Superfluid density in the presence of persistent current in superfluid4He

The superfluid density _s in the presence of persistent current(v _n –v _s 0) is investigated using the Doppler-shifted fourth-sound technique. In the vortex-free Landau state, _s remains constant within our experimental resolution of two parts in 10 ⁵ . This is not inconsistent with a theoretical prediction by Khalatnikov. Where vortices are present outside the Landau region, a fractional change in _s becomes as large as 1.2%, depending on rotation velocity and temperature, and shows a relatively complex hysteresis behavior.This research is supported by NSF and ONR.     

Does a persistent current exist in a superfluid helium film?

The transfer rate of helium film was measured in a container with typical dimensions of 1 cm. The film flow was induced thermally. Superimposed to the film flow was a rotation of the container. If a velocity difference between substrate and superfluid component were possible, the critical film flow rate would be expected to depend on the angular velocity of the rotation. No such dependence was found. We conclude that a sizable persistent current in a helium film in this geometry is not possible. This result is in agreement with measurements of Wang and Rudnick and in contradiction to those of Henkelet al.     

A possible crystallographic explanation for the five-fold diffraction symmetry in icosahedral phases

X-ray and electron diffraction data from the Al-Cu-Fe icosahedral phase are compared and analysed on the basis of the microcrystalline and multi-domain model developed by the author. It is shown that a crystallographic explanation is now possible for both the enigmatic five-fold symmetry and non-periodicity of reflections observed in electron diffraction patterns of icosahedral phases.     

A possible observation of quantum nucleation in superfluid He4 near crystallization

The overpressurization of superfluid He⁴ under crystallization is studied experimentally. The effect of a substrate and He³ impurities on the nucleation rate W is observed. The dependence of the metastable state lifetime versus the overpressurization and temperature is measured in the range 10^–7–1 s and 0.52–1.75 K. The results are compared with the theoretical predictions for the classic and quantum nucleation. The surface relief effect is considered. It is shown that relative to a flat surface, a cone-shaped pit is a site corresponding to a smaller nucleation energy. In this case a change of the nucleation rate versus the metastability degree and temperature in the classic region is analyzed. As a result, the most reliable qualitative manifestation of quantum nucleation is the independence of the metastable degree under the constant rate W upon temperature, which is observed below 1 K in the experiment.     

Critical current for the flow of superfluid3He in a confined geometry

We determine in a simple model the depression of the critical current in the B phase of superfluid³He due to the presence of boundaries. Results are given for a parallel-plate and a cylindrical geometry, using both analytical and numerical solutions to the Ginzburg-Landau equations.     

A fast-acting superconducting switch for protection of superconducting coils in the persistent current mode

Superconducting switches which are normally used as shorting switches to operate superconducting coils in the persistent current mode are unsuitable for field energy removal from a coil in case of quenching by a parallel resistor because of the low resistance in the non-superconducting state. Moreover these switches have a long turn-off time compared with the characteristic transient time from the superconducting to normal state of high current density coils.The superconducting switch described in this paper permits switch off of current from 20–90 A within a few milliseconds with a normal resistance of about 200 Ω. The switch is activated inductively by a special winding configuration.     

Molecular characterization of monoclonal antibodies against aflatoxins: a possible explanation for the highest sensitivity

We screened and established seven hybridoma cell lines that secrete anti-aflatoxin monoclonal antibodies with different sensitivities. Among these antibodies, 1C11 exhibited the highest sensitivity against all four major kinds of aflatoxins (AFB1, AFB2, AFG1, and AFG2) (IC(50) 0.0012-0.018 ng mL(-1) in the enzyme linked immunosorbent assay (ELISA) system, visual limit of detection of 0.03-0.25 ng mL(-1)). To better understand the interactions between these antibodies and aflatoxins, as well as to guide their potential sensitivity improvement in recombinant antibodies, we used multiple sequence alignment and molecular modeling combined with molecular docking to clarify the molecular mechanism of the highest sensitivity of 1C11 against aflatoxins. Our results show that hydrogen bond and hydrophobic interaction formed by Ser-H49 and Phe-H103 in the antibody with the hapten played the most important roles in determining the binding affinity. Further experiments performed on antibody mutants, designed on the basis of the computational models, supported the prediction of the interaction mode between the antibody and the hapten. Although the factors that influence antibody sensitivity are highly interdependent, our experimental and modeling studies clearly demonstrate how structural differences influence the binding properties of antibodies against the target hapten with different sensitivities.     

Superflow and the depairing critical current for spin singlet-triplet states of superfluid Fermi liquid

The unitary states of superfluid Fermi liquid with singlet D and triplet P type of pairing are investigated in the framework of the weak coupling approximation. The superflow pair-breaking critical current is calculated at zero temperature and in the Ginzburg-Landau region for various values of the respective strengths of singlet and triplet components of the pairing interaction. The dependence of the mass superflow on the a ₁ (F ₁ ^s ) Landau amplitude is determined. The mixed singlet-triplet states BS (a mixture of BW anisotropic and D-wave states) and 2DS (a mixture of 2D planar and D-wave states) are found to be stable for some region of the superfluid velocity.     

Experimental determination of the temperature dependence of the superfluid electron density in high-temperature superconductors

It is established that the temperature dependence of the effective density of superfluid electrons for Cu(1) lattice sites calculated within the framework of the Bardeen-Cooper-Schriffer (BCS) theory is at variance with the experimental data obtained using Mössbauer spectroscopy for YBa₂Cu₃O₇, YBa₂Cu₄O₈, Tl₂Ba₂Ca₂Cu₃O₁₀, Bi₂Sr₂Ca₂Cu₃O₁₀, and HgBa₂Ca₂Cu₃O₈ compounds. At the same time, the experimental data for Cu(2) lattice sites are in satisfactory agreement with BCS results.     

Persistent currents in saturated He II films detected through film flow measurements: Addendum to “Does a persistent current exist in a superfluid helium film?”

The existence of a persistent current in a saturated He II film which is adsorbed on the walls of a container of typical dimensions 1 cm is demonstrated. The persistent current is produced by rotation and detected by measuring the critical film flow rate.     

A neuron adaptive detecting approach of harmonic current for APFand its realization of analog circuit

There have been a number of harmonic current detecting methods for the active power filter (APF), including the filtration approach by fixed frequency filters, the composition method of the imaginary and the real power based on the instantaneous reactive power theory, etc. In this paper, firstly, according to the adaptive noise canceling technology in signal processing, an adaptive detecting approach of harmonic current based on a neuron is presented. Then, on the basis of the configuration and learning algorithm for the developed system, the realization scheme of an analog circuit of the system is discussed. Thirdly, using PSPICE software, computer simulation studies of the circuit are performed. Finally, experimental studies are carried out. The performance and feasibility of the approach are tested and verified by the simulation and experimental results     

Classical scattering of a sphere by a vortex—A possible explanation of the Steyert-Taylor-Kitchens experiment

A classical model for the scattering of a small particle by a rectilinear vortex in liquid He II is studied for the purpose of explaining the experimental results of Steyert, Taylor, and Kitchens. Although many of their observations are accounted for, verification of the theory would require a re-analysis of the experimental data. A classical analogue of an Iordanskii force is also discussed.Work partially supported by the U. S. Atomic Energy Commission under contract No. AT(11-1)-1569.     

An analog of the normal current density effect in barrier discharge

We have experimentally studied the regimes of homogeneous barrier discharge operation in air at reduced pressure and observed behavior analogous to the normal current density effect in a dc discharge.     

Anisotropic gap distortion due to superflow and the depairing critical current in superfluid 3He-B

The specific heats of UAs and the isostructural nonmagnetic homolog ThAs have been measured in the temperature range 5–300 K. While the latter compound displays a regular smooth curve C _p (T), UAs shows two sharp anomalies. The first anomaly, around 64 K, may be ascribed to the magnetic transition from type IA to type I antiferromagnetic structure; the second anomaly, at 122.8 K, corresponds to the Néel temperature. An analysis of the experimental curve C _p (T) for UAs has been carried out by several different methods to get the magnetic contribution to the specific heat with the best possible accuracy. The resulting magnetic entropy depends on the method and its maximum value at 250 K is 0.8 R ln 4, assuming a high-temperature value of the electronic heat capacity coefficient – 33 mJ/K² mole. No anomaly at 41 K was observed whatever thermal treatment was used to prepare the UAs samples.     

A model of electron emission from a wedge in the space-charge-limited current regime

The process of electron emission from a wedge-shaped cathode in the space-charge-limited current regime has been theoretically studied. The field distribution in the interelectrode gap is described using a simple analytical model, which is based on the matching of self-similar solutions for electron flows at the vertex region and at the periphery. The dependence of the perveance on the wedge angle in the wedge cathode-flat anode system is determined.