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Densities Comparable (density + comparable)
Selected AbstractsOccurrence and density of Halobates micans (Hemiptera: Gerridae) in the eastern South Indian OceanENTOMOLOGICAL SCIENCE, Issue 2 2007Terumi IKAWA Abstract Two species of ocean skaters, Halobates germanus and Halobates micans, live in the tropical and subtropical waters of the Indian Ocean. From December 1992 to December 1993, Halobates was intensively sampled in the easternmost region of the South Indian Ocean (13,18.5°S, 114,121E°), from which there have been a small number of records of Halobates. No H. germanus was caught, but a total of 1190 H. micans were collected, with densities estimated at 13 900,28 100 individuals/km2. This suggests that H. micans lives in the study area at high densities comparable to those in the Atlantic and the Pacific Oceans. We also discuss the possible effects of ocean currents and winds on the geographic distributions of the two Halobates species in the eastern South Indian Ocean. [source] The scale size of chondrule formation regions: Constraints imposed by chondrule cooling ratesMETEORITICS & PLANETARY SCIENCE, Issue 12 2001Lon L. Hood The presence of fine-grained rims around chondrules in most unequilibrated chondrites also indicates that a significant quantity of micron-sized dust was present in chondrule formation regions. Here, we assume that the persistent external energy source needed to explain chondrule cooling rates consists primarily of radiation from surrounding heated chondrules, fine dust, and gas after the formation event. Using an approximate one-dimensional numerical model for the outward diffusion of thermal radiation from such a system, the scale sizes of formation regions required to yield acceptable cooling rates are determined for a range of possible chondrule, dust, and gas parameters. Results show that the inferred scale sizes depend sensitively on the number densities of micron-sized dust and on their adopted optical properties. In the absence of dust, scale sizes > 1000 km are required for plausible maximum chondrule number densities and heated gas parameters. In the presence of dust with mass densities comparable to those of the chondrules and with absorptivities and emissivities of ,0.01 calculated for Mie spheres with a pure mineral composition, scale sizes as small as ,100 km are possible. If dust absorptivities and emissivities approach unity (as may occur for particles with more realistic shapes and compositions), then scale sizes as small as ×10 km are possible. Considering all uncertainties in model parameters, it is concluded that small scale sizes (10,100 km) for chondrule formation regions are allowed by the experimentally inferred cooling rates. [source] Simultaneous ram pressure and tidal stripping; how dwarf spheroidals lost their gasMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006Lucio Mayer ABSTRACT We perform high-resolution N -body+SPH (smoothed particle hydrodynamics) simulations of gas-rich dwarf galaxy satellites orbiting within a Milky Way-sized halo and study for the first time the combined effects of tides and ram pressure. The structure of the galaxy models and the orbital configurations are chosen in accordance with those expected in a Lambda cold dark matter (,CDM) universe. While tidal stirring of disky dwarfs produces objects whose stellar structure and kinematics resembles that of dwarf spheroidals after a few orbits, ram pressure stripping is needed to entirely remove their gas component. Gravitational tides can aid ram pressure stripping by diminishing the overall potential of the dwarf, but tides also induce bar formation which funnels gas inwards making subsequent stripping more difficult. This inflow is particularly effective when the gas can cool radiatively. Assuming a low density of the hot Galactic corona consistent with observational constraints, dwarfs with Vpeak < 30 km s,1 can be completely stripped of their gas content on orbits with pericenters of 50 kpc or less. Instead, dwarfs with more massive dark haloes and Vpeak > 30 km s,1 lose most or all of their gas content only if a heating source keeps the gas extended, partially counteracting the bar-driven inflow. We show that the ionizing radiation from the cosmic ultraviolet (UV) background at z > 2 can provide the required heating. In these objects, most of the gas is removed or becomes ionized at the first pericenter passage, explaining the early truncation of the star formation observed in Draco and Ursa Minor. Galaxies on orbits with larger pericenters and/or falling into the Milky Way halo at lower redshift can retain significant amounts of the centrally concentrated gas. These dwarfs would continue to form stars over a longer period of time, especially close to pericenter passages, as observed in Fornax and other dwarf spheroidal galaxies (dSphs) of the Local Group. The stripped gas breaks up into individual clouds pressure confined by the outer gaseous medium that have masses, sizes and densities comparable to the H i clouds recently discovered around M31. [source] Salt Marsh Restoration in Connecticut: 20 Years of Science and ManagementRESTORATION ECOLOGY, Issue 3 2002R. Scott Warren Abstract In 1980 the State of Connecticut began a tidal marsh restoration program targeting systems degraded by tidal restrictions and impoundments. Such marshes become dominated by common reed grass (Phragmites australis) and cattail (Typha angustifolia and T. latifolia), with little ecological connection to Long Island Sound. The management and scientific hypothesis was that returning tidal action, reconnecting marshes to Long Island Sound, would set these systems on a recovery trajectory. Specific restoration targets (i.e., pre-disturbance conditions or particular reference marshes) were considered unrealistic. However, it was expected that with time restored tides would return ecological functions and attributes characteristic of fully functioning tidal salt marshes. Here we report results of this program at nine separate sites within six marsh systems along 110 km of Long Island Sound shoreline, with restoration times of 5 to 21 years. Biotic parameters assessed include vegetation, macroinvertebrates, and use by fish and birds. Abiotic factors studied were soil salinity, elevation and tidal flooding, and soil water table depth. Sites fell into two categories of vegetation recovery: slow, ca. 0.5%, or fast, more than 5% of total area per year. Although total cover and frequency of salt marsh angiosperms was positively related to soil salinity, and reed grass stand parameters negatively so, fast versus slow recovery rates could not be attributed to salinity. Instead, rates appear to reflect differences in tidal flooding. Rapid recovery was characterized by lower elevations, greater hydroperiods, and higher soil water tables. Recovery of other biotic attributes and functions does not necessarily parallel those for vegetation. At the longest studied system (rapid vegetation recovery) the high marsh snail Melampus bidentatus took two decades to reach densities comparable with a nearby reference marsh, whereas the amphipod Orchestia grillus was well established on a slow-recovery marsh, reed grass dominated after 9 years. Typical fish species assemblages were found in restoration site creeks and ditches within 5 years. Gut contents of fish in ditches and on the high marsh suggest that use of restored marsh as foraging areas may require up to 15 years to reach equivalence with reference sites. Bird species that specialize in salt marshes require appropriate vegetation; on the oldest restoration site, breeding populations comparable with reference marshland had become established after 15 years. Use of restoration sites by birds considered marsh generalists was initially high and was still nearly twice that of reference areas even after 20 years. Herons, egrets, and migratory shorebirds used restoration areas extensively. These results support our prediction that returning tides will set degraded marshes on trajectories that can bring essentially full restoration of ecological functions. This can occur within two decades, although reduced tidal action can delay restoration of some functions. With this success, Connecticut's Department of Environmental Protection established a dedicated Wetland Restoration Unit. As of 1999 tides have been restored at 57 separate sites along the Connecticut coast. [source] Are the Australian poultry industries vulnerable to large outbreaks of highly pathogenic avian influenza?AUSTRALIAN VETERINARY JOURNAL, Issue 5 2009SA Hamilton Objective To describe the structure of the Australian poultry industry and discuss the potential for highly pathogenic avian influenza (HPAI) to spread between Australian poultry farms. Procedure High densities of poultry farms, frequent contacts between farms by service providers, the supply of live poultry markets (LPM) and the presence of free-range duck flocks in affected regions have been identified as risk factors for the spread of HPAI between flocks in outbreaks causing the death or destruction of over 1 million poultry overseas. Data on 1,594 commercial Australian chicken meat, chicken egg, duck and turkey farms were collected by a telephone questionnaire of farm managers to assess the risk of a HPAI outbreak in Australia. Results and Discussion Five regions of Australia had farm densities comparable to overseas regions that experienced widespread HPAI. Common service providers routinely contacted different classes and types of farms over wide geographic areas. However, no responding farms supplied LPM and the majority of duck farms did not produce free-range ducks. Conclusion Outbreaks of HPAI have the potential to cause serious impacts on the Australian poultry industry. The risk posted by LPM and free-range ducks is limited, but the movement of genetic stock and common service providers could spread infection between companies, industries or geographical regions. Biosecurity measures are therefore considered critical to limit the secondary spread of infection should an outbreak occur. [source] Tissue-engineered injectable bone regeneration for osseointegrated dental implantsCLINICAL ORAL IMPLANTS RESEARCH, Issue 5 2004Yoichi Yamada Abstract: The present study investigated a correlation between osseointegration in dental implants and an injectable tissue-engineered bone, using mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP). Initially, the teeth in the mandible region were extracted and the healing period was 1 month. Bone defects on both sides of the mandible were prepared with a trephine bar. The defects were implanted with graft materials as follows: PRP, dog MSCs (dMSCs), and PRP, autogenous particulate cancellous bone and marrow (PCBM), and control (defect only). Two months later, the animals were evaluated by histology, and at the same time dental implants were installed. Two months later, the animals were sacrificed and nondecalcified sections were evaluated histologically and histometrically. According to the histological observations, the dMSCs/PRP group had well-formed mature bone and neovascularization, compared with the control (defect only) and PRP groups, as was the same for the PCBM group. A higher marginal bone level was observed around implants with PRP, PCBM, and dMSCs/PRP compared with the control. Furthermore, the values describing the amount of bone,implant contact (BIC) at the bone/implant interface were significantly different between the PRP, PCBM, dMSCs/PRP, and control groups. Significant differences were also found between the dMSCs/PRP and control groups in bone density. The findings of this experimental study indicate that the use of a mixture of dMSCs/PRP results in good results such as the amount of BIC and bone density comparable with that achieved by PCBM. Résumé L'étude présente a analysé une corrélation entre l'ostéïntégration d'implants dentaires et un os injectable traité en utilisant des cellules souches mésenchymateuses (MSC) et du plasma riche en plaquette (PRP). Initialement, les dents de la région mandibulaire ont été avulsées et la période de guérison a été d'un mois. Les lésions osseuses des deux côtés de la mandibule ont été préparées avec un trépan. Les lésions ont été traitées avec les matériaux de greffe suivants : PRP, MSC canin (dMSC) et PRP, moelle l'os spongieux en petites particules autogènes (PCBM) et contrôle (lésion seulement). Deux mois plus tard, les animaux ont étéévalués et en même temps les implants dentaires ont été placés. Deux mois plus tard, les animaux ont été euthanasiés et des coupes non-décalcifiées ont étéévaluées histologiquement et histométriquement. Suivant les observations histologiques, le groupe dMSC/PRP avait de l'os mûr bien formé et une néovascularisation comparé au contrôle et aux groupes PRP, comme pour le groupe PCBM. Un niveau osseux marginal plus important a été observé autour des implants avec PRP, PCBM et dMSC/PRP comparé au contrôle. De plus les valeurs décrivant la quantité de contact os/implant à l'interface os/implant étaient significativement différentes entre les groupes PRP, PCBM, dMSC/PRP et contrôles. Des différences significatives étaient aussi trouvées entre les groupes dMSC/PRP et contrôle en ce qui concernait la densité osseuse. Ces découvertes indiquent que l'utilisation d'un mélange dMSC/PRP résulte en de bons résultats tels que la quantité de contact os-implant et la densité osseuse comparéà ce qui se passe après l'utilisation du PCBM. Zusammenfassung Gewebemanipulierte injizierbare Knochenregenerate für osseointegrierte dentale Implantate Die vorliegende Studie untersuchte eine Korrelation zwischen der Osseointegration bei dentalen Implantaten und einem injizierbaren gewebemanipulierten Knochenregenerat aus mesenchymalen Stammzellen (MSCs) und plättchenreichem Plasma (PRP). Zuerst wurden die Zähne im Unterkiefer extrahiert. Darauf folgte eine Heilungsperiode von 1 Monat. Auf beiden Seiten der Unterkiefer wurden mit einer Hohlfräse Knochendefekte präpariert. Die Defekte wurden mit folgenden Transplantatmaterialien aufgefüllt: PRP, Hunde MSCs (dMSCs) und PRP, autologer zerkleinerter Knochen und Knochenmark (PCBM) und kein Füllmaterial (Kontrolle). Zwei Monate später wurden die Tiere histologisch untersucht und es wurden dentale Implantate eingesetzt. Nach weiteren zwei Monaten wurden die Tiere geopfert und nicht entkalkte Schnitte wurden histologisch und histometrisch ausgewertet. Gemäss der histologischen Beobachtungen zeigten die dMSCs/PRP Gruppe im Vergleich zur Kontrollgruppe und zur PRP Gruppe gut ausgebildeten reifen Knochen und neue Gefässe. Das Selbe galt für die PCBM Gruppe. Bei den Implantaten mit PRP, PCBM und dMSCs/PRP konnte im Vergleich zur Kontrollgruppe ein höheres marginales Knocheniveau beobachtet werden. Zudem waren die Werte, welche das Ausmass an Knochen-Implantat-Kontakt an der Kochen/Implantat Berührungsfläche beschreiben, zwischen den PRP, PCBM, dMSCs/PRP und der Kontrollgruppe signifikant verschieden. Signifikante Unterschiede wurden auch bezüglich Knochendichte zwischen der dMSCs/PRP und der Kontrollgruppe gefunden. Die Ergebnisse dieser experimentellen Studie zeigen, dass die Anwendung eines Gemisches aus dMSCs/PRP zu guten Resultaten bezüglich Ausmass an Knochen-Implantat-Kontakt und Knochendichte führt. Die erzielten Resultate sind mit den mit PCBM erreichten vergleichbar. Resumen El presente estudio investigó la correlación entre osteointegración en implantes dentales y un tejido-elaborado óseo inyectable, usando células madre mesenquimales (MSCs) y plasma rico en plaquetas (PRP). Inicialmente, se extrajeron los dientes de la mandíbula y el periodo de cicatrización fue de un mes. Se prepararon defectos óseos en ambos lados de la mandíbula con una fresa trépano. Los defectos se implantaron con material de injerto de la siguiente manera: PRP, MSCs de perro (dMSCs) y PRP, partículas de hueso esponjoso y médula autógenos (PCBM), y control (defecto solo). Dos meses mas tarde, los animales se evaluaron por histología, al mismo tiempo se instalaron implantes dentales. Dos meses mas tarde se sacrificaron los animales y se evaluaron secciones no descalcificadas histológica e histometricamente. De acuerdo con las observaciones histológicas, el grupo dMSCs/PRP había formado bien un hueso maduro y una neovascularización, comparado con el control (defecto solo) y grupos PRP, también fue igual para el grupo PCBM. Se observó un nivel óseo marginal mas alto alrededor de los implantes con PRP, PCBM, y dMSCs/PRP comparados con el control. Mas aun, los valores que describen la cantidad de contacto hueso-implante en la interfase hueso/implante fueron significativamente diferentes entre los grupos PRP, PCBM, dMSCs/PRP, y de control en la densidad ósea. Estos hallazgos de este estudio experimental indican que el uso de una mezcla de dMSCs/PRP resulta en buenos resultados tales como la cantidad de contacto hueso-implante y densidad ósea comparable a aquella lograda por PCBM. [source] | ||||||||||||||||