Large bandwidth, highly efficient optical gratings through high index materials

We analyze the diffraction characteristics of dielectric gratings that feature a high index grating layer, and devise, through rigorous numerical calculations, large bandwidth, highly efficient, high dispersion dielectric gratings in reflection, transmission, and immersed transmission geometry. A dielectric TIR grating is suggested, whose -1dB spectral bandwidth is doubled as compared to its all-glass equivalent. The short wavelength diffraction efficiency is additionally improved by allowing for slanted lamella. The grating surpasses a blazed gold grating over the full octave. An immersed transmission grating is devised, whose -1dB bandwidth is tripled as compared to its all-glass equivalent, and that surpasses an equivalent classical transmission grating over nearly the full octave. A transmission grating in the classical scattering geometry is suggested, that features a buried high index layer. This grating provides effectively 100% diffraction efficiency at its design wavelegth, and surpasses an equivalent fused silica grating over the full octave.Comment: 15 pages, 7 figure

Transpiration of a spruce and beech stand under soil drought conditions in the Tharandt Forest

To evaluate the water balance of a site, requirements of the forest stand under changing environmental conditions have to be considered. Among the different components of the site water balance, stand transpiration represents the physiological response of the trees and can be taken as a link to carbon relations. A regulating and hence critical parameter mediating between water and carbon balance is canopy conductance. Water-use efficiency is an indicator of this relationship. At a spruce and beech site, xylem sap flow measurements were applied to estimate canopy transpiration (Ec ) and canopy conductance (gc ). During the growing season of 2006, Ec at the spruce site (161 mm season-1) was significantly lower than at the beech site (182 mm season-1) while the total-year balances were similar. This was related to a period of soil drought during summer which was more pronounced at the spruce site than at the beech site. In contrast to beech, canopy conductance of spruce was reduced to minimal values independent of atmospheric conditions, and water-use efficiency was increased. From the findings it can be concluded that site conditions and tree species lead to measurable differences in the water balance of sites which should accordingly be expressed in water-balance models. The presented measured data are fundamental to value transpiration-related indicators of water-balance models.Für die Bewertung des Standortwasserhaushaltes sind die Anforderungen der Bestockung unter sich ändernden Umweltbedingungen mit zu berücksichtigen. Von den unterschiedlichen Wasserhaushaltskomponenten gibt die Bestandestranspiration die physiologische Reaktion der Bäume wider und steht somit auch dem Kohlenstoffhaushalt am nächsten. Eine regulierende und somit kritische Größe stellt die Bestandesleitfähigkeit dar, die zwischen Wasser- und Kohlenstoffhaushalt vermittelt. Als Indikator für diese Regulation wird das Verhältnis von Kohlenstoffaufnahme zu Wasserabgabe, die sog. Wassernutzungseffizienz, herangezogen. An einem Fichten- und Buchenstandort wurde mittels Xylemsaftflussmessungen die Bestandestranspiration (Ec) und -leitfähigkeit (gc) bestimmt. Von Mai bis Oktober 2006 lag Ec am Fichtenstandort (161 mm Saison-1) deutlich unter Ec von Buche mit 182 mm Saison-1 während die Gesamtjahresbilanz ähnlich war. Dies stand in Beziehung mit einer Phase sommerlicher Bodentrockenheit, die sich am Fichtenstandort deutlicher als am Buchenstandort auswirkte. Im Gegensatz zu Buche war während der Bodentrockenheit die Bestandesleitfähigkeit von Fichte, unabhängig von atmosphärischen Bedingungen, auf minimale Werte reduziert und die Wassernutzungseffizienz erhöht. Aus den Befunden kann gefolgert werden, dass Standortverhältnisse und Baumarten zu messbaren Unterschieden im Standortswasserhaushalt führen, die auch in Wasserhaushaltsmodellen darstellbar sein sollten. Die vorliegenden Messdaten sind grundlegend, um transpirationsbezogene Indikatoren von Wasserhaushaltsmodellen zu bewerten

A spectral Galerkin exponential Euler time-stepping scheme for parabolic SPDEs on two-dimensional domains with a C2-boundary

We consider the numerical approximation of second-order semi-linear parabolic stochastic partial differential equations interpreted in the mild sense which we solve on general two-dimensional domains with a $\mathcal{C}^2$ boundary with homogeneous Dirichlet boundary conditions. The equations are driven by Gaussian additive noise, and several Lipschitz-like conditions are imposed on the nonlinear function. We discretize in space with a spectral Galerkin method and in time using an explicit Euler-like scheme. For irregular shapes, the necessary Dirichlet eigenvalues and eigenfunctions are obtained from a boundary integral equation method. This yields a nonlinear eigenvalue problem, which is discretized using a boundary element collocation method and is solved with the Beyn contour integral algorithm. We present an error analysis as well as numerical results on an exemplary asymmetric shape, and point out limitations of the approach.Comment: 23 pages, 7 figure

The Use of Tobacco Pipes in Identifying and Separating Contexts on Smuttynose Island, Maine

Five years of excavation on Smuttynose Island, Isles of Shoals, Maine has recovered a large number of artifacts. These artifacts are related to nearly four hundred years of European use and occupation of the island, and include over 7,000 fragments of white clay tobacco pipes. Unfortunately, the specific soil conditions of the site often made field identification of different contexts difficult during the excavation process. This paper explores the use of clay pipes in the separation and identification of different stratigraphic contexts. Questions addressed include the utility of various stem-bore dating methods, and the use of identifying the origin of pipes and how this can be used to link specific stratigraphic contexts to known historical occupations of the island. This particularly includes the early migratory period of the Gulf of Maine cod fishery. Finally, this paper provides a chronological framework for further study and interpretation of the archaeology of Smuttynose Island

Unsteady thermal convection in the North-East-German basin

We describe a Voronoi box based finite volume method for the numerical simulation of thermal convection in sedimental basins. The method shows a temperature maximum principle and consistent velocity approximation. We present results of simulation runs in vertical slices of the North-East German basin. These indicate that the system is far from a stationary state, it shows quasi-periodic, and possibly chaotic behaviour. The chaos hypothesis is formulated based on the analysis of the Nusselt number time series obtaind from simulation runs

The Seventeenth Century Brewhouse and Bakery at Ferryland, Newfoundland

In 2001 archaeologists working at the 17th-century English settlement at Ferryland, Newfoundland, uncovered evidence of an early structure beneath a mid-to-late century gentry dwelling. A preliminary analysis of the architectural features and material culture from related deposits tentatively identified the structure as a brewhouse and bakery, likely the same “brewhouse room” mentioned in a 1622 letter from the colony. Further analysis of this material in 2010 confirmed the identification and dating of this structure. Comparison of the Ferryland brewhouse to data from both documentary and archaeological sources revealed some unusual features. When analyzed within the context of the original Calvert period settlement, these features provide additional evidence for the interpretation of the initial settlement at Ferryland not as a corporate colony such as Jamestown or Cupids, but as a small country manor home for George Calvert and his family

Realization of a monolithic high-reflectivity cavity mirror from a single silicon crystal

We report on the first experimental realization of a high-reflectivity cavity mirror that solely consists of a single silicon crystal. Since no material was added to the crystal, the urgent problem of 'coating thermal noise' that currently limits classical as well as quantum measurements is avoided. Our mirror is based on a surface nanostructure that creates a resonant surface waveguide. In full agreement with a rigorous model we realized a reflectivity of (99.79+/-0.01)% at a wavelength of 1.55 {\mu}m, and achieved a cavity finesse of 2784. We anticipate that our achievement will open the avenue to next generation high-precision experiments targeting fundamental questions of physics.Comment: Phys. Rev. Lett., accepte

The social construction of human-robot co-work by means of prototype work settings

Whether we look at Europe, the USA or Japan, in many areas in the world new possibilities of employing robotic systems in work settings essentially rely on direct collaborative interaction be-tween human workers and collaborative robots leading to new distributions of agency between them and making available robotic operations as resources for performing different forms of work, work which otherwise would remain out of reach for robotic automation for the time being. In this paper we introduce our concepts of studying the social construction of these collaborative work settings and the distribution of agency, accordingly. Referring to the basic idea of actor-network theory that technology in use should be analysed in a symmetrical manner, treating all the human and nonhuman entities involved as actors, our concept of distributed agency goes beyond actor-network theory in that it introduces the notion of gradualised action, which allows distinguishing between different levels of distributed agency. Therefore, we can precisely describe, in which way and to what extent activities and actor positions are delegated to robot co-workers or remain with its human counterpart. For analysing how the distribution of agency between human and robot co-workers is socially constructed in different stages, first in laboratory settings and then in increas-ingly realistic real-world settings, we interpret the spectrum of manifestations of human-robot col-laboration as prototypically realised scenarios at different stages of elaboration. In doing so we introduce the current state of collaborative robots in the areas of industrial production and care work as they represent contrastive cases: In industrial production collaborative robots are the next step in a long-standing history of robotic automation whereas in care work the new robots are also the first robots to be employed there. We believe that in both fields a perspective on collaborative work between humans and robots as a socio-technical constellation is helpful in order to be able to identify new distributions of work tasks