Global geometry of T2 symmetric spacetimes with weak regularity

We define the class of weakly regular spacetimes with T2 symmetry, and investigate their global geometry structure. We formulate the initial value problem for the Einstein vacuum equations with weak regularity, and establish the existence of a global foliation by the level sets of the area R of the orbits of symmetry, so that each leaf can be regarded as an initial hypersurface. Except for the flat Kasner spacetimes which are known explicitly, R takes all positive values. Our weak regularity assumptions only require that the gradient of R is continuous while the metric coefficients belong to the Sobolev space H1 (or have even less regularity).Comment: 5 page

_Limusaurus_ and bird digit identity

_Limusaurus_ is a remarkable herbivorous ceratosaur unique among theropods in having digits II, III and IV, with only a small metacarpal vestige of digit I. This raises interesting questions regarding the controversial identity of avian wing digits. The early tetanuran ancestors of birds had tridactyl hands with digital morphologies corresponding to digits I, II & III of other dinosaurs. In bird embryos, however, the pattern of cartilage formation indicates that their digits develop from positions that become digits II, III, & IV in other amniotes. _Limusaurus_ has been argued to provide evidence that the digits of tetanurans, currently considered to be I, II and III, may actually be digits II, III, & IV, thus explaining the embryological position of bird wing digits. However, morphology and gene expression of the anterior bird wing digit specifically resemble digit I, not II, of other amniotes. We argue that digit I loss in _Limusaurus_ is derived and thus irrelevant to understanding the development of the bird wing

Two-slit diffraction with highly charged particles: Niels Bohr's consistency argument that the electromagnetic field must be quantized

We analyze Niels Bohr's proposed two-slit interference experiment with highly charged particles that argues that the consistency of elementary quantum mechanics requires that the electromagnetic field must be quantized. In the experiment a particle's path through the slits is determined by measuring the Coulomb field that it produces at large distances; under these conditions the interference pattern must be suppressed. The key is that as the particle's trajectory is bent in diffraction by the slits it must radiate and the radiation must carry away phase information. Thus the radiation field must be a quantized dynamical degree of freedom. On the other hand, if one similarly tries to determine the path of a massive particle through an inferometer by measuring the Newtonian gravitational potential the particle produces, the interference pattern would have to be finer than the Planck length and thus undiscernable. Unlike for the electromagnetic field, Bohr's argument does not imply that the gravitational field must be quantized.Comment: 8 pages, 4 figures. To appear in Proc. Natl. Acad. Sc

Measurement of thermal conductance of silicon nanowires at low temperature

We have performed thermal conductance measurements on individual single crystalline silicon suspended nanowires. The nanowires (130 nm thick and 200 nm wide) are fabricated by e-beam lithography and suspended between two separated pads on Silicon On Insulator (SOI) substrate. We measure the thermal conductance of the phonon wave guide by the 3 method. The cross-section of the nanowire approaches the dominant phonon wavelength in silicon which is of the order of 100 nm at 1K. Above 1.3K the conductance behaves as T3, but a deviation is measured at the lowest temperature which can be attributed to the reduced geometry

Effects of digestate on the environment and on plant production - results of a research project

Composts and digestates can influence soil fertility and plant health. These influences can be positive or negative, depending of the quality of the composts. A currently important question is to know, if digestates differ from composts in these aspects. A Swiss project is concerned with the estimation of the potential of Swiss composts and digestates to influence soil fertility and plant health positively. For this, one hundred composts and digestates representative of the different composting systems and qualities available on the Swiss market were analyzed. The organic matter and nutrient content of the composts varied greatly between the composts and the digestates; the materials of origin were the major factor influencing these values. The respiration rate and enzyme activities also varied greatly; they are particularly important in digestates. The organic matter of digestates is less stable than that of composts. The N-mineralization potential from the majority of the digestates added to soil is high, in comparison to young composts. When digestates are not correctly treated or stored, however, they can immobilize nitrogen in the soil. This problem is hardly correlated with the management of the digestate in the first stage after leaving the fermenter. Especially products which have become too dry during this period lost their ammonia-nitrogen, and hence immobilized nitrogen in the soil. The risk of phytotoxicity is higher in digestates than in composts. This limits the possibility for use of digestate. With a post-treatment of digestate, it is possible to produce high quality compost with a high compatibility with plant growth and with a more stabilized organic matter. In field experiments, digestates increased the pH-value and the biological activity of soil to the same extent than composts. These effects were observable also one season after compost application. No immobilization of nitrogen was observed

Effects of compost and digestate on environment and plant production – results of two research projects

A yearly amount of 9.3x106t compost and digestate derived from separately collected organic waste is produced in the 25 European Union member states. The improvement of soil properties is a major benefit of compost application. However, little is known about the occurrence of organic pollutants in compost. In order to estimate the potential of Swiss composts and digestates to influence soil fertility and plant health, one hundred products representative for the different composting systems and qualities available on the Swiss market were analyzed in two research projects. In the first study, polycyclic aromatic hydrocarbons (PAHs), ortho substituted and dioxin-like polychlorinated biphenyls (PCBs, DL PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), tetrabromobisphenol A (TBBPA), perfluorinated alkyl substances (PFAS), pesticides, chlorinated paraffins (CPs), phthalates and nonylphenol (NP) were analyzed. All compound classes were detected except for NP. PFAS, HBCD, TBBPA, some compounds out of PBDEs and pesticides were found in compost and digestate for the first time. Concentrations of most compounds were in the low ppb range. Contents of PAHs were between 600 and 12473 μg/kg dry weight (dw) and contents of HBCD and CPs between 17 and 384 μg/kg dw. Tests with springtails (Folsomia candida) have been shown to be a versatile tool for ecotoxicological assessment. Within these tests, inhibiting and stimulating effects due to compost application were observed. Except for high PAHs contents, no major problem with regard to contamination of compost and digestate was identified. In the second study, the physical, chemical and biological properties of the composts and digestats, and their influence on soil fertility and plant growth, were characterized. The organic substance and the nutrient content of the composts varied largely between the composts with the feedstock materials as major influencing factors. The respiration rate and enzyme activities exhibited large variations as well, particularly in the youngest composts. These differences decreased when the composts became more mature. Maturity, the degradation stage of the organic matter, depended not only on the age of the compost, but also on the management of the process. The N-mineralization potential of compost added to soil showed that a high proportion of young composts immobilized the nitrogen in the soil. Two compost parameters allowed to predict the risk of nitrogen immobilization in soil: the NO3- and the humic acids contents. The phytotoxicity of the composts varied largely even in mature composts, showing that the storage of the compost plays a decisive role. While the majority of composts protected cucumber plants against Pythium ultimum, only a few composts suppressed Rhizoctonia solani in basil. With respect to disease suppression, the management of the maturation process seems to play a major role. In field experiments, some biologically immature composts immobilized nitrogen in soil and reduced growth of maize. With additional fertilization, however, it was possible to compensate this effect. Digestates and composts increased the pH-value and the biological activity of soil. These effects were observable also one maize season after compost application. In conclusion, the management of the composting process seems to influence the biological quality of the composts and digestats to a higher extent than the feedstock materials or the composting system. More attention should be paid to this biological quality, in order to produce composts with more beneficial effects on crops