Large gap magnetic suspension system

The design of a large gap magnetic suspension system is discussed. Some of the topics covered include: the system configuration, permanent magnet material, levitation magnet system, superconducting magnets, resistive magnets, superconducting levitation coils, resistive levitation coils, levitation magnet system, and the nitrogen cooled magnet system

Non-parametric Reconstruction of Cluster Mass Distribution from Strong Lensing: Modelling Abell 370

We describe a new non-parametric technique for reconstructing the mass distribution in galaxy clusters with strong lensing, i.e., from multiple images of background galaxies. The observed positions and redshifts of the images are considered as rigid constraints and through the lens (ray-trace) equation they provide us with linear constraint equations. These constraints confine the mass distribution to some allowed region, which is then found by linear programming. Within this allowed region we study in detail the mass distribution with minimum mass-to-light variation; also some others, such as the smoothest mass distribution. The method is applied to the extensively studied cluster Abell 370, which hosts a giant luminous arc and several other multiply imaged background galaxies. Our mass maps are constrained by the observed positions and redshifts (spectroscopic or model-inferred by previous authors) of the giant arc and multiple image systems. The reconstructed maps obtained for \a370 reveal a detailed mass distribution, with substructure quite different from the light distribution. The method predicts the bimodal nature of the cluster and that the projected mass distribution is indeed elongated along the axis defined by the two dominant cD galaxies. But the peaks in the mass distribution appear to be offset from the centres of the cDs. We also present an estimate for the total mass of the central region of the cluster. This is in good agreement with previous mass determinations. The total mass of the central region is M=(2.0-2.7) 10^14 Msun/h50, depending on the solution chosen.Comment: 14 pages(19 postscript figures), minor corrections, MNRAS in pres

The Effect of Teaching Science Using Hawkins Method in Developing Scientific Curiosity among Students of Intermediate Basic Stage

This study aimed at investigating the effect of teaching science using Hawkins methods in developing scientific curiosity among students of 6th grade from one of Zarqa city school/Jordan in the first semester of the academic year 2018/2019. The subjects of the study consisted of 63 students, divided into two groups: the experimental group of 32 students was taught the “Electricity in our life” unit using Hawkins method and the control group 31 was taught the same unit by the traditional method. To achieve the objectives of the study, a quasi-experimental approach was used. A valid and reliable curiosity scale was prepared  and applied on the subjects of the study before conducting the experiment to test the equivalence of the two groups, and after conducting  the experiment to  achieve the aim of the study. The result revealed statistically significant differences  in the students' curiosity due to the method of teaching in favor of the experimental group which was taught according to Hawkins method. In light of the result, the study recommended that science teachers should use Hawkins method in teaching science

Generic closed loop controller for power regulation in dual active bridge DC-DC converter with current stress minimization

This paper presents a comprehensive and generalized analysis of the bidirectional dual active bridge (DAB) DC/DC converter using triple phase shift (TPS) control to enable closed loop power regulation while minimizing current stress. The key new achievements are: a generic analysis in terms of possible conversion ratios/converter voltage gains (i.e. Buck/Boost/Unity), per unit based equations regardless of DAB ratings, and a new simple closed loop controller implementable in real time to meet desired power transfer regulation at minimum current stress. Per unit based analytical expressions are derived for converter AC RMS current as well as power transferred. An offline particle swarm optimization (PSO) method is used to obtain an extensive set of TPS ratios for minimizing the RMS current in the entire bidirectional power range of - 1 to 1 per unit. The extensive set of results achieved from PSO presents a generic data pool which is carefully analyzed to derive simple useful relations. Such relations enabled a generic closed loop controller design that can be implemented in real time avoiding the extensive computational capacity that iterative optimization techniques require. A detailed Simulink DAB switching model is used to validate precision of the proposed closed loop controller under various operating conditions. An experimental prototype also substantiates the results achieved

Electro-absorption of silicene and bilayer graphene quantum dots

We study numerically the optical properties of low-buckled silicene and AB-stacked bilayer graphene quantum dots subjected to an external electric field, which is normal to their surface. Within the tight-binding model, the optical absorption is calculated for quantum dots, of triangular and hexagonal shapes, with zigzag and armchair edge terminations. We show that in triangular silicene clusters with zigzag edges a rich and widely tunable infrared absorption peak structure originates from transitions involving zero energy states. The edge of absorption in silicene quantum dots undergoes red shift in the external electric field for triangular clusters, whereas blue shift takes place for hexagonal ones. In small clusters of bilayer graphene with zigzag edges the edge of absorption undergoes blue/red shift for triangular/hexagonal geometry. In armchair clusters of silicene blue shift of the absorption edge takes place for both cluster shapes, while red shift is inherent for both shapes of the bilayer graphene quantum dots.Comment: 7 pages, 7 figure

Geochemistry of fluid inclusions in the Vazante zinc deposit, Minas Gerais, Brazil

The Vazante deposit in Minas Gerais, southeast-central Brazil is the world’s largest known occurrence of hypogene non-sulfide zinc (HNSZ) mineralization, originally consisting of about 28.5 million tonnes of ore at an average grade of 18% zinc. The zinc mineralization consists mainly of willemite with lesser, broadly coeval sphalerite and is hosted by sheared Proterozoic slaty dolomites. The Vazante deposit lies at the southern end of the 120 km long Vazante-Unaí trend, the largest district of Zn-Pb mineralization in Brazil, which consists of both hypogene non-sulfide and sulfide deposits. All of the Vazante-Unaí mineralization lies within the Brasília fold belt in the western part of the Bambuí foreland basin and is thought to be a product of fluids mobilized by the 630-610 Ma Brasiliano orogeny. Little is known about the nature of the fluids that form HNSZ deposits beyond fluid inclusion bulk salinities and homogenization temperatures. The present study of the Vazante deposit is the first to measure the elemental composition of potential mineralizing fluids in a HNSZ deposit, and was carried out using LA-ICP-MS and microthermometry. The analyses were all performed on fluid inclusions hosted by sphalerite, as no primary fluid inclusions were identified in willemite. Most of the primary fluid inclusions in sphalerite were found to contain aqueous liquid and vapor in highly variable proportions. Some primary fluid inclusions (~20%) consist entirely of aqueous liquid. Most secondary fluid inclusions were found to consist of a single aqueous liquid phase with about 10% consisting of aqueous liquid + vapor. A few fluid inclusions were observed to contain rhombohedral crystals, which are interpreted to be accidental carbonate mineral inclusions rather than daughter minerals based on their inconsistent occurrence within fluid inclusion assemblages, variable sizes in proportion to their host fluid inclusion sizes, and the abundance of carbonate mineral inclusions in the sphalerite matrix. Microthermometry was performed only on the liquid-vapor primary fluid inclusions and yielded highly variable homogenization temperatures ranging between 47 and 352° C. This high degree of variability is interpreted to be a product either of the deformation and low grade metamorphism that affected the Vazante-Unaí trend during the Brasiliano orogeny, or of necking down during cooling. Salinities were also found to be highly variable, ranging from 0.9 to 22 equivalent weight percent NaCl, and are interpreted to reflect mixing of a saline fluid with a dilute fluid. No correlation between salinity and homogenization temperature was observed. LA-ICP-MS analyses were preformed after the microthermometry analyses to determine the elemental compositions of the fluid inclusions. Absolute elemental concentrations varied widely in keeping with the wide range of fluid inclusion salinities, but the atomic ratios of elements with respect to Na were relatively constant as a function of salinity, consistent with the pattern expected from the dilution of a saline fluid. Average atomic ratios were K/Na = 0.36, Mg/Na = 0.078, Ca/Na = 0.12, and Sr/Na = 0.001. Ba was consistently detected in the fluid inclusions at concentrations of 10’s to 100’s of ppm. Pb was quantifiable in about 14% of the fluid inclusions in concentrations of 100’s to 1000’s of ppm. Vazante fluid inclusion compositions obtained from the present study were compared to Morro Agudo fluid inclusion compositions obtained from previous studies. Vazante and Morro Agudo fluid inclusions were found to have similar K/Na and Ba/Na ratios but Vazante fluid inclusions were found to have significantly lower Mg/Na, Ca/Na, and Sr/Na ratios and to be overall more dilute. Also, none of the Morro Agudo fluid inclusions contained any detectable Pb. Thus, the Vazante and Morro Agudo deposits and their corresponding different styles of mineralization appear to have been formed by different fluids. The compositions of Vazante fluid inclusions were also compared to the compositions of fluid inclusions in Mississippi Valley-type (MVT) deposits in the central United States and in the Irish deposits. Vazante fluid inclusions were found to have higher Ba/Na, K/Na, and Mg/Na but lower Ca/Na and Sr/Na atomic ratios than Ozark MVT fluid inclusions. Vazante fluid inclusions were also found to be distinct from Irish fluid inclusions, having higher Ca/Na, K/Na, and Mg/Na ratios but lower Ba/Na and Sr/Na ratios than Irish fluid inclusions. The fluid inclusion microthermometry and LA-ICP-MS data suggest that the Vazante mineralization formed as a result of dilution of a brine. Willemite and sphalerite solubility are identically sensitive to salinity, but willemite solubility decreases more strongly than sphalerite solubility with respect to pH increase. If the diluting fluid had a higher pH than the brine, then the higher fraction of dilute fluid present in Vazante fluid inclusions compared to Morro Agudo fluid inclusions may mean that the pH of the ore fluid mixture at Vazante was higher than at Morro Agudo, which would favor willemite precipitation and explain its predominance at Vazante. This hypothesis was tested using reaction path modeling, in which potential end member ore fluids were extracted from the fluid inclusion data and allowed to mix. The results confirmed that willemite precipitation should predominate over sphalerite when a cool, dilute, basic, oxidizing fluid mixes with a hotter, saline, acidic, reducing fluid, and produce an overall ore mineral assemblage that resembles what is observed in the field

Modelling of transient heat transfer in annealing furnaces

This is a study of heat transfer in a lift-off furnace which is employed in the batch annealing of a stack of coils of steel strip. The objective of the project is to investigate the various factors which govern the furnace design and the heat transfer resistances, so as to reduce the time of the annealing cycle, and hence minimize the operating costs. The work involved mathematical modelling of patterns of gas flow and modes of heat transfer. These models are: Heat conduction and its conjectures in the steel coils;Convective heat transfer in the plates separating the coils in the stack and in other parts of the furnace; and Radiative and convective heat transfer in the furnace by using the long furnace model. An important part of the project is the development of numerical methods and computations to solve the transient models. A limited number of temperature measurements was available from experiments on a test coil in an industrial furnace. The mathematical model agreed well with these data. The model has been used to show the following characteristics of annealing furnaces, and to suggest further developments which would lead to significant savings: - The location of the limiting temperature in a coil is nearer to the hollow core than to the outer periphery. - Thermal expansion of the steel tends to open the coils, reduces their thermal conductivity in the radial direction, and hence prolongs the annealing cycle. Increasing the tension in the coils and/or heating from the core would overcome this heat transfer resistance. - The shape and dimensions of the convective channels in the plates have significant effect on heat convection in the stack. An optimal design of a channel is shown to be of a width-to-height ratio equal to 9. - Increasing the cooling rate, by using a fluidized bed instead of the normal shell and tube exchanger, would shorten the cooling time by about 15%, but increase the temperature differential in the stack. - For a specific charge weight, a stack of different-sized coils will have a shorter annealing cycle than one of equally-sized coils, provided that production constraints allow the stacking order to be optimal. - Recycle of hot flue gases to the firing zone of the furnace would produce a. decrease in the thermal efficiency up to 30% but decreases the heating time by about 26%

Magnetic suspension and balance system advanced study

An improved compact design for a superconducting magnetic suspension and balance system for an 8 ft. x 8 ft. transonic wind tunnel is developed. The original design of an MSBS in NASA Cr-3802 utilized 14 external superconductive coils and a superconductive solenoid in the airplane test model suspended in a wind tunnel. The improvements are in the following areas: test model solenoid options, dynamic force limits on the model, magnet cooling options, structure and cryogenic designs, power supply specifications, and cost and performance evaluations. The improvements are: MSBS cost reduction of 28%, weight; reduction of 43%, magnet system ampere-meter reduction of 38%, helium liquifier capacity reduction by 33%, magnet system stored energy reduction by 55%, AC loss to liquid helium reduced by 76%, system power supply reduced by 68%, test coil pole strength increased by 19%, wing magnetization increased by 40%, and control frequency limit increased by 200% from 10 Hz to 30 Hz. The improvements are due to: magnetic holmium coil forms in the test model, better rare earth permanent magnets in the wings, fiberglass-epoxy structure replacing stainless steel, better coil configuration, and new saddle roll coil design