bluuebunny/crossref_metadata_2025 huggingface dataset:
Mapping wheat powdery mildew resistance derived fromAegilops markgrafii
Authors: Weidner Annette , Röder Marion S. , Börner Andreas
Published: May 2012

The pattern of inheritance of powdery mildew resistance expressed by two bread wheat (cultivar ‘Alcedo’)/Aegilops markgrafiiintrogression lines was explored using F2populations bred from crosses made with the powdery mildew-susceptible cultivar ‘Kanzler’. Disease reaction was tested at both seedling and adult plant stages. Two resistance loci, designatedQPm.ipk-1AandQPm.ipk-7A, were identified as mapping to the distal ends of chromosome arms 1AS and 7AL, respectively. WhereasQPm.ipk-1Awas expressed throughout the plant's life,QPm.ipk-7Awas only effective at the seedling stage. The map location of both resistance loci indicated that resistances originated fromA. markgrafii.The possible genetic relationship of these disease-resistant genes to knownPmgenes is discussed in the context of synteny.
Development of a one‐dimensional ecosystem model including the iron cycle applied to the Oyashio region, western subarctic Pacific
Authors: Shigemitsu M. , Okunishi T. , Nishioka J. , Sumata H. , Hashioka T. , Aita M. N. , Smith S. L. , Yoshie N. , Okada N. , Yamanaka Y.
Published: May 2012

To investigate the iron cycle at Station A4 in the Oyashio region of the western subarctic Pacific, we developed a 1‐D ecosystem model consisting of 14 components including the iron cycle. The parameters associated with the iron cycle were optimized by assimilating monthly averaged data from time series observations for depth‐integrated net primary production, nitrate, silicate, dissolved and particulate iron within the surface mixed layer (ML) and at two depths (200 and 300 m depth). The model successfully reproduced the observations and demonstrated that (1) on an annual basis, winter mixing of subsurface water supplies more dissolved iron (Fed) to the ML than does dust dissolution, (2) Fed concentration in the ML rapidly declines to near‐depletion during the peak period of the diatom bloom in spring, which results in an increasing consumption ratio of silicate to nitrogenous nutrients by diatoms as they become more iron‐limited, causing a more rapid decrease of silicate compared to that of nitrogenous nutrients in the ML, followed by the silicate limitation of diatoms, and (3) Fed supplied to the ML by dust dissolution and desorption from particulate iron, by alleviating iron limitation of phytoplankton, supports their continuous utilization of nitrate from spring to fall even though Fed concentration in the ML remains low after the peak spring bloom. The model explained quantitatively the above behavior of Fed and other nutrients associated with Fed over the annual cycle in the Oyashio region.
U.S. Senate may consider Law of the Sea treaty again
Authors: Showstack Randy
Published: May 2012

U.S. ambassador David Balton hopes that the third time will be the charm. The U.S. Senate's Committee on Foreign Relations currently is considering holding hearings for a third time regarding U.S. accession to the United Nations Convention on the Law of the Sea, a framework governing uses of the world's oceans. The committee could hold hearings as early as this month, Balton, deputy assistant secretary for oceans and fisheries at the U.S. Department of State, said at the AGU Science Policy Conference on 2 May.
Weather extremes could affect agriculture
Authors: Balcerak Ernie
Published: May 2012

As Earth's climate warms, agricultural producers will need to adapt. Changes, especially increases in extreme events, are already having an impact on food production, according to speakers at a 1 May session on agriculture and food security at the AGU Science Policy Conference. Christopher Field, director of the Department of Global Ecology at the Carnegie Institution for Science of Washington, D. C., pointed out the complex factors that come into play in understanding food security, including spatially varying controls and stresses, incomplete models, and the potential for threshold responses. Factors that are likely to cause problems include increasing population; increasing preference for meat, which needs more land and energy inputs to produce; climate change; and increasing use of agricultural lands for biomass energy.
U.S. Earth Observing System beginning a rapid decline, report states
Authors: Showstack Randy
Published: May 2012

The U.S. Earth Observing System “is beginning a rapid decline in capability as long‐running missions end and key new missions are delayed, lost, or canceled,” according to a 2 May report by the U.S. National Research Council (NRC) titledEarth Science and Applications From Space: A Midterm Assessment of NASA's Implementation of the Decadal Survey. By 2020 the number of NASA and National Oceanic and Atmospheric Administration (NOAA) Earth observing instruments in space is likely to decline to as little as 25% of the current number, a concern that reinforces earlier studies that have warned that the U.S. system of environmental satellites is at risk of collapse, according to the report. “The projected loss of observing capability will have profound consequences on science and society, from weather forecasting to responding to natural hazards,” said NRC committee chair Dennis Hartmann, professor of atmospheric sciences at the University of Washington, Seattle. The report does not include planned or proposed missions that are not yet funded. The report notes, though, that “even the most optimistic projected launch cadence remains significantly below what would be required to prevent a major decline in NASA and NOAA's orbiting space assets.”
Developing a national stream morphology data exchange: Needs, challenges, and opportunities
Authors: Collins Mathias J. , Gray John R. , Peppler Marie C. , Fitzpatrick Faith A. , Schubauer‐Berigan Joseph P.
Published: May 2012

Stream morphology data, primarily consisting of channel and foodplain geometry and bed material size measurements, historically have had a wide range of applications and uses including culvert/ bridge design, rainfall‐ runoff modeling, food inundation mapping (e.g., U.S. Federal Emergency Management Agency food insurance studies), climate change studies, channel stability/sediment source investigations, navigation studies, habitat assessments, and landscape change research. The need for stream morphology data in the United States, and thus the quantity of data collected, has grown substantially over the past 2 decades because of the expanded interests of resource management agencies in watershed management and restoration. The quantity of stream morphology data collected has also increased because of state‐of‐the‐art technologies capable of rapidly collecting high‐resolution data over large areas with heretofore unprecedented precision. Despite increasing needs for and the expanding quantity of stream morphology data, neither common reporting standards nor a central data archive exist for storing and serving these often large and spatially complex data sets. We are proposing an open‐ access data exchange for archiving and disseminating stream morphology data.
Interdisciplinary research produces results in the understanding of planetary caves
Authors: Titus Timothy , Boston Penelope J.
Published: May 2012

First International Planetary Cave Research Workshop: Implications for Astrobiology, Climate, Detection, and Exploration; Carlsbad, New Mexico, 25–28 October 2011 With the advent of high‐resolution spatial imaging, the idea of caves on other planets has moved from the pages of science fiction into the realm of hard‐core science—complete with hypotheses, models, experiments, and observational data. Recently acquired data from spacecraft, together with terrestrial analogs and numerical models, are providing new insights into caves on Earth as well as caves on other terrestrial planetary bodies (e.g., Moon, Mars, and Titan).
Navigating graduate school and beyond: A career guide for graduate students and a must read for every advisor
Authors: Schultz Colin
Published: May 2012

Beginning his scientific career as an engineering student at PSG College of Technology, in Coimbatore, India, Sundar A. Christopher has negotiated and navigated the higher‐education system to become the chairman of the Department of Atmospheric Sciences at the University of Alabama in Huntsville. Drawing on his own experiences and on insights gleaned from the students who have passed through his graduate‐level professional development course, Christopher takes a lighthearted look at peer review, proposal writing, managing budgets, and making the most of conferences in the AGU bookNavigating Graduate School and Beyond: A Career Guide for Graduate Students and a Must Read for Every Advisor. In this interview, Eos speaks to Christopher about overcoming the bureaucratic, logistical, and personal hurdles that too often lead students to disillusionment and conflict.
Simulating thermokarst lakes
Authors: Balcerak Ernie
Published: May 2012

Thermokarst lakes, which form from thawing permafrost, alter landscapes and hydrology and can release significant amounts of methane to the atmosphere. To learn more about the dynamics of thermokarst lakes, Kessler et al. created a three‐dimensional numerical model of these lakes that includes the surrounding topography. They simulated 10,000 years of evolution of two small thermokarst lakes on the northern Seward Peninsula in Alaska and studied the pattern of methane production and emission over time. They found that the rate of methane production depends on the rate of expansion of thermokarst lakes into ancient permafrost and that local topography strongly influences the rate of expansion and drainage of the lakes. One lake, located in relatively flat surroundings, expanded rapidly and drained many times, while the other, surrounded by steeper slopes, grew more slowly and drained only partially. Thus, topography is an important control on thermokarst lake dynamics and methane emission. (Journal of Geophysical Research‐Biogeosciences, doi:10.1029/2011JG001796, 2012)
Silicic acid biogeochemistry in the Gulf of California
Authors: Balcerak Ernie
Published: May 2012

Silicon is an essential nutrient for the growth of siliceous phytoplankton, which accounts for a significant amount of marine primary production. Constraints on silicic acid limit primary production and carbon export, so biogeochemical silicon cycling influences the carbon cycle and climate. Silicon cycling has been studied mostly in iron‐limited regions of the ocean, and not much is known about the effects of iron availability on silicon cycling in coastal upwelling systems. Pichevin et al. investigated nutrient profiles and sedimentary records from the Gulf of California, which is not limited by iron year‐round. They found that iron limitation even in this type of setting is an important factor in silicon cycling in coastal upwelling regions. (Paleoceanography, doi:10.1029/2011PA002237, 2012)
Satellite tracks seasonal changes in atmospheric heavy water
Authors: Schultz Colin
Published: May 2012

From 10 to 30 kilometers in altitude, the steadily decreasing temperatures in the upper troposphere and lower stratopshere cause water vapor containing the hydrogen isotope deuterium—HDO, or heavy water—to preferentially condense out of the air, falling back toward the surface as ice. This selective depletion of heavy water leads, in theory, to a 90% drop in the ratio of heavy water to regular water vapor concentrations as compared to surface levels. The observational record, however, does not always align so well with theoretical predictions. Researchers suspect that skewed heavy water concentrations are due to atmospheric mixing, where deuterium‐ laden water from lower altitudes is transported upward. By tracking changes in the HDO/H2O ratio, researchers hope to tease out the history of evaporation, condensation, and convection that affect a particular atmospheric region.
Measuring biogeochemical responses to pulses of water
Authors: Balcerak Ernie
Published: May 2012

Hydrologic pulses, temporary increases in water inputs such as bouts of precipitation, can affect biogeochemical processes in ecosystems by providing water and nutrient resources. However, ecosystem responses to the water vary. Harms and Grimm conducted experiments to determine how hydrologic pulses and existing moisture conditions interact to affect the biogeochemistry of desert floodplains. During dry and monsoon seasons at their study site in the floodplains of the San Pedro River in Arizona, the researchers experimentally added pulses of water and then measured emissions of several trace gases that are indicators of biological processes. They found that the size of the added hydrologic pulse strongly interacted with existing soil moisture conditions in determining emissions of some trace gases. For instance, following dry conditions, pulses of water stimulated carbon dioxide, methane, and nitric oxide emissions, with larger water pulses stimulating more emissions. However, when soil was already wet, the addition of water pulses had less effect on the emission of these gases. (Journal of Geophysical Research‐Biogeosciences, doi:10.1029/2011JG001775, 2012)
Development of mantle seismic anisotropy during subduction‐induced 3‐D flow
Authors: Faccenda M. , Capitanio F. A.
Published: May 2012

The dynamics of subduction can be indirectly constrained by studying the induced mantle flow. However, inferring the circulation of the mantle around subducting plates from the interpretation of shear wave splitting patterns remains elusive. We calculated the strain‐induced lattice preferred orientation (LPO) developed in 3‐D models of subduction where retreat motions are maximized and found that in the mantle layer entrained with the downgoing slab the seismic anisotropy is trench‐perpendicular, and becomes trench‐parallel deeper, where the toroidal flow accommodates slab retreat. Synthetic SKS splitting shows that in the fore‐arc slab rollback favors trench‐parallel polarization of the fast shear wave component, while plate advance enhances trench‐perpendicular seismic anisotropy. The interference between these two competing mechanisms yields subslab delay times of 0.5 to 1.3 sec, comparable with those observed at most natural subduction zones. The magnitude of the subslab trench‐parallel splitting is independent of the rate at which the slab migrates, instead it is proportional to the amount of retreat.
Dynamics of plant histone modifications in response to DNA damage
Authors: Drury Georgina E. , Dowle Adam A. , Ashford David A. , Waterworth Wanda M. , Thomas Jerry , West Christopher E.
Published: May 2012

DNA damage detection and repair take place in the context of chromatin, and histone proteins play important roles in these events. Post-translational modifications of histone proteins are involved in repair and DNA damage signalling processes in response to genotoxic stresses. In particular, acetylation of histones H3 and H4 plays an important role in the mammalian and yeast DNA damage response and survival under genotoxic stress. However, the role of post-translational modifications to histones during the plant DNA damage response is currently poorly understood. Several different acetylated H3 and H4 N-terminal peptides following X-ray treatment were identified using MS analysis of purified histones, revealing previously unseen patterns of histone acetylation in Arabidopsis. Immunoblot analysis revealed an increase in the relative abundance of the H3 acetylated N-terminus, and a global decrease in hyperacetylation of H4 in response to DNA damage induced by X-rays. Conversely, mutants in the key DNA damage signalling factor ATM (ATAXIA TELANGIECTASIA MUTATED) display increased histone acetylation upon irradiation, linking the DNA damage response with dynamic changes in histone modification in plants.
Vector‐based miR‐15a/16‐1 plasmid inhibits colon cancer growth in vivo
Authors: Dai Lixia , Wang Wei , Zhang Shuang , Jiang Qingyuan , Wang Ruibo , Dai Lei , Cheng Lin , Yang Yang , Wei Yu‐Quan , Deng Hong‐Xin
Published: May 2012

miR‐15 (microRNA 15) and miR‐16 are frequently deleted or down‐regulated in many cancer cell lines and various tumour tissues, suggesting that miR‐15a/16‐1 plays important roles in tumour progression and might be a method for cancer treatment. We have developed a vector‐based plasmid to explore the anti‐tumour efficacy of miR‐15a/16‐1 in colon cancer in vivo. It is proposed that miR‐15a and miR‐16‐1 target cyclin B1 (CCNB1), which associates with several tumorigenic features such as survival and proliferation. The levels of miR‐15a and miR‐16‐1 in colon cancer cells were inversely correlated with CCNB1 expression, and there was consensus between miR‐15a/16‐1 and CCNB1 mRNA sequences by analysing homology. Vector‐based miR‐15a/16‐1 expression plasmid was constructed and transfected into HCT 116 and SW620 colon cancer cells in vitro. The effects produced on cell viability and angiogenesis were analysed using flow cytometric analysis, colony formation analysis and tube formation analysis. CCNB1 expression down‐regulation was checked by Western blotting. Systemic delivery of miR‐15a/16‐1 plasmids encapsulated in cationic liposome led to a significant inhibition of subcutaneous tumour growth and angiogenesis in tumour tissues, whereas no effects were observed with liposome carrying the non‐specific plasmid. In summary, miR‐15a/16‐1 has been applied in colon cancer treatment in vivo, and resulted in effective colon tumour xenografts growth arrest and angiogenesis decrease. These findings suggest that systemic delivery of vector‐based miR‐15a/16‐1 expression plasmid can be an approach to colon cancer therapy.
Nitric oxide induces segregation of decay accelerating factor (DAF or CD55) from the membrane lipid‐rafts and its internalization in human endometrial cells
Authors: Banadakoppa Manu , Goluszko Pawel , Liebenthal Daniel , Yallampalli Chandra
Published: May 2012

Recent studies suggest that DAF (decay accelerating factor), a complement regulatory protein, present in lipid rafts, is utilized by Dr fimbriated Escherichia coli for their binding and internalization. Previous studies in our laboratory have shown that NO (nitric oxide) can reduce the invasion of Dr(+) E. coli and the severity of uterine infection in pregnant rats. Also, the expression level of DAF both at the mRNA and protein levels has been shown to be reduced by NO. Therefore NO mediated down‐regulation of DAF appears to be an important factor in reducing the susceptibility to E. coli infection. However, it is unclear if NO can actually modulate the membrane association of DAF and therefore initial bacterial binding to cells. We found that NO induces the delocalization of DAF from the GM1‐rich lipid rafts. Using biochemical and cell biological approaches in a uterine epithelial cell model (Ishikawa cells), DAF accumulates in caveolae upon exposure to NO. Interaction of DAF with the caveolar protein, caveolin1, leads to their internalization by endosomes. NO‐induced delocalization of DAF from the lipid raft and its accumulation in caveolae are mediated through a cGMP (cyclic guanosine monophosphate) pathway. The acute localized synthesis of NO and its influence on DAF localization may represent an important unrecognized phenomenon of host defence against Dr(+) E. coli bacteria, as well as many disease conditions that involve complement system.
Lieb-Thirring inequality for a model of particles with point interactions
Authors: Frank Rupert L. , Seiringer Robert
Published: May 2012

We consider a model of quantum-mechanical particles interacting via point interactions of infinite scattering length. In the case of fermions we prove a Lieb-Thirring inequality for the energy, i.e., we show that the energy is bounded from below by a constant times the integral of the particle density to the power \documentclass[12pt]{minimal}\begin{document}$\frac{5}{3}$\end{document}53.
Relativistic Scott correction in self-generated magnetic fields
Authors: Erdős László , Fournais Søren , Solovej Jan Philip
Published: May 2012

We consider a large neutral molecule with total nuclear charge Z in a model with self-generated classical magnetic field and where the kinetic energy of the electrons is treated relativistically. To ensure stability, we assume that Zα < 2/π, where α denotes the fine structure constant. We are interested in the ground state energy in the simultaneous limit Z → ∞, α → 0 such that κ = Zα is fixed. The leading term in the energy asymptotics is independent of κ, it is given by the Thomas-Fermi energy of order Z7/3 and it is unchanged by including the self-generated magnetic field. We prove the first correction term to this energy, the so-called Scott correction of the form S(αZ)Z2. The current paper extends the result of Solovej et al. [Commun. Pure Appl. Math. LXIII, 39–118 (2010)] on the Scott correction for relativistic molecules to include a self-generated magnetic field. Furthermore, we show that the corresponding Scott correction function S, first identified by Solovej et al. [Commun. Pure Appl. Math. LXIII, 39–118 (2010)], is unchanged by including a magnetic field. We also prove new Lieb-Thirring inequalities for the relativistic kinetic energy with magnetic fields.
Critical rotational speeds for superfluids in homogeneous traps
Authors: Correggi M. , Pinsker F. , Rougerie N. , Yngvason J.
Published: May 2012

We present an asymptotic analysis of the effects of rapid rotation on the ground state properties of a superfluid confined in a two-dimensional trap. The trapping potential is assumed to be radial and homogeneous of degree larger than two in addition to a quadratic term. Three critical rotational velocities are identified, marking, respectively, the first appearance of vortices, the creation of a “hole” of low density within a vortex lattice, and the emergence of a giant vortex state free of vortices in the bulk. These phenomena have previously been established rigorously for a “flat” trap with fixed boundary but the “soft” traps considered in the present paper exhibit some significant differences, in particular the giant vortex regime, that necessitate a new approach. These differences concern both the shape of the bulk profile and the size of vortices relative to the width of the annulus where the bulk of the superfluid resides. Close to the giant vortex transition the profile is of Thomas-Fermi type in “flat” traps, whereas it is gaussian for soft traps, and the “last” vortices to survive in the bulk before the giant vortex transition are small relative to the width of the annulus in the former case but of comparable size in the latter.
Silicon-based reproducible and active surface-enhanced Raman scattering substrates for sensitive, specific, and multiplex DNA detection
Authors: Jiang Z. Y. , Jiang X. X. , Su S. , Wei X. P. , Lee S. T. , He Y.
Published: May 2012

Silicon-based active and reproducible surface-enhanced Raman scattering (SERS) substrate, i.e., silver nanoparticles decorated-silicon wafers (AgNPs@Si), is employed for constructing high-performance sensors. Significantly, the AgNPs@Si, facilely prepared via in situ AgNPs growth on silicon wafers, features excellent SERS reproducibility and high enhancement factor. Our experiment further demonstrates such resultant silicon-based SERS substrate is efficacious for multiplex, sensitive, and specific DNA detection. In particular, single-base mismatched DNA with low concentrations is readily discriminated by using the AgNPs@Si. Moreover, the silicon-based sensor exhibits adequate multiplexing capacity, enabling unambiguous identification of the dual-target DNA detection.
Symmetry of extremals of functional inequalities via spectral estimates for linear operators
Authors: Dolbeault Jean , Esteban Maria J. , Loss Michael
Published: May 2012

We prove new symmetry results for the extremals of the Caffarelli-Kohn-Nirenberg inequalities in any dimension larger or equal than 2 , in a range of parameters for which no explicit results of symmetry were previously known.
Fano antiresonance and perfect spin-filtering in a diamondlike quantum network device: Nonequilibrium Green’s function approach
Authors: Fu Hua-Hua , Yao Kai-Lun
Published: May 2012

Electronic transport through a diamondlike quantum network device composed of multiple quantum dots (QDs) is theoretically studied by means of the nonequilibrium Green’s function approach. In this system, by producing an energy difference between the site energy of the upper and down QDs through adjusting the gate voltages, the linear conductance spectrum shows a valley structure with a zero point due to the occurrence of Fano antiresonance. As the energy difference increases or the network chain size increases to a not very large value, the antiresonant valleys in the conductance spectra change to well-defined insulating bands with very steep edges. Moreover, the conditions for the occurrence of the Fano antiresonance and its relation with the formation of the well-defined insulating bands are studied. By introducing a Zeeman effect due to an external magnetic field, the spin-splitting conductance spectra show several highly to 100% spin-polarized windows, which proposes that this network device can be used as a perfect spin filter and generate a completely spin-polarized current. In addition, the many-body effect due to the intradot electron-electron interaction on the profile of the insulating bands is also investigated. It is found that the main characteristics of the well-defined insulating band remain and the highly spin-polarized window splits into several sub-ones still possessing the very steep edges, indicating that the many-body effect does not affect its application for a perfect spin filter.
Electronic effects of Se and Pb dopants in TlBr
Authors: Smith Holland M. , Phillips David J. , Sharp Ian D. , Beeman Jeffrey W. , Chrzan Daryl C. , Haegel Nancy M. , Haller Eugene E. , Ciampi Guido , Kim Hadong , Shah Kanai S.
Published: May 2012

Deep levels in Se- and Pb-doped bulk TlBr detectors were characterized with photo-induced conductivity transient spectroscopy (PICTS) and cathodoluminescence (CL). Se-doped TlBr revealed two traps with energies of 0.35 and 0.45 eV in PICTS spectra. The Pb-doped material revealed three levels with energies of 0.11, 0.45, and 0.75 eV. CL measurements in both materials correlate with optical transitions involving some of the identified levels. The ambipolar carrier lifetimes of Se-doped and Pb-doped TlBr were measured with microwave reflectivity transients and found to be significantly lower than the lifetime of undoped TlBr.
Nonlinear size-dependent melting of the silica-encapsulated silver nanoparticles
Authors: Tang Chengying , Sung Yun-Mo , Lee Joonho
Published: May 2012

In spite of the recent report of the in situ high-resolution transmission electron microscopy observation of the melting of Ag nanoparticles (NPs) in Chen et al. [Appl. Phys. Lett. 96, 253104 (2010)], no consistent experimental investigation coupled with theoretical analysis has been reported so far. We report the size-dependence of the melting temperature (Tm) of Ag NPs by both differential scanning calorimetry experiments and thermodynamic assessments. Thermodynamically calculated Tm for the Ag NPs showed a nonlinear function with respect to the inverse of the particle size and agreed well with the present and reported experimental results within an error of 1 K.
Tendency of spherically imploding plasma liners formed by merging plasma jets to evolve toward spherical symmetry
Authors: Cassibry J. T. , Stanic M. , Hsu S. C. , Witherspoon F. D. , Abarzhi S. I.
Published: May 2012

We have performed three-dimensional (3D) simulations using smoothed particle hydrodynamics (SPH) in order to study the effects of discrete plasma jets on the processes of plasma liner formation, implosion on vacuum, and expansion. It was found that the pressure histories of the inner portion of the liner from 3D SPH simulations with a uniform liner and with 30 discrete plasma jets were qualitatively and quantitatively similar from peak compression through the complete stagnation of the liner. The 3D simulations with a uniform liner were first benchmarked against results from one-dimensional radiation-hydrodynamic simulations [T. J. Awe et al., Phys. Plasmas 18, 072705 (2011)]. Two-dimensional plots of the pressure field show that the discrete jet SPH case evolves towards a profile that is almost indistinguishable from the SPH case with a uniform liner, thus indicating that non-uniformities due to discrete jets are smeared out by late stages of the implosion. The processes of plasma liner formation and implosion on vacuum were shown to be robust against Rayleigh-Taylor instability growth. Finally, interparticle mixing for a liner imploding on vacuum was investigated. The mixing rate was found to be very small until after the peak compression for the 30 jet simulations.
Gauge properties of the guiding center variational symplectic integrator
Authors: Squire J. , Qin H. , Tang W. M.
Published: May 2012

Variational symplectic algorithms have recently been developed for carrying out long-time simulation of charged particles in magnetic fields [H. Qin and X. Guan, Phys. Rev. Lett. 100, 035006 (2008); H. Qin, X. Guan, and W. Tang, Phys. Plasmas (2009); J. Li, H. Qin, Z. Pu, L. Xie, and S. Fu, Phys. Plasmas 18, 052902 (2011)]. As a direct consequence of their derivation from a discrete variational principle, these algorithms have very good long-time energy conservation, as well as exactly preserving discrete momenta. We present stability results for these algorithms, focusing on understanding how explicit variational integrators can be designed for this type of system. It is found that for explicit algorithms, an instability arises because the discrete symplectic structure does not become the continuous structure in the t→0 limit. We examine how a generalized gauge transformation can be used to put the Lagrangian in the “antisymmetric discretization gauge,” in which the discrete symplectic structure has the correct form, thus eliminating the numerical instability. Finally, it is noted that the variational guiding center algorithms are not electromagnetically gauge invariant. By designing a model discrete Lagrangian, we show that the algorithms are approximately gauge invariant as long as A and φ are relatively smooth. A gauge invariant discrete Lagrangian is very important in a variational particle-in-cell algorithm where it ensures current continuity and preservation of Gauss’s law [J. Squire, H. Qin, and W. Tang (to be published)].
Silicon fab-compatible contacts to n-InP and p-InGaAs for photonic applications
Authors: Jain S. , Sysak M. , Swaidan M. , Bowers J.
Published: May 2012

We report on silicon fab-compatible non-gold ohmic contacts to n-InP and p-InGaAs using Ti/W and Pd/Ge/W based metallization schemes where gold is replaced by aluminum as a thick probe layer. Specific contact resistivity of <1 × 10−7 Ω cm2 and < 2 × 10−6 Ω cm2 is obtained on n-InP and p-InGaAs after 450 °C anneal using circular transmission line model (CTLM) patterns. In addition, by varying the atomic ratio of Pd/Ge we, propose a common metal contact to both group III–V epitaxial layers with a specific contact resistivity <1 × 10−5 Ω cm2.
Tunneling resistance and its effect on the electrical conductivity of carbon nanotube nanocomposites
Authors: Bao W. S. , Meguid S. A. , Zhu Z. H. , Weng G. J.
Published: May 2012

In this paper, we examined the effect of electron tunneling upon the electrical conductivity of carbon nanotube (CNT) polymer nanocomposites. A CNT percolating network model was developed to account for the random distribution of the CNT network using Monte Carlo simulations, where the tunneling resistance between CNTs was established based on the electron transport theory. Our work shows several novel features that result from this tunneling resistance: (i) direct contact resistance is the result of one-dimensional electron ballistic tunneling between two adjacent CNTs, (ii) the nanoscale CNT-CNT contact resistance should be represented by the Landauer-Büttiker (L-B) formula, which accounts for both tunneling and direct contact resistances, and (iii) the difference in contact resistance between single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) can be modeled by the channel number in the L-B model. The model predictions reveal that the contact resistance due to electron tunneling effects in nanocomposites with dispersed SWCNTs plays a more dominant role than those with MWCNTs. These results compare favorably with existing experimental data and demonstrate that the proposed model can properly estimate the electrical conductivity of nanocomposites containing homogeneously dispersed percolating CNT network.
Sodium ionic conduction in complex hydrides with [BH4]− and [NH2]− anions
Authors: Matsuo Motoaki , Kuromoto Shingo , Sato Toyoto , Oguchi Hiroyuki , Takamura Hitoshi , Orimo Shin-ichi
Published: May 2012

We report the experimental results of structural and sodium ionic conductive properties of the Na(BH4)–Na(NH2)–NaI system. Na(BH4)0.5(NH2)0.5 with [BH4]− and [NH2]− complex anions formed by combining Na(BH4) and Na(NH2) complex hydrides shows the most superior sodium ionic conductivity of 2 × 10−6 S/cm at 300 K because of the specific antiperovskite-type structure with vacancies in the Na+ site Furthermore, Na(BH4)0.5(NH2)0.5 shows a high electrochemical stability of at least 6 V (vs Na+/Na). The result suggests that Na(BH4)0.5(NH2)0.5 could be a potential candidate for solid electrolyte.
Trace analysis of non-basal plane misfit stress relaxation in (202¯1) and (303¯1¯) semipolar InGaN/GaN heterostructures
Authors: Hardy Matthew T. , Hsu Po Shan , Wu Feng , Koslow Ingrid L. , Young Erin C. , Nakamura Shuji , Romanov Alexey E. , DenBaars Steven P. , Speck James S.
Published: May 2012

We have studied primary and secondary slip systems in the relaxation of lattice mismatch stresses in (202¯1) and (303¯1¯) semipolar InxGa1−xN/GaN heterostructures by analyzing the geometry of traces associated with dislocations employing cathodoluminescence, x-ray diffraction, and transmission electron microscopy. For (202¯1) InxGa1−xN/GaN heterostructures, the primary relaxation is by dislocation glide on the c-plane 112¯0(0001) slip system and secondary relaxation is by dislocation glide on inclined planes including the m-plane 〈112¯0〉{11¯00} slip system. For (303¯1¯) grown heterostructures non-basal slip, namely dislocation glide on the m-plane slip system, is the initial stress relaxation pathway.
A pathway between Bernal and rhombohedral stacked graphene layers with scanning tunneling microscopy
Authors: Xu P. , Yang Yurong , Qi D. , Barber S. D. , Ackerman M. L. , Schoelz J. K. , Bothwell T. B. , Barraza-Lopez Salvador , Bellaiche L. , Thibado P. M.
Published: May 2012

Horizontal shifts in the top layer of highly oriented pyrolytic graphite, induced by a scanning tunneling microscope (STM) tip, are presented. Excellent agreement is found between STM images and those simulated using density functional theory. First-principle calculations identify that the low-energy barrier direction of the top layer displacement is toward a structure where none of the carbon pz orbitals overlap, while the high-energy barrier direction is toward AA stacking. Each directional shift yields a real-space surface charge density similar to graphene; however, the low-energy barrier direction requires only one bond length to convert ABA (Bernal) to ABC (rhombohedral).
Analysis of vacancy-induced amorphization of single-layer graphene
Authors: Carpenter Corinne , Ramasubramaniam Ashwin , Maroudas Dimitrios
Published: May 2012

We report results of a systematic molecular-dynamics study on the vacancy-induced amorphization of single-layer graphene. An inserted vacancy concentration between 5% and 10% marks the onset of the amorphization transition. The computed amorphized configurations are in agreement with recent experimental observations. We find that the transition becomes less abrupt with vacancy concentration as the temperature increases and determine the surface roughness of the defective graphene as a function of vacancy concentration. We also find that the electronic density of states of vacancy-amorphized graphene is characterized by introduction of localized states near the Fermi level of perfect single-layer graphene.
Large-scale generic test stand for testing of multiple configurations of air filters utilizing a range of particle size distributions
Authors: Giffin Paxton K. , Parsons Michael S. , Unz Ronald J. , Waggoner Charles A.
Published: May 2012

The Institute for Clean Energy Technology (ICET) at Mississippi State University has developed a test stand capable of lifecycle testing of high efficiency particulate air filters and other filters specified in American Society of Mechanical Engineers Code on Nuclear Air and Gas Treatment (AG-1) filters. The test stand is currently equipped to test AG-1 Section FK radial flow filters, and expansion is currently underway to increase testing capabilities for other types of AG-1 filters. The test stand is capable of producing differential pressures of 12.45 kPa (50 in. w.c.) at volumetric air flow rates up to 113.3 m3/min (4000 CFM). Testing is performed at elevated and ambient conditions for temperature and relative humidity. Current testing utilizes three challenge aerosols: carbon black, alumina, and Arizona road dust (A1-Ultrafine). Each aerosol has a different mass median diameter to test loading over a wide range of particles sizes. The test stand is designed to monitor and maintain relative humidity and temperature to required specifications. Instrumentation is implemented on the upstream and downstream sections of the test stand as well as on the filter housing itself. Representative data are presented herein illustrating the test stand's capabilities. Digital images of the filter pack collected during and after testing is displayed after the representative data are discussed. In conclusion, the ICET test stand with AG-1 filter testing capabilities has been developed and hurdles such as test parameter stability and design flexibility overcome.
Effect of oxygen-related surface adsorption on the efficiency and stability of ZnO nanorod array ultraviolet light-emitting diodes
Authors: Liu W. Z. , Xu H. Y. , Ma J. G. , Liu C. Y. , Liu Y. X. , Liu Y. C.
Published: May 2012

Ultraviolet light-emitting diodes using MgZnO-coated and bare ZnO nanorod arrays as active layers were manufactured. Both types were exposed to ambient air over a 1-yr period to assess their stability. By monitoring the electroluminescence evolution with air-exposure time and comparing the changes of electroluminescence and x-ray photoelectron spectra before and after vacuum desorption, it is concluded that surface-adsorbed O2 and OH− species, as acceptor and donor surface states, quench ultraviolet electroluminescence, and favor undesirable surface-mediated nonradiative and deep-level recombination. The MgZnO coating prevents surface adsorption, and so the coated nanorod device shows higher efficiency and stability than the uncoated one.
Partially filled intermediate band of Cr-doped GaN films
Authors: Sonoda S.
Published: May 2012

We investigated the band structure of sputtered Cr-doped GaN (GaCrN) films using optical absorption, photoelectron yield spectroscopy, and charge transport measurements. It was found that an additional energy band is formed in the intrinsic band gap of GaN upon Cr doping, and that charge carriers in the material move in the inserted band. Prototype solar cells showed enhanced short circuit current and open circuit voltage in the n-GaN/GaCrN/p-GaN structure compared to the GaCrN/p-GaN structure, which validates the proposed concept of an intermediate-band solar cell.
Two regimes of self-propelled motion of a torus rotating about its centerline in a viscous incompressible fluid at intermediate Reynolds numbers
Authors: Moshkin N. P. , Suwannasri Pairin
Published: May 2012

In the present work, the problem of the motion of a self-propelled torus in a viscous incompressible fluid is investigated numerically. The surface of the torus rotates with constant velocity around its centerline. The rotating boundary of a torus generates inertia in the surrounding fluid. The outer and inner surfaces produce inertia in opposite directions. There are two self-motion regimes. In one of them, the torus moves in the direction of the inner surface motion due to the larger production of inertia by the outer portion of the torus boundary. The direction of propulsion is the same as in the case of a zero Reynolds number. In the other regime the torus moves in opposite direction due to the high momentum flux associated with the jet of fluid expelled from the hole. The drag coefficients and flow patterns are analyzed at Reynolds numbers Re = 20 − 60, (Reynolds number defined by velocity of a uniform stream and a smaller diameter of torus), the aspect ratios Ar = 2, 3 (aspect ratio defined as ratio of torus diameter to cross-section diameter), and a range of rotational rate −5.6 ⩽ α ⩽ 2.5 (α defined as ratio of tangential tank-treading motion of torus surface to the uniform far-field velocity).
Thermo-optic switch based on transmission-dip shifting in a double-slot photonic crystal waveguide
Authors: Cui Kaiyu , Zhao Qiang , Feng Xue , Huang Yidong , Li Yongzhuo , Wang Da , Zhang Wei
Published: May 2012

Optical switch based on an ultra-compact double-slot photonic crystal waveguide (DS-PCWG) with a titanium/aluminum microheater is demonstrated. The operating principle relies on shifting a transmission-dip caused by the defect mode coupling in photonic band gap (PBG). Based on the unique mode coupling in PBG, low switching power of 9.2 mW and high extinction ratio of 17 dB are achieved experimentally while the length of DS-PCWG is only 16 μm.
Columnar thermoelectric elements of linked spheres for miniature electric generation modules
Authors: Takagi Kenta , Ozaki Kimihiro , Kawaguchi Yasuhiro , Yumi Hideki
Published: May 2012

Thermoelectric elements that were formed from vertically aligned microspheres were fabricated from 500-µm monosized spherical particles of Fe2VAl alloys with a particle assembly that used pulsed current micro-welding. P-n pairs of the elements consisting of three particles generated relatively large temperature differences ΔT despite being 1.5 mm tall. At ΔT = 19 K, the five pairs generated a voltage of 21 mV and a maximum generation power of 40 µW, which converted to 0.21 V/cm2 voltage per unit area and 0.4 mW/cm2 power density, respectively. Moreover, we demonstrated the feasibility of building a massive array with 100 elements.
High-power, stable Ka/V dual-band gyrotron traveling-wave tube amplifier
Authors: Hung Chien-Lun
Published: May 2012

A dual-band amplifier can reduce the size, cost, and weight of a transmitter in dual-band radar and communication systems. This study proposes and theoretically investigates a gyrotron traveling-wave tube (gyro-TWT) amplifier capable of dual-band operation. Possible oscillations in the coaxial interaction waveguide are stabilized by the lossy inner cylinder. Under stable operating conditions, the gyro-TWT is predicted to provide a peak power of 375 kW with 71 dB saturated gain and 3.8 GHz bandwidth in the Ka-band and a peak power of 150 kW with 35 dB saturated gain and 1.7 GHz bandwidth in the V-band.
Contingency in requests of signing chimpanzees (Pan troglodytes)
Authors: Leitten Lisa , Jensvold Mary Lee A. , Fouts Roger S. , Wallin Jason M.
Published: May 2012

Conversational interactions depend on partners making contingent responses. This experiment examined the responses of five chimpanzees (Pan troglodytes), Washoe, Moja, Tatu, Dar and Loulis, to four conversational conditions. Following the chimpanzee’s request, a human interlocutor either: (1) complied with the request, (2) provided an unrequested item or activity, (3) refused to comply or (4) did not respond to the request. The chimpanzees’ responses were contingent on the conversational input of the interlocutor. When their requests were satisfied, the chimpanzees most often ceased signing. However, when their requests were misunderstood, refused or not acknowledged, the chimpanzees repeated and revised. This pattern of responses is comparable to patterns of conversational responses in human children. Keywords: chimpanzees; American Sign Language; requests; pragmatics; conversation; gesture; communication; Pan troglodytes
Scenarios of robot-assisted play for children with cognitive and physical disabilities
Authors: Robins Ben , Dautenhahn Kerstin , Ferrari Ester , Kronreif Gernot , Prazak-Aram Barbara , Marti Patrizia , Iacono Iolanda , Gelderblom Gert Jan , Bernd Tanja , Caprino Francesca , Laudanna Elena
Published: May 2012

This article presents a novel set of ten play scenarios for robot-assisted play for children with special needs. This set of scenarios is one of the key outcomes of the IROMEC project that investigated how robotic toys can become social mediators, encouraging children with special needs to discover a range of play styles, from solitary to collaborative play (with peers, carers/teachers, parents etc.). The target user groups in the project were children with Mild Mental Retardation,1 children with Severe Motor Impairment and children with Autism. The play scenarios were developed against specific educational and therapeutic objectives that were discussed with panels of experts (teachers therapists parents) in various countries, during several user panel meetings for each of the above mentioned target user groups. These objectives were classified with reference to the ICF-CY, the International Classification of Functioning – version for Children and Youth. The article presents a detailed description of the play scenarios, each with its relevant educational and therapeutic objectives in five key developmental areas (i.e. sensory development, communication and interaction, Cognitive development, motor development and social and emotional development). While the play scenarios described in this paper originally were developed for and tested with the above user groups and with the IROMEC robot, the play scenarios can potentially be applied to other user groups and to a wide range of other applications involving human-robot interaction using different robotic toys. Keywords: human-robot interaction; assistive technology; play scenarios; autism; mild mental retardation; sever motor impairment; assisted play
If it looks like a dog
Authors: Sinatra Anne M. , Sims Valerie K. , Chin Matthew G. , Lum Heather C.
Published: May 2012

This study was designed to compare the natural free form communication that takes place when a person interacts with robotic entities versus live animals. One hundred and eleven participants interacted with one of four entities: an AIBO robotic dog, Legobot, Dog or Cat. It was found that participants tended to rate the Dog as more capable than the other entities, and often spoke to it more than the robotic entities. However, participants were not positively biased toward live entities, as the Cat often was thought of and spoken to similarly to the AIBO robot. Results are consistent with a model in which both appearance and interactivity lead to the development of beliefs about a live or robotic entity in an interaction. Keywords: Human-robot interaction; human-animal interaction; AIBO; free form communication; attributions; human-entity interaction
The Action Game
Authors: Jansen Bart , Cornelis Jan
Published: May 2012

This article introduces a computational model which illustrates how a population of agents can coordinate a vocabulary for goal oriented behavior through repeated local interactions, called “Action Games”. Using principles of self organization and specific assumptions on their behavior, the agents learn the goals and a vocabulary for them. It is shown that the proposed model can be used to investigate the coordination of vocabularies for goal oriented behavior both in a vertical (e.g. between a single teacher and student) and in a horizontal (e.g. in a population of agents which have no a priori repertoire of goals and no vocabularies) transmission scheme. Furthermore, it is shown that in this model shared vocabularies can only be learned from multiple demonstrations consisting of exactly these actions that are strictly required to reach the goal. Keywords: robot imitation; self organization; vocabularies