bluuebunny/crossref_metadata_2025 huggingface dataset:
Decadal variability in the Arctic Ocean shown in hydrochemical data
Authors: Ikeda M. , Colony R. , Yamaguchi H. , Ikeda T.
Published: November 2005

The recent distribution of Russian hydrochemical data collected from the Arctic Basin provides useful information on ocean interior variabilities. Among various chemical components, silicate is the most valuable for showing the boundary between the silicate‐rich Pacific Water and the opposite Atlantic Water. Here, it is assumed that the silicate distribution receives minor influence from seasonal biological productivity and Siberian Rivers outflow. It shows a clear maximum around 100‐m depth in the Canada Basin. The vertical gradient below 100 m provides information on the vertical motion of the upper boundary of the Atlantic Water at a decadal time scale: i.e., the boundary shifts upward (downward), as realized by the silicate reduction (increase) at a fixed depth, responding to a more intense (weaker) Polar Vortex or the positive (negative) phase of the Arctic Oscillation. This valuable hydrochemical data set has provided a tool for verifying Arctic Ocean models with decadal responses to atmospheric variabilities.
Response of the Greenland‐Scotland overflow to changing deep water supply from the Arctic Mediterranean
Authors: Wilkenskjeld Stiig , Quadfasel Detlef
Published: November 2005

A simple two‐layer channel model with a topographic barrier is used to study the response of the overflows across the Greenland‐Scotland Ridge to changes in the available volume of deep and intermediate waters in the Nordic Seas. Hydraulic control determines the deep exchange through the different gaps in the ridge while a geostrophic balance in the north provides the respective upstream conditions. In the model the overflow through Denmark Strait is more sensitive to changes in the deep water supply than that of the Faeroe‐Bank Channel, but no sudden breakdown of the exchanges across the ridge is seen when the supply decreases. Transport variations in the East‐Greenland Current have only minor influence on the total overflow.
Mapping the structure and depth of lava tubes using ground penetrating radar
Authors: Miyamoto Hideaki , Haruyama Jun'ichi , Kobayashi Takao , Suzuki Keiiti , Okada Tatsuaki , Nishibori Toshiyuki , Showman Adam P. , Lorenz Ralph , Mogi Katsuro , Crown David A. , Rodriguez Jose A. P. , Rokugawa Shuichi , Tokunaga Tomochika , Masumoto Kazuhiko
Published: November 2005

The formation of lava tubes is one of the most significant factors controlling the emplacement of lava flows. However, extents and structures of lava tubes are typically not precisely known due to the difficulty in finding lava tubes in the field. We developed a new stepped‐frequency ground penetrating radar (GPR) system with shielded antennas, which allows measurements that have both high spatial resolution and large penetration depth. We performed two types of measurements over an inactive lava flow and show that this method can easily detect the existence of a lava tube. Importantly, phase reversals of the reflection signals can help identify reflections from a lava tube. Using these reflection patterns, we estimate the vertical dimension and the depth of a lava tube at Fuji volcano, which are validated by survey measurements. The presented method may be the most practical way to map terrestrial and perhaps extraterrestrial lava tubes.
Observed twentieth century land surface air temperature and precipitation covariability
Authors: Déry Stephen J. , Wood Eric F.
Published: November 2005

Significant positive trends in surface air temperatures (SATs) and precipitation were observed over 71% and 27%, respectively, of the global land surface during the twentieth century. Although the terrestrial surface is becoming warmer and wetter, the covariability between annual SAT and precipitation is not well understood. Significant anticorrelations between annual values of SAT and precipitation exist over 24% of the global land surface. Regional‐scale interannual climate variability alternates between two dominant regimes, namely relatively warm and dry or cool and wet conditions. The out‐of‐phase positive trends in terrestrial SATs and precipitation observed during the twentieth century provide an important climate simulation benchmark.
Precipitation controls Sahel greening trend
Authors: Hickler Thomas , Eklundh Lars , Seaquist Jonathan W. , Smith Benjamin , Ardö Jonas , Olsson Lennart , Sykes Martin T. , Sjöström Martin
Published: November 2005

The Sahel region has been identified as a “hot spot” of global environmental change, but understanding of the roles of different climatic and anthropogenic forcing factors driving change in the region is incomplete. We show that a process‐based ecosystem model driven by climatic and atmospheric CO2 data alone closely reproduces the satellite‐observed greening trend of the Sahel vegetation and its interannual variability between 1982 and 1998. Changes in precipitation were identified as the primary driver of the aggregated simulated vegetation changes. According to the model, the increasing carbon uptake through vegetation was associated with an increasing relative carbon sink; but integrated over the whole period, the Sahel was predicted to be a net source of carbon.
A decrease in discharge‐normalized DOC export by the Yukon River during summer through autumn
Authors: Striegl Robert G. , Aiken George R. , Dornblaser Mark M. , Raymond Peter A. , Wickland Kimberly P.
Published: November 2005

Climate warming is having a dramatic effect on the vegetation distribution and carbon cycling of terrestrial subarctic and arctic ecosystems. Here, we present hydrologic evidence that warming is also affecting the export of dissolved organic carbon and bicarbonate (DOC and HCO3−) at the large basin scale. In the 831,400 km2 Yukon River basin, water discharge (Q) corrected DOC export significantly decreased during the growing season from 1978–80 to 2001–03, indicating a major shift in terrestrial to aquatic C transfer. We conclude that decreased DOC export, relative to total summer through autumn Q, results from increased flow path, residence time, and microbial mineralization of DOC in the soil active layer and groundwater. Counter to current predictions, we argue that continued warming could result in decreased DOC export to the Bering Sea and Arctic Ocean by major subarctic and arctic rivers, due to increased respiration of organic C on land.
Modeling atmospheric stable water isotopes and the potential for constraining cloud processes and stratosphere‐troposphere water exchange
Authors: Schmidt Gavin A. , Hoffmann Georg , Shindell Drew T. , Hu Yongyun
Published: November 2005

Stable water isotope tracers (HDO and H218O) are incorporated into the ModelE version of the Goddard Institute for Space Studies Atmospheric (GISS) General Circulation Model (GCM). Details of the moist convective parameterisation, cloud phase, background ozone, isotope kinetics and vertical resolution are varied and we examine their impacts, particularly in the upper troposphere (UT) and lower stratosphere. We find that isotopes in precipitation, except in Antarctica, are largely unaffected by these changes and thus are not a useful metric for evaluating model skill above the lower troposphere. Simulated isotopic entry values into the stratosphere over all experiments range between −750 and −600‰ for HDO, and −130 to −90‰ for H218O, demonstrating that the mixing processes simulated by the model can explain a significant part of the observed offset from pure Rayleigh distillation. Isotope fields are shown to be sensitive to the parameterisation of cloud physics and representation of UT processes and therefore may be useful in constraining modeled cloud physics and mechanisms of stratosphere‐troposphere water vapour exchange.
Four decades of ozonesonde measurements over Antarctica
Authors: Solomon Susan , Portmann Robert W. , Sasaki Toru , Hofmann David J. , Thompson David W. J.
Published: November 2005

Ozonesonde observations from Syowa and the South Pole over more than 40 years are described and intercompared. Observations from the two sites reveal remarkable agreement, supporting and extending the understanding gained from either individually. Both sites exhibit extensive Antarctic ozone losses in a relatively narrow altitude range from about 12 to 24 km in October, and the data are consistent with temperature‐dependent chemistry involving chlorine on polar stratospheric clouds as the cause of the ozone hole. The maximum October ozone losses at higher altitudes near 18 km (70 hPa) appear to be transported to lower levels near the tropopause on a timescale of a few months, which is likely to affect the timing of the effects of ozone depletion on possible tropospheric climate changes. Both sites also show greater ozone losses in the lowermost stratosphere after the volcanic eruption of Mt. Pinatubo, supporting the view that surface chemistry can be enhanced by volcanic perturbations and that the very deep ozone holes observed in the early 1990s reflected such enhancements. Sparse data from the Syowa station in the early 1980s also suggest that enhanced ozone losses due to the El Chichon eruption may have contributed to the beginning of a measurable ozone hole. Observations at both locations show that some ozone depletion now occurs during much if not all year at lower altitudes near 12–14 km. Correlations between temperature and ozone provide new insights into ozone losses, including its nonlinear character, maximum effectiveness, and utility as a tool to distinguish dynamical effects from chemical processes. These data also show that recent changes in ozone do not yet indicate ozone recovery linked to changing chlorine abundances but provide new tools to probe observations for the first such future signals.
Hygroscopicity and volatility of 4–10 nm particles during summertime atmospheric nucleation events in urban Atlanta
Authors: Sakurai Hiromu , Fink Melissa A. , McMurry Peter H. , Mauldin Lee , Moore Katharine F. , Smith James N. , Eisele Fred L.
Published: November 2005

Continuous measurements of hygroscopicity and volatility of atmospheric aerosol particles of 4–10 nm diameter were conducted with a nanometer tandem differential mobility analyzer (Nano TDMA) during the Aerosol Nucleation and Real‐time Characterization Experiment (ANARChE), which took place in Atlanta in July and August 2002. In the Nano TDMA measurements, particles were exposed to either a high humidity (∼90% RH) or an elevated temperature (∼100°C) downstream of the first differential mobility analyzer (DMA) and were then resized by the second DMA to determine the change in size due to water uptake or evaporation. There were several days when nucleation occurred and high concentrations of sub‐20 nm particles were observed, and during those events, particles of 4–10 nm diameter were very hygroscopic and nonvolatile. These observations, together with parallel Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS) measurements of sub‐20 nm particle composition, suggest that the particles were mostly composed of ammoniated sulfates. This finding strongly supports the hypothesis that the nucleation and subsequent growth of nanoparticles were driven by reactions involving sulfuric acid and ammonia during this study.
Isotopomer fractionation in the UV photolysis of N2O: Comparison of theory and experiment
Authors: Prakash Meher K. , Weibel Jason D. , Marcus R. A.
Published: November 2005

In the photodissociation of N2O, absorption cross sections differ with isotopic substitution, leading to a wavelength‐dependent fractionation of the various isotopomers. Several models ranging from shifts by zero‐point energy differences to propagation of wave packets on the excited electronic state potential energy surface have been proposed to explain the observed fractionations. We present time‐independent fractionation calculations for the isotopomers 447, 448, 456, 546, and 556. Besides largely agreeing with the experimental data, these calculations have the advantage of not being computationally intensive, as well as satisfying the physical facts that the asymmetric stretch and the doubly degenerate bending vibration are the principal Franck‐Condon active modes in the photodissociation. The latter is reflected in the actual dissociation and in the high rotational excitation and lack of vibrational excitation of the N2 product. The calculations are based on a multidimensional reflection principle using an ab initio potential energy surface. The theory for the absorption cross section and isotopomer fractionation accompanying photodissociation is described. The absolute value of the theoretically calculated absorption cross section is very close (90%) to the experimentally observed value. The present computations also provide data for the slope of a three‐isotope plot of the fractionation of 447/446 relative to 448/446, using the fractionations at different wavelengths. The resulting slope is compared with a perturbation theoretical expression for direct photodissociation given elsewhere.
Estimation of the contribution of intercontinental transport during the PEACE campaign by using a global model
Authors: Takigawa Masayuki , Sudo Kengo , Akimoto Hajime , Kita Kazuyuki , Takegawa Nobuyuki , Kondo Yutaka , Takahashi Masaaki
Published: November 2005

A quasi–real–time calculation system for the global distribution of ozone (O3) and its precursors, including CO, NOx, and nonmethane hydrocarbons (NMHCs), has been newly developed by using a 3–D chemical–transport model. The model is driven by meteorological data from the National Centers for Environmental Prediction (NCEP), and produces daily 7–day forecast of the distribution of chemical species. The model was used in daily flight planning for the Pacific Exploration of Asian Continental Emission (PEACE)–A and –B aircraft measurement campaigns in January and April–May 2002, respectively. Model–calculated meteorological fields show good agreement with aircraft observations. The model also reproduced events such as polluted air masses in the lower troposphere (LT) corresponding to post–frontal outflow, a high–concentration CO plume in the upper troposphere (UT) in late spring, and the observed plume that was transported by deep convection over central China. The amount of CO transported into the free troposphere (FT) by deep convection was estimated to be about 6 Tg CO over China in May 2002. Meridional and seasonal variations in the long–range transport (LRT) of CO tracers, Asian CO tracers, and CO tracers produced from the oxidation of CH4 and NMHCs were all evaluated using tagged CO tracers. LRT CO comprised about 36% of the total CO budget in December–February 2001/2002, and about 20% in March–May 2002 in the free troposphere over Japan. In late spring, the concentration of Asian CO over southern Japan decreased compared to that in winter because the wind direction shifted from northwesterly to easterly or southerly.
Dynamics of pothole growth as defined by field data and geometrical description
Authors: Springer Gregory S. , Tooth Stephen , Wohl Ellen E.
Published: November 2005

This paper examines cylindrical pothole growth on streambeds using empirical analyses of field data and geometric constraints. Pothole depths (d) and average radii () at three localities have the relationship = kd, where k and ɛ are regression coefficients (R2 ≥ 0.72). Observed ɛ (0.57, 0.67, 0.85) translate to d increasing faster than r at all localities. The strong correlations and absence of potholes with very low or high ratios of depth/diameter suggest that small concavities act as pothole seeds and enlargement is quasi‐systematic. Exploiting the power relationship, growing potholes can be represented as deepening and radially expanding cylinders. Absolute and relative distributions of erosion can be calculated for floors and walls using this geometrical approach. Volumetrically, more substrate is eroded from pothole walls than floors during growth for ɛ > 0.5. Among sample populations, as much as 70% more material is eroded from walls than floors (ɛ = 0.85). Wall and floor surface areas differ by 1 or more orders of magnitude for observed ɛ, and as a result, erosion rates are fastest atop floors. Differences in erosion rates may reflect the efficacy of erosion phenomena. Low‐angle impacts of tools on walls presumably have low erosion efficiencies. Efficacies are presumably influenced by substrate properties, and floor and wall erosion rates are most comparable in the weakest observed strata, although substantially more material is removed from walls at this locality (ɛ = 0.85). Additional data is needed, but quantifiable relationships may exist between geometries, substrates, and erosion phenomena.
Effect of seafloor depth on phytoplankton blooms in high‐nitrate, low‐chlorophyll (HNLC) regions
Authors: Tyrrell T. , Merico A. , Waniek J. J. , Wong C. S. , Metzl N. , Whitney F.
Published: November 2005

We calculated correlations between seafloor depth and phytoplankton blooms in all three main high‐nitrate, low‐chlorophyll (HNLC) regions, but with a particular focus on the subarctic North Pacific area. It has long been known that the central parts of the east and west subarctic North Pacific are HNLC regions. The deep western basin of the Bering Sea is also HNLC, whereas the wide continental shelf of the eastern Bering Sea is not. We carried out a statistical comparison of spatial maps of (1) seafloor depth and (2) chlorophyll a concentration from satellite data. This comparison reveals that shallow waters have, on average, higher peak chlorophyll a concentrations (more intense phytoplankton blooms) than deep waters (p ≪ 0.01). Possible artifacts of the satellite data are considered but it is concluded that the signal is genuine, in part because the same patterns are found in in situ data. There are several possible explanations for the observed correlation; the most probable, we suggest, is that iron diffusing out of the seafloor causes alleviation of iron limitation in shallow waters.
Antiviral prodrugs – the development of successful prodrug strategies for antiviral chemotherapy
Authors: De Clercq Erik , Field Hugh J
Published: November 2005

Following the discovery of the first effective antiviral compound (idoxuridine) in 1959, nucleoside analogues, especially acyclovir (ACV) for the treatment of herpesvirus infections, have dominated antiviral therapy for several decades. However, ACV and similar acyclic nucleosides suffer from low aqueous solubility and low bioavailability following oral administration. Derivatives of acyclic nucleosides, typically esters, were developed to overcome this problem and valaciclovir, the valine ester of ACV, was among the first of a new series of compounds that were readily metabolized upon oral administration to produce the antiviral nucleosidein vivo, thus increasing the bioavailility by several fold. Concurrently, famciclovir was developed as an oral formulation of penciclovir. These antiviral ‘prodrugs’ thus established a principle that has led to many successful drugs including both nucleoside and nucleotide analogues for the control of several virus infections, notably those caused by herpes‐, retro‐ and hepatitisviruses. This review will chart the origins and development of the most important of the antiviral prodrugs to date.

British Journal of Pharmacology(2006)147, 1–11. doi:10.1038/sj.bjp.0706446
4‐methyl benzylamine stimulates food consumption and counteracts the hypophagic effects of amphetamine acting on brainShaker‐likeKv1.1 channels
Authors: Pirisino Renato , Galeotti Nicoletta , Livi Silvia , Raimondi Laura , Ghelardini Carla
Published: November 2005

4‐methyl benzylamine (4‐MBZ; 28 μg, 231 nmol) elicits a hyperphagic response in starved mice in contrast to the hypophagia induced by the parent compound benzylamine (BZ; 33 μg, 231 nmol) or by amphetamine (AMPH, 2 μg).

In mice starved for only 4 h, and therefore with little stimulation to eat, the maximal increase in food consumption induced by intracerebroventricular (i.c.v.)‐injected 4‐MBZ was 190% over that of the controls (ED508.3±2.7 μg mouse−1; 68±22 nmol mouse−1), whereas after i.p. administration, these values were 160% and approximately 129 mg kg−1, respectively.

The hyperphagic effect of 4‐MBZ was reduced by more than 60% in mice pretreated with antisense oligodeoxyribonucleotide (aODN1) previously found to selectively inhibit (over 50%) the expression ofShaker‐likeKv1.1 channels.

In mice highly stimulated to eat after 12‐h fasting, 4‐MBZ (28 μg) significantly reduced (to about 70%) the hypophagic response by AMPH (2 μg) or BZ (33 μg). Conversely, these two compounds reduced (respectively, by 69 and 44%) the hyperphagic response of 4‐MBZ in 4‐h fasting mice.

4‐MBZ (28 μg) also reduced the hypermotility and the stimulation of inspection activity elicited by AMPH in mice and the release of DA stimulated by AMPH (2 μg) from the nucleus accumbens of rats.

We hypothesize that 4‐MBZ elicits hyperphagic effects probably by openingShaker‐likeKv1.1 subtypes in the brain, whereas AMPH and BZ are hypophagic by blocking these channels.

British Journal of Pharmacology(2006)147, 218–224. doi:10.1038/sj.bjp.0706465
Applications of a time correlation function theory for the fifth-order Raman response function I: Atomic liquids
Authors: DeVane Russell , Ridley Christina , Space Brian , Keyes T.
Published: November 2005

Multidimensional spectroscopy has the ability to provide great insight into the complex dynamics and time-resolved structure of liquids. Theoretically describing these experiments requires calculating the nonlinear-response function, which is a combination of quantum-mechanical time correlation functions (TCFs), making it extremely difficult to calculate. Recently, a new theory was presented in which the two-dimensional Raman quantum response function R(5)(t1,t2) was expressed with a two-time, computationally tractable, classical TCF. Writing the response function in terms of classical TCFs brings the full power of atomistically detailed molecular dynamics to the problem. In this paper, the new TCF theory is employed to calculate the fifth-order Raman response function for liquid xenon and investigate several of the polarization conditions for which experiments can be performed on an isotropic system. The theory is shown to reproduce line-shape characteristics predicted by earlier theoretical work.
Statistical characterizations of spatiotemporal patterns generated in the Swift–Hohenberg model
Authors: Hu Shaowen , Nathan Girish , Kouri Donald J. , Hoffman David K. , Gunaratne Gemunu H.
Published: November 2005

Two families of statistical measures are used for quantitative characterization of nonequilibrium patterns and their evolution. The first quantifies the disorder in labyrinthine patterns, and captures features like the domain size, defect density, variations in wave number, etc. The second class of characteristics can be used to quantify the disorder in more general nonequilibrium structures, including those observed during domain growth. The presence of distinct stages of relaxation in spatiotemporal dynamics under the Swift–Hohenberg equation is analyzed using both classes of measures.
Impulsive stabilization and synchronization of a class of chaotic delay systems
Authors: Li Chuandong , Liao Xiaofeng , Yang Xiaofan , Huang Tingwen
Published: November 2005

The problems of control and synchronization of a class of chaotic systems with time delay via the impulsive control approach are investigated. Based on the Lyapunov-like stability theory for impulsive functional differential equations, several sufficient conditions are derived to guarantee chaos control and synchronization. Furthermore, we address the chaos quasisynchronization in the presence of single-parameter mismatch. Several illustrated examples are also given to show the effectiveness of the proposed methods.
Chemicophysical surface treatment and the experimental demonstration of Schottky-Mott rules for metal∕semiconductor heterostructure interfaces
Authors: Motayed Abhishek , Mohammad S. Noor
Published: November 2005

Metal∕semiconductor (M∕S) heterostructure is of wide interest in a number of areas including physics, chemistry, materials science, materials engineering, chemical engineering, and electrical engineering. It is an important element of modern technology. The present investigation describes a novel experimental technique to address the influence of interfacial chemical passivation on the Schottky-Mott [Naturwiss. 26, 843 (1938); Cambridge Philos. Soc. 34, 568 (1938)] rules for M∕S heterostructure, and to try to establish these rules. The success of the experiment derives from three remarkable findings: First, a semiconductor (AlxGa1−xN), which is robust and relatively less susceptible to an easy reaction with foreign chemicals, is needed for the demonstration. Second, reactive ion etching together with wet chemical etching by certain selected chemical (such as KOH), but not by others (for example, H3PO4 or aqua regia), can clean the semiconductor surface well, and remove∕passivate the dangling chemical bonds from this surface. Third, a judicious selection of deposition parameters for the deposition of metal(s) preferably on a certain selected semiconductor can lead to metal deposition on the semiconductor surface by van der Waals type of epitaxy. Transmission electron microscopy and x-ray diffraction indicate that M∕S heterostructures, thus prepared, are very different from others; they appear to provide convincing experimental verification of the Schottky-Mott rules, and to establish these rules without any ambiguity. Others fail to do it.
Sulfur hexafluoride’s liquid-vapor coexistence curve, interfacial properties, and diffusion coefficients as predicted by a simple rigid model
Authors: Olivet Aurelio , Duque Daniel , Vega Lourdes F.
Published: November 2005

We present here molecular-dynamics simulation results of the vapor-liquid coexistence curve, surface tension, and self-diffusion coefficients of sulfur hexafluoride. Sulfur hexafluoride is modeled as a rigid molecule, following the model proposed by Pawley [Mol. Phys. 43, 1321 (1981)]. Vapor-liquid coexistence curve and surface tension are obtained through direct molecular-dynamic simulations in the NVT ensemble. Simulation results are able to reproduce the qualitative shape of the vapor-liquid envelope. However, lower densities, a higher critical temperature, and an overestimated surface tension are obtained here. Those deviations are explained on the basis of the rigidity of the molecular model used. Self-diffusion coefficients are calculated from simulations in the NVE ensemble for different gas states at atmospheric pressure. The rigid model performs better for dynamical properties since simulation results provide very good agreement with available experimental data in this case.
Kinetics of diffusion-limited catalytically activated reactions: An extension of the Wilemski–Fixman approach
Authors: Bénichou O. , Coppey M. , Moreau M. , Oshanin G.
Published: November 2005

We study the kinetics of diffusion-limited catalytically activated A+B→B reactions taking place in three-dimensional systems, in which an annihilation of diffusive A particles by diffusive traps B may happen only if the encounter of an A with any of the Bs happens within a special catalytic subvolumen: these subvolumens being immobile and uniformly distributed within the reaction bath. Suitably extending the classical approach of Wilemski and Fixman [J. Chem. Phys. 58, 4009 (1973)] to such three-molecular diffusion-limited reactions, we calculate analytically an effective reaction constant and show that it comprises several terms associated with the residence and joint residence times of Brownian paths in finite domains. The effective reaction constant exhibits a nontrivial dependence on the reaction radii, the mean density of catalytic subvolumens, and particles’ diffusion coefficients. Finally, we discuss the fluctuation-induced kinetic behavior in such systems.
Behavior of polarizable models in presence of strong electric fields. I. Origin of nonlinear effects in water point-charge systems
Authors: Chelli Riccardo , Barducci Alessandro , Bellucci Luca , Schettino Vincenzo , Procacci Piero
Published: November 2005

In the current opinion, the inclusion of polarization response in classical computer simulations is considered as one of the most important and urgent improvements to be implemented in modern empirical potential models. In this work we focus on the capability of polarizable models, based on the pairwise Coulomb interactions, to model systems where strong electric fields enter into play. As shown by Masia, Probst, and Rey (MPR) [in J. Chem. Phys. 121, 7362 (2004)], when a molecule interacts with point charges, polarizable models show underpolarization with respect to ab initio methods. We prove that this underpolarization, clearly related to nonlinear polarization effects, cannot be simply ascribed to the lack of hyperpolarization in the polarizable models, as suggested by MPR. Analysis of the electron-density rearrangement induced on a water molecule by a point charge reveals a twofold level of polarization response. One level involves intramolecular charge transfer on the whole molecular volume, with the related polarization exhibiting a seemingly linear behavior with the external electric field. The other nonlinear polarization level occurs only at strong electric fields and is found to be strictly correlated to the quantum-mechanical nature of the water molecule. The latter type of polarization has a local character, being limited to the space region of the water lone pairs.
Dissociative recombination of the weakly bound NO-dimer cation: Cross sections and three-body dynamics
Authors: Petrignani Annemieke , Andersson Patrik U. , Pettersson Jan B. C. , Thomas Richard D. , Hellberg Fredrik , Ehlerding Anneli , Larsson Mats , van der Zande Wim J.
Published: November 2005

Dissociative recombination (DR) of the dimer ion (NO)2+ has been studied at the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm. The experiments were aimed at determining details on the strongly enhanced thermal rate coefficient for the dimer, interpreting the dissociation dynamics of the dimer ion, and studying the degree of similarity to the behavior in the monomer. The DR rate reveals that the very large efficiency of the dimer rate with respect to the monomer is limited to electron energies below 0.2eV. The fragmentation products reveal that the breakup into the three-body channel NO+O+N dominates with a probability of 0.69±0.02. The second most important channel yields NO+NO fragments with a probability of 0.23±0.03. Furthermore, the dominant three-body breakup yields electronic and vibrational ground-state products, NO(υ=0)+N(S4)+O(P3), in about 45% of the cases. The internal product-state distribution of the NO fragment shows a similarity with the product-state distribution as predicted by the Franck-Condon overlap between a NO moiety of the dimer ion and a free NO. The dissociation dynamics seem to be independent of the NO internal energy. Finally, the dissociation dynamics reveal a correlation between the kinetic energy of the NO fragment and the degree of conservation of linear momentum between the O and N product atoms. The observations support a mechanism in which the recoil takes place along one of the NO bonds in the dimer.
Fluid-dynamic equations for granular particles in a host medium
Authors: Bisi M. , Spiga G.
Published: November 2005

A kinetic model for a granular gas interacting with a given background by binary dissipative collisions is analyzed, with particular reference to the derivation of macroscopic equations for the fundamental observables. Particles are modelled as inelastic hard spheres under the assumption of collision dominated regime (small mean free path). Closure of the relevant moment equations is achieved by resorting to a maximum entropy principle, and two specific entropy functionals have been worked out in detail, in the class of the admissible ones for the relevant linear extended Boltzmann equation. Considered macroscopic fields include density, mass velocity, and granular temperature. In the hydrodynamic limit when the mean free path tends to zero, a single drift-diffusion equation of Navier-Stokes type is recovered for the only hydrodynamic variable of the physical problem.
Fractal dimensions in perceptual color space: A comparison study using Jackson Pollock’s art
Authors: Mureika J. R.
Published: November 2005

The fractal dimensions of color-specific paint patterns in various Jackson Pollock paintings are calculated using a filtering process that models perceptual response to color differences (L*a*b* color space). The advantage of the L*a*b* space filtering method over traditional red-green-blue (RGB) spaces is that the former is a perceptually uniform (metric) space, leading to a more consistent definition of “perceptually different” colors. It is determined that the RGB filtering method underestimates the perceived fractal dimension of lighter-colored patterns but not of darker ones, if the same selection criteria is applied to each. Implications of the findings to Fechner’s “principle of the aesthetic middle” and Berlyne’s work on perception of complexity are discussed.
Electronic and optical properties of α, γ, and β phases of MgH2: A first-principles GW investigation
Authors: Moysés Araújo C. , Lebègue S. , Eriksson O. , Arnaud B. , Alouani M. , Ahuja R.
Published: November 2005

The electronic structure of α, γ, and β phases of MgH2 is studied using the state of the art all-electron projector-augmented-wave GW approximation. Both the ground-state and the high-pressure transformations are considered in this investigation. We have found an indirect (direct) band gap of 5.58eV (6.52eV) for α-MgH2 in good agreement with the experimental findings. For the γ and β phases, we have found indirect (direct) band-gap values of 5.24eV (5.33eV) and 3.90eV (4.72eV), respectively. The optical properties are investigated by means of the complex dielectric function, which is calculated within the framework of a full-potential linearized augmented plane-wave method and corrected by the scissor operation. All phases are found to be color neutral insulators.
Millisecond time-range analysis of space-charge distribution and electroluminescence in insulating polymers under transient electric stress
Authors: Fukuma M. , Teyssedre G. , Laurent C. , Fukunaga K.
Published: November 2005

The combined analysis of the space charge and electroluminescence (EL) in insulating polymers provides useful information on charge transport and energy dissipation. We are particularly interested in defining critical transport regimes leading to energy releases potentially harmful for the material. These critical regimes can be characterized by investigating the internal charge distribution when electroluminescence is detected. The dc case has been adequately covered: however, very few results are reported involving transient electric stress because its investigation needs a very fast space-charge detection setup. We have carried out such an analysis in the case of low-density polyethylene and polyethylene naphthalate (PEN) films by using fast acquisition techniques for both, the space-charge profile (resolution of 40μs in time and 15μm in depth) and the electroluminescence acquisition (250μs time resolution). The films were subjected to a voltage ramp up to a targeted level followed by a stabilization and a short circuit, the whole wave form lasting for 50 ms. Voltage rise rates from 300 to 3000kV∕s and fields up to 200kV∕mm were used as well as ac stress in a frequency range from 0.2 to 50 Hz. Mobile charges following the voltage application were in evidence in PEN. Two contributions have been distinguished in the EL excitation mechanisms: one is due to hot carrier impact processes driven by dV∕dt, and the other is linked with recombination and controlled by the dc transport properties of the material.
Microfabricated high-finesse optical cavity with open access and small volume
Authors: Trupke M. , Hinds E. A. , Eriksson S. , Curtis E. A. , Moktadir Z. , Kukharenka E. , Kraft M.
Published: November 2005

We present a microfabricated optical cavity, which combines a very small mode volume with high finesse. In contrast to other micro-resonators, such as microspheres, the structure we have built gives atoms and molecules direct access to the high-intensity part of the field mode, enabling them to interact strongly with photons in the cavity for the purposes of detection and quantum-coherent manipulation. Light couples directly in and out of the resonator through an optical fiber, avoiding the need for sensitive coupling optics. This renders the cavity particularly attractive as a component of a lab-on-a-chip, and as a node in a quantum network.
Spin-dependent tunneling through high-k LaAlO3
Authors: Garcia V. , Bibes M. , Maurice J.-L. , Jacquet E. , Bouzehouane K. , Contour J.-P. , Barthélémy A.
Published: November 2005

We report on the use of the LaAlO3 (LAO) high-k dielectric as a tunnel barrier in magnetic tunnel junctions. From tunnel magnetoresistance (TMR) measurements on epitaxial La2∕3Sr1∕3MnO3∕LAO∕La2∕3Sr1∕3MnO3 junctions, we estimate a spin polarization of 77% at low temperature for the La2∕3Sr1∕3MnO3∕LAO interface. Remarkably, the TMR of La2∕3Sr1∕3MnO3∕LAO∕Co junctions at low bias is negative, evidencing a negative spin polarization of Co at the interface with LAO, and its bias dependence is very similar to that of La2∕3Sr1∕3MnO3∕SrTiO3∕Co junctions. We discuss possible reasons for this behavior.
Carrier concentration, mobility, and electron effective mass in chlorine-doped n-type Zn1−xMnxSe epilayers grown by molecular-beam epitaxy
Authors: Daniel B. , Agarwal K. C. , Lupaca-Schomber J. , Klingshirn C. , Hetterich M.
Published: November 2005

We investigate n-type chlorine-doped ZnMnSe epilayers with various Mn contents and doping concentrations. In ZnSe, the maximum dopability was 6×1019cm−3, which reduces to 1.1×1019cm−3 at 13% Mn content. At a constant ZnCl2 doping source temperature, the doping concentration decreases continuously with increasing Mn content in the sample. From our optical measurements, we found a lower electron effective mass in Zn0.87Mn0.13Se samples compared to ZnSe. Additionally, the incorporation of Mn increases the resistivity and decreases the mobility of the free charge carriers in the samples.
High ac-voltage sensitivity of a quartz needle sensor used in noncontact scanning force microscopy
Authors: Hartmann C. , Mertin W. , Bacher G.
Published: November 2005

The ac-voltage sensitivity of a needle sensor used in a scanning force microscope has been investigated. The voltage sensitivity varies depending if the needle sensor is used as an active or passive device. Using it as an active device, we achieve a voltage sensitivity down to 100μV if the frequency and phase of the excitation voltage of the needle sensor is matched to the voltage of the device under test.
Growth of Ag icosahedral nanocrystals on a SrTiO3(001) support
Authors: Silly Fabien , Castell Martin R.
Published: November 2005

We have investigated the structure and morphology of self-assembled silver nanocrystals supported on a SrTiO3(001)−(2×1) substrate using scanning tunneling microscopy. Ag forms nanocrystals with five-fold symmetry which have an icosahedral shape. Nanocrystals with point, edge, and face orientation (five-fold, two-fold, and three-fold symmetry, respectively) have been studied. The images of these nanocrystals allow a crystallographic identification of the supported shape of the icosahedral form.
Thermally driven nanomechanical deflection of hybrid nanowires
Authors: Ikuno Takashi , Honda Shin-ichi , Yasuda Tatsuro , Oura Kenjiro , Katayama Mitsuhiro , Lee Jung Goo , Mori Hirotaro
Published: November 2005

We observed thermally induced nanomechanical deflection of a hybrid inorganic nanowire (NW) synthesized by pulsed-laser deposition, the structure of which is a carbon nanotube template sandwiched by aluminum oxide and tungsten oxide thin layers. The hybrid NW was gradually bent at a specimen temperature ranging from room temperature to 800 °C, due to the different coefficients of thermal expansion of the coated layers. This mechanical deflection exhibited repeatability.
Monte Carlo determination of crystallite size of porous silicon from x-ray line broadening
Authors: Martín-Palma R. J. , Pascual L. , Herrero P. , Martínez-Duart J. M.
Published: November 2005

The nanometric structure of porous silicon makes this material very suitable for its use in many different fields, including optoelectronics and biological applications. Porous silicon can be basically described as an amorphous matrix in which silicon nanocrystals are embedded. In the present work, the distribution in size of the Si grains that compose porous silicon as a function of porosity was determined based on x-ray line broadening. For this purpose, a Monte Carlo interference-function-fitting algorithm was used. The main advantage of this method is that it gives the complete particle size distribution and not just averaged values. The results from the distribution in size of porous silicon were fitted to a log normal distribution and were correlated with the corresponding photoluminescent spectra.
Surface behavior of La2∕3Ca1∕3MnO3 epitaxial thin films
Authors: Abad Ll. , Martínez B. , Balcells Ll.
Published: November 2005

The role of the surface layers in La2∕3Ca1∕3MnO3 magnetic oxide epitaxial thin films is analyzed. We show that the topmost layers do play a very relevant role on the transport properties acting as an insulating barrier. Atomic force microscopy (AFM) measurements in the current sensing mode exhibit typical features of tunneling conduction. The analysis of the I-V curves by using the Simmons model give values of barrier thickness in good agreement with nonmagnetic layer thickness estimates from magnetic measurements. Ex situ annealing in air at high temperature clearly improve the magnetotransport properties of the films reducing the surface insulating barrier.
Substrate effect on the thickness of spin-coated ultrathin polymer film
Authors: Cheung K. P. , Grover R. , Wang Y. , Gurkovich C. , Wang G. , Scheinbeim J.
Published: November 2005

In this work, we report clear evidence of a strong substrate effect on the thickness of a spin-coated polymer film in the ultrathin (<30nm) regime. We observed a film thickness to spin speed relationship that clearly cannot be described by the classic power-law model. This “anomalous” film thickness phenomenon is quite different from those previously reported in the literature. We propose a new “non-Newtonian” bottom layer model to explain the phenomenon.
Do Rotation Coordinates Provide the Substrate for a Mental Protractor?
Authors: Greene Ernest , Frawley William
Published: November 2005

In previous studies, we have found that the accuracy in judging collinearity of lines or dots varies considerably from one subject to another as a function of the relative angle of the stimulus elements. A model of errors generally shows large excursions across several subranges of angular position. These do not appear to be motor errors, at least not ones that are well separated from perceptual mechanisms. The errors are most likely generated at primary visual cortex, or beyond. We examined and modeled accuracy in judging collinearity of dot pairs, varying the angular position of the dots through 360°, the distance between the dots (stimulus span), and the distance at which the subject was required to respond (response span). Subjects manifested idiosyncratic profiles of error across angular positions, as reported previously. But across the tested range of spans, from 4 to 8 deg, the errors tended to be the same, irrespective of stimulus or response span. This suggests that the judgments are based on a radial (angular) measure of spatial position. We discuss these results in the context of proposals that the brain maps spatial position using rotation coordinates. These new data are consistent with the hypothesis that subjects use the z-axis coordinates as a mental protractor for judging angular position and collinearity.
The Role of Edges in Object Recognition by Pigeons
Authors: Peissig Jessie J , Young Michael E , Wasserman Edward A , Biederman Irving
Published: November 2005

In three experiments, we explored how pigeons use edges, corresponding to orientation and depth discontinuities, in visual recognition tasks. In experiment 1, we compared the pigeon's ability to recognize line drawings of four different geons when trained with shaded images. The birds were trained with either a single view or five different views of each object. Because the five training views had markedly different appearances and locations of shaded surfaces, reflectance edges, etc, the pigeons might have been expected to rely more on the orientation and depth discontinuities that were preserved over rotation and in the line drawings. In neither condition, however, was there any transfer from the rendered images to the outline drawings. In experiment 2, some pigeons were trained with line drawings and shaded images of the same objects associated with the same response (consistent condition), whereas other pigeons were trained with a line drawing and a shaded image of two different objects associated with the same response (inconsistent condition). If the pigeons perceived any correspondence between the stimulus types, then birds in the consistent condition should have learned the discrimination more quickly than birds in the inconsistent condition. But, there was no difference in performance between birds in the consistent and inconsistent conditions. In experiment 3, we explored pigeons' processing of edges by comparing their discrimination of shaded images or line drawings of four objects. Once trained, the pigeons were tested with planar rotations of those objects. The pigeons exhibited different patterns of generalization depending on whether they were trained with line drawings or shaded images. The results of these three experiments suggest that pigeons may place greater importance on surface features indicating materials, such as food or water. Such substances do not have definite boundaries—cued by edges—which are thought to be central to human recognition.