Weakly Enforced Boundary Conditions for the NURBS-Based Finite Cell Method

In this paper, we present a variationally consistent formulation for the weak enforcement of essential boundary conditions as an extension to the finite cell method, a fictitious domain method of higher order. The absence of boundary fitted elements in fictitious domain or immersed boundary methods significantly restricts a strong enforcement of essential boundary conditions to models where the boundary of the solution domain coincides with the embedding analysis domain. Penalty methods and Lagrange multiplier methods are adequate means to overcome this limitation but often suffer from various drawbacks with severe consequences for a stable and accurate solution of the governing system of equations. In this contribution, we follow the idea of NITSCHE [29] who developed a stable scheme for the solution of the Laplace problem taking weak boundary conditions into account. An extension to problems from linear elasticity shows an appropriate behavior with regard to numerical stability, accuracy and an adequate convergence behavior. NURBS are chosen as a high-order approximation basis to benefit from their smoothness and flexibility in the process of uniform model refinement

Science and Values on the High Desert: Dams and Irrigation on the Deschutes River, Oregon

More than a century of irrigation water withdrawals, reclamation, and the construction of the Pelton-Round Butte hydroelectric complex have altered the Deschutes River in central Oregon. An examination of these human impacts in the Deschutes Basin finds the geomorphic and hydrologic impacts downstream of the hydroelectric complex to be less substantial than typically expected, while irrigation water withdrawals in the upper basin remain a serious issue. Mitigation and restoration efforts have achieved success in the larger context of the status quo of water rights and water use in the American West, though much work remains before anadromous fish reestablish a presence in the Deschutes Basin

Engineering of Neutral Excitons and Exciton Complexes in Transition Metal Dichalcogenide Monolayers through External Dielectric Screening

In order to fully exploit the potential of transition metal dichalcogenide monolayers (TMD-MLs), the well-controlled creation of atomically sharp lateral heterojunctions within these materials is highly desirable. A promising approach to create such heterojunctions is the local modulation of the electronic structure of an intrinsic TMD-ML via dielectric screening induced by its surrounding materials. For the realization of this non-invasive approach, an in-depth understanding of such dielectric effects is required. We report on the modulations of excitonic transitions in TMD-MLs through the effect of dielectric environments including low-k and high-k dielectric materials. We present absolute tuning ranges as large as 37 meV for the optical band gaps of WSe 2 and MoSe 2 MLs and relative tuning ranges on the order of 30% for the binding energies of neutral excitons in WSe 2 MLs. The findings suggest the possibility to reduce the electronic band gap of WSe 2 MLs by 120 meV, paving the way towards dielectrically defined lateral heterojunctions.Comment: 11 pages + 6 pages supporting informatio

The economics of managing crop diversity on-farm: Case studies from the genetic resources policy initiative

The purpose of this book is to assess a variety of economic issues as they relate to agro-biodiversity and show how addressing these issues can assist in agro-biodiversity policy-making. This is illustrated using empirical data from some of the countries (Ethiopia, Nepal and Zambia) which are part of the Genetic Resources Policy Initiative. The empirical chapters apply the relevant economic methods, including regression analysis, choice experiments, hedonic pricing, contingent valuation and farm business income analysis. The authors discuss the economics of managing crop diversity on-farm in the context of crop variety attribute preferences, farmers' perception of agro-biodiversity loss, and value addition and marketing of the products of traditional crop varieties. The case studies include detailed analysis of traditional varieties of groundnut, maize, rice, sorghum, and teff. The results are relevant not only to GRPI countries but also to other countries concerned with the sustainable utilization of these resources. Overall, the studies illustrate how genetic resources issues can be integrated into rural development interventions

Consequences of critical interchain couplings and anisotropy on a Haldane chain

Effects of interchain couplings and anisotropy on a Haldane chain have been investigated by single crystal inelastic neutron scattering and density functional theory (DFT) calculations on the model compound SrNi$_2$V$_2$O$_8$. Significant effects on low energy excitation spectra are found where the Haldane gap ($\Delta_0 \approx 0.41J$; where $J$ is the intrachain exchange interaction) is replaced by three energy minima at different antiferromagnetic zone centers due to the complex interchain couplings. Further, the triplet states are split into two branches by single-ion anisotropy. Quantitative information on the intrachain and interchain interactions as well as on the single-ion anisotropy are obtained from the analyses of the neutron scattering spectra by the random phase approximation (RPA) method. The presence of multiple competing interchain interactions is found from the analysis of the experimental spectra and is also confirmed by the DFT calculations. The interchain interactions are two orders of magnitude weaker than the nearest-neighbour intrachain interaction $J$ = 8.7~meV. The DFT calculations reveal that the dominant intrachain nearest-neighbor interaction occurs via nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty $d$ orbital of V ions. The present single crystal study also allows us to correctly position SrNi$_2$V$_2$O$_8$ in the theoretical $D$-$J_{\perp}$ phase diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where it lies within the spin-liquid phase.Comment: 12 pages, 12 figures, 3 tables PRB (accepted). in Phys. Rev. B (2015

Robustness Assessment of Deployable Gossamer Structural Space Systems

The growing interest of science and industry in space, especially for commercial use in communications, climate and earth observation, as well as space exploration, is leading to the demand for increasingly efficient and lighter technical systems. For economic use, weight savings and the associated development of alternative and advanced designs are necessary, such as deployable, ultralight weight structural systems, so-called Gossamer structures that enable a wide variety of space applications to be realized. To this end, the thesis will investigate one of the most important aspects of deployable ultra-lightweight structural space systems, their robustness. This is investigated on different levels of complexity and finally quantified for the Gossamer structural space system as a whole. Although such structural systems are characterized by their very large outer dimensions, with a filigree design featuring very thin walls, and have a superior mass-area or mass-length ratio, thus offering great advantages in terms of economy and mission technology, they are at the same time more susceptible to disturbances, variation and imperfections, compared to traditional designs. The analysis of robustness, understood as a quantifiable metric, as well as the integration of robustness considerations and corresponding methods, can identify and determine these vulnerabilities and reduce them already during the development and design process by countermeasures. As a result, a structural system with minimized vulnerabilities and increased structural performance in the form of robustness can be achieved. In order to provide a first overview a general classification of existing Gossamer structural space systems and existing approaches for robustness assessment and quantification are analyzed. However, very different approaches are reported in the various fields of technology and engineering, with some highly theoretical and some only partially transferable. For this reason, a new methodology is developed and discussed in this thesis, which considers the characteristics of two-dimensional deployable Gossamer structural space systems and allows for a technical assessment of individual subsystem and overall system robustness. This is mainly shown by the example of the DLR solar sail demonstrator Gossamer-1. With the focus on quantification, it is essential to determine influencing variables and parameters, such as disturbances and deviations, which characterize the robustness of such structural systems. In practical experiments geometrical changes, such as shape and form deviations, caused by the manufacturing process, tooling and long-term stowage, changes in material properties due to environmental influences in space, as well as load changes due to interaction of components are investigated. Based on this, the here presented thesis investigates the effects of the determined influences on the robustness of deployable fiber composite booms and its subsystem, in mechanical bending tests as well as in numerical calculations. The resulting robustness parameters are subsequently used to quantify subsystem and overall system robustness facilitating the here developed method. Consequently, this thesis enables direct comparability and assessment of ultra-light weight Gossamer structural space systems based on their robustness as quantified metric

Constraints on regional drivers of relative sea-level change around Cordova, Alaska

New records of paleoenvironmental change from two lakes near Cordova, south central Alaska, combined with analysis of previously reported sediment sequences from the adjacent Copper River Delta, provide quantitative constraints on a range of Earth system processes through their expression in relative sea-level change. Basal sediment ages from Upper Whitshed Lake indicate ice-free conditions by at least 14,140 – 15,040 cal yr BP. While Upper and Lower Whitshed Lakes provide only upper limits to relative sea-level change, interbedded layers of freshwater peat and intertidal silt extending more than 11 m below present sea level in Copper River Delta indicate net submergence over the last 6000 years and multiple earthquake deformation cycles. In contrast, Lower Whitshed Lake, situated just above present high tide level, records only one episode of marine sedimentation, commencing AD 1120 – 1500, that we interpret as the result of isostatic subsidence due to Little Ice Age mass accumulation of the Chugach Mountain glaciers. Lower Whitshed Lake also records isostatic uplift at the end of the Little Ice Age before the end of marine sedimentation caused by ~1.5 m coseismic uplift in the great Alaska earthquake of AD 1964. We successfully explain the records of relative sea-level change from both Copper River Delta and the Whitshed Lakes by integrating the effects of eustatic sea-level rise, glacial isostasy, earthquake deformation cycles, sediment loading, sediment compaction and late Holocene changes in glacier mass into a single model. This approach provides initial quantitative constraints on the individual contributions of these processes. Taking reasonable estimates of eustasy, post-Last Glacial Maximum and Neoglacial glacial isostatic adjustment and a simple earthquake deformation cycle, we demonstrate that sediment loading and sediment compaction are both contributors to relative sea-level rise at Copper River Delta, together producing subsidence averaging approximately 1.2 mm yr-1 over the mid to late Holocene. Further isolation basin studies have the potential to greatly improve our understanding of the individual contributions of these processes in this highly dynamic region

Materials, Structures and Manufacturing: An Integrated Approach to Develop Expandable Structures

Membrane dominated space structures are lightweight and package efficiently for launch; however, they must be expanded (deployed) in-orbit to achieve the desired geometry. These expandable structural systems include solar sails, solar power arrays, antennas, and numerous other large aperture devices that are used to collect, reflect and/or transmit electromagnetic radiation. In this work, an integrated approach to development of thin-film damage tolerant membranes is explored using advanced manufacturing. Bio-inspired hierarchical structures were printed on films using additive manufacturing to achieve improved tear resistance and to facilitate membrane deployment. High precision, robust expandable structures can be realized using materials that are both space durable and processable using additive manufacturing. Test results show this initial work produced higher tear resistance than neat film of equivalent mass. Future research and development opportunities for expandable structural systems designed using an integrated approach to structural design, manufacturing, and materials selection are discussed