482 research outputs found

    Algebraic invariants, mutation, and commensurability of link complements

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    We construct a family of hyperbolic link complements by gluing tangles along totally geodesic four-punctured spheres, then investigate the commensurability relation among its members. Those with different volume are incommensurable, distinguished by their scissors congruence classes. Mutation produces arbitrarily large finite subfamilies of nonisometric manifolds with the same volume and scissors congruence class. Depending on the choice of mutation, these manifolds may be commensurable or incommensurable, distinguished in the latter case by cusp parameters. All have trace field Q(i,\sqrt{2}), but some have integral traces while others do not.Comment: Minor changes following referee's suggestion

    MAGSEAL Edge Breaking Safety Device

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    Team 22 was approached by the Magnetic Seal Corporation to solve a problem: develop simple electro-mechanical safety guarding for an edge-breaking and chamfering lathe. To accomplish this, the current situation was thoroughly researched, the machine inspected by the team, and a preliminary patent search conducted to survey the current body of knowledge for machine guarding. Through lessons learned from this literature search, including mounting methods, shape considerations, and a means to electrically link the guard engagement to machine operation, 120 concepts were generated by the team and classified into four groups. A Quality Function Deployment comparison was performed and in addition to sponsor feedback, a preliminary design for the guard was modeled, drawn, and prototyped. This design uses a steel frame to hold interchangeable polycarbonate panes with three con- toured holes cut therein. One hole is provided for the operator to break the outside diameter of a part, another hole expressly for the inside diameter, and a relief by which a grinding wheel can approach and apply a chamfer feature into the part at variable angles. The holes are arranged and sized so that an operator cannot fit both edge-breaking stone and finger at once, and were a slip to occur, the hand would naturally move either against the frame wherein the pane would prevent contact, or away from the machine entirely. Aluminum sheathing is used to fully enclose the operation and prevent egress of debris or dust into the operator area. A two pin support approach was theorized, but not prototyped, for attachment of the guard to the machine. Through inspection of this prototype and simulation within a faithful 3-D replica of the edge-breaking machine, this design was verified to fulfill MAGSEAL\u27s requirements. The use of the safety guard will not increase cycle time and hypothesized to not be an inconvenience to the operator. Additional work will be carried out to fit the device to the lathe, incorporate electrical integration into the power system, and adapt the guard to the full range of processed parts

    The State of Preschool 2009

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    Provides data on state-funded pre-K programs for the 2008-09 school year and examines the recession's effects on expanding enrollment and raising standards. Ranks states by percentage of children enrolled, funding per child, and quality benchmarks met

    Association of Pyrethroid Pesticide Exposure With Attention-Deficit/Hyperactivity Disorder in a Nationally Representative Sample of U.S. Children

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    Background Pyrethroid pesticides cause abnormalities in the dopamine system and produce an ADHD phenotype in animal models, with effects accentuated in males versus females. However, data regarding behavioral effects of pyrethroid exposure in children is limited. We examined the association between pyrethroid pesticide exposure and ADHD in a nationally representative sample of US children, and tested whether this association differs by sex. Methods Data are from 8–15 year old participants (N = 687) in the 2001–2002 National Health and Nutrition Examination Survey. Exposure was assessed using concurrent urinary levels of the pyrethroid metabolite 3-phenoxybenzoic acid (3-PBA). ADHD was defined by either meeting Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition criteria on the Diagnostic Interview Schedule for Children (DISC) or caregiver report of a prior diagnosis. ADHD symptom counts were determined via the DISC. Multivariable logistic regression examined the link between pyrethroid exposure and ADHD, and poisson regression investigated the link between exposure and ADHD symptom counts. Results Children with urinary 3-PBA above the limit of detection (LOD) were twice as likely to have ADHD compared with those below the LOD (adjusted odds ratio [aOR] 2.42; 95 % confidence interval [CI] 1.06, 5.57). Hyperactive-impulsive symptoms increased by 50 % for every 10-fold increase in 3-PBA levels (adjusted count ratio 1.50; 95 % CI 1.03, 2.19); effects on inattention were not significant. We observed possible sex-specific effects: pyrethroid biomarkers were associated with increased odds of an ADHD diagnosis and number of ADHD symptoms for boys but not girls. Conclusions We found an association between increasing pyrethroid pesticide exposure and ADHD which may be stronger for hyperactive-impulsive symptoms compared to inattention and in boys compared to girls. Given the growing use of pyrethroid pesticides, these results may be of considerable public health import

    A Latent Profile Analysis of Aggression and Victimization across Relationship Types Among Veterans Who Use Substances

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    Objective: This study examined patterns of violence victimization and aggression in both intimate partner and non-partner relationships among veterans, and used latent profile analysis to identify subtypes of violence involvement. Methods: Participants were 841 substance use treatment-seeking veterans (94% male) from a large VA Medical Center who completed screening measures for a randomized controlled trial. Self-report measures were: substance use, legal problems, depression, and violence involvement. Results: Past year violence involvement, including both intimate partner (IPV) and non-partner (NPV) were common in the sample; although NPV occurred at somewhat higher rates. When including either IPV or NPV aggression or victimization, over 48% reported involvement with physical violence, 31% with violence involving injury and 86% with psychological aggression. Latent profile analysis including both aggression and victimization in partner and non-partner relationships indicated a four profile solution: no-low violence (NLV, n = 701), predominantly IPV (n = 35), predominantly NPV (n = 83), and high general violence (HGV, n = 22). Multinomial logistic regression analyses revealed that compared to the no-low violence group, the remaining three groups differed in demographics, depressive symptoms, alcohol and other drug use, and legal involvement. Individuals within each profile had different patterns of substance use and legal involvement with the participants with an HGV profile reporting the most legal problems. Conclusions: IPV and NPV are relatively common among veterans seeking substance use treatment. Characteristics of violence and associated substance use, mental health, and legal difficulties may be useful in considering how to tailor substance use and mental health services
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