Electrical generation of pure spin currents in a two-dimensional electron gas

Pure spin currents are measured in micron-wide channels of GaAs two-dimensional electron gas (2DEG). Spins are injected and detected using quantum point contacts, which become spin polarized at high magnetic field. High sensitivity to the spin signal is achieved in a nonlocal measurement geometry, which dramatically reduces spurious signals associated with charge currents. Measured spin relaxation lengths range from 30 to 50 microns, much longer than has been reported in GaAs 2DEG's. The technique developed here provides a flexible tool for the study of spin polarization and spin dynamics in mesoscopic structures defined in 2D semiconductor systems

Picture book on Marine Gastropods

Gastropods includes snails, slugs and their relatives is a hyper diverse with respect to number of species, structure and habitat and many other attributes. Gastropods are characterised by having single shell and an operculum. Widely ranging in size, the shell has been modified enormously in many groups. A total of 80,000 to 100,000 mollusc species are known world over. About 3271 species of molluscs are found in India, of which 1900 marine species of gastropods are known to date. These resources are exploited by either mechanised trawlers, bottom set gillnets or by diving. Very few species forms a regular fishery and most of them are obtained in smaller magnitude making them unnoticed. While these resources are smaller in magnitude compared to other fisheries, they play an important role as raw materials for the multi-million dollar ‘SHELLCRAFT INDUSTRIES’ world over. In India, the resource is harvested in almost all the landing centres of both the coasts. In southeast coast of India, where the most part of landings of marine gastropods are occurring is considered a hub of shellcraft industry. A total of more than 250 species has been recorded and representing forty odd families in gastropods. The Federation of Sea Shell Handicrafts Merchants Association (FOSSHMA), estimates around 90 active seashell handicrafts traders in India, comprising of 20 very active, 30 minimal functioning and 40 dormant units. The major destinations of export is found to be the United States of America, Australia, Europe, Japan, Philippines, Vietnam, Africa, Malaysia, Belgium, Croatia, England, Haiti Island, Sri Lanka,France, Netherlands, Germany, South Africa etc. The major species exported are Conus sp, Umbonium sp, Chicoreus ramosus, Lambis lambis, Babylonia spirata, B. zeylanica, Telescopium sp, Terebralia sp, Tonna spp and Cerithium sp. Around 20-25 species are imported by shellcraft industries and the major species imported are Busycon sp, Haliotis sp, Cypraea tigris, Mitrella sp. The major importing countries includes USA, Mexico, New Zealand, South Africa, Australia, Philippines, Spain and other African countries. This picture book contains 165 photographs of seashells used in the Indian seashell industries clustered under the common name of the respective species along with vernacular (Tamil) names

1-(Benz­yloxy)naphthalene

In the title compound, C17H14O, the dihedral angle between the naphthyl ring system and the benzyl group is 83.22 (4)°. Both of these moieties are planar, with mean deviations from their least-squares planes, defined by the naphthyl ring C atoms and the O atom, and the phenyl ring C atoms and the benzyl α-C atom, of 0.0176 (1) and 0.0024 (13) Å, respectively. The crystal structure is stabilized by C—H⋯π and π–π inter­actions [centroid–centroid distance = 3.7817 (10) Å]

Gastropod landing, utilisation and trade in India: A case study from Kollam, India

Gastropods used both for decorative and edible purposes are a valuable resource along the east and west coast of India and the Andaman and Nicobar Islands. Even though the molluscan production in India was comparatively insignificant in earlier times, it increased due to the demand for edible as well as ornamental gastropods from around the globe coupled with their importance in generating additional income as a bycatch. Shakthikulangara and Neendakara landing centres of the Kollam district of Kerala ranks among the major gastropod landing centres along the west coast of India. Based on the cost and earnings analysed from the primary data collected from Shakthikulangara and Neendakara area, various productivity ratios are analysed which indicates that the fishing for gastropods registered a shift in operations from harvesting as a by-catch resource to targeted fishing. The study reveals the scope of gastropod fishery in Kerala as well as the lack of shellcraft industry in the state. Also, the reduced availability of gastropods due to the extensive exploitation is investigated

Ornamental gastropod shell trade in India : A macroeconomic assessment

The capture fisheries results in landing of sizeable amount of by-catch which includes molluscs, crustaceans (certain varieties of crabs, and Squilla spp.), finfishes (non-edible varieties), sea snakes and echinoderms

Emerging giant resonant exciton induced by Ta-substitution in anatase TiO2_{2}: a tunable correlation effect

Titanium dioxide (TiO$_2$) has rich physical properties with potential implications in both fundamental physics and new applications. Up-to-date, the main focus of applied research is to tune its optical properties, which is usually done via doping and/or nano-engineering. However, understanding the role of $d$-electrons in materials and possible functionalization of $d$-electron properties are still major challenges. Herewith, within a combination of an innovative experimental technique, high energy optical conductivity, and of the state-of-the-art {\it ab initio} electronic structure calculations, we report an emerging, novel resonant exciton in the deep ultraviolet region of the optical response. The resonant exciton evolves upon low concentration Ta-substitution in anatase TiO$_{2}$ films. It is surprisingly robust and related to strong electron-electron and electron-hole interactions. The $d$- and $f$- orbitals localization, due to Ta-substitution, plays an unexpected role, activating strong electronic correlations and dominating the optical response under photoexcitation. Our results shed light on a new optical phenomenon in anatase TiO$_{2}$ films and on the possibility of tuning electronic properties by Ta substitution

Intermittency transitions to strange nonchaotic attractors in a quasiperiodically driven Duffing oscillator

Different mechanisms for the creation of strange nonchaotic attractors (SNAs) are studied in a two-frequency parametrically driven Duffing oscillator. We focus on intermittency transitions in particular, and show that SNAs in this system are created through quasiperiodic saddle-node bifurcations (Type-I intermittency) as well as through a quasiperiodic subharmonic bifurcation (Type-III intermittency). The intermittent attractors are characterized via a number of Lyapunov measures including the behavior of the largest nontrivial Lyapunov exponent and its variance as well as through distributions of finite-time Lyapunov exponents. These attractors are ubiquitous in quasiperiodically driven systems; the regions of occurrence of various SNAs are identified in a phase diagram of the Duffing system.Comment: 24 pages, RevTeX 4, 12 EPS figure

Transverse Electronic Transport through DNA Nucleotides with Functionalized Graphene Electrodes

Graphene nanogaps and nanopores show potential for the purpose of electrical DNA sequencing, in particular because single-base resolution appears to be readily achievable. Here, we evaluated from first principles the advantages of a nanogap setup with functionalized graphene edges. To this end, we employed density functional theory and the non-equilibrium Green's function method to investigate the transverse conductance properties of the four nucleotides occurring in DNA when located between the opposing functionalized graphene electrodes. In particular, we determined the electrical tunneling current variation as a function of the applied bias and the associated differential conductance at a voltage which appears suitable to distinguish between the four nucleotides. Intriguingly, we observe for one of the nucleotides a negative differential resistance effect.Comment: 19 pages, 7 figure

Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films

We report room-temperature ferromagnetism in highly conducting transparent anatase Ti1-xTaxO2 (x~0.05) thin films grown by pulsed laser deposition on LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), x-ray diffraction (XRD), proton induced x-ray emission (PIXE), x-ray absorption spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) indicated negligible magnetic contaminants in the films. The presence of ferromagnetism with concomitant large carrier densities was determined by a combination of superconducting quantum interference device (SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD) and was supported by first-principle calculations. SXMCD and XAS measurements revealed a 90% contribution to ferromagnetism from the Ti ions and a 10% contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites though carrier activation was only 50% at 5% Ta concentration implying compensation by cationic defects. The role of Ti vacancy and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS) respectively. It was found that in films with strong ferromagnetism, the Ti vacancy signal was strong while Ti3+ signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localised magnetic moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to ferromagnetism in wide-band-gap semiconducting oxides without any magnetic elements.Comment: 21 pages, 10 figures, to appear in Philosophical Transaction - Royal Soc.

Distribution of Hydrocarbons and Microbial Populations Related to Sedimentation Processes in Lower Cook Inlet and Norton Sound, Alaska

In spring and summer 1978 and spring 1979 an integrated study was carried out to examine the interrelationships of physical (sediment deposition), chemical (organic carbon and hydrocarbon concentrations), and biological (microbial populations and activities) factors in the Cook Inlet and Norton Sound regions with respect to the probable sinks and fates of hydrocarbon contaminants within these ecosystems. Most of the fine-grained sediment entering Cook Inlet is transported out of the inlet into Shelikof Strait. However, significant sediment accumulation occurs within areas of Kamishak and Kachemak bays. In Norton Sound, sediment from the Yukon River is transported counterclockwise around the embayment and approximately 50% is deposited in the nearshore regions of the sound. In both regions, areas of high sediment accumulation are richer in organic carbon and hydrocarbon derived from land than are areas of low sediment accumulation. In general, areas with high sediment accumulation rates for fine-grained particles are also areas of relatively high microbial activity. Results suggest that these elevated microbial activities reflect biodegradation of detrital carbon associated with these particles. Also, the Cook Inlet and Norton Sound region were found to be free from petroleum hydrocarbon contamination (with the exception of one area in Cook Inlet). No evidence was found of hydrocarbon accumulation resulting from a gas seepage in Norton Sound, nor for accumulation of hydrocarbons in sediments of lower Cook Inlet and Shelikof Strait from oil well operations in upper Cook Inlet.Key words: arctic marine ecosystems, sedimentation, microorganism, hydrocarbons, lower Cook Inlet, Norton SoundMots clés: écosystèmes marins arctiques, sédimentation, micro-organismes, hydrocarbons, sud de l'inlet Cook, bras de mer Norto