Composition, Phase Structure, and Corrosion of Nickel-Free and Nickel-Containing Stainless Steel Orthodontic Wires

Stainless steel wires have long been used in orthodontics. The austenitic stainless steel used in orthodontics contains approximately 18 wt% chromium and 8 wt% nickel. Nickel improves the corrosion resistance and helps maintain the austenite structure of stainless steel. Nickel is the most allergenic metal and is the most common metal associated with contact dermatitis in orthodontics. Nickel-free wires have been developed, and it was the goal of this study to compare nickel-free and nickel-containing stainless steel orthodontic wires to determine and compare their composition, phase structure, and corrosion properties. For each test, nickel-free and conventional stainless steel wires were compared from four companies: Acme Monaco, Dentaurum, Leone, and Scheu-Dental. Phase structure was determined using x-ray diffraction. Composition was measured using scanning electron microscopy with energy dispersive spectroscopy. For each wire, straight lengths were sectioned into 1-inch segments, arranged side-by-side, to create a 1-inch by 1-inch planar array of wires secured with sticky wax. Resultant XRD pattern peaks were indexed using standard methods or via ICDD files. Electrochemical corrosion tests were completed using a 3-electrode cell with a potentiostat and Gamry corrosion test software. Fusayama-Meyer artificial saliva solution was used as the electrolyte at room temperature. For each wire brand, wire lengths were isolated using nail polish, exposing a consistent surface area to account for varying diameters of the wires among brands. Open circuit potential, polarization resistance, and corrosion current density were determined. Data were compared using one-way analysis of variance (ANOVA) at a 0.05 significance value with a Tukey\u27s Studentized Range (HSD) Test post hoc analysis, where required. Two nickel-free wires had detectable amounts of nickel. All nickel-free stainless steel wires had an increased amount of manganese, chromium, and molybdenum with decreased iron content. The orthodontic stainless steel wires are mostly austenitic, but martensite may be present in both types. Although there were significant differences among the wires for the three corrosion parameters, there was not a general difference between nickel-free and conventional stainless steel wires. Overall, despite composition differences between the nickel-free and nickel-containing stainless steel wires, they generally had the same phase structure and similar corrosion properties

Extended paretian rules and relative utilitarianism

This paper introduces the 'Extended Pareto' axiom on Social welfare functions and gives a characterization of the axiom when it is assumed that the Social Welfare Functions that satisfy it in a framework of preferences over lotteries also satisfy the restrictions (on the domain and range of preferences) implied by the von-Neumann-Morgenstern axioms. With the addition of two other axioms: Anonymity and Weak IIA* it is shown that there is a unique Social Welfare Function called Relative Utilitarianism that consists of normalizing individual utilities between zero and one and then adding them

Prediction of secondary structures for large RNA molecules

The prediction of correct secondary structures of large RNAs is one of the unsolved challenges of computational molecular biology. Among the major obstacles is the fact that accurate calculations scale as O(n⁴), so the computational requirements become prohibitive as the length increases. We present a new parallel multicore and scalable program called GTfold, which is one to two orders of magnitude faster than the de facto standard programs mfold and RNAfold for folding large RNA viral sequences and achieves comparable accuracy of prediction. We analyze the algorithm's concurrency and describe the parallelism for a shared memory environment such as a symmetric multiprocessor or multicore chip. We are seeing a paradigm shift to multicore chips and parallelism must be explicitly addressed to continue gaining performance with each new generation of systems. We provide a rigorous proof of correctness of an optimized algorithm for internal loop calculations called internal loop speedup algorithm (ILSA), which reduces the time complexity of internal loop computations from O(n⁴) to O(n³) and show that the exact algorithms such as ILSA are executed with our method in affordable amount of time. The proof gives insight into solving these kinds of combinatorial problems. We have documented detailed pseudocode of the algorithm for predicting minimum free energy secondary structures which provides a base to implement future algorithmic improvements and improved thermodynamic model in GTfold. GTfold is written in C/C++ and freely available as open source from our website.M.S.Committee Chair: Bader, David; Committee Co-Chair: Heitsch, Christine; Committee Member: Harvey, Stephen; Committee Member: Vuduc, Richar

Leader reputation and default in sovereign debt

This paper compares default incentives in competitive sovereign debt markets when leaders can be either democratically elected or dictators. When leaders can be replaced as in democracies, the incentives for repayment are mainly the ego rents from office and the possibility of getting a corrupt leader from replacement. In a dictatorship, on the other hand, the cost of not repaying loans is the permanent loss of reputation and the loss of future access to credit. There is a trade off between repayment and risk sharing. We show, counter-intuitively, that when ego rents are low, and value of reputation to dictators is high, then democracies repay more often and have lower risk premia than dictatorships

Extended paretian rules and relative utilitarianism.

This paper introduces the 'Extended Pareto' axiom on Social welfare functions and gives a characterization of the axiom when it is assumed that the Social Welfare Functions that satisfy it in a framework of preferences over lotteries also satisfy the restrictions (on the domain and range of preferences) implied by the von-Neumann-Morgenstern axioms. With the addition of two other axioms: Anonymity and Weak IIA* it is shown that there is a unique Social Welfare Function called Relative Utilitarianism that consists of normalizing individual utilities between zero and one and then adding them.Group Preferences; Multi-profile;

Malaysia’s 2013 election: the nation, and the National Front

If ever an election victory could be interpreted as a humiliation by the winning side, then the Malaysian federal election, held in May this year, was profoundly humiliating for the National Front (Barisan Nasional, or BN). BN won government for the thirteenth time, and extended its uninterrupted hold on federal government in Malaysia. It also continues to hold a majority of states in the federation. In this sense, BN’s political primacy—as the sole government Malaysia has ever known—remains in place, in the nation it argues its predecessors brought in to being in 1957 (Cheah Boon Kheng 2002; Hooker 2003). Aside from remaining in government, however, BN has nevertheless had to reconcile itself to a new political environment, in which its domination of the architecture of ‘the national’ is no longer guaranteed. Berita, Autumn 2013: 14–20

Exploring N-rich phases in LixNy clusters for hydrogen storage at nano-scale

We have performed cascade genetic algorithm and ab initio atomistic thermodynamics under the framework of first-principles density functional theory to study the (meta-)stability of a wide range of LixNy clusters. We found that hybrid xc-functional is essential to address this problem as a local/semi-local functional simply fails even to predict a qualitative prediction. Most importantly, we find that though in bulk Lithium Nitride, Li rich phase, i.e. Li3N, is the stable stoichiometry, in small LixNy clusters N-rich phases are more stable at thermodynamic equilibrium. We further show a that these N-rich clusters are promising hydrogen storage material because of their easy adsorption and desorption ability at respectively low (< 300K) and moderately high temperature (> 600K).Comment: 5 pages, 4 figure

Development and the interaction of enforcement institutions

We examine how institutions that enforce contracts between two parties, producers and consumers, interact in a competitive market with one-sided symmetric information and productivity shocks. We compare an informal enforcement mechanism, reputation, the efficacy of which is enhanced by consumers investing in “connectedness,” with a formal mechanism, legal enforcement, the effectiveness of which can be reduced by producers by means of bribes. When legal enforcement is poor, consumers connect more with one another to improve informal enforcement; in contrast, a well-connected network of consumers reduces producers’ incentives to bribe. In equilibrium, the model predicts a positive relationship between the the frequency of productivity shocks, bribing, and the use of informal enforcement, providing a physical explanation of why developing countries often fail to have efficient legal systems. Firm-level estimations confirm the partial equilibrium implications of the model