bluuebunny/crossref_metadata_2025 huggingface dataset:
Crustal structure beneath the gravity lineations in the Gravity Lineations, Intraplate Melting, Petrologic and Seismic Expedition (GLIMPSE) study area from seismic refraction data
Authors: Holmes R. Chadwick , Webb Spahr C. , Forsyth Donald W.
Published: July 2007

The active source seismic component of the Gravity Lineations, Intraplate Melting, Petrologic and Seismic Expedition (GLIMPSE) experiment investigated the velocity structure and crustal thickness of the Pacific plate along a ∼450 km line paralleling the southern East Pacific Rise where prominent intraplate ridges lie within lows of the lineated free‐air gravity pattern. Compressional wave traveltime data collected by 10 ocean bottom seismometers indicate that the median crustal thickness is ∼6.2 km and increases to ∼8.2 km beneath the Sojourn Ridge. The conspicuous absence of crustal thinning beneath both the Sojourn and Hotu‐Matua ridge systems is strong support against a boudinage‐style model for the formation of these volcanic complexes. Our results suggest the ridge loads are partially supported by both plate flexure and underplating, with an additional mantle component inferred from the analysis of gravity data, Rayleigh wave tomography, and teleseismic body wave delays. Small‐scale convection could produce the observed crustal thickness pattern but fails to explain the geochemical and formation age trends along the ridges. We prefer a model where the channelized flow of low‐density material in the upper mantle, possibly undergoing small‐scale convection, is advected toward the ridge crest. Lows in the gravity field reflect the density contrast within the asthenosphere, and decompression melting amid upwelling limbs of the convective cells sustains the development of the associated ridge systems.
Atmospheric oxidation pathways of propane and its by‐products: Acetone, acetaldehyde, and propionaldehyde
Authors: Rosado‐Reyes Claudette M. , Francisco Joseph S.
Published: July 2007

Propane (C3H8) is one of the most abundant nonmethane hydrocarbons in the atmosphere. It is a fuel widely used, derived from petroleum products during oil and natural gas processing. It can be oxidized in the atmosphere via its reactions with hydroxyl (OH) radicals and chlorine (Cl) atoms and serves as an indicator for the presence of such oxidants. During the atmospheric degradation of propane, various carbonyl compounds are formed, with acetone, acetaldehyde, and propionaldehyde among the most prominent. Carbonyl compounds are relevant because of their toxicity and ability to produce free radicals by photolysis that give rise to stable products, thus providing valuable information about atmospheric oxidation processes. The exact mechanisms of the oxidation pathways of propane have not been properly characterized, although several speculations have been made that determine the oxidation products. The present study investigates the oxidation mechanism of propane, acetone, acetaldehyde, and propionaldehyde by ab inito molecular orbital methods. Detailed pathways leading to experimentally observed products are presented. Equilibrium geometries and energetics, as well as vibrational frequencies of species, transition states, and prereactive complexes are determined at the QCISD(T)/6‐311G(2df,2p)//MP2(full)/6‐31G(d).
Future climate impacts of direct radiative forcing of anthropogenic aerosols, tropospheric ozone, and long‐lived greenhouse gases
Authors: Chen Wei‐Ting , Liao Hong , Seinfeld John H.
Published: July 2007

Long‐lived greenhouse gases (GHGs) are the most important driver of climate change over the next century. Aerosols and tropospheric ozone (O3) are expected to induce significant perturbations to the GHG‐forced climate. To distinguish the equilibrium climate responses to changes in direct radiative forcing of anthropogenic aerosols, tropospheric ozone, and GHG between present day and year 2100, four 80‐year equilibrium climates are simulated using a unified tropospheric chemistry‐aerosol model within the Goddard Institute for Space Studies (GISS) general circulation model (GCM) II′. Concentrations of sulfate, nitrate, primary organic (POA) carbon, secondary organic (SOA) carbon, black carbon (BC) aerosols, and tropospheric ozone for present day and year 2100 are obtained a priori by coupled chemistry‐aerosol GCM simulations, with emissions of aerosols, ozone, and precursors based on the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenario (SRES) A2. Changing anthropogenic aerosols, tropospheric ozone, and GHG from present day to year 2100 is predicted to perturb the global annual mean radiative forcing by +0.18 (considering aerosol direct effects only), +0.65, and +6.54 W m−2 at the tropopause, and to induce an equilibrium global annual mean surface temperature change of +0.14, +0.32, and +5.31 K, respectively, with the largest temperature response occurring at northern high latitudes. Anthropogenic aerosols, through their direct effect, are predicted to alter the Hadley circulation owing to an increasing interhemispheric temperature gradient, leading to changes in tropical precipitation. When changes in both aerosols and tropospheric ozone are considered, the predicted patterns of change in global circulation and the hydrological cycle are similar to those induced by aerosols alone. GHG‐induced climate changes, such as amplified warming over high latitudes, weakened Hadley circulation, and increasing precipitation over the Tropics and high latitudes, are consistent with predictions of a number of previous GCM studies. Finally, direct radiative forcing of anthropogenic aerosols is predicted to induce strong regional cooling over East and South Asia. Wintertime rainfall over southeastern China and the Indian subcontinent is predicted to decrease because of the increased atmospheric stability and decreased surface evaporation, while the geographic distribution of precipitation is also predicted to be altered as a result of aerosol‐induced changes in wind flow.
A multiproxy assessment of the western equatorial Pacific hydrography during the last 30 kyr
Authors: de Garidel‐Thoron Thibault , Rosenthal Yair , Beaufort Luc , Bard Edouard , Sonzogni Corinne , Mix Alan C.
Published: July 2007

Sea surface temperature (SST) and salinity of the Western Pacific Warm Pool (WPWP) reflect global climate effects such as the El Niño–Southern Oscillation phenomenon. However, reconstructions of past changes in the WPWP from the geologic record vary depending on the specific proxy record used. Here we develop a multiproxy record of the last deglaciation from a radiocarbon‐dated sediment core (MD97‐2138) retrieved in the heart of the WPWP. SST reconstructions for the past 30,000 years based on planktonic foraminiferal Mg/Ca (Globigerinoides ruber and Globigerinoides sacculifer), alkenone unsaturation index, and foraminiferal transfer functions differ notably. Mg/Ca‐based SST estimates from the surface dwelling species G. ruber in MD97‐2138 indicate a larger surface cooling (3° ± 0.6°C) during the Last Glacial Maximum (LGM) than inferred from Mg/Ca ratios in G. sacculifer (2.3° ± 0.7°C), statistical transfer functions based on planktonic foraminiferal species assemblages, and Uk37′ (1°–2°C). These estimates are consistent with estimates from other WPWP cores, thereby suggesting that the discrepancy is due to proxy compatibility rather than differences in cores qualitity. Postdepositional dissolution above the lysocline might have altered the Mg/Ca‐based temperature estimates in our site, but this effect is insufficient to resolve discrepancies between Mg/Ca in G. ruber and the other proxies. We suggest that the lower estimates obtained from Mg/Ca in G. sacculifer, faunal transfer functions, and Uk37′ might reflect subsurface temperature changes rather than strict surface estimates. Accounting for potential artefacts, including dissolution and bioturbation, we suggest that the glacial WPWP SST was about 2.5° ± 0.7°C cooler than during the Holocene, whereas the subsurface/upper thermocline temperature change was only about 1.8° ± 0.7°C. Interpreting variations in δ18OSW in terms of salinity changes suggests a possibly slight decrease in surface salinity at the site of MD97‐2138 during the LGM. Though LGM freshening in MD97‐2138 is not robust to postdeposition dissolution effects, this inferred freshening appears to be a general feature of the western equatorial Pacific.
Extensional faulting on Tinos Island, Aegean Sea, Greece: How many detachments?
Authors: Brichau Stéphanie , Ring Uwe , Carter Andrew , Monié Patrick , Bolhar Robert , Stockli Daniel , Brunel Maurice
Published: July 2007

Zircon and apatite fission track (ZFT and AFT) and (U‐Th)/He, 40Ar/39Ar hornblende, and U‐Pb zircon ages from the granites of Tinos Island in the Aegean Sea, Greece, suggest, together with published ZFT data, that there are three extensional detachments on Tinos. The Tinos granites crosscut the Tinos detachment. Cooling of the granites was controlled by the Livadi detachment, which occurs structurally above the Tinos detachment. Our U‐Pb zircon age is 14.6 ± 0.2 Ma and two 40Ar/39Ar hornblende ages are 14.4 ± 0.4 and 13.7 ± 0.4 Ma. ZFT and AFT ages go from 14.4 ± 1.2 to 12.2 ± 1.0 Ma and 12.8 ± 2.4 to 11.9 ± 2.0 Ma. (U‐Th)/He ages are from 10.4 ± 0.2 to 9.9 ± 0.2 Ma (zircon) and 11.9 ± 0.5 to 10.0 ± 0.3 Ma (apatite). All ages decrease northeastward in the direction of hanging wall transport on the Livadi detachment and age‐distance relationships yield a slip rate of 2.6 (+3.3 / −1.0) km Ma−1. This rate is smaller than a published slip rate of 6.5 km Ma−1 for the Vari detachment, which is another detachment structurally above the Tinos detachment. Because of the different rates and because published ZFT ages from the footwall of the Vari detachment are ∼10 Ma, we propose that the Vari detachment has to be distinguished from the older Livadi detachment. We discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the Vari detachment cut down into the footwall of the Livadi detachment successively exhuming deeper structural units. The thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation.
Numerical analyses of subsurface flow in a steep hillslope under rainfall: The role of the spatial heterogeneity of the formation hydraulic properties
Authors: Fiori Aldo , Russo David
Published: July 2007

The paper aims at analyzing subsurface flow and streamflow generation in steep hillslopes after rainfall. The principal scope of the work is to assess the role played by the spatial variability of the hydraulic properties on the subsurface flow patterns and hillslope discharge. We try to address this task through a three‐dimensional numerical model which solves the Richards equation under prescribed initial and boundary conditions. Along an established practice, the relevant hydraulic parameters are modeled as random space functions with given statistical properties. Realistic features of the spatially variable formation parameters and the precipitation data are incorporated into the simulation model. It is found that spatial heterogeneity has a significant impact on the movement of water in the hillslope and the streamflow generation. In particular, the heterogeneous systems are more sensitive to rain input and display an increase of both the water table and saturation which is faster than the homogeneous case. The same is for water velocity, which is everywhere larger when heterogeneity is considered. As a consequence, the dynamics of subsurface stormflow (recognized as the leading mechanism for streamflow generation in the simulations) and the outflow discharge produced by the hillslope after a rain event are enhanced by heterogeneity. Despite of the possible lack of generality of the numerical experiments, they provide useful insight into the complex dynamics occurring in hillslope systems. The simulations show the importance of including realistic spatial heterogeneity in hillslope hydrology studies.
Moving beyond heterogeneity and process complexity: A new vision for watershed hydrology
Authors: McDonnell J. J. , Sivapalan M. , Vaché K. , Dunn S. , Grant G. , Haggerty R. , Hinz C. , Hooper R. , Kirchner J. , Roderick M. L. , Selker J. , Weiler M.
Published: July 2007

Field studies in watershed hydrology continue to characterize and catalogue the enormous heterogeneity and complexity of rainfall runoff processes in more and more watersheds, in different hydroclimatic regimes, and at different scales. Nevertheless, the ability to generalize these findings to ungauged regions remains out of reach. In spite of their apparent physical basis and complexity, the current generation of detailed models is process weak. Their representations of the internal states and process dynamics are still at odds with many experimental findings. In order to make continued progress in watershed hydrology and to bring greater coherence to the science, we need to move beyond the status quo of having to explicitly characterize or prescribe landscape heterogeneity in our (highly calibrated) models and in this way reproduce process complexity and instead explore the set of organizing principles that might underlie the heterogeneity and complexity. This commentary addresses a number of related new avenues for research in watershed science, including the use of comparative analysis, classification, optimality principles, and network theory, all with the intent of defining, understanding, and predicting watershed function and enunciating important watershed functional traits.
Two‐dimensional numerical models of open‐top hydrothermal convection at high Rayleigh and Nusselt numbers: Implications for mid‐ocean ridge hydrothermal circulation
Authors: Fontaine Fabrice J. , Wilcock William S. D.
Published: July 2007

Mid‐ocean ridges host vigorous hydrothermal systems that remove large quantities of heat from the oceanic crust. Inferred Nusselt numbers (Nu), which are the ratios of the total heat flux to the heat flux that would be transported by conduction alone, range from 8 to several hundred. Such vigorous convection is not fully described by most numerical models of hydrothermal circulation. A major difficulty arises at high Nu from the numerical solution of the temperature equation. To avoid classical numerical artifacts such as nonphysical oscillatory behavior and artificial diffusion, we implement the Multidimensional Positive Definite Advection Transport Algorithm (MPDATA) technique, which solves the temperature equation using an iterated upwind corrected scheme. We first validate the method by comparing results for models with uniform fluid properties in closed‐ and open‐top systems to existing solutions with Nu ≤ ∼20. We then incorporate realistic fluid properties and run models for Nu up to 50–60. Solutions are characterized by an unstable bottom thermal boundary layer where thermal instabilities arise locally. The pattern of heat extraction is periodic to chaotic. At any Nu > ∼13 the venting temperatures in a given plume are chaotic and oscillate from ∼350° to 450°C. Individual plumes can temporarily stop short of the surface for intervals ranging from tens to hundreds of years at times when other plumes vent with an increased flow rate. The solutions also display significant recirculation, and as a result large areas of downflow are relatively warm with temperatures commonly exceeding 150°C at middepths. Our results have important implications for mid‐ocean ridge hydrothermal systems and suggest the following: (1) The reaction zones of mid‐ocean ridge hydrothermal systems are enlarged by thermal instabilities that migrate laterally toward upflow zones. This will substantially increase the volume of rock involved in chemical reactions compared to steady state configurations. (2) Hydrothermal discharge can stop temporarily as zones of venting are dynamically replaced by zones of seawater recharge. (3) Anhydrite precipitation occurring at temperatures exceeding ∼150°C will likely occur throughout a large portion of recharge zone and will not necessarily clog downflow pathways as efficiently as has been recently inferred.
Maximum entropy production, cloud feedback, and climate change
Authors: Paltridge Garth W. , Farquhar Graham D. , Cuntz Matthias
Published: July 2007

A steady‐state energy‐balance climate model based on a global constraint of maximum entropy production is used to examine cloud feedback and the response of surface temperature T to doubled atmospheric CO2. The constraint ensures that change in zonal cloud amount θ necessarily involves change in the convergence KX of meridional energy flow. Without other feedbacks, the changes in θ, KX and T range from about 2%, 2 Wm−2 and 1.5 K respectively at the equator to −2%, −2 Wm−2 and 0.5 K at the poles. Global‐average cloud effectively remains unchanged with increasing CO2 and has little effect on global‐average temperature. Global‐average cloud decreases with increasing water vapour and amplifies the positive feedback of water vapour and lapse rate. The net result is less cloud at all latitudes and a rise in T of the order of 3 K at the equator and 1 K at the poles. Ice‐albedo and solar absorption feedbacks are not considered.
Decadal warming of the coldest Antarctic Bottom Water flow through the Vema Channel
Authors: Zenk Walter , Morozov Eugene
Published: July 2007

A decadal warming trend of Antarctic Bottom Water flowing through the Vema Channel is reanalyzed. Our data base consists of 94 high precision, full depth stations from 19 visits to the Vema Sill plus twelve stopovers at two additional key locations. Originally a long‐term temperature increase in the near‐bottom jet was noted from 1992 onward, after a period of rather constant abyssal temperatures since 1972. From today's perspective the apparent stagnant temperature level until 1991 can be interpreted as a period of feeble rising in comparison with a perspicuous warming trend of 2.8 mK yr−1 in the following 15 years. However, the clearly manifested temperature rise is superimposed with fluctuations. For the first time the available time series appears long enough to indicate an associated slight freshening of the bottom water. An attempt is made to trace the observed variability back to its source region in the Weddell Sea.
Navier‐Stokes flow and transport simulations using real fractures shows heavy tailing due to eddies
Authors: Cardenas M. Bayani , Slottke Donald T. , Ketcham Richard A. , Sharp John M.
Published: July 2007

Two‐dimensional Navier‐Stokes flow and transport simulations are conducted for a 15‐cm long fracture mapped via X‐ray computed tomography. (1) The actual fracture with irregular aperture, (2) a truncated fracture where the largest aperture area is excluded from the domain, (3) the truncated fracture with further thinning of other large aperture areas, and (4) a fracture with uniform vertical aperture equal to the actual fracture's mean aperture, are subjected to the same pressure gradient. Slight variations in fracture characteristics result in significantly different flow and transport behavior. Flux is much larger for the uniform‐aperture fracture compared to the actual fracture. A pronounced eddy is present at the largest aperture zone of the actual fracture resulting in a power‐law tail absent in other cases. The uniform aperture fracture has the largest effective dispersion coefficient estimated via inversion of a 1D analytical model. The analytical model fit to the other cases is not as robust as in the uniform aperture case.
Propofol Exerts Greater Neuroprotection with Disodium Edetate than without It
Authors: Kotani Yoshinori , Nakajima Yoshimi , Hasegawa Tatsuya , Satoh Masahiko , Nagase Hisamitsu , Shimazawa Masamitsu , Yoshimura Shinichi , Iwama Toru , Hara Hideaki
Published: July 2007

The main objective of this study, on mice, was to compare the neuroprotective effects of propofol with those of propofol plus disodium edetate (propofol EDTA). We also administered propofol EDTA (0.005% (w/v) EDTA) to mice intravenously, and measured the changes in zinc concentrations occurring after permanent middle cerebral artery occlusion. In the in vivo study, propofol EDTA displayed stronger neuroprotective effects than propofol alone. Furthermore, we examined the neuroprotective effects of EDTA administered alone, and found that EDTA Na significantly reduced the infarct volume. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive cells in the ischemic penumbra was reduced more by propofol EDTA than by propofol alone. We performed in the in vitro study in five groups (aerobic, vehicle (control), propofol, EDTA, and propofol plus EDTA). Propofol and EDTA each protected PC12 cells against oxygen—glucose deprivation-induced cell damage, and the effect of propofol was increased by adding EDTA. Because the chelating action of EDTA was a potential causal mechanism, we examined the effect of propofol EDTA on intracerebral zinc homeostasis. When propofol EDTA was given intravenously 10 mins before cerebral ischemia, the zinc concentration decreased significantly in the cortical area, but not in the subcortex. In conclusion, (a) propofol provides neuroprotection against both in vivo and in vitro ischemic damage, and its effects are enhanced when EDTA is added; and (b) EDTA itself protects against ischemic neuronal damage, possibly, owing to its zinc-chelating action.
Saturation process induced by vortex-merging in numerical Vlasov-Maxwell experiments of stimulated Raman backscattering
Authors: Albrecht-Marc M. , Ghizzo A. , Johnston T. W. , Réveillé T. , Del Sarto D. , Bertrand P.
Published: July 2007

The influence of low-frequency nonlinear Bernstein-Greene-Kruskal (BGK)-type waves induced by trapped electrons in backward stimulated Raman scattering is investigated in optical mixing. Semi-Lagrangian Vlasov-Maxwell simulations show two nonlinear behaviors. First, there is a Morales-O’Neil plasma wave frequency downshift retuned by a small wavenumber shift which maintains the Stimulated Raman Scattering (SRS) resonance. The saturation of Raman backscattering begins with phase space vortex merging followed by a transition to lower wavenumbers following the (nonlinear) dispersion relation, resembling weak turbulence.
Particle spin in a turbulent shear flow
Authors: Mortensen P. H. , Andersson H. I. , Gillissen J. J. J. , Boersma B. J.
Published: July 2007

The translational and rotational motions of small spherical particles dilutely suspended in a turbulent channel flow have been investigated. Three different particle classes were studied in an Eulerian-Lagrangian framework to examine the effect of the response times on the particle statistics. The results for the fluctuating particle velocities were consistent with earlier observations. The mean particle spin exceeded the mean fluid angular velocity in a region close to the channel walls. The fluctuating components of the particle spin were consistently lower than the corresponding fluid angular velocities for the heaviest particles.
On the linear stability of turbulent plane strain flow in a rotating frame
Authors: Akylas E. , Langer C. A. , Kassinos S. C. , Demosthenous E.
Published: July 2007

We apply inviscid rapid distortion theory to the limiting hyperbolic case of turbulent plain strain flow in a rotating frame and investigate the dependence of the evolution of the turbulent kinetic energy on the frame rotation rate. We derive an analytical two-dimensional solution that, unlike previous oversimplified pressureless analyses, allows for an accurate approximation of the three-dimensional initially isotropic problem. From the analytical solutions, we determine the correct stability criterion for the evolution of the turbulent kinetic energy in this flow. Also, we calculate the asymptotic states of the turbulence, in terms of the normalized Reynolds stresses and structure dimensionality tensor components, which coincide with the exact three-dimensional numerical results.
Asymptotic analysis of chaotic particle sedimentation and trapping in the vicinity of a vertical upward streamline
Authors: Angilella Jean-Régis
Published: July 2007

The sedimentation of a heavy Stokes particle in a laminar plane or axisymmetric flow is investigated by means of asymptotic methods. We focus on the occurrence of Stommel’s retention zones and on the splitting of their separatrices. The goal of this paper is to analyze under which conditions these retention zones can form, and under which conditions they can break and induce chaotic particle settling. The terminal velocity of the particle in still fluid is of the order of the typical velocity of the flow, and the particle response time is much smaller than the typical flow time scale. It is observed that if the flow is steady and has an upward streamline where the vertical velocity has a strict local maximum, then inertialess particle trajectories can take locally the form of elliptic Stommel cells, provided the particle terminal velocity is close enough to the local peak flow velocity. These structures only depend on the local flow topology and do not require the flow to have closed streamlines or stagnation points. If, in addition, the flow is submitted to a weak time-periodic perturbation, classical expansions enable one to write the particle dynamics as a Hamiltonian system with one degree of freedom, plus a perturbation containing both the dissipative terms of the particle motion equation and the flow unsteadiness. Melnikov’s method therefore provides accurate criteria to predict the splitting of the separatrices of the elliptic cell mentioned above, leading to chaotic particle trapping and chaotic settling. The effect of particle inertia and flow unsteadiness on the occurrence of simple zeros in Melnikov’s function is discussed. Particle motion in a plane cellular flow and in a vertical pipe is then investigated to illustrate these results.
Hit and miss of classical nucleation theory as revealed by a molecular simulation study of crystal nucleation in supercooled sulfur hexafluoride
Authors: Leyssale Jean-Marc , Delhommelle Jérôme , Millot Claude
Published: July 2007

Classical nucleation theory pictures the homogeneous nucleation of a crystal as the formation of a spherical crystalline embryo, possessing the properties of the macroscopic crystal, inside a parent supercooled liquid. In this work we study crystal nucleation in moderately supercooled sulfur hexafluoride by umbrella sampling simulations. The nucleation free energy evolves from 5.2kBT at T=170K to 39.1kBT at T=195K. The corresponding critical nucleus size ranges from 40molecules at T=170Kto266molecules at T=195K. Both nucleation free energy and critical nucleus size are shown to evolve with temperature according to the equations derived from the classical nucleation theory. Inspecting the obtained nuclei we show, however, that they present quite anisotropic shapes in opposition to the spherical assumption of the theory. Moreover, even though the critical nuclei possess the structure of the stable bcc plastic phase, the only mechanically stable crystal phase for SF6 in the temperature range investigated, they are shown to be less ordered than the corresponding macroscopic crystal. Their crystalline order is nevertheless shown to increase regularly with their size. This is confirmed by a study of a nucleus growth from a critical size to a size of the order of 104molecules. Similarly to the fact that it does not affect the temperature dependence of the nucleation free energy and of the critical nucleus size, the ordering of the nucleus with size does not affect the growth rate of the nucleus.
Electromagnetic model and calculations of the surface-enhanced Raman-shifted emission from Langmuir-Blodgett films on metal nanostructures
Authors: Giannini V. , Sánchez-Gil J. A. , García-Ramos J. V. , Méndez E. R.
Published: July 2007

We present a theoretical study of the electromagnetic contribution to surface-enhanced Raman scattering (SERS) from a Langmuir-Blodgett film close to a metal surface. This macroscopic dipolar model fully accounts for the Raman-shifted emission so that meaningful SERS (electromagnetic) enhancement factors that do not depend only on the local electromagnetic field enhancement at the pump frequency are defined. For a plane metal surface, analytical SERS enhancement factors that are consistent for all pump beam polarization and molecular orientation are obtained. In order to investigate SERS on complex nanostructured metal surfaces, we introduce this model into the formally exact, Green’s theorem surface integral equation formulation of the scattered electromagnetic field. This formulation is thus employed to calculate numerically the near-field and far-field emissions at the Raman-shifted frequency for very rough, random nanostructured surfaces, with emphasis on the impact of collective processes for varying pump frequency and Raman shift. Our results reveal that the widely used ∣E∣4 approximation tends to overestimate average SERS enhancement factors.
Generalized phenomenological model for the effect of electromigration on interfacial reaction
Authors: Hsu Chia-Ming , Wong David Shan-Hill , Chen Sinn-Wen
Published: July 2007

Intermetallic compound (IMC) formation is important for the reliability of microelectronic devices. In this work, a generalized phenomenological model was developed to explain the effects of electromigration on IMC growth by considering reaction and diffusion of two species. When both reaction and mass transfer are important, the model predicts cathode enhancement and anode thinning if the electromigration effect on the dominant diffusion species is more pronounced. Cathode suppression and anode enhancement occur when the electromigration effect on the minor diffusion species is more pronounced. Simultaneous cathode and anode suppressions happen when there are two diffusion species and the diffusion and electromigration fluxes are comparable. Simultaneous cathode and anode enhancements occur when mass transfer is the limiting step and diffusion flux is negligible compared to electromigration. This model was found to be consistent with experiment data on IMC growth in the literature given the limited amount of information on effective charge of various species.
Examination of plasma-wall interactions in Hall effect thrusters by means of calibrated thermal imaging
Authors: Mazouffre S. , Dannenmayer K. , Pérez-Luna J.
Published: July 2007

A semiempirical time-dependent thermal model of Hall effect thrusters was developed to compute evolution of the thruster channel wall temperature during a transient regime. The model accounts for heat conduction through dielectric walls and radiative transfer as the channel is considered as a thermal enclosure. The graybody view factors are experimentally determined during the cooling period that follows a power shutdown. The model permits the assessment of the amount of power delivered to walls by fitting calculated temperature profiles to experimental profiles obtained by means of calibrated infrared imaging. Plasma-surface interactions are examined in this contribution for three types of thrusters, namely, SPT100-ML, PPS®1350-G, and the 5-kW-class PPSX000-ML. The electrical input power range that is probed stretches out from 500Wto5kW. The energy flux passed to the discharge chamber dielectric walls varies between 0.1 and 2W∕cm2. The overall amount of power delivered to the external and internal walls is found to vary linearly with the applied power. It is in favor of an energy loss mechanism driven by ion bombardment. A departure from the linear trend is observed at high discharge voltage. Production of multiply charged ion species could be an explanation. The impact of thruster design and wall material on power losses inside the thruster channel is also investigated from both a technological and a physics standpoint.
Effect of shape on magnetic response for slotted Co nanorings
Authors: Agarwal Nipun , Smith David J. , McCartney Martha R.
Published: July 2007

Remanent states and magnetization reversal for slotted Co nanorings have been investigated using Lorentz microscopy and off-axis electron holography. The 30-nm-thick Co slotted rings were patterned individually and in arrays using electron-beam lithography and lift-off. Different combinations of ring sizes, ring widths, slot angles, and interelement distances were studied using orthogonal applied field directions (perpendicular and parallel to the slot direction). Typical outer diameters (ODs) were in the range of 300–650nm with slot angles (α) from 30° to 180°. Single-vortex, double-vortex, and flux-closure states without any vortex were found to be the most common remanent configurations. The nanorings showed considerable flux leakage near the slotted region for some size and shape combinations. Slotted Co nanorings with small OD (300nm or less) and moderate slot angles (α=30°) would be strong candidate shapes for future patterned media applications.
GaN quantum dots grown on AlxGa1−xN layer by plasma-assisted molecular beam epitaxy
Authors: Hori Y. , Oda O. , Bellet-Amalric E. , Daudin B.
Published: July 2007

We report on the growth of GaN quantum dots on an AlxGa1−xN layer. Taking advantage of the delayed strain relaxation of AlGaN on an AlN template, we were able to grow GaN quantum dots on an AlGaN layer with Al content as low as 34%. Real-time monitoring of the variations of the in-plane lattice parameter revealed that the growth of the self-organized GaN quantum dots depended not only on the in-plane lattice mismatch but also on the chemical composition of the underlying layer. The morphological properties of the GaN quantum dots were studied by atomic force microscopy. The size distribution of the quantum dots varied from bimodal to monomodal at 80% Al content. Monomodal quantum dots decreased the aspect ratio when the Al content of the AlGaN layer decreased, which is consistent with a reduced elastic relaxation compensated for by a decrease of interfacial energy.
Surface potential mapping on crystalline silicon on glass solar modules
Authors: Breitenstein Otwin , Gupta Rajesh , Schneider Jens
Published: July 2007

Thin film solar modules may suffer from internal shunts or other defects like open interconnections. Shunts are detectable in solar modules e.g., by lock-in thermography (LIT). However, since the local potentials in a module are floating, the quantitative interpretation of LIT results is complicated. In crystalline silicon on glass (CSG) thin film silicon solar modules, not only the individual cell potentials may vary, but also the lateral potential within one cell. In this contribution, sequentially contacting surface potential mapping (PM) is proposed for imaging the local surface potential in CSG modules. The measurements were performed in the dark with an applied forward bias and under illumination of the module with an electrical load. The results are displayed in special formats like the cell bias image or the potential deviation image, which are very sensitive to any defects or inhomogeneities in the module. After introducing the experimental technique, PSpice simulations of different defects like shorts and opens in CSG modules are performed. The simulated local potentials are used to construct potential mapping images of different defects under different measurement conditions in different display modes. These simulations are then compared with experimental results obtained on fractions of CSG modules. Characteristic defects can be identified by characteristic PM image structures. We find that PM is a convenient and reliable tool to image inhomogeneities especially in CSG thin film modules. In combination with LIT imaging, this technique allows one to identify any kind of electric inhomogeneities in such modules, which are leading to a reduced performance. The application of this technique to other solar modules is discussed as well.
Eu
3
+
as a probe for rare-earth dopant site structure in nano-glass-ceramics
Authors: Driesen K. , Tikhomirov V. K. , Görller-Walrand C.
Published: July 2007

Eu 3 + -doped transparent nano-glass-ceramics, 32(SiO2)9(AlO1.5)31.5(CdF2)18.5(PbF2)5.5(ZnF2):3.5(EuF3)mol %, have been prepared aiming at the investigation of the site structure of the Eu3+ rare-earth dopant. In this nano-glass-ceramic host, other rare-earth dopants, such as Er3+, Tm3+, Ho3+, and Dy3+, also have served as a dopant; however the Eu3+ ion is a preferably sensitive probe for a rare-earth dopant site structure due to its unique purely magnetic and purely electric dipole moment optical transitions involving the nondegenerate excited D50 and ground F70 states. The splitting in the respective emission and absorption spectra in the crystalline field of the nano-glass-ceramics and its parent glass has been studied. It has been concluded that the major site of the rare-earth dopant in the nano-glass-ceramics is nearly cubic, with an orthorhombic distortion according to the sequence Oh→D4h→D2h, and the majority of the rare-earth dopants substitute onto the Pb2+ site in the PbF2 nanocrystals embedded in the glass network. A vibronic contribution to the strength of the D50→F72 electric dipole moment transition has been found and the respective dominating contributing vibration mode has been proposed to be and to change as a2u→b1u→au, according to lowering the site symmetry in a sequence Oh→D4h→D2h.
Oxygen species in HfO2 films: An in situ x-ray photoelectron spectroscopy study
Authors: Driemeier C. , Wallace R. M. , Baumvol I. J. R.
Published: July 2007

The chemical bonding of O atoms in HfO2 films on Si was investigated by in situ x-ray photoelectron spectroscopy in the O 1s spectral region. In addition to trivial O forming only O-Hf bonds, O 1s signals corresponding to nontrivial secondary O (Osec) were also observed. By ruling out possible roles of impurities as well as by comparing O 1s signals for different thermochemical processing routes, Osec chemical origins were inferred. Moreover, angle-resolved photoelectron analysis was employed to quantitatively separate surface and bulk Osec contributions. Surface Osec was assigned to surface O-H groups generated either by room temperature water vapor exposure or by 600 °C H2 annealing. Bulk Osec was assigned to O-O or O-H bonds and, as indicated by thermodynamic calculations and complementary structural analysis, is located in HfO2 amorphous regions and grain boundaries. This bulk Osec can be partly removed by annealing in reducing atmospheres. For some of the processing routes employed here, we observed additional, water-induced bulk Osec, which was attributed to dissociative water absorption in HfO2 amorphous regions and O-depleted grain boundaries.
Small-angle neutron scattering in materials science: Recent practical applications
Authors: Melnichenko Yuri B. , Wignall George D.
Published: July 2007

Modern materials science and engineering relies increasingly on detailed knowledge of the structure and interactions in “soft” and “hard” materials, but there have been surprisingly few microscopic techniques for probing the structures of bulk samples of these substances. Small-angle neutron scattering (SANS) was first recognized in Europe as a major technique for this purpose and, over the past several decades, has been a growth area in both academic and industrial materials research to provide structural information on length scales ∼10–1000Å (or 1–100nm). The technique of ultrahigh resolution small-angle neutron scattering (USANS) raises the upper resolution limit for structural studies by more than two orders of magnitude and (up to ∼30μm) and hence overlaps with light scattering and microscopy. This review illustrates the ongoing vitality of SANS and USANS in materials research via a range of current practical applications from both soft and hard matter nanostructured systems.
Tunable and movable liquid microlens in situ fabricated within microfluidic channels
Authors: Dong Liang , Jiang Hongrui
Published: July 2007

The authors report on a tunable and movable liquid microlens in situ fabricated through fluid manipulation within microfluidics. Taking advantage of surface tensions at the microscale, the microlens is formed by a liquid droplet interfacing air. Through pneumatic control of the droplet, the microlens can be tuned in focal length and moved within the microfluidic channel on demand, thus being highly reconfigurable. A focal length tuning range from 1.5to8.9mm is demonstrated. The in-plane optical axis of the microlens provides the flexibility in designing micro-optics within microfluidics, as demonstrated by realizing a planar fluorescence detection device.
Surface energy transfer from rhodamine 6G to gold nanoparticles: A spectroscopic ruler
Authors: Sen Tapasi , Sadhu Suparna , Patra Amitava
Published: July 2007

Here, the authors report the energy transfer from rhodamine 6G dyes to gold nanoparticles. There is a pronounced effect on the photoluminescence and a shortening of the lifetime of the dye when interacting with the Au nanoparticles. The calculated distance (d) between the donor and acceptor varies from 86.06to102.47Å with changing the concentrations of Au and dye. Analysis suggests that the energy transfer from dye to the Au nanoparticles is a surface energy transfer process and follows a 1∕d4 distance dependence.
Switchable nonlinear metalloferroelectric photonic crystals
Authors: Mishina E. , Zaitsev A. , Ilyin N. , Sherstyuk N. , Sigov A. , Golovko Yu. , Muhortov V. , Kolesnikov A. , Lozovik Yu. , Yemtsova M. , Rasing Th.
Published: July 2007

Two types of low-voltage electroswitchable nonlinear photonic crystals were fabricated providing spatial-frequency control of second harmonic generation radiation of visible light. A two-dimensional photonic crystal was fabricated by focused ion beam etching of a ferroelectric BaSrTiO3 thin film and switched by an electric field applied by an interdigital electrode system, which simultaneously acted as a one-dimensional photonic crystal. The fabricated device operated at a second harmonic wavelength around 400nm with an efficiency incomparably higher than in the case of linear optics.
Magnetodielectric effect in double perovskite La2CoMnO6 thin films
Authors: Singh M. P. , Truong K. D. , Fournier P.
Published: July 2007

We report on the magnetodielectric properties of well-ordered epitaxial La2CoMnO6 films. The temperature dependence of the dielectric constant is measured in the 10–105Hz frequency range under applied magnetic fields up to 50kOe. As temperature is lowered, the dielectric constant decreases in the ferromagnetic regime and approaches a plateau below 100K. A significant enhancement in the dielectric constant under applied magnetic field is observed only in the ferromagnetic phase regime culminating around the transition temperature, while it is absent in the paramagnetic phase regime. Using Arrott plots, we also demonstrate that these films exhibit a second-order phase transition at their Curie temperature. The observed magnetodielectric characteristics of the films are interpreted using the phenomenological theory.
Depletion-mode GaAs metal-oxide-semiconductor field-effect transistor with amorphous silicon interface passivation layer and thin HfO2 gate oxide
Authors: Zhu F. , Koveshnikov S. , Ok I. , Kim H. S. , Zhang M. , Lee T. , Thareja G. , Yu L. , Lee J. C. , Tsai W. , Tokranov V. , Yakimov M. , Oktyabrsky S.
Published: July 2007

The authors have demonstrated a n-type GaAs depletion-mode metal-oxide-semiconductor field-effect Transistor with normalized transconductance gm of 266mS∕mm, peak electron mobility of 1124cm2V−1s−1, and low hysteresis. The good device characteristics are attributed to the use of amorphous silicon interface passivation layer and HfO2 gate dielectric. The pulse Id-Vg characteristics show that even higher channel mobility (>2000cm2V−1s−1) can be achieved by reducing the interfacial and bulk traps in the gate stack.
Effect of acceptor on efficiencies of exciplex-type organic light emitting diodes
Authors: Su W. M. , Li W. L. , Xin Q. , Su Z. S. , Chu B. , Bi D. F. , He H. , Niu J. H.
Published: July 2007

The relationship between the electroluminescent (EL) efficiencies of interfacial exciplex emission and the lowest unoccupied molecular orbital (LUMO) of the acceptors systematically investigated. A nearly linear relationship was observed between LUMOs of acceptors and exciplex efficiency for a fixed donor of 4,4′,4″-tris[3-methyl-phenyl(phenyl)amino]-triphenylamine in exciplex-type devices. This result indicates that the lower the LUMO of the acceptor is, the higher the EL efficiency of the exciplex is. The effect of acceptor on the efficiencies of exciplex-type devices is attributable to the interactions between the donor and acceptor molecules, which were closely related to the matched LUMOs and intermolecular conformations overlap between donor and acceptor molecules.
Combinatorial promoter design for engineering noisy gene expression
Authors: Murphy Kevin F. , Balázsi Gábor , Collins James J.
Published: July 2007

Understanding the behavior of basic biomolecular components as parts of larger systems is one of the goals of the developing field of synthetic biology. A multidisciplinary approach, involving mathematical and computational modeling in parallel with experimentation, is often crucial for gaining such insights and improving the efficiency of artificial gene network design. Here we used such an approach and developed a combinatorial promoter design strategy to characterize how the position and multiplicity of
tet
O
2
operator sites within the
GAL1
promoter affect gene expression levels and gene expression noise in
Saccharomyces cerevisiae
. We observed stronger transcriptional repression and higher gene expression noise as a single operator site was moved closer to the TATA box, whereas for multiple operator-containing promoters, we found that the position and number of operator sites together determined the dose–response curve and gene expression noise. We developed a generic computational model that captured the experimentally observed differences for each of the promoters, and more detailed models to successively predict the behavior of multiple operator-containing promoters from single operator-containing promoters. Our results suggest that the independent binding of single repressors is not sufficient to explain the more complex behavior of the multiple operator-containing promoters. Taken together, our findings highlight the importance of joint experimental–computational efforts and some of the challenges of using a bottom-up approach based on well characterized, isolated biomolecular components for predicting the behavior of complex, synthetic gene networks, e.g., the whole can be different from the sum of its parts.
Intracellular crowding defines the mode and sequence of substrate uptake byEscherichia coliand constrains its metabolic activity
Authors: Beg Q. K. , Vazquez A. , Ernst J. , de Menezes M. A. , Bar-Joseph Z. , Barabási A.-L. , Oltvai Z. N.
Published: July 2007

The influence of the high intracellular concentration of macromolecules on cell physiology is increasingly appreciated, but its impact on system-level cellular functions remains poorly quantified. To assess its potential effect, here we develop a flux balance model ofEscherichia colicell metabolism that takes into account a systems-level constraint for the concentration of enzymes catalyzing the various metabolic reactions in the crowded cytoplasm. We demonstrate that the model's predictions for the relative maximum growth rate of wild-type and mutantE. colicells in single substrate-limited media, and the sequence and mode of substrate uptake and utilization from a complex medium are in good agreement with subsequent experimental observations. These results suggest that molecular crowding represents a bound on the achievable functional states of a metabolic network, and they indicate that models incorporating this constraint can systematically identify alterations in cellular metabolism activated in response to environmental change.