bluuebunny/crossref_metadata_2025 huggingface dataset:
Missing feedbacks, asymmetric uncertainties, and the underestimation of future warming
Authors: Torn Margaret S. , Harte John
Published: May 2006

Historical evidence shows that atmospheric greenhouse gas (GhG) concentrations increase during periods of warming, implying a positive feedback to future climate change. We quantified this feedback for CO2 and CH4 by combining the mathematics of feedback with empirical ice‐core information and general circulation model (GCM) climate sensitivity, finding that the warming of 1.5–4.5°C associated with anthropogenic doubling of CO2 is amplified to 1.6–6.0°C warming, with the uncertainty range deriving from GCM simulations and paleo temperature records. Thus, anthropogenic emissions result in higher final GhG concentrations, and therefore more warming, than would be predicted in the absence of this feedback. Moreover, a symmetrical uncertainty in any component of feedback, whether positive or negative, produces an asymmetrical distribution of expected temperatures skewed toward higher temperature. For both reasons, the omission of key positive feedbacks and asymmetrical uncertainty from feedbacks, it is likely that the future will be hotter than we think.
Evidence for newly closed magnetosheath field lines at the dayside magnetopause under northward IMF
Authors: Lavraud B. , Thomsen M. F. , Lefebvre B. , Schwartz S. J. , Seki K. , Phan T. D. , Wang Y. L. , Fazakerley A. , Rème H. , Balogh A.
Published: May 2006

We analyze the structure of the high‐latitude magnetopause under steady interplanetary magnetic field (IMF). We use 56 magnetopause encounters of Cluster spacecraft from 2001 to 2003 to explore the statistical properties of the magnetosheath electron boundary layer, observed outside the high‐latitude dayside magnetopause. We focus on the occurrence of low absolute parallel heat flux in this layer and its dependence on the magnetic field clock angle simultaneously measured by Cluster. The low absolute parallel heat fluxes result from the presence of bidirectional heated electrons in the magnetosheath electron boundary layer and are primarily observed when the local magnetic field is northward. The bidirectional heated electrons are interpreted as the signature of newly closed magnetosheath field lines that have reconnected at the high‐latitude magnetopause, tailward of the cusp, in both hemispheres. This study strongly suggests that double high‐latitude reconnection is a tenable mechanism for the formation of the low‐latitude boundary layer and potentially of the cold, dense plasma sheet under northward IMF. Although the efficiency (in terms of mass and energy transfer) of this mechanism is still to be investigated, it is an obvious way of capturing solar wind plasma under northward IMF.
Global auroral proton precipitation observed by IMAGE‐FUV: Noon and midnight brightness dependence on solar wind characteristics and IMF orientation
Authors: Coumans Valérie , Gérard Jean‐Claude , Hubert Benoît , Meurant Matthieu
Published: May 2006

The brightness of proton aurora observed near solar maximum at summer and winter solstices with the FUV‐SI12 global imager on board the IMAGE satellite has been correlated with the solar wind and the interplanetary magnetic field characteristics measured by ACE satellite instruments. By contrast to the electron aurora, we find a strong correlation both on nightside and dayside between the proton precipitated power and the solar wind dynamic pressure calculated with 1‐hour averaged solar wind data. For both southward and northward IMF, the proton power increases with ∣Bz∣, but much more rapidly on the nightside for southward IMF orientation. Correlations for the nightside aurora were also calculated with a series of solar wind‐magnetosphere coupling functions. We find highest correlation coefficients for expressions containing the dynamic pressure or involving the solar wind electric field in the Y‐Z plane. The influence of the solar wind dynamic pressure on the proton aurora is tentatively explained by the effect of the pressure on the shape of the magnetosphere, generating stretching of the magnetotail and proton precipitation but also by other coupling processes between the solar wind and the magnetosphere. Adding FUV‐WIC and SI13 electron aurora images in the study, we determine how proton and electron precipitations simultaneously react to solar wind and IMF characteristics and Kp. Results shows that protons are more reactive to dynamic pressure variations than electrons when Bz is positive, while the influence on of both types of particles is similar for negative Bz. The precipitating proton flux is found proportionally larger compared with the electron flux when the total auroral flux increases for low activity level. Instead, for high activity level, the proportion of the proton and the electron powers are similar when auroral power increases. Consequently, it is suggested that similar mechanisms cause proton and electron auroral precipitation for high activity levels, while they appear somewhat decoupled for lower activity conditions.
Energetic outer zone electron loss timescales during low geomagnetic activity
Authors: Meredith Nigel P. , Horne Richard B. , Glauert Sarah A. , Thorne Richard M. , Summers Danny , Albert Jay M. , Anderson Roger R.
Published: May 2006

Following enhanced magnetic activity the fluxes of energetic electrons in the Earth's outer radiation belt gradually decay to quiet‐time levels. We use CRRES observations to estimate the energetic electron loss timescales and to identify the principal loss mechanisms. Gradual loss of energetic electrons in the region 3.0 ≤ L ≤ 5.0 occurs during quiet periods (Kp < 3−) following enhanced magnetic activity on timescales ranging from 1.5 to 3.5 days for 214 keV electrons to 5.5 to 6.5 days for 1.09 MeV electrons. The intervals of decay are associated with large average values of the ratio fpe/fce (>7), indicating that the decay takes place in the plasmasphere. We compute loss timescales for pitch‐angle scattering by plasmaspheric hiss using the PADIE code with wave properties based on CRRES observations. The resulting timescales suggest that pitch angle scattering by plasmaspheric hiss propagating at small or intermediate wave normal angles is responsible for electron loss over a wide range of energies and L shells. The region where hiss dominates loss is energy‐dependent, ranging from 3.5 ≤ L ≤ 5.0 at 214 keV to 3.0 ≤ L ≤ 4.0 at 1.09 MeV. Plasmaspheric hiss at large wave normal angles does not contribute significantly to the loss rates. At E = 1.09 MeV the loss timescales are overestimated by a factor of ∼5 for 4.5 ≤ L ≤ 5.0. We suggest that resonant wave‐particle interactions with EMIC waves, which become important at MeV energies for larger L (L > ∼4.5), may play a significant role in this region.
Strain accommodation by magmatism and faulting as rifting proceeds to breakup: Seismicity of the northern Ethiopian rift
Authors: Keir Derek , Ebinger C. J. , Stuart G. W. , Daly E. , Ayele A.
Published: May 2006

The volcanically active Main Ethiopian rift (MER) marks the transition from continental rifting in the East African rift to incipient seafloor spreading in Afar. We use new seismicity data to investigate the distribution of strain and its relationship with magmatism immediately prior to continental breakup. From October 2001 to January 2003, seismicity was recorded by up to 179 broadband instruments that covered a 250 km × 350 km area. A total of 1957 earthquakes were located within the network, a selection of which was used for accurate location with a three‐dimensional velocity model and focal mechanism determination. Border faults are inactive except for a cluster of seismicity at the structurally complex intersection of the MER and the older Red Sea rift, where the Red Sea rift flank is downwarped into the younger MER. Earthquakes are localized to ∼20‐km‐wide, right‐stepping en echelon zones of Quaternary magmatism and faulting, which are underlain by mafic intrusions that rise to 8–10 km subsurface. Seismicity in these “magmatic segments” is characterized by low‐magnitude swarms coincident with Quaternary faults, fissures, and chains of eruptive centers. All but three focal mechanisms show normal dip‐slip motion; the minimum compressive stress is N103°E, perpendicular to Quaternary faults and aligned volcanic cones. The earthquake catalogue is complete above ML 2.1, and the estimated b value is 1.13 ± 0.05. The seismogenic zone lies above the 20‐km‐wide intrusion zones; intrusion may trigger faulting in the upper crust. New and existing data indicate that during continental breakup, intrusion of magma beneath ∼20‐km‐wide magmatic segments accommodates the majority of strain and controls the locus of seismicity and faulting in the upper crust.
Radiated seismic energy based on dynamic rupture models of faulting
Authors: Ma Shuo , Archuleta Ralph J.
Published: May 2006

By modeling spontaneous ruptures, we study the mechanism dependence of radiated seismic energy from three hypothetical crustal events, 30° dipping reverse fault, 60° dipping normal fault, and a vertical strike‐slip fault, and the 1994 blind‐thrust Northridge earthquake. Embedded in a homogeneous half‐space, all three hypothetical faults have the same area and are subjected to the same shear and normal stress conditions and frictional parameters. Dynamic simulations produce apparent stress of 0.53 MPa, 0.23 MPa, and 0.34 MPa for the reverse, normal, and strike‐slip faults, respectively. The energy distribution on a distant surface shows that a large fraction of energy is concentrated in the forward direction of rupture propagation. We use spontaneous rupture models to compute the radiated energy from the 1994 Northridge earthquake. The initial stress drop distribution is based on a kinematic slip distribution. Using a linear slip‐weakening friction law, we modify both the initial stress and yield stress until the dynamic rupture produces near‐source synthetics that are consistent with the data. The total radiated seismic energy from our model is 6.0 × 1014 J; seismic moment 1.47 × 1019 Nm; apparent stress 1.5 MPa; fracture energy 3.2 × 1014 J; and slip‐weakening distance 0.25 m. The energy flux distribution is heterogeneous with strong directivity effects. These results suggest that correcting for directivity could be difficult, but necessary, for teleseismic and regional estimates of radiated energy. Dynamic source models constrained by ground motions can provide a stable and accurate energy estimate for large earthquakes.
A study of the physical, chemical, and optical properties of ambient aerosol particles in Southeast Asia during hazy and nonhazy days
Authors: See S. W. , Balasubramanian R. , Wang W.
Published: May 2006

Many Southeast Asian countries have been constantly plagued by recurring smoke haze episodes as a result of traditional slash‐and‐burn practices in agricultural areas to clear crop lands or uncontrolled forest fires. However, our current knowledge on the physiochemical and optical properties of ambient aerosols associated with regional haze phenomenon is still fairly limited. Therefore a comprehensive field study was carried out in Singapore from March 2001 to March 2002 under varying weather conditions to gain a better understanding of the characteristics. The physical (size distribution of mass and number concentrations), chemical (mass concentrations of chemical components: 14 ions, 24 metals, elemental carbon (EC) and organic carbon (OC)), and optical (light absorption (bap) and scattering (bsp) by particles) characteristics of ambient aerosol particles were investigated. The results are reported separately for clear and hazy days by categorizing the days as clear or hazy on the basis of visibility data. It was observed that the average concentrations of PM2.5 and most chemical components increased approximately by a factor of 2 on hazy days. Backward air trajectories together with the hot spot distributions in the region indicated that the degradation in Singapore's air quality on hazy days was attributable to large‐scale forest fires in Sumatra. This visibility degradation was quantitatively measured on the basis of the light absorption and scattering by particles. As expected, scattering rather than absorption controlled atmospheric visibility, and PM2.5 particles present on hazy days were more efficient at scattering light than those found on clear days.
Radio holographic filtering, error estimation, and quality control of radio occultation data
Authors: Gorbunov M. E. , Lauritsen K. B. , Rhodin A. , Tomassini M. , Kornblueh L.
Published: May 2006

Processing of radio occultation data requires filtering and quality control for the noise reduction and sorting out corrupted data samples. We introduce a radio holographic filtering algorithm based on the synthesis of canonical transform (CT2) and radio holographic focused synthesized aperture (RHFSA) methods. The field in the CT2‐transformed space is divided by a reference signal to subtract the regular phase variation and to compress the spectrum. Next, it is convolved with a Gaussian filter window and multiplied by the reference signal to restore the phase variation. This algorithm is simple to implement, and it is numerically efficient. Numerical simulation of processing radio occultations with a realistic receiver noise indicates a good performance of the method. We introduce a new technique of the error estimation of retrieved bending angle profiles based on the width of the running spectra of the transformed wavefield multiplied with the reference signal. We describe a quality control method for the discrimination of corrupted samples in the L2 channel, which is most susceptible to signal tracking errors. We apply the quality control and error estimation techniques for the processing of data acquired by Challenging Minisatellite Payload (CHAMP) and perform a statistical comparison of CHAMP data with the analyses of the German Weather Service (DWD). The statistical analysis shows a good agreement between the CHAMP and DWD error estimates and the observed CHAMP–DWD differences. This corroborates the efficiency of the proposed quality control and error estimation techniques.
Determination of regional distributions and seasonal variations of land surface heat fluxes from Landsat‐7 Enhanced Thematic Mapper data over the central Tibetan Plateau area
Authors: Ma Yaoming , Zhong Lei , Su Zhongbo , Ishikawa Hirohiko , Menenti Massimo , Koike Toshio
Published: May 2006

In this study, a parameterization method based on Landsat‐7 ETM data and field observations has been proposed and tested for deriving surface reflectance, surface temperature, NDVI, MSAVI, vegetation coverage, LAI, net radiation flux, soil heat flux, sensible heat flux and latent heat flux over heterogeneous landscape. As a case study, the methodology was applied to the experimental area of the CAMP/Tibet, which located at the central Tibetan Plateau. Two scenes of Landsat‐7 ETM data were used in this study. The scene of 9 June 2002 was selected as a case of summer, and the scene of 2 December 2002 was selected as a case of winter. To validate the proposed methodology, the ground‐measured surface reflectance, surface temperature, net radiation flux, soil heat flux, sensible heat flux and latent heat flux are compared to Landsat‐7 ETM derived values. The results show that the derived surface variables and land surface heat fluxes in two different months over the study area are in good accordance with the land surface status. These parameters show a wide range due to the strong contrast of surface features. Also, the estimated land surface variables and land surface heat fluxes are in good agreement with ground measurements, and all their absolute percent difference is less than 9.9% in the validation sites. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface variables and land surface heat fluxes using the Landsat‐7 ETM data and filed observations over the study area.
Inverse stochastic moment analysis of steady state flow in randomly heterogeneous media
Authors: Hernandez A. F. , Neuman S. P. , Guadagnini A. , Carrera J.
Published: May 2006

Nonlocal stochastic moment equations have been used successfully to analyze steady state and transient flow in randomly heterogeneous media conditional on measured values of medium properties. We present a nonlinear geostatistical inverse algorithm for steady state flow that makes it possible to further condition such analyses on measured values of state variables. Our approach accounts for all scales of spatial variability resolvable by the computational grid. It is based on recursive finite element approximations of exact nonlocal first and second conditional moment equations. Hydraulic conductivity is parameterized geostatistically on the basis of measured values at discrete locations and unknown values at discrete “pilot points.” Prior estimates of pilot point values are obtained (optionally) by generalized kriging. Posterior estimates at pilot points and (optionally) at measurement points are obtained by calibrating mean flow against measured values of head. The parameters are projected onto a computational grid via kriging. Maximum likelihood calibration allows estimating not only hydraulic but also (optionally) unknown variogram parameters with or without prior information about the former. The approach yields covariance matrices for parameter estimation as well as head and flux prediction errors, the latter being obtained a posteriori. We implement our inverse approach on highly and mildly heterogeneous media under superimposed mean uniform and convergent flows in a bounded two‐dimensional domain. Our examples illustrate how conductivity and head data act separately and jointly to reduce parameter estimation errors and to model predictive uncertainty. We also evaluate the functional form of the log conductivity variogram and its parameters using likelihood‐based model discrimination criteria.
Seismic anisotropy in the uppermost mantle, back‐arc region of the northeast Japan arc: Petrophysical analyses of Ichinomegata peridotite xenoliths
Authors: Michibayashi Katsuyoshi , Abe Natsue , Okamoto Atsushi , Satsukawa Takako , Michikura Kenta
Published: May 2006

A dense network of seismic stations has been deployed across the northeast Japan arc to investigate mantle wedge structures. To attain independent petrophysical constraints, we determined the seismic properties of Ichinomegata mantle xenoliths from the back‐arc region that were brought to the surface from the mantle lithosphere by volcanic eruptions. We calculated the seismic properties of the xenoliths from olivine and pyroxene crystal‐preferred orientations and single crystal elastic constants. The small magnitude of measured S‐wave splitting (delay time of 0.22 s in the area where the xenoliths were entrained) can be explained by the average seismic properties of mantle xenoliths for an approximately 20‐km thick horizontal anisotropic layer, indicating that the mantle lithosphere could be one of the dominant sources of seismic anisotropy; this layer is possibly related to deformation in the uppermost mantle lithosphere due to back‐arc spreading along the northeast Japan arc.
Upper and intermediate circulation in the western equatorial Pacific Ocean in October 1999 and April 2000
Authors: Gouriou Y. , Delcroix T. , Eldin G.
Published: May 2006

The upper and intermediate circulation (0–1200 m) in the western equatorial Pacific Ocean is examined thanks to Lowered Acoustic Doppler Current Profiler (LADCP) measurements carried out during two cruises in October 1999 and April 2000. Several new features of the equatorial circulation are discussed. It is shown that the secondary South Subsurface CounterCurrent (sSSCC) laying at 6°S–400 m depth, had a deep extension at 165°E with a maximum core velocity around 5°S–1000 m. Furthermore the Equatorial Intermediate Current (EIC) and the Lower EIC (LEIC) displayed a strong temporal variability between 165°E and 180°, as these two westward currents were replaced by eastward flow along the equator on the second cruise. Finally during the April 2000 cruise the zonal velocity profile carried out at the equator east of the Gilbert Island (around 175°E) broke into small vertical scales, possibly reflecting topographic effect and/or destabilization mechanism that leads to the formation of long zonal jet‐like structures.
Discharge temperature–discharge rate correlation of Japanese hot springs driven by buoyancy and its application to permeability mapping
Authors: Muraoka H. , Sakaguchi K. , Nakao S. , Kimbara K.
Published: May 2006

A bi‐logarithmic plot of the discharge temperature versus flow rate of 3,686 hot springs in Japan shows a broad but positive correlation. This correlation is semiquantitatively explained as buoyancy‐driven Darcy flow using a one‐dimensional advection flow equation for hot water in a porous media assuming a 1 km reservoir depth and 104 m2 discharge area for each hot spring. The permeability of the best fit curve to the relation is 10−13 m2 that is a typical value for relatively low‐temperature geothermal fields at a reservoir temperature less than 260°C. This is consistent with the relatively low reservoir temperature for these hot springs. Based on the relation, the permeability of each hot spring area can be estimated from the discharge temperature and discharge rate values, and permeability mapping for the 1 km skin depth is performed for almost all of Japan.
Modern‐age buildup of CO2 and its effects on seawater acidity and salinity
Authors: Loáiciga Hugo A.
Published: May 2006

The impacts of increases in atmospheric CO2 since the midst of the 18th century on average seawater salinity and acidity are evaluated. Assuming that the rise in the planetary mean surface temperature continues unabated, and that it eventually causes the melting of terrestrial ice and permanent snow, it is calculated that the average seawater salinity would be lowered not more than 0.61‰ from its current 35‰. It is also calculated –using an equilibrium model of aqueous carbonate species in seawater open to the atmosphere‐ that the increase in atmospheric CO2 from 280 ppmv (representative of 18th‐century conditions) to 380 ppmv (representative of current conditions) raises the average seawater acidity approximately 0.09 pH units across the range of seawater temperature considered (0 to 30°C). A doubling of CO2 from 380 ppmv to 760 ppmv (the 2 × CO2 scenario) increases the seawater acidity approximately 0.19 pH units across the same range of seawater temperature. In the latter case, the predicted increase in acidity results in a pH within the water‐quality limits for seawater of 6.5 and 8.5 and a change in pH less than 0.20 pH units. This paper's results concerning average seawater salinity and acidity show that, on a global scale and over the time scales considered (hundreds of years), there would not be accentuated changes in either seawater salinity or acidity from the observed or hypothesized rises in atmospheric CO2 concentrations.
Orientation dynamics in isotropic phases of model oligofluorenes: Glass or liquid crystal
Authors: Somma E. , Chi C. , Loppinet B. , Grinshtein J. , Graf R. , Fytas G. , Spiess H. W. , Wegner G.
Published: May 2006

Orientation molecular dynamics were investigated in a series of “defect-free” oligofluorenes by depolarized dynamic light scattering and dynamic NMR spectroscopy. Typical liquid crystalline pretransitional dynamics were observed upon cooling the isotropic phase to the liquid crystalline phase with strong increase of the scattered intensity and slowing down of the characteristic time of the probed collective relaxation. This is well accounted for by the Landau-de Gennes theory, however, with a strong temperature dependence of the viscosity coefficient, reflecting the proximity of the glass transition. For the trimer the two transitions almost overlap and the molecular orientation coincide with the α-relaxation associated with the glass transition. The NMR measurements confirm that the time scale of the dynamics is completely governed by the glass process, yet the geometry of the motion is anisotropic, yielding order parameters ranging from 0.15 to 0.25 for the long axis in the liquid crystalline phase. The glass transition is therefore geometrically restricted with poorly ordered mesophase which is consistent with the weak transverse phonons in the light scattering experiment down to Tg+20K.
Measurement of the dynamic elastic properties of a thin coating
Authors: Alfano Marco , Pagnotta Leonardo
Published: May 2006

The use of thin coatings as protective layers for mechanical components has dramatically increased in the last two decades. The performance of a coated system depends mainly on a knowledge of the basic mechanical properties of coatings and, therefore, experimental techniques for determining Young’s modulus and Poisson’s ratio are needed. In this technical note a procedure is presented that allows the well known sonic resonance methods, for the elastic characterization of homogeneous and isotropic materials, to be extended to thin square plates. It requires the measurement of two of the first four natural frequencies of the sample in order to obtain the dynamic elastic properties of the material of which it is made. The procedure is based on suitable approximate relationships relating the resonant frequencies to size, density, and elastic constants of the material. These relations are derived from an extensive series of numerical analyses carried out by a finite element code. In addition, inexpensive experimental equipment to measure the resonant frequencies is also proposed. The procedure has been applied to a freestanding chemical vapor deposited diamond coating and the measured values are consistent with previous observations based on other methods.
Pathway to a lower cost high repetition rate ignition facility
Authors: Obenschain S. P. , Colombant D. G. , Schmitt A. J. , Sethian J. D. , McGeoch M. W.
Published: May 2006

An approach to a high-repetition ignition facility based on direct drive with the krypton-fluoride laser is presented. The objective is development of a “Fusion Test Facility” that has sufficient fusion power to be useful as a development test bed for power plant materials and components. Calculations with modern pellet designs indicate that laser energies well below a megajoule may be sufficient. A smaller driver would result in an overall smaller, less complex and lower cost facility. While this facility might appear to have most direct utility to inertial fusion energy, the high flux of neutrons would also be able to address important issues concerning materials and components for other approaches to fusion energy. The physics and technological basis for the Fusion Test Facility are presented along with a discussion of its applications.
Quantum optimal control: Hessian analysis of the control landscape
Authors: Shen Zhenwen , Hsieh Michael , Rabitz Herschel
Published: May 2006

Seeking an effective quantum control entails searching over a landscape defined as the objective as a functional of the control field. This paper considers the problem of driving a state-to-state transition in a finite level quantum system, and analyzes the local topology of the landscape of the final transition probability in terms of the variables specifying the control field. Numerical calculation of the eigenvalues of the Hessian of the transition probability with respect to the control field variables reveals systematic structure in the spectra reflecting the existence of a generic and simple control landscape topology. An illustration shows that the number of nonzero Hessian eigenvalues is determined by the number of quantum states in the system. The Hessian eigenvectors associated with its nonzero eigenvalues are shown to give insight into the cooperative roles of the control variables. The practical consequences of these findings for quantum control are discussed.
Imaging and vibrational spectroscopy of single pyridine molecules on Ag(110) using a low-temperature scanning tunneling microscope
Authors: Hahn J. R. , Ho W.
Published: May 2006

A scanning tunneling microscope (STM) was used to extract the images of single, isolated pyridine molecules adsorbed on Ag(110) and to record their vibrational spectrum at 13K. On the STM image, the pyridine molecule appears as an elongated protrusion along the [001] direction on top of a silver atom, indicating that it is bonded through its nitrogen lone pair electrons. STM inelastic electron tunneling spectroscopy of the adsorbed pyridine revealed C–D and C–H stretch modes at 282 and 378meV, respectively.
Approaches for the calculation of vibrational frequencies in liquids: Comparison to benchmarks for azide/water clusters
Authors: Li Shuzhou , Schmidt J. R. , Corcelli S. A. , Lawrence C. P. , Skinner J. L.
Published: May 2006

Ultrafast vibrational spectroscopy experiments, together with molecular-level theoretical interpretation, can provide important information about the structure and dynamics of complex condensed phase systems, including liquids. The theoretical challenge is to calculate the instantaneous vibrational frequencies of a molecule in contact with a molecular environment, accurately and quickly, and to this end a number of different methods have been developed. In this paper we critically analyze these different methods by comparing their results to accurate benchmark calculations on azide/water clusters. We also propose an optimized quantum mechanics/molecular mechanics method, which for this problem is superior to the other methods.
Noncommutative geometry and the standard model vacuum
Authors: Barrett John W. , Dawe Martins Rachel A.
Published: May 2006

The space of Dirac operators for the Connes-Chamseddine spectral action for the standard model of particle physics coupled to gravity is studied. The model is extended by including right-handed neutrino states, and the S0-reality axiom is not assumed. The possibility of allowing more general fluctuations than the inner fluctuations of the vacuum is proposed. The maximal case of all possible fluctuations is studied by considering the equations of motion for the vacuum. While there are interesting nontrivial vacua with Majorana-type mass terms for the leptons, the conclusion is that the equations are too restrictive to allow solutions with the standard model mass matrix.
The double photoionization of hydrogen iodide molecules
Authors: Alagia M. , Brunetti B. G. , Candori P. , Falcinelli S. , Moix Teixidor M. , Pirani F. , Richter R. , Stranges S. , Vecchiocattivi F.
Published: May 2006

The double photoionization of HI molecules has been investigated using vacuum ultraviolet synchrotron radiation in the energy range between 27 and 35eV. The product ions have been detected by the use of time-of-flight mass spectrometry and the threshold energy for HI2+ and H++I+ formation has been determined. These results have been interpreted by the use of a theoretical model which has been previously applied by us to HBr2+ and HCl2+. On the basis of the reliability of such a model, an assessment of the systematic trends of the bond features along the HX2+ (X=F, Cl, Br, I) homologous series is given in this paper. In particular, the increase of the stability of these dications, in their lowest electronic states, when going towards the heavier molecules, has been rationalized considering the systematic variation of the charge transfer coupling between the H–X2+ and the H+–X+ states.
Quenched by ice: Transient grating measurements of vibronic dynamics in bromine-doped ice
Authors: Goldschleger I. U. , Senekerimyan V. , Krage M. S. , Seferyan H. , Janda K. C. , Apkarian V. A.
Published: May 2006

In both water and in ice, the absorption spectra of bromine are dramatically broadened and blueshifted, and all fluorescence is quenched. Time resolved, electronically resonant transient grating measurements are carried out to characterize the vibronic dynamics of the trapped molecule in its electronic B(Π0u3) state in ice. Independent of the initial excitation energy, after the first half-period of motion, a vibrational packet is observed to oscillate near the bottom of the potential, near ν=1. The oscillations undergo a chirped decay to a terminal frequency of 169cm−1 on a time scale of τν=1240fs, to form the stationary ν=0 level. The electronic population in the B state decays in τe=1500fs. Adiabatic following to the cage-compression coordinate is a plausible origin of the chirp. Analysis of the absorption spectrum is provided to recognize that solvent coordinates are directly excited in the process. The observed blueshift of the absorption is modeled by considering the Br2–OH2 complex. Two-dimensional simulations, that explicitly include the solvent coordinate, reproduce both the time data and the absorption spectrum. The observed sharp vibrational recursions can be explained by overdamped motion along the solvent coordinate, and wave packet focusing by fast dissipation during the first half-period of motion of the molecular coordinate.
Dispersion interferometer based on a CO2 laser for TEXTOR and burning plasma experiments
Authors: Bagryansky P. A. , Khilchenko A. D. , Kvashnin A. N. , Lizunov A. A. , Voskoboynikov R. V. , Solomakhin A. L. , Koslowski H. R. ,   TEXTOR team
Published: May 2006

A dispersion interferometer based on a continuous-wave CO2 laser source (λ=9.57 μm) with double plasma passage for measurements of the line-integrated electron density in the TEXTOR tokamak and the GDT linear system has been developed and tested in experiments. A sensitivity of 〈nel〉min=2×1017 m−2 and a temporal resolution of 1 ms have been achieved. The interferometer does not need any rigid frame for vibration insulation. Its basic components are installed compactly on an optical bench placed on a stable support outside of the torus. The possibility for the development of a multichannel dispersion interferometer for the next generation of fusion devices (e.g., W7-X, ITER) is discussed.
Parametric generation of multimegahertz acoustic oscillations in laser-generated multibubble system in bulk water
Authors: Kudryashov Sergey I. , Lyon Kevin , Allen Susan D.
Published: May 2006

Using a nanosecond CO2 laser for explosive surface boiling of bulk water, oscillatory acoustic transients from steam bubbles were recorded using a contact photoacoustic technique. Multiple well-resolved, high-amplitude multimegahertz spectral features reflecting parametric interactions between oscillations of cavitating steam bubbles were revealed in the fast Fourier transformation spectra of these transients. A potential parametric generation mechanism for these oscillation modes of steam bubbles is discussed.
Ultralow resistance Si-containing Ti∕Al∕Mo∕Au Ohmic contacts with large processing window for AlGaN∕GaN heterostructures
Authors: Mohammed Fitih M. , Wang Liang , Adesida Ilesanmi
Published: May 2006

We report on the electrical and microstructural characterization of Si-containing Ti∕Al∕Mo∕Au contacts for AlGaN∕GaN heterostructures. Excellent Ohmic contact formation with contact resistance and specific contact resistivity as low as 0.12Ωmm and 3.8×10−7Ωcm2, respectively, have been obtained by the optimization of Si distribution in the metallization. The presence of Si strongly affects the Ohmic performance and microstructural makeup of the annealed contacts. Greater enhancement in Ohmic performance is achieved when optimized amount of Si is dispersed throughout the metallization.
Evidence for strong flux pinning by small, dense nanoprecipitates in a Sm-doped YBa2Cu3O7−δ coated conductor
Authors: Song Xueyan , Chen Zhijun , Kim Sang-II , Feldmann D. Matthew , Larbalestier David , Reeves Jodi , Xie Yiyuan , Selvamanickam Venkat
Published: May 2006

About 17vol.% of ∼10nm sized (Y,Sm)2O3 precipitates have been developed in a metal-organic chemical vapor deposition grown Sm-doped YBa2Cu3O7−δ coated conductor. The precipitate spacing of ∼15nm suggests strong vortex-precipitate pinning interactions, which are evidenced by a shift in the peak in the flux pinning force curve, an enhanced irreversibility field exceeding 8T at 77K, and a lack of temperature scaling of the flux pinning force over the temperature range of 65–82K.
Multiple and virtual photon processes in radiation-induced magnetoresistance oscillations in two-dimensional electron systems
Authors: Lei X. L. , Liu S. Y.
Published: May 2006

Recently discovered new structures and zero-resistance states outside the well-known oscillations are demonstrated to arise from multiphoton assisted processes, by a detailed analysis of microwave photoresistance in two-dimensional electron systems under enhanced radiation. The concomitant resistance dropping and the peak narrowing observed in the experiments are also reproduced. We show that the radiation-induced suppression of average resistance comes from virtual photon effect and exists throughout the whole magnetic field range.
Theoretical study of electron transport in boron nanotubes
Authors: Lau Kah Chun , Pandey Ravindra , Pati Ranjit , Karna Shashi P.
Published: May 2006

The electron transport in single-walled boron nanotube (BNT) is studied using the Landauer-Büttiker [R. Landauer, J. Phys.: Condens: Matter 1, 8099 (1989); M. Büttiker, Phys. Rev. Lett. 57, 1761 (1986)] multichannel approach in conjunction with the tight-binding method. In the range of the calculated length (1–5.0nm) of the tubes, the calculations predict a ballistic transport in BNT and find a relatively low resistance for BNTs as compared to that of the single-walled carbon nanotubes (CNTs) of comparable length. A lower resistance in the case of BNT than the CNT may be attributed to electron-deficient nature of boron characterized by the presence of two-center, and multicenter bonds in the former.
Lewis-Base Adducts of Lead(II) Compounds. VII. Synthetic and Structural Studies of Some 1:1 Adducts of Linear Polyamines With Lead(II) Nitrate
Authors: Harrowfield JM , Miyamae H , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 1 : 1 adducts of lead(II) nitrate with the linear multidentate polyamines ethane-1,2-diamine ('en'(= '2')), H2N(CH2)2NH(CH2)2NH2(' dien ' = '22') and H2N(CH2)xNH(CH2)yNH(CH2)zNH2 ( xyztet = '222tet' (= ' trien '), '232tet', '323tet'). Crystal/refinement data are as follows: [(en) Pb (NO3)2](∞|∞) is monoclinic, P 21/c, a 5.388(2), b 12.440(5), c 13.123(3) Ǻ, β 102.33(3)°, Z = 4 f.u .; R 0.037 for No 2698 'observed' (I > 3σ(I)) reflections. [( dien ) Pb (NO3)2](∞|∞) is orthorhombic, Ccma , a 9.800(2), b 10.840(2), c 20.521(5), Z = 8; R 0.045, No 991. [( trien ) Pb (NO3)2](∞|∞) is orthorhombic, P 212121, a 14.815(3), b 10.975(3), c 8.410(2) Ǻ, Z = 4; R 0.050, No 1360; [(232tet) Pb (NO3)2](∞|∞) is isomorphous, a 14.524(6), b 11.221(1), c 8.860(2) Ǻ, R 0.036, No 2371. [(323tet) Pb (NO3)2](∞|∞) is monoclinic, P21/c, a 8.195(4), b 14.407(7), c 13.312(4) Ǻ, β 91.05(3)°, Z = 4; R 0.049, No 1644. In general, the degree of complexity of the adduct diminishes as the ligand size increases: whereas the en adduct is a compact one-dimensional two stranded polymer with nearly all nitrate oxygens involved in tight bridging interactions, the extent of bridging diminishes in the adducts of the larger amines, until, for the 323tet species, a monomer is obtained involving a lead coordination sphere containing the ligand and a pair of bidentate nitrate groups. The 1 : 2 adduct with en is also recorded, and is a dimer with quasi-i internal symmetry. [(en)2Pb(NO3)2]2 is monoclinic, P21, a 6.661(2), b 14.226(8), C 13.618(4)Ǻ, β 96.51(2)°; R 0.072, No 1713.
Lewis-Base Adducts of Lead(II) Compounds. XV. Synthesis and Structure of Some Adducts of Bis(2-pyridyl)amine With Lead(II) Salts
Authors: Harrowfield JM , Miyamae H , Skelton BW , Soudi AA , White AH
Published: May 2006

Several complexes of bis(2-pyridyl)amine ('dpa') with lead(II) salts have been synthesized and subjected to room-temperature single-crystal X-ray studies. 1:1 Adducts have been obtained with lead(II) bromide and iodide. They have similar unit cells, also similar to those of a variety of other N,N′-heteroaromatic bidentate ligand adducts with metal(II) halides, and the C2/c cell described elsewhere in this series may be regarded as archetypical. [(dpa)PbBr2](∞|∞) is monoclinic, P21/a, a 9.791(4), b 9.720(4), c 16.498(4) Ǻ, β 95.96(4)′, Z = 4 f.u.; conventional R on |F| at convergence was 0.066 for No = 2717 'observed' (I > 3σ(I)) reflections. [(dpa)PbI2](∞|∞) is monoclinic, P21/c, a 8.299(2), b 10.229(3), c 16.905(5) Ǻ, β 101.47(2)°, Z = 4 f.u.; R was 0.044 for No 2140. Both complexes, like their 2,2'-bipyridine and 1,10-phenanthroline analogues, are linear polymers with six-coordinate (cis-N2)Pb(μ-X)4 environments linked in infinite ... (μ-X)2Pb(μ-X)2… one-dimensional chains, and with dpa being bidentate. A 2:1 adduct of bis(2-pyridyl)amine with lead(II) acetate ('Pb(ac)2') is also described. [(dpa)2Pb(ac)2](∞|∞) is monoclinic, C 2/c, a 28.835(5), b 10.868(3), c 7.665(2) Ǻ, β 94.21(2)°, Z = 4; R was 0.029 for No 1854. The complex is a linear polymer along c; the lead atom lies on a crystallographic twofold axis with a coordination environment comprising a pair of symmetry-related dpa ligands, in this case unidentate (Pb-N 3.092(6) Ǻ), and a pair of symmetry-related bidentate acetate ligands (Pb-O 2.465(4) and 2.568(5) Ǻ) with the first oxygen atom performing an additional bridging function to adjacent symmetry-related lead atoms (Pb-O 2.663(4)Ǻ).
Lewis-Base Adducts of Lead(II) Compounds. XVIII. Synthetic and Structural Studies of Some 1:1 and 2:1 Adducts of 2,4,6-Tris (2-pyridyl)-1,3,5-triazine With Lead(II) Nitrate
Authors: Harrowfield JM , Kepert DL , Miyamae H , Skelton BW , Soudi AA , White AH
Published: May 2006

Adducts of lead(II) nitrate with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (' trz ') have been synthesized and structurally characterized by room-temperature single-crystal X-ray studies, for 1:1 and 1:2 stoichiometry. Crystals of [( trz ) Pb (NO3)2](∞|∞) are monoclinic, P 21/c, a 10.531 (1), b 12.856(2), c 16.874(3) Ǻ, β 102.83(1)°, Z = 4 f.u .; R was 0.027 for No = 2773 'observed' (I > 3σ(I)) reflections. The complex is an infinite polymer; the plane of the tridentate trz ligand lies normal to the polymer axis ( Pb -N(central; distal) 2.523(5); 2.594(5), 2.568(5) Ǻ) with unsymmetrically bidentate nitrate groups to either side ( Pb -O 2.598(6), 2.928(7); 2.556(6), 2.911(7) Ǻ). The third oxygen of each nitrate group bridges to the next lead atom in the polymer chain ( Pb -O 3.008(5), 3.083(6)Ǻ). [( trz )2Pb(NO3)2] is monoclinic, C 2/c, a 15.723(5), b 10.034(2), c 24.379(15) Ǻ, β 106.84(4)°, Z = 4 f.u .; R was 0.038 for No 3030. The compound is a methanol monosolvate. The complex species is mononuclear, with the lead atom located on a crystallographic 2 axis and 10-coordinated by pairs of symmetry-related tridentate trz ( Pb -N(central; distal) 2.779(4); 2.800(5), 2.818(5) Ǻ) and bidentate nitrate ligands ( Pb -O 2.796(6), 2.689(5)Ǻ). A hexahydrate has also been obtained (triclinic, Pī a 23.580(9), b 10.147(4), c 9.762(4)Ǻ, α 113.14(3), β 92.11(3), γ 101.60(3)°, Z = 2 f.u ; R 0.041 for No 5633); although metal-ligand distances are similar to those found in the methanol solvate, and quasi-2 symmetry is retained, a very different stereochemistry is evident in respect of the relative dispositions of the ligands about the (quasi)-2 axis, involving a substantial twist of the two nitrate ligands relative to the triazines, and a flattening of the latter. The coordination polyhedron is different in the two 1:2 adducts. In the methanol solvate the stereochemistry is pentagonal antiprismatic whereas in the hexahydrate it is bicapped square antiprismatic.
Lewis-Base Adducts of Lead(II) Compounds. XIX. Synthetic and Structural Studies of Some 1:1 Adducts of 2,4,6-Tris (2-pyridyl)-1,3,5-triazine With Lead(II) (Pseudo-)Halides
Authors: Harrowfield JM , Miyamae H , Skelton BW , Soudi AA , White AH
Published: May 2006

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for 1:1 adducts of 2,4,6-tris(2-pyridyl) 1,3,5-triazine (' trz ') with lead(II) chloride, bromide, iodide and thiocyanate, the chloride and bromide being methanol monosolvates. [( trz )PbCl2](∞|∞). MeOH is monoclinic, P 2/c, a 9.178(2), b 14.833(3), c
7.347(8) Ǻ, β 93.89(2)°, Z = 2 f.u .; R was 0.042 for No = 1451 'observed' (I > 3σ(I)) reflections; the bromide is related, having a derivative triclinic cell, Pī, a 9.259(3), b 15.153(6), c 7.428(2) Ǻ, α 90.28(3), β 94.62(2), γ 91.15(3)°, Z = 2 f.u .; R was 0.047 for No 2729. [( trz )PbI2](∞|∞), also solvated, is triclinic, Pī , a 15.266(9), b 8.9448(8), c 8.148(11) Ǻ, α 80.60(6), β 77.05(7), γ 83.45(3)°, Z = 2; R was 0.032 for No 3222. In all three compounds an infinite PbX2PbX2Pb polymer is found with the plane of the tridentate trz lying quasi normal to the polymer axis. Pb -N distances lie between 2.63(1) and 2.803(8) Ǻ; Pb-Cl are 2.848(3) and 3.074(3), Pb -Br 2.963(2)-3.257(2) and Pb-I 3.192(3)-3.466(2) Ǻ. The thiocyanate, monoclinic, C 2/c, a 16.974(6), b 6.410(2), c 39.49(2) Ǻ, β 96.33(4)°, Z = 8, R 0.13 for No 2465, is a column of dimeric units stacked up b, successive lead atoms being bridged by thiocyanate sulfur atoms packed in between them, and quasi-parallel to a, and by thiocyanates parallel to b which link pairs of lead atoms in each dimer with the same b coordinate by pairs of bridging nitrogens and bridging sulfurs from the adjacent pair.
A Further Three New Lichen Depsidones
Authors: Elix JA , Elix JA , Adler MT , Adler MT , Wardlaw JH , Wardlaw JH
Published: May 2006

The new depsidones subnorstictic acid (1,4,10-trihydroxy-8-methyl-3,7-dioxo-1,3-dihydro-7H-isobenzofuro-[4,5-b][1,4]benzodioxepin-11-carbaldehyde) (4), decarboxyalectoronic acid [3,8-dihydroxy-1,6-di(2'-oxo-heptyl)-11H-dibenzo[ b,e ][1,4]dioxepin-11-one] (8) and di-O-methylphysodic acid [3,8-dimethoxy-11-oxo-1-(2'-oxoheptyl)-6-pentyl-11H-dibenzo[ b,e ][1,4]dioxepin-7-carboxylic acid] (15) have been identified in lichen extracts.
Metformin prevents embryonic resorption induced by hyperandrogenisation with dehydroepiandrosterone in mice
Authors: Solano M. E. , Elia E. , Luchetti C. G. , Sander V. , Di Girolamo G. , Gonzalez C. , Motta A. B.
Published: May 2006

The present study examined the mechanism by which metformin prevents dehydroepiandrosterone (DHEA)-induced embryonic resorption in mice. Treatment with DHEA (6 mg/100 g bodyweight, 24 and 48 h post implantation) induced 88 ± 1 % embryonic resorption and the diminution of both serum oestradiol (E) and progesterone (P) levels. However, when metformin (50 mg/kg bodyweight) was given together with DHEA, embryo resorption (43 ± 3% v. 35 ± 5% in controls) and both serum E and P levels were not significantly different from controls. Glucose and insulin levels were increased in the DHEA-treated mice but when metformin was administered together with DHEA these parameters were similar to control values. Treatment with DHEA increased ovarian oxidative stress and diminished uterine nitric oxide synthase (NOS) activity; however, when metformin was administered together with DHEA, both ovarian oxidative stress and uterine NOS activity were not different from controls. Metformin treatment did not modify the percentage of CD4+ and CD8+ T cells from both axillar and retroperitoneal lymph nodes but prevented the increase of serum tumour necrosis factor α produced in DHEA-treated mice. These results show that metformin acts in DHEA-induced embryonic resorption in mice by modulating endocrine parameters, ovarian oxidative stress and uterine NOS activity.