bluuebunny/crossref_metadata_2025 huggingface dataset:
Aspects of an Institutionalizing Political System: China, 1958–1965
Authors: Bachman David
Published: December 2006

This article uses newly available Chinese sources to take a different look at aspects of the Chinese political system and the Chinese state during 1958 to 1965. While not challenging the literature on elite power issues, it demonstrates that much more was going on within the Chinese state than has been widely appreciated. In particular, the article focuses on the formal legal process, where it appears that the use of courts was extensive throughout the per-Cultural Revolution period and where the verdict of not guilty, not punished occurred more frequently in China than it did in American federal criminal cases; on the growing breakdown of the Party elite; and on China's preparation for war, basically an ongoing process of the Chinese state from 1962 on, with extensive militarization even earlier.
Symmetries, ansätze and exact solutions of nonlinear second-order evolution equations with convection terms, II
Authors: CHERNIHA ROMAN , SEROV MYKOLA
Published: December 2006

New results concerning Lie symmetries of nonlinear reaction-diffusion-convection equations, which supplement in a natural way the results published in the European Journal of Applied Mathematics (9(1998) 527–542) are presented.
An intrusion layer in stationary incompressible fluids: Part 1: Periodic waves
Authors: FORBES LAWRENCE K. , HOCKING GRAEME C. , FARROW DUNCAN E.
Published: December 2006

Waves on a neutrally buoyant intrusion layer moving into otherwise stationary fluid are studied. There are two interfacial free surfaces, above and below the moving layer, and a train of waves is present. A small amplitude linearized theory shows that there are two different flow types, in which the two interfaces are either in phase or else move oppositely. The former flow type occurs at high phase speed and the latter is a low-speed solution. Nonlinear solutions are computed for large amplitude waves, using a spectral type numerical method. They extend the results of the linearized analysis, and reveal the presence of limiting flow types in some circumstances.
Factors contributing to the stability of anticoagulation control and outcome of thromboembolic prophylaxis in the older population
Authors: Wynne Hilary , Khan Tayyaba , Sconce Elizabeth , Kamali Farhad
Published: December 2006

Meta-analyses of randomized controlled trials have reported the efficacy of dose-adjusted warfarin therapy (target International Normalised Ratio (INR) 2–3) in reducing stroke risk in atrial fibrillation by 68%, with aspirin reducing relative risk by 22%. Absolute benefit for an individual patient depends on the presence of the risk factors for stroke; these include previous stroke, transient ischaemic attack, hypertension, diabetes, valvular heart disease, heart failure and advanced age. In spite of reported benefit, many people with atrial fibrillation and a high risk of stroke are not receiving anticoagulation: disappointingly, risk stratification is not being sufficiently used to guide treatment.
DO FIRING COSTS AFFECT THE INCIDENCE OF FIRM BANKRUPTCY?
Authors: SAMANIEGO ROBERTO M.
Published: January 2007

An overlooked topic is the treatment of worker claims when firms are shutting down. In fact, when firms close, worker claims such as severance pay often go unfulfilled. To evaluate the quantitative importance of this observation, this paper develops a general equilibrium model with close attention to the exit margin, and examines how macroeconomic outcomes vary with the treatment of firing costs on exit. In the model, the impact of firing costs on employment weakens by a third when closing plants do not have to pay them, even though closure accounts for considerably less than one-third of total job destruction. Thus, the distribution of firm characteristics is a new channel for labor market rigidities to affect aggregates. The model also accounts for cross-country differences in the relationship between the structure of job flows and firm turnover.
Effects of the seasonal cycle on the development and termination of the Indian Ocean Zonal Dipole Mode
Authors: Halkides D. J. , Han Weiqing , Webster Peter J.
Published: December 2006

Effects of the seasonal cycles of atmospheric surface forcings on the development and termination of the Indian Ocean Zonal Dipole Mode (IOZDM) are studied using a nonlinear, 4‐1/2 layer ocean model partially coupled to an advective atmospheric mixed layer model in which sea surface temperature (SST) feeds back only to air temperature and specific humidity. A series of experiments are performed for the period of 1984–1998 to isolate processes. The results indicate the seasonal cycle of atmospheric forcing aids development and decay of cold SST anomalies (SSTA) in the eastern basin associated with strong, positive dipole events. During the strong IOZDM years of 1994 and 1997, seasonal southeasterlies associated with the Asian summer monsoon reinforce coastal upwelling associated with the IOZDM near Sumatra‐Java in boreal summer and fall, assisting initiation and increasing the peak amplitudes of these events. However, near the equator, fall equatorial westerlies deepen the thermocline in the eastern basin, reducing the cold SSTA in the eastern equatorial region and near Sumatra and Java. This contributes to the early termination of the 1994 IOZDM. In boreal winter the monsoon wind reversal reduces coastal upwelling along Sumatra and Java, further contributing to IOZDM termination. Moreover, the seasonal equatorial westerlies during fall and the monsoon wind reversal during winter counter southeasterly wind anomalies associated with the IOZDM in the eastern antinode region, reducing the total wind speed, weakening entrainment cooling and surface turbulent heat loss and thus further assisting IOZDM termination.
Predicting cloud droplet number concentration in Community Atmosphere Model (CAM)‐Oslo
Authors: Storelvmo Trude , Kristjánsson Jon Egill , Ghan Steven J. , Kirkevåg Alf , Seland Øyvind , Iversen Trond
Published: December 2006

A new framework for calculating cloud droplet number, including a continuity equation for cloud droplet number concentration, has been developed and implemented in an extended version of the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 2.0.1 (CAM‐2.0.1). The new continuity equation for cloud droplet number concentration consists of a nucleation term and several microphysical sink terms. The nucleation term is calculated on the basis of a parameterization of activation of cloud condensation nuclei (CCN). A subgrid distribution of vertical velocity is used to calculate the range of supersaturations determining the activation within each model grid box. The aerosol types considered in this study are sea salt, sulfate, black carbon, organic carbon, and mineral dust. The horizontal and vertical distributions of sulfate and carbonaceous aerosols are calculated on the basis of AEROCOM (http://nansen.ipsl.jussieu.fr/AEROCOM) sources. Microphysical sink terms for cloud droplets are obtained from a prognostic cloud water scheme, assuming a direct proportionality between loss of cloud water and loss of cloud droplets. On the basis of the framework described above, the cloud droplet number concentration and cloud droplet effective radius are determined. Cloud microphysical and radiative properties compare reasonably well with satellite observations, giving an indication of the soundness of our approach. Our method of fitting the aerosol size distribution with lognormal modes has been evaluated and was found not to introduce systematic errors in our approach. The aerosol indirect effect estimated in the new framework ranges from −0.13 W/m2 to −0.72 W/m2, which is significantly smaller than in most other comparable studies. This is largely due to the introduction of microphysical sinks for cloud droplets and a cloud droplet activation scheme which accounts for the so‐called competition effect among CCN. As we are not allowing aerosol effects on cloud microphysics and radiation to feed back on the model meteorology, our estimates of the aerosol indirect effect do not include changes in relative humidity and cloud cover.
Microphysical and dynamical controls on cirrus cloud optical depth distributions
Authors: Kay Jennifer E. , Baker Marcia , Hegg Dean
Published: December 2006

We assess microphysical and dynamical controls on cirrus cloud optical depth distributions [P(σ)] along idealized air parcel trajectories. We find P(σ) shape depends primarily on the ratio of the ice crystal fallout timescale to timescales of other microphysical and dynamical processes. With homogeneous freezing only, two P(σ) regimes emerged. In the limited fallout regime, relatively slow fallout allows complete depletion of the ice supersaturation, and P(σ) has a peak at large optical depth values (σ > 1). In contrast, in the fallout‐dominated regime, relatively rapid fallout results in persistent high‐ice supersaturation and multiple freezing events, and P(σ) has a monotonically decreasing shape dominated by small optical depth values. The addition of heterogeneous freezing alters the homogeneous‐freezing P(σ) shape only in the limited fallout regime. Here glaciated ice nuclei (IN) do not inhibit homogeneous freezing but can change P(σ) by reducing the optical depth of the P(σ) peak and adding a monotonically decreasing tail at low optical depth values. Surprisingly, glaciated IN do not significantly change P(σ) values or shape in the fallout‐dominated regime. Fluctuations in vertical velocity and accompanying temperature changes have relatively little impact on P(σ) unless the fluctuation timescales are shorter than fallout timescales, but longer than ice crystal growth timescales. As temperature fluctuations increase in amplitude, new freezing events affect P(σ) as long as fluctuation timescales approach or exceed freezing timescales. Our modeled P(σ) qualitatively resemble observed P(σ), indicating these results could aid in GCM cirrus P(σ) parameterization and help diagnose the controls on cirrus P(σ).
Precollisional, multistage exhumation of subducted continental crust: The Sesia Zone, western Alps
Authors: Babist J. , Handy M. R. , Konrad‐Schmolke M. , Hammerschmidt K.
Published: December 2006

The Sesia Zone within the Tertiary arc of the western Alps is a relic of the subducted part of the Adriatic continental margin along the SE border of the Tethyan ocean. The Sesia Zone comprises three basement nappes which individuated during Late Cretaceous (65–80 Ma) subduction to different depths at high‐pressure (HP, blueschist, eclogite facies) conditions (peak pressures of 1.0–1.2, 1.0–1.5, and 1.5–2.0 GPa). The thrusts bounding these nappes developed where the crust was previously thinned during Jurassic rifting. Crustal‐scale shear zones partly overprinted these early thrusts and exhumed coherent slices of crust containing HP rocks. Initial exhumation of the internal part of the accreted margin involved thrusting (D1) and transpressional shearing (D2) along a subvertical, E‐W trending mylonitic shear zone under retrograde blueschist‐ to greenschist‐facies conditions. This exhumation was nearly isothermal to a depth of about 25 km, where the basement nappes were juxtaposed. Subsequent exhumation of these nappes to a common depth of about 15–20 km occurred in the footwall of a greenschist‐facies, top‐SE extensional shear zone (D3) preserved in some of the highest mountain peaks of the Sesia Zone. New Rb‐Sr mineral ages constrain D2 to have occurred at about 60–65 Ma and D3 at about 45–55 Ma. Thus top‐SE extensional exhumation was broadly coeval with Eocene, SE directed subduction of the Liguro‐Piemont oceanic lithosphere beneath the Adriatic margin. Slow cooling and erosional denudation of the Sesia Zone from 45 to 30 Ma occurred in the hanging wall of the Gressoney extensional shear zone (D4), which itself contributed to the exhumation of Eocene HP and ultra‐HP oceanic rocks in its footwall. By 30 Ma, HP rocks of the Sesia Zone were intruded by shallow granitic plutons which were eroded and redeposited within volcanoclastic sediments. Oligo‐Miocene Insubric backfolding and thrusting (D5) only exhumed northeastern parts of the Sesia Zone, where HP metamorphism is absent or was overprinted by Tertiary temperature‐dominated metamorphism. Most exhumation of continental HP rocks in the Sesia Zone therefore preceded Tertiary Alpine collision and coincided with Late Cretaceous to Early Tertiary subduction of the Adriatic and Tethyan lithosphere. The transition from D2 to D3 in the Sesia Zone is interpreted to mark a change from high‐stress, oblique SE directed subduction and accretion of the distal Adriatic continental margin to NW retreating, low‐stress subduction of the Liguro‐Piemont oceanic lithosphere.
An investigation of thundersnow and deep snow accumulations
Authors: Crowe Christina , Market Patrick , Pettegrew Brian , Melick Chris , Podzimek Josef
Published: December 2006

A comparison of 30 years of hourly surface weather observations (1960–1991) from first‐order stations and 24‐hour snowfall data from climate network stations over the upper Midwestern United States reveals an indirect association between the relatively rare occurrence of thundersnow (<1 event yr−1 in this dataset) and the accumulation of significant 24‐hour snowfall (>15 cm) in 19 of 22 cases identified. Although no direct relationship is found between the location of thundersnow and the deepest 24‐hour snow totals, significant snow accumulations frequently occurred in proximity (<1° latitude) to thundersnow events. The presence of thundersnow tended to indicate a parent extratropical cyclone capable of producing significant snowfall totals; should thundersnow be anticipated, the operational meteorologist can have much greater confidence in forecasting deeper snow totals.
Isorenieratane record in black shales from the Paris Basin, France: Constraints on recycling of respired CO2 as a mechanism for negative carbon isotope shifts during the Toarcian oceanic anoxic event
Authors: van Breugel Yvonne , Baas Marianne , Schouten Stefan , Mattioli Emanuela , Sinninghe Damsté Jaap S.
Published: December 2006

The prominent negative stable carbon isotope excursion in both carbonate and organic carbon recorded in organic‐rich sediments deposited during the Toarcian oceanic anoxic event (OAE) has commonly been explained by recycling of 13C‐depleted CO2 (the so‐called Küspert model). More recently, the massive release of 13C‐depleted methane or other forms of 13C‐depleted carbon was also proposed to account for the observed negative δ13C excursions in organic carbon of terrigenous as well as of marine origin. The occurrence of diagenetic products of the carotenoid isorenieratene (isorenieratane and other aryl isoprenoids) in Toarcian black shales has been regarded as supporting evidence for the Küspert hypothesis as they point to strong stratification of the epicontinental seas. A section of a drill core straddling the Toarcian of the Paris Basin (Cirfontaine‐en‐Ornois) contained intact isorenieratane, providing evidence that photosynthetic green sulphur bacteria were present at the time of deposition, even prior to the OAE. However, the isorenieratane abundances are very low in the section where the negative δ13C excursion in organic carbon and phytane, a chemical fossil derived from chlorophyll, occurs. The abundance of the isorenieratene derivatives increases, once the δ13C records have shifted to more positive values. The δ13C of isorenieratane (generally circa −13.1 ± 0.5 ‰) indicates that the respired CO2 contribution at the chemocline was low and is thus not likely to be the main cause of the prominent up to 7‰ negative δ13C shift recorded in Toarcian organic carbon records.
A New Model for the Evolution of Carnivory in the Bladderwort Plant (Utricularia): Adaptive Changes in Cytochrome c Oxidase (COX) Provide Respiratory Power
Authors: Laakkonen L. , Jobson R. W. , Albert V. A.
Published: January 2007

Abstract: The evolution of carnivorous plants has been modeled as a selective tradeoff between photosynthetic costs and benefits in nutrient‐poor habitats. Although possibly applicable for pitfall and flypaper trappers, more variables may be required for active trapping systems. Bladderwort (Utricularia) suction traps react to prey stimuli with an extremely rapid release of elastic instability. Trap setting requires considerable energy to engage an active ion transport process whereby water is pumped out through the thin bladder walls to create negative internal pressure. Accordingly, empirical estimates have shown that respiratory rates in bladders are far greater than in leafy structures. Cytochrome c oxidase (COX) is a multi‐subunit enzyme that catalyzes the respiratory reduction of oxygen to water and couples this reaction to translocation of protons, generating a transmembrane electrochemical gradient that is used for the synthesis of adenosine triphosphate (ATP). We have previously demonstrated that two contiguous cysteine residues in helix 3 of COX subunit I (COX I) have evolved under positive Darwinian selection. This motif, absent in = 99.9 % of databased COX I proteins from eukaryotes, Archaea, and Bacteria, lies directly at the docking point of COX I helix 3 and cytochrome c. Modeling of bovine COX I suggests the possibility that a vicinal disulfide bridge at this position could cause premature helix termination. The helix 3–4 loop makes crucial contacts with the active site of COX, and we postulate that the C–C motif might cause a conformational change that decouples (or partly decouples) electron transport from proton pumping. Such decoupling would permit bladderworts to optimize power output (which equals energy times rate) during times of need, albeit with a 20 % reduction in overall energy efficiency of the respiratory chain. A new model for the evolution of bladderwort carnivory is proposed that includes respiration as an additional tradeoff parameter.
Respiration and Photosynthesis of Bladders and Leaves of Aquatic Utricularia Species
Authors: Adamec L.
Published: January 2007

Abstract: In aquatic species of carnivorous Utricularia, about 10—50% of the total biomass consists of bladders. Utricularia bladders are physiologically very active organs though their chlorophyll content may greatly be reduced. To specify energetic costs of carnivory, respiration (RD) and net photosynthetic rate (PN) were compared in bladders and leaves or shoot segments of six aquatic Utricularia species with differentiated (U. ochroleuca, U. intermedia, U. floridana) or non‐differentiated shoots (U. vulgaris, U. australis, U. bremii) under optimum conditions (20°C, [CO2] 0.20 mM, 400 μmol m‐2 s‐1 PAR). RD of bladders of six Utricularia species (5.1 — 8.6 mmol kg‐1FW h‐1) was 75 — 200% greater, than that in leaves in carnivorous or photosynthetic shoots (1.7 — 6.1 mmol kg‐1FW h‐1). Within individual species, this difference was statistically significant at p < 0.002 ‐ 0.01. However, PN in photosynthetic leaves/shoots (40 ‐ 117 mmol kg‐1FW h‐1) exceeded that in bladders (5.2 ‐ 14.7 mmol kg‐1FW h‐1) 7 ‐ 10 times. RD of empty bladders of U. ochroleuca was exactly the same as that in bladders containing prey. Though Utricularia bladders are essential for uptake of growth limiting mineral nutrients N and P from prey as the main benefit of carnivory, the current results support previous work showing that bladder function requires greater metabolic (maintenance) cost and very low photosynthetic efficiency (great RD: PN ratio).
Understanding the Dynamics of Collaborative Multi-Party Discourse
Authors: Cowell Andrew J , Gregory Michelle L , Bruce Joe , Haack Jereme , Love Doug , Rose Stuart , Andrew Adrienne H
Published: December 2006

In this paper, we discuss the efforts underway at the Pacific Northwest National Laboratory in understanding the dynamics of multi-party discourse across a number of communication modalities, such as email, instant messaging traffic and meeting data. Two prototype systems are discussed. The Conversation Analysis Tool (ChAT) is an experimental test-bed for the development of computational linguistic components and enables users to easily identify topics or persons of interest within multi-party conversations, including who talked to whom, when, the entities that were discussed, etc. The Retrospective Analysis of Communication Events (RACE) prototype, leveraging many of the ChAT components, is an application built specifically for knowledge workers and focuses on merging different types of communication data so that the underlying message can be discovered in an efficient, timely fashion.
Dielectric study of neutral and charged hydrogels during the swelling process
Authors: Yılmaz Y. , Gelir A. , Salehli F. , Nigmatullin R. R. , Arbuzov A. A.
Published: December 2006

Dielectric spectroscopy measurements of conductivity were applied for understanding the change in the internal morphology of the neutral and permanently charged polyacrylamide (PAAm) hydrogels during the swelling process. For the first time four distinct peaks (each corresponding to a different swelling stage) in the conductivity of the neutral gel were observed during the swelling of this gel. These peaks are related to the distribution of dense polymer regions (they are defined as the “blobs”) appearing in a microstructure of the given PAAm gel having at least four average sizes. For the charged gel the heterogeneity decreases due to the internal electric field of the charged sites. Thus, this characteristic behavior in the conductivity becomes almost negligible for the gel charged with permanent SO3− groups. It seems this fact causes considerable decrease in amplitude of the peaks and overall decrease the conductivity during the whole swelling process especially at high frequencies. The new theory of dielectric relaxation based on the fractional kinetics containing the complex power-law exponents was used for verifying these swelling processes and received an excellent confirmation in description of the real part of the complex conductivity Re[σ(ω)] by the fitting function that follows from the suggested theory. The calculated power-law exponents describe the behavior of Re[σ(ω,m∕m0)] in the available frequency range (30Hz–13MHz) and for all values of the relative masses (volumes) measured in the process of the experiment. The excellent coincidence between the new theory and measured data gives a possibility to suggest more reliable physical picture of the swelling process that takes place in neutral/charged gels.
Synthesis and thermoelectric properties of double-atom-filled skutterudite compounds CamCenFexCo4−xSb12
Authors: Tang Xinfeng , LI Han , Zhang Qingjie , Niino Masayuki , Goto Takashi
Published: December 2006

Single-phase CamCenFexCo4−xSb12 compounds filled by Ca and Ce were synthesized by using melting-quench-diffusion annealing reaction method. The structure and thermoelectric properties of double atoms filled skutterudite compounds were investigated. The results of Rietveld refinement indicate high reliabilities of filling fractions consistent with the inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis, CamCenFexCo4−xSb12 compounds possess skutterudite structure, and Sb-icosahedron voids were filled with Ca or Ce. The thermal parameter BCa∕Ce (6.0) of Ca∕Ce is much larger than that of BSb (0.3) and BFe∕Co (0.3) of Sb and Fe∕Co. The specific chemical states of atoms were obtained from x-ray photoelectron spectroscopy quantitative analysis, which shows that Sb has five chemical states and the relative content is correlative with the total filling fraction; the filling atoms have three filling positions and tend to fill the center position of the Sb-icosahedron voids, preferentially. With the same filling fraction, carrier concentration and electrical conductivity of p-type CamCenFexCo4−xSb12 are intervenient between that of single atom filled compounds CamFexCo4−xSb12 and CenFexCo4−xSb12, and decreased with increasing Ca and Ce, especially Ce, filling fraction. The Seebeck coefficients are increased with increasing total filling fraction, and the influence of Ce filling fraction to the Seebeck coefficients is more notable than that of Ca, and with the same filling fraction, the lattice thermal conductivity of CamCenFexCo4−xSb12 is smaller than that of CamFexCo4−xSb12 and CenFexCo4−xSb12; furthermore, when the total filling fraction (m+n) is about 0.3 and the respective filling fraction of Ca and Ce is approximately identical, the lattice thermal conductivity reached the minimum value. The greatest ZT value of 1.2 was obtained at 750K for p-type Ca0.18Ce0.12Fe1.45Co2.55Sb12 compound.
Theoretical study of phosphorescence in dye doped light emitting diodes
Authors: Minaev Boris , Jansson Emil , Ågren Hans , Schrader Sigurd
Published: December 2006

Phosphorescence of platinum(II) octaethyl porphyrin (PtOEP), which has been used in organic light emitting diodes to overcome the efficiency limit imposed by the formation of triplet excitons, is studied by time-dependent (TD) density functional theory (DFT). The spin-orbit coupling (SOC) effects and the phosphorescence radiative lifetime (τpr), calculated by the TD DFT method with the quadratic response technique, are analyzed for a series of porphyrins in order to elucidate the internal heavy atom effect on τpr. While the significance of the dπ orbital admixture into the lowest unoccupied molecular orbital eg(π*), proposed by Gouterman et al. [J. Chem. Phys. 56, 4073 (1972)], is supported by our SOC calculations, we find that the charge-transfer (CT) mechanism is more important; the CT state of the A2g3 symmetry provides effective SOC mixing with the ground state, and a large A2g3-Eu3 transition dipole moment gives the main contribution to the radiative phosphorescence rate constant. The IR and Raman spectra in the ground state and first excited triplet state (T1) are studied for proper assignment of vibronic patterns. An orbital angular momentum of the T1 state is not quenched completely by the Jahn-Teller effect. A large zero-field splitting is predicted for PtP and PtOEP which results from a competition between the SOC and Jahn-Teller effects. A strong vibronic activity is found for the eg mode at 230cm−1 in PtP phosphorescence which is shifted to 260cm−1 in PtOEP. This out-of-plane vibration of the Pt atom produces considerable change of the SOC mixing. The role of charge-transfer state of dππ* type is stressed for the explanation of the electroluminescent properties of the dye doped light emitting diode.
Comparison of wave propagation studies in plasmas using three-dimensional finite-difference time-domain and ray-tracing methods
Authors: Chaudhury Bhaskar , Chaturvedi Shashank
Published: December 2006

Power-flow trajectories of electromagnetic waves through a spatially nonuniform plasma have been computed using direct solutions of Maxwell’s equations using the three-dimensional finite-difference time-domain (FDTD) method. This method yields accurate information on refraction as well as absorption effects. The method can be used to compute power-flow trajectories for plasmas with arbitrarily varying density profiles, including effects due to arbitrarily shaped conducting or dielectric surfaces bounding the plasma. Furthermore, since FDTD is computationally expensive, especially for parametric studies, it is desirable to use ray tracing to estimate refraction effects. A quantitative comparison is performed between two different methods of obtaining exact and approximate solutions of Maxwell’s equations in order to assess their relative utility in different situations. In the present work, we limit ourselves to a cold, collisional, unmagnetized plasma, where the response to electromagnetic waves is fully specified by a dispersion relation based on magnetoionic theory. It is shown that ray tracing in such plasmas yields accurate results only when two conditions are satisfied. Firstly, the density scale length should be long as compared to the free-space wavelength of the incident wave. Secondly, the conduction current should be small as compared to the displacement current in the medium. The second condition is one which has been identified for the first time.
Nuclear spin relaxation of sodium cations in bacteriophage Pf1 solutions
Authors: Sobieski D. N. , Krueger N. R. , Vyas S. , Augustine M. P.
Published: January 2007

The nuclear magnetic resonance (NMR) spectra for the I=3∕2 Na23 cation dissolved into filamentous bacteriophage Pf1 solutions display line splittings and relaxation times consistent with an interaction between the Na23 nuclear quadrupole moment and the electric field gradient produced by the negatively charged Pf1 particles. The Na23 NMR line splittings and relaxation rates corresponding to magnetization recovery and single, double, and triple quantum coherence decays are measured in Pf1 solutions and compared to theoretical values. The deviation of the observed dc spectral density J(0) from the equal first harmonic J(ω0) and second harmonic J(2ω0) values as J(ω0)=J(2ω0)≠J(0) in these solutions suggests that ion migration in the electric field gradient of the Pf1 particles produces an anisotropic relaxation mechanism. Correlation functions and thus spectral densities for this process are calculated from solutions to the Fokker-Planck equation for radial motion in an electric potential and used to estimate measured relaxation rates. Appropriate electric potentials are generated from the solutions to the Poisson-Boltzmann equation for a charged Pf1 particle in aqueous phase, functions that lead to theoretical estimates of NMR line splittings consistent with experimental observations.
Micromagnetic investigation on the coercivity mechanism of the SmCo5∕Sm2Co17 high-temperature magnets
Authors: Rong Chuan-Bing , Zhang Hong-Wei , Chen Ren-Jie , Shen Bao-Gen , He Shu-Li
Published: January 2007

The coercivity mechanism of the precipitation-hardened Sm(Co,Fe,Cu,Zr)z magnets at different temperature have been investigated by micromagnetic calculations. It was found that the coercivity mechanism varies with the temperature. The magnetization reversal is mainly controlled by domain-wall pinning when the temperature T is lower than 800 K, while it is dominated by coherent rotation at higher temperature. The quantitative analysis shows that the reduced coercivity is linearly related to the difference of domain-wall energy between 1:5 and 2:17 phases at T≤800 K, while it is mainly determined by the ratio of exchange constant between the two phases at T>800 K. The temperature dependence of coercivity Hc(T) is the competitive result of the microstructure parameter αex(T) and the anisotropy field. The anomalous Hc(T) near the Curie temperature of 1:5 phase is caused by the fast drop of intergrain exchange coupling and thus the fast increase of αex(T). The micromagnetic calculations show that the anomalous Hc(T) also can be obtained in the nanocomposite-type SmCo5∕Sm2Co17 with an appropriate microstructure.
n
-alkanes on Pt(111) and on C(0001)∕Pt(111): Chain length dependence of kinetic desorption parameters
Authors: Tait Steven L. , Dohnálek Zdenek , Campbell Charles T. , Kay Bruce D.
Published: December 2006

We have measured the desorption of seven small n-alkanes (CNH2N+2, N=1–4,6,8,10) from the Pt(111) and C(0001) surfaces by temperature programed desorption. We compare these results to our recent study of the desorption kinetics of these molecules on MgO(100) [J. Chem. Phys. 122, 164708 (2005)]. There we showed an increase in the desorption preexponential factor by several orders of magnitude with increasing n-alkane chain length and a linear desorption energy scaling with a small y-intercept value. We suggest that the significant increase in desorption prefactor with chain length is not particular to the MgO(100) surface, but is a general effect for desorption of the small n-alkanes. This argument is supported by statistical mechanical arguments for the increase in the entropy gain of the molecules upon desorption. In this work, we demonstrate that this hypothesis holds true on both a metal surface and a graphite surface. We observe an increase in prefactor by five orders of magnitude over the range of n-alkane chain lengths studied here. On each surface, the desorption energies of the n-alkanes are found to increase linearly with the molecule chain length and have a small y-intercept value. Prior results of other groups have yielded a linear desorption energy scaling with chain length that has unphysically large y-intercept values. We demonstrate that by allowing the prefactor to increase according to our model, a reanalysis of their data resolves this y-intercept problem to some degree.
Ion beam generation from sheath field of grid electrode and its application to surface treatment
Authors: Cho Yong-Sung , Lee Hae June , Park Chung-Hoo , Lee Ho-Jun , Lee Sung-Kwan
Published: December 2006

As plasma immersion ion implantation using a conducting grid is very useful to reduce the effect of capacitance and charging in surface modification, it is broadly applied in the fields of insulating material implantation. On the other hand, there have been only few attempts to analyze the sheath dynamics including the conducting grid. If the bias voltage applied to the conducting grid is in the range of hundreds of volts for sputtering, or the energy for local restructuring of the atomic arrangement is much lower than voltage for implantation, the surface charge and space charge substantially affect the incident ion energy and ion current to the surface. The formation of the space and surface charges during one bias pulse period are thus analyzed through a one-dimensional and a two-dimensional particle-in-cell simulation. Experiment with the optimally designed grid on the basis of the simulation results is conducted, and the results of both cases with grid and without grid are compared. The improvement of adhesion is yielded by increasing surface roughness and chemical change in the polyurethane treatment using the conducting grid.
Reversible paramagnetism to ferromagnetism in transition metal-doped TiO2 nanocrystals prepared by microwave irradiation
Authors: Glaspell Garry , Panda Asit B. , El-Shall M. S.
Published: December 2006

Ti O 2 nanoparticles doped with 1%, 5%, and 10% M (M=Co, Fe, and Ni) were prepared by microwave irradiation and characterized using x-ray diffraction, transmission electron microscopy, and magnetometry. The as-prepared samples are found to be paramagnetic at room temperature, with the magnetic susceptibility following the Curie-Weiss law in the investigated range of 2–300K. However, transformation from paramagnetism to room-temperature ferromagnetism (RTFM) was observed by hydrogenating the samples at 400°C. Reheating in air converted the samples back to paramagnetic while rehydrogenating the samples again induced ferromagnetism. It is argued that the reversible RTFM observed is due to interaction between the dopant metal ions and oxygen vacancies produced during hydrogenation. X-ray diffraction of the hydrogenated Co- and Fe-doped samples shows only a single TiO2 phase suggesting that the observed RTFM may be intrinsic, but for the Ni-doped samples the magnetism may arise from metallic Ni on the surfaces of the TiO2 nanoparticles.
Quantitative nanoscale modulus measurements and elastic imaging of SnO2 nanobelts
Authors: Zheng Yuegui , Geer Robert E. , Dovidenko Katharine , Kopycinska-Müller Malgorzata , Hurley Donna C.
Published: December 2006

A comparative study of the elastic modulus and uniformity of single-crystal SnO2 nanobelts is presented employing two nondestructive techniques based on atomic force microscopy: differential ultrasonic force microscopy (d-UFM) and atomic force acoustic microcopy (AFAM). In mapping mode both techniques revealed a uniform elastic response across the surface of the nanobelts as expected for single-crystal nanostructures. Comparative analyses of the local indentation modulus (probe area≈100–400nm2) were undertaken using both techniques at multiple points on the same SnO2 nanobelt exhibiting a (102) surface crystalline orientation as determined by electron backscatter diffraction. Both d-UFM and AFAM exhibited excellent quantitative agreement yielding indentation moduli of 151±14 and 154±18GPa, respectively. These values are significantly below the expected value of the (102) indentation modulus of 358GPa for crystalline SnO2 determined from the Green’s function model of Barnett and Lothe [Phys. Nors. 8, 13 (1975)] adapted by Vlassak et al. [J. Mech. Phys. Solids 51, 1701 (2003)]. This observation is consistent with recent nanoindentation (destructive) measurements of (101¯) oriented SnO2 nanobelts that yielded an indentation modulus of 66±10GPa, well below the expected value of 308GPa. In addition to confirming the quantitative consistency and overall accuracy of nanoscale modulus measurements using d-UFM and AFAM, the overall trend in these data contradicts recent molecular dynamics studies that call for increased elastic moduli in similar nanobelt structures.
Numerical analysis of the radial breathing mode of armchair and zigzag single-walled carbon nanotubes under deformation
Authors: Cao Guoxin , Chen Xi , Kysar Jeffrey W.
Published: December 2006

An ab initio analysis based on the density functional theory is carried out to investigate the effects of axial strain and radial pressure on the radial breathing mode (RBM) frequency of individual single-walled carbon nanotubes with armchair and zigzag chiralities. It is found that the RBM frequency is not sensitive to axial tensile strain or small axial compressive strain. When the axial compressive strain exceeds a critical value, the RBM frequency is significantly reduced. On the other hand, the RBM frequency is highly sensitive to the radial pressure; a pressure of 1GPa can increase the RBM frequency by about 8cm−1. Under a high radial pressure, the difference between the frequencies of the positive and negative half periods of the RBM vibration sharply increases, which may lead to the separation of the RBM peaks. Very good agreement is found between the present numerical analysis and previous experimental results.
Anomalous conductivity and secondary electron emission in Hall effect thrusters
Authors: Garrigues L. , Hagelaar G. J. M. , Boniface C. , Boeuf J. P.
Published: December 2006

This paper is devoted to the study of the effects of electron-wall interactions on cross magnetic field electron momentum and energy losses in Hall effect thrusters. By coupling a semianalytical model of the wall sheath similar to models used by several authors in this context, with a two-dimensional hybrid simulation of a Hall effect thruster, we find that the cross magnetic field conductivity enhanced by electron-wall collisions and secondary electron emission is not sufficient to explain the conductivity deduced from experiments. Calculated current-voltage curves including electron-wall collisions from a standard sheath model as the sole “anomalous” conductivity mechanism do not reproduce the measurements, especially at high discharge voltages, and for various wall ceramics. Results also show that a one-dimensional description of electron-wall collisions with a constant radial plasma density profile as used by many authors leads to an overestimation of the contribution of electron-wall interactions to cross magnetic field conductivity.
Optical polarization anisotropy and hole states in pyramidal quantum dots
Authors: Karlsson K. F. , Troncale V. , Oberli D. Y. , Malko A. , Pelucchi E. , Rudra A. , Kapon E.
Published: December 2006

The authors present a polarization-resolved photoluminescence study of single semiconductor quantum dots (QDs) interconnected to quantum wires, measured both in a top geometry, and in a less conventional cleaved-edge geometry. Strong polarization anisotropy is revealed for all observed transitions, and it is deduced that closely spaced QD hole states exhibit nearly pure heavy-or light-hole character. These effects are attributed to the large aspect ratio of the dot shape.
The impact of negative-bias-temperature-instability on the carrier generation lifetime of metal-oxynitride-silicon capacitors
Authors: Volkos S. N. , Efthymiou E. S. , Bernardini S. , Hawkins I. D. , Peaker A. R. , Petkos G.
Published: December 2006

N -type metal-oxynitride-silicon capacitors were subjected to a negative bias voltage at an elevated temperature. Under this condition, Negative-bias-temperature-instability (NBTI) was evidenced in capacitance-voltage (CV) characteristics with an accompanying decrease, as determined from inversion layer-related (i.e., generation lifetime) deep-level-transient-spectroscopy (DLTS) measurements, in the carrier generation lifetime. An analysis of the dominant defect supplying minority carriers to the inversion layer at the silicon-oxynitride interface revealed a significant change brought about by NBTI. A full recovery of the carrier generation lifetime was observed after several days at zero bias voltage, and room temperature conditions had elapsed following NBTI. Concurrently, a passivation, as inferred from conventional DLTS measurements, of the NBTI-induced trap density occurred at the silicon-oxynitride interface. These relaxation and deactivation phenomena were discussed in the context of a plausible model involving a reaction at the silicon-oxynitride interface between trivalent silicon dangling bond defects and hydrogenous species.
Effect of texture on the magnetostriction of grain-aligned composite Terfenol-D
Authors: Kwon Oh Yeoul , Kim Hee Yeoun , Hong Soon Hyung , Son De Rac
Published: December 2006

Grain-aligned composite Terfenol-D was fabricated via unidirectional solidification, followed by the infiltration of epoxy. The fraction of the RFe2 phase in composite Terfenol-D depends on the iron/rare earth (RE=Tb,Dy) ratio of the as-grown Terfenol-D and the direction of the RFe2 phase in the as-grown Terfenol-D changes from ⟨110⟩ to ⟨111⟩ with an increasing iron/rare earth ratio. For a series of grain-aligned composite Terfenol-D with different RFe2 fractions, the magnetostriction was found to increase from 813to1013ppm with increases in the RFe2 fraction. A model for the magnetostriction of grain-aligned composite Terfenol-D was developed based on the modified uniform strain condition. The modified uniform strain model was then used to predict the magnetostriction of grain-aligned composite Terfenol-D from the fraction of the RFe2 phase, the elastic modulus for each crystal direction of the RFe2 phase obtained in a texture analysis, and the saturation magnetostriction value of each preferred direction. The predicted magnetostriction of grain-aligned composite Terfenol-D, which considers the elastic modulus with respect to the crystal direction of the magnetostrictive phase, is in agreement with the experimental results. In conclusion, in grain-aligned composite Terfenol-D fabricated using the crystal growth technique the preferred direction should be considered for predicting the magnetostriction of grain-aligned composite Terfenol-D.
Anomalous small angle x-ray scattering determination of ion distribution around a polyelectrolyte biopolymer in salt solution
Authors: Horkay Ferenc , Hecht Anne Marie , Rochas Cyrille , Basser Peter J. , Geissler Erik
Published: December 2006

The distribution of counterions in solutions of high molecular mass hyaluronic acid, in near-physiological conditions where mono- and divalent ions are simultaneously present, is studied by small angle neutron scattering and anomalous small angle x-ray scattering. The solutions contain either sodium or rubidium chloride together with varying concentrations of calcium or strontium chloride. The effects of monovalent-divalent ion exchange dominate the amplitude and the form of the counterion cloud. In the absence of divalent ions, the shape of the anomalous scattering signal from the monovalent ions is consistent with the distribution calculated from the Poisson-Boltzmann equation, as found by other workers. In mixtures of monovalent and divalent ions, however, as the divalent ion concentration increases, both the diameter and the amplitude of the monovalent ion cloud decrease. The divalent counterions always occupy the immediate neighborhood of the charged polyanion. Above a given concentration their anomalous scattering signal saturates. Even in a large excess of divalent ions, ion exchange is incomplete.
Spatial distribution of deep level defects in crack-free AlGaN grown on GaN with a high-temperature AlN interlayer
Authors: Sun Q. , Wang H. , Jiang D. S. , Jin R. Q. , Huang Y. , Zhang S. M. , Yang H. , Jahn U. , Ploog K. H.
Published: December 2006

The deep level luminescence of crack-free Al0.25Ga0.75N layers grown on a GaN template with a high-temperature grown AlN interlayer has been studied using spatially resolved cathodoluminescence (CL) spectroscopy. The CL spectra of Al0.25Ga0.75N grown on a thin AlN interlayer present a deep level aquamarine luminescence (DLAL) band at about 2.6eV and a deep level violet luminescence (DLVL) band at about 3.17eV. Cross-section line scan CL measurements on a cleaved sample edge clearly reveal different distributions of DLAL-related and DLVL-related defects in AlGaN along the growth direction. The DLAL band of AlGaN is attributed to evolve from the yellow luminescence band of GaN, and therefore has an analogous origin of a radiative transition between a shallow donor and a deep acceptor. The DLVL band is correlated with defects distributed near the GaN∕AlN∕AlGaN interfaces. Additionally, the lateral distribution of the intensity of the DLAL band shows a domainlike feature which is accompanied by a lateral phase separation of Al composition. Such a distribution of deep level defects is probably caused by the strain field within the domains.
Improvement of field emission from screen-printed carbon nanotubes by He∕(N2,Ar) atmospheric pressure plasma treatment
Authors: Kyung S. J. , Park J. B. , Lee J. H. , Yeom G. Y.
Published: December 2006

A screen-printed carbon nanotube (CNT) paste for applications to field emission emitters was treated with He, He∕Ar, and He∕N2 atmospheric pressure plasmas. The effect of the different plasma treatments on the field emission characteristics of the screen-printed CNTs was investigated. The atmospheric pressure plasma applied to the screen-printed CNT paste for 10s resulted in a reduction in the turn-on electric field. In particular, the application of a He∕N2 plasma treatment decreased the turn-on electric field from 3.13to1.29V∕μm and increased the field enhancement factor from 737 to 2775 after the treatment. These results suggest that an adequate atmospheric pressure plasma treatment of screen-printed CNTs can be effective in enhancing the field emission properties.
Irreversibility line and low-field grain-boundary pinning in electron-doped superconducting thin films
Authors: Sergeenkov S. , Lanfredi A. J. C. , Araujo-Moreira F. M.
Published: December 2006

ac magnetic susceptibilities of electron-doped Pr1.85Ce0.15CuO4 (PCCO) and Sm1.85Ce0.15CuO4 (SCCO) granular thin films have been measured as a function of temperature and magnetic-field strength. Depending on the level of homogeneity of our films, two different types of the irreversibility line (IL), Tirr≡Tp(H), defined as the intergrain-loss peak temperature in the imaginary part of the susceptibility and obeying the law 1−Tp∕TC∝Hq, have been found. Namely, more homogeneous PCCO films (with a grain size of the order of 2μm) are best-fitted with q=2∕3 while less homogeneous SCCO films (with a grain size of the order of 500nm) follow the IL law with q=1. The obtained results are described via the critical-state model taking into account the low-field grain-boundary pinning. The extracted pinning-force densities in more granular SCCO films turn out to be four times larger than their counterparts in less granular PCCO films.