bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-dimensional force-free magnetic fields described by some nonlinear equations
Authors: Khater A. H. , Callebaut D. K. , Abdelkawy M. A.
Published: December 2010

A force-free magnetic field arises as a special case in the magnetostatic equation in plasmas when only the magnetic energy density is relevant while all other energy densities are negligible and so only the magnetic pressure is considered. In this article, we find the exact solutions of two-dimensional force-free magnetic fields described by Liouville, sine, double sine, sinh-Poisson, and power force-free magnetic equations. We use the generalized tanh method. In all those cases, the ratio of the current density and the magnetic field is not constant as it happens, e.g., in the solar atmosphere.
Mathematical analysis of the dimensional scaling technique for the Schrödinger equation with power-law potentials
Authors: Ding Zhonghai , Chen Goong , Lin Chang-Shou
Published: December 2010

The dimensional scaling (D-scaling) technique is an innovative asymptotic expansion approach to study the multiparticle systems in molecular quantum mechanics. It enables the calculation of ground and excited state energies of quantum systems without having to solve the Schrödinger equation. In this paper, we present a mathematical analysis of the D-scaling technique for the Schrödinger equation with power-law potentials. By casting the D-scaling technique in an appropriate variational setting and studying the corresponding minimization problem, the D-scaling technique is justified rigorously. A new asymptotic dimensional expansion scheme is introduced to compute asymptotic expansions for ground state energies.
Geometric properties of the magnetic Laplacian on the Euclidean 4-space
Authors: Kazmierowski Dominique , Zinoun Azzouz , Intissar Ahmed
Published: December 2010

When the four-dimensional Euclidean space is endowed with a covariant derivative that is either self-dual or antiself-dual and of constant curvature, the corresponding magnetic Laplacian is closely related to the sub-Laplacian of the quaternionic Heisenberg group. Some geometric properties of this operator are studied. In particular, it is proved that there exists a canonical orthogonal complex structure which provides a factorization in the sense of Schrödinger.
Integral representation of Dirac distribution using the Tsallis q-exponential function
Authors: Mamode Malik
Published: December 2010

Jauregui and Tsallis have recently given a new integral representation of the Dirac distribution in terms of q-exponential function, generalizing the well-known representation in plane waves. We prove rigorously this result using the analytical representation of Schwartz distributions and the tools of complex analysis.
Comparative time-resolved study of the XeF2 etching of Mo and Si
Authors: Veyan J.-F. , Aureau D. , Gogte Y. , Campbell P. , Yan X.-M. , Chabal Y. J.
Published: December 2010

In situ and time-resolved infrared absorption spectroscopic measurements reveal that, under typical processing conditions (∼300 K, approximately Torr pressures), XeF2 reacts efficiently but very differently with Mo and Si substrates. This kinetic study of the surface etching processes, based on the time evolution of both reactants and products, demonstrates that the mechanisms for Mo and Si etching are different. While XeF2 produces substantial roughening and a thick fluorosilyl layer on the crystalline Si surface (>200 nm), it only reacts with the surface atoms of amorphous Mo with substantially slower kinetics. The measured kinetics are quantified by simulation and the final profile experimentally obtained on etched Si surface is shown to be consistent with a recent theoretical study of the characteristic diffusion-controlled etching of silicon.
Effect of Mn concentration and atomic structure on the magnetic properties of Ge thin films
Authors: Ferri F. A. , Pereira-da-Silva M. A. , Zanatta A. R. , Varella A. L. S. , de Oliveira A. J. A.
Published: December 2010

This work reports on the magnetic properties of Ge100−xMnx (x=0–24 at. %) films prepared by cosputtering a Ge+Mn target and submitted to cumulative thermal annealing treatments up to 500 °C. Both as-deposited and annealed films were investigated by means of compositional analysis, Raman scattering spectroscopy, magnetic force microscopy, superconducting quantum interference device magnetometry, and electrical resistivity measurements. All as-deposited films (either pure or containing Mn) exhibit an amorphous structure, which changes to crystalline as the annealing treatments are performed at increasing temperatures. In fact, the magnetic properties of the present Ge100−xMnx films are very sensitive to the Mn content and whether their atomic structure is amorphous or crystalline. More specifically: whereas the amorphous Ge100−xMnx films (with high x) present a characteristic spin glass behavior at low temperature; after crystallization, the films (with moderate Mn contents) are ferromagnetic at room temperature. Moreover, the magnetic behavior of the films scales with their Mn concentration and tends to be more pronounced after crystallization. Finally, the semiconducting behavior of the films, experienced by previous optical studies, was confirmed through electrical measurements, which also indicate the dependence of the resistivity with the atomic composition of the films.
Distinguishing impurity concentrations in GaAs and AlGaAs using very shallow undoped heterostructures
Authors: Mak W. Y. , Das Gupta K. , Beere H. E. , Farrer I. , Sfigakis F. , Ritchie D. A.
Published: December 2010

We have developed a method of fabricating very shallow, gateable, undoped two-dimensional electron gases (2DEG) and making very low resistivity contacts to these. We studied the evolution of mobility as a function of the depth of the 2DEG (from 310 to 30 nm). We extract quantitative information about the background impurity concentrations in GaAs and AlGaAs, the interface roughness, and the charge in the surface states. Surface charge sets an intrinsic limit to the mobility of very shallow 2DEGs. It is probably impossible to fabricate such shallow high-mobility 2DEGs using modulation doping due to the need to accommodate a spacer layer.
Negative refractive index designed in a periodic composite of lossy microplasmas and microresonators
Authors: Sakai Osamu , Shimomura Takuya , Tachibana Kunihide
Published: December 2010

A novel metamaterial with negative refractive index was designed using a spatially periodic composite of microplasmas and microresonators. Microresonators, which are double-helix metal wires in this report, work as an origin of macroscopic negative permeability material, as well as discharge electrodes. If a resonance frequency of the resonators is well below electron plasma frequency of the microplasmas where their permittivity is negative in the real part with a certain imaginary part, the macroscopic refractive index becomes negative just above the resonance frequency where the macroscopic permeability is negative, even if microplasmas are fairly lossy; due to such a loss or conductive component in permittivity, electromagnetic waves are not evanescent but propagating. This result indicates that plasmas can play important roles in parameter control of a metamaterial with a complex refractive index.
Atomic structure, electronic structure, and band offsets at Ge:GeO:GeO2 interfaces
Authors: Lin L. , Xiong K. , Robertson J.
Published: December 2010

The band gaps of GeO2 and GeO are calculated to be 6.1 and 4.0 eV, respectively, using hybrid density functionals that do not require band gap corrections. The conduction band offsets for Ge:GeO2 and Ge:GeO interfaces are calculated to be 0.8 and 0.4 eV, respectively, relatively small and similar to those found by photoemission. The atomic structure of solid GeO is found to have threefold coordinated Ge and O sites with planar oxygen sites.
Low symmetry monoclinic MC phase in epitaxial BiFeO3 thin films on LaSrAlO4 substrates
Authors: Chen Zuhuang , Luo Zhenlin , Qi Yajun , Yang Ping , Wu Shuxiang , Huang Chuanwei , Wu Tom , Wang Junling , Gao Chen , Sritharan Thirumany , Chen Lang
Published: December 2010

We reported that the tetragonal-like phase identified in strained epitaxial BiFeO3 films on a (001) LaSrAlO4 single crystal substrates is monoclinic MC, based on high resolution synchrotron x-ray studies and piezoresponse force microscopy measurements. This MC phase has different symmetry with the rhombohedral-like monoclinic MA phase found in BiFeO3 films grown on low mismatch SrTiO3 substrates. Transmission electron microscopy revealed that the films on LaSrAlO4 substrates have a high crystalline quality and coherent interface.
Thermoelectric-induced spin currents in single-molecule magnet tunnel junctions
Authors: Zhang Zhengzhong , Jiang Liang , Wang Ruiqiang , Wang Baigeng , Xing D. Y.
Published: December 2010

A molecular spin-current generator is proposed, which consists of a single-molecule magnet (SMM) coupled to two normal metal electrodes with temperature gradient. It is shown that this tunneling junction can generate a highly spin-polarized current by thermoelectric effects, whose flowing direction and spin polarization can be changed by adjusting the gate voltage applied to the SMM. This device can be realized with current technologies and may have practical use in spintronics and quantum information.
Experimental and theoretical evidence of enhanced ferromagnetism in sonochemical synthesized BiFeO3 nanoparticles
Authors: Fang Liang , Liu Jian , Ju Sheng , Zheng Fengang , Dong Wen , Shen Mingrong
Published: December 2010

BiFeO 3 nanoparticles were synthesized by a sonochemical method and their magnetic behavior was investigated both experimentally and theoretically. With an aid of ultrasonic irradiation, the saturated magnetization of BiFeO3 nanoparticles at room temperature was found to be increased effectively, from 0.007 to 0.012 μB/Fe. The postannealing and x-ray photoemission spectroscopy results demonstrate that oxygen vacancies can be generated due to the ultrasonic irradiation and play an important role to increase the ferromagnetism. Our first-principles calculation results are in good agreement with the experimental observations.
Highly conducting zinc oxide thin films achieved without postgrowth annealing
Authors: Singh Budhi , Khan Zaheer Ahmed , Khan Imran , Ghosh Subhasis
Published: December 2010

Heavily doped zinc oxide thin films were grown by radio frequency magnetron sputtering. High level of Al doping has been achieved at high growth temperatures (TG), thereby avoiding the need for postgrowth annealing. It is further shown that due to ionized impurity scattering, mobility decreases with increasing TG. Optical transmission spectra show that the bandgap varies from 3.22 to 3.68 eV with increasing Al content due to the combined effect of Burstien–Moss effect and bandgap renormalization.
Magnetostriction and anisotropy compensation in TbxDy0.9−xNd0.1Fe1.93 [0.2≤x≤0.4]
Authors: Jammalamadaka S Narayana , Markandeyulu G. , Balasubramaniam Krishnan
Published: December 2010

Structure and magnetostriction of TbxDy0.9−xNd0.1Fe1.93 (0.2≤x≤0.4) compounds are investigated. All the compounds are found to stabilize in MgCu2-type C15 cubic Laves phase structure. The easy magnetization direction changes from ⟨100⟩(x=0.2) to ⟨111⟩(x=0.3) through an intermediate state at x=0.25. Anisotropy compensation is realized near x=0.25 for the TbxDy0.9−xNd0.1Fe1.93 compounds. The Laves phase compound Tb0.4Dy0.5Nd0.1Fe1.93 has large spontaneous magnetostriction (1670×10−6) and a low anisotropy at room temperature which could make it a good candidate material for magnetostriction applications.
Fundamental oscillation of resonant tunneling diodes above 1 THz at room temperature
Authors: Suzuki Safumi , Asada Masahiro , Teranishi Atsushi , Sugiyama Hiroki , Yokoyama Haruki
Published: December 2010

Fundamental oscillations up to 1.04 THz were achieved in resonant tunneling diodes at room temperature. A graded emitter and thin barriers were introduced in GaInAs/AlAs double-barrier resonant tunneling diodes for reductions of the transit time in the collector depletion region and the resonant tunneling time, respectively. Output powers were 7 μW at 1.04 THz and around 10 μW in 0.9–1 THz region. A change in oscillation frequency of about 4% with bias voltage was also obtained.
Large group delay in a microwave metamaterial analog of electromagnetically induced transparency
Authors: Zhang Lei , Tassin Philippe , Koschny Thomas , Kurter Cihan , Anlage Steven M. , Soukoulis C. M.
Published: December 2010

We report on our experimental work concerning a planar metamaterial exhibiting classical electromagnetically induced transparency (EIT). Using a structure with two mirrored split-ring resonators as the dark element and a cut wire as the radiative element, we demonstrate that an EIT-like resonance can be achieved without breaking the symmetry of the structure. The mirror symmetry of the metamaterial’s structural element results in a selection rule inhibiting magnetic dipole radiation for the dark element, and the increased quality factor leads to low absorption (<10%) and large group index (of the order of 30).
Graphene growth by molecular beam epitaxy on the carbon-face of SiC
Authors: Moreau E. , Godey S. , Ferrer F. J. , Vignaud D. , Wallart X. , Avila J. , Asensio M. C. , Bournel F. , Gallet J.-J.
Published: December 2010

Graphene layers have been grown by molecular beam epitaxy (MBE) on the (0001¯) C-face of SiC and have been characterized by atomic force microscopy, low energy electron diffraction (LEED), and UV photoelectron spectroscopy. Contrary to the graphitization process, the step-terrace structure of SiC is fully preserved during the MBE growth. LEED patterns show multiple orientation domains which are characteristic of graphene on SiC (0001¯), indicating non-Bernal rotated graphene planes. Well-defined Dirac cones, typical of single-layer graphene, have been observed in the valence band for few graphene layers by synchrotron spectroscopy, confirming the electronic decoupling of graphene layers.
Band structures of graphene hexagonal lattice semiconductor quantum dots
Authors: Peng Juan , Li Shu-Shen
Published: December 2010

Electronic structures of coupled semiconductor quantum dots (QDs) arranged as graphene hexagonal lattice are studied theoretically using the tight-binding method. In our calculations, the electrons can hop to the third-nearest-neighbors, and the overlap matrix as well as the multicenter integral are taken into account. The novel two-dimensional Dirac-like electronic excitations in graphene are found in these artificial planar QD structures. The results provide the theoretical basis for searching Dirac fermions in QD materials and have great significance for investigating and making semiconductor QD devices.
Quantum growth of a metal/insulator system: Lead on sapphire
Authors: Hong Hawoong , Gray Aaron , Xu Ruqing , Zhang Longxiang , Chiang T.-C.
Published: December 2010

We report the observation of quantum growth behavior in a metal-on-insulator system. Using insulating substrates, with their large band gaps, should maximize quantum confinement effects. In a study of Pb film growth and thermal processing on sapphire, we have observed robust preferred island height selection over a wide thickness range—a hallmark of quantum confinement effects—up to 250 °C. By contrast, room temperature is the limit for Pb films prepared on Si(111). These results provide the evidence connecting the quantum growth behavior of overlayers with the substrate band gap.
Direct band Ge photoluminescence near 1.6 μm coupled to Ge-on-Si microdisk resonators
Authors: Shambat Gary , Cheng Szu-Lin , Lu Jesse , Nishi Yoshio , Vuckovic Jelena
Published: December 2010

We fabricate and optically characterize germanium microdisks formed out of epitaxial germanium grown on silicon. Resonators coupled to fiber tapers display clear whispering gallery modes in transmission and photoluminescence with quality factors limited by germanium’s material absorption. Continuous wave pumping of the cavities resulted in a dominant heating effect for the cavity modes in both transmission and photoluminescence. Pulsed optical pumping proved to be more effective in minimizing heating, but was not sufficient to observe material gain or lasing. We believe that significantly higher doping levels are critical in order to achieve lasing at reasonable pump conditions.
Perveance and ion bunch structure from a “compact, high-pressure” laser ion source
Authors: Yeates P. , Costello J. T. , Kennedy E. T.
Published: December 2010

The Dublin City University (DCU) laser ion source (LIS) is a “compact high-pressure” laser ion source utilizing a table top Q-switched laser. The DCU-LIS combines high laser fluence (F>4 kJ cm−2), high laser intensity (I>1011 W cm−2) with a short field free region (L=48 mm) and high source potential (Vext>40 kV) in order to offset recombination losses within the plasma and maximize the proportion of highly charged ions which are extracted from the plasma plume. Such a configuration also provides high peak currents (Ip>3 mA), high current densities (J>5 mA cm−2), and high charge states (Cu6+) in the extracted ion-bunch train. However, to obtain and utilize these parameter values in a high pressure LIS requires characterization and control of a number of processes related to ion dynamics and space charge effects on the extracted ions at the plasma plume-anode-extraction gap interface. Relevant issues include electric field distortion, Debye shielding, beam divergence, overfocusing, and perveance (P) in addition to current density profiles for the extracted ion beam. In this paper we focus on these issues and their impact on charge particle extraction and acceleration with a view to elucidating the parameter regimes within which the DCU-LIS performance envelope is optimal.
The fractal dimension of cell membrane correlates with its capacitance: A new fractal single-shell model
Authors: Wang Xujing , Becker Frederick F. , Gascoyne Peter R. C.
Published: December 2010

The scale-invariant property of the cytoplasmic membrane of biological cells is examined by applying the Minkowski–Bouligand method to digitized scanning electron microscopy images of the cell surface. The membrane is found to exhibit fractal behavior, and the derived fractal dimension gives a good description of its morphological complexity. Furthermore, we found that this fractal dimension correlates well with the specific membrane dielectric capacitance derived from the electrorotation measurements. Based on these findings, we propose a new fractal single-shell model to describe the dielectrics of mammalian cells, and compare it with the conventional single-shell model (SSM). We found that while both models fit with experimental data well, the new model is able to eliminate the discrepancy between the measured dielectric property of cells and that predicted by the SSM.
Materiality and Creative Production: The Case of the Mile End Neighborhood in Montréal
Authors: Rantisi Norma M , Leslie Deborah
Published: December 2010

Recent studies on the economic significance of creativity have emphasized the role that quality of life plays in attracting talent to cities. In these studies, quality of life is seen in terms of its role in enhancing consumption. In this paper we build on a corpus of literature that considers how quality of life attributes can enhance creative production. On the basis of a study of fashion and graphic designers in Montréal, we consider the role played by material factors, such as loft-style buildings, low-cost rents, mixed-use zoning, and public space, in nurturing and supporting creativity in one of Montréal's off-beat neighborhoods. We argue that these conditions cultivate creative production by enabling a set of artistic practices and diverse encounters.
Global Architects: Learning and Innovation through Communities and Constellations of Practice
Authors: Faulconbridge James R
Published: December 2010

It is surprising that, despite widespread interest in the cultural industries, few questions have been asked about the geographies of learning and innovation in architecture. Particularly relevant to global architects are debates about the way stretched relational spaces and ‘global’ communities of practice connect individuals, firms, and regions into networks of learning that ‘perforate’ scales. This paper seeks to apply such debates to the case of global architects and to examine the spatiality of the practices that allow learning and lead to innovation in their work. It is shown that global architects participate in ‘local’ communities of practice that rely on face-to-face interaction, talk, and ‘buzz’. These ‘local’ communities are also part of ‘global’ constellations of practice constructed by forms of circulation: in particular, travel by architects and the circulation of texts and images in the media, which facilitate learning through human–nonhuman interactions. It is, therefore, suggested that in order to more effectively analyse the geographies of learning and innovation—in architecture but also other industries—focus needs to fall on (1) the geography of talk/buzz and communities of practice; but also (2) the geography of human–nonhuman interactions that form constellations of practice. Such a focus reveals that apparently local communities of practice are more often than not connected into global spaces of learning and innovation through constellations of practice produced by nonhumans.
Behind the ‘Heathrow Hassle’: A Political and Cultural Economy of the Privatized Airport
Authors: McNeill Donald
Published: December 2010

I seek to specify the nature of the regulation and management of airport space, drawing on a case study of London Heathrow, and discuss the public and corporate discontent with the airport's owners and operators, BAA, over the condition of the airport. I examine the linkages between economic and organizational discourses of airport management and ownership, and the internal economy of (dis)organization that has underpinned Heathrow's poor image, aligning this with the highly leveraged and government-regulated financial regimes that BAA and Heathrow operate within. I argue that a detailed engagement with the political and cultural economy of the airport is required to understand the functioning of such significant strategic spaces within cities.
Performing Resistance? Re-Reading Practices of Urban Cycling on London's South Bank
Authors: Spinney Justin
Published: December 2010

Despite a burgeoning literature on mobilities in general and cycling in particular as a transport, leisure, and political practice, there remains a lack of research on cycling in pedestrian public spaces. There is, however, a substantial body of literature in relation to skateboarding in public spaces which with few exceptions theorises it as resistant to preexisting dominant design codes and social norms. Using the example of London's South Bank this paper focuses on the urban cycling practices of bike trials and BMX in order to illustrate that these practices are perhaps not as ‘resistant’ as previous accounts have argued. Whilst accounts of skateboarding have tended to draw upon a body–architecture dialectics and subcultural theory, using ethnographic methods this paper discusses the practice and reception of display, sociality, and authority inherent in these public performances. In doing so the paper demonstrates that these styles of riding largely perform the social and cultural norms enshrined in the redevelopment of the South Bank. The result is a performed reading of these practices and spaces which sees power as always becoming. In line with this, the paper also questions the logic of current strategies which seek to displace riders and skaters to peripheral ‘private’ skate parks based on an erroneous reading of such practices as always resistant.
Regional Well-Being in Tropical Queensland, Australia: Developing a Dissatisfaction Index to Inform Government Policy
Authors: Larson Silva
Published: December 2010

This paper investigates the perceived well-being of residents of two coastal rural areas located in the central part of the Great Barrier Reef region in Australia. Typically, well-being studies concentrate on collating data from respondents about their perceptions of levels of satisfaction on specific predetermined points. However, recording respondents' satisfactions with various contributors to their well-being does not provide researchers with an indication of how important those contributors are to the respondents. This paper presents an approach to the analysis of well-being that combines the perceived importance of the well-being factors with the reported levels of satisfaction with the factor, aggregated to a regional level. A total of 372 individuals were asked to comment on how satisfied they were with twenty-seven well-being factors from the domains of society, the natural environment, and the economy and services. The highest reported satisfaction rates were associated with family relations, family safety, family health, family education levels, and work (> 75%). Information about the perceived importance of the well-being factors was also recorded and combined with information about levels of satisfaction, thus creating an index of dissatisfaction—an index that allows one to identify an ‘action list’, or set of regional priorities that, if addressed by policy makers, has the potential to enhance regional well-being. Several high-scoring factors in the index, such as condition of the landscape and beaches and access to nature, came from the domain of the natural environment, indicating the importance of integrated approaches to well-being that also include environmental concerns.
Less and Less Favoured? Britain's Regions in the Energy Crunch
Authors: Jones Calvin
Published: December 2010

Recent pronouncements by the International Energy Agency suggest that the world faces a potentially very serious shortage of liquid oil in the next decade. Meanwhile, alternative sources of energy, fossil fuel or otherwise, are problematic for political, technical, or environmental reasons. This paper suggests that these developments may herald a fundamental change in the economic landscape—and one that will further widen the gap between wealthy and poor regions in the developed world, with poorer regions being very vulnerable to the difficulties associated with this change. The nature of the ‘energy crunch’ is presented, as are arguments that suggest the UK is less well prepared than other European competitors for increased energy costs and price volatility. The paper then presents data for GB regions, suggesting that upcoming energy challenges might herald an era of greater regional economic divergence.
Flood Perception and Mitigation: The Role of Severity, Agency, and Experience in the Purchase of Flood Protection, and the Communication of Flood Information
Authors: Soane Emma , Schubert Iljana , Challenor Peter , Lunn Rebecca , Narendran Sunitha , Pollard Simon
Published: December 2010

Protection of human life and property from flooding is a strategic priority in the UK. We examine how to encourage home owners to protect themselves and their residences. A model of factors that influence the decision to buy flood-protection devices is tested using survey data from 2109 home owners. The results show that the majority of respondents have not purchased domestic flood protection ( N = 1732; 82.1%). Purchase of flood-protection devices was influenced by age; perceived seriousness; and beliefs about, and trust in, the role of regulators in managing flooding. In younger respondents the perceived seriousness of the dangers of flooding acted as precursors and barriers to action depending on individual sense of responsibility and agency. The second part of the study examines responsiveness to information. Information about flooding alone was insufficient to promote behavioural change, particularly among people who had not experienced a flood or who believed that they were not in a flood zone. Implications for understanding flood protection, managing agency issues, and flood-communication campaigns are discussed.
Mobile Broadband Services and the Availability of Instant Access to Cyberspace
Authors: Kellerman Aharon
Published: December 2010

Recent developments and innovations in ICTs (information and communications technologies) and their wide and growing adoption have changed the status of cyberspace vis-à-vis physical space, as well as that of users of information and communications devices. The most important change concerning cyberspace has been its permanent and instant availability to users through broadband services, bringing about its integration with physical space, at least from the perspective of users. I attempt to highlight this change, its significance, and its potential implications. A short review of the literature on cyberspace as a spatial entity is followed by a presentation of the growing adoption of various mobile technologies for users of the Internet, and the rapidly growing mobile broadband traffic, notably of streaming information, coupled with extended mobile Internet uses, mainly for entertainment. These discussions will lead us to the suggestion of several implications of instantly accessed cyberspace by mobile broadband users—access which is available without location and time restrictions.
Identification of Everyday Objects on the Basis of Gaborized Outline Versions
Authors: Sassi Michaël , Vancleef Kathleen , Machilsen Bart , Panis Sven , Wagemans Johan
Published: December 2010

Using outlines derived from a widely used set of line drawings, we created stimuli geared towards the investigation of contour integration and texture segmentation using shapes of everyday objects. Each stimulus consisted of Gabor elements positioned and oriented curvilinearly along the outline of an object, embedded within a larger Gabor array of homogeneous density. We created six versions of the resulting Gaborized outline stimuli by varying the orientations of elements inside and outside the outline. Data from two experiments, in which participants attempted to identify the objects in the stimuli, provide norms for identifiability and name agreement, and show differences in identifiability between stimulus versions. While there was substantial variability between the individual objects in our stimulus set, further analyses suggest a number of stimulus properties which are generally predictive of identification performance. The stimuli and the accompanying normative data, both available on our website ( http://www.gestaltrevision.be/sources/gaboroutlines ), provide a useful tool to further investigate contour integration and texture segmentation in both normal and clinical populations, especially when top-down influences on these processes, such as the role of prior knowledge of familiar objects, are of main interest.
Recognition and Eye Movements with Partially Hidden Pictures of Faces and Cars in Different Orientations
Authors: Wade Nicholas J , Tatler Benjamin W
Published: December 2010

Inverted faces are more difficult to identify than upright ones. This even applies when pictures of faces are partially hidden in geometrical designs so that it takes some seconds to recognise them. Similar, though not as pronounced, orientation preferences apply to familiar objects. We compared the recognition times and patterns of eye movements for two sets of familiar symmetrical objects. Pictures of faces and of cars were embedded in patterns of concentric circles in order to render them difficult to recognise. They were presented in four orientations, at 90° intervals from upright. Two experiments were conducted with the same set of stimuli; experiment 1 required participants to respond in terms of faces or cars, and in experiment 2 responses were made to the orientation of the embedded image independently of its class. Upright faces were recognised more accurately and faster than those in other orientations; fixation durations were longer for upright faces even before recognition. These results applied to both experiments. Orientation effects for cars were not pronounced and distinctions between 90°, 180°, and 270° embedded images were not consistent; this was the case in both experiments.
The Reduction of the Effect of the Müller—Lyer Illusion on Saccade Amplitude by Classic Adaptation
Authors: Knox Paul C
Published: December 2010

The effect of Müller—Lyer stimuli on saccade amplitude varies across studies. One methodological difference between studies is stimulus display time; studies with long stimulus display times tend to report smaller effects than studies with short display times. Is it possible that long display times might provide conditions in which saccade adaption takes place? Five adult subjects were exposed to runs of the same illusion-inducing Müller—Lyer stimulus, presented for 1 s, interspersed with probe trials in which a point target was presented for 200 ms. While saccade amplitude was consistently larger with ‘in-configurations’ than with ‘out-configurations’ at the beginning of runs, amplitude declined over runs with the in-configuration. On average, it was constant in out-configuration runs. The net effect was a decline in the apparent effect size (in-amp - out-amp / out-amp) of the Müller—Lyer stimulus. Probe trial saccade amplitude increased in ‘out’ runs and decreased in ‘in’ runs. These effects were not present in control experiments, in which stimulus display time was 200 ms. One explanation for this pattern of results is that long stimulus presentation times allow for the generation of retinal error signals. This in turn leads to saccade adaptation, causing an underestimation of the effect of this type of stimulus on saccade amplitude.
Face-to-Face Coalition
Authors: Andrews Timothy J , Thompson Peter
Published: December 2010

The perception and recognition of familiar faces are thought to depend critically on an analysis of the internal features of the face. However, other studies have shown that combining highly familiar internal features with an inappropriate set of familiar external features produces a composite face whose identity is dominated by the external features. Here, we show that this illusion depends on the distinctiveness of the external features.
Mapping Emotion Category Boundaries Using a Visual Expectation Paradigm
Authors: Cheal Jenna L , Rutherford M D
Published: December 2010

Past research showing categorical perception of emotional facial expressions has relied on identification and discrimination tasks that require an explicit response via keypress. Here we report a new paradigm for investigating the category boundary of emotional facial expressions that, instead, relies on an implicit response—eye direction. Participants were trained to expect a target stimulus on a particular side of the monitor, predicted by an emotional expression on a face image. An eye-tracker then recorded eye movements of participants as they viewed novel intermediate facial-expression stimuli. Anticipatory eye movement was taken as evidence of categorisation. Results from two experiments suggest that this implicit method can be used to determine category boundaries, and that the boundaries found with this method are similar to those found with the keypress response.
Inverting Faces Does Not Abolish Cultural Diversity in Eye Movements
Authors: Rodger Helen , Kelly David J , Blais Caroline , Caldara Roberto
Published: December 2010

Face processing is widely understood to be a basic, universal visual function effortlessly achieved by people from all cultures and races. The remarkable recognition performance for faces is markedly and specifically affected by picture-plane inversion: the so-called face-inversion effect (FIE), a finding often used as evidence for face-specific mechanisms. However, it has recently been shown that culture shapes the way people deploy eye movements to extract information from faces. Interestingly, the comparable lack of experience with inverted faces across cultures offers a unique opportunity to establish the extent to which such cultural perceptual biases in eye movements are robust, but also to assess whether face-specific mechanisms are universally tuned. Here we monitored the eye movements of Western Caucasian (WC) and East Asian (EA) observers while they learned and recognised WC and EA inverted faces. Both groups of observers showed a comparable impairment in recognising inverted faces of both races. WC observers deployed a scattered inverted triangular scanpath with a bias towards the mouth, whereas EA observers uniformly extended the focus of their fixations from the centre towards the eyes. Overall, our data show that cultural perceptual differences in eye movements persist during the FIE, questioning the universality of face-processing mechanisms.
The role of fire in southern Scandinavian forests during the late Holocene
Authors: Bradshaw Richard H. W. , Lindbladh Matts , Hannon Gina E.
Published: December 2010

Charcoal fragments preserved in small, wet basins are used to characterise the fire regime of temperate and mixed boreal forest (hemiboreal) zones of southern Scandinavia during the last 3500 years. There was far less charcoal recorded from the temperate zone than the hemiboreal zone during the last 3500 years, yet the low temperate zone values showed a clear trend of continuous increase until 1500 AD, after which the values decreased sharply. The record from the hemiboreal region showed a greater temporal variability with far higher charcoal influx values than in the temperate zone. There were significant positive correlations between charcoal influx and Betula, Calluna and Pinus pollen abundance and negative correlations with pollen indicators of anthropogenic impact such as Rumex and Cerealia. Charcoal influx in the temperate zone showed a strong association with the period of major anthropogenic impact, whereas the hemiboreal data reacted more to climatic change. The temporal and spatial pattern of charcoal influx was only a minor explanatory factor for vegetation composition at a regional scale in southern Scandinavia. The fire return interval was often long and irregular in most of the region and anthropogenic factors such as grazing, mowing and establishment of arable fields were probably more important than fire as drivers of vegetation change.
Wildfires in boreal ecosystems: past, present and some emerging trends
Authors: Girardin Martin P. , Ali Adam A. , Hély Christelle
Published: December 2010

With the emergence of a new forest management paradigm based on the emulation of natural disturbance regimes, interest in fire-related studies has increased in the boreal forest management community. A key issue in this regard is the improvement of our understanding of the variability in past disturbances and its linkages with climate and ecosystems. The surge in research activity has further been exacerbated by the increasing awareness of climate change, which has already exposed boreal forests to greater fire risk in recent decades. It is anticipated that further warming and drying will further enhance fire frequency and area burned in many boreal forests. Better predictions of future fire activity will contribute to better long-term forest planning in managed boreal forests. The 12 papers presented in this special issue exemplify this increased research activity by bringing together studies from diverse disciplines and presenting the latest advances regarding methodological approaches for reconstruction and modelling of past, present and future fire activity. Here we aim to summarise, evaluate and set into context some of the new insights arising from these studies and also to discuss some considerations to be taken into account in future research activities.
Future dryness in the southwest US and the hydrology of the early 21st century drought
Authors: Cayan Daniel R. , Das Tapash , Pierce David W. , Barnett Tim P. , Tyree Mary , Gershunov Alexander
Published: December 2010

Recently the Southwest has experienced a spate of dryness, which presents a challenge to the sustainability of current water use by human and natural systems in the region. In the Colorado River Basin, the early 21st century drought has been the most extreme in over a century of Colorado River flows, and might occur in any given century with probability of only 60%. However, hydrological model runs from downscaled Intergovernmental Panel on Climate Change Fourth Assessment climate change simulations suggest that the region is likely to become drier and experience more severe droughts than this. In the latter half of the 21st century the models produced considerably greater drought activity, particularly in the Colorado River Basin, as judged from soil moisture anomalies and other hydrological measures. As in the historical record, most of the simulated extreme droughts build up and persist over many years. Durations of depleted soil moisture over the historical record ranged from 4 to 10 years, but in the 21st century simulations, some of the dry events persisted for 12 years or more. Summers during the observed early 21st century drought were remarkably warm, a feature also evident in many simulated droughts of the 21st century. These severe future droughts are aggravated by enhanced, globally warmed temperatures that reduce spring snowpack and late spring and summer soil moisture. As the climate continues to warm and soil moisture deficits accumulate beyond historical levels, the model simulations suggest that sustaining water supplies in parts of the Southwest will be a challenge.
Nucleosome-mediated cooperativity between transcription factors
Authors: Mirny Leonid A.
Published: December 2010

Cooperative binding of transcription factors (TFs) to promoters and other regulatory regions is essential for precise gene expression. The classical model of cooperativity requires direct interactions between TFs, thus constraining the arrangement of TF sites in regulatory regions. Recent genomic and functional studies, however, demonstrate a great deal of flexibility in such arrangements with variable distances, numbers of sites, and identities of TF sites located in cis-regulatory regions. Such flexibility is inconsistent with cooperativity by direct interactions between TFs. Here, we demonstrate that strong cooperativity among noninteracting TFs can be achieved by their competition with nucleosomes. We find that the mechanism of nucleosome-mediated cooperativity is analogous to cooperativity in another multimolecular complex: hemoglobin. This surprising analogy provides deep insights, with parallels between the heterotropic regulation of hemoglobin (e.g., the Bohr effect) and the roles of nucleosome-positioning sequences and chromatin modifications in gene expression. Nucleosome-mediated cooperativity is consistent with several experimental studies, is equally applicable to repressors and activators, allows substantial flexibility in and modularity of regulatory regions, and provides a rationale for a broad range of genomic and evolutionary observations. Striking parallels between cooperativity in hemoglobin and in transcriptional regulation point to a general mechanism that can be used in various biological systems.
Model of pediatric pituitary hormone deficiency separates the endocrine and neural functions of the LHX3 transcription factor in vivo
Authors: Colvin Stephanie C. , Malik Raleigh E. , Showalter Aaron D. , Sloop Kyle W. , Rhodes Simon J.
Published: December 2010

The etiology of most pediatric hormone deficiency diseases is poorly understood. Children with combined pituitary hormone deficiency (CPHD) have insufficient levels of multiple anterior pituitary hormones causing short stature, metabolic disease, pubertal failure, and often have associated nervous system symptoms. Mutations in developmental regulatory genes required for the specification of the hormone-secreting cell types of the pituitary gland underlie severe forms of CPHD. To better understand these diseases, we have created a unique mouse model of CPHD with a targeted knockin mutation (
Lhx3
W227ter), which is a model for the human
LHX3
W224ter disease. The
LHX3
gene encodes a LIM-homeodomain transcription factor, which has essential roles in pituitary and nervous system development in mammals. The introduced premature termination codon results in deletion of the carboxyl terminal region of the LHX3 protein, which is critical for pituitary gene activation. Mice that lack all LHX3 function do not survive beyond birth. By contrast, the homozygous
Lhx3
W227ter mice survive, but display marked dwarfism, thyroid disease, and female infertility. Importantly, the
Lhx3
W227ter mice have no apparent nervous system deficits. The
Lhx3
W227ter mouse model provides a unique array of hormone deficits and facilitates experimental approaches that are not feasible with human patients. These experiments demonstrate that the carboxyl terminus of the LHX3 transcription factor is not required for viability. More broadly, this study reveals that the in vivo actions of a transcription factor in different tissues are molecularly separable.
Dynamic self-assembly and control of microfluidic particle crystals
Authors: Lee Wonhee , Amini Hamed , Stone Howard A. , Di Carlo Dino
Published: December 2010

Engineered two-phase microfluidic systems have recently shown promise for computation, encryption, and biological processing. For many of these systems, complex control of dispersed-phase frequency and switching is enabled by nonlinearities associated with interfacial stresses. Introducing nonlinearity associated with fluid inertia has recently been identified as an easy to implement strategy to control two-phase (solid-liquid) microscale flows. By taking advantage of inertial effects we demonstrate controllable self-assembling particle systems, uncover dynamics suggesting a unique mechanism of dynamic self-assembly, and establish a framework for engineering microfluidic structures with the possibility of spatial frequency filtering. Focusing on the dynamics of the particle–particle interactions reveals a mechanism for the dynamic self-assembly process; inertial lift forces and a parabolic flow field act together to stabilize interparticle spacings that otherwise would diverge to infinity due to viscous disturbance flows. The interplay of the repulsive viscous interaction and inertial lift also allow us to design and implement microfluidic structures that irreversibly change interparticle spacing, similar to a low-pass filter. Although often not considered at the microscale, nonlinearity due to inertia can provide a platform for high-throughput passive control of particle positions in all directions, which will be useful for applications in flow cytometry, tissue engineering, and metamaterial synthesis.