bluuebunny/crossref_metadata_2025 huggingface dataset:
Time series of winter convection in the Greenland Sea
Authors: Ronski S. , Budéus G.
Published: April 2005

In spite of the lack of bottom reaching convection in the Greenland Sea since the 1980s, convection continues to ventilate the Greenland Gyre down to intermediate depth. The variability of this ventilation activity is determined here annually for eight winters according to a multiple criteria catalogue, applied to annual summer conductivity‐temperature‐depth transects along 75°N. The comparison of the ventilation depths with the meteorological forcing, the ice cover, and the stratification of the water column shows the decisive influence of the hydrographic structure in the upper and intermediate layers. Ice, on the other hand, is not necessary for convection to occur. Ice formation does not even lead to particularly deep convection. A stability maximum, which currently dominates the vertical structure of the water column at medium depth, limits the ventilation depths effectively.
Pyro‐cumulonimbus injection of smoke to the stratosphere: Observations and impact of a super blowup in northwestern Canada on 3–4 August 1998
Authors: Fromm Michael , Bevilacqua Richard , Servranckx René , Rosen James , Thayer Jeffrey P. , Herman Jay , Larko David
Published: April 2005

We report observations and analysis of a pyro‐cumulonimbus event in the midst of a boreal forest fire blowup in Northwest Territories Canada, near Norman Wells, on 3–4 August 1998. We find that this blowup caused a five‐fold increase in lower stratospheric aerosol burden, as well as multiple reports of anomalous enhancements of tropospheric gases and aerosols across Europe 1 week later. Our observations come from solar occultation satellites (POAM III and SAGE II), nadir imagers (GOES, AVHRR, SeaWiFS, DMSP), TOMS, lidar, and backscattersonde. First, we provide a detailed analysis of the 3 August eruption of extreme pyro‐convection. This includes identifying the specific pyro‐cumulonimbus cells that caused the lower stratospheric aerosol injection, and a meteorological analysis. Next, we characterize the altitude, composition, and opacity of the post‐convection smoke plume on 4–7 August. Finally, the stratospheric impact of this injection is analyzed. Satellite images reveal two noteworthy pyro‐cumulonimbus phenomena: (1) an active‐convection cloud top containing enough smoke to visibly alter the reflectivity of the cloud anvil in the Upper Troposphere Lower Stratosphere (UTLS) and (2) a smoke plume, that endured for at least 2 hours, atop an anvil. The smoke pall deposited by the Norman Wells pyro‐convection was a very large, optically dense, UTLS‐level plume on 4 August that exhibited a mesoscale cyclonic circulation. An analysis of plume color/texture from SeaWiFS data, aerosol index, and brightness temperature establishes the extreme altitude and “pure” smoke composition of this unique plume. We show what we believe to be a first‐ever measurement of strongly enhanced ozone in the lower stratosphere mingled with smoke layers. We conclude that two to four extreme pyro‐thunderstorms near Norman Wells created a smoke injection of hemispheric scope that substantially increased stratospheric optical depth, transported aerosols 7 km above the tropopause (above ∼430 K potential temperature), and also perturbed lower stratospheric ozone.
NOAA AVHRR derived aerosol optical depth over land
Authors: Hauser A. , Oesch D. , Foppa N. , Wunderle S.
Published: April 2005

Aerosol optical depth was retrieved from a time series of NOAA‐16 AVHRR data from May 2001 through December 2002 for Central Europe (40.5°N–50.0°N, 0°E–17°E). In contrast to classical methods, no a priori knowledge of the surface reflectance is necessary, but instead the surface reflectance is estimated from a time series including the previous 44 days. Additionally, the area where aerosol optical depth can be retrieved is no longer limited to certain land cover types. Only bright surface targets are excluded in the retrieval. To retrieve the aerosol optical depth, the radiative transfer code SMAC is used. Afterwards the data are averaged within a 25 × 25 pixel region to increase the retrieval precision. The resulting standard deviation of the aerosol optical depth within this region is used as a quality control parameter and suitable for a post‐processing of the initial aerosol retrieval. This post‐processing leads to a substantial increase in the retrieval accuracy when compared to ground‐based AERONET measurements. Over 650 co‐incident AVHRR retrievals and AERONET measurements were compared, and a correlation coefficient of 0.70 was found. Altogether, the proposed method offers the potential to generate an aerosol climatology based on NOAA AVHRR data, which dates back to the early 1980s.
Variations of electron density based on long‐term incoherent scatter radar and ionosonde measurements over Millstone Hill
Authors: Lei Jiuhou , Liu Libo , Wan Weixing , Zhang Shun‐Rong
Published: April 2005

Measurements from the incoherent scatter radar (ISR) and ionosonde over Millstone Hill (42.6°N, 288.5°E) are analyzed to explore ionospheric temporal variations. The F2 layer peak density NmF2, peak height hmF2, and scale height H are derived from a Chapman α layer fitting to observed ISR electron density profiles. Diurnal, seasonal, and solar activity variations of the ionospheric characteristics are presented. Our study on the solar activity dependence of NmF2, hmF2, and H indicates that the peak parameters (NmF2 and hmF2) of the F2 layer increase with daily F10.7 index and saturate (or increase with a much lower rate) for very high F10.7; however, they show almost linear dependence with the solar proxy index F10.7p = (F10.7 + F10.7A)/2, where F10.7A is the 81‐day running mean of daily F10.7. This suggests that the overall effect of solar EUV and neutral atmosphere changes on the solar activity variation of ionospheric ionization is linear with F10.7p. The rate of change in the ionospheric characteristics with solar activity exhibits a seasonal and local time variation. Over Millstone Hill, NmF2 in summer is characterized by the evening peak in its diurnal variation, and NmF2 exhibits winter anomaly under low and high solar activity levels. The temporal variations of the topside effective scale height H0 can be explained in terms of those in the slab thickness. The IRI model overestimates the Ne effective topside scale height over Millstone Hill; therefore our analysis for the effective topside scale height from the Millstone Hill measurements might help to improve the IRI topside profiles at middle latitudes.
Contrasting trends in North Atlantic deep‐water formation in the Labrador Sea and Nordic Seas during the Holocene
Authors: Renssen Hans , Goosse Hugues , Fichefet Thierry
Published: April 2005

The Holocene North Atlantic deep‐water formation is studied in a 9,000‐year long simulation with a coupled climate model of intermediate complexity, forced by changes in orbital forcing and atmospheric trace gas concentrations. During the experiment, deep‐water formation in the Nordic Seas is reduced due to an enhanced influx of sea ice from the Central Arctic, decreasing both surface salinity and density, whereas deep‐water formation in the Labrador Sea increases due to surface cooling. This leads to changes in the distribution of oceanic heat transported northwards by the Atlantic Ocean, with less heat released (−120 Wm−2 in February) in the Nordic Seas, amplifying the surface cooling and increasing the sea‐ice cover. In the Labrador Sea, the oceanic heat release increases slightly (+14 Wm−2), thus dampening locally the cooling trend. The overall Atlantic overturning strength remains constant throughout the experiment. Over the Nordic Seas, reduced evaporation contributes to the surface freshening.
Measurements and implications of the relationship between lightning and terrestrial gamma ray flashes
Authors: Cummer Steven A. , Zhai Yuhu , Hu Wenyi , Smith David M. , Lopez Liliana I. , Stanley Mark A.
Published: April 2005

We report observations and analysis of 30 kHz radio emissions (sferics) from lightning discharges associated with 26 terrestrial gamma ray flashes (TGFs) recorded by the RHESSI satellite over the Caribbean and Americas, between 1500 and 4000 km away from the magnetic field sensors located at Duke University. Thirteen of the TGFs are found to occur within −3/+1 ms of lightning discharges of positive polarity from the direction of the RHESSI subsatellite point, strongly indicating that the TGFs are linked to these discharges. The event timing and sferic direction finding reveals that the discharges occur within a ∼300 km radius circle around the RHESSI subsatellite point. Although the positive polarity of all 13 discharges is consistent with runaway breakdown, the lightning charge moment changes are approximately two orders of magnitude smaller than present high altitude runaway breakdown theory predicts. Implications of these measurements are discussed.
Anomalous electronic transport and magnetic instability in Eu1−xLaxB6 (x=0.0, 0.1, 0.2, and 0.3)
Authors: Rhyee Jong-Soo , Cho B. K.
Published: April 2005

We investigated the anomalous magnetic and transport properties for Eu1−xLaxB6 (x=0.0, 0.1, 0.2, and 0.3) series compounds. From the magnetization measurements, it was found that the ferromagnetic state with Tc≈15K for EuB6 evolves to an antiferromagnetic-like state with Néel temperature TN≈8.5K for Eu1−xLaxB6 (x=0.3). Frustrated unstable magnetic state is induced by a small doping of La in Eu1−xLaxB6 (x=0.1 and 0.2). Interestingly, the gap-like increase of resistivity ρ(T) appears at low temperatures for Eu1−xLaxB6 (x=0.1 and 0.2), while a sudden drop of ρ(T) was observed at TN for Eu1−xLaxB6 (x=0.3), which is likely due to a loss of magnetic scattering. Here, we discuss the role of unstable magnetization on the anomalous transport properties in the intermediate doped region of Eu1−xLaxB6 (x=0.1, and 0.2).
Effect of doping on flux pinning of GdBa2Cu3O7−y
Authors: Zhang L. , Xu X. B. , Ding S. Y. , Zheng M. H. , Xiao L. , Ren H. T. , Jiao Y. L. , Wang X. L. , Lin Z. W. , Zhu J. G.
Published: April 2005

Cylindrical single grains of GdBa2Cu3Oy (Gd-123) with a diameter of 25mm were successfully fabricated by melt-texture growth (MTG) process in air to study the influence of different starting powders on flux pinning. Measurements of the magnetic critical current density (Jc) showed that it was possible to fabricate large Gd-123 single grain with a high Jc at high temperatures and fields by means of properly controlling the starting powders of Gd2O3, BaCO3, and CuO before the MTG process.
Site disorder and spin-glass ordering in PrAu2Si2
Authors: Ryan D. H. , Voyer C. J. , Swainson I. P. , Krimmel A. , Hemberger J. , Loidl A.
Published: April 2005

We have used Au197 Mössbauer spectroscopy along with both neutron and x-ray diffraction to search for site disorder and noncollinear magnetic ordering in PrAu2Si2. There is no evidence of a transferred hyperfine field at the Au site down to 1.7 K allowing us to rule out both collinear antiferromagnetic order and spin-glass ordering of the Pr moments. Full-pattern Rietveld refinement of both neutron and x-ray diffraction data taken over a wide angle range allows us to exclude Au∕Si site disorder at the 1% level. We conclude that the Pr moments do not order above 1.7 K in PrAu2Si2, and that the susceptibility peak is likely a dynamic effect.
Weak ferromagnetic order and possible high-Tc superconductivity in the RuCa2RCu2O8+δ ruthenium-cuprate
Authors: Ku H. C. , Yang C. Y. , Chang B. C. , Lin B. N. , Hsu Y. Y. , Tai M. F.
Published: April 2005

Weak ferromagnetic order with ordering temperature Tm∼47K and possible superconducting transition with Tc∼37K are observed for the ruthenium-cuprate RuCa2PrCu2O8+δ with the orthorhombic distortion of the tetragonal RuSr2GdCu2O8+δ-type [with Tm∼136K and Tc(max)∼65K] phase. Anomalous temperature dependent magnetization Mm(T) in both field-cooled and zero-field-cooled modes and isothermal magnetic hysteresis Mm(Ba) below and above Tm and Tc indicates a very complicated coexistence and interplay between weak-ferromagnetic order and possible superconductivity.
Magnetic and transport properties of ternary indides of type R2CoIn8 (R=Ce, Pr, and Dy)
Authors: Joshi Devang A. , Tomy C. V. , Paulose P. L. , Nagarajan R. , Nirmala R. , Malik S. K.
Published: April 2005

We have synthesized and investigated the magnetic and transport properties of a series of compounds, R2CoIn8 (R=rare earth). Compounds form in single phase with a tetragonal structure (space group P4∕mmm, no. 162). The Ce compound shows heavy fermion behavior. The magnetic susceptibility of Pr2CoIn8 shows a marked deviation from the Curie–Weiss behavior at low temperatures, which is attributed to the crystalline electric field effects. Heat capacity and magnetization measurements show that Dy2CoIn8 undergoes a magnetic transition at 17K and a second transition near 5K, the latter of which may be due to spin reorientation. Magnetization of this compound shows two metamagnetic transitions approximately at 3.6T and 8.3T.
Comment and calculation on duality exchange in Gd2In
Authors: Yazdani A.
Published: April 2005

Since Gd2In intermetallic compound contains two types of Gd, three-phase transition in low field is demonstrated by the following conclusions: (I) A strong negative exchange as short range exchange (Jn,nsh) in the distance Rc=3.3Å. (II) A relatively weak antiferromagnetic exchange (JInnn) as long range interaction in the distance Rc=4.6Å. (III) Two kinds of exchange fluctuations, resulted by competition λmin(k=0) and λmin(k=π). (IV) Above the critical field, the external field perturbs the magnetic ions in antiferromagnetic (AFM) state, imposing a FM-AFM crossover and so a triplet competition starts to grow. (V) The calculation of Tc and Tn and experimental results are in a good agreement.
Length scale competition in nonlinear Klein—Gordon models: A collective coordinate approach
Authors: Cuenda Sara , Sánchez Angel
Published: April 2005

Working within the framework of nonlinear Klein–Gordon models as a paradigmatic example, we show that length scale competition, an instability of solitons subjected to perturbations of an specific length, can be understood by means of a collective coordinate approach in terms of soliton position and width. As a consequence, we provide a natural explanation of the phenomenon in much simpler terms than any previous treatment of the problem. Our technique allows us to study the existence of length scale competition in most soliton bearing nonlinear models and can be extended to coherent structures with more degrees of freedom.
An investigation of nonadiabatic interactions in Cl(Pj2)+D2 via crossed-molecular-beam scattering
Authors: Parsons Bradley F. , Chandler David W.
Published: April 2005

We have determined limits on the cross section for both electronically nonadiabatic excitation and quenching in the Cl(Pj2)+D2 system. Our experiment incorporates crossed-molecular-beam scattering with state-selective Cl(P1∕2,3∕22) detection and velocity-mapped ion imaging. By colliding atomic chlorine with D2, we address the propensity for collisions that result in a change of the spin-orbit level of atomic chlorine either through electronically nonadiabatic spin-orbit excitation Cl(P3∕22)+D2→Cl*(P1∕22)+D2 or through electronically nonadiabatic spin-orbit quenching Cl*(P1∕22)+D2→Cl(P3∕22)+D2. In the first part of this report, we estimate an upper limit for the electronically nonadiabatic spin-orbit excitation cross section at a collision energy of 5.3kcal∕mol, which lies above the energy of the reaction barrier (4.9kcal∕mol). Our analysis and simulation of the experimental data determine an upper limit for the excitation cross section as σNA⩽0.012Å2. In the second part of this paper we investigate the propensity for electronically nonadiabatic spin-orbit quenching of Cl* following a collision with D2 or He. We perform these experiments at collision energies above and below the energy of the reaction barrier. By comparing the amount of scattered Cl* in our images to the amount of Cl* lost from the atomic beam we obtain the maximum cross section for electronically nonadiabatic quenching as σNA⩽15−15+44Å2 for a collision energy of 7.6kcal∕mol. Our experiments show the probability for electronically nonadiabatic quenching in Cl*+D2 to be indistinguishable to that for the kinematically identical system of Cl*+He.
Spatial scale-dependent tracer diffusion in bulk polycarbonate studied by holographic relaxation
Authors: Veniaminov A. , Sillescu H. , Bartsch E.
Published: April 2005

The diffusion of a photochromic dye tracer in polycarbonate was studied by a holographic relaxation technique (forced Rayleigh scattering) at temperatures close to the glass transition temperature. By varying the holographic grating period the results could be interpreted via the spatial scale dependence of apparent diffusion coefficients within a two-state diffusion model. This indicates inhomogeneities on the scale of a few micrometers in the polymer glass.
A growing string method for the reaction pathway defined by a Newton trajectory
Authors: Quapp Wolfgang
Published: April 2005

The reaction path is an important concept of theoretical chemistry. We use a projection operator for the following of the Newton trajectory (NT) along the reaction valley of the potential energy surface. We describe the numerical scheme for the string method, adapting the proposal of a growing string (GS) by [Peters et al.,J. Chem. Phys. 120, 7877 (2004)]. The combination of the Newton projector and the growing string idea is an improvement of both methods, and a great saving of the number of iterations needed to find the pathway over the saddle point. This combination GS-NT is at the best of our knowledge new. We employ two different corrector methods: first, the use of projected gradient steps, and second a conjugated gradient method, the CG+ method of Liu, Nocedal, and Waltz, generalized by projectors. The executed examples are Lennard-Jones clusters, LJ7 and LJ22, and an N-methyl-alanyl-acetamide (alanine dipeptide) rearrangement between the minima C7ax and C5. For the latter, the growing stŕing calculation is interfaced with the GASSIAN03 quantum chemical software package.
Validity of quasinormal approximation in turbulent channel flow
Authors: Vedula Prakash , Moser Robert D. , Zandonade Paulo S.
Published: April 2005

The validity of the quasinormal approximation, which relates the fourth-order velocity correlations to second-order velocity correlations, is tested using data obtained from direct numerical simulation (DNS) of turbulent channel flow at Reτ≈590. Results indicate that the quasinormal approximation is accurate throughout the channel except for a thin layer near the wall (y+<50), where the approximation breaks down for small separations (r+<200). Comparison to an analysis of the quasinormal approximation in isotropic turbulence indicates that except very near the wall, the quasinormal errors are of comparable magnitude in the channel and isotropic turbulence. This suggests that use of the quasinormal approximation in turbulence models such as EDQNM and optimal large eddy simulation (LES) will be comparably accurate in the channel at y+>50 as it is for isotropic turbulence. This study is motivated by the need to model fourth-order correlations in optimal LES. To evaluate the impact of errors like those observed on optimal LES models, an optimal LES model incorporating the quasinormal approximation was used in isotropic turbulence and the simulation results were compared to those from LES models based solely on DNS data. The use of the quasinormal approximation in our optimal LES model resulted in degradation of the high wavenumber spectrum, a sign of a somewhat reduced dissipation of the model. However, the results are sufficiently encouraging to warrant further development of LES models using the quasinormal approximation.
Time-resolved imaging of the reaction coordinate
Authors: Mabbs Richard , Pichugin Kostyantyn , Sanov Andrei
Published: April 2005

Time-resolved photoelectron imaging of negative ions is employed to study the dynamics along the reaction coordinate in the photodissociation of IBr−. The results are discussed in a side-by-side comparison with the dissociation of I2−, examined under similar experimental conditions. The I2− anion, extensively studied in the past, is used as a reference system for interpreting the IBr− results. The data provide rigorous dynamical tests of the anion electronic potentials. The evolution of the energetics revealed in the time-resolved (780 nm pump, 390 nm probe) I2− and IBr− photoelectron images is compared to the predictions of classical trajectory calculations, with the time-resolved photoelectron spectra modeled assuming a variety of neutral states accessed in the photodetachment. In light of good overall agreement of the experimental data with the theoretical predictions, the results are used to construct an experimental image of the IBr− dissociation potential as a function of the reaction coordinate.
Adsorption of carbon on Pd clusters of nanometer size: A first-principles theoretical study
Authors: Neyman Konstantin M. , Inntam Chan , Gordienko Alexei B. , Yudanov Ilya V. , Rösch Notker
Published: April 2005

Adsorbed atomic C species can be formed in the course of surface reactions and commonly decorate metal catalysts. We studied computationally C adsorption on Pd nanoclusters using an all-electron scalar relativistic density functional method. The metal particles under investigation, Pd55, Pd79, Pd85, Pd116, Pd140, and Pd146, were chosen as fragments of bulk Pd in the form of three-dimensional octahedral or cuboctahedral crystallites, exposing (111) and (100) facets as well as edge sites. These cluster models are shown to yield size-converged adsorption energies. We examined which surface sites of these clusters are preferentially occupied by adsorbed C. According to calculations, surface C atoms form strongly adsorbed carbide species (with adsorption energies of more than 600kJmol−1) bearing a significant negative charge. Surface sites allowing high, fourfold coordination of carbon are overall favored. To avoid effects of adsorbate-adsorbate interaction in the cluster models for carbon species in the vicinity of cluster edges, we reduced the local symmetry of selected adsorption complexes on the nanoclusters by lowering the global symmetry of the nanocluster models from point group Oh to D4h. On (111) facets, threefold hollow sites in the center are energetically preferred; adsorbed C is calculated to be slightly less stable when displaced to the facet borders.
Amide I vibrational circular dichroism of polypeptides: Generalized fragmentation approximation method
Authors: Choi Jun-Ho , Kim Joong-Soo , Cho Minhaeng
Published: April 2005

Fragment analyses of vibrational circular dichroic response of dipeptides were carried out recently [Choi and Cho, J. Chem. Phys. 120, 4383 (2004)]. In the present paper, by using a minimal size unit peptide containing two chiral carbons covalently bonded to the peptide group, a generalized fragmentation approximation method is discussed and applied to the calculations of infrared-absorption and vibrational circular dichroism (VCD) intensities of amide I vibrations in various secondary structure polypeptides. Unlike the dipole strength determining IR-absorption intensity, the rotational strength is largely determined by the cross terms that are given by the inner product between the transition electric dipole and the transition magnetic dipole of two different peptides. This explains why the signs and magnitudes of VCD peaks are far more sensitive to the relative orientation and distance between different peptide bonds in a given protein. In order to test the validity of fragmentation approximation, three different segments in a globular protein ubiquitin, i.e., right-handed α-helix, β-sheet, and β-turn regions, were chosen for density-functional theory (DFT) calculations of amide I vibrational properties and the numerically simulated IR-absorption and VCD spectra by using the fragmentation method are directly compared with DFT results. It is believed that the fragmentation approximation method will be of use in numerically simulating vibrational spectra of proteins in solutions.
Classical and quantum mechanical infrared echoes from resonantly coupled molecular vibrations
Authors: Noid W. G. , Loring Roger F.
Published: April 2005

The nonlinear response function associated with the infrared vibrational echo is calculated for a quantum mechanical model of resonantly coupled, anharmonic oscillators at zero temperature. The classical mechanical response function is determined from the quantum response function by setting ℏ→0, permitting the comparison of the effects of resonant vibrational coupling among an arbitrary number of anharmonic oscillators on quantum and classical vibrational echoes. The quantum response function displays a time dependence that reflects both anharmonicity and resonant coupling, while the classical response function depends on anharmonicity only through a time-independent amplitude, and shows a time dependence controlled only by the resonant coupling. In addition, the classical response function grows without bound in time, a phenomenon associated with the nonlinearity of classical mechanics, and absent in quantum mechanics. This unbounded growth was previously identified in the response function for a system without resonant vibrational energy transfer, and is observed to persist in the presence of resonant coupling among vibrations. Quantitative agreement between classical and quantum response functions is limited to a time scale of duration inversely proportional to the anharmonicity.
Photodissociation dynamics of N2O at 130 nm: The N2(AΣu+3,BΠg3)+O(PJ=2,1,3) channels
Authors: Witinski Mark F. , Ortiz-Suárez Marivi , Davis H. Floyd
Published: April 2005

Oxygen Rydberg time-of-flight spectroscopy was used to study the vacuum ultraviolet photodissociation dynamics of N2O near 130 nm. The O(PJ3) products were tagged by excitation to high-n Rydberg levels and subsequently field ionized at a detector. In agreement with previous work, we find that O(PJ3) formation following excitation to the repulsive N2O D(Σ+1) state produces the first two electronically excited states of the N2 counterfragment, N2(AΣu+3) and N2(BΠg3). The O(PJ3) translational energy distribution reveals that the overall branching ratio between N2(AΣu+3) and N2(BΠg3) formation is approximately 1.0:1.0 for J=1 and 2, with slightly less N2(BΠg3) produced in coincidence with O(P03). The angular distributions were found to be independent of J and highly anisotropic, with β=1.5±0.2.
Photodissociation channels for N2O near 130 nm studied by product imaging
Authors: Lambert H. M. , Davis E. W. , Tokel O. , Dixit A. A. , Houston P. L.
Published: April 2005

The photodissociation of N2O at wavelengths near 130 nm has been investigated by velocity-mapped product imaging. In all, five dissociation channels have been detected, leading to the following products: O(S1)+N2(XΣ1), N(D2)+NO(XΠ2), N(P2)+NO(XΠ2), O(P3)+N2(AΣ+u3), and O(P3)+N2(BΠg3). The most significant channel is to the products O(S1)+N2(XΣ1), with strong vibrational excitation in the N2. The O(P3)+N2(A,B):N(D2,P2)+NO branching ratio is measured to be 1.4±0.5, while the N2(A)+O(PJ3):N2(B)+O(PJ3) branching ratio is determined to be 0.84±0.09. The spin-orbit distributions for the O(PJ3), N(PJ2), and N(DJ2) products were also determined. The angular distributions of the products are in qualitative agreement with excitation to the N2O(D̃Σ+1) state, with participation as well by the Πv3 state.
Ultrashort-pulse laser plasmas: Fraction of hot electrons escaping from the target and electron spectra in planar and spherical geometry
Authors: Fill Ernst E.
Published: April 2005

Hot electrons generated upon interaction of ultrashort, intense laser pulses with solid targets have many applications in various fields of physics. In this paper a simple theory is developed which allows calculation of the fraction of electrons which escape from the target and the altered electron energy distribution at a distance from the target. The theory is worked out in planar and spherical geometry. It is exact if the electrons are instantaneously generated. In planar geometry all particles eventually return to the target. In spherical geometry, however, a fraction of the electrons are found to escape and, moreover, the electron energy spectrum at large distances approaches an asymptotical one. Two examples of initial electron distributions are treated in detail, viz., an exponential and a Lorentzian distribution.
Electron-wall interaction in Hall thrusters
Authors: Raitses Y. , Staack D. , Keidar M. , Fisch N. J.
Published: April 2005

Electron-wall interaction effects in Hall thrusters are studied through measurements of the plasma response to variations of the thruster channel width and the discharge voltage. The discharge voltage threshold is shown to separate two thruster regimes. Below this threshold, the electron energy gain is constant in the acceleration region and therefore, secondary electron emission (SEE) from the channel walls is insufficient to enhance electron energy losses at the channel walls. Above this voltage threshold, the maximum electron temperature saturates. This result seemingly agrees with predictions of the temperature saturation, which recent Hall thruster models explain as a transition to space-charge saturated regime of the near-wall sheath. However, in the experiment, the maximum saturation temperature exceeds by almost three times the critical value estimated under the assumption of a Maxwellian electron energy distribution function. The channel narrowing, which should also enhance electron-wall collisions, causes unexpectedly larger changes of the plasma potential distribution than does the increase of the electron temperature with the discharge voltage. An enhanced anomalous crossed-field mobility (near wall or Bohm-type) is suggested by a hydrodynamic model as an explanation to the reduced electric field measured inside a narrow channel. We found, however, no experimental evidence of a coupling between the maximum electron temperature and the location of the accelerating voltage drop, which might have been expected due to the SEE-induced near-wall conductivity.
Structures and electrical properties of Bi5FeTi3O15 thin films
Authors: Zhang Shan-Tao , Chen Yan-Feng , Liu Zhi-Guo , Ming Nai-Ben , Wang Jia , Cheng Guang-Xu
Published: April 2005

Thin films of layered ferroelectric oxide Bi5FeTi3O15 have been fabricated on Pt-coated Si substrates by pulsed laser deposition. Temperature-dependent Raman studies reveal the phase-transition temperature of 550 °C, consistent with other reports. A new mode at 685cm−1 is observed and ascribed to the Bi–Fe–O perovskite block. With an applied field of 105kV∕cm, the leakage current density is 5.2×10−7A∕cm2, indicating the high room-temperature resistivity in the order of 1012Ωcm. With an applied external electric field of 210kV∕cm, the remnant polarization and coercive field of the films are measured to be 6.4μC∕cm2 and 112kV∕cm, respectively. The nonvolatile polarization of the films decreases about 15% of the initial value after 7.2×109 switching cycles. As for the dielectric properties, at 0.1 MHz, the measured dielectric constant and loss tangent are 172 and 0.024, respectively. The ferroelectric properties are comparable with that of other Bi-layered oxides, such as rare-earth substituted Bi4Ti3O12 films, which are promising candidates for application in ferroelectric memory.
Electron Bernstein wave-bootstrap current synergy in the National Spherical Torus Experiment
Authors: Harvey R. W. , Taylor G.
Published: April 2005

Current driven by electron Bernstein waves (EBW) and by the electron bootstrap effect are calculated separately and concurrently with a kinetic code to determine the degree of synergy between them. A target β=40% NSTX [M. Ono, S. Kaye, M. Peng et al., Proceedings of the 17th IAEA Fusion Energy Conference, edited by M. Spak (IAEA, Vienna, Austria, 1999), Vol. 3, p. 1135] plasma is examined. A simple bootstrap model in the collisional-quasilinear CQL3D Fokker–Planck code (National Technical Information Service document No. DE93002962) is used in these studies: the transiting electron distributions are connected in velocity space at the trapped-passing boundary to trapped-electron distributions that are displaced radially by a half-banana-width outwards/inwards for the co-passing/counter-passing regions. This model agrees well with standard bootstrap current calculations over the outer 60% of the plasma radius. Relatively small synergy net bootstrap current is obtained for EBW power up to 4 MW. Locally, bootstrap current density increases in proportion to increased plasma pressure, and this effect can significantly affect the radial profile of driven current.
The origin of the long time correlations of the density fluctuations in the scrape-off layer of the Tore Supra Tokamak
Authors: Devynck P. , Ghendrih P. , Sarazin Y.
Published: April 2005

It is shown that intermittent density bursts observed in the scrape-off layer of Tore Supra [J. Jacquinot, Nucl. Fusion 43, 1583 (2003)] are detected in packs on the probe. In such a pack, typically two to three bursts are separated by time intervals smaller than the mean separation time. The long tails above 50μs observed on the autocorrelation function of the density fluctuations are found to be the temporal correlation between the individual bursts within their pack. Packs of density bursts can be detected in two limiting states of the turbulence: when the coupling between density and potential is strong and large density bursts split during their radial propagation or at the opposite when the coupling is weak so that different density bursts can propagate radially along the potential valleys. The lack of spatial resolution of the diagnostic does not allow to discriminate between the two mechanisms.
Rear surface spallation on single-crystal silicon in nanosecond laser micromachining
Authors: Ren Jun , Orlov Sergei S. , Hesselink Lambertus
Published: April 2005

Rear surface spallation of single-crystal silicon under 5-ns laser pulse ablation at intensities of 0.6–60GW∕cm2 is studied through postablation examination of the ablated samples. The spallation threshold energy and the spallation depth’s dependences on the energy and target thickness are measured. From the linear relation between the spallation threshold energy and the target thickness, an estimation of the material spall strength around 1.4GPa is obtained, in reasonable agreement with the spall strength estimation of 0.8–1.2GPa at a strain rate of 107s−1 using Grady’s model for brittle materials. The experiment reveals the internal fracturing process over an extended zone in silicon, which is controlled by the competition between the shock pressure load and the laser ablation rate. The qualities of the laser microstructuring and micromachining results are greatly improved by using an acoustic impedance matching approach.
Energy distribution of gap states in hydrogenated amorphous silicon by post-transit photocurrent spectroscopy: Validity of an indium-tin oxide/silicon oxide double-layer gate
Authors: Sakata I. , Yamanaka M.
Published: April 2005

Reduction of junction leakage currents is important to exactly obtain the energy distribution of gap states in hydrogenated amorphous silicon (a-Si:H) by post-transit photocurrent spectroscopy (PTPS). A double-layer transparent conducting gate composed of indium-tin-oxide (ITO) and silicon oxide (SiOx) is an effective means for this purpose in Schottky barrier (SB) diodes. However, there has been some concern that the presence of the SiOx layer could affect the PTPS results. We demonstrate from careful experimental studies that the insertion of the SiOx layer between ITO and a-Si:H does not give any additional structure in the energy distribution of gap states of a-Si:H measured by PTPS and the SB diodes with the ITO–SiOx double-layer gate are suited for exact PTPS measurements.
Viscosity of liquid undercooled tungsten
Authors: Paradis Paul-François , Ishikawa Takehiko , Yoda Shinichi
Published: April 2005

Knowledge of the viscosity and its temperature dependence is essential to improve metallurgical processes as well as to validate theoretical and empirical models of liquid metals. However, data for metals with melting points above 2504K could not be determined yet due to contamination and containment problems. Here we report the viscosity of tungsten, the highest melting point metal (3695K), measured by a levitation technique. Over the 3350–3700-K temperature range, which includes the undercooled region by 345K, the viscosity data could be fitted as η(T)=0.108exp[1.28×105∕(RT)](mPas). At the melting point, the datum agrees with the proposed theoretical and empirical models of liquid metals but presents atypical temperature dependence, suggesting a basic change in the mechanism of momentum transfer.
Determining quantum eigenfunctions in three-dimensional nanoscale structures
Authors: Sullivan Dennis M. , Citrin D. S.
Published: April 2005

As semiconductor devices become ever smaller, their behavior is more likely to be determined by quantum mechanics than by classical physics. The starting point for the analysis of most nanoscale devices is the determination of the eigenstates and eigenfunctions of the structure. We present a method to solve the time-dependent Schrödinger equation that is capable of determining the eigenenergies and eigenfunctions of arbitrary three-dimensional nanostructures. The heart of this method is a formulation of the time-dependent Schrödinger equation into the finite-difference time-domain method. No approximations are made except the finite differencing of the derivatives for implementation in a computer.
Structural modulation on multilayered bismuth cuprate observed by x-ray reciprocal space mapping
Authors: Kaneko Satoru , Akiyama Kensuke , Shimizu Yoshitada , Yuasa Hiroyasu , Hirabayashi Yasuo , Ohya Seishiro , Saito Keisuke , Funakubo Hiroshi , Yoshimoto Mamoru
Published: April 2005

Epitaxial Bi2Sr2Ca1Cu2Ox(Bi-2212)∕Bi2Sr2Cu1Ox(Bi-2201) multilayer was investigated by x-ray diffraction methods in order to investigate the effect of internal strain on structural modulation. In multilayered structure, the effect of internal strain is more prominent than in an aliovalent substitution, such as a substitution of La3+ for Sr2+. X-ray reciprocal space mapping (XRSM) was taken on the ω-2θ plane (cross-section XRSM) in order to estimate the lattice constants along the in-plane and out-of-plane directions, and θ-2θ scan was used to verify the multilayered structure. Another XRSM method, plan-view XRSM, was employed to verify the in-plane symmetry of structural modulation on the ω-ψ plane. The structural modulation was observed on both the cross-section and plan-view XRSM. The lattice constants together with the modulation vector in multilayer were varied by the multilayer periods without any substitution in the original structure.
Wave propagation in vortices and vortex bursting
Authors: Moet H. , Laporte F. , Chevalier G. , Poinsot T.
Published: April 2005

The propagation of pressure waves in a Lamb–Oseen vortex has been investigated both by three-dimensional direct numerical simulations as well as a set of large-eddy simulations. The pressure wave is initiated by locally increasing the core radius of a Lamb–Oseen vortex at its edge. This wave travels along the vortex axis towards the region with a thinner core radius. Behind the wave the axial velocity increases so that sufficient swirl may trigger the helical instability. An abrupt change of flow structure in the vortex core is observed in the case of intersecting pressure waves: this phenomenon is known as vortex bursting. A vortex system composed of two symmetric counter-rotating vortices, which is similar to that of an aircraft has also been investigated by means of large-eddy simulations. In the far-field region the system develops linear instabilities such as the Crow instability, which is characterized by a large-scale symmetric sinusoidal deformation resulting in the reconnection of the two vortices. It also demonstrates the occurrence of helical instability and vortex bursting.
Thermal energy He3 spin-echo spectrometer for ultrahigh resolution surface dynamics measurements
Authors: Fouquet P. , Jardine A. P. , Dworski S. , Alexandrowicz G. , Allison W. , Ellis J.
Published: April 2005

We present details of a He3 spin-echo spectrometer, designed to make possible a wide range of new surface dynamics measurements. The apparatus operates at beam energy of 8meV, sufficiently high to enable processes such as surface Bragg diffraction and permit inelastic and quasielastic scattering measurements at up to momentum transfers of about 4Å−1. We describe the requirements for the machine, details of the major components used to fulfil these requirements, and the performance of the overall spectrometer. The machine can access a Fourier time range of 0.01ps–1ns, and yields a resolution of 3μeV for inelastic spectrum reconstruction, although under favorable circumstances quasielastic broadenings as narrow as 20neV can be resolved, allowing correspondingly slower processes to be studied.
Implosion hydrodynamics of fast ignition targets
Authors: Stephens R. B. , Hatchett S. P. , Tabak M. , Stoeckl C. , Shiraga H. , Fujioka S. , Bonino M. , Nikroo A. , Petrasso R. , Sangster T. C. , Smith J. , Tanaka K. A.
Published: April 2005

The fast ignition (FI) concept requires the generation of a compact, dense, pure fuel mass accessible to an external ignition source. The current base line FI target is a shell fitted with a reentrant cone extending to near its center. Conventional direct- or indirect-drive collapses the shell near the tip of the cone and then an ultraintense laser pulse focused to the inside cone tip generates high-energy electrons to ignite the dense fuel. A theoretical and experimental investigation was undertaken of the collapse of such targets, validating modeling, and exploring the trade-offs available, in such an asymmetric geometry, to optimize compaction of the fuel and maintain the integrity of the cone. The collapse is complex. Away from the cone, the shell collapses much as does a conventional implosion, generating a hot, low-density inner core. But because of the open side, hot plasma exhausts out toward the tip of the cone. This hot plasma is advantageous for implosion diagnostics; it can provide protons for angular dependent measurements of the shell wall, neutrons for temperature measurements, and self-emission for contamination measurements. But for FI it is a liability; the hot, low-density inner core impedes the compaction of the cold fuel, lowering the implosion/burn efficiency and the gain. Approaches to optimizing this shell design are discussed.
Keto defect sites in fluorene-based organic field-effect transistors: The origin of rapid degradation on the performance of the device
Authors: Noh Yong-Young , Kim Dong-Yu , Yoshida Yuji , Yase Kiyoshi , Jung Byung-Jun , Lim Eunhee , Shim Hong-Ku , Azumi Reiko
Published: April 2005

The effect of keto defects in fluorene units on the performance of organic field-effect transistors (OFETs) was examined based on fluorene end-capped fused bithiophenes (BFTT) and biphenyl end-capped fused bithiophene oligomers (BPTT). The formation of keto defects after various periods of UV illumination in air on BFTT films was confirmed by the increase of the long-wavelength emission at 2.1–2.3eV in the photoluminescent (PL) spectrum and the generation of a Fourier transfer infrared (FTIR) peak at 1721cm−1, corresponding to the carbonyl stretching mode of the fluorenone moiety. For both BPTT films irradiated in air and BFTT in nitrogen, i.e., a keto-free system, no increase in long-wavelength emission in the PL spectrum, was found and the peak corresponding to the carbonyl stretching mode of the fluorenone moiety was absent in the FTIR spectrum. The threshold voltage, i.e., switch-on voltage, of the OFETs was increased and the field-effect mobility and on-state drain current were rapidly decreased after the formation of ketonic defects, since these defects induce the formation of numerous trap sites in the band gap of the semiconducting conjugated oligomer. The density of trap sites (Nt) generated after the formation of keto defects was determined using space-charge-limited current spectroscopy. A Nt of around 2.7×1015cm−3 was found for the BFTT film due to the formation of keto defects after 6h of UV irradiation.
Role of thermal instabilities and anomalous transport in threshold of detachment and multifacetted asymmetric radiation from the edge (MARFE)
Authors: Tokar M. Z. , Kelly F. A. , Loozen X.
Published: April 2005

A model for the plasma edge in limiter tokamaks is elaborated, which permits us to investigate the synergy of impurity radiation, particle recycling, and edge turbulence phenomena in the formation of large-scale structures, in particular, of multifacetted asymmetric radiation from the edge. The model includes a description for the anomalous transport of charged particles induced by drift microinstabilities most typical under edge conditions. Computations show that the pattern of structures, developing when a critical plasma density is approached, is essentially determined by the poloidal inhomogeneities introduced from the Shafranov shift of magnetic surfaces and from the ballooning character of edge turbulence.
Temperature-dependent Fowler–Nordheim tunneling and a compensation effect in anodized Al-Al2O3-Au diodes
Authors: Hickmott T. W.
Published: April 2005

Current-voltage (I–V) curves of Al-Al2O3-Au diodes with anodized Al2O3 thicknesses between 12 and 54nm have been measured between 100 and 320K. Diodes are rectifying at 300K. There is a marked decrease in rectification of I–V curves as temperature decreases from 300to100K. Part of the decrease is due to a decrease in current when Au is positive (applied voltage VA>0V); part of the decrease is due to an increase in current for VA<0V as temperature decreases. A reversal of the rectification direction has been observed at 100K. I–V curves for increasing VA>0V are affected by the polarization of the diode by a negative voltage. I–V curves for decreasing VA are independent of previous history and are due to Fowler–Nordheim tunneling, J=CF2exp(−B∕F). Values of B and C are temperature dependent. B is used to obtain an effective barrier height for tunneling, ϕE. ϕE increases from ∼1.5to∼2.5eV as temperature decreases from 300to100K for VA>0V. For VA<0V, ϕE∼2.3eV at 100K and increases to ∼2.8eV at 160K, except for the diode with 12nm of Al2O3. There is a relation between B and C lnC=r+sB, where r and s are constants, which is analogous to a compensation effect or Meyer–Neldel relation for data that obey an Arrhenius equation. A model is proposed in which the tunnel barrier is determined by an impurity band in Al2O3.
Progress in the kinetic theory of electrostatic harmonics of plasma waves
Authors: Yoon Peter H.
Published: April 2005

This paper performs numerical analysis to verify the theoretical predictions of Yoon [“Effects of spontaneous fluctuations in the generalized weak turbulence theory,” Phys. PlasmasPHPAEN 12, 042306 (2005)], according to which the higher harmonics of the electron plasma frequency, generated during the course of electron beam-plasma interaction start to grow initially with fast quasilinear growth rate, which is roughly n times higher than the fundamental Langmuir mode growth rate, n being the harmonic number, but the rapid initial growth soon slows down to the level of fundamental mode growth rate. It is also shown that when the initial wave levels for the harmonics are relatively high, then the overall dynamics is largely dictated by the slow nonlinear growth rate, but when the initial wave levels associated with the harmonic components are artificially suppressed, then the fast quasilinear growth stage is prolonged.