bluuebunny/crossref_metadata_2025 huggingface dataset:
‘Paying for the Emergency by displacing the settlers’: global coffee and rural restructuring in late colonial Kenya
Authors: Hyde David
Published: March 2009

Global coffee markets entered into a deep cyclical downturn from the mid 1950s. As producers, notably Brazil and Colombia, continued to increase their output, intense struggles arose among global competitors for larger slices of a contracting market. The prospect of an economic catastrophe, following the release of Brazil's surplus stocks, preoccupied Kenya's colonial government, which was dependent on tax revenues derived from coffee sales, and was less able to support the settler-dominated industry in the face of the increased costs incurred by the Mau Mau Emergency after 1952. This left European settlers exposed, with many barely able to recover their costs of production. What began as a counter-insurgency strategy, by allowing an elite of African farmers to grow Arabica coffee (a privilege formerly reserved to settlers) was enlarged and accelerated in response to unrelenting global market pressures. These compelled the colonial government to beckon low-cost African farmers into coffee production, in a bid to save its tax base and ensure the survival of the coffee sector. Even though the Coffee Marketing Board confiscated much of their income, African farmers proved well able to rally family labour and achieve surpluses. Rationalization of production and the re-organization of the commodity chain to maintain high quality at lower cost were decisive in both reconfiguring the economic and social relationships that underpinned Kenya's independence in 1963 and securing the country's place on the world market. The aim here is to explain the crisis, and its grip on Kenya's economy during the transition to independence and beyond.
Discovery of an extended, halo-like stellar population around the Large Magellanic Cloud
Authors: Majewski Steven R. , Nidever David L. , Muñoz Ricardo R. , Patterson Richard J. , Kunkel William E. , Carlin Jeffrey L.
Published: March 2009

We describe an ongoing, large-scale, photometric and spectroscopic survey of the Large Magellanic Cloud (LMC) periphery. This survey uses WashingtonM,T2+DDO51 photometry to identify distant LMC red giant branch (RGB) star candidates; multi-object spectroscopy is used to confirm the stellar surface gravities of these RGB stars and their association with the LMC (e.g., through radial velocities). The survey now encompasses hundreds of fields ranging from the LMC center with full azimuthal coverage around the LMC and out to 23° from the LMC center. We have confirmed the existence of RGB stars with (the unusual) Magellanic velocities out to the radial limit of this survey coverage. From data in a subsample of these fields, we show that this extended population of stars makes up a diffuse structure enveloping the LMC with a two-dimensional distribution resembling a classical halo with a shallow de Vaucouleurs profile and a broad metallicity spread around a typical mean value of [Fe/H] ~ −1.0.
Modeling a high velocity LMC: The formation of the Magellanic Stream
Authors: Mastropietro Chiara
Published: March 2009

I use high resolution N-body/SPH simulations to model the new proper motion of the Large Magellanic Cloud (LMC) within the Milky Way (MW) halo and investigate the effects of gravitational and hydrodynamical forces on the formation of the Magellanic Stream (MS). Both the LMC and the MW are fully self consistent galaxy models embedded in extended cuspy ΛCDM dark matter halos. I find that ram-pressure from a low density ionized halo is sufficient to remove a large amount of gas from the LMC's disk forming a trailing Stream that extends more than 120 degrees from the Cloud. Tidal forces elongate the satellite's disk but do not affect its vertical structure. No stars become unbound showing that tidal stripping is almost effectless.
The star formation process in the Magellanic Clouds
Authors: Oliveira J. M.
Published: March 2009

The Magellanic Clouds offer unique opportunities to study star formation both on the global scales of an interacting system of gas-rich galaxies, as well as on the scales of individual star-forming clouds. The interstellar media of the Small and Large Magellanic Clouds and their connecting bridge, span a range in (low) metallicities and gas density. This allows us to study star formation near the critical density and gain an understanding of how tidal dwarfs might form; the low metallicity of the SMC in particular is typical of galaxies during the early phases of their assembly, and studies of star formation in the SMC provide a stepping stone to understand star formation at high redshift where these processes can not be directly observed. In this review, I introduce the different environments encountered in the Magellanic System and compare these with the Schmidt-Kennicutt law and the predicted efficiencies of various chemo-physical processes. I then concentrate on three aspects that are of particular importance: the chemistry of the embedded stages of star formation, the Initial Mass Function, and feedback effects from massive stars and its ability to trigger further star formation.
Integrated spectral properties of star clusters in the Magellanic Clouds
Authors: Ahumada Andrea V. , Talavera M. L. , Clariá J. J. , Santos J. F. C. , Bica E. , Parisi M. C. , Torres M. C.
Published: March 2009

We present flux-calibrated integrated spectra in the optical spectral range of concentrated star clusters in the Large and Small Magellanic Clouds (LMC-SMC), approximately half of which constitute unstudied objects. We have mainly estimated ages and foreground interstellar reddening values from the comparison of the line strengths and continuum distribution of the cluster spectra with those of template spectra with known parameters. Also reddening values were estimated by interpolation between the extinction maps of Burstein & Heiles (1982) (BH). A good agreement between ages and reddenings derived through the different procedures was found. The ages of the 27 LMC star clusters range from 5 to 125 Myr, while those of the 13 SMC vary from 4 to 350 Myr.
Nonlinear modeling of InP devices for W-band applications
Authors: Resca Davide , Di Giacomo Valeria , Raffo Antonio , Cignani Rafael , Santarelli Alberto , Vannini Giorgio , Filicori Fabio , Schreurs Dominique , Medjdoub Farid , Thouvenin Nicolas , Gaquière Christophe
Published: March 2009

A recently proposed technique for the distributed modeling of extrinsic parasitic effects in electron devices is used for the very first time in conjunction with a lumped equivalent circuit model for the intrinsic device.

Nonlinear modeling of 0.1 μm InP HEMTs for W-band applications is considered here, leading to extremely accurate predictions of harmonic distortion and power added efficiency at the fundamental frequencies of 27 and 94 GHz.

The distributed parasitic network is identified through accurate electromagnetic simulations up to the upper frequency limit of the millimeter-wave band (300 GHz), while standard pulsedI/VandS-parameter measurements up to 67 GHz are used for the identification of the intrinsic device model.
A correlation of capacitive RF-MEMS reliability to AlN dielectric film spontaneous polarization
Authors: Papandreou Eleni , Papaioannou George , Lisec Tomas
Published: March 2009

This paper investigates the effect of spontaneous polarization of magnetron-sputtered aluminum nitride on the electrical properties and reliability of Radio Frequency – Micro-Electro-Mechanical Systems capacitive switches. The assessment is performed with the aid of application of thermally stimulated polarization currents in metal-insulator-metal capacitors and temperature dependence of device capacitance. The study reveals the presence of a surface charge, which is smaller than that expected from material spontaneous polarization, but definitely is responsible for the low degradation rate under certain bias polarization life tests.
Possible oceanic feedback in the extratropics in relation to the North Atlantic SST tripole
Authors: Mochizuki Takashi , Awaji Toshiyuki , Sugiura Nozomi
Published: March 2009

We analyze the results of 4‐dimensional variational data assimilation experiments using a coupled general circulation model and identify signals from a possible extratropical oceanic feedback relating to the North Atlantic Sea Surface Temperature (SST) tripole. Examination of the optimized control variables (coupling parameters) and the resultant climate fields reveals that the model errors in the North Atlantic climate variations are very sensitive to the intensity of the extratropical air‐sea thermal coupling. This results in the enhancement of the atmospheric responses to SST changes particularly around 40°N, 50°W, when the model errors are most effectively corrected. Since an adjoint approach enables us to detect the sensitivity to fluctuations in the model variables, our results suggest that this oceanic thermal feedback in the extratropics is a key physical process influencing the North Atlantic Oscillation and the associated North Atlantic SST tripole.
The “Sirente crater field,” Italy, revisited
Authors: Speranza F. , Nicolosi I. , Ricchetti N. , Etiope G. , Rochette P. , Sagnotti L. , De Ritis R. , Chiappini M.
Published: March 2009

A scientific debate has developed in the last few years as to whether a 130 m diameter sag pond surrounded by a saddle‐shaped rim and neighboring smaller sags from the Sirente Plain (Abruzzi, Italy) represent the only known Italian meteoritic crater field, a mud volcano, or an anthropogenic feature. To decipher the nature of the Sirente landforms, we carried out geophysical and geochemical investigations. Geoelectric profiles document two karstified shelf carbonate ridges lying at 10–40 m depth below calcareous lacustrine silts (and deeper more conductive sediments, likely soils/tephra) filling the plain. The smaller sags lie just above the ridges, implying a karstic origin, whereas the main sag (also resting above a carbonate ridge) shows no roots in excess of 10–20 m depth, in contrast to the “crater” interpretation. High‐resolution magnetic surveys reveal negative/positive anomaly stripes in correspondence with the buried ridges/valleys, respectively. The smaller sags, as well as the main crater are located in the domain of negative residuals. The positive long‐wavelength magnetic signature is likely due to the strongly susceptive soils/tephra filling the buried valleys. Magnetic modeling shows that the field observed over the crater is incompatible with the field generated by a buried meteorite with realistic characteristics. The smaller sags are characterized by small magnetic anomaly couplets, perfectly reproducible considering the susceptibility contrast between the fill‐in soil and the surrounding silts. Our data show that the Sirente crater and the minor depressions are simply the results of human activity and karstic processes, respectively.
Satellite‐based near‐real‐time estimation of irrigated crop water consumption
Authors: Tang Qiuhong , Peterson Shannon , Cuenca Richard H. , Hagimoto Yutaka , Lettenmaier Dennis P.
Published: March 2009

Estimation of evapotranspiration using satellite sensors offers the potential for improved water management in irrigated areas. However, previous applications of remote sensing to estimate crop water use have been retrospective in nature, whereas the spatial resolution of sensors that provide information in real time has been thought to be too coarse for such purposes. We describe application of a variation of the Moderate Resolution Imaging Spectroradiometer (MODIS) standard evapotranspiration algorithm for near‐real‐time method for estimation of actual evapotranspiration based entirely on satellite data. The latency of the approach is typically 3 days to 1 week, although the lag could be reduced. The method works best over areas where there is substantial diversity in vegetation types within the remote sensing window; the contrast in vegetation between irrigated and adjacent unirrigated areas meets this requirement well. The satellite sensors/products are MODIS land cover (MOD12Q1), surface reflectance (MOD09GQ), vegetation indices (MOD13Q1), land surface temperature/emissivity (MOD11A1), and albedo (MCD43A3) and NOAA/NESDIS surface radiation budget (SRB) products derived from the Geostationary Operational Environmental Satellites. The MODIS/SRB evapotranspiration estimates agree favorably with ground flux tower observations and evapotranspiration estimates from a much higher resolution Landsat‐based (METRIC) method over irrigated areas of the Klamath River Basin, with instantaneous evapotranspiration biases less than 10% and daily evapotranspiration biases less than 15%. There is a tendency for the MODIS/SRB approach to underestimate, and for the METRIC‐based algorithm to overestimate, seasonal evapotranspiration relative to the tower flux observations.
Daily heterotrophic respiration model considering the diurnal temperature variability in the soil
Authors: Chen J. M. , Huang S. E. , Ju W. , Gaumont‐Guay D. , Black T. A.
Published: March 2009

In daily, monthly, and annual respiration models for regional and global applications, the diurnal variation of temperature is generally ignored. As the effect of temperature on respiration is nonlinear, this ignorance may cause considerable errors in respiration estimation, but these errors have not yet been systematically investigated. This is in fact a central issue in temporal scaling of ecosystem models which are often applied in time steps equal to or larger than a day. In this study, we develop an integrated daily heterotrophic respiration model, and demonstrate first theoretically the importance of considering the diurnal amplitude of soil temperature and the vertical soil carbon distribution pattern in daily respiration estimation using the daily mean temperature. Measurements of soil respiration with roots exclusion made in a mature black spruce site in Saskatchewan, Canada, in July–September 2004 are used to validate the model. Daily heterotrophic respiration rates were underestimated by up to 15%, with a mean value of 4.5%, when only the mean daily temperature was used. This underestimation occurred under the conditions that the diurnal temperature amplitude in the forest was less than 12°C and the vertical distribution of organic carbon in the top 15–30 cm was uniform. Based on the integrated daily model, this underestimation at the same site would be 38% if the amplitude increases to 20°C, and in soils with steep vertical carbon distributions with a 20°C diurnal amplitude, it can increase to 44%. The magnitude of this underestimation is theoretically proportional to [ln(Q10)]2. During the experimental period, the value of Q10 for heterotrophic respiration was found to be 4.0–4.5. If Q10 = 2.0, this underestimation is reduced to about 10% at a diurnal temperature amplitude of 20°C.
Rheology of concentrated granular suspensions and possible implications for debris flow modeling
Authors: Sosio Rosanna , Crosta Giovanni B.
Published: March 2009

Granular suspensions are of major relevance for many geophysical flows. We investigated the rheological behavior of three samples taken from a debris flow deposit at varying solid concentration (from 38.0 to 54.2% by volume) and grain size distribution. Experiments were performed first on the fraction finer than 0.075 mm and then on suspensions with fine sand (up to 0.425 mm in size and percentages varying from 10 to 50%). A vane apparatus connected to a rotational rheometer was used, and experiments showed a reproducibility within ±12%. Results were processed by the Tikhonov regularization method in order to convert the shear stress (τ) versus rotation velocity (ω) curves to shear stress (τ) versus shear rate () flow curves. At shear rates lower than 3–5 s−1, shear stress is rate‐independent. At higher shear rates, the shear stress increases depending on the maximum grain particles included within the suspension. We used the Herschel‐Bulkley and Bingham models to describe the monotonous increase of the flow curves. Varying the grain size distribution of the samples, the power and consistency indexes range within 0.75–1.35 and 0.44–40.8 Pa s−n, where n is the exponent of ; the viscosity coefficient varies from 1.0 to 47.2 Pa s; and the shear stress varies from 28 to 1959 Pa. For materials mainly composed of silt and clay with a variable sand content, (1) an increase in the particle size changes the rheological behavior from shear thinning to shear thickening, and (2) the percentage of sand affects both the frictional character of the flow and the magnitude of the rheological parameters.
Modeling the effect of size reduction on the stratification of a large wind‐driven lake using an uncertainty‐based approach
Authors: Rueda Francisco , Vidal Javier , Schladow Geoffrey
Published: March 2009

An important source of uncertainty affecting the results of 3‐D hydrodynamic models of wind‐driven lakes, and one which is rarely formally addressed, arises in the development of spatially and temporally varying wind fields used as surface boundary conditions. We analyze one of the sources of uncertainty in this process and propose a simple and straightforward method to assess the uncertainty in model results arising from the construction of wind fields for surface boundary conditions. Taking into account such uncertainty in model results, it is demonstrated that a 3‐D hydrodynamic model is able to represent mathematically the evolution of the stratification in a large wind‐driven lake. Using the Salton Sea as a case study, and taking model uncertainty into consideration, we demonstrate that a reduction of the lake size, as has been proposed for restoration of the Salton Sea, will induce a stronger and more persistent stratification. These changes in stratification are shown to be statistically significant. As the number of weather stations used to reconstruct the wind field over water increases from three to five, agreement between field and simulated data improves, possibly because of reduced uncertainty in the spatial interpolation of wind data. Differences in stratification between the Salton Sea as it currently exists and as it could exist if restoration plans are implemented, with the lake occupying the northern end of the basin and its surface area reduced by 80%, are the result of the spatial variability of the wind and changes in the magnitude of the wind‐driven mechanical energy fluxes into the lake.
The Effect of Retro-Cueing on an ERP Marker of VSTM Maintenance
Authors: Murray Alexandra , Kuo Bo-Cheng , Stokes Mark , Nobre Anna
Published: March 2009

Previous research has found that Contralateral Delay Activity (CDA) is correlated with the number of items maintained in Visual Short Term Memory from one visual field (VF) (Vogel & Machizawa, 2004). CDA is usually elicited by a to-be-remembered array after a prospective cue (pro-cue) signalling the relevant side of the visual display, and is interpreted as a putative electrophysiological signature of WM maintenance. Attention can also be directed to the contents of VSTM, after the presentation of a visual array, using a retroactive cue (retro-cue) (Nobre, Griffin, & Rao, 2008). Because retro-cueing directs attention within a memory trace, potentially reducing the load of items to be maintained, we hypothesised that this would significantly attenuate the CDA. Participants were initially presented with a spatial pro-cue which reduced the number of to-be-remembered items to one side. After a delay, a memory array of either four (low load) or eight (high load) items was displayed. A retro-cue then cued participants to one location within the relevant VF, further reducing the load of to-be-remembered items; or provided no information, requiring participants to hold all items in the relevant VF. At the end of the trial, participants performed a same/different judgement on a test stimulus. Retro-cues significantly improved VSTM performance. Unexpectedly, the CDA was found to be abolished by the presentation of both spatially predictive and neutral cues, independently of the VSTM load participants had to maintain.
Metal-Ligand Bonding
Authors: Moore E A , Janes Rob
Published: March 2009

To appreciate the chemistry and physical properties of complexes of the transition series, an understanding of metal-ligand interactions applied to complexes of the d-block is needed. Metal Ligand Bonding aims to provide this through an accessible, detailed, non-mathematical approach. Initial chapters detail the crystal-field model, using it to describe the use of magnetic measurements to distinguish complexes with different electronic configurations and geometries. Subsequent chapters look at the molecular orbital theory of transition metal complexes using a pictorial approach. Bonding in octahedral complexes is explored and electronic spectra and magnetic properties are given extensive coverage. The material addressed in this book forms the foundation of undergraduate lecture courses on d-block chemistry and facilitates learning through various key features, including: full colour diagrams; in-text questions with answers; revision exercises and clearly defined learning outcomes to encourage a reflective approach to study; an associated website; and experimental data and observations from everyday life. A basic knowledge of atomic and molecular orbitals as applied to main group elements is assumed.
Eicosapentaenoic acid stimulates AMP-activated protein kinase and increases visfatin secretion in cultured murine adipocytes
Authors: Lorente-Cebrián Silvia , Bustos Matilde , Marti Amelia , Martinez J. Alfredo , MORENO-ALIAGA Maria J.
Published: March 2009

Visfatin is an adipokine highly expressed in visceral AT (adipose tissue) of humans and rodents, the production of which seems to be dysregulated in excessive fat accumulation and conditions of insulin resistance. EPA (eicosapentaenoic acid), an n−3 PUFA (polyunsaturated fatty acid), has been demonstrated to exert beneficial effects in obesity and insulin resistance conditions, which have been further linked to its reported ability to modulate adipokine production by adipocytes. TNF-α (tumour necrosis factor-α) is a pro-inflammatory cytokine whose production is increased in obesity and is involved in the development of insulin resistance. Control of adipokine production by some insulin-sensitizing compounds has been associated with the stimulation of AMPK (AMP-activated protein kinase). The aim of the present study was to examine in vitro the effects of EPA on visfatin production and the potential involvement of AMPK both in the absence or presence of TNF-α. Treatment with the pro-inflammatory cytokine TNF-α (1 ng/ml) did not modify visfatin gene expression and protein secretion in primary cultured rat adipocytes. However, treatment of these primary adipocytes with EPA (200 μmol/l) for 24 h significantly increased visfatin secretion (P<0.001) and mRNA gene expression (P<0.05). Moreover, the stimulatory effect of EPA on visfatin secretion was prevented by treatment with the AMPK inhibitor Compound C, but not with the PI3K (phosphoinositide 3-kinase) inhibitor LY294002. Similar results were observed in 3T3-L1 adipocytes. Moreover, EPA strongly stimulated AMPK phosphorylation alone or in combination with TNF-α in 3T3-L1 adipocytes and pre-adipocytes. The results of the present study suggest that the stimulatory action of EPA on visfatin production involves AMPK activation in adipocytes.
Gendered Islam and Modernity in the Nation-Space: Women's Modernism in the Jamaat-e-Islami of Pakistan
Authors: Jamal Amina
Published: March 2009

Feminist scholarship on women in religious and right-wing social and political movements has moved from a reductive focus on causal or motivational factors to more sophisticated analyses explicating processes of agency and subject formation. With the aim of expanding and deepening this conceptual space, I will discuss some of my interactions with a group of women in the Jamaat-e-Islami in Pakistan, as we attempted to explore the complex meanings of ‘the modern’ that informed the self-understanding of my interviewees. My work corroborates some of the contemporary scholarship on what is referred to as Political Islam in arguing that Islamist movements in Muslim societies are also the catalysts of modernization, rather than simply its interlocutors. This article argues that these processes of social and political organizing entail particular interrogations and the reconstituting of identities in ways that blur the line between ‘the religious’ and ‘the secular’. On the one hand, we need to understand Jamaat women's self-construction as religious or pious women; on the other hand, we must grasp the specificity of their claims to act as modern subjects situated in the time of political and cultural modernity.
Do Bangladeshi Factory Workers Need Saving? Sisterhood in the Post-Sweatshop Era
Authors: Siddiqi Dina M.
Published: March 2009

This article revisits the figure of the ‘third world sweatshop worker’, long iconic of the excesses of the global expansion of flexible accumulation in late twentieth-century capitalism. I am interested in how feminist activists concerned with the uneven impact of neo-liberal policies can engage in progressive political interventions without participating in the ‘culture of global moralism’ that continues to surround conventional representations of third world workers. I situate my analysis in the national space of Bangladesh, where the economy is heavily dependent on the labour of women factory workers in the garment industry and where local feminist understandings of the ‘sweatshop economy’ have not always converged with global feminist/left concerns about the exploitation inherent in the (now not so new) New International Division of Labor. The tensions or disjunctures between ‘global’ and ‘local’ feminist viewpoints animate the concerns of this article. I argue that de-contextualized critiques derived from abstract notions of individual rights, and corresponding calls for change from above — calls on the conscience of the feminist and the consumer, for instance — can entail troubling analytical simplifications. They highlight some relations of power while erasing others, thereby enacting a different kind of violence and at times undermining mobilizations on the ground. I draw attention to the multiple fields of power through which much of the activism across borders continues to be produced and reproduced discursively. This kind of framing fits all too easily into existing cultural scripts about gender and race elsewhere, and produces ethical obligations to ‘save’ women workers.
Effect of perpendicular magnetic recording media nucleation field on thermal stability
Authors: Shi Zhupei , Tang Kai , He Jizhong , Zhang Jane , Duan Shanlin
Published: March 2009

We developed a new component level thermal decay test that directly measures decays in media signal and noise, which are combined to obtain signal-to-noise ratio (SNR) decay. The SNR decay on spin stand is in good agreement with the hard disk drive bit error rate decay data. The effect of recording linear density (KFCI) on the SNR decay is studied, which is mainly attributed to the demagnetization field change with the recording density. Applying this test to a group of media with a broad range of nucleation field (Hn), it is found that the SNR decay correlates better with the Hn than with the thermal stability factor (KuV/kBT). For a perpendicular magnetic recording media with Hn∼−2000 Oe exhibits zero SNR decay, it indicates strong robustness thermal stability.
Investigation of valence states and electronic structure of ferromagnetic double-perovskite La2MnNiO6 by using synchrotron radiation
Authors: Kang J.-S. , Kim G. , Lee H. J. , Kolesnik S. , Dabrowski B. , Lee Hangil , Kim J.-Y. , Lee Jieun , Kim Bongjae , Min B. I.
Published: March 2009

The electronic structure of ferromagnetic double-perovskite La2MnNiO6 has been investigated by employing Mn and Ni 2p→3d resonant photoemission spectroscopy (RPES) and soft x-ray absorption spectroscopy (XAS). The Mn and Ni 2p XAS measurements show that Mn ions are formally tetravalent (3d3) and that Ni ions are formally divalent (3d8). Mn and Ni 2p→3d RPES shows that the occupied Mn 3d3 (t2g3↑) states are sharp and located around 2 eV below EF, while the occupied Ni 3d8 (t2g3↑t2g3↓eg2↑) states are broader than the Mn 3d states and they extend from EF to ∼5 eV below EF.
High resolution study of etch figures on CaF2 (111)
Authors: Motzer Christian , Reichling Michael
Published: March 2009

Calcium difluoride crystals cleaved along the (111) direction are etched with the dislocation site selective etchants HNO3, HCl, H2SO4, and H3PO4 and their surfaces are inspected ex situ with scanning force microscopy (AFM). Force microscopy yields characteristic features of the etch pits at the nanometer scale such as terracing and ditrigonal patterns. The method enables direct quantitative measurements of etch pit structures to derive kinetic data revealing details of the dissolution mechanism. Orthophosphoric acid is found to yield the best scaleable etching figures at ambient and elevated temperatures, as for this etchant, the dissolution is reaction-rate controlled. The scanning tip can induce a precipitationlike process by adherent traces of sulfuric or phosphoric acid that can be removed by a treatment with nitric acid following the regular etching procedure.
Cross stream chain migration in nanofluidic channels: Effects of chain length, channel height, and chain concentration
Authors: Kohale Swapnil C. , Khare Rajesh
Published: March 2009

We use molecular dynamics simulations to study the shear flow of a polymer solution in a nanochannel by using an explicit, atomistic model of the solvent. The length scales representing the chain size, channel size, and the molecular scale structure in these nanochannels are comparable. The diffusion and hydrodynamic interactions in the system are governed by the intermolecular interactions in the explicit solvent model that is used in the simulations. We study the cross stream migration of flexible polymer chains in a solution that is subjected to a planar Couette flow in a nanochannel. We present a detailed study of the effects of chain length, channel size, and solution concentration on the cross stream chain migration process. Our results show that when a dilute solution containing a longer and a shorter chain is subjected to shear flow, the longer chains that are stretched by the flow migrate away from the channel walls, while the shorter chains that do not stretch also do not exhibit this migration behavior. The thickness of the chain depletion layer at the channel surface resulting from cross stream migration is found to increase with an increase in the channel height. On the other hand, this degree of migration away from the channel walls is found to decrease with an increase in the solution concentration. In solutions with concentrations comparable to or greater than the overlap concentration, the depletion layer thickness in shear flow is found to be comparable or slightly smaller than that observed in the absence of flow.
Modeling and simulation of coating growth on nanofibers
Authors: Wilder J. , Clemons C. B. , Kreider K. L. , Young G. W. , Evans E. , Zhang G.
Published: March 2009

This work presents modeling and simulation results of a procedure to coat nanofibers and core-clad nanostructures with thin film materials using plasma enhanced physical vapor deposition. In the experimental effort that motivates the modeling, electrospun polymer nanofibers are coated with metallic materials under different operating conditions to observe changes in the coating morphology. The modeling effort focuses on linking simple models at the reactor, nanofiber, and atomic levels to form a comprehensive model. Numerical simulations that link the concentration field with the evolution of the coating free surface predict that as the Damköhler number is increased the coating morphology changes from a wavy to a nodular to a dendritic needle-type form as observed experimentally.
On the fabrication of all-glass optical fibers from crystals
Authors: Ballato J. , Hawkins T. , Foy P. , Kokuoz B. , Stolen R. , McMillen C. , Daw M. , Su Z. , Tritt T. M. , Dubinskii M. , Zhang J. , Sanamyan T. , Matthewson M. J.
Published: March 2009

The highly nonequilibrium conditions under which optical fibers conventionally are drawn afford considerable, yet underappreciated, opportunities to realize fibers comprised of novel materials or materials that themselves cannot be directly fabricated into fiber form using commercial scalable methods. Presented here is an in-depth analysis of the physical, compositional, and selected optical properties of silica-clad erbium-doped yttrium aluminosilicate glass optical fibers derived from undoped, 0.25, and 50 wt % Er3+-doped yttrium aluminum garnet (YAG) crystals. The YAG-derived fibers were found to be noncrystalline as evidenced by x-ray diffraction and corroborated by spectroscopic measurements. Elemental analysis across the core/clad interface strongly suggests that diffusion plays a large role in this amorphization. Despite the noncrystalline nature of the fibers, they do exhibit acceptable low losses (∼0.15–0.2 dB/m) for many applications, broad-band emissions in the near-infrared, and enhanced thermal conductivity along their length while maintaining equivalent mechanical strength with respect to conventional silica optical fibers. Further, considerably higher rare-earth doping levels are realized than can be achieved by conventional solution or vapor-phase doping schemes. A discussion of opportunities for such approaches to nontraditional fiber materials is presented.
Effect of electric field on the nanoindentation of zinc sulfide
Authors: Yang Fuqian , Dang Hongmei
Published: March 2009

Local softening was observed for the nanoindentation of a polycrystalline ZnS in an electric field. The indentation load was in the range of 35–100 μN, and the electric field intensity was in the range of 0.5–2 V/mm. The indentation hardness decreased with increasing the electric field intensity. This effect was likely due to the electromechanical interaction which changed the effective resolved shear stress and the average velocity of charged dislocations. A critical increment in the resolved shear stress was obtained at which the average velocity of the charged dislocations is the same as that in the absence of electric field.
The effect of noise on the complete synchronization of two bidirectionally coupled piecewise linear chaotic systems
Authors: Xiao Yuzhu , Xu Wei , Li Xiuchun , Tang Sufang
Published: March 2009

In this paper, we study the synchronization of two bidirectionally coupled piecewise linear chaotic systems when the coupling strength is disturbed by the common or different noise. Based on stochastic differential equation theory, we verify that the noise can really induce the occurrence of synchronization, and the sufficient conditions of synchronization with probability 1 are established. We also find that with the common noise it is easier to induce the synchronization than with different noise. Moreover, two examples are provided and some numerical simulations are performed to verify the theoretical results.
Experimental studies on fast-ion transport by Alfvén wave avalanches on the National Spherical Torus Experiment
Authors: Podestà M. , Heidbrink W. W. , Liu D. , Ruskov E. , Bell R. E. , Darrow D. S. , Fredrickson E. D. , Gorelenkov N. N. , Kramer G. J. , LeBlanc B. P. , Medley S. S. , Roquemore A. L. , Crocker N. A. , Kubota S. , Yuh H.
Published: March 2009

Fast-ion transport induced by Alfvén eigenmodes (AEs) is studied in beam-heated plasmas on the National Spherical Torus Experiment [Ono et al., Nucl. Fusion 40, 557 (2000)] through space, time, and energy resolved measurements of the fast-ion population. Fast-ion losses associated with multiple toroidicity-induced AEs (TAEs), which interact nonlinearly and terminate in avalanches, are characterized. A depletion of the energy range >20 keV, leading to sudden drops of up to 40% in the neutron rate over 1 ms, is observed over a broad spatial range. It is shown that avalanches lead to a relaxation of the fast-ion profile, which in turn reduces the drive for the instabilities. The measured radial eigenmode structure and frequency of TAEs are compared with the predictions from a linear magnetohydrodynamics stability code. The partial disagreement suggests that nonlinearities may compromise a direct comparison between experiment and linear theory.
Spectral relationships between kicked Harper and on-resonance double kicked rotor operators
Authors: Lawton Wayne , Mouritzen Anders S. , Wang Jiao , Gong Jiangbin
Published: March 2009

Kicked Harper operators and on-resonance double kicked rotor operators model quantum systems whose semiclassical limits exhibit chaotic dynamics. Recent computational studies indicate a striking resemblance between the spectra of these operators. In this paper we apply C∗-algebra methods to explain this resemblance. We show that each pair of corresponding operators belongs to a common rotation C∗-algebra Bα, prove that their spectra are equal if α is irrational, and prove that the Hausdorff distance between their spectra converges to zero as q increases if α=p/q with p and q coprime integers. Moreover, we show that corresponding operators in Bα are homomorphic images of mother operators in the universal rotation C∗-algebra Aα that are unitarily equivalent and hence have identical spectra. These results extend analogous results for almost Mathieu operators. We also utilize the C∗-algebraic framework to develop efficient algorithms to compute the spectra of these mother operators for rational α and present preliminary numerical results that support the conjecture that their spectra are Cantor sets if α is irrational. This conjecture for almost Mathieu operators, called the ten Martini problem, was recently proven after intensive efforts over several decades. This proof for the almost Mathieu operators utilized transfer matrix methods, which do not exist for the kicked operators. We outline a strategy, based on a special property of loop groups of semisimple Lie groups, to prove this conjecture for the kicked operators.
Development of empirical bond-order-type interatomic potential for amorphous carbon structures
Authors: Kumagai T. , Hara S. , Choi J. , Izumi S. , Kato T.
Published: March 2009

A bond-order-type interatomic potential has been developed for reproducing amorphous carbon (a-C) structures. Several improvements have been incorporated into the conventional Brenner potential so that the material properties of carbon crystals remain unchanged. The main characteristics of the potential function developed in the present research are the use of a screening function instead of a cutoff function and the introduction of a dihedral angle potential around the bond between two threefold coordinated atoms. By using the developed interatomic potential, we can reproduce the material properties of a-C structures, such as the fraction of sp3-bonded atoms, radial distribution function, and ring statistics. It is found that the correction term enhances the formation of cluster structures in a-C, which is confirmed in the first-principles calculation.
Low dimensional description of pedestrian-induced oscillation of the Millennium Bridge
Authors: Abdulrehem Mahmoud M. , Ott Edward
Published: March 2009

When it opened to pedestrian traffic in the year 2000, London’s Millennium Bridge exhibited an unwanted, large side-to-side oscillation, which was apparently due to a resonance between the stepping frequency of walkers and one of the bridge modes. Models for this event, and similar events on other bridges, have been proposed. The model most directly addressing the synchronization mechanism of individual walkers and the resulting global response of the bridge-pedestrian system is the one developed by Eckhardt et al. [Phys. Rev. E 75, 021110 (2007)]. This model treats individual walkers with a phase oscillator description and is inherently high dimensional with system dimensionality (N+2), where N is the number of walkers. In the present work we use a method proposed by Ott and Antonsen [Chaos 18, 037113 (2008)] to reduce the model of Eckhardt et al. to a low dimensional dynamical system, and we employ this reduced description to study the global dynamics of the bridge/pedestrian interaction. More generally, this treatment serves as an interesting example of the possibility of low dimensional macroscopic behavior in large systems of coupled oscillators.
On the activation and passivation of precursors for process-induced positive charges in Hf-dielectric stacks
Authors: Chang M. H. , Zhao C. Z. , Ji Z. , Zhang J. F. , Groeseneken G. , Pantisano L. , De Gendt S. , Heyns M. M.
Published: March 2009

Hf-based dielectric stack is replacing SiON as gate dielectric even though our understanding of it is incomplete. It has been reported that a thermal exposure above 450°C can lead to positive charging in both unoptimized SiO2 layer and Hf-based dielectric stack. At present, there is little information on how this process-induced positive charging (PIPC) occurs in the Hf-based stack and how to suppress it. The objective of the current work is to improve our understanding by addressing three key issues. First, the activation of PIPC precursors after device fabrication is investigated and it will be shown that the loss of certain species from the gate edge through lateral diffusion is responsible for it. Second, the passivation of the precursor is studied and the relevant species are explored. It is found that both water- and chlorine-related species play a role. Finally, the reactivation of the passivated precursor is examined and the results show that it is not thermally accelerated.
Giant magnetodielectric effect and magnetic field tunable dielectric resonance in spinel MnZn ferrite
Authors: Chen Yajie , Zhang Xiao-Yu , Vittoria Carmine , Harris V. G.
Published: March 2009

The sensitive response of the dielectric permittivity under the application of magnetic fields in Mn0.60Zn0.40Fe2.12O4+δ polycrystalline ferrite is presented. A magnetic field of 3.5 kOe induced a giant magnetodielectric {MD=[ε′(H)−ε′(0)]/ε′(0)} response, of 1800% at f=7 MHz, at room temperature. The ferrite exhibits a large magnetic field-induced frequency response of 180 Hz/Oe. We suggest that this effect arises primarily from a spin-dependent space charge polarization mechanism in response to the application of dc magnetic fields.
Analysis of a SeCl4-graphite intercalate surface by thermovoltage scanning tunneling microscopy
Authors: Seifritz J. , Wagner Th. , Weyers B. , Möller R.
Published: March 2009

The local thermoelectric properties of a SeCl4-graphite intercalate compound (SeCl4-GIC) are studied by means of scanning-tunneling microscopy (STM). The analysis by micro-Raman spectroscopy suggested two domains, a “carbonlike” and a “SeCl4-GIC-like.” By using the thermovoltage that arises if a temperature difference between the tunneling tip and the sample of a STM is applied, areas with a difference in the local density of states can be distinguished with high lateral resolution. The differences in the local thermopower may be as large as several hundred μV/K. The aim was to estimate the contribution of the different domains to the thermopower of SeCl4-GIC.
Linear-nonlinear interaction’s effect on the power dependence of nonlinear distortion products
Authors: Henrie Justin , Christianson Andrew , Chappell William J.
Published: March 2009

An unusual power dependence of the nonlinear distortion produced by a two-tone test has been observed in several different physical systems. We show that the interaction between the nonlinear and linear elements of a system can dramatically transform the overall nonlinear behavior of the system from that of the nonlinear component in isolation. In particular, we show that when interaction with the linear elements of an electric circuit is appropriately accounted for, rather simple models of nonlinearity display the unusual power dependence of nonlinear distortion products observed in a variety of physical systems.
Correlation between the microstructure and electroluminescence properties of Er-doped metal-oxide semiconductor structures
Authors: Kanjilal A. , Rebohle L. , Skorupa W. , Helm M.
Published: March 2009

Optical response of a rare earth (RE)-doped SiO2 layer is known to deteriorate markedly at room temperature due to RE clustering. The key challenge is therefore to probe the ongoing processes at the microscopic level and the subsequent impact on the luminescence properties with increasing RE concentration. Here, we report how the Er electroluminescence in a metal-oxide-semiconductor structure has been affected by increasing Er content. Our results indicate that the Er oxide clustering is anticipated by the formation of Si-based oxygen-deficiency centers during postimplantation annealing and leads to a strong quenching of the short-wavelength (350–500 nm) Er electroluminescence.
Active phase control of a Ag near-field superlens via the index mismatch approach
Authors: Lee Kwangchil , Jung Youngjean , Kang Gumin , Park Haesung , Kim Kyoungsik
Published: March 2009

We recognize that the phase control of optical transfer function is profoundly important in realizing nanoimaging beyond the diffraction limit. The difficulty of the optical phase measurement in the near field, required for the conventional adaptive control method, motivates us to achieve active phase control in the superlens imaging system. The visibility and resolving capabilities are significantly enhanced through the index mismatch approach by tuning the wavelength of the incident light.
Chimpanzee Faces are ‘Special’ to Humans
Authors: Taubert Jessica
Published: March 2009

A longstanding proposal is that primates, including humans, might have an innate representation of face structure. But, if humans have such a representation, how broad is its form: limited to coding conspecifics, or general enough to cover related species? The results reported here show adult humans process faces of chimpanzees in a way previously assumed to be exclusive to human faces. The composite effect was used to provide the first direct test of so-called holistic processing. Despite no lifetime experience of chimpanzees, adult humans showed a substantial composite effect for chimpanzee faces, and also an inversion effect. There was no similar evidence of holistic processing for faces of species of greater phylogenic distance from humans, including gorillas, spider monkeys, sheep, chickens, and Jacky lizards; nor was there any effect for non-face objects. In contrast to the holistic processing results, discrimination of chimpanzee faces was, as expected, poor. In the context of evidence that poor discrimination of heterospecific faces arises from a process of perceptual narrowing in infancy, our results suggest that adults retain some aspects of a broader bandwidth present in neonates (holistic processing) but lose others (discrimination).