Large Relative Angles Research Articles

A new detection set-up to search the X17 boson

An excess of electron-positron pairs at large relative angle emitted in the 3H(p,e+e−)4He, 7Li(p,e+e−)8Be, and 11B(p,e+e−)12C nuclear processes has been recently observed. These anomalies are compatible with the creation of a boson with mass of about 17 MeV, not foreseen in the standard model. To probe the possible existence of the so called X17 boson, we propose to study for the first time the 3He(n,e+e−)4He reaction at the n_TOF facility at CERN. The experimental program and performance of the detector prototype are discussed.

Динамика плоского движения космического крана-манипулятора типа руки с учетом изгиба звеньев

The paper considers the plane motion dynamics of a three-link crane-manipulator consisting of two rods elastic in bending and a massive solid body attached to them at their end (load capture). All links are interconnected by hinge joints with the given (controlled) relative rotation angles. The first link is also connected to the mobile base. The system mathematical model was developed to calculate its non-stationary oscillations and dynamic loading of links at arbitrary in time and large relative angles of the links rotation as the solid bodies. The rods bending deformations (elastic transverse displacements and rotation angles of the axes) were considered to be insignificant (linear). Each rod ending was represented by the Ritz method using two given shape functions with the unknown coefficients, which were taken as the generalized coordinates. In this case, the “cantilever” bending forms of each rod with the given transverse displacement and angle of rotation at their ends were used. A simplified version was considered: each rod bending was represented by only one given form of its bending by a single moment applied at the end. System oscillation equations were obtained based on the principle of probable displacements in the generalized coordinates (four equations or two in a simplified form). Since rotation angles at the ends of the elastic rods were added to the given rotation angles of the non-deformable rods, total angles were left under the signs of sines and cosines without linearization for convenience of calculations and increasing accuracy. As a result, such equations of non-stationary oscillations remained non-linear. They were integrated by numerical methods using standard programs in one of the computer algebra systems. Examples are provided with the comparative results estimates obtained in the two-term and one-term approximations of the function in regard to the bending form of the system bending rod joints.

Time-domain simulation of sum-frequency hydrodynamic performance of a TLP-type floating wind turbine in multidirectional seas

Previous studies (Ren et al., 2022) by the authors have confirmed that the second-order diffracted wave loads are very sensitive to the wave directional spreading of the so-called storm-swell mixed seas where the storm-driven local seas combined with long-period swells propagating from different angles. In this paper, particular attention is paid to estimate the sum-frequency hydrodynamic forces and motion responses of a TLP-type floating wind turbine (FWT) in such complex sea states. A time-domain potential flow model is developed for the second-order interaction between the multidirectional irregular waves and moored structures. The boundary value problems for the scattered potential are solved by a higher-order boundary element method (HOBEM). The fourth-order Adams–Bashforth–Moulton method is used to update the wave surface and the Newmark method combined with the Newton–Raphson iteration scheme is adopted to solve the body motion equations.For validation, a freely floating hemisphere in unidirectional bichromatic waves is investigated and good agreement is found by comparing with Kim and Yue's frequency-domain results. Numerical tests are conducted on the TLP-type FWT with different combinations of incident angles and spreading factors of the storm-swell mixed seas. The effects of the wave headings and directional spreading on the sum-frequency hydrodynamic response are discussed. It is noted that when the swells approach the storm seas from large relative angles, the sum-frequency vertical response of the FWT can be up to seven times greater than that in the collinear mixed seas. In addition, the present model can extend the rotor-floater-tether coupled dynamic simulator of FWT to more realistic seas such as storm-swell mixed seas.

A comprehensive analysis of differential cross sections and analyzing powers in the proton\u2013deuteron break-up channel at 135 MeV

A selection of measured cross sections and vector analyzing powers, A_{x} and A_{y}, are presented for the vec {p}{d} break-up reaction. The data are taken with a polarized proton beam with a kinetic energy of 135 MeV using the Big Instrument for Nuclear-polarization Analysis (BINA) at KVI, the Netherlands. With this setup, A_{x} is extracted for the first time for a large range of energies as well as polar and azimuthal angles of the two outgoing protons. For most of the configurations, the results at small and large relative azimuthal angles differ in behavior when comparing experimental data with the theoretical calculations. We also performed a more global comparison of our data with theoretical calculations. The cross-section results show huge values of chi ^{2}/d.o.f.. The absolute values of chi ^{2}/d.o.f. for the components of vector analyzing powers, A_{x} and A_{y}, are smaller than the ones for the cross section, partly due to larger uncertainties for these observables. However, also for these observables no satisfactory agreement is found for all angular combinations. This implies that the present models of a three-nucleon force are not able to provide a satisfactory description of experimental data.

Stabilization of a straight longitudinal dune under bimodal wind with large directional variation.

It has been observed that the direction in which a sand dune extends its crest line depends on seasonal variation of wind direction; when the variation is small, the crest line develops more or less perpendicularly to the mean wind direction to form a transverse dune with some undulation. In the case of bimodal wind with a large relative angle, however, the dune extends its crest along the mean wind direction and evolves into an almost straight longitudinal dune. Motivated by these observations, we investigate the dynamical stability of isolated dunes using the crest line model, where the dune dynamics is represented by its crest line motion. First, we extend the previous linear stability analysis under the unidirectional wind to the case with nonzero slant angle between the wind direction and the normal direction of the crest line, and show that the stability diagram does not depend on the slant angle. Second, we examine how the linear stability is affected by the seasonal changes of wind direction in the case of bimodal wind with equal strength and duration. For the transverse dune, we find that the stability is virtually the same with that for the unidirectional wind as long as the dune evolution during a season is small. On the other hand, in the case of the longitudinal dune, the dispersions of the growth rates for the perturbation are drastically different from those of the unidirectional wind, and we find that the largest growth rate is always located at k=0. This is because the growth of the perturbation with k≠0 is canceled by the alternating wind from opposite sides of the crest line even though it grows during each duration period of the bimodal wind. For a realistic parameter set, the system is in the wavy unstable regime of the stability diagram for the unidirectional wind, thus the straight transverse dune is unstable to develop undulation and eventually evolves into a string of barchans when the seasonal variation of wind direction is small, but the straight longitudinal dune is stabilized under the large variation of bimodal wind direction. We also perform numerical simulations on the crest line model, and find that the results are consistent with our linear analysis and the previous reports that show that the longitudinal dunes tend to have a straight ridge elongating over time.

Correlations between jets and charged particles in PbPb and pp collisions at s N N = 2.76 $$ \sqrt{s_{\mathrm{NN}}}=2.76 $$ TeV

The quark-gluon plasma is studied via medium-induced changes to correlations between jets and charged particles in PbPb collisions compared to pp reference data. This analysis uses data sets from PbPb and pp collisions with integrated luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, collected at sqrt(s[NN]) = 2.76 TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity (Delta eta) and relative azimuthal angle (Delta phi) with respect to reconstructed jet directions. Charged particles are correlated with all jets with transverse momentum (pt) above 120 GeV, and with the leading and subleading jets (the highest and second-highest in pt, respectively) in a selection of back-to-back dijet events. Modifications in PbPb data relative to pp reference data are characterized as a function of PbPb collision centrality and charged particle pt. A centrality-dependent excess of low-pt particles is present for all jets studied, and is most pronounced in the most central events. This excess of low-pt particles follows a Gaussian-like distribution around the jet axis, and extends to large relative angles of Delta eta approximately 1 and Delta phi approximately 1.

Dependence of the Raman spectrum characteristics on the number of layers and stacking orientation in few-layer graphene

Few-layer graphene (FLG) samples prepared by two methods (chemical vapor deposition (CVD) followed by transfer onto SiO2/Si substrate and mechanical exfoliation) are characterized by combined optical contrast and micro-Raman mapping experiments. We examine the behavior of the integrated intensity ratio of the 2D and G bands (A2D/AG) and of the 2D band width (Γ2D) as a function of the number of layers (N). For our mechanically exfoliated FLG, A2D/AG decreases and Γ2D increases with N as expected for commensurately stacked FLG. For CVD FLG, both similar and opposite behaviors are observed and are ascribed to different stacking orders. For small (respectively, large) relative rotation angle between consecutive layers (θ), the values of the A2D/AG ratio is smaller (respectively, larger) and the 2D band is broader (respectively, narrower) than for single-layer graphene. Moreover, the A2D/AG ratio decreases (respectively, increases) and, conversely, Γ2D increases (respectively, decreases) as a function of N for small (respectively, large) θ. An intermediate behavior has also been found and is interpreted as the presence of both small and large θ within the studied area. These results confirm that neither A2D/AG nor Γ2D are definitive criteria to identify single-layer graphene, or to count N in FLG.

In-plane angular-dependent exchange bias and blocking temperature of a Cr2O3 () film system prepared by post annealing

A ()-oriented Cr2O3 film was prepared, and the in-plane angular dependence of both its exchange bias (Hex) and blocking temperature (TB) were investigated. By changing the applied magnetic field direction, we modulated the relative angle between the magnetic anisotropy direction of Cr2O3 and the applied magnetic field direction. We found that TB ∼ Néel temperature (TN) for a sufficiently large relative angle, while TB is smaller than TN for a small relative angle, reflecting a change in the effective exchange coupling energy. By tuning the applied magnetic field direction, we demonstrated extrinsic control of Hex and TB.

Optical absorption spectrum of rotated trilayer graphene

Using ab initio calculations we have studied the optical linear response of different configurations of twisted trilayer graphene systems. We have found that when one of the outer layers is rotated the system shows an angle-dependent optical spectrum as its twisted bilayer counterpart; however, in this case there are two absorption peaks located in the visible range of the spectrum and one more in the intermediate infrared range for large relative rotation angles. When two layers are rotated the spectrum exhibits only two absorption peaks in the visible range revealing information about the two relative rotation angles between the layers in the structure. All these absorption peaks in the visible range shift to the intermediate infrared range for small angles.

Improving Safety and Performance of Small-Scale Vertical Axis Wind Turbines

Although horizontal axis wind turbines (HAWT) are considered more efficient in operation than their vertical axis wind turbine (VAWT) counterpart and are more commonly used in wind farms as large wind turbines, the VAWT may offer greater advantages in safety and operation when it comes to their application within the urban environment. Yaw control systems are an essential requirement for the safe operation of HAWT, which are costly and require high levels of maintenance, but are inherently unnecessary for VAWT. At low blade speed ratios, the performance of VAWT degrades owing to strong dynamic stall effects. This necessitates VAWT operation at high blade speed ratios to suppress them. However, the consequent large rotational speeds lead to hazardous operation especially in confined urban areas. Thus to improve the low blade speed performance, a preliminary experimental investigation has been carried out at the Aerodynamics Laboratory of the University of New South Wales on an H-type VAWT blade that employed zero-net mass flux actuation. This technique has traditionally been used for static stall delay and flow separation mitigation on aircraft wings. In the present study, large relative angles of incidence were simulated by sinusoidally oscillating the blade about its quarter-chord, and resulted in the formation of dynamic stall vortices. The application of zero-net mass flux actuation was found to have a beneficial effect on the blade aerodynamic performance by either suppressing dynamic stall or delaying its onset to higher angles of attack. This study, therefore, suggests that reduced oscillatory loads and more robust output power can be achieved with zero-net mass flux actuation on VAWT operating at low blade-speed ratios. Consequently, the findings have positive practical implications for the design of small-scale VAWT for widespread use in the urban environment.

Spin-torque induced rf oscillation in magnetic tunnel junctions with an Fe-rich CoFeB free layer

A steady magnetization precession induced by spin-torque was studied in magnetic tunnel junctions with an Fe-rich CoFeB free layer under a perpendicular magnetic field. The Fe-rich CoFeB free layer showed a low critical current (Ic) for spin-torque induced switching. The low value of Ic for the Fe-rich CoFeB free layer enabled us to observe the spin-torque induced rf oscillation even at a low dc bias current (Idc). The oscillation frequency increased with increasing Idc, indicating the out-of-plane precessional mode. Owing to the perpendicular magnetic anisotropy in the Fe-rich CoFeB free layer, the large relative angle between the free and pinned layers was achieved under the perpendicular magnetic field. The out-of-plane precession of the magnetization and the large relative angle resulted in the large rf output power of 175 nW.

On large angle multiple gluon radiation

Jet shape observables which involve measurements restricted to a part of phase space are sensitive to multiplication of soft gluon with large relative angles and give rise to specific single logarithmically enhanced (SL) terms (non-global logs). We consider associated distributions in two variables which combine measurement of a jet shape V in the whole phase space (global) and that of the transverse energy flow away from the jet direction, Eout (non-global). We show that associated distributions factorize into the global distribution in V and a factor that takes into account SL contributions from multi-gluon ``hedgehog'' configurations in all orders. The latter is the same that describes the single-variable Eout distribution, but evaluated at a rescaled energy VQ.

WIDE-ANGLE α-t COINCIDENCE MEASUREMENT IN THE BREAKUP OF 7Li ON 27Al

We have performed wide-angle in-plane coincidence measurements of the alpha particles and tritons emitted in the 48-MeV 7 Li projectile breakup reaction on 27 Al . The data have been analyzed using the post-form distorted-wave Born-approximation (DWBA) theory of breakup reactions where Coulomb and nuclear breakup as well as their interference terms are included. The theory is able to provide a good description of the experimental data particularly at large relative angles between the fragments. The interference between the Coulomb and nuclear breakup modes is found to be significant.

Many-body Coulomb perturbation of azimuthal alpha - alpha correlations.

The perturbation of azimuthal \ensuremath{\alpha}-\ensuremath{\alpha} correlations by many-body Coulomb interactions with other emitted particles is investigated. Individual emissions are simulated by modeling instantaneous emission from the surface of a hot rotating gas. Upon emission, the particle trajectories are calculated by means of classical calculations which incorporate the many-body Coulomb interaction between the emitted particles and the emitting source. For high-multiplicity events, the initial azimuthal correlation between emitted \ensuremath{\alpha} particles can be attenuated by final-state Coulomb interactions. The effect is most pronounced for \ensuremath{\alpha} particles emitted close to the barrier, but it appears of minor importance for \ensuremath{\alpha} particles emitted at large relative angles and at energies well above the Coulomb barrier. \textcopyright{} 1996 The American Physical Society.

Multifragmentation induced by relativistic α-projectiles

Multifragmentation of the system α + 197 Au has been studied at incident energies of 1 and 3.6 GeV/nucleon with the new 4π setup, “FASA”. A very high mean IMF multiplicity of 〈 M〉 IMF =5.1 ± 0.8 is observed at the higher incident energy. Applying the statistical multifragmentation model of Gross, a breakup density ϱ ϱ 0 of about 1 7 is deduced from the relative velocity between two IMFs at large relative angles. The excitation energy increases from 4.5 MeV/nucleon at the lower beam energy to 5.5 MeV/nucleon at the higher beam energy. The time difference between the emission of two IMFs is less than 100 fm/c, justifying to call this process a simultaneous breakup.

Sensitivities of the relative velocity between fragments on the decay mechanism

Relative velocity spectra of two intermediate mass fragments (IMF) emitted in 18O induced reactions on 197Au at E/ A=84MeV were investigated. The average relative velocity measured at small and also large relative angles is satisfactorily reproduced by calculations that model the sequential emission of IMF's and light particles on the basis of statistical model calculations. A similar agreement is found for the average relative velocity measured in α+ 197Au reactions at E/ A=800MeV. Thus, no conclusive evidence for a transition from a conventional multi-sequential decay to a true multifragmentation process can be found at an excitation energy between 3 and 4 MeV per nucleon.

Fundamental Study of Wave Impact Loads on Ship Bow (3rd Report)

As part of their studies conducted regarding the wave impact loads acting on the ship bow and the structural responses thereto by a series of drop tests, the authors analyzed the scale effect, or the influence of the scale of bow models therein used on the results of the drop tests.It is often claimed that the estimated impulsive pressure determined by a model test varies with the scale of the model. To see if such a claim was well-founded or not, the authors carried out the drop test using a 1/15 scale model and compared the results with those obtained using the 1/3 scale model in the previous tests. The results of this comparative study may be summarized as follows.At first, the maximum impulsive pressure obtained using the 1/15 scale model was considerably smaller than that determined using the 1/3 scale model. This difference became small with large relative impact angle α. Such a difference must have come from the difference in relative size of the pressure gauges fitted to these two models. On the other hand, the equivalent static pressure Peq obtained using the 1/15 scale model and that obtained using the 1/3 scale model remained the same, if the size of the panel was proportional to the size of the model. That is, Peq didn't vary with the scale of the model.Further, investigation was made of the effects of the size and the location of the panel on Peq. Peq indicated a considerable change according to the size and location of the panel when the impact angle α was 0°, but the change became smaller with large α of, say, α=5°.

Fundamental Study of Wave Impact Load on Ship Bow (1st Report)

As part of their studies conducted regarding the wave impact loads acting on the ship bow and the structural responses thereto by a series of drop tests, the authors analyzed the scale effect, or the influence of the scale of bow models therein used on the results of the drop tests.It is often claimed that the estimated impulsive pressure determined by a model test varies with the scale of the model. To see if such a claim was well-founded or not, the authors carried out the drop test using a 1/15 scale model and compared the results with those obtained using the 1/3 scale model in the previous tests. The results of this comparative study may be summarized as follows.At first, the maximum impulsive pressure obtained using the 1/15 scale model was considerably smaller than that determined using the 1/3 scale model. This difference became small with large relative impact angle α. Such a difference must have come from the difference in relative size of the pressure gauges fitted to these two models. On the other hand, the equivalent static pressure Peq obtained using the 1/15 scale model and that obtained using the 1/3 scale model remained the same, if the size of the panel was proportional to the size of the model. That is, Peq didn't vary with the scale of the model.Further, investigation was made of the effects of the size and the location of the panel on Peq. Peq indicated a considerable change according to the size and location of the panel when the impact angle α was 0°, but the change became smaller with large α of, say, α=5°.

Determination of the Multipolarity of Nuclear Electromagnetic Transitions Using a Magnetic Pair Spectrometer

An intermediate-image magnetic pair spectrometer has been modified so as to respond to positron-electron internal pairs emitted at large relative angles ($50\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\lesssim}\ensuremath{\theta}\ensuremath{\lesssim}90\ifmmode^\circ\else\textdegree\fi{}$) thereby making the pair-line transmission depend sensitively on the multipolarity of electromagnetic transitions above 2 MeV. The modification consists of a specially designed spiral baffle system which selects pairs emitted within 105\ifmmode^\circ\else\textdegree\fi{} azimuthal sectors on opposite sides of the axis. Measurements are made of the net yield of an internal-pair-conversion coincidence line, both in the normal spectrometer operation (pairs with relative angles $0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\lesssim}90\ifmmode^\circ\else\textdegree\fi{}$) and with the spiral baffle installed, giving a reduction ratio ${R}_{\ensuremath{\omega}}=\frac{{Y}_{\mathrm{with}\mathrm{baffle}}}{{Y}_{\mathrm{without}\mathrm{baffle}}}$. Experimental ratios were determined for 14 known transitions including $E0$, $E1$, $M1$, $E2$, $M2$, and $E3$ multipoles between 3 and 7 MeV. Theoretical calculations were carried out on the spectrometer transmission, when using the baffle, for $E0$, $E1$ through $E4$, and $M1$ through $M4$ transitions from nonaligned nuclei over a wide energy range. These transmissions were combined with previous calculations of the transmission without the baffle in order to derive curves of ${R}_{\ensuremath{\omega}}(l)$ versus transition energy for the various multipoles. A best fit to the experimental ratios for the known multipoles was made in the calculations by adjusting slightly the values of the mean spectrometer-entrace angle and the sector angle $\ensuremath{\omega}$ of the baffle. The various ratio curves thus obtained are spaced widely enough apart to allow clear multipole assignments to be made in most cases. For mixed transitions from aligned nuclei, calculations were made of correction factors to be applied to the experimentally determined ratios. It is shown how the correction factors can be derived from separate measurements of the angular distributions of the corresponding gamma rays. The method has been applied to a number of previously unassigned transitions in ${\mathrm{Be}}^{10}$, ${\mathrm{B}}^{10}$, ${\mathrm{C}}^{14}$, and ${\mathrm{N}}^{14}$ leading to new spin and parity information on certain levels in these nuclei. In particular, it is found that the ${\mathrm{Be}}^{10}$ 6.18-MeV level and the ${\mathrm{C}}^{14}$ 6.58-MeV level are both ${0}^{+}$ and the ${\mathrm{N}}^{14}$ 5.10-MeV level has odd parity.