdom); Babaei, Ferydon [Department of Physics, University of Qom, Qom (Iran, Islamic Republic of)

2017-01-30

Highlights: • Graded helical square tower-like terraced sculptured Mn thin films are produced with different number of arms. • XRD, AFM, FESEM and optical analyses as well as theoretical calculations are carried out. • Intensity of Plasmon peaks depend on the polarization, the incident angle, and the distance from the shadowing block. • The presence of defects in these sculptured structures can be predicted by theoretical investigation. • Experimental and theoretical investigations show consistent results. - Abstract: Graded helical square tower-like terraced sculptured Mn thin films (GHSTTS) are produced in three stages with different number of arms using oblique angle deposition together with rotation of substrate holder about its surface normal, plus a shadowing block fixed at the centre of the substrate holder. The structural characterization of the produced samples was obtained using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). Results showed a structural gradient with distance from the edge of the shadowing block, which in turn is responsible for the decrease in the volume of void fraction and increase of grain size. Plasmon absorption peaks observed in the optical analysis of these nano-structures showed that their wavelength region and intensity depend on the polarization and the incident angle of light, as well as the distance from the edge of the shadowing block. According to our model and discrete dipole approximation (DDA) calculations, when the number of parallel nano-rods of different lengths and radii are increased the peak in the spectrum shifts to shorter wavelengths (blue shift). Also when the diameters of the nano-rods increases (a situation that occurs with increasing film thickness) the results is again a blue shift in the spectrum. The presence of defects in these sculptured structures caused by the shadowing effect is predicted by the theoretical DDA investigation of their optical spectra

How reverse turns may mediate the formation of helical segments in proteins: an x-ray model.

OpenAIRE

Perczel, A; Foxman, B M; Fasman, G D

1992-01-01

The three-dimensional structure of a protein is the assembly of different secondary structural elements, such as alpha-helices, beta-pleated sheets, and beta-turns. Although the conformation of hundreds of proteins has been elaborated in the solid state, only a vague understanding of the mechanism of their conformational folding is known. One facet of this topic is the conformational interconversion of one or more beta-turns to a helical structure (and vice versa), which may also be related t...

Dynamics of zonal flows in helical systems.

Science.gov (United States)

Sugama, H; Watanabe, T-H

2005-03-25

A theory for describing collisionless long-time behavior of zonal flows in helical systems is presented and its validity is verified by gyrokinetic-Vlasov simulation. It is shown that, under the influence of particles trapped in helical ripples, the response of zonal flows to a given source becomes weaker for lower radial wave numbers and deeper helical ripples while a high-level zonal-flow response, which is not affected by helical-ripple-trapped particles, can be maintained for a longer time by reducing their bounce-averaged radial drift velocity. This implies a possibility that helical configurations optimized for reducing neoclassical ripple transport can simultaneously enhance zonal flows which lower anomalous transport.

Parameterization and measurements of helical magnetic fields

International Nuclear Information System (INIS)

Fischer, W.; Okamura, M.

1997-01-01

Magnetic fields with helical symmetry can be parameterized using multipole coefficients (a n , b n ). We present a parameterization that gives the familiar multipole coefficients (a n , b n ) for straight magnets when the helical wavelength tends to infinity. To measure helical fields all methods used for straight magnets can be employed. We show how to convert the results of those measurements to obtain the desired helical multipole coefficients (a n , b n )

Synthesis of Norbornene Derived Helical Copolymer by Simple Molecular Marriage Approach to Produce Smart Nanocarrier.

Science.gov (United States)

Mane, Shivshankar R; Sathyan, Ashlin; Shunmugam, Raja

2017-03-22

A novel library of norbornene derived helical copolymer has been synthesized through the coupling of two homopolymers via Molecular Marriage Approach. The helicity is governed by the non-covalent interactions like hydrogen bonding, π-π stacking and the influence of hydrophobic and hydrophilic motifs. The detailed characterization of the copolymer (Copoly 1) has been provided and the super structures are confirmed through dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The observed size of the aggregates was about 200 nm. The density functional theory (DFT) is favorably supported for the formation of proposed structure of Copoly 1. Circular dichroism (CD) measurement has confirmed the one handed helical structure of the copolymer. Reservoir capability of this pH responsive polymer (Copoly 1) to encapsulate anti-cancer drug doxorubicin (DOX) warrants its potential applications in the field of bio-medical sciences.

Conceptual design of the superconducting magnet system for the helical fusion reactor

International Nuclear Information System (INIS)

Yanagi, Nagato; Hamaguchi, Shinji; Takahata, Kazuya; Natsume, Kyohei

2013-01-01

Current status of conceptual design of superconducting magnet system and low temperature system for the helical fusion reactor are introduced. There are three kinds of candidates of superconducting magnets such as Cable-in-conduit (CIC), Low-Temperature Superconductor (LTS) and High-Temperature Superconductor (HTS). Their characteristic properties, coil designs and cooling systems are stated. The freezer and low temperature distribution system, bus line and current lead, and excitation power source for superconducting coil are reported. The various elements of superconducting magnet system of FFHR-d1, partial cross section of FFHR helical coil using CIC, conceptual diagram of helical coil winding method of FFHR using CIC, relation among mass flow of supercritical helium supplied into CIC conductor and temperature increasing and pressure loss, cross section structure of LTS indirect-cooling conductor at 100 kA, cross section of 100-kA HTS conductor, connection method of helical coil segment and YBCO conductor are illustrated. (S.Y.)

Supramolecular Architectures and Mimics of Complex Natural Folds Derived from Rationally Designed alpha-Helical Protein Structures

Science.gov (United States)

Tavenor, Nathan Albert

Protein-based supramolecular polymers (SMPs) are a class of biomaterials which draw inspiration from and expand upon the many examples of complex protein quaternary structures observed in nature: collagen, microtubules, viral capsids, etc. Designing synthetic supramolecular protein scaffolds both increases our understanding of natural superstructures and allows for the creation of novel materials. Similar to small-molecule SMPs, protein-based SMPs form due to self-assembly driven by intermolecular interactions between monomers, and monomer structure determines the properties of the overall material. Using protein-based monomers takes advantage of the self-assembly and highly specific molecular recognition properties encodable in polypeptide sequences to rationally design SMP architectures. The central hypothesis underlying our work is that alpha-helical coiled coils, a well-studied protein quaternary folding motif, are well-suited to SMP design through the addition of synthetic linkers at solvent-exposed sites. Through small changes in the structures of the cross-links and/or peptide sequence, we have been able to control both the nanoscale organization and the macroscopic properties of the SMPs. Changes to the linker and hydrophobic core of the peptide can be used to control polymer rigidity, stability, and dimensionality. The gaps in knowledge that this thesis sought to fill on this project were 1) the relationship between the molecular structure of the cross-linked polypeptides and the macroscopic properties of the SMPs and 2) a means of creating materials exhibiting multi-dimensional net or framework topologies. Separate from the above efforts on supramolecular architectures was work on improving backbone modification strategies for an alpha-helix in the context of a complex protein tertiary fold. Earlier work in our lab had successfully incorporated unnatural building blocks into every major secondary structure (beta-sheet, alpha-helix, loops and beta

Overview of results from the Large Helical Device

International Nuclear Information System (INIS)

Yamada, H.

2010-11-01

The physical understanding of net-current free helical plasmas has progressed in the Large Helical Device (LHD) since the last Fusion Energy Conference in Geneva, 2008. The experimental results from LHD have promoted detailed physical documentation of features specific to net-current-free 3-D helical plasmas as well as complementary to the tokamak approach. The primary heating source is NBI with a heating power of 23 MW, and ECH with 3.7 MW plays an important role in local heating and power modulation in transport studies. The maximum central density has reached 1.2 x 10 21 m -3 due to the formation of an Internal Diffusion Barrier (IDB) at the magnetic field of 2.5 T. The IDB has been maintained for 3 s by refueling with repetitive pellet injection. The plasma with a central ion temperature reaching 5.6 keV exhibits the formation of an Internal Transport Barrier (ITB). The ion thermal diffusivity decreases to the level predicted by neoclassical transport. This ITB is accompanied by spontaneous toroidal rotation and an Impurity Hole which generates an impurity-free core. Impurity Hole is due to a large outward convection of impurities in spite of the negative radial electric field. The magnitude of the Impurity Hole is enhanced in the magnetic configuration with larger helical ripple and for higher Z impurities. Another mechanism to suppress impurity contamination has been identified at the plasma edge with a stochastic magnetic field. A helical system shares common physics issues with tokamaks such as 3-D equilibria, transport in a stochastic magnetic field, plasma response to a Resonant Magnetic Perturbation (RMP), divertor physics, and the role of radial electric field and meso-scale structure. (author)

Lasing thresholds of helical photonic structures with different positions of a single light-amplifying helix turn

Energy Technology Data Exchange (ETDEWEB)

Blinov, L M; Palto, S P [A.V. Shubnikov Institute of Crystallography, Russian Academy of Sciences, Moscow, Russian Federaion (Russian Federation)

2013-09-30

Numerical simulation is used to assess the lasing threshold of helical structures of cholesteric liquid crystals (CLCs) in which only one turn amplifies light. This turn is located either in the centre of symmetric structures of various sizes or in an arbitrary place in asymmetric structures of preset size. In all cases, we find singularities in light amplification by a one-dimensional CLC structure for the most important band-edge modes (m1, m2 and m3) and plot the threshold gain coefficient k{sub th} against the position of the amplifying turn. For the symmetric structures, the lasing threshold of the m1 mode is shown to vary linearly with the inverse of the square of the cavity length. Moreover, modes with a lower density of photonic states (DOS) in the cavity may have a lower lasing threshold. This can be accounted for by the dependence of the density of photonic states on the position of the amplifying turn and, accordingly, by the nonuniform electromagnetic field intensity distribution along the cavity for different modes. In the asymmetric structures, the same field energy distribution is responsible for a correlation between k{sub th} and DOS curves. (lasers)

Evidence for Mixed Helicity in Erupting Filaments

Science.gov (United States)

Muglach, K.; Wang, Y.-M.; Kliem, B.

2009-09-01

Erupting filaments are sometimes observed to undergo a rotation about the vertical direction as they rise. This rotation of the filament axis is generally interpreted as a conversion of twist into writhe in a kink-unstable magnetic flux rope. Consistent with this interpretation, the rotation is usually found to be clockwise (as viewed from above) if the post-eruption arcade has right-handed helicity, but counterclockwise if it has left-handed helicity. Here, we describe two non-active-region filament events recorded with the Extreme-Ultraviolet Imaging Telescope on the Solar and Heliospheric Observatory in which the sense of rotation appears to be opposite to that expected from the helicity of the post-event arcade. Based on these observations, we suggest that the rotation of the filament axis is, in general, determined by the net helicity of the erupting system, and that the axially aligned core of the filament can have the opposite helicity sign to the surrounding field. In most cases, the surrounding field provides the main contribution to the net helicity. In the events reported here, however, the helicity associated with the filament "barbs" is opposite in sign to and dominates that of the overlying arcade.

Helicity and potential vorticity in the surface boundary layer turbulence

Science.gov (United States)

Chkhetiani, Otto; Kurgansky, Michael; Koprov, Boris; Koprov, Victor

2016-04-01

An experimental measurement of all three components of the velocity and vorticity vectors, as well as the temperature and its gradient, and potential vorticity, has been developed using four acoustic anemometers. Anemometers were placed at vertices of a tetrahedron, the horizontal base of which was a rectangular triangle with equal legs, and the upper point was exactly above the top of the right angle. The distance from the surface to the tetrahedron its base was 5.5 m, and the lengths of legs and a vertical edge were 5 m. The measurements were carried out of total duration near 100 hours both in stable and unstable stratification conditions (at the Tsimlyansk Scientific Station in a uniform area of virgin steppe 700 x 650 m, August 2012). A covariance-correlation matrix for turbulent variations in all measured values has been calculated. In the daytime horizontal and vertical components of the helicity are of the order of -0.03 and +0.01 m s-2, respectively. The nighttime signs remain unchanged, but the absolute values are several times smaller. It is confirmed also by statistics of a relative helicity. The cospectra and spectral correlation coefficients have been calculated for all helicity components. The time variations in the components of "instantaneous" relative helicity and potential vorticity are considered. Connections of helicity with Monin-Obukhov length and the wind vertical profile structure are discussed. This work was supported by the Russian Science Foundation (Project No 14-27-00134).

Applications of 2D helical vortex dynamics

DEFF Research Database (Denmark)

Okulov, Valery; Sørensen, Jens Nørkær

2010-01-01

In the paper, we show how the assumption of helical symmetry in the context of 2D helical vortices can be exploited to analyse and to model various cases of rotating flows. From theory, examples of three basic applications of 2D dynamics of helical vortices embedded in flows with helical symmetry...... of the vorticity field are addressed. These included some of the problems related to vortex breakdown, instability of far wakes behind rotors and vortex theory of ideal rotors....

Theoretical aspects of magnetic helicity

International Nuclear Information System (INIS)

Hammer, J.H.

1985-01-01

The magnetic helicity, usually defined as K=integralA.Bdv, where A is the vector potential and B the magnetic field, measures the topological linkage of magnetic fluxes. Helicity manifests itself in the twistedness and knottedness of flux tubes. Its significance is that it is an ideal MHD invariant. While the helicity formalism has proven very useful in understanding reversed field pinch and spheromak behavior, some problems exist in applying the method consistently for complex (e.g., toroidal) conductor geometries or in situations where magnetic flux penetrates conducting walls. Recent work has attempted to generalize K to allow for all possible geometries

Influence of crystallite size and temperature on the antiferromagnetic helices of terbium and holmium metal

Energy Technology Data Exchange (ETDEWEB)

Bick, Jens-Peter; Michels, Andreas [Universitaet des Saarlandes, D-66041 Saarbruecken (Germany); University of Luxembourg, L-1511 Luxembourg (Luxembourg); Ferdinand, Adrian; Birringer, Rainer [Universitaet des Saarlandes, D-66041 Saarbruecken (Germany); Baller, Joerg; Sanctuary, Roland [University of Luxembourg, L-1511 Luxembourg (Luxembourg); Philippi, Stefan [Leibniz Institute for Solid State and Materials Research, D-01069 Dresden (Germany); Lott, Dieter [GKSS Research Center, D-21502 Geesthacht (Germany); Balog, Sandor [Paul Scherrer Institute, CH-5232 Villigen (Switzerland); Rotenberg, Eli [Lawrence Berkeley National Laboratory, California 94720 (United States); Kaindl, Guenter [Freie Universitaet Berlin, D-14195 Berlin-Dahlem (Germany); Doebrich, Kristian M. [Freie Universitaet Berlin, D-14195 Berlin-Dahlem (Germany); Max-Born-Institut, D-12489 Berlin (Germany)

2011-07-01

We report on the results of grain-size and temperature-dependent magnetization, specific-heat, neutron-scattering, and angle-resolved photoelectron spectroscopy (ARPES) experiments on the heavy rare-earth metals terbium and holmium, with particular emphasis on the temperature regions where the helical antiferromagnetic phases exist. In contrast to Ho, we find that the helical structure in Tb is relative strongly affected by microstructural disorder, specifically, it can no longer be detected for the smallest studied grain size of D=18 nm. Moreover, in coarse-grained Tb a helical structure persists even in the ferromagnetic regime, down to about T=215 K, in agreement with the ARPES data, which reveal a nesting feature of the Fermi surface at the L point of the Brillouin zone at T=210 K.

Effects of Magnetic and Kinetic Helicities on the Growth of Magnetic Fields in Laminar and Turbulent Flows by Helical Fourier Decomposition

Energy Technology Data Exchange (ETDEWEB)

Linkmann, Moritz; Sahoo, Ganapati; Biferale, Luca [Department of Physics and INFN, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Rome (Italy); McKay, Mairi; Berera, Arjun [School of Physics and Astronomy, University of Edinburgh, Peter Guthrie Tait Road, EH9 3FD, Edinburgh (United Kingdom)

2017-02-10

We present a numerical and analytical study of incompressible homogeneous conducting fluids using a helical Fourier representation. We analytically study both small- and large-scale dynamo properties, as well as the inverse cascade of magnetic helicity, in the most general minimal subset of interacting velocity and magnetic fields on a closed Fourier triad. We mainly focus on the dependency of magnetic field growth as a function of the distribution of kinetic and magnetic helicities among the three interacting wavenumbers. By combining direct numerical simulations of the full magnetohydrodynamics equations with the helical Fourier decomposition, we numerically confirm that in the kinematic dynamo regime the system develops a large-scale magnetic helicity with opposite sign compared to the small-scale kinetic helicity, a sort of triad-by-triad α -effect in Fourier space. Concerning the small-scale perturbations, we predict theoretically and confirm numerically that the largest instability is achived for the magnetic component with the same helicity of the flow, in agreement with the Stretch–Twist–Fold mechanism. Vice versa, in the presence of Lorentz feedback on the velocity, we find that the inverse cascade of magnetic helicity is mostly local if magnetic and kinetic helicities have opposite signs, while it is more nonlocal and more intense if they have the same sign, as predicted by the analytical approach. Our analytical and numerical results further demonstrate the potential of the helical Fourier decomposition to elucidate the entangled dynamics of magnetic and kinetic helicities both in fully developed turbulence and in laminar flows.

Electronic transport in single-helical protein molecules: Effects of multiple charge conduction pathways and helical symmetry

Energy Technology Data Exchange (ETDEWEB)

Kundu, Sourav, E-mail: sourav.kunduphy@gmail.com; Karmakar, S.N.

2016-07-15

We propose a tight-binding model to investigate electronic transport properties of single helical protein molecules incorporating both the helical symmetry and the possibility of multiple charge transfer pathways. Our study reveals that due to existence of both the multiple charge transfer pathways and helical symmetry, the transport properties are quite rigid under influence of environmental fluctuations which indicates that these biomolecules can serve as better alternatives in nanoelectronic devices than its other biological counterparts e.g., single-stranded DNA.

Total scalp irradiation using helical tomotherapy

International Nuclear Information System (INIS)

Orton, Nigel; Jaradat, Hazim; Welsh, James; Tome, Wolfgang

2005-01-01

Homogeneous irradiation of the scalp poses technical and dosimetric challenges due to the extensive, superficial, curved treatment volume. Conventional treatments on a linear accelerator use multiple matched electron fields or a combination of electron and photon fields. Problems with these techniques include dose heterogeneity in the target due to varying source-to-skin distance (SSD) and angle of beam incidence, significant dose to the brain, and the potential for overdose or underdose at match lines between the fields. Linac-based intensity-modulated radiation therapy (IMRT) plans have similar problems. This work presents treatment plans for total scalp irradiation on a helical tomotherapy machine. Helical tomotherapy is well-suited for scalp irradiation because it has the ability to deliver beamlets that are tangential to the scalp at all points. Helical tomotherapy also avoids problems associated with field matching and use of more than one modality. Tomotherapy treatment plans were generated and are compared to plans for treatment of the same patient on a linac. The resulting tomotherapy plans show more homogeneous target dose and improved critical structure dose when compared to state-of-the-art linac techniques. Target equivalent uniform dose (EUD) for the best tomotherapy plan was slightly higher than for the linac plan, while the volume of brain tissue receiving over 30 Gy was reduced by two thirds. Furthermore, the tomotherapy plan can be more reliably delivered than linac treatments, because the patient is aligned prior to each treatment based on megavoltage computed tomography (MVCT)

Employing Helicity Amplitudes for Resummation

NARCIS (Netherlands)

Moult, I.; Stewart, I.W.; Tackmann, F.J.; Waalewijn, W.J.

2015-01-01

Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are

Helicity multiplexed broadband metasurface holograms.

Science.gov (United States)

Wen, Dandan; Yue, Fuyong; Li, Guixin; Zheng, Guoxing; Chan, Kinlong; Chen, Shumei; Chen, Ming; Li, King Fai; Wong, Polis Wing Han; Cheah, Kok Wai; Pun, Edwin Yue Bun; Zhang, Shuang; Chen, Xianzhong

2015-09-10

Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices.

Collagenolytic Matrix Metalloproteinase Activities toward Peptomeric Triple-Helical Substrates.

Science.gov (United States)

Stawikowski, Maciej J; Stawikowska, Roma; Fields, Gregg B

2015-05-19

Although collagenolytic matrix metalloproteinases (MMPs) possess common domain organizations, there are subtle differences in their processing of collagenous triple-helical substrates. In this study, we have incorporated peptoid residues into collagen model triple-helical peptides and examined MMP activities toward these peptomeric chimeras. Several different peptoid residues were incorporated into triple-helical substrates at subsites P3, P1, P1', and P10' individually or in combination, and the effects of the peptoid residues were evaluated on the activities of full-length MMP-1, MMP-8, MMP-13, and MMP-14/MT1-MMP. Most peptomers showed little discrimination between MMPs. However, a peptomer containing N-methyl Gly (sarcosine) in the P1' subsite and N-isobutyl Gly (NLeu) in the P10' subsite was hydrolyzed efficiently only by MMP-13 [nomenclature relative to the α1(I)772-786 sequence]. Cleavage site analysis showed hydrolysis at the Gly-Gln bond, indicating a shifted binding of the triple helix compared to the parent sequence. Favorable hydrolysis by MMP-13 was not due to sequence specificity or instability of the substrate triple helix but rather was based on the specific interactions of the P7' peptoid residue with the MMP-13 hemopexin-like domain. A fluorescence resonance energy transfer triple-helical peptomer was constructed and found to be readily processed by MMP-13, not cleaved by MMP-1 and MMP-8, and weakly hydrolyzed by MT1-MMP. The influence of the triple-helical structure containing peptoid residues on the interaction between MMP subsites and individual substrate residues may provide additional information about the mechanism of collagenolysis, the understanding of collagen specificity, and the design of selective MMP probes.

Vorticity field, helicity integral and persistence of entanglement in reaction-diffusion systems

International Nuclear Information System (INIS)

Trueba, J L; Arrayas, M

2009-01-01

We show that a global description of the stability of entangled structures in reaction-diffusion systems can be made by means of a helicity integral. A vorticity vector field is defined for these systems, as in electromagnetism or fluid dynamics. We have found under which conditions the helicity is conserved or lost through the boundaries of the medium, so the entanglement of structures observed is preserved or disappears during time evolution. We illustrate the theory with an example of knotted entanglement in a FitzHugh-Nagumo model. For this model, we introduce new non-trivial initial conditions using the Hopf fibration and follow the time evolution of the entanglement. (fast track communication)

Vorticity field, helicity integral and persistence of entanglement in reaction-diffusion systems

Energy Technology Data Exchange (ETDEWEB)

Trueba, J L; Arrayas, M [Area de Electromagnetismo, Universidad Rey Juan Carlos, Camino del Molino s/n, 28943 Fuenlabrada, Madrid (Spain)

2009-07-17

We show that a global description of the stability of entangled structures in reaction-diffusion systems can be made by means of a helicity integral. A vorticity vector field is defined for these systems, as in electromagnetism or fluid dynamics. We have found under which conditions the helicity is conserved or lost through the boundaries of the medium, so the entanglement of structures observed is preserved or disappears during time evolution. We illustrate the theory with an example of knotted entanglement in a FitzHugh-Nagumo model. For this model, we introduce new non-trivial initial conditions using the Hopf fibration and follow the time evolution of the entanglement. (fast track communication)

The geometrical origin of the strain-twist coupling in double helices

Directory of Open Access Journals (Sweden)

Kasper Olsen

2011-03-01

Full Text Available A simple geometrical explanation for the counterintuitive phenomenon when twist leads to extension in double helices is presented. The coupling between strain and twist is investigated using a tubular description. It is shown that the relation between strain and rotation is universal and depends only on the pitch angle. For pitch angles below 39.4° strain leads to further winding, while for larger pitch angles strain leads to unwinding. The zero-twist structure, with a pitch angle of 39.4°, is at the unique point between winding and unwinding and independent of the mechanical properties of the double helix. The existence of zero-twist structures, i.e. structures that display neither winding, nor unwinding under strain is discussed. Close-packed double helices are shown to extend rather than shorten when twisted. Numerical estimates of this elongation upon winding are given for DNA, chromatin, and RNA.

Geometrical principles of homomeric β-barrels and β-helices: Application to modeling amyloid protofilaments.

Science.gov (United States)

Hayward, Steven; Milner-White, E James

2017-10-01

Examples of homomeric β-helices and β-barrels have recently emerged. Here we generalize the theory for the shear number in β-barrels to encompass β-helices and homomeric structures. We introduce the concept of the "β-strip," the set of parallel or antiparallel neighboring strands, from which the whole helix can be generated giving it n-fold rotational symmetry. In this context, the shear number is interpreted as the sum around the helix of the fixed register shift between neighboring identical β-strips. Using this approach, we have derived relationships between helical width, pitch, angle between strand direction and helical axis, mass per length, register shift, and number of strands. The validity and unifying power of the method is demonstrated with known structures including α-hemolysin, T4 phage spike, cylindrin, and the HET-s(218-289) prion. From reported dimensions measured by X-ray fiber diffraction on amyloid fibrils, the relationships can be used to predict the register shift and the number of strands within amyloid protofilaments. This was used to construct models of transthyretin and Alzheimer β(40) amyloid protofilaments that comprise a single strip of in-register β-strands folded into a "β-strip helix." Results suggest both stabilization of an individual β-strip helix and growth by addition of further β-strip helices can involve the same pair of sequence segments associating with β-sheet hydrogen bonding at the same register shift. This process would be aided by a repeat sequence. Hence, understanding how the register shift (as the distance between repeat sequences) relates to helical dimensions will be useful for nanotube design. © 2017 Wiley Periodicals, Inc.

Small-x Asymptotics of the Quark Helicity Distribution.

Science.gov (United States)

Kovchegov, Yuri V; Pitonyak, Daniel; Sievert, Matthew D

2017-02-03

We construct a numerical solution of the small-x evolution equations derived in our recent work [J. High Energy Phys. 01 (2016) 072.JHEPFG1029-847910.1007/JHEP01(2016)072] for the (anti)quark transverse momentum dependent helicity TMDs and parton distribution functions (PDFs) as well as the g_{1} structure function. We focus on the case of large N_{c}, where one finds a closed set of equations. Employing the extracted intercept, we are able to predict directly from theory the behavior of the quark helicity PDFs at small x, which should have important phenomenological consequences. We also give an estimate of how much of the proton's spin carried by the quarks may be at small x and what impact this has on the spin puzzle.

Single-superfield helical-phase inflation

Energy Technology Data Exchange (ETDEWEB)

Ketov, Sergei V., E-mail: ketov@tmu.ac.jp [Department of Physics, Tokyo Metropolitan University, Minami-ohsawa 1-1, Hachioji-shi, Tokyo 192-0397 (Japan); Kavli Institute for the Physics and Mathematics of the Universe (IPMU), The University of Tokyo, Chiba 277-8568 (Japan); Institute of Physics and Technology, Tomsk Polytechnic University, 30 Lenin Ave., Tomsk 634050 (Russian Federation); Terada, Takahiro, E-mail: takahiro@hep-th.phys.s.u-tokyo.ac.jp [Department of Physics, The University of Tokyo, Tokyo 113-0033 (Japan); Deutsches Elektronen-Synchrotron (DESY), 22607 Hamburg (Germany)

2016-01-10

Large-field inflation in supergravity requires the approximate global symmetry needed to protect flatness of the scalar potential. In helical-phase inflation, the U(1) symmetry of the Kähler potential is assumed, the phase part of the complex scalar of a chiral superfield plays the role of inflaton, and the radial part is strongly stabilized. The original model of helical phase inflation, proposed by Li, Li and Nanopoulos (LLN), employs an extra (stabilizer) superfield. We propose a more economical new class of the helical phase inflationary models without a stabilizer superfield. As the specific examples, the quadratic, the natural, and the Starobinsky-type inflationary models are studied in our approach.

A real-scale helical coil winding trial of the Large Helical Device

International Nuclear Information System (INIS)

Senba, T.; Yamamoto, T.; Tamaki, T.; Asano, K.; Suzuki, S.; Yamauchi, T.; Uchida, K.; Nakanishi, K.; Yamagiwa, T.; Suzuki, S.; Miyoshi, R.; Sasa, H.; Watanabe, S.; Tatemura, M.; Hatada, N.; Yamaguchi, S.; Imagawa, S.; Yanagi, N.; Satow, T.; Yamamoto, J.; Motojima, O.

1995-01-01

A real-scale helical coil winding trial of the Large Helical Device (LHD) has been conducted for a study of coil winding configuration and winding methods and for exhibiting the state of the art. It includes construction and test run of a specifically designed winding machine and development of various manufacturing methods for accurate coil winding. It has been carried out in Hitachi Works before in situ winding, and has provided much needed engineering data for construction of the LHD. (orig.)

Evidence for α-helices in the gas phase: a case study using Melittin from honey bee venom.

Science.gov (United States)

Florance, Hannah V; Stopford, Andrew P; Kalapothakis, Jason M; McCullough, Bryan J; Bretherick, Andrew; Barran, Perdita E

2011-09-07

Gas phase methodologies are increasingly used to study the structure of proteins and peptides. A challenge to the mass spectrometrist is to preserve the structure of the system of interest intact and unaltered from solution into the gas phase. Small peptides are very flexible and can present a number of conformations in solution. In this work we examine Melittin a 26 amino acid peptide that forms the active component of honey bee venom. Melittin is haemolytic and has been shown to form an α-helical tetrameric structure by X-ray crystallography [M. Gribskov et al., The RCSB Protein Data Bank, 1990] and to be helical in high concentrations of methanol. Here we use ion mobility mass spectrometry, molecular dynamics and gas-phase HDX to probe its structure in the gas phase and specifically interrogate whether the helical form can be preserved. All low energy calculated structures possess some helicity. In our experiments we examine the peptide following nano-ESI from solutions with varying methanol content. Ion mobility gives collision cross sections (CCS) that compare well with values found from molecular modelling and from other reported structures, but with inconclusive results regarding the effect of solvent. There is only a slight increase in CCS with charge, showing minimal coloumbically driven unfolding. HDX supports preservation of some helical content into the gas phase and again shows little difference in the exchange rates of species sprayed from different solvents. The [M + 3H](3+) species has two exchanging populations both of which exhibit faster exchange rates than observed for the [M + 2H](2+) species. One interpretation for these results is that the time spent being analysed is sufficient for this peptide to form a helix in the 'ultimate' hydrophobic environment of a vacuum.

On the helicity of open magnetic fields

International Nuclear Information System (INIS)

Prior, C.; Yeates, A. R.

2014-01-01

We reconsider the topological interpretation of magnetic helicity for magnetic fields in open domains, and relate this to the relative helicity. Specifically, our domains stretch between two parallel planes, and each of these ends may be magnetically open. It is demonstrated that, while the magnetic helicity is gauge-dependent, its value in any gauge may be physically interpreted as the average winding number among all pairs of field lines with respect to some orthonormal frame field. In fact, the choice of gauge is equivalent to the choice of reference field in the relative helicity, meaning that the magnetic helicity is no less physically meaningful. We prove that a particular gauge always measures the winding with respect to a fixed frame, and propose that this is normally the best choice. For periodic fields, this choice is equivalent to measuring relative helicity with respect to a potential reference field. However, for aperiodic fields, we show that the potential field can be twisted. We prove by construction that there always exists a possible untwisted reference field.

Hydrogen recycling and transport in the helical divertor of TEXTOR

Energy Technology Data Exchange (ETDEWEB)

Clever, Meike

2010-07-01

The aim of this thesis was to investigate the hydrogen recycling at the target plates of the helical divertor in TEXTOR and by this the capability of this divertor configuration to access such favourable operational regimes. In order to study the different divertor density regimes in TEXTOR, discharges were performed in which the total plasma density was increased continuously up to the density limit. The recycling was investigated in a fixed helical divertor structure where four helical strike points with a poloidal width of about 8-10 cm are created at the divertor target plates. The experimental investigation of the hydrogen recycling was carried out using mainly spectroscopic methods supplemented by Langmuir probe, interferometric and atomic beam measurements. In the framework of this thesis a spectroscopic multi camera system has been built that facilitates the simultaneous observation of four different spectral lines, recording images of the divertor target plates and the plasma volume close to the target. The system facilitates the simultaneous measurement of the poloidal and toroidal pattern of the recycling flux at the divertor target without the need for sweeping the plasma structure. The simultaneous observation of different spectral lines reduces the uncertainty in the analysis based on several lines, as the contribution from uncertainties in the reproducibility of plasma parameters in different discharges are eliminated and only the uncertainty of the measurement method limits the accuracy. The spatial resolution of the system in poloidal and toroidal direction (0.8 mm{+-}0.01 mm) is small compared to the separation of the helical strike points, the capability of the measurement method to resolve these structures is therefore limited by the line-of-sight integration and the penetration depth of the light emitting species. The measurements showed that the recycling flux increases linearly with increasing plasma density, a high recycling regime is not

Hydrogen recycling and transport in the helical divertor of TEXTOR

International Nuclear Information System (INIS)

Clever, Meike

2010-01-01

The aim of this thesis was to investigate the hydrogen recycling at the target plates of the helical divertor in TEXTOR and by this the capability of this divertor configuration to access such favourable operational regimes. In order to study the different divertor density regimes in TEXTOR, discharges were performed in which the total plasma density was increased continuously up to the density limit. The recycling was investigated in a fixed helical divertor structure where four helical strike points with a poloidal width of about 8-10 cm are created at the divertor target plates. The experimental investigation of the hydrogen recycling was carried out using mainly spectroscopic methods supplemented by Langmuir probe, interferometric and atomic beam measurements. In the framework of this thesis a spectroscopic multi camera system has been built that facilitates the simultaneous observation of four different spectral lines, recording images of the divertor target plates and the plasma volume close to the target. The system facilitates the simultaneous measurement of the poloidal and toroidal pattern of the recycling flux at the divertor target without the need for sweeping the plasma structure. The simultaneous observation of different spectral lines reduces the uncertainty in the analysis based on several lines, as the contribution from uncertainties in the reproducibility of plasma parameters in different discharges are eliminated and only the uncertainty of the measurement method limits the accuracy. The spatial resolution of the system in poloidal and toroidal direction (0.8 mm±0.01 mm) is small compared to the separation of the helical strike points, the capability of the measurement method to resolve these structures is therefore limited by the line-of-sight integration and the penetration depth of the light emitting species. The measurements showed that the recycling flux increases linearly with increasing plasma density, a high recycling regime is not

Splitting of α-Helical Structure as Molecular Basis for Abolishing an Amyloid Formation by Multiple Glycosylation: A Molecular Dynamics Simulation Study

Energy Technology Data Exchange (ETDEWEB)

Choi, Youngjin [Hoseo University, Asan (Korea, Republic of); Cho, Eunae; Jung, Seunho [Konkuk University, Seoul (Korea, Republic of)

2016-07-15

Molecular details played by glycosylation are complicated by the subtle nature of variations in the glycan structure, and this complexity is one of the research barriers to establish structure-function relationship on the protein modification. This is particularly true for understanding the exact structural consequence of the glycosylation of the biological proteins. The present MD simulation revealed molecular-level mechanism of the glycosylation effect on the peptide to understand the experimentally observed phenomenon for inhibiting amyloid formation in the model peptide. The galactose residue on the Ser17 undermined the helical integrity of main protein region by enhancing sugar–amino acid interaction and perturbing natural interactions between amino acid residues.

Impact of helical boundary conditions on nonlinear 3D magnetohydrodynamic simulations of reversed-field pinch

International Nuclear Information System (INIS)

Veranda, M; Bonfiglio, D; Cappello, S; Chacón, L; Escande, D F

2013-01-01

Helical self-organized reversed-field pinch (RFP) regimes emerge both numerically—in 3D visco-resistive magnetohydrodynamic (MHD) simulations—and experimentally, as in the RFX-mod device at high current (I P above 1 MA). These states, called quasi-single helicity (QSH) states, are characterized by the action of a MHD mode that impresses a quasi-helical symmetry to the system, thus allowing a high degree of magnetic chaos healing. This is in contrast with the multiple helicity (MH) states, where magnetic fluctuations create a chaotic magnetic field degrading the confinement properties of the RFP. This paper reports an extensive numerical study performed in the frame of 3D visco-resistive MHD which considers the effect of helical magnetic boundary conditions, i.e. of a finite value of the radial magnetic field at the edge (magnetic perturbation, MP). We show that the system can be driven to a selected QSH state starting from both spontaneous QSH and MH regimes. In particular, a high enough MP can force a QSH helical self-organization with a helicity different from the spontaneous one. Moreover, MH states can be turned into QSH states with a selected helicity. A threshold in the amplitude of MP is observed above which is able to influence the system. Analysis of the magnetic topology of these simulations indicates that the dominant helical mode is able to temporarily sustain conserved magnetic structures in the core of the plasma. The region occupied by conserved magnetic surfaces increases reducing secondary modes' amplitude to experimental-like values. (paper)

HEMISPHERIC HELICITY TREND FOR SOLAR CYCLE 24

International Nuclear Information System (INIS)

Hao Juan; Zhang Mei

2011-01-01

Using vector magnetograms obtained with the Spectro-polarimeter (SP) on board Hinode satellite, we studied two helicity parameters (local twist and current helicity) of 64 active regions that occurred in the descending phase of solar cycle 23 and the ascending phase of solar cycle 24. Our analysis gives the following results. (1) The 34 active regions of the solar cycle 24 follow the so-called hemispheric helicity rule, whereas the 30 active regions of the solar cycle 23 do not. (2) When combining all 64 active regions as one sample, they follow the hemispheric helicity sign rule as in most other observations. (3) Despite the so-far most accurate measurement of vector magnetic field given by SP/Hinode, the rule is still weak with large scatters. (4) The data show evidence of different helicity signs between strong and weak fields, confirming previous result from a large sample of ground-based observations. (5) With two example sunspots we show that the helicity parameters change sign from the inner umbra to the outer penumbra, where the sign of penumbra agrees with the sign of the active region as a whole. From these results, we speculate that both the Σ-effect (turbulent convection) and the dynamo have contributed in the generation of helicity, whereas in both cases turbulence in the convection zone has played a significant role.

Ion temperature gradient modes in toroidal helical systems

Energy Technology Data Exchange (ETDEWEB)

Kuroda, T. [Graduate University for Advanced Studies, Toki, Gifu (Japan); Sugama, H.; Kanno, R.; Okamoto, M.

2000-04-01

Linear properties of ion temperature gradient (ITG) modes in helical systems are studied. The real frequency, growth rate, and eigenfunction are obtained for both stable and unstable cases by solving a kinetic integral equation with proper analytic continuation performed in the complex frequency plane. Based on the model magnetic configuration for toroidal helical systems like the Large Helical Device (LHD), dependences of the ITG mode properties on various plasma equilibrium parameters are investigated. Particularly, relative effects of {nabla}B-curvature drifts driven by the toroidicity and by the helical ripples are examined in order to compare the ITG modes in helical systems with those in tokamaks. (author)

Ion temperature gradient modes in toroidal helical systems

International Nuclear Information System (INIS)

Kuroda, T.; Sugama, H.; Kanno, R.; Okamoto, M.

2000-04-01

Linear properties of ion temperature gradient (ITG) modes in helical systems are studied. The real frequency, growth rate, and eigenfunction are obtained for both stable and unstable cases by solving a kinetic integral equation with proper analytic continuation performed in the complex frequency plane. Based on the model magnetic configuration for toroidal helical systems like the Large Helical Device (LHD), dependences of the ITG mode properties on various plasma equilibrium parameters are investigated. Particularly, relative effects of ∇B-curvature drifts driven by the toroidicity and by the helical ripples are examined in order to compare the ITG modes in helical systems with those in tokamaks. (author)

Generalized helicity and Beltrami fields

International Nuclear Information System (INIS)

Buniy, Roman V.; Kephart, Thomas W.

2014-01-01

We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional 1/4 ∫ Ω trF μν F μν d 4 x subject to the local constraint ε μναβ trF μν F αβ =0 satisfies the covariant non-abelian Beltrami equation. -- Highlights: •We introduce the covariant non-abelian helicity and Beltrami equation. •The Yang–Mills action and instanton term constraint lead to the Beltrami equation. •Solutions of the Beltrami equation conserve helicity

Molecular Dynamics with Helical Periodic Boundary Conditions

Czech Academy of Sciences Publication Activity Database

Kessler, Jiří; Bouř, Petr

2014-01-01

Roč. 35, č. 21 (2014), s. 1552-1559 ISSN 0192-8651 R&D Projects: GA ČR GAP208/11/0105; GA MŠk(CZ) LH11033 Grant - others:GA AV ČR(CZ) M200551205; GA MŠk(CZ) LM2010005 Institutional support: RVO:61388963 Keywords : periodic boundary conditions * helical symmetry * molecular dynamics * protein structure * amyloid fibrils Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.589, year: 2014

Helical-D pinch

International Nuclear Information System (INIS)

Schaffer, M.J.

1997-08-01

A stabilized pinch configuration is described, consisting of a D-shaped plasma cross section wrapped tightly around a guiding axis. The open-quotes helical-Dclose quotes geometry produces a very large axial (toroidal) transform of magnetic line direction that reverses the pitch of the magnetic lines without the need of azimuthal (poloidal) plasma current. Thus, there is no need of a open-quotes dynamoclose quotes process and its associated fluctuations. The resulting configuration has the high magnetic shear and pitch reversal of the reversed field pinch (RFP). (Pitch = P = qR, where R = major radius). A helical-D pinch might demonstrate good confinement at q << 1

Employing helicity amplitudes for resummation in SCET

International Nuclear Information System (INIS)

Moult, Ian; Stewart, Iain W.; Tackmann, Frank J.; Waalewijn, Wouter J.; Nikhef, Amsterdam

2016-05-01

Helicity amplitudes are the fundamental ingredients of many QCD calculations for multi-leg processes. We describe how these can seamlessly be combined with resummation in Soft-Collinear Effective Theory (SCET), by constructing a helicity operator basis for which the Wilson coefficients are directly given in terms of color-ordered helicity amplitudes. This basis is crossing symmetric and has simple transformation properties under discrete symmetries.

MHD stability analysis of helical system plasmas

International Nuclear Information System (INIS)

Nakamura, Yuji

2000-01-01

Several topics of the MHD stability studies in helical system plasmas are reviewed with respect to the linear and ideal modes mainly. Difference of the method of the MHD stability analysis in helical system plasmas from that in tokamak plasmas is emphasized. Lack of the cyclic (symmetric) coordinate makes an analysis more difficult. Recent topic about TAE modes in a helical system is also described briefly. (author)

SU-E-T-197: Helical Cranial-Spinal Treatments with a Linear Accelerator

Energy Technology Data Exchange (ETDEWEB)

Anderson, J; Bernard, D; Liao, Y; Templeton, A; Turian, J; Chu, J [Rush University Medical Center, Chicago, IL (United States)

2014-06-01

Purpose: Craniospinal irradiation (CSI) of systemic disease requires a high level of beam intensity modulation to reduce dose to bone marrow and other critical structures. Current helical delivery machines can take 30 minutes or more of beam-on time to complete these treatments. This pilot study aims to test the feasibility of performing helical treatments with a conventional linear accelerator using longitudinal couch travel during multiple gantry revolutions. Methods: The VMAT optimization package of the Eclipse 10.0 treatment planning system was used to optimize pseudo-helical CSI plans of 5 clinical patient scans. Each gantry revolution was divided into three 120° arcs with each isocenter shifted longitudinally. Treatments requiring more than the maximum 10 arcs used multiple plans with each plan after the first being optimized including the dose of the others (Figure 1). The beam pitch was varied between 0.2 and 0.9 (couch speed 5- 20cm/revolution and field width of 22cm) and dose-volume histograms of critical organs were compared to tomotherapy plans. Results: Viable pseudo-helical plans were achieved using Eclipse. Decreasing the pitch from 0.9 to 0.2 lowered the maximum lens dose by 40%, the mean bone marrow dose by 2.1% and the maximum esophagus dose by 17.5%. (Figure 2). Linac-based helical plans showed dose results comparable to tomotherapy delivery for both target coverage and critical organ sparing, with the D50 of bone marrow and esophagus respectively 12% and 31% lower in the helical linear accelerator plan (Figure 3). Total mean beam-on time for the linear accelerator plan was 8.3 minutes, 54% faster than the tomotherapy average for the same plans. Conclusions: This pilot study has demonstrated the feasibility of planning pseudo-helical treatments for CSI targets using a conventional linac and dynamic couch movement, and supports the ongoing development of true helical optimization and delivery.

Detergent-associated solution conformations of helical and beta-barrel membrane proteins.

Science.gov (United States)

Mo, Yiming; Lee, Byung-Kwon; Ankner, John F; Becker, Jeffrey M; Heller, William T

2008-10-23

Membrane proteins present major challenges for structural biology. In particular, the production of suitable crystals for high-resolution structural determination continues to be a significant roadblock for developing an atomic-level understanding of these vital cellular systems. The use of detergents for extracting membrane proteins from the native membrane for either crystallization or reconstitution into model lipid membranes for further study is assumed to leave the protein with the proper fold with a belt of detergent encompassing the membrane-spanning segments of the structure. Small-angle X-ray scattering was used to probe the detergent-associated solution conformations of three membrane proteins, namely bacteriorhodopsin (BR), the Ste2p G-protein coupled receptor from Saccharomyces cerevisiae, and the Escherichia coli porin OmpF. The results demonstrate that, contrary to the traditional model of a detergent-associated membrane protein, the helical proteins BR and Ste2p are not in the expected, compact conformation and associated with detergent micelles, while the beta-barrel OmpF is indeed embedded in a disk-like micelle in a properly folded state. The comparison provided by the BR and Ste2p, both members of the 7TM family of helical membrane proteins, further suggests that the interhelical interactions between the transmembrane helices of the two proteins differ, such that BR, like other rhodopsins, can properly refold to crystallize, while Ste2p continues to prove resistant to crystallization from an initially detergent-associated state.

Helical CT scan for emergent patients with cerebrovascular diseases

International Nuclear Information System (INIS)

Matsumoto, Masato; Sato, Naoki; Nakano, Masayuki; Watanabe, Youichi; Kodama, Namio

1995-01-01

We studied 44 emergent patients with cerebrovascular diseases (18 cases of subarachnoid hemorrhage, 15 of occlusive lesions, 7 of intracerebral hematoma and 4 of suspected subarachnoid hemorrhage) using helical CT scan. The helical CT scan was performed with contrast medium at a rate of 3 ml/sec with a delay of 20 sec, and was carried out before conventional angiography. The reconstruction time of 3D-CTA was within 10 min. We were able to obtain findings for the lesion on 3D-CTA before those on conventional angiography. The 3D-CTA yielded excellent images of the vascular structures and anatomical relationships of the aneurysm, its neck and parent artery, and surrounding arteries. However, it proved difficult to visualize vessels of less than 1 mm in diameter, especially the perforating arteries. In occlusive diseases, the degree of stenosis depended on the changes in CT number threshold: at present, evaluations of the lesions should be made by conventional angiography. 3D-CTA using helical CT scan can thus be applied for emergent patients with cerebrovascular diseases. Surgical simulation images of 3D-CTA were especially useful at the time of operation. (author)

Helical CT scan for emergent patients with cerebrovascular diseases

Energy Technology Data Exchange (ETDEWEB)

Matsumoto, Masato; Sato, Naoki; Nakano, Masayuki; Watanabe, Youichi; Kodama, Namio [Fukushima Medical Coll. (Japan)

1995-08-01

We studied 44 emergent patients with cerebrovascular diseases (18 cases of subarachnoid hemorrhage, 15 of occlusive lesions, 7 of intracerebral hematoma and 4 of suspected subarachnoid hemorrhage) using helical CT scan. The helical CT scan was performed with contrast medium at a rate of 3 ml/sec with a delay of 20 sec, and was carried out before conventional angiography. The reconstruction time of 3D-CTA was within 10 min. We were able to obtain findings for the lesion on 3D-CTA before those on conventional angiography. The 3D-CTA yielded excellent images of the vascular structures and anatomical relationships of the aneurysm, its neck and parent artery, and surrounding arteries. However, it proved difficult to visualize vessels of less than 1 mm in diameter, especially the perforating arteries. In occlusive diseases, the degree of stenosis depended on the changes in CT number threshold: at present, evaluations of the lesions should be made by conventional angiography. 3D-CTA using helical CT scan can thus be applied for emergent patients with cerebrovascular diseases. Surgical simulation images of 3D-CTA were especially useful at the time of operation. (author).

Generalized helicity and Beltrami fields

Energy Technology Data Exchange (ETDEWEB)

Buniy, Roman V., E-mail: roman.buniy@gmail.com [Schmid College of Science, Chapman University, Orange, CA 92866 (United States); Isaac Newton Institute, University of Cambridge, Cambridge, CB3 0EH (United Kingdom); Kephart, Thomas W., E-mail: tom.kephart@gmail.com [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Isaac Newton Institute, University of Cambridge, Cambridge, CB3 0EH (United Kingdom)

2014-05-15

We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional 1/4 ∫{sub Ω}trF{sub μν}F{sup μν}d{sup 4}x subject to the local constraint ε{sup μναβ}trF{sub μν}F{sub αβ}=0 satisfies the covariant non-abelian Beltrami equation. -- Highlights: •We introduce the covariant non-abelian helicity and Beltrami equation. •The Yang–Mills action and instanton term constraint lead to the Beltrami equation. •Solutions of the Beltrami equation conserve helicity.

CURRENT AND KINETIC HELICITY OF LONG-LIVED ACTIVITY COMPLEXES

International Nuclear Information System (INIS)

Komm, Rudolf; Gosain, Sanjay

2015-01-01

We study long-lived activity complexes and their current helicity at the solar surface and their kinetic helicity below the surface. The current helicity has been determined from synoptic vector magnetograms from the NSO/SOLIS facility, and the kinetic helicity of subsurface flows has been determined with ring-diagram analysis applied to full-disk Dopplergrams from NSO/GONG and SDO/HMI. Current and kinetic helicity of activity complexes follow the hemispheric helicity rule with mainly positive values (78%; 78%, respectively, with a 95% confidence level of 31%) in the southern hemisphere and negative ones (80%; 93%, respectively, with a 95% confidence level of 22% and 14%, respectively) in the northern hemisphere. The locations with the dominant sign of kinetic helicity derived from Global Oscillation Network Group (GONG) and SDO/HMI data are more organized than those of the secondary sign even if they are not part of an activity complex, while locations with the secondary sign are more fragmented. This is the case for both hemispheres even for the northern one where it is not as obvious visually due to the large amount of magnetic activity present as compared to the southern hemisphere. The current helicity shows a similar behavior. The dominant sign of current helicity is the same as that of kinetic helicity for the majority of the activity complexes (83% with a 95% confidence level of 15%). During the 24 Carrington rotations analyzed here, there is at least one longitude in each hemisphere where activity complexes occur repeatedly throughout the epoch. These ''active'' longitudes are identifiable as locations of strong current and kinetic helicity of the same sign

Simplification of the helical TEN2 laser

Science.gov (United States)

Krahn, K.-H.

1980-04-01

The observation that the helical TEN2 laser can effectively be simplified by giving up the use of decoupling elements as well as by abolishing the segmentation of the electrode structure is examined. Although, as a consequence of this simplification, the operating pressure range was slightly decreased, the output power could be improved by roughly 30%, a result which is attributed to the new electrode geometry exhibiting lower inductance and lower damping losses.

Structural transitions and guest/host complexing of liquid crystal helical nanofilaments induced by nanoconfinement.

Science.gov (United States)

Kim, Hanim; Ryu, Seong Ho; Tuchband, Michael; Shin, Tae Joo; Korblova, Eva; Walba, David M; Clark, Noel A; Yoon, Dong Ki

2017-02-01

A lamellar liquid crystal (LC) phase of certain bent-core mesogenic molecules can be grown in a manner that generates a single chiral helical nanofilament in each of the cylindrical nanopores of an anodic aluminum oxide (AAO) membrane. By introducing guest molecules into the resulting composite chiral nanochannels, we explore the structures and functionality of the ordered guest/host LC complex, verifying the smectic-like positional order of the fluidic nematic LC phase, which is obtained by the combination of the LC organization and the nanoporous AAO superstructure. The guest nematic LC 4'- n -pentyl-4-cyanobiphenyl is found to form a distinctive fluid layered ordered LC complex at the nanofilament/guest interface with the host 1,3-phenylene bis[4-(4-nonyloxyphenyliminomethyl)benzoate], where this interface contacts the AAO cylinder wall. Filament growth form is strongly influenced by mixture parameters and pore dimensions.

Helical Root Buckling: A Transient Mechanism for Stiff Interface Penetration

Science.gov (United States)

Silverberg, Jesse; Noar, Roslyn; Packer, Michael; Harrison, Maria; Cohen, Itai; Henley, Chris; Gerbode, Sharon

2011-03-01

Tilling in agriculture is commonly used to loosen the topmost layer of soil and promote healthy plant growth. As roots navigate this mechanically heterogeneous environment, they encounter interfaces between the compliant soil and the underlying compacted soil. Inspired by this problem, we used 3D time-lapse imaging of Medicago Truncatula plants to study root growth in two-layered transparent hydrogels. The layers are mechanically distinct; the top layer is more compliant than the bottom. We observe that the roots form a transient helical structure as they attempt to penetrate the bi-layer interface. Interpreting this phenotype as a form of buckling due to root elongation, we measured the helix size as a function of the surrounding gel modulus. Our measurements show that by twisting the root tip during growth, the helical structure recruits the surrounding medium for an enhanced penetration force allowing the plants access to the lower layer of gel.

Effect of Ovality on Maximum External Pressure of Helically Coiled Steam Generator Tubes with a Rectangular Wear

Energy Technology Data Exchange (ETDEWEB)

Shin, Dong In; Lim, Eun Mo; Huh, Nam Su [Seoul National Univ. of Science and Technology, Seoul (Korea, Republic of); Choi, Shin Beom; Yu, Je Yong; Kim, Ji Ho; Choi, Suhn [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2013-10-15

A structural integrity of steam generator tubes of nuclear power plants is one of crucial parameters for safe operation of nuclear power plants. Thus, many studies have been made to provide engineering methods to assess integrity of defective tubes of commercial nuclear power plants considering its operating environments and defect characteristics. As described above, the geometric and operating conditions of steam generator tubes in integral reactor are significantly different from those of commercial reactor. Therefore, the structural integrity assessment of defective tubes of integral reactor taking into account its own operating conditions and geometric characteristics, i. e., external pressure and helically coiled shape, should be made to demonstrate compliance with the current design criteria. Also, ovality is very specific characteristics of the helically coiled tube because it is occurred during the coiling processes. The wear, occurring from FIV (Flow Induced Vibration) and so on, is main degradation of steam generator tube. In the present study, maximum external pressure of helically coiled steam generator tube with wear is predicted based on the detailed 3-dimensional finite element analysis. As for shape of wear defect, the rectangular shape is considered. In particular, the effect of ovality on the maximum external pressure of helically coiled tubes with rectangular shaped wear is investigated. In the present work, the maximum external pressure of helically coiled steam generator tube with rectangular shaped wear is investigated via detailed 3-D FE analyses. In order to cover a practical range of geometries for defective tube, the variables affecting the maximum external pressure were systematically varied. In particular, the effect of tube ovality on the maximum external pressure is evaluated. It is expected that the present results can be used as a technical backgrounds for establishing a practical structural integrity assessment guideline of

Modelling simple helically delivered dose distributions

International Nuclear Information System (INIS)

Fenwick, John D; Tome, Wolfgang A; Kissick, Michael W; Mackie, T Rock

2005-01-01

In a previous paper, we described quality assurance procedures for Hi-Art helical tomotherapy machines. Here, we develop further some ideas discussed briefly in that paper. Simple helically generated dose distributions are modelled, and relationships between these dose distributions and underlying characteristics of Hi-Art treatment systems are elucidated. In particular, we describe the dependence of dose levels along the central axis of a cylinder aligned coaxially with a Hi-Art machine on fan beam width, couch velocity and helical delivery lengths. The impact on these dose levels of angular variations in gantry speed or output per linear accelerator pulse is also explored

Evolution and breakdown of helical vortex wakes behind a wind turbine

International Nuclear Information System (INIS)

Nemes, A; Jacono, D Lo; Sheridan, J; Blackburn, H M; Sherry, M

2014-01-01

The wake behind a three-bladed Glauert model rotor in a water channel was investigated. Planar particle image velocimetry was used to measure the velocity fields on the wake centre-line, with snapshots phase-locked to blade position of the rotor. Phase- locked averages of the velocity and vorticity fields are shown, with tip vortex interaction and entanglement of the helical filaments elucidated. Proper orthogonal decomposition and topology-based vortex identification are used to filter the PIV images for coherent structures and locate vortex cores. Application of these methods to the instantaneous data reveals unsteady behaviour of the helical filaments that is statistically quantifiable

MAGNETIC HELICITY FLUX IN THE PRESENCE OF SHEAR

International Nuclear Information System (INIS)

Hubbard, Alexander; Brandenburg, Axel

2011-01-01

Magnetic helicity has risen to be a major player in dynamo theory, with the helicity of the small-scale field being linked to the dynamo saturation process for the large-scale field. It is a nearly conserved quantity, which allows its evolution equation to be written in terms of production and flux terms. The flux term can be decomposed in a variety of fashions. One particular contribution that has been expected to play a significant role in dynamos in the presence of mean shear was isolated by Vishniac and Cho. Magnetic helicity fluxes are explicitly gauge dependent however, and the correlations that have come to be called the Vishniac-Cho flux were determined in the Coulomb gauge, which turns out to be fraught with complications in shearing systems. While the fluxes of small-scale helicity are explicitly gauge dependent, their divergences can be gauge independent. We use this property to investigate magnetic helicity fluxes of the small-scale field through direct numerical simulations in a shearing-box system and find that in a numerically usable gauge the divergence of the small-scale helicity flux vanishes, while the divergence of the Vishniac-Cho flux remains finite. We attribute this seeming contradiction to the existence of horizontal fluxes of small-scale magnetic helicity with finite divergences.

Magnetic Helicity Flux in the Presence of Shear

Science.gov (United States)

Hubbard, Alexander; Brandenburg, Axel

2011-01-01

Magnetic helicity has risen to be a major player in dynamo theory, with the helicity of the small-scale field being linked to the dynamo saturation process for the large-scale field. It is a nearly conserved quantity, which allows its evolution equation to be written in terms of production and flux terms. The flux term can be decomposed in a variety of fashions. One particular contribution that has been expected to play a significant role in dynamos in the presence of mean shear was isolated by Vishniac & Cho. Magnetic helicity fluxes are explicitly gauge dependent however, and the correlations that have come to be called the Vishniac-Cho flux were determined in the Coulomb gauge, which turns out to be fraught with complications in shearing systems. While the fluxes of small-scale helicity are explicitly gauge dependent, their divergences can be gauge independent. We use this property to investigate magnetic helicity fluxes of the small-scale field through direct numerical simulations in a shearing-box system and find that in a numerically usable gauge the divergence of the small-scale helicity flux vanishes, while the divergence of the Vishniac-Cho flux remains finite. We attribute this seeming contradiction to the existence of horizontal fluxes of small-scale magnetic helicity with finite divergences.

Transport barrier in Helical system

International Nuclear Information System (INIS)

Ida, Katsumi

1998-01-01

Experiments on the transport barrier in Helical plasmas are reviewed. There are two mechanisms of transport improvement, that results in the formation of the transport barrier. One is the improvement of neoclassical transport by reducing the ripple loss with radial electric field, which exist only in helical plasma. The other is the improvement of anomalous transport due to the suppression of fluctuations associated with a radial electric field shear both in tokamak and helical plasma. The formation of the transport barrier can be triggered by the radial electric field shear associated with the transition of the radial electric field (L/H transition or ion-electron root transition) or the peaked density or the optimization of magnetic field shear. The mechanisms of transport barrier formation are also discussed. (author). 60 refs

Toroidal helical quartz forming machine

International Nuclear Information System (INIS)

Hanks, K.W.; Cole, T.R.

1977-01-01

The Scyllac fusion experimental machine used 10 cm diameter smooth bore discharge tubes formed into a simple toroidal shape prior to 1974. At about that time, it was discovered that a discharge tube was required to follow the convoluted shape of the load coil. A machine was designed and built to form a fused quartz tube with a toroidal shape. The machine will accommodate quartz tubes from 5 cm to 20 cm diameter forming it into a 4 m toroidal radius with a 1 to 5 cm helical displacement. The machine will also generate a helical shape on a linear tube. Two sets of tubes with different helical radii and wavelengths have been successfully fabricated. The problems encountered with the design and fabrication of this machine are discussed

Simulation of injector dynamics during steady inductive helicity injection current drive in the HIT-SI experiment

Energy Technology Data Exchange (ETDEWEB)

Hansen, C., E-mail: hansec@uw.edu [PSI-Center, University of Washington, Seattle, Washington 98195 (United States); Columbia University, New York, New York 10027 (United States); Marklin, G. [PSI-Center, University of Washington, Seattle, Washington 98195 (United States); Victor, B. [HIT-SI Group, University of Washington, Seattle, Washington 98195 (United States); Akcay, C. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Jarboe, T. [HIT-SI Group, University of Washington, Seattle, Washington 98195 (United States); PSI-Center, University of Washington, Seattle, Washington 98195 (United States)

2015-04-15

We present simulations of inductive helicity injection in the Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI) device that treats the entire plasma volume in a single dynamic MHD model. A new fully 3D numerical tool, the PSI-center TETrahedral mesh code, was developed that provides the geometric flexibility required for this investigation. Implementation of a zero-β Hall MHD model using PSI-TET will be presented including formulation of a new self-consistent magnetic boundary condition for the wall of the HIT-SI device. Results from simulations of HIT-SI are presented focusing on injector dynamics that are investigated numerically for the first time. Asymmetries in the plasma loading between the two helicity injectors and progression of field reversal in each injector are observed. Analysis indicates cross-coupling between injectors through confinement volume structures. Injector impedance is found to scale with toroidal current at fixed density, consistent with experimental observation. Comparison to experimental data with an injector drive frequency of 14.5 kHz shows good agreement with magnetic diagnostics. Global mode structures from Bi-Orthogonal decomposition agree well with experimental data for the first four modes.

Chiral charge erasure via thermal fluctuations of magnetic helicity

International Nuclear Information System (INIS)

Long, Andrew J.; Sabancilar, Eray

2016-01-01

We consider a relativistic plasma of fermions coupled to an Abelian gauge field and carrying a chiral charge asymmetry, which might arise in the early Universe through baryogenesis. It is known that on large length scales, λ≳1/(αμ_5), the chiral anomaly opens an instability toward the erasure of chiral charge and growth of magnetic helicity. Here the chemical potential μ_5 parametrizes the chiral asymmetry and α is the fine-structure constant. We study the process of chiral charge erasure through the thermal fluctuations of magnetic helicity and contrast with the well-studied phenomenon of Chern-Simons number diffusion. Through the fluctuation-dissipation theorem we estimate the amplitude and time scale of helicity fluctuations on the length scale λ, finding δ H∼λT and τ∼αλ"3T"2 for a relativistic plasma at temperature T. We argue that the presence of a chiral asymmetry allows the helicity to grow diffusively for a time t∼T"3/(α"5μ_5"4) until it reaches an equilibrium value H∼μ_5T"2/α, and the chiral asymmetry is partially erased. If the chiral asymmetry is small, μ_5< T/α, this avenue for chiral charge erasure is found to be slower than the chiral magnetic effect for which t∼T/(α"3μ_5"2). This mechanism for chiral charge erasure can be important for the hypercharge sector of the Standard Model as well as extensions including U(1) gauge interactions, such as asymmetric dark matter models.

Induced helical backbone conformations of self-organizable dendronized polymers.

Science.gov (United States)

Rudick, Jonathan G; Percec, Virgil

2008-12-01

information to rationalize function as retrostructural analysis. Retrostructural analysis validates our hypothesis that the self-assembling dendrons induce a helical backbone conformation in cylindrical self-organizable dendronized polymers. This helical conformation mediates unprecedented functions. Self-organizable dendronized polymers have emerged as powerful building blocks for nanoscience by virtue of their dimensions and ability to self-organize. Discrete cylindrical and spherical structures with well-defined dimensions can be visualized and manipulated individually. More importantly, they provide a robust framework for elucidating functions available only at the nanoscale. This Account will highlight structures and functions generated from self-organizable dendronized polymers that enable integration of the nanoworld with its macroscopic universe. Emphasis is placed on those structures and functions derived from the induced helical backbone conformation of cylindrical self-organizable dendronized polymers.

Magnetic Helicity Estimations in Models and Observations of the Solar Magnetic Field. III. Twist Number Method

Energy Technology Data Exchange (ETDEWEB)

Guo, Y. [School of Astronomy and Space Science and Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210023 (China); Pariat, E.; Moraitis, K. [LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, F-92190 Meudon (France); Valori, G. [University College London, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT (United Kingdom); Anfinogentov, S. [Institute of Solar-Terrestrial Physics SB RAS 664033, Irkutsk, P.O. box 291, Lermontov Street, 126a (Russian Federation); Chen, F. [Max-Plank-Institut für Sonnensystemforschung, D-37077 Göttingen (Germany); Georgoulis, M. K. [Research Center for Astronomy and Applied Mathematics of the Academy of Athens, 4 Soranou Efesiou Street, 11527 Athens (Greece); Liu, Y. [W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); Thalmann, J. K. [Institute of Physics, Univeristy of Graz, Universitätsplatz 5/II, A-8010 Graz (Austria); Yang, S., E-mail: guoyang@nju.edu.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2017-05-01

We study the writhe, twist, and magnetic helicity of different magnetic flux ropes, based on models of the solar coronal magnetic field structure. These include an analytical force-free Titov–Démoulin equilibrium solution, non-force-free magnetohydrodynamic simulations, and nonlinear force-free magnetic field models. The geometrical boundary of the magnetic flux rope is determined by the quasi-separatrix layer and the bottom surface, and the axis curve of the flux rope is determined by its overall orientation. The twist is computed by the Berger–Prior formula, which is suitable for arbitrary geometry and both force-free and non-force-free models. The magnetic helicity is estimated by the twist multiplied by the square of the axial magnetic flux. We compare the obtained values with those derived by a finite volume helicity estimation method. We find that the magnetic helicity obtained with the twist method agrees with the helicity carried by the purely current-carrying part of the field within uncertainties for most test cases. It is also found that the current-carrying part of the model field is relatively significant at the very location of the magnetic flux rope. This qualitatively explains the agreement between the magnetic helicity computed by the twist method and the helicity contributed purely by the current-carrying magnetic field.

Localization of functional receptor epitopes on the structure of ciliary neurotrophic factor indicates a conserved, function-related epitope topography among helical cytokines.

Science.gov (United States)

Panayotatos, N; Radziejewska, E; Acheson, A; Somogyi, R; Thadani, A; Hendrickson, W A; McDonald, N Q

1995-06-09

By rational mutagenesis, receptor-specific functional analysis, and visualization of complex formation in solution, we identified individual amino acid side chains involved specifically in the interaction of ciliary neurotrophic factor (CNTF) with CNTFR alpha and not with the beta-components, gp130 and LIFR. In the crystal structure, the side chains of these residues, which are located in helix A, the AB loop, helix B, and helix D, are surface accessible and are clustered in space, thus constituting an epitope for CNTFR alpha. By the same analysis, a partial epitope for gp130 was also identified on the surface of helix A that faces away from the alpha-epitope. Superposition of the CNTF and growth hormone structures showed that the location of these epitopes on CNTF is analogous to the location of the first and second receptor epitopes on the surface of growth hormone. Further comparison with proposed binding sites for alpha- and beta-receptors on interleukin-6 and leukemia inhibitory factor indicated that this epitope topology is conserved among helical cytokines. In each case, epitope I is utilized by the specificity-conferring component, whereas epitopes II and III are used by accessory components. Thus, in addition to a common fold, helical cytokines share a conserved order of receptor epitopes that is function related.

System assessment of helical reactors in comparison with tokamaks

International Nuclear Information System (INIS)

Yamazaki, K.; Imagawa, S.; Muroga, T.; Sagara, A.; Okamura, S.

2002-10-01

A comparative assessment of tokamak and helical reactors has been performed using equivalent physics/engineering model and common costing model. Higher-temperature plasma operation is required in tokamak reactors to increase bootstrap current fraction and to reduce current-drive (CD) power. In helical systems, lower-temperature operation is feasible and desirable to reduce helical ripple transport. The capital cost of helical reactor is rather high, however, the cost of electricity (COE) is almost same as that of tokamak reactor because of smaller re-circulation power (no CD power) and less-frequent blanket replacement (lower neutron wall loading). The standard LHD-type helical reactor with 5% beta value is economically equivalent to the standard tokamak with 3% beta. The COE of lower-aspect ratio helical reactor is on the same level of high-β N tokamak reactors. (author)

Using Magnetic Helicity Diagnostics to Determine the Nature of Solar Active-Region Formation

Science.gov (United States)

Georgoulis, Manolis K.

Employing a novel nonlinear force-free (NLFF) method that self-consistently infers instantaneous free magnetic-energy and relative magnetic-helicity budgets from single photospheric vector magnetograms, we recently constructed the magnetic energy-helicity (EH) diagram of solar active regions. The EH diagram implies dominant relative helicities of left-handed or right-handed chiralities for the great majority of active regions. The amplitude (budget) of these helicities scales monotonically with the free magnetic energy. This constructive, strongly preferential accumulation of a certain sense of magnetic helicity seems to disqualify recently proposed mechanisms relying on a largely random near-surface convection for the formation of the great majority of active regions. The existing qualitative formation mechanism for these regions remains the conventional Omega-loop emergence following a buoyant ascension from the bottom of the convection zone. However, exceptions to this rule include even eruptive active regions: NOAA AR 11283 is an obvious outlier to the EH diagram, involving significant free magnetic energy with a small relative magnetic helicity. Relying on a timeseries of vector magnetograms of this region, our methodology shows nearly canceling amounts of both senses of helicity and an overall course from a weakly left-handed to a weakly right-handed structure, in the course of which a major eruption occurs. For this and similarly behaving active regions the latest near-surface formation scenario might conceivably be employed successfully. Research partially supported by the EU Seventh Framework Programme under grant agreement No. PIRG07-GA-2010-268245 and by the European Union Social Fund (ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: Thales. Investing in knowledge society through the European Social Fund.

THE EFFECTS OF SPATIAL SMOOTHING ON SOLAR MAGNETIC HELICITY PARAMETERS AND THE HEMISPHERIC HELICITY SIGN RULE

Energy Technology Data Exchange (ETDEWEB)

Ocker, Stella Koch [Department of Physics, Oberlin College, Oberlin, OH 44074 (United States); Petrie, Gordon, E-mail: socker@oberlin.edu, E-mail: gpetrie@nso.edu [National Solar Observatory, Boulder, CO 80303 (United States)

2016-12-01

The hemispheric preference for negative/positive helicity to occur in the northern/southern solar hemisphere provides clues to the causes of twisted, flaring magnetic fields. Previous studies on the hemisphere rule may have been affected by seeing from atmospheric turbulence. Using Hinode /SOT-SP data spanning 2006–2013, we studied the effects of two spatial smoothing tests that imitate atmospheric seeing: noise reduction by ignoring pixel values weaker than the estimated noise threshold, and Gaussian spatial smoothing. We studied in detail the effects of atmospheric seeing on the helicity distributions across various field strengths for active regions (ARs) NOAA 11158 and NOAA 11243, in addition to studying the average helicities of 179 ARs with and without smoothing. We found that, rather than changing trends in the helicity distributions, spatial smoothing modified existing trends by reducing random noise and by regressing outliers toward the mean, or removing them altogether. Furthermore, the average helicity parameter values of the 179 ARs did not conform to the hemisphere rule: independent of smoothing, the weak-vertical-field values tended to be negative in both hemispheres, and the strong-vertical-field values tended to be positive, especially in the south. We conclude that spatial smoothing does not significantly affect the overall statistics for space-based data, and thus seeing from atmospheric turbulence seems not to have significantly affected previous studies’ ground-based results on the hemisphere rule.

Helical magnetic axis configuration combined with l = 1 and weak l = -1 torsatron fields

International Nuclear Information System (INIS)

Kikuchi, Hitoshi; Saito, Katsunori; Gesso, Hirokazu; Shiina, Shoichi

1989-01-01

The superposition of a relatively weak l = -1 torsatron field on a main l = 1 torsatron field leads to the improvement of the confinement properties due to the formation of a local magnetic well, which results from the local curvature of the helical magnetic axis with a larger excursion in the major radius direction. This l±1 helical magnetic axis system has a comparatively simple, compact coil structure. Here the vacuum configuration properties of l = ±1 system are described. (author)

Spin versus helicity in processes involving transversity

CERN Document Server

Mekhfi, Mustapha

2011-01-01

We construct the spin formalism in order to deal in a direct and natural way with processes involving transversity which are now of increasing popularity. The helicity formalism which is more appropriate for collision processes of definite helicity has been so far used also to manage processes with transversity, but at the price of computing numerous helicity amplitudes generally involving unnecessary kinematical variables.In a second step we work out the correspondence between both formalisms and retrieve in another way all results of the helicity formalism but in simpler forms.We then compute certain processes for comparison.A special process:the quark dipole magnetic moment is shown to be exclusively treated within the spin formalism as it is directly related to the transverse spin of the quark inside the baryon.

New formulae for magnetic relative helicity and field line helicity

Science.gov (United States)

Aly, Jean-Jacques

2018-01-01

We consider a magnetic field {B} occupying the simply connected domain D and having all its field lines tied to the boundary S of D. We assume here that {B} has a simple topology, i.e., the mapping {M} from positive to negative polarity areas of S associating to each other the two footpoints of any magnetic line, is continuous. We first present new formulae for the helicity H of {B} relative to a reference field {{B}}r having the same normal component {B}n on S, and for its field line helicity h relative to a reference vector potential {{C}}r of {{B}}r. These formulae make immediately apparent the well known invariance of these quantities under all the ideal MHD deformations that preserve the positions of the footpoints on S. They express indeed h and H either in terms of {M} and {B}n, or in terms of the values on S of a pair of Euler potentials of {B}. We next show that, for a specific choice of {{C}}r, the field line helicity h of {B} fully characterizes the magnetic mapping {M} and then the topology of the lines. Finally, we give a formula that describes the rate of change of h in a situation where the plasma moves on the perfectly conducting boundary S without changing {B}n and/or non-ideal processes, described by an unspecified term {N} in Ohm’s law, are at work in some parts of D.

ADDITIVE SELF-HELICITY AS A KINK MODE THRESHOLD

International Nuclear Information System (INIS)

Malanushenko, A.; Longcope, D. W.; Fan, Y.; Gibson, S. E.

2009-01-01

In this paper, we propose that additive self-helicity, introduced by Longcope and Malanushenko, plays a role in the kink instability for complex equilibria, similar to twist helicity for thin flux tubes. We support this hypothesis by a calculation of additive self-helicity of a twisted flux tube from the simulation of Fan and Gibson. As more twist gets introduced, the additive self-helicity increases, and the kink instability of the tube coincides with the drop of additive self-helicity, after the latter reaches the value of H A /Φ 2 ∼ 1.5 (where Φ is the flux of the tube and H A is the additive self-helicity). We compare the additive self-helicity to twist for a thin subportion of the tube to illustrate that H A /Φ 2 is equal to the twist number, studied by Berger and Field, when the thin flux tube approximation is applicable. We suggest that the quantity H A /Φ 2 could be treated as a generalization of a twist number, when the thin flux tube approximation is not applicable. A threshold on a generalized twist number might prove extremely useful studying complex equilibria, just as the twist number itself has proven useful studying idealized thin flux tubes. We explicitly describe a numerical method for calculating additive self-helicity, which includes an algorithm for identifying a domain occupied by a flux bundle and a method of calculating potential magnetic field confined to this domain. We also describe a numerical method to calculate twist of a thin flux tube, using a frame parallelly transported along the axis of the tube.

Counting and tensorial properties of twist-two helicity-flip nucleon form factors

International Nuclear Information System (INIS)

Chen Zhang; Ji Xiangdong

2005-01-01

We perform a systematic analysis on the off-forward matrix elements of the twist-two quark and gluon helicity-flip operators. By matching the allowed quantum numbers and their crossing channel counterparts (a method developed by Ji and Lebed), we systematically count the number of independent nucleon form factors in off-forward scattering of matrix elements of these quark and gluon spin-flip operators. In particular, we find that the numbers of independent nucleon form factors of twist-two, helicity-flip quark (gluon) operators are 2n-1 (2n-5) if n is odd, and 2n-2 (2n-6) if n is even, with n≥2 (n≥4). We also analyze and write down the tensorial/Lorentz structure and kinematic factors of the expansion of these operators' matrix elements in terms of the independent form factors. These generalized form factors define the off-forward quark and gluon helicity-flip distributions in the literature

Helicity and other conservation laws in perfect fluid motion

Science.gov (United States)

Serre, Denis

2018-03-01

In this review paper, we discuss helicity from a geometrical point of view and see how it applies to the motion of a perfect fluid. We discuss its relation with the Hamiltonian structure, and then its extension to arbitrary space dimensions. We also comment about the existence of additional conservation laws for the Euler equation, and its unlikely integrability in Liouville's sense.

Helicity non-conserving form factor of the proton

Energy Technology Data Exchange (ETDEWEB)

Voutier, E.; Furget, C.; Knox, S. [Universite Joseph Fourier, Grenoble (France)] [and others

1994-04-01

The study of the hadron structure in the high Q{sup 2} range contributes to the understanding of the mechanisms responsible for the confinement of quarks and gluons. Among the numerous experimental candidates sensitive to these mechanisms, the helicity non-conserving form factor of the proton is a privileged observable since it is controlled by non-perturbative effects. The authors investigate here the feasibility of high Q{sup 2} measurements of this form factor by means of the recoil polarization method in the context of the CEBAF 8 GeV facility. For that purpose, they discuss the development of a high energy proton polarimeter, based on the H({rvec p},pp) elastic scattering, to be placed at the focal plane of a new hadron spectrometer. It is shown that this experimental method significantly improves the knowledge of the helicity non-conserving form factor of the proton up to 10 GeV{sup 2}/c{sup 2}.

NIMROD simulations and physics assessment of possible designs for a next generation Steady Inductive Helicity Injection HIT device

Science.gov (United States)

Penna, James; Morgan, Kyle; Grubb, Isaac; Jarboe, Thomas

2017-10-01

The Helicity Injected Torus - Steady Inductive 3 (HIT-SI3) experiment forms and maintains spheromaks via Steady Inductive Helicity Injection (SIHI) using discrete injectors that inject magnetic helicity via a non-axisymmetric perturbation and drive toroidally symmetric current. Newer designs for larger SIHI-driven spheromaks incorporate a set of injectors connected to a single external manifold to allow more freedom for the toroidal structure of the applied perturbation. Simulations have been carried out using the NIMROD code to assess the effectiveness of various imposed mode structures and injector schema in driving current via Imposed Dynamo Current Drive (IDCD). The results are presented here for varying flux conserver shapes on a device approximately 1.5 times larger than the current HIT-SI3 experiment. The imposed mode structures and spectra of simulated spheromaks are analyzed in order to examine magnetic structure and stability and determine an optimal regime for IDCD sustainment in a large device. The development of scaling laws for manifold operation is also presented, and simulation results are analyzed and assessed as part of the development path for the large scale device.

Distributed temperature sensors development using an stepped-helical ultrasonic waveguide

Science.gov (United States)

Periyannan, Suresh; Rajagopal, Prabhu; Balasubramaniam, Krishnan

2018-04-01

This paper presents the design and development of the distributed ultrasonic waveguide temperature sensors using some stepped-helical structures. Distributed sensing has several applications in various industries (oil, glass, steel) for measurement of physical parameters such as level, temperature, viscosity, etc. This waveguide incorporates a special notch or bend for obtaining ultrasonic wave reflections from the desired locations (Gage-lengths) where local measurements are desired. In this paper, a multi-location measurement wave-guide, with a measurement capability of 18 locations in a single wire, has been fabricated. The distribution of these sensors is both in the axial as well as radial directions using a stepped-helical spring configuration. Also, different high temperature materials have been chosen for the wave-guide. Both lower order axi-symmetric guided ultrasonic modes (L(0,1) and T(0,1)) were employed. These wave modes were generated/received (pulse-echo approach) using conventional longitudinal and shear transducers, respectively. Also, both the wave modes were simultaneously generated/received and compared using shear transducer for developing the distributed helical wave-guide sensors. The effect of dispersion of the wave modes due to curvature effects will also be discussed.

Clinical application of helical CT colonography

International Nuclear Information System (INIS)

Zeng Huiliang; Zhu Xinjin; Liang Rujian; Liang Jianhao; Ou Weiqian; Wen Haomao

2009-01-01

Objective: To investigate the clinical value of 16-slice helical CT colonography in the diagnosis of colon tumor and polypus. Methods: 16-slice helical CT volumetric scanning was performed in 18 patients with colonic disease, including colonic tumor (n=16) and colonic polypus (n=2). 3D images, virtual endoscopy and multiplanar reformation were obtained in the AW4.1 workstation. CT appearances were compared with operation and fiberoptic colonoscopy. Results: Satisfied results were achieved from 18 patients, no difference found in results between CT colonography and operation in 16 patients with colonic tumor. Conclusion: 16-slice helical CT colonography is of great value in preoperative staging of colonic tumor and have a high value in clinical application. (authors)

Neutrino's helicity in a gravitational field

International Nuclear Information System (INIS)

Pansart, J.P.

1996-01-01

By using approximated solutions of Dirac's equation, we show that there is no helicity reversal for light neutrinos in the Schwarzschild metric nor in an expanding universe. The actual coupling between a particle spin and the angular momentum of a heavy rotating body induces a possible helicity reversal but with an unobservable probability proportional to m 2 p / E 2 , where m p is the particle mass and E its energy. In these calculations, the helicity is defined through the spin orientation with respect to the current and not with respect to the linear momentum. This definition gives simple expressions and is equal to the usual definition in the case of a flat space. (N.T.)

Introduction to the m = 1 helicity source

International Nuclear Information System (INIS)

Platts, D.A.; Jarboe, T.R.; Wright, B.L.

1985-01-01

The m = 1 Helicity Source, formerly called the Kinked Z-pinch, was developed as part of the Electrode Studies program at Los Alamos. The Electrode Studies program was initiated to study the control of electrode erosion in long discharge duration spheromak sources. Erosion control is necessary to reduce plasma impurities and to obtain adequate electrode lifetimes. The first task of the Electrode Studies program is to determine, from among a variety of configurations including the coaxial one, a helicity source geometry with good prospects for erosion control. The more efficient the helicity source the easier it will be to control erosion, but the source most also be easy to diagnose and modify if it is to be a useful test bed. The various erosion control techniques which have been proposed will require extensive experimentation to evaluate and optimize. Proposed techniques include, using refractory metals, profiling of the electrodes and magnetic fields, and various gas injection schemes including porous electrodes. It is considered necessary to do these experiments on an optimized helicity source so that the electrode geometries and plasma properties will be relevant. Therefore the present Electrode Studies program is aimed at developing an improved helicity source design

Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence

Energy Technology Data Exchange (ETDEWEB)

Bodo, G.; Rossi, P. [INAF/Osservatorio Astrofisico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese (Italy); Cattaneo, F. [Department of Astronomy and Astrophysics, The University of Chicago, 5640 S. Ellis Avenue, Chicago IL 60637 (United States); Mignone, A., E-mail: bodo@oato.inaf.it [Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, 10125 Torino (Italy)

2017-07-10

We examine the relationship between magnetic flux generation, taken as an indicator of large-scale dynamo action, and magnetic helicity, computed as an integral over the dynamo volume, in a simple dynamo. We consider dynamo action driven by magneto-rotational turbulence (MRT) within the shearing-box approximation. We consider magnetically open boundary conditions that allow a flux of helicity in or out of the computational domain. We circumvent the problem of the lack of gauge invariance in open domains by choosing a particular gauge—the winding gauge—that provides a natural interpretation in terms of the average winding number of pairwise field lines. We use this gauge precisely to define and measure the helicity and the helicity flux for several realizations of dynamo action. We find in these cases that the system as a whole does not break reflectional symmetry and that the total helicity remains small even in cases when substantial magnetic flux is generated. We find no particular connection between the generation of magnetic flux and the helicity or the helicity flux through the boundaries. We suggest that this result may be due to the essentially nonlinear nature of the dynamo processes in MRT.

Role of α-Helical Structure in Organic Solvent-Activated Homodimer of Elastase Strain K

Directory of Open Access Journals (Sweden)

Chee Fah Wong

2011-09-01

Full Text Available Recombinant elastase strain K overexpressed from E. coli KRX/pCon2(3 was purified to homogeneity by a combination of hydrophobic interaction chromatography and ion exchange chromatography, with a final yield of 48% and a 25-fold increase in specific activity. The purified protein had exhibited a first ever reported homodimer size of 65 kDa by SDS-PAGE and MALDI-TOF, a size which is totally distinct from that of typically reported 33 kDa monomer from P. aeruginosa. The organic solvent stability experiment had demonstrated a stability pattern which completely opposed the rules laid out in previous reports in which activity stability and enhancement were observed in hydrophilic organic solvents such as DMSO, methanol, ethanol and 1-propanol. The high stability and enhancement of the enzyme in hydrophilic solvents were explained from the view of alteration in secondary structures. Elastinolytic activation and stability were observed in 25 and 50% of methanol, respectively, despite slight reduction in α-helical structure caused upon the addition of the solvent. Further characterization experiments had postulated great stability and enhancement of elastase strain K in broad range of temperatures, pHs, metal ions, surfactants, denaturing agents and substrate specificity, indicating its potential application in detergent formulation.

Helicity amplitudes for matter-coupled gravity

International Nuclear Information System (INIS)

Aldrovandi, R.; Novaes, S.F.; Spehler, D.

1992-07-01

The Weyl-van der Waerden spinor formalism is applied to the evaluation of helicity invariant amplitudes in the framework of linearized gravitation. The graviton couplings to spin-0, 1 - 2 , 1, and 3 - 2 particles are given, and, to exhibit the reach of this method, the helicity amplitudes for the process electron + positron → photon + graviton are obtained. (author)

Hydrodynamic studies of CNT nanofluids in helical coil heat exchanger

Science.gov (United States)

Babita; Sharma, S. K.; Mital Gupta, Shipra; Kumar, Arinjay

2017-12-01

Helical coils are extensively used in several industrial processes such as refrigeration systems, chemical reactors, recovery processes etc to accommodate a large heat transfer area within a smaller space. Nanofluids are getting great attention due to their enhanced heat transfer capability. In heat transfer equipments, pressure drop is one of the major factors of consideration for pumping power calculations. So, the present work is aimed to study hydrodynamics of CNT nanofluids in helical coils. In this study, pressure drop characteristics of CNT nanofluid flowing inside horizontal helical coils are investigated experimentally. The helical coil to tube diameter was varied from 11.71 to 27.34 keeping pitch of the helical coil constant. Double distilled water was used as basefluid. SDBS and GA surfactants were added to stablilize CNT nanofluids. The volumetric fraction of CNT nanofluid was varied from 0.003 vol% to 0.051 vol%. From the experimental data, it was analyzed that the friction factor in helical coils is greater than that of straight tubes. Concentration of CNT in nanofluids also has a significant influence on the pressure drop/friction factor of helical coils. At a constant concentration of CNT, decreasing helical coil to tube diameter from 27.24 to 11.71, fanning friction factor of helical coil; f c increases for a constant value of p/d t. This increase in the value of fanning friction factor can be attributed to the secondary flow of CNT nanofluid in helical coils.

Assembly of Huntingtin headpiece into α-helical bundles.

Science.gov (United States)

Ozgur, Beytullah; Sayar, Mehmet

2017-05-24

Protein aggregation is a hallmark of neurodegenerative disorders. In this group of brain-related disorders, a disease-specific "host" protein or fragment misfolds and adopts a metastatic, aggregate-prone conformation. Often, this misfolded conformation is structurally and thermodynamically different from its native state. Intermolecular contacts, which arise in this non-native state, promote aggregation. In this regard, understanding the molecular principles and mechanisms that lead to the formation of such a non-native state and further promote the formation of the critical nucleus for fiber growth is essential. In this study, the authors analyze the aggregation propensity of Huntingtin headpiece (htt NT ), which is known to facilitate the polyQ aggregation, in relation to the helix mediated aggregation mechanism proposed by the Wetzel group. The authors demonstrate that even though htt NT displays a degenerate conformational spectrum on its own, interfaces of macroscopic or molecular origin can promote the α-helix conformation, eliminating all other alternatives in the conformational phase space. Our findings indicate that htt NT molecules do not have a strong orientational preference for parallel or antiparallel orientation of the helices within the aggregate. However, a parallel packed bundle of helices would support the idea of increased polyglutamine concentration, to pave the way for cross-β structures.

Progressive and resonant wave helices application to electron paramagnetic resonance; Helices a ondes progressives et resonnantes application a la resonance paramagnetique electronique

Energy Technology Data Exchange (ETDEWEB)

Volino, F [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

1969-07-01

We show that helices can be used as resonant systems. Their properties are theoretically and experimentally studied. We describe resonant helices for electron paramagnetic resonance in X-band and develop a comparison between their sensitivity and the sensitivity of a normal resonant cavity. For cylindrical samples less than 3 mm diameter, the helix is more sensitive and can produce more intense microwave magnetic fields. (author) [French] Il est montre que les helices peuvent etre utilisees comme systeme resonnant. Leurs proprietes sont discutees theoriquement et experimentalement. Des helices resonnantes en bande X pour la resonance paramagnetique electronique sont decrites et leur sensibilite est comparee a celle des cavites resonnantes. Pour des echantillons cylindriques de moins de 3 mm de diametre, l'helice est plus sensible et peut produire des champs magnetiques hyper fins plus intenses. (auteur)

Highlights from the assembly of the helical field coils for the Advanced Toroidal Facility

International Nuclear Information System (INIS)

Benson, R.D.

1985-01-01

The helical field (HF) coils in the Advanced Toroidal Facility (ATF) device consist of a set of 24 identical segments connected to form a continuous pair of helical coils wrapped around a toroidal vacuum vessel. Each segment weighs approximately 1364 kg (3000 lb) and is composed of 14 water-cooled copper plate conductors bolted to a cast stainless steel structural support member with a T-shape cross section (known as the structural tee). The segment components are electrically insulated with Kapton adhesive tape, G-10, Tefzel, and rubber to withstand 2.5 kV. As a final insulator and structural support, the entire segment is vacuum impregnated with epoxy. This paper offers a brief overview of the processes used to assemble the component parts into a completed segment, including identification of items that required special attention. 4 figs

Magnetic properties of the Ce2Fe17-x Mn x helical magnets up to high magnetic fields

International Nuclear Information System (INIS)

Kuchin, A.G.; Mushnikov, N.V.; Bartashevich, M.I.; Prokhnenko, O.; Khrabrov, V.I.; Lapina, T.P.

2007-01-01

Magnetic properties of the Ce 2 Fe 17- x Mn x , x=0-2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5-1 are helical antiferromagnets and those with 1 B that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce 2 Fe 17- x Mn x compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce 2 Fe 17- x Mn x helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce 2 Fe 17- x Mn x , x=0.5-2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated

Particle orbit analysis for LHD helical axis configurations

International Nuclear Information System (INIS)

Guasp, J.; Yamazaki, K.; Motojima, O.

1993-04-01

Fast ion orbits for helical magnetic axis configurations in LHD (Large Helical Device) are analyzed and compared with the standard circular axis case. Boundaries between passing and helically trapped particle regions show clear differences: in the non-planar axis case the helically trapped region spreads, near the magnetic axis, over a much wider band across the 90deg pitch angle value and shows a very marked asymmetry. The locally trapped particle region is also wider than in the standard case. The differences in the loss cone boundaries of the two cases are rather small, however, the effects of re-entering criteria are very important in both cases. On the contrary, effects of finite coil size are not significant. (author)

Helically linked mirror arrangement

International Nuclear Information System (INIS)

Ranjan, P.

1986-08-01

A scheme is described for helical linking of mirror sections, which endeavors to combine the better features of toroidal and mirror devices by eliminating the longitudinal loss of mirror machines, having moderately high average β and steady state operation. This scheme is aimed at a device, with closed magnetic surfaces having rotational transform for equilibrium, one or more axisymmetric straight sections for reduced radial loss, a simple geometrical axis for the links and an overall positive magnetic well depth for stability. We start by describing several other attempts at linking of mirror sections, made both in the past and the present. Then a description of our helically linked mirror scheme is given. This example has three identical straight sections connected by three sections having helical geometric axes. A theoretical analysis of the magnetic field and single-particle orbits in them leads to the conclusion that most of the passing particles would be confined in the device and they would have orbits independent of pitch angle under certain conditions. Numerical results are presented, which agree well with the theoretical results as far as passing particle orbits are concerned

Helicity and evanescent waves. [Energy transport velocity, helicity, Lorentz transformation

Energy Technology Data Exchange (ETDEWEB)

Agudin, J L; Platzeck, A M [La Plata Univ. Nacional (Argentina); Albano, J R [Instituto de Astronomia y Fisica del Espacio, Buenos Aires, Argentina

1978-02-20

It is shown that the projection of the angular momentum of a circularly polarized electromagnetic evanescent wave along the mean velocity of energy transport (=helicity) can be reverted by a Lorentz transformation, in spite of the fact that this velocity is c.

Magnetic islands created by resonant helical windings

International Nuclear Information System (INIS)

Fernandes, A.S.; Heller, M.V.; Caldas, I.L.

1986-01-01

The triggering of disruptive instabilities by resonant helical windings in large aspect-ratio tokamaks is associated to destruction of magnetic surfaces. The Chirikov condition is applied to estimate analytically the helical winding current thresholds for ergodization of the magnetic field lines. (Autor) [pt

Progressive and resonant wave helices application to electron paramagnetic resonance; Helices a ondes progressives et resonnantes application a la resonance paramagnetique electronique

Energy Technology Data Exchange (ETDEWEB)

Volino, F. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

1969-07-01

We show that helices can be used as resonant systems. Their properties are theoretically and experimentally studied. We describe resonant helices for electron paramagnetic resonance in X-band and develop a comparison between their sensitivity and the sensitivity of a normal resonant cavity. For cylindrical samples less than 3 mm diameter, the helix is more sensitive and can produce more intense microwave magnetic fields. (author) [French] Il est montre que les helices peuvent etre utilisees comme systeme resonnant. Leurs proprietes sont discutees theoriquement et experimentalement. Des helices resonnantes en bande X pour la resonance paramagnetique electronique sont decrites et leur sensibilite est comparee a celle des cavites resonnantes. Pour des echantillons cylindriques de moins de 3 mm de diametre, l'helice est plus sensible et peut produire des champs magnetiques hyper fins plus intenses. (auteur)

Superposition of helical beams by using a Michelson interferometer.

Science.gov (United States)

Gao, Chunqing; Qi, Xiaoqing; Liu, Yidong; Weber, Horst

2010-01-04

Orbital angular momentum (OAM) of a helical beam is of great interests in the high density optical communication due to its infinite number of eigen-states. In this paper, an experimental setup is realized to the information encoding and decoding on the OAM eigen-states. A hologram designed by the iterative method is used to generate the helical beams, and a Michelson interferometer with two Porro prisms is used for the superposition of two helical beams. The experimental results of the collinear superposition of helical beams and their OAM eigen-states detection are presented.

NMR studies of the fifth transmembrane segment of Na+,K+-ATPase reveals a non-helical ion-binding region

DEFF Research Database (Denmark)

Underhaug, Jarl; Jakobsen, Louise Odgaard; Esmann, Mikael

2006-01-01

The structure of a synthetic peptide corresponding to the fifth membrane-spanning segment (M5) in Na(+),K(+)-ATPase in sodium dodecyl sulfate (SDS) micelles was determined using liquid-state nuclear magnetic resonance (NMR) spectroscopy. The spectra reveal that this peptide is substantially less...... transmembrane element of the Ca(2+)-ATPase. Furthermore, this region spans the residues implicated in Na(+) and K(+) transport, where they are likely to offer the flexibility needed to coordinate Na(+) as well as K(+) during active transport....... alpha-helical than the corresponding M5 peptide of Ca(2+)-ATPase. A well-defined alpha-helix is shown in the C-terminal half of the peptide. Apart from a short helical stretch at the N-terminus, the N-terminal half contains a non-helical region with two proline residues and sequence similarity to a non-structured...

Dynamic helical CT mammography of breast cancer

International Nuclear Information System (INIS)

Yamamoto, Akira; Fukushima, Hitoshi; Okamura, Ryuji; Nakamura, Yoshiaki; Morimoto, Taisuke; Urata, Yoji; Mukaihara, Sumio; Hayakawa, Katsumi

2006-01-01

The purpose of this study was to determine whether dynamic helical computed tomography (CT)-mammography could assist in selecting the most appropriate surgical method in women with breast cancer. Preoperative contrast-enhanced helical CT scanning of the breast was performed on 133 female patients with suspicion of breast cancer at the same time as clinical, mammographic, and/or ultrasonographic examinations. The patients were scanned in the prone position with a specially designed CT-compatible device. A helical scan was made with rapid intravenous bolus injection (3 ml/s) of 100 ml of iodine contrast material. Three-dimensional maximum intensity projection (MIP) images were reconstructed, and CT findings were correlated with surgical and histopathological findings. Histopathological analysis revealed 84 malignant lesions and seven benign lesions. The sensitivity, specificity, and accuracy levels of the CT scanning were 94.6%, 58.6%, and 78.9%. Helical scanning alone revealed additional contralateral carcinomas in three of four patients and additional ipsilateral carcinomas in three of five patients. However, the technique gave false-positive readings in 24 patients. The preoperative CT-mammogram altered the surgical method in six patients. Dynamic helical CT-mammography in the prone position may be one of the choices of adjunct imaging in patients with suspected breast cancer scheduled for surgery. (author)

Helical self-organization and hierarchical self-assembly of an oligoheterocyclic pyridine-pyridazine strand into extended supramolecular fibers.

Science.gov (United States)

Cuccia, Louis A; Ruiz, Eliseo; Lehn, Jean-Marie; Homo, Jean-Claude; Schmutz, Marc

2002-08-02

The synthesis and characterization of an alternating pyridine-pyridazine strand comprising thirteen heterocycles are described. Spontaneous folding into a helical secondary structure is based on a general molecular self-organization process enforced by the conformational information encoded within the primary structure of the molecular strand itself. Conformational control based on heterocyclic "helicity codons" illustrates a strategy for designing folding properties into synthetic oligomers (foldamers). Strong intermolecular interactions of the highly ordered lock-washer subunits of compound 3 results in hierarchical supramolecular self-assembly into protofibrils and fibrils. Compound 3 also forms mechanically stable two-dimensional Langmuir-Blodgett and cast thin films.

Resonant helical fields in tokamaks

International Nuclear Information System (INIS)

Okano, V.

1990-01-01

Poincare maps of magnetic field lines of a toroidal helical system were made. The magnetic field is a linear superposition of the magnetic fields produced by a toroidal plasma in equilibrium and by external helical currents. Analytical expression for the Poincare maps was no obtained since the magnetic field do not have symmetry. In order to obtain the maps, the equation minus derivative of l vector times B vector = 0 was numerically integrated. In the Poincare maps, the principal and the secondary magnetic island were observed. (author)

Microbunch preserving in-line system for an APPLE II helical radiator at the LCLS baseline

Energy Technology Data Exchange (ETDEWEB)

Geloni, Gianluca [European XFEL Project Team, Hamburg (Germany); Kocharyan, Vitali; Saldin, Evgeni [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

2011-05-15

In a previous work we proposed a scheme for polarization control at the LCLS baseline, which exploited the microbunching from the planar undulator. After the baseline undulator, the electron beam is transported through a drift by a FODO focusing system, and through a short helical radiator. The microbunching structure can be preserved, and intense coherent radiation is emitted in the helical undulator at fundamental harmonic. The driving idea of this proposal is that the background linearly-polarized radiation from the baseline undulator is suppressed by spatial filtering. Filtering is achieved by letting radiation and electron beam through Be slits upstream of the helical radiator, where the radiation spot size is about ten times larger than the electron beam transverse size. Several changes considered in the present paper were made to improve the previous design. Slits are now placed immediately behind the helical radiator. The advantage is that the electron beam can be spoiled by the slits, and narrower slits width can be used for spatial filtering. Due to this fundamental reason, the present setup is shorter than the previous one. The helical radiator is now placed immediately behind the SHAB undulator. It is thus sufficient to use the existing FODO focusing system of the SHAB undulator for transporting themodulated electron beam. This paper presents complete GENESIS code calculations for the new design, starting from the baseline undulator entrance up to the helical radiator exit including the modulated electron beam transport by the SHAB FODO focusing system. (orig.)

Microbunch preserving in-line system for an APPLE II helical radiator at the LCLS baseline

International Nuclear Information System (INIS)

Geloni, Gianluca; Kocharyan, Vitali; Saldin, Evgeni

2011-05-01

In a previous work we proposed a scheme for polarization control at the LCLS baseline, which exploited the microbunching from the planar undulator. After the baseline undulator, the electron beam is transported through a drift by a FODO focusing system, and through a short helical radiator. The microbunching structure can be preserved, and intense coherent radiation is emitted in the helical undulator at fundamental harmonic. The driving idea of this proposal is that the background linearly-polarized radiation from the baseline undulator is suppressed by spatial filtering. Filtering is achieved by letting radiation and electron beam through Be slits upstream of the helical radiator, where the radiation spot size is about ten times larger than the electron beam transverse size. Several changes considered in the present paper were made to improve the previous design. Slits are now placed immediately behind the helical radiator. The advantage is that the electron beam can be spoiled by the slits, and narrower slits width can be used for spatial filtering. Due to this fundamental reason, the present setup is shorter than the previous one. The helical radiator is now placed immediately behind the SHAB undulator. It is thus sufficient to use the existing FODO focusing system of the SHAB undulator for transporting themodulated electron beam. This paper presents complete GENESIS code calculations for the new design, starting from the baseline undulator entrance up to the helical radiator exit including the modulated electron beam transport by the SHAB FODO focusing system. (orig.)

Using helical compressors for coke gas condensation

Energy Technology Data Exchange (ETDEWEB)

Privalov, V E; Rezunenko, Yu I; Lelyanov, N V; Zarnitzkii, G Eh; Gordienko, A A; Derebenko, I F; Venzhega, A G; Leonov, N P; Gorokhov, N N

1982-08-01

Coke oven gas compression is discussed. Presently used multilevel piston compressors are criticized. The paper recommends using helical machines which combine advantages of using volume condensing compressors and compact high-efficiency centrifugal machines. Two kinds of helical compressors are evaluated: dry and oil-filled; their productivities and coke oven gas chemical composition are analyzed. Experiments using helical compressors were undertaken at the Yasinovskii plant. Flowsheet of the installation is shown. Performance results are given in a table. For all operating conditions content of insolubles in oil compounds is found to be lower than the acceptable value (0.08%). Compressor productivity measurements with variable manifold pressure are evaluated. Figures obtained show that efficient condensation of raw coke oven gas is possible. Increasing oil-filled compressor productivity is recommended by decreasing amount of oil injected and simultaneously increasing rotation speed. The dry helical compressor with water seal is found to be most promising for raw coke oven gas condensation. (10 refs.)

Helical structure of longitudinal vortices embedded in turbulent wall-bounded flow

DEFF Research Database (Denmark)

Velte, Clara Marika; Hansen, Martin Otto Laver; Okulov, Valery

2009-01-01

Embedded vortices in turbulent wall-bounded flow over a flat plate, generated by a passive rectangular vane-type vortex generator with variable angle \\beta to the incoming flow in a low-Reynolds number flow (Re = 2600 based on the inlet grid mesh size L = 0:039 m and free stream velocity U....... This is important for flow control, since one thereby can determine the axial velocity induced by the helical vortex as well as the swirl redistributing the axial velocity component for a given device angle \\beta. This also simplifies theoretical studies, e.g. to understand and predict the stability of the vortex...

Relativistic helicity and link in Minkowski space-time

International Nuclear Information System (INIS)

Yoshida, Z.; Kawazura, Y.; Yokoyama, T.

2014-01-01

A relativistic helicity has been formulated in the four-dimensional Minkowski space-time. Whereas the relativistic distortion of space-time violates the conservation of the conventional helicity, the newly defined relativistic helicity conserves in a barotropic fluid or plasma, dictating a fundamental topological constraint. The relation between the helicity and the vortex-line topology has been delineated by analyzing the linking number of vortex filaments which are singular differential forms representing the pure states of Banach algebra. While the dimension of space-time is four, vortex filaments link, because vorticities are primarily 2-forms and the corresponding 2-chains link in four dimension; the relativistic helicity measures the linking number of vortex filaments that are proper-time cross-sections of the vorticity 2-chains. A thermodynamic force yields an additional term in the vorticity, by which the vortex filaments on a reference-time plane are no longer pure states. However, the vortex filaments on a proper-time plane remain to be pure states, if the thermodynamic force is exact (barotropic), thus, the linking number of vortex filaments conserves

Reduced bispectrum seeded by helical primordial magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Hortúa, Héctor Javier [Universidad Nacional de Colombia-Bogotá, Facultad de Ciencias, Departamento de Física, Carrera 30 Calle 45-03, C.P. 111321 Bogotá (Colombia); Castañeda, Leonardo, E-mail: hjhortuao@unal.edu.co, E-mail: lcastanedac@unal.edu.co [Grupo de Gravitación y Cosmología, Observatorio Astronómico Nacional, Universidad Nacional de Colombia, cra 45 No 26-85, Edificio Uriel Gutierréz, Bogotá, D.C. (Colombia)

2017-06-01

In this paper, we investigate the effects of helical primordial magnetic fields (PMFs) on the cosmic microwave background (CMB) reduced bispectrum. We derive the full three-point statistics of helical magnetic fields and numerically calculate the even contribution in the collinear configuration. We then numerically compute the CMB reduced bispectrum induced by passive and compensated PMF modes on large angular scales. There is a negative signal on the bispectrum due to the helical terms of the fields and we also observe that the biggest contribution to the bispectrum comes from the non-zero IR cut-off for causal fields, unlike the two-point correlation case. For negative spectral indices, the reduced bispectrum is enhanced by the passive modes. This gives a lower value of the upper limit for the mean amplitude of the magnetic field on a given characteristic scale. However, high values of IR cut-off in the bispectrum, and the helical terms of the magnetic field relaxes this bound. This demonstrates the importance of the IR cut-off and helicity in the study of the nature of PMFs from CMB observations.

Helicity antenna showers for hadron colliders

Energy Technology Data Exchange (ETDEWEB)

Fischer, Nadine; Skands, Peter [Monash University, School of Physics and Astronomy, Clayton, VIC (Australia); Lifson, Andrew [Monash University, School of Physics and Astronomy, Clayton, VIC (Australia); ETH Zuerich, Zurich (Switzerland)

2017-10-15

We present a complete set of helicity-dependent 2 → 3 antenna functions for QCD initial- and final-state radiation. The functions are implemented in the Vincia shower Monte Carlo framework and are used to generate showers for hadron-collider processes in which helicities are explicitly sampled (and conserved) at each step of the evolution. Although not capturing the full effects of spin correlations, the explicit helicity sampling does permit a significantly faster evaluation of fixed-order matrix-element corrections. A further speed increase is achieved via the implementation of a new fast library of analytical MHV amplitudes, while matrix elements from Madgraph are used for non-MHV configurations. A few examples of applications to QCD 2 → 2 processes are given, comparing the newly released Vincia 2.200 to Pythia 8.226. (orig.)

Helicity antenna showers for hadron colliders

Science.gov (United States)

Fischer, Nadine; Lifson, Andrew; Skands, Peter

2017-10-01

We present a complete set of helicity-dependent 2→ 3 antenna functions for QCD initial- and final-state radiation. The functions are implemented in the Vincia shower Monte Carlo framework and are used to generate showers for hadron-collider processes in which helicities are explicitly sampled (and conserved) at each step of the evolution. Although not capturing the full effects of spin correlations, the explicit helicity sampling does permit a significantly faster evaluation of fixed-order matrix-element corrections. A further speed increase is achieved via the implementation of a new fast library of analytical MHV amplitudes, while matrix elements from Madgraph are used for non-MHV configurations. A few examples of applications to QCD 2→ 2 processes are given, comparing the newly released Vincia 2.200 to Pythia 8.226.

The helical tomotherapy thread effect

International Nuclear Information System (INIS)

Kissick, M.W.; Fenwick, J.; James, J.A.; Jeraj, R.; Kapatoes, J.M.; Keller, H.; Mackie, T.R.; Olivera, G.; Soisson, E.T.

2005-01-01

Inherent to helical tomotherapy is a dose variation pattern that manifests as a 'ripple' (peak-to-trough relative to the average). This ripple is the result of helical beam junctioning, completely unique to helical tomotherapy. Pitch is defined as in helical CT, the couch travel distance for a complete gantry rotation relative to the axial beam width at the axis of rotation. Without scattering or beam divergence, an analytical posing of the problem as a simple integral predicts minima near a pitch of 1/n where n is an integer. A convolution-superposition dose calculator (TomoTherapy, Inc.) included all the physics needed to explore the ripple magnitude versus pitch and beam width. The results of the dose calculator and some benchmark measurements demonstrate that the ripple has sharp minima near p=0.86(1/n). The 0.86 factor is empirical and caused by a beam junctioning of the off-axis dose profiles which differ from the axial profiles as well as a long scatter tail of the profiles at depth. For very strong intensity modulation, the 0.86 factor may vary. The authors propose choosing particular minima pitches or using a second delivery that starts 180 deg off-phase from the first to reduce these ripples: 'Double threading'. For current typical pitches and beam widths, however, this effect is small and not clinically important for most situations. Certain extremely large field or high pitch cases, however, may benefit from mitigation of this effect

Buckling of anisotropic films on cylindrical substrates: insights for self-assembly fabrication of 3D helical gears

International Nuclear Information System (INIS)

Yin Jie; Chen Xi

2010-01-01

We propose an effective way of fabricating true three-dimensional helical gear-like structures (with inclined gear teeth) by using self-assembled stress-driven buckling of anisotropic films on compliant cylindrical substrates. Key parameters characterizing the helical undulation profile, in particular the gear teeth number and the inclined teeth angle, are investigated numerically using finite element simulations. Based on the insights from numerical calculations, a simplified theoretical model is established to effectively predict the teeth number. The results show that the anisotropic modulus ratio has a larger effect on the teeth number than the anisotropy angle. The orientation of gear teeth is related to the coupled effects of the anisotropic modulus ratio, anisotropy angle, substrate curvature and substrate aspect ratio. In general, the undulation orientation tends to be perpendicular to the direction of minimum bending stiffness in the film. The findings in this paper provide useful guidance for the self-assembly fabrication of helical gears and other 3D structures at various length scales.

Helical 1:1 α/Sulfono-γ-AA Heterogeneous Peptides with Antibacterial Activity

Energy Technology Data Exchange (ETDEWEB)

She, Fengyu; Nimmagadda, Alekhya; Teng, Peng; Su, Ma; Zuo, Xiaobing; Cai, Jianfeng

2016-05-09

As one of the greatest threats facing in 21st century, antibiotic resistance is now a major public health concern. Host-defense peptides (HDPs) offer an alternative approach to combat emerging multidrug-resistant bacteria. It is known that helical HDPs such as magainin 2 and its analogs adopt cationic amphipathic conformations upon interaction with bacterial membranes, leading to membrane disruption and subsequent bacterial cell death. We have previously shown that amphipathic sulfono-γ-AApeptides could mimic magainin 2 and exhibit bactericidal activity. In this article, we demonstrate for the first time that amphipathic helical 1:1 α/sulfono-γ-AA heterogeneous peptides, in which regular amino acids and sulfono-γ-AApeptide building blocks are alternatively present in a 1:1 pattern, display potent antibacterial activity against both Gram-positive and Gram-negative bacterial pathogens. Small Angle X-ray Scattering (SAXS) suggests that the lead sequences adopt defined helical structures. The subsequent studies including 2 fluorescence microscopy and time-kill experiments indicate that these hybrid peptides exert antimicrobial activity by mimicking the mechanism of HDPs. Our findings may lead to the development of HDP-mimicking antimicrobial peptidomimetics that combat drug-resistant bacterial pathogens. In addition, our results also demonstrate the effective design of a new class of helical foldamer, which could be employed to interrogate other important biological targets such as protein-protein interactions in the future.

A proline-hinge alters the characteristics of the amphipathic α-helical AMPs.

Science.gov (United States)

Lee, Jong Kook; Gopal, Ramamourthy; Park, Seong-Cheol; Ko, Hyun Sook; Kim, Yangmee; Hahm, Kyung-Soo; Park, Yoonkyung

2013-01-01

HP (2-20) is a 19-aa, amphipathic, α-helical peptide with antimicrobial properties that was derived from the N-terminus of Helicobacter pylori ribosomal protein L1. We previously showed that increasing the net hydrophobicity of HP (2-20) by substituting Trp for Gln(17) and Asp(19) (Anal 3) increased the peptide's antimicrobial activity. In hydrophobic medium, Anal 3 forms an amphipathic structure consisting of an N-terminal random coil region (residues 2-5) and an extended helical region (residues 6-20). To investigate the structure-activity relationship of Anal 3, we substituted Pro for Glu(9) (Anal 3-Pro) and then examined the new peptide's three-dimensional structure, antimicrobial activity and mechanism of action. Anal 3-Pro had an α-helical structure in the presence of trifluoroethanol (TFE) and sodium dodecyl sulfate (SDS). NMR spectroscopic analysis of Anal 3-Pro's tertiary structure in SDS micelles confirmed that the kink potential introduced by Pro(10) was responsible for the helix distortion. We also found that Anal 3-Pro exhibited about 4 times greater antimicrobial activity than Anal 3. Fluorescence activated flow cytometry and confocal fluorescence microscopy showed that incorporating a Pro-hinge into Anal 3 markedly reduced its membrane permeability so that it accumulated in the cytoplasm without remaining in the cell membrane. To investigate the translocation mechanism, we assessed its ability to release of FITC-dextran. The result showed Anal 3-Pro created a pore Candida albicans revealed that Anal 3-Pro and buforin II exert similar effects on cell membranes, whereas magainin 2 exerts a different, more damaging, effect. In addition, Anal 3-Pro assumed a helix-hinge-helix structure in the presence of biological membranes and formed micropores in both bacterial and fungal membranes, through which it entered the cytoplasm and tightly bound to DNA. These results indicate that the bending region of Anal 3- Pro peptide is prerequisite for effective

Helical type thermonuclear device and control method

International Nuclear Information System (INIS)

Ishigaki, Yukio.

1990-01-01

In a conventional helical type thermonuclear device, electric current flows in the toroidal direction under magnetic fields of helical coils and vertical magnetic coils, by which a circulating electric field is caused. Therefore, there is a problem that electrons as a seed are generated by cosmic rays, etc., the electrons are confined in a magnetic field boundary, are accelerated by the circulating electric field, to reach a high energy level, collide against structures in a vacuum vessel and emit a great amount of X-rays. Then, compensation coils for offsetting the magnetic fields generated upon energization and deenergization of the vertical magnetic coils and the power source therefor are disposed at the positions opposing to each other on both sides of the vertical magnetic coils for controlling the variation coefficient rate of electric current upon energization and deenergization of the vertical magnetic coils. Since the compensation coils also offset the magnetic field generated upon energization and deenergization of the vertical magnetic field coils by this control, the circulating magnetic field is not caused in the vacuum vessel to reduce the X-ray radiation by electrons at high energy level. (N.H.)

Experiments on helical modes in magnetized thin foil-plasmas

Science.gov (United States)

Yager-Elorriaga, David

2017-10-01

This paper gives an in-depth experimental study of helical features on magnetized, ultrathin foil-plasmas driven by the 1-MA linear transformer driver at University of Michigan. Three types of cylindrical liner loads were designed to produce: (a) pure magneto-hydrodynamic (MHD) modes (defined as being void of the acceleration-driven magneto-Rayleigh-Taylor instability, MRT) using a non-imploding geometry, (b) pure kink modes using a non-imploding, kink-seeded geometry, and (c) MRT-MHD coupled modes in an unseeded, imploding geometry. For each configuration, we applied relatively small axial magnetic fields of Bz = 0.2-2.0 T (compared to peak azimuthal fields of 30-40 T). The resulting liner-plasmas and instabilities were imaged using 12-frame laser shadowgraphy and visible self-emission on a fast framing camera. The azimuthal mode number was carefully identified with a tracking algorithm of self-emission minima. Our experiments show that the helical structures are a manifestation of discrete eigenmodes. The pitch angle of the helix is simply m / kR , from implosion to explosion, where m, k, and R are the azimuthal mode number, axial wavenumber, and radius of the helical instability. Thus, the pitch angle increases (decreases) during implosion (explosion) as R becomes smaller (larger). We found that there are one, or at most two, discrete helical modes that arise for magnetized liners, with no apparent threshold on the applied Bz for the appearance of helical modes; increasing the axial magnetic field from zero to 0.5 T changes the relative weight between the m = 0 and m = 1 modes. Further increasing the applied axial magnetic fields yield higher m modes. Finally, the seeded kink instability overwhelms the intrinsic instability modes of the plasma. These results are corroborated with our analytic theory on the effects of radial acceleration on the classical sausage, kink, and higher m modes. Work supported by US DOE award DE-SC0012328, Sandia National Laboratories

Adsorption of zinc ions on bone char using helical coil-packed bed columns and its mass transfer modeling

DEFF Research Database (Denmark)

Moreno-Pérez, J.; Bonilla-Petriciolet, A.; Rojas-Mayorga, C. K.

2016-01-01

This study reports the assessment of helical coil-packed bed columns for Zn2+ adsorption on bone char. Zn2+ adsorption breakthrough curves have been obtained using helical coil columns with different characteristics and a comparison has been conducted with respect to the results of straight fixed-bed...... columns. Results showed that the helical coil adsorption columns may offer an equivalent removal performance than that obtained for the traditional packed bed columns but using a compact structure. However, the coil diameter, number of turns, and feed flow appear to be crucial parameters for obtaining...... the best performance in this packed-bed geometry. A mass transfer model for a mobile fluid flowing through a porous media was used for fitting and predicting the Zn2+ breakthrough curves in helical coil bed columns. Results of adsorbent physicochemical characterization showed that Zn2+ adsorption on bone...

High performance operational limits of tokamak and helical systems

International Nuclear Information System (INIS)

Yamazaki, Kozo; Kikuchi, Mitsuru

2003-01-01

The plasma operational boundaries of tokamak and helical systems are surveyed and compared with each other. Global confinement scaling laws are similar and gyro-Bohm like, however, local transport process is different due to sawtooth oscillations in tokamaks and ripple transport loss in helical systems. As for stability limits, achievable tokamak beta is explained by ideal or resistive MHD theories. On the other hand, beta values obtained so far in helical system are beyond ideal Mercier mode limits. Density limits in tokamak are often related to the coupling between radiation collapse and disruptive MHD instabilities, but the slow radiation collapse is dominant in the helical system. The pulse length of both tokamak and helical systems is on the order of hours in small machines, and the longer-pulsed good-confinement plasma operations compatible with radiative divertors are anticipated in both systems in the future. (author)

ALS-causing profilin-1-mutant forms a non-native helical structure in membrane environments.

Science.gov (United States)

Lim, Liangzhong; Kang, Jian; Song, Jianxing

2017-11-01

Despite having physiological functions completely different from superoxide dismutase 1 (SOD1), profilin 1 (PFN1) also carries mutations causing amyotrophic lateral sclerosis (ALS) with a striking similarity to that triggered by SOD1 mutants. Very recently, the C71G-PFN1 has been demonstrated to cause ALS by a gain of toxicity and the acceleration of motor neuron degeneration preceded the accumulation of its aggregates. Here by atomic-resolution NMR determination of conformations and dynamics of WT-PFN1 and C71G-PFN1 in aqueous buffers and in membrane mimetics DMPC/DHPC bicelle and DPC micelle, we deciphered that: 1) the thermodynamic destabilization by C71G transforms PFN1 into coexistence with the unfolded state, which is lacking of any stable tertiary/secondary structures as well as restricted ps-ns backbone motions, thus fundamentally indistinguishable from ALS-causing SOD1 mutants. 2) Most strikingly, while WT-PFN1 only weakly interacts with DMPC/DHPC bicelle without altering the native structure, C71G-PFN1 acquires abnormal capacity in strongly interacting with DMPC/DHPC bicelle and DPC micelle, energetically driven by transforming the highly disordered unfolded state into a non-native helical structure, similar to what has been previously observed on ALS-causing SOD1 mutants. Our results imply that one potential mechanism for C71G-PFN1 to initiate ALS might be the abnormal interaction with membranes as recently established for SOD1 mutants. Copyright © 2017 Elsevier B.V. All rights reserved.

A Prospective Evaluation of Helical Tomotherapy

International Nuclear Information System (INIS)

Bauman, Glenn; Yartsev, Slav; Rodrigues, George; Lewis, Craig; Venkatesan, Varagur M.; Yu, Edward; Hammond, Alex; Perera, Francisco; Ash, Robert; Dar, A. Rashid; Lock, Michael; Baily, Laura; Coad, Terry C; Trenka, Kris C.; Warr, Barbara; Kron, Tomas; Battista, Jerry; Van Dyk, Jake

2007-01-01

Purpose: To report results from two clinical trials evaluating helical tomotherapy (HT). Methods and Materials: Patients were enrolled in one of two prospective trials of HT (one for palliative and one for radical treatment). Both an HT plan and a companion three-dimensional conformal radiotherapy (3D-CRT) plan were generated. Pretreatment megavoltage computed tomography was used for daily image guidance. Results: From September 2004 to January 2006, a total of 61 sites in 60 patients were treated. In all but one case, a clinically acceptable tomotherapy plan for treatment was generated. Helical tomotherapy plans were subjectively equivalent or superior to 3D-CRT in 95% of plans. Helical tomotherapy was deemed equivalent or superior in two thirds of dose-volume point comparisons. In cases of inferiority, differences were either clinically insignificant and/or reflected deliberate tradeoffs to optimize the HT plan. Overall imaging and treatment time (median) was 27 min (range, 16-91 min). According to a patient questionnaire, 78% of patients were satisfied to very satisfied with the treatment process. Conclusions: Helical tomotherapy demonstrated clear advantages over conventional 3D-CRT in this diverse patient group. The prospective trials were helpful in deploying this technology in a busy clinical setting

Review of the helicity formalism; Revision del formalismo de helicidad

Energy Technology Data Exchange (ETDEWEB)

Barreiro, F; Cerrada, M; Fernandez, E

1972-07-01

Our purpose in these notes has been to present a brief and general review of the helicity formalism. We begin by discussing Lorentz invariance, spin and helicity ideas, in section 1 . In section 2 we deal with the construction of relativistic states and scattering amplitudes in the helicity basis and we study their transformation properties under discrete symmetries. Finally we present some more sophisticated topics like kinematical singularities of helicity amplitudes, kinematical constraints and crossing relations 3, 4, 5 respectively. (Author) 8 refs.

Helicity evolution at small x

International Nuclear Information System (INIS)

Kovchegov, Yuri V.; Pitonyak, Daniel; Sievert, Matthew D.

2016-01-01

We construct small-x evolution equations which can be used to calculate quark and anti-quark helicity TMDs and PDFs, along with the g 1 structure function. These evolution equations resum powers of α s ln 2  (1/x) in the polarization-dependent evolution along with the powers of α s ln (1/x) in the unpolarized evolution which includes saturation effects. The equations are written in an operator form in terms of polarization-dependent Wilson line-like operators. While the equations do not close in general, they become closed and self-contained systems of non-linear equations in the large-N c and large-N c   N f limits. As a cross-check, in the ladder approximation, our equations map onto the same ladder limit of the infrared evolution equations for the g 1 structure function derived previously by Bartels, Ermolaev and Ryskin http://dx.doi.org/10.1007/s002880050285.

Multiple helical modes of vortex breakdown

DEFF Research Database (Denmark)

Sørensen, Jens Nørkær; Naumov, I. V.; Okulov, Valery

2011-01-01

Experimental observations of vortex breakdown in a rotating lid-driven cavity are presented. The results show that vortex breakdown for cavities with high aspect ratios is associated with the appearance of stable helical vortex multiplets. By using results from stability theory generalizing Kelvi......’s problem on vortex polygon stability, and systematically exploring the cavity flow, we succeeded in identifying two new stable vortex breakdown states consisting of triple and quadruple helical multiplets....

Experimental Evidence of Helical Flow in Porous Media

DEFF Research Database (Denmark)

Ye, Yu; Chiogna, Gabriele; Cirpka, Olaf A.

2015-01-01

Helical flow leads to deformation of solute plumes and enhances transverse mixing in porous media. We present experiments in which macroscopic helical flow is created by arranging different materials to obtain an anisotropic macroscopic permeability tensor with spatially variable orientation....... The resulting helical flow entails twisting streamlines which cause a significant increase in lateral mass exchange and thus a large enhancement of plume dilution (up to 235%) compared to transport in homogenous media. The setup may be used to effectively mix solutes in parallel streams similarly to static...... mixers, but in porous media....

Radiation Field of a Square, Helical Beam Antenna

DEFF Research Database (Denmark)

Knudsen, Hans Lottrup

1952-01-01

square helices are used. Further, in connection with corresponding rigorous formulas for the field from a circular, helical antenna with a uniformly progressing current wave of constant amplitude the present formulas may be used for an investigation of the magnitude of the error introduced in Kraus......' approximate calculation of the field from a circular, helical antenna by replacing this antenna with an ``equivalent'' square helix. This investigation is carried out by means of a numerical example. The investigation shows that Kraus' approximate method of calculation yields results in fair agreement...

Geometric analysis of alloreactive HLA α-helices.

Science.gov (United States)

Ribarics, Reiner; Karch, Rudolf; Ilieva, Nevena; Schreiner, Wolfgang

2014-01-01

Molecular dynamics (MD) is a valuable tool for the investigation of functional elements in biomolecules, providing information on dynamic properties and processes. Previous work by our group has characterized static geometric properties of the two MHC α-helices comprising the peptide binding region recognized by T cells. We build upon this work and used several spline models to approximate the overall shape of MHC α-helices. We applied this technique to a series of MD simulations of alloreactive MHC molecules that allowed us to capture the dynamics of MHC α-helices' steric configurations. Here, we discuss the variability of spline models underlying the geometric analysis with varying polynomial degrees of the splines.

Helicity conservation and twisted Seifert surfaces for superfluid vortices.

Science.gov (United States)

Salman, Hayder

2017-04-01

Starting from the continuum definition of helicity, we derive from first principles its different contributions for superfluid vortices. Our analysis shows that an internal twist contribution emerges naturally from the mathematical derivation. This reveals that the spanwise vector that is used to characterize the twist contribution must point in the direction of a surface of constant velocity potential. An immediate consequence of the Seifert framing is that the continuum definition of helicity for a superfluid is trivially zero at all times. It follows that the Gauss-linking number is a more appropriate definition of helicity for superfluids. Despite this, we explain how a quasi-classical limit can arise in a superfluid in which the continuum definition for helicity can be used. This provides a clear connection between a microscopic and a macroscopic description of a superfluid as provided by the Hall-Vinen-Bekarevich-Khalatnikov equations. This leads to consistency with the definition of helicity used for classical vortices.

On Helical Projection and Its Application in Screw Modeling

Directory of Open Access Journals (Sweden)

Riliang Liu

2014-04-01

Full Text Available As helical surfaces, in their many and varied forms, are finding more and more applications in engineering, new approaches to their efficient design and manufacture are desired. To that end, the helical projection method that uses curvilinear projection lines to map a space object to a plane is examined in this paper, focusing on its mathematical model and characteristics in terms of graphical representation of helical objects. A number of interesting projective properties are identified in regard to straight lines, curves, and planes, and then the method is further investigated with respect to screws. The result shows that the helical projection of a cylindrical screw turns out to be a Jordan curve, which is determined by the screw's axial profile and number of flights. Based on the projection theory, a practical approach to the modeling of screws and helical surfaces is proposed and illustrated with examples, and its possible application in screw manufacturing is discussed.

Scale Dependence of Magnetic Helicity in the Solar Wind

Science.gov (United States)

Brandenburg, Axel; Subramanian, Kandaswamy; Balogh, Andre; Goldstein, Melvyn L.

2011-01-01

We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-in-flow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k approximately equal to 2AU(sup -1) (or frequency nu approximately equal to 2 microHz) at distances below 2.8AU and at k approximately equal to 30AU(sup -1) (or nu approximately equal to 25 microHz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10(sup 45) Mx(sup 2) cycle(sup -1) at large scales and to a three times lower value at smaller scales.

Asymmetric fan beams (AFB) for improvement of the craniocaudal dose distribution in helical tomotherapy delivery

International Nuclear Information System (INIS)

Gladwish, Adam; Kron, Tomas; McNiven, Andrea; Bauman, Glenn; Van Dyk, Jake

2004-01-01

Helical tomotherapy (HT) is a novel radiotherapy technique that utilizes intensity modulated fan beams that deliver highly conformal dose distributions in a helical beam trajectory. The most significant limitation in dose delivery with a constant fan beam thickness (FBT) is the penumbra width of the dose distribution in the craniocaudal direction, which is equivalent to the FBT. We propose to employ a half-blocked fan beam at start and stop location to reduce the penumbra width by half. By opening the jaw slowly during the helical delivery until the desired FBT is achieved it is possible to create a sharper edge in the superior and inferior direction from the target. The technique was studied using a tomotherapy beam model implemented on a commercial treatment planning system (Theraplan Plus V3.0). It was demonstrated that the dose distribution delivered using a 25 mm fan beam can be improved significantly, to reduce the dose to normal structures located superiorly and inferiorly of the target. Dosimetry for this technique is straightforward down to a FBT of 15 mm and implementation should be simple as no changes in couch movement are required compared to a standard HT delivery. We conclude that the use of asymmetric collimated fan beams for the start and stop of the helical tomotherapeutic dose delivery has the potential of significantly improving the dose distribution in helical tomotherapy

Helical axis stellarator equilibrium model

International Nuclear Information System (INIS)

Koniges, A.E.; Johnson, J.L.

1985-02-01

An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift

PRODUCTIVITY OF SOLAR FLARES AND MAGNETIC HELICITY INJECTION IN ACTIVE REGIONS

International Nuclear Information System (INIS)

Park, Sung-hong; Wang Haimin; Chae, Jongchul

2010-01-01

The main objective of this study is to better understand how magnetic helicity injection in an active region (AR) is related to the occurrence and intensity of solar flares. We therefore investigate the magnetic helicity injection rate and unsigned magnetic flux, as a reference. In total, 378 ARs are analyzed using SOHO/MDI magnetograms. The 24 hr averaged helicity injection rate and unsigned magnetic flux are compared with the flare index and the flare-productive probability in the next 24 hr following a measurement. In addition, we study the variation of helicity over a span of several days around the times of the 19 flares above M5.0 which occurred in selected strong flare-productive ARs. The major findings of this study are as follows: (1) for a sub-sample of 91 large ARs with unsigned magnetic fluxes in the range from (3-5) x 10 22 Mx, there is a difference in the magnetic helicity injection rate between flaring ARs and non-flaring ARs by a factor of 2; (2) the GOES C-flare-productive probability as a function of helicity injection displays a sharp boundary between flare-productive ARs and flare-quiet ones; (3) the history of helicity injection before all the 19 major flares displayed a common characteristic: a significant helicity accumulation of (3-45) x 10 42 Mx 2 during a phase of monotonically increasing helicity over 0.5-2 days. Our results support the notion that helicity injection is important in flares, but it is not effective to use it alone for the purpose of flare forecast. It is necessary to find a way to better characterize the time history of helicity injection as well as its spatial distribution inside ARs.

Geometry Dynamics of α-Helices in Different Class I Major Histocompatibility Complexes

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Reiner Ribarics

2015-01-01

Full Text Available MHC α-helices form the antigen-binding cleft and are of particular interest for immunological reactions. To monitor these helices in molecular dynamics simulations, we applied a parsimonious fragment-fitting method to trace the axes of the α-helices. Each resulting axis was fitted by polynomials in a least-squares sense and the curvature integral was computed. To find the appropriate polynomial degree, the method was tested on two artificially modelled helices, one performing a bending movement and another a hinge movement. We found that second-order polynomials retrieve predefined parameters of helical motion with minimal relative error. From MD simulations we selected those parts of α-helices that were stable and also close to the TCR/MHC interface. We monitored the curvature integral, generated a ruled surface between the two MHC α-helices, and computed interhelical area and surface torsion, as they changed over time. We found that MHC α-helices undergo rapid but small changes in conformation. The curvature integral of helices proved to be a sensitive measure, which was closely related to changes in shape over time as confirmed by RMSD analysis. We speculate that small changes in the conformation of individual MHC α-helices are part of the intrinsic dynamics induced by engagement with the TCR.

Image quality of high-resolution CT with 16-channel multidetector-row CT. Comparison between helical scan and conventional step-shoot scan

International Nuclear Information System (INIS)

Sumikawa, Hiromitsu; Johkoh, Takeshi; Koyama, Mitsuhiro

2005-01-01

The aim of this study was to evaluate the image quality of high-resolution CT (HRCT) reconstructed from volumetric data with 16-channel multidetector-row CT (MDCT). Eleven autopsy lungs that were diagnosed histopathologically were scanned by 16-channel MDCT with the step-and-shoot scan mode and three helical scan modes. Each helical mode had each size of focal spot, pitch, and time of gantry rotation. HRCT images were reconstructed from the volumetric data with each helical mode and axial sequence data. Two observers evaluated the image quality and noted the most appropriate diagnosis for each imaging. Visualization of abnormal structures with one helical mode was equal to those with axial mode, whereas those with the other two helical modes were inferior to those with axial mode (Wilcoxon signed rank test; p<0.0001). There was no significant difference in diagnostic efficacy between modes. The image quality of HRCT with appropriate helical mode is equal to that with axial mode and diagnostic efficacy is equal among all modes. These results may indicate that sufficient HRCT images can be obtained by only one helical scan without the addition of conventional axial scans. (author)

Metallic and 3D-printed dielectric helical terahertz waveguides.

Science.gov (United States)

Vogt, Dominik Walter; Anthony, Jessienta; Leonhardt, Rainer

2015-12-28

We investigate guidance of Terahertz (THz) radiation in metallic and 3D-printed dielectric helical waveguides in the frequency range from 0.2 to 1 THz. Our experimental results obtained from THz time-domain spectroscopy (THz-TDS) measurements are in very good agreement with finite-difference time-domain (FDTD) simulations. We observe single-mode, low loss and low dispersive propagation of THz radiation in metallic helical waveguides over a broad bandwidth. The 3D-printed dielectric helical waveguides have substantially extended the bandwidth of a low loss dielectric tube waveguide as observed from the experimental and simulation results. The high flexibility of the helical design allows an easy incorporation into bench top THz devices.

INTERPRETING ERUPTIVE BEHAVIOR IN NOAA AR 11158 VIA THE REGION'S MAGNETIC ENERGY AND RELATIVE-HELICITY BUDGETS

International Nuclear Information System (INIS)

Tziotziou, Kostas; Georgoulis, Manolis K.; Liu Yang

2013-01-01

In previous works, we introduced a nonlinear force-free method that self-consistently calculates the instantaneous budgets of free magnetic energy and relative magnetic helicity in solar active regions (ARs). Calculation is expedient and practical, using only a single vector magnetogram per computation. We apply this method to a time series of 600 high-cadence vector magnetograms of the eruptive NOAA AR 11158 acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory over a five-day observing interval. Besides testing our method extensively, we use it to interpret the dynamical evolution in the AR, including eruptions. We find that the AR builds large budgets of both free magnetic energy and relative magnetic helicity, sufficient to power many more eruptions than the ones it gave within the interval of interest. For each of these major eruptions, we find eruption-related decreases and subsequent free-energy and helicity budgets that are consistent with the observed eruption (flare and coronal mass ejection (CME)) sizes. In addition, we find that (1) evolution in the AR is consistent with the recently proposed (free) energy-(relative) helicity diagram of solar ARs, (2) eruption-related decreases occur before the flare and the projected CME-launch times, suggesting that CME progenitors precede flares, and (3) self terms of free energy and relative helicity most likely originate from respective mutual terms, following a progressive mutual-to-self conversion pattern that most likely stems from magnetic reconnection. This results in the non-ideal formation of increasingly helical pre-eruption structures and instigates further research on the triggering of solar eruptions with magnetic helicity firmly placed in the eruption cadre

Alteration of helical vortex core without change in flow topology

DEFF Research Database (Denmark)

Velte, Clara Marika; Okulov, Valery; Hansen, Martin Otto Laver

2011-01-01

topology. The helical symmetry as such is preserved, although the characteristic parameters of helical symmetry of the vortex core transfer from a smooth linear variation to a different trend under the influence of a non-uniform pressure gradient, causing an increase in helical pitch without changing its......The abrupt expansion of the slender vortex core with changes in flow topology is commonly known as vortex breakdown. We present new experimental observations of an alteration of the helical vortex core in wall bounded turbulent flow with abrupt growth in core size, but without change in flow...

Bioinspired coupled helical coils for soft tissue engineering of tubular structures - Improved mechanical behavior of tubular collagen type I templates.

Science.gov (United States)

Janke, H P; Bohlin, J; Lomme, R M L M; Mihaila, S M; Hilborn, J; Feitz, W F J; Oosterwijk, E

2017-09-01

The design of constructs for tubular tissue engineering is challenging. Most biomaterials need to be reinforced with supporting structures such as knittings, meshes or electrospun material to comply with the mechanical demands of native tissues. In this study, coupled helical coils (CHCs) were manufactured to mimic collagen fiber orientation as found in nature. Monofilaments of different commercially available biodegradable polymers were wound and subsequently fused, resulting in right-handed and left-handed polymer helices fused together in joints where the filaments cross. CHCs of different polymer composition were tested to determine the tensile strength, strain recovery, hysteresis, compressive strength and degradation of CHCs of different composition. Subsequently, seamless and stable hybrid constructs consisting of PDSII® USP 2-0 CHCs embedded in porous collagen type I were produced. Compared to collagen alone, this hybrid showed superior strain recovery (93.5±0.9% vs 71.1±12.6% in longitudinal direction; 87.1±6.6% vs 57.2±4.6% in circumferential direction) and hysteresis (18.9±2.7% vs 51.1±12.0% in longitudinal direction; 11.5±4.6% vs 46.3±6.3% in circumferential direction). Furthermore, this hybrid construct showed an improved Young's modulus in both longitudinal (0.5±0.1MPavs 0.2±0.1MPa; 2.5-fold) and circumferential (1.65±0.07MPavs (2.9±0.3)×10 -2 MPa; 57-fold) direction, respectively, compared to templates created from collagen alone. Moreover, hybrid template characteristics could be modified by changing the CHC composition and CHCs were produced showing a mechanical behavior similar to the native ureter. CHC-enforced templates, which are easily tunable to meet different demands may be promising for tubular tissue engineering. Most tubular constructs lack sufficient strength and tunability to comply with the mechanical demands of native tissues. Therefore, we embedded coupled helical coils (CHCs) produced from biodegradable polymers - to

Performance analyses of helical coil heat exchangers. The effect of external coil surface modification on heat exchanger effectiveness

Science.gov (United States)

Andrzejczyk, Rafał; Muszyński, Tomasz

2016-12-01

The shell and coil heat exchangers are commonly used in heating, ventilation, nuclear industry, process plant, heat recovery and air conditioning systems. This type of recuperators benefits from simple construction, the low value of pressure drops and high heat transfer. In helical coil, centrifugal force is acting on the moving fluid due to the curvature of the tube results in the development. It has been long recognized that the heat transfer in the helical tube is much better than in the straight ones because of the occurrence of secondary flow in planes normal to the main flow inside the helical structure. Helical tubes show good performance in heat transfer enhancement, while the uniform curvature of spiral structure is inconvenient in pipe installation in heat exchangers. Authors have presented their own construction of shell and tube heat exchanger with intensified heat transfer. The purpose of this article is to assess the influence of the surface modification over the performance coefficient and effectiveness. The experiments have been performed for the steady-state heat transfer. Experimental data points were gathered for both laminar and turbulent flow, both for co current- and countercurrent flow arrangement. To find optimal heat transfer intensification on the shell-side authors applied the number of transfer units analysis.

Helical Polyacetylenes Induced via Noncovalent Chiral Interactions and Their Applications as Chiral Materials.

Science.gov (United States)

Maeda, Katsuhiro; Yashima, Eiji

2017-08-01

Construction of predominantly one-handed helical polyacetylenes with a desired helix sense utilizing noncovalent chiral interactions with nonracemic chiral guest compounds based on a supramolecular approach is described. As with the conventional dynamic helical polymers possessing optically active pendant groups covalently bonded to the polymer chains, this noncovalent helicity induction system can show significant chiral amplification phenomena, in which the chiral information of the nonracemic guests can transfer with high cooperativity through noncovalent bonding interactions to induce an almost single-handed helical conformation in the polymer backbone. An intriguing "memory effect" of the induced macromolecular helicity is observed for some polyacetylenes, which means that the helical conformations induced in dynamic helical polyacetylene can be transformed into metastable static ones by tuning their helix-inversion barriers. Potential applications of helical polyacetylenes with controlled helix sense constructed by the "noncovalent helicity induction and/or memory effect" as chiral materials are also described.

Low-energy properties of fractional helical Luttinger liquids

NARCIS (Netherlands)

Meng, T.; Fritz, L.|info:eu-repo/dai/nl/371569559; Schuricht, D.|info:eu-repo/dai/nl/369284690; Loss, D.

2014-01-01

We investigate the low-energy properties of (quasi) helical and fractional helical Luttinger liquids. In particular, we calculate the Drude peak of the optical conductivity, the density of states, as well as charge transport properties of the interacting system with and without attached Fermi liquid

Heat transfer characteristics of a helical heat exchanger

International Nuclear Information System (INIS)

San, Jung-Yang; Hsu, Chih-Hsiang; Chen, Shih-Hao

2012-01-01

Heat transfer performance of a helical heat exchanger was investigated. The heat exchanger is composed of a helical tube with rectangular cross section and two cover plates. The ε–Ntu relation of the heat exchanger was obtained using a numerical method. In the analysis, the flow in the tube (helical flow) was considered to be mixed and the flow outside the tube (radial flow) was unmixed. In the experiment, the Darcy friction factor (f) and convective heat transfer coefficient (h) of the radial flow were measured. The radial flow was air and the helical flow was water. Four different channel spacing (0.5, 0.8, 1.2 and 1.6 mm) were individually considered. The Reynolds numbers were in the range 307–2547. Two correlations, one for the Darcy friction factor and the other for the Nusselt number, were proposed. - Highlights: ► We analyze the heat transfer characteristics of a helical heat exchanger and examine the effectiveness–Ntu relation. ► Increasing number of turns of the heat exchanger would slightly increase the effectiveness. ► There is an optimum Ntu value corresponding to a maximum effectiveness. ► We measure the Darcy friction factor and Nusselt number of the radial flow and examine the correlations.

Control of the Helicity Content of a Gun-Generated Spheromak by Incorporating a Conducting Shell into a Magnetized Coaxial Plasma Gun

Science.gov (United States)

Matsumoto, Tadafumi; Sekiguchi, Jun'ichi; Asai, Tomohiko

In the formation of magnetized plasmoid by a magnetized coaxial plasma gun (MCPG), the magnetic helicity content of the generated plasmoid is one of the critical parameters. Typically, the bias coil to generate a poloidal flux is mounted either on the outer electrode or inside the inner electrode. However, most of the flux generated in the conventional method spreads even radially outside of the formation region. Thus, only a fraction of the total magnetic flux is actually exploited for helicity generation in the plasmoid. In the proposed system, the plasma gun incorporates a copper shell mounted on the outer electrode. By changing the rise time of the discharge bias coil current and the geometrical structure of the shell, the magnetic field structure and its time evolution can be controlled. The effect of the copper shell has been numerically simulated for the actual gun structure, and experimentally confirmed. This may increase the magnetic helicity content results, through increased poloidal magnetic field.

Single-Handed Helical Polybissilsesquioxane Nanotubes and Mesoporous Nanofibers Prepared by an External Templating Approach Using Low-Molecular-Weight Gelators

Directory of Open Access Journals (Sweden)

Jing Hu

2017-01-01

Full Text Available Chiral low-molecular-weight gelators (LMWGs derived from amino acids can self-assemble into helical fibers and twisted/coiled nanoribbons by H-bonding and π–π interaction. Silica nanotubes with single-handed helices have been prepared using chiral LMWGs through sol–gel transcription. Molecular-scale chirality exists at the inner surfaces. Here, we discuss single-handed helical aromatic ring-bridged polybissilsesquioxane nanotubes and mesoporous nanofibers prepared using chiral LMWGs. This review aims at describing the formation mechanisms of the helical nanostructures, the origination of optical activity, and the applications for other helical nanomaterial preparation, mainly based on our group’s results. The morphology and handedness can be controlled by changing the chirality and kinds of LMWGs and tuning the reaction conditions. The aromatic rings arrange in a partially crystalline structure. The optical activity of the polybissilsesquioxane nanotubes and mesoporous nanofibers originates from chiral defects, including stacking and twisting of aromatic groups, on the inner surfaces. They can be used as the starting materials for preparation of silica, silicon, carbonaceous, silica/carbon, and silicon carbide nanotubes.

Unraveling double stranded alpha-helical coiled coils: an x-ray diffraction study on hard alpha-keratin fibers.

Science.gov (United States)

Kreplak, L; Doucet, J; Briki, F

2001-04-15

Transformations of proteins secondary and tertiary structures are generally studied in globular proteins in solution. In fibrous proteins, such as hard alpha-keratin, that contain long and well-defined double stranded alpha-helical coiled coil domains, such study can be directly done on the native fibrous tissue. In order to assess the structural behavior of the coiled coil domains under an axial mechanical stress, wide angle x-ray scattering and small angle x-ray scattering experiments have been carried out on stretched horse hair fibers at relative humidity around 30%. Our observations of the three major axial spacings as a function of the applied macroscopic strain have shown two rates. Up to 4% macroscopic strain the coiled coils were slightly distorted but retained their overall conformation. Above 4% the proportion of coiled coil domains progressively decreased. The main and new result of our study is the observation of the transition from alpha-helical coiled coils to disordered chains instead of the alpha-helical coiled coil to beta-sheet transition that occurs in wet fibers.

Starch Catabolism by a Prominent Human Gut Symbiont Is Directed by the Recognition of Amylose Helices

Energy Technology Data Exchange (ETDEWEB)

Koropatkin, Nicole M.; Martens, Eric C.; Gordon, Jeffrey I.; Smith, Thomas J. (WU); (Danforth)

2009-01-12

The human gut microbiota performs functions that are not encoded in our Homo sapiens genome, including the processing of otherwise undigestible dietary polysaccharides. Defining the structures of proteins involved in the import and degradation of specific glycans by saccharolytic bacteria complements genomic analysis of the nutrient-processing capabilities of gut communities. Here, we describe the atomic structure of one such protein, SusD, required for starch binding and utilization by Bacteroides thetaiotaomicron, a prominent adaptive forager of glycans in the distal human gut microbiota. The binding pocket of this unique {alpha}-helical protein contains an arc of aromatic residues that complements the natural helical structure of starch and imposes this conformation on bound maltoheptaose. Furthermore, SusD binds cyclic oligosaccharides with higher affinity than linear forms. The structures of several SusD/oligosaccharide complexes reveal an inherent ligand recognition plasticity dominated by the three-dimensional conformation of the oligosaccharides rather than specific interactions with the composite sugars.

Chiral monolithic absorbent constructed by optically active helical-substituted polyacetylene and graphene oxide: preparation and chiral absorption capacity.

Science.gov (United States)

Li, Weifei; Wang, Bo; Yang, Wantai; Deng, Jianping

2015-02-01

Chiral monolithic absorbent is successfully constructed for the first time by using optically active helical-substituted polyacetylene and graphene oxide (GO). The preparative strategy is facile and straightforward, in which chiral-substituted acetylene monomer (Ma), cross-linker (Mb), and alkynylated GO (Mc) undergo copolymerization to form the desired monolithic absorbent in quantitative yield. The resulting monoliths are characterized by circular dichroism, UV-vis absorption, scanning electron microscopy (SEM), FT-IR, Raman, energy-dispersive spectrometer (EDS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), XPS, and thermogravimetric analysis (TGA) techniques. The polymer chains derived from Ma form chiral helical structures and thus provide optical activity to the monoliths, while GO sheets contribute to the formation of porous structures. The porous structure enables the monolithic absorbents to demonstrate a large swelling ratio in organic solvents, and more remarkably, the helical polymer chains provide optical activity and further enantio-differentiating absorption ability. The present study establishes an efficient and versatile methodology for preparing novel functional materials, in particular monolithic chiral materials based on substituted polyacetylene and GO. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A multi-modular helical magnetic millirobot navigating in curved tubular environments

Directory of Open Access Journals (Sweden)

Seungmun Jeon

2017-05-01

Full Text Available This paper proposes a novel multi-modular helical magnetic millirobot (MHMM able to navigate in curved tubular environments. The proposed MHMM is basically composed of head, middle, and tail modules serially connected by a universal joint, and can employ more modules if necessary. The head module is a helical body with a magnetic rotary tip attached to the front end. Thus, once located in a curved tube filled with a fluid, the MHMM can effectively generate navigating or unclogging motions simply actuated by an external rotating magnetic field. This paper also examines the dynamic characteristics of the MHMM under various working conditions to manipulate the MHMM in a stable and safe manner. Then, it demonstrates various controlled motions of the MHMM in an in-vitro pulsatile flow environment to show the validity of the proposed structure and method.

Spin helical states and spin transport of the line defect in silicene lattice

Energy Technology Data Exchange (ETDEWEB)

Yang, Mou; Chen, Dong-Hai; Wang, Rui-Qiang [Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Bai, Yan-Kui, E-mail: ykbai@semi.ac.cn [College of Physical Science and Information Engineering and Hebei Advance Thin Films Laboratory, Hebei Normal University, Shijiazhuang, Hebei 050024 (China)

2015-02-06

We investigated the electronic structure of a silicene-like lattice with a line defect under the consideration of spin–orbit coupling. In the bulk energy gap, there are defect related bands corresponding to spin helical states localized beside the defect line: spin-up electrons flow forward on one side near the line defect and move backward on the other side, and vice versa for spin-down electrons. When the system is subjected to random distribution of spin-flipping scatterers, electrons suffer much less spin-flipped scattering when they transport along the line defect than in the bulk. An electric gate above the line defect can tune the spin-flipped transmission, which makes the line defect as a spin-controllable waveguide. - Highlights: • Band structure of silicene with a line defect. • Spin helical states around the line defect and their probability distribution features. • Spin transport along the line defect and that in the bulk silicene.

Two conceptual designs of helical fusion reactor FFHR-d1A based on ITER technologies and challenging ideas

Science.gov (United States)

Sagara, A.; Miyazawa, J.; Tamura, H.; Tanaka, T.; Goto, T.; Yanagi, N.; Sakamoto, R.; Masuzaki, S.; Ohtani, H.; The FFHR Design Group

2017-08-01

The Fusion Engineering Research Project (FERP) at the National Institute for Fusion Science (NIFS) is conducting conceptual design activities for the LHD-type helical fusion reactor FFHR-d1A. This paper newly defines two design options, ‘basic’ and ‘challenging.’ Conservative technologies, including those that will be demonstrated in ITER, are chosen in the basic option in which two helical coils are made of continuously wound cable-in-conduit superconductors of Nb3Sn strands, the divertor is composed of water-cooled tungsten monoblocks, and the blanket is composed of water-cooled ceramic breeders. In contrast, new ideas that would possibly be beneficial for making the reactor design more attractive are boldly included in the challenging option in which the helical coils are wound by connecting high-temperature REBCO superconductors using mechanical joints, the divertor is composed of a shower of molten tin jets, and the blanket is composed of molten salt FLiNaBe including Ti powers to increase hydrogen solubility. The main targets of the challenging option are early construction and easy maintenance of a large and three-dimensionally complicated helical structure, high thermal efficiency, and, in particular, realistic feasibility of the helical reactor.

Resistive interchange mode destabilized by helically trapped energetic ions and its effects on energetic ions and bulk plasmas

International Nuclear Information System (INIS)

Du, X.D.; Toi, K.; Osakabe, M.

2014-10-01

A resistive interchange mode with bursting behavior and rapid frequency chirping in the range less than 10 kHz is observed for the first time in the magnetic hill region of net current-free, low beta LHD (Large Helical Device) plasmas during high power injection of perpendicular neutral beams. The mode resonates with the precession motion of helically trapped energetic beam ions, following the resonant condition. The radial mode structure is found to be very similar to that of usual pressure-driven interchange mode, of which radial displacement eigenfunction has an even function around the rational surface. This beam driven mode is excited when the beta value of helically trapped energetic ions exceed a certain threshold. The radial transport of helically trapped energetic ions induced by the mode transiently generates significant radial electric field near the plasma peripheral region. Thus generated radial electric field clearly suppresses micro turbulence and improves bulk plasma confinement, suggesting strong flow shear generation. (author)

A proline-hinge alters the characteristics of the amphipathic α-helical AMPs.

Directory of Open Access Journals (Sweden)

Jong Kook Lee

Full Text Available HP (2-20 is a 19-aa, amphipathic, α-helical peptide with antimicrobial properties that was derived from the N-terminus of Helicobacter pylori ribosomal protein L1. We previously showed that increasing the net hydrophobicity of HP (2-20 by substituting Trp for Gln(17 and Asp(19 (Anal 3 increased the peptide's antimicrobial activity. In hydrophobic medium, Anal 3 forms an amphipathic structure consisting of an N-terminal random coil region (residues 2-5 and an extended helical region (residues 6-20. To investigate the structure-activity relationship of Anal 3, we substituted Pro for Glu(9 (Anal 3-Pro and then examined the new peptide's three-dimensional structure, antimicrobial activity and mechanism of action. Anal 3-Pro had an α-helical structure in the presence of trifluoroethanol (TFE and sodium dodecyl sulfate (SDS. NMR spectroscopic analysis of Anal 3-Pro's tertiary structure in SDS micelles confirmed that the kink potential introduced by Pro(10 was responsible for the helix distortion. We also found that Anal 3-Pro exhibited about 4 times greater antimicrobial activity than Anal 3. Fluorescence activated flow cytometry and confocal fluorescence microscopy showed that incorporating a Pro-hinge into Anal 3 markedly reduced its membrane permeability so that it accumulated in the cytoplasm without remaining in the cell membrane. To investigate the translocation mechanism, we assessed its ability to release of FITC-dextran. The result showed Anal 3-Pro created a pore <1.8 nm in diameter, which is similar to buforin II. Notably, scanning electron microscopic observation of Candida albicans revealed that Anal 3-Pro and buforin II exert similar effects on cell membranes, whereas magainin 2 exerts a different, more damaging, effect. In addition, Anal 3-Pro assumed a helix-hinge-helix structure in the presence of biological membranes and formed micropores in both bacterial and fungal membranes, through which it entered the cytoplasm and tightly

Dynamic and Progressive Control of DNA Origami Conformation by Modulating DNA Helicity with Chemical Adducts.

Science.gov (United States)

Chen, Haorong; Zhang, Hanyu; Pan, Jing; Cha, Tae-Gon; Li, Shiming; Andréasson, Joakim; Choi, Jong Hyun

2016-05-24

DNA origami has received enormous attention for its ability to program complex nanostructures with a few nanometer precision. Dynamic origami structures that change conformation in response to environmental cues or external signals hold great promises in sensing and actuation at the nanoscale. The reconfiguration mechanism of existing dynamic origami structures is mostly limited to single-stranded hinges and relies almost exclusively on DNA hybridization or strand displacement. Here, we show an alternative approach by demonstrating on-demand conformation changes with DNA-binding molecules, which intercalate between base pairs and unwind DNA double helices. The unwinding effect modulates the helicity mismatch in DNA origami, which significantly influences the internal stress and the global conformation of the origami structure. We demonstrate the switching of a polymerized origami nanoribbon between different twisting states and a well-constrained torsional deformation in a monomeric origami shaft. The structural transformation is shown to be reversible, and binding isotherms confirm the reconfiguration mechanism. This approach provides a rapid and reversible means to change DNA origami conformation, which can be used for dynamic and progressive control at the nanoscale.

Drift mode calculations for the Large Helical Device

International Nuclear Information System (INIS)

Rewoldt, G.; Ku, L.-P.; Tang, W.M.; Sugama, H.; Nakajima, N.; Watanabe, K.Y.; Murakami, S.; Yamada, H.; Cooper, W.A.

2000-01-01

A fully kinetic assessment of the stability properties of toroidal drift modes has been obtained for a case for the Large Helical Device (LHD) [A.Iiyoshi, et al., Plasma Physics and Controlled Nuclear Fusion Research, 1998, Nucl.Fusion 39, 1245 (1999)]. This calculation retains the important effects in the linearized gyrokinetic equation, using the lowest-order ''ballooning representation'' for high toroidal mode number instabilities in the electrostatic limit. Results for toroidal drift waves destabilized by trapped particle dynamics and ion temperature gradients are presented, using three-dimensional magnetohydrodynamics equilibria reconstructed from experimental measurements. The effects of helically-trapped particles and helical curvature are investigated

Theoretical modeling of transport barriers in helical plasmas

International Nuclear Information System (INIS)

Toda, S.; Itoh, K.; Ohyabu, N.

2008-10-01

A unified transport modelling to explain electron Internal Transport Barriers (e-ITB) in helical plasmas and Internal Diffusion Barriers (IDB) observed in Large Helical Device (LHD) is proposed. The e-ITB can be predicted with the effect of zonal flows to obtain the e-ITB in the low collisional regime when the radial variation of the particle anomalous diffusivity is included. Transport analysis in this article can newly show that the particle fuelling induces the IDB formation when this unified transport modelling is used in the high collisional regime. The density limit for the IDB in helical plasmas is also examined including the effect of the radiation loss. (author)

Magnetic Helical Micro- and Nanorobots: Toward Their Biomedical Applications

Directory of Open Access Journals (Sweden)

Famin Qiu

2015-03-01

Full Text Available Magnetic helical micro- and nanorobots can perform 3D navigation in various liquids with a sub-micrometer precision under low-strength rotating magnetic fields (<10 mT. Since magnetic fields with low strengths are harmless to cells and tissues, magnetic helical micro/nanorobots are promising tools for biomedical applications, such as minimally invasive surgery, cell manipulation and analysis, and targeted therapy. This review provides general information on magnetic helical micro/nanorobots, including their fabrication, motion control, and further functionalization for biomedical applications.

Utility of three-dimensional helical CT in the diagnosis of breast cancer

International Nuclear Information System (INIS)

Maeda, Yoshiaki; Hata, Yoshinobu; Matsuoka, Shinnichi; Nakajima, Nobuhisa; Ito, Toichi; Osada, Tadahiro; Sano, Fumio

2004-01-01

Although utility of three-dimensional (3D) helical CT for preoperative examination of breast cancer has been discussed, the accuracy of the helical CT in diagnosing breast cancer has not been fully evaluated. In this study 56 malignant and 28 benign breast tumors were evaluated preoperatively with 3D-helical CT, and their imaging results were compared with pathological findings of surgical specimens. Helical CT identified the presence of malignancy in 54 out of the 56 cancer cases tested and the sensitivity and specificity in distinguishing between malignant and benign tumors were 82% and 57%, respectively. The sensitivity and specificity in diagnosing the presence of metastatic axillary lymph nodes using helical CT were 70% and 80%, respectively. The sensitivity and specificity in diagnosing the presence of extensive intraductal component (EIC) using helical CT were 71% and 86%, respectively. Helical CT visualized all of the tumors in multifocal breast cancer cases. In conclusion, 3D-helical CT is a useful modality for preoperative examination of breast cancer, especially for assessing axillary lymph node status, and EIC, and will be helpful for conducting sentinel lymph node biopsy (SNLB) and breast-conserving surgery. (author)

Radiation characteristics of helical tomotherapy

International Nuclear Information System (INIS)

Jeraj, Robert; Mackie, Thomas R.; Balog, John; Olivera, Gustavo; Pearson, Dave; Kapatoes, Jeff; Ruchala, Ken; Reckwerdt, Paul

2004-01-01

Helical tomotherapy is a dedicated intensity modulated radiation therapy (IMRT) system with on-board imaging capability (MVCT) and therefore differs from conventional treatment units. Different design goals resulted in some distinctive radiation field characteristics. The most significant differences in the design are the lack of flattening filter, increased shielding of the collimators, treatment and imaging operation modes and narrow fan beam delivery. Radiation characteristics of the helical tomotherapy system, sensitivity studies of various incident electron beam parameters and radiation safety analyses are presented here. It was determined that the photon beam energy spectrum of helical tomotherapy is similar to that of more conventional radiation treatment units. The two operational modes of the system result in different nominal energies of the incident electron beam with approximately 6 MeV and 3.5 MeV in the treatment and imaging modes, respectively. The off-axis mean energy dependence is much lower than in conventional radiotherapy units with less than 5% variation across the field, which is the consequence of the absent flattening filter. For the same reason the transverse profile exhibits the characteristic conical shape resulting in a 2-fold increase of the beam intensity in the center. The radiation leakage outside the field was found to be negligible at less than 0.05% because of the increased shielding of the collimators. At this level the in-field scattering is a dominant source of the radiation outside the field and thus a narrow field treatment does not result in the increased leakage. The sensitivity studies showed increased sensitivity on the incident electron position because of the narrow fan beam delivery and high sensitivity on the incident electron energy, as common to other treatment systems. All in all, it was determined that helical tomotherapy is a system with some unique radiation characteristics, which have been to a large extent

Helical CT of traumatic injuries of the thoracic aorta

International Nuclear Information System (INIS)

Mengozzi, E.; Burzi, M.; Miceli, M.; Lipparini, M.; Sartoni Galloni, S.

2000-01-01

Acute thoracic aortic injuries account for up to 10-20% of fatalities in high-speed deceleration road accidents and have an estimated immediate fatality rate of 80-90%. Untreated survivors to acute trauma (10-20%) have a dismal prognosis: 30% of them die within 6 hours, 40-50% die within 24 hours, and 90% within 4 months. It was investigated the diagnostic accuracy of Helical Computed Tomography (Helical CT) in acute traumatic injuries of the thoracic aorta, and the role of this technique in the diagnostic management of trauma patients with a strong suspicion of aortic rupture. It was compared retrospectively the chest Helical CT findings of 256 trauma patients examined June 1995 through August 1999. Chest Helical CT examinations were performed according to trauma score, to associated traumatic lesions and to plain chest radiographic findings. All the examinations were performed with no intravenous contrast agent administration and the pitch 2 technique. After a previous baseline study, contrast-enhanced scans were acquired with pitch 1 in 87 patients. Helical CT showed aortic lesions in 9 of 256 patients examined. In all the 9 cases it was found a mediastinal hematoma and all of them had positive plain chest radiographic findings of mediastinal enlargement. Moreover, in 6 cases aortic knob blurring was also evident on plain chest film and in 5 cases depressed left mainstem bronchus and trachea deviation rightwards were observed. All aortic lesions were identified on axial scans and located at the isthmus of level. Aortic rupture was always depicted as pseudo diverticulum of the proximal descending tract and intimal flap. It was also found that periaortic hematoma in 6 cases and intramural hematoma in 1 case. There were non false positive results in the series: 7 patients with Helical CT diagnosis of aortic rupture were submitted to conventional aortography that confirmed both type and extension of the lesions as detected by Helical CT, and all findings were

The dominant role of side chains in supramolecular double helical organisation in synthetic tripeptides

Science.gov (United States)

Sharma, Ankita; Tiwari, Priyanka; Dutt Konar, Anita

2018-06-01

Peptide self-assembled nanostructures have attracted attention recently owing to their promising applications in diversified avenues. To validate the importance of sidechains in supramolecular architectural stabilization, herein this report describes the self-assembly propensities involving weak interactions in a series of model tripeptides Boc-Xaa-Aib-Yaa-OMe I-IV, (where Xaa = 4-F-Phe/NMeSer/Ile & Yaa = Tyr in peptide I-III respectively and Xaa = 4-F-Phe & Yaa = Ile in peptide IV) differing in terminal side chains. The solid state structural analysis reveals that tripeptide (I) displays supramolecular preference for double helical architecture. However, when slight modification has been introduced in the N-terminal side chains disfavour the double helical organisation (Peptide II and III). Indeed the peptides display sheet like ensemble within the framework. Besides replacement of C-terminal Tyr by Ile in peptide I even do not promote the architecture, emphasizing the dominant role of balance of side chains in stabilizing double helical organisation. The CD measurements, concentration dependant studies, NMR titrations and ROESY spectra are well in agreement with the solid state conformational investigation. Moreover the morphological experiments utilizing FE-SEM, support the heterogeneity present in the peptides. Thus this work may not only hold future promise in understanding the structure and function of neurodegenerative diseases but also assist in rational design of protein modification in biologically active peptides.

Controllable helical deformations on printed anisotropic composite soft actuators

Science.gov (United States)

Wang, Dong; Li, Ling; Serjouei, Ahmad; Dong, Longteng; Weeger, Oliver; Gu, Guoying; Ge, Qi

2018-04-01

Helical shapes are ubiquitous in both nature and engineering. However, the development of soft actuators and robots that mimic helical motions has been hindered primarily due to the lack of efficient modeling approaches that take into account the material anisotropy and the directional change of the external loading point. In this work, we present a theoretical framework for modeling controllable helical deformations of cable-driven, anisotropic, soft composite actuators. The framework is based on the minimum potential energy method, and its model predictions are validated by experiments, where the microarchitectures of the soft composite actuators can be precisely defined by 3D printing. We use the developed framework to investigate the effects of material and geometric parameters on helical deformations. The results show that material stiffness, volume fraction, layer thickness, and fiber orientation can be used to control the helical deformation of a soft actuator. In particular, we found that a critical fiber orientation angle exists at which the twist of the actuator changes the direction. Thus, this work can be of great importance for the design and fabrication of soft actuators with tailored deformation behavior.

Preparation, characterization and infrared emissivity study of helical polyurethane-SiO2 core-shell composite

International Nuclear Information System (INIS)

Wang Zhiqiang; Zhou Yuming; Yao Qingzhao; Sun Yanqing

2009-01-01

Helical polyurethane-SiO 2 (HPU-SiO 2 ) core-shell composite was prepared after surface modification of SiO 2 nanoparticles. HPU-SiO 2 was characterized by Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet (UV) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results indicate that the helical polyurethane has been successfully grafted onto the surfaces of the modified SiO 2 . HPU-SiO 2 composite exhibits clearly core-shell structure. The ultraviolet absorption and crystallizability of HPU-SiO 2 are changed due to the shell of helical polyurethane, which possesses regular single-handed conformation and inter-chain hydrogen bonds. The infrared emissivity of HPU-SiO 2 was also investigated. The result indicates that the interfacial interactions between organic shell and inorganic core induce the infrared emissivity value being reduced from 0.781 for SiO 2 to 0.503 for HPU-SiO 2 .

Numerical analysis of fluid flow and heat transfer in a helical ...

African Journals Online (AJOL)

Helical channels are widely applied in different application areas. In a converging diverging nozzle, helical channels are mainly used for cooling of its wall. The characteristics of fluid flow and heat transfer inside helical duct for a converging diverging nozzle is not commonly dealt in present literatures. In this paper CFD ...

The Enhanced Intramolecular Energy Transfer and Strengthened ff Luminescence of a Stable Helical Eu Complex in Ionic Liquids

Directory of Open Access Journals (Sweden)

Yuki Hasegawa

2018-01-01

Full Text Available The luminescence of a Eu complex (EuL is enhanced by stabilization of the coordination structure in highly viscous ionic liquids. The EuL was found to maintain a stable single helical structure both in organic solvents and in the ionic liquids [BMIM][PF6] and [EMIM][PF6]. A colorless solution of EuL dissolved in [BMIM][PF6] exhibits bright red luminescence with a quantum yield of 32.3%, a value that is much higher than that in acetonitrile (12%. Estimated rate constants for the energy relaxation pathway indicate that the energy transfer efficiency is enhanced in [BMIM][PF6] as a result of the suppression of molecular fluctuations in the ligands. Additionally, a highly luminescent helical structure is preserved in [EMIM][PF6] up to 120 °C.

New reconstruction algorithm in helical-volume CT

International Nuclear Information System (INIS)

Toki, Y.; Rifu, T.; Aradate, H.; Hirao, Y.; Ohyama, N.

1990-01-01

This paper reports on helical scanning that is an application of continuous scanning CT to acquire volume data in a short time for three-dimensional study. In a helical scan, the patient couch sustains movement during continuous-rotation scanning and then the acquired data is processed to synthesize a projection data set of vertical section by interpolation. But the synthesized section is not thin enough; also, the image may have artifacts caused by couch movement. A new reconstruction algorithm that helps resolve such problems has been developed and compared with the ordinary algorithm. The authors constructed a helical scan system based on TCT-900S, which can perform 1-second rotation continuously for 30 seconds. The authors measured section thickness using both algorithms on an AAPM phantom, and we also compared degree of artifacts on clinical data

Resonant helical fields in the TBR tokamak

International Nuclear Information System (INIS)

Bender, O.W.

1986-01-01

The influence of external resonant helical fields (RHF) in the tokamak TBR plasma discharges was investigated. These fields were created by helical windings wounded on the TBR vessel with the same helicity of rational magnetic surfaces, producing resonant efects on these surfaces. The characteristics of the MHZ activity (amplitude, frequency and poloidal and toroidal wave numbers, m=2,3,4 and n=1, respectively) during the plasma discharges were modified by eletrical winding currents of the order of 2% of the plasma current. These characterisitics were measured for diferent discharges safety factors at the limiter (q) between 3 and 4, with and without the RHF, with the atenuation of the oscillation amplitudes and the increasing of their frequencies. The existente of expontaneous and induced magnetic islands were investigated. The data were compared with results obtained in other tokamaks. (author) [pt

Recent Results of Helical Nonneutral Plasmas on Compact Helical System (CHS)

International Nuclear Information System (INIS)

Himura, H.; Yamamoto, Y.; Sanpei, A.; Masamune, S.; Wakabayashi, H.; Isobe, M.

2006-01-01

First of all, non-constant space potential φs and electron density ne on magnetic surfaces of helical nonneutral plasmas are verified experimentally. The difference in φs enlarges significantly at the outer region inside the closed magnetic surfaces, and the corresponding equipotential surfaces are inferred to shift upward vertically with respect to magnetic surfaces. Meanwhile, larger value of ne is clearly observed in the downward region (z < 0) of magnetic surfaces, which seems to be consistent with the φs measurement. These results are the first evidence which strongly suggests the equilibrium proposed for nonneutral plasmas confined in closed magnetic surfaces. Secondly, in order to investigate the mechanism of the multiple disruption of helical nonneutral plasmas observed in experiments, space and time evolutions of electron flux are measured carefully inside the magnetic surfaces, when the plasma disruption occurs. Surprisingly, a set of data show that the observed disruption is at first happened at ρ ∼ 0.8, where ρ is the normalized minor radius, and then, it seems to propagate inside magnetic surfaces

Catechol-Acylhydrazone-Liganden für die Bildung heterodinuklearer Helicate

OpenAIRE

Latorre Martínez, Irene Cristina

2011-01-01

The interest for artificial helical structures has steadily grown since the first definition by Lehn and the investigations done later on. Not only the spectacular properties and potential applications of these compounds are important features of these substances but also their special characteristics are interesting for the supramolecular chemists. The synthesis of ligands with special donor atoms at the coordination sites is the crucial point and makes the selective binding of f- and d- met...

Space vehicle electromechanical system and helical antenna winding fixture

Science.gov (United States)

Judd, Stephen; Dallmann, Nicholas; Guenther, David; Enemark, Donald; Seitz, Daniel; Martinez, John; Storms, Steven

2017-12-26

A space vehicle electromechanical system may employ an architecture that enables convenient and practical testing, reset, and retesting of solar panel and antenna deployment on the ground. A helical antenna winding fixture may facilitate winding and binding of the helical antenna.

Theory of dynamics in long pulse helical plasmas

International Nuclear Information System (INIS)

Itoh, K.; Sanuki, H.; Toda, S.; Yokoyama, M.; Itoh, S.-I.; Yagi, M.; Fukuyama, A.

2001-01-01

Self-organized dynamics of toroidal helical plasma, which is induced by the nonlinear transport property, is discussed. Neoclassical ripple diffusion is a dominant mechanism that drives the radial electric field. The bifurcation nature of the electric field generation gives rise to the electric field domain interface, across which the electric field changes strongly. This domain interface is an origin of internal transport barrier in helical systems. This nonlinearity gives rise to the self-organized oscillations; the electric field pulsation is one of the examples. Based on the model of density limit, in which the competition between the transport loss and radiation loss is analyzed, dynamics near the density limit of helical systems is also discussed. (author)

Numerical Analysis of Helical Pile-Soil Interaction under Compressive Loads

Science.gov (United States)

Polishchuk, A. I.; Maksimov, F. A.

2017-11-01

The results of the field tests of full-scale steel helical piles in clay soils intended for prefabricated temporary buildings foundations are presented in this article. The finite element modeling was used for the evaluation of stress distribution of the clay soil around helical piles. An approach of modeling of the screw-pile geometry has been proposed through the Finite Element Analysis. Steel helical piles with a length of 2.0 m, shaft diameter of 0.108 m and a blade diameter of 0.3 m were used in the experiments. The experiments have shown the efficiency of double-bladed helical piles in the clay soils compared to single-bladed piles. It has been experimentally established that the introduction of the second blade into the pile shaft provides an increase of the bearing capacity in clay soil up to 30% compared to a single-bladed helical pile with similar geometrical dimensions. The numerical results are compared with the measurements obtained by a large scale test and the bearing capacity has been estimated. It has been found that the model results fit the field results. For a double-bladed helical pile it was revealed that shear stresses upon pile loading are formed along the lateral surface forming a cylindrical failure surface.

Magnet design with 100-kA HTS STARS conductors for the helical fusion reactor

Science.gov (United States)

Yanagi, N.; Terazaki, Y.; Ito, S.; Tamura, H.; Hamaguchi, S.; Mito, T.; Hashizume, H.; Sagara, A.

2016-12-01

The high-temperature superconducting (HTS) option is employed for the conceptual design of the LHD-type helical fusion reactor FFHR-d1. The 100-kA-class STARS (Stacked Tapes Assembled in Rigid Structure) conductor is used for the magnet system including the continuously wound helical coils. Protection of the magnet system in case of a quench is a crucial issue and the hot-spot temperature during an emergency discharge is estimated based on the zero-dimensional and one-dimensional analyses. The number of division of the coil winding package is examined to limit the voltage generation. For cooling the HTS magnet, helium gas flow is considered and its feasibility is examined by simple analysis as a first step.

Energy fluxes in helical magnetohydrodynamics and dynamo action

Indian Academy of Sciences (India)

... large-scale magnetic field arising due to non-helical interactions and (2) inverse energy flux of magnetic energy caused by helical interactions. Based on our flux results, a primitive model for galactic dynamo has been constructed. Our calculations yield dynamo time-scale for a typical galaxy to be of the order of 108 years.

Roles of effective helical ripple rates in nonlinear stability of externally induced magnetic islands

Energy Technology Data Exchange (ETDEWEB)

Nishimura, Seiya, E-mail: n-seiya@kobe-kosen.ac.jp [Kobe City College of Technology, Kobe, Hyogo 651-2194 (Japan)

2015-02-15

Magnetic islands are externally produced by resonant magnetic perturbations (RMPs) in toroidal plasmas. Spontaneous annihilation of RMP-induced magnetic islands called self-healing has been observed in helical systems. A possible mechanism of the self-healing is shielding of RMP penetration by helical ripple-induced neoclassical flows, which give rise to neoclassical viscous torques. In this study, effective helical ripple rates in multi-helicity helical systems are revisited, and a multi-helicity effect on the self-healing is investigated, based on a theoretical model of rotating magnetic islands. It is confirmed that effective helical ripple rates are sensitive to magnetic axis positions. It is newly found that self-healing thresholds also strongly depend on magnetic axis positions, which is due to dependence of neoclassical viscous torques on effective helical ripple rates.

Circular-Polarization-Selective Transmission Induced by Spin-Orbit Coupling in a Helical Tape Waveguide

Science.gov (United States)

Liu, Yahong; Guo, Qinghua; Liu, Hongchao; Liu, Congcong; Song, Kun; Yang, Biao; Hou, Quanwen; Zhao, Xiaopeng; Zhang, Shuang; Navarro-Cía, Miguel

2018-05-01

Spin-orbit coupling of light, describing the interaction between the polarization (spin) and spatial degrees of freedom (orbit) of light, plays an important role in subwavelength scale systems and leads to many interesting phenomena, such as the spin Hall effect of light. Here, based on the spin-orbit coupling, we design and fabricate a helical tape waveguide (HTW), which can realize a circular-polarization-selective process. When the incident circularly polarized wave is of the same handedness as the helix of the HTW, a nearly complete transmission is observed; in contrast, a counterrotating circular polarization of incident wave results in a much lower transmission or is even totally blocked by the HTW. Indeed, both simulations and experiments reveal that the blocked component of power leaks through the helical aperture of the HTW and forms a conical beam analogous to helical Cherenkov radiation due to the conversion from the spin angular momentum to the orbital angular momentum. Our HTW structure demonstrates its potential as a polarization selector in a broadband frequency range.

Analytic, High-beta Solutions of the Helical Grad-Shafranov Equation

International Nuclear Information System (INIS)

Smith, D.R.; Reiman, A.H.

2004-01-01

We present analytic, high-beta (β ∼ O(1)), helical equilibrium solutions for a class of helical axis configurations having large helical aspect ratio, with the helix assumed to be tightly wound. The solutions develop a narrow boundary layer of strongly compressed flux, similar to that previously found in high beta tokamak equilibrium solutions. The boundary layer is associated with a strong localized current which prevents the equilibrium from having zero net current

Characteristic features of edge transport barrier formed in helical divertor configuration of the Large Helical Device

International Nuclear Information System (INIS)

Toi, K.; Ohdachi, S.; Watanabe, F.

2006-10-01

In a helical divertor configuration of the Large Helical Device (LHD), transport barrier was formed through low to high confinement (L-H) transition in the plasma edge region including ergodic field layer of which region is in the magnetic hill. The plasma stored energy or the averaged bulk plasma beta dia > (derived from diamagnetic measurement) starts to increase just after the transition. In the case that both dia > and line-averaged electron density e > at the transition are relatively high as dia >≥1.5% and e >≥2x10 19 m -3 , the increase is hampered by rapid growth of edge MHD modes and/or small ELM like activities just after the transition. On the other hand, the transition at lower e > (≤1.5x10 19 m -3 ) and dia > (<2%) leads to a continuous increase in the stored energy with a time scale longer than the global energy confinement time, without suffering from these MHD activities near the edge. The ETB typically formed in electron density profile extends into ergodic field layer defined in the vacuum field. The width of ETB is almost independent of the toroidal field strength from 0.5T to 1.5T and is much larger than the poloidal ion gyro-radius. When resonant helical field perturbations are applied to expand a magnetic island size at the rational surface of the rotational transform ι/2π=1 near the edge, the L-H transition is triggered at lower electron density compared with the case without the field perturbations. The application of large helical field perturbations also suppresses edge MHD modes and ELM like activities. (author)

Gynecological applications of helical CT using SmartPrep

Energy Technology Data Exchange (ETDEWEB)

Sakurada, Akira; Kakizaki, Dai; Abe, Kimihiko [Tokyo Medical Coll. (Japan)

1999-11-01

SmartPrep is software program for scanning a given region of interest (ROI) at optimal contrast density. An operator can arbitrarily define ROI and preset the CT value at which scanning should be started. After the injection of a contrast medium, system conducts continuous monitoring of the ROI and the operator starts helical scanning of the planned region when the present CT value has been reached. In comparison with conventional helical CT that requires a period of time from the beginning of contrast medium injection to the beginning of scanning, SmartPrep minimizes personal error and better depicts the artery-predominant phase under optimal conditions. In this study we examine the usefulness of contrast-enhanced helical CT using SmartPrep in the evaluation of gynecological disease. When the contrast medium was injected into the dorsal vein of the hand at a rate of 3 ml/sec, strong staining of pelvic arteries was observed in the CT images started at 17 to 23 sec after injection. The early-phase helical CT obtained under these conditions provided good depiction of lesions in cases of placenta accreta and invasive mole, as well as clear demonstration of tumor angiogenesis and evaluation of laterality in cases of cervical cancer. Comparison of the early and delayed phase also facilitated easier evaluation of lymph nodes than conventional comparison of simple and contrast-enhanced CT. The results thus suggest the usefulness of contrast-enhanced helical CT using SmartPrep in gynecology. (author)

Helical CT in evaluation of the bronchial tree

International Nuclear Information System (INIS)

Perhomaa, M.; Laehde, S.; Rossi, O.; Suramo, I.

1997-01-01

Purpose: To establish a protocol for and to assess the value of helical CT in the imaging of the bronchial tree. Material and Methods: Noncontrast helical CT was performed in 30 patients undergoing fiberoptic bronchoscopy for different reasons. Different protocols were compared; they included overlapping 10 mm, 5 mm, or 3 mm slices and non-tilted, cephalad or caudal tilted images. Ordinary cross-sectional and multiplanar 2D reformats were applied for visualization of the bronchial branches. The effect of increasing the helical pitch was tested in one patient. Results: A total of 92.1-100% of the segmental bronchi present in the helical acquisitions were identified by the different protocols. The collimation had no significant impact on the identification of the bronchial branches, but utilization of 3-mm overlapping slices made it easier to distinguish the nearby branches and provided better longitudinal visualization of the bronchi in 2D reformats. The tilted scans illustrated the disadvantage of not covering all segmental bronchi in one breath-hold. An increase of the pitch from 1 to 1.5 did not cause noticeable blurring of the images. CT and bronchoscopic findings correlated well in the area accessible to bronchoscopy, but CT detected 5 additional pathological lesions (including 2 cancers) in the peripheral lung. Conclusion: Helical CT supplemented with bronchography-like 2D reformats provides an effective method complementary to bronchoscopy in the examination of the bronchial tree. (orig.)

Combined process "helical rolling-pressing" and its effect on the microstructure of ferrous and non-ferrous materials

Science.gov (United States)

Naizabekov, Abdrakhman; Lezhnev, Sergey; Arbuz, Alexandr; Panin, Evgeniy

2018-02-01

Ultrafine-grained materials are one of the most promising structural and functional materials. However, the known methods of obtaining them are not enough powerful and technologically advanced for profitable industrial applications. Development of the combined process "helical rolling-pressing" is an attempt to bring technology to produce ultrafine-grained materials to the industry. The combination of intense processing of the surface by helical rolling and the entire cross section of workpiece in equal channel angular matrix, with intense deformation by torsion between rolls and matrix will increase the degree of deformation per pass and allows to mutually compensate disadvantages of these methods in the case of their separate use. This paper describes the development of a laboratory stand and study of influence of combined process "helical rolling-pressing"on the microstructure of tool steel, technical copper and high alloy stainless high-temperature steel.

Dynamics of helicity transport and Taylor relaxation

International Nuclear Information System (INIS)

Diamond, P.H.; Malkov, M.

2003-01-01

A simple model of the dynamics of Taylor relaxation is derived using symmetry principles alone. No statistical closure approximations are invoked or detailed plasma model properties assumed. Notably, the model predicts several classes of nondiffusive helicity transport phenomena, including traveling nonlinear waves and superdiffusive turbulent pulses. A universal expression for the scaling of the effective magnetic Reynolds number of a system undergoing Taylor relaxation is derived. Some basic properties of intermittency in helicity transport are examined

Equilibrium calculations for helical axis stellarators

International Nuclear Information System (INIS)

Hender, T.C.; Carreras, B.A.

1984-04-01

An average method based on a vacuum flux coordinate system is presented. This average method permits the study of helical axis stellarators with toroidally dominated shifts. An ordering is introduced, and to lowest order the toroidally averaged equilibrium equations are reduced to a Grad-Shafranov equation. Also, to lowest order, a Poisson-type equation is obtained for the toroidally varying corrections to the equilibium. By including these corrections, systems that are toroidally dominated, but with significant helical distortion to the equilibrium, may be studied. Numerical solutions of the average method equations are shown to agree well with three-dimensional calculations

Ratio of ellipticities between 192 and 208 nm (R1 ): An effective electronic circular dichroism parameter for characterization of the helical components of proteins and peptides.

Science.gov (United States)

Banerjee, Raja; Sheet, Tridip

2017-11-01

Circular dichroism (CD) spectroscopy represents an important tool for characterization of the peptide and protein secondary structures that mainly arise from the conformational disposition of the peptide backbone in solution. In 1991 Manning and Woody proposed that, in addition to the signal intensity, the ratio between [θ]nπ* and [θ]ππ*ǁ ((R 2 ) ≅ [θ] 222 /[θ] 208 ), along with [θ]ππ*⊥ and [θ]ππ*ǁ ((R 1 ) ≅ [θ] 192 /[θ] 208 ), may be utilized towards identifying the peptide/protein conformation (especially 3 10 - and α-helices). However, till date the use of the ratiometric ellipticity component for helical structure analysis of peptides and proteins has not been reported. We studied a series of temperature dependent CD spectra of a thermally stable, model helical peptide and its related analogs in water as a function of added 2,2,2-trifluoroethanol (TFE) in order to explore their landscape of helicity. For the first time, we have experimentally shown here that the R 1 parameter can characterize better the individual helices, while the other parameter R 2 and the signal intensity do not always converge. We emphasize the use of the R 1 ratio of ellipticities for helical characterization because of the common origin of these two bands (exciton splitting of the amide π→ π* transition in a helical polypeptide). This approach may become worthwhile and timely with the increasing accessibility of CD synchrotron sources. © 2017 Wiley Periodicals, Inc.

On Measurement of Helicity Parameters in Top Quark Decay

OpenAIRE

Nelson, Charles A.; Adler, Jr, L. J.

2000-01-01

To enable an evaluation of future measurements of the helicity parameters for " t --> W b " decay in regard to " T_FS violation", this paper considers the effects of an additional pure-imaginary coupling, (i g/2 Lambda) or (i g), associated with a specific, single additional Lorentz structure, i = S, P, S + P, ... Sizable " T_FS violation" signatures can occur for low-effective mass scales (< 320 GeV), but in most cases can be more simply excluded by 10% precision measurement of the probabili...

A helical naphthopyran dopant for photoresponsive cholesteric liquid crystals

OpenAIRE

Kim, Yuna; Frigoli, Michel; Vanthuyne, Nicolas; Tamaoki, Nobuyuki

2017-01-01

The first photoresponsive cholesteric liquid crystal comprising a photoisomerizable helical naphthopyran derivative dopant and a nematic liquid crystal is reported. An unprecedented helical twisting power switching ratio of over 90% allowed us to demonstrate multi-cycle rotational motion of micro-objects by UV light irradiation.

Feasibility study of helical tomotherapy for total body or total marrow irradiation

International Nuclear Information System (INIS)

Hui, Susanta K.; Kapatoes, Jeff; Fowler, Jack; Henderson, Douglas; Olivera, Gustavo; Manon, Rafael R.; Gerbi, Bruce; Mackie, T. R.; Welsh, James S.

2005-01-01

Total body radiation (TBI) has been used for many years as a preconditioning agent before bone marrow transplantation. Many side effects still plague its use. We investigated the planning and delivery of total body irradiation (TBI) and selective total marrow irradiation (TMI) and a reduced radiation dose to sensitive structures using image-guided helical tomotherapy. To assess the feasibility of using helical tomotherapy (A) we studied variations in pitch, field width, and modulation factor on total body and total marrow helical tomotherapy treatments. We varied these parameters to provide a uniform dose along with a treatment times similar to conventional TBI (15-30 min). (B) We also investigated limited (head, chest, and pelvis) megavoltage CT (MVCT) scanning for the dimensional pretreatment setup verification rather than total body MVCT scanning to shorten the overall treatment time per treatment fraction. (C) We placed thermoluminescent detectors (TLDs) inside a Rando phantom to measure the dose at seven anatomical sites, including the lungs. A simulated TBI treatment showed homogeneous dose coverage (±10%) to the whole body. Doses to the sensitive organs were reduced by 35%-70% of the target dose. TLD measurements on Rando showed an accurate dose delivery (±7%) to the target and critical organs. In the TMI study, the dose was delivered conformally to the bone marrow only. The TBI and TMI treatment delivery time was reduced (by 50%) by increasing the field width from 2.5 to 5.0 cm in the inferior-superior direction. A limited MVCT reduced the target localization time 60% compared to whole body MVCT. MVCT image-guided helical tomotherapy offers a novel method to deliver a precise, homogeneous radiation dose to the whole body target while reducing the dose significantly to all critical organs. A judicious selection of pitch, modulation factor, and field size is required to produce a homogeneous dose distribution along with an acceptable treatment time. In

Flow-induced vibration analysis of a helical coil steam generator experiment using large eddy simulation

Energy Technology Data Exchange (ETDEWEB)

Yuan, Haomin; Solberg, Jerome; Merzari, Elia; Kraus, Adam; Grindeanu, Iulian

2017-10-01

This paper describes a numerical study of flow-induced vibration in a helical coil steam generator experiment conducted at Argonne National Laboratory in the 1980s. In the experiment, a half-scale sector model of a steam generator helical coil tube bank was subjected to still and flowing air and water, and the vibrational characteristics were recorded. The research detailed in this document utilizes the multi-physics simulation toolkit SHARP developed at Argonne National Laboratory, in cooperation with Lawrence Livermore National Laboratory, to simulate the experiment. SHARP uses the spectral element code Nek5000 for fluid dynamics analysis and the finite element code DIABLO for structural analysis. The flow around the coil tubes is modeled in Nek5000 by using a large eddy simulation turbulence model. Transient pressure data on the tube surfaces is sampled and transferred to DIABLO for the structural simulation. The structural response is simulated in DIABLO via an implicit time-marching algorithm and a combination of continuum elements and structural shells. Tube vibration data (acceleration and frequency) are sampled and compared with the experimental data. Currently, only one-way coupling is used, which means that pressure loads from the fluid simulation are transferred to the structural simulation but the resulting structural displacements are not fed back to the fluid simulation

Helical CT of ureteral disease

International Nuclear Information System (INIS)

Cikman, Pablo; Bengio, Ruben; Bulacio, Javier; Zirulnik, Esteban; Garimaldi, Jorge

2000-01-01

Among the new applications of helical CT is the study of the ureteral pathology. The objective of this paper was to evaluate patients with suspected pathology of this organ and the repercussion in the therapeutic plans. We studied 23 patients with a helical CT protocol, without IV contrast injection and performed multiplanar reconstruction (MPR). We called this procedure Pielo CT. Thirteen ureteral stones were detected, 6 calculi, 2 urinary tract tumors, dilatation of the system in a patient with neo-bladder. In 2 patients, in whom ureteral pathology was ruled out, we found other alterations that explained the symptoms, (gallbladder stones, disk protrusion). The Pielo CT let decide a therapeutical approach in 20 or 21 patients with ureteral pathology. (author)

A self-biased 3D tunable helical antenna in ferrite LTCC substrate

KAUST Repository

Ghaffar, Farhan A.; Shamim, Atif

2015-01-01

A ferrite LTCC based helical antenna which also provides magneto-static bias for its frequency tuning is presented in this work. The 3D helical-cum-bias winding design avoids the use of large external electromagnets which are traditionally used with ferrite based tunable antennas. This reduces the overall size of the design while making it efficient by getting rid of demagnetization effect experienced at the air-to-ferrite interface. RF choke and DC blocking capacitor, required to isolate the RF and DC passing through a single structure, are integrated within the multi-layer Ferrite LTCC substrate. Magnetostatic and microwave simulations have been carried out for the design optimization. The prototype antenna demonstrates a tuning range of 10 % around 13 GHz. An optimized design with an air cavity is also presented which reduces the biasing power requirement by 40 %.

A self-biased 3D tunable helical antenna in ferrite LTCC substrate

KAUST Repository

Ghaffar, Farhan A.

2015-07-19

A ferrite LTCC based helical antenna which also provides magneto-static bias for its frequency tuning is presented in this work. The 3D helical-cum-bias winding design avoids the use of large external electromagnets which are traditionally used with ferrite based tunable antennas. This reduces the overall size of the design while making it efficient by getting rid of demagnetization effect experienced at the air-to-ferrite interface. RF choke and DC blocking capacitor, required to isolate the RF and DC passing through a single structure, are integrated within the multi-layer Ferrite LTCC substrate. Magnetostatic and microwave simulations have been carried out for the design optimization. The prototype antenna demonstrates a tuning range of 10 % around 13 GHz. An optimized design with an air cavity is also presented which reduces the biasing power requirement by 40 %.

Relational dynamics in the multi-helices knowledge production system

DEFF Research Database (Denmark)

Thai, Thi Minh; Hjortsø, Carsten Nico Portefée

-level dynamics are characterized by political ambidexterity that enables the state to maintain control by privileging traditional science and education constituencies, and at the same time support the transition of the knowledge production system towards international methodology and quality standards through......Drawing on the triple helix framework and organizational institutionalism, this article applies a qualitative research approach to analyze structures, institutional logics, power relations that shape inter-organizational relations and the structuration of a knowledge production system...... in an emerging economy. Findings highlight the emergence of a fifth-helices knowledge production system includes the state, science and education, industry, international actors, and society. The system comprises two major segments, one associated with the traditional command economy and characterized...

Tokamak startup using point-source dc helicity injection.

Science.gov (United States)

Battaglia, D J; Bongard, M W; Fonck, R J; Redd, A J; Sontag, A C

2009-06-05

Startup of a 0.1 MA tokamak plasma is demonstrated on the ultralow aspect ratio Pegasus Toroidal Experiment using three localized, high-current density sources mounted near the outboard midplane. The injected open field current relaxes via helicity-conserving magnetic turbulence into a tokamaklike magnetic topology where the maximum sustained plasma current is determined by helicity balance and the requirements for magnetic relaxation.

Results of auricular helical rim reconstruction with post-auricular tube flap.

Science.gov (United States)

Iljin, Aleksandra; Lewandowicz, Edward; Antoszewski, Bogusław; Zieliński, Tomasz

2016-01-01

The aim of the study was to present our experience with post-auricular tube flap (ptf) and clinical evaluation of the results following auricular helical rim reconstruction with this technique in patients after trauma. We analyzed the results in 12 patients who underwent three-staged auricular helical rim reconstruction with ptf following trauma in the Department of Plastic, Reconstructive and Aesthetic Surgery between 2005-2014. The patients were followed-up for at least 1 year. We evaluated early and long-term results after surgery including plastic surgeon's and patient's opinion. Postoperative results were satisfactory (very good) in 10 cases, both in the opinion of the plastic surgeon and patients. Transient venous congestion of the helix occurred in two cases (16.6%). This complication did not have any influence on estimation of the results after surgery. Delayed wound healing in the poles of the reconstructed helical edge, as well as non-aesthetic helical scars with imperfections of helical rim, were seen in another two patients (16.6%). 1. Post-auricular tube flap reconstructions after helical rim trauma allowed for complete restoration of contour, size and orientation of the helix and the whole operated ear, which confirms the efficiency of the applied technique. 2. Reconstructive surgery with post-auricular tube flap in patients with auricular helical rim defects contributed to postoperative satisfaction in both patients and doctors' estimations.

Helicity amplitudes and electromagnetic decays of hyperon resonances

International Nuclear Information System (INIS)

Cauteren, T. van; Ryckebusch, J.; Metsch, B.; Petry, H.R.

2005-01-01

We present results for the helicity amplitudes of the lowest-lying hyperon resonances Y * , computed within the framework of the Bonn Constituent-Quark model, which is based on the Bethe-Salpeter approach. The seven parameters entering the model were fitted to the best-known baryon masses. Accordingly, the results for the helicity amplitudes are genuine predictions. Some hyperon resonances are seen to couple more strongly to a virtual photon with finite Q 2 than to a real photon. Other Y * 's, such as the S 01 (1670) Λ-resonance or the S 11 (1620) Σ-resonance, couple very strongly to real photons. We present a qualitative argument for predicting the behaviour of the helicity asymmetries of baryon resonances at high Q 2 . (orig.)

Double Helical Gear Performance Results in High Speed Gear Trains

Science.gov (United States)

Handschuh, Robert F.; Ehinger, Ryan; Sinusas, Eric; Kilmain, Charles

2010-01-01

The operation of high speed gearing systems in the transmissions of tiltrotor aircraft has an effect on overall propulsion system efficiency. Recent work has focused on many aspects of high-speed helical gear trains as would be used in tiltrotor aircraft such as operational characteristics, comparison of analytical predictions to experimental data and the affect of superfinishing on transmission performance. Baseline tests of an aerospace quality system have been conducted in the NASA Glenn High-Speed Helical Gear Train Test Facility and have been described in earlier studies. These earlier tests had utilized single helical gears. The results that will be described in this study are those attained using double helical gears. This type of gear mesh can be configured in this facility to either pump the air-oil environment from the center gap between the meshing gears to the outside of tooth ends or in the reverse direction. Tests were conducted with both inward and outward air-oil pumping directions. Results are compared to the earlier baseline results of single helical gears.

Experimental investigation of solar powered diaphragm and helical pumps

Science.gov (United States)

For several years, many types of solar powered water pumping systems were evaluated, and in this paper, diaphragm and helical solar photovoltaic (PV) powered water pumping systems are discussed. Data were collected on diaphragm and helical pumps which were powered by different solar PV arrays at mul...

Three-dimensional helical CT for treatment planning of breast cancer

Energy Technology Data Exchange (ETDEWEB)

Hiramatsu, Hideko; Enomoto, Kohji; Ikeda, Tadashi [Keio Univ., Tokyo (Japan). School of Medicine] [and others

1999-01-01

The role of three-dimensional (3D) helical CT in the treatment planning of breast cancer was evaluated. Of 36 patients examined, 30 had invasive ductal carcinoma, three had invasive lobular carcinoma, one had DCIS, one had DCIS with minimal invasion, and 1 had Paget`s disease. Patients were examined in the supine position. The whole breast was scanned under about 25 seconds of breath-holding using helical CT (Proceed, Yokogawa Medical Systems, or High-speed Advantage, GE Medical Systems). 3D imaging was obtained with computer assistance (Advantage Windows, GE Medical Systems). Linear and/or spotty enhancement on helical CT was considered to suggest DCIS or intraductal spread in the area surrounding the invasive cancer. Of 36 patients, 24 showed linear and/or spotty enhancement on helical CT, and 22 of those 24 patients had DCIS or intraductal spread. In contrast, 12 of 36 patients were considered to have little or no intraductal spread on helical CT, and eight of the 12 patients had little or no intraductal spread on pathological examination. The sensitivity, specificity, and accuracy rates for detecting intraductal spread on MRI were 85%, 80%, and 83%, respectively. 3D helical CT was considered useful in detecting intraductal spread and planning surgery, however, a larger study using a precise correlation with pathology is necessary. (author)

Study of electric field pulsation in helical plasmas

International Nuclear Information System (INIS)

Toda, S; Itoh, K

2011-01-01

A model for the experimental results of the periodic oscillation of the electric field, so-called the electric field pulsation, observed in the Compact Helical Device (Fujisawa et al 1998 Phys. Rev. Lett. 81 2256) and the Large Helical Device (Shimizu et al 2010 Plasma Fusion Res. 5 S1015) is presented. A self-generated oscillation of the radial electric field is shown as the simulation result in helical plasmas. The reduction of the anomalous transport diffusivity in the core region is observed due to the strong shear of the radial electric field when the positive electric field is shown in the core region in the periodic oscillation of E r . Two different time scales are found in the self-generated oscillation, which are the transport time scale and the fast time scale at the transition of the radial electric field. This oscillation because of the hysteresis characteristic is attributed to the electric field pulsation observed in helical plasmas. The parameter region of the condition for the self-generated oscillation is derived. It is shown that the multiple solutions of the radial electric field for the ambipolar condition are necessary but not sufficient for obtaining the self-generated oscillation.

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven ...

Indian Academy of Sciences (India)

tribpo

Key words. Sun—dynamo, helicity, turbulent convection. Extended abstract. Recent numerical simulations lead to the result that turbulence is much more mag- netically driven than believed. ... positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicity which is negative ...

Study of Pelvicaliceal Anatomy by Helical Computerized Tomography

International Nuclear Information System (INIS)

Al-Qahtani, Fahd N.; Ali, Gaber A.; Kamal, Baher A.; Taha, Saud A.

2003-01-01

To evaluate the role of 3-dimensional images produced by computerized tomography (CT), using intravenous contrast, to study pelvicaliceal anatomy.This might be of help in endourological procedure. The study was conducted in the King Fahd Hospital of the University, King Faisal University. Dammam,Kingdom of Saudi Arabia. The study took place from July 2002 through to October 2002 .Helical CT was carried for patients who were investigated using excretory urography for any reason. A CT was carried out to the kidneys only within 10 minutes ( between 5 and 15 minute films of excretory urography).Images were reprocessed by 3-dimension construction after subtracting all structures except for the palvicaliceal system. Thity-six normal kidneys were studied. The upper pole was drained by a single caliceal infundibulum in all 36(100%) kidneys.the middle segement of the kidney was drained by 2 infundibula in 32 (89%) kidneys. Four (11%) kidneys have no middle caliceal infudibula. The lower pole was drained by 2 caliceal infundibula in 23 (64%) and a single infundibulum in 13 (36%) kidneys. The minor calices draining each renal segment were seen clearly. Three-dimensional images derived by helical CT are feasible for evaluating the anatomy of palvicaliceal system,and, can be of help in endourological procedures. (author)/

Synthesis of Helquats Based on Phenanthridinium Units: Four-Step Procedure to Novel Extended Helical Dications

Czech Academy of Sciences Publication Activity Database

Sonawane, Manoj R.; Vávra, Jan; Šaman, David; Císařová, I.; Teplý, Filip

2015-01-01

Roč. 47, č. 22 (2015), s. 3479-3488 ISSN 0039-7881 Grant - others:GA AV ČR(CZ) M200551208 Institutional support: RVO:61388963 Keywords : helical structures * rhodium * catalysis * cycloadditions * heterocycles * Sonogashira coupling Subject RIV: CC - Organic Chemistry Impact factor: 2.652, year: 2015

Peptide design using alpha,beta-dehydro amino acids: from beta-turns to helical hairpins.

Science.gov (United States)

Mathur, Puniti; Ramakumar, S; Chauhan, V S

2004-01-01

Incorporation of alpha,beta-dehydrophenylalanine (DeltaPhe) residue in peptides induces folded conformations: beta-turns in short peptides and 3(10)-helices in larger ones. A few exceptions-namely, alpha-helix or flat beta-bend ribbon structures-have also been reported in a few cases. The most favorable conformation of DeltaPhe residues are (phi,psi) approximately (-60 degrees, -30 degrees ), (-60 degrees, 150 degrees ), (80 degrees, 0 degrees ) or their enantiomers. DeltaPhe is an achiral and planar residue. These features have been exploited in designing DeltaPhe zippers and helix-turn-helix motifs. DeltaPhe can be incorporated in both right and left-handed helices. In fact, consecutive occurrence of three or more DeltaPhe amino acids induce left-handed screw sense in peptides containing L-amino acids. Weak interactions involving the DeltaPhe residue play an important role in molecular association. The C--H.O==C hydrogen bond between the DeltaPhe side-chain and backbone carboxyl moiety, pi-pi stacking interactions between DeltaPhe side chains belonging to enantiomeric helices have shown to stabilize folding. The unusual capability of a DeltaPhe ring to form the hub of multicentered interactions namely, a donor in aromatic C--H.pi and C--H.O==C and an acceptor in a CH(3).pi interaction suggests its exploitation in introducing long-range interactions in the folding of supersecondary structures. Copyright 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2004

Field of a helical Siberian Snake

Energy Technology Data Exchange (ETDEWEB)

Luccio, A. [Brookhaven National Lab., Upton, NY (United States)

1995-02-01

To preserve the spin polarization of a beam of high energy protons in a circular accelerator, magnets with periodic magnetic field, called Siberian Snakes are being used. Recently, it was proposed to build Siberian Snakes with superconducting helical dipoles. In a helical, or twisted dipole, the magnetic field is perpendicular to the axis of the helix and rotates around it as one proceeds along the magnet. In an engineering study of a 4 Tesla helical snake, the coil geometry is derived, by twisting, from the geometry of a cosine superconducting dipole. While waiting for magnetic measurement data on such a prototype, an analytical expression for the field of the helice is important, to calculate the particle trajectories and the spin precession in the helix. This model will also allow to determine the optical characteristics of the snake, as an insertion in the lattice of the accelerator. In particular, one can calculate the integrated multipoles through the magnet and the equivalent transfer matrix. An expression for the field in the helix body, i.e., excluding the fringe field was given in a classical paper. An alternate expression can be found by elaborating on the treatment of the field of a transverse wiggler obtained under the rather general conditions that the variables are separable. This expression exactly satisfies Maxwell`s div and curl equations for a stationary field, {del} {center_dot} B = 0, {del} x B = 0. This approach is useful in that it will allow one to use much of the work already done on the problem of inserting wigglers and undulators in the lattice of a circular accelerator.

EVOLUTION OF SPINNING AND BRAIDING HELICITY FLUXES IN SOLAR ACTIVE REGION NOAA 10930

Energy Technology Data Exchange (ETDEWEB)

Ravindra, B. [Indian Institute of Astrophysics, Koramangala, Bangalore 560 034 (India); Yoshimura, Keiji [Department of Physics, Montana State University Bozeman, MT 59717 (United States); Dasso, Sergio, E-mail: ravindra@iiap.res.in, E-mail: yosimura@solar.physics.montana.edu, E-mail: dasso@df.uba.ar [Instituto de Astronomia y Fisica del Espacio (CONICET-UBA), 1428 Buenos Aires (Argentina)

2011-12-10

The line-of-sight magnetograms from Solar Optical Telescope Narrowband Filter Imager observations of NOAA Active Region 10930 have been used to study the evolution of spinning and braiding helicities over a period of five days starting from 2006 December 9. The north (N) polarity sunspot was the follower and the south (S) polarity sunspot was the leader. The N-polarity sunspot in the active region was rotating in the counterclockwise direction. The rate of rotation was small during the first two days of observations and it increased up to 8 Degree-Sign hr{sup -1} on the third day of the observations. On the fourth and fifth days it remained at 4 Degree-Sign hr{sup -1} with small undulations in its magnitude. The sunspot rotated about 260 Degree-Sign in the last three days. The S-polarity sunspot did not complete more than 20 Degree-Sign in five days. However, it changed its direction of rotation five times over a period of five days and injected both the positive and negative type of spin helicity fluxes into the corona. Through the five days, both the positive and negative sunspot regions injected equal amounts of spin helicity. The total injected helicity is predominantly negative in sign. However, the sign of the spin and braiding helicity fluxes computed over all the regions were reversed from negative to positive five times during the five-day period of observations. The reversal in spinning helicity flux was found before the onset of the X3.4-class flare, too. Though, the rotating sunspot has been observed in this active region, the braiding helicity has contributed more to the total accumulated helicity than the spinning helicity. The accumulated helicity is in excess of -7 Multiplication-Sign 10{sup 43} Mx{sup 2} over a period of five days. Before the X3.4-class flare that occurred on 2006 December 13, the rotation speed and spin helicity flux increased in the S-polarity sunspot. Before the flare, the total injected helicity was larger than -6

Mechanics of patterned helical Si springs on Si substrate.

Science.gov (United States)

Liu, D L; Ye, D X; Khan, F; Tang, F; Lim, B K; Picu, R C; Wang, G C; Lu, T M

2003-12-01

The elastic response, including the spring constant, of individual Si helical-shape submicron springs, was measured using a tip-cantilever assembly attached to a conventional atomic force microscope. The isolated, four-turn Si springs were fabricated using oblique angle deposition with substrate rotation, also known as the glancing angle deposition, on a templated Si substrate. The response of the structures was modeled using finite elements, and it was shown that the conventional formulae for the spring constant required modifications before they could be used for the loading scheme used in the present experiment.

Imaging of Composites by Helical X-Ray Computed Tomography

DEFF Research Database (Denmark)

Wang, Ying; Pyka, Grzegorz; Jespersen, Kristine Munk

Understanding the fatigue damage mechanisms of composite materials used in wind turbine rotor blades could potentially enhance the reliability and energy efficiency of wind turbines by improving the structure design. In this paper, the fatigue damage propagating mechanisms of unidirectional glass...... fibre composites was characterised by helical X-ray CT. The staining approach was used and it was effective to enhance the visibility of thin matrix cracks and partly closed fibre breaks instead of widely opened cracks. Fibre breaks in the centre UD bundle were found to occur locally, instead of being...

Nonideal, helical, vortical magnetohydrodynamic steady states

International Nuclear Information System (INIS)

Agim, Y.Z.; Montgomery, D.

1991-01-01

The helically-deformed profiles of driven, dissipative magnetohydrodynamic equilibria are constructed through second order in helical amplitude. The resultant plasma configurations are presented in terms of contour plots of magnetic flux function, pressure, current flux function and the mass flux function, along with the stability boundary at which they are expected to appear. For the Wisconsin Phaedrus-T Tokamak, plasma profiles with significant m = 3, n = 1 perturbation seem feasible; for these, the plasma pressure peaks off-axis. For the smaller aspect ratio case, the configuration with m 1,n =1 is thought to be relevant to the density perturbation observed in JET after a pellet injection. (author)

Equilibrium studies of helical axis stellarators

International Nuclear Information System (INIS)

Hender, T.C.; Carreras, B.A.; Garcia, L.; Harris, J.H.; Rome, J.A.; Cantrell, J.L.; Lynch, V.E.

1984-01-01

The equilibrium properties of helical axis stellarators are studied with a 3-D equilibrium code and with an average method (2-D). The helical axis ATF is shown to have a toroidally dominated equilibrium shift and good equilibria up to at least 10% peak beta. Low aspect ratio heliacs, with relatively large toroidal shifts, are shown to have low equilibrium beta limits (approx. 5%). Increasing the aspect ratio and number of field periods proportionally is found to improve the equilibrium beta limit. Alternatively, increasing the number of field periods at fixed aspect ratio which raises and lowers the toroidal shift improves the equilibrium beta limit

Long range correlations and folding angle with applications to α-helical proteins

Science.gov (United States)

Krokhotin, Andrey; Nicolis, Stam; Niemi, Antti J.

2014-03-01

The conformational complexity of chain-like macromolecules such as proteins and other linear polymers is much larger than that of point-like atoms and molecules. Unlike particles, chains can bend, twist, and even become knotted. Thus chains might also display a much richer phase structure. Unfortunately, it is not very easy to characterize the phase of a long chain. Essentially, the only known attribute is the radius of gyration. The way how it changes when the degree of polymerization becomes different, and how it evolves when the ambient temperature and solvent properties change, is commonly used to disclose the phase. But in any finite length chain there are corrections to scaling that complicate the detailed analysis of the phase structure. Here we introduce a quantity that we call the folding angle to identify and scrutinize the phase structure, as a complement to the radius of gyration. We argue for a mean-field level relationship between the folding angle and the scaling exponent in the radius of gyration. We then estimate the value of the folding angle in the case of crystallographic α-helical protein structures in the Protein Data Bank. We also show how the experimental value of the folding angle can be obtained computationally, using a semiclassical Born-Oppenheimer description of α-helical chiral chains.

A three-dimensional-weighted cone beam filtered backprojection (CB-FBP) algorithm for image reconstruction in volumetric CT-helical scanning

International Nuclear Information System (INIS)

Tang Xiangyang; Hsieh Jiang; Nilsen, Roy A; Dutta, Sandeep; Samsonov, Dmitry; Hagiwara, Akira

2006-01-01

Based on the structure of the original helical FDK algorithm, a three-dimensional (3D)-weighted cone beam filtered backprojection (CB-FBP) algorithm is proposed for image reconstruction in volumetric CT under helical source trajectory. In addition to its dependence on view and fan angles, the 3D weighting utilizes the cone angle dependency of a ray to improve reconstruction accuracy. The 3D weighting is ray-dependent and the underlying mechanism is to give a favourable weight to the ray with the smaller cone angle out of a pair of conjugate rays but an unfavourable weight to the ray with the larger cone angle out of the conjugate ray pair. The proposed 3D-weighted helical CB-FBP reconstruction algorithm is implemented in the cone-parallel geometry that can improve noise uniformity and image generation speed significantly. Under the cone-parallel geometry, the filtering is naturally carried out along the tangential direction of the helical source trajectory. By exploring the 3D weighting's dependence on cone angle, the proposed helical 3D-weighted CB-FBP reconstruction algorithm can provide significantly improved reconstruction accuracy at moderate cone angle and high helical pitches. The 3D-weighted CB-FBP algorithm is experimentally evaluated by computer-simulated phantoms and phantoms scanned by a diagnostic volumetric CT system with a detector dimension of 64 x 0.625 mm over various helical pitches. The computer simulation study shows that the 3D weighting enables the proposed algorithm to reach reconstruction accuracy comparable to that of exact CB reconstruction algorithms, such as the Katsevich algorithm, under a moderate cone angle (4 deg.) and various helical pitches. Meanwhile, the experimental evaluation using the phantoms scanned by a volumetric CT system shows that the spatial resolution along the z-direction and noise characteristics of the proposed 3D-weighted helical CB-FBP reconstruction algorithm are maintained very well in comparison to the FDK

Kinetic theory of rf current drive and helicity injection

International Nuclear Information System (INIS)

Mett, R.R.

1992-01-01

Current drive and helicity injection by plasma waves are examined with the use of kinetic theory. The Vlasov equation yields a general current drive formula that contains resonant and nonresonant (ponderomotivelike) contributions. Standard quasilinear current drive is described by the former, while helicity current drive may be contained in the latter. Since direct analytical comparison of the sizes of the two terms is, in general, difficult, a new approach is taken. Solution of the drift-kinetic equation shows that the standard Landau damping/transit time magnetic pumping quasilinear diffusion coefficient is the only contribution to steady-state current drive to leading order in ε=ρ L /l, where ρ L is the Larmor radius and l is the inhomogeneity scale length. All nonresonant contributions, including the helicity, appear at higher order, after averages are taken over a flux surface, over azimuth, and over time. Consequently, at wave frequencies well below the electron cyclotron frequency, a wave helicity flux perpendicular to the magnetic field does not influence the parallel motion of electrons to leading order and therefore will not drive a significant current. Any current associated with a wave helicity flux is then either ion current (and thus inefficient) or electron current stemming from effects not included in the drift-kinetic treatment, such as cyclotron, collisional, or nonlinear (i.e., not quasilinear)

Helical-tokamak hybridization concepts for compact configuration exploration and MHD stabilization

International Nuclear Information System (INIS)

Oishi, T.; Yamazaki, K.; Arimoto, H.; Baba, K.; Hasegawa, M.; Ozeki, H.; Shoji, T.; Mikhailov, M.I.

2010-11-01

To search for low-aspect-ratio torus systems, a lot of exotic confinement concepts are proposed so far historically. One of the authors previously proposed the tokamak-helical hybrid called TOKASTAR (Tokamak-Stellarator Hybrid) to improve the magnetic local shear near the bad curvature region. This is characterized by simple and compact coil systems with enough divertor space relevant to reactor designs. Based on this TOKASTAR concept, a toroidal mode number N=2 C (compact) -TOKASTAR machine (R - 35 mm) was constructed. The rotational transform of this compact helical configuration is rather small to confine hot ions, but can be utilized as a compact electron plasma machine for multi-purposes. The C-TOKASTAR has a pair of spherically winding helical coils and a pair of poloidal coils. Existence of magnetic surface and electron confinement property in C-TOKASTAR device were investigated by an electron-emission impedance method. Calculation of the particle orbit also supports that closed magnetic surface is formed in the cases that the ratio between poloidal and helical coil current is appropriate. Another aspect of the research using TOKASTAR configuration includes the evaluation of the effect of the outboard helical field application to tokamak plasmas. It is considered that outboard helical field has roles to assist the initiation of plasma current, to improve MHD stability, and so on. To check these roles, we made TOKASTAR-2 machine (R - 0.12 m, B - 1 kG) with ohmic heating central coil, eight toroidal field coils, a pair of vertical field coils and two outboard helical field coil segments. The electron cyclotron heating plasma start-up and plasma current disruption control experiments might be expected in this machine. Calculation of magnetic field line tracing has revealed that magnetic surface can be formed using additional outer helical coils. (author)

Computational study of the fibril organization of polyglutamine repeats reveals a common motif identified in beta-helices.

Science.gov (United States)

Zanuy, David; Gunasekaran, Kannan; Lesk, Arthur M; Nussinov, Ruth

2006-04-21

The formation of fibril aggregates by long polyglutamine sequences is assumed to play a major role in neurodegenerative diseases such as Huntington. Here, we model peptides rich in glutamine, through a series of molecular dynamics simulations. Starting from a rigid nanotube-like conformation, we have obtained a new conformational template that shares structural features of a tubular helix and of a beta-helix conformational organization. Our new model can be described as a super-helical arrangement of flat beta-sheet segments linked by planar turns or bends. Interestingly, our comprehensive analysis of the Protein Data Bank reveals that this is a common motif in beta-helices (termed beta-bend), although it has not been identified so far. The motif is based on the alternation of beta-sheet and helical conformation as the protein sequence is followed from the N to the C termini (beta-alpha(R)-beta-polyPro-beta). We further identify this motif in the ssNMR structure of the protofibril of the amyloidogenic peptide Abeta(1-40). The recurrence of the beta-bend suggests a general mode of connecting long parallel beta-sheet segments that would allow the growth of partially ordered fibril structures. The design allows the peptide backbone to change direction with a minimal loss of main chain hydrogen bonds. The identification of a coherent organization beyond that of the beta-sheet segments in different folds rich in parallel beta-sheets suggests a higher degree of ordered structure in protein fibrils, in agreement with their low solubility and dense molecular packing.

Elbow helical axes of motion are not the same in physiologic and kinetic joint simulators.

Science.gov (United States)

Muriuki, Muturi G; Mohagheh-Motlagh, Amin; Smolinski, Patrick J; Miller, Mark Carl

2012-08-31

Physiologic and kinetic joint simulators have been widely used for investigations of joint mechanics. The two types of simulator differ in the way joint motion is achieved; through prescribed motions and/or forces in kinetic joint simulators and by tendon loads in physiologic joint simulators. These two testing modalities have produced important insights, as in elucidating the importance of soft tissue structures to joint stability. However, the equivalence of the modalities has not been tested. This study sequentially tested five cadaveric elbows using both a physiologic simulator and a robot/6DOF system. Using position data from markers on the humerus and ulna, we calculated and compared the helical axes of motion of the specimens as the elbows were flexed from full extension. Six step size increments were used in the helical axis calculation. Marker position data at each test's full extension and full flexion point were also used to calculate a datum (overall) helical axis. The angles between the datum axis and step-wise movements were computed and stored. Increasing step size monotonically decreased the variability and the average conical angle encompassing the helical axes; a repeated measures ANOVA using test type (robot or physiologic simulator) and step size found that both type and step caused statistically significant differences (p<0.001). The large changes in helical axis angle observed for small changes in elbow flexion angle, especially in the robot tests, are a caveat for investigators using similar control algorithms. Controllers may need to include increased joint compliance and/or C(1) continuity to reduce variability. Copyright © 2012 Elsevier Ltd. All rights reserved.

Disulfide-stabilized Helical Hairpin Structure and Activity of a Novel Antifungal Peptide EcAMP1 from Seeds of Barnyard Grass (Echinochloa crus-galli)*

Science.gov (United States)

Nolde, Svetlana B.; Vassilevski, Alexander A.; Rogozhin, Eugene A.; Barinov, Nikolay A.; Balashova, Tamara A.; Samsonova, Olga V.; Baranov, Yuri V.; Feofanov, Alexey V.; Egorov, Tsezi A.; Arseniev, Alexander S.; Grishin, Eugene V.

2011-01-01

This study presents purification, activity characterization, and 1H NMR study of the novel antifungal peptide EcAMP1 from kernels of barnyard grass Echinochloa crus-galli. The peptide adopts a disulfide-stabilized α-helical hairpin structure in aqueous solution and thus represents a novel fold among naturally occurring antimicrobial peptides. Micromolar concentrations of EcAMP1 were shown to inhibit growth of several fungal phytopathogens. Confocal microscopy revealed intensive EcAMP1 binding to the surface of fungal conidia followed by internalization and accumulation in the cytoplasm without disturbance of membrane integrity. Close spatial structure similarity between EcAMP1, the trypsin inhibitor VhTI from seeds of Veronica hederifolia, and some scorpion and cone snail toxins suggests natural elaboration of different functions on a common fold. PMID:21561864

Disulfide-stabilized helical hairpin structure and activity of a novel antifungal peptide EcAMP1 from seeds of barnyard grass (Echinochloa crus-galli).

Science.gov (United States)

Nolde, Svetlana B; Vassilevski, Alexander A; Rogozhin, Eugene A; Barinov, Nikolay A; Balashova, Tamara A; Samsonova, Olga V; Baranov, Yuri V; Feofanov, Alexey V; Egorov, Tsezi A; Arseniev, Alexander S; Grishin, Eugene V

2011-07-15

This study presents purification, activity characterization, and (1)H NMR study of the novel antifungal peptide EcAMP1 from kernels of barnyard grass Echinochloa crus-galli. The peptide adopts a disulfide-stabilized α-helical hairpin structure in aqueous solution and thus represents a novel fold among naturally occurring antimicrobial peptides. Micromolar concentrations of EcAMP1 were shown to inhibit growth of several fungal phytopathogens. Confocal microscopy revealed intensive EcAMP1 binding to the surface of fungal conidia followed by internalization and accumulation in the cytoplasm without disturbance of membrane integrity. Close spatial structure similarity between EcAMP1, the trypsin inhibitor VhTI from seeds of Veronica hederifolia, and some scorpion and cone snail toxins suggests natural elaboration of different functions on a common fold.

Investigating the role of GXXXG motifs in helical folding and self-association of plasticins, Gly/Leu-rich antimicrobial peptides.

Science.gov (United States)

Carlier, Ludovic; Joanne, Pierre; Khemtémourian, Lucie; Lacombe, Claire; Nicolas, Pierre; El Amri, Chahrazade; Lequin, Olivier

2015-01-01

Plasticins (PTC) are dermaseptin-related antimicrobial peptides characterized by a large number of leucine and glycine residues arranged in GXXXG motifs that are often described to promote helix association within biological membranes. We report the structure and interaction properties of two plasticins, PTC-B1 from Phyllomedusa bicolor and a cationic analog of PTC-DA1 from Pachymedusa dacnicolor, which exhibit membrane-lytic activities on a broad range of microorganisms. Despite a high number of glycine, CD and NMR spectroscopy show that the two plasticins adopt mainly alpha-helical conformations in a wide variety of environments such as trifluoroethanol, detergent micelles and lipid vesicles. In DPC and SDS, plasticins adopt well-defined helices that lie parallel to the micelle surface, all glycine residues being located on the solvent-exposed face. Spectroscopic data and cross-linking experiments indicate that the GXXXG repeats in these amphipathic helices do not provide a strong oligomerization interface, suggesting a different role from GXXXG motifs found in transmembrane helices. Copyright © 2014 Elsevier B.V. All rights reserved.

The Use of Faraday Rotation Sign Maps as a Diagnostic for Helical Jet Magnetic Fields

International Nuclear Information System (INIS)

Reichstein, Andrea; Gabuzda, Denise

2012-01-01

We present maps of the sign of the Faraday Rotation measure obtained from multi-frequency radio observations made with the Very Long Baseline Array (VLBA). The Active Galactic Nuclei (AGN) considered have B-field structures with a central 'spine' of B-field orthogonal to the jet and/or a longitudinal B-field near one or both edges of the jet. This structure can plausibly be interpreted as being caused by a helical/toroidal jet magnetic field. Faraday Rotation is a rotation of the plane of polarization that occurs when the polarized radiation passes through a magnetized plasma. The sign of the RM is determined by the direction of the line-of-sight B-field in the region causing the Faraday Rotation, and an ordered toroidal or helical magnetic field associated with an AGN jet will thus produce a distinctive bilateral distribution of the RMs across the jet. We present and discuss RM-sign maps and their possible interpretation regarding the magnetic field geometries for several sources.

Finite element analysis of helical flows in human aortic arch: A novel index

OpenAIRE

Lee, Cheng-Hung; Liu, Kuo-Sheng; Jhong, Guan-Heng; Liu, Shih-Jung; Hsu, Ming-Yi; Wang, Chao-Jan; Hung, Kuo-Chun

2014-01-01

This study investigates the helical secondary flows in the aortic arch using finite element analysis. The relationship between helical flow and the configuration of the aorta in patients of whose three-dimensional images constructed from computed tomography scans was examined. A finite element model of the pressurized root, arch, and supra-aortic vessels was developed to simulate the pattern of helical secondary flows. Calculations indicate that most of the helical secondary flow was formed i...

Dosimetric aspects of breast radiotherapy with three-dimensional and intensity-modulated radiotherapy helical tomotherapy planning modules

International Nuclear Information System (INIS)

Yadav, Poonam; Yan, Yue; Ignatowski, Tasha; Olson, Anna

2017-01-01

In this work, we investigated the dosimetric differences between the intensity-modulated radiotherapy (IMRT) plans and the three-dimensional (3D) helical plans based on the TomoTherapy system. A total of 15 patients with supine setup were randomly selected from the data base. For patients with lumpectomy planning target volume (PTV), regional lymph nodes were also included as part of the target. For dose sparing, the significant differences between the helical IMRT and helical 3D were only found in the heart and contralateral breast. For the dose to the heart, helical IMRT reduced the maximum point dose by 6.98 Gy compared to the helical 3D plan (p = 0.01). For contralateral breast, the helical IMRT plans significantly reduced the maximum point dose by 5.6 Gy compared to the helical 3D plan. However, compared to the helical 3D plan, the helical IMRT plan increased the volume for lower dose (13.08% increase in V 5 Gy , p = 0.01). In general, there are no significant differences in dose sparing between helical IMRT and helical 3D plans.

Exact solutions for helical magnetohydrodynamic equilibria. II. Nonstatic and nonbarotropic solutions

International Nuclear Information System (INIS)

Villata, M.; Ferrari, A.

1994-01-01

In the framework of the analytical study of magnetohydrodynamic (MHD) equilibria with flow and nonuniform density, a general family of well-behaved exact solutions of the generalized Grad--Shafranov equation and of the whole set of time-independent MHD equations completed by the nonbarotropic ideal gas equation of state is obtained, both in helical and axial symmetry. The helical equilibrium solutions are suggested to be relevant to describe the helical morphology of some astrophysical jets

Energetic ion driven Alfven eigenmodes in Large Helical Device plasmas with three-dimensional magnetic structure and their impact on energetic ion transport

International Nuclear Information System (INIS)

Toi, K; Yamamoto, S; Nakajima, N; Ohdachi, S; Sakakibara, S; Osakabe, M; Murakami, S; Watanabe, K Y; Goto, M; Kawahata, K; Kolesnichenko, Ya I; Masuzaki, S; Morita, S; Narihara, K; Narushima, Y; Takeiri, Y; Tanaka, K; Tokuzawa, T; Yamada, H; Yamada, I; Yamazaki, K

2004-01-01

In the Large Helical Device (LHD), energetic ion driven Alfven eigenmodes (AEs) and their impact on energetic ion transport have been studied. The magnetic configuration of the LHD is three-dimensional and has negative magnetic shear over a whole plasma radius in the low beta regime. These features introduce the characteristic structures of the shear Alfven spectrum. In particular, a core-localized type of toroidicity-induced AE (TAE) is most likely because the TAE gap frequency rapidly increases towards the plasma edge. Moreover, helicity-induced AEs (HAEs) can be generated through a toroidal mode coupling as well as poloidal one in the three-dimensional configuration. The following experimental results have been obtained in LHD plasmas heated by tangential neutral beam injection: (1) observation of core-localized TAEs having odd as well as even parity, (2) eigenmode transition of the core-localized TAE to global AEs (GAEs), which phenomenon is very similar to that in a reversed shear tokamak, (3) observation of HAEs of which the frequency is about eight times higher than the TAE gap frequency, (4) enhanced radial transport/loss of energetic ions caused by bursting TAEs in a relatively high beta regime, and (5) seed formation of internal transport barriers induced by TAE-induced energetic ion transport. These results will be important and interesting information for AE physics in toroidal plasmas

Stretchable Helical Architecture Inorganic-Organic Hetero Thermoelectric Generator

KAUST Repository

Rojas, Jhonathan Prieto; Singh, Devendra; Conchouso Gonzalez, David; Carreno, Armando Arpys Arevalo; Foulds, Ian G.; Hussain, Muhammad Mustafa

2016-01-01

To achieve higher power output from a thermoelectric generator (TEG), one needs to maintain a larger temperature difference between hot and cold end. In that regard, a stretchable TEG can be interesting to adaptively control the temperature difference. Here we show, the development of simple yet versatile and highly stretchable thermoelectric generators (TEGs), by combining well-known inorganic thermoelectric materials Bismuth Telluride and Antimony Telluride (Bi2Te3 and Sb2Te3) with organic substrates (Off-Stoichiometry Thiol-Enes polymer platform – OSTE, polyimide or paper) and novel helical architecture (double-arm spirals) to achieve over 100% stretchability. First, an OSTE-based TEG design demonstrates higher open circuit voltage generation at 100% strain than at rest, although it exhibits high internal resistance and a relatively complex fabrication process. The second, simpler TEG design, achieves a significant resistance reduction and two different structural substrates (PI and paper) are compared. The paper-based TEG generates 17 nW (ΔT = 75 °C) at 60% strain, which represents more than twice the power generation while at rest (zero strain). On the other hand, polyimide produces more conductive TE films and higher power (~35 nW at ΔT = 75 °C) but due to its higher thermal conductivity, power does not increase at stretch. In conclusion, highly stretchable TEGs can lead to higher temperature gradients (thus higher power generation), given that thermal conductivity of the structural material is low enough. Furthermore, either horizontal or vertical displacement can be achieved with double-arm helical architecture, hence allowing to extend the device to any nearby and mobile heat sink for continuous, effectively higher power generation.

Stretchable Helical Architecture Inorganic-Organic Hetero Thermoelectric Generator

KAUST Repository

Rojas, Jhonathan Prieto

2016-10-26

To achieve higher power output from a thermoelectric generator (TEG), one needs to maintain a larger temperature difference between hot and cold end. In that regard, a stretchable TEG can be interesting to adaptively control the temperature difference. Here we show, the development of simple yet versatile and highly stretchable thermoelectric generators (TEGs), by combining well-known inorganic thermoelectric materials Bismuth Telluride and Antimony Telluride (Bi2Te3 and Sb2Te3) with organic substrates (Off-Stoichiometry Thiol-Enes polymer platform – OSTE, polyimide or paper) and novel helical architecture (double-arm spirals) to achieve over 100% stretchability. First, an OSTE-based TEG design demonstrates higher open circuit voltage generation at 100% strain than at rest, although it exhibits high internal resistance and a relatively complex fabrication process. The second, simpler TEG design, achieves a significant resistance reduction and two different structural substrates (PI and paper) are compared. The paper-based TEG generates 17 nW (ΔT = 75 °C) at 60% strain, which represents more than twice the power generation while at rest (zero strain). On the other hand, polyimide produces more conductive TE films and higher power (~35 nW at ΔT = 75 °C) but due to its higher thermal conductivity, power does not increase at stretch. In conclusion, highly stretchable TEGs can lead to higher temperature gradients (thus higher power generation), given that thermal conductivity of the structural material is low enough. Furthermore, either horizontal or vertical displacement can be achieved with double-arm helical architecture, hence allowing to extend the device to any nearby and mobile heat sink for continuous, effectively higher power generation.

Evolution of sausage and helical modes in magnetized thin-foil cylindrical liners driven by a Z-pinch

Science.gov (United States)

Yager-Elorriaga, D. A.; Lau, Y. Y.; Zhang, P.; Campbell, P. C.; Steiner, A. M.; Jordan, N. M.; McBride, R. D.; Gilgenbach, R. M.

2018-05-01

In this paper, we present experimental results on axially magnetized (Bz = 0.5 - 2.0 T), thin-foil (400 nm-thick) cylindrical liner-plasmas driven with ˜600 kA by the Michigan Accelerator for Inductive Z-Pinch Experiments, which is a linear transformer driver at the University of Michigan. We show that: (1) the applied axial magnetic field, irrespective of its direction (e.g., parallel or anti-parallel to the flow of current), reduces the instability amplitude for pure magnetohydrodynamic (MHD) modes [defined as modes devoid of the acceleration-driven magneto-Rayleigh-Taylor (MRT) instability]; (2) axially magnetized, imploding liners (where MHD modes couple to MRT) generate m = 1 or m = 2 helical modes that persist from the implosion to the subsequent explosion stage; (3) the merging of instability structures is a mechanism that enables the appearance of an exponential instability growth rate for a longer than expected time-period; and (4) an inverse cascade in both the axial and azimuthal wavenumbers, k and m, may be responsible for the final m = 2 helical structure observed in our experiments. These experiments are particularly relevant to the magnetized liner inertial fusion program pursued at Sandia National Laboratories, where helical instabilities have been observed.

Clinical application of helical CT 3D reconstruction for the dental orthopaedics

International Nuclear Information System (INIS)

Han Benyi; Jiang Xiaolu; Li Hongru

2005-01-01

Objective: To evaluate the clinical application of helical CT 3D reconstruction technique in the dental orthopaedics. Methods: The helical CT was performed with 3.0 mm slice thickness and 1.0 pitch in 41 patients with dental orthopaedics. The 3D reconstructions, including maximum intensity projection (MIP), surface shaded display (SSD), and multiplanar reconstructions (MPR), were made for all the cases. Results: Thirty-seven of the 41 patients showed malalignment, tilt, rotation, overlap of the teeth and the different space between the longitudinal axes of the teeth. Twenty-five cases of them have shown 36 buried teeth in all. The axial images covered all the information. SSD demonstrated the external contours and entire morphologies of the teeth and the mandible with the relationship of the teeth alignment and the mandible. MIP clearly manifested the full view and the longitudinal alignment of the teeth. Among the 36 buried teeth, there were 29 palatally and 7 labially presented teeth, and they were morphologically delineated on MIP through various angles. Conclusion: The helical CT 3D reconstruction is a new technique to display the stereoscopic configuration of teeth. The combination of axial images and MIP, SSD, and MPR provides valuable anatomic and diagnostic information helpful for the surgeons to structure and determine the treatment protocol for the dental orthopaedics. (authors)

The evolution of helical cosmic magnetic fields as predicted by MHD closure theory

Energy Technology Data Exchange (ETDEWEB)

Saveliev, Andrey; Sigl, Guenter [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Jedamzik, Kartsen [Univ. Montpellier-2. (France). Laboratoire Univers et Particules de Montpellier

2013-04-15

We extend our recent derivation of the time evolution equations for the energy content of magnetic fields and turbulent motions for incompressible, homogeneous, and isotropic turbulence to include the case of non-vanishing helicity. These equations are subsequently numerically integrated in order to predict the present day primordial magnetic field strength and correlation length, depending on its initial helicity and magnetic energy density. We find that all prior analytic predictions for helical magnetic fields, such as the epoch when they become maximally helical and their subsequent growth of correlation length L {proportional_to} a{sup 1/3} and decrease of magnetic field strength B {proportional_to} a{sup -1/3} with scale factor a are well confirmed by the simulations. An initially fully helical primordial magnetic field is a factor 4 x 10{sup 4} stronger at the present epoch then its non-helical counterpart when generated during the electroweak epoch.

Intravenous digital subtraction angiography and helical computed tomography in evaluation of living renal donors

International Nuclear Information System (INIS)

Watarai, Yoshihiko; Usuki, Tomoaki; Takeuchi, Ichiro; Nonomura, Katsuya; Koyanagi, Tomohiko; Kubo, Kozo; Hirano, Tetsuo; Togashi, Masaki; Ohashi, Nobuo

2001-01-01

The present study was carried out to evaluate the accuracy of helical computed tomography (CT) and intravenous digital subtraction angiography (IV-DSA) on anatomical assessment of renal vasculature for living renal donors. Forty-two healthy potential renal donors were prospectively evaluated and 35 subsequently underwent donor nephrectomy after helical CT and IV-DSA evaluation. The vascular and non-vascular findings were compared between the findings on helical CT, IV-DSA and surgery. Ten prehilar branches and five accessory renal arteries were found at nephrectomy. Overall, operative findings agreed with the findings by IV-DSA in 89% and by helical CT in 83%. In delineating accessory arteries, IV-DSA had a sensitivity of 60% and specificity of 97%, whereas helical CT had a sensitivity of 40% and specificity of 100%. In delineating prehilar branches, IV-DSA had a sensitivity of 90% and specificity of 100%, whereas helical CT had a sensitivity of 70% and specificity of 100%. Accessory arteries and prehilar branches that were not detected by helical CT or IV-DSA, were less than 2 mm in diameter and did not require vascular reconstruction. Renal veins were delineated in 63% by IV-DSA, whereas they were clearly imaged by helical CT in all cases, including a case with a circumaortic renal vein. Non-vascular findings were obtained in 64% by helical CT, including two renal tumors. None of these findings were obtained by IV-DSA. Helical CT and IV-DSA provide comparably sufficient information on renal artery vasculature. However, helical CT provides significantly more information on venous and non-vascular findings as a single-imaging modality. (author)

Transport properties of a discrete helical electrostatic quadrupole

International Nuclear Information System (INIS)

Meitzler, C.R.; Antes, K.; Datte, P.; Huson, F.R.; Xiu, L.

1991-01-01

The helical electrostatic quadrupole (HESQ) lens has been proposed as a low energy beam transport system which permits intense H - beams to be focused into an RFQ without seriously increasing the beam's emittance. A stepwise continuous HESQ lens has been constructed, and preliminary tests have shown that the structure does provide focusing. In order to understand the transport properties of this device, further detailed studies have been performed. Emittances were measured 3.5 cm from the end of the HESQ at two different voltages on the HESQ electrodes. A comparison of these experimental results with a linear model of the HESQ beam transport is made. 4 refs., 5 figs

Dosimetric aspects of breast radiotherapy with three-dimensional and intensity-modulated radiotherapy helical tomotherapy planning modules

Energy Technology Data Exchange (ETDEWEB)

Yadav, Poonam [Department of Human Oncology, University of Wisconsin-Madison, Madison, WI (United States); Service of Radiation Therapy, University of Wisconsin Aspirus Cancer Center, Wisconsin Rapids, WI (United States); Yan, Yue, E-mail: yyan5@mdanderson.org [Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX (United States); Ignatowski, Tasha [Service of Radiation Therapy, University of Wisconsin Aspirus Cancer Center, Wisconsin Rapids, WI (United States); Olson, Anna [Department of Human Oncology, University of Wisconsin-Madison, Madison, WI (United States); Service of Radiation Therapy, University of Wisconsin Aspirus Cancer Center, Wisconsin Rapids, WI (United States)

2017-04-01

In this work, we investigated the dosimetric differences between the intensity-modulated radiotherapy (IMRT) plans and the three-dimensional (3D) helical plans based on the TomoTherapy system. A total of 15 patients with supine setup were randomly selected from the data base. For patients with lumpectomy planning target volume (PTV), regional lymph nodes were also included as part of the target. For dose sparing, the significant differences between the helical IMRT and helical 3D were only found in the heart and contralateral breast. For the dose to the heart, helical IMRT reduced the maximum point dose by 6.98 Gy compared to the helical 3D plan (p = 0.01). For contralateral breast, the helical IMRT plans significantly reduced the maximum point dose by 5.6 Gy compared to the helical 3D plan. However, compared to the helical 3D plan, the helical IMRT plan increased the volume for lower dose (13.08% increase in V{sub 5} {sub Gy}, p = 0.01). In general, there are no significant differences in dose sparing between helical IMRT and helical 3D plans.

Helical muon beam cooling channel engineering design

International Nuclear Information System (INIS)

Johnson, Rolland

2015-01-01

The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb 3 Sn-based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb 3 Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb 3 Sn solenoid as originally planned. Instead, a complementary project was approved by the

Helical muon beam cooling channel engineering design

Energy Technology Data Exchange (ETDEWEB)

Johnson, Rolland [Muons, Inc., Batavia, IL (United States)

2015-08-07

The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb₃Sn-based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb₃Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb₃Sn solenoid as originally planned. Instead, a complementary

Monte-Carlo calculation of perpendicular neutral-beam injection in helical systems

International Nuclear Information System (INIS)

Hanatani, K.; Wakatani, M.; Uo, K.

1981-01-01

The effect of a helical field ripple on the slowing-down process of the fast ions created by neutral injection is investigated numerically. For this purpose, the guiding-centre orbits are followed in a model magnetic field without plasma current, on the assumption that the slowing-down process is to be classical. Optimum injection angles in two types of helical magnetic traps are compared. One is the Heliotron-E configuration with a large rotational transform and deep helical ripple; the other one is the conventional stellarator field with a small rotational transform and shallow helical ripple. In contrast to the stellarator, the heating efficiency as calculated for Heliotron-E does not decrease monotonically when the injection angle is perpendicular to the toroidal direction; a heating efficiency of above 70% was obtained for perpendicular injection into a high-density plasma with negligible charge-exchange loss. The difference in heating efficiency versus injection angle between heliotron and conventional stellarator fields is explained by a difference in drift motion of the helically trapped fast ions. (author)

Chirality of Intermediate Filaments and Magnetic Helicity of Active Regions

Science.gov (United States)

Lim, Eun-Kyung; Chae, J.

2009-05-01

Filaments that form either between or around active regions (ARs) are called intermediate filaments. Even though there have been many theoretical studies, the origin of the chirality of filaments is still unknown. We investigated how intermediate filaments are related to their associated ARs, especially from the point of view of magnetic helicity and the orientation of polarity inversion lines (PILs). The chirality of filaments has been determined based on the orientations of barbs observed in the full-disk Hα images taken at Big Bear Solar Observatory during the rising phase of solar cycle 23. The sign of magnetic helicity of ARs has been determined using S/inverse-S shaped sigmoids from Yohkoh SXT images. As a result, we have found a good correlation between the chirality of filaments and the magnetic helicity sign of ARs. Among 45 filaments, 42 filaments have shown the same sign as helicity sign of nearby ARs. It has been also confirmed that the role of both the orientation and the relative direction of PILs to ARs in determining the chirality of filaments is not significant, against a theoretical prediction. These results suggest that the chirality of intermediate filaments may originate from magnetic helicity of their associated ARs.

Helical wire stress analysis of unbonded flexible riser under irregular response

Science.gov (United States)

Wang, Kunpeng; Ji, Chunyan

2017-06-01

A helical wire is a critical component of an unbonded flexible riser prone to fatigue failure. The helical wire has been the focus of much research work in recent years because of the complex multilayer construction of the flexible riser. The present study establishes an analytical model for the axisymmetric and bending analyses of an unbonded flexible riser. The interlayer contact under axisymmetric loads in this model is modeled by setting radial dummy springs between adjacent layers. The contact pressure is constant during the bending response and applied to determine the slipping friction force per unit helical wire. The model tracks the axial stress around the angular position at each time step to calculate the axial force gradient, then compares the axial force gradient with the slipping friction force to judge the helical wire slipping region, which would be applied to determine the bending stiffness for the next time step. The proposed model is verified against the experimental data in the literature. The bending moment-curvature relationship under irregular response is also qualitatively discussed. The stress at the critical point of the helical wire is investigated based on the model by considering the local flexure. The results indicate that the present model can well simulate the bending stiffness variation during irregular response, which has significant effect on the stress of helical wire.

Plasma transport simulation modeling for helical confinement systems

International Nuclear Information System (INIS)

Yamazaki, K.; Amano, T.

1991-08-01

New empirical and theoretical transport models for helical confinement systems are developed based on the neoclassical transport theory including the effect of radial electric field and multi-helicity magnetic components, and the drift wave turbulence transport for electrostatic and electromagnetic modes, or the anomalous semi-empirical transport. These electron thermal diffusivities are compared with CHS (Compact Helical System) experimental data, which indicates that the central transport coefficient of the ECH plasma agrees with the neoclassical axi-symmetric value and the transport outside the half radius is anomalous. On the other hand, the transport of NBI-heated plasmas is anomalous in the whole plasma region. This anomaly is not explained by the electrostatic drift wave turbulence models in these flat-density-profile discharges. For the detailed prediction of plasma parameters in LHD (Large Helical Device), 3-D(dimensional) equilibrium/1-D transport simulations including empirical or drift wave turbulence models are carried out, which suggests that the global confinement time of LHD is determined mainly by the electron anomalous transport near the plasma edge region rather than the helical ripple transport in the core region. Even if the ripple loss can be eliminated, the increase of the global confinement is 10%. However, the rise in the central ion temperature is more than 20%. If the anomalous loss can be reduced to the half level of the present scaling, like so-called 'H-mode' of the tokamak discharge, the neoclassical ripple loss through the ion channel becomes important even in the plasma core. The 5% radial inward shift of the plasma column with respect to the major radius is effective for improving plasma confinement and raising more than 50% of the fusion product by reducing this neoclassical asymmetric ion transport loss and increasing 10% in the plasma radius. (author)

Nonlinear behavior of multiple-helicity resistive interchange modes near marginally stable states

International Nuclear Information System (INIS)

Sugama, Hideo; Nakajima, Noriyoshi; Wakatani, Masahiro.

1991-05-01

Nonlinear behavior of resistive interchange modes near marginally stable states is theoretically studied under the multiple-helicity condition. Reduced fluid equations in the sheared slab configuration are used in order to treat a local transport problem. With the use of the invariance property of local reduced fluid model equations under a transformation between the modes with different rational surfaces, weakly nonlinear theories for single-helicity modes by Hamaguchi and Nakajima are extended to the multiple-helicity case and applied to the resistive interchange modes. We derive the nonlinear amplitude equations of the multiple-helicity modes, from which the convective transport in the saturated state is obtained. It is shown how the convective transport is enhanced by nonlinear interaction between modes with different rational surfaces compared with the single-helicity case. We confirm that theoretical results are in good agreement with direct numerical simulations. (author)

Strong coupling between a permalloy ferromagnetic contact and helical edge channel in a narrow HgTe quantum well

Energy Technology Data Exchange (ETDEWEB)

Kononov, A.; Egorov, S. V. [Russian Academy Sciences, Institute of Solid State Physics (Russian Federation); Kvon, Z. D.; Mikhailov, N. N.; Dvoretsky, S. A. [Institute of Semiconductor Physics (Russian Federation); Deviatov, E. V., E-mail: dev@issp.ac.ru [Russian Academy Sciences, Institute of Solid State Physics (Russian Federation)

2016-11-15

We experimentally investigate spin-polarized electron transport between a permalloy ferromagnet and the edge of a two-dimensional electron system with band inversion, realized in a narrow, 8 nm wide, HgTe quantum well. In zero magnetic field, we observe strong asymmetry of the edge potential distribution with respect to the ferromagnetic ground lead. This result indicates that the helical edge channel, specific for the structures with band inversion even at the conductive bulk, is strongly coupled to the ferromagnetic side contact, possibly due to the effects of proximity magnetization. This allows selective and spin-sensitive contacting of helical edge states.

Investigation into the heat transfer performance of helically ribbed surfaces

International Nuclear Information System (INIS)

Firth, R.J.

1981-12-01

The first part of an investigation into flow and heat transfer in annular channels and seven pin clusters is described. One of the main aims of the project is to improve cluster heat transfer prediction codes for helically ribbed surfaces. A study is made of the heat transfer and flow characteristics of a helically ribbed pin in an annular channel. It is shown that the swirling flow, which is induced by the helical ribs, gives rise to substantially enhanced diffusivity levels. This phenomenon had not been taken into account by previous analysis techniques. The methods for analysing heat transfer and pressure drop data from annular channels which were originally developed for non-swirling flow are generalised to accommodate swirling flow. The new methods are shown to be consistent with empirical data. Roughness parameter data is presented for helically ribbed surfaces with an axial rib pitch into height ratio of about 7. (author)

Role of bundle helices in a regulatory crosstalk in the trimeric betaine transporter BetP.

Science.gov (United States)

Gärtner, Rebecca M; Perez, Camilo; Koshy, Caroline; Ziegler, Christine

2011-12-02

The Na(+)-coupled betaine symporter BetP regulates transport activity in response to hyperosmotic stress only in its trimeric state, suggesting a regulatory crosstalk between individual protomers. BetP shares the overall fold of two inverted structurally related five-transmembrane (TM) helix repeats with the sequence-unrelated Na(+)-coupled symporters LeuT, vSGLT, and Mhp1, which are neither trimeric nor regulated in transport activity. Conformational changes characteristic for this transporter fold involve the two first helices of each repeat, which form a four-TM-helix bundle. Here, we identify two ionic networks in BetP located on both sides of the membrane that might be responsible for BetP's unique regulatory behavior by restricting the conformational flexibility of the four-TM-helix bundle. The cytoplasmic ionic interaction network links both first helices of each repeat in one protomer to the osmosensing C-terminal domain of the adjacent protomer. Moreover, the periplasmic ionic interaction network conformationally locks the four-TM-helix bundle between the same neighbor protomers. By a combination of site-directed mutagenesis, cross-linking, and betaine uptake measurements, we demonstrate how conformational changes in individual bundle helices are transduced to the entire bundle by specific inter-helical interactions. We suggest that one purpose of bundle networking is to assist crosstalk between protomers during transport regulation by specifically modulating the transition from outward-facing to inward-facing state. Copyright © 2011 Elsevier Ltd. All rights reserved.

Observation of helix associations for insertion of a retinal molecule and distortions of helix structures in bacteriorhodopsin

Science.gov (United States)

Urano, Ryo; Okamoto, Yuko

2015-12-01

We applied a newly proposed prediction method for membrane protein structures to bacteriorhodopsin that has distorted transmembrane helices in the native structure. This method uses an implicit membrane model, which restricts sampling space during folding in a membrane region, and includes helix bending. Replica-exchange simulations were performed with seven transmembrane helices only without a retinal molecule. Obtained structures were classified into clusters of similar structures, which correspond to local-minimum free energy states. The two lowest free energy states corresponded to a native-like structure with the correct empty space for retinal and a structure with this empty space filled with a helix. Previous experiments of bacteriorhodopsin suggested that association of transmembrane helices enables them to make a room for insertion of a retinal. Our results are consistent with these results. Moreover, distortions of helices in the native-like structures were successfully reproduced. In the distortions, whereas the locations of kinks for all helices were similar to those of Protein Data Bank's data, the amount of bends was more similar for helices away from the retinal than for those close to the retinal in the native structure. This suggests a hypothesis that the amino-acid sequence specifies the location of kinks in transmembrane helices and that the amount of distortions depends on the interactions with the surrounding molecules such as neighboring helices, lipids, and retinal.

Recent helicity source and power supply improvements in CTX

International Nuclear Information System (INIS)

Henins, I.; Knox, S.O.; Jarboe, T.R.; Barnes, C.W.

1985-01-01

Since the last CT Symposium, two major changes in CTX have been the introduction of pulse forming networks (PFNs) to drive the coaxial electrode helicity source, and the very recent installation of a larger source with electrode diameters about twice of the previous ones. The power supplies used for CTX have ranged from the simple connection of the capacitor bank across the electrode collector plates (slow mode) to the more sophisticated PFNs, described here, which optimize the energy transfer from the capacitor bank to the magnetic fields of the spheromak. Using the PFNs, the formation and sustainment phase to peak toroidal plasma current lasts longer (approx. =0.7 ms) than in the slow mode (approx. =0.05 ms), thus lowering the peak current that must flow through the electrode surfaces. Also, by supplying the source electrodes with both a square pulse current waveform and a quasi-steady source flux, phi/sub g/, one can generate helicity at a constant source lambda/sub g/ parameter. The use of a larger diameter helicity source will improve the energy efficiency of helicity injection and allow higher source current for the same surface current density because of the larger electrode surface area

Extension of operation regimes and investigation of three-dimensional current-less plasmas in the Large Helical Device

International Nuclear Information System (INIS)

Kaneko, O.

2012-11-01

The Large Helical Device (LHD) has shown the advantages of heliotron plasma for fusion reactor from operational point of view not only such as disruption free and steady state operation, but also as high density and stable high beta operation. Since the last Fusion Energy Conference in Daejon in 2010 (Yamada, 2011 Nucl. Fusion 51 094021), physical understanding as well as parameter improvement of net-current free helical plasmas has progressed successively. The current efforts are focused on optimization of plasma edge condition to extend the operation regime towards higher ion temperature and more stable high density. In LHD a part of open helical divertors are being modified to the baffle-structured closed ones to aim at active control of the edge plasma. It has been demonstrated that the neutral pressure in the closed helical divertor was more than 10 times higher than that in the open helical divertor. The central ion temperature has exceeded 7 keV. This high-T i plasma was obtained by a carbon pellet injection and the kinetic-energy confinement was improved by a factor of 1.5. Transport analysis of the high-T i plasmas has shown that the ion-thermal conductivity and the viscosity reduced after the pellet injection. Study of physics in 3-D geometry is highlighted in the topics of the response to Resonant Magnetic Perturbation such as ELM mitigation and divertor detachment. Novel approaches of non-local and non-diffusive transport have also been advanced. In this paper, highlighted results in these two years are overviewed. (author)

Diffusion with finite-helicity field tensor: A mechanism of generating heterogeneity

Science.gov (United States)

Sato, N.; Yoshida, Z.

2018-02-01

Topological constraints on a dynamical system often manifest themselves as breaking of the Hamiltonian structure; well-known examples are nonholonomic constraints on Lagrangian mechanics. The statistical mechanics under such topological constraints is the subject of this study. Conventional arguments based on phase spaces, Jacobi identity, invariant measure, or the H theorem are no longer applicable since all these notions stem from the symplectic geometry underlying canonical Hamiltonian systems. Remembering that Hamiltonian systems are endowed with field tensors (canonical 2-forms) that have zero helicity, our mission is to extend the scope toward the class of systems governed by finite-helicity field tensors. Here, we introduce a class of field tensors that are characterized by Beltrami vectors. We prove an H theorem for this Beltrami class. The most general class of energy-conserving systems are non-Beltrami, for which we identify the "field charge" that prevents the entropy to maximize, resulting in creation of heterogeneous distributions. The essence of the theory can be delineated by classifying three-dimensional dynamics. We then generalize to arbitrary (finite) dimensions.

New Modular Heliotron system compatible with closed helical divertor and good plasma confinement

International Nuclear Information System (INIS)

Yamazaki, K.; Watanabe, K.Y.

1994-04-01

A new helical system ('Modular Heliotron') with improved modular coils compatible with efficient closed helical divertor and good plasma confinement property is proposed based on a Heliotron system with continuous helical coils and one pair of poloidal coils. The physics optimization of this system as a function of the gap angle between adjacent modular coils has been carried out by means of vacuum magnetic surface calculations and finite-beta plasma analyses, and a new improved coil system is invented by combining sectored helical field coils with sectored returning poloidal field coils. The Modular Heliotron with standard coil winding law (reference Modular Heliotron) was previously proposed, but it is found that this is not appropriate to keep clean helical divertor and high beta configuration when the coil gap becomes large. By modulating the modular coil winding with outside-plus and inside-minus pitch modulation, almost the same good magnetic configuration as that of a conventional Heliotron can be produced. The optimal gap angle is determined as a function of the modulation parameter. This improved Modular Heliotron permits larger gap angle between adjacent modules and produces more clean helical divertor configuration than the reference Modular Heliotron. All these helical system are created by only modular coils without poloidal coils. (author)

Linear local stability of electrostatic drift modes in helical systems

International Nuclear Information System (INIS)

Yamagishi, O.; Nakajima, N.; Sugama, H.; Nakamura, Y.

2003-01-01

We investigate the stability of the drift wave in helical systems. For this purpose, we solve the linear local gyrokinetic-Poisson equation, in the electrostatic regime. As a model of helical plasmas, Large helical Device (LHD) is considered. The equation we apply is rather exact in the framework of linear gyrokinetic theory, where only the approximation is the ballooning representation. In this paper, we consider only collisionless cases. All the frequency regime can be naturally reated without any assumptions, and in such cases, ion temperature gradient modes (ITG), trapped electron modes (TEM), and electron temperature gradient modes (ETG) are expected to become unstable linearly independently. (orig.)

Neutronics Design of Helical Type DEMO Reactor FFHR-d1

Energy Technology Data Exchange (ETDEWEB)

Tanaka, T.; Sagara, A.; Goto, T.; Yanagi, N.; Masuzaki, S.; Tamura, H.; Miyazawa, J.; Muroga, T., E-mail: teru@nifs.ac.jp [National Institute for Fusion Science, Toki (Japan)

2012-09-15

Full text: Neutronics design study has been performed in a newly started conceptual design activity for a helical type DEMO reactor FFHR-d1. Features of the FFHR-d1 design are enlargement of the basic configurations of reactor components and extrapolation of plasma parameters from those of the helical type plasma experimental machine Large Helical Device (LHD) to achieve the highest feasibility. From the neutronics point of view, a blanket space of FFHR-d1 is severely limited at the inboard of the torus. This is due to the core plasma position shifting to the inboard side under the confinement condition extrapolated from LHD. The first step of the neutronics investigation using the MCNP code has been performed with a simple torus model simulating thin inboard blanket space. A Flibe+Be/Ferritic steel breeding blanket showed preferable performances for both tritium breeding and shielding, and has been adapted as a reference blanket system for FFHR-d1. The investigations indicate that a combination of a 15 cm thick breeding blanket, 55 cm thick WC+B4C shield, i.e., the blanket space of 70 cm, could suppress the fast neutron flux and nuclear heating in the helical coils to the design targets for the neutron wall loading of 1.5 MW/m{sup 2}. Since the outboard side can provide a large space for a 60 cm thick breeding blanket, a fully-covered tritium breeding ratio (TBR) of 1.31 has been obtained in the simple torus model. The neutronics design study has proceeded to the second step using a 3-D helical reactor model. The most important issue in the 3-D neutronics design is a compatibility with the helical divertor design. To achieve a higher TBR and shielding performance, the core plasma has to be covered by the breeding blanket layers as possible. However, the dimensions of the blanket layers are limited by magnetic field lines connecting an edge of the core plasma and divertor pumping ports. After repeating modification of the blanket configuration, the global TBR of 1

Modification of Spalart-Allmaras model with consideration of turbulence energy backscatter using velocity helicity

International Nuclear Information System (INIS)

Liu, Yangwei; Lu, Lipeng; Fang, Le; Gao, Feng

2011-01-01

The correlation between the velocity helicity and the energy backscatter is proved in a DNS case of 256 3 -grid homogeneous isotropic decaying turbulence. The helicity is then proposed to be employed to improve turbulence models and SGS models. Then Spalart-Allmaras turbulence model (SA) is modified with the helicity to take account of the energy backscatter, which is significant in the region of corner separation in compressors. By comparing the numerical results with experiments, it can be concluded that the modification for SA model with helicity can appropriately represent the energy backscatter, and greatly improves the predictive accuracy for simulating the corner separation flow in compressors. -- Highlights: → We study the relativity between the velocity helicity and the energy backscatter. → Spalart-Allmaras turbulence model is modified with the velocity helicity. → The modified model is employed to simulate corner separation in compressor cascade. → The modification can greatly improve the accuracy for predicting corner separation. → The helicity can represent the energy backscatter in turbulence and SGS models.

Quasiparticle dynamics in reshaped helical Dirac cone of topological insulators.

Science.gov (United States)

Miao, Lin; Wang, Z F; Ming, Wenmei; Yao, Meng-Yu; Wang, Meixiao; Yang, Fang; Song, Y R; Zhu, Fengfeng; Fedorov, Alexei V; Sun, Z; Gao, C L; Liu, Canhua; Xue, Qi-Kun; Liu, Chao-Xing; Liu, Feng; Qian, Dong; Jia, Jin-Feng

2013-02-19

Topological insulators and graphene present two unique classes of materials, which are characterized by spin-polarized (helical) and nonpolarized Dirac cone band structures, respectively. The importance of many-body interactions that renormalize the linear bands near Dirac point in graphene has been well recognized and attracted much recent attention. However, renormalization of the helical Dirac point has not been observed in topological insulators. Here, we report the experimental observation of the renormalized quasiparticle spectrum with a skewed Dirac cone in a single Bi bilayer grown on Bi(2)Te(3) substrate from angle-resolved photoemission spectroscopy. First-principles band calculations indicate that the quasiparticle spectra are likely associated with the hybridization between the extrinsic substrate-induced Dirac states of Bi bilayer and the intrinsic surface Dirac states of Bi(2)Te(3) film at close energy proximity. Without such hybridization, only single-particle Dirac spectra are observed in a single Bi bilayer grown on Bi(2)Se(3), where the extrinsic Dirac states Bi bilayer and the intrinsic Dirac states of Bi(2)Se(3) are well separated in energy. The possible origins of many-body interactions are discussed. Our findings provide a means to manipulate topological surface states.

A broadband helical saline water liquid antenna for wearable systems

Science.gov (United States)

Li, Gaosheng; Huang, Yi; Gao, Gui; Yang, Cheng; Lu, Zhonghao; Liu, Wei

2018-04-01

A broadband helical liquid antenna made of saline water is proposed. A transparent hollow support is employed to fabricate the antenna. The rotation structure is fabricated with a thin flexible tube. The saline water with a concentration of 3.5% can be injected into or be extracted out from the tube to change the quantity of the solution. Thus, the tunability of the radiation pattern could be realised by applying the fluidity of the liquid. The radiation feature of the liquid antenna is compared with that of a metal one, and fairly good agreement has been achieved. Furthermore, three statements of the radiation performance corresponding to the ratio of the diameter to the wavelength of the helical saline water antenna have been proposed. It has been found that the resonance frequency increases when the length of the feeding probe or the radius of the vertical part of the liquid decreases. The fractional bandwidth can reach over 20% with a total height of 185 mm at 1.80 GHz. The measured results indicate reasonable approximation to the simulated. The characteristics of the liquid antenna make it a good candidate for various wireless applications, especially the wearable systems.

Divertors for Helical Devices: Concepts, Plans, Results, and Problems

International Nuclear Information System (INIS)

Koenig, R.; Grigull, P.; McCormick, K.

2004-01-01

With Large Helical Device (LHD) and Wendelstein 7-X (W7-X), the development of helical devices is now taking a large step forward on the path to a steady-state fusion reactor. Important issues that need to be settled in these machines are particle flux and heat control and the impact of divertors on plasma performance in future continuously burning fusion plasmas. The divertor concepts that will initially be explored in these large machines were prepared in smaller-scale devices like Heliotron E, Compact Helical System (CHS), and Wendelstein 7-AS (W7-AS). While advanced divertor scenarios relevant for W7-X were already studied in W7-AS, other smaller-scale experiments like Heliotron-J, CHS, and National Compact Stellarator Experiment will be used for the further development of divertor concepts. The two divertor configurations that are being investigated are the helical and the island divertor, as well as the local island divertor, which was successfully demonstrated on CHS and just went into operation on LHD. At present, on its route to a fully closed helical divertor, LHD operates in an open helical divertor configuration. W7-X will be equipped right from the start with an actively cooled discrete island divertor that will allow quasi-continuous operation. The divertor design is very similar to the one explored on W7-AS. For sufficiently large island sizes and not too long field line connection lengths, this divertor gives access to a partially detached quasi-steady-state operating scenario in a newly found high-density H-mode operating regime, which benefits from high energy and low impurity confinement times, with edge radiation levels of up to 90% and sufficient neutral compression in the subdivertor region (>10) for active pumping. The basic physics of the different divertor concepts and associated implementation problems, like asymmetries due to drifts, accessibility of essential operating scenarios, toroidal asymmetries due to symmetry breaking error fields

Long helical filaments are not seen encircling cells in electron cryotomograms of rod-shaped bacteria

International Nuclear Information System (INIS)

Swulius, Matthew T.; Chen, Songye; Jane Ding, H.; Li, Zhuo; Briegel, Ariane; Pilhofer, Martin; Tocheva, Elitza I.; Lybarger, Suzanne R.; Johnson, Tanya L.; Sandkvist, Maria; Jensen, Grant J.

2011-01-01

Highlights: → No long helical filaments are seen near or along rod-shaped bacterial inner membranes by electron cryo-tomography. → Electron cryo-tomography has the resolution to detect single filaments in vivo. -- Abstract: How rod-shaped bacteria form and maintain their shape is an important question in bacterial cell biology. Results from fluorescent light microscopy have led many to believe that the actin homolog MreB and a number of other proteins form long helical filaments along the inner membrane of the cell. Here we show using electron cryotomography of six different rod-shaped bacterial species, at macromolecular resolution, that no long (>80 nm) helical filaments exist near or along either surface of the inner membrane. We also use correlated cryo-fluorescent light microscopy (cryo-fLM) and electron cryo-tomography (ECT) to identify cytoplasmic bundles of MreB, showing that MreB filaments are detectable by ECT. In light of these results, the structure and function of MreB must be reconsidered: instead of acting as a large, rigid scaffold that localizes cell-wall synthetic machinery, moving MreB complexes may apply tension to growing peptidoglycan strands to ensure their orderly, linear insertion.

Imploding to equilibrium of helically symmetric theta pinches

International Nuclear Information System (INIS)

Sharky, N.N.

1978-01-01

The time-dependent, single-fluid, dissipative magnetohydrodynamic equations are solved in helical coordinates (r,phi), where phi = THETA-kz, k = 2π/L and L is the periodicity length in the z-direction. The two-dimensional numerical calculations simulate theta pinches which have an l = 1 helical field added to them. Given the applied magnetic fields and the initial state of the plasma, we study the time evolution of the system. The plasma is found to experience two kinds of oscillations, occurring on different time scales. These are the radial compression oscillations, and the slower helical oscillations of the plasma column. The plasma motion is followed until these oscillations disappear and an equilibrium is nearly reached. Hence given the amplitude and the rise time of the applied magnetic fields, the calculations allow one to relate the initial state of a cold, homogeneous plasma to its final equilibrium state where it is heated and compressed

Experimental determination of limit angle of helical anisotropy in amorphous magnetic microwires

International Nuclear Information System (INIS)

Chizhik, A.; Zhukov, A.; Blanco, J.M.; Gonzalez, J.; Gawronski, P.

2009-01-01

The influence of the torsion stress on the surface magnetic structure in Co-rich amorphous glass covered microwires has been investigated. The limit angle of the surface helical anisotropy induced by the torsion stress has been determined in agreement with the model which considers the torsion stress as a interference of two tensile stresses of opposite signs directed at 45 deg. and 135 deg. relative to the longitudinal axis of the wire

Structure determination of a peptide model of the repeated helical domain in Samia cynthia ricini silk fibroin before spinning by a combination of advanced solid-state NMR methods.

Science.gov (United States)

Nakazawa, Yasumoto; Asakura, Tetsuo

2003-06-18

Fibrous proteins unlike globular proteins, contain repetitive amino acid sequences, giving rise to very regular secondary protein structures. Silk fibroin from a wild silkworm, Samia cynthia ricini, consists of about 100 repeats of alternating polyalanine (poly-Ala) regions of 12-13 residues in length and Gly-rich regions. In this paper, the precise structure of the model peptide, GGAGGGYGGDGG(A)(12)GGAGDGYGAG, which is a typical repeated sequence of the silk fibroin, was determined using a combination of three kinds of solid-state NMR studies; a quantitative use of (13)C CP/MAS NMR chemical shift with conformation-dependent (13)C chemical shift contour plots, 2D spin diffusion (13)C solid-state NMR under off magic angle spinning and rotational echo double resonance. The structure of the model peptide corresponding to the silk fibroin structure before spinning was determined. The torsion angles of the central Ala residue, Ala(19), in the poly-Ala region were determined to be (phi, psi) = (-59 degrees, -48 degrees ) which are values typically associated with alpha-helical structures. However, the torsion angles of the Gly(25) residue adjacent to the C-terminal side of the poly-Ala chain were determined to be (phi, psi) = (-66 degrees, -22 degrees ) and those of Gly(12) and Ala(13) residues at the N-terminal of the poly-Ala chain to be (phi, psi) = (-70 degrees, -30 degrees ). In addition, REDOR experiments indicate that the torsion angles of the two C-terminal Ala residues, Ala(23) and Ala(24), are (phi, psi) = (-66 degrees, -22 degrees ) and those of N-terminal two Ala residues, Ala(13) and Ala(14) are (phi, psi) = (-70 degrees, -30 degrees ). Thus, the local structure of N-terminal and C-terminal residues, and also the neighboring residues of alpha-helical poly-Ala chain in the model peptide is a more strongly wound structure than found in typical alpha-helix structures.

Use of helicity methods in evaluating loop integrals: a QCD example

International Nuclear Information System (INIS)

Koerner, J.G.; Sieben, P.

1991-01-01

We discuss the use of helicity methods in evaluating loop diagrams by analyzing a specific example: the one-loop concentration to e + e - → qanti qg in massless QCD. By using covariant helicity representations for the spinor and vector wave functins we obtain the helicity amplitudes directly from the Feynman loop diagrams by covariant contraction. The necessary loop integrations are considerably simplified since one encounters only scalar loop integrals after contraction. We discuss crossing relations that allow one to obtain the corresponding one-loop helicity amplitudes for the crossed processes as e.g. qanti q → (W, Z, γ * ) + g including the real photon cases. As we treat the spin degrees of freedom in four dimensions and only continue momenta to n dimensions (dimensional reduction scheme) we explicate how our results are related to the usual dimensional regularization results. (orig.)

Magnetic helices as metastable states of finite XY ferromagnetic chains: An analytical study

Science.gov (United States)

Popov, Alexander P.; Pini, Maria Gloria

2018-04-01

We investigated a simple but non trivial model, consisting of a chain of N classical XY spins with nearest neighbor ferromagnetic interaction, where each of the two end-point spins is assumed to be exchange-coupled to a fully-pinned fictitious spin. In the mean field approximation, the system might be representative of a soft ferromagnetic film sandwiched between two magnetically hard layers. We show that, while the ground state is ferromagnetic and collinear, the system can attain non-collinear metastable states in the form of magnetic helices. The helical solutions and their stability were studied analytically in the absence of an external magnetic field. There are four possible classes of solutions. Only one class is metastable, and its helical states contain an integer number of turns. Among the remaining unstable classes, there is a class of helices which contain an integer number of turns. Therefore, an integer number of turns in a helical configuration is a necessary, but not a sufficient, condition for metastability. These results may be useful to devise future applications of metastable magnetic helices as energy-storing elements.

Superconducting Helical Snake Magnet for the AGS

CERN Document Server

Willen, Erich; Escallier, John; Ganetis, George; Ghosh, Arup; Gupta, Ramesh C; Harrison, Michael; Jain, Animesh K; Luccio, Alfredo U; MacKay, William W; Marone, Andrew; Muratore, Joseph F; Okamura, Masahiro; Plate, Stephen R; Roser, Thomas; Tsoupas, Nicholaos; Wanderer, Peter

2005-01-01

A superconducting helical magnet has been built for polarized proton acceleration in the Brookhaven AGS. This "partial Snake" magnet will help to reduce the loss of polarization of the beam due to machine resonances. It is a 3 T magnet some 1940 mm in magnetic length in which the dipole field rotates with a pitch of 0.2053 degrees/mm for 1154 mm in the center and a pitch of 0.3920 degrees/mm for 393 mm in each end. The coil cross-section is made of two slotted cylinders containing superconductor. In order to minimize residual offsets and deflections of the beam on its orbit through the Snake, a careful balancing of the coil parameters was necessary. In addition to the main helical coils, a solenoid winding was built on the cold bore tube inside the main coils to compensate for the axial component of the field that is experienced by the beam when it is off-axis in this helical magnet. Also, two dipole corrector magnets were placed on the same tube with the solenoid. A low heat leak cryostat was built so that t...

Helical CT in acute lower gastrointestinal bleeding

International Nuclear Information System (INIS)

Ernst, Olivier; Leroy, Christophe; Sergent, Geraldine; Bulois, Philippe; Saint-Drenant, Sophie; Paris, Jean-Claude

2003-01-01

The purpose of this study was to assess the usefulness of helical CT in depicting the location of acute lower gastrointestinal bleeding. A three-phase helical CT of the abdomen was performed in 24 patients referred for acute lower gastrointestinal bleeding. The diagnosis of the bleeding site was established by CT when there was at least one of the following criteria: spontaneous hyperdensity of the peribowel fat; contrast enhancement of the bowel wall; vascular extravasation of the contrast medium; thickening of the bowel wall; polyp or tumor; or vascular dilation. Diverticula alone were not enough to locate the bleeding site. The results of CT were compared with the diagnosis obtained by colonoscopy, enteroscopy, or surgery. A definite diagnosis was made in 19 patients. The bleeding site was located in the small bowel in 5 patients and the colon in 14 patients. The CT correctly located 4 small bowel hemorrhages and 11 colonic hemorrhages. Diagnosis of the primary lesion responsible for the bleeding was made in 10 patients. Our results suggest that helical CT could be a good diagnostic tool in acute lower gastrointestinal bleeding to help the physician to diagnose the bleeding site. (orig.)

Origins of the helical wrapping of phenyleneethynylene polymers about single-walled carbon nanotubes.

Science.gov (United States)

Von Bargen, Christopher D; MacDermaid, Christopher M; Lee, One-Sun; Deria, Pravas; Therien, Michael J; Saven, Jeffery G

2013-10-24

The highly charged, conjugated polymer poly[p-{2,5-bis(3-propoxysulfonicacidsodiumsalt)}phenylene]ethynylene (PPES) has been shown to wrap single-wall carbon nanotubes (SWNTs), adopting a robust helical superstructure. Surprisingly, PPES adopts a helical rather than a linear conformation when adhered to SWNTs. The complexes formed by PPES and related polymers upon helical wrapping of a SWNT are investigated using atomistic molecular dynamics (MD) simulations in the presence and absence of aqueous solvent. In simulations of the PPES/SWNT system in an aqueous environment, PPES spontaneously takes on a helical conformation. A potential of mean force, ΔA(ξ), is calculated as a function of ξ, the component of the end-to-end vector of the polymer chain projected on the SWNT axis; ξ is a monotonic function of the polymer's helical pitch. ΔA(ξ) provides a means to quantify the relative free energies of helical conformations of the polymer when wrapped about the SWNT. The aqueous system possesses a global minimum in ΔA(ξ) at the experimentally observed value of the helical pitch. The presence of this minimum is associated with preferred side chain conformations, where the side chains adopt conformations that provide van der Waals contact between the tubes and the aliphatic components of the side chains, while exposing the anionic sulfonates for aqueous solvation. The simulations provide a free energy estimate of a 0.2 kcal/mol/monomer preference for the helical over the linear conformation of the PPES/SWNT system in an aqueous environment.

Controlling lanthanide exchange in triple-stranded helicates. A way to optimize molecular light-upconversion

Energy Technology Data Exchange (ETDEWEB)

Zare, Davood; Nozary, Homayoun; Piguet, Claude [Department of Inorganic, Analytical and Applied Chemistry, University of Geneva (Switzerland); Suffren, Yan; Hauser, Andreas [Department of Physical Chemistry, University of Geneva (Switzerland)

2017-11-13

The kinetic lability of hexadentate gallium-based tripods is sufficient to ensure thermodynamic self-assembly of luminescent heterodimetallic [GaLn(L3){sub 3}]{sup 6+} helicates on the hour time scale, where Ln is a trivalent 4f-block cation. The inertness is, however, large enough for preserving the triple-helical structure when [GaLn(L3){sub 3}]{sup 6+} is exposed to lanthanide exchange. The connection of a second gallium-based tripod further slows down the exchange processes to such an extent that spectroscopically active [CrErCr(L4){sub 3}]{sup 9+} can be diluted into closed-shell [GaYGa(L4){sub 3}]{sup 9+} matrices without metal scrambling. This feature is exploited for pushing molecular-based energy-transfer upconversion (ETU) at room temperature. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

A numerical study of the stabilitiy of helical vortices using vortex methods

International Nuclear Information System (INIS)

Walther, J H; Guenot, M; Machefaux, E; Rasmussen, J T; Chatelain, P; Okulov, V L; Soerensen, J N; Bergdorf, M; Koumoutsakos, P

2007-01-01

We present large-scale parallel direct numerical simulations using particle vortex methods of the instability of the helical vortices. We study the instability of a single helical vortex and find good agreement with inviscid theory. We outline equilibrium configurations for three double helical vortices-similar to those produced by three blade wind turbines. The simulations confirm the stability of the inviscid model, but predict a breakdown of the vortical system due to viscosity

A numerical study of the stabilitiy of helical vortices using vortex methods

Energy Technology Data Exchange (ETDEWEB)

Walther, J H [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Guenot, M [Enginering College in Industrial Systems, FR-17041, La Rochelle (France); Machefaux, E [Enginering College in Industrial Systems, FR-17041, La Rochelle (France); Rasmussen, J T [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Chatelain, P [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland); Okulov, V L [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Soerensen, J N [Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Lyngby (Denmark); Bergdorf, M [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland); Koumoutsakos, P [Computational Laboratory, ETH Zurich, CH-8092 Zurich (Switzerland)

2007-07-15

We present large-scale parallel direct numerical simulations using particle vortex methods of the instability of the helical vortices. We study the instability of a single helical vortex and find good agreement with inviscid theory. We outline equilibrium configurations for three double helical vortices-similar to those produced by three blade wind turbines. The simulations confirm the stability of the inviscid model, but predict a breakdown of the vortical system due to viscosity.

Principles for structure analysis of carbon nanotubes by HRTEM

Energy Technology Data Exchange (ETDEWEB)

Xudong, Fan; Bursill, L A

1995-10-01

An efficient algorithm is derived for generating all possible seamless carbon nanotube structure models. This makes use of multijugate helical lattices, a concept borrowed from some biological structures. Principles for helicity and structure analysis of carbon nanotubes using high-resolution electron microscopy and image processing techniques are then developed. Applicability is tested on experimentally obtained images. The limitations of this approach are examined. Provided the tubules contain less than three to five layers the individual component layer helicities and the order of assembly may be obtained from the high-resolution many-beam bright - and dark-field image reconstructions. 16 refs., 11 figs.

Principles for structure analysis of carbon nanotubes by HRTEM

International Nuclear Information System (INIS)

Fan Xudong; Bursill, L.A.

1995-01-01

An efficient algorithm is derived for generating all possible seamless carbon nanotube structure models. This makes use of multijugate helical lattices, a concept borrowed from some biological structures. Principles for helicity and structure analysis of carbon nanotubes using high-resolution electron microscopy and image processing techniques are then developed. Applicability is tested on experimentally obtained images. The limitations of this approach are examined. Provided the tubules contain less than three to five layers the individual component layer helicities and the order of assembly may be obtained from the high-resolution many-beam bright - and dark-field image reconstructions. 16 refs., 11 figs

Comparison between helical computed tomography angiography and intraoperative findings

Directory of Open Access Journals (Sweden)

Abijit Shetty

2014-01-01

Conclusions: Helical CT is important in delineating the arterial, venous, and ureteral anatomy and can show the important incidental findings. Left renal donors and males have more variations in their renal anatomy. Technically challenging laparoscopic nephrectomy on the multiple-vessel-side donor is possible with the aid of helical CT. The importance of the CT in evaluating donor renal anatomy for a technically challenging laparoscopic donor nephrectomy is commendable.

A helical scintillating fiber hodoscope

CERN Document Server

Altmeier, M; Bisplinghoff, J; Bissel, T; Bollmann, R; Busch, M; Büsser, K; Colberg, T; Demiroers, L; Diehl, O; Dohrmann, F; Engelhardt, H P; Eversheim, P D; Felden, O; Gebel, R; Glende, M; Greiff, J; Gross, A; Gross-Hardt, R; Hinterberger, F; Jahn, R; Jeske, M; Jonas, E; Krause, H; Lahr, U; Langkau, R; Lindemann, T; Lindlein, J; Maier, R; Maschuw, R; Mayer-Kuckuck, T; Meinerzhagen, A; Naehle, O; Pfuff, M; Prasuhn, D; Rohdjess, H; Rosendaal, D; Von Rossen, P; Sanz, B; Schirm, N; Schulz-Rojahn, M; Schwarz, V; Scobel, W; Thomas, S; Trelle, H J; Weise, E; Wellinghausen, A; Wiedmann, W; Woller, K; Ziegler, R

1999-01-01

A novel scintillating fiber hodoscope in helically cylindric geometry has been developed for detection of low multiplicity events of fast protons and other light charged particles in the internal target experiment EDDA at the Cooler Synchrotron COSY. The hodoscope consists of 640 scintillating fibers (2.5 mm diameter), arranged in four layers surrounding the COSY beam pipe. The fibers are helically wound in opposing directions and read out individually using 16-channel photomultipliers connected to a modified commercial encoding system. The detector covers an angular range of 9 deg. <= THETA<=72 deg. and 0 deg. <=phi (cursive,open) Greek<=360 deg. in the lab frame. The detector length is 590 mm, the inner diameter 161 mm. Geometry and granularity of the hodoscope afford a position resolution of about 1.3 mm. The detector design took into consideration a maximum of reliability and a minimum of maintenance. An LED array may be used for monitoring purposes. (author)

Helical post stellarator. Part 1: Vacuum configuration

International Nuclear Information System (INIS)

Moroz, P.E.

1997-08-01

Results on a novel type of stellarator configuration, the Helical Post Stellarator (HPS), are presented. This configuration is different significantly from all previously known stellarators due to its unique geometrical characteristics and unique physical properties. Among those are: the magnetic field has only one toroidal period (M = 1), the plasma has an extremely low aspect ratio, A ∼ 1, and the variation of the magnetic field, B, along field lines features a helical ripple on the inside of the torus. Among the main advantages of a HPS for a fusion program are extremely compact, modular, and simple design compatible with significant rotational transform, large plasma volume, and improved particle transport characteristics

Generation of helical gears with new surfaces topology by application of CNC machines

Science.gov (United States)

Litvin, F. L.; Chen, N. X.; Hsiao, C. L.; Handschuh, Robert F.

1993-01-01

Analysis of helical involute gears by tooth contact analysis shows that such gears are very sensitive to angular misalignment that leads to edge contact and the potential for high vibration. A new topology of tooth surfaces of helical gears that enables a favorable bearing contact and a reduced level of vibration is described. Methods for grinding of the helical gears with the new topology are proposed. A TCA (tooth contact analysis) program for simulation of meshing and contact of helical gears with the new topology has been developed. Numerical examples that illustrate the proposed ideas are discussed.

Synthesis, structure, and electrochemistry and magnetic properties of a novel 1D homochiral MnIII(5-Brsalen) coordination polymer with left-handed helical character

Science.gov (United States)

Dong, Dapeng; Yu, Naisen; Zhao, Haiyan; Liu, Dedi; Liu, Jia; Li, Zhenghua; Liu, Dongping

2016-01-01

A novel homochiral manganese (III) Mn(5-Brsalen) coordination polymer with left-handed helical character by spontaneous resolution on crystallization by using Mn(5-Brsalen) and 4,4-bipyridine, [MnIII(5-Brsalen)(4,4-bipy)]·ClO4·CH3OH (1) (4,4-bipy = 4,4-bipyridine) has been synthesized and structurally characterized by X-ray single-crystal diffraction, elemental analysis and infrared spectroscopy. In compound 1, each manganese(III) anion is six-coordinate octahedral being bonded to four atoms of 5-Brsalen ligand in an equatorial plane and two nitrogen atoms from a 4,4-bipyridine ligand in axial positions. The structure of compound 1 can be described a supramolecular 2D-like structure which was formed by the intermolecular π-stacking interactions between the neighboring chains of the aromatic rings of 4,4-bipyridine and 5-Brsalen molecules. UV-vis absorption spectrum, electrochemistry and magnetic properties of the compound 1 have also been studied.

Two exciton states in discrete and continuum alpha-helical proteins

International Nuclear Information System (INIS)

Latha, M.M.; Merlin, G.

2012-01-01

The dynamics of alpha-helical proteins is described by proposing a model Hamiltonian representing two exciton bound states. The dynamics is studied by constructing the equations of motion using a two exciton eigen-function in the discrete level. A numerical analysis shows the existence of two excitons in alpha-helical proteins and its propagation as solitons along the hydrogen bonding spines. The lattice model is also treated in the continuum limit which is a valid approximation in the low temperature, long wavelength limit. The resulting equation is studied using the multiple scale perturbation analysis which also shows the transfer of two exciton energy through alpha-helical proteins in the form of solitons with no change in velocity and amplitude. -- Highlights: ► The dynamics of alpha-helical proteins with two exciton states is studied. ► The dynamics is studied both in the discrete and continuum levels. ► The resulting equations are solved numerically and analytically. ► The solution supports the propagation of the energy in the form of solitons.

New modular heliotron system compatible with closed helical divertor and good plasma confinement

International Nuclear Information System (INIS)

Yamazaki, K.; Watanabe, K.Y.

1995-01-01

A new helical system ('modular heliotron') with improved modular coils compatible with an efficient closed helical divertor and a good plasma confinement property is proposed, based on a heliotron system with continuous helical coils and one pair of poloidal coils. The physics optimization of this system as a function of the gap angle between adjacent modular coils has been carried out by means of vacuum magnetic surface calculations and finite-beta plasma analyses, and a new improved coil system is invented by combining sectored helical field coils with sectored returning poloidal field coils. A modular heliotron with standard coil winding law (the reference modular heliotron) was previously proposed, but it is found that this was not appropriate to keep a clean helical divertor and high beta configuration when the coil gap becomes large. By modulating the modular coil winding with outside-plus and inside-minus pitch modulation, almost the same good magnetic configuration as that of a conventional heliotron can be produced. The optimal gap angle is determined as a function of the modulation parameter. This improved modular heliotron permits a larger gap angle between adjacent modules and produces a cleaner helical divertor configuration than the reference modular heliotron. All these helical systems are created by only modular coils without poloidal coils. (author). Letter-to-the-editor. 11 refs, 7 figs

Linked and knotted beams of light, conservation of helicity and the flow of null electromagnetic fields

International Nuclear Information System (INIS)

Irvine, William T M

2010-01-01

Maxwell's equations allow for some remarkable solutions consisting of pulsed beams of light which have linked and knotted field lines. The preservation of the topological structure of the field lines in these solutions has previously been ascribed to the fact that the electric and magnetic helicities, a measure of the degree of linking and knotting between field lines, are conserved. Here we show that the elegant evolution of the field is due to the stricter condition that the electric and magnetic fields be everywhere orthogonal. The field lines then satisfy a 'frozen field' condition and evolve as if they were unbreakable filaments embedded in a fluid. The preservation of the orthogonality of the electric and magnetic field lines is guaranteed for null, shear-free fields such as the ones considered here by a theorem of Robinson. We calculate the flow field of a particular solution and find it to have the form of a Hopf fibration moving at the speed of light in a direction opposite to the propagation of the pulsed light beam, a familiar structure in this type of solution. The difference between smooth evolution of individual field lines and conservation of electric and magnetic helicities is illustrated by considering a further example in which the helicities are conserved, but the field lines are not everywhere orthogonal. The field line configuration at time t = 0 corresponds to a nested family of torus knots but unravels upon evolution.

Structure and non-structure of centrosomal proteins.

Science.gov (United States)

Dos Santos, Helena G; Abia, David; Janowski, Robert; Mortuza, Gulnahar; Bertero, Michela G; Boutin, Maïlys; Guarín, Nayibe; Méndez-Giraldez, Raúl; Nuñez, Alfonso; Pedrero, Juan G; Redondo, Pilar; Sanz, María; Speroni, Silvia; Teichert, Florian; Bruix, Marta; Carazo, José M; Gonzalez, Cayetano; Reina, José; Valpuesta, José M; Vernos, Isabelle; Zabala, Juan C; Montoya, Guillermo; Coll, Miquel; Bastolla, Ugo; Serrano, Luis

2013-01-01

Here we perform a large-scale study of the structural properties and the expression of proteins that constitute the human Centrosome. Centrosomal proteins tend to be larger than generic human proteins (control set), since their genes contain in average more exons (20.3 versus 14.6). They are rich in predicted disordered regions, which cover 57% of their length, compared to 39% in the general human proteome. They also contain several regions that are dually predicted to be disordered and coiled-coil at the same time: 55 proteins (15%) contain disordered and coiled-coil fragments that cover more than 20% of their length. Helices prevail over strands in regions homologous to known structures (47% predicted helical residues against 17% predicted as strands), and even more in the whole centrosomal proteome (52% against 7%), while for control human proteins 34.5% of the residues are predicted as helical and 12.8% are predicted as strands. This difference is mainly due to residues predicted as disordered and helical (30% in centrosomal and 9.4% in control proteins), which may correspond to alpha-helix forming molecular recognition features (α-MoRFs). We performed expression assays for 120 full-length centrosomal proteins and 72 domain constructs that we have predicted to be globular. These full-length proteins are often insoluble: Only 39 out of 120 expressed proteins (32%) and 19 out of 72 domains (26%) were soluble. We built or retrieved structural models for 277 out of 361 human proteins whose centrosomal localization has been experimentally verified. We could not find any suitable structural template with more than 20% sequence identity for 84 centrosomal proteins (23%), for which around 74% of the residues are predicted to be disordered or coiled-coils. The three-dimensional models that we built are available at http://ub.cbm.uam.es/centrosome/models/index.php.

What Helicity Can Tell Us about Solar Magnetic Fields Alexei A ...

Indian Academy of Sciences (India)

Concept of magnetic/current helicity was introduced to solar physics about 15 ... represented by a thin flux tube model with flux , one can show that magnetic helicity,. Hm = (2π). −1 2 ... For example, spiral pattern of filaments forming sunspot ...

Institute for Fusion Research and Large Helical Device program

International Nuclear Information System (INIS)

Iiyoshi, Atsuo

1989-01-01

In the research on nuclear fusion, the final objective is to materialize nuclear fusion reactors, and for the purpose, it is necessary to cause nuclear combustion by making the plasma of higher than 100 million deg and confine it for a certain time. So far in various universities, the researches on diversified fusion processes have been advanced, but in February, 1986, the Science Council issued the report 'Nuclear fusion research in universities hereafter'. As the next large scale device, an external conductor system helical device was decided, and it is desirable to found the organization for joint utilization by national universities to promote the project. The researches on the other processes are continued by utilizing the existing facilitie. The reason of selecting a helical device is the data base of the researches carried out so far can be utilized sufficiently, it is sufficiently novel even after 10 years from now, and many researchers can be collected. The place of the research is Toki City, Gifu Prefecture, where the Institute of Plasma Physics, Nagoya University, is to be moved. The basic concept of the superconducting helical device project, the trend of nuclear fusion development in the world, the physical research using a helical system and so on are reported. (Kako, I.)

A structural framework for a near-minimal form of life: mass and compositional analysis of the helical mollicute Spiroplasma melliferum BC3.

Directory of Open Access Journals (Sweden)

Shlomo Trachtenberg

Full Text Available Spiroplasma melliferum is a wall-less bacterium with dynamic helical geometry. This organism is geometrically well defined and internally well ordered, and has an exceedingly small genome. Individual cells are chemotactic, polar, and swim actively. Their dynamic helicity can be traced at the molecular level to a highly ordered linear motor (composed essentially of the proteins fib and MreB that is positioned on a defined helical line along the internal face of the cell's membrane. Using an array of complementary, informationally overlapping approaches, we have taken advantage of this uniquely simple, near-minimal life-form and its helical geometry to analyze the copy numbers of Spiroplasma's essential parts, as well as to elucidate how these components are spatially organized to subserve the whole living cell. Scanning transmission electron microscopy (STEM was used to measure the mass-per-length and mass-per-area of whole cells, membrane fractions, intact cytoskeletons and cytoskeletal components. These local data were fit into whole-cell geometric parameters determined by a variety of light microscopy modalities. Hydrodynamic data obtained by analytical ultracentrifugation allowed computation of the hydration state of whole living cells, for which the relative amounts of protein, lipid, carbohydrate, DNA, and RNA were also estimated analytically. Finally, ribosome and RNA content, genome size and gene expression were also estimated (using stereology, spectroscopy and 2D-gel analysis, respectively. Taken together, the results provide a general framework for a minimal inventory and arrangement of the major cellular components needed to support life.

Point contacts and localization in generic helical liquids

Science.gov (United States)

Orth, Christoph P.; Strübi, Grégory; Schmidt, Thomas L.

2013-10-01

We consider two helical liquids on opposite edges of a two-dimensional topological insulator, which are connected by one or several local tunnel junctions. In the presence of spatially inhomogeneous Rashba spin-orbit coupling, the spin of the helical edge states is momentum dependent, and this spin texture can be different on opposite edges. We demonstrate that this has a strong impact on the electron transport between the edges. In particular, in the case of many random tunnel contacts, the localization length depends strongly on the spin textures of the edge states.

Electrical resistivity and dielectric properties of helical microorganism cells coated with silver by electroless plating

Energy Technology Data Exchange (ETDEWEB)

Cai, Jun, E-mail: jun_cai@buaa.edu.cn [Bionic and Micro/Nano/Bio Manufacturing Technology Research Center, School of Mechanical Engineering and Automation, Beihang University, Beijing 100191 (China); Lan, Mingming; Zhang, Deyuan; Zhang, Wenqiang [Bionic and Micro/Nano/Bio Manufacturing Technology Research Center, School of Mechanical Engineering and Automation, Beihang University, Beijing 100191 (China)

2012-09-01

Highlights: Black-Right-Pointing-Pointer We use the microorganism cells as forming templates to fabricate the bio-based conductive particles. Black-Right-Pointing-Pointer The microorganism cells selected as forming templates are Spirulina platens, which are of natural helical shape and high aspect ratio. Black-Right-Pointing-Pointer The sliver-coated Spirulina cells are a kind of lightweight conductive particles. Black-Right-Pointing-Pointer The composites containing sliver-coated Spirulina cells exhibit a lower percolation value. - Abstract: In this paper, microorganism cells (Spirulina platens) were used as forming templates for the fabrication of the helical functional particles by electroless silver plating process. The morphologies and ingredients of the coated Spirulina cells were analyzed with scanning electron microscopy and energy dispersive spectrometer. The crystal structures were characterized by employing the X-ray diffraction. The electrical resistivity and dielectric properties of samples containing different volume faction of sliver-coated Spirulina cells were measured and investigated by four-probe meter and vector network analyzer. The results showed that the Spirulina cells were successfully coated with a uniform silver coating and their initial helical shapes were perfectly kept. The electrical resistivity and dielectric properties of the samples had a strong dependence on the volume content of sliver-coated Spirulina cells and the samples could achieve a low percolation value owing to high aspect ratio and preferable helical shape of Spirulina cells. Furthermore, the conductive mechanism was analyzed with the classic percolation theory, and the values of {phi}{sub c} and t were obtained.

Plasma transport simulation modelling for helical confinement systems

International Nuclear Information System (INIS)

Yamazaki, K.; Amano, T.

1992-01-01

New empirical and theoretical transport models for helical confinement systems are developed on the basis of the neoclassical transport theory, including the effect of the radial electric field and of multi-helicity magnetic components as well as the drift wave turbulence transport for electrostatic and electromagnetic modes or the anomalous semi-empirical transport. These electron thermal diffusivities are compared with experimental data from the Compact Helical System which indicate that the central transport coefficient of a plasma with electron cyclotron heating agrees with neoclassical axisymmetric value and the transport outside the half-radius is anomalous. On the other hand, the transport of plasmas with neutral beam injection heating is anomalous in the whole plasma region. This anomaly is not explained by the electrostatic drift wave turbulence models in these discharges with flat density profiles. For a detailed prediction of the plasma parameters in the Large Helical Device (LHD), 3-D equilibrium/1-D transport simulations including empirical or drift wave turbulence models are performed which suggest that the global confinement time of the LHD is determined mainly by the electron anomalous transport in the plasma edge region rather than by the helical ripple transport in the core region. Even if the ripple loss can be eliminated, the increase in global confinement is 10%. However, the rise in the central ion temperature is more than 20%. If the anomalous loss can be reduced to half of the value used in the present scaling, as is the case in the H-mode of tokamak discharges, the neoclassical ripple loss through the ion channel becomes important even in the plasma core. The 5% radial inward shift of the plasma column with respect to the major radius improves the plasma confinement and increases the fusion product by more than 50% by reducing the neoclassical asymmetric ion transport loss and increasing the plasma radius (10%). (author). 32 refs, 7 figs

Probing conserved helical modules of portal complexes by mass spectrometry-based hydrogen/deuterium exchange.

Science.gov (United States)

Kang, Sebyung; Poliakov, Anton; Sexton, Jennifer; Renfrow, Matthew B; Prevelige, Peter E

2008-09-05

The Double-stranded DNA bacteriophage P22 has a ring-shaped dodecameric complex composed of the 84 kDa portal protein subunit that forms the central channel of the phage DNA packaging motor. The overall morphology of the P22 portal complex is similar to that of the portal complexes of Phi29, SPP1, T3, T7 phages and herpes simplex virus. Secondary structure prediction of P22 portal protein and its threading onto the crystal structure of the Phi29 portal complexes suggested that the P22 portal protein complex shares conserved helical modules that were found in the dodecameric interfaces of the Phi29 portal complex. To identify the amino acids involved in intersubunit contacts in the P22 portal ring complexes and validate the threading model, we performed comparative hydrogen/deuterium exchange analysis of monomeric and in vitro assembled portal proteins of P22 and the dodecameric Phi29 portal. Hydrogen/deuterium exchange experiments provided evidence of intersubunit interactions in the P22 portal complex similar to those in the Phi29 portal that map to the regions predicted to be conserved helical modules.

The helical ventricular myocardial band: global, three-dimensional, functional architecture of the ventricular myocardium.

Science.gov (United States)

Kocica, Mladen J; Corno, Antonio F; Carreras-Costa, Francesc; Ballester-Rodes, Manel; Moghbel, Mark C; Cueva, Clotario N C; Lackovic, Vesna; Kanjuh, Vladimir I; Torrent-Guasp, Francisco

2006-04-01

We are currently witnessing the advent of new diagnostic tools and therapies for heart diseases, but, without serious scientific consensus on fundamental questions about normal and diseased heart structure and function. During the last decade, three successive, international, multidisciplinary symposia were organized in order to setup fundamental research principles, which would allow us to make a significant step forward in understanding heart structure and function. Helical ventricular myocardial band of Torrent-Guasp is the revolutionary new concept in understanding global, three-dimensional, functional architecture of the ventricular myocardium. This concept defines the principal, cumulative vectors, integrating the tissue architecture (i.e. form) and net forces developed (i.e. function) within the ventricular mass. Here we expose the compendium of Torrent-Guasp's half-century long functional anatomical investigations in the light of ongoing efforts to define the integrative approach, which would lead to new understanding of the ventricular form and function by linking across multiple scales of biological organization, as defined in ongoing Physiome project. Helical ventricular myocardial band of Torrent-Guasp may also, hopefully, allow overcoming some difficulties encountered in contemporary efforts to create a comprehensive mathematical model of the heart.

Local and nonlocal advected invariants and helicities in magnetohydrodynamics and gas dynamics I: Lie dragging approach

International Nuclear Information System (INIS)

Webb, G M; Dasgupta, B; McKenzie, J F; Hu, Q; Zank, G P

2014-01-01

In this paper advected invariants and conservation laws in ideal magnetohydrodynamics (MHD) and gas dynamics are obtained using Lie dragging techniques. There are different classes of invariants that are advected or Lie dragged with the flow. Simple examples are the advection of the entropy S (a 0-form), and the conservation of magnetic flux (an invariant 2-form advected with the flow). The magnetic flux conservation law is equivalent to Faraday's equation. The gauge condition for the magnetic helicity to be advected with the flow is determined. Different variants of the helicity in ideal fluid dynamics and MHD including: fluid helicity, cross helicity and magnetic helicity are investigated. The fluid helicity conservation law and the cross-helicity conservation law in MHD are derived for the case of a barotropic gas. If the magnetic field lies in the constant entropy surface, then the gas pressure can depend on both the entropy and the density. In these cases the conservation laws are local conservation laws. For non-barotropic gases, we obtain nonlocal conservation laws for fluid helicity and cross helicity by using Clebsch variables. These nonlocal conservation laws are the main new results of the paper. Ertel's theorem and potential vorticity, the Hollman invariant, and the Godbillon–Vey invariant for special flows for which the magnetic helicity is zero are also discussed. (paper)

Design and testing of a coil-unit barrel for helical coil electromagnetic launcher

Science.gov (United States)

Yang, Dong; Liu, Zhenxiang; Shu, Ting; Yang, Lijia; Ouyang, Jianming

2018-01-01

A coil-unit barrel for a helical coil electromagnetic launcher is described. It provides better features of high structural strength and flexible adjustability. It is convenient to replace the damaged coil units and easy to adjust the number of turns in the stator coils due to the modular design. In our experiments, the highest velocity measured for a 4.5-kg projectile is 47.3 m/s and the mechanical reinforcement of the launcher could bear 35 kA peak current. The relationship between the energy conversion efficiency and the inductance gradient of the launcher is also studied. In the region of low inductance gradient, the efficiency is positively correlated with the inductance gradient. However, in the region of high inductance gradient, the inter-turn arc erosion becomes a major problem of limiting the efficiency and velocity of the launcher. This modular barrel allows further studies in the inter-turn arc and the variable inductance gradient helical coil launcher.

Silver baits for the "miraculous draught" of amphiphilic lanthanide helicates.

Science.gov (United States)

Terazzi, Emmanuel; Guénée, Laure; Varin, Johan; Bocquet, Bernard; Lemonnier, Jean-François; Emery, Daniel; Mareda, Jiri; Piguet, Claude

2011-01-03

The axial connection of flexible thioalkyls chains of variable length (n=1-12) within the segmental bis-tridentate 2-benzimidazole-8-hydroxyquinoline ligands [L12(Cn) -2 H](2-) provides amphiphilic receptors designed for the synthesis of neutral dinuclear lanthanides helicates. However, the stoichiometric mixing of metals and ligands in basic media only yields intricate mixtures of poorly soluble aggregates. The addition of Ag(I) in solution restores classical helicate architectures for n=3, with the quantitative formation of the discrete D(3) -symmetrical [Ln(2) Ag2(L12(C3) -2 H)(3) ](2+) complexes at millimolar concentration (Ln=La, Eu, Lu). The X-ray crystal structure supports the formation of [La(2) Ag(2) (L12(C3) -2 H)(3) ][OTf](2) , which exists in the solid state as infinite linear polymers bridged by S-Ag-S bonds. In contrast, molecular dynamics (MD) simulations in the gas phase and in solution confirm the experimental diffusion measurements, which imply the formation of discrete molecular entities in these media, in which the sulfur atoms of each lipophilic ligand are rapidly exchanged within the Ag(I) coordination sphere. Turned as a predictive tool, MD suggests that this Ag(I) templating effect is efficient only for n=1-3, while for n>3 very loose interactions occur between Ag(I) and the thioalkyl residues. The subsequent experimental demonstration that only 25 % of the total ligand speciation contributes to the formation of [Ln(2) Ag(2) (L12(C12) -2 H)(3) ](2+) in solution puts the bases for a rational approach for the design of amphiphilic helical complexes with predetermined molecular interfaces. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A semi-analytical study on helical springs made of shape memory polymer

International Nuclear Information System (INIS)

Baghani, M; Naghdabadi, R; Arghavani, J

2012-01-01

In this paper, the responses of shape memory polymer (SMP) helical springs under axial force are studied both analytically and numerically. In the analytical solution, we first derive the response of a cylindrical tube under torsional loadings. This solution can be used for helical springs in which both the curvature and pitch effects are negligible. This is the case for helical springs with large ratios of the mean coil radius to the cross sectional radius (spring index) and also small pitch angles. Making use of this solution simplifies the analysis of the helical springs to that of the torsion of a straight bar with circular cross section. The 3D phenomenological constitutive model recently proposed for SMPs is also reduced to the 1D shear case. Thus, an analytical solution for the torsional response of SMP tubes in a full cycle of stress-free strain recovery is derived. In addition, the curvature effect is added to the formulation and the SMP helical spring is analyzed using the exact solution presented for torsion of curved SMP tubes. In this modified solution, the effect of the direct shear force is also considered. In the numerical analysis, the 3D constitutive equations are implemented in a finite element program and a full cycle of stress-free strain recovery of an SMP (extension or compression) helical spring is simulated. Analytical and numerical results are compared and it is shown that the analytical solution gives accurate stress distributions in the cross section of the helical SMP spring besides the global load–deflection response. Some case studies are presented to show the validity of the presented analytical method. (paper)

N-terminal diproline and charge group effects on the stabilization of helical conformation in alanine-based short peptides: CD studies with water and methanol as solvent.

Science.gov (United States)

Goyal, Bhupesh; Srivastava, Kinshuk Raj; Durani, Susheel

2017-06-01

Protein folding problem remains a formidable challenge as main chain, side chain and solvent interactions remain entangled and have been difficult to resolve. Alanine-based short peptides are promising models to dissect protein folding initiation and propagation structurally as well as energetically. The effect of N-terminal diproline and charged side chains is assessed on the stabilization of helical conformation in alanine-based short peptides using circular dichroism (CD) with water and methanol as solvent. A1 (Ac-Pro-Pro-Ala-Lys-Ala-Lys-Ala-Lys-Ala-NH 2 ) is designed to assess the effect of N-terminal homochiral diproline and lysine side chains to induce helical conformation. A2 (Ac-Pro-Pro-Glu-Glu-Ala-Ala-Lys-Lys-Ala-NH 2 ) and A3 (Ac-dPro-Pro-Glu-Glu-Ala-Ala-Lys-Lys-Ala-NH 2 ) with N-terminal homochiral and heterochiral diproline, respectively, are designed to assess the effect of Glu...Lys (i, i + 4) salt bridge interactions on the stabilization of helical conformation. The CD spectra of A1, A2 and A3 in water manifest different amplitudes of the observed polyproline II (PPII) signals, which indicate different conformational distributions of the polypeptide structure. The strong effect of solvent substitution from water to methanol is observed for the peptides, and CD spectra in methanol evidence A2 and A3 as helical folds. Temperature-dependent CD spectra of A1 and A2 in water depict an isodichroic point reflecting coexistence of two conformations, PPII and β-strand conformation, which is consistent with the previous studies. The results illuminate the effect of N-terminal diproline and charged side chains in dictating the preferences for extended-β, semi-extended PPII and helical conformation in alanine-based short peptides. The results of the present study will enhance our understanding on stabilization of helical conformation in short peptides and hence aid in the design of novel peptides with helical structures. Copyright © 2017 European Peptide

LARGE-SCALE MAGNETIC HELICITY FLUXES ESTIMATED FROM MDI MAGNETIC SYNOPTIC CHARTS OVER THE SOLAR CYCLE 23

Energy Technology Data Exchange (ETDEWEB)

Yang Shangbin; Zhang Hongqi, E-mail: yangshb@nao.cas.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing (China)

2012-10-10

To investigate the characteristics of large-scale and long-term evolution of magnetic helicity with solar cycles, we use the method of Local Correlation Tracking to estimate the magnetic helicity evolution over solar cycle 23 from 1996 to 2009 using 795 MDI magnetic synoptic charts. The main results are as follows: the hemispheric helicity rule still holds in general, i.e., the large-scale negative (positive) magnetic helicity dominates the northern (southern) hemisphere. However, the large-scale magnetic helicity fluxes show the same sign in both hemispheres around 2001 and 2005. The global, large-scale magnetic helicity flux over the solar disk changes from a negative value at the beginning of solar cycle 23 to a positive value at the end of the cycle, while the net accumulated magnetic helicity is negative in the period between 1996 and 2009.

LARGE-SCALE MAGNETIC HELICITY FLUXES ESTIMATED FROM MDI MAGNETIC SYNOPTIC CHARTS OVER THE SOLAR CYCLE 23

International Nuclear Information System (INIS)

Yang Shangbin; Zhang Hongqi

2012-01-01

To investigate the characteristics of large-scale and long-term evolution of magnetic helicity with solar cycles, we use the method of Local Correlation Tracking to estimate the magnetic helicity evolution over solar cycle 23 from 1996 to 2009 using 795 MDI magnetic synoptic charts. The main results are as follows: the hemispheric helicity rule still holds in general, i.e., the large-scale negative (positive) magnetic helicity dominates the northern (southern) hemisphere. However, the large-scale magnetic helicity fluxes show the same sign in both hemispheres around 2001 and 2005. The global, large-scale magnetic helicity flux over the solar disk changes from a negative value at the beginning of solar cycle 23 to a positive value at the end of the cycle, while the net accumulated magnetic helicity is negative in the period between 1996 and 2009.

Extracting 3D parametric curves from 2D images of helical objects.

OpenAIRE

Willcocks, Chris; Jackson, Philip T.G.; Nelson, Carl J.; Obara, Boguslaw

2016-01-01

Helical objects occur in medicine, biology, cosmetics, nanotechnology, and engineering. Extracting a 3D parametric curve from a 2D image of a helical object has many practical applications, in particular being able to extract metrics such as tortuosity, frequency, and pitch. We present a method that is able to straighten the image object and derive a robust 3D helical curve from peaks in the object boundary. The algorithm has a small number of stable parameters that require little tuning, and...

Development of Integrated Simulation System for Helical Plasmas

Energy Technology Data Exchange (ETDEWEB)

Nakamura, Y.; Yokoyama, M.; Nakajima, N.; Fukuyama, A.; Watanabe, K. Y.; Funaba, H.; Suzuki, Y.; Murakami, S.; Ida, K.; Sakakibara, S.; Yamada, H.

2005-07-01

Recent progress of computers (parallel/vector-parallel computers, PC clusters, for example) and numerical codes for helical plasmas like three-dimensional MHD equilibrium codes, combined with the development of the plasma diagnostics technique, enable us to do the detailed theoretical analyses of the individual experimental observations. Now, it is pointed out that the experimental data analysis from the viewpoints of integrated physics is an important issue to understand the confinement physics globally. In addition to that, there are international movements towards the integrated numerical simulation study. One is several proposals of integrated modeling of burning tokamak plasmas, motivated by the ITER activity. The integrated numerical simulation will be a good help to draw up new experimental plans especially for burning plasma experiments. Another movement is international collaborations on the confinement database and neoclassical transport in helical plasmas/stellarators. These backgrounds motivate us to start the development of the integrated simulation system which has a modular structure and user-friendly interfaces. The integrated simulation system, which is based on the hierarchical and multi-scale (time and space) modeling, will also be a platform for theoreticians to test their own model such as turbulent transport model. In this paper, we will show the strategy of developing the integrated simulation system and present status of the development. Especially, we discuss the modeling of the time evolution of the plasma net current profile, which is equivalent to the time evolution of the rotational transform profile, in the resistive time scale. (Author)