Non-metallic Tubes Research Articles

A–V formulation for numerical modelling of superconductor magnetization in true 3D geometry

We present the numerical procedure suitable for computing the distribution of electrical currents in a superconductor with geometry extending in all three spatial dimensions when it is exposed to a magnetic field changing in time. Its main advantage is that it solves the problem in terms of vector potential, of the magnetic field. Such an A-formulation is usually the default option for magnetic field calculations in commercial finite element codes. We have used it in the past when a two-dimensional (2D) approximation was found to be sufficient to predict AC losses of single wires, cables, and coils with circular turns. Incorporation of superconductor properties based on the critical state model is straightforward in 2D because the flow of current is restricted to one direction only. The main challenge in extending the method to three dimensions is to cope with the situation when currents could flow in any direction. We have found that assuming that the local current density in a superconductor is always parallel to the local electrical field, and that its modulus is limited by the critical current density, provides sufficient input for accomplishing a new working equation, linking the vector of current density to the time derivative of the magnetic vector potential. Our method successfully passed testing on the benchmark problem of superconducting cube magnetization. It is also used to interpret the magnetization measured on two cylindrical superconducting objects in the transverse field: one was a tube made from bulk BSCCO and the other a REBCO coated conductor tape helically wound on a non-metallic tube. Computed magnetization loops in both cases show good agreement with experiments and confirm the validity of the method.

Scattering and absorption of ultracold atoms by nanotubes

We investigate theoretically how cold atoms, including Bose–Einstein condensates, are scattered from, or absorbed by, nanotubes with a view to analysing recent experiments. In particular, we consider the role of potential strength, quantum reflection, atomic interactions and tube vibrations on atom loss rates. Lifshitz theory calculations deliver a significantly stronger scattering potential than that found in experiment and we discuss possible reasons for this. We found that the scattering potential for dielectric tubes can be calculated to a good approximation using a modified pairwise summation approach, which is efficient and easily extendable to arbitrary geometries. Quantum reflection of atoms from a nanotube may become a significant factor at low temperatures, especially for non-metallic tubes. Interatomic interactions are shown to increase the rate at which atoms are lost to the nanotube and lead to non-trivial dynamics. Thermal nanotube vibrations do not significantly increase loss rates or reduce condensate fractions, but lower frequency oscillations can dramatically heat the cloud.

The Effect of Grooves on Initial Peak Load and Plastic Work for Nonmetallic Tubes Statically

In this paper an experimental study of the effect of grooves on initial peak load and work done by plastic deformation of material is presented. A series of tests were conducted on polyvinylchloride PVC circular tubes with grooves and without grooves loaded statically and axially. The specimens with grooves were tested with constant depth of groove and constant axial length of groove. Load-deflection characteristics for the PVC circular tubes specimens and the influence of collapsing load were illustrated in this work. The experimental results were compared with proposed mathematical model giving a good agreement. Also in this work, it was showed that the value of plastic work decreases with increasing the number of grooves.

Experimental Study of the Effect of Semi-Apical Angle on Initial Peak Load and Plastic Work for Nonmetallic Tubes

This article investigate the effect of semi-apical angle on the collapse load characteristics of thin truncated circular cones during axial crumpling .The PVC tubes axial crumpling resistance (the relation ship between crumpling force and axial deflection) is described with mathematical models, which are derived depending on previous research and experimental present work .The mathematical models for present work gave good agreement with experimental results. The study showed that the values of initial peak load and plastic work decrease with increasing the semi-apical angle degree at constant thickness tubes and constant large diameter of end bottom of tubes and constant length.

A portable Halbach magnet that can be opened and closed without force: The NMR-CUFF

Portable equipment for nuclear magnetic resonance (NMR) is becoming increasingly attractive for use in a variety of applications. One of the main scientific challenges in making NMR portable is the design of light-weight magnets that possess a strong and homogeneous field. Existing NMR magnets can provide such magnetic fields, but only for small samples or in small regions, or are rather heavy. Here we show a simple yet elegant concept for a Halbach-type permanent magnet ring, which can be opened and closed with minimal mechanical force. An analytical solution for an ideal Halbach magnet shows that the magnetic forces cancel if the structure is opened at an angle of 35.3° relative to its poles. A first prototype weighed only 3.1kg, and provided a flux density of 0.57T with a homogeneity better than 200ppm over a spherical volume of 5mm in diameter without shimming. The force needed to close it was found to be about 20N. As a demonstration, intact plants were imaged and water (xylem) flow measured. Magnets of this type (NMR-CUFF=Cut-open, Uniform, Force Free) are ideal for portable use and are eminently suited to investigate small or slender objects that are part of a larger or immobile whole, such as branches on a tree, growing fruit on a plant, or non-metallic tubing in industrial installations. This new concept in permanent-magnet design enables the construction of openable, yet strong and homogeneous magnets, which aside from use in NMR or MRI could also be of interest for applications in accelerators, motors, or magnetic bearings.

Structure and electronic properties of nitrogen-containing carbon nanotubes

The structure and electronic properties of nitrogen-containing carbon nanotubes are investigated using self-consistent field crystal orbital method. The models of these tubes are constructed by substitution of some carbon atoms with nitrogen atoms in the armchair carbon nanotube. The calculated band structures show that these nanotubes can be metals or semiconductors depending on the relative position of nitrogen and carbon atoms. The most stable non-metallic tubes are narrow energy gap (EG) semiconductors. Metallic tubes have two overlapped partially filled bands. The influence of Fermi vector positions on metal–insulator phase transition is discussed in the metallic NC tubes.

Finish Ratings of Gypsum Wallboards

The term “finish rating” is used in NFPA 70, National Electrical Code (NEC)1 to describe the required performance of finish materials installed as thermal barriers for electrical nonmetallic tubing. Finish rating data is most commonly associated with assemblies containing combustible wood framing, although the definition has also been extended to assemblies with noncombustible metal framing. To date, however, very little finish rating data has been available for common finish materials installed over metal framing. To supplement the available information, finish rating tests were conducted on identical wall sections finished with standard 1/2″ gypsum wallboard from five different manufacturers, constructed with metal and wood stud framing. All 10 assemblies tested demonstrated finish ratings of 15 minutes or more.

A nonintrusive auto-transformer technique for the measurement of void fraction

Winding low resistance wires around the tube of the test section in a method analogous to the auto-transformer winding was proved experimentally successful for the measurement of void fraction in the two-phase medium inside the tube. This novel technique is based upon the fact that the two-phase mixture becomes the region for a magnetic field where any change in the void fraction produces a change in the permeability of the two-phase mixture. The present technique is suitable for two-phase flows, which are contained in nonmetallic tubes.

Efficient method for the isolation by HPLC of a major metabolite of the carcinogen 2-amino-3-methylimidazo [4,5-f]quinoline(IQ), the 5-hydroxy derivative

Previous difficulties in the standard HPLC separation of the 5-hydroxy derivative, a major metabolite of the food mutagen and carcinogen 2-amino-3-methylimidazo[4,5-f]-quinoline(IQ), with the properties of a chelating agent, were resolved by utilizing a nonmetallic tubing and column and a BRP-1 stationary phase. This system separates the already known metabolites by reverse phase mode, but presents the unique advantage of resolving chelating compounds like 5-hydroxy-IQ as a single, clean peak. The procedure may be generally applicable to this class of chemicals.

An Evaluation of Smoke Toxicity and Toxic Hazard of Electrical Nonmetallic Tubing Combustion Products

Small-scale smoke toxicity tests were performed on polyvinylchloride-based electrical nonmetallic tubing (PVC/ENT) using the National Bureau of Stan dards (NBS) protocol for nonflaming combustion. An LC50 of 28.5 mg/L (± 9.25) was determined, placing PVC/ENT smoke in a toxicity category comparable to smoke from wood.

Industrial x-ray equipment

Winding low resistance wires around the tube of the test section in a method analogous to the auto-transformer winding was proved experimentally successful for the measurement of void fraction in the two-phase medium inside the tube. This novel technique is based upon the fact that the two-phase mixture becomes the region for a magnetic field where any change in the void fraction produces a change in the permeability of the two-phase mixture. The present technique is suitable for two-phase flows, which are contained in nonmetallic tubes.