bluuebunny/crossref_metadata_2025 huggingface dataset:
Origin of color centers in the flux-grown europium gallium garnet
Authors: Aleksandrovsky A. S. , Arkhipkin V. G. , Bezmaternykh L. N. , Gudim I. A. , Krylov A. S. , Vagizov F.
Published: April 2008

Europium gallium garnet (EuGG) single crystals were grown from fluxes with various contents. Optical absorption spectra of EuGG grown from a flux containing calcium show an additional band in the ultraviolet and blue regions of the spectra as compared to the case of a calcium-free flux. Mössbauer spectra of the samples grown from the fluxes with different additives show no signs of other valence states of the europium ions except for 3+. However, they indicate changes in the crystal field due to the entrance of additive ions. The nature of the additional absorption must be the same as that for calcium-doped gadolinium gallium garnet, i.e., anion vacancies. Mössbauer isotope shifts and quadrupole splitting for EuGG are determined.
Molecular dynamics of hydrogen dissociation on an oxygen covered Pt(111) surface
Authors: Ludwig Jeffery , Vlachos Dionisios G.
Published: April 2008

The dissociation of hydrogen on a Pt(111) surface covered with a p(2×2) oxygen phase was investigated using quasiclassical, six-dimensional molecular dynamics. The potential energy surface (PES) used in these simulations was obtained by an iterative novelty sampling algorithm. Compared to molecular beam experiments performed under similar conditions, the simulations give an accurate prediction of the reaction probability via a direct dissociation pathway. When compared to previously reported reaction probability curves for the clean Pt(111) surface, we find that the presence of an oxygen overlayer inhibits the direct pathway to hydrogen dissociation. This inhibition is a function of incident energy and cannot be described by a simple site blocking model. An indirect pathway to dissociation, which was observed in experiments, is not properly captured by the PES. Spatially resolved “reaction maps” indicate that the preferred site for hydrogen dissociation on an oxygen covered Pt surface is the top site of the Pt atom farthest from the adsorbed oxygen atom.
Self-induced transparency in colloidal liquids by Z-scan-based optical trapping
Authors: Dai Qiao-Feng , Liu Hai-Ying , Liu Jin , Wu Li-Jun , Guo Qi , Hu Wei , Yang Xiang-Bo , Liu Song-Hao , Lan Sheng , Gopal Achanta Venu , Trofimov V. A.
Published: April 2008

We demonstrated a transition from a disordered to an ordered state in a colloidal liquid by utilizing Z-scan-based optical trapping. The Z-scan process plays a role of gradually and continuously narrowing and deepening the optical potential well. When the trapping power was increased above a certain level, a self-induced transparency occurs, leading to a significant enhancement in transmission. The dynamic transition was confirmed by monitoring the diffraction pattern of the trapping region.
Analytical expression for the electric potential in the plasma sheath near an arc-cathode
Authors: Askari S. , Minoo H.
Published: April 2008

An expression for the spatial dependence of the electric potential in a collisionless plasma sheath near an electron-emitting cathode is presented. The applicability of this expression for an arc cathode is demonstrated. Comparison with the numerical solutions of the model equations indicates that the sheath thickness and potential variation predicted by this expression are accurate in a wide range of the electron-emission yield.
Nonadiabatic electron wavepacket dynamics of molecules in an intense optical field: An ab initio electronic state study
Authors: Yonehara Takehiro , Takatsuka Kazuo
Published: April 2008

A theory of quantum electron wavepacket dynamics that nonadiabatically couples with classical nuclear motions in intense optical fields is studied. The formalism is intended to track the laser-driven electron wavepackets in terms of the linear combination of configuration-state functions generated with ab initio molecular orbitals. Beginning with the total quantum Hamiltonian for electrons and nuclei in the vector potential of classical electromagnetic field, we reduce the Hamiltonian into a mixed quantum-classical representation by replacing the quantum nuclear momentum operators with the classical counterparts. This framework gives equations of motion for electron wavepackets in an intense laser field through the time dependent variational principle. On the other hand, a generalization of the Newtonian equations provides a matrix form of forces acting on the nuclei for nonadiabatic dynamics. A mean-field approximation to the force matrix reduces this higher order formalism to the semiclassical Ehrenfest theory in intense optical fields. To bring these theories into a practical quantum chemical package for general molecules, we have implemented the relevant ab initio algorithms in it. Some numerical results in the level of the semiclassical Ehrenfest-type theory with explicit use of the nuclear kinematic (derivative) coupling and the velocity form for the optical interaction are presented.
Solving the electron and electron-nuclear Schrödinger equations for the excited states of helium atom with the free iterative-complement-interaction method
Authors: Nakashima Hiroyuki , Hijikata Yuh , Nakatsuji Hiroshi
Published: April 2008

Very accurate variational calculations with the free iterative-complement-interaction (ICI) method for solving the Schrödinger equation were performed for the 1sNs singlet and triplet excited states of helium atom up to N=24. This is the first extensive applications of the free ICI method to the calculations of excited states to very high levels. We performed the calculations with the fixed-nucleus Hamiltonian and moving-nucleus Hamiltonian. The latter case is the Schrödinger equation for the electron-nuclear Hamiltonian and includes the quantum effect of nuclear motion. This solution corresponds to the nonrelativistic limit and reproduced the experimental values up to five decimal figures. The small differences from the experimental values are not at all the theoretical errors but represent the physical effects that are not included in the present calculations, such as relativistic effect, quantum electrodynamic effect, and even the experimental errors. The present calculations constitute a small step toward the accurately predictive quantum chemistry.
Planar-type spin valves based on low-molecular-weight organic materials with La0.67Sr0.33MnO3 electrodes
Authors: Ikegami Tomonori , Kawayama Iwao , Tonouchi Masayoshi , Nakao Satoru , Yamashita Yoshiro , Tada Hirokazu
Published: April 2008

The spin injection and transport properties of low-molecular-weight organic semiconductors such as pentacene and bis(l,2,5-thiadiazolo)-p-quinobis(l,3-dithiole) (BTQBT) were investigated utilizing planar-type spin-valve devices with half-metallic La0.67Sr0.33MnO3 electrodes. The devices showed clear spin-valve characteristics with a magnetoresistance (MR) ratio of up to 29% at 5K. The MR ratio was found to depend on the gap spacing of the electrodes, the applied bias voltage, temperature, and the crystallinity of the films. It was also affected by gas adsorption onto the films, indicating that the spins were scattered by carriers and/or radical ions in the films generated through charge transfer from gas molecules.
Site-selective formation of Si nanocrystal in SiO2 by femtosecond laser irradiation and Al deoxidization effects
Authors: Uchida Noriyuki , Mikami Youhei , Kintoh Hiroshi , Murakami Kouichi , Fukata Naoki , Mitome Masanori , Hase Muneaki , Kitajima Masahiro
Published: April 2008

We have developed a robust method for fabricating Si nanoregions in silica glass using femtosecond laser processing. We attained a vivid formation of silicon-rich nanoregions site-selectively generated in SiO2 by irradiation of femtosecond laser pulses to the interface of a SiO2 substrate and deposited aluminum (Al) thin film, where the Al element acts as a gettering site for O atoms. Growth of high-density Si nanocrystals and amorphous Si was observed by transmission electron microscopy in the region that was multiply irradiated with the femtosecond laser. Furthermore, local annealing with a cw laser enhances the Si nanocrystal growth, which was determined by micro-Raman measurements.
Exploring the new three-dimensionalab initiointeraction energy surface of the Ar–HF complex: Rovibrational calculations for Ar–HF and Ar–DF with vibrationally excited diatoms
Authors: Jankowski Piotr
Published: April 2008

Several features and the performance of the recently published [P. Jankowski and M. Ziólkowski, Mol. Phys. 104, 2293 (2006)] three-dimensional intermolecular potential energy surface for the Ar–HF complex have been investigated. This full-dimensional surface has been obtained using the method of the local expansion of the exact interaction energy surface [P. Jankowski, J. Chem. Phys. 121, 1655 (2004)] in the Taylor series with respect to intramolecular coordinates. The interaction energies have been calculated with the coupled-cluster supermolecular method with single, double, and noniterative triple excitations. The convergence of the interaction energy with respect to the size of the basis set is discussed. The two-dimensional surfaces resulting from averaging of the full-dimensional surface over the intramolecular vibration of HF have been obtained and directly compared to the empirical H6(4,3,2) set of surfaces proposed by Hutson [J. Chem. Phys. 96, 6752 (1992)]. A very good agreement has been observed. The averaged potentials have been used to calculate the rovibrational energy levels of the Ar–HF and Ar–DF complexes and compared to the experimental data. The accuracy of rovibrational calculations achieved with the new surface is much better than with any of the ab initio surfaces available so far. Predictions of the rovibrational energy levels and spectroscopic constants have also been done for Ar–HF with HF in the v=4,5 vibrational states, and for Ar–DF and DF in the v=3,4 states. The full-dimensional surface studied in this paper is the first ab initio surface which is fully compatible with the empirical H6(4,3,2) surface proposed by Hutson.
Nonmetallic left-handed material based on negative-positive anisotropy in low-dimensional quantum structures
Authors: Ginzburg Pavel , Orenstein Meir
Published: April 2008

Nonmetallic left-handed material by assembly of low-dimensional quantum structures is theoretically proposed. Specifically, we predict relatively wideband, tunable left-handed material by employing structures comprised of semiconductor quantum wells and quantum dots. Well established epitaxial growth of semiconductor material allows a feasible composition of such metamaterials. The advantages of the proposed scheme is the potential ability to invert the material losses to gain by electrical pumping and the possibility to switch the material regime from left-handed to right-handed by applying external voltage, which are not affordable in the recently proposed left-handed material configurations.
Tin laser-produced plasma source modeling at 13.5nm for extreme ultraviolet lithography
Authors: White J. , O’Sullivan G. , Zakharov S. , Choi P. , Zakharov V. , Nishimura H. , Fujioka S. , Nishihara K.
Published: April 2008

Extreme ultraviolet lithography semiconductor manufacturing requires a 13.5nm light source. Laser-produced plasma emission from Sn V–Sn XIV ions is one proposed industry solution. The effect of laser pulse width and spatial profile on conversion efficiency is analyzed over a range of power densities using a two-dimensional radiative magnetohydrodynamic code and compared to experiment using a 1.064μm, neodymium:yttrium aluminium garnet laser on a planar tin target. The calculated and experimental conversion efficiencies and the effects of self-absorption in the plasma edge are compared. Best agreement between theory and experiment is found for an 8.0ns Gaussian pulse.
The polydisperse cell model: Nonlinear screening and charge renormalization in colloidal mixtures
Authors: Torres Aldemar , Téllez Gabriel , van Roij René
Published: April 2008

We propose a model for the calculation of renormalized charges and osmotic properties of mixtures of highly charged colloidal particles. The model is a generalization of the cell model and the notion of charge renormalization as introduced by Alexander et al. [J. Chem. Phys. 80, 5776 (1984)]. The total solution is partitioned into as many different cells as components in the mixture. The radii of these cells are determined self-consistently for a given set of parameters from the solution of the nonlinear Poisson–Boltzmann equation with appropriate boundary conditions. This generalizes Alexanders’s model where the (unique) Wigner–Seitz cell radius is solely fixed by the colloid packing fraction. We illustrate the technique by considering a binary mixture of the colloids with the same sign of charge. The present model can be used to calculate thermodynamic properties of highly charged colloidal mixtures at the level of linear theories, while taking the effect of nonlinear screening into account.
Phase coexistence in polydisperse athermal polymer-colloidal mixture
Authors: Hlushak S. P. , Kalyuzhnyi Yu. V. , Cummings P. T.
Published: April 2008

A theoretical scheme developed earlier [Y. V. Kalyuzhnyi et al., Chem. Phys. Lett. 443, 243 (2007)] is used to calculate the full phase diagram of polydisperse athermal polymer-colloidal mixture with polydispersity in both colloidal and polymeric components. In the limiting case of bidisperse polymer-colloidal mixture, theoretical results are compared against computer simulation results. We present the cloud and shadow curves, critical binodals, and distribution functions of the coexisting phases and discuss the effects of polydispersity on their behavior. According to our analysis polydispersity extends the region of the phase instability, shifting the critical point to the lower values of the pressure and density. For the high values of the pressure polydispersity causes strong fractionation effects, with the large size colloidal particles preferring the low-density shadow phase and long chain length polymeric particles preferring the high-density shadow phase.
Photoabsorption spectra of small fullerenes and Si-heterofullerenes
Authors: Koponen Laura , Puska Martti J. , Nieminen Risto M.
Published: April 2008

We study the spectral properties of two kinds of derivatives of the carbon fullerene C60, small fullerenes and Si-heterofullerenes, by ab initio calculations. The principal method of study is the time-dependent density-functional theory in its full time-propagation form. C20, C28, C32, C36, and C50, the most stable small fullerenes in the range of C20–C50, are found to have characteristic features in their optical absorption spectra, originating from the geometry of the molecules in question. The comparison of measured and calculated absorption spectra is found to be a useful tool in differentiating between different, almost isoenergetic ground state structure candidates of small fullerenes. Substitutionally doped fullerenes are of interest due to their enhanced chemical reactivity. It is suggested that the doping degree can be obtained by studying the absorption spectra. For example, it is observed that the spectra gradually change when doping C60 up to C48Si12 so that absorption in the visible and near infrared regions increases.
Dynamics of molecular diffusion of rhodamine 6G in silica nanochannels
Authors: Kievsky Y. Y. , Carey B. , Naik S. , Mangan N. , ben-Avraham D. , Sokolov I.
Published: April 2008

We describe a method to study diffusion of rhodamine 6G dye in single silica nanochannels using arrays of silica nanochannels. Dynamics of the molecules inside single nanochannel is found from the change of the dye concentration in solution with time. A 108 decrease in the dye diffusion coefficient relative to water was observed. In comparison to single fluorescent molecule studies, the presented method does not require fluorescence of the diffusing molecules.
Single-photon level ultrafast all-optical switching
Authors: Han Xiao-Feng , Weng Yu-Xiang , Wang Rui , Chen Xi-Hao , Luo Kai-Hong , Wu Ling-An , Zhao Jimin
Published: April 2008

We demonstrate an approach to all-optical switching, where a weak beam controls a strong beam, based on three-wave mixing optical parametric amplification in a nonlinear crystal. Ultrafast switching within 400fs has been achieved with a 130fs single-photon level switch beam containing, on average, 0.75 photon/pulse, which can turn on/off a signal pulse containing 5.9×108 photons. The transverse patterns for the on and off states are well defined and the switch has a large bandwidth of up to 10nm.
Quantum transport in In0.75Ga0.25As quantum wires
Authors: Simmonds P. J. , Sfigakis F. , Beere H. E. , Ritchie D. A. , Pepper M. , Anderson D. , Jones G. A. C.
Published: April 2008

In addition to quantized conductance plateaus at integer multiples of 2e2∕h, the differential conductance G=dI∕dV shows plateaus at 0.25(2e2∕h) and 0.75(2e2∕h) under applied source-drain bias in In0.75Ga0.25As quantum wires defined by insulated split gates. This observation is consistent with a spin-gap model for the 0.7 structure. Using a tilted magnetic field to induce Landau level crossings, the g factor was measured to be ∼9 by the coincidence method. This material, with a mobility of 1.8×105cm2∕Vs at a carrier density of 1.4×1011cm−2, may prove useful for further study of electron-electron interaction effects in quantum wires.
Enhanced charge collection and reduced recombination of CdS∕TiO2 quantum-dots sensitized solar cells in the presence of single-walled carbon nanotubes
Authors: Lee Wonjoo , Lee Jungwoo , Lee Sangjin , Yi Whikun , Han Sung-Hwan , Cho Byung Won
Published: April 2008

This paper reports the modification of CdS∕TiO2 quantum-dot sensitized solar cells by using single-walled carbon nanotubes (SWCNTs) on indium-doped tin oxide (ITO) electrodes. The presence of the SWCNT layers on an ITO electrode increased the short-circuit current under the irradiation condition and also reduced the charge recombination process under the dark condition. The power conversion efficiency of CdS∕TiO2 on ITO increased 50.0% in the presence of SWCNTs due to the improved charge-collecting efficiency and reduced recombination.
Synergistic effects of vacuum ultraviolet radiation, ion bombardment, and heating in 193nm photoresist roughening and degradation
Authors: Nest D. , Graves D. B. , Engelmann S. , Bruce R. L. , Weilnboeck F. , Oehrlein G. S. , Andes C. , Hudson E. A.
Published: April 2008

The roles of ultraviolet/vacuum ultraviolet (UV/VUV) photons, Ar+ ion bombardment and heating in the roughening of 193nm photoresist have been investigated. Atomic force microscopy measurements show minimal surface roughness after UV/VUV-only or ion-only exposures at any temperature. Simultaneous UV/VUV, ion bombardment, and heating to surface temperatures of 60–100°C result in increased surface roughness, and is comparable to argon plasma-exposed samples. Ion bombardment creates a modified near-surface layer while UV/VUV radiation results in loss of carbon-oxygen bonds up to a depth of ∼100nm. Enhanced roughness is only observed in the presence of all three effects.
Temperature dependent Schottky barrier height and Fermi level pinning on Au/HBC/GaAs diodes
Authors: Özcan Soner , Smoliner Jürgen , Dienel Thomas , Fritz Torsten
Published: April 2008

Au/hexa-peri-hexabenzocoronene [C42H18∕(HBC)]∕GaAs heterostructures were investigated by ballistic electron emission microscopy. At room temperature, the Schottky barrier height at the Au/HBC interface was measured to be 1.3eV, while the Fermi level at the HBC-GaAs interface is pinned 1.2eV below the GaAs conduction band. Decreasing the temperature down to T=10K, the Au/HBC Schottky barrier height increases to 1.55eV and the Fermi level pinning at the HBC-GaAs interface reaches a value of 1.4eV, close to the valence band of GaAs. These high values make HBC a promising interfacial layer in order to increase, for example, the open circuit voltage of GaAs Schottky barrier solar cells.
Experimental evidence of magnetic anisotropy induction by superconductivity in superlattices
Authors: Monton C. , Ramos C. A. , Guimpel J. , Zysler R. D.
Published: April 2008

We present a study of Nb∕Co superlattices by ferromagnetic resonance. We find that when the superconductor enters the Meissner state, an anisotropy field around 400Oe, parallel to the applied field, appears in the ferromagnetic layers, consistent with the superconducting flux expelled from the superconducting layers. This anisotropy field is an important key to understand previous results showing that the superconductor layers modify the magnetic state of the ferromagnetic layers.
High performance pnp AlGaN∕GaN heterojunction bipolar transistors on GaN substrates
Authors: Kumakura Kazuhide , Makimoto Toshiki
Published: April 2008

We fabricated pnp AlGaN∕GaN heterojunction bipolar transistors (HBTs) with various emitter areas on GaN substrates and investigated their common-emitter current-voltage and high-power characteristics at room temperature. The HBTs with an emitter area of 30×50μm2 exhibited a high performance: a maximum current gain of 85 at a collector current of 30mA and a maximum collector current density of 7.3kA∕cm2 at a collector-emitter voltage of 30V, which corresponds to the maximum power dissipation density of 219kW∕cm2. The current gain and the collector current density increased compared to those on sapphire substrates. For the HBT with the emitter area of 270×450μm2, the current gain was still as high as 47 and the maximum collector current reached as high as 1A, and this single HBT showed a high-power dissipation of 30W. This high performance of the HBTs is ascribed to the low dislocation density and relatively high thermal conductivity of the GaN substrate. Although the emitter crowding and self-heating effects remain, the obtained values are highest among pnp nitride-based HBTs.
Another method for domain wall movement by a nonuniform transverse magnetic field
Authors: You Chun-Yeol
Published: April 2008

We propose another method for domain wall (DW) movement in nanowire geometry. We find that a DW moves to an energy minimum position in order to minimize the Zeeman energy under a nonuniform transverse magnetic field. DW dynamics under a spatially nonuniform transverse magnetic field has been investigated by means of micromagnetic simulations. The nonuniform transverse magnetic field driven DW motion has a superior nature which includes a rigidity of the domain structure during the movement of the DWs in addition to all of the advantages of conventional field driven DW movement. The direction of the DW movement only depends on the magnetization direction inside of the DW itself, not on the one of the domains. Therefore, it is possible to achieve field driven DW motion with rigid domain structures.
Negative index materials based on metal nanoclusters
Authors: Wu Qi , Park Wounjhang
Published: April 2008

We present a negative index metamaterial architecture based on metal nanoclusters. The nanoclusters support magnetic Mie resonances and exhibit negative permeability, which can be combined with negative permittivity to achieve negative refractive index. We demonstrate two designs using silver nanoclusters with either silver films or silver coated nanowires in optical frequency region. Refractive index of −1 and figure of merit of 2 are achieved by sandwiching nanoclusters between silver films. Our simulations show the flexibility in constructing negative index materials using metal nanoclusters due to their tunable operating frequencies and the freedom in the choice of the material compositions.
Stress enhanced self-diffusion in Si: Entropy effect in anisotropic elastic environment
Authors: Rushchanskii Konstantin Z. , Pochet Pascal , Lançon Frédéric
Published: April 2008

We present a multiscale analysis on stress enhanced vacancy-mediated diffusion in strained Si that explicitly includes the Jahn–Teller structural distortion around vacancies. The resulting anisotropy combined with biaxial deformations applied to (100)-oriented films lead to an orientational dependency of the vacancy formation energy. At finite temperatures, it results in a strong entropy effect when thermal activation allows occupancy of high energy defect states. Kinetic Lattice Monte Carlo simulations reveal that the effective activation energy is a strongly nonlinear function of strain at small deformations. At larger deformations, it becomes linear where as the occupancy of the excited states becomes insignificant.
Sources, fate and transport of atmospheric mercury from Asia
Authors: Jaffe Dan , Strode Sarah
Published: April 2008

Environmental context. Mercury is a global problem and more than half of all anthropogenic emissions are from Asia. In this paper we review the sources of mercury coming from Asia, the environmental fate of these emissions and their global transport. Asian emissions of mercury are responsible for a small, but significant share of the mercury that deposits throughout the world, especially in the northern hemisphere.
Abstract. Asian anthropogenic emissions of mercury to the atmosphere contribute 54% of all anthropogenic emissions. For this reason, it is important to understand how these emissions impact both the regional and global mercury cycle. The largest share of mercury emissions in Asia is due to coal combustion and smelting. Approximately half of the Asian anthropogenic emissions are emitted as Hg0. The remainder are emitted as gaseous Hg2+ compounds and particle-bound Hg (PHg). These latter forms of Hg are susceptible to relatively rapid removal from the atmosphere. The Asian emissions lead to very high concentrations of airborne Hg in urban and rural areas of Asia. Modelling the fate and transport of the Asian emissions using the Goddard Earth Observing System (GEOS)-Chem model of global tropospheric chemistry shows that these emissions are associated with high deposition of Hg within Asia, but there is little data with which to evaluate this model result. Observations downwind of Asia show that Hg0 is the dominant form in Asian plumes, with generally small, but variable amounts of other forms. Thus we conclude that most of the Asian Hg2+ and PHg have been removed in the source region. In addition, downwind observations show that total emissions are significantly larger than indicated by the anthropogenic emission inventory. This likely reflects either an underestimate of the anthropogenic emissions or emissions of Hg from land. Plumes containing enhancements in Asian Hg0, but not other species, have been detected as far away as North America. Because only Asian Hg0 is transported long distances, the deposition is distributed relatively uniformly in the northern hemisphere. In North America, Asian anthropogenic emissions account for 7–20% of all deposition, with an average of 16%.
Methylmercury exposure and health effects in humans
Authors: Choi Anna L. , Grandjean Philippe
Published: April 2008

Environmental Context. Dietary intake of fish and other seafood products is the dominant source of human exposure to methylmercury, a toxicant that can have serious adverse effects on the developing nervous system and may promote heart diseases. The existing evidence of human toxicity should inspire prudent choices in maintaining fish intakes to secure an ample supply of essential nutrients, while at the same time choosing species that are low in mercury concentrations. The combination of essential nutrients and avoidance of this toxic contaminant will benefit brain development and human health in general. In addition, current contamination levels suggest that intensified efforts are needed to reduce and eliminate mercury release to the environment. Abstract. Methylmercury (MeHg) is a worldwide contaminant found in seafood and freshwater fish, which constitute the dominant source of human exposure to this substance. The developing human brain is particularly susceptible to injury caused by MeHg, which easily passes the placental barrier. Epidemiological studies in fishing populations have found subtle though lasting adverse effects on brain functions of children who were exposed prenatally to MeHg from seafood diets. This contaminant also seems capable of promoting the development of heart disease. Fish and seafood also contain important nutrients, such as omega-3 fatty acids that may provide beneficial effects, thereby possibly counteracting or obscuring the adverse effects of MeHg. This article reviews the existing evidence on MeHg developmental neurotoxicity and the emerging evidence that MeHg may promote the development of heart diseases. MeHg risks may have been underestimated in the past, in part because of the confounding effects of nutrients from seafood and fish. Improved control of mercury release to the environment is indicated. In addition, regulatory agencies should provide better guidance to consumers in maintaining a balanced diet that includes seafood as low as possible in mercury.
Fine-scale variation of historical fire regimes in sagebrush-steppe and juniper woodland: an example from California, USA
Authors: Miller Richard F. , Heyerdahl Emily K.
Published: April 2008

Coarse-scale estimates of fire intervals across the mountain big sagebrush (Artemisia tridentata spp. vaseyana (Rydb.) Beetle) alliance range from decades to centuries. However, soil depth and texture can affect the abundance and continuity of fine fuels and vary at fine spatial scales, suggesting fire regimes may vary at similar scales. We explored variation in fire frequency across 4000 ha in four plant associations with differing soils in which mountain big sagebrush and western juniper (Juniperus occidentalis subsp. occidentalis Hook.) were diagnostic or a transitory component. We reconstructed fire frequency from fire-scarred ponderosa pine (Pinus ponderosa P. & C. Lawson) in one association. The other three associations lacked fire-scarred trees so we inferred fire frequency from establishment or death dates of western juniper and a model of the rate of post-fire succession we developed from current vegetation along a chronosequence of time-since-fire. Historical fire frequency varied at fine spatial scales in response to soil-driven variation in fuel abundance and continuity and spanned the range of frequencies currently debated. Fire intervals ranged from decades in areas of deep, productive soils where fine fuels were likely abundant and continuous, to centuries in areas of shallow, coarse soils where fine fuel was likely limited.
Evaluating the effectiveness of contour-felled log erosion barriers as a post-fire runoff and erosion mitigation treatment in the western United States
Authors: Robichaud P. R. , Wagenbrenner J. W. , Brown R. E. , Wohlgemuth P. M. , Beyers J. L.
Published: April 2008

Between 1998 and 2002, six sites were established immediately after large wildfires in the western United States to determine the effectiveness of contour-felled log erosion barriers in mitigating post-wildfire runoff and erosion. In each pair of matched, burned, and small watersheds (1–13 ha), one was treated with contour-felled log erosion barriers and one was left untreated as a control. For 4 to 6 post-fire years, runoff and sediment yields were measured and correlated with rain properties. High-intensity rainfall produced most of the measured runoff and sediment yields except in the southern California site, where long-duration rain events produced most of the runoff and erosion. For small rain events (less than the 2-year return period for the 10-min duration), the runoff, peak flows, and sediment yields were lower in the treated watersheds than in the control watersheds, but there was no treatment effect for rain events with larger return periods. Improper installation and degradation over time reduced the effectiveness of contour-felled log erosion barriers. Rainfall characteristics and installation procedures should be carefully considered before choosing contour-felled log erosion barriers for post-fire hillslope stabilisation.
Selective disruption of the mammalian secretory apparatus enhances or eliminates calcium current modulation in nerve endings
Authors: Silinsky Eugene M.
Published: April 2008

Modulation of secretion via G protein-coupled receptors (GPCRs) serves an important regulatory function in neuronal and nonneuronal secretory cells. Most secretory cells possess voltage-gated calcium channels, share homologues of the core complex of three proteins (the SNAREs) that constitute the secretory apparatus, and are modulated by GPCR activation. Activators of GPCRs generally inhibit the release of neurotransmitter substances to a maximum of only 50–60% of the control level, suggesting that complex protein–protein interactions may govern the efficacy of this form of modulation. In this article, molecular genetic approaches are used in combination with botulinum toxins (selective molecular scalpels that cleave the SNAREs at highly restricted loci) to address this issue. The results suggest that the cleavage of either of the plasma membrane SNAREs (syntaxin or SNAP-25) prevents modulation of calcium currents by A1adenosine receptors at mammalian motor nerve endings. In contrast, cleavage of the synaptic vesicle SNARE (synaptobrevin) in conjunction with deletion of the vesicle-docking protein Rab3A greatly enhances the efficacy of calcium current modulation.
From biosilicification to tailored materials: Optimizing hydrophobic domains and resistance to protonation of polyamines
Authors: Belton David J. , Patwardhan Siddharth V. , Annenkov Vadim V. , Danilovtseva Elena N. , Perry Carole C.
Published: April 2008

Considerable research has been directed toward identifying the mechanisms involved in biosilicification to understand and possibly mimic the process for the production of superior silica-based materials while simultaneously minimizing pollution and energy costs. Molecules isolated from diatoms and, most recently sponges, thought to be key to this process contain polyamines with a propylamine backbone and variable levels of methylation. In a chemical approach to understanding the role of amine (especially propylamine) structures in silicification we have explored three key structural features: (
i
) the degree of polymerization, (
ii
) the level of amine methylation, and (
iii
) the size of the amine chain spacers. In this article, we show that there are two factors critical to their function: the ability of the amines to produce microemulsions and the presence of charged and uncharged amine groups within a molecule, with the latter feature helping to catalyze silicic acid condensation by a proton donor/acceptor mechanism. The understanding of amine–silicate interactions obtained from this study has enabled the controlled preparation of hollow and nonporous siliceous materials under mild conditions (circumneutral pH, room temperature, and in all aqueous systems) possibly compatible with the conditions used by biosystems. The “rules” identified from our study were further used predictively to modulate the activity of a given amine. We believe that the outcomes of the present contribution will form the basis for an approach to controlling the growth of inorganic materials by using tailor-made organic molecules.
The MUT9p kinase phosphorylates histone H3 threonine 3 and is necessary for heritable epigenetic silencing in
Chlamydomonas
Authors: Casas-Mollano J. Armando , Jeong Byeong-ryool , Xu Jianping , Moriyama Hideaki , Cerutti Heriberto
Published: April 2008

Changes in chromatin organization are emerging as key regulators in nearly every aspect of DNA-templated metabolism in eukaryotes. Histones undergo many, largely reversible, posttranslational modifications that affect chromatin structure. Some modifications, such as trimethylation of histone H3 on Lys 4 (H3K4me3), correlate with transcriptional activation, whereas others, such as methylation of histone H3 on Lys 27 (H3K27me), are associated with silent chromatin. Posttranslational histone modifications may also be involved in the inheritance of chromatin states. Histone phosphorylation has been implicated in a variety of cellular processes but, because of the dynamic nature of this modification, its potential role in long-term gene silencing has remained relatively unexplored. We report here that a
Chlamydomonas reinhardtii
mutant defective in a Ser/Thr protein kinase (MUT9p), which phosphorylates histones H3 and H2A, shows deficiencies in the heritable repression of transgenes and transposons. Moreover, based on chromatin immunoprecipitation analyses, phosphorylated H3T3 (H3T3ph) and monomethylated H3K4 (H3K4me1) are inversely correlated with di/trimethylated H3K4 and associate preferentially with silenced transcription units. Conversely, the loss of those marks in mutant strains correlates with the transcriptional reactivation of transgenes and transposons. Our results suggest that H3T3ph and H3K4me1 function as reinforcing epigenetic marks for the silencing of euchromatic loci in
Chlamydomonas
.
Spatial and Linguistic Aspects of Visual Imagery in Sentence Comprehension
Authors: Bergen Benjamin K. , Lindsay Shane , Matlock Teenie , Narayanan Srini
Published: April 2008

There is mounting evidence that language comprehension involves the activation of mental imagery of the content of utterances (; ; ; ; ; ; ). This imagery can have motor or perceptual content. Three main questions about the process remain under‐explored, however. First, are lexical associations with perception or motion sufficient to yield mental simulation, or is the integration of lexical semantics into larger structures, like sentences, necessary? Second, what linguistic elements (e.g., verbs, nouns, etc.) trigger mental simulations? Third, how detailed are the visual simulations that are performed? A series of behavioral experiments address these questions, using a visual object categorization task to investigate whether up‐ or down‐related language selectively interferes with visual processing in the same part of the visual field (following ). The results demonstrate that either subject nouns or main verbs can trigger visual imagery, but only when used in literal sentences about real space—metaphorical language does not yield significant effects—which implies that it is the comprehension of the sentence as a whole and not simply lexical associations that yields imagery effects. These studies also show that the evoked imagery contains detail as to the part of the visual field where the described scene would take place.
Adaptive Non‐Interventional Heuristics for Covariation Detection in Causal Induction: Model Comparison and Rational Analysis
Authors: Hattori Masasi , Oaksford Mike
Published: April 2008

In this article, 41 models of covariation detection from 2 × 2 contingency tables were evaluated against past data in the literature and against data from new experiments. A new model was also included based on a limiting case of the normative phi‐coefficient under an extreme rarity assumption, which has been shown to be an important factor in covariation detection () and data selection (; , ). The results were supportive of the new model. To investigate its explanatory adequacy, a rational analysis using two computer simulations was conducted. These simulations revealed the environmental conditions and the memory restrictions under which the new model best approximates the normative model of covariation detection in these tasks. They thus demonstrated the adaptive rationality of the new model.
“What if…”: The Use of Conceptual Simulations in Scientific Reasoning
Authors: Trickett Susan Bell , Trafton J. Gregory
Published: April 2008

The term conceptual simulation refers to a type of everyday reasoning strategy commonly called “what if” reasoning. It has been suggested in a number of contexts that this type of reasoning plays an important role in scientific discovery; however, little direct evidence exists to support this claim. This article proposes that conceptual simulation is likely to be used in situations of informational uncertainty, and may be used to help scientists resolve that uncertainty. We conducted two studies to investigate the relationship between conceptual simulation and informational uncertainty. Study 1 was an in vivo study of expert scientists; the results suggest that scientists do use conceptual simulation in situations of informational uncertainty, and that they use conceptual simulation to make inferences from their data using the analogical reasoning process of alignment by similarity detection. Study 2 experimentally manipulated experts' level of uncertainty and provides further support for the hypothesis that conceptual simulation is more likely to be used in situations of informational uncertainty. Finally, we discuss the relationship between conceptual simulation and other types of reasoning using qualitative mental models.
Mapping the Color Space of Saccadic Selectivity in Visual Search
Authors: Xu Yun , Higgins Emily C. , Xiao Mei , Pomplun Marc
Published: April 2008

Color coding is used to guide attention in computer displays for such critical tasks as baggage screening or air traffic control. It has been shown that a display object attracts more attention if its color is more similar to the color for which one is searching. However, what does similar precisely mean? Can we predict the amount of attention that a display color will receive during a search for a given target color? To tackle this question, two color‐search experiments measuring the selectivity of saccadic eye movements and mapping out its underlying color space were conducted. A variety of mathematical models, predicting saccadic selectivity for given target and display colors, were devised and evaluated. The results suggest that applying a Gaussian function to a weighted Euclidean distance in a slightly modified HSI color space is the best predictor of saccadic selectivity in the chosen paradigm. Hue and intensity information by itself provides a basis for useful predictors, spanning a possibly spherical color space of saccadic selectivity. Although the current models cannot predict saccadic selectivity values for a wide variety of visual search tasks, they reveal some characteristics of color search that are of both theoretical and applied interest, such as for the design of human–computer interfaces.
Tracking the Continuity of Language Comprehension: Computer Mouse Trajectories Suggest Parallel Syntactic Processing
Authors: Farmer Thomas A. , Cargill Sarah A. , Hindy Nicholas C. , Dale Rick , Spivey Michael J.
Published: April 2008

Although several theories of online syntactic processing assume the parallel activation of multiple syntactic representations, evidence supporting simultaneous activation has been inconclusive. Here, the continuous and non‐ballistic properties of computer mouse movements are exploited, by recording their streaming x, y coordinates to procure evidence regarding parallel versus serial processing. Participants heard structurally ambiguous sentences while viewing scenes with properties either supporting or not supporting the difficult modifier interpretation. The curvatures of the elicited trajectories revealed both an effect of visual context and graded competition between simultaneously active syntactic representations. The results are discussed in the context of 3 major groups of theories within the domain of sentence processing.
Race Categorization Modulates Holistic Face Encoding
Authors: Michel Caroline , Corneille Olivier , Rossion Bruno
Published: April 2008

Recent studies have shown that same‐race (SR) faces are processed more holistically than other‐race (OR) faces, a difference that may underlie the greater difficulty at recognizing OR than SR faces (the “other‐race effect”). This article provides original evidence suggesting that the holistic processing of faces may be sensitive to the observers' racial categorization of the face. In Experiment 1, Caucasian participants performed a face‐composite task with Caucasian faces, Asian faces, and racially ambiguous morphed face stimuli. Identical morphed face stimuli were processed more holistically when categorized as SR than as OR faces. Experiment 2 further suggests that this finding was not underlain by strategic or training effects. Overall, these results support the view that one's categorization of a face as belonging to the same or another race plays a critical role in the holistic processing of this face.
Flowers for the Doctor: Pro-Natalism and Abortion in Fascist Milan
Authors: Willson Perry R.
Published: April 2008

This article explores the reasons for the failure of the Fascist attempts to raise the Italian birth rate through an examination of the pro-natalist campaign in the great industrial and commercial city of Milan and its surrounding province. It then considers one of the specific ways in which the birth rate was kept down - illegal abortion - focusing in particular on the dramatic events surrounding the arrest of an illegal abortionist in the small textile town of Rho in 1928.
Un Americano a Roma: A 1950s’ Satire of Americanization
Authors: Ellwood David
Published: April 2008

The satirical film,Un americano a Romais examined as a commentary on the absorption by Italians, and especially Italian youth, of fads and fashions deriving from America during the economic boom. Although no masterpiece, the film is an important reflection on Italian identity at a time of rapid and bewildering change. It reveals that, while America became ‘everyone's second culture’, loyalty to domestic traditions and customs remained strong.
Justice, television and delegitimation: on the cultural codification of the Italian political crisis
Authors: Sassatelli Roberta
Published: April 2008

Pier Paolo Giglioli, Sandra Cavicchioli and Giolo Fele,Rituali di degradazione. Anatomia del processo Cusani, Il Mulino, Bologna, 1997, 243 pp., ISBN 88–15–05713–7 pbk, 28,000 Lire.

Recent developments in Italian politics, such as the emergence ofForza Italia, became possible only after a much deeper process had taken place, the delegitimation of Italian politicians. In the early 1990s, much of the political class which had dominated Italian politics since the Second World War was publicly exposed and removed from politics. The old parties of government, the Christian Democrats (DC) and the Socialists (PSI), were swept aside. What appeared to be a civilized evolution had its visible peak in the difficult struggle conducted by a few magistrates, the Milan-basedMani pulite(Clean hands) team, against political corruption. The so-calledTangentopoli(Kickback city) investigations have been indicated as the turning point of contemporary Italian politics. They certainly represent the moment when a rhetoric of ‘old’ and ‘new’ was divulged, when the Italian Republic began to be felt as a collapsing venture, giving an opportunity for change and reform which has not yet been grasped.
The death (and re-birth) of the hero: charisma and manufactured charisma in modern Italy
Authors: Gundle Stephen
Published: April 2008

In the twentieth century Italy has witnessed an unusual variety of charismatic political figures. Given the tradition of the Risorgimento and in particular the influence of Garibaldi, several of these donned the mantle of heroism. However, in modern conditions this heroism was largely a matter of showmanship. With the rise of mass communications, political leaders were compelled to reinvent the nature and forms of their appeal to the people and also to engage with the languages of popular entertainment. It is argued that cinema heralded a profound change in the nature of charisma and that television subsequently undermined it by rendering political leaders familiar and reducing the distance necessary for stage management.