bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconciling channel formation processes with the nature of elevated outflow systems at Ophir and Aurorae Plana, Mars
Authors: Leverington David W.
Published: October 2009

Many Hesperian outflow channels head at elevations compatible with aquifer recharge beneath the Martian south polar cap, and such channels are widely interpreted as the products of this recharge. Some outflow channels head at greater elevations that are inconsistent with southern recharge, including three systems located in Aurorae Planum and eastern Ophir Planum. These three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west. However, the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands, inconsistencies between hypothesized processes and the nature of regional topography and mineralogy, and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface. In contrast, a volcanic origin for the Ophir and Aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms, the volcanotectonic nature of the Valles Marineris system and adjacent upland plains, and the nature of available analog landforms and processes. Though numerous uncertainties remain, a volcanic interpretation of these outflow systems can more simply account for the existence of component channels. The attributes of other elevated outflow systems on Mars similarly appear to be most consistent with volcanic origins. If the Ophir and Aurorae systems formed volcanically, thermal considerations imply minimum erupted lava volumes of 6.4 × 103km3for Allegheny Vallis and 6.2 × 104km3for Elaver Vallis.
A storage model approach to the assessment of snow depth trends
Authors: Woody Jonathan , Lund Robert , Grundstein Andrew J. , Mote Thomas L.
Published: October 2009

This paper introduces a stochastic storage model capable of assessing trends in daily snow depth series. The model allows for seasonal features, which permits the analysis of daily data. Breakpoint times, which occur when the observing station changes location or instrumentation, are shown to greatly influence estimated trend margins and are accounted for in this analysis. The model is fitted by numerically minimizing a sum of squares of daily prediction errors. Standard errors for the model parameters, useful in making trend inferences, are presented. The methods are illustrated in the analysis of a century of daily snow depth observations from Napoleon, North Dakota. The results here show that snow depths are significantly declining at Napoleon, with spring ablation occurring earlier, and that breakpoint features are very influential in deriving realistic trend estimates.
An investigation of amorphous Ge2Se3 structure for phase change memory devices using fluctuation electron microscopy
Authors: Jarvis K. , Carpenter R. W. , Davis M. , Campbell K. A.
Published: October 2009

Medium range order in amorphous thin films of Ge2Se3, a phase change memory material, was examined using electron nanodiffraction fluctuation electron microscopy. Variance measurements showed that medium range order existed at 0.36 and 0.58 Å−1. The film was not at equilibrium and contained a few monoclinic nanocrystals with weak Bragg maxima at 0.33, 0.54, and 0.63 Å−1, which are related to the GeSe2 equilibrium phase at this composition. We also determined the variance for amorphous silicon (a-Si) and amorphous silica (a-SiO2) and those results agree with others in the literature. It is expected that the medium range order is related to nucleation of the crystallization reaction in Ge2Se3.
Compact model for forward subthreshold characteristics in polymer semiconductor transistors
Authors: Sambandan S. , Kist R. J. P. , Lujan R. , Ng T. , Arias A. C. , Street R. A.
Published: October 2009

We present a compact model for polymer thin film transistors (TFTs) operating in forward subthreshold region. Due to the threshold voltage shift in these devices, the bias point of a device operating for a sufficiently long time moves toward the subthreshold region. Therefore, modeling subthreshold operation in polymer semiconductor based TFTs is important. We particularly address two areas where polymer TFTs are different from other disordered materials such as amorphous silicon. Firstly, the shape of the density of deep states cannot be assumed to be purely exponential. Such an assumption does not provide fine modeling of the subthreshold slope. Secondly, for subthreshold operation particularly under high drain-source bias, we need to include Poole–Frenkel type transport mechanisms such as variable range hopping and space charge limited current. This paper includes these features and develops a compact closed form model.
Full Coulomb collision operator in the moment expansion
Authors: Ji Jeong-Young , Held Eric D.
Published: October 2009

The full Coulomb collision operator and its moments including nonlinear terms are analytically calculated in the moment expansion. In coupling nonlinear terms, the product formula which expresses a product of two harmonic tensors as a series of single harmonic tensors is derived. The collision operators and moments are written in explicit formulas for arbitrary moments and for arbitrary temperature and mass ratios. These expressions easily reduce to formulas for the small mass-ratio approximation or for like species.
Transmission-based detection of nuclides with nuclear resonance fluorescence using a quasimonoenergetic photon source
Authors: Hagmann C. A. , Hall J. M. , Johnson M. S. , McNabb D. P. , Kelley J. H. , Huibregtse C. , Kwan E. , Rusev G. , Tonchev A. P.
Published: October 2009

We provide a detailed experimental validation of the concept of transmission-based isotope detection. The dominant background processes in this class of systems were measured by studying the detection of U238 with a quasimonochromatic (ΔE∕E∼3%) photon beam. A notch develops in the spectrum transmitted through our test objects due to the preferential attenuation of photons with an energy that resonantly excites a bound nuclear state in U238 near 2 MeV. The notch was measured downstream of our test objects by means of resonant photon scattering from a secondary U238 target. The dominant backgrounds measured in the notch detector due to radioactive decay and elastic scattering of the transmitted beam are presented. Processes that refill the notch with off-resonance photons will obscure the signal and result in a higher probability of false negatives. A measurement of the refill process produced a null result, and we report an upper limit on the magnitude of the notch fill factor.
Space-charge-limited currents in organics with trap distributions: Analytical approximations versus numerical simulation
Authors: Paasch Gernot , Scheinert Susanne
Published: October 2009

Analytical approximations for space-charge-limited currents (SCLCs) in systems with exponential or Gaussian trap distributions were widely used in analyzing organic diodes. The current follows a power law with a transition into the trap-free SCLC at high voltages and an Ohmic low voltage limit. The power coefficient γ is connected with either the decay constant or the variance of the distributions. Within these formulations, it is not possible to check the relevance of the numerous approximations needed to derive them. This concerns especially the relations of the contact work functions and of the layer thickness with the trap concentration, the position of the center of the trap distribution and its maximum value. Application of the analytical approximations to results of full numerical simulations allows one to set limits for the parameter ranges in which the approximations can be applied. In the case of the exponential distribution the analytical approximation is rather good for high trap concentrations and thicker layers. However, the simulations reveal a number of additional peculiarities. Such, the high voltage limit is usually not the trap-free SCLC but Ohmic and determined only by the anode barrier, the low voltage limit leads to a diodelike dependence with a large ideality factor and scaling with layer thickness and position of the trap distribution is extremely limited. In the case of the Gaussian trap distribution the simulations show indeed that the formula together with the connection between the power coefficient and the variance of the distribution fails completely. Thus, in principle, earlier analyzes of experimental data should be revised by using numerical simulations.
Hole mobility and transport mechanisms in λ-DNA
Authors: Jakobsson Mattias , Stafström Sven
Published: October 2009

We have performed a study of charge transport in λ-DNA using a recently developed model based on Marcus theory and dynamic Monte Carlo simulations. The model accounts for charge delocalization over multiple adjacent identical nucleobases. Such delocalized states are found to act as traps for charge transport and therefore have a negative impact on the charge carrier (hole) mobility. Both the electric field and temperature dependence of the mobility in λ-DNA is reported in this paper. Furthermore, the detailed information produced by the simulation allow us to plot the progress of a hole propagating through the DNA sequence and this is used to identify the bottlenecks that limits the charge transport process.
General formulation of pressure and stress tensor for arbitrary many-body interaction potentials under periodic boundary conditions
Authors: Thompson Aidan P. , Plimpton Steven J. , Mattson William
Published: October 2009

Three distinct forms are derived for the force virial contribution to the pressure and stress tensor of a collection of atoms interacting under periodic boundary conditions. All three forms are written in terms of forces acting on atoms, and so are valid for arbitrary many-body interatomic potentials. All three forms are mathematically equivalent. In the special case of atoms interacting with pair potentials, they reduce to previously published forms. (i) The atom-cell form is similar to the standard expression for the virial for a finite nonperiodic system, but with an explicit correction for interactions with periodic images. (ii) The atom form is particularly suited to implementation in modern molecular dynamics simulation codes using spatial decomposition parallel algorithms. (iii) The group form of the virial allows the contributions to the virial to be assigned to individual atoms.
Vertical hybrid microcavity based on a polymer layer sandwiched between porous silicon photonic crystals
Authors: Sychev F. Yu. , Razdolski I. E. , Murzina T. V. , Aktsipetrov O. A. , Trifonov T. , Cheylan S.
Published: October 2009

A vertical hybrid microcavity is fabricated by sandwiching a polymer layer between distributed Bragg reflectors (DBRs) composed of porous silicon photonic crystals. The DBRs are made by electrochemical etching of Si and consist of alternating porous Si layers of high and low porosity, the top DBR being a freestanding film. The hybrid microcavity demonstrates a deep microcavity mode placed within a 200 nm wide photonic band gap, and reveals a many-fold enhancement of the third-order nonlinearity of the microcavity layer. The fabrication technique employed is rather simple, enabling the use of a variety of functional materials as the microcavity spacer.
Anisotropic optical constants of in-plane oriented polyfluorene thin films on rubbed substrate
Authors: Zhu De-Xi , Shen Wei-Dong , Zhen Hong-Yu
Published: October 2009

We present a photometric method to determine the anisotropic optical constants of several aligned polyfluorene films. These polymers exhibit liquid crystal characteristic under heat treatment and polymer chains are preferentially in-plane oriented on a rubbed alignment layer. A self-consistent dispersion formula of Forouhi–Bloomer model is introduced to fit the measured polarized reflectance and transmittance curves by a global optimization algorithm. The very good agreements between the experimental and theoretical spectra allow us to shed light on the parallel and perpendicular components of optical constant. On this basis, light-emitting devices are fabricated using the anisotropic active films. The measured polarized electroluminescence spectra confirm the optical birefringence.
Picosecond photoassisted electron emission from gated p-silicon high density field emitter array
Authors: Chiang Chin-Jen , Yankelevich Diego R. , Heritage Jonathan P.
Published: October 2009

A 1 mm square array of oxidation sharpened p-type Si field emitter tips (2.4 μm spacing and 1 μm gate aperture) produces 40 ps rise time pulsed electron emission into the vacuum when excited by 110 fs duration optical pulses (λ=0.78 μm). The observed emission quantum yield for pulsed excitation of 0.04% is partially accounted for by gate shadowing and overlap of optical absorption depth and an estimated depletion layer thickness. These results suggest that more efficient photoexcited picosecond time scale electron emission is possible from optimized semiconductor field emitter structures.
Understanding the changes in mechanical properties due to the crystalline-to-amorphization transition in SiC
Authors: Xue Kun , Niu Li-Sha
Published: October 2009

Atomic-scale simulations of tensile testing are performed on a series of silicon carbide (SiC) with varying chemical disorder to investigate the changes in mechanical properties due to the accumulation of irradiation damage. The accumulation of chemical disorder, which drives the crystalline-to-amorphization (c-a) transition, plays a significant role on the variations of Young’s modulus and strength, but in different manners. Young’s modulus decreases almost linearly with increasing chemical disorder below some threshold (χ≡NC–C/NC–Si<∼0.54). However, strength exhibits abrupt substantial reduction with the presence of a slight chemical disorder (χ=0.045). Above the threshold, the degradations of Young’s modulus and strength tend to saturate, indicating the completion of c-a transition. The variations of the mechanical properties as a function of chemical disorder are closely correlated with the crossover from homogenous elastic deformation to localized plastic flow percolating through the system. The crossover arises from the interplay between uncorrelated atomic slipping confined within topological disordered clusters and the constraint from topological ordered ligaments. The crossover is also manifested in fracture mechanisms switching from lattice instability to some type of “ductile” fracture preceded by nanocavity percolation.
Bright three-band white light generated from CdSe/ZnSe quantum dot-assisted Sr3SiO5:Ce3+,Li+-based white light-emitting diode with high color rendering index
Authors: Jang Ho Seong , Kwon Byoung-Hwa , Yang Heesun , Jeon Duk Young
Published: October 2009

In this study, bright three-band white light was generated from the CdSe/ZnSe quantum dot (QD)-assisted Sr3SiO5:Ce3+,Li+-based white light-emitting diode (WLED). The CdSe/ZnSe core/shell structure was confirmed by energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. The CdSe/ZnSe QDs showed high quantum efficiency (79%) and contributed to the high luminous efficiency (ηL) of the fabricated WLED. The WLED showed bright natural white with excellent color rendering property (ηL=26.8 lm/W, color temperature=6140 K, and color rendering index=85) and high stability against the increase in forward bias currents from 20 to 70 mA.
An isolated line-shape model based on the Keilson–Storer function for velocity changes. II. Molecular dynamics simulations and the Q(1) lines for pure H2
Authors: Tran H. , Hartmann J.-M. , Chaussard F. , Gupta M.
Published: October 2009

This paper presents comparisons between molecular dynamics simulations (MDSs) and the Keilson and Storer (KS) model for collision-induced translational velocity changes in pure H2 at room temperature from four different points of view. The first considers various autocorrelation functions associated with the velocity. The second and third comparisons are made for the collision kernels and for the time evolutions of some conditional probabilities for changes in the velocity modulus and orientation. Finally, the evolutions, with density, of the half widths of the Q(1) lines of the isotropic Raman (1–0) fundamental band and of the (2–0) overtone quadrupole band are investigated. The results demonstrate that, while the KS approach gives a poor description of detailed velocity-to-velocity changes, it leads to accurate results for the correlation functions and spectral shapes, quantities resulting from large averages over the velocity. On the opposite, collision kernels derived from MDS lead to accurate predictions of all considered quantities. The results open promising perspectives for modeling of the spectral shapes of other systems. They also stress the value of direct calculations of speed-dependent broadening and shifting parameters from the intermolecular potential to avoid their determination from measured spectra and permit fully meaningful tests of the models.
Comment on “Can existing models quantitatively describe the mixing behavior of acetone with water” [J. Chem. Phys. 130, 124516 (2009)]
Authors: Kang Myungshim , Perera Aurelien , Smith Paul E.
Published: October 2009

A recent publication indicated that simulations of acetone-water mixtures using the KBFF model for acetone indicate demixing at mole fractions less than 0.28 of acetone, in disagreement with experiment and two previously published studies. Here, we indicate some inconsistancies in the current study which could help to explain these differences.
Correlating dopant distributions and electrical properties of boron-doped silicon nanowires
Authors: Schlitz Ruth A. , Perea Daniel E. , Lensch-Falk Jessica L. , Hemesath Eric R. , Lauhon Lincoln J.
Published: October 2009

Quantitative nonuniform radial doping profiles in vapor liquid solid grown boron-doped silicon nanowires are correlated with axial variations in electrical properties. Boron concentrations measured by atom probe tomography are lower for the core material grown from a gold catalyst than for material deposited on the nanowire surface. Transistors fabricated along a single nanowire exhibit a transition from nonlinear contact-dominated behavior to linear behavior with increasing thickness of the dopant-enriched surface layer. Simple models confirm that the surface is doped to a level that enables the contact resistance to become comparable to the channel resistance, suggesting that unintentional surface doping may play a role in lowering contact resistances in some nanowire devices.
Even-odd parity oscillations in spin polarization of a quantum dot array
Authors: An Xing-Tao , Liu Jian-Jun
Published: October 2009

We propose a quantum dot (QD) array device which contains a bridge coupling between two leads. Due to the quantum interference and the Rashba spin-orbit interaction, the spin of the electrons through the device is polarized. Moreover, we find odd-even parity oscillations of spin polarization of the electrons through the system. We study the spin accumulations in every QD and find that there is difference between the spin accumulations of the QDs directly and indirectly coupling to leads. These results demonstrate that the bridge coupling is a flexible and feasible way to manipulate the electron spin of the QD array.
Redox potentials and pKa for benzoquinone from density functional theory based molecular dynamics
Authors: Cheng Jun , Sulpizi Marialore , Sprik Michiel
Published: October 2009

The density functional theory based molecular dynamics (DFTMD) method for the computation of redox free energies presented in previous publications and the more recent modification for computation of acidity constants are reviewed. The method uses a half reaction scheme based on reversible insertion/removal of electrons and protons. The proton insertion is assisted by restraining potentials acting as chaperones. The procedure for relating the calculated deprotonation free energies to Brønsted acidities (pKa) and the oxidation free energies to electrode potentials with respect to the normal hydrogen electrode is discussed in some detail. The method is validated in an application to the reduction of aqueous 1,4-benzoquinone. The conversion of hydroquinone to quinone can take place via a number of alternative pathways consisting of combinations of acid dissociations, oxidations, or dehydrogenations. The free energy changes of all elementary steps (ten in total) are computed. The accuracy of the calculations is assessed by comparing the energies of different pathways for the same reaction (Hess’s law) and by comparison to experiment. This two-sided test enables us to separate the errors related with the restrictions on length and time scales accessible to DFTMD from the errors introduced by the DFT approximation. It is found that the DFT approximation is the main source of error for oxidation free energies.
Density scaling in viscous liquids: From relaxation times to four-point susceptibilities
Authors: Coslovich D. , Roland C. M.
Published: October 2009

We present numerical calculations of a four-point dynamic susceptibility, χ4(t), for the Kob–Andersen Lennard-Jones mixture as a function of temperature T and density ρ. Over a relevant range of T and ρ, the full t-dependence of χ4(t) and thus the maximum in χ4(t), which is proportional to the dynamic correlation volume, are invariant for state points for which the scaling variable ργ/T is constant. The value of the material constant γ is the same as that which superposes the relaxation time τ of the system versus ργ/T. Thus, the dynamic correlation volume is a unique function of τ for any thermodynamic condition in the regime where density scaling holds. Finally, we examine the conditions under which the density scaling properties are related to the existence of strong correlations between pressure and energy fluctuations.
A Multiperiod School Location Planning Approach with Free School Choice
Authors: Müller Sven , Haase Knut , Kless Sascha
Published: October 2009

The subject of this paper is a new approach to multiperiod school location planning in urban areas. Most of the existing approaches in the field do not consider free school choice nor are they able to consider substitution effects between school locations. We minimize the location and transport costs with respect to students choosing the school with the highest utility. Since these school choice probabilities (determined by a mixed multinominal logit model) depend on the available schools, we have to consider two steps. First, we generate for each period a set of scenarios indicating which school is open and which is not. For each scenario we allocate the students to available schools according to capacity and utility. Second, we select for each period one scenario in order to minimize total costs. Problems with a long planning horizon and a large number of demand points are solvable. We apply this approach to schools of the City of Dresden, Germany.
Geodemographic Code and the Production of Space
Authors: Uprichard Emma , Burrows Roger , Parker Simon
Published: October 2009

There is a growing body of research relating to the ways in which digital code contributes to the production of space. In much of this work this issue is approached by first examining particular spaces and then considering the code and its effects on those spaces. In contrast, we explore the production of space from another angle, examining the ways in which an example of code—geodemographic classification—is constructed, and then questioning what it is about the emergent production of space that may feed back recursively into the production of that code.
Living in an Oasis: Middle-Class Disaffiliation and Selective Belonging in an English Suburb
Authors: Watt Paul
Published: October 2009

This paper aims to address the oft-mentioned dearth of research on the suburbs by examining processes of sociospatial segregation and middle-class disaffiliation in London's eastern suburban periphery. By drawing upon aspects of Bourdieu's theoretical framework, the paper shows how the home-owning, middle-class, largely white residents of the ‘Woodlands’ private housing estate attempted to shore up their threatened sense of exclusivity in relation to the nearby deprived ‘Eastside’ suburb. The empirical material is drawn from survey and interview research on incomers to Woodlands. For its affluent incoming residents, Woodlands' dominant place image was that of an ‘oasis’ within Eastside, an area dominated by a large council-built housing estate. Although the Woodlands incomers were physically resident in Eastside, they symbolically and practically disengaged from ‘local’ places, notably shops, pubs, and schools, and their lower class and not-quite-white populations. The author argues that the Woodlands incomers adhered to a spatially selective version of what Savage et al refer to as ‘elective belonging’. Such selective belonging denotes a spatially uneven attachment rooted in residents' schizophrenic relationship to the suburban area, embracing the Woodlands oasis whilst abjuring the ‘other Eastside’.
Patterns and Challenges of Urban Nature Conservation—A Study of Southern Sweden
Authors: Borgström Sara T
Published: October 2009

The current, dominating strategy of nature conservation within urban landscapes is to formally protect remaining patches of unexploited nature in nature reserves. However, integration of nature conservation frameworks into urban planning requires reconsideration of key issues, such as why, where, and how to protect nature in a purposeful way. As part of that process I statistically evaluate current nature conservation in 209 municipalities in southern Sweden by analysing the number, size, age, and land cover patterns of 1869 nature reserves in relation to the degree of urbanisation. The analyses reveal that in urban municipalities the nature reserves are fewer, but larger, and have a higher diversity of land covers. Having large nature reserves may be especially important in urban landscapes, since it is often highly fragmented. The land cover compositions show no differences between urban and rural nature reserves. However, urban nature reserves differ more from their surroundings compared with rural nature reserves, according to the identified changes in representation of land cover types with an increasing degree of urbanisation. The most urgent future challenge identified is to develop urban nature conservation strategies that are integrated into the urban context including other green areas and built-up areas, the land-use history, and the requirements for local ecosystem services across the landscape.
Researching Technoscientific Concerns in the Making: Narrative Structures, Public Responses, and Emerging Nanotechnologies
Authors: Macnaghten Phil
Published: October 2009

In this paper I engage with debates on technoscientific governance, narrative, and emergent public attitudes. Building on a piece of social research addressing public responses to the social and ethical dimensions of emerging nanotechnologies, I develop a methodology and mode of analysis designed to take into account four distinctive features of nanotechnology discourse and its constitution in the public sphere, namely: its unfamiliarity; its promissory quality; its uncanniness; and its metaphysical assumptions of progress. Through an analysis of common narratives that shape and structure lay public responses to the technology, and in response to framings of how the technology and its applications are being crafted in the public domain, I argue that nanotechnologies offer a site for an intense future politics centred on dilemmas of body invasion, unanticipated risks, nature's revenge, control, inequalities, and pace of change. I conclude with a set of reflections on the role of the critical social sciences in such a future technopolitics.
Changes in Enforcement Styles among Environmental Enforcement Officials in China
Authors: Lo Carlos Wing-Hung , Fryxell Gerald E , Van Rooij Benjamin
Published: October 2009

This study examines changes in enforcement styles among environmental enforcement officials in the context of China's rapidly changing institutional environments, using panel data collected in Guangzhou in 2000 and 2006. Altogether, five enforcement style elements were examined—accommodation, prioritization, educational, formalism, and coercion. It was found that in 2006 respondents reported greater reliance on education, formalism, and coercion than in 2000. During the same period 2000–06, no significant changes were found for the enforcement styles of accommodation and prioritization or in the respondents' perceptions of their organization's enforcement effectiveness. From regression models in which enforcement styles were used to predict perceived organizational enforcement effectiveness, it was observed that the coefficient for formalism had changed substantially over this period, from being significantly negative to significantly positive, which may be evidence of a general shift from ‘rule by man’ to ‘rule by law’ in China. This study has benefited from the concept of regulatory enforcement style elements, as it allows for an empirical understanding of regulatory enforcement beyond the common and normative dichotomy of deterrence versus cooperation.
Connecting Place and the Everyday Practices of Parenting: Insights from Auckland, New Zealand
Authors: Witten Karen , Kearns Robin , McCreanor Tim , Penney Liane , Faalau Fuafiva
Published: October 2009

This paper asks how the material differences between suburban neighbourhoods influence parents' experience of place and their everyday practices of parenting. Building on a view of place as ‘becoming’, we examine how the accessibility of community amenities and the in-place production and maintenance of social practices contribute to the cohesiveness of neighbourhoods and the social capital resources available to parents. We draw on a 2002–03 study of experiences of Maori, Pakeha (European), and Samoan parents residing in six diverse Auckland neighbourhoods. Analysis of the parents' narratives highlight aspects of the neighbourhood environment that give meaning to participants' daily experiences of parenting, and foster or impede the social relations of place. Beyond purely locational issues, the nuanced relationships between material and sociocultural resources of neighbourhood profoundly influence local patterns of parenting practice. We conclude that place matters in parenting but the salience of the neighbourhood for accessing material and social capital resources varies for parents of different ethnic groups. ‘Jumping’ spatial scale to meet resource needs through the active creation of amenities was more common for minority ethnic groups.
The Construction of Curved Shapes
Authors: Jowers Iestyn , Earl Christopher
Published: October 2009

Application of a shape grammar involves the repetitive task of matching and replacing subshapes of a design under transformation, and as such is well suited for computer implementation. As a result, ever since the conception of the shape grammar formalism, efforts have been made to develop computer programs that automate shape grammar applications. Much of this effort has been directed towards the problem of subshape detection, which involves recognising subshapes embedded in a design. Solutions to this problem have been presented for shapes composed of rectilinear geometric elements, such as straight lines, and algorithms based on these solutions have been implemented in a variety of shape grammar interpreters. However, there has been less research concerning the solution of the subshape detection problem for shapes composed of nonrectilinear geometric elements, such as curve segments. In this paper a method of intrinsic matching is presented, which enables comparison of the embedding properties of parametric curves. This method has been employed in order to develop shape algorithms which can be implemented in shape grammar interpreters for shapes composed of parametric curve segments, arranged in two-dimensional or three-dimensional space.
Re-inventing model-based decision support with Australian dryland farmers. 1. Changing intervention concepts during 17 years of action research
Authors: McCown R. L. , Carberry P. S. , Hochman Z. , Dalgliesh N. P. , Foale M. A.
Published: October 2009

The idea that simulation models of agricultural production can serve as tools for farmers remains a compelling idea even after 3 decades of mostly disappointing development efforts. This paper is the first in a series that reports on 17 years of systems research that used models differently from the Decision Support System idea that has dominated the field. The starting point of FARMSCAPE (Farmers’, Advisers’, Researchers’, Monitoring, Simulation, Communication And Performance Evaluation) was finding whether farmers could value simulation when conditions for appreciation were improved by (a) specifying the simulator for individual paddocks in question and (b) delivering customised simulation to decision makers as a supporting service rather than software as a decision support product. The first aim of the program has been to learn how to effectively intervene in farm management practice using complex, abstract models of croplands, specified with local soil, climate, and management data. The second aim has been to learn how a resulting service that farmers value can be delivered cost effectively by a third party.
This first paper deals with an aspect of the first aim, i.e. valued decision support intervention. In the terms used by Checkland (1981), the activities that served this systems practice aim were guided by ‘what we thought we were doing’ in intervening in farmers’ practice, i.e. our systems thinking. This first paper concerns FARMSCAPE systems thinking and how it evolved over 17 years as we learned successively through discovery of a new concept or representation in the literature to overcome limitations of the then-current conceptual framework. Subsequent papers deal with customising scientific monitoring and simulation for farmers, communication as engagement in situations of practice, understanding decision support intervention as facilitation of personal knowledge construction, and piloting commercial delivery of a simulation-based service to farmers and their advisers.
Response to selection for grazing tolerance in winter-active populations of phalaris (Phalaris aquatica L.). 1. Persistence under grazing in three environments
Authors: Culvenor R. A. , Boschma S. P. , Reed K. F. M.
Published: October 2009

Forage grass cultivars must have adequate grazing tolerance for use in the grazing systems for which they are intended. Response to 2 cycles of selection for persistence under heavy grazing pressure was examined in 3 winter-active breeding populations of the productive perennial grass, phalaris (Phalaris aquatica L.), from 2000 to 2003, at Bulart in western Victoria and Rye Park on the Southern Tablelands and Tamworth on the North-West Slopes of New South Wales. There was one continuously grazed and one rotationally grazed set of plots at Bulart to examine the effect of grazing management.
All sites were affected by drought in later years but drought stress was most severe at Tamworth. A strongly positive linear response to selection was observed in an analysis of persistence measured as frequency of phalaris plant base across the 3 sites (excluding the rotational treatment at Bulart), but response interacted with site. By 2003, linear response averaged 14% frequency units or 34–40% proportional response per cycle at Rye Park and the continuously grazed plots at Bulart, sites that were environmentally suited to survival of phalaris. In contrast, response to selection was absent or slightly negative at Tamworth where conditions were drier and hotter. Populations responded similarly in analyses across all 3 sites but 1 population was less responsive when analyses were restricted to Bulart and Rye Park. Herbage mass measurements in 2001 at Bulart and 2002 at Rye Park indicated positive responses to selection, which were increasingly linked to frequency over time. Rotationally grazed plots at Bulart displayed higher frequency than continuously grazed plots after 3 years of grazing.
The experiment showed that grazing tolerance was a heritable trait in the populations tested when environmental constraints were not limiting and that useful improvements in persistence had been obtained compared with existing cultivars.
Response to selection for grazing tolerance in winter-active populations of phalaris (Phalaris aquatica L.). 2. Correlated response in yield potential, plant characteristics, and alkaloid levels
Authors: Culvenor R. A. , Boschma S. P. , Reed K. F. M.
Published: October 2009

Phenotypic changes in populations of perennial grasses are known to occur in response to natural or deliberate selection under grazing. These changes may have agronomic significance. Associated changes in morphology and yield potential of young stands in response to 2 cycles of selection for grazing tolerance were examined in 3 winter-active breeding populations of the perennial grass, phalaris (Phalaris aquatica L.). Levels of alkaloids which potentially could affect palatability were also examined. There was a decline in seedling growth and autumn and winter yield in spaced plants of 6.3–7.5% per cycle pooled across populations. Seedling growth measured in sown swards at 2 sites was not affected by selection. Visually estimated sward yield in the second year, ignoring large gaps, agreed with the spaced plant results but the decline was not significant at P ≤ 0.05 when herbage yield was measured by mowing, probably due to effects of plant density. On balance, it was concluded that a decline in individual plant yield of 6–7% per cycle had occurred but this could be compensated by higher density, particularly over time as differences in persistence under grazing developed. The most pronounced morphological response to selection under grazing was towards a more densely tillered growth habit, although one exception occurred. There was also a tendency towards a more prostrate growth habit and later heading, but this was significant only for the most erect and earliest maturing population. Two cycles of selection did not significantly affect summer activity or area of plant base in any population. Tryptamine alkaloids were below the level likely to affect palatability but tended to increase with selection, particularly in a very low tryptamine base population, which suggested that they may play a role in persistence.
Because of potentially deleterious effects on yield, care is required in using this selection method. A balance of yield potential and grazing tolerance appropriate to the management system is needed.
Senthil Muthuswamy: A new road map for cancer
Authors: Sedwick Caitlin
Published: October 2009

Senthil Muthuswamy uses 3D cell culture to explore the influence of cell polarity on oncogenic transformation.
Keratins regulate protein biosynthesis through localization of GLUT1 and -3 upstream of AMP kinase and Raptor
Authors: Vijayaraj Preethi , Kröger Cornelia , Reuter Ursula , Windoffer Reinhard , Leube Rudolf E. , Magin Thomas M.
Published: October 2009

Keratin intermediate filament proteins form cytoskeletal scaffolds in epithelia, the disruption of which affects cytoarchitecture, cell growth, survival, and organelle transport. However, owing to redundancy, the global function of keratins has not been defined in full. Using a targeted gene deletion strategy, we generated transgenic mice lacking the entire keratin multiprotein family. In this study, we report that without keratins, embryonic epithelia suffer no cytolysis and maintain apical polarity but display mislocalized desmosomes. All keratin-null embryos die from severe growth retardation at embryonic day 9.5. We find that GLUT1 and -3 are mislocalized from the apical plasma membrane in embryonic epithelia, which subsequently activates the energy sensor adenosine monophosphate kinase (AMPK). Analysis of the mammalian target of rapamycin (mTOR) pathway reveals that AMPK induction activates Raptor, repressing protein biosynthesis through mTORC1's downstream targets S6 kinase and 4E-binding protein 1. Our findings demonstrate a novel keratin function upstream of mTOR signaling via GLUT localization and have implications for pathomechanisms and therapy approaches for keratin disorders and the analysis of other gene families.
AP-1 and KIF13A coordinate endosomal sorting and positioning during melanosome biogenesis
Authors: Delevoye Cédric , Hurbain Ilse , Tenza Danièle , Sibarita Jean-Baptiste , Uzan-Gafsou Stéphanie , Ohno Hiroshi , Geerts Willie J.C. , Verkleij Arie J. , Salamero Jean , Marks Michael S. , Raposo Graça
Published: October 2009

Specialized cell types exploit endosomal trafficking to deliver protein cargoes to cell type–specific lysosome-related organelles (LROs), but how endosomes are specified for this function is not known. In this study, we show that the clathrin adaptor AP-1 and the kinesin motor KIF13A together create peripheral recycling endosomal subdomains in melanocytes required for cargo delivery to maturing melanosomes. In cells depleted of AP-1 or KIF13A, a subpopulation of recycling endosomes redistributes to pericentriolar clusters, resulting in sequestration of melanosomal enzymes like Tyrp1 in vacuolar endosomes and consequent inhibition of melanin synthesis and melanosome maturation. Immunocytochemistry, live cell imaging, and electron tomography reveal AP-1– and KIF13A-dependent dynamic close appositions and continuities between peripheral endosomal tubules and melanosomes. Our results reveal that LRO protein sorting is coupled to cell type–specific positioning of endosomes that facilitate endosome–LRO contacts and are required for organelle maturation.
It takes two to tango to the melanosome
Authors: Lakkaraju Aparna , Carvajal-Gonzalez Jose Maria , Rodriguez-Boulan Enrique
Published: October 2009

The role of clathrin adaptor proteins in sorting cargo in the biosynthetic and recycling routes is an area of intense research. In this issue, Delevoye et al. (2009. J. Cell Biol. doi:10.1083/jcb.200907122) show that a close interaction between the clathrin adaptor AP-1 and a kinesin motor KIF13A is essential for delivering melanogenic enzymes from recycling endosomes to nascent melanosomes and for organelle biogenesis.
Efficiency considerations in triangular adaptive mesh refinement
Authors: Behrens Jörn , Bader Michael
Published: October 2009

Locally or adaptively refined meshes have been successfully applied to simulation applications involving multi-scale phenomena in the geosciences. In particular, for situations with complex geometries or domain boundaries, meshes with triangular or tetrahedral cells demonstrate their superior ability to accurately represent relevant realistic features.

On the other hand, these methods require more complex data structures and are therefore less easily implemented, maintained and optimized. Acceptance in the Earth-system modelling community is still low. One of the major drawbacks is posed by indirect addressing due to unstructured or dynamically changing data structures and correspondingly lower efficiency of the related computations.

In this paper, we will derive several strategies to circumvent the mentioned efficiency constraint. In particular, we will apply recent computational sciences methods in combination with results of classical mathematics (space-filling curves) in order to linearize the complex data and access structure.
A new antimicrobial peptide isolated from Oudneya africana seeds
Authors: Hammami Riadh , Hamida Jeannette Ben , Vergoten Gérard , Lacroix Jean‐Marie , Slomianny Marie‐Christine , Mohamed Neffati , Fliss Ismail
Published: October 2009

Oudneya africana R. Br. (Brassicaceae), a wild‐growing plant in the arid region of Tunisia, is used in ethno‐medicinal treatment of microbial infections. Validation of ethno‐therapeutic claims pertaining to the plant was sought by investigating its antimicrobial activity. A proteinaceous extract of the seeds, called AS‐3000, showed activity against various organisms including L. monocytogenes, E. coli, B. subtilis, E. hirae, P. aeruginosa, S. aureus and C. albicans. Extract AS‐3000 exhibited a synergistic effect against L. ivanovii when combined with vancomycin or chloramphenicol. The post‐antibiotic inhibitory effect of the ampicillin/AS‐3000 combination was 2.3‐fold greater than for the antibiotic alone. The mode of action of AS‐3000 on Listeria and Escherichia was visible using SEM. These results support the use of O. africana for treating microbial infections.
Policy options for alcohol price regulation: the importance of modelling population heterogeneity
Authors: Meier Petra Sylvia , Purshouse Robin , Brennan Alan
Published: October 2009

Context and aims Internationally, the repertoire of alcohol pricing policies has expanded to include targeted taxation, inflation‐linked taxation, taxation based on alcohol‐by‐volume (ABV), minimum pricing policies (general or targeted), bans of below‐cost selling and restricting price‐based promotions. Policy makers clearly need to consider how options compare in reducing harms at the population level, but are also required to demonstrate proportionality of their actions, which necessitates a detailed understanding of policy effects on different population subgroups. This paper presents selected findings from a policy appraisal for the UK government and discusses the importance of accounting for population heterogeneity in such analyses.

Method We have built a causal, deterministic, epidemiological model which takes account of differential preferences by population subgroups defined by age, gender and level of drinking (moderate, hazardous, harmful). We consider purchasing preferences in terms of the types and volumes of alcoholic beverages, prices paid and the balance between bars, clubs and restaurants as opposed to supermarkets and off‐licenses.

Results Age, sex and level of drinking fundamentally affect beverage preferences, drinking location, prices paid, price sensitivity and tendency to substitute for other beverage types. Pricing policies vary in their impact on different product types, price points and venues, thus having distinctly different effects on subgroups. Because population subgroups also have substantially different risk profiles for harms, policies are differentially effective in reducing health, crime, work‐place absence and unemployment harms.

Conclusion Policy appraisals must account for population heterogeneity and complexity if resulting interventions are to be well considered, proportionate, effective and cost‐effective.