Negative Bubbles Research Articles

Explosion of Electron Bubbles Trapped on Vortices in He-II

Electrons injected into liquid helium become trapped in a spherical cavity from which the liquid is almost completely excluded. When a negative pressure is applied to the liquid the size of the electron bubble increases, and at a critical negative pressure Pcthe bubble explodes. We have observed these explosions and have measured Pcas a function of temperature. At low temperatures an electron bubble can become bound to a quantized vortex. The flow of the helium around the quantized vortex leads to a reduction in the magnitude of Pc. We will report measurements of this reduction in Pcand will make a comparison of the results with theoretical predictions.

Flow patterns in a pilot plant‐scale turbulent fluidized bed reactor: Concurrent application of tracers and fiber optic sensors

AbstractHydrodynamics of a turbulent fluidized bed is studied by means of the concurrent application of fiber optic sensors and a helium tracer.It is observed that in the vicinity of the column wall there is a high bubble activity region. Low bubble activity and negative bubble velocities are reported for the dense phase near the column centre‐line region.A temperature increase from 22 to 145°C results in a more homogeneous turbulent fluidized bed with smaller bubbles and more gas flowing through an expanded dense bed emulsion phase.Mass transfer coefficients between bubble‐emulsion (kbe) and bubble‐annulus (kba) are evaluated. The dominant mass transfer path was the one from the bubbles to the annular region with kba being several times greater than kbe.

Bound states of rotons to impurities in He II

Rotons and impurities such as ions or solvated /sup 3/He particles can interact via dipolar forces from the flow fields of the roton and the motion of the impurity through the background fluid. Stable bound states of rotons to impurities can occur with near-zero total momentum. We give explicit results of bound-state calculations for solvated /sup 3/He, the positive helium ion, and the negative electron bubble.

New types of magnetic domain structure in orthoferrite

Mutual interaction of domains in bubble materials causes new types of domain structure. These structures, which are observed in an orthoferrite platelet, are classified into five categories: 1) periodic bubble domains in the valleys of a wavy wall; 2) coexistence of positive and negative bubbles on both sides of a wavy wall; 3) bubbles within a ring domain; 4) concentric ring domains; and 5) coexistence of positive and negative bubbles. Experimental observations by means of magnetooptical effect were performed to investigate the stabilities, controllabilities, and physical properties of the domains. The domain structures 3), 4), 5) are stable even in zero bias field and the structures 1), 2), 3), 5) can be transferred without changing the configuration.

Crossing, Hermitian Analyticity, and the Connection between Spin and Statistics

The analytic S-matrix framework is further developed. First some results of earlier works are collected and the physical-region analyticity properties recently derived from macroscopic causality conditions are described. These entail that scattering functions are analytic at physical points except on positive-α Landau surfaces, and that there they are iε limits of analytic functions from certain well-defined directions, except possibly at certain points where four or more positive-α surfaces intersect. A general iε rule that also covers these exceptional points is then stated. It is then shown that the scattering function defined by analytic continuation is either symmetric or antisymmetric under interchange of variables describing identical particles and that the sign induced by the interchange is independent of the particular scattering function in which the variables appear. The physical-region analyticity properties of bubble-diagram functions are then derived from the general iε rule. These functions are products of scattering functions and conjugate scattering functions integrated over physical internal-particle variables, as in the terms of unitarity equations. They are shown to be analytic in the physical region except on Landau surfaces and, more specifically, except on those Landau surfaces that correspond to Landau diagrams that are supported by the bubble diagram in question, with the further restriction that the Landau α's must be positive or negative for lines lying within positive or negative bubbles, respectively. Also, the basic rule for continuation around these singularities is derived. A new general derivation of the pole-factorization theorem is given, which is based on slightly weaker assumptions than earlier proofs. Particular attention is paid to the over-all sign. A general derivation of the crossing and Hermitian analyticity properties of scattering functions is then given. On the basis of the deduced general rules for constructing the paths of continuation that connect the crossed and Hermitian conjugate points, the various related points are found to be boundary values of a single physical sheet. In particular, a certain sequence of continuations is shown to take one back to the original point. From this fact it follows that abnormal statistics are incompatible with simultaneous unitarity in both the direct and crossed channels. The proof given here does not depend on the notion of interchange of variables other than those of identical particles. Earlier proofs depended on the unphysical notion of interchange of variables representing conjugate particles. Finally it is shown that the analytically continued M functions with normal-ordered variables are precisely the scattering functions: no extra signs are needed or permitted. Aside from the general i rule, the analyticity assumptions are these: (1) The discontinuity around a singularity of a bubble diagram B has no residue at a physical-particle mass value (in an appropriate variable) unless the singularity corresponds to a diagram that is supported by B and has the single-particle-exchange form that corresponds to a pole at that mass value. (2) The residue just described has the pole-factorization property. (3) Confluences of infinite numbers of singularity surfaces do not invalidate the results established by assuming that this number is locally finite. Assumption (1) entails that all relevant singularities of scattering functions lie on Landau surfaces. That is the basic assumption.

On the instability and rupture of droplets and bubbles in strong electric fields

An approximate quantitative theory of the equilibrium of a bubble or droplet in a uniform electric field is developed and applied to earlier experimental results. An explanation of the oscillation of bubbles in strong fields and the difference in behavior of positive and negative bubbles is explained on the basis of the discharge of electricity from points.