Bursts in discontinuous Aeolian saltation

Close to the onset of Aeolian particle transport through saltation we find in wind tunnel experiments a regime of discontinuous flux characterized by bursts of activity. Scaling laws are observed in the time delay between each burst and in the measurements of the wind fluctuations at the fluid threshold Shields number $\theta_c$. The time delay between each burst decreases on average with the increase of the Shields number until sand flux becomes continuous. A numerical model for saltation including the wind-entrainment from the turbulent fluctuations can reproduce these observations and gives insight about their origin. We present here also for the first time measurements showing that with feeding it becomes possible to sustain discontinuous flux even below the fluid threshold

Forage legume impact on soil fertility and N balance

Dairy production systems in Europe are to a large extent based on ley-arable rotations. In the ley phase of such rotations nitrogen accumulation occurs as a result of (1) organic carbon accumulation in soil not disturbed by tillage operations and (2) a considerable nitrogen surplus in grasslands, particularly under grazing regimes where a large part of the N in ingested grass is recycled to soil via urine and faeces. The accumulation of N and C in grasslands starts soon after establishment, the rate asymptotically declining with age and depends on practices such as fertiliser level, animal feed composition, stocking density, length of grazing and the botanical composition of the sward. In these pasture systems, key perennial legumes are white clover (Trifolium repens L.) red clover (Trifolium pratense L.) and lucerne (Medicago sativa). They are used because of their valuable contribution to production, feed quality and N inputs via biological fixation of atmospheric N2 (Ledgard et al., 2010) Grassland cultivation almost always results in a substantial residual effect and the mineralization of N often exceeds the requirement of the succeeding crop. Thus, there is a high risk of nitrate leaching following sward cultivation. Management practices to control nitrate losses include delayed ploughing until late winter or spring, the use of efficient catch crops after ploughing and a reduction in fertilizer N application to cereals after ploughing. The objective of this paper is to illustrate by examples the importance of management for N fertility building and efficient utilization in crop rotations containing forage legumes

An on-line solid phase extraction procedure for the routine quantification of urinary methylmalonic acid by liquid chromatography-tandem mass spectrometry

Background: The goal of this study was to develop and to validate an improved isotope-dilution-liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of methylmalonic acid (MMA) in urine. Methods: A previously described sample preparation protocol requires two solvent extraction steps, including evaporation. The first extraction is to extract the analyte from the sample, and second occurs following derivatization of the extract. In the method described here, the second evaporation step was substituted by on-line solid phase extraction employing column-switching and a permanent co-polymer based extraction cartridge. A standard validation protocol was applied to investigate the performance of the method. Results: The method was found to be linear in the clinically relevant range of concentrations (6-100 mu mol/L). Total coefficients of variation were below 10% and inaccuracy was <10% for quality control samples at three concentrations. Conclusions: By omitting one evaporation step, the semi-automated method described in this article enables for more convenient work-flow in the quantification of urinary MMA compared to the previous protocol. This is of relevance for MMA measurement in the routine clinical laboratory setting. Validation demonstrated acceptable analytical performance. Clin Chem Lab Med 2010;48:1647-50

Coupling of shells in a carbon nanotube quantum dot

We systematically study the coupling of longitudinal modes (shells) in a carbon nanotube quantum dot. Inelastic cotunneling spectroscopy is used to probe the excitation spectrum in parallel, perpendicular and rotating magnetic fields. The data is compared to a theoretical model including coupling between shells, induced by atomically sharp disorder in the nanotube. The calculated excitation spectra show good correspondence with experimental data.Comment: 8 pages, 4 figure

Singlet-Triplet Physics and Shell Filling in Carbon Nanotube Double Quantum Dots

An artifcial two-atomic molecule, also called a double quantum dot (DQD), is an ideal system for exploring few electron physics. Spin-entanglement between just two electrons can be explored in such systems where singlet and triplet states are accessible. These two spin-states can be regarded as the two states in a quantum two-state system, a so-called singlet-triplet qubit. A very attractive material for realizing spin based qubits is the carbon nanotube (CNT), because it is expected to have a very long spin coherence time. Here we show the existence of a gate-tunable singlet-triplet qubit in a CNT DQD. We show that the CNT DQD has clear shell structures of both four and eight electrons, with the singlet-triplet qubit present in the four-electron shells. We furthermore observe inelastic cotunneling via the singlet and triplet states, which we use to probe the splitting between singlet and triplet, in good agreement with theory.Comment: Supplement available at: http://www.fys.ku.dk/~hij/public/singlet-triple_supp.pd

Electron transport in single wall carbon nanotube weak links in the Fabry-Perot regime

We fabricated reproducible high transparency superconducting contacts consisting of superconducting Ti/Al/Ti trilayers to gated single-walled carbon nanotubes (SWCNTs). The reported semiconducting SWCNT have normal state differential conductance up to $3e^2/h$ and exhibit clear Fabry-Perot interference patterns in the bias spectroscopy plot. We observed subharmonic gap structure in the differential conductance and a distinct peak in the conductance at zero bias which is interpreted as a manifestation of a supercurrent. The gate dependence of this supercurrent as well as the excess current are examined and compared to a coherent theory of superconducting point contacts with good agreement.Comment: 10 pages, 4 figure

Bulk and surface magnetoinductive breathers in binary metamaterials

We study theoretically the existence of bulk and surface discrete breathers in a one-dimensional magnetic metamaterial comprised of a periodic binary array of split-ring resonators. The two types of resonators differ in the size of their slits and this leads to different resonant frequencies. In the framework of the rotating-wave approximation (RWA) we construct several types of breather excitations for both the energy-conserved and the dissipative-driven systems by continuation of trivial breather solutions from the anticontinuous limit to finite couplings. Numerically-exact computations that integrate the full model equations confirm the quality of the RWA results. Moreover, it is demonstrated that discrete breathers can spontaneously appear in the dissipative-driven system as a results of a fundamental instability.Comment: 10 pages, 16 figure

Introduction to the Symposium Convergence on Delaware: Corporate Bankruptcy and Corporate Governance

Bankruptcy is back. The use of Chapter 11 by large, publicly held firms was a subject of much debate in the academic and popular press in the late 1980s and the early 1990s. Firms such as Texaco, Revco, LTV, Federated Department Stores, Maxwell Communications, TWA, and Eastern Airlines all filed for bankruptcy during that time. The economic boom of the mid- and late 1990s, however, resulted in a relative dearth of high-profile bankruptcy cases. The recent economic downturn has moved corporate reorganizations back into the spotlight. The Chapter 11 filings by firms such as Enron, Global Crossing, the Loewen Group, US Airways, United Airlines, and WorldCom have focused attention once again on Chapter 11. Yet today\u27s bankruptcy practice has changed notably since our last wave of major bankruptcies. The most visible change in the reorganization of large, publicly held companies in the past fifteen years has been the rise of the Delaware bankruptcy court. As of 1990, a firm looking to reorganize under Chapter 11 would most likely file its bankruptcy petition in the Southern District of New York. Today, such firms look first and foremost to Delaware, Indeed, other courts are changing their practices to mirror those of Delaware. This switch in the lead venue of reorganization practice raises two sets of questions. The first set of questions focuses directly on this trend. Delaware\u27s prominence in corporate law has spawned a decades-old debate over why firms choose Delaware and whether the forces that drive firms to Delaware create a body of corporate law that advances or impedes societal interests. The rise of the Delaware bankruptcy court raises similar inquiries. In short, we need to explore why firms now choose to file for reorganization in Delaware, and whether the switch to Delaware is one that should be applauded or condemned