Predicting future duration from present age: A critical assessment

Using a temporal version of the Copernican principle, Gott has proposed a statistical predictor of future longevity based on present age (Gott III, J. R., 1993, Nature, 363, 315) and applied the predictor to a variety of examples, including the longevity of the human species. Although Gott's proposal contains a grain of truth, it does not have the universal predictive power that he attributes to it.     

15N-Traceruntersuchungen zum Mechanismus der N2O-Bildung in Böden

Nitrous oxide is a potential environmental hazard responsible for the green house effect and the destruction of the ozone layer in the lower stratosphere. Biological denitrification under anaerobic conditions in soils results in the formation of both N₂O and N₂, whereby highly nitrogen-fertilized agricultural soils contribute to a considerable extent of the N₂O emission. Latest results in the literature indicate that nitrous oxide can also be formed as a byproduct of the microbial nitrification. This is of importance for soils in central Germany because of the non-existence of typical denitrification conditions in a semiaride climate.

This study was conducted to measure the path of N₂O formation in Haplic Phaeozen: using [¹⁵N] ammonium and [¹⁵N] nitrat and a GC-MS aided incubation system. The kinetic isotope method was used to evaluate the experimental data. The results are:

- Under anaerobic conditions (～ 90% of the water holding capacity = WHC) N₂O originates mainly from the nitrate pool by denitrification.

- As expected, the N₂O formation is low under aerobic conditions (～ 80% WHC) but the gas originates directly from the ammonium and not from the nitrate pool, probably as a byproduct of the nitrification process.     

Properties of Graphene/Waterborne Polyurethane Nanocomposites Cast from Colloidal Dispersion Mixtures

Nanocomposites of waterborne polyurethane (WPU) reinforced with functionalized graphene sheets (FGSs) were effectively prepared by casting from a colloidal dispersion of FGS and WPU, and the morphology and physical properties were examined. The finer aqueous FGS dispersions or WPU with smaller particles yielded nanocomposites with enhanced electrical conductivity and thermal resistance due to finely dispersed FGS. The FGS nucleated the crystallization of the polycaprolactone (PCL) segments in WPU and improved its modulus. However, FGS inhibited crystal growth and deteriorated the tensile properties at high deformation, i.e., tensile strength and elongation at break, because the interaction between FGS and WPU hindered the chain rearrangement of WPU in the nanocomposite.     

A Novel Pyrene Fluorescent Sensor Based on the π–π Interaction Between Pyrene and Graphene of Graphene–Cadmium Telluride Quantum Dot Nanocomposites

In this article, water-soluble graphene–cadmium telluride quantum dot nanocomposites were fabricated through the synthesis of cadmium telluride quantum dots in the presence of graphene aqueous dispersion. It was found that pyrene could remarkably quench fluorescence of graphene–cadmium telluride quantum dot nanocomposites. On this basis, a novel method for the determination of pyrene was developed. Factors affecting the pyrene detection were investigated, and the optimum conditions were determined. Under the optimum conditions, a linear relationship could be established between the quenching of fluorescence intensity of graphene–cadmium telluride quantum dot nanocomposites and the pyrene concentration in the range of 6.00 × 10^?8–2.00 × 10^?6 mol L^?1 with a correlation coefficient of 0.9959. The detection limit was 4.02 × 10^?8 mol L^?1. Furthermore, the nanocomposites were applied to practical determination of pyrene in different water samples with satisfactory results.     

Analytical Study of Raw Materials of Zinc Oxide Used for Enamels on Industrial Ceramics: Quantitative Analysis of Zinc,Lead, and Sulfur in These Samples by X‐ray Fluorescence and Flame Atomic Absorption Spectrometry

An analytical study is carried out to optimize X‐ray fluorescence (XRF) and flame atomic absorption spectrometry (FAAS) quantitative analysis of Zn, Pb, and S in ZnO samples commonly used to obtain industrial ceramic enamels. Pb and S in the raw materials often contaminate ZnO and are very detrimental in industrial applications. Thus, very accurate analytical determination of these elements in ceramic samples is extremely important. First of all, a mineralogical study by X‐ray diffraction (XRD) on the different components in these raw materials and the materials produced during the firing process is performed in order to establish the mineral forms in a reference sample for analysis by XRF spectrometry. The working conditions are optimized for XRF multielemental analysis, using the sample in the form of pellets, due to high loss on ignition (LOI) values. The preparation of suitable standards and working conditions for FAAS analysis have also been optimized. The content of these elements was determined by FAAS for the reference sample and several samples for industrial use, and the results were compared with those obtained by XRF. Comparison of the results obtained from XRF and FAAS analysis of Pb and Zn show more accurate values for FAAS. For ZnO, an accuracy of 0.11% with ±0.1% precision by FAAS and 0.46% accuracy with ±0.2% precision by XRF are found. For PbO, 1.06% accuracy and ±0.06% precision using FAAS and 5.6% accuracy and ±0.35% precision by XRF were found. For SO₃ determined only by XRF, accuracy was 4.76% with ±0.25% precision. These values are highly satisfactory given that these two elements are only found in small proportions.     

Using the natural 15N abundance to assess the main nitrogen inputs into the sand dune area of the North-Western Negev desert (ISRAEL)

The variation of the natural ¹⁵N abundance is often used to evaluate the origin of nitrogen or the pathways of N input into ecosystems. We tried to use this approach to assess the main input pathways of nitrogen into the sand dune area of the north-western Negev Desert (Israel). The following two pathways are the main sources for nitrogen input into the system:

1. Biological fixation of atmospheric nitrogen by cyanobacteria present in biological crusts and by N₂-fixing vascular plants (e.g. the shrub Retama raetam);

2. Atmospheric input of nitrogen by wet deposition with rainfall, dry deposition of dust containing N compounds, and gaseous deposition.

Samples were taken from selected environmental compartments such as biological crusts, sand underneath these crusts (down to a depth of 90?cm), N₂-fixing and non-N₂-fixing plants, atmospheric bulk deposition as well as soil from arable land north of the sandy area in three field campaigns in March 1998, 1999 and 2000. The δ¹⁵N values measured were in the following ranges: grass ?2.5‰ to +1.5‰; R. reatam: +0.5‰ to +4.5‰; non-N₂-fixing shrubs +1‰ to +7‰; sand beneath the biological crusts +4‰ to +20‰ (soil depth 2–90?cm); and arable land to the north up to 10‰. Thus, the natural ¹⁵N abundance of the different N pools varies significantly. Accordingly, it should be feasible to assess different input pathways from the various ¹⁵N abundances of nitrogen. For example, the biological N fixation rates of the Fabaceae shrub R. reatam from the ¹⁵N abundances measured were calculated to be 46–86% of biomass N derived from the atmosphere. The biological crusts themselves generally show slight negative ¹⁵N values (?3‰ to ?0.5‰), which can be explained by biological N fixation. However, areas with a high share of lichens, which are unable to fix atmospheric nitrogen, show very negative values down to ?10‰. The atmospheric N bulk deposition, which amounts to 1.9–3.8?kg?N/ha?yr, has a ¹⁵N abundance between 4.4‰ and 11.6‰ and is likely to be caused by dust from the arable land to the north. Thus, it cannot be responsible for the very negative values of lichens measured either. There must be an additional N input from the atmosphere with negative δ¹⁵N values, e.g. gaseous N forms (NO _x , NH₃). To explain these conflicting findings, detailed information is still needed on the wet, particulate and gaseous atmospheric deposition of nitrogen.     

Graphene under perpendicular incidence of electromagnetic waves: Gaps and band structure

We study the energy spectrum for the problem of graphene's carriers under perpendicular incidence of electromagnetic waves. To obtain the spectrum, we solve the Dirac equation under such a field. Then a generalized Mathieu equation is obtained. The limiting cases of strong and weak fields, as well as long and short wavelengths, are analyzed. The energy spectrum is obtained numerically by using the Whittaker method, and a perturbation method is used to obtain the analytical separatrix curve between allowed and forbidden states. The energy spectrum presents bands, and a gap at the Fermi energy. The gap is linear on the electromagnetic wave intensity.     

Design of self-cleaning TiO2 coating on clay roofing tiles

The phenomenon of heterogeneous photocatalysis takes place in the degradation process of many organic contaminants on solid surfaces. Photocatalysis is based on the excitation of the semiconductor by irradiation with supraband gap photons and the migration of electron-hole pairs to the surface of the photocatalysts, leading to the reaction of the holes with adsorbed H₂O and OH^? to form hydroxyl radicals. Due to the stability and photosensitivity of TiO₂ semiconductors, this system is well studied and is of great interest from an ecological and industrial point of view for use in the field of building materials. Clay roofing tiles, due to their long-term exploitation, are subject to physical, chemical and biological degradation that leads to deterioration. Ceramic systems have a high percentage of total porosity and considering their non-tolerance of organic coating, the use of surface active materials (SAM) that induce porosity in TiO₂ coatings is of vital significance. Photocatalytic coatings applied on clay roofing tiles under industrial conditions were designed by varying the quantity of TiO₂ (mass/cm²) on the tile surface (thin and thick TiO₂ layer). The positive changes in specific surface area and mesopore structure of the designed coatings were made by the addition of PEG 600 as a surface active material. It was shown that a thin photocatalytic layer (0.399 mg suspension/cm² tile surface), applied onto ceramic tiles under industrial conditions, had better photocatalytic activity in methylene blue decomposition, hydrophilicity and antimicrobial activity than a thick photocatalytic coating (0.885 mg suspension/cm²).