bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties of Sm5Fe17 melt-spun ribbon
Authors: Saito Tetsuji
Published: May 2007

The relationship between the structures and magnetic properties of Sm5Fe17 melt-spun ribbons was studied. The melt-spun ribbons obtained by annealing of amorphous Sm5Fe17 melt-spun ribbon consisted of the Sm5Fe17 phase when annealed at 973K for 0h (i.e., when the furnace was immediately turned off after heating) or the Sm5Fe17 phase together with a small amount of the SmFe12 phase when produced by annealing at 973K for 1h. The coercivity of the annealed Sm–Fe melt-spun ribbons was strongly dependent on the annealing conditions. The maximum coercivity of the annealed Sm5Fe17 melt-spun ribbons exceeded 36kOe.
Superconductivity in zero-dimensional indium nanoparticles
Authors: Wu F.-Y. , Yang C. C. , Wu C.-M. , Wang C.-W. , Li W.-H.
Published: May 2007

An In nanoparticle powder was fabricated by employing the thermal evaporation method. Size analysis using x-ray diffraction profiles analysis and atomic force microscopy images indicates an average particle diameter of 36(2)nm and a Gaussian size distribution with a half-width of 3nm. The superconducting critical temperature of the In nanopowder increases slightly to 3.57(3)K, which was found to be extremely insensitive to the applied magnetic field. The critical magnetic field reaches ∼5T, which is a factor of 170 times higher than that of bulk In.
Low temperature neutron diffraction studies showing evidence for charge-exchange-type magnetic ordering in Mn doped SrRuO3
Authors: Singh Brajendra , Sundar Manoharan S. , Sahu R. K. , Krishnan P. S. R. , Shinde A. B. , Jain Karishma
Published: May 2007

Sr Ru O 3 is a 4d transition metal oxide having a metallic and itinerant ferromagnetic character with TC∼165K. Mn doping in SrRuO3 induces antiferromagnetic interaction, with the equiatomic composition SrRu0.5Mn0.5O3 showing TC∼125K. Temperature dependent zero field cooled and field cooled magnetization data, resistivity data, and neutron diffraction studies on SrRu0.5Mn0.5O3 show the signature of the presence of two ferromagnetic zigzag chains coupled antiferromagnetically, called charge exchange (CE)-type antiferromagnetic ordering; this is contrary to the role of Ru+4, which is reported to remove charge ordering in manganites. The presence of significant amount of Mn+3 ions plays an important role in stabilizing the CE-type antiferromagnetic ordering.
Photoemission study of the Fe(001)∕MgO interface for varying oxidation conditions of magnesium oxide
Authors: Müller Martina , Matthes Frank , Schneider Claus M.
Published: May 2007

The nature of interface bonding essentially determines the spin polarization of tunneling currents through ferromagnet/insulator interfaces. We focus on the influence of ultrathin off-stoichiometric MgO coverages on the spin-polarized electronic structure of the (001) surface of bcc-Fe. By applying a combination of low-energy spin-resolved and core-level photoelectron spectroscopy, we show that the MgO stoichiometry has a direct impact on the interfacial spin polarization. The results underline the importance of controlling the chemical composition and bonding at ferromagnet/oxide interfaces to further optimize spin-dependent tunneling devices.
Three-dimensional magnetic flux-closure domain patterns in MnAs thin films on GaAs(001)
Authors: Engel-Herbert R. , Hesjedal T. , Schaadt D. M.
Published: May 2007

The magnetic microstructure of single-crystalline MnAs films on GaAs(001) has been investigated. Magnetic force microscopy (MFM) reveals a three-dimensional magnetization pattern that is in disagreement with the simple domain picture observed by surface-sensitive magnetic imaging. Here, we present a consistent micromagnetic picture of MnAs thin films in the ferromagnetic stripe phase, which appears in the course of the phase transition. A number of equilibrium magnetization patterns of the stripes are found that are, in fact, based on flux-closure domain patterns in the basal plane of MnAs. The simulation of a stripe array yields excellent agreement with the measured surface magnetization. The experimentally observed stray field contrast was confirmed by MFM contrast simulations based on these equilibrium magnetization patterns.
Magnetostriction in the Bose-Einstein condensate quantum magnet NiCl2–4SC(NH2)2 (Invited)
Authors: Zapf V. S. , Correa V. F. , Batista C. D. , Murphy T. P. , Palm E. D. , Jaime M. , Tozer S. , Lacerda A. , Paduan-Filho A.
Published: May 2007

The quantum magnet NiCl2–4SC(NH2)2 is a candidate for observing Bose-Einstein condensation of spin degrees of freedom in applied magnetic fields. An XY antiferromagnetic ordered state occurs in a dome-shaped region of the temperature-field phase diagram between Hc1=2.1T and Hc2=12.6T and below 1.2K. Bose-Einstein condensation corresponds to the field-induced quantum phase transition into the ordered state. We investigate magnetostriction in single crystals of this compound at dilution refrigerator temperatures in magnetic fields up to 18T, and as a function of magnetic field angle. We show that significant changes in the lattice parameters are induced by magnetic fields, and argue that these result from antiferromagnetic couplings between the Ni spins along the tetragonal c axis. The magnetic phase diagram as a function of temperature, field, and field angle can be extracted from these data. We discuss the implications of these results to Bose-Einstein condensation in this system.
Nonlinear magnetic response from the Ru0.9Sr2YCu2.1O7.9 magnetosuperconductor and its resultant phase separation
Authors: Živković I. , Awana V. P. S. , Kishan H. , Balamurugan S. , Takayama-Muromachi E. , Felner I.
Published: May 2007

We investigated the third harmonic nonlinear susceptibility of the Ru0.9Sr2YCu2.1O7.9 magnetosuperconductor and found the presence of two well separated negative peaks. The peak at TM=140K is connected to the previously well known main magnetic ordering of the Ru sublattice, and the peak at around 180K is probably associated with the formation of superparamagnetic particles above TM. The negative signals for both peaks will be discussed in terms of ensuing magnetic orderings of Ru spins at these temperatures. Further, these results will be compared with a recent study of nonlinear susceptibility on RuSr2GdCu2O8.
Grain boundary evaluation in sequentially laterally solidified polycrystalline-silicon devices
Authors: Valletta A. , Bonfiglietti A. , Rapisarda M. , Mariucci L. , Fortunato G. , Brotherton S. D.
Published: May 2007

A systematic study has been made of the conduction process in polycrystalline-silicon thin film transistors (poly-Si TFTs) using carrier flow parallel and perpendicular to sub-grain-boundaries in sequentially laterally solidified material. The objective of this investigation was to obtain an unambiguous characterization of grain boundary (GB) behavior. By studying orthogonal TFTs in this anisotropic material, it was possible to distinguish grain boundary carrier trapping from intragrain trapping. In conventional poly-Si, the material is isotropic over distances greater than the grain size of ∼300nm, and there is no direct and clear-cut way of distinguishing between intragrain and intergrain trapping centers. In the experimental samples, the thermal activation energy of the channel current was measured in the two orthogonal directions, and the difference in activation energy was related to carrier flow over perpendicular sub-GBs. The detailed interpretation of the experimental results was facilitated by two-dimensional numerical simulations, demonstrating that a planar barrier GB, which simply resulted in a potential barrier within the channel, was fundamentally incompatible with the experimental drain current activation energy data. It was only possible to obtain a satisfactory representation of all the experimental data by using a finite width GB, in which carrier flow was controlled by transport across the resistive GB region, rather than by emission over a barrier. This representation of the sub-GB permitted the essential combination of reduced field effect mobility, for orthogonal carrier flow, and a drain current activation energy, which was close to zero.
In-plane self-arrangement of high-density InAs quantum dots on GaAsSb∕GaAs(001) by molecular beam epitaxy
Authors: Kanto Toru , Yamaguchi Koichi
Published: May 2007

InAs quantum dots (QDs) were grown on GaAsSb∕GaAs(001) buffer layers by molecular beam epitaxy using a Stranski-Krastanov mode. A high QD density of about 1×1011 cm−2 was obtained for an Sb flux ratio of more than 0.14. In the case of high-density QD growth on the GaAsSb layers, many nanoholes were observed on the surface and located beside the QDs. In addition, one-dimensional QD chains were formed near nanogrooves and step edges. As the InAs growth proceeded, an in-plane arrangement of the InAs QDs was partially formed along ⟨010⟩ directions. It is considered that the in-plane arrangement of the QDs originates from the QD chains and the nanogrooves, aligned along ⟨010⟩ step edges. From transmission electron microscopy and photoluminescence measurements, it was found that the high-density InAs QDs on the GaAsSb buffer layer reveal high crystal quality.
Preparation and structure of porous dielectrics by plasma enhanced chemical vapor deposition
Authors: Gates S. M. , Neumayer D. A. , Sherwood M. H. , Grill A. , Wang X. , Sankarapandian M.
Published: May 2007

The preparation of ultralow dielectric constant porous silicon, carbon, oxygen, hydrogen alloy dielectrics, called “pSiCOH,” using a production 200mm plasma enhanced chemical vapor deposition tool and a thermal treatment is reported here. The effect of deposition temperature on the pSiCOH film is examined using Fourier transform infrared (FTIR) spectroscopy, dielectric constant (k), and film shrinkage measurements. For all deposition temperatures, carbon in the final porous film is shown to be predominantly Si–CH3 species, and lower k is shown to correlate with increased concentration of Si–CH3. NMR and FTIR spectroscopies clearly detect the loss of a removable, unstable, hydrocarbon (CHx) phase during the thermal treatment. Also detected are increased cross-linking of the Si–O skeleton, and concentration changes for three distinct structures of carbon. In the as deposited films, deposition temperature also affects the hydrocarbon (CHx) content and the presence of CO and CC functional groups.
Quantum SU(3) Skyrme model with noncanonical embedded SO(3) soliton
Authors: Jurčiukonis D. , Norvaišas E.
Published: May 2007

The new ansatz which is the SO(3) group soliton was defined for the SU(3) Skyrme model. The model is considered in noncanonical bases SU(3)⊃SO(3) for the state vectors. A complete canonical quantization of the model has been investigated in the collective coordinate formalism for the fundamental SU(3) representation of the unitary field. The independent quantum variable manifold covers all the eight dimension SU(3) group manifold due to the new ansatz. The explicit expressions of the Lagrangian and Hamiltonian densities are derived for this modified quantum skyrmion.
Photoluminescence and self-interference in germanium-doped silica films
Authors: Yang Y. M. , Yang L. W. , Cai M. Q. , Chu Paul K.
Published: May 2007

Germanium-doped silica films were prepared by magnetron cosputtering and postannealing. The photoluminescence properties and their dependence on the Ge contents and annealing temperature were investigated. Our experiments indicate that the observed light emission originates from the neutral oxygen vacancy defects. The substructures in the luminescence bands of the films were found to result from multiple-beam interferences of the emission in the optical cavity formed by the transparent films.
Dependence on chain length of NMR relaxation times in mixtures of alkanes
Authors: Freed Denise E.
Published: May 2007

Many naturally occurring fluids, such as crude oils, consist of a very large number of components. It is often of interest to determine the composition of the fluids in situ. Diffusion coefficients and nuclear magnetic resonance (NMR) relaxation times can be measured in situ and depend on the size of the molecules. It has been shown [D. E. Freed et al., Phys. Rev. Lett. 94, 067602 (2005)] that the diffusion coefficient of each component in a mixture of alkanes follows a scaling law in the chain length of that molecule and in the mean chain length of the mixture, and these relations were used to determine the chain length distribution of crude oils from NMR diffusion measurements. In this paper, the behavior of NMR relaxation times in mixtures of chain molecules is addressed. The author explains why one would expect scaling laws for the transverse and longitudinal relaxation times of mixtures of short chain molecules and mixtures of alkanes, in particular. It is shown how the power law dependence on the chain length can be calculated from the scaling laws for the translational diffusion coefficients. The author fits the literature data for NMR relaxation in binary mixtures of alkanes and finds that its dependence on chain length agrees with the theory. Lastly, it is shown how the scaling laws in the chain length and the mean chain length can be used to determine the chain length distribution in crude oils that are high in saturates. A good fit is obtained between the NMR-derived chain length distributions and the ones from gas chromatography.
Impact of interfacial layer control using Gd2O3 in HfO2 gate dielectric on GaAs
Authors: Dalapati Goutam Kumar , Tong Yi , Loh Wei Yip , Mun Hoe Keat , Cho Byung Jin
Published: May 2007

Structural and electrical properties of HfO2 and HfO2∕Gd2O3 gate stacks on p-GaAs substrates have been investigated. It has been demonstrated that the presence of thin layer of Gd2O3 between HfO2 and GaAs improves metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, frequency dispersion, and leakage current. It is also found that HfO2∕Gd2O3 stack can reduce the interfacial GaAs-oxide formation, thus reduce the outdiffusion of elemental Ga and As during post-thermal annealing process. Such suppression of outdiffusion significantly improves the electrical properties of the dielectric stacks.
Angle multiplexed storage with object beam alone
Authors: Yau Hon-Fai , Liu Jung-Ping
Published: May 2007

Making use of the interference of incident light waves and the accompanying fanning waves in a photorefractive LiNbO3 crystal, the authors have recorded binary images as well as gray-tone images in a crystal with only an object beam. Angle multiplexing has also been demonstrated with this one beam recording method. Basing on a model that the recording is accomplished through the interference of the object light and its fanning light, the authors have estimated the minimal angular separation for achieving a cross-talk-free multiplexing.
Synthesis and photoluminescence properties of well-aligned Ga-doped N-rich SiOxNy nanowire bundles
Authors: Zhang X. T. , Liu Z. , Zheng Z. , Hark S. K. , Fu Y. B. , Zhang G. B.
Published: May 2007

Well-aligned Ga-doped N-rich SiOxNy bundles were synthesized on Si substrates by chemical vapor deposition. According to the x-ray photoelectron spectroscopy spectra of the Si 2p3∕2 region, the relative shifts of N 1s and chemical stabilities of all the possible tetrahedrons, the most probable four tetrahedral phases in the bundles are Si–N4, Si–N3O, Si–O3N, and Si–O4, corresponding to bonding units of Si3N4, Si2ON2, Si6O9N2, and SiO2. Elemental mappings, by using electron energy loss spectroscopy, confirm that elements Si, O, and N are homogeneously distributed. An intense ultraviolet light emission is observed by using vacuum ultraviolet synchrotron radiation as an excitation light source.
Deep levels controlling the electrical properties of Fe-implanted GaInP∕GaAs
Authors: Fraboni Beatrice , Piana Erio , Cesca Tiziana , Gasparotto Andrea , Longo Massimo , Jakomin Roberto , Tarricone Luciano
Published: May 2007

The authors investigated the electrical compensation induced by deep levels introduced in metal organic vapor phase epitaxy grown n+-InGaP∕GaAs epitaxial layers by high temperature Fe implantation. The activation of the Fe2+-related deep levels has been assessed by current-voltage analyses performed at different temperatures. In the framework of the space charge limited current model, they determined the energy location in the gap of the deep levels that control the electrical properties of the semi-insulating epilayers. A donor level which acts as an electron trap located at EC−0.5eV and a Fe-related acceptor level which is responsible for the stable increase of resistivity located at EV+0.72eV were identified.
Strain analysis in ultrathin SiGe-on-insulator layers formed from strained Si-on-insulator substrates by Ge-condensation process
Authors: Tezuka Tsutomu , Hirashita Norio , Moriyama Yoshihiko , Nakaharai Shu , Sugiyama Naoharu , Takagi Shin-ichi
Published: May 2007

Ultrathin strained SiGe-on-insulator (sSGOI) layers were fabricated by Ge condensation, in which Si1−xGex layers on strained Si-on-insulator (sSOI) substrates were oxidized, and their strain and defects were investigated. With increasing the Ge fraction x, the compressive strain in the SGOI layers was found to linearly increase up to ∼2%. The linear strain dependence on x was offset by the preexisting tensile strain in the sSOI substrate compared to that of conventional SGOI layers formed on unstrained SOI substrates. As a result, pseudomorphic sSGOI layers were obtained on the sSOI substrate up to higher x (∼0.75) than on a SOI substrate.
Efficient solution-processed infrared photovoltaic cells: Planarized all-inorganic bulk heterojunction devices via inter-quantum-dot bridging during growth from solution
Authors: Klem Ethan J. D. , MacNeil Dean D. , Cyr Paul W. , Levina Larissa , Sargent Edward H.
Published: May 2007

Solution-processed thin-film organic, inorganic, and hybrid photovoltaic devices have achieved power conversion efficiencies as high as 5%. However, these devices remain limited by their capture of visible energy; more than a half of the sun’s power lies in the infrared. Herein the authors demonstrate photovoltaic devices effective across the visible and all the way out to 1700nm. Only through the use of ethanedithiol as a bridging molecule to affect interparticle linking were they able to achieve fabrication of smooth, continuous quantum dot films on rough, high-surface area transparent metal oxides. This allowed them to increase light absorption while maintaining efficient charge separation and extraction and at the same time avoiding electrical short circuits. They obtained monochromatic infrared power conversion efficiencies of 1.3%, a 50-fold gain over the previous published record of 0.025% in IR solution-processed photovoltaics. The authors demonstrate quantum size-effect tuning of device band gaps relevant to multijunction solar cells.
Anisotropic electric conduction derived from self-organized nanogroove array on Li-doped NiO epitaxial film
Authors: Matsuda Akifumi , Akiba Shusaku , Kasahara Masayasu , Watanabe Takahiro , Akita Yasuyuki , Yoshimoto Mamoru
Published: May 2007

The self-assembly formation of straight and periodic nanogroove arrays was carried out on the surface of Li-doped NiO thin films by use of atomic steps on the substrate. The nanostructure was formed by annealing Li-doped NiO (111) epitaxial thin film prepared on an atomically stepped α-Al2O3 (0001) substrate via pulsed laser deposition at room temperature. V-shaped nanogrooves, with a depth of ∼20nm and an open-end width of ∼50nm, were observed over the entire substrate and characterized by cross-sectional transmission-electron microscopy. The separation of the aligned nanogrooves was from 80to100nm, comparable to the size of the atomic steps on the substrate. Anisotropic electric conduction was definitely attained for the Li-doped NiO thin film with the nanogroove array. A resistance ratio up to about 100 was obtained for both directions parallel and perpendicular to the nanogrooves. The resultant anisotropy was considered to be mainly caused by anisotropic grain growth due to self-organized reconstruction of the NiO film during annealing.
Miniature sensor suitable for electronic nose applications
Authors: Pinnaduwage Lal A. , Gehl Anthony C. , Allman Steve L. , Johansson Alicia , Boisen Anja
Published: May 2007

A major research effort has been devoted over the years for the development of chemical sensors for the detection of chemical and explosive vapors. However, the deployment of such chemical sensors will require the use of multiple sensors (probably tens of sensors) in a sensor package to achieve selective detection. In order to keep the overall detector unit small, miniature sensors with sufficient sensitivity of detection will be needed. We report sensitive detection of dimethyl methylphosphonate (DMMP), a stimulant for the nerve agents, using a miniature sensor unit based on piezoresistive microcantilevers. The sensor can detect parts-per-trillion concentrations of DMMP within 10s exposure times. The small size of the sensor makes it ideally suited for electronic nose applications.
Influence of the quantum-confined Stark effect in an InGaN∕GaN quantum well on its coupling with surface plasmon for light emission enhancement
Authors: Chen Cheng-Yen , Lu Yen-Cheng , Yeh Dong-Ming , Yang C. C.
Published: May 2007

The authors analyze the contribution of the screening of the quantum-confined Stark effect (QCSE) to the emission enhancement behavior in the process of surface plasmon (SP) coupling with an InGaN∕GaN quantum well (QW), which is 20nm away from a Ag thin film that supports the SP. From the measurements of excitation power dependent photoluminescence and time-resolved photoluminescence (TRPL) spectroscopy, and the fitting to the TRPL data based on a rate-equation model, it is found that when the excitation level is high, the QCSE screening effect not only contributes significantly to the emission enhancement but also increases the SP coupling rate because of the blueshift of emission spectrum caused by the screening effect. Therefore, the emission strength from SP radiation, relative to that from QW radiative recombination, increases with the excited carrier density. Also, a saturation behavior of SP-QW coupling is observed from the fitting procedure.
Copper barrier properties of a low-dielectric-constant organocyclosiloxane prepared by plasma-enhanced polymerization
Authors: Yoshino Takenobu , Hata Nobuhiro , Kawahara Jun , Kikkawa Takamaro
Published: May 2007

An excellent barrier effect against copper (Cu) ion drift of an organocyclosiloxane (OCS) low-dielectric-constant film is studied by electric measurements. The OCS film, which was formed by plasma-enhanced polymerization, had two kinds of organic groups such as alkyl and vinyl groups extending from each silicon (Si) atom in a six-membered ring of silica (Si–O). Time to breakdown of Cu/OCS/Si metal-insulator-semiconductor (MIS) capacitors measured with positive bias stress was equal to that with negative bias stress, and an almost zero flatband voltage shift was observed after applying a bias-temperature stress. From these results, the authors conclude that Cu+ ion drift into OCS is suppressed. By forming 30-nm-thick OCS on a porous silica (po-SiO) film, the predicted lifetime of Cu/OCS/po-SiO MIS structure exceeds 10yr at 473K under 0.2MV∕cm, suggesting that thin OCS is attractive for po-SiO as a drift barrier for Cu+ ions. It is proposed that the contact between Cu and Si–O skeletal bonds is suppressed by organic groups in OCS, preventing the ionization of Cu atoms and their drift.
Optical thermometry through infrared excited green upconversion emissions in Er3+–Yb3+ codoped Al2O3
Authors: Dong B. , Liu D. P. , Wang X. J. , Yang T. , Miao S. M. , Li C. R.
Published: May 2007

Fluorescence intensity ratio (FIR) variation of green upconversion emissions at 523 and 545nm in the Er3+–Yb3+ codoped Al2O3 has been studied as a function of temperature using a 978nm semiconductor laser diode as an excitation source. In the temperature range of 295–973K, the maximum sensitivity and the temperature revolution derived from the FIR technique are approximately 0.0051K−1 and 0.3K, respectively. The Er3+–Yb3+ codoped Al2O3 material with the highest operating temperature up to 973K, the higher temperature revolution, and the fluorescence efficiency indicated that it is promising for applications in optical high temperature sensor.
Multiple scattering in evolving media
Authors: Snieder Roel , Page John
Published: May 2007

With high sensitivity to evolving environments, multiply scattered acoustic and elastic waves are being used to probe temporal changes in physical systems, from volcanoes to bubbles in a turbulent fluid.
The physics in your fork
Authors: Bloomfield Louis A.
Published: May 2007

A manufacturer of good cutlery balances competing requirements of strength, ability to hold an edge, and resistance to rusting.
Toward an internally consistent pressure scale
Authors: Fei Yingwei , Ricolleau Angele , Frank Mark , Mibe Kenji , Shen Guoyin , Prakapenka Vitali
Published: May 2007

Our ability to interpret seismic observations including the seismic discontinuities and the density and velocity profiles in the earth's interior is critically dependent on the accuracy of pressure measurements up to 364 GPa at high temperature. Pressure scales based on the reduced shock-wave equations of state alone may predict pressure variations up to 7% in the megabar pressure range at room temperature and even higher percentage at high temperature, leading to large uncertainties in understanding the nature of the seismic discontinuities and chemical composition of the earth's interior. Here, we report compression data of gold (Au), platinum (Pt), the NaCl-B2 phase, and solid neon (Ne) at 300 K and high temperatures up to megabar pressures. Combined with existing experimental data, the compression data were used to establish internally consistent thermal equations of state of Au, Pt, NaCl-B2, and solid Ne. The internally consistent pressure scales provide a tractable, accurate baseline for comparing high pressure–temperature experimental data with theoretical calculations and the seismic observations, thereby advancing our understanding fundamental high-pressure phenomena and the chemistry and physics of the earth's interior.
Effect of congenital blindness on the semantic representation of some everyday concepts
Authors: Connolly Andrew C. , Gleitman Lila R. , Thompson-Schill Sharon L.
Published: May 2007

This study explores how the lack of first-hand experience with color, as a result of congenital blindness, affects implicit judgments about “higher-order” concepts, such as “fruits and vegetables” (FV), but not others, such as “household items” (HHI). We demonstrate how the differential diagnosticity of color across our test categories interacts with visual experience to produce, in effect, a category-specific difference in implicit similarity. Implicit pair-wise similarity judgments were collected by using an odd-man-out triad task. Pair-wise similarities for both FV and for HHI were derived from this task and were compared by using cluster analysis and regression analyses. Color was found to be a significant component in the structure of implicit similarity for FV for sighted participants but not for blind participants; and this pattern remained even when the analysis was restricted to blind participants who had good explicit color knowledge of the stimulus items. There was also no evidence that either subject group used color knowledge in making decisions about HHI, nor was there an indication of any qualitative differences between blind and sighted subjects' judgments on HHI.
Cholesterol Controls Lipid Endocytosis through Rab11
Authors: Takahashi Miwa , Murate Motohide , Fukuda Mitsunori , Sato Satoshi B. , Ohta Akinori , Kobayashi Toshihide
Published: May 2007

Cellular cholesterol increases when cells reach confluency in Chinese hamster ovary (CHO) cells. We examined the endocytosis of several lipid probes in subconfluent and confluent CHO cells. In subconfluent cells, fluorescent lipid probes including poly(ethylene glycol)derivatized cholesterol, 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3β-ol, and fluorescent sphingomyelin analogs were internalized to pericentriolar recycling endosomes. This accumulation was not observed in confluent cells. Internalization of fluorescent lactosylceramide was not affected by cell confluency, suggesting that the endocytosis of specific membrane components is affected by cell confluency. The crucial role of cellular cholesterol in cell confluency–dependent endocytosis was suggested by the observation that the fluorescent sphingomyelin was transported to recycling endosomes when cellular cholesterol was depleted in confluent cells. To understand the molecular mechanism(s) of cell confluency– and cholesterol-dependent endocytosis, we examined intracellular distribution of rab small GTPases. Our results indicate that rab11 but not rab4, altered intracellular localization in a cell confluency–associated manner, and this alteration was dependent on cell cholesterol. In addition, the expression of a constitutive active mutant of rab11 changed the endocytic route of lipid probes from early to recycling endosomes. These results thus suggest that cholesterol controls endocytic routes of a subset of membrane lipids through rab11.
The Transmembrane Domain of Acid Trehalase Mediates Ubiquitin-independent Multivesicular Body Pathway Sorting
Authors: Huang Ju , Reggiori Fulvio , Klionsky Daniel J.
Published: May 2007

Trehalose serves as a storage source of carbon and plays important roles under various stress conditions. For example, in many organisms trehalose has a critical function in preserving membrane structure and fluidity during dehydration/rehydration. In the yeast Saccharomyces cerevisiae, trehalose accumulates in the cell when the nutrient supply is limited but is rapidly degraded when the supply of nutrients is renewed. Hydrolysis of trehalose in yeast depends on neutral trehalase and acid trehalase (Ath1). Ath1 resides and functions in the vacuole; however, it appears to catalyze the hydrolysis of extracellular trehalose. Little is known about the transport route of Ath1 to the vacuole or how it encounters its substrate. Here, through the use of various trafficking mutants we showed that this hydrolase reaches its final destination through the multivesicular body (MVB) pathway. In contrast to the vast majority of proteins sorted into this pathway, Ath1 does not require ubiquitination for proper localization. Mutagenesis analyses aimed at identifying the unknown targeting signal revealed that the transmembrane domain of Ath1 contains the information sufficient for its selective sequestration into MVB internal vesicles.
Accumulation of Polyadenylated mRNA, Pab1p, eIF4E, and eIF4G with P-Bodies inSaccharomyces cerevisiae
Authors: Brengues Muriel , Parker Roy
Published: May 2007

Recent experiments have shown that mRNAs can move between polysomes and P-bodies, which are aggregates of nontranslating mRNAs associated with translational repressors and the mRNA decapping machinery. The transitions between polysomes and P-bodies and how the poly(A) tail and the associated poly(A) binding protein 1 (Pab1p) may affect this process are unknown. Herein, we provide evidence that poly(A)+mRNAs can enter P-bodies in yeast. First, we show that both poly(A)−and poly(A)+mRNA become translationally repressed during glucose deprivation, where mRNAs accumulate in P-bodies. In addition, both poly(A)+transcripts and/or Pab1p can be detected in P-bodies during glucose deprivation and in stationary phase. Cells lacking Pab1p have enlarged P-bodies, suggesting that Pab1p plays a direct or indirect role in shifting the equilibrium of mRNAs away from P-bodies and into translation, perhaps by aiding in the assembly of a type of mRNP within P-bodies that is poised to reenter translation. Consistent with this latter possibility, we observed the translation initiation factors (eIF)4E and eIF4G in P-bodies at a low level during glucose deprivation and at high levels in stationary phase. Moreover, Pab1p exited P-bodies much faster than Dcp2p when stationary phase cells were given fresh nutrients. Together, these results suggest that polyadenylated mRNAs can enter P-bodies, and an mRNP complex including poly(A)+mRNA, Pab1p, eIF4E, and eIF4G2 may represent a transition state during the process of mRNAs exchanging between P-bodies and translation.
Efficient Interaction between Two GTPases Allows the Chloroplast SRP Pathway to Bypass the Requirement for an SRP RNA
Authors: Jaru-Ampornpan Peera , Chandrasekar Sowmya , Shan Shu-ou
Published: May 2007

Cotranslational protein targeting to membranes is regulated by two GTPases in the signal recognition particle (SRP) and the SRP receptor; association between the two GTPases is slow and is accelerated 400-fold by the SRP RNA. Intriguingly, the otherwise universally conserved SRP RNA is missing in a novel chloroplast SRP pathway. We found that even in the absence of an SRP RNA, the chloroplast SRP and receptor GTPases can interact efficiently with one another; the kinetics of interaction between the chloroplast GTPases is 400-fold faster than their bacterial homologues, and matches the rate at which the bacterial SRP and receptor interact with the help of SRP RNA. Biochemical analyses further suggest that the chloroplast SRP receptor is pre-organized in a conformation that allows optimal interaction with its binding partner, so that conformational changes during complex formation are minimized. Our results highlight intriguing differences between the classical and chloroplast SRP and SRP receptor GTPases, and help explain how the chloroplast SRP pathway can mediate efficient targeting of proteins to the thylakoid membrane in the absence of the SRP RNA, which plays an indispensable role in all the other SRP pathways.
Involvement of Transportin 2–mediated HuR Import in Muscle Cell Differentiation
Authors: van der Giessen Kate , Gallouzi Imed-Eddine
Published: May 2007

Muscle fiber formation requires the sequential expression of myogenic regulatory factors (MRFs) such as MyoD and myogenin. The messenger RNAs encoding these two proteins are regulated posttranscriptionally through their ability to associate with the RNA-binding protein HuR. HuR localizes first to the nucleus and then to the cytoplasm during muscle differentiation. Therefore, we examined the link between this localization and the promyogenic function of HuR. We show that early in muscle differentiation, HuR is localized to the nucleus of myoblasts by active Transportin 2 (TRN2)-mediated import. In differentiated muscle fibers, however, the TRN2-HuR complex is disrupted, leading to the cytoplasmic localization of HuR, as well as to the stabilization of MyoD and myogenin mRNAs. Interrupting the TRN2-HuR complex using RNA interference against TRN2, or the cell-permeable peptides (AP) fused to the HuR nucleocytoplasmic shuttling domain (HNS), enhanced the efficiency of myofiber formation. Together, our data suggest that HuR import is disrupted in differentiated muscle fibers and this event constitutes an important regulatory step during myogenesis.
A Knockout Mouse Approach Reveals that TCTP Functions as an Essential Factor for Cell Proliferation and Survival in a Tissue- or Cell Type–specific Manner
Authors: Chen Sung Ho , Wu Peih-Shan , Chou Chiang-Hung , Yan Yu-Ting , Liu Hsuan , Weng Shih-Yen , Yang-Yen Hsin-Fang
Published: May 2007

Translationally controlled Tumor Protein (TCTP) is an evolutionally highly conserved protein which has been implicated in many cellular functions that are related to cell growth, death, and even the allergic response of the host. To address the physiological roles of TCTP, we generated TCTP knockout mice by targeted gene disruption. Heterozygous mutants appeared to be developmentally normal. However, homozygous mutants (TCTP−/−) were embryonic lethal. TCTP−/−embryos were smaller in size than the control littermates at all postimplantation stages examined. Although TCTP is widely expressed in both extraembryonic and embryonic tissues, the most prominent defect of the TCTP−/−embryo at embryonic stage day 5.5 (E5.5) was in its epiblast, which had a reduced number of cells compared with wild-type controls. The knockout embryos also suffered a higher incidence of apoptosis in epiblast starting about E6.5 and subsequently died around E9.5–10.5 with a severely disorganized structure. Last, we demonstrated that TCTP−/−and control mouse embryonic fibroblasts manifested similar proliferation activities and apoptotic sensitivities to various death stimuli. Taken together, our results suggest that despite that TCTP is widely expressed in many tissues or cell types, it appears to regulate cell proliferation and survival in a tissue- or cell type–specific manner.
Availability of non-carotenoid antioxidants affects the expression of a carotenoid-based sexual ornament
Authors: Pike Thomas W , Blount Jonathan D , Lindström Jan , Metcalfe Neil B
Published: May 2007

Carotenoids are responsible for much of the yellow, orange and red pigmentation in the animal kingdom, and the importance of such coloration as an honest signal of individual quality has received widespread attention. In particular, owing to the multiple roles of carotenoids as pigments, antioxidants and immunostimulants, carotenoid-based coloration has been suggested to advertise an individual's antioxidant or immune defence capacity. However, it has recently been argued that carotenoid-based signals may in fact be advertising the availability of different antioxidants, many of which (including various vitamins, antioxidant enzymes and minerals) are colourless and so would be uninformative as components of a visual signal, yet often have greater biological activity than carotenoids. We tested this hypothesis by feeding male sticklebacks (
Gasterosteus aculeatus
) a diet containing a fixed level of carotenoids and either low or high, but biologically realistic levels of the colourless antioxidant vitamins C and E. High-antioxidant diet males produced significantly more intensely coloured (but not larger) carotenoid-based regions of nuptial coloration and were preferred over size-matched males of the opposite diet treatment in mate-choice trials. Furthermore, there were positive correlations between an individual's somatic antioxidant activity and signal intensity. Our data suggest that carotenoid-based ornaments may honestly signal an individual's availability of non-carotenoid antioxidants, allowing females to make adaptive mate-choice decisions.
Evolving the selfish herd: emergence of distinct aggregating strategies in an individual-based model
Authors: Wood Andrew J , Ackland Graeme J
Published: May 2007

From zebra to starlings, herring and even tadpoles, many creatures move in an organized group. The emergent behaviour arises from simple underlying movement rules, but the evolutionary pressure which favours these rules has not been conclusively identified. Various explanations exist for the advantage to the individual of group formation: reduction of predation risk; increased foraging efficiency or reproductive success. Here, we adopt an individual-based model for group formation and subject it to simulated predation and foraging; the haploid individuals evolve via a genetic algorithm based on their relative success under such pressure. Our work suggests that flock or herd formation is likely to be driven by predator avoidance. Individual fitness in the model is strongly dependent on the presence of other phenotypes, such that two distinct types of evolved group can be produced by the same predation or foraging conditions, each stable against individual mutation. We draw analogies with multiple Nash equilibria theory of iterated games to explain and categorize these behaviours. Our model is sufficient to capture the complex behaviour of dynamic collective groups, yet is flexible enough to manifest evolutionary behaviour.
Mating success of resident versus non-resident males in a territorial butterfly
Authors: Bergman Martin , Gotthard Karl , Berger David , Olofsson Martin , Kemp Darrell J , Wiklund Christer
Published: May 2007

Male–male competition over territorial ownership suggests that winning is associated with considerable benefits. In the speckled wood butterfly,Pararge aegeria, males fight over sunspot territories on the forest floor; winners gain sole residency of a sunspot, whereas losers patrol the forest in search of females. It is currently not known whether residents experience greater mating success than non-residents, or whether mating success is contingent on environmental conditions. Here we performed an experiment in which virgin females ofP. aegeriawere allowed to choose between a resident and a non-resident male in a large enclosure containing one territorial sunspot. Resident males achieved approximately twice as many matings as non-residents, primarily because matings were most often preceded by a female being discovered when flying through a sunspot. There was no evidence that territorial residents were more attractiveper se, with females seen to reject them as often as non-residents. Furthermore, in the cases where females were discovered outside of the sunspot, they were just as likely to mate with non-residents as residents. We hypothesize that the proximate advantage of territory ownership is that light conditions in a large sunspot greatly increase the male's ability to detect and intercept passing receptive females.
The isotopic ecology of African mole rats informs hypotheses on the evolution of human diet
Authors: Yeakel Justin D , Bennett Nigel C , Koch Paul L , Dominy Nathaniel J
Published: May 2007

The diets ofAustralopithecus africanusandParanthropus robustusare hypothesized to have included C4plants, such as tropical grasses and sedges, or the tissues of animals which themselves consumed C4plants. Yet inferences based on the craniodental morphology ofA. africanusandP. robustusindicate a seasonal diet governed by hard, brittle foods. Such mechanical characteristics are incompatible with a diet of grasses or uncooked meat, which are too tough for efficient mastication by flat, low-cusped molars. This discrepancy, termed the C4conundrum, has led to the speculation that C4plant underground storage organs (USOs) were a source of nutrition for hominin species. We test this hypothesis by examining the isotopic ecology of African mole rats, which consume USOs extensively. We measuredδ18O andδ13C of enamel and bone apatite from fossil and modern species distributed across a range of habitats. We show thatδ18O values vary little and thatδ13C values vary along the C3to C4/CAM-vegetative axis. Relatively highδ13C values exist in modernCryptomys hottentotus natalensisandCryptomysspp. recovered from hominin-bearing deposits. These values overlap those reported forA. africanusandP. robustusand we conclude that the USO hypothesis for hominin diets retains certain plausibility.
Synthetic protocell biology: from reproduction to computation
Authors: Solé Ricard V , Munteanu Andreea , Rodriguez-Caso Carlos , Macía Javier
Published: May 2007

Cells are the building blocks of biological complexity. They are complex systems sustained by the coordinated cooperative dynamics of several biochemical networks. Their replication, adaptation and computational features emerge as a consequence of appropriate molecular feedbacks that somehow define what life is. As the last decades have brought the transition from the description-driven biology to the synthesis-driven biology, one great challenge shared by both the fields of bioengineering and the origin of life is to find the appropriate conditions under which living cellular structures can effectively emerge and persist. Here, we review current knowledge (both theoretical and experimental) on possible scenarios of artificial cell design and their future challenges.
Models of primitive cellular life: polymerases and templates in liposomes
Authors: Monnard Pierre-Alain , Luptak Andrej , Deamer David W
Published: May 2007

Nutrient transport, polymerization and expression of genetic information in cellular compartments are hallmarks of all life today, and must have appeared at some point during the origin and early evolution of life. Because the first cellular life lacked membrane transport systems based on highly evolved proteins, they presumably depended on simpler processes of nutrient uptake. Using a system consisting of an RNA polymerase and DNA template entrapped in submicrometre-sized lipid vesicles (liposomes), we found that the liposome membrane could be made sufficiently permeable to allow access of ionized substrate molecules as large as
nucleoside triphosphates
(NTPs) to the enzyme. The encapsulated polymerase transcribed the template-specific base sequences of the DNA to the RNA that was synthesized. These experiments demonstrate that units of genetic information can be associated with a functional catalyst in a single compartment, and that transcription of gene-sized DNA fragments can be achieved by relying solely on passive diffusion to supply NTPs substrates.
Coevolution of metabolic networks and membranes: the scenario of progressive sequestration
Authors: Szathmáry Eörs
Published: May 2007

Many regard metabolism as one of the central phenomena (or criteria) of life. Yet, the earliest infrabiological systems may have been devoid of metabolism: such systems would have been extreme heterotrophs. We do not know what level of complexity is attainable for chemical systems without enzymatic aid. Lack of template-instructed enzymatic catalysis may put a ceiling on complexity owing to inevitable spontaneous decay and wear and tear of chemodynamical machines. Views on the origin of metabolism critically depend on the assumptions concerning the sites of synthesis and consumption of organic compounds. If these sites are different, non-enzymatic origin of autotrophy is excluded. Whether autotrophy is secondary or not, it seems that protocell boundaries may have become more selective with time, concurrent with the enzymatization of the metabolic network. Primary heterotrophy and autotrophy imply pathway innovation and retention, respectively. The idea of metabolism–membrane coevolution leads to a scenario of progressive sequestration of the emerging living system from its exterior milieu. Comparative data on current protein enzymes may shed some light on such a primeval process by analogy, since two main ideas about enzymatization (the retroevolution and the patchwork scenarios) may not necessarily be mutually exclusive and the earliest enzymatic system may have used ribozymes rather than proteins.
Planktonic copepods reacting selectively to hydrodynamic disturbances
Authors: Strickler J. Rudi , Balázsi Gábor
Published: May 2007

In the water column, planktonic copepods encounter small-scale hydrodynamic disturbances generated by fellow zooplankters. Our question is whether or not the copepods can distinguish between hydrodynamic disturbances created by predators, prey, conspecifics and/or mates. We used a Schlieren optical system with a density gradient in the water volume and filmed at 48 frames per second to record the behaviour of copepods during encounters with an artificial hydrodynamic disturbance. We observed the reactions ofCyclops scutiferandEpischura nordenskiolditowards disturbances of different strengths. We also re-examined an earlier report on tandem swimming inC. scutiferwhile attempting to mate, using novel mathematical tools to analyse possible correlations between the two mates. We conclude that the information within the hydrodynamic disturbances created by swimming zooplankters has enough content for differentiated reactions. We also suggest that the adaptive value of tandem swimming during mating results in offspring capable of executing escape reactions comparable in strength to the disturbances.