Wave Propagation in Lossy and Superconducting Circular Waveguides

We present an accurate approach to compute the attenuation of waves, propagating in circular waveguides with lossy and superconducting walls. A set of transcendental equation is developed by matching the fields at the surface of the wall with the electrical properties of the wall material. The propagation constant kz is found by numerically solving for the root of the equation. The complex conductivity of the superconductor is obtained from the Mattis-Bardeen equations. We have compared the loss of TE11 mode computed using our technique with that using the perturbation and Stratton’s methods. The results from the three methods agree very well at a reasonable range of frequencies above the cutoff. The curves, however, deviate below cutoff and at millimeter wave frequencies. We attribute the discrepancies to the dispersive effect and the presence of the longitudinal fields in a lossy waveguide. At frequencies below the gap, the superconducting waveguide exhibits lossless transmission behavior. Above the gap frequency, Cooper-pair breaking becomes dominant and the loss increases significantly

Excitation spectroscopy of vortex lattices in a rotating Bose-Einstein condensate

Excitation spectroscopy of vortex lattices in rotating Bose-Einstein condensates is described. We numerically obtain the Bogoliubov-deGenne quasiparticle excitations for a broad range of energies and analyze them in the context of the complex dynamics of the system. Our work is carried out in a regime in which standard hydrodynamic assumptions do not hold, and includes features not readily contained within existing treatments.Comment: 4 pages, 4 figures. Submitted for publicatio

Enhancing the stability of protein-polysaccharides emulsions via Maillard reaction for better oil encapsulation in spray-dried powders by pH adjustment

Lipid oxidation remains a major problem faced by the dairy industry. The bio-active ingredient (oil/milkfat) can be shielded by encapsulation within a secondary material. Emulsion stability is one of the main requirements for the production of oil/fat microcapsules with low levels of free surface fat and better encapsulation efficiency. This study focused on the use of sodium caseinate (NaCas)-lactose complex; conjugated via the Maillard reaction, as encapsulating materials, and investigated the effect of pH on the stability of protein-polysaccharide oil-in-water (O/W) emulsions. Subsequently, the properties of spray dried oil microcapsules, including encapsulation efficiency, insolubility, wettability, and microstructure, were analysed. The results demonstrated that better NaCas-lactose interactions were achieved at pH 11, with enhanced adsorption of the conjugates at the oil droplet particles and subsequently better emulsifying properties and stability. Additionally, a better oil entrapment (95.2 ± 3.7%) by the cross-linked protein and lactose was achieved when the pH of NaCas-lactose mixture was adjusted to 11 as compared to a pH of 7.5 (73.1 ± 2%). The outcome showed that it was possible to achieve stable microcapsules with oil loading as high as 80%, and with similar functional properties as those with 40% oil loading

EXPERIMENTAL INVESTIGATION OF OPEN LOOP MULTI-STAGE IMPEDANCE PUMPING SYSTEM

Impedance pump is a simple valveless pumping mechanism, where an elastic tube is joined to a more rigid one; a periodic asymmetrical pinching on the elastic tube will produce a unidirectional flow. This pumping concept offers a low energy, low noise alternative at both micro and macro scales. This paper describes an experimental investigation of the performance of a two-stage, open loop impedance pump. The results show that, when compared to a single stage open loop impedance pump, the two-stage impedance pump can achieve a significant pressure head and flow rate increment. A pressure head increment of 240 Pa is obtained in the single stage system compared to 480 Pa for the two-stage system. The corresponding flow rates were 5 mL/s and 8 mL/s respectively. This is an indication that impedance pumping system can be scaled up to achieve a variety of pumping assignments