Sarath Kumar, S. R.; Cha, Dong Kyu; Alshareef, Husam N.(Journal of Applied Physics, AIP Publishing, 2011-10-24)[Article]
Lattice dynamics, low-temperature electrical transport, and high-temperature thermoelectric properties of (In, Yb)-doped CoSb3thin films on different substrates are reported. Pulsed laser deposition under optimized conditions yielded single-phase polycrystalline skutterudite films. Raman spectroscopy studies suggested that In and Yb dopants occupy the cage sites in the skutterudite lattice. Low-temperature electrical transport studies revealed the n-type semiconducting nature of the films with extrinsic and intrinsic conduction mechanisms, in sharp contrast to the degenerate nature reported for identical bulk samples. Calculations yielded a direct bandgap close to 50 meV with no evidence of an indirect gap. The carrier concentration of the films was identical to that reported for the bulk and increased with temperature beyond 250 K. The higher resistivity exhibited is attributed to the enhanced grain boundary scattering in films with a high concentration of grains. The maximum power factor of ∼0.68 W m−1 K−1 obtained at 660 K for the film on glass is found to be nearly four times smaller compared to that reported for the bulk. The observed difference in the power factors of the films on different substrates is explained on the basis of the diffusion of oxygen from the substrates and the formation of highly conducting CoSb2 phase upon the oxidation of CoSb3.
We examined the diel behavior among the jellyfish Periphylla periphylla in Lurefjorden, Norway in a sampling campaign and by a > 3-month continuous acoustic study. Jellyfish distribution and behavior were recorded by an upward-facing, bottom-mounted echo sounder at 280-m depth. The population was typically divided into four groups, each with different behavior. Individuals of behavioral Mode 1 undertook synchronous diel vertical migrations (DVM) within the upper 100 m. Individuals of behavioral Mode 2, stayed at ~ 160-200-m depth during the day, and also exhibited synchronized DVM, ascending at dusk and descending at dawn. The smaller individuals of behavioral Mode 3 swam continuously up and down throughout both day and night, yet occurred below Mode 2 individuals in daytime (~ 200 m-bottom), while their vertical range encompassed the entire water column during night. Mode 4 behavior was displayed by large jellyfish located between ~ 130 m and the bottom. These animals shifted between remaining motionless and relocating in rapid steps during both day and night. These four main behavioral patterns persisted throughout the registration period, although the synchronously migrating Mode 2 behavior became weaker in spring. This acoustic study has unveiled more diverse migration behaviors than previously derived from net sampling and remote-operated vehicles methods and emphasizes the importance of studying individuals. DVM is complex because individuals in a plankton population may simultaneously engage in a range of various contrasting behaviors.
Lezama-Ochoa, A; Ballón, M; Woillez, M; Grados, D; Irigoien, Xabier; Bertrand, A(Marine Ecology Progress Series, Inter-Research Science Center, 2011-10-20)[Article]
Macrozooplankton plays a key role in pelagic ecosystems as a link between lower
trophic levels and fish. However, although its ecological role is usually considered in polar ecosystems,
it is rarely considered in temperate ones. To obtain comprehensive information on the
macrozooplankton distribution in the Bay of Biscay we adapted a bi-frequency acoustic method
developed for the Humboldt Current system. This method can be used to extract continuous and
simultaneous high-resolution information on the spatiotemporal patterns of biomass distributions
of macrozooplankton and pelagic fish throughout the diel cycle. The 2 distributions were mapped
using geostatistical techniques. We applied kriging with external drifts, which accounts for both
diel and across-shore changes in macrozooplankton biomass. We then used a cross-variogram to
determine the scale-dependent relationships between macrozooplankton and fish. The results
show how macrozooplankton and fish are distributed according to the different ecological
domains (coast, shelf, shelf-break and offshore) along the Spanish and French coasts. Specific
macrozooplankton hotspots were observed, but macrozooplankton was generally more abundant
offshore than inshore, whereas fish showed the opposite trend. This pattern was confirmed by the
aggregation sizes, which increased towards oceanic waters for macrozooplankton and decreased
for fish. Finally, the correlation between fish and macrozooplankton was positive on a small scale
(<30 nautical miles) and negative on a large scale (>30 nautical miles).
Gaaloul, Fakhreddine; Alouini, Mohamed-Slim; Radaydeh, Redha Mahmoud Mesleh(IEEE Transactions on Vehicular Technology, Institute of Electrical and Electronics Engineers (IEEE), 2011-10-19)[Technical Report]
This paper investigates the performance of two low-complexity combining schemes, which are based on one- or two-phase observation, to mitigate multipath fading in dual-hop amplify-and-forward relaying systems. For the one-phase-based combining, a single-antenna station is assumed to relay information from a multiple-antenna transmitter to a multiple-antenna receiver, and the activation of the receive antennas is adaptively performed based on the second-hop statistics, regardless of the first-hop conditions. On the other hand, the two-phase-based combining suggests using multiple single-antenna stations between the multiple-antenna transmitter and the single-antenna receiver, where the suitable set of active relays is identified according to the precombining end-to-end fading conditions. To facilitate comparisons between the two schemes, formulations for the statistics of the combined signal-to-noise ratio and some performance measures are presented. Numerical and simulation results are shown to clarify the tradeoff between the achieved diversity-array gain, the processing complexity, and the power consumption.
Tahini, H. A.; Chroneos, Alexander; Grimes, R. W.; Schwingenschlögl, Udo(Applied Physics Letters, AIP Publishing, 2011-10-18)[Article]
Density functional theory calculations are used to investigate the formation and diffusion of tin-vacancy pairs (SnV) in germanium(Ge). Depending upon the Fermi energy, SnV pairs can form in neutral, singly negative, or doubly negative charged states. The activation energies of diffusion, also as function of the Fermi energy, are calculated to lie between 2.48-3.65 eV, in agreement with and providing an interpretation of available experimental work.
Zhu, Zhiyong; Cheng, Yingchun; Schwingenschlögl, Udo(Physical Review B, American Physical Society (APS), 2011-10-14)[Article]
Fully relativistic first-principles calculations based on density functional theory are performed to study the spin-orbit-induced spin splitting in monolayer systems of the transition-metal dichalcogenides MoS2, MoSe2, WS2, and WSe2. All these systems are identified as direct-band-gap semiconductors. Giant spin splittings of 148–456 meV result from missing inversion symmetry. Full out-of-plane spin polarization is due to the two-dimensional nature of the electron motion and the potential gradient asymmetry. By suppression of the Dyakonov-Perel spin relaxation, spin lifetimes are expected to be very long. Because of the giant spin splittings, the studied materials have great potential in spintronics applications.
Kaloni, Thaneshwor P.; Cheng, Yingchun; Faccio, R.; Schwingenschlögl, Udo(Journal of Materials Chemistry, Royal Society of Chemistry (RSC), 2011-10-14)[Article]
We study the oxidation of monovacancies in graphene by oxygen molecules using first principles calculations. In particular, we address the local magnetic moments which develop at monovacancies and show that they remain intact when a molecule is adsorbed such that the dangling carbon bonds are not fully saturated. However, the lowest energy configuration does not maintain dangling bonds and is found to be semiconducting. Our data can explain the experimentally observed behavior of graphene under exposure to an oxygen plasma.
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