Beginning Of Oscillation Research Articles

An Experimental Study of Sweepout and Entrainment in the Advanced Reactor Downcomer

Sweepout from the water surface by gas (vapor or air) flow plays an important role in analyzing the mass and momentum transfer in the reactor downcomer of multidimensional geometry during a loss-of-coolant accident by decreasing the water level in the downcomer. The core water level will tend to decrease rapidly if a considerable amount of the entrained water stream and droplets pass through the break in lieu of flooding the reactor. The amount of entrained water is mostly determined by the interacting gas flow rate, the geometric condition, and the interfacial area between the gas and the water. The sweepout is observed to take place in three rather distinct regions: at the beginning of oscillation, at the full wave, and at the wave peak (droplet separation). The beginning of oscillation normally occurs as a result of the Helmholtz instability, which is defined in terms of the difference between the gas and the liquid velocities. The horizontal water surface is waved greatly before the gas flow reaches the critical point of droplet detachment. In the full-wave region, the droplets from the rough wave are swept into the gas flow and driven to the break. The water stream and droplets near the wave-peak region pass through the break at extremely high velocities.In view of these observations this paper investigates the relation between the gas flow rate and the amount of bypass as a function of time. The test facility was constructed in a 1/10 linear scaled-down model from the 1400-MW(electric) Advanced Power Reactor 1400 (APR1400), which has four direct vessel injection lines, four cold legs, and two hot legs. The air was injected through the three intact cold legs and passed through the broken cold leg. The sweepout was visualized from the acrylic test vessel. When the water level was located at the bottom of the break nozzle, the amount of bypass increased at the high Reynolds number of the gas. In the test the downcomer water level rapidly decreased for the initial minute. Then, given the Reynolds number of the gas, the sweepout hardly occurred as the water level approached the critical point 10 min into the test. So far, the experiment and the analysis for the sweepout have been limited to small annuli, flat plates, and T-junctions, which yielded the two-dimensional flow field. The current experimental results shed light on the flow mechanism and the semiempirical relations for the three-dimensional sweepout in a large-diameter annulus such as the reactor downcomer. The sweepout and entrainment are physically understood by visual inspection of flow in the downcomer. An engineering correlation is developed to predict the multidimensional sweepout and entrainment in the annular downcomer.

Influence of the magnetic field and uniaxial pressure on the current instability in the hopping conductivity region

In this specific work we present results of the investigation of the current oscillations in the hopping conductivity region at magnetic field and aniaxial stress, where the dependences of threshold field beginning of oscillations on temperature and on magnetic field and uniaxial pressure are determined. The model to explain the experimental results is presented. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Affleck-Dine mechanism with a negative thermal logarithmic potential

We investigate whether the Affleck-Dine (AD) mechanism works when the contribution of the two-loop thermal correction to the potential is negative in gauge-mediated supersymmetry breaking models. The AD field is trapped far away from the origin by the negative thermal correction for a long time until the temperature of the Universe becomes low enough. The most striking feature is that the Hubble parameter becomes much smaller than the mass scale of the radial component of the AD field, during the trap. Then, the amplitude of the AD field decreases so slowly that the baryon number is not fixed even after the onset of radial oscillation. The resultant baryon asymmetry crucially depends on whether the Hubble parameter H is larger than the mass scale of the phase component of the AD field, ${M}_{\ensuremath{\theta}},$ at the beginning of oscillation. If $H<{M}_{\ensuremath{\theta}}$ holds, the formation of Q balls plays an essential role in determining the baryon number, which is found to be washed out due to the nonlinear dynamics of Q-ball formation. On the other hand, if $H>{M}_{\ensuremath{\theta}}$ holds, it is found that the dynamics of Q-ball formation does not affect the baryon asymmetry, and that it is possible to generate the right amount of baryon asymmetry.

Different signaling pathway between sphingosine-1-phosphate and lysophosphatidic acid in Xenopus oocytes: functional coupling of the sphingosine-1-phosphate receptor to PLC-xbeta in Xenopus oocytes.

In Xenopus oocytes, both sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA) activate Ca2+-dependent oscillatory Cl- currents by acting through membrane-bound receptors. External application of 50 microM S1P elicited a long-lasting oscillatory current that continued over 30 min from the beginning of oscillation, with 300 nA (n = 11) as a usual maximum peak of current, whereas 1-microM LPA treatment showed only transiently oscillating but more vigorous current responses, with 2,800 nA (n = 18) as a maximum peak amplitude. Both phospholipid-induced Ca2+-dependent Cl- currents were observed in the absence of extracellular Ca2+, were blocked by intracellular injection of the Ca2+ chelator, EGTA, and could not be elicited by treatment with thapsigargin, an inhibitor of endoplasmic reticulum (ER) Ca2+ ATPase. Intracellular Ca2+ release appeared to be from inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ store, because Cl- currents were blocked by heparin injection. Pretreatment with the aminosteroid, U-73122, an inhibitor of G protein-mediated phospholipase C (PLC) activation, to oocytes inhibited the current responses evoked both by S1P and LPA. However, when they were injected with 10 ng of antisense oligonucleotide (AS-ODN) against Xenopus phospholipase C (PLC-xbeta), oocytes could not respond to S1P application, whereas they responded normally to LPA, indicating that the S1P signaling pathway goes through PLC-xbeta, whereas LPA signaling goes through another unknown PLC. To determine the types of G proteins involved, we introduced AS-ODNs against four types of G-protein alpha subunits that were identified in Xenopus laevis; G(q)alpha, G11alpha, G0alpha, and G(i1)alpha. Among AS-ODNs against the G alphas tested, AS-G(q)alpha and AS-G(i1)alpha to S1P and AS-G(q)alpha and AS-G11alpha to LPA specifically reduced current responses, respectively, to about 20-30% of controls. These results demonstrate that LPA and S1P, although they have similar structural features, release intracellular Ca2+ from the IP3-sensitive pool, use different components in their signal transduction pathways in Xenopus oocytes.

Non-catalyzed oscillation reaction in aniline-KBrO3−H2SO4 system, I. Potentiometric study of oscillations

The non-catalyzed oscillation reaction of the aniline-KBrO3−H2SO4 system has been followed potentiometrically. The concentration regions of the beginning of oscillation are given in a triangular diagram. Also studied was the dependence of the induction period on concentration of the participants, which was described by a kinetic equation. The oscillation region extends to lower KBrO3 concentrations, the number of the oscillation jumps increases, and the induction period is shortened with increasing acidity.

Transient Behavior of He-Ne Lasers

An experimental study on He-Ne laser (1.15 µ) under pulsed H.F. excitation reveals that there exist delay in oscillation build-up and a peak in the output at the beginning of oscillation. From qualitative discussions on the behavior of photon density and inversion density on the basis of coupled rate equations, these transient phenomena are shown reasonable. Contributions of various factors related to lasing mechanism are clarified from numerical calculations of simplified rate equations by the use of electronic computers. Both loss terms for the photon and the inversion effect strongly the shape of the curve of the solution. The increase of the former produces an oscillating build-up, while the contribution of the latter is opposite. Resultant contribution of the loss terms is also analysed. A reasonable set of the coefficients is found to lead to a solution having the delay which agrees with the experiment.

A Study of the Oscillations Occurring in the Circuits of the Pliotron

The currents in the grid and plate circuits of a pliotron are studied oscillographically, both for the transient conditions at the beginning of oscillations, and for the steady oscillating state. Magnetic, electric, and combined magnetic and electric couplings between the grid and plate circuits are tested. The effects obtained are explained, and the experimentally determined periods of oscillation checked against the suitably calculated values.