bluuebunny/crossref_metadata_2025 huggingface dataset:
A corpus-based sociolinguistic study of amplifiers in British English
Authors: Xiao Richard , Tao Hongyin
Published: February 2008

Amplifiers such as ‘very’, ‘so’, ‘absolutely’ and ‘totally’ are a common type of intensifiers in the English language. While earlier studies have explored the meaning and grammar of amplifiers, as well as their connection with sociolinguistic variables, notably genre categories, few have explored extralinguistic parameters on the basis of substantive corpus data. In this article we use the British National Corpus (BNC), the largest balanced corpus of British English available today, to explore variations in the use of amplifiers in terms of a wide range of sociolinguistic variables. Specifically, we examine 33 amplifiers across the following dimensions: discourse mode and register, gender, age, education level, audience gender and age, as well as publication date. Our results paint a complex picture. Some tendencies are clear, for example, amplifiers are more common in speech than in writing, higher levels of education correlate positively with higher frequencies of use, and there is an overall decrease in the use of amplifiers over an intervening thirty year period. However, other areas merely defy simple generalizations. For example, gender differences between men and women vary from speaking to writing, so do the differences among individual amplifiers and among age groups. Our results raise interesting issues pertaining to both traditional sociolinguistic concerns and the emerging field of corpus linguistics.
The Guided Autobiography Method: A Learning Experience
Authors: Thornton James E.
Published: February 2008

This article discusses the proposition that learning is an unexplored feature of the guided autobiography method and its developmental exchange. Learning, conceptualized and explored as the embedded and embodied processes, is essential in narrative activities of the guided autobiography method leading to psychosocial development and growth in dynamic, temporary social groups. The article is organized in four sections and summary. The first section provides a brief overview of the guided autobiography method describing the interplay of learning and experiencing in temporary social groups. The second section offers a limited review on learning and experiencing as processes that are essential for development, growth, and change. The third section reviews the small group activities and the emergence of the “developmental exchange” in the guided autobiography method. Two theoretical constructs provide a conceptual foundation for the developmental exchange: a counterpart theory of aging as development and collaborative-situated group learning theory. The summary recaps the main ideas and issues that shape the guided autobiography method as learning and social experience using the theme, “Where to go from here.”
Genetic variants in IRF6 and the risk of facial clefts: single‐marker and haplotype‐based analyses in a population‐based case‐control study of facial clefts in Norway
Authors: Jugessur Astanand , Rahimov Fedik , Lie Rolv T. , Wilcox Allen J. , Gjessing Håkon K. , Nilsen Roy M. , Nguyen Truc Trung , Murray Jeffrey C.
Published: February 2008

Mutations in the gene encoding interferon regulatory factor 6 (IRF6) underlie a common form of syndromic clefting known as Van der Woude syndrome. Lip pits and missing teeth are the only additional features distinguishing the syndrome from isolated clefts. Van der Woude syndrome, therefore, provides an excellent model for studying the isolated forms of clefting. From a population‐based case‐control study of facial clefts in Norway (1996–2001), we selected 377 cleft lip with or without cleft palate (CL/P), 196 cleft palate only (CPO), and 763 control infant‐parent triads for analysis. We genotyped six single nucleotide polymorphisms within the IRF6 locus and estimated the relative risks (RR) conferred on the child by alleles and haplotypes of the child and of the mother. On the whole, there were strong statistical associations with CL/P but not CPO in our data. In single‐marker analyses, mothers with a double‐dose of the ‘a’‐allele at rs4844880 had an increased risk of having a child with CL/P (RR=1.85, 95% confidence interval: 1.04–3.25; P=0.036). An RR of 0.38 (95% confidence interval: 0.16–0.92; P=0.031) was obtained when the child carried a single‐dose of the ‘a’‐allele at rs2235371 (the p.V274I polymorphism). The P‐value for the overall test was <0.001. In haplotype analyses, several of the fetal and maternal haplotype relative risks were statistically significant individually but were not strong enough to show up on the overall test (P=0.113). Taken together, these findings further support a role for IRF6 variants in clefting of the lip and provide specific risk estimates in a Norwegian population. Genet. Epidemiol. 2008. © 2008 Wiley‐Liss, Inc.
Vibrational computing: Simulation of a full adder by optimal control
Authors: Bomble L. , Lauvergnat D. , Remacle F. , Desouter-Lecomte M.
Published: February 2008

Within the context of vibrational molecular quantum computing, we investigate the implementation of a full addition of two binary digits and a carry that provides the sum and the carry out. Four qubits are necessary and they are encoded into four different normal vibrational modes of a molecule. We choose the bromoacetyl chloride molecule because it possesses four bright infrared active modes. The ground and first excited states of each mode form the one-qubit computational basis set. Two approaches are proposed for the realization of the full addition. In the first one, we optimize a pulse that implements directly the entire addition by a single unitary transformation. In the second one, we decompose the full addition in elementary quantum gates, following a scheme proposed by Vedral et al. [Phys. Rev. A 54, 147 (1996)]. Four elementary quantum gates are necessary, two two-qubit CNOT gates (controlled NOT) and two three-qubit TOFFOLI gates (controlled-controlled NOT). All the logic operations consist in one-qubit flip. The logic implementation is therefore quasiclassical and the readout is based on a population analysis of the vibrational modes that does not take the phases into account. The fields are optimized by the multitarget extension of the optimal control theory involving all the transformations among the 24 qubit states. A single cycle of addition without considering the preparation or the measure or copy of the result can be carried out in a very competitive time, on a picosecond time scale.
Quantitative determination of linear and second-harmonic generation optical effective responses of achiral or chiral materials in planar structures: Theory and materials
Authors: Rodriguez Vincent
Published: February 2008

A theoretical formalism designed to quantify linear optical and second-order nonlinear optical responses of achiral or chiral anisotropic materials in planar structure is presented. In particular, the theory includes linear optical activity that is governed by the gyrotropic components and second-harmonic generation optical rotatory dispersion, the magnitude of which depends on the ratio of chiral and achiral χ(2) components. Examples are given which reproduce complex interference effects and other subtle optical effects that are encountered in layered structures. Detailed experimental second harmonic generation studies of quartz and dihydrogen phosphate that quantify linear and nonlinear optical activities of these materials are reported.
Temperature dependence of the electrical conductivity of imidazolium ionic liquids
Authors: Leys Jan , Wübbenhorst Michael , Preethy Menon Chirukandath , Rajesh Ravindran , Thoen Jan , Glorieux Christ , Nockemann Peter , Thijs Ben , Binnemans Koen , Longuemart Stéphane
Published: February 2008

The electrical conductivities of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids and of 1-hexyl-3-methylimidazolium ionic liquids with different anions were determined in the temperature range between 123 and 393K on the basis of dielectric measurements in the frequency range from 1to107Hz. Most of the ionic liquids form a glass and the conductivity values obey the Vogel-Fulcher-Tammann equation. The glass transition temperatures are increasing with increasing length of the alkyl chain. The fragility is weakly dependent on the alkyl chain length but is highly sensitive to the structure of the anion.
Nonequilibrium molecular dynamics simulations with a backward-forward trajectories sampling for multidimensional infrared spectroscopy of molecular vibrational modes
Authors: Hasegawa Taisuke , Tanimura Yoshitaka
Published: February 2008

A full molecular dynamics (MD) simulation approach to calculate multidimensional third-order infrared (IR) signals of molecular vibrational modes is proposed. Third-order IR spectroscopy involves three-time intervals between three excitation and one probe pulses. The nonequilibrium MD (NEMD) simulation allows us to calculate molecular dipoles from nonequilibrium MD trajectories for different pulse configurations and sequences. While the conventional NEMD approach utilizes MD trajectories started from the initial equilibrium state, our approach does from the intermediate state of the third-order optical process, which leads to the doorway-window decomposition of nonlinear response functions. The decomposition is made before the second pump excitation for a two-dimensional case of IR photon echo measurement, while it is made after the second pump excitation for a three-dimensional case of three-pulse IR photon echo measurement. We show that the three-dimensional IR signals are efficiently calculated by using the MD trajectories backward and forward in time for the doorway and window functions, respectively. We examined the capability of the present approach by evaluating the signals of two- and three-dimensional IR vibrational spectroscopies for liquid hydrogen fluoride. The calculated signals might be explained by anharmonic Brownian model with the linear-linear and square-linear system-bath couplings which was used to discuss the inhomogeneous broadening and dephasing mechanism of vibrational motions. The predicted intermolecular librational spectra clearly reveal the unusually narrow inhomogeneous linewidth due to the one-dimensional character of HF molecule and the strong hydrogen bond network.
Optical measurement of thermal transport in suspended carbon nanotubes
Authors: Hsu I-Kai , Kumar Rajay , Bushmaker Adam , Cronin Stephen B. , Pettes Michael T. , Shi Li , Brintlinger Todd , Fuhrer Michael S. , Cumings John
Published: February 2008

Thermal transport in carbon nanotubes is explored using different laser powers to heat suspended single-walled carbon nanotubes ∼5μm in length. The temperature change along the length of a nanotube is determined from the temperature-induced shifts in the G band Raman frequency. The spatial temperature profile reveals the ratio of the contact thermal resistance to the intrinsic thermal resistance of the nanotube. Moreover, the obtained temperature profiles allow differentiation between diffusive and ballistic phonon transport. Diffusive transport is observed in all nanotubes measured and the ratio of thermal contact resistance to intrinsic nanotube thermal resistance is found to range from 0.02 to 17.
Molecular simulation strategy for mechanical modeling of amorphous/porous low-dielectric constant materials
Authors: Yuan Cadmus A. , van der Sluis Olaf , Zhang G. Q. , Ernst Leo J. , van Driel Willem D. , Flower Amy E. , van Silfhout Richard B. R.
Published: February 2008

We propose an amorphous/porous molecular connection network generation algorithm for simulating the material stiffness of a low-k material (SiOC:H). Based on a given concentration of the basic building blocks, this algorithm will generate an approximate and large amorphous network. The molecular topology is obtained by distributing these blocks randomly into a predefined framework. Subsequently, a structural relaxation step including local and global perturbations is applied to achieve the most likely stereochemical structure. Thus, the obtained mechanical properties of the low-k materials have been verified with the experimental data.
High quality InAsSb grown on InP substrates using AlSb∕AlAsSb buffer layers
Authors: Wu Bing-Ruey , Liao Chichih , Cheng K. Y.
Published: February 2008

High quality InAsSb grown on semi-insulating InP substrates by molecular beam epitaxy was achieved using AlSb∕AlAsSb structure as the buffer layer. A 1000Å InAsSb layer grown on top of 1μm AlSb∕AlAsSb buffer layer showed a room temperature electron mobility of ∼12000cm2∕Vs. High structural quality and low misfit defect density were also demonstrated in the InAsSb layer. This novel AlSb∕AlAsSb buffer layer structure with the AlAsSb layer lattice matched to InP substrates could enhance the performance of optoelectronic devices utilizing 6.1Å family of compound semiconductor alloys.
Real-time detection of bacterial spores using coherent anti-Stokes Raman spectroscopy
Authors: Dogariu A. , Goltsov A. , Pestov D. , Sokolov A. V. , Scully M. O.
Published: February 2008

We demonstrate a realistic method for detection of anthrax-type spores in real time based on their chemical fingerprints using coherent anti-Stokes Raman scattering. Specifically, we demonstrate that coherent Raman scattering can be used to successfully identify spores with high accuracy and high selectivity in less than 50ms.
Three envelope approach for ultrafast pulse characterization in a pump-probe experiment
Authors: Yellampalle Balakishore , Chia Elbert E. M. , Kim Kiyong , Taylor Antoinette J. , Averitt Richard
Published: February 2008

We demonstrate an approach for the complete characterization of temporally identical ultrashort pulses at the focal point in a pump-probe experiment for potential use of pump-probe data deconvolution. Our approach uses three envelope measurements, autocorrelation, fundamental, and second harmonic spectra, combined with an error minimization pulse retrieval scheme. The three envelope approach is suitable when the measured envelopes have low noise and minimal systematic errors.
Pumped pure spin current and shot noise spectra in a two-level Rashba dot
Authors: Lü Hai-Feng , Guo Yong
Published: February 2008

The authors analyze theoretically the pumped spin current and current noise spectra in a two-level Rashba dot connected to two ferromagnetic electrodes with parallel magnetic configuration. It is found that the interlevel spin flips induced by the Rashba spin-orbit interaction can generate a pure spin current, whose strength is determined by both the energy spacing between two levels and the spin-flip strength. It is further pointed out that the total charge current noise at a finite bias voltage can be used to determine whether the pumped current is a pure spin type or not.
Analytical-statistical model to accurately estimate diffusional nanoparticle deposition on inverted surfaces at low pressure
Authors: Asbach Christof , Stahlmecke Burkhard , Fissan Heinz , Kuhlbusch Thomas A. J. , Wang Jing , Pui David Y. H.
Published: February 2008

Particle contamination is a major concern in clean manufacturing. We present a model that predicts the diffusional particle contamination probability on inverted surfaces under the influence of gravity and thermophoresis at low pressure level. The model follows an analytical-statistical approach that can be solved using common spreadsheet software; therefore, not requiring major computational resources. The model revealed that thermophoresis can effectively eliminate diffusional deposition. Assuming that a contamination probability of 0.1% is acceptable, a thermal gradient of 10K∕cm protects against the deposition of all particles ⩾30nm with an initial distance of 1mm or more.
Enhancement in magnetoelectric response in CoFe2O4–BaTiO3 heterostructure
Authors: Zhang Yi , Deng Chaoyong , Ma Jing , Lin Yuanhua , Nan Ce-Wen
Published: February 2008

Co Fe 2 O 4 – Ba Ti O 3 heterostructure was epitaxially grown on the (001)-SrTiO3 substrate via pulsed laser deposition, in which the bottom BaTiO3 layer epitaxially grown on the substrate acts as a buffer layer and effectively reduces the coherent constraint in the magnetic layer arising from the substrate. Microstructure studies from x-ray diffraction and electron microscopies showed good coherent epitaxy thin films of the (001)-CoFe2O4 and (001)-BaTiO3 on the substrate, which exhibits simultaneously strong ferroelectric and ferromagnetic responses. An obvious direct magnetoelectric coupling effect was observed in the thin films, which shows an enhancement compared to previous NiFe2O4–BaTiO3 heterostructures.
Wavelength dependent phase locking in quantum cascade laser Y-junctions
Authors: Hoffmann L. K. , Hurni C. A. , Schartner S. , Mujagić E. , Andrews A. M. , Klang P. , Schrenk W. , Semtsiv M. P. , Masselink W. T. , Strasser G.
Published: February 2008

Midinfrared quantum cascade lasers with monolithically integrated Y-junctions are investigated. Two different emission wavelengths of 10.5 and 4.2μm were realized in two different material systems, lattice-matched GaAs∕AlGaAs on GaAs and strain-compensated InGaAs∕InAlAs∕AlAs on InP. With identical Y-junction dimensions, phase locking is observed in both structures. In GaAs based devices, fundamental lateral modes are present in the coupled waveguides, which are coherently synchronized at the Y-junction. In InP based devices, modes of higher order are excited, which originate from coupling. The generation of multiple modes yields an out-of-phase fraction which reduces the level of coherence.
Half-metallic electronic structures of quaternary ferromagnetic chalcospinels: CdxCu1−xCr2S4 and CdxCu1−xCr2Se4
Authors: Wang Y.-H. A. , Gupta A. , Chshiev M. , Butler W. H.
Published: February 2008

First-principles calculations indicate that the chalcogenide spinels CdxCu1−xCr2S4 and CdxCu1−xCr2Se4 can be ferromagnetic metals, half-metals, or semiconductors depending on the Cd concentration x. In particular, CdxCu1−xCr2S4 can be tuned to be effectively half-metallic for x values between 0.25 and 0.875 and CdxCu1−xCr2Se4 can be half-metallic for x between 0.625 and 0.875. For x<0.25 for CdxCu1−xCr2S4 and for x<0.625 for CdxCu1−xCr2Se4, these materials are predicted to be ferromagnetic metals. For x>0.875 both systems are predicted to be ferromagnetic semiconductors.
Epitaxial (001) BiFeO3 membranes with substantially reduced fatigue and leakage
Authors: Jang H. W. , Baek S. H. , Ortiz D. , Folkman C. M. , Eom C. B. , Chu Y. H. , Shafer P. , Ramesh R. , Vaithyanathan V. , Schlom D. G.
Published: February 2008

We report substantially reduced fatigue and electrical leakage in BiFeO3 membranes fabricated by releasing epitaxial (001) BiFeO3 films from the Si substrates on which they were grown. Fatigue-free switching behavior of up to 1010cycles was observed for BiFeO3 membranes with Pt top electrodes, while as-grown films break down at ∼109cycles. This is attributed to the low coercive field of BiFeO3 membranes and their being free from substrate clamping. In contrast, (111) BiFeO3 films exhibit significant fatigue at the same electric field. Epitaxial (001) BiFeO3 membranes with low coercive field are very promising for lead-free ferroelectric memory and magnetoelectric devices.
Electroless nickel/gold Ohmic contacts to p-type GaN
Authors: Lewis L. , Casey D. P. , Jeyaseelan A. V. , Rohan J. F. , Maaskant P. P.
Published: February 2008

A solution based approach to forming Ohmic contacts to p-type GaN is described. Electroless plated Ni∕Au contacts are shown to compare favorably with traditional evaporated contacts, with contact resistivities ρc in the region of 10−2Ωcm2. These values are readily achieved after a rapid thermal annealing in an O2 atmosphere. The tunneling nature of the contact is confirmed via temperature dependant measurements. X-ray diffraction measurements confirm the similarity between evaporated and plated contacts. Current-photocurrent (I-L) and current-voltage (I-V) measurements from light emitting diodes formed using an electroless p-type contact are shown. Electroless deposition of the contact metals allows for a reduction in processing time and cost.
Suppression of exciton annihilation at high current densities in organic light-emitting diode resulting from energy-level alignments of carrier transport layers
Authors: Matsushima Toshinori , Adachi Chihaya
Published: February 2008

We manufactured an organic light-emitting diode (OLED) in which the hole and electron transport layers are chemically doped with p- and n-type dopants and energy levels in between neighboring carrier transport layers and emitting molecules are aligned. From the results of the electroluminescence (EL) characteristics of the OLED, we found that (1) the OLED has an extremely low driving voltage of 2.65±0.050.05V at a current density of 100mA∕cm2; (2) the onset voltage of EL (≈2.4V) corresponds to the photon energy of emitting molecules (≈2.5eV), while the onset voltage of currents is ≈1.8V; and (3) a decrease in EL efficiency at high current densities can be suppressed by matching the energy levels.
Ytterbium-doped solid core photonic bandgap fiber for laser operation around 980nm
Authors: Pureur V. , Bigot L. , Bouwmans G. , Quiquempois Y. , Douay M. , Jaouen Y.
Published: February 2008

We report on the design and characterization of an ytterbium-doped solid core photonic bandgap fiber laser operating at 977nm. By adjusting the fiber optogeometrical parameters, we favored laser gain in the three level configuration thanks to the introduction of bandgap losses in the wavelength range above 1000nm; avoiding thus laser operation in the four level configuration. A slope efficiency of η∼65% has been obtained for a 99%–4% laser cavity.
Optically induced ultrafast quenching of the semiconductor quantum well luminescence
Authors: Amo A. , Ballarini D. , Sanvitto D. , Kozhemyakina E. , Viña L. , Lemaître A. , Bajoni D. , Bloch J.
Published: February 2008

We present an experimental configuration that enables the ultrafast, transient quenching of the excitonic photoluminescence in quantum wells. Our scheme is based on two, delayed, short pulses experiment. A first pulse excites carriers in the system, while a second pulse induces an ultrafast redistribution of excitons that results in abrupt dips in the photoluminescence. We present a model that quantitatively accounts for the measured dip depth. The magnitude of the dip, determined by the temperature change of the carriers, can be controlled by varying the power and delay of the second pulse.
Two-photon energy transfer enhanced three-dimensional optical memory in quantum-dot and azo-dye doped polymers
Authors: Li Xiangping , Chon James W. M. , Evans Richard A. , Gu Min
Published: February 2008

A three-dimensional bit-by-bit optical memory system in quantum-dot and azo-dye doped polymers is demonstrated in this paper. It is shown that two-photon absorption can be used to excite resonance energy transfer from luminescent CdS quantum dots to azo-dye molecules. As a result, the isomerization of azo-dye molecules leads to a pronounced refractive index change. This two-photon-excited energy transfer process in the quantum-dot and azo-dye polymer not only allows for high efficient multilayer information recording into the volume of thick samples but also offers a refractive index window for readout.
Nonpolar GaN-based microcavity using AlN∕GaN distributed Bragg reflector
Authors: Zhu T. , Dussaigne A. , Christmann G. , Pinquier C. , Feltin E. , Martin D. , Butté R. , Grandjean N.
Published: February 2008

Nonpolar GaN based microcavity (MC) made of a bottom AlN∕GaN distributed Bragg reflector (DBR) and a top dielectric SiO2∕SiNx DBR has been fabricated on a-plane GaN template. The 13 pair AlN∕GaN DBR, centered around 372nm, exhibits a peak reflectivity of ∼95% together with a flat stopband of 30nm width. The cavity mode centered around 390nm is characterized by a full width at half maximum of 4nm. The optical properties of both the DBR and MC are well reproduced when accounting for linear birefringence effects.
Broadband moth-eye antireflection coatings on silicon
Authors: Sun Chih-Hung , Jiang Peng , Jiang Bin
Published: February 2008

We report a bioinspired templating technique for fabricating broadband antireflection coatings that mimic antireflective moth eyes. Wafer-scale, subwavelength-structured nipple arrays are directly patterned on silicon using spin-coated silica colloidal monolayers as etching masks. The templated gratings exhibit excellent broadband antireflection properties and the normal-incidence specular reflection matches with the theoretical prediction using a rigorous coupled-wave analysis (RCWA) model. We further demonstrate that two common simulation methods, RCWA and thin-film multilayer models, generate almost identical prediction for the templated nipple arrays. This simple bottom-up technique is compatible with standard microfabrication, promising for reducing the manufacturing cost of crystalline silicon solar cells.
Negative differential mobility in GaAs at ultrahigh fields: Comparison between an experiment and simulations
Authors: Vainshtein Sergey , Yuferev Valentin , Palankovski Vassil , Ong Duu-Sheng , Kostamovaara Juha
Published: February 2008

Direct measurement of the electron velocity vn at an extreme electric field E is problematic due to impact ionization. The dependence vn(E) obtained by a Monte Carlo method can be verified, however, by comparing simulated and experimental data on superfast switching in a GaAs bipolar transistor structure, in which the switching transient is very sensitive to this dependence at high electric fields (up to 0.6MV∕cm). Such a comparison allows the conclusion to be made that the change from negative to positive differential mobility predicted earlier at E∼0.3MV∕cm should not happen until the electric field exceeds 0.6MV∕cm.
High performance polythiophene thin-film transistors doped with very small amounts of an electron acceptor
Authors: Ma Liang , Lee Wi Hyoung , Park Yeong Don , Kim Jong Soo , Lee Hwa Sung , Cho Kilwon
Published: February 2008

The relationship between the electrical properties and the microstructure of poly(3-hexylthiophene) (P3HT) films doped with an electron acceptor, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) has been studied. The introduction of F4-TCNQ in very small quantities improved the device performance of P3HT thin-film transistors significantly. The field-effect mobility of a device doped with only 0.2wt% F4-TCNQ was enhanced by a factor of 30 with respect to that of a pure P3HT device. The threshold voltages of the P3HT thin-film transistors can also be controlled by adjusting the F4-TCNQ concentration. These improvements are attributed to the doping-induced formation of charge-transfer complexes and improved molecular orientation of the P3HT.
Study of the wetting layer of InAs∕GaAs nanorings grown by droplet epitaxy
Authors: Zhao C. , Chen Y. H. , Xu B. , Tang C. G. , Wang Z. G. , Ding F.
Published: February 2008

The properties of the wetting layer (WL) of InAs nanorings grown by droplet epitaxy have been studied. The heavy-hole (HH) and light-hole (LH) related transitions of the In(Ga)As WL were observed by reflectance difference spectroscopy. From the temperature dependent photoluminescence behavior of InAs rings, the channel for carriers to redistribute was found to be the compressed GaAs instead of the In(Ga)As layer, which strongly indicated that the wetting layer was depleted around the rings. Futhermore, a complex evolution of the WL with In deposition amount has been observed.
Spatial distribution of crown shaped light emission from a periodic inverted polygonal deflector embedded in an InGaN∕GaN light emitting diode
Authors: Kim Hyung Gu , Cuong Tran Viet , Jeong Hyun , Woo Seung Hee , Cha Ok Hwan , Suh Eun-Kyung , Hong Chang-Hee , Cho Hyung Koun , Kong Bo Hyun , Jeong Mun Seok
Published: February 2008

We investigated spatial light emission from a periodic inverted polygonal deflector, which included six {10-1-1} facets and six {11-2-2} facets embedded in an InGaN∕GaN light emitting diode by using confocal scanning electroluminescence microscopy. We found a noticeable crown shape with the contrast of luminescence intensity and wavelength observed on these facets mainly due to the variation of growth rate for the InGaN quantum wells. In addition, a very low intensity and blueshifted emission wavelength on the {11-2-2} facets indicated the deficiency of indium incorporation and/or much thinner well thickness as compared to that of the {10-1-1} facets.
Nanometer thick single crystal Y2O3 films epitaxially grown on Si (111) with structures approaching perfection
Authors: Nieh C. W. , Lee Y. J. , Lee W. C. , Yang Z. K. , Kortan A. R. , Hong M. , Kwo J. , Hsu C.-H.
Published: February 2008

Cubic phase Y2O3 films 1.6–10nm thick of excellent quality have been epitaxially grown on Si (111) with Y2O3(111)∥Si(111) using electron beam evaporation of Y2O3 in ultrahigh vacuum. Structural and morphological studies were carried out by x-ray scattering and reflectivity and high-resolution transmission electron microscopy, with the growth being in situ monitored by reflection high energy electron diffraction. There are two Y2O3 domains in the initial stage of the oxide growth with equal population, and the B-type domain of Y2O3[21¯1¯]∥Si[112¯] becomes predominating over the A-type domain of Y2O3[21¯1¯]∥Si[21¯1¯] with increasing film thickness. Besides the excellent crystallinity of the films as derived from the small ω-rocking curve width of 0.014°, our results also show atomically sharp smooth surface and interfaces.
Compliance of a microfibril subjected to shear and normal loads
Authors: Liu Jingzhou , Hui Chung-Yuen , Shen Lulin , Jagota Anand
Published: February 2008

Many synthetic bio-inspired adhesives consist of an array of microfibrils attached to an elastic backing layer, resulting in a tough and compliant structure. The surface region is usually subjected to large and nonlinear deformations during contact with an indenter, leading to a strongly nonlinear response. In order to understand the compliance of the fibrillar regions, we examine the nonlinear deformation of a single fibril subjected to a combination of shear and normal loads. An exact closed-form solution is obtained using elliptic functions. The prediction of our model compares well with the results of an indentation experiment.
Oxygen mass transfer in a model three-dimensional artery
Authors: Coppola G , Caro C
Published: February 2008

Arterial geometry is commonly non-planar and associated with swirling blood flow. In this study, we examine the effect of arterial three-dimensionality on the distribution of wall shear stress (WSS) and the mass transfer of oxygen from the blood to the vessel wall in a U-bend, by modelling the blood vessels as either cylindrical or helical conduits. The results show that under physiological flow conditions, three-dimensionality can reduce both the range and extent of low WSS regions and substantially increase oxygen flux through the walls. The Sherwood number and WSS distributions between the three-dimensional helical model and a human coronary artery show remarkable qualitative agreement, implying that coronary arteries may potentially be described with a relatively simple idealized three-dimensional model, characterized by a small number of well-defined geometric parameters. The flow pattern downstream of a planar bend results in separation of the
Sh
number and WSS effects, a finding that implies means of investigating them individually.
Analysis of the sensitivity properties of a model of vector-borne bubonic plague
Authors: Buzby Megan , Neckels David , Antolin Michael F , Estep Donald
Published: February 2008

Model sensitivity is a key to evaluation of mathematical models in ecology and evolution, especially in complex models with numerous parameters. In this paper, we use some recently developed methods for sensitivity analysis to study the parameter sensitivity of a model of vector-borne bubonic plague in a rodent population proposed by Keeling & Gilligan. The new sensitivity tools are based on a variational analysis involving the adjoint equation. The new approach provides a relatively inexpensive way to obtain derivative information about model output with respect to parameters. We use this approach to determine the sensitivity of a quantity of interest (the force of infection from rats and their fleas to humans) to various model parameters, determine a region over which linearization at a specific parameter reference point is valid, develop a global picture of the output surface, and search for maxima and minima in a given region in the parameter space.
Cubic membranes: a structure-based design for DNA uptake
Authors: Almsherqi Zakaria , Hyde Stephen , Ramachandran Malarmathy , Deng Yuru
Published: February 2008

Cubic membranes are soft three-dimensional crystals found within cell organelles in a variety of living systems, despite the aphorism of Fedorov: ‘crystallization is death’. They consist of multi-bilayer lipid–protein stacks, folded onto anticlastic surfaces that resemble triply periodic minimal surfaces, forming highly swollen crystalline sponges. Although cubic membranes have been observed in numerous cell types and under different pathophysiological conditions, knowledge about the formation and potential function(s) of non-lamellar, cubic structures in biological systems is scarce. We report that mitochondria with this cubic membrane organization isolated from starved amoeba
Chaos carolinense
interact sufficiently with short segments of phosphorothioate oligonucleotides (PS-ODNs) to give significant ODNs uptake. ODNs condensed within the convoluted channels of cubic membrane by an unknown passive targeting mechanism. Moreover, the interaction between ODNs and cubic membrane is sufficient to retard electrophoretic mobility of the ODN component in the gel matrix. These ODN–cubic membrane complexes are readily internalized within the cytoplasm of cultured mammalian cells. Transmission electron microscopic analysis confirms ODNs uptake by cubic membranes and internalization of ODN–cubic membrane complexes into the culture cells. Cubic membranes thus may offer a new, potentially benign medium for gene transfection.
Spatio-temporal information in an artificial olfactory mucosa
Authors: Sánchez-Montañés Manuel A , Gardner Julian W , Pearce Timothy C
Published: February 2008

Deploying chemosensor arrays in close proximity to stationary phases imposes stimulus-dependent spatio-temporal dynamics on their response and leads to improvements in complex odour discrimination. These spatio-temporal dynamics need to be taken into account explicitly when considering the detection performance of this new odour sensing technology, termed an artificial olfactory mucosa. For this purpose, we develop here a new measure of spatio-temporal information that combined with an analytical model of the artificial mucosa, chemosensor and noise dynamics completely characterizes the discrimination capability of the system. This spatio-temporal information measure allows us to quantify the contribution of both space and time to discrimination performance and may be used as part of optimization studies or calculated directly from an artificial mucosa output. Our formal analysis shows that exploiting both space and time in the mucosa response always outperforms the use of space alone and is further demonstrated by comparing the spatial versus spatio-temporal information content of mucosa experimental data. Together, the combination of the spatio-temporal information measure and the analytical model can be applied to extract the general principles of the artificial mucosa design as well as to optimize the physical and operating parameters that determine discrimination performance.
On the geodesic property of strain field patterns in elastoplastic composites
Authors: Jeulin Dominique , Li Wei , Ostoja-Starzewski Martin
Published: February 2008

Under study is the geodesic (i.e. shortest path) character of strain fields occurring in inelastic response of matrix-inclusion composites. The spatially random morphology of composites is created by generating the inclusions centres through a sequential inhibition process based on a planar Poisson point field preventing any disc overlaps. Both phases (inclusions and matrix) are elastic–plastic hardening with the matrix being more compliant and weaker than the inclusions, and perfect bonding holding everywhere, so that the plastic flow occurs between the inclusions. A quantitative comparison of a response pattern obtained by computational mechanics with that found only by mathematical morphology indicates that (i) the regions of plastic flow are close (or even very close) to geodesics and (ii) a purely geometric (and orders of magnitude more rapid than by computational mechanics) assessment of these regions is possible.
A computationally efficient estimator for mutual information
Authors: Evans Dafydd
Published: February 2008

Mutual information quantifies the determinism that exists in a relationship between random variables, and thus plays an important role in exploratory data analysis. We investigate a class of non-parametric estimators for mutual information, based on the nearest neighbour structure of observations in both the joint and marginal spaces. Unless both marginal spaces are one-dimensional, we demonstrate that a well-known estimator of this type can be computationally expensive under certain conditions, and propose a computationally efficient alternative that has a time complexity of order

(
N
 log 
N
) as the number of observations
N
→∞.
Breakdown and delayed cospeciation in the arbuscular mycorrhizal mutualism
Authors: Merckx Vincent , Bidartondo Martin I
Published: February 2008

The ancient arbuscular mycorrhizal association between the vast majority of plants and the fungal phylum Glomeromycota is a dominant nutritional mutualism worldwide. In the mycorrhizal mutualism, plants exchange photosynthesized carbohydrates for mineral nutrients acquired by fungi from the soil. This widespread cooperative arrangement is broken by ‘cheater’ plant species that lack the ability to photosynthesize and thus become dependent upon three-partite linkages (cheater–fungus–photosynthetic plant). Using the first fine-level coevolutionary analysis of mycorrhizas, we show that extreme fidelity towards fungi has led cheater plants to lengthy evolutionary codiversification. Remarkably, the plants' evolutionary history closely mirrors that of their considerably older mycorrhizal fungi. This demonstrates that one of the most diffuse mutualistic networks is vulnerable to the emergence, persistence and speciation of highly specific cheaters.
No effect of blue on winning contests in judo
Authors: Dijkstra Peter D , Preenen Paul T.Y
Published: February 2008

A study by Rowe
et al
. reported a winning bias for judo athletes wearing a blue outfit relative to those wearing a white one during the 2004 Olympics. It was suggested that blue is associated with a higher likelihood of winning through differential effects of colour on opponent visibility and/or an intimidating effect on the opponent. However, we argue that there is no colour effect on winning in judo. We show that alternative factors, namely allocation biases, asymmetries in prior experience and differences in recovery time are possible confounding factors in the analysis of Rowe
et al
. After controlling for these factors, we found no difference in blue and white wins. We further analysed contest outcomes of 71 other major judo tournaments and also found no winning bias. Our findings have implications for sports policy makers: they suggest that a white–blue outfit pairing ensures an equal level of play.
Species–genus ratios reflect a global history of diversification and range expansion in marine bivalves
Authors: Krug Andrew Z , Jablonski David , Valentine James W
Published: February 2008

The distribution of marine bivalve species among genera and higher taxa takes the form of the classic hollow curve, wherein few lineages are species rich and many are species poor. The distribution of species among genera (S/G ratio) varies with latitude, with temperate S/G's falling within the null expectation, and tropical and polar S/G's exceeding it. Here, we test several hypotheses for this polar overdominance in the species richness of small numbers of genera. We find a significant positive correlation between the latitudinal range of a genus and its species richness, both globally and within regions. Genus age and species richness are also positively related, but this relationship breaks down when the analysis is limited to genera endemic to climate zones or with narrow latitudinal ranges. The data suggest a link between speciation and range-expansion, with genera expanding out of the tropical latitudinal bins tending to speciate more prolifically, both globally and regionally. These genera contain more species within climate zones than taxa endemic to that zone. Range expansion thus appears to be fundamentally coupled with speciation, producing the skewed distribution of species among genera, both globally and regionally, whereas clade longevity is achieved through extinction—resistance conferred by broad geographical ranges.
A junk-food hypothesis for gannets feeding on fishery waste
Authors: Grémillet David , Pichegru Lorien , Kuntz Grégoire , Woakes Anthony G , Wilkinson Sarah , Crawford Robert J.M , Ryan Peter G
Published: February 2008

Worldwide fisheries generate large volumes of fishery waste and it is often assumed that this additional food is beneficial to populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape gannetsMorus capensisand of their feeding environment in the Benguela upwelling zone. The natural prey of Cape gannets (pelagic fishes) is depleted and birds now feed extensively on fishery wastes. These are beneficial to non-breeding birds, which show reduced feeding effort and high survival. By contrast, breeding gannets double their diving effort in an attempt to provision their chicks predominantly with high-quality, live pelagic fishes. Owing to a scarcity of this resource, they fail and most chicks die. Our study supports the junk-food hypothesis for Cape gannets since it shows that non-breeding birds can survive when complementing their diet with fishery wastes, but that they struggle to reproduce if live prey is scarce. This is due to the negative impact of low-quality fishery wastes on the growth patterns of gannet chicks. Marine management policies should not assume that fishery waste is generally beneficial to scavenging seabirds and that an abundance of this artificial resource will automatically inflate their populations.
Long-term fitness benefits of polyandry in a small mammal, the bank voleClethrionomys glareolus
Authors: Klemme Ines , Ylönen Hannu , Eccard Jana Anja
Published: February 2008

Polyandry, i.e. mating with multiple males within one reproductive event, is a common female mating strategy but its adaptive function is often unclear. We tested whether polyandrous females gain genetic benefits by comparing fitness traits of monandrous (mated twice with a single male) and polyandrous (mated twice with two different males) female bank volesClethrionomys glareolus. We raised the offspring in the laboratory until adulthood and measured their body size, before releasing them to outdoor enclosures to overwinter. At the onset of the breeding season in the following spring, we found that offspring of polyandrous females performed significantly better at reproduction than those of monandrous females. This was mainly due to sons of polyandrous females producing significantly more offspring than those of monandrous females. No significant differences were found for offspring body mass or winter survival between the two treatments. Our results appear to provide evidence that bank vole females gain long-term benefits from polyandry.
Fire-mediated dieback and compositional cascade in an Amazonian forest
Authors: Barlow Jos , Peres Carlos A
Published: February 2008

The only fully coupled land–atmosphere global climate model predicts a widespread dieback of Amazonian forest cover through reduced precipitation. Although these predictions are controversial, the structural and compositional resilience of Amazonian forests may also have been overestimated, as current vegetation models fail to consider the potential role of fire in the degradation of forest ecosystems. We examine forest structure and composition in the Arapiuns River basin in the central Brazilian Amazon, evaluating post-fire forest recovery and the consequences of recurrent fires for the patterns of dominance of tree species. We surveyed tree plots in unburned and once-burned forests examined 1, 3 and 9 years after an unprecedented fire event, in twice-burned forests examined 3 and 9 years after fire and in thrice-burned forests examined 5 years after the most recent fire event. The number of trees recorded in unburned primary forest control plots was stable over time. However, in both once- and twice-burned forest plots, there was a marked recruitment into the 10–20 cm diameter at breast height tree size classes between 3 and 9 years post-fire. Considering tree assemblage composition 9 years after the first fire contact, we observed (i) a clear pattern of community turnover among small trees and the most abundant shrubs and saplings, and (ii) that species that were common in any of the four burn treatments (unburned, once-, twice- and thrice-burned) were often rare or entirely absent in other burn treatments. We conclude that episodic wildfires can lead to drastic changes in forest structure and composition, with cascading shifts in forest composition following each additional fire event. Finally, we use these results to evaluate the validity of the savannization paradigm.
Observed change of the standardized precipitation index, its potential cause and implications to future climate change in the Amazon region
Authors: Li Wenhong , Fu Rong , Juárez Robinson I. Negrón , Fernandes Katia
Published: February 2008

Observations show that the standard precipitation index (SPI) over the southern Amazon region decreased in the period of 1970–1999 by 0.32 per decade, indicating an increase in dry conditions. Simulations of constant pre-industrial climate with recent climate models indicate a low probability (
p
=0%) that the trends are due to internal climate variability. When the 23 models are forced with either anthropogenic factors or both anthropogenic and external natural factors, approximately 13% of sampled 30-year SPI trends from the models are found to be within the range of the observed SPI trend at 95% confidence level. This suggests a possibility of anthropogenic and external forcing of climate change in the southern Amazon. On average, the models project no changes in the frequency of occurrence of low SPI values in the future; however, those models which produce more realistic SPI climatology, variability and trend over the period 1970–1999 show more of a tendency towards more negative values of SPI in the future. The analysis presented here suggests a potential anthropogenic influence on Amazon drying, which warrants future, more in-depth, study.
Navigating Amazonia under uncertainty: past, present and future environmental governance
Authors: Boyd Emily
Published: February 2008

One of the major environmental challenges of the twenty-first century is the continued rapid deforestation of Amazonia. The 2005 dieback crisis emphasizes the unprecedented challenges facing Brazil. The examination of past and present institutions for ecosystem management, in Amazonia, shows structural barriers across public, private and community arrangements. The adaptive governance concept helps to understand why these institutions are failing to deliver sustainable futures. In looking forward, it is encouraging to see that important networks of knowledge and a number of novel initiatives are emerging in Brazil. These new arrangements are novel in the way that they seem to be adaptive and navigate structures in the hope of overcoming insurmountable drivers of deforestation.