Generalized orientations and the Bloch invariant

Abstract. For compact hyperbolic 3-manifolds we lift the Bloch invariant defined by Neumann and Yang to an integral class in K3(C). Applying the Borel and the Bloch regulators, one gets back the volume and the Chern-Simons invariant of the manifold. We also discuss the non-compact case, in which there appears a Z/2-ambiguity

Adsorptionsuntersuchungen an Organokieselsäurepolymeren

BET-Oberflächen und Isothermen von n-Hexan, Benzen, Wasser und Stickstoff wurden an vier Organokieselsäurepolymeren vermessen, die sich im Vernetzungsgrad der Doppelvierring-Kieselsäureeinheiten Si8O20 und in der Struktur der Brücken unterscheiden. Ein Polymer ist mikroporös, die anderen sind makroporös. Alle Polymere verhalten sich hydrophob. Neben der Adsorption tritt Quellung bei der Einwirkung organischer Adsorptive auf. Die Zusammenhänge zwischen der Länge der Brücken und der Porosität werden diskutiert

Synchronization of organ pipes: experimental observations and modeling

We report measurements on the synchronization properties of organ pipes. First, we investigate influence of an external acoustical signal from a loudspeaker on the sound of an organ pipe. Second, the mutual influence of two pipes with different pitch is analyzed. In analogy to the externally driven, or mutually coupled self-sustained oscillators, one observes a frequency locking, which can be explained by synchronization theory. Further, we measure the dependence of the frequency of the signals emitted by two mutually detuned pipes with varying distance between the pipes. The spectrum shows a broad ``hump'' structure, not found for coupled oscillators. This indicates a complex coupling of the two organ pipes leading to nonlinear beat phenomena.Comment: 24 pages, 10 Figures, fully revised, 4 big figures separate in jpeg format. accepted for Journal of the Acoustical Society of Americ

Unconventional carrier-mediated ferromagnetism above room temperature in ion-implanted (Ga, Mn)P:C

Ion implantation of Mn ions into hole-doped GaP has been used to induce ferromagnetic behavior above room temperature for optimized Mn concentrations near 3 at.%. The magnetism is suppressed when the Mn dose is increased or decreased away from the 3 at.% value, or when n-type GaP substrates are used. At low temperatures the saturated moment is on the order of one Bohr magneton, and the spin wave stiffness inferred from the Bloch-law T^3/2 dependence of the magnetization provides an estimate Tc = 385K of the Curie temperature that exceeds the experimental value, Tc = 270K. The presence of ferromagnetic clusters and hysteresis to temperatures of at least 330K is attributed to disorder and proximity to a metal-insulating transition.Comment: 4 pages, 4 figures (RevTex4

Crystallographic structure of ultrathin Fe films on Cu(100)

We report bcc-like crystal structures in 2-4 ML Fe films grown on fcc Cu(100) using scanning tunneling microscopy. The local bcc structure provides a straightforward explanation for their frequently reported outstanding magnetic properties, i.e., ferromagnetic ordering in all layers with a Curie temperature above 300 K. The non-pseudomorphic structure, which becomes pseudomorphic above 4 ML film thickness is unexpected in terms of conventional rules of thin film growth and stresses the importance of finite thickness effects in ferromagnetic ultrathin films.Comment: 4 pages, 3 figures, RevTeX/LaTeX2.0

Variabilidad de rindes de trigo y fertilización nitrogenada

p.115-122En la primera parte del trabajo se presenta un modelo teórico de respuesta del cultivo de trigo a una serie de factores de producción. El objetivo del mismo es permitir la estimación del valor esperado de rinde, E (Y), y la varianza de rinde, V (Y), para cualquier nivel de uso de insumo. En la segunda parte se usa el modelo anterior para analizar el proceso de respuesta del cultivo de trigo al uso de fertilizante nitrogenado. Se utilizan datos experimentales correspondientes a la zona triguera II. Una función polinomial es ajustada a datos de ensayos llevados a cabo en la zona II Norte y en la zona II Sur. Una prueba estadística para detectar la presencia de heterocedasticidad (el Test de Park) permite estimar la influencia del nivel de fertilización nitrogenada sobre la variabilidad de rindes. Se concluye que (1) las dosis óptimas son considerablemente (30-50 por ciento) mayores en la zona II surque en la II Norte, (2) las diferencias (entre zonas) de dosis óptima son mayores cuanto menores son las relaciones de precio fertilizante-trigo y (3) la utilización de fertilizante nitrogenado no parece aumentad el riesgo económico de producción

Predicting soil erosion with RUSLE in mediterranean agricultural systems at catchment scale

Accurate assessment of soil loss is essential for sustainable agricultural production, management and conservation planning, especially in productive rain-fed agro-ecosystems and protected areas. The European Union considers soil as a non-renewable resource and identifies that soil degradation has strong impacts on soil and water resources. In this work the Revised Universal Soil Loss Equation model was applied within a geographic information system in the Estaña catchment (Spanish Pre-Pyrenees) as representative of a Mediterranean agro-ecosystem to elaborate a map of soil erosion at high spatial resolution (5 x 5 m of cell size). The soil erodibility factor (K) is calculated from three different approaches to evaluate the importance of spatial variations in soil texture, field infiltration measurements (Kfs) and amount of coarse fragments. The average value of estimated soil loss for the whole study area is 2.3 Mg ha-1 yr-1 and the highest rates are estimated in crops in steep areas (5.8 Mg ha-1 yr-1) and trails (18.7 Mg ha-1 yr-1). Cultivated soils with high soil erosion rates (higher than 8 Mg ha-1 yr-1) represent 20% of the cultivated area. The average value of soil loss in areas with human disturbances (4.21 Mg ha-1 yr-1) is 4.4 times higher than that estimated for areas with natural vegetation (0.96 Mg ha-1 yr-1). Field validation with 137Cs shows that the estimated value of soil loss in barley fields with the K-Kfs-rocks factor improves the model predictions in comparison with those obtained with the K-texture and K-Kfs factors. The RUSLE model predicts a decrease in soil erosion in fields in accordance with the increase of the age of abandonment. Predicted values of soil erosion and measured soil organic matter and stoniness in old abandoned fields agree with those in areas of natural forest and indicate the recovery of the original conditions of the soil. Statistical analysis highlights that the C factor contributes most of the variability of the values of predicted soil erosion, the K and LS factors contribute in a similar way and the P factor contributes least to the variability of soil erosion. Cultivated soils developed over clay materials in high slope areas are the most susceptible to soil degradation processes in comparison with soils developed over limestones in gentle and medium slope areas. The recovery of terraces in steep fields and conservation of crop residues are proposed as soil conservation practices to reduce the magnitude of soil loss in the study area.This research was financially supported by the following project: “Soil erosion and carbon dynamic in Mediterranean agroecosystems: radioisotopic modelling at different spatial and temporal scales” (MEDEROCAR, CGL2008-00831/BTE) funded by the Spanish Ministry of Science and Innovation.Peer reviewe

Using LES to Study Reacting Flows and Instabilities in Annular Combustion Chambers

Great prominence is put on the design of aeronautical gas turbines due to increasingly stringent regulations and the need to tackle rising fuel prices. This drive towards innovation has resulted sometimes in new concepts being prone to combustion instabilities. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber, which remained out of reach until very recently and the development of massively parallel computers. Since one of the most limiting factors in performing Large Eddy Simulation (LES) of real combustors is estimating the adequate grid, the effects of mesh resolution are investigated by computing full annular LES of a realistic helicopter combustion chamber on three grids, respectively made of 38, 93 and 336 million elements. Results are compared in terms of mean and fluctuating fields. LES captures self-established azimuthal modes. The presence and structure of the modes is discussed. This study therefore highlights the potential of LES for studying combustion instabilities in annular gas turbine combustors

The proeutectoid cementite transformation in steels

A comprehensive, critical, and up to date review is presented for the proeutectoid cementite transformation in steels. It is believed that many of the new findings, features, and concepts presented here for this classic phase transformation in steels serve as a model which may be more broadly applicable to test against many other phase transformations systems as well. There were a number of early investigations of cementite morphology, and this review considers those early results in light of many newer studies that provide critical new insight into cementite morphologies in both two and three dimensions. A number of different orientation relationships (ORs) between proeutectoid cementite and the austenite matrix from which it forms have been reported in the literature, in some cases leading to confusion, and they are critically evaluated here, as are the habit plane, growth direction, and interfacial structure of various morphologies of proeutectoid cementite. Quantitative experimental and theoretical investigations of the growth kinetics of the proeutectoid cementite transformation are considered next, and the nucleation site of proeutectoid cementite in austenite is also discussed in some detail. This review considers all of these issues in a critical way in which differences, commonalities, important features, and redundancies are sorted out, in order to present a unified picture that will add some clarity to this subject. The different features and issues of this transformation that are considered in detail throughout this review are finally brought together in a comprehensive way in the last major section of this paper on ‘Formation mechanism(s) of proeutectoid cementite’, in order to provide a complete, modern view of the formation of proeutectoid cementite from austenite. To the best knowledge of the present authors, before this review a thorough assessment of this classic phase transformation in steels had not been undertaken since 1962, when Professor Hubert I. Aaronson covered this topic in a section of the book entitled ‘The Decomposition of Austenite by Diffusional Processes’. In large part due to a number of ground breaking new findings on the proeutectoid cementite transformation since then (particularly in the last decade), it is very timely for a new review on this topic