bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal properties of sand from Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS): Spatial variations within the Proctor Crater dune field on Mars
Authors: Fenton Lori K. , Mellon Michael T.
Published: June 2006

Thermal inertia, a parameter calculated from surface temperatures obtained from spacecraft, has long been used to quantify the amount of loose, fine‐grained material on the Martian surface. With little “ground truth” available, studies often refer to Martian dune fields to calibrate thermal inertias. The well‐understood physical properties of dune sand make it an ideal basis for comparison to more complex surfaces. However, higher‐resolution data sets available from the TES (Thermal Emission Spectrometer onboard Mars Global Surveyor) and THEMIS (Thermal Emission Imaging System onboard Mars Odyssey) show spatial variations in the thermal properties within dune fields, calling into question their effectiveness as controls for thermal inertia studies. In order to explain these variations, we apply a thermal model developed for TES data to a commonly investigated dune field in Noachis Terra, that on the floor of Proctor Crater. We show that in this dune field, the thermal variations on the scale of 30 J m−2 s−0.5 K−1 are present and correlate spatially with aeolian features in the dune field. These variations correspond to three types of surfaces observed in the Mars Orbital Camera Narrow Angle (MOC NA) images: (1) dune sand, (2) interdunes exposing the surface underlying the dune field, and (3) sand‐covered interdunes, or dune troughs. Both the interdunes and the dune troughs have cooler nighttime temperatures than the dune sand, corresponding to lower thermal inertia values. The dune troughs may be sand‐covered areas with either minor amounts of dust accumulation or a mean sand grain size lower than that of dune sand. Because fine sand grains tend to preferentially accumulate on dune crests rather than in dune troughs, the second hypothesis is considered less likely than the first. This has implications for the recent sedimentary history of the dune field: Dust accumulation in dune troughs may imply that sand saltation is not prevalent enough to scour away all of the dust settling out from suspension in the atmosphere; however, it is prevalent enough to keep the dunes crests themselves clear of dust.
Kinetic aspects of foreshock cavities
Authors: Schwartz Steven J. , Sibeck David , Wilber Mark , Meziane Karim , Horbury Timothy S.
Published: June 2006

We have investigated the kinetic signatures within, and at the edges of, a foreshock cavity. Such cavities are believed to be formed when an isolated collection of interplanetary magnetic field lines connect to quasi‐parallel regions of the Earth's bow shock, allowing energetic ions to flow upstream and excavate a local cavity. Observations by the Cluster spacecraft show precisely this configuration. The suprathermal ions can be seen just outside the edges of the cavity within a restricted range of gyrophases, consistent with their gyromotion tangential to the layer containing the cavity. Foreshock cavities, if sufficiently common, may play significant roles in triggering magnetospheric events. Thus our confirmation of their relatively simple formation mechanism lends support to their inferred frequency.
Particle acceleration at perpendicular shock waves: Model and observations
Authors: Zank G. P. , Li Gang , Florinski V. , Hu Qiang , Lario D. , Smith C. W.
Published: June 2006

On the basis of a recently developed nonlinear guiding center theory for the perpendicular spatial diffusion coefficient κ⊥ used to describe the transport of energetic particles, we construct a model for diffusive particle acceleration at highly perpendicular shocks, i.e., shocks whose upstream magnetic field is almost orthogonal to the shock normal. We use κ⊥ to investigate energetic particle anisotropy and injection energy at shocks of all obliquities, finding that at 1 AU, for example, parallel and perpendicular shocks can inject protons with equal facility. It is only at highly perpendicular shocks that very high injection energies are necessary. Similar results hold for the termination shock. Furthermore, the inclusion of self‐consistent wave excitation at quasiparallel shocks in evaluating the particle acceleration timescale ensures that it is significantly smaller than that for highly perpendicular shocks at low to intermediate energies and comparable at high energies. Thus higher proton energies are achieved at quasiparallel rather than highly perpendicular interplanetary shocks within 1 AU. However, both injection energy and the acceleration timescale at highly perpendicular shocks are sensitive to assumptions about the ratio of the two‐dimensional (2‐D) correlation length scale to the slab correlation length scale λ2D/λ∥. Model proton spectra and intensity profiles accelerated by a highly perpendicular interplanetary shock are compared to an identical but parallel interplanetary shock, revealing important distinctions. Finally, we present observations of highly perpendicular interplanetary shocks that show that the absence of upstream wave activity does not inhibit particle acceleration at a perpendicular shock. The accelerated particle distributions closely resemble those expected of diffusive shock acceleration, and observed at oblique shocks, an example of which is shown.
Black carbon measurement in a coastal area of south China
Authors: Cheng Y. , Lee S. C. , Ho K. F. , Wang Y. Q. , Cao J. J. , Chow J. C. , Watson J. G.
Published: June 2006

To better understand anthropogenic pollution originating in Asia and its transport into the global atmosphere, black carbon (BC) emissions were measured continuously from June 2004 to May 2005 at Hok Tsui (22.13°N, 114.15°E). Hok Tsui is a continental outflow, downwind monitoring site, located in a coastal area near Hong Kong. Using an Aethalometer, hourly BC concentrations ranged from 63.0 ng/m3 to 17.3 μg/m3, showing a clear seasonal pattern with high concentrations in winter, spring, and fall and low values in summer. During the winter, high BC concentrations occurred frequently as a result of southward long‐range transport of polluted air masses in the boundary layer over the Asian continent. Anthropogenic emissions in coastal areas of southeastern China were the major potential sources for the observed pollutants. During the summer, high BC concentrations were measured occasionally when the air masses came from the northwest. These anthropogenic pollutants were found to be regional in nature, originating from sources in the Pearl River Delta (PRD) region, which included emissions from residential and agricultural combustion, industry, power plants, motor vehicles, and ships.
Linking snowpack microphysics and albedo evolution
Authors: Flanner Mark G. , Zender Charles S.
Published: June 2006

Snow aging causes reflectance to vary significantly on timescales of days. This variability influences the strength of snow albedo feedback and can affect the timing of snowmelt. However, climate models have yet to incorporate important controls on snow aging and albedo evolution. We develop a physically based model that predicts evolution of dry, pure snow specific surface area, and apply aspherical ice particle theory to link these results with albedo evolution. This is the first theoretical study to quantify the relative roles of initial size distribution, vertical temperature gradient, and snow density in snow albedo evolution. Vapor diffusion caused by curvature differences causes rapid albedo decay in the first day following snowfall. Vertical temperature gradient generally dominates grain growth processes afterward but is modulated by snow density, irregularity in particle spacing, and temperature. These processes operate as a coupled system, which we uniquely represent without abrupt transitions between regimes. Model results agree very well with measurements of isothermal snow evolution and are within reasonable range of temperature gradient observations. We show that different snow state regimes cause albedo of nonmelting snow surfaces with identical initial albedo to vary by 0.12 or more after 14 days. Lack of quality observational data illuminates the need for well‐controlled snow studies that simultaneously monitor specific surface area, temperature gradient, and albedo. Accounting for snow aging processes, especially temperature gradient, will improve understanding and assessment of snow albedo feedback and climate sensitivity. The modeling framework we develop will also be useful for air‐snow chemistry studies that consider specific surface area.
Inverse modeling of argon step‐release data from lunar impact spherules
Authors: Levine Jonathan , Rohde Robert A.
Published: June 2006

We use argon step‐release measurements to model the initial distribution of argon isotopes in 177 lunar impact spherules. The speed of modern computers permits us to approach this inverse problem in new ways, and the techniques we develop may be extended to study a wide range of samples, diffusing species, and geometries. Lunar spherules, by virtue of their simple shapes and histories, seem to be excellent candidates for inverse modeling. Nevertheless, impact spherules preserve chemical or material heterogeneities that are relics of their parent materials. As a result, we find that the distribution of argon isotopes in most impact spherules is more complex than can be meaningfully constrained by a practical number of precise measurements. The spatial distribution of argon from different sources, such as solar implantation, would be better probed in spherules by other techniques, such as stepwise etching.
Degree‐1 convection in the Martian mantle and the origin of the hemispheric dichotomy
Authors: Roberts James H. , Zhong Shijie
Published: June 2006

The surface of Mars appears dramatically different between the northern and southern hemispheres. Any endogenic origin for this hemispheric dichotomy must involve a pattern of mantle convection that reflects the shape of the dichotomy, primarily spherical harmonic degree‐1. We investigated two mechanisms by which degree‐1 convection may be initiated in the Martian mantle: (1) an endothermic phase change near the CMB and (2) viscosity layering in the mid‐mantle. Using two‐dimensional (2‐D) and 3‐D spherical finite‐element convection models, we explored the conditions under which each mechanism can produce degree‐1 structures. The phase transition is only effective at generating degree‐1 structures when the mantle viscosity is constant or weakly temperature‐dependent (activation energy <100 kJ/mol), but the degree‐1 pattern requires several billion years to develop. Increasing convective vigor in phase change models leads to reduced wavelengths for convective structures. Degree‐1 convection can also develop in a layered viscosity mantle, with temperature‐ and depth‐dependent viscosity. An overall sublithospheric radial viscosity variation of a factor of 100 including a factor of 8–25 jump in the midmantle can lead to formation of degree‐1 structure in a timescale ranging from 100 My to several hundred My, consistent with the timescale for the formation of the dichotomy. Neither convective vigor nor the internal heating rate greatly affects the formation of degree‐1 structures. We propose that degree‐1 mantle convection induced by a layered viscosity structure may be responsible for the formation of the crustal dichotomy.
Relationship between hydrological characteristics and dissolved organic carbon concentration and mass in northern prairie wetlands using a conservative tracer approach
Authors: Waiser Marley J.
Published: June 2006

The semiarid prairie pothole region of the North American Great Plains is characterized by millions of small, shallow, closed basin wetlands. These wetlands are hydrologically dynamic, often losing considerable water volume and depth seasonally in response to high evaporative stress and/or infiltration rates. However, the consequences of such water loss on wetland water chemistry parameters, in particular dissolved organic carbon (DOC), remain relatively unstudied. Seasonal changes in DOC concentrations in 12 freshwater and saline wetlands at the St. Denis National Wildlife Refuge near Saskatoon, Saskatchewan, Canada, were examined over an 8‐year period (1993–2000). Specific conductivity in the study ponds ranged from 312 μS cm−1 to 33,493 μS cm−1 (seasonal means). DOC concentrations in all study ponds were high (>10 mg L−1) and increased across a gradient of increasing salinity (mean DOC values from fresh water to saline ranged from 19.7 mg L−1 to 102.7 mg L−1). In the majority of ponds, DOC concentrations increased seasonally from spring through fall. On average this increase was 21 mg L−1, with fall values averaging 60% greater than spring. The greatest DOC increases were observed in saline ponds which lost most of their water by evaporation. Although DOC in these ponds was highly correlated with the conservative tracer, chloride, the slopes of these regression lines were always less than 1 as were the DOC:chloride ratios, indicating nonconservative DOC behavior. Additionally, chloride concentrations increased much faster seasonally than did DOC. Taken together, these data indicated that although DOC was not behaving conservatively, at least some of the observed DOC increases could be explained by simple evapoconcentration. These data also suggested that saline ponds appeared to experience net seasonal removal of DOC. Possible removal mechanisms for DOC include infiltration to the pond margin, bacterial utilization, and photolysis. Freshwater ponds, which lost most of their water by infiltration to the pond margin, on the other hand, displayed less seasonal variation in DOC concentrations. In these ponds, the relationship between DOC and chloride ion was not as strong as in the saline ponds; the slope of this relationship was always >1, as were DOC:chloride ratios. These data indicated that although DOC was being lost to the pond margin as water infiltrated, freshwater ponds accumulated DOC seasonally. Decomposition and excretion of DOC by macrophytes, as well as by pelagic and attached phytoplankton, are the likely within pond sources of DOC here. The rapid response of these small, shallow aquatic systems to water loss make them ideal microcosms in which to study effects of climate on DOC concentrations and other water chemistry parameters.
A framework for urban storm water modeling and control analysis with analytical models
Authors: Chen Jieyun , Adams Barry J.
Published: June 2006

This paper introduces a framework for urban storm water modeling and control analysis with analytical models, which consist of a number of functional components, such as rainfall‐runoff transformation, pollutant buildup and wash‐off, and pollutant removal in storage/treatment facilities, etc. As the key component, the rainfall‐runoff transformation, which characterizes runoff generation mechanism in the drainage area, is employed not only to transform the probability distributions of the rainfall characteristics into the probability distribution of runoff in an effort to develop storm water quantity control measures, such as runoff volume of spills and runoff control efficiency, but also to derive the probability distributions of pollutant loads and develop storm water quality control measures, such as the average event mean concentrations and annual pollutant loads to receiving waters. While each component or module is initially developed separately and can function independently, all these components are virtually an integral part of the framework considering that the pollutant wash‐off load model is essentially an integration of the rainfall‐runoff transformation and pollutant buildup models. In light of the proposed framework, which may serve as a map to this study, this paper summarizes theoretical basis while emphasizing major procedures with a case study for the development of the integrated analytical model based on the derived probability distribution approach.
Large‐eddy simulation of a diurnal cycle of the atmospheric boundary layer: Atmospheric stability and scaling issues
Authors: Kumar Vijayant , Kleissl Jan , Meneveau Charles , Parlange Marc B.
Published: June 2006

A simulation of a diurnal cycle of atmospheric boundary layer (ABL) flow over a homogeneous terrain is performed using large‐eddy simulation (LES) with the Lagrangian scale‐dependent dynamic subgrid‐scale model. The surface boundary condition is derived from the field observations of surface heat flux from the HATS experiment (Horst et al., 2004; Kleissl et al., 2004). The simulation results display good general agreement with previous modeling and experimental studies with regard to characteristic features such as growth of the convective boundary layer by entrainment, nocturnal jet, and multilayered flow structure of the nocturnal regime. To gain a better understanding of the physical parameters affecting the statistics of the flow, we study the dependence of a subgrid parameter (dynamic Smagorinsky coefficient), resolved turbulent kinetic energy, and resolved vertical velocity variance upon atmospheric stability. The profiles of these turbulent variables plotted as a function of Obukhov length show “hysteretic” behavior that implies nonunique dependence. The subsequent use of local Richardson number as the scaling parameter shows a decrease in this “hysteresis,” but there is an increased scatter in the profiles with increasing height. Conversely, profiles plotted as a function of local Obukhov length (based on the fluxes at the local vertical level) show almost no hysteresis, confirming the validity of Nieuwstadt's local scaling hypothesis. Although the local scaling hypothesis was formulated for the stable boundary layer, we find that it applies to the entire stability range of the diurnal cycle.
Multifractality and rainfall extremes: A review
Authors: Veneziano Daniele , Langousis Andreas , Furcolo Pierluigi
Published: June 2006

The multifractal representation of rainfall and its use to predict rainfall extremes have advanced significantly in recent years. This paper summarizes this body of work and points at some open questions. The need for a coherent overview comes in part from the use of different terminology, notation, and analysis methods in the literature and in part from the fact that results are dispersed and not always readily available. Two important trends have marked the use of multifractals for rainfall and its extremes. One is the recent shift of focus from asymptotic scaling properties (mainly for the intensity‐duration‐frequency curves and the areal reduction factor) to the exact extreme distribution under nonasymptotic conditions. This shift has made the results more relevant to hydrologic applications. The second trend is a more sparing use of multifractality in modeling, reflecting the limits of scale invariance in space‐time rainfall. This trend has produced models that are more consistent with observed rainfall characteristics, again making the results more suitable for application. Finally, we show that rainfall extremes can be analyzed using rather rough models, provided the parameters are fitted to an appropriate range of large‐deviation statistics.
Seasonal variability in the stratospheric aerosol layer in the current volcanically‐quiescent period over two tropical stations in India using the twilight sounding method
Authors: Padma Kumari B. , Londhe A. L. , Jadhav D. B. , Trimbake H. K.
Published: June 2006

The twilight photometry technique is used to study the variability of stratospheric aerosol layer over the tropical Indian inland stations, Pune (18.5°N, 73.9°E) and Karad (17.0°N, 74.2°E) during the volcanically quiescent period January 2000 to December 2003. The stratospheric aerosol loading is computed from the aerosol vertical profiles derived by twilight scattering technique. The time variation of monthly mean stratospheric aerosol loading shows small‐scale variations in the background stratospheric aerosol loading with maximum loading in the winter.
An isolated cloud band around a typhoon in the western tropical Pacific
Authors: Ushiyama T. , Shirooka R. , Chuda T. , Kubota H. , Iwasaki S. , Chen J. , Takeuchi K. , Uyeda H.
Published: June 2006

Satellite imagery and C‐band radar on the R/V Mirai detected an isolated convective cloud band over the western tropical Pacific, and dropsondes observed the surrounding atmospheric environment. The reasonable development mechanism of this unusual cloud band is investigated using observational and numerical simulation data. Although theoretically, the surrounding atmospheric profile supported convective rolls, only a single cloud band was developed. Numerical simulations revealed a single cloud band and roll structure without condensate in the boundary layer. A westerly jet just above the cloud band influenced the environment with strong vertical shear supporting convective rolls; this was maintained by a typhoon at a distance of 1500 km away. A large‐scale convergence in the meridional wind was also accompanied with this westerly jet. This special environment made by a typhoon could develop the unusual single cloud band.
Salt release from warming sea ice
Authors: Widell Karolina , Fer Ilker , Haugan Peter M.
Published: June 2006

In a field study in the Arctic, ejection of dense, saline plumes was observed 1 m below warm land‐fast first‐year sea ice, under conditions where the heat balance at the ice‐ocean interface predicted melting. We describe the observed momentum, heat and salt fluxes in the boundary layer under the ice and the structure of the plume events. Measured downward salt flux was well correlated with upward oceanic heat flux. Our measurements indicate that turbulent heat forcing from below can play an important role for the desalination of warm and saline, hence permeable, sea ice.
Revealing Structure in Visualizations of Dense 2D and 3D Parallel Coordinates
Authors: Johansson Jimmy , Ljung Patric , Jern Mikael , Cooper Matthew
Published: June 2006

Parallel coordinates is a well-known technique used for visualization of multivariate data. When the size of the data sets increases the parallel coordinates display results in an image far too cluttered to perceive any structure. We tackle this problem by constructing high-precision textures to represent the data. By using transfer functions that operate on the high-precision textures, it is possible to highlight different aspects of the entire data set or clusters of the data. Our methods are implemented in both standard 2D parallel coordinates and 3D multi-relational parallel coordinates. Furthermore, when visualizing a larger number of clusters, a technique called ‘feature animation’ may be used as guidance by presenting various cluster statistics. A case study is also performed to illustrate the analysis process when analysing large multivariate data sets using our proposed techniques.
PRISAD: A Partitioned Rendering Infrastructure for Scalable Accordion Drawing (Extended Version)
Authors: Slack James , Hildebrand Kristian , Munzner Tamara
Published: June 2006

We present PRISAD, the first generic rendering infrastructure for information visualization applications that use the accordion drawing technique: rubber-sheet navigation with guaranteed visibility for marked areas of interest. Our new rendering algorithms are based on the partitioning of screen-space, which allows us to handle dense data set regions correctly. The algorithms in previous work led to incorrect visual representations because of overculling, and to inefficiencies due to overdrawing multiple items in the same region. Our pixel-based drawing infrastructure guarantees correctness by eliminating over-culling, and improves rendering performance with tight bounds on overdrawing. PRITree and PRISeq are applications built on PRISAD, with the feature sets of TreeJuxtaposer and SequenceJuxtaposer, respectively. We describe our PRITree and PRISeq data set traversal algorithms, which are used for efficient rendering, culling, and layout of data sets within the PRISAD framework. We also discuss PRITree node marking techniques, which offer order-of-magnitude improvements to both memory and time performance vs previous range storage and retrieval techniques. Our PRITree implementation features a fivefold increase in rendering speed for non-trivial tree structures, and also reduces memory requirements in some real-world data sets by up to eight times, so we are able to handle trees of several million nodes. PRISeq renders 15 times faster and handles data sets 20 times larger than previous work. The software is available as open source from http://olduvai.sourceforge.net .
Surface Glyphs for Efficient Visualization of Spatial Multivariate Data
Authors: Forsell Camilla , Seipel Stefan , Lind Mats
Published: June 2006

We present a first effort to evaluate the possible utility of a new type of surface glyphs intended for visualizations of multivariate spatial data. The glyphs are based on results from vision research suggesting that our perception of metric 3D structure is distorted and imprecise relative to the actual scene before us; only a class of qualitative properties of the scene is perceived with accuracy. These properties are best characterized as being invariant over affine but not Euclidean transformations. A large number of possible 3D glyphs for the visualization of spatial data can be constructed using such properties. One group of such glyphs is based on the local sign of surface curvature. We investigated this group in two visualization experiments. The results show that available sources of 3D structural information were sufficient for our subjects to make fast and accurate judgments. Some implications for visualization are also discussed.
A Sky Dome Visualisation for Identification of Astronomical Orientations
Authors: Zotti Georg
Published: June 2006

It has long been known that ancient temples were frequently oriented along the cardinal directions or to certain points along the horizon where the Sun or the Moon rises or sets on special days of the year. In the last decades, archaeologists have found evidence of even older building structures buried in the soil, with doorways that also appear to have distinct orientations.

This paper presents a novel diagram combining archaeological maps with a folded-apart, flattened view of the whole sky, showing the local horizon and the daily paths of the Sun, Moon and brighter stars. By use of this diagram, interesting groupings of astronomical orientation directions, for example, to certain sunrise and sunset points could be identified, which were evidently used to mark certain days of the year. Orientations towards rising and setting points of a few significant stars very likely indicated the beginning of the agricultural year in the middle neolithic period.
Give Chance a Chance: Modeling Density to Enhance Scatter Plot Quality through Random Data Sampling
Authors: Bertini Enrico , Santucci Giuseppe
Published: June 2006

The problem of visualizing huge amounts of data is well known in information visualization. Dealing with a large number of items forces almost any kind of Infovis technique to reveal its limits in terms of expressivity and scalability. In this paper we focus on 2D scatter plots, proposing a ‘feature preservation’ approach, based on the idea of modeling the visualization in a virtual space in order to analyze its features (e.g., absolute density, relative density, etc.). In this way we provide a formal framework to measure the visual overlapping, obtaining precise quality metrics about the visualization degradation and devising automatic sampling strategies able to improve the overall image quality. Metrics and algorithms have been improved through suitable user studies.
Visualization Aided Performance Tuning of Irregular Task-Parallel Computations
Authors: Blochinger Wolfgang , Kaufmann Michael , Siebenhaller Martin
Published: June 2006

This paper deals with a visualization-based approach to performance analyzing and tuning of highly irregular task-parallel applications. At its core lies a novel automatic layout algorithm for execution graphs which is based on Sugiyama's framework. Our visualization enables the application designer to reliably detect manifestations of parallel overhead and to investigate on their individual root causes. We particularly focus on structural properties of task-parallel computations which are hard to detect in a more analytical way, for example, false sharing and false parallelism. In addition, we discuss embedding our visualization into an integrated development environment, realizing a seamless work-flow for implementation, execution, analysis, and tuning of parallel programs.
Concept Maps for Designing Adaptive Knowledge Maps
Authors: Crampes Michel , Ranwez Sylvie , Villerd Jean , Velickovski Filip , Mooney Chris , Emery Andrew , Mille Nicholas
Published: June 2006

Concept Maps (CMaps) are an excellent method to visually represent and interact with a knowledge domain. A Knowledge Map (KMap) is a further complicated instance of a CMap, containing many instances of concepts and concept relations that add to the complexity of a visual representation. Adaptivity is also a key requirement for KMaps that we will demonstrate through practical example. This paper presents both a method, called ‘Domain-View-Controller’ (DVC) and a software environment specifically designed to create adaptive KMaps from CMaps. These tools give professional knowledge designers the means for specifying the domain knowledge of end users, allowing them to build well-organized adaptive KMaps with partial automated assistance. This paper also presents a scheme for the fully automated process of creating KMaps from domain specifications, giving end users the ability to display complex knowledge without having the expertise of knowledge engineers. The paper focuses on a real-world example from the domain of music to illustrate the underlying principles.
Learning from Architects: Complementary Concept Mapping Approaches
Authors: Burkhard Remo Aslak
Published: June 2006

The research scope in concept mapping research can be extended with the investigation of complementary concept mapping approaches, which are visual representations that complement the classical node link diagrams from Novak. To do so, concept mapping researchers can draw inspiration from architects. This article presents four strategies of architects to map concepts. The analysis shows what concept mapping researchers can benefit from architects: first, from the practice of architects to use complementary visualizations, which is investigated in the research field of Knowledge Visualization. Second, from their practice to structure information, which is investigated in the research field of Information Architecture. Both research fields are relevant for concept mapping researchers who investigate new formal approaches that complement the concept mapping approach taken by Novak. Third, the article discusses examples of complementary concept maps in different business situations.
A Comparison between Concept Maps, Mind Maps, Conceptual Diagrams, and Visual Metaphors as Complementary Tools for Knowledge Construction and Sharing
Authors: Eppler Martin J
Published: June 2006

In this article, Novak's concept mapping technique is compared to three other types of visualization formats, namely mind maps, conceptual diagrams, and visual metaphors. The application parameters and the respective advantages and disadvantages of each format for learning and knowledge sharing are reviewed and discussed. It is argued that the combination of these four visualization types can play to the strength of each one. The article then provides real-life examples from such a use in undergraduate and graduate university teaching. The results provide first indications that the different visualization formats can be used in complementary ways to enhance motivation, attention, understanding and recall. The implications for a complementary use of these visualization formats in class room and meeting contexts are discussed and a future research agenda in this domain is articulated.
Comoving acceleration of overdense electron-positron plasma by colliding ultra-intense laser pulses
Authors: Liang Edison
Published: June 2006

Particle-in-cell (PIC) simulation results of sustained acceleration of electron-positron (e+e−) plasmas by comoving electromagnetic (EM) pulses are presented. When a thin slab of overdense e+e− plasma is irradiated with linear-polarized ultra-intense short laser pulses from both sides, the pulses are transmitted when the plasma is compressed to thinner than ∼2 relativistic skin depths. A fraction of the plasma is then captured and efficiently accelerated by self-induced J×B forces. For 1μm laser and 1021Wcm−2 intensity, the maximum energy exceeds GeV in a picosecond.
On the discrete Peyrard-Bishop model of DNA: Stationary solutions and stability
Authors: Cuenda Sara , Sánchez Angel
Published: June 2006

As a first step in the search of an analytical study of mechanical denaturation of DNA in terms of the sequence, we study stable, stationary solutions in the discrete, finite, and homogeneous Peyrard-Bishop DNA model. We find and classify all the stationary solutions of the model, as well as analytic approximations of them, both in the continuum and in the discrete limits. Our results explain the structure of the solutions reported by Theodorakopoulos et al. [Phys. Rev. Lett. 93, 258101 (2004)] and provide a way to proceed to the analysis of the generalized version of the model incorporating the genetic information.
Photoionization and photodissociation of HCl(BΣ+1,J=) near 236 and 239nm using three-dimensional ion imaging
Authors: Chichinin A. I. , Maul C. , Gericke K.-H.
Published: June 2006

The electronically excited states HCl*(E,υ′=0,J′=0) and HCl*(V,υ′=12,J′=0) have been prepared by two-photon resonant absorption of ground state HCl via Q(0) transitions at 238.719 and at 236.000nm, respectively. The consequent one-or two-photon excitation at the same wavelength results in the production of H+, Cl+, and HCl+ ions. The speed distributions and anisotropy parameters β for these ions have been determined by three-dimensional photofragment ion imaging based on a position-sensitive delay-line anode assembly. Several results are presented: first, we measured velocity (speed and angle) distributions for HCl+ due to the electron recoil in the photoionization of HCl*. Such distributions give information on the photoionization process and on the vibrational distribution of HCl+ after the laser pulse. Second, the measured β parameters for Cl+ and H+ distributions give information on the symmetries of the upper states in the one-photon photoexcitation of HCl*. Third, the measured speed distributions for H+ help to understand the mechanism of the photodissociation of HCl+ ions.
Deuteron spin lattice relaxation in amorphous ices
Authors: Scheuermann M. , Geil B. , Winkel K. , Fujara F.
Published: June 2006

Temperature-dependent deuteron spin lattice relaxation times T1 have been obtained from water in its three amorphous states at ambient pressure: low density amorphous (LDA), high density amorphous (HDA), and very high density amorphous (VHDA). It is found that in all of these states the magnetization recovery is essentially monoexponential and that T1 of LDA is significantly longer than that of the higher density forms. Thus, T1 can be used as a monitor parameter to study the kinetics of the transitions from HDA to LDA and from VHDA to LDA. During the transformation of VHDA to LDA an intermediate state is formed, which, according to its T1 at low temperature, is clearly determined to be HDA-like. However, and most significantly, the transition from VHDA to this HDA-like state and further on to LDA occurs at temperatures significantly above the kinetic stability limit of native HDA produced at 77K. These findings contribute to the current discussion on the nature of HDA and VHDA by strengthening the view that the annealing of VHDA at ambient pressure produces a relaxed HDA-like state.
On a new self-consistent-field theory for the canonical ensemble
Authors: Baeurle Stephan A. , Efimov Garii V. , Nogovitsin Evgenij A.
Published: June 2006

A significant amount of many-body problems of quantum or classical equilibrium statistical mechanics are conveniently treated at fixed temperature and system size. In this paper, we present a new functional integral approach for solving canonical ensemble problems over the entire coupling range, relying on the method of Gaussian equivalent representation of Efimov and Ganbold [Phys. Status Solidi 168, 165 (1991)]. We demonstrate its suitability and competitiveness for performing approximate calculations of thermodynamic and structural quantities on the example of a repulsive potential model, widely used in soft matter theory.
Mechanism of CO oxidation reaction on O-covered Pd(111) surfaces studied with fast x-ray photoelectron spectroscopy: Change of reaction path accompanying phase transition of O domains
Authors: Nakai Ikuyo , Kondoh Hiroshi , Shimada Toru , Resta Andrea , Andersen Jesper N. , Ohta Toshiaki
Published: June 2006

We studied the mechanism of CO oxidation on O-precovered Pd(111) surfaces by means of fast x-ray photoelectron spectroscopy (XPS). The oxygen overlayer is compressed upon CO coadsorption from a p(2×2) structure into a (√3×√3)R30° structure and then into a p(2×1) structure with increasing CO coverage. These three O phases exhibit distinctly different reactivities. (1) The p(2×2) phase does not react with CO unless the surface temperature is sufficiently high (<290K). (2) In the (√3×√3)R30° phase, the reaction occurs exclusively at island peripheries. CO molecules in a high-density phase formed under CO exposure react with oxygen atoms, leading to quite a small apparent activation energy. (3) The reaction proceeds uniformly over the islands in the p(2×1) phase.
Dispersed fluorescence spectroscopy of the GeCl2 Ã–X̃ transition
Authors: Lin Yu-Shu , Chen Cheng-Chung , Chang Bor-Chen
Published: June 2006

The laser-induced fluorescence excitation spectrum of the GeCl2 Ã–X̃ transition at ultraviolet wavelengths (300–320nm) was recorded in a direct current discharge supersonic free jet expansion. The excitation spectrum contains several sharp peaks and a congested diffuse structure. Dispersed fluorescence spectra following the excitation of these GeCl2 ultraviolet bands were successfully acquired for the first time. The analysis of the dispersed fluorescence spectra reveals the detailed vibrational structure of the X̃A11 state. We have assigned the vibrational structures corresponding to different isotopomers (Ge35Cl2, Ge35Cl37Cl, and Ge37Cl2). The vibrational fundamental frequencies were determined: 409cm−1 (symmetric stretch), 159cm−1 (bend), and 352cm−1 (antisymmetric stretch) for the X̃A11 state of GeCl2. Vibrational parameters of the ground electronic state including vibrational frequencies, anharmonicity, and bend-stretch coupling constant were determined. Our dispersed fluorescence spectra also clarify the vibrational assignments of the hot bands and provide more experimental data for unraveling the nature of the congested diffuse structure at shorter wavelengths in the excitation spectrum.
Persistent nuclear wave packet oscillation coexistent with incoherent vibrational population at excited F centers in KI
Authors: Koyama Takeshi , Takahashi Youtarou , Nakajima Makoto , Suemoto Tohru
Published: June 2006

We investigated nuclear wave packet dynamics in the excited state of KI F centers at 10K using time-resolved luminescence spectroscopy. Observed transient spectrum is divided into oscillatory and non-oscillatory components. The former lasts over 11ps without appreciable damping and is attributed to the oscillation of the wave packet consisting mainly of the A1g mode around the center. The non-oscillatory part rises quickly after photo-excitation exhibiting a cooling of incoherent vibrational population. This behavior suggests the fast energy dissipation due to the dephasing of the bulk phonon modes.
Walker’s theorem without coordinates
Authors: Derdzinski Andrzej , Roter Witold
Published: June 2006

We provide a coordinate-free version of the local classification, due to Walker [Q. J. Math. 1, 69 (1950)], of null parallel distributions on pseudo-Riemannian manifolds. The underlying manifold is realized, locally, as the total space of a fiber bundle, each fiber of which is an affine principal bundle over a pseudo-Riemannian manifold. All structures just named are naturally determined by the distribution and the metric, in contrast with the noncanonical choice of coordinates in the usual formulation of Walker’s theorem.
Giant magnetoresistance in transition-metal-doped ZnO films
Authors: Wang Jing , Gu Zhengbin , Lu Minghui , Wu Di , Yuan Changsheng , Zhang Shantao , Chen Yanfeng , Zhu Shining , Zhu Yongyuan
Published: June 2006

Magnetic and transport properties were investigated in Zn0.94Mn0.03Co0.03O thin films prepared by dual radio frequency magnetron sputtering technique. A negative magnetoresistance (MR=[ρ(H)−ρ(0)]∕ρ(0)) of −95% at 2K and a positive MR of 48% at 10K were established in the films. The anomalous magnetic and magnetic-related transport properties in transition-metal-doped ZnO films are discussed in terms of magnetic polarons.
High corrosion stability of DyBa2Cu3Oz thin films relative to YBa2Cu3Oz films: A possible relation between corrosion and c-axis correlated extended defects
Authors: Murugesan M. , Obara H. , Nakagawa Y. , Yamasaki H. , Mawatari Y. , Kosaka S.
Published: June 2006

An enhanced stability towards corrosion was noted for DyBa2Cu3Oz relative to YBa2Cu3Oz. Between pure and Ca doped films, Ca doped films were found to be more corrosion resistant towards aqueous environment. The observed high corrosion stability in DyBa2Cu3Oz can be explained by the improved microstructure and the absence of c-axis correlated extended defects (EDs), while the remarkable increase in corrosion stability for the Ca doped films is presumed to be due to the notable improvement in the grain boundary region and the absence of ED. It is confirmed that the films with c-axis correlated ED are highly prone to corrosion by moisture.
Plasma acceleration from radio-frequency discharge in dielectric capillary
Authors: Dunaevsky A. , Raitses Y. , Fisch N. J.
Published: June 2006

A capacitive rf discharge was demonstrated in a dielectric capillary for generation of quasineutral plasma flow with energies of several tens of eV. A potential gradient at the open end of the capillary and high-temperature electrons in the capillary discharge promote the ion acceleration. The plasma flow was generated from a ceramic capillary with inner diameter of ∼0.8mm and a length of ∼10mm, at a gas flow rate of 2–10SCCM (SCCM denotes cubic centimeter per minute at STP) and input power of 15–20W. The ion energy spectrum consists of high-energy accelerated ions and a low-energy tail formed due to ionization in the acceleration region. The relatively wide plume angle of ∼65° indicates that the acceleration region is placed outside the capillary and has a convex shape. Estimated total efficiency at 2SCCM Xe flow rate and 15W input power reaches 2%–3%. This approach may be attractive for micropropulsion applications due to its simplicity, low weight and small dimensions of the source, and the absence of a cathode neutralizer.
Growth of high-quality GaAs on Ge∕Si1−xGex on nanostructured silicon substrates
Authors: Vanamu G. , Datye A. K. , Dawson R. , Zaidi Saleem H.
Published: June 2006

Heteroepitaxial growth of GaAs∕Ge∕SiGe films on submicrostructured Si substrates is reported. One-dimensional, nanometer-linewidth, submicrometer period features were fabricated in Si substrates using interferometric lithography, reactive ion etching, and wet-chemical etching techniques. The quality of the GaAs layers grown on these structures was investigated using high-resolution x-ray diffraction, transmission electron microscopy, scanning electron microscopy, photoluminescence, and etch pit density measurements. The defect density of GaAs epilayers grown on submicrostructured Si at ∼6×105cm−2 was two orders of magnitude lower compared with that grown on planar silicon. The optical quality of the GaAs∕Ge∕SiGe on submicrostructured Si was comparable to that of single crystal GaAs.
Two-dimensional structure of charge packets in polyethylene under high dc fields
Authors: Fukuma Masumi , Fukunaga Kaori , Laurent Christian
Published: June 2006

The puzzling behavior of space charge inside solid dielectrics has been revealed by space charge measurement techniques. In particular, positive and negative “charge packets” propagating through the bulk with a repetitive character are thought to be related to prebreakdown mechanisms. Here, we investigated the space charge distribution in a lateral direction by using our recently developed two-dimensional pulsed electroacoustic setup and discovered that the structure of the charge packets is not homogeneous in the lateral direction. This could change drastically the common view as regards their generation and propagation mechanisms as well as their relationship to breakdown.
Stable polarization gratings recorded in azo-dye-doped liquid crystals
Authors: Gorkhali Suraj P. , Cloutier Sylvain G. , Crawford Gregory P. , Pelcovits Robert A.
Published: June 2006

We report on the design, fabrication, electro-optical performance, and stability of switchable polarization gratings formed in azo-dye-doped nematic liquid crystals. Stable gratings are demonstrated even after applying saturating electric fields (8V∕μm) and after heating to extreme temperatures (T=190°C). A simple phenomenological model is presented to show that the Freedericksz threshold voltage depends on surface and volume contributions. The observed thresholdless behavior indicates that the grating stability is consistent with a surface-stabilizing effect.
Strong enhancement of Er3+ emission at room temperature in silicon-on-insulator photonic crystal waveguides
Authors: Galli M. , Politi A. , Belotti M. , Gerace D. , Liscidini M. , Patrini M. , Andreani L. C. , Miritello M. , Irrera A. , Priolo F. , Chen Y.
Published: June 2006

We have realized silicon-on-insulator photonic crystal (PhC) waveguides with intense 1.54μm emission at room temperature. The slabs contain a thin layer of SiO2 with Er3+ doped silicon nanoclusters embedded at the center of the Si core and are patterned with a triangular lattice of holes. An enhancement by more than two orders of magnitude of the Er3+ near-normal emission is observed when the transition is in resonance with an appropriate mode of the PhC slab. The results are in very good agreement with calculated photonic bands and emission spectra. These findings are important for the realization of Si-compatible efficient light emitters at telecom wavelengths.
Low resistivity p-ZnO films fabricated by sol-gel spin coating
Authors: Cao Yongge , Miao Lei , Tanemura Sakae , Tanemura Masaki , Kuno Yohei , Hayashi Yasuhiko
Published: June 2006

N-doped and In-N-codoped ZnO films were fabricated on quartz glass substrate by sol-gel spin coating. Their p-type conductivities were characterized by the Hall measurements, revealing low resistivities of the order of 10−1Ωcm. Thin-film junctions comprising an undoped ZnO layer and a N-doped ZnO layer displayed the typical rectifying characteristics, suggesting formation of p-n homojunctions at the interfaces.
Low damping in epitaxial sputtered iron films
Authors: Scheck C. , Cheng L. , Bailey W. E.
Published: June 2006

We show that sputtered, pure epitaxial iron films can have high-frequency loss as low as, or lower than, any known metallic ferromagnetic heterostructure. Minimum 34GHz ferromagnetic resonance linewidths of 41±2Oe are demonstrated, some ∼5%–10% lower than the previous minimum reported for molecular beam epitaxially deposited Fe. Intrinsic and extrinsic damping have been separated over 0–40GHz, giving a lower bound for intrinsic LL(G) relaxation rates of λ or G=85±5MHz (α=0.0027±0.0001) and for extrinsic η∼30–50MHz. Swept-frequency measurements indicate the potential for integrated frequency domain devices with Q>100 at 30–40Ghz.