bluuebunny/crossref_metadata_2025 huggingface dataset:
Tropospheric chemistry over the lower Great Plains of the United States 2. Trace gas profiles and distributions
Authors: Luke Winston T. , Dickerson Russell R. , Ryan William F. , Pickering Kenneth E. , Nunnermacker Linda J.
Published: February 2012

Convective clouds and thunderstorms redistribute air pollutants vertically, and by altering the chemistry and radiative balance of the upper troposphere, these local actions can have global consequences. To study these effects, measurements of trace gases ozone, O3, carbon monoxide, CO, and odd nitrogen were made aboard the NCAR Sabreliner on 18 flights over the southern Great Plains during June 1985. To demonstrate chemical changes induced by vertical motions in the atmosphere and to facilitate comparison with computer model calculations, these data were categorized according to synoptic flow patterns. Part 1 of this two‐part paper details the alternating pulses of polar and maritime air masses that dominate the vertical mixing in this region. In this paper, trace gas measurements are presented as altitude profiles (0–12 km) with statistical distributions of mixing ratios for each species in each flow pattern. The polar flow regime is characterized by northwesterly winds, subsiding air, and convective stability. Concentrations of CO and total odd nitrogen (NOy) are relatively high in the shallow planetary boundary layer (PBL) but decrease rapidly with altitude. Ozone, on the other hand, is uniformly distributed, suggesting limited photochemical production; in fact, nitric oxide, NO, mixing ratios fell below 10 ppt (parts per 1012by volume) in the midtroposphere. The maritime regime is characterized by southerly surface winds, convective instability, and a deep PBL; uniformly high concentrations of trace gases were found up to 4 km on one flight. Severe storms occur in maritime flow, especially when capped by a dry layer, and they transport large amounts of CO, O3, and NOyinto the upper troposphere. Median NO levels at high altitude exceeded 300 ppt. Lightning produces spikes of NO (but not CO) with mixing ratios sometimes exceeding 1000 ppt. This flow pattern tends to leave the midtroposphere relatively clean with concentrations of trace gases similar to those observed in the polar category. During frontal passage both stratiform and convective clouds mix pollutants more uniformly into the middle and upper levels; high mixing ratios of CO are found at all altitudes, and O3levels are highest of any category, implicating photochemical production. These results illustrate the importance of convection in tropospheric chemistry. Use of average trace gas profiles or eddy diffusion parameterized vertical mixing can lead to errors of 30 to 50% in O3and CO concentrations and an order of magnitude for odd nitrogen.
Some trace gas emissions from North American biomass fires with an assessment of regional and global fluxes from biomass burning
Authors: Laursen Krista K. , Hobbs Peter V. , Radke Lawrence F. , Rasmussen Rei A.
Published: February 2012

Emission factors for several trace gases were determined using airborne measurements from 13 biomass fires in North America. Emissions of methane (CH4), nonmethane hydrocarbons (NMHC), hydrogen (H2) and ammonia (NH3) were found to be positively correlated with the ratio of carbon monoxide (CO) to carbon dioxide (CO2) emission factors, both within each fire and between fires. This indicates that these four species are produced predominantly when combustion is inefficient. Methyl chloride (CH3Cl) emission factors were positively correlated with the ratio of CO to CO2emission factors within the majority of the fires. However, a linear regression of the average CH3Cl emission factor for each fire onto the average ratio of the CO to CO2emission factors produced a negative correlation coefficient. This indicates that the variance in CH3Cl emissions between fires is not due to differences in overall combustion efficiency. (According to previous research, differences in fuel chlorine content are mainly responsible for the differences in emissions of CH3Cl between fires.) The average NOxemission factors for three biomass fires in southern California were found to be significantly higher than the average NOxemission factors for the remaining 10 fires studied. It is suggested that this difference is due to an enhanced nitrogen content (possibly the result of pollutant deposition and in some cases nitrogen fixation) of the fuels consumed, and the consumption of large amounts of foliage during the three fires. The average NOx/CO2molar ratio determined from this study (2.1 × 10−3) is consistent with results from other airborne and laboratory studies of biomass burning emissions. However, the N2O/CO2molar ratios resulting from this study are roughly a factor of 2 larger than N2O/CO2molar ratios obtained from laboratory studies. It is hypothesized that the higher N2O/CO2molar ratios presented here are primarily due to emissions of N2O from the soil Overall average emission factors derived from this study were used to estimate the fluxes of several trace gases from temperate and boreal biomass fires. In addition, a new method is outlined for estimating fluxes of CH4, NMHC, H2and NH3from global biomass burning. The annual emissions of these four species from worldwide biomass burning are determined by this method to be 39, 17, 21 and 4.5 Tg yr−1, respectively. Our results indicate that the worldwide emissions of CH4, NMHC, H2and NH3from biomass burning represent 8%, 17%, 24% and 7%, respectively, of the total global emissions of these four species.
Hydroxyl X2II pure rotational transitions
Authors: Goorvitch D. , Goldman A. , Dothe Hoang , Tipping R. H. , Chackerian C.
Published: February 2012

We present a list of frequencies, term values, Einstein A values, and assignments for the pure rotational transitions of the X2II state of the OH molecule. This list includes transitions from 3 to 2015 cm−1 for Δv = 0, v″ = 0 – 4, and J″ = 0.5 − 49.5. The A values were computed using recent advances in calculating wave functions for a coupled system and an experimentally derived electric dipole moment function (Nelson et al. 1990) which exhibits curvature.
Dew and frost chemistry at a midcontinent site, United States
Authors: Wagner George H. , Steele Kenneth F. , Peden Mark E.
Published: February 2012

From July 1989 to July 1990 a total of 98 dew and 9 frost samples were collected at the University of Arkansas Agricultural Experiment Station, Fayetteville. The total water flux from dews and frosts per year was less than 2% of that from rains. Acid and nutrient fluxes were also much lower in dew. In the following series of ions the number in parentheses gives the percent of the yearly flux of the ion in dew compared to rain for the same time period: H+ (0.06), Ca2+(25), Mg2 + (11), K+ (21), Na+ (4), NH4+ (10), Cl− (4), NO3− (5), and SO2−4 (5). In contrast, the concentration of the various ions in dew, except H+, is generally several times that in rain. Dew is primarily a Ca(HCO3)2 and (NH4)2SO4 solution; whereas rain is primarily a NH4HSO4 solution. The mean pH of dew is 6.37 compared to 4.99 for rain. The average acetate‐formate concentration of dew in equivalents was (1) equal to about 53% of the nitrate‐sulfate concentration in rain for April‐June and (2) 10 times more concentrated than in rain for the year. The steps governing dew composition are indicated to be (1) formation on dry deposition solids (2) dissolution of the soluble portion of the dry deposition by dew water, and (3) sorption of gaseous NH3, acetic, and formic acids into the dew solution.
Measurements and model calculations of HCl column amounts and related parameters over McMurdo during the austral spring in 1989
Authors: Liu X. , Blatherwick R. D. , Murcray F. J. , Keys J. G. , Solomon S.
Published: February 2012

Solar spectra obtained from a ground‐based Fourier transform infrared instrument at McMurdo, Antarctica in the spring of 1989 have been analyzed to determine total HCl column amounts. A one‐dimensional photochemical model was used to simulate the rate of recovery of HCl in the springtime. Low column amounts (about 1 × 1015 molecules cm−2) were observed in early September and may be attributed to the heterogeneous conversion of HCl to active chlorine species during the polar night. The rate of recovery of HCl is consistent with its production by chlorine atoms reacting with methane and is dependent on concentrations of active chlorine species and NO molecules in the altitude region from 12 to 22 km. High HCl column amounts (about 7 × 1015 molecules cm−2) were observed following recovery in late October, suggesting that the lower stratosphere in the polar region had descended relative to mid‐latitudes and that the degree of dechlorination of the transported air was very small.
Simplicity
Authors: van Helden Paul
Published: February 2012

Scientists should remember that some of the most successful theories have been the most simple; complex theories risk losing their usefulness in a thicket of detail and exceptions.
Extracellular nucleotide inhibits cell proliferation and negatively regulates Toll‐like receptor 4 signalling in human progenitor endothelial cells
Authors: Xiao Zhilin , Yang Mei , Fang Li , Lv Qingshan , He Qing , Deng Minjie , Liu Xueting , Chen Xiaobin , Chen Meifang , Xie Xiumei , Hu Jinyue
Published: February 2012

Extracellular nucleotides mediate a wide range of physiological effects by interacting with plasma membrane P2 purinergic receptors. P2 receptors are expressed in certain kinds of stem cells, and function to induce cytokine expression and to modulate cell proliferation. We have analysed the expression and the function of P2 receptors in human umbilical cord blood‐derived EPCs (endothelial progenitor cells). EPCs expressed P2X4,6,7 and P2Y2,4,11,13,14 receptors and extracellular ATP inhibited EPCs proliferation. As in a previous study, EPCs expressed functional TLR4 (Toll‐like receptor 4) and activation of TLR4 by LPS (lipopolysaccharide) evoked a pro‐inflammatory immune response. When human EPCs were stimulated with LPS and nucleotides, ATP or UTP inhibited the expression of pro‐inflammatory cytokines including MCP‐1 (monocyte chemoattractant protein‐1), IFNα (interferon α), TNFα (tumour necrosis factor α) and adhesion molecule VCAM‐1 (vascular cell adhesion molecule 1) induced by LPS. ATP and UTP also down‐regulated the gene expression of TLR4, CD14 and MyD88 (myeloid differentiation factor 88), a TLR adaptor molecule, and protein expression of CD14 and MyD88. Moreover, the phosphorylation of NF‐κB (nuclear factor κB) p65 induced by TLR4 activation was inhibited partly by ATP or UTP at concentrations of 1–5 μM. These results suggest that extracellular nucleotides negatively regulate EPCs proliferation and TLR4 signalling.
Development of the Communication Complexity Scale
Authors: Brady Nancy C. , Fleming Kandace , Thiemann-Bourque Kathy , Olswang Lesley , Dowden Patricia , Saunders Muriel D. , Marquis Janet
Published: February 2012

Purpose

Accurate description of an individual’s communication status is critical in both research and practice. Describing the communication status of individuals with severe intellectual and developmental disabilities is difficult because these individuals often communicate with presymbolic means that may not be readily recognized. Our goal was to design a communication scale and summary score for interpretation that could be applied across populations of children and adults with limited (often presymbolic) communication forms.

Method

The Communication Complexity Scale (CCS) was developed by a team of researchers and tested with 178 participants with varying levels of presymbolic and early symbolic communication skills. Correlations between standardized and informant measures were completed, and expert opinions were obtained regarding the CCS.

Results

CCS scores were within expected ranges for the populations studied, and interrater reliability was high. Comparison across other measures indicated significant correlations with standardized tests of language. Scores on informant report measures tended to place children at higher levels of communication. Expert opinions generally favored the development of the CCS.

Conclusions

The scale appears to be useful for describing a given individual’s level of presymbolic or early symbolic communication. Further research is needed to determine whether it is sensitive to developmental growth in communication.
Facilitating Emergent Literacy: Efficacy of a Model That Partners Speech-Language Pathologists and Educators
Authors: Girolametto Luigi , Weitzman Elaine , Greenberg Janice
Published: February 2012

Purpose

This study examined the efficacy of a professional development program for early childhood educators that facilitated emergent literacy skills in preschoolers. The program, led by a speech-language pathologist, focused on teaching alphabet knowledge, print concepts, sound awareness, and decontextualized oral language within naturally occurring classroom interactions.

Method

Twenty educators were randomly assigned to experimental and control groups. Educators each recruited 3 to 4 children from their classrooms to participate. The experimental group participated in 18 hr of group training and 3 individual coaching sessions with a speech-language pathologist. The effects of intervention were examined in 30 min of videotaped interaction, including storybook reading and a post-story writing activity.

Results

At posttest, educators in the experimental group used a higher rate of utterances that included print/sound references and decontextualized language than the control group. Similarly, the children in the experimental group used a significantly higher rate of utterances that included print/sound references and decontextualized language compared to the control group.

Conclusion

These findings suggest that professional development provided by a speech-language pathologist can yield short-term changes in the facilitation of emergent literacy skills in early childhood settings. Future research is needed to determine the impact of this program on the children’s long-term development of conventional literacy skills.
Compression and focusing a laser produced plasma using a plasma optical system
Authors: Pagano C. , Goncharov A. A. , Lunney J. G.
Published: February 2012

Axi-symmetric compression and focusing of a low temperature laser produced copper plasma with an electrostatic plasma optical system was investigated for the first time. The degree of plasma concentration was quantified using Langmuir ion measurements of the ion flow and optical measurements of the thickness distributions of copper depositions on glass substrates. Both the ion flow and the deposition measurements showed strong concentration of the ion-plasma flow towards the axis. The ion current density at the focus was compressed by a factor up to 9.The on-axis deposition rate was increased by about the same factor.
Laser produced streams of Ge ions accelerated and optimized in the electric fields for implantation into SiO2 substrates
Authors: Rosinski M. , Giuffrida L. , Parys P. , Gasior P. , Fazio E. , Mezzasalma A. M. , Torrisi L. , Ando L. , Wolowski J.
Published: February 2012

Ge crystals were prepared by means of laser-induced ion implantation technique. A Nd:YAG pulsed laser (repetition rate: 10 Hz; pulse duration: 3.5 ns; pulse energy: ∼0.5 J) was used both as an ion source and to carry out the ablation processes. The optimization of the laser-generated ion beam parameters in a broad energy and current density range has been obtained controlling the electrostatic field parameters. Numerical simulations of the focusing system, performed adopting an OPERA 3D code, and an investigation of the ion characteristics, using the ion time-of-flight method, have allowed to optimize the preparation parameters. The structural properties of the samples were investigated by means of x-ray photoelectron, micro-Raman spectroscopies, and scanning electron microscopy techniques. Experimental results show that, by appropriately varying the ion implantation parameters and by a post-preparation annealing treatment, it is possible to achieve the development of a micrometer-sized crystalline Ge phase and/or an amorphous one.
Magnetic field induced quantum criticality at a Lifshitz transition with interactions
Authors: Schlottmann P.
Published: February 2012

Motivated by a discontinuous transition observed in CeIn3 in high magnetic fields, the effects of the Landau quantization and interactions on a Lifshitz transition are studied. The Landau quantization leads to a quasi-one-dimensional behavior for the direction parallel to the field. The repulsive Coulomb interactions give rise to a gas of strongly coupled particles. The density correlation function is calculated for a special long-ranged interaction potential. It is concluded that, in the ground state, an electron (or hole) pocket is emptied in a discontinuous fashion as a function of the chemical potential (or magnetic field). This discontinuity is gradually smeared by the temperature, in agreement with experiments for CeIn3.
Effect of Mn substitution for Fe on magnetic and magnetostrictive properties of SmFe2 compound
Authors: Wang Y. , Ren W. J. , Wang Z. H. , Zhang Y. Q. , Li J. , Zhang Z. D.
Published: February 2012

The structural, magnetic, and magnetostrictive properties of Sm(Fe1−xMnx)2 (0 ≤ x ≤ 0.20) alloys have been investigated. The alloys are almost single phase cubic Laves Sm(Fe, Mn)2 when x ≤ 0.15. The lattice parameter increases and Curie temperature and the magnetization at 295 K decrease with increasing Mn content of the Sm(Fe1−xMnx)2 compounds. The spin-reorientation temperature for ⟨110⟩ to ⟨111⟩ of Sm(Fe1−xMnx)2 decreases from 200 K for x = 0 to 140 K for x = 0.15, indicating the increasing anisotropy of the Mn-substituted compounds. The magnetostriction coefficient λ111 of the Sm(Fe1−xMnx)2 compounds slightly decreases with Mn substitution and maintains a value larger than 1900 ppm for 0 ≤ x ≤ 0.15. The linear anisotropic magnetostriction λa = λ‖ − λ⊥ for the Sm(Fe1−xMnx)2 alloys decreases with increasing Mn content, which may be ascribed to the decrease of λ111 and the increased anisotropy.
Geometric structure, electronic structure, and spin transition of several FeII spin-crossover molecules
Authors: Tuan Nguyen Anh
Published: February 2012

We present a density functional study on the geometric structure, electronic structure, and spin transition of a series of FeII spin-crossover (SCO) molecules, i.e., [Fe(abpt)2(NCS)2] (1), [Fe(abpt)2(NCSe)2] (2), and [Fe(dpbo)(HIm)2] (3) with dpbo = {diethyl(E,E)-2,2′-[1,2-phenylbis(iminomethylidyne)]bis[3-oxobutanoate](2–)-N,N’,O3,O3’}, and abpt = {4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole} in order to explore more about the way to control SCO behavior of transition metal complexes. Our calculated results show that the spin transition of these FeII molecules is accompanied with charge transfer between the Fe atom and ligands. This causes change in the electrostatic energy (ΔU) as well as the total electronic energy of SCO molecules. Moreover, our calculated results demonstrate an important contribution of the interionic interactions to ΔU, and there is the relation between ΔU and the thermal hysteresis behavior of SCO molecules. These results should be helpful for developing new SCO molecules.
High temperature Seebeck coefficient and resistance measurement system for thermoelectric materials in the thin disk geometry
Authors: Böttger P. H. Michael , Flage-Larsen E. , Karlsen O. B. , Finstad Terje G.
Published: February 2012

A versatile apparatus to measure the cross-plane Seebeck coefficient and the resistivity of bulk samples shaped as disks or thin plates, over a temperature range of 300 K–620 K with possible extension to higher temperatures, is presented. It is constructed from readily available equipment and instrumentation with parts that are easily manufactured. The Seebeck coefficient is measured over an average region of the sample under steady-state conditions. The sample resistance is measured using a four-point alternating current method and scaled to room temperature measurements with known geometry to calculate resistivity. A variety of sample shapes are supported. Most importantly, the support of the thin disk geometry allows for the very same samples to be used in a laser flash instrument. The design allows for rough vacuum, high vacuum, or purging with inert gases in the sample chamber. Measurements on thermoelectric ZnSb and a Ni reference material are presented.
Simulation studies of positron acceleration in a shock wave in a nonuniform external magnetic field
Authors: Iwata Takashi , Takahashi Seiichi , Ohsawa Yukiharu
Published: February 2012

Positron acceleration in a shock wave in an electron-positron-ion plasma is studied with one-dimensional, fully kinetic, electromagnetic particle simulations, with particular attention paid to the effect of inhomogeneity of external magnetic field B0. First, acceleration to γ ∼ 104, where γ is the Lorentz factor, is demonstrated for a shock wave in a uniform B0 with the shock speed νsh close to c cos θ, where c is the speed of light and θ is the angle between B0 and the wave normal. The acceleration is not saturated till the end of the simulation run. Then, the effect of nonuniformity of B0 is investigated: Comparisons are made between the case in which the difference (νsh − c cos θ) at the shock front changes from negative to positive values as the shock wave propagates and the case with this relation reversed. The latter is found to create a greater number of high-energy particles than the former.
Peculiarities of magnetically ordered phase formation during anion and cation substitutions in MnFeAsyP1−y and Mn2−xFexAs0.5P0.5 systems
Authors: Valkov V. I. , Golovchan A. V. , Szymczak H. , Dyakonov V. P.
Published: February 2012

Experimental and theoretical results of the study of MnFeAsyP1−y (0.15 ≤ y ≤ 0.66) and Mn2−xFexAs0.5P0.5 (0.5 ≤ x ≤ 1.0) systems were analyzed in order to determine the main factors responsible for the mechanism by which antiferromagnetic phase is formed in each of the two systems. It is shown that in the case of cation substitution in the Mn2−xFexAs0.5P0.5 system the main contribution to the mechanism of changing the magnetic ordering phase type is due to a considerable change of electron filling of the magnetically active d-band. As for the MnFeAsyP1−y system with anion substitution, destabilization of the ferromagnetic phase and formation of the antiferromagnetic phase with decreasing As concentration may be due to the changes in the density of electronic states because of a considerable reduction of the unit cell volume.
Thermal conductivity of solid monohydroxyl alcohols in polyamorphous states
Authors: Krivchikov A. I. , Korolyuk O. A. , Sharapova I. V.
Published: February 2012

New measurements of the thermal conductivity of solid ethyl alcohol C2H5OH in the interval from 2 K to the melting temperature are presented. An annealing effect in the thermal conductivity of the orientationally ordered phase of the alcohol has been observed over a wide range of temperatures. This phase was obtained as a result of an irreversible first-order phase transition from an orientationally disordered crystal with a cubic structure at T = 109 K. The thermal conductivity was observed to increase as the monoclinic lattice changed from a less stable phase to a more stable one. The growth may be due to the improved quality of the completely ordered crystal. A comparative analysis of the temperature dependences of the thermal conductivity κ(T) is made for the solid monohydroxyl alcohols CH3OH, C2H5OH, С2D5OD, C3H7OH, and C4H9OH in their disordered orientational and structural states. At low temperatures the thermal conductivity of the series of monohydroxyl structural glasses of the alcohols increases linearly with the mass of the alcohol molecule.
Composition dependence of elastic constants in wurtzite AlGaInN alloys
Authors: Łopuszyński M. , Majewski J. A.
Published: February 2012

In this paper, we analyze the dependence of elastic constants cij on composition for random wurtzite quaternary AlxGayIn1-x-yN alloy in the whole concentration range. The study takes as its starting point the cij parameters for zinc blende phase calculated earlier by the authors on the basis of valence force field model. To obtain the wurtzite constants from cubic material parameters the Martin transformation is used. The deviations from linear Vegard-like dependence of cij on composition are analyzed and accurate quadratic fits to calculated moduli are presented. The influence of nonlinear internal strain term in the Martin transformation is also investigated. Our general results for quaternary AlxGayIn1-x-yN alloys are compared with the recent ab initio calculations for ternaries GaxIn1-xN and AlxIn1-xN (Gorczyca and Łepkowski, Phys. Rev. B 83 203 201, 2011) and good qualitative agreement is found.
Reduced magnetohydrodynamic theory of oblique plasmoid instabilities
Authors: Baalrud S. D. , Bhattacharjee A. , Huang Y.-M.
Published: February 2012

The three-dimensional nature of plasmoid instabilities is studied using the reduced magnetohydrodynamic equations. For a Harris equilibrium with guide field, represented by Bo=Bpotanh(x/λ)ŷ+Bzoẑ, a spectrum of modes are unstable at multiple resonant surfaces in the current sheet, rather than just the null surface of the poloidal field Byo(x)=Bpotanh(x/λ), which is the only resonant surface in 2D or in the absence of a guide field. Here, Bpo is the asymptotic value of the equilibrium poloidal field, Bzo is the constant equilibrium guide field, and λ is the current sheet width. Plasmoids on each resonant surface have a unique angle of obliquity θ≡arctan(kz/ky). The resonant surface location for angle θ is xs=λarctanh(μ), where μ=tanθBzo/Bpo and the existence of a resonant surface requires |θ|<arctan(Bpo/Bzo). The most unstable angle is oblique, i.e., θ≠0 and xs≠0, in the constant-ψ regime, but parallel, i.e., θ=0 and xs=0, in the nonconstant-ψ regime. For a fixed angle of obliquity, the most unstable wavenumber lies at the intersection of the constant-ψ and nonconstant-ψ regimes. The growth rate of this mode is γmax/Γo≃SL1/4(1-μ4)1/2, in which Γo=VA/L, VA is the Alfvén speed, L is the current sheet length, and SL is the Lundquist number. The number of plasmoids scales as N~SL3/8(1-μ2)-1/4(1+μ2)3/4.
Current states of a doubly connected superconductor with two point contacts
Authors: Koverya V. P. , Krevsun A. V. , Bondarenko S. I. , Levchenko N. M.
Published: February 2012

The distribution of the transport current in branches of a doubly connected superconductor (DCS) with two clamping point contacts is investigated experimentally when the contacts are in the different states: (a) one or both contacts are in the critical state, (b) both are in the supercritical (resistive) state. In the state (a) the transport current frozen in the DCS and injected through one of the contacts can be increased or decreased by tuning the value and polarity of the current passing through the other contact. In the state (b), the current self-oscillations the amplitude and the frequency of which depend on the value of the injected transport current appear in the branches of the DCS. A role of the parametric Josephson inductance and resistivity of the contact in formation of its critical state and in distribution of the current in the branches of the DCS is discussed.
Low-temperature resistance minimum in granular hole-doped cobaltites
Authors: Chiang Y. N. , Dzyuba M. O. , Shevchenko O. G. , Khirnyi V. F.
Published: February 2012

It is for the first time that in three-dimensional granular cobaltites (La1−x Srx)1−yAgyCoO3 with a grain size of about 1 μm and replacement ratios x = 0.35 and y = 0, 0.05 a “metal–nonmetal” conductivity transition was observed, presumably associated with the AFM ordering of granule moments. This transition manifests itself as a minimum in the temperature dependence of resistance of the samples. An explanation of the nature of the minimum is proposed, based on the intragranular mechanism of electron correlation on the basis of the Zener double-exchange and on the intergranular mechanism of spin-polarized electron tunneling between the nearest neighbors under the antiferromagnetic exchange interaction of granule moments. Numerical calculation of the system conductance is made via the model based on summation of intragranular phase conductivities of the electronic system and on the computation of the total impedance of the system as a sum of resistances of individual granules with a given resistive contribution of intergranular tunneling. It is found that the external magnetic field of up to 10 T does not affect the depth of the minimum and its position on the temperature scale, suggesting that the intergranular antiferromagnetic interaction is stable to external magnetic fields.
The influence of intensive plastic deformation on thermopower low-temperature peak and resistivity of polycrystalline copper
Authors: Svetlov V. N. , Solovjov A. L. , Stepanov V. B.
Published: February 2012

The temperature dependence and the absolute value of the minimum of differential difference thermoelectric power (TEP) were investigated experimentally as a function of plastic deformation in polycrystalline copper samples with different content of impurities: conditionally pure (99.99% Cu) and conditionally impure (99.9% Cu). Simultaneously the relative electrical resistivity normalized to the value of residual resistance at 4.2 K was measured. The nonmonotonic character of the deformation dependences of the resistivity and TEP minimum account for the evolution of the defect structure in specimens with increasing strain.
Dispersion-corrected density functional theory calculations of the molecular binding of n-alkanes on Pd(111) and PdO(101)
Authors: Antony Abbin , Hakanoglu Can , Asthagiri Aravind , Weaver Jason F.
Published: February 2012

We investigated the molecular binding of n-alkanes on Pd(111) and PdO(101) using conventional density functional theory (DFT) and the dispersion-corrected DFT-D3 method. In agreement with experimental findings, DFT-D3 predicts that the n-alkane desorption energies scale linearly with the molecule chain length on both surfaces, and that n-alkanes bind more strongly on PdO(101) than on Pd(111). The desorption energies computed using DFT-D3 are slightly higher than the measured values for n-alkanes on Pd(111), though the agreement between computation and experiment is a significant improvement over conventional DFT. The measured desorption energies of n-alkanes on PdO(101) and the energies computed using DFT-D3 agree to within better than 2.5 kJ/mol (< 5%) for chain lengths up to n-butane. The DFT-D3 calculations predict that the molecule-surface dispersion energy for a given n-alkane is similar in magnitude on Pd(111) and PdO(101), and that dative bonding between the alkanes and coordinatively unsaturated Pd atoms is primarily responsible for the enhanced binding of n-alkanes on PdO(101). From analysis of the DFT-D3 results, we estimate that the strength of an alkane η2(H, H) interaction on PdO(101) is ∼16 kJ/mol, while a single η1 H-Pd dative bond is worth about 10 kJ/mol.
Dressed adiabatic and diabatic potentials to study conical intersections for F + H2
Authors: Das Anita , Sahoo Tapas , Mukhopadhyay Debasis , Adhikari Satrajit , Baer Michael
Published: February 2012

We follow a suggestion by Lipoff and Herschbach [Mol. Phys. 108, 1133 (2010)10.1080/00268971003662912] and compare dressed and bare adiabatic potentials to get insight regarding the low-energy dynamics (e.g., cold reaction) taking place in molecular systems. In this particular case, we are interested to study the effect of conical intersections (ci) on the interacting atoms. For this purpose, we consider vibrational dressed adiabatic and vibrational dressed diabatic potentials in the entrance channel of reactive systems. According to our study, the most one should expect, in case of F + H2, is a mild effect of the (1, 2) ci on its reactive/exchange process−an outcome also supported by experiment. This happens although the corresponding dressed and bare potential barriers (and the corresponding van der Waals potential wells) differ significantly from each other.
First principles study of Seebeck coefficients of doped semiconductors ZnTe1−xFx and ZnTe1−yNy
Authors: Yang X. H.
Published: February 2012

The electron densities of states in semiconductors of n-doped ZnTe1−xFx and p-doped ZnTe1−yNy are calculated with the first principles based on density functional theory. The F and N atoms induce steep density of states (DOSs) in conduction and valence band edges, respectively, owing to the high electronegativities of F and N elements as compared to Te. The calculated results show that the lower the carrier concentration, the sharper the DOS, and the smaller distances of Fermi level and chemical potential (µ) from the band edge. It is the sharper DOS and smaller µ that lead to the larger Seebeck coefficients. For the same carrier concentration and temperature, the Seebeck coefficients in ZnTe1−yNy are much larger than the ones in ZnTe1−xFx in the whole temperature range due to the much sharper DOS near the valence band edge. Moreover, the power factors in ZnTe1−yNy are larger than those in ZnTe1−xFx below ∼1200 K, in spite of the lower electrical conductivities in ZnTe1−yNy. The investigation in this paper further demonstrates that only engineering the semiconductors with sharp DOSs near the band edges through heavily doping hetero-elements can the electrical transport properties be enhanced significantly.
Bistatic scattering characterization of a three-dimensional broadband cloaking structure
Authors: Alitalo Pekka , Culhaoglu Ali E. , Osipov Andrey V. , Thurner Stefan , Kemptner Erich , Tretyakov Sergei A.
Published: February 2012

Here we present the results of full experimental characterization of broadband cloaking of a finite-sized metallic cylinder at X-band. The cloaking effect is characterized by measuring the bistatic scattering patterns of uncloaked and cloaked objects in free space and then comparing these with each other. The results of the measurements demonstrate a broadband cloaking effect and are in good agreement with numerical predictions.
When does the non-variational nature of second-order Møller-Plesset energies manifest itself? All-electron correlation energies for open-shell atoms from K to Br
Authors: McCarthy Shane P. , Thakkar Ajit J.
Published: February 2012

All-electron correlation energies Ec are not very well known for open-shell atoms with more than 18 electrons. The complete basis-set (CBS) limits of second-order Møller-Plesset (MP2) perturbation theory energies are obtained for open-shell atoms by computations in large basis sets combined with a knowledge of the MP2/CBS limit for the next larger closed-shell atom with the same valence shell structure. Then higher-order correlation corrections are found by coupled-cluster calculations using basis sets that are not quite as large. The method is validated for the open-shell atoms from Al to Cl for which Ec is reasonably well established. Then, the method is used to obtain non-relativistic Ec values, probably accurate to 3%, for the open-shell atoms of the fourth period: K, Sc–Cu, and Ga–Br. These energies are compared with the predictions of 19 density functionals and may be useful for the parameterization of new ones. The results show that MP2 overestimates |Ec| for atoms heavier than Fe.
A new TriBeam system for three-dimensional multimodal materials analysis
Authors: Echlin McLean P. , Mottura Alessandro , Torbet Christopher J. , Pollock Tresa M.
Published: February 2012

The unique capabilities of ultrashort pulse femtosecond lasers have been integrated with a focused ion beam (FIB) platform to create a new system for rapid 3D materials analysis. The femtosecond laser allows for in situ layer-by-layer material ablation with high material removal rates. The high pulse frequency (1 kHz) of ultrashort (150 fs) laser pulses can induce material ablation with virtually no thermal damage to the surrounding area, permitting high resolution imaging, as well as crystallographic and elemental analysis, without intermediate surface preparation or removal of the sample from the chamber. The TriBeam system combines the high resolution and broad detector capabilities of the DualBeamTM microscope with the high material removal rates of the femtosecond laser, allowing 3D datasets to be acquired at rates 4–6 orders of magnitude faster than 3D FIB datasets. Design features that permit coupling of laser and electron optics systems and positioning of a stage in the multiple analysis positions are discussed. Initial in situ multilayer data are presented.
Angle-resolved metastable fragment yields spectra of N2 and CO in K-edge excitation energy region
Authors: Gejo Tatsuo , Tamura Takashi , Honma Kenji , Shigemasa Eiji , Hikosaka Yasumasa , Tamenori Yusuke
Published: February 2012

Angle-resolved metastable fragments yields spectra have been measured in the N 1s ionization region of the N2 and C 1s ionization region of CO. These spectra are compared with zero kinetic energy electron and photoelectron spectra. It has been shown that an isotropic metastable fragments yields spectra are almost identical with the ZEKE spectrum, whereas metastable fragments yields spectra with the Σ–Σ transition show similarity with photoelectron spectra. This means that these spectra clearly contain information about two shake-up mechanisms: conjugate and direct shake-up processes. All the peaks in the metastable photofragment spectra can be assigned as either satellite states or double/triple excitation states. Thus, it was shown that angle-resolved metastable photofragment spectroscopy could be used to help characterize multi-electron excitation states in general.
Broadband microwave spectroscopy in Corbino geometry at 3He temperatures
Authors: Steinberg Katrin , Scheffler Marc , Dressel Martin
Published: February 2012

A broadband microwave spectrometer has been constructed to determine the complex conductivity of thin metal films at frequencies from 45 MHz to 20 GHz working in the temperature range from 0.45 K to 2 K (in a 3He cryostat). The setup follows the Corbino approach: a vector network analyzer measures the complex reflection coefficient of a microwave signal hitting the sample as termination of a coaxial transmission line. As the calibration of the setup limits the achievable resolution, we discuss the sources of error hampering different types of calibration. Test measurements of the complex conductivity of a heavy-fermion material demonstrate the applicability of the calibration procedures.
Characteristics of an underwater direct current discharge in bubbles and the temperature distribution in the bubbles
Authors: Xiong Ranhua , Nikiforov Anton Yu. , Vanraes Patrick , Leys Christophe
Published: February 2012

An underwater direct current (DC) discharge in artificially produced air bubbles is investigated. Electrical and optical emission properties of the plasma and temperature distribution in bubbles evaluated by using computational fluid dynamics (CFD) are presented. The behavior of plasma inside a bubble significantly depends on the bubble size. The discharge with water as a cathode is characterized by streamer nature, whereas the plasma with water as an anode appears diffuse and homogenous. The gas temperature is estimated from emission of the plasma, and it is much higher when water is a cathode. Bubble dynamics is investigated by CFD simulation, and results are in good agreement with experimental data. It shows the temperature distribution in bubbles strongly depends on the bubble dynamics, and gas-water interface has a sharp temperature gradient and acts as an efficient heat sink.
Suppression of higher mode excitation in a high gain relativistic klystron amplifier
Authors: Wu Y. , Xu Z. , Jin X. , Li Z. H. , Tang C. X.
Published: February 2012

Suppressing higher mode excitation is very important in the high gain relativistic klystron amplifier because higher mode can seriously degrade klystron performance and cause pulse shortening. The mechanism of higher mode self-excitation is explored in the PIC simulation, and it is shown the coupling between cavities is the main cause of higher mode self-excitation. The coupling forms the positive feedback loop for higher mode to be excited just like that in the oscillator circuit. The formula for startup current of higher mode self-excitation is developed based on the coupling between cavities. And the corresponding methods are taken to avoid higher mode self-excitation. Finally, mode control is realized in the RKA with output power up to 1.02 GW when driven power is only few kilowatts.
Silver nano particle formation on Ar plasma – treated cinnamyl alcohol
Authors: Dahle S. , Marschewski M. , Wegewitz L. , Viöl W. , Maus-Friedrichs W.
Published: February 2012

Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy are employed to study the adsorption of silver on cinnamyl alcohol films prepared on Au(111) substrates by thermal evaporation. Additionally, the impact of an Ar atmosphere dielectric barrier discharge plasma applied to the cinnamyl alcohol film preliminary to the Ag adsorption is investigated. In both cases silver nano particles with an average diameter of 9 nm are formed. These particles do not interact chemically with the underlying cinnamyl alcohol film. We do not find any influence of the preliminary Ar plasma-treatment on the adsorption behavior at all.
“External forces” are indispensable for the occurrence of exchange bias?
Authors: Feng Wuwei , Jiang Nai-Yuan , Huang Shin-Da , Chen Hung-Ming , Cheng Chih-Wei , Chern G. , Yu Chin-Chung
Published: February 2012

We demonstrate here a double-shifted exchange bias which spontaneously exists in the as-deposited [Pt/Co]n/IrMn multilayers without resorting to any “external forces,” such as deposition with field, field annealing, (zero) field cooling with specific procedures. The observed results indicate that the exchange bias might occur spontaneously when a ferromagnetic layer is in contact with an antiferromagnetic layer; herein it is tentatively attributed to interactions among perpendicular anisotropy of [Pt/Co]n multilayers, its intrinsic demagnetization field, and magnetic anisotropy of the IrMn layer. The thickness and the magnitude of magnetic anisotropy of the ferromagnetic multilayer are crucial for the adjustment of asymmetric double-shifted exchange bias which can also be tuned to exist in the in-plane or out-of-plane directions.
Ultrafast ring opening in 1,3-cyclohexadiene investigated by simplex-based spectral unmixing
Authors: White J. L. , Kim J. , Petrović V. S. , Bucksbaum P. H.
Published: February 2012

We use spectral unmixing to determine the number of transient photoproducts and to track their evolution following the photo-excitation of 1,3-cyclohexadiene (CHD) to form 1,3,5-hexatriene (HT) in the gas phase. The ring opening is initiated with a 266 nm ultraviolet laser pulse and probed via fragmentation with a delayed intense infrared 800 nm laser pulse. The ion time-of-flight (TOF) spectra are analyzed with a simplex-based spectral unmixing technique. We find that at least three independent spectra are needed to model the transient TOF spectra. Guided by mathematical and physical constraints, we decompose the transient TOF spectra into three spectra associated with the presence of CHD, CHD+, and HT, and show how these three species appear at different times during the ring opening.
Impact ionization in quantum well infrared photodetectors with different number of periods
Authors: Dong Shan , Li Ning , Chen Sihai , Liu Xihui , Lu Wei
Published: February 2012

This paper presents the detailed investigation of the photocurrent accompanied with impact ionization effect in In0.15Ga0.85As/GaAs multiple quantum well infrared photodetectors (QWIPs) with 10 and 50 periods. The sample with 50 periods exhibits remarkable enhancement at high electric field while a negative differential conductivity (NDC) phenomenon is observed in the sample with 10 periods. The enhancement at high electric field is attributed to impact ionization across the conduction-band-edge discontinuity between incident hot electrons and the electrons confined in the wells. The different behavior of these two samples indicates that the length of the multiplication region strongly affects the multiplication factor M. We also measured the photocurrent of GaAs/Al0.15Ga0.85As QWIPs, which do not show an obvious multiplication phenomenon. This is attributed to a different impact ionization coefficient α. A theoretical model of the multiplication factor M varying with impact ionization coefficient α, capture probability pc, and well number N is provided to clarify these phenomena and compared with experimental result.
Tuning upconversion emission by controlling particle shape in NaYF4:Yb3+/Er3+ nanocrystals
Authors: Gao Dangli , Zhang Xiangyu , Gao Wei
Published: February 2012

Rod-shaped and plate-shaped NaYF4:Yb3+/Er3+ nanocrystals (NCs) have been synthesized via a facile oleic acid-assisted hydrothermal route. The intensity and color tunability by shape controlling of NCs is demonstrated by up and down frequency conversions in NaYF4:Yb3+/Er3+ NCs. The results obviously show that rod-shaped NCs present much stronger upconversion luminescence intensity and smaller ratio of green to red emission intensity than that of plate-shaped NCs. The underlying reason of luminescence enhancement by shape controlling is explored, and a mechanism of the enhancement based on the decrease of nonradiation relaxation probability and the increase of energy transfer efficiency from Yb3+ to Er3+ is proposed for nanorods.
Magnetocapacitance effect in nonmultiferroic YFeO3 single crystal
Authors: Cheng Z. X. , Shen H. , Xu J. Y. , Liu P. , Zhang S. J. , Wang J. L. , Wang X. L. , Dou S. X.
Published: February 2012

YFeO3 single crystal displays two relaxor-like dielectric relaxations, one at low temperature (170 − 300 K) and one at high temperature (370 − 520 K), which are attributed to the activation of electrons and oxygen vacancies, respectively. Above the temperature at which electrons are activated, the sample displays a large magnetocapacitance effect. Comparison of the impedance Cole-Cole plots measured with and without applied magnetic field reveals that the occurrence of magnetocapacitance effect is accompanied with an increasing in DC conductivity under magnetic field after the activation of electrons, which is explained by the enhancement of electron jumping in Fe2+-O-Fe3+ chains by magnetic field. Thus the magnetocapacitance effect in YFeO3 single crystal can be explained by the combination of the Maxwell-Wagner space charge effect and/or magnetoresistance effect, depending on the frequency range.
Structurally determined directionality identifies the boundary between mobile and immobile domains in a disordered material
Authors: de Souza Vanessa K. , Harrowell Peter
Published: February 2012

The structure and available degrees of freedom of an amorphous configuration can determine the location of dynamic heterogeneities. In the same way, these features can also determine the directionality of the particle motion. In this paper we propose that directionality can be attributed to those particles that only participate in a single unconstrained motion. The consequences of this suggestion in terms of the spatial distribution of particles with high directionality are explored using a random bond model.