Exploration and categorization of pre-service physics teachers' alternative conceptions in superconductivity and nanotechnology

An exploratory case study research design was followed to explore and categorize 23 pre-service physics teachers’ understanding in the fields of superconductivity and nanotechnology at the Sultan Qaboos University in Oman. To elicit their responses, a five-stage categorical framework analysis was used. The five stages included identification of the thematic framework, familiarization, coding, placing the categories on a chart and finally, interpretation. A conceptual survey test (Conceptual Survey of Superconductivity and Nanotechnology) was administered to the pre-service physics teachers to form four independently homogenous ability focus groups. This was followed by focus group discussions whose data were analyzed to group their conceptions in both the epistemological as well as ontological categories. From the focus group discussions, six categories were considered from previous studies, namely; lateral alternative conceptions, ontological conceptions, naïve physics, Ohm’s p-primes, mixed conceptions and loose ideas. Since this was a pre-instructional study, naïve physics ideas and lateral alternative conceptions were dominant. Naïve physics refers to the untrained student or human perception of various physical phenomena while lateral alternative conception refers the misconceptions individuals have on ideas that may be inconsistent with scientifically acceptable facts. Findings indicate that the pre-service teachers’ conceptions deviated from canonical scientific concepts, are diversified and inconsistent. The knowledge on pre-instructional conceptions will influence the development of evidence-based pedagogy, which is fundamental to the development of an effective physics education curriculum.Institute for Science and Technology Education (ISTE)M. Sc. (Physics Education

Impact Of Fault Current Limiters And Demand Response On Electric Utility Asset Management Programs

Over-currents are known to be the dominant cause of power system component failures or deterioration from full functionality. Some of these effects may remain unknown and could later result in catastrophic failures of the entire or large portions of the system. There are plenty of devices/methods available to limit the undesirable consequences of the over-current events. These devices/methods have great impact on system reliability by reducing stress on power system components and increasing their useful lifetime. Due to the importance of the subject, there is tremendous need to analyze and compare these devices/methods in terms of reliability. However, few researches have been reported on analyzing reliability impacts of these devices. Reported studies, in the meantime, appear to have investigated these effects qualitatively rather than quantitatively. This is mainly due to lack of a mathematical model to study the direct impacts of over-current values on system reliability. The main stream of reliability calculations are normally based on statistical measures of system outages rather than electrical parameters such as over-current values. Over-currents usually appear in two common forms of fault currents and overload currents. Fault Current Limiters (FCL) and protection devices are commonly used to limit the impact of fault currents. FCL’s limit the magnitude of fault currents and protection devices limit the exposure time of the component to the fault current and therefore have great impact on increasing the lifetime of the components. Overloads, on the other hand, have smaller magnitudes than those of fault currents but can still be destructive because of normally much longer exposure times. Overcoming overload problems usually requires control strategies such as generation rescheduling, and/or load shedding, and optimized usage of existing assets. Using Demand Response (DR) programs are one of the most effective ways of reducing overload burdens on the power system. In this dissertation, simulation models are developed and used to determine the effect of FCL on reducing the magnitude of fault currents. Various case studies will be performed to calculate the effectiveness of FCL’s in real power system applications. Then, security/dependability studies on the protection systems will be performed to analyze and calculate their effectiveness in reducing exposure times to fault currents. Based on the calculated indices, proper selection of protection schemes can be made based on the desired level of dependability/security. In the next part of the work, a mathematical model is developed to calculate the effect of fault current magnitude and duration on the reliability and asset management. Using the developed model and results of the earlier sections of this research work, the impact of protection systems and FCL devices on reliability and asset management programs are quantitatively calculated and compared. The results from such studies will assist in maintenance planning and in proper selection of the fault current limiting devices with regards to desired reliability and asset management programs. DR programs are introduced and modeled in this dissertation as an effective tool in reducing overload burdens on power system components. Using the developed mathematical model, DR programs are studied and compared in terms of reliability improvement that they provide by preventing unnecessary increase in the component failure rates

Index to NASA Tech Briefs, January - June 1966

Index to NASA technological innovations for January-June 196

Rapid Prototyping and Design of a Fast Random Number Generator

Information in the form of online multimedia, bank accounts, or password usage for diverse applications needs some form of security. the core feature of many security systems is the generation of true random or pseudorandom numbers. Hence reliable generators of such numbers are indispensable. the fundamental hurdle is that digital computers cannot generate truly random numbers because the states and transitions of digital systems are well understood and predictable. Nothing in a digital computer happens truly randomly. Digital computers are sequential machines that perform a current state and move to the next state in a deterministic fashion. to generate any secure hash or encrypted word a random number is needed. But since computers are not random, random sequences are commonly used. Random sequences are algorithms that generate a pattern of values that appear to be random but after some time start repeating. This thesis implements a digital random number generator using MATLAB, FGPA prototyping, and custom silicon design. This random number generator is able to use a truly random CMOS source to generate the random number. Statistical benchmarks are used to test the results and to show that the design works. Thus the proposed random number generator will be useful for online encryption and security

Synthesis and Physical Characterization of Solid-State Materials.

Two quantitative X-ray powder diffraction methods were used to analyze Phosphogypsum, a currently underutilized solid by-product of phosphoric acid production. Three kinds of synthetic mixtures were prepared to reflect the variable composition of phosphogypsum: AG (anhydrite and gypsum), QCD (quartz, calcite, and dolomite), and AGQCD. Compositions derived from the Whole Pattern fitting method for the binary and ternary mixtures agreed reasonably well with known values, with residuals \rm\langle R\sp2\rangle = 0.10 for eleven AG samples, and \rm\langle R\sp2\rangle = 0.018 for thirteen QCD samples. However, in the five-component mixtures, overlap of anhydrite, dolomite and gypsum peaks prevented quantitation. Compositions derived from the Matrix Flushing method were generally superior, with \rm\langle R\sp2\rangle = 0.009 for eleven AG mixtures, \rm\langle R\sp2\rangle = 0.0004 for thirteen QCD mixtures, and \rm\langle R\sp2\rangle = 0.0197 for nine AGQCD mixtures. The most notable exception in the determination of AG mixtures with 0-10% gypsum. The measured compositions were distorted in favor of gypsum, apparently due to the affinity of gypsum for water. Two single crystal structures, one organometallic and the other inorganic, were determined. \rm\lbrack (phen)\sb2Cu\rbrack \sp{+}(hfacac)\sp{-} crystallizes in triclinic space group P1 with: a = 10.284(0)A, b = 11.685(0)A, c = 12.519(0)A and \rm\alpha = 114.97(0)\sp\circ ,\ \beta = 90.77(0)\sp\circ ,\ \chi = 105.78(0)\sp\circ .\ Ba\sb{1-x}K\sb{x}BiO\sb3,\ x = 0.419(0), a superconductor with \rm Tc = 29.5\sp\circ K. It crystallizes in cubic space group with Pm3m symmetry and a cell constant of a = 4.2948(0)A. The diffraction-quality crystal of \rm Ba\sb{1-x}K\sb{x}BiO\sb3 was synthesized by electrosynthesis in a molten KOH flux at \rm 225\sp\circ C. The synthesis required ultra-pure KOH (99.99%), \rm Ba(OH)\sb2{\cdot}8H\sb2O (99.8%), \rm Bi\sb2O\sb3 (99.9998%), and a cover gas of water-saturated ultra-pure Ar. The melt composition was based on weight ratios K/Ba = 17.2 and K/Bi = 12.5. The electrode deposition potential was 0.677 volts, starting current $\rm I\cong 20\ \mu A.$ Every attempt was made to maintain a current density of less than \rm 0.5mA/cm\sp2, to ensure slow crystal growth

Defect-based testing of LTS digital circuits

A Defect-Based Test (DBT) methodology for Superconductor Electronics (SCE) is presented in this thesis, so that commercial production and efficient testing of systems can be implemented in this technology in the future. In the first chapter, the features and prospects for SCE have been presented. The motivation for this research and the outline of the thesis were also described in Chapter 1. It has been shown that high-end applications such as Software-Defined Radio (SDR) and petaflop computers which are extremely difficult to implement in top-of-the-art semiconductor technologies can be realised using SCE. But, a systematic structural test methodology had yet to be developed for SCE and has been addressed in this thesis. A detailed introduction to Rapid Single-Flux Quantum (RSFQ) circuits was presented in Chapter 2. A Josephson Junction (JJ) was described with associated theory behind its operation. The JJ model used in the simulator used in this research work was also presented. RSFQ logic with logic protocols as well as the design and implementation of an example D-type flip-flop (DFF) was also introduced. Finally, advantages and disadvantages of RSFQ circuits have been discussed with focus on the latest developments in the field. Various techniques for testing RSFQ circuits were discussed in Chapter 3. A Process Defect Monitor (PDM) approach was presented for fabrication process analysis. The presented defect-monitor structures were used to gather measurement data, to find the probability of the occurrence of defects in the process which forms the first step for Inductive Fault Analysis (IFA). Results from measurements on these structures were used to create a database for defects. This information can be used as input for performing IFA. "Defect-sprinkling" over a fault-free circuit can be carried out according to the measured defect densities over various layers. After layout extraction and extensive fault simulation, the resulting information will indicate realistic faults. In addition, possible Design-for-Testability (DfT) schemes for monitoring Single-Flux Quantum (SFQ) pulses within an RSFQ circuit has also been discussed in Chapter 3. The requirement for a DfT scheme is inevitable for RSFQ circuits because of their very high frequency of operation and very low operating temperature. It was demonstrated how SFQ pulses can be monitored at an internal node of an SCE circuit, introducing observability using Test-Point Insertion (TPI). Various techniques were discussed for the introduction of DfT and to avoid the delay introduced by the DfT structure if it is required. The available features in the proposed design for customising the detector make it attractive for a detailed DBT of RSFQ circuits. The control of internal nodes has also been illustrated using TPI. The test structures that were designed and implemented to determine the occurrence of defects in the processes can also be used to locate the position for the insertion of the above mentioned DfT structures