bluuebunny/crossref_metadata_2025 huggingface dataset:
Ray tracing simulation for radiation trapping of the He I resonance transitions in a linear plasma device
Authors: Kajita Shin , Nishijima Daisuke , Hollmann Eric M. , Ohno Noriyasu
Published: June 2009

A ray tracing code combined with a He I collisional-radiative (CR) model has been developed to investigate effects of radiation trapping on the population distribution of He atoms in a weakly ionized plasma. The code accurately reproduces experimentally observed vertical profiles of emission intensities in a linear plasma device. On the other hand, the CR code and that modified with the optical escape factor method to include the radiation trapping effects show that vertical profiles significantly deviate from measured ones at the periphery of the plasma column. This work therefore demonstrates that accurate matching of line intensity profiles over the entire plasma column requires a ray tracing code, not just an optical escape factor approximation.
Light polarization control in strain-engineered GaAsN/GaAsN:H heterostructures
Authors: Trotta R. , Polimeni A. , Capizzi M. , Martelli F. , Rubini S. , Francardi M. , Gerardino A. , Mariucci L.
Published: June 2009

The expansion of the GaAsN lattice following hydrogen incorporation is spatially patterned so as to generate an anisotropic stress in the sample growth plane. The resulting in-plane symmetry breaking determines an in-plane polarization dependence of the light emitted along the crystal growth direction in agreement with optical selection rules and strain field calculations.
Growing correlation length in supercooled water
Authors: Moore Emily B. , Molinero Valeria
Published: June 2009

The evolution of the structure of water from the stable high temperature liquid to its glass, low-density amorphous ice (LDA), is studied through large-scale molecular dynamics simulations with the mW model [J. Phys. Chem. B 113, 4008 (2009)]. We characterize the density, translational, and orientational ordering of liquid water from the high temperature stable liquid to the low-density glass LDA at the critical cooling rate for vitrification. A continuous transition to a tetrahedrally ordered low-density liquid is observed at 50 K below the temperature of maximum density and 25 K above a temperature of minimum density. The structures of the low-density liquid and glass are consistent with that of a continuous random tetrahedral network. The liquid-liquid transformation temperature TLL, defined by the maximum isobaric expansivity, coincides with the maximum rate of change in the local structure of water. Long-range structural fluctuations of patches of four-coordinated molecules form in the liquid. The correlation length of the four-coordinated patches in the liquid increases according to a power law in the range 300 K to TLL+10 K; a maximum is predicted at TLL. To the best of our knowledge this is the first direct estimation of the Widom line of supercooled water through the analysis of structural correlations.
Transversal and longitudinal mode selections in double-corrugation coaxial slow-wave devices
Authors: Ge Xingjun , Zhong Huihuang , Qian Baoliang , Liu Lie , Liu Yonggui , Li Limin , Shu Ting , Zhang Jiande
Published: June 2009

To reduce the dimensions of relativistic backward wave oscillators (RBWOs) operating in the low frequency regime of less than 2 GHz, the theory of transversal and longitudinal mode selections are introduced in this paper. The transversal mode selection is achieved using the property of “surface wave” of the coaxial slow-wave structure (SWS) to excite the quasi transverse electromagnetic (quasi-TEM) mode without the higher transverse magnetic (TM) modes and it is proved that the coaxial SWS may decrease the transversal dimension of the SWS sections. In addition, the S-parameter method is employed to investigate the longitudinal resonant characteristic of the finite-length SWS, and the scheme of longitudinal mode selection is put forward. It is proposed that the introduction of a well-designed coaxial extractor to slow-wave devices can help to achieve the longitudinal mode selection and reduce the period number of the SWS, which not only can make the devices more compact, but also can avoid the destructive competition between various longitudinal modes, therefore can enhance the efficiency and stabilize the frequency. To sum up, the physical mechanisms of transversal and longitudinal mode selections ensure that the microwave is produced with a single mode and a narrow band. Based on the above discussion, a compact L-band coaxial RBWO is investigated and optimized in detail with the particle-in-cell KARAT code (V. P. Tarakanov, Berkeley Research Associates, Inc., 1992). In simulation, the L-band coaxial RBWO, driven by a 700 kV, 11 kA electron beam, comes to a nonlinear steady state in 20 ns. High-power microwave of quasi-TEM mode is generated with an average power of 2.66 GW, a frequency of 1.6 GHz, and power conversion efficiency of 34.5% in durations of 30–60 ns.
Coupled azimuthal and radial flows and oscillations in a rotating plasma
Authors: Karimov A. R. , Stenflo L. , Yu M. Y.
Published: June 2009

Nonlinear coupling between the radial, axial, and azimuthal flows in a cold rotating plasma is considered nonperturbatively by first constructing a basis solution for a rotating flow. Simple but exact solutions that describe an expanding plasma with oscillatory flow fields are then obtained. These solutions show that the energy in the radial and axial flow components can be transferred to the azimuthal component but not the vice versa. Nonlinear electron velocity oscillations in the absence of electron density oscillations at the same frequency are shown to exist.
Electronic transport property of single-crystalline hexagonal tungsten trioxide nanowires
Authors: Wang S. J. , Lu W. J. , Cheng G. , Cheng K. , Jiang X. H. , Du Z. L.
Published: June 2009

Hexagonal WO3 nanowires were prepared on Si substrate by thermal evaporation of WO3 powder. A single WO3 nanowire was assembled on a pair of Pt electrodes by electric field assembly. The electrical transport behavior indicates that the back-to-back SBs structure is formed, which show nonlinear and asymmetric I-V properties. Through measurement of the I-V curve and the calculation of barrier height difference under illumination, it is found that the electrical asymmetry results from the asymmetric barrier height of the two Schottky barriers, which are dominated by the surface states of nanowire caused by O2 adsorption in the electric assembling process.
Change of the trap energy levels of the atomic layer deposited HfLaOx films with different La concentration
Authors: An Chee-Hong , Lee Myung Soo , Choi Ju-Yun , Kim Hyoungsub
Published: June 2009

Ultrathin HfO2 and HfLaOx films with La/(Hf+La) ratios of 42%, 57%, and 64% were synthesized with an atomic layer deposition process. By measuring the leakage current at different temperatures, the conduction mechanism of HfO2 and HfLaOx films was shown to follow the Poole–Frenkel emission model under a gate injection condition. Based on the temperature and field-dependence measurements, the intrinsic trap energy levels were found to be 1.42, 1.34, 1.03, and 0.98 eV for the HfLaOx samples with La/(Hf+La) ratios of 0%, 42%, 57%, and 64%, respectively, showing a decreasing behavior as the La content increased.
Probing misalignment in exchange biased systems: A dynamic approach
Authors: Le Graët C. , Spenato D. , Pogossian S. P. , Dekadjevi D. T. , Ben Youssef J.
Published: June 2009

An experimental method based on ferromagnetic resonance is proposed to quantify the misalignment between ferromagnetic and antiferromagnetic easy axis in exchange biased systems. Our experimental study deals with Ni81Fe19/Al2O3 and exchange biased Ni81Fe19/NiO bilayers. Performing ferromagnetic resonance studies, we demonstrate that the misalignment is present in the exchange biased system. It is revealed by an asymmetry of the resonance field angular dependence. Using a simple model, the angle of misalignment is determined.
Electronic structure characterization of La2NiMnO6 epitaxial thin films using synchrotron-radiation photoelectron spectroscopy and optical spectroscopy
Authors: Kitamura M. , Ohkubo I. , Matsunami M. , Horiba K. , Kumigashira H. , Matsumoto Y. , Koinuma H. , Oshima M.
Published: June 2009

Electronic structures of La2NiMnO6 epitaxial films are characterized using synchrotron-radiation photoelectron spectroscopy and optical spectroscopy. X-ray absorption spectra reveal that the valence states of Ni2+ and Mn4+ are dominant. The electronic structure at the valence band maximum is mainly derived from the Mn 3d state. The conduction band minimum is composed mostly of the Mn 3d-O 2p hybridized state. The optical gap is estimated to be about 1.5 eV based on the optical conductivity derived from optical spectra.
Enhanced exciton-phonon interactions in photoluminescence of ZnO nanopencils
Authors: Ahn Cheol Hyoun , Mohanta Sanjay Kumar , Lee Nae Eung , Cho Hyung Koun
Published: June 2009

We report enhanced exciton-phonon interactions in the photoluminescence (PL) of ZnO nanopencils compared with ZnO nanorods grown on ZnO/Si templates by thermal evaporation. Although the low temperature (<100 K) PL spectra of ZnO nanorods and nanopencils were dominated by the strong donor-bound exciton, the PL spectra at elevated temperatures (>100 K) showed dominant contributions from the free exciton emissions and phonon-replicas of free excitons for nanorods and nanopencils, respectively. This discrepancy in the behaviors of excitonic emissions of the ZnO nanorods and nanopencils was related to surface defects causing different strengths of exciton-phonon coupling. The different excitonic emissions of the nanorods and nanopencils revealed a 52 meV redshift in the room temperature PL of nanopencils.
Diamond Schottky-pn diode with high forward current density and fast switching operation
Authors: Makino Toshiharu , Tanimoto Satoshi , Hayashi Yusuke , Kato Hiromitsu , Tokuda Norio , Ogura Masahiko , Takeuchi Daisuke , Oyama Kazuhiro , Ohashi Hiromichi , Okushi Hideyo , Yamasaki Satoshi
Published: June 2009

We fabricated a diamond diode, namely a Schottky-pn diode (SPND), which is composed of a fully depleted n-type active layer sandwiched between a highly doped p-type layer and a Schottky metal layer. The SPND has superior characteristics that overcome the weak points of both a Schottky barrier diode and a pn diode. That is, the SPND showed high current density (over 4000 A/cm2) with low specific resistance (0.4 mΩ cm2) at a forward bias of 6 V while maintaining a high rectification ratio of ∼1010. Moreover, the SPND showed extremely fast turn-off speed of nanosecond order.
Morphology in semimagnetic Pb1−xMnxSe nanocrystals: Thermal annealing effects
Authors: Dantas N. O. , Silva R. S. , Pelegrini F. , Marques G. E.
Published: June 2009

Samples of Pb1−xMnxSe nanocrystals were synthesized by fusion method and characterized by optical absorption, atomic force microscopy, x-ray diffraction, and electron paramagnetic resonance (EPR) techniques. Effects of Mn2+ ion incorporation into PbSe nanocrystals are manifested by well resolved optical spectra for different concentrations of Mn. The EPR spectra of as grown and thermal annealed Pb1−xMnxSe samples show that the magnetic properties of these Mn-doped nanocrystals can be tuned by thermal processes using different annealing times.
Strong perpendicular magnetic anisotropy in Ni/Co(111) single crystal superlattices
Authors: Girod S. , Gottwald M. , Andrieu S. , Mangin S. , McCord J. , Fullerton Eric E. , Beaujour J.-M. L. , Krishnatreya B. J. , Kent A. D.
Published: June 2009

Single crystal Ni/Co(111) superlattices have been grown by molecular beam epitaxy. The Ni thickness is 3 ML whereas the Co thickness varies from 0.2 to 4 ML. The superlattices were studied using magnetometry and ferromagnetic resonance spectroscopy and they all exhibit strong perpendicular to the plane magnetic anisotropy. The maximum magnetocrystalline anisotropy is obtained for one cobalt monolayer. Kerr microscopy measurements show the variation of domain pattern as the Co layer thickness changes.
Prediction of the formation of stable periodic self-interstitial cluster chains [(I4)m,m=1–4] in Si under biaxial strain
Authors: Bondi Robert J. , Lee Sangheon , Hwang Gyeong S.
Published: June 2009

Using density functional theory calculations, we examined the structure and stability of extendable self-interstitial cluster configurations (In,n=12,16) with four-atom periodicity in crystalline silicon under biaxial strain (−4%≤ε≤4%) on Si(100). In the absence of strain, the ground state configurations of I12 and I16 share a common structure (I12-like) with C2h symmetry and a four-atom repeating unit; however, we identified an extended configuration based on I4 (D2d symmetry) cluster aggregates [(I4)m(m=3,4)] along ⟨110⟩ that is more favorable under certain magnitudes of strain. While both the I12-like and (I4)m configurations exhibit relative stabilities that are a function of both strain and orientation, the larger (I4)m orientation effect is the primary reason that these structures are preferred in both highly tensile and highly compressive environments. This suggests that I4 derivatives may participate in the growth transition of Si self-interstitial clusters in the compact-to-extended size regime (10≤n≤20) under strain.
Rectification of spin-bias-induced charge currents
Authors: Zhai Feng , Zhao Xiaofang , Xu H. Q.
Published: June 2009

When a spin bias is applied to a two-terminal device, a charge current will be generated. We demonstrate the rectification of such a current by studying spin-dependent transport through a quantum point contact (QPC) modulated by a spin-orbit interaction. When the polarization orientation of the spin bias (which is the spin-quantization axis) is along the transverse direction of the QPC, the two spin-conserved transmissions show a distinct variation with the incident energy. As a result, the charge current can turn from zero to a remarkable value by switching the spin bias from one lead to the other lead.
The influence of temperature and electric field on field emission energy distribution of an individual single-wall carbon nanotube
Authors: Wu Ping , Huang N. Y. , Deng S. Z. , Liang S. D. , Chen Jun , Xu N. S.
Published: June 2009

The influence of temperature and electric field on field emission energy distribution (FEED) is studied. It is found that higher temperature energizes more higher-energy electrons. FEED peaks shift toward low energy linearly with the increase in applied voltage because of the electric field penetration. The theoretic current-voltage characteristic is fitted to the experimental data by the density of states, field enhancement factor, and temperature, from which the average energy of emitted electrons and then Fermi level of the carbon nanotube (CNT) is ascertained. This research confirms that the electric field competes with temperature and provides a method to ascertain the Fermi level of CNT.
Nonlinear optical infrared microscopy with chemical specificity
Authors: Lee Eun Seong , Lee Jae Yong
Published: June 2009

We demonstrate a realization of nonlinear optical infrared microscopy that is capable of chemically specific imaging with high spatial resolution. It exploits the nonlinear refraction of the target material that is thermally induced by resonantly absorbed mid-infrared radiation and probed with a short wavelength near-infrared laser beam. The O–H and C–H2 vibrational modes in a water-oil mixture sample are selectively imaged at two different midinfrared wavelengths and the spatial resolution is measured to be 1.1 μm in the condition of numerical aperture 0.5, which is not attainable with conventional infrared microscopes.
Enhancement of field emission of the ZnO film by the reduced work function and the increased conductivity via hydrogen plasma treatment
Authors: You J. B. , Zhang X. W. , Cai P. F. , Dong J. J. , Gao Y. , Yin Z. G. , Chen N. F. , Wang R. Z. , Yan H.
Published: June 2009

The ZnO films deposited by magnetron sputtering were treated by H/O plasma. It is found that the field emission (FE) characteristics of the ZnO film are considerably improved after H-plasma treatment and slightly deteriorated after O-plasma treatment. The improvement of FE characteristics is attributed to the reduced work function and the increased conductivity of the ZnO:H films. Conductive atomic force microscopy was employed to investigate the effect of the plasma treatment on the nanoscale conductivity of ZnO, these findings correlate well with the FE data and facilitate a clearer description of electron emission from the ZnO:H films.
In situ passivation and blue luminescence of silicon clusters using a cluster beam/H2O codeposition production method
Authors: Brewer A. , von Haeften K.
Published: June 2009

Si clusters are produced in a gas aggregation source and fly through ultrahigh vacuum onto a cold target where they are codeposited with water vapor. Melting of the ice yields immediately a suspension of nanoparticles that emits intense, nondegrading luminescence in the blue wavelength range. Spectroscopic analysis reveals a Si/SiO core-shell structure where the luminescence stems from oxygen deficient defects. The main advantage of our production method is that it yields the luminescent Si nanoparticles in one step.
Thiol-based self-assembly nanostructures in promoting interfacial adhesion for copper-epoxy joint
Authors: Wong Cell K. Y. , Yuen Matthew M. F. , Xu Bing
Published: June 2009

Adhesion promotion between copper-epoxy interfaces without roughening the copper substrates is critical for new generation electronic devices. This paper demonstrates a pronounced adhesion promotion of a copper-epoxy joint from 4.8 J m−2 for the untreated samples to 159 J m−2 for the interfaces prepared with a thiol-based self-assembly molecular layer (SAM). The 33-fold improvement was related to the presence of nanostructures with the SAM treatment. The adhesion enhancement is attributed to both chemical bonding between copper and epoxy and the formation of nanosized features on copper substrates. The thiol promoter enhances the interfacial adhesion with no roughening of the substrates.
Surface tension of heavy water under high magnetic fields
Authors: Iino Masaaki , Fujimura Yuu
Published: June 2009

The surface tension of deuterium oxide-air interface was precisely measured under magnetic fields up to 10 T. The surface tension increased by 2.37±0.14 mN/m (3.30±0.19%) at 10 T. It was found that the surface tension increased linearly with an increase in the square of the magnetic field, the proportionality constant of which showed a marked isotope effect.
Vortex matching effect in engineered thin films of NbN
Authors: Thakur Ajay D. , Ooi Shuuichi , Chockalingam Subbaiah P. , Jesudasan John , Raychaudhuri Pratap , Hirata Kazuto
Published: June 2009

We report robust vortex matching effects in antidot arrays fabricated on thin films of NbN. The near absence of hysteresis between field sweep directions indicates a negligible residual pinning in the host thin films. Owing to the very small coherence length of NbN thin films (ξ<5 nm), the observations suggest the possibility of probing physics of vortices at true nanometer length scales in suitably fabricated structures.
Maximal energy that can be converted by a dielectric elastomer generator
Authors: Koh Soo Jin Adrian , Zhao Xuanhe , Suo Zhigang
Published: June 2009

Mechanical energy can be converted to electrical energy by using a dielectric elastomer generator. The elastomer is susceptible to various modes of failure, including electrical breakdown, electromechanical instability, loss of tension, and rupture by stretch. The modes of failure define a cycle of maximal energy that can be converted. This cycle is represented on planes of work-conjugate coordinates and may be used to guide the design of practical cycles.
Design of electron wave filters in monolayer graphene by tunable transmission gap
Authors: Chen Xi , Tao Jia-Wei
Published: June 2009

We have investigated the transmission in monolayer graphene barrier at nonzero angle of incidence. Taking the influence of parallel wave vector into account, the transmission as the function of incidence energy has a gap due to the evanescent waves in two cases of Klein tunneling and classical motion. The modulation of the transmission gap by the incidence angle, the height, and width of potential barrier may lead to potential applications in graphene-based electronic devices.
Dielectric relaxation and relaxor behavior in bilayered perovskites
Authors: González-Abreu Y. , Peláiz-Barranco A. , Araújo E. B. , Júnior A. Franco
Published: June 2009

Sr 0.5 Ba 0.5 Bi 2 Nb 2 O 9 ferroelectric ceramics exhibit a complex dielectric behavior, showing typical relaxor behavior. The relaxation processes are described by the Cole–Cole model [K. S. Cole and R. H. Cole, J. Chem. Phys. 9, 341 (1941)]. At temperatures below 490 K, the dielectric relaxation is associated to the relaxorlike ferroelectric behavior, resulting from the inhomogeneous distribution of barium due to its preference for the bismuth site. Above that, the interaction between the dipoles, which form the microdomains above the relaxor ferroelectric peak and the electrons, which are due to the ionization of the oxygen vacancies are discussed as the probable origin of the relaxation.
A theoretical study on thermoelectric properties of graphene nanoribbons
Authors: Ouyang Yijian , Guo Jing
Published: June 2009

We investigate the thermoelectric properties of graphene nanoribbons (GNRs) by solving atomistic electron and phonon transport equations in the nonequilibrium Green’s function formalism. The dependence of thermopower on temperature and chemical potential is compared to that of graphene, which shows the important role of quasi-one-dimensional geometry in determining the thermoelectric properties of a GNR. The edge roughness and lattice vacancy are found to increase the thermopower but decrease the thermoelectric ZT factor because the decrease in the electronic conductance outweighs the decrease in the thermal conductance and the increase in the thermopower.
Micromorphological evidence for mineral weathering pathways in a coastal acid sulfate soil sequence with Mediterranean-type climate, South Australia
Authors: Poch R. M. , Thomas B P. , Fitzpatrick R. W. , Merry R. H.
Published: June 2009

Soil micromorphology, using light microscopy and scanning electron microscopy (SEM), was used to describe detailed soil morphological and compositional changes and determine mineral weathering pathways in acid sulfate soils (ASS) from the following 2 contrasting coastal environments in Barker Inlet, South Australia: (i) a tidal mangrove forest with sulfidic material at St Kilda, and (ii) a former supratidal samphire area at Gillman that was drained in 1954 causing sulfuric material to form from sulfidic material. Pyrite framboids and cubes were identified in sulfidic material from both sites and are associated with sapric and hemic materials. Gypsum crystals, interpreted as a product of sulfide oxidation, were observed to have formed in lenticular voids within organic matter in the tidal mangrove soils at St Kilda. Sulfide oxidation was extensive in the drained soil at Gillman, evidenced by the formation of iron oxyhydroxide pseudomorphs (goethite crystallites and framboids) after pyrite and jarosite, and of gypsum crystals. Gypsum crystals occur where a local source of calcium such as shells or calcareous sand is present. Sporadic oxidation episodes are indicated by the formation of iron oxide and jarosite coatings around coarse biogenic voids. These observations indicate that mineral transformation pathways are strongly influenced by soil physico-chemical characteristics (i.e. oxidation rate, Eh, pH, soil solution chemistry, mineralogy, and spatial distribution of sulfides). This information has been used to illustrate the interrelationships of pyrite, carbonate, gypsum, jarosite, and organic matter and help predict soil evolution under changing hydro-geochemical, redoximorphic, and thermal conditions in soils from coastal environments.
Impact of soil conditions on hydrology and water quality for a brown clay in the north-eastern cereal zone of Australia
Authors: Freebairn D. M. , Wockner G. H. , Hamilton N. A. , Rowland P.
Published: June 2009

Hydrology and water quality impacts of alternative land management practices are poorly quantified for semi-arid environments in the northern Australia cropping zone, yet wide-scale changes in tillage practices and land use were being recommended based on experience from other environments.
The objective of this study was to explore changes in soil profile and catchment hydrology and water quality associated with different soil surface conditions created by different tillage and grazing practices. Soil water, runoff, and suspended sediment concentrations were monitored on 4 contour bay catchments over an 18-year period. Soil conditions were described by soil moisture, soil cover, and surface roughness in order to explore functional relationships between management, hydrology, and water quality. The site was chosen to represent the drier margins of cropping in southern Queensland where clay soils with high water-holding capacity, in conjunction with fallowing to store water for later crop growth, are an essential risk management tool.
Accumulation of soil water in fallows was inefficient, with fallow efficiencies ranging from –7 to 40% due to high evaporation and runoff losses. Runoff amount was determined by soil water content, which was strongly influenced by antecedent rainfall, water use, and evaporation patterns. Surface cover and roughness had subtle influences on runoff, and a greater effect on suspended sediment concentration. Runoff and suspended sediment losses were considerably lower under pasture than cropping.
A participative approach between farmers and scientists was demonstrated to be an efficient method to carry out an extensive and long-term catchment study at a remote location. This study provides benchmark data for future hydrologic and water quality investigations.
Diagnostic screening of urban soil contaminants using diffuse reflectance spectroscopy
Authors: Bray J. G. P. , Rossel R. Viscarra , McBratney A. B.
Published: June 2009

There is increasing demand for cheap and rapid screening tests for soil contaminants in environmental consultancies. Diffuse reflectance spectroscopy (DRS) in the visible-near infrared (vis-NIR) and mid infrared (MIR) has the potential to meet this demand. The aims of this paper were to develop diagnostic screening tests for heavy metals and polycyclic aromatic hydrocarbons (PAH) in soil using vis-NIR and MIR DRS. Cadmium, copper, lead, and zinc were analysed, as were total PAH and benzo[a]pyrene. An ordinal logistic regression technique was used for the screening and predictions of either contaminated or uncontaminated soil at different thresholds. We calculated the rates of false positive and false negative predictions and derived Receiver Operating Characteristic curves to explore how the choice of a threshold affects their proportion. Zinc and copper had the best prediction accuracies of the heavy metals, with 89% and 85%, respectively. Cadmium and lead had the lowest prediction accuracies, with 68% and 67%, respectively. PAH predictions averaged 78.9%. With an average prediction accuracy of 79.9%, MIR analysis was only slightly more accurate than vis-NIR analysis, which had an average prediction accuracy of 77.5%. However, vis-NIR may be used in situ, thereby reducing cost and time of analysis and providing diagnosis in ‘real-time’. DRS in the vis-NIR can substantially decrease both the time and cost associated with screening for soil contaminants.
Burning management and carbon sequestration of upland heather moorland in the UK
Authors: Farage Peter , Ball Andrew , McGenity Terry J. , Whitby Corinne , Pretty Jules
Published: June 2009

The use of fire in land management has come under increasing scrutiny with regard to its potential effects on sustainability and climate change. Moorlands in the United Kingdom have traditionally used rotational burning of the heather (Calluna vulgaris) to improve the grazing and habitat, especially for grouse (Lagopus lagopus scoticus). However, these ecosystems overlie carbon-rich soils and concerns have been raised about the merits of this practice. In order to assess the impact of rotational burning on carbon balance, an investigation was undertaken on a grouse moor in the Yorkshire Dales, UK. This showed that the quantity of carbon stored above ground in heather biomass ranged from 600 to 1325 g C/m2 (typical for UK upland heaths). However, the national UK carbon inventory assumes 200 g C/m2, thereby appearing to underestimate considerably the importance of these habitats for carbon storage above ground.
Analysis of 2 burns in subsequent years showed that 16 ± 4% and 24 ± 5% (± s.e.) of the above-ground material was consumed in the fires, resulting in the direct release of 103 ± 22 and 201 ± 62 g/m2 of carbon, respectively. Indirect carbon losses, which other studies have shown to be primarily due to erosion, were estimated to release another 5–21 g C/m2.year. The significance of other major greenhouse gas fluxes was assessed for the whole system using published parameters and models. We show that, over the burning cycle of 15–20 years, losses of carbon from burning are <10% of the total losses of carbon from the system, implying that careful burning management at this site does not have a major detrimental effect on the carbon budget, which for this moor lies within the range of an annual net loss of 34 g C/m2.year to a net uptake of 146 g C/m2.year.
Environmental and edaphic drivers of bacterial communities involved in soil N-cycling
Authors: Forbes M.S. , Broos K. , Baldock J.A. , Gregg A.L. , Wakelin S.A.
Published: June 2009

The cycling of N in soil is supported both directly and indirectly by numerous microbial processes. These processes affect ecosystem fertility, but can also generate forms of N which have detrimental environmental impacts, such as N2O. Understanding drivers of biological communities involved in key N-transformations is therefore of much interest. The effects of physicochemical and environmental properties on the relative size (abundance within total DNA pool) of biological communities involved in 3 key N transformations were investigated. Soils from 14 locations spanning a rainfall gradient across 3 agricultural regions (Clare, Mallee, Balaclava) were sampled, with samples taken from the surface and at depth from each site. Based on PCA of physicochemical and environmental properties, the soils fell into 2 distinct groupings: Clare and Mallee + Balaclava ‘types’. The abundance of functional genes involved in N2 fixation (nifH), ammonia oxidation (amoA), and nitrate reduction (narG) was quantified in DNA extracted from the soils using real-time PCR. The abundance of the nifH gene varied significantly with site (P = 0.03) but not depth, and no regional association with nifH gene abundance was found. Multivariate analysis indicated that the abundance of nifH was positively correlated with soil total C (ρ = 0.382; P = 0.006). Similarly, the abundance of narG varied with site (P < 0.001) and not soil depth. The abundance of narG was positively correlated with increasing rainfall (ρ = 0.417; P = 0.002). The abundance of amoA did not significantly vary between soils, but significantly decreased with soil depth (P = 0.006). The abundance of amoA was negatively correlated with soil electrical conductivity and positively with organic C (combined ρ = 0.44; P = 0.003). Whereas there was no relationship between the abundance of nifH and amoA or narG, the abundance of amoA was positively correlated with the abundance of narG (P < 0.001). These results indicate that the abundance of the N cycling genes is independently affected by different physicochemical or environmental properties. The interactions between soil, environment, and the functionally significant biological communities they support are complex. To gain fuller understanding of soil N cycling, the ecology of the various biological components affecting N-transformations must be investigated simultaneously.
Carbon storage in a Ferrosol under subtropical rainforest, tree plantations, and pasture is linked to soil aggregation
Authors: Richards Anna E. , Dalal Ram C. , Schmidt Susanne
Published: June 2009

Soil is a large sink for carbon (C), with the potential to significantly reduce the net increase in atmospheric CO2 concentration. However, we previously showed that subtropical tree plantations store less C into long-term soil pools than rainforest or pasture. To explore reasons for differences in C storage between different land-use systems, we examined the relationships between soil aggregation, iron and aluminium oxide and hydroxide content, and soil organic C (SOC) under exotic C4 pasture (Pennisetum clandestinum), native hoop pine (Araucaria cunninghamii) plantations, and rainforest. We measured SOC concentrations of water-stable and fully dispersed aggregates to assess the location of soil C. Concentrations of dithionite- and oxalate-extractable iron and aluminium were also determined to assess their role in SOC sequestration. Soil under rainforest and pasture contained more C in intra-aggregate particulate organic matter (iPOM, >53 μm) than hoop pine plantations, indicating that in rainforest and pasture, greater stabilisation of SOC occurred via soil aggregation. SOC was not significantly correlated with dithionite- and oxalate-extractable Fe and Al in these systems, indicating that sorption sites of Fe and Al oxides and hydroxides were saturated. We concluded that soil C under rainforest and pasture is stabilised by incorporation within soil aggregates, which results in greater storage of C in soil under pasture than plantations following land-use change. The reduced storage of C as iPOM in plantation soil contributes to the negative soil C budget of plantations compared with rainforest and pasture, even 63 years after establishment. The results have relevance for CO2 mitigation schemes based on tree plantations.
Linking social norms to efficient conservation investment in payments for ecosystem services
Authors: Chen Xiaodong , Lupi Frank , He Guangming , Liu Jianguo
Published: June 2009

An increasing amount of investment has been devoted to protecting and restoring ecosystem services worldwide. The efficiency of conservation investments, including payments for ecosystem services (PES), has been found to be affected by biological, political, economic, demographic, and social factors, but little is known about the effects of social norms at the neighborhood level. As a first attempt to quantify the effects of social norms, we studied the effects of a series of possible factors on people's intentions of maintaining forest on their Grain-to-Green Program (GTGP) land plots if the program ends. GTGP is one of the world's largest PES programs and plays an important role in global conservation efforts. Our study was conducted in China's Wolong Nature Reserve, home to the world-famous endangered giant pandas and >4,500 farmers. We found that, in addition to conservation payment amounts and program duration, social norms at the neighborhood level had significant impacts on program re-enrollment, suggesting that social norms can be used to leverage participation to enhance the sustainability of conservation benefits from PES programs. Moreover, our results demonstrate that economic and demographic trends also have profound implications for sustainable conservation. Thus, social norms should be incorporated with economic and demographic trends for efficient conservation investments.
Secretory phospholipase A2-IID is an effector molecule of CD4+CD25+regulatory T cells
Authors: von Allmen Caroline E. , Schmitz Nicole , Bauer Monika , Hinton Heather J. , Kurrer Michael O. , Buser Regula B. , Gwerder Myriam , Muntwiler Simone , Sparwasser Tim , Beerli Roger R. , Bachmann Martin F.
Published: June 2009

Suppression by natural CD4+CD25+regulatory T cells (Tregs) is one mechanism by which tolerance is maintained. However, the way in which Tregs mediate suppression is not well understood. Here, we show that secreted phospholipase A2 (sPLA2)-IID is selectively produced by Tregs. sPLA2-IID is a potent mediator of Treg function, because it strongly suppressed proliferation of CD4+and CD8+T cells in vitro and in vivo in a manner independent of its catalytic activity. Furthermore, sPLA2-IID promoted the differentiation of Tregs, presumably via attenuating signaling through the PI3K/Akt/mammalian target of rapamycin pathway. Importantly, administration of a sPLA2-IID-Fc fusion protein inhibited disease development in murine models of colitis and multiple sclerosis, suggesting that sPLA2-IID's immunosuppressive function might be exploited therapeutically.
The private rejection of unfair offers and emotional commitment
Authors: Yamagishi Toshio , Horita Yutaka , Takagishi Haruto , Shinada Mizuho , Tanida Shigehito , Cook Karen S.
Published: June 2009

In a series of experiments, we demonstrate that certain players of an economic game reject unfair offers even when this behavior
increases
rather than decreases inequity. A substantial proportion (30–40%, compared with 60–70% in the standard ultimatum game) of those who responded rejected unfair offers even when rejection reduced only their own earnings to 0, while not affecting the earnings of the person who proposed the unfair split (in an impunity game). Furthermore, even when the responders were not able to communicate their anger to the proposers by rejecting unfair offers in a
private
impunity game, a similar rate of rejection was observed. The rejection of unfair offers that
increases
inequity cannot be explained by the social preference for inequity aversion or reciprocity; however, it does provide support for the model of emotion as a commitment device. In this view, emotions such as anger or moral disgust lead people to disregard the immediate consequences of their behavior, committing them to behave consistently to preserve integrity and maintain a reputation over time as someone who is reliably committed to this behavior.
Biological consequences of earlier snowmelt from desert dust deposition in alpine landscapes
Authors: Steltzer Heidi , Landry Chris , Painter Thomas H. , Anderson Justin , Ayres Edward
Published: June 2009

Dust deposition to mountain snow cover, which has increased since the late 19
th
century, accelerates the rate of snowmelt by increasing the solar radiation absorbed by the snowpack. Snowmelt occurs earlier, but is decoupled from seasonal warming. Climate warming advances the timing of snowmelt and early season phenological events (e.g., the onset of greening and flowering); however, earlier snowmelt without warmer temperatures may have a different effect on phenology. Here, we report the results of a set of snowmelt manipulations in which radiation-absorbing fabric and the addition and removal of dust from the surface of the snowpack advanced or delayed snowmelt in the alpine tundra. These changes in the timing of snowmelt were superimposed on a system where the timing of snowmelt varies with topography and has been affected by increased dust loading. At the community level, phenology exhibited a threshold response to the timing of snowmelt. Greening and flowering were delayed before seasonal warming, after which there was a linear relationship between the date of snowmelt and the timing of phenological events. Consequently, the effects of earlier snowmelt on phenology differed in relation to topography, which resulted in increasing synchronicity in phenology across the alpine landscape with increasingly earlier snowmelt. The consequences of earlier snowmelt from increased dust deposition differ from climate warming and include delayed phenology, leading to synchronized growth and flowering across the landscape and the opportunity for altered species interactions, landscape-scale gene flow via pollination, and nutrient cycling.
Morphological record of oxygenic photosynthesis in conical stromatolites
Authors: Bosak Tanja , Liang Biqing , Sim Min Sub , Petroff Alexander P.
Published: June 2009

Conical stromatolites are thought to be robust indicators of the presence of photosynthetic and phototactic microbes in aquatic environments as early as 3.5 billion years ago. However, phototaxis alone cannot explain the ubiquity of disrupted, curled, and contorted laminae in the crests of many Mesoproterozoic, Paleoproterozoic, and some Archean conical stromatolites. Here, we demonstrate that cyanobacterial production of oxygen in the tips of modern conical aggregates creates contorted laminae and submillimeter-to-millimeter-scale enmeshed bubbles. Similarly sized fossil bubbles and contorted laminae may be present only in the crestal zones of some conical stromatolites 2.7 billion years old or younger. This implies not only that cyanobacteria built Proterozoic conical stromatolites but also that fossil bubbles may constrain the timing of the evolution of oxygenic photosynthesis.
Intraday LeBaron effects
Authors: Bianco Simone , Corsi Fulvio , Renò Roberto
Published: June 2009

We study the relation at intraday level between serial correlation and volatility of the Standard and Poor (S&P) 500 stock index futures returns. At daily and weekly levels, serial correlation and volatility forecasts have been found to be negatively correlated (LeBaron effect). After finding a significant attenuation of the original effect over time, we show that a similar but more pronounced effect holds by using intraday measures, by such as realized volatility and variance ratio. We also test the impact of unexpected volatility, defined as the part of volatility which cannot be forecasted, on the presence of intraday serial correlation in the time series by employing a model for realized volatility based on the heterogeneous market hypothesis. We find that intraday serial correlation is negatively correlated to volatility forecasts, whereas it is positively correlated to unexpected volatility.
Major flowering time gene,
FLOWERING LOCUS C
, regulates seed germination in
Arabidopsis thaliana
Authors: Chiang George C. K. , Barua Deepak , Kramer Elena M. , Amasino Richard M. , Donohue Kathleen
Published: June 2009

FLOWERING LOCUS C
(
FLC
) is a major regulator of flowering responses to seasonal environmental factors. Here, we document that
FLC
also regulates another major life-history transition-seed germination, and that natural variation at the
FLC
locus and in
FLC
expression is associated with natural variation in temperature-dependent germination.
FLC
-mediated germination acts through additional genes in the flowering pathway (
FT
,
SOC1
, and
AP1
) before involving the abscisic acid catabolic pathway (via
CYP707A2
) and gibberellins biosynthetic pathway (via
GA20ox1
) in seeds. Also,
FLC
regulation of germination is largely maternally controlled, with
FLC
peaking and
FT
,
SOC1
, and
AP1
levels declining at late stages of seed maturation. High
FLC
expression during seed maturation is associated with altered expression of hormonal genes (
CYP707A2
and
GA20ox1
) in germinating seeds, indicating that gene expression before the physiological independence of seeds can influence gene expression well after any physical connection between maternal plants and seeds exists. The major role of
FLC
in temperature-dependent germination documented here reveals a much broader adaptive significance of natural variation in
FLC
. Therefore, pleiotropy between these major life stages likely influences patterns of natural selection on this important gene, making
FLC
a promising case for examining how pleiotropy influences adaptive evolution.
Expected rate of fisheries-induced evolution is slow
Authors: Andersen Ken H. , Brander Keith
Published: June 2009

Commercial fisheries exert high mortalities on the stocks they exploit, and the consequent selection pressure leads to fisheries-induced evolution of growth rate, age and size at maturation, and reproductive output. Productivity and yields may decline as a result, but little is known about the rate at which such changes are likely to occur. Fisheries-induced evolution of exploited populations has recently become a subject of concern for policy makers, fisheries managers, and the general public, with prominent calls for mitigating management action. We make a general evolutionary impact assessment of fisheries by calculating the expected rate of fisheries-induced evolution and the consequent changes in yield. Rates of evolution are expected to be ≈0.1–0.6% per year, and the consequent reductions in fisheries yield are <0.7% per year. These rates are at least a factor of 5 lower than published values based on experiments and analyses of population time series, and we explain why the published rates may be overestimates. Dealing with evolutionary effects of fishing is less urgent than reducing the direct detrimental effects of overfishing on exploited stocks and on their marine ecosystems.
Kinetic theories of dynamics and persistent caging in a one-dimensional lattice gas
Authors: Abel Steven M. , Steve Tse Ying-Lung , Andersenb Hans C.
Published: June 2009

The one-dimensional, single-occupancy lattice gas exhibits highly cooperative particle motion and provides an interesting challenge for theoretical methods designed to describe caging in liquids. We employ this model in an effort to gain insight into caging phenomena in more realistic models of liquids, using a diagrammatic kinetic theory of density fluctuations to develop a series of approximations to the kinetic equations for the van Hove self-correlation function. The approximations are formulated in terms of the irreducible memory function, and we assess their efficacy by comparing their solutions with computer simulation results and the well-known subdiffusive behavior of a tagged particle at long times. The first approximation, a mode coupling theory, factorizes the 4-point propagators that contribute to the irreducible memory function into products of independent single-particle propagators. This approximation fails to capture the subdiffusive behavior of a tagged particle at long times. Analysis of the mode coupling approximation in terms of the diagrammatic kinetic theory leads to the development of two additional approximations that can be viewed as diagrammatic extensions or modifications of mode coupling theory. The first, denoted MC1, captures the long-time subdiffusive behavior of a tagged particle. The second, denoted MC2, captures the subdiffusive behavior of a tagged particle and also yields the correct amplitude of its mean square displacement at long times. Numerical and asymptotic solutions of the approximate kinetic equations share many qualitative and quantitative features with simulation results at all timescales.