Shear Bond Strength Comparison between Two Orthodontic Adhesives and Self-Ligating and Conventional Brackets

Objective: To evaluate and compare the shear bond strengths of two adhesives using two types of brackets: a conventional and a self-ligating bracket system. Materials and Methods: Sixty extracted human premolars were collected. The premolars were randomly divided into three groups of 20 teeth. All three groups were direct bonded. Groups 1 and 2 used light-cured adhesive and primer (Transbond XT) with a conventional (Orthos) and a self-ligating bracket (Damon 2), respectively. Group 3 used a light-cured primer (Orthosolo) and a light-cured adhesive (Blūgloo) with a self-ligating bracket (Damon 2). The specimens were stored in distilled water at 37°C for 40 ± 2 hours, after which they were debonded and inspected for Adhesive Remnant Index (ARI) scoring. Results: The mean shear bond strength was 15.2 MPa for group 1, 23.2 MPa for group 2, and 24.8 MPa for group 3. A one-way analysis of variance and post hoc Tukey test showed significant differences in bond strength (P \u3c .001) between group 1 and groups 2 and 3 but no significant difference (P \u3e .05) between groups 2 and 3. A Weibull analysis demonstrated that all three groups provided sufficient bond strength with over 90% survival rate at normal masticatory and orthodontic force levels. A Kruskal-Wallis test showed no significant difference (P \u3e .05) in ARI scores among all three groups. Conclusions: All three groups demonstrated clinically acceptable bond strength. The Damon 2 self-ligating bracket exhibited satisfactory in vitro bond strength with both adhesive systems used

Variations on the Theme of Remembering: A National Survey of How Canadians Use the Past

This paper in collective remembering is based on a telephone survey of 3,419 adult residents of Canada. The questionnaire contains over 70 questions. The interviews average over 20 minutes in length. Part of the Canadians and Their Pasts project, the survey seeks to assess how Canadians use the past in daily life. How many engage in activities related to the past, such as reading books, viewing photos, or visiting museums and historic sites? How do they evaluate different sources of information about the past? What types of past — family, province, nation, ethnic group — are most important to them? The paper suggests that the construction and reconstruction of autobiographical memory is a fundamental aspect of one’s uses of the past. It also proposes that wider collective pasts are particularly important among members of minority and alternative groups. And that the past of the nation-state figures more prominently in these citizens’ reflections than Roy Rosenzweig and David Thelen observed in their similar study, The Presence of the Past: Popular Uses of History in American Life (1998).Cette étude de remémoration collective s’appuie sur une enquête téléphonique menée auprès de 3,419 adultes résidant au Canada. Comportant plus de 70 questions et nécessitant des entretiens de plus de 20 minutes, l’enquête, effectuée dans le cadre du projet Les Canadiens et leurs passés, vise à évaluer l’utilisation du passé dans la vie de tous les jours. Combien de Canadiens et de Canadiennes se livrent à des activités liées au passé, telles que lire un livre, regarder des photos ou visiter un musée ou un lieu historique? Comment évaluent-ils les différentes sources d’information sur le passé? Quels types de passé priment pour eux : celui de leur famille, de leur province, de leur pays, de leur groupe ethnique? Le présent article avance l’idée que la construction et la reconstruction du souvenir autobiographique sont des aspects fondamentaux de l’utilisation du passé. Il affirme que les passés collectifs sont tout particulièrement importants chez les membres des minorités et des groupes divergents. Et il laisse entendre que le passé de l’État-nation est beaucoup plus présent dans les réflexions de ces citoyens que ne l’ont constaté Roy Rosenzweig et David Thelen dans leur étude semblable, The Presence of the Past: Popular Uses of History in American Life (1998)

The First Direct and Enantioselective Cross-Aldol Reaction of Aldehydes

The first enantioselective catalytic direct cross-aldol reaction that employs nonequivalent aldehydes has been accomplished using proline as the reaction catalyst. Structural variation in both the aldol donor (R_1 = Me, n-Bu, Bn, 91 to >99%) and aldol acceptor (R_2 = I-Pr, I-Bu, c-C6H11, Et, Ph, 97−99% ee) are possible while maintaining high reaction efficiency (75−88% yield). Significantly, this new aldol variant allows facile enantioselective access to a broad range of β-hydroxy aldehydes which are valuable intermediates in polyketide syntheses

Two-Step Synthesis of Carbohydrates by Selective Aldol Reactions

Studies of carbohydrates have been hampered by the lack of chemical strategies for the expeditious construction and coupling of differentially protected monosaccharides. Here, a synthetic route based on aldol coupling of three aldehydes is presented for the de novo production of polyol differentiated hexoses in only two chemical steps. The dimerization of α-oxyaldehydes, catalyzed by l-proline, is then followed by a tandem Mukaiyama aldol addition-cyclization step catalyzed by a Lewis acid. Differentially protected glucose, allose, and mannose stereoisomers can each be selected, in high yield and stereochemical purity, simply by changing the solvent and Lewis acid used. The reaction sequence also efficiently produces ^(13)C-labeled analogs, as well as structural variants such as 2-amino– and 2-thio–substituted derivatives

Realistic protein-protein association rates from a simple diffusional model neglecting long-range interactions, free energy barriers, and landscape ruggedness

We develop a simple but rigorous model of protein-protein association kinetics based on diffusional association on free energy landscapes obtained by sampling configurations within and surrounding the native complex binding funnels. Guided by results obtained on exactly solvable model problems, we transform the problem of diffusion in a potential into free diffusion in the presence of an absorbing zone spanning the entrance to the binding funnel. The free diffusion problem is solved using a recently derived analytic expression for the rate of association of asymmetrically oriented molecules. Despite the required high steric specificity and the absence of long-range attractive interactions, the computed rates are typically on the order of 10^4-10^6 M-1 s-1, several orders of magnitude higher than rates obtained using a purely probabilistic model in which the association rate for free diffusion of uniformly reactive molecules is multiplied by the probability of a correct alignment of the two partners in a random collision. As the association rates of many protein-protein complexes are also in the 10^5-10^6 M-1 s-1, our results suggest that free energy barriers arising from desolvation and/or side-chain freezing during complex formation or increased ruggedness within the binding funnel, which are completely neglected in our simple diffusional model, do not contribute significantly to the dynamics of protein-protein association. The transparent physical interpretation of our approach that computes association rates directly from the size and geometry of protein-protein binding funnels makes it a useful complement to Brownian dynamics simulations.Comment: 9 pages, 5 figures, 1 table. One figure and a few comments added for clarificatio

TBD(exp 3)

When asked by the Aeronautical Engineering staff to design a viable supersonic commercial transport, most of the students were well aware that Boeing, McDonnell Douglas, and other aircraft companies had been studying a cadre of transports for more than 30 years and had yet to present a viable aircraft. In the spirit of aviation progress and with much creative license, the TBD design team spearheaded the problem with the full intention of presenting a marketable high speed civil transport in spring of 1992. The project commenced with various studies of future market demands. With the market expansion of American business overseas, the airline industry projects a boom of over 200 million passengers by the year 2000. This will create a much higher demand for time efficient and cost effective inter-continental travel; this is the challenge of the high speed civil transport. The TBD(exp 3), a 269 passenger, long-range civil transport was designed to cruise at Mach 3.0 utilizing technology predicted to be available in 2005. Unlike other contemporary commercial airplane designs, the TBD(exp 3) incorporates a variable geometry wing for optimum performance. This design characteristic enabled the TBD(exp 3) to be efficient in both subsonic and supersonic flight. The TBD(exp 3) was designed to be economically viable for commercial airline purchase, be comfortable for passengers, meet FAR Part 25, and the current FAR 36 Stage 3 noise requirements. The TBD(exp 3) was designed to exhibit a long service life, maximize safety, ease of maintenance, as well as be fully compatible with all current high-traffic density airport facilities

The First General Enantioselective Catalytic Diels−Alder Reaction with Simple α,β-Unsaturated Ketones

The first general approach to enantioselective catalysis of the Diels−Alder reaction with simple ketone dienophiles has been accomplished. The use of iminium catalysis has enabled enantioselective access to a fundamental Diels−Alder reaction variant that has previously been unavailable using chiral Lewis acid catalysis. A new chiral amine catalyst has been developed that allows a variety of monodentate cyclic and acyclic ketones to successfully participate in enantioselective [4 + 2] cycloadditions. A wide spectrum of cyclic and acyclic diene substrates can also be accommodated in this new organocatalytic transformation. A computational model is provided that is in accord with the sense of enantioinduction observed for all reactions conducted during the course of this study

Expression of the neural stem cell markers NG2 and L1 in human angiomyolipoma: are angiomyolipomas neoplasms of stem cells?

Angiomyolipomas are benign tumors of the kidney which express phenotypes of smooth muscle, fat, and melanocytes. These tumors appear with increased frequency in the autosomal dominant disorder tuberous sclerosis and are the leading cause of morbidity in adults with tuberous sclerosis. While benign, these tumors are capable of provoking life threatening hemorrhage and replacement of the kidney parenchyma, resulting in renal failure. The histogenesis of these tumors is currently unclear, although currently, we believe these tumors arise from perivascular epithelioid cells of which no normal counterpart has been convincingly demonstrated. Recently, stem cell precursors have been recognized that can give rise to smooth muscle and melanocytes. These precursors have been shown to express the neural stem cell marker NG2 and L1. In order to determine whether angiomyolipomas, which exhibit smooth muscle and melanocytic phenotypes, express NG2 and L1, we performed immunocytochemistry on a cell line derived from a human angiomyolipoma, and found that these cells are uniformly positive. Immunohistochemistry of human angiomyolipoma specimens revealed uniform staining of tumor cells, while renal cell carcinomas revealed positivity only of angiogenic vessels. These results support a novel histogenesis of angiomyolipoma as a defect in differentiation of stem cell precursors

“I want to know my bloodline”: New Brunswickers and Their Pasts

New Brunswick is a product of wars fought from 1689 to 1815. During these wars, all of which included battles on North American soil, the social relations among the First Nations, French, and British inhabitants were forged, often in blood. These conflicts became the foundation for mutable but seemingly mutually exclusive identities that are documented in a recent survey of New Brunswickers on how they engage the past in their everyday lives. In this paper, we describe the eighteenth-century context in which many New Brunswick cultural identities were constructed and address the findings of the Canadians and Their Pasts survey in a province where popular engagement with history is complicated by diverse perceptions of the past. Résumé Le Nouveau-Brunswick est le produit de guerres ayant eu lieu entre 1689 et 1815. Pendant ces guerres, qui ont toutes eu des batailles en sol nord-américain, des relations sociales se sont tissées entre les Premières nations, les Français et les Britanniques; souvent, ils étaient unis par les liens du sang. Ces conflits sont à la source d’identités mutables, mais qui étaient, en apparence, mutuellement exclusives et qui ont fait l’objet d’une récente enquête qui portait sur les gens du Nouveau-Brunswick et sur la façon qu’ils évoquent le passé au quotidien. Dans cet exposé, nous décrivons le contexte du 18e siècle dans lequel de nombreuses identités culturelles du Nouveau-Brunswick se sont formées et nous nous penchons sur les résultats du sondage portant sur les Canadiens et leur passé et ce, dans une province où l’engagement populaire envers l’histoire se complique par les diverses perceptions du passé

Atomic structure of dislocation kinks in silicon

We investigate the physics of the core reconstruction and associated structural excitations (reconstruction defects and kinks) of dislocations in silicon, using a linear-scaling density-matrix technique. The two predominant dislocations (the 90-degree and 30-degree partials) are examined, focusing for the 90-degree case on the single-period core reconstruction. In both cases, we observe strongly reconstructed bonds at the dislocation cores, as suggested in previous studies. As a consequence, relatively low formation energies and high migration barriers are generally associated with reconstructed (dangling-bond-free) kinks. Complexes formed of a kink plus a reconstruction defect are found to be strongly bound in the 30-degree partial, while the opposite is true in the case of 90-degree partial, where such complexes are found to be only marginally stable at zero temperature with very low dissociation barriers. For the 30-degree partial, our calculated formation energies and migration barriers of kinks are seen to compare favorably with experiment. Our results for the kink energies on the 90-degree partial are consistent with a recently proposed alternative double-period structure for the core of this dislocation.Comment: 12 pages, two-column style with 8 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#rn_di