bluuebunny/crossref_metadata_2025 huggingface dataset:
Two decades of terrestrial carbon fluxes from a carbon cycle data assimilation system (CCDAS)
Authors: Rayner P. J. , Scholze M. , Knorr W. , Kaminski T. , Giering R. , Widmann H.
Published: June 2005

This paper presents the space‐time distribution of terrestrial carbon fluxes for the period 1979–1999 generated by a terrestrial carbon cycle data assimilation system (CCDAS). CCDAS is based around the Biosphere Energy Transfer Hydrology model. We assimilate satellite observations of photosynthetically active radiation and atmospheric CO2 concentration observations in a two‐step process. The control variables for the assimilation are the parameters of the carbon cycle model. The optimized model produces a moderate fit to the seasonal cycle of atmospheric CO2 concentration and a good fit to its interannual variability. Long‐term mean fluxes show large uptakes over the northern midlatitudes and uptakes over tropical continents partly offsetting the prescribed efflux due to land use change. Interannual variability is dominated by the tropics. On interannual timescales the controlling process is net primary productivity (NPP) while for decadal changes the main driver is changes in soil respiration. An adjoint sensitivity analysis reveals that uncertainty in long‐term storage efficiency of soil carbon is the largest contributor to uncertainty in net flux.
Terrigenous dissolved organic matter in the Arctic Ocean and its transport to surface and deep waters of the North Atlantic
Authors: Benner Ronald , Louchouarn Patrick , Amon Rainer M. W.
Published: June 2005

Surface waters of the Arctic Ocean have the highest concentrations of dissolved organic carbon (DOC) and terrigenous dissolved organic matter (DOM) of all ocean basins. Concentrations of dissolved lignin phenols in polar surface waters are 7‐fold to 16‐fold higher than those in the Atlantic and Pacific oceans, and stable carbon isotopic compositions of DOM are depleted in 13C by 1–2‰ relative to those in the Atlantic and Pacific. The large contribution of terrigenous DOM from Arctic rivers is responsible for the elevated concentrations of DOC in polar surface waters. The distribution of terrigenous DOM in polar surface waters is very heterogeneous, but on average we estimate 14–24% of the DOC is of terrestrial origin. Stable nitrogen isotopic compositions were useful for distinguishing DOM of Pacific and Atlantic origins as well as terrigenous and marine origins. The size distribution and composition of lignin phenols provide some evidence of photochemical transformations of terrigenous DOM, but it appears this process is not extensive in polar surface waters. The extent to which terrigenous DOM is removed from the Arctic Ocean by microbial degradation is less clear and warrants further study. Physical transport of terrigenous DOC to the North Atlantic is a major mechanism for its removal from the Arctic. The East Greenland Current alone exports 4.4–6.6 Tg of terrigenous DOC annually to the North Atlantic. Terrigenous DOC of Arctic origin was identified for the first time in components of North Atlantic Deep Water. Preliminary estimates indicate that ∼1 Tg of terrigenous DOC is exported from the Arctic in Denmark Strait Overflow Water with an additional ∼0.7 Tg in Classical Labrador Sea Water. Together, these exports compose approximately 25–33% of the terrigenous DOC discharged annually to the Arctic via rivers.
Modeling temporal variations of electrical resistivity associated with pore pressure change in a kilometer‐scale natural system
Authors: Hautot Sophie
Published: June 2005

From 1995 to 1998 the natural electric field was monitored with an array of 20 dipoles on a ridge separating two reservoir lakes in the French Alps. The experiment was run to study the correlation between the electric potential variations and transient deformations of the ridge in association with the annual cycle of lake level variations. Large distortion of the induced electric field is observed and is found almost purely static and well correlated to the geology. A simple DC 3‐D model is constructed, and resistivity structures that create the distortion are identified. The electrically resistive crystalline bedrock strongly amplifies the static distortion caused by the heterogeneous geology on the ridge. The temporal variations of the electric distortion observed over two years are associated with the lake level cycle. The model suggests that a resistivity variation of the order of 20% in the bedrock can account for the observed seasonal time‐varying distortion. The resistivity change could be explained in terms of pore and crack geometry change controlled by stress. This study suggests that in particular geological contexts, electrical resistivity changes in structures can be detected through an amplification of the static distortion of the induced electric field. The results provide a framework to interpret some observations of electric field variations possibly associated with tectonic activity. The galvanic coupling model proposed here is an alternative to the streaming potential effect model, and it defines new criteria for the surface detection of groundwater in the crust.
Mathematical simulations of anisotropy of magnetic susceptibility on composite fabrics
Authors: Martín‐Hernández Fátima , Kunze Karsten , Julivert Manuel , Hirt Ann M.
Published: June 2005

The anisotropy of magnetic susceptibility (AMS) is an integral measure of the preferred orientation of all minerals present in a rock. When the AMS is carried by paramagnetic minerals alone, the principal directions of the susceptibility ellipsoid should reflect the crystallographic orientation of the minerals. The relationship between the AMS and deformation depends on several factors, which control the development of lattice‐preferred orientation (LPO) in a rock. A mathematical model is presented that simulates the magnetic susceptibility ellipsoid for samples composed of more than one mineral phase. Measurements of the AMS are compared with fabric‐based anisotropy models for black slates from the Navia‐Alto Sil slate belt in northern Spain. The AMS is carried by paramagnetic minerals, as has been confirmed by high‐field torque magnetometry, low‐temperature AMS and magnetization curves. The LPO of mica and chlorite has been determined by X‐ray texture goniometry. Pole figures and orientation ellipsoids show the changes in the degree of alignment of the phyllosilicates. The models have been tested in samples displaying three types of pole figures: a high‐intensity point maximum, a medium‐intensity elliptical maximum, and a girdle‐shaped distribution. At one site displaying kink bands the LPO shows variations between these types at the outcrop scale. The case studies illustrate the success in modeling different LPO types.
Control of impact crater fracture systems on subsurface hydrology, ground subsidence, and collapse, Mars
Authors: Rodríguez Jose Alexis Palmero , Sasaki Sho , Dohm James M. , Tanaka Ken L. , Strom Bob , Kargel Jeff , Kuzmin Ruslan , Miyamoto Hideaki , Spray John G. , Fairén Alberto G. , Komatsu Goro , Kurita Kei , Baker Victor
Published: June 2005

Noachian layered materials are pervasively exposed throughout the highlands of Mars. The layered deposits, in places many kilometers thick, exhibit impact craters of diverse morphologic characteristics, ranging from highly degraded to pristine, most of which formed during the period of heavy bombardment. In addition, exhumed impact craters, ancient channels, and fluvial and alluvial fans are visible in the layered deposits through MOC imagery. These features are more abundant in Noachian terrains, which indicates relatively high erosion rates during ancient Mars that competed with heavy meteoritic bombardment. The Noachian layered materials are thus expected to contain numerous buried impact craters in various states of preservation. Here, we propose that impact craters (buried and exposed) and associated fracture systems dominate the basement structural fabric of the ancient highlands and that they have significantly influenced the hydrogeology. Diversity in the occurrence of high and low densities of impact craters and associated fracture systems controls the magnitude of the local effects of magmatic‐driven hydrothermal activity. In and surrounding the Tharsis region, for example, the formation of chaotic terrains (the source regions of the circum‐Chryse outflow channel system) and a large diversity of collapse structures, including impact crater moats and pit chains, appear to be the result of enhanced hydrothermal activity.
Interactions between bed forms: Topography, turbulence, and transport
Authors: Jerolmack Douglas , Mohrig David
Published: June 2005

Results are presented examining the interaction between two sandy bed forms under low–sediment transport conditions in a small laboratory flume. The initial artificially made bed forms were out of equilibrium with the flow field. Temporal evolution of bed forms was monitored using time‐lapse photography in order to characterize bed form adjustment to the imposed flow. Velocity measurements were collected using an acoustic Doppler velocimeter to characterize both mean flow and turbulence associated with different bed form geometries. Sandy bed forms all had identical initial geometries; however, the initial distance between bed form crests was varied between experiments. Overall deformation of the bed varied as a function of initial bed form spacing; however, bed forms evolved unpredictably as periods of relatively slow change were punctuated by periods of rapidly changing geometry. Subtle changes in bed form trough geometry were found to have a strong influence on turbulence and therefore sediment transport. Comparison with field studies suggests that the mechanisms described herein are active in natural systems.
Data requirements for identifying macroscopic water stress parameters: A study on grapevines
Authors: Hupet F. , Trought M. C. T. , Greven M. , Green S. R. , Clothier B. E.
Published: June 2005

We have tested the inverse modeling approach to derive macroscopic water stress parameters (MWSP) using different types of information, such as soil water content, pressure head, and transpiration rate. This testing was performed by numerical experiments considering a multilayered soil growing grapevines under three different irrigation regimes and two contrasted water stress scenarios. The results indicate that measurements of the soil water content alone do not contain enough information to estimate MWSP. Nonuniqueness is likely to occur, and the MWSP estimates may contain large uncertainties. However, the incorporation of only transpiration measurements into the objective function does allow the deriving of accurate MWSP. This contrast is mainly due to the difference of sensitivity to the MWSP, which is much higher for the transpiration than for the soil water content. Results obtained using only soil water pressure head measurements are similar to or poorer than those obtained using transpiration data. Moreover, visual inspection of response surfaces of the objective function suggests that the incorporation of further information in addition to transpiration into the objective function is not of great value for the identification of MWSP. Uncertainties for the MWSP estimated using the three types of information combined are in most cases only 1.3 times smaller than when transpiration measurements alone are incorporated into the objective function. Beyond the specific results obtained for the estimation of MWSP we find that the parameters estimates and their associated uncertainties are strongly dependent upon the type, quantity, and quality of the information included into the objective function. Hence inverse modeling may provide a means to design better experiments.
Structures induced by small moonlets in Saturn's rings: Implications for the Cassini Mission
Authors: Seiß M. , Spahn F. , Sremčević M. , Salo H.
Published: June 2005

Particle simulations are carried out to study density features caused by small moonlets embedded in a dense planetary ring. The creation of a “propeller” like structure is found together with adjacent density wakes. Both features are clear indications for the existence of moonlets in the rings. We confirmed that the propeller scales with the Hill‐radius in radial direction whereas its azimuthal extent is determined by the ratio between the moonlet‐mass and the ring‐viscosity. Our findings bear direct implications for the analysis of the Cassini imaging (ISS) and occultation (UVIS) data: (i) for the detection of embedded larger bodies (>30 m) in Saturn's rings, and (ii) for remotely probing transport properties of the rings. The existence of a moonlet population may point to a catastrophic disruption of a parent body as a formation scenario for rings.
Warm flux tubes in the E‐ring plasma torus: Initial Cassini magnetometer observations
Authors: Leisner J. S. , Russell C. T. , Khurana K. K. , Dougherty M. K. , André N.
Published: June 2005

Initial Cassini magnetometer observations in the E‐ring plasma torus reveal the presence of previously unreported diamagnetic decreases in the magnetic field. The decrease in magnetic pressure on these flux tubes implies the presence of additional plasma energy densities up to 1 keV/cm3. They are less stretched than surrounding flux tubes suggesting the centrifugal force acting on them is less, possibly because they have a lower mass content or lower azimuthal velocity than their neighbors. Outward from these isolated tubes, at about 6 Saturn radii, an irregular transition from predominantly cool to predominantly warm flux tubes is observed. A similar boundary is observed in the jovian magnetosphere at the outer edge of the Io torus. Both the saturnian and jovian boundaries are candidates for the interchange instability but other processes may also be acting. ULF waves are associated with some, but not all, of these flux tubes.
Thermosteric sea level rise, 1955–2003
Authors: Antonov J. I. , Levitus S. , Boyer T. P.
Published: June 2005

For the 1955–2003 period, the thermal expansion of the 0–700 m layer of the World Ocean contributed approximately 0.33 mm/year to global sea level rise. About half of this thermosteric trend is due to warming of the Atlantic Ocean. Approximately one third of the total thermosteric rise is due to the warming of the Pacific Ocean. For the period of available TOPEX/Poseidon (T/P) satellite altimetry data (1993–2003), the linear trend of thermosteric sea level (0–700 m) is 1.23 mm/year, 60% of which is due to the trends in the Pacific Ocean. For the 0–3000 m layer of the entire World Ocean, the linear trend of thermosteric sea level is 0.40 mm/year for 1955–1959 through 1994–1998. For the 50°S–65°N region that we previously reported (Antonov et al., 2002) which was characterized by a 0.50 mm/year trend for 1955–1959 through 1992–1996, our new estimate is 0.47 mm/year for this same period.
Nestin-Expressing Cells Divide and Adopt a Complex Electrophysiologic Phenotype after Transient Brain Ischemia
Authors: Kronenberg Golo , Wang Li-Ping , Synowitz Michael , Gertz Karen , Katchanov Juri , Glass Rainer , Harms Christoph , Kempermann Gerd , Kettenmann Helmut , Endres Matthias
Published: June 2005

The intermediate filament nestin is upregulated in response to cerebral ischemia; the significance of this, however, is incompletely understood. Here, we used transgenic mice that express green fluorescent protein (GFP) under control of the nestin promotor to characterize the fate of nestin-expressing cells up to 8 weeks after 30 mins occlusion of the middle cerebral artery (MCAo) and reperfusion. The population of nestin-GFP + cells increased in the ischemic lesion rim and core within 4 days, did not become TUNEL-positive, and was detectable up to 8 weeks in the lesion scar. Nestin-GFP + cells proliferated in situ and underwent approximately one round of cell division. They were not recruited in large numbers from the subventricular zone (SVZ) as indicated by absence of colabeling with intracerebroventricularly injected dye DiI in the majority of nestin-GFP + cells. Nestin-GFP + cells expressed the chondroitin sulfate proteoglycan NG2 and nestin protein, but typically lacked mature astrocytic markers, that is, glial fibrillary acid protein (GFAP) or S100 β. Vice versa, the majority of GFAP + cells lacked nestin-expression and surrounded the ischemic lesion by 4 days. Whole-cell patch-clamp recordings in acute brain slices from controls showed that only about half of nestin-GFP + cells displayed complex membrane properties. In contrast, 4 days after the insult all nestin-GFP + cells expressed these properties. We hypothesize that the change in physiologic properties induced by the ischemic insult is directed toward a specific function of nestin-expressing cells.
Persistent Arterial Hyperammonemia Increases the Concentration of Glutamine and Alanine in the Brain and Correlates with Intracranial Pressure in Patients with Fulminant Hepatic Failure
Authors: Tofteng Flemming , Hauerberg John , Hansen Bent A , Pedersen Carsten B , Jørgensen Linda , Larsen Fin S
Published: June 2005

In this prospective study of patients with fulminant hepatic failure (FHF), we tested the hypothesis that arterial hyperammonemia results in cerebral accumulation of the osmotic active amino acids glutamine and alanine, processes that were expected to correlate with intracranial pressure (ICP). By using in vivo brain microdialysis technique together with ICP monitoring in 17 FHF patients (10 females/7 males; median age 49 (range 18 to 66) years), we found that arterial ammonia concentration correlated to brain content of glutamine ( r=0.47; P > 0.05) but not to alanine. A persisting high arterial ammonia concentration (above 200 μmol/L) characterized patients who developed high ICP ( n=8) while patients who did not experience surges of increased ICP ( n=9) had a decline in the ammonia level ( P > 0.05). Moreover, brain glutamine and alanine concentrations were higher at baseline and increased further in patients who developed intracranial hypertension compared with patients who experienced no surges of high ICP. Brain glutamine concentration increased 32% from baseline to 6536 (697 to 9712) μmol/L ( P > 0.05), and alanine 44% from baseline to 104 (81 to 381) μmol/L ( P > 0.05). Brain concentration of glutamine ( r=0.59, P > 0.05), but not alanine, correlated to ICP. Also arterial ammonia concentration correlated to ICP ( r=0.73, P > 0.01). To conclude, this study shows that persistence of arterial hyperammonemia is associated with profound changes in the cerebral concentration of glutamine and alanine. The elevation of brain glutamine concentration correlated to ICP in patients with FHF.
Free Radical-Mediated Damage to Barrier Function is not Associated with Altered Brain Morphology in High-Altitude Headache
Authors: Bailey Damian M , Roukens Robin , Knauth Michael , Kallenberg Kai , Christ Stefan , Mohr Alex , Genius Just , Storch-Hagenlocher Birgitte , Meisel Fabien , McEneny Jane , Young Ian S , Steiner Thorsten , Hess Klaus , Baärtsch Peter
Published: June 2005

The present study combined molecular and neuroimaging techniques to examine if free radical-mediated damage to barrier function in hypoxia would result in extracellular edema, raise intracranial pressure (ICP) and account for the neurological symptoms typical of high-altitude headache (HAH) also known as acute mountain sickness (AMS). Twenty-two subjects were randomly exposed for 18 h to 12% (hypoxia) and 21% oxygen (O2 (normoxia)) for collection of venous blood (0 h, 8 h, 15 h, 18 h) and CSF (18 h) after lumbar puncture (LP). Electron paramagnetic resonance (EPR) spectroscopy identified a clear increase in the blood and CSF concentration of O2 and carbon-centered free radicals ( P > 0.05 versus normoxia) subsequently identified as lipid-derived alkoxyl (LO•) and alkyl (LC•) species. Magnetic resonance imaging (MRI) demonstrated a mild increase in brain volume (7.0 ± 4.8mL or 0.6% ± 0.4%, P > 0.05 versus normoxia) that resolved within 6 h of normoxic recovery. However, there was no detectable evidence for gross barrier dysfunction, elevated lumbar pressures, T2 prolongation or associated neuronal and astroglial damage. Clinical AMS was diagnosed in 50% of subjects during the hypoxic trial and corresponding headache scores were markedly elevated ( P > 0.05 versus non-AMS). A greater increase in brain volume was observed, though this was slight, independent of oxidative stress, barrier dysfunction, raised lumbar pressure, vascular damage and measurable evidence of cerebral edema and only apparent in the most severe of cases. These findings suggest that free-radical-mediated vasogenic edema is not an important pathophysiological event that contributes to the mild brain swelling observed in HAH.
Celling Black Bodies: Black Women in the Global Prison Industrial Complex
Authors: Sudbury Julia
Published: June 2005

The past two decades have witnessed an explosion in the population of women prisoners in Europe, North America and Australasia, accompanied by a boom in prison construction. This article argues that this new pattern of women's incarceration has been forged by three overlapping phenomena. The first is the fundamental shift in the role of the state that has occurred as a result of the neo-liberal globalization. The second and related phenomenon is the emergence and subsequent global expansion of what has been labeled a ‘prison industrial complex’ made up of a intricate web of relations between state penal institutions, politicians and profit-driven prison corporations. The third is the emergence of a US-led global war on drugs which is symbiotically related and mutually constituted by the transnational trade in criminalized drugs. These new regimes of accumulation and discipline, I argue, build on older systems of racist and patriarchal exploitation to ensure the super-exploitation of black women within the global prison industrial complex. The article calls for a new anti-racist feminist analysis that explores how the complex matrix of race, class, gender and nationality meshes with contemporary globalized geo-political and economic realities. The prison industrial complex plays a critical role in sustaining the viability of the new global economy and black women are increasingly becoming the raw material that fuels its expansion and profitability. The article seeks to reveal the profitable synergies between drug enforcement, the prison industry, international financial institutions, media and politicians that are sending women to prison in ever increasing numbers.
Colloids as model systems for problems in statistical physics
Authors: Babič D. , Schmitt C. , Bechinger C.
Published: June 2005

Owing to their mesoscopic length scales, colloidal suspensions provide ideal model systems suitable for addressing many problems in the field of statistical physics. Exemplarily, we highlight the versatile nature of such systems by discussing experiments with stochastic resonance and a practical realization of a recently proposed ratchet cellular automaton.
Stochastic resonance: Theory and numerics
Authors: Casado-Pascual Jesús , Gómez-Ordóñez José , Morillo Manuel
Published: June 2005

We address the phenomenon of stochastic resonance in a noisy bistable system driven by a time-dependent periodic force (not necessarily sinusoidal) and in its two-state approximation. Even for driving forces with subthreshold amplitudes, the behavior of the system response might require a nonlinear description. We introduce analytical and numerical tools to analyze the power spectral amplification and the signal-to-noise ratio in a nonlinear regime. Our analysis shows the importance of the effects of the driving force on the system fluctuations in a nonlinear regime. These effects can be usefully exploited to achieve high quality output signals with gains larger than unity, which is impossible within a linear regime.
From diffusion to anomalous diffusion: A century after Einstein’s Brownian motion
Authors: Sokolov I. M. , Klafter J.
Published: June 2005

Einstein’s explanation of Brownian motion provided one of the cornerstones which underlie the modern approaches to stochastic processes. His approach is based on a random walk picture and is valid for Markovian processes lacking long-term memory. The coarse-grained behavior of such processes is described by the diffusion equation. However, many natural processes do not possess the Markovian property and exhibit anomalous diffusion. We consider here the case of subdiffusive processes, which correspond to continuous-time random walks in which the waiting time for a step is given by a probability distribution with a diverging mean value. Such a process can be considered as a process subordinated to normal diffusion under operational time which depends on this pathological waiting-time distribution. We derive two different but equivalent forms of kinetic equations, which reduce to known fractional diffusion or Fokker–Planck equations for waiting-time distributions following a power law. For waiting time distributions which are not pure power laws one or the other form of the kinetic equation is advantageous, depending on whether the process slows down or accelerates in the course of time.
Performance characteristics of Brownian motors
Authors: Linke Heiner , Downton Matthew T. , Zuckermann Martin J.
Published: June 2005

Brownian motors are nonequilibrium systems that rectify thermal fluctuations to achieve directed motion, using spatial or temporal asymmetry. We provide a tutorial introduction to this basic concept using the well-known example of a flashing ratchet, discussing the micro- to nanoscopic scale on which such motors can operate. Because of the crucial role of thermal noise, the characterization of the performance of Brownian motors must include their fluctuations, and we review suitable performance measures for motor coherency and efficiency. Specifically, we highlight that it is possible to determine the energy efficiency of Brownian motors by measuring their velocity fluctuations, without detailed knowledge of the motor function and its energy input. Finally, we exemplify these concepts using a model for an artificial single-molecule motor with internal degrees of freedom.
Random walks, diffusion limited aggregation in a wedge, and average conformal maps
Authors: Sander Leonard M. , Somfai Ellák
Published: June 2005

We investigate diffusion-limited aggregation (DLA) in a wedge geometry. Arneodo and collaborators have suggested that the ensemble average of DLA cluster density should be close to the noise-free selected Saffman-Taylor finger. We show that a different, but related, ensemble average, that of the conformal maps associated with random clusters, yields a nontrivial shape which is also not far from the Saffman-Taylor finger. However, we have previously demonstrated that the same average of DLA in a channel geometry is not the Saffman-Taylor finger. This casts doubt on the idea that the average of noisy diffusion-limited growth is governed by a simple transcription of noise-free results.
Relevance of πσ* states in the photoinduced processes of adenine, adenine dimer, and adenine–water complexes
Authors: Ritze H.-H. , Lippert H. , Samoylova E. , Smith V. R. , Hertel I. V. , Radloff W. , Schultz T.
Published: June 2005

Ab initio calculations and time-resolved photoionization spectroscopy were carried out to characterize the role of the lowest two πσ* excited states for the photoinduced processes in the adenine monomer, adenine dimer, and adenine–water clusters. The calculations show—with respect to the monomer—a stabilization of 0.11–0.14 eV for the πσ* states in different isomers of adenine dimer and an even bigger stabilization of 0.14–0.36 eV for isomers of adenine-(H2O)1 and adenine-(H2O)3. Hence, the stabilized πσ* states should play an important role in the excited-state relaxation of partially or fully solvated adenine. This conclusion is supported by experimental results: In the adenine monomer, strong nπ* state signals are observed. Those signals are reduced in adenine dimer and vanish in water clusters due to the competing relaxation via the πσ* states.
Radiative association of He+ with H2 at temperatures below 100 K
Authors: Mrugała Felicja , Kraemer Wolfgang P.
Published: June 2005

The paper presents a theoretical study of the low-energy dynamics of radiative association processes in the He++H2 collision system. Formation of the triatomic HeH2+ ion in its bound rotation-vibration states on the potential-energy surfaces of the ground and of the first excited electronic states is investigated. Close-coupling calculations are performed to determine detailed state-to-state characteristics (bound←free transition rates, radiative and dissociative widths of resonances) as well as temperature-average characteristics (rate constants, photon emission spectra) of the two-state (X←A) reaction He+(S2)+H2(XΣg+1)→HeH2+(XA′2)+hν and of the single-state (A←A) reaction He+(S2)+H2(XΣg+1)→HeH2+(AA′2)+hν. The potential-energy surfaces of the X- and A-electronic states of HeH2+ and the dipole moment surfaces determined ab initio in an earlier work [Kraemer, Špirko, and Bludsky, Chem. Phys. 276, 225 (2002)] are used in the calculations. The rate constants k(T) as functions of temperature are calculated for the temperature interval 1⩽T⩽100K. The maximum k(T) values are predicted as 3.3×10−15s−1cm3 for the X←A reaction and 2.3×10−20s−1cm3 for the A←A reaction at temperatures around 2 K. Rotationally predissociating states of the He+−H2 complex, correlating with the υ=0,j=2 state of free H2, are found to play a crucial role in the dynamics of the association reactions at low temperatures; their contribution to the k(T) function of the X←A reaction at T<30K is estimated as larger than 80%. The calculated partial rate constants and emission spectra show that in the X←A reaction the HeH2+(X) ion is formed in its highly excited vibrational states. This is in contrast with the vibrational state population of the ion when formed via the (X←X) reaction He(S1)+H2+(XΣg+2)→HeH2+(XA′2)+hν.
Annealing enhanced hydrogen absorption in nanocrystalline Pd∕Au sensing films
Authors: Zhao Z. , Carpenter M. A.
Published: June 2005

The enhanced hydrogen absorption and sensitivity of nanocrystalline Pd(60at.%)∕Au(40at.%) thin films were realized through the development of a thermal annealing process and a determination of its underlying enhancement mechanism. 20-nm-thick films were deposited by magnetron sputtering and then annealed at temperatures ranging from 100 to 400 °C. Optical reflectance and x-ray diffraction (XRD) analyses were utilized to investigate the H2 response and microstructure characteristics of the as-deposited and annealed films as a function of the annealing temperature. The as-deposited films exhibited a consistently low H absorption, evidenced by a small reflectance-signal change at even a 4% H2 concentration, while displaying a 5-second response time. The combined stress and composition analyses by XRD indicate that the as-deposited film is under a compressive stress of ∼560MPa and has an unexpectedly low Pd (40%) content in the ∼7-nm nanocrystallites, in contrast to the overall film Pd concentration (60%), with Pd enrichment occurring in the disordered grain boundary. The low H absorption characteristics can be overcome by a thermal annealing process, and it was determined that a 200 °C annealing temperature was most desirable. The annealing process resulted in a 4× to 6× enhancement of the signal change, with a minimal effect on the response time. The annealing also stabilized the microstructure, allowing for enhanced sensing stability, reliability, and durability. The underlying mechanism for hydrogen absorption enhancement is comprised of three heat-promoted events within the film microstructure: grain growth, a reduction of the internal compressive stress, and atomic intermixing of Pd from its enrichment and disordered state at the grain boundary into the Pd∕Au grain lattice.
Absorption intensities and emission cross sections of principal intermanifold and inter-Stark transitions of Er3+(4f11) in polycrystalline ceramic garnet Y3Al5O12
Authors: Sardar Dhiraj K. , Russell Charles C. , Gruber John B. , Allik Toomas H.
Published: June 2005

A comparative spectroscopic study is performed on Er3+(4f11) ions doped in polycrystalline ceramic garnet Y3Al5O12 (YAG) and single-crystal laser rod, both containing nominal 50 at. % of Er3+. The standard Judd–Ofelt (JO) model is applied to the room-temperature absorption intensities of Er3+(4f11) transitions in both hosts to obtain the phenomenological intensity parameters. These parameters are subsequently used to determine the radiative decay rates, radiative lifetimes, and branching ratios of the Er3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds LJ2S+1 of Er3+(4f11) in these garnet hosts. The emission cross sections of the intermanifold Er3+I13∕24→I15∕24 (1.5 μm) transition as well as the principal inter-Stark transition Y1→Z4 (1550 nm) within the corresponding multiplet manifolds have been determined. The room-temperature fluorescence lifetimes of the I13∕24→I15∕24 (1.5 μm) transition in both polycrystalline ceramic and single-crystal YAG samples were measured. From the radiative lifetimes determined from the JO model and the measured fluorescence lifetimes, the quantum efficiencies for both samples were determined. The comparative study of Er3+(4f11) ions performed suggests that polycrystalline ceramic YAG is an excellent alternative to single-crystal YAG rod for certain applications.
On conductivity changes in shocked potassium chloride
Authors: Bourne N. K. , Townsend D. , Braithwaite M.
Published: June 2005

A previous work has reported that shock loading of ionic crystals produces an induced polarization and changes in electrical conductivity. However, previous measurements recorded an integrated electrical signal comprising the induced electrical field and that due to current flow. For this reason a differential system was designed to separate these effects that was adapted from that used in the investigation of the conductivity of hydrogen under shock. The measurement removes voltages produced in the shock-induced electrical field, allowing determination of those resulting from resistance changes. Although the mechanical response of potassium chloride to shock has been studied extensively, the electrical response is less studied. Here, experiments are reported in which it is shocked to various stresses in order to observe conductivity changes. The range of stresses induced includes several mechanical thresholds, including the elastic-plastic transition, the B1:B2 phase transformation, and the overdriving of the shock faster than the elastic wave. The behavior observed when single crystal and targets pressed from granular material (to close to full density) are shocked around each of these thresholds is presented. The effects of loading to a particular stress in a single step or in multiple steps are discussed.
Magnetism of sol-gel fabricated CoFe2O4∕SiO2 nanocomposites
Authors: Vejpravová J. , Sechovský V. , Plocek J. , Nižňanský D. , Hutlová A. , Rehspringer J.-L.
Published: June 2005

Details of synthesis and characterization of sol-gel-produced CoFe2O4 nanoparticles embedded in the amorphous SiO2 matrix are presented together with results of an extended magnetization study of these materials. The particle size was found to increase from 6to15nm by varying the temperature of a subsequent annealing from 800to1100°C. All samples exhibited superparamagnetic behavior with values of the blocking temperature TB increasing with the particle size. At temperatures above TB the magnetization curves follow the expected Langevin scaling of M vs H∕T, which is consistent with the formation of the superparamagnetic state. For T<TB, the coercivity field Hc was found to be proportional to T and the frequency-dependent ac susceptibility was found to obey the Néel–Arrhenius law. Both observations are compatible with a model of noninteracting randomly oriented single-domain particles.
Facet degradation of GaN heterostructure laser diodes
Authors: Schoedl Thomas , Schwarz Ulrich T. , Kümmler Volker , Furitsch Michael , Leber Andreas , Miler Andreas , Lell Alfred , Härle Volker
Published: June 2005

We investigated the degradation of cleaved facets of (Al,In)GaN laser diodes in different atmospheres. We found that operation in water-free atmospheres with sufficient oxygen shows a slow degradation. Operation in atmospheres with water vapor causes a fast degradation and an oxidation on the facet. This deposition is a permanent damage to the laser diode. If the laser diode is operated in pure nitrogen, we find a thick deposition on the facet, which shows high absorption. This deposition can be removed by either high optical output powers or by operation in atmospheres with sufficient oxygen. We also explain the influence of these coatings to the degradation behavior and see these coatings as the reason for unstable kinks in the L–I characteristics during operation.
Transverse-electric-field-enhanced response in InAs∕AlGaAs∕GaAs quantum-dot infrared photodetectors
Authors: Chen Shen-De , Chen Ying-Ying , Lee Si-Chen
Published: June 2005

By introducing a 2-nm-Al0.3Ga0.7As capping layer on the InAs quantum dots, a transverse-electric- (TE) field-enhanced multicolor quantum-dot (QD) infrared photodetector has been achieved. The TE-enhanced peaks are due to the transition from the S-like ground state to the P-like first excited states induced by the strain field effects on the quantum dot. After rapid thermal annealing, the TE dominant peaks can be changed to transverse-magnetic- (TM) field-enhanced and vice versa. This is because the rapid thermal annealing creates defects at the boundary of QDs and their surrounding material, which release the compressive strain within the QDs.
Integral equation theory of random copolymer melts: Self-consistent treatment of intramolecular and intermolecular correlations
Authors: Sung Bong June , Yethiraj Arun
Published: June 2005

A self-consistent integral equation theory is presented for the conformational properties and spinodal lines of random copolymer melts. The theory combines field-theoretic methods with the polymer reference interaction site model (PRISM) theory. The many-chain problem is replaced by a single chain where the sites interact via a bare plus a self-consistently determined medium-induced potential, and the conformational properties are obtained using a variational method. The theoretical prediction for the spinodal line is qualitatively similar to that of non-self-consistent PRISM theory. The theory predicts macroscopic phase separation for all values of the monomer correlation strength, λ. The inverse spinodal temperature is a nonmonotonic function of λ with a maximum at λmax. For large values of λ(≈1), the values of spinodal temperatures are almost identical to those of non-self-consistent PRISM theory. For low values of λ, however, the theory predicts higher values for spinodal temperatures than non-self-consistent PRISM theory. The theory predicts significant changes in the mean-square end-to-end distance as the temperature is decreased.
Coupled dielectric waveguides: variational estimations
Authors: Melnichuk O. P. , Popov I. Yu.
Published: June 2005

Two dielectric waveguides coupled through small windows are considered. In the case of single coupling window we prove the existence of an eigenvalue below the threshold. It’s estimation is obtained. If there is the periodic set of coupling windows a band below the threshold exists. Using variational estimations of the band edges we prove that there exists a gap between the band and the threshold. This result shows that the system has a property of photonic band gap material (photonic crystal). It can be used for construction of optical fiber systems.
Hybrid states of two and three level atoms
Authors: Billionnet Claude
Published: June 2005

We calculate atom-photon resonances in the Wigner-Weisskopf model, admitting two photons and choosing a particular coupling function. We also present a rough description of the set of resonances in a model for a three-level atom coupled to a scalar-photon field. We give a general picture of matter-field resonances that these results fit into.
Development of a relaxation-inducing cluster expansion formalism for treating strong relaxation and correlation effects
Authors: Jana Debasis , Mukherjee Debashis
Published: June 2005

We present in this paper a comprehensive account of an explicitly spin-free coupled cluster theory for treating energy differences of open-shell states relative to a closed-shell ground state, where the open-shell states of interest are dominated by a few simple configuration state functions. We develop a valence-universal coupled cluster formalism to achieve this via a novel cluster expansion ansatz for the valence part of the wave operator, where the orbital relaxation and the correlation relaxation accompanying ionization/excitation from the ground state are taken care of to all orders in compact, efficient, and explicitly spin-free manner. The essential difference of our proposed ansatz from the ordinary and the normal-ordered cluster ansatz in vogue is that (a) we allow the valence cluster operators to be connected among themselves with spectator valence lines only and (b) we use suitable combinatoric factors accompanying powers of cluster operators thus connected, which are equal to the number of ways the operators can be joined, leading to the same excitation (the automorphic factor). We emphasize that such an ansatz does not generate terms (diagrams) with chains of cluster operators joined among themselves via spectator lines only. Barring only a few, almost all the terms in the working equations determining the cluster amplitudes involve contraction of the Hamiltonian with the cluster operators via at least one nonspectator line, leading to what we call a “strongly connected” series. The structure of the working equation is remarkably similar to the single-reference closed-shell equation, with a few additional terms. The presence of contractions among cluster operators via spectator lines introduces the additional physical effects of orbital and correlation relaxation using low-body cluster operators. As an illustrative application of the new multireference coupled cluster (CC) theory, we consider in this paper computation of ionization potentials (IPs) of one-valence problem with only one active orbital. The numerical applications are made for both the core- and the inner- and outer-valence IPs for several molecular systems. The numerical values demonstrate the superiority of the relaxation-inducing CC theory, as compared to the normal-ordered ansatz.
Dielectric heating effects of dual-frequency liquid crystals
Authors: Wen Chien-Hui , Wu Shin-Tson
Published: June 2005

A noncontact birefringence probing method is developed to monitor the temperature rise of dual-frequency liquid crystals (DFLCs) due to the dielectric heating effect. This method allows us to determine the temperature change accurately without using a thermocouple. The dielectric heating effects of three DFLC mixtures are investigated quantitatively. By properly choosing the molecular structures, the dielectric heating effect can be minimized while keeping other desirable physical properties uncompromised.
Effects of high-field electrical stress on the conduction properties of ultrathin La2O3 films
Authors: Miranda E. , Molina J. , Kim Y. , Iwai H.
Published: June 2005

Electron transport in high-field stressed metal-insulator-silicon devices with ultrathin (<5nm) lanthanum oxide layers is investigated. We show that the leakage current flowing through the structure prior to degradation is direct and Fowler-Nordheim tunneling conduction, while that after stress exhibits diode-like behavior with series and parallel resistances. In this latter case, a closed-form expression for the current–voltage characteristic, based on the Lambert W function, is presented. Current evolution from one regime to the other during constant voltage stress takes place by means of discrete current steps of nearly identical magnitude, which would be indicative of the occurrence of multiple dielectric breakdowns across the insulating layer.
Mechanical properties of chemical vapor deposition-grown multiwalled carbon nanotubes
Authors: Gaillard Jay , Skove Malcolm , Rao Apparao M.
Published: June 2005

The bending modulus (Young’s modulus) of several chemical vapor deposition-grown multiwalled nanotubes (MWNTs) have been measured using a vibrating reed technique. Three different precursors were used to produce MWNTs with differing densities of defects in the tube walls. Individual MWNTs were electrostatically driven in air over a dark-field light microscope and the bending modulus of the nanotubes was determined from the frequency of the first vibrational resonance. A correlation between the defect density and the bending modulus was found which implies that the bending modulus is relatively more sensitive to wall defects than the nanotube diameter.
Evaluation of the effect of polymer coating on the lateral pressure tuning of fiber Bragg gratings
Authors: Paul J. , Zhao L. P. , Ngoi B. K. A. , Fang Z. P.
Published: June 2005

We report the analysis of the expected effect of polymeric coating on the lateral pressure tuning of fiber Bragg gratings (FBGs). The dependence of the coating thickness and the stiffness of the polymer on the peak wavelength shift sensitivity and birefringence were evaluated using finite element analysis. A suitable polymeric coating with an optimum value of thickness could reduce the birefringence to an insignificant near-zero value and the peak shift sensitivity could be enhanced to almost ten times as high as that of bare FBGs.
A Wannier function made from distributed Gaussians
Authors: Karabulut Hasan
Published: June 2005

A new Wannier function made from distributed Gaussians is reported. Convolution integrals of the Wannier functions are studied and analytical expressions for the convolution integral are given. A new expression for a set of coefficients introduced in an earlier publication [J. Math. Phys. 38, 4815 (1997)] is derived. Using this new expression, the peculiar behavior of another set of coefficients introduced in the same publication in a particular limit is explained.
On observation of freeze-dried smectite plane views of nanolayers
Authors: Laribi S. , Jouffrey B. , Fleureau J.-M.
Published: June 2005

Observations were carried out on a purified and deshydrated smectite using scanning and transmission electron microscopy. They show extremely thin layers in the planar orientation (thickness of the order of a few nanometers). An important part of them is also bent with variable radii of curvature, often of the order of a few hundreds of nanometers. Some of the samples are complicated in shape, and present a succession of folds. Samples mainly grow as layers and not as a pile-up of layers. Electron energy loss spectroscopy shows that the Si∕Al local ratio is of the order of 2 as expected.
Buffer-enhanced room-temperature growth and characterization of epitaxial ZnO thin films
Authors: Sasaki Atsushi , Hara Wakana , Matsuda Akifumi , Tateda Norihiro , Otaka Sei , Akiba Shusaku , Saito Keisuke , Yodo Tokuo , Yoshimoto Mamoru
Published: June 2005

The room-temperature epitaxial growth of ZnO thin films on NiO buffered sapphire (0001) substrate was achieved by using the laser molecular-beam-epitaxy method. The obtained ZnO films had the ultrasmooth surface reflecting the nanostepped structure of the sapphire substrate. The crystal structure at the surface was investigated in situ by means of coaxial impact-collision ion scattering spectroscopy. It was proved that the buffer-enhanced epitaxial ZnO thin films grown at room temperature had +c polarity, while the polarity of high-temperature grown ZnO thin films on the sapphire was −c. Photoluminescence spectra at room temperature were measured for the epitaxial ZnO films, showing only the strong ultraviolet emission near 380nm.