Upwelling rates for the equatorial Pacific Ocean derived from the bomb 14C distribution

A north-south cross section of bomb-produced radiocarbon (14C) in the upper 1000 m of the central equatorial Pacific Ocean (CEP) was measured in April, 1979 during Leg 3 of the NORPAX shuttle experiment. The 14C shows an equatorial mixed layer depletion of ∼40‰ compared to subtropical surface waters. Upwelling of deeper, 14C depleted water maintains this minimum. Two subsurface tongues of high 14C water, found north and south of the equator, are associated with high salinity water and probably result from exchange with subtropical surface water. The continued increase in mixed layer 14C levels in the CEP (up to 1979) indicates the importance of 14C input from these subsurface 14C maxima. Equatorward meridional advection resulting from geostrophic flow is the predominant supply of water upwelling at the equator and controls the 14C distribution in the CEP. The results of multi-layer mixing model calculations indicate an upwelling transport rate of 47 Sverdrups (5S–4N) and a maximum depth of upwelling of 225 m (σ0 = 26.5). These equatorial circulation characteristics explain the 14C, ΣCO2, oxygen, salinity and tritium distributions measured during Leg 3. The time history of mixed layer bomb 14C concentrations in the CEP indicate an exchange time of 4–6 years between the subtropical and equatorial surface oceans

Transport Properties of Carbon Nanotube C60_{60} Peapods

We measure the conductance of carbon nanotube peapods from room temperature down to 250mK. Our devices show both metallic and semiconducting behavior at room temperature. At the lowest temperatures, we observe single electron effects. Our results suggest that the encapsulated C$_{60}$ molecules do not introduce substantial backscattering for electrons near the Fermi level. This is remarkable given that previous tunneling spectroscopy measurements show that encapsulated C$_{60}$ strongly modifies the electronic structure of a nanotube away from the Fermi level.Comment: 9 pages, 4 figures. This is one of two manuscripts replacing the one orginally submitted as arXiv:cond-mat/0606258. The other one is arXiv:0704.3641 [cond-mat

Industrial Application of Heterostructure Device Simulation,”

Abstract-We give an overview of the state-of-theart of heterostructure RF-device simulation for industrial application based on III-V compound semiconductors. Results for Heterostructure Bipolar Transistors (HBTs) and for High Electron Mobility Transistors (HEMTs) are presented in good agreement with measured data of industrially relevant devices

Persistence of intense, climate-driven runoff late in Mars history

Mars is dry today, but numerous precipitation-fed paleo-rivers are found across the planet’s surface. These rivers’ existence is a challenge to models of planetary climate evolution. We report results indicating that, for a given catchment area, rivers on Mars were wider than rivers on Earth today. We use the scale (width and wavelength) of Mars paleo-rivers as a proxy for past runoff production. Using multiple methods, we infer that intense runoff production of >(3–20) kg/m 2 per day persisted until 1 Ga. Our improved history of Mars’ river runoff places new constraints on the unknown mechanism that caused wet climates on Mars

Tunneling spectroscopy of few-monolayer NbSe2_2 in high magnetic field: Ising protection and triplet superconductivity

In conventional Bardeen-Cooper-Scrieffer (BCS) superconductors, Cooper pairs of electrons of opposite spin (i.e. singlet structure) form the ground state. Equal spin triplet pairs (ESTPs), as in superfluid $^3$He, are of great interest for superconducting spintronics and topological superconductivity, yet remain elusive. Recently, odd-parity ESTPs were predicted to arise in (few-)monolayer superconducting NbSe$_2$, from the non-colinearity between the out-of-plane Ising spin-orbit field (due to the lack of inversion symmetry in monolayer NbSe$_2$) and an applied in-plane magnetic field. These ESTPs couple to the singlet order parameter at finite field. Using van der Waals tunnel junctions, we perform spectroscopy of superconducting NbSe$_2$ flakes, of 2--25 monolayer thickness, measuring the quasiparticle density of states (DOS) as a function of applied in-plane magnetic field up to 33T. In flakes $\lesssim$ 15 monolayers thick the DOS has a single superconducting gap. In these thin samples, the magnetic field acts primarily on the spin (vs orbital) degree of freedom of the electrons, and superconductivity is further protected by the Ising field. The superconducting energy gap, extracted from our tunnelling spectra, decreases as a function of the applied magnetic field. However, in bilayer NbSe$_2$, close to the critical field (up to 30T, much larger than the Pauli limit), superconductivity appears to be more robust than expected from Ising protection alone. Our data can be explained by the above-mentioned ESTPs

Assessing connectivity between an overlying aquifer and a coal seam gas resource using methane isotopes, dissolved organic carbon and tritium

Coal seam gas (CSG) production can have an impact on groundwater quality and quantity in adjacent or overlying aquifers. To assess this impact we need to determine the background groundwater chemistry and to map geological pathways of hydraulic connectivity between aquifers. In south-east Queensland (Qld), Australia, a globally important CSG exploration and production province, we mapped hydraulic connectivity between the Walloon Coal Measures (WCM, the target formation for gas production) and the overlying Condamine River Alluvial Aquifer (CRAA), using groundwater methane (CH4) concentration and isotopic composition (δ13C-CH4), groundwater tritium (3H) and dissolved organic carbon (DOC) concentration. A continuous mobile CH4 survey adjacent to CSG developments was used to determine the source signature of CH4 derived from the WCM. Trends in groundwater δ13C-CH4 versus CH4 concentration, in association with DOC concentration and 3H analysis, identify locations where CH4 in the groundwater of the CRAA most likely originates from the WCM. The methodology is widely applicable in unconventional gas development regions worldwide for providing an early indicator of geological pathways of hydraulic connectivity

Strong tuning of Rashba spin orbit interaction in single InAs nanowires

A key concept in the emerging field of spintronics is the gate voltage or electric field control of spin precession via the effective magnetic field generated by the Rashba spin orbit interaction. Here, we demonstrate the generation and tuning of electric field induced Rashba spin orbit interaction in InAs nanowires where a strong electric field is created either by a double gate or a solid electrolyte surrounding gate. In particular, the electrolyte gating enables six-fold tuning of Rashba coefficient and nearly three orders of magnitude tuning of spin relaxation time within only 1 V of gate bias. Such a dramatic tuning of spin orbit interaction in nanowires may have implications in nanowire based spintronic devices.Comment: Nano Letters, in pres

Nanoelectromechanical coupling in fullerene peapods probed via resonant electrical transport experiments

Fullerene peapods, that is carbon nanotubes encapsulating fullerene molecules, can offer enhanced functionality with respect to empty nanotubes. However, the present incomplete understanding of how a nanotube is affected by entrapped fullerenes is an obstacle for peapods to reach their full potential in nanoscale electronic applications. Here, we investigate the effect of C60 fullerenes on electron transport via peapod quantum dots. Compared to empty nanotubes, we find an abnormal temperature dependence of Coulomb blockade oscillations, indicating the presence of a nanoelectromechanical coupling between electronic states of the nanotube and mechanical vibrations of the fullerenes. This provides a method to detect the C60 presence and to probe the interplay between electrical and mechanical excitations in peapods, which thus emerge as a new class of nanoelectromechanical systems.Comment: 7 pages, 3 figures. Published in Nature Communications. Free online access to the published version until Sept 30th, 2010, see http://www.nature.com/ncomms/journal/v1/n4/abs/ncomms1034.htm