Influência da angulação do implante e tipo de intermediário na distribuição das tensões

The aim of this study was to evaluate the influence of implant angulation and abutment type (UCLA and Estheticone) on stress distribution in screw-retained implant-supported prostheses through photoelasticity. Three models were fabricated with photoelastic resin PL-2 (Vishay, Micro-Measurements Group, Inc Raleigh, N.C., USA) containing one external hexagon implant with 3.75x10mm (Master screw, Conexão Sistemas de Prótese Ltda., Arujá, São Paulo) with 0°, 17° and 30° degrees and a screw-retained prostheses with UCLA and Estheticone abutments. The assembly was positioned in a circular polariscope; axial and oblique (45° degrees) loads of 100N were applied in fixed points on the occlusal crown surfaces by a universal testing machine. The stress generated was photographed and analyzed qualitatively with appropriate software (Adobe Photoshop®). The results demonstrated the same number of fringes for both abutment types for each angulation, with fringes increasing in the same way. A higher number of fringes were closer in the oblique loading mode. It was concluded that there was no significant difference in stress distribution in prostheses with UCLA and Estheticone abutments. Higher stress concentrations were observed with increased implant angulation. Stress concentration and intensity were higher in the oblique load than in axial load application.

SEASONAL, HABITAT AND SEX-SPECIFIC PATTERNS OF FOOD UTILIZATION BY RED-WINGED BLACKBIRDS (Agelaius phoeniceous) IN EASTERN ONTARIO AND THEIR ECONOMIC IMPORTANCE

Crop depredation by red-winged blackbirds (Agelaius phoeniceus) causes serious economic losses to agricultural crops each year in both Canada and the United States. The concentration of vulnerable, monocultural crops, particularly corn, during periods when large flocks of blackbirds congregate in roosting areas prior to migration has invariably led to heavy feeding pressure (Stone et al., 1972; Wiens and Dyer, 1975; Tyler et al., 1978). Efforts to reduce damage levels by mechanical and chemical dispersal agents have been largely unsuccessful, at least in terms of a long-term solution to the problem. Recently, the lethal control of blackbird populations using surfactants has been proposed. However, the potential repercussions of the removal of substantial numbers of birds from northern breeding areas are virtually unknown (Robertson et al., 1978). Much of the research dealing with the feeding ecology of red-winged blackbirds has been limited to fall and winter periods when large aggregations of birds are actively involved in crop depredation (Goddad, 1969; Williams, 1976; Dolbeer et al., 1978) or pose a potential health hazard (Monroe and Cronholm, 1976). However, what is not known is the degree to which the removal of deleterious weed seed and insect pests cited in several studies (Bird and Smith, 1964; Mott et al., 1972; Robertson et al., 1978) might be of potential value to agriculture. The issue of whether the benefits derived from redwing foraging compensate for the negative aspects associated with crop depredation and health hazards remains largely unresolved. The present study attempted to evaluate the pest status of this species using diet information derived from food habits analysis conducted during the residency of red- winged blackbirds in a northern breeding area. By determining how the feeding ecology of red-winged blackbirds varies on a seasonal basis, among different breeding habitats and between sexes, we hoped to determine more realistically which segments of the population might be responsible for the greatest benefits or detriments and, thereby, more accurately evaluate the economic impact of the species as a whole. To achieve this aim, the study provides an accurate description of the common insects and weed pests utilized by redwings. By determining the relative proportions of those items known to be detrimental, we hoped to illustrate, at least qualitatively, the degree to which redwing foraging is comprised of both beneficial and harmful components.

LYOCELL AND COTTON FIBERS AS REINFORCEMENTS FOR A THERMOSET POLYMER

Cellulose fibers obtained from the textile industry (lyocell) were investigated as a potential reinforcement for thermoset phenolic matrices, to improve their mechanical properties. Textile cotton fibers were also considered. The fibers were characterized in terms of their chemical composition and analyzed using TGA, SEM, and X-ray. The thermoset (non-reinforced) and composites (phenolic matrices reinforced with randomly dispersed fibers) were characterized using TG, DSC, SEM, DMTA, the Izod impact strength test, and water absorption capacity analysis. The composites that were reinforced with lyocell fibers exhibited impact strengths of nearly 240 Jm(-1), whereas those reinforced with cotton fibers exhibited impact strengths of up to 773 Jm(-1). In addition to the aspect ratio, the higher crystallinity of cotton fibers compared to lyocell likely plays a role in the impact strength of the composite reinforced by the fibers. The SEM images showed that the porosity of the textile fibers allowed good bulk diffusion of the phenolic resin, which, in turn, led to both good adhesion of fiber to matrix and fewer microvoids at the interface.

Not in the Legends

In writing “Not in the Legends”, one of the images and concepts which constantly returned was that of pilgrimage. I began to write these poems while studying abroad in London, after having passed the previous semester in France and travelling around Europe. There was something in the repetition of sightseeing— walking six miles in Luxembourg to see the grave of General Patton, taking photographs of the apartment where Sylvia Plath ended her life, bowing before the bones of saints, searching through Père Lachaise for the grave of Théodore Gericault— which struck me as numinous and morbid. At the same time, I came to love living abroad and I grew discontent with both remaining and returning. I wanted the opportunity to live everywhere all the time and not have to choose between home and away. Returning from abroad, I turned my attention to the landscape of my native country. I found in the New England pilgrims a narrative of people who had left their home in search of growth and freedom. In these journeys I began to appreciate the significance of place and tried to understand what it meant to move from one place to another, how one chose a home, and why people searched for meaning in specific locations. The processes of moving from student to worker and from childhood to adulthood have weighed on me. I began to see these transitions towards maturity as travels to a different land. Memory and nostalgia are their own types of pilgrimage in their attempts to return to lost places, as is the reading of literature. These pilgrimages, real and metaphorical, form the thematic core of the collection. I read the work of many poets who came before me, returning to the places where the Canon was forged. Those poets have a large presence in the work I produced. I wondered how I, as a young poet, could earn my own place in the tradition and sought models in much the same way a painter studies the brushstrokes of a master. In the process, I have tried to uncover what it means to be a poet. Is it something like being a saint? Is it something like being a colonist? Or is to be the one who goes in search of saints and colonists? In trying to measure my own life and work based on the precedent, I have questioned what role era and generation have on the formation of identity. I focused my reading heavily on the early years of English poetry, trying to find the essence of the time when the language first achieved the transcendence of verse. In following the development of English poetry through Coleridge, John Berryman, and Allison Titus, I have explored the progression of those basic virtues in changing contexts. Those bearings, applied to my modern context, helped to shape the poetry I produced. Many of the poems in “Not in the Legends” are based on my own personal experience. In my recollections I have tried to interrogate nostalgia rather than falling into mere reminiscence. Rather than allowing myself poems of love and longing, I have tried to find the meaning of those emotions. A dominant conflict exists between adventure and comfort which mirrors the central engagement with the nature of being “here” or “there”. It is found in scenes of domesticity and wilderness as I attempt to understand my own simultaneous desire for both. For example, in “Canned Mangoes…” the intrusion of nature, even in a context as innocuous as a poem by Sir Walter Raleigh, unravels ordinary comforts of the domestic sphere. The character of “The Boy” from Samuel Beckett’s Waiting for Godot proved such an interesting subject for me because he is one who can transcend the normal boundaries of time and place. The title suggests connections to both place and time. “Legends” features the dual meaning of both myths and the keys to maps. To propose something “Not in the Legends” is to find something which has no precedent in our histories and our geographies, something beyond our field of knowledge and wholly new. One possible interpretation I devised was that each new generation lives a novel existence, the future being the true locus of that which is beyond our understanding. The title comes from Keats’ “Hyperion, a Fragment”, and details the aftermath of the Titanomachy. The Titans, having fallen to the Olympians, are a representation of the passing of one generation for the next. Their dejection is expressed by Saturn, who laments: Not in my own sad breast, Which is its own great judge and searcher out, Can I find reason why ye should be thus: Not in the legends of the first of days… (129-132) The emotions of the conquered Titans are unique and without antecedent. They are experiencing feelings which surpass all others in history. In this, they are the equivalent of the poet who feels that his or her own sufferings are special. In contrast are Whitman’s lines from “Song of Myself” which serve as an epigraph to this collection. He contends for a sense of continuity across time, a realization that youth, age, pleasure, and suffering have always existed and will always exist. Whitman finds consolation in this unity, accepting that kinship with past generations is more important that his own individuality. These opposing views offer two methods of presenting the self in history. The instinct of poetry suggests election. The poet writes because he feels his experiences are special, or because he believes he can serve as a synecdoche for everyone. I have fought this instinct by trying to contextualize myself in history. These poems serve as an attempt at prosopography with my own narrative a piece of the whole. Because the earth abides forever, our new stories get printed over the locations of the old and every place becomes a palimpsest of lives and acts. In this collection I have tried to untangle some of those layers, especially my own, to better understand the sprawling legend of history.

Optimal design of AC EMI filters with damping networks and effect on the systems power factor

The cutoff frequencies of an EMI filter are normally given by the noise attenuation requirements the filter has to fulfill. In order to select the component values of the filter elements, i.e. inductances and capacitances, an additional design criterium is needed. In this paper the effect of the EMI filter input and output impedances are considered. The input impedance influences the filters effect on the system displacement power factor and the output impedance plays a key role in the system stability. The effect of filter element values, the number of filter stages as well as additional damping networks are considered and a design procedure is provided. For this analysis a two-port description of the input filters employing ABCD-parameters is used.

Hybrid behavioral-analytical loss model for a high frequency and low load DC/DC buck converter

This work presents a behavioral-analytical hybrid loss model for a buck converter. The model has been designed for a wide operating frequency range up to 4MHz and a low power range (below 20W). It is focused on the switching losses obtained in the power MOSFETs. Main advantages of the model are the fast calculation time (below 8.5 seconds) and a good accuracy, which makes this model suitable for the optimization process of the losses in the design of a converter. It has been validated by simulation and experimentally with one GaN power transistor and three Si MOSFETs. Results show good agreement between measurements and the model

Envelope Amplifier Based on a Hybrid Series Converter With The Slow-envelope Technique

High frequency dc-dc switching converters are used as envelope amplifiers in RF transmitters. The dc-dc converter should operate at very high frequency to track an envelope in the MHz range to supply the power amplifier. One of the circuits suitable for this application is a hybrid topology composed of a switched converter and a linear regulator in series that work together to adjust the output voltage to track the envelope with accuracy. This topology can take advantage of the reduced slew-rate technique where switching dc-dc converter provides the RF envelope with limited slew rate in order to avoid high switching frequency and high power losses, while the linear regulator performs fine adjustment in order to obtain the exact replica of the RF envelope. The combination of this control technique with this topology is proposed in this paper. Envelopes with different bandwidth will be considered to optimize the efficiency of the dc-dc converter. The calculations and experiments have been done to track a 2MHz envelope in the range 0-12V for an EER RF transmitter.

Advances in random matrix theory, zeta functions, and sphere packing

Over four hundred years ago, Sir Walter Raleigh asked his mathematical assistant to find formulas for the number of cannonballs in regularly stacked piles. These investigations aroused the curiosity of the astronomer Johannes Kepler and led to a problem that has gone centuries without a solution: why is the familiar cannonball stack the most efficient arrangement possible? Here we discuss the solution that Hales found in 1998. Almost every part of the 282-page proof relies on long computer verifications. Random matrix theory was developed by physicists to describe the spectra of complex nuclei. In particular, the statistical fluctuations of the eigenvalues (“the energy levels”) follow certain universal laws based on symmetry types. We describe these and then discuss the remarkable appearance of these laws for zeros of the Riemann zeta function (which is the generating function for prime numbers and is the last special function from the last century that is not understood today.) Explaining this phenomenon is a central problem. These topics are distinct, so we present them separately with their own introductory remarks.

The Bulletin of the North Carolina Department of Agriculture.

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The Bulletin of the North Carolina Department of Agriculture.

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