bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the early stages of self-assembly in nanophase materials. II. Role of symmetry and dimensionality
Authors: Kozak John J. , Nicolis G.
Published: February 2011

We study the early stages of self-assembly of elementary building blocks of nanophase materials, considering explicitly their structure and the symmetry and the dimensionality of the reaction space. Previous work [Kozak et al., J. Chem. Phys. 134, 154701 (2007)] focused on characterizing self-assembly on small square-planar templates. Here we consider larger lattices of square-planar symmetry having N = 255 sites, and both hexagonal and triangular lattices of N = 256 sites. Furthermore, to assess the consequences of a depletion zone above a basal layer (λ = 1), we study self-assembly on an augmented diffusion space defined by λ = 2 and λ = 5 stacked layers having the same characteristics as the basal plane. The effective decrease in the efficiency of self-assembly of individual nanophase units when the diffusion space is expanded, by increasing the template size and/or by enlarging the depletion zone, is then quantified. The results obtained reinforce our earlier conclusion that the most significant factor influencing the kinetics of formation of a final self-assembled unit is the number of reaction pathways from one or more precursor states. We draw attention to the relevance of these results to zeolite synthesis and reactions within pillared clays.
Time-dependent manipulation of ultracold ion bunches
Authors: Reijnders M. P. , Debernardi N. , van der Geer S. B. , Mutsaers P. H. A. , Vredenbregt E. J. D. , Luiten O. J.
Published: February 2011

The combination of an ultracold ion source based on photoionization of a laser-cooled gas and time-dependent acceleration fields enables precise manipulation of ion beams. We demonstrate reduction in the longitudinal energy spread and transverse (de)focusing of the beam by applying time-dependent acceleration voltages. In addition, we show how time-dependent acceleration fields can be used to control both the sign and strength of the spherical aberrations. The experimental results are in close agreement with detailed charged particle tracking simulations and can be explained in terms of a simple analytical model.
Electronic structure analysis of threading screw dislocations in 4H–SiC using electron holography
Authors: Chung Suk , Berechman Ronen A. , McCartney Martha R. , Skowronski Marek
Published: February 2011

Off-axis electron holography has been used to map the electrostatic potential distribution of threading screw dislocations in differently n-doped 4H–SiC epitaxial layers. Observed phase contrast indicated the presence of a negatively charged dislocation core. Comparison between experimental and simulated potential profiles indicated that the density of trapped charges increased for a higher doped epilayer. Assuming a single level of the trap at the core, the ionization energy of the trap was calculated to be 0.89±0.22 eV.
Evaluation of Sr2CoMoO6−δ as anode material in solid-oxide fuel cells: A neutron diffraction study
Authors: Aguadero A. , Alonso J. A. , Martínez-Coronado R. , Martínez-Lope M. J. , Fernández-Díaz M. T.
Published: February 2011

The oxygen-deficient Sr2CoMoO6−δ double perovskite has been proposed as an anode material in solid-oxide fuel cells (SOFC). The evolution of its crystal structure has been followed by “in situ” temperature-dependent neutron powder diffraction from 23 °C (RT) to 867 °C in the heating and cooling runs in ultrahigh vacuum (PO2≈10−6 Torr) in order to simulate the reducing atmosphere corresponding to the working conditions of an anode in a SOFC. At RT the sample is described as tetragonal in the I4/m space group. When this oxide is heated above Tt=262 °C it undergoes a tetragonal I4/m to cubic Fm-3m phase transition. This phase transition takes place at a temperature around 25 °C lower than that previously described for the oxidized sample, and it is affected by a significant hysteresis (Tt=174 °C in the cooling run). The absence of tilting of the CoO6 and MoO6 octahedra in the high-temperature cubic phase favors the orbital overlap and the electronic conductivity; a high mobility of the oxygen atoms is derived from the elevated displacement parameters, for instance 3.2 Å2 at 867 °C. Both factors contribute to the excellent performance described for this mixed ionic-electronic conductor (MIEC) oxide as anode in single fuel cells. The dilatometric analysis shows a change of slope at around 270 °C that can be correlated with this tetragonal-to-cubic phase transition. The obtained thermal expansion coefficient (TEC) in the tetragonal region, between 50 and 270 °C is 14.5×10−6 K−1 whereas in the cubic region, between 270 and 850 °C, the TEC is 11.2×10−6 K−1. These figures are comparable to those obtained from the mentioned structural analysis; moreover the TEC for the cubic phase perfectly matches those of the usual electrolytes in a SOFC.
On the correlation of Young’s modulus and the fracture strength of metallic glasses
Authors: Yuan C. C. , Xi X. K.
Published: February 2011

It is generally believed that there is no simple relationship between ultimate fracture strength and stiffness for an elastically isotropic material. By taking bulk metallic glasses (BMGs) as model materials, the relation between ultimate fracture strength and elastic moduli was analyzed within Griffith theory framework. The observed correlation between elastic moduli and fracture strength in BMGs reveals the effects of BMG defects and plastic zone size on the crack resistance of these model materials.
TiO
2
-based metal-insulator-metal selection device for bipolar resistive random access memory cross-point application
Authors: Shin Jungho , Kim Insung , Biju Kuyyadi P. , Jo Minseok , Park Jubong , Lee Joonmyoung , Jung Seungjae , Lee Wootae , Kim Seonghyun , Park Sangsu , Hwang Hyunsang
Published: February 2011

We report a simple metal-insulator-metal (MIM)-type selection device that can alleviate the sneak current path in cross-point arrays. By connecting a nanometer-scale Pt/TiO2/TiN selection device to a Pt/TiO2−x/TiO2/W resistive random access memory (RRAM), we could significantly reduce read disturbance from unselected memory cells. This selection device could be easily integrated into an RRAM device, in which it suppressed the sneak current and significantly improved the readout margin compared to that obtained for an RRAM not using a selection device. The introduction of this MIM device can fulfill the requirement for an appropriate selection device for bipolar-type RRAM cross-point applications.
Instability of electrowetting on a dielectric substrate
Authors: Park Jonghyun , Feng Xi-Qiao , Lu Wei
Published: February 2011

The wetting angle of a liquid droplet on a dielectric substrate can be tuned by an applied electric field. Recent experiments revealed an intriguing phenomenon where the contact line between a droplet and a substrate may lose stability under a relatively large field, leading to the ejection of small droplets from the edge of the mother droplet. While this behavior may pose a limit on the achievable wetting angle, it also provides an interesting approach to produce patterns of tiny droplets. We propose a phase field model to explain the mechanism, which combines thermodynamics and convective viscous flow. Our study suggests that instability is preceded by a contact angle reduction and extrusion of a thin layer from the edge of the droplet. While instability appears when the electric field is above a critical value, it can be suppressed with increased surface energy of the droplet.
Magnetic and electrical behavior of Al doped La0.7Ca0.3MnO3 manganites
Authors: Tiwari Shailja , Phase D. M. , Choudhary R. J. , Mund H. S. , Ahuja B. L.
Published: February 2011

The effects of doping on magnetic and electrical transport mechanism of polycrystalline samples La0.7Ca0.3Mn1−xAlxO3 (x=0,0.02,0.04,0.06,0.08,0.1) have been investigated. Magnetization data reveal that long-range ferromagnetic ordering persists in all samples and the saturation moment decreases linearly as x increases. Resistivity data have been fitted with the variable range hopping model to estimate the density of state at Fermi level. It was observed that the substitution of Al in the series leads to a decrease in conductivity of the doped manganites samples, with conduction being controlled by the disorder induced localization of charge carriers.
Smooth soliton solutions of a new integrable equation by Qiao
Authors: Sakovich Sergei
Published: February 2011

We find a transformation which relates a new third-order integrable nonlinear evolution equation, introduced recently by Qiao, with the well-known modified Korteweg–de Vries equation. Then we use this transformation to derive smooth soliton solutions of the new equation from the known rational and soliton solutions of the old one.
Constrained active space unrestricted mean-field methods for controlling spin-contamination
Authors: Tsuchimochi Takashi , Scuseria Gustavo E.
Published: February 2011

We have recently proposed a novel approach for obtaining high-spin restricted open-shell Hartree–Fock wave functions by imposing constraints on the unrestricted Hartree–Fock (UHF) method [T. Tsuchimochi and G. E. Scuseria, J. Chem. Phys. 133, 141102 (2010)]. We here extend these ideas to the case where the constraints are released in an active space but imposed elsewhere. If the active space is properly chosen, our constrained UHF (CUHF) method greatly benefits from a controlled broken-symmetry effect while avoiding the massive spin contamination of traditional UHF. We also revisit and apply L$\rm {\ddot{o}}$öwdin's projection operator to CUHF and obtain multireference wave functions with moderate computational cost. We report singlet–triplet energy splittings showing that our constrained scheme outperforms fully unrestricted methods. This constrained approach can be readily used in spin density functional theory with similar favorable effects.
Temperature effect on negative bias-induced instability of HfInZnO amorphous oxide thin film transistor
Authors: Kwon Dae Woong , Kim Jang Hyun , Chang Ji Soo , Kim Sang Wan , Kim Wandong , Park Jae Chul , Song Ihun , Kim Chang Jung , Jung U In , Park Byung-Gook
Published: February 2011

Negative bias-induced instability of amorphous hafnium indium zinc oxide (α-HIZO) thin film transistors (TFTs) was investigated at various temperatures. In order to examine temperature-induced effects, fabricated TFTs with different combinations of gate insulator and gate metal were stressed by a negative gate bias at various temperatures. As a result, it is proved that negative bias-induced hole-trapping in the gate insulators and temperature-enhanced electron injection from the gate metals occurs at the same time at all temperatures, and the instability of HIZO TFT is more affected by the dominant factor out of the two mechanisms.
Calculation of spin-current densities using gauge-including atomic orbitals
Authors: Taubert Stefan , Sundholm Dage , Jusélius Jonas
Published: February 2011

The gauge-including magnetically induced current method for calculating the components of the current-density tensor using gauge-including atomic orbitals has been extended to treating open-shell molecules. The applicability of the method is demonstrated by calculations of first-order induced current densities on cyclobutadiene, Al3, and B3 at correlated ab initio levels of theory. For comparison, current-density calculations were also performed on the lowest closed-shell singlet state of cyclobutadiene as well on the closed-shell \documentclass[12pt]{minimal}\begin{document}${\rm Al}_3^-$\end{document} Al 3− and \documentclass[12pt]{minimal}\begin{document}${\rm B}_3^-$\end{document}B3− anions. The ring-current susceptibilities of the open-shell species are computed at the Hartree-Fock self-consistent-field, second-order Møller– Plesset perturbation theory, and coupled-cluster singles and doubles levels, whereas for the closed-shell systems also density functional theory calculations were employed. Explicit values for the current strengths caused by α and β electrons as well as the difference, representing the spin current, were obtained by numerical integration of the current-density contributions passing a plane perpendicular to the molecular ring. Comparisons of the present results to those recently obtained for the lowest triplet state of biphenyl emphasize that electron correlation effects must be considered for obtaining an accurate description of spin-current densities.
Hydrogen bond and halogen bond inside the carbon nanotube
Authors: Wang Weizhou , Wang Donglai , Zhang Yu , Ji Baoming , Tian Anmin
Published: February 2011

The hydrogen bond and halogen bond inside the open-ended single-walled carbon nanotubes have been investigated theoretically employing the newly developed density functional M06 with the suitable basis set and the natural bond orbital analysis. Comparing with the hydrogen or halogen bond in the gas phase, we find that the strength of the hydrogen or halogen bond inside the carbon nanotube will become weaker if there is a larger intramolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom donor to the antibonding orbital of the X–H or X–Hal bond involved in the formation of the hydrogen or halogen bond and will become stronger if there is a larger intermolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom acceptor to the antibonding orbital of the X–H or X–Hal bond. According to the analysis of the molecular electrostatic potential of the carbon nanotube, the driving force for the electron-density transfer is found to be the negative electric field formed in the carbon nanotube inner phase. Our results also show that the X–H bond involved in the formation of the hydrogen bond and the X–Hal bond involved in the formation of the halogen bond are all elongated when encapsulating the hydrogen bond and halogen bond within the carbon nanotube, so the carbon nanotube confinement may change the blue-shifting hydrogen bond and the blue-shifting halogen bond into the red-shifting hydrogen bond and the red-shifting halogen bond. The possibility to replace the all electron nanotube-confined calculation by the simple polarizable continuum model is also evaluated.
Structural and optical properties of liquid CO2 for pressures up to 1 TPa
Authors: Boates B. , Hamel S. , Schwegler E. , Bonev S. A.
Published: February 2011

We report on the use of first-principles molecular dynamics calculations to examine properties of liquid carbon dioxide in the pressure–temperature range of 0–1 TPa and 200–100 000 K. The computed equations of state points are used to predict a series of shock Hugoniots with initial starting conditions that are relevant to existing and ongoing shock-wave experiments. A comparison with published measurements up to 70 GPa shows excellent agreement. We find that the liquid undergoes a gradual phase transition along the Hugoniot and have characterized this transition based on changes in bonding and structural properties as well as the conductivity and reflectivity of the fluid.
Alkane adsorption in Na-exchanged chabazite: The influence of dispersion forces
Authors: Göltl Florian , Hafner Jürgen
Published: February 2011

The importance of dispersion forces for the correct description of the adsorption of short alkanes in Na-exchanged and purely siliceous chabazite has been investigated at different levels of theory: (i) standard density-functional (DFT) calculations using the Perdew, Burke, and Ernzerhof (PBE) exchange–correlation functional in the generalized gradient approximation, (ii) dispersion corrections based on empirical force fields according to Grimme [J. Computat. Chem. 134, 1463 (2004)– PBE-d], (iii) calculations based on the van der Waals density functional (vdW-DF) proposed by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)], and (iv) using the random phase approximation (RPA) in combination with the adiabatic-connection fluctuation-dissipation theorem (RPA-ACFDT), using wave-functions calculated at the DFT and Hartree–Fock (HF) levels. A full relaxation of the adsorbate–zeolite complex was performed at the PBE, PBE-d, and vdW-DF levels. RPA and RPA-HF energies were calculated for the optimized configurations. A critical analysis of the results shows that the most accurate description is achieved at the RPA level with HF exchange energies, while both PBE-d and vdW-DF overestimate the strength of the interaction with the acid site.
High-resolution core-level photoemission study of CF4-treated Gd2O3(Ga2O3) gate dielectric on Ge probed by synchrotron radiation
Authors: Pi T.-W. , Huang M. L. , Lee W. C. , Chu L. K. , Lin T. D. , Chiang T. H. , Wang Y. C. , Wu Y. D. , Hong M. , Kwo J.
Published: February 2011

High-resolution core-level photoemission analysis using synchrotron radiation was used to investigate the superior electrical performance of aGa2O3(Gd2O3) gate dielectric on Ge(001) after CF4 treatment. Prior to the treatment, a thin germanate-like oxide layer that formed at the interface prevented Ge from diffusing to the surface. The Ge surface retained a small amount of buckled dimers from the as-grown sample. The buckled dimers were quickly removed by CF4 plasma treatment followed by an annealing process, resulting in a more uniform interface than that of the as-grown sample. The detailed interfacial electronic structure for the untreated and treated samples are presented.
A method to estimate the planar, instantaneous body force distribution from velocity field measurements
Authors: Albrecht Thomas , Weier Tom , Gerbeth Gunter , Metzkes Hans , Stiller Jörg
Published: February 2011

We present a simple method to derive a planar, instantaneous body force distribution from a given two-dimensional velocity field without knowledge of the pressure field, under the specific restriction that the body force is dominated by one component only. Spatial integration then completely recovers this component. Particle image velocimetry and direct numerical simulations of a wall jet induced by a known body force were conducted to validate the method, demonstrating a good agreement of the original and reconstructed force fields.
Higher-order energy-conserving gyrokinetic theory
Authors: Mishchenko Alexey , Brizard Alain J.
Published: February 2011

A higher-order self-consistent energy-conserving gyrokinetic system of equations is derived. It is shown that additional terms appear in the quasineutrality condition. These terms are nonlinear in the electric field. The derivation includes higher-order terms in the gyrokinetic Hamiltonian (needed for the energy conservation) and employs a variational principle that automatically provides all the conservation laws through the Noether theorem. The equations derived here can be applied in certain transition layers such as the stellarator transport barriers caused by the transition between the electron and ion root regimes. The theory may also be of interest for the edge plasma, where the nonlinear terms in the quasineutrality equation could be relevant. The equations derived are simple enough and can readily be used in gyrokinetic codes.
Raman study of interfacial load transfer in graphene nanocomposites
Authors: Srivastava Iti , Mehta Rutvik J. , Yu Zhong-Zhen , Schadler Linda , Koratkar Nikhil
Published: February 2011

We tracked the strain-sensitive characteristic Raman G-band shift of graphene platelets in polydimethyl-siloxane (PDMS) nanocomposites revealing the filler-to-matrix interactions. We obtained large debonding strains of ∼7% for graphene in PDMS, with the peak shift rate with strain being ∼2.4 cm−1/composite strain % in comparison to single-walled carbon nanotube composites, where a relatively low rate of ∼0.1 cm−1/composite strain % was obtained, suggesting enhanced load-transfer effectiveness for graphene. A surprising observation was that for large strains (>1.5%) the graphene fillers went into compression under uniaxial tensile deformation and vice versa. We propose that this effect is related to the high mobility of the PDMS chains at room temperature.
Charged colloid-polymer mixtures: A study on electrostatic depletion attraction
Authors: Peláez-Fernández M. , Moncho-Jordá A. , Callejas-Fernández J.
Published: February 2011

In this work, light scattering methods have been used to study the effect of adding charged polymer chains on the structural and dynamic properties of a charged colloidal system. The experimental measurements of the static structure factor Scc(q) show that as the polymer concentration increases, the main peak moves to higher q-values, which is interpreted in terms of the electrostatically enhanced depletion attraction induced by the polymer. Moreover, we found that the shift of the peak depends on the interplay between two relevant length scales, the polymer radius of gyration, Rg, and the Debye length, κ−1. To reach these conclusions, the polymer reference interaction site model has been employed to explain the experimental results and to study how the effective depletion attraction depends on the polymer concentration, Rg and κ−1. Additionally, the measurements of the dynamic structure factor f(q, τ) indicate that the colloidal diffusion increases with the polymer concentration. Both static and dynamic analysis point out that the repulsion between colloids becomes weaker as the charged polymer is added.
Low-frequency nanotesla sensitivity in Metglas/piezoelectric/carbon fiber/piezoelectric composites with active tip mass
Authors: Park Chee-Sung , Avirovik Dragan , Bressers Scott , Priya Shashank
Published: February 2011

We report nanotesla sensitivity in Metglas/piezoelectric/carbon fiber/piezoelectric laminates with active tip mass operating in the vicinity of second bending mode. The peak magnetoelectric response for the laminate with an active tip mass (1 g) in longitudinal-transversal mode under Hdc=8 Oe and Hac=1 Oe was found to be ∼1.08 V/cm Oe at 43 Hz (first bending mode) and ∼19 V/cm Oe at 511 Hz (second bending mode). At the standard 1 kHz frequency, the maximum resolution of 5 nT was measured under Hac=0.5 Oe.
Scaling of the viscosity of the Lennard-Jones chain fluid model, argon, and some normal alkanes
Authors: Galliero Guillaume , Boned Christian , Fernández Josefa
Published: February 2011

In this work, we have tested the efficiency of two scaling approaches aiming at relating shear viscosity to a single thermodynamic quantity in dense fluids, namely the excess entropy and the thermodynamic scaling methods. Using accurate databases, we have applied these approaches first to a model fluid, the flexible Lennard-Jones chain fluid (from the monomer to the hexadecamer), then to real fluids, such as argon and normal alkanes. To enlarge noticeably the range of thermodynamics conditions for which these scaling methods are applicable, we have shown that the use of the residual viscosity instead of the total viscosity is preferable in the scaling procedures. It has been found that both approaches, using the adequate scaling, are suitable for the Lennard-Jones chain fluid model for a wide range of thermodynamic conditions whatever the chain length when scaling law exponents and prefactors are adjusted for each chain length. Furthermore, these results were found to be well respected by the corresponding real fluids.
Theory of quasiballistic transport through nanocrystalline silicon dots
Authors: Mori Nobuya , Minari Hideki , Uno Shigeyasu , Mizuta Hiroshi , Koshida Nobuyoshi
Published: February 2011

A model to describe the underlying physics of high-energy electron emission from a porous silicon diode is presented. The model is based on an atomistic tight-binding method combined with semiclassical Monte Carlo simulation. It well reproduces essential features of experimental findings. An initial acceleration region is shown to play a crucial role in generating quasiballistic electron emission.
Imbalanced mobilities causing S-shaped IV curves in planar heterojunction organic solar cells
Authors: Tress Wolfgang , Petrich Annette , Hummert Markus , Hein Moritz , Leo Karl , Riede Moritz
Published: February 2011

We show that S-kinks in the current voltage characteristics, which decrease the fill factor significantly, can be caused by a strong imbalance of charge carrier mobilities (hole mobility in donor and electron mobility in acceptor) in planar/flat heterojunction organic solar cells. Electrical simulations according to a drift-diffusion model predict the occurrence of an S-kink for a mobility mismatch factor larger than 100. By combining a low-mobility donor material, (1,2,3,4,9,10,11,12-octaphenyl-diindeno[1,2,3-cd:1′,2′,3′-lm]perylene), with the acceptors C60 and N,N′-dimethylperylene-3,4:9,10-dicarboximide, which show different electron mobilities, we experimentally verify the predictions. Our results demonstrate that not only interface effects but also the photoactive material itself can cause S-kinks.
Multifrequency terahertz lasing from codoped silicon crystals
Authors: Pavlov S. G. , Eichholz R. , Abrosimov N. V. , Redlich B. , Hübers H.-W.
Published: February 2011

Stimulated terahertz emission in the range from 4.5 to 6.4 THz has been realized from a single silicon crystal doped by two hydrogen-like donor centers, phosphorus and antimony, when pumped by midinfrared radiation from a free electron laser. Intracenter as well as Raman lasing has been observed. Simultaneous laser emission from both donors occurs when the pump photon energy is sufficient for photoionization of the antimony donors. The laser processes of both donors are not influenced by each other. Therefore the codoping approach can be extended to other group-V donors including more than two dopants in a single crystal.
Photodissociation dynamics of H2O: Effect of unstable resonances on the $\tilde B\,^{1}{\rm \!A}_{1}$B̃1A1 electronic state
Authors: Cheng Yuan , Yuan Kaijun , Cheng Lina , Guo Qing , Dai Dongxu , Yang Xueming
Published: February 2011

We report a tunable vacuum ultraviolet photodissociation study of H2O from different unstable resonances in the $\tilde B^1\!{\rm A}_1$B̃1A1 electronic state, using the H-atom Rydberg tagging technique. The quantum state resolved OH product translational energy distributions and angular distributions have been measured. Experimental results illustrate, for the first time, that excitation to the different unstable resonances has very different effect on the OH(X) and OH(A) product channels. The OH(X) product rotational distributions vary only slightly, while the OH(A) product rotational distributions and state-resolved angular distributions change dramatically as the photolysis energy increases. Effect of parent rotational excitation on the OH(A) product has also been observed. Through careful simulations to the experimental spectra, OH(A)/OH(X) branching ratios have been determined at five photolysis wavelengths. The general agreement between theory and experiment in the branching ratios is good. The branching ratios for the OH(A) product from different parent rotational levels are close to the nuclear spin-statistics value, which is also consistent with the extremely low rotational temperature of the H2O beam in the current experiment.
Room-temperature semiconductor coherent Smith–Purcell terahertz sources
Authors: Smith Don D. , Belyanin Alexey
Published: February 2011

We propose a room-temperature semiconductor source of coherent narrowband Smith–Purcell radiation (SPR) in the low-to-mid terahertz range. The device is a planar Gunn diode with a metallic grating deposited near the drift region. Stimulated SPR is generated as domains move under the grating. Radiation frequency is determined by the domain velocity and grating period—it is not transit-time limited. The approach is photolithographically tunable, readily scales to arrays, and is compatible with any planar Gunn technology. Integration with a planar antenna improves radiation efficiency and enables far-field optimization. We develop an analytic theory of the devices which agrees well with simulations. Results indicate that this method may achieve technologically relevant power density levels and warrants experimental investigation.
Jumonji domain-containing protein 6 (Jmjd6) is required for angiogenic sprouting and regulates splicing of VEGF-receptor 1
Authors: Boeckel Jes-Niels , Guarani Virginia , Koyanagi Masamichi , Roexe Tino , Lengeling Andreas , Schermuly Ralph T. , Gellert Pascal , Braun Thomas , Zeiher Andreas , Dimmeler Stefanie
Published: February 2011

JmjC domain-containing proteins play a crucial role in the control of gene expression by acting as protein hydroxylases or demethylases, thereby controlling histone methylation or splicing. Here, we demonstrate that silencing of Jumonji domain-containing protein 6 (Jmjd6) impairs angiogenic functions of endothelial cells by changing the gene expression and modulating the splicing of the VEGF-receptor 1 (Flt1). Reduction of Jmjd6 expression altered splicing of Flt1 and increased the levels of the soluble form of Flt1, which binds to VEGF and placental growth factor (PlGF) and thereby inhibits angiogenesis. Saturating VEGF or PlGF or neutralizing antibodies directed against soluble Flt1 rescued the angiogenic defects induced by Jmjd6 silencing. Jmjd6 interacts with the splicing factors U2AF65 that binds to Flt1 mRNA. In conclusion, Jmjd6 regulates the splicing of Flt1, thereby controlling angiogenic sprouting.
Blanks, a nuclear siRNA/dsRNA-binding complex component, is required for
Drosophila
spermiogenesis
Authors: Gerbasi Vincent R. , Preall Jonathan B. , Golden Daniel E. , Powell David W. , Cummins Timothy D. , Sontheimer Erik J.
Published: February 2011

Small RNAs and a diverse array of protein partners control gene expression in eukaryotes through a variety of mechanisms. By combining siRNA affinity chromatography and mass spectrometry, we have identified the double-stranded RNA-binding domain protein Blanks to be an siRNA- and dsRNA-binding protein from
Drosophila
S2 cells. We find that Blanks is a nuclear factor that contributes to the efficiency of RNAi. Biochemical fractionation of a Blanks-containing complex shows that the Blanks complex is unlike previously described RNA-induced silencing complexes and associates with the DEAD-box helicase RM62, a protein previously implicated in RNA silencing. In flies, Blanks is highly expressed in testes tissues and is necessary for postmeiotic spermiogenesis, but loss of Blanks is not accompanied by detectable transposon derepression. Instead, genes related to innate immunity pathways are up-regulated in
blanks
mutant testes. These results reveal Blanks to be a unique component of a nuclear siRNA/dsRNA-binding complex that contributes to essential RNA silencing-related pathways in the male germ line.
Testosterone administration impairs cognitive empathy in women depending on second-to-fourth digit ratio
Authors: van Honk Jack , Schutter Dennis J. , Bos Peter A. , Kruijt Anne-Wil , Lentjes Eef G. , Baron-Cohen Simon
Published: February 2011

During social interactions we automatically infer motives, intentions, and feelings from bodily cues of others, especially from the eye region of their faces. This cognitive empathic ability is one of the most important components of social intelligence, and is essential for effective social interaction. Females on average outperform males in this cognitive empathy, and the male sex hormone testosterone is thought to be involved. Testosterone may not only down-regulate social intelligence organizationally, by affecting fetal brain development, but also activationally, by its current effects on the brain. Here, we show that administration of testosterone in 16 young women led to a significant impairment in their cognitive empathy, and that this effect is powerfully predicted by a proxy of fetal testosterone: the right-hand second digit-to-fourth digit ratio. Our data thus not only demonstrate down-regulatory effects of current testosterone on cognitive empathy, but also suggest these are preprogrammed by the very same hormone prenatally. These findings have importance for our understanding of the psychobiology of human social intelligence.
Nanopatterned protein microrings from a diatom that direct silica morphogenesis
Authors: Scheffel André , Poulsen Nicole , Shian Samuel , Kröger Nils
Published: February 2011

Diatoms are eukaryotic microalgae that produce species-specifically structured cell walls made of SiO2(silica). Formation of the intricate silica structures of diatoms is regarded as a paradigm for biomolecule-controlled self-assembly of three-dimensional, nano- to microscale-patterned inorganic materials. Silica formation involves long-chain polyamines and phosphoproteins (silaffins and silacidins), which are readily soluble in water, and spontaneously form dynamic supramolecular assemblies that accelerate silica deposition and influence silica morphogenesis in vitro. However, synthesis of diatom-like silica structure in vitro has not yet been accomplished, indicating that additional components are required. Here we describe the discovery and intracellular location of six novel proteins (cingulins) that are integral components of a silica-forming organic matrix (microrings) in the diatomThalassiosira pseudonana. The cingulin-containing microrings are specifically associated with girdle bands, which constitute a substantial part of diatom biosilica. Remarkably, the microrings exhibit protein-based nanopatterns that closely resemble characteristic features of the girdle band silica nanopatterns. Upon the addition of silicic acid the microrings become rapidly mineralized in vitro generating nanopatterned silica replicas of the microring structures. A silica-forming organic matrix with characteristic nanopatterns was also discovered in the diatomCoscinodiscus wailesii, which suggests that preassembled protein-based templates might be general components of the cellular machinery for silica morphogenesis in diatoms. These data provide fundamentally new insight into the molecular mechanisms of biological silica morphogenesis, and may lead to the development of self-assembled 3D mineral forming protein scaffolds with designed nanopatterns for a host of applications in nanotechnology.
Elongation factor 4 (EF4/LepA) accelerates protein synthesis at increased Mg2+concentrations
Authors: Pech Markus , Karim Zhala , Yamamoto Hiroshi , Kitakawa Madoka , Qin Yan , Nierhaus Knud H.
Published: February 2011

Elongation factor 4 (EF4) is one of the most conserved proteins present in bacteria as well as in mitochondria and chloroplasts of eukaryotes. Although EF4 has the unique ability to catalyze the back-translocation reaction on posttranslocation state ribosomes, the physiological role of EF4 remains unclear. Here we demonstrate that EF4 is stored at the membrane ofEscherichia colicells and released into the cytoplasm upon conditions of high ionic strength or low temperature. Under such conditions, wild-typeE. colicells overgrow mutant cells lacking the EF4 gene within 5–10 generations. Elevated intracellular Mg2+concentrations or low temperature retard bacterial growth and inhibit protein synthesis, probably because of formation of aberrant elongating ribosomal states. We suggest that EF4 binds to these stuck ribosomes and remobilizes them, consistent with the EF4-dependent enhancement (fivefold) in protein synthesis observed under these unfavorable conditions. The strong selective advantage conferred by the presence of EF4 at high intracellular ionic strength or low temperatures explains the ubiquitous distribution and high conservation of EF4.
ORAI1-mediated calcium influx is required for human cytotoxic lymphocyte degranulation and target cell lysis
Authors: Maul-Pavicic Andrea , Chiang Samuel C. C. , Rensing-Ehl Anne , Jessen Birthe , Fauriat Cyril , Wood Stephanie M. , Sjöqvist Sebastian , Hufnagel Markus , Schulze Ilka , Bass Thilo , Schamel Wolfgang W. , Fuchs Sebastian , Pircher Hanspeter , McCarl Christie-Ann , Mikoshiba Katsuhiko , Schwarz Klaus , Feske Stefan , Bryceson Yenan T. , Ehl Stephan
Published: February 2011

Lymphocytes mediate cytotoxicity by polarized release of the contents of cytotoxic granules toward their target cells. Here, we have studied the role of the calcium release-activated calcium channel ORAI1 in human lymphocyte cytotoxicity. Natural killer (NK) cells obtained from an ORAI1-deficient patient displayed defective store-operated Ca2+entry (SOCE) and severely defective cytotoxic granule exocytosis leading to impaired target cell lysis. Similar findings were obtained using NK cells from a stromal interaction molecule 1-deficient patient. The defect occurred at a late stage of the signaling process, because activation of leukocyte functional antigen (LFA)-1 and cytotoxic granule polarization were not impaired. Moreover, pharmacological inhibition of SOCE interfered with degranulation and target cell lysis by freshly isolated NK cells and CD8+effector T cells from healthy donors. In addition to effects on lymphocyte cytotoxicity, synthesis of the chemokine macrophage inflammatory protein-1β and the cytokines TNF-α and IFN-γ on target cell recognition was impaired in ORAI1-deficient NK cells, as previously described for T cells. By contrast, NK cell cytokine production induced by combinations of IL-12, IL-15, and IL-18 was not impaired by ORAI1 deficiency. Taken together, these results identify a critical role for ORAI1-mediated Ca2+influx in granule exocytosis for lymphocyte cytotoxicity as well as for cytokine production induced by target cell recognition.
Nonhomologous end joining drives poly(ADP-ribose) polymerase (PARP) inhibitor lethality in homologous recombination-deficient cells
Authors: Patel Anand G. , Sarkaria Jann N. , Kaufmann Scott H.
Published: February 2011

Poly(ADP-ribose) polymerase (PARP) inhibitors are strikingly toxic to cells with defects in homologous recombination (HR). The mechanistic basis for these findings is incompletely understood. Here, we show that PARP inhibitor treatment induces phosphorylation of DNA-dependent protein kinase substrates and stimulates error-prone nonhomologous end joining (NHEJ) selectively in HR-deficient cells. Notably, inhibiting DNA-dependent protein kinase activity reverses the genomic instability previously reported in these cells after PARP inhibition. Moreover, disabling NHEJ by using genetic or pharmacologic approaches rescues the lethality of PARP inhibition or down-regulation in cell lines lacking BRCA2, BRCA1, or ATM. Collectively, our results not only implicate PARP1 catalytic activity in the regulation of NHEJ in HR-deficient cells, but also indicate that deregulated NHEJ plays a major role in generating the genomic instability and cytotoxicity in HR-deficient cells treated with PARP inhibitors.
Early onset of neural synchronization in the contextual associations network
Authors: Kveraga Kestutis , Ghuman Avniel Singh , Kassam Karim S. , Aminoff Elissa A. , Hämäläinen Matti S. , Chaumon Maximilien , Bar Moshe
Published: February 2011

Objects are more easily recognized in their typical context. However, is contextual information activated early enough to facilitate the perception of individual objects, or is contextual facilitation caused by postperceptual mechanisms? To elucidate this issue, we first need to study the temporal dynamics and neural interactions associated with contextual processing. Studies have shown that the contextual network consists of the parahippocampal, retrosplenial, and medial prefrontal cortices. We used functional MRI, magnetoencephalography, and phase synchrony analyses to compare the neural response to stimuli with strong or weak contextual associations. The context network was activated in functional MRI and preferentially synchronized in magnetoencephalography (MEG) for stimuli with strong contextual associations. Phase synchrony increased early (150–250 ms) only when it involved the parahippocampal cortex, whereas retrosplenial–medial prefrontal cortices synchrony was enhanced later (300–400 ms). These results describe the neural dynamics of context processing and suggest that context is activated early during object perception.
Proper formation of whisker barrelettes requires periphery-derived Smad4-dependent TGF-β signaling
Authors: da Silva Susana , Hasegawa Hiroshi , Scott Alexandra , Zhou Xiang , Wagner Amanda K. , Han Bao-Xia , Wang Fan
Published: February 2011

Mammalian somatosensory topographic maps contain specialized neuronal structures that precisely recapitulate the spatial pattern of peripheral sensory organs. In the mouse, whiskers are orderly mapped onto several brainstem nuclei as a set of modular structures termed barrelettes. Using a dual-color iontophoretic labeling strategy, we found that the precise topography of barrelettes is not a result of ordered positions of sensory neurons within the ganglion. We next explored another possibility that formation of the whisker map is influenced by periphery-derived mechanisms. During the period of peripheral sensory innervation, several TGF-β ligands are exclusively expressed in whisker follicles in a dynamic spatiotemporal pattern. Disrupting TGF-β signaling, specifically in sensory neurons by conditional deletion of
Smad4
at the late embryonic stage, results in the formation of abnormal barrelettes in the principalis and interpolaris brainstem nuclei and a complete absence of barrelettes in the caudalis nucleus. We further show that this phenotype is not derived from defective peripheral innervation or central axon outgrowth but is attributable to the misprojection and deficient segregation of trigeminal axonal collaterals into proper barrelettes. Furthermore,
Smad4
-deficient neurons develop simpler terminal arbors and form fewer synapses. Together, our findings substantiate the involvement of whisker-derived TGF-β/Smad4 signaling in the formation of the whisker somatotopic maps.
Understanding current causes of women's underrepresentation in science
Authors: Ceci Stephen J. , Williams Wendy M.
Published: February 2011

Explanations for women's underrepresentation in math-intensive fields of science often focus on sex discrimination in grant and manuscript reviewing, interviewing, and hiring. Claims that women scientists suffer discrimination in these arenas rest on a set of studies undergirding policies and programs aimed at remediation. More recent and robust empiricism, however, fails to support assertions of discrimination in these domains. To better understand women's underrepresentation in math-intensive fields and its causes, we reprise claims of discrimination and their evidentiary bases. Based on a review of the past 20 y of data, we suggest that some of these claims are no longer valid and, if uncritically accepted as current causes of women's lack of progress, can delay or prevent understanding of contemporary determinants of women's underrepresentation. We conclude that differential gendered outcomes in the real world result from differences in resources attributable to choices, whether free or constrained, and that such choices could be influenced and better informed through education if resources were so directed. Thus, the ongoing focus on sex discrimination in reviewing, interviewing, and hiring represents costly, misplaced effort: Society is engaged in the present in solving problems of the past, rather than in addressing meaningful limitations deterring women's participation in science, technology, engineering, and mathematics careers today. Addressing today's causes of underrepresentation requires focusing on education and policy changes that will make institutions responsive to differing biological realities of the sexes. Finally, we suggest potential avenues of intervention to increase gender fairness that accord with current, as opposed to historical, findings.
Oral delivery of RNase P ribozymes by
Salmonella
inhibits viral infection in mice
Authors: Bai Yong , Gong Hao , Li Hongjian , Vu Gia-Phong , Lu Sangwei , Liu Fenyong
Published: February 2011

Safe, effective, and tissue-specific delivery is a central issue for the therapeutic application of nucleic-acid-based gene interfering agents, such as ribozymes and siRNAs. In this study, we constructed a functional RNase P-based ribozyme (M1GS RNA) that targets the overlapping mRNA region of M80.5 and protease, two murine cytomegalovirus (MCMV) proteins essential for viral replication. In addition, a novel attenuated strain of
Salmonella
, which exhibited efficient gene transfer activity and little cytotoxicity and pathogenicity in mice, was constructed and used for delivery of anti-MCMV ribozyme. In MCMV-infected macrophages treated with the constructed attenuated
Salmonella
strain carrying the functional M1GS RNA construct, we observed an 80–85% reduction in the expression of M80.5/protease and a 2,500-fold reduction in viral growth. Oral inoculation of the attenuated
Salmonella
strain in mice efficiently delivered antiviral M1GS RNA into spleens and livers, leading to substantial expression of the ribozyme without causing significant adverse effects in the animals. Furthermore, the MCMV-infected mice that were treated orally with
Salmonella
carrying the functional M1GS sequence displayed reduced viral gene expression, decreased viral titers, and improved survival compared to the untreated mice or mice treated with
Salmonella
containing control ribozyme sequences. Our results provide direct evidence that oral delivery of M1GS RNA by
Salmonella
-based vectors effectively inhibits viral gene expression and replication in mice. Moreover, this study demonstrates the utility of
Salmonella
-mediated oral delivery of RNase P ribozyme for gene-targeting applications in vivo.
Cocaine dynamically regulates heterochromatin and repetitive element unsilencing in nucleus accumbens
Authors: Maze Ian , Feng Jian , Wilkinson Matthew B. , Sun HaoSheng , Shen Li , Nestler Eric J.
Published: February 2011

Repeated cocaine exposure induces persistent alterations in genome-wide transcriptional regulatory networks, chromatin remodeling activity and, ultimately, gene expression profiles in the brain's reward circuitry. Virtually all previous investigations have centered on drug-mediated effects occurring throughout active euchromatic regions of the genome, with very little known concerning the impact of cocaine exposure on the regulation and maintenance of heterochromatin in adult brain. Here, we report that cocaine dramatically and dynamically alters heterochromatic histone H3 lysine 9 trimethylation (H3K9me3) in the nucleus accumbens (NAc), a key brain reward region. Furthermore, we demonstrate that repeated cocaine exposure causes persistent decreases in heterochromatization in this brain region, suggesting a potential role for heterochromatic regulation in the long-term actions of cocaine. To identify precise genomic loci affected by these alterations, chromatin immunoprecipitation followed by massively parallel DNA sequencing (ChIP-Seq) was performed on NAc. ChIP-Seq analyses confirmed the existence of the H3K9me3 mark mainly within intergenic regions of the genome and identified specific patterns of cocaine-induced H3K9me3 regulation at repetitive genomic sequences. Cocaine-mediated decreases in H3K9me3 enrichment at specific genomic repeats [e.g., long interspersed nuclear element (LINE)-1 repeats] were further confirmed by the increased expression of LINE-1 retrotransposon-associated repetitive elements in NAc. Such increases likely reflect global patterns of genomic destabilization in this brain region after repeated cocaine administration and open the door for future investigations into the epigenetic and genetic basis of drug addiction.