Aluminum - Bronze Compacts and their Possible Use as a Bearing Material

In the modern aspect of powder metallurgy, the first use of a sintering process was in making filaments for incandescent electric lamps.In the short while from the day of Edison to the pres­ent, the science of working with metal powders has advanced by leaps and bounds.

Improvement of γ-ray energy resolution of LaBr3:Ce3+ scintillation detectors by Sr2+ and Ca2+ co-doping

Commercially available LaBr3:5% Ce3+ scintillators show with photomultiplier tube readout about 2.7% energy resolution for the detection of 662 keV γ-rays. Here we will show that by co-doping LaBr3:Ce3+ with Sr2+ or Ca2+ the resolution is improved to 2.0%. Such an improvement is attributed to a strong reduction of the scintillation light losses that are due to radiationless recombination of free electrons and holes during the earliest stages (1–10 ps) inside the high free charge carrier density parts of the ionization track.

Improvement of LaBr3:5%Ce scintillation properties by Li+, Na+, Mg2+, Ca2+, Sr2+, and Ba2+ co-doping

This paper reports on the effects of Li+, Na+, Mg2+, Ca2+, Sr2+, and Ba2+ co-doping on the scintillation properties of LaBr3:5%Ce3+. Pulse-height spectra of various gamma and X-ray sources with energies from 8 keV to 1.33 MeV were measured from which the values of light yield and energy resolution were derived. Sr2+ and Ca2+ co-doped crystals showed excellent energy resolution as compared to standard LaBr3:Ce. The proportionality of the scintillation response to gamma and X-rays of Ca2+, Sr2+, and Ba2+ co-doped samples also considerably improves. The effects of the co-dopants on emission spectra, decay time, and temperature stability of the light yield were studied. Multiple thermoluminescence glow peaks, decrease of the light yield at temperatures below 295 K, and additional long scintillation decay components were observed and related to charge carrier traps appearing in LaBr3:Ce3+ with Ca2+, Sr2+, and Ba2+ co-doping.

Influence of hemostatic agents upon the outcome of periapical surgery: dressings with anesthetic and vasoconstrictor or aluminum chloride

OBJECTIVE To evaluate the effects of different hemostatic agents upon the outcome of periapical surgery. DESIGN A retrospective study was made of patients subjected to periapical surgery between 2006-2009 with the ultrasound technique and using MTA as retrograde filler material. We included patients with a minimum follow-up of 12 months, divided into two groups according to the hemostatic agent used: A) dressings impregnated in anesthetic solution with adrenalin; or B) aluminum chloride paste (Expasyl). Radiological controls were made after 6 and 12 months, and on the last visit. The global evolution scale proposed by von Arx and Kurt (1999) was used to establish the outcome of periapical surgery. RESULTS A total of 96 patients (42 males and 54 females) with a mean age of 40.7 years were included. There were 50 patients in the aluminum chloride group and 46 patients in the anesthetic solution with vasoconstrictor group. No significant differences were observed between the two groups in terms of outcome after 12 months - the success rate being 58.6% and 61.7% in the anesthetic solution with vasoconstrictor and aluminum chloride groups, respectively (p > 0.05). CONCLUSION The outcome after 12 months of follow-up was better in the aluminum chloride group than in the anesthetic solution with vasoconstrictor group, though the difference was not significant.

Aluminum toxicity to tropical montane forest tree seedlings in southern Ecuador: response of biomass and plant morphology to elevated Al concentrations

In acid tropical forest soils (pH < 5.5) increased mobility of aluminum might limit aboveground productivity. Therefore, we evaluated Al phytotoxicity of three native tree species of tropical montane forests in southern Ecuador. An hydroponic dose-response experiment was conducted. Seedlings of Cedrela odorata L., Heliocarpus americanus L., and Tabebuia chrysantha (Jacq.) G. Nicholson were treated with 0, 300, 600, 1200, and 2400 mu M Al and an organic layer leachate. Dose-response curves were generated for root and shoot morphologic properties to determine effective concentrations (EC). Shoot biomass and healthy leaf area decreased by 44 % to 83 % at 2400 mu M Al, root biomass did not respond (C. odorata), declined by 51 % (H. americanus), or was stimulated at low Al concentrations of 300 mu M (T. chrysantha). EC10 (i.e. reduction by 10 %) values of Al for total biomass were 315 mu M (C. odorata), 219 mu M (H. americanus), and 368 mu M (T. chrysantha). Helicarpus americanus, a fast growing pioneer tree species, was most sensitive to Al toxicity. Negative effects were strongest if plants grew in organic layer leachate, indicating limitation of plant growth by nutrient scarcity rather than Al toxicity. Al toxicity occurred at Al concentrations far above those in native organic layer leachate.

Relation between Excitation Power Density and Er3+ Doping Yielding the Highest Absolute Upconversion Quantum Yield

The upconversion quantum yield (UCQY) is one of the most significant parameters for upconverter materials. A high UCQY is essential for a succesful integration of upconversion in many applications, such as harvesting of the solar radiation. However, little is known about which doping level of the rare-earth ions yields the highest UCQY in the different host lattices and what are the underlying causes. Here, we investigate which Er3+ doping yields the highest UCQY in the host lattices β-NaYF4 and Gd2O2S under 4I15/2 → 4I13/2 excitation. We show for both host lattices that the optimum Er3+ doping is not fixed and it actually decreases as the irradiance of the excitation increases. To find the optimum Er3+ doping for a given irradiance, we determined the peak position of the internal UCQY as a function of the average Er−Er distance. For this purpose, we used a fit on experimental data, where the average Er−Er distance was calculated from the Er3+ doping of the upconverter samples and the lattice parameters of the host materials. We observe optimum average Er−Er distances for the host lattices β-NaYF4 and Gd2O2S with differences <14% at the same irradiance levels, whereas the optimum Er3+ doping are around 2× higher for β-NaYF4 than for Gd2O2S. Estimations by extrapolation to higher irradiances indicate that the optimum average Er−Er distance converges to values around 0.88 and 0.83 nm for β-NaYF4 and Gd2O2S, respectively. Our findings point to a fundamental relationship and focusing on the average distance between the active rare-earth ions might be a very efficient way to optimize the doping of rare-earth ions with regard to the highest achievable UCQY.

Aluminum toxicity in a tropical montane forest ecosystem in southern Ecuador

Aluminum phytotoxicity frequently occurs in acid soils (pH < 5.5) and was therefore discussed to affect ecosystem functioning of tropical montane forests. The susceptibility to Al toxicity depends on the sensitivity of the plant species and the Al speciation in soil solution, which can vary highly depending e.g., on pH, ionic strength, and dissolved organic matter. An acidification of the ecosystem and periodic base metal deposition from Saharan dust may control plant available Al concentrations in the soil solutions of tropical montane rainforests in south Ecuador. The overall objective of my study was to assess a potential Al phytotoxicity in the tropical montane forests in south Ecuador. For this purpose, I exposed three native Al non-accumulating tree species (Cedrela odorata L., Heliocarpus americanus L., and Tabebuia chrysantha (Jacq.) G. Nicholson) to increased Al concentrations (0 – 2400 μM Al) in a hydroponic experiment, I established dose-response curves to estimate the sensitivity of the tree species to increased Al concentrations, and I investigated the mechanisms behind the observed effects induced by elevated Al concentrations. Furthermore, the response of Al concentrations and the speciation in soil solution to Ca amendment in the study area were determined. In a final step, I assessed all major Al fluxes, drivers of Al concentrations in ecosystem solutions, and indicators of Al toxicity in the tropical montane rainforest in Ecuador in order to test for indications of Al toxicity. In the hydroponic experiment, a 10 % reduction in aboveground biomass production occurred at 126 to 376 μM Al (EC10 values), probably attributable to decreased Mg concentrations in leaves and reduced potosynthesis. At 300 μM Al, increased root biomass production of T. chrysantha was observed. Phosphorus concentrations in roots of C. odorata and T. chrysantha were significantly highest in the treatment with 300 μM Al and correlated significantly with root biomass, being a likely reason for stimulated root biomass production. The degree of organic complexation of Al in the organic layer leachate, which is central to plant nutrition because of the high root density, and soil solution from the study area was very high (mean > 99 %). The resulting low free Al concentrations are not likely to affect plant growth, although the concentrations of potentially toxic Al3+ increased with soil depth due to higher total Al and lower dissolved organic matter concentrations in soil solutions. The Ca additions caused an increase of Al in the organic layer leachate, probably because Al3+ was exchanged against the added Ca2+ ions while pH remained constant. The free ion molar ratios of Ca2+:Al3+ (mean ratio ca. 400) were far above the threshold (≤ 1) for Al toxicity, because of a much higher degree of organo-complexation of Al than Ca. High Al fluxes in litterfall (8.8 – 14.2 kg ha−1 yr−1) indicate a high Al circulation through the ecosystem. The Al concentrations in the organic layer leachate were driven by the acidification of the ecosystem and increased significantly between 1999 and 2008. However, the Ca:Al molar ratios in organic layer leachate and all aboveground ecosystem solutions were above the threshold for Al toxicity. Except for two Al accumulating and one non-accumulating tree species, the Ca:Al molar ratios in tree leaves from the study area were above the Al toxicity threshold of 12.5. I conclude that toxic effects in the hydroponic experiment occurred at Al concentrations far above those in native organic layer leachate, shoot biomass production was likely inhibited by reduced Mg uptake, impairing photosynthesis, and the stimulation of root growth at low Al concentrations can be possibly attributed to improved P uptake. Dissolved organic matter in soil solutions detoxifies Al in acidic tropical forest soils and a wide distribution of Al accumulating tree species and high Al fluxes in the ecosystem do not necessarily imply a general Al phytotoxicity.