High Rotational Frequencies Research Articles

Formation of a three-dimensional scrape-off layer in a fast rotating resonant magnetic perturbation field at TEXTOR

Measurements of electron density ne(r,t) and temperature Te(r,t) fields in the far edge (r/a>0.98) of the tokamak TEXTOR during application of a fast rotating resonant magnetic perturbations (RMP) show an in-phase modulation of both ne and Te coherent to the rotation frequency of the external RMP field, which is correlated to the local rotating magnetic topology. The comparison provides experimental evidence that a three-dimensional scrape-off layer is preserved for high RMP field rotation frequencies of νRMP=974Hz. Additionally, we obtain the geometrical dimensions of the 3D helical flux tubes in terms of the helical and radial width and compare them to the magnetic topology modeled in vacuum approximation in a quasi-static approach. The geometrical dimensions of the experimentally detected flux tubes increase linearly with increasing perturbation current as prescribed by the magnetic topology. For high RMP amplitudes the pressure drop inside the helical flux tube is limited by an effectively enhanced radial transport.

IMPRINTS OF THE NUCLEAR SYMMETRY ENERGY ON GRAVITATIONAL WAVES FROM DEFORMED PULSARS

The density dependence of nuclear symmetry energy is a critical input for understanding many interesting phenomena in astrophysics and cosmology. We report here effects of the nuclear symmetry energy partially constrained by terrestrial laboratory experiments on the strength of gravitational waves (GWs) from deformed pulsars at both low and high rotational frequencies.

Biexcitability and Early Afterdepolarization-Mediated Cardiac Arrhythmias

Under normal conditions in ventricular tissue, both planar wave propagation and spiral wave reentry are mediated by Na current (INa)-mediated depolarization. Under diseased conditions in which repolarization reserve is reduced, however, secondary depolarizations can occur in the plateau or repolarizing phase of the action potential (AP) due to reactivation of the L-type calcium current (ICa,L), known as early afterdepolarizations (EADs). Under these conditions, we observed a novel behavior in which both INa-mediated spiral wave reentry and ICa,L-mediated spiral wave reentry coexisted in the same homogeneous tissue. INa-mediated spiral waves were similar to those observed under normal condition, with high rotation frequency (∼10 Hz) and nearly full repolarization between beats. ICa,L-mediated spiral waves, however, rotated much slower (2-3 Hz) with membrane voltage remaining above −40 mV, at which INa is inactivated. We call this novel property of an excitable medium biexcitability. In heterogeneous tissue with transmural AP gradients, pause-induced EADs initiated ICa,L-mediated rotors from the M-cell region. The resulting arrhythmia was characterized by co-existing ICa,L- and INa-mediated wavefronts, with a frequency and electrocardiographic appearance resembling Torsades de Pointes. The arrhythmia either terminated spontaneously or degenerated to ventricular fibrillation. We propose biexcitability as a novel mechanism of Torsades de Pointes in long QT syndromes.

VORTEX LATTICE STATE OF A SUPERFLUID FERMI GAS IN THE UNITARY REGION

In this paper, we study the structure of vortex lattices in a trapped superfluid Fermi gas in the unitary region near the superfluid transition temperature. A phenomenological approach based on the Ginzburg-Landau theory is used. Two types of stable triangular vortex lattices are found numerically at the same rotation frequency. In type (A), the trap center is occupied by a vortex; in type (B), there are three vortices closest to the trap center which is unoccupied. The lattice structures at different rotation frequencies and temperatures are analyzed. The vortex density increases linearly with the rotation frequency, very close to the analytical estimation. The superfluid and type-(B) vortex lattice do not disappear together. At high rotation frequencies, the vortex lattice disappears, but there exists a localized superfluid state near the trap center. The superfluid vanishes at a critical rotation frequency consistent with the theory for the upper critical magnetic field of type-II superconductors.

Investigation of the temperature rise due to eddy currents in large chopper disks operated at polarized neutron beamlines

The detrimental temperature rise due to eddy currents in large chopper disks from aluminium alloy operated at high rotation frequencies was investigated experimentally and compared to calculations obtained with finite element analyses. We found that for magnetic field strengths which are commonly used for polarized neutron beam guidance, the temperature rise is only about 20 K, a value which does not compromise the use of these aluminium choppers. Furthermore, the induced magnetic field due to the eddy currents does not significantly affect the polarizing field. These findings will form the basis of our chopper development from this material.

Prospects for isomeric energy release

The state of experimental studies and promising proposals for the application of nuclear isomers presented as controlled energy or γ-ray sources are reviewed. The properties of isomeric states, methods of their production, and approaches to their efficient stimulation using various types of radiation are analyzed. The long-lived isomers, which can be accumulated in reactor irradiations or in other nuclear interactions with abundant yield, are listed. The isomers are estimated according to their specific energy accumulated per nucleus and the level of the cross section for their formation in reactions with neutrons. The nuclei are classified as promising either for obtaining controlled γ-ray pulses, for the enhanced release of the radioactive decay energy, or for experimental studies on detecting forbidden electromagnetic transitions from the ground to isomeric state. In all cases, the possibility of external-stimulus action on nuclear transitions has key significance, which should become the subject of investigations. The results of successful observation of stimulation of isomers are described at excitation energy E* > 1 MeV in the reactions with bremsstrahlung photons and Coulomb excitation in the ion beam. The essential increase in the K-hindered transitions with increasing energy and also the K-mixing at high rotational frequency for high-spin levels are discussed. The attention is focused on attempts to detect the triggering induced by the radiation in the x-ray range, in particular, that of the 178m2Hf isomer with the help of x-ray sources and the synchrotron radiation. Proposals for experiments with other isomers are considered. The possibility of affecting the nuclear states by means of ionization of electron shells of a corresponding atom is discussed as promising, and various schemes of similar experiments are proposed. The atomic cross sections are eight orders of magnitude higher than the nuclear ones; therefore, the stimulation of an isomer can occur even if the conversion from atomic excitations to nuclear ones has a low probability.

Rotating surface solitons

We introduce a novel type of surface waves that form at the edge of guiding structures consisting of several concentric rings. Such surface waves rotate steadily upon propagation and, in contrast with nonrotating waves, for high rotation frequencies they do not exhibit power thresholds for their existence. There exists an upper limit for the surface wave rotation frequency, which depends on the radius of the outer guiding ring and on its depth.

Rotation of an atomic Bose–Einstein condensate with and without a quantized vortex

We theoretically examine the rotation of an atomic Bose–Einstein condensate in an elliptical trap, both in the absence and presence of a quantized vortex. Two methods of introducing the rotating potential are considered—adiabatically increasing the rotation frequency at fixed ellipticity, and adiabatically increasing the trap ellipticity at fixed rotation frequency. Extensive simulations of the Gross–Pitaevskii equation are employed to map out the points where the condensate becomes unstable and ultimately forms a vortex lattice. We highlight the key features of having a quantized vortex in the initial condensate. In particular, we find that the presence of the vortex causes the instabilities to shift to lower or higher rotation frequencies, depending on the direction of the vortex relative to the trap rotation.

Microscopic structure of deformed and superdeformed collective bands in rotating nuclei

We investigate in self-consistent cranked Nilsson plus quasiparticle random-phase approximation the structure of $^{190,192,194}\mathrm{Hg}$ in their evolution from normal to superdeformation and from low to high rotational frequencies. The analysis of the energy levels suggests a splitting of few normally deformed bands into two or more branches. The investigation of the dynamical moments of inertia supports the octupole character of the low-lying negative parity superdeformed bands, in agreement with previous theoretical predictions and experimental findings. As a more direct confirm of their octupole nature, we obtain strong $E1$ transitions linking those bands to the yrast superdeformed band, in agreement with experiments. A similar result is shown to hold also for $^{152}\mathrm{Dy}$. Like in $^{152}\mathrm{Dy}$, the collectivity of the low-lying scissors mode gets enhanced with the onset of superdeformation.

Influence of melt convection on microstructure evolution of Nd‐Fe‐B alloys using a forced crucible rotation technique

AbstractThe forced crucible rotation technique has been applied to the solidification of Nd‐Fe‐B alloys. Specially sealed samples were subjected to well‐defined forced rotation during induction heating and solidification. The resulting microstructure of the Nd‐Fe‐B alloys in consideration of melt convection has been investigated using scanning electron probe microscopy. The determination of the α‐Fe volume fraction by measuring the magnetic moment in a vibrating sample magnetometer (VSM) resulted in a distinct reduction of the α‐Fe volume fraction in samples with high crucible rotation frequencies. Furthermore, a new category of experiment has been started where a tailored magnetic field was applied in order to study the microstructure evolution due to an enhancement or suppression of the melt convection by additional alternating magnetic fields. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrasonic micro-motor using miniature piezoelectric tube with diameter of 1.0 mm

At the present moment, the smallest piezoelectric ultrasonic micro-motors utilizing miniature PZT piezoelectric ceramic tubes were developed. The motor consists of a PZT-metal composite tube stator, two steel rotors and a thin shaft that keeps the two rotors pressing on both ends of the stator elastically. The dimensions of the PZT tube are 1.0 mm in outer diameter, 0.6 mm in inner diameter and 5.0 mm in length. The diameter and total length of the assembled micro-motor is 1.0 mm and 8 mm (including an adjusting spring), respectively. The tube-type micro-motor is driven by two pairs of alternative voltages with phase shift 90° between the adjacent electrodes and operated in the first circular-bending vibration mode of the stator with the resonance frequency about 58 kHz. The experimental results show that the tube-type micro-motors have perfect performances: (i) high rotation frequency over 3000 rpm and (ii) large starting torque over 7.8 μN m under the conditions of the input voltage of 110 V p–p and the resonance frequency. The micro-motor is well suitable for operating in micro-spaces, such as in intravascular, micro-robots and micro-craft applications.

Optical Detection of Two Intermediate-Mass Binary Pulsar Companions

We report the detection of probable optical counterparts for two intermediate-mass binary pulsar (IMBP) systems, PSR J1528-3146 and PSR J1757-5322. Recent radio pulsar surveys have uncovered a handful of these systems with putative massive white dwarf companions, thought to have an evolutionary history different from that of the more numerous class of low-mass binary pulsars with He white dwarf companions. The study of IMBP companions via optical observations offers us several new diagnostics: the evolution of main-sequence stars near the white dwarf-neutron star boundary, the physics of white dwarfs close to the Chandrasekhar limit, and insights into the recycling process by which old pulsars are spun up to high rotation frequencies. We were unsuccessful in our attempt to detect optical counterparts of PSR J1141-6545, PSR J1157-5112, PSR J1435-6100, and PSR J1454-5846.

Ni58: An Unpaired Band Crossing at New Heights of Angular Momentum for Rotating Nuclei

High-spin states in 58Ni have been investigated by means of the fusion-evaporation reaction 28Si(32S, 2p)58Ni at 130 MeV beam energy. Discrete-energy levels are observed in 58Ni at record-breaking 42 MeV excitation energy and angular momenta in excess of 30h. The states form regular rotational bands with unprecedented high rotational frequencies. A comparison with configuration dependent cranked Nilsson-Strutinsky calculations reveals an exceptional two-band crossing scenario, the interaction strength of which is strongly shape dependent.

134 分布荷重を受ける回転円形膜の振動特性

Vibrations of a rotating circular membrane under distributed load are investigated. Bending stiffness is ignored and von Karman theory is applied to formulate equilibrium equations and vibration equation around the equilibrium states. The equations are numerically solved taking account of buckling and vibration modes are obtained. The result is shown to be consistent with vibration modes of a spring-mass system which simulates elasticity of membrane. An experiment of a rotating circular membrane under gravity in vacuum is carried out and a vibration mode is found to agree with the vibrations observed when high rotation frequencies.

Observation of the second proton alignment inTm160

High-spin states in the doubly odd nucleus $^{160}\mathrm{Tm}$ have been investigated using the $^{130}\mathrm{Te}$($^{35}\mathrm{Cl}$,5n) reaction and the Euroball \ensuremath{\gamma}-ray detector array. The previously established rotational structures in $^{160}\mathrm{Tm}$ were extended, leading to the first observation of the second $({h}_{11/2}){}^{2}$ proton band crossing in this nucleus. This crossing is found to occur at a higher rotational frequency in $^{160}\mathrm{Tm}$ than in lighter Tm isotopes. This trend resembles that of the first $({h}_{11/2}){}^{2}$ proton band crossing found in neighboring Er nuclei and is associated with a predicted increase in deformation as a function of neutron number in these isotopes.

Reappearance of the pairing correlations at finite temperature

Rotational and deformation dependence of isovector and isoscalar pairing correlations at finite temperature are studied in an exactly solvable cranked deformed shell model Hamiltonian. It is shown that isovector pairing correlations, as expected, decrease with increasing deformation and the isoscalar pairing correlations remain constant at temperature, T=0. However, it is observed that at finite temperature both isovector and isoscalar pairing correlations are enhanced with increasing deformation, which contradict the mean-field predictions. It is also demonstrated that the pair correlations, which are quenched at T=0 and high rotational frequency re-appear at finite temperature. The changes in the individual multipole pairing fields as a function of rotation and deformation are analyzed in detail.

Sustainable water management in smallholder irrigation schemes: Understanding the impact of field water management on maize productivity on two irrigation schemes in Zimbabwe

Smallholder irrigation globally can be recognised as a crucial common property resource for the sustenance of rural livelihoods in semi-arid regions. This is particularly true for Zimbabwe where 70% of the population is situated in rural areas characterised by low and unpredictable rainfall patterns. This paper looks at the performance of smallholder irrigation schemes based on a technical evaluation of field water management and crop performance. Field water management was assessed by looking at the application efficiency ( E a), tail water ratio (TWR), deep percolation ratio (DPR), requirement efficiency ( E r) and distribution uniformity (DU). Crop performance and productivity was evaluated by looking at weekly crop heights and the overall crop yield. The study was conducted on two irrigation schemes in Zimbabwe’s dry region V in Manicaland province. The two schemes (Chakohwa and Gudyanga irrigation schemes) are surface schemes using the border irrigation gmethod. E a of less than 30% was common at Chakohwa whilst that at Gudyanga ranged above 50% with the remainder being lost as deep percolation in most cases. The irrigation borders were dyked at the end resulting in ponding and excess water application at the ends. Generally farmers at Chakohwa irrigation scheme have an unpredictable irrigation rotation thus influencing them to hoard water ( E r = 100%) whenever their turn came. The high rotation frequency (7 days), low infiltration rates and short borders (80 m) at Gudyanga irrigation scheme saw the farmers under applying in some cases ( E r < 100%). Over application was only done by those farmers with a poor suction head and poorly levelled borders. There were no significant differences between the yields obtained across the schemes though within Chakohwa, yields were generally high for farmers near the water source compared to those at the tail end.

Toward complete spectroscopy of128Prand rotational structures in126Pr

Over 240 transitions and three new rotational bands have been observed in the well-deformed, odd-odd ${}_{59}^{128}{\mathrm{Pr}}_{69}$ nucleus. The high-spin states were populated in two experiments using the ${}^{92}\mathrm{Mo}{(}^{40}\mathrm{Ca},3pn)$ reaction at beam energies of 170 and 184 MeV. Several structures were confirmed in the former experiment using the Clarion and HyBall arrays with the recoil mass spectrometer at Oak Ridge National Laboratory. Gammasphere, in conjunction with the Microball, were employed in the latter experiment at Argonne National Laboratory to extend the sequences to very high spins. Rotational structures in ${}^{126}\mathrm{Pr}$ were also identified in the $\ensuremath{\alpha}\mathrm{pn}$ channel of the same reaction. The recent discrepancies of spin assignments for the yrast bands in ${}^{126,128}\mathrm{Pr}$ and the interpretation of the lowest crossing in the $\ensuremath{\pi}{h}_{11/2}$ band in ${}^{127}\mathrm{Pr}$ are discussed. An adiabatic crossing of the intruder ${i}_{13/2}$ neutron with one of the normal-deformed bands in ${}^{128}\mathrm{Pr}$ is observed at high rotational frequency. Experimental trends in the signature inversion phenomenon of the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{h}_{11/2}$ bands in the $A\ensuremath{\approx}130$ region are defined and prove to be surprisingly irregular with respect to those found in the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{i}_{13/2}$ bands of the $A\ensuremath{\approx}160$ region.

1218 インデューサ入口に生じる逆流の数値計算

In a pump for a rocket engine which operates under high rotational frequency and low NPSH, an inducer is equipped in order to keep performance from dropping when cavitation occurs. As the flow rate is lower, swirling backflow occurs at the inlet of the inducer. And then, the backflow makes various problems. So in this study, we simulated the flow field in the inducer by using CFD code "CFX-TASCflow". The calculations were executed for various flow rate, and the backflow was observed especialy at low flow rate like as the experiment. In addition, The effect of swept-back on the leading edge for the backflow was also studied.

Study of 169Hf at high rotational frequency

High-spin properties of the nucleus 169Hf have been studied through the fusion evaporation reaction 96Zr(76Ge,3n)169Hf at a beam energy of 310 MeV. The known rotational bands have been extended considerably and 6 new bands have been established, four of which form coupled bands with pronounced M1 connections. Quasiparticle assignments are suggested for the new band structures, and it appears that coupling to vibrational degrees of freedom plays a role. Both coupled bands involve the excitation of quasiprotons. In the region of highest spin, a large alignment gain is interpreted in terms of a mixed crossing where an h 9/2 and an h 11/2 quasiproton provide the two signatures of the aligning configuration.