First-principles electronic theory of non-collinear magnetic order in transition-metal nanowires

The structural, electronic and magnetic properties of one-dimensional 3d transition-metal (TM) monoatomic chains having linear, zigzag and ladder geometries are investigated in the frame-work of first-principles density-functional theory. The stability of long-range magnetic order along the nanowires is determined by computing the corresponding frozen-magnon dispersion relations as a function of the 'spin-wave' vector q. First, we show that the ground-state magnetic orders of V, Mn and Fe linear chains at the equilibrium interatomic distances are non-collinear (NC) spin-density waves (SDWs) with characteristic equilibrium wave vectors q that depend on the composition and interatomic distance. The electronic and magnetic properties of these novel spin-spiral structures are discussed from a local perspective by analyzing the spin-polarized electronic densities of states, the local magnetic moments and the spin-density distributions for representative values q. Second, we investigate the stability of NC spin arrangements in Fe zigzag chains and ladders. We find that the non-collinear SDWs are remarkably stable in the biatomic chains (square ladder), whereas ferromagnetic order (q =0) dominates in zigzag chains (triangular ladders). The different magnetic structures are interpreted in terms of the corresponding effective exchange interactions J(ij) between the local magnetic moments μ(i) and μ(j) at atoms i and j. The effective couplings are derived by fitting a classical Heisenberg model to the ab initio magnon dispersion relations. In addition they are analyzed in the framework of general magnetic phase diagrams having arbitrary first, second, and third nearest-neighbor (NN) interactions J(ij). The effect of external electric fields (EFs) on the stability of NC magnetic order has been quantified for representative monoatomic free-standing and deposited chains. We find that an external EF, which is applied perpendicular to the chains, favors non-collinear order in V chains, whereas it stabilizes the ferromagnetic (FM) order in Fe chains. Moreover, our calculations reveal a change in the magnetic order of V chains deposited on the Cu(110) surface in the presence of external EFs. In this case the NC spiral order, which was unstable in the absence of EF, becomes the most favorable one when perpendicular fields of the order of 0.1 V/Å are applied. As a final application of the theory we study the magnetic interactions within monoatomic TM chains deposited on graphene sheets. One observes that even weak chain substrate hybridizations can modify the magnetic order. Mn and Fe chains show incommensurable NC spin configurations. Remarkably, V chains show a transition from a spiral magnetic order in the freestanding geometry to FM order when they are deposited on a graphene sheet. Some TM-terminated zigzag graphene-nanoribbons, for example V and Fe terminated nanoribbons, also show NC spin configurations. Finally, the magnetic anisotropy energies (MAEs) of TM chains on graphene are investigated. It is shown that Co and Fe chains exhibit significant MAEs and orbital magnetic moments with in-plane easy magnetization axis. The remarkable changes in the magnetic properties of chains on graphene are correlated to charge transfers from the TMs to NN carbon atoms. Goals and limitations of this study and the resulting perspectives of future investigations are discussed.

Prevalencia de síntomas musculo-esqueléticos en trabajadores de una institución de educación superior en el departamento de Arauca, Colombia, 2015

Introducción Los desórdenes musculo esqueléticos representan uno de los problemas de salud ocupacional más comunes de trabajadores, lo cual genera ausentismo laboral y aumento en los costos de enfermedades laborales. Objetivo Estimar la prevalencia de síntomas osteomusculares y su relación con factores de riesgo ocupacional, en personal docente y administrativo de una institución de educación superior en el Departamento de Arauca para el año 2015. Métodos Estudio analítico de corte transversal en una muestra de 116 trabajadores. Se utilizaron dos instrumentos: “La Encuesta Nacional de Condiciones de Trabajo” del Instituto Nacional de Seguridad e Higiene en el Trabajo de España (INSHT) y el “Cuestionario Ergopar”, validados al Español. Se obtuvo previa autorización del Comité de ética de la Universidad del Rosario. El análisis estadístico se realizó con el IBM SPSS Statistics versión 20.0. Resultados: Los síntomas osteomusculares con mayor prevalencia fueron en cuello (86,2%), espalda lumbar (61,2%), manos muñecas (59,5%) y pies (52,6%); no se observaron diferencias estadísticamente significantes entre administrativos e instructores. En el lugar de trabajo los factores de riesgo con mayor prevalencia fueron exposición a temperaturas extremas (48,3%), aberturas y huecos desprotegidos, escaleras, plataformas, desniveles (44%) significativamente mayor en instructores (52,6%) que en personal administrativo (27,5%) (p= 0,010). Conclusiones: Los síntomas osteomusculares más prevalentes fueron aquellos propios de la actividad docente: cuello, espalda lumbar, manos muñecas y pies. El personal de la institución en especial los docentes está expuesto a factores de riesgo físico, químico y ergonómico. Las condiciones de trabajo son adecuadas. No se encontró asociación estadística entre exposición a factores de riesgo en el puesto de trabajo y prevalencia de síntomas osteomusculares. Se debe establecer acciones dirigidas a evitar lesiones musculo esqueléticas en la población.

Get to know your local games shop

Provides information on the mathematical potential of commercial board games. Mastermind; Snakes and Ladders; Ludo.

Organotin-oxo clusters

This thesis reports on the development and expansion of reliable synthetic di-and multi-tin precursors for the assembly of oligomeric organotin-oxo compounds in which the shape, dimension and tin nuclearity can be controlled. The reaction of polymeric diorganotin oxides, (R2SnO)m (R = Me, Et, n-Bu, n-Oct, c-Hex, i-Pr, Ph), with saturated aqueous NH4X solutions (X = F, Cl, Br, I, OAc) in refluxing 1,4-dioxane afforded in high yields dimeric tetraorganodistannoxanes, [R2(X)SnOSn(X)R2]2, and in a few cases diorganotin dihalides or diacetates, R2SnX2. This method appears to be particularly good for the synthesis of halogenated tetraorganodistannoxanes but a less suitable method for the preparation of dicarboxylato tetraorganodistannoxanes. Identification of [R2(OH)SnOSn(X)R2]2 (R = n-Bu; X = Cl, Br) and [R2(OH)SnOSn(X)R2][R2(X)SnOSn(X)R2] suggest a serial substitution mechanism starting from [R2(OH)SnOSn(OH)R2]2. A series of α, ω -bis(triphenylstannyl)alkanes, [Ph3Sn]2(CH2)n (n = 3-8, 10, 12) and some of their derivatives were synthesised and characterised. These α, ω-bis(triphenylstannyl)alkanes, [Ph3Sn]2(CH2)n were converted to the corresponding halides [R(Cl)2Sn]2(CH2)n (R = CH2SiMe3) and subsequently to the polymeric oxides {[R(0)Sn]2(CH2)n}m. Reaction of {[R(O)Sn]2(CH2)n}m with [R(Cl)2Sn]2(CH2)n. (n = 3, n' = 4 and n = 4, n' = 3) in toluene at 100°C results in a mixture of symmetric and asymmetric double ladders, where different spacer chain lengths (n and n') provide the source of asymmetry. The coexistence at high temperature of separate 119Sn NMR signals belonging to symmetric and asymmetric double ladders suggests an equilibrium that is slow on the 119Sn NMR time scale and the position of which is temperature dependent. However, 119Sn NMR spectroscopic experiments of {[R(0)Sn]2(CH2)3}m with [R(Cl)2Sn]2(CH2)n for longer spacers (n - 5, 6, 8, 10, 12) reveal that molecular self-assembly of symmetric spacer-bridged di-tin precursors of equal chain length is preferred over asymmetric species. An ether-bridged di-tin tetrachloride [R(Cl)2Sn(CH2)3]2O (R = CH2SiMe3) and its corresponding polymeric oxide {[R(O)Sn(CH2)3]2O}m were synthesised and characterised. Reaction of [R(Cl)2Sn(CH2)3]2O with {[R(O)Sn(CH2)3]2O}m results in a unique functionalised double ladder {{[RSn(Cl)](CH2)3O(CH2)3[RSn(Cl)]}O}4 whose structure in the solid state was determined by X-ray analysis. Identification of tetrameric functionalised double ladder as well as dimeric and monomeric species suggest the existence of an equilibrium in solution. The feasibility of the functionalised double ladder to form host-guest complexes with a variety of metal cations is investigated using electrospray mass spectrometry (ESMS). Evidence for such complexes is found only for sodium cations. The reaction between {[R(O)Sn]2(CH2)n}m (n = 3, 4, 8, 10) and triflic acid is described. The initial formed products [RSn(CH2)nSnR](OTf)4 are easily hydrolysed. For n = 3, self-assembly leads to a discrete double ladder type structure, {{[RSn(OH)](CH2)3[RSn(H2O)]}O}44OTf, which is the first example of a cationic double ladder. For n ≥ 3, hydrolysis gives polymeric products, as demonstrated by the crystal structure of {[(H2O)(OH)RSn]2(CH2)4-2OTf2H2O}m. Two spacer-bridged terra-tin octachlorides [R(Cl)2Sn(CH2)3Sn(Cl)2]2(CH2)n (R = CH2SiMes; n = 1, 8) and their corresponding polymeric oxides {[R(O)Sn(CH2)3Sn(O)]2(CH2)n}m were successfully synthesised and characterised. Attempts were made to synthesise quadruple ladders from these precursors. Reactions of [R(Cl)2Sn(CH2)3Sn(Cl)2]2CH2 with {[R(O)Sn(CH2)3Sn(O)]2CH2}m or (Y-Bu2SnO)3 result in, mostly insoluble, amorphous solids. Reactions of [R(Cl)2Sn(CH2)3Sn(Cl)2]2(CH2)8 with {[R(O)Sn(CH2)3Sn(O)]2(CH2)8}m or (t-Bu2SnO)s result in new tin-containing species which are presumably oligomeric. The synthesis of a series of alkyl-bridged di-tin hexacarboxylates [(RCO2)3Sn]2(CH2)n (n = 3, 4; R = Ph, c-C6H11, CH3, C1CH2) is also reported. The hydrolysis of these compounds is facile and complex. There appears to be no correlation between spacer chain length and hydrolysis product. However, the conjugate acid strength of the carboxylate does appear to be important. In general only insoluble amorphous polymeric organotin-oxo compounds were obtained.

Raining blood and money

A fictocritical piece based on a fire in New York.
A girl jumps from the ninth floor of the Asch Building. People on the sidewalk are screaming for her not to jump. But she has to jump. As she stands on the ledge, her back against the open window, the fire is burning the clothes off her back. She has her head bent forward so her hair doesn't catch alight as she waves a handkerchief at the crowd. The windows on the floor beneath her start to explode. Tongues of flame lick at her feet. So she jumps. It's a definite jump, as she bends her knees before she leaps over the edge. It's not a graceful jump. Her arms begin to flail as she struggles to stay upright. There are gasps from the crowd, a few screams. Some people turn away. Others are transfixed, watching her as she falls. Suddenly, her dress catches on a hook jutting out of wall below and she is suspended in the air, mid-fall. But the ladders still can't reach her and so it is just a cruel pause in her inevitable death. She hangs there like a ragdoll until her dress burns itself free from her body and she resumes her fall. She lands on the pavement on the west - ward side of New York University building. Thud-dead...

A estratégia reprodutiva dos peixes migradores frente às escadas do Complexo Canoas (Rio Paranapanema, Bacia do Alto Paraná)

Pós-graduação em Ciências Biológicas (Zoologia) - IBB

Reproductive migration of fish and movement in a series of reservoirs in the Upper Parana River basin, Brazil

AbstractThis study evaluates the effectiveness of two fish passes at two hydropower dams (Canoas I and II) in the Upper Parana basin, which form part of a cascade of three reservoirs. Fish from 12 migratory species (3089 specimens) were captured during their ascending, reproductive migration and were tagged with hydrostatic tags. The recapture data (294 specimens over two consecutive years) showed that there is a strong tendency for the maintenance of ascending migration through reservoirs with fish passes but with differences in migratory activity within the same species. No eggs, larvae or juveniles of these species were found in samples collected over 5 years in the reservoirs above the fish passes. These data suggest that fish passes have contributed to the restoration of the migratory routes of adult fish but that in the absence of suitable spawning or nursery habitats for these species; they probably act as ecological traps and do not contribute to the recruitment of the species.

Doenças osteoarticulares em pequenos animais

Osteoarticular diseases are very frequent in small animals, especially dogs. Osteoarthritis is the most common degenerative arthropathy in cats and dogs. It is one of the most important skeletal disease in small animals and it is divided into two broad classes: secondary and genetics. The secondary is originated from situations that can cause joint instability like as trauma, ligament problems and obesity among others. The gene for osteoarthritis comes from hereditary problems such as hip dysplasia, elbow dysplasia and other diseases that can cause articular instability. The hereditary osteoarticular diseases are important only because they can result in the osteoarthritis. It is important to prevent the joint instability and consequently the clinical signs that affect the quality of life of the animals. The most common clinical signs are intermittent claudication, a decrease in performance, reluctance to jump and climb ladders among others. To prevent the clinical signs or mitigate them, the treatments need to be focused on pain control and especially restoration of the affected joint. The treatments most used are the medical and surgery. Anti-inflammatory and analgesics are used in large scale for pain control and to inhibit inflammatory mediators. Furthermore, medical treatment includes weight reduction, physiotherapy and proper nutrition along with anti-inflammatory and analgesics. Surgical treatments are indicated if there is an inadequate response to medical treatment. Physiotherapy is often used in conjunction with other treatments. Besides the reduction of weight is essential and obesity is unacceptable. Cats also suffer from osteoarthritis, but the diagnosis is rarer than in dogs. Usually the cat’s owners relate the reluctance to jump and drop in performance with senility, and when the disease is diagnosed is already in... (Complete abstract click electronic access below)

Entwicklung einer Online-Kopplung der Gelelektrophorese mit der induktiv gekoppelten Plasma-Massenspektrometrie und deren Anwendung in der Bioanalytik

Die Elementmassenspektrometrie wurde in den letzten Jahren sehr erfolgreich zur Aufklärung verschiedener Fragestellungen in der Bioanalytik eingesetzt. Hierbei spielen vor allem Kopplungstechniken von Trennmethoden wie der Flüssigchromatographie (LC) oder der Kapillarelektrophorese (CE) mit der induktiv gekoppelten Plasma-Massenspektrometrie (ICP-MS) als Multielementdetektor mit hervorragenden Quantifizierungseigenschaften eine entscheidende Rolle bei der Untersuchung von Biopolymeren und deren Wechselwirkung mit verschiedenen Metallen. So wurden beispielsweise verschiedene Methoden für die Trennung und Detektion von Metalloproteinen oder DNA-Metall-Addukten in unterschiedlichen Probenmaterialien entwickelt. Die traditionelle und leistungsstärkste Trennmethode für Biopolymere aller Art, die Gelelektrophorese, wurde jedoch bislang nicht in einem Online-Verfahren an die ICP-MS gekoppelt, um solche Fragestellungen zu bearbeiten. Verschiedene Versuche auf der Basis der Laserablation wurden in diese Richtung unternommen, wobei diese Techniken als sehr umständlich und zeitaufwändig anzusehen sind. In dieser Arbeit wird erstmals die technische Realisierung einer Online-Kopplung der Gelelektrophorese mit der ICP-MS beschrieben. Das System basiert auf einem Prinzip aus der präparativen Gelelektrophorese, in welcher eine kontinuierliche Elution der getrennten Komponenten aus dem Gel während der laufenden Elektrophorese durchgeführt wird. Die eluierten Komponenten werden mit dem Elutionspuffer direkt in das Zerstäubersystem des ICP-MS geführt. Die ersten Untersuchungen wurden am Beispiel der Fragemente von doppelsträngiger DNA (dsDNA) durchgeführt. Kommerziell erhältliche Standardlösungen wurden mit der Online-GE-ICP-MS mittels Detektion von 31P an einem hochauflösenden Massenspektrometer mit einer Massenauflösung von 4000 analysiert. Die Trennbedingungen (z.B. pH-Wert oder Ionenstärke der Pufferlösungen) wurden für die Trennung von dsDNA-Fragementen in Agarosegelen optimiert und auf verschiedene dsDNA-Fragmente angewandt. In einem nächsten Schritt wurden die Quantifizierungsmöglichkeiten für Biopolymere untersucht. Sehr kleine Mengen an dsDNA konnten mit einer Präzision von weniger als 3% quantifiziert werden. Hierfür kamen verschiedene Möglichkeiten der externen Kalibration zum Einsatz, wie der Kalibration mit einem Phosphat-Standard oder einem kommerziell erhältlichen quantitativen dsDNA-Standard. Um das Potenzial der entwickelten Methode für die Untersuchung von Biopolymer-Metall-Wechselwirkungen zu demonstrieren, wurden Oligonukleotide mit Cisplatin unter physiologischen Bedingungen inkubiert und die Reaktionsprodukte mit der Online-GE-ICP-MS mittels 31P- und 195Pt-Detektion untersucht. Verschiedene Cisplatin-Oligonukleotid-Addukte konnten auf diese Weise beobachtet werden, was zur Identifizierung die Anwendung der MALDI-TOF-MS als komplementärer Form der Massenspektrometrie notwendig machte. Abschließend wurde die Isotopenverdünnungsanalyse zum Zweck der Quantifizierung herangezogen.

Regulation of apoptosis during the pathogenesis of non -melanoma skin cancer

Previous studies from our lab have shown distinctive patterns of expression of bcl-2 gene family members in human nonmelanoma skin cancer (NMSC). To further evaluate the significance of these observations and to study the effects of cell death deregulation during skin carcinogenesis, we generated a transgenic mouse model (HK1.bcl-2) using the human keratin 1 promoter to target the expression of a human bcl-2 minigene to the epidermis. Transgenic protein expression was confirmed in all the layers of the epidermis except the stratum corneum using immunohistochemistry. Multifocal epidermal hyperplasia, without associated hyperkeratosis, was observed in newborn HK1.bcl-2 mice. Immunofluorescence staining using monoclonal antibodies specific for a variety of differentiation markers revealed aberrant expression of keratin 6 (K6) in the transgenic epidermis. Epidermal proliferative indexes, assessed by anti-BrdUrd immunofluorescence staining, were similar in control and transgenic newborn mice, but suprabasal proliferating cells were seen within the hyperplastic areas of the transgenic mouse skin. Spontaneous apoptotic indices of the epidermis were similar in both control and HK1.bcl-2 transgenic newborn mice, however, after UV-B irradiation, the number of "sunburn cells" was significantly higher in the control compared to the HK1.bcl-2 transgenic animals.^ Adult HK1.bcl-2 and control littermate mice were used in UV-B and chemical carcinogenesis protocols including DMBA + TPA. UV-B irradiated control and HK1.bcl-2 mice had comparable incidence of tumors than the controls, but the mean latency period was significantly shorter in the HK1.bcl-2 transgenic. Both control and transgenic animals included in chemical carcinogenesis protocols required application of both the initiating (DMBA) and promoting (TPA) agents to develop tumors. The frequency, number, and latency of tumor formation was similar in both groups of animals, however, HK1.bcl-2 mice exhibited a rate of conversion from benign papilloma to carcinoma 2.5 times greater than controls.^ Similar carcinogenesis experiments were performed using newborn mice. HK1.bcl-2 mice treated with UV-B plus TPA have a three fold greater incidence of tumor formation compared to controls littermates. HK1.bcl-2 transgenic animals also exhibited a shorter latency for papilloma formation when treated with DMBA plus TPA.^ HK1.bcl-2/v-Ha-ras double transgenic mice shared phenotypic features of both HK1.v-Ha-ras and HK1.bcl-2 transgenic mice, and exhibited focal areas of augmented hyperplasia. These double transgenic mice were susceptible to tumor formation by treatment with TPA alone.^ Cultures of primary keratinocytes were established from control, HK1.bcl-2, HK1.Ha-ras, and HK1.bcl-2/v-Ha-ras newborn mice. Cell viability was determined after exposure of the cells to UV-B irradiation, DMBA, TPA, or TGF-$\beta$1. Internucleosomal DNA fragmentation ("ladders") and morphological cellular changes compatible with apoptotic cell death were observed after the application of all these agents. HK1.bcl-2 keratinocytes were resistant to cell death induction by all of these agents except TGF-$\beta$1. HK1.Ha-ras cells had a higher spontaneous rate of cell death which could be compensated by co-expression of bcl-2.^ These findings suggest that bcl-2 dependent cell death suppression may be an important component of multistep skin carcinogenesis. ^

Mapping protein-protein interactions by affinity-directed mass spectrometry.

A precise and rapid method for identifying sites of interaction between proteins was demonstrated; the basis of the method is direct mass spectrometric readout from the complex to determine the specific components of the proteins that interact--a method termed affinity-directed mass spectrometry. The strategy was used to define the region of interaction of a protein growth factor with a monoclonal antibody. A combination of proteolytic digestion and affinity-directed mass spectrometry was used to rapidly determine the approximate location of a continuous binding epitope within the growth factor. The precise boundaries of the binding epitope were determined by affinity-directed mass spectrometric analysis of sets of synthetic peptide ladders that span the approximate binding region. In addition to the mapping of such linear epitopes, affinity-directed mass spectrometry can be applied to the mapping of other types of molecule-molecule contacts, including ligand-receptor and protein-oligonucleotide interactions.

Fumonisins and Alternaria alternata lycopersici toxins: sphinganine analog mycotoxins induce apoptosis in monkey kidney cells.

Fusarium moniliforme toxins (fumonisins) and Alternaria alternata lycopersici (AAL) toxins are members of a new class of sphinganine analog mycotoxins that occur widely in the food chain. These mycotoxins represent a serious threat to human and animal health, inducing both cell death and neoplastic events in mammals. The mechanisms by which this family of chemical congeners induce changes in cell homeostasis were investigated in African green monkey kidney cells (CV-1) by assessing the appearance of apoptosis, cell cycle regulation, and putative components of signal transduction pathways involved in apoptosis. Structurally, these mycotoxins resemble the sphingoid bases, sphingosine and sphinganine, that are reported to play critical roles in cell communication and signal transduction. The addition of fumonisin B1 or AAL toxin, TA, to CV-1 cells induced the stereotypical hallmarks of apoptosis, including the formation of DNA ladders, compaction of nuclear DNA, and the subsequent appearance of apoptotic bodies. Neither mycotoxin induced cell death, DNA ladders, or apoptotic bodies in CV-1 cells expressing simian virus 40 large T antigen (COS-7) at toxin concentrations that readily killed CV-1 cells. Fumonisin B1 induced cell cycle arrest in the G1 phase in CV-1 cells but not in COS-7 cells. AAL toxin TA did not arrest cell cycle progression in either cell line. The induction of apoptosis combined with the widespread presence of these compounds in food crops and animal feed identifies a previously unrecognized health risk to humans and livestock. These molecules also represent a new class of natural toxicants that can be used as model compounds to further characterize the molecular and biochemical pathways leading to apoptosis.

Use of space by domestic chicks housed in complex aviaries.

To improve the understanding of the development of locomotor capacity in layer hens, we measured how female laying hen chicks (n=120) of four different strains (LSL-lite, Hyline Brown, Dekalb White, Lohmann Brown; 3 groups of 10 chicks per line) utilized the ground, the air, elevated horizontal (platforms and perches) and inclined surfaces (ramps and ladders) in an aviary until 9 weeks of age. We used infra-red video recordings to perform all-occurrences sampling of locomotive behavioural and perching events that occurred on the ground—where bedding material, food and water were provided, in the air, and on elevated horizontal and inclined surfaces within weekly 30-min sampling periods. Chicks preferred level ground during the first week of life compared to weeks 5–9 (P<0.0001) and performed 52% of all behavioural events in this section. Elevated surface use began at 2 weeks of age and increased over time (P=0.003), where most behaviour was performed in S2 (45% of all events). Chicks preferred horizontal to inclined surfaces, which were used from weeks 2–5 with maximum use occurring during weeks 2 and 3. Lohmann LSL chicks used the space above the ground most frequently (P=0.05) and performed more aerial ascent/descent behaviour than other lines (P<0.0001). Overall activity levels declined with age (P<0.0001). In summary layer chicks almost exclusively locomoted on the ground but utilized elevated horizontal surfaces (perch, first platform) as early as 2 weeks. These results provide information for improving space use in rearing aviaries by introducing lower perches, platforms and ramps/ladders to accommodate age-dependent locomotor abilities.

Injury and frequency of use of playground equipment in public schools and parks in Brisbane, Australia

Objective: The purpose of this study was to determine the frequency of use of play equipment in public schools and parks in Brisbane, Australia, and to estimate an annual rate of injury per use of equipment, overall and for particular types of equipment. Methods: Injury data on all children injured from playground equipment and seeking medical attention at the emergency department of either of the two children's hospitals in the City of Brisbane were obtained for the years 1996 and 1997. Children were observed at play on five different pieces of play equipment in a random sample of 16 parks and 16 schools in the City of Brisbane. Children injured in the 16 parks and schools were counted, and rates of injury and use were calculated. Results: The ranked order for equipment use in the 16 schools was climbing equipment (3762 uses), horizontal ladders (2309 uses), and slides (856 uses). Each horizontal ladder was used 2.6 times more often than each piece of climbing equipment. Each horizontal ladder was used 7.8 times more than each piece of climbing equipment in the sample of public parks. Slides were used 4.6 times more than climbing equipment in parks and 1.2 times more in public schools. The annual injury rate for the 16 schools and 16 parks under observation was 0.59/100000 and 0.26/100000 uses of equipment, respectively. Conclusions: This study shows that annual number of injuries per standardized number of uses could be used to determine the relative risk of particular pieces of playground equipment. The low overall rate of injuries/100000 uses of equipment in this study suggests that the benefit of further reduction of injury in this community may be marginal and outweigh the economic costs in addition to reducing challenging play opportunities.