bluuebunny/crossref_metadata_2025 huggingface dataset:
A mean-field model for amorphization in crystalline solid solutions
Authors: Li Huaming , Li Mo
Published: June 2011

Based on our understanding of the atomic mechanisms of melting in binary crystalline solid solutions, we propose a unified two-order-parameter mean-field model to describe solid-state amorphization under polymorphic constraints. In this framework, we treat both thermal melting and amorphization on equal footing as a topological-order-to-disorder transition. The primary order parameter is defined such that it represents the loss of the long-range order. The elastic strain field induced by composition disorder that plays an important role at low temperature is described by a bilinear coupling with the primary order parameter. We show that solid-state amorphization can be considered as an extension of a melting transition at low temperature under polymorphic constraints. This theory can also address endothermic melting as well as exothermic melting at low temperature. We present phase diagrams and the corresponding thermodynamic quantities for a model binary crystalline solution system at and near the transitions.
Ultra-low-power superconductor logic
Authors: Herr Quentin P. , Herr Anna Y. , Oberg Oliver T. , Ioannidis Alexander G.
Published: June 2011

We have developed a new superconducting digital technology, Reciprocal Quantum Logic, that uses ac power carried on a transmission line, which also serves as a clock. Using simple experiments, we have demonstrated zero static power dissipation, thermally limited dynamic power dissipation, high clock stability, high operating margins, and a low bit-error rate. These features indicate that the technology is scalable to far more complex circuits at a significant level of integration. On the system level, Reciprocal Quantum Logic combines the high speed and low-power signal levels of single-flux-quantum signals with the design methodology of semiconductor digital logic, including low static power dissipation, low latency combinational logic, and efficient device count.
Features in optical absorption and photocurrent spectra of organic solar cells due to organic/organic interface
Authors: Ismail Yasser A. M. , Soga Tetsuo , Jimbo Takashi
Published: June 2011

We surprisingly found that, organic/organic interface had a direct and pronounced impact on optical absorption and photocurrent spectra of organic solar cell at a favorable wavelength region of the visible solar spectrum. The organic/organic interface was formed as a result of connection between coumarin 6 (C6): [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) blend films and indium-tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) electrode. Optical absorption measurement was carried out for ITO/PEDOT:PSS/C6:PCBM films, while external quantum efficiency measurement was carried out for ITO/PEDOT:PSS/C6:PCBM/Al solar cells, with varying C6:PCBM blend concentration. We found that, the C6:PCBM blend in the ITO/PEDOT:PSS/C6:PCBM films had an additional feature in the absorption spectra at the wavelength range of 520–800 nm, at which the C6 dye, PCBM, PEDOT:PSS, and ITO were transparent. An additional feature, also, appeared in photocurrent spectra of the C6:PCBM films in the ITO/PEDOT:PSS/C6:PCBM/Al solar cells at the same wavelength range. The new features in the optical absorption and photocurrent spectra of the investigated solar cells originated, in all probability, due to optically induced sup-band transitions in the C6:PCBM blend films at the interface with ITO/PEDOT:PSS electrode. Thus, the C6:PCBM blend films produced a charge carrier generation interface due to connection with ITO/PEDOT:PSS electrode. As a result of this charge carrier generation interface, the power conversion efficiency of the corresponding solar cell is improved. Taking into consideration these new findings, the high-band-gap organic materials will take more importance as sensitizers in organic optoelectronic applications.
Photoluminescence dynamics of ensemble and individual CdSe/ZnS quantum dots with an alloyed core/shell interface
Authors: Ratchford Daniel , Dziatkowski Konrad , Hartsfield Thomas , Li Xiaoqin , Gao Yan , Tang Zhiyong
Published: June 2011

A comprehensive study of the photoluminescence dynamics in newly developed CdSe/ZnS quantum dots with alloyed core/shell interfaces is presented. Time-correlated single photon counting is used to measure the decay of exciton luminescence from both the ensemble and individual quantum dots. For decreasing emission wavelength (i.e., for smaller dots), the ensemble data reveal increasing total decay rates with greater variation. This systematic change is expected for emitters with stronger quantum confinement and more influenced by the surface/interface trap states. In experiments performed on single quantum dots, the photoluminescence trajectories exhibit two-state blinking behavior. The distributions of the “off”-state probability density are described by an average power-law exponent of 1.5 ± 0.2, while the average decay rate of emission from the threshold-discriminated “on”-states is estimated to be 0.035 ± 0.004 ns−1. We suggest that in core/shell quantum dots with a large bandgap offset, the compositionally graded energy profile at the interface may not be smooth enough to suppress nonradiative Auger recombination and prevent blinking.
Swift heavy-ion irradiation-induced shape and structural transformation in cobalt nanoparticles
Authors: Sprouster D. J. , Giulian R. , Araujo L. L. , Kluth P. , Johannessen B. , Cookson D. J. , Ridgway M. C.
Published: June 2011

The shape and structural evolution of Co nanoparticles embedded in SiO2 and subjected to swift heavy-ion irradiation have been investigated over a wide energy and fluence range. Modifications of the nanoparticle size and shape were characterized with transmission electron microscopy and small-angle x-ray scattering. Nanoparticles below a threshold diameter remained spherical in shape and progressively decreased in size under irradiation due to dissolution. Nanoparticles above the threshold diameter transformed into nanorods with their major dimension parallel to the incident ion direction. Modifications of the atomic-scale structure of the Co nanoparticles were identified with x-ray absorption spectroscopy. Analysis of the x-ray absorption near-edge spectra showed that prior to irradiation all Co atoms were in a metallic state, while after irradiation Co atoms were in both oxidized and metallic environments, the former consistent with dissolution. The evolution of the nanoparticle short-range order was determined from extended x-ray absorption fine structure spectroscopy. Structural changes in the Co nanoparticles as a function of ion fluence included an increase in disorder and asymmetric deviation from a Gaussian interatomic distance distribution coupled with a decrease in bondlength. Such changes resulted from the irradiation-induced decrease in nanoparticle size and subsequent dissolution.
A strong magneto-optical activity in rare-earth La3+ substituted M-type strontium ferrites
Authors: Hu Feng , Fernandez-Garcia Lucia , Liu Xian-Song , Zhu De-Ru , Suárez Marta , Luis Menéndez Jose
Published: June 2011

M-type strontium ferrites with substitution of Sr2+ by rare-earth La3+ were prepared by conventional ceramic technology. The structure, magnetic properties, and magneto-optical Kerr activity of Sr1−xLaxFe12O19 (x = 0, 0.05, 0.10, 0.15, 0.20) were investigated by x-ray diffraction (XRD), vibrating sample magnetometer (VSM), and magneto-optical ellipsometry, respectively. X-ray diffraction showed that the samples sintered at 1290 °C for 3 h were single M-type hexagonal ferrites. The magnetic properties were remarkably changed due to the valence change of Fe ions induced by the substitution of La ions. Most significantly, an important magneto-optical activity was induced in the La3+ substituted M-type strontium ferrites around 3 eV.
Energy level decay processes in Ho3+-doped tellurite glass relevant to the 3 μm transition
Authors: Gomes Laércio , Milanese Daniel , Lousteau Joris , Boetti Nadia , Jackson Stuart D.
Published: June 2011

The primary excited state decay processes relating to the 5I6 → 5I7 ∼ 2.9 μm laser transition in singly Ho3+-doped tellurite (TZBG) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 5I6 energy level at 1151 nm and 5I7 energy level at 1958 nm has established that the rate of energy transfer up-conversion between holmium ions excited to the 5I7 level is negligible for Ho3+ concentrations up to 4 mol. %. Excited state absorption was not observed from either the 5I7 or 5I6 levels and the luminescence from the 5I7 and 5I6 energy levels was measured to peak at ∼2050 nm and ∼2930 nm, respectively. The 5I6 level has a low luminescence efficiency of ∼8.9% due to strong nonradiative multiphonon relaxation. In contrast, decay from the 5I7 level is essentially fully radiative. A linear decrease in the decay time of the 5I6 level with Ho3+ concentration augmentation results from energy transfer to OH− ions in the glass (with NOH ∼ 8.2 × 1017 ions cm−3) and reduces the luminescence efficiency of the 5I6 level to 8% for [Ho3+] = 4 mol. %. Numerical simulation of a fiber laser incorporating 4 mol. % Ho3+ showed that a population inversion of ∼7.8% is reached for square pulses of 100 μs duration and a repetition frequency of 20 Hz at a moderate pump intensity of 418 kW cm−2 if energy transfer to OH− radicals is neglected.
Thin liquid film lubrication under external electrical fields: Roles of liquid intermolecular interactions
Authors: Xie Guoxin , Luo Jianbin , Liu Shuhai , Guo Dan , Zhang Chenhui
Published: June 2011

One of the important features of the nanoscale liquid film lubrication is the formation of ordered layers at the solid/liquid interface. In this paper, the effect of the intermolecular interaction in liquid lubricant films on the formation of ordered layers after applying external electric fields (EEFs) has been investigated by measuring the central-film-thicknesses of liquids in concentrated point contacts and then inferring the thin film rheology. It has been found that the film formation properties of both pure liquid n-alkanes and liquid n-alcohols with relatively long chains have weak responses to EEFs, while those of their mixed solutions could be enhanced more notably by EEFs. In addition, the effect of the dispersive interactions between solvent molecules on the formation of ordered layers in thin lubrication films under EEFs was also discussed.
Two- and four-component relativistic generalized-active-space coupled cluster method: Implementation and application to BiH
Authors: Sørensen Lasse K. , Olsen Jeppe , Fleig Timo
Published: June 2011

A string-based coupled-cluster method of general excitation rank and with optimal scaling which accounts for special relativity within the four-component framework is presented. The method opens the way for the treatment of multi-reference problems through an active-space inspired single-reference based state-selective expansion of the model space. The evaluation of the coupled-cluster vector function is implemented by considering contractions of elementary second-quantized operators without setting up the amplitude equations explicitly. The capabilities of the new method are demonstrated in application to the electronic ground state of the bismuth monohydride molecule. In these calculations simulated multi-reference expansions with both doubles and triples excitations into the external space as well as the regular coupled-cluster hierarchy up to full quadruples excitations are compared. The importance of atomic outer core-correlation for obtaining accurate results is shown. Comparison to the non-relativistic framework is performed throughout to illustrate the additional work of the transition to the four-component relativistic framework both in implementation and application. Furthermore, an evaluation of the highest order scaling for general-order expansions is presented.
The interfacial amorphous double layer and the homogeneous nucleation in reflow of a Sn-Zn solder on Cu substrate
Authors: Pan Chien-Cheng , Lin Kwang-Lung
Published: June 2011

To illustrate the interfacial reaction mechanism, the Sn-Zn[Sn–8.5Zn–0.5Ag-0.01Al-0.1Ga (wt%)] solder was reflowed on Cu substrate at 250 °C for 15 s followed by immediate quench in liquid nitrogen. The frozen interfacial microstructure was investigated with high resolution transmission electron microscope. An amorphous double layer was formed at the interface which consists of a 5 nm pure Cu region and a Cu-Zn diffusion region. Nanocrystalline intermetallic compound (IMC) Cu5Zn8 were observed in the Cu-Zn diffusion region. These nanocrystalline IMCs are suggested to form via a homogeneous nucleation process.
Combination of exchange-bias and long-range interlayer couplings in Fe/fct-Mn/Co trilayers
Authors: Wang Chih-Hsiung , Huang Ya-Yun , Lin Wen-Chin
Published: June 2011

In this study, Fe/Mn/Co trilayers were grown on Cu(100) to investigate the combination of exchange-bias coupling and long-range interlayer coupling. The crystalline structures of fct-Co and fct-Mn were confirmed by low energy electron diffraction (LEED) and I/V-LEED. The magnetic hysteresis loops were measured by magneto-optical Kerr effect as a function of Fe and Mn thickness. When the fct-Mn was increased to 24 ML, the Co and Fe layers underwent incoherent two-step magnetization switching with a special feature. The interlayer coupling preferred coherent rotation of Fe and Co, but the exchange bias coupling of Mn/Co increased the coercivity of the Co layer, prohibiting rotation simultaneous with the Fe layer. As a result, during the Fe flipping, the Co layer first rotated in accordance with the Fe layer and then turned back to the initial orientation. Our simulation also demonstrated a similar phenomenon when the exchange bias coupling and interlayer coupling were of comparable magnitude.
Synthesis, characterization and ferroelectric properties of lead-free K0.5Na0.5NbO3 nanotube arrays
Authors: Zhou Di , Gu Haoshuang , Hu Yongming , Tian Huyong , Wang Zhao , Qian Zheli , Wang Yu
Published: June 2011

Lead-free K0.5Na0.5NbO3 (KNN) nanotube arrays were synthesized by a sol-gel method with anodic aluminum oxide templates. The obtained KNN nanotubes exhibited a polycrystalline and monoclinic perovskite structure with diameters of ∼200 nm and wall thickness of ∼30–40 nm, respectively. The polarization-electric loop curve of the nanotubes array were examined showing the values of 2Pr and 2Ec at about 3.4 μC/cm2 and 13 kV/cm, respectively, under a maximum electric field of 12.5 kV/cm. The piezoelectric characteristics of individual KNN nanotube array was also identified through piezoresponse force microscopy.
Voltage preamplifier for extensional quartz sensors used in scanning force microscopy
Authors: Morawski Ireneusz , Blicharski Józef , Voigtländer Bert
Published: June 2011

Extensional-mode quartz resonators are being increasingly used as force sensors in dynamic scanning force microscopy or atomic force microscopy (AFM). We propose a voltage preamplifier in order to amplify the charge induced on quartz electrodes. The proposed solution has some advantages over the typically used current-to-voltage converters. First, the gain does not depend on the inner parameters of the quartz resonator, which are usually unknown for the specific resonator and may even vary during the measurement. Second, with such an amplifier a better signal-to-noise ratio can be achieved. Finally, we present AFM images of the Si(111) and the SiO2 surfaces obtained by the voltage preamplifier with simultaneously recorded tunneling current.
Three-dimensional ferromagnetic architectures with multiple metastable states
Authors: Nasirpouri F. , Engbarth M. A. , Bending S. J. , Peter L. M. , Knittel A. , Fangohr H. , Milošević M. V.
Published: June 2011

We demonstrate controllable dual-bath electrodeposition of nickel on architecture-tunable three-dimensional (3D) silver microcrystals. Magnetic hysteresis loops of individual highly faceted Ag-Ni core-shell elements reveal magnetization reversal that comprises multiple sharp steps corresponding to different stable magnetic states. Finite-element micromagnetic simulations on smaller systems show several jumps during magnetization reversal which correspond to transitions between different magnetic vortex states. Structures of this type could be realizations of an advanced magnetic data storage architecture whereby each element represents one multibit, storing a combination of several conventional bits depending on the overall number of possible magnetic states associated with the 3D core-shell shape.
Improving near-field confinement of a bowtie aperture using surface plasmon polaritons
Authors: Srisungsitthisunti Pornsak , Ersoy Okan K. , Xu Xianfan
Published: June 2011

Bowtie aperture is known to produce subdiffraction-limited optical spot with high intensity. In this work, we investigate integrating a bowtie aperture with circular grooves to reduce the divergence of the near-field produced by the bowtie aperture. Numerical results indicate that surface waves reflected from circular grooves improve the field confinement of a bowtie aperture along the polarization axis. These circular grooves with period near half the wavelength of surface plasmon polaritons reduce the spot size by as much as 40% at distances between 20 and 100 nm from the surface and create a more symmetrical optical spot.
Effect of SiC wafer miscut angle on the morphology and Hall mobility of epitaxially grown graphene
Authors: Dimitrakopoulos Christos , Grill Alfred , McArdle Timothy J. , Liu Zihong , Wisnieff Robert , Antoniadis Dimitri A.
Published: June 2011

We show that the surface morphology and electrical properties of graphene grown on SiC(0001) wafers depend strongly on miscut angle, even for nominally “on-axis” wafers. Graphene grown on pit-free surfaces with narrow terraces (miscut above 0.28°) shows substantially lower Hall mobility than graphene on surfaces with miscut angles below 0.1° that have wider terraces with some pits. The effect of pits on mobility is not detrimental if flat, pit-free areas with dimensions larger than the carrier mean free path remain between pits. Using these results, we optimized the growth process, achieving room-temperature mobility up to 3015 cm2/V s at N=2.0×1012 cm−2.
Magnetic exchange couplings evaluated with Rung 3.5 density functionals
Authors: Phillips Jordan J. , Peralta Juan E. , Janesko Benjamin G.
Published: June 2011

Rung 3.5 exchange-correlation functionals are assessed for the calculation of magnetic exchange coupling parameters and atomic spin populations for a variety of inorganic and organic magnetic systems. Density functional theory calculations of exchange couplings sensitively depend on nonlocal contributions to the exchange-correlation functional. Semilocal functionals, Rungs 1-3 on “Jacob's Ladder” of density functional approximations, yield excessively delocalized electrons and overestimated absolute exchange couplings. Fourth-rung hybrid functionals admixing nonlocal exchange improve the results. We show that new “Rung 3.5” functionals give magnetic properties intermediate between semilocal and hybrid functionals, providing additional evidence that these functionals incorporate some desirable aspects of nonlocal exchange. Results for ferromagnetic complexes indicate areas for future improvement.
Moyal multiplier algebras of the test function spaces of type S
Authors: Soloviev M. A.
Published: June 2011

The Gel'fand-Shilov spaces of type S are considered as topological algebras with respect to the Moyal star product and their corresponding algebras of multipliers are defined and investigated. In contrast to the well-studied case of Schwartz's space S, these multipliers are allowed to have nonpolynomial growth or infinite order singularities. The Moyal multiplication is thereby extended to certain classes of ultradistributions, hyperfunctions, and analytic functionals. The main theorem of the paper characterizes those elements of the dual of a given test function space that are the Moyal multipliers of this space. The smallest nontrivial Fourier-invariant space in the scale of S-type spaces is shown to play a special role, because its corresponding Moyal multiplier algebra contains the largest algebra of functions for which the power series defining their star products are absolutely convergent. Furthermore, it contains analogous algebras associated with cone-shaped regions, which can be used to formulate a causality condition in quantum field theory on noncommutative space-time.
A InGaN/GaN quantum dot green (λ=524 nm) laser
Authors: Zhang Meng , Banerjee Animesh , Lee Chi-Sen , Hinckley John M. , Bhattacharya Pallab
Published: June 2011

The characteristics of self-organized InGaN/GaN quantum dot lasers are reported. The laser heterostructures were grown on c-plane GaN substrates by plasma-assisted molecular beam epitaxy and the laser facets were formed by focused ion beam etching with gallium. Emission above threshold is characterized by a peak at 524 nm (green) and linewidth of 0.7 nm. The lowest measured threshold current density is 1.2 kA/cm2 at 278 K. The slope and wall plug efficiencies are 0.74 W/A and ∼1.1%, respectively, at 1.3 kA/cm2. The value of T0=233 K in the temperature range of 260–300 K.
Thermal emittance measurements of a cesium potassium antimonide photocathode
Authors: Bazarov Ivan , Cultrera Luca , Bartnik Adam , Dunham Bruce , Karkare Siddharth , Li Yulin , Liu Xianghong , Maxson Jared , Roussel William
Published: June 2011

Thermal emittance measurements of a CsK2Sb photocathode at several laser wavelengths are presented. The emittance is obtained with a solenoid scan technique using a high voltage dc photoemission gun. The thermal emittance is 0.56±0.03 mm mrad/mm(rms) at 532 nm wavelength. The results are compared with a simple photoemission model and found to be in a good agreement.
Rotationally resolved infrared spectrum of the Na+-D2 complex: An experimental and theoretical study
Authors: Poad B. L. J. , Dryza V. , Kłos J. , Buchachenko A. A. , Bieske E. J.
Published: June 2011

The infrared spectrum of mass-selected Na+-D2 complexes is recorded in the D-D stretch vibration region (2915-2972 cm−1) by detecting Na+ photofragments resulting from photo-excitation of the complexes. Analysis of the rotationally resolved spectrum confirms a T-shaped equilibrium geometry for the complex and a vibrationally averaged intermolecular bond length of 2.461 Å. The D-D stretch band centre occurs at 2944.04 cm−1, representing a −49.6 cm−1 shift from the Q1(0) transition of the free D2 molecule. Variational rovibrational energy level calculations are performed for Na+-D2 utilising an ab initio potential energy surface developed previously for investigating the Na+-H2 complex [B. L. J. Poad et al., J. Chem. Phys. 129, 184306 (2008)]10.1063/1.3005785. The theoretical approach predicts a dissociation energy for Na+-D2 of 923 cm−1 with respect to the Na++ D2 limit, reproduces the experimental rotational constants to within 1-2%, and gives a simulated spectrum closely matching the experimental infrared spectrum.
Comparative characterization of rhombohedral and tetragonal PZN-PT single crystals
Authors: Kobor D. , Tine M. , Hajjaji A. , Lebrun L. , Pruvost S. , Guyomar D.
Published: June 2011

Ferroelectric single crystals Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN–PT) are promising full materials for nonresonant or large bandwidth transducers due to the large values of their piezoelectric properties (dij, kij) and their mechanical quality factor (Qij). However the properties of these materials depend greatly on the content of titanium which influences very significantly the symmetry of the crystal. In this paper we try to understand the influence of the percentage of Titanium in these crystals by studying the two compositions that are in very different phases at room temperature (rhombohedral and tetragonal symmetries). Crystals of pure PZN–4.5PT and PZN-12PT were grown by a Flux technique. The typical single crystals obtained are brown yellow. The room temperature dielectric permittivity along the <001> direction is about 900 for the PZN-12PT, which is smaller than that of the PZN–4.5PT (5840). The Curie point Tc of the tetragonal crystal is about 220 °C (which is higher than that of the rhombohedral one (166 °C)), while the ferroelectric phase transition temperature is 130 °C for the PZN-4.5PT single crystal. The remnant polarization and coercive field of <001> oriented crystals measured at 1 kHz are around 40 μC/cm2 and 3.30 kV/cm, respectively for the PZN-4.5PT, 27μC/cm2 and 11.1 kV/cm for the PZN-12PT single crystal. The d33 versus uniaxial stress shows that this coefficient is more stable for the single crystal with low Ti than for that with high rate of Ti. The study of temperature stability on these crystals shows a possible presence of an unidentified phase in the low and negative range temperature for the PZN-4.5PT.
Regulation of aromatase expression by 1α,25(OH)2 vitamin D3 in rat testicular cells
Authors: Zanatta Leila , Bouraïma-Lelong Hélène , Delalande Christelle , Silva Fátima R. M. B. , Carreau Serge
Published: June 2011

It is well known that the vitamin D endocrine system is involved in physiological and biochemical events in numerous tissues, especially gut, bone and kidney but also testis. Therefore, in this study the effect and mechanisms of action of 1α,25(OH)2 vitamin D3 (1,25D) on aromatase gene expression in immature rat Sertoli cells were evaluated. Vitamin D receptor transcripts were present in immature Sertoli cells as well as in adult testicular germ cells and somatic cells. The treatment of immature Sertoli cells with 100 nM 1,25D increased the amount of aromatase transcript, mainly in 30-day-old rats. The protein kinase A (PKA) blocker, H89, partially inhibited the 1,25D effect. The stimulation of aromatase gene expression in 30-day-old Sertoli cells by the agonist 1α,25(OH)2 lumisterol3, and the suppression of the 1,25D effect by the antagonists 1β,25(OH)2 vitamin D3 and (23S)-25-dehydro-1α (OH)-vitamin D3-26,23-lactone suggested, besides a genomic effect of 1,25D, the existence of non-genomic activation of the membrane-bound vitamin D receptor involving the PKA pathway.
Differential resistance of mammalian sperm chromatin to oxidative stress as assessed by a two-tailed comet assay
Authors: Enciso María , Johnston Stephen D. , Gosálvez Jaime
Published: June 2011

Protamines of eutherian species are cysteine-rich molecules that become cross-linked by disulfide bonds during epididymal transit, whereas the protamines of most marsupial species lack cysteine residuals. The present study made use of the differences in protamine structure between eutherian and metatherian mammal spermatozoa to examine the comparative resistance of sperm DNA to oxidative damage in three eutherian species (Mus musculus, Homo sapiens, Sus domesticus) and three metatherian species (Vombatus ursinus, Phascolarctos cinereus, Macropus giganteus). Sperm DNA fragmentation of samples exposed to increasing concentrations of hydrogen peroxide was assessed by means of the two-tailed comet assay. The sperm DNA of the marsupial species studied were significantly more sensitive to oxidative stress than the spermatozoa of eutherian species. Such susceptibility is consistent with the lack of disulfide cross-linking in marsupial sperm chromatin and suggests that the oxidation of thiols to disulfides for chromatin condensation during epididymal transit in eutherian mammals is likely to be important in order to provide stability and protect these cells from the genotoxic effects of adverse environments.
Mitochondrial inhibition during preimplantation embryogenesis shifts the transcriptional profile of fetal mouse brain
Authors: Fullston Tod , Mitchell Megan , Wakefield Sarah , Lane Michelle
Published: June 2011

Environmental stress results in perturbations to mitochondrial function in the preimplantation embryo and hinders subsequent embryo and possibly offspring development. Global gene expression in fetal mouse brain was investigated following targeted mitochondrial inhibition by amino-oxyacetate (AOA) from the 2-cell to the blastocyst stage. Blastocysts were transferred to pseudopregnant recipients and RNA extracted from Day 18 fetal brains for microarray interrogation. Exposure to 5 μM AOA during preimplantation embryo development induced differential expression of 166 genes (>1.25 fold) in the fetal brain, relative to control medium-cultured embryos. Altered expression pathways included carbohydrate metabolism, neurological development, cellular proliferation and death, DNA replication, recombination and repair. Of 28 genes exhibiting the greatest change in expression, qPCR confirmed that 16 were significantly altered. Targeted qPCR assessment of a further 20 genes associated with methylation, acetylation and mitochondrial dysfunction revealed that three were significantly altered (Immp1l, Nars2, Sat2) and Dmap1 exhibited a sex-specific response to AOA exposure. Only 2/48 genes had significantly altered expression by qPCR (Nola3, Timm8b) in fetal brains exposed to 50 μM AOA embryo culture, excluding an AOA dose-dependent response. It was concluded that perturbation of mitochondrial function induced by 5 μM AOA during preimplantation embryo development alters gene expression in the neonatal brain in a manner that suggests that proper brain development may be compromised.
Comparative oncogenomics identifies breast tumors enriched in functional tumor-initiating cells
Authors: Herschkowitz Jason I. , Zhao Wei , Zhang Mei , Usary Jerry , Murrow George , Edwards David , Knezevic Jana , Greene Stephanie B. , Darr David , Troester Melissa A. , Hilsenbeck Susan G. , Medina Daniel , Perou Charles M. , Rosen Jeffrey M.
Published: June 2011

The claudin-low subtype is a recently identified rare molecular subtype of human breast cancer that expresses low levels of tight and adherens junction genes and shows high expression of epithelial-to-mesenchymal transition (EMT) genes. These tumors are enriched in gene expression signatures derived from human tumor-initiating cells (TICs) and human mammary stem cells. Through cross-species analysis, we discovered mouse mammary tumors that have similar gene expression characteristics as human claudin-low tumors and were also enriched for the human TIC signature. Such claudin-low tumors were similarly rare but came from a number of distinct mouse models, including the p53 null transplant model. Here we present a molecular characterization of 50 p53 null mammary tumors compared with other mouse models and human breast tumor subtypes. Similar to human tumors, the murine p53 null tumors fell into multiple molecular subtypes, including two basal-like, a luminal, a claudin-low, and a subtype unique to this model. The claudin-low tumors also showed high gene expression of EMT inducers, low expression of the miR-200 family, and low to absent expression of both claudin 3 and E-cadherin. These murine subtypes also contained distinct genomic DNA copy number changes, some of which are similarly altered in their cognate human subtype counterpart. Finally, limiting dilution transplantation revealed that p53 null claudin-low tumors are highly enriched for TICs compared with the more common adenocarcinomas arising in the same model, thus providing a unique preclinical mouse model to investigate the therapeutic response of TICs.
Acidic nuclear phosphoprotein 32kDa (ANP32)B-deficient mouse reveals a hierarchy of ANP32 importance in mammalian development
Authors: Reilly Patrick T. , Afzal Samia , Gorrini Chiara , Lui Koren , Bukhman Yury V. , Wakeham Andrew , Haight Jillian , Ling Teo Wei , Cheung Carol C. , Elia Andrew J. , Turner Patricia V. , Mak Tak Wah
Published: June 2011

The highly conserved ANP32 proteins are proposed to function in a broad array of physiological activities through molecular mechanisms as diverse as phosphatase inhibition, chromatin regulation, caspase activation, and intracellular transport. On the basis of previous analyses of mice bearing targeted mutations of
Anp32a
or
Anp32e
, there has been speculation that all ANP32 proteins play redundant roles and are dispensable for normal development. However, more recent work has suggested that ANP32B may in fact have functions that are not shared by other ANP32 family members. Here we report that
ANP32B
expression is associated with a poor prognosis in human breast cancer, consistent with the increased levels of
Anp32b
mRNA present in proliferating wild-type (WT) murine embryonic fibroblasts and stimulated WT B and T lymphocytes. Moreover, we show that, contrary to previous assumptions,
Anp32b
is very important for murine embryogenesis. In a mixed genetic background, ANP32B-deficient mice displayed a partially penetrant perinatal lethality that became fully penetrant in a pure C57BL/6 background. Surviving ANP32B-deficient mice showed reduced viability due to variable defects in various organ systems. Study of compound mutants lacking ANP32A, ANP32B, and/or ANP32E revealed previously hidden roles for ANP32A in mouse development that became apparent only in the complete absence of ANP32B. Our data demonstrate a hierarchy of importance for the mammalian
Anp32
genes, with
Anp32b
being the most critical for normal development.
Using a Genetic Mixture Model to Study Phenotypic Traits: Differential Fecundity among Yukon River Chinook Salmon
Authors: Bromaghin Jeffrey F. , Evenson Danielle F. , McLain Thomas H. , Flannery Blair G.
Published: June 2011

Fecundity is a vital population characteristic that is directly linked to the productivity of fish populations. Historic data from Yukon River (Alaska) Chinook salmonOncorhynchus tshawytschasuggest that length‐adjusted fecundity differs among populations within the drainage and either is temporally variable or has declined. Yukon River Chinook salmon have been harvested in large‐mesh gill‐net fisheries for decades, and a decline in fecundity was considered a potential evolutionary response to size‐selective exploitation. The implications for fishery conservation and management led us to further investigate the fecundity of Yukon River Chinook salmon populations. Matched observations of fecundity, length, and genotype were collected from a sample of adult females captured from the multipopulation spawning migration near the mouth of the Yukon River in 2008. These data were modeled by using a new mixture model, which was developed by extending the conditional maximum likelihood mixture model that is commonly used to estimate the composition of multipopulation mixtures based on genetic data. The new model facilitates maximum likelihood estimation of stock‐specific fecundity parameters without first using individual assignment to a putative population of origin, thus avoiding potential biases caused by assignment error. The hypothesis that fecundity of Chinook salmon has declined was not supported; this result implies that fecundity exhibits high interannual variability. However, length‐adjusted fecundity estimates decreased as migratory distance increased, and fecundity was more strongly dependent on fish size for populations spawning in the middle and upper portions of the drainage. These findings provide insights into potential constraints on reproductive investment imposed by long migrations and warrant consideration in fisheries management and conservation. The new mixture model extends the utility of genetic markers to new applications and can be easily adapted to study any observable trait or condition that may vary among populations.
Observation of Atlantic Sturgeon Predation by a Flathead Catfish
Authors: Flowers H. Jared , Bonvechio Timothy F. , Peterson Douglas L.
Published: June 2011

Sturgeons (family Acipenseridae) are a highly threatened taxon worldwide; populations have declined for several reasons, including overfishing and habitat modification. It has been suggested that the widely introduced, highly piscivorous, flathead catfish Pylodictis olivaris is responsible for the decline of certain sturgeon populations in North America. Here we present the first field observation of flathead catfish predation on a sturgeon of any species, an Atlantic sturgeon Acipenser oxyrinchus in the Satilla River, Georgia. Our finding demonstrates a potential impact of flathead catfish predation on sturgeon populations; however, more research is needed to describe the full magnitude of such effects on sturgeon populations.
Temporal Variation in Prevalence of Viral Hemorrhagic Septicemia Virus Type IVb among Upper St. Lawrence River Smallmouth Bass
Authors: Eckerlin Geofrey E. , Farrell John M. , Casey Rufina N. , Hope Kristine M. , Groocock Geoffrey H. , Bowser Paul R. , Casey James
Published: June 2011

We investigated a newly introduced pathogen in a wild population of smallmouth bass Micropterus dolomieu in the St. Lawrence River to illuminate unknown temporal and demographic prevalence patterns. We used real‐time quantitative reverse‐transcription polymerase chain reaction to assess viral hemorrhagic septicemia virus (VHSV) genotype IVb (VHSV‐IVb) viral N‐gene levels. Our objectives were to characterize the distribution and abundance of this newly introduced pathogen within a naïve population of economically valuable sport fish through an annual cycle. We also sought to describe VHSV‐IVb levels across demographic groups (males and females; adults and subadults). Strong temporal variation in prevalence of VHSV‐IVb was evident through the annual cycle; peaks in prevalence corresponded to the smallmouth bass spawning period and a temperature range of 10–14°C. No difference in VHSV‐IVb prevalence between male and female smallmouth bass was detected. However, a markedly higher prevalence was observed in subadult fish than in adult fish. Owing to the observed temporal patterns in prevalence, surveillance programs for VHSV‐IVb in smallmouth bass should concentrate effort on springtime sampling and should include subadult fish.
Fish Entrainment Rates through Towboat Propellers in the Upper Mississippi and Illinois Rivers
Authors: Killgore K. Jack , Miranda L. E. , Murphy Catherine E. , Wolff Douglas M. , Hoover Jan Jeffrey , Keevin Thomas M. , Maynord Steven T. , Cornish Mark A.
Published: June 2011

A specially designed net was used to study fish entrainment and injury through towboat propellers in 13 pools of the Upper Mississippi and Illinois rivers. The net was attached to the stern of a 48.8‐m‐long towboat with twin propellers (in Kort propulsion nozzles), and sampling typically took place while the towboat pushed 15 loaded barges upstream at a time. In total, 254 entrainment samples over 894 km of the 13 study pools were collected. The sampling efforts produced 16,005 fish representing 15 families and at least 44 species; fish ranged in total length from 3 to 123 cm, but only 12.5‐cm or longer fish were analyzed because smaller fish could escape through the mesh of the trawl. Clupeidae (68% of total catch) and Sciaenidae (21%) were the dominant families. We detected no effects of towboat operation variables (speed and engine [i.e., propeller] revolutions per minute [RPM]) on entrainment rate (i.e., fish/km), but entrainment rate showed a wedge‐shaped distribution relative to hydraulic and geomorphic characteristics of the channel. Entrainment rate was low (<1 fish/km) in wide sections of the river, deep water, and swift current (or time periods characterized by faster flow); however, entrainment in narrow sections with shallow, slow water was highly variable and occasionally reached high levels (>30 fish/km). Although total entrainment rate was not related to engine RPM, the probability of being struck by a propeller increased with fish length and engine RPM. Limits on engine RPM in narrow, shallow, and sluggish reaches could reduce entrainment impact, particularly for large‐bodied fish.
Effectiveness and Trade‐Offs Associated with Hydraulic Egg Collections from Natural Salmon and Steelhead Redds for Conservation Hatchery Programs
Authors: Berejikian Barry A. , Gable Joshua T. , Vidergar Dmitri T.
Published: June 2011

Maintaining a large genetically effective number of breeders (Nb) in supplemented salmon populations is considered vital to their long‐term sustainability, yet may be difficult to consistently achieve in practice, especially in conservation hatchery programs that require small numbers of eggs for captive rearing. We evaluated efforts to hydraulically collect eggs from naturally produced redds, as implemented by conservation hatchery programs for Endangered Species Act listed populations of Snake River Chinook salmon Oncorhynchus tshawytscha and Hood Canal steelhead O. mykiss; we then compared the estimated Nb represented in the hydraulically collected captive populations with the Nb obtained by the more conventional approach (i.e., adult collection and artificial spawning). Egg collection goals in the steelhead and Chinook salmon conservation hatchery programs were met in most cases and were never exceeded. The embryo viability and egg‐to‐fry survival consistently exceeded 90% and were no less than would be expected through artificial spawning. Demographic estimates suggested that a greater Nb in the captive population would be obtained by hydraulic redd sampling than by artificial spawning of captured adults to produce a specific, limited number of eggs. Hydraulic redd sampling allows sexual selection to occur naturally on the spawning grounds and does not require barrier weirs, handling of adults, or the removal of a female's entire fecundity from natural production. The high rate of survival to emergence for hydraulically collected eggs (>95%) suggests that eggs are not damaged by the collection process, but the fate of uncollected eggs that are disturbed during the process is unknown. Hydraulic redd sampling requires fairly frequent redd surveys to time collections at the proper stage of embryonic development, and access to some redds in remote areas can be difficult. Hydraulic sampling of eyed eggs appears to have largely accomplished the goals of these small‐ to moderately‐sized conservation hatchery programs.
The Role of Age of Acquisition in Memory: Effects on Judgements of Learning and Recall
Authors: Illman Nathan A. , Morrison Catriona M.
Published: June 2011

Judgements of learning (JOLs) are self-made predictions of the likelihood that one will later recall information. The influence of stimulus characteristics on JOLs and recall continues to receive attention, yet there are still a number of unexplored lexical word features that may exert an effect on mnemonic processing. Using a standard cue–target paradigm, we focused on the role of word age of acquisition (AoA) and evaluated the role of both cue and target AoA on responses. We replicated the robust delayed-JOL effect and used a novel items analysis approach to examine the relationship between intrinsic word features and accuracy and reaction times for both JOLs and recall. A consistent effect of target AoA was found, even after controlling for a range of covariates previously shown to impact JOLs and recall. These results expand the role of AoA in word processing and suggest that it is a key variable in memory and metacognition; they also support Koriat's (1997) cue utilization framework.
The modulation of spatial congruency by object-based attention: Analysing the “locus” of the modulation
Authors: Luo Chunming , Lupiáñez Juan , Funes María Jesús , Fu Xiaolan
Published: June 2011

Earlier studies have demonstrated that spatial cueing differentially reduces stimulus–stimulus congruency (e.g., spatial Stroop) interference but not stimulus–response congruency (e.g., Simon; e.g., Lupiáñez & Funes, 2005). This spatial cueing modulation over spatial Stroop seems to be entirely attributable to object-based attention (e.g., Luo, Lupiáñez, Funes, & Fu, 2010). In the present study, two experiments were conducted to further explore whether the cueing modulation of spatial Stroop is object based and/or space based and to analyse the “locus” of this modulation. In Experiment 1, we found that the cueing modulation over spatial Stroop is entirely object based, independent of stimulus–response congruency. In Experiment 2, we observed that the modulation of object-based attention over the spatial Stroop only occurred at a short cue–target interval (i.e., stimulus onset asynchrony; SOA), whereas the stimulus–response congruency effect was not modulated either by object-based or by location-based attentional cueing. The overall pattern of results suggests that the spatial cueing modulation over spatial Stroop arises from object-based attention and occurs at the perceptual stage of processing.
Rhesus monkeys lack a consistent peak-end effect
Authors: Xu Eric R. , Knight Emily J. , Kralik Jerald D.
Published: June 2011

In humans, the order of receiving sequential rewards can significantly influence the overall subjective utility of an outcome. For example, people subjectively rate receiving a large reward by itself significantly higher than receiving the same large reward followed by a smaller one (Do, Rupert, & Wolford, 2008). This result is called the peak-end effect. A comparative analysis of order effects can help determine the generality of such effects across primates, and we therefore examined the influence of reward-quality order on decision making in three rhesus macaque monkeys ( Macaca mulatta). When given the choice between a high–low reward sequence and a low–high sequence, all three monkeys preferred receiving the high-value reward first. Follow-up experiments showed that for two of the three monkeys their choices depended specifically on reward-quality order and could not be accounted for by delay discounting. These results provide evidence for the influence of outcome order on decision making in rhesus monkeys. Unlike humans, who usually discount choices when a low-value reward comes last, rhesus monkeys show no such peak-end effect.
Very large refrigerant capacity at room temperature with reproducible magnetocaloric effect in Fe0.975Ni0.025Rh
Authors: Manekar Meghmalhar , Roy S B
Published: June 2011

We present the results of magnetocaloric effect (MCE) measurements on Fe0.975Ni0.025Rh. The MCE is estimated using both the isothermal field-dependent magnetization and the temperature-dependent magnetization in constant magnetic fields. We find a very large effective refrigerant capacity of nearly 492.8 J kg−1, with the hot end at about 307 K, which is reproducible over many field cycles. We compare this refrigerant capacity with those of two well known systems, namely Gd5Ge1.9Si2Fe0.1 and MnFeP0.45As0.55, which show a large MCE near room temperature, and also with our earlier results on the parent Fe–Rh alloy. The large effective refrigerant capacity in our sample is one of the largest achieved yet at room temperature with a significant improvement over the parent Fe–Rh system.
The influence of spherical cavity surface charge distribution on the sequence of partial discharge events
Authors: Illias Hazlee A , Chen George , Lewin Paul L
Published: June 2011

In this work, a model representing partial discharge (PD) behaviour of a spherical cavity within a homogeneous dielectric material has been developed to study the influence of cavity surface charge distribution on the electric field distribution in both the cavity and the material itself. The charge accumulation on the cavity surface after a PD event and charge movement along the cavity wall under the influence of electric field magnitude and direction has been found to affect the electric field distribution in the whole cavity and in the material. This in turn affects the likelihood of any subsequent PD activity in the cavity and the whole sequence of PD events. The model parameters influencing cavity surface charge distribution can be readily identified; they are the cavity surface conductivity, the inception field and the extinction field. Comparison of measurement and simulation results has been undertaken to validate the model.