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Sample records for short-period pulse helical

  1. Demonstration of a high-field short-period superconducting helical undulator suitable for future TeV-scale linear collider positron sources.

    PubMed

    Scott, D J; Clarke, J A; Baynham, D E; Bayliss, V; Bradshaw, T; Burton, G; Brummitt, A; Carr, S; Lintern, A; Rochford, J; Taylor, O; Ivanyushenkov, Y

    2011-10-21

    The first demonstration of a full-scale working undulator module suitable for future TeV-scale positron-electron linear collider positron sources is presented. Generating sufficient positrons is an important challenge for these colliders, and using polarized e(+) would enhance the machine's capabilities. In an undulator-based source polarized positrons are generated in a metallic target via pair production initiated by circularly polarized photons produced in a helical undulator. We show how the undulator design is developed by considering impedance effects on the electron beam, modeling and constructing short prototypes before the successful fabrication, and testing of a final module.

  2. Long-pulse plasma discharge on the Large Helical Device

    NASA Astrophysics Data System (ADS)

    Kumazawa, R.; Mutoh, T.; Saito, K.; Seki, T.; Nakamura, Y.; Kubo, S.; Shimozuma, T.; Yoshimura, Y.; Igami, H.; Ohkubo, K.; Takeiri, Y.; Oka, Y.; Tsumori, K.; Osakabe, M.; Ikeda, K.; Nagaoka, K.; Kaneko, O.; Miyazawa, J.; Morita, S.; Narihara, K.; Shoji, M.; Masuzaki, S.; Kobayashi, M.; Ogawa, H.; Goto, M.; Morisaki, T.; Peterson, B. J.; Sato, K.; Tokuzawa, T.; Ashikawa, N.; Nishimura, K.; Funaba, H.; Chikaraishi, H.; Watari, T.; Watanabe, T.; Sakamoto, M.; Ichimura, M.; Takase, Y.; Notake, T.; Takeuchi, N.; Torii, Y.; Shimpo, F.; Nomura, G.; Takahashi, C.; Yokota, M.; Kato, A.; Zhao, Y.; Kwak, J. G.; Yoon, J. S.; Yamada, H.; Kawahata, K.; Ohyabu, N.; Ida, K.; Nagayama, Y.; Noda, N.; Komori, A.; Sudo, S.; Motojima, O.; LHD experiment Group

    2006-03-01

    A long-pulse plasma discharge of more than 30 min duration was achieved on the Large Helical Device (LHD). A plasma of ne = 0.8 × 1019 m-3 and Ti0 = 2.0 keV was sustained with PICH = 0.52 MW, PECH = 0.1 MW and averaged PNBI = 0.067 MW. The total injected heating energy was 1.3 GJ. One of the keys to the success of the experiment was a dispersion of the local plasma heat load to divertors, accomplished by sweeping the magnetic axis inward and outward. Causes limiting the long pulse plasma discharge are discussed. An ion impurity penetration limited further long-pulse discharge in the 8th experimental campaign (2004).

  3. Full-wave simulations on ultrashort-pulse reflectometry for helical plasmas

    SciTech Connect

    Hojo, H.; Fukuchi, A.; Itakura, A.; Mase, A.

    2004-10-01

    The full-wave simulations on ultrashort-pulse reflectometry for helical plasmas are studied based on the FDTD method in two dimensions. The propagation of an ultrashort-pulse electromagnetic wave is computed in helical plasmas modeled for the Large Helical Device magnetic field configuration. The density-profile reconstruction is performed by the Abel inversion method with the time delay data for the reflected waves from plasma, and it is shown that the reconstructed density profile coincides well with the original profile.

  4. Increasing the magnetic helicity content of a plasma by pulsing a magnetized source.

    PubMed

    Woodruff, S; Stallard, B W; McLean, H S; Hooper, E B; Bulmer, R; Cohen, B I; Hill, D N; Holcomb, C T; Moller, J; Wood, R D

    2004-11-12

    By operating a magnetized coaxial gun in a pulsed mode it is possible to produce large voltage pulses of duration approximately 500 mus while reaching a few kV, giving a discrete input of helicity into a spheromak. In the sustained spheromak physics experiment (SSPX), it is observed that pulsing serves to nearly double the stored magnetic energy and double the temperature. We discuss these results by comparison with 3D MHD simulations of the same phenomenon.

  5. The origin of short-period comets

    SciTech Connect

    Bailey, M.E.; Stagg, C.R. Calgary Univ. )

    1990-07-01

    If the observed number of short-period comets can be accounted for by a spherically symmetric model of the Oort cloud, in conjunction with an inner core of merely moderate central concentration, then the observed correlation between the ecliptic plane and the inclinations of Jupiter-family short-period comets may be seen as partly due to the calculated decrease in capture probability with inclination, and partly to the effects of cometary decay and observational selection. The implied constraint on the inner core becomes even more severe, if a hypothetical comet disk in the Uranus-Neptune zone either makes a significant contribution to the observed short-period comets or if these comets' mean lifetime is greater than 3000 years. 32 refs.

  6. Rotational swashplate pulse continuously variable transmission based on helical gear axial meshing transmission

    NASA Astrophysics Data System (ADS)

    Sun, Jiandong; Fu, Wenyu; Lei, Hong; Tian, E.; Liu, Ziping

    2012-11-01

    The current research on pulse continuously variable transmission(CVT) is mainly focused on reducing the pulse degree and making pulse degrees a constant value. Current research mainly confined to find out new design parameters by using the method of optimization, and reduce the pulse degree of pulse CVT and its range of variation. But the fact is that the reduction of the pulse degree is not significant. This article presents a new structure of mechanical pulse CVT—the rotational swashplate pulse CVT with driven by helical gear axial meshing. This transmission is simple and compact in structure and low in pulsatile rate (it adopts 6 guide rods), and the pulsatile degree is irrelevant to the transmission ratio. Theoretically, pulsatile rate could be reduced to zero if appropriate curved surface of the swashplate is used. Compared with the connecting rod pulse CVT, the present structure uses helical gear mechanism as transmission part and it avoids unbalanced inertial force in the former model. This paper analyzes the principle of driving of this transmission, presents its mechanical structure, and discusses its motion characteristics. Experimental prototype of this type of CVT has been manufactured. Tests for the transmission efficiency(when the rotational speed of the output shaft is the maximum) and the angular velocity of the output shaft have been carried out, and data have been analyzed. The experimental results show that the speed of the output shaft for the experimental prototype is slightly lower than the theoretical value, and the transmission efficiency of the experimental prototype is about 70%. The pulse degree of the CVT discussed in this paper is less than the existing pulse CVT of other types, and it is irrelevant to the transmission ratio of the CVT. The research provides the new idea to the CVT study.

  7. Flux amplification and sustainment of ST plasmas by multi-pulsed coaxial helicity injection on HIST

    NASA Astrophysics Data System (ADS)

    Higashi, T.; Ishihara, M.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

    2010-11-01

    The Helicity Injected Spherical Torus (HIST) device has been developed towards high-current start up and sustainment by Multi-pulsed Coaxial Helicity Injection (M-CHI) method. Multiple pulses operation of the coaxial plasma gun can build the magnetic field of STs and spheromak plasmas in a stepwise manner. So far, successive gun pulses on SSPX at LLNL were demonstrated to maintain the magnetic field of spheromak in a quasi-steady state against resistive decay [1]. The resistive 3D-MHD numerical simulation [2] for STs reproduced the current amplification by the M-CHI method and confirmed that stochastic magnetic field was reduced during the decay phase. By double pulsed operation on HIST, the plasma current was effectively amplified against the resistive decay. The life time increases up to 10 ms which is longer than that in the single CHI case (4 ms). The edge poloidal fields last between 0.5 ms and 6 ms like a repetitive manner. During the second driven phase, the toroidal ion flow is driven in the same direction as the plasma current as well as in the initial driven phase. At the meeting, we will discuss a current amplification mechanism based on the merging process with the plasmoid injected secondly from the gun. [1] B. Hudson et al., Phys. Plasmas Vol.15, 056112 (2008). [2] Y. Kagei et al., J. Plasma Fusion Res. Vol.79, 217 (2003).

  8. Mechanisms of amplification of ultrashort electromagnetic pulses in gyrotron traveling wave tube with helically corrugated waveguide

    NASA Astrophysics Data System (ADS)

    Ginzburg, N. S.; Zotova, I. V.; Sergeev, A. S.; Zaslavsky, V. Yu.; Zheleznov, I. V.; Samsonov, S. V.; Mishakin, S. V.

    2015-11-01

    A time-domain self consistent theory of a gyrotron traveling wave tube with a helically corrugated operating waveguide has been developed. Based on this model, the process of short pulse amplification was studied in regimes of grazing and intersection of the dispersion curves of the electromagnetic wave and the electron beam. In the first case, the possibility of amplification without pulse form distortion was demonstrated for the pulse spectrum width of the order of the gain bandwidth. In the second case, when the electrons' axial velocity was smaller than the wave's group velocity, it was shown that the slippage of the incident signal with respect to the electron beam provides feeding of the signal by "fresh" electrons without initial modulation. As a result, the amplitude of the output pulse can exceed the amplitude of its saturated value for the case of the grazing regime, and, for optimal parameters, the peak output power can be even larger than the kinetic power of the electron beam.

  9. Mechanisms of amplification of ultrashort electromagnetic pulses in gyrotron traveling wave tube with helically corrugated waveguide

    SciTech Connect

    Ginzburg, N. S. Zaslavsky, V. Yu.; Zotova, I. V.; Sergeev, A. S.; Zheleznov, I. V.; Samsonov, S. V.; Mishakin, S. V.

    2015-11-15

    A time-domain self consistent theory of a gyrotron traveling wave tube with a helically corrugated operating waveguide has been developed. Based on this model, the process of short pulse amplification was studied in regimes of grazing and intersection of the dispersion curves of the electromagnetic wave and the electron beam. In the first case, the possibility of amplification without pulse form distortion was demonstrated for the pulse spectrum width of the order of the gain bandwidth. In the second case, when the electrons' axial velocity was smaller than the wave's group velocity, it was shown that the slippage of the incident signal with respect to the electron beam provides feeding of the signal by “fresh” electrons without initial modulation. As a result, the amplitude of the output pulse can exceed the amplitude of its saturated value for the case of the grazing regime, and, for optimal parameters, the peak output power can be even larger than the kinetic power of the electron beam.

  10. Reconstruction of edge density profiles on Large Helical Device using ultrashort-pulse reflectometry.

    PubMed

    Yokota, Yuya; Mase, Atsushi; Kogi, Yuichiro; Tokuzawa, Tokihiko; Kawahata, Kazuo; Nagayama, Yoshio; Hojo, Hitoshi

    2008-10-01

    Reflectometry has been expected to be one of the key diagnostics to measure density profiles. We have applied an ultrashort-pulse reflectometry (USPR) system to Large Helical Device in the National Institute for Fusion Science. Wide frequency band system is required to obtain wide density profile since an incident wave is reflected at the density layer corresponding to its cutoff frequency. The reflectometry utilizes an impulse with less than 30 ps pulse width as a source. Since the bandwidth of an impulse has an inverse relation to the pulse width, we can cover the frequency range of micro- to millimeter waves (18-40 GHz) with a single source. The density profiles can be reconstructed by collecting time-of-flight (TOF) signals for each frequency component of an impulse reflected from the corresponding cutoff layer. We utilize the signal record analysis (SRA) method to reconstruct the density profiles from the TOF signal. The effectiveness of the SRA method for the profile reconstruction is confirmed by a simulation study of the USPR using a finite-difference time domain method.

  11. Nonlinear MHD simulation of current drive by multi-pulsed coaxial helicity injection in spherical torus

    NASA Astrophysics Data System (ADS)

    Kanki, Takashi; Nagata, Masayoshi; Kagei, Yasuhiro

    2011-10-01

    The dynamics of structures of magnetic field, current density, and plasma flow generated during multi-pulsed coaxial helicity injection in spherical torus is investigated by 3-D nonlinear MHD simulations. During the driven phase, the flux and current amplifications occur due to the merging and magnetic reconnection between the preexisting plasma in the confinement region and the ejected plasma from the gun region involving the n = 1 helical kink distortion of the central open flux column (COFC). Interestingly, the diamagnetic poloidal flow which tends toward the gun region is then observed due to the steep pressure gradients of the COFC generated by ohmic heating through an injection current winding around the inboard field lines, resulting in the formation of the strong poloidal flow shear at the interface between the COFC and the core region. This result is consistent with the flow shear observed in the HIST. During the decay phase, the configuration approaches the axisymmetric MHD equilibrium state without flow because of the dissipation of magnetic fluctuation energy to increase the closed flux surfaces, suggesting the generation of ordered magnetic field structure. The parallel current density λ concentrated in the COFC then diffuses to the core region so as to reduce the gradient in λ, relaxing in the direction of the Taylor state.

  12. Improving the output voltage waveform of an intense electron-beam accelerator based on helical type Blumlein pulse forming line

    NASA Astrophysics Data System (ADS)

    Cheng, Xin-Bing; Liu, Jin-Liang; Zhang, Hong-Bo; Feng, Jia-Huai; Qian, Bao-Liang

    2010-07-01

    The Blumlein pulse forming line (BPFL) consisting of an inner coaxial pulse forming line (PFL) and an outer coaxial PFL is widely used in the field of pulsed power, especially for intense electron-beam accelerators (IEBA). The output voltage waveform determines the quality and characteristics of the output beam current of the IEBA. Comparing with the conventional BPFL, an IEBA based on a helical type BPFL can increase the duration of the output voltage in the same geometrical volume. However, for the helical type BPFL, the voltage waveform on a matched load may be distorted which influences the electron-beam quality. In this paper, an IEBA based on helical type BPFL is studied theoretically. Based on telegrapher equations of the BPFL, a formula for the output voltage of IEBA is obtained when the transition section is taken into account, where the transition section is between the middle cylinder of BPFL and the load. From the theoretical analysis, it is found that the wave impedance and transit time of the transition section influence considerably the main pulse voltage waveform at the load, a step is formed in front of the main pulse, and a sharp spike is also formed at the end of the main pulse. In order to get a well-shaped square waveform at the load and to improve the electron-beam quality of such an accelerator, the wave impedance of the transition section should be equal to that of the inner PFL of helical type BPFL and the transit time of the transition section should be designed as short as possible. Experiments performed on an IEBA with the helical type BPFL show reasonable agreement with theoretical analysis.

  13. Preferred Hosts for Short-Period Exoplanets

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-12-01

    In an effort to learn more about how planets form around their host stars, a team of scientists has analyzed the population of Kepler-discovered exoplanet candidates, looking for trends in where theyre found.Planetary OccurrenceSince its launch in 2009, Kepler has found thousands of candidate exoplanets around a variety of star types. Especially intriguing is the large population of super-Earths and mini-Neptunes planets with masses between that of Earth and Neptune that have short orbital periods. How did they come to exist so close to their host star? Did they form in situ, or migrate inwards, or some combination of both processes?To constrain these formation mechanisms, a team of scientists led by Gijs Mulders (University of Arizona and NASAs NExSS coalition) analyzed the population of Kepler planet candidates that have orbital periods between 2 and 50 days.Mulders and collaborators used statistical reconstructions to find the average number of planets, within this orbital range, around each star in the Kepler field. They then determined how this planet occurrence rate changed for different spectral types and therefore the masses of the host stars: do low-mass M-dwarf stars host more or fewer planets than higher-mass, main-sequence F, G, or K stars?Challenging ModelsAuthors estimates for the occurrence rate for short-period planets of different radii around M-dwarfs (purple) and around F, G, and K-type stars (blue). [Mulders et al. 2015]The team found that M dwarfs, compared to F, G, or K stars, host about half as many large planets with orbital periods of P 50 days. But, surprisingly, they host significantly more small planets, racking up an average of 3.5 times the number of planets in the size range of 12.8 Earth-radii.Could it be that M dwarfs have a lower total mass of planets, but that mass is distributed into more, smaller planets? Apparently not: the authors show that the mass of heavy elements trapped in short-orbital-period planets is higher for M

  14. Effects of multi-pulsed coaxial helicity injection on dynamics of spherical torus

    NASA Astrophysics Data System (ADS)

    Kanki, T.; Nagata, M.; Kagei, Y.

    2012-10-01

    The mechanism to rebuild the magnetic fields and to amplify the currents in the high-q spherical torus (ST) by the multi-pulsed coaxial helicity injection is investigated using the resistive nonlinear 3D-MHD simulations. During the driven phase, the dynamics is almost axisymmetric because the magnetic fluctuation level of n=0 mode compared with other higher modes is much larger. The toroidal current It is effectively amplified due to the merging of plasmoid ejected from the gun region with the pre-existing ST in the confinement region. The poloidal flux is not significantly amplified because the current sheet generated by the merging process does not rapidly decay. The negative toroidal flow vt is then induced in the direction of It around the central open flux column (OFC) region by inductive toroidal electric field Et (=-vzBr) because of the plasmoid ejection. The strong poloidal flow vz (=ErBt) is also driven from the gun to confinement region due to the Lorentz force. As the result of vz, the flow vortices associated with the dynamo effect are caused around the upper confinement region. During the decay phase, the closed field lines are regenerated due to the dissipation of magnetic fluctuations. The helical distortion of the OFC becomes small, and then ordered magnetic field structures without flows are built. Just after turning off the external electric field, the poloidal flow from the confinement to gun region is caused by the pressure gradients. The parallel current density λ concentrated in the OFC diffuses to the core region, but does not relax in the direction of the Taylor state due to the pressure gradients.

  15. Detection of short-period global waves from nightglow observations

    NASA Astrophysics Data System (ADS)

    Shved, G. M.; Karpova, N. V.; Ammosov, P. P.; Gavrilyeva, G. A.; Perminov, V. I.; Semenov, A. I.

    2009-06-01

    Atmospheric temperature oscillations at similar frequencies have been detected in the spectra of variations in the rotational temperatures of the OH and O2 nighttime emissions, simultaneously observed at two spaced stations in the range of periods ˜1-3 h. These oscillations are probably caused by global waves: short-period solar tides and/or free oscillations of the atmosphere.

  16. Photoacoustic spectroscopy of short-period gyrotropic superlattices

    SciTech Connect

    Mityurich, G.S.; Starodubtsev, E.G.

    1994-12-31

    The Rosencwaig-Gersho photoacoustic transformation is extended to the case of the short-period superlattices formed by gytropic nonmagnetic cubic crystals. The potentialities of photoacoustic spectroscopy when applied to superlattices and the control of their parameters are considered. 18 refs., 4 figs.

  17. Analytic short period lunar and solar perturbations of artificial satellites.

    NASA Technical Reports Server (NTRS)

    Fisher, D.

    1972-01-01

    The short period luni-solar theory of Kozai is generalized for arbitrary obliquity of the ecliptic and inclination of the moon's orbit to the ecliptic. Analytic first order lunar perturbations to the elements are derived. The theory is illustrated by an application to the communication satellite Intelsat 3F3.

  18. Analytic short period lunar and solar perturbations of artificial satellites

    NASA Technical Reports Server (NTRS)

    Fisher, D.

    1972-01-01

    A short period luni-solar theory was generalized for application to arbitrary obliquity of the ecliptic and inclination of the moon's orbit to the ecliptic. Analytic first order lunar perturbations to the elements were derived. The theory is illustrated by an application to the communication satellite Intelsat 3F3.

  19. Autocovariance prediction of short period Earth rotation parameters.

    NASA Astrophysics Data System (ADS)

    Kosek, W.

    The autocovariance prediction of equidistant model and Earth Rotation Parameters (ERP) time series are presented. It enables computation of a forecast without any a priori information. It has been applied to short period polar motion and Length of Day (LOD) time series. The differences between the predicted short-period polar motion and LOD data computed for the 7th, 14th and 21st day in the future for different starting prediction epochs point out on irregular variations in Earth rotation. Similar computations were made using the autoregressive prediction method. The irregular (unpredictable) variations computed by the autoregressive prediction are very similar to those computed by the autocovariance prediction. The frequency and time-frequency analysis of these irregular variations shows that they affect oscillations with different periods from about 20 to ≡130 days and in different epochs.

  20. Generation of 3 GW microwave pulses in X-band from a combination of a relativistic backward-wave oscillator and a helical-waveguide compressor

    SciTech Connect

    Bratman, V. L.; Denisov, G. G.; Kolganov, N. G.; Mishakin, S. V.; Samsonov, S. V.; Cross, A. W.; He, W.; Zhang, L.; McStravick, M.; Whyte, C. G.; Young, A. R.; Ronald, K.; Robertson, C. W.; Phelps, A. D. R.

    2010-11-15

    The phenomenon of passive compression of frequency-modulated (FM) pulses in a dispersive media (DM) was used to increase the peak microwave power up to the multigigawatt level. A helically corrugated waveguide was used as the DM, while a relativistic X-band backward-wave oscillator (RBWO) with a descending-during-the-pulse accelerating voltage served as a source of FM pulses. Compression of pulses down to a halfwidth of 2.2 ns accompanied by a 4.5-fold power increase up to a value of about 3.2 GW has been demonstrated.

  1. Planetary perturbations and the origins of short-period comets

    SciTech Connect

    Quinn, T.; Tremaine, S.; Duncan, M. Queen's Univ., Kingston )

    1990-06-01

    To investigate the dynamical plausibility of possible sources for the short-period comets, a representative sample of comet orbits in the field of the sun and the giant planets was integrated, with the aim to determine whether the distribution of orbits from a proposed source that reach observable perihelia (q less than 2.5 AU) matches the observed distribution of short-period orbits. It is found that the majority of the short-period comets, those with orbital period P less than 20 yr (the Jupiter family), cannot arise from isotropic orbits with perihelia near Jupiter's orbit, because the resulting observable comet orbits have the wrong distribution in period, inclination, and argument of perihelion. The simulations also show that Jupiter-family comets cannot arise from isotropic orbits with perihelia in the Uranus-Neptune region. On the other hand, a source of low-inclination Neptune-crossing orbits yields a distribution of observable Jupiter-family comets that is consistent with the data in all respects. These results imply that the Jupiter-family comets arise from a disk source in the outer solar system rather than from the Oort comet cloud. 30 refs.

  2. Formation of Short-Period Binary Pulsars in Globular Clusters.

    PubMed

    Rasio; Pfahl; Rappaport

    2000-03-20

    We present a new dynamical scenario for the formation of short-period binary millisecond pulsars in globular clusters. Our work is motivated by the recent observations of 20 radio pulsars in 47 Tuc. In a dense cluster such as 47 Tuc, most neutron stars acquire binary companions through exchange interactions with primordial binaries. The resulting systems have semimajor axes in the range approximately 0.1-1 AU and neutron star companion masses approximately 1-3 M middle dot in circle. For many of these systems, we find that when the companion evolves off the main sequence and fills its Roche lobe, the subsequent mass transfer is dynamically unstable. This leads to a common envelope phase and the formation of short-period neutron star-white dwarf binaries. For a significant fraction of these binaries, the decay of the orbit due to gravitational radiation will be followed by a period of stable mass transfer driven by a combination of gravitational radiation and tidal heating of the companion. The properties of the resulting short-period binaries match well those of observed binary pulsars in 47 Tuc. PMID:10702129

  3. Planetary perturbations and the origins of short-period comets

    NASA Astrophysics Data System (ADS)

    Quinn, T.; Tremaine, S.; Duncan, M.

    1990-06-01

    To investigate the dynamical plausibility of possible sources for the short-period comets, a representative sample of comet orbits in the field of the sun and the giant planets was integrated, with the aim to determine whether the distribution of orbits from a proposed source that reach observable perihelia (q less than 2.5 AU) matches the observed distribution of short-period orbits. It is found that the majority of the short-period comets, those with orbital period P less than 20 yr (the 'Jupiter family'), cannot arise from isotropic orbits with perihelia near Jupiter's orbit, because the resulting observable comet orbits have the wrong distribution in period, inclination, and argument of perihelion. The simulations also show that Jupiter-family comets cannot arise from isotropic orbits with perihelia in the Uranus-Neptune region. On the other hand, a source of low-inclination Neptune-crossing orbits yields a distribution of observable Jupiter-family comets that is consistent with the data in all respects. These results imply that the Jupiter-family comets arise from a disk source in the outer solar system rather than from the Oort comet cloud.

  4. Ultra-short period binaries from the Catalina Surveys

    SciTech Connect

    Drake, A. J.; Djorgovski, S. G.; Graham, M. J.; Mahabal, A. A.; Donalek, C.; Williams, R.; García-Álvarez, D.; Catelan, M.; Torrealba, G.; Prieto, J. L.; Abraham, S.; Larson, S.; Christensen, E.

    2014-08-01

    We investigate the properties of 367 ultra-short period binary candidates selected from 31,000 sources recently identified from Catalina Surveys data. Based on light curve morphology, along with WISE, Sloan Digital Sky Survey, and GALEX multi-color photometry, we identify two distinct groups of binaries with periods below the 0.22 day contact binary minimum. In contrast to most recent work, we spectroscopically confirm the existence of M dwarf+M dwarf contact binary systems. By measuring the radial velocity variations for five of the shortest-period systems, we find examples of rare cool white dwarf (WD)+M dwarf binaries. Only a few such systems are currently known. Unlike warmer WD systems, their UV flux and optical colors and spectra are dominated by the M-dwarf companion. We contrast our discoveries with previous photometrically selected ultra-short period contact binary candidates and highlight the ongoing need for confirmation using spectra and associated radial velocity measurements. Overall, our analysis increases the number of ultra-short period contact binary candidates by more than an order of magnitude.

  5. CLATHRATE HYDRATES FORMATION IN SHORT-PERIOD COMETS

    SciTech Connect

    Marboeuf, Ulysse; Mousis, Olivier; Petit, Jean-Marc; Schmitt, Bernard

    2010-01-01

    The initial composition of current models of cometary nuclei is only based on two forms of ice: crystalline ice for long-period comets and amorphous ice for short-period comets. A third form of ice, i.e., clathrate hydrate, could exist within the short-period cometary nuclei, but the area of formation of this crystalline structure in these objects has never been studied. Here, we show that the thermodynamic conditions in the interior of short-period comets allow the existence of clathrate hydrates in Halley-type comets. We show that their existence is viable in the Jupiter family comets only when the equilibrium pressure of CO clathrate hydrate is at least 1 order of magnitude lower than the usually assumed theoretical value. We calculate that the amount of volatiles that could be trapped in the clathrate hydrate layer may be orders of magnitude greater than the daily amount of gas released at the surface of the nucleus at perihelion. The formation and the destruction of the clathrate hydrate cages could then explain the diversity of composition of volatiles observed in comets, as well as some pre-perihelion outbursts. We finally show that the potential clathrate hydrate layer in comet 67P/Churyumov-Gerasimenko would, unfortunately, be deep inside the nucleus, out of reach of the Rosetta lander. However, such a clathrate hydrate layer would show up by the gas composition of the coma.

  6. Formation of Short-Period Binary Pulsars in Globular Clusters.

    PubMed

    Rasio; Pfahl; Rappaport

    2000-03-20

    We present a new dynamical scenario for the formation of short-period binary millisecond pulsars in globular clusters. Our work is motivated by the recent observations of 20 radio pulsars in 47 Tuc. In a dense cluster such as 47 Tuc, most neutron stars acquire binary companions through exchange interactions with primordial binaries. The resulting systems have semimajor axes in the range approximately 0.1-1 AU and neutron star companion masses approximately 1-3 M middle dot in circle. For many of these systems, we find that when the companion evolves off the main sequence and fills its Roche lobe, the subsequent mass transfer is dynamically unstable. This leads to a common envelope phase and the formation of short-period neutron star-white dwarf binaries. For a significant fraction of these binaries, the decay of the orbit due to gravitational radiation will be followed by a period of stable mass transfer driven by a combination of gravitational radiation and tidal heating of the companion. The properties of the resulting short-period binaries match well those of observed binary pulsars in 47 Tuc.

  7. Transient short-period oscillations in Super Soft Sources

    NASA Astrophysics Data System (ADS)

    Ness, J.

    2014-07-01

    Novae are powered by nuclear runaway reactions that take place on the surface of a white dwarf. The nova ejecta block all emission produced by nuclear burning until the start of the Super Soft Source (SSS) phase when X-rays become visible after the ejecta have cleared sufficiently. Recently, transient short-period (<100s) oscillations have been found in Swift/XRT light curves taken during the SSS phase of three novae. We performed a systematic search for short-period oscillations in all available continuous XMM and Chandra SSS light curves and found short-period oscillation in LMC 2009a (33s), RS Oph (35s), KT Eri (35s), V339 Del (54s), and Cal 83 (67s). Period-time maps clearly illustrate the transient nature of the period both in terms of period value and signal strength. A similar systematic study of all Swift/XRT observations is under way (Beardmore et al.). If interpreted as g-mode oscillations, excited by the ɛ mechanism, theoretical relations between period, luminosity, and white dwarf mass can be explored to determine the white dwarf mass.

  8. The possibility for a short-period hybrid staggered undulator.

    SciTech Connect

    Sasaki, S.; Experimental Facilities Division

    2005-01-01

    A short-period hybrid-type staggered undulator is proposed. A proper combination of vanadium Permendur (VP) pole and NdFeB magnet provide approximately 40% larger peak field strength than a conventional staggered undulator. The peak field of a 15-mm-period hybrid staggered undulator exceeds 0.8 T at a gap of 6 mm. Also, by using dysprosium as a pole and PrFeB as a magnet at liquid nitrogen temperature (77K), even higher peak field ({approx} 0.94 T) can be achieved at the same gap.

  9. Theory of short periodic orbits for partially open quantum maps.

    PubMed

    Carlo, Gabriel G; Benito, R M; Borondo, F

    2016-07-01

    We extend the semiclassical theory of short periodic orbits [M. Novaes et al., Phys. Rev. E 80, 035202(R) (2009)PLEEE81539-375510.1103/PhysRevE.80.035202] to partially open quantum maps, which correspond to classical maps where the trajectories are partially bounced back due to a finite reflectivity R. These maps are representative of a class that has many experimental applications. The open scar functions are conveniently redefined, providing a suitable tool for the investigation of this kind of system. Our theory is applied to the paradigmatic partially open tribaker map. We find that the set of periodic orbits that belongs to the classical repeller of the open map (R=0) is able to support the set of long-lived resonances of the partially open quantum map in a perturbative regime. By including the most relevant trajectories outside of this set, the validity of the approximation is extended to a broad range of R values. Finally, we identify the details of the transition from qualitatively open to qualitatively closed behavior, providing an explanation in terms of short periodic orbits. PMID:27575138

  10. Theory of short periodic orbits for partially open quantum maps.

    PubMed

    Carlo, Gabriel G; Benito, R M; Borondo, F

    2016-07-01

    We extend the semiclassical theory of short periodic orbits [M. Novaes et al., Phys. Rev. E 80, 035202(R) (2009)PLEEE81539-375510.1103/PhysRevE.80.035202] to partially open quantum maps, which correspond to classical maps where the trajectories are partially bounced back due to a finite reflectivity R. These maps are representative of a class that has many experimental applications. The open scar functions are conveniently redefined, providing a suitable tool for the investigation of this kind of system. Our theory is applied to the paradigmatic partially open tribaker map. We find that the set of periodic orbits that belongs to the classical repeller of the open map (R=0) is able to support the set of long-lived resonances of the partially open quantum map in a perturbative regime. By including the most relevant trajectories outside of this set, the validity of the approximation is extended to a broad range of R values. Finally, we identify the details of the transition from qualitatively open to qualitatively closed behavior, providing an explanation in terms of short periodic orbits.

  11. A Mechanism for Producing Short-Period Binaries

    NASA Astrophysics Data System (ADS)

    Eggleton, Peter P.; Kisseleva-Eggleton, Ludmila

    2006-08-01

    When three point masses form a hierarchical triple system, the short-period orbit can be severely modified by the long-period orbit if the two orbits are inclined to each other by more than about 39^deg (sin^{-1}sqrt{2/5}). Such an inclination can induce ‘Kozai cycles’ (Kozai, 1962), in which the eccentricity of the inner orbit cycles by a large amount while its period and therefore semimajor axis remains roughly constant. During those periastra when the eccentricity is largest, tidal friction may become important, and this can result in a secular shrinkage of the orbit, until it becomes circularised at a period of a few days. However, apsidal motion due to either GR or to the quadrupolar distortion of the components (if they are no longer treated as point masses) can reduce the range of eccentricity. We explore the limits on outer and inner orbital period that these perturbations imply. If the components are F/G/K/M dwarfs, then rotationally-driven dynamo activity can become important at the short periods that can occur in the right circumstances. It can cause the period to shorten further. The result may be a contact binary, and/or a merger in which the two stars of the inner pair coalesce to form a single rapidly rotating star. We suggest that this may be the origin of AB Dor, a very rapidly rotating K dwarf that is probably about 50 Myr old.

  12. Theory of short periodic orbits for partially open quantum maps

    NASA Astrophysics Data System (ADS)

    Carlo, Gabriel G.; Benito, R. M.; Borondo, F.

    2016-07-01

    We extend the semiclassical theory of short periodic orbits [M. Novaes et al., Phys. Rev. E 80, 035202(R) (2009), 10.1103/PhysRevE.80.035202] to partially open quantum maps, which correspond to classical maps where the trajectories are partially bounced back due to a finite reflectivity R . These maps are representative of a class that has many experimental applications. The open scar functions are conveniently redefined, providing a suitable tool for the investigation of this kind of system. Our theory is applied to the paradigmatic partially open tribaker map. We find that the set of periodic orbits that belongs to the classical repeller of the open map (R =0 ) is able to support the set of long-lived resonances of the partially open quantum map in a perturbative regime. By including the most relevant trajectories outside of this set, the validity of the approximation is extended to a broad range of R values. Finally, we identify the details of the transition from qualitatively open to qualitatively closed behavior, providing an explanation in terms of short periodic orbits.

  13. VLT Spectroscopy of Four Short Period Cataclysmic Variables

    NASA Astrophysics Data System (ADS)

    Skinner, Julie N.; Howell, S. B.; Mason, E.

    2006-12-01

    VLT UVES spectroscopy of four short period, non-magnetic cataclysmic variable stars is presented. The stars observed were GW Lib, BW Scl, VY Aqr, and Z Cha. The 0.1A resolution spectra were uses to measure line strengths and velocity information. Using these measured values, physical parameters, such as the stellar masses, the binary inclination, and the nature of the accretion disk were determined. Mass constraints in the stars BW Scl and GW Lib strongly suggest that the mass donors are likely to be degenerate stars with masses less than 0.06 M-sun. Skinner's research was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation through Scientific Program Order No. 3 (AST-0243875) of the Cooperative Agreement No. AST-0132798 between the Association of Universities for Research in Astronomy (AURA) and the NSF.

  14. The atmospheric circulation of ultra-short period exoplanets

    NASA Astrophysics Data System (ADS)

    Kataria, Tiffany; Showman, Adam P.; Fortney, Jonathan J.; Stevenson, Kevin B.; Lewis, Nikole K.

    2015-01-01

    Even though ultra-short period exoplanets comprise only a small fraction of the total exoplanet population, they present a useful probe into the role of fast rotation rates and small orbital distances on atmospheric dynamics. In this regime, advective timescales are longer than radiative timescales such that the temperature contrasts from dayside to nightside are large (>500 K at photospheric pressures); this strong day-night forcing, coupled with the planet's fast rotation rate (and hence small Rossby deformation radius) yields multiple, narrow (~40 degrees) jets in the atmosphere. Here we will present two cases illustrative of the dynamical regime for ultra-short period exoplanets, and how we can use general circulation models to constrain observations of their atmospheres. First, we will present models of WASP-43b, a Jupiter-mass planet in a 19.5-hour orbit around a K7 star. Because WASP-43b has an equilibrium temperature similar to that of HD 209458b, we can explore the role of rotation rate on the dynamics at a fixed stellar flux. We then compare our models to spectrophotometric observations obtained with HST/WFC3 and show how our 5× solar model provides the best match to the data. Next, we explore the dynamical regime of 55 Cnc e, a 7 Earth-mass, 2 Earth-radius planet in a 0.7 day orbit around a K star. Because smaller planets have a large diversity in possible compositions, we compare hydrogen-, water- and carbon dioxide-dominated models and show how differences in opacity structure lead to differences in temperature structure and circulation. We also demonstrate how future observations can distinguish between these possible compositions of 55 Cnc e, particularly in emission.

  15. Developing of 2D helical waves in semiconductor under the action of femtosecond laser pulse and external electric field

    NASA Astrophysics Data System (ADS)

    Trofimov, Vyacheslav A.; Egorenkov, Vladimir A.; Loginova, Mariya M.

    2015-08-01

    We analyze laser-induced periodic structure developing in a semiconductor under the condition of both optical bistability existence and action of 2D external electric field. Optical bistability occurs because of nonlinear dependence of semiconductor absorption coefficient on charged particles concentration. The electron mobility, diffusion of electrons and laser-induced electric field are taken into account for laser pulse propagation analyzing. 2D external electric field together with electric field, induced by free electrons and ionized donors, governs the charged particle motion. Under certain conditions, the additional positive inverse loop between electron motion and electric field, caused by redistribution of free charged particles, appears. As a result, the helical wave for free charged particle concentration of electron-hole plasma in semiconductor develops under the electric field action. For computer simulation of a problem under consideration, a new finite-difference scheme is proposed. The main feature of proposed method consists in constructed two-step iteration process. We pay a special attention for calculation of initial functions distributions. For their calculation we solve the set of 2D stationary partial differential equations by using additional iteration process that is similar to the iteration process, applied for the main problem solution.

  16. Desensitization to media violence over a short period of time.

    PubMed

    Fanti, Kostas A; Vanman, Eric; Henrich, Christopher C; Avraamides, Marios N

    2009-01-01

    This study investigated the desensitization to violence over a short period of time. Participants watched nine violent movie scenes and nine comedy scenes, and reported whether they enjoyed the violent or comedy scenes and whether they felt sympathetic toward the victim of violence. Using latent growth modeling, analyses were carried out to investigate how participants responded to the different scenes across time. The findings of this study suggested that repeated exposure to media violence reduces the psychological impact of media violence in the short term, therefore desensitizing viewers to media violence. As a result, viewers tended to feel less sympathetic toward the victims of violence and actually enjoy more the violence portrayed in the media. Additionally, desensitization to media violence was better represented by a curvilinear pattern, whereas desensitization to comedy scenes was better represented by a linear pattern. Finally, trait aggression was not related to the pattern of change over time, although significant effects were found for initial reports of enjoyment and sympathy. PMID:19172659

  17. Short-period Stellar Activity Cycles with Kepler Photometry

    NASA Astrophysics Data System (ADS)

    Arkhypov, Oleksiy V.; Khodachenko, Maxim L.; Lammer, Helmut; Güdel, Manuel; Lüftinger, Theresa; Johnstone, Colin P.

    2015-07-01

    We study the short-periodic component of stellar activity with a cycle period of {P}{cyc}\\lt {10}3 days using the Kepler mission photometry of fast-rotating (1\\lt P\\lt 4 days) stars with spectra of M4V to F3V. Applying the originally developed two non-spectral methods, we measured the effective period of stellar cycles in 462 objects. The obtained results are in accordance with previous measurements by Vida et al. and do not seem to result from a beating effect. The performed measurements of Pcyc cluster in a specific branch that covers the previously unstudied region in the Saar & Brandenburg diagram and connects the branch of inactive stars with the area populated by super-active objects. It is shown that the formation of the discovered branch is due to the α-quenching effect, which saturates the magnetic dynamo and decreases the cycle periods with the increase of the inverted Rossby number. This finding is important in the context of the discussion on catastrophic quenching and other heuristic approximations of the nonlinear α-effect.

  18. Short Period Secular Variation Seen in Satellite Data

    NASA Astrophysics Data System (ADS)

    Mandea, M.; Olsen, N.

    2006-12-01

    Observatory monthly means provide an excellent opportunity to study the temporal changes of the magnetic field at a given location. Unfortunately, the uneven distribution of the present observatory network makes it difficult to determine the global field change pattern. We present a new approach developed to extract satellite monthly means at a regular network of "virtual observatories" located at 400km altitude, and based on CHAMP magnetic measurements. Comparison of these virtual observatory monthly means with the corresponding ground observatory values shows a remarkably well correlated signal at monthly and annual time-scales. Using monthly means for 2001-2005 from these "virtual observatories" we investigate the space-time structure of the short-period variation of the Earth's magnetic field by means of a Spherical Harmonic Expansion, followed by a separation into external (magnetospheric) and internal part. Analysing the time series of the magnetic field at the "virtual observatories" a geomagnetic jerk taking place during the first months of the year 2003 has been found. The occurrence of this jerk is rather limited and this characteristic is also discussed.

  19. Short-period terrestrial planets and radial velocity stellar jitter.

    NASA Astrophysics Data System (ADS)

    Dumusque, Xavier

    2015-01-01

    Stellar jitter is the main limitation to ultra-precise radial velocity (RV) measurements. It currently precludes our ability to detect a planet like the Earth. Short-period terrestrial planets present first the advantage of inducing a stronger RV signal. In addition, the signal produced by these planets have a period completely different than stellar activity. This allows us, when the observational strategy is adequate, to decorrelate the planetary signal from the jitter induced by the star using filtering techniques. I will show the examples of Kepler-78b and Corot-7b, where the amplitude of the planetary signal can be detected, despite the stellar activity jitter that is 5 and 3 times larger, respectively. The cases of Alpha Cen Bb will also be reviewed, with a new reduction of the published data that increases the significance of the planetary signal.This project is funded by ETAEARTH, a transnational collaboration between European countries and the US (the Swiss Space Office, the Harvard Origin of Life Initiative, the Scottish Universities Physics Alliance, the University of Geneva, the Smithsonian Astrophysical Observatory, the Italian National Astrophysical Institute, the University of St. Andrews, Queens University Belfast, and the University of Edinburgh) setup to optimize the synergy between space-and ground-based data whose scientific potential for the characterization of extrasolar planets can only be fully exploited when analyzed together.

  20. Cyclical Period Changes in Short-Period Dwarf Novae

    NASA Astrophysics Data System (ADS)

    Baptista, R.; Borges, B. W.; Bond, H. E.; Jablonski, F.; Steiner, J. E.; Grauer, A. D.

    2004-01-01

    The observed-minus-calculated (O-C) diagrams of the eclipse timings of three dwarf novae of the SU UMa sub-class are presented and discussed. The (O-C) diagrams cover 28 24 and 15 years respectively for Z~Cha V2051~Oph and V4140~Sgr and show clear orbital period changes. Z~Cha shows conspicuous cyclical changes of period 28+/-2 yr and amplitude 60+/-12 s. V2051~Oph shows a cyclical period change of period 22+/-2 yr and amplitude 17+/-3 s. The (O-C) diagram of V4140~Sgr shows less convincing evidence but can also be explained in terms of a cyclical period modulation with an amplitude of about 16s and a time scale of 6.9+/-0.3 years. The best explanation for these observations is that of a solar-type magnetic activity cycle in the secondary star modulating its radius and consequently the mass transfer rate and the orbital separation on time scales of years. These results support the recent findings of Ak Ozkan & Mattei that the quiescent magnitudes and outburst interval of a sample of dwarf novae (including many SU UMa stars) show cyclical variations produced by solar-type magnetic activity cycles. Our results also confirm that the fully-convective secondary stars of these short period binaries still possess non-negligible magnetic fields.

  1. UV Chromospheric Activity in Cool, Short-Period Contact Binaries

    NASA Technical Reports Server (NTRS)

    Hrivnak, Bruce J.

    2000-01-01

    We have completed our analysis of the IUE spectra of the short-period contact binary OO Aql. OO Aql is a rare W UMa-type eclipsing binary in which the two solar-type stars may have only recently evolved into contact. The binary has an unusually high mass ratio (0.84), and a relatively long orbital period (0.506 d) for its spectral type (mid-G). Twelve ultraviolet spectra of OO Aql were obtained in 1988 with the IUE satellite, including a series of consecutive observations that cover nearly a complete orbital cycle. Chromospheric activity is studied by means of the Mg II h+k emission at 2800 A. The Mg II emission is found to vary, even when the emission is normalized to the adjacent continuum flux. This variation may be correlated with orbital phase in the 1988 observations. It also appears that the normalized Mg H emission varies with time, as seen in spectra obtained at two different epochs in 1988 and when compared with two spectra obtained several years earlier. The level of chromospheric activity in OO Aql is less than that of other W UMa-type binaries of similar colors, but this is attributed to its early stage of contact binary evolution. Ultraviolet light curves were composed from measurements of the ultraviolet continuum in the spectra. These were analyzed along with visible light curves of OO Aql to determine the system parameters. The large wavelength range in the light curves enabled a well-constrained fit to a cool spot in the system. A paper on these results is scheduled for publication in the February 2001 issue of the Astronomical Journal.

  2. Generation of Helical and Axial Magnetic Fields by the Relativistic Laser Pulses in Under-dense Plasma: Three-Dimensional Particle-in-Cell Simulation

    NASA Astrophysics Data System (ADS)

    Zheng, Chun-Yang; Zhu, Shao-Ping; He, Xian-Tu

    2002-07-01

    The quasi-static magnetic fields created in the interaction of relativistic laser pulses with under-dense plasmas have been investigated by three-dimensional particle-in-cell simulation. The relativistic ponderomotive force can drive an intense electron current in the laser propagation direction, which is responsible for the generation of a helical magnetic field. The axial magnetic field results from a difference beat of wave-wave, which drives a solenoidal current. In particular, the physical significance of the kinetic model for the generation of the axial magnetic field is discussed.

  3. Helicity-selective phase-matching and quasi-phase matching of circularly polarized high-order harmonics: towards chiral attosecond pulses

    NASA Astrophysics Data System (ADS)

    Kfir, Ofer; Grychtol, Patrik; Turgut, Emrah; Knut, Ronny; Zusin, Dmitriy; Fleischer, Avner; Bordo, Eliyahu; Fan, Tingting; Popmintchev, Dimitar; Popmintchev, Tenio; Kapteyn, Henry; Murnane, Margaret; Cohen, Oren

    2016-06-01

    Phase matching of circularly polarized high-order harmonics driven by counter-rotating bi-chromatic lasers was recently predicted theoretically and demonstrated experimentally. In that work, phase matching was analyzed by assuming that the total energy, spin angular momentum and linear momentum of the photons participating in the process are conserved. Here we propose a new perspective on phase matching of circularly polarized high harmonics. We derive an extended phase matching condition by requiring a new propagation matching condition between the classical vectorial bi-chromatic laser pump and harmonics fields. This allows us to include the influence of the laser pulse envelopes on phase matching. We find that the helicity dependent phase matching facilitates generation of high harmonics beams with a high degree of chirality. Indeed, we present an experimentally measured chiral spectrum that can support a train of attosecond pulses with a high degree of circular polarization. Moreover, while the degree of circularity of the most intense pulse approaches unity, all other pulses exhibit reduced circularity. This feature suggests the possibility of using a train of attosecond pulses as an isolated attosecond probe for chiral-sensitive experiments.

  4. Rotation of a Pulsed Jet, or Plume, in a Rotating Flow: A Source of Helicity for an α-ω Astrophysical Dynamo

    NASA Astrophysics Data System (ADS)

    Beckley, Howard F.; Colgate, Stirling A.; Romero, Van D.; Ferrel, Ragnar

    2003-12-01

    A fluid-flow experiment was performed in water to investigate how an expanding pulsed jet rotates when injected off-axis into a rotating annular flow. The pulsed jet simulates a large-scale rising plume in a stellar or accretion disk environment. In the experiment, the pulsed jet was injected parallel to, but radially displaced from, the axis of rotation. The jet was observed to counterrotate Δφ~π/2 to π rad relative to the rotating frame before dispersing into the background flow. The counterrotation of an expanding pulsed jet in a rotating frame is the key result of the experiment. The counterrotation of the jet occurs because of the increased moment of inertia due to its expansion and conserved angular momentum. Rapid turbulent entrainment of the pulsed jet with the background flow during radial divergence when striking the end wall limits the net rotation of the jet. Shear within the differentially rotating background flow enhances the net rotation of the jet. Naturally occurring buoyant plumes in rotating flows should exhibit this same coherent nature, i.e., the same direction of rotation, the same vertical motion, and the same finite angle of rotation for every plume. This should make pulsed jets, or plumes, when occurring in a conducting medium, nearly ideal for producing helicity for the α-ω dynamo. In the experiment, Couette flow was established in water between two coaxial cylinders with an outer radius R0=15 cm, an inner radius R1=7.5 cm, and height Z=10 cm. The Reynolds number of the experiment was Re~=105 in order to simulate the behavior of turbulent entrainment at high Reynolds number. The differential rotation of the background flow was varied from constant rotation, dΩ/dR=0, to Ω~1/R. The flow was made visible by pulsed hydrogen electrolysis from a tungsten wire and by dispersed guanidine in water. The flow was imaged using a digital video camcorder. These measurements are a precursor to the design and development of an α-ω dynamo

  5. Short period, high field cryogenic undulator for extreme performance x-ray free electron lasers

    NASA Astrophysics Data System (ADS)

    O'Shea, F. H.; Marcus, G.; Rosenzweig, J. B.; Scheer, M.; Bahrdt, J.; Weingartner, R.; Gaupp, A.; Grüner, F.

    2010-07-01

    Short period, high field undulators can enable short wavelength free electron lasers (FELs) at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems. We describe an ongoing initiative to develop such an undulator based on an approach that utilizes novel cryogenic materials. While this effort was begun in the context of extending the photon energy regime of a laser-plasma accelerator based electron source, we consider here implications of its application to sub-fs scenarios in which more conventional injectors are employed. The use of such low-charge, ultrashort beams, which has recently been proposed as a method of obtaining single-spike performance in x-ray FELs, is seen in simulation to give unprecedented beam brightness. This brightness, when considered in tandem with short wavelength, high field undulators, enables extremely high performance FELs. Two examples discussed in this paper illustrate this point well. The first is the use of the SPARX injector at 2.1 GeV with 1 pC of charge to give 8 GW peak power in a single spike at 6.5 Å with a photon beam peak brightness greater than 1035photons/(smm2mrad20.1%BW), which will also reach LCLS wavelengths on the 5th harmonic. The second is the exploitation of the LCLS injector with 0.25 pC, 150 as pulses to lase at 1.5 Å using only 4.5 GeV energy; beyond this possibility, we present start-to-end simulations of lasing at unprecedented short wavelength, 0.15 Å, using 13.65 GeV LCLS design energy.

  6. A triple origin for the lack of tight coplanar circumbinary planets around short-period binaries

    NASA Astrophysics Data System (ADS)

    Hamers, Adrian; Perets, Hagai B.; Portegies Zwart, Simon

    2015-12-01

    Detection of transiting circumbinary planets is more tractable around short-period binaries. However, sofar, no such binaries have been found with orbits shorter than 7 days. Short-period main sequence binaries have been suggested to form in triple systems, through a combination of secular Kozai-Lidov cycles and tidal friction (KLCTF). Here, we show that coplanar circumbinary transiting planets are unlikely to exist around short-period binaries, due to triple evolution. We use secular analysis, N-body simulations and analytic considerations as well as population synthesis models to characterize their overall properties. We find that the existence of a circumbinary planet in a triple is likely to produce one of the following outcomes. (1) Sufficiently massive planets in tight and/or coplanar orbits around the inner binary can partially or completely quench the KL evolution, `shielding' the inner binary from the secular effects of the tertiary, and not allowing the KLCTF process to take place. In this case, the inner binary will not shrink to become a short-period binary. (2) KL evolution is not quenched and it drives the planetary orbit into high eccentricities, giving rise to an unstable configuration, in which the planet is most likely ejected from the system. (3) KL evolution is not quenched, but the planet survives the KLCTF evolution and the formation of the short-period binary; the planet orbit is likely to be much wider than the currently observed inner binary orbit, and is likely to be inclined in respect to the binary orbit, as well as eccentric. These outcomes lead to two main conclusions: (1) it is unlikely to find a (massive) planet on a tight and coplanar orbit around a short-period main-sequence binary, and (2) the frequency, masses and orbits of non-coplanar circumbinary planets in short-period binaries are constrained by their secular evolution.

  7. Chaotic motion in a comet disk beyond Neptune - The delivery of short-period comets

    SciTech Connect

    Torbett, M.V. )

    1989-10-01

    Recent Monte Carlo simulations have demonstrated that a source with a spherical distribution of orbital angular momenta such as the Oort Cloud cannot give rise to the highly flattened distribution of short-period comets. It was also demonstrated that the problem of delivery could be resolved if short-period comets originate in a low inclination disk of comets beyond the orbit of Neptune. Numerical integrations of cometary motion in this disk show that perturbations by the four major planets can result in chaotic motions which, on long timescales, can deliver comets to low inclination Neptune-crossing orbits. Multistage gravitational scattering by the major planets can then, according to theory, supply short-period comets with orbital elements matching observations. 34 refs.

  8. A survey for very short-period planets in the Kepler data

    SciTech Connect

    Jackson, Brian; Stark, Christopher C.; Chambers, John; Adams, Elisabeth R.; Deming, Drake

    2013-12-20

    We conducted a search for very short-period transiting objects in the publicly available Kepler data set. Our preliminary survey has revealed four planetary candidates, all with orbital periods less than 12 hr. We have analyzed the data for these candidates using photometric models that include transit light curves, ellipsoidal variations, and secondary eclipses to constrain the candidates' radii, masses, and effective temperatures. Even with masses of only a few Earth masses, the candidates' short periods mean that they may induce stellar radial velocity signals (a few m s{sup –1}) detectable by currently operating facilities. The origins of such short-period planets are unclear, but we discuss the possibility that they may be the remnants of disrupted hot Jupiters. Whatever their origins, if confirmed as planets, these candidates would be among the shortest-period planets ever discovered. Such planets would be particularly amenable to discovery by the planned TESS mission.

  9. Tidal decay and stable Roche-lobe overflow of short-period gaseous exoplanets

    NASA Astrophysics Data System (ADS)

    Jackson, Brian; Jensen, Emily; Peacock, Sarah; Arras, Phil; Penev, Kaloyan

    2016-11-01

    Many gaseous exoplanets in short-period orbits are on the verge or are in the process of Roche-lobe overflow (RLO). Moreover, orbital stability analysis shows tides can drive many hot Jupiters to spiral inevitably toward their host stars. Thus, the coupled processes of orbital evolution and RLO likely shape the observed distribution of close-in exoplanets and may even be responsible for producing some of the short-period rocky planets. However, the exact outcome for an overflowing planet depends on its internal response to mass loss, and the accompanying orbital evolution can act to enhance or inhibit RLO. In this study, we apply the fully-featured and robust Modules for Experiments in Stellar Astrophysics suite to model RLO of short-period gaseous planets. We show that, although the detailed evolution may depend on several properties of the planetary system, it is largely determined by the core mass of the overflowing gas giant. In particular, we find that the orbital expansion that accompanies RLO often stops and reverses at a specific maximum period that depends on the core mass. We suggest that RLO may often strand the remnant of a gas giant near this orbital period, which provides an observational prediction that can corroborate the hypothesis that short-period gas giants undergo RLO. We conduct a preliminary comparison of this prediction to the observed population of small, short-period planets and find some planets in orbits that may be consistent with this picture. To the extent that we can establish some short-period planets are indeed the remnants of gas giants, that population can elucidate the properties of gas giant cores, the properties of which remain largely unconstrained.

  10. Tidal decay and stable Roche-lobe overflow of short-period gaseous exoplanets

    NASA Astrophysics Data System (ADS)

    Jackson, Brian; Jensen, Emily; Peacock, Sarah; Arras, Phil; Penev, Kaloyan

    2016-06-01

    Many gaseous exoplanets in short-period orbits are on the verge or are in the process of Roche-lobe overflow (RLO). Moreover, orbital stability analysis shows tides can drive many hot Jupiters to spiral inevitably toward their host stars. Thus, the coupled processes of orbital evolution and RLO likely shape the observed distribution of close-in exoplanets and may even be responsible for producing some of the short-period rocky planets. However, the exact outcome for an overflowing planet depends on its internal response to mass loss, and the accompanying orbital evolution can act to enhance or inhibit RLO. In this study, we apply the fully-featured and robust Modules for Experiments in Stellar Astrophysics suite to model RLO of short-period gaseous planets. We show that, although the detailed evolution may depend on several properties of the planetary system, it is largely determined by the core mass of the overflowing gas giant. In particular, we find that the orbital expansion that accompanies RLO often stops and reverses at a specific maximum period that depends on the core mass. We suggest that RLO may often strand the remnant of a gas giant near this orbital period, which provides an observational prediction that can corroborate the hypothesis that short-period gas giants undergo RLO. We conduct a preliminary comparison of this prediction to the observed population of small, short-period planets and find some planets in orbits that may be consistent with this picture. To the extent that we can establish some short-period planets are indeed the remnants of gas giants, that population can elucidate the properties of gas giant cores, the properties of which remain largely unconstrained.

  11. Distribution of pulmonary ventilation and perfusion during short periods of weightlessness

    NASA Technical Reports Server (NTRS)

    Michels, D. B.; West, J. B.

    1978-01-01

    Airborne experiments were conducted on four trained normal male subjects (28-40 yr) to study pulmonary function during short periods (22-27 sec) of zero gravity obtained by flying a jet aircraft through appropriate parabolic trajectories. The cabin was always pressurized to a sea-level altitude. The discussion is limited to pulmonary ventilation and perfusion. The results clearly demonstrate that gravity is the major factor causing nonuniformity in the topographical distribution of pulmonary ventilation. More importantly, the results suggest that virtually all the topographical nonuniformity of ventilation, blood flow, and lung volume observed under 1-G conditions are eliminated during short periods of zero gravity.

  12. Electron acceleration based on a laser pulse propagating through a plasma in the simultaneous presence of a helical wiggler and an obliquely applied external magnetic field

    NASA Astrophysics Data System (ADS)

    Gashti, M. A.; Jafari, S.

    2016-06-01

    Electron acceleration based on a laser pulse propagating through plasma channel has been studied in the simultaneous presence of a helical magnetic wiggler and an obliquely applied external magnetic field. A numerical study of electron energy and electron trajectory has been made using the fourth-order Runge-kutta method. Numerical results indicate that electron energy increases with decreasing θ -angle of the obliquely external magnetic field. Besides, it increases with increasing the amplitude of the obliquely magnetic field. It is also found that the electron attains a higher energy at shorter distances for higher amplitude of the wiggler field Ωw . Therefore, employing a magnetic wiggler field is very beneficial for electron acceleration in short distances. Further new results reveal that in the absence of the wiggler field (Ωw=0) , the electron energy increases with increasing the laser intensity, whereas in the presence of the wiggler field (Ωwneq0) , the electron energy increases with decreasing the laser intensity. As a result, employing a wiggler magnetic field in the laser-based electron accelerators can be worthwhile in the design of table top accelerators and it can enhance the electron energy at lower laser intensities.

  13. Design of polarizers for a mega-watt long-pulse millimeter-wave transmission line on the large helical device.

    PubMed

    Ii, T; Kubo, S; Shimozuma, T; Kobayashi, S; Okada, K; Yoshimura, Y; Igami, H; Takahashi, H; Ito, S; Mizuno, Y; Okada, K; Makino, R; Kobayashi, K; Goto, Y; Mutoh, T

    2015-02-01

    The polarizer is one of the critical components in a high-power millimeter-wave transmission line. It requires full and highly efficient coverage of any polarization states, high-power tolerance, and low-loss feature. Polarizers with rounded shape at the edge of the periodic groove surface are designed and fabricated by the machining process for a mega-watt long-pulse millimeter-wave transmission line of the electron cyclotron resonance heating system in the large helical device. The groove shape of λ/8- and λ/4-type polarizers for an 82.7 GHz transmission line is optimally designed in an integral method developed in the vector theories of diffraction gratings so that the efficiency to realize any polarization state can be maximized. The dependence of the polarization states on the combination of the two polarizer rotation angles (Φλ/8, Φλ/4) is examined experimentally in a low-power test with the newly developed polarization monitor. The results show that the measured polarization characteristics are in good agreement with the calculated ones.

  14. Design of polarizers for a mega-watt long-pulse millimeter-wave transmission line on the large helical device

    SciTech Connect

    Ii, T. Kubo, S.; Shimozuma, T.; Kobayashi, S.; Okada, K.; Yoshimura, Y.; Igami, H.; Takahashi, H.; Ito, S.; Mizuno, Y.; Okada, K.; Mutoh, T.; Makino, R.; Kobayashi, K.; Goto, Y.

    2015-02-15

    The polarizer is one of the critical components in a high-power millimeter-wave transmission line. It requires full and highly efficient coverage of any polarization states, high-power tolerance, and low-loss feature. Polarizers with rounded shape at the edge of the periodic groove surface are designed and fabricated by the machining process for a mega-watt long-pulse millimeter-wave transmission line of the electron cyclotron resonance heating system in the large helical device. The groove shape of λ/8- and λ/4-type polarizers for an 82.7 GHz transmission line is optimally designed in an integral method developed in the vector theories of diffraction gratings so that the efficiency to realize any polarization state can be maximized. The dependence of the polarization states on the combination of the two polarizer rotation angles (Φ{sub λ/8}, Φ{sub λ/4}) is examined experimentally in a low-power test with the newly developed polarization monitor. The results show that the measured polarization characteristics are in good agreement with the calculated ones.

  15. Cooperative Learning Combined with Short Periods of Lecturing: A Good Alternative in Teaching Biochemistry

    ERIC Educational Resources Information Center

    Fernandez-Santander, Ana

    2008-01-01

    The informal activities of cooperative learning and short periods of lecturing has been combined and used in the university teaching of biochemistry as part of the first year course of Optics and Optometry in the academic years 2004-2005 and 2005-2006. The lessons were previously elaborated by the teacher and included all that is necessary to…

  16. ExploreNEOs. VIII. Dormant Short-period Comets in the Near-Earth Asteroid Population

    NASA Astrophysics Data System (ADS)

    Mommert, M.; Harris, A. W.; Mueller, M.; Hora, J. L.; Trilling, D. E.; Bottke, W. F.; Thomas, C. A.; Delbo, M.; Emery, J. P.; Fazio, G.; Smith, H. A.

    2015-10-01

    We perform a search for dormant comets, asteroidal objects of cometary origin, in the near-Earth asteroid (NEA) population based on dynamical and physical considerations. Our study is based on albedos derived within the ExploreNEOs program and is extended by adding data from NEOWISE and the Akari asteroid catalog. We use a statistical approach to identify asteroids on orbits that resemble those of short-period near-Earth comets (NECs) using the Tisserand parameter with respect to Jupiter, the aphelion distance, and the minimum orbital intersection distance with respect to Jupiter. From the sample of NEAs on comet-like orbits, we select those with a geometric albedo pV ≤ 0.064 as dormant comet candidates, and find that only ˜50% of NEAs on comet-like orbits also have comet-like albedos. We identify a total of 23 NEAs from our sample that are likely to be dormant short-period NECs and, based on a de-biasing procedure applied to the cryogenic NEOWISE survey, estimate both magnitude-limited and size-limited fractions of the NEA population that are dormant short-period comets. We find that 0.3%-3.3% of the NEA population with H ≤ 21, and ({9}-5+2)% of the population with diameters d ≥ 1 km, are dormant short-period NECs.

  17. CRTS discovery of an outburst from a short period binary system

    NASA Astrophysics Data System (ADS)

    Drake, A. J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M. J.; Donalek, C.; Williams, R.; Catelan, M.; Christensen, E.; Larson, S. M.

    2016-06-01

    Here we report the discovery of an outburst from known short period binary system 2MASS_J16211735+4412541. On 2016-06-03.45 UT, 2MASS_J162117 wasdetected by CRTS as a transient event ( CSS160603:162117+441254) with V_CSS=13.3.

  18. Origins of Solar Systems Workshop: The Origin, Evolution, and Detectability of Short Period Comets

    NASA Technical Reports Server (NTRS)

    Stern, S. Alan

    1993-01-01

    The origin of the short period comets (SPC) (periods less than 200 years), the dynamical formation of their present reservoir(s), the cause and rate of their transport to the inner planetary region where they can be detected, and the magnitude of selection effects in their discovery are important research questions directly coupled to the goals of understanding the origin and evolution of the Solar System. To address these questions in an intensive way, an interdisciplinary, five month long Workshop from Jan. to May 1993 at Southwest Research Institute (SwRI) in San Antonio was convened. The goal of this Workshop was to advance the state of understanding about the origins, dynamical evolution, and present location of short period comets and their reservoir(s).

  19. Transformation of short-periodic high-inclination orbits of circumsolar submillimeter dust

    SciTech Connect

    Bazei, A.A.; Kramer, E.N.

    1995-11-01

    Disintegration of short-periodic comets is one of the sources of cosmic dust in the Solar System. Initially dust particles move approximately in the orbits of parent comets, in particular, in high-inclination orbits. In a few million years, some of these particles (the smallest ones) go over to the short-periodic, high-inclination orbits due to the Poynting-Robertson effect. The numerical integration of the equations of motion at this stage of evolution gives rise to somewhat surprising results. For example, when integrating the equations of motion as far back as 6000 years from the time of meteor observation, the real meteor particle gains the perihelion distance smaller than the solar radius (!). Our calculations show that the time of falling onto the Sun is shorter for a article moving in a high-inclination orbit. This is due to the superposition of gravitational perturbation and radiation effects.

  20. Short period light variation of the Algol-type binary U Coronae Borealis

    NASA Astrophysics Data System (ADS)

    Narusawa, Shin-Ya; Waki, Yoshifumi; Ioroi, Masayuki; Nakamura, Yasuhisa; Takeuti, Mine

    The short period variability in the light curve of U CrB, an Algol-type binary, was examined with the published data of van Gent (1989). The period of variability was approximately 0.05 d and the amplitude was 0.05 mag. The superposition of several modes was suggested. The properties of the light variability were compared with those of the early-type main-sequence pulsating stars.

  1. Effect of disorder on the optical properties of short period superlattices

    NASA Technical Reports Server (NTRS)

    Strozier, J. A.; Zhang, Y. A.; Horton, C.; Ignatiev, A.; Shih, H. D.

    1993-01-01

    The optical properties of disordered short period superlattices are studied using a one-dimensional tight-binding model. A difference vector and disorder structure factor are proposed to characterize the disordered superlattice. The density of states, participation number, and optical absorption coefficients for both ordered and disordered superlattices are calculated as a function of energy. The results show that introduction of disorder into an indirect band gap material enhances the optical transition near the indirect band edge.

  2. Search for Random Fluctuations in Periods of Short-period Cepheids

    NASA Astrophysics Data System (ADS)

    Berdnikov, L. N.; Stevens, I. R.

    2010-02-01

    Data from SMEI instrument (onboard the CORIOLIS spacecraft) for 16 brightest Cepheids were analyzed with the Eddington-Plakidis method and random fluctuations in periods for four of them, SU Cas (P=1.95d), δ Cep (P=5.37d), κ Pav (P=9.09d), and α UMi (P=3.97d) were detected. Such fluctuations for short period Cepheids were found for the first time.

  3. Ultra-Short-Period Planets in K2: New Results From SuPerPiG

    NASA Astrophysics Data System (ADS)

    Adams, Elisabeth; Jackson, Brian; Endl, Michael

    2016-10-01

    Ultra-short-period planets, with orbital periods of less than 1 day, are a challenge to theories of planet formation. The SuPerPiG collaboration (Short-Period Planet Group) reports on 19 candidates identified in Campaigns 0-5 of the K2 mission. Planet candidates range in size from 0.7-16 Earth radii and in orbital period from 4.2 to 23.5 hours. One candidate (EPIC 203533312, Kp=12.5) is among the shortest-period planet candidates discovered to date (P=4.2 hours), and, if confirmed as a planet, must have a density of at least rho=8.9 g/cm^3 in order to not be tidally disrupted. Five candidates have nominal radius values in the sub-Jovian desert (R_P=3-11 R_E and P<=1.5 days) where theoretical models do not favor their long-term stability; the only confirmed planet in this range is thought to be disintegrating (EPIC 201637175). Based on an assessment of our survey's completeness, we estimate an occurrence rate for ultra-short-period planets among K2 target stars that is about half that estimated from the Kepler sample, raising questions as to whether K2 systems are intrinsically different from Kepler systems, possibly as a result of their different galactic location.

  4. Light Curve Analyses of the Short Period, Totally Eclipsing Binaries V449 & V463 And

    NASA Astrophysics Data System (ADS)

    Okimoto, Jensen; Schwartz, W. H.; Sanders, S. J.; Bradstreet, D. H.

    2014-01-01

    As part of our ongoing research on short period eclipsing binaries which do not have published precision light curves and/or analyses, we placed V449 & V463 And on our observing schedule for the fall of 2013. V449 And (GSC 3281-2158; Mis V1190) was reported by Kazarovet (2005) to be a short period (0.33853 day) overcontact system ranging from V = 12.2 - 12.9 mag. We have obtained more than 1300 total observations in V and Rc. Preliminary light curve analysis reveals a W-type overcontact system with the primary eclipse being total and a temperature difference between the stars of ~300 K. The light curves themselves are fairly symmetrical (not typical for these types of systems) except for a more rapid rise in the ascending branch after secondary eclipse than symmetry would predict. This seems quite peculiar, as most W-UMa light curves exhibit asymmetries primarily between maxima (the O’Connell effect). Detailed modeling including hot and/or cool spots will be presented, as well as a period study based upon the limited timings available. V463 And (GSC 2764-1417; NSV 14514) was discovered by Khruslov and reported in IBVS 5699 (2006) to be a short period (0.406095 day) system ranging from V = 12.15 - 13.05 mag. Our thoroughly covered V and Rc light curves show that the secondary eclipse is total. Subsequent analysis indicates the system is most likely a near-contact binary with a temperature difference of ~1200 K between the components. The light curves also demonstrate very significant asymmetries, especially near secondary eclipse. The O’Connell effect is 0.08 mag in Rc between the two maxima and the first maxima is significantly asymmetrically shaped. Modeling results including spot analysis and a period study will be presented in this poster.

  5. Study on the Geomagnetic Short Period Variations of the Northwestern Yunnan

    NASA Astrophysics Data System (ADS)

    Yuan, Y.; Li, Q.; Cai, J.

    2015-12-01

    The Northwestern Yunnan is located in the interaction area between the Eurasian plate and the India plate. This area has been the ideal place for the research of continental dynamics and the prediction for risk region of strong earthquake for its complex tectonic environment and frequent seismic activity. Therefore the study on the geomagnetic short period variations is of great significance in the exploration of deep electrical structure, analysis of the seismic origin and deep geodynamics in the Northwestern Yunnan of China . This paper is based on the geomagnetic data from the magnetometer array with 8 sites built in the northwestern Yunnan to explore the deep electrical structure by the method of geomagnetic depth sounding. Firstly, we selected a total of 183 geomagnetic short period events at the range of 6min to 120min period. And we found a north northwest dividing line, of which two sides has the opposite value in the vertical component variation amplitude, which indicates the obvious conductivity anomaly underground. Secondly, the contour maps of the ratio of vertical component and horizontal component variation amplitude ΔZ/ΔH in different periods reflects the changes of a high conductivity belt's direction and position. In addition, the induction arrows maps within the period of 2 - 256min also shows that on the two sides of the dividing line the induction vectors deviate from each other, and the amplitude and direction of vectors varies with periods regularly. In the light of this, we infer that a high conductivity belt probably exists, which stretches from the deep crust to uppermost mantle and changes with depth constantly with the reference of magnetotelluric sounding. In the end of this paper, the staggered grid finite difference method is used to model the simplified three-dimensional high conductivity anomaly, and the result shows magnetic field distributions are consistent with the observed geomagnetic short period variations characteristics in

  6. Short periodic orbit approach to resonances and the fractal Weyl law.

    PubMed

    Pedrosa, J M; Wisniacki, D; Carlo, G G; Novaes, M

    2012-03-01

    We investigate the properties of the semiclassical short periodic orbit approach for the study of open quantum maps that was recently introduced [Novaes, Pedrosa, Wisniacki, Carlo, and Keating, Phys. Rev. E 80, 035202(R) (2009)]. We provide solid numerical evidence, for the paradigmatic systems of the open baker and cat maps, that by using this approach the dimensionality of the eigenvalue problem is reduced according to the fractal Weyl law. The method also reproduces the projectors |ψ(n)(R)><ψ(n)(L)|, which involves the right and left states associated with a given eigenvalue and is supported on the classical phase-space repeller.

  7. Studies of short-period comets on the eve of Rosetta

    NASA Astrophysics Data System (ADS)

    Pozuelos, F. J.; Moreno, F.; Aceituno, F.; Casanova, V.; Sota, A.; López-Moreno, J. J.; Cometas-Obs Team

    2015-05-01

    We present an extended study of the dust environment of a sample of short-period comets and their dynamical history. With this aim, we characterized the dust tails when the comets are active, and we make a statistical study to determine their dynamical evolution. The targets selected were 22P/Kopff, 30P/Reinmuth 1, 78P/Gehrels 2, 81P/Wild 2, 103P/Hartley 2, 115P/Maury, 118P/Shoemaker-Levy 4, 123P/West-Hartley, 157P/Tritton, 185P/Petriew, P/2011 W2 (Rinner).

  8. A superconducting short period undulator for a harmonic generation FEL experiment

    SciTech Connect

    Ingold, G.; Solomon, L.; Ben-Zvi, I.; Krinsky, S.; Li, D.; Lynch, D.; Sheehan, J.; Woodle, M.; Qiu, X.Z.; Yu, L.H.; Zhang, X.; Sampson, W.; Gardner, M.; Robins, K.; Lehrman, I.; Heuer, R.; Sheehan, J.; Weissenburger, D.

    1993-07-01

    A three stage superconducting (SC) undulator for a high gain harmonic generation (HGE) FEL experiment in the infrared is under construction at the NSLS in collaboration with Grumman Corporation. A novel undulator technology suitable for short period (6--40mm) undulators will be employed for all three stages, the modulator, the dispersive section and the radiator. The undulator triples the frequency of a 10.4{mu}m CO{sub 2} seed laser. So far a 27 period (one third of the final radiator) prototype radiator has been designed, built and tested.

  9. A superconducting short period undulator for a harmonic generation FEL experiment

    SciTech Connect

    Ingold, G.; Solomon, L.; Ben-Zvi, I.; Krinsky, S.; Li, D.; Lynch, D.; Sheehan, J.; Woodle, M.; Qiu, X.Z.; Yu, L.H.; Zhang, X.; Sampson, W.; Gardner, M.; Robins, K. ); Lehrman, I.; Heuer, R.; Sheehan, J.; Weissenburger, D. )

    1993-01-01

    A three stage superconducting (SC) undulator for a high gain harmonic generation (HGE) FEL experiment in the infrared is under construction at the NSLS in collaboration with Grumman Corporation. A novel undulator technology suitable for short period (6--40mm) undulators will be employed for all three stages, the modulator, the dispersive section and the radiator. The undulator triples the frequency of a 10.4[mu]m CO[sub 2] seed laser. So far a 27 period (one third of the final radiator) prototype radiator has been designed, built and tested.

  10. Inter-hemispheric Comparison of Mesospheric Short-period Gravity Wave Propagation

    NASA Astrophysics Data System (ADS)

    Nielsen, K.; Taylor, M. J.; Collins, R. L.; Irving, B. K.; Negale, M.; Siskind, D. E.; Eckermann, S. D.; Hoppel, K.; Harvey, V.; Russell, J. M.

    2011-12-01

    Mesospheric short-period (≤1-hr) gravity waves are of great importance for dynamics in the mesosphere-lower thermosphere (MLT) region, and are typically measured by instruments capable of high temporal and/or spatial resolutions such as lidars and airglow imagers. These waves have been studied extensively at low- and mid-latitudes where known wave sources are well established. The results show strong dependence on the background wind and temperature fields, which can act as a barrier prohibiting vertical propagation of the waves, as well as providing a ducted environment in which the waves can travel large horizontal distances. In fact, results show that up to 75% of these waves may exhibit ducted wave motion. Recent airglow imaging measurements over Antarctica have revealed a large number of short-period gravity waves in absence of the prominent wave sources present at lower latitudes. In contrast to results at lower latitudes, very few waves (˜5%) observed over Halley (76°S) exhibited Doppler ducted motion. In this work, we utilize airglow imagery, SABER temperature measurements, together with the Navy's high-altitude numerical weather prediction system, NOGAPS-ALPHA, to investigate propagation conditions (particularly, the role of thermal ducting) over Rothera (68°S). Data acquired from a newly installed airglow imager operating at Poker Flat, Alaska (65°N) and the co-located lidar provide an opportunity to perform an inter-hemispheric comparison of propagation conditions over two polar sites at similar latitudes.

  11. Inversion of Source Parameters for Moderate Earthquakes Using Short-Period Teleseismic P Waves

    NASA Astrophysics Data System (ADS)

    Chu, Risheng; Ni, Sidao; Pitarka, Arben; Helmberger, Don V.

    2014-07-01

    In this paper, we introduce a new method for estimating the source parameters of moderate earthquakes ( M w ~5.0) by modeling short-period teleseismic waveforms. This method uses a grid-search algorithm to minimize misfits between observed data and synthetic seismograms in depth, magnitude, and mechanism domain in a relative high-frequency range of 0.8-2.0 Hz, similar to the traditional cut-and-paste method used in regional modeling ( Zhu and Helmberger, Bull Sesimol Soc Am 86:1634-1641, 1996). In this frequency range, a significant challenge is determining the initial P-wave polarity because of a low signal-to-noise ratio (SNR). Therefore we first determine source properties for a master earthquake with a relative strong SNR. Both the travel time and amplitude corrections are developed relative to the reference 1D model along each path used in inverting the master event. We then applied these corrections to other earthquakes clustered in the same area to constrain the initial P polarities. Thus the focal mechanisms can be determined reasonably well. We inverted focal mechanisms for a small set of events beneath Qeshm Island in southern Iran and demonstrate the importance of radiation pattern at short periods.

  12. Spectroscopy of the enigmatic short-period cataclysmic variable IR Com in an extended low state

    NASA Astrophysics Data System (ADS)

    Manser, C. J.; Gänsicke, B. T.

    2014-07-01

    We report the occurrence of a deep low state in the eclipsing short-period cataclysmic variable (CV) IR Com, lasting more than two years. Spectroscopy obtained in this state shows the system as a detached white dwarf plus low-mass companion, indicating that accretion has practically ceased. The spectral type of the companion derived from the SDSS spectrum is M6-7, somewhat later than expected for the orbital period of IR Com. Its radial velocity amplitude, K2 = 419.6 ± 3.4 km s-1, together with the inclination of 75°-90° implies 0.8 < Mwd <1.0 M⊙. We estimate the white dwarf temperature to be ≃15 000 K, and the absence of Zeeman splitting in the Balmer lines rules out magnetic fields in excess of ≃5 MG. IR Com still defies an unambiguous classification, in particular the occurrence of a deep, long low state is so far unique among short-period CVs that are not strongly magnetic.

  13. PLANET HUNTERS: ASSESSING THE KEPLER INVENTORY OF SHORT-PERIOD PLANETS

    SciTech Connect

    Schwamb, Megan E.; Lintott, Chris J.; Lynn, Stuart; Smith, Arfon M.; Simpson, Robert J.; Fischer, Debra A.; Giguere, Matthew J.; Brewer, John M.; Parrish, Michael; Schawinski, Kevin

    2012-08-01

    We present the results from a search of data from the first 33.5 days of the Kepler science mission (Quarter 1) for exoplanet transits by the Planet Hunters citizen science project. Planet Hunters enlists members of the general public to visually identify transits in the publicly released Kepler light curves via the World Wide Web. Over 24,000 volunteers reviewed the Kepler Quarter 1 data set. We examine the abundance of {>=}2 R{sub Circled-Plus} planets on short-period (<15 days) orbits based on Planet Hunters detections. We present these results along with an analysis of the detection efficiency of human classifiers to identify planetary transits including a comparison to the Kepler inventory of planet candidates. Although performance drops rapidly for smaller radii, {>=}4 R{sub Circled-Plus} Planet Hunters {>=}85% efficient at identifying transit signals for planets with periods less than 15 days for the Kepler sample of target stars. Our high efficiency rate for simulated transits along with recovery of the majority of Kepler {>=}4 R{sub Circled-Plus} planets suggests that the Kepler inventory of {>=}4 R{sub Circled-Plus} short-period planets is nearly complete.

  14. Detection of short-period waves by the images of two all-sky cameras

    NASA Astrophysics Data System (ADS)

    Koltovskoi, Igor; Gavrilyeva, Galina; Ammosov, Petr; Ammosova, Anastasiia

    2016-07-01

    The short-period gravity waves by the images of two all-sky cameras, registered at different heights (˜97 km and ˜87 km) are detected. The first camera detects gravity waves in the visible region by emission of atomic oxygen (557,7 nm) at a height of 97 km. Second camera detects hydroxyl molecule emission in the near infrared region at a height of 87 km. Both cameras installed at Maymaga station (63°N, 129.5°E). According to two cameras data horizontal characteristics (propagation direction, horizontal phase velocity, period and horizontal wavelength) of gravity waves was obtained. Considering the night 06.02.2013 most of the night there is a slow motion (˜20-30 m/s) of short-period gravity waves (wave length up to 10 km) in the direction of the south-east. In the morning the reverse direction of propagation is observed. In the evening (˜17: 30 UT) begins intensive movement of larger scale gravity waves (˜40 km) in the direction of the north-east at a velocity of 70 to 160 m/s.

  15. Seasonal Investigation of Variance in Short Period Mesospheric Wave Structure at Low Latitudes.

    NASA Astrophysics Data System (ADS)

    Karnam, Hema; Taylor, Mike; Gunther, Jake

    2006-10-01

    As a part of the Maui-MALT program, the Utah State University Mesospheric Temperature Mapper (MTM) has operated continuously at Maui-Hawaii since November 2001. Over 1000 nights of high quality data on Mesospheric temperatures using the near infra red OH and O2 emission layers (centered at 87 and 94 km respectively) have been obtained over the past four years. In this study, we have analyzed data from 2003 (295 nights) to perform an initial investigation of the variance in OH and O2 signal in the frequency band corresponding to short period (12 min- 1 hour) . This was done by spectrally filtering the data into selected bands (approximately 1 hour wide). The data have been used to study variability in wave content on a night-to-night as well as a seasonal basis. Short period waves were present throughout the year and indicate no obvious summer to winter difference in wave power. On sporadic nights throughout the year, both OH and O2 show remarkable enhancements of wave power (factor of 10). Here, we present the results of this initial study.

  16. Time functions of deep earthquakes from broadband and short-period stacks

    USGS Publications Warehouse

    Houston, H.; Benz, H.M.; Vidale, J.E.

    1998-01-01

    To constrain dynamic source properties of deep earthquakes, we have systematically constructed broadband time functions of deep earthquakes by stacking and scaling teleseismic P waves from U.S. National Seismic Network, TERRAscope, and Berkeley Digital Seismic Network broadband stations. We examined 42 earthquakes with depths from 100 to 660 km that occurred between July 1, 1992 and July 31, 1995. To directly compare time functions, or to group them by size, depth, or region, it is essential to scale them to remove the effect of moment, which varies by more than 3 orders of magnitude for these events. For each event we also computed short-period stacks of P waves recorded by west coast regional arrays. The comparison of broadband with short-period stacks yields a considerable advantage, enabling more reliable measurement of event duration. A more accurate estimate of the duration better constrains the scaling procedure to remove the effect of moment, producing scaled time functions with both correct timing and amplitude. We find only subtle differences in the broadband time-function shape with moment, indicating successful scaling and minimal effects of attenuation at the periods considered here. The average shape of the envelopes of the short-period stacks is very similar to the average broadband time function. The main variations seen with depth are (1) a mild decrease in duration with increasing depth, (2) greater asymmetry in the time functions of intermediate events compared to deep ones, and (3) unexpected complexity and late moment release for events between 350 and 550 km, with seven of the eight events in that depth interval displaying markedly more complicated time functions with more moment release late in the rupture than most events above or below. The first two results are broadly consistent with our previous studies, while the third is reported here for the first time. The greater complexity between 350 and 550 km suggests greater heterogeneity in

  17. Tunnelling and current density in short period strained AlN/GaN superlattices

    NASA Astrophysics Data System (ADS)

    Asenova, Iglika; Valcheva, Evgenia; Arnaudov, Dimo

    2014-09-01

    In this paper we theoretically analyze the under-barrier perpendicular transport in short period strained III-nitride superlattices via a generalized model. The transmission coefficient of unbiased and biased structures, as well as the tunnel current at room temperature, are calculated via the transfer matrix formalism and the effective mass approximation. The inherent to the III-nitrides electric polarization fields taken into account and the exact solution of the Schrödinger equation is used in the calculation process. The minizone structure is shown to periodically disintegrate and reform as the externally applied electric field increases, while the tunnel current density shows nonlinear behavior and negative differential conductance. The theoretical results we obtain are compared and found to be consistent with the experimental ones.

  18. Band gaps and internal electric fields in semipolar short period InN/GaN superlattices

    SciTech Connect

    Gorczyca, I.; Skrobas, K.; Suski, T.; Christensen, N. E.; Svane, A.

    2014-06-09

    The electronic structures and internal electric fields of semipolar short-period mInN/nGaN superlattices (SLs) have been calculated for several compositions (m, n). Two types of SL are considered, (112{sup ¯}2) and (202{sup ¯}1), corresponding to growth along the wurtzite s2 and s6 directions, respectively. The results are compared to similar calculations for polar SLs (grown in the c-direction) and nonpolar SLs (grown in the a- and m-directions). The calculated band gaps for the semipolar SLs lie between those calculated for the nonpolar and polar SLs: For s2-SLs they fall slightly below the band gaps of a-plane SLs, whereas for s6-SLs they are considerably smaller.

  19. Multiband Photometry of Southern Very Short Period Eclipsing Binaries. I. V676 Centauri

    NASA Astrophysics Data System (ADS)

    Gray, J. D.; Samec, R. G.; Woissol, S. L.

    1996-05-01

    In this paper, we extend our study of solar-type binaries near the the low period limit to include Southern hemisphere systems. Observations are being taken at Cerro Tololo Inter-American Observatory, Chile. Here, we report B,V,R,I observations of V676 Centauri. Our three nights of data were taken in May of 1991 with a dry ice cooled Ga-As photometer attached to the 1.0-m reflector. Two new primary and two secondary epochs of minimum light were determined from the observations, and more than 100 minima were collected from the literature. Our period study spans some 35 years. The light curves show a rather large difference in eclipse depths for a W UMa binary. An O'Connell effect lends evidence of spot activity in this very short period ( 0.291 d) system. A preliminary photometric analysis of the light curves is presented.

  20. Ischial Tuberosity Avulsion Stress Fracture after Short Period of Repetitive Training

    PubMed Central

    Yang, Bo-Kyu; Ahn, Young-Joon; Im, Se-Hyuk; Park, Sang-Hyun

    2016-01-01

    Fatigue fracture of the pelvis is the form of fracture due to repetitive micro-stress accumulation, can be affected by a number of factors such as patient's nutritional status, biomechanics, social status and so on. Still there is no study about precise standard degree of external force that lead to stress fracture, but it may caused by compression force, traction force or complex force and others. Avulsion stress to ischial tuberosity or anterior superior iliac spine by attached muscle is known as the main factor for the avulsion fracture. This report will deal with 19 years old conscripted policeman who occurred ischial tuberosity avulsion fracture after training of 6-hour running for 5 days accompanying hip hyper-flexion motion. This reports aims to provide case study of stress fracture occurred after 5 days of exercise which is relatively short period who had no specific trauma history or pain. PMID:27777924

  1. AM CVn Stars: Structure and Evolution of Ultra-Short Period Interacting Binaries

    NASA Technical Reports Server (NTRS)

    Froning, Cynthia

    2005-01-01

    This is the final report of a FUSE program to study the physics of accretion and outflows in ultra-compact, helium dominated, disk-accreting binaries. With FUSE, we observed the AM CVn binary V803 Cen, which is one of only two AM CVn systems observed by FUSE to date. V803 Cen is a short-period interacting binary in which a hydrogen-deficient white dwarf transfers mass to another white dwarf via a hot, steady-state accretion disk. Unlike other cataclysmic variables (CVs), AM CVn stars have undergone double common envelope evolution (one for each white dwarf in the binary) and so probe an alternate route of evolution in binary stars. Our goals in this project were to investigate how the structure of the accretion disk and the link between the disk and wind outflows are affected by the absence of hydrogen in the system and by the compact size of the binary and the accretion disk.

  2. Fourier analysis of short-period SMC Cepheids: A comparison with Galactic Cepheids

    NASA Astrophysics Data System (ADS)

    Buchler, J. Robert; Moskalik, Pawel

    1994-12-01

    A Fourier analysis has been made of the Small Magellanic Cloud (SMC) classical Cepheid data of Smith et al. It is shown that the grouping into fundamental and first overtone pulsators, implied by the period-luminosity diagram, survives when the Fourier coefficients are plotted versus period. A comparison with the Galactic Cepheid data corroborates the existing evidence that the short period Galactic s-Cepheids are indeed first overtone pulsators. The only long period overtone Cepheid in the sample that is reliably covered (P = 3.49 d) also conforms with the corresponding s-Cepheids. On the other hand, the hypothesis of Gieren et al. that the long period s-Cepheids are fundamental pulsators is refuted. The data show systematic differences between the SMC Cepheids and their Galactic counterparts, differences that are of theoretical interest. The need for a further observational effort devoted to SMC and to Large Magellanic cloud (LMC) Cepheids is stressed.

  3. Pitch Controllability Based on Airplane Model without Short-Period Approximation—Flight Simulator Experiment—

    NASA Astrophysics Data System (ADS)

    Sato, Osamu; Kobayashi, Osamu

    Pitch controllability of an airplane is very important for longitudinal flying qualities, therefore, much research has been conducted. However, it has not been clarified why pitch handling qualities degrades in the low speed, e.g. take-off and landing flight phases. On this topic, this paper investigates the effect of several parameters of the short-period mode and phugoid mode using a flight simulator. The results show the following conclusions: The difference between the initial phase angles in two modal components in the pitch attitude response to elevator step input plays the most important role in the pitch handling qualities among modal parameters; and the difference of the two modal natural frequencies has small effect on the pitch controllability even when flight speed decreases.

  4. Characteristics of short-period internal waves in the Kara Sea inferred from satellite SAR data

    NASA Astrophysics Data System (ADS)

    Kozlov, I. E.; Kudryavtsev, V. N.; Zubkova, E. V.; Zimin, A. V.; Chapron, B.

    2015-12-01

    In this paper we present the results of short-period internal wave (SIW) observations in the Kara Sea on the basis of satellite ENVISAT ASAR data between July and October 2007. Altogether, 248 internal wave (IW) packets and solitons are identified in 89 SAR images. Detailed spatial statistics of IW signatures and their properties in the Kara Sea is presented. The primary regions of IW activity are the areas near the Kara Gates Strait, the southeastern part of the Novaya Zemlya Trough, and in the vicinity of Cape Zhelaniya. We identify the regions where large IW packets are observed with wavelengths up to 2-3 km and the front length exceeding 200 km. The mean interpacket distance for observed IWs is about 20 km, but it may reach 50-60 km. Consequent IW packets are observed to travel up to 500 km from the presumed generation points. The results of satellite observations are compared with results of previous studies.

  5. Infrared reflectance of AlN-GaN short period superlattice films

    NASA Astrophysics Data System (ADS)

    MacMillan, M. F.; Devaty, R. P.; Choyke, W. J.; Khan, M. Asif; Kuznia, J.

    1996-08-01

    The room-temperature infrared reflectance of AlN-GaN short period superlattice films has been measured. These superlattice films were deposited by switched atomic layer metalorganic chemical vapor deposition onto GaN or AlN buffer layers deposited on basal plane sapphire substrates. The measured reflectance spectra are compared to calculated spectra using an effective medium theory to model the dielectric function of the superlattice. The optical properties of the individual materials making up the samples are modeled with Lorentz oscillators using only bulk input parameters. The effects of film and substrate anisotropy and off-normal incidence are included in the calculation. Using this modeling technique, it is possible to obtain thickness estimates for the superlattice film and the buffer layer. The complicated structures seen in the reststrahl region reflectance of these films are also analyzed by comparison to the calculated spectra.

  6. New Constraints on the False Positive Rate for Short-Period Kepler Planet Candidates

    NASA Astrophysics Data System (ADS)

    Colón, Knicole D.; Morehead, Robert C.; Ford, Eric B.

    2015-01-01

    The Kepler space mission has discovered thousands of potential planets orbiting other stars, thereby setting the stage for in-depth studies of different populations of planets. We present new multi-wavelength transit photometry of small (Rp < 6 Earth radii), short-period (P < 6 days) Kepler planet candidates acquired with the Gran Telescopio Canarias. Multi-wavelength transit photometry allows us to search for wavelength-dependent transit depths and subsequently identify eclipsing binary false positives (which are especially prevalent at the shortest orbital periods). We combine these new observations of three candidates with previous results for five other candidates (Colón & Ford 2011 and Colón, Ford, & Morehead 2012) to provide new constraints on the false positive rate for small, close-in candidates. In our full sample, we identify four candidates as viable planets and four as eclipsing binary false positives. We therefore find a higher false positive rate for small, close-in candidates compared to the lower false positive rate of ~10% determined by other studies for the full sample of Kepler planet candidates (e.g. Fressin et al. 2013). We also discuss the dearth of known planets with periods less than ~2.5 days and radii between ~3 and 11 Earth radii (the so-called 'sub-Jovian desert'), since the majority of the candidates in our study are located in or around this 'desert.' The lack of planets with these orbital and physical properties is not expected to be due to observational bias, as short-period planets are generally easier to detect (especially if they are larger or more massive than Earth). We consider the implications of our results for the other ~20 Kepler planet candidates located in this desert. Characterizing these candidates will allow us to better understand the formation processes of this apparently rare class of planets.

  7. Towards a Fundamental Understanding of Short Period Eclipsing Binary Systems Using Kepler Data

    NASA Astrophysics Data System (ADS)

    Prsa, Andrej

    Kepler's ultra-high precision photometry is revolutionizing stellar astrophysics. We are seeing intrinsic phenomena on an unprecedented scale, and interpreting them is both a challenge and an exciting privilege. Eclipsing binary stars are of particular significance for stellar astrophysics because precise modeling leads to fundamental parameters of the orbiting components: masses, radii, temperatures and luminosities to better than 1-2%. On top of that, eclipsing binaries are ideal physical laboratories for studying other physical phenomena, such as asteroseismic properties, chromospheric activity, proximity effects, mass transfer in close binaries, etc. Because of the eclipses, the basic geometry is well constrained, but a follow-up spectroscopy is required to get the dynamical masses and the absolute scale of the system. A conjunction of Kepler photometry and ground- based spectroscopy is a treasure trove for eclipsing binary star astrophysics. This proposal focuses on a carefully selected set of 100 short period eclipsing binary stars. The fundamental goal of the project is to study the intrinsic astrophysical effects typical of short period binaries in great detail, utilizing Kepler photometry and follow-up spectroscopy to devise a robust and consistent set of modeling results. The complementing spectroscopy is being secured from 3 approved and fully funded programs: the NOAO 4-m echelle spectroscopy at Kitt Peak (30 nights; PI Prsa), the 10- m Hobby-Eberly Telescope high-resolution spectroscopy (PI Mahadevan), and the 2.5-m Sloan Digital Sky Survey III spectroscopy (PI Mahadevan). The targets are prioritized by the projected scientific yield. Short period detached binaries host low-mass (K- and M- type) components for which the mass-radius relationship is sparsely populated and still poorly understood, as the radii appear up to 20% larger than predicted by the population models. We demonstrate the spectroscopic detection viability in the secondary

  8. Observing and Modeling the Optical Counterparts of Short-Period Binary Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Schroeder, Joshua

    In this dissertation, I explore the subject of short-period binary millisecond pulsars discovered by the Fermi Gamma-ray Space Telescope and radio follow-up teams, and present observations of fields containing eight recently discovered short-period (Porb < 1 d) binary millisecond pulsars using the telescopes at MDM Observatory. The goal of these observations was to detect the optical counterparts of the binaries and, for the best-suited counterparts detected, to observe the photometric variation of the companion that happens over the course of the orbit in various filters. The hope was to then use the light curves to model the systems and obtain constraints on the mass of the neutron stars which are likely to be some of the most massive neutron stars in the galaxy. Optical counterparts to four of these systems are detected, one of which, PSR J2214+3000, is a novel detection. Additionally, I present the fully orbital phase-resolved B, V , and R light curves of the optical counterparts to two objects, PSR J1810+1744 and PSR J2215+5135, for which I employ the ELC model of Orosz & Hauschildt (2000) to measure the unknown system parameters. For PSR J1810+1744 I find that the system parameters cannot be fit even assuming that 100% of the spin-down luminosity of the pulsar is irradiating the secondary, and so radial velocity measurements of this object will be required for the complete solution. However, PSR J2215+5135 exhibits light curves that are extremely well constrained using the ELC model and we find that the mass of the neutron star is constrained by these and the radio observations to be MNS > 1.75 solar masses; at the 3-sigma level. I also find a discrepancy between the model temperature and the measured colors of this object which I interpret as possible evidence for an additional high-temperature source such as a quiescent disk. Given this and the fact that PSR J2215+5135 contains a relatively high mass companion (Mc > 0.1 solar masses), I propose that similar

  9. Roche lobe effects on expanded upper atmospheres of short-periodic giant exoplanets

    NASA Astrophysics Data System (ADS)

    Jaritz, G. F.; Endler, S.; Langmayr, D.; Lammer, H.; Grießmeier, J.-M.; Erkaev, N. V.; Biernat, H. K.

    2005-08-01

    Theoretical studies and recent observational evidence of the expansion of the atmospheres of short-periodic exoplanets show that the atmospheres extend up to several planetary radii. This indicates that the atmospheres experience blow-off conditions. Because of the short orbital distance to their host stars, the expansion of the upper atmosphere is no longer radially symmetric, but depends on the direction to the central body, resulting in a deformation of the expanded atmosphere. We show the connection between atmospheric expansion, tidal forces and effects of the Roche potential and find that HD 209458 b, OGLE-TR-10 b and OGLE-TR-111 b are most likely in a state of classical hydrodynamical blow-off, because the distance where blow-off can occur is less than the distance to the Lagrangian point L1. On the other hand, OGLE-TR-56 b, OGLE-TR-113 b, OGLE-TR-132 b and TreS-1 experience a geometrical blow-off defined by the Roche lobe as proposed by Lecavelier des Etangs et al. (2004, A&A, 418, L1). Our results have important implications for the evolution of short periodic gas giants, because the Roche lobe overflow of the atmosphere can lead to lower mass loss rates over the exoplanets history, compared to gas giants which experience hydrodynamic expansion and loss unaffected by this boundary. Thus, massive exoplanets like OGLE-TR-56 b in very close orbital distances are subject to geometrical blow-off conditions, this results in a total mass loss for this particular exoplanet of the order of about 3 × 10-2 M_pl over the planets age, even if current mass loss rates of about 2 × 1011 g s-1 are calculated. If the exoplanet effected by the geometrical blow-off is more massive, the mass loss rate is even lower. However, giant exoplanets like HD 209458 b, OGLE-TR-10 b and OGLE-TR-111 b at orbital distances of about 0.05 AU may experience classical hydrodynamic blow-off conditions, which can result in higher mass loss rates. Thus, such planets may shrink to their core

  10. Pulse

    MedlinePlus

    ... resting for at least 10 minutes. Take the exercise heart rate while you are exercising. ... pulse rate can help determine if the patient's heart is pumping. ... rate gives information about your fitness level and health.

  11. The first orbital parameters and period variation of the short-period eclipsing binary AQ Boo

    NASA Astrophysics Data System (ADS)

    Wang, Shuai; Zhang, Liyun; Pi, Qingfeng; Han, Xianming L.; Zhang, Xiliang; Lu, Hongpeng; Wang, Daimei; Li, TongAn

    2016-10-01

    We obtained the first VRI CCD light curves of the short-period contact eclipsing binary AQ Boo, which was observed on March 22 and April 19 in 2014 at Xinglong station of National Astronomical Observatories, and on January 20, 21 and February 28 in 2015 at Kunming station of Yunnan Observatories of Chinese Academy of Sciences, China. Using our six newly obtained minima and the minima that other authors obtained previously, we revised the ephemeris of AQ Boo. By fitting the O-C (observed minus calculated) values of the minima, the orbital period of AQ Boo shows a decreasing tendency P˙ = - 1.47(0.17) ×10-7 days/year. We interpret the phenomenon by mass transfer from the secondary (more massive) component to the primary (less massive) one. By using the updated Wilson & Devinney program, we also derived the photometric orbital parameters of AQ Boo for the first time. We conclude that AQ Boo is a near contact binary with a low contact factor of 14.43%, and will become an over-contact system as the mass transfer continues.

  12. Detection of short period coronal intensity oscillations and observing programme during 1998 and 1999 eclipses

    NASA Astrophysics Data System (ADS)

    Singh, Jagdev

    An experiment to search for short-period intensity oscillations in the solar corona was conducted during the total solar eclipse of 1995 October 24 at Kalpi (26^ circ 08^' ' N, 79^' ' 45^' ' E), India. The analysis of the data shows that measured coronal intensity in the continuum, centered around 5500 AA with a pass-band of about 240 AA, recorded at 20 hertz using a thermoelectric-water cooled phtomultiplier varied with time during the eclipse. The power spectrum analysis of the data reveals that most of the power is contained in 6 frequencies below 0.2 Hz. A least square analysis gives the period of the 6 frequency components to be 56.5, 19.5, 13.5, 8.0, 6.1 and 5.3 s. These oscillations are found to be sinusoidal and their amplitude are found to lie in the range of 0.2 - 1.3% of the coronal brightness. The verification and determination of the oscillation scale length and changes in these oscillations with solar radii will help in understanding the heating of solar corona. The details of the experiment to be conducted during the total solar eclipses of 1998 and 1999 to study these oscillations as a function of solar radius will be discussed. It is planned to develop a multi-channel photometer using R647 Hamamatsu photomultiplier tubes to observe the corona at 6 different locations at the solar corona.

  13. A SHORT-PERIOD CENSOR OF SUB-JUPITER MASS EXOPLANETS WITH LOW DENSITY

    SciTech Connect

    Szabo, Gy. M.; Kiss, L. L.

    2011-02-01

    Despite the existence of many short-period hot Jupiters, there is not one hot Neptune with an orbital period less than 2.5 days. Here, we discuss a cluster analysis of the currently known 106 transiting exoplanets to investigate a possible explanation for this observation. We find two distinct clusters in the mass-density space, one with hot Jupiters with a wide range of orbital periods (0.8-114 days) and a narrow range of planet radii (1.2 {+-} 0.2 R{sub J} ) and another one with a mixture of super-Earths, hot Neptunes, and hot Jupiters, exhibiting a surprisingly narrow period distribution (3.7 {+-} 0.8 days). These two clusters follow strikingly different distributions in the period-radius parameter plane. The branch of sub-Jupiter mass exoplanets is censored by the orbital period at the large-radius end: no planets with mass between 0.02 and 0.8 M{sub J} or with radius between 0.25 and 1.0 R{sub J} are known with P{sub orb} < 2.5 days. This clustering is not predicted by current theories of planet formation and evolution, which we also review briefly.

  14. A generalized behavioral model for rotating short period comets with spectral orbital elements and axial orientation

    NASA Technical Reports Server (NTRS)

    Fanale, F. P.; Salvail, J. R.

    1984-01-01

    A generalized model for short period comets is developed which integrates in a fairly rigorous manner the isolation history of regions on rotating comets with specified axial orientation and the complex feedback processes involving heat, gas and dust transport, dust mantle development and coma opacity. Attention is focused on development, reconfiguration and partial or complete launching of dust mantles and the reciprocal effects of these three processes on ice surface temperature and gas and dust production. The dust mantle controls the H2O flux not only by its effect on the temperature at the ice interface but (dominantly) by its dynamic stability which strongly influences vapor diffusivity. The model includes the effects of latitude, rotation and spin axis orientation are included and applied to an initially homogeneous sphere of H2O ice and silicate using the orbital parameters of comet Encke. Numerous variations of the model, using combinations of grain size distribution, dust-to-ice ratio, latitude and spin axis orientation, are presented and discussed. Resulted for a similar nonrotating, constant Sun orientation models are also included.

  15. Studies of cortical interactions over short periods of time during the search for verbal associations.

    PubMed

    Nikolaev, A R; Ivanitskii, G A; Ivanitskii, A M

    2001-01-01

    Interactions between cortical areas were studied during the search for verbal associations and reading of words. The functional anatomy and the sequence of involvement of cortical areas during the solution of these tasks have been described previously, in studies using positron emission tomography and multichannel recordings of evoked potentials combined with identification of the locations of dipole sources [8, 9, 19, 25]. Cortical interactions reflected in terms of the synchronization of EEG rhythms were studied by developing a method based on correlating curve wavelets, which allows the moments at which this synchronization occurs to be identified over short periods of time comparable with the speeds of individual thought operations (up to 100 msec). Three main stages were identified in the search for associations. During the first 200 msec after stimulus presentation, cortical connections were seen between the right and left frontal areas; at 200-500 msec, there were connections between the frontal and the temporal-parietal areas; finally, at 450-700 sec, there were connections between the left temporal and the right frontal-central-temporal areas. These results are in good agreement with data obtained previously using other methods and supplement them with mapping data on cortical connections. A number of differences in the mechanisms of information processing during the search for associations and reading were also identified.

  16. Long-term orbital evolution of short-period comets found in Project Cosmo-DICE

    NASA Technical Reports Server (NTRS)

    Nakamura, Tsuko; Yoshikawa, Makoto

    1992-01-01

    Orbital evolutions of about 160 short-period (SP) comets are numerically integrated for 4400 years in the framework of a realistic dynamical model. By the round-trip error in closure test, a reliable time space of the integrated orbits is estimated for each comet. Majority of the SP comets with their Tisserand's constant(J) between 2.8 and 3.1 are found to evolve within the past 1000-2000 years from the orbits whose perihelia are near the Jovian orbit to the orbits with perihelia of 1-2 AU. This evolution is much more rapid than that expected from Monte Carlo simulations based on symmetric distribution of planetary perturbations, thus suggesting that asymmetry of perturbation distribution play an important role in cometary evolution. Several comets are shown to evolve from the near-Saturn orbits and then to be handed over under the control of Jupiter. We also find that a few comets were captured from long-period orbits (a = 75-125 AU) via only a few close encounters with Jupiter. It is confirmed that the captured SP comets of low-inclination with 2.7 less than J less than 3.1 show more or less strong chaotic behavior. On the other hand, comets with longer orbital period and/or of high inclination reveal slow or quasi-periodic orbital evolution.

  17. The Unusual Short Period Binary V342 Aquilae; Does it Break the Evolutionary Theory Mold

    NASA Astrophysics Data System (ADS)

    Hartman, C.; Polidan, R. S.; Welty, A. D.; Wade, R.; Etzel, P. B.; Bruhweiler, F. C.

    Analysis of the eclipsing (period = 3.39 days) binary V342 Aquilae at visible wavelengths reveals that the system is heavily enshrouded with gas, masking the identity of the underlying stars. In the ultraviolet V342 Aquilae shows six times more attenuation at phases outside of eclipse than most Algols. It is likely, then, that V342 Aquilae is the most enshrouded short period Algol system known. Our ultraviolet spectra show very pronounced Fe II absorption lines arising from ground and metastable levels, indicating an extensive circumstellar gas envelope. The strength of this absorption shows both an orbital and a cycle-to-cycle variability. The eclipse spectra display very strong emission from lines such as C II, Si IV, and C IV, with a striking similarity to the interacting binary TT Hydrae (B9.5V+K0III). We have deduced that the system consists of a late B star with a late GIII-IV companion and a mass ratio on the order of 0.5. A detailed description of the observations, as well as deduced geometrical and physical properties of the system are presented. The apparent conflict of these observations with presently understood theory of binary evolution will be discussed. Wade wishes to acknowledge the support of NASA grant NAG 5-1698.

  18. Reciprocal-Space Analysis of Compositional Modulation in Short-Period Superlattices Using Position-Sensitive X-Ray Detection

    SciTech Connect

    Ahrenkiel, S.P.; Follstaedt, D.M.; Lee, S.R.; Millunchick, J.M.; Norman, A.G.; Reno, J.L.; Twesten, R.D.

    1998-11-10

    Epitaxial growth of AlAs-InAs short-period superlattices on (001) InP can lead to heterostructures exhibiting strong, quasi-periodic, lateral modulation of the alloy composition; transverse satellites arise in reciprocal space as a signature of the compositional modulation. Using an x-ray diffractometer equipped with a position-sensitive x-ray detector, we demonstrate reciprocal-space mapping of these satellites as an efficient, nondestructive means for detecting and characterizing the occurrence of compositional modulation. Systematic variations in the compositional modulation due to the structural design and the growth conditions of the short-period superlattice are characterized by routine mapping of the lateral satellites. Spontaneous compositional modulation occurs along the growth front during molecular-beam epitaxy of (AlAs) (InAs)n short-period superlattices. The modulation is quasi-periodic and forms a lateral superlattice superimposed on the intended SPS structure. Corresponding transverse satellites arise about each reciprocal lattice point, and x-ray diffraction can be routinely used to map their local reciprocal-space structure. The integrated intensity, spacing, orientation, and shape of these satellites provide a reliable means for nondestructively detecting and characterizing the compositional modulation in short-period superlattices. The analytical efficiency afforded by the use of a PSD has enabled detailed study of systematic vacations in compositional modulation as a function of the average composition, the period, and the growth rate of the short- period superlattice

  19. THE VERY SHORT PERIOD M DWARF BINARY SDSS J001641-000925

    SciTech Connect

    Davenport, James R. A.; Becker, Andrew C.; Hawley, Suzanne L.; Gunning, Heather C.; Munshi, Ferah A.; Albright, Meagan; West, Andrew A.; Bochanski, John J.; Holtzman, Jon; Hilton, Eric J.

    2013-02-10

    We present follow-up observations and analysis of the recently discovered short period low-mass eclipsing binary, SDSS J001641-000925. With an orbital period of 0.19856 days, this system has one of the shortest known periods for an M dwarf binary system. Medium-resolution spectroscopy and multi-band photometry for the system are presented. Markov Chain Monte Carlo modeling of the light curves and radial velocities yields estimated masses for the stars of M {sub 1} = 0.54 {+-} 0.07 M {sub Sun} and M {sub 2} = 0.34 {+-} 0.04 M {sub Sun }, and radii of R {sub 1} = 0.68 {+-} 0.03 R {sub Sun} and R {sub 2} = 0.58 {+-} 0.03 R {sub Sun }, respectively. This solution places both components above the critical Roche overfill limit, providing strong evidence that SDSS J001641-000925 is the first verified M-dwarf contact binary system. Within the follow-up spectroscopy we find signatures of non-solid body rotation velocities, which we interpret as evidence for mass transfer or loss within the system. In addition, our photometry samples the system over nine years, and we find strong evidence for period decay at the rate of P-dot {approx} 8 s yr{sup -1}. Both of these signatures raise the intriguing possibility that the system is in over-contact, and actively losing angular momentum, likely through mass loss. This places SDSS J001641-000925 as not just the first M-dwarf over-contact binary, but one of the few systems of any spectral type known to be actively undergoing coalescence. Further study of SDSS J001641-000925 is ongoing to verify the nature of the system, which may prove to be a unique astrophysical laboratory.

  20. Magnetic activity and orbital period variation of the short-period eclipsing binary DV Psc

    SciTech Connect

    Pi, Qing-feng; Zhang, Li-Yun; Zhang, Xi-liang

    2014-03-01

    We present six new BVR{sub c}I{sub c} CCD light curves of a short-period RS CVn binary DV Psc obtained in 2010-2012. The light curve distortions change on both short and long timescales, which is explained by two starspots on the primary component. Moreover, five new flare events were detected and the flare ratio of DV Psc is about 0.082 flares per hour. There is a possible relation between the phases (longitude) of the flares and starspots for all of the available data of late-type binaries, which implies a correlation of the stellar activity of the spots and flares. The cyclic oscillation, with a period of 4.9 ± 0.4 yr, may result from the magnetic activity cycle, identified by the variability of Max. I-Max. II. Until now, there were no spectroscopic studies of chromospheric activity indicators of the H{sub β} and H{sub γ} lines for DV Psc. Our observations of these indicators show that DV Psc is active, with excess emissions. The updated O – C diagram with an observing time span of about 15 yr shows an upward parabola, which indicates a secular increase in the orbital period of DV Psc. The orbital period secularly increases at a rate of dP/dt = 2.0×10{sup –7} days yr{sup –1}, which might be explained by the angular momentum exchanges or mass transfer from the secondary to primary component.

  1. On the composition of earth's short-period seismic noise field

    USGS Publications Warehouse

    Koper, K.D.; Seats, K.; Benz, H.

    2010-01-01

    In the classic microseismic band of 5-20 sec, seismic noise consists mainly of fundamental mode Rayleigh and Love waves; however, at shorter periods seismic noise also contains a significant amount of body-wave energy and higher mode surface waves. In this study we perform a global survey of Earth's short-period seismic noise field with the goal of quantifying the relative contributions of these propagation modes. We examined a year's worth of vertical component data from 18 seismic arrays of the International Monitoring System that were sited in a variety of geologic environments. The apertures of the arrays varied from 2 to 28 km, constraining the periods we analyzed to 0.25-2.5 sec. Using frequency-wavenumber analysis we identified the apparent velocity for each sample of noise and classified its mode of propagation. The dominant component was found to be Lg, occurring in about 50% of the noise windows. Because Lg does not propagate across ocean-continent boundaries, this energy is most likely created in shallow water areas near coastlines. The next most common component was P-wave energy, which accounted for about 28% of the noise windows. These were split between regional P waves (Pn=Pg at 6%), mantle bottoming P waves (14%), and core-sensitive waves (PKP at 8%). This energy is mostly generated in deep water away from coastlines, with a region of the North Pacific centered at 165?? W and 40?? N being especially prolific. The remainder of the energy arriving in the noise consisted of Rg waves (28%), a large fraction of which may have a cultural origin. Hence, in contrast to the classic micro-seismic band of 5-20 sec, at shorter periods fundamental mode Rayleigh waves are the least significant component.

  2. Short-Period Mesospheric Gravity Waves and Diurnal Tidal Interactions at a Critical Layer

    NASA Astrophysics Data System (ADS)

    Ejiri, M. K.; Taylor, M. J.; Franke, S. J.

    2007-05-01

    The US Maui-MALT program is designed to investigate the properties and dynamics of the low-latitude mesosphere and lower thermosphere region (MLT) in exceptional detail. On June 29, 2003, the University of Illinois Meteor Wind Radar (MWR) at Kihei, Maui (20.8°N, 156.4°W) observed a diurnal tidal wave with an amplitude twice as large as normal at mesospheric height (80--100 km) for 7 hours (1400--2100 UT). At the same time, the Utah State University Mesospheric Temperature Mapper (MTM) measured OH and O2 band emission intensities and temperatures at nearby Haleakala Crater, Maui (20.8°N, 156.2°W). The MTM observed a short-period gravity wave (GW) event propagating through this region for most of the night from 600 to 1500 UT. The GWs disappeared from the O2 band data (peak altitude: ~94 km) and the OH band data (~87 km) around 1400 UT and 1430 UT, respectively. Qualitative and quantitative investigations of relationship between the observed GW dissipations and the increasing background wind field show the following. 1. The wave dissipation observed in both emissions was caused by wave absorption at a critical layer (CL) when the background wind speed exceeded the wave phase speed. 2. The wave absorption at the CL appears to accelerate the background wind. 3. The acceleration occurred over a wide altitude range (80--100 km) because the CL was moving down in association with downward progression of the diurnal tidal wave. 4. The change in background wind speed caused by the GW absorption at the CL was comparable with the induced tidal effect.

  3. The Advanced Helical Generator

    SciTech Connect

    Reisman, D B; Javedani, J B; Ellsworth, G F; Kuklo, R M; Goerz, D A; White, A D; Tallerico, L J; Gidding, D A; Murphy, M J; Chase, J B

    2009-10-26

    A high explosive pulsed power (HEPP) generator called the Advanced Helical Generator (AHG) has been designed, built, and successfully tested. The AHG incorporates design principles of voltage and current management to obtain a high current and energy gain. Its design was facilitated by the use of modern modeling tools as well as high precision manufacture. The result was a first-shot success. The AHG delivered 16 Mega-Amperes of current and 11 Mega-Joules of energy to a quasi-static 80 nH inductive load. A current gain of 154 times was obtained with a peak exponential rise time of 20 {micro}s. We will describe in detail the design and testing of the AHG.

  4. Dust environment and dynamical history of a sample of short-period comets

    NASA Astrophysics Data System (ADS)

    Pozuelos, F. J.; Moreno, F.; Aceituno, F.; Casanova, V.; Sota, A.; López-Moreno, J. J.; Castellano, J.; Reina, E.; Diepvens, A.; Betoret, A.; Häusler, B.; Gonález, C.; Rodríguez, D.; Bryssinck, E.; Cortés, E.; García, F.; García, F.; Limón, F.; Grau, F.; Fratev, F.; Baldrís, F.; Rodriguez, F. A.; Montalbán, F.; Soldán, F.; Muler, G.; Almendros, I.; Temprano, J.; Bel, J.; Sánchez, J.; Lopesino, J.; Báez, J.; Hernández, J. F.; Martín, J. L.; Ruiz, J. M.; Vidal, J. R.; Gaitán, J.; Salto, J. L.; Aymamí, J. M.; Bosch, J. M.; Henríquez, J. A.; Martín, J. J.; Lacruz, J.; Tremosa, L.; Lahuerta, L.; Reszelsky, M.; Rodríguez, M.; Camarasa, M.; Campas, M.; Canales, O.; Dekelver, P. J.; Moreno, Q.; Benavides, R.; Naves, R.; Dymoc, R.; García, R.; Lahuerta, S.; Climent, T.

    2014-08-01

    Aims: In this work, we present an extended study of the dust environment of a sample of short-period comets and their dynamical history. With this aim, we characterize the dust tails when the comets are active, and we make a statistical study to determine their dynamical evolution. The targets selected were 22P/Kopff, 30P/Reinmuth 1, 78P/Gehrels 2, 115P/Maury, 118P/Shoemaker-Levy 4, 123P/West-Hartley, 157P/Tritton, 185/Petriew, and P/2011 W2 (Rinner). Methods: We use two different observational data sets: a set of images taken at the Observatorio de Sierra Nevada and, the Afρ curves provided by the amateur astronomical association Cometas-Obs. To model these observations, we use our Monte Carlo dust tail code. From this analysis, we derive the dust parameters, which best describe the dust environment: dust loss rates, ejection velocities, and size distribution of particles. On the other hand, we use a numerical integrator to study the dynamical history of the comets, which allows us to determine with a 90% confidence level the time spent by these objects in the region of Jupiter family comets. Results: From the Monte Carlo dust tail code, we derived three categories according to the amount of dust emitted: weakly active (115P, 157P, and Rinner), moderately active (30P, 123P, and 185P), and highly active (22P, 78P, and 118P). The dynamical studies showed that the comets of this sample are young in the Jupiter family region, where the youngest ones are 22P (~100 yr), 78P (~500 yr), and 118P (~600 yr). The study points to a certain correlation between comet activity and time spent in the Jupiter family region, although this trend is not always fulfilled. The largest particle sizes are not tightly constrained, so that the total dust mass derived should be regarded as a lower limit. Appendices are available in electronic form at http://www.aanda.org

  5. SOHO/SWAN OBSERVATIONS OF SHORT-PERIOD SPACECRAFT TARGET COMETS

    SciTech Connect

    Combi, M. R.; Lee, Y.; Patel, T. S.; Maekinen, J. T. T.; Bertaux, J.-L.; Quemerais, E.

    2011-04-15

    SWAN, the Solar Wind ANisotropies all-sky hydrogen Ly{alpha} camera on the Solar and Heliospheric Observatory spacecraft that makes all-sky images of interplanetary neutral hydrogen, has an ongoing campaign to make special observations of comets, both short- and long-period ones, in addition to the serendipitous observations of comets as part of the all-sky monitoring program. We report here on a study of several short-period comets that were detected by SWAN: 21P/Giacobini-Zinner (1998 and 2005 apparitions), 19P/Borrelly (2001 apparition), 81P/Wild 2 (1997 apparition), and 103P/Hartley 2 (1997 apparition). SWAN observes comets over long continuous stretches of their visible apparitions and therefore provides excellent temporal coverage of the water production. For some of the observations we are also able to analyze an entire sequence of images over many days to several weeks/months using our time-resolved model and extract daily average water production rates over continuous periods of several days to months. The short-term (outburst) and long-term behavior can be correlated with other observations. The overall long-term variation is examined in light of seasonal effects seen in the pre- to post-perihelion differences. For 21P/Giacobini-Zinner and 81P/Wild 2 the activity variations over each apparition were more continuously monitored but nonetheless consistent with previous observations. For 19P/Borrelly we found a very steep variation of water production rates, again consistent with some previous observations, and a variation over six months around perihelion that was reasonably consistent with the spin-axis model of Schleicher et al. and the illumination of the main active areas. During the 1997-1998 apparition of 103P/Hartley 2, the target comet of the EPOXI mission (the Deep Impact extended mission), we found a variation with heliocentric distance ({approx}r{sup -3.6}) that was almost as steep as 19P/Borrelly and, given the small measured radius near

  6. Seismic Site Effects from the Seafloor Motion Recorded by the Short-period Ocean Bottom Seismometers

    NASA Astrophysics Data System (ADS)

    Lin, J. Y.; Cheng, W. B.; Chin, S. J.; Hsu, S. K.; Dong, J. J.

    2014-12-01

    For decades, it has been mentioned that submarine slope failures are spatially linked to the presence of gas hydrates/gas-charged sediments. When triggered by earthquakes, oversteepen and instable sediments may prompt breakouts of the slopes containing gas hydrates and cause submarine landslides and tsunamis. Widely distributed BSRs have been observed in the area offshore of southwestern Taiwan where the active accretionary complex meets with the passive China continental margin. In the region, large or small scale landslides were also reported based on seismic interpretations. In order to clarify the link between earthquake, landslide and the presence of gas hydrate, we evaluate the response of seafloor sediments in regard to passive dynamic loads. Horizontal-to-vertical (H/V) spectral ratios are used to characterize the local sediment response. Ambient noise as well as distant earthquakes are used as generators of the passive dynamic loads. Based on this study, we aim to characterize the site in terms of its physical properties and the local site effect produced by shallow marine sediments. The results show that the maximum H/V ratios appeared in the range of 5-10 Hz, where the horizontal amplitudes increased by an order of magnitude relative to the vertical amplitude. The stations located in the northwestern part of study area were characterized by another relatively small peak at proximately 2 Hz, which may indicates the presence of a discontinuity of sediments. For most stations, the H/V ratios estimated based on the earthquake (i.e. strong input signal) and noise (background, micro-seismic noise) records were characterized by different pattern. No distinct peak is observed for the H/V pattern calculated during earthquakes. This phenomenon may suggest that no clear sedimentary boundary exist when a stronger motion applies. Estimating H/V spectral ratios of data recorded by the seven short period OBSs (Ocean Bottom Seismometer) deployed in the southwest Taiwan

  7. Studying Short-Period Comets and Long-Period Comets Detected by WISE/NEOWISE

    NASA Astrophysics Data System (ADS)

    Kramer, Emily A.; Fernández, Yanga R.; Bauer, James M.; Stevenson, Rachel; Mainzer, Amy K.; Grav, Tommy; Masiero, Joseph; Walker, Russell G.; Lisse, Carey M.

    2014-11-01

    The Wide-field Infrared Survey Explorer (WISE) mission surveyed the sky in four infrared wavelength bands (3.4, 4.6, 12 and 22-micron) between January 2010 and February 2011 [1, 2]. During the mission, WISE serendipitously observed 160 comets, including 21 newly discovered objects. About 89 of the comets observed by WISE displayed a significant dust tail in the 12 and 22-micron (thermal emission) bands, showing a wide range of activity levels and dust morphology. Since the observed objects are a mix of both long-period comets (LPCs) and short-period comets (SPCs), differences in their activity can be used to better understand the thermal evolution that each of these populations has undergone. For the comets that displayed a significant dust tail, we have estimated the sizes and ages of the particles using dynamical models based on the Finson-Probstein method [3, 4]. For a selection of 40 comets, we have then compared these models to the data using a novel tail-fitting method that allows the best-fit model to be chosen analytically rather than subjectively. For comets that were observed multiple times by WISE, the dust tail particle properties were estimated separately, and then compared. We find that the dust tails of both LPCs and SPCs are primarily comprised of ~mm to cm sized particles, which were the result of emission that occurred several months to several years prior to the observations. The LPCs nearly all have strong dust emission close to the comet's perihelion distance, and the SPCs mostly have strong dust emission close to perihelion, but some have strong dust emission well before perihelion. Acknowledgments: This publication makes use of data products from (1) WISE, which is a joint project of UCLA and JPL/Caltech, funded by NASA; and (2) NEOWISE, which is a project of JPL/Caltech, funded by the Planetary Science Division of NASA. EK was supported by a NASA Earth and Space Sciences Fellowship. RS gratefully acknowledges support from the NASA

  8. Short-period near-contact binary systems at the beginning of the overcontact phase

    NASA Astrophysics Data System (ADS)

    Qian, Shengbang

    2002-11-01

    A detailed analysis of orbital period changes of seven near-contact binary stars (NCBs) (BL And, V473 Cas, XZ CMi, BV Eri, RU Eri, UU Lyn and GR Tau) with period less than 1 d has been performed and their respective O-C diagrams are formed and discussed. It is found that all systems analysed show secular period decreasing. For V473 Cas, the analysis of the period change was performed based on data collected by Moschner, Frank & Bastian. For XZ CMi, its period shows some complex changes, a possible cyclic oscillation is discovered to superpose on the secular decrease that can be explained either by the presence of a third body or by magnetic activity cycles of the components. Since the third-body assumption is consistent with the photometric solution of Rafert, XZ CMi may be a truly triple system. For BV Eri, the period decrease is only supported by weak evidence. All the seven systems are short-period NCBs with AF-type primary components where both components are filling or nearly filling the critical Roche lobe. As the period decreases, the separation between both components will be reducing and thus these systems will evolve into A-type overcontact binaries. The period decrease may be caused by mass transfer or/and by angular momentum loss via magnetic braking. Combined with the published data on the other systems of the same type, a possible statistical connection between orbital period P and its rate of decrease dP/dt is obtained: dP/dt=-5.3 × 10-7×P+ 1.3 × 10-7 d yr-1. This correlation indicates that the smaller the orbital period P is, the smaller its rate of change dP/dt will be. The correlation found in this paper indicates that there may be a smooth transition from A- and F-type NCBs with period decreases to the A- and F-type overcontact binaries that have period increases, and in that sense one may postulate that the NCBs may be the progenitors of the A-type W UMa systems and will be oscillating around a marginal-contact state as predicted by thermal

  9. SOHO/SWAN Observations of Short-period Spacecraft Target Comets

    NASA Astrophysics Data System (ADS)

    Combi, M. R.; Lee, Y.; Patel, T. S.; Mäkinen, J. T. T.; Bertaux, J.-L.; Quémerais, E.

    2011-04-01

    SWAN, the Solar Wind ANisotropies all-sky hydrogen Lyα camera on the Solar and Heliospheric Observatory spacecraft that makes all-sky images of interplanetary neutral hydrogen, has an ongoing campaign to make special observations of comets, both short- and long-period ones, in addition to the serendipitous observations of comets as part of the all-sky monitoring program. We report here on a study of several short-period comets that were detected by SWAN: 21P/Giacobini-Zinner (1998 and 2005 apparitions), 19P/Borrelly (2001 apparition), 81P/Wild 2 (1997 apparition), and 103P/Hartley 2 (1997 apparition). SWAN observes comets over long continuous stretches of their visible apparitions and therefore provides excellent temporal coverage of the water production. For some of the observations we are also able to analyze an entire sequence of images over many days to several weeks/months using our time-resolved model and extract daily average water production rates over continuous periods of several days to months. The short-term (outburst) and long-term behavior can be correlated with other observations. The overall long-term variation is examined in light of seasonal effects seen in the pre- to post-perihelion differences. For 21P/Giacobini-Zinner and 81P/Wild 2 the activity variations over each apparition were more continuously monitored but nonetheless consistent with previous observations. For 19P/Borrelly we found a very steep variation of water production rates, again consistent with some previous observations, and a variation over six months around perihelion that was reasonably consistent with the spin-axis model of Schleicher et al. and the illumination of the main active areas. During the 1997-1998 apparition of 103P/Hartley 2, the target comet of the EPOXI mission (the Deep Impact extended mission), we found a variation with heliocentric distance (~r -3.6) that was almost as steep as 19P/Borrelly and, given the small measured radius near aphelion, this places a

  10. Helical localized wave solutions of the scalar wave equation.

    PubMed

    Overfelt, P L

    2001-08-01

    A right-handed helical nonorthogonal coordinate system is used to determine helical localized wave solutions of the homogeneous scalar wave equation. Introducing the characteristic variables in the helical system, i.e., u = zeta - ct and v = zeta + ct, where zeta is the coordinate along the helical axis, we can use the bidirectional traveling plane wave representation and obtain sets of elementary bidirectional helical solutions to the wave equation. Not only are these sets bidirectional, i.e., based on a product of plane waves, but they may also be broken up into right-handed and left-handed solutions. The elementary helical solutions may in turn be used to create general superpositions, both Fourier and bidirectional, from which new solutions to the wave equation may be synthesized. These new solutions, based on the helical bidirectional superposition, are members of the class of localized waves. Examples of these new solutions are a helical fundamental Gaussian focus wave mode, a helical Bessel-Gauss pulse, and a helical acoustic directed energy pulse train. Some of these solutions have the interesting feature that their shape and localization properties depend not only on the wave number governing propagation along the longitudinal axis but also on the normalized helical pitch.

  11. Helical localized wave solutions of the scalar wave equation.

    PubMed

    Overfelt, P L

    2001-08-01

    A right-handed helical nonorthogonal coordinate system is used to determine helical localized wave solutions of the homogeneous scalar wave equation. Introducing the characteristic variables in the helical system, i.e., u = zeta - ct and v = zeta + ct, where zeta is the coordinate along the helical axis, we can use the bidirectional traveling plane wave representation and obtain sets of elementary bidirectional helical solutions to the wave equation. Not only are these sets bidirectional, i.e., based on a product of plane waves, but they may also be broken up into right-handed and left-handed solutions. The elementary helical solutions may in turn be used to create general superpositions, both Fourier and bidirectional, from which new solutions to the wave equation may be synthesized. These new solutions, based on the helical bidirectional superposition, are members of the class of localized waves. Examples of these new solutions are a helical fundamental Gaussian focus wave mode, a helical Bessel-Gauss pulse, and a helical acoustic directed energy pulse train. Some of these solutions have the interesting feature that their shape and localization properties depend not only on the wave number governing propagation along the longitudinal axis but also on the normalized helical pitch. PMID:11488494

  12. Helicity content and tokamak applications of helicity

    SciTech Connect

    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.

  13. A high-average power tapered FEL amplifier at submillimeter frequencies using sheet electron beams and short-period wigglers

    SciTech Connect

    Bidwell, S.W.; Radack, D.J.; Antonsen, T.M. Jr.; Booske, J.H.; Carmel, Y.; Destler, W.W.; Granatstein, V.L.; Levush, B.; Latham, P.E.; Zhang, Z.X.

    1990-01-01

    A high-average-power FEL amplifier operating at submillimeter frequencies is under development at the University of Maryland. Program goals are to produce a CW, {approximately}1 MW, FEL amplifier source at frequencies between 280 GHz and 560 GHz. To this end, a high-gain, high-efficiency, tapered FEL amplifier using a sheet electron beam and a short-period (superconducting) wiggler has been chosen. Development of this amplifier is progressing in three stages: (1) beam propagation through a long length ({approximately}1 m) of short period ({lambda}{sub {omega}} = 1 cm) wiggler, (2) demonstration of a proof-of-principle amplifier experiment at 98 GHz, and (3) designs of a superconducting tapered FEL amplifier meeting the ultimate design goal specifications. 17 refs., 1 fig., 1 tab.

  14. Concentric waves and short-period oscillations observed in the ionosphere after the 2013 Moore EF5 tornado

    NASA Astrophysics Data System (ADS)

    Nishioka, Michi; Tsugawa, Takuya; Kubota, Minoru; Ishii, Mamoru

    2013-11-01

    We detected clear concentric waves and short-period oscillations in the ionosphere after an Enhanced Fujita scale (EF)5 tornado hit Moore, Oklahoma, U.S., on 20 May 2013 using dense wide-coverage ionospheric total electron content (TEC) observations in North America. These concentric waves were nondispersive, with a horizontal wavelength of ~120 km and a period of ~13 min. They were observed for more than 7 h throughout North America. TEC oscillations with a period of ~4 min were also observed to the south of Moore for more than 8 h. A comparison between the TEC observations and infrared cloud image from the GOES satellite indicates that the concentric waves and short-period oscillations are caused by supercell-induced atmospheric gravity waves and acoustic resonances, respectively. This observational result provides the first clear evidence of a severe meteorological event causing atmospheric waves propagating upward in the upper atmosphere and reaching the ionosphere.

  15. Short period wave generation in Moss Landing Harbor caused by offshore landslides induced by the Loma Prieta earthquake

    SciTech Connect

    Gardner-Taggart, J.M.; Barminski, R.F. Jr. )

    1991-07-01

    Short period waves were observed in the Moss Landing Harbor approximately 2 minutes after the October 17, 1989 Loma Prieta earthquake. Offshore submarine landslides in the region of wave generation was noted by scuba divers and recorded by side scanning sonographs, fathometer records and ROV video footage taken in the area after the quake. These waves are believed to have been generated by offshore submarine landslides along the canyon walls of the Monterey Canyon directly offshore of the Moss Landing Marine Laboratories.

  16. Demonstration of inverse free-electron laser seeding in a sub-80 K, short period cryogenic undulator

    NASA Astrophysics Data System (ADS)

    OʼShea, F. H.; Knyazik, Andrey; Marinelli, A.; Rosenzweig, J. B.; Dunning, M.; Hast, C.; Hemsing, E.; Jobe, K.; Nelson, J.; Weathersby, S.; Xiang, D.; Holy, F.; Grüner, F.; Bahrdt, J.

    2014-12-01

    Short period, high field undulators have been shown to permit operation of x-ray free-electron lasers with short gain-lengths, and at unprecedented short wavelengths. In addition, the reduced beam energy required to reach resonance with a given radiation wavelength in short period undulators could prove useful in advanced inverse free-electron laser (IFEL) seeding schemes for future light sources, such as high-gain harmonic generation and echo-enabled harmonic generation, or in IFEL acceleration. We report here the in situ beam testing of a 9 mm period length cryogenic undulator having undulator parameter near unity in the context appropriate for advanced seeding and acceleration schemes, a linear accelerator. Because of the short period length of the undulator, a 47 MeV high-brightness electron beam could be used to produce near infrared photons via the undulator radiation mechanism. The undulator radiation was observed through a filter and the spectral response of the undulator is compared to simulation. Finally, an 800 nm seed laser was introduced in order to generate an energy modulation via the IFEL mechanism. Resonance between the electron beam and the laser seed was achieved without detailed knowledge of the temperature dependent undulator magnetic field through the observation of the undulator radiation. The energy modulation (and concomitant energy spread increase) of the electron beam was observed both directly in an electron beam spectrometer and indirectly via coherent transition radiation after conversion to a density modulation in a longitudinally dispersive chicane.

  17. The OmegaWhite Survey for short period variable stars - II. An overview of results from the first four years

    NASA Astrophysics Data System (ADS)

    Toma, R.; Ramsay, G.; Macfarlane, S.; Groot, P. J.; Woudt, P. A.; Dhillon, V.; Jeffery, C. S.; Marsh, T.; Nelemans, G.; Steeghs, D.

    2016-11-01

    OmegaWhite is a wide-field, high cadence, synoptic survey targeting fields in the southern Galactic plane, with the aim of discovering short period variable stars. Our strategy is to take a series of 39 s exposures in the g band of a 1 deg2 of sky lasting 2 h using the OmegaCAM wide field imager on the VLT Survey Telescope (VST). We give an overview of the initial 4 yr of data which covers 134 deg2 and includes 12.3 million light curves. As the fields overlap with the VLT Survey Telescope Hα Photometric Survey of the Galactic plane and Bulge (VPHAS+), we currently have ugriHα photometry for ˜1/3 of our fields. We find that a significant fraction of the light curves have been affected by the diffraction spikes of bright stars sweeping across stars within a few dozen of pixels over the two hour observing time interval due to the alt-az nature of the VST. We select candidate variable stars using a variety of variability statistics, followed by a manual verification stage. We present samples of several classes of short period variables, including: an ultra compact binary, a DQ white dwarf, a compact object with evidence of a 100 min rotation period, three CVs, one eclipsing binary with an 85 min period, a symbiotic binary which shows evidence of a 31 min photometric period, and a large sample of candidate δ Sct type stars including one with a 9.3 min period. Our overall goal is to cover 400 deg2, and this study indicates we will find many more interesting short period variable stars as a result.

  18. The OmegaWhite Survey for short period variable stars II: An overview of results from the first four years

    NASA Astrophysics Data System (ADS)

    Toma, R.; Ramsay, G.; Macfarlane, S.; Groot, P. J.; Woudt, P. A.; Dhillon, V.; Jeffery, C. S.; Marsh, T.; Nelemans, G.; Steeghs, D.

    2016-08-01

    OmegaWhite is a wide-field, high cadence, synoptic survey targeting fields in the southern Galactic plane, with the aim of discovering short period variable stars. Our strategy is to take a series of 39 s exposures in the g band of a 1 square degree of sky lasting 2 h using the OmegaCAM wide field imager on the VLT Survey Telescope (VST). We give an overview of the initial 4 years of data which covers 134 square degrees and includes 12.3 million light curves. As the fields overlap with the VLT Survey Telescope Hα Photometric Survey of the Galactic plane and Bulge (VPHAS+), we currently have ugriHα photometry for ˜1/3 of our fields. We find that a significant fraction of the light curves have been affected by the diffraction spikes of bright stars sweeping across stars within a few dozen of pixels over the two hour observing time interval due to the alt-az nature of the VST. We select candidate variable stars using a variety of variability statistics, followed by a manual verification stage. We present samples of several classes of short period variables, including: an ultra compact binary, a DQ white dwarf, a compact object with evidence of a 100 min rotation period, three CVs, one eclipsing binary with an 85 min period, a symbiotic binary which shows evidence of a 31 min photometric period, and a large sample of candidate δ Sct type stars including one with a 9.3 min period. Our overall goal is to cover 400 square degrees, and this study indicates we will find many more interesting short period variable stars as a result.

  19. Multidisciplinary experiment on studying short-period variability of the sedimentary process in the northeastern part of the Black Sea

    NASA Astrophysics Data System (ADS)

    Klyuvitkin, A. A.; Ostrovskii, A. G.; Novigatskii, A. N.; Lisitzin, A. P.

    2016-07-01

    The principal aim of this work is to reveal the regularities of short-period synoptic variability of vertical flows and the composition of settling sedimentary material, to obtain information on the quantitative characteristics of the processes that influence sound-scattering layers in the water layer above the continental slope behind the shelf edge in the northeastern part of the Black Sea. The results were obtained due to improvement of the equipment and the procedures for performing sea experiments on studying physicogeological, biological, and hydrophysical processes in the upper illuminated layer of phytoplankton development.

  20. Search for circum-planetary material and orbital period variations of short-period Kepler exoplanet candidates

    NASA Astrophysics Data System (ADS)

    Garai, Z.; Zhou, G.; Budaj, J.; Stellingwerf, R. F.

    2014-12-01

    A unique short-period ({P = 0.65356(1)} d) Mercury-size Kepler exoplanet candidate KIC012557548b has been discovered recently by {Rappaport et al. (2012)}. This object is a transiting disintegrating exoplanet with a circum-planetary material-comet-like tail. Close-in exoplanets, like KIC012557548b, are subjected to the greatest planet-star interactions. This interaction may have various forms. In certain cases it may cause formation of the comet-like tail. Strong interaction with the host star, and/or presence of an additional planet may lead to variations in the orbital period of the planet. Our main aim is to search for comet-like tails similar to KIC012557548b and for long-term orbital period variations. We are curious about frequency of comet-like tail formation among short-period Kepler exoplanet candidates. We concentrate on a sample of 20 close-in candidates with a period similar to KIC012557548b from the Kepler mission. We first improved the preliminary orbital periods and obtained the transit light curves. Subsequently we searched for the signatures of a circum-planetary material in these light curves. For this purpose the final transit light curve of each planet was fitted with a theoretical light curve, and the residuals were examined for abnormalities. We then searched for possible long-term changes of the orbital periods using the method of phase dispersion minimization. In 8 cases out of 20 we found some interesting peculiarities, but none of the exoplanet candidates showed signs of a comet-like tail. It seems that the frequency of comet-like tail formation among short-period Kepler exoplanet candidates is very low. We searched for comet-like tails based on the period criterion. Based on our results we can conclude that the short-period criterion is not enough to cause comet-like tail formation. This result is in agreement with the theory of the thermal wind and planet evaporation (Perez-Becker & Chiang 2013). We also found 3 cases of candidates which

  1. Helicity in superfluids

    NASA Astrophysics Data System (ADS)

    Kedia, Hridesh; Kleckner, Dustin; Proment, Davide; Irvine, William T. M.

    Ideal fluid flow conserves a special quantity known as helicity, in addition to energy, momentum and angular momentum. Helicity can be understood as a measure of the knottedness of vortex lines of the flow, providing an important geometric tool to study diverse physical systems such as turbulent fluids and plasmas. Since superfluids flow without resistance just like ideal (Euler) fluids, a natural question arises: Is there an extra conserved quantity akin to helicity in superfluids? We address the question of a ''superfluid helicity'' theoretically and examine its consequences in numerical simulations.

  2. Three-dimensional full waveform inversion of short-period teleseismic wavefields based upon the SEM-DSM hybrid method

    NASA Astrophysics Data System (ADS)

    Monteiller, Vadim; Chevrot, Sébastien; Komatitsch, Dimitri; Wang, Yi

    2015-08-01

    We present a method for high-resolution imaging of lithospheric structures based on full waveform inversion of teleseismic waveforms. We model the propagation of seismic waves using our recently developed direct solution method/spectral-element method hybrid technique, which allows us to simulate the propagation of short-period teleseismic waves through a regional 3-D model. We implement an iterative quasi-Newton method based upon the L-BFGS algorithm, where the gradient of the misfit function is computed using the adjoint-state method. Compared to gradient or conjugate-gradient methods, the L-BFGS algorithm has a much faster convergence rate. We illustrate the potential of this method on a synthetic test case that consists of a crustal model with a crustal discontinuity at 25 km depth and a sharp Moho jump. This model contains short- and long-wavelength heterogeneities along the lateral and vertical directions. The iterative inversion starts from a smooth 1-D model derived from the IASP91 reference Earth model. We invert both radial and vertical component waveforms, starting from long-period signals filtered at 10 s and gradually decreasing the cut-off period down to 1.25 s. This multiscale algorithm quickly converges towards a model that is very close to the true model, in contrast to inversions involving short-period waveforms only, which always get trapped into a local minimum of the cost function.

  3. Short-period cyclic loading system for in situ X-ray observation of anelastic properties at high pressure

    NASA Astrophysics Data System (ADS)

    Yoshino, Takashi; Yamazaki, Daisuke; Tange, Yoshinori; Higo, Yuji

    2016-10-01

    To determine the anelastic properties of materials of the Earth's interior, a short-period cyclic loading system was installed for in situ X-ray radiographic observation under high pressure to the multi-anvil deformation DIA press at the bending magnet beam line BL04B1 at SPring-8. The hydraulic system equipped with a piston controlled by a solenoid was designed so as to enable producing smooth sinusoidal stress in a wide range of oscillation period from 0.2 to 100 s and generating variable amplitudes. Time resolved X-ray radiography imaging of the sample and reference material provides their strain as a function of time during cyclic loading. A synchrotron X-ray radiation source allows us to resolve their strain variation with time even at the short period (<1 s). The minimum resolved strain is as small as 10-4, and the shortest oscillation period to detect small strain is 0.5 s. Preliminary experimental results exhibited that the new system can resolve attenuation factor Q-1 at upper mantle conditions. These results are in quantitative agreement with previously reported data obtained at lower pressures.

  4. Short period ScP phase amplitude calculations for core-mantle boundary with intermediate scale topography

    NASA Astrophysics Data System (ADS)

    Shen, Zhichao; Ni, Sidao; Wu, Wenbo; Sun, Daoyuan

    2016-04-01

    The core-mantle boundary (CMB) topography plays a key role in constraining geodynamic modeling and core-mantle coupling. It's effective to resolve the intermediate lateral scale topography (hundreds of km) with short period core reflected seismic phases (ScP) due to their small Fresnel-zones at short epicentral distances (<3336 km (30°)). We developed a method based on the ray theory and representation theorem to calculate short period ScP synthetics for intermediate lateral scale CMB topography. The CMB topography we introduced here is axisymmetric and specified with two parameters: H (height) and L (diameter, or lateral length scale). Our numerical computation shows that a bump (H > 0) and dip (H < 0) model would cause defocusing/weakening and focusing/amplifying effects on ScP amplitude. Moreover, the effect of frequency and combination of L and H are quantified with the amplification coefficients. Then we applied this method to estimate a possible CMB topography beneath northeastern Japan, and a CMB model with L = 140 km, H = 1.2 km overall matches the observed pattern of 2D PcP/ScP amplitude ratios. However, it is difficult to totally rule out other factors that may also affect PcP/ScP pattern because of limitation of ray-based algorithms we used here. A hybrid method combining ray theory and numerical method is promising for studying complicated 3D structure and CMB topography in the future.

  5. Spontaneous lateral composition modulation in InAlAs and InGaAs short-period superlattices

    SciTech Connect

    Follstaedt, D.M.; Twesten, R.D.; Millunchick, J.M.; Lee, S.R.; Jones, E.D.; Ahrenkiel, S.P.; Zhang, Y.; Mascarenhas, A.

    1997-07-11

    The microstructure of spontaneous lateral composition modulation along the [110] direction has been studied in (InAs){sub n}/(AlAs){sub m} short-period superlattices grown by molecular beam epitaxy on (001) InP. X-ray diffraction and transmission electron microscopy show that global strain ({var_epsilon}) in the superlattice reduces the degree of composition modulation, which disappears for the absolute value of {var_epsilon} > 0.7%. For tensile strains of {var_epsilon} {approx} +0.4%, they find that In-rich columns become regularly spaced and correlated with cusps in the growth surface. A similar correlation is seen in (InAs){sub n}/(GaAs){sub m} short-period superlattices between the enriched columns and the peaks and valleys of {l_brace}114{r_brace}{sub A} facets on the surface. The enriched columns in the (InAs){sub n}/(GaAs){sub m} layer (and the facets) extend for much longer distances ({approximately}0.2--0.4 {micro}m) in the [1{bar 1}0] direction than do the columns in the (InAs){sub n}/(AlAs){sub m} layer ({approximately} 56 nm).

  6. Effect of the Proximity of the Wing First-Bending Frequency and the Short-Period Frequency on the Airplane Dynamic-Response Factor

    NASA Technical Reports Server (NTRS)

    Huss, Carl R.; Donegan, James J.

    1959-01-01

    The results are presented in the form of preliminary design charts which give a comparison between the dynamic-response factors of the semi-rigid case and the airplane longitudinal short-period case and between the dynamic-response factors of the semi-rigid case and the steady-state value of the airplane longitudinal short-period response. These charts can be used to estimate the first-order effects of the addition of a wing-bending degree of freedom on the short-period dynamic-response factor and on the maximum dynamic-response factor when compared with the steady-state response of the system.

  7. Flow of Planets, Not Weak Tidal Evolution, Produces the Short-Period Planet Distribution with More Planets than Expected

    NASA Astrophysics Data System (ADS)

    Taylor, Stuart F.

    2013-01-01

    The most unexpected planet finding is arguably the number of those with shorter periods than theorists had expected, because most such close planets had been expected to migrate into the star in shorter timescales than the ages of the stars. Subsequent effort has been made to show how tidal dissipation in stars due to planets could be weaker than expected, but we show how the occurrence distribution of differently-sized planets is more consistent with the explanation that these planets have more recently arrived as a flow of inwardly migrating planets, with giant planets more likely to be found while gradually going through a short period stage. This continual ``flow'' of new planets arriving from further out is presumably supplied by the flow likely responsible for the short period pileup of giant planets (Socrates+ 2011). We have previously shown that the shortest period region of the exoplanet occurrence distribution has a fall-off shaped by inward tidal migration due to stellar tides, that is, tides on the star caused by the planets (Taylor 2011, 2012). The power index of the fall-off of giant and intermediate radius planet candidates found from Kepler data (Howard+ 2011) is close to the index of 13/3 which is expected for planets in circular orbits undergoing tidal migration. However, there is a discrepancy of the strength of the tidal migration determined using fits to the giant and medium planets distributions. This discrepancy is best resolved by the explanation that more giant than medium radii planets migrate through these short period orbits. We also present a correlation between higher eccentricity of planetary orbits with higher Fe/H of host stars, which could be explained by high eccentricity planets being associated with recent episodes of other planets into stars. By the time these planets migrate to become hot Jupiters, the pollution may be mixed into the star. The clearing of other planets by migrating hot giant planets may result in hot Jupiters

  8. Short-period X-ray oscillations in super-soft novae and persistent super-soft sources

    NASA Astrophysics Data System (ADS)

    Ness, J.-U.; Beardmore, A. P.; Osborne, J. P.; Kuulkers, E.; Henze, M.; Piro, A. L.; Drake, J. J.; Dobrotka, A.; Schwarz, G.; Starrfield, S.; Kretschmar, P.; Hirsch, M.; Wilms, J.

    2015-06-01

    Context. Transient short-period (<100 s) oscillations have been found in the X-ray light curves of three novae during their super-soft source (SSS) phase and in one persistent SSS. Aims: We pursue an observational approach to determine possible driving mechanisms and relations to fundamental system parameters such as the white dwarf mass. Methods: We performed a systematic search for short-period oscillations in all available XMM-Newton and Chandra X-ray light curves of persistent SSS and novae during their SSS phase. To study time evolution, we divided each light curve into short time-segments and computed power spectra. We then constructed a dynamic power spectrum from which we identified transient periodic signals even when only present for a short time. We base our confidence levels on simulations of false-alarm probability for the chosen oversampling rate of 16, corrected for multiple testing based on the number of time segments. From all time segments of each system, we computed fractions of time when periodic signals were detected. Results: In addition to the previously known systems with short-period oscillations, RS Oph (35 s), KT Eri (35 s), V339 Del (54 s), and Cal 83 (67 s), we found one additional system, LMC 2009a (33 s), and also confirm the 35 s period from Chandra data of KT Eri. The oscillation amplitudes are of about <15% of the respective count rates and vary without any clear dependence on the X-ray count rate. The fractions of the time when the respective periods were detected at 2σ significance (duty cycle) are 11.3%, 38.8%, 16.9%, 49.2%, and 18.7% for LMC 2009a, RS Oph, KT Eri, V339 Del, and Cal 83, respectively. The respective highest duty cycles found in a single observation are 38.1%, 74.5%, 61.4%, 67.8%, and 61.8%. Conclusions: Since fast rotation periods of the white dwarfs as origin of these transient oscillations are speculative, we concentrate on pulsation mechanisms. We present initial considerations predicting the oscillation

  9. Formation and Evolution of Circumbinary Planets, and the Apparent Lack of CPBs Around Short-Period Binaries

    NASA Astrophysics Data System (ADS)

    Haghighipour, Nader

    2015-12-01

    The success of the Kepler space telescope in detecting planets in circumbinary orbits strongly suggests that planet formation around binary stars is robust and planets of a variety of sizes and orbital configurations may exist in such complex environments. Accurate modeling of Kepler data has also indicated that some of these planets orbit their central binaries in close proximity to the boundary of orbital stability. This finding, combined with the unsuccessful attempts in forming circumbinary planets (CBPs) close to the orbital stability limit has lent strong support to the idea that almost all currently known CBPs have formed at large distances and undergone substantial radial migration. A survey of the currently known CBPs further indicates that these planets are mainly Neptune-mass and there seems to be a lack of planets of Jupiter-mass or larger in P-type orbits. Furthermore, an examination of the observational data obtained by the Kepler telescope seems to suggest an absence of CBPs around short-period binaries. Finally, recent detections of episodic transits in the two newly discovered circumbinary systems, Kepler 413b and Kepler 453b, as well as the discovery of Kepler non-transiting CBPs, (please see the abstract by Fabrycky et al) have indicated that in general, the orbits of planets and their host binaries are not co-planar. We present a new model for the formation and evolution of CBPs in which the migration of CBPs has been studied for low and high eccentricity binaries, and for different values of binary period. Results of our extensive hydrodynamical simulations show that planet-disk interaction in low-eccentricity binaries can account for the migration of CBPs and the proximity of their final orbits to the boundary of stability. In eccentric binaries, the situation is, however, more complex and in order to explain the final orbital architecture of the system, other factors such as planet-planet interaction have to be taken into account. We show

  10. Double Helical Fluid Containment

    NASA Astrophysics Data System (ADS)

    Lowry, Brian

    2003-11-01

    In the absence of gravity or at micro-scales, helical wires can support cylindrical volumes of fluid of infinite length, making them convenient as conduits. However, fixed contact line double helical fluid volumes have the additional property that they can be drained to zero volume without loss of stability to constant pressure disturbances. Thus the two-wire support is a convenient microgravity or micro-scale container as well as conduit. For evenly spaced wires, continuous draining of a cylindrical volume to zero is possible for double helices ranging from moderate pitch to the parallel wire case. Double helices of steeper pitch are stable as cylinders and at zero volume, but are unstable for some range of intermediate volumes. This unstable zone is very strongly dependent on the offset between the helical wires, varying rapidly for offsets other than 180 degrees. Preliminary experimental results validate the theoretical predictions.

  11. Heat Loss by Helicity Injection II

    SciTech Connect

    Fowler, T K

    2006-04-25

    Arguments are reviewed showing that helicity transport always flattens the temperature profile, yielding unit current amplification in SSPX and flat temperature profiles in RFP's whenever the dynamo is active. The argument is based on transport theory yielding a hyper-resistivity {Lambda} {approx} (c{sup 2}/{omega}{sub pc}{sup 2}){chi}{sub c} with electron thermal diffusivity {chi}{sub c}, valid for any process producing a random-walk in electron constants of motion in the unperturbed field. The theory could be tested by deriving {Lambda} from helicity transport in SSPX, by analogy with recent analysis yielding {chi}{sub c} from heat transport. If the predicted ratio {Lambda}/{chi}{sub c} is confirmed, efforts to increase current amplification in SSPX must be based on scenario scenarios consistent with slow helicity transport compared to heat s transport (pulsed reactor, multipulse, neutral beam injection).

  12. Energy levels of very short-period (GaAs) sub n -(AlAs) sub n superlattices

    SciTech Connect

    Ge, W.; Sturge, M.D.; Schmidt, W.D. ); Pfeiffer, L.N.; West, K.W. )

    1990-07-02

    The energy levels of very short-period (GaAs){sub {ital n}}-(AlAs){sub {ital n}} superlattices ({ital n}{le}4) were investigated by photoluminescence (PL). The results show that these superlattices are type II but the lowest conduction bands are {ital X}{sub {ital x},{ital y}} for {ital n}{le}3 and {ital X}{sub {ital z}} for {ital n}=4, respectively. (Here {ital X}{sub {ital z}} is the valley with {bold k} parallel to the growth axis.) In both cases the {ital X} valleys are very close to each other. PL decay, PL excitation, and PL under uniaxial stress confirm this identification. Al{sub 0.5}Ga{sub 0.5}As shows very different behavior, showing that even for {ital n}=1 our samples are true superlattices.

  13. Interfacial intermixing in InAs/GaSb short-period-superlattices grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Luna, E.; Satpati, B.; Rodriguez, J. B.; Baranov, A. N.; Tournié, E.; Trampert, A.

    2010-01-01

    The unique properties of the noncommon-atom InAs/GaSb short-period-superlattices (SPSL) strongly depend on the interface structure. These interfaces are characterized using transmission electron microscopy (TEM). The compositional sharpness is obtained from the comparison of the experimental contrast in g002 two-beam dark-field TEM images with simulated intensity profiles, which are calculated assuming that the element distribution profiles are described by sigmoidal functions. The interfacial intermixing, defined by the chemical width, is obtained for SPSL with different periods and layer thicknesses, even in the extreme case of nominally less than 3 ML thick InAs layers. Nominal 1 ML InSb layers intentionally inserted are also identified.

  14. Short-period circumnutations found in sunflower hypocotyls in satellite orbit. A reappraisal of data from Spacelab-1

    NASA Technical Reports Server (NTRS)

    Bardal, Tom Kr; Johnsson, Anders; Chapman, David K.; Sager, J. C. (Principal Investigator)

    2003-01-01

    We have further analysed data from an experiment performed in satellite orbit, in Spacelab-1. In micro-gravity the hypocotyls of Helianthus annuus, cv. "Teddy Bear", showed short period circumnutations (periods around 30 minutes) as well as the already reported long period nutations (with an average period of about 115 minutes). We applied various types of signal analysis (Fourier and wavelet analysis) to the data series. The long period circumnutations have a larger amplitude than the short term circumnutations. Both short and long period circumnutations exist in one and the same hypocotyl. (This is in contrast to our ground control experiments, where were found only the long-period nutations.) The period of the nutations changed throughout the experiment. These results are extending the conclusions drawn after the Spacelab experiment (Brown et al. 1990). In particular they emphasize the existence of both short- and long-period circumnutations in micro-gravity.

  15. Interfacial intermixing in InAs/GaSb short-period-superlattices grown by molecular beam epitaxy

    SciTech Connect

    Luna, E.; Satpati, B.; Trampert, A.; Rodriguez, J. B.; Baranov, A. N.; Tournie, E.

    2010-01-11

    The unique properties of the noncommon-atom InAs/GaSb short-period-superlattices (SPSL) strongly depend on the interface structure. These interfaces are characterized using transmission electron microscopy (TEM). The compositional sharpness is obtained from the comparison of the experimental contrast in g{sub 002} two-beam dark-field TEM images with simulated intensity profiles, which are calculated assuming that the element distribution profiles are described by sigmoidal functions. The interfacial intermixing, defined by the chemical width, is obtained for SPSL with different periods and layer thicknesses, even in the extreme case of nominally less than 3 ML thick InAs layers. Nominal 1 ML InSb layers intentionally inserted are also identified.

  16. On the use of volumetric strain meters to infer additional characteristics of short-period seismic radiation

    USGS Publications Warehouse

    Borcherdt, R.D.; Johnston, M.J.S.; Glassmoyer, G.

    1989-01-01

    Volumetric strain meters (Sacks-Evertson design) are installed at 15 sites along the San Andreas fault system, to monitor long-term strain changes for earthquake prediction. Deployment of portable broadband, high-resolution digital recorders (GEOS) at several of the sites extends the detection band for volumetric strain to periods shorter than 5 ?? 10-2 sec and permits the simultaneous observation of seismic radiation fields using conventional short-period pendulum seismometers. Recordings of local and regional earthquakes indicate that dilatometers respond to P energy but not direct shear energy and that straingrams can be used to resolve superimposed reflect P and S waves for inference of wave characteristics not permitted by either sensor alone. Simultaneous measurements of incident P- and S-wave amplitudes are used to introduce a technique for single-station estimates of wave field inhomogeneity, free-surface reflection coefficients and local material P velocity. -from Authors

  17. Short-Period Superlattices of (GaP)n(AlP)n Grown by Metalorganic Vapor Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Morii, Akio; Ohno, Isao; Kanda, Atsushi; Arai, Kazumasa; Tokudome, Koichi; Hara, Kazuhiko; Yoshino, Junji; Kukimoto, Hiroshi

    1991-07-01

    Short-period superlattices of (GaP)n(AlP)n have been grown by metalorganic vapor phase epitaxy. X-ray diffraction measurements have confirmed the formation of the structures, where n ranges from 4 to 10. Low-temperature photoluminescence has shown characteristic emission peaks, which shift toward higher energies and tend to increase in intensity with decreasing n. These results, together with the band discontinuity between GaP and AlP which was estimated from that between GaP and Al0.6Ga0.4P, strongly indicate that the (GaP)n(AlP)n system forms the superlattices of a type-II band alignment.

  18. Ultra-short-period Planets in K2 SuPerPiG Results for Campaigns 0-5

    NASA Astrophysics Data System (ADS)

    Adams, Elisabeth R.; Jackson, Brian; Endl, Michael

    2016-08-01

    We analyzed data from Campaigns 0-5 of the K2 mission and report 19 ultra-short-period candidate planets with orbital periods of less than one day (nine of which have not been previously reported). Planet candidates range in size from 0.7 to 16 Earth radii and in orbital period from 4.2 to 23.5 hr. One candidate (EPIC 203533312, Kp = 12.5) is among the shortest-period planet candidates discovered to date (P=4.2 hr), and, if confirmed as a planet, must have a density of at least ρ =8.9 {{g}} {{cm}}-3 to not be tidally disrupted. Five candidates have nominal radius values in the sub-Jovian desert ({R}P=3{--}11 {R}\\oplus and P≤slant 1.5 days) where theoretical models do not favor their long-term stability; the only confirmed planet in this range is thought to be disintegrating (EPIC 201637175). In addition to the planet candidates, we report on four objects that may not be planetary, including one with intermittent transits (EPIC 211152484) and three initially promising candidates that are likely false positives based on characteristics of their light curves and on radial velocity follow-up. A list of 91 suspected eclipsing binaries identified at various stages in our vetting process is also provided. Based on an assessment of our survey's completeness, we estimate an occurrence rate for ultra-short-period planets among K2 target stars that is about half that estimated from the Kepler sample, raising questions as to whether K2 systems are intrinsically different from Kepler systems, possibly as a result of their different galactic location.

  19. Ultra-short-period Planets in K2 SuPerPiG Results for Campaigns 0–5

    NASA Astrophysics Data System (ADS)

    Adams, Elisabeth R.; Jackson, Brian; Endl, Michael

    2016-08-01

    We analyzed data from Campaigns 0–5 of the K2 mission and report 19 ultra-short-period candidate planets with orbital periods of less than one day (nine of which have not been previously reported). Planet candidates range in size from 0.7 to 16 Earth radii and in orbital period from 4.2 to 23.5 hr. One candidate (EPIC 203533312, Kp = 12.5) is among the shortest-period planet candidates discovered to date (P=4.2 hr), and, if confirmed as a planet, must have a density of at least ρ =8.9 {{g}} {{cm}}-3 to not be tidally disrupted. Five candidates have nominal radius values in the sub-Jovian desert ({R}P=3{--}11 {R}\\oplus and P≤slant 1.5 days) where theoretical models do not favor their long-term stability; the only confirmed planet in this range is thought to be disintegrating (EPIC 201637175). In addition to the planet candidates, we report on four objects that may not be planetary, including one with intermittent transits (EPIC 211152484) and three initially promising candidates that are likely false positives based on characteristics of their light curves and on radial velocity follow-up. A list of 91 suspected eclipsing binaries identified at various stages in our vetting process is also provided. Based on an assessment of our survey's completeness, we estimate an occurrence rate for ultra-short-period planets among K2 target stars that is about half that estimated from the Kepler sample, raising questions as to whether K2 systems are intrinsically different from Kepler systems, possibly as a result of their different galactic location.

  20. THIRD COMPONENT SEARCH AND ABUNDANCES OF THE VERY DUSTY SHORT-PERIOD BINARY BD +20 Degree-Sign 307

    SciTech Connect

    Fekel, Francis C.; Cordero, Maria J.; Galicher, Raphael; Zuckerman, B.; Melis, Carl; Weinberger, Alycia J. E-mail: majocord@indiana.edu E-mail: ben@astro.ucla.edu E-mail: weinberger@dtm.ciw.edu

    2012-04-10

    We have obtained near-infrared adaptive optics imaging and collected additional radial velocity observations to search for a third component in the extremely dusty short-period binary system BD +20 Degree-Sign 307. Our image shows no evidence for a third component at separations greater than 19 AU. Our four seasons of radial velocities have a constant center-of-mass velocity and are consistent with the systemic velocities determined at two earlier epochs. Thus, the radial velocities also provide no support for a third component. Unfortunately, the separation domains covered by our imaging and radial velocity results do not overlap. Thus, we examined the parameters for possible orbits of a third component that could have been missed by our current observations. With our velocities we determined improved circular orbital elements for the 3.4 day double-lined binary. We also performed a spectroscopic abundance analysis of the short-period binary components and conclude that the stars are a mid- and a late-F dwarf. We find that the iron abundances of both components, [Fe/H] = 0.15, are somewhat greater than the solar value and comparable to that of stars in the Hyades. Despite the similarity of the binary components, the lithium abundances of the two stars are very unequal. The primary has log {epsilon} (Li) = 2.72, while in the secondary log {epsilon} (Li) {<=}1.46, which corresponds to a difference of at least a factor of 18. The very disparate lithium abundances in very similar stars make it impossible to ascribe a single age to them. While the system is likely at least 1 Gyr old, it may well be as old as the Sun.

  1. Daily short-period gravitation can prevent functional and structural changes in arteries of simulated microgravity rats.

    PubMed

    Sun, Biao; Zhang, Li-Fan; Gao, Fang; Ma, Xiao-Wu; Zhang, Miao-Li; Liu, Jian; Zhang, Le-Ning; Ma, Jin

    2004-09-01

    This study was designed to clarify whether simulated microgravity-induced differential adaptational changes in cerebral and hindlimb arteries could be prevented by daily short-period restoration of the normal distribution of transmural pressure across arterial vasculature by either dorsoventral or footward gravitational loading. Tail suspension (Sus) for 28 days was used to simulate cardiovascular deconditioning due to microgravity. Daily standing (STD) for 1, 2, or 4 h, or +45 degrees head-up tilt (HUT) for 2 or 4 h was used to provide short-period dorsoventral or footward gravitational loading as countermeasure. Functional studies showed that Sus alone induced an enhancement and depression in vasoconstrictor responsiveness of basilar and femoral arterial rings, respectively, as previously reported. These differential functional alterations can be prevented by either of the two kinds of daily gravitational loading treatments. Surprisingly, daily STD for as short as 1 h was sufficient to prevent the differential functional changes that might occur due to Sus alone. In morphological studies, the effectiveness of daily 4-h HUT or 1-h STD in preventing the differential remodeling changes in the structure of basilar and anterior tibial arteries induced by Sus alone was examined by histomorphometry. The results showed that both the hypertrophic and atrophic changes that might occur, respectively, in cerebral and hindlimb arteries due to Sus alone were prevented not only by daily HUT for 4 h but also by daily STD even for 1 h. These data indicate that daily gravitational loading by STD for as short as 1 h is sufficient to prevent differential adaptational changes in function and structure of vessels in different anatomic regions induced by a medium-term simulated microgravity.

  2. Short-period Rayleigh wave tomography for Kilauea and Mauna Loa volcanoes, Hawaii, from ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Ballmer, S.; Haney, M. M.; Wolfe, C. J.; Okubo, P.; Thurber, C. H.

    2013-12-01

    Imaging with ambient seismic noise has proven to be a useful complement to earthquake tomography. Ambient noise's surface wave energy at short periods (peaked at ~0.2 Hz) allows imaging of shallow structure (i.e., the uppermost ~10 km), with resolution dependent on the geometry of available inter-station propagation paths instead of earthquake-receiver paths. In addition, data is generated continuously allowing for relatively uniform imaging capabilities through time. These advantages are of great interest in imaging the shallow seismic structure of volcanic systems, since magmatic plumbing systems extend all the way to the surface and can structurally change with time. We here present the first demonstration of ambient noise tomography for the volcanic systems of Kilauea and Mauna Loa on the Island of Hawai'i. Using continuous noise records between May 2007 and December 2009 from the permanent network operated by the USGS Hawaiian Volcano Observatory, we calculate noise correlation functions (NCFs) (vertical components only) at 0.1-0.9 Hz for more than 700 short-period station pairs. The presence of extended intervals in which volcanic tremor from Pu'u O'o and Halema'uma'u obscures the Green's functions above 0.3 Hz for all station pairs requires the exclusion of those intervals from the analysis. We use the NCF's summed absolute amplitude as a criterion to identify days that are contaminated by tremor. Stacks of the remaining 169 daily, uncontaminated NCFs are used to perform group velocity measurements with automatic frequency time analysis in 0.01 Hz intervals. We ensure quality of the measurements by manually selecting frequency bands in which we trust the automatic measurement for each dispersion curve. Assuming straight (i.e. great circle) propagation paths, we linearly invert for Rayleigh wave group velocity maps at each frequency. Our results in the frequency band from ~0.15 to 0.25 Hz show prominent anomalous high-velocities beneath Kilauea's rift zones

  3. Helical superconducting black holes.

    PubMed

    Donos, Aristomenis; Gauntlett, Jerome P

    2012-05-25

    We construct novel static, asymptotically five-dimensional anti-de Sitter black hole solutions with Bianchi type-VII(0) symmetry that are holographically dual to superconducting phases in four spacetime dimensions with a helical p-wave order. We calculate the precise temperature dependence of the pitch of the helical order. At zero temperature the black holes have a vanishing entropy and approach domain wall solutions that reveal homogenous, nonisotropic dual ground states with an emergent scaling symmetry.

  4. A Case of Cellular Fibrous Histiocytoma on the Right Elbow with Repeated Relapse within a Short Period.

    PubMed

    Tsunoda, Kanako; Oikawa, Hiroki; Maeda, Fumihiko; Takahashi, Kazuhiro; Akasaka, Toshihide

    2015-01-01

    Cellular fibrous histiocytoma, a variant of fibrous histiocytoma, is a designation used for lesions showing increased cellularity with a fascicular growth pattern and frequent extension into the subcutis. Here we describe a case of cellular fibrous histiocytoma showing repeated recurrence in a 36-year-old woman who initially presented with a 2-cm cutaneous tumor on her right elbow. Histopathologically, the first resected specimen demonstrated irregularly arranged collagen fibers mixed with scattered proliferating plump to spindle-shaped fibrohistiocytes. However, examination of the resected specimens obtained after recurrence showed that the cellularity had increased, the spindle-shaped cells showing monomorphic proliferation with a fascicular and storiform growth pattern extending into the subcutis, as well as an increase of Ki-67 positivity. Since the lesion showed repeated relapse within a short period, we performed wide-field resection of the tumor with a 3-cm margin. Currently, 48 months after surgery, there has been no local recurrence or metastasis, but continuous strict follow-up will be necessary. PMID:25759652

  5. A Case of Cellular Fibrous Histiocytoma on the Right Elbow with Repeated Relapse within a Short Period

    PubMed Central

    Tsunoda, Kanako; Oikawa, Hiroki; Maeda, Fumihiko; Takahashi, Kazuhiro; Akasaka, Toshihide

    2015-01-01

    Cellular fibrous histiocytoma, a variant of fibrous histiocytoma, is a designation used for lesions showing increased cellularity with a fascicular growth pattern and frequent extension into the subcutis. Here we describe a case of cellular fibrous histiocytoma showing repeated recurrence in a 36-year-old woman who initially presented with a 2-cm cutaneous tumor on her right elbow. Histopathologically, the first resected specimen demonstrated irregularly arranged collagen fibers mixed with scattered proliferating plump to spindle-shaped fibrohistiocytes. However, examination of the resected specimens obtained after recurrence showed that the cellularity had increased, the spindle-shaped cells showing monomorphic proliferation with a fascicular and storiform growth pattern extending into the subcutis, as well as an increase of Ki-67 positivity. Since the lesion showed repeated relapse within a short period, we performed wide-field resection of the tumor with a 3-cm margin. Currently, 48 months after surgery, there has been no local recurrence or metastasis, but continuous strict follow-up will be necessary. PMID:25759652

  6. On the Nature of the Bright Short-Period X-ray Source in the Circinus Galaxy Field

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin C.; Tennant, Allyn F.; Wu, Kinwah; Swartz, Douglas A.; Ghosh, Kajal K.

    2003-01-01

    The spectrum and light curve of the bright X-ray source CG X-1 in the field of the Circinus galaxy are re-examined. Previous analyses have concluded that the source is an accreting black hole of mass approx. greater than 50 solar masses although it was noted that the light curve resembles that of an AM Her system. Here we show that the short period and an assumed main sequence companion constrain the mass of the companion to less than 1 solar mass. Further a possible eclipse seen during one of the Chandra observations and a subsequent XMM-Newton observation constrains the mass of the compact object to less than 60 solar masses. If such a system lies in the Circinus galaxy, then the accreting object must either radiate anisotropically or strongly violate the Eddington limit. Even if the emission is beamed, then the companion star which intercepts this flux during eclipse will be driven out of thermal equilibrium and evaporate within approx. 10(exp 3) yr. We find that the observations cannot rule out an AM Her system in the Milky Way and that such a system can account for the variations seen in the light curve.

  7. On the Nature of the Bright Short-Period X-Ray Source in the Circinus Galaxy Field

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin C.; Wu, Kinwah; Tennant, Allyn F.; Swartz, Douglas A.; Ghosh, Kajal K.

    2004-01-01

    The spectrum and light curve of the bright X-ray source CG X-1 in the field of the Circinus galaxy are reexamined. Previous analyses have concluded that the source is an accreting black hole of mass > or approx. 50 solar masses although it has been noted that the light curve resembles that of an AM Herculis system. Here we show that the short period and an assumed main-sequence companion constrain the mass of the companion to less than 1 solar mass. Furthermore, a possible eclipse seen during one of the Chandra observations and a subsequent XMM-Newton observation constrain the mass of the compact object to less than 60 solar masses. If such a system lies in the Circinus galaxy, then the accreting object must either radiate anisotropically or strongly violate the Eddington limit. Even if the emission is beamed, then the companion star that intercepts this flux during eclipse will be driven out of thermal equilibrium and evaporate within approx. 10(exp 3) yr. We find that the observations cannot rule out an AM Herculis system in the Milky Way and that such a system can account for the variations seen in the light curve.

  8. Quantification of atomic intermixing in short-period InAs/GaSb superlattices for infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Ashuach, Y.; Kauffmann, Y.; Saguy, C.; Grossman, S.; Klin, O.; Weiss, E.; Zolotoyabko, E.

    2013-05-01

    Cross-sectional scanning tunneling microscopy (XSTM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) are applied for characterizing the MBE-grown short-period InAs/GaSb superlattices for mid- and long-wavelength infrared detection. The focus of this study is on atomic intermixing in close proximity to the interfaces, which is a key issue for device performance. HAADF-STEM permits visualization of the anion-cation dumbbells in individual sub-layers and is even capable to resolve anions and cations separated by 0.15 nm within a dumbbell. On this basis, the interfacial width is extracted with high accuracy. XSTM technique allows us direct counting of certain kinds of atoms within atomic rows, which sheds light on compositional fluctuations and isovalent atomic intermixing. Both methods reveal rather abrupt interfaces with InAs-on-GaSb interfaces being slightly wider than GaSb-on-InAs interfaces. According to HAADF-STEM, in the set of investigated samples, the 90%-to-10% interface width is confined within 2.6-4.4 monolayers (0.8-1.3 nm). In all the samples studied, XSTM analysis showed some residual concentration (on the level of a few atomic percent) of Sb atoms in the middle of the InAs sub-layers, as a result of As/Sb substitutions during growth. The level of intermixing is diminishing with increasing the thickness of individual InAs layers.

  9. In-plane and growth direction electron cyclotron effective mass in short period InAs/GaSb semiconductor superlattices

    SciTech Connect

    Suchalkin, S.; Belenky, G.; Svensson, S. P.; Laikhtman, B.; Smirnov, D.; Tung, L. C.; Bandara, S.

    2011-08-15

    In plane and growth direction electron effective mass in short period InAs/GaSb semiconductor superlattices (SL) was measured using cyclotron resonance at different orientations of magnetic field with respect to SL growth direction. It was demonstrated that the electron spectrum near the bottom of the SL subband has 3D character, with the in-plane effective masses ranging from 0.023 m{sub 0} to 0.028 m{sub 0} and growth direction effective masses of 0.03-0.034 m{sub 0} depending on the SL period and growth conditions. The measured effective masses are close to those calculated in the weak coupling limit of the Kronig-Penney model. In this limit the SL electron effective mass is a weighted average of the electron effective masses of corresponding bulk materials. Correlation between the magnitude of cyclotron mobility, amplitude of negative magnetoresistance, and steepness of the long wavelength side of the photoluminescence spectrum indicate that the crystalline structure disorder is a major factor contributing to the momentum relaxation time of the electrons.

  10. SHORT-PERIOD g-MODE PULSATIONS IN LOW-MASS WHITE DWARFS TRIGGERED BY H-SHELL BURNING

    SciTech Connect

    Córsico, A. H.; Althaus, L. G.

    2014-09-20

    The detection of pulsations in white dwarfs with low mass offers the possibility of probing their internal structures through asteroseismology and placing constraints on the binary evolutionary processes involved in their formation. In this Letter, we assess the impact of stable H burning on the pulsational stability properties of low-mass He-core white dwarf models resulting from binary star evolutionary calculations. We found that besides a dense spectrum of unstable radial modes and nonradial g and p modes driven by the κ mechanism due to the partial ionization of H in the stellar envelope, some unstable g modes with short pulsation periods are also powered by H burning via the ε mechanism of mode driving. This is the first time that ε destabilized modes are found in models representative of cool white dwarf stars. The short periods recently detected in the pulsating low-mass white dwarf SDSS J111215.82+111745.0 could constitute the first evidence of the existence of stable H burning in these stars, in particular in the so-called extremely low-mass white dwarfs.

  11. Impacts of Thermal and Wind structures on Mesospheric Short-period Gravity Wave Propagation at High Latitudes

    NASA Astrophysics Data System (ADS)

    Nielsen, Kim; Taylor, Michael J.; Siskind, David; Collins, Richard; Harvey, V. Lynn; Russell, James; Irving, Brita; Negale, Michael

    2012-07-01

    Mesospheric short-period (<1-hr) gravity waves are of great importance for dynamics in the mesosphere-lower thermosphere (MLT) region, and are typically measured by instruments capable of high temporal and/or spatial resolutions, such as lidars and airglow imagers. These waves have been studied extensively at low- and mid-latitudes where known wave sources are well established. The results show strong dependence on the background wind and temperature fields, which can act as a barrier prohibiting vertical propagation of the waves, as well as providing a ducted environment in which the waves can travel large horizontal distances. In fact, results show that up to 75% of these waves may exhibit ducted wave motion. Recent efforts to quantify the existence and nature of these waves over the Antarctic continent have lead to a long-term (10 years) data set obtained with airglow imagers. Our results suggest that these southern polar waves are predominantly freely propagating in the airglow region, in stark contrast to results at other latitudes. A new study in the Arctic enables a comparison between the two data sets. In this work, we investigate the propagation nature of the observed wave field and attempt to identify dominant source regions and potential sources of polar gravity waves through ray tracing.

  12. PG 0308 + 096 and PG 1026 + 002 - Two new short period binary stars resulting from common-envelope evolution

    NASA Technical Reports Server (NTRS)

    Saffer, Rex A.; Wade, Richard A.; Liebert, James; Green, Richard F.; Sion, Edward M.; Bechtold, J.; Foss, Diana; Kidder, K.

    1993-01-01

    Ultraviolet spectroscopy, optical spectroscopy, and spectrophotometry have been used to study the excess UV stars PG 0308 + 096 and PG 1026 + 002. Both objects are short-period binary systems, each containing a DA white dwarf star and a dM star. Orbital periods of approximately 0.284 day for PG 0308 + 096, and aproximately 0.597 day for PG 1026, have been found by spectroscopic analysis of the H-alpha emission line. Ly-alpha and Balmer line profile fitting were used to estimate the mass of white dwarf stars; mass estimates for the dM stars are based on their spectral types. The orbital inclinations are derived from these masses, the periods, and amplitudes of the H-alpha radial velocity curves. The equivalent width of the H-alpha emission line, in each binary system, varies with the orbital phase in such a manner as to imply that it arises, in large part at least, from the hemisphere of the M star that faces the white dwarf star.

  13. Constraining the formation of black holes in short-period black hole low-mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Repetto, Serena; Nelemans, Gijs

    2015-11-01

    The formation of stellar-mass black holes (BHs) is still very uncertain. Two main uncertainties are the amount of mass ejected in the supernova (SN) event (if any) and the magnitude of the natal kick (NK) the BH receives at birth (if any). Repetto et al., studying the position of Galactic X-ray binaries containing BHs, found evidence for BHs receiving high NKs at birth. In this paper, we extend that study, taking into account the previous binary evolution of the sources as well. The seven short-period BH X-ray binaries that we use are compact binaries consisting of a low-mass star orbiting a BH in a period less than 1 d. We trace their binary evolution backwards in time, from the current observed state of mass transfer, to the moment the BH was formed, and we add the extra information on the kinematics of the binaries. We find that several systems could be explained by no NK, just mass ejection, while for two systems (and possibly more) a high kick is required. So unless the latter have an alternative formation, such as within a globular cluster, we conclude that at least some BHs get high kicks. This challenges the standard picture that BH kicks would be scaled down from neutron star kicks. Furthermore, we find that five systems could have formed with a non-zero NK but zero mass ejected (i.e. no SN) at formation, as predicted by neutrino-driven NKs.

  14. Helicity, Reconnection, and Dynamo Effects

    SciTech Connect

    Ji, Hantao

    1998-11-01

    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.

  15. Predicted detection rates of regional-scale meteorite impacts on Mars with the InSight short-period seismometer

    NASA Astrophysics Data System (ADS)

    Teanby, N. A.

    2015-08-01

    In 2016 NASA will launch the InSight discovery-class mission, which aims to study the detailed internal structure of Mars for the first time. Short- and long-period seismometers form a major component of InSight's payload and have the potential to detect seismic waves generated by meteorite impacts. Large globally detectable impact events producing craters with diameters of ∼ 100 m have been investigated previously and are likely to be rare (Teanby, N.A., Wookey, J. [2011]. Phys. Earth Planet. Int. 186, 70-80), but smaller impacts producing craters in the 0.5-20 m range are more numerous and potentially occur sufficiently often to be detectable on regional scales (≲1000 km). At these distances, seismic waves will have significant high frequency content and will be suited to detection with InSight's short-period seismometer SEIS-SP. In this paper I estimate the current martian crater production function from observations of new craters (Malin, M.C. et al. [2006]. Science 314, 1573-1577; Daubar, I.J. et al. [2013]. Icarus 225, 506-516), model results (Williams, J.P., Pathare, A.V., Aharonson, O. [2014]. Icarus 235, 23-36), and standard isochrons (Hartmann, W.K. [2005]. Icarus 174, 294-320). These impact rates are combined with an empirical relation between impact energy, source-receiver distance, and peak seismogram amplitude, derived from a compilation of seismic recordings of terrestrial and lunar impacts, chemical explosions, and nuclear tests. The resulting peak seismogram amplitude scaling law contains significant uncertainty, but can be used to predict impact detection rates. I estimate that for a short-period instrument, with a noise spectral density of 10-8 ms-2 Hz-1/2 in the 1-16 Hz frequency band, approximately 0.1-30 regional impacts per year should be detectable with a nominal value of 1-3 impacts per year. Therefore, small regional impacts are likely to be a viable source of seismic energy for probing Mars' crustal and upper mantle structure. This is

  16. Frequency Dependence of Short Period Seismic Noise from Two Decades of Observations at Warramunga Seismic Array (WRA), Australia

    NASA Astrophysics Data System (ADS)

    Gal, M.; Reading, A. M.; Ellingsen, S. P.; Koper, K. D.; Tkalcic, H.; Hemer, M. A.

    2014-12-01

    The analysis of the seismic ambient noise field has recently received increased attention owing to its success in mapping the Earth's shallow and deep structures. The origin of the passive seismic wavefield is associated with deep ocean and coastal regions where ocean waves, under certain conditions, can excite seismic waves (microseisms) that propagate as surface and body waves. Previous seismological studies mainly focused on the observation of the strongest microseisms that are associated with the frequency range 0.1-0.3Hz. In our study, we focus on short period microseisms (0.325-0.725Hz) and examine the frequency dependant wave field and temporal variations over two decades. We use data recorded over two decades (1991-2012) from the Warramunga array (WRA) in central Australia. The analysis is carried out using IAS Capon beamforming that shows robust estimates of slowness and backazimuth, and is able to resolve multiple wave arrivals. Continuous data records are divided into one hour long recordings and evaluated for multiple arrivals in 8 separate frequency bands. We find multiple surface and body wave sources, which display seasonality and frequency dependence and remain stationary for two decades. We observe, for surface waves, that Rayleigh waves dominate for low frequencies while higher frequencies show a transition to leaky Rayleigh waves. The strong stationarity of the signal over multiple years, supports the suggestion that bathymetry and other site effects, such as coast line geometry, create favourable conditions for the generation of ocean induced surface waves. For body waves, source locations are identified in deep ocean regions for low frequencies and in shallow waters for higher frequencies. We further discuss correlation between arrivals and a WAVEWATCH III ocean wave hindcast for strong events. Fig 1: a) Shows the slowness of strongest incoming arrivals for 1 hour of WRA data over two decades. b) Displays the surface waves paths of incoming

  17. Short-Period Normal-mode Synthetics and Fr{é}chet kernels for Spherically Symmetric Earth Models

    NASA Astrophysics Data System (ADS)

    Yang, H.; Zhao, L.; Hung, S.

    2007-12-01

    Determination of three dimensional multiscale Earth structures requires high-quality seismic data and accurate synthetic waveforms. To extract and interpret the full waveform information from widely available broadband data, we need to be able to calculate complete broadband synthetic seismograms. Normal-mode theory provides the exact solutions to the wave equation in spherically symmetric Earth models, and the efficiency afforded by the usage of precalculated eigenfunction databases makes normal-mode summation the preferred approach for calculating long-period synthetic seismograms in 1-D reference models. In this study, we extend the normal-mode summation to short period by attacking the problems encountered in computing normal-mode eigenfrequencies and eigenfunctions at higher frequencies. Flexible radial sampling scheme based on the WKBJ approximation is adopted to ensure the accuracy of the secular equation when the radial eigenfunctions are highly oscillatory. This allows us to compute accurate normal-mode eigenfunctions up to much higher frequencies (~ 1Hz for Spheroidal and ~ 2Hz for Toroidal modes). Although errors can still be large for certain modes, they are almost all inner-core shear modes, and numerical experiments show that they have no contribution to seismograms on the surface. In contrast, omitting only 0.1% mantle modes at random can lead to noisy synthetics. The capability to compute normal modes up to high frequencies enables us to obtain accurate and complete synthetic seismograms that can be used to both extract waveform information from all seismic phases and to compute their full-wave Fr{é}chet kernels, which opens up possibilities in global and regional high-resolution tomography as well as studies on the seismic structure in the deep mantle and the inner core.

  18. Photometric Studies of Three Neglected Short-period Contact Binaries GN Bootis, BL Leonis, and V1918 Cygni

    NASA Astrophysics Data System (ADS)

    Yang, Y.-G.; Qian, S.-B.; Dai, H.-F.

    2013-03-01

    We present new photometry for three short-period contact binaries, GN Boo, BL Leo, and V1918 Cyg, observed from 2008 December to 2012 April using several small telescopes in China. Photometric models were deduced from new observations using the updated Wilson-Devinney Code. The results show that GN Boo and BL Leo are W-type contact binaries, while V1918 Cyg is an A-type one. The mass ratios and fill-out factors are q = 0.320(± 0.002) and f = 5.8(± 0.1)% for GN Boo, q = 0.476(± 0.005) and f = 21.3(± 1.1)% for BL Leo, q = 0.264(± 0.002), and f = 49.7(± 0.7)% for V1918 Cyg, respectively. From the (O - C) curves, it is discovered that the orbital periods of three binaries have varied in a complicated way, i.e., cyclic oscillation for GN Boo, long-term period decrease for BL Leo, and both for V1918 Cyg. The cyclic variations for GN Boo and V1918 Cyg may probably be attributed to the magnetic activity of the primary component or light-time effect due to the third body. Meanwhile, the secular period decreases for BL Leo and V1918 Cyg may result from mass transfer from the primary to the secondary, accompanying the mass and angular momentum loss from the central system. Finally, GN Boo, BL Leo, and V1918 Cyg will evolve into deep contact binaries. Additionally, a statistical study of 37 contact binaries with decreasing periods is given. We obtained the relations of q - f and q - dln P/dt, and preliminarily determined the mass loss rate of dln M/dt from the binary system.

  19. A short period of high-intensity interval training improves skeletal muscle mitochondrial function and pulmonary oxygen uptake kinetics.

    PubMed

    Christensen, Peter M; Jacobs, Robert A; Bonne, Thomas; Flück, Daniela; Bangsbo, Jens; Lundby, Carsten

    2016-06-01

    The aim of the present study was to examine whether improvements in pulmonary oxygen uptake (V̇o2) kinetics following a short period of high-intensity training (HIT) would be associated with improved skeletal muscle mitochondrial function. Ten untrained male volunteers (age 26 ± 2 yr; mean ± SD) performed six HIT sessions (8-12 × 60 s at incremental test peak power; 271 ± 52 W) over a 2-wk period. Before and after the HIT period, V̇o2 kinetics was modeled during moderate-intensity cycling (110 ± 19 W). Mitochondrial function was assessed with high-resolution respirometry (HRR), and maximal activities of oxidative enzymes citrate synthase (CS) and cytochrome c oxidase (COX) were accordingly determined. In response to HIT, V̇o2 kinetics became faster (τ: 20.4 ± 4.4 vs. 28.9 ± 6.1 s; P < 0.01) and fatty acid oxidation (ETFP) and leak respiration (LN) both became elevated (P < 0.05). Activity of CS and COX did not increase in response to training. Both before and after the HIT period, fast V̇o2 kinetics (low τ values) was associated with large values for ETFP, electron transport system capacity (ETS), and electron flow specific to complex II (CIIP) (P < 0.05). Collectively, these findings support that selected measures of mitochondrial function obtained with HRR are important for fast V̇o2 kinetics and better markers than maximal oxidative enzyme activity in describing the speed of the V̇o2 response during moderate-intensity exercise.

  20. Quasi-periodic VLF emissions with short-period modulation and their relationship to whistlers: a case study

    NASA Astrophysics Data System (ADS)

    Titova, Elena; Demekhov, Andrei; Kozlovsky, Alexander; Manninen, Jyrki; Pasmanik, Dmitry

    We study properties of quasiperiodic (QP) VLF emissions recorded on December 24, 2011 during the VLF campaign in Northern Finland. The main attention is paid to interrelationships between different characteristic periods in the QP spectra. In particular, we analyze regular variations in the QP repetition intervals (1 - 10 min) during the event from 15:30 to 22 UT, their changes during substorms, and short periodic (several-second) modulation observed within separate QP elements. We explained the variations of periods of QP emissions in terms of the model of auto-oscillation regime of the cyclotron instability in the magnetosphere. During the considered event lasting about 7 hours we observed a regular increase in the time intervals between the QP elements. We relate this increase with weakening of the magnetospheric source of energetic electrons. Significant variations in the QP period occurred during substorms. These variations can be due to a substorm-related increase in the energetic-electron flux and/or due to the precipitation of these electrons into the ionosphere which changes the reflection coefficient of VLF waves. We analyze the fine structure of QP element spectra and reveal the periods related to the time scales of guided propagation of whistler-mode waves along the magnetic field line, which suggests that ducted propagation regime took place for the QP emissions. The periods were about 6--9 s for frequencies 3.5--1.2 kHz respectively, which was similar to the period of almost simultaneously observed two-hop whistlers In the low-frequency part of QP spectra periodic emissions with меньшими periods of about 3 s were observed. Analysis of fine structure of QP elements shows that their formation is affected by both linear effects (i.e., group-velocity dispersion) and nonlinear effects related

  1. Doing more with short period data: Determining magnitudes from clipped and over-run seismic data at Mount St. Helens

    NASA Astrophysics Data System (ADS)

    Wellik, John J., II

    How can we calculate earthquake magnitudes when the signal is clipped and over-run? When a volcano is very active, the seismic record may saturate (i.e., the full amplitude of the signal is not recorded) or be over-run (i.e., the end of one event is covered by the start of a new event). The duration, and sometimes the amplitude, of an earthquake signal are necessary for determining event magnitudes; thus, it may be impossible to calculate earthquake magnitudes when a volcano is very active. This problem is most likely to occur at volcanoes with limited networks of short period seismometers. This study outlines two methods for calculating earthquake magnitudes when events are clipped and over-run. The first method entails modeling the shape of earthquake codas as a power law function and extrapolating duration from the decay of the function. The second method draws relations between clipped duration (i.e., the length of time a signal is clipped) and the full duration. These methods allow for magnitudes to be determined within 0.2 to 0.4 units of magnitude. This error is within the range of analyst hand-picks and is within the acceptable limits of uncertainty when quickly quantifying volcanic energy release during volcanic crises. Most importantly, these estimates can be made when data are clipped or over-run. These methods were developed with data from the initial stages of the 2004-2008 eruption at Mount St. Helens. Mount St. Helens is a well-studied volcano with many instruments placed at varying distances from the vent. This fact makes the 2004-2008 eruption a good place to calibrate and refine methodologies that can be applied to volcanoes with limited networks.

  2. Dearth of short-period Neptunian exoplanets: A desert in period-mass and period-radius planes

    NASA Astrophysics Data System (ADS)

    Mazeh, T.; Holczer, T.; Faigler, S.

    2016-05-01

    A few studies have reported a significant dearth of exoplanets with Neptune mass and radius with orbital periods below 2-4 d. This cannot be explained by observational biases because many Neptunian planets with longer orbital periods have been detected. The existence of this desert is similar to the appearance of the so-called brown-dwarf desert that suggests different formation mechanisms of planets and stellar companions with short orbital periods. Similarly, the Neptunian desert might indicate different mechanisms of formation and evolution for hot Jupiters and short-period super-Earths. We here follow a previous study and examine the location and shape of the desert in both the period-mass and period-radius planes, using the currently available large samples of planets. The desert in the period-mass plane has a relatively sharp upper edge, with a planetary mass that is inversely proportional to the planetary orbital period, while the lower, somewhat blurred, boundary is located along masses that are apparently linearly proportional to the period. The desert in the period-radius plane of the transiting planets is less clear. It seems as if the radius along the upper boundary is inversely proportional to the period to the power of one-third, while the lower boundary shows a radius that is proportional to the period to the power of two-thirds. The combination of the two upper bounds of the desert, in the period-mass and period-radius planes, yields a planetary mass-radius relation of Rp/RJup ≃ (1.2 ± 0.3)(Mp/MJup)0.27 ± 0.11 for 0.1 ≲ Mp/MJup ≲ 1. The derived shape of the desert, which might extend up to periods of 5-10 d, could shed some light on the formation and evolution of close-in planets.

  3. First multi-colour photometric study of the short period K-type contact binary NSVS 2701634

    NASA Astrophysics Data System (ADS)

    Martignoni, M.; Acerbi, F.; Barani, C.

    2016-07-01

    We present the first CCD sets of complete light curves for the W Ursae Majoris W-type system NSVS 2701634. The observations were performed in the B, V and Ic bands using the 0.25 m telescope of the "Stazione Astronomica Betelgeuse" Italy, during 8 nights in April 2015. From our observations we were able to confirm and revise the short-period (0.24 days) variation found by Shaw and collaborators in their online list Using our 12 times of minimum light, the orbital period variations of NSVS 2701634 are studied for the first time. The general trend of the (O-C) curve reveals that its period is varying by a downward parabola that means that period is decreasing, this fact could be explained by a mass transfer between the components of the system. The light curves were modelled using the Wilson-Devinney code and the elements obtained from this analysis are used to compute the physical parameters of the system in order to study its evolutionary status. A reasonable fit of the synthetic light curves of the data indicated that NSVS 2701634 is an late-type (K3 -K4+K6) contact binary system of W-Subtype of the W Ursae Majoris systems, with a mass ratio of q = 2.60, a degree of contact factor f = 15.3% and inclination i = 72°. The light curves show asymmetries at the maxima that are fitted adding an hot spot on the surface of the more massive star, known as inverse O'Connell effect. From an estimation of the absolute dimensions of the system and from the logM-logL diagram, it is seen that both components of NSVS 2701634 follow the general pattern of the W subtype W Ursae Majoris systems.

  4. The origin and evolution of short-period Miras in the solar neighborhood: Constraints on the life cycle of old stars

    NASA Technical Reports Server (NTRS)

    Jura, M.

    1994-01-01

    The spatial distribution of the short-period (P less than 300 days) oxygen-rich Miras in the solar neighborhood can be fitted with an exponential scale height above the Galactic plane of about 600 pc. Using the Gliese catalog of local main-sequence stars, we estimate that the density of suitable G-type progenitor dwarfs within 20 pc of the Sun for these short-period Miras is 6 x 10(exp -4)/cu pc. The portion of the H-R diagram near the main-sequence turnoff of these velocity-selected Gliese stars is intermediate between that of the old open cluster NGC 188 and that of the metal-rich globular cluster, 47 Tuc. We infer that the main-sequence progenitors of the short-period Miras have masses near 1.0 solar mass, and we estimate that these Miras have ages approximately 9 x 10(exp 9). We also identify a few old disk red giants in the neighborhood of the Sun. On the basis of very limited information, we estimate that the total amount of mass lost from these stars during their first ascent up the red giant branch is less than or equal to 0.1 solar mass. We derive a duration of the short-period Mira phase of close to 5 x 10(exp 5) yr. This estimate for the duration of the short period Mira phase is longer than our estimate of 2 x 10(exp 5) yr for the duration of the Mira phase for stars with periods longer than 300 days. From their infrared colors, we estimate a typical mass-loss rate from the short-period Miras of approximately 1 x 10(exp -7) solar mass/yr.

  5. Helical plasma thruster

    SciTech Connect

    Beklemishev, A. D.

    2015-10-15

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR{sup ®} rocket engine.

  6. Helical plasma thruster

    NASA Astrophysics Data System (ADS)

    Beklemishev, A. D.

    2015-10-01

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR® rocket engine.

  7. Helical screw viscometer

    DOEpatents

    Aubert, J.H.; Chapman, R.N.; Kraynik, A.M.

    1983-06-30

    A helical screw viscometer for the measurement of the viscosity of Newtonian and non-Newtonian fluids comprising an elongated cylindrical container closed by end caps defining a circular cylindrical cavity within the container, a cylindrical rotor member having a helical screw or ribbon flight carried by the outer periphery thereof rotatably carried within the cavity whereby the fluid to be measured is confined in the cavity filling the space between the rotor and the container wall. The rotor member is supported by axle members journaled in the end caps, one axle extending through one end cap and connectable to a drive source. A pair of longitudinally spaced ports are provided through the wall of the container in communication with the cavity and a differential pressure meter is connected between the ports for measuring the pressure drop caused by the rotation of the helical screw rotor acting on the confined fluid for computing viscosity.

  8. Helical-D pinch

    SciTech Connect

    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-D{close_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}dynamo{close_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.

  9. Transport of marked pebbles in short periods of time on a coarse clastic beach (Marina di Pisa, Italy)

    NASA Astrophysics Data System (ADS)

    Bertoni, D.; Ciavola, P.; Grottoli, E.; Sarti, G.

    2012-04-01

    in short periods of time.

  10. Helicity and celestial magnetism

    NASA Astrophysics Data System (ADS)

    Moffatt, H. K.

    2016-06-01

    This informal article discusses the central role of magnetic and kinetic helicity in relation to the evolution of magnetic fields in geophysical and astrophysical contexts. It is argued that the very existence of magnetic fields of the intensity and scale observed is attributable in large part to the chirality of the background turbulence or random-wave field of flow, the simplest measure of this chirality being non-vanishing helicity. Such flows are responsible for the generation of large-scale magnetic fields which themselves exhibit magnetic helicity. In the geophysical context, the turbulence has a `magnetostrophic' character in which the force balance is primarily that between buoyancy forces, Coriolis forces and Lorentz forces associated with the dynamo-generated magnetic field; the dominant nonlinearity here arises from the convective transport of buoyant elements erupting from the `mushy zone' at the inner core boundary. At the opposite extreme, in a highly conducting low-density plasma, the near-invariance of magnetic field topology (and of associated helicity) presents the challenging problem of `magnetic relaxation under topological constraints', of central importance both in astrophysical contexts and in controlled-fusion plasma dynamics. These problems are reviewed and open issues, particularly concerning saturation mechanisms, are reconsidered.

  11. Helically linked mirror arrangement

    SciTech Connect

    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 ..beta.. 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.

  12. Band gap tuning and optical absorption in type-II InAs/GaSb mid infrared short period superlattices: 14 bands Kṡp study

    NASA Astrophysics Data System (ADS)

    AbuEl-Rub, Khaled M.

    2012-09-01

    The MBE growth of short-period InAs/GaSb type-II superlattice structures, varied around 20.5 Å InAs/24 Å GaSb were [J. Applied physics, 96, 2580 (2004)] carried out by Haugan et al. These SLs were designed to produce devices with an optimum mid-infrared photoresponse and a sharpest photoresponse cutoff. We have used a realistic and reliable 14-band k.p formalism description of the superlattice electronic band structure to calculate the absorption coefficient in such short-period InAs/GaSb type-II superlattices. The parameters for this formalism are known from fitting to independent experiments for the bulk materials. The band-gap energies are obtained without any fitting parameters, and are in good agreement with experimental data.

  13. Helicity transport through the photosphere

    NASA Astrophysics Data System (ADS)

    Schuck, P. W.; Antiochos, S. K.; Linton, M.

    2013-12-01

    Solar eruptions are driven by energy and helicity transported through the photosphere and into the Corona. However, the mechanism by which helicity is transferred from the solar dynamo to coronal structures is pooly understood. We recast the Berger and Field (1984) helicity transport equation in manifestly gauge invariant form and examine the individual terms leading to the transport of helicity through the emergence of closed field, and twisting and tangling of potential fields. These theoretical results are applied to erupting active regions observed by SDO/HMI. The plasma velocity fields in the photosphere, necessary for computing energy and helicity fluxes are determined using an upgraded version of DAVE4VM that incorporates the spherical geometry of the solar images. We find that the bulk of the helicity into the corona is injected by twisting motions, and we discuss the implications of our results for understanding coronal activity. This work was supported, in part, by NASA.

  14. Helicity transport through the photosphere

    NASA Astrophysics Data System (ADS)

    Schuck, P. W.; Antiochos, S. K.; Linton, M.

    2013-05-01

    Solar eruptions are driven by energy and helicity transported through the photosphere and into the Corona. However, the mechanism by which helicity is transferred from the solar dynamo to coronal structures is pooly understood. We recast the Berger and Field (1984) helicity transport equation in manifestly gauge invariant form and examine the individual terms leading to the transport of helicity through the emergence of closed field, and twisting and tangling of potential fields. These theoretical results are applied to erupting active regions observed by SDO/HMI. The plasma velocity fields in the photosphere, necessary for computing energy and helicity fluxes are determined using an upgraded version of DAVE4VM that incorporates the spherical geometry of the solar images. We find that the bulk of the helicity into the corona is injected by twisting motions, and we discuss the implications of our results for understanding coronal activity.

  15. Conservation of helicity in superfluids

    NASA Astrophysics Data System (ADS)

    Kedia, Hridesh; Kleckner, Dustin; Proment, Davide; Irvine, William T. M.

    2015-03-01

    Helicity arises as a special conserved quantity in ideal fluids, in addition to energy, momentum and angular momentum. As a measure of the knottedness of vortex lines, Helicity provides an important tool for studying a wide variety of physical systems such as plasmas and turbulent fluids. Superfluids flow without resistance just like ideal (Euler) fluids, making it natural to ask whether their knottedness is similarly preserved. We address the conservation of helicity in superfluids theoretically and examine its consequences in numerical simulations.

  16. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, Changbiao.

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically transported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron's relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  17. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, Changbiao

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically transported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron`s relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  18. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, C.

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically imported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron's relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  19. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, C.

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically imported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron`s relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  20. Short-period volcanic gas precursors to phreatic eruptions: Insights from Poás Volcano, Costa Rica

    USGS Publications Warehouse

    de Moor, Maarten; Aiuppa, Alessandro; Pacheco, Javier; Avard, Geoffroy; Kern, Christoph; Liuzzo, Marco; Martinez, Maria; Giudice, Gaetano; Fischer, Tobias P.

    2016-01-01

    Volcanic eruptions involving interaction with water are amongst the most violent and unpredictable geologic phenomena on Earth. Phreatic eruptions are exceptionally difficult to forecast by traditional geophysical techniques. Here we report on short-term precursory variations in gas emissions related to phreatic blasts at Poás volcano, Costa Rica, as measured with an in situ multiple gas analyzer that was deployed at the edge of the erupting lake. Gas emitted from this hyper-acid crater lake approaches magmatic values of SO2/CO2 1–6 days prior to eruption. The SO2 flux derived from magmatic degassing through the lake is measureable by differential optical absorption spectrometry (sporadic campaign measurements), which allows us to constrain lake gas output and input for the major gas species during eruptive and non-eruptive periods. We can further calculate power supply to the hydrothermal system using volatile mass balance and thermodynamics, which indicates that the magmatic heat flux into the shallow hydrothermal system increases from ∼27 MW during quiescence to ∼59 MW during periods of phreatic events. These transient pulses of gas and heat from the deeper magmatic system generate both phreatic eruptions and the observed short-term changes in gas composition, because at high gas flux scrubbing of sulfur by the hydrothermal system is both kinetically and thermodynamically inhibited whereas CO2gas is always essentially inert in hyperacid conditions. Thus, the SO2/CO2 of lake emissions approaches magmatic values as gas and power supply to the sub-limnic hydrothermal system increase, vaporizing fluids and priming the hydrothermal system for eruption. Our results suggest that high-frequency real-time gas monitoring could provide useful short-term eruptive precursors at volcanoes prone to phreatic explosions.

  1. Helicity-Density And Normalized-Helicity Maps Of Flows

    NASA Technical Reports Server (NTRS)

    Degani, David; Levy, Yuval; Seginer, Arnan

    1991-01-01

    Maps of helicity density and normalized helicity useful as graphical representations of important features of three-dimensional flow fields containg vortexes. Emphasize complicated and important parts of flow field, identify vortexes, differentiate between primary and secondary vortexes, indicate sense of swirling motion, locate free singular points, and trace vortex-core streamlines emanating from these points.

  2. Magnetic design constraints of helical solenoids

    SciTech Connect

    Lopes, M. L.; Krave, S. T.; Tompkins, J. C.; Yonehara, K.; Flanagan, G.; Kahn, S. A.; Melconian, K.

    2015-01-30

    Helical solenoids have been proposed as an option for a Helical Cooling Channel for muons in a proposed Muon Collider. Helical solenoids can provide the required three main field components: solenoidal, helical dipole, and a helical gradient. In general terms, the last two are a function of many geometric parameters: coil aperture, coil radial and longitudinal dimensions, helix period and orbit radius. In this paper, we present design studies of a Helical Solenoid, addressing the geometric tunability limits and auxiliary correction system.

  3. Helicity patterns on the Sun

    NASA Astrophysics Data System (ADS)

    Pevtsov, A.

    Solar magnetic fields exhibit hemispheric preference for negative (pos- itive) helicity in northern (southern) hemisphere. The hemispheric he- licity rule, however, is not very strong, - the patterns of opposite sign helicity were observed on different spatial scales in each hemisphere. For instance, many individual sunspots exhibit patches of opposite he- licity inside the single polarity field. There are also helicity patterns on scales larger than the size of typical active region. Such patterns were observed in distribution of active regions with abnormal (for a give hemisphere) helicity, in large-scale photospheric magnetic fields and coronal flux systems. We will review the observations of large-scale pat- terns of helicity in solar atmosphere and their possible relationship with (sub-)photospheric processes. The emphasis will be on large-scale pho- tospheric magnetic field and solar corona.

  4. Suppression and control of leakage field in electromagnetic helical microwiggler

    SciTech Connect

    Ohigashi, N.; Tsunawaki, Y.; Imasaki, K.

    1995-12-31

    Shortening the period of electromagnetic wiggler introduces both the radical increase of the leakage field and the decrease of the field in the gap region. The leakage field is severer problem in planar electromagnetic wiggler than in helical wiggler. Hence, in order to develop a short period electromagnetic wiggler, we have adopted {open_quotes}three poles per period{close_quotes} type electromagnetic helical microwiggler. In this work, we inserted the permanent magnet (PM) blocks with specific magnetized directions in the space between magnetic poles, for suppressing the leakage field flowing out from a pole face to the neighboring pole face. These PM-blocks must have higher intrinsic coersive force than saturation field of pole material. The gap field due to each pole is adjustable by controlling the leakage fields, that is, controlling the position of each iron screw set in each retainer fixing the PM-blocks. At present time, a test wiggler with period 7.8mm, periodical number 10 and gap length 4.6mm has been manufactured. Because the ratio of PM-block aperture to gap length is important parameter to suppress the leakage field, the parameter has been surveyed experimentally for PM-blocks with several dimensions of aperture. The field strength of 3-5kG (K=0.2-0.4) would be expected in the wiggler.

  5. Influence of the electron velocity spread and the beam width on the efficiency and mode competition in the high-power pulsed gyrotron for 300 GHz band collective Thomson scattering diagnostics in the large helical device

    NASA Astrophysics Data System (ADS)

    Dumbrajs, O.; Saito, T.; Tatematsu, Y.; Yamaguchi, Y.

    2016-09-01

    We present results of a theoretical study of influence of the electron velocity spread and the radial width on the efficiency and mode competition in a 300-kW, 300-GHz gyrotron operating in the T E22 ,2 mode. This gyrotron was developed for application to collective Thomson scattering diagnostics in the large helical device and 300-kW level high power single T E22 ,2 mode oscillation has been demonstrated [Yamaguchi et al., J. Instrum. 10, c10002 (2015)]. Effects of a finite voltage rise time corresponding to the real power supply of this gyrotron are also considered. Simulations tracking eight competing modes show that the electron velocity spread and the finite beam width influence not only the efficiency of the gyrotron operation but also the mode competition scenario during the startup phase. A combination of the finite rise time with the electron velocity spread or the finite beam width affects the mode competition scenario. The simulation calculation reproduces the experimental observation of high power single mode oscillation of the T E22 ,2 mode as the design mode. This gives a theoretical basis of the experimentally obtained high power oscillation with the design mode in a real gyrotron and moreover shows a high power oscillation regime of the design mode.

  6. 1SWASP J075102.16+342405.3: A deep overcontact binary system with a period under the short period cut-off

    NASA Astrophysics Data System (ADS)

    Jiang, Linqiao; Qian, Sheng-Bang; Zhang, Jia; Liu, Nianping

    2015-12-01

    New photometry of two different seasons for the extremely short period eclipsing binary 1SWASP J075102.16+342405.3 were performed. The two sets of derived light curves show a large difference in their shape, i.e., the 2013 light curves show big asymmetry, whereas the 2014 light curve is almost symmetric. All light curves were analysed using the 2013 version of the Wilson-Devinney (W-D) code. The obtained solutions show that 1SWASP J075102.16+342405.3 is of the A subtype W UMa contact system with an extremely high fill-out of f ≈ 96% and a high mass ratio of 0.70-0.78. Furthermore, a third light contributing to the total flux of the system was found. All these properties make the system a very special short-period source. The analysis of the 2013 light curves proved that the changes in the light curve shape are caused by magnetic activities. By means of all available times of minimum light, the variation of the orbital period was studied. It was found that the O - C diagram implies an increasing orbital period over a time span of eight years, which may be caused by the mass transfer from the less massive component to the more massive one; however, we are more inclined to say that it is only a part of a long period cyclic variation which can be explained by the light-travel time effect (LTTE) via the third body.

  7. Investigating short-period mesospheric gravity wave propagation and momentum flux at low-latitudes using simultaneous Na lidar and temperature mapper measurements

    NASA Astrophysics Data System (ADS)

    Ejiri, M. K.; Taylor, M. J.; Pautet, P. D.; Zhao, Y.; Liu, A. Z.

    The US Maui-MALT program is designed to investigate the properties and dynamics of the low-latitude mesosphere and lower thermosphere region MLT in exceptional detail A key component of this study is the investigation of short-period gravity waves and their propagation and dissipation characteristics at MLT height High-resolution measurements of the background wind temperature field using the University of Illinois Na wind temperature lidar have been combined with simultaneous image measurements of the NIR OH and O 2 airglow intensity and rotational temperature obtained by the Utah State University Mesospheric Temperature Mapper MTM to perform an in-depth investigation of five selected short-period less than 20 min gravity wave events In each case the waves were observed under differing background conditions and we have determined their intrinsic properties and nature of propagation i e freely propagating or ducted This has allowed us to quantify their associated horizontal momentum fluxes at two different altitudes 87 and 94 km within MLT and hence investigate their impact on this region at low-latitudes

  8. Growth of InAs/GaSb short-period superlattices for high-resolution mid-wavelength infrared focal plane array detectors

    NASA Astrophysics Data System (ADS)

    Walther, M.; Schmitz, J.; Rehm, R.; Kopta, S.; Fuchs, F.; Fleißner, J.; Cabanski, W.; Ziegler, J.

    2005-05-01

    InAs/GaSb short-period superlattices (SLs) with a broken gap type-II band alignment are investigated for the fabrication of photovoltaic pin-photodetectors on GaSb substrates. The structures were grown by molecular beam epitaxy using valved cracker cells for arsenic and antimony. Effective bandgap and strain in the SL were adjusted by varying the thickness of the InAs and GaSb layers in the SL and the controlled formation of InSb-like or GaAs-like bonds at the interfaces. MBE growth conditions were investigated and optimized in order to achieve good morphological, electrical and optical properties. IR-photodiodes with a cut-off wavelength of 5.4 μm reveal quantum efficiencies around 30% and detectivity values exceeding 10 13 Jones at 77 K. A focal plane array camera with 256×256 detector elements and 40 μm pitch based on InAs/GaSb short-period SLs was fabricated for the first time. The camera system reveals an excellent thermal resolution with a noise equivalent temperature difference below 12 mK for an integration time of 5 ms using f/2 optics. The detector performance, comparable with state of the art mercury-cadmium-telluride IR detectors, makes this material system very interesting for the fabrication of advanced thermal imaging systems.

  9. Turbulent Dynamos and Magnetic Helicity

    SciTech Connect

    Ji, Hantao

    1999-04-01

    It is shown that the turbulent dynamo alpha-effect converts magnetic helicity from the turbulent field to the mean field when the turbulence is electromagnetic while the magnetic helicity of the mean-field is transported across space when the turbulence is elcetrostatic or due to the elcetron diamagnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity expect for a battery effect which vanishes in the limit of magnetohydrodynamics. Implications for astrophysical situations, especially for the solar dynamo, are discussed.

  10. Dispersion of helically corrugated waveguides: Analytical, numerical, and experimental study

    NASA Astrophysics Data System (ADS)

    Burt, G.; Samsonov, S. V.; Ronald, K.; Denisov, G. G.; Young, A. R.; Bratman, V. L.; Phelps, A. D.; Cross, A. W.; Konoplev, I. V.; He, W.; Thomson, J.; Whyte, C. G.

    2004-10-01

    Helically corrugated waveguides have recently been studied for use in various applications such as interaction regions in gyrotron traveling-wave tubes and gyrotron backward-wave oscillators and as a dispersive medium for passive microwave pulse compression. The paper presents a summary of various methods that can be used for analysis of the wave dispersion of such waveguides. The results obtained from an analytical approach, simulations with the three-dimensional numerical code MAGIC, and cold microwave measurements are analyzed and compared.

  11. Helicity multiplexed broadband metasurface holograms

    PubMed Central

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

    2015-01-01

    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. PMID:26354497

  12. Magnetic Helicity and Planetary Dynamos

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2012-01-01

    A model planetary dynamo based on the Boussinesq approximation along with homogeneous boundary conditions is considered. A statistical theory describing a large-scale MHD dynamo is found, in which magnetic helicity is the critical parameter

  13. Tunable Helical Origami

    NASA Astrophysics Data System (ADS)

    Chen, Zi; Dai, Eric; Zheng, Huang

    2014-03-01

    Origami, the Japanese art of paper folding, is traditionally viewed as an amusing pastime and medium of artistic expression. However, in recent years, origami has begun to inspire innovations in science and engineering. For example, K. Miura led the study of a paper folding pattern in regards to deployment of solar panels to outer space, resulting in more efficient packing and unpacking of the solar panels into tightly constrained spaces. In this work, we study the geometric and mechanical properties of a twisting origami pattern. The pattern created by the fold exhibits several interesting properties, including rigid foldibility, and finely tunable helical coiling, with control over pitch, radius, and handedness of the helix. In addition, the pattern closely mimics the twist buckling patterns shown by thin materials, for example, a mobius strip. In our work, we relate the six parameters of the twisting origami pattern to generate a fully tunable graphical model of the fold. In addition, we demonstrate that the morphogenesis of such folding pattern can be modeled through finite element analysis. We hope our research into the diagonal fold brings insight into the potential scientific and engineering applications of origami and spark further research into how the traditional paper art can be applied as a simple, inexpensive model for complex problems.

  14. Helical Fiber Amplifier

    DOEpatents

    Koplow, Jeffrey P.; Kliner, Dahy; Goldberg, Lew

    2002-12-17

    A multi-mode gain fiber is provided which affords substantial improvements in the maximum pulse energy, peak power handling capabilities, average output power, and/or pumping efficiency of fiber amplifier and laser sources while maintaining good beam quality (comparable to that of a conventional single-mode fiber source). These benefits are realized by coiling the multimode gain fiber to induce significant bend loss for all but the lowest-order mode(s).

  15. Magnetic Helicity, Tilt, and Twist

    NASA Astrophysics Data System (ADS)

    Pevtsov, Alexei A.; Berger, Mitchell A.; Nindos, Alexander; Norton, Aimee A.; van Driel-Gesztelyi, Lidia

    2014-12-01

    Since its introduction to astro- and solar physics, the concept of helicity has proven to be useful in providing critical insights into physics of various processes from astrophysical dynamos, to magnetic reconnection and eruptive phenomena. Signature of helicity was also detected in many solar features, including orientation of solar active regions, or Joy's law. Here we provide a summary of both solar phenomena and consider mutual relationship and its importance for the evolution of solar magnetic fields.

  16. Microwave Studies of Perfluoropentane and its Helicity

    NASA Astrophysics Data System (ADS)

    Fournier, Joseph A.; Bohn, Robert K.; Montgomery, John A.; , Jr.

    2009-06-01

    Unlike hydrocarbons, fluorocarbons are helical in their all-trans most stable conformations. A definitive experimental determination of the helical angle has not been accomplished because single crystal X-ray studies are not available due to the lack of suitable crystallization solvents, but a value of 17^° from exactly trans is generally accepted from X-ray fiber studies. Using a pulsed-jet Fourier Transform microwave spectrometer, we have observed and assigned the rotational spectra of the lowest energy all-anti C_2 symmetry form of perfluoro-n-pentane and all three of its ^{13}C isotopomers. A, B, and C values of the parent species are 990.6394(4) MHz, 314.00020(14) MHz, and 304.37034(14) MHz, respectively. A range of effective r_0 structures incorporating various model constraints are consistent with about 16^° torsion and a Kraitchman analysis of the parent and ^{13}C species gives 13.3^°. Ab initio calculations are consistent with the experimental results.

  17. Employing helicity amplitudes for resummation

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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 p p →H +0 , 1, 2 jets, p p →W /Z /γ +0 , 1, 2 jets, and p p →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.

  18. omega-Helices in proteins.

    PubMed

    Enkhbayar, Purevjav; Boldgiv, Bazartseren; Matsushima, Norio

    2010-05-01

    A modification of the alpha-helix, termed the omega-helix, has four residues in one turn of a helix. We searched the omega-helix in proteins by the HELFIT program which determines the helical parameters-pitch, residues per turn, radius, and handedness-and p = rmsd/(N - 1)(1/2) estimating helical regularity, where "rmsd" is the root mean square deviation from the best fit helix and "N" is helix length. A total of 1,496 regular alpha-helices 6-9 residues long with p < or = 0.10 A were identified from 866 protein chains. The statistical analysis provides a strong evidence that the frequency distribution of helices versus n indicates the bimodality of typical alpha-helix and omega-helix. Sixty-two right handed omega-helices identified (7.2% of proteins) show non-planarity of the peptide groups. There is amino acid preference of Asp and Cys. These observations and analyses insist that the omega-helices occur really in proteins.

  19. omega-Helices in proteins.

    PubMed

    Enkhbayar, Purevjav; Boldgiv, Bazartseren; Matsushima, Norio

    2010-05-01

    A modification of the alpha-helix, termed the omega-helix, has four residues in one turn of a helix. We searched the omega-helix in proteins by the HELFIT program which determines the helical parameters-pitch, residues per turn, radius, and handedness-and p = rmsd/(N - 1)(1/2) estimating helical regularity, where "rmsd" is the root mean square deviation from the best fit helix and "N" is helix length. A total of 1,496 regular alpha-helices 6-9 residues long with p < or = 0.10 A were identified from 866 protein chains. The statistical analysis provides a strong evidence that the frequency distribution of helices versus n indicates the bimodality of typical alpha-helix and omega-helix. Sixty-two right handed omega-helices identified (7.2% of proteins) show non-planarity of the peptide groups. There is amino acid preference of Asp and Cys. These observations and analyses insist that the omega-helices occur really in proteins. PMID:20496104

  20. The Pulse Line Ion Accelerator Concept

    SciTech Connect

    Briggs, Richard J.

    2006-02-15

    The Pulse Line Ion Accelerator concept was motivated by the desire for an inexpensive way to accelerate intense short pulse heavy ion beams to regimes of interest for studies of High Energy Density Physics and Warm Dense Matter. A pulse power driver applied at one end of a helical pulse line creates a traveling wave pulse that accelerates and axially confines the heavy ion beam pulse. Acceleration scenarios with constant parameter helical lines are described which result in output energies of a single stage much larger than the several hundred kilovolt peak voltages on the line, with a goal of 3-5 MeV/meter acceleration gradients. The concept might be described crudely as an ''air core'' induction linac where the PFN is integrated into the beam line so the accelerating voltage pulse can move along with the ions to get voltage multiplication.

  1. Short-period superlattices of AlN/Al{sub 0.08}Ga{sub 0.92}N grown on AlN substrates

    SciTech Connect

    Nikishin, S.A.; Borisov, B.A.; Chandolu, A.; Kuryatkov, V.V.; Temkin, H.; Holtz, M.; Mokhov, E.N.; Makarov, Yu.; Helava, H.

    2004-11-08

    High-quality short-period superlattices of AlN/Al{sub 0.08}Ga{sub 0.92}N have been grown by gas-source molecular-beam epitaxy with ammonia on Al face of AlN (0001) substrates. A significant reduction was achieved in the dislocation density, down to 3x10{sup 8} cm{sup -2}. Complete removal of residual Al{sub 2}O{sub 3} surface oxide is needed in order to obtain low dislocation density in homoepitaxy on AlN. We show that the presence of Al{sub 2}O{sub 3} islands with the surface coverage as low as 0.2% results in increased dislocation density.

  2. Blue stragglers as remnants of stellar mergers - The discovery of short-period eclipsing binaries in the globular cluster NGC 5466

    NASA Astrophysics Data System (ADS)

    Mateo, Mario; Harris, Hugh C.; Nemec, James; Olszewski, Edward W.

    1990-08-01

    Results are reported from a search for short-period variables among blue stragglers in the central region of NGC 5466, based on analysis of 248 B and V CCD images obtained with the U.S. Naval Observatory 1-m, Palomar Observatory 1.5-m, and Steward Observatory 2.3-m telescopes during 1987-1989. The data are presented in extensive tables and graphs and characterized in detail. Nine variable blue stragglers are identified, of which three are eclipsing binaries with periods 0.298-0.511 d (two contact binaries of W UMa type and one detached or semidetached binary) and six are pulsating SX Phe stars. Theoretical models indicate that all of the noneclipsing blue stragglers could be merged close binaries, although other formation mechanisms cannot be completely ruled out.

  3. Blue stragglers as remnants of stellar mergers - The discovery of short-period eclipsing binaries in the globular cluster NGC 5466

    SciTech Connect

    Mateo, M.; Harris, H.C.; Nemec, J.; Olszewski, E.W. Naval Observatory, Flagstaff, AZ British Columbia Univ., Vancouver Steward Observatory, Tucson, AZ )

    1990-08-01

    Results are reported from a search for short-period variables among blue stragglers in the central region of NGC 5466, based on analysis of 248 B and V CCD images obtained with the U.S. Naval Observatory 1-m, Palomar Observatory 1.5-m, and Steward Observatory 2.3-m telescopes during 1987-1989. The data are presented in extensive tables and graphs and characterized in detail. Nine variable blue stragglers are identified, of which three are eclipsing binaries with periods 0.298-0.511 d (two contact binaries of W UMa type and one detached or semidetached binary) and six are pulsating SX Phe stars. Theoretical models indicate that all of the noneclipsing blue stragglers could be merged close binaries, although other formation mechanisms cannot be completely ruled out. 111 refs.

  4. IUE spectrophotometry of the DA4 primary in the short-period white dwarf-red dwarf spectroscopic binary Case 1

    NASA Technical Reports Server (NTRS)

    Sion, E. M.; Guinan, E. F.; Wesemael, F.

    1984-01-01

    Low-resolution ultraviolet International Ultraviolet Explorer spectra of the DA white dwarf Case 1 are presented. The spectra show the presence of the 1400 A feature, already discovered in several other DA stars, and of a shallower trough in the 1550-1700 A range. A model atmosphere analysis of the ultraviolet energy distribution of the Ly-alpha red wing yields T(e) = 13,000 + or - 500 K. Possible interpretations of the 1400 A feature are reviewed. Case 1 is the coolest white dwarf found in a short-period, detached white dwarf-red dwarf binary, and its cooling time is consistent with estimates of the efficiency of angular momentum removal mechanisms in the phases subsequent to common envelope binary evolution.

  5. A short period of fasting before surgery conserves basal metabolism and suppresses catabolism according to indirect calorimetry performed under general anesthesia.

    PubMed

    Yoshimura, Shinichiro; Fujita, Yoshihito; Hirate, Hiroyuki; Kusama, Nobuyoshi; Azami, Takafumi; Sobue, Kazuya

    2015-06-01

    It is recommended that the period of fasting before elective surgery should be shortened to facilitate a rapid recovery by preventing catabolism. We examined the effects of a short period of fasting on metabolism by performing indirect calorimetry (IC) under general anesthesia. A prospective observational study involving 26 consecutive patients who underwent elective surgery and whose metabolism was evaluated using IC during anesthesia was conducted. The patients were divided into two groups, those who fasted for <8 h (group S) and those who fasted for >10 h (group L). Oxygen consumption, the volume of carbon dioxide emissions (VCO2), the respiratory quotient (RQ), resting energy expenditure (REE), and basal energy expenditure (BEE) were compared. The REE, VCO2, and RQ of group L (17.7 ± 2.3 kcal/kg/day, 118.5 ± 20.8 ml/min, and 0.71 ± 0.12, respectively) were significantly lower than those of group S (19.7 ± 2.3 kcal/kg/day, 143.6 ± 30.9 ml/min, and 0.81 ± 0.09, respectively) (P < 0.05). In group L, the relationship between REE and BEE was weaker (r(2) = 0.501) and the BEE-REE slope was less steep (REE = 0.419BEE + 509.477) than those seen in group S (r(2) = 0.749 and REE = 1.113BEE - 376.111, respectively). Our findings suggest that a short period of fasting (<8 h) before surgery is more strongly associated with the conservation of basal metabolism.

  6. Dust environment and dynamical history of a sample of short-period comets . II. 81P/Wild 2 and 103P/Hartley 2

    NASA Astrophysics Data System (ADS)

    Pozuelos, F. J.; Moreno, F.; Aceituno, F.; Casanova, V.; Sota, A.; López-Moreno, J. J.; Castellano, J.; Reina, E.; Climent, A.; Fernández, A.; San Segundo, A.; Häusler, B.; González, C.; Rodriguez, D.; Bryssinck, E.; Cortés, E.; Rodriguez, F. A.; Baldris, F.; García, F.; Gómez, F.; Limón, F.; Tifner, F.; Muler, G.; Almendros, I.; de los Reyes, J. A.; Henríquez, J. A.; Moreno, J. A.; Báez, J.; Bel, J.; Camarasa, J.; Curto, J.; Hernández, J. F.; González, J. J.; Martín, J. J.; Salto, J. L.; Lopesino, J.; Bosch, J. M.; Ruiz, J. M.; Vidal, J. R.; Ruiz, J.; Sánchez, J.; Temprano, J.; Aymamí, J. M.; Lahuerta, L.; Montoro, L.; Campas, M.; García, M. A.; Canales, O.; Benavides, R.; Dymock, R.; García, R.; Ligustri, R.; Naves, R.; Lahuerta, S.; Pastor, S.

    2014-11-01

    Aims: This paper is a continuation of the first paper in this series, where we presented an extended study of the dust environment of a sample of short-period comets and their dynamical history. On this occasion, we focus on comets 81P/Wild 2 and 103P/Hartley 2, which are of special interest as targets of the spacecraft missions Stardust and EPOXI. Methods: As in the previous study, we used two sets of observational data: a set of images, acquired at Sierra Nevada and Lulin observatories, and the Afρ data as a function of the heliocentric distance provided by the amateur astronomical association Cometas-Obs. The dust environment of comets (dust loss rate, ejection velocities, and size distribution of the particles) was derived from our Monte Carlo dust tail code. To determine their dynamical history we used the numerical integrator Mercury 6.2 to ascertain the time spent by these objects in the Jupiter family Comet region. Results: From the dust analysis, we conclude that both 81P/Wild 2 and 103P/Hartley 2 are dusty comets, with an annual dust production rate of 2.8 × 109 kg yr-1 and (0.4-1.5) × 109 kg yr-1, respectively. From the dynamical analysis, we determined their time spent in the Jupiter family Comet region as ~40 yr in the case of 81P/Wild 2 and ~1000 yr for comet 103P/Hartley 2. These results imply that 81P/Wild 2 is the youngest and the most active comet of the eleven short-period comets studied so far, which tends to favor the correlation between the time spent in JFCs region and the comet activity previously discussed.

  7. X-ray standing-wave study of (AlAs){sub m}(GaAs){sub n} short-period superlattices

    SciTech Connect

    Lessmann, A.; Brennan, S.; Munkholm, A.; Materlik, G.

    1999-04-01

    X-ray standing-waves (XSW) are used for an investigation of the structure of (AlAs){sub m}(GaAs){sub n} short-period superlattices (SL{close_quote}s). The XSW induced modulation of x-ray fluorescence from the Al, As, and Ga atoms and the total photoelectron yield are monitored around the 0th order SL satellite (AlAs)(GaAs)(004,0) and the GaAs(004) substrate Bragg reflection. From the specific shape of these modulations and the sample reflectivity, an atomic model about the interfaces is derived. This is accomplished by comparing the experimental data with dynamical calculations of x-ray wavefield distribution and reflectivity, which are based on the Takagi-Taupin equation. The fluorescence measurements at the 0th order SL satellite reveal a high crystalline order in the AlAs layers of the short-period SL, whereas in the GaAs layers, a fraction of the Ga and As atoms is not on the ideal lattice positions. From the analysis, a model of the atomic distribution along the [001] direction can be determined. This reveals that at each internal interface in the GaAs layers, two Ga atom planes are shifted by up to 0.035 nm and one As atom plane by 0.023 nm. At each interface, the shifts are directed towards the substrate. In addition, the XSW field at the GaAs(004) substrate reflection results in a moir{acute e} or beating effect in the SL structure, which can be used to determine the information depth {Lambda}{sub e} of total electron-yield measurements in a more detailed approach. {copyright} {ital 1999} {ital The American Physical Society}

  8. Selective control for helical microswimmers

    NASA Astrophysics Data System (ADS)

    Katsamba, Panayiota; Lauga, Eric

    2015-11-01

    One of the greatest aspirations for artificial microswimmers is their application in non-invasive medicine. For any practical use, adequate mechanisms enabling control of multiple artificial swimmers is of paramount importance. Here we propose a multi-helical, freely-jointed motor as a novel selective control mechanism. We show that the nonlinear step-out behavior of a magnetized helix driven by a rotating magnetic field can be exploited, when used in conjunction with other helices, to obtain a velocity profile that is non-negligible only within a chosen interval of operating frequencies. Specifically, the force balance between the competing opposite-handed helices is tuned to give no net motion at low frequencies while in the middle frequency range, the swimming velocity increases monotonically with the driving frequency if two opposite helices are used, thereby allowing speed adjustment by varying the driving frequency. We illustrate this idea in detail on a two-helix system, and demonstrate how to generalize to N helices, both numerically and theoretically. We finish by explaining how to solve the inverse problem and design an artificial swimmer with an arbitrarily-complex velocity vs. frequency relationship.

  9. Flexible helical-axis stellarator

    DOEpatents

    Harris, Jeffrey H.; Hender, Timothy C.; Carreras, Benjamin A.; Cantrell, Jack L.; Morris, Robert N.

    1988-01-01

    An 1=1 helical winding which spirals about a conventional planar, circular central conductor of a helical-axis stellarator adds a significant degree of flexibility by making it possible to control the rotational transform profile and shear of the magnetic fields confining the plasma in a helical-axis stellarator. The toroidal central conductor links a plurality of toroidal field coils which are separately disposed to follow a helical path around the central conductor in phase with the helical path of the 1=1 winding. This coil configuration produces bean-shaped magnetic flux surfaces which rotate around the central circular conductor in the same manner as the toroidal field generating coils. The additional 1=1 winding provides flexible control of the magnetic field generated by the central conductor to prevent the formation of low-order resonances in the rotational transform profile which can produce break-up of the equilibrium magnetic surfaces. Further, this additional winding can deepen the magnetic well which together with the flexible control provides increased stability.

  10. Reconstruction of 2D seismic wavefield from Long-Period Seismogram and Short-Period Seismogram Envelope by Seismic Gradiometry applied to the Hi-net Array

    NASA Astrophysics Data System (ADS)

    Maeda, Takuto; Nishida, Kiwamu; Takagi, Ryota; Obara, Kazushige

    2016-04-01

    The high-sensitive seismograph network (Hi-net) operated by National Research Institute for Earth Science and Disaster Prevention (NIED) has about 800 stations with average separation of 20 km all over the Japanese archipelago. Although it is equipped with short-period seismometers, we also can observe long-period seismic wave up to 100 s in periods for significantly large earthquakes. In this case, we may treat long-period seismic waves as a 2D wavefield with station separations shorter than wavelength rather than individual traces at stations. In this study, we attempt to reconstruct 2D wavefield and obtain its propagation properties from seismic gradiometry (SG) method. The SG estimates the wave amplitude and its spatial derivative coefficients from discrete station record by the Taylor series approximation with an inverse problem. By using spatial derivatives in horizontal directions, we can obtain properties of propagating wave packet such as the arrival direction, slowness, geometrical spreading and radiation pattern. In addition, by using spatial derivatives together with free-surface boundary condition, we may decompose the vector elastic 2D wavefield estimated by the SG into divergence and rotation components. First, we applied the seismic gradiometry to a synthetic long-period (20-50 s) seismogram dataset computed by numerical simulation in realistic 3D medium at the Hi-net station layout as a feasibility test. We confirmed that the wave amplitude and its spatial derivatives are very well reproduced with average correlation coefficients higher than 0.99 in this period range. Applications to a real large earthquakes show that the amplitude and phase of the wavefield are well reconstructed with additional information of arrival direction and its slowness. The reconstructed wavefield contained a clear contrast in slowness between body and surface waves, regional non-great-circle-path wave propagation which may be attributed to scattering. Slowness

  11. Generalized helicity and Beltrami fields

    SciTech Connect

    Buniy, Roman V.; Kephart, Thomas W.

    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.

  12. Attenuation of short-period P, PcP, ScP, and pP waves in the earth's mantle

    SciTech Connect

    Bock, G.; Clements, J.R.

    1982-05-10

    The parameter t* (ratio of body wave travel time to the average quality factor Q) was estimated under various assumptions of the nature of the earthquake sources for short-period P, PcP, and ScP phases originating from earthquakes in the Fiji-Tonga region and recorded at the Warramunga Seismic Array at Tennant Creek (Northern Territory, Australia). Spectral ratios were calculated for the amplitudes of PcP to P and of pP to P. The data reveal a laterally varying Q structure in the Fiji-Tonga region. The high-Q lithosphere descending beneath the Tonga Island arc is overlain above 350 km depth by a wedgelike zone of high attenuation with an average Q/sub ..cap alpha../ between 120 and 200 at short periods. The upper mantle farther to the west of the Tonga island arc is less attenuating, with Q/sub ..cap alpha../, between 370 and 560. Q/sub ..cap alpha../ is about 500 in the upper mantle on the oceanic side of the subduction zone. The t* estimates of this study are much smaller than estimates from the free oscillation model SL8. This can be partly explained by regional variations of Q in the upper mantle. If no lateral Q variations occur in the lower mantle, a frequency-dependent Q can make the PcP and ScP observations consistent with model SL8. Adopting the absorption band model to describe the frequency dependence of Q, the parameter tau/sub 2/, the cut-off period of the high-frequency end of the absorption band, was determined. For different source models with finite corner frequencies, the average tau/sub 2/ for the mantle is between 0.01 and 0.10 s (corresponding to frequencies between 16 and 1.6 Hz) as derived from the PcP data, and between 0.06 and 0.12 s (2.7 and 1.3 Hz), as derived from the ScP data.

  13. Infrared Reflectance and Ultrahigh Vacuum Cathodoluminescence of Aluminum Nitride-Gallium Nitride Short Period Superlattice Films and P-Type Porous 6h Silicon Carbide Layers

    NASA Astrophysics Data System (ADS)

    MacMillan, Michael F.

    The room temperature infrared reflectance of AlN -GaN short period superlattice films was measured. These superlattice films were deposited by switched atomic layer metal organic chemical vapor deposition onto GaN or AlN buffer layers deposited on basal plane sapphire substrates. The measured reflectance spectra are compared to calculated spectra generated using an effective medium theory to model the dielectric function of the superlattice. Optical properties of the individual materials comprising the samples are modeled with Lorentz oscillators using bulk input parameters. The effects of film and substrate anisotropy and off normal incidence are included in the calculation. Using this modeling technique, thickness estimates for the total superlattice film and the buffer layer are obtained. Cathodoluminescence of AlN-GaN short period superlattice films was measured at 6K, 77K and room temperature, and at several electron acceleration voltages to allow depth profiling of the samples. An ultraviolet peak located above the band gap energy of GaN is present in all samples and persists from 6K to room temperature. Using the film and buffer thicknesses determined by the reflectance measurement this ultraviolet peak is identified as originating from the superlattice layer. Preliminary results indicate that this peak is due to quantum confinement in the GaN layers. The room temperature infrared reflectance of thick p-type porous 6H SiC layers was measured. Samples were fabricated by anodization of p-type 6H SiC bulk crystals in dilute HF. Striking differences are seen between the reststrahl region reflectance of these porous layers and that of bulk 6H SiC crystals. Several effective medium models, which assume different morphologies of the component materials, 6H SiC and air, were used to model the dielectric function of porous SiC. Calculated reflectance spectra, generated using these dielectric functions, are compared to experimental porous SiC spectra, allowing us to

  14. Brownian motion of helical flagella.

    PubMed

    Hoshikawa, H; Saito, N

    1979-07-01

    We develops a theory of the Brownian motion of a rigid helical object such as bacterial flagella. The statistical properties of the random forces acting on the helical object are discussed and the coefficients of the correlations of the random forces are determined. The averages , and are also calculated where z and theta are the position along and angle around the helix axis respectively. Although the theory is limited to short time interval, direct comparison with experiment is possible by using the recently developed cinematography technique. PMID:16997210

  15. Spatial fluctuation enhancement and nonradiative-recombination-center generation due to high Si-doping into GaAs/AlAs short-period-superlattices

    NASA Astrophysics Data System (ADS)

    Kobori, H.; Shigetani, A.; Umezu, I.; Sugimura, A.

    2006-04-01

    Through the time-resolved photoluminescence (TR-PL) measurement for excitons, we have studied the enhancement of spatial fluctuation (SF) and the generation of nonradiative-recombination-centers (NRC) due to high Si-doping into GaAs/AlAs short-period-superlattices (SPS's). We have carried out the exciton transport analysis according to Krivorotov et al. [I.N. Krivorotov, T. Chang, G.D. Gilliland, L.P. Fu, K.K. Bajaj, Phys. Rev. B 58 (1998) 10687]. From this analysis, we have obtained the temperature dependence of the exciton diffusivity, the concentration of the NRC and the average distant between adjacent localized states of excitons. The temperature dependence of the exciton diffusivity is found to be given by the sum of the temperature-independent contribution and the activation-type contribution. For the exciton diffusivity in undoped GaAs/AlAs SPS's, only the activation-type contribution has been observed. Therefore, we point out the possibility that the temperature-independent contribution comes from the tunneling through the impurities. In this experiment, the activation energy and the concentration of the NRC are found to be larger than those of undoped GaAs/AlAs SPS's. We infer that high Si-doping into GaAs/AlAs SPS causes the enhancement of the SF and the generation of NRC.

  16. GaAsSb/GaAsN short-period superlattices as a capping layer for improved InAs quantum dot-based optoelectronics

    SciTech Connect

    Utrilla, A. D.; Ulloa, J. M. Guzman, A.; Hierro, A.

    2014-07-28

    The application of a GaAsSb/GaAsN short-period superlattice capping layer (CL) on InAs/GaAs quantum dots (QDs) is shown to be an option for providing improved luminescence properties to this system. Separating both GaAsSb and GaAsN ternaries during the growth in 2 monolayer-thick phases solves the GaAsSbN immiscibility-related problems. Strong fluctuations in the CL composition and strain field as well as in the QD size distribution are significantly reduced, and a more regular CL interface is also obtained. Room-temperature (RT) photoluminescence (PL) is obtained for overall N contents as high as 3%, yielding PL peak wavelengths beyond 1.4 μm in samples with a type-II band alignment. High external quantum efficiency electroluminescence and photocurrent from the QD ground state are also demonstrated at RT in a single QD-layer p-i-n device. Thus, it becomes possible to combine and transfer the complementary benefits of Sb- and N-containing GaAs alloys to InAs QD-based optoelectronics.

  17. Interface study and performance of large layer pair ultra-short period W/B{sub 4}C X-ray multilayer

    SciTech Connect

    Pradhan, P. C. Nayak, M.; Mondal, P.; Lodha, G. S.

    2015-06-24

    The nature of interfaces in ultra short period W/B{sub 4}C multilayers (MLs) is studied using hard x-ray reflectivity and cross sectional transmission electron microscope. W/B{sub 4}C MLs are fabricated using magnetron sputtering system with systematic varying thickness of both W and B{sub 4}C layers from ∼5 to 30 Å keeping number of layer pairs fixed at 10. It is observed that in low period W/B{sub 4}C ML, as the layer thickness decreases, the interdiffusion plays a significant role because of the discontinuous nature of film. This gives variation of density and roughness of the layer as well as generates thickness errors in the ML structure due to volume changes which is originated by interdifusion process. Finally, W/B{sub 4}C MLs with large number of layer pairs (300) are fabricated with periodicity d= 20 Å which gives ∼54 % of reflectivity at energy 8.047 keV.

  18. Sex and age differences in meat composition of Yeso sika deer (Cervus nippon yesoensis) reared for a short period after capture in the wild.

    PubMed

    Hayashida, Maki; Souma, Kousaku; Sugo, Kazuki; Araki, Shin-Ichi; Ishizaka, Fumiaki; Ueda, Masami; Kasai, Takamasa; Masuko, Takayoshi

    2015-02-01

    Yeso sika deer captured in winter around Lake Akan in Hokkaido were reared for 8-10 months at Tokyo University of Agriculture in Abashiri. Six 1-year-old females and males and six 2-year-old or older (adult) females and males were slaughtered and their carcasses were processed. The chemical composition, mineral contents and fatty acid composition of the loin were measured. No marked influence of gender or age was noted in the chemical composition of loin. In the mineral contents, significant differences were noted. The potassium and sulfur contents were lower and the sodium content was higher in adult deer meat (P < 0.05, respectively) and the potassium content was higher in male deer meat (P < 0.05). Arsenic, cadmium or lead were not detected. In the unsaturated fatty acid, a significant interaction was detected (P < 0.05), and it was high in 1-year-old female deer meat and low in 1-year-old male deer meat. Significant gender or age differences were noted only in the mineral contents in the loin of deer reared for a short period after capture.

  19. Discovery of the strongly eccentric, short-period binary nature of the B-type system HD 313926 by the MOST satellite

    NASA Astrophysics Data System (ADS)

    Rucinski, Slavek M.; Kuschnig, Rainer; Matthews, Jaymie M.; Dimitrov, Wojtek; Pribulla, Theodor; Guenther, David B.; Moffat, Anthony F. J.; Sasselov, Dimitar; Walker, Gordon A. H.; Weiss, Werner W.

    2007-09-01

    The MOST photometric space mission discovered an eclipsing binary among its guide stars in 2006 June which combines a relatively large eccentricity e = 0.20 with an orbital period of only 2.27 d. HD 313926 appears to consist of two early-type stars of spectral type B3-B7. It has the largest eccentricity among known early-type binaries with periods less than 3.5 d. Despite the large components indicated by its spectral type and light curve model, and its short period, the orbit of HD 313926 has not yet circularized so it is probably very young, even compared with other young B stars. Based on data from MOST, a Canadian Space Agency mission jointly operated by Dynacon Inc., the University of Toronto Institute for Aerospace Studies and the University of British Columbia, with the assistance of the University of Vienna, and on data from the David Dunlap Observatory, University of Toronto. E-mail: rucinski@astro.utoronto.ca

  20. Sex and age differences in meat composition of Yeso sika deer (Cervus nippon yesoensis) reared for a short period after capture in the wild.

    PubMed

    Hayashida, Maki; Souma, Kousaku; Sugo, Kazuki; Araki, Shin-Ichi; Ishizaka, Fumiaki; Ueda, Masami; Kasai, Takamasa; Masuko, Takayoshi

    2015-02-01

    Yeso sika deer captured in winter around Lake Akan in Hokkaido were reared for 8-10 months at Tokyo University of Agriculture in Abashiri. Six 1-year-old females and males and six 2-year-old or older (adult) females and males were slaughtered and their carcasses were processed. The chemical composition, mineral contents and fatty acid composition of the loin were measured. No marked influence of gender or age was noted in the chemical composition of loin. In the mineral contents, significant differences were noted. The potassium and sulfur contents were lower and the sodium content was higher in adult deer meat (P < 0.05, respectively) and the potassium content was higher in male deer meat (P < 0.05). Arsenic, cadmium or lead were not detected. In the unsaturated fatty acid, a significant interaction was detected (P < 0.05), and it was high in 1-year-old female deer meat and low in 1-year-old male deer meat. Significant gender or age differences were noted only in the mineral contents in the loin of deer reared for a short period after capture. PMID:25186458

  1. Influence of internal electric fields on band gaps in short period GaN/GaAlN and InGaN/GaN polar superlattices

    SciTech Connect

    Gorczyca, I. Skrobas, K.; Suski, T.; Christensen, N. E.; Svane, A.

    2015-08-21

    The electronic structures of short period mGaN/nGa{sub y}Al{sub 1−y}N and mIn{sub y}Ga{sub 1-y}N/nGaN superlattices grown along the wurtzite c axis have been calculated for different alloy compositions y and various small numbers m of well- and n of barrier-monolayers. The general trends in gap behavior can, to a large extent, be related to the strength of the internal electric field, E, in the GaN and InGaN quantum wells. In the GaN/GaAlN superlattices, E reaches 4 MV/cm, while in the InGaN/GaN superlattices, values as high as E ≈ 6.5 MV/cm are found. The strong electric fields are caused by spontaneous and piezoelectric polarizations, the latter contribution dominating in InGaN/GaN superlattices. The influence of different arrangements of In atoms (indium clustering) on the band gap values in InGaN/GaN superlattices is examined.

  2. Molecular beam epitaxy of ZnSSe/CdSe short-period superlattices for III–V/II–VI multijunction solar cells

    SciTech Connect

    Sorokin, S. V. Gronin, S. V.; Sedova, I. V.; Klimko, G. V.; Evropeitsev, E. A.; Baidakova, M. V.; Sitnikova, A. A.; Toropov, A. A.; Ivanov, S. V.

    2015-08-15

    Results on the molecular-beam epitaxy growth of short-period alternately-strained ZnS{sub x}Se{sub 1−x}/CdSe superlattices which are pseudomorphic to GaAs (001) substrates and possess effective band-gap values within the range of E{sub g} ≈ 2.5–2.7 eV are presented. Oscillations of the specular-spot intensity in reflection high-energy electron diffraction are used for in situ control of the superlattice parameters. A method to determine the SL parameters (compositions and thicknesses of the constituent layers) based on combined analysis of the grown structures by low-temperature photoluminescence and X-ray diffractometry is developed. It is found that the parameters of the grown ZnS{sub x}Se{sub 1−x}/CdSe superlattices are close to their design values and the density of extended defects in the structures is low even though the structure thickness (∼300 nm) considerably exceeds the critical thickness for bulk II–VI layers with the same lattice-constant mismatch.

  3. Lithium in a short-period tidally locked binary of M67: Implications for stellar evolution, Galactic Lithium evolution, and cosmology

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; King, Jeremy R.; Boesgaard, Ann M.; Ryan, Sean G.

    1994-01-01

    In open clusters, late-F stars exhibit a Li maximum (the Li 'peak' region) at lower abundance with age, which could be due either to stellar depletion or Galactic Li enrichment (or some other cause). We have observed a short-period tidally locked binary (SPTLB) on the Li peak region in the old cluster M67 to distinguish between alternatives. SPTLBs which synchronized in the early pre-main sequence would avoid the rotational mixing which, according to Yale models, may be responsible for depleting Li with age in open cluster dwarfs. We find that both components of the M67 SPTLB have a Li abundance lying about a factor of 2 or more above any other M67 single star and about a factor of 3 or more above the mean Li peak region abundance in M67. Our results suggest that the initial Li abundance in M67 is at least as high as approximately 3.0 = 12 + log (N(sub Li)/N(sub H)). Our high M67 SPTLB Li abundance and those in other clusters support the combination of Zahn's tidal circularization and the Yale rotational mixing theories and may indicate that the halo Li plateau (analogous to the cluster Li peak region) abundance has been depleted from a higher primordial value. Implications are discussed.

  4. Band gaps and built-in electric fields in InAlN/GaN short period superlattices: Comparison with (InAlGa)N quaternary alloys

    NASA Astrophysics Data System (ADS)

    Gorczyca, I.; Suski, T.; Christensen, N. E.; Svane, A.

    2016-04-01

    The general trends in the behavior of the band gaps in short period superlattices (SLs) composed from InAlN and GaN layers and grown along the wurtzite c axis have been analyzed for different alloy compositions and several thicknesses of quantum wells and barriers. The composition dependence of the gaps is compared to that of the quaternary alloys I nyA l1 -x -yG axN with the same effective contents of In, Al, and Ga as the SLs. The differences in the gaps are explained mainly by the built-in electric fields in the SLs caused by spontaneous and piezoelectric polarizations. Other factors, such as internal strain caused by lattice mismatch between wells and barriers and wave function hybridization, are taken into account. A simplified approach to determine the built-in electric fields directly from the dielectric properties of the constituent materials has been applied and verified by comparison to ab initio calculations for selected SLs. The calculated band gaps are compared with existing experimental data.

  5. Three-Dimensional Reconstruction of Helical Polymers

    PubMed Central

    Egelman, Edward H.

    2015-01-01

    The field of three-dimensional electron microscopy began more than 45 years ago with a reconstruction of a helical phage tail, and helical polymers continue to be important objects for three-dimensional reconstruction due to the centrality of helical protein and nucleoprotein polymers in all aspects of biology. We are now witnessing a fundamental revolution in this area, made possible by direct electron detectors, which has led to near-atomic resolution for a number of important helical structures. Most importantly, the possibility of achieving such resolution routinely for a vast number of helical samples is within our reach. One of the main problems in helical reconstruction, ambiguities in assigning the helical symmetry, is overcome when one reaches a resolution where secondary structure is clearly visible. However, obstacles still exist due to the intrinsic variability within many helical filaments. PMID:25912526

  6. Three-dimensional reconstruction of helical polymers.

    PubMed

    Egelman, Edward H

    2015-09-01

    The field of three-dimensional electron microscopy began more than 45years ago with a reconstruction of a helical phage tail, and helical polymers continue to be important objects for three-dimensional reconstruction due to the centrality of helical protein and nucleoprotein polymers in all aspects of biology. We are now witnessing a fundamental revolution in this area, made possible by direct electron detectors, which has led to near-atomic resolution for a number of important helical structures. Most importantly, the possibility of achieving such resolution routinely for a vast number of helical samples is within our reach. One of the main problems in helical reconstruction, ambiguities in assigning the helical symmetry, is overcome when one reaches a resolution where secondary structure is clearly visible. However, obstacles still exist due to the intrinsic variability within many helical filaments.

  7. The transport of relative canonical helicity

    SciTech Connect

    You, S.

    2012-09-15

    The evolution of relative canonical helicity is examined in the two-fluid magnetohydrodynamic formalism. Canonical helicity is defined here as the helicity of the plasma species' canonical momentum. The species' canonical helicity are coupled together and can be converted from one into the other while the total gauge-invariant relative canonical helicity remains globally invariant. The conversion is driven by enthalpy differences at a surface common to ion and electron canonical flux tubes. The model provides an explanation for why the threshold for bifurcation in counter-helicity merging depends on the size parameter. The size parameter determines whether magnetic helicity annihilation channels enthalpy into the magnetic flux tube or into the vorticity flow tube components of the canonical flux tube. The transport of relative canonical helicity constrains the interaction between plasma flows and magnetic fields, and provides a more general framework for driving flows and currents from enthalpy or inductive boundary conditions.

  8. Progress in Non-solenoidal Startup via Local Helicity Injection in the Pegasus Experiment

    NASA Astrophysics Data System (ADS)

    Fonck, R. J.; Barr, J. L.; Bongard, M. W.; Burke, M. G.; Hinson, E. T.; Perry, J. M.; Redd, A. J.; Schlossberg, D. J.; Schoenbeck, N. L.; Shriwise, P. C.; Thome, K. E.

    2012-10-01

    The operating space for localized helicity injection for non-solenoidal startup is constrained by helicity input and dissipation rates and a geometric limit on plasma current set by Taylor relaxation. To test the understanding of dissipation mechanisms during helicity-driven startup, the helicity injection startup and growth is being expanded to ˜0.3 MA plasma currents and longer pulse lengths on the Pegasus experiment. Following initiation via active current sources, passive electrodes can be used to grow discharges for relatively long pulse lengths. Bursts of MHD activity are observed during helicity injection, and correlate with rapid equilibrium changes, including inward motion of the magnetic axis, redistribution of the toroidal current, and strong ion heating with ion temperatures ˜1 keV observed. The plasma arc injector impedance and the associated helicity injection rate appear to be constrained by a double-layer space charge limit at low currents and by the Alfv'en-Lawson limit for strong electron beams at high currents. Additions to the experiment include an expanded poloidal field coil system for added plasma control, new divertor coils, new plasma gun-electrode injector assemblies, expanded gas fueling techniques, and eventually a doubling of the toroidal field.

  9. Baryogenesis from decaying magnetic helicity

    NASA Astrophysics Data System (ADS)

    Kamada, Kohei; Long, Andrew J.

    2016-09-01

    As a result of the Standard Model chiral anomalies, baryon number is violated in the early Universe in the presence of a hypermagnetic field with varying helicity. We investigate whether the matter/antimatter asymmetry of the Universe can be created from the decaying helicity of a primordial (hyper)magnetic field before and after the electroweak phase transition. In this model, baryogenesis occurs without (B -L )-violation, since the (B +L ) asymmetry generated by the hypermagnetic field counteracts the washout by electroweak sphalerons. At the electroweak crossover, the hypermagnetic field becomes an electromagnetic field, which does not source (B +L ). Although the sphalerons remain in equilibrium for a time, washout is avoided since the decaying magnetic helicity sources chirality. The relic baryon asymmetry is fixed when the electroweak sphaleron freezes out. Under reasonable assumptions, a baryon asymmetry of nB/s ≃4 ×10-12 can be generated from a maximally helical, right-handed (hyper)magnetic field that has a field strength of B0≃10-14 Gauss and coherence length of λ0≃1 pc today. Relaxing an assumption that relates λ0 to B0, the model predicts nB/s ≳10-10, which could potentially explain the observed baryon asymmetry of the Universe.

  10. Note: Helical nanobelt force sensors

    SciTech Connect

    Hwang, G.; Hashimoto, H.

    2012-12-15

    We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 Multiplication-Sign 10{sup -10} Pa{sup -1}), low stiffness (0.03125 N/m), large-displacement capability ({approx}10 {mu}m), and good fatigue resistance, they are well suited to function as stand-alone, compact ({approx}20 {mu}m without the plug-in support), light ({approx}5 g including the plug-in support), versatile and large range ({approx}{mu}N) and high resolution ({approx}nN) force sensors.

  11. Non-solenoidal Startup through Local Helicity Injection in the Pegasus Toroidal Experiment

    NASA Astrophysics Data System (ADS)

    Bongard, M. W.; Barr, J. L.; Burke, M. G.; Fonck, R. J.; Hinson, E. T.; Perry, J. M.; Redd, A. J.; Schlossberg, D. J.; Schoenbeck, N. L.; Shriwise, P. C.; Thome, K. E.

    2012-10-01

    Non-solenoidal plasma startup via local helicity injection is governed by helicity balance and Taylor relaxation constraints. Local helicity injection capabilities at Pegasus have been increased, supporting an expansion of the existing operational space towards Ip˜ 0.3 MA and characterization of helicity dissipation mechanisms during plasma startup, growth, and sustainment. After discharge initiation with an active current source, helicity injection may be provided by passive electrodes to continue its evolution and extend pulse length. Local magnetic measurements confirm that a local field null is transiently created by injected current streams prior to relaxation into a tokamak-like state and sustained helicity injection. Bursts of MHD activity during the growth phase are correlated with rapid equilibrium changes, redistribution of the toroidal current density, and observations of strong ion heating (Ti ˜ 1 keV). The impedance of active injectors and thereby their helicity input rate appears constrained by a double-layer space charge limit at low currents and the Alfv'en-Lawson limit for intense electron beams at high currents. Facility and diagnostic upgrades include an expanded poloidal field coil system for improved plasma control, new divertor coils, new plasma gun-electrode injector assemblies, a Thomson scattering system, expanded gas fueling techniques, and support for doubling the toroidal field.

  12. Detailed noise measurements on the SR-7A propeller: Tone behavior with helical tip Mach number

    NASA Technical Reports Server (NTRS)

    Dittmar, James H.; Hall, David G.

    1991-01-01

    Detailed noise measurements were taken on the SR-7A propeller to investigate the behavior of the noise with helical tip Mach number and then to level off as Mach number was increased further. This behavior was further investigated by obtaining detailed pressure-time histories of data. The pressure-time histories indicate that a portion of the primary pressure pulse is progressively cancelled by a secondary pulse which results in the noise leveling off as the helical tip Mach number is increased. This second pulse appears to originate on the same blade as the primary pulse and is in some way connected to the blade itself. This leaves open the possibility of redesigning the blade to improve the cancellation; thereby, the propeller noise is reduced.

  13. Searching for evidence for different activity drivers in long- and short-period comets from the WISE/NEOWISE data set

    NASA Astrophysics Data System (ADS)

    Kramer, E.; Fernandez, Y.; Bauer, J.; Stevenson, R.; Mainzer, A.; Grav, T.; Masiero, J.; Walker, R.; Lisse, C.; WISE Team

    2014-07-01

    Introduction: The Wide-field Infrared Survey Explorer (WISE) mission surveyed the sky in four infrared wavelength bands (3.4, 4.6, 12 and 22 μ m) between January 2010 and February 2011 [1,2]. During the mission, WISE serendipitously observed over 150 comets, including 21 newly discovered objects. About half of the comets observed by WISE displayed a significant dust tail in the 12 and 22 μ m (thermal emission) bands. The Figure below shows a sampling of six comets in the 22 μ m band, showing the range of activity levels and dust morphology present in the data. Since the observed objects are a mix of both long-period (LP) and short-period (SP) comets, differences in activity can be used to better understand the thermal processing that each of these populations has undergone. Approach: For the comets that displayed a significant dust tail, we have estimated the sizes and ages of the particles using dynamical models based on the Finson-Probstein method [3,4]. The main parameter in these models is the ratio of solar radiation pressure to solar gravity, called β. We have then compared these models to the data using a novel tail-fitting method that allows the best-fit model to be chosen analytically rather than subjectively. For comets that were observed multiple times by WISE, the particle properties were estimated separately, and then compared. Results: The ages of the dust tails seen vary in age from a few months to several years, with the average for both SP and LP comets being between 1--2 years. While many of the dust tails are comprised of grains emitted near perihelion, several comets exhibit tails that depart from this trend significantly. For both the SP and LP comets, the median β value was about 0.01, suggesting that the tail particles are on the order of tens of microns in size. Our preliminary analysis suggests that while the sizes and ages of the particles that comprise the dust tails of LP and SP comets are similar, the heliocentric distance at which

  14. Zodiacal Exoplanets in Time (ZEIT). III. A Short-period Planet Orbiting a Pre-main-sequence Star in the Upper Scorpius OB Association

    NASA Astrophysics Data System (ADS)

    Mann, Andrew W.; Newton, Elisabeth R.; Rizzuto, Aaron C.; Irwin, Jonathan; Feiden, Gregory A.; Gaidos, Eric; Mace, Gregory N.; Kraus, Adam L.; James, David J.; Ansdell, Megan; Charbonneau, David; Covey, Kevin R.; Ireland, Michael J.; Jaffe, Daniel T.; Johnson, Marshall C.; Kidder, Benjamin; Vanderburg, Andrew

    2016-09-01

    We confirm and characterize a close-in ({P}{{orb}} = 5.425 days), super-Neptune sized ({5.04}-0.37+0.34 {R}\\oplus ) planet transiting K2-33 (2MASS J16101473-1919095), a late-type (M3) pre-main-sequence (11 Myr old) star in the Upper Scorpius subgroup of the Scorpius–Centaurus OB association. The host star has the kinematics of a member of the Upper Scorpius OB association, and its spectrum contains lithium absorption, an unambiguous sign of youth (\\lt 20 Myr) in late-type dwarfs. We combine photometry from K2 and the ground-based MEarth project to refine the planet’s properties and constrain the host star’s density. We determine K2-33’s bolometric flux and effective temperature from moderate-resolution spectra. By utilizing isochrones that include the effects of magnetic fields, we derive a precise radius (6%–7%) and mass (16%) for the host star, and a stellar age consistent with the established value for Upper Scorpius. Follow-up high-resolution imaging and Doppler spectroscopy confirm that the transiting object is not a stellar companion or a background eclipsing binary blended with the target. The shape of the transit, the constancy of the transit depth and periodicity over 1.5 yr, and the independence with wavelength rule out stellar variability or a dust cloud or debris disk partially occulting the star as the source of the signal; we conclude that it must instead be planetary in origin. The existence of K2-33b suggests that close-in planets can form in situ or migrate within ˜10 Myr, e.g., via interactions with a disk, and that long-timescale dynamical migration such as by Lidov–Kozai or planet–planet scattering is not responsible for all short-period planets.

  15. Zodiacal Exoplanets in Time (ZEIT). III. A Short-period Planet Orbiting a Pre-main-sequence Star in the Upper Scorpius OB Association

    NASA Astrophysics Data System (ADS)

    Mann, Andrew W.; Newton, Elisabeth R.; Rizzuto, Aaron C.; Irwin, Jonathan; Feiden, Gregory A.; Gaidos, Eric; Mace, Gregory N.; Kraus, Adam L.; James, David J.; Ansdell, Megan; Charbonneau, David; Covey, Kevin R.; Ireland, Michael J.; Jaffe, Daniel T.; Johnson, Marshall C.; Kidder, Benjamin; Vanderburg, Andrew

    2016-09-01

    We confirm and characterize a close-in ({P}{{orb}} = 5.425 days), super-Neptune sized ({5.04}-0.37+0.34 {R}\\oplus ) planet transiting K2-33 (2MASS J16101473-1919095), a late-type (M3) pre-main-sequence (11 Myr old) star in the Upper Scorpius subgroup of the Scorpius-Centaurus OB association. The host star has the kinematics of a member of the Upper Scorpius OB association, and its spectrum contains lithium absorption, an unambiguous sign of youth (\\lt 20 Myr) in late-type dwarfs. We combine photometry from K2 and the ground-based MEarth project to refine the planet’s properties and constrain the host star’s density. We determine K2-33’s bolometric flux and effective temperature from moderate-resolution spectra. By utilizing isochrones that include the effects of magnetic fields, we derive a precise radius (6%-7%) and mass (16%) for the host star, and a stellar age consistent with the established value for Upper Scorpius. Follow-up high-resolution imaging and Doppler spectroscopy confirm that the transiting object is not a stellar companion or a background eclipsing binary blended with the target. The shape of the transit, the constancy of the transit depth and periodicity over 1.5 yr, and the independence with wavelength rule out stellar variability or a dust cloud or debris disk partially occulting the star as the source of the signal; we conclude that it must instead be planetary in origin. The existence of K2-33b suggests that close-in planets can form in situ or migrate within ˜10 Myr, e.g., via interactions with a disk, and that long-timescale dynamical migration such as by Lidov-Kozai or planet-planet scattering is not responsible for all short-period planets.

  16. BD Andromedae: A new short-period RS CVn eclipsing binary star with a distant tertiary body in a highly eccentric orbit

    SciTech Connect

    Kim, Chun-Hwey; Song, Mi-Hwa; Yoon, Jo-Na; Jeong, Min-Ji; Han, Wonyong

    2014-06-20

    A photometric study of BD And was made through the analysis of two sets of new BVR light curves. The light curves with migrating photometric waves outside eclipse show that BD And is a short-period RS CVn-type binary star. The analysis of all available timings reveals that the orbital period has varied in a strictly cyclical way with a period of 9.2 yr. The periodic variation most likely arises from the light-time effect due to a tertiary moving in a highly elliptical orbit (e {sub 3} = 0.76). The Applegate mechanism could not operate properly in the eclipsing pair. The light curves were modeled with two large spots on the hotter star and a large third light amounting to about 14% of the total systemic light. BD And is a triple system: a detached binary system consisting of two nearly equal solar-type stars with an active primary star and a G6-G7 tertiary dwarf. The absolute dimensions of the eclipsing pair and tertiary components were determined. The three components with a mean age of about 5.8 Gyr are located at midpositions in main-sequence bands. The radius of the secondary is about 17% larger than that deduced from stellar models. The orbital and radiometric characteristics of the tertiary are intensively investigated. One important feature is that the mutual inclination between two orbits is larger than 60°, implying that Kozai cycles had occurred very efficiently in the past. The possible past and future evolutions of the BD And system, driven by KCTF and MBTF, are also discussed.

  17. Predictive supracolloidal helices from patchy particles

    PubMed Central

    Guo, Ruohai; Mao, Jian; Xie, Xu-Ming; Yan, Li-Tang

    2014-01-01

    A priori prediction of supracolloidal architectures from nanoparticle and colloidal assembly is a challenging goal in materials chemistry and physics. Despite intense research in this area, much less has been known about the predictive science of supracolloidal helices from designed building blocks. Therefore, developing conceptually new rules to construct supracolloidal architectures with predictive helicity is becoming an important and urgent task of great scientific interest. Here, inspired by biological helices, we show that the rational design of patchy arrangement and interaction can drive patchy particles to self-assemble into biomolecular mimetic supracolloidal helices. We further derive a facile design rule for encoding the target supracolloidal helices, thus opening the doors to the predictive science of these supracolloidal architectures. It is also found that kinetics and reaction pathway during the formation of supracolloidal helices offer a unique way to study supramolecular polymerization, and that well-controlled supracolloidal helices can exhibit tailorable circular dichroism effects at visible wavelengths. PMID:25387544

  18. Predictive supracolloidal helices from patchy particles

    NASA Astrophysics Data System (ADS)

    Guo, Ruohai; Mao, Jian; Xie, Xu-Ming; Yan, Li-Tang

    2014-11-01

    A priori prediction of supracolloidal architectures from nanoparticle and colloidal assembly is a challenging goal in materials chemistry and physics. Despite intense research in this area, much less has been known about the predictive science of supracolloidal helices from designed building blocks. Therefore, developing conceptually new rules to construct supracolloidal architectures with predictive helicity is becoming an important and urgent task of great scientific interest. Here, inspired by biological helices, we show that the rational design of patchy arrangement and interaction can drive patchy particles to self-assemble into biomolecular mimetic supracolloidal helices. We further derive a facile design rule for encoding the target supracolloidal helices, thus opening the doors to the predictive science of these supracolloidal architectures. It is also found that kinetics and reaction pathway during the formation of supracolloidal helices offer a unique way to study supramolecular polymerization, and that well-controlled supracolloidal helices can exhibit tailorable circular dichroism effects at visible wavelengths.

  19. An experimental superconducting helical undulator

    SciTech Connect

    Caspi, S.; Taylor, C.

    1995-12-31

    Improvements in the technology of superconducting magnets for high energy physics and recent advancements in SC materials with the artificial pinning centers (APC){sup 2}, have made a bifilar helical SC device an attractive candidate for a single-pass free electron laser (FEL){sup 3}. Initial studies have suggested that a 6.5 mm inner diameter helical device, with a 27 mm period, can generate a central field of 2-2.5 Tesla. Additional studies have also suggested that with a stored energy of 300 J/m, such a device can be made self-protecting in the event of a quench. However, since the most critical area associated with high current density SC magnets is connected with quenching and training, a short experimental device will have to be built and tested. In this paper we discuss technical issues relevant to the construction of such a device, including a conceptual design, fields, and forces.

  20. Helical screw expander evaluation project

    NASA Technical Reports Server (NTRS)

    Mckay, R.

    1982-01-01

    A one MW helical rotary screw expander power system for electric power generation from geothermal brine was evaluated. The technology explored in the testing is simple, potentially very efficient, and ideally suited to wellhead installations in moderate to high enthalpy, liquid dominated field. A functional one MW geothermal electric power plant that featured a helical screw expander was produced and then tested with a demonstrated average performance of approximately 45% machine efficiency over a wide range of test conditions in noncondensing, operation on two-phase geothermal fluids. The Project also produced a computer equipped data system, an instrumentation and control van, and a 1000 kW variable load bank, all integrated into a test array designed for operation at a variety of remote test sites. Data are presented for the Utah testing and for the noncondensing phases of the testing in Mexico. Test time logged was 437 hours during the Utah tests and 1101 hours during the Mexico tests.

  1. Helical Antimicrobial Sulfono- {gamma} -AApeptides

    SciTech Connect

    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.

  2. On the nature of short-period oscillations of the main Black Sea pycnocline, submesoscale eddies, and response of the marine environment to the catastrophic shower of 2012

    NASA Astrophysics Data System (ADS)

    Zatsepin, A. G.; Ostrovskii, A. G.; Kremenetskiy, V. V.; Piotukh, V. B.; Kuklev, S. B.; Moskalenko, L. V.; Podymov, O. I.; Baranov, V. I.; Korzh, A. O.; Stanichny, S. V.

    2013-11-01

    Field studies performed at the Shirshov Institute of Oceanology, Russian Academy of Sciences (SIO RAS), Black Sea hydrophysical polygon in 2012 are illustrated. The variations in the vertical distribution of the hydrophysical characteristics (water temperature, salinity, and density, as well as current velocity) in the upper 200-m layer of the Black Sea above the continental slope in the cold season, obtained using an Aqualog autonomous profiler on a moored buoy station, have been analyzed. It has been established that the position of the permanent pycno-halocline and the hydrosulphuric zone upper boundary intensively oscillate with a characteristic period of 5-10 days. These oscillations cause short-period variations in the thickness of the oxigenated layer by 20-40 m, which reaches one-third of the total thickness of the layer. Measurements performed with autonomous stations (bottom ADCP, thermochain) at the experimental subsatellite polygon in the Gelendzhik coastal zone, as well as meteorological, ship, and satellite data obtained during the catastrophic rains and flooding on July 6-7, 2012, and afterward, have been simultaneously analyzed. It has been established that a catastrophic flow of turbid fresh water into the sea caused the formation of a belt of freshened (by 1.0-2.7 psu) less dense water with a high suspension concentration on the shelf and the upper continental slope. This water formed a quasi-geostrophic northwestward along-shore current, the velocity of which reached 40-50 cm/s. Therefore, the freshened and turbid water mostly escaped from the Gelendzhik region northwestward for two days after the flood, and the remaining water became free of suspension owing to its settlement during approximately the same period. The fields of the current velocity and suspension concentration in a submesoscale cyclonic eddy, identified on the satellite image, were measured at the hydrophysical polygon. It has been established that a high (when compared to the

  3. KELT-1b: A STRONGLY IRRADIATED, HIGHLY INFLATED, SHORT PERIOD, 27 JUPITER-MASS COMPANION TRANSITING A MID-F STAR

    SciTech Connect

    Siverd, Robert J.; Pepper, Joshua; Stassun, Keivan G.; Beatty, Thomas G.; Scott Gaudi, B.; Eastman, Jason D.; Street, Rachel; Fulton, Benjamin J.; Collins, Karen; Bieryla, Allyson; Latham, David W.; Berlind, Perry; Calkins, Michael L.; Esquerdo, Gilbert A.; Furesz, Gabor; Geary, John C.; Buchhave, Lars A.; Jensen, Eric L. N.; Crepp, Justin R.; DePoy, D. L.; and others

    2012-12-20

    We present the discovery of KELT-1b, the first transiting low-mass companion from the wide-field Kilodegree Extremely Little Telescope-North (KELT-North) transit survey. A joint analysis of the spectroscopic, radial velocity, and photometric data indicates that the V = 10.7 primary is a mildly evolved mid-F star with T{sub eff} = 6516 {+-} 49 K, log g 4.228{sup +0.014}{sub -0.021}, and [Fe/H] = 0.052 {+-} 0.079, with an inferred mass M{sub *} = 1.335 {+-} 0.063 M{sub Sun} and radius R{sub *} 1.471{sup +0.045}{sub -0.035} R{sub Sun }. The companion is a low-mass brown dwarf or a super-massive planet with mass M{sub P} = 27.38 {+-} 0.93 M{sub Jup} and radius R{sub P} = 1.116{sup +0.038}{sub -0.029} R{sub Jup}. The companion is on a very short ({approx}29 hr) period circular orbit, with an ephemeris T{sub c} (BJD{sub TDB}) = 2455909.29280 {+-} 0.00023 and P = 1.217501 {+-} 0.000018 days. KELT-1b receives a large amount of stellar insolation, resulting in an estimated equilibrium temperature assuming zero albedo and perfect redistribution of T{sub eq} = 2423{sup +34}{sub -27} K. Comparison with standard evolutionary models suggests that the radius of KELT-1b is likely to be significantly inflated. Adaptive optics imaging reveals a candidate stellar companion to KELT-1 with a separation of 588 {+-} 1 mas, which is consistent with an M dwarf if it is at the same distance as the primary. Rossiter-McLaughlin measurements during transit imply a projected spin-orbit alignment angle {lambda} = 2 {+-} 16 deg, consistent with a zero obliquity for KELT-1. Finally, the vsin I{sub *} = 56 {+-} 2 km s{sup -1} of the primary is consistent at {approx}2{sigma} with tidal synchronization. Given the extreme parameters of the KELT-1 system, we expect it to provide an important testbed for theories of the emplacement and evolution of short-period companions, as well as theories of tidal dissipation and irradiated brown dwarf atmospheres.

  4. High-Precision Locations and the Stress Field from Instrumental Seismicity, Moment Tensors, and Short-Period Mechanisms through the Mina Deflection, Central Walker Lane

    NASA Astrophysics Data System (ADS)

    Ruhl, C. J.; Smith, K. D.

    2012-12-01

    include the 1934 M 6.5 Excelsior Mountains event south of Mina, NV, and the 1932 M 7.1 Cedar Mountains earthquake east of the Pilot Mountains. Another persistent feature in the seismicity is an ~40 km long arcuate distribution of activity extending from approximately Queen Valley, north of the White Mountains, to Mono Lake that appears to reflect a southwestern boundary to northeast-striking structures in the MD. Here we develop high-precision relocations of instrumental seismicity in the MD from 1984 through 2012, including relocations of the 2004 sequence, and account for the historical seismic record. MT solutions from published reports and computed from recent M 3.5+ earthquakes as well as available and developed short-period focal mechanisms are compiled to evaluate the stress field to assess mechanisms of slip accommodation. Based on the complex distribution of fault orientations, the stress field varies locally northward from the SWL throughout the MD; however, in many cases, fault plane alignments can be isolated from high-precision locations, providing better constraints on stress and slip orientations.

  5. Helicity in dynamical processes in the atmosphere

    NASA Astrophysics Data System (ADS)

    Kurgansky, Michael; Maksimenkov, Leonid; Khapaev, Alexey; Chkhetiani, Otto

    2016-04-01

    In modern geophysical fluid dynamics and dynamic meteorology, a notable interest is observed to the notion of helicity ("kinetic helicity" to be distinguished from "magnetic helicity" widely used in magnetohydrodynamics, astrophysics and Solar physics), which is defined by the scalar product of 3D vectors of velocity and vorticity. In this contribution, we bring together different, both known in the literature and novel formulations of the helicity balance equation, by also taking into account the effects of air compressibility and Earth rotation. Equations and relationships are presented that are valid under different approximations customarily made in the dynamic meteorology, e.g. Boussinesq approximation, quasi-static approximation, quasi-geostrophic approximation. An emphasis is placed on the helicity budget analysis in large-scale atmospheric motions. An explicit expression is presented for the rate of helicity injection from the free atmosphere into a non-linear Ekman boundary layer. This injection is shown to be exactly balanced by the helicity viscous destruction within the boundary layer. It is conjectured that this helicity injection may characterize the intensity of atmospheric circulation in extratropical latitudes of both terrestrial hemispheres. Examples are provided based on re-analyses data. Vertical distribution of helicity and superhelicity in different Ekman boundary layers is also discussed.

  6. Probing and controlling liquid crystal helical nanofilaments.

    PubMed

    Zhu, Chenhui; Wang, Cheng; Young, Anthony; Liu, Feng; Gunkel, Ilja; Chen, Dong; Walba, David; Maclennan, Joseph; Clark, Noel; Hexemer, Alexander

    2015-05-13

    We report the first in situ measurement of the helical pitch of the helical nanofilament B4 phase of bent-core liquid crystals using linearly polarized, resonant soft X-ray scattering at the carbon K-edge. A strong, anisotropic scattering peak corresponding to the half-pitch of the twisted smectic layer structure was observed. The equilibrium helical half-pitch of NOBOW is found to be 120 nm, essentially independent of temperature. However, the helical pitch can be tuned by mixing guest organic molecules with the bent-core host, followed by thermal annealing.

  7. Helical axis stellarator with noninterlocking planar coils

    DOEpatents

    Reiman, Allan; Boozer, Allen H.

    1987-01-01

    A helical axis stellarator using only noninterlocking planar, non-circular coils, generates magnetic fields having a magnetic well and large rotational transform with resultant large equilibrium beta.

  8. Building blocks for subleading helicity operators

    NASA Astrophysics Data System (ADS)

    Kolodrubetz, Daniel W.; Moult, Ian; Stewart, Iain W.

    2016-05-01

    On-shell helicity methods provide powerful tools for determining scattering amplitudes, which have a one-to-one correspondence with leading power helicity operators in the Soft-Collinear Effective Theory (SCET) away from singular regions of phase space. We show that helicity based operators are also useful for enumerating power suppressed SCET operators, which encode subleading amplitude information about singular limits. In particular, we present a complete set of scalar helicity building blocks that are valid for constructing operators at any order in the SCET power expansion. We also describe an interesting angular momentum selection rule that restricts how these building blocks can be assembled.

  9. Magnetic helicity in emerging solar active regions

    SciTech Connect

    Liu, Y.; Hoeksema, J. T.; Bobra, M.; Hayashi, K.; Sun, X.; Schuck, P. W.

    2014-04-10

    Using vector magnetic field data from the Helioseismic and Magnetic Imager instrument aboard the Solar Dynamics Observatory, we study magnetic helicity injection into the corona in emerging active regions (ARs) and examine the hemispheric helicity rule. In every region studied, photospheric shearing motion contributes most of the helicity accumulated in the corona. In a sample of 28 emerging ARs, 17 follow the hemisphere rule (61% ± 18% at a 95% confidence interval). Magnetic helicity and twist in 25 ARs (89% ± 11%) have the same sign. The maximum magnetic twist, which depends on the size of an AR, is inferred in a sample of 23 emerging ARs with a bipolar magnetic field configuration.

  10. Helical tomotherapy superficial dose measurements

    SciTech Connect

    Ramsey, Chester R.; Seibert, Rebecca M.; Robison, Benjamin; Mitchell, Martha

    2007-08-15

    Helical tomotherapy is a treatment technique that is delivered from a 6 MV fan beam that traces a helical path while the couch moves linearly into the bore. In order to increase the treatment delivery dose rate, helical tomotherapy systems do not have a flattening filter. As such, the dose distributions near the surface of the patient may be considerably different from other forms of intensity-modulated delivery. The purpose of this study was to measure the dose distributions near the surface for helical tomotherapy plans with a varying separation between the target volume and the surface of an anthropomorphic phantom. A hypothetical planning target volume (PTV) was defined on an anthropomorphic head phantom to simulate a 2.0 Gy per fraction IMRT parotid-sparing head and neck treatment of the upper neck nodes. A total of six target volumes were created with 0, 1, 2, 3, 4, and 5 mm of separation between the surface of the phantom and the outer edge of the PTV. Superficial doses were measured for each of the treatment deliveries using film placed in the head phantom and thermoluminescent dosimeters (TLDs) placed on the phantom's surface underneath an immobilization mask. In the 0 mm test case where the PTV extends to the phantom surface, the mean TLD dose was 1.73{+-}0.10 Gy (or 86.6{+-}5.1% of the prescribed dose). The measured superficial dose decreases to 1.23{+-}0.10 Gy (61.5{+-}5.1% of the prescribed dose) for a PTV-surface separation of 5 mm. The doses measured by the TLDs indicated that the tomotherapy treatment planning system overestimates superficial doses by 8.9{+-}3.2%. The radiographic film dose for the 0 mm test case was 1.73{+-}0.07 Gy, as compared to the calculated dose of 1.78{+-}0.05 Gy. Given the results of the TLD and film measurements, the superficial calculated doses are overestimated between 3% and 13%. Without the use of bolus, tumor volumes that extend to the surface may be underdosed. As such, it is recommended that bolus be added for these

  11. NMR Assignments for a Helical 40 kDa Membrane Protein

    SciTech Connect

    Oxenoid, Kirill; Kim, Hak J.; Jacob, Jaison; Soennichsen, Frank D.; Sanders, Charles R.

    2004-04-28

    Backbone nuclear magnetic resonance (NMR) assignments were achieved for diacylglycerol kinase (DAGK) in detergent micelles. DAGK is a homotrimeric integral membrane protein comprised of 121 residue subunits, each having three transmembrane segments. Assignments were made using TROSY-based pulse sequences. DAGK was found to be an almost exclusively helical protein. This work points to the feasibility of both solving the structure of DAGK using solution NMR methods and using NMR as a primary tool in structural studies of other helical integral membrane proteins of similar size and complexity.

  12. Human Skin as Arrays of Helical Antennas in the Millimeter and Submillimeter Wave Range

    NASA Astrophysics Data System (ADS)

    Feldman, Yuri; Puzenko, Alexander; Ben Ishai, Paul; Caduff, Andreas; Agranat, Aharon J.

    2008-03-01

    Recent studies of the minute morphology of the skin by optical coherence tomography showed that the sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. A computer simulation study of these structures in millimeter and submillimeter wave bands show that the human skin functions as an array of low-Q helical antennas. Experimental evidence is presented that the spectral response in the sub-Terahertz region is governed by the level of activity of the perspiration system. It is also correlated to physiological stress as manifested by the pulse rate and the systolic blood pressure.

  13. Human skin as arrays of helical antennas in the millimeter and submillimeter wave range.

    PubMed

    Feldman, Yuri; Puzenko, Alexander; Ben Ishai, Paul; Caduff, Andreas; Agranat, Aharon J

    2008-03-28

    Recent studies of the minute morphology of the skin by optical coherence tomography showed that the sweat ducts in human skin are helically shaped tubes, filled with a conductive aqueous solution. A computer simulation study of these structures in millimeter and submillimeter wave bands show that the human skin functions as an array of low-Q helical antennas. Experimental evidence is presented that the spectral response in the sub-Terahertz region is governed by the level of activity of the perspiration system. It is also correlated to physiological stress as manifested by the pulse rate and the systolic blood pressure. PMID:18517913

  14. Helical coil thermal hydraulic model

    NASA Astrophysics Data System (ADS)

    Caramello, M.; Bertani, C.; De Salve, M.; Panella, B.

    2014-11-01

    A model has been developed in Matlab environment for the thermal hydraulic analysis of helical coil and shell steam generators. The model considers the internal flow inside one helix and its associated control volume of water on the external side, both characterized by their inlet thermodynamic conditions and the characteristic geometry data. The model evaluates the behaviour of the thermal-hydraulic parameters of the two fluids, such as temperature, pressure, heat transfer coefficients, flow quality, void fraction and heat flux. The evaluation of the heat transfer coefficients as well as the pressure drops has been performed by means of the most validated literature correlations. The model has been applied to one of the steam generators of the IRIS modular reactor and a comparison has been performed with the RELAP5/Mod.3.3 code applied to an inclined straight pipe that has the same length and the same elevation change between inlet and outlet of the real helix. The predictions of the developed model and RELAP5/Mod.3.3 code are in fairly good agreement before the dryout region, while the dryout front inside the helical pipes is predicted at a lower distance from inlet by the model.

  15. Spheromak Power and Helicity Balance

    SciTech Connect

    Thomassen, K.I.

    2000-05-18

    This note addresses the division of gun power and helicity between the open line volume and the closed flux surface volume in a steady state flux core spheromak. Our assumptions are that fine scale turbulence maintains each region close to a Taylor state, {mu}{sub o}J = {lambda}B. The gun region that feeds these two volumes surrounded by a flux conserver is shown topologically below. (The actual geometry is toroidal). Flux and current from the magnetized gun flow on open lines around the entire closed surface containing the spheromak. The gun current flows down the potential gradient, the potential difference between the two ends of each line being the gun voltage. Here, the gun voltage excludes the sheath drops at each end. When these volumes have different values of {lambda} (ratio of {mu}{sub o}B{sup -2}j {center_dot} B in each region) in the open line volume V{sub 1} and the closed spheromak volume V{sub 2} the efficiency of transferring the gun power to the spheromak to sustain the ohmic loss is the {lambda}-ratio of these regions, in the limit V{sub 1} << V{sub 2}. This result follows immediately from helicity balance in that limit. Here we give an accounting of all the gun power, and do not assume a small edge (open line) region.

  16. Hydrodynamic characteristics of the helical flow pump.

    PubMed

    Ishii, Kohei; Hosoda, Kyohei; Nishida, Masahiro; Isoyama, Takashi; Saito, Itsuro; Ariyoshi, Koki; Inoue, Yusuke; Ono, Toshiya; Nakagawa, Hidemoto; Sato, Masami; Hara, Sintaro; Lee, Xinyang; Wu, Sheng-Yuan; Imachi, Kou; Abe, Yusuke

    2015-09-01

    The helical flow pump (HFP) was invented to be an ideal pump for developing the TAH and the helical flow TAH (HFTAH) using two HFPs has been developed. However, since the HFP is quite a new pump, hydrodynamic characteristics inside the pump are not clarified. To analyze hydrodynamic characteristics of the HFP, flow visualization study using the particle image velocimetry and computational fluid dynamics analysis were performed. The experimental and computational models were developed to simulate the left HFP of the HFTAH and distributions of flow velocity vectors, shear stress and pressure inside the pump were examined. In distribution of flow velocity vectors, the vortexes in the vane were observed, which indicated that the HFP has a novel and quite unique working principle in which centrifugal force rotates the fluid in the helical volutes and the fluid is transferred from the inlet to the outlet helical volutes according to the helical structure. In distribution of shear stress, the highest shear stress that was considered to be occurred by the shunt flow across the impeller was found around the entrance of the inlet helical volute. However, it was not so high to cause hemolysis. This shunt flow is thought to be improved by redesigning the inlet and outlet helical volutes. In distribution of pressure, negative pressure was found near the entrance of the inlet helical volute. However, it was not high. Negative pressure is thought to be reduced with an improvement in the design of the impeller or the vane shape. PMID:25784463

  17. The AGS synchrotron with four helical magnets

    SciTech Connect

    Tsoupas N.; Huang, H.; Roser, T.; MacKay, W.W.; Trbojevic, D.

    2012-05-20

    The idea of using two partial helical magnets was applied successfully to the AGS synchrotron to preserve the proton beam polarization. In this paper we explore in details the idea of using four helical magnets placed symmetrically in the AGS ring. The placement of four helical magnets in the AGS ring provides many advantages over the present setup of the AGS which uses two partial helical magnets. First, the symmetric placement of the four helical magnets allows for a better control of the AGS optics with reduced values of the beta functions especially near beam injection, second, the vertical spin direction during beam injection and extraction is closer to vertical, and third, it provides for a larger 'spin tune gap', which allows the vertical and horizontal tunes to be placed, and prevent the horizontal and vertical intrinsic spin resonances of the AGS to occur during the acceleration cycle. Although the same spin gap can be obtained with a single or two partial helices, the required high field strength of a single helix makes its use impractical, and that of the double helix rather difficult. In this paper we will provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and compare these results with the present setup of the AGS that uses two partial helical magnets.

  18. Simplified Fabrication of Helical Copper Antennas

    NASA Technical Reports Server (NTRS)

    Petro, Andrew

    2006-01-01

    A simplified technique has been devised for fabricating helical antennas for use in experiments on radio-frequency generation and acceleration of plasmas. These antennas are typically made of copper (for electrical conductivity) and must have a specific helical shape and precise diameter.

  19. Structure and interactions of biological helices

    NASA Astrophysics Data System (ADS)

    Kornyshev, Alexei A.; Lee, Dominic J.; Leikin, Sergey; Wynveen, Aaron

    2007-07-01

    Helices are essential building blocks of living organisms, be they molecular fragments of proteins ( α -helices), macromolecules (DNA and collagen), or multimolecular assemblies (microtubules and viruses). Their interactions are involved in packing of meters of genetic material within cells and phage heads, recognition of homologous genes in recombination and DNA repair, stability of tissues, and many other processes. Helical molecules form a variety of mesophases in vivo and in vitro. Recent structural studies, direct measurements of intermolecular forces, single-molecule manipulations, and other experiments have accumulated a wealth of information and revealed many puzzling physical phenomena. It is becoming increasingly clear that in many cases the physics of biological helices cannot be described by theories that treat them as simple, unstructured polyelectrolytes. The present article focuses on the most important and interesting aspects of the physics of structured macromolecules, highlighting various manifestations of the helical motif in their structure, elasticity, interactions with counterions, aggregation, and poly- and mesomorphic transitions.

  20. Best packing of identical helices

    NASA Astrophysics Data System (ADS)

    Huh, Youngsik; Hong, Kyungpyo; Kim, Hyoungjun; No, Sungjong; Oh, Seungsang

    2016-10-01

    In this paper we prove the unique existence of a ropelength-minimizing conformation of the θ-spun double helix in a mathematically rigorous way, and find the minimal ropelength {{{Rop}}}* (θ )=-\\tfrac{8π }{t} where t is the unique solution in [-θ ,0] of the equation 2-2\\cos (t+θ )={t}2. Using this result, the pitch angles of the standard, triple and quadruple helices are around 39.3771^\\circ , 42.8354^\\circ and 43.8351^\\circ , respectively, which are almost identical with the approximated pitch angles of the zero-twist structures previously known by Olsen and Bohr. We also find the ropelength of the standard N-helix.

  1. The quantum Hall effect helicity

    SciTech Connect

    Shrivastava, Keshav N.

    2015-04-16

    The quantum Hall effect in semiconductor heterostructures is explained by two signs in the angular momentum j=l±s and g=(2j+1)/(2l+1) along with the Landau factor (n+1/2). These modifications in the existing theories explain all of the fractional charges. The helicity which is the sign of the product of the linear momentum with the spin p.s plays an important role for the understanding of the data at high magnetic fields. In particular it is found that particles with positive sign in the spin move in one direction and those with negative sign move in another direction which explains the up and down stream motion of the particles.

  2. Thermal deformation of helical gears

    NASA Astrophysics Data System (ADS)

    Zhang, Yong; Fei, Ye-tai; Liu, Shan-lin

    2010-08-01

    The analytical equation for the thermal field of a helical gear under normal working condition in a stable thermal field is established using mathematical physics, and the thermal deformation of the gear can be computed using this equation. The variations of gear geometric parameters, such as radial dimension, tooth depth, spiral angle, pressure angle, flank clearance and etc., are investigated with respect to the temperature change. According to the analytical and computational results obtained using the equation, the thermal deformation of the gear is strongly dependent on the choice of parameters, which is also confirmed using simulation software (COMSOL Multiphysic software). This is significant for the improvement of the rotation precision and working efficiency of screw gears.

  3. Adding helicity to inflationary magnetogenesis

    SciTech Connect

    Caprini, Chiara; Sorbo, Lorenzo E-mail: sorbo@physics.umass.edu

    2014-10-01

    The most studied mechanism of inflationary magnetogenesis relies on the time-dependence of the coefficient of the gauge kinetic term F{sub μν} F{sup μν}. Unfortunately, only extremely finely tuned versions of the model can consistently generate the cosmological magnetic fields required by observations. We propose a generalization of this model, where also the pseudoscalar invariant F{sub μν}  F-tilde {sup μν} is multiplied by a time dependent function. The new parity violating term allows more freedom in tuning the amplitude of the field at the end of inflation. Moreover, it leads to a helical magnetic field that is amplified at large scales by magnetohydrodynamical processes during the radiation dominated epoch. As a consequence, our model can satisfy the observational lower bounds on fields in the intergalactic medium, while providing a seed for the galactic dynamo, if inflation occurs at an energy scale ranging from 10{sup 5} to 10{sup 10} GeV. Such energy scale is well below that suggested by the recent BICEP2 result, if the latter is due to primordial tensor modes. However, the gauge field is a source of tensors during inflation and generates a spectrum of gravitational waves that can give a sizable tensor to scalar ratio r=O(0.2) even if inflation occurs at low energies. This system therefore evades the Lyth bound. For smaller values of r, lower values of the inflationary energy scale are required. The model predicts fully helical cosmological magnetic fields and a chiral spectrum of primordial gravitational waves.

  4. Overview of The Pulse Line Ion Accelerator

    SciTech Connect

    Briggs, R.J.; Bieniosek, F.M.; Coleman, J.E.; Eylon, S.; Henestroza, E.; Leitner, M.; Logan, B.G.; Reginato, L.L.; Roy, P.K.; Seidl, P.A.; Waldron, W.L.; Yu, S.S.; Barnard, J.J.; Caporaso, G.J.; Friedman, A.; Grote, D.P.; Nelson, S.D.

    2006-06-29

    An overview of the Pulse Line Ion Accelerator (PLIA) concept and its development is presented. In the PLIA concept a pulse power driver applied to one end of a helical pulse line creates a traveling wave pulse that accelerates and axially confines a heavy ion beam pulse The motivation for its development at the IFE-VNL is the acceleration of intense, short pulse, heavy ion beams to regimes of interest for studies of High Energy Density Physics and Warm Dense Matter. Acceleration scenarios with constant parameter helical lines are described which result in output energies of a single stage much larger than the several hundred kilovolt peak voltages on the line, with a goal of 3-5 MeV/meter acceleration gradients. The main attraction of the concept is the very low cost it promises. It might be described crudely as an ''air core'' induction linac where the pulse-forming network is integrated into the beam line so the accelerating voltage pulse can move along with the ions to get voltage multiplication.

  5. Magnetic Helicity in a Cyclic Convective Dynamo

    NASA Astrophysics Data System (ADS)

    Miesch, Mark S.; Zhang, Mei; Augustson, Kyle C.

    2016-05-01

    Magnetic helicity is a fundamental agent for magnetic self-organization in magnetohydrodynamic (MHD) dynamos. As a conserved quantity in ideal MHD, it establishes a strict topological coupling between large and small-scale magnetic fields. The generation of magnetic fields on scales larger than the velocity field is linked to an upscale transfer of magnetic helicity, either locally in spectral space as in the inverse cascade of magnetic helicity in MHD turbulence or non-locally, as in the turbulent alpha-effect of mean-field dynamo theory. Thus, understanding the generation, transport, and dissipation of magnetic helicity is an essential prerequisite to understanding manifestations of magnetic self-organization in the solar dynamo, including sunspots, the prominent dipole and quadrupole moments, and the 22-year magnetic activity cycle. We investigate the role of magnetic helicity in a convective dynamo model that exhibits regular magnetic cycles. The cycle is marked by coherent bands of toroidal field that persist within the convection zone and that are antisymmetric about the equator. When these toriodal bands interact across the equator, it initiates a global restructuring of the magnetic topology that contributes to the reversal of the dipole moment. Thus, the polar field reversals are preceeded by a brief reversal of the subsurface magnetic helicity. There is some evidence that the Sun may exhibit a similar magnetic helicity reversal prior to its polar field reversals.

  6. Enhanced helical swimming in Boger fluids

    NASA Astrophysics Data System (ADS)

    Godinez, Francisco; Mendez-Rojano, Rodrigo; Zenit, Roberto; Lauga, Eric

    2014-11-01

    We conduct experiments with force-free magnetically-driven helical swimmers in Newtonian and viscoelastic (Boger) fluids. In order assess the effect of viscoelasticity on the swimming performance, we conduct experiments for swimmers with different helical tail geometries. We use helices with the same wave length and total length but vary the angle of the helix. As previously reported by the computational study of Spagniole and collaborators, we found that the swimming performance can either increase, decrease or remain unchanged, depending on the geometry of the tail. With the right geometry, the enhancement can be up to a factor of two.

  7. Helices in the wake of precipitation fronts.

    PubMed

    Thomas, Shibi; Lagzi, István; Molnár, Ferenc; Rácz, Zoltán

    2013-08-01

    A theoretical study of the emergence of helices in the wake of precipitation fronts is presented. The precipitation dynamics is described by the Cahn-Hilliard equation and the fronts are obtained by quenching the system into a linearly unstable state. Confining the process onto the surface of a cylinder and using the pulled-front formalism, our analytical calculations show that there are front solutions that propagate into the unstable state and leave behind a helical structure. We find that helical patterns emerge only if the radius of the cylinder R is larger than a critical value R>R(c), in agreement with recent experiments. PMID:24032809

  8. Helical flux ropes in solar prominences

    NASA Technical Reports Server (NTRS)

    Martens, P. C. H.; Van Ballegooijen, A. A.

    1990-01-01

    The present numerical method for the computation of force-free, cancelling magnetic structures shows that flux cancellation at the neutral line in a sheared magnetic arcade generates helical field lines that can support a prominence's plasma. With increasing flux cancellation, the axis of the helical fields moves to greater heights; this is suggestive of a prominence eruption. Two alternative scenarios are proposed for the formation of polar crown prominences which yield the correct axial magnetic field sign. Both models are noted to retain the formation of helical flux tubes through flux cancellation as their key feature.

  9. Steering Chiral Swimmers along Noisy Helical Paths

    NASA Astrophysics Data System (ADS)

    Friedrich, Benjamin M.; Jülicher, Frank

    2009-08-01

    Chemotaxis along helical paths towards a target releasing a chemoattractant is found in sperm cells and many microorganisms. We discuss the stochastic differential geometry of the noisy helical swimming path of a chiral swimmer. A chiral swimmer equipped with a simple feedback system can navigate in a concentration gradient of chemoattractant. We derive an effective equation for the alignment of helical paths with a concentration gradient which is related to the alignment of a dipole in an external field and discuss the chemotaxis index.

  10. Dense Helical Electron Bunch Generation in Near-Critical Density Plasmas with Ultrarelativistic Laser Intensities

    PubMed Central

    Hu, Ronghao; Liu, Bin; Lu, Haiyang; Zhou, Meilin; Lin, Chen; Sheng, Zhengming; Chen, Chia-erh; He, Xiantu; Yan, Xueqing

    2015-01-01

    The mechanism for emergence of helical electron bunch(HEB) from an ultrarelativistic circularly polarized laser pulse propagating in near-critical density(NCD) plasma is investigated. Self-consistent three-dimensional(3D) Particle-in-Cell(PIC) simulations are performed to model all aspects of the laser plasma interaction including laser pulse evolution, electron and ion motions. At a laser intensity of 1022 W/cm2, the accelerated electrons have a broadband spectrum ranging from 300 MeV to 1.3 GeV, with the charge of 22 nano-Coulombs(nC) within a solid-angle of 0.14 Sr. Based on the simulation results, a phase-space dynamics model is developed to explain the helical density structure and the broadband energy spectrum. PMID:26503634

  11. Cooperative pulses

    NASA Astrophysics Data System (ADS)

    Braun, Michael; Glaser, Steffen J.

    2010-11-01

    We introduce the concept of cooperative (COOP) pulses which are designed to compensate each other's imperfections. In multi-scan experiments, COOP pulses can cancel undesired signal contributions, complementing and generalizing phase cycles. COOP pulses can be efficiently optimized using an extended version of the optimal-control-based gradient ascent pulse engineering (GRAPE) algorithm. The advantage of the COOP approach is experimentally demonstrated for broadband and band-selective pulses.

  12. Dissecting π-helices: sequence, structure and function.

    PubMed

    Kumar, Prasun; Bansal, Manju

    2015-11-01

    A new procedure for the identification of regular secondary structures using a C(α) trace has identified 659 π-helices in 3582 protein chains, solved at high resolution. Taking advantage of this significantly expanded database of π-helices, we have analysed the functional and structural roles of π-helices and determined the position-wise amino acid propensity within and around them. These helices range from 5 to 18 residues in length with the average twist and rise being 85.2 ± 7.2° and 1.28 ± 0.31 Å, respectively. A total of 546 (~ 83%) out of 659 π-helices occur in conjunction with α-helices, with 101 π-helices being interspersed between two α-helices. The majority of interspersed π-helices were found to be conserved across a large number of structures within a protein family and produce a significant bend in the overall helical segment as well as local distortions in the neighbouring α-helices. The presence of a π-helical fragment leads to appropriate orientation of the constituent residues, so as to facilitate favourable interactions and also help in proper folding of the protein chain. In addition to intra helical 6→1 N-H···O hydrogen bonds, π-helices are also stabilized by several other non-bonded interactions. π-Helices show distinct positional residue preferences, which are different from those of α-helices.

  13. Emergence of helicity in rotating stratified turbulence

    NASA Astrophysics Data System (ADS)

    Marino, Raffaele; Mininni, Pablo D.; Rosenberg, Duane; Pouquet, Annick

    2013-03-01

    We perform numerical simulations of decaying rotating stratified turbulence and show, in the Boussinesq framework, that helicity (velocity-vorticity correlation), as observed in supercell storms and hurricanes, is spontaneously created due to an interplay between buoyancy and rotation common to large-scale atmospheric and oceanic flows. Helicity emerges from the joint action of eddies and of inertia-gravity waves (with inertia and gravity with respective associated frequencies f and N), and it occurs when the waves are sufficiently strong. For N/f<3 the amount of helicity produced is correctly predicted by a quasilinear balance equation. Outside this regime, and up to the highest Reynolds number obtained in this study, namely Re≈10000, helicity production is found to be persistent for N/f as large as ≈17, and for ReFr2 and ReRo2, respectively, as large as ≈100 and ≈24000.

  14. Building blocks for subleading helicity operators

    DOE PAGES

    Kolodrubetz, Daniel W.; Moult, Ian; Stewart, Iain W.

    2016-05-24

    On-shell helicity methods provide powerful tools for determining scattering amplitudes, which have a one-to-one correspondence with leading power helicity operators in the Soft-Collinear Effective Theory (SCET) away from singular regions of phase space. We show that helicity based operators are also useful for enumerating power suppressed SCET operators, which encode subleading amplitude information about singular limits. In particular, we present a complete set of scalar helicity building blocks that are valid for constructing operators at any order in the SCET power expansion. In conclusion, we also describe an interesting angular momentum selection rule that restricts how these building blocks canmore » be assembled.« less

  15. Passive micromixers with dual helical channels

    NASA Astrophysics Data System (ADS)

    Liu, Keyin; Yang, Qing; Chen, Feng; Zhao, Yulong; Meng, Xiangwei; Shan, Chao; Li, Yanyang

    2015-02-01

    In this study, a three-dimensional (3D) micromixer with cross-linked double helical microchannels is studied to achieve rapid mixing of fluids at low Reynolds numbers (Re). The 3D micromixer takes full advantages of the chaotic advection model with helical microchannels; meanwhile, the proposed crossing structure of double helical microchannels enables two flow patterns of repelling flow and straight flow in the fluids to promote the agitation effect. The complex 3D micromixer is realized by an improved femtosecond laser wet etching (FLWE) technology embedded in fused silica. The mixing results show that cross-linked double helical microchannels can achieve excellent mixing within 3 cycles (300 μm) over a wide range of low Re (1.5×10-3~600), which compare well with the conventional passive micromixers. This highly-effective micromixer is hoped to contribute to the integration of microfluidic systems.

  16. Motion of multiple helical vortices

    NASA Astrophysics Data System (ADS)

    Velasco Fuentes, Oscar

    2015-11-01

    In 1912 Joukowsky deduced that in an unbounded ideal fluid a set of helical vortices--when these are equal, coaxial and symmetrically arranged--would translate and rotate steadily while the vortices preserve their form and relative position. Each vortex is an infinite tube whose cross-section is circular (with radius a) and whose centerline is a helix of pitch L and radius R. The motion is thus determined by three non-dimensional parameters only: the number of vortices N, the vortex radius α = a / R and the vortex pitch τ = L / 2 πR . Here, we express the linear and angular velocities of the vortices as the sum of the mutually induced velocities found by Okulov (2004) and the self-induced velocities found by Velasco Fuentes (2015). We verified that our results are accurate over the whole range of values of the vortices' pitch and radius by numerically computing the vortex motion with two smoothed versions of the Biot-Savart law. It was found that the translation velocity U grows with the number of vortices (N) but decreases as the vortices' radius and pitch (a and τ, respectively) increase; in contrast, the rotation velocity Ω grows with N and a but has a local minimum around τ = 1 for fixed values of N and a.

  17. Spheromak Power and Helicity Balance

    SciTech Connect

    Thomassen, K.I.

    2000-05-18

    This note addresses the division of gun power and helicity between the open line volume and the closed flux surface volume in a steady state flux core spheromak. Our assumptions are that fine scale turbulence maintains each region close to an axisymmetric Taylor state, {mu}{sub o}j = {lambda}B. The gun region that feeds these two volumes surrounded by a flux conserver is shown topologically below. (The actual geometry is toroidal). Flux and current from the magnetized gun flow on open lines around the entire closed surface containing the spheromak. The gun current flows down the potential gradient, the potential difference between the two ends of each line being the gun voltage. Here, the gun voltage excludes the sheath drops at each end. These volumes have different values of {lambda} in each region (open line volume V{sub 1} and closed spheromak volume V{sub 2}) and we want to calculate the efficiency of transferring the gun power to the spheromak to sustain the ohmic loss in steady state.

  18. CURRENT HELICITY OF ACTIVE REGIONS AS A TRACER OF LARGE-SCALE SOLAR MAGNETIC HELICITY

    SciTech Connect

    Zhang, H.; Gao, Y.; Xu, H.; Moss, D.; Kleeorin, N.; Rogachevskii, I.; Kuzanyan, K.; Sokoloff, D.

    2012-05-20

    We demonstrate that the current helicity observed in solar active regions traces the magnetic helicity of the large-scale dynamo generated field. We use an advanced two-dimensional mean-field dynamo model with dynamo saturation based on the evolution of the magnetic helicity and algebraic quenching. For comparison, we also studied a more basic two-dimensional mean-field dynamo model with simple algebraic alpha-quenching only. Using these numerical models we obtained butterfly diagrams both for the small-scale current helicity and also for the large-scale magnetic helicity, and compared them with the butterfly diagram for the current helicity in active regions obtained from observations. This comparison shows that the current helicity of active regions, as estimated by -A {center_dot} B evaluated at the depth from which the active region arises, resembles the observational data much better than the small-scale current helicity calculated directly from the helicity evolution equation. Here B and A are, respectively, the dynamo generated mean magnetic field and its vector potential. A theoretical interpretation of these results is given.

  19. Studies of Solar Helicity Using Vector Magnetograms

    NASA Technical Reports Server (NTRS)

    Hagyard, Mona J.; Pevstov, Alexei A.

    1999-01-01

    observations of photospheric magnetic fields made with vector magnetographs have been used recently to study solar helicity. In this paper we indicate what can and cannot be derived from vector magnetograms, and point out some potential problems in these data that could affect the calculations of 'helicity'. Among these problems are magnetic saturation, Faraday rotation, low spectral resolution, and the method of resolving the ambiguity in the azimuth.

  20. Duality and helicity: A symplectic viewpoint

    NASA Astrophysics Data System (ADS)

    Elbistan, M.; Duval, C.; Horváthy, P. A.; Zhang, P.-M.

    2016-10-01

    The theorem which says that helicity is the conserved quantity associated with the duality symmetry of the vacuum Maxwell equations is proved by viewing electromagnetism as an infinite dimensional symplectic system. In fact, it is shown that helicity is the moment map of duality acting as an SO (2) group of canonical transformations on the symplectic space of all solutions of the vacuum Maxwell equations.

  1. Fourier-Bessel reconstruction of helical assemblies.

    PubMed

    Diaz, Ruben; Rice, William J; Stokes, David L

    2010-01-01

    Helical symmetry is commonly used for building macromolecular assemblies. Helical symmetry is naturally present in viruses and cytoskeletal filaments and also occurs during crystallization of isolated proteins, such as Ca-ATPase and the nicotinic acetyl choline receptor. Structure determination of helical assemblies by electron microscopy has a long history dating back to the original work on three-dimensional (3D) reconstruction. A helix offers distinct advantages for structure determination. Not only can one improve resolution by averaging across the constituent subunits, but each helical assembly provides multiple views of these subunits and thus provides a complete 3D data set. This review focuses on Fourier methods of helical reconstruction, covering the theoretical background, a step-by-step guide to the process, and a practical example based on previous work with Ca-ATPase. Given recent results from helical reconstructions at atomic resolution and the development of graphical user interfaces to aid in the process, these methods are likely to continue to make an important contribution to the field of structural biology. PMID:20888960

  2. Gluons in glueballs: Spin or helicity?

    SciTech Connect

    Mathieu, Vincent; Buisseret, Fabien; Semay, Claude

    2008-06-01

    In the past decade, lattice QCD has been able to compute the low-lying glueball spectrum with accuracy. Like other effective approaches of QCD, potential models still have difficulties to cope with gluonic hadrons. Assuming that glueballs are bound states of valence gluons with zero current mass, it is readily understood that the use of a potential model, intrinsically noncovariant, could be problematic in this case. The main challenge for this kind of model is actually to find a way to introduce properly the more relevant degree of freedom of the gluon: spin or helicity. In this work, we use the so-called helicity formalism of Jacob and Wick to describe two-gluon glueballs. We show, in particular, that this helicity formalism exactly reproduces the J{sup PC} numbers which are observed in lattice QCD when the constituent gluons have a helicity-1, without introducing extra states as is the case in most of the potential models. These extra states appear when gluons are seen as spin-1 particles. Using a simple spinless Salpeter model with Cornell potential within the helicity formalism, we obtain a glueball mass spectrum which is in good agreement with lattice QCD predictions for helicity-1 gluons provided instanton-induced interactions are taken into account.

  3. Helicity Annihilation in Trefoil Reconnection: Simulations

    NASA Astrophysics Data System (ADS)

    Kerr, Robert M.

    2015-11-01

    The simulated evolution and self-reconnection of a perturbed trefoil vortex knot is compared to the experiment. To have a single initial reconnection, as in the experiments, the trefoil is perturbed by 4 weak vortex rings. Visualizations show that the simulations and experiments undergo similar topological changes. Quantitative comparisons using the helicity and global topological number show that both are preserved for a long period before reconnection begins, as in the experiments. Unlike the experiments, once reconnection begins, a significant fraction of the helicity is dissipated and the global topological number changes by a discrete amount in a fixed time. Helicity spectra and physical space correlations show that the change in helicity is associated with the appearance of negative helicity at lower wavenumbers and in the outer regions of the trefoil. Furthermore, using a range of Reynolds numbers, with the highest comparable to the experiments, it is demonstrated that a Reynolds number independent fraction of the initial helicity is dissipated in a finite time. This observation does not violate any current mathematics restricting the strong growth of Navier-Stokes norms as the viscosity goes to zero due to the structure of the trefoil.

  4. Alternative Methods for Field Corrections in Helical Solenoids

    SciTech Connect

    Lopes, M. L.; Krave, S. T.; Tompkins, J. C.; Yonehara, K.; Flanagan, G.; Kahn, S. A.; Melconian, K.

    2015-05-01

    Helical cooling channels have been proposed for highly efficient 6D muon cooling. Helical solenoids produce solenoidal, helical dipole, and helical gradient field components. Previous studies explored the geometric tunability limits on these main field components. In this paper we present two alternative correction schemes, tilting the solenoids and the addition of helical lines, to reduce the required strength of the anti-solenoid and add an additional tuning knob.

  5. PULSE SORTER

    DOEpatents

    Wade, E.J.

    1958-07-29

    An apparatus is described for counting and recording the number of electrical pulses occurring in each of a timed sequence of groups of pulses. The particular feature of the invention resides in a novel timing circuit of the univibrator type which provides very accurately timed pulses for opening each of a series of coincidence channels in sequence. The univibrator is shown incorporated in a pulse analyzing system wherein a series of pulse counting channels are periodically opened in order, one at a time, for a predetermtned open time interval, so that only one channel will be open at the time of occurrence of any of the electrical pulses to be sorted.

  6. Effective desynchronization with a resetting pulse train followed by a single pulse

    NASA Astrophysics Data System (ADS)

    Tass, P. A.

    2001-07-01

    A combined pulse train, single-pulse stimulation technique is presented here which makes it possible to effectively desynchronize a cluster of globally coupled phase oscillators in the presence of noise. Such a composite stimulus consists of a resetting short periodic high-frequent pulse train followed by a desynchronizing single pulse. The pulse train entrains and, thus, restarts the collective oscillation independently of its initial dynamic state. With a fixed delay after the pulse train, a single pulse is delivered which desynchronizes the cluster by hitting it in a vulnerable state. After the desynchronization the cluster wants to become synchronized again since the incoherent state is unstable. Nevertheless, repeated administration of the same composite stimulus blocks the resynchronization. Compared to double-pulse phase resetting and with regard to neurological applications, this method is particularly mild and can be applied to effectively maintain incoherency in a population of oscillatory neurons that tend to synchronize their firing. The composite stimulation approach sheds new light on the mechanism of standard deep brain stimulation and suggests an improved, milder and demand-controlled deep brain stimulation technique for patients with Parkinson's disease or essential tremor.

  7. A unified convention for biological assemblies with helical symmetry

    SciTech Connect

    Tsai, Chung-Jung; Nussinov, Ruth

    2011-08-01

    A new representation of helical structure by four parameters, [n{sub 1}, n{sub 2}, twist, rise], is able to generate an entire helical construct from asymmetric units, including cases of helical assembly with a seam. Assemblies with helical symmetry can be conveniently formulated in many distinct ways. Here, a new convention is presented which unifies the two most commonly used helical systems for generating helical assemblies from asymmetric units determined by X-ray fibre diffraction and EM imaging. A helical assembly is viewed as being composed of identical repetitive units in a one- or two-dimensional lattice, named 1-D and 2-D helical systems, respectively. The unification suggests that a new helical description with only four parameters [n{sub 1}, n{sub 2}, twist, rise], which is called the augmented 1-D helical system, can generate the complete set of helical arrangements, including coverage of helical discontinuities (seams). A unified four-parameter characterization implies similar parameters for similar assemblies, can eliminate errors in reproducing structures of helical assemblies and facilitates the generation of polymorphic ensembles from helical atomic models or EM density maps. Further, guidelines are provided for such a unique description that reflects the structural signature of an assembly, as well as rules for manipulating the helical symmetry presentation.

  8. Pulse Oximetry

    MedlinePlus

    ... www.thoracic.org amount of gases (oxygen and carbon dioxide) that are in your blood. To get an ... Also, a pulse oximeter does not measure your carbon dioxide level. How accurate is the pulse oximeter? The ...

  9. The influence of helical background fields on current helicity and electromotive force of magnetoconvection

    NASA Astrophysics Data System (ADS)

    Rüdiger, G.; Küker, M.

    2016-07-01

    Motivated by the empirical finding that the known hemispheric rules for the current helicity at the solar surface are not strict, we demonstrate the excitation of small-scale current helicity by the influence of large-scale helical magnetic background fields on nonrotating magnetoconvection. This is shown within a quasilinear analytic theory of driven turbulence and by nonlinear simulations of magnetoconvection that the resulting small-scale current helicity has the same sign as the large-scale current helicity, while the ratio of both pseudoscalars is of the order of the magnetic Reynolds number of the convection. The same models do not provide finite values of the small-scale kinetic helicity. On the other hand, a turbulence-induced electromotive force is produced including the diamagnetic pumping term, as well as the eddy diffusivity but, however, no α effect. It has thus been argued that the relations for the simultaneous existence of small-scale current helicity and α effect do not hold for the model of nonrotating magnetoconvection under consideration. Calculations for various values of the magnetic Prandtl number demonstrate that, for the considered diffusivities, the current helicity increases for growing magnetic Reynolds number, which is not true for the velocity of the diamagnetic pumping, which is in agreement with the results of the quasilinear analytical approximation.

  10. Evaluation of helicity generation in the tropical storm Gonu

    NASA Astrophysics Data System (ADS)

    Farahani, Majid M.; Khansalari, Sakineh; Azadi, Majid

    2016-06-01

    Helicity is a valuable dynamical concept for the study of rotating flows. Consequently helicity flux, indicative of the source or sink of helicity, owns comparable importance. In this study, while reviewing the existing methods, a mathematical relation between helicity and helicity-flux is introduced, discussed and examined. The computed values of helicity and helicity fluxes in an actual case, using the classical and this proposed method are compared. The down-stream helicity flux including sources and sinks of helicity is considered for the tropical storm Gonu that occurred over the coasts of Oman and Iran on June 2-7, 2007. Results show that the buoyancy, through the upper troposphere down to a height within boundary layer, is the main source in producing helicity, and surface friction from earth surface up to a height within boundary layer, is the main dissipating element of helicity. The dominance of buoyancy forcing over the dissipative friction forcing results in generation of vortex or enhancement of it after bouncing the land. Furthermore, the increase (decrease) of helicity results in an increase (decrease) in the height of the level in which maximum helicity flux occurs. It is suggested that the maximum helicity flux occurs at the top of the turbulent boundary layer, so that the height of boundary layer could be obtained.

  11. Fabrication and experimentation of FRP helical spring

    NASA Astrophysics Data System (ADS)

    Ekanthappa, J.; Shiva Shankar, G. S.; Amith, B. M.; Gagan, M.

    2016-09-01

    In present scenario, the automobile industry sector is showing increased interest in reducing the unsprung weight of the automobile & hence increasing the fuel Efficiency. One of the feasible sub systems of a vehicle where weight reduction may be attempted is vehicle- suspension system. Usage of composite material is a proven way to lower the component weight without any compromise in strength. The composite materials are having high specific strength, more elastic strain energy storage capacity in comparison with those of steel. Therefore, helical coil spring made of steel is replaceable by composite cylindrical helical coil spring. This research aims at preparing a re-usable mandrel (mould) of Mild steel, developing a setup for fabrication, fabrication of FRP helical spring using continuous glass fibers and Epoxy Resin (Polymer). Experimentation has been conducted on fabricated FRP helical spring to determine its strength parameters & for failure analysis. It is found that spring stiffness (K) of Glass/Epoxy helical-spring is greater than steel-coil spring with reduced weight.

  12. Thermoelectric Analysis for Helical Power Generation Systems

    NASA Astrophysics Data System (ADS)

    Meng, Xiangning; Fujisaka, Takeyuki; Suzuki, Ryosuke O.

    2014-06-01

    The performance of a three-dimensional helical thermoelectric generation (TEG) system is examined by exposing it to a temperature difference with hot and cold sources. The helical paths for the two thermal fluids give the TEG device the potential to efficiently convert thermal energy. The characteristic performance of the helical system is numerically analyzed by using the finite-volume method in a compact system. The helical system is compared with a straight system in which all the thermoelectric (TE) elements present equivalent geometry. The difference in the TE performance between the two systems is not significant when the TE surfaces are maintained at constant temperatures. Both the electromotive force and the current in the TEG system increase linearly with the temperature difference Δ T applied at the two module surfaces. The current preferentially flows through a main path determined by the geometry of the TE element. The merits of the helical design are its compactness, space saving, and smooth fluid flow due to gravity, compared with the straight system.

  13. PULSE GENERATOR

    DOEpatents

    Roeschke, C.W.

    1957-09-24

    An improvement in pulse generators is described by which there are produced pulses of a duration from about 1 to 10 microseconds with a truly flat top and extremely rapid rise and fall. The pulses are produced by triggering from a separate input or by modifying the current to operate as a free-running pulse generator. In its broad aspect, the disclosed pulse generator comprises a first tube with an anode capacitor and grid circuit which controls the firing; a second tube series connected in the cathode circuit of the first tube such that discharge of the first tube places a voltage across it as the leading edge of the desired pulse; and an integrator circuit from the plate across the grid of the second tube to control the discharge time of the second tube, determining the pulse length.

  14. Working member of a helical downhole motor for drilling wells

    SciTech Connect

    Kochnev, A.M.; Vshivkov, A.N.; Goldobin, V.B.

    1993-06-22

    A working member of a helical downhole motor is described for drilling wells comprising: separate tubular sections having helical teeth arranged in succession and interconnected by connecting elements, each connecting element having the form of a ring, rigidly secured at the tubular sections and having helical teeth of a pitch and a direction equal to a pitch and a direction, respectively, of the helical teeth of the tubular sections, whereas a profile of the helical teeth of the ring is equidistant to a profile of the helical teeth of the sections.

  15. The helical structure of DNA facilitates binding

    NASA Astrophysics Data System (ADS)

    Berg, Otto G.; Mahmutovic, Anel; Marklund, Emil; Elf, Johan

    2016-09-01

    The helical structure of DNA imposes constraints on the rate of diffusion-limited protein binding. Here we solve the reaction-diffusion equations for DNA-like geometries and extend with simulations when necessary. We find that the helical structure can make binding to the DNA more than twice as fast compared to a case where DNA would be reactive only along one side. We also find that this rate advantage remains when the contributions from steric constraints and rotational diffusion of the DNA-binding protein are included. Furthermore, we find that the association rate is insensitive to changes in the steric constraints on the DNA in the helix geometry, while it is much more dependent on the steric constraints on the DNA-binding protein. We conclude that the helical structure of DNA facilitates the nonspecific binding of transcription factors and structural DNA-binding proteins in general.

  16. Nondispersive optical activity of meshed helical metamaterials.

    PubMed

    Park, Hyun Sung; Kim, Teun-Teun; Kim, Hyeon-Don; Kim, Kyungjin; Min, Bumki

    2014-11-17

    Extreme optical properties can be realized by the strong resonant response of metamaterials consisting of subwavelength-scale metallic resonators. However, highly dispersive optical properties resulting from strong resonances have impeded the broadband operation required for frequency-independent optical components or devices. Here we demonstrate that strong, flat broadband optical activity with high transparency can be obtained with meshed helical metamaterials in which metallic helical structures are networked and arranged to have fourfold rotational symmetry around the propagation axis. This nondispersive optical activity originates from the Drude-like response as well as the fourfold rotational symmetry of the meshed helical metamaterials. The theoretical concept is validated in a microwave experiment in which flat broadband optical activity with a designed magnitude of 45° per layer of metamaterial is measured. The broadband capabilities of chiral metamaterials may provide opportunities in the design of various broadband optical systems and applications.

  17. The helical structure of DNA facilitates binding

    NASA Astrophysics Data System (ADS)

    Berg, Otto G.; Mahmutovic, Anel; Marklund, Emil; Elf, Johan

    2016-09-01

    The helical structure of DNA imposes constraints on the rate of diffusion-limited protein binding. Here we solve the reaction–diffusion equations for DNA-like geometries and extend with simulations when necessary. We find that the helical structure can make binding to the DNA more than twice as fast compared to a case where DNA would be reactive only along one side. We also find that this rate advantage remains when the contributions from steric constraints and rotational diffusion of the DNA-binding protein are included. Furthermore, we find that the association rate is insensitive to changes in the steric constraints on the DNA in the helix geometry, while it is much more dependent on the steric constraints on the DNA-binding protein. We conclude that the helical structure of DNA facilitates the nonspecific binding of transcription factors and structural DNA-binding proteins in general.

  18. Manipulation of wavefront using helical metamaterials.

    PubMed

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

    2016-08-01

    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.

  19. Structural Transition from Helices to Hemihelices

    PubMed Central

    Su, Tianxiang; Bertoldi, Katia; Clarke, David R.

    2014-01-01

    Helices are amongst the most common structures in nature and in some cases, such as tethered plant tendrils, a more complex but related shape, the hemihelix forms. In its simplest form it consists of two helices of opposite chirality joined by a perversion. A recent, simple experiment using elastomer strips reveals that hemihelices with multiple reversals of chirality can also occur, a richness not anticipated by existing analyses. Here, we show through analysis and experiments that the transition from a helical to a hemihelical shape, as well as the number of perversions, depends on the height to width ratio of the strip's cross-section. Our findings provides the basis for the deterministic manufacture of a variety of complex three-dimensional shapes from flat strips. PMID:24759785

  20. Helicity and singular structures in fluid dynamics

    PubMed Central

    Moffatt, H. Keith

    2014-01-01

    Helicity is, like energy, a quadratic invariant of the Euler equations of ideal fluid flow, although, unlike energy, it is not sign definite. In physical terms, it represents the degree of linkage of the vortex lines of a flow, conserved when conditions are such that these vortex lines are frozen in the fluid. Some basic properties of helicity are reviewed, with particular reference to (i) its crucial role in the dynamo excitation of magnetic fields in cosmic systems; (ii) its bearing on the existence of Euler flows of arbitrarily complex streamline topology; (iii) the constraining role of the analogous magnetic helicity in the determination of stable knotted minimum-energy magnetostatic structures; and (iv) its role in depleting nonlinearity in the Navier-Stokes equations, with implications for the coherent structures and energy cascade of turbulence. In a final section, some singular phenomena in low Reynolds number flows are briefly described. PMID:24520175

  1. Primordial magnetic helicity from stochastic electric currents

    NASA Astrophysics Data System (ADS)

    Calzetta, Esteban; Kandus, Alejandra

    2014-04-01

    We study the possibility that primordial magnetic fields generated in the transition between inflation and reheating posses magnetic helicity, HM. The fields are induced by stochastic currents of scalar charged particles created during the mentioned transition. We estimate the rms value of the induced magnetic helicity by computing different four-point scalar quantum electrodynamics Feynman diagrams. For any considered volume, the magnetic flux across its boundaries is in principle not null, which means that the magnetic helicity in those regions is gauge dependent. We use the prescription given by Berger and Field and interpret our result as the difference between two magnetic configurations that coincide in the exterior volume. In this case, the magnetic helicity gives only the number of magnetic links inside the considered volume. We calculate a concrete value of HM for large scales and analyze the distribution of magnetic defects as a function of the scale. Those defects correspond to regular as well as random fields in the considered volume. We find that the fractal dimension of the distribution of topological defects is D=1/2. We also study if the regular fields induced on large scales are helical, finding that they are and that the associated number of magnetic defects is independent of the scale. In this case, the fractal dimension is D=0. We finally estimate the intensity of fields induced at the horizon scale of reheating and evolve them until the decoupling of matter and radiation under the hypothesis of the inverse cascade of magnetic helicity. The resulting intensity is high enough and the coherence length long enough to have an impact on the subsequent process of structure formation.

  2. [Examination of motion artifacts for helical and non-helical scanning modes in head CT].

    PubMed

    Fujimura, Ichiro; Ichikawa, Katsuhiro; Terakawa, Shoichi; Hara, Takanori; Miura, Yohei

    2011-01-01

    For head computed tomography (CT), non-helical scanning has been recommended even in the widely used multi-slice CT (MSCT). Also, an acute stroke imaging standardization group has recommended the non-helical mode in Japan. However, no detailed comparison has been reported for current MSCT with more than 16 slices. In this study, we compared the non-helical and helical modes for head CT, focusing on temporal resolution and motion artifacts. The temporal resolution was evaluated by using temporal sensitivity profiles (TSPs) measured using a temporal impulse method. In both modes, the TSPs and temporal modulation transfer factors (MTFs) were measured for various pitch factors using 64-slice CT (Aquilion 64, Toshiba). Two motion phantoms were scanned to evaluate motion artifacts, and then quantitative analyses for motion artifacts and helical artifacts were performed by measuring multiple regions of interest (ROIs) in the phantom images. In addition, the rates of artifact occurrence for retrospective clinical cases were compared. The temporal resolution increased as the pitch factor was increased. Remarkable streak artifacts appeared in the non-helical images of the motion phantom, in spite of the equivalent effective temporal resolution. In clinical analysis, results consistent with the phantom studies were shown. These results indicated that the low pitch helical mode would be effective for emergency head CT with patient movement.

  3. Equilibrium calculations for helical axis stellarators

    SciTech Connect

    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.

  4. Conversion from mutual helicity to self-helicity observed with IRIS

    NASA Astrophysics Data System (ADS)

    Li, L. P.; Peter, H.; Chen, F.; Zhang, J.

    2014-10-01

    Context. In the upper atmosphere of the Sun observations show convincing evidence for crossing and twisted structures, which are interpreted as mutual helicity and self-helicity. Aims: We use observations with the new Interface Region Imaging Spectrograph (IRIS) to show the conversion of mutual helicity into self-helicity in coronal structures on the Sun. Methods: Using far UV spectra and slit-jaw images from IRIS and coronal images and magnetograms from SDO, we investigated the evolution of two crossing loops in an active region, in particular, the properties of the Si IV line profile in cool loops. Results: In the early stage two cool loops cross each other and accordingly have mutual helicity. The Doppler shifts in the loops indicate that they wind around each other. As a consequence, near the crossing point of the loops (interchange) reconnection sets in, which heats the plasma. This is consistent with the observed increase of the line width and of the appearance of the loops at higher temperatures. After this interaction, the two new loops run in parallel, and in one of them shows a clear spectral tilt of the Si IV line profile. This is indicative of a helical (twisting) motion, which is the same as to say that the loop has self-helicity. Conclusions: The high spatial and spectral resolution of IRIS allowed us to see the conversion of mutual helicity to self-helicity in the (interchange) reconnection of two loops. This is observational evidence for earlier theoretical speculations. Movie associated with Fig. 1 and Appendix A are available in electronic form at http://www.aanda.org

  5. Short-Period Seismometer Development at JPL

    NASA Technical Reports Server (NTRS)

    Martin, R.

    1995-01-01

    Determining the structure of the interior of Mars has been a high priority for every Mars exploration strategy developed in the past 20 years, and is one of the primary goals of the InterMarsnet mission. Seismology is by far the most effective and detailed tool for investigating the radial and lateral distribution of density and elastic properties within a planet. Whereas long-period signals contain information from surface waves and normal modes from relatively large events, as well as the tidal response of the planet, the ability to record the high-frequency portion of the seismic spectrum (0.05 > f > 50 Hz) is essential for using the body waves of small to moderate events for probing the interior and analyzing the source characteristics of martian quakes.

  6. Quantum chaotic resonances from short periodic orbits.

    PubMed

    Novaes, M; Pedrosa, J M; Wisniacki, D; Carlo, G G; Keating, J P

    2009-09-01

    We present an approach to calculating the quantum resonances and resonance wave functions of chaotic scattering systems, based on the construction of states localized on classical periodic orbits and adapted to the dynamics. Typically only a few such states are necessary for constructing a resonance. Using only short orbits (with periods up to the Ehrenfest time), we obtain approximations to the longest-living states, avoiding computation of the background of short living states. This makes our approach considerably more efficient than previous ones. The number of long-lived states produced within our formulation is in agreement with the fractal Weyl law conjectured recently in this setting. We confirm the accuracy of the approximations using the open quantum baker map as an example.

  7. 3382 Cassidy: A Short Period Asteroid

    NASA Astrophysics Data System (ADS)

    Risley, Ethan

    2013-04-01

    The asteroid 3382 Cassidy was observed from the Etscorn Campus Observatory (ECO, 2012) at New Mexico Institute of Mining and Technology in Socorro, NM, on nine nights over a span of 43 days in 2012 September-November. A bimodal synodic period of 4.254 ± 0.002 h and an amplitude of 0.15 ± 0.02 mag were obtained.

  8. Irregular short period variations in Earth rotation

    NASA Astrophysics Data System (ADS)

    Kosek, Wieslaw

    Irregular variations in Earth Rotation Parameters (ERP) were detected by the autocovariance and autoregressive prediction methods applied in the forward and backward directions of time. Time variable Fourier Transform Band Pass Filter (FTBPF) spectra of the unpredictable variations of the ERP reveal that pole coordinates data are mostly disturbed in the spectral range from about 50 to 250 days while length of day (LOD) data are mostly disturbed in the spectral range from about 20 to 110 days. The most energetic irregular variations in the ERP occurred in the beginning of 1988 and 1995 years.

  9. 3382 Cassidy: A Short Period Asteroid

    NASA Astrophysics Data System (ADS)

    Risley, Ethan

    2013-04-01

    The asteroid 3382 Cassidy was observed from the Etscorn Campus Observatory (ECO, 2012) at New Mexico Institute of Mining and Technology in Socorro, NM, on nine nights over a span of 43 days in 2012 September-November. A bimodal synodic period of 4.254 ± 0.002 h and an amplitude of 0.15 ± 0.02 mag were obtained.

  10. Short Periodicities in Latitudinal Variation of Sunspots

    NASA Astrophysics Data System (ADS)

    Kim, Bang-Yeop; Chang, Heon-Young

    2011-06-01

    The latitudinal variation of sunspots appearing during the period from 1874 to 2009 has been studied in terms of centerof- latitude (COL). The butterfly diagram has been used to study the evolution of the magnetic field and the dynamics at the bottom of the solar convection zone. Short-term periodicities have been of particular interest, in that they are somehow related to the structure and dynamics of the solar interior. We thus have focused our investigation on shortterm periodicities. We first calculated COL by averaging the latitude of sunspots with the weight function in area. Then, we analyzed the time series of COL using the wavelet transform technique. We found that a periodicity of ~5 years is the most dominant feature in the time series of COL, with the exception of the ~11 year solar cycle itself. This periodicity can be easily understood by considering small humps between the minima in the area-weighted butterfly diagram. However, we find that periodicities of ~1.3 (0.064), ~1.5 (0.056), or ~1.8 (0.046) years ( 1/ month ), which have been previously suggested as evidence of links between the changing structure of the sunspot zone and the tachocline rotation rate oscillations, are insignificant and inconsistent. We therefore conclude that the only existing short-term periodicity is of ~5 years, and that periodicities of ~1.3, ~1.5, or ~1.8 years are likely to be artifacts due to random noise of small sunspots.

  11. Pulse stretcher

    DOEpatents

    Horton, J.A.

    1994-05-03

    Apparatus for increasing the length of a laser pulse to reduce its peak power without substantial loss in the average power of the pulse is disclosed. The apparatus uses a White cell having a plurality of optical delay paths of successively increasing number of passes between the field mirror and the objective mirrors. A pulse from a laser travels through a multi-leg reflective path between a beam splitter and a totally reflective mirror to the laser output. The laser pulse is also simultaneously injected through the beam splitter to the input mirrors of the optical delay paths. The pulses from the output mirrors of the optical delay paths go simultaneously to the laser output and to the input mirrors of the longer optical delay paths. The beam splitter is 50% reflective and 50% transmissive to provide equal attenuation of all of the pulses at the laser output. 6 figures.

  12. Pulse Voltammetry

    NASA Astrophysics Data System (ADS)

    Stojek, Zbigniew

    The idea of imposing potential pulses and measuring the currents at the end of each pulse was proposed by Barker in a little-known journal as early as in 1958 [1]. However, the first reliable trouble-free and affordable polarographs offering voltammetric pulse techniques appeared on the market only in the 1970s. This delay was due to some limitations on the electronic side. In the 1990s, again substantial progress in electrochemical pulse instrumentation took place. This was related to the introduction of microprocessors, computers, and advanced software.

  13. A Prospective Evaluation of Helical Tomotherapy

    SciTech Connect

    Bauman, Glenn ||. E-mail: glenn.bauman@lhsc.on.ca; Yartsev, Slav; Rodrigues, George ||; Lewis, Craig; Hammond, Alex; Perera, Francisco; Ash, Robert, Dar, A. Rashid |; Venkatesan, Varagur M. |; Yu, Edward; Lock, Michael; Battista, Jerry; Van Dyk, Jake ||; Baily, Laura; Coad, Terry C; Trenka, Kris C.; Warr, Barbara; Kron, Tomas

    2007-06-01

    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.

  14. Helicity as a Component of Filament Formation

    NASA Astrophysics Data System (ADS)

    Mackay, D. H.; Gaizauskas, V.

    2003-09-01

    In this paper we seek the origin of the axial component of the magnetic field in filaments by adapting theory to observations. A previous paper (Mackay, Gaizauskas, and van Ballegooijen, 2000) showed that surface flows acting on potential magnetic fields for 27 days the maximum time between the emergence of magnetic flux and the formation of large filaments between the resulting activity complexes cannot explain the chirality or inverse polarity nature of the observed filaments. We show that the inclusion of initial helicity, for which there is observational evidence, in the flux transport model results in sufficiently strong dextral fields of inverse polarity to account for the existence and length of an observed filament within the allotted time. The simulations even produce a large length of dextral chirality when just small amounts of helicity are included in the initial configuration. The modeling suggests that the axial field component in filaments can result from a combination of surface (flux transport) and sub-surface (helicity) effects acting together. Here surface effects convert the large-scale helicity emerging in active regions into a smaller-scale magnetic-field component parallel to the polarity inversion line so as to form a magnetic configuration suitable for a filament.

  15. Magnetic Helicity of Alfven Simple Waves

    NASA Technical Reports Server (NTRS)

    Webb, Gary M.; Hu, Q.; Dasgupta, B.; Zank, G. P.; Roberts, D.

    2010-01-01

    The magnetic helicity of fully nonlinear, multi-dimensional Alfven simple waves are investigated, by using relative helicity formulae and also by using an approach involving poloidal and toroidal decomposition of the magnetic field and magnetic vector potential. Different methods to calculate the magnetic vector potential are used, including the homotopy and Biot-Savart formulas. Two basic Alfven modes are identified: (a) the plane 1D Alfven simple wave given in standard texts, in which the Alfven wave propagates along the z-axis, with wave phase varphi=k_0(z-lambda t), where k_0 is the wave number and lambda is the group velocity of the wave, and (b)\\ the generalized Barnes (1976) simple Alfven wave in which the wave normal {bf n} moves in a circle in the xy-plane perpendicular to the mean field, which is directed along the z-axis. The plane Alfven wave (a) is analogous to the slab Alfven mode and the generalized Barnes solution (b) is analogous to the 2D mode in Alfvenic, incompressible turbulence. The helicity characteristics of these two basic Alfven modes are distinct. The helicity characteristics of more general multi-dimensional simple Alfven waves are also investigated. Applications to nonlinear Aifvenic fluctuations and structures observed in the solar wind are discussed.

  16. Magnetic Helicity of Alfven Simple Waves

    NASA Astrophysics Data System (ADS)

    Webb, G. M.; Hu, Q.; Dasgupta, B.; Zank, G. P.; Roberts, D.

    2010-12-01

    The magnetic helicity of fully nonlinear, multi-dimensional Alfven simple waves are investigated, by using relative helicity formulae and also by using an approach involving poloidal and toroidal decomposition of the magnetic field and magnetic vector potential. Different methods to calculate the magnetic vector potential are used, including the homotopy and Biot-Savart formulas. Two basic Alfven modes are identified: (a) the plane 1D Alfven simple wave given in standard texts, in which the Alfven wave propagates along the z-axis, with wave phase \\varphi=k0(z-λ t), where k0 is the wave number and λ is the group velocity of the wave, and (b) the generalized Barnes (1976) simple Alfvén wave in which the wave normal n moves in a circle in the xy-plane perpendicular to the mean field, which is directed along the z-axis. The plane Alfven wave (a) is analogous to the slab Alfven mode and the generalized Barnes solution (b) is analogous to the 2D mode in Alfvenic, incompressible turbulence. The helicity characteristics of these two basic Alfven modes are distinct. The helicity characteristics of more general multi-dimensional simple Alfven waves are also investigated. Applications to nonlinear Alfvenic fluctuations and structures observed in the solar wind are discussed.

  17. Multislice helical CT: image temporal resolution.

    PubMed

    Hui, H; Pan, T; Shen, Y

    2000-05-01

    A multislice helical computed tomography (CT) halfscan (HS) reconstruction algorithm is proposed for cardiac applications. The imaging performances (in terms of the temporal resolution, z-axis resolution, image noise, and image artifacts) of the HS algorithm are compared to the existing algorithms using theoretical models and clinical data. A theoretical model of the temporal resolution performance (in terms of the temporal sensitivity profile) is established for helical CT, in general, i.e., for any number of detector rows and any reconstruction algorithm used. It is concluded that the HS reconstruction results in improved image temporal resolution than the corresponding 180 degrees LI (linear interpolation) reconstruction and is more immune to the inconsistent data problem induced by cardiac motions. The temporal resolution of multislice helical CT with the HS algorithm is comparable to that of single-slice helical CT with the HS algorithm. In practice, the 180 degrees LI and HS-LI algorithms can be used in parallel to generate two image sets from the same scan acquisition, one (180 degrees LI) for improved z-resolution and noises, and the other (HS-LI) for improved image temporal resolution.

  18. QCD Evolution of Helicity and Transversity TMDs

    SciTech Connect

    Prokudin, Alexei

    2014-01-01

    We examine the QCD evolution of the helicity and transversity parton distribution functions when including also their dependence on transverse momentum. Using an appropriate definition of these polarized transverse momentum distributions (TMDs), we describe their dependence on the factorization scale and rapidity cutoff, which is essential for phenomenological applications.

  19. Deformation of flexible micro helices under flow

    NASA Astrophysics Data System (ADS)

    Daieff, Marine; Lindner, Anke; Du Roure, Olivia; Morozov, Alexander; Pham, Jonathan; Crosby, Alfred

    The interaction of small helices with fluids is important because of its relevance to both fundamental science and technological applications, such as swimming microrobots or microflow sensors. Helically shaped flagella are also exploited by swimming microorganisms to move through their surrounding fluids. Here we study experimentally the deformation of flexible helical ribbons under flow in a microfluidic channel. The size of the helix is typically microscale for the diameter and nanoscale for the thickness. We focus on two different aspects: the overall shape of the helix and the viscous frictional properties. The frictional coefficients determined by our experiments are consistent with calculated values in the context of resistive force theory. Deformation of helices by viscous flow is well-described by non-linear finite extensibility. Due to the non-uniform distribution of the pitch under distributed loading, we identify both linear and nonlinear behavior along the contour length of a single helix. Utilizing our system, we explore the impact of non-Newtonian fluid properties on the mechanics of helix-fluid interactions.

  20. Phase diagram of two interacting helical states

    NASA Astrophysics Data System (ADS)

    Santos, Raul A.; Gutman, D. B.; Carr, Sam T.

    2016-06-01

    We consider two coupled time-reversal-invariant helical edge modes of the same helicity, such as would occur on two stacked quantum spin Hall insulators. In the presence of interaction, the low-energy physics is described by two collective modes, one corresponding to the total current flowing around the edge and the other one describing relative fluctuations between the two edges. We find that quite generically, the relative mode becomes gapped at low temperatures, but only when tunneling between the two helical modes is nonzero. There are two distinct possibilities for the gapped state depending on the relative size of different interactions. If the intraedge interaction is stronger than the interedge interaction, the state is characterized as a spin-nematic phase. However, in the opposite limit, when the interaction between the helical edge modes is strong compared to the interaction within each mode, a spin-density wave forms, with emergent topological properties. First, the gap protects the conducting phase against localization by weak nonmagnetic impurities; second, the protected phase hosts localized zero modes on the ends of the edge that may be created by sufficiently strong nonmagnetic impurities.

  1. Artificial, parallel, left-handed DNA helices.

    PubMed

    Tian, Cheng; Zhang, Chuan; Li, Xiang; Li, Yingmei; Wang, Guansong; Mao, Chengde

    2012-12-19

    This communication reports an engineered DNA architecture. It contains multiple domains of half-turn-long, standard B-DNA duplexes. While each helical domain is right-handed and its two component strands are antiparallel, the global architecture is left-handed and the two component DNA strands are oriented parallel to each other.

  2. Muon Beam Helical Cooling Channel Design

    SciTech Connect

    Johnson, Rolland; Ankenbrandt, Charles; Flanagan, G; Kazakevich, G M; Marhauser, Frank; Neubauer, Michael; Roberts, T; Yoshikawa, C; Derbenev, Yaroslav; Morozov, Vasiliy; Kashikhin, V S; Lopes, Mattlock; Tollestrup, A; Yonehara, Katsuya; Zloblin, A

    2013-06-01

    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.

  3. Helical axis stellarator with noninterlocking planar coils

    DOEpatents

    Reiman, A.; Boozer, A.H.

    1984-03-06

    The present invention generates stellarator fields having favorable properties (magnetic well and large rotational transform) by a simple coil system consisting only of unlinked planar non-circular coils. At large rotational transform toroidal effects on magnetic well and rotational transform are small and can be ignored. We do so herein, specializing in straight helical systems.

  4. A novel miniaturized passively Q-switched pulse-burst laser for engine ignition.

    PubMed

    Ma, Yufei; Li, Xudong; Yu, Xin; Fan, Rongwei; Yan, Renpeng; Peng, Jiangbo; Xu, Xinrui; Sun, Rui; Chen, Deying

    2014-10-01

    A novel miniaturized Cr⁴⁺:YAG passively Q-switched Nd:YAG pulse-burst laser under 808 nm diode-laser pulse-pumping was demonstrated for the purpose of laser-induced plasma ignition, in which pulse-burst mode can realize both high repetition rate and high pulse energy simultaneously in a short period. Side-pumping configuration and two different types of laser cavities were employed. The pumping pulse width was constant at 250 μs. For the plane-plane cavity, the output beam profile was flat-top Gaussian and the measured M² value was 4.1 at the maximum incident pump energy of 600 mJ. The pulse-burst laser contained a maximum of 8 pulses, 7 pulses and 6 pulses for pulse-burst repetition rate of 10 Hz, 50 Hz and 100 Hz, respectively. The energy obtained was 15.5 mJ, 14.9 mJ and 13.9 mJ per pulse for pulse-burst repetition rate of 10 Hz, 50 Hz and 100 Hz, respectively. The maximum repetition rate of laser pulses in pulse-burst was 34.6 kHz for 8 pulses at the incident pump energy of 600 mJ and the single pulse width was 13.3 ns. The thermal lensing effect of Nd:YAG rod was investigated, and an plane-convex cavity was adopted to compensate the thermal lensing effect of Nd:YAG rod and improve the mode matching. For the plane-convex cavity, the output beam profile was quasi-Gaussian and the measured M2 value was 2.2 at the incident pump energy of 600 mJ. The output energy was 10.6 mJ per pulse for pulse-burst repetition rate of 100 Hz. The maximum repetition rate of laser pulses in pulse-burst was 27.4 kHz for 6 pulses at the incident pump energy of 600 mJ and the single pulse width was 14.2 ns. The experimental results showed that this pulse-burst laser can produce high repetition rate (>20 kHz) and high pulse energy (>10 mJ) simultaneously in a short period for both two different cavities. PMID:25322040

  5. Two-dimensional surface chirality control by solvent-induced helicity inversion of a helical polyacetylene on graphite.

    PubMed

    Sakurai, Shin-ichiro; Okoshi, Kento; Kumaki, Jiro; Yashima, Eiji

    2006-05-01

    We report the direct evidence for the macromolecular helicity inversion of a helical poly(phenylacetylene) bearing l- or d-alanine pendants with a long alkyl chain in different solvents by atomic force microscopy observations of the diastereomeric helical structures. The diastereomeric helical poly(phenylacetylene)s induced in polar and nonpolar solvents self-assembled into ordered, two-dimensional helix bundles with controlled molecular packing, helical pitch, and handedness on graphite upon exposure of each solvent. The macromolecular helicity deposited on graphite from a polar solvent further inverted to the opposite handedness by exposure to a specific nonpolar solvent, and these changes in the surface chirality based on the inversion of helicity could be visualized by atomic force microscopy with molecular resolution, and the results were quantified by X-ray diffraction of the oriented liquid crystalline, diastereomeric helical polymer films.

  6. The Effects of Spatial Smoothing on Solar Magnetic Helicity and the Hemispheric Helicity Sign Rule

    NASA Astrophysics Data System (ADS)

    Koch Ocker, Stella; Petrie, Gordon

    2016-05-01

    The hemispheric sign rule for solar magnetic helicity, which states that negative/positive helicity occurs preferentially in the northern/southern hemisphere, provides clues to the causes of twisted, flaring magnetic fields. However, previous studies on the hemisphere rule may have been significantly affected by seeing from atmospheric turbulent motions. Using Hinode/SOT-SP data spanning from 2006 to 2012, we studied the effects of two important data processing steps that imitate the effects of atmospheric seeing: noise reduction by ignoring pixel values that are weaker than the estimated noise threshold, and Gaussian spatial smoothing. We applied these processing techniques to the helicity distribution maps for active regions NOAA 11158 and NOAA 11243, along with the average helicities of 36 active regions, in order to imitate and understand the effects of seeing from atmospheric turbulence. We found that rather than changing trends in the helicity distributions, Gaussian smoothing and noise reduction enhanced existing trends by pushing outliers towards the mean or removing them altogether. We also found that, when separated for weak and strong magnetic fields, the average helicities of the 36 active regions conformed to the hemisphere rule for weak field helicities and breached the rule for strong field helicities. In general, we found that data processing did not affect whether the hemisphere rule held for data taken from space-based instruments, and thus that seeing from atmospheric turbulence did not significantly affect previous studies' ground-based results on the hemisphere rule. This work was carried out through the National Solar Observatory Research Experiences for Undergraduates (REU) Program, which is funded by the National Science Foundation (NSF). The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the NSF.

  7. Applications of Elliptically Polarized, Few-Cycle Attosecond Pulses

    NASA Astrophysics Data System (ADS)

    Starace, Anthony F.

    2016-05-01

    Use of elliptically-polarized light opens the possibility of investigating effects that are not accessible with linearly-polarized pulses. This talk presents two new physical effects that are predicted for ionization of the helium atom by few-cycle, elliptically polarized attosecond pulses. For double ionization of He by an intense elliptically polarized attosecond pulse, we predict a nonlinear dichroic effect (i.e., the difference of the two-electron angular distributions in the polarization plane for opposite helicities of the ionizing pulse) that is sensitive to the carrier-envelope phase, ellipticity, peak intensity I, and temporal duration of the pulse. For single ionization of He by two oppositely circularly polarized, time-delayed attosecond pulses we predict that the photoelectron momentum distributions in the polarization plane have helical vortex structures that are exquisitely sensitive to the time-delay between the pulses, their relative phase, and their handedness. Both of these effects manifest the ability to control the angular distributions of the ionized electrons by means of the attosecond pulse parameters. Our predictions are obtained numerically by solving the six-dimensional two-electron time-dependent Schrödinger equation for the case of elliptically polarized attosecond pulses. They are interpreted analytically by means of perturbation theory analyses of the two ionization processes. This work is supported in part by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Award No. DE-FG03-96ER14646.

  8. PULSE AMPLIFIER

    DOEpatents

    Johnstone, C.W.

    1958-06-17

    The improvement of pulse amplifiers used with scintillation detectors is described. The pulse amplifier circuit has the advantage of reducing the harmful effects of overloading cause by large signal inputs. In general the pulse amplifier circuit comprises two amplifier tubes with the input pulses applied to one amplifier grid and coupled to the second amplifier tube through a common cathode load. The output of the second amplifier is coupled from the plate circuit to a cathode follower tube grid and a diode tube in connected from grid to cathode of the cathode follower tube. Degenerative feedback is provided in the second amplifier by coupling a signal from the cathode follower cathode to the second amplifier grid. The circuit proqides moderate gain stability, and overload protection for subsequent pulse circuits.

  9. Magnetic field analysis and achievable on-axis field for helical undulators.

    SciTech Connect

    Kim, S. H.; Accelerator Systems Division

    2008-01-01

    The on- and off-axis magnetic fields for infinitely long, helical undulators were analyzed for linear and nonlinear poles. An analytical expression of the on-axis field for linear poles was derived in terms of coil current density, undulator period length, and coil dimensions. The derived expression showed that, when the undulator dimensions were scaled according to the period ratios, the on-axis fields were proportional to the periods, which is in agreement with calculations of model undulators. For undulators with nonlinear steel poles, when the undulator dimensions were scaled, the field distributions remained unchanged for a constant value of (current density x period). It was also shown that, for two scaled undulators, one with linear and one with nonlinear poles, the off-axis field components, normalized to the respective on-axis fields, had the same field distributions near the axis within the calculation errors. This implies that the derived normalized off-axis field for linear poles may be used for beam dynamic analysis in the fields of undulators with nonlinear poles within the beam chamber. Achievable on-axis fields were calculated for short-period undulators with parameters close to those for the proposed International Linear Collider (ILC) positron production undulators. The required undulator parameters for the ILC appear to be achievable depending on the Nb{sub 3}Sn superconductor packing factor in the coil and on how close the chosen operating current is to the critical current.

  10. Autonomously folded α-helical lockers promote RNAi*

    PubMed Central

    Guyader, Christian P. E.; Lamarre, Baptiste; De Santis, Emiliana; Noble, James E.; Slater, Nigel K.; Ryadnov, Maxim G.

    2016-01-01

    RNAi is an indispensable research tool with a substantial therapeutic potential. However, the complete transition of the approach to an applied capability remains hampered due to poorly understood relationships between siRNA delivery and gene suppression. Here we propose that interfacial tertiary contacts between α-helices can regulate siRNA cytoplasmic delivery and RNAi. We introduce a rationale of helical amphipathic lockers that differentiates autonomously folded helices, which promote gene silencing, from helices folded with siRNA, which do not. Each of the helical designs can deliver siRNA into cells via energy-dependent endocytosis, while only autonomously folded helices with pre-locked hydrophobic interfaces were able to promote statistically appreciable gene silencing. We propose that it is the amphipathic locking of interfacing helices prior to binding to siRNA that enables RNAi. The rationale offers structurally balanced amphipathic scaffolds to advance the exploitation of functional RNAi. PMID:27721465

  11. Autonomously folded α-helical lockers promote RNAi*

    NASA Astrophysics Data System (ADS)

    Guyader, Christian P. E.; Lamarre, Baptiste; de Santis, Emiliana; Noble, James E.; Slater, Nigel K.; Ryadnov, Maxim G.

    2016-10-01

    RNAi is an indispensable research tool with a substantial therapeutic potential. However, the complete transition of the approach to an applied capability remains hampered due to poorly understood relationships between siRNA delivery and gene suppression. Here we propose that interfacial tertiary contacts between α-helices can regulate siRNA cytoplasmic delivery and RNAi. We introduce a rationale of helical amphipathic lockers that differentiates autonomously folded helices, which promote gene silencing, from helices folded with siRNA, which do not. Each of the helical designs can deliver siRNA into cells via energy-dependent endocytosis, while only autonomously folded helices with pre-locked hydrophobic interfaces were able to promote statistically appreciable gene silencing. We propose that it is the amphipathic locking of interfacing helices prior to binding to siRNA that enables RNAi. The rationale offers structurally balanced amphipathic scaffolds to advance the exploitation of functional RNAi.

  12. Vacuum systems for the ILC helical undulator

    SciTech Connect

    Malyshev, O. B.; Scott, D. J.; Bailey, I. R.; Barber, D. P.; Baynham, E.; Bradshaw, T.; Brummitt, A.; Carr, S.; Clarke, J. A.; Cooke, P.; Dainton, J. B.; Ivanyushenkov, Y.; Malysheva, L. I.; Moortgat-Pick, G. A.; Rochford, J.; Department of Physics, University of Liverpool Oxford St. Liverpool L69 7ZE; Cockcroft Institute, Warrington WA4 4AD

    2007-07-15

    The International Linear Collider (ILC) positron source uses a helical undulator to generate polarized photons of {approx}10 MeV at the first harmonic. Unlike many undulators used in synchrotron radiation sources, the ILC helical undulator vacuum chamber will be bombarded by photons, generated by the undulator, with energies mostly below that of the first harmonic. Achieving the vacuum specification of {approx}100 nTorr in a narrow chamber of 4-6 mm inner diameter, with a long length of 100-200 m, makes the design of the vacuum system challenging. This article describes the vacuum specifications and calculations of the flux and energy of photons irradiating the undulator vacuum chamber and considers possible vacuum system design solutions for two cases: cryogenic and room temperature.

  13. Electronic structure calculations on helical conducting polymers.

    PubMed

    Ripoll, Juan D; Serna, Andrei; Guerra, Doris; Restrepo, Albeiro

    2010-10-21

    We present a study of the electronic structure and derived properties of polyfurane (PFu), polypyrrol (PPy), and polythiophene (PTh). Two spatial arrangements are considered: trans chain (tc-PFu, tc-PPy, tc-PTh) and cis α-helical (α-PFu, α-PPy, α-PTh). Even at the small sizes considered here, helical conformations appear to be stable. Band gaps of pure, undoped oligomers fall into the semiconductor range. Density of states (DOS) analysis suggest dense valence and conduction bands. Bond length alternation analysis predicts almost complete delocalization of the π clouds in all spatial arrangements. Doping with electron donors or electron-withdrawing impurities reduces all band gaps close to the metallic regime in addition to increasing the DOS for the valence and conduction bands.

  14. Properties of dc helicity injected tokamak plasmas

    SciTech Connect

    Darrow, D.S.; Ono, M.; Forest, C.B.; Greene, G.J.; Hwang, Y.S.; Park, H.K. ); Taylor, R.J.; Pribyl, P.A.; Evans, J.D.; Lai, K.F.; Liberati, J.R. )

    1990-06-01

    Several dc helicity injection experiments using an electron beam technique have been conducted on the Current Drive Experiment (CDX) (Phys. Rev. Lett. {bold 59}, 2165 (1987)) and the Continuous Current Tokamak (CCT) (Phys. Rev. Lett. {bold 63}, 2365 (1989)). The data strongly suggest that tokamak plasmas are being formed and maintained by this method. The largest currents driven to date are 1 kA in CDX ({ital q}{sub {ital a}} =5) and 6 kA in CCT ({ital q}{sub {ital a}} =3.5). An initial comparison of discharge properties with helicity theory indicates rough agreement. Current drive energy efficiencies are 9% and 23% of Ohmic efficiency in two cases analyzed. Strong radial electric fields are observed in these plasmas that cause poloidal rotation and, possibly, improved confinement.

  15. Helical Muon Beam Cooling Channel Engineering Design

    SciTech Connect

    Kashikhin, V.S.; Lopes, M.L.; Romanov, G.V.; Tartaglia, M.A.; Yonehara, K.; Yu, M.; Zlobin, A.V.; Flanagan, G.; Johnson, R.P.; Kazakevich, G.M.; Marhauser, F.; /MUONS Inc., Batavia

    2012-05-01

    The Helical Cooling Channel (HCC), a novel technique for six-dimensional (6D) ionization cooling of muon beams, has shown considerable promise based on analytic and simulation studies. However, the implementation of this revolutionary method of muon cooling requires new techniques for the integration of hydrogen-pressurized, high-power RF cavities into the low-temperature superconducting magnets of the HCC. We present the progress toward a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb{sub 3}Sn based HCC test section. We include discussions on the pressure and thermal barriers needed within the cryostat to maintain operation of the magnet at 4.2 K while operating the RF and energy absorber at a higher temperature. Additionally, we include progress on the Nb{sub 3}Sn helical solenoid design.

  16. Viscosity of Sheared Helical filament Suspensions

    NASA Astrophysics Data System (ADS)

    Sartucci, Matthew; Urbach, Jeff; Blair, Dan; Schwenger, Walter

    The viscosity of suspensions can be dramatically affected by high aspect ratio particles. Understanding these systems provides insight into key biological functions and can be manipulated for many technological applications. In this talk, the viscosity as a function of shear rate of suspensions of helical filaments is compared to that of suspensions of straight rod-like filaments. Our goal is to determine the impact of filament geometry on low volume fraction colloidal suspensions in order to identify strategies for altering viscosity with minimal volume fraction. In this research, the detached flagella of the bacteria Salmonella Typhimurium are used as a model system of helical filaments and compared to mutated straight flagella of the Salmonella. We compare rheological measurements of the suspension viscosity in response to shear flow and use a combination of the rheology and fluorescence microscopy to identify the microstructural changes responsible for the observed rheological response.

  17. Helicity of a toroidal vortex with swirl

    NASA Astrophysics Data System (ADS)

    Bannikova, E. Yu.; Kontorovich, V. M.; Poslavsky, S. A.

    2016-04-01

    Based on the solutions of the Bragg-Hawthorne equation, we discuss the helicity of a thin toroidal vortex in the presence of swirl, orbital motion along the torus directrix. The relation between the helicity and circulations along the small and large linked circumferences (the torus directrix and generatrix) is shown to depend on the azimuthal velocity distribution in the core of the swirling ring vortex. In the case of nonuniform swirl, this relation differs from the well-known Moffat relation, viz., twice the product of such circulations multiplied by the number of linkages. The results can find applications in investigating the vortices in planetary atmospheres and the motions in the vicinity of active galactic nuclei.

  18. A Helical Magnet Design for RHIC^*.

    NASA Astrophysics Data System (ADS)

    Willen, E.; Gupta, R.; Kelly, E.; Muratore, J.

    1997-05-01

    Helical dipole magnets are required in a project for the Relativistic Heavy Ion Collider (RHIC) to control and preserve the beam polarization in order to allow the collision of polarized proton beams. The project requires superconducting magnets with a 100 mm coil aperture and a 4 Tesla field in which the field rotates 360 degrees over a distance of 2.4 meters. A design restraint is that the magnets operate at relatively low current (less than 500 amperes) in order to minimize the heat load from the current leads. A magnet has been developed that uses a small diameter superconducting cable wound into helical grooves machined into a thick-walled aluminum cylinder. The design and test results of this prototype magnet will be described. ^*Work supported by the U.S. Department of Energy.

  19. Guided wave helical ultrasonic tomography of pipes.

    PubMed

    Leonard, Kevin R; Hinders, Mark K

    2003-08-01

    Ultrasonic guided waves have been used for a wide variety of ultrasonic inspection techniques. We describe here a new variation called helical ultrasound tomography (HUT) that uses guided ultrasonic waves along with tomographic reconstruction algorithms that have been developed by seismologists for what they call "cross borehole" tomography. In HUT, the Lamb-like guided waves travel the various helical criss-cross paths between two parallel circumferential transducer arrays instead of the planar criss-cross seismic paths between two boreholes. Although the measurement itself is fairly complicated, the output of the tomographic reconstruction is a readily interpretable map of a quantity of interest such as pipe wall thickness. In this paper we demonstrate HUT via laboratory scans on steel pipe segments into which controlled thinnings have been introduced.

  20. Coherent electron transport in a helical nanotube

    NASA Astrophysics Data System (ADS)

    Liang, Guo-Hua; Wang, Yong-Long; Du, Long; Jiang, Hua; Kang, Guang-Zhen; Zong, Hong-Shi

    2016-09-01

    The quantum dynamics of carriers bound to helical tube surfaces is investigated in a thin-layer quantization scheme. By numerically solving the open-boundary Schrödinger equation in curvilinear coordinates, geometric effect on the coherent transmission spectra is analysed in the case of single propagating mode as well as multimode. It is shown that, the coiling endows the helical nanotube with different transport properties from a bent cylindrical surface. Fano resonance appears as a purely geometric effect in the conductance, the corresponding energy of quasibound state is obviously influenced by the torsion and length of the nanotube. We also find new plateaus in the conductance. The transport of double-degenerate mode in this geometry is reminiscent of the Zeeman coupling between the magnetic field and spin angular momentum in quasi-one-dimensional structure.

  1. Helical Tomotherapy for Parotid Gland Tumors

    SciTech Connect

    Lee, Tae Kyu; Rosen, Isaac I.; Gibbons, John P.; Fields, Robert S.; Hogstrom, Kenneth R.

    2008-03-01

    Purpose: To investigate helical tomotherapy (HT) intensity-modulated radiotherapy (IMRT) as a postoperative treatment for parotid gland tumors. Methods and Materials: Helical tomotherapy plans were developed for 4 patients previously treated with segmental multileaf collimator (SMLC) IMRT. A primary planning target volume (PTV64) and two secondary PTVs (PTV60, PTV54) were defined. The clinical goals from the SMLC plans were applied as closely as possible to the HT planning. The SMLC plans included bolus, whereas HT plans did not. Results: In general, the HT plans showed better target coverage and target dose homogeneity. The minimum doses to the desired coverage volume were greater, on average, in the HT plans for all the targets. Minimum PTV doses were larger, on average, in the HT plans by 4.6 Gy (p = 0.03), 4.8 Gy (p = 0.06), and 4.9 Gy (p = 0.06) for PTV64, PTV60, and PTV54, respectively. Maximum PTV doses were smaller, on average, by 2.9 Gy (p = 0.23), 3.2 Gy (p = 0.02), and 3.6 Gy (p = 0.03) for PTV64, PTV60, and PTV54, respectively. Average dose homogeneity index was statistically smaller in the HT plans, and conformity index was larger for PTV64 in 3 patients. Tumor control probabilities were higher for 3 of the 4 patients. Sparing of normal structures was comparable for the two techniques. There were no significant differences between the normal tissue complication probabilities for the HT and SMLC plans. Conclusions: Helical tomotherapy treatment plans were comparable to or slightly better than SMLC plans. Helical tomotherapy is an effective alternative to SMLC IMRT for treatment of parotid tumors.

  2. Automatic generation of tree level helicity amplitudes

    NASA Astrophysics Data System (ADS)

    Stelzer, T.; Long, W. F.

    1994-11-01

    The program MadGraph is presented which automatically generates postscript Feynman diagrams and Fortran code to calculate arbitrary tree level helicity amplitudes by calling HELAS[1] subroutines. The program is written in Fortran and is available in Unix and VMS versions. MadGraph currently includes standard model interactions of QCD and QFD, but is easily modified to include additional models such as supersymmetry.

  3. Automatic generation of tree level helicity amplitudes

    NASA Astrophysics Data System (ADS)

    Stelzer, T.; Long, W. F.

    1994-07-01

    The program MadGraph is presented which automatically generates postscript Feynman diagrams and Fortran code to calculate arbitrary tree level helicity amplitudes by calling HELAS[1] subroutines. The program is written in Fortran and is available in Unix and VMS versions. MadGraph currently includes standard model interactions of QCD and QFD, but is easily modified to include additional models such as supersymmetry.

  4. Field of a helical Siberian Snake

    SciTech Connect

    Luccio, A.

    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.

  5. Bacteria that glide with helical tracks

    PubMed Central

    Nan, Beiyan; McBride, Mark J.; Chen, Jing; Zusman, David R.; Oster, George

    2014-01-01

    Many bacteria glide smoothly on surfaces, but with no discernable propulsive organelles on their surface. Recent experiments with Myxococcus xanthus and Flavobacterium johnsoniae show that both distantly related bacterial species glide utilizing proteins that move in helical tracks, albeit with significantly different motility mechanisms. Both species utilize proton motive force for movement. However, the motors that power gliding in M. xanthus have been identified, while the F. johnsoniae motors remain to be discovered. PMID:24556443

  6. Helical Cerenkov effect, a novel radiation source

    SciTech Connect

    Soln, J. )

    1994-10-01

    The observability of the helical Cerenkov effect as a novel radiation source is discussed. Depending on the value of the index of refraction of the medium, the strength of the uniform magnetic field, and the electron beam energy, helical Cerenkov radiation can occur in the same spectral regions as the ordinary Cerenkov effect, that is, from microwave to visible wavelengths. From the kinematics point of view, the author argues that for a microwave wavelength of 10[sup [minus]1] cm this effect should be observable in a medium with an index of refraction of 1.4, with a beam energy of 3 MeV, and a uniform magnetic field of 4 T. On the specific level, however, for the sake of simplicity, he discusses the observability of this effect for visible light with the central wavelength of 5 [times] 10[sup [minus]5] cm which can be achieved with 2 MeV in beam energy, silica aerogel as a medium (with an index of refraction of 1.075), and uniform magnetic fields from 5 to 10 T. For a 10-T magnetic field, he calculates that in the visible region of 250 to 750 nm an electron will produce a photon per 10 cm of traveled length. As to the stimulated helical Cerenkov emission, the author estimates that respectable gains are possible even if the beam passes close to the dielectric rather than through it. In addition to being potentially a new radiation source, the helical Cerenkov effect could possibly be used as a detector of radiation by energetic electrons that are trapped in a medium by strong magnetic fields.

  7. Environmental-health aspects of pulse-modulated microwaves.

    PubMed

    Neshev, N N; Kirilova, E I

    1996-01-01

    Our theoretical model describes the potential influence of irradiation with pulse-modulated microwaves on the conformational oscillations of enzymes in living organisms. Certain values of pulse-repetition time, determined by the period of conformational oscillations of the corresponding type of enzyme, can produce the effect at extremely low power levels. Synchronized oscillations in identical enzyme molecules produce in turn large-scale oscillations within living cells. Thus, short periods of exposure to pulse-modulated microwaves could be beneficial to cellular function, whereas maintaining the amplitude of such oscillations at a maximum for long periods may have a stressful effect on biochemical processes. The model discloses the possible environmental-health risks of long-term exposure in ambient fields that are created by radar, navigation, and communication systems. PMID:8869530

  8. Pulse Data.

    ERIC Educational Resources Information Center

    Hands On!, 1998

    1998-01-01

    Presents an activity using computer software to investigate the role of the heart and blood, how the blood system responds to exercise, and how pulse rate is a good measure of physical condition. (ASK)

  9. Overview of the Helicity Injected Torus Program

    NASA Astrophysics Data System (ADS)

    Nelson, B. A.; Jarboe, T. R.; Hamp, W. T.; Izzo, V. A.; O'Neill, R. G.; Redd, A. J.; Sieck, P. E.; Smith, R. J.

    2004-11-01

    The Helicity Injected Torus with Steady Inductive Helicity Injection (SIHI) spheromak experiment (HIT-SI) [Jarboe, Fus. Tech., (36)1, p.85, 1999] addresses critical issues for spheromaks, including current drive, operation at high beta, and confinement. HIT-SI features an optimal high-beta plasma shape and current profile, steady-state operation, minimal plasma-wall interaction, and injected power always flowing into the plasma. HIT-SI has a ``bow-tie'' shaped 1 cm thick Cu flux conserver with major radius R = 0.33 m and axial extent of 0.57 m. A half torus helicity injector at each end of the flux conserver produces conjugate sinusoidal flux (4 MW peak) and loop voltages (20 MW peak) at 5 kHz by IGBT-based switching power amplifiers. Injector flux and loop voltages are phase controlled to maintain power flow always inward. Insulating breaks for the oscillating flux and loop voltage are provided by a novel double viton o-ring system. HIT-SI uses the diagnostic suite previously used by the HIT-II experiment, (presented in an accompanying poster.) Results and 3D MHD simulations will be presented.

  10. Magnetic Helical Microswimmers in Poiseuille Flow

    NASA Astrophysics Data System (ADS)

    Acemoglu, Alperen; Yesilyurt, Serhat

    2014-11-01

    We analyze the motion of artificial magnetic microswimmers which mimic the swimming of natural organisms at low Reynolds numbers. Artificial magnetic microswimmers consist of a rigidly connected helical tail and a magnetic head. Magnetic swimmers are actuated with three orthogonal electromagnetic coil pairs. The swimmer motion is examined in the laminar flow which is introduced to channel with syringe pump. We recorded videos for forward (pusher-like swimming / in the head direction) and backward (puller-like swimming / in the tail direction) motion of swimmers. Swimmers have non-stable helical trajectories for forward motion and stable straight trajectories for backward motion. The flow effects on trajectories are observed for swimmers with different geometric parameters in the circular channels. Experiment results show that helical wavelengths of the trajectories are affected with the flow. Additionally, the flow has more pronounced effect on the trajectories of the swimmers in wide channels. Moreover, circular confinement in narrow channels leads to more stable trajectories; in wide channels swimmers follow complex trajectories. A CFD model is used to compare experiments with simulations and to analyze the effects of hydrodynamic interactions.

  11. Helical swimming in viscoelastic and porous media

    NASA Astrophysics Data System (ADS)

    Liu, Bin

    2012-02-01

    Many bacteria swim by rotating helical flagella. These cells often live in polymer suspensions, which are viscoelastic. Recently there have been several theoretical and experimental studies showing that viscoelasticity can either enhance or suppress propulsion, depending on the details of the microswimmer. To help clarify this situation, we study experimentally the motility of the flagellum using a scaled-up model system - a motorized helical coil that rotates along its axial direction. A free-swimming speed is obtained when the net force on the helix is zero. When the helix is immersed in a viscoelastic (Boger) fluid, we find an increase in the force-free swimming speed as compared with the Newtonian case. The enhancement is maximized at a Deborah number of approximately one, and the magnitude depends not only on the elasticity of the fluid but also on the geometry of the helix. In the second part of my talk, I will discuss how spatial confinements, such as a porous medium, affect the flagellated swimming. For clarity, the porous media are modeled as cylindrical cavities with solid walls. A modified boundary element method allows us to investigate a situation that the helical flagella are very close to the wall, with high spatial resolution and relatively low computational cost. To our surprise, at fixed power consumption, a highly coiled flagellum swims faster in narrower confinements, while an elongated flagellum swims faster in a cavity with a wider opening. We try understanding these effects with simple physical pictures.

  12. Mechanical Resonances of Helically Coiled Carbon Nanowires

    NASA Astrophysics Data System (ADS)

    Saini, D.; Behlow, H.; Podila, R.; Dickel, D.; Pillai, B.; Skove, M. J.; Serkiz, S. M.; Rao, A. M.

    2014-07-01

    Despite their wide spread applications, the mechanical behavior of helically coiled structures has evaded an accurate understanding at any length scale (nano to macro) mainly due to their geometrical complexity. The advent of helically coiled micro/nanoscale structures in nano-robotics, nano-inductors, and impact protection coatings has necessitated the development of new methodologies for determining their shear and tensile properties. Accordingly, we developed a synergistic protocol which (i) integrates analytical, numerical (i.e., finite element using COMSOL®) and experimental (harmonic detection of resonance; HDR) methods to obtain an empirically validated closed form expression for the shear modulus and resonance frequency of a singly clamped helically coiled carbon nanowire (HCNW), and (ii) circumvents the need for solving 12th order differential equations. From the experimental standpoint, a visual detection of resonances (using in situ scanning electron microscopy) combined with HDR revealed intriguing non-planar resonance modes at much lower driving forces relative to those needed for linear carbon nanotube cantilevers. Interestingly, despite the presence of mechanical and geometrical nonlinearities in the HCNW resonance behavior the ratio of the first two transverse modes f2/f1 was found to be similar to the ratio predicted by the Euler-Bernoulli theorem for linear cantilevers.

  13. Helical antimicrobial polypeptides with radial amphiphilicity

    PubMed Central

    Xiong, Menghua; Lee, Michelle W.; Mansbach, Rachael A.; Song, Ziyuan; Bao, Yan; Peek, Richard M.; Yao, Catherine; Chen, Lin-Feng; Ferguson, Andrew L.; Wong, Gerard C. L.; Cheng, Jianjun

    2015-01-01

    α-Helical antimicrobial peptides (AMPs) generally have facially amphiphilic structures that may lead to undesired peptide interactions with blood proteins and self-aggregation due to exposed hydrophobic surfaces. Here we report the design of a class of cationic, helical homo-polypeptide antimicrobials with a hydrophobic internal helical core and a charged exterior shell, possessing unprecedented radial amphiphilicity. The radially amphiphilic structure enables the polypeptide to bind effectively to the negatively charged bacterial surface and exhibit high antimicrobial activity against both gram-positive and gram-negative bacteria. Moreover, the shielding of the hydrophobic core by the charged exterior shell decreases nonspecific interactions with eukaryotic cells, as evidenced by low hemolytic activity, and protects the polypeptide backbone from proteolytic degradation. The radially amphiphilic polypeptides can also be used as effective adjuvants, allowing improved permeation of commercial antibiotics in bacteria and enhanced antimicrobial activity by one to two orders of magnitude. Designing AMPs bearing this unprecedented, unique radially amphiphilic structure represents an alternative direction of AMP development; radially amphiphilic polypeptides may become a general platform for developing AMPs to treat drug-resistant bacteria. PMID:26460016

  14. Mechanical Resonances of Helically Coiled Carbon Nanowires

    PubMed Central

    Saini, D.; Behlow, H.; Podila, R.; Dickel, D.; Pillai, B.; Skove, M. J.; Serkiz, S. M.; Rao, A. M.

    2014-01-01

    Despite their wide spread applications, the mechanical behavior of helically coiled structures has evaded an accurate understanding at any length scale (nano to macro) mainly due to their geometrical complexity. The advent of helically coiled micro/nanoscale structures in nano-robotics, nano-inductors, and impact protection coatings has necessitated the development of new methodologies for determining their shear and tensile properties. Accordingly, we developed a synergistic protocol which (i) integrates analytical, numerical (i.e., finite element using COMSOL®) and experimental (harmonic detection of resonance; HDR) methods to obtain an empirically validated closed form expression for the shear modulus and resonance frequency of a singly clamped helically coiled carbon nanowire (HCNW), and (ii) circumvents the need for solving 12th order differential equations. From the experimental standpoint, a visual detection of resonances (using in situ scanning electron microscopy) combined with HDR revealed intriguing non-planar resonance modes at much lower driving forces relative to those needed for linear carbon nanotube cantilevers. Interestingly, despite the presence of mechanical and geometrical nonlinearities in the HCNW resonance behavior the ratio of the first two transverse modes f2/f1 was found to be similar to the ratio predicted by the Euler-Bernoulli theorem for linear cantilevers. PMID:24986377

  15. Buckling transition in long α-helices

    SciTech Connect

    Palenčár, Peter; Bleha, Tomáš

    2014-11-07

    The treatment of bending and buckling of stiff biopolymer filaments by the popular worm-like chain model does not provide adequate understanding of these processes at the microscopic level. Thus, we have used the atomistic molecular-dynamic simulations and the Amber03 force field to examine the compression buckling of α-helix (AH) filaments at room temperature. It was found that the buckling instability occurs in AHs at the critical force f{sub c} in the range of tens of pN depending on the AH length. The decrease of the force f{sub c} with the contour length follows the prediction of the classic thin rod theory. At the force f{sub c} the helical filament undergoes the swift and irreversible transition from the smoothly bent structure to the buckled one. A sharp kink in the AH contour arises at the transition, accompanied by the disruption of the hydrogen bonds in its vicinity. The kink defect brings in an effective softening of the AH molecule at buckling. Nonbonded interactions between helical branches drive the rearrangement of a kinked AH into the ultimate buckled structure of a compact helical hairpin described earlier in the literature.

  16. Manipulation of wavefront using helical metamaterials.

    PubMed

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

    2016-08-01

    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. PMID:27505790

  17. Total scalp irradiation using helical tomotherapy

    SciTech Connect

    Orton, Nigel . E-mail: nporton@facstaff.wisc.edu; Jaradat, Hazim; Welsh, James; Tome, Wolfgang

    2005-09-30

    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)

  18. Nuclear design of Helical Cruciform Fuel rods

    SciTech Connect

    Shirvan, K.; Kazimi, M. S.

    2012-07-01

    In order to increase the power density of current and new light water reactor designs, the Helical Cruciform Fuel (HCF) rods are proposed. The HCF rods are equivalent to a cylindrical rod, with the fuel in a cruciform shaped, twisted axially. The HCF rods increase the surface area to volume ratio and inter-subchannel mixing behavior due to their cruciform and helical shapes, respectively. In a previous study, the HCF rods have shown the potential to up-rate existing PWRs by 50% and BWRs by 25%. However, HCF rods do display different neutronics modeling and performance. The cruciform cross section of HCF rods creates radially asymmetric heat generation and temperature distribution. The nominal HCF rod's beginning of life reactivity is reduced, compared to a cylindrical rod with the same fuel volume, by 500 pcm, due to increase in absorption in cladding. The rotation of these rods accounts for reactivity changes, which depends on the H/HM ratio of the pin cell. The HCF geometry shows large sensitivities to U{sup 235} or gadolinium enrichments compared to a cylindrical geometry. In addition, the gadolinium-containing HCF rods show a stronger effect on neighboring HCF rods than in case of cylindrical rods, depending on the orientation of the HCF rods. The helical geometry of the rods introduces axial shadowing of about 600 pcm, not seen in typical cylindrical rods. (authors)

  19. Quantifying foot deformation using finite helical angle.

    PubMed

    Pothrat, Claude; Goislard de Monsabert, Benjamin; Vigouroux, Laurent; Viehweger, Elke; Berton, Eric; Rao, Guillaume

    2015-10-15

    Foot intrinsic motion originates from the combination of numerous joint motions giving this segment a high adaptive ability. Existing foot kinematic models are mostly focused on analyzing small scale foot bone to bone motions which require both complex experimental methodology and complex interpretative work to assess the global foot functionality. This study proposes a method to assess the total foot deformation by calculating a helical angle from the relative motions of the rearfoot and the forefoot. This method required a limited number of retro-reflective markers placed on the foot and was tested for five different movements (walking, forefoot impact running, heel impact running, 90° cutting, and 180° U-turn) and 12 participants. Overtime intraclass correlation coefficients were calculated to quantify the helical angle pattern repeatability for each movement. Our results indicated that the method was suitable to identify the different motions as different amplitudes of helical angle were observed according to the flexibility required in each movement. Moreover, the results showed that the repeatability could be used to identify the mastering of each motion as this repeatability was high for well mastered movements. Together with existing methods, this new protocol could be applied to fully assess foot function in sport or clinical contexts.

  20. Bifurcated helical core equilibrium states in tokamaks

    NASA Astrophysics Data System (ADS)

    Cooper, W. A.; Chapman, I. T.; Schmitz, O.; Turnbull, A. D.; Tobias, B. J.; Lazarus, E. A.; Turco, F.; Lanctot, M. J.; Evans, T. E.; Graves, J. P.; Brunetti, D.; Pfefferlé, D.; Reimerdes, H.; Sauter, O.; Halpern, F. D.; Tran, T. M.; Coda, S.; Duval, B. P.; Labit, B.; Pochelon, A.; Turnyanskiy, M. R.; Lao, L.; Luce, T. C.; Buttery, R.; Ferron, J. R.; Hollmann, E. M.; Petty, C. C.; van Zeeland, M.; Fenstermacher, M. E.; Hanson, J. M.; Lütjens, H.

    2013-07-01

    Tokamaks with weak to moderate reversed central shear in which the minimum inverse rotational transform (safety factor) qmin is in the neighbourhood of unity can trigger bifurcated magnetohydrodynamic equilibrium states, one of which is similar to a saturated ideal internal kink mode. Peaked prescribed pressure profiles reproduce the ‘snake’ structures observed in many tokamaks which has led to a novel explanation of the snake as a bifurcated equilibrium state. Snake equilibrium structures are computed in simulations of the tokamak à configuration variable (TCV), DIII-D and mega amp spherical torus (MAST) tokamaks. The internal helical deformations only weakly modulate the plasma-vacuum interface which is more sensitive to ripple and resonant magnetic perturbations. On the other hand, the external perturbations do not alter the helical core deformation in a significant manner. The confinement of fast particles in MAST simulations deteriorate with the amplitude of the helical core distortion. These three-dimensional bifurcated solutions constitute a paradigm shift that motivates the applications of tools developed for stellarator research in tokamak physics investigations.

  1. Progress in development of the neutron profile monitor for the large helical device

    SciTech Connect

    Ogawa, K. Kobuchi, T.; Isobe, M.; Takeiri, Y.; Takada, E.; Uchida, Y.; Ochiai, K.; Tomita, H.; Uritani, A.

    2014-11-15

    The neutron profile monitor stably operated at a high-count-rate for deuterium operations in the Large Helical Device has been developed to enhance the research on the fast-ion confinement. It is composed of a multichannel collimator, scintillation-detectors, and a field programmable gate array circuit. The entire neutron detector system was tested using an accelerator-based neutron generator. This system stably acquires the pulse data without any data loss at high-count-rate conditions up to 8 × 10{sup 5} counts per second.

  2. Pulse stretcher

    DOEpatents

    Horton, James A.

    1994-01-01

    Apparatus (20) for increasing the length of a laser pulse to reduce its peak power without substantial loss in the average power of the pulse. The apparatus (20) uses a White cell (10) having a plurality of optical delay paths (18a-18d) of successively increasing number of passes between the field mirror (13) and the objective mirrors (11 and 12). A pulse (26) from a laser (27) travels through a multi-leg reflective path (28) between a beam splitter (21) and a totally reflective mirror (24) to the laser output (37). The laser pulse (26) is also simultaneously injected through the beam splitter (21) to the input mirrors (14a-14d) of the optical delay paths (18a-18d). The pulses from the output mirrors (16a-16d) of the optical delay paths (18a-18d) go simultaneously to the laser output (37) and to the input mirrors ( 14b-14d) of the longer optical delay paths. The beam splitter (21) is 50% reflective and 50% transmissive to provide equal attenuation of all of the pulses at the laser output (37).

  3. Growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices on +c-GaN template in dynamic atomic layer epitaxy

    NASA Astrophysics Data System (ADS)

    Kusakabe, Kazuhide; Hashimoto, Naoki; Itoi, Takaomi; Wang, Ke; Imai, Daichi; Yoshikawa, Akihiko

    2016-04-01

    The growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices (SPSs) were investigated with their application to ordered alloys in mind. The SPSs were grown on +c-GaN template at 650 °C by dynamic atomic layer epitaxy in conventional plasma-assisted molecular beam epitaxy. It was found that coherent structured InN/GaN SPSs could be fabricated when the thickness of the GaN barrier was 4 ML or above. Below 3 ML, the formation of SPSs was quite difficult owing to the increased strain in the SPS structure caused by the use of GaN as a template. The effective or average In composition of the (InN)1/(GaN)4 SPSs was around 10%, and the corresponding InN coverage in the ˜1 ML-thick InN wells was 50%. It was found that the effective InN coverage in ˜1 ML-thick InN wells could be varied with the growth conditions. In fact, the effective In composition could be increased up to 13.5%, i.e., the corresponding effective InN coverage was about 68%, by improving the capping/freezing speed by increasing the growth rate of the GaN barrier layer.

  4. ICPP: Results from Helical Axis Stellarators

    NASA Astrophysics Data System (ADS)

    Blackwell, B. D.

    2000-10-01

    Helical axis stellarators produce magnetic surfaces of high rotational transform and moderate shear solely by means of external currents, with the promise of high β. Several machines with quite different toroidal, helical, and ``bumpy'' Fourier components of magnetic field are now operating. The H-1 Heliac (1m, 1Tesla: Canberra, Australia), an M=3, low aspect ratio flexible heliac has been operated up to 0.5 Tesla with RF heating up to Ti ~ 100eV. Confinement transitions observed in this plasma exhibit many features of improved confinement regimes in tokamaks obtained at much larger power. ECH at 28GHz is being commissioned, and results from a suite of scattering, scalar and vector tomographic and multipoint probe and optical measurements will be presented. The M=4 Flexible Heliac ``TJ-II'' (1.5m, 1.2T: CIEMAT, Madrid) has accumulated a database of ECH plasma (1T) for a variety of configurations, (iota ~ 1.3--2.24) and a comprehensive set of diagnostics. Temperatures up to 2keV were measured by Thomson scattering/ECE. Observations include stored energy dependence, evidence of internal transport barriers, ELM-like bursts of magnetic activity and E×B sheared flows near rational surfaces in the plasma boundary. A new advanced configuration, the helical-axis heliotron, ``Heliotron J'' (1.2m, 1.5T: IAE, Kyoto University), the successor to Heliotron E, uses a ``bumpy'' magnetic component to improve high-energy particle confinement and reduce neoclassical transport. A combination of toroidal and helical coils produces a range of configurations. First plasma was successfully produced on December 1999, by ECH at 53GHz(2ω_ce). Following field mapping and final installation of diagnostics, the full experiment will start July 2000. The Helically Symmetric Experiment, ``HSX'' (Univ. Wisconsin, Madison) employs computer optimized non-planar coils to exploit a quasi-symmetry that minimizes toroidal magnetic field harmonics, confirmed by recent mapping of the drift orbits

  5. Cryo-EM Structure Determination Using Segmented Helical Image Reconstruction.

    PubMed

    Fromm, S A; Sachse, C

    2016-01-01

    Treating helices as single-particle-like segments followed by helical image reconstruction has become the method of choice for high-resolution structure determination of well-ordered helical viruses as well as flexible filaments. In this review, we will illustrate how the combination of latest hardware developments with optimized image processing routines have led to a series of near-atomic resolution structures of helical assemblies. Originally, the treatment of helices as a sequence of segments followed by Fourier-Bessel reconstruction revealed the potential to determine near-atomic resolution structures from helical specimens. In the meantime, real-space image processing of helices in a stack of single particles was developed and enabled the structure determination of specimens that resisted classical Fourier helical reconstruction and also facilitated high-resolution structure determination. Despite the progress in real-space analysis, the combination of Fourier and real-space processing is still commonly used to better estimate the symmetry parameters as the imposition of the correct helical symmetry is essential for high-resolution structure determination. Recent hardware advancement by the introduction of direct electron detectors has significantly enhanced the image quality and together with improved image processing procedures has made segmented helical reconstruction a very productive cryo-EM structure determination method.

  6. Faraday signature of magnetic helicity from reduced depolarization

    SciTech Connect

    Brandenburg, Axel; Stepanov, Rodion

    2014-05-10

    Using one-dimensional models, we show that a helical magnetic field with an appropriate sign of helicity can compensate the Faraday depolarization resulting from the superposition of Faraday-rotated polarization planes from a spatially extended source. For radio emission from a helical magnetic field, the polarization as a function of the square of the wavelength becomes asymmetric with respect to zero. Mathematically speaking, the resulting emission occurs then either at observable or at unobservable (imaginary) wavelengths. We demonstrate that rotation measure (RM) synthesis allows for the reconstruction of the underlying Faraday dispersion function in the former case, but not in the latter. The presence of positive magnetic helicity can thus be detected by observing positive RM in highly polarized regions in the sky and negative RM in weakly polarized regions. Conversely, negative magnetic helicity can be detected by observing negative RM in highly polarized regions and positive RM in weakly polarized regions. The simultaneous presence of two magnetic constituents with opposite signs of helicity is shown to possess signatures that can be quantified through polarization peaks at specific wavelengths and the gradient of the phase of the Faraday dispersion function. Similar polarization peaks can tentatively also be identified for the bi-helical magnetic fields that are generated self-consistently by a dynamo from helically forced turbulence, even though the magnetic energy spectrum is then continuous. Finally, we discuss the possibility of detecting magnetic fields with helical and non-helical properties in external galaxies using the Square Kilometre Array.

  7. Evolution of field line helicity during magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Russell, A. J. B.; Yeates, A. R.; Hornig, G.; Wilmot-Smith, A. L.

    2015-03-01

    We investigate the evolution of field line helicity for magnetic fields that connect two boundaries without null points, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field connectivity and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a complex magnetic field, the evolution of field line helicity is dominated by a work-like term that is evaluated at the field line endpoints, namely, the scalar product of the generalized field line velocity and the vector potential. Furthermore, the flux integral of this term over certain areas is very small compared to the integral of the unsigned quantity, which indicates that changes of field line helicity happen in a well-organized pairwise manner. It follows that reconnection is very efficient at redistributing helicity in complex magnetic fields despite having little effect on the total helicity.

  8. Evolution of field line helicity during magnetic reconnection

    SciTech Connect

    Russell, A. J. B. Hornig, G.; Wilmot-Smith, A. L.; Yeates, A. R.

    2015-03-15

    We investigate the evolution of field line helicity for magnetic fields that connect two boundaries without null points, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field connectivity and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a complex magnetic field, the evolution of field line helicity is dominated by a work-like term that is evaluated at the field line endpoints, namely, the scalar product of the generalized field line velocity and the vector potential. Furthermore, the flux integral of this term over certain areas is very small compared to the integral of the unsigned quantity, which indicates that changes of field line helicity happen in a well-organized pairwise manner. It follows that reconnection is very efficient at redistributing helicity in complex magnetic fields despite having little effect on the total helicity.

  9. Cryo-EM Structure Determination Using Segmented Helical Image Reconstruction.

    PubMed

    Fromm, S A; Sachse, C

    2016-01-01

    Treating helices as single-particle-like segments followed by helical image reconstruction has become the method of choice for high-resolution structure determination of well-ordered helical viruses as well as flexible filaments. In this review, we will illustrate how the combination of latest hardware developments with optimized image processing routines have led to a series of near-atomic resolution structures of helical assemblies. Originally, the treatment of helices as a sequence of segments followed by Fourier-Bessel reconstruction revealed the potential to determine near-atomic resolution structures from helical specimens. In the meantime, real-space image processing of helices in a stack of single particles was developed and enabled the structure determination of specimens that resisted classical Fourier helical reconstruction and also facilitated high-resolution structure determination. Despite the progress in real-space analysis, the combination of Fourier and real-space processing is still commonly used to better estimate the symmetry parameters as the imposition of the correct helical symmetry is essential for high-resolution structure determination. Recent hardware advancement by the introduction of direct electron detectors has significantly enhanced the image quality and together with improved image processing procedures has made segmented helical reconstruction a very productive cryo-EM structure determination method. PMID:27572732

  10. SMART Observation of Magnetic Helicity in Solar Filaments

    NASA Astrophysics Data System (ADS)

    Hagino, M.; Kitai, R.; Shibata, K.

    2006-08-01

    We examined the magnetic helicity of solar filaments from their structure in the chromosphere and corona. The H-alpha telescope of the Solar Magnetic Activity Research Telescope (SMART) observed 239 intermediate filaments from 2005 July 1 to 2006 May 15. The intermediate filament usually locates between two active regions. Using these images, we identified the filament spine and its barbs, and determined the chromospheric filament helicity from the mean angle between each barbs and a spine. We found that 71% (78 of 110) of intermediate filaments in the northern hemisphere are negative helicity and 67% (87 of 129) of filaments in the southern hemisphere are positive, which agreed with the well-known hemispheric tendency of the magnetic helicity. Additionally, we studied the coronal helicity of intermediate filaments. The coronal filament helicity is defined as the crossing angle of threads formed a filament. The helicity pattern of coronal filaments obtained with EIT/SOHO 171A also shows the helicity hemispheric tendency. Namely, 65% (71 of 110) of coronal filaments in the northern hemisphere exhibit negative helicity and the 65% (84 of 129) of filaments in the southern hemisphere show negative helicity. These data were observed in the same day with the SMART H-alpha data. Moreover, we found 12 filament eruptions in our data. The 7 of 12 filaments show the clear opposite sign of the hemispheric tendency of the magnetic helicity. The helicity seems to be change during temporal evolution. This results suggest that filament instability may be driven by the opposite sign helicity injection from the foot point of the barb.

  11. New Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence

    NASA Astrophysics Data System (ADS)

    Banerjee, Supratik; Galtier, Sebastien

    2016-04-01

    Hall magnetohydrodynamics is a mono-fluid plasma model appropriate for probing Final{some of the} physical processes (other than pure kinetic effects) at length scales smaller than the scales of standard MHD. In sub-ionic space plasma turbulence (e.g. the solar wind) this fluid model has been proved to be useful. Three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses three inviscid invariants which are the total energy, the magnetic helicity and the generalized helicity. In this presentation, we would like to discuss new exact relations for helicities (magnetic helicities and generalized helicities) which are derived for homogeneous stationary (not necessarily isotropic) Hall MHD turbulence (and also for its inertialess electron MHD limit) in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e. the scalar product of two different increments and are written simply as ηM = di < δ ( {b} × {j}) \\cdot δ {b} >, with ηM the average magnetic helicity flux rate, {b} the magnetic field, {j} the current and ± ηG = < δ ( {v} × {Ω} ) \\cdot δ {Ω} > , with ηM the average generalized helicity flux rate, {v} the fluid velocity and {Ω} = {b} + dI {ω} being the generalized helicity where ω is simply the fluid vorticity ( = nabla × {v}). It provides, therefore, a direct measurement of the dissipation rates for the corresponding helicities even in case of an anisotropic plasma turbulence. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations while the magnetic helicity cascade is linked to the right polarized fluctuations. The newly derived relations also show that like energy, a non-zero helicity flux can only be associated to a departure of Beltrami flow state. {Reference} S. Banerjee & S. Galtier, {Chiral Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence} (submitted).

  12. Helical muon beam cooling channel engineering design

    SciTech Connect

    Johnson, Rolland

    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

  13. Resistive Interchange Modes Destabilized by Helically Trapped Energetic Ions in a Helical Plasma

    NASA Astrophysics Data System (ADS)

    Du, X. D.; Toi, K.; Osakabe, M.; Ohdachi, S.; Ido, T.; Tanaka, K.; Yokoyama, M.; Yoshinuma, M.; Ogawa, K.; Watanabe, K. Y.; Isobe, M.; Nagaoka, K.; Ozaki, T.; Sakakibara, S.; Seki, R.; Shimizu, A.; Suzuki, Y.; Tsuchiya, H.

    2015-04-01

    A new bursting m =1 /n =1 instability (m ,n : poloidal and toroidal mode numbers) with rapid frequency chirping down has been observed for the first time in a helical plasma with intense perpendicular neutral beam injection. This is destabilized in the plasma peripheral region by resonant interaction between helically trapped energetic ions and the resistive interchange mode. A large radial electric field is induced near the edge due to enhanced radial transport of the trapped energetic ions by the mode, and leads to clear change in toroidal plasma flow, suppression of microturbulence, and triggering an improvement of bulk plasma confinement.

  14. Coordination chemistry strategies for dynamic helicates: time-programmable chirality switching with labile and inert metal helicates.

    PubMed

    Miyake, Hiroyuki; Tsukube, Hiroshi

    2012-11-01

    'Chirality switching' is one of the most important chemical processes controlling many biological systems. DNAs and proteins often work as time-programmed functional helices, in which specific external stimuli alter the helical direction and tune the time scale of subsequent events. Although a variety of organic foldamers and their hybrids with natural helices have been developed, we highlight coordination chemistry strategies for development of structurally and functionally defined metal helicates. These metal helicates have characteristic coordination geometries, redox reactivities and spectroscopic/magnetic properties as well as complex chiralities. Several kinds of inert metal helicates maintain rigid helical structures and their stereoisomers are separable by optical resolution techniques, while labile metal helicates offer dynamic inversion of their helical structures via non-covalent interactions with external chemical signals. The latter particularly have dynamically ordered helical structures, which are controlled by the combinations of metal centres and chiral ligands. They further function as time-programmable switches of chirality-derived dynamic rotations, translations, stretching and shape flipping, which are useful applications in nanoscience and related technology.

  15. Helical growth in plant organs: mechanisms and significance.

    PubMed

    Smyth, David R

    2016-09-15

    Many plants show some form of helical growth, such as the circular searching movements of growing stems and other organs (circumnutation), tendril coiling, leaf and bud reversal (resupination), petal arrangement (contortion) and leaf blade twisting. Recent genetic findings have revealed that such helical growth may be associated with helical arrays of cortical microtubules and of overlying cellulose microfibrils. An alternative mechanism of coiling that is based on differential contraction within a bilayer has also recently been identified and underlies at least some of these growth patterns. Here, I provide an overview of the genes and cellular processes that underlie helical patterning. I also discuss the diversity of helical growth patterns in plants, highlighting their potential adaptive significance and comparing them with helical growth patterns in animals. PMID:27624832

  16. Dispersion phenomena in helical flow in a concentric annulus.

    PubMed

    Song, Young Seok; Brenner, Howard

    2009-12-14

    We examined dispersion phenomena of solutes in helical flow in a concentric annulus through a multiscale approach. The helical flow was developed by the combination of the Poiseuille flow and Couette flow. Here, we present an analytic model that can address the multidimensional Taylor dispersion in the helical flow under a lateral field of thermophoresis (or thermal diffusion) in the gapwise direction. Macroscopic parameters including the average solute velocity and dispersivity were analyzed using relevant microscopic physicochemical properties. The mathematically obtained results were validated by the numerical simulation carried out in this study. The findings show that macrotransport processes are robust and straightforward to handle multidimensional dispersion phenomena of solutes in helical flow. This study is expected to provide a theoretical platform for applications of helical flow such as tube exchangers, oil drilling, and multidimensional field flow fractionations (e.g., helical flow field flow fractionation). PMID:20001025

  17. Dispersion phenomena in helical flow in a concentric annulus

    NASA Astrophysics Data System (ADS)

    Song, Young Seok; Brenner, Howard

    2009-12-01

    We examined dispersion phenomena of solutes in helical flow in a concentric annulus through a multiscale approach. The helical flow was developed by the combination of the Poiseuille flow and Couette flow. Here, we present an analytic model that can address the multidimensional Taylor dispersion in the helical flow under a lateral field of thermophoresis (or thermal diffusion) in the gapwise direction. Macroscopic parameters including the average solute velocity and dispersivity were analyzed using relevant microscopic physicochemical properties. The mathematically obtained results were validated by the numerical simulation carried out in this study. The findings show that macrotransport processes are robust and straightforward to handle multidimensional dispersion phenomena of solutes in helical flow. This study is expected to provide a theoretical platform for applications of helical flow such as tube exchangers, oil drilling, and multidimensional field flow fractionations (e.g., helical flow field flow fractionation).

  18. Dispersion phenomena in helical flow in a concentric annulus.

    PubMed

    Song, Young Seok; Brenner, Howard

    2009-12-14

    We examined dispersion phenomena of solutes in helical flow in a concentric annulus through a multiscale approach. The helical flow was developed by the combination of the Poiseuille flow and Couette flow. Here, we present an analytic model that can address the multidimensional Taylor dispersion in the helical flow under a lateral field of thermophoresis (or thermal diffusion) in the gapwise direction. Macroscopic parameters including the average solute velocity and dispersivity were analyzed using relevant microscopic physicochemical properties. The mathematically obtained results were validated by the numerical simulation carried out in this study. The findings show that macrotransport processes are robust and straightforward to handle multidimensional dispersion phenomena of solutes in helical flow. This study is expected to provide a theoretical platform for applications of helical flow such as tube exchangers, oil drilling, and multidimensional field flow fractionations (e.g., helical flow field flow fractionation).

  19. Helicity Inferences Stemming from a Mean-Field Solar Dynamo

    NASA Astrophysics Data System (ADS)

    Pipin, Valery

    The global magnetic field of the Sun is generated by dynamo instability that stems from interactions of magnetic field with the large and small-scale flows. Theoretically, it is expected that such interactions produce a helical magnetic field which evolves following to magnetic helicity conservation law. We discuss some consequences of magnetic helicity conservation for the mean-field solar dynamo. We also discuss the observational aspect of the problem including the recent results about observations of the current helicity of solar active regions, the magnetic helicity of the global magnetic field as revealed by SOHO/MDI observations, and the problem of magnetic helicity transport from the solar convection zone to the outer atmosphere.

  20. Density of states of helically symmetric boron carbon nitride nanotubes.

    PubMed

    Carvalho, A C M; Bezerra, C G; Lawlor, J A; Ferreira, M S

    2014-01-01

    Motivated by the existence of helical wrapping patterns in composite nanotube systems, in this work we study the effects of the helical incorporation of carbon atoms in boron nitride nanotubes. We consider the substitutional carbon atoms distributed in stripes forming helical patterns along the nanotube axis. The density of states and energy band gap were calculated adopting Green function formalism by using the Rubio-Sancho technique in order to solve the matrix Dyson equation. We report the effects of the helical atomic distribution of carbon atoms on the behaviour of the density of states and the energy band gap. In particular, we show that the electronic energy band gap displays a non-monotonical dependence on the helical pattern, oscillating as a function of the helical angle θ.

  1. Non-Kolmogorov cascade of helicity-driven turbulence.

    PubMed

    Kessar, Mouloud; Plunian, Franck; Stepanov, Rodion; Balarac, Guillaume

    2015-09-01

    We solve the Navier-Stokes equations with two simultaneous forcings. One forcing is applied at a given large scale and it injects energy. The other forcing is applied at all scales belonging to the inertial range and it injects helicity. In this way we can vary the degree of turbulence helicity from nonhelical to maximally helical. We find that increasing the rate of helicity injection does not change the energy flux. On the other hand, the level of total energy is strongly increased and the energy spectrum gets steeper. The energy spectrum spans from a Kolmogorov scaling law k^{-5/3} for a nonhelical turbulence, to a non-Kolmogorov scaling law k^{-7/3} for a maximally helical turbulence. In the latter case we find that the characteristic time of the turbulence is not the turnover time but a time based on the helicity injection rate. We also analyze the results in terms of helical modes decomposition. For a maximally helical turbulence one type of helical mode is found to be much more energetic than the other one, by several orders of magnitude. The energy cascade of the most energetic type of helical mode results from the sum of two fluxes. One flux is negative and can be understood in terms of a decimated model. This negative flux, however, is not sufficient to lead an inverse energy cascade. Indeed, the other flux involving the least energetic type of helical mode is positive and the largest. The least energetic type of helical mode is then essential and cannot be neglected.

  2. On the Origin of Magnetic Helicity in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Tian, Lirong; Alexander, David

    2008-01-01

    Twenty-three active regions associated with pronounced sigmoidal structure in Yohkoh soft X-ray observations are selected to investigate the origin of magnetic helicity in the solar corona. We calculate the radial magnetic flux of each polarity, the rate of magnetic helicity injection, and total flux of the helicity injection (Δ HLCT) over 4-5 days using MDI 96 minute line-of-sight magnetograms and a local correlation tracking technique. We also estimate the contribution from differential rotation to the overall helicity budget (Δ Hrot). It is found that of the seven active regions for which the flux emergence exceeds 1.0 × 1022 Mx, six exhibited a helicity flux injection exceeding 1.0 × 1043 Mx2 (i.e., Δ H = Δ HLCT - Δ Hrot). Moreover, the rate of helicity injection and the total helicity flux are larger (smaller) during periods of more (less) increase of magnetic flux. Of the remaining 16 active regions, with flux emergence less than 1022 Mx, only 4 had significant injection of helicity, exceeding 1043 Mx2. Typical contributions from differential rotation over the same period were 2-3 times smaller than that of the strong magnetic field emergence. These statistical results signify that the strong emergence of magnetic field is the most important origin of the coronal helicity, while horizontal motions and differential rotation are insufficient to explain the measured helicity injection flux. Furthermore, the study of the helicity injection in nineteen newly emerging active regions confirms the result on the important role played by strong magnetic flux emergence in controlling the injection of magnetic helicity into the solar corona.

  3. Ureterolithiasis: classical and atypical findings on unenhanced helical computed tomography.

    PubMed

    Vaswani, Kuldeep K; El-Dieb, Adam; Vitellas, Kenneth M; Bennett, William F; Bova, James G

    2002-03-01

    Evaluation of patients with acute flank pain using helical computed tomography (CT) is a well-accepted, rapid, and safe procedure in the emergency setting. Various primary and secondary signs are described in the literature for evaluation of these patients. Our purpose is to demonstrate both the classical findings associated with ureteral calculi on unenhanced helical CT and atypical findings and potential pitfalls. We also provide readers with a systematic approach to interpreting unenhanced helical CT scans performed for acute flank pain.

  4. Development of steady-state operation using ion cyclotron heating in the Large Helical Device

    NASA Astrophysics Data System (ADS)

    Kasahara, H.; Seki, T.; Saito, K.; Seki, R.; Kumazawa, R.; Yoshimura, Y.; Kubo, S.; Shimozuma, T.; Igami, H.; Takahashi, H.; Nagasaki, K.; Ueda, Y.; Tokitani, M.; Ashikawa, N.; Shoji, M.; Wakatsuki, T.; Kamio, S.; Tsuchiya, H.; Yoshimura, S.; Tamura, N.; Suzuki, C.; Yamada, H.; Mutoh, T.

    2014-06-01

    Using a handshake shape (HAS) antenna phasing dipole for ion cyclotron heating (ICH), the heating efficiency was higher than that using a previous poloidal array antenna in the Large Helical Device. In order to sustain the dipole operation, real-time feedback for impedance matching and maintaining the same phase and power was adopted during long-pulse discharge. The HAS antenna was designed to reduce parasitic losses associated with energetic particle and radio-frequency (RF) sheath effects by field-aligned current concentration on the midplane. Local hot spots and the inhomogeneity of the diverter heat profile in the toroidal direction were reduced. The long-pulse discharge with an electron density (ne0) of 1 × 1019 m-3, center electron temperature (Te0) of 2.5 keV, a plasma duration time (td) of 19 min, and RF heating power (PRF) of 1 MW was achieved by ICH and electron cyclotron heating.

  5. Ultraviolet GaN photodetectors on Si via oxide buffer heterostructures with integrated short period oxide-based distributed Bragg reflectors and leakage suppressing metal-oxide-semiconductor contacts

    SciTech Connect

    Szyszka, A. E-mail: adam.szyszka@pwr.wroc.pl; Haeberlen, M.; Storck, P.; Thapa, S. B.; Schroeder, T.

    2014-08-28

    Based on a novel double step oxide buffer heterostructure approach for GaN integration on Si, we present an optimized Metal-Semiconductor-Metal (MSM)-based Ultraviolet (UV) GaN photodetector system with integrated short-period (oxide/Si) Distributed Bragg Reflector (DBR) and leakage suppressing Metal-Oxide-Semiconductor (MOS) electrode contacts. In terms of structural properties, it is demonstrated by in-situ reflection high energy electron diffraction and transmission electron microscopy-energy dispersive x-ray studies that the DBR heterostructure layers grow with high thickness homogeneity and sharp interface structures sufficient for UV applications; only minor Si diffusion into the Y{sub 2}O{sub 3} films is detected under the applied thermal growth budget. As revealed by comparative high resolution x-ray diffraction studies on GaN/oxide buffer/Si systems with and without DBR systems, the final GaN layer structure quality is not significantly influenced by the growth of the integrated DBR heterostructure. In terms of optoelectronic properties, it is demonstrated that—with respect to the basic GaN/oxide/Si system without DBR—the insertion of (a) the DBR heterostructures and (b) dark current suppressing MOS contacts enhances the photoresponsivity below the GaN band-gap related UV cut-off energy by almost up to two orders of magnitude. Given the in-situ oxide passivation capability of grown GaN surfaces and the one order of magnitude lower number of superlattice layers in case of higher refractive index contrast (oxide/Si) systems with respect to classical III-N DBR superlattices, virtual GaN substrates on Si via functional oxide buffer systems are thus a promising robust approach for future GaN-based UV detector technologies.

  6. Helical structure of Bordetella pertussis fimbriae.

    PubMed Central

    Steven, A C; Bisher, M E; Trus, B L; Thomas, D; Zhang, J M; Cowell, J L

    1986-01-01

    The helical structures of Bordetella pertussis fimbriae of serotypes 2 and 6 were determined by optical diffraction analysis of electron micrographs of negatively stained paracrystalline bundles of purified fimbriae. The fimbrial structure is based on an axial repeat of 13 nm that contains five repeating units in two complete turns of a single-start helix. This structure was confirmed by direct measurements of mass per unit length for individual fimbriae performed by dark-field scanning transmission electron microscopy of unstained specimens. These data further established that the helically repeating unit is a monomer of fimbrial protein (Mr congruent to 22,000 for type 2 and Mr congruent to 21,500 for type 6). Radial density profiles calculated from the scanning transmission electron micrographs showed that the fimbria has peak density at its center, i.e., no axial channel, consistent with the results of conventional negative-staining electron microscopy. The radial profile gives an outermost diameter of approximately 7.5 nm, although the peripheral density is, on average, diffuse, allowing sufficient intercalation between adjacent fimbriae to give a center-to-center spacing of approximately 5.5 nm in the paracrystals. Despite serological and biochemical differences between type 2 and type 6 fimbriae, the packing arrangements of their fimbrial subunits are identical. From this observation, we infer that the respective subunits may have in common conserved regions whose packing dictates the helical geometry of the fimbria. It is plausible that a similar mechanism may underlie the phenomenon of phase variations in other systems of bacterial fimbriae. Images PMID:2875062

  7. The helical decomposition and the instability assumption

    NASA Technical Reports Server (NTRS)

    Waleffe, Fabian A.

    1993-01-01

    Direct numerical simulations show that the triadic transfer function T(k,p,q) peaks sharply when q (or p) is much smaller than k. The triadic transfer function T(k,p,q) gives the rate of energy input into wave number k from all interactions with modes of wave number p and q, where k, p, q form a triangle. This observation was thought to suggest that energy is cascaded downscale through non-local interactions with local transfer and that there was a strong connection between large and small scales. Both suggestions were in contradiction with the classical Kolmogorov picture of the energy cascade. The helical decomposition was found useful in distinguishing between kinematically independent interactions. That analysis has gone beyond the question of non-local interaction with local transfer. In particular, an assumption about the statistical direction of triadic energy transfer in any kinematically independent interaction was introduced (the instability assumption). That assumption is not necessary for the conclusions about non-local interactions with local transfer recalled above. In the case of turbulence under rapid rotation, the instability assumption leads to the prediction that energy is transferred in spectral space from the poles of the rotation axis toward the equator. The instability assumption is thought to be of general validity for any type of triad interactions (e.g. internal waves). The helical decomposition and the instability assumption offer detailed information about the homogeneous statistical dynamics of the Navier-Stokes equations. The objective was to explore the validity of the instability assumption and to study the contributions of the various types of helical interactions to the energy cascade and the subgrid-scale eddy-viscosity. This was done in the context of spectral closures of the Direct Interaction or Quasi-Normal type.

  8. Helical Magnetic Fields from Sphaleron Decay and Baryogenesis

    SciTech Connect

    Copi, Craig J.; Ferrer, Francesc; Vachaspati, Tanmay; Achucarro, Ana

    2008-10-24

    Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields, though the helicity created is smaller than earlier analytical estimates. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics.

  9. Helical Magnetic Fields from Sphaleron Decay and Baryogenesis

    NASA Astrophysics Data System (ADS)

    Copi, Craig J.; Ferrer, Francesc; Vachaspati, Tanmay; Achúcarro, Ana

    2008-10-01

    Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields, though the helicity created is smaller than earlier analytical estimates. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics.

  10. Applying of helicity in an analysis of a severe sandstorm

    NASA Astrophysics Data System (ADS)

    Tao, Jian-hong; Wang, Jin-song; Feng, Jian-ying; Chang, Yue; Liu, Xiao-li

    2005-08-01

    The helicity of a severe sandstorm happened in Northwest China was analyzed by using global reanalysis grid data of NCEP/NCAR for 4 times a day. As an important physical parameter in analyzing and predicting severe convective weather, the helicity also has good indication in the forecasting of sandstorm. The distribution of helicity over the sandstorm area was negative at higher levels and positive at lower levels. There was definite relationship between the evolvement of helicity's negative value at higher levels and the occurrence of sandstorm.

  11. The global distribution of magnetic helicity in the solar corona

    NASA Astrophysics Data System (ADS)

    Yeates, A. R.; Hornig, G.

    2016-10-01

    By defining an appropriate field line helicity, we apply the powerful concept of magnetic helicity to the problem of global magnetic field evolution in the Sun's corona. As an ideal-magnetohydrodynamic invariant, the field line helicity is a meaningful measure of how magnetic helicity is distributed within the coronal volume. It may be interpreted, for each magnetic field line, as a magnetic flux linking with that field line. Using magneto-frictional simulations, we investigate how field line helicity evolves in the non-potential corona as a result of shearing by large-scale motions on the solar surface. On open magnetic field lines, the helicity injected by the Sun is largely output to the solar wind, provided that the coronal relaxation is sufficiently fast. But on closed magnetic field lines, helicity is able to build up. We find that the field line helicity is non-uniformly distributed, and is highly concentrated in twisted magnetic flux ropes. Eruption of these flux ropes is shown to lead to sudden bursts of helicity output, in contrast to the steady flux along the open magnetic field lines. Movies are available at http://www.aanda.org

  12. The formation of helical mesoporous silica nanotubes

    NASA Astrophysics Data System (ADS)

    Wan, Xiaobing; Pei, Xianfeng; Zhao, Huanyu; Chen, Yuanli; Guo, Yongmin; Li, Baozong; Hanabusa, Kenji; Yang, Yonggang

    2008-08-01

    Three chiral cationic gelators were synthesized. They can form translucent hydrogels in pure water. These hydrogels become highly viscous liquids under strong stirring. Mesoporous silica nanotubes with coiled pore channels in the walls were prepared using the self-assemblies of these gelators as templates. The mechanism of the formation of this hierarchical nanostructure was studied using transmission electron microscopy at different reaction times. The results indicated that there are some interactions between the silica source and the gelator. The morphologies of the self-assemblies of gelators changed gradually during the sol-gel transcription process. It seems that the silica source directed the organic self-assemblies into helical nanostructures.

  13. Spin transport in helical biological systems

    SciTech Connect

    Díaz, Elena; Gutierrez, Rafael

    2014-08-20

    Motivated by the recent experimental demonstration of spin selective effects in monolayers of double-stranded DNA oligomers, our work presents a minimal model to describe electron transmission through helical fields. Our model highlight that the lack of inversion symmetry due to the chirality of the potential is a key factor which will lead to a high spin-polarization (SP). We also study the stability of the SP against fluctuations of the electronic structure induced by static disorder affecting the on-site energies. In the energy regions where the spin-filtering occurs, our results remain stable against moderate disorders although the SP is slightly reduced.

  14. Helicon wave excitation with helical antennas

    SciTech Connect

    Light, M.; Chen, F.F.

    1995-04-01

    Components of the wave magnetic field in a helicon discharge have been measured with a single-turn, coaxial magnetic probe. Left- and right-handed helical antennas, as well as plane-polarized antennas, were used; and the results were compared with the field patterns computed for a nonuniform plasma. The results show that the right-hand circularly polarized mode is preferentially excited with all antennas, even those designed to excite the left-hand mode. For right-hand excitation, the radial amplitude profiles are in excellent agreement with computations. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  15. Generalized unitarity and six-dimensional helicity

    SciTech Connect

    Bern, Zvi; Dennen, Tristan; Huang, Yu-tin; Ita, Harald; Carrasco, John Joseph

    2011-04-15

    We combine the unitarity method with the six-dimensional helicity formalism of Cheung and O'Connell to construct loop-level scattering amplitudes. As a first example, we construct dimensionally regularized QCD one-loop four-point amplitudes. As a nontrivial multiloop example, we confirm that the recently constructed four-loop four-point amplitude of N=4 super-Yang-Mills theory, including nonplanar contributions, is valid for dimensions D{<=}6. We comment on the connection of our approach to the recently discussed Higgs infrared regulator and on dual conformal properties in six dimensions.

  16. [Helical CT of urinary tract: clinical applications].

    PubMed

    Roy, C; Tuchmann, C; Guth, S; Lang, H; Saussine, C; Jacqmin, D

    2000-09-01

    Helical CT is the most useful imaging modality to evaluate kidney diseases. Different imaging protocols are used to assess the correct diagnosis in each clinical situation. The nephrographic phase (between 90 and 100 s of delay after injection) is more accurate than the cortical phase (between 30 and 40 s of delay) to depict and characterise small renal masses. Multiplanar and 3D reconstruction are useful to plan partial kidney surgery or percutaneous surgery of lithiasis. In emergency, spiral CT, if available, is suitable to assess renal colic. Spiral CT is the best modality to evaluate traumatic kidney.

  17. Inverse moments equilibria for helical anisotropic systems

    NASA Astrophysics Data System (ADS)

    Cooper, W. A.; Hirshman, S. P.; Depassier, M. C.

    1987-11-01

    An energy functional is devised for magnetic confinement schemes that have anisotropic plasma pressure. The minimization of this energy functional is demonstrated to reproduce components of the magnetohydrodynamic (MHD) force balance relation in systems with helical symmetry. An iterative steepest descent procedure is applied to the Fourier moments of the inverse magnetic flux coordinates to minimize the total energy and thus generate anisotropic pressure MHD equilibria. Applications to straight ELMO Snaky Torus (NTIS Document No. DE-84002406) configurations that have a magnetic well on the outermost flux surfaces have been obtained.

  18. Helical Luttinger liquid in topological insulator nanowires.

    PubMed

    Egger, R; Zazunov, A; Yeyati, A Levy

    2010-09-24

    We derive and analyze the effective low-energy theory for interacting electrons in a cylindrical nanowire made of a strong topological insulator. Three different approaches provide a consistent picture for the band structure, where surface states forming inside the bulk gap correspond to one-dimensional bands indexed by total angular momentum. When a half-integer magnetic flux pierces the nanowire, we find a strongly correlated helical Luttinger liquid topologically protected against weak disorder. We describe how transport experiments can detect this state.

  19. Dissipation of Energy, Cross Helicity, and Magnetic Helicity in Ideal MHD

    NASA Astrophysics Data System (ADS)

    Aluie, Hussein; Eyink, Gregory L.; Vishniac, Ethan T.

    2007-11-01

    The ``invariants'' of ideal MHD--energy, cross helicity, and magnetic helicity--need not be conserved in the limit of zero viscosity and resistivity if the solution fields become singular. This is observed to occur in MHD turbulence, where the effective dissipation is due to nonlinear cascade of the invariants to small-scales. We study the large-scale balances of the three invariants via a ``coarse-graining'' approach related to Wilson-Kadanoff renormalization group. The ideal dissipation in this framework is due to ``turbulent stress'' and ``turbulent EMF'' generated by eliminated plasma motions below the coarse-graining length. We derive upper bounds on these turbulent contributions to the MHD equations and improve the necessary conditions of [1] for ideal dissipation. In particular, we show that the conditions for turbulent dissipation/forward cascade of magnetic helicity are so severe--infinite 3rd-order moments of the velocity & magnetic fields!--that they are unlikely to ever naturally occur. We also establish local balance equations in space-time of the three invariants, both for measurable ``coarsed-grained'' variables and also for ``bare'' fields. On this basis we give physical interpretations of the turbulent cascades, in terms of work concepts for energy and in terms of topological linkage [2] for the two helicities. [1] Caflisch et al. 1997 Comm. Math. Phys. 184, 443-455 [2] Moffatt, H. K. 1969 J. Fluid Mech. 35, 117-129.

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

    NASA Astrophysics Data System (ADS)

    Kundu, Sourav; Karmakar, S. N.

    2016-07-01

    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.

  1. Dynamic characteristics of pulsed supersonic fuel sprays

    NASA Astrophysics Data System (ADS)

    Pianthong, K.; Matthujak, A.; Takayama, K.; Milton, B. E.; Behnia, M.

    2008-06-01

    This paper describes the dynamic characteristics of pulsed, supersonic liquid fuel sprays or jets injected into ambient air. Simple, single hole nozzles were employed with the nozzle sac geometries being varied. Different fuel types, diesel fuel, bio-diesel, kerosene, and gasoline were used to determine the effects of fuel properties on the spray characteristics. A vertical two-stage light gas gun was employed as a projectile launcher to provide a high velocity impact to produce the liquid jet. The injection pressure was around 0.88-1.24 GPa in all cases. The pulsed, supersonic fuel sprays were visualized by using a high-speed video camera and shadowgraph method. The spray tip penetration and velocity attenuation and other characteristics were examined and are described here. An instantaneous spray tip velocity of 1,542 m/s (Mach number 4.52) was obtained. However, this spray tip velocity can be sustained for only a very short period (a few microseconds). It then attenuates very quickly. The phenomenon of multiple high frequency spray pulses generated by a single shot impact and the changed in the angle of the shock structure during the spray flight, which had already been observed in previous studies, is again noted. Multiple shock waves from the conical nozzle spray were also clearly captured.

  2. PULSE COUNTER

    DOEpatents

    Trumbo, D.E.

    1959-02-10

    A transistorized pulse-counting circuit adapted for use with nuclear radiation detecting detecting devices to provide a small, light weight portable counter is reported. The small size and low power requirements of the transistor are of particular value in this instance. The circuit provides an adjustable count scale with a single transistor which is triggered by the accumulated charge on a storage capacitor.

  3. Helicity of the Solar Magnetic Field

    NASA Astrophysics Data System (ADS)

    Tiwari, Sanjiv Kumar

    2009-11-01

    Magnetic helicity is a physical quantity that measures the degree of linkages and twistedness in the field lines. It is given by a volume integral over the scalar product of magnetic field B and its vector potential A. Direct computation of magnetic helicity in the solar atmosphere is not possible due to two reasons. First, we do not have the observations at different heights in the solar atmosphere to compute the volume integral. Second, the vector potential A is non-unique owing to gauge variance. Many researchers incorrectly inferred twist, a component of magnetic helicity, from the force-free parameter α. We clarified the physical meaning of α and its relation with the magnetic helicity. Also, a direct method is proposed for the computation of global α values of sunspots. An analytical bipole was generated to study the effect of polarimetric noise on the estimation of various magnetic parameters. We find that the effect of polarimetric noise, present in the recent vector magnetograms e.g., from Hinode (Solar Optical Telescope/Spectro- Polarimeter (SOT/SP)), on the magnetic parameters like α and magnetic energy, is negligible. We examined the fine structures of local current and α in the sunspots. Local α patches of opposite signs are present in the umbra of each sunspot. The amplitude of the spatial variation of local α in the umbra is typically of the order of the global α of the sunspot. We find that the local α and current are distributed as alternately positive and negative filaments in the penumbra. The amplitude of azimuthal variation of the local α in the penumbra is approximately an order of magnitude larger than that in the umbra. The contributions of the local positive and negative currents and α in the penumbra cancel each other giving almost no contribution for their global values for whole sunspot. We have introduced the concept of signed shear angle (SSA) for sunspots and establish its importance for non force

  4. Gyrotron beam generation with helical magnetic fields

    NASA Astrophysics Data System (ADS)

    Jackson, R. H.; Sedlak, C. A.

    1983-08-01

    This report presents the results of an investigation into the basic properties of a new type of electron gun for generating high transverse velocity beams, the bifilar helix - Pierce gun or H-gun. The H-gun differs significantly from presently used magnetron injection guns (MIGs) in that first a laminar, low transverse velocity beam is formed and then transverse velocity is imparted by propagating the beam through the magnetic field of a bifilar helix. In order to evaluate the H-gun, an analytic and computational study was conducted to examine the relationships between the magnetic fields (axial and helical), and the beam properties after existing the helical field. The effects of the helix field entrance profile, the helix-axial field gyroresonance, and helix field gradients have been taken into account in the investigation. Based on the results of this research, conditions have been specified which will produce a high transverse velocity beam with low axial velocity spread. In particular, it has been found that an adiabatic helix entrance profile can provide a flexible means of generating high quality beams for gyro-devices.

  5. Determining How Magnetic Helicity Injection Really Works

    SciTech Connect

    Paul M. Bellan

    2001-10-09

    OAK-B135 The goal of the Caltech program is to determine how helicity injection works by investigating the actual dynamics and topological evolution associated with magnetic relaxation. A new coaxial helicity injection source has been constructed and brought into operation. The key feature of this source is that it has maximum geometric simplicity. Besides being important for fusion research, this work also has astrophysical implications. Photos obtained using high-speed cameras show a clear sequence of events in the formation process. In particular, they show initial merging/reconnection processes, jet-like expansion, kinking, and separation of the plasma from the source. Various diagnostics have been developed, including laser induced fluorescence and soft x-ray detection using high speed diodes. Gas valves have been improved and a patent disclosure relating to puffed gas valves has been filed. Presentations on this work have been given in the form of invited talks at several university physics departments that were previously unfamiliar with laboratory plasma experiments.

  6. Cosmic acceleration and the helicity-0 graviton

    SciTech Connect

    Rham, Claudia de; Heisenberg, Lavinia; Gabadadze, Gregory; Pirtskhalava, David

    2011-05-15

    We explore cosmology in the decoupling limit of a nonlinear covariant extension of Fierz-Pauli massive gravity obtained recently in arXiv:1007.0443. In this limit the theory is a scalar-tensor model of a unique form defined by symmetries. We find that it admits a self-accelerated solution, with the Hubble parameter set by the graviton mass. The negative pressure causing the acceleration is due to a condensate of the helicity-0 component of the massive graviton, and the background evolution, in the approximation used, is indistinguishable from the {Lambda}CDM model. Fluctuations about the self-accelerated background are stable for a certain range of parameters involved. Most surprisingly, the fluctuation of the helicity-0 field above its background decouples from an arbitrary source in the linearized theory. We also show how massive gravity can remarkably screen an arbitrarily large cosmological constant in the decoupling limit, while evading issues with ghosts. The obtained static solution is stable against small perturbations, suggesting that the degravitation of the vacuum energy is possible in the full theory. Interestingly, however, this mechanism postpones the Vainshtein effect to shorter distance scales. Hence, fifth force measurements severely constrain the value of the cosmological constant that can be neutralized, making this scheme phenomenologically not viable for solving the old cosmological constant problem. We briefly speculate on a possible way out of this issue.

  7. Neutrino helicity reversal and fundamental symmetries

    NASA Astrophysics Data System (ADS)

    Jentschura, U. D.; Wundt, B. J.

    2014-07-01

    A rather elusive helicity reversal occurs in a gedanken experiment in which a massive left-handed Dirac neutrino, traveling at a velocity u < c, is overtaken on a highway by a speeding vehicle (traveling at velocity v with u < v < c). Namely, after passing the neutrino, looking back, one would see a right-handed neutrino (which has never been observed in nature). The Lorentz-invariant mass of the right-handed neutrino is still the same as before the passing. The gedanken experiment thus implies the existence of right-handed, light neutrinos, which are not completely sterile. Furthermore, overtaking a bunch of massive right-handed Dirac neutrinos leads to gradual de-sterilization. We discuss the helicity reversal and the concomitant sterilization and de-sterilization mechanisms by way of an illustrative example calculation, with a special emphasis on massive Dirac and Majorana neutrinos. We contrast the formalism with a modified Dirac neutrino described by a Dirac equation with a pseudoscalar mass term proportional to the fifth current.

  8. Long polypeptide 310-helices at atomic resolution

    PubMed Central

    Bavoso, Alfonso; Benedetti, Ettore; Di Blasio, Benedetto; Pavone, Vincenzo; Pedone, Carlo; Toniolo, Claudio; Bonora, Gian Maria

    1986-01-01

    The crystal-state preferred conformation of the terminally blocked homooctapeptide from the Cα,α-dimethylated α-aminoisobutyric acid (Aib) residue, pBrBz-(Aib)8-OBut, in which pBrBz is para-bromobenzoyl and OBut is tert-butoxy, determined by x-ray diffraction analysis using direct methods, was found to be a 310-helix stabilized by six consecutive intramolecular N—H....O=C hydrogen bonds of the C10-III (or III′) type. This is the first observation at atomic resolution of a regular 310-helix longer than two complete turns. The solid-state structural analysis was extended to the terminally blocked, α-aminoisobutyric acid-rich octapeptide corresponding to the 2-9 sequence of the peptaibol antibiotics emerimicins III and IV, pBrBz-Aib3-L-Val-Gly-L-Leu-Aib2-OMe. Again, this peptide adopts a (right-handed) 310-helical structure, although slightly distorted at the level of the L-leucine residue. The role of specific amino acid sequence and peptide main-chain length in stabilizing either the 310- or the α-helical conformation and their possible implications on the nature of the channel formed by peptaibol antibiotics in the membrane are also briefly discussed. PMID:16593674

  9. Quantification of a Helical Origami Fold

    NASA Astrophysics Data System (ADS)

    Dai, Eric; Han, Xiaomin; Chen, Zi

    2015-03-01

    Origami, the Japanese art of paper folding, is traditionally viewed as an amusing pastime and medium of artistic expression. However, in recent years, origami has served as a source of inspiration for innovations in science and engineering. Here, we present the geometric and mechanical properties of a twisting origami fold. The origami structure created by the fold exhibits several interesting properties, including rigid foldibility, local bistability and finely tunable helical coiling, with control over pitch, radius and handedness of the helix. In addition, the pattern generated by the fold closely mimics the twist buckling patterns shown by thin materials, for example, a mobius strip. We use six parameters of the twisting origami pattern to generate a fully tunable graphical model of the fold. Finally, we present a mathematical model of the local bistability of the twisting origami fold. Our study elucidates the mechanisms behind the helical coiling and local bistability of the twisting origami fold, with potential applications in robotics and deployable structures. Acknowledgment to Branco Weiss Fellowship for funding.

  10. Transport of helical gyrotactic swimmers in channels

    NASA Astrophysics Data System (ADS)

    Alqarni, M. S.; Bearon, R. N.

    2016-07-01

    We develop a mechanistic model that describes the transport of gyrotactic cells with propulsive force and propulsive torque that are not parallel. In sufficiently weak shear this yields helical swimming trajectories, whereas in stronger shear cells can attain a stable equilibrium orientation. We obtain the stable equilibrium solution for cell orientation as a function of the shear strength and determine the feasibility region for equilibrium solutions. We compute numerically the trajectories of cells in two dimensional vertical channel flow where the shear is non-uniform. Depending on the parameter values, we show that helical swimmers may display classical gyrotactic focussing towards the centre of the channel or can display a new phenomenon of focussing away from the centre of the channel. This result can be explained by consideration of the equilibrium solution for cell orientation. In this study we consider only dilute suspensions where there is no feedback from cell swimming on the hydrodynamics, and both cell-wall and cell-cell interactions are neglected.

  11. CURRENT AND KINETIC HELICITY OF LONG-LIVED ACTIVITY COMPLEXES

    SciTech Connect

    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.

  12. VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. II. A SHORT-PERIOD COMPANION ORBITING AN F STAR WITH EVIDENCE OF A STELLAR TERTIARY AND SIGNIFICANT MUTUAL INCLINATION

    SciTech Connect

    Fleming, Scott W.; Ge Jian; De Lee, Nathan; Jiang Peng; Lee, Brian; Nelson, Ben; Barnes, Rory; Beatty, Thomas G.; Gaudi, B. Scott; Shappee, Benjamin J.; Crepp, Justin R.; Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I.; Ferreira, Leticia; Porto de Mello, Gustavo F.; Gary, Bruce; Hebb, Leslie; Stassun, Keivan; Ghezzi, Luan; and others

    2012-09-15

    We report the discovery via radial velocity (RV) measurements of a short-period (P = 2.430420 {+-} 0.000006 days) companion to the F-type main-sequence star TYC 2930-00872-1. A long-term trend in the RV data also suggests the presence of a tertiary stellar companion with P > 2000 days. High-resolution spectroscopy of the host star yields T{sub eff} = 6427 {+-} 33 K, log g = 4.52 {+-} 0.14, and [Fe/H] = -0.04 {+-} 0.05. These parameters, combined with the broadband spectral energy distribution (SED) and a parallax, allow us to infer a mass and radius of the host star of M{sub 1} = 1.21 {+-} 0.08 M{sub Sun} and R{sub 1} = 1.09{sup +0.15}{sub -0.13} R{sub Sun }. The minimum mass of the inner companion is below the hydrogen-burning limit; however, the true mass is likely to be substantially higher. We are able to exclude transits of the inner companion with high confidence. Further, the host star spectrum exhibits a clear signature of Ca H and K core emission, indicating stellar activity, but a lack of photometric variability and small vsin I suggest that the primary's spin axis is oriented in a pole-on configuration. The rotational period of the primary estimated through an activity-rotation relation matches the orbital period of the inner companion to within 1.5 {sigma}, suggesting that the primary and inner companion are tidally locked. If the inner companion's orbital angular momentum vector is aligned with the stellar spin axis as expected through tidal evolution, then it has a stellar mass of {approx}0.3-0.4 M{sub Sun }. Direct imaging limits the existence of stellar companions to projected separations <30 AU. No set of spectral lines and no significant flux contribution to the SED from either companion are detected, which places individual upper mass limits of M{sub {l_brace}2,3{r_brace}} {approx}< 1.0 M{sub Sun }, provided they are not stellar remnants. If the tertiary is not a stellar remnant, then it likely has a mass of {approx}0.5-0.6 M{sub Sun }, and its

  13. VERY-LOW-MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. III. A SHORT-PERIOD BROWN DWARF CANDIDATE AROUND AN ACTIVE G0IV SUBGIANT

    SciTech Connect

    Ma Bo; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Wang Ji; Barnes, Rory; Agol, Eric; Crepp, Justin R.; Dutra-Ferreira, Leticia; Porto de Mello, G. F.; Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I.; Ghezzi, Luan; Hebb, Leslie; Stassun, Keivan G.; Wisniewski, John P.; Bizyaev, Dmitry; and others

    2013-01-01

    We present an eccentric, short-period brown dwarf candidate orbiting the active, slightly evolved subgiant star TYC 2087-00255-1, which has effective temperature T{sub eff} = 5903 {+-} 42 K, surface gravity log (g) = 4.07 {+-} 0.16 (cgs), and metallicity [Fe/H] = -0.23 {+-} 0.07. This candidate was discovered using data from the first two years of the Multi-object APO Radial Velocity Exoplanets Large-area Survey, which is part of the third phase of Sloan Digital Sky Survey. From our 38 radial velocity measurements spread over a two-year time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 3.571 {+-} 0.041 km s{sup -1}, period P = 9.0090 {+-} 0.0004 days, and eccentricity e = 0.226 {+-} 0.011. Adopting a mass of 1.16 {+-} 0.11 M{sub Sun} for the subgiant host star, we infer that the companion has a minimum mass of 40.0 {+-} 2.5 M{sub Jup}. Assuming an edge-on orbit, the semimajor axis is 0.090 {+-} 0.003 AU. The host star is photometrically variable at the {approx}1% level with a period of {approx}13.16 {+-} 0.01 days, indicating that the host star spin and companion orbit are not synchronized. Through adaptive optics imaging we also found a point source 643 {+-} 10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 M{sub Sun} if it is physically associated with TYC 2087-00255-1 and has the same age. Future proper motion observation should be able to resolve if this tertiary object is physically associated with TYC 2087-00255-1 and make TYC 2087-00255-1 a triple body system. Core Ca II H and K line emission indicate that the host is chromospherically active, at a level that is consistent with the inferred spin period and measured v{sub rot}sin i, but unusual for a subgiant of this T{sub eff}. This activity could be explained by ongoing tidal spin-up of the host star by the companion.

  14. Helical grip for the cable cars of San Francisco

    NASA Technical Reports Server (NTRS)

    Peyran, R. J.

    1979-01-01

    A helical cable car grip to minimize high maintenance costs of San Francisco's cable car operation is presented. The grip establishes a rolling contact between the cable and grip to reduce sliding friction and associated cable wear. The design, development, and testing of the helical cable car grip are described.

  15. Experimental investigation of solar powered diaphragm and helical pumps

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  16. Numerical Simulations of Helicity Condensation in the Solar Corona

    NASA Technical Reports Server (NTRS)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-01-01

    The helicity condensation model has been proposed by Antiochos (2013) to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the system. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of, for example, a bipolar active region. The calculations demonstrate that, contrary to common belief, coronal loops having opposite helicity do not reconnect, whereas loops having the same sense of helicity do reconnect. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  17. Water tuned the helical nanostructures and supramolecular chirality in organogels.

    PubMed

    Liu, Changxia; Jin, Qingxian; Lv, Kai; Zhang, Li; Liu, Minghua

    2014-04-11

    Water was found to tune the self-assembled nanostructures of a cationic amphiphile in organic solvents from nanofibers to helical tapes, helical tubes and chiral nanotwists with various pitch lengths depending on water content. Inversion of CD spectra was observed in the water-triggered polar and non-polar solvent gels.

  18. Helical channel design and technology for cooling of muon beams

    SciTech Connect

    Yonehara, K; Derbenev, Y.S.; Johnson, R.P.; /MUONS Inc., Batavia

    2010-08-01

    Novel magnetic helical channel designs for capture and cooling of bright muon beams are being developed using numerical simulations based on new inventions such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF) cavities. We are close to the factor of a million six-dimensional phase space (6D) reduction needed for muon colliders. Recent experimental and simulation results are presented.

  19. Computing magnetic energy and helicity fluxes from series of magnetograms .

    NASA Astrophysics Data System (ADS)

    Démoulin, P.; Pariat, E.

    Magnetic energy and helicity fluxes can now be derived from measurements of the photospheric magnetic and velocity fields. We show that only photospheric flux-tube motions are needed to estimate the full fluxes. The derived maps of flux densities permit to localize where energy and helicity input occurs in active regions (ARs). The precision of the energy flux density is dominantly limited by the precision obtained on the transverse component of the magnetic field. On the contrary, the helicity flux density requires only the measurement of the vertical component of the magnetic field. Previously, the magnetic helicity maps were strongly affected by a false definition of the helicity flux density involving the magnetic vector potential. Applied to observations, this approach introduces important fake polarities. We define a better helicity flux density; it reduces the fake polarities by more than an order of magnitude. The spatial distribution of helicity injected into the studied ARs is much more coherent than previously thought, and presents a dominant sign in each AR. Finally, the correct helicity flux density could be derived from magnetograms if coronal connectivities are known.

  20. The magnetic helicity spectrum from solar vector magnetograms

    NASA Astrophysics Data System (ADS)

    Brandenburg, Axel; Zhang, Hongqi; Sokoloff, Dmitry

    2016-05-01

    The gauge-invariant (or relative) magnetic helicity is often measured to characterize the degree of magnetic complexity of active regions. However, magnetic helicity is expected to have different signs on different length scales that can be identified with the large- and small-scale fields used in dynamo theory. To address this, it is important to determine magnetic helicity spectra as functions of wavenumber. These spectra are defined such that the integral over all wavenumbers gives the usual magnetic helicity density in a particular patch of interest. Using vector magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory for active region NOAA 11515, which was on the southern hemisphere, we show that the magnetic helicity spectrum has positive sign on scales below 30 Mm, but negative sign on larger scales. This active region was rather complex and its magnetic helicity was within 26% of its theoretical maximum value. This is much more than that of NOAA 11158, which was also rather complex, but only within 5% of its theoretical maximum value. Since the contribution of larger length scales turned out to be important in the case of NOAA 11515, its total magnetic helicity is dominated by the negative values from large length scales, which explains the unusual sign for the southern hemisphere. Measuring magnetic helicity spectra with DKIST may become an important tool to learn about the workings of the underlying dynamo.

  1. Pulsed hydrojet

    DOEpatents

    Bohachevsky, I.O.; Torrey, M.D.

    1986-06-10

    An underwater pulsed hydrojet propulsion system is provided for accelerating and propelling a projectile or other vessel. A reactant, such as lithium, is fluidized and injected into a water volume. The resulting reaction produces an energy density in a time effective to form a steam pocket. Thrust flaps or baffles direct the pressure from the steam pocket toward an exit nozzle for accelerating a water volume to create thrust. A control system regulates the dispersion of reactant to control thrust characteristics.

  2. Accumulation of heavy particles around a helical vortex filament

    NASA Astrophysics Data System (ADS)

    IJzermans, Rutger H. A.; Hagmeijer, Rob; van Langen, Pieter J.

    2007-10-01

    The motion of small heavy particles near a helical vortex filament in incompressible flow is investigated. Both the configurations of a helical vortex filament in free space and a helical vortex filament in a concentric pipe are considered, and the corresponding helically symmetric velocity fields are expressed in terms of a stream function. Particle motion is assumed to be driven by Stokes drag, and the flow fields are assumed to be independent from the motion of particles. Numerical results show that heavy particles may be attracted to helical trajectories. The stability of these attraction trajectories is demonstrated by linear stability analysis. In addition, the correlation between the attraction trajectories and the streamline topologies is investigated.

  3. Chiral exact relations for helicities in Hall magnetohydrodynamic turbulence.

    PubMed

    Banerjee, Supratik; Galtier, Sébastien

    2016-03-01

    Besides total energy, three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses two inviscid invariants, which are the magnetic helicity and the generalized helicity. Exact relations are derived for homogeneous (nonisotropic) stationary Hall MHD turbulence (and also for its inertialess electron MHD limit) with nonzero helicities and in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e., the scalar product of two different increments. It provides, therefore, a direct measurement of the dissipation rates for the corresponding invariant flux. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations, while the magnetic helicity cascade is linked to the right polarized fluctuations. PMID:27078460

  4. Hierarchically arranged helical fibre actuators driven by solvents and vapours.

    PubMed

    Chen, Peining; Xu, Yifan; He, Sisi; Sun, Xuemei; Pan, Shaowu; Deng, Jue; Chen, Daoyong; Peng, Huisheng

    2015-12-01

    Mechanical responsiveness in many plants is produced by helical organizations of cellulose microfibrils. However, simple mimicry of these naturally occurring helical structures does not produce artificial materials with the desired tunable actuations. Here, we show that actuating fibres that respond to solvent and vapour stimuli can be created through the hierarchical and helical assembly of aligned carbon nanotubes. Primary fibres consisting of helical assemblies of multiwalled carbon nanotubes are twisted together to form the helical actuating fibres. The nanoscale gaps between the nanotubes and micrometre-scale gaps among the primary fibres contribute to the rapid response and large actuation stroke of the actuating fibres. The compact coils allow the actuating fibre to rotate reversibly. We show that these fibres, which are lightweight, flexible and strong, are suitable for a variety of applications such as energy-harvesting generators, deformable sensing springs and smart textiles. PMID:26367106

  5. Hierarchically arranged helical fibre actuators driven by solvents and vapours

    NASA Astrophysics Data System (ADS)

    Chen, Peining; Xu, Yifan; He, Sisi; Sun, Xuemei; Pan, Shaowu; Deng, Jue; Chen, Daoyong; Peng, Huisheng

    2015-12-01

    Mechanical responsiveness in many plants is produced by helical organizations of cellulose microfibrils. However, simple mimicry of these naturally occurring helical structures does not produce artificial materials with the desired tunable actuations. Here, we show that actuating fibres that respond to solvent and vapour stimuli can be created through the hierarchical and helical assembly of aligned carbon nanotubes. Primary fibres consisting of helical assemblies of multiwalled carbon nanotubes are twisted together to form the helical actuating fibres. The nanoscale gaps between the nanotubes and micrometre-scale gaps among the primary fibres contribute to the rapid response and large actuation stroke of the actuating fibres. The compact coils allow the actuating fibre to rotate reversibly. We show that these fibres, which are lightweight, flexible and strong, are suitable for a variety of applications such as energy-harvesting generators, deformable sensing springs and smart textiles.

  6. Chiral exact relations for helicities in Hall magnetohydrodynamic turbulence.

    PubMed

    Banerjee, Supratik; Galtier, Sébastien

    2016-03-01

    Besides total energy, three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses two inviscid invariants, which are the magnetic helicity and the generalized helicity. Exact relations are derived for homogeneous (nonisotropic) stationary Hall MHD turbulence (and also for its inertialess electron MHD limit) with nonzero helicities and in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e., the scalar product of two different increments. It provides, therefore, a direct measurement of the dissipation rates for the corresponding invariant flux. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations, while the magnetic helicity cascade is linked to the right polarized fluctuations.

  7. Hierarchical Helical Order in the Twisted Growth of Plant Organs

    NASA Astrophysics Data System (ADS)

    Wada, Hirofumi

    2012-09-01

    The molecular and cellular basis of left-right asymmetry in plant morphogenesis is a fundamental issue in biology. A rapidly elongating root or hypocotyl of twisting mutants of Arabidopsis thaliana exhibits a helical growth with a handedness opposite to that of the underlying cortical microtubule arrays in epidermal cells. However, how such a hierarchical helical order emerges is currently unknown. We propose a model for investigating macroscopic chiral asymmetry in Arabidopsis mutants. Our elastic model suggests that the helical pattern observed is a direct consequence of the simultaneous presence of anisotropic growth and tilting of cortical microtubule arrays. We predict that the root helical pitch angle is a function of the microtubule helical angle and elastic moduli of the tissues. The proposed model is versatile and is potentially important for other biological systems ranging from protein fibrous structures to tree trunks.

  8. Hierarchically arranged helical fibre actuators driven by solvents and vapours.

    PubMed

    Chen, Peining; Xu, Yifan; He, Sisi; Sun, Xuemei; Pan, Shaowu; Deng, Jue; Chen, Daoyong; Peng, Huisheng

    2015-12-01

    Mechanical responsiveness in many plants is produced by helical organizations of cellulose microfibrils. However, simple mimicry of these naturally occurring helical structures does not produce artificial materials with the desired tunable actuations. Here, we show that actuating fibres that respond to solvent and vapour stimuli can be created through the hierarchical and helical assembly of aligned carbon nanotubes. Primary fibres consisting of helical assemblies of multiwalled carbon nanotubes are twisted together to form the helical actuating fibres. The nanoscale gaps between the nanotubes and micrometre-scale gaps among the primary fibres contribute to the rapid response and large actuation stroke of the actuating fibres. The compact coils allow the actuating fibre to rotate reversibly. We show that these fibres, which are lightweight, flexible and strong, are suitable for a variety of applications such as energy-harvesting generators, deformable sensing springs and smart textiles.

  9. An Investigation of Pulse Transit Time as a Non-Invasive Blood Pressure Measurement Method

    NASA Astrophysics Data System (ADS)

    McCarthy, B. M.; O'Flynn, B.; Mathewson, A.

    2011-08-01

    The objective of this paper is to examine the Pulse Transit Method (PTT) as a non-invasive means to track Blood Pressure over a short period of time. PTT was measured as the time it takes for an ECG R-wave to propagate to the finger, where it is detected by a photoplethysmograph sensor. The PTT method is ideal for continuous 24-hour Blood Pressure Measurement (BPM) since it is both cuff-less and non-invasive and therefore comfortable and unobtrusive for the patient. Other techniques, such as the oscillometric method, have shown to be accurate and reliable but require a cuff for operation, making them unsuitable for long term monitoring. Although a relatively new technique, the PTT method has shown to be able to accurately track blood pressure changes over short periods of time, after which re-calibration is necessary. The purpose of this study is to determine the accuracy of the method.

  10. The Writhe of Helical Structures in the Solar Corona

    NASA Technical Reports Server (NTRS)

    Toeroek, T.; Berger, M. A.; Kliem, B.

    2010-01-01

    Context. Helicity is a fundamental property of magnetic fields, conserved in ideal MHD. In flux rope topology, it consists of twist and writhe helicity. Despite the common occurrence of helical structures in the solar atmosphere, little is known about how their shape relates to the writhe, which fraction of helicity is contained in writhe, and how much helicity is exchanged between twist and writhe when they erupt. Aims. Here we perform a quantitative investigation of these questions relevant for coronal flux ropes. Methods. The decomposition of the writhe of a curve into local and nonlocal components greatly facilitates its computation. We use it to study the relation between writhe and projected S shape of helical curves and to measure writhe and twist in numerical simulations of flux rope instabilities. The results are discussed with regard to filament eruptions and coronal mass ejections (CMEs). Results. (1) We demonstrate that the relation between writhe and projected S shape is not unique in principle, but that the ambiguity does not affect low-lying structures, thus supporting the established empirical rule which associates stable forward (reverse) S shaped structures low in the corona with positive (negative) helicity. (2) Kink-unstable erupting flux ropes are found to transform a far smaller fraction of their twist helicity into writhe helicity than often assumed. (3) Confined flux rope eruptions tend to show stronger writhe at low heights than ejective eruptions (CMEs). This argues against suggestions that the writhing facilitates the rise of the rope through the overlying field. (4) Erupting filaments which are S shaped already before the eruption and keep the sign of their axis writhe (which is expected if field of one chirality dominates the source volume of the eruption), must reverse their S shape in the course of the rise. Implications for the occurrence of the helical kink instability in such events are discussed.

  11. Local order and mobility of water molecules around ambivalent helices.

    PubMed

    Bhattacharjee, Nicholus; Biswas, Parbati

    2011-10-27

    Water on a protein surface plays a key role in determining the structure and dynamics of proteins. Compared to the properties of bulk water, many aspects of the structure and dynamics of the water surrounding the proteins are less understood. It is interesting therefore to explore how the properties of the water within the solvation shell around the peptide molecule depend on its specific secondary structure. In this work we investigate the orientational order and residence times of the water molecules to characterize the structure, energetics, and dynamics of the hydration shell water around ambivalent peptides. Ambivalent sequences are identical sequences which display multiple secondary structures in different proteins. Molecular dynamics simulations of representative proteins containing variable helix, variable nonhelix, and conserved helix are also used to explore the local structure and mobility of water molecules in their vicinity. The results, for the first time, depict a different water distribution pattern around the conserved and variable helices. The water molecules surrounding the helical segments in variable helices are found to possess a less locally ordered structure compared to those around their corresponding nonhelical counterparts and conserved helices. The long conserved helices exhibit extremely high local residence times compared to the helical conformations of the variable helices, whereas the residence times of the nonhelical conformations of the variable helices are comparable to those of the short conserved helices. This differential pattern of the structure and dynamics of water molecules in the vicinity of conserved/variable helices may lend valuable insights for understanding the role of solvent effects in determining sequence ambivalency and help in improving the accuracy of water models used in the simulations of proteins.

  12. Schemes for generation of isolated attosecond pulses of pure circular polarization

    NASA Astrophysics Data System (ADS)

    Hernández-García, C.; Durfee, C. G.; Hickstein, D. D.; Popmintchev, T.; Meier, A.; Murnane, M. M.; Kapteyn, H. C.; Sola, I. J.; Jaron-Becker, A.; Becker, A.

    2016-04-01

    We propose and analyze two schemes capable of generating isolated attosecond pulses of pure circular polarization, based on results of numerical simulations. Both schemes utilize the generation of circularly polarized high-order-harmonics by crossing two circularly polarized counter-rotating pulses in a noncollinear geometry. Our results show that in this setup isolation of a single attosecond pulse can be achieved either by restricting the driver pulse duration to a few cycles or by temporally delaying the two crossed driver pulses. We further propose to compensate the temporal walk-off between the pulses across the focal spot and increasing the conversion efficiency by using angular spatial chirp to provide perfectly matched pulse fronts. The isolation of pure circularly polarized attosecond pulses, along with the opportunity to select their central energy and helicity in the noncollinear technique, opens new perspectives from which to study ultrafast dynamics in chiral systems and magnetic materials.

  13. Construction of the Helicity Injected Torus with Steady Inductive Helicity Injection (HIT-SI)

    NASA Astrophysics Data System (ADS)

    Sieck, P. E.; Gu, P.; Hamp, W. T.; Izzo, V. A.; Jarboe, T. R.; Nelson, B. A.; Rogers, J. A.

    2001-10-01

    HIT-SI is a ``bow tie'' spheromak designed to implement Steady Inductive Helicity Injection (SIHI). The engineering requirements of SIHI lead to several unique design features, including a multiply connected electrically insulating o-ring seal and a close-fitting passive flux conserver that is electrically insulated from the plasma. Prototype tests have been performed to verify the performance of the o-ring seal and the plasma sprayed zirconia insulation. An engineering test of the new HIT-SI front end will be done before it replaces the present HIT-II front end on HIT. Startup and one millisecond of sustainment will be done to test breakdown and verify power supply requirements. The power supplies and external coils are designed to provide 20 MW at 5 kHz to 50 kHz for 1 ms to the helicity injection circuits for this test. Progress in the construction and assembly of HIT-SI will be presented.

  14. Role of glycosaminoglycans in determining the helicity of paired helical filaments.

    PubMed Central

    Arrasate, M.; Pérez, M.; Valpuesta, J. M.; Avila, J.

    1997-01-01

    It is known from previous work that tau is the main component of paired helical filaments (PHFs) and that it can assemble in vitro into polymers resembling PHFs when high concentrations of protein are used. In the search for molecules that can facilitate tau polymerization, a component of neurofibrillary tangles, heparan sulfate (or its more sulfated form, heparin), and other glycosaminoglycans have been tested. Glycosaminoglycans, in the sulfated but not in the unsulfated form, facilitate not only tau assembly but also the formation of polymers resembling PHFs. Conversely, PHFs were found to contain heparan sulfate and chondroitin sulfate. Heparinase or chondroitinase treatment of PHFs results in the formation of straight structures. All of these results suggest a role for sulfated glycosaminoglycans in determining the helicity of PHFs. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 PMID:9327745

  15. Landau Theory of Helical Fermi Liquids.

    PubMed

    Lundgren, Rex; Maciejko, Joseph

    2015-08-01

    We construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator. In the presence of rotation symmetry, interactions between quasiparticles are described by ten independent Landau parameters per angular momentum channel, by contrast with the two (symmetric and antisymmetric) Landau parameters for a conventional spin-degenerate Fermi liquid. We project quasiparticle states onto the Fermi surface and obtain an effectively spinless, projected Landau theory with a single projected Landau parameter per angular momentum channel that captures the spin-momentum locking or nontrivial Berry phase of the Fermi surface. As a result of this nontrivial Berry phase, projection to the Fermi surface can increase or lower the angular momentum of the quasiparticle interactions. We derive equilibrium properties, criteria for Fermi surface instabilities, and collective mode dispersions in terms of the projected Landau parameters. We briefly discuss experimental means of measuring projected Landau parameters.

  16. Chaotic coordinates for the Large Helical Device

    SciTech Connect

    Hudson, S. R.; Suzuki, Y.

    2014-10-15

    The theory of quadratic-flux-minimizing (QFM) surfaces is reviewed, and numerical techniques that allow high-order QFM surfaces to be efficiently constructed for experimentally relevant, non-integrable magnetic fields are described. As a practical example, the chaotic edge of the magnetic field in the Large Helical Device (LHD) is examined. A precise technique for finding the boundary surface is implemented, the hierarchy of partial barriers associated with the near-critical cantori is constructed, and a coordinate system, which we call chaotic coordinates, that is based on a selection of QFM surfaces is constructed that simplifies the description of the magnetic field, so that flux surfaces become “straight” and islands become “square.”.

  17. Cool and hot flux ropes, their helicity

    NASA Astrophysics Data System (ADS)

    Nindos, Alexander

    2016-07-01

    We will review recent indirect and direct evidence for the existence of magnetic flux ropes in the solar atmosphere. Magnetic flux ropes may appear as S-shaped or reverse S-shaped (sigmoidal) structures in regions that are likely to erupt, and may also show in nonlinear force-free field extrapolations that use data from photospheric vector magnetograms as boundary condition. The availability of high sensitivity data recorded with unprecedented spatial and temporal resolution in hot EUV wavelengths by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) has revealed the existence of coherent structures identified as hot flux ropes. In this presentation, we will review the properties of both cool and hot flux ropes with an emphasis on the frequency of their occurrence in large flares and on their magnetic helicity content.

  18. Helical Membrane Protein Conformations and their Environment

    PubMed Central

    Cross, Timothy A.; Murray, Dylan T.; Watts, Anthony

    2013-01-01

    Evidence that membrane proteins respond conformationally and functionally to their environment is gaining pace. Structural models, by necessity, have been characterized in preparations where the protein has been removed from its native environment. Different structural methods have used various membrane mimetics that have recently included lipid bilayers as a more native-like environment. Structural tools applied to lipid bilayer-embedded integral proteins are informing us about important generic characteristics of how membrane proteins respond to the lipid environment as compared with their response to other non-lipid environments. Here, we review the current status of the field, with specific reference to observations of some well-studied α-helical membrane proteins, as a starting point to aid the development of possible generic principals for model refinement. PMID:23996195

  19. Helicity evolution at small-x

    DOE PAGES

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

    2016-01-13

    We construct small-x evolution equations which can be used to calculate quark and anti-quark helicity TMDs and PDFs, along with the g1 structure function. These evolution equations resum powers of αs ln2(1/x) in the polarization-dependent evolution along with the powers of αs ln(1/x) in the unpolarized evolution which includes saturation efects. 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-Nc and large-Nc & Nf limits. As a cross-check, in the ladder approximation, our equationsmore » map onto the same ladder limit of the infrared evolution equations for g1 structure function derived previously by Bartels, Ermolaev and Ryskin.« less

  20. Novel Design of Superconducting Helical Dipole Magnet

    NASA Astrophysics Data System (ADS)

    Meinke, R.; Senti, M.; Stelzer, G.

    1997-05-01

    Superconducting helical dipole magnets with a nominal field of 4 Tesla are needed for the spin physics program at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The magnets are required to operate at a relatively low current of 400 A since many of these magnets have to be independently controlled. The Advanced Magnet Lab, Inc., in Palm Bay, FL has designed and built two prototype magnets using advanced computer controlled coil winding technology. The AML design is extremely cost effective since it avoids magnet specific tooling despite the required complex coil pattern and any precision machined inserts or spacers. It is the first time an accelerator magnet of this technology has reached a field above 4 Tesla. Results from the prototype testing at BNL are presented.

  1. Winding light beams along elliptical helical trajectories

    NASA Astrophysics Data System (ADS)

    Wen, Yuanhui; Chen, Yujie; Zhang, Yanfeng; Chen, Hui; Yu, Siyuan

    2016-07-01

    Conventional caustic methods in real or Fourier space produced accelerating optical beams only with convex trajectories. We developed a superposition caustic method capable of winding light beams along nonconvex trajectories. We ascertain this method by constructing a one-dimensional (1D) accelerating beam moving along a sinusoidal trajectory, and subsequently extending to two-dimensional (2D) accelerating beams along arbitrarily elliptical helical trajectories. We experimentally implemented the method with a compact and robust integrated optics approach by fabricating micro-optical structures on quartz glass plates to perform the spatial phase and amplitude modulation to the incident light, generating beam trajectories highly consistent with prediction. The theoretical and implementation methods can in principle be extended to the construction of accelerating beams with a wide variety of nonconvex trajectories, thereby opening up a route of manipulating light beams for fundamental research and practical applications.

  2. PULSE COLUMN

    DOEpatents

    Grimmett, E.S.

    1964-01-01

    This patent covers a continuous countercurrent liquidsolids contactor column having a number of contactor states each comprising a perforated plate, a layer of balls, and a downcomer tube; a liquid-pulsing piston; and a solids discharger formed of a conical section at the bottom of the column, and a tubular extension on the lowest downcomer terminating in the conical section. Between the conical section and the downcomer extension is formed a small annular opening, through which solids fall coming through the perforated plate of the lowest contactor stage. This annular opening is small enough that the pressure drop thereacross is greater than the pressure drop upward through the lowest contactor stage. (AEC)

  3. HELICITY CONSERVATION IN NONLINEAR MEAN-FIELD SOLAR DYNAMO

    SciTech Connect

    Pipin, V. V.; Sokoloff, D. D.; Zhang, H.; Kuzanyan, K. M.

    2013-05-01

    It is believed that magnetic helicity conservation is an important constraint on large-scale astrophysical dynamos. In this paper, we study a mean-field solar dynamo model that employs two different formulations of the magnetic helicity conservation. In the first approach, the evolution of the averaged small-scale magnetic helicity is largely determined by the local induction effects due to the large-scale magnetic field, turbulent motions, and the turbulent diffusive loss of helicity. In this case, the dynamo model shows that the typical strength of the large-scale magnetic field generated by the dynamo is much smaller than the equipartition value for the magnetic Reynolds number 10{sup 6}. This is the so-called catastrophic quenching (CQ) phenomenon. In the literature, this is considered to be typical for various kinds of solar dynamo models, including the distributed-type and the Babcock-Leighton-type dynamos. The problem can be resolved by the second formulation, which is derived from the integral conservation of the total magnetic helicity. In this case, the dynamo model shows that magnetic helicity propagates with the dynamo wave from the bottom of the convection zone to the surface. This prevents CQ because of the local balance between the large-scale and small-scale magnetic helicities. Thus, the solar dynamo can operate in a wide range of magnetic Reynolds numbers up to 10{sup 6}.

  4. Deducing the symmetry of helical assemblies: Applications to membrane proteins.

    PubMed

    Coudray, Nicolas; Lasala, Ralph; Zhang, Zhening; Clark, Kathy M; Dumont, Mark E; Stokes, David L

    2016-08-01

    Helical reconstruction represents a convenient and powerful approach for structure determination of macromolecules that assemble into helical arrays. In the case of membrane proteins, formation of tubular crystals with helical symmetry represents an attractive alternative, especially when their small size precludes the use of single-particle analysis. An essential first step for helical reconstruction is to characterize the helical symmetry. This process is often daunting, due to the complexity of helical diffraction and to the low signal-to-noise ratio in images of individual assemblies. Furthermore, the large diameters of the tubular crystals produced by membrane proteins exacerbates the innate ambiguities that, if not resolved, will produce incorrect structures. In this report, we describe a set of tools that can be used to eliminate ambiguities and to validate the choice of symmetry. The first approach increases the signal-to-noise ratio along layer lines by incoherently summing data from multiple helical assemblies, thus producing several candidate indexing schemes. The second approach compares the layer lines from images with those from synthetic models built with the various candidate schemes. The third approach uses unit cell dimensions measured from collapsed tubes to distinguish between these candidate schemes. These approaches are illustrated with tubular crystals from a boron transporter from yeast, Bor1p, and a β-barrel channel from the outer membrane of E. coli, OmpF.

  5. Helicity transport from solar convection zone to interplanetary space

    NASA Astrophysics Data System (ADS)

    Zhang, Mei

    2013-07-01

    Magnetic helicity is a physical quantity that describes field topology. It is also a conserved quantity as Berger in 1984 demonstrated that the total magnetic helicity is still conserved in the corona even when there is a fast magnetic reconnection. It is generally believed that solar magnetic fields, together with their helicity, are created in the convection zone by various dynamo processes. These fields and helicity are transported into the corona through solar photosphere and finally released into the interplanetary space via various processes such as coronal mass ejections (CMEs) and solar winds. Here I will give a brief review on our recent works, first on helicity observations on the photosphere and how to understand these observations via dynamo models. Mostly, I will talk about what are the possible consequences of magnetic helicity accumulation in the corona, namely, the formation of magnetic flux ropes, CMEs taking place as an unavoidable product of coronal evolution, and flux emergences as a trigger of CMEs. Finally, I will address on in what a form magnetic field in the interplanetary space would accommodate a large amount of magnetic helicity that solar dynamo processes have been continuously producing.

  6. What is the Most Important Origin of the Coronal Helicity?

    NASA Astrophysics Data System (ADS)

    Tian, L.

    23 active regions (ARs) with well-defined SXR sigmoids are selected to study which is the more important origin of the coronal helicity -- the emergence of magnetic fields or photospheric horizontal motions. The radial magnetic flux of each polarity, the helicity injection rate, and total helicity flux (Δ Hlct) are calculated using local correlation tracking technique and {MDI 96m} line-of-sight magnetograms, and the helicity budget of the differential rotation (Δ Hrot) is also estimated. It is found that six ARs inject helicity flux greater than 1.0× 1043 {Mx}^2 (Δ H=Δ Hlct-Δ Hrot), in a sample of seven ARs with emerging magnetic flux greater than 1.0× 1022 Mx. On the other hand, in sixteen ARs with emerging magnetic flux less than 1.0× 1022 Mx, only four ARs inject helicity flux greater than 1.0× 1043 Mx^2, which denotes the main contribution of the horizontal motions. The statistical results suggest that the horizontal motions are not important to the coronal helicity injection when there is little magnetic field emergence.

  7. Extreme Helicity and Intense Convective Towers in Hurricane Bonnie

    NASA Technical Reports Server (NTRS)

    Molinari, John; Vollaro, David

    2008-01-01

    Helicity was calculated in Hurricane Bonnie (1998) using tropospheric-deep dropsonde soundings from the NASA Convection and Moisture Experiment. Large helicity existed downshear of the storm center with respect to the ambient vertical wind shear. It was associated with veering, semicircular hodographs created by strong, vortex-scale, radial-vertical flow induced by the shear. The most extreme values of helicity, among the largest ever reported in the literature, occurred in the vicinity of deep convective cells in the downshear-left quadrant. These cells reached as high as 17.5 km and displayed the temporal and spatial scales of supercells. Convective available potential energy (CAPE) averaged 861 J/kg downshear, but only about one-third as large upshear. The soundings nearest the deep cells were evaluated using two empirical supercell parameters that make use of CAPE, helicity, and/or shear. These parameters supported the possible existence of supercells as a consequence of the exceptional helicity combined with moderate but sufficient CAPE. Ambient vertical wind shear exceeded 12 m/s for 30 h, yet the hurricane maintained 50 m/s maximum winds. It is hypothesized that the long-lived convective cells enabled the storm to resist the negative impact of the shear. Supercells in large-helicity, curved-hodograph environments appear to provide a useful conceptual model for intense convection in the hurricane core. Helicity calculations might also give some insight into the behavior of vortical hot towers, which share some characteristics with supercells.

  8. Pool-cooled superconducting magnet design of large helical device

    NASA Astrophysics Data System (ADS)

    Suzuki, S.; Miyazawa, H.; Saito, R.; Iida, F.; Ogata, H.; Yamazaki, Y.; Motojima, Osamu; Yamamoto, Junya; Fujiwara, Masami; Takeo, M.

    1990-03-01

    The Large Helical Device is the next generation in helical equipment for nuclear fusion. The large scale superconducting magnets are going to be applied to these coils. The major and minor radius of the helical coil system are 4 and 0.96 m respectively and the magnetic field is 4 T at the plasma center and 8 T at the coil surface. The coil system stores about 2 GJ of total energy. The superconductor of the helical coil is pure aluminum stabilized Nb-Ti compacted strand cable with copper housing. The coils have a stainless-steel helium can that is filled with liquid helium. This pool-cooled superconducting helical coil system satisfies the fully stabilized condition. The superconducting poloidal coils are composed of six (three pairs) circular coils and use forced-cooled superconductors to reduce the eddy current losses by the field changing operation. The helical and poloidal coil system are built in the large bell-jar (vacuum vessel for thermal insulation) with outer diameter of 13 m. Conductor design and stability of superconducting magnets for helical and poloidal coil systems are described.

  9. Helicity, topology, and Kelvin waves in reconnecting quantum knots

    NASA Astrophysics Data System (ADS)

    Clark di Leoni, P.; Mininni, P. D.; Brachet, M. E.

    2016-10-01

    Helicity is a topological invariant that measures the linkage and knottedness of lines, tubes, and ribbons. As such, it has found myriads of applications in astrophysics, fluid dynamics, atmospheric sciences, and biology. In quantum flows, where topology-changing reconnection events are a staple, helicity appears as a key quantity to study. However, the usual definition of helicity is not well posed in quantum vortices, and its computation based on counting links and crossings of centerline vorticity can be downright impossible to apply in complex and turbulent scenarios. We present a definition of helicity which overcomes these problems and which gives the expected result in the large-scale limit. With it, we show that certain reconnection events can excite Kelvin waves and other complex motions of the centerline vorticity, which slowly deplete helicity as they interact nonlinearly, thus linking the theory of vortex knots with observations of quantum fluids. This process also results in the depletion of helicity in a fully turbulent quantum flow, in a way reminiscent of the decay of helicity in classical fluids.

  10. Deducing the symmetry of helical assemblies: Applications to membrane proteins.

    PubMed

    Coudray, Nicolas; Lasala, Ralph; Zhang, Zhening; Clark, Kathy M; Dumont, Mark E; Stokes, David L

    2016-08-01

    Helical reconstruction represents a convenient and powerful approach for structure determination of macromolecules that assemble into helical arrays. In the case of membrane proteins, formation of tubular crystals with helical symmetry represents an attractive alternative, especially when their small size precludes the use of single-particle analysis. An essential first step for helical reconstruction is to characterize the helical symmetry. This process is often daunting, due to the complexity of helical diffraction and to the low signal-to-noise ratio in images of individual assemblies. Furthermore, the large diameters of the tubular crystals produced by membrane proteins exacerbates the innate ambiguities that, if not resolved, will produce incorrect structures. In this report, we describe a set of tools that can be used to eliminate ambiguities and to validate the choice of symmetry. The first approach increases the signal-to-noise ratio along layer lines by incoherently summing data from multiple helical assemblies, thus producing several candidate indexing schemes. The second approach compares the layer lines from images with those from synthetic models built with the various candidate schemes. The third approach uses unit cell dimensions measured from collapsed tubes to distinguish between these candidate schemes. These approaches are illustrated with tubular crystals from a boron transporter from yeast, Bor1p, and a β-barrel channel from the outer membrane of E. coli, OmpF. PMID:27255388

  11. Tapered pulse tube for pulse tube refrigerators

    DOEpatents

    Swift, Gregory W.; Olson, Jeffrey R.

    1999-01-01

    Thermal insulation of the pulse tube in a pulse-tube refrigerator is maintained by optimally varying the radius of the pulse tube to suppress convective heat loss from mass flux streaming in the pulse tube. A simple cone with an optimum taper angle will often provide sufficient improvement. Alternatively, the pulse tube radius r as a function of axial position x can be shaped with r(x) such that streaming is optimally suppressed at each x.

  12. Multipinhole SPECT helical scan parameters and imaging volume

    SciTech Connect

    Yao, Rutao Deng, Xiao; Wei, Qingyang; Dai, Tiantian; Ma, Tianyu; Lecomte, Roger

    2015-11-15

    Purpose: The authors developed SPECT imaging capability on an animal PET scanner using a multiple-pinhole collimator and step-and-shoot helical data acquisition protocols. The objective of this work was to determine the preferred helical scan parameters, i.e., the angular and axial step sizes, and the imaging volume, that provide optimal imaging performance. Methods: The authors studied nine helical scan protocols formed by permuting three rotational and three axial step sizes. These step sizes were chosen around the reference values analytically calculated from the estimated spatial resolution of the SPECT system and the Nyquist sampling theorem. The nine helical protocols were evaluated by two figures-of-merit: the sampling completeness percentage (SCP) and the root-mean-square (RMS) resolution. SCP was an analytically calculated numerical index based on projection sampling. RMS resolution was derived from the reconstructed images of a sphere-grid phantom. Results: The RMS resolution results show that (1) the start and end pinhole planes of the helical scheme determine the axial extent of the effective field of view (EFOV), and (2) the diameter of the transverse EFOV is adequately calculated from the geometry of the pinhole opening, since the peripheral region beyond EFOV would introduce projection multiplexing and consequent effects. The RMS resolution results of the nine helical scan schemes show optimal resolution is achieved when the axial step size is the half, and the angular step size is about twice the corresponding values derived from the Nyquist theorem. The SCP results agree in general with that of RMS resolution but are less critical in assessing the effects of helical parameters and EFOV. Conclusions: The authors quantitatively validated the effective FOV of multiple pinhole helical scan protocols and proposed a simple method to calculate optimal helical scan parameters.

  13. Self-organization of protein with helical domains

    NASA Astrophysics Data System (ADS)

    Frenkel, Zakhar M.; Melker, Alexander I.

    2002-02-01

    In this contribution, we report on a study of the self- organization of isolated polypeptides. The process is computer simulated by the method of molecular dynamics. We observed that the helical structures have a very impotent role in the protein self-organization. We have found conditions under which such structures to be stable. The process and result of self-organization under these conditions were sharply different from others, unable to maintain the helical structures. The structures obtained have a strong resemblance to the native conformations of the corresponding real proteins in a case of proteins composed by helical domains.

  14. Neoclassical Transport in the Helical Reversed-Field Pinch

    NASA Astrophysics Data System (ADS)

    Gobbin, M.; Spizzo, G.; Marrelli, L.; White, R. B.

    2010-11-01

    Test particle evaluation of the diffusion coefficient in a fusion plasma in the reversed-field pinch (RFP) configuration shows distinct similarities with stellarators when the plasma spontaneously evolves towards a helical shape. The almost total absence of superbanana particles at the levels of helical deformation seen in experiment (Bh/B=10%) causes transport to be proportional to collision frequency (at low collisions). This fact excludes the possibility that the minimum conceivable transport could be inversely proportional to collision frequency, which is typical of unoptimized stellarators. This result strengthens the perspectives of the helical RFP as a fusion configuration.

  15. Josephson junction through a disordered topological insulator with helical magnetization

    NASA Astrophysics Data System (ADS)

    Zyuzin, Alexander; Alidoust, Mohammad; Loss, Daniel

    2016-06-01

    We study supercurrent and proximity vortices in a Josephson junction made of disordered surface states of a three-dimensional topological insulator with a proximity induced in-plane helical magnetization. In a regime where the rotation period of helical magnetization is larger than the junction width, we find supercurrent 0 -π crossovers as a function of junction thickness, magnetization strength, and parameters inherent to the helical modulation and surface states. The supercurrent reversals are associated with proximity induced vortices, nucleated along the junction width, where the number of vortices and their locations can be manipulated by means of the superconducting phase difference and the parameters mentioned above.

  16. Tailoring chiro-optical effects by helical nanowire arrangement

    NASA Astrophysics Data System (ADS)

    Esposito, Marco; Tasco, Vittorianna; Todisco, Francesco; Benedetti, Alessio; Tarantini, Iolena; Cuscunà, Massimo; Dominici, Lorenzo; de Giorgi, Milena; Passaseo, Adriana

    2015-10-01

    In this work, we experimentally investigate the chiro-optical properties of 3D metallic helical systems at optical frequencies. Both single and triple-nanowire geometries have been studied. In particular, we found that in single-helical nanostructures, the enhancement of chiro-optical effects achievable by geometrical design is limited, especially with respect to the operation wavelength and the circular polarization conversion purity. Conversely, in the triple-helical nanowire configuration, the dominant interaction is the coupling among the intertwined coaxial helices which is driven by a symmetric spatial arrangement. Consequently, a general improvement in the g-factor, extinction ratio and signal-to-noise-ratio is achieved in a broad spectral range. Moreover, while in single-helical nanowires a mixed linear and circular birefringence results in an optical activity strongly dependent on the sample orientation and wavelength, in the triple-helical nanowire configuration, the obtained purely circular birefringence leads to a large optical activity up to 8°, independent of the sample angle, and extending in a broad band of 500 nm in the visible range. These results demonstrate a strong correlation between the configurational internal interactions and the chiral feature designation, which can be effectively exploited for nanoscale chiral device engineering.In this work, we experimentally investigate the chiro-optical properties of 3D metallic helical systems at optical frequencies. Both single and triple-nanowire geometries have been studied. In particular, we found that in single-helical nanostructures, the enhancement of chiro-optical effects achievable by geometrical design is limited, especially with respect to the operation wavelength and the circular polarization conversion purity. Conversely, in the triple-helical nanowire configuration, the dominant interaction is the coupling among the intertwined coaxial helices which is driven by a symmetric spatial

  17. Helical Spin Order from Topological Dirac and Weyl Semimetals

    SciTech Connect

    Sun, Xiao-Qi; Zhang, Shou-Cheng; Wang, Zhong

    2015-08-14

    In this paper, we study dynamical mass generation and the resultant helical spin orders in topological Dirac and Weyl semimetals, including the edge states of quantum spin Hall insulators, the surface states of weak topological insulators, and the bulk materials of Weyl semimetals. In particular, the helical spin textures of Weyl semimetals manifest the spin-momentum locking of Weyl fermions in a visible manner. Finally, the spin-wave fluctuations of the helical order carry electric charge density; therefore, the spin textures can be electrically controlled in a simple and predictable manner.

  18. Conservation of writhe helicity under anti-parallel reconnection

    PubMed Central

    Laing, Christian E.; Ricca, Renzo L.; Sumners, De Witt L.

    2015-01-01

    Reconnection is a fundamental event in many areas of science, from the interaction of vortices in classical and quantum fluids, and magnetic flux tubes in magnetohydrodynamics and plasma physics, to the recombination in polymer physics and DNA biology. By using fundamental results in topological fluid mechanics, the helicity of a flux tube can be calculated in terms of writhe and twist contributions. Here we show that the writhe is conserved under anti-parallel reconnection. Hence, for a pair of interacting flux tubes of equal flux, if the twist of the reconnected tube is the sum of the original twists of the interacting tubes, then helicity is conserved during reconnection. Thus, any deviation from helicity conservation is entirely due to the intrinsic twist inserted or deleted locally at the reconnection site. This result has important implications for helicity and energy considerations in various physical contexts. PMID:25820408

  19. Helicity representation for deep inelastic collisions of heavy ions

    NASA Astrophysics Data System (ADS)

    Strutinsky, V. M.; Vydrug-Vlasenko, S. M.

    1980-09-01

    Quantum-mechanical cross-section for the inelastic collisions characterized by large values of the angular momenta is analysed. For the case of a planar mechanism of the reaction the approximation of the small helicity is drawn.

  20. Nanomotor-based biocatalytic patterning of helical metal microstructures.

    PubMed

    Manesh, Kalayil Manian; Campuzano, Susana; Gao, Wei; Lobo-Castañón, María Jesús; Shitanda, Isao; Kiantaj, Kiarash; Wang, Joseph

    2013-02-21

    A new nanomotor-based surface-patterning technique based on the movement of a magnetically powered enzyme-functionalized flexible nanowire swimmer offers the ability to create complex helical metal microstructures.

  1. Amphipathic Alpha-Helical Peptide Compositions as Antiviral Agents

    NASA Technical Reports Server (NTRS)

    Glenn, Jeffrey (Inventor); Cho, Nam-Joon (Inventor); Frank, Curtis W. (Inventor); Cheong, Kwang Ho (Inventor)

    2014-01-01

    The invention features methods and compositions that exploit the ability of amphipathic alpha-helical (AH) peptides to cause disruption of lipid-containing vesicles, such as enveloped viruses, in a size-dependent manner.

  2. Helicity charging and eruption of magnetic flux from the Sun

    NASA Technical Reports Server (NTRS)

    Rust, David M.; Kumar, A.

    1994-01-01

    The ejection of helical toroidal fields from the solar atmosphere and their detection in interplanetary space are described. The discovery that solar magnetic fields are twisted and that they are segregated by hemisphere according to their chirality has important implications for the escape process. The roles played by erupting prominences, coronal mass ejections (CME's) and active region (AR) loops in expressing the escape of magnetic flux and helicity are discussed. Sporadic flux escape associated with filament eruptions accounts for less than one-tenth the flux loss. Azimuthal flux loss by CME's could account for more, but the major contributor to flux escape may be AR loop expansion. It is shown how the transfer of magnetic helicity from the sun's interior into emerged loops ('helicity charging') could be the effective driver of solar eruptions and of flux loss from the sun.

  3. A Halogen-Bond-Induced Triple Helicate Encapsulates Iodide.

    PubMed

    Massena, Casey J; Wageling, Nicholas B; Decato, Daniel A; Martin Rodriguez, Enrique; Rose, Ariana M; Berryman, Orion B

    2016-09-26

    The self-assembly of higher-order anion helicates in solution remains an elusive goal. Herein, we present the first triple helicate to encapsulate iodide in organic and aqueous media as well as the solid state. The triple helicate self-assembles from three tricationic arylethynyl strands and resembles a tubular anion channel lined with nine halogen bond donors. Eight strong iodine⋅⋅⋅iodide halogen bonds and numerous buried π-surfaces endow the triplex with remarkable stability, even at elevated temperatures. We suggest that the natural rise of a single-strand helix renders its linear halogen-bond donors non-convergent. Thus, the stringent linearity of halogen bonding is a powerful tool for the synthesis of multi-strand anion helicates. PMID:27411932

  4. Macroscopic ordering of helical pores for arraying guest molecules noncentrosymmetrically

    PubMed Central

    Li, Chunji; Cho, Joonil; Yamada, Kuniyo; Hashizume, Daisuke; Araoka, Fumito; Takezoe, Hideo; Aida, Takuzo; Ishida, Yasuhiro

    2015-01-01

    Helical nanostructures have attracted continuous attention, not only as media for chiral recognition and synthesis, but also as motifs for studying intriguing physical phenomena that never occur in centrosymmetric systems. To improve the quality of signals from these phenomena, which is a key issue for their further exploration, the most straightforward is the macroscopic orientation of helices. Here as a versatile scaffold to rationally construct this hardly accessible structure, we report a polymer framework with helical pores that unidirectionally orient over a large area (∼10 cm2). The framework, prepared by crosslinking a supramolecular liquid crystal preorganized in a magnetic field, is chemically robust, functionalized with carboxyl groups and capable of incorporating various basic or cationic guest molecules. When a nonlinear optical chromophore is incorporated in the framework, the resultant complex displays a markedly efficient nonlinear optical output, owing to the coherence of signals ensured by the macroscopically oriented helical structure. PMID:26416086

  5. Domain boundary formation in helical multishell gold nanowires.

    PubMed

    Hoshi, T; Fujiwara, T

    2009-07-01

    Helical multishell gold nanowires are studied theoretically for the formation mechanism of the helical domain boundary. Nanowires with a wire length of more than 10 nm are relaxed by quantum mechanical molecular dynamics simulation with a tight-binding form Hamiltonian. In the results, non-helical nanowires are transformed into helical ones with the formation of atom pair defects at the domain boundary, where the defective atom pair is moved from an inner shell. Analysis of local electronic structure shows a competitive feature of the energy gain of reconstruction on the wire surface and the energy loss of the defect formation. A simple energy scaling theory gives a general explanation of domain boundary formation.

  6. Macroscopic ordering of helical pores for arraying guest molecules noncentrosymmetrically

    NASA Astrophysics Data System (ADS)

    Li, Chunji; Cho, Joonil; Yamada, Kuniyo; Hashizume, Daisuke; Araoka, Fumito; Takezoe, Hideo; Aida, Takuzo; Ishida, Yasuhiro

    2015-09-01

    Helical nanostructures have attracted continuous attention, not only as media for chiral recognition and synthesis, but also as motifs for studying intriguing physical phenomena that never occur in centrosymmetric systems. To improve the quality of signals from these phenomena, which is a key issue for their further exploration, the most straightforward is the macroscopic orientation of helices. Here as a versatile scaffold to rationally construct this hardly accessible structure, we report a polymer framework with helical pores that unidirectionally orient over a large area (~10 cm2). The framework, prepared by crosslinking a supramolecular liquid crystal preorganized in a magnetic field, is chemically robust, functionalized with carboxyl groups and capable of incorporating various basic or cationic guest molecules. When a nonlinear optical chromophore is incorporated in the framework, the resultant complex displays a markedly efficient nonlinear optical output, owing to the coherence of signals ensured by the macroscopically oriented helical structure.

  7. Bidirectional helical motility of cytoplasmic dynein around microtubules.

    PubMed

    Can, Sinan; Dewitt, Mark A; Yildiz, Ahmet

    2014-07-28

    Cytoplasmic dynein is a molecular motor responsible for minus-end-directed cargo transport along microtubules (MTs). Dynein motility has previously been studied on surface-immobilized MTs in vitro, which constrains the motors to move in two dimensions. In this study, we explored dynein motility in three dimensions using an MT bridge assay. We found that dynein moves in a helical trajectory around the MT, demonstrating that it generates torque during cargo transport. Unlike other cytoskeletal motors that produce torque in a specific direction, dynein generates torque in either direction, resulting in bidirectional helical motility. Dynein has a net preference to move along a right-handed helical path, suggesting that the heads tend to bind to the closest tubulin binding site in the forward direction when taking sideways steps. This bidirectional helical motility may allow dynein to avoid roadblocks in dense cytoplasmic environments during cargo transport.

  8. 3D printing of a multifunctional nanocomposite helical liquid sensor

    NASA Astrophysics Data System (ADS)

    Guo, Shuang-Zhuang; Yang, Xuelu; Heuzey, Marie-Claude; Therriault, Daniel

    2015-04-01

    A multifunctional 3D liquid sensor made of a PLA/MWCNT nanocomposite and shaped as a freeform helical structure was fabricated by solvent-cast 3D printing. The 3D liquid sensor featured a relatively high electrical conductivity, the functionality of liquid trapping due to its helical configuration, and an excellent sensitivity and selectivity even for a short immersion into solvents.A multifunctional 3D liquid sensor made of a PLA/MWCNT nanocomposite and shaped as a freeform helical structure was fabricated by solvent-cast 3D printing. The 3D liquid sensor featured a relatively high electrical conductivity, the functionality of liquid trapping due to its helical configuration, and an excellent sensitivity and selectivity even for a short immersion into solvents. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00278h

  9. Precision synthesis, structure and function of helical polymers

    PubMed Central

    OKAMOTO, Yoshio

    2015-01-01

    Helical structures are chiral, which means that if we can synthesize a polymer having a stable one-handed helicity, the polymer is optically active. In 1979, we succeeded in the synthesis of a one-handed helical polymer from an optically inactive achiral monomer, triphenylmethyl methacrylate (TrMA). This is the first example of the asymmetric synthesis of an optically active one-handed helical polymer. The polymer (PTrMA) exhibited an unexpected high chiral recognition ability and afforded a practically useful chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) by coating it on silica gel. In addition, we also succeeded in the development of very useful CSPs for HPLC using the phenylcarbamate derivatives of polysaccharides, cellulose and amylose. These CSPs can efficiently resolve a broad range of chiral compounds, and have been used all over the world for separating and analyzing chiral compounds. PMID:26062738

  10. Precision synthesis, structure and function of helical polymers.

    PubMed

    Okamoto, Yoshio

    2015-01-01

    Helical structures are chiral, which means that if we can synthesize a polymer having a stable one-handed helicity, the polymer is optically active. In 1979, we succeeded in the synthesis of a one-handed helical polymer from an optically inactive achiral monomer, triphenylmethyl methacrylate (TrMA). This is the first example of the asymmetric synthesis of an optically active one-handed helical polymer. The polymer (PTrMA) exhibited an unexpected high chiral recognition ability and afforded a practically useful chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) by coating it on silica gel. In addition, we also succeeded in the development of very useful CSPs for HPLC using the phenylcarbamate derivatives of polysaccharides, cellulose and amylose. These CSPs can efficiently resolve a broad range of chiral compounds, and have been used all over the world for separating and analyzing chiral compounds. PMID:26062738

  11. Traveling wave instability in helical coil flow

    NASA Astrophysics Data System (ADS)

    Webster, D. R.; Humphrey, J. A. C.

    1997-02-01

    Complementary flow visualization photographs and numerical calculations are presented for the transitional state between the laminar and turbulent flow regimes in a helically coiled pipe. The flow visualization covers a Reynolds number range from 3800 to 8650 (890

  12. Overview of the Large Helical Device project

    NASA Astrophysics Data System (ADS)

    Iiyoshi, A.; Komori, A.; Ejiri, A.; Emoto, M.; Funaba, H.; Goto, M.; Ida, K.; Idei, H.; Inagaki, S.; Kado, S.; Kaneko, O.; Kawahata, K.; Kobuchi, T.; Kubo, S.; Kumazawa, R.; Masuzaki, S.; Minami, T.; Miyazawa, J.; Morisaki, T.; Morita, S.; Murakami, S.; Muto, S.; Mutoh, T.; Nagayama, Y.; Nakamura, Y.; Nakanishi, H.; Narihara, K.; Nishimura, K.; Noda, N.; Ohdachi, S.; Ohyabu, N.; Oka, Y.; Osakabe, M.; Ozaki, T.; Peterson, B. J.; Sagara, A.; Sakakibara, S.; Sakamoto, R.; Sasao, H.; Sasao, M.; Sato, K.; Sato, M.; Seki, T.; Shimozuma, T.; Shoji, M.; Suzuki, H.; Takeiri, Y.; Tanaka, K.; Toi, K.; Tokuzawa, T.; Tsumori, K.; Tsuzuki, K.; Watanabe, K. Y.; Watari, T.; Yamada, H.; Yamada, I.; Yamaguchi, S.; Yokoyama, M.; Akiyama, R.; Chikaraishi, H.; Haba, K.; Hamaguchi, S.; Iima, M.; Imagawa, S.; Inoue, N.; Iwamoto, K.; Kitagawa, S.; Kodaira, J.; Kubota, Y.; Maekawa, R.; Mito, T.; Nagasaka, T.; Nishimura, A.; Takahashi, C.; Takahata, K.; Takita, Y.; Tamura, H.; Tsuzuki, T.; Yamada, S.; Yamauchi, K.; Yanagi, N.; Yonezu, H.; Hamada, Y.; Matsuoka, K.; Murai, K.; Ohkubo, K.; Ohtake, I.; Okamoto, M.; Satoh, S.; Satow, T.; Sudo, S.; Tanahashi, S.; Yamazaki, K.; Fujiwara, M.; Motojima, O.

    1999-09-01

    The Large Helical Device (LHD) has successfully started running plasma confinement experiments after a long construction period of eight years. During the construction and machine commissioning phases, a variety of milestones were attained in fusion engineering which successfully led to the first operation, and the first plasma was ignited on 31 March 1998. Two experimental campaigns were carried out in 1998. In the first campaign, the magnetic flux mapping clearly demonstrated a nested structure of magnetic surfaces. The first plasma experiments were conducted with second harmonic 84 and 82.6 GHz ECH at a heating power input of 0.35 MW. The magnetic field was set at 1.5 T in these campaigns so as to accumulate operational experience with the superconducting coils. In the second campaign, auxiliary heating with NBI at 3 MW has been carried out. Averaged electron densities of up to 6 × 1019m-3, central temperatures ranging from 1.4 to 1.5 keV and stored energies of up to 0.22 MJ have been attained despite the fact that the impurity level has not yet been minimized. The obtained scaling of energy confinement time has been found to be consistent with the ISS95 scaling law with some enhancement.

  13. Physical Gelation of α-Helical Copolypeptides.

    PubMed

    Vacogne, Charlotte D; Schopferer, Michael; Schlaad, Helmut

    2016-07-11

    Owing to its rod-like α-helical secondary structure, the synthetic polypeptide poly(γ-benzyl-l-glutamate) (PBlG) can form physical and thermoreversible gels in helicogenic solvents such as toluene. The versatility of PBlG can be increased by introducing functionalizable comonomers, such as allylglycine (AG). In this work we examined the secondary structure of PBlG and a series of statistical poly(γ-benzyl-l-glutamate-co-allylglycine) copolypeptides, varying in composition and chain length, by circular dichroism (CD), Fourier-transform infrared (FTIR) and Raman spectroscopy, and wide-angle X-ray scattering (WAXS). The secondary structure of PBlG and the copolypeptides presented dissimilarities that increased with increasing AG molar fraction, especially when racemic AG units were incorporated. The physical gelation behavior of these copolypeptides was analyzed by temperature-sweep (1)H NMR and rheological measurements. The study revealed that both copolypeptide composition and chain length affected secondary structure, gelation temperature, and gel stiffness. PMID:27233111

  14. Helical surface reconstruction based on CMM

    NASA Astrophysics Data System (ADS)

    Pan, Zhikang; Zhu, Lianqing; Chen, Qingshan; Guo, Yangkuan

    2011-05-01

    The reconstruction of helical surface plays an important role in many engineering and scientific applications. This paper tends to establish an effective processing scheme of surface reconstruction of scatter 3D points, and make an in-depth exploration for the preprocessing technology of scatter points set and the algorithm of three-dimension model surface reconstruction. This paper has three main aspects: data acquisition, data preprocess and surface reconstruction. First, by comparing several measuring equipments, the screw parts are scanned via CMM (Coordinate Measuring Machine). Initial 3D point clouds are obtained by setting the scanning route according to the shape of the targets. Second, Using "3σ" criteria point de-noising is applied to the initial data points. Then Heap Sort is used to sort these points, being convenient for saving data and reconstructing the surface. Third, this paper presents a surface reconstruction method based on triangulation algorithm. The triangular meshes are generated based on Delaunay triangulation technique in two dimensions. And Loop Subdivision is adopted in order to get manifold meshes. Finally the surface reconstruction of an involute worm and an Archimedes worm shows that this approach is feasible.

  15. Helical surface reconstruction based on CMM

    NASA Astrophysics Data System (ADS)

    Pan, Zhikang; Zhu, Lianqing; Chen, Qingshan; Guo, Yangkuan

    2010-12-01

    The reconstruction of helical surface plays an important role in many engineering and scientific applications. This paper tends to establish an effective processing scheme of surface reconstruction of scatter 3D points, and make an in-depth exploration for the preprocessing technology of scatter points set and the algorithm of three-dimension model surface reconstruction. This paper has three main aspects: data acquisition, data preprocess and surface reconstruction. First, by comparing several measuring equipments, the screw parts are scanned via CMM (Coordinate Measuring Machine). Initial 3D point clouds are obtained by setting the scanning route according to the shape of the targets. Second, Using "3σ" criteria point de-noising is applied to the initial data points. Then Heap Sort is used to sort these points, being convenient for saving data and reconstructing the surface. Third, this paper presents a surface reconstruction method based on triangulation algorithm. The triangular meshes are generated based on Delaunay triangulation technique in two dimensions. And Loop Subdivision is adopted in order to get manifold meshes. Finally the surface reconstruction of an involute worm and an Archimedes worm shows that this approach is feasible.

  16. Towards online patient imaging during helical radiotherapy.

    PubMed

    Yu, L; Poole, C M; Lancaster, C M; Sylvander, S R

    2015-03-01

    Exit-detector data from helical radiation therapy have been studied extensively for delivery verification and dose reconstruction. Since the same radiation source is used for both imaging and treatment, this work investigates the possibility of utilising exit-detector raw data for imaging purposes. This gives rise to potential clinical applications such as retrospective daily setup verification and inter-fractional setup error detection. The exit-detector raw data were acquired and independently analysed using Python programming language. The raw data were extracted from the treatment machine's onboard computer, and converted into 2D array files. The contours of objects (phantom or patient) were acquired by applying a logarithmic function to the ratio of two sinograms, one with the object in the beam and one without. The setup variation between any two treatment deliveries can be detected by applying the same function to their corresponding exit-detector sinograms. The contour of the object was well defined by the secondary radiation from the treatment beam and validated with the imaging beam, although no internal structures were discernible due to the interference from the primary radiation. The sensitivity of the setup variation detection was down to 2 mm, which was mainly limited by the resolution of the exit-detector itself. The exit-detector data from treatment procedures contain valuable photon exit fluence maps which can be utilised for contour definition and verification of patient alignment without reconstruction.

  17. Helical Screw Expander Evaluation Project. Final report

    SciTech Connect

    McKay, R.

    1982-03-01

    A functional 1-MW geothermal electric power plant that featured a helical screw expander was produced and then tested in Utah in 1978 to 1979 with a demonstrated average performance of approximately 45% machine efficiency over a wide range of test conditions in noncondensing operation on two-phase geothermal fluids. The Project also produced a computer-equipped data system, an instrumentation and control van, and a 1000-kW variable load bank, all integrated into a test array designed for operation at a variety of remote test sites. Additional testing was performed in Mexico in 1980 under a cooperative test program using the same test array, and machine efficiency was measured at 62% maximum with the rotors partially coated with scale, compared with approximately 54% maximum in Utah with uncoated rotors, confirming the importance of scale deposits within the machine on performance. Data are presented for the Utah testing and for the noncondensing phases of the testing in Mexico. Test time logged was 437 hours during the Utah tests and 1101 hours during the Mexico tests.

  18. Abstract folding space analysis based on helices

    PubMed Central

    Huang, Jiabin; Backofen, Rolf; Voß, Björn

    2012-01-01

    RNA has many pivotal functions especially in the regulation of gene expression by ncRNAs. Identification of their structure is an important requirement for understanding their function. Structure prediction alone is often insufficient for this task, due to algorithmic problems, parameter inaccuracies, and biological peculiarities. Among the latter, there are base modifications, cotranscriptional folding leading to folding traps, and conformational switching as in the case of riboswitches. All these require more in-depth analysis of the folding space. The major drawback, which all methods have to cope with, is the exponential growth of the folding space. Therefore, methods are often limited in the sequence length they can analyze, or they make use of heuristics, sampling, or abstraction. Our approach adopts the abstraction strategy and remedies some problems of existing methods. We introduce a position-specific abstraction based on helices that we term helix index shapes, or hishapes for short. Utilizing a dynamic programming framework, we have implemented this abstraction in the program RNAHeliCes. Furthermore, we developed two hishape-based methods, one for energy barrier estimation, called HiPath, and one for abstract structure comparison, termed HiTed. We demonstrate the superior performance of HiPath compared to other existing methods and the competitive accuracy of HiTed. RNAHeliCes, together with HiPath and HiTed, are available for download at http://www.cyanolab.de/software/RNAHeliCes.htm. PMID:23104999

  19. Helical path separation for guided wave tomography

    SciTech Connect

    Huthwaite, P.; Seher, M.

    2015-03-31

    The pipe wall loss caused by corrosion can be quantified across an area by transmitting guided Lamb waves through the region and measuring the resulting signals. Typically the dispersive relationship for these waves, resulting in the wave velocity being a function of thickness, is exploited which enables the wall thickness to be determined from a velocity reconstruction. The accuracy and quality of this reconstruction is commonly limited by the angle of view available from the transducer arrays. These arrays are often attached as a pair of ring arrays either side of the inspected region, and due to the cyclic nature of the pipe, waves are able to travel in an inifinite number of helical paths between any two transducers. The first arrivals can be separated relatively easily by time gating, but by using just these components the angle of view is strongly restricted. To improve the viewing angle, it is necessary to separate the wavepackets. This paper provides an outline of a separation approach: initially the waves are backpropagated to their source to align the different signals, then a filtering technique is applied to select the desired components. The technique is applied to experimental data and demonstrated to robustly separate the signals.

  20. Towards online patient imaging during helical radiotherapy.

    PubMed

    Yu, L; Poole, C M; Lancaster, C M; Sylvander, S R

    2015-03-01

    Exit-detector data from helical radiation therapy have been studied extensively for delivery verification and dose reconstruction. Since the same radiation source is used for both imaging and treatment, this work investigates the possibility of utilising exit-detector raw data for imaging purposes. This gives rise to potential clinical applications such as retrospective daily setup verification and inter-fractional setup error detection. The exit-detector raw data were acquired and independently analysed using Python programming language. The raw data were extracted from the treatment machine's onboard computer, and converted into 2D array files. The contours of objects (phantom or patient) were acquired by applying a logarithmic function to the ratio of two sinograms, one with the object in the beam and one without. The setup variation between any two treatment deliveries can be detected by applying the same function to their corresponding exit-detector sinograms. The contour of the object was well defined by the secondary radiation from the treatment beam and validated with the imaging beam, although no internal structures were discernible due to the interference from the primary radiation. The sensitivity of the setup variation detection was down to 2 mm, which was mainly limited by the resolution of the exit-detector itself. The exit-detector data from treatment procedures contain valuable photon exit fluence maps which can be utilised for contour definition and verification of patient alignment without reconstruction. PMID:25636244

  1. Visualizing Helical Metals on Topological Insulators

    NASA Astrophysics Data System (ADS)

    Yazdani, Ali

    2012-02-01

    During the last few years, it has become apparent that there can be a distinct type of insulator, which can occur because of the topology of electronic wavefunctions in materials comprised of heavier elements. Strong interaction between the spin and the orbital angular momentum of electrons in these compounds alters the sequence in energy of their electronic states. The key consequence of this topological characteristic (and the way to distinguish a topological insulator from an ordinary one) is the presence of metallic electrons with helical spin texture at their surfaces. I will describe experiments that directly visualize these novel quantum states of matter and demonstrate their unusual properties through spectroscopic mapping with the scanning tunneling microscope (STM). These experiments show that the spin texture of these states protects them against backscattering and localization. These states appear to penetrate through barriers that stop other electronic states. I will also describe more ongoing efforts focused on unraveling the physics of topological surface states and their potential for device-like applications. [4pt] References: [0pt] P. Roushan et al, Nature 460 1106 (2009). [0pt] J. Seo et al, Nature 466 343 (2010). [0pt] H. Beidenkopf et al, to appear Nature Physics (2011).

  2. Stable double helical iodine chains inside single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Yao, Zhen; Liu, Chun-Jian; Lv, Hang; Liu, Bing-Bing

    2016-08-01

    The helicity of stable double helical iodine chains inside single-walled carbon nanotubes (SWCNTs) is studied by calculating the systematic interaction energy. Our results present clear images of stable double helical structures inside SWCNTs. The optimum helical radius and helical angle increase and decrease with increasing diameter, respectively. The tube's diameter plays a leading role in the helicity of encapsulated structures, while the tube's chirality may induce different metastable structures. This study indicates that the observed double helical iodine chains in experiments are not necessarily the optimum structures, but may also be metastable structures.

  3. Scale Dependence of Magnetic Helicity in the Solar Wind

    NASA Technical Reports Server (NTRS)

    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.

  4. Measuring Coronal Energy and Helicity Buildup with SDO/HMI

    NASA Astrophysics Data System (ADS)

    Schuck, P. W.; Antiochos, S. K.; Barnes, G.; Leka, K. D.

    2014-12-01

    Solar eruptions are driven by energy and helicity transported through the photosphere and into the corona. However, the mechanism by which energy and helicity emerge from the solar interior to form the observed coronal structures is poorly understood. SDO/HMI data are the first space-based full-disk vector field observations of the Sun with a near 100% duty cycle and, therefore, represent an unprecedented opportunity to quantify the energy end helicity fluxes through the photosphere. However, because of the SDO satellite's highly inclined geostationary orbit, the relative velocity of the instrument varies by ±3~km/s which introduces major orbital artifacts. We have developed a procedure for mitigating these artifacts and have applied this analysis to AR11084 to produce a cleaned data set. Our analysis procedure is described, in detail, and the results for AR11084 presented. We have also recast the Berger and Field (1984) helicity transport equation in manifestly gauge invariant form and derived the terms quantifying the injection of helicity into the corona by the emergence of closed field, versus helicity injection by the stressing of pre-emerged flux. The plasma velocity fields in the photosphere, necessary for computing energy and helicity fluxes are determined using an upgraded version of DAVE4VM that incorporates the spherical geometry of the solar images. We find that the bulk of the helicity into the corona is injected by twisting motions, and we discuss the implications of our results for understanding solar activity and especially for data-driven modeling of solar eruptions.This work was supported, in part, by NASA

  5. Vibratory high pressure coal feeder having a helical ramp

    DOEpatents

    Farber, Gerald

    1978-01-01

    Apparatus and method for feeding powdered coal from a helical ramp into a high pressure, heated, reactor tube containing hydrogen for hydrogenating the coal and/or for producing useful products from coal. To this end, the helical ramp is vibrated to feed the coal cleanly at an accurately controlled rate in a simple reliable and trouble-free manner that eliminates complicated and expensive screw feeders, and/or complicated and expensive seals, bearings and fully rotating parts.

  6. SCALE DEPENDENCE OF MAGNETIC HELICITY IN THE SOLAR WIND

    SciTech Connect

    Brandenburg, Axel; Subramanian, Kandaswamy; Balogh, Andre; Goldstein, Melvyn L. E-mail: kandu@iucaa.ernet.in E-mail: melvyn.l.goldstein@nasa.gov

    2011-06-10

    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 {approx} 2 AU{sup -1} (or frequency {nu} {approx} 2 {mu}Hz) at distances below 2.8 AU and at k {approx} 30 AU{sup -1} (or {nu} {approx} 25 {mu}Hz) 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.

  7. Numerical Simulations of Helicity Condensation in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-05-01

    The helicity condensation model has been proposed by Antiochos to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences are observed to form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the corona. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of a bipolar active region, for example. The calculations demonstrate that, contrary to common belief, opposite helicity twists do not lead to significant reconnection in such a coronal system, whereas twists with the same sense of helicity do produce substantial reconnection. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  8. Electrical characterization of all-optical helicity-dependent switching in ferromagnetic Hall crosses

    NASA Astrophysics Data System (ADS)

    El Hadri, M. S.; Pirro, P.; Lambert, C.-H.; Bergeard, N.; Petit-Watelot, S.; Hehn, M.; Malinowski, G.; Montaigne, F.; Quessab, Y.; Medapalli, R.; Fullerton, E. E.; Mangin, S.

    2016-02-01

    We present an experimental study of all-optical helicity-dependent switching (AO-HDS) of ferromagnetic Pt/Co/Pt heterostructures with perpendicular magnetic anisotropy. The sample is patterned into a Hall cross and the AO-HDS is measured via the anomalous Hall effect. This all-electrical probing of the magnetization during AO-HDS enables a statistical quantification of the switching ratio for different laser parameters, such as the threshold power to achieve AO-HDS and the exposure time needed to reach complete switching at a given laser power. We find that the AO-HDS is a cumulative process, a certain number of optical pulses is needed to obtain a full and reproducible helicity-dependent switching. The deterministic switching of the ferromagnetic Pt/Co/Pt Hall cross provides a full "opto-spintronic device," where the remanent magnetization can be all-optically and reproducibly written and erased without the need of an external magnetic field.

  9. Re-configurable multi-level temperature sensing by ultrasonic "spring-like" helical waveguide

    NASA Astrophysics Data System (ADS)

    Periyannan, Suresh; Rajagopal, Prabhu; Balasubramaniam, Krishnan

    2016-04-01

    This paper introduces a novel technique for multi-level temperature measurement using a single reconfigurable ultrasonic wire waveguide that is configured in the form of a helical spring. In this embodiment, the multiple sensing levels located along the length of the helical waveguide wire can be repositioned by stretching or collapsing the spring to provide measurements at different desired spacing in a given area/volume. This method can measure over a wide range of temperatures. The transduction is performed using Piezo-electric crystals that are attached to one end of the waveguide which act as transmitter as well as receiver. The wire will have multiple reflector embodiments (notches was used here) that allow reflections of input L(0,1) mode guided ultrasonic wave, in pulse echo mode, back to the crystal. Using the time of fight measurement at multiple predefined reflector locations, the local average temperatures are measured and compared with co-located thermocouples. The finite element modeling simulation was used to study the effect of excitation frequency and the mean coil diameter of the "spring-like" waveguide. This technique improves on the limitations of a straight waveguide technique earlier reported.

  10. α-Synuclein Oligomers with Broken Helical Conformation Form Lipoprotein Nanoparticles*

    PubMed Central

    Varkey, Jobin; Mizuno, Naoko; Hegde, Balachandra G.; Cheng, Naiqian; Steven, Alasdair C.; Langen, Ralf

    2013-01-01

    α-Synuclein (αS) is a membrane-binding protein with sequence similarity to apolipoproteins and other lipid-carrying proteins, which are capable of forming lipid-containing nanoparticles, sometimes referred to as “discs.” Previously, it has been unclear whether αS also possesses this property. Using cryo-electron microscopy and light scattering, we found that αS can remodel phosphatidylglycerol vesicles into nanoparticles whose shape (ellipsoidal) and dimensions (in the 7–10-nm range) resemble those formed by apolipoproteins. The molar ratio of αS to lipid in nanoparticles is ∼1:20, and αS is oligomeric (including trimers and tetramers). Similar nanoparticles form when αS is added to vesicles of mitochondrial lipids. This observation suggests a mechanism for the previously reported disruption of mitochondrial membranes by αS. Circular dichroism and four-pulse double electron electron resonance experiments revealed that in nanoparticles αS assumes a broken helical conformation distinct from the extended helical conformation adopted when αS is bound to intact vesicles or membrane tubules. We also observed αS-dependent tubule and nanoparticle formation in the presence of oleic acid, implying that αS can interact with fatty acids and lipids in a similar manner. αS-related nanoparticles might play a role in lipid and fatty acid transport functions previously attributed to this protein. PMID:23609437

  11. Biomimetic Hierarchical Assembly of Helical Supraparticles from Chiral Nanoparticles.

    PubMed

    Zhou, Yunlong; Marson, Ryan L; van Anders, Greg; Zhu, Jian; Ma, Guanxiang; Ercius, Peter; Sun, Kai; Yeom, Bongjun; Glotzer, Sharon C; Kotov, Nicholas A

    2016-03-22

    Chiroptical materials found in butterflies, beetles, stomatopod crustaceans, and other creatures are attributed to biocomposites with helical motifs and multiscale hierarchical organization. These structurally sophisticated materials self-assemble from primitive nanoscale building blocks, a process that is simpler and more energy efficient than many top-down methods currently used to produce similarly sized three-dimensional materials. Here, we report that molecular-scale chirality of a CdTe nanoparticle surface can be translated to nanoscale helical assemblies, leading to chiroptical activity in the visible electromagnetic range. Chiral CdTe nanoparticles coated with cysteine self-organize around Te cores to produce helical supraparticles. D-/L-Form of the amino acid determines the dominant left/right helicity of the supraparticles. Coarse-grained molecular dynamics simulations with a helical pair-potential confirm the assembly mechanism and the origin of its enantioselectivity, providing a framework for engineering three-dimensional chiral materials by self-assembly. The helical supraparticles further self-organize into lamellar crystals with liquid crystalline order, demonstrating the possibility of hierarchical organization and with multiple structural motifs and length scales determined by molecular-scale asymmetry of nanoparticle interactions.

  12. Tailoring chiro-optical effects by helical nanowire arrangement.

    PubMed

    Esposito, Marco; Tasco, Vittorianna; Todisco, Francesco; Benedetti, Alessio; Tarantini, Iolena; Cuscunà, Massimo; Dominici, Lorenzo; De Giorgi, Milena; Passaseo, Adriana

    2015-11-21

    In this work, we experimentally investigate the chiro-optical properties of 3D metallic helical systems at optical frequencies. Both single and triple-nanowire geometries have been studied. In particular, we found that in single-helical nanostructures, the enhancement of chiro-optical effects achievable by geometrical design is limited, especially with respect to the operation wavelength and the circular polarization conversion purity. Conversely, in the triple-helical nanowire configuration, the dominant interaction is the coupling among the intertwined coaxial helices which is driven by a symmetric spatial arrangement. Consequently, a general improvement in the g-factor, extinction ratio and signal-to-noise-ratio is achieved in a broad spectral range. Moreover, while in single-helical nanowires a mixed linear and circular birefringence results in an optical activity strongly dependent on the sample orientation and wavelength, in the triple-helical nanowire configuration, the obtained purely circular birefringence leads to a large optical activity up to 8°, independent of the sample angle, and extending in a broad band of 500 nm in the visible range. These results demonstrate a strong correlation between the configurational internal interactions and the chiral feature designation, which can be effectively exploited for nanoscale chiral device engineering.

  13. PROMINENCE FORMATION ASSOCIATED WITH AN EMERGING HELICAL FLUX ROPE

    SciTech Connect

    Okamoto, Takenori J.; Tsuneta, Saku; Katsukawa, Yukio; Suematsu, Yoshinori; Lites, Bruce W.; Kubo, Masahito; Yokoyama, Takaaki; Berger, Thomas E.; Shine, Richard A.; Tarbell, Theodore D.; Title, Alan M.; Shimizu, Toshifumi

    2009-05-20

    The formation and evolution process and magnetic configuration of solar prominences remain unclear. In order to study the formation process of prominences, we examine continuous observations of a prominence in NOAA AR 10953 with the Solar Optical Telescope on the Hinode satellite. As reported in our previous Letter, we find a signature suggesting that a helical flux rope emerges from below the photosphere under a pre-existing prominence. Here we investigate more detailed properties and photospheric indications of the emerging helical flux rope, and discuss their relationship to the formation of the prominence. Our main conclusions are: (1) a dark region with absence of strong vertical magnetic fields broadens and then narrows in Ca II H-line filtergrams. This phenomenon is consistent with the emergence of the helical flux rope as photospheric counterparts. The size of the flux rope is roughly 30,000 km long and 10,000 km wide. The width is larger than that of the prominence. (2) No shear motion or converging flows are detected, but we find diverging flows such as mesogranules along the polarity inversion line. The presence of mesogranules may be related to the emergence of the helical flux rope. (3) The emerging helical flux rope reconnects with magnetic fields of the pre-existing prominence to stabilize the prominence for the next several days. We thus conjecture that prominence coronal magnetic fields emerge in the form of helical flux ropes that contribute to the formation and maintenance of the prominence.

  14. Tailoring chiro-optical effects by helical nanowire arrangement.

    PubMed

    Esposito, Marco; Tasco, Vittorianna; Todisco, Francesco; Benedetti, Alessio; Tarantini, Iolena; Cuscunà, Massimo; Dominici, Lorenzo; De Giorgi, Milena; Passaseo, Adriana

    2015-11-21

    In this work, we experimentally investigate the chiro-optical properties of 3D metallic helical systems at optical frequencies. Both single and triple-nanowire geometries have been studied. In particular, we found that in single-helical nanostructures, the enhancement of chiro-optical effects achievable by geometrical design is limited, especially with respect to the operation wavelength and the circular polarization conversion purity. Conversely, in the triple-helical nanowire configuration, the dominant interaction is the coupling among the intertwined coaxial helices which is driven by a symmetric spatial arrangement. Consequently, a general improvement in the g-factor, extinction ratio and signal-to-noise-ratio is achieved in a broad spectral range. Moreover, while in single-helical nanowires a mixed linear and circular birefringence results in an optical activity strongly dependent on the sample orientation and wavelength, in the triple-helical nanowire configuration, the obtained purely circular birefringence leads to a large optical activity up to 8°, independent of the sample angle, and extending in a broad band of 500 nm in the visible range. These results demonstrate a strong correlation between the configurational internal interactions and the chiral feature designation, which can be effectively exploited for nanoscale chiral device engineering. PMID:26467488

  15. Ion Compensation for Space Charge in the Helical Electron Beams of Gyrotrons

    NASA Astrophysics Data System (ADS)

    Manuilov, V. N.; Semenov, V. E.

    2016-06-01

    We solve analytically the problem about ion compensation for the space charge of a helical electron beam in a gyrotron operated in the long-pulse regime. Elementary processes, which take place during ionization of residual gas in the tube under typical pressures of 10-6-10-7 mm Hg, are considered. It is shown that distribution of the space charge is affected mainly by the electrons of the initial beam and slow-moving ions produced by ionization of the residual gas. Steady-state density of ions in the operating space of the gyrotron after the end of the transitional processes is found, as well as the electron density profile in the channel of electron beam transportation. The results obtained allow us to evaluate the pitch-factor variations caused by partial compensations for the potential "sagging" in the gyrotron cavity, thus being useful for analysis of starting currents, efficiency, and mode competition in high-power gyrotrons.

  16. Torsional mode ultrasonic helical waveguide sensor for re-configurable temperature measurement

    NASA Astrophysics Data System (ADS)

    Periyannan, Suresh; Rajagopal, Prabhu; Balasubramaniam, Krishnan

    2016-06-01

    This paper introduces an ultrasonic torsional mode based technique, configured in the form of a helical "spring-like" waveguide, for multi-level temperature measurement. The multiple sensing levels can be repositioned by stretching or collapsing the spring to provide simultaneous measurements at different desired spacing in a given area/volume. The transduction is performed using piezo-electric crystals that generate and receive T(0,1) mode in a pulse echo mode. The gage lengths and positions of measurements are based on machining multiple reflector notches in the waveguide at required positions. The time of fight (TOF) measurements between the reflected signals from the notches provide local temperatures that compare well with co-located thermocouples.

  17. Helical plasma striations in liners in the presence of an external axial magnetic field

    NASA Astrophysics Data System (ADS)

    Atoyan, L.; Hammer, D. A.; Kusse, B. R.; Byvank, T.; Cahill, A. D.; Greenly, J. B.; Pikuz, S. A.; Shelkovenko, T. A.

    2016-02-01

    Awe et al. found on the 20 MA Z machine [Acta Phys. Pol. A 115, 956 (2009)] that applying an externally generated axial magnetic field to an imploding liner leads to a helical pattern in the liner when viewed with soft x-ray radiography ([Phys. Rev. Lett. 111, 235005 (2013)] and [Phys. Plasmas 21, 056303 (2014)]). Here, we show that this phenomenon is also observed in extreme ultraviolet self-emission images of 10 mm long cylindrical metal liners having varying diameters and varying wall thicknesses on a 1 MA, 100-200 ns pulsed power generator. The magnetic field in these experiments is created using either twisted return current wires positioned close to the liner, generating a time-varying Bz, or a Helmholtz coil, generating a steady-state Bz.

  18. ADJUSTABLE DOUBLE PULSE GENERATOR

    DOEpatents

    Gratian, J.W.; Gratian, A.C.

    1961-08-01

    >A modulator pulse source having adjustable pulse width and adjustable pulse spacing is described. The generator consists of a cross coupled multivibrator having adjustable time constant circuitry in each leg, an adjustable differentiating circuit in the output of each leg, a mixing and rectifying circuit for combining the differentiated pulses and generating in its output a resultant sequence of negative pulses, and a final amplifying circuit for inverting and square-topping the pulses. (AEC)

  19. Tubular crystals and helical arrays: structural determination of HIV-1 capsid assemblies using iterative helical real-space reconstruction.

    PubMed

    Zhang, Peijun; Meng, Xin; Zhao, Gongpu

    2013-01-01

    Helical structures are important in many different life forms and are well-suited for structural studies by cryo-EM. A unique feature of helical objects is that a single projection image contains all the views needed to perform a three-dimensional (3D) crystallographic reconstruction. Here, we use HIV-1 capsid assemblies to illustrate the detailed approaches to obtain 3D density maps from helical objects. Mature HIV-1 particles contain a conical- or tubular-shaped capsid that encloses the viral RNA genome and performs essential functions in the virus life cycle. The capsid is composed of capsid protein (CA) oligomers which are helically arranged on the surface. The N-terminal domain (NTD) of CA is connected to its C-terminal domain (CTD) through a flexible hinge. Structural analysis of two- and three-dimensional crystals provided molecular models of the capsid protein (CA) and its oligomer forms. We determined the 3D density map of helically assembled HIV-1 CA hexamers at 16 Å resolution using an iterative helical real-space reconstruction method. Docking of atomic models of CA-NTD and CA-CTD dimer into the electron density map indicated that the CTD dimer interface is retained in the assembled CA. Furthermore, molecular docking revealed an additional, novel CTD trimer interface.

  20. Tubular Crystals and Helical Arrays: Structural Determination of HIV-1 Capsid Assemblies Using Iterative Helical Real-Space Reconstruction

    PubMed Central

    Zhang, Peijun; Meng, Xin; Zhao, Gongpu

    2013-01-01

    Helical structures are important in many different life forms and are well-suited for structural studies by cryo-EM. A unique feature of helical objects is that a single projection image contains all the views needed to perform a three-dimensional (3D) crystallographic reconstruction. Here, we use HIV-1 capsid assemblies to illustrate the detailed approaches to obtain 3D density maps from helical objects. Mature HIV-1 particles contain a conical- or tubular-shaped capsid that encloses the viral RNA genome and performs essential functions in the virus life cycle. The capsid is composed of capsid protein (CA) oligomers which are helically arranged on the surface. The N-terminal domain (NTD) of CA is connected to its C-terminal domain (CTD) through a flexible hinge. Structural analysis of two- and three-dimensional crystals provided molecular models of the capsid protein (CA) and its oligomer forms. We determined the 3D density map of helically assembled HIV-1 CA hexamers at 16 Å resolution using an iterative helical real-space reconstruction method. Docking of atomic models of CA-NTD and CA-CTD dimer into the electron density map indicated that the CTD dimer interface is retained in the assembled CA. Furthermore, molecular docking revealed an additional, novel CTD trimer interface. PMID:23132072