Effectiveness of Dentin Bonding Agents

The interface between a composite resin restoration and dentin is still a problem with regard to secondary caries and esthetics. With conventional restorative techniques the absence of bonding between the restorative material and the dentin produces marginal gaps. These gaps are populated with microorganisms or trap pigments. Therefore, adhesive techniques are required for functional and esthetic restorations. In extracted teeth stored in 0.1% thymol solution, 8 cylindrical cavities (diameter: 3 mm; depth: 2 mm) and 8 class V cavities (1/2 of the margin in dentin) were prepared in each group and filled with composite resin. Before actual placement the following dentin adhesives were used: Scotchbond 2 (3M), Gluma (Bayer), Scotchbond LC (3M), Dentin Adhesit (Ivoclar), Dentin Adhesive (Kulzer) and Durafill-Bond (Kulzer) as a control. Before and after thermocycling (TC) (2000 cycles, 5° C to 55° C) replicas were taken and a quantitative margin analysis in the SEM was performed at 200 x magnification. To analyze the data, a rating scale (four criteria) was used to characterize the marginal configuration. Statistical analysis of the results showed that the materials Gluma, Scotchbond LC and Scotchbond 2 yielded significantly (p \u3c 0.05) better margins than the other materials in both cylindrical and class V cavities. Before TC values \u3e 90% were found with Gluma, Scotchbond LC and Scotchbond 2 in Class V cavities. However, after TC, these values decreased significantly to 66% for Gluma, 42% for Scotchbond LC and 81% for Scotchbond 2. Scotchbond 2 showed approximately 80% excellent margins in both cavity forms after TC. A subsequent clinical study should be done to confirm these favourable results in vivo

Comment on "On the Origin of the Highest Energy Cosmic Rays"

We show that the photodisintegration of heavy cosmic ray nuclei with energies above 10^20 eV is dominated by interactions with photons from the cosmic microwave background radiation, rather than from infrared ones. This implies that the observed air shower events with energies 2-3 10^20 eV cannot originate from Fe nuclei coming from distances beyond 10 MpcComment: 1 page, 2 figure

Is the halo responsible for the microlensing events?

We discuss whether the astrophysical objects responsible for the recently reported microlensing events of sources in the Large Magellanic Cloud can be identified as the brown dwarf components of the spheroid of our galaxy, rather than the constituents of a dark baryonic halo.Comment: 10 pages, Postscript file (3 figures included). Talk given by E.R. in the 6^th Workshop on Neutrino Telescopes, Venice, February 199

Gravitational lensing as folds in the sky

We revisit the gravitational lensing phenomenon using a new visualization technique. It consists in projecting the observers sky into the source plane, what gives rise to a folded and stretched surface. This provides a clear graphical tool to visualize some interesting well-known effects, such as the development of multiple images of a source, the structure of the caustic curves, the parity of the images and their magnification as a function of the source position.Comment: 11 pages, 8 figure

Peatlands and the carbon cycle: from local processes to global implications - a synthesis

Peatlands cover only 3% of the Earth's land surface but boreal and subarctic peatlands store about 15-30% of the world's soil carbon ( C) as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling. This paper synthesizes the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands in the context of climate change. The main drivers controlling most are related to some aspects of hydrology. Despite high spatial and annual variability in Net Ecosystem Exchange ( NEE), the differences in cumulative annual NEE are more a function of broad scale geographic location and physical setting than internal factors, suggesting the existence of strong feedbacks. In contrast, trace gas emissions seem mainly controlled by local factors. Key uncertainties remain concerning the existence of perturbation thresholds, the relative strengths of the CO2 and CH4 feedback, the links among peatland surface climate, hydrology, ecosystem structure and function, and trace gas biogeochemistry as well as the similarity of process rates across peatland types and climatic zones. Progress on these research areas can only be realized by stronger co-operation between disciplines that address different spatial and temporal scales

Quantitative Margin Analysis in the Scanning Electron Microscope.

Interface between restorative materials and tooth hard substances must be morphologically as perfect as possible to avoid plaque accumulation and subsequent secondary caries or pulpal diseases. Therefore the marginal behavior of restorations is an important parameter to predict their longevity. Morphologically, the quality of margins is characterized by different well defined criteria. Using a replica technique it is possible to assess the complete marginal circumference of restorations in the SEM. Margins of restorations show a large variety of their morphology. This publication describes a method to quantify the quality of dental restorations. The restoration margins are traced on the SEM screen with a digitizer and an interface to measure the margin\u27s length. Simultaneously the margin quality is assessed and assigned to the corresponding lengths. The % distribution of the quality criteria for each restoration is then calculated. Using a comparative light microscope, the replicas are aligned and mounted identically in the SEM for longitudinal studies. The results presented are limited to tests for the accuracy of the method. Using 5 criteria to characterize the margin quality, it was found that the difference between two measurements by the same operator, 4 weeks apart was 3% ± 2.6%. The largest difference for one group was 9%. In another accuracy test where 4 criteria for margin characterization were used, the difference between two measurements was 1.9% ± 0.9%. The largest difference between two groups found was 3.4%. This method can be used for longitudinal studies in vivo, but also for in vitro screening tests with new materials

Making space for art: a spatial perspective of disruptive and defensive institutional work in Venezuela’s art world

The physical and material aspects of space, such as geographical distance or boundaries, have social and symbolic consequences that impact how people influence and are influenced by institutions. Social actors can however contest how space is conceived, perceived and lived, thus making space a crucial lever in the disruption and defense of institutions. However, we lack understanding of the spatial aspects of such institutional struggles. In exploring how space is leveraged in institutional work, our study foregrounds the socio-political nature of space, building on and expanding the theorization of Lefebvre. We draw on an in depth longitudinal analysis of the material, social and symbolic aspects of the spatial dimensions of disruptive and defensive institutional work over the past twenty years in Venezuela’s art world. Following the Bolivarian Revolution in the late 1990s, the incoming government transformed the organization of the national cultural landscape, resulting in a prolonged period of institutional disruption and defense. We demonstrate that actors use the material, social, and symbolic dimensions of space to challenge and maintain their key values and practices, and that those three dimensions are intertwined

EPIQR-TOBUS: a new generation of refurbishment decision aid methods

In a large majority of European countries, the amount of maintenance and refurbishment works represents nearly 50% of the total amount spent in the building sector. New requirements are being added to the necessity of maintaining or re-establishing the building stock's usage value. They are linked to the determination to reduce energy consumption, pollutant emissions, work site wastes, to improve the Indoor Environment Quality (IEQ) and all the modern conveniences inside buildings. Two European projects, EPIQR (réf. nr.: JOR3-CT96-0044) and TOBUS (réf. nr.: JOR3-CT98-Û235), developed in the IIIrd and IVth framework programs put the foundations of a new generation of refurbishment decision aid tools. A structured diagnosis scheme covering the state of deterioration of the building elements, energy performance, indoor environment quality, functional obsolescence offer a new concept which helps architects and engineers to approach the building refurbishment with a global view of the whole process, to take informed decisions, to construct coherent refurbishment scenarii and calculate a reasonable investment budget in the very first stage of the refurbishment project. EPIQR project addresses residential buildings and it has been finished in 1998, TOBUS addresses office buildings and it is still in course. The support of these methods is a multimedia computer program. Several modules help the users to treat the data collected during a diagnosis survey, to set up refurbishment scenarii and calculate their cost or energy performance, and finally to visualise the results in a comprehensive way and to prepare quality reports. This paper presents the structure and the main features of the method and softwar

Validation and application of an urban turbulence parameterisation scheme for mesoscale atmospheric models

Growing population, extensive use (and abuse) of the natural resources, increasing pollutants emissions in the atmosphere: these are a few obstacles (and not the least) one has to face with nowadays to ensure the sustainability of our planet in general, and of the air quality in particular. In the case of air pollution, the processes that govern the transport and the chemical transformation of pollutants are highly complex and non-linear. The use of numerical models for simulating meteorological fields, which in turn will determine the transport of pollutants in the atmosphere, is thus a very appropriate tool to describe and understand the air pollution problematic. This work focuses on the meteorological simulation, using a mesoscale model. The stress is particularly put on the parameterisation of urban induced effects on the meteorological fields above a city. A detailed urban parameterisation scheme has been implemented in a mesoscale model in a previous work. This new scheme takes into account the presence of a city in a more accurate way as the traditional method usually used in mesoscale models. In the first part of this work, the urban module was validated for a one-dimensional off-line simulation within and above a street canyon in the city of Basel/Switzerland. The simulation results were compared with measurements taken within and above the same street canyon during an intensive observation period in the frame of the BUBBLE project (Basel UrBan Boundary Layer Experiment). The comparison with the measurements and with a simulation using the traditional urban parameterisation showed that the detailed urban scheme improved the quality of the simulation of turbulent fluxes and meteorological parameters (wind, temperature) in the urban canopy. Further on, the mesoscale was applied for a three-dimensional simulation over the city of Basel and its surroundings. The results showed that the model is able to reproduce the wind pattern that prevailed during the simulated episode, and that the accuracy of the temperature simulation in the city is improved with the urban module. In the third part of this work, an air quality study was performed over the Mexico City basin. The mesoscale model simulated the meteorological conditions for the chosen episode (1 and 2 March 1997). The results were then passed to TAPOM, a Eulerian photochemical model that calculates the space and time distribution of air pollutants. The simulated concentrations over the basin showed good agreement with the observed values. The validated model could then be used to test some emissions reduction scenarios for Mexico City. The use of the detailed urban parameterisation scheme for meteorological fields and air pollutants concentration simulation improved the quality of the results in almost all the applied situations. Consequently, the full modelling tool presented and validated in this work can be used for air quality modelling studies over cities and their surroundings

Unzipping DNA with Optical Tweezers: High Sequence Sensitivity and Force Flips

AbstractForce measurements are performed on single DNA molecules with an optical trapping interferometer that combines subpiconewton force resolution and millisecond time resolution. A molecular construction is prepared for mechanically unzipping several thousand-basepair DNA sequences in an in vitro configuration. The force signals corresponding to opening and closing the double helix at low velocity are studied experimentally and are compared to calculations assuming thermal equilibrium. We address the effect of the stiffness on the basepair sensitivity and consider fluctuations in the force signal. With respect to earlier work performed with soft microneedles, we obtain a very significant increase in basepair sensitivity: presently, sequence features appearing at a scale of 10 basepairs are observed. When measured with the optical trap the unzipping force exhibits characteristic flips between different values at specific positions that are determined by the base sequence. This behavior is attributed to bistabilities in the position of the opening fork; the force flips directly reflect transitions between different states involved in the time-averaging of the molecular system