bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarized edge emission from GaN-based light-emitting diodes sandwiched by dielectric/metal hybrid reflectors
Authors: Yan L. J. , Sheu J. K. , Huang F. W. , Lee M. L.
Published: December 2010

Edge-emitting c-plane GaN/sapphire-based light-emitting diodes (LEDs) sandwiched by two dielectric/metal hybrid reflectors on both sapphire and GaN surfaces were studied to determine their light emission polarization. The hybrid reflectors comprised dielectric multiple thin films and a metal layer. The metal layers of Au or Ag used in this study were designed to enhance the polarization ratio from S-polarization (transverse electric wave, TE) to P-polarization (transverse magnetic wave, TM). The two sets of optimized dielectric multi thin films served as matching layers for wide-angle incident light on both sapphire and GaN surfaces. To determine which reflector scheme would achieve a higher polarization ratio, simulations of the reflectance at the hybrid reflectors on sapphire (or GaN) interface were performed before the fabrication of experimental LEDs. Compared with conventional c-plane InGaN/GaN/sapphire LEDs without dielectric/metal hybrid reflectors, the experimental LEDs exhibited higher polarization ratio (ITE-max/ITM-max) with r=2.174 (∼3.37 dB) at a wavelength of 460 nm. In contrast, the original polarized light (without dielectric/metal hybrid reflectors) was partially contributed (r=1.398) by C-HH or C-LH (C band to the heavy-hole sub-band or C band to the crystal-field split-off sub-band) transitions along the a-plane or m-plane direction.
Metastable oxygen incorporation into thin film NiO by low temperature active oxidation: Influence on hole conduction
Authors: Aydogdu Gulgun H. , Ruzmetov Dmitry , Ramanathan Shriram
Published: December 2010

The ability to controllably tune cation valence state and resulting electrical conductivity of transition metal-oxides such as NiO is of great interest for a range of solid state electronic and energy devices and more recently in understanding electron correlation phenomena at complex oxide interfaces. Here, we demonstrate that it is possible to enhance electrical conductivity of NiO thin films by one order of magnitude by photoexcitation and three orders of magnitude by ozone treatment at as low as 310 K. The change occurs within nearly 2000 s and, thereafter, reaches a self-limiting value. A surprising difference is seen at 400 K: ultraviolet photon and ozone treatments cause only a marginal reduction in resistance in the first few minutes and, then, the resistance begins to increase and recovers its original value. This unusual reversal is explained by considering metastable incorporation of oxygen in NiO and oxygen equilibration with the environment. Variation in nickel valence state prior to and after photoexcitation and ozone treatment, investigated by x-ray photoelectron spectroscopy, provides mechanistic insights into resistance trends. This study demonstrates photon-assisted and ozone oxidation as effective low temperature routes to tune the electrical properties as well as metastably incorporate oxygen into oxides with direct influence on electrical conduction properties.
Radiofrequency field absorption by carbon nanotubes embedded in a conductive host
Authors: Shuba Mikhail V. , Slepyan Gregory Ya. , Maksimenko Sergey A. , Hanson George W.
Published: December 2010

Understanding the electromagnetic response of carbon nanotubes (CNTs) in the radio frequency range is very important for experimental development of therapeutic and diagnostic CNT applications, including selective thermolysis of cancer cells and thermoacoustic imaging. In this study, we present the theory of electromagnetic wave scattering by several finite length CNT configurations, including singlewall CNT’s having a surfactant coating, CNT bundles, and multiwall CNTs. Absorption cross-sections of these structures in a conductive host region are theoretically studied in the radio frequency range. Strong local field enhancement due to edge effects is predicted to be inherent to metallic singlewall CNTs in the near-field zone, providing an additional mechanism of energy dissipation in a conductive host. Due to the screening effect the application of singlewall CNTs for the enhancement of energy dissipation is more effective than the application of multiwall CNTs or CNT bundles at the same mass fraction of CNT inclusions. The presence of a lossy dielectric (surfactant) coating can significantly increase the absorption cross section of singlewall CNTs.
Nanometer size effect on the structure and magnetic properties of high oxygen content ferromagnetic PrMnO3+δ nanoparticles
Authors: Zhang T. , Fang Y. Z. , Dressel M. , Wang X. P. , Fang Q. F.
Published: December 2010

Structure and magnetic properties of undoped PrMnO3+δ nanoparticles with average particle size ranging from 40–500 nm have been investigated. Compared with bulk PrMnO3 compound with A type antiferromagnetic ordering below TN=95 K, PrMnO3+δ nanoparticles exhibit ferromagnetic ordering. With decreasing particle size, the MnO6 octahedra distortion increases, the cell volume shrinks, the average Mn–O bond length increases and the Mn–O–Mn bond angle decreases; the ferromagnetism becomes weak and the Curie temperature decreases gradually, and meanwhile, the spin glass behavior becomes more obvious. However, in contrast to antiferromagnetic nanoparticles, no exchange bias phenomenon was observed in our case. These interesting results are attributed to the excessive oxygen content and surface effects.
Raman scattering studies of p-type Sb-doped ZnO thin films
Authors: Samanta Kousik , Bhattacharya Pijush , Katiyar Ram S.
Published: December 2010

Antimony doped p-type ZnO films were grown on Al2O3 (0001) substrate by pulsed laser deposition. The structural properties of Zn1−xSbxO (3% and 5%) thin films were investigated by Raman scattering studies. The softening of local lattice due to the formation of (SbZn−2VZn) acceptor complexes was detected as the shift in E2high mode toward lower frequency side in ZnSbO thin films. Additional optical modes observed at 277, 333, 483, and 534 cm−1 are due to the breaking of translational symmetry in w-ZnO by Sb doping. The Zn–Sb related local vibrational mode was detected around 237 cm−1 in 5% Sb doped ZnO thin film. Room temperature Hall measurements exhibited low resistivity of 0.017 Ω cm, high hole concentration of 6.25×1018 cm−3, and mobility of 57.44 cm2/V s in the 5% Sb-doped ZnO thin film.
Compensation mechanism in silicon-doped gallium arsenide nanowires
Authors: Ketterer B. , Mikheev E. , Uccelli E. , Fontcuberta i Morral A.
Published: December 2010

P-type gallium arsenide nanowires were grown with different silicon doping concentrations. The incorporation is monitored by Raman spectroscopy of the local vibrational modes. For Si-concentrations up to 1.4×1018 cm−3, silicon incorporates mainly in arsenic sites. For higher concentrations, we observe the formation of silicon pairs. This is related to the Coulomb interaction between charged defects during growth. An electrical deactivation of more than 85% of the silicon acceptors is deduced for nominal silicon concentration of 4×1019 cm−3. This work is important to understand the limiting mechanisms of doping in compound semiconductor nanowires.
Nonlinear quasisteady state benchmark of global gyrokinetic codes
Authors: Lapillonne X. , McMillan B. F. , Görler T. , Brunner S. , Dannert T. , Jenko F. , Merz F. , Villard L.
Published: December 2010

Two global gyrokinetic codes are benchmarked against each other by comparing simulation results in the case of ion temperature gradient driven turbulence, in the adiabatic electron response limit. The two codes are the Eulerian code GENE and the Lagrangian particle-in-cell code ORB5 which solve the gyrokinetic equations. Linear results are presented, including growth rates, real frequencies, and mode structure comparisons. Nonlinear simulations without sources are carried out with particular attention to considering the same initial conditions, showing identical linear phase and first nonlinear burst. Very good agreement is also achieved between simulations obtained using a Krook-type heat source, which enables to reach a quasisteady state and thus to compare the heat diffusivity traces over a statistically meaningful time interval. For these nonlinear results, the radial zonal flow structure and shearing rate profile are also discussed. The very detailed comparisons presented may serve as reference for benchmarking other gyrokinetic simulation codes, in particular those which consider global geometry.
Laser frequency upshift and self-defocusing under avalanche breakdown of air
Authors: Verma Updesh , Sharma A. K.
Published: December 2010

A theoretical model of avalanche breakdown of air by a Gaussian laser beam and frequency upshift is developed. The laser beam, below the threshold for tunnel ionization, heats the seed electrons to high energy and initiates avalanche ionization of the air. The ensuing plasma density profile that has maximum on axis and falls off radially causes refraction divergence of the beam. The temporal evolution of plasma density causes self-phase modulation of the laser, causing frequency broadening and spectral emission in the visible.
Nonstationary ponderomotive self-focusing of a Gaussian laser pulse in a plasma
Authors: Tripathi Deepak , Bhasin Lalita , Uma R. , Tripathi V. K.
Published: December 2010

A model of relaxing ponderomotive nonlinearity is developed to study the nonstationary self-focusing of a Gaussian laser pulse in a plasma. The ponderomotive force acts on the electrons instantaneously but the plasma density redistribution via the process of ambipolar diffusion is taken to evolve on the time scale τR≅r0/cs, where r0 is the laser spot size and cs is the sound speed. The paraxial ray approximation is used to solve the wave equation. The focusing is stronger at the rear of the pulse than at the front, causing considerable distortion of the pulse when pulse duration is comparable to nonlinearity relaxation time. The saturation effect of nonlinearity leads to focusing of any portion of the pulse to a minimum spot size r0fmin at an optimum distance zop and then the spot size increases. fmin and zop depend on the intensity of the portion of the pulse.
Neoclassical equilibria as starting point for global gyrokinetic microturbulence simulations
Authors: Vernay T. , Brunner S. , Villard L. , McMillan B. F. , Jolliet S. , Tran T. M. , Bottino A. , Graves J. P.
Published: December 2010

The implementation of linearized operators describing inter- and like-species collisions in the global gyrokinetic particle-in-cell code ORB5 [S. Jolliet, Comput. Phys. Commun. 177, 409 (2007)] is presented. A neoclassical axisymmetric equilibrium with self-consistent electric field can be obtained with no assumption made on the radial width of the particle trajectories. The formulation thus makes it possible to study collisional transport in regions where the neoclassical approximation breaks down such as near the magnetic axis. The numerical model is validated against both analytical results as well as other simulation codes. The effects of the poloidally asymmetric Fourier modes of the electric field are discussed, and the contribution of collisional kinetic electrons is studied. In view of subsequent gyrokinetic simulations of turbulence started from a neoclassical equilibrium, the problem of numerical noise inherent to the particle-in-cell approach is addressed. A novel algorithm for collisional gyrokinetic simulation switching between a local and a canonical Maxwellian background for, respectively, carrying out the collisional and collisionless dynamics is proposed, and its beneficial effects together with a coarse graining procedure [Y. Chen and S. E. Parker, Phys. Plasmas 14, 082301 (2007)] on noise and weight spreading reduction are discussed.
Electromechanical robustness of monolayer graphene with extreme bending
Authors: Briggs Benjamin D. , Nagabhirava Bhaskar , Rao Gayathri , Geer Robert , Gao Haiyuan , Xu Yang , Yu Bin
Published: December 2010

We report on the electromechanical robustness of graphene in an extreme condition of deformation: uniaxial bending. A large-angle-bent graphene monolayer was obtained with a predefined template. Structural/mechanical analysis is conducted, followed by electronic transport measurement. Raman spectroscopy analysis suggests negligible strain in the significantly bent graphene, showing mechanical robustness of the two-dimensional carbon nanostructure. The impact on band structure with respect to key deformation parameters (bending angle and curvature radius) were investigated using sp3 tight-binding simulation. Results show insignificant local band modification at bending locations. Even with extreme deformation, excellent carrier mobility in monolayer graphene is preserved.
Conditions for establishing quasistable double layers in the Earth’s auroral upward current region
Authors: Main D. S. , Newman D. L. , Ergun R. E.
Published: December 2010

The strength and stability of simulated double layers at the ionosphere-auroral cavity boundary have been studied as a function of cold ionospheric electron temperature and density. The simulations are performed with an open boundary one-dimensional particle-in- cell (PIC) simulation and are initialized by imposing a density cavity within the simulation domain. The PIC simulation includes H+ and O+ ion beams, a hot H+ background population, cold ionospheric electrons, and a hot electron population. It is shown that a double layer remains quasistable for a variety of initial conditions and plasma parameters. The average potential drop of the double layer is found to increase as the cold electron temperature decreases. However, in terms of cold electron density, the average potential drop of the double layer is found to increase up to some critical cold electron density and decreases above this value. Comparisons with FAST observations are made and agreement is found between simulation results and observations in the shape and width of the double layer. This study helps put a constraint on the plasma conditions in which a DL can be expected to form and remain quasistable.
Midwave infrared quantum dot avalanche photodiode
Authors: Ramirez David A. , Shao Jiayi , Hayat Majeed M. , Krishna Sanjay
Published: December 2010

We report the first demonstration of a GaAs based avalanche photodiode (APD) operating in the midwave infrared region (3–5 μm). In the device, called the quantum dot avalanche photodiode, an intersubband quantum dots-in-a-well detector is coupled with an APD through a tunnel barrier. Using this approach, we have increased the photocurrent and reached a conversion efficiency of 12%, which is one of the highest reported conversion efficiencies for any quantum dot detector.
Probing the electron density in undoped, Si-doped, and Mg-doped InN nanowires by means of Raman scattering
Authors: Cuscó R. , Domènech-Amador N. , Artús L. , Gotschke T. , Jeganathan K. , Stoica T. , Calarco R.
Published: December 2010

We report a Raman scattering determination of the electron density in InN nanowires from the analysis of longitudinal optical-phonon-plasmon coupled modes. A Raman peak assigned to the L− coupled mode is observed in both undoped and doped InN nanowires. This peak exhibits a shift to higher (lower) frequencies in the Si-doped (Mg-doped) nanowires and allows us to estimate the electron density in the nanowires. A significant residual electron density is found in the undoped nanowires, which increases in Si-doped nanowires and is partially compensated in Mg-doped nanowires.
Mechanism of ultrahigh Mn concentration in epitaxially grown wurtzite Ga1−xMnxN
Authors: Chen Z. T. , Wang L. , Yang X. L. , Wang C. D. , Zhang G. Y.
Published: December 2010

The mechanism of Mn doping in epitaxially grown wurtzite Ga1−xMnxN has been investigated by using first-principles calculations. Although the Mn solubility limit is calculated to be as low as 0.032% under thermodynamical equilibrium, it can be increased by about two orders due to the role of growth surface, reaching several atomic percent, and can be further increased by hydrogen passivation. This work indicates that Ga1−xMnxN can be grown epitaxially with Mn concentration as high as that were used in most theoretical predictions, making it reasonable to expect practical room-temperature ferromagnetic Ga1−xMnxN suitable for spin injector.
Control of vortex chirality in regular polygonal nanomagnets using in-plane magnetic field
Authors: Yakata S. , Miyata M. , Nonoguchi S. , Wada H. , Kimura T.
Published: December 2010

The authors have proposed a control method of the magnetic vortex chirality in regular polygonal nanomagnets with an odd number of sides. The asymmetric nucleation energy of the vortex from the uniformly magnetized state enables us to simply control the vortex chirality by an in-plane magnetic field. The reliability of the proposed method has been numerically and experimentally confirmed in the triangle, pentagonal, heptagonal, and nonagonal Permalloy nanomagnets. The authors also confirmed that the vortex chirality is uncontrollable when the number of the side is even.
Comment on “Nonlinear gyrokinetic theory with polarization drift” [Phys. Plasmas 17, 082304 (2010)]
Authors: Leerink S. , Parra F. I. , Heikkinen J. A.
Published: December 2010

In this comment, we show that by using the discrete particle distribution function the changes of the phase-space volume of gyrocenter coordinates due to the fluctuating E×B velocity do not explicitly appear in the Poisson equation and the [Sosenko et al., Phys. Scr. 64, 264 (2001)] result is recovered. It is demonstrated that there is no contradiction between the work presented by Sosenko et al. and the work presented by [Wang et al., Phys. Plasmas 17, 082304 (2010)].
First principles study of Ag, Au, and Cu surface segregation in FePt-L1
Authors: Chepulskii Roman V. , Curtarolo Stefano
Published: December 2010

Doping FePt nanoparticles could be a possible approach to achieve high L10 order and magnetic anisotropy. To address stability, first-principles studies of surface segregation of dilute Ag/Au/Cu solutes at and near the (001)/(100)/(111) surfaces of FePt-L10 are performed. It is found that a strong surface segregation tendency at first outer layer is present in all the cases. For Cu, segregation is less than half of Ag and Au. Ag and Cu segregate to Fe sites at surfaces and preferentially substitute for Fe in the bulk, whereas Au substitutes for Fe at surfaces and for Fe and Pt in the bulk.
Large enhancement of the anomalous Hall effect in Co/Pt multilayers sandwiched by MgO layers
Authors: Zhang S. L. , Teng J. , Zhang J. Y. , Liu Y. , Li J. W. , Yu G. H. , Wang S. G.
Published: December 2010

We report a large enhanced anomalous Hall effect (AHE) in the Co/Pt multilayers sandwiched by two MgO layers. The Hall resistivity (ρxy) was over an order of magnitude larger than that in pure Co/Pt multilayers. By optimizing the thickness of MgO layers, a high field sensitivity value of 2445 V/A T for Hall sensors was achieved. The enhancement of AHE is mainly attributed to the MgO–Pt interfacial effect.
Efficiency dependence on alkali metal compound/Al bilayer cathode in organic light-emitting diodes
Authors: Zhou D. Y. , Cai S. D. , Gu W. , Liao L. S. , Lee S. T.
Published: December 2010

The use of alkali metal compound/Al bilayer cathodes of LiF/Al and Liq/Al caused a dramatic luminous efficiency change of one order of magnitude in organic light-emitting diodes (OLEDs) comprising 2-methyl-9,10-bis(naphthalene-2-yl)anthracene (MADN) as an electron-transporting layer (ETL). In contrast, the use of the same two electrodes yielded similar efficiency in OLEDs comprising of tris(8-hydroxyquinoline) aluminum(III) (Alq3) as an ETL. The dramatic change is attributed to different behaviors of LiF/Al and Liq/Al cathodes toward the ETL. It is revealed that organic alkali metal complex/Al, such as Liq/Al, is superior to inorganic alkali metal compound/Al, such as LiF/Al, as a standard bilayer cathode to investigate the effectiveness of electron-transporting materials for high-efficiency OLEDs.
Surface localized exciton emission from undoped SnO2 nanocrystal films
Authors: Pan S. S. , Tian Y. H. , Luo Y. Y. , Zhang Y. X. , Wang S. , Li G. H.
Published: December 2010

We report the UV photoluminescence properties of SnO2 nanocrystalline films. A free exciton decay centered at 3.7 eV and a strong surface localized exciton emission peak at 3.3 eV have been observed at room temperature. The peak energy of the surface localized exciton emission exhibits a redshift with increasing temperature and a blueshift with increasing excitation intensity. The surface localized exciton emission is considered to originate from the radiative recombination of exciton within the surface region of SnO2 nanocrystals. The surface defects and local disorder are believed to be responsible for the formation of band tail states at the conduction band and potential well within the band tails.
Collisionless shock generation in high-speed counterstreaming plasma flows by a high-power laser
Authors: Morita T. , Sakawa Y. , Kuramitsu Y. , Dono S. , Aoki H. , Tanji H. , Kato T. N. , Li Y. T. , Zhang Y. , Liu X. , Zhong J. Y. , Takabe H. , Zhang J.
Published: December 2010

The experimental demonstration of the formation of a strong electrostatic (ES) collisionless shock has been carried out with high-speed counterstreaming plasmas, produced by a high-power laser irradiation, without external magnetic field. The nearly four times density jump observed in the experiment shows a high Mach-number shock. This large density jump is attributed to the compression of the downstream plasma by momentum transfer by ion reflection of the upstream plasma. Particle-in-cell (PIC) simulation shows the production of a collisionless high Mach-number ES shock with counterstreaming interaction of two plasma slabs with different temperatures and densities, as pointed out by Sorasio et al. [Phys. Rev. Lett. 96, 045005 (2006)]. It is speculated that the shock discontinuity is balanced with the momentum of incoming and reflected ions and the predominant pressure of the electrons in the downstream with PIC simulation.
Nobel physics prize honors achievements in graphene
Authors: Wilson Mark
Published: December 2010

In 2004 the laureates sparked, and then participated in, an explosion of experimental and theoretical work on the single-layer material.
Optical absorption of single molecules observed by three groups
Authors: Miller Johanna
Published: December 2010

Even with a tightly focused laser beam, only about one one-millionth of the incident light is absorbed.
LIGO relocation would boost gravitational-wave science
Authors: Feder Toni
Published: December 2010

Whether one detector is moved to Australia or left in Washington State, the upgraded version of the three-pronged Laser Interferometer Gravitational-Wave Observatory is expected to deliver results.
Chandrasekhar’s role in 20th-century science
Authors: Dyson Freeman
Published: December 2010

Once the astrophysics community had come to grips with a calculation performed by a 19-year-old student sailing off to graduate school, the heavens could never again be seen as a perfect and tranquil dominion.
Beauty and the quest for beauty in science
Authors: Chandrasekhar S.
Published: December 2010

Science, like the arts, admits aesthetic criteria; we seek theories that display “a proper conformity of the parts to one another and to the whole” while still showing “some strangeness in their proportion.”
Erosion pillars, from circuits to the cosmos
Authors: Vonk Matthew
Published: December 2010

The visually fascinating, elongated shapes that result from anisotropic erosion are the products of varied and sometimes surprising physics.
Two experiments, two takes on electric bacteria
Authors: Smart Ashley G.
Published: December 2010

Biologists know that certain kinds of microbes can convert organic waste into useful electric current. They just aren’t yet sure how.
Deconvolution of dynamic mechanical networks
Authors: Hinczewski Michael , von Hansen Yann , Netz Roland R.
Published: December 2010

Time-resolved single-molecule biophysical experiments yield data that contain a wealth of dynamic information, in addition to the equilibrium distributions derived from histograms of the time series. In typical force spectroscopic setups the molecule is connected via linkers to a readout device, forming a mechanically coupled dynamic network. Deconvolution of equilibrium distributions, filtering out the influence of the linkers, is a straightforward and common practice. We have developed an analogous dynamic deconvolution theory for the more challenging task of extracting kinetic properties of individual components in networks of arbitrary complexity and topology. Our method determines the intrinsic linear response functions of a given object in the network, describing the power spectrum of conformational fluctuations. The practicality of our approach is demonstrated for the particular case of a protein linked via DNA handles to two optically trapped beads at constant stretching force, which we mimic through Brownian dynamics simulations. Each well in the protein free energy landscape (corresponding to folded, unfolded, or possibly intermediate states) will have its own characteristic equilibrium fluctuations. The associated linear response function is rich in physical content, because it depends both on the shape of the well and its diffusivity—a measure of the internal friction arising from such processes as the transient breaking and reformation of bonds in the protein structure. Starting from the autocorrelation functions of the equilibrium bead fluctuations measured in this force clamp setup, we show how an experimentalist can accurately extract the state-dependent protein diffusivity using a straightforward two-step procedure.
ADP-ribosylation factor machinery mediates endocytosis in plant cells
Authors: Naramoto Satoshi , Kleine-Vehn Jürgen , Robert Stéphanie , Fujimoto Masaru , Dainobu Tomoko , Paciorek Tomasz , Ueda Takashi , Nakano Akihiko , Van Montagu Marc C. E. , Fukuda Hiroo , Friml Jiří
Published: December 2010

Endocytosis is crucial for various cellular functions and development of multicellular organisms. In mammals and yeast, ADP-ribosylation factor (ARF) GTPases, key components of vesicle formation, and their regulators ARF-guanine nucleotide exchange factors (GEFs) and ARF-GTPase-activating protein (GAPs) mediate endocytosis. A similar role has not been established in plants, mainly because of the lack of the canonical ARF and ARF-GEF components that are involved in endocytosis in other eukaryotes. In this study, we revealed a regulatory mechanism of endocytosis in plants based on ARF GTPase activity. We identified that ARF-GEF GNOM and ARF-GAP VASCULAR NETWORK DEFECTIVE 3 (VAN3), both of which are involved in polar auxin transport-dependent morphogenesis, localize at the plasma membranes as well as in intracellular structures. Variable angle epifluorescence microscopy revealed that GNOM and VAN3 localize to partially overlapping discrete foci at the plasma membranes that are regularly associated with the endocytic vesicle coat clathrin. Genetic studies revealed that GNOM and VAN3 activities are required for endocytosis and internalization of plasma membrane proteins, including PIN-FORMED auxin transporters. These findings identified ARF GTPase-based regulatory mechanisms for endocytosis in plants. GNOM and VAN3 previously were proposed to function solely at the recycling endosomes and
trans
-Golgi networks, respectively. Therefore our findings uncovered an additional cellular function of these prominent developmental regulators.
MicroRNA miR-125b causes leukemia
Authors: Bousquet Marina , Harris Marian H. , Zhou Beiyan , Lodish Harvey F.
Published: December 2010

MicroRNA miR-125b has been implicated in several kinds of leukemia. The chromosomal translocation t(2;11)(p21;q23) found in patients with myelodysplasia and acute myeloid leukemia leads to an overexpression of miR-125b of up to 90-fold normal. Moreover, miR-125b is also up-regulated in patients with B-cell acute lymphoblastic leukemia carrying the t(11;14)(q24;q32) translocation. To decipher the presumed oncogenic mechanism of miR-125b, we used transplantation experiments in mice. All mice transplanted with fetal liver cells ectopically expressing miR-125b showed an increase in white blood cell count, in particular in neutrophils and monocytes, associated with a macrocytic anemia. Among these mice, half died of B-cell acute lymphoblastic leukemia, T-cell acute lymphoblastic leukemia, or a myeloproliferative neoplasm, suggesting an important role for miR-125b in early hematopoiesis. Furthermore, coexpression of miR-125b and the BCR-ABL fusion gene in transplanted cells accelerated the development of leukemia in mice, compared with control mice expressing only BCR-ABL, suggesting that miR-125b confers a proliferative advantage to the leukemic cells. Thus, we show that overexpression of miR-125b is sufficient both to shorten the latency of BCR-ABL–induced leukemia and to independently induce leukemia in a mouse model.
Inflammation-induced tumorigenesis in the colon is regulated by caspase-1 and NLRC4
Authors: Hu Bo , Elinav Eran , Huber Samuel , Booth Carmen J. , Strowig Till , Jin Chengcheng , Eisenbarth Stephanie C. , Flavell Richard A.
Published: December 2010

Chronic inflammation is a known risk factor for tumorigenesis, yet the precise mechanism of this association is currently unknown. The inflammasome, a multiprotein complex formed by NOD-like receptor (NLR) family members, has recently been shown to orchestrate multiple innate and adaptive immune responses, yet its potential role in inflammation-induced cancer has been little studied. Using the azoxymethane and dextran sodium sulfate colitis-associated colorectal cancer model, we show that caspase-1–deficient (Casp1
−/−
) mice have enhanced tumor formation. Surprisingly, the role of caspase-1 in tumorigenesis was not through regulation of colonic inflammation, but rather through regulation of colonic epithelial cell proliferation and apoptosis. Consequently, caspase-1–deficient mice demonstrate increased colonic epithelial cell proliferation in early stages of injury-induced tumor formation and reduced apoptosis in advanced tumors. We suggest a model in which the NLRC4 inflammasome is central to colonic inflammation-induced tumor formation through regulation of epithelial cell response to injury.
‘Schools and Continuing Professional Development in England – State of the Nation’ research study: policy context, aims and design
Authors: Pedder David , Opfer V. Darleen , McCormick Robert , Storey Anne
Published: December 2010

This article introduces the Schools and Continuing Professional Development State of the Nation study (SoNS). Discussion of English policy together with an account of the study's aims and research design provide a context for the other articles included in this special issue. A key assumption behind the research, and the prevailing CPD policy context in England, is that organisational conditions in schools are highly influential in the development of sustained and effective classroom‐based, collaborative, inquiry‐oriented CPD. Therefore, the aims of the study investigated the range and kinds of support that schools in England provide as well as the range and kinds of CPD activities in which teachers were able to participate. Teachers’ professional learning practices and perspectives were researched in relation to three main themes: (a) the benefits, status and effectiveness of CPD; (b) the planning and organisation of CPD; and (c) access to CPD. These questions were explored through a mixed methods design consisting of three strands: (a) literature review; (b) qualitative research (school snapshots); and (c) a national survey of primary and secondary teachers in England. Discussion of processes and procedures of data analysis is followed by a summary of our conceptual model of schools and teachers’ CPD.
‘State of the Nation’: a discussion of some of the project's key findings
Authors: Earley Peter
Published: December 2010

This paper considers several of the key findings of the State of the Nation research. Specific reference is made to three areas – impact evaluation, strategic leadership of professional development, and barriers and constraints to effective CPD practice – which are considered with reference to findings from the other TDA‐funded projects conducted at about the same time.
Losing control in front of a fearful face: The effect of emotional information on cognitive control
Authors: Zhou Jifan , Gao Tao , Zhang Yunfan , Liang Junying , Shui Rende , Shen Mowei
Published: December 2010

How is our cognitive control system modulated by emotional information, especially fearful stimuli? An intuitive hypothesis is that fearful stimuli would enhance cognitive control so that people could switch from the ongoing task to emergent events more quickly to secure themselves. To test this hypothesis, we investigated the influence of emotional information on the shift function of cognitive control by using the task-cueing procedure, in which face images were presented as cues. With the gender of faces indicating which task to do, we manipulated the emotional valence of faces (neutral vs. fearful), finding that the switch costs were larger in the trials containing fearful cues than in the trials containing neutral cues (Experiment 1). This effect was not caused by enlarging task-set interference (Experiment 2), nor by slowing down cue encoding (Experiment 3). Contrary to the intuitive hypothesis, our results suggested that the endogenous task-set reconfiguration process was impaired when fearful faces were presented. We speculated that the benefit of decreasing cognitive flexibility in face of fearful stimuli is to speed up response in a dangerous environment, and this accelerating response is achieved by suppressing the goal-directed system to permit the fast, automatic stimulus-driven system to govern behaviours.
Contrasting Graded Effects of Semantic Similarity and Association across the Concreteness Spectrum
Authors: Crutch Sebastian J. , Jackson Ella C.
Published: December 2010

Evidence from healthy individuals and neuropsychological patients with deep dyslexia or semantic refractory access dysphasia suggests that abstract and concrete concepts have different dependencies upon associative and similarity-based representational frameworks. However, the importance of information about semantic similarity for concepts that lie across the full concreteness spectrum has not been investigated. Here we report the performance of healthy individuals on an odd-one-out task involving semantically related word triplets that showed continuous variation for the key variables of concreteness, similarity strength, and association strength. In addition, data from a stroke aphasic patient tested on a matching-to-sample task based on the same abstract, middle-concreteness, and concrete stimuli are also presented. The effects of similarity and association strength upon performance were both shown to interact significantly with concreteness, but in opposite directions. The effect of semantic similarity increased with concreteness but the effect of association decreased with concreteness. This research provides further evidence for the proposal that abstract and concrete words have different dependencies upon associative and similarity-based information. It also develops the proposal by providing data that are consistent with a graded and not binary or ungraded model of the relationship between concreteness and these two forms of semantic relationship.
Observation and physical practice: Coding of simple motor sequences
Authors: Gruetzmacher Nicole , Panzer Stefan , Blandin Yannick , Shea Charles H.
Published: December 2010

An experiment was conducted to determine the coordinate system used in the development of movement codes during observation and utilized on later physical practice performance of a simple spatial–temporal movement sequence. The task was to reproduce a 1.3-s spatial–temporal pattern of elbow flexions and extensions. An intermanual transfer paradigm with a retention test and two transfer tests was used: a mirror transfer test where the same pattern of muscle activation and limb joint angles was required and a nonmirror transfer test where the visual–spatial pattern of the sequence was reinstated on the transfer test. The results indicated a strong advantage for participants in the physical practice condition when transferred to the mirror condition in which the motor coordinates (e.g., pattern of muscle activation and joint angles) were reinstated relative to transfer performance when the visual–spatial coordinates were reinstated (visual and spatial location of the target waveform). The observation group, however, demonstrated an advantage when the visual–spatial coordinates were reinstated. These results demonstrate that codes based in motor coordinates can be developed relatively quickly for simple rapid movement sequences when participants are provided physical practice, but observational practice limits the system to the development of codes based in visual–spatial coordinates. Performances of control participants, who were not permitted to practise or observe the task, were quite poor on all tests.
Modality Effects in Memory for Basic Stimulus Attributes: A Temporal and Nontemporal Comparison
Authors: Ogden Ruth S. , Jones Luke A.
Published: December 2010

Previous research suggests that there are significant differences in the operation of reference memory for stimuli of different modalities, with visual temporal entries appearing to be more durable than auditory entries (Ogden, Wearden, & Jones, 2008, 2010). Ogden et al. (2008, 2010) demonstrated that when participants were required to store multiple auditory temporal standards over a period of delay there was significant systematic interference to the representation of the standard characterized by shifts in the location of peak responding. No such performance deterioration was observed when multiple visually presented durations were encoded and maintained. The current article explored whether this apparent modality-based difference in reference memory operation is unique to temporal stimuli or whether similar characteristics are also apparent when nontemporal stimuli are encoded and maintained. The modified temporal generalization method developed in Ogden et al. (2008) was employed; however, standards and comparisons varied by pitch (auditory) and physical line length (visual) rather than duration. Pitch and line length generalization results indicated that increasing memory load led to more variable responding and reduced recognition of the standard; however, there was no systematic shift in the location of peak responding. Comparison of the results of this study with those of Ogden et al. (2008, 2010) suggests that although performance deterioration as a consequence of increases in memory load is common to auditory temporal and nontemporal stimuli and visual nontemporal stimuli, systematic interference is unique to auditory temporal processing.
Ama1p-activated anaphase-promoting complex regulates the destruction of Cdc20p during meiosis II
Authors: Tan Grace S. , Magurno Jennifer , Cooper Katrina F.
Published: December 2010

The execution of meiotic divisions in Saccharomyces cerevisiae is regulated by anaphase-promoting complex/cyclosome (APC/C)–mediated protein degradation. During meiosis, the APC/C is activated by association with Cdc20p or the meiosis-specific activator Ama1p. We present evidence that, as cells exit from meiosis II, APC/CAma1mediates Cdc20p destruction. APC/CAma1recognizes two degrons on Cdc20p, the destruction box and destruction degron, with either domain being sufficient to mediate Cdc20p destruction. Cdc20p does not need to associate with the APC/C to bind Ama1p or be destroyed. Coimmunoprecipitation analyses showed that the diverged amino-terminal region of Ama1p recognizes both Cdc20p and Clb1p, a previously identified substrate of APC/CAma1. Domain swap experiments revealed that the C-terminal WD region of Cdh1p, when fused to the N-terminal region of Ama1p, could direct most of Ama1p functions, although at a reduced level. In addition, this fusion protein cannot complement the spore wall defect in ama1Δ strains, indicating that substrate specificity is also derived from the WD repeat domain. These findings provide a mechanism to temporally down-regulate APC/CCdc20activity as the cells complete meiosis II and form spores.
The kinesin KIF9 and reggie/flotillin proteins regulate matrix degradation by macrophage podosomes
Authors: Cornfine Susanne , Himmel Mirko , Kopp Petra , el Azzouzi Karim , Wiesner Christiane , Krüger Marcus , Rudel Thomas , Linder Stefan
Published: December 2010

Podosomes are actin-based matrix contacts in a variety of cell types, most notably monocytic cells, and are characterized by their ability to lyse extracellular matrix material. Besides their dependence on actin regulation, podosomes are also influenced by microtubules and microtubule-dependent transport processes. Here we describe a novel role for KIF9, a previously little-characterized member of the kinesin motor family, in the regulation of podosomes in primary human macrophages. We find that small interfering RNA (siRNA)/short-hairpin RNA–induced knockdown of KIF9 significantly affects both numbers and matrix degradation of podosomes. Overexpression and microinjection experiments reveal that the unique C-terminal region of KIF9 is crucial for these effects, presumably through binding of specific interactors. Indeed, we further identify reggie-1/flotillin-2, a signaling mediator between intracellular vesicles and the cell periphery, as an interactor of the KIF9 C-terminus. Reggie-1 dynamically colocalizes with KIF9 in living cells, and, consistent with KIF9-mediated effects, siRNA-induced knockdown of reggies/flotillins significantly impairs matrix degradation by podosomes. In sum, we identify the kinesin KIF9 and reggie/flotillin proteins as novel regulators of macrophage podosomes and show that their interaction is critical for the matrix-degrading ability of these structures.
Autophagy facilitates glycolysis during Ras-mediated oncogenic transformation
Authors: Lock Rebecca , Roy Srirupa , Kenific Candia M. , Su Judy S. , Salas Eduardo , Ronen Sabrina M. , Debnath Jayanta
Published: December 2010

The protumorigenic functions for autophagy are largely attributed to its ability to promote cancer cell survival in response to diverse stresses. Here we demonstrate an unexpected connection between autophagy and glucose metabolism that facilitates adhesion-independent transformation driven by a strong oncogenic insult—mutationally active Ras. In cells ectopically expressing oncogenic H-Ras as well as human cancer cell lines harboring endogenous K-Ras mutations, autophagy is induced following extracellular matrix detachment. Inhibiting autophagy due to the genetic deletion or RNA interference–mediated depletion of multiple autophagy regulators attenuates Ras-mediated adhesion-independent transformation and proliferation as well as reduces glycolytic capacity. Furthermore, in contrast to autophagy-competent cells, both proliferation and transformation in autophagy-deficient cells expressing oncogenic Ras are insensitive to reductions in glucose availability. Overall, increased glycolysis in autophagy-competent cells facilitates Ras-mediated adhesion-independent transformation, suggesting a unique mechanism by which autophagy may promote Ras-driven tumor growth in specific metabolic contexts.
Interactions of CstF-64, CstF-77, and symplekin: Implications on localisation and function
Authors: Ruepp Marc-David , Schweingruber Christoph , Kleinschmidt Nicole , Schümperli Daniel
Published: December 2010

Cleavage/polyadenylation of mRNAs and 3′ processing of replication-dependent histone transcripts are both mediated by large complexes that share several protein components. Functional studies of these shared proteins are complicated by the cooperative binding of the individual subunits. For CstF-64, an additional difficulty is that symplekin and CstF-77 bind mutually exclusively to its hinge domain. Here we have identified CstF-64 and symplekin mutants that allowed us to distinguish between these interactions and to elucidate the role of CstF-64 in the two processing reactions. The interaction of CstF-64 with symplekin is limiting for histone RNA 3′ processing but relatively unimportant for cleavage/polyadenylation. In contrast, the nuclear accumulation of CstF-64 depends on its binding to CstF-77 and not to symplekin. Moreover, the CstF-64 paralogue CstF-64Tau can compensate for the loss of CstF-64. As CstF-64Tau has a lower affinity for CstF-77 than CstF-64 and is relatively unstable, it is the minor form. However, it may become up-regulated when the CstF-64 level decreases, which has biological implications for spermatogenesis and probably also for other regulatory events. Thus, the interactions between CstF-64/CstF-64Tau and CstF-77 are important for the maintenance of stoichiometric nuclear levels of the CstF complex components and for their intracellular localization, stability, and function.
Aberrant mitochondrial fission in neurons induced by protein kinase Cδ under oxidative stress conditions in vivo
Authors: Qi Xin , Disatnik Marie-Helene , Shen Ning , Sobel Raymond A. , Mochly-Rosen Daria
Published: December 2010

Neuronal cell death in a number of neurological disorders is associated with aberrant mitochondrial dynamics and mitochondrial degeneration. However, the triggers for this mitochondrial dysregulation are not known. Here we show excessive mitochondrial fission and mitochondrial structural disarray in brains of hypertensive rats with hypertension-induced brain injury (encephalopathy). We found that activation of protein kinase Cδ (PKCδ) induced aberrant mitochondrial fragmentation and impaired mitochondrial function in cultured SH-SY5Y neuronal cells and in this rat model of hypertension-induced encephalopathy. Immunoprecipitation studies indicate that PKCδ binds Drp1, a major mitochondrial fission protein, and phosphorylates Drp1 at Ser 579, thus increasing mitochondrial fragmentation. Further, we found that Drp1 Ser 579 phosphorylation by PKCδ is associated with Drp1 translocation to the mitochondria under oxidative stress. Importantly, inhibition of PKCδ, using a selective PKCδ peptide inhibitor (δV1-1), reduced mitochondrial fission and fragmentation and conferred neuronal protection in vivo and in culture. Our study suggests that PKCδ activation dysregulates the mitochondrial fission machinery and induces aberrant mitochondrial fission, thus contributing to neurological pathology.