bluuebunny/crossref_metadata_2025 huggingface dataset:
Court rules on U.S. Greenhouse Gas Regulation
Authors: Zielinski Sarah
Published: April 2007

The U.S. Supreme Court has ruled that greenhouse gases are ‘pollutants’ under the federal Clean Air Act and that the U.S. government has the authority to regulate them. Twelve states and several non‐profit organizations had sued the U.S. Environmental Protection Agency after EPA ruled in 2003 that it lacked authority to regulate greenhouse gas emissions from automobiles. The Court, in its 5‐4 ruling, objected to EPA's “laundry list of reasons not to regulate” greenhouse gases and said that EPA “offered no reasoned explanation for its refusal to decide whether greenhouse gases cause or contribute to climate change.” EPA was ordered to revisit its decision on regulating greenhouse gas emissions from automobiles. The full Court opinion on Massachusetts us. EPA is available at http://www.supremecourtus.gov/opinions/06pdf/05‐1120.pdf
Timing of peak oil uncertain
Authors: Zielinksi Sarah
Published: April 2007

According to the Hubbert peak theory, oil production in any geographic area will follow a bellshaped curve. The timing of the ‘peak’ in global oil production is important because after that point, there will be less and less oil available for consumption. A new report from the U.S. Government Accountability Office found that most studies estimate that peak oil production will occur sometime between now and 2040. The uncertainty in these estimates could be reduced with better information about worldwide supply and demand, and alternative fuels and transportation technologies could mitigate the effects of a global decline in oil production. However, the report found no coordinated U.S. federal strategy to address these issues. The report, “Uncertainty about Future Oil Supply Makes It Important to Develop a Strategy for Addressing a Peak and Decline in Oil Production,” is available at http://www.gao.gov/cgi‐bin/getrpt?GAO‐07‐283
Tsunami hits the Solomon Islands
Authors: Zielinski Sarah
Published: April 2007

A magnitude 8.1 earthquake shook the Solomon Islands on 1 April at approximately 7:40 A.M. local time. The earthquake generated a tsunami several meters high that struck many of the islands. The earthquake occurred along the boundary of the Pacific plate where the Australia, Woodlark, and Solomon Sea plates subduct beneath it, according to the U.S. Geological Survey's Earthquake Hazards Program. At least 34 people were killed by the tsunami and several dozen more are still missing, according to the National Disaster Council in the Solomon Islands. The NDC estimates that 900–2500 homes were destroyed by the tsunami, displacing about 5500 people
Outstanding student paper awards
Authors: Anonymous
Published: April 2007

The following members received Outstanding Student Paper Awards at the 2006 AGU Fall Meeting, in San Francisco, Calif Winners in other sections and focus groups will be announced in subsequent issues of Eos.
Tourism and Hospitality SME Training Needs and Provision: A Sub-Regional Analysis
Authors: Dewhurst Helen , Dewhurst Peter , Livesey Rachel
Published: April 2007

This paper contends that tourism destination competitiveness depends upon a viable community of small tourism and hospitality firms that often collectively represent the destination product. It is argued that the requirement for tourism destinations to deliver high-quality service and products, coupled with the labour intensive nature of the industry, results in a need for businesses to recruit and retain well-educated and well-trained professionals. The findings of a sub-regional research project that explored small tourism and hospitality firm attitudes to training and training provision are presented. It is concluded that, while there is a range of tailored training provision available to such firms, they perceive several key barriers to prevent them from fully engaging with this. In conclusion, it is suggested that it may be the ‘lifestyle’-oriented nature of many such firms that is the most fundamental determining factor in training orientation.
Expanding into Asia: The Human Resource Challenge
Authors: Doherty Liz , Klenert Anna , Manfredi Simonetta
Published: April 2007

This paper presents the main findings of a piece of research conducted for Compass Group plc. The main aim of the research was to identify sources of Asian graduates to manage Compass' expanding food service outlets in Asia and to support their broadly geocentric international strategy. The paper demonstrates that business-oriented English-speaking graduates are available in Asia, and also that Asian students (both business students and hospitality students) educated in the UK are very interested in working for Compass in Asia, provided that the benefits package is attractive enough and that career development routes are offered. The arguments for pursuing either a geocentric or a polycentric human resourcing strategy are discussed.
Enhanced magnetocaloric effect in single crystalline Nd0.5Sr0.5MnO3
Authors: Venkatesh R. , Pattabiraman M. , Sethupathi K. , Rangarajan G. , Narayana Jammalamadaka S.
Published: April 2007

The magnetocaloric effect in single crystalline Nd0.5Sr0.5MnO3 (NSMO 0.5) is investigated by computing the field dependent entropy change (ΔS) and adiabatic temperature change (ΔTad). At the charge ordering temperature (TCO), the value of ΔSmax is found to be much higher than ΔSmax reported in polycrystalline samples. This “giant” entropy change is attributed to interplay (stronger in single crystals) among spin, charge, lattice, and orbital degrees of freedom resulting in a field induced transition at TCO. In contrast, the change in entropy associated with Curie temperature (TC) is very low. The direct measurements of the field induced temperature change (ΔT) are in agreement with the computed value of ΔS. The presence of short-range correlations with charge/orbital order (COO) above and below TC may be responsible for the suppression of the negative MCE at TC. A critical exponent analysis of the paramagnetic (PM) to ferromagnetic (FM) transition using magnetization data yields mean-field-like values, which is likely to be operative in inhomogeneous systems such as NSMO 0.5 with correlated COO clusters larger than lattice parameter.
Electronic structures and magnetic properties of layered compound RCrSb3 (R=La,Yb)
Authors: Choi H. C. , Shim J. H. , Kwon S. K. , Min B. I.
Published: April 2007

R Cr Sb 3 (R: rare-earth ions) exhibits unconventional magnetic behaviors due to their layered structures and the complex interactions of Cr 3d and R 4f electrons. We have explored the electronic structures of LaCrSb3, YbCrSb3, and also LaVSb3 for a comparison by using the linearized muffin-tin orbital band method. For LaCrSb3 and LaVSb3, the rigid band model is well applicable to understanding their electronic and magnetic states. However, for LaCrSb3 and YbCrSb3, the extension of the rigid band model fails, because Yb ions in YbCrSb3 are in a divalent state of Yb2+ with fully occupied 4f bands, which differ from the trivalent La3+ in LaCrSb3.
Metamagnetic transitions in RFe2(H,D)4.2 compounds (R=Y,Tb)
Authors: Leblond T. , Paul-Boncour V. , Guillot M. , Isnard O.
Published: April 2007

The Tb for Y substitution in YFe2D4.2 leads to an increase of cell volume, a canted ferrimagnetic structure at low temperature, and a shift of the magnetovolumic transition temperature to higher value. The study of the structural and magnetic properties of TbFe2H4.2 and TbFe2D4.2 indicates a significant (H,D) isotope effect implying a larger cell volume and a higher transition temperature for the hydride compared to the deuteride.
Observation and identification of zonal flows in a basic plasma physics experiment
Authors: Sokolov V. , Wei X. , Sen A. K.
Published: April 2007

The role of self-generated zonal flows (ZF) in transport regulation in magnetic confinement devices via its shear is a potent concept and a physics issue [P. H. Diamond, S-I Itoh, K. Itoh, and T. S. Hahm, Plasma Phys. Controlled Fusion 47, R35 (2005)]. A basic physics experimental study of ZF associated with ITG (ion temperature gradient) drift modes has been performed in the Columbia Linear Machine [R. Scarmozzino, A. K. Sen, and G. A. Navratil, Phys. Rev. Lett. 57, 1729 (1986)]. The difficult problem of detection of ZF has been solved via a novel diagnostic using the paradigm of FM (frequency modulation) in radio transmission. Using this and discrete short time Fourier transform, a power spectrum peak was found at an ITG (“carrier”) frequency of ∼120kHz and FM sidebands at a frequency of ∼2kHz. ZF was definitively identified with azimuthal (poloidal) and axial (toroidal) symmetry (kθ≈0,k‖≈0) and radially inhomogeneous (kr≠0) flow structures in cylindrical plasmas. However, the stabilizing effect of ZF shear appears to be small and no significant isotopic effects are observed.
Influence of the Damköhler number on turbulence-scalar interaction in premixed flames. II. Model development
Authors: Chakraborty N. , Swaminathan N.
Published: April 2007

The modeling of Damköhler number, Da, effects on the interaction of turbulence and scalar fields in premixed flames is studied using two freely propagating statistically planar flames calculated by direct numerical simulation (DNS). One flame having Da>1 shows attributes of turbulent combustion in the corrugated flamelets regime while the other having Da<1 depicts characteristics of the thin reaction zones regime. The interaction process is characterized by the tensor inner product of the scalar and velocity gradients. It is found that the interaction process dissipates the scalar gradients in the Da>1 flame whereas it produces the scalar gradients in the Da<1 flame. It is argued and also shown that the Damköhler number dependence should explicitly appear in the models for the turbulence-scalar interaction in order to represent the above physics correctly. Simple unified models, in the Reynolds averaged Navier-Stokes (RANS) framework, for the interaction processes involving a local Damköhler number dependence are proposed and validated against the DNS data. The proposed models are shown to degenerate simply to passive scalar models when there are no chemical reactions in the flow or when the chemical reactions are passive. The predictions of these models are also compared to the values obtained using the models available in the literature. It is found that the explicit Da dependence is required to capture the DNS results correctly. Extension of the proposed RANS models to large eddy simulation is also discussed.
Experimental observations of instabilities in rotating plane Couette flow
Authors: Hiwatashi Kazuaki , Alfredsson P. H. , Tillmark Nils , Nagata M.
Published: April 2007

The transition from the two-dimensional (2D) longitudinal roll cell state to 3D flows in the rotating plane Couette system, predicted by the theoretical investigation [M. Nagata, J. Fluid Mech. 358, 357 (1998)], is examined experimentally. The streamwise and spanwise wave numbers of observed steady 3D flows seem to agree with those predicted by the theory when the rotation rate is relatively large. However, we observe unsteady 3D states in the region where the theory predicts stable steady 3D flows when the rotation rate is small.
Density functional theory analysis of the structural and electronic properties of TiO2 rutile and anatase polytypes: Performances of different exchange-correlation functionals
Authors: Labat Frédéric , Baranek Philippe , Domain Christophe , Minot Christian , Adamo Carlo
Published: April 2007

The two polymorphs of TiO2, rutile and anatase, have been investigated at the ab initio level using different Hamiltonians with all-electron Gaussian and projector augmented plane wave basis sets. Their equilibrium lattice parameters, relative stabilities, binding energies, and band structures have been evaluated. The calculations have been performed at the Hartree-Fock, density functional theory (DFT), and hybrid (B3LYP and PBE0) levels. As regards DFT, the local density and generalized gradient (PBE) approximations have been used. Our results show an excellent agreement with the experimental band structures and binding energies for the B3LYP and PBE0 functionals, while the best structural descriptions are obtained at the PBE0 level. However, no matter which Hamiltonian and method are used, anatase is found more stable than rutile, in contrast with recent experimental reports, although the relative stabilities of the two phases are very close to each other. Nevertheless, based on the overall results, the hybrid PBE0 functional appears as a good compromise to obtain an accurate description of both structural and electronic properties of solids.
Photonic superdiffusive motion in resonance line radiation trapping Partial frequency redistribution effects
Authors: Alves-Pereira A. R. , Nunes-Pereira E. J. , Martinho J. M. G. , Berberan-Santos M. N.
Published: April 2007

The relation between the jump length probability distribution function and the spectral line profile in resonance atomic radiation trapping is considered for partial frequency redistribution (PFR) between absorbed and reemitted radiation. The single line opacity distribution function [M. N. Berberan-Santos et al., J. Chem. Phys. 125, 174308 (2006)] is generalized for PFR and used to discuss several possible redistribution mechanisms (pure Doppler broadening; combined natural and Doppler broadening; and combined Doppler, natural, and collisional broadening). It is shown that there are two coexisting scales with a different behavior: the small scale is controlled by the intricate PFR details while the large scale is essentially given by the atom rest frame redistribution asymptotic. The pure Doppler and combined natural, Doppler, and collisional broadening are characterized by both small- and large-scale superdiffusive Lévy flight behaviors while the combined natural and Doppler case has an anomalous small-scale behavior but a diffusive large-scale asymptotic. The common practice of assuming complete redistribution in core radiation and frequency coherence in the wings of the spectral distribution is incompatible with the breakdown of superdiffusion in combined natural and Doppler broadening conditions.
Asymmetrically solvated anion with both kinetic and thermodynamic stabilities: Theoretical studies on the cluster anions (HF)n− (n=3–6)
Authors: Hao Xi-Yun , Xu Xin
Published: April 2007

At the level of MP2 with the aug-cc-pVDZ and aug-cc-pVTZ basis sets supplemented with diffuse bond functions, the authors searched the potential energy surfaces of (HF)n− (n=3–6). In accordance with the literature, they found that the symmetrically solvated-electron anion (3(FH){e}) possesses the largest vertical detachment energy (VDE), while the dipole-bound anion ((FH)3{e}) is the lowest isomer in energy for (HF)3−. Their calculations demonstrated that, with the increase of the cluster size, the asymmetric (FH)a{e}(HF)b cluster is stabilized with a simultaneously increased VDE. Thus they predicted that, for (HF)6−, the (FH)4{e}(HF)2 cluster is both kinetically and thermodynamically most stable, possessing the largest VDE and being the global minimum at the same time.
Surface plasmon enhanced photoluminescence of conjugated polymers
Authors: Park Hong-Ju , Vak Doojin , Noh Yong-Young , Lim Bogyu , Kim Dong-Yu
Published: April 2007

To produce surface plasmons, silver nanostructures were fabricated using a thermal evaporation method and the surface plasmon wavelength was tuned via an annealing. These nanostructures were located between the indium tin oxide (ITO) and poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate) for the coupling of the surface plasmon resonance with organic fluorophores. To prevent the quenching of emission, spacer was placed between the light emitting polymers and the ITO substrate. As a result, the authors were able to observe an increase in photoluminescence of conjugated polymers using the silver nanostructures.
Experimental determination of the band gap dependence of Auger recombination in InGaAs∕InP multiple quantum well lasers at room temperature
Authors: Massé N. F. , Adams A. R. , Sweeney S. J.
Published: April 2007

The band gap dependencies of the threshold current and its radiative component are measured using high pressure techniques. Detailed theoretical calculations show that the band gap dependence of the internal losses plays a significant role in the band gap dependence of the radiative current. Temperature dependence measurements show that the radiative current accounts for 20% of the total threshold current at room temperature. This allows us to determine the pressure dependence of the non-radiative Auger recombination current, and hence to experimentally obtain the variation of the Auger coefficient C with band gap.
High electron mobility InN
Authors: Jones R. E. , Li S. X. , Haller E. E. , van Genuchten H. C. M. , Yu K. M. , Ager J. W. , Liliental-Weber Z. , Walukiewicz W. , Lu H. , Schaff W. J.
Published: April 2007

Irradiation of InN films with 2MeV He+ ions followed by thermal annealing below 500°C creates films with high electron concentrations and mobilities, as well as strong photoluminescence. Calculations show that electron mobility in irradiated samples is limited by triply charged donor defects. Subsequent thermal annealing removes a fraction of the defects, decreasing the electron concentration. There is a large increase in electron mobility upon annealing; the mobilities approach those of the as-grown films, which have 10 to 100 times smaller electron concentrations. Spatial ordering of the triply charged defects is suggested to cause the unusual increase in electron mobility.
Polarized laser emission from an anisotropic one-dimensional photonic crystal laser
Authors: Kim Sun Woong , Park Byoungchoo , Lee Y. P.
Published: April 2007

The authors studied the laser emission from an anisotropic one-dimensional (1D) photonic crystal (PC) laser. An active medium layer, consisted of an epoxy resin doped with fluorescent dye, was sandwiched between two anisotropic 1D PC films. Efficient laser emissions were generated by optical pumping at relatively low lasing thresholds. The wavelengths of the emitted lasers were 611 and 618nm, which correspond to the two split eigenmodes at the low-energy band edges due to the anisotropy of the PCs. The authors also demonstrated that the polarization of the lasing emission can be controlled by adjusting the birefringence of the PCs.
Hole escape processes detrimental to photoluminescence efficiency in a blue InGaN multiple-quantum-well diode under reverse bias conditions
Authors: Inoue T. , Fujiwara K. , Sheu J. K.
Published: April 2007

Photoluminescence (PL) properties of a blue In0.3Ga0.7N multiple-quantum-well (MQW) diode with an additional n+-doped In0.18Ga0.82N electron reservoir layer (ERL) have been investigated at 20K as a function of reverse bias under indirect barrier excitation. A PL intensity ratio of MQW/ERL is observed to be significantly quenched by increasing the reverse field due to electron-hole separation and carrier escape, in spite of observed blueshifts, when the excitation power is decreased by two orders of magnitude. The PL intensity reduction suggests that the hole escape process plays an important role for determination of the PL efficiency under the reverse bias.
Low-energy linear oxygen plasma source
Authors: Anders André , Yushkov George Yu.
Published: April 2007

A new version of a constricted plasma source is described, characterized by all metal-ceramic construction, a linear slit exit of 180mm length, and cw operation (typically 50kHz) at an average power of 1.5kW. The plasma source is here operated with oxygen gas, producing streaming plasma that contains mainly positive molecular and atomic ions, and to a much lesser degree, negative ions. The maximum total ion current obtained was about 0.5A. The fraction of atomic ions reached more than 10% of all ions when the flow rate was less then 10SCCM O2, corresponding to a chamber pressure of about 0.5Pa for the selected pumping speed. The energy distribution functions of the different ion species were measured with a combined mass spectrometer and energy analyzer. The time-averaged distribution functions were broad and ranged from about 30to90eV at 200kHz and higher frequencies, while they were only several eV broad at 50kHz and lower frequencies, with the maximum located at about 40eV for the grounded anode case. This maximum was shifted down to about 7eV when the anode was floating, indicating the important role of the plasma potential for the ion energy for a given substrate potential. The source could be scaled to greater length and may be useful for functionalization of surfaces and plasma-assisted deposition of compound films.
Fast fragmentation of metal oxide nanoparticles via reduction in oxyhydrogen flame
Authors: Pikhitsa Peter V. , Choi Mansoo , Yang Sangsun , Kim Jae-Young , Jang Hoyoung , Park Jae-Hoon
Published: April 2007

Fast fragmentation of 20nm iron oxide and 60nm tin oxide nanoparticles into a few nanometer nanoparticles in a diffusion oxyhydrogen flame is reported. The phenomenon is explained by the in situ reduction of generated 20–60nm nanoparticles. The fragmentation occurs due to reduction induced instability in the oxygen-deficient surface. Simulated experiments with electron irradiation and characterization with x-ray absorption spectroscopy substantiated this mechanism. This finding may open a route to continuously generate a few nanometer scale nanoparticles of various oxides in a flame synthesis.
Ultrahigh finesse Fabry-Pérot superconducting resonator
Authors: Kuhr S. , Gleyzes S. , Guerlin C. , Bernu J. , Hoff U. B. , Deléglise S. , Osnaghi S. , Brune M. , Raimond J.-M. , Haroche S. , Jacques E. , Bosland P. , Visentin B.
Published: April 2007

The authors have built a microwave Fabry-Pérot resonator made of diamond-machined copper mirrors coated with superconducting niobium. Its damping time (Tc=130ms at 51GHz and 0.8K) corresponds to a finesse of 4.6×109, the highest ever reached for a Fabry-Pérot in any frequency range. This result opens many perspectives for quantum information processing, decoherence and nonlocality studies.
Operation of nanosilicon ballistic electron emitter in liquid water and hydrogen generation effect
Authors: Koshida Nobuyoshi , Ohta Toshiyuki , Gelloz Bernard
Published: April 2007

The usefulness of the ballistic emitter in liquid has been studied for nanocrystalline silicon (nc-Si) diode. Here the authors show that the nc-Si ballistic emitter operates well in liquid water, and that hydrogen gas is produced from the device surface only by electron incidence into water without using any counterelectrodes. The mechanism of direct hydrogen generation is discussed in relation to the interaction between energy-tunable hot electrons and water. The present result develops a concept of electron emission device as an active electrode in liquid. Advantageous features and the usefulness of this effect are also addressed.
Effects of alloy intermixing on the lateral confinement potential in InAs∕GaAs self-assembled quantum dots probed by intersublevel absorption spectroscopy
Authors: Zibik E. A. , Ng W. H. , Wilson L. R. , Skolnick M. S. , Cockburn J. W. , Gutierrez M. , Steer M. J. , Hopkinson M.
Published: April 2007

The effect of thermal annealing on the conduction band states in self-assembled quantum dots has been investigated using far-infrared absorption spectroscopy. Broadening of the absorption linewidth associated with the ground state (s) to first excited state (p) transitions indicates that annealed quantum dots become less uniform in the lateral direction but more uniform in the growth direction as evidenced by photoluminescence measurements. A significant decrease in the s to p transition energy and the p-state splitting has been observed upon annealing. The avoided crossing as the transition energy approaches the optical phonon energy provides evidence of strong electron-phonon coupling in quantum dots.
Tetracene air-gap single-crystal field-effect transistors
Authors: Xia Yu , Kalihari Vivek , Frisbie C. Daniel , Oh Nam K. , Rogers John A.
Published: April 2007

The authors report the fabrication and characterization of tetracene single-crystal field-effect transistors (FETs) utilizing an air or vacuum gap as the gate dielectric. The linear mobility of the device can be as high as 1.6cm2∕Vs in air, with a subthreshold slope lower than 0.5VnF∕decadecm2. By changing the orientation of the same crystal on the air-gap substrate, surface charge transport along different crystallographic directions was measured. There is pronounced anisotropy in the mobility; temperature dependent measurements show the mobility is activated (in contrast to air-gap FETs based on rubrene) and that the activation energy is independent of transport direction. Gate electrode displacement current was also recorded for these devices, allowing accurate determination of the gate induced surface charge and the fraction of trapped charge.
Imaging current flow in lobster nerve cord using the acoustoelectric effect
Authors: Witte Russell , Olafsson Ragnar , Huang Sheng-Wen , O’Donnell Matthew
Published: April 2007

Ultrasound traversing a biologic fluid or tissue generates a local change in electrical conductivity known as the acoustoelectric effect. The authors exploit this interaction to image ionic current injected into the abdominal segment of the lobster nerve cord. A pair of recording electrodes detected the acoustoelectric signal induced by pulses of focused ultrasound (1.4 or 7.5MHz). The signal was linear with injected current at 2MPa (0.7μV∕mAcm2) and pressure at 75mA∕cm2 (23μV∕MPa). Acoustoelectric imaging of biocurrents potentially enhances spatial resolution of traditional electrophysiology and merits further study as an imaging modality for neural applications.
Carrier-envelope phase stabilized 5.6fs, 1.2mJ pulses
Authors: Mashiko Hiroki , Nakamura Christopher M. , Li Chengquan , Moon Eric , Wang He , Tackett Jason , Chang Zenghu
Published: April 2007

The authors report the generation of 1.2mJ pulses with a duration of 5.6fs from a neon filled hollow-core fiber seeded with carrier-envelope phase stabilized 2.2mJ, 25fs pulses. The carrier-envelope phase after the fiber was measured by a second, out-loop f-to-2f interferometer. With seed pulse power locked, the carrier-envelope phase of the two-cycle pulses is controlled to a standard deviation of 370mrad. The peak power of the carrier-envelope phase stabilized pulses, 0.2TW, is twice that previously generated. The significance of seed pulse energy stability for carrier-envelope phase stabilization of few-cycle laser pulses is demonstrated.
Al
x
Ga
1
−
x
N
-based avalanche photodiodes with high reproducible avalanche gain
Authors: Tut Turgut , Gokkavas Mutlu , Inal Ayse , Ozbay Ekmel
Published: April 2007

The authors report high performance solar-blind photodetectors with reproducible avalanche gain as high as 1560 under ultraviolet illumination. The solar-blind photodetectors have a sharp cutoff around 276nm. The dark currents of the 40μm diameter devices are measured to be lower than 8fA for bias voltages up to 20V. The responsivity of the photodetectors is 0.13A∕W at 272nm under 20V reverse bias. The thermally limited detectivity is calculated as D*=1.4×1014cmHz1∕2W−1 for a 40μm diameter device.
Focused-ion-beam-directed nucleation of InAs quantum dots
Authors: McKay H. A. , Dehne A. , Lee J. Y. , Millunchick J. M.
Published: April 2007

GaAs buffer layers were patterned with Ga+ ions via a focused ion beam and then overgrown with InAs. Atomic force microscopy reveals a strong influence of the ion dose upon subsequent formation of InAs quantum dots. Uniformly dosed areas show an apparent reduction in the critical thickness for quantum dot formation and the area density of the dots increases with increasing ion dose, which is related to ion beam induced roughening of the surface.
Improving gold phytoextraction in desert willow (Chilopsis linearis) using thiourea: a spectroscopic investigation
Authors: Rodríguez Elena , Peralta-Videa José R. , Sánchez-Salcido Blanca , Parsons Jason G. , Romero Jaime , Gardea-Torresdey Jorge L.
Published: April 2007

Environmental context. The conventional methods used for the extraction of gold from mine tailings and runoff are costly and often require harsh chemical treatment. Using plants to extract gold is more environmentally friendly and economically feasible. Plants are especially appealing because they can uptake low levels of gold and accumulate them in their tissues, whereas conventional methods are less effective at extracting gold at low levels. Thiourea has been proposed as an alternative gold chelator that could help in gold phytomining. It is less toxic than cyanide, which is the chemical commonly used to dissolve gold from mine ores. Abstract. Phytomining, the use of plants to recover noble metals, is developing as a feasible option to extract gold from mine tailings. In this study, thiourea (TU) was used to increase gold availability and to enhance gold accumulation by the desert plant Chilopsis linearis. Seedlings of C. linearis were grown in a hydroponic solution containing 25 μM Au and TU at 25, 50, 100, 200, and 400 μM. After two weeks of growth, the concentration of Au, micro- and macronutrients was determined using inductively coupled plasma–optical emission spectroscopy. In addition, X-ray absorption spectroscopy was used to determine the oxidation state and the coordination of the Au atom within the plant tissues. The effect of TU on plant growth was determined as well. The results of the present study demonstrated that TU at 25 μM was able to increase the Au uptake by C. linearis plants grown in hydroponics without any toxic effect. However, the translocation to stem and leaves was better at 100 and 200 μM of TU, respectively. The addition of TU to hydroponic solutions did not affect the uptake of Ca, Mg, P, and K. However, TU induced an increase in uptake of S, Fe, Cu, and Zn and a decrease in Mn uptake. When Au was chelated with TU, the plant transformed 64% of the Au–TU complex to Au(0) and the other 36% remained in the ionic form.
Stability constants for metal arsenates
Authors: Lee Janice S. , Nriagu Jerome O.
Published: April 2007

Environmental context. The behaviour of arsenic compounds is controlled by their solubility, which in turn controls both the forms and mobility of arsenic in the environment. Current knowledge on arsenic chemistry may be distorted because information available on the solubility of arsenic compounds usually does not include possible formation of metal–arsenate complexes. Our results show the formation of stable metal–arsenate complexes that have not been considered before, and this new data can be used to further examine the effect of these complexes on controlling the fate and transport of arsenic in the environment.
Abstract. The formation of solid metal arsenates could conceivably reduce the concentrations of arsenate and metal ions in natural and contaminated aqueous ecosystems, and possibly in human body fluids. In this study, solid metal arsenates were dissolved isothermally in solutions with different molar concentrations of arsenic acid. The saturated solutions were analysed and the results processed to derive the solubility products (Ksp) for solid phases and association constants (K) for metal arsenate ion-pairs. Ion chromatography was used to confirm the presence of ion-pairs, some of which had never before been considered. Association constants were determined for the following ion-pairs: FeHAsO4+ (log K = 4.88), CoHAsO40 (log K = 1.50), ZnHAsO40 (log K = 3.28), SrH2AsO4+ (log K = 1.72), and Ag2H2AsO4+ (log K = 4.50). The following metal ions apparently do not form stable complexes with HAsO42–: Cd2+, Cr3+, Cu2+, Mg2+, Mn2+, Ni2+, Pb2+, and Sn2+. Standard state solubility products (Ksp°) were redetermined for the following compounds: Ag3AsO4, Cd3(AsO4)2, Co3(AsO4)2, CrAsO4, Cu3(AsO4)2, FeAsO4, Mg3(AsO4)2, MnHAsO4, NiHAsO4, PbHAsO4, Sn3(AsO4)2, Sr3(AsO4)2, Zn3(AsO4)2·Zn3(AsO4)2·8H2O (koettigite), Cu2Al7(AsO4)4(OH)13·12H2O (ceruleite), and Pb2CuAsO4CrO4OH (fornacite). Our results show the formation of ion-pairs for some metal arsenates and indicate that previous studies have overestimated the solubilities of many arsenates.
Performance of a new diffusive sampler for Hg0 determination in the troposphere
Authors: Skov Henrik , Sørensen Britt T. , Landis Matthew S. , Johnson Matthew S. , Sacco Paolo , Goodsite Michael E. , Lohse Christian , Christiansen Kenneth S.
Published: April 2007

Environmental context. Mercury is of concern to both the public and to the scientific community because it is found at high levels in some marine predators, prompting the US EPA and others to make guidelines restricting the consumption of some species. Most mercury in the environment is emitted to the atmosphere, but it is not known how it is transferred from the atmosphere to the marine environment. Therefore, it is important to study the connection between emission of mercury, its transport and removal from the atmosphere. We have developed a new sampler that is inexpensive, easy to use and with a sufficiently high detection limit that it can be used to measure the low mercury concentrations in the atmosphere at a reasonable time resolution.
Abstract. Mercury behaves uniquely in the atmosphere due to its volatility and long lifetime. The existing methods for measuring atmospheric mercury are either expensive or labour intensive. The present paper presents a new measurement technique, the diffusive sampler, that is portable, inexpensive, easy to use, and does not need a power supply. The sampler is sufficiently sensitive that it can measure mercury at low ambient levels with an exposure time of 1 to 3 days. The sampler is based on the Radiello diffusive sampler, which was used to collect volatile organic compounds. In the present paper, the method is validated under controlled laboratory conditions. The uptake rate of the Radiello diffusive sampler is determined using known concentrations of gaseous elemental mercury, and is measured as a function of wind speed, relative humidity and temperature. The Radiello sampler has a detection limit of 0.14 ng m–3 for 1 day of exposure and thus can be used to measure mercury concentrations at the low levels found in ambient air. The Radiello sampler is therefore useful for mapping concentrations close to sources and sinks, in addition to ambient concentrations. For example, the sampler can be used to describe the geographical extent of Arctic mercury depletion episodes where gaseous elemental mercury is removed and stays close to 0 ng m–3 for days, and it can be a powerful tool for mapping gradients around point sources and other areas of interest.
Distinct contribution of electrostatics, initial conformational ensemble, and macromolecular stability in RNA folding
Authors: Laederach Alain , Shcherbakova Inna , Jonikas Magdalena A. , Altman Russ B. , Brenowitz Michael
Published: April 2007

We distinguish the contribution of the electrostatic environment, initial conformational ensemble, and macromolecular stability on the folding mechanism of a large RNA using a combination of time-resolved “Fast Fenton” hydroxyl radical footprinting and exhaustive kinetic modeling. This integrated approach allows us to define the folding landscape of the L-21
Tetrahymena thermophila
group I intron structurally and kinetically from its earliest steps with unprecedented accuracy. Distinct parallel pathways leading the RNA to its native form upon its Mg
2+
-induced folding are observed. The structures of the intermediates populating the pathways are not affected by variation of the concentration and type of background monovalent ions (electrostatic environment) but are altered by a mutation that destabilizes one domain of the ribozyme. Experiments starting from different conformational ensembles but folding under identical conditions show that whereas the electrostatic environment modulates molecular flux through different pathways, the initial conformational ensemble determines the partitioning of the flux. This study showcases a robust approach for the development of kinetic models from collections of local structural probes.
Cyanobacterial clock, a stable phase oscillator with negligible intercellular coupling
Authors: Amdaoud M. , Vallade M. , Weiss-Schaber C. , Mihalcescu I.
Published: April 2007

Accuracy in cellular function has to be achieved despite random fluctuations (noise) in the concentrations of different molecular constituents inside and outside the cell. The circadian oscillator in cyanobacteria is an example of resilience to noise. This resilience could be either the consequence of intercellular communication or the intrinsic property of the built-in biochemical network. Here we investigate the intercellular coupling hypothesis. A short theoretical depiction of interacting noisy phase oscillators, confirmed by numerical simulations, allows us to discriminate the effect of coupling from noise. Experimentally, by studying the phase of concurrent populations of different initial phases, we evaluate a very small upper limit of the intercellular coupling strength. In addition,
in situ
entrainment experiments confirm our ability to detect a coupling of the circadian oscillator to an external force and to describe explicitly the dynamic change of the mean phase. We demonstrate, therefore, that the cyanobacterial clock stability is a built-in property as the intercellular coupling effect is negligible.
Complex spatial group patterns result from different animal communication mechanisms
Authors: Eftimie R. , de Vries G. , Lewis M. A.
Published: April 2007

We present previously undescribed spatial group patterns that emerge in a one-dimensional hyperbolic model for animal group formation and movement. The patterns result from the assumption that the interactions governing movement depend not only on distance between conspecifics, but also on how individuals receive information about their neighbors and the amount of information received. Some of these patterns are classical, such as stationary pulses, traveling waves, ripples, or traveling trains. However, most of the patterns have not been reported previously. We call these patterns zigzag pulses, semizigzag pulses, breathers, traveling breathers, and feathers.
Reevolution of sexuality breaks Dollo's law
Authors: Domes Katja , Norton Roy A. , Maraun Mark , Scheu Stefan
Published: April 2007

The dominance of sexual reproduction is still an unresolved enigma in evolutionary biology. Strong advantages of sex have to exist, because only a few parthenogenetic taxa persist over evolutionary timescales. Oribatid mites (Acari) include outstanding exceptions to the rule that parthenogenetically reproducing taxa are of recent origin and doomed to extinction. In addition to the existence of large parthenogenetic clusters in oribatid mites, phylogenetic analyses of this study and model-based reconstruction of ancestral states of reproduction imply that Crotoniidae have reevolved sexuality from parthenogenetic ancestors within one of those clusters. This reversal in reproductive mode is unique in the animal kingdom and violates Dollo's law that complex ancestral states can never be reacquired. The reevolution of sexuality requires that ancestral genes for male production are maintained over evolutionary time. This maintenance likely is true for oribatid mites because spanandric males exist in various species, although mechanisms that enable the storage of genetically ancestral traits are unclear. Our findings present oribatid mites as a unique model system to explore the evolutionary significance of parthenogenetic and sexual reproduction.
Stepwise formation of the bacterial flagellar system
Authors: Liu Renyi , Ochman Howard
Published: April 2007

Elucidating the origins of complex biological structures has been one of the major challenges of evolutionary studies. The bacterial flagellum is a primary example of a complex apparatus whose origins and evolutionary history have proven difficult to reconstruct. The gene clusters encoding the components of the flagellum can include >50 genes, but these clusters vary greatly in their numbers and contents among bacterial phyla. To investigate how this diversity arose, we identified all homologs of all flagellar proteins encoded in the complete genome sequences of 41 flagellated species from 11 bacterial phyla. Based on the phylogenetic occurrence and histories of each of these proteins, we could distinguish an ancient core set of 24 structural genes that were present in the common ancestor to all Bacteria. Within a genome, many of these core genes show sequence similarity only to other flagellar core genes, indicating that they were derived from one another, and the relationships among these genes suggest the probable order in which the structural components of the bacterial flagellum arose. These results show that core components of the bacterial flagellum originated through the successive duplication and modification of a few, or perhaps even a single, precursor gene.
The same genomic region conditions clonal deletion and clonal deviation to the CD8αα and regulatory T cell lineages in NOD versus C57BL/6 mice
Authors: Holler Phillip D. , Yamagata Tetsuya , Jiang Wenyu , Feuerer Markus , Benoist Christophe , Mathis Diane
Published: April 2007

Clonal deviation is a mechanism by which immature thymocytes expressing a self-reactive T cell antigen receptor (TCR) are rescued from clonal deletion by adopting an alternative differentiation pathway resistant to apoptosis. Here, we confirm and generalize previous indications that genetic alleles in NOD mice condition ineffective clonal deviation toward the CD8αα lineage, a peculiar population of TCRαβ lymphocytes that electively colonizes the intraepithelial lymphocyte pool in the gut. Thymic selection of CD8αα cells was very age-dependent, occurring almost exclusively in the postnatal period. Fewer CD8αα cells were found in the thymus and intraepithelial lymphocytes of BDC2.5 TCR transgenic mice on the NOD than on the C57BL/6 (B6) background; this paucity extended to standard NOD mice, albeit to a lesser extent. CD8αα cells resided in the BDC2.5 pancreatic infiltrate, and they were more abundant on the B6 than the NOD background, correlating with aggressivity of the lesion. A (B6g7× NOD)F2intercross in agonist-challenged BDC2.5 fetal thymic organ cultures demonstrated the existence of a major quantitative trait locus on chromosome 3, coincident with an interval associated with resistance to clonal deletion. A replicate linkage confirmed these positions and showed that the same region also controls clonal deviation toward the CD4+FoxP3+regulatory T cell lineage. That clonal deviation toward the CD8αα and regulatory T cell pathways share genetic control further highlights the similarities between these two “rescue lineages,” consistent with an immunoregulatory role for CD8αα cells.
Network of general and specialty J protein chaperones of the yeast cytosol
Authors: Sahi Chandan , Craig Elizabeth Anne
Published: April 2007

J proteins are obligate cochaperones of Hsp70s, stimulating their ATPase activity and thus allowing them to function in multiple cellular processes. In most cellular compartments, an Hsp70 works with multiple, structurally divergent J proteins. To better understand the functional specificity of J proteins and the complexity of the Hsp70:J protein network, we undertook a comprehensive analysis of 13 J proteins of the cytosol of the yeast
Saccharomyces cerevisiae
. Phenotypes caused by the absence of four proteins, Sis1, Jjj1, Jjj3, and Cwc23, could not be rescued by overexpression of any other cytosolic J protein, demonstrating the distinctive nature of J proteins. In one case, that of Zuo1, the phenotypic effects of the absence of a J protein could be rescued by overexpression of only one other J protein, Jjj1, which, like Zuo1, is ribosome-associated. In contrast, the severe growth phenotype caused by the absence of the cytosol's most abundant J protein, Ydj1, was substantially rescued by expression of J domain-containing fragments of many cytosolic J proteins. We conclude that many functions of Hsp70 chaperone machineries only require stimulation of Hsp70's ATPase activity by J protein partners. However, a subset of Hsp70 functions requires specific J protein partners, likely demanding either sublocalization within the compartment or binding to specific client proteins.
miR-150, a microRNA expressed in mature B and T cells, blocks early B cell development when expressed prematurely
Authors: Zhou Beiyan , Wang Stephanie , Mayr Christine , Bartel David P. , Lodish Harvey F.
Published: April 2007

MicroRNAs (miRNAs) are a family of ≈22-nt noncoding RNAs that can posttranscriptionally regulate gene expression. Several miRNAs are specifically expressed in hematopoietic cells. Here we show that one such miRNA, miR-150, is mainly expressed in the lymph nodes and spleen and is highly up-regulated during the development of mature T and B cells; expression of miR-150 is sharply up-regulated at the immature B cell stage. Overexpression of miR-150 in hematopoietic stem cells, followed by bone marrow transplantation, had little effect on the formation of either mature CD8- and CD4-positive T cells or granulocytes or macrophages, but the formation of mature B cells was greatly impaired. Furthermore, premature expression of miR-150 blocked the transition from the pro-B to the pre-B stage. Our results indicate that miR-150 most likely down-regulates mRNAs that are important for pre- and pro-B cell formation or function, and its ectopic expression in these cells blocks further development of B cells.
Identification of a novel functional specificity signal within the GPI anchor signal sequence of carcinoembryonic antigen
Authors: Nicholson Thomas B. , Stanners Clifford P.
Published: April 2007

Exchanging the glycophosphatidylinositol (GPI) anchor signal sequence of neural cell adhesion molecule (NCAM) for the signal sequence of carcinoembryonic antigen (CEA) generates a mature protein with NCAM external domains but CEA-like tumorigenic activity. We hypothesized that this resulted from the presence of a functional specificity signal within this sequence and generated CEA/NCAM chimeras to identify this signal. Replacing the residues (GLSAG) 6–10 amino acids downstream of the CEA anchor addition site with the corresponding NCAM residues resulted in GPI-anchored proteins lacking the CEA-like biological functions of integrin modulation and differentiation blockage. Transferring this region from CEA into NCAM in conjunction with the upstream proline (PGLSAG) was sufficient to specify the addition of the CEA anchor. Therefore, this study identifies a novel specificity signal consisting of six amino acids located within the GPI anchor attachment signal, which is necessary and sufficient to specify the addition of a particular functional GPI anchor and, thereby, the ultimate function of the mature protein.
The tumor suppressor microRNA let-7 represses the HMGA2 oncogene
Authors: Lee Yong Sun , Dutta Anindya
Published: April 2007

HMGA2, a high-mobility group protein, is oncogenic in a variety of tumors, including benign mesenchymal tumors and lung cancers. Knockdown of Dicer in HeLa cells revealed that the HMGA2 gene is transcriptionally active, but its mRNA is destabilized in the cytoplasm through the microRNA (miRNA) pathway. HMGA2 was derepressed upon inhibition of let-7 in cells with high levels of the miRNA. Ectopic expression of let-7 reduced HMGA2 and cell proliferation in a lung cancer cell. The effect of let-7 on HMGA2 was dependent on multiple target sites in the 3′ untranslated region (UTR), and the growth-suppressive effect of let-7 on lung cancer cells was rescued by overexpression of the HMGA2 ORF without a 3′UTR. Our results provide a novel example of suppression of an oncogene by a tumor-suppressive miRNA and suggest that some tumors activate the oncogene through chromosomal translocations that eliminate the oncogene’s 3′UTR with the let-7 target sites.