bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the oxygen 18 concentration in precipitation with ambient climatic and geographic parameters
Authors: Liebminger Andreas , Haberhauer Georg , Varmuza Kurt , Papesch Wolfgang , Heiss Gerhard
Published: March 2006

Recent exploratory analysis of a data set from the Austrian Network of Isotopes in Precipitation (ANIP) together with climatic data revealed significant correlations between isotopic compositions in precipitation and climatic conditions (A. Liebminger et al., 2006). Based on these results multivariate models have been developed in order to predict the oxygen 18 concentration from local climatic and geographic parameters. The best two models are applied to 201 new locations for which long term climatic and geographic parameters are available. The resulting modeled oxygen 18 values exhibit good compliance with known correlations of oxygen 18 with temperature and altitude. Isotope distribution charts lead to a reasonable picture of the distribution of oxygen 18 in Austrian precipitation.
Formation of HNO3 and NO3− in the anthropogenically‐influenced eastern Mediterranean marine boundary layer
Authors: Vrekoussis M. , Liakakou E. , Mihalopoulos N. , Kanakidou M. , Crutzen P. J. , Lelieveld J.
Published: March 2006

To investigate the seasonal behaviour of nitrate radicals (NO3) as a source of nitric acid (HNO3) and particulate nitrate (NO3−) in the eastern Mediterranean atmosphere, we conducted NO3 measurements on the island of Crete for more than two years. Ancillary measurements of chemical compounds and meteorological parameters were used to analyse the observations. Nighttime production of HNO3 plus NO3−, as initiated by NO3 radicals, accounts for about 50–65% of the total production rate depending on season. The remainder is produced by the hydroxyl radical (OH) reaction with nitrogen dioxide during daytime. On a yearly mean basis, about 17% of the HNO3 plus NO3− formation results from the reaction of NO3 radicals with dimethylsulfide of marine origin. This shows important interactions between biogenic and anthropogenic compounds contributing to nutrient deposition to the sea.
A new method to determine depth‐dependent carbon export fluxes using vertical 230Th profiles
Authors: Hirose Katsumi
Published: March 2006

Because of their particle‐reactive properties, radiogenic thorium isotopes in oceanic waters have been used in studies for the particle removal processes. In particular, 234Th has extensively been utilized to determine the carbon export flux from the euphotic zone. On the other hand, 230Th in seawater has so far mainly provided information on residence times, settling velocities and adsorption‐desorption rates of 230Th in the water column. Here we introduce a new model to calculate the carbon export flux from vertical 230Th profiles. According to this model, the carbon export flux is directly related to the POC/230Th ratio in sinking or suspended particulate matter. The carbon export flux can be directly calculated from vertical profiles of POC and particulate 230Th, which should become an effective means to constrain ocean biogeochemical models.
Monsoon forcing, hydrodynamics of the Kuroshio Current, and tectonic effects on sedimentary carbon and sulfur cycling in the Okinawa Trough since 90 ka
Authors: Kao S. J. , Roberts A. P. , Hsu S. C. , Chang Y. P. , Lyons W. B. , Chen M. T.
Published: March 2006

Monsoon forcing and hydrodynamic effects controlled carbon and sulfur biogeochemistry over the last 90 ka in a 43‐m core from the Okinawa Trough (OT). Total organic carbon (TOC) contents co‐vary with summer insolation at 30°N suggesting monsoon forcing of primary productivity and organic carbon burial. Before the last glacial maximum (LGM), total sulfur (TS) contents varied concomitantly with TOC. However, sea level rise and intensified Kuroshio inflow during the Holocene enhanced deepwater ventilation, which resulted in TS‐depleted sediments with low degree of pyritization (DOP). By contrast, DOP values were high during the previous highstand (at ∼80 ka BP), when sea level was similar to that in the Holocene, as well as during the LGM when deepwater circulation was relatively weak. A topographic barrier is proposed to have sufficiently blocked the Kuroshio Current out of the OT during the previous sea level highstand, which weakened deepwater ventilation and led to reducing diagenetic conditions. Tectonic rifting in the southern OT at 60‐30 ka BP enabled the major change in hydrodynamics and sediment biogeochemistry.
Isotopic constraints on non‐photochemical sulfate production in the Arctic winter
Authors: McCabe Justin R. , Savarino Joel , Alexander Becky , Gong Sunling , Thiemens Mark H.
Published: March 2006

The oxygen isotopic composition (Δ17O) of non‐seasalt sulfate (NSS) aerosol was measured in samples from Alert, Canada over one year (July 1999–June 2000) and used to quantify the S(IV) oxidants. Measurements of Δ17O in NSS are used to evaluate the relative contributions of O3, H2O2, and OH oxidation leading to the formation of SO42− compared to a model of Feichter et al. (1996). The isotopic values suggest that there is a twofold overestimate of ozone oxidation in the model during winter. The isotopic composition is consistent with 10 to 18% contribution from a non‐photochemical oxidation pathway, likely Fe3+/Mn2+‐catalyzed O2 oxidation, during the dark Arctic winter. Isotopic evidence also invokes a 3 to 10% contribution of a mass dependent oxidant during springtime Arctic ozone depletion events.
Magnitude determination using initial P waves: A single‐station approach
Authors: Wu Yih‐Min , Yen Hsin‐Yi , Zhao Li , Huang Bor‐Shouh , Liang Wen‐Tzong
Published: March 2006

Prompted by recent success in the research and application of earthquake early warning systems, we conducted an investigation into the relationship between the magnitudes of earthquakes and the properties of the first three seconds of the P waves at a single station. Using waveforms at station NACB of the Broadband Array in Taiwan for Seismology from 46 earthquakes within 100‐km epicentral distance, we found a linear correlation between the magnitudes and the logarithmic characteristic periods of the initial P waves for earthquakes up to magnitude 6.5. We also detected a deterministic relationship between the magnitudes and the peak amplitudes of the initial P waves for earthquakes of magnitude M < 6.5. While further study needs to be done on the behavior of the initial P‐wave peak amplitudes from larger earthquakes, we propose here that the characteristic periods and peak amplitudes of the first three seconds of the P waves be used jointly in onsite (single‐station) earthquake early warning operations.
Phenomenological solar contribution to the 1900–2000 global surface warming
Authors: Scafetta N. , West B. J.
Published: March 2006

We study the role of solar forcing on global surface temperature during four periods of the industrial era (1900–2000, 1900–1950, 1950–2000 and 1980–2000) by using a sun‐climate coupling model based on four scale‐dependent empirical climate sensitive parameters to solar variations. We use two alternative total solar irradiance satellite composites, ACRIM and PMOD, and a total solar irradiance proxy reconstruction. We estimate that the sun contributed as much as 45–50% of the 1900–2000 global warming, and 25–35% of the 1980–2000 global warming. These results, while confirming that anthropogenic‐added climate forcing might have progressively played a dominant role in climate change during the last century, also suggest that the solar impact on climate change during the same period is significantly stronger than what some theoretical models have predicted.
Spatiotemporal filtering using principal component analysis and Karhunen‐Loeve expansion approaches for regional GPS network analysis
Authors: Dong D. , Fang P. , Bock Y. , Webb F. , Prawirodirdjo L. , Kedar S. , Jamason P.
Published: March 2006

Spatial filtering is an effective way to improve the precision of coordinate time series for regional GPS networks by reducing so‐called common mode errors, thereby providing better resolution for detecting weak or transient deformation signals. The commonly used approach to regional filtering assumes that the common mode error is spatially uniform, which is a good approximation for networks of hundreds of kilometers extent, but breaks down as the spatial extent increases. A more rigorous approach should remove the assumption of spatially uniform distribution and let the data themselves reveal the spatial distribution of the common mode error. The principal component analysis (PCA) and the Karhunen‐Loeve expansion (KLE) both decompose network time series into a set of temporally varying modes and their spatial responses. Therefore they provide a mathematical framework to perform spatiotemporal filtering. We apply the combination of PCA and KLE to daily station coordinate time series of the Southern California Integrated GPS Network (SCIGN) for the period 2000 to 2004. We demonstrate that spatially and temporally correlated common mode errors are the dominant error source in daily GPS solutions. The spatial characteristics of the common mode errors are close to uniform for all east, north, and vertical components, which implies a very long wavelength source for the common mode errors, compared to the spatial extent of the GPS network in southern California. Furthermore, the common mode errors exhibit temporally nonrandom patterns.
Global stratospheric HOCl distributions retrieved from infrared limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)
Authors: von Clarmann T. , Glatthor N. , Grabowski U. , Höpfner M. , Kellmann S. , Linden A. , Mengistu Tsidu Gizaw , Milz M. , Steck T. , Stiller G. P. , Fischer H. , Funke B.
Published: March 2006

Vertical profiles of stratospheric HOCl were retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aboard the Envisat research satellite. These are the first HOCl measurements with global coverage. The ν2 transitions between 1215.725 and 1275.550 cm−1 were used for inference of the vertical profiles. The maximal volume mixing ratios were found in the tropics at altitudes of ∼35 km (daytime) and ∼37 km (nighttime), with values up to 0.22 ppbv and 0.23 ppbv for zonal mean values at 5° latitude binning. The peak altitude of nonpolar nighttime measurements is on average higher by 2.4 ± 0.3 km compared to nonpolar daytime measurements and higher by 2.2 ± 0.3 km at high latitudes poleward of ±45° compared to respective equatorward latitudes. The diurnal variability is largest at 30°S at 46 km altitude, reaching amplitudes of 0.11 ppbv. In the Antarctic a secondary peak at 23–25 km (0.14 ppbv) was found on 19–24 September 2002, which is attributed to heterogeneous chemistry. An estimated single‐profile precision of 0.03–0.08 ppbv could be achieved at an altitude resolution of 9 km in an altitude range between 20 and 50 km. Taking the trend into account, these measurements are reasonably consistent with former far‐infrared measurements.
Coupling aerosol size distributions and size‐resolved hygroscopicity to predict humidity‐dependent optical properties and cloud condensation nuclei spectra
Authors: Gasparini Roberto , Collins Don R. , Andrews Elisabeth , Sheridan Patrick J. , Ogren John A. , Hudson James G.
Published: March 2006

Aerosol size distributions and size‐resolved hygroscopicity were measured with a Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) system during the May 2003 Atmospheric Radiation Measurement Program (ARM) Aerosol Intensive Operational Period (IOP) at a rural site in northern Oklahoma. Size and hygroscopicity information were combined in order to model the aerosol as a population of multicomponent particles, each consisting of organic carbon, elemental carbon, mineral dust, ammonium sulfate, and water, or some subset of these components. Comparisons of both derived optical properties and derived cloud condensation nuclei (CCN) spectra with direct measurements are used to provide independent validation of this multicomponent aerosol model. The aerosol hygroscopic growth factor, f(RH), relating total submicron scattering at high relative humidity to that at low relative humidity, is predicted with this aerosol model. The f(RH) values computed using measurements made with the Aerosol Observing System are closer to those predicted when the hygroscopic fraction of the aerosol is assumed to be in the metastable state than to those values predicted assuming the aerosol is crystalline. Overpredictions of f(RH) are generally limited to the measured f(RH) plus 0.15 over the RH range from 40 to 80% RH. Underpredictions are enhanced at RH greater than ∼65%, suggesting underestimation of the increase in scattering enhancement with increasing RH. The multicomponent aerosol model is also used to predict the cumulative and differential critical supersaturation distributions of the aerosol population. The resulting derived CCN spectra are compared to spectra measured directly with two Desert Research Institute (DRI) CCN spectrometers. Among the 1490 pairs of DMA/TDMA‐predicted and DRI‐measured CCN concentrations at various critical supersaturations from 0.02–1.05%, the sample number‐weighted mean R2 value for the linear regressions is 0.74. CCN concentrations are slightly overpredicted at both the lowest (0.02–0.04%) and highest (0.80–1.05%) supersaturations measured. Overall, the multicomponent aerosol model based on the measurements of size distributions and size‐resolved hygroscopicity yields reasonable predictions of the humidity‐dependent optical properties and of the CCN spectra of the aerosol.
New Satellite Will Forecast Ionospheric Disturbances
Authors: Hunton Donald , Retterer John M. , Jeong Laila , Kelley Michael C. , de la Beaujardiére Odile
Published: March 2006

Low‐latitude ionospheric irregularities have a detrimental effect on the performance of communications, navigation, and surveillance systems. A satellite will be launched in an equatorial orbit to predict when and where these irregularities will occur. Sophisticated models will use data from the satellite and from numerous ground‐based ionospheric measurements to produce a real‐time forecast of the global ionosphere and the irregularities within.
18FDG PET in Vascular Dementia: Differentiation from Alzheimer's Disease Using Voxel-Based Multivariate Analysis
Authors: Kerrouche Nacer , Herholz Karl , Mielke Rüdiger , Holthoff Vjera , Baron Jean-Claude
Published: March 2006

The brain metabolic pattern of vascular dementia (VaD) remains poorly characterized. Univariate voxel-based analysis ignores the functional correlations among structures and may lack sensitivity and specificity. Here, we applied a novel voxel-based multivariate technique to a large (18F)2-fluoro-2-deoxy-D-glucose positron emission tomography data set. The sample consisted of 153 subjects, one-third each being probable subcortical VaD, probable Alzheimer disease (AD) (matched for Mini-Mental-State examination (MMSE) and age), and normal controls (NCs). We first applied principal component (PC) analysis and removed PCs significantly correlated to age. The remainders were used as feature vectors in a canonical variate analysis to generate canonical variates (CVs), that is, linear combinations of PC-scores. The first two CVs efficiently separated the groups. CV1 separated VaD from AD with 100% accuracy, whereas CV2 separated NC from demented subjects with 72% sensitivity and 96% specificity. Images depicting CV1 and CV2 showed that lower metabolism differentiating VaD from AD mainly concerned the deep gray nuclei, cerebellum, primary cortices, middle temporal gyrus, and anterior cingulate gyrus, whereas lower metabolism in AD versus VaD concerned mainly the hippocampal region and orbitofrontal, posterior cingulate, and posterior parietal cortices. The hypometabolic pattern common to VaD and AD mainly concerned the posterior parietal, precuneus, posterior cingulate, prefrontal, and anterior hippocampal regions, and linearly correlated with the MMSE. This study shows the potential of voxel-based multivariate methods to highlight independent functional networks in dementing diseases. By maximizing the separation between groups, this method extracted a metabolic pattern that efficiently differentiated VaD and AD.
Bench to Bedside: The Quest for Quality in Experimental Stroke Research
Authors: Dirnagl Ulrich
Published: March 2006

Over the past decades, great progress has been made in clinical as well as experimental stroke research. Disappointingly, however, hundreds of clinical trials testing neuroprotective agents have failed despite efficacy in experimental models. Recently, several systematic reviews have exposed a number of important deficits in the quality of preclinical stroke research. Many of the issues raised in these reviews are not specific to experimental stroke research, but apply to studies of animal models of disease in general. It is the aim of this article to review some quality-related sources of bias with a particular focus on experimental stroke research. Weaknesses discussed include, among others, low statistical power and hence reproducibility, defects in statistical analysis, lack of blinding and randomization, lack of quality-control mechanisms, deficiencies in reporting, and negative publication bias. Although quantitative evidence for quality problems at present is restricted to preclinical stroke research, to spur discussion and in the hope that they will be exposed to meta-analysis in the near future, I have also included some quality-related sources of bias, which have not been systematically studied. Importantly, these may be also relevant to mechanism-driven basic stroke research. I propose that by a number of rather simple measures reproducibility of experimental results, as well as the step from bench to bedside in stroke research may be made more successful. However, the ultimate proof for this has to await successful phase III stroke trials, which were built on basic research conforming to the criteria as put forward in this article.
Optimizing C4+ and C5+ beams of the Kei2 electron cyclotron resonance ion source using a special gas-mixing technique
Authors: Drentje A. G. , Muramatsu M. , Kitagawa A.
Published: March 2006

With the prototype electron cyclotron resonance ion source for the next carbon therapy facility in Japan a series of measurements has been performed in order (a) to find the best condition for producing high beam currents of C4+ ions, and (b) to study the effect of “special” gas mixing by using a chemical compound as a feed gas. The effect would then appear as an increase in high charge state production in this case of C5+ ions. In “regular” gas-mixing experiments it is well known that an isotopic phenomenon occurs: a heavier isotope of the mixing gas is increasing the production of high charge states of the beam gas ions. A similar isotopic effect has been found in the present experiment: with deuterated methane (CD4 gas) the C5+ beam currents are about 10% higher than with regular methane (CH4 gas). The “mixing-gas” ratio D (or H) to C can be decreased by choosing, e.g., butane gas; in this case the isotopic effect for C5+ production is even stronger (>15%). For production of C4+ ions the isotopic effect appears to be absent. Clearly this is related to the much easier production. It turns out that the relative amount of carbon is much more important: butane gives about 10% higher C4+-ion currents than methane.
Viscoelastic effects on early stage of spinodal decomposition in dynamically asymmetric polymer blends
Authors: Takenaka Mikihito , Takeno Hiroyuki , Hashimoto Takeji , Nagao Michihiro
Published: March 2006

Spinodal decomposition induced by a rapid pressure change was investigated for a dynamically asymmetric polymer blend [deuterated polybutadiene (DPB)/polyisoprene (PI)] with a composition of 50∕50wt∕wt by using time-resolved small angle neutron scattering. The time change in the scattered intensity distribution with wave number (q) during the spinodal decomposition was found to be approximated by the Doi-Onuki theory [M. Doi and A. Onuki, J. Phys. II 2, 1631 (1992)]. The theoretical analysis yielded the q dependence of the Onsager kinetic coefficient which is characterized by the q−2 dependence at qξve>1 with the characteristic length ξve being much larger than the radius of gyration of DPB or PI. The estimated ξve agrees well with that obtained previously in the relaxation processes induced by pressure change within the one phase region for the same blend.
Negative-ion yield in low-pressure radio frequency discharges in hydrogen: Particle modeling and vibrational kinetics
Authors: Diomede P. , Longo S. , Capitelli M.
Published: March 2006

A theoretical study of the complex interplay between the vibrational kinetics and the plasma dynamics in low-pressure hydrogen plasmas produced by radio frequency discharges is performed. The study is realized by means of a one-dimensional particle model with five species (e, H+, H2+, H3+, and H−) while the vibrational/dissociation kinetics is based on a continuum model and the two are self-consistently coupled. In particular, we analyze the influence of pressure.
Investigation of multiaxis molecular motion by off-magic angle spinning deuteron NMR
Authors: Huang Yuanyuan , Vold Robert L. , Hoatson Gina L.
Published: March 2006

The relatively new deuteron NMR method of off-axis-magic angle spinning (OMAS) has been extended and used to investigate multiaxis rotational jump motion. Floquet theory is developed for simulating deuteron OMAS spectra with multisite jumps at different rates about noncoincident axes, and efficient procedures are presented for computing the sideband line shapes. It is demonstrated experimentally that reproducible adjustment of the angle between the rotor axis and the static magnetic field is feasible with precision approaching ±0.01°. This leads to the reintroduction of a scaled, first-order quadrupole coupling that defines a new kinetic window and makes deuteron OMAS much more sensitive than ordinary magic angle spinning to motion on the kilohertz time scale. Temperature-dependent deuteron OMAS line shapes of octanoic acid/urea-d4 inclusion compound have been recorded and fitted, using least-squares procedures, to provide rates of rotation about both CN and CO bonds. The Arrhenius activation parameters for rotation about CN bonds, Ea=60.4±2.4kJ∕mol and ln(A)=24.9±0.3, agree well with previous values determined by selective inversion experiments. However, OMAS yields Ea=26.3±0.4kJ∕mole and ln(A)=24.9±0.3 for whole-body rotation about the CO bond axis in contrast to previous analysis of static quadrupole echo (QE) line shapes which gave Ea=22.3±0.3kJ∕mole and ln(A)=24.8±0.6 for the same sample. The underlying homogeneous linewidths of OMAS spectra are much smaller than those of QE spectra, and this provides higher precision and less systematic error in the determination of rates.
Experiments and modification on electron cyclotron resonance ion sources at the Institute of Modern Physics
Authors: Zhang Z. M. , Zhao H. W. , Sun L. T. , Cao Y. , Zhang X. Z. , Guo X. H. , Li X. X. , Li J. Y. , Feng Y. C. , Wang H. , Ma B. H. , Zhao H. Y. , He W. , Shang Y.
Published: March 2006

Uranium ion beams were produced from electron cyclotron resonance (ECR) ion sources by sputtering method this year at the Institute of Modern Physics. At first, we chose the Lanzhou ECR No. 3 ion source to implement the production experiment of U ion beams. Finally, 11eμA of U28+, 5eμA of U32+, and 1.5eμA of U35+ were obtained. A U26+ ion beam produced by the LECR2 ion source was accelerated successfully by the cyclotron. This means that the Heavy Ion Research Facility in Lanzhou (HIRFL) has accomplished the acceleration of the ion beam of the heaviest element according to the designed parameters. The Lanzhou ECR ion source No. 2 (LECR2), which was built in 1997, has served the HIRFL for eight years and needed to be upgraded to provide more intense high charge state ion beams for HIRFL cooling storage ring. We started the upgrading project of LECR2 last year, and the modified design just has been finished.
Simulations of H− extraction
Authors: Becker R.
Published: March 2006

Having established the mathematical formulation for the numerical simulation of the extraction of H− ions from a plasma in final form [R. Becker, AIP Conf. Proc. 763, 194 (2005)] and implemented into the frame of the well-known simulation program IGUN [R. Becker and W. B. Herrmannsfeldt, Rev. Sci. Instrum.63, 2756 (1992)], examples of known high-performing ion sources could be studied. The formulation is not sensitive to the creation of H− ions either on the wall (preferably in cesiated sources) or in the volume of the plasma (all kinds of sources). Therefore, the cesiated SNS source as well as the noncesiated DESY source could be simulated. Both sources have been well characterized by measurements, which makes the comparison with simulations very interesting.
Abrupt variation in ion current with biased disk voltage in the electron cyclotron resonance ion source
Authors: Taki G. S. , Sarma P. R. , Chakraborty D. K. , Bhandari R. K. , Ray P. K. , Drentje A. G.
Published: March 2006

The performance of the biased disk in the 6.4GHz electron cyclotron resonance ion source at VECC, Kolkata was studied at a pressure of ∼1×10−7Torr. We observed an abrupt variation of beam current with bias voltage. For low negative bias voltages (from 0 to −5V) the beam current gradually decreases and then shows a sudden change in magnitude at a voltage of about −6V. The higher the charge state, the higher is the magnitude of this change. For H+ also the current changes abruptly, but the jump is from a higher to a lower current. This indicates a sudden change in the charge-state distribution of the beam, likely corresponding to a suddenly improved confinement.
Radially uniform circular sweep of ion beam
Authors: Akhmetov T. D. , Davydenko V. I. , Ivanov A. A. , Kobets V. V. , Medvedko A. S. , Skorobogatov D. N. , Tiunov M. A.
Published: March 2006

A spiral sweep of the ion beam was suggested tо provide sufficiently uniform irradiation of a circular target. It is shown that if the beam radius is small enough, the radius of the beam center should increase as a square root of time to provide uniform radial irradiation of the target. In the complex for Boron Neutron Capture Therapy developed at the Budker Institute of Nuclear Physics, the proton beam sweep will be performed by a sweeper with uniform magnetic field with strength up to 500G and axial length ∼20cm, rotating at 100–2000Hz, and scanning over the radius at a 1–10Hz frequency. The sweeper field is produced by four longitudinal flat current windings placed near the inner walls of a box-shaped yoke with the inner opening of a square cross section. A similar sweeping technique can be used in a 200keV oxygen implanter, which is also under development at the Budker Institute.
Characteristics of the KVI electron cyclotron resonance ion source
Authors: Kremers H. R. , Beijers J. P. M. , Brandenburg S.
Published: March 2006

In this article, an update will be given of last year’s activities to modify the CAPRICE-type ECR ion source into an AECR-type ECR ion source as developed in Berkely, Argonne and Jyväskylä. Here we will present measurements on the radial and the axial magnetic field, the vacuum system, report on the ECR plasma produced by the KVI-AECR ion source.
Fast slit-beam extraction and chopping for neutron generator
Authors: Kalvas T. , Hahto S. K. , Gicquel F. , King M. , Vainionpää J. H. , Reijonen J. , Leung K. N. , Miller T. G.
Published: March 2006

High-intensity fast white neutron pulses are needed for pulsed fast neutron transmission spectroscopy (PFNTS). A compact tritium–tritium fusion reaction neutron generator with an integrated ion beam chopping system has been designed, simulated, and tested for PFNTS. The design consists of a toroidal plasma chamber with 20 extraction slits, concentric cylindrical electrodes, chopper plates, and a central titanium-coated beam target. The total ion beam current is 1A. The beam chopping is done at 30keV energy with a parallel-plate deflector integrated with an Einzel lens. Beam pulses with 5ns width can be achieved with a 15ns rise/fall time ±1500V sweep on the chopper plates. The neutrons are produced at 120keV energy. A three-dimensional simulation code based on Vlasov iteration was developed for simulating the ion optics of this system. The results with this code were found to be consistent with other simulation codes. So far we have measured 50ns ion beam pulses from the system.
Towards benchmark second-order correlation energies for large atoms. II. Angular extrapolation problems
Authors: Flores J. R. , Słupski R. , Jankowski K.
Published: March 2006

We have studied the use of the asymptotic expansions (AEs) for the angular momentum extrapolation (to l→∞) of atomic second-order Møller-Plesset (MP2) correlation energies of symmetry-adapted pairs (SAPs). The AEs have been defined in terms of partial wave (PW) increments to the SAP correlation energies obtained with the finite element MP2 method (FEM-MP2), as well as with the variational perturbation method in a Slater-type orbital basis. The method employed to obtain AEs from PW increments is general in the sense that it can be applied to methods other than MP2 and, if modified, to molecular systems. Optimal AEs have been determined for all types of SAPs possible in large atoms using very accurate FEM PW increments up to lmax=45. The impact of the error of the PW increments on the coefficients of the AEs is computed and taken into account in our procedure. The first AE coefficient is determined to a very high accuracy, whereas the second involves much larger errors. The optimum l values (lopt) for starting the extrapolation procedures are determined and their properties, interesting from the practical point of view, are discussed. It is found that the values of the first AE coefficients obey expressions of the type derived by Kutzelnigg and Morgan [J. Chem. Phys. 96, 4484 (1992); 97, 8821(E) (1992)] for He-type systems in the bare-nucleus case provided they are modified by fractional factors in the case of triplet and unnatural singlet SAPs. These expressions give extremely accurate values for the first AE coefficient both for the STO and the FEM Hartree-Fock orbitals. We have compared the performance of our angular momentum extrapolations with those of some of the principal expansion extrapolations performed with correlation consistent basis sets employed in the literature and indicated the main sources of inaccuracy.
Recombination of ozone via the chaperon mechanism
Authors: Ivanov Mikhail V. , Schinke Reinhard
Published: March 2006

The recombination of ozone via the chaperon mechanism, i.e., ArO+O2→Ar+O3 and ArO2+O→Ar+O3, is studied by means of classical trajectories and a pairwise additive Ar−O3 potential energy surface. The recombination rate coefficient has a strong temperature dependence, which approximately can be described by T−n with n≈3. It is negligible for temperatures above 700 K or so, but it becomes important for low temperatures. The calculations unambiguously affirm the conclusions of Hippler et al. [J. Chem. Phys. 93, 6560 (1990)] and Luther et al. [Phys. Chem. Chem. Phys. 7, 2764 (2005)] that the chaperon mechanism makes a sizable contribution to the recombination of O3 at room temperature and below. The dependence of the chaperon recombination rate coefficient on the isotopomer, studied for two different isotope combinations, is only in rough qualitative agreement with the experimental data. The oxygen atom isotope exchange reaction involving ArO and ArO2 van der Waals complexes is also investigated; the weak binding of O or O2 to Ar has only a small effect.
Self-similarity of single-channel transmission for electron transport in nanowires
Authors: Gelin M. F. , Li Zhenyu , Kosov D. S.
Published: March 2006

We demonstrate that the single-channel transmission in the resonance tunneling regime exhibits self-similarity as a function of the nanowire length and the energy of incident electrons. The self-similarity is used to design the nonlinear transformation of the nanowire length and energy which, on the basis of known values of transmission for a certain region on the energy-length plane, yields transmissions for other regions on this plane. Test calculations with a one-dimensional tight-binding model illustrate the described transformations. Density function theory based transport calculations of Na atomic wires confirm the existence of the self-similarity in the transmission.
Kohn’s theory of the insulating state: A quantum-chemistry viewpoint
Authors: Resta Raffaele
Published: March 2006

The qualitative difference between insulators and conductors not only manifests itself in the excitation spectra but also—according to Kohn's theory [Phys. Rev. 133, A171 (1964)]—in a different organization of the electrons in their ground state: the wave function is localized in insulators and delocalized in conductors. Such localization, however, is hidden in a rather subtle way in the many-body wave function. The theory has been substantially revisited and extended in modern times, invariably within a periodic-boundary-condition framework, i.e., ideally addressing an infinite condensed system. Here we show how the localization/delocalization of the many-body wave function shows up when considering either three-dimensional clusters of increasing size or quasi-one-dimensional systems (linear polymers, nanotubes, and nanowires) of increasing length, within the ordinary “open” boundary conditions adopted for finite systems. We also show that the theory, when specialized to uncorrelated wave functions, has a very close relationship with Boy's theory of localization [Rev. Mod. Phys. 32, 296 (1960)]: the Boys orbitals in the bulk of the sample behave in a qualitatively different way in insulating versus conducting cases.
The generalized active space concept for the relativistic treatment of electron correlation. III. Large-scale configuration interaction and multiconfiguration self-consistent-field four-component methods with application to UO2
Authors: Fleig Timo , Jensen Hans Jørgen Aa. , Olsen Jeppe , Visscher Lucas
Published: March 2006

We present an implementation for large-scale relativistic electronic structure calculations including spin-dependent contributions and electron correlation in a fully variational procedure. The modular implementation of the double group configuration interaction (CI) program into a multiconfiguration self-consistent-field (MCSCF) code allows for the treatment of large CI expansions in both the spinor optimization step and the post-MCSCF dynamic electron correlation step. As an illustration of the potential of the new code, we calculate the spectroscopic properties of the UO2 molecule where we study the ground state and a few excited states in vertical and adiabatic calculations.
Surface nanostructuring and optical activation of lithium fluoride crystals by ion beam irradiation
Authors: Mussi V. , Granone F. , Boragno C. , Buatier de Mongeot F. , Valbusa U. , Marolo T. , Montereali R. M.
Published: March 2006

We present results on simultaneous nanostructuring and optical activation of lithium fluoride crystals by 800eV off-normal Ar+ sputtering at different ion doses. The samples were studied by atomic force microscopy and optical spectroscopy. After ion irradiation smoothening of the initial random roughness is achieved and well-defined self-organized ripple structures appear, having a mean periodicity of 30nm and a mean height of 3nm. The simultaneous optical activation of the irradiated samples is due to the stable formation of electronic defects with intense photoluminescence in the visible spectral range.
Quenching of rotationally excited CO by collisions with H2
Authors: Yang Benhui , Stancil P. C. , Balakrishnan N. , Forrey R. C.
Published: March 2006

Quantum close-coupling and coupled-states approximation scattering calculations of rotational energy transfer in CO due to collisions with H2 are presented for collision energies between 10−6 and 15000cm−1 using the H2–CO interaction potentials of Jankowski and Szalewicz [J. Chem. Phys. 123, 104301 (2005); 108, 3554 (1998)]. State-to-state cross sections and rate coefficients are reported for the quenching of CO initially in rotational levels j2=1–3 by collisions with both para- and ortho-H2. Comparison with the available theoretical and experimental results shows good agreement, but some discrepancies with previous calculations using the earlier potential remain. Interestingly, elastic and inelastic cross sections for the quenching of CO (j2=1) by para-H2 reveal significant differences at low collision energies. The differences in the well depths of the van der Waals interactions of the two potential surfaces lead to different resonance structures in the cross sections. In particular, the presence of a near-zero-energy resonance for the earlier potential which has a deeper van der Waals well yields elastic and inelastic cross sections that are about a factor of 5 larger than that for the newer potential at collision energies lower than 10−3cm−1.
Efficient calculation of low energy statistical rates for gas phase dissociation using umbrella sampling
Authors: Mella Massimo
Published: March 2006

Monte Carlo (MC) simulations can be used to compute microcanonical statistical rates of gas phase dissociation reactions. Unfortunately, the MC approach may suffer from a slow convergence and large statistical errors for energies just above the dissociation threshold. In this work, umbrella sampling is proposed as a device to reduce the statistical error of MC rate constants. The method is tested by computing the classical dissociation rate for the reaction [H5O2+]*→H2O+H3O+ over the range of internal energy 38<E⩽100kcal∕mol. Comparing with other literature methods, it is found that umbrella sampling reduces the computational effort by up to two orders of magnitude when used in conjunction with a careful choice of sampling distributions. The comparison between MC rate constants and classical Rice-Ramsperberg-Kassel harmonic theory shows that anharmonicity plays an important role in the dissociation process of the Zundel cation (H5O2+) at all energies.
Comment on “About the calculation of exchange coupling constants using density-functional theory: The role of the self-interaction error” [J. Chem. Phys. 123, 164110 (2005)]
Authors: Adamo C. , Barone V. , Bencini A. , Broer R. , Filatov M. , Harrison N. M. , Illas F. , Malrieu J. P. , de P. R. Moreira I.
Published: March 2006

The use of density functional theory to obtain energy differences related to magnetic coupling constants is debated with special emphasis to the claims by Ruiz et al. [J. Chem. Phys.123, 164110 (2005)] that good agreement with experiment using the B3LYP potential is obtained by ignoring spin symmetry in case self-interaction error cannot be removed.
Reply to “Comment on ‘About the calculation of exchange coupling constants using density-functional theory: The role of the self-interaction error’” [J. Chem. Phys.123, 164110 (2005)]
Authors: Ruiz Eliseo , Cano Joan , Alvarez Santiago , Polo Víctor
Published: March 2006

This reply focuses on two crucial aspects, the role of the self-interaction error on the calculation of the exchange coupling constants, which has been proposed by other authors and ourselves, and the excellent agreement between the results obtained with our theoretical approach and the experimental data for all kinds of magnetic transition metal compounds.
Effect of surface field on the morphology of a symmetric diblock copolymer under cylindrical confinement
Authors: Chen Peng , He Xuehao , Liang Haojun
Published: March 2006

We have used lattice Monte Carlo simulations to investigate the molecular assembly of symmetric diblock copolymer melts within cylindrical nanochannels. We studied the effect that the surface field has on the copolymer morphology in three cylinders having different diameters. Upon varying the strength of the surface field, we observed a variety of morphologies, including stacked-disk, single-helix, catenoid-cylinder, gyroidal, stacked-circle, and concentric cylindrical barrel structures. The results of these simulations should be helpful when designing polymeric nanomaterials confined in cylindrical nanochannels.
Laser-based measurement of elastic and mechanical properties of layered polycrystalline silicon structures with projection masks
Authors: Bennis A. , Lomonosov A. M. , Shen Z. H. , Hess P.
Published: March 2006

The Young’s modulus, density, and thickness of a 20.3μm polycrystalline silicon layer deposited on a silicon wafer covered with a ∼2.5-μm-thick silicon-oxide interface layer were measured using projection masks to generate surface acoustic waves (SAWs) with higher harmonics approaching 600MHz. The propagating SAW train was detected with a laser probe-beam-deflection setup. The characteristic strongly nonlinear dispersion effect allowed the simultaneous extraction of several unknown film properties. The dispersion was described theoretically by the boundary element method model. A Young’s modulus of 152GPa, a density of 2.25g∕cm3, and a film thickness of 20.3μm were determined for the polycrystalline silicon film.
Ge on Si p-i-n photodiodes operating at 10Gbit∕s
Authors: Colace Lorenzo , Balbi Michele , Masini Gianlorenzo , Assanto Gaetano , Luan Hsin-Chiao , Kimerling Lionel C.
Published: March 2006

We report on fast p-i-n photodetectors operating in the near infrared and realized in pure germanium on silicon. The diodes were fabricated by chemical vapor deposition at 600°C without affecting the crystal quality and allowing the integration with standard silicon processes. We demonstrate responsivities of 0.4 and 0.2A∕W at 1.3 and 1.55μm, respectively, as well as operation at 10Gbit∕s.
Self-aligned TiSi2∕Si heteronanocrystal nonvolatile memory
Authors: Zhu Yan , Zhao Dengtao , Li Ruigang , Liu Jianlin
Published: March 2006

The titanium silicide/silicon (TiSi2∕Si) heteronanocrystals are fabricated on SiO2 thin films. The metal-oxide-semiconductor structure embedding the TiSi2∕Si heteronanocrystals shows superior performance over the Si dot device. The charge loss rate in the TiSi2∕Si heteronanocrystal device is 7.5 times less than that of the Si dot device. It is also found that the TiSi2∕Si heteronanocrystal device has wider memory window than the Si dot counterpart.
Quantum size effects manifest in infrared spectra of single bismuth nanowires
Authors: Cornelius T. W. , Toimil-Molares M. E. , Neumann R. , Fahsold G. , Lovrincic R. , Pucci A. , Karim S.
Published: March 2006

Infrared transmission spectroscopy measurements on single bismuth nanowires of various diameters d are presented. The spectra show a strong absorption whose onset is blueshifted proportionally to 1∕d2. We ascribe the absorption to interband transitions. The blueshift results from quantum size effects since they lead to the d-dependent splitting of the energy bands and to a respective shift of energy gaps.
Self-organized growth of Mn nanocluster arrays on Si(111)-(7×7) surfaces
Authors: Wang Hui , Zou Zhi-Qiang
Published: March 2006

We demonstrate the formation of well-ordered arrays of Mn nanoclusters of nearly identical sizes on a Si(111)-(7×7) surface. The Mn atoms are found not to react with the Si substrate at temperatures below ∼260°C. At room temperature, the Mn clusters occupy both halves of the (7×7) unit cell and arrange themselves into a honeycomb structure, whereas at a temperature of 258°C, they exclusively occupy the faulted half of the unit cell and form an array with hexagonal symmetry. The self-organization process of the nanocluster array of Mn is different from that previously reported for the group-IIIA metals, due to stronger Mn–substrate and Mn–Mn interactions.
Fabricating subwavelength array structures using a near-field photolithographic method
Authors: Chang Wei-Lun , Chang Yu-Jen , Wei Pei-Kuen , Tsao Pei Hsi
Published: March 2006

This work presents a photolithographic approach for producing high aspect ratio arrays in photoresist. The photomask is composed of hexagonal/square rod arrays with a thickness of 0.2μm and a period of 600nm. Illuminating the photomask with a blue laser generates periodically focused beams up to 1μm long and less than 300nm wide. A hexagonal rod array provides a better focused beam than a square array due to its higher symmetry. Finite-difference time-domain calculations elucidate the existence of long focused beams above the photomask. Optical near-field measurements verified those subwavelength beams originating from the rod regions.
Mode locking of lateral modes in broad-area semiconductor lasers by subharmonic optical pulse injection
Authors: Kaiser Joachim , Fischer Ingo , Elsässer Wolfgang
Published: March 2006

We generate stable mode-locking of different lateral modes in broad-area semiconductor lasers (BALs) by local injection of short optical pulses repeated at subharmonics of the lateral mode separation. The locking results in a persistent, periodic spatiotemporal dynamics consisting of a laterally alternating intensity modulation with a repetition rate of 3.4GHz, which can be regarded as an enhancement and stabilization of the spontaneous dynamic filamentation that is frequently observed in free running BALs.
Anisotropic plasma effects on electron capture process in an anisotropic plasma
Authors: Shin Dong-Soo , Jung Young-Dae
Published: March 2006

The anisotropic and plasma screening effects on the electron capture process are investigated in an anisotropic plasma in the presence of an external electric field. The Bohr–Lindhard model with the impact parameter analysis is applied to obtain the electron capture probability in the anisotropic plasma as a function of the impact parameter, Debye length, and collision energy. The result shows that the electron capture cross section decreases with increasing collision energy. It is also found that the anisotropic effect strongly suppresses the electron capture cross section in the anisotropic plasma.
Silicon and silicon oxide etching rate enhancement by nitrogen containing gas addition in remote perfluorocarbon plasmas
Authors: Bai Bo , An Jujin , Sawin Herbert H.
Published: March 2006

The addition of 3% nitrogen to a mixture of perfluorocarbon/oxygen/argon in a remote toroidal plasma source was shown to double the etching rate of both silicon dioxide and silicon in a downstream process. It is believed that the nitrogen blocks the surface recombination sites for COF2 formation on the wall of the transfer tube, thereby transporting more fluorine atoms to the downstream process chamber and increasing the etching rate.
Microscopic interfacial structures and magnetic properties of ultrathin Co∕Si(111) films
Authors: Tsay J. S. , Fu T. Y. , Lin M. H. , Yang C. S. , Yao Y. D.
Published: March 2006

The relation between magnetic properties and microscopic structure for a metal/semiconductor system is described. Cobalt films on a CoSi interface possess an in-plane easy axis of magnetization as the result of magnetocrystalline anisotropy of the Co∕CoSi interface. On a Si(111)-7×7 surface, direct evidence for the formation of CoSi2 compounds at the interface was found by the appearance of doubled spot defects in scanning tunneling microscopic images. The interfacial effects cause the easy axis of magnetization of a Co∕Si interface to be canted out of plane.
Passive imaging of localized reflectors and interfaces in open media
Authors: Larose Eric , Montaldo Gabriel , Derode Arnaud , Campillo Michel
Published: March 2006

Previous experiments in open media showed the possibility of reconstructing the direct (ballistic) wave between two passive sensors from the time correlations of elastic or acoustic scattered wave fields. Here we illustrate how the passive imaging technique can also retrieve detailed features of the Green’s function, beyond the ballistic wave. Two ultrasonic experiments are presented. In the first one we reconstruct the complete signature of two well-separated scatterers with a perfect distribution of distant sources. In the second experiment we image an aluminum/water interface with only a few sources. The lack of sources is compensated for by taking advantage of a multiple scattering slab.