bluuebunny/crossref_metadata_2025 huggingface dataset:
Qualitative analysis and solutions of bounded travelling waves for the fluidized-bed modelling equation
Authors: Zhang Weiguo , Bian Lanyun , Zhao Yan
Published: March 2010

We apply the theory of planar dynamical systems to carry out a qualitative analysis for the planar dynamical system corresponding to the fluidized-bed modelling equation. We obtain the global phase portraits of this system under various parameter conditions and the existence conditions of bounded travelling-wave solutions of this equation. According to the discussion on relationships between the behaviours of bounded travelling-wave solutions and the dissipation coefficients ε and δ, we find a critical value λ0 for arbitrary travelling-wave velocity υ. This equation has a unique damped oscillatory solution as ∥ε + δυ∥ < λ0 and ∥ε + δυ∥ ≠ 0, while it has a unique monotone kink profile solitary-wave solution as ∥ε + δυ∥ > λ0. By means of the undetermined coefficients method, we obtain the exact bell profile solitary-wave solution and monotone kink profile solitary-wave solution. Meanwhile, we obtain the approximate damped oscillatory solution. We point out the positions of these solutions in the global phase portraits. Finally, based on integral equations that reflect the relationships between the approximate damped oscillatory solutions and the implicit exact damped oscillatory solutions, error estimates for the approximate damped oscillatory solutions are presented.
Impacts of artisanal fishing on key functional groups and the potential vulnerability of coral reefs
Authors: LOKRANTZ JERKER , NYSTRÖM MAGNUS , NORSTRÖM ALBERT V. , FOLKE CARL , CINNER JOSHUA E.
Published: March 2010

Fishing can have major impacts on the structure of coral reef ecosystems. Overfishing of herbivores is particularly detrimental, as it makes the coral system more likely to undergo shifts to macroalgal dominance in the event of coral mass mortality. Knowing when important processes, such as herbivory, are becoming brittle is important because it can provide an opportunity for managers to avoid undesirable ecosystem-level changes. This study investigates the impact of artisanal fishing on three important functional groups of herbivores (grazers, scrapers and excavators) on five coral-dominated reefs outside Zanzibar (Tanzania). There was a negative correlation between fishing pressure and fish biomass, abundance, diversity and species richness. Moreover, fishing had a negative influence on the demographic structure of functional groups, particularly excavators, manifesting itself as a skewness towards smaller individuals within populations. Artisanal fishing can have significant impacts on key functional groups of herbivorous reef fishes which may increase the vulnerability of coral reefs to undesirable ecosystem shifts.
Changing distribution and abundance of Swan GooseAnser cygnoidesin the Yangtze River floodplain: the likely loss of a very important wintering site
Authors: ZHANG YONG , CAO LEI , BARTER MARK , FOX ANTHONY D. , ZHAO MEIJUAN , MENG FANJUAN , SHI HONGQUAN , JIANG YONG , ZHU WENZHONG
Published: March 2010

Virtually the entire population of the globally ‘Vulnerable’ Swan GooseAnser cygnoideswinters in the Yangtze floodplain. Historically, the species was widely distributed throughout the floodplain but now approximately 95% of the population is confined to three closely-situated wetlands in Anhui and Jiangxi Provinces. Recent counts indicate that at one of these sites, Shengjin Lake (in Anhui), a decline of about 10,000–20,000 birds, to about 1,000 currently, has taken place during the last five years. The likely cause of the decline in Swan Goose abundance at Shengjin Lake is the recent decrease in submerged vegetation, particularly tuber-producingVallisneriawhich is the species’s main food; this decrease has been linked with the introduction of intensive aquaculture in the main areas used by Swan Geese within the lake. Earlier range contractions in the Yangtze floodplain may also be linked to reductions in submerged vegetation cover at other sites, where intensive aquaculture has also been implicated. Changes in lake hydrology following construction of the Three Gorges Dam may also have adversely affected submerged vegetation productivity. Key information needs for the effective implementation of conservation measures for Swan Goose include an understanding of (1) the fitness consequences of Swan Geese being forced to switch to different foods; (2) how aquaculture can be managed to minimise impacts on submerged vegetation; (3) the impact of changing lake hydrology on key Swan Goose food plants; and (4) the optimal management of wetlands to ensure that adequate food is both produced during the summer period and is available throughout the winter.
Confidence Bounds for the Estimation of the Volume Phase Fraction from a Single Image in a Nickel Base Superalloy
Authors: Blanc Rémi , Baylou Pierre , Germain Christian , Da Costa Jean-Pierre
Published: March 2010

We propose an image-based framework to evaluate the uncertainty in the estimation of the volume fraction of specific microstructures based on the observation of a single section. These microstructures consist of cubes organized on a cubic mesh, such as monocrystalline nickel base superalloys. The framework is twofold: a model-based stereological analysis allows relating two-dimensional image observations to three-dimensional microstructure features, and a spatial statistical analysis allows computing approximate confidence bounds while assessing the representativeness of the image. The reliability of the method is assessed on synthetic models. Volume fraction estimation variances and approximate confidence intervals are computed on real superalloy images in the context of material characterization.
A geographic approach to place and natural resource use in local food systems
Authors: Duram Leslie , Oberholtzer Lydia
Published: March 2010

This article illuminates the geographic concept of ‘place’ in local foods. Because the social aspects of local food have been more fully addressed in previous literature, this review focuses instead on the ecological aspects of farming and food. First, the literature on natural resource use in agriculture provides contextual understanding of water use, biodiversity, soils and agro-ecological methods. The complex relationship between climate change and agriculture is described and models assessing the impacts of climate change on agriculture are detailed. The geography of local food is specifically addressed by describing methods for assessing natural resource use in local food, including food miles, consumer transportation, scale and community, agricultural methods and diet. Finally, future research paths are suggested to provide a comprehensive evaluation of the environmental impact of local food. Such research would encompass the geography of local food through development of broader, more inclusive strategy, including the concept of the ‘ecological appetite’ of crops and foods, the union of both social and ecological aspects of resource use, the linkages between rural and urban producers and consumers and the inclusion of farmers’ ecological knowledge. Overall, the geography of local food seeks to assess the where of food production and consumption, while incorporating key issues of how (agro-ecological methods benefiting the community) and what (locally appropriate crops).
Green marketing: Are environmental and social objectives compatible with profit maximization?
Authors: Woolverton Andrea , Dimitri Carolyn
Published: March 2010

Along with others, we recognize the impact of human action on environmental quality. At the same time, we note that businesses have entered the ‘green market’. The goal of this paper is to open a discussion about green marketing. We raise questions regarding how firm governance impacts the ability of firms to incorporate environmental objectives into profit maximization. Additionally, we discuss the green marketing strategies that firms have chosen to use, as well as public and private options available for eco-label monitoring and enforcement to avoid additional consumer confusion.
Technoscience, anaerobic digester technology and the dairy industry: Factors influencing North Country New York dairy farmer views on alternative energy technology
Authors: Welsh Rick , Grimberg Stefan , Gillespie Gilbert W. , Swindal Megan
Published: March 2010

Structural change in the US dairy industry toward fewer and very large farms has fueled interest and government funding of research into the feasibility of constructing anaerobic digesters (ADs) on large operations as a waste management strategy. Some groups opposed to increasing scale and concentration in the livestock sectors, including dairy, also oppose ADs because of the connection with larger scale operations and the potential for facilitating increased concentration in agricultural production. But the connection between AD technology and large scale is a social construction promoted by its incorporation into the debates over agricultural industrialization. The technology per se is essentially scale neutral and its scale-implications are artifacts of design choices, as is seen by its successful application to both very small farms around the world and large-scale agricultural enterprises in the USA. Using a survey of dairy farmers in New York, we find that interest in AD technology occurs at all farm sizes; and that factors other than farm size are important in determining interest in the technology. We conclude that the technoscientific question raised by these findings is: will applications to, and interest by, smaller dairy farmer operators result in shifts in policy and funding priorities toward more diverse agricultural research agendas regarding AD technology?
Alternative agriculture in an energy- and resource-depleting future
Authors: Kirschenmann Frederick
Published: March 2010

Industrial principles of specialization, simplification and concentration began to be applied to agriculture after the Second World War with positive production results. But it is now widely recognized that this agriculture and food system faces daunting challenges in the decades ahead, including increased human population growth, natural resource depletion, ecological degradation, climate change and escalating energy costs. These challenges have refocused the attention of agriculturalists and food scientists on the question of how we can continue to feed the human species. But these challenges also provide opportunities to rethink and redesign our food system. Agriculturalists are recognizing that resilience is at least as important to food security as maximum production, and consumer concerns provide us with unprecedented opportunities for farmers and consumers to come together as ‘food citizens’ to determine appropriate changes in our food system. To that end it is important to examine the various production systems and infrastructures in an effort to select the most viable options for long-term sustainability.
Embedded‐sensor network design for snow cover measurements around snow pillow and snow course sites in the Sierra Nevada of California
Authors: Rice Robert , Bales Roger C.
Published: March 2010

The design of sensor networks for measuring the mean and spatial distribution of snow depth at the scale of 1–16 km2 was evaluated by deploying an embedded‐sensor network consisting of ultrasonic snow depth sensors to capture the variable physiographic features around an operational snow course in Yosemite National Park in the Sierra Nevada of California. Manual snow surveys were also carried out during accumulation and ablation periods. Four years of continuous data from the embedded‐sensor network showed that snow depths during both accumulation and ablation periods can vary as much as 50% based on variability in topography and vegetation across a 0.4 ha study area. Spatial snow surveys showed that such a sensor network can be deployed so as to capture both the variability and mean for accumulation and ablation periods across a 1 km2 area surrounding the sensor network, with a broader network required to extend this to 4 and 16 km2 areas. In forested areas, higher canopy densities, greater than 60% closure, were associated with the lowest snow depths. Analysis of historical snow course records from 14 sites in Yosemite, including the 10 spatial measurements made during each monthly snow course survey, showed snow depths across the 300 m snow course transects to be relatively uniform, with 68% of all monthly values having standard deviations no more than 10% of the mean. Although existing snow courses do little to help define the spatial patterns of snow distribution at the 1–16 km2 scales, it is feasible to extend the representativeness of current operational networks by deploying low‐cost embedded‐sensor networks nearby. Such networks should be strategically located to also capture elevational differences in snow accumulation and melt, as well as local‐scale variability in canopy cover and aspect.
Revealing coseismic displacements and the deformation zones of the 1999 Chi‐Chi earthquake in the Tsaotung area, central Taiwan, using digital cadastral data
Authors: Lee Yuan‐Hsi , Wu Kun‐Che , Rau Ruey‐Juan , Chen He‐Chin , Lo Wei , Cheng Kai‐Chien
Published: March 2010

The 1999 Chi‐Chi, Taiwan, earthquake (Mw 7.6) was the largest earthquake to strike Taiwan in the twentieth century. This earthquake is associated with a 100 km long surface rupture. In order to reveal the details of displacement near the surface rupture, we use a digital cadastral system to calculate coseismic displacement around the Tsaotung area, central Taiwan. The digital cadastral system was originally conceived to survey land and building boundaries. In the Tsaotung area, Taiwan authorities have taken digital cadastral measurements before and after the Chi‐Chi earthquake. The cadastral system affords high‐density control points that reach ∼1421 points/km2, a system denser than that of the GPS. Accuracy is to within ±11 cm, a level that is higher than spot imaging and one that allows us to study surface deformation in detail. Coseismic displacement is ∼4.3–4.6 m at distance from the surface rupture and decreases to 3–4 m near the surface rupture. The azimuth of horizontal displacements is ∼310°–315° and rotates to 280°–305° near the surface rupture. This produced a compression, left‐lateral deformation zone with ∼10−3 compression strain near the surface rupture. Coseismic displacement of the footwall is 1–1.2 m in 110°, which is similar to that from using GPS data. In the Tsaotung thrust slice, we observed that the azimuth of horizontal displacement rotates from a NW trend to a south trend as a result of slip partitioning and gravity slide effect.
A note on Doppler processing of coherent radar backscatter from the water surface: With application to ocean surface wave measurements
Authors: Hwang Paul A. , Sletten Mark A. , Toporkov Jakov V.
Published: March 2010

The technique for extracting wave period and wave direction from radar backscattering intensity is well developed, but the determination of spectral density or wave height is hindered by the complex nature of the modulation transfer function. In contrast to backscattering intensity, the Doppler signal of a coherent radar is originated from the radial velocity of the scattering objects. Its oscillatory component is contributed by ocean waves. The peak component of the Doppler velocity spectrum can be used to obtain the spectral peak wave period and the significant wave height can be calculated from the variance of the Doppler velocity. Analyses of coherent radar measurements collected from the ocean show that with radar range coverage on the order of 10 dominant wavelengths, a good estimate of peak wave period and significant wave height is achievable with radar data as short as a few seconds.
Combined observations of rock mass movements using satellite SAR interferometry, differential GPS, airborne digital photogrammetry, and airborne photography interpretation
Authors: Strozzi Tazio , Delaloye Reynald , Kääb Andreas , Ambrosi Christian , Perruchoud Eric , Wegmüller Urs
Published: March 2010

Recent global warming, through the related retreat of mountain glaciers, causes a growing number of different slope instabilities requiring accurate and cost‐effective monitoring. We investigate the potential of combined remote sensing observations from satellite and airborne microwave and optical sensors for an efficient survey of mountainous ground displacements. The evolution of a paraglacial deep‐seated rock mass movement due to glacier retreat in the Swiss Alps has been observed between 1976 and 2008 with satellite synthetic aperture radar (SAR) interferometry, differential GPS, and airborne digital photogrammetry. Analysis of differential SAR interferograms revealed an acceleration of the landslide from ∼4 cm/yr in the slope‐parallel direction during the mid‐1990s to more than 30 cm/yr in the summer of 2008. Differential GPS surveys performed between the summers of 2007 and 2008 indicate seasonal variations of the landslide activity. The photogrammetric analysis revealed no significant movement (i.e., <1 cm/yr) between 1976 and 1995 and provides an overview of the total displacement between 1995 and 2006 with high spatial resolution. In situ and airborne photography interpretation suggests that the landslide was activated at earliest by the end of the Last Glaciation but without any significant long‐lasting activity during the Holocene and that the exponentially increasing reactivation since the 1990s is the result of ongoing debutressing of the valley flank due to the glacier retreat in combination with strong precipitation and snowmelt events. We conclude that the employed remote sensing techniques complement each other well within a landslide hazard assessment procedure.
Constraining the timescales of sediment sequestration associated with large woody debris using cosmogenic 7Be
Authors: Fisher G. B. , Magilligan F. J. , Kaste J. M. , Nislow K. H.
Published: March 2010

The beneficial ecogeomorphic functions associated with large woody debris (LWD) in fluvial environments are well documented and include positive sediment impacts such as channel margin sequestration, increased substrate heterogeneity, and decreased channel embeddedness, as well as numerous secondary benefits such as nutrient retention and increased habitat heterogeneity. Despite an extensive literature documenting such positive sediment attributes of LWD in forested channels, a quantitative analysis of in‐channel sediment storage times associated with channel obstructions has traditionally been difficult to assess. In this study along a 9 km stretch of the Ducktrap River in coastal Maine we present a novel application of fallout cosmogenic 7Be (t1/2 = 53 days) coupled with a constant initial activity (CIA) sediment aging model to quantitatively assess transitional bed load storage times in bars associated with in‐channel obstructions (LWD and boulders). We find that reach‐scale variability in unit stream power and LWD frequency affect sediment storage times, with transport‐limited reaches providing longer‐term sediment sequestration (generally > 100 days) associated with in‐channel obstructions than supply limited ones (<100 days). Estimates of sediment baraccumulation rates also varied between reaches from 0.2 g cm−2 d−1 in the supply limited reach to 0.7 g cm−2 d−1 in the transport‐limited reach. Last, greater frequency of sites, increased sediment volumes and storage times, and naturally viable recruitment mechanisms for LWD in forested channels document its superior ecogeomorphic function when compared to boulders in this study, even in the Ducktrap river, where twentieth century logging has greatly reduced the size, frequency, and geomorphic efficacy of in‐channel wood. This study has implications for channel restoration efforts and documents a novel application of 7Be and CIA methodology to constraining transitional bed load storage times in the fluvial environment.
Bayesian geostatistical design: Task‐driven optimal site investigation when the geostatistical model is uncertain
Authors: Nowak W. , de Barros F. P. J. , Rubin Y.
Published: March 2010

Geostatistical optimal design optimizes subsurface exploration for maximum information toward task‐specific prediction goals. Until recently, most geostatistical design studies have assumed that the geostatistical description (i.e., the mean, trends, covariance models and their parameters) is given a priori. This contradicts, as emphasized by Rubin and Dagan (1987a), the fact that only few or even no data at all offer support for such assumptions prior to the bulk of exploration effort. We believe that geostatistical design should (1) avoid unjustified a priori assumptions on the geostatistical description, (2) instead reduce geostatistical model uncertainty as secondary design objective, (3) rate this secondary objective optimal for the overall prediction goal, and (4) be robust even under inaccurate geostatistical assumptions. Bayesian Geostatistical Design follows these guidelines by considering uncertain covariance model parameters. We transfer this concept from kriging‐like applications to geostatistical inverse problems. We also deem it inappropriate to consider parametric uncertainty only within a single covariance model. The Matérn family of covariance functions has an additional shape parameter. Controlling model shape by a parameter converts covariance model selection to parameter identification and resembles Bayesian model averaging over a continuous spectrum of covariance models. This is appealing since it generalizes Bayesian model averaging from a finite number to an infinite number of models. We illustrate how our approach fulfills the above four guidelines in a series of synthetic test cases. The underlying scenarios are to minimize the prediction variance of (1) contaminant concentration or (2) arrival time at an ecologically sensitive location by optimal placement of hydraulic head and log conductivity measurements. Results highlight how both the impact of geostatistical model uncertainty and the sampling network design vary according to the choice of objective function.
Thermal skin effect of pipes in streambeds and its implications on groundwater flux estimation using diurnal temperature signals
Authors: Cardenas M. Bayani
Published: March 2010

Heat tracing is widely used for quantifying groundwater flux across the river‐streambed interface. This study investigates the potential for a thermal skin effect (TSE) whereby temperature measured inside a pipe buried in sediment is lagged and damped compared to temperature outside of the pipe, violating the assumption that monitored temperatures are representative of the saturated sediment. Numerical simulations show that 1–3 inch diameter pipes lead to an additional lag of tens of minutes to almost 1.5 h when diurnal temperature signals originating from the river and propagating into the sediment are monitored. The lag increases with pipe diameter and diminishes when steel is used instead of PVC. The temperatures taken from inside the pipe lead to substantial errors when they are used as targets for fitting with a forward heat transport model. The errors are large when the fit is made to the timing of the temperature signals but is small when the fit is made to the amplitude of the signal while ignoring the timing. This is because the TSE leads to little damping of the amplitude of the temperature fluctuations and mostly exhibits as extra lag. Therefore, methods that take advantage of the amplitude of the signal, such as time series analysis using amplitude ratios, are not sensitive to the TSE. Time series data can be corrected by subtracting the response time of the water‐filled pipe or by adding the response time as a phase shift to analytical models.
Speaking truth to power?
Authors: Rose Steven
Published: March 2010

Speaking truth to power has never been an easy task and often comes with repercussions even for today's scientific advisors. But, Steven Rose argues, there is no such thing as disinterested scientific advice; it may therefore be necessary to rethink the role and composition of scientific advisory panels.
Einstein's grandchildren
Authors: Jacobs Howy
Published: March 2010

The new German government has boldly promised to “lead Germany to first place in the world in education, science and research.” Howy Jacobs explores this promise and whether it will lure Einstein's grandchildren back across the pond.
Of guerillas and cafés
Authors: Wolinsky Howard
Published: March 2010

From Guerilla tactics to French café culture and festivals: scientists are exploring new venues to talk to the people. Howard Wolinsky investigates the latest science outreach programmes.
Langerhans cells as targets for immunotherapy against skin cancer
Authors: Stoitzner Patrizia , Sparber Florian , Tripp Christoph H
Published: March 2010

Cancer is the second most common cause of death in the world. Treatment of cancer is very challenging and immunotherapy has been developed as a potential way to fight cancer. The main obstacle with immunotherapy is that cancer cells evolve from healthy body cells in response to an accumulation of genetic mutations. As a consequence, the immune system struggles to detect the abnormal cells as they are mainly recognized as self. This implies that equipping the immune system to eliminate cancer cells is tricky, yet represents a very efficient way to constrain the growth of tumors. We became interested in developing immunotherapeutical strategies against skin cancer in the context of our observations that Langerhans cells (LC) are very potent antigen presenting cells and are able to incorporate protein antigens and present them to CD4+ and CD8+ T cells in the skin‐draining lymph nodes. As a consequence, we developed an immunization strategy through the skin, termed epicutaneous immunization. Protein antigen applied onto barrier‐disrupted skin induces long‐lasting cytotoxic T‐cell responses, potent enough to control and inhibit tumor growth. In this review, we suggest that immunization strategies through the skin could be a promising new approach for the treatment of skin cancer.
Langerhans cells: critical regulators of skin immunity?
Authors: Clausen Björn E , Kel Junda M
Published: March 2010

Langerhans cells (LC) are members of the heterogenous family of professional antigen presenting dendritic cells (DC). They are identified by the C‐type lectin receptor Langerin and form a contiguous network in the epidermis. Consequently, LC are an integral part of the skin barrier to the environment and were considered to be critical inducers of skin immunity, whereas dermal DC were largely overlooked. However, with the identification of a distinct subset of Langerin expressing dermal DC, the situation in the skin has become more complex and the relative contribution of the different cutaneous DC populations in balancing immunity and tolerance has become a matter of active debate. Here, we briefly review the classical paradigm and recent challenges of LC function, before focusing on advances concerning their role in contact hypersensitivity and ultraviolet radiation‐induced immunosuppression obtained within vivoLC ablation models. We then discuss novel LC/DC‐specific gene targeting approaches currently used to dissect the role of the regulatory cytokines transforming growth factor‐β and interleukin‐10 to govern LC and DC functionin vivo. This second generation of LC‐specific genetically engineered mice will considerably extend our understanding of the molecular control of LC function in regulating skin immunity and tolerance in the near future.
Association of the 19S proteasomal ATPases with the ATPase‐binding domain of CIITA is essential for CIITA stability and MHC class II expression
Authors: Bhat Kavita Purnanda , Truax Agnieszka Dorota , Brooks Jeanne Kaye , Greer Susanna Fletcher
Published: March 2010

Major histocompatibility class II (MHC class II) molecules are glycoproteins that present extracellular antigens to CD4+ T cells and are essential for initiation of adaptive immune responses. MHC class II expression requires recruitment of a master regulator, the class II transactivator (CIITA), to the MHC class II promoter. Others and we have earlier linked CIITA to the ubiquitin‐proteasome system by showing that mono‐ubiquitination of CIITA increases its transactivity, whereas poly‐ubiquitination of CIITA leads to its degradation. We have further shown that the 26S proteasome also has non‐proteolytic functions in MHC class II transcription, as 19S ATPase subunits of the 26S proteasome positively regulate MHC class II transcription and are necessary for stable promoter binding of CIITA. Although these basic requirements of the proteasome to initiate MHC class II transcription are known, how CIITA is recruited, stabilized, and degraded remains unclear. Here, we identify a novel N‐terminal 19S ATPase‐binding domain of CIITA. The ATPase‐binding domain lies within the proline/serine/threonine‐rich region of CIITA and encompasses a majority of the CIITA degron sequence. Absence of the ATPase‐binding domain increases the half‐life of CIITA, but blocks MHC class II surface expression, indicating that CIITA requires interaction with the 19S ATPases for both appropriate deployment and destruction.
Observation of a nonaxisymmetric magnetohydrodynamic self-organized state
Authors: Cothran C. D. , Brown M. R. , Gray T. , Schaffer M. J. , Marklin G. , Lukin V. S.
Published: March 2010

A nonaxisymmetric stable magnetohydrodynamic (MHD) equilibrium within a prolate cylindrical conducting boundary has been produced experimentally at Swarthmore Spheromak Experiment (SSX) [M. R. Brown et al., Phys. Plasmas 6, 1717 (1999)]. It has m=1 toroidal symmetry, helical distortion, and flat λ profile. Each of these observed characteristics are in agreement with the magnetically relaxed minimum magnetic energy Taylor state. The Taylor state is computed using the methods described by A. Bondeson et al. [Phys. Fluids 24, 1682 (1981)] and by J. M. Finn et al. [Phys. Fluids 24, 1336 (1981)] and is compared in detail to the measured internal magnetic structure. The lifetime of this nonaxisymmetric compact torus (CT) is comparable to or greater than that of the axisymmetric CTs produced at SSX; thus suggesting confinement is not degraded by its nonaxisymmetry. For both one- and two-spheromak initial state plasmas, this same equilibrium consistently emerges as the final state.
Thermodynamic phase diagram for hydrogen on polar InP(111)B surfaces
Authors: Shu Haibo , Chen Xiaoshuang , Dong Ruibin , Wang Xiaofang , Lu Wei
Published: March 2010

Thermodynamic stability of hydrogenated polar InP(111)B surfaces is systematically studied by performing first-principles density functional calculations. Employing a thermodynamic approach, the hydrogen chemical potential is considered as functions of temperature and pressure. The calculated Gibbs free energies demonstrate that the surface structures of InP(111)B strongly depend on growth condition and surface compositions. The (2×2) surfaces with 3PH2+PH3, 3H+PH3, 3H, and P trimer, and the (3×3) surface with In adatom are stable phases under different chemical potentials of P and H, respectively. Moreover, our calculations suggest that the ideal surface and most of (3×3) surfaces are just metastable due to their deviation from electron counting rule. The calculated surface phase diagrams as the functions of temperature and pressure of H2 reveal that the (2×2) surface with P trimer is stable under the experimental growth condition (550–800 K). Once the samples are cooled down in a H-rich ambient, the hydrogenated InP(111)B surfaces are more favorable.
Electrically controlled magnetic switching based on graphene-magnet composite structures
Authors: Semenov Y. G. , Zavada J. M. , Kim K. W.
Published: March 2010

A nonvolatile magnetic switch is proposed by utilizing the unique properties of graphene-ferromagnet composite structures. The basic mechanism relies on the role of graphene in mediating and modulating the effective exchange bias between adjacent magnetic layers, which can lead to electrically controlled rotation of magnetic bits. Readout of magnetization states is also achieved electrically through the magnetoresistance effect in the graphene channel. The proposed switch can be used to realize both the memory and programmable logic elements. Theoretical estimates illustrate the feasibility of the concept as well as its potential advantage of low power consumption (∼10−19 J) for the intrinsic switching operation.
Specific heat and magnetic order of La0.2Ca0.8MnO3
Authors: Markovich V. , Wieckowski J. , Gutowska M. , Szewczyk A. , Wisniewski A. , Martin C. , Gorodetsky G.
Published: March 2010

Measurements of specific heat of the electron-doped La0.2Ca0.8MnO3 manganite are reported for 2<T<400 K. It was found that La0.2Ca0.8MnO3 exhibits an orbital ordering at TOO=204 K and a long-range antiferromagnetic order below TN=178 K. The entropy changes (ΔS) around both TOO[ΔS(TOO)≈0.38 J/mol K] and TN[ΔS(TN)≈3.58 J/mol K] were determined. The entropy change associated with the orbital ordering was found to be much smaller than that for charge ordered manganites. The low temperature specific heat indicates that La0.2Ca0.8MnO3 has rather high Debye temperature ΘD=685 K in comparison with existing results for electron-doped La1−xCaxMnO3 manganites. Moreover, the presence of a large 1/T2 hyperfine contribution and of a considerable linear term, unexpected for La0.2Ca0.8MnO3 with antiferromagnetic insulating ground state, was revealed. The possible relationship between the behavior of the heat capacity and the phase separation is discussed.
Self-assembly and magnetic properties of MnAs nanowires on GaAs(001) substrate
Authors: Xu F. , Huang P. W. , Huang J. H. , Lee W. N. , Chin T. S. , Ku H. C. , Du Y. W.
Published: March 2010

The in-plane aligned MnAs nanowires have been grown by molecular-beam epitaxy on GaAs(001) substrates at high growth temperature (≥450 °C). A discontinuous growth with break intervals (50 s’ interval per 10 s’ growth) was employed. The obtained nanowires were identified to be mainly type-B hexagonal MnAs. The influences of growth temperature and As4/Mn flux ratio on the nanowires’ morphology were investigated. Both high growth temperature and high As4/Mn flux ratio are necessary for the growth of uniaxially aligned MnAs nanowires with high aspect ratio. The magnetic anisotropy of the nanowires and their multimodal size distributions contribute to the large coercivity and special shape of the M-H loops along the magnetic easy axis, which is [11¯02]MnAs∥[110]GaAs. However, the longer growth time would lead to the both azimuthal alignments of the MnAs wires and the weakening of the magnetic anisotropy.
Comment on “Microwave attenuation of hydrogen plasma in carbon nanotubes” [J. Appl. Phys. 104, 124315 (2008)]
Authors: Moradi Afshin
Published: March 2010

In a recent article, Babaei and Solari [J. Appl. Phys. 104, 124315 (2008)] studied the effects of the electron temperature, and the external static magnetic field on the attenuation (ATT) of the microwave in the hydrogen plasma embedded inside the carbon nanotubes (CNTs), which were grown by iron-catalyzed high-pressure disproportionation (HiPco). They showed that the position of ATT peak shifts significantly toward high frequency with increasing thermal frequency and in the presence of an external magnetic field in the Faraday configuration, for υc<20 GHz, the ATT coefficient increases with increasing cyclotron frequency, and for υc>20 GHz, the ATT level variations extremely increase, where υc is the cyclotron frequency. Here we derive the correct form of the microwave absorption coefficient of the magnetized hydrogen plasma embedded inside the CNTs and show that the absorption band moves from low to high frequencies when the magnetic field strength increases. Also, we show that the ATT of the microwave in the system is not sensitive to the thermal frequency.
Magnetoelectric and multiferroic properties of variously oriented epitaxial BiFeO3–CoFe2O4 nanostructured thin films
Authors: Yan Li , Wang Zhiguang , Xing Zengping , Li Jiefang , Viehland D.
Published: March 2010

We report the ferroelectric, ferromagnetic, and magnetoelectric (ME) properties of self-assembled epitaxial BiFeO3–CoFe2O4 (BFO–CFO) nanostructure composite thin films deposited on (001), (110), and (111) SrTiO3 (STO) single crystal substrates. These various properties are shown to depend on orientation. The maximum values of the relative dielectric constant, saturation polarization, longitudinal piezoelectric coefficient, saturation magnetization, and ME coefficient at room temperature were 143, 86 μm/cm2, 50 pm/V, 400 emu/cc, and 20 mV/cm Oe, respectively.
High performance airbrushed organic thin film transistors
Authors: Chan Calvin K. , Richter Lee J. , Dinardo Brad , Jaye Cherno , Conrad Brad R. , Ro Hyun Wook , Germack David S. , Fischer Daniel A. , DeLongchamp Dean M. , Gundlach David J.
Published: March 2010

Spray-deposited poly-3-hexylthiophene (P3HT) transistors were characterized using electrical and structural methods. Thin-film transistors with octyltrichlorosilane treated gate dielectrics and spray-deposited P3HT active layers exhibited a saturation regime mobility as high as 0.1 cm2 V−1 s−1, which is comparable to the best mobilities observed in high molecular mass P3HT transistors prepared using other methods. Optical and atomic force microscopy showed the presence of individual droplets with an average diameter of 20 μm and appreciable large-scale film inhomogeneities. Despite these inhomogeneities, near-edge x-ray absorption fine structure spectroscopy of the device-relevant channel interface indicated excellent orientation of the P3HT.
A compact, passive setup for low vibration noise measurements in the frequency band (300–2000) Hz
Authors: Saraceni Mario , Bonaldi Michele , Castellani Lorenzo , Conti Livia , Gounda Abdul Basheed , Longo Stefano , Pegoraro Matteo
Published: March 2010

In this paper we report about the setup we designed to isolate at about 1.5 kHz from mechanical noise an experimental payload of about 6.6 kg mass. We discuss the design guidelines and optimization by finite element analysis and we characterize the suspension performance by experimental measurements. While providing an attenuation of about 180 dB in all spatial directions at 1.5 kHz, our passive system is very compact and can be easily replicated whenever the need of a volume of few liters with very low vibration noise level in the 1–2 kHz range is needed.
Drift tube soft-landing for the production and characterization of materials: Applied to Cu clusters
Authors: Davila Stephen J. , Birdwell David O. , Verbeck Guido F.
Published: March 2010

We have recently developed a soft-landing (SL) instrument that is capable of depositing ions onto substrates for preparative and developmental research of new materials using a laser ablation source. This instrument was designed with a custom drift tube and a split-ring ion optic for the isolation of selected ions. The drift tube allows for the separation and thermalization of ions formed after laser ablation through collisions with an inert bath gas. These collisions allow the ions to be landed at energies below 1 eV onto substrates. The split-ring ion optic is capable of directing ions toward the detector or a landing substrate for selected components. Experiments will be shown ablating Cu using an Nd:YAG (1064 and 532 nm) for cluster formation and landing onto a muscovite (mica) surface. The laser ablation of Cu in 8 Torr of He gas gives a spectrum that contains multiple peaks corresponding to Cun, CunOm clusters, and their corresponding isomers. Atomic force microscopy and drift tube measurements were performed to characterize the performance characteristics of the instrument.
Quantifying chain reptation in entangled polymer melts: Topological and dynamical mapping of atomistic simulation results onto the tube model
Authors: Stephanou Pavlos S. , Baig Chunggi , Tsolou Georgia , Mavrantzas Vlasis G. , Kröger Martin
Published: March 2010

The topological state of entangled polymers has been analyzed recently in terms of primitive paths which allowed obtaining reliable predictions of the static (statistical) properties of the underlying entanglement network for a number of polymer melts. Through a systematic methodology that first maps atomistic molecular dynamics (MD) trajectories onto time trajectories of primitive chains and then documents primitive chain motion in terms of a curvilinear diffusion in a tubelike region around the coarse-grained chain contour, we are extending these static approaches here even further by computing the most fundamental function of the reptation theory, namely, the probability ψ(s,t) that a segment s of the primitive chain remains inside the initial tube after time t, accounting directly for contour length fluctuations and constraint release. The effective diameter of the tube is independently evaluated by observing tube constraints either on atomistic displacements or on the displacement of primitive chain segments orthogonal to the initial primitive path. Having computed the tube diameter, the tube itself around each primitive path is constructed by visiting each entanglement strand along the primitive path one after the other and approximating it by the space of a small cylinder having the same axis as the entanglement strand itself and a diameter equal to the estimated effective tube diameter. Reptation of the primitive chain longitudinally inside the effective constraining tube as well as local transverse fluctuations of the chain driven mainly from constraint release and regeneration mechanisms are evident in the simulation results; the latter causes parts of the chains to venture outside their average tube surface for certain periods of time. The computed ψ(s,t) curves account directly for both of these phenomena, as well as for contour length fluctuations, since all of them are automatically captured in the atomistic simulations. Linear viscoelastic properties such as the zero shear rate viscosity and the spectra of storage and loss moduli obtained on the basis of the obtained ψ(s,t) curves for three different polymer melts (polyethylene, cis-1,4-polybutadiene, and trans-1,4-polybutadiene) are consistent with experimental rheological data and in qualitative agreement with the double reptation and dual constraint models. The new methodology is general and can be routinely applied to analyze primitive path dynamics and chain reptation in atomistic trajectories (accumulated through long MD simulations) of other model polymers or polymeric systems (e.g., bidisperse, branched, grafted, etc.); it is thus believed to be particularly useful in the future in evaluating proposed tube models and developing more accurate theories for entangled systems.
Defect-related tunneling mechanism of efficiency droop in III-nitride light-emitting diodes
Authors: Bochkareva N. I. , Voronenkov V. V. , Gorbunov R. I. , Zubrilov A. S. , Lelikov Y. S. , Latyshev P. E. , Rebane Y. T. , Tsyuk A. I. , Shreter Y. G.
Published: March 2010

The quantum efficiency of GaN-based light-emitting diodes (LEDs) is investigated at temperatures 77–300 K. It is found that the efficiency droop is due to a decrease in the internal quantum efficiency (IQE) in the low-energy part of the emission spectrum. The efficiency starts to decrease at a temperature independent forward voltage of Umax≈2.9 V. At this voltage tunneling current through the LED-structure begins to dominate. It is suggested that the external quantum efficiency droop is related to reduction of the IQE due to tunneling leakage of carriers from the quantum well (QW) to defect states in barriers, and to reduction of the injection efficiency by excess tunneling current under QW through deep defect states in barriers.
Photometer for monitoring the thickness of inkjet printed films for organic electronic and sensor applications
Authors: Im Jisun , Sengupta Sandip K. , Whitten James E.
Published: March 2010

Inkjet printed organic thin films are being used for a variety of electronic and sensor applications with advantages that include ease of fabrication and reproducibility. Construction and use of a low-cost photometer based on a light-emitting diode (LED) light source and a photodiode detector are described. The photometer attaches to the exit of the printer with the transparent substrate onto which the film is printed passing between the LED and photodiode. By measuring the output voltage of the detector, the transmittance and absorbance of the inkjet printed film can be calculated in real-time. Since absorbance is linearly proportional to thickness in the Beer–Lambert regime, the thickness of the film may be monitored and controlled by varying the number of passes through the printer. Use of the photometer is demonstrated for inkjet printed films of monolayer-protected colloidal gold nanoparticles that function as chemical vapor sensors. The photometer may find applications in both research and quality control related to the manufacture of organic electronic devices and sensors and enables “feedback-controlled” inkjet printing.
Time-resolved photoelectron spectroscopy of wavepackets through a conical intersection in NO2
Authors: Arasaki Yasuki , Takatsuka Kazuo , Wang Kwanghsi , McKoy Vincent
Published: March 2010

We report the results of theoretical studies of the time-resolved femtosecond photoelectron spectroscopy of quantum wavepackets through the conical intersection between the first two A2′ states of NO2. The Hamiltonian explicitly includes the pump-pulse interaction, the nonadiabatic coupling due to the conical intersection between the neutral states, and the probe interaction between the neutral states and discretized photoelectron continua. Geometry- and energy-dependent photoionization matrix elements are explicitly incorporated in these studies. Photoelectron angular distributions are seen to provide a clearer picture of the ionization channels and underlying wavepacket dynamics around the conical intersection than energy-resolved spectra. Time-resolved photoelectron velocity map images are also presented.
Role of excited-impurity quasiparticles for amplification of radiation in an erbium-doped glass fiber amplifier
Authors: Renk K. F.
Published: March 2010

In this paper, I will show that excited-impurity quasiparticles may play an essential role for the amplification of radiation in an erbium-doped glass fiber amplifier. A quasiparticle consists of an excited state of an erbium ion interacting with other erbium ions and with the thermal bath via phonon-assisted energy transfer processes. The quasiparticles populate energy levels of a quasiband. Fermi’s statistics determines the average occupation numbers of the levels. The quasiparticle model leads to an analytical expression for the gain coefficient of an erbium-doped glass fiber amplifier, or generally, of a fiber amplifier or fiber laser.
Electrical switching behavior from ultrathin potential barrier of self-assembly molecules tuned by interfacial charge trapping
Authors: Li Yun , Qiu Danfeng , Cao Liqiang , Shao Chenxu , Pan Lijia , Pu Lin , Xu Jianbin , Shi Yi
Published: March 2010

The investigation of the self-assembly molecules of n-octyltrichlorosilane (OTS) as an ultrathin potential barrier in an organic two-terminal structure is presented. Electrical switching behavior with a large increase in current density is observed, and the mechanism of the electrical transition is mainly related to the OTS potential barrier tuned by charge trapping at the interface of OTS with the organic semiconductor layer. The switching behavior reveals the importance of the interfacial properties of self-assembly molecules in controlling the vertical charge transport.