Nondestructive measurements of implant-bone interface shear modulus and effects of implant geometry in pull-out tests

Push-out and pull-out tests are used for destructive evaluation of implant-bone interface strength. Because nondestructive mechanical tests would allow maintenance of an intact interface for subsequent morphological study, we developed such a test to determine the shear modulus of the interface by measuring the shear deformation of a thin layer adjacent to the implant. A polyurethane foam model was used to test the experimental setup on a group of nine cylindrical implants with three different lengths (15-48 mm) and three different diameters (5-9.7 mm). The shear modulus of the interface, as calculated from the pull-out test, was validated against the shear modulus of the foam derived from tensile tests. The two values of shear modulus were well correlated (R2 = 0.8, p < 0.001), thus encouraging further application of the setup for tests of implant-bone interface mechanics. In addition, we also examined the effects of implant length and diameter. The length of the implants had a significant influence on the interface shear modulus (p < 0.05), indicating that comparisons of the variable should only be made of implants with the same length. The length and diameter of the implants were not critical parameters for the ultimate fixation strength

Influence of crop rotation and flutolanil on the diversity of fungi on peanut shells

Les agents pathogènes du sol qui affectent les arachides (Arachis hypogaea) survivent ou hivernent souvent sur les écales d'arachides laissées sur ou dans le sol. Les effets de diverses rotations de cultures sur la flore fongique des écales d'arachides ont été comparés par trois tests en champ menés en 1992 et en 1993. Dans deux des tests, les parcelles d'arachides cultivées de façon continue ont été traitées ou non traitées avec le fongicide flutolanil. Les pratiques de rotation ont varié avec la localisation, et les cultures en rotation avec les arachides étaient le coton (Gossypium hirsutum), le seigle (Secale céréale), l'herbe de Bahia (Paspalum notatum), et le maïs (Zea mays). Au total,31 genres de champignon ont été isolés des écales. Plus des deux tiers des isolats étaient des Deutéromycètes, suivis en fréquence par les Basidiomycètes, les Ascomycètes et les Phycomycètes. Les pratiques de rotation ont affecté l'incidence de plusieurs champignons pathogènes (par exemple, les Fusarium spp. et le Lasiodiplodia theobromae) sur les écales d'arachides, mais les résultats n'ont pas été cohérents entre les tests et les années. L'herbe de Bahia ou le maïs cultivés en rotation avec les arachides ont réduit la fréquence du Rhizoctonia solani AG-4 dans les écales. Le Rhizoctonia solani AG-2-2 et le Macrophomina phaseolina ont été isolés à des niveaux plus élevés dans la rotation herbe de Bahia-arachide. Quand les arachides étaient cultivées en rotation avec le coton avec ou sans une culture de couverture de seigle, les parcelles recouvertes de seigle avaient des taux d'isolement moindres pour les champignons totaux en 1992 que les parcelles sans seigle, mais aucune différence n'a été observée en 1993. De plus, plusieurs espèces de Fusarium ont été isolées plus fréquemment des écales provenant de parcelles en rotation avec le seigle. Le flutolanil a diminué significativement les taux d'isolement de plusieurs champignons, incluant le R. solani AG-4, dans un des essais en 1992. L'ensemble des champignons isolés (en combinant tous les isolats de champignon) sur les parcelles traitées au flutolanil étaient plus élevés en 1993, mais pas en 1992 sur un des sites. Les taux d'isolement pour les différents genres et espèces de champignon différaient sur les deux milieux utilisés (agar à l'extrait de malt et agar au sel de malt). En particulier, l’AIternaria alternata et des espèces de Fusarium ont été isolés plus fréquemment sur l'agar au sel de malt, tandis que L theobromae, R. solani AG-4 et Trichoderma spp. Étaient plus souvent rencontrés sur l'agar à l'extrait de malt.Soilborne pathogens of peanut (Arachis hypogaea) often survive or over winter on peanut shells left on or in the soil. The effects of different crop rotations on the peanut shell mycobiota were compared in three field trials in 1992 and repeated in 1993. In two of the trials, plots grown continuously to peanut were either treated with the fungicide flutolanil or left untreated. Rotation practices varied with location and the crops in rotation with peanut were cotton (Gossypium hirsutum), rye (Secale cereale), bahiagrass (Paspalum notatum), and corn (Zea mays). In total, 31 different gene of fungi were isolated from shells. Over two-thirds of the isolates were Deuteromycotina, followed in frequency by Basidiomycetes, Ascomycetes, and Phycomycetes. The rotation practices affected the incidence of several pathogenic fungi (e.g., Fusarium spp., and Lasiodiplodia theobromae) in the peanut shells, but the results were not consistent across trials or years. Bahiagrass or corn grown in rotation with peanut reduced the frequency of Rhizoctonia solani AG-4 in shells. Rhizoctonia solani AG-2-2 and Macrophomina phaseolina were isolated at a greater level in the bahiagrass-peanut rotation. Where peanut was rotated with cotton with or without a winter cover crop of rye, plots containing rye had lower isolation rates for total fungi in 1992 than those without rye, but there was no différence in 1993. Also, several species of Fusarium were isolated more frequently from shells from plots rotated with rye. Flutolanil significantly lowered isolation rates of several fungi, including R. solani AG-4, in one trial in 1992. Total fungi isolated (all fungal isolates combined) in the flutolanil-treated plots were greater in 1993, but not in 1992 at one site. Isolation rates for the different gene and species of fungi differed on the two media utilized (malt-extract agar and malt-salt agar). In particular, Alternaria alternata and species of Fusarium were isolated more frequently on malt-salt agar, whereas L theobromae, R. solani AG-4 and Trichoderma spp. were more common on malt-extract agar

Parallel plate model for trabecular bone exhibits volume fraction-dependent bias

Unbiased stereological methods were used in conjunction with microcomputed tomographic (micro-CT) scans of human and animal bone to investigate errors created when the parallel plate model was used to calculate morphometric parameters. Bone samples were obtained from the human proximal tibia, canine distal femur, rat tail, and pig spine and scanned in a micro-CT scanner. Trabecular thickness, trabecular spacing, and trabecular number were calculated using the parallel plate model. Direct thickness, and spacing and connectivity density were calculated using unbiased three-dimensional methods. Both thickness and spacing calculated using the plate model were well correlated to the direct three-dimensional measures (r(2) = 0. 77-0.92). The correlation between trabecular number and connectivity density varied greatly (r(2) = 0.41-0.94). Whereas trabecular thickness was consistently underestimated using the plate model, trabecular spacing was underestimated at low volume fractions and overestimated at high volume fractions. Use of the plate model resulted in a volume-dependent bias in measures of thickness and spacing (p < 0.001). This was a result of the fact that samples of low volume fraction were much more "rod-like" than those of the higher volume fraction. Our findings indicate that the plate model provides biased results, especially when populations with different volume fractions are compared. Therefore, we recommend direct thickness measures when three-dimensional data sets are available

Comparisons of Limb Structural Properties in Free-Ranging Chimpanzees From Kibale, Gombe, Mahale and Taï Communities

Structural characteristics of limbs bones provide insight into how an animal dynamically loads its limbs during life. Cause-and-effect relationships between loading and the osteogenic response it elicits are complex. In spite of such complexities, cross-sectional geometric properties can be useful indicators of locomotor repertoires. Typical comparisons use primates that are distinguished by broad habitual locomotor differences, usually with samples garnered from several museum collections. Intraspecific variability is difficult to investigate in such samples because behavior or life histories, which are tools for interpreting intraspecific variability, are limited. Clearly intraspecific variation both in morphology and behavior/life history exists. Here we expand an ongoing effort towards understanding intraspecific variation in limb structural properties by comparing free-ranging chimpanzees that have associated behavioral and life history data. Humeral and femoral data from eleven adult chimpanzees (Pan troglodytes) of Kibale National Park (Uganda) are compared to 29 adult habituated chimpanzees from Gombe (Tanzania), Mahale Mountains (Tanzania), and Taï Forest (Côte d’Ivoire) National Park communities. Overall, limb structural morphology of Kibale chimpanzees most resembles limb structural morphology of Mahale chimpanzees. Shape ratios and percentage cortical areas of Kibale chimpanzees are most similar to non-Gombe chimpanzees, while Kibale structural properties (e.g., maximum rigidity) are most similar to non-Taï structural properties. Even after adding Kibale females, Taï females continue to stand out from females in other communities. This research was supported in part by the L.S.B. Leakey Foundation and the National Science Foundation (DDIG, BCS-0002686).Human Evolutionary Biolog

First direct measurements of hydraulic jumps in an active submarine density current

For almost half a century, it has been suspected that hydraulic jumps, which consist of a sudden decrease in downstream velocity and increase in flow thickness, are an important feature of submarine density currents such as turbidity currents and debris flows. Hydraulic jumps are implicated in major seafloor processes, including changes from channel erosion to fan deposition, flow transformations from debris flow to turbidity current, and large-scale seafloor scouring. We provide the first direct evidence of hydraulic jumps in a submarine density current and show that the observed hydraulic jumps are in phase with seafloor scours. Our measurements reveal strong vertical velocities across the jumps and smaller than predicted decreases in downstream velocity. Thus, we demonstrate that hydraulic jumps need not cause instantaneous and catastrophic deposition from the flow as previously suspected. Furthermore, our unique data set highlights problems in using depth-averaged velocities to calculate densimetric Froude numbers for gravity currents

Measurements of Scintillation Efficiency and Pulse-Shape for Low Energy Recoils in Liquid Xenon

Results of observations of low energy nuclear and electron recoil events in liquid xenon scintillator detectors are given. The relative scintillation efficiency for nuclear recoils is 0.22 +/- 0.01 in the recoil energy range 40 keV - 70 keV. Under the assumption of a single dominant decay component to the scintillation pulse-shape the log-normal mean parameter T0 of the maximum likelihood estimator of the decay time constant for 6 keV < Eee < 30 keV nuclear recoil events is equal to 21.0 ns +/- 0.5 ns. It is observed that for electron recoils T0 rises slowly with energy, having a value ~ 30 ns at Eee ~ 15 keV. Electron and nuclear recoil pulse-shapes are found to be well fitted by single exponential functions although some evidence is found for a double exponential form for the nuclear recoil pulse-shape.Comment: 11 pages, including 5 encapsulated postscript figure

Some investigations into non passive listening

Our knowledge of the function of the auditory nervous system is based upon a wealth of data obtained, for the most part, in anaesthetised animals. More recently, it has been generally acknowledged that factors such as attention profoundly modulate the activity of sensory systems and this can take place at many levels of processing. Imaging studies, in particular, have revealed the greater activation of auditory areas and areas outside of sensory processing areas when attending to a stimulus. We present here a brief review of the consequences of such non-passive listening and go on to describe some of the experiments we are conducting to investigate them. In imaging studies, using fMRI, we can demonstrate the activation of attention networks that are non-specific to the sensory modality as well as greater and different activation of the areas of the supra-temporal plane that includes primary and secondary auditory areas. The profuse descending connections of the auditory system seem likely to be part of the mechanisms subserving attention to sound. These are generally thought to be largely inactivated by anaesthesia. However, we have been able to demonstrate that even in an anaesthetised preparation, removing the descending control from the cortex leads to quite profound changes in the temporal patterns of activation by sounds in thalamus and inferior colliculus. Some of these effects seem to be specific to the ear of stimulation and affect interaural processing. To bridge these observations we are developing an awake behaving preparation involving freely moving animals in which it will be possible to investigate the effects of consciousness (by contrasting awake and anaesthetized), passive and active listening

Limits on spin-dependent WIMP-nucleon cross-sections from the first ZEPLIN-II data

The first underground data run of the ZEPLIN-II experiment has set a limit on the nuclear recoil rate in the two-phase xenon detector for direct dark matter searches. In this paper the results from this run are converted into the limits on spin-dependent WIMP-proton and WIMP-neutron cross-sections. The minimum of the curve for WIMP-neutron cross-section corresponds to 0.07 pb at a WIMP mass of around 65 GeV.Comment: 12 pages, 2 figures, to be published in Physics Letters

Deconstructing superorganisms and societies to address big questions in biology

Social insect societies are long-standing models for understanding social behaviour and evolution. Unlike other advanced biological societies (such as the multicellular body), the component parts of social insect societies can be easily deconstructed and manipulated. Recent methodological and theoretical innovations have exploited this trait to address an expanded range of biological questions. We illustrate the broadening range of biological insight coming from social insect biology with four examples. These new frontiers promote open-minded, interdisciplinary exploration of one of the richest and most complex of biological phenomena: sociality

Sensitivity of the IceCube Detector to Astrophysical Sources of High Energy Muon Neutrinos

We present the results of a Monte-Carlo study of the sensitivity of the planned IceCube detector to predicted fluxes of muon neutrinos at TeV to PeV energies. A complete simulation of the detector and data analysis is used to study the detector's capability to search for muon neutrinos from sources such as active galaxies and gamma-ray bursts. We study the effective area and the angular resolution of the detector as a function of muon energy and angle of incidence. We present detailed calculations of the sensitivity of the detector to both diffuse and pointlike neutrino emissions, including an assessment of the sensitivity to neutrinos detected in coincidence with gamma-ray burst observations. After three years of datataking, IceCube will have been able to detect a point source flux of E^2*dN/dE = 7*10^-9 cm^-2s^-1GeV at a 5-sigma significance, or, in the absence of a signal, place a 90% c.l. limit at a level E^2*dN/dE = 2*10^-9 cm^-2s^-1GeV. A diffuse E-2 flux would be detectable at a minimum strength of E^2*dN/dE = 1*10^-8 cm^-2s^-1sr^-1GeV. A gamma-ray burst model following the formulation of Waxman and Bahcall would result in a 5-sigma effect after the observation of 200 bursts in coincidence with satellite observations of the gamma-rays.Comment: 33 pages, 13 figures, 6 table