Sound propagation over uneven ground and irregular topography

The development of theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere is discussed. Irregular topography here is understood to imply a ground surface that (1) is not idealizable as being perfectly flat or (2) that is not idealizable as having a constant specific acoustic impedance. The study focuses on circumstances where the propagation is similar to what might be expected for noise from low-altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence

Bound states in a quasi-two-dimensional Fermi gas

We consider the problem of N identical fermions of mass M and one distinguishable particle of mass m interacting via short-range interactions in a confined quasi-two-dimensional (quasi-2D) geometry. For N=2 and mass ratios M/m<13.6, we find non-Efimov trimers that smoothly evolve from 2D to 3D. In the limit of strong 2D confinement, we show that the energy of the N+1 system can be approximated by an effective two-channel model. We use this approximation to solve the 3+1 problem and we find that a bound tetramer can exist for mass ratios M/m as low as 5 for strong confinement, thus providing the first example of a universal, non-Efimov tetramer involving three identical fermions.Comment: 5 pages, 4 figure

Observation of an orbital interaction-induced Feshbach resonance in 173-Yb

We report on the experimental observation of a novel inter-orbital Feshbach resonance in ultracold 173-Yb atoms, which opens the possibility of tuning the interactions between the 1S0 and 3P0 metastable state, both possessing vanishing total electronic angular momentum. The resonance is observed at experimentally accessible magnetic field strengths and occurs universally for all hyperfine state combinations. We characterize the resonance in the bulk via inter-orbital cross-thermalization as well as in a three-dimensional lattice using high-resolution clock-line spectroscopy.Comment: 5 pages, 4 figure

A comparative analysis of Simplified General Circulation Models of the atmosphere of Venus

Within the context of a working group supported by ISSI (Bern, Switzerland), we have made an intercomparison work between Global Circulation Models using simpli?ed parameterizations for radiative forcing and other physical processes. Even with similar schemes and parameters, the different GCMs produce different circulations, illustrating interesting differences between dynamical model cores

Supersolidity in electron-hole bilayers with a large density imbalance

We consider an electron-hole bilayer in the limit of extreme density imbalance, where we have a single particle in one layer interacting attractively with a Fermi liquid in the other parallel layer. Using an appropriate variational wave function for the dressed exciton, we provide strong evidence for the existence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in electron-hole bilayers with a large density imbalance. Furthermore, within this unusual limit of FFLO, we find that a dilute gas of minority particles forms excitons that condense into a two-dimensional "supersolid".Comment: 6 pages, 2 figure

Open sea OWC motions and mooring loads monitoring at BiMEP

This is the author accepted manuscript.Despite the large number of wave energy converter concepts proposed over the past three decades, only a few field measurement datasets are available in the public domain. The sparse nature of device performance and reliability data coupled with a general lack of design convergence means that technological and economic progress within the sector is fragmented. Fundamental to ensuring device efficiency and survivability is the acquisition of long-term, open sea, device and mooring system response data, combined with comprehensive numerical modelling. With mooring systems representing approximately 10% of marine renewable energy device CAPEX, the evolution of shared mooring systems and the use of novel materials with load reduction capabilities represent clear strategies to achieve more favourable project finances. This paper will report on design of the mooring load monitoring system as well as preliminary analysis of several load cases identified from field data recorded during the winter of the first deployment. Comparisons are made to numerical simulations of the device and mooring system subjected to representative environmental conditions. The measured mooring line tensions also provide operational design criteria (i.e. load capacity and durability requirements) for two elastomeric tethers which will replace the polyester ropes currently used in the seaward catenary lines.The research leading to this paper is part of the OPERA (Open Sea Operating Experience to Reduce Wave Energy Cost) project which is funded from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654.444

Linear magnetoresistance in commercial n-type silicon due to inhomogeneous doping

Free electron theory tells us that resistivity is independent of magnetic field. In fact, most observations match the semiclassical prediction of a magnetoresistance that is quadratic at low fields before saturating. However, a non-saturating linear magnetoresistance has been observed in exotic semiconductors such as silver chalcogenides, lightly-doped InSb, N-doped InAs, MnAs-GaAs composites, PrFeAsO, and epitaxial graphene. Here we report the observation of a large linear magnetoresistance in the ohmic regime in commonplace commercial n-type silicon wafer. It is well-described by a classical model of spatially fluctuating donor densities, and may be amplified by altering the aspect ratio of the sample to enhance current-jetting: increasing the width tenfold increased the magnetoresistance at 8 T from 445 % to 4707 % at 35 K. This physical picture may well offer insights into the large magnetoresistances recently observed in n-type and p-type Si in the non-ohmic regime.Comment: submitted to Nature Material

Extension of Lake Whatcom phosphorus ban: environmental impact assessment

Lake Whatcom is the main source of drinking water for over 96,000 people in Whatcom County including 82,000 residents of the City of Bellingham. Unfortunately, Lake Whatcom is currently listed under the Washington State Department of Ecology\u27s 303D list as an impaired water body due to lack of dissolved oxygen. The main cause of low oxygen levels in the lake is excess phosphorus. Phosphorus is a nutrient necessary for all plant life. However, when too much of it enters aquatic systems, it can cause an imbalance in the aquatic ecosystem. In the past, phosphorus that was used in fertilizers and detergents has entered Lake Whatcom watershed through stormwater runoff. Phosphorus in the lake has contributed to an increase in algal blooms. If these blooms are allowed to continue to grow in the lake, they will have a negative impact on drinking water quality, aesthetics, public services and utilities, recreation in Lake Whatcom, energy and natural resources, as well as quality of life for fish and other wildlife. This environmental impact assessment offers two alternatives to the no-action option regarding phosphorus in the watershed. The first alternative (original ban) would be to return to the original 2005 ordinance restricting the use of phosphorus. This was a control ordinance on commercial fertilizers labeled as containing more than 0% phosphorus by weight. It was based on an honor system, and not enforced. There were also educational materials provided to people living in the watershed on how phosphorus affects the lake, with low phosphorus fertilizers for people to use. The use of phosphorus on first year planting is still allowed within the watershed under the original ban alternative. Additionally, many private land owners could still bring in other materials containing phosphorus such as composts, mulches, etc. The second alternative is the new ordinance that was recently passed by the City Council in January 2011. This new ban limits the use of fertilizers, mulches, wood chips, composts, and other products containing phosphorus for all land uses (with the exception of forestry) within the Lake Whatcom watershed. It also requires retail to post signage notifying customers of the prohibited uses of soil amendments containing over 0% phosphorus on landscaping and horticultural applications. There is already an adequate amount of phosphorus in the soil for plants to grow, and added nutrients are not actually necessary. If no action is taken to limit the amount of added phosphorus coming into the watershed, stormwater runoff will continue to carry more nutrients into the lake, degrading the quality of the water

Tin(II) Ureide Complexes:Synthesis, Structural Chemistry and Evaluation as SnO precursors

In an attempt to tailor precursors for application in the deposition of phase pure SnO, we have evaluated a series of tin (1-6) ureide complexes. The complexes were successfully synthesized by employing N,N′-Trialkyl-functionalized ureide ligands, in which features such as stability, volatility, and decomposition could be modified with variation of the substituents on the ureide ligand in an attempt to find the complex with the ideal electronic, steric, or coordinative properties, which determine the fate of the final products. The tin(II) ureide complexes 1-6 were synthesized by direct reaction [Sn{NMe2}2] with aryl and alkyl isocyanates in a 1:2 molar ratio. All the complexes were characterized by NMR spectroscopy as well as elemental analysis and, where applicable, thermogravimetric (TG) analysis. The single-crystal X-ray diffraction studies of 2, 3, 4, and 6 revealed that the complexes crystallize in the monoclinic space group P2(1)/n (2 and 4) or in the triclinic space group P-1 (3 and 6) as monomers. Reaction with phenyl isocyanate results in the formation of the bimetallic species 5, which crystallizes in the triclinic space group P-1, a consequence of incomplete insertion into the Sn-NMe2 bonds, versus mesityl isocyanate, which produces a monomeric double insertion product, 6, under the same conditions, indicating a difference in reactivity between phenyl isocyanate and mesityl isocyanate with respect to insertion into Sn-NMe2 bonds. The metal centers in these complexes are all four-coordinate, displaying either distorted trigonal bipyramidal or trigonal bipyramidal geometries. The steric influence of the imido-ligand substituent has a clear effect on the coordination mode of the ureide ligands, with complexes 2 and 6, which contain the cyclohexyl and mesityl ligands, displaying κ2-O,N coordination modes, whereas κ2-N,N′ coordination modes are observed for the sterically bulkier tert-butyl and adamantyl derivatives, 3 and 4. The thermogravimetric analysis of the complexes 3 and 4 exhibited excellent physicochemical properties with clean single-step curves and low residual masses in their TG analyses suggesting their potential utility of these systems as MOCVD and ALD precursors.</p