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Sample records for 199mhg perturbed angular

  1. (Perturbed angular correlations in zirconia ceramics)

    SciTech Connect

    Not Available

    1990-01-01

    This is the progress report for the first year of the currently-approved three year funding cycle. We have carried on a vigorous program of experimental and theoretical research on microscopic properties of zirconia and ceria using the Perturbed Angular Correlation (PAC) experimental technique. The experimental method was described in the original proposal and in a number of references as well as several of the technical reports that accompany this progress report.

  2. Drell-Yan lepton angular distributions in perturbative QCD

    NASA Astrophysics Data System (ADS)

    Lambertsen, Martin; Vogelsang, Werner

    2016-06-01

    We present a comprehensive comparison of the available experimental data for the Drell-Yan lepton angular coefficients λ and ν to calculations at leading and next-to-leading order of perturbative QCD. To obtain the next-to-leading order corrections, we make use of publicly available numerical codes that allow us to compute the Drell-Yan cross section at second order in perturbation theory and from which the contributions we need can be extracted. Our comparisons reveal that perturbative QCD is able to describe the experimental data overall rather well, especially at colliders, but also in the fixed-target regime. On the basis of the angular coefficients alone, there appears to be little (if any) convincing evidence for effects that go beyond fixed-order collinear factorized perturbation theory, although the presence of such effects is not ruled out.

  3. Fully digital time differential perturbed angular correlation (TDPAC) spectrometer

    NASA Astrophysics Data System (ADS)

    Herden, C.; Röder, J.; Gardner, J. A.; Becker, K. D.

    2008-09-01

    A new generation time differential perturbed angular correlation (PAC) spectrometer has been designed and built. The design strategy and details of the data collection and reduction methodology are reported. First results obtained by the new spectrometer are reported and compared with PAC data obtained by more conventional means.

  4. Studying oxygen vacancies in ceramics by perturbed angular correlation spectroscopy

    SciTech Connect

    Su, Han-Tzong; Wang, Ruiping; Fuchs, H.; Gardner, J.A. . Dept. of Physics); Evenson, W.E. . Dept. of Physics); Sommers, J.A. )

    1990-01-01

    Perturbed angular correlation measurements in tetragonal and cubic zirconia and in ceria are described. A physically reasonable and self-consistent interpretation of these data implies that oxygen vacancies are trapped at a second neighbor position by Cd in tetragonal zirconia and by In in ceria. For Cd in tetragonal zirconia, the vacancy trap energy is found to be 0.44 eV, and the energy barrier between adjacent trap sites is approximately 0.8 eV. The activation energy of an oxygen vacancy hopping between trap sites around {sup 111}Cd in ceria is found to be 0.55 eV. The activation energy for oxygen vacancy hopping in cubic zirconia, as detected by {sup 181}Ta PAC, is about 1.0 eV and independent of the Y concentration. 12 refs., 4 figs.

  5. Contribution from cosmological scalar perturbations to the angular velocity spectrum of extragalactic sources

    SciTech Connect

    Marakulin, A. O. Sazhina, O. S.; Sazhin, M. V.

    2012-07-15

    The possibility of the influence of adiabatic scalar perturbations on the angular velocity spectrum of extragalactic sources is considered. The multipole expansion coefficients of the angular velocity field in terms of vector spherical harmonics are calculated. We show that there is no contribution from adiabatic perturbations to the angular spectrum for a spatially flat Universe at the dusty stage, while there is a contribution only to the electric multiple coefficients at the stage of {Lambda}-term domination. The cases of long-wavelength and short-wavelength perturbations are considered separately. The relationship between the multipole angular velocity spectrum and the primordial scalar perturbation spectrum is discussed.

  6. Contribution from cosmological scalar perturbations to the angular velocity spectrum of extragalactic sources

    NASA Astrophysics Data System (ADS)

    Marakulin, A. O.; Sazhina, O. S.; Sazhin, M. V.

    2012-07-01

    The possibility of the influence of adiabatic scalar perturbations on the angular velocity spectrum of extragalactic sources is considered. The multipole expansion coefficients of the angular velocity field in terms of vector spherical harmonics are calculated. We show that there is no contribution from adiabatic perturbations to the angular spectrum for a spatially flat Universe at the dusty stage, while there is a contribution only to the electric multiple coefficients at the stage of Λ-term domination. The cases of long-wavelength and short-wavelength perturbations are considered separately. The relationship between the multipole angular velocity spectrum and the primordial scalar perturbation spectrum is discussed.

  7. Linear force and moment equations for an annular smooth shaft seal perturbed both angularly and laterally

    NASA Technical Reports Server (NTRS)

    Fenwick, J.; Dijulio, R.; Ek, M. C.; Ehrgott, R.

    1982-01-01

    Coefficients are derived for equations expressing the lateral force and pitching moments associated with both planar translation and angular perturbations from a nominally centered rotating shaft with respect to a stationary seal. The coefficients for the lowest order and first derivative terms emerge as being significant and are of approximately the same order of magnitude as the fundamental coefficients derived by means of Black's equations. Second derivative, shear perturbation, and entrance coefficient variation effects are adjudged to be small.

  8. Interpretation of perturbed angular distribution results for19F implanted into diamond

    NASA Astrophysics Data System (ADS)

    Connell, S.; Sellschop, J. P. F.; Stemmet, M. C.; Appel, H.; Bharuth-Ram, K.; Verwoerd, W. S.

    1990-08-01

    Perturbed Angular Distribution measurements have been made on natural diamond using recoil implanted fluorine ions as probes. Two distinct lattice sites for fluorine in diamond were found. Site identifications prompted by theoretical cluster calculations are presented. The PAD data are well described by a texture theory, though the origin of the texture effects is presently not known.

  9. Static Magnetic Properties of Films Measured by Means of Angular Perturbative Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Oliveira, Alexandre; Melo, Abner; da Costa, Ricardo; Chesman, Carlos

    In this work we introduced a new technique to measure magnetic anisotropies and magnetoelectrical properties, such as Anisotropic Magnetoresistance (AMR) and Giant Magnetoresistance (GMR) amplitudes. The Perturbative Magnetoresistance (PMR) consist of a regular collinear four probe magnetoresistance set up with an AC magnetic field (hac) applied perpendicular to the DC (Hdc) one. hac amplitude is about 1.0 Oe and oscillate at 270 Hz. We successfully interpreted the signal response from the voltage measured by lock-in amplifier and proposed a model based on energy minimization to extract magnetic anisotropies, AMR and GMR amplitudes. Measuring the in-plane angular dependency of PMR signal we were able to identify the usual magnetic anisotropy, such as uniaxial, unidirectional and cubic. Taking into account the perturbative nature of this technique (small hac amplitude and low frequency), we argue that angular PMR can be used to investigate some dynamic magnetic effects where static technique can not provide such information. A distinct feature of angular PMR is the capability to be used in saturated and non-saturated regime, so revealing magnetic properties dependency on applied field strength. We addressed the Rotatable Anisotropy as an example in this work.

  10. Second order classical perturbation theory for atom surface scattering: Analysis of asymmetry in the angular distribution

    SciTech Connect

    Zhou, Yun Pollak, Eli; Miret-Artés, Salvador

    2014-01-14

    A second order classical perturbation theory is developed and applied to elastic atom corrugated surface scattering. The resulting theory accounts for experimentally observed asymmetry in the final angular distributions. These include qualitative features, such as reduction of the asymmetry in the intensity of the rainbow peaks with increased incidence energy as well as the asymmetry in the location of the rainbow peaks with respect to the specular scattering angle. The theory is especially applicable to “soft” corrugated potentials. Expressions for the angular distribution are derived for the exponential repulsive and Morse potential models. The theory is implemented numerically to a simplified model of the scattering of an Ar atom from a LiF(100) surface.

  11. Perturbed angular correlation study of radiation-induced defects in Rh metal

    NASA Astrophysics Data System (ADS)

    Chawda, M.; Patel, N.; Sebastian, K. C.; Somayajulu, D. R. S.; Sarkar, M.; Singh, R. P.; Murlithar, S.; Awasthi, D. K.

    2006-06-01

    Radiation-induced defects are studied in cubic rhodium metal, using the local probe technique 'Time differential perturbed angular correlation (TDPAC) at liquid N-2 temperature. Isochronal annealing was done at 300, 1073 and 1473 K temperatures. The irradiated sample showed two quadrupole interaction frequencies at 1150 and 93 MHz. The low frequency disappeared at room-temperature annealing, which was assigned to In trapped at a vacancy, whereas the higher frequency remained up to high temperatures and was attributed to In trapped at Rh-C complexes in the Rh matrix.

  12. Perturbed angular correlation experiments on the pressure-induced structural modification of bovine serum albumin.

    PubMed

    Ceolín, M

    2000-09-11

    The hydrodynamic behaviour of the bovine serum albumin (BSA) was studied by means of the Perturbed Angular Correlation (PAC) technique as a function of the hydrostatic pressure (up to 4.1 kbar) applied to the sample. The results have clearly shown that at moderated pressures (around 1.5 kbar) the BSA molecule suffers structural modifications which produces an increase of the molecular volume and the rotational correlation time of the molecule. About the reversibility of the process, our results indicate that the changes are fully irreversible. Our experiments are the first devoted to the study of the high-pressure behaviour of biological molecules using the PAC technique. PMID:10989128

  13. Magnetic interaction in NdScGe: a local investigation by perturbed angular correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Mishra, S. N.; Dhar, S. K.

    2004-02-01

    The magnetic and electric hyperfine interactions for the 111Cd probe nucleus in the equi-atomic ferromagnetic compound NdScGe (T_{\\mathrm {c}}\\sim 200 K) have been investigated by the time differential perturbed angular correlation (TDPAC) technique. The Cd probe occupying the Sc site experiences a large magnetic hyperfine field with saturation value Bhf(0) = -8.5 T. By comparing the results with the hyperfine field data in Nd metal and estimates made with the RKKY interaction, we find an indication for sizeable spin polarization of the conduction electrons in NdScGe. In addition, we find evidence of lattice softening near the Curie temperature reflected by an abrupt decrease in the quadrupole interaction frequency ngrQ(T).

  14. Hyperfine magnetic field at Ta impurities in nickel: Perturbed angular correlation and first principle calculation study

    NASA Astrophysics Data System (ADS)

    Cekić, B. Dj.; Umićević, A. B.; Belošević-Čavor, J. N.; Koteski, V. J.; Ivanovski, V. N.; Stojković, M. N.

    2008-03-01

    The hyperfine magnetic field (H) in 0.2 at.% Hf-Ni alloy is measured at the 181Ta probe using the time-differential perturbed angular correlation (TDPAC) method, in the temperature range 78-675 K. The obtained value of 8.6 (3) T at room temperature is in good agreement with the previously reported measurements for similar Hf concentrations in Ni. X-ray powder diffraction (XRPD) experiments confirmed that small atomic concentrations of Hf atoms (<1 at.%) mainly substitute on Ni lattice sites in the fcc crystal lattice without forming any intermetallic phase. In addition, ab-initio calculation using all-electron augmented plane waves plus local orbitals (APW+lo) formalism is performed and the obtained result for the hyperfine magnetic field at Ta site is in accordance with the measurement.

  15. Quantum beats in the 3γ annihilation decay of Positronium observed by perturbed angular distribution

    NASA Astrophysics Data System (ADS)

    Ivanov, Eugeniu; Vata, Ion; Dudu, Dorin; Rusen, Ion; Stefan, Nitisor

    2008-10-01

    We have applied conventional Time Differential Perturbed Angular Correlation (TDPAC) method to observe the anisotropy oscillations in the 3γ annihilation decay of polarized Positronium in a weak magnetic field. The effect, as predicted theoretically and experimentally demonstrated by Barishevsky et al. [V.G. Barishevsky, O.N. Metelitsa, V.V. Tikhomirov, Oscillations of the positronium decay γ-quantum angular distribution in a magnetic field, J. Phys. B: At. Mol. Opt. Phys.22 (1989) 2835], is induced by the coherent admixture of the m = 0 states of ortho-Positronium ( o-Ps) and para-Positronium ( p-Ps) in interaction with the magnetic field. The following experimental characteristics are to be considered: the oscillation frequency corresponds to the difference in energy of the Ps atom levels in magnetic field and is proportional with H2; in a fixed geometry the modulation depth (oscillations amplitude) depends on the mean positron polarization; privileged angles of the polarization vector, magnetic field and detectors are required for optimizing the observed oscillations amplitude. The normalized difference spectrum function ( R( t)) obtained from time spectra measured in vacuum and in different gaseous atmospheres (Ar, H 2, N 2) have the oscillations amplitude constant and we conclude that the Ps atoms are not fully thermalized over a time interval of about 400 ns. The R( t) functions obtained for o-Ps annihilation decays, in dry air or Ar-O mixture, have the oscillations amplitude time dependent due, probably, to the paramagnetism of the Oxygen molecules.

  16. On angularly perturbed Laplace equations in the unit ball of IR{sup n+2} and their distributional boundary values

    SciTech Connect

    Massopust, P.R.

    1997-08-01

    All solutions of an in its angular coordinates continuously perturbed Laplace-Beltrami equation in the open unit ball IB{sup n+2} {contained_in} IR{sup n+2}, n {ge} 1, are characterized. Moreover, it is shown that such pertubations yield distributional boundary values which are different from, but algebraically and topologically equivalent to, the hyperfunctions of Lions & Magenes. This is different from the case of radially perturbed Laplace-Beltrami operators (cf. [7]) where one has stability of distributional boundary values under such perturbations.

  17. Time differential perturbed angular correlation (TDPAC) studies of the 133Ba ion uptake in bone crystals.

    PubMed

    Rimbert, J N; Kellershohn, C; Dumas, F; Hubert, C

    1981-03-01

    TDPAC measurements of the 356-81 keV gamma-ray cascade resulting from electron capture decay of 133Ba have been performed at room temperature on BaCl2 (aqueous solution and polycrystalline powder), and on samples where the 133Ba nucleus is bound to bone powder, and also to synthesised hydroxylapatite, all after absorption in vitro. As expected, the angular correlation is not perturbed in the solution. However, in the polycrystalline chloride the time dependence of the anisotropy of the cascade of 133Cs nuclide indicates that the decaying nucleus undergoes electric interactions due to different electric field gradients acting at the site of the nucleus. In 133Ba-bone powder the results show a static quadrupolar interaction differing with the absorption contact time during sample preparation, indicating that depth of 133Ba ion fixation in the bone crystal is dependent on this contact time. These results seem to be confirmed by the TDPAC measurements performed on 133Ba-hydroxylapatite samples where the contact times for absorption of active-ion 133Ba and hydroxylapatite in suspension were very different. PMID:7220599

  18. Perturbed angular correlation study of the ion exchange of indium into silicalite zeolites

    NASA Astrophysics Data System (ADS)

    Ramallo-López, J. M.; Requejo, F. G.; Rentería, M.; Bibiloni, A. G.; Miró, E. E.

    1999-09-01

    Two indium-containing silicalite zeolites (In/H ZSM5) catalysts prepared by wet impregnation and ionic exchange were characterized by the Perturbed Angular Correlation (PAC) technique using 111In as probe to determine the nature of the indium species. Some of these species take part in the catalytic reaction of the selective reduction (SCR) of NOx with methane. PAC experiments were performed at 500ºC in air before and after reduction reoxidation treatments on the catalysts in order to determine the origin of the different hyperfine interactions and then the degree of ionic exchange. Complementary catalytic activity characterizations were also performed. PAC experiments performed on the catalyst obtained by wet impregnation showed that all In-atoms form In2O3 crystallites while almost 70% of In-atoms form In2O3 in the catalyst obtained by ionic exchange. The PAC experiments of both catalysts performed after the reduction reoxidation treatment revealed the presence of two hyperfine interactions, different from those corresponding to indium in In2O3. These hyperfine interactions should be associated to disperse In species responsible of the catalytic activity located in the ionic exchange-sites of the zeolites.

  19. Stability of erythrocyte ghosts: a gamma-ray perturbed angular correlation study.

    PubMed Central

    Kruse, C A; Tin, G W; Baldeschwieler, J D

    1983-01-01

    The structural integrity of erythrocyte ghosts made by the preswell and slow-dialysis techniques has been studied in vitro by use of gamma-ray perturbed angular correlation (PAC) techniques and also by standard in vitro leakage methods employing sequestered labeled markers. Complexes of 111In3+ and nitrilotriacetate were encapsulated in ghosts made from human, rabbit, rat, and mouse erythrocytes, and their leakage was monitored by both methods. In addition, 125I-labeled bovine serum albumin was encapsulated, and ghost integrity was monitored by conventional leakage measurements. With the PAC technique the percentage of material released from human ghosts was determined quantitatively, and the results were equivalent to those obtained by the conventional method. In addition, at various times after intravenous injection, tissue distribution of the ghosts in the mouse was studied. The percent injected dose per gram of tissue of the labeled surface proteins of erythrocyte ghosts in circulation approximated that of the entrapped labeled albumin. This suggests that the ghost membrane and contents are strongly associated in vivo. Large 125I-labeled bovine serum albumin molecules and small 111In3+-nitrilotriacetate complexes were delivered in high quantitites to the lung initially, and to the liver and spleen. Because erythrocyte ghosts have the ability to entrap a wide range of substances and deliver them to specific organs, ghosts may be preferable to other drug carriers or drug therapy for treatment of certain disorders. PMID:6572379

  20. Studies of point-defect interactions in solids using perturbed angular correlations

    SciTech Connect

    Schuhmann, R.B.

    1988-01-01

    Vacancy defect production and migration in {sup 111}In doped Au, Pt and Ni following plastic deformation are studied via {sup 111}Cd perturbed {gamma}-{gamma} angular correlations (TDPAC). In all three metals, deformation produces the same defect species as are seen following irradiation. In Au, a particular In-vacancy complex which is probably a trapped divacancy exists in two distinct configurations. Thermal conversion from one configuration to the other occurs near 200K. In Pt, an In-vacancy complex exhibits a strongly temperature dependent electric field gradient, indicating the presence of local resonant modes. In Ni, a relaxed In-trivacancy complex forms via simple, single-step trapping of a migrating trivacancy. Once formed, the In-trivacancy complex in Ni can trap up to four guest H or D atoms. These are bound to the complex with an energy of {approximately}0.5 eV, irrespective of isotopic mass. By monitoring the damping of the TDPAC precession not associated with a bound defect, the author observed release of untrapped interstitial H from the lattice. These experiments give a consistent, microscopic picture of H diffusion and release from Ni. The use of BaF{sub 2} scintillators allows for an eightfold improvement in TDPAC time resolution. This makes possible experiments in systems previously inaccessible due to large precessional frequencies. The author demonstrates the utility of BaF{sub 2} in several examples, including {sup 100}RhNi, {sup 99}TcFe, {sup 101}RuFe, {sup 100}RhCo and {sup 100}RhFe, systems which had not been studied previously due to time resolution limitation. The Larmor frequency for {sup 100}RhFe, 5565 Mrad/s, is the highest frequency ever measured via TDPAC.

  1. Atomic jump frequencies in intermetallic compounds studied using perturbed angular correlation of gamma rays

    NASA Astrophysics Data System (ADS)

    Newhouse, Randal Leslie

    Atomic jump frequencies were determined in a variety of intermetallic compounds through analysis of nuclear relaxation of spectra measured using the nuclear hyperfine technique, perturbed angular correlation (PAC) of gamma rays. Observed at higher temperatures, this relaxation is attributed to fluctuations in the orientation or magnitude of electric field gradients (EFG) at nuclei of 111In/Cd probe atoms as the atoms make diffusive jumps. Jump frequencies were obtained by fitting dynamically relaxed PAC spectra using either an empirical relaxation function or using ab initio relaxation models created using the program PolyPacFit. Jump frequency activation enthalpies were determined from measurements over a range of temperatures. Diffusion was studied in the following systems: 1) Pseudo-binary alloys having the L12 crystal structure such as In3(La1-xPrx). The goal was to see how jump frequencies were affected by random disorder. 2) The family of layered phases, LanCoIn3n+2 ( n=0,1,2,3…∞). The goal was to see how jump frequencies varied with the spacing of Co layers, which were found to block diffusion. 3) Phases having the FeGa3 structure. The goal was to analyze dynamical relaxation for probe atoms having multiple inequivalent jump vectors. 4) Phases having the tetragonal Al4Ba structure. The goal was to search for effects in the PAC spectra caused by fluctuations in magnitudes of EFGs without fluctuations in orientations. Ab initio relaxation models were developed to simulate and fit dynamical relaxation for PAC spectra of FeGa3, and several phases with the Al4Ba structure in order to determine underlying microscopic jump frequencies. In the course of this work, site preferences also were observed for 111In/Cd probe atoms in several FeGa 3 and Al4Ba phases.

  2. Resonance and absorption spectra of the Schwarzschild black hole for massive scalar perturbations: A complex angular momentum analysis

    SciTech Connect

    Decanini, Yves; Raffaelli, Bernard; Folacci, Antoine

    2011-10-15

    We reexamine some aspects of scattering by a Schwarzschild black hole in the framework of complex angular momentum techniques. More precisely, we consider, for massive scalar perturbations, the high-energy behavior of the resonance spectrum and of the absorption cross section by emphasizing analytically the role of the mass. This is achieved (i) by deriving asymptotic expansions for the Regge poles of the S-matrix and then for the associated weakly damped quasinormal frequencies and (ii) by taking into account the analytic structure of the greybody factors which allows us to extract by resummation the physical information encoded in the absorption cross section.

  3. Perturbed Angular Correlation of the stretched cascade in the decay of 180mHf using a digital spectrometer

    NASA Astrophysics Data System (ADS)

    Jäger, Markus; Butz, Tilman

    2012-05-01

    We report on the measurement of the nuclear quadrupole interaction (NQI) at Hf sites using the nuclear probe 180mHf in HfF4·HF·2H2O at 300 K by exploiting all possible start quanta in the stretched cascade with a digital Time Differential Perturbed Angular Correlation (TDPAC) spectrometer. With conventional spectrometers, multiple prompt start signals would paralyze the router. The gain in coincidence rate is about a factor of 5 compared to a conventional spectrometer using a single start only. With multiple starts 180mHf is a promising new isomeric nuclear probe in TDPAC experiments. As an additional feature we implemented the possibility to measure up to four cascades simultaneously in order to save data collection time or to measure isobaric contaminations like 111mCd and 111In.

  4. Nuclear quadrupole interaction at 181Ta in hafnium dioxide fiber: Time differential perturbed angular correlation measurements and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Banerjee, D.; Das, P.; Guin, R.; Das, S. K.

    2012-09-01

    The thermal behavior of hafnium dioxide fiber has been investigated with the aid of time differential perturbed angular correlation (TDPAC) technique along with XRD and SEM measurements. This study has proved a good thermal stability of the fibrous material up to 1173 K and the fiber loses its crystallinity to a meager extent at 1673 K. No phase transition has been observed up to 1673 K in this fiber. TDPAC parameters for the HfO2 fiber annealed at 1173 K are ωQ=124.6 (3) Mrad/s and η=0.36 (1). These values remain unaltered for the HfO2 fiber annealed even at 1673 K. Electronic structure calculations based on the density functional theory (DFT) for HfO2 doped with tantalum impurity have been performed and the calculated EFG parameters are in reasonable agreement with the experimental values.

  5. A Perturbed-Angular-Correlation Study of Hyperfine Interactions at 181Ta in α-Fe2O3

    NASA Astrophysics Data System (ADS)

    Pasquevich, A. F.; Junqueira, A. C.; Carbonari, A. W.; Saxena, R. N.

    2004-11-01

    The hyperfine interactions at 181Ta ions on Fe3+ sites in α-Fe2O3 (hematite) were studied in the temperature range 11 1100 K by means of the perturbed angular correlation (PAC) technique. The 181Hf(β-)181Ta probe nuclei were introduced chemically into the sample during the preparation. The hyperfine interaction measurements allow to observe the magnetic phase transition and to characterize the supertransferred hyperfine magnetic field Bhf and the electric field gradient (EFG) at the impurity sites. The angles between Bhf and the principal axes of the EFG were determined. The Morin transition was also observed. The results are compared with those of similar experiments carried out using 111Cd probe.

  6. Oxidation of Hafnium and Diffusion of Hafnium Atoms in Hexagonal Close-Packed Hafnium; Microscopic Investigations by Perturbed Angular Correlations

    NASA Astrophysics Data System (ADS)

    Dey, Chandi C.

    2012-11-01

    Time-differential perturbed angular correlation (TDPAC) studies in hafnium metal (~5%Zr) have been carried out at different temperatures. It is found that hafnium metal on heating at 873 K continuously for two days in air, transforms partially and abruptly to HfO2 while no component of oxide has been observed for heating up to 773 K and during initial heating at 873 K for 1 day. This result is strikingly different to that expected from the Arrhenius theory. Also, a strong nuclear relaxation effect has been observed at 873 K due to rapid fluctuation of hafnium atoms in hexagonal closepacked (hcp) hafnium. At this temperature, ~ 5% probe nuclei experience static perturbation due to monoclinic HfO2, ~ 50% experience fluctuating interaction, and ~ 5% produce static defect configuration of hcp hafnium. With lowering of temperature, defect configurations of hafnium increase at the cost of fluctuating interaction. An almost total fluctuating interaction observed in hcp hafnium at a temperature much lower than its melting point is another interesting phenomenon.

  7. Low temperature structural modification in Rb2ZrF6: Investigations by perturbed angular correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Dey, S. K.; Dey, C. C.; Saha, S.

    2016-06-01

    Temperature dependent perturbed angular correlation (PAC) measurements in crystalline compounds Rb2ZrF6 and Cs2HfF6 have been performed in the temperature range 298-753 K. In Rb2ZrF6, four discrete quadrupole interaction frequencies have been observed at room temperature which correspond to four minor structural modifications. From previous measurements, on the other hand, two structural modifications of this compound were known. A displacive phase transition, probably, occurs at low temperature due to rotation of the ZrF62- octahedron and produces different structural modifications. From present measurements in Rb2ZrF6, two quadrupole interaction frequencies [ωQ=26.1(3) Mrad/s, η=0.55(2), δ=5(1)% and ωQ=148.7(3) Mrad/s, η=0.538(5), δ=1.2%] have been found at room temperature which were not found from previous studies. In Cs2HfF6, these new structural modifications have not been observed.

  8. A compact digital time differential perturbed angular correlation-spectrometer using field programmable gate arrays and various timestamp algorithms.

    PubMed

    Jäger, Markus; Iwig, Kornelius; Butz, Tilman

    2011-06-01

    A user-friendly fully digital time differential perturbed angular correlation (TDPAC)-spectrometer with six detectors and fast digitizers using field programmable gate arrays (FPGA) is described and performance data are given. The new spectrometer has an online data analysis feature, a compact size, and a time resolution such as conventional analog spectrometers. Its calculation intensive part was implemented inside the digitizer. This gives the possibility to change parameters (energy windows, constant fraction trigger delay) and see their influence immediately in the γ-γ correlation diagrams. Tests were performed which showed that the time resolution using a (60)Co source with energy window set at 1.17 MeV and 1.33 MeV is 265 ps with LaBr(3)(Ce) scintillators and 254 ps with BaF(2) scintillators. A true constant fraction algorithm turned out to be slightly better than the constant fraction of amplitude method. The spectrometer performance was tested with a TDPAC measurement using a (44)Ti in rutile source and a positron lifetime measurement using (22)Na. The maximum possible data rate of the spectrometer is 1.1 × 10(6) γ quanta per detector and second. PMID:21721728

  9. A compact digital time differential perturbed angular correlation-spectrometer using field programmable gate arrays and various timestamp algorithms

    SciTech Connect

    Jaeger, Markus; Butz, Tilman; Iwig, Kornelius

    2011-06-15

    A user-friendly fully digital time differential perturbed angular correlation (TDPAC)-spectrometer with six detectors and fast digitizers using field programmable gate arrays (FPGA) is described and performance data are given. The new spectrometer has an online data analysis feature, a compact size, and a time resolution such as conventional analog spectrometers. Its calculation intensive part was implemented inside the digitizer. This gives the possibility to change parameters (energy windows, constant fraction trigger delay) and see their influence immediately in the {gamma}-{gamma} correlation diagrams. Tests were performed which showed that the time resolution using a {sup 60}Co source with energy window set at 1.17 MeV and 1.33 MeV is 265 ps with LaBr{sub 3}(Ce) scintillators and 254 ps with BaF{sub 2} scintillators. A true constant fraction algorithm turned out to be slightly better than the constant fraction of amplitude method. The spectrometer performance was tested with a TDPAC measurement using a {sup 44}Ti in rutile source and a positron lifetime measurement using {sup 22}Na. The maximum possible data rate of the spectrometer is 1.1 x 10{sup 6} {gamma} quanta per detector and second.

  10. Interaction of positronium atoms, with paramagnetic molecules, measured by perturbed angular distribution in 3γ annihilation decay

    NASA Astrophysics Data System (ADS)

    Ivanov, Eugeniu; Vata, Ion; Teodorian, Stefan; Rusen, Ion; Stefan, Nitisor

    2009-01-01

    Positronium in the triplet spin state (S = 1) decays by 3γ annihilation having a life time of about 140 ns in vacuum. Positronium annihilation is affected by magnetic fields which mix the M = 0 state of ortho-positronium with the M = 0 state of para-positronium. The mixing fraction depends on the magnetic field intensity and causes quantum beats in the time distribution of γ annihilation decay. This effect was predicted by Barishevsky et al. [V.G. Barishevsky, O.N. Metelitsa, V.V. Tikhomirov, J. Phys. B Atom. Mol. Opt. Phys. 22 (1989) 2835]. The time differential perturbed angular correlation method (TDPAC), combined with long-lived positron life time spectroscopy (PLTS), has been used to observe these quantum beats. It is found that the characteristics of the annihilation time distribution are not influenced by the presence of diamagnetic species such as Ar, N2 and H2 but are affected by the presence of the paramagnetic O2 molecule. Our results are encouraging in developing a new method for investigating magnetic fields on an atomic scale.

  11. PAC (perturbed angular correlation) analysis of defect motion by Blume's stochastic model for I = 5/2 electric quadrupole interactions

    SciTech Connect

    Evenson, W.E. . Dept. of Physics and Astronomy); Gardner, J.A.; Wang, Ruiping . Dept. of Physics); Su, Han-Tzong ); McKale, A.G. )

    1990-01-01

    Using Blume's stochastic model and the approach of Winkler and Gerdau, we have computed-time-dependent effects on perturbed angular correlation (PAC) spectra due to defect motion in solids in the case of I = (5/2) electric quadrupole interactions. We report detailed analysis for a family of simple models: XYZ + Z'' models, in which the symmetry axis of an axial efg is allowed to fluctuate among orientations along x, y, and z axes, and a static axial efg oriented along the z axis is added to the fluctuating efgs. When the static efg is zero, this model is termed the XYZ'' model. Approximate forms are given for G{sub 2}(t) in the slow and rapid fluctuation regimes, i.e. suitable for the low and high temperature regions, respectively. Where they adequately reflect the underlying physical processes, these expressions allow one to fit PAC data for a wide range of temperatures and dopant concentrations to a single model, thus increasing the uniqueness of the interpretation of the defect properties. Application of the models are given for zirconia and ceria ceramics. 14 refs.

  12. A compact digital time differential perturbed angular correlation-spectrometer using field programmable gate arrays and various timestamp algorithms

    NASA Astrophysics Data System (ADS)

    Jäger, Markus; Iwig, Kornelius; Butz, Tilman

    2011-06-01

    A user-friendly fully digital time differential perturbed angular correlation (TDPAC)-spectrometer with six detectors and fast digitizers using field programmable gate arrays (FPGA) is described and performance data are given. The new spectrometer has an online data analysis feature, a compact size, and a time resolution such as conventional analog spectrometers. Its calculation intensive part was implemented inside the digitizer. This gives the possibility to change parameters (energy windows, constant fraction trigger delay) and see their influence immediately in the γ-γ correlation diagrams. Tests were performed which showed that the time resolution using a 60Co source with energy window set at 1.17 MeV and 1.33 MeV is 265 ps with LaBr3(Ce) scintillators and 254 ps with BaF2 scintillators. A true constant fraction algorithm turned out to be slightly better than the constant fraction of amplitude method. The spectrometer performance was tested with a TDPAC measurement using a 44Ti in rutile source and a positron lifetime measurement using 22Na. The maximum possible data rate of the spectrometer is 1.1 × 106 γ quanta per detector and second.

  13. Temperature dependence of electric field gradient in LaCoO3 perovskite investigated by perturbed angular correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Junqueira, Astrogildo C.; Carbonari, Artur W.; Saxena, Rajendra N.; Mestnik-Filho, José; Dogra, Rakesh

    2005-11-01

    The time differential perturbed angular correlation (TDPAC) technique was used to study the temperature dependence of electric field gradient (EFG) in LaCoO3 perovskite using {}^{111}\\mathrm {In}\\rightarrow {}^{111}\\mathrm {Cd} and {}^{181}\\mathrm {Hf} \\rightarrow {}^{181}\\mathrm {Ta} nuclear probes. The radioactive parent nuclei 111In and 181Hf were introduced into the oxide lattice through a chemical process during sample preparation and were found to occupy only the Co sites in LaCoO3. The PAC measurements with 111Cd and 181Ta probes were made in the temperature range of 4.2-1146 K and 4.2-1004 K, respectively. No long-range magnetic order was observed up to 4.2 K. The EFGs at 111Cd and 181Ta show very similar temperature dependences. They increase slowly between 4.2 and about 77 K and then decrease almost linearly with increasing temperature until about 500-600 K, where a broad peak-like structure is observed, followed by linear decrease at still higher temperatures. These discontinuities at about 77 K and 500-600 K have been interpreted as thermally activated spin state transitions from the low-spin (t2g6eg0) ground state configuration to the intermediate-spin (t2g5eg1) state and from the intermediate-spin to the high-spin (t2g4eg2) state of the Co3+ ion, confirming previous observation in other recent studies. An indication of a Jahn-Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out.

  14. Time-differential perturbed angular correlation study of the electric field gradient in Ti2Rh MoSi2-type compound

    NASA Astrophysics Data System (ADS)

    Wodniecki, P.; Kulińska, A.; Wodniecka, B.

    The electric field gradient (EFG) at the 181Hf→181Ta site in Ti2Rh C11 b -type compound was measured as a function of temperature using time-differential perturbed angular correlation (TDPAC) technique. The room temperature results show one EFG with the parameters of: ν Q =336(1) MHz→V zz =5.9×1017 V cm-2, η=0.1. Very week linear temperature dependence of this EFG was measured with the slope of 3.6 (2)×10-5 K-1. The results are compared with those for other isostructural compounds.

  15. Time-differential perturbed angular correlation study of the electric field gradient in Ti2Rh MoSi2-type compound

    NASA Astrophysics Data System (ADS)

    Wodniecki, P.; Kulińska, A.; Wodniecka, B.

    2007-06-01

    The electric field gradient (EFG) at the 181Hf→181Ta site in Ti2Rh C11 b -type compound was measured as a function of temperature using time-differential perturbed angular correlation (TDPAC) technique. The room temperature results show one EFG with the parameters of: ν Q = 336(1) MHz→V zz =5.9 × 1017 V cm - 2, η = 0.1. Very week linear temperature dependence of this EFG was measured with the slope of 3.6 (2) × 10 - 5 K - 1. The results are compared with those for other isostructural compounds.

  16. Three-hadron angular correlations in high-energy proton-proton and nucleus-nucleus collisions from perturbative QCD

    SciTech Connect

    Ayala, Alejandro; Ortiz, Antonio; Paic, Guy; Jalilian-Marian, Jamal; Magnin, J.; Tejeda-Yeomans, Maria Elena

    2011-08-15

    We study three-hadron azimuthal angular correlations in high-energy proton-proton and central nucleus-nucleus collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider at midrapidity. We use the leading-order parton matrix elements for 2{yields}3 processes and include the effect of parton energy loss in the quark-gluon plasma using the modified fragmentation function approach. For the case when the produced hadrons have either the same or not too different momenta, we observe two away-side peaks at 2{pi}/3 and 4{pi}/3. We consider the dependence of the angular correlations on energy loss parameters that have been used in studies of single inclusive hadron production at RHIC. Our results on the angular dependence of the cross section agree well with preliminary data by the PHENIX Collaboration. We comment on the possible contribution of 2{yields}3 processes to dihadron angular correlations and how a comparison of the two processes may help characterize the plasma further.

  17. PAC (perturbed angular correlation) perturbation factor for spin 5/2 nuclei subject to a rapidly fluctuation EFC (electric field gradient)

    SciTech Connect

    Evenson, W.E. . Dept. of Physics and Astronomy); McKale, A.G.; Su, H.T.; Gardner, J.A. . Dept. of Physics)

    1990-01-01

    We report numerical computations of the PAC perturbation factor G{sub 2}(t) for spin 5/2 nuclei subject to a static EFG symmetric about the z-axis and an additional axially-symmetric EFG hose symmetry axis fluctuates randomly among the x,y,z directions. For sufficiently large fluctuation rates, the numerical results are described by the expression for the static interaction alone with the addition of relaxation terms. Results of applying this model to {sup 111}Cd TDPAC measurements on tetragonal ZrO{sub 2} are described briefly. The model allows one to evaluate the probability that oxygen vacancies are trapped, the energy of association of vacancy-metal pairs, and the vacancy activation energy of motion. 4 refs., 3 figs.

  18. Online time-differential perturbed angular correlation study with an 19O beam - Residence sites of oxygen atoms in highly oriented pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Sato, W.; Ueno, H.; Watanabe, H.; Miyoshi, H.; Yoshimi, A.; Kameda, D.; Ito, T.; Shimada, K.; Kaihara, J.; Suda, S.; Kobayashi, Y.; Shinohara, A.; Ohkubo, Y.; Asahi, K.

    2008-01-01

    The online time-differential perturbed angular correlation (TDPAC) method was applied to a study of the physical states of a probe 19F, the β- decay product of 19O (t1/2 = 26.9 s), implanted in highly oriented pyrolytic graphite. The observed magnitude of the electric field gradient at the probe nucleus, ∣Vzz∣ = 2.91(17) × 1022 V m-2, suggests that the incident 19O atoms are stabilized at an interlayer position with point group C3v. Exhibiting observed TDPAC spectra having a clear sample-to-detector configuration dependence, we demonstrate the applicability of the present online method with a short-lived radioactive 19O beam.

  19. Dynamic lattice distortions in Sr2RuO4: microscopic studies by perturbed angular correlation spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Mishra, S. N.; Rots, M.; Cottenier, S.

    2010-09-01

    Applying time differential perturbed angular correlation (TDPAC) spectroscopy and ab initio calculations, we have investigated possible lattice instabilities in Sr2RuO4 by studying the electric quadrupole interaction of a 111Cd probe at the Ru site. We find evidence for a dynamic lattice distortion, revealed from the observations of: (i) a rapidly fluctuating electric-field gradient (EFG) tensor showing non-Arrhenius relaxation, (ii) an anomalous temperature dependence of the quadrupole interaction frequency, and (iii) a monotonic increase of the EFG asymmetry (η) below 300 K. We argue that the observed dynamic lattice distortion is caused by strong spin fluctuations associated with the inherent magnetic instability in Sr2RuO4.

  20. Dynamic lattice distortions in Sr2RuO4: microscopic studies by perturbed angular correlation spectroscopy and ab initio calculations.

    PubMed

    Mishra, S N; Rots, M; Cottenier, S

    2010-09-29

    Applying time differential perturbed angular correlation (TDPAC) spectroscopy and ab initio calculations, we have investigated possible lattice instabilities in Sr(2)RuO(4) by studying the electric quadrupole interaction of a (111)Cd probe at the Ru site. We find evidence for a dynamic lattice distortion, revealed from the observations of: (i) a rapidly fluctuating electric-field gradient (EFG) tensor showing non-Arrhenius relaxation, (ii) an anomalous temperature dependence of the quadrupole interaction frequency, and (iii) a monotonic increase of the EFG asymmetry (η) below 300 K. We argue that the observed dynamic lattice distortion is caused by strong spin fluctuations associated with the inherent magnetic instability in Sr(2)RuO(4). PMID:21386555

  1. A weak magnetism observed in SnO2 doped with Fe by means of Perturbed Gamma-Gamma Angular Correlation and Mössbauer Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ramos, J. M.; Carbonari, A. W.; Martucci, T.; Costa, M. S.; Cabrera-Pasca, G. A.; Macedo, M. A. V.; Saxena, R. N.

    Nano-structured samples of SnO2 doped with Fe prepared by the sol-gel method were studied by the Perturbed Gamma-Gamma Angular Correlation (PAC) Spectroscopy using 111In (111Cd) probe nuclei as well as by 57Fe Mšssbauer spectroscopy. The samples were prepared from very pure metallic Sn and Fe. Carrier-free 111In nuclei were introduced during the sol-gel process of sample preparation for PAC measurements. The PAC measurements were carried out after annealing the samples at different temperatures and the results show a combined electric quadrupole and magnetic dipole interaction for probe nuclei that do not occupy the regular Sn sites. The hyperfine parameters revealed weak magnetic interactions.

  2. Local probe studies of Fe hyperfine field in CaFe2As2 by time differential perturbed angular distribution (TDPAD) spectroscopy and ab initio methods

    NASA Astrophysics Data System (ADS)

    Mohanta, S. K.; Mishra, S. N.; Davane, S. M.; Kumar, Neeraj; Thamizhavel, A.; Layek, S.; Hossain, Z.; Srivastava, S. K.

    2013-03-01

    Applying the γ-ray perturbed angular distribution technique we have measured the magnetic hyperfine field and spin relaxation time of recoil implanted 54Fe in single and polycrystalline CaFe2As2 over the temperature range 20-360 K, encompassing both tetragonal and orthorhombic structural phases of the material. The magnetic response of Fe in the high temperature tetragonal phase (T ⩾ 180 K), show Curie-Weiss type local susceptibility and Korringa like spin relaxation, reflecting the presence of localized moment on Fe. In the orthorhombic phase, the spin rotation spectra of 54Fe show two magnetic hyperfine field components, both exhibiting quasi two dimensional magnetic ordering. The experimentally measured hyperfine field and Fe moment show good agreement with results obtained from ab initio calculations performed within the frame work of local spin density approximation (LSDA).

  3. Studies of interaction between He and elements with mass number 140 in Fe by time-differential perturbed-angular-correlation measurements

    NASA Astrophysics Data System (ADS)

    Ohkubo, Yoshitaka; Taniguchi, Akihiro; Xu, Qiu; Tanigaki, Minoru; Sato, Koichi

    2014-08-01

    Room-temperature time-differential perturbed-angular-correlation (TDPAC) spectra of 140Ce arising through 140Ba-140La from 140Cs in He-doped Fe, unannealed and annealed in vacuum at various temperatures, were obtained in order to examine whether Ce (or rather, La and Ba) and He form complexes having a definite geometrical structure in Fe, as suggested by first-principles density-functional theory calculations. No clear signal of such complexes was observed in the TDPAC spectra. However, the TDPAC spectra indicate that Ce and He form complexes having a variety of geometrical structures. Comparison with reported TDPAC results on 111Cd arising from 111In in He-doped stainless steel shows that the parent atoms (La and Ba) of 140Ce trap He atoms more efficiently than In atoms do, indicating stronger bonding of He to the former atoms, while different from the present case, 111Cd (In)-He complexes form a unique geometrical structure.

  4. Electric field gradients at 181Ta probe in ZrNi: Results from perturbed angular correlation and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Dey, C. C.; Das, Rakesh; Srivastava, S. K.

    2015-07-01

    Results of temperature dependent perturbed angular correlation (PAC) measurements in the equiatomic ZrNi alloy have been reported for the first time using 181Hf probe. At room temperature, values of quadrupole frequency and asymmetry parameter for the major component (~80%) are found to be ωQ=26.8(4) Mrad/s, and η=0.413(7). The resulting electric field gradient comes out to be Vzz=2.99 ×1017 V/cm2 and this corresponds to the probe nuclei occupying the regular substitutional Zr sites. In ZrNi system, no magnetic interaction is observed down to 77 K indicating absence of any magnetism in this material. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies on an inactive but similarly prepared sample confirm the dominant presence of the orthorhombic ZrNi phase in the sample. A complementary density functional theory (DFT) calculation results in Vzz=-2.35×1017 V/cm2, η=0.46 at the 181Ta probe impurity site and zero magnetic moment on each atomic site, in close agreement with the experimental results. Furthermore, it is found that electric field gradient for the regular component follows a T3/2 temperature dependence between 77 and 353 K, beyond which it varies linearly with temperature.

  5. Oxygen ordering in the high-Tc superconductor HgBa2CaCu2O6+δ as revealed by perturbed angular correlation

    NASA Astrophysics Data System (ADS)

    Mendonça, T. M.; Correia, J. G.; Haas, H.; Odier, P.; Tavares, P. B.; da Silva, M. R.; Lopes, A. M. L.; Pereira, A. M.; Gonçalves, J. N.; Amaral, J. S.; Darie, C.; Araujo, J. P.

    2011-09-01

    Lattice sites and collective ordering of oxygen atoms in HgBa2CaCu2O6+δ were studied using the perturbed angular correlation (PAC) technique at ISOLDE/CERN. The electric field gradients (EFG) at 199mHg nuclei have been measured as functions of oxygen doping on the Hg planes, above and below Tc. In comparison with the results obtained for oxygen and fluorine doping in Hg-1201, the analysis shows a different oxygen ordering exhibited by Hg-1212. Moreover, for all studied cases, the experimental results show that at a local scale there is non uniform oxygen distribution. A series of ab initio EFG calculations allowed to infer that at low concentrations, regions without oxygen coexist with regions where O2δ dumbbell molecules are located at the center of the Hg mesh. On the other side, at high concentrations, O2δ dumbbell molecules coexist with single Oδ atoms occupying the center of the Hg mesh. The present results suggest that oxygen sits on the Hg planes in the form of a molecule and not as a single atom.

  6. Magnetic behavior of La-doped Fe{sub 3}O{sub 4} studied by perturbed angular correlation spectroscopy with {sup 111}Cd and {sup 140}Ce

    SciTech Connect

    Matos, I. T. Bosch-Santos, B.; Cabrera-Pasca, G. A.; Carbonari, A. W.

    2015-05-07

    In this paper, the local magnetic properties of La-doped Fe{sub 3}O{sub 4} (5% and 10%) bulk and Nanoparticles (NPs) samples were studied by measuring hyperfine interactions in a wide range of temperature from 10 to 900 K with perturbed γ-γ angular correlation spectroscopy using {sup 111}In({sup 111}Cd) and {sup 140}La({sup 140}Ce) as probe nuclei. Results for the temperature dependence of the magnetic hyperfine field (B{sub hf}) for bulk and NP samples, pure and doped with La show that its behavior follows a second order Brillouin-like transition from which the Curie temperature (T{sub C}) was determined (T{sub C} ∼ 855 K). Results also show two different regions in NP samples: the core where a minor fraction of probe nuclei with well defined magnetic dipole frequency was observed and the shell where a major fraction with broad distributed electric quadrupolar frequency (surface effect in NP) was observed. The Verwey transition T{sub V} ∼ 120 K, due the order disorder phase, was also observed in all samples. The results are discussed in terms of the magnetic exchange interaction between Fe{sup 2+} and Fe{sup 3+} ions in the two regions of NP.

  7. Magnetic behavior of La-doped Fe3O4 studied by perturbed angular correlation spectroscopy with 111Cd and 140Ce

    NASA Astrophysics Data System (ADS)

    Matos, I. T.; Bosch-Santos, B.; Cabrera-Pasca, G. A.; Carbonari, A. W.

    2015-05-01

    In this paper, the local magnetic properties of La-doped Fe3O4 (5% and 10%) bulk and Nanoparticles (NPs) samples were studied by measuring hyperfine interactions in a wide range of temperature from 10 to 900 K with perturbed γ-γ angular correlation spectroscopy using 111In(111Cd) and 140La(140Ce) as probe nuclei. Results for the temperature dependence of the magnetic hyperfine field (Bhf) for bulk and NP samples, pure and doped with La show that its behavior follows a second order Brillouin-like transition from which the Curie temperature (TC) was determined (TC ˜ 855 K). Results also show two different regions in NP samples: the core where a minor fraction of probe nuclei with well defined magnetic dipole frequency was observed and the shell where a major fraction with broad distributed electric quadrupolar frequency (surface effect in NP) was observed. The Verwey transition TV ˜ 120 K, due the order disorder phase, was also observed in all samples. The results are discussed in terms of the magnetic exchange interaction between Fe2+ and Fe3+ ions in the two regions of NP.

  8. Perturbed Angular Correlation Study of the Static and Dynamic Aspects of Cadmium and Mercury Atoms Inside and Attached to a C60 Fullerene Cage

    NASA Astrophysics Data System (ADS)

    Das, Satyendra K.; Guin, Rashmohan; Banerjee, Debasish; Johnston, Karl; Das, Parnika; Butz, Tilman; Amaral, Vitor S.; Correia, Joao G.; Barbosa, Marcelo B.

    2014-11-01

    30 keV 111mCd and 50 keV 199mHg beams from ISOLDE were used to implant on preformed targets of C60 with a thickness of 1 mg cm-2. Endofullerene compounds, viz. 111mCd@C60 and 199mHg@C60 formed during implantation were separated by filtration through micropore filter paper followed by solvent extraction. Dried samples of the endofullerene compounds were counted for the time differential perturbed angular correlation (TDPAC) measurement using the coincidence of the 151 - 245 keV cascade of 111mCd and the 374 - 158 keV cascade of 199mHg on a six LaBr3(Ce) detector system coupled with digital electronics. The results for 111mCd@C60 indicate a single static component (27%) and a fast relaxing component (73%), the latter implying that the cadmium atom moves rapidly inside the cage at room temperature. The quadrupole interaction frequency and asymmetry parameter of the cadmium atom occupying the static site in C60 are wQ=8.21(36) Mrad s-1 and η = 0.41(9), respectively. The fast relaxation constant is 0.0031(4) ns-1. Similarly, mercury atoms also exhibit a single static and a fast component. The static site has a quadrupole frequency wQ=283.0(12.4) Mrad s-1 and η =0 with a fraction of 30%. The fast relaxation constant is 0.045(8) ns-1 with a fraction of 70%, very similar to that of cadmium.

  9. Hyperfine interaction measurements in LaCrO3 and LaFeO3 perovskites using perturbed angular correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Dogra, R.; Junqueira, A. C.; Saxena, R. N.; Carbonari, A. W.; Mestnik-Filho, J.; Moralles, M.

    2001-06-01

    The perturbed angular correlation (PAC) technique was used to study the hyperfine interactions in the antiferromagnetic and paramagnetic regions of the distorted perovskites LaCrO3 and LaFeO3. The dilute 111In-->111Cd nuclear probes were introduced into the samples through a chemical process. The present measurements cover the temperature ranges from 15 to 848 K for LaCrO3 and 77 to 1324 K for LaFeO3. Two distinct electric-quadrupole interactions were observed in each compound. The lower quadrupole frequency was assigned to the transition-metal atom site while the higher frequency was attributed to the lanthanum site in both cases. Temperature dependence of the electric-quadrupole interaction parameters indicated structural phase transitions at around 512 and 1223 K, respectively, in LaCrO3 and LaFeO3. The phase transitions were associated with the change from an orthorhombic to rhombohedral structure and characterized by a sudden increase in the electric field gradient Vzz and a decrease in the asymmetry parameter η for both sites. PAC spectra measured below the Néel temperature revealed that at 0 K the supertransferred magnetic hyperfine field on 111Cd at the Cr site in LaCrO3 (2.4 T) is much smaller than at the Fe site in LaFeO3 (19.4 T). The magnetic field on 111Cd at La sites in both compounds is of the order of 0.3 T. Additional measurements were made to determine the magnetic hyperfine field using the probe nucleus 140La-->140Ce. The result reconfirmed that a relatively weak hyperfine field is supertransferred to the probe atoms at La sites.

  10. Magnetic and Structural Properties of LANTHANUM(2-X) Strontium(x) Copper OXYGEN(4+DELTA) Studied with Time - Perturbed Angular Correlations

    NASA Astrophysics Data System (ADS)

    Saylor, Janet Marie

    Structural and magnetic properties of the high temperature superconductor La_{2-x}Sr_{x} CuO_{4-y} have been studied with ^{111} In/^{111}Cd perturbed angular gammagamma-correlations (PAC). In these measurements ppm of the radioactive probe, ^{111}In, is diffused into small samples by heat treatment. During the 2.8 day half-life of ^{111}In, the hyperfine spectrum of the I = 5/2, 85 ns. excited state of ^{111}Cd can be studied. A number of complex combined magnetic-dipole -electric-quadrupole interactions are observed. These depend simply on the sample preparation which controls the types and concentration of oxygen defects which exist in the sample. In particular, we have found that vacuum annealing results in a unique PAC spectrum. In this case, which only occurs when the samples are nearly exactly oxygen stoichiometric, the ^{111}Cd probe sits at the La site with no oxygen defects nearby. The principle axis of the electric field gradient ( omega_{o} = 240 Mrad/s) is found to be nearly parallel to the tetragonal c-axis and perpendicular to the hyperfine field ( omega_{L} = 10 Mrad/s). The temperature dependence and orientation of the hyperfine field, the electric field gradient and its asymmetry parameter (eta~ 0.1) have been studied for lightly doped La_{2-x }Sr_{x}CuO _4. We found first that hyperfine field is proportional to bulk magnetization, and second that eta is proportional orthorhombic distortion (To = 530 K). This unique sensitivity of our probe to both the magnetic and structural phase transitions in La _2CuO_{4+delta }, combined with the microscopic information on oxygen stoichiometry it can provide, have made ^{111}In/^{111 }Cd PAC ideal for studies of complex phase diagram of La_{2-x}Sr _{x}CuO _4. Results from these investigations include the first microscopic determination of the oxygen stoichiometry of La_{2-x}Sr _{x}CuO _4 and observation of the maximum Neel temperature; measurement of the magnetic critical exponent, beta = 0.50(4), and the

  11. LOCAL MAGNETIC BEHAVIOR OF 54Fe in EuFe2As2 AND Eu0.5K0.5Fe2As2: MICROSCOPIC STUDY USING TIME DIFFERENTIAL PERTURBED ANGULAR DISTRIBUTION (TDPAD) SPECTROSCOPY

    NASA Astrophysics Data System (ADS)

    Mohanta, S. K.; Mishra, S. N.; Davane, S. M.; Layek, S.; Hossain, Z.

    2013-12-01

    In this paper, we report the time differential perturbed angular distribution measurements of 54Fe on a polycrystalline EuFe2As2 and Eu0.5K0.5Fe2As2. The hyperfine field and nuclear spin-relaxation rate are strongly temperature dependent in the paramagnetic state suggesting strong spin fluctuation in the parent compound. The local susceptibility show Curie-Weiss-like temperature dependence and Korringa-like relaxation in the tetragonal phase indicating the presence of local moment. In the orthorhombic phase, the hyperfine field behavior suggesting quasi two-dimensional magnetic ordering. The experimental results are in a good agreement with first-principle calculations based on density functional theory.

  12. Angular Scaling In Jets

    SciTech Connect

    Jankowiak, Martin; Larkoski, Andrew J.; /SLAC

    2012-02-17

    We introduce a jet shape observable defined for an ensemble of jets in terms of two-particle angular correlations and a resolution parameter R. This quantity is infrared and collinear safe and can be interpreted as a scaling exponent for the angular distribution of mass inside the jet. For small R it is close to the value 2 as a consequence of the approximately scale invariant QCD dynamics. For large R it is sensitive to non-perturbative effects. We describe the use of this correlation function for tests of QCD, for studying underlying event and pile-up effects, and for tuning Monte Carlo event generators.

  13. First-principles and time-differential γ-γ perturbed-angular-correlation spectroscopy study of structural and electronic properties of Ta-doped TiO2 semiconductor

    NASA Astrophysics Data System (ADS)

    Darriba, G. N.; Errico, L. A.; Eversheim, P. D.; Fabricius, G.; Rentería, M.

    2009-03-01

    The, time-differential γ-γ perturbed-angular-correlation (TDPAC) technique using ion-implanted H181f(→T181a) tracers was applied to study the hyperfine interactions of T181a impurities in the rutile structure of TiO2 single crystals. The experiments were performed in air in the temperature range of 300-1273 K, allowing the electric-field-gradient (EFG) tensor characterization (in magnitude, asymmetry, and orientation) at T181a probe atoms located in defect-free cation sites of the structure. The measured EFG is parallel to the [001] crystal axis, as occurs at Ti sites, but normal to the EFG orientation observed at C111d impurities in TiO2 single crystals [L. A. Errico , Phys. Rev. Lett. 89, 055503 (2002)]. In addition, ab initio calculations were performed using the full-potential augmented plane wave plus local orbital method that allow us to treat the electronic structure of the doped system and the atomic relaxations induced by the Ta impurity in a fully self-consistent way. We considered different dilutions of the doped system (using the supercell approach) and studied the electronic properties and structural atomic relaxation dependence on the charge state of the impurity. The accuracy of the calculations and the excellent agreement of the predicted magnitude, asymmetry, and orientation of the EFG tensor with the experimental results enable us to infer the EFG sign, not accessible with conventional TDPAC experiments. The comparison of the measured EFG at Ta sites with experimental and ab initio theoretical results reported in the literature at Cd, Ta, and Ti sites in TiO2 allowed us to obtain a deeper insight on the role played by metal impurities in oxide semiconductors.

  14. Magnetic interactions in equi-atomic rare-earth intermetallic alloys RScGe (R = Ce, Pr, Nd and Gd) studied by time differential perturbed angular correlation spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Mishra, S N

    2009-03-01

    Applying the time differential perturbed angular correlation (TDPAC) technique we have measured electric and magnetic hyperfine fields of the 111Cd impurity in equi-atomic rare-earth intermetallic alloys RScGe (R = Ce, Pr and Gd) showing antiferro- and ferromagnetism with unusually high ordering temperatures. The Cd nuclei occupying the Sc site show high magnetic hyperfine fields with saturation values Bhf(0) = 21 kG, 45 kG and 189 kG in CeScGe, PrScGe and GdScGe, respectively. By comparing the results with the hyperfine field data of Cd in rare-earth metals and estimations from the RKKY model, we find evidence for the presence of additional spin density at the probe nucleus, possibly due to spin polarization of Sc d band electrons. The principal electric field gradient component Vzz in CeScGe, PrScGe and GdScGe has been determined to be 5.3 × 1021 V m-2, 5.5 × 1021 V m-2 and 5.6 × 1021 V m-2, respectively. Supplementing the experimental measurements, we have carried out ab initio calculations for pure and Cd-doped RScGe compounds with R = Ce, Pr, Nd and Gd using the full potential linearized augmented plane wave (FLAPW) method based on density functional theory (DFT). From the total energies calculated with and without spin polarization we find ferrimagnetic ground states for CeScGe and PrScGe while NdScGe and GdScGe are ferromagnetic. In addition, we find a sizable magnetic moment at the Sc site, increasing from ≈0.10 μB in CeScGe to ≈0.3 μB in GdScGe, confirming the spin polarization of Sc d band electrons. The calculated electric field gradient and magnetic hyperfine fields of the Cd impurity closely agree with the experimental values. We believe spin polarization of Sc 3d band electrons, strongly hybridized with spin polarized 5d band electrons of the rare-earth, enables a long range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between RE 4f moments which in turn leads to high magnetic ordering temperatures in RScGe compounds.

  15. Magnetic interactions in equi-atomic rare-earth intermetallic alloys RScGe (R = Ce, Pr, Nd and Gd) studied by time differential perturbed angular correlation spectroscopy and ab initio calculations.

    PubMed

    Mishra, S N

    2009-03-18

    Applying the time differential perturbed angular correlation (TDPAC) technique we have measured electric and magnetic hyperfine fields of the (111)Cd impurity in equi-atomic rare-earth intermetallic alloys RScGe (R = Ce, Pr and Gd) showing antiferro- and ferromagnetism with unusually high ordering temperatures. The Cd nuclei occupying the Sc site show high magnetic hyperfine fields with saturation values B(hf)(0) = 21 kG, 45 kG and 189 kG in CeScGe, PrScGe and GdScGe, respectively. By comparing the results with the hyperfine field data of Cd in rare-earth metals and estimations from the RKKY model, we find evidence for the presence of additional spin density at the probe nucleus, possibly due to spin polarization of Sc d band electrons. The principal electric field gradient component V(zz) in CeScGe, PrScGe and GdScGe has been determined to be 5.3 × 10(21) V m(-2), 5.5 × 10(21) V m(-2) and 5.6 × 10(21) V m(-2), respectively. Supplementing the experimental measurements, we have carried out ab initio calculations for pure and Cd-doped RScGe compounds with R = Ce, Pr, Nd and Gd using the full potential linearized augmented plane wave (FLAPW) method based on density functional theory (DFT). From the total energies calculated with and without spin polarization we find ferrimagnetic ground states for CeScGe and PrScGe while NdScGe and GdScGe are ferromagnetic. In addition, we find a sizable magnetic moment at the Sc site, increasing from ≈0.10 μ(B) in CeScGe to ≈0.3 μ(B) in GdScGe, confirming the spin polarization of Sc d band electrons. The calculated electric field gradient and magnetic hyperfine fields of the Cd impurity closely agree with the experimental values. We believe spin polarization of Sc 3d band electrons, strongly hybridized with spin polarized 5d band electrons of the rare-earth, enables a long range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between RE 4f moments which in turn leads to high magnetic ordering temperatures in

  16. Renormalized Lie perturbation theory

    SciTech Connect

    Rosengaus, E.; Dewar, R.L.

    1981-07-01

    A Lie operator method for constructing action-angle transformations continuously connected to the identity is developed for area preserving mappings. By a simple change of variable from action to angular frequency a perturbation expansion is obtained in which the small denominators have been renormalized. The method is shown to lead to the same series as the Lagrangian perturbation method of Greene and Percival, which converges on KAM surfaces. The method is not superconvergent, but yields simple recursion relations which allow automatic algebraic manipulation techniques to be used to develop the series to high order. It is argued that the operator method can be justified by analytically continuing from the complex angular frequency plane onto the real line. The resulting picture is one where preserved primary KAM surfaces are continuously connected to one another.

  17. Angular Momentum

    ERIC Educational Resources Information Center

    Shakur, Asif; Sinatra, Taylor

    2013-01-01

    The gyroscope in a smartphone was employed in a physics laboratory setting to verify the conservation of angular momentum and the nonconservation of rotational kinetic energy. As is well-known, smartphones are ubiquitous on college campuses. These devices have a panoply of built-in sensors. This creates a unique opportunity for a new paradigm in…

  18. Angular Cheilitis

    MedlinePlus

    ... the mouth. Overview Angular cheilitis (perlèche) is a chronic inflammatory condition of the corners of the mouth. Usually associated with a fungal ( Candidal ) or bacterial ( Staphylococcal ) infection, those ... people of all ages. Chronic pooling of saliva encourages fungal and bacterial growth, ...

  19. Angular momentum

    NASA Astrophysics Data System (ADS)

    Shakur, Asif; Sinatra, Taylor

    2013-12-01

    The gyroscope in a smartphone was employed in a physics laboratory setting to verify the conservation of angular momentum and the nonconservation of rotational kinetic energy. As is well-known, smartphones are ubiquitous on college campuses. These devices have a panoply of built-in sensors. This creates a unique opportunity for a new paradigm in the physics laboratory. Many traditional physics experiments can now be performed very conveniently in a pedagogically enlightening environment while simultaneously reducing the laboratory budget substantially by using student-owned smartphones.

  20. Phonons with orbital angular momentum

    NASA Astrophysics Data System (ADS)

    Ayub, M. K.; Ali, S.; Mendonca, J. T.

    2011-10-01

    Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.

  1. Phonons with orbital angular momentum

    SciTech Connect

    Ayub, M. K.; Ali, S.; Mendonca, J. T.

    2011-10-15

    Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.

  2. Topology and perturbation theory

    NASA Astrophysics Data System (ADS)

    Manjavidze, J.

    2000-08-01

    This paper contains description of the fields nonlinear modes successive quantization scheme. It is shown that the path integrals for absorption part of amplitudes are defined on the Dirac (δ-like) functional measure. This permits arbitrary transformation of the functional integral variables. New form of the perturbation theory achieved by mapping the quantum dynamics in the space WG of the (action, angle)-type collective variables. It is shown that the transformed perturbation theory contributions are accumulated exactly on the boundary ∂WG. Abilities of the developed formalism are illustrated by the Coulomb problem. This model is solved in the WC=(angle, angular momentum, Runge-Lentz vector) space and the reason of its exact integrability is emptiness of ∂WC.

  3. The angular momentum of the Oort cloud

    NASA Technical Reports Server (NTRS)

    Weissman, Paul R.

    1991-01-01

    An evaluation is made of the work of Marochnik et al. (1988), which estimated that the angular momentum of the Oort cloud is 2-3 orders of magnitude greater than the planetary system's total angular momentum. It is noted that most of the angular momentum in the currently observed Oort cloud is the result of the effects of external perturbers over the solar system's history, and it is demonstrated that the total current angular momentum is probably in the 6.0 x 10 to the 50th to 1.1 x 10 to the 51st g sq cm/sec range; original angular momentum was probably a factor of 5 below such values.

  4. The angular momentum of the Oort cloud

    SciTech Connect

    Weissman, P.R. )

    1991-01-01

    An evaluation is made of the work of Marochnik et al. (1988), which estimated that the angular momentum of the Oort cloud is 2-3 orders of magnitude greater than the planetary system's total angular momentum. It is noted that most of the angular momentum in the currently observed Oort cloud is the result of the effects of external perturbers over the solar system's history, and it is demonstrated that the total current angular momentum is probably in the 6.0 x 10 to the 50th to 1.1 x 10 to the 51st g sq cm/sec range; original angular momentum was probably a factor of 5 below such values. 21 refs.

  5. Time-differential perturbed-angular-correlation and emission Moessbauer studies on {sup 99}Ru dispersed in YBa{sub 2}Cu{sub 3}O{sub 6.8} and YBa{sub 2}Cu{sub 3}O{sub 6}

    SciTech Connect

    Ohkubo, Y.; Kobayashi, Y.; Harasawa, K.; Ambe, S.; Okada, T.; Ambe, F.; Asai, K.; Shibata, S.

    1995-06-29

    The hyperfine interactions at {sup 99}Ru({sup $IMP@99}Rh) dispersed in YBa{sub 2}Cu{sub 3}O{sub 6.8} and YBa{sub 2}Cu{sub 3}O{sub 6} were studied by means of time-differential perturbed-angular-correlation (TDPAC) and emission Moessbauer spectroscopy. The TDPAC and Moessbauer measurements show that Ru ions are in the tetravalent state and exclusively occupy the Cu-1 sites, which form one-dimensional Cu-O chains in the orthorhombic phase. The oxygen coordinations around the Ru ions are discussed on the basis of the observed electric field gradients at {sup 99}Ru in YBa{sub 2}Cu{sub 3}O{sub 6.8} and YBa{sub 2}Cu{sub 3}O{sub 6}. 35 refs., 6 figs., 1 tab.

  6. PERTURBING LIGNIFICATION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Perturbing lignification is possible in multiple and diverse ways. Without obvious growth/development phenotypes, transgenic angiosperms can have lignin levels reduced to half the normal level, can have compositions ranging from very high-guaiacyl/low-syringyl to almost totally syringyl, and can eve...

  7. Cosmological Perturbations

    NASA Astrophysics Data System (ADS)

    Lesgourges, J.

    2013-08-01

    We present a self-contained summary of the theory of linear cosmological perturbations. We emphasize the effect of the six parameters of the minimal cosmological model, first, on the spectrum of Cosmic Microwave Background temperature anisotropies, and second, on the linear matter power spectrum. We briefly review at the end the possible impact of a few non-minimal dark matter and dark energy models.

  8. Primordial power spectrum of tensor perturbations in Finsler spacetime

    NASA Astrophysics Data System (ADS)

    Li, Xin; Wang, Sai

    2016-02-01

    We first investigate the gravitational wave in the flat Finsler spacetime. In the Finslerian universe, we derive the perturbed gravitational field equation with tensor perturbations. The Finslerian background spacetime breaks rotational symmetry and induces parity violation. Then we obtain the modified primordial power spectrum of the tensor perturbations. The parity violation feature requires that the anisotropic effect contributes to the TT, TE, EE, BB angular correlation coefficients with l'=l+1 and TB, EB with l'=l. The numerical results show that the anisotropic contributions to the angular correlation coefficients depend on m, and TE and ET angular correlation coefficients are different.

  9. Gyroscope test of gravitation: An analysis of the important perturbations

    NASA Technical Reports Server (NTRS)

    Oconnell, R. F.

    1971-01-01

    Two perturbations, the earth's quadrupole moment and the earth's revolution around the sun, are discussed. Schiff's proposed gyroscope test of gravitation is analyzed, along with the capability of deciphering each separate contribution to the angular velocity of spin precession.

  10. Perturbative fragmentation

    SciTech Connect

    Kopeliovich, B. Z.; Pirner, H.-J.; Potashnikova, I. K.; Schmidt, Ivan; Tarasov, A. V.

    2008-03-01

    The Berger model of perturbative fragmentation of quarks to pions is improved by providing an absolute normalization and keeping all terms in a (1-z) expansion, which makes the calculation valid at all values of fractional pion momentum z. We also replace the nonrelativistic wave function of a loosely bound pion by the more realistic procedure of projecting to the light-cone pion wave function, which in turn is taken from well known models. The full calculation does not confirm the (1-z){sup 2} behavior of the fragmentation function (FF) predicted in [E. L. Berger, Z. Phys. C 4, 289 (1980); Phys. Lett. 89B, 241 (1980] for z>0.5, and only works at very large z>0.95, where it is in reasonable agreement with phenomenological FFs. Otherwise, we observe quite a different z-dependence which grossly underestimates data at smaller z. The disagreement is reduced after the addition of pions from decays of light vector mesons, but still remains considerable. The process dependent higher twist terms are also calculated exactly and found to be important at large z and/or p{sub T}.

  11. Phenomenological Determination of the Orbital Angular Momentum

    SciTech Connect

    Ramsey, Gordon P.

    2009-08-04

    Measurements involving the gluon spin, {delta}G(x, t) and the corresponding asymmetry, A(x,t) = {delta}G(x,t)/G(x,t) play an important role in quantitative understanding of proton structure. We have modeled the asymmetry perturbatively and calculated model corrections to obtain information about non-perturbative spin-orbit effects. These models are consistent with existing COMPASS and HERMES data on the gluon asymmetry. The J{sub z} = (1/2) sum rule is used to generate values of orbital angular momentum at LO and NLO. For models consistent with data, the orbital angular momentum is small. Our studies specify accuracy that future measurements should achieve to constrain theoretical models for nucleon structure.

  12. Hadronic Structure from Perturbative Dressing

    NASA Astrophysics Data System (ADS)

    Arash, Firooz

    2005-09-01

    Perturbative dressing of a valence quark in QCD produces the internal structure of an extended object, the so-called Valon. The valon structure is universal and independent of the hosting hadron. Polarized and unpolarized proton and pion structure functions are calculated in the valon representation. One finds that although all the available data on g1p,n,d are easily reproduced, a sizable orbital angular momentum associated with the partonic structure of the valon is required in order to have a spin 1/2 valon.

  13. Cosmological perturbations in unimodular gravity

    SciTech Connect

    Gao, Caixia; Brandenberger, Robert H.; Cai, Yifu; Chen, Pisin E-mail: rhb@hep.physics.mcgill.ca E-mail: chen@slac.stanford.edu

    2014-09-01

    We study cosmological perturbation theory within the framework of unimodular gravity. We show that the Lagrangian constraint on the determinant of the metric required by unimodular gravity leads to an extra constraint on the gauge freedom of the metric perturbations. Although the main equation of motion for the gravitational potential remains the same, the shift variable, which is gauge artifact in General Relativity, cannot be set to zero in unimodular gravity. This non-vanishing shift variable affects the propagation of photons throughout the cosmological evolution and therefore modifies the Sachs-Wolfe relation between the relativistic gravitational potential and the microwave temperature anisotropies. However, for adiabatic fluctuations the difference between the result in General Relativity and unimodular gravity is suppressed on large angular scales. Thus, no strong constraints on the theory can be derived.

  14. Partonic orbital angular momentum

    NASA Astrophysics Data System (ADS)

    Arash, Firooz; Taghavi-Shahri, Fatemeh; Shahveh, Abolfazl

    2013-04-01

    Ji's decomposition of nucleon spin is used and the orbital angular momentum of quarks and gluon are calculated. We have utilized the so called valon model description of the nucleon in the next to leading order. It is found that the average orbital angular momentum of quarks is positive, but small, whereas that of gluon is negative and large. Individual quark flavor contributions are also calculated. Some regularities on the total angular momentum of the quarks and gluon are observed.

  15. On Angular Momentum

    DOE R&D Accomplishments Database

    Schwinger, J.

    1952-01-26

    The commutation relations of an arbitrary angular momentum vector can be reduced to those of the harmonic oscillator. This provides a powerful method for constructing and developing the properties of angular momentum eigenvectors. In this paper many known theorems are derived in this way, and some new results obtained. Among the topics treated are the properties of the rotation matrices; the addition of two, three, and four angular momenta; and the theory of tensor operators.

  16. A Comparative Time Differential Perturbed Angular Correlation Study of the Nuclear Quadrupole Interaction in HfF4·HF·2H2O Using 180mHf and 181Hf(β-)181Ta as Nuclear Probes: Is Ta an Innocent Spy?

    NASA Astrophysics Data System (ADS)

    Butz, Tilman; Das, Satyendra K.; Manzhur, Yurij

    2009-02-01

    We report on a comparative study of the nuclear quadrupole interaction of the nuclear probes 180mHf and 181Hf(β -)181Ta in HfF4・HF・2H2O using time differential perturbed angular correlations (TDPAC) at 300 K. For the first probe, assuming a Lorentzian frequency distribution, we obtained ωQ= 103(4) Mrad/s, an asymmetry parameter η = 0.68(3), a linewidth δ = 7.3(3.9)%, and full anisotropy within experimental accuracy. For the second probe, assuming a Lorentzian frequency distribution, we obtained three fractions: (1) with 56.5(7)%, ωQ= 126.64(4) Mrad/s and η = 0.9241(4) with a rather small distribution δ = 0.40(8)% which is attributed to HfF4・HF・2H2O; (2) with 4.6(4)%, ωQ = 161.7(3) Mrad/s and η = 0.761(4) assuming no line broadening which is tentatively attributed to a small admixture of Hf2OF6・H2O; (3) the remainder of 39.0(7)% accounts for a rapid loss of anisotropy and is modelled by a perturbation function with a sharp frequency multiplied by an exponential factor exp(-λ t) with λ = 0.55(2) ns-1. Whereas the small admixture of Hf2OF6・H2O escapes detection by the 180mHf probe, there is no rapid loss of roughly half the anisotropy as is the case with 181Hf(β -)181Ta. This loss could in principle be due to fluctuating electric field gradients originating from movements of nearest neighbour HF adducts and/or H2O molecules after nuclear transmutation to the foreign atom Ta which are absent for the isomeric probe. Alternatively, paramagnetic Ta ions could lead to fluctuating magnetic dipole fields which, when combined with fluctuating electric field gradients, could also lead to a rapid loss of anisotropy. In any case, Ta is not an "innocent spy" in this compound. Although 180mHf is not a convenient probe for conventional spectrometers, the use of fast digitizers and software coincidences would allow to use all γ -quanta in the stretched cascade which would greatly improve the efficiency of the spectrometer. 180mHf could also serve as a Pu

  17. Angular Acceleration Without Torque?

    NASA Astrophysics Data System (ADS)

    Kaufman, Richard D.

    2012-01-01

    Hardly. Just as Robert Johns qualitatively describes angular acceleration by an internal force in his article "Acceleration Without Force?" here we will extend the discussion to consider angular acceleration by an internal torque. As we will see, this internal torque is due to an internal force acting at a distance from an instantaneous center.2

  18. Angular Acceleration without Torque?

    ERIC Educational Resources Information Center

    Kaufman, Richard D.

    2012-01-01

    Hardly. Just as Robert Johns qualitatively describes angular acceleration by an internal force in his article "Acceleration Without Force?" here we will extend the discussion to consider angular acceleration by an internal torque. As we will see, this internal torque is due to an internal force acting at a distance from an instantaneous center.

  19. DVL Angular Velocity Recorder

    NASA Technical Reports Server (NTRS)

    Liebe, Wolfgang

    1944-01-01

    In many studies, especially of nonstationary flight motion, it is necessary to determine the angular velocities at which the airplane rotates about its various axes. The three-component recorder is designed to serve this purpose. If the angular velocity for one flight attitude is known, other important quantities can be derived from its time rate of change, such as the angular acceleration by differentiations, or - by integration - the angles of position of the airplane - that is, the angles formed by the airplane axes with the axis direction presented at the instant of the beginning of the motion that is to be investigated.

  20. Transient dynamics of perturbations in astrophysical disks

    NASA Astrophysics Data System (ADS)

    Razdoburdin, D. N.; Zhuravlev, V. V.

    2015-11-01

    We review some aspects of a major unsolved problem in understanding astrophysical (in particular, accretion) disks: whether the disk interiors can be effectively viscous in spite of the absence of magnetorotational instability. A rotational homogeneous inviscid flow with a Keplerian angular velocity profile is spectrally stable, making the transient growth of perturbations a candidate mechanism for energy transfer from regular motion to perturbations. Transient perturbations differ qualitatively from perturbation modes and can grow substantially in shear flows due to the nonnormality of their dynamical evolution operator. Because the eigenvectors of this operator, also known as perturbation modes, are not pairwise orthogonal, they can mutually interfere, resulting in the transient growth of their linear combinations. Physically, a growing transient perturbation is a leading spiral whose branches are shrunk as a result of the differential rotation of the flow. We discuss in detail the transient growth of vortex shearing harmonics in the spatially local limit, as well as methods for identifying the optimal (fastest growth) perturbations. Special attention is given to obtaining such solutions variationally by integrating the respective direct and adjoint equations forward and backward in time. The presentation is intended for experts new to the subject.

  1. Angular velocity discrimination

    NASA Technical Reports Server (NTRS)

    Kaiser, Mary K.

    1990-01-01

    Three experiments designed to investigate the ability of naive observers to discriminate rotational velocities of two simultaneously viewed objects are described. Rotations are constrained to occur about the x and y axes, resulting in linear two-dimensional image trajectories. The results indicate that observers can discriminate angular velocities with a competence near that for linear velocities. However, perceived angular rate is influenced by structural aspects of the stimuli.

  2. A UNIFIED THEORY FOR THE EFFECTS OF STELLAR PERTURBATIONS AND GALACTIC TIDES ON OORT CLOUD COMETS

    SciTech Connect

    Collins, Benjamin F.; Sari, Re'em

    2010-11-15

    We examine the effects of passing field stars on the angular momentum of a nearly radial orbit of an Oort cloud comet bound to the Sun. We derive the probability density function of the change in angular momentum from one stellar encounter, assuming a uniform and isotropic field of perturbers. We show that the total angular momentum follows a Levy flight, and determine its distribution function. If there is an asymmetry in the directional distribution of perturber velocities, the marginal probability distribution of each component of the angular momentum vector can be different. The constant torque attributed to Galactic tides arises from a non-cancellation of perturbations with an impact parameter of order the semimajor axis of the comet. When the close encounters are rare, the angular momentum is best modeled by the stochastic growth of stellar encounters. If trajectories passing between the comet and the Sun occur frequently, the angular momentum exhibits the coherent growth attributed to the Galactic tides.

  3. Hyperfine Magnetic Field Measurements in the Heusler Alloys COBALT(2)-TITANIUM-Z, COBALT(2)-MAGNESIUM-Z (z = Silicon, Germanium, and Tin) and COBALT(2)-MAGNESIUM- Gallium Using the Moessbauer Effect (me) and the Time Differential Perturbed Angular Correlation (tdpac) Techniques

    NASA Astrophysics Data System (ADS)

    Lahamer, Amer Said

    1990-01-01

    Measurements of the hyperfine magnetic field in a series of Heusler alloys were performed. The probes were in (^{119}Sn) and cadmium (^{111}Cd). These measurements were performed at the University of Cincinnati in Cincinnati, Ohio. Two techniques were used. The first technique was the Mossbauer effect, which was used to measure the hyperfine magnetic field on ^{119 }Sn in Co_2TiZ (Z = Si, Ge, and Sn), and the second technique was the Time Differential Perturbed Angular Correlation which was used to measure the hyperfine magnetic field on ^ {111}Cd in the Co_2MnZ (Z = Si, Ge, Sn, and Ga). The probes are expected to go to the Z sites of the alloys. The hyperfine magnetic field measurements on ^{119}Sn in Co _2TiZ (Z = Si, Ge, and Sn) alloys were done at room, dry ice and liquid nitrogen temperatures by using the Mossbauer effect technique. The data were fitted by using a least squares fit from which three parameters were extracted. These parameters are the isomer shift, the quadrupole splitting and the hyperfine magnetic field. Temperature variation measurements of the hyperfine magnetic field were performed on ^{111 }Cd in Co_2MnZ (Z = Si, Ge, Sn, and Ga) alloys. The data were fitted again by using a least squares fit from which the Larmor frequency which is related to the hyperfine magnetic field was extracted. Also the Fourier Transforms were taken of the data, on the one hand to confirm the results of the least squares fit and on the other hand to look for more frequencies. Results of the Fourier Transforms show that some of the probe, ^{111}In, did go to the Co site in the Co_2MnZ (Z = Ga, Si, and Ge) alloys. The hmf on ^{111 }Cd in the Co site of these alloys is found to be 68 kOe which is consistent with the value found in the literature. Two theoretical models were examined for the trends of hyperfine magnetic field on ^{119 }Sn and ^{111}Cd in Co_2MnZ (Z = Si, Ge, Sn, and Ga) alloys. These are the Campbell and Blandin model and the Stearns' overlap model

  4. Angular momentum radio

    NASA Astrophysics Data System (ADS)

    Thidé, B.; Tamburini, F.; Then, H.; Someda, C. G.; Mari, Elletra; Parisi, G.; Spinello, F.; Romanato, Fra

    2014-02-01

    Wireless communication amounts to encoding information onto physical observables carried by electromagnetic (EM) fields, radiating them into surrounding space, and detecting them remotely by an appropriate sensor connected to an informationdecoding receiver. Each observable is second order in the fields and fulfills a conservation law. In present-day radio only the EM linear momentum observable is fully exploited. A fundamental physical limitation of this observable, which represents the translational degrees of freedom of the charges (typically an oscillating current along a linear antenna) and the fields, is that it is single-mode. This means that a linear-momentum radio communication link comprising one transmitting and one receiving antenna, known as a single-input-single-output (SISO) link, can provide only one transmission channel per frequency (and polarization). In contrast, angular momentum, which represents the rotational degrees of freedom, is multi-mode, allowing an angular-momentum SISO link to accommodate an arbitrary number of independent transmission channels on one and the same frequency (and polarization). We describe the physical properties of EM angular momentum and how they can be exploited, discuss real-world experiments, and outline how the capacity of angular momentum links may be further enhanced by employing multi-port techniques, i.e., the angular momentum counterpart of linear-momentum multiple-input-multiple-output (MIMO).

  5. Do cosmological perturbations have zero mean?

    SciTech Connect

    Armendariz-Picon, Cristian

    2011-03-01

    A central assumption in our analysis of cosmic structure is that cosmological perturbations have a constant ensemble mean, which can be set to zero by appropriate choice of the background. This property is one of the consequences of statistical homogeneity, the invariance of correlation functions under spatial translations. In this article we explore whether cosmological perturbations indeed have zero mean, and thus test one aspect of statistical homogeneity. We carry out a classical test of the zero mean hypothesis against a class of alternatives in which primordial perturbations have inhomogeneous non-vanishing means, but homogeneous and isotropic covariances. Apart from Gaussianity, our test does not make any additional assumptions about the nature of the perturbations and is thus rather generic and model-independent. The test statistic we employ is essentially Student's t statistic, applied to appropriately masked, foreground-cleaned cosmic microwave background anisotropy maps produced by the WMAP mission. We find evidence for a non-zero mean in a particular range of multipoles, but the evidence against the zero mean hypothesis goes away when we correct for multiple testing. We also place constraints on the mean of the temperature multipoles as a function of angular scale. On angular scales smaller than four degrees, a non-zero mean has to be at least an order of magnitude smaller than the standard deviation of the temperature anisotropies.

  6. Fluidic angular velocity sensor

    NASA Technical Reports Server (NTRS)

    Berdahl, C. M. (Inventor)

    1986-01-01

    A fluidic sensor providing a differential pressure signal proportional to the angular velocity of a rotary input is described. In one embodiment the sensor includes a fluid pump having an impeller coupled to a rotary input. A housing forming a constricting fluid flow chamber is connected to the fluid input of the pump. The housing is provided with a fluid flow restrictive input to the flow chamber and a port communicating with the interior of the flow chamber. The differential pressure signal measured across the flow restrictive input is relatively noise free and proportional to the square of the angular velocity of the impeller. In an alternative embodiment, the flow chamber has a generally cylindrical configuration and plates having flow restrictive apertures are disposed within the chamber downstream from the housing port. In this embodiment, the differential pressure signal is found to be approximately linear with the angular velocity of the impeller.

  7. Metamaterial broadband angular selectivity

    NASA Astrophysics Data System (ADS)

    Shen, Yichen; Ye, Dexin; Wang, Li; Celanovic, Ivan; Ran, Lixin; Joannopoulos, John D.; Soljačić, Marin

    2014-09-01

    We demonstrate how broadband angular selectivity can be achieved with stacks of one-dimensionally periodic photonic crystals, each consisting of alternating isotropic layers and effective anisotropic layers, where each effective anisotropic layer is constructed from a multilayered metamaterial. We show that by simply changing the structure of the metamaterials, the selective angle can be tuned to a broad range of angles; and, by increasing the number of stacks, the angular transmission window can be made as narrow as desired. As a proof of principle, we realize the idea experimentally in the microwave regime. The angular selectivity and tunability we report here can have various applications such as in directional control of electromagnetic emitters and detectors.

  8. Angular diameter distances reconsidered in the Newman and Penrose formalism

    NASA Astrophysics Data System (ADS)

    Kling, Thomas P.; Aly, Aly

    2016-02-01

    Using the Newman and Penrose spin coefficient (NP) formalism, we provide a derivation of the Dyer-Roeder equation for the angular diameter distance in cosmological space-times. We show that the geodesic deviation equation written in NP formalism is precisely the Dyer-Roeder equation for a general Friedman-Robertson-Walker (FRW) space-time, and then we examine the angular diameter distance to redshift relation in the case that a flat FRW metric is perturbed by a gravitational potential. We examine the perturbation in the case that the gravitational potential exhibits the properties of a thin gravitational lens, demonstrating how the weak lensing shear and convergence act as source terms for the perturbed Dyer-Roeder equation.

  9. Density perturbation theory

    SciTech Connect

    Palenik, Mark C.; Dunlap, Brett I.

    2015-07-28

    Despite the fundamental importance of electron density in density functional theory, perturbations are still usually dealt with using Hartree-Fock-like orbital equations known as coupled-perturbed Kohn-Sham (CPKS). As an alternative, we develop a perturbation theory that solves for the perturbed density directly, removing the need for CPKS. This replaces CPKS with a true Hohenberg-Kohn density perturbation theory. In CPKS, the perturbed density is found in the basis of products of occupied and virtual orbitals, which becomes ever more over-complete as the size of the orbital basis set increases. In our method, the perturbation to the density is expanded in terms of a series of density basis functions and found directly. It is possible to solve for the density in such a way that it makes the total energy stationary even if the density basis is incomplete.

  10. Vector potential and metric perturbations of a rotating black hole

    NASA Technical Reports Server (NTRS)

    Chrzanowski, P. L.

    1975-01-01

    The assumption of factorized Green's functions together with the inhomogeneous Teukolsky equations are used to derive analytic expressions for homogeneous metric (and vector potential) perturbations of a Kerr black hole. These homogeneous solutions are used to construct solutions to the perturbation equations when sources are present. What one finds are particularly simple formulas for the energy and angular momentum flux in the asymptotic regions at plus or minus infinity.-

  11. "Angular" plasma cell cheilitis.

    PubMed

    da Cunha Filho, Roberto Rheingantz; Tochetto, Lucas Baldissera; Tochetto, Bruno Baldissera; de Almeida, Hiram Larangeira; Lorencette, Nádia Aparecida; Netto, José Fillus

    2014-03-01

    Plasma cell cheilitis is an extremely rare disease, characterized by erythematous-violaceous, ulcerated and asymptomatic plaques, which evolve slowly. The histological characteristics include dermal infiltrate composed of mature plasmocytes. We report a case of Plasma cell angular cheilitis in a 58-year-old male, localized in the lateral oral commissure. PMID:24656273

  12. Automated Lattice Perturbation Theory

    SciTech Connect

    Monahan, Christopher

    2014-11-01

    I review recent developments in automated lattice perturbation theory. Starting with an overview of lattice perturbation theory, I focus on the three automation packages currently "on the market": HiPPy/HPsrc, Pastor and PhySyCAl. I highlight some recent applications of these methods, particularly in B physics. In the final section I briefly discuss the related, but distinct, approach of numerical stochastic perturbation theory.

  13. Angular momentum and star formation

    NASA Astrophysics Data System (ADS)

    Strittmatter, P. A.

    The present investigation is mainly concerned with the importance of high angular resolution observations in studies of star formation and, in particular, with elucidating the role which angular momentum plays in the process. A brief report is included on recent high angular resolution observations made with the Steward Observatory speckle camera system. A consideration of the angular momentum in interstellar clouds indicates that rotation precludes quasi-spherical contraction. A number of solutions to this angular momentum problem are examined, taking into account questions concerning the help provided by high angular resolution observations for an elucidation of the various possible scenarios of star formation. Technical aspects involved in obtaining suitable data are investigated. It is concluded that high angular resolution observations hold considerable promise for solving at least some of the problems associated with the role of angular momentum in star formation.

  14. Angular momentum projected semiclassics

    NASA Astrophysics Data System (ADS)

    Hasse, Rainer W.

    1987-06-01

    By using angular momentum projected plane waves as wave functions, we derive semiclassical expressions for the single-particle propagator, the partition function, the nonlocal density matrix, the single-particle density and the one particle-one hole level density for fixed angular momentum and fixed z-component or summed over the z-components. Other quantities can be deduced from the propagator. In coordinate space ( r, r') the relevant quantities depend on |r-r'| instead of | r- r'| and in Wigner space ( R, P) they become proportional to the angular momentum constraints δ(| R × P|/ h̵-l) and δ( R × P) z/ h̵-m) . As applications we calculate the single-particle and one-particle-one hole level densities for harmonic oscillator and Hill-Wheeler box potentials and the imaginary part of the optical potential and its volume integral with an underlying harmonic oscillator potential and a zero range two-body interaction.

  15. Frame independent cosmological perturbations

    SciTech Connect

    Prokopec, Tomislav; Weenink, Jan E-mail: j.g.weenink@uu.nl

    2013-09-01

    We compute the third order gauge invariant action for scalar-graviton interactions in the Jordan frame. We demonstrate that the gauge invariant action for scalar and tensor perturbations on one physical hypersurface only differs from that on another physical hypersurface via terms proportional to the equation of motion and boundary terms, such that the evolution of non-Gaussianity may be called unique. Moreover, we demonstrate that the gauge invariant curvature perturbation and graviton on uniform field hypersurfaces in the Jordan frame are equal to their counterparts in the Einstein frame. These frame independent perturbations are therefore particularly useful in relating results in different frames at the perturbative level. On the other hand, the field perturbation and graviton on uniform curvature hypersurfaces in the Jordan and Einstein frame are non-linearly related, as are their corresponding actions and n-point functions.

  16. Quark Orbital Angular Momentum

    NASA Astrophysics Data System (ADS)

    Burkardt, Matthias

    2016-06-01

    Generalized parton distributions provide information on the distribution of quarks in impact parameter space. For transversely polarized nucleons, these impact parameter distributions are transversely distorted and this deviation from axial symmetry leads on average to a net transverse force from the spectators on the active quark in a DIS experiment. This force when acting along the whole trajectory of the active quark leads to transverse single-spin asymmetries. For a longitudinally polarized nucleon target, the transverse force implies a torque acting on the quark orbital angular momentum (OAM). The resulting change in OAM as the quark leaves the target equals the difference between the Jaffe-Manohar and Ji OAMs.

  17. Inflationary tensor perturbations after BICEP2.

    PubMed

    Caligiuri, Jerod; Kosowsky, Arthur

    2014-05-16

    The measurement of B-mode polarization of the cosmic microwave background at large angular scales by the BICEP experiment suggests a stochastic gravitational wave background from early-Universe inflation with a surprisingly large amplitude. The power spectrum of these tensor perturbations can be probed both with further measurements of the microwave background polarization at smaller scales and also directly via interferometry in space. We show that sufficiently sensitive high-resolution B-mode measurements will ultimately have the ability to test the inflationary consistency relation between the amplitude and spectrum of the tensor perturbations, confirming their inflationary origin. Additionally, a precise B-mode measurement of the tensor spectrum will predict the tensor amplitude on solar system scales to 20% accuracy for an exact power-law tensor spectrum, so a direct detection will then measure the running of the tensor spectral index to high precision. PMID:24877926

  18. Uniaxial angular accelerometers

    NASA Astrophysics Data System (ADS)

    Seleznev, A. V.; Shvab, I. A.

    1985-05-01

    The basic mechanical components of an angular accelerometer are the sensor, the damper, and the transducer. Penumatic dampers are simplest in construction, but the viscosity of air is very low and, therefore, dampers with special purpose oils having a high temperature stability (synthetic silicon or organosilicon oils) are most widely used. The most common types of viscous dampers are lamellar with meshed opposed arrays of fixed and movable vanes in the dashpot, piston dampers regulated by an adjustable-length capillary tube, and dampers with paddle wheel in closed tank. Another type of damper is an impact-inertial one with large masses absorbing the rotational energy upon collision with the sensor. Conventional measuring elements are resistive, capacitive, electromagnetic, photoelectric, and penumatic or hydraulic. Novel types of angular accelerometers are based on inertia of gas jets, electron beams, and ion beams, the piezoelectric effect in p-n junctions of diode and transistors, the electrokinetic effect in fluids, and cryogenic suspension of the sensor.

  19. The Perturbed Puma Model

    NASA Astrophysics Data System (ADS)

    Rong, Shu-Jun; Liu, Qiu-Yu

    2012-04-01

    The puma model on the basis of the Lorentz and CPT violation may bring an economical interpretation to the conventional neutrinos oscillation and part of the anomalous oscillations. We study the effect of the perturbation to the puma model. In the case of the first-order perturbation which keeps the (23) interchange symmetry, the mixing matrix element Ue3 is always zero. The nonzero mixing matrix element Ue3 is obtained in the second-order perturbation that breaks the (23) interchange symmetry.

  20. Orbital angular momentum microlaser.

    PubMed

    Miao, Pei; Zhang, Zhifeng; Sun, Jingbo; Walasik, Wiktor; Longhi, Stefano; Litchinitser, Natalia M; Feng, Liang

    2016-07-29

    Structured light provides an additional degree of freedom for modern optics and practical applications. The effective generation of orbital angular momentum (OAM) lasing, especially at a micro- and nanoscale, could address the growing demand for information capacity. By exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser producing a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. The polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission. Our OAM microlaser could find applications in the next generation of integrated optoelectronic devices for optical communications in both quantum and classical regimes. PMID:27471299

  1. Orbital angular momentum microlaser

    NASA Astrophysics Data System (ADS)

    Miao, Pei; Zhang, Zhifeng; Sun, Jingbo; Walasik, Wiktor; Longhi, Stefano; Litchinitser, Natalia M.; Feng, Liang

    2016-07-01

    Structured light provides an additional degree of freedom for modern optics and practical applications. The effective generation of orbital angular momentum (OAM) lasing, especially at a micro- and nanoscale, could address the growing demand for information capacity. By exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser producing a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. The polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission. Our OAM microlaser could find applications in the next generation of integrated optoelectronic devices for optical communications in both quantum and classical regimes.

  2. On the relation between angular momentum and angular velocity

    NASA Astrophysics Data System (ADS)

    Silva, J. P.; Tavares, J. M.

    2007-01-01

    Students of mechanics usually have difficulties when they learn about the rotation of a rigid body. These difficulties are rooted in the relation between angular momentum and angular velocity, because these vectors are not parallel, and we need in general to utilize a rotating frame of reference or a time dependent inertia tensor. We discuss a series of problems that introduce both difficulties.

  3. Chiral Perturbation Theory

    NASA Astrophysics Data System (ADS)

    Tiburzi, Brian C.

    The era of high-precision lattice QCD has led to synergy between lattice computations and phenomenological input from chiral perturbation theory. We provide an introduction to chiral perturbation theory with a bent towards understanding properties of the nucleon and other low-lying baryons. Four main topics are the basis for this chapter. We begin with a discussion of broken symmetries and the procedure to construct the chiral Lagrangian. The second topic concerns specialized applications of chiral perturbation theory tailored to lattice QCD, such as partial quenching, lattice discretization, and finite-volume effects. We describe inclusion of the nucleon in chiral perturbation theory using a heavy-fermion Euclidean action. Issues of convergence are taken up as our final topic. We consider expansions in powers of the strange-quark mass, and the appearance of unphysical singularities in the heavy-particle formulation. Our aim is to guide lattice practitioners in understanding the predictions chiral perturbation theory makes for baryons, and show how the lattice will play a role in testing the rigor of the chiral expansion at physical values of the quark masses.

  4. Intrinsic Angular Momentum of Light.

    ERIC Educational Resources Information Center

    Santarelli, Vincent

    1979-01-01

    Derives a familiar torque-angular momentum theorem for the electromagnetic field, and includes the intrinsic torques exerted by the fields on the polarized medium. This inclusion leads to the expressions for the intrinsic angular momentum carried by the radiation traveling through a charge-free medium. (Author/MA)

  5. Vortex perturbation dynamics

    NASA Technical Reports Server (NTRS)

    Criminale, W. O.; Lasseigne, D. G.; Jackson, T. L.

    1995-01-01

    An initial value approach is used to examine the dynamics of perturbations introduced into a vortex under strain. Both the basic vortex considered and the perturbations are taken as fully three-dimensional. An explicit solution for the time evolution of the vorticity perturbations is given for arbitrary initial vorticity. Analytical solutions for the resulting velocity components are found when the initial vorticity is assumed to be localized. For more general initial vorticity distributions, the velocity components are determined numerically. It is found that the variation in the radial direction of the initial vorticity disturbance is the most important factor influencing the qualitative behavior of the solutions. Transient growth in the magnitude of the velocity components is found to be directly attributable to the compactness of the initial vorticity.

  6. Angular signal radiography.

    PubMed

    Li, Panyun; Zhang, Kai; Bao, Yuan; Ren, Yuqi; Ju, Zaiqiang; Wang, Yan; He, Qili; Zhu, Zhongzhu; Huang, Wanxia; Yuan, Qingxi; Zhu, Peiping

    2016-03-21

    Microscopy techniques using visible photons, x-rays, neutrons, and electrons have made remarkable impact in many scientific disciplines. The microscopic data can often be expressed as the convolution of the spatial distribution of certain properties of the specimens and the inherent response function of the imaging system. The x-ray grating interferometer (XGI), which is sensitive to the deviation angle of the incoming x-rays, has attracted significant attention in the past years due to its capability in achieving x-ray phase contrast imaging with low brilliance source. However, the comprehensive and analytical theoretical framework is yet to be presented. Herein, we propose a theoretical framework termed angular signal radiography (ASR) to describe the imaging process of the XGI system in a classical, comprehensive and analytical manner. We demonstrated, by means of theoretical deduction and synchrotron based experiments, that the spatial distribution of specimens' physical properties, including absorption, refraction and scattering, can be extracted by ASR in XGI. Implementation of ASR in XGI offers advantages such as simplified phase retrieval algorithm, reduced overall radiation dose, and improved image acquisition speed. These advantages, as well as the limitations of the proposed method, are systematically investigated in this paper. PMID:27136780

  7. The Angular Gyrus

    PubMed Central

    2013-01-01

    There is considerable interest in the structural and functional properties of the angular gyrus (AG). Located in the posterior part of the inferior parietal lobule, the AG has been shown in numerous meta-analysis reviews to be consistently activated in a variety of tasks. This review discusses the involvement of the AG in semantic processing, word reading and comprehension, number processing, default mode network, memory retrieval, attention and spatial cognition, reasoning, and social cognition. This large functional neuroimaging literature depicts a major role for the AG in processing concepts rather than percepts when interfacing perception-to-recognition-to-action. More specifically, the AG emerges as a cross-modal hub where converging multisensory information is combined and integrated to comprehend and give sense to events, manipulate mental representations, solve familiar problems, and reorient attention to relevant information. In addition, this review discusses recent findings that point to the existence of multiple subdivisions in the AG. This spatial parcellation can serve as a framework for reporting AG activations with greater definition. This review also acknowledges that the role of the AG cannot comprehensibly be identified in isolation but needs to be understood in parallel with the influence from other regions. Several interesting questions that warrant further investigations are finally emphasized. PMID:22547530

  8. Annihilation of angular momentum bias during thrusting and spinning-up maneuvers

    NASA Technical Reports Server (NTRS)

    Longuski, J. M.; Kia, T.; Breckenridge, W. G.

    1989-01-01

    During spinning-up and thrusting maneuvers of rockets and spacecraft, undesired transverse torques (from error sources such as thruster misalignment, center-of-mass offset and thruster mismatch) perturb the angular momentum vector from its original orientation. In this paper a maneuver scheme is presented which virtually annihilates the angular momentum vector bias, even though the magnitude and direction of the perturbing body-fixed torques are unknown. In the analysis it is assumed that the torques are small and constant and that the spacecraft or rocket can be approximated by a rigid body, which may be asymmetric. Typical maneuvers of the Galileo spacecraft are simulated to demonstrate the technique.

  9. Barothropic relaxing media under pressure perturbations: Nonlinear dynamics

    NASA Astrophysics Data System (ADS)

    Kuetche, Victor K.

    2015-12-01

    In this paper, we delve into the dynamics of a barothropic relaxing medium under pressure perturbations originating from blast wave explosions in the milieu. Analyzing the problem within the viewpoint of the Lyakhov formalism of geodynamic systems, we derive a complex-valued nonlinear evolution equation which models the wave propagation of the pressure perturbations within the barothropic medium. As a result, we find that the previous system can be circularly polarized and hence support traveling rotating pressure excitations which profiles strongly depend upon their angular momenta. In the wake of these results, we address some physical implications of the findings alongside their potential applications.

  10. Cosmological perturbations in antigravity

    NASA Astrophysics Data System (ADS)

    Oltean, Marius; Brandenberger, Robert

    2014-10-01

    We compute the evolution of cosmological perturbations in a recently proposed Weyl-symmetric theory of two scalar fields with oppositely signed conformal couplings to Einstein gravity. It is motivated from the minimal conformal extension of the standard model, such that one of these scalar fields is the Higgs while the other is a new particle, the dilaton, introduced to make the Higgs mass conformally symmetric. At the background level, the theory admits novel geodesically complete cyclic cosmological solutions characterized by a brief period of repulsive gravity, or "antigravity," during each successive transition from a big crunch to a big bang. For simplicity, we consider scalar perturbations in the absence of anisotropies, with potential set to zero and without any radiation. We show that despite the necessarily wrong-signed kinetic term of the dilaton in the full action, these perturbations are neither ghostlike nor tachyonic in the limit of strongly repulsive gravity. On this basis, we argue—pending a future analysis of vector and tensor perturbations—that, with respect to perturbative stability, the cosmological solutions of this theory are viable.

  11. Even perturbations of the self-similar Vaidya space-time

    SciTech Connect

    Nolan, Brien C.; Waters, Thomas J.

    2005-05-15

    We study even parity metric and matter perturbations of all angular modes in self-similar Vaidya space-time. We focus on the case where the background contains a naked singularity. Initial conditions are imposed, describing a finite perturbation emerging from the portion of flat space-time preceding the matter-filled region of space-time. The most general perturbation satisfying the initial conditions is allowed to impinge upon the Cauchy horizon (CH), where the perturbation remains finite: There is no 'blue-sheet' instability. However, when the perturbation evolves through the CH and onto the second future similarity horizon of the naked singularity, divergence necessarily occurs: This surface is found to be unstable. The analysis is based on the study of individual modes following a Mellin transform of the perturbation. We present an argument that the full perturbation remains finite after resummation of the (possibly infinite number of) modes.

  12. Liouvillian perturbations of black holes

    NASA Astrophysics Data System (ADS)

    Couch, W. E.; Holder, C. L.

    2007-10-01

    We apply the well-known Kovacic algorithm to find closed form, i.e., Liouvillian solutions, to the differential equations governing perturbations of black holes. Our analysis includes the full gravitational perturbations of Schwarzschild and Kerr, the full gravitational and electromagnetic perturbations of Reissner-Nordstrom, and specialized perturbations of the Kerr-Newman geometry. We also include the extreme geometries. We find all frequencies ω, in terms of black hole parameters and an integer n, which allow Liouvillian perturbations. We display many classes of black hole parameter values and their corresponding Liouvillian perturbations, including new closed-form perturbations of Kerr and Reissner-Nordstrom. We also prove that the only type 1 Liouvillian perturbations of Schwarzschild are the known algebraically special ones and that type 2 Liouvillian solutions do not exist for extreme geometries. In cases where we do not prove the existence or nonexistence of Liouvillian perturbations we obtain sequences of Diophantine equations on which decidability rests.

  13. Electromagnetically induced angular Talbot effect

    NASA Astrophysics Data System (ADS)

    Qiu, Tianhui; Yang, Guojian

    2015-12-01

    The discrete angular spectrum (angular Talbot effect) of a periodic grating illuminated by a suitable spherical wave front has been observed recently (Azaña and Chatellus 2104 Phys. Rev. Lett. 112 213902). In this paper we study the possibility of such a phenomenon being realized with a medium that has no macroperiodic structure itself. Tunable electromagnetically induced grating (EIG) could be such a kind of medium. We obtain an EIG based on the periodically modulated strong susceptibility due to the third-order nonlinear effect generated in a double Λ-type four-level atomic system, and show the angular Talbot effect of an amplitude EIG, as well as a hybrid EIG, as the condition of the discrete phase-modulation shift of the illumination light front is satisfied. EIG parameters are tunable and the EIG-based angular Talbot effect may have the same potential applications as its periodic grating counterpart has.

  14. Transverse angular momentum of photons

    SciTech Connect

    Aiello, Andrea

    2010-05-15

    We develop the quantum theory of transverse angular momentum of light beams. The theory applies to paraxial and quasiparaxial photon beams in vacuum and reproduces the known results for classical beams when applied to coherent states of the field. Both the Poynting vector, alias the linear momentum, and the angular-momentum quantum operators of a light beam are calculated including contributions from first-order transverse derivatives. This permits a correct description of the energy flow in the beam and the natural emergence of both the spin and the angular momentum of the photons. We show that for collimated beams of light, orbital angular-momentum operators do not satisfy the standard commutation rules. Finally, we discuss the application of our theory to some concrete cases.

  15. Angular Momentum Ejection and Recoil*

    NASA Astrophysics Data System (ADS)

    Ohia, O.; Coppi, B.

    2009-11-01

    The spontaneous rotation phenomenon observed in axisymmetric magnetically confined plasmas has been explained by the ``accretion theory'' [1] that considers the plasma angular momentum as gained from its interaction with the magnetic field and the surrounding material wall. The ejection of angular momentum to the wall, and the consequent recoil are attributed to modes excited at the edge while the transport of the (recoil) angular momentum from the edge toward the center is attributed to a different kind of mode. The toroidal phase velocity of the edge mode, to which the sign of the ejected angular momentum is related, is considered to change its direction in the transition from the H-regime to the L-regime. For the latter case, edge modes with phase velocity in the direction of vdi are driven by the temperature gradient of a cold ion population at the edge and damped on the ``hot'' ion population. The ``balanced'' double interaction [2] of the mode with the two populations, corresponding to a condition of marginal stability, leads to ejection of hot ions and loss of angular momentum in the direction of vdi while the cold population acquires angular momentum in the opposite direction. In the H-regime resistive ballooning modes with phase velocities in the direction of vde are viewed as the best candidates for the excited edge modes. *Sponsored in part by the U.S. DOE. [1] B. Coppi, Nucl. Fusion 42, 1 (2002) [2] B. Coppi and F. Pegoraro, Nucl. Fusion 17, 969 (1977)

  16. Aspects of perturbative unitarity

    NASA Astrophysics Data System (ADS)

    Anselmi, Damiano

    2016-07-01

    We reconsider perturbative unitarity in quantum field theory and upgrade several arguments and results. The minimum assumptions that lead to the largest time equation, the cutting equations and the unitarity equation are identified. Using this knowledge and a special gauge, we give a new, simpler proof of perturbative unitarity in gauge theories and generalize it to quantum gravity, in four and higher dimensions. The special gauge interpolates between the Feynman gauge and the Coulomb gauge without double poles. When the Coulomb limit is approached, the unphysical particles drop out of the cuts and the cutting equations are consistently projected onto the physical subspace. The proof does not extend to nonlocal quantum field theories of gauge fields and gravity, whose unitarity remains uncertain.

  17. Intermolecular perturbation theory

    NASA Astrophysics Data System (ADS)

    Hayes, I. C.; Hurst, G. J. B.; Stone, A. J.

    The new intermolecular perturbation theory described in the preceding papers is applied to some van der Waals molecules. HeBe is used as a test case, and the perturbation method converges well at interatomic distances down to about 4 a0, giving results in excellent agreement with supermolecule calculations. ArHF and ArHCl have been studied using large basis sets, and the results agree well with experimental data. The ArHX configuration is favoured over the ArXH configuration mainly because of larger polarization and charge-transfer contributions. In NeH2 the equilibrium geometry is determined by a delicate balance between opposing effects; with a double-zeta-polarization basis the correct configuration is predicted.

  18. Cosmic microwave background bispectrum on small angular scales

    SciTech Connect

    Pitrou, Cyril; Uzan, Jean-Philippe; Bernardeau, Francis

    2008-09-15

    This article investigates the nonlinear evolution of cosmological perturbations on sub-Hubble scales in order to evaluate the unavoidable deviations from Gaussianity that arise from the nonlinear dynamics. It shows that the dominant contribution to modes coupling in the cosmic microwave background temperature anisotropies on small angular scales is driven by the sub-Hubble nonlinear evolution of the dark matter component. The perturbation equations, involving, in particular, the first moments of the Boltzmann equation for photons, are integrated up to second order in perturbations. An analytical analysis of the solutions gives a physical understanding of the result as well as an estimation of its order of magnitude. This allows one to quantify the expected deviation from Gaussianity of the cosmic microwave background temperature anisotropy and, in particular, to compute its bispectrum on small angular scales. Restricting to equilateral configurations, we show that the nonlinear evolution accounts for a contribution that would be equivalent to a constant primordial non-Gaussianity of order f{sub NL}{approx}25 on scales ranging approximately from l{approx}1000 to l{approx}3000.

  19. Uncertainty principle for angular position and angular momentum

    NASA Astrophysics Data System (ADS)

    Franke-Arnold, Sonja; Barnett, Stephen M.; Yao, Eric; Leach, Jonathan; Courtial, Johannes; Padgett, Miles

    2004-08-01

    The uncertainty principle places fundamental limits on the accuracy with which we are able to measure the values of different physical quantities (Heisenberg 1949 The Physical Principles of the Quantum Theory (New York: Dover); Robertson 1929 Phys. Rev. 34 127). This has profound effects not only on the microscopic but also on the macroscopic level of physical systems. The most familiar form of the uncertainty principle relates the uncertainties in position and linear momentum. Other manifestations include those relating uncertainty in energy to uncertainty in time duration, phase of an electromagnetic field to photon number and angular position to angular momentum (Vaccaro and Pegg 1990 J. Mod. Opt. 37 17; Barnett and Pegg 1990 Phys. Rev. A 41 3427). In this paper, we report the first observation of the last of these uncertainty relations and derive the associated states that satisfy the equality in the uncertainty relation. We confirm the form of these states by detailed measurement of the angular momentum of a light beam after passage through an appropriate angular aperture. The angular uncertainty principle applies to all physical systems and is particularly important for systems with cylindrical symmetry.

  20. The Angular Momentum of Light

    NASA Astrophysics Data System (ADS)

    Andrews, David L.; Babiker, Mohamed

    2012-11-01

    Preface D. L. Andrews and M. Babiker; 1. Light beams carrying orbital angular momentum J. B. Götte and S. M. Barnett; 2. Vortex transformation and vortex dynamics in optical fields G. Molina-Terriza; 3. Vector beams in free space E. J. Galvez; 4. Optical beams with orbital angular momentum in nonlinear media A. S. Desyatnikov and Y. S. Kivshar; 5. Ray optics, wave optics and quantum mechanics G. Nienhuis; 6. Quantum formulation of angle and orbital angular momentum J. B. Götte and S. M. Barnett; 7. Dynamic rotational frequency shift I. Bialynicki-Birula and Z. Bialynicka-Birula; 8. Spin-orbit interactions of light in isotropic media K. Y. Bliokh, A. Aiello and M. A. Alonso; 9. Quantum electrodynamics, angular momentum and chirality D. L. Andrews and M. Babiker; 10. Trapping of charged particles by Bessel beams I. Bialynicki-Birula, Z. Bialynicka-Birula and N. Drozd; 11. Theory of atoms in twisted light M. Babiker, D. L. Andrews and V. E. Lembessis; 12. An experimentalist's introduction to orbital angular momentum for quantum optics J. Romero, D. Giovannini, S. Franke-Arnold and M. J. Padgett; 13. Measurement of light's orbital angular momentum M. P. J. Lavery, J. Courtial and M. J. Padgett; 14. Efficient generation of optical twisters using helico-conical beams V. R. Daria, D. Palima and J. Glückstad; 15. Self similar modes of coherent diffusion with orbital angular momentum O. Firstenberg, M. Shuker, R. Pugatch and N. Davidson; 16. Dimensionality of azimuthal entanglement M. van Exter, E. Eliel and H. Woerdman; Index.

  1. Rotation of the polarization vector from distant radio galaxies in the perturbed FRW metric

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Sankha Subhra

    2016-06-01

    Analysis of the correlation between the angular positions of distant radio galaxies on the sky and the orientations of their polarization vectors with respect to their major axes indicates a dipolar anisotropy in the large scale. We consider a single mode of large-scale scalar perturbation to the FRW metric. Using Newman-Penrose formalism, we calculate the rotation of the galaxy major axis with respect to the polarization vector as the elliptic image and the polarization vector are carried through the perturbed spacetime. The dependence of the rotation on the polar angular coordinate of the galaxy is qualitatively similar to the claimed dipole pattern.

  2. Factors influencing perceived angular velocity

    NASA Technical Reports Server (NTRS)

    Kaiser, Mary K.; Calderone, Jack B.

    1991-01-01

    Angular velocity perception is examined for rotations both in depth and in the image plane and the influence of several object properties on this motion parameter is explored. Two major object properties are considered, namely, texture density which determines the rate of edge transitions for rotations in depth, i.e., the number of texture elements that pass an object's boundary per unit of time, and object size which determines the tangential linear velocities and 2D image velocities of texture elements for a given angular velocity. Results of experiments show that edge-transition rate biased angular velocity estimates only when edges were highly salient. Element velocities had an impact on perceived angular velocity; this bias was associated with 2D image velocity rather than 3D tangential velocity. Despite these biases judgements were most strongly determined by the true angular velocity. Sensitivity to this higher order motion parameter appeared to be good for rotations both in depth (y-axis) and parallel to the line of sight (z-axis).

  3. Angular Power Spectrum in Modular Invariant Inflation Model

    SciTech Connect

    Hayashi, Mitsuo J.; Okame, Y.; Takagi, K.; Watanabe, T.; Hirai, S.; Takami, T.

    2008-05-29

    A scalar potential of inflation is proposed and the angular power spectra of the adiabatic density perturbations are computed. The potential consists of three scalar fields, S, Y and T, together with two free parameters. By fitting the parameters to cosmological data at the fixed point T = 1, we find that the potential behaves like the single-field potential of S, which slowly rolls down. We further show that the inflation predictions corresponding to this potential provide a good fit to the recent three-year WMAP data, e.g. the spectral index n{sub s} = 0.951.The TT and TE angular power spectra obtained from our model almost completely coincide with the corresponding results obtained from the {lambda}CDM model. We conclude that our model is considered to be an adequate theory of inflation that explains the present data.

  4. Resilience of hybrid optical angular momentum qubits to turbulence

    PubMed Central

    Farías, Osvaldo Jiménez; D'Ambrosio, Vincenzo; Taballione, Caterina; Bisesto, Fabrizio; Slussarenko, Sergei; Aolita, Leandro; Marrucci, Lorenzo; Walborn, Stephen P.; Sciarrino, Fabio

    2015-01-01

    Recent schemes to encode quantum information into the total angular momentum of light, defining rotation-invariant hybrid qubits composed of the polarization and orbital angular momentum degrees of freedom, present interesting applications for quantum information technology. However, there remains the question as to how detrimental effects such as random spatial perturbations affect these encodings. Here, we demonstrate that alignment-free quantum communication through a turbulent channel based on hybrid qubits can be achieved with unit transmission fidelity. In our experiment, alignment-free qubits are produced with q-plates and sent through a homemade turbulence chamber. The decoding procedure, also realized with q-plates, relies on both degrees of freedom and renders an intrinsic error-filtering mechanism that maps errors into losses. PMID:25672667

  5. Resilience of hybrid optical angular momentum qubits to turbulence.

    PubMed

    Farías, Osvaldo Jiménez; D'Ambrosio, Vincenzo; Taballione, Caterina; Bisesto, Fabrizio; Slussarenko, Sergei; Aolita, Leandro; Marrucci, Lorenzo; Walborn, Stephen P; Sciarrino, Fabio

    2015-01-01

    Recent schemes to encode quantum information into the total angular momentum of light, defining rotation-invariant hybrid qubits composed of the polarization and orbital angular momentum degrees of freedom, present interesting applications for quantum information technology. However, there remains the question as to how detrimental effects such as random spatial perturbations affect these encodings. Here, we demonstrate that alignment-free quantum communication through a turbulent channel based on hybrid qubits can be achieved with unit transmission fidelity. In our experiment, alignment-free qubits are produced with q-plates and sent through a homemade turbulence chamber. The decoding procedure, also realized with q-plates, relies on both degrees of freedom and renders an intrinsic error-filtering mechanism that maps errors into losses. PMID:25672667

  6. Discrete reductive perturbation technique

    SciTech Connect

    Levi, Decio; Petrera, Matteo

    2006-04-15

    We expand a partial difference equation (P{delta}E) on multiple lattices and obtain the P{delta}E which governs its far field behavior. The perturbative-reductive approach is here performed on well-known nonlinear P{delta}Es, both integrable and nonintegrable. We study the cases of the lattice modified Korteweg-de Vries (mKdV) equation, the Hietarinta equation, the lattice Volterra-Kac-Van Moerbeke equation and a nonintegrable lattice KdV equation. Such reductions allow us to obtain many new P{delta}Es of the nonlinear Schroedinger type.

  7. Baryon chiral perturbation theory

    NASA Astrophysics Data System (ADS)

    Scherer, S.

    2012-03-01

    We provide a short introduction to the one-nucleon sector of chiral perturbation theory and address the issue of power counting and renormalization. We discuss the infrared regularization and the extended on-mass-shell scheme. Both allow for the inclusion of further degrees of freedom beyond pions and nucleons and the application to higher-loop calculations. As applications we consider the chiral expansion of the nucleon mass to order Script O(q6) and the inclusion of vector and axial-vector mesons in the calculation of nucleon form factors. Finally, we address the complex-mass scheme for describing unstable particles in effective field theory.

  8. Controlling the Spins Angular Momentum in Ferromagnets with Sequences of Picosecond Acoustic Pulses

    PubMed Central

    Kim, Ji-Wan; Vomir, Mircea; Bigot, Jean-Yves

    2015-01-01

    Controlling the angular momentum of spins with very short external perturbations is a key issue in modern magnetism. For example it allows manipulating the magnetization for recording purposes or for inducing high frequency spin torque oscillations. Towards that purpose it is essential to modify and control the angular momentum of the magnetization which precesses around the resultant effective magnetic field. That can be achieved with very short external magnetic field pulses or using intrinsically coupled magnetic structures, resulting in a transfer of spin torque. Here we show that using picosecond acoustic pulses is a versatile and efficient way of controlling the spin angular momentum in ferromagnets. Two or three acoustic pulses, generated by femtosecond laser pulses, allow suppressing or enhancing the magnetic precession at any arbitrary time by precisely controlling the delays and amplitudes of the optical pulses. A formal analogy with a two dimensional pendulum allows us explaining the complex trajectory of the magnetic vector perturbed by the acoustic pulses. PMID:25687970

  9. Phenomenology of preequilibrium angular distributions

    SciTech Connect

    Kalbach, C.; Mann, F.M.

    1980-05-01

    The systematics of continuum angular distributions from a wide variety of light ion nuclear reactions have been studied. To first order, the shape of the angular distributions have been found to depend only on the energy of the outgoing particle and on the division of the cross section into multi-step direct and multi-step compound parts. The angular distributions can be described in terms of Legendre polynomials with the reduced polynomial coefficients exhibiting a simple dependence on the outgoing particle energy. Two integer and four continuous parameters with universal values are needed to describe the coefficients for outgoing energies of 2 to 60 MeV in all the reaction types studied. This parameterization combined with a modified Griffin model computer code permits the calculation of double differential cross sections for light ion continuum reactions where no data is available.

  10. Variations in atmospheric angular momentum

    NASA Technical Reports Server (NTRS)

    Rosen, R. D.; Salstein, D. A.

    1981-01-01

    Twice-daily values of the atmosphere's angular momentum about the polar axis during the five years from 1976 through 1980 are presented in graphs and a table. The compilation is based on a global data set, incorporating 90 percent of the mass of the atmosphere. The relationship between changes in the angular momentum of the atmosphere and changes in the length of day is described, as are the main sources of error in the data. The variability in angular momentum is revealed in a preliminary fashion by means of a spectral decomposition. The data presented should stimulate comparisons with other measures of the length of day and so provide a basis for greater understanding of Earth-atmosphere interactions.

  11. Interferometric measurement of angular motion

    NASA Astrophysics Data System (ADS)

    Peña Arellano, Fabián Erasmo; Panjwani, Hasnain; Carbone, Ludovico; Speake, Clive C.

    2013-04-01

    This paper describes the design and realization of a homodyne polarization interferometer for measuring angular motion. The optical layout incorporates carefully designed cat's eye retroreflectors that maximize the measurable range of angular motion and facilitate initial alignment. The retroreflectors are optimized and numerically characterized in terms of defocus and spherical aberrations using Zemax software for optical design. The linearity of the measurement is then calculated in terms of the aberrations. The actual physical interferometer is realized as a compact device with optical components from stock and without relying on adjustable holders. Evaluation of its performance using a commercial autocollimator confirmed a reproducibility within 0.1%, a non-linearity of less than 1 ppm with respect to the autocollimator, an upper limit to its sensitivity of about 5 × 10-11 rad/sqrt{textrm {Hz}} from audioband down to 100 mHz and an angular measurement range of more than ±1°.

  12. Canonical floquet perturbation theory

    NASA Astrophysics Data System (ADS)

    Pohlen, David J.

    1992-12-01

    Classical Floquet theory is examined in order to generate a canonical transformation to modal variables for periodic system. This transformation is considered canonical if the periodic matrix of eigenvectors is symplectic at the initial time. Approaches for symplectic normalization of the eigenvectors had to be examined for each of the different Poincare eigenvalue cases. Particular attention was required in the degenerate case, which depended on the solution of a generalized eigenvector. Transformation techniques to ensure real modal variables and real periodic eigenvectors were also needed. Periodic trajectories in the restricted three-body case were then evaluated using the canonical Floquet solution. The system used for analyses is the Sun-Jupiter system. This system was especially useful since it contained two of the more difficult Poincare eigenvalue cases, the degenerate case and the imaginary eigenvalue case. The perturbation solution to the canonical modal variables was examined using both an expansion of the Hamiltonian and using a representation that was considered exact. Both methods compared quite well for small perturbations to the initial condition. As expected, the expansion solution failed first due to truncation after the third order term of the expansion.

  13. Non-Colinearity of Angular Velocity and Angular Momentum

    ERIC Educational Resources Information Center

    Burr, A. F.

    1974-01-01

    Discusses the principles, construction, and operation of an apparatus which serves to demonstrate the non-colinearity of the angular velocity and momentum vectors as well as the inertial tensors. Applications of the apparatus to teaching of advanced undergraduate mechanics courses are recommended. (CC)

  14. Solar cell angular position transducer

    NASA Technical Reports Server (NTRS)

    Sandford, M. C.; Gray, D. L. (Inventor)

    1980-01-01

    An angular position transducer utilizing photocells and a light source is disclosed. The device uses a fully rotatable baffle which is connected via an actuator shaft to the body whose rotational displacement is to be measured. The baffle blocks the light path between the light source and the photocells so that a constant semicircular beam of light reaches the photocells. The current produced by the photocells is fed through a resistor, a differential amplifier measures the voltage drop across the resistor which indicates the angular position of the actuator shaft and hence of the object.

  15. Energy and angular momentum transfer in binary galaxies

    NASA Technical Reports Server (NTRS)

    Namboodiri, P. M. S.; Kochhar, R. K.

    1990-01-01

    The authors numerically studied tidal effects of a massive perturber on a satellite galaxy. The model consists of a spherical satellite galaxy and a point mass perturber and the encounter is non-penetrating. A wide range of density ratios and eccentricities of the relative orbits have been considered. The disruption of the satellite galaxy has been observed when the numerical value of the fractional change in the energy is greater than two. The changes in the energy and angular momentum show smooth variation in the case of unbound orbits and irregular variation in the bound orbit cases. It is shown that for a constant pericentral distance, increasing the density ratio decreases the tidal effects; and for a given density ratio an increase in the eccentricity decreases the tidal effects.

  16. Quasi-periodic oscillations of perturbed tori

    NASA Astrophysics Data System (ADS)

    Parthasarathy, Varadarajan; Manousakis, Antonios; Kluźniak, Włodzimierz

    2016-05-01

    We performed axisymmetric hydrodynamical simulations of oscillating tori orbiting a non-rotating black hole. The tori in equilibrium were constructed with a constant distribution of angular momentum in a pseudo-Newtonian potential (Kluźniak-Lee). Motions of the torus were triggered by adding subsonic velocity fields: radial, vertical and diagonal to the tori in equilibrium. As the perturbed tori evolved in time, we measured L2 norm of density and obtained the power spectrum of L2 norm which manifested eigenfrequencies of tori modes. The most prominent modes of oscillation excited in the torus by a quasi-random perturbation are the breathing mode and the radial and vertical epicyclic modes. The radial and the plus modes, as well as the vertical and the breathing modes will have frequencies in an approximate 3:2 ratio if the torus is several Schwarzschild radii away from the innermost stable circular orbit. Results of our simulations may be of interest in the context of high-frequency quasi-periodic oscillations observed in stellar-mass black hole binaries, as well as in supermassive black holes.

  17. Noncontact measurement of angular deflection

    NASA Technical Reports Server (NTRS)

    Bryant, E. L.

    1978-01-01

    Technique for measuring instantaneous angular deflection of object requires no physical contact. Technique utilizes two flat refractors, converging lens, and different photocell. Distinction of method is its combination of optical and electromechanical components into feedback system in which measurement error is made to approach zero. Application is foreseen in measurement of torsional strain.

  18. The lunar angular momentum problem

    NASA Technical Reports Server (NTRS)

    Weidenschilling, S. J.

    1984-01-01

    Formation of the Moon by classical Darwin-type fission of a rapidly spinning proto-Earth is discussed. The relationship of angular momentum to accretion disks is examined. The co-accretion scenario and Darwin-type fission are compared and evaluated.

  19. Olympic Wrestling and Angular Momentum.

    ERIC Educational Resources Information Center

    Carle, Mark

    1988-01-01

    Reported is the use of a wrestling photograph in a noncalculus introductory physics course. The photograph presents a maneuver that could serve as an example for a discussion on equilibrium, forces, torque, and angular motion. Provided are some qualitative thoughts as well as quantitative calculations. (YP)

  20. Flatbands under Correlated Perturbations

    NASA Astrophysics Data System (ADS)

    Bodyfelt, Joshua D.; Leykam, Daniel; Danieli, Carlo; Yu, Xiaoquan; Flach, Sergej

    2014-12-01

    Flatband networks are characterized by the coexistence of dispersive and flatbands. Flatbands (FBs) are generated by compact localized eigenstates (CLSs) with local network symmetries, based on destructive interference. Correlated disorder and quasiperiodic potentials hybridize CLSs without additional renormalization, yet with surprising consequences: (i) states are expelled from the FB energy EFB, (ii) the localization length of eigenstates vanishes as ξ ˜1 /ln (E -EFB) , (iii) the density of states diverges logarithmically (particle-hole symmetry) and algebraically (no particle-hole symmetry), and (iv) mobility edge curves show algebraic singularities at EFB . Our analytical results are based on perturbative expansions of the CLSs and supported by numerical data in one and two lattice dimensions.

  1. Flatbands under correlated perturbations.

    PubMed

    Bodyfelt, Joshua D; Leykam, Daniel; Danieli, Carlo; Yu, Xiaoquan; Flach, Sergej

    2014-12-01

    Flatband networks are characterized by the coexistence of dispersive and flatbands. Flatbands (FBs) are generated by compact localized eigenstates (CLSs) with local network symmetries, based on destructive interference. Correlated disorder and quasiperiodic potentials hybridize CLSs without additional renormalization, yet with surprising consequences: (i) states are expelled from the FB energy E_{FB}, (ii) the localization length of eigenstates vanishes as ξ∼1/ln(E-E_{FB}), (iii) the density of states diverges logarithmically (particle-hole symmetry) and algebraically (no particle-hole symmetry), and (iv) mobility edge curves show algebraic singularities at E_{FB}. Our analytical results are based on perturbative expansions of the CLSs and supported by numerical data in one and two lattice dimensions. PMID:25526142

  2. Discrete Newtonian cosmology: perturbations

    NASA Astrophysics Data System (ADS)

    Ellis, George F. R.; Gibbons, Gary W.

    2015-03-01

    In a previous paper (Gibbons and Ellis 2014 Discrete Newtonian cosmology Class. Quantum Grav. 31 025003), we showed how a finite system of discrete particles interacting with each other via Newtonian gravitational attraction would lead to precisely the same dynamical equations for homothetic motion as in the case of the pressure-free Friedmann-Lemaître-Robertson-Walker cosmological models of general relativity theory, provided the distribution of particles obeys the central configuration equation. In this paper we show that one can obtain perturbed such Newtonian solutions that give the same linearized structure growth equations as in the general relativity case. We also obtain the Dmitriev-Zel’dovich equations for subsystems in this discrete gravitational model, and show how it leads to the conclusion that voids have an apparent negative mass.

  3. Perturbed effects at radiation physics

    NASA Astrophysics Data System (ADS)

    Külahcı, Fatih; Şen, Zekâi

    2013-09-01

    Perturbation methodology is applied in order to assess the linear attenuation coefficient, mass attenuation coefficient and cross-section behavior with random components in the basic variables such as the radiation amounts frequently used in the radiation physics and chemistry. Additionally, layer attenuation coefficient (LAC) and perturbed LAC (PLAC) are proposed for different contact materials. Perturbation methodology provides opportunity to obtain results with random deviations from the average behavior of each variable that enters the whole mathematical expression. The basic photon intensity variation expression as the inverse exponential power law (as Beer-Lambert's law) is adopted for perturbation method exposition. Perturbed results are presented not only in terms of the mean but additionally the standard deviation and the correlation coefficients. Such perturbation expressions provide one to assess small random variability in basic variables.

  4. Molecular above-threshold-ionization angular distributions with attosecond bichromatic intense XUV laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2012-01-01

    Angular distributions of molecular above-threshold ionization (MATI) in bichromatic attosecond extreme ultraviolet (XUV) linear polarization laser pulses have been theoretically investigated. Multiphoton ionization in a prealigned molecular ion H2+ produces clear MATI spectra which show a forward-backward asymmetry in angular and momentum distributions which is critically sensitive to the carrier envelope phase (CEP) φ, the time delay Δτ between the two laser pulses, and the photoelectron kinetic energies Ee. The features of the asymmetry in MATI angular distributions are described well by multiphoton perturbative ionization models. Phase differences of continuum electron wave functions can be extracted from the CEP φ and time delay Δτ dependent ionization asymmetry ratio created by interfering multiphoton ionization pathways. At large internuclear distances MATI angular distributions exhibit more complex features due to laser-induced electron diffraction where continuum electron wavelengths are less than the internuclear distance.

  5. Cosmological perturbations in massive bigravity

    SciTech Connect

    Lagos, Macarena; Ferreira, Pedro G. E-mail: p.ferreira1@physics.ox.ac.uk

    2014-12-01

    We present a comprehensive analysis of classical scalar, vector and tensor cosmological perturbations in ghost-free massive bigravity. In particular, we find the full evolution equations and analytical solutions in a wide range of regimes. We show that there are viable cosmological backgrounds but, as has been found in the literature, these models generally have exponential instabilities in linear perturbation theory. However, it is possible to find stable scalar cosmological perturbations for a very particular choice of parameters. For this stable subclass of models we find that vector and tensor perturbations have growing solutions. We argue that special initial conditions are needed for tensor modes in order to have a viable model.

  6. Canonical density matrix perturbation theory.

    PubMed

    Niklasson, Anders M N; Cawkwell, M J; Rubensson, Emanuel H; Rudberg, Elias

    2015-12-01

    Density matrix perturbation theory [Niklasson and Challacombe, Phys. Rev. Lett. 92, 193001 (2004)] is generalized to canonical (NVT) free-energy ensembles in tight-binding, Hartree-Fock, or Kohn-Sham density-functional theory. The canonical density matrix perturbation theory can be used to calculate temperature-dependent response properties from the coupled perturbed self-consistent field equations as in density-functional perturbation theory. The method is well suited to take advantage of sparse matrix algebra to achieve linear scaling complexity in the computational cost as a function of system size for sufficiently large nonmetallic materials and metals at high temperatures. PMID:26764847

  7. Separability of Gravitational Perturbation in Generalized Kerr-Nut Sitter Space-Time

    NASA Astrophysics Data System (ADS)

    Oota, Takeshi; Yasui, Yukinori

    Generalized Kerr-NUT-de Sitter space-time is the most general space-time which admits a rank-2 closed conformal Killing-Yano tensor. It contains the higher-dimensional Kerr-de Sitter black holes with partially equal angular momenta. We study the separability of gravitational perturbations in the generalized Kerr-NUT-de Sitter space-time. We show that a certain type of tensor perturbations admits the separation of variables. The linearized perturbation equations for the Einstein condition are transformed into the ordinary differential equations of Fuchs type.

  8. Plate tectonics conserves angular momentum

    NASA Astrophysics Data System (ADS)

    Bowin, C.

    2009-03-01

    A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4 E+27 kgm2s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites

  9. Hybrid perturbation scheme for wide beamwidth circularly polarized stacked patch microstrip antenna for satellite communication

    NASA Astrophysics Data System (ADS)

    Hossain, Mohammad Shakawat

    Circularly polarized microstrip antennas are popular for satellite communications due to their circularly polarized orientation. They are used frequently in modern day satellite communication. In order to achieve wide angular coverage in satellite communication, a wide beamwidth is required from the antenna. Traditional single layer microstrip antenna inherently demonstrates low angular beamwidth of approximately 600 to 800and thereby lacks wide angular coverage when used for satellite communication. The objective of this thesis is to design a single-fed stacked microstrip antenna using different perturbation techniques in order to achieve a wide angular beamwidth. This thesis presents a new design for a circularly polarized antenna based on the hybrid perturbation scheme. First, a method of stacked patch-ring with negative perturbation was used to generate a significantly larger beamwidth of 1060. The axial ratio (AR) bandwidth obtained is also significantly larger compared to the case when square rings are used as parasitic and driven rings with a single feed. A simulated impedance bandwidth (S11< - 10 dB) of 16%, 3 dB AR bandwidth of 8% and a peak gain of 8.65 dBic are obtained from this design. Next, a new design of stacked hybrid antenna is presented, which uses hybrid perturbations to generate circular polarization radiation. An enhanced beamwidth of 1260 was obtained. The simulation results are confirmed by the measured results.

  10. Full-sky formulae for weak lensing power spectra from total angular momentum method

    SciTech Connect

    Yamauchi, Daisuke; Taruya, Atsushi; Namikawa, Toshiya E-mail: namikawa@yukawa.kyoto-u.ac.jp

    2013-08-01

    We systematically derive full-sky formulae for the weak lensing power spectra generated by scalar, vector and tensor perturbations from the total angular momentum (TAM) method. Based on both the geodesic and geodesic deviation equations, we first give the gauge-invariant expressions for the deflection angle and Jacobi map as observables of the CMB lensing and cosmic shear experiments. We then apply the TAM method, originally developed in the theoretical studies of CMB, to a systematic derivation of the angular power spectra. The TAM representation, which characterizes the total angular dependence of the spatial modes projected along a line-of-sight, can carry all the information of the lensing modes generated by scalar, vector, and tensor metric perturbations. This greatly simplifies the calculation, and we present a complete set of the full-sky formulae for angular power spectra in both the E-/B-mode cosmic shear and gradient-/curl-mode lensing potential of deflection angle. Based on the formulae, we give illustrative examples of non-vanishing B-mode cosmic shear and curl-mode of deflection angle in the presence of the vector and tensor perturbations, and explicitly compute the power spectra.

  11. On Dunkl angular momenta algebra

    NASA Astrophysics Data System (ADS)

    Feigin, Misha; Hakobyan, Tigran

    2015-11-01

    We consider the quantum angular momentum generators, deformed by means of the Dunkl operators. Together with the reflection operators they generate a subalgebra in the rational Cherednik algebra associated with a finite real reflection group. We find all the defining relations of the algebra, which appear to be quadratic, and we show that the algebra is of Poincaré-Birkhoff-Witt (PBW) type. We show that this algebra contains the angular part of the Calogero-Moser Hamiltonian and that together with constants it generates the centre of the algebra. We also consider the gl( N ) version of the subalge-bra of the rational Cherednik algebra and show that it is a non-homogeneous quadratic algebra of PBW type as well. In this case the central generator can be identified with the usual Calogero-Moser Hamiltonian associated with the Coxeter group in the harmonic confinement.

  12. Neoclassical Angular Momentum Flux Revisited

    NASA Astrophysics Data System (ADS)

    Wong, S. K.; Chan, V. S.

    2004-11-01

    The toroidal angular momentum flux in neoclassical transport theory of small rotations depends on the second order (in ion poloidal gyroradius over plasma scale length) ion distribution function. Owing to the complexity of the calculation, the result obtained a long time ago for circular cross-section tokamak plasmas in the banana regime [M.N. Rosenbluth, et al., Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1971), Vol. 1, p. 495] has never been reproduced. Using a representation of the angular momentum flux based on the solution of an adjoint equation to the usual linearized drift kinetic equation, and performing systematically a large-aspect-ratio expansion, we have obtained the flux for flux surfaces of arbitrary shape. We have found the same analytic form for the temperature gradient driven part of the flux, but the overall numerical multiplier is different and has the opposite sign. Implications for rotations in discharges with no apparent momentum input will be discussed.

  13. NUCLEI AT HIGH ANGULAR MOMENTUM

    SciTech Connect

    Diamond, R.M.; Stephens, F.S.

    1980-06-01

    It appears that most nuclei show a compromise between purely collective and purely non-collective behavior at very high spins.non~collective behavior in nuclei has been seen only as high as 36 or 37{bar h}, at which point a more collective structure seems to develop. The concepts underlying the study of high angular momentum states are discussed. The factors that limit angular momentum in nuclei are considered. The currently emerging state of physics of very high spin states is reviewed. The detailed calculations currently made for high spin states are described, focusing not on the calculations themselves, but on the physical input to them and results that come out. Production of high-spin states using heavy-ion reactions is reviewed. Studies of {gamma}-rays de-exciting the evaporation residues from heavy-ion reactions are covered. Two types of {gamma} rays occur: those that cool the nucleus to or toward the yrast line, called "statistical," and those that are more or less parallel to the yrast line and remove the angular momentum, called "yrast~like." Collective rotation, in simplest form the motion of a deformed nucleus around an axis perpendicular to its symmetry axis, is also covered.

  14. Achromatic orbital angular momentum generator

    NASA Astrophysics Data System (ADS)

    Bouchard, Frédéric; Mand, Harjaspreet; Mirhosseini, Mohammad; Karimi, Ebrahim; Boyd, Robert W.

    2014-12-01

    We describe a novel approach for generating light beams that carry orbital angular momentum (OAM) by means of total internal reflection in an isotropic medium. A continuous space-varying cylindrically symmetric reflector, in the form of two glued hollow axicons, is used to introduce a nonuniform rotation of polarization into a linearly polarized input beam. This device acts as a full spin-to-orbital angular momentum convertor. It functions by switching the helicity of the incoming beam's polarization, and by conservation of total angular momentum thereby generates a well-defined value of OAM. Our device is broadband, since the phase shift due to total internal reflection is nearly independent of wavelength. We verify the broad-band behaviour by measuring the conversion efficiency of the device for three different wavelengths corresponding to the RGB colours, red, green and blue. An average conversion efficiency of 95% for these three different wavelengths is observed. This device may find applications in imaging from micro- to astronomical systems where a white vortex beam is needed.

  15. Resumming the string perturbation series

    NASA Astrophysics Data System (ADS)

    Grassi, Alba; Mariño, Marcos; Zakany, Szabolcs

    2015-05-01

    We use the AdS/CFT correspondence to study the resummation of a perturbative genus expansion appearing in the type II superstring dual of ABJM theory. Although the series is Borel summable, its Borel resummation does not agree with the exact non-perturbative answer due to the presence of complex instantons. The same type of behavior appears in the WKB quantization of the quartic oscillator in Quantum Mechanics, which we analyze in detail as a toy model for the string perturbation series. We conclude that, in these examples, Borel summability is not enough for extracting non-perturbative information, due to non-perturbative effects associated to complex instantons. We also analyze the resummation of the genus expansion for topological string theory on local , which is closely related to ABJM theory. In this case, the non-perturbative answer involves membrane instantons computed by the refined topological string, which are crucial to produce a well-defined result. We give evidence that the Borel resummation of the perturbative series requires such a non-perturbative sector.

  16. On dark energy isocurvature perturbation

    SciTech Connect

    Liu, Jie; Zhang, Xinmin; Li, Mingzhe E-mail: limz@nju.edu.cn

    2011-06-01

    Determining the equation of state of dark energy with astronomical observations is crucially important to understand the nature of dark energy. In performing a likelihood analysis of the data, especially of the cosmic microwave background and large scale structure data the dark energy perturbations have to be taken into account both for theoretical consistency and for numerical accuracy. Usually, one assumes in the global fitting analysis that the dark energy perturbations are adiabatic. In this paper, we study the dark energy isocurvature perturbation analytically and discuss its implications for the cosmic microwave background radiation and large scale structure. Furthermore, with the current astronomical observational data and by employing Markov Chain Monte Carlo method, we perform a global analysis of cosmological parameters assuming general initial conditions for the dark energy perturbations. The results show that the dark energy isocurvature perturbations are very weakly constrained and that purely adiabatic initial conditions are consistent with the data.

  17. Computing singularities of perturbation series

    SciTech Connect

    Kvaal, Simen; Jarlebring, Elias; Michiels, Wim

    2011-03-15

    Many properties of current ab initio approaches to the quantum many-body problem, both perturbational and otherwise, are related to the singularity structure of the Rayleigh-Schroedinger perturbation series. A numerical procedure is presented that in principle computes the complete set of singularities, including the dominant singularity which limits the radius of convergence. The method approximates the singularities as eigenvalues of a certain generalized eigenvalue equation which is solved using iterative techniques. It relies on computation of the action of the Hamiltonian matrix on a vector and does not rely on the terms in the perturbation series. The method can be useful for studying perturbation series of typical systems of moderate size, for fundamental development of resummation schemes, and for understanding the structure of singularities for typical systems. Some illustrative model problems are studied, including a helium-like model with {delta}-function interactions for which Moeller-Plesset perturbation theory is considered and the radius of convergence found.

  18. Statistical anisotropy of the curvature perturbation from vector field perturbations

    SciTech Connect

    Dimopoulos, Konstantinos; Karciauskas, Mindaugas; Lyth, David H.; Rodriguez, Yeinzon E-mail: m.karciauskas@lancaster.ac.uk E-mail: yeinzon.rodriguez@uan.edu.co

    2009-05-15

    The {delta}N formula for the primordial curvature perturbation {zeta} is extended to include vector as well as scalar fields. Formulas for the tree-level contributions to the spectrum and bispectrum of {zeta} are given, exhibiting statistical anisotropy. The one-loop contribution to the spectrum of {zeta} is also worked out. We then consider the generation of vector field perturbations from the vacuum, including the longitudinal component that will be present if there is no gauge invariance. Finally, the {delta}N formula is applied to the vector curvaton and vector inflation models with the tensor perturbation also evaluated in the latter case.

  19. Measurements on B-hadron angular correlations at 7 TeV with the CMS experiment

    NASA Astrophysics Data System (ADS)

    Sala, Leonardo; CMS Collaboration

    2012-09-01

    A measurement of the angular correlations between beauty and anti-beauty hadrons produced in LHC proton-proton collisions at √s = 7 TeV is presented, probing for the first time the small angular separation region. The B hadrons are identified by the presence of secondary vertices from their decays and their kinematics reconstructed combining the decay vertex with the primary interaction vertex. The results are compared with predictions based on perturbative QCD calculations at leading and next-to-leading order.

  20. Two-dimensional angular filter array for angular domain imaging with 3D printed angular filters

    NASA Astrophysics Data System (ADS)

    Ng, Eldon; Carson, Jeffrey J. L.

    2013-02-01

    Angular Domain Imaging (ADI) is a technique that is capable of generating two dimensional shadowgrams of attenuating targets embedded in a scattering medium. In ADI, an angular filter array (AFA) is positioned between the sample and the detector to distinguish between quasi-ballistic photons and scattered photons. An AFA is a series of micro-channels with a high aspect ratio. Previous AFAs from our group were constructed by micro-machining the micro-channels into a silicon wafer, limiting the imaging area to a one dimensional line. Two dimensional images were acquired via scanning. The objective of this work was to extend the AFA design to two dimensions to allow for two dimensional imaging with minimal scanning. The second objective of this work was to perform an initial characterization of the imaging capabilities of the 2D AFA. Our approach was to use rapid 3D prototyping techniques to generate an array of micro-channels. The imaging capabilities were then evaluated by imaging a 0.9 mm graphite rod submerged in a scattering media. Contrast was observed to improve when a second angular filter array was placed in front of the sample to mask the incoming light.

  1. Elementary derivation of the perturbation equations of celestial mechanics

    NASA Technical Reports Server (NTRS)

    Burns, J. A.

    1976-01-01

    The equations of celestial mechanics that govern the temporal rates of change of orbital elements are completely derived using elementary dynamics and proceeding only from Newton's equation and its solution. Two orbital equations and the four most meaningful orbital elements - semimajor axis, eccentricity, inclination, and longitude of pericenter - are written in terms of the orbital energy (E) and angular momentum (H) per unit mass. The six resulting equations are differentiated with respect to time to see the effect on the orbital elements of small changes in E and H. The usual perturbation equations in terms of disturbing-force components are then derived by computing the manner in which perturbing forces change E and H. The results are applied in a qualitative discussion of the orbital evolution of particles in nonspherical gravitational fields, through atmospheres, and under the action of tides.

  2. Plate tectonics conserves angular momentum

    NASA Astrophysics Data System (ADS)

    Bowin, C.

    2010-03-01

    A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4+27 kg m2 s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies revealed by geoid anomalies of the degree 4-10 packet of the Earth's spherical harmonic coefficients. These linear positive geoid anomalies underlie plate subduction zones and are presumed due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant

  3. Cosmological perturbations during radion stabilization

    NASA Astrophysics Data System (ADS)

    Ashcroft, P. R.; van de Bruck, C.; Davis, A.-C.

    2005-01-01

    We consider the evolution of cosmological perturbations during radion stabilization, which we assume to happen after a period of inflation in the early universe. Concentrating on the Randall-Sundrum brane world scenario, we find that, if matter is present both on the positive and negative tension branes, the coupling of the radion to matter fields could have significant impact on the evolution of the curvature perturbation and on the production of entropy perturbations. We investigate both the case of a long-lived and a short-lived radion and outline similarities and differences to the curvaton scenario.

  4. Uncertainty relations for angular momentum

    NASA Astrophysics Data System (ADS)

    Dammeier, Lars; Schwonnek, René; Werner, Reinhard F.

    2015-09-01

    In this work we study various notions of uncertainty for angular momentum in the spin-s representation of SU(2). We characterize the ‘uncertainty regions’ given by all vectors, whose components are specified by the variances of the three angular momentum components. A basic feature of this set is a lower bound for the sum of the three variances. We give a method for obtaining optimal lower bounds for uncertainty regions for general operator triples, and evaluate these for small s. Further lower bounds are derived by generalizing the technique by which Robertson obtained his state-dependent lower bound. These are optimal for large s, since they are saturated by states taken from the Holstein-Primakoff approximation. We show that, for all s, all variances are consistent with the so-called vector model, i.e., they can also be realized by a classical probability measure on a sphere of radius \\sqrt{s(s+1)}. Entropic uncertainty relations can be discussed similarly, but are minimized by different states than those minimizing the variances for small s. For large s the Maassen-Uffink bound becomes sharp and we explicitly describe the extremalizing states. Measurement uncertainty, as recently discussed by Busch, Lahti and Werner for position and momentum, is introduced and a generalized observable (POVM) which minimizes the worst case measurement uncertainty of all angular momentum components is explicitly determined, along with the minimal uncertainty. The output vectors for the optimal measurement all have the same length r(s), where r(s)/s\\to 1 as s\\to ∞ .

  5. Variable Distance Angular Symbology Reader

    NASA Technical Reports Server (NTRS)

    Schramm, Harry F., Jr. (Inventor); Corder, Eric L. (Inventor)

    2006-01-01

    A variable distance angular symbology, reader utilizes at least one light source to direct light through a beam splitter and onto a target. A target may be angled relative to the impinging light beam up to and maybe even greater than 45deg. A reflected beam from the target passes through the beam splitter and is preferably directed 90deg relative to the light source through a telecentric lens to a scanner which records an image of the target such as a direct part marking code.

  6. Two-axis angular effector

    DOEpatents

    Vaughn, Mark R.; Robinett, III, Rush D.; Phelan, John R.; Van Zuiden, Don M.

    1997-01-21

    A new class of coplanar two-axis angular effectors. These effectors combine a two-axis rotational joint analogous to a Cardan joint with linear actuators in a manner to produce a wider range of rotational motion about both axes defined by the joint. This new class of effectors also allows design of robotic manipulators having very high strength and efficiency. These effectors are particularly suited for remote operation in unknown surroundings, because of their extraordinary versatility. An immediate application is to the problems which arise in nuclear waste remediation.

  7. Third-Body Perturbation Effects on Satellite Formations

    NASA Astrophysics Data System (ADS)

    T. Roscoe, Christopher W.; Vadali, Srinivas R.; Alfriend, Kyle T.

    2013-12-01

    The effects of third-body perturbations on satellite formations are investigated using differential orbital elements to describe the relative motion. Absolute and differential effects of the lunar perturbation on satellite formations are derived analytically based on the simplified model of the circular restricted three-body problem. This analytical description includes averaged long-term effects on the orbital elements, including the full transformation between the osculating elements and the lunar-averaged elements, which is absent from previous research. A simplified Earth-Moon system model is used, but the results are applicable to any formation reference orbit about the Earth. Simulations are performed to determine the effects of the lunar perturbation on example formations in upper MEO, highly eccentric orbits by using the formation design criteria of Phases I and II of the NASA Magnetospheric Multiscale mission. The changes in angular differential orbital elements ( δ ω, δΩ, and δ M 0) and in science return quality due to this perturbation are compared to changes due to J 2. The method is then expanded to include the inclination of the Moon's orbit and results are compared to simulation using the NASA General Mission Analysis Tool.

  8. Coping with perturbations to a layout somersault in tumbling.

    PubMed

    King, M A; Yeadon, M R

    2003-07-01

    Tumbling is a dynamic movement requiring control of the linear and angular momenta generated during the approach and takeoff phases. Both of these phases are subject to some variability even when the gymnast is trying to perform a given movement repeatedly. This paper used a simulation model of tumbling takeoff to establish how well gymnasts can cope with perturbations of the approach and takeoff phases. A five segment planar simulation model with torque generators at each joint was developed to simulate tumbling takeoffs. The model was customised to an elite gymnast by determining subject specific inertia and torque parameters and a simulation was produced which closely matched a performance of a layout somersault by the gymnast. The performance of a layout somersault was found to be sensitive to the approach characteristics and the activation timings but relatively insensitive to the elasticity of the track and maximum muscle strength. Appropriate variation of the activation timings used during the takeoff phase was capable of coping with moderate perturbations of the approach characteristics. A model of aerial movement established that variation of body configuration in the flight phase was capable of adjusting for takeoff perturbations that would lead to rotation errors of up to 8%. Providing the errors in perceiving approach characteristics are less than 5% or 5 degrees and the errors in timing activations are less than 7ms, perturbations in the approach can be accommodated using adjustments during takeoff and flight. PMID:12757800

  9. Causal compensated perturbations in cosmology

    NASA Technical Reports Server (NTRS)

    Veeraraghavan, Shoba; Stebbins, Albert

    1990-01-01

    A theoretical framework is developed to calculate linear perturbations in the gravitational and matter fields which arise causally in response to the presence of stiff matter sources in a FRW cosmology. It is shown that, in order to satisfy energy and momentum conservation, the gravitational fields of the source must be compensated by perturbations in the matter and gravitational fields, and the role of such compensation in containing the initial inhomogeneities in their subsequent evolution is discussed. A complete formal solution is derived in terms of Green functions for the perturbations produced by an arbitrary source in a flat universe containing cold dark matter. Approximate Green function solutions are derived for the late-time density perturbations and late-time gravitational waves in a universe containing a radiation fluid. A cosmological energy-momentum pseudotensor is defined to clarify the nature of energy and momentum conservation in the expanding universe.

  10. Isocurvature perturbations in extra radiation

    SciTech Connect

    Kawasaki, Masahiro; Miyamoto, Koichi; Nakayama, Kazunori; Sekiguchi, Toyokazu E-mail: miyamone@icrr.u-tokyo.ac.jp E-mail: oyokazu.sekiguchi@nagoya-u.jp

    2012-02-01

    Recent cosmological observations, including measurements of the CMB anisotropy and the primordial helium abundance, indicate the existence of an extra radiation component in the Universe beyond the standard three neutrino species. In this paper we explore the possibility that the extra radiation has isocurvatrue fluctuations. A general formalism to evaluate isocurvature perturbations in the extra radiation is provided in the mixed inflaton-curvaton system, where the extra radiation is produced by the decay of both scalar fields. We also derive constraints on the abundance of the extra radiation and the amount of its isocurvature perturbation. Current observational data favors the existence of an extra radiation component, but does not indicate its having isocurvature perturbation. These constraints are applied to some particle physics motivated models. If future observations detect isocurvature perturbations in the extra radiation, it will give us a hint to the origin of the extra radiation.

  11. Robust stability under additive perturbations

    NASA Technical Reports Server (NTRS)

    Bhaya, A.; Desoer, C. A.

    1985-01-01

    A MIMO linear time-invariant feedback system 1S(P,C) is considered which is assumed to be U-stable. The plant P is subjected to an additive perturbation Delta P which is proper but not necessarily stable. It is proved that the perturbed system is U-stable if and only if Delta P(I + Q x Delta P) exp -1 is U-stable.

  12. Controlling neutron orbital angular momentum.

    PubMed

    Clark, Charles W; Barankov, Roman; Huber, Michael G; Arif, Muhammad; Cory, David G; Pushin, Dmitry A

    2015-09-24

    The quantized orbital angular momentum (OAM) of photons offers an additional degree of freedom and topological protection from noise. Photonic OAM states have therefore been exploited in various applications ranging from studies of quantum entanglement and quantum information science to imaging. The OAM states of electron beams have been shown to be similarly useful, for example in rotating nanoparticles and determining the chirality of crystals. However, although neutrons--as massive, penetrating and neutral particles--are important in materials characterization, quantum information and studies of the foundations of quantum mechanics, OAM control of neutrons has yet to be achieved. Here, we demonstrate OAM control of neutrons using macroscopic spiral phase plates that apply a 'twist' to an input neutron beam. The twisted neutron beams are analysed with neutron interferometry. Our techniques, applied to spatially incoherent beams, demonstrate both the addition of quantum angular momenta along the direction of propagation, effected by multiple spiral phase plates, and the conservation of topological charge with respect to uniform phase fluctuations. Neutron-based studies of quantum information science, the foundations of quantum mechanics, and scattering and imaging of magnetic, superconducting and chiral materials have until now been limited to three degrees of freedom: spin, path and energy. The optimization of OAM control, leading to well defined values of OAM, would provide an additional quantized degree of freedom for such studies. PMID:26399831

  13. Perturbations of the Black Hole-Torus System: Instabilities and QPOs

    NASA Astrophysics Data System (ADS)

    Donmez, Orhan

    2016-07-01

    The existence of the black hole (BH)-torus system has been given a considerable attention to explain the variability of X-ray and Gamma-ray (γ-ray) data. The perturbation of the black hole-torus system creates instabilities and some of these instabilities are responsible for a quasi-periodic oscillation. In this talk, we present the results from numerical simulation of the dynamical instability of a pressure-supported relativistic torus, rotating around the black hole with a constant specific angular momentum on a fixed space-time background, in case of perturbation. The types of instabilities and their amplitudes strongly depend on what kind of perturbation is applied. The types of perturbations can be a blob of hot gas, Bondi-Hoyle accretion from a finite distance, radial and angular velocity perturbations of the stable accreted torus, and non-spherical accretion as a consequence of isotropic fall of the spherical-shell which has finite thickness. We study the effects of perturbations onto the torus-black hole system by solving the hydrodynamical equations and we have found that the torus around the black hole would have an instability, which is called the Papaloizou-Pringle, and a quasi-periodic oscillation only if we choose a suitable perturbations and initial data. It is noted that, while the perturbations, which are called blob of hot gas, radial velocity perturbations and Bondi-Hoyle accretion, create the Papaloizou-Pringle instability, the Papaloizou-Pringle instability is softly developed and removed in a short time scale for spherical shell accretion. Our studies also indicate that QPOs are common phenomena on the disc around the black holes. If the accretion disc or torus has a quasi-periodic behavior, it emits continuous radiation during the oscillation.

  14. Gauge invariant perturbations of self-similar Lemaitre-Tolman-Bondi spacetime: Even parity modes with l{>=}2

    SciTech Connect

    Waters, Thomas J.; Nolan, Brien C.

    2009-04-15

    In this paper we consider gauge invariant linear perturbations of the metric and matter tensors describing the self-similar Lemaitre-Tolman-Bondi (timelike dust) spacetime containing a naked singularity. We decompose the angular part of the perturbation in terms of spherical harmonics and perform a Mellin transform to reduce the perturbation equations to a set of ordinary differential equations with singular points. We fix initial data so the perturbation is finite on the axis and the past null cone of the singularity, and follow the perturbation modes up to the Cauchy horizon. There we argue that certain scalars formed from the modes of the perturbation remain finite, indicating linear stability of the Cauchy horizon.

  15. Useful angular selectivity in oblique columnar aluminum

    NASA Astrophysics Data System (ADS)

    Ditchburn, R. J.; Smith, G. B.

    1991-03-01

    A useful magnitude of angular selective transmittance of incident unpolarized light is demonstrated in obliquely deposited aluminum. Required deposition procedures and anisotropic optical properties are discussed. Angular selectivity is very strong at visible wavelengths but both experiment and theory indicate that a single oblique layer with well defined columns gives high transmittance at near-infrared wavelengths compared with normal films. There are ways of reducing this to enhance the energy control capability. Both solar and luminous angular selectivity are reported.

  16. The Angular Momentum of the Solar System

    NASA Astrophysics Data System (ADS)

    Cang, Rongquin; Guo, Jianpo; Hu, Juanxiu; He, Chaoquiong

    2016-05-01

    The angular momentum of the Solar System is a very important physical quantity to the formation and evolution of the Solar System. Previously, the spin angular momentum of the Sun and the orbital angular momentum of the Eight Giant Planets were only taken into consideration, when researchers calculated the angular momentum of the Solar System. Nowadays, it seems narrow and conservative. Using Eggleton's code, we calculate the rotational inertia of the Sun. Furthermore, we obtain that the spin angular momentum of the Sun is 1.8838 x 10^41 kg m^2 s^-1. Besides the spin angular momentum of the Sun and the orbital angular momentum of the Eight Giant Planets, we also account for the orbital angular momentum of the Asteroid Belt, the Kuiper Belt, the Oort Cloud, the Ninth Giant Planet and the Solar Companion. We obtain that the angular momentum of the whole Solar System is 3.3212 x 10^45 kg m^2 s^-1.

  17. Configuration interaction calculations with infinite angular = expansions

    SciTech Connect

    Goldman, S.P.; Glickman, T.

    1996-05-01

    The Modified Configuration Interaction (MCI) method improves the angular convergence of Configuration Interaction (CI) calculations by several orders of magnitude by mixing a priori a large number of angular basis functions. With MCI one can therefore use basis functions with very large angular momentum quantum numbers, overcoming an important limitation of conventional CI. Although this is desirable given the excellent convergence obtained, the large number of angular integrations and the calculation of n-j symbols with large values of l to high accuracy, make the angular calculations lengthy. In this work a new angular representation for CI calculations is presented that is much more efficient and powerful. Instead of the large number of angular functions of MCI the authors use a basis set containing an infinite linear combination of angular functions. All the necessary integrations involving these infinite expansions are done in closed form and are actually easy and fast to compute. The linear coefficients in the angular expansion are optimized in terms of a few non-linear parameters. Several examples will be presented with applications to two-electron systems.

  18. Gravitational waves from perturbed stars

    NASA Astrophysics Data System (ADS)

    Ferrari, V.

    2011-12-01

    Non radial oscillations of neutron stars are associated with the emission of gravitational waves. The characteristic frequencies of these oscillations can be computed using the theory of stellar perturbations, and they are shown to carry detailed information on the internal structure of the emitting source. Moreover, they appear to be encoded in various radiative processes, as for instance, in the tail of the giant flares of Soft Gamma Repeaters. Thus, their determination is central to the theory of stellar perturbation. A viable approach to the problem consists in formulating this theory as a problem of resonant scattering of gravitational waves incident on the potential barrier generated by the spacetime curvature. This approach discloses some unexpected correspondences between the theory of stellar perturbations and the theory of quantum mechanics, and allows us to predict new relativistic effects.

  19. Gravitational waves from perturbed stars

    NASA Astrophysics Data System (ADS)

    Ferrari, V.

    2011-03-01

    Non radial oscillations of neutron stars are associated with the emission of gravitational waves. The characteristic frequencies of these oscillations can be computed using the theory of stellar perturbations, and they are shown to carry detailed information on the internal structure of the emitting source. Moreover, they appear to be encoded in various radiative processes, as for instance in the tail of the giant flares of Soft Gamma Repeaters. Thus, their determination is central to the theory of stellar perturbation. A viable approach to the problem consists in formulating this theory as a problem of resonant scattering of gravitational waves incident on the potential barrier generated by the spacetime curvature. This approach discloses some unexpected correspondences between the theory of stellar perturbations and the theory of quantum mechanics, and allows us to predict new relativistic effects.

  20. Jet Perturbation by HE target

    SciTech Connect

    Poulsen, P; Kuklo, R M

    2001-03-01

    We have previously reported the degree of attenuation and perturbation by a Cu jet passing through Comp B explosive. Similar tests have now been performed with high explosive (HE) targets having CJ pressures higher than and lower than the CJ pressure of Comp B. The explosives were LX-14 and TNT, respectively. We found that the measured exit velocity of the jet where it transitions from perturbed to solid did not vary significantly as a function of HE type for each HE thickness. The radial momentum imparted to the perturbed jet segment did vary as a function of HE type, however, and we report the radial spreading of the jet and the penetration of a downstream target as a function of HE type and thickness.

  1. Perturbed motion at small eccentricities

    NASA Astrophysics Data System (ADS)

    Emel'yanov, N. V.

    2015-09-01

    In the study of the motion of planets and moons, it is often necessary to have a simple approximate analytical motion model, which takes into account major perturbations and preserves almost the same accuracy at long time intervals. A precessing ellipse model is used for this purpose. In this paper, it is shown that for small eccentricities this model of the perturbed orbit does not correspond to body motion characteristics. There is perturbed circular motion with a constant zero mean anomaly. The corresponding solution satisfies the Lagrange equations with respect to Keplerian orbital elements. There are two families of solutions with libration and circulation changes in the mean anomaly close to this particular solution. The paper shows how the eccentricity and mean anomaly change in these solutions. Simple analytical models of the motion of the four closest moons of Jupiter consistent with available ephemerides are proposed, which in turn are obtained by the numerical integration of motion equations and are refined by observations.

  2. Effects of the type and direction of support surface perturbation on postural responses

    PubMed Central

    2014-01-01

    Background Postural control is organized around a task goal. The two most frequently used types of tasks for postural control research are translational (translation along the anterior-posterior axis) and rotational (rotation in sagittal plane) surface perturbations. These types of perturbations rotate the ankle joint, causing different magnitudes and directions of body sway. The purpose of this study was to investigate the effects of the type (translation vs. rotation) and direction (forward/toe up vs. backward/toe down) of the perturbation on postural responses. Method Nineteen healthy subjects were tested with four perturbations, i.e., forward and backward translation and toe up and toe down rotation. The onset latency and magnitude of muscle activations, angular changes, and COM displacements were measured. In addition, the kinematic data were divided into two phases. The initial phase reflected the balance disturbance induced by the platform movement, and the reversal phase reflected the balance reaction. Results The results showed that, in the initial phase, rotational perturbation induced earlier ankle movement and faster and larger vertical COM displacement, while translational and forward/toe up perturbations induced larger head and trunk angular change and faster and larger horizontal COM displacement. In the reversal phase, balance reaction was attained by multi-joint movements. Translational and forward/toe up perturbations that induced larger upper body instability evoked faster muscle activation as well as faster and larger hip or knee joint movements. Conclusions These findings provide insights into an appropriate support surface perturbation for the evaluation and training of balance. PMID:24708582

  3. Thermal perturbation of the Sun

    NASA Technical Reports Server (NTRS)

    Twigg, L. W.; Endal, A. S.

    1981-01-01

    An investigation of thermal perturbations of the solar convective zone via changes in the mixing length parameter were carried out, with a view toward understanding the possible solar radius and luminosity changes cited in the literature. The results show that: (a) a single perturbation of alpha is probably not the cause of the solar radius change and (b) the parameter W = d lambda nR./d lambda nL. can not be characterized by a single value, as implied in recent work.

  4. Angular-Rate Estimation Using Quaternion Measurements

    NASA Technical Reports Server (NTRS)

    Azor, Ruth; Bar-Itzhack, Y.; Deutschmann, Julie K.; Harman, Richard R.

    1998-01-01

    In most spacecraft (SC) there is a need to know the SC angular rate. Precise angular rate is required for attitude determination, and a coarse rate is needed for attitude control damping. Classically, angular rate information is obtained from gyro measurements. These days, there is a tendency to build smaller, lighter and cheaper SC, therefore the inclination now is to do away with gyros and use other means and methods to determine the angular rate. The latter is also needed even in gyro equipped satellites when performing high rate maneuvers whose angular-rate is out of range of the on board gyros or in case of gyro failure. There are several ways to obtain the angular rate in a gyro-less SC. When the attitude is known, one can differentiate the attitude in whatever parameters it is given and use the kinematics equation that connects the derivative of the attitude with the satellite angular-rate and compute the latter. Since SC usually utilize vector measurements for attitude determination, the differentiation of the attitude introduces a considerable noise component in the computed angular-rate vector.

  5. Mean Angular Momenta of Primary Photofission Products

    SciTech Connect

    Bezshyyko, O.A.; Kadenko, I.M.; Plujko, V.A.; Yermolenko, R.V.; Mazur, V.M.; Strilchuk, N.V.; Vishnevsky, I.M.; Zheltonozhsky, V.A.

    2005-05-24

    Isomer ratios and mean angular momenta for photofission products of 237Np and 238U are obtained. The technique of gamma-ray spectrometry for isomeric ratio determination was used. Fissionable nuclei were irradiated by bremsstrahlung spectrum of microtron M-30 with electron energy 16 MeV. Calculations of mean angular momenta were performed by modified version of the EMPIRE II code.

  6. Orbital angular momentum in the nucleon

    SciTech Connect

    Garvey, Gerald T.

    2010-05-15

    Analysis of the measured value of the integrated d-bar-u-bar asymmetry (I{sub fas} = 0.147 +- 0.027) in the nucleon show it to arise from nucleon fluctuations into baryon plus pion. Requiring angular momentum conservation in these fluctuations shows the associated orbital angular momentum is equal to the value of the flavor asymmetry.

  7. Flux-torque cross-coupling analysis of FOC schemes: Novel perturbation rejection characteristics.

    PubMed

    Amezquita-Brooks, Luis; Liceaga-Castro, Eduardo; Liceaga-Castro, Jesús; Ugalde-Loo, Carlos E

    2015-09-01

    Field oriented control (FOC) is one of the most successful control schemes for electrical machines. In this article new properties of FOC schemes for induction motors (IMs) are revealed by studying the cross-coupling of the flux-torque subsystem. Through the use of frequency-based multivariable tools, it is shown that FOC has intrinsic stator currents disturbance rejection properties due to the existence of a transmission zero in the flux-torque subsystem. These properties can be exploited in order to select appropriate feedback loop configurations. One of the major drawbacks of FOC schemes is their high sensitivity to slip angular velocity perturbations. These perturbations are related to variations of the rotor time constant, which are known to be problematic for IM control. In this regard, the effect that slip angular velocity perturbations have over the newly found perturbation rejection properties is also studied. In particular, although perturbation rejection is maintained, deviations to the equilibrium point are induced; this introduces difficulties for simultaneous flux and torque control. The existence of equilibrium point issues when flux and torque are simultaneously controlled is documented for the first time in this article. PMID:26187346

  8. A collision history-based approach to Sensitivity/Perturbation calculations in the continuous energy Monte Carlo code SERPENT

    SciTech Connect

    Giuseppe Palmiotti

    2015-05-01

    In this work, the implementation of a collision history-based approach to sensitivity/perturbation calculations in the Monte Carlo code SERPENT is discussed. The proposed methods allow the calculation of the eects of nuclear data perturbation on several response functions: the eective multiplication factor, reaction rate ratios and bilinear ratios (e.g., eective kinetics parameters). SERPENT results are compared to ERANOS and TSUNAMI Generalized Perturbation Theory calculations for two fast metallic systems and for a PWR pin-cell benchmark. New methods for the calculation of sensitivities to angular scattering distributions are also presented, which adopts fully continuous (in energy and angle) Monte Carlo estimators.

  9. AGK Rules in Perturbative QCD

    NASA Astrophysics Data System (ADS)

    Bartels, Jochen

    2006-06-01

    I summarize the present status of the AGK cutting rules in perturbative QCD. Particular attention is given to the application of the AGK analysis to diffraction and multiple scattering in DIS at HERA and to pp collisions at the LHC. I also discuss the bootstrap conditions which appear in pQCD.

  10. VHS Movies: Perturbations for Morphogenesis.

    ERIC Educational Resources Information Center

    Holmes, Danny L.

    This paper discusses the concept of a family system in terms of an interactive system of interrelated, interdependent parts and suggests that VHS movies can act as perturbations, i.e., change promoting agents, for certain dysfunctional family systems. Several distinct characteristics of a family system are defined with particular emphasis on…

  11. Adaptation Strategies in Perturbed /s/

    ERIC Educational Resources Information Center

    Brunner, Jana; Hoole, Phil; Perrier, Pascal

    2011-01-01

    The purpose of this work is to investigate the role of three articulatory parameters (tongue position, jaw position and tongue grooving) in the production of /s/. Six normal speakers' speech was perturbed by a palatal prosthesis. The fricative was recorded acoustically and through electromagnetic articulography in four conditions: (1) unperturbed,…

  12. Basics of QCD perturbation theory

    SciTech Connect

    Soper, D.E.

    1997-06-01

    This is an introduction to the use of QCD perturbation theory, emphasizing generic features of the theory that enable one to separate short-time and long-time effects. The author also covers some important classes of applications: electron-positron annihilation to hadrons, deeply inelastic scattering, and hard processes in hadron-hadron collisions. 31 refs., 38 figs.

  13. Generalized perturbations in neutrino mixing

    NASA Astrophysics Data System (ADS)

    Liao, Jiajun; Marfatia, D.; Whisnant, K.

    2015-10-01

    We derive expressions for the neutrino mixing parameters that result from complex perturbations on (1) the Majorana neutrino mass matrix (in the basis of charged lepton mass eigenstates) and on (2) the charged lepton mass matrix, for arbitrary initial (unperturbed) mixing matrices. In the first case, we find that the phases of the elements of the perturbation matrix, and the initial values of the Dirac and Majorana phases, strongly impact the leading-order corrections to the neutrino mixing parameters and phases. For experimentally compatible scenarios wherein the initial neutrino mass matrix has μ -τ symmetry, we find that the Dirac phase can take any value under small perturbations. Similarly, in the second case, perturbations to the charged lepton mass matrix can generate large corrections to the mixing angles and phases of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix. As an illustration of our generalized procedure, we apply it to a situation in which nonstandard scalar and nonstandard vector interactions simultaneously affect neutrino oscillations.

  14. Seven topics in perturbative QCD

    SciTech Connect

    Buras, A.J.

    1980-09-01

    The following topics of perturbative QCD are discussed: (1) deep inelastic scattering; (2) higher order corrections to e/sup +/e/sup -/ annihilation, to photon structure functions and to quarkonia decays; (3) higher order corrections to fragmentation functions and to various semi-inclusive processes; (4) higher twist contributions; (5) exclusive processes; (6) transverse momentum effects; (7) jet and photon physics.

  15. Invisible Electronic States and Their Dynamics Revealed by Perturbations

    NASA Astrophysics Data System (ADS)

    Merer, Anthony J.

    2011-06-01

    Sooner or later everyone working in the field of spectroscopy encounters perturbations. These can range in size from a small shift of a single rotational level to total destruction of the vibrational and rotational patterns of an electronic state. To some workers perturbations are a source of terror, but to others they are the most fascinating features of molecular spectra, because they give information about molecular dynamics, and about states that would otherwise be invisible as a result of unfavorable selection rules. An example of the latter is the essentially complete characterization of the tilde{b}^3A_2 state of SO_2 from the vibronic perturbations it causes in the tilde{a}^3B_1 state. The S_1-trans state of acetylene is a beautiful example of dynamics in action. The level patterns of the three bending vibrations change dramatically with increasing vibrational excitation as a result of the vibrational angular momentum and the approach to the isomerization barrier. Several vibrational levels of the S_1-cis isomer, previously thought to be unobservable, can now be assigned. They obtain their intensity through interactions with nearby levels of the trans isomer.

  16. A Computer Program for the Reactivity and Kinetic Parameters for Two-Dimensional Triangular Geometry by Transport Perturbation Theory.

    Energy Science and Technology Software Center (ESTSC)

    1990-04-25

    Version 00 TPTRIA calculates reactivity, effective delayed neutron fractions and mean generation time for two-dimensional triangular geometry on the basis of neutron transport perturbation theory. DIAMANT2 (also designated as CCC-414), is a multigroup two-dimensional discrete ordinates transport code system for triangular and hexagonal geometry which calculates direct and adjoint angular fluxes.

  17. A transport based one-dimensional perturbation code for reactivity calculations in metal systems

    SciTech Connect

    Wenz, T.R.

    1995-02-01

    A one-dimensional reactivity calculation code is developed using first order perturbation theory. The reactivity equation is based on the multi-group transport equation using the discrete ordinates method for angular dependence. In addition to the first order perturbation approximations, the reactivity code uses only the isotropic scattering data, but cross section libraries with higher order scattering data can still be used with this code. The reactivity code obtains all the flux, cross section, and geometry data from the standard interface files created by ONEDANT, a discrete ordinates transport code. Comparisons between calculated and experimental reactivities were done with the central reactivity worth data for Lady Godiva, a bare uranium metal assembly. Good agreement is found for isotopes that do not violate the assumptions in the first order approximation. In general for cases where there are large discrepancies, the discretized cross section data is not accurately representing certain resonance regions that coincide with dominant flux groups in the Godiva assembly. Comparing reactivities calculated with first order perturbation theory and a straight {Delta}k/k calculation shows agreement within 10% indicating the perturbation of the calculated fluxes is small enough for first order perturbation theory to be applicable in the modeled system. Computation time comparisons between reactivities calculated with first order perturbation theory and straight {Delta}k/k calculations indicate considerable time can be saved performing a calculation with a perturbation code particularly as the complexity of the modeled problems increase.

  18. Effects of angular correlations on particle-particle propagation in infinite nuclear matter

    NASA Astrophysics Data System (ADS)

    Romero-Barrientos, J.; Arellano, H. F.

    2016-05-01

    The effect of angular correlations on self-consistent solutions for single-particle (sp) potentials in infinite nuclear matter is investigated. To this end we treat explicitly the angular dependence of the particle-particle (pp) propagator in Brueckner-Hartree-Fock (BHF) equation for the g matrix. It is observed that the exact angular dependence of the pp propagator yields highly fluctuating structures, posing stringent difficulties in the actual search of self-consistent solutions for the sp energy. A perturbative approach is presented to evaluate the effect of the angular correlations in the self-consistent solutions. Solutions at Fermi momenta kF in the range 1.20 - 1.75 fm-1 are reported using Argonne v 18 nucleon- nucleon potential. Although the sp potentials are sensitive to the treatment of the angular behaviour of the propagator, such sensitivity appears at momenta well above the Fermi surface. As a result, the saturation properties of symmetric nuclear matter differ marginally from those calculated using angle-averaged energy denominators in pp propagators.

  19. The Serret-Andoyer formalism in rigid-body dynamics: I. Symmetries and perturbations

    NASA Astrophysics Data System (ADS)

    Gurfil, P.; Elipe, A.; Tangren, W.; Efroimsky, M.

    2007-08-01

    This paper reviews the Serret-Andoyer (SA) canonical formalism in rigid-body dynamics, and presents some new results. As is well known, the problem of unsupported and unperturbed rigid rotator can be reduced. The availability of this reduction is offered by the underlying symmetry, that stems from conservation of the angular momentum and rotational kinetic energy. When a perturbation is turned on, these quantities are no longer preserved. Nonetheless, the language of reduced description remains extremely instrumental even in the perturbed case. We describe the canonical reduction performed by the Serret-Andoyer (SA) method, and discuss its applications to attitude dynamics and to the theory of planetary rotation. Specifically, we consider the case of angular-velocity-dependent torques, and discuss the variation-of-parameters-inherent antinomy between canonicity and osculation. Finally, we address the transformation of the Andoyer variables into action-angle ones, using the method of Sadov.

  20. Angular momentum in the Local Group

    SciTech Connect

    Dunn, A.; Laflamme, R.

    1994-04-01

    We briefly review models for the Local Group and the acquisition of its angular momentum. We describe early attempts to understand the origin of the spin of the galaxies discussing the hypothesis that the Local Group has little angular momentum. Finally we show that using Peebles` least action principle there should be a rather large amount of orbital angular momentum compared to the magnitude of the spin of its galaxies. Therefore the Local Group cannot be thought as tidally isolated. Using Peebles` trajectories we give a possible set of trajectories for Local Group galaxies which would predict their spin.

  1. Stellar Angular Diameter Relations for Microlensing Surveys

    NASA Astrophysics Data System (ADS)

    Adams, Arthur; Boyajian, Tabetha S.; von Braun, Kaspar

    2016-01-01

    Determining the physical properties of microlensing events depends on having accurate angular radii of the source star. Using long-baseline optical interferometry we are able to determine the angular sizes of nearby stars with uncertainties less than 2 percent. We present empirical estimates of angular diameters for both dwarfs/subgiants and giant stars as functions of five color indices which are relevant to planned microlensing surveys. We find in all considered colors that metallicity does not play a statistically significant role in predicting stellar size for the samples of stars considered.

  2. Angular momentum dependence of complex fragment emission

    SciTech Connect

    Sobotka, L.G.; Sarantites, D.G.; Li, Z.; Dines, E.L.; Halbert, M.L.; Hensley, D.C.; Lisle, J.C.; Schmitt, R.P.; Majka, Z.; Nebbia, G.

    1987-12-01

    The angular momentum dependence of large fragment production in long-lived reactions is studied by measurements of fragment cross sections from reactions with substantially different angular momentum distributions and the coincident ..gamma..-ray multiplicity distributions. The results indicate that the primary l-wave distributions move to larger mean values and decrease in width and skewness with increasing mass symmetry in the decay channel. The results also confirm that the partition of angular momentum kinetic energy relaxed heavy-ion reactions is that expected for a rigidly rotating intermediate.

  3. Optical Mixing of Rydberg Angular Momenta

    SciTech Connect

    Corless, J.D.; Stroud, C.R., Jr.

    1997-07-01

    When optical frequency fields are used to couple a ground state to a Rydberg state, the resonant dipole coupling is to a low angular momentum state. Higher angular momentum states are typically thought not to play a role in the excitation. The extremely large dipole matrix elements coupling Rydberg states of the same n but differing l , however, allow optical fields of modest strengths to produce Rabi frequencies larger than optical frequencies. We demonstrate that these optical fields can therefore readily excite the higher angular momentum states, and we examine the consequences of this coupling. {copyright} {ital 1997} {ital The American Physical Society}

  4. Vector perturbations of galaxy number counts

    NASA Astrophysics Data System (ADS)

    Durrer, Ruth; Tansella, Vittorio

    2016-07-01

    We derive the contribution to relativistic galaxy number count fluctuations from vector and tensor perturbations within linear perturbation theory. Our result is consistent with the the relativistic corrections to number counts due to scalar perturbation, where the Bardeen potentials are replaced with line-of-sight projection of vector and tensor quantities. Since vector and tensor perturbations do not lead to density fluctuations the standard density term in the number counts is absent. We apply our results to vector perturbations which are induced from scalar perturbations at second order and give numerical estimates of their contributions to the power spectrum of relativistic galaxy number counts.

  5. Neptune's story. [Triton's orbit perturbation

    NASA Technical Reports Server (NTRS)

    Goldreich, P.; Murray, N.; Longaretti, P. Y.; Banfield, D.

    1989-01-01

    It is conjectured that Triton was captured from a heliocentric orbit as the result of a collision with what was then one of Neptune's regular satellites. The immediate post-capture orbit was highly eccentric. Dissipation due to tides raised by Neptune in Triton caused Triton's orbit to evolve to its present state in less than one billion years. For much of this time Triton was almost entirely molten. While its orbit was evolving, Triton cannibalized most of the regular satellites of Neptune and also perturbed Nereid, thus accounting for that satellite's highly eccentric and inclined orbit. The only regular satellites of Neptune that survived were those that formed well within 5 Neptune radii, and they move on inclined orbits as the result of chaotic perturbations forced by Triton.

  6. Identifying Network Perturbation in Cancer.

    PubMed

    Grechkin, Maxim; Logsdon, Benjamin A; Gentles, Andrew J; Lee, Su-In

    2016-05-01

    We present a computational framework, called DISCERN (DIfferential SparsE Regulatory Network), to identify informative topological changes in gene-regulator dependence networks inferred on the basis of mRNA expression datasets within distinct biological states. DISCERN takes two expression datasets as input: an expression dataset of diseased tissues from patients with a disease of interest and another expression dataset from matching normal tissues. DISCERN estimates the extent to which each gene is perturbed-having distinct regulator connectivity in the inferred gene-regulator dependencies between the disease and normal conditions. This approach has distinct advantages over existing methods. First, DISCERN infers conditional dependencies between candidate regulators and genes, where conditional dependence relationships discriminate the evidence for direct interactions from indirect interactions more precisely than pairwise correlation. Second, DISCERN uses a new likelihood-based scoring function to alleviate concerns about accuracy of the specific edges inferred in a particular network. DISCERN identifies perturbed genes more accurately in synthetic data than existing methods to identify perturbed genes between distinct states. In expression datasets from patients with acute myeloid leukemia (AML), breast cancer and lung cancer, genes with high DISCERN scores in each cancer are enriched for known tumor drivers, genes associated with the biological processes known to be important in the disease, and genes associated with patient prognosis, in the respective cancer. Finally, we show that DISCERN can uncover potential mechanisms underlying network perturbation by explaining observed epigenomic activity patterns in cancer and normal tissue types more accurately than alternative methods, based on the available epigenomic data from the ENCODE project. PMID:27145341

  7. Anisotropic CMB distortions from non-Gaussian isocurvature perturbations

    NASA Astrophysics Data System (ADS)

    Ota, Atsuhisa; Sekiguchi, Toyokazu; Tada, Yuichiro; Yokoyama, Shuichiro

    2015-03-01

    We calculate the CMB μ-distortion, langleμrangle, and the angular power spectrum of its cross-correlation with the temperature anisotropy, langleμTrangle, in the presence of the non-Gaussian neutrino isocurvature density (NID) mode. While the pure Gaussian NID perturbations give merely subdominant contributions to langleμrangle and do not create langleμTrangle, we show large langleμTrangle can be realized in case where, especially, the NID perturbations 𝒮(x) are proportional to the square of a Gaussian field g(x), i.e. 𝒮(x)propto g2(x). Such Gaussian-squared perturbations contribute to not only the power spectrum, but also the bispectrum of CMB anisotropies. The constraints from the power spectrum is given by 𝒫𝒮𝒮(k0)~𝒫g2(k0)lesssim10-10 at k0=0.05 Mpc-1. We also forecast constraints from the CMB temperature and E-mode polarisation bispectra, and show that 𝒫g(k0)lesssim10-5 would be allowed from the Planck data. We find that langleμrangle and |l(l+1)CμTl| can respectively be as large as 10-9 and 10-14 with uncorrelated scale-invariant NID perturbations for 𝒫g(k0)=10-5. When the spectrum of the Gaussian field is blue-tilted (with spectral index ngsimeq1.5), langleμTrangle can be enhanced by an order of magnitude.

  8. R evolution: Improving perturbative QCD

    SciTech Connect

    Hoang, Andre H.; Jain, Ambar; Stewart, Iain W.; Scimemi, Ignazio

    2010-07-01

    Perturbative QCD results in the MS scheme can be dramatically improved by switching to a scheme that accounts for the dominant power law dependence on the factorization scale in the operator product expansion. We introduce the ''MSR scheme'' which achieves this in a Lorentz and gauge invariant way and has a very simple relation to MS. Results in MSR depend on a cutoff parameter R, in addition to the {mu} of MS. R variations can be used to independently estimate (i.) the size of power corrections, and (ii.) higher-order perturbative corrections (much like {mu} in MS). We give two examples at three-loop order, the ratio of mass splittings in the B*-B and D*-D systems, and the Ellis-Jaffe sum rule as a function of momentum transfer Q in deep inelastic scattering. Comparing to data, the perturbative MSR results work well even for Q{approx}1 GeV, and power corrections are reduced compared to MS.

  9. Path integral for inflationary perturbations

    NASA Astrophysics Data System (ADS)

    Prokopec, Tomislav; Rigopoulos, Gerasimos

    2010-07-01

    The quantum theory of cosmological perturbations in single-field inflation is formulated in terms of a path integral. Starting from a canonical formulation, we show how the free propagators can be obtained from the well-known gauge-invariant quadratic action for scalar and tensor perturbations, and determine the interactions to arbitrary order. This approach does not require the explicit solution of the energy and momentum constraints, a novel feature which simplifies the determination of the interaction vertices. The constraints and the necessary imposition of gauge conditions is reflected in the appearance of various commuting and anticommuting auxiliary fields in the action. These auxiliary fields are not propagating physical degrees of freedom but need to be included in internal lines and loops in a diagrammatic expansion. To illustrate the formalism we discuss the tree-level three-point and four-point functions of the inflaton perturbations, reproducing the results already obtained by the methods used in the current literature. Loop calculations are left for future work.

  10. R evolution: Improving perturbative QCD

    NASA Astrophysics Data System (ADS)

    Hoang, André H.; Jain, Ambar; Scimemi, Ignazio; Stewart, Iain W.

    2010-07-01

    Perturbative QCD results in the MS¯ scheme can be dramatically improved by switching to a scheme that accounts for the dominant power law dependence on the factorization scale in the operator product expansion. We introduce the “MSR scheme” which achieves this in a Lorentz and gauge invariant way and has a very simple relation to MS¯. Results in MSR depend on a cutoff parameter R, in addition to the μ of MS¯. R variations can be used to independently estimate (i.) the size of power corrections, and (ii.) higher-order perturbative corrections (much like μ in MS¯). We give two examples at three-loop order, the ratio of mass splittings in the B*-B and D*-D systems, and the Ellis-Jaffe sum rule as a function of momentum transfer Q in deep inelastic scattering. Comparing to data, the perturbative MSR results work well even for Q˜1GeV, and power corrections are reduced compared to MS¯.

  11. Perturbation growth in accreting filaments

    NASA Astrophysics Data System (ADS)

    Clarke, S. D.; Whitworth, A. P.; Hubber, D. A.

    2016-05-01

    We use smoothed particle hydrodynamic simulations to investigate the growth of perturbations in infinitely long filaments as they form and grow by accretion. The growth of these perturbations leads to filament fragmentation and the formation of cores. Most previous work on this subject has been confined to the growth and fragmentation of equilibrium filaments and has found that there exists a preferential fragmentation length-scale which is roughly four times the filament's diameter. Our results show a more complicated dispersion relation with a series of peaks linking perturbation wavelength and growth rate. These are due to gravo-acoustic oscillations along the longitudinal axis during the sub-critical phase of growth. The positions of the peaks in growth rate have a strong dependence on both the mass accretion rate onto the filament and the temperature of the gas. When seeded with a multiwavelength density power spectrum, there exists a clear preferred core separation equal to the largest peak in the dispersion relation. Our results allow one to estimate a minimum age for a filament which is breaking up into regularly spaced fragments, as well as an average accretion rate. We apply the model to observations of filaments in Taurus by Tafalla & Hacar and find accretion rates consistent with those estimated by Palmeirim et al.

  12. Gravitational waves carrying orbital angular momentum

    NASA Astrophysics Data System (ADS)

    Bialynicki-Birula, Iwo; Bialynicka-Birula, Zofia

    2016-02-01

    Spinorial formalism is used to map every electromagnetic wave into the gravitational wave (within the linearized gravity). In this way we can obtain the gravitational counterparts of Bessel, Laguerre-Gauss, and other light beams carrying orbital angular momentum.

  13. Calculates Angular Quadrature Weights and Cosines.

    Energy Science and Technology Software Center (ESTSC)

    1988-02-18

    DSNQUAD calculates the angular quadrature weights and cosines for use in CCC-254/ANISN-ORNL. The subroutines in DSNQUAD were lifted from the XSDRN-PM code, which is supplied with the CCC-475/ SCALIAS-77 package.

  14. Angular-divergence calculation for Experimental Advanced Superconducting Tokamak neutral beam injection ion source based on spectroscopic measurements

    SciTech Connect

    Chi, Yuan; Hu, Chundong; Zhuang, Ge

    2014-02-15

    Calorimetric method has been primarily applied for several experimental campaigns to determine the angular divergence of high-current ion source for the neutral beam injection system on the Experimental Advanced Superconducting Tokamak (EAST). A Doppler shift spectroscopy has been developed to provide the secondary measurement of the angular divergence to improve the divergence measurement accuracy and for real-time and non-perturbing measurement. The modified calculation model based on the W7AS neutral beam injectors is adopted to accommodate the slot-type accelerating grids used in the EAST's ion source. Preliminary spectroscopic experimental results are presented comparable to the calorimetrically determined value of theoretical calculation.

  15. A new integrated optical angular velocity sensor

    NASA Astrophysics Data System (ADS)

    Ciminelli, Caterina; Peluso, Francesco; Armenise, Mario N.

    2005-03-01

    Very compact and low-cost rotation sensors are strongly required for any moving systems in several applications. Integrated optical angular velocity sensors seem to be very promising in terms of low cost, compactness, light weight and high-performance. In the paper a new integrated optical angular velocity sensor having a passive resonant configuration is proposed. Preliminary results are really encouraging and demonstrate the possibility of using the sensor in gyro systems for satellite applications.

  16. Angular performance measure for tighter uncertainty relations

    SciTech Connect

    Hradil, Z.; Rehacek, J.; Klimov, A. B.; Rigas, I.; Sanchez-Soto, L. L.

    2010-01-15

    The uncertainty principle places a fundamental limit on the accuracy with which we can measure conjugate quantities. However, the fluctuations of these variables can be assessed in terms of different estimators. We propose an angular performance that allows for tighter uncertainty relations for angle and angular momentum. The differences with previous bounds can be significant for particular states and indeed may be amenable to experimental measurement with the present technology.

  17. Angular wander measurements of maser clusters

    NASA Astrophysics Data System (ADS)

    Mutel, Robert L.

    Angular wander measurements of the relative positions of closely spaced maser features provides a powerful probe of interstellar turbulence associated with regions of star formation. Differential angular wander is easily measured in a maser complex and can strongly distinguish between shallow and steep power-law turbulence. The best candidates for such measurements appear to be the 6 and 12 GHz type II methanol masers.

  18. Geometric absorption of electromagnetic angular momentum

    NASA Astrophysics Data System (ADS)

    Konz, C.; Benford, Gregory

    2003-10-01

    Circularly polarized electromagnetic fields carry both energy and angular momentum. We investigate the conditions under which a circularly polarized wave field transfers angular momentum to a perfectly conducting macroscopic object, using exact electromagnetic wave theory in a steady-state calculation. We find that axisymmetric perfect conductors cannot absorb or radiate angular momentum when illuminated. However, any asymmetry allows absorption. A rigorous, steady-state solution of the boundary value problem for the reflection from a perfectly conducting infinite wedge shows that waves convey angular momentum at the edges of asymmetries. Conductors can also radiate angular momentum, so their geometric absorption coefficient for angular momentum can be negative. Such absorption or radiation depends solely on the specific geometry of the conductor. The geometric absorption coefficient can be as high as 0.8, and the coefficient for radiation can be -0.4, larger than typical material absorption coefficients. We apply the results to recent experiments which spun roof-shaped aluminum sheets with polarized microwave beams. Applications of geometric, instead of material, absorption can be quite varied. Though experiments testing these ideas will be simpler at microwavelengths, the ideas work for optical ones as well.

  19. Cosmological perturbations: Vorticity, isocurvature and magnetic fields

    NASA Astrophysics Data System (ADS)

    Christopherson, Adam J.

    2014-10-01

    In this paper, I review some recent, interlinked, work undertaken using cosmological perturbation theory — a powerful technique for modeling inhomogeneities in the universe. The common theme which underpins these pieces of work is the presence of nonadiabatic pressure, or entropy, perturbations. After a brief introduction covering the standard techniques of describing inhomogeneities in both Newtonian and relativistic cosmology, I discuss the generation of vorticity. As in classical fluid mechanics, vorticity is not present in linearized perturbation theory (unless included as an initial condition). Allowing for entropy perturbations, and working to second order in perturbation theory, I show that vorticity is generated, even in the absence of vector perturbations, by purely scalar perturbations, the source term being quadratic in the gradients of first order energy density and isocurvature, or nonadiabatic pressure perturbations. This generalizes Crocco's theorem to a cosmological setting. I then introduce isocurvature perturbations in different models, focusing on the entropy perturbation in standard, concordance cosmology, and in inflationary models involving two scalar fields. As the final topic, I investigate magnetic fields, which are a potential observational consequence of vorticity in the early universe. I briefly review some recent work on including magnetic fields in perturbation theory in a consistent way. I show, using solely analytical techniques, that magnetic fields can be generated by higher order perturbations, albeit too small to provide the entire primordial seed field, in agreement with some numerical studies. I close this paper with a summary and some potential extensions of this work.

  20. Superconvergent perturbation method in quantum mechanics

    SciTech Connect

    Scherer, W. )

    1995-02-27

    An analog of Kolmogorov's superconvergent perturbation theory in classical mechanics is constructed for self-adjoint operators. It is different from the usual Rayleigh-Schroedinger perturbation theory and yields expansions for eigenvalues and eigenvectors in terms of functions of the perturbation parameter.

  1. Geometric Hamiltonian structures and perturbation theory

    SciTech Connect

    Omohundro, S.

    1984-08-01

    We have been engaged in a program of investigating the Hamiltonian structure of the various perturbation theories used in practice. We describe the geometry of a Hamiltonian structure for non-singular perturbation theory applied to Hamiltonian systems on symplectic manifolds and the connection with singular perturbation techniques based on the method of averaging.

  2. Gravitational perturbations of the Schwarzschild spacetime: A practical covariant and gauge-invariant formalism

    NASA Astrophysics Data System (ADS)

    Martel, Karl; Poisson, Eric

    2005-05-01

    We present a formalism to study the metric perturbations of the Schwarzschild spacetime. The formalism is gauge invariant, and it is also covariant under two-dimensional coordinate transformations that leave the angular coordinates unchanged. The formalism is applied to the typical problem of calculating the gravitational waves produced by material sources moving in the Schwarzschild spacetime. We examine the radiation escaping to future null infinity as well as the radiation crossing the event horizon. The waveforms, the energy radiated, and the angular-momentum radiated can all be expressed in terms of two gauge-invariant scalar functions that satisfy one-dimensional wave equations. The first is the Zerilli-Moncrief function, which satisfies the Zerilli equation, and which represents the even-parity sector of the perturbation. The second is the Cunningham-Price-Moncrief function, which satisfies the Regge-Wheeler equation, and which represents the odd-parity sector of the perturbation. The covariant forms of these wave equations are presented here, complete with covariant source terms that are derived from the stress-energy tensor of the matter responsible for the perturbation.

  3. Weak lensing generated by vector perturbations and detectability of cosmic strings

    SciTech Connect

    Yamauchi, Daisuke; Namikawa, Toshiya; Taruya, Atsushi E-mail: namikawa@utap.phys.s.u-tokyo.ac.jp

    2012-10-01

    We study the observational signature of vector metric perturbations through the effect of weak gravitational lensing. In the presence of vector perturbations, the non-vanishing signals for B-mode cosmic shear and curl-mode deflection angle, which have never appeared in the case of scalar metric perturbations, naturally arise. Solving the geodesic and geodesic deviation equations, we drive the full-sky formulas for angular power spectra of weak lensing signals, and give the explicit expressions for E-/B-mode cosmic shear and gradient-/curl-mode deflection angle. As a possible source for seeding vector perturbations, we then consider a cosmic string network, and discuss its detectability from upcoming weak lensing and CMB measurements. Based on the formulas and a simple model for cosmic string network, we calculate the angular power spectra and expected signal-to-noise ratios for the B-mode cosmic shear and curl-mode deflection angle. We find that the weak lensing signals are enhanced for a smaller intercommuting probability of the string network, P, and they are potentially detectable from the upcoming cosmic shear and CMB lensing observations. For P ∼ 10{sup −1}, the minimum detectable tension of the cosmic string will be down to Gμ ∼ 5 × 10{sup −8}. With a theoretically inferred smallest value P ∼ 10{sup −3}, we could even detect the string with Gμ ∼ 5 × 10{sup −10}.

  4. A detection system with broad angular acceptance for particle identification and angular distribution measurements

    NASA Astrophysics Data System (ADS)

    Carnelli, P. F. F.; Arazi, A.; Fernández Niello, J. O.; Capurro, O. A.; Cardona, M. A.; de Barbará, E.; Figueira, J. M.; Hojman, D.; Martí, G. V.; Martinez Heimann, D.; Negri, A. E.; Pacheco, A. J.

    2013-10-01

    A new detection system for time-optimized heavy-ion angular distribution measurements has been designed and constructed. This device is composed by an ionization chamber with a segmented-grid anode and three position-sensitive silicon detectors. This particular arrangement allows identifying reaction products emitted within a 30° wide angular range with better than 1° angular resolution. As a demonstration of its capabilities, angular distributions of the elastic scattering cross-section and the production of alpha particles in the 7Li+27Al system, at an energy above the Coulomb barrier, are presented.

  5. Bringing "The Moth" to Light: A Planet-Perturbed Disk Scenario for the HD 61005 System

    NASA Astrophysics Data System (ADS)

    Esposito, Thomas M.; Fitzgerald, Michael P.; Graham, James R.; Kalas, Paul G.; Millar-Blanchaer, Max; Wang, Jason

    2015-12-01

    The HD 61005 debris disk ("The Moth") is notable for its unusual swept-back "wing" morphology, brightness asymmetries, dust ring offset, and a cleared region inside of ~50 AU. Here we present Gemini Planet Imager data that reveal this disk in scattered light down to Jupiter-like separations of <10 AU. Complementary W.M. Keck NIRC2/AO J,H,K imaging shows the disk's outer regions with high angular resolution. Based on these data, we propose a new explanation for the disk's features: that of an unseen planet on an inclined, eccentric orbit perturbing the disk material. To test this scenario, we used secular perturbation theory to construct 3-D dust distributions that informed 2-D scattered-light models, which we then compared with the data via an MCMC analysis. We found that the best-fit models reproduced morphological disk features similar to those observed, indicating that the perturber scenario is plausible for this system.

  6. RECONSTRUCTING COSMOLOGICAL MATTER PERTURBATIONS USING STANDARD CANDLES AND RULERS

    SciTech Connect

    Alam, Ujjaini; Sahni, Varun; Starobinsky, Alexei A. E-mail: varun@iucaa.ernet.i

    2009-10-20

    For a large class of dark energy (DE) models, for which the effective gravitational constant is a constant and there is no direct exchange of energy between DE and dark matter (DM), knowledge of the expansion history suffices to reconstruct the growth factor of linearized density perturbations in the non-relativistic matter component on scales much smaller than the Hubble distance. In this paper, we develop a non-parametric method for extracting information about the perturbative growth factor from data pertaining to the luminosity or angular size distances. A comparison of the reconstructed density contrast with observations of large-scale structure and gravitational lensing can help distinguish DE models such as the cosmological constant and quintessence from models based on modified gravity theories as well as models in which DE and DM are either unified or interact directly. We show that for current supernovae (SNe) data, the linear growth factor at z = 0.3 can be constrained to 5% and the linear growth rate to 6%. With future SNe data, such as expected from the Joint Dark Energy Mission, we may be able to constrain the growth factor to 2%-3% and the growth rate to 3%-4% at z = 0.3 with this unbiased, model-independent reconstruction method. For future baryon acoustic oscillation data which would deliver measurements of both the angular diameter distance and the Hubble parameter, it should be possible to constrain the growth factor at z = 2.5%-9%. These constraints grow tighter with the errors on the data sets. With a large quantity of data expected in the next few years, this method can emerge as a competitive tool for distinguishing between different models of dark energy.

  7. Reconstructing cosmological matter perturbations using standard candles and rulers

    SciTech Connect

    Alam, Ujjaini; Sahni, Varun; Starobinsky, Alexei A

    2008-01-01

    For a large class of dark energy (DE) models, for which the effective gravitational constant is a constant and there is no direct exchange of energy between DE and dark matter (DM), knowledge of the expansion history suffices to reconstruct the growth factor of linearized density perturbations in the non-relativistic matter component on scales much smaller than the Hubble distance. In this paper, we develop a non-parametric method for extracting information about the perturbative growth factor from data pertaining to the luminosity or angular size distances. A comparison of the reconstructed density contrast with observations of large-scale structure and gravitational lensing can help distinguish DE models such as the cosmological constant and quintessence from models based on modified gravity theories as well as models in which DE and DM are either unified or interact directly. We show that for current supernovae (SNe) data, the linear growth factor at z = 0.3 can be constrained to 5% and the linear growth rate to 6%. With future SNe data, such as expected from the Joint Dark Energy Mission, we may be able to constrain the growth factor to 2%-3% and the growth rate to 3%-4% at z = 0.3 with this unbiased, model-independent reconstruction method. For future baryon acoustic oscillation data which would deliver measurements of both the angular diameter distance and the Hubble parameter, it should be possible to constrain the growth factor at z = 2.5%-9%. These constraints grow tighter with the errors on the data sets. With a large quantity of data expected in the next few years, this method can emerge as a competitive tool for distinguishing between different models of dark energy.

  8. Identifying Network Perturbation in Cancer

    PubMed Central

    Logsdon, Benjamin A.; Gentles, Andrew J.; Lee, Su-In

    2016-01-01

    We present a computational framework, called DISCERN (DIfferential SparsE Regulatory Network), to identify informative topological changes in gene-regulator dependence networks inferred on the basis of mRNA expression datasets within distinct biological states. DISCERN takes two expression datasets as input: an expression dataset of diseased tissues from patients with a disease of interest and another expression dataset from matching normal tissues. DISCERN estimates the extent to which each gene is perturbed—having distinct regulator connectivity in the inferred gene-regulator dependencies between the disease and normal conditions. This approach has distinct advantages over existing methods. First, DISCERN infers conditional dependencies between candidate regulators and genes, where conditional dependence relationships discriminate the evidence for direct interactions from indirect interactions more precisely than pairwise correlation. Second, DISCERN uses a new likelihood-based scoring function to alleviate concerns about accuracy of the specific edges inferred in a particular network. DISCERN identifies perturbed genes more accurately in synthetic data than existing methods to identify perturbed genes between distinct states. In expression datasets from patients with acute myeloid leukemia (AML), breast cancer and lung cancer, genes with high DISCERN scores in each cancer are enriched for known tumor drivers, genes associated with the biological processes known to be important in the disease, and genes associated with patient prognosis, in the respective cancer. Finally, we show that DISCERN can uncover potential mechanisms underlying network perturbation by explaining observed epigenomic activity patterns in cancer and normal tissue types more accurately than alternative methods, based on the available epigenomic data from the ENCODE project. PMID:27145341

  9. Magnetic field and angular momentum evolution models

    NASA Astrophysics Data System (ADS)

    Gallet, F.

    2013-11-01

    The magnetic field in young stellar object is clearly the most important component when one dealing with the angular momentum evolution of solar-like stars. It controls this latter one from the pre-main sequence, during the ``disk locking'' phase where the stars magnetically interact with their surrounding disk, to the main-sequence through powerful stellar winds that remove angular momentum from the stellar surface. We present new models for the rotational evolution of solar-like stars between 1 Myr and 10 Gyr with the aim to reproduce the distributions of rotational periods observed for star forming regions and young open clusters within this age range. Our simulations are produced by a recent model dedicated to the study of the angular momentum evolution of solar-type stars. This model include a new wind braking law based on recent numerical simulations of magnetized stellar winds and a specific dynamo and mass-loss prescription are used to link the angular momentum loss-rate to angular velocity evolution. The model additionally allows for a core/envelope decoupling with an angular momentum transfer between these two regions. Since this former model didn't include any physical star/disk interaction description, two star/disk interaction processes are eventually added to it in order to reproduce the apparent small angular velocities to which the stellar surface is subject during the disk accretion phase. We have developed rotational evolution models for slow, median and fast rotators including two star/disk interaction scenarios that are the magnetospheric ejection and the accretion powered stellar winds processes. The models appear to fail at reproducing the rotational behaviour of solar-type stars except when a more intense magnetic field is used during the disk accretion phase.

  10. The massive Dirac field on a rotating black hole spacetime: angular solutions

    NASA Astrophysics Data System (ADS)

    Dolan, Sam R.; Gair, Jonathan R.

    2009-09-01

    The massive Dirac equation on a Kerr-Newman background may be solved by the method of separation of variables. The radial and angular equations are coupled via an angular eigenvalue, which is determined from the Chandrasekhar-Page (CP) equation. Obtaining accurate angular eigenvalues is a key step in studying scattering, absorption and emission of the fermionic field. Here we introduce a new method for finding solutions of the CP equation. First, we introduce a novel representation for the spin-half spherical harmonics. Next, we decompose the angular solutions of the CP equation (the mass-dependent spin-half spheroidal harmonics) in the spherical basis. The method yields a three-term recurrence relation which may be solved numerically via continued-fraction methods, or perturbatively to obtain a series expansion for the eigenvalues. In the case μ = ±ω (where ω and μ are the frequency and mass of the fermion) we obtain eigenvalues and eigenfunctions in a closed form. We study the eigenvalue spectrum and the zeros of the maximally co-rotating mode. We compare our results with previous studies, and uncover and correct some errors in the literature. We provide series expansions, tables of eigenvalues and numerical fits across a wide parameter range and present plots of a selection of eigenfunctions. It is hoped that this study will be a useful resource for all researchers interested in the Dirac equation on a rotating black hole background.

  11. "Phonon" scattering beyond perturbation theory

    NASA Astrophysics Data System (ADS)

    Qiu, WuJie; Ke, XueZhi; Xi, LiLi; Wu, LiHua; Yang, Jiong; Zhang, WenQing

    2016-02-01

    Searching and designing materials with intrinsically low lattice thermal conductivity (LTC) have attracted extensive consideration in thermoelectrics and thermal management community. The concept of part-crystalline part-liquid state, or even part-crystalline part-amorphous state, has recently been proposed to describe the exotic structure of materials with chemical- bond hierarchy, in which a set of atoms is weakly bonded to the rest species while the other sublattices retain relatively strong rigidity. The whole system inherently manifests the coexistence of rigid crystalline sublattices and fluctuating noncrystalline substructures. Representative materials in the unusual state can be classified into two categories, i.e., caged and non-caged ones. LTCs in both systems deviate from the traditional T -1 relationship ( T, the absolute temperature), which can hardly be described by small-parameter-based perturbation approaches. Beyond the classical perturbation theory, an extra rattling-like scattering should be considered to interpret the liquid-like and sublattice-amorphization-induced heat transport. Such a kind of compounds could be promising high-performance thermoelectric materials, due to the extremely low LTCs. Other physical properties for these part-crystalline substances should also exhibit certain novelty and deserve further exploration.

  12. Ultrafast angular momentum transfer in multisublattice ferrimagnets.

    PubMed

    Bergeard, N; López-Flores, V; Halté, V; Hehn, M; Stamm, C; Pontius, N; Beaurepaire, E; Boeglin, C

    2014-01-01

    Femtosecond laser pulses can be used to induce ultrafast changes of the magnetization in magnetic materials. However, one of the unsolved questions is that of conservation of the total angular momentum during the ultrafast demagnetization. Here we report the ultrafast transfer of angular momentum during the first hundred femtoseconds in ferrimagnetic Co0.8Gd0.2 and Co0.74Tb0.26 films. Using time-resolved X-ray magnetic circular dichroism allowed for time-resolved determination of spin and orbital momenta for each element. We report an ultrafast quenching of the magnetocrystalline anisotropy and show that at early times the demagnetization in ferrimagnetic alloys is driven by the local transfer of angular momenta between the two exchange-coupled sublattices while the total angular momentum stays constant. In Co0.74Tb0.26 we have observed a transfer of the total angular momentum to an external bath, which is delayed by ~150 fs. PMID:24614016

  13. Dirac Green function for angular projection potentials.

    PubMed

    Zeller, Rudolf

    2015-11-25

    The aim of this paper is twofold: first, it is shown that the angular dependence of the Dirac Green function can be described analytically for potentials with non-local dependence on the angular variables if they are chosen as projection potentials in angular momentum space. Because the local dependence on the radial variable can be treated to any precision with present computing capabilities, this means that the Green function can be calculated practically exactly. Second, it is shown that a result of this kind not only holds for a single angular projection potential but also more generally, for instance if space is divided into non-overlapping cells and a separate angular projection potential is used in each cell. This opens the way for relativistic density-functional calculations within a different perspective than the conventional one. Instead of trying to obtain the density for a given potential approximately as well as possible, the density is determined exactly for non-local potentials which can approximate arbitrary local potentials as well as desired. PMID:26523824

  14. An orbital angular momentum spectrometer for electrons

    NASA Astrophysics Data System (ADS)

    Harvey, Tyler; Grillo, Vincenzo; McMorran, Benjamin

    2016-05-01

    With the advent of techniques for preparation of free-electron and neutron orbital angular momentum (OAM) states, a basic follow-up question emerges: how do we measure the orbital angular momentum state distribution in matter waves? Control of both the energy and helicity of light has produced a range of spectroscopic applications, including molecular fingerprinting and magnetization mapping. Realization of an analogous dual energy-OAM spectroscopy with matter waves demands control of both initial and final energy and orbital angular momentum states: unlike for photons, final state post-selection is necessary for particles that cannot be annihilated. We propose a magnetic field-based mechanism for quantum non-demolition measurement of electron OAM. We show that OAM-dependent lensing is produced by an operator of form U =exp iLzρ2/ℏb2 where ρ =√{x2 +y2 } is the radial position operator, Lz is the orbital angular momentum operator along z, and b is the OAM dispersion length. We can physically realize this operator as a term in the time evolution of an electron in magnetic round lens. We discuss prospects and practical challenges for implementation of a lensing orbital angular momentum measurement. This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under the Early Career Research Program Award # DE-SC0010466.

  15. Angular momentum conservation for dynamical black holes

    SciTech Connect

    Hayward, Sean A.

    2006-11-15

    Angular momentum can be defined by rearranging the Komar surface integral in terms of a twist form, encoding the twisting around of space-time due to a rotating mass, and an axial vector. If the axial vector is a coordinate vector and has vanishing transverse divergence, it can be uniquely specified under certain generic conditions. Along a trapping horizon, a conservation law expresses the rate of change of angular momentum of a general black hole in terms of angular momentum densities of matter and gravitational radiation. This identifies the transverse-normal block of an effective gravitational-radiation energy tensor, whose normal-normal block was recently identified in a corresponding energy conservation law. Angular momentum and energy are dual, respectively, to the axial vector and a previously identified vector, the conservation equations taking the same form. Including charge conservation, the three conserved quantities yield definitions of an effective energy, electric potential, angular velocity and surface gravity, satisfying a dynamical version of the so-called first law of black-hole mechanics. A corresponding zeroth law holds for null trapping horizons, resolving an ambiguity in taking the null limit.

  16. Dirac Green function for angular projection potentials

    NASA Astrophysics Data System (ADS)

    Zeller, Rudolf

    2015-11-01

    The aim of this paper is twofold: first, it is shown that the angular dependence of the Dirac Green function can be described analytically for potentials with non-local dependence on the angular variables if they are chosen as projection potentials in angular momentum space. Because the local dependence on the radial variable can be treated to any precision with present computing capabilities, this means that the Green function can be calculated practically exactly. Second, it is shown that a result of this kind not only holds for a single angular projection potential but also more generally, for instance if space is divided into non-overlapping cells and a separate angular projection potential is used in each cell. This opens the way for relativistic density-functional calculations within a different perspective than the conventional one. Instead of trying to obtain the density for a given potential approximately as well as possible, the density is determined exactly for non-local potentials which can approximate arbitrary local potentials as well as desired.

  17. Molecular-frame photoelectron angular distributions Molecular-frame photoelectron angular distributions

    NASA Astrophysics Data System (ADS)

    Lucchese, Robert R.; Stolow, Albert

    2012-10-01

    Angle-resolved photoelectron measurements in molecular ionization continue to grow in importance due to their sensitivity to molecular dynamics combined with their avoidance of deleterious averaging over molecular orientation. This special issue contains only regularly refereed articles and provides an account of current experimental and theoretical studies of such molecular-frame photoelectron angular distributions (MFPADs). Recent experimental activity in this field has been stimulated by advances in light sources such as x-ray free electron lasers, attosecond XUV laser pulses and phase-stable ultrashort strong laser fields. This effort is further amplified by recent developments in coincidence detection and molecular-frame alignment/orientation techniques. Beyond perturbative light-matter interactions, strong field processes such as tunnel ionization, above threshold ionization and rescattering phenomena such as high harmonic generation and laser-induced electron diffraction are beginning to probe molecular-frame photoelectron-molecule scattering dynamics. Theoretical developments are playing an equally important role in furthering molecular-frame photoelectron science. This issue contains several purely theoretical papers that aim to provide insight into possible schemes for using MFPADs in the study of molecular dynamics. Because the details of the electron-molecule scattering dynamics are important to the interpretation of experimental data, significant progress is made by a close collaboration between theory and experiment. There are a number of such contributions in this issue that combine theory and experiment to obtain a detailed understanding of the observed processes. One recurring theme is the use of measured MFPADs as probes of the molecular state and to uncover information about the dynamics of molecular systems. Contributions in this issue consider using MFPADs to investigate molecular geometry or the rotational, vibrational or electronic state of a

  18. Variation in Angular Velocity and Angular Acceleration of a Particle in Rectilinear Motion

    ERIC Educational Resources Information Center

    Mashood, K. K.; Singh, V. A.

    2012-01-01

    We discuss the angular velocity ([image omitted]) and angular acceleration ([image omitted]) associated with a particle in rectilinear motion with constant acceleration. The discussion was motivated by an observation that students and even teachers have difficulty in ascribing rotational motion concepts to a particle when the trajectory is a…

  19. Angular correlations in the two-photon decay of heliumlike heavy ions

    SciTech Connect

    Surzhykov, A.; Fratini, F.; Volotka, A.; Santos, J. P.; Indelicato, P.; Plunien, G.; Stoehlker, Th.; Fritzsche, S.

    2010-04-15

    The two-photon decay of heavy, helium-like ions is investigated based on second-order perturbation theory and Dirac's relativistic equation. Special attention has been paid to the angular emission of the two photons (i.e., how the angular correlation function depends on the shell structure of the ions in their initial and final states). Moreover, the effects from the (electric and magnetic) nondipole terms in the expansion of the electron-photon interaction are discussed. Detailed calculations have been carried out for the two-photon decay of the 1s2s {sup 1}S{sub 0}, 1s2s {sup 3}S{sub 1}, and 1s2p {sup 3}P{sub 0} states of helium-like Xe{sup 52+}, Au{sup 77+}, and U{sup 90+} ions.

  20. Characterization of Optical Components for the Cosmology Large Angular Scale Surveyor (CLASS)

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuo; Essinger-Hileman, Thomas; Xu, Zhilei; Marriage, Tobias

    2016-06-01

    Inflation theory posits a rapid expansion at the beginning of the universe that explains the homogeneity, isotropy and flatness of our universe. The theory postulates perturbations to space-time with both scalar and tensor components, the latter of which would give rise to a "B-mode" polarization in the Cosmic Microwave Background (CMB). The Cosmology Large Angular Scale Surveyor (CLASS), with its broadband frequency coverage and rapid front-end modulation, has the unique ability to map the entire B-mode angular power spectrum where there the inflationary signal is expected to dominate. In this poster, I give an overview of CLASS and present work on the characterization of CLASS optical components, including infrared filters, using a custom Fourier Transform Interferometer.

  1. Instability in stratified accretion flows under primary and secondary perturbations

    NASA Astrophysics Data System (ADS)

    Nasraoui, S.; Salhi, A.; Lehner, T.

    2015-04-01

    We consider horizontal linear shear flow (shear rate denoted by Λ ) under vertical uniform rotation (ambient rotation rate denoted by Ω0 ) and vertical stratification (buoyancy frequency denoted by N ) in unbounded domain. We show that, under a primary vertical velocity perturbation and a radial density perturbation consisting of a one-dimensional standing wave with frequency N and amplitude proportional to w0sin(ɛ N x /w0) ≈ɛ N x (≪1 ) , where x denotes the radial coordinate and ɛ a small parameter, a parametric instability can develop in the flow, provided N2>8 Ω0(2 Ω0-Λ ) . For astrophysical accretion flows and under the shearing sheet approximation, this implies N2>8 Ω02(2 -q ) , where q =Λ /Ω0 is the local shear gradient. In the case of a stratified constant angular momentum disk, q =2 , there is a parametric instability with the maximal growth rate (σm/ɛ ) =3 √{3 }/16 for any positive value of the buoyancy frequency N . In contrast, for a stratified Keplerian disk, q =1.5 , the parametric instability appears only for N >2 Ω0 with a maximal growth rate that depends on the ratio Ω0/N and approaches (3 √{3 }/16 )ɛ for large values of N .

  2. Exact-to-precision generalized perturbation for neutron transport calculation

    SciTech Connect

    Wang, C.; Abdel-Khalik, H. S.

    2013-07-01

    This manuscript extends the exact-to-precision generalized perturbation theory (E{sub P}GPT), introduced previously, to neutron transport calculation whereby previous developments focused on neutron diffusion calculation only. The E{sub P}GPT collectively denotes new developments in generalized perturbation theory (GPT) that place premium on computational efficiency and defendable accuracy in order to render GPT a standard analysis tool in routine design and safety reactor calculations. EPGPT constructs a surrogate model with quantifiable accuracy which can replace the original neutron transport model for subsequent engineering analysis, e.g. functionalization of the homogenized few-group cross sections in terms of various core conditions, sensitivity analysis and uncertainty quantification. This is achieved by reducing the effective dimensionality of the state variable (i.e. neutron angular flux) by projection onto an active subspace. Confining the state variations to the active subspace allows one to construct a small number of what is referred to as the 'active' responses which are solely dependent on the physics model rather than on the responses of interest, the number of input parameters, or the number of points in the state phase space. (authors)

  3. Energy angular momentum closed-loop guidance

    NASA Astrophysics Data System (ADS)

    Patera, Russell P.

    2015-03-01

    A novel guidance algorithm for launch vehicle ascent to the desired mission orbit is proposed. The algorithm uses total specific energy and orbital angular momentum as new state vector parameters. These parameters are ideally suited for the ascent guidance task, since the guidance algorithm steers the launch vehicle along a pre-flight optimal trajectory in energy angular momentum space. The guidance algorithm targets apogee, perigee, inclination and right ascension of ascending node. Computational complexities are avoided by eliminating time in the guidance computation and replacing it with angular momentum magnitude. As a result, vehicle acceleration, mass, thrust, length of motor burns, and staging times are also eliminated from the pitch plane guidance calculations. The algorithm does not involve launch vehicle or target state propagation, which results in minimal computational effort. Proof of concept of the new algorithm is presented using several numerical examples that illustrate performance results.

  4. Inequalities for angular derivatives and boundary interpolation

    NASA Astrophysics Data System (ADS)

    Bolotnikov, Vladimir; Elin, Mark; Shoikhet, David

    2013-03-01

    The classical Julia-Wolff-Carathéodory theorem asserts that the angular derivative of a holomorphic self-mapping of the open unit disk (Schur function) at its boundary fixed point is a positive number. Cowen and Pommerenke (J Lond Math Soc 26:271-289, 1982) proved that if a Schur function has several boundary regular fixed (or mutual contact) points, then the angular derivatives at these points are subject to certain inequalities. We develop a unified approach to establish relations between angular derivatives of Schur functions with a prescribed (possibly, infinite) collection of either mutual contact points or boundary fixed points. This approach yields diverse inequalities improving both classical and more recent results. We apply them to study the Nevanlinna-Pick interpolation problem with boundary data. Our methods lead to fairly explicit formulas describing the set of solutions.

  5. Improved numerical projection of angular momentum

    NASA Astrophysics Data System (ADS)

    O'Mara, Kevin; Johnson, Calvin

    2015-10-01

    Nuclear many-body states have good angular momenta, but many theoretical building blocks such as deformed Slater determinants do not. Hence one must numerically project out states of good angular momenta, usually through a computationally taxing three-dimensional integral. We took an existing code for angular-momentum projected Hartree-Fock and improved its performance, partly through judicious ordering of the loops, precomputing arrays of important combinatorics, and careful application of parallelization. We also investigated a novel inversion scheme. This work is potentially applicable to multiple approaches in many-body calculations, and should also be generalizable to particle number projection. Supported by SDSU Summer Undergraduate Research Program and by DOE Award Number DE-FG02-96ER40985.

  6. Electromagnetic angular momentum transport in Saturn's rings

    NASA Technical Reports Server (NTRS)

    Goertz, C. K.; Morfill, G. E.; Ip, W.; Gruen, E.; Havnes, O.

    1986-01-01

    It is shown here that submicrometer dust particles sporadically elevated above Saturn's ring are subject to electromagnetic forces which will reduce their angular momentum inside synchronous orbit and increase it outside. When the dust is reabsorbed by the ring the angular momentum of the ring is decreased (increased) inside (outside) of synchronous orbit. For the case of the spokes in Saturn's B-ring it is estimated that the timescale for transporting ring material due to this angular momentum coupling effect is comparable to the viscous transport time or even smaller. It is suggested that the minimum in the optical depth of the B-ring at synchronous orbit is due to this effect.

  7. Angular momentum conservation in dipolar energy transfer.

    PubMed

    Guo, Dong; Knight, Troy E; McCusker, James K

    2011-12-23

    Conservation of angular momentum is a familiar tenet in science but has seldom been invoked to understand (or predict) chemical processes. We have developed a general formalism based on Wigner's original ideas concerning angular momentum conservation to interpret the photo-induced reactivity of two molecular donor-acceptor assemblies with physical properties synthetically tailored to facilitate intramolecular energy transfer. Steady-state and time-resolved spectroscopic data establishing excited-state energy transfer from a rhenium(I)-based charge-transfer state to a chromium(III) acceptor can be fully accounted for by Förster theory, whereas the corresponding cobalt(III) adduct does not undergo an analogous reaction despite having a larger cross-section for dipolar coupling. Because this pronounced difference in reactivity is easily explained within the context of the angular momentum conservation model, this relatively simple construct may provide a means for systematizing a broad range of chemical reactions. PMID:22194572

  8. Angular correlations and high energy evolution

    SciTech Connect

    Kovner, Alex; Lublinsky, Michael

    2011-11-01

    We address the question of to what extent JIMWLK evolution is capable of taking into account angular correlations in a high energy hadronic wave function. Our conclusion is that angular (and indeed other) correlations in the wave function cannot be reliably calculated without taking into account Pomeron loops in the evolution. As an example we study numerically the energy evolution of angular correlations between dipole scattering amplitudes in the framework of the large N{sub c} approximation to JIMWLK evolution (the 'projectile dipole model'). Target correlations are introduced via averaging over an (isotropic) ensemble of anisotropic initial conditions. We find that correlations disappear very quickly with rapidity even inside the saturation radius. This is in accordance with our physical picture of JIMWLK evolution. The actual correlations inside the saturation radius in the target QCD wave function, on the other hand, should remain sizable at any rapidity.

  9. Storm Track Response to Perturbations in Climate

    NASA Astrophysics Data System (ADS)

    Mbengue, Cheikh Oumar

    This thesis advances our understanding of midlatitude storm tracks and how they respond to perturbations in the climate system. The midlatitude storm tracks are regions of maximal turbulent kinetic energy in the atmosphere. Through them, the bulk of the atmospheric transport of energy, water vapor, and angular momentum occurs in midlatitudes. Therefore, they are important regulators of climate, controlling basic features such as the distribution of surface temperatures, precipitation, and winds in midlatitudes. Storm tracks are robustly projected to shift poleward in global-warming simulations with current climate models. Yet the reasons for this shift have remained unclear. Here we show that this shift occurs even in extremely idealized (but still three-dimensional) simulations of dry atmospheres. We use these simulations to develop an understanding of the processes responsible for the shift and develop a conceptual model that accounts for it. We demonstrate that changes in the convective static stability in the deep tropics alone can drive remote shifts in the midlatitude storm tracks. Through simulations with a dry idealized general circulation model (GCM), midlatitude storm tracks are shown to be located where the mean available potential energy (MAPE, a measure of the potential energy available to be converted into kinetic energy) is maximal. As the climate varies, even if only driven by tropical static stability changes, the MAPE maximum shifts primarily because of shifts of the maximum of near-surface meridional temperature gradients. The temperature gradients shift in response to changes in the width of the tropical Hadley circulation, whose width is affected by the tropical static stability. Storm tracks generally shift in tandem with shifts of the subtropical terminus of the Hadley circulation. We develop a one-dimensional diffusive energy-balance model that links changes in the Hadley circulation to midlatitude temperature gradients and so to the storm

  10. Synthetic aperture methods for angular scatter imaging

    NASA Astrophysics Data System (ADS)

    Guenther, Drake A.; Ranganathan, Karthik; McAllister, Michael J.; Rigby, K. W.; Walker, William F.

    2004-04-01

    Angular scatter offers a new source of tissue contrast and an opportunity for tissue characterization in ultrasound imaging. We have previously described the application of the translating apertures algorithm (TAA) to coherently acquire angular scatter data over a range of scattering angles. While this approach works well at the focus, it suffers from poor depth of field (DOF) due to a finite aperture size. Furthermore, application of the TAA with large focused apertures entails a tradeoff between spatial resolution and scattering angle resolution. While large multielement apertures improve spatial resolution, they encompass many permutations of transmit/receive element pairs. This results in the simultaneous interrogation of multiple scattering angles, limiting angular resolution. We propose a synthetic aperture imaging scheme that achieves both high spatial resolution and high angular resolution. In backscatter acquisition mode, we transmit successively from single transducer elements, while receiving on the same element. Other scattering angles are interrogated by successively transmitting and receiving on different single elements chosen with the appropriate spatial separation between them. Thus any given image is formed using only transmit/receive element pairs at a single separation. This synthetic aperture approach minimizes averaging across scattering angles, and yields excellent angular resolution. Likewise, synthetic aperture methods allow us to build large effective apertures to maintain a high spatial resolution. Synthetic dynamic focusing and dynamic apodization are applied to further improve spatial resolution and DOF. We present simulation results and experimental results obtained using a GE Logiq 700MR system modified to obtain synthetic aperture TAA data. Images of wire targets exhibit high DOF and spatial resolution. We also present a novel approach for combining angular scatter data to effectively reduce grating lobes. With this approach we have

  11. Perturbations i have Known and Loved

    NASA Astrophysics Data System (ADS)

    Field, Robert W.

    2011-06-01

    A spectroscopic perturbation is a disruption of a ^1Σ-^1Σ-like regular pattern that can embody level-shifts, extra lines, and intensity anomalies. Once upon a time, when a band was labeled ``perturbed,'' it was considered worthless because it could at best yield molecular constants unsuited for archival tables. Nevertheless, a few brave spectroscopists, notably Albin Lagerqvist and Richard Barrow, collected perturbations because they knew that the pattern of multiple perturbations formed an intricate puzzle that would eventually reveal the presence and electronic symmetry of otherwise unobservable electronic states. There are many kinds of patterns of broken patterns. In my PhD thesis I showed how to determine absolute vibrational assignments for the perturber from patterns among the observed values of perturbation matrix elements. When a ^3Π state is perturbed, its six (Ω, parity) components capture a pattern of level shifts and intensity anomalies that reveals more about the nature of the perturber than a simple perturbation of the single component of a ^1Σ state. In perturbation-facilitated OODR, a perturbed singlet level acts as a spectroscopic doorway through which the entire triplet manifold may be systematically explored. For polyatomic molecule vibrations, a vibrational polyad (a group of mutually perturbing vibrational levels, among which the perturbation matrix elements are expected to follow harmonic oscillator scaling rules) can contain more components than a ^3Π state and intrapolyad patterns can be exquisitely sensitive not merely to the nature of an interloper within the polyad but also to the eigenvector character of the vibronic state from which the polyad is viewed. Variation of scaled polyad interaction parameters from one polyad to the next, a pattern of patterns, can signal proximity to an isomerization barrier. Everything in Rydberg-land seems to scale as N⋆-3, yet a trespassing valence state causes all scaling and propensity rules go

  12. Probing Angular Correlations in Sequential Double Ionization

    SciTech Connect

    Fleischer, A.; Woerner, H. J.; Arissian, L.; Liu, L. R.; Meckel, M.; Rippert, A.; Doerner, R.; Villeneuve, D. M.; Corkum, P. B.; Staudte, A.

    2011-09-09

    We study electron correlation in sequential double ionization of noble gas atoms and HCl in intense, femtosecond laser pulses. We measure the photoelectron angular distributions of Ne{sup +} relative to the first electron in a pump-probe experiment with 8 fs, 800 nm, circularly polarized laser pulses at a peak intensity of a few 10{sup 15} W/cm{sup 2}. Using a linear-linear pump-probe setup, we further study He, Ar, and HCl. We find a clear angular correlation between the two ionization steps in the sequential double ionization intensity regime.

  13. Time-resolved orbital angular momentum spectroscopy

    SciTech Connect

    Noyan, Mehmet A.; Kikkawa, James M.

    2015-07-20

    We introduce pump-probe magneto-orbital spectroscopy, wherein Laguerre-Gauss optical pump pulses impart orbital angular momentum to the electronic states of a material and subsequent dynamics are studied with 100 fs time resolution. The excitation uses vortex modes that distribute angular momentum over a macroscopic area determined by the spot size, and the optical probe studies the chiral imbalance of vortex modes reflected off the sample. First observations in bulk GaAs yield transients that evolve on time scales distinctly different from population and spin relaxation, as expected, but with surprisingly large lifetimes.

  14. Absolute angular positioning in ultrahigh vacuum

    SciTech Connect

    Schief, H.; Marsico, V.; Kern, K.

    1996-05-01

    Commercially available angular resolvers, which are routinely used in machine tools and robotics, are modified and adapted to be used under ultrahigh-vacuum (UHV) conditions. They provide straightforward and reliable measurements of angular positions for any kind of UHV sample manipulators. The corresponding absolute reproducibility is on the order of 0.005{degree}, whereas the relative resolution is better than 0.001{degree}, as demonstrated by high-resolution helium-reflectivity measurements. The mechanical setup and possible applications are discussed. {copyright} {ital 1996 American Institute of Physics.}

  15. Angular momentum in spin-phonon processes

    NASA Astrophysics Data System (ADS)

    Garanin, D. A.; Chudnovsky, E. M.

    2015-07-01

    Quantum theory of spin relaxation in the elastic environment is revised with account of the concept of a phonon spin recently introduced by Zhang and Niu [L. Zhang and Q. Niu, Phys. Rev. Lett. 112, 085503 (2014), 10.1103/PhysRevLett.112.085503]. Similar to the case of the electromagnetic field, the division of the angular momentum associated with elastic deformations into the orbital part and the part due to phonon spins proves to be useful for the analysis of the balance of the angular momentum. Such analysis sheds important light on microscopic processes leading to the Einstein-de Haas effect.

  16. On the vector model of angular momentum

    NASA Astrophysics Data System (ADS)

    Saari, Peeter

    2016-09-01

    Instead of (or in addition to) the common vector diagram with cones, we propose to visualize the peculiarities of quantum mechanical angular momentum by a completely quantized 3D model. It spotlights the discrete eigenvalues and noncommutativity of components of angular momentum and corresponds to outcomes of measurements—real or computer-simulated. The latter can be easily realized by an interactive worksheet of a suitable program package of algebraic calculations. The proposed complementary method of visualization helps undergraduate students to better understand the counterintuitive properties of this quantum mechanical observable.

  17. Angular distribution of emission from hyperbolic metamaterials

    PubMed Central

    Gu, Lei; Livenere, J. E.; Zhu, G.; Tumkur, T. U.; Hu, H.; Cortes, C. L.; Jacob, Z.; Prokes, S. M.; Noginov, M. A.

    2014-01-01

    We have studied angular distribution of emission of dye molecules deposited on lamellar metal/dielectric and Si/Ag nanowire based metamaterials with hyperbolic dispersion. In agreement with the theoretical prediction, the emission pattern of dye on top of lamellar metamaterial is similar to that on top of metal. At the same time, the effective medium model predicts the emission patterns of the nanowire array and the dye film deposited on glass to be nearly identical to each other. This is not the case of our experiment. We tentatively explain the nearly Lambertian (∝cosθ) angular distribution of emission of the nanowire based sample by a surface roughness. PMID:25476126

  18. Angular Resolution of Multi-Lisa Constellations

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Gong, Xue-Fei

    2010-04-01

    In this article, we present a detailed derivation of the angular resolution of arbitrary sets of LISA (Laser Interferometer Space Antenna) constellations with a toy model for gravitational wave signals, and further generalized to more complicated cases with slowly varying gravitational wave signals of well-defined frequency at any time instant. For future space-borne LISA-like gravitational wave detectors, our results may serve as a conservative quick estimate of the detector's angular resolution and hopefully moreover a reference for the configuration designs.

  19. Matter perturbations in scaling cosmology

    NASA Astrophysics Data System (ADS)

    Fuño, A. Romero; Hipólito-Ricaldi, W. S.; Zimdahl, W.

    2016-04-01

    A suitable nonlinear interaction between dark matter with an energy density ρM and dark energy with an energy density ρX is known to give rise to a non-canonical scaling ρM ∝ ρXa-ξ, where ξ is a parameter which generally deviates from ξ = 3. Here, we present a covariant generalization of this class of models and investigate the corresponding perturbation dynamics. The resulting matter power spectrum for the special case of a time-varying Lambda model is compared with data from the Sloan Digital Sky Survey (SDSS) DR9 catalogue (Ahn et al.). We find a best-fitting value of ξ = 3.25 which corresponds to a decay of dark matter into the cosmological term. Our results are compatible with the Lambda Cold Dark Matter model at the 2σ confidence level.

  20. Perturbativity in the seesaw mechanism

    NASA Astrophysics Data System (ADS)

    Asaka, Takehiko; Tsuyuki, Takanao

    2016-02-01

    We consider the Standard Model extended by right-handed neutrinos to explain massive neutrinos through the seesaw mechanism. The new fermion can be observed when it has a sufficiently small mass and large mixings to left-handed neutrinos. If such a particle is the lightest right-handed neutrino, its contribution to the mass matrix of active neutrinos needs to be canceled by that of a heavier one. Yukawa couplings of the heavier one are then larger than those of the lightest one. We show that the perturbativity condition gives a severe upper bound on the mixing of the lightest right-handed neutrino, depending on the masses of heavier ones. Models of high energy phenomena, such as leptogenesis, can be constrained by low energy experiments.

  1. Perturbations of vortex ring pairs

    NASA Astrophysics Data System (ADS)

    Gubser, Steven S.; Horn, Bart; Parikh, Sarthak

    2016-02-01

    We study pairs of coaxial vortex rings starting from the action for a classical bosonic string in a three-form background. We complete earlier work on the phase diagram of classical orbits by explicitly considering the case where the circulations of the two vortex rings are equal and opposite. We then go on to study perturbations, focusing on cases where the relevant four-dimensional transfer matrix splits into two-dimensional blocks. When the circulations of the rings have the same sign, instabilities are mostly limited to wavelengths smaller than a dynamically generated length scale at which single-ring instabilities occur. When the circulations have the opposite sign, larger wavelength instabilities can occur.

  2. Sudakov safety in perturbative QCD

    NASA Astrophysics Data System (ADS)

    Larkoski, Andrew J.; Marzani, Simone; Thaler, Jesse

    2015-06-01

    Traditional calculations in perturbative quantum chromodynamics (pQCD) are based on an order-by-order expansion in the strong coupling αs. Observables that are calculable in this way are known as "safe." Recently, a class of unsafe observables was discovered that do not have a valid αs expansion but are nevertheless calculable in pQCD using all-orders resummation. These observables are called "Sudakov safe" since singularities at each αs order are regulated by an all-orders Sudakov form factor. In this paper, we give a concrete definition of Sudakov safety based on conditional probability distributions, and we study a one-parameter family of momentum sharing observables that interpolate between the safe and unsafe regimes. The boundary between these regimes is particularly interesting, as the resulting distribution can be understood as the ultraviolet fixed point of a generalized fragmentation function, yielding a leading behavior that is independent of αs.

  3. Robust control with structured perturbations

    NASA Technical Reports Server (NTRS)

    Keel, Leehyun

    1988-01-01

    Two important problems in the area of control systems design and analysis are discussed. The first is the robust stability using characteristic polynomial, which is treated first in characteristic polynomial coefficient space with respect to perturbations in the coefficients of the characteristic polynomial, and then for a control system containing perturbed parameters in the transfer function description of the plant. In coefficient space, a simple expression is first given for the l(sup 2) stability margin for both monic and non-monic cases. Following this, a method is extended to reveal much larger stability region. This result has been extended to the parameter space so that one can determine the stability margin, in terms of ranges of parameter variations, of the closed loop system when the nominal stabilizing controller is given. The stability margin can be enlarged by a choice of better stabilizing controller. The second problem describes the lower order stabilization problem, the motivation of the problem is as follows. Even though the wide range of stabilizing controller design methodologies is available in both the state space and transfer function domains, all of these methods produce unnecessarily high order controllers. In practice, the stabilization is only one of many requirements to be satisfied. Therefore, if the order of a stabilizing controller is excessively high, one can normally expect to have a even higher order controller on the completion of design such as inclusion of dynamic response requirements, etc. Therefore, it is reasonable to have a lowest possible order stabilizing controller first and then adjust the controller to meet additional requirements. The algorithm for designing a lower order stabilizing controller is given. The algorithm does not necessarily produce the minimum order controller; however, the algorithm is theoretically logical and some simulation results show that the algorithm works in general.

  4. Cosmological perturbations in f(T) gravity

    SciTech Connect

    Chen, Shih-Hung; Dent, James B.; Dutta, Sourish; Saridakis, Emmanuel N.

    2011-01-15

    We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbein, we extract the corresponding dispersion relation, which provides a constraint on the f(T) Ansaetze that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from {Lambda}CDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons.

  5. Polarized Structure Function of Nucleon and Orbital Angular Momentum

    NASA Astrophysics Data System (ADS)

    Arash, Firooz; Taghavi-Shahri, Fatemeh

    2007-06-01

    We have utilized the concept of valon model to calculate the spin structure function of a constituent quark. This structure is universal and arises from perturbative dressing of a valence quark in QCD. With a convolution method the polarized structure functions of proton, neutron, and deuteron are obtained. Our results agree rather well with all available experimental data. It suggests that the sea quark contribution to the spin of nucleon is consistent with zero, in agreement with HERMES data. It also reveals that while the total quark contribution to the spin of a constituent quark, or valon, is almost constant and equal to one, the gluon contribution grows with the increase of Q2, and hence, requiring a sizable negative angular momentum contribution. This component, as well as singlet and non-singlet parts are calculated in the Next-to-Leading order in QCD. We speculate that the gluon contribution to the spin of proton is in the order of 50%. Furthermore, we have determined the polarized valon distribution in a nucleon.

  6. Angular distribution of turbulence in wave space

    NASA Technical Reports Server (NTRS)

    Coleman, G.; Ferziger, J. H.; Bertoglio, J. P.

    1987-01-01

    An alternative to the one-point closure model for turbulence, the large eddy simulation (LES), together with its more exact relative, direct numerical simulation (DNS) are discussed. These methods are beginning to serve as partial substitutes for turbulence experiments. The eddy damped quasi-normal Markovian (EDQNM) theory is reviewed. Angular distribution of the converted data was examined in relationship to EDQNM.

  7. Inclusion of angular momentum in FREYA

    SciTech Connect

    Randrup, Jørgen; Vogt, Ramona

    2015-05-18

    The event-by-event fission model FREYA generates large samples of complete fission events from which any observable can extracted, including fluctuations of the observables and the correlations between them. We describe here how FREYA was recently refined to include angular momentum throughout. Subsequently we present some recent results for both neutron and photon observables.

  8. Spacecraft Angular State Estimation After Sensor Failure

    NASA Technical Reports Server (NTRS)

    Bauer, Frank (Technical Monitor); BarItzhack, Itzhack Y.; Harman, Richard R.

    2002-01-01

    This work describes two algorithms for computing the angular rate and attitude in case of a gyro failure in a spacecraft (SC) with a special mission profile. The source of the problem is presented, two algorithms are suggested, an observability study is carried out, and the efficiency of the algorithms is demonstrated.

  9. A Novel Permanent Magnetic Angular Acceleration Sensor

    PubMed Central

    Zhao, Hao; Feng, Hao

    2015-01-01

    Angular acceleration is an important parameter for status monitoring and fault diagnosis of rotary machinery. Therefore, we developed a novel permanent magnetic angular acceleration sensor, which is without rotation angle limitations and could directly measure the instantaneous angular acceleration of the rotating system. The sensor rotor only needs to be coaxially connected with the rotating system, which enables convenient sensor installation. For the cup structure of the sensor rotor, it has a relatively small rotational inertia. Due to the unique mechanical structure of the sensor, the output signal of the sensor can be directed without a slip ring, which avoids signal weakening effect. In this paper, the operating principle of the sensor is described, and simulated using finite element method. The sensitivity of the sensor is calibrated by torsional pendulum and angle sensor, yielding an experimental result of about 0.88 mV/(rad·s−2). Finally, the angular acceleration of the actual rotating system has been tested, using both a single-phase asynchronous motor and a step motor. Experimental result confirms the operating principle of the sensor and indicates that the sensor has good practicability. PMID:26151217

  10. Inclusion of Angular Momentum in FREYA

    NASA Astrophysics Data System (ADS)

    Randrup, Jørgen; Vogt, Ramona

    The event-by-event fission model FREYA generates large samples of complete fission events from which any observable can extracted, including fluctuations of the observables and the correlations between them. We describe here how FREYA was recently refined to include angular momentum throughout. Subsequently we present some recent results for both neutron and photon observables.

  11. The Role of Angularity in Route Choice

    NASA Astrophysics Data System (ADS)

    Turner, Alasdair

    The paths of 2425 individual motorcycle trips made in London were analyzed in order to uncover the route choice decisions made by drivers. The paths were derived from global positioning system (GPS) data collected by a courier company for each of their drivers, using algorithms developed for the purpose of this paper. Motorcycle couriers were chosen due to the fact that they both know streets very well and that they do not rely on the GPS to guide their navigation. Each trace was mapped to the underlying road network, and two competing hypotheses for route choice decisions were compared: (a) that riders attempt to minimize the Manhattan distance between locations and (b) that they attempt to minimize the angular distance. In each case, the distance actually traveled was compared to the minimum possible either block or angular distance through the road network. It is usually believed that drivers who know streets well will navigate trips that reduce Manhattan distance; however, here it is shown that angularity appears to play an important role in route choice. 63% of trips made took the minimum possible angular distance between origin and destination, while 51% of trips followed the minimum possible block distance. This implies that impact of turns on cognitive distance plays an important role in decision making, even when a driver has good knowledge of the spatial network.

  12. Heteromodal conceptual processing in the angular gyrus

    PubMed Central

    Bonner, Michael F.; Peelle, Jonathan E.; Cook, Philip A.; Grossman, Murray

    2013-01-01

    Concepts bind together the features commonly associated with objects and events to form networks in long-term semantic memory. These conceptual networks are the basis of human knowledge and underlie perception, imagination, and the ability to communicate about experiences and the contents of the environment. Although it is often assumed that this distributed semantic information is integrated in higher-level heteromodal association cortices, open questions remain about the role and anatomic basis of heteromodal representations in semantic memory. Here we used combined neuroimaging evidence from functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) to characterize the cortical networks underlying concept representation. Using a lexical decision task, we examined the processing of concepts in four semantic categories that varied on their sensory-motor feature associations (sight, sound, manipulation, and abstract). We found that the angular gyrus was activated across all categories regardless of their modality-specific feature associations, consistent with a heteromodal account for the angular gyrus. Exploratory analyses suggested that categories with weighted sensory-motor features additionally recruited modality-specific association cortices. Furthermore, DTI tractography identified white matter tracts connecting these regions of modality-specific functional activation with the angular gyrus. These findings are consistent with a distributed semantic network that includes a heteromodal, integrative component in the angular gyrus in combination with sensory-motor feature representations in modality-specific association cortices. PMID:23333416

  13. A Novel Permanent Magnetic Angular Acceleration Sensor.

    PubMed

    Zhao, Hao; Feng, Hao

    2015-01-01

    Angular acceleration is an important parameter for status monitoring and fault diagnosis of rotary machinery. Therefore, we developed a novel permanent magnetic angular acceleration sensor, which is without rotation angle limitations and could directly measure the instantaneous angular acceleration of the rotating system. The sensor rotor only needs to be coaxially connected with the rotating system, which enables convenient sensor installation. For the cup structure of the sensor rotor, it has a relatively small rotational inertia. Due to the unique mechanical structure of the sensor, the output signal of the sensor can be directed without a slip ring, which avoids signal weakening effect. In this paper, the operating principle of the sensor is described, and simulated using finite element method. The sensitivity of the sensor is calibrated by torsional pendulum and angle sensor, yielding an experimental result of about 0.88 mV/(rad·s(-2)). Finally, the angular acceleration of the actual rotating system has been tested, using both a single-phase asynchronous motor and a step motor. Experimental result confirms the operating principle of the sensor and indicates that the sensor has good practicability. PMID:26151217

  14. Singular perturbation applications in neutron transport

    SciTech Connect

    Losey, D.C.; Lee, J.C.

    1996-09-01

    This is a paper on singular perturbation applications in neutron transport for submission at the next ANS conference. A singular perturbation technique was developed for neutron transport analysis by postulating expansion in terms of a small ordering parameter {eta}. Our perturbation analysis is carried, without approximation, through {Omicron}({eta}{sup 2}) to derive a material interface correction for diffusion theory. Here we present results from an analytical application of the perturbation technique to a fixed source problem and then describe and implementation of the technique in a computational scheme.

  15. Kato expansion in quantum canonical perturbation theory

    NASA Astrophysics Data System (ADS)

    Nikolaev, Andrey

    2016-06-01

    This work establishes a connection between canonical perturbation series in quantum mechanics and a Kato expansion for the resolvent of the Liouville superoperator. Our approach leads to an explicit expression for a generator of a block-diagonalizing Dyson's ordered exponential in arbitrary perturbation order. Unitary intertwining of perturbed and unperturbed averaging superprojectors allows for a description of ambiguities in the generator and block-diagonalized Hamiltonian. We compare the efficiency of the corresponding computational algorithm with the efficiencies of the Van Vleck and Magnus methods for high perturbative orders.

  16. Singularity perturbed zero dynamics of nonlinear systems

    NASA Technical Reports Server (NTRS)

    Isidori, A.; Sastry, S. S.; Kokotovic, P. V.; Byrnes, C. I.

    1992-01-01

    Stability properties of zero dynamics are among the crucial input-output properties of both linear and nonlinear systems. Unstable, or 'nonminimum phase', zero dynamics are a major obstacle to input-output linearization and high-gain designs. An analysis of the effects of regular perturbations in system equations on zero dynamics shows that whenever a perturbation decreases the system's relative degree, it manifests itself as a singular perturbation of zero dynamics. Conditions are given under which the zero dynamics evolve in two timescales characteristic of a standard singular perturbation form that allows a separate analysis of slow and fast parts of the zero dynamics.

  17. The effects of a lateral in-flight perturbation on lower extremity biomechanics during drop landings.

    PubMed

    Yom, Jae P; Simpson, Kathy J; Arnett, Scott W; Brown, Cathleen N

    2014-10-01

    One potential ACL injury situation is due to contact with another person or object during the flight phase, thereby causing the person to land improperly. Conversely, athletes often have flight-phase collisions but do land safely. Therefore, to better understand ACL injury causation and methods by which people typically land safely, the purpose of this study was to determine the effects of an in-flight perturbation on the lower extremity biomechanics displayed by females during typical drop landings. Seventeen collegiate female recreational athletes performed baseline landings, followed by either unexpected laterally-directed perturbation or sham (nonperturbation) drop landings. We compared baseline and perturbation trials using paired-samples t tests (P < .05) and 95% confidence intervals for lower-extremity joint kinematics and kinetics and GRF. The results demonstrated that perturbation landings compared with baseline landings exhibited more extended joint positions of the lower extremity at initial contact; and, during landing, greater magnitudes for knee abduction and hip adduction displacements; peak magnitudes of vertical and medial GRF; and maximum moments of ankle extensors, knee extensors, and adductor and hip adductors. We conclude that a lateral in-flight perturbation leads to abnormal GRF and angular motions and joint moments of the lower extremity. PMID:25010630

  18. Angular momentum evolution of Algol binaries

    NASA Astrophysics Data System (ADS)

    Ibanoǧlu, C.; Soydugan, F.; Soydugan, E.; Dervişoǧlu, A.

    2006-11-01

    We have compiled the well-determined absolute parameters of Algol-type binaries. The lists contain the parameters of 74 detached and 61 semidetached close binaries. The double-lined eclipsing binaries provide not only the most accurate determinations of stellar mass, radius and temperatures but also distance-independent luminosity for each of their individual components. The distributions of the primary and secondary masses of detached binaries (DBs) are similar, whilst the secondary masses of the semidetached binaries (SDBs) are mostly smaller than 2 Msolar with a peak in the M2-bin (0.21-1.0). The components of the DBs are almost all located in the main-sequence band. On the contrary, the secondary components of the SDBs have larger radii and luminosity with respect to the same mass and the same effective temperature of main-sequence counterparts. They occupy a region of the Hertzsprung-Russell diagram between terminal-age main sequence and giants. Moreover, the total angular momenta and specific angular momenta are larger for the SDBs of orbital periods with P > 5 d than those of the shorter period ones. The specific angular momenta of SDBs with periods longer than 5 d are 65 per cent greater than that of the short period group with the same mass. The DBs and the SDBs with orbital periods longer and shorter than 5 d are separated into three groups in the J/M5/3 - q diagram. The SDBs with mass ratios greater than 0.3 and P > 5 d have almost the same angular momentum to those of DBs. However, the SDBs with short periods have the smallest angular momentum even though they have the same mass ratios. This result reveals that angular momentum loss (AML) considerably affects the evolution of close binary systems. Recently, Chen, Li & Qian suggested that, in addition to magnetic braking, a circumbinary disc may play an important role in AML from Algol-type binaries. Their calculations indicated that the evolution of Algol-type binaries can be significantly affected by

  19. Miniaturized photoelectric angular sensor with simplified design

    NASA Astrophysics Data System (ADS)

    Dumbravescu, Niculae; Schiaua, Silviu

    1999-09-01

    In building the movable elements of robots, peripheral devices and measuring apparata, increasing the resolution of the angular sensor systems, based on incremental rotary encoders, is essential, together with decreasing the complexity, dimensions and weight. Especially when the angular sensor is integrated in a measuring system, belonging to a programmed light airplane for surveillance, the key issue is to reduce both dimensions and weight. This can be done using a simplified design, which consists in the following solutions: replacement of the fragile Cr on glass substrate, 1.5 mm thick (normally used for the fabrication of incremental disks), with light Cr on polycarbonate substrate, with only 0.15 mm thick; the absence of collimating optics (based on microlenses, used in IR emitter-photocell receiver assembly), as a result of the good coupling efficiency (due to the possible approaching of these elements at minimum 0.45 mm); the shrinkage of the disk's diameters to only 14 mm; the use of surface mounting devices and the related surface mounting technology, enabling to reduce dimensions and weight. The maximum number of slits on a 14 mm diameter dividing disk, usually obtained in a Cr on polycarbonate version, being approx. 1000, no problem occurs in our case, for 360 slits. The requested angular resolution (only 0.5 degrees for the light airplane), using the whole classical '4x digital multiplication' is not necessary, but a lower one of only 2x, resulting in a simplified electronics. The proposed design permitted, that an original arrangement, for building a small size, lightweight, heavy-duty incremental transducer based angular sensor system, to be obtained, useful not only in avionics, but also in robotics, or other special applications. Besides, extending the number of fixed gratings (masks) allows, that many primary signals to be derived, and a further increase in resolution of even 6 angular minutes to be obtained from the initial 360 slits.

  20. Perturbation theory in light-cone quantization

    SciTech Connect

    Langnau, A.

    1992-01-01

    A thorough investigation of light-cone properties which are characteristic for higher dimensions is very important. The easiest way of addressing these issues is by analyzing the perturbative structure of light-cone field theories first. Perturbative studies cannot be substituted for an analysis of problems related to a nonperturbative approach. However, in order to lay down groundwork for upcoming nonperturbative studies, it is indispensable to validate the renormalization methods at the perturbative level, i.e., to gain control over the perturbative treatment first. A clear understanding of divergences in perturbation theory, as well as their numerical treatment, is a necessary first step towards formulating such a program. The first objective of this dissertation is to clarify this issue, at least in second and fourth-order in perturbation theory. The work in this dissertation can provide guidance for the choice of counterterms in Discrete Light-Cone Quantization or the Tamm-Dancoff approach. A second objective of this work is the study of light-cone perturbation theory as a competitive tool for conducting perturbative Feynman diagram calculations. Feynman perturbation theory has become the most practical tool for computing cross sections in high energy physics and other physical properties of field theory. Although this standard covariant method has been applied to a great range of problems, computations beyond one-loop corrections are very difficult. Because of the algebraic complexity of the Feynman calculations in higher-order perturbation theory, it is desirable to automatize Feynman diagram calculations so that algebraic manipulation programs can carry out almost the entire calculation. This thesis presents a step in this direction. The technique we are elaborating on here is known as light-cone perturbation theory.

  1. Non-perturbative approach for curvature perturbations in stochastic δ N formalism

    SciTech Connect

    Fujita, Tomohiro; Kawasaki, Masahiro; Tada, Yuichiro E-mail: kawasaki@icrr.u-tokyo.ac.jp

    2014-10-01

    In our previous paper [1], we have proposed a new algorithm to calculate the power spectrum of the curvature perturbations generated in inflationary universe with use of the stochastic approach. Since this algorithm does not need the perturbative expansion with respect to the inflaton fields on super-horizon scale, it works even in highly stochastic cases. For example, when the curvature perturbations are very large or the non-Gaussianities of the curvature perturbations are sizable, the perturbative expansion may break down but our algorithm enables to calculate the curvature perturbations. We apply it to two well-known inflation models, chaotic and hybrid inflation, in this paper. Especially for hybrid inflation, while the potential is very flat around the critical point and the standard perturbative computation is problematic, we successfully calculate the curvature perturbations.

  2. Separable wave equations for gravitoelectromagnetic perturbations of rotating charged black strings

    NASA Astrophysics Data System (ADS)

    Miranda, Alex S.; Morgan, Jaqueline; Kandus, Alejandra; Zanchin, Vilson T.

    2015-12-01

    Rotating charged black strings are exact solutions of four-dimensional Einstein-Maxwell equations with a negative cosmological constant and a non-trivial spacetime topology. According to the AdS/CFT correspondence, these black strings are dual to rotating thermal states of a strongly interacting quantum field theory with nonzero chemical potential that lives in a cylinder. The dynamics of linear fluctuations in the dual field theory can be studied from the perturbation equations for classical fields in a black-string spacetime. With this motivation in mind, we develop here a completely gauge and tetrad invariant perturbation approach to deal with the gravitoelectromagnetic fluctuations of rotating charged black strings in the presence of sources. As usual, for any charged black hole, a perturbation in the background electromagnetic field induces a metric perturbation and vice versa. In spite of this coupling and the non-vanishing angular momentum, we show that linearization of equations of the Newman-Penrose formalism leads to four separated second-order complex equations for suitable combinations of the spin coefficients, the Weyl and the Maxwell scalars. Then, we generalize the Chandrasekhar transformation theory by the inclusion of sources and apply it to reduce the perturbation problem to four decoupled inhomogeneous wave equations—a pair for each sector of perturbations. The radial part of such wave equations can be put into Schrödinger-like forms after Fourier transforming them with respect to time. We find that the resulting effective potentials form two pairs of supersymmetric partner potentials and, as a consequence, the fundamental variables of one perturbation sector are related to the variables of the other sector. The relevance of such a symmetry in connection to the AdS/CFT correspondence is discussed, and future applications of the pertubation theory developed here are outlined.

  3. Characterization of the Head Stabilization Response to a Lateral Perturbation During Walking in Older Adults

    NASA Technical Reports Server (NTRS)

    Buccello-Stout, Regina R.; Cromwell, Ronita L.; Bloomberg, Jacob J.

    2009-01-01

    A main contributor of fractures in older adults is from a lateral fall. The decline in sensory systems results in difficulty maintaining balance stability. Head stabilization contributes to postural control by serving as a stable platform for the sensory systems. The purpose of this study was to characterize the head stabilization response to a lateral perturbation while walking. A total of 16 healthy older adults, aged 66-81 years, walked across a foam pathway 6 times. One piece of the foam pathway covered a movable platform that translated to the left when the subject stepped on the foam. Three trials were randomized in which the platform shifted. Angular rate sensors placed on the center of mass of the head and trunk collected head and trunk movement in all three planes of motion. The roll plane was analyzed to examine motion in the plane of the perturbation. Subjects stepped onto the platform with the right foot. Recovery step time and distance were recorded. The first trial was analyzed to capture the novelty of the perturbation. Results indicate a significant difference in footfall distance t=0.004, p<0.05, as well as the speed of foot recovery t=0.001, p<0.05, between natural and perturbed walking. Results indicate that the head t=0.005, p<0.05, and trunk t=0.0001, p<0.05, velocities increase during perturbed compared to natural walking. Older adults place their recovery foot down faster when perturbed to re-establish their base of support. Head and trunk segments are less stable and move with greater velocities to reestablish stability when perturbed.

  4. Changes in Head Stability Control in Response to a Lateral Perturbation while Walking in Older Adults

    NASA Technical Reports Server (NTRS)

    Buccello, Regina R.; Cromwell, Ronita L.; Bloomberg, Jacob J.

    2008-01-01

    Falling is a main contributor of injury in older adults. The decline in sensory systems associated with aging limits information needed to successfully compensate for unexpected perturbations. Therefore, sensory changes result in older adults having problems maintaining balance stability when experiencing an unexpected lateral perturbation (e.g. slip) in the environment. The goal of this study was to determine head stability movement strategies used by older adults when experiencing an unexpected lateral perturbation during walking. A total of 16 healthy adults, aged 66-81 years, walked across a foam pathway 6 times. One piece of the foam pathway covered a movable platform that translated to the left when the subject stepped on the foam. Three trials were randomized in which the platform shifted. Angular rate sensors were placed on the center of mass for the head and trunk segments to collect head and trunk movement in all three planes of motion. The predominant movement strategies for maintaining head stability were determined from the results of the cross-correlation analyses between the head and trunk segments. The Chi square test of independence was used to evaluate the movement pattern distributions of head-trunk coordination during perturbed and non-perturbed walking. When perturbed, head stabilization was significantly challenged in the yaw and roll planes of motion. Subjects demonstrated a movement pattern of the head leading the trunk in an effort to stabilize the head. The older adult subjects used this head stabilization movement pattern to compensate for sensory changes when experiencing the unexpected lateral perturbation.

  5. Quantum field perturbation theory revisited

    NASA Astrophysics Data System (ADS)

    Matone, Marco

    2016-03-01

    Schwinger's formalism in quantum field theory can be easily implemented in the case of scalar theories in D dimension with exponential interactions, such as μDexp (α ϕ ). In particular, we use the relation exp (α δ/δ J (x ) )exp (-Z0[J ])=exp (-Z0[J +αx]) with J the external source, and αx(y )=α δ (y -x ). Such a shift is strictly related to the normal ordering of exp (α ϕ ) and to a scaling relation which follows by renormalizing μ . Next, we derive a new formulation of perturbation theory for the potentials V (ϕ )=λ/n ! :ϕn: , using the generating functional associated to :exp (α ϕ ):. The Δ (0 )-terms related to the normal ordering are absorbed at once. The functional derivatives with respect to J to compute the generating functional are replaced by ordinary derivatives with respect to auxiliary parameters. We focus on scalar theories, but the method is general and similar investigations extend to other theories.

  6. Perturbative theory for Brownian vortexes

    NASA Astrophysics Data System (ADS)

    Moyses, Henrique W.; Bauer, Ross O.; Grosberg, Alexander Y.; Grier, David G.

    2015-06-01

    Brownian vortexes are stochastic machines that use static nonconservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. Here we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak nonconservative driving. The first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers.

  7. Chiral perturbation theory with nucleons

    SciTech Connect

    Meissner, U.G.

    1991-09-01

    I review the constraints posed on the interactions of pions, nucleons and photons by the spontaneously broken chiral symmetry of QCD. The framework to perform these calculations, chiral perturbation theory, is briefly discussed in the meson sector. The method is a simultaneous expansion of the Greens functions in powers of external moments and quark masses around the massless case, the chiral limit. To perform this expansion, use is made of a phenomenological Lagrangian which encodes the Ward-identities and pertinent symmetries of QCD. The concept of chiral power counting is introduced. The main part of the lectures of consists in describing how to include baryons (nucleons) and how the chiral structure is modified by the fact that the nucleon mass in the chiral limit does not vanish. Particular emphasis is put on working out applications to show the strengths and limitations of the methods. Some processes which are discussed are threshold photopion production, low-energy compton scattering off nucleons, {pi}N scattering and the {sigma}-term. The implications of the broken chiral symmetry on the nuclear forces are briefly described. An alternative approach, in which the baryons are treated as very heavy fields, is touched upon.

  8. Non-Perturbative Field Theories.

    NASA Astrophysics Data System (ADS)

    Stephenson, David

    Available from UMI in association with The British Library. Requires signed TDF. Some non-perturbative aspects of field theories are studied by applying lattice gauge theory techniques. The low-lying hadronic mass spectrum is calculated numerically using quenched lattice quantum chromodynamics. The results of large numerical simulations performed on a distributed array processor are presented and analysed. Particular emphasis is stressed upon the understanding of systematic and statistical errors in the calculation. In addition, the pion decay constant and the chiral condensate are evaluated. An attempt is made to relate the numerical findings to the experimentally measured quantities. A pioneering attempt to understand Yukawa couplings is discussed. A toy Fermion-Higgs system is studied numerically on a transputer array. Dynamical fermions are included in the investigation of the behavior of the system over a wide range of Yukawa couplings. A phase diagram is found for the model which shows evidence of spontaneous chiral symmetry breaking transitions. Extensions of the model are discussed together some speculations concerning the behaviour of Yukawa couplings in general. The possibility of using the lattice as a model for space-time is investigated by studying the propagation of particles on a fractal lattice. In addition, the use of truncated fractals as novel regulators is studied numerically in the hope that the problem of fermion doubling will be alleviated.

  9. Perturbative theory for Brownian vortexes.

    PubMed

    Moyses, Henrique W; Bauer, Ross O; Grosberg, Alexander Y; Grier, David G

    2015-06-01

    Brownian vortexes are stochastic machines that use static nonconservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. Here we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak nonconservative driving. The first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers. PMID:26172698

  10. Gravitational perturbation of the BTZ black hole induced by test particles and weak cosmic censorship in AdS spacetime

    SciTech Connect

    Rocha, Jorge V.; Cardoso, Vitor

    2011-05-15

    We analyze the gravitational perturbations induced by particles falling into a three dimensional, asymptotically AdS black hole geometry. More specifically, we solve the linearized perturbation equations obtained from the geodesic motion of a ringlike distribution of test particles in the BTZ background. This setup ensures that the U(1) symmetry of the background is preserved. The nonasymptotic flatness of the background raises difficulties in attributing the significance of energy and angular momentum to the conserved quantities of the test particles. This issue is well known but, to the best of our knowledge, has never been addressed in the literature. We confirm that the naive expressions for energy and angular momentum are the correct definitions. Finally, we put an asymptotically AdS version of the weak cosmic censorship to a test: by attempting to overspin the BTZ black hole with test particles it is found that the black hole cannot be spun-up past its extremal limit.

  11. Scalar Quantum Electrodynamics: Perturbation Theory and Beyond

    SciTech Connect

    Bashir, A.; Gutierrez-Guerrero, L. X.; Concha-Sanchez, Y.

    2006-09-25

    In this article, we calculate scalar propagator in arbitrary dimensions and gauge and the three-point scalar-photon vertex in arbitrary dimensions and Feynman gauge, both at the one loop level. We also discuss constraints on their non perturbative structure imposed by requirements of gauge invariance and perturbation theory.

  12. Degenerate Open Shell Density Perturbation Theory

    NASA Astrophysics Data System (ADS)

    Palenik, Mark; Dunlap, Brett

    The density perturbation theory (DPT) methodology we have developed applies the Hohenberg-Kohn theorem to perturbations in density functional theory. At each order, the energy is directly minimized with respect to the density at all lower orders. The difference between the perturbed and unperturbed densities is expanded in terms of a finite number of basis functions, and a single matrix inversion in this space reduces the complexity of the problem to that of non-interacting perturbation theory. For open-shell systems with symmetry, however, the situation becomes more complex. Typically, the perturbation will break the symmetry leading to a zeroth-order shift in the Kohn-Sham potential. Because the symmetry breaking is independent of the strength of the perturbation, the mapping from the initial to the perturbed KS potential is discontinuous and techniques from perturbation theory for noninteracting particles fail. We describe a rigorous formulation of DPT for use in systems that display an initial degeneracy, such as atoms and Fe55Cp*12 clusters and present initial calculations on these systems.

  13. Ultra-sensitive and super-resolving angular rotation measurement based on photon orbital angular momentum using parity measurement.

    PubMed

    Zhang, Zijing; Qiao, Tianyuan; Ma, Kun; Cen, Longzhu; Zhang, Jiandong; Wang, Feng; Zhao, Yuan

    2016-08-15

    Photon orbital angular momentum has led to many novel insights and applications in quantum measurement. Photon orbital angular momentum can increase the resolution and sensitivity of angular rotation measurement. However, quantum measurement strategy can further surpass this limit and improve the resolution of angular rotation measurement. This Letter proposes and demonstrates a parity measurement method in angular rotation measurement scheme for the first time. Parity measurement can make the resolution superior to the limit of the existing method. The sensitivity can be improved with higher orbital angular momentum photons. Moreover, this Letter gives a detailed discussion of the change of resolution and sensitivity in the presence of photon loss. PMID:27519107

  14. Intelligent perturbation algorithms for space scheduling optimization

    NASA Technical Reports Server (NTRS)

    Kurtzman, Clifford R.

    1991-01-01

    Intelligent perturbation algorithms for space scheduling optimization are presented in the form of the viewgraphs. The following subject areas are covered: optimization of planning, scheduling, and manifesting; searching a discrete configuration space; heuristic algorithms used for optimization; use of heuristic methods on a sample scheduling problem; intelligent perturbation algorithms are iterative refinement techniques; properties of a good iterative search operator; dispatching examples of intelligent perturbation algorithm and perturbation operator attributes; scheduling implementations using intelligent perturbation algorithms; major advances in scheduling capabilities; the prototype ISF (industrial Space Facility) experiment scheduler; optimized schedule (max revenue); multi-variable optimization; Space Station design reference mission scheduling; ISF-TDRSS command scheduling demonstration; and example task - communications check.

  15. Covariant generalization of cosmological perturbation theory

    SciTech Connect

    Enqvist, Kari; Hoegdahl, Janne; Nurmi, Sami; Vernizzi, Filippo

    2007-01-15

    We present an approach to cosmological perturbations based on a covariant perturbative expansion between two worldlines in the real inhomogeneous universe. As an application, at an arbitrary order we define an exact scalar quantity which describes the inhomogeneities in the number of e-folds on uniform density hypersurfaces and which is conserved on all scales for a barotropic ideal fluid. We derive a compact form for its conservation equation at all orders and assign it a simple physical interpretation. To make a comparison with the standard perturbation theory, we develop a method to construct gauge-invariant quantities in a coordinate system at arbitrary order, which we apply to derive the form of the nth order perturbation in the number of e-folds on uniform density hypersurfaces and its exact evolution equation. On large scales, this provides the gauge-invariant expression for the curvature perturbation on uniform density hypersurfaces and its evolution equation at any order.

  16. Angular description for 3D scattering centers

    NASA Astrophysics Data System (ADS)

    Bhalla, Rajan; Raynal, Ann Marie; Ling, Hao; Moore, John; Velten, Vincent J.

    2006-05-01

    The electromagnetic scattered field from an electrically large target can often be well modeled as if it is emanating from a discrete set of scattering centers (see Fig. 1). In the scattering center extraction tool we developed previously based on the shooting and bouncing ray technique, no correspondence is maintained amongst the 3D scattering center extracted at adjacent angles. In this paper we present a multi-dimensional clustering algorithm to track the angular and spatial behaviors of 3D scattering centers and group them into features. The extracted features for the Slicy and backhoe targets are presented. We also describe two metrics for measuring the angular persistence and spatial mobility of the 3D scattering centers that make up these features in order to gather insights into target physics and feature stability. We find that features that are most persistent are also the most mobile and discuss implications for optimal SAR imaging.

  17. Precompound nucleon angular distributions in the continuum

    SciTech Connect

    Blann, M.; Scobel, W.; Plechaty, E.

    1985-08-01

    Angular distributions for nucleon induced reactions (incident energies 14 to 90 MeV) leading to precompound nucleon emission in the continuum (emitted particle energies 9-70 MeV) are calculated based on nucleon-nucleon scattering kinematics for an incident nucleon on a Fermi gas. Analytic expressions due to Kikuchi and Kawai are used for the single scattering kernel. The geometry dependent hybrid model is used to generate the differential cross sections for first, second, etc. order scattering, these weightings being used to fold the single scattering kernel. Results are found to reproduce all experimental angular distributions quite well at angles in the 20/sup 0/ to 90/sup 0/ range. Ad-hoc modifications to approximate quantal effects and Coulomb deflections are explored, but the results do not seem to offer a consistent means of reproducing back angle yields, and give generally poorer results at very forward angles.

  18. Performance criteria for dosimeter angular response

    SciTech Connect

    Roberson, P.L.; Fox, R. A.; Cummings, F. M.; McDonald, J. C.; Jones, K.L.

    1988-06-01

    This report provides criteria for evaluating the response of personnel dosimeters to radiation at nonperpendicular incidence. The US Department of Energy Laboratory Accreditation Program (DOELAP) ensures that dosimetry systems at DOE facilities meet acceptable standards for precision and accuracy. In the past, these standards were limited to tests for system variability, energy dependence, and level of detection. The proposed criteria will broaden the scope of DOELAP to include the angular response of personnel dosimeters. Because occupational exposures in the workplace are rarely due to radiation from only one direction, dosimeters must accurately assign individual dose equivalent from irradiation at any forward angle of incidence. Including an angular response criterion in DOELAP would improve the quality of personnel monitoring provided that the criterion is developed from appropriate dose quantities. This report provides guidance for assigning individual dose equivalents for radiation fields at nonperpendicular incidence to the dosimeter. 21 refs., 10 figs., 10 tabs.

  19. From transverse angular momentum to photonic wheels

    NASA Astrophysics Data System (ADS)

    Aiello, Andrea; Banzer, Peter; Neugebauer, Martin; Leuchs, Gerd

    2015-12-01

    Scientists have known for more than a century that light possesses both linear and angular momenta along the direction of propagation. However, only recent advances in optics have led to the notion of spinning electromagnetic fields capable of carrying angular momenta transverse to the direction of motion. Such fields enable numerous applications in nano-optics, biosensing and near-field microscopy, including three-dimensional control over atoms, molecules and nanostructures, and allowing for the realization of chiral nanophotonic interfaces and plasmonic devices. Here, we report on recent developments of optics with light carrying transverse spin. We present both the underlying principles and the latest achievements, and also highlight new capabilities and future applications emerging from this young yet already advanced field of research.

  20. Satellite Angular Rate Estimation From Vector Measurements

    NASA Technical Reports Server (NTRS)

    Azor, Ruth; Bar-Itzhack, Itzhack Y.; Harman, Richard R.

    1996-01-01

    This paper presents an algorithm for estimating the angular rate vector of a satellite which is based on the time derivatives of vector measurements expressed in a reference and body coordinate. The computed derivatives are fed into a spacial Kalman filter which yields an estimate of the spacecraft angular velocity. The filter, named Extended Interlaced Kalman Filter (EIKF), is an extension of the Kalman filter which, although being linear, estimates the state of a nonlinear dynamic system. It consists of two or three parallel Kalman filters whose individual estimates are fed to one another and are considered as known inputs by the other parallel filter(s). The nonlinear dynamics stem from the nonlinear differential equation that describes the rotation of a three dimensional body. Initial results, using simulated data, and real Rossi X ray Timing Explorer (RXTE) data indicate that the algorithm is efficient and robust.

  1. The Cosmology Large Angular Scale Surveyor

    NASA Astrophysics Data System (ADS)

    Marriage, Tobias; Ali, A.; Amiri, M.; Appel, J. W.; Araujo, D.; Bennett, C. L.; Boone, F.; Chan, M.; Cho, H.; Chuss, D. T.; Colazo, F.; Crowe, E.; Denis, K.; Dünner, R.; Eimer, J.; Essinger-Hileman, T.; Gothe, D.; Halpern, M.; Harrington, K.; Hilton, G.; Hinshaw, G. F.; Huang, C.; Irwin, K.; Jones, G.; Karakla, J.; Kogut, A. J.; Larson, D.; Limon, M.; Lowry, L.; Mehrle, N.; Miller, A. D.; Miller, N.; Moseley, S. H.; Novak, G.; Reintsema, C.; Rostem, K.; Stevenson, T.; Towner, D.; U-Yen, K.; Wagner, E.; Watts, D.; Wollack, E.; Xu, Z.; Zeng, L.

    2014-01-01

    Some of the most compelling inflation models predict a background of primordial gravitational waves (PGW) detectable by their imprint of a curl-like "B-mode" pattern in the polarization of the Cosmic Microwave Background (CMB). The Cosmology Large Angular Scale Surveyor (CLASS) is a novel array of telescopes to measure the B-mode signature of the PGW. By targeting the largest angular scales (>2°) with a multifrequency array, novel polarization modulation and detectors optimized for both control of systematics and sensitivity, CLASS sets itself apart in the field of CMB polarization surveys and opens an exciting new discovery space for the PGW and inflation. This poster presents an overview of the CLASS project.

  2. Tubulin-perturbing naphthoquinone spiroketals.

    PubMed

    Balachandran, Raghavan; Hopkins, Tamara D; Thomas, Catherine A; Wipf, Peter; Day, Billy W

    2008-02-01

    Several natural and synthetic naphthoquinone spiroketals are potent inhibitors of the thioredoxin-thioredoxin reductase redox system. Based on the antimitotic and weak antitubulin actions noted for SR-7 ([8-(furan-3-ylmethoxy)-1-oxo-1,4-dihydronaphthalene-4-spiro-2'-naphtho[1'',8''-de][1',3'][dioxin]), a library of related compounds was screened for tubulin-perturbing properties. Two compounds, TH-169 (5'-hydroxy-4'H-spiro[1,3-dioxolane-2,1'-naphthalen]-4'-one) and TH-223 (5'-methoxy-4'H-spiro[1,3-dioxane-2,1'-naphthalen]-4'-one), had substantial effects on tubulin assembly and were antiproliferative at low micromolar concentrations. TH-169 was the most potent at blocking GTP-dependent polymerization of 10 mum tubulin in vitro with a remarkable 50% inhibitory concentration of ca. 400 nm. It had no effect on paclitaxel-induced microtubule assembly and did not cause microtubule hypernucleation. TH-169 failed to compete with colchicine for binding to beta-tubulin. The 50% antiproliferative concentration of TH-169 against human cancer cells was at or slightly below 1 mum. Flow cytometry showed that 1 mum TH-169 caused an increase in G(2)/M and hypodiploid cells. TH-169 eliminated the PC-3 cells' polyploid population and increased their expression of p21(WAF1) and Hsp70 in a concentration-dependent manner. The antiproliferative effect of TH-169 was irreversible and independent of changes in caspases, actin, tubulin, glyceraldehyde phosphate dehydrogenase or Bcl-x(S/L). This structurally simple naphthoquinone spiroketal represents a small molecule, tubulin-interactive agent with a novel apoptotic pathway and attractive biological function. PMID:18194192

  3. Behavior of nuclei at high angular momentum

    SciTech Connect

    Stephens, F.S.

    1982-07-01

    The present report begins with a brief overview of nuclear shapes and level structures at high-spin values. The new spectroscopy associated with angular-momentum alignments is described, and some of the exciting possibilities of this spectroscopy are explored. Nuclear moments of inertia are discussed and a somewhat different one is defined, together with a method for measuring it and some early results. Finally a few comments on the future prospects for high-spin physics are offered.

  4. Diaphyseal angular deformities in three foals.

    PubMed

    White, K K

    1983-02-01

    Angular limb deformities in 3 foals were found to originate in the diaphyseal region of the 3rd metacarpal (2) and metatarsal (1) bones. In each case, treatment consisted of wedge ostectomy followed by compression plating. Two foals survived for useful performance; the 3rd was euthanatized because of ischemia of the operated limb. The condition appeared to resemble a similar syndrome in man involving tibial curvature. PMID:6826451

  5. Time-dependent photoelectron angular distributions

    NASA Astrophysics Data System (ADS)

    Wang, Xiangyang

    1999-09-01

    I show that the angular distribution of electrons photoionized from gas phase targets by short light pulses is time-dependent, when the orbital momentum composition of the photocurrent changes with excitation energy so evolves with the time of detection. A theory of time- dependent photoionization is outlined and general formulas of time-dependent photoelectron flux and angular distribution are given. Two general propagator methods suitable to describe the time-dependent photoionization and scattering processes are developed. The photoionization process is viewed as a local excitation followed by a half scattering. The local excitation process is solved theoretically in a small region around the target core. This approach has been generalized to describe the evolution of a wavepacket in an unbound system. An asymptotic propagator theorem is discovered and used to derive analytic expressions for asymptotic propagators. The origin of the time dependence is explored by parameterizing the time delay and orbital momentum coupling in a two channel model. K-shell photoionization of N2 and CO are calculated with this time- dependent photoionization theory, implemented using a multiple scattering model. Numerical results demonstrate that the time dependence of photoelectron angular distributions is a realistic effect.

  6. Angular Fock coefficients: Refinement and further development

    NASA Astrophysics Data System (ADS)

    Liverts, Evgeny Z.; Barnea, Nir

    2015-10-01

    The angular coefficients ψk ,p(α ,θ ) of the Fock expansion characterizing the S -state wave function of the two-electron atomic system are calculated in hyperspherical angular coordinates α and θ . To solve the problem the Fock recurrence relations separated into the independent individual equations associated with definite power j of the nucleus charge Z are applied. The "pure" j components of the angular Fock coefficients, orthogonal to the hyperspherical harmonics Yk l, are found for even values of k . To this end, the specific coupling equation is proposed and applied. Effective techniques for solving the individual equations with the simplest nonseparable and separable right-hand sides are proposed. Some mistakes or misprints made earlier in representations of ψ2 ,0, are noted and corrected. All j components of ψ4 ,1 and the majority of components and subcomponents of ψ3 ,0 are calculated and presented. All calculations are carried out with the help of Wolfram Mathematica.

  7. The Cosmology Large Angular Scale Surveyor (CLASS)

    NASA Technical Reports Server (NTRS)

    Harrington, Kathleen; Marriange, Tobias; Aamir, Ali; Appel, John W.; Bennett, Charles L.; Boone, Fletcher; Brewer, Michael; Chan, Manwei; Chuss, David T.; Colazo, Felipe; Denis, Kevin; Moseley, Samuel H.; Rostem, Karwan; Wollack, Edward

    2016-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array designed to characterize relic primordial gravitational waves from in ation and the optical depth to reionization through a measurement of the polarized cosmic microwave background (CMB) on the largest angular scales. The frequencies of the four CLASS telescopes, one at 38 GHz, two at 93 GHz, and one dichroic system at 145/217 GHz, are chosen to avoid spectral regions of high atmospheric emission and span the minimum of the polarized Galactic foregrounds: synchrotron emission at lower frequencies and dust emission at higher frequencies. Low-noise transition edge sensor detectors and a rapid front-end polarization modulator provide a unique combination of high sensitivity, stability, and control of systematics. The CLASS site, at 5200 m in the Chilean Atacama desert, allows for daily mapping of up to 70% of the sky and enables the characterization of CMB polarization at the largest angular scales. Using this combination of a broad frequency range, large sky coverage, control over systematics, and high sensitivity, CLASS will observe the reionization and recombination peaks of the CMB E- and B-mode power spectra. CLASS will make a cosmic variance limited measurement of the optical depth to reionization and will measure or place upper limits on the tensor-to-scalar ratio, r, down to a level of 0.01 (95% C.L.).

  8. Nuclear structure at high angular momentum

    SciTech Connect

    Stephens, F.S.

    1980-06-01

    This review paper begins by discussing the limits faced in the attempts to get nuclei to hold very high angular momentum. The method presently used to produce nuclei with the maximum angular momentum is described. Then the physics of high-spin states is taken up; some properties of a purely collective, classical rotor are described, and the effects of coupling single-particle motion to this are considered. Next, backbending, its causes, and a new spectroscopy of bands and backbends at high spin values are discussed. Noncollective states occur when the nuclear angular momentum is carried by a few high-j particles and is aligned along a symmetry axis. There results an irregular yrast line, along which there are no collective transitions. Noncollective behavior in the lead region, the hafnium region, and the N = 82 region is examined. Then the discussion moves on to collective behavior and recent studies on continuum spectra. Evidence for rotation is given, and effective moments of inertia for this rotation are evaluated. Finally, current ..gamma..-ray energy correlation studies are described. 68 references, 36 figures. (RWR)

  9. A Neural Circuit for Angular Velocity Computation

    PubMed Central

    Snider, Samuel B.; Yuste, Rafael; Packer, Adam M.

    2010-01-01

    In one of the most remarkable feats of motor control in the animal world, some Diptera, such as the housefly, can accurately execute corrective flight maneuvers in tens of milliseconds. These reflexive movements are achieved by the halteres, gyroscopic force sensors, in conjunction with rapidly tunable wing steering muscles. Specifically, the mechanosensory campaniform sensilla located at the base of the halteres transduce and transform rotation-induced gyroscopic forces into information about the angular velocity of the fly's body. But how exactly does the fly's neural architecture generate the angular velocity from the lateral strain forces on the left and right halteres? To explore potential algorithms, we built a neuromechanical model of the rotation detection circuit. We propose a neurobiologically plausible method by which the fly could accurately separate and measure the three-dimensional components of an imposed angular velocity. Our model assumes a single sign-inverting synapse and formally resembles some models of directional selectivity by the retina. Using multidimensional error analysis, we demonstrate the robustness of our model under a variety of input conditions. Our analysis reveals the maximum information available to the fly given its physical architecture and the mathematics governing the rotation-induced forces at the haltere's end knob. PMID:21228902

  10. A neural circuit for angular velocity computation.

    PubMed

    Snider, Samuel B; Yuste, Rafael; Packer, Adam M

    2010-01-01

    In one of the most remarkable feats of motor control in the animal world, some Diptera, such as the housefly, can accurately execute corrective flight maneuvers in tens of milliseconds. These reflexive movements are achieved by the halteres, gyroscopic force sensors, in conjunction with rapidly tunable wing steering muscles. Specifically, the mechanosensory campaniform sensilla located at the base of the halteres transduce and transform rotation-induced gyroscopic forces into information about the angular velocity of the fly's body. But how exactly does the fly's neural architecture generate the angular velocity from the lateral strain forces on the left and right halteres? To explore potential algorithms, we built a neuromechanical model of the rotation detection circuit. We propose a neurobiologically plausible method by which the fly could accurately separate and measure the three-dimensional components of an imposed angular velocity. Our model assumes a single sign-inverting synapse and formally resembles some models of directional selectivity by the retina. Using multidimensional error analysis, we demonstrate the robustness of our model under a variety of input conditions. Our analysis reveals the maximum information available to the fly given its physical architecture and the mathematics governing the rotation-induced forces at the haltere's end knob. PMID:21228902

  11. Optical angular momentum in a rotating frame.

    PubMed

    Speirits, Fiona C; Lavery, Martin P J; Padgett, Miles J; Barnett, Stephen M

    2014-05-15

    It is well established that light carrying orbital angular momentum (OAM) can be used to induce a mechanical torque causing an object to spin. We consider the complementary scenario: will an observer spinning relative to the beam axis measure a change in OAM as a result of their rotational velocity? Remarkably, although a linear Doppler shift changes the linear momentum of a photon, the angular Doppler shift induces no change in the angular momentum. Further, we examine the rotational Doppler shift in frequency imparted to the incident light due to the relative motion of the beam with respect to the observer and consider what must happen to the measured wavelength if the speed of light c is to remain constant. We show specifically that the OAM of the incident beam is not affected by the rotating observer and that the measured wavelength is shifted by a factor equal and opposite to that of the frequency shift induced by the rotational Doppler effect. PMID:24978243

  12. Resolution analysis of an angular domain imaging system with two dimensional angular filters

    NASA Astrophysics Data System (ADS)

    Ng, Eldon; Carson, Jeffrey J. L.

    2013-02-01

    Angular Domain Imaging (ADI) employs an angular filter to distinguish between quasi-ballistic and scattered photons based on trajectory. A 2D angular filter array was constructed using 3D printing technology to generate an array of micro-channels 500 μm x 500 μm with a length of 12 cm. The main barrier to 2D imaging with the 2D angular filter array was the shadows cast on the image by the 500 μm walls of the angular filter. The objective of this work was to perform a resolution analysis of the 2D angular filter array. The approach was to position the AFA with a two dimensional positioning stage to obtain images of areas normally obstructed by the walls of the AFA. A digital light processor was also incorporated to generate various light patterns to improve the contrast of the images. A resolution analysis was completed by imaging a knife edge submerged in various uniform scattering media (Intralipid® dilutions with water). The edge response functions obtained were then used to compute the line spread function and the theoretical resolution of the imaging system. The theoretical system resolution was measured to be between 110 μm - 180 μm when the scattering level was at or below 0.7% Intralipid®. The theoretical resolution was in agreement with a previous resolution analysis of a silicon-based angular filter with a similar aspect ratio. The measured resolution was also found to be smaller than the size of an individual channel, suggesting that the resolution of an AFA based ADI system is not dependent on the size of the micro-channel.

  13. Parity-violating effects in an exotic perturbation of the rigid rotator

    NASA Astrophysics Data System (ADS)

    Pallares-Rivera, A.; Kirchbach, M.

    2015-03-01

    The perturbation of the free rigid rotator by the trigonometric Scarf potential is shown to conserve its energy excitation patterns and change only the wave functions towards spherical harmonics rescaled by a function of an unspecified parity, or mixtures of such rescaled harmonics of equal magnetic quantum numbers and different angular momenta. In effect, no parity can be assigned to the states of the rotational bands emerging in this exotic way, and the electric dipole operator is allowed to acquire non-vanishing expectation values.

  14. Analytic spectra of CMB anisotropies and polarization generated by scalar perturbations in synchronous gauge

    NASA Astrophysics Data System (ADS)

    Cai, Z.; Zhang, Y.

    2012-05-01

    The temperature anisotropies and polarization of the cosmic microwave background (CMB) radiation not only serve as indispensable cosmological probes, but also provide a unique channel to detect relic gravitational waves (RGW) at very long wavelengths. Analytical studies of the anisotropies and polarization improve our understanding of various cosmic processes and help to separate the contribution of RGW from that of density perturbations. We present a detailed analytical calculation of CMB temperature anisotropies αk and polarization βk generated by scalar metric perturbations in synchronous gauge, parallel to our previous work with RGW as a generating source. This is realized primarily by an analytic time integration of Boltzmann’s equation, yielding the closed forms of αk and βk. Approximations, such as the tight-coupling approximation for photons a priori to the recombination and the long-wavelength limit for scalar perturbations, are used. The residual gauge modes in scalar perturbations are analyzed and a proper joining condition of scalar perturbations at the radiation-matter equality is chosen, ensuring the continuity of energy perturbation. The resulting analytic expressions of the multipole moments of polarization aEl and of temperature anisotropies aTl are explicit functions of the scalar perturbations, recombination time, recombination width, photon-free streaming damping factor, baryon fraction, initial amplitude, primordial scalar spectral index and the running index. These results show that a longer recombination width yields higher amplitudes of polarization on large scales and more damping on small scales, and that a late recombination time shifts the peaks of C^{XX^{\\prime }}_l to larger angular scales. Calculations show that aEl is generated in the presence of the quadrupole α2 of temperature anisotropies via scattering, both having similar structures and being smaller than the total aTl, which consists of the contributions from the

  15. Curvature perturbation spectrum in two-field inflation with a turning trajectory

    SciTech Connect

    Pi, Shi; Sasaki, Misao E-mail: misao@yukawa.kyoto-u.ac.jp

    2012-10-01

    We revisit a two-component inflaton model with a turning trajectory in the field space, where the field slowly rolls down along the trajectory. We consider the case when the effective mass in the direction perpendicular to the trajectory, namely the isocurvature direction, is either of the same order as or much larger than the Hubble parameter. Assuming that the turning angular velocity is small, we compute analytically the corrections to the power spectrum of curvature perturbation caused by the mediation of the heavy isocurvature perturbation, and compare our analytic results with the numerical ones. Especially, when M{sub eff}{sup 2} >> H{sup 2}, we find that it is proportional to M{sub eff}{sup −2}. This result is consistent with the one obtained previously by an effective field theory approach.

  16. Comparison of Radiation Pressure Perturbations on Rocket Bodies and Debris at Geosynchronous Earth Orbit

    NASA Astrophysics Data System (ADS)

    Wetterer, C.; Hill, K.; Jah, M.

    2014-09-01

    Recent research has highlighted the need for physically consistent radiation pressure and Bidirectional Reflectance Distribution Function (BRDF) models. This paper seeks to evaluate the impact of BRDF-consistent radiation pressure models compared to changes in the other BRDF parameters. The differences in orbital position arising because of changes in the shape, attitude, angular rates, BRDF parameters, and radiation pressure model are plotted as a function of time for simulated rocket bodies and debris at geo-synchronous orbit (GEO). The initial position and velocity of the space object is kept fixed, and the orbital position difference between a baseline or-bit and the perturbed orbit are plotted as a function of time. This is similar to how the effects of perturbations have been visualized in the past in commonly used astrodynamics references.

  17. Calculating nonadiabatic pressure perturbations during multifield inflation

    NASA Astrophysics Data System (ADS)

    Huston, Ian; Christopherson, Adam J.

    2012-03-01

    Isocurvature perturbations naturally occur in models of inflation consisting of more than one scalar field. In this paper, we calculate the spectrum of isocurvature perturbations generated at the end of inflation for three different inflationary models consisting of two canonical scalar fields. The amount of nonadiabatic pressure present at the end of inflation can have observational consequences through the generation of vorticity and subsequently the sourcing of B-mode polarization. We compare two different definitions of isocurvature perturbations and show how these quantities evolve in different ways during inflation. Our results are calculated using the open source Pyflation numerical package which is available to download.

  18. Vector perturbations in a contracting Universe

    SciTech Connect

    Battefeld, T.J.; Brandenberger, R.

    2004-12-15

    In this note we show that vector perturbations exhibit growing mode solutions in a contracting Universe, such as the contracting phase of the pre big bang or the cyclic/ekpyrotic models of the Universe. This is not a gauge artifact and will in general lead to the breakdown of perturbation theory--a severe problem that has to be addressed in any bouncing model. We also comment on the possibility of explaining, by means of primordial vector perturbations, the existence of the observed large-scale magnetic fields. This is possible since they can be seeded by vorticity.

  19. Cosmological perturbations and the Weinberg theorem

    NASA Astrophysics Data System (ADS)

    Akhshik, Mohammad; Firouzjahi, Hassan; Jazayeri, Sadra

    2015-12-01

    The celebrated Weinberg theorem in cosmological perturbation theory states that there always exist two adiabatic scalar modes in which the comoving curvature perturbation is conserved on super-horizon scales. In particular, when the perturbations are generated from a single source, such as in single field models of inflation, both of the two allowed independent solutions are adiabatic and conserved on super-horizon scales. There are few known examples in literature which violate this theorem. We revisit the theorem and specify the loopholes in some technical assumptions which violate the theorem in models of non-attractor inflation, fluid inflation, solid inflation and in the model of pseudo conformal universe.

  20. Evolution of non-spherical perturbations.

    NASA Astrophysics Data System (ADS)

    Boschan, P.

    1995-06-01

    In this paper I investigate the evolution of primordial non-spherical positive and negative fluctuations. They can be calculated by second order of perturbation theory. I solved analytically the second order equation for arbitrary density parameter {OMEGA}_M0_ and cosmological constant {LAMBDA} using the approximation introduced by Martell & Freundling (???). The second order solution is compared with the exact one in the spherical case. I find that the initial deformation grows rapidly for positive perturbations, while the negative perturbations (voids) are stable against deformations.

  1. Perturbation calculation of thermodynamic density of states

    SciTech Connect

    Brown, Greg; Schulthess, Thomas C; Nicholson, Don M; Eisenbach, Markus; Stocks, George Malcolm

    2011-01-01

    The density of states g( ) is frequently used to calculate the temperature-dependent properties of a thermodynamic system. Here a derivation is given for calculating the warped density of states g ( ) resulting from the addition of a perturbation. The method is validated for a classical Heisenberg model of bcc Fe and the errors in the free energy are shown to be second order in the perturbation. Taking the perturbation to be the difference between a first-principles quantum-mechanical energy and a corresponding classical energy, this method can significantly reduce the computational effort required to calculate g( ) for quantum systems using the Wang-Landau approach.

  2. HIV-associated memory B cell perturbations

    PubMed Central

    Hu, Zhiliang; Luo, Zhenwu; Wan, Zhuang; Wu, Hao; Li, Wei; Zhang, Tong; Jiang, Wei

    2015-01-01

    Memory B-cell depletion, hyperimmunoglobulinemia, and impaired vaccine responses are the hallmark of B cell perturbations inhuman immunodeficiency virus (HIV) disease. Although B cells are not the targets for HIV infection, there is evidence for B cell, especially memory B cell dysfunction in HIV disease mediated by other cells or HIV itself. This review will focus on HIV-associated phenotypic and functional alterations in memory B cells. Additionally, we will discuss the mechanism underlying these perturbations and the effect of anti-retroviral therapy (ART) on these perturbations. PMID:25887082

  3. Perturbing macroscopic magnetohydrodynamic stability for toroidal plasmas

    NASA Astrophysics Data System (ADS)

    Comer, Kathryn J.

    We have introduced a new perturbative technique to rapidly explore the dependence of long wavelength ideal magnetohydrodynamic (MHD) instabilities on equilibrium profiles, shaping properties, and wall parameters. Traditionally, these relations are studied with numerical parameter scans using computationally intensive stability codes. Our perturbative technique first finds the equilibrium and stability using traditional methods. Subsequent small changes in the original equilibrium parameters change the stability. We quickly find the new stability with an expansion of the energy principle, rather than with another run of the stability codes. We first semi-analytically apply the technique to the screw pinch after eliminating compressional Alfven wave effects. The screw pinch results validate the approach, but also indicate that allowable perturbations to equilibria with certain features may be restricted. Next, we extend the approach to toroidal geometry using experimental equilibria and a simple constructed equilibrium, with the ideal MHD stability code GATO. Stability properties are successfully predicted from perturbed toroidal equilibria when only the vacuum beyond the plasma is perturbed (through wall parameter variations), rather than the plasma itself. Small plasma equilibrium perturbations to both experimental and simple equilibria result in very large errors to the predicted stability, and valid results are found only over a narrow range of most perturbations. Despite the large errors produced when changing plasma parameters, the wall perturbations revealed two useful applications of this technique. Because the calculations are non-iterative matrix multiplications, the convergence issues that can disrupt a full MHD stability code are absent. Marginal stability, therefore, is much easier to find with the perturbative technique. Also, the perturbed results can be input as the initial guess for the eigenvalue for a full stability code, and improve subsequent

  4. A Model for Gaussian Perturbations of Graphene

    NASA Astrophysics Data System (ADS)

    Dodson, C. T. J.

    2015-11-01

    Graphene consists nominally of a regular planar hexagonal carbon lattice monolayer. However, its structure experiences perturbations in the presence of external influences, whether from substrate properties, thermal or electromagnetic fields, or ambient fluid movement. Here we give an information geometric model to represent the state space of perturbations as a Riemannian pseudosphere with scalar curvature close to -1/2. This would allow the representation of a trajectory of states under a given ambient or process change, so opening the possibility for geometrically formulated dynamical models to link structural perturbations to the physics.

  5. Acoustic Eigenvalues of a Quasispherical Resonator: Second Order Shape Perturbation Theory for Arbitrary Modes

    PubMed Central

    Mehl, James B.

    2007-01-01

    The boundary-shape formalism of Morse and Ingard is applied to the acoustic modes of a deformed spherical resonator (quasisphere) with rigid boundaries. For boundary shapes described by r = a [1 − ε ℱ(θ, ϕ)], where ε is a small scale parameter and ℱ is a function of order unity, the frequency perturbation is calculated to order ε2. The formal results apply to acoustic modes whose angular dependence is designated by the indices ℓ and m. Specific examples are worked out for the radial (ℓ = 0) and triplet (ℓ = 1) modes, for prolate and oblate spheroids, and for triaxial ellipsoids. The exact eigenvalues for the spheroids, and eigenvalue determined with finite-element calculations, are shown to agree with perturbation theory through terms of order ε2. This work is an extension of the author’s previous papers on the acoustic eigenfrequencies of deformed spherical resonators, which were limited to the second-order perturbation for radial modes [J. Acoust. Soc. Am. 71, 1109-1113 (1982)] and the first order-perturbation for arbitrary modes [J. Acoust. Soc. Am. 79, 278–285 (1986)]. PMID:27110463

  6. Design of a wearable perturbator for human knee impedance estimation during gait.

    PubMed

    Tucker, Michael R; Moser, Adrian; Lambercy, Olivier; Sulzer, James; Gassert, Roger

    2013-06-01

    Mechanical impedance modulation is the key to natural, stable and efficient human locomotion. An improved understanding of this mechanism is necessary for the development of the next generation of intelligent prosthetic and orthotic devices. This paper documents the design methodologies that were employed to realize a knee perturbator that can experimentally estimate human knee impedance during gait through the application of angular velocity perturbations. The proposed experiment requires a light, transparent, wearable, and remotely actuated device that closely follows the movement of the biological joint. A genetic algorithm was used to design a polycentric hinge whose instantaneous center of rotation is optimized to be kinematically compatible with the human knee. A wafer disc clutch was designed to switch between a high transparency passive mode and a high impedance actuated mode. A remote actuation and transmission scheme was designed to enable high power output perturbations while minimizing the device's mass. Position and torque sensors were designed for device control and to provide data for post-processing and joint impedance estimation. Pending the fabrication and mechanical testing of the device, we expect this knee perturbator to be a valuable tool for experimental investigation of locomotive joint impedance modulation. PMID:24187191

  7. Perturbations of black p-branes

    SciTech Connect

    Abdalla, Elcio; Fernandez Piedra, Owen Pavel; Oliveira, Jeferson de; Molina, C.

    2010-03-15

    We consider black p-brane solutions of the low-energy string action, computing scalar perturbations. Using standard methods, we derive the wave equations obeyed by the perturbations and treat them analytically and numerically. We have found that tensorial perturbations obtained via a gauge-invariant formalism leads to the same results as scalar perturbations. No instability has been found. Asymptotically, these solutions typically reduce to a AdS{sub (p+2)}xS{sup (8-p)} space which, in the framework of Maldacena's conjecture, can be regarded as a gravitational dual to a conformal field theory defined in a (p+1)-dimensional flat space-time. The results presented open the possibility of a better understanding the AdS/CFT correspondence, as originally formulated in terms of the relation among brane structures and gauge theories.

  8. The Perturbational MO Method for Saturated Systems.

    ERIC Educational Resources Information Center

    Herndon, William C.

    1979-01-01

    Summarizes a theoretical approach using nonbonding MO's and perturbation theory to correlate properties of saturated hydrocarbons. Discussion is limited to correctly predicted using this method. Suggests calculations can be carried out quickly in organic chemistry. (Author/SA)

  9. Controlling roll perturbations in fruit flies.

    PubMed

    Beatus, Tsevi; Guckenheimer, John M; Cohen, Itai

    2015-04-01

    Owing to aerodynamic instabilities, stable flapping flight requires ever-present fast corrective actions. Here, we investigate how flies control perturbations along their body roll angle, which is unstable and their most sensitive degree of freedom. We glue a magnet to each fly and apply a short magnetic pulse that rolls it in mid-air. Fast video shows flies correct perturbations up to 100° within 30 ± 7 ms by applying a stroke-amplitude asymmetry that is well described by a linear proportional-integral controller. For more aggressive perturbations, we show evidence for nonlinear and hierarchical control mechanisms. Flies respond to roll perturbations within 5 ms, making this correction reflex one of the fastest in the animal kingdom. PMID:25762650

  10. SHARP ENTRYWISE PERTURBATION BOUNDS FOR MARKOV CHAINS

    PubMed Central

    THIEDE, ERIK; VAN KOTEN, BRIAN; WEARE, JONATHAN

    2015-01-01

    For many Markov chains of practical interest, the invariant distribution is extremely sensitive to perturbations of some entries of the transition matrix, but insensitive to others; we give an example of such a chain, motivated by a problem in computational statistical physics. We have derived perturbation bounds on the relative error of the invariant distribution that reveal these variations in sensitivity. Our bounds are sharp, we do not impose any structural assumptions on the transition matrix or on the perturbation, and computing the bounds has the same complexity as computing the invariant distribution or computing other bounds in the literature. Moreover, our bounds have a simple interpretation in terms of hitting times, which can be used to draw intuitive but rigorous conclusions about the sensitivity of a chain to various types of perturbations. PMID:26491218

  11. Cosmological perturbations in mimetic Horndeski gravity

    NASA Astrophysics Data System (ADS)

    Arroja, Frederico; Bartolo, Nicola; Karmakar, Purnendu; Matarrese, Sabino

    2016-04-01

    We study linear scalar perturbations around a flat FLRW background in mimetic Horndeski gravity. In the absence of matter, we show that the Newtonian potential satisfies a second-order differential equation with no spatial derivatives. This implies that the sound speed for scalar perturbations is exactly zero on this background. We also show that in mimetic G3 theories the sound speed is equally zero. We obtain the equation of motion for the comoving curvature perturbation (first order differential equation) and solve it to find that the comoving curvature perturbation is constant on all scales in mimetic Horndeski gravity. We find solutions for the Newtonian potential evolution equation in two simple models. Finally we show that the sound speed is zero on all backgrounds and therefore the system does not have any wave-like scalar degrees of freedom.

  12. Casimir energy for perturbed surfaces of revolution

    NASA Astrophysics Data System (ADS)

    Morales-Almazan, Pedro

    2016-03-01

    In this paper, we explore the zeta function arising from a small perturbation on a surface of revolution and the effect of this on the functional determinant and on the change of the Casimir energy associated with the surface.

  13. Controlling roll perturbations in fruit flies

    PubMed Central

    Beatus, Tsevi; Guckenheimer, John M.; Cohen, Itai

    2015-01-01

    Owing to aerodynamic instabilities, stable flapping flight requires ever-present fast corrective actions. Here, we investigate how flies control perturbations along their body roll angle, which is unstable and their most sensitive degree of freedom. We glue a magnet to each fly and apply a short magnetic pulse that rolls it in mid-air. Fast video shows flies correct perturbations up to 100° within 30 ± 7 ms by applying a stroke-amplitude asymmetry that is well described by a linear proportional–integral controller. For more aggressive perturbations, we show evidence for nonlinear and hierarchical control mechanisms. Flies respond to roll perturbations within 5 ms, making this correction reflex one of the fastest in the animal kingdom. PMID:25762650

  14. Angular Momentum and Galaxy Formation Revisited

    NASA Astrophysics Data System (ADS)

    Romanowsky, Aaron J.; Fall, S. Michael

    2012-12-01

    Motivated by a new wave of kinematical tracers in the outer regions of early-type galaxies (ellipticals and lenticulars), we re-examine the role of angular momentum in galaxies of all types. We present new methods for quantifying the specific angular momentum j, focusing mainly on the more challenging case of early-type galaxies, in order to derive firm empirical relations between stellar j sstarf and mass M sstarf (thus extending earlier work by Fall). We carry out detailed analyses of eight galaxies with kinematical data extending as far out as 10 effective radii, and find that data at two effective radii are generally sufficient to estimate total j sstarf reliably. Our results contravene suggestions that ellipticals could harbor large reservoirs of hidden j sstarf in their outer regions owing to angular momentum transport in major mergers. We then carry out a comprehensive analysis of extended kinematic data from the literature for a sample of ~100 nearby bright galaxies of all types, placing them on a diagram of j sstarf versus M sstarf. The ellipticals and spirals form two parallel j sstarf-M sstarf tracks, with log-slopes of ~0.6, which for the spirals are closely related to the Tully-Fisher relation, but for the ellipticals derives from a remarkable conspiracy between masses, sizes, and rotation velocities. The ellipticals contain less angular momentum on average than spirals of equal mass, with the quantitative disparity depending on the adopted K-band stellar mass-to-light ratios of the galaxies: it is a factor of ~3-4 if mass-to-light ratio variations are neglected for simplicity, and ~7 if they are included. We decompose the spirals into disks and bulges and find that these subcomponents follow j sstarf-M sstarf trends similar to the overall ones for spirals and ellipticals. The lenticulars have an intermediate trend, and we propose that the morphological types of galaxies reflect disk and bulge subcomponents that follow separate, fundamental j sstarf

  15. ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED

    SciTech Connect

    Romanowsky, Aaron J.; Fall, S. Michael

    2012-12-15

    Motivated by a new wave of kinematical tracers in the outer regions of early-type galaxies (ellipticals and lenticulars), we re-examine the role of angular momentum in galaxies of all types. We present new methods for quantifying the specific angular momentum j, focusing mainly on the more challenging case of early-type galaxies, in order to derive firm empirical relations between stellar j{sub *} and mass M{sub *} (thus extending earlier work by Fall). We carry out detailed analyses of eight galaxies with kinematical data extending as far out as 10 effective radii, and find that data at two effective radii are generally sufficient to estimate total j{sub *} reliably. Our results contravene suggestions that ellipticals could harbor large reservoirs of hidden j{sub *} in their outer regions owing to angular momentum transport in major mergers. We then carry out a comprehensive analysis of extended kinematic data from the literature for a sample of {approx}100 nearby bright galaxies of all types, placing them on a diagram of j{sub *} versus M{sub *}. The ellipticals and spirals form two parallel j{sub *}-M{sub *} tracks, with log-slopes of {approx}0.6, which for the spirals are closely related to the Tully-Fisher relation, but for the ellipticals derives from a remarkable conspiracy between masses, sizes, and rotation velocities. The ellipticals contain less angular momentum on average than spirals of equal mass, with the quantitative disparity depending on the adopted K-band stellar mass-to-light ratios of the galaxies: it is a factor of {approx}3-4 if mass-to-light ratio variations are neglected for simplicity, and {approx}7 if they are included. We decompose the spirals into disks and bulges and find that these subcomponents follow j{sub *}-M{sub *} trends similar to the overall ones for spirals and ellipticals. The lenticulars have an intermediate trend, and we propose that the morphological types of galaxies reflect disk and bulge subcomponents that follow

  16. On perturbations of a quintom bounce

    SciTech Connect

    Cai Yifu; Qiu Taotao; Zhang Xinmin; Brandenberger, Robert; Piao Yunsong E-mail: qiutt@mail.ihep.ac.cn E-mail: yspiao@gucas.ac.cn

    2008-03-15

    A quintom universe with an equation of state crossing the cosmological constant boundary can provide a bouncing solution dubbed the quintom bounce and thus resolve the big bang singularity. In this paper, we investigate the cosmological perturbations of the quintom bounce both analytically and numerically. We find that the fluctuations in the dominant mode in the post-bounce expanding phase couple to the growing mode of the perturbations in the pre-bounce contracting phase.

  17. Non Perturbative Aspects of Field Theory

    SciTech Connect

    Bashir, A.

    2009-04-20

    For any quantum field theory (QFT), there exists a set of Schwinger-Dyson equations (SDE) for all its Green functions. However, it is not always straight forward to extract quantitatively exact physical information from this set of equations, especially in the non perturbative regime. The situation becomes increasingly complex with growing number of external legs. I give a qualitative account of the hunt for the non perturbative Green functions in gauge theories.

  18. Asymmetric angular-selective thermal emission

    NASA Astrophysics Data System (ADS)

    Sakr, Enas; Dhaka, Shailja; Bermel, Peter

    2016-03-01

    Thermal emission from blackbodies and flat metallic surfaces is non-directional, following the Lambert cosine law. However, highly directional thermal emission could be useful for improving the efficiency of a broad range of different applications, including thermophotovoltaics, spectroscopy and infra-red light sources. This is particularly true if strong symmetry breaking could ensure emission only in one particular direction. In this work, we investigate the possibility of tailoring asymmetric thermal emission using structured metasurfaces. These are built from surface grating unit elements that support asymmetric localization of thermal surface plasmon polaritons. The angular dependence of emissivity is studied using a rigorous coupled wave analysis (RCWA) of absorption, plus Kirchhoff's law of thermal radiation. It is further validated using a direct thermal simulation of emission originating from the metal. Asymmetric angular selectivity with near-blackbody emissivity is demonstrated for different shallow blazed grating structures. We study the effect of changing the period, depth and shape of the grating unit cell on the direction angle, angular spread, and magnitude of coupled radiation mode. In particular, a periodic sawtooth structure with a period of 1.5λ and angle of 8°was shown to create significant asymmetry of at least a factor of 3. Such structures can be considered arbitrary directional sources that can be carefully patterned on metallic surfaces to yield thermal lenses with designed focal lengths, targeted to particular concentration ratios. The benefit of this approach is that it can enhance the view factor between thermal emitters and receivers, without restricting the area ratio or separation distance.

  19. Lunar influence on equatorial atmospheric angular momentum

    NASA Astrophysics Data System (ADS)

    Bizouard, Christian; Zotov, Leonid; Sidorenkov, Nikolay

    2014-11-01

    This study investigates the relationship between the equatorial atmospheric angular momentum oscillation in the nonrotating frame and the quasi-diurnal lunar tidal potential. Between 2 and 30 days, the corresponding equatorial component, called Celestial Atmospheric Angular Momentum (CEAM), is mostly constituted of prograde circular motions, especially of a harmonic at 13.66 days, a sidelobe at 13.63 days, and of a weekly broadband variation. A simple equilibrium tide model explains the 13.66 day pressure term as a result of the O1 lunar tide. The powerful episodic fluctuations between 5 and 8 days possibly reflect an atmospheric normal mode excited by the tidal waves Q1 (6.86 days) and σ1 (7.095 days). The lunar tidal influence on the spectral band from 2 to 30 days is confirmed by two specific features, not occurring for seasonal band dominated by the solar thermal effect. First, Northern and Southern Hemispheres contribute equally and synchronously to the CEAM wind term. Second, the pressure and wind terms are proportional, which follows from angular momentum budget considerations where the topographic and friction torques on the solid Earth are much smaller than the one resulting from the equatorial bulge. Such a configuration is expected for the case of tidally induced circulation, where the surface pressure variation is tesseral and cannot contribute to the topographic torque, and tidal winds blow only at high altitudes. The likely effects of the lunar-driven atmospheric circulation on Earth's nutation are estimated and discussed in light of the present-day capabilities of space geodetic techniques.

  20. Thermally unstable perturbations in stratified conducting atmospheres

    NASA Astrophysics Data System (ADS)

    Reale, Fabio; Serio, Salvatore; Peres, Giovanni

    1994-10-01

    We investigate the thermal stability of isobaric perturbations in a stratified isothermal background atmosphere with solar abundances, as resulting from the competition of optically thin plasma radiative cooling and of heating conducted from the surrounding atmosphere. We have analyzed the threshold line between stable and unstable perturbations, in the plane of the two important control parameters: the initial size of the perturbation and the temperature of the unperturbed medium; this line changes with the pressure of the unperturbed atmosphere. We have extended the results of linear perturbation analysis by means of numerical calculations of the evolution of spherical isobaric perturbations, using a two-dimensional hydrodynamic code including Spitzer heat conduction. We explore a wide range of the parameters appropriate to the solar and stellar upper atmospheres: the background uniform temperature is between 105 K and 107 K, the initial pressure betweeen 0.1 and 10 dyn/sq cm, and the perturbation size between 105 and 1010 cm. The numerical results are in substantial agreement with the linear analysis. We discuss possible implications of our results also in terms of observable effects, especially concerning plasma downflows, and propose thermal instability as a possible candidate to explain the observed redshifts in solar and stellar transition region lines.

  1. Angular distributions of neutron-nucleus collisions

    SciTech Connect

    Mukhopadhyay, Tapan; Lahiri, Joydev; Basu, D. N.

    2011-06-15

    We derive the total and the differential cross sections with respect to angle for neutron-induced reactions from an analytical model having a simple functional form to demonstrate the quantitative agreement with the measured cross sections. The energy dependence of the neutron-nucleus interaction cross sections are estimated successfully for energies ranging from 5 to 600 MeV. In this work, the effect of the imaginary part of the nuclear potential is treated more appropriately compared to our earlier work. The angular distributions for neutron scattering also agree reasonably well with the experimental data at forward angles.

  2. Linear and angular retroreflecting interferometric alignment target

    DOEpatents

    Maxey, L. Curtis

    2001-01-01

    The present invention provides a method and apparatus for measuring both the linear displacement and angular displacement of an object using a linear interferometer system and an optical target comprising a lens, a reflective surface and a retroreflector. The lens, reflecting surface and retroreflector are specifically aligned and fixed in optical connection with one another, creating a single optical target which moves as a unit that provides multi-axis displacement information for the object with which it is associated. This displacement information is useful in many applications including machine tool control systems and laser tracker systems, among others.

  3. Angular correlation studies in noble gases

    NASA Technical Reports Server (NTRS)

    Coleman, P. G.

    1990-01-01

    There has been a recent revival of interest in the measurement of angular correlation of annihilation photons from the decay of positrons and positronium in gases. This revival has been stimulated by the possibility offered by the technique to shed new light on the apparently low positronium formation fraction in the heavier noble gases and to provide information on positronium quenching processes in gases such as oxygen. There is also the potential for learning about positronium slowing down in gases. This review focuses on experimental noble gas work and considers what new information has been, and may be, gained from these studies.

  4. Convert Acoustic Resonances to Orbital Angular Momentum

    NASA Astrophysics Data System (ADS)

    Jiang, Xue; Li, Yong; Liang, Bin; Cheng, Jian-chun; Zhang, Likun

    2016-07-01

    We use acoustic resonances in a planar layer of half-wavelength thickness to twist wave vectors of an in-coming plane wave into a spiral phase dislocation of an outgoing vortex beam with orbital angular momentum (OAM). The mechanism is numerically and experimentally demonstrated by producing an airborne Bessel-like vortex beam. Our acoustic resonance-based OAM production differs from existing means for OAM production by enormous phased spiral sources or by elaborate spiral profiles. Our study can advance the capability of generating phase dislocated wave fields for further applications of acoustic OAM.

  5. Convert Acoustic Resonances to Orbital Angular Momentum.

    PubMed

    Jiang, Xue; Li, Yong; Liang, Bin; Cheng, Jian-Chun; Zhang, Likun

    2016-07-15

    We use acoustic resonances in a planar layer of half-wavelength thickness to twist wave vectors of an in-coming plane wave into a spiral phase dislocation of an outgoing vortex beam with orbital angular momentum (OAM). The mechanism is numerically and experimentally demonstrated by producing an airborne Bessel-like vortex beam. Our acoustic resonance-based OAM production differs from existing means for OAM production by enormous phased spiral sources or by elaborate spiral profiles. Our study can advance the capability of generating phase dislocated wave fields for further applications of acoustic OAM. PMID:27472113

  6. Near horizon extremal geometry perturbations: dynamical field perturbations vs. parametric variations

    NASA Astrophysics Data System (ADS)

    Hajian, K.; Seraj, A.; Sheikh-Jabbari, M. M.

    2014-10-01

    In [1] we formulated and derived the three universal laws governing Near Horizon Extremal Geometries (NHEG). In this work we focus on the Entropy Perturbation Law (EPL) which, similarly to the first law of black hole thermodynamics, relates perturbations of the charges labeling perturbations around a given NHEG to the corresponding entropy perturbation. We show that field perturbations governed by the linearized equations of motion and symmetry conditions which we carefully specify, satisfy the EPL. We also show that these perturbations are limited to those coming from difference of two NHEG solutions (i.e. variations on the NHEG solution parameter space). Our analysis and discussions shed light on the "no-dynamics" statements of [2, 3].

  7. Perturbation amplitude affects linearly estimated neuromechanical wrist joint properties.

    PubMed

    Klomp, Asbjorn; de Groot, Jurriaan H; de Vlugt, Erwin; Meskers, Carel G M; Arendzen, J Hans; van der Helm, Frans C T

    2014-04-01

    System identification techniques have been used to separate intrinsic muscular and reflexive contributions to joint impedance, which is an essential step in the proper choice of patient specific treatment. These techniques are, however, only well developed for linear systems. Assuming linearity prescribes the neuromuscular system to be perturbed only around predefined operating points. In this study, we test the validity of a commonly used linear model by analyzing the effects of flexion-extension displacement amplitude (2(°), 4(°), and 8(°)) on damping, stiffness, and reflex gain of the wrist joint, at different background torque levels (0, 1, and 2 N · m). With displacement amplitude, intrinsic damping increased, while intrinsic stiffness and reflex gains decreased. These changes were dependent on the level of wrist torque. The dependency of the neuromuscular system properties on even small variations in angular displacement is evident and has to be accounted for when comparing different studies and clinical interpretations using linear identification techniques. Knowledge of the behavior of the neuromuscular system around operating points is an essential step toward the development of nonlinear models that allow for discrimination between patients and controls in a larger range of loading conditions. PMID:24216632

  8. Axions and the galactic angular momentum distribution

    NASA Astrophysics Data System (ADS)

    Banik, N.; Sikivie, P.

    2013-12-01

    We analyze the behavior of axion dark matter before it falls into a galactic gravitational potential well. The axions thermalize sufficiently fast by gravitational self-interactions that almost all go to their lowest-energy state consistent with the total angular momentum acquired from tidal torquing. That state is a state of rigid rotation on the turnaround sphere. It predicts the occurrence and detailed properties of the caustic rings of dark matter for which observational evidence had been found earlier. We show that the vortices in the axion Bose-Einstein condensate (BEC) are attractive, unlike those in superfluid He4 and dilute gases. We expect that a large fraction of the vortices in the axion BEC join into a single big vortex along the rotation axis of the galaxy. The resulting enhancement of caustic rings explains the typical size of the rises in the Milky Way rotation curve attributed to caustic rings. We show that baryons and ordinary cold dark matter particles are entrained by the axion BEC and acquire the same velocity distribution. The resulting baryonic angular momentum distribution gives a good qualitative fit to the distributions observed in dwarf galaxies. We give estimates of the minimum fraction of dark matter that is composed of axions.

  9. Understanding GRETINA using angular correlation method

    NASA Astrophysics Data System (ADS)

    Austin, Madeline

    2015-10-01

    The ability to trace the path of gamma rays through germanium is not only necessary for taking full advantage of GRETINA but also a promising possibility for homeland security defense against nuclear threats. This research tested the current tracking algorithm using the angular correlation method by comparing results from raw and tracked data to the theoretical model for Co-60. It was found that the current tracking method is unsuccessful in reproducing angular correlation. Variations to the tracking algorithm were made in the FM value, tracking angle, number of angles of separation observed, and window of coincidence in attempt to improve correlation results. From these variations it was observed that having a larger FM improved results, reducing the number of observational angles worsened correlation, and that overall larger tracking angles improved with larger windows of coincidence and vice-verse. Future research would be to refine the angle of measurement for raw data and to explore the possibility of an energy dependence by testing other elements. This work is supported by the United States Department of Energy, Office of Science, under Contract Number DE-AC02-06CH11357

  10. Practical scaling law for photoelectron angular distributions

    SciTech Connect

    Guo Dongsheng; Zhang Jingtao; Xu Zhizhan; Li Xiaofeng; Fu Panming; Freeman, R.R.

    2003-10-01

    A practical scaling law that predicts photoelectron angular distributions (PADs) is derived using angular distribution formulas which explicitly contain spontaneous emission. The scaling law is used to analyze recent PAD measurements in above-threshold ionization, and to predict results of future experiments. Our theoretical and numerical studies show that, in the non-relativistic regime and long-wavelength approximation, the shapes of PADs are determined by only three dimensionless numbers: (1) u{sub p}{identical_to}U{sub p}/({Dirac_h}/2{pi}){omega}, the ponderomotive number (ponderomotive energy in units of laser photon energy); (2) {epsilon}{sub b}{identical_to}E{sub b}/({Dirac_h}/2{pi}){omega}, the binding number (atomic binding energy in units of the laser photon energy); (3) j, the absorbed-photon number. The scaling law is shown to be useful in predictions of results from strong-field Kapitza-Dirac effect measurements; specifically, the application of this scaling law to recently reported Kapitza-Dirac diffraction is discussed. Possible experimental tests to verify the scaling law are suggested.

  11. Axial-conductances angular filter investigation

    NASA Astrophysics Data System (ADS)

    Hannan, P. W.; Pedersen, J. F.

    1984-04-01

    This report describes the concept, analysis, design, construction, and tests of an angular filter using an axial-conductance medium. The filter provides rejection that increases with incidence angle in the E plane. It is essentially invisible at broadside incidence, does not have critical tolerances on dimensions or materials, and operates over a wide frequency band. Analysis of an ideal homogeneous axial-conductance medium shows that the optimum value for the axial loss tangent is unity. With this value, the homogeneous medium provides approximately 8 dB of absorptive rejection per wavelength of filter thickness at a 45 E-plane incidence angle. Analysis of a practical inhomogeneous axial-conductance medium shows that some loss is introduced at broadside incidence, and that two types of waves can exist in the medium when only one wave is incident at an oblique angle. When the practical medium has dimensions that are properly chosen, its broadside loss can be negligible, and its rejection versus incidence angle can approximate that of the ideal medium. Tests of inhomogeneous samples in simulator wave guide confirm these analytical results. A screen printing method for depositing thick-film resistive ink on thin dielectric sheets has been investigated. With this method a 5x5 foot angular filter, designed for operation at 10 GHz, has been constructed containing over 70,000 axial-conductance elements.

  12. Perturbations of the Robertson-Walker space

    NASA Astrophysics Data System (ADS)

    Hwang, Jai Chan

    This dissertation contains three parts consisting of thirteen chapters. Each chapter is self-contained, and can be read independently. In chapter 1, we have presented a complete set of cosmological perturbation equations using the covariant equations. We also present an explicit solution for the evolution of large scale cosmological density perturbations assuming a perfect fluid. In chapter 2, two independent gauge-invariant variables are derived which are continuous at any transition where there is a discontinuous change in pressure. In chapter 3, we present a Newtonian counterpart to the general relativistic covariant approach to cosmological perturbations. In chapter 4, we present a simple way of deriving cosmological perturbation equations in generalized gravity theories which accounts for metric perturbations in gauge-invariant way. We apply this approach to the f(phi,R)-omega(phi)phi, cphi;c Lagrangian. In chapter 5, we have derived second order differential equations for cosmological perturbations in a Robertson-Walker space, for each of the following gravity theories: f(R) gravity, generalized scalar-tensor gravity, gravity with non-minimally coupled scalar field, and induced gravity. Asymptotic solutions are derived for the large and small scale limits. In chapter 6, classical evolution of density perturbations in the large scale limit is clarified in the generalized gravity theories. In chapter 7, we apply our method to a theory with the Lagrangian L approximately f(R) + gamma RR;c;c. In chapter 8, T(M)ab;b equals 0 is shown in a general ground. In chapter 9, the origin of the Friedmann-like behavior of the perturbed model in the large scale limit is clarified in a comoving gauge. Thus, when the imperfect fluid contributions are negligible, the large scale perturbations in a nearly flat background evolve like separate Friedmann models. In chapter 10, we generalize the perturbation equations applicable to a class of generalized gravity theories with multi

  13. Non-hard sphere thermodynamic perturbation theory

    NASA Astrophysics Data System (ADS)

    Zhou, Shiqi

    2011-08-01

    A non-hard sphere (HS) perturbation scheme, recently advanced by the present author, is elaborated for several technical matters, which are key mathematical details for implementation of the non-HS perturbation scheme in a coupling parameter expansion (CPE) thermodynamic perturbation framework. NVT-Monte Carlo simulation is carried out for a generalized Lennard-Jones (LJ) 2n-n potential to obtain routine thermodynamic quantities such as excess internal energy, pressure, excess chemical potential, excess Helmholtz free energy, and excess constant volume heat capacity. Then, these new simulation data, and available simulation data in literatures about a hard core attractive Yukawa fluid and a Sutherland fluid, are used to test the non-HS CPE 3rd-order thermodynamic perturbation theory (TPT) and give a comparison between the non-HS CPE 3rd-order TPT and other theoretical approaches. It is indicated that the non-HS CPE 3rd-order TPT is superior to other traditional TPT such as van der Waals/HS (vdW/HS), perturbation theory 2 (PT2)/HS, and vdW/Yukawa (vdW/Y) theory or analytical equation of state such as mean spherical approximation (MSA)-equation of state and is at least comparable to several currently the most accurate Ornstein-Zernike integral equation theories. It is discovered that three technical issues, i.e., opening up new bridge function approximation for the reference potential, choosing proper reference potential, and/or using proper thermodynamic route for calculation of fex - ref, chiefly decide the quality of the non-HS CPE TPT. Considering that the non-HS perturbation scheme applies for a wide variety of model fluids, and its implementation in the CPE thermodynamic perturbation framework is amenable to high-order truncation, the non-HS CPE 3rd-order or higher order TPT will be more promising once the above-mentioned three technological advances are established.

  14. Time differential perturbed angular correlation of 111In-EDTA linked to the single free cysteine of bovine serum albumin.

    PubMed

    Ceolín, M; Martínez, J A; Ermácora, M R

    1997-09-25

    By means of a facile chemical modification of the bovine serum albumin molecule, it was possible to measure its hydrodynamic radius with high accuracy (approximately 3%) using the TDPAC technique. The new approach presented here allows a wide use of the TDPAC technique to perform high precision studies of backbone dynamics of almost any protein. PMID:9350519

  15. Use of Earth’s Magnetic Field for Mitigating Gyroscope Errors Regardless of Magnetic Perturbation

    PubMed Central

    Afzal, Muhammad Haris; Renaudin, Valérie; Lachapelle, Gérard

    2011-01-01

    Most portable systems like smart-phones are equipped with low cost consumer grade sensors, making them useful as Pedestrian Navigation Systems (PNS). Measurements of these sensors are severely contaminated by errors caused due to instrumentation and environmental issues rendering the unaided navigation solution with these sensors of limited use. The overall navigation error budget associated with pedestrian navigation can be categorized into position/displacement errors and attitude/orientation errors. Most of the research is conducted for tackling and reducing the displacement errors, which either utilize Pedestrian Dead Reckoning (PDR) or special constraints like Zero velocity UPdaTes (ZUPT) and Zero Angular Rate Updates (ZARU). This article targets the orientation/attitude errors encountered in pedestrian navigation and develops a novel sensor fusion technique to utilize the Earth’s magnetic field, even perturbed, for attitude and rate gyroscope error estimation in pedestrian navigation environments where it is assumed that Global Navigation Satellite System (GNSS) navigation is denied. As the Earth’s magnetic field undergoes severe degradations in pedestrian navigation environments, a novel Quasi-Static magnetic Field (QSF) based attitude and angular rate error estimation technique is developed to effectively use magnetic measurements in highly perturbed environments. The QSF scheme is then used for generating the desired measurements for the proposed Extended Kalman Filter (EKF) based attitude estimator. Results indicate that the QSF measurements are capable of effectively estimating attitude and gyroscope errors, reducing the overall navigation error budget by over 80% in urban canyon environment. PMID:22247672

  16. Search for quark compositeness in dijet angular distributions from pp collisions at sqrt(s) = 7 TeV

    SciTech Connect

    Chatrchyan, Serguei; et al.

    2012-05-01

    A search for quark compositeness using dijet angular distributions from pp collisions at sqrt(s) = 7 TeV is presented. The search has been carried out using a data sample corresponding to an integrated luminosity of 2.2 inverse femtobarns, recorded by the CMS experiment at the LHC. Normalized dijet angular distributions have been measured for dijet invariant masses from 0.4 TeV to above 3 TeV and compared with a variety of contact interaction models, including those which take into account the effects of next-to-leading-order QCD corrections. The data are found to be in agreement with the predictions of perturbative QCD, and lower limits are obtained on the contact interaction scale, ranging from 7.5 up to 14.5 TeV at 95% confidence level.

  17. Mode coupling of Schwarzschild perturbations: Ringdown frequencies

    SciTech Connect

    Pazos, Enrique; Brizuela, David; Martin-Garcia, Jose M.; Tiglio, Manuel

    2010-11-15

    Within linearized perturbation theory, black holes decay to their final stationary state through the well-known spectrum of quasinormal modes. Here we numerically study whether nonlinearities change this picture. For that purpose we study the ringdown frequencies of gauge-invariant second-order gravitational perturbations induced by self-coupling of linearized perturbations of Schwarzschild black holes. We do so through high-accuracy simulations in the time domain of first and second-order Regge-Wheeler-Zerilli type equations, for a variety of initial data sets. We consider first-order even-parity (l=2, m={+-}2) perturbations and odd-parity (l=2, m=0) ones, and all the multipoles that they generate through self-coupling. For all of them and all the initial data sets considered we find that--in contrast to previous predictions in the literature--the numerical decay frequencies of second-order perturbations are the same ones of linearized theory, and we explain the observed behavior. This would indicate, in particular, that when modeling or searching for ringdown gravitational waves, appropriately including the standard quasinormal modes already takes into account nonlinear effects.

  18. Cohomology Methods in Causal Perturbation Theory

    NASA Astrophysics Data System (ADS)

    Grigore, D. R.

    2010-01-01

    Various problems in perturbation theory of (quantum) gauge models can be rephrased in the language of cohomology theory. This was already noticed in the functional formulation of perturbative gauge theories. Causal perturbation theory is a fully quantum approach: is works only with the chronological products which are defined as operator-valued distributions in the Fock space of the model. The use of causal perturbation theory leads to similar cohomology problems; the main difference with respect to the functional methods comes from the fact that the gauge transformation of the causal approach is, essentially, the linear part of the non-linear BRST transformation. Using these methods it is possible to give a nice determination of the interaction Lagrangians for gauge models (Yang-Mills and gravitation in the linear approximation); one obtains with this method the unicity of the interaction Lagrangian up to trivial terms. The case of quantum gravity is highly non-trivial and can be generalized with this method to the massive graviton case. Going to higher orders of perturbation theory one finds quantum anomalies. Again the cohomological methods can be used to determine the generic form of these anomalies. Finally, one can investigate the arbitrariness of the chronological products in higher orders and reduce this problem to cohomology methods also.

  19. Supersymmetry restoration in superstring perturbation theory

    NASA Astrophysics Data System (ADS)

    Sen, Ashoke

    2015-12-01

    Superstring perturbation theory based on the 1PI effective theory approach has been useful for addressing the problem of mass renormalization and vacuum shift. We derive Ward identities associated with space-time supersymmetry transformation in this approach. This leads to a proof of the equality of renormalized masses of bosons and fermions and identities relating fermionic amplitudes to bosonic amplitudes after taking into account the effect of mass renormalization. This also relates unbroken supersymmetry to a given order in perturbation theory to absence of tadpoles of massless scalars to higher order. The results are valid at the perturbative vacuum as well as in the shifted vacuum when the latter describes the correct ground state of the theory. We apply this to SO(32) heterotic string theory on Calabi-Yau 3-folds where a one loop Fayet-Iliopoulos term apparently breaks supersymmetry at one loop, but analysis of the low energy effective field theory indicates that there is a nearby vacuum where supersymmetry is restored. We explicitly prove that the perturbative amplitudes of this theory around the shifted vacuum indeed satisfy the Ward identities associated with unbroken supersymmetry. We also test the general arguments by explicitly verifying the equality of bosonic and fermionic masses at one loop order in the shifted vacuum, and the appearance of two loop dilaton tadpole in the perturbative vacuum where supersymmetry is expected to be broken.

  20. Cosmological perturbations in teleparallel Loop Quantum Cosmology

    NASA Astrophysics Data System (ADS)

    Haro, Jaime

    2013-11-01

    Cosmological perturbations in Loop Quantum Cosmology (LQC) are usually studied incorporating either holonomy corrections, where the Ashtekar connection is replaced by a suitable sinus function in order to have a well-defined quantum analogue, or inverse-volume corrections coming from the eigenvalues of the inverse-volume operator. In this paper we will develop an alternative approach to calculate cosmological perturbations in LQC based on the fact that, holonomy corrected LQC in the flat Friedmann-Lemaître-Robertson-Walker (FLRW) geometry could be also obtained as a particular case of teleparallel F(T) gravity (teleparallel LQC). The main idea of our approach is to mix the simple bounce provided by holonomy corrections in LQC with the non-singular perturbation equations given by F(T) gravity, in order to obtain a matter bounce scenario as a viable alternative to slow-roll inflation. In our study, we have obtained an scale invariant power spectrum of cosmological perturbations. However, the ratio of tensor to scalar perturbations is of order 1, which does not agree with the current observations. For this reason, we suggest a model where a transition from the matter domination to a quasi de Sitter phase is produced in order to enhance the scalar power spectrum.

  1. Local perturbations perturb—exponentially–locally

    SciTech Connect

    De Roeck, W. Schütz, M.

    2015-06-15

    We elaborate on the principle that for gapped quantum spin systems with local interaction, “local perturbations [in the Hamiltonian] perturb locally [the groundstate].” This principle was established by Bachmann et al. [Commun. Math. Phys. 309, 835–871 (2012)], relying on the “spectral flow technique” or “quasi-adiabatic continuation” [M. B. Hastings, Phys. Rev. B 69, 104431 (2004)] to obtain locality estimates with sub-exponential decay in the distance to the spatial support of the perturbation. We use ideas of Hamza et al. [J. Math. Phys. 50, 095213 (2009)] to obtain similarly a transformation between gapped eigenvectors and their perturbations that is local with exponential decay. This allows to improve locality bounds on the effect of perturbations on the low lying states in certain gapped models with a unique “bulk ground state” or “topological quantum order.” We also give some estimate on the exponential decay of correlations in models with impurities where some relevant correlations decay faster than one would naively infer from the global gap of the system, as one also expects in disordered systems with a localized groundstate.

  2. Cosmological perturbations on the phantom brane

    NASA Astrophysics Data System (ADS)

    Bag, Satadru; Viznyuk, Alexander; Shtanov, Yuri; Sahni, Varun

    2016-07-01

    We obtain a closed system of equations for scalar perturbations in a multi-component braneworld. Our braneworld possesses a phantom-like equation of state at late times, weff < ‑1, but no big-rip future singularity. In addition to matter and radiation, the braneworld possesses a new effective degree of freedom—the `Weyl fluid' or `dark radiation'. Setting initial conditions on super-Hubble spatial scales at the epoch of radiation domination, we evolve perturbations of radiation, pressureless matter and the Weyl fluid until the present epoch. We observe a gradual decrease in the amplitude of the Weyl-fluid perturbations after Hubble-radius crossing, which results in a negligible effect of the Weyl fluid on the evolution of matter perturbations on spatial scales relevant for structure formation. Consequently, the quasi-static approximation of Koyama and Maartens provides a good fit to the exact results during the matter-dominated epoch. We find that the late-time growth of density perturbations on the brane proceeds at a faster rate than in ΛCDM. Additionally, the gravitational potentials Φ and Ψ evolve differently on the brane than in ΛCDM, for which Φ = Ψ. On the brane, by contrast, the ratio Φ/Ψ exceeds unity during the late matter-dominated epoch (z lesssim 50). These features emerge as smoking gun tests of phantom brane cosmology and allow predictions of this scenario to be tested against observations of galaxy clustering and large-scale structure.

  3. Improved WKB analysis of cosmological perturbations

    SciTech Connect

    Casadio, Roberto; Luzzi, Mattia; Venturi, Giovanni; Finelli, Fabio

    2005-02-15

    Improved Wentzel-Kramers-Brillouin (WKB)-type approximations are presented in order to study cosmological perturbations beyond the lowest order. Our methods are based on functions which approximate the true perturbation modes over the complete range of the independent (Langer) variable, from subhorizon to superhorizon scales, and include the region near the turning point. We employ both a perturbative Green's function technique and an adiabatic (or semiclassical) expansion (for a linear turning point) in order to compute higher order corrections. Improved general expressions for the WKB scalar and tensor power spectra are derived for both techniques. We test our methods on the benchmark of power-law inflation, which allows comparison with exact expressions for the perturbations, and find that the next-to-leading order adiabatic expansion yields the amplitude of the power spectra with excellent accuracy, whereas the next-to-leading order with the perturbative Green's function method does not improve the leading order result significantly. However, in more general cases, either or both methods may be useful.

  4. Rolling axions during inflation: perturbativity and signatures

    NASA Astrophysics Data System (ADS)

    Peloso, Marco; Sorbo, Lorenzo; Unal, Caner

    2016-09-01

    The motion of a pseudo-scalar field X during inflation naturally induces a significant amplification of the gauge fields to which it is coupled. The amplified gauge fields can source characteristic scalar and tensor primordial perturbations. Several phenomenological implications have been discussed in the cases in which (i) X is the inflaton, and (ii) X is a field different from the inflaton, that experiences a temporary speed up during inflation. In this second case, visible sourced gravitational waves (GW) can be produced at the CMB scales without affecting the scalar perturbations, even if the scale of inflation is several orders of magnitude below what is required to produce a visible vacuum GW signal. Perturbativity considerations can be used to limit the regime in which these results are under perturbative control. We revised limits recently claimed for the case (i), and we extend these considerations to the case (ii). We show that, in both cases, these limits are satisfied by the applications that generate signals at CMB scales. Applications that generate gravitational waves and primordial black holes at much smaller scales are at the limit of the validity of this perturbativity analysis, so we expect those results to be valid up to possibly order one corrections.

  5. A spectral analysis of the earth's angular momentum budget

    NASA Technical Reports Server (NTRS)

    Eubanks, T. M.; Steppe, J. A.; Dickey, J. O.; Callahan, P. S.

    1985-01-01

    The exchange of angular momentum between the solid earth and the atmosphere from January 1976 through March 1982 is investigated using estimates of the earth's rotation from optical astrometry and lunar laser ranging and meteorological estimates of the atmospheric angular momentum M(atm). The physics of the earth's angular momentum budget is described, and earth rotation measurements are related to changes in the angular momentum of the fluid parts of the earth. The availability and reliability of earth rotation and M(atm) data are reported, and the possibility of estimating the exchange of angular momentum with the oceans and with the core is examined. Estimates of the power spectrum, cospectral coherence, and linear transfer functions and an analysis of the unmodeled part of the angular momentum budget are presented and discussed. The amplitude and phase of the semiannual, monthly, and fortnightly tidal variations in the length of day are estimated after removing observed atmospheric excitation.

  6. Motion fading is driven by perceived, not actual angular velocity.

    PubMed

    Kohler, P J; Caplovitz, G P; Hsieh, P-J; Sun, J; Tse, P U

    2010-06-01

    After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. Here we examine the relationship between such 'motion fading' and perceived angular velocity. Using several different dot patterns that generate emergent virtual contours, we demonstrate that whenever there is a difference in the perceived angular velocity of two patterns of dots that are in fact rotating at the same angular velocity, there is also a difference in the time to undergo motion fading for those two patterns. Conversely, whenever two patterns show no difference in perceived angular velocity, even if in fact rotating at different angular velocities, we find no difference in the time to undergo motion fading. Thus, motion fading is driven by the perceived rather than actual angular velocity of a rotating stimulus. PMID:20371254

  7. Angular momenta creation in relativistic electron-positron plasma.

    PubMed

    Tatsuno, T; Berezhiani, V I; Pekker, M; Mahajan, S M

    2003-07-01

    Creation of angular momentum in a relativistic electron-positron plasma is explored. It is shown that a chain of angular momentum carrying vortices is a robust asymptotic state sustained by the generalized nonlinear Schrödinger equation characteristic to the system. The results may suggest a possible electromagnetic origin of angular momenta when it is applied to the MeV epoch of the early Universe. PMID:12935260

  8. Peculiarities of Angular Distribution of Electrons at Si <100> Channeling

    NASA Astrophysics Data System (ADS)

    Bogdanov, O. V.; Pivovarov, Yu L.; Takabayashi, Y.; Tukhfatullin, T. A.

    2012-05-01

    The properties of both angular and spatial distribution of 255 MeV electrons at <100> channeling in silicon crystal has been investigated experimentally at the linac injector of SAGA light source and by computer simulations. The simulation of trajectories, angular and spatial distributions of electrons on the screen monitor has been performed taking into account initial spatial as well as angular beam divergence of electron beam. Both experimental data and simulations show the brilliant effect of so-called "doughnut scattering".

  9. Efficient checkpointing schemes for depletion perturbation solutions on memory-limited architectures

    SciTech Connect

    Stripling, H. F.; Adams, M. L.; Hawkins, W. D.

    2013-07-01

    We describe a methodology for decreasing the memory footprint and machine I/O load associated with the need to access a forward solution during an adjoint solve. Specifically, we are interested in the depletion perturbation equations, where terms in the adjoint Bateman and transport equations depend on the forward flux solution. Checkpointing is the procedure of storing snapshots of the forward solution to disk and using these snapshots to recompute the parts of the forward solution that are necessary for the adjoint solve. For large problems, however, the storage cost of just a few copies of an angular flux vector can exceed the available RAM on the host machine. We propose a methodology that does not checkpoint the angular flux vector; instead, we write and store converged source moments, which are typically of a much lower dimension than the angular flux solution. This reduces the memory footprint and I/O load of the problem, but requires that we perform single sweeps to reconstruct flux vectors on demand. We argue that this trade-off is exactly the kind of algorithm that will scale on advanced, memory-limited architectures. We analyze the cost, in terms of FLOPS and memory footprint, of five checkpointing schemes. We also provide computational results that support the analysis and show that the memory-for-work trade off does improve time to solution. (authors)

  10. Non-gravitational perturbations and satellite geodesy

    SciTech Connect

    Milani, A.; Nobill, A.M.; Farinella, P.

    1987-01-01

    This book presents the basic ideas of the physics of non-gravitational perturbations and the mathematics required to compute their orbital effects. It conveys the relevance of the different problems that must be solved to achieve a given level of accuracy in orbit determination and in recovery of geophysically significant parameters. Selected Contents are: Orders of Magnitude of the Perturbing Forces, Tides and Apparent Forces, Tools from Celestial Mechanics, Solar Radiation Pressure-Direct Effects: Satellite-Solar Radiation Interaction, Long-Term Effects on Semi-Major Axis, Radiation Pressure-Indirect Effects: Earth-Reflected Radiation Pressure, Anisotropic Thermal Emission, Drag: Orbital Perturbations by a Drag-Like Force, and Charged Particle Drag.

  11. Perturbations in a regular bouncing universe

    SciTech Connect

    Battefeld, T.J.; Geshnizjani, G.

    2006-03-15

    We consider a simple toy model of a regular bouncing universe. The bounce is caused by an extra timelike dimension, which leads to a sign flip of the {rho}{sup 2} term in the effective four dimensional Randall Sundrum-like description. We find a wide class of possible bounces: big bang avoiding ones for regular matter content, and big rip avoiding ones for phantom matter. Focusing on radiation as the matter content, we discuss the evolution of scalar, vector and tensor perturbations. We compute a spectral index of n{sub s}=-1 for scalar perturbations and a deep blue index for tensor perturbations after invoking vacuum initial conditions, ruling out such a model as a realistic one. We also find that the spectrum (evaluated at Hubble crossing) is sensitive to the bounce. We conclude that it is challenging, but not impossible, for cyclic/ekpyrotic models to succeed, if one can find a regularized version.

  12. Non-perturbative quantum geometry III

    NASA Astrophysics Data System (ADS)

    Krefl, Daniel

    2016-08-01

    The Nekrasov-Shatashvili limit of the refined topological string on toric Calabi-Yau manifolds and the resulting quantum geometry is studied from a non-perturbative perspective. The quantum differential and thus the quantum periods exhibit Stokes phenomena over the combined string coupling and quantized Kähler moduli space. We outline that the underlying formalism of exact quantization is generally applicable to points in moduli space featuring massless hypermultiplets, leading to non-perturbative band splitting. Our prime example is local ℙ1 + ℙ1 near a conifold point in moduli space. In particular, we will present numerical evidence that in a Stokes chamber of interest the string based quantum geometry reproduces the non-perturbative corrections for the Nekrasov-Shatashvili limit of 4d supersymmetric SU(2) gauge theory at strong coupling found in the previous part of this series. A preliminary discussion of local ℙ2 near the conifold point in moduli space is also provided.

  13. Interactions of Blast Waves with Perturbed Interfaces

    NASA Astrophysics Data System (ADS)

    Henry de Frahan, Marc; Johnsen, Eric

    2015-11-01

    Richtmyer-Meshkov and Rayleigh-Taylor instabilities induce hydrodynamic mixing in many important physical systems such as inertial confinement fusion, supernova collapse, and scramjet combustion. Blast waves interacting with perturbed interfaces are prevelant in such applications and dictate the mixing dynamics. This study increases our understanding of blast-driven hydrodynamic instabilities by providing models for the time-dependent perturbation growth and vorticity production mechanisms. The strength and length of the blast wave determine the different growth regimes and the importance of the Richtmyer-Meshkov or Rayleigh-Taylor growth. Our analysis is based on simulations of a 2D planar blast wave, modeled by a shock (instantaneous acceleration) followed by a rarefaction (time-dependent deceleration), interacting with a sinusoidal perturbation at an interface between two fluids. A high-order accurate Discontinuous Galerkin method is used to solve the multifluid Euler equations.

  14. Hypersurface-invariant approach to cosmological perturbations

    NASA Astrophysics Data System (ADS)

    Salopek, D. S.; Stewart, J. M.

    1995-01-01

    Using Hamilton-Jacobi theory, we develop a formalism for solving semiclassical cosmological perturbations which does not require an explicit choice of time hypersurface. The Hamilton-Jacobi equation for gravity interacting with matter (either a scalar or dust field) is solved by making an ansatz which includes all terms quadratic in the spatial curvature. Gravitational radiation and scalar perturbations are treated on an equal footing. Our technique encompasses linear perturbation theory and it also describes some mild nonlinear effects. As a concrete example of the method, we compute the galaxy-galaxy correlation function as well as large-angle microwave background fluctuations for power-law inflation, and we compare with recent observations.

  15. Elementary theorems regarding blue isocurvature perturbations

    NASA Astrophysics Data System (ADS)

    Chung, Daniel J. H.; Yoo, Hojin

    2015-04-01

    Blue CDM-photon isocurvature perturbations are attractive in terms of observability and may be typical from the perspective of generic mass relations in supergravity. We present and apply three theorems useful for blue isocurvature perturbations arising from linear spectator scalar fields. In the process, we give a more precise formula for the blue spectrum associated with the axion model of Kasuya and Kawasaki [Axion Isocurvature Fluctuations with Extremely Blue Spectrum, Phys. Rev. D 80, 023516 (2009).], which can in a parametric corner give a factor of O (10 ) correction. We explain how a conserved current associated with Peccei-Quinn symmetry plays a crucial role and explicitly plot several example spectra including the breaks in the spectra. We also resolve a little puzzle arising from a naive multiplication of isocurvature expression that sheds light on the gravitational imprint of the adiabatic perturbations on the fields responsible for blue isocurvature fluctuations.

  16. Perturbation measurement of waveguides for acoustic thermometry

    NASA Astrophysics Data System (ADS)

    Lin, H.; Feng, X. J.; Zhang, J. T.

    2013-09-01

    Acoustic thermometers normally embed small acoustic transducers in the wall bounding a gas-filled cavity resonator. At high temperature, insulators of transducers loss electrical insulation and degrade the signal-to-noise ratio. One essential solution to this technical trouble is to couple sound by acoustic waveguides between resonator and transducers. But waveguide will break the ideal acoustic surface and bring perturbations(Δf+ig) to the ideal resonance frequency. The perturbation model for waveguides was developed based on the first-order acoustic theory in this paper. The frequency shift Δf and half-width change g caused by the position, length and radius of waveguides were analyzed using this model. Six different length of waveguides (52˜1763 mm) were settled on the cylinder resonator and the perturbation (Δf+ig) were measured at T=332 K and p=250˜500 kPa. The experiment results agreed with the theoretical prediction very well.

  17. Perturbation analysis of electromagnetic geodesic acoustic modes

    SciTech Connect

    Ren, Haijun

    2014-06-15

    Lagrangian displacement and magnetic field perturbation response to the geodesic acoustic mode is analyzed by using the ideal magnetohydrodynamic equations in a large-aspect-ratio tokamak. δB{sub θ}, the poloidal component of magnetic field perturbation, has poloidal wave number m = 2 created by the poloidal displacement ξ{sub θ}. The parallel perturbation of magnetic field, δB{sub ∥}, has a poloidally asymmetric structure with m = 1 and is on the same order of magnitude with δB{sub θ} to the leading order. The radial displacement ξ{sub r} is of order O(βϵξ{sub θ}) but plays a significant role in determining δB{sub ∥}, where β is the plasma/magnetic pressure ratio and ϵ is the inverse aspect ratio.

  18. Noncontacting method for measuring angular deflection

    NASA Technical Reports Server (NTRS)

    Bryant, E. L. (Inventor)

    1980-01-01

    An apparatus is described for indicating the instantaneous angular deflection of an object about a selected axis without mechanical contact with the object. Light from a light source is transmitted through a flat refractor to a converging lens which focuses the light through another flat refractor onto a differential photocell. The first flat refractor is attached to the object such that when the object is deflected about the selected axis the refractor is also deflected about that axis. The two flat refractors are identical and they are placed an equal distance from the converging lens as are the light source and the photocell. The output of the photocell which is a function of image displacement is fed to a high gain amplifier that drives a galvanometer which rotates the second flat refractor. The second refractor is rotated so that the image displacement is very nearly zero making the galvanometer current a measure of the deflection of the object about the selected axis.

  19. Arbitrarily tunable orbital angular momentum of photons

    PubMed Central

    Pan, Yue; Gao, Xu-Zhen; Ren, Zhi-Cheng; Wang, Xi-Lin; Tu, Chenghou; Li, Yongnan; Wang, Hui-Tian

    2016-01-01

    Orbital angular momentum (OAM) of photons, as a new fundamental degree of freedom, has excited a great diversity of interest, because of a variety of emerging applications. Arbitrarily tunable OAM has gained much attention, but its creation remains still a tremendous challenge. We demonstrate the realization of well-controlled arbitrarily tunable OAM in both theory and experiment. We present the concept of general OAM, which extends the OAM carried by the scalar vortex field to the OAM carried by the azimuthally varying polarized vector field. The arbitrarily tunable OAM we presented has the same characteristics as the well-defined integer OAM: intrinsic OAM, uniform local OAM and intensity ring, and propagation stability. The arbitrarily tunable OAM has unique natures: it is allowed to be flexibly tailored and the radius of the focusing ring can have various choices for a desired OAM, which are of great significance to the benefit of surprising applications of the arbitrary OAM. PMID:27378234

  20. Angular Clustering of Obscured Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Gandhi, Poshak; Garcet, O.; Disseau, L.; Pacaud, F.; Pierre, M.; Gueguen, A.; Alloin, D.; Chiappetti, L.; Gosset, E.; Maccagni, D.; Surdej, J.; Valtchanov, I.

    2006-09-01

    We describe the properties of X-ray point-like sources detected over 4.2 sq. degs. of the largest contiguous survey with XMM-Newton to date (the XMM-LSS survey) to fluxes of F2-10 keV 8x10-15 erg/s/cm2 and F0.5-2 keV 2x10-15 erg/s/cm2 respectively. For 1200 sources in the soft band, we find a two-point angular correlation function (ACF) signal similar to previous work, but no correlation for 400 sources in the hard band. A sample of 200 faint sources with hard X-ray spectra does show a 2-3 sigma positive signal with a power-law normalization theta0>40 arcsec. We discuss implications, including the fact that a large correlation length for obscured AGN is inconsistent with simple AGN Unification based on orientation only.

  1. Colliding particles carrying nonzero orbital angular momentum

    NASA Astrophysics Data System (ADS)

    Ivanov, Igor P.

    2011-05-01

    Photons carrying nonzero orbital angular momentum (twisted photons) are well-known in optics. Recently, using Compton backscattering to boost optical twisted photons to high energies was suggested. Twisted electrons in the intermediate energy range have also been produced recently. Thus, collisions involving energetic twisted particles seem to be feasible and represent a new tool in high-energy physics. Here we discuss some generic features of scattering processes involving twisted particles in the initial and/or final state. In order to avoid additional complications arising from nontrivial polarization states, we focus here on scalar fields only. We show that processes involving twisted particles allow one to perform a Fourier analysis of the plane-wave cross section with respect to the azimuthal angles of the initial particles. In addition, using twisted states, one can probe the autocorrelation function of the amplitude, which is inaccessible in the plane-wave collisions. Finally, we discuss prospects for experimental study of these effects.

  2. Internal reflection sensors with high angular resolution

    NASA Astrophysics Data System (ADS)

    Shavirin, I.; Strelkov, O.; Vetskous, A.; Norton-Wayne, L.; Harwood, R.

    1996-07-01

    We discuss the use of total internal reflection for the production of sensors with high angular resolution. These sensors are intended for measurement of the angle between a sensor's axis and the direction to a source of radiation or reflecting object. Sensors of this type are used in controlling the position of machine parts in robotics and industry, orienting space vehicles and astronomic devices in relation to the Sun, and as autocollimators for checking angles of deviation. This kind of sensor was used in the Apollo space vehicle some 20 years ago. Using photodetectors with linear and area CCD arrays has opened up new application possibilities for appropriately designed sensors. A generalized methodology is presented applicable to a wide range of tasks. Some modifications that can improve the performance of the basic design are described.

  3. Passive optical element with selective angular reflection

    SciTech Connect

    Tremblay, C.; Rheault, F.; Boulay, R.; Tremblay, R.

    1987-02-01

    This work is related to the development of passive selective transmission materials that will contribute to regularize the solar thermal gain. We propose an original solution to the problem of seasonal control of energetic input into buildings through windows. A passive optical element with selective angular reflection is used to solve this problem. This optical element allows sunlight to enter windows during the fall and winter, whereas, owing to the different astronomical path of the sun, it stops and rejects direct sunlight by means of the optical effect called total internal reflection (TIR) during the central spring-Summer period. The purpose of this paper is to describe the optical element in some detail, to develop the principal design equations, and give the results of the optimization of optical and geometrical parameters.

  4. Wideband phase-locked angular modulator

    NASA Technical Reports Server (NTRS)

    Nguyen, L.

    1989-01-01

    A phase-locked loop (PLL) angular modulator scheme has been proposed which has the characteristics of wideband modulation frequency response. The modulator design is independent of the PLL closed-loop transfer function H(s), thereby allowing independent optimization of the loop's parameters as well as the modulator's parameters. A phase modulator implementing the proposed scheme was built to phase modulate a low-noise phase-locked signal source at the output frequency of 2290 MHz. The measurement results validated the analysis by demonstrating that the resulting baseband modulation bandwidth exceeded that of the phase-locked loop by over an order of magnitude. However, it is expected to be able to achieve much wider response still.

  5. Angular relation of axes in perceptual space

    NASA Technical Reports Server (NTRS)

    Bucher, Urs

    1992-01-01

    The geometry of perceptual space needs to be known to model spatial orientation constancy or to create virtual environments. To examine one main aspect of this geometry, the angular relation between the three spatial axes was measured. Experiments were performed consisting of a perceptual task in which subjects were asked to set independently their apparent vertical and horizontal plane. The visual background provided no other stimuli to serve as optical direction cues. The task was performed in a number of different body tilt positions with pitches and rolls varied in steps of 30 degs. The results clearly show the distortion of orthogonality of the perceptual space for nonupright body positions. Large interindividual differences were found. Deviations from orthogonality up to 25 deg were detected in the pitch as well as in the roll direction. Implications of this nonorthogonality on further studies of spatial perception and on the construction of virtual environments for human interaction is also discussed.

  6. Optical communication beyond orbital angular momentum.

    PubMed

    Trichili, Abderrahmen; Rosales-Guzmán, Carmelo; Dudley, Angela; Ndagano, Bienvenu; Ben Salem, Amine; Zghal, Mourad; Forbes, Andrew

    2016-01-01

    Mode division multiplexing (MDM) is mooted as a technology to address future bandwidth issues, and has been successfully demonstrated in free space using spatial modes with orbital angular momentum (OAM). To further increase the data transmission rate, more degrees of freedom are required to form a densely packed mode space. Here we move beyond OAM and demonstrate multiplexing and demultiplexing using both the radial and azimuthal degrees of freedom. We achieve this with a holographic approach that allows over 100 modes to be encoded on a single hologram, across a wide wavelength range, in a wavelength independent manner. Our results offer a new tool that will prove useful in realizing higher bit rates for next generation optical networks. PMID:27283799

  7. Optical communication beyond orbital angular momentum

    NASA Astrophysics Data System (ADS)

    Trichili, Abderrahmen; Rosales-Guzmán, Carmelo; Dudley, Angela; Ndagano, Bienvenu; Ben Salem, Amine; Zghal, Mourad; Forbes, Andrew

    2016-06-01

    Mode division multiplexing (MDM) is mooted as a technology to address future bandwidth issues, and has been successfully demonstrated in free space using spatial modes with orbital angular momentum (OAM). To further increase the data transmission rate, more degrees of freedom are required to form a densely packed mode space. Here we move beyond OAM and demonstrate multiplexing and demultiplexing using both the radial and azimuthal degrees of freedom. We achieve this with a holographic approach that allows over 100 modes to be encoded on a single hologram, across a wide wavelength range, in a wavelength independent manner. Our results offer a new tool that will prove useful in realizing higher bit rates for next generation optical networks.

  8. Optical communication beyond orbital angular momentum

    PubMed Central

    Trichili, Abderrahmen; Rosales-Guzmán, Carmelo; Dudley, Angela; Ndagano, Bienvenu; Ben Salem, Amine; Zghal, Mourad; Forbes, Andrew

    2016-01-01

    Mode division multiplexing (MDM) is mooted as a technology to address future bandwidth issues, and has been successfully demonstrated in free space using spatial modes with orbital angular momentum (OAM). To further increase the data transmission rate, more degrees of freedom are required to form a densely packed mode space. Here we move beyond OAM and demonstrate multiplexing and demultiplexing using both the radial and azimuthal degrees of freedom. We achieve this with a holographic approach that allows over 100 modes to be encoded on a single hologram, across a wide wavelength range, in a wavelength independent manner. Our results offer a new tool that will prove useful in realizing higher bit rates for next generation optical networks. PMID:27283799

  9. Coherent control of photoelectron wavepacket angular interferograms

    NASA Astrophysics Data System (ADS)

    Hockett, P.; Wollenhaupt, M.; Baumert, T.

    2015-11-01

    Coherent control over photoelectron wavepackets, via the use of polarization-shaped laser pulses, can be understood as a time and polarization-multiplexed process, where the final (time-integrated) observable coherently samples all instantaneous states of the light-matter interaction. In this work, we investigate this multiplexing via computation of the observable photoelectron angular interferograms resulting from multi-photon atomic ionization with polarization-shaped laser pulses. We consider the polarization sensitivity of both the instantaneous and cumulative continuum wavefunction; the nature of the coherent control over the resultant photoelectron interferogram is thus explored in detail. Based on this understanding, the use of coherent control with polarization-shaped pulses as a methodology for a highly multiplexed coherent quantum metrology is also investigated, and defined in terms of the information content of the observable.

  10. Chiral symmetries associated with angular momentum

    NASA Astrophysics Data System (ADS)

    Bhattacharya, M.; Kleinert, M.

    2014-03-01

    In quantum mechanics courses, symmetries of a physical system are usually introduced as operators which commute with the Hamiltonian. In this paper we will consider chiral symmetries which anticommute with the Hamiltonian. Typically, introductory courses at the (under)graduate level do not discuss these simple, useful and beautiful symmetries at all. The first time a student encounters them is when the Dirac equation is discussed in a course on relativistic quantum mechanics, or when particle-hole symmetry is studied in the context of superconductivity. In this paper, we will show how chiral symmetries can be simply elucidated using the theory of angular momentum, which is taught in virtually all introductory quantum mechanics courses.

  11. Angular momentum effects in subbarrier fusion

    SciTech Connect

    Halbert, M.L.; Beene, J.R.; Hensley, D.C.; Honkanen, K.; Semkow, T.M.; Abenante, V.; Sarantites, D.G.; Li, Z.

    1988-01-01

    Angular-momentum distributions sigma/sub L/ for the compound nucleus /sup 164/Yb were deduced from measurements of ..gamma..-ray multiplicity for all significant evaporation residues from fusion of /sup 64/Ni and /sup 100/Mo at and below the Coulomb barrier. The excitation functions can be reproduced with coupled-channels calculations only if additional coupling beyond the known inelastic strengths is included. Even with this augmented coupling, however, at the lowest bombarding energies the experimental sigma/sub L/ extend to higher L values than the predictions. Single-barrier penetration models for a potential with an energy-dependent depth and shape fitted to the excitation function likewise underestimate the role of high-L partial waves. Somewhat better success is achieved with models in which fission is allowed to occur at distances comparable with or even larger than the Coulomb barrier radius. 24 refs., 3 figs., 2 tabs.

  12. Arbitrarily tunable orbital angular momentum of photons.

    PubMed

    Pan, Yue; Gao, Xu-Zhen; Ren, Zhi-Cheng; Wang, Xi-Lin; Tu, Chenghou; Li, Yongnan; Wang, Hui-Tian

    2016-01-01

    Orbital angular momentum (OAM) of photons, as a new fundamental degree of freedom, has excited a great diversity of interest, because of a variety of emerging applications. Arbitrarily tunable OAM has gained much attention, but its creation remains still a tremendous challenge. We demonstrate the realization of well-controlled arbitrarily tunable OAM in both theory and experiment. We present the concept of general OAM, which extends the OAM carried by the scalar vortex field to the OAM carried by the azimuthally varying polarized vector field. The arbitrarily tunable OAM we presented has the same characteristics as the well-defined integer OAM: intrinsic OAM, uniform local OAM and intensity ring, and propagation stability. The arbitrarily tunable OAM has unique natures: it is allowed to be flexibly tailored and the radius of the focusing ring can have various choices for a desired OAM, which are of great significance to the benefit of surprising applications of the arbitrary OAM. PMID:27378234

  13. Angular biasing in implicit Monte-Carlo

    SciTech Connect

    Zimmerman, G.B.

    1994-10-20

    Calculations of indirect drive Inertial Confinement Fusion target experiments require an integrated approach in which laser irradiation and radiation transport in the hohlraum are solved simultaneously with the symmetry, implosion and burn of the fuel capsule. The Implicit Monte Carlo method has proved to be a valuable tool for the two dimensional radiation transport within the hohlraum, but the impact of statistical noise on the symmetric implosion of the small fuel capsule is difficult to overcome. We present an angular biasing technique in which an increased number of low weight photons are directed at the imploding capsule. For typical parameters this reduces the required computer time for an integrated calculation by a factor of 10. An additional factor of 5 can also be achieved by directing even smaller weight photons at the polar regions of the capsule where small mass zones are most sensitive to statistical noise.

  14. The asymptotics of the solution of an equation with a small parameter in a domain with angular points

    SciTech Connect

    Lelikova, Elena F

    2010-12-07

    The asymptotic behaviour of solutions of the first boundary-value problem for a second-order elliptic equation in a domain with angular points is investigated for the case when a small parameter is involved in the equation only as a factor multiplying one of the highest order derivatives and the limit equation is an ordinary differential equation. Although the order of the limit equation coincides with that of the original equation, the problem in question is singularly perturbed. The asymptotic behaviour of the solution of this problem is studied by the method of matched asymptotic expansions. Bibliography: 11 titles.

  15. Instability of charged Lovelock black holes: Vector perturbations and scalar perturbations

    NASA Astrophysics Data System (ADS)

    Takahashi, Tomohiro

    2013-01-01

    We examine the stability of charged Lovelock black hole solutions under vector-type and scalar-type perturbations. We find suitable master variables for the stability analysis; the equations for these variables are Schrödinger-type equations with two components, and these Schrödinger operators are symmetric. By these master equations, we show that charged Lovelock black holes are stable under vector-type perturbations. For scalar-type perturbations, we show the criteria for instability and check these numerically. In our previous paper [T. Takahashi, Prog. Theor. Phys. 125, 1289 (2011)], we have shown that nearly extreme black holes show instability under tensor-type perturbations. In this paper, we find that black holes with a small charge show instability under scalar-type perturbations even if they have a relatively large mass.

  16. Extreme-mass-ratio inspiral corrections to the angular velocity and redshift factor of a mass in circular orbit about a Kerr black hole

    NASA Astrophysics Data System (ADS)

    Shah, Abhay G.; Friedman, John L.; Keidl, Tobias S.

    2012-10-01

    This is the first of two papers on computing the self-force in a radiation gauge for a particle of mass m moving in circular, equatorial orbit about a Kerr black hole. In the extreme-mass-ratio inspiral (EMRI) framework, with mode-sum renormalization, we compute the renormalized value of the quantity H≔(1)/(2)hαβuαuβ, gauge-invariant under gauge transformations generated by a helically symmetric gauge vector; here, hαβ is the metric perturbation, uα the particle’s 4-velocity. We find the related order m correction to the particle’s angular velocity at fixed renormalized redshift (and to its redshift at fixed angular velocity), each of which can be written in terms of H. The radiative part of the metric perturbation is constructed from a Hertz potential that is extracted from the Weyl scalar by an algebraic inversion T. S. Keidl , Phys. Rev. D 82, 124012 (2010). We then write the spin-weighted spheroidal harmonics as a sum over spin-weighted spherical harmonics Yℓms and use mode-sum renormalization to find the renormalization coefficients by matching a series in L=ℓ+1/2 to the large-L behavior of the expression for H. The nonradiative parts of the perturbed metric associated with changes in mass and angular momentum are calculated in the Kerr gauge.

  17. Angular Approach Scanning Ion Conductance Microscopy.

    PubMed

    Shevchuk, Andrew; Tokar, Sergiy; Gopal, Sahana; Sanchez-Alonso, Jose L; Tarasov, Andrei I; Vélez-Ortega, A Catalina; Chiappini, Ciro; Rorsman, Patrik; Stevens, Molly M; Gorelik, Julia; Frolenkov, Gregory I; Klenerman, David; Korchev, Yuri E

    2016-05-24

    Scanning ion conductance microscopy (SICM) is a super-resolution live imaging technique that uses a glass nanopipette as an imaging probe to produce three-dimensional (3D) images of cell surface. SICM can be used to analyze cell morphology at nanoscale, follow membrane dynamics, precisely position an imaging nanopipette close to a structure of interest, and use it to obtain ion channel recordings or locally apply stimuli or drugs. Practical implementations of these SICM advantages, however, are often complicated due to the limitations of currently available SICM systems that inherited their design from other scanning probe microscopes in which the scan assembly is placed right above the specimen. Such arrangement makes the setting of optimal illumination necessary for phase contrast or the use of high magnification upright optics difficult. Here, we describe the designs that allow mounting SICM scan head on a standard patch-clamp micromanipulator and imaging the sample at an adjustable approach angle. This angle could be as shallow as the approach angle of a patch-clamp pipette between a water immersion objective and the specimen. Using this angular approach SICM, we obtained topographical images of cells grown on nontransparent nanoneedle arrays, of islets of Langerhans, and of hippocampal neurons under upright optical microscope. We also imaged previously inaccessible areas of cells such as the side surfaces of the hair cell stereocilia and the intercalated disks of isolated cardiac myocytes, and performed targeted patch-clamp recordings from the latter. Thus, our new, to our knowledge, angular approach SICM allows imaging of living cells on nontransparent substrates and a seamless integration with most patch-clamp setups on either inverted or upright microscopes, which would facilitate research in cell biophysics and physiology. PMID:27224490

  18. Delocalized correlations in twin light beams with orbital angular momentum.

    PubMed

    Marino, A M; Boyer, V; Pooser, R C; Lett, P D; Lemons, K; Jones, K M

    2008-08-29

    We generate intensity-difference-squeezed Laguerre-Gauss twin beams of light carrying orbital angular momentum by using four-wave mixing in a hot atomic vapor. The conservation of orbital angular momentum in the four-wave mixing process is studied as well as the spatial distribution of the quantum correlations obtained with different configurations of orbital angular momentum. Intensity-difference squeezing of up to -6.7 dB is demonstrated with beams carrying orbital angular momentum. Delocalized spatial correlations between the twin beams are observed. PMID:18851611

  19. CHARACTERIZATION OF THE RESONANT CAUSTIC PERTURBATION

    SciTech Connect

    Chung, Sun-Ju

    2009-11-01

    Four of nine exoplanets found by microlensing were detected by the resonant caustic, which represents the merging of the planetary and central caustics at the position when the projected separation of a host star and a bounded planet is s approx 1. One of the resonant caustic lensing events, OGLE-2005-BLG-169, was a caustic-crossing high-magnification event with A {sub max}approx 800 and the source star was much smaller than the caustic, nevertheless the perturbation was not obviously apparent on the light curve of the event. In this paper, we investigate the perturbation pattern of the resonant caustic to understand why the perturbations induced by the caustic do not leave strong traces on the light curves of high-magnification events despite a small source/caustic size ratio. From this study, we find that the regions with small magnification excess around the center of the resonant caustic are rather widely formed, and the event passing the small-excess region produces a high-magnification event with a weak perturbation that is small relative to the amplification caused by the star and thus does not noticeably appear on the light curve of the event. We also find that the positive excess of the inside edge of the resonant caustic and the negative excess inside the caustic become stronger and wider as q increases, and thus the resonant caustic-crossing high-magnification events with the weak perturbation occur in the range of q <= 10{sup -4}. We determine the probability of the occurrence of events with the small excess |epsilon| <= 3% in high-magnification events induced by a resonant caustic. As a result, we find that for Earth-mass planets with a separation of approx2.5 AU the resonant caustic high-magnification events with the weak perturbation can occur with a significant frequency.

  20. Perturbative Lagrangian approach to gravitational instability.

    NASA Astrophysics Data System (ADS)

    Bouchet, F. R.; Colombi, S.; Hivon, E.; Juszkiewicz, R.

    1995-04-01

    This paper deals with the time evolution in the matter era of perturbations in Friedman-Lemaitre models with arbitrary density parameter {OMEGA}, with either a zero cosmological constant, {LAMBDA}=0, or with a non-zero cosmological constant in a spatially flat Universe. Unlike the classical Eulerian approach where the density contrast is expanded in a perturbative series, this analysis relies instead on a perturbative expansion of particles trajectories in Lagrangian coordinates. This brings a number of advantages over the classical analysis. In particular, it enables the description of stronger density contrasts. Indeed the linear term in the Lagrangian perturbative series is the famous Zeldovich approximate solution (1970). The idea to consider the higher order terms was introduced by Moutarde et al. (1991), generalized by Bouchet et al. (1992), and further developed by many others. We present here a systematic and detailed account of this approach. We give analytical results (or fits to numerical results) up to the third order (which is necessary to compute, for instance, the four point spatial correlation function or the corrections to the linear evolution of the two-point correlation function, as well as the secondary temperature anisotropies of the Cosmic Microwave Background). We then proceed to explore the link between the Lagrangian description and statistical measures. We show in particular that Lagrangian perturbation theory provides a natural framework to compute the effect of redshift distortions, using the skewness of the density distribution function as an example. Finally, we show how well the second order theory does as compared to other approximations in the case of spherically symmetric perturbations. We also compare this second order approximation and Zeldovich solution to N-body simulations with scale-free (n=-2) Gaussian initial conditions. We find that second order theory is both simple and powerful.

  1. Nonlinear Growth of Singular Vector Based Perturbations

    NASA Astrophysics Data System (ADS)

    Reynolds, C. A.

    2002-12-01

    The nonlinearity of singular vector-based perturbation growth is examined within the context of a global atmospheric forecast model. The characteristics of these nonlinearities and their impact on the utility of SV-based diagnostics are assessed both qualitatively and quantitatively. Nonlinearities are quantified by examining the symmetry of evolving positive and negative "twin" perturbations. Perturbations initially scaled to be consistent with estimates of analysis uncertainty become significantly nonlinear by 12 hours. However, the relative magnitude of the nonlinearities is a strong function of scale and metric. Small scales become nonlinear very quickly while synoptic scales can remain significantly linear out to three day. Small shifts between positive and negative perturbations can result in significant nonlinearities even when the basic anomaly patterns are quite similar. Thus, singular vectors may be qualitatively useful even when nonlinearities are large. Post-time pseudo-inverse experiments show that despite significant nonlinear perturbation growth, the nonlinear forecast corrections are similar to the expected linear corrections, even at 72 hours. When the nonlinear correction does differ significantly from the expected linear correction, the nonlinear correction is usually better, indicating that in some cases the pseudo-inverse correction effectively suppresses error growth outside the subspace defined by the leading (dry) singular vectors. Because a significant portion of the nonlinear growth occurs outside of the dry singular vector subspace, an a priori nonlinearity index based on the full perturbations is not a good predictor of when pseudo-inverse based corrections will be ineffective. However, one can construct a reasonable predictor of pseudo-inverse ineffectiveness by focusing on nonlinearities in the synoptic scales or in the singular vector subspace only.

  2. Perturbative approach to Markovian open quantum systems

    PubMed Central

    Li, Andy C. Y.; Petruccione, F.; Koch, Jens

    2014-01-01

    The exact treatment of Markovian open quantum systems, when based on numerical diagonalization of the Liouville super-operator or averaging over quantum trajectories, is severely limited by Hilbert space size. Perturbation theory, standard in the investigation of closed quantum systems, has remained much less developed for open quantum systems where a direct application to the Lindblad master equation is desirable. We present such a perturbative treatment which will be useful for an analytical understanding of open quantum systems and for numerical calculation of system observables which would otherwise be impractical. PMID:24811607

  3. Evolution of perturbations in an inflationary universe

    NASA Technical Reports Server (NTRS)

    Frieman, J. A.; Will, C. M.

    1982-01-01

    The evolution of inhomogeneous density perturbations in a model of the very early universe that is dominated for a time by a constant energy density of a false quantum-mechanical vacuum is analyzed. During this period, the universe inflates exponentially and supercools exponentially, until a phase transition back to the true vacuum reheats the matter and radiation. Focus is on the physically measurable, coordinate-independent modes of inhomogeneous perturbations of this model and it is found that all modes either are constant or are exponentially damped during the inflationary era.

  4. Death to perturbative QCD in exclusive processes?

    SciTech Connect

    Eckardt, R.; Hansper, J.; Gari, M.F.

    1994-04-01

    The authors discuss the question of whether perturbative QCD is applicable in calculations of exclusive processes at available momentum transfers. They show that the currently used method of determining hadronic quark distribution amplitudes from QCD sum rules yields wave functions which are completely undetermined because the polynomial expansion diverges. Because of the indeterminacy of the wave functions no statement can be made at present as to whether perturbative QCD is valid. The authors emphasize the necessity of a rigorous discussion of the subject and the importance of experimental data in the range of interest.

  5. Perturbations in bouncing and cyclic models

    NASA Astrophysics Data System (ADS)

    Biswas, Tirthabir; Mayes, Riley; Lattyak, Colleen

    2016-03-01

    Being able to reliably track perturbations across bounces and turnarounds in cyclic and bouncing cosmology lies at the heart of being able to compare the predictions of these models with the cosmic microwave background observations. This has been a challenging task due to the unknown nature of the physics involved during the bounce as well as the technical challenge of matching perturbations precisely between the expansion and contraction phases. In this paper, we present some general techniques (analytical and numerical) that can be applied to understand the physics of the fluctuations, especially those with "long" wavelengths, and apply our techniques to nonsingular cosmological models such as the bounce inflation and cyclic inflation.

  6. Non-Gaussianity from isocurvature perturbations

    SciTech Connect

    Kawasaki, Masahiro; Nakayama, Kazunori; Sekiguchi, Toyokazu; Suyama, Teruaki; Takahashi, Fuminobu E-mail: nakayama@icrr.u-tokyo.ac.jp E-mail: suyama@icrr.u-tokyo.ac.jp

    2008-11-15

    We develop a formalism for studying non-Gaussianity in both curvature and isocurvature perturbations. It is shown that non-Gaussianity in the isocurvature perturbation between dark matter and photons leaves distinct signatures in the cosmic microwave background temperature fluctuations, which may be confirmed in future experiments, or possibly even in the currently available observational data. As an explicit example, we consider the quantum chromodynamics axion and show that it can actually induce sizable non-Gaussianity for the inflationary scale, H{sub inf} = O(10{sup 9}-10{sup 11}) GeV.

  7. Continuum methods in lattice perturbation theory

    SciTech Connect

    Becher, Thomas G

    2002-11-15

    We show how methods of continuum perturbation theory can be used to simplify perturbative lattice calculations. We use the technique of asymptotic expansions to expand lattice loop integrals around the continuum limit. After the expansion, all nontrivial dependence on momenta and masses is encoded in continuum loop integrals and the only genuine lattice integrals left are tadpole integrals. Using integration-by-parts relations all of these can be expressed in terms of a small number of master integrals. Four master integrals are needed for bosonic one loop integrals, sixteen in QCD with Wilson or staggered fermions.

  8. Robustness of braneworld scenarios against tensorial perturbations

    NASA Astrophysics Data System (ADS)

    Bazeia, D.; Losano, L.; Menezes, R.; Olmo, Gonzalo J.; Rubiera-Garcia, D.

    2015-11-01

    Inspired by the peculiarities of the effective geometry of crystalline structures, we reconsider thick brane scenarios from a metric-affine perspective. We show that for a rather general family of theories of gravity, whose Lagrangian is an arbitrary function of the metric and the Ricci tensor, the background and scalar field equations can be written in first-order form, and tensorial perturbations have a non negative definite spectrum, which makes them stable under linear perturbations regardless of the form of the gravity Lagrangian. We find, in particular, that the tensorial zero modes are exactly the same as predicted by Einstein’s theory regardless of the scalar field and gravitational Lagrangians.

  9. Perturbative renormalization of the electric field correlator

    NASA Astrophysics Data System (ADS)

    Christensen, C.; Laine, M.

    2016-04-01

    The momentum diffusion coefficient of a heavy quark in a hot QCD plasma can be extracted as a transport coefficient related to the correlator of two colour-electric fields dressing a Polyakov loop. We determine the perturbative renormalization factor for a particular lattice discretization of this correlator within Wilson's SU(3) gauge theory, finding a ∼ 12% NLO correction for values of the bare coupling used in the current generation of simulations. The impact of this result on existing lattice determinations is commented upon, and a possibility for non-perturbative renormalization through the gradient flow is pointed out.

  10. Conservative perturbation theory for nonconservative systems

    NASA Astrophysics Data System (ADS)

    Shah, Tirth; Chattopadhyay, Rohitashwa; Vaidya, Kedar; Chakraborty, Sagar

    2015-12-01

    In this paper, we show how to use canonical perturbation theory for dissipative dynamical systems capable of showing limit-cycle oscillations. Thus, our work surmounts the hitherto perceived barrier for canonical perturbation theory that it can be applied only to a class of conservative systems, viz., Hamiltonian systems. In the process, we also find Hamiltonian structure for an important subset of Liénard system—a paradigmatic system for modeling isolated and asymptotic oscillatory state. We discuss the possibility of extending our method to encompass an even wider range of nonconservative systems.

  11. Computing model independent perturbations in dark energy and modified gravity

    SciTech Connect

    Battye, Richard A.; Pearson, Jonathan A. E-mail: jonathan.pearson@durham.ac.uk

    2014-03-01

    We present a methodology for computing model independent perturbations in dark energy and modified gravity. This is done from the Lagrangian for perturbations, by showing how field content, symmetries, and physical principles are often sufficient ingredients for closing the set of perturbed fluid equations. The fluid equations close once ''equations of state for perturbations'' are identified: these are linear combinations of fluid and metric perturbations which construct gauge invariant entropy and anisotropic stress perturbations for broad classes of theories. Our main results are the proof of the equation of state for perturbations presented in a previous paper, and the development of the required calculational tools.

  12. Intercentrosomal angular separation during mitosis plays a crucial role for maintaining spindle stability

    NASA Astrophysics Data System (ADS)

    Sutradhar, S.; Basu, S.; Paul, R.

    2015-10-01

    Cell division through proper spindle formation is one of the key puzzles in cell biology. In most mammalian cells, chromosomes spontaneously arrange to achieve a stable bipolar spindle during metaphase which eventually ensures proper segregation of the DNA into the daughter cells. In this paper, we present a robust three-dimensional mechanistic model to investigate the formation and maintenance of a bipolar mitotic spindle in mammalian cells under different physiological constraints. Using realistic parameters, we test spindle viability by measuring the spindle length and studying the chromosomal configuration. The model strikingly predicts a feature of the spindle instability arising from the insufficient intercentrosomal angular separation and impaired sliding of the interpolar microtubules. In addition, our model successfully reproduces chromosomal patterns observed in mammalian cells, when activity of different motor proteins is perturbed.

  13. Calibration of the head direction network: a role for symmetric angular head velocity cells.

    PubMed

    Stratton, Peter; Wyeth, Gordon; Wiles, Janet

    2010-06-01

    Continuous attractor networks require calibration. Computational models of the head direction (HD) system of the rat usually assume that the connections that maintain HD neuron activity are pre-wired and static. Ongoing activity in these models relies on precise continuous attractor dynamics. It is currently unknown how such connections could be so precisely wired, and how accurate calibration is maintained in the face of ongoing noise and perturbation. Our adaptive attractor model of the HD system that uses symmetric angular head velocity (AHV) cells as a training signal shows that the HD system can learn to support stable firing patterns from poorly-performing, unstable starting conditions. The proposed calibration mechanism suggests a requirement for symmetric AHV cells, the existence of which has previously been unexplained, and predicts that symmetric and asymmetric AHV cells should be distinctly different (in morphology, synaptic targets and/or methods of action on postsynaptic HD cells) due to their distinctly different functions. PMID:20354898

  14. Intercentrosomal angular separation during mitosis plays a crucial role for maintaining spindle stability.

    PubMed

    Sutradhar, S; Basu, S; Paul, R

    2015-10-01

    Cell division through proper spindle formation is one of the key puzzles in cell biology. In most mammalian cells, chromosomes spontaneously arrange to achieve a stable bipolar spindle during metaphase which eventually ensures proper segregation of the DNA into the daughter cells. In this paper, we present a robust three-dimensional mechanistic model to investigate the formation and maintenance of a bipolar mitotic spindle in mammalian cells under different physiological constraints. Using realistic parameters, we test spindle viability by measuring the spindle length and studying the chromosomal configuration. The model strikingly predicts a feature of the spindle instability arising from the insufficient intercentrosomal angular separation and impaired sliding of the interpolar microtubules. In addition, our model successfully reproduces chromosomal patterns observed in mammalian cells, when activity of different motor proteins is perturbed. PMID:26565279

  15. Compact planetary systems perturbed by an inclined companion. II. Stellar spin-orbit evolution

    SciTech Connect

    Boué, Gwenaël; Fabrycky, Daniel C.

    2014-07-10

    The stellar spin orientation relative to the orbital planes of multiplanet systems is becoming accessible to observations. Here, we analyze and classify different types of spin-orbit evolution in compact multiplanet systems perturbed by an inclined outer companion. Our study is based on classical secular theory, using a vectorial approach developed in a separate paper. When planet-planet perturbations are truncated at the second order in eccentricity and mutual inclination, and the planet-companion perturbations are developed at the quadrupole order, the problem becomes integrable. The motion is composed of a uniform precession of the whole system around the total angular momentum, and in the rotating frame, the evolution is periodic. Here, we focus on the relative motion associated with the oscillations of the inclination between the planet system and the outer orbit and of the obliquities of the star with respect to the two orbital planes. The solution is obtained using a powerful geometric method. With this technique, we identify four different regimes characterized by the nutation amplitude of the stellar spin axis relative to the orbital plane of the planets. In particular, the obliquity of the star reaches its maximum when the system is in the Cassini regime where planets have more angular momentum than the star and where the precession rate of the star is similar to that of the planets induced by the companion. In that case, spin-orbit oscillations exceed twice the inclination between the planets and the companion. Even if the mutual inclination is only ≅ 20°, this resonant case can cause the spin-orbit angle to oscillate between perfectly aligned and retrograde values.

  16. Gauge-invariant cosmological perturbation theory with seeds

    SciTech Connect

    Durrer, R. )

    1990-10-15

    Gauge-invariant cosmological perturbation theory is extended to handle perturbations induced by seeds. A calculation of the Sachs-Wolfe effect is presented. A second-order differential equation for the growth of density perturbations is derived and the perturbation of Liouville's equation for collisionless particles is also given. The results are illustrated by a simple analytic example of a single texture knot, where we calculate the induced perturbations of the energy of microwave photons, of baryonic matter, and of collisionless particles.

  17. Circumstellar Debris Disks: Diagnosing the Unseen Perturber

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika R.; Naoz, Smadar; Vican, Laura; Farr, Will M.

    2016-07-01

    The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai–Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N-body simulations. We demonstrate that a Kozai–Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai–Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.

  18. Degenerate adiabatic perturbation theory: Foundations and applications

    NASA Astrophysics Data System (ADS)

    Rigolin, Gustavo; Ortiz, Gerardo

    2014-08-01

    We present details and expand on the framework leading to the recently introduced degenerate adiabatic perturbation theory [Phys. Rev. Lett. 104, 170406 (2010), 10.1103/PhysRevLett.104.170406], and on the formulation of the degenerate adiabatic theorem, along with its necessary and sufficient conditions [given in Phys. Rev. A 85, 062111 (2012), 10.1103/PhysRevA.85.062111]. We start with the adiabatic approximation for degenerate Hamiltonians that paves the way to a clear and rigorous statement of the associated degenerate adiabatic theorem, where the non-Abelian geometric phase (Wilczek-Zee phase) plays a central role to its quantitative formulation. We then describe the degenerate adiabatic perturbation theory, whose zeroth-order term is the degenerate adiabatic approximation, in its full generality. The parameter in the perturbative power-series expansion of the time-dependent wave function is directly associated to the inverse of the time it takes to drive the system from its initial to its final state. With the aid of the degenerate adiabatic perturbation theory we obtain rigorous necessary and sufficient conditions for the validity of the adiabatic theorem of quantum mechanics. Finally, to illustrate the power and wide scope of the methodology, we apply the framework to a degenerate Hamiltonian, whose closed-form time-dependent wave function is derived exactly, and also to other nonexactly solvable Hamiltonians whose solutions are numerically computed.

  19. Aharonov-Bohm Effect in Perturbation Theory.

    ERIC Educational Resources Information Center

    Purcell, Kay M.; Henneberger, Walter C.

    1978-01-01

    The Aharonov-Bohn effect is obtained in first-order perturbation theory. It is shown that the effect occurs only when the initial state is a superposition of eigenstates of Lz corresponding to eigenvalues having opposite sign. (Author/GA)

  20. Entropy perturbations in N-flation

    SciTech Connect

    Cai Ronggen; Hu Bin; Piao Yunsong

    2009-12-15

    In this paper we study the entropy perturbations in N-flation by using the {delta}N formalism. We calculate the entropy corrections to the power spectrum of the overall curvature perturbation P{sub {zeta}}. We obtain an analytic form of the transfer coefficient T{sub RS}{sup 2}, which describes the correlation between the curvature and entropy perturbations, and investigate its behavior numerically. It turns out that the entropy perturbations cannot be neglected in N-flation because the amplitude of entropy components is approximately in the same order as the adiabatic one at the end of inflation T{sub RS}{sup 2}{approx}O(1). The spectral index n{sub S} is calculated and it becomes smaller after the entropy modes are taken into account, i.e., the spectrum becomes redder, compared to the pure adiabatic case. Finally we study the modified consistency relation of N-flation, and find that the tensor-to-scalar ratio (r{approx_equal}0.006) is greatly suppressed by the entropy modes, compared to the pure adiabatic one (r{approx_equal}0.017) at the end of inflation.

  1. On the divergences of inflationary superhorizon perturbations

    SciTech Connect

    Enqvist, K; Nurmi, S; Podolsky, D; Rigopoulos, G I E-mail: sami.nurmi@helsinki.fi E-mail: gerasimos.rigopoulos@helsinki.fi

    2008-04-15

    We discuss the infrared divergences that appear to plague cosmological perturbation theory. We show that, within the stochastic framework, they are regulated by eternal inflation so that the theory predicts finite fluctuations. Using the {Delta}N formalism to one loop, we demonstrate that the infrared modes can be absorbed into additive constants and the coefficients of the diagrammatic expansion for the connected parts of two-and three-point functions of the curvature perturbation. As a result, the use of any infrared cutoff below the scale of eternal inflation is permitted, provided that the background fields are appropriately redefined. The natural choice for the infrared cutoff would, of course, be the present horizon; other choices manifest themselves in the running of the correlators. We also demonstrate that it is possible to define observables that are renormalization-group-invariant. As an example, we derive a non-perturbative, infrared finite and renormalization point-independent relation between the two-point correlators of the curvature perturbation for the case of the free single field.

  2. What Perturbs the ggrdgr Rings of Uranus?

    PubMed

    French, R G; Kangas, J A; Elliot, J L

    1986-01-31

    The gamma and delta rings have by far the largest radial perturbations of any of the nine known Uranian rings. These two rings deviate from Keplerian orbits, having typical root-mean-square residuals of about 3 kilometers (compared to a few hundred meters for the other seven known rings). Possible causes for the perturbations include nearby shepherd satellites and Lindblad resonances. If shepherd satellites are responsible, they could be as large as several tens of kilometers in diameter. The perturbation patterns of the gamma and delta rings have been examined for evidence of Lindblad resonances of azimuthal wave number m = 0, 1, 2, 3, and 4. The beta ring radial residuals are well matched by a 2:1 Lindblad resonance. If this represents a real physical phenomenon and is not an artifact of undersampling, then the most plausible interpretation is that there is an undiscovered satellite orbiting 76,522 +/- 8 kilometers from Uranus, with an orbital period of 15.3595 +/- 0.0001 hours and a radius of 75 to 100 kilometers. Such a satellite would be easily detected by the Voyager spacecraft when it encounters Uranus. The 2:1 resonance location is 41 +/- 9 kilometers inside the delta ring, which makes it unlikely that the resonance is due to a viscous instability within the ring. In contrast, no low-order Lindblad resonance matches the gamma ring perturbations, which are probably caused by one or more shepherd satellites large enough to be clearly visible in Voyager images. PMID:17776019

  3. On-Shell Methods in Perturbative QCD

    SciTech Connect

    Bern, Zvi; Dixon, Lance J.; Kosower, David A.

    2007-04-25

    We review on-shell methods for computing multi-parton scattering amplitudes in perturbative QCD, utilizing their unitarity and factorization properties. We focus on aspects which are useful for the construction of one-loop amplitudes needed for phenomenological studies at the Large Hadron Collider.

  4. Magnetic perturbation inspection of inner bearing races

    NASA Technical Reports Server (NTRS)

    Barton, J. R.; Lankford, J.

    1972-01-01

    Approximately 100 inner race bearings were inspected nondestructively prior to endurance testing. Two of the bearings which failed during testing spalled at the sites of subsurface inclusions previously detected by using magnetic field perturbation. At other sites initially judged to be suspect, subsurface inclusion-nucleated cracking was observed. Inspection records and metallurgical sectioning results are presented and discussed.

  5. Partially Quenched Chiral Perturbation Theory to NNLO

    SciTech Connect

    Laehde, Timo; Bijnens, Johan; Danielsson, Niclas

    2006-07-11

    This paper summarizes the recent calculations of the masses and decay constants of the pseudoscalar mesons at the two-loop level, or NNLO, in Partially Quenched Chiral Perturbation theory (PQ{chi}PT). Possible applications include chiral extrapolations of Lattice QCD, as well as the determination of the low-energy constants (LEC:s) of QCD.

  6. Staggered heavy baryon chiral perturbation theory

    NASA Astrophysics Data System (ADS)

    Bailey, Jon A.

    2008-03-01

    Although taste violations significantly affect the results of staggered calculations of pseudoscalar and heavy-light mesonic quantities, those entering staggered calculations of baryonic quantities have not been quantified. Here I develop staggered chiral perturbation theory in the light-quark baryon sector by mapping the Symanzik action into heavy baryon chiral perturbation theory. For 2+1 dynamical quark flavors, the masses of flavor-symmetric nucleons are calculated to third order in partially quenched and fully dynamical staggered chiral perturbation theory. To this order the expansion includes the leading chiral logarithms, which come from loops with virtual decuplet-like states, as well as terms of O(mπ3), which come from loops with virtual octet-like states. Taste violations enter through the meson propagators in loops and tree-level terms of O(a2). The pattern of taste symmetry breaking and the resulting degeneracies and mixings are discussed in detail. The resulting chiral forms are appropriate to lattice results obtained with operators already in use and could be used to study the restoration of taste symmetry in the continuum limit. I assume that the fourth root of the fermion determinant can be incorporated in staggered chiral perturbation theory using the replica method.

  7. Cell cycle population effects in perturbation studies

    PubMed Central

    O'Duibhir, Eoghan; Lijnzaad, Philip; Benschop, Joris J; Lenstra, Tineke L; van Leenen, Dik; Groot Koerkamp, Marian JA; Margaritis, Thanasis; Brok, Mariel O; Kemmeren, Patrick; Holstege, Frank CP

    2014-01-01

    Growth condition perturbation or gene function disruption are commonly used strategies to study cellular systems. Although it is widely appreciated that such experiments may involve indirect effects, these frequently remain uncharacterized. Here, analysis of functionally unrelated Saccharyomyces cerevisiae deletion strains reveals a common gene expression signature. One property shared by these strains is slower growth, with increased presence of the signature in more slowly growing strains. The slow growth signature is highly similar to the environmental stress response (ESR), an expression response common to diverse environmental perturbations. Both environmental and genetic perturbations result in growth rate changes. These are accompanied by a change in the distribution of cells over different cell cycle phases. Rather than representing a direct expression response in single cells, both the slow growth signature and ESR mainly reflect a redistribution of cells over different cell cycle phases, primarily characterized by an increase in the G1 population. The findings have implications for any study of perturbation that is accompanied by growth rate changes. Strategies to counter these effects are presented and discussed. PMID:24952590

  8. Singular perturbation equations for flexible satellites

    NASA Technical Reports Server (NTRS)

    Huang, T. C.; Das, A.

    1973-01-01

    The dynamic model of a flexible satellite with n generalized structural position coordinates requires the solution of a set of N coupled nonlinear ordinary or partial differential equations. For single composite body satellites, N is equal to (n + 3). For dual-spin systems, N is equal to (n + 9). These equations usually involve time derivatives up to the second order. For large values of n, linearization of the system has so far been the only practicable way of solution. The present study shows a method of avoiding this linearization by reducing the N equations to three or nine nonlinear, coupled, first-order ordinary differential equations involving only the angular velocities of the composite bodies. The solutions for these angular velocities lead to linear equations in the n generalized structural position coordinates, which can then be solved by known methods.

  9. Dose perturbation due to the polysulfone cap surrounding a Fletcher-Williamson colpostat.

    PubMed

    Price, Michael J; Kry, Stephen F; Eifel, Patricia J; Salehpour, Mohammad; Mourtada, Firas

    2010-01-01

    We conducted a metrological evaluation of the dosimetric impact due to the polysulfone cap used with the Fletcher-Williamson (FW) colpostat for 192Ir high-dose rate and pulsed-dose rate intracavitary brachytherapy using Monte Carlo simulations. Polysulfone caps with diameter of 30 mm, 25 mm, 20 mm, and 16 mm (mini-ovoid) were simulated and the absorbed dose rate in the surrounding water was calculated and compared to the dose rate for a bare 192Ir source in water. The dose perturbation depended on the cap diameter, distance away from the cap surface, and angular position around the cap. The largest dose rate reductions were found to be in the direction of the tumor bed where the cap is thickest. The range of perturbation over all depths and cap diameters was +2.8% (dose enhancement) to -6.8% (dose reduction). The FW colpostat cap's material composition should be modified to reduce this dosimetric effect or brachytherapy treatment planning dose algorithms should be improved to account for this perturbation. PMID:20160700

  10. An elaborate data set on human gait and the effect of mechanical perturbations

    PubMed Central

    Hnat, Sandra K.; van den Bogert, Antonie J.

    2015-01-01

    Here we share a rich gait data set collected from fifteen subjects walking at three speeds on an instrumented treadmill. Each trial consists of 120 s of normal walking and 480 s of walking while being longitudinally perturbed during each stance phase with pseudo-random fluctuations in the speed of the treadmill belt. A total of approximately 1.5 h of normal walking (>5000 gait cycles) and 6 h of perturbed walking (>20,000 gait cycles) is included in the data set. We provide full body marker trajectories and ground reaction loads in addition to a presentation of processed data that includes gait events, 2D joint angles, angular rates, and joint torques along with the open source software used for the computations. The protocol is described in detail and supported with additional elaborate meta data for each trial. This data can likely be useful for validating or generating mathematical models that are capable of simulating normal periodic gait and non-periodic, perturbed gaits. PMID:25945311

  11. Radial transport with perturbed magnetic field

    SciTech Connect

    Hazeltine, R. D.

    2015-05-15

    It is pointed out that the viscosity coefficient describing radial transport of toroidal angular momentum is proportional to the second power of the gyro-radius—like the corresponding coefficients for particle and heat transport—regardless of any geometrical symmetry. The observation is widely appreciated, but worth emphasizing because some literature gives the misleading impression that asymmetry can allow radial moment transport in first-order.

  12. ANGULAR MOMENTUM CHANGING TRANSITIONS IN PROTON-RYDBERG HYDROGEN ATOM COLLISIONS

    SciTech Connect

    Vrinceanu, D.; Onofrio, R.; Sadeghpour, H. R. E-mail: onofrior@gmail.com

    2012-03-01

    Collisions between electrically charged particles and neutral atoms are central for understanding the dynamics of neutral gases and plasmas in a variety of physical situations of terrestrial and astronomical interest. Specifically, redistribution of angular momentum states within the degenerate shell of highly excited Rydberg atoms occurs efficiently in distant collisions with ions. This process is crucial in establishing the validity of the local thermal equilibrium assumption and may also play a role in determining a precise ionization fraction in primordial recombination. We provide an accurate expression for the non-perturbative rate coefficient of collisions between protons and H(nl) ending in a final state H(nl'), with n being the principal quantum number and l, l' the initial and final angular momentum quantum numbers, respectively. The validity of this result is confirmed by results of classical trajectory Monte Carlo simulations. Previous results, obtained by Pengelly and Seaton only for dipole-allowed transitions l {yields} l {+-} 1, overestimate the l-changing collisional rate coefficients approximately by a factor of six, and the physical origin of this overestimation is discussed.

  13. Consequential angular momentum loss and the period gap of cataclysmic variables

    NASA Astrophysics Data System (ADS)

    King, A. R.; Kolb, U.

    1995-01-01

    We consider cataclysmic variable evolution driven partially by angular momentum losses which are themselves the result of mass transfer (e.g., via mass loss from an accretion disk). We show that such consequential angular momentum loss (CAML) mechanisms have great difficulty in reproducing the main features of the CV period gap. To interrupt mass transfer at all, CAML-driven systems must be unstable to dynamical-timescale mass transfer above the gap. Further, extremely tight constraints on the system parameters (e.g., the masses) are required to account for the observed width of the CV period gap: the CAML mechanism must essentially bring the system to the brink of thermal-timescale mass transfer instability. It is not obvious that these requirements can be satisfied in any given case, and they make the system very vulnerable to unstable mass transfer through small perturbations of the CAML process. A magnetic disk wind, as recently suggested by Livio and Pringle, cannot provide a large enough orbital torque to make a gap of the observed width except for unacceptably small white dwarf masses.

  14. Symmetry broken and restored coupled-cluster theory: I. Rotational symmetry and angular momentum

    NASA Astrophysics Data System (ADS)

    Duguet, T.

    2015-02-01

    We extend coupled-cluster (CC) theory performed on top of a Slater determinant breaking rotational symmetry to allow for the exact restoration of the angular momentum at any truncation order. The main objective relates to the description of near-degenerate finite quantum systems with an open-shell character. As such, the newly developed many-body formalism offers a wealth of potential applications and further extensions dedicated to the ab initio description of, e.g., doubly open-shell atomic nuclei and molecule dissociation. The formalism, which encompasses both single-reference CC theory and projected Hartree-Fock theory as particular cases, permits the computation of usual sets of connected diagrams while consistently incorporating static correlations through the highly non-perturbative restoration of rotational symmetry. Interestingly, the yrast spectroscopy of the system, i.e. the lowest energy associated with each angular momentum, is accessed within a single calculation. A key difficulty presently overcome relates to the necessity to handle generalized energy and norm kernels for which naturally terminating CC expansions could be eventually obtained. The present work focuses on SU(2) but can be extended to any (locally) compact Lie group and to discrete groups, such as most point groups. In particular, the formalism will be soon generalized to U(1) symmetry associated with particle number conservation. This is relevant to Bogoliubov CC theory that was recently applied to singly open-shell nuclei.

  15. Modification of the DSN radio frequency angular tropospheric refraction model

    NASA Technical Reports Server (NTRS)

    Berman, A. L.

    1977-01-01

    The previously derived DSN Radio Frequency Angular Tropospheric Refraction Model contained an assumption which was subsequently seen to be at a variance with the theoretical basis of angular refraction. The modification necessary to correct the model is minor in that the value of a constant is changed.

  16. Spatial Angular Compounding for Elastography without the Incompressibility Assumption

    PubMed Central

    Rao, Min; Varghese, Tomy

    2007-01-01

    Spatial-angular compounding is a new technique that enables the reduction of noise artifacts in ultrasound elastography. Previous results using spatial angular compounding, however, were based on the use of the tissue incompressibility assumption. Compounded elastograms were obtained from a spatially-weighted average of local strain estimated from radiofrequency echo signals acquired at different insonification angles. In this paper, we present a new method for reducing the noise artifacts in the axial strain elastogram utilizing a least-squares approach on the angular displacement estimates that does not use the incompressibility assumption. This method produces axial strain elastograms with higher image quality, compared to noncompounded axial strain elastograms, and is referred to as the least-squares angular-compounding approach for elastography. To distinguish between these two angular compounding methods, the spatial-angular compounding with angular weighting based on the tissue incompressibility assumption is referred to as weighted compounding. In this paper, we compare the performance of the two angular-compounding techniques for elastography using beam steering on a linear-array transducer. Quantitative experimental results demonstrate that least-squares compounding provides comparable but smaller improvements in both the elastographic signal-to-noise ratio and the contrast-to-noise ratio, as compared to the weighted-compounding method. Ultrasound simulation results suggest that the least-squares compounding method performs better and provide accurate and robust results when compared to the weighted compounding method, in the case where the incompressibility assumption does not hold. PMID:16761786

  17. Quark and Gluon Orbital Angular Momentum: Where Are We?

    NASA Astrophysics Data System (ADS)

    Lorcé, Cédric; Liu, Keh-Fei

    2016-06-01

    The orbital angular momentum of quarks and gluons contributes significantly to the proton spin budget and attracted a lot of attention in the recent years, both theoretically and experimentally. We summarize the various definitions of parton orbital angular momentum together with their relations with parton distributions functions. In particular, we highlight current theoretical puzzles and give some prospects.

  18. One particularity of energy-angular secondary electrons spectrum

    NASA Astrophysics Data System (ADS)

    Borisov, S. S.; Zaitsev, S. I.

    2006-05-01

    In this work we discuss the problems of the energy-angular spectrum of backscattered and true secondary electrons simulation using the discrete (DLA) and the continuous (CLA) loss approximations. The presence of an angular spectrum artefact - the deviation from the sinusoidal distribution over the range of 177-18O° from the beam direction is shown.

  19. Angular distribution of light scattered from heavily doped silica fibres

    SciTech Connect

    Alekseev, V V; Likhachev, M E; Bubnov, M M; Salganskii, M Yu; Khopin, V F; Gur'yanov, Aleksei N; Dianov, Evgenii M

    2011-10-31

    This paper describes an experimental setup for precision measurements of the angular distribution of light scattered by optical fibres in a wide angular range and demonstrates that the models of anomalous scattering proposed to date need to be refined. We have found and interpreted a discrepancy between the Rayleigh scattering coefficients measured by different techniques.

  20. On the non-uniform distribution of the angular elements of near-Earth objects

    NASA Astrophysics Data System (ADS)

    JeongAhn, Youngmin; Malhotra, Renu

    2014-02-01

    We examine the angular distributions of near-Earth objects (NEOs) which are often regarded as uniform. The apparent distribution of the longitude of ascending node, Ω, is strongly affected by well-known seasonal effects in the discovery rate of NEOs. The deviation from the expected π-periodicity in the apparent distribution of Ω indicates that its intrinsic distribution is slightly enhanced along a mean direction, Ω‾=111°; approximately 53% of NEOs have Ω values within ±90° of Ω‾. We also find that each subgroup of NEOs (Amors, Apollos and Atens) has different observational selection effects which cause different non-uniformities in the apparent distributions of their arguments of perihelion ω, and longitudes of perihelion ϖ. For their intrinsic distributions, our analysis reveals that the Apollo asteroids have non-uniform ω due to secular dynamics associated with inclination-eccentricity-ω coupling, and the Amors’ ϖ distribution is peaked towards the secularly forced eccentricity vector. The Apollos’ ω distribution is axial, favoring values near 0° and 180°; the two quadrants centered at 0° and 180° account for 55% of the Apollos’ ω values. The Amors’ ϖ distribution peaks near ϖ‾=4°; 61% of Amors have ϖ within ±90° of this peak. We show that these modest but statistically significant deviations from uniform random distributions of angular elements are owed to planetary perturbations, primarily Jupiter’s. It is remarkable that this strongly chaotic population of minor planets reveals the presence of Jupiter in its angular distributions.

  1. Methods for measuring and transporting angular momentum in general relativity

    NASA Astrophysics Data System (ADS)

    Nichols, David; Flanagan, Eanna; Stein, Leo; Vines, Justin

    2016-03-01

    For an observer in a curved spacetime, elements of the dual space of the set of linearized Poincare transformations from the observer's tangent space to itself can naturally be interpreted as local linear and angular momenta. We give an operational procedure by which the observer can measure such local linear and angular momenta from the local spacetime geometry. These momenta can be interpreted as approximate versions of the linear and angular momenta of the spacetime about the observer's location. The measurement algorithm allows for a more accurate determination of the linear and angular momentum of stationary, asymptotically flat systems than previous proposals do. We also describe a prescription by which observers at different locations can compare values of their measured linear and angular momentum by using a specific transport equation, which refines previous proposals. These operational definitions may also prove useful for clarifying the physical interpretation of Bondi-Metzner-Sachs asymptotic charges in asymptotically flat spacetimes.

  2. High-dimensional quantum nature of ghost angular Young's diffraction

    SciTech Connect

    Chen Lixiang; Leach, Jonathan; Jack, Barry; Padgett, Miles J.; Franke-Arnold, Sonja; She Weilong

    2010-09-15

    We propose a technique to characterize the dimensionality of entangled sources affected by any environment, including phase and amplitude masks or atmospheric turbulence. We illustrate this technique on the example of angular ghost diffraction using the orbital angular momentum (OAM) spectrum generated by a nonlocal double slit. We realize a nonlocal angular double slit by placing single angular slits in the paths of the signal and idler modes of the entangled light field generated by parametric down-conversion. Based on the observed OAM spectrum and the measured Shannon dimensionality spectrum of the possible quantum channels that contribute to Young's ghost diffraction, we calculate the associated dimensionality D{sub total}. The measured D{sub total} ranges between 1 and 2.74 depending on the opening angle of the angular slits. The ability to quantify the nature of high-dimensional entanglement is vital when considering quantum information protocols.

  3. CLASS: The Cosmology Large Angular Scale Surveyor

    NASA Technical Reports Server (NTRS)

    Essinger-Hileman, Thomas; Ali, Aamir; Amiri, Mandana; Appel, John W.; Araujo, Derek; Bennett, Charles L.; Boone, Fletcher; Chan, Manwei; Cho, Hsiao-Mei; Chuss, David T.; Colazo, Felipe; Crowe, Erik; Denis, Kevin; Dunner, Rolando; Eimer, Joseph; Gothe, Dominik; Halpern, Mark; Kogut, Alan J.; Miller, Nathan; Moseley, Samuel; Rostem, Karwan; Stevenson, Thomas; Towner, Deborah; U-Yen, Kongpop; Wollack, Edward

    2014-01-01

    The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment to measure the signature of a gravitational wave background from inflation in the polarization of the cosmic microwave background (CMB). CLASS is a multi-frequency array of four telescopes operating from a high-altitude site in the Atacama Desert in Chile. CLASS will survey 70% of the sky in four frequency bands centered at 38, 93, 148, and 217 GHz, which are chosen to straddle the Galactic-foreground minimum while avoiding strong atmospheric emission lines. This broad frequency coverage ensures that CLASS can distinguish Galactic emission from the CMB. The sky fraction of the CLASS survey will allow the full shape of the primordial B-mode power spectrum to be characterized, including the signal from reionization at low-length. Its unique combination of large sky coverage, control of systematic errors, and high sensitivity will allow CLASS to measure or place upper limits on the tensor-to-scalar ratio at a level of r = 0:01 and make a cosmic-variance-limited measurement of the optical depth to the surface of last scattering, tau. (c) (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  4. Semiclassical model for attosecond angular streaking.

    PubMed

    Smolarski, M; Eckle, P; Keller, U; Dörner, R

    2010-08-16

    Attosecond angular streaking is a new technique to achieve unsurpassed time accuracy of only a few attoseconds. Recently this has been successfully used to set an upper limit on the electron tunneling delay time in strong laser field ionization. The measurement technique can be modeled with either the time-dependent Schrödinger equation (TDSE) or a more simple semiclassical approach that describes the process in two steps in analogy to the three-step model in high harmonic generation (HHG): step one is the tunnel ionization and step two is the classical motion in the strong laser field. Here we describe in detail a semiclassical model which is based on the ADK theory for the tunneling step, with subsequent classical propagation of the electron in the laser field. We take into account different ellipticities of the laser field and a possible wavelength-dependent ellipticity that is typically observed for pulses in the two-optical-cycle regime. This semiclassical model shows excellent agreement with the experimental result. PMID:20721150

  5. Angular Synchronization by Eigenvectors and Semidefinite Programming

    PubMed Central

    Singer, A.

    2010-01-01

    The angular synchronization problem is to obtain an accurate estimation (up to a constant additive phase) for a set of unknown angles θ1, …, θn from m noisy measurements of their offsets θi − θj mod 2π. Of particular interest is angle recovery in the presence of many outlier measurements that are uniformly distributed in [0, 2π) and carry no information on the true offsets. We introduce an efficient recovery algorithm for the unknown angles from the top eigenvector of a specially designed Hermitian matrix. The eigenvector method is extremely stable and succeeds even when the number of outliers is exceedingly large. For example, we successfully estimate n = 400 angles from a full set of m=(4002) offset measurements of which 90% are outliers in less than a second on a commercial laptop. The performance of the method is analyzed using random matrix theory and information theory. We discuss the relation of the synchronization problem to the combinatorial optimization problem Max-2-Lin mod L and present a semidefinite relaxation for angle recovery, drawing similarities with the Goemans-Williamson algorithm for finding the maximum cut in a weighted graph. We present extensions of the eigenvector method to other synchronization problems that involve different group structures and their applications, such as the time synchronization problem in distributed networks and the surface reconstruction problems in computer vision and optics. PMID:21179593

  6. Millimetre Wave with Rotational Orbital Angular Momentum

    PubMed Central

    Zhang, Chao; Ma, Lu

    2016-01-01

    Orbital angular momentum (OAM) has been widely studied in fibre and short-range communications. The implementation of millimetre waves with OAM is expected to increase the communication capacity. Most experiments demonstrate the distinction of OAM modes by receiving all of the energy in the surface vertical to the radiation axis in space. However, the reception of OAM is difficult in free space due to the non-zero beam angle and divergence of energy. The reception of OAM in the space domain in a manner similar to that in optical fibres (i.e., receiving all of the energy rings vertical to the radiation axis) is impractical, especially for long-distance transmission. Here, we fabricate a prototype of the antenna and demonstrate that rather than in the space domain, the OAM can be well received in the time domain via a single antenna by rotating the OAM wave at the transmitter, i.e., the radio wave with rotational OAM. The phase and frequency measured in the experiment reveal that for different OAM modes, the received signals act as a commonly used orthogonal frequency division multiplexing (OFDM) signal in the time domain. This phase rotation has promising prospects for use in the practical reception of different OAMs of millimetre waves in long-distance transmission. PMID:27596746

  7. Interannual variation of global atmospheric angular momentum

    SciTech Connect

    Chen, Tsing-Chang; Yen, Ming-Cheng; Tribbia, J.J.

    1996-10-01

    The relative atmospheric angular momentum (RAM) integrated over the globe is an explicit variable representing the state of the atmospheric general circulation. After removing the annual, semiannual, and higher-frequency components, the filtered global RAM time series for the past 14 years (1979-92) is highly correlated with both the Southern Oscillation index and the tropical Pacific sea surface temperature averaged over Area NINO-3 (5{degrees}S-5{degrees}N, 150{degrees}W-90{degrees}W). The interannual variation of global RAM is coherent with the poleward propagation of RAM anomalies. The global RAM anomalies reach their minimum values when westerly anomalies emerge in the Tropics and higher latitudes during a cold El Nino-Southern Oscillation (ENSO) event. On the other hand, global RAM anomalies attain their maximum values when westerly anomalies arrive at the subtropics of both hemispheres during a warm ENSO event. It is demonstrated that the poleward propagation of RAM anomalies results from the flip-flop oscillation of the anomalous circulation between cold and warm ENSO events. 11 refs., 3 figs.

  8. The missing angular momentum of superconductors.

    PubMed

    Hirsch, J E

    2008-06-11

    We point out that the Meissner effect, the process by which a superconductor expels magnetic field from its interior, represents an unsolved puzzle within the London-Bardeen-Cooper-Schrieffer theoretical framework used to describe the physics of conventional superconductors, because it appears to give rise to non-conservation of angular momentum. Possible ways to avoid this inconsistency within the conventional theory of superconductivity are argued to be far-fetched. Consequently, we argue that unless/until a consistent explanation is put forth, the existence of the Meissner effect represents an anomaly that casts doubt on the validity of the conventional framework. Instead, we point out that three elements of the unconventional theory of hole superconductivity (that are not part of the conventional theory) allow for a consistent explanation of the Meissner effect, namely: (i) that the charge distribution in superconductors is macroscopically inhomogeneous, (ii) that superconducting electrons reside in mesoscopic orbits of radius 2λ(L) (λ(L) = London penetration depth), and (iii) that spin-orbit coupling plays an essential role in superconductivity. PMID:21694324

  9. Angular velocity and centripetal acceleration relationship

    NASA Astrophysics Data System (ADS)

    Monteiro, Martín; Cabeza, Cecilia; Marti, Arturo C.; Vogt, Patrik; Kuhn, Jochen

    2014-05-01

    During the last few years, the growing boom of smartphones has given rise to a considerable number of applications exploiting the functionality of the sensors incorporated in these devices. A sector that has unexpectedly taken advantage of the power of these tools is physics teaching, as reflected in several recent papers. In effect, the use of smartphones has been proposed in several physics experiments spanning mechanics, electromagnetism, optics, oscillations, and waves, among other subjects. Although mechanical experiments have received considerable attention, most of them are based on the use of the accelerometer. An aspect that has received less attention is the use of rotation sensors or gyroscopes. An additional advance in the use of these devices is given by the possibility of obtaining data using the accelerometer and the gyroscope simultaneously. The aim of this paper is to consider the relation between the centripetal acceleration and the angular velocity. Instead of using a formal laboratory setup, in this experiment a smartphone is attached to the floor of a merry-go-round, found in many playgrounds. Several experiments were performed with the roundabout rotating in both directions and with the smart-phone at different distances from the center. The coherence of the measurements is shown.

  10. Cyclic transformation of orbital angular momentum modes

    NASA Astrophysics Data System (ADS)

    Schlederer, Florian; Krenn, Mario; Fickler, Robert; Malik, Mehul; Zeilinger, Anton

    2016-04-01

    The spatial modes of photons are one realization of a QuDit, a quantum system that is described in a D-dimensional Hilbert space. In order to perform quantum information tasks with QuDits, a general class of D-dimensional unitary transformations is needed. Among these, cyclic transformations are an important special case required in many high-dimensional quantum communication protocols. In this paper, we experimentally demonstrate a cyclic transformation in the high-dimensional space of photonic orbital angular momentum (OAM). Using simple linear optical components, we show a successful four-fold cyclic transformation of OAM modes. Interestingly, our experimental setup was found by a computer algorithm. In addition to the four-cyclic transformation, the algorithm also found extensions to higher-dimensional cycles in a hybrid space of OAM and polarization. Besides being useful for quantum cryptography with QuDits, cyclic transformations are key for the experimental production of high-dimensional maximally entangled Bell-states.

  11. Millimetre Wave with Rotational Orbital Angular Momentum.

    PubMed

    Zhang, Chao; Ma, Lu

    2016-01-01

    Orbital angular momentum (OAM) has been widely studied in fibre and short-range communications. The implementation of millimetre waves with OAM is expected to increase the communication capacity. Most experiments demonstrate the distinction of OAM modes by receiving all of the energy in the surface vertical to the radiation axis in space. However, the reception of OAM is difficult in free space due to the non-zero beam angle and divergence of energy. The reception of OAM in the space domain in a manner similar to that in optical fibres (i.e., receiving all of the energy rings vertical to the radiation axis) is impractical, especially for long-distance transmission. Here, we fabricate a prototype of the antenna and demonstrate that rather than in the space domain, the OAM can be well received in the time domain via a single antenna by rotating the OAM wave at the transmitter, i.e., the radio wave with rotational OAM. The phase and frequency measured in the experiment reveal that for different OAM modes, the received signals act as a commonly used orthogonal frequency division multiplexing (OFDM) signal in the time domain. This phase rotation has promising prospects for use in the practical reception of different OAMs of millimetre waves in long-distance transmission. PMID:27596746

  12. Angular Distribution and Angular Dispersion in Collision of 19F+27Al at 114 MeV

    NASA Astrophysics Data System (ADS)

    Wang, Qi; Dong, Yu-Chuan; Li, Song-Lin; Duan, Li-Min; Xu, Hu-Shan; Xu, Hua-Gen; Chen, Ruo-Fu; Wu, He-Yu; Han, Jian-Long; Li, Zhi-Chang; Lu, Xiu-Qin; Zhao, Kui; Liu, Jian-Cheng; Sergey, Yu-Kun

    2004-10-01

    Angular distributions of fragments B, C, N, O, F, Ne, Na, Mg and Al induced by the collision of 19F+27Al at 114 MeV have been measured. Angular dispersion parameters are extracted from the experimental data and compared with the theoretical ones. The dynamic dispersions for dissipative products depend strongly on the charge number Z of the fragments.

  13. Non-adiabatic perturbations in multi-component perfect fluids

    SciTech Connect

    Koshelev, N.A.

    2011-04-01

    The evolution of non-adiabatic perturbations in models with multiple coupled perfect fluids with non-adiabatic sound speed is considered. Instead of splitting the entropy perturbation into relative and intrinsic parts, we introduce a set of symmetric quantities, which also govern the non-adiabatic pressure perturbation in models with energy transfer. We write the gauge invariant equations for the variables that determine on a large scale the non-adiabatic pressure perturbation and the rate of changes of the comoving curvature perturbation. The analysis of evolution of the non-adiabatic pressure perturbation has been made for several particular models.

  14. Evolution of the curvature perturbations during warm inflation

    SciTech Connect

    Matsuda, Tomohiro

    2009-06-15

    This paper considers warm inflation as an interesting application of multi-field inflation. Delta-N formalism is used for the calculation of the evolution of the curvature perturbations during warm inflation. Although the perturbations considered in this paper are decaying after the horizon exit, the corrections to the curvature perturbations sourced by these perturbations can remain and dominate the curvature perturbations at large scales. In addition to the typical evolution of the curvature perturbations, inhomogeneous diffusion rate is considered for warm inflation, which may lead to significant non-Gaussianity of the spectrum.

  15. Thermostat-Like Perturbations of an Oscillator

    NASA Astrophysics Data System (ADS)

    Freidlin, Mark

    2016-07-01

    We consider an oscillator with one degree of freedom perturbed by a deterministic thermostat-like perturbation and another system, in particular, another oscillator, coupled with the first one. If the Hamiltonian of the first system has saddle points, the whole system has, in a sense, a stochastic behavior on long time intervals. Under certain conditions, one can introduce the relative entropy and describe metastability and other large deviation effects in this deterministic system. If the coupled system is also an oscillator, the long time evolution of the energy of this oscillator has a diffusion approximation. To get these results one has to regularize the system. But the results are, to some extent, independent of the regularization: the stochasticity is due to instabilities at saddle points of the original system.

  16. Resummation Approach in QCD Analytic Perturbation Theory

    NASA Astrophysics Data System (ADS)

    Bakulev, Alexander P.; Potapova, Irina V.

    2011-10-01

    We discuss the resummation approach in QCD Analytic Perturbation Theory (APT). We start we a simple example of asymptotic ower series for a zero-dimensional analog of the scalar g φ model. Then we give a short historic preamble of APT and show that renormgroup improvement of the QCD perturbation theory dictates to use the Fractional APT (FAPT). After that we discuss the (F)PT resummation of nonpower series and provide the one-, two-, and three-loop resummation recipes. We show the results of applications of these recipes to the estimation of the Adler function D(Q) in the N=4 region of Q and of the Higgs-boson-decay width Γ(mH2) for M=100-180 GeV.

  17. Perturbative type II amplitudes for BPS interactions

    NASA Astrophysics Data System (ADS)

    Basu, Anirban

    2016-02-01

    We consider the perturbative contributions to the {{ R }}4, {D}4{{ R }}4 and {D}6{{ R }}4 interactions in toroidally compactified type II string theory. These BPS interactions do not receive perturbative contributions beyond genus three. We derive Poisson equations satisfied by these moduli dependent string amplitudes. These T-duality invariant equations have eigenvalues that are completely determined by the structure of the integrands of the multi-loop amplitudes. The source terms are given by boundary terms of the moduli space of Riemann surfaces corresponding to both separating and non-separating nodes. These are determined directly from the string amplitudes, as well as from U-duality constraints and logarithmic divergences of maximal supergravity. We explicitly solve these Poisson equations in nine and eight-dimensions.

  18. A Renormalisation Group Method. III. Perturbative Analysis

    NASA Astrophysics Data System (ADS)

    Bauerschmidt, Roland; Brydges, David C.; Slade, Gordon

    2015-05-01

    This paper is the third in a series devoted to the development of a rigorous renormalisation group method for lattice field theories involving boson fields, fermion fields, or both. In this paper, we motivate and present a general approach towards second-order perturbative renormalisation, and apply it to a specific supersymmetric field theory which represents the continuous-time weakly self-avoiding walk on . Our focus is on the critical dimension . The results include the derivation of the perturbative flow of the coupling constants, with accompanying estimates on the coefficients in the flow. These are essential results for subsequent application to the 4-dimensional weakly self-avoiding walk, including a proof of existence of logarithmic corrections to their critical scaling. With minor modifications, our results also apply to the 4-dimensional -component spin model.

  19. Study of the spectrum of inflaton perturbations

    SciTech Connect

    Glenz, Matthew M.; Parker, Leonard

    2009-09-15

    We examine the spectrum of inflaton fluctuations resulting from any given long period of exponential inflation. Infrared and ultraviolet divergences in the inflaton dispersion summed over all modes do not appear in our approach. We show how the scale invariance of the perturbation spectrum arises. We also examine the spectrum of scalar perturbations of the metric that is created by the inflaton fluctuations that have left the Hubble sphere during inflation and the spectrum of density perturbations that they produce at reentry after inflation has ended. When the inflaton dispersion spectrum is renormalized during the expansion, we show (for the case of the quadratic inflaton potential) that the density perturbation spectrum approaches a mass-independent limit as the inflaton mass approaches zero, and remains near that limiting value for masses less than about 1/4 of the inflationary Hubble constant. We show that this limiting behavior does not occur if one only makes the Minkowski space subtraction, without the further adiabatic subtractions that involve time derivatives of the expansion scale factor a(t). We also find a parametrized expression for the energy density produced by the change in a(t) as inflation ends. If the end of inflation were sufficiently abrupt, then the temperature corresponding to this energy density could be very significant. We also show that fluctuations of the inflaton field that are present before inflation starts are not dissipated during inflation and could have a significant observational effect today. The mechanism for this is caused by the initial fluctuations through stimulated emission from the vacuum.

  20. Tests of Chiral Perturbation Theory with COMPASS

    SciTech Connect

    Friedrich, Jan

    2010-12-28

    The COMPASS experiment at CERN studies with high precision pion-photon induced reactions on nuclear targets via the Primakoff effect. This offers the possibility to test chiral perturbation theory (ChPT) in various channels: Pion Compton scattering allows to clarify the longstanding question of the pion polarisabilities, single neutral pion production is related to the chiral anomaly, and for the two-pion production cross sections exist as yet untested ChPT predictions.

  1. Geometric perturbation theory and plasma physics

    SciTech Connect

    Omohundro, S.M.

    1985-04-04

    Modern differential geometric techniques are used to unify the physical asymptotics underlying mechanics, wave theory and statistical mechanics. The approach gives new insights into the structure of physical theories and is suited to the needs of modern large-scale computer simulation and symbol manipulation systems. A coordinate-free formulation of non-singular perturbation theory is given, from which a new Hamiltonian perturbation structure is derived and related to the unperturbed structure. The theory of perturbations in the presence of symmetry is developed, and the method of averaging is related to reduction by a circle group action. The pseudo-forces and magnetic Poisson bracket terms due to reduction are given a natural asymptotic interpretation. Similar terms due to changing reference frames are related to the method of variation of parameters, which is also given a Hamiltonian formulation. These methods are used to answer a question about nearly periodic systems. The answer leads to a new secular perturbation theory that contains no ad hoc elements. Eikonal wave theory is given a Hamiltonian formulation that generalizes Whitham's Lagrangian approach. The evolution of wave action density on ray phase space is given a Hamiltonian structure using a Lie-Poisson bracket. The relationship between dissipative and Hamiltonian systems is discussed. A new type of attractor is defined which attracts both forward and backward in time and is shown to occur in infinite-dimensional Hamiltonian systems with dissipative behavior. The theory of Smale horseshoes is applied to gyromotion in the neighborhood of a magnetic field reversal and the phenomenon of reinsertion in area-preserving horseshoes is introduced. The central limit theorem is proved by renormalization group techniques. A natural symplectic structure for thermodynamics is shown to arise asymptotically from the maximum entropy formalism.

  2. Stability of SIRS system with random perturbations

    NASA Astrophysics Data System (ADS)

    Lu, Qiuying

    2009-09-01

    Epidemiological models with bilinear incidence rate λSI usually have an asymptotically stable trivial equilibrium corresponding to the disease-free state, or an asymptotically stable non-trivial equilibrium (i.e. interior equilibrium) corresponding to the endemic state. In this paper, we consider an epidemiological model, which is an SIRS model with or without distributed time delay influenced by random perturbations. We present the stability conditions of the disease-free equilibrium of the associated stochastic SIRS system.

  3. Perturbation Theory for Superfluid in Nonuniform Potential

    NASA Astrophysics Data System (ADS)

    Koshida, Shinji; Kato, Yusuke

    2016-05-01

    Perturbation theory of superfluid fraction in terms of nonuniform potential is constructed. We find that the coefficient of the leading term is determined by the dynamical structure factor or density fluctuation of the system. The results for the ideal Bose gas and the interacting Bose system with linear dispersion are consistent to implications from Landau's criterion. We also find that the superfluidity of Tomonaga-Luttinger liquid with K>2 is shown to be stable against nonuniform potential.

  4. Intelligent perturbation algorithms to space scheduling optimization

    NASA Technical Reports Server (NTRS)

    Kurtzman, Clifford R.

    1991-01-01

    The limited availability and high cost of crew time and scarce resources make optimization of space operations critical. Advances in computer technology coupled with new iterative search techniques permit the near optimization of complex scheduling problems that were previously considered computationally intractable. Described here is a class of search techniques called Intelligent Perturbation Algorithms. Several scheduling systems which use these algorithms to optimize the scheduling of space crew, payload, and resource operations are also discussed.

  5. Perturbations of nested branes with induced gravity

    SciTech Connect

    Sbisà, Fulvio; Koyama, Kazuya E-mail: kazuya.koyama@port.ac.uk

    2014-06-01

    We study the behaviour of weak gravitational fields in models where a 4D brane is embedded inside a 5D brane equipped with induced gravity, which in turn is embedded in a 6D spacetime. We consider a specific regularization of the branes internal structures where the 5D brane can be considered thin with respect to the 4D one. We find exact solutions corresponding to pure tension source configurations on the thick 4D brane, and study perturbations at first order around these background solutions. To perform the perturbative analysis, we adopt a bulk-based approach and we express the equations in terms of gauge invariant and master variables using a 4D scalar-vector-tensor decomposition. We then propose an ansatz on the behaviour of the perturbation fields when the thickness of the 4D brane goes to zero, which corresponds to configurations where gravity remains finite everywhere in the thin limit of the 4D brane. We study the equations of motion using this ansatz, and show that they give rise to a consistent set of differential equations in the thin limit, from which the details of the internal structure of the 4D brane disappear. We conclude that the thin limit of the ''ribbon'' 4D brane inside the (already thin) 5D brane is well defined (at least when considering first order perturbations around pure tension configurations), and that the gravitational field on the 4D brane remains finite in the thin limit. We comment on the crucial role of the induced gravity term on the 5D brane.

  6. Angular dependent light emission from planar waveguides

    SciTech Connect

    Peter, Jaison; Prabhu, Radhakrishna; Radhakrishnan, P.; Vallabhan, C. P. G.; Nampoori, V. P. N.; Kailasnath, M.

    2015-01-07

    We have investigated the angular dependence of amplified spontaneous emission (ASE) and laser emission from an asymmetric and free-standing polymer thin films doped with rhodamine 6G, which is transversely pumped by a pulsed Nd:YAG laser. A semi-leaky waveguide or quasi-waveguide structure has been developed by spin coating technique. In these waveguides, the light was confined by the film/air-film/glass substrate interfaces. At the film/substrate interface, a portion of light will reflect back into the film (guided mode) and the remaining refracted to the substrate resulting in cutoff modes. A blue-shift in ASE has been observed when the pump power was increased from 8 to 20 mW allowing a limited range of tuning of emission wavelength. To study the directionality of the ASE from the waveguide, we have measured the output intensity and FWHM of emission spectra as a function of viewing angle (θ) from the plane parallel to film. From the detailed examination of the output emission spectra, as +θ increases from 0° there has been an initial decrease in output intensity, but at a particular angle ≈10° an increase in output intensity was observed. This additional peak in output intensity as +θ is a clear indication of coexistence of the cutoff mode. We also present a compact solid-state laser based on leaky mode propagation from the dye-doped polymer free-standing film (∼50 μm thickness) waveguide. The partial reflections from the broad lateral surfaces of the free-standing films provided the optical feedback for the laser emission with high directionality. For a pump power of 22 mW, an intense line with FWHM <0.2 nm was observed at 578 nm.

  7. Cosmic perturbations through the cyclic ages

    SciTech Connect

    Erickson, Joel K.; Gratton, Steven; Steinhardt, Paul J.; Turok, Neil

    2007-06-15

    We analyze the evolution of cosmological perturbations in the cyclic model, paying particular attention to their behavior and interplay over multiple cycles. Our key results are: (1) galaxies and large scale structure present in one cycle are generated by the quantum fluctuations in the preceding cycle without interference from perturbations or structure generated in earlier cycles and without interfering with structure generated in later cycles; (2) the ekpyrotic phase, an epoch of gentle contraction with equation of state w>>1 preceding the hot big bang, makes the universe homogeneous, isotropic and flat within any given observer's horizon; and (3) although the universe is uniform within each observer's horizon, the structure of the cyclic universe on very large scales is more complex, owing to the effects of superhorizon length perturbations, and cannot be described globally as a Friedmann-Robertson-Walker cosmology. In particular, we show that the ekpyrotic contraction phase is so effective in smoothing, flattening and isotropizing the universe within the horizon that this phase alone suffices to solve the horizon and flatness problems even without an extended period of dark energy domination (a kind of low energy inflation). Instead, the cyclic model rests on a genuinely novel, noninflationary mechanism (ekpyrotic contraction) for resolving the classic cosmological conundrums.

  8. Non-perturbative effects in spin glasses.

    PubMed

    Castellana, Michele; Parisi, Giorgio

    2015-01-01

    We present a numerical study of an Ising spin glass with hierarchical interactions--the hierarchical Edwards-Anderson model with an external magnetic field (HEA). We study the model with Monte Carlo (MC) simulations in the mean-field (MF) and non-mean-field (NMF) regions corresponding to d ≥ 4 and d < 4 for the d-dimensional ferromagnetic Ising model respectively. We compare the MC results with those of a renormalization-group (RG) study where the critical fixed point is treated as a perturbation of the MF one, along the same lines as in the -expansion for the Ising model. The MC and the RG method agree in the MF region, predicting the existence of a transition and compatible values of the critical exponents. Conversely, the two approaches markedly disagree in the NMF case, where the MC data indicates a transition, while the RG analysis predicts that no perturbative critical fixed point exists. Also, the MC estimate of the critical exponent ν in the NMF region is about twice as large as its classical value, even if the analog of the system dimension is within only ~2% from its upper-critical-dimension value. Taken together, these results indicate that the transition in the NMF region is governed by strong non-perturbative effects. PMID:25733337

  9. Noninflationary model with scale invariant cosmological perturbations

    SciTech Connect

    Peter, Patrick; Pinho, Emanuel J. C.; Pinto-Neto, Nelson

    2007-01-15

    We show that a contracting universe which bounces due to quantum cosmological effects and connects to the hot big-bang expansion phase, can produce an almost scale invariant spectrum of perturbations provided the perturbations are produced during an almost matter dominated era in the contraction phase. This is achieved using Bohmian solutions of the canonical Wheeler-DeWitt equation, thus treating both the background and the perturbations in a fully quantum manner. We find a very slightly blue spectrum (n{sub S}-1>0). Taking into account the spectral index constraint as well as the cosmic microwave background normalization measure yields an equation of state that should be less than {omega} < or approx. 8x10{sup -4}, implying n{sub S}-1{approx}O(10{sup -4}), and that the characteristic curvature scale of the Universe at the bounce is L{sub 0}{approx}10{sup 3}l{sub Pl}, a region where one expects that the Wheeler-DeWitt equation should be valid without being spoiled by string or loop quantum gravity effects. We have also obtained a consistency relation between the tensor-to-scalar ratio T/S and the scalar spectral index as T/S{approx}4.6x10{sup -2}{radical}(n{sub S}-1), leading to potentially measurable differences with inflationary predictions.

  10. Relativistic Positioning System in perturbed spacetime

    NASA Astrophysics Data System (ADS)

    Kostić, Uroš; Horvat, Martin; Gomboc, Andreja

    2015-11-01

    We present a variant of a Global Navigation Satellite System called a Relativistic Positioning System (RPS), which is based on emission coordinates. We modelled the RPS dynamics in a spacetime around Earth, described by a perturbed Schwarzschild metric, where we included the perturbations due to Earth multipoles (up to the 6th), the Moon, the Sun, Venus, Jupiter, solid tide, ocean tide, and Kerr rotation effect. The exchange of signals between the satellites and a user was calculated using a ray-tracing method in the Schwarzschild spacetime. We find that positioning in a perturbed spacetime is feasible and is highly accurate already with standard numerical procedures: the positioning algorithms used to transform between the emission and the Schwarzschild coordinates of the user are very accurate and time efficient—on a laptop it takes 0.04 s to determine the user’s spatial and time coordinates with a relative accuracy of {10}-28-{10}-26 and {10}-32-{10}-30, respectively.

  11. Dark matter dispersion tensor in perturbation theory

    NASA Astrophysics Data System (ADS)

    Aviles, Alejandro

    2016-03-01

    We compute the dark matter velocity dispersion tensor up to third order in perturbation theory using the Lagrangian formalism, revealing growing solutions at the third and higher orders. Our results are general and can be used for any other perturbative formalism. As an application, corrections to the matter power spectrum are calculated, and we find that some of them have the same structure as those in the effective field theory of large-scale structure, with "EFT-like" coefficients that grow quadratically with the linear growth function and are further suppressed by powers of the logarithmic linear growth factor f ; other corrections present additional k dependence. Due to the velocity dispersions, there exists a free-streaming scale that suppresses the whole 1-loop power spectrum. Furthermore, we find that as a consequence of the nonlinear evolution, the free-streaming length is shifted towards larger scales, wiping out more structure than that expected in linear theory. Therefore, we argue that the formalism developed here is better suited for a perturbation treatment of warm dark matter or neutrino clustering, where the velocity dispersion effects are well known to be important. We discuss implications related to the nature of dark matter.

  12. Using Lagrangian perturbation theory for precision cosmology

    SciTech Connect

    Sugiyama, Naonori S.

    2014-06-10

    We explore the Lagrangian perturbation theory (LPT) at one-loop order with Gaussian initial conditions. We present an expansion method to approximately compute the power spectrum LPT. Our approximate solution has good convergence in the series expansion and enables us to compute the power spectrum in LPT accurately and quickly. Non-linear corrections in this theory naturally satisfy the law of conservation of mass because the relation between matter density and the displacement vector of dark matter corresponds to the conservation of mass. By matching the one-loop solution in LPT to the two-loop solution in standard perturbation theory, we present an approximate solution of the power spectrum which has higher order corrections than the two-loop order in standard perturbation theory with the conservation of mass satisfied. With this approximation, we can use LPT to compute a non-linear power spectrum without any free parameters, and this solution agrees with numerical simulations at k = 0.2 h Mpc{sup –1} and z = 0.35 to better than 2%.

  13. Predicting pathway perturbations in Down syndrome.

    PubMed

    Gardiner, K

    2003-01-01

    Comparative annotation of human chromosome 21 genomic sequence with homologous regions of mouse chromosomes 16, 17 and 10 has identified 170 orthologous gene pairs. Functional annotation of these genes, based on literature reports and computationally-derived predictions, shows that a broad range of cellular processes are represented. A goal of Down syndrome research is to determine which of these processes are perturbed by overexpression of chromosome 21 genes, and which may, therefore, contribute to the cognitive deficits that characterize Down syndrome. Eleven chromosome 21 genes are annotated to interact with or be affected by components of the MAP Kinase pathway and eight are involved in Ca2+/calcineurin signaling. Both pathways are critical for normal neurological function, and consequently their perturbations are proposed as candidates for phenotypic relevance. We present evidence suggesting that the MAP Kinase pathway is perturbed in the Ts65Dn mouse model of Down syndrome at 4-6 months of age. Analysis is complicated by the observation that overexpression of chromosome 21 genes in trisomy may be affected by method of detection, organism, tissue or brain region, and/or developmental age. PMID:15068236

  14. Perturbative gravity in the causal approach

    NASA Astrophysics Data System (ADS)

    Grigore, D. R.

    2010-01-01

    Quantum theory of the gravitation in the causal approach is studied up to the second order of perturbation theory in the causal approach. We emphasize the use of cohomology methods in this framework. After describing in detail the mathematical structure of the cohomology method we apply it in three different situations: (a) the determination of the most general expression of the interaction Lagrangian; (b) the proof of gauge invariance in the second order of perturbation theory for the pure gravity system—massless and massive; (c) the investigation of the arbitrariness of the second-order chronological products compatible with renormalization principles and gauge invariance (i.e. the renormalization problem in the second order of perturbation theory). In case (a) we investigate pure gravity systems and the interaction of massless gravity with matter (described by scalars and spinors) and massless Yang-Mills fields. We obtain a difference with respect to the classical field theory due to the fact that in quantum field theory one cannot enforce the divergenceless property on the vector potential and this spoils the divergenceless property of the usual energy-momentum tensor. To correct this one needs a supplementary ghost term in the interaction Lagrangian. In all three case, the computations are more simple than by the usual methods.

  15. Perturbative Critical Behavior from Spacetime Dependent Couplings

    SciTech Connect

    Dong, Xi; Horn, Bart; Silverstein, Eva; Torroba, Gonzalo

    2012-08-03

    We find novel perturbative fixed points by introducing mildly spacetime-dependent couplings into otherwise marginal terms. In four-dimensional QFT, these are physical analogues of the small-{epsilon} Wilson-Fisher fixed point. Rather than considering 4-{epsilon} dimensions, we stay in four dimensions but introduce couplings whose leading spacetime dependence is of the form {lambda}x{sup {kappa}}{mu}{sup {kappa}}, with a small parameter {kappa} playing a role analogous to {epsilon}. We show, in {phi}{sup 4} theory and in QED and QCD with massless flavors, that this leads to a critical theory under perturbative control over an exponentially wide window of spacetime positions x. The exact fixed point coupling {lambda}{sub *}(x) in our theory is identical to the running coupling of the translationally invariant theory, with the scale replaced by 1/x. Similar statements hold for three-dimensional {phi}{sup 6} theories and two-dimensional sigma models with curved target spaces. We also describe strongly coupled examples using conformal perturbation theory.

  16. Topological quantum order: Stability under local perturbations

    SciTech Connect

    Bravyi, Sergey; Hastings, Matthew B.; Michalakis, Spyridon

    2010-09-15

    We study zero-temperature stability of topological phases of matter under weak time-independent perturbations. Our results apply to quantum spin Hamiltonians that can be written as a sum of geometrically local commuting projectors on a D-dimensional lattice with certain topological order conditions. Given such a Hamiltonian H{sub 0}, we prove that there exists a constant threshold {epsilon}>0 such that for any perturbation V representable as a sum of short-range bounded-norm interactions, the perturbed Hamiltonian H=H{sub 0}+{epsilon}V has well-defined spectral bands originating from low-lying eigenvalues of H{sub 0}. These bands are separated from the rest of the spectra and from each other by a constant gap. The band originating from the smallest eigenvalue of H{sub 0} has exponentially small width (as a function of the lattice size). Our proof exploits a discrete version of Hamiltonian flow equations, the theory of relatively bounded operators, and the Lieb-Robinson bound.

  17. Combining coupled cluster and perturbation theory

    NASA Astrophysics Data System (ADS)

    Nooijen, Marcel

    1999-12-01

    Single reference coupled cluster (CC) singles and doubles theory is combined with low-order perturbation theory (PT) to treat ground state electron correlation. Two variants of the general scheme are discussed that differ in the type of amplitudes that are approximated perturbatively and which are treated to infinite order. The combined CC/PT methods to include ground state correlation are merged with equation-of-motion (EOM) and similarity transformed EOM methods to describe excitation spectra of the highly correlated s-tetrazine, MnO4- and Ni(CO)4 systems. It is shown that the computationally efficient CC/PT schemes can reproduce full CCSD results even if perturbation theory by itself is a very poor approximation, as is the case for many transition metal compounds. In a second test CC/PT is applied to determine ground state equilibrium molecular structures and harmonic vibrational frequencies for a set of small molecules. Using either variant of CC/PT, full CCSD geometries are easily recovered, while vibrational frequencies can be more sensitive to details of the approximation.

  18. Baryonic matter perturbations in decaying vacuum cosmology

    SciTech Connect

    Marttens, R.F. vom; Zimdahl, W.; Hipólito-Ricaldi, W.S. E-mail: wiliam.ricaldi@ufes.br

    2014-08-01

    We consider the perturbation dynamics for the cosmic baryon fluid and determine the corresponding power spectrum for a Λ(t)CDM model in which a cosmological term decays into dark matter linearly with the Hubble rate. The model is tested by a joint analysis of data from supernovae of type Ia (SNIa) (Constitution and Union 2.1), baryonic acoustic oscillations (BAO), the position of the first peak of the anisotropy spectrum of the cosmic microwave background (CMB) and large-scale-structure (LSS) data (SDSS DR7). While the homogeneous and isotropic background dynamics is only marginally influenced by the baryons, there are modifications on the perturbative level if a separately conserved baryon fluid is included. Considering the present baryon fraction as a free parameter, we reproduce the observed abundance of the order of 5% independently of the dark-matter abundance which is of the order of 32% for this model. Generally, the concordance between background and perturbation dynamics is improved if baryons are explicitly taken into account.

  19. Multifrequency perturbations in matter-wave interferometry

    NASA Astrophysics Data System (ADS)

    Günther, A.; Rembold, A.; Schütz, G.; Stibor, A.

    2015-11-01

    High-contrast matter-wave interferometry is essential in various fundamental quantum mechanical experiments as well as for technical applications. Thereby, contrast and sensitivity are typically reduced by decoherence and dephasing effects. While decoherence accounts for a general loss of quantum information in a system due to entanglement with the environment, dephasing is due to collective time-dependent external phase shifts, which can be related to temperature drifts, mechanical vibrations, and electromagnetic oscillations. In contrast to decoherence, dephasing can, in principle, be reversed. Here, we demonstrate in experiment and theory a method for the analysis and reduction of the influence of dephasing noise and perturbations consisting of several external frequencies in an electron interferometer. This technique uses the high spatial and temporal resolution of a delay-line detector to reveal and remove dephasing perturbations by second-order correlation analysis. It allows matter-wave experiments under perturbing laboratory conditions and can be applied, in principle, to electron, atom, ion, neutron, and molecule interferometers.

  20. Gamma Ray Emission Tomography and Angular Correlation Measurements to Study the Distribution and Binding Site of Selenium.

    NASA Astrophysics Data System (ADS)

    Dahni, Anwar

    Available from UMI in association with The British Library. The distribution of ^ {75}Se in tissue equivalent materials was investigated employing Gamma ray Emission Topography with a rectilinear scanner utilizing NaI(Tl) and BGO detectors. The reconstructed images, using Filtered Back Projection and Iterative techniques were presented in 2D colour and 3D representations. Using a lead collimator of aperture 1.5 x 20 mm and 70 length, the distribution of selenium with variation of volume and concentration was examined and clearly seen. Several corrections such as background, scattering, attenuation compensation and X-ray characteristic suppression, were performed to improve the quality of the images which was evaluated in terms of the fidelity factor. The possibility of quantifying an image was considered with regard to spatial resolution and least detectable concentration. The spatial resolution was measured using two small vials containing the same concentration of selenium, the value obtained was the same as the width of the collimator aperture. The value of the least detectable concentration of selenium however, was difficult to find, due to the many ambiguous factors involved. The binding site of selenium which is based on quadrupole interaction with the surrounding electric field, was investigated employing Perturbed Angular Correlation (PAC) experiments using NaI(Tl) and BaF_2 detectors. Using NaI(Tl) detectors, it was difficult to observe the perturbation, due to the poor time resolution. The BaF_2 detector according to the literature has a shorter light emission decay time constant (0.6 ns), suggested that a better time resolution than that found with the NaI(Tl) detectors could be obtained. A Perturbed Angular Correlation experiment employing BaF _2 detectors and a fast-slow coincidence system was set up. The time differential PAC of selenium in solution showed an unperturbed angular correlation pattern. The main problem is the very short half life of the

  1. Angular magnetoresistance in semiconducting undoped amorphous carbon thin films

    NASA Astrophysics Data System (ADS)

    Sagar, Rizwan Ur Rehman; Saleemi, Awais Siddique; Zhang, Xiaozhong

    2015-05-01

    Thin films of undoped amorphous carbon thin film were fabricated by using Chemical Vapor Deposition and their structure was investigated by using High Resolution Transmission Electron Microscopy and Raman Spectroscopy. Angular magnetoresistance (MR) has been observed for the first time in these undoped amorphous carbon thin films in temperature range of 2 ˜ 40 K. The maximum magnitude of angular MR was in the range of 9.5% ˜ 1.5% in 2 ˜ 40 K. The origin of this angular MR was also discussed.

  2. How orbital angular momentum affects beam shifts in optical reflection

    SciTech Connect

    Merano, M.; Hermosa, N.; Woerdman, J. P.; Aiello, A.

    2010-08-15

    It is well known that reflection of a Gaussian light beam (TEM{sub 00}) by a planar dielectric interface leads to four beam shifts when compared to the geometrical-optics prediction. These are the spatial Goos-Haenchen (GH) shift, the angular GH shift, the spatial Imbert-Fedorov (IF) shift, and the angular IF shift. We report here, theoretically and experimentally, that endowing the beam with orbital angular momentum leads to coupling of these four shifts; this is described by a 4x4 mixing matrix.

  3. Angular momentum evolution during star and planetary system formation

    NASA Astrophysics Data System (ADS)

    Davies, Claire L.; Greaves, Jane S.

    2014-01-01

    We focused on analysing the role played by protoplanetary disks in the evolution of angular momentum during star formation. If all the angular momentum contained within collapsing pre-stellar cores was conserved during their formation, proto-stars would reach rotation rates exceeding their break-up velocities before they reached the main sequence (Bodenheimer 1995). In order to avoid this occuring, methods by which proto-stars can lose angular momentum must exist. Angular momentum can be transferred from star to disk via stellar magnetic field lines through a process called magnetic braking (Camenzind 1990; Königl 1991). Alternatively, the stellar angular momentum can be lost from the star-disk system entirely via stellar- or disk-winds (e.g. Pelletier & Pudritz 1992; Matt & Pudritz 2005). The proportion of lost stellar angular momentum retained within the protoplanetary disk is important to studies of planetary system formation. If the bulk motion within the disk remains Keplerian, any increase of angular momentum in the disk causes an outward migration of disk material and an expansion of the disk. Therefore, an increase in disk angular momentum may cause a reduction in the disk surface density, often used to indicate the disk's ability to form planets. We made use of multi-wavelength data available in the literature to directly calculate the stellar and disk angular momenta for two nearby regions of star formation. Namely, these were the densely populated and highly irradiated Orion Nebula Cluster (ONC) and the comparitively sparse Taurus-Auriga region. Due to the limited size of the ONC dataset, we produced an average surface density profile for the region. We modelled the stars as solid body rotators due to their fully convective nature (Krishnamurthi et al. 1997) and assumed the disks are flat and undergo Keplerian rotation about the same rotation axis as the star. We observed the older disks within each of the two star forming regions to be preferentially

  4. Angular vibrations of cryogenically cooled double-crystal monochromators.

    PubMed

    Sergueev, I; Döhrmann, R; Horbach, J; Heuer, J

    2016-09-01

    The effect of angular vibrations of the crystals in cryogenically cooled monochromators on the beam performance has been studied theoretically and experimentally. A simple relation between amplitude of the vibrations and size of the focused beam is developed. It is shown that the double-crystal monochromator vibrations affect not only the image size but also the image position along the optical axis. Several methods to measure vibrations with the X-ray beam are explained and analyzed. The methods have been applied to systematically study angular crystal vibrations at monochromators installed at the PETRA III light source. Characteristic values of the amplitudes of angular vibrations for different monochromators are presented. PMID:27577762

  5. Electro-optic analyzer of angular momentum hyperentanglement.

    PubMed

    Wu, Ziwen; Chen, Lixiang

    2016-01-01

    Characterizing a high-dimensional entanglement is fundamental in quantum information applications. Here, we propose a theoretical scheme to analyze and characterize the angular momentum hyperentanglement that two photons are entangled simultaneously in spin and orbital angular momentum. Based on the electro-optic sampling with a proposed hyper-entanglement analyzer and the simple matrix operation using Cramer rule, our simulations show that it is possible to retrieve effectively both the information about the degree of polarization entanglement and the spiral spectrum of high-dimensional orbital angular momentum entanglement. PMID:26911530

  6. Angular magnetoresistance in semiconducting undoped amorphous carbon thin films

    SciTech Connect

    Sagar, Rizwan Ur Rehman; Saleemi, Awais Siddique; Zhang, Xiaozhong

    2015-05-07

    Thin films of undoped amorphous carbon thin film were fabricated by using Chemical Vapor Deposition and their structure was investigated by using High Resolution Transmission Electron Microscopy and Raman Spectroscopy. Angular magnetoresistance (MR) has been observed for the first time in these undoped amorphous carbon thin films in temperature range of 2 ∼ 40 K. The maximum magnitude of angular MR was in the range of 9.5% ∼ 1.5% in 2 ∼ 40 K. The origin of this angular MR was also discussed.

  7. Electro-optic analyzer of angular momentum hyperentanglement

    NASA Astrophysics Data System (ADS)

    Wu, Ziwen; Chen, Lixiang

    2016-02-01

    Characterizing a high-dimensional entanglement is fundamental in quantum information applications. Here, we propose a theoretical scheme to analyze and characterize the angular momentum hyperentanglement that two photons are entangled simultaneously in spin and orbital angular momentum. Based on the electro-optic sampling with a proposed hyper-entanglement analyzer and the simple matrix operation using Cramer rule, our simulations show that it is possible to retrieve effectively both the information about the degree of polarization entanglement and the spiral spectrum of high-dimensional orbital angular momentum entanglement.

  8. Detection of a spinning object using light's orbital angular momentum.

    PubMed

    Lavery, Martin P J; Speirits, Fiona C; Barnett, Stephen M; Padgett, Miles J

    2013-08-01

    The linear Doppler shift is widely used to infer the velocity of approaching objects, but this shift does not detect rotation. By analyzing the orbital angular momentum of the light scattered from a spinning object, we observed a frequency shift proportional to product of the rotation frequency of the object and the orbital angular momentum of the light. This rotational frequency shift was still present when the angular momentum vector was parallel to the observation direction. The multiplicative enhancement of the frequency shift may have applications for the remote detection of rotating bodies in both terrestrial and astronomical settings. PMID:23908234

  9. Electro-optic analyzer of angular momentum hyperentanglement

    PubMed Central

    Wu, Ziwen; Chen, Lixiang

    2016-01-01

    Characterizing a high-dimensional entanglement is fundamental in quantum information applications. Here, we propose a theoretical scheme to analyze and characterize the angular momentum hyperentanglement that two photons are entangled simultaneously in spin and orbital angular momentum. Based on the electro-optic sampling with a proposed hyper-entanglement analyzer and the simple matrix operation using Cramer rule, our simulations show that it is possible to retrieve effectively both the information about the degree of polarization entanglement and the spiral spectrum of high-dimensional orbital angular momentum entanglement. PMID:26911530

  10. Control of Angular Intervals for Angle-Multiplexed Holographic Memory

    NASA Astrophysics Data System (ADS)

    Kinoshita, Nobuhiro; Muroi, Tetsuhiko; Ishii, Norihiko; Kamijo, Koji; Shimidzu, Naoki

    2009-03-01

    In angle-multiplexed holographic memory, the full width at half maximum of the Bragg selectivity curves is dependent on the angle formed between the medium and incident laser beams. This indicates the possibility of high density and high multiplexing number by varying the angular intervals between adjacent holograms. We propose an angular interval scheduling for closely stacking holograms into medium even when the angle range is limited. We obtained bit error rates of the order of 10-4 under the following conditions: medium thickness of 1 mm, laser beam wavelength of 532 nm, and angular multiplexing number of 300.

  11. Scanning Twyman interferometer for measuring small angular displacement

    NASA Astrophysics Data System (ADS)

    Ma, Jianguo; Tong, Yue

    2010-12-01

    We present a simple but effective method for measuring small angular displacement based on a scanning Twyman interferometer ,in which, one of the two mirrors is mounted on the piezoelectric ceramic (PZT) droved by saw-tooth voltage, the status of interference fringes changes from static to dynamic. A photoelectric detector detects this dynamic photo-signal and changes into electronic signal. The signal is inputted into an oscillograph. The oscillogram will present interference crests. The method for measuring small angular displacement is based on the linear relation between the angular displacement and the crest shift on the oscillogram.

  12. Scanning Twyman interferometer for measuring small angular displacement

    NASA Astrophysics Data System (ADS)

    Ma, Jianguo; Tong, Yue

    2011-05-01

    We present a simple but effective method for measuring small angular displacement based on a scanning Twyman interferometer ,in which, one of the two mirrors is mounted on the piezoelectric ceramic (PZT) droved by saw-tooth voltage, the status of interference fringes changes from static to dynamic. A photoelectric detector detects this dynamic photo-signal and changes into electronic signal. The signal is inputted into an oscillograph. The oscillogram will present interference crests. The method for measuring small angular displacement is based on the linear relation between the angular displacement and the crest shift on the oscillogram.

  13. Generation and detection of orbital angular momentum via metasurface.

    PubMed

    Jin, Jinjin; Luo, Jun; Zhang, Xiaohu; Gao, Hui; Li, Xiong; Pu, Mingbo; Gao, Ping; Zhao, Zeyu; Luo, Xiangang

    2016-01-01

    Beams carrying orbital angular momentum possess a significant potential for modern optical technologies ranging from classical and quantum communication to optical manipulation. In this paper, we theoretically design and experimentally demonstrate an ultracompact array of elliptical nanoholes, which could convert the circularly polarized light into the cross-polarized vortex beam. To measure the topological charges of orbital angular momentum in a simple manner, another elliptical nanoholes array is designed to generate reference beam as a reference light. This approach may provide a new way for the generation and detection of orbital angular momentum in a compact device. PMID:27052796

  14. Generation and detection of orbital angular momentum via metasurface

    NASA Astrophysics Data System (ADS)

    Jin, Jinjin; Luo, Jun; Zhang, Xiaohu; Gao, Hui; Li, Xiong; Pu, Mingbo; Gao, Ping; Zhao, Zeyu; Luo, Xiangang

    2016-04-01

    Beams carrying orbital angular momentum possess a significant potential for modern optical technologies ranging from classical and quantum communication to optical manipulation. In this paper, we theoretically design and experimentally demonstrate an ultracompact array of elliptical nanoholes, which could convert the circularly polarized light into the cross-polarized vortex beam. To measure the topological charges of orbital angular momentum in a simple manner, another elliptical nanoholes array is designed to generate reference beam as a reference light. This approach may provide a new way for the generation and detection of orbital angular momentum in a compact device.

  15. Turbulent equipartition and homogenization of plasma angular momentum.

    PubMed

    Gürcan, O D; Diamond, P H; Hahm, T S

    2008-04-01

    A physical model of turbulent equipartition (TEP) of plasma angular momentum is developed. We show that using a simple, model insensitive ansatz of conservation of total angular momentum, a TEP pinch of angular momentum can be obtained. We note that this term corresponds to a part of the pinch velocity previously calculated using quasilinear gyrokinetic theory. We observe that the nondiffusive TEP flux is inward, and therefore may explain the peakedness of the rotation profiles observed in certain experiments. Similar expressions for linear toroidal momentum and flow are computed and it is noted that there is an additional effect due the radial profile of moment of inertia density. PMID:18517961

  16. Angular resolution of air-shower array-telescopes

    NASA Technical Reports Server (NTRS)

    Linsley, J.

    1985-01-01

    A fundamental limit on the angular resolution of air shower array-telescopes is set by the finite number of shower particles coupled with the finite thickness of the particle swarm. Consequently the angular resolution which can be achieved in practice depends in a determinant manner on the size and number of detectors in an array-telescope, as well as on the detector separation and the timing resolution. It is also necessary to examine the meaning of particle density in whatever type of detector is used. Results are given which can be used to predict the angular resolution of a given instrument for showers of various sizes, and to compare different instruments.

  17. Indirect precise angular control using four-wave mixing

    SciTech Connect

    Zhang, Wei; Ding, Dong-Sheng; Shi, Bao-Sen Guo, Guang-Can; Jiang, Yun-Kun

    2014-04-28

    Here, we show indirect precise angular control using a four-wave mixing (FWM) process. This was performed with a superposition of light with orbital angular momentum in an M-Type configuration of a hot {sup 85}Rb atomic ensemble. A gear-shaped interference pattern is observed at FWM light with a donut-shaped input signal. The gear could be rotated and is controlled through the change of the polarization of the pump laser. Our experimental results that are based on nonlinear coherent interactions have applications in image processing and precise angular control.

  18. Generation and detection of orbital angular momentum via metasurface

    PubMed Central

    Jin, Jinjin; Luo, Jun; Zhang, Xiaohu; Gao, Hui; Li, Xiong; Pu, Mingbo; Gao, Ping; Zhao, Zeyu; Luo, Xiangang

    2016-01-01

    Beams carrying orbital angular momentum possess a significant potential for modern optical technologies ranging from classical and quantum communication to optical manipulation. In this paper, we theoretically design and experimentally demonstrate an ultracompact array of elliptical nanoholes, which could convert the circularly polarized light into the cross-polarized vortex beam. To measure the topological charges of orbital angular momentum in a simple manner, another elliptical nanoholes array is designed to generate reference beam as a reference light. This approach may provide a new way for the generation and detection of orbital angular momentum in a compact device. PMID:27052796

  19. Excitation of stable Alfven eigenmodes by application of alternating magnetic field perturbations in the Compact Helical System

    SciTech Connect

    Ito, T.; Toi, K.; Isobe, M.; Nagaoka, K.; Takeuchi, M.; Akiyama, T.; Matsuoka, K.; Minami, T.; Nishimura, S.; Okamura, S.; Shimizu, A.; Suzuki, C.; Yoshimura, Y.; Takahashi, C.; Matsunaga, G.

    2009-09-15

    Stable toroidicity-induced Alfven eigenmodes (TAEs) with low toroidal mode number (n=1 and n=2) were excited by application of alternating magnetic field perturbations generated with a set of electrodes inserted into the edge region of neutral beam injection heated plasmas on the Compact Helical System [K. Nishimura, K. Matsuoka, M. Fujiwara et al., Fusion Technol. 17, 86 (1990)]. The gap locations of TAEs excited by the electrodes are in the plasma peripheral region of {rho}>0.7 ({rho} is the normalized minor radius) where energetic ion drive is negligibly small, while some AEs are excited by energetic ions in the plasma core region of {rho}<0.4. The damping rate of these stable TAEs derived from plasma responses to applied perturbations is fairly large, that is, {approx}9% to {approx}12% of the angular eigenfrequency. This large damping rate is thought to be dominantly caused by continuum damping and radiative damping.

  20. A perturbation theory study of electron vortices in electromagnetic fields: the case of infinitely long line charge and magnetic dipole.

    PubMed

    Xie, L; Wang, P; Pan, X Q

    2014-08-01

    The novel discovery of electron vortices carrying quantized orbital angular momentum motivated intensive research of their basic properties as well as applications, e.g. structural characterization of magnetic materials. In this paper, the fundamental interactions of electron vortices within infinitely long atomic-column-like electromagnetic fields are studied based on the relativistically corrected Pauli-Schrödinger equation and the perturbation theory. The relative strengths of three fundamental interactions, i.e. the electron-electric potential interaction, the electron-magnetic potential/field interaction and the spin-orbit coupling are discussed. The results suggest that the perturbation energies of the last two interactions are in an order of 10(3)-10(4) smaller than that of the first one for electron vortices. In addition, it is also found that the strengths of these interactions are strongly dependant on the spatial distributions of the electromagnetic field as well as the electron vortices. PMID:24690540