bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of spatial concentration fluctuations on effective kinetics in diffusion‐reaction systems
Authors: Tartakovsky A. M. , de Anna P. , Le Borgne T. , Balter A. , Bolster D.
Published: December 2011

The effect of spatial concentration fluctuations on the reaction of two solutes, A + B ⇀ C, is considered. In the absence of fluctuations, the concentration of solutes decays as Adet = Bdet ∼ t−1. Contrary to this, experimental and numerical studies suggest that concentrations decay significantly slower. Existing theory suggests a t−d/4 scaling in the asymptotic regime (d is the dimensionality of the problem). Here we study the effect of fluctuations using the classical diffusion‐reaction equation with random initial conditions. Initial concentrations of the reactants are treated as correlated random fields. We use the method of moment equations to solve the resulting stochastic diffusion‐reaction equation and obtain a solution for the average concentrations that deviates from ∼t−1 to ∼t−d/4 behavior at characteristic transition time t*. We also derive analytical expressions for t* as a function of Damköhler number and the coefficient of variation of the initial concentration.
Lexical and Phonological Effects in Early Word Production
Authors: Sosa Anna V. , Stoel-Gammon Carol
Published: December 2011

Purpose

This study examines the influence of word frequency, phonological neighborhood density (PND), age of acquisition (AoA), and phonotactic probability on production variability and accuracy of known words by toddlers with no history of speech, hearing, or language disorders.

Method

Fifteen toddlers between 2;0 (years;months) and 2;5 produced monosyllabic target words varying in word frequency, PND, AoA, and phonotactic probability. Phonetic transcription was used to determine (a) whole-word variability and (b) proportion of whole-word proximity (PWP; Ingram, 2002) of each target word produced.

Results

Results show a significant effect of PND on PWP and variability (words from dense neighborhoods had higher PWP and lower variability than those from sparse neighborhoods), a significant effect of word frequency on variability (high-frequency words were less variable) but not proximity, and a significant effect of AoA on proximity (earlier acquired words had lower PWP) but not variability.

Conclusions

Results provide new information regarding the role that lexical and phonological factors play in the speech of young children; specifically, several factors are identified that influence variability of production. Additionally, by examining lexical and phonological factors simultaneously, the current study isolates differential effects of the individual factors. Implications for our understanding of emerging phonological representations are discussed.

Supplemental Material

https://doi.org/10.23641/asha.6170360
Animation of Graphic Symbols Representing Verbs and Prepositions: Effects on Transparency, Name Agreement, and Identification
Authors: Schlosser Ralf W. , Shane Howard , Sorce James , Koul Rajinder , Bloomfield Emma , Debrowski Lisa , DeLuca Tim , Miller Stephanie , Schneider Danielle , Neff Allison
Published: December 2011

Purpose

The effects of animation on transparency, name agreement, and identification of graphic symbols for verbs and prepositions were evaluated in preschoolers of 3 age groups.

Methods

A mixed-group design was used; in each age group, half of the children were randomly allocated to 1 of 2 orders of symbol formats. The 52 children were asked to guess the meaning of symbols and to identify a target symbol among foils given the spoken label.

Results

Animated symbols were more transparent than static symbols, although this was more pronounced for verbs. Animated verbs were named more accurately than static verbs, but there was no difference between animated and static prepositions. Verbs were identified more accurately compared with prepositions, but there was no difference between symbol formats. Older children guessed, named, and identified symbols more effectively than younger children.

Conclusion

Animation enhances transparency and name agreement, especially for verbs, which reduces the instructional burden that comes with nontransparent symbols. Animation does not enhance identification accuracy. Verbs are easier to identify than prepositions. A developmental effect was observed for each measure. Limitations and implications for future research are discussed.
Consequences of Broad Auditory Filters for Identification of Multichannel-Compressed Vowels
Authors: Souza Pamela , Wright Richard , Bor Stephanie
Published: December 2011

Purpose

In view of previous findings (Bor, Souza, & Wright, 2008) that some listeners are more susceptible to spectral changes from multichannel compression (MCC) than others, this study addressed the extent to which differences in effects of MCC were related to differences in auditory filter width.

Method

Listeners were recruited in 3 groups: listeners with flat sensorineural loss, listeners with sloping sensorineural loss, and a control group of listeners with normal hearing. Individual auditory filter measurements were obtained at 500 and 2000 Hz. The filter widths were related to identification of vowels processed with 16-channel MCC and with a control (linear) condition.

Results

Listeners with flat loss had broader filters at 500 Hz but not at 2000 Hz compared with listeners with sloping loss. Vowel identification was poorer for MCC compared with linear amplification. Listeners with flat loss made more errors than listeners with sloping loss, and there was a significant relationship between filter width and the effects of MCC.

Conclusions

Broadened auditory filters can reduce the ability to process amplitude-compressed vowel spectra. This suggests that individual frequency selectivity is a factor that influences benefit of MCC when a high number of compression channels are used.
Infants Exposed to Fluent Natural Speech Succeed at Cross-Gender Word Recognition
Authors: van Heugten Marieke , Johnson Elizabeth K.
Published: December 2011

Purpose

To examine the possibility that early signal-to-word form mapping capabilities are robust enough to handle substantial indexical variation in the realization of words.

Method

Two groups of 7.5-month-olds were tested with the Headturn Preference Procedure. Half of the infants were exposed to words embedded in passages spoken by their mothers and tested on lists of trained and novel isolated words spoken by their fathers. The other half of the infants were yoked pairs listening to unfamiliar speakers.

Results

In the test phase, infants listened longer to trained than to novel words, indicating that they successfully segmented the words from the passages. This result was not modulated by infants' familiarity with the speaker.

Conclusions

Under more naturalistic listening conditions, 7.5-month-olds exhibit the ability to recognize words in the face of substantial indexical variation regardless of whether speakers are familiar. This suggests that early word representations are, at least to some extent, independent of the speaker’s gender and may reflect sophisticated abstraction capabilities on the part of the infants, which would render extreme episodic models of early speech perception untenable. Additional research using similarly ecologically valid testing methods is called for to elucidate the precise nature of early word representations.
Random Versus Blocked Practice in Treatment for Childhood Apraxia of Speech
Authors: Maas Edwin , Farinella Kimberly A.
Published: December 2011

Purpose

To compare the relative effects of random vs. blocked practice schedules in treatment for childhood apraxia of speech (CAS). Although there have been repeated suggestions in the literature to use random practice in CAS treatment, no systematic studies exist that have directly compared random with blocked practice in this population.

Method

Using an alternating treatments single-subject design with multiple baselines across behaviors, the authors compared random and blocked practice in 4 children diagnosed with CAS in terms of retention and transfer. Random and blocked practice were implemented in the context of a version of Dynamic Temporal and Tactile *Cueing treatment (Strand, Stoeckel, & Baas, 2006). Perceptual accuracy of target utterances was scored, and effect sizes were calculated to quantify the magnitude of treatment effects.

Results

Findings were mixed, with 2 children showing a blocked practice advantage, 1 child showing a random practice advantage, and 1 child showing no clear improvement in either condition.

Conclusions

These findings suggest that the random practice advantage observed in the nonspeech motor learning literature may not extend to treatment for CAS. Furthermore, the findings add to the small body of literature indicating that integral stimulation treatment can lead to improvements in speech production for children with CAS.
Stochastic resonance on a modular neuronal network of small-world subnetworks with a subthreshold pacemaker
Authors: Yu Haitao , Wang Jiang , Liu Chen , Deng Bin , Wei Xile
Published: December 2011

We study the phenomenon of stochastic resonance on a modular neuronal network consisting of several small-world subnetworks with a subthreshold periodic pacemaker. Numerical results show that the correlation between the pacemaker frequency and the dynamical response of the network is resonantly dependent on the intensity of additive spatiotemporal noise. This effect of pacemaker-driven stochastic resonance of the system depends extensively on the local and the global network structure, such as the intra- and inter-coupling strengths, rewiring probability of individual small-world subnetwork, the number of links between different subnetworks, and the number of subnetworks. All these parameters play a key role in determining the ability of the network to enhance the noise-induced outreach of the localized subthreshold pacemaker, and only they bounded to a rather sharp interval of values warrant the emergence of the pronounced stochastic resonance phenomenon. Considering the rather important role of pacemakers in real-life, the presented results could have important implications for many biological processes that rely on an effective pacemaker for their proper functioning.
Sensitivity analysis of stochastic attractors and noise-induced transitions for population model with Allee effect
Authors: Bashkirtseva I. , Ryashko L.
Published: December 2011

We study a stochastically forced predator-prey model with Allee effect. In the deterministic case, this model exhibits non-trivial stable equilibrium or limit cycle corresponding to the coexistence of both species. Computational methods based on the stochastic sensitivity functions technique are suggested for the analysis of the dispersion of random states in stochastic attractors. Our method allows to construct confidence domains and estimate the threshold value of the intensity for noise generating a transition from the coexistence to the extinction.
Unstable periodic orbits and noise in chaos computing
Authors: Kia Behnam , Dari Anna , Ditto William L. , Spano Mark L.
Published: December 2011

Different methods to utilize the rich library of patterns and behaviors of a chaotic system have been proposed for doing computation or communication. Since a chaotic system is intrinsically unstable and its nearby orbits diverge exponentially from each other, special attention needs to be paid to the robustness against noise of chaos-based approaches to computation. In this paper unstable periodic orbits, which form the skeleton of any chaotic system, are employed to build a model for the chaotic system to measure the sensitivity of each orbit to noise, and to select the orbits whose symbolic representations are relatively robust against the existence of noise. Furthermore, since unstable periodic orbits are extractable from time series, periodic orbit-based models can be extracted from time series too. Chaos computing can be and has been implemented on different platforms, including biological systems. In biology noise is always present; as a result having a clear model for the effects of noise on any given biological implementation has profound importance. Also, since in biology it is hard to obtain exact dynamical equations of the system under study, the time series techniques we introduce here are of critical importance.
Variability of spatio-temporal patterns in non-homogeneous rings of spiking neurons
Authors: Yanchuk Serhiy , Perlikowski Przemyslaw , Popovych Oleksandr V. , Tass Peter A.
Published: December 2011

We show that a ring of unidirectionally delay-coupled spiking neurons may possess a multitude of stable spiking patterns and provide a constructive algorithm for generating a desired spiking pattern. More specifically, for a given time-periodic pattern, in which each neuron fires once within the pattern period at a predefined time moment, we provide the coupling delays and/or coupling strengths leading to this particular pattern. The considered homogeneous networks demonstrate a great multistability of various travelling time- and space-periodic waves which can propagate either along the direction of coupling or in opposite direction. Such a multistability significantly enhances the variability of possible spatio-temporal patterns and potentially increases the coding capability of oscillatory neuronal loops. We illustrate our results using FitzHugh-Nagumo neurons interacting via excitatory chemical synapses as well as limit-cycle oscillators.
Simultaneous step meandering and bunching instabilities controlled by Ehrlich-Schwoebel barrier and elastic interaction
Authors: Yu Yan-Mei , Voigt Axel , Guo Xiaoshu , Liu Yong
Published: December 2011

Through phase-field simulations, we investigate simultaneous step meandering and bunching instabilities with the presence of Ehrlich-Schwoebel barrier and elastic interaction. The meandering instability induced by the Ehrlich-Schwoebel barrier is found to be dependent on the elastic interaction at low adatom deposition rate. The ordered step meandering-bunching structure is designed by using the predefined magnitude distribution of the force monopoles on vicinal surfaces based on interplay between the Ehrlich-Schwoebel barrier and the elastic interaction.
Balanced ternary addition using a gated silicon nanowire
Authors: Mol J. A. , van der Heijden J. , Verduijn J. , Klein M. , Remacle F. , Rogge S.
Published: December 2011

Ternary logic has the lowest cost of complexity, here, we demonstrate a CMOS hardware implementation of a ternary adder using a silicon metal-on-insulator single electron transistor. Gate dependent rectifying behavior of a single electron transistor (SET) results in a robust three-valued output as a function of the potential of the single electron transistor island. Mapping logical, ternary inputs to the three gates controlling the potential of the single electron transistor island allows us to perform complex, inherently ternary operations, on a single transistor.
Instability of nonsymmetric nonmonotone equilibria of the Vlasov-Maxwell system
Authors: Ben-Artzi Jonathan
Published: December 2011

We consider the \documentclass[12pt]{minimal}\begin{document}$1\frac{1}{2}$\end{document}112-dimensional relativistic Vlasov-Maxwell system that describes the time-evolution of a plasma. We find a relatively simple criterion for spectral instability of a wide class of equilibria. This class includes non-homogeneous equilibria that need not satisfy any additional symmetry properties (as was the case in previous results), nor should they be monotone in the particle energy. The criterion is given in terms of the spectral properties of two Schrödinger operators that arise naturally from Maxwell's equations. The spectral analysis of these operators is quite delicate, and some general functional analytic tools are developed to treat them. These tools can be applied to similar systems in higher dimensions, as long as their domain is finite or periodic.
Direct imaging of the spatial diffusion of excitons in single semiconductor nanowires
Authors: Fickenscher M. A. , Jackson H. E. , Smith L. M. , Yarrison-Rice J. M. , Kang J. H. , Paiman S. , Gao Q. , Tan H. H. , Jagadish C.
Published: December 2011

We use spatially and temporally resolved photoluminescence to measure exciton diffusion in single zinc blende GaAs/AlGaAs core/shell and mixed phase InP nanowires. Excitons in the single phase GaAs/AlGaAs nanowires are seen to diffuse rapidly throughout the nanowire with a measured diffusion constant ranging from 45 to 100 cm2/s, while in the mixed phase, InP nanowire electrons and holes are seen to rapidly localize to the quantum confined states in the zinc blende and wurtzite segments, respectively. The diffusion constant in the GaAs/AlGaAs nanowire is similar to the best hole mobilities observed in modulation doped heterostructures.
Metal oxide resistive memory switching mechanism based on conductive filament properties
Authors: Bersuker G. , Gilmer D. C. , Veksler D. , Kirsch P. , Vandelli L. , Padovani A. , Larcher L. , McKenna K. , Shluger A. , Iglesias V. , Porti M. , Nafría M.
Published: December 2011

By combining electrical, physical, and transport/atomistic modeling results, this study identifies critical conductive filament (CF) features controlling TiN/HfO2/TiN resistive memory (RRAM) operations. The leakage current through the dielectric is found to be supported by the oxygen vacancies, which tend to segregate at hafnia grain boundaries. We simulate the evolution of a current path during the forming operation employing the multiphonon trap-assisted tunneling (TAT) electron transport model. The forming process is analyzed within the concept of dielectric breakdown, which exhibits much shorter characteristic times than the electroforming process conventionally employed to describe the formation of the conductive filament. The resulting conductive filament is calculated to produce a non-uniform temperature profile along its length during the reset operation, promoting preferential oxidation of the filament tip. A thin dielectric barrier resulting from the CF tip oxidation is found to control filament resistance in the high resistive state. Field-driven dielectric breakdown of this barrier during the set operation restores the filament to its initial low resistive state. These findings point to the critical importance of controlling the filament cross section during forming to achieve low power RRAM cell switching.
Electrostatic solitary structures in presence of non-thermal electrons and a warm electron beam on the auroral field lines
Authors: Singh S. V. , Lakhina G. S. , Bharuthram R. , Pillay S. R.
Published: December 2011

Electrostatic solitary waves (ESWs) have been observed by satellites in the auroral region of the Earth’s magnetosphere. These ESWs are found to be having both positive and negative electrostatic potentials. Using the Sagdeeev psuedo-potential technique, arbitrary amplitude electron-acoustic solitary waves/double layers are studied in an unmagnetized plasma consisting of non-thermally distributed hot electrons, fluid cold electrons, a warm electron beam, and ions. The inertia of the warm electrons, and not the beam speed, is essential for the existence of positive potential solitary structures. Existence domains for positive as well as negative potential electrostatic solitons/double layers are obtained. For the typical auroral region parameters, the electric field amplitude of the negative potential solitons is found to be in the range ∼(3–30) mV/m and ∼(5–80) mV/m for the positive potential solitons. For the negative potential solitons/double layers, the amplitudes are higher when their widths are smaller. On the other hand, the amplitude of the positive potential structures increase with their widths.
Energy relaxation of intermolecular motions in supercooled water and ice: A molecular dynamics study
Authors: Yagasaki Takuma , Saito Shinji
Published: December 2011

We investigate the energy relaxation of intermolecular motions in liquid water at temperatures ranging from 220 K to 300 K and in ice at 220 K using molecular dynamics simulations. We employ the recently developed frequency resolved transient kinetic energy analysis, which provides detailed information on energy relaxation in condensed phases like two-color pump-probe spectroscopy. It is shown that the energy cascading in liquid water is characterized by four processes. The temperature dependences of the earlier three processes, the rotational-rotational, rotational-translational, and translational-translational energy transfers, are explained in terms of the density of states of the intermolecular motions. The last process is the slow energy transfer arising from the transitions between potential energy basins caused by the excitation of the low frequency translational motion. This process is absent in ice because the hydrogen bond network rearrangement, which accompanies the interbasin transitions in liquid water, cannot take place in the solid phase. We find that the last process in supercooled water is well approximated by a stretched exponential function. The stretching parameter, β, decreases from 1 to 0.72 with decreasing temperature. This result indicates that the dynamics of liquid water becomes heterogeneous at lower temperatures.
Determination of secondary phases in kesterite Cu2ZnSnS4 thin films by x-ray absorption near edge structure analysis
Authors: Just Justus , Lützenkirchen-Hecht Dirk , Frahm Ronald , Schorr Susan , Unold Thomas
Published: December 2011

Secondary phases in Cu2ZnSnS4 (CZTS) are investigated by x-ray absorption spectroscopy. Evaluating the x-ray absorption near edge structure at the sulfur K-edge, we show that secondary phases exhibit sufficiently distinct features to allow their quantitative determination with high accuracy. We are able to quantify the ZnS fraction with an absolute accuracy of ±3%, by applying linear combination analysis using reference spectra. We find that even in CZTS thin films with [Sn]/[Zn] ≈ 1, a significant amount of ZnS can be present. A strong correlation of the ZnS-content with the degradation of the electrical performance of solar cells is observed.
Facile creation of bio-inspired superhydrophobic Ce-based metallic glass surfaces
Authors: Liu Kesong , Li Zhou , Wang Weihua , Jiang Lei
Published: December 2011

A bio-inspired synthesis strategy was conducted to fabricate superhydrophobic Ce-based bulk metallic glass (BMG) surfaces with self-cleaning properties. Micro-nanoscale hierarchical structures were first constructed on BMG surfaces and then modified with the low surface energy coating. Surface structures, surface chemical compositions, and wettability were characterized by combining scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, and contact angle measurements. Research indicated that both surface multiscale structures and the low surface free energy coating result in the final formation of superhydrophobicity.
Collapse kinetics of vibrated granular chains
Authors: Jeng Pei-Ren , Chen Kuan Hua , Hwang Gwo-jen , Lien Chenhsin , To Kiwing , Chou Y. C.
Published: December 2011

The kinetics of the collapse of the coil state into condensed states is studied with vibrated granular chain composed of N metal beads partially immersed in water. The radius of gyration of the chain, Rg is measured. For short chains (N < 140), disk-like condensed state is formed and Rg decreases with time such that the function ΔRg2 (≡ Rg2 − Rg2(∞)) = A e−t/τ, where the relaxation time τ follows a power-law dependence on the chain length N with an exponent γ = 1.9 ± 0.2. For the chains with length N ≥ 300, rod-like clusters are observed during the initial stage of collapse and Rg2 = Rg2(0) – Btβ, with β = 0.6 ± 0.1. In the coarsening stage, the exponential dependence of ΔRg2 on time still holds, however, the relaxation time τ fluctuates and has no simple dependence on N. Furthermore, the time dependence of the averaged radius of gyration of the individual clusters, Rg,cl can be described by the theory of Lifshitz and Slyozov. A peak in the structure function of long chains is observed in the initial stage of the collapse transition. The collapse transition in the bead chains is a first order phase transition. However, features of the spinodal decomposition are also observed.
Exact results for finite quantum Hall systems of electrons at filling factor one: Disk geometry
Authors: Ciftja Orion
Published: December 2011

We obtain exact analytical expressions for the total energy per particle and related quantities corresponding to a finite quantum Hall system of electrons in a disk geometry when filling factor of the Landau level is one. Such exact results apply to finite systems of electrons with an arbitrary number of particles. The reported calculations for finite systems of electrons in a disk geometry complement earlier calculations for finite systems of electrons in a simpler spherical geometry. The results we provide can serve as benchmarks to gauge the accuracy of various theoretical approximations and numerical methods used to study the properties of strongly correlated many-body systems.
The indirect to direct band gap transition in multilayered MoS2 as predicted by screened hybrid density functional theory
Authors: Ellis Jason K. , Lucero Melissa J. , Scuseria Gustavo E.
Published: December 2011

Molybdenite (MoS2) undergoes a transition from an indirect to direct gap semiconductor exhibiting strong photoluminescence when confined in a 2D monolayer. We investigate the effect of interlayer interactions on the band structure and density of states using the screened hybrid functional of Heyd, Scuseria, and Ernzerhof. We show that for the bulk and monolayer systems, our short-range screened hybrid functional produces band gaps in good agreement with experiment. Our functional includes only interlayer interactions of non-van der Waals origin, predicts properties consistent with recent experiments, and provides predictions for few-layered systems.
Long-lasting flexible organic solar cells stored and tested entirely in air
Authors: Omrane B. , Landrock C. K. , Chuo Y. , Hohertz D. , Aristizabal J. , Kaminska B. , Kavanagh K. L.
Published: December 2011

We report on improved stability of poly(3-hexylthiopene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester bulk heterojunction solar cells using an indium tin oxide (ITO) anode and an indium metal cathode. Except for the ITO anode the devices are fabricated, stored, and tested entirely in air without encapsulation, exhibiting less than 10% loss in power conversion efficiency after 200 days. X-ray photoelectron spectroscopy shows that this improvement in ambient stability is correlated with the diffusion of indium from the cathode into the active polymer. The In oxidizes presumably resulting in a reduction in P3HT polymer chain degradation.
Anisotropy effect on global minimum structures of clusters: Two-center Lennard-Jones model
Authors: Feng Yan , Wu Jing , Cheng Longjiu , Liu Haiyan
Published: December 2011

Using a two-center Lennard-Jones (2CLJ) model, the simplest anisotropic case, we investigated how anisotropy affects global minimum structures of clusters and obtained some interesting results. The anisotropy parameter, R, is defined as the ratio of the bond length of 2CLJ dimer to the LJ equilibrium pair separation, where a larger R value means higher anisotropy. For low R values, the structures resemble those of the Lennard-Jones atomic clusters. However, as the pairwise interaction becomes more anisotropic, the “magic numbers” change, and several novel cluster patterns emerge as particularly stable structures, and the global minima change from icosahedral, to polyicosahedral and to novel irregular structures. Moreover, increasing the anisotropy effectively softens the 2CLJ potential. Given the general importance of the LJ cluster as a simple model cluster, 2CLJ model can provide a straightforward and useful analysis of the effect of molecular shape on the structures of clusters.
Molecular dynamics simulation of Bauschinger’s effect in deformed copper single crystal in different strain ranges
Authors: Zhu D. , Zhang H. , Li D. Y.
Published: December 2011

Plastic pre-strain may decrease the yield strength of metallic materials when stressed in the opposite direction, known as Bauschinger’s effect, which could considerably influence the performance of the materials. However, various processes on microscopic level associated with the Bauschinger’s effect are still not clear. In this study, defect generation, movement and annihilation in single crystal copper during cyclic tension-compression loading processes were simulated using the molecular dynamics method. It was observed that Bauschinger’s effect was asymmetrical and the strain hardening was more profound during compression. After plastic compression, the tensile fracture strain was increased. The absorbed energy was self-adjusted during the tension-compression cycles and kept relatively stable during the loading cycles. Efforts were made to understand the mechanisms responsible for these phenomena.
Multi-level phase change memory devices with Ge2Sb2Te5 layers separated by a thermal insulating Ta2O5 barrier layer
Authors: Gyanathan Ashvini , Yeo Yee-Chia
Published: December 2011

This work investigates multi-level phase change random access memory (PCRAM) devices comprising two Ge2Sb2Te5 (GST) layers sandwiching a thermal insulating Ta2O5 barrier layer. The PCRAM cell comprises a phase change material stack between a top and a bottom electrode. The phase change material stack comprises a nitrogen doped GST (NGST) layer on a thin Ta2O5 barrier layer on an undoped GST layer. It is demonstrated that one of the phase change layers in the GST stack can be selectively amorphized by using a voltage pulse. This enables multi-level resistance switching. The differences in resistivities, as well as the different melting and crystallization temperatures of both the NGST and GST layers, contribute to the multi-level switching dynamics of the PCRAM device. The thermal conductivity of Ta2O5 with respect to GST is also another factor influencing the multi-level switching. Extensive electrical characterization of the PCRAM devices was performed. Thermal analysis was used to examine the physics behind the multi-level switching mechanism of these devices.
Nanofluid heat capacities
Authors: Starace Anne K. , Gomez Judith C. , Wang Jun , Pradhan Sulolit , Glatzmaier Greg C.
Published: December 2011

Significant increases in the heat capacity of heat transfer fluids are needed not only to reduce the costs of liquid heating and cooling processes, but also to bring clean energy producing technologies like concentrating solar power (CSP) to price parity with conventional energy generation. It has been postulated that nanofluids could have higher heat capacities than conventional fluids. In this work, nano- and micron-sized particles were added to five base fluids (poly-α olefin, mineral oil, ethylene glycol, a mixture of water and ethylene glycol, and calcium nitrate tetrahydrate), and the resulting heat capacities were measured and compared with those of the neat base fluids and the weighted average of the heat capacities of the components. The particles used were inert metals and metal oxides that did not undergo any phase transitions over the temperature range studied. In the nanofluids studied here, we found no increase in heat capacity upon the addition of the particles larger than the experimental error.
Electrical noise characteristics of a doped silicon microcantilever heater-thermometer
Authors: Corbin Elise A. , King William P.
Published: December 2011

We measure the electrical noise characteristics of doped silicon microcantilevers during cantilever self-heating over the temperature range 296–781 K. The dominant noise source is 1/f below about 10 kHz, while at higher frequency, the dominant noise source is Johnson noise. The 1/f noise matches the Hooge model. The noise floor is about 10 nV/Hz1/2 and depends upon temperature, matching the theoretical Johnson noise. The Johnson noise-limited temperature resolution is about 1 μK/Hz1/2.
Size effect on magnetic coupling in all-ferromagnetic superlattices
Authors: Padhan P. , Prellier W.
Published: December 2011

The switching of ferromagnetic-to-antiferromagnetic coupling of magnetization in the superlattices consisting of two ferromagnetic metals La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) grown on (001) oriented SrTiO3 has been observed by changing the orientation of the field from out–of–plane to in–plane direction. Such switching of magnetic coupling strongly depends on the stacking order of La0.7Sr0.3MnO3 and SrRuO3 layers in the superlattice of 20 unit cell (u.c.)/n (= 3 or 5) u.c. thickness configuration. This is explained by the structural distortion in the MnO6 and RuO6 octahedra along the out-of-plane direction due to the observed stress.
Synthesis of submicron metastable phase of silicon using femtosecond laser-driven shock wave
Authors: Tsujino Masashi , Sano Tomokazu , Sakata Osami , Ozaki Norimasa , Kimura Shigeru , Takeda Shingo , Okoshi Masayuki , Inoue Narumi , Kodama Ryosuke , Kobayashi Kojiro F. , Hirose Akio
Published: December 2011

We measured the grain size of metastable phase of Si synthesized by shock compression. We analyzed the crystalline structures of the femtosecond laser-driven shock compressed silicon with x-ray diffraction measurements. We found that submicron grains of metastable Si-VIII exist in the silicon. We suggest that the pressure loading time is too short for the nucleated high-pressure phases to grow in case of the femtosecond laser-driven shock compression, therefore Si-VIII grains of submicron size are obtained. We are expecting to discover other unique crystalline structures induced by the femtosecond laser-driven shock wave.
Communication: The reason why +c ZnO surface is less stable than −c ZnO surface: First-principles calculation
Authors: Ito Seitaro , Shimazaki Tomomi , Kubo Momoji , Koinuma Hideomi , Sumiya Masatomo
Published: December 2011

It has been experimentally shown that an O(−c)-polar ZnO surface is more stable than a Zn(+c)-polar surface in H2 ambient. We applied first-principles calculations to investigating the polarity dependence on the stability at the electronic level. The calculations revealed that the −c surface terminated with H atom was stable maintaining a wurtzite structure, whereas the +c surface was unstable due to the change of coordination numbers of Zn at the topmost surface from four (wurtzite) to six (rock salt). This causes the generation of O2 molecules, resulting in instability at the +c surface.
On elastic waves and related phenomena in lattice materials and structures
Authors: Phani A. Srikantha
Published: December 2011

Lattice materials possessing a spatially periodic microstructure are suitable in weight sensitive multifunctional structural applications such as sandwich panels. They not only possess high specific stiffness but also provide opportunities to tailor acoustic and thermal properties through designing their unit cell topology. This paper seeks to understand their mechanical response under static and dynamic loads from a structural mechanics perspective combining Bloch wave theory with Finite Element Method (FEM). Bringing together results from earlier works, it is shown that three eigenvalue problems, containing the frequency and wave vector as the unknowns, can be used to analyze bulk and surface wave phenomena. The application of eigenvalue problems to band-gaps (spatially extended response), edge effects of Saint Venant type (spatially localised response), and buckling of long cellular structures is shown.
Dispersion considerations affecting phonon-mass impurity scattering rates
Authors: Hopkins Patrick E.
Published: December 2011

This work presents a derivation of phonon-mass impurity scattering rates applicable to dispersive phonon systems. This form of mass impurity scattering is compared with the previously accepted form assuming a nondispersive crystal by calculating the thermal conductivity of Si. The mass impurity scattering rate determined from this approach considering dispersion is in excellent agreement with theoretical calculations, where the scattering rates determined from the dispersionless model under predict the role of phonon-mass impurity scattering in thermal transport by over an order of magnitude.
Piezoelectric superlattices as multi-field internally resonating metamaterials
Authors: Senesi M. , Ruzzene M.
Published: December 2011

Piezoelectric superlattices are investigated as examples of internally resonating metamaterials. The multi-field coupling characteristics of the considered configuration is identified as the mechanism enabling the generation of the internal resonances, and the related achievement of unusual wave properties. Numerical studies on two-dimensional piezoelectric superlattices illustrate the coupled behavior of this class of periodic systems. In addition, analytical studies developed on the basis of the long wavelength approximation support the interpretation of the coupling as an internally resonant mechanism, and allow the analysis of the influence of lattice topology on the frequencies of internal resonance.
A tolerogenic role for Toll-like receptor 9 is revealed by B-cell interaction with DNA complexes expressed on apoptotic cells
Authors: Miles Katherine , Heaney Jonathan , Sibinska Zaneta , Salter Donald , Savill John , Gray David , Gray Mohini
Published: December 2011

Intracellular protein complexes containing nucleic acids are common targets of autoantibodies in many autoimmune diseases. Central tolerance to these antigens is incomplete, yet nucleosomal DNA is expressed on the surface of cells dying by apoptosis. It is commonly believed that autoimmunity is prevented by the rapid uptake of apoptotic cells (ACs) by neighbors or professional phagocytes to which they deliver anti-inflammatory signals. Self-reactive, innate-like B cells contact and are selected by intracellular antigens expressed on ACs; however, how self-tolerance is maintained is not well understood. Here we report that IL-10 production by B cells, stimulated by contact with ACs, results from the engagement of Toll-like receptor 9 (TLR9) within the B cell after recognition of DNA-containing complexes on the surface of ACs. Until now, TLR9 ligation has been considered an inflammatory signal, but we have confirmed a hitherto unexpected immunoregulatory role by demonstrating the absence of the protective effect of ACs during experimental autoimmune encephalitis (EAE) in TLR9-deficient mice. Human circulating CD27+B cells also respond to DNA-bearing ACs, but not to DNase-treated cells, by secreting IL-10. Chronic autoimmune disease may arise if this tolerance mechanism is not reimposed after episodes of inflammation, or if the regulatory B-cell response is subverted.
Structural basis for DNA recognition and loading into a viral packaging motor
Authors: Büttner Carina R. , Chechik Maria , Ortiz-Lombardía Miguel , Smits Callum , Ebong Ima-Obong , Chechik Victor , Jeschke Gunnar , Dykeman Eric , Benini Stefano , Robinson Carol V. , Alonso Juan C. , Antson Alfred A.
Published: December 2011

Genome packaging into preformed viral procapsids is driven by powerful molecular motors. The small terminase protein is essential for the initial recognition of viral DNA and regulates the motor’s ATPase and nuclease activities during DNA translocation. The crystal structure of a full-length small terminase protein from the Siphoviridae bacteriophage SF6, comprising the N-terminal DNA binding, the oligomerization core, and the C-terminal β-barrel domains, reveals a nine-subunit circular assembly in which the DNA-binding domains are arranged around the oligomerization core in a highly flexible manner. Mass spectrometry analysis and four further crystal structures show that, although the full-length protein exclusively forms nine-subunit assemblies, protein constructs missing the C-terminal β-barrel form both nine-subunit and ten-subunit assemblies, indicating the importance of the C terminus for defining the oligomeric state. The mechanism by which a ring-shaped small terminase oligomer binds viral DNA has not previously been elucidated. Here, we probed binding in vitro by using EPR and surface plasmon resonance experiments, which indicated that interaction with DNA is mediated exclusively by the DNA-binding domains and suggested a nucleosome-like model in which DNA binds around the outside of the protein oligomer.
End-Cretaceous marine mass extinction not caused by productivity collapse
Authors: Alegret Laia , Thomas Ellen , Lohmann Kyger C
Published: December 2011

An asteroid impact at the end of the Cretaceous caused mass extinction, but extinction mechanisms are not well-understood. The collapse of sea surface to sea floor carbon isotope gradients has been interpreted as reflecting a global collapse of primary productivity (Strangelove Ocean) or export productivity (Living Ocean), which caused mass extinction higher in the marine food chain. Phytoplankton-dependent benthic foraminifera on the deep-sea floor, however, did not suffer significant extinction, suggesting that export productivity persisted at a level sufficient to support their populations. We compare benthic foraminiferal records with benthic and bulk stable carbon isotope records from the Pacific, Southeast Atlantic, and Southern Oceans. We conclude that end-Cretaceous decrease in export productivity was moderate, regional, and insufficient to explain marine mass extinction. A transient episode of surface ocean acidification may have been the main cause of extinction of calcifying plankton and ammonites, and recovery of productivity may have been as fast in the oceans as on land.
Pluripotency factor-mediated expression of the leptin receptor (OB-R) links obesity to oncogenesis through tumor-initiating stem cells
Authors: Feldman Douglas Edmund , Chen Chialin , Punj Vasu , Tsukamoto Hidekazu , Machida Keigo
Published: December 2011

Misregulation of a pluripotency-associated transcription factor network in adult tissues is associated with the expansion of rare, highly malignant tumor-initiating stem cells (TISCs) through poorly understood mechanisms. We demonstrate that robust and selective expression of the receptor for the adipocyte-derived peptide hormone leptin (OB-R) is a characteristic feature of TISCs and of a broad array of embryonic and induced pluripotent stem cells and is mediated directly by the core pluripotency-associated transcription factors OCT4 and SOX2. TISCs exhibit sensitized responses to leptin, including the phosphorylation and activation of the pluripotency-associated oncogene STAT3 and induction of
Oct4
and
Sox2
, thereby establishing a self-reinforcing signaling module. Exposure of cultured mouse embryonic stem cells to leptin sustains pluripotency in the absence of leukemia inhibitory factor. By implanting TISCs into leptin-deficient
ob/ob
mice or into comparably overweight

Lepr
db/db

mice that produce leptin, we provide evidence of a central role for the leptin-TISC–signaling axis in promoting obesity-induced tumor growth. Differential responses to extrinsic, adipocyte-derived cues may promote the expansion of tumor cell subpopulations and contribute to oncogenesis.
High pressure ices
Authors: Hermann Andreas , Ashcroft N. W. , Hoffmann Roald
Published: December 2011

H
2
O will be more resistant to metallization than previously thought. From computational evolutionary structure searches, we find a sequence of new stable and meta-stable structures for the ground state of ice in the 1–5 TPa (10 to 50 Mbar) regime, in the static approximation. The previously proposed
Pbcm
structure is superseded by a
Pmc
2
1
phase at
p
 = 930 GPa, followed by a predicted transition to a
P
2
1
crystal structure at
p
 = 1.3 TPa. This phase, featuring higher coordination at O and H, is stable over a wide pressure range, reaching 4.8 TPa. We analyze carefully the geometrical changes in the calculated structures, especially the buckling at the H in O-H-O motifs. All structures are insulating—chemistry burns a deep and (with pressure increase) lasting hole in the density of states near the highest occupied electronic levels of what might be component metallic lattices. Metallization of ice in our calculations occurs only near 4.8 TPa, where the metallic
C
2/
m
phase becomes most stable. In this regime, zero-point energies much larger than typical enthalpy differences suggest possible melting of the H sublattice, or even the entire crystal.
Open and transparent: the review process of the Semantic Web journal
Authors: JANOWICZ Krzysztof , HITZLER Pascal
Published: December 2011

While open access is established in the world of academic publishing, open reviews are rare. The Semantic Web journal goes further than just open review by implementing an open and transparent review process in which reviews are publicly available, and the assigned editors and reviewers are known by name, and are published together with accepted manuscripts. In this article we introduce the steps to realize such a process from the conceptual design, over the implementation, a overview of the results so far, and up to lessons learned.
The scholarly publishing industry in China: overview and opportunities
Authors: Jei XU , WAHLS Matthias
Published: December 2011

The rapid growth of government investment in scientific research in China over past decades has also caused the scholarly publishing industry to go through great changes. Nevertheless, there is a big gap between the state of China's scholarly publishing industry and the current demands of international scientific communication. Globalization and digitization developments are currently widening this gap. Based on desk research, face‐to‐face interviews, observations, and experience, we identify the current business challenges for scholarly publishing in China, and provide a list of suggestions to narrow the gap.
Book Reviews
Authors: OKERSON Ann Shumelda
Published: December 2011

Open Access: What You Need to Know Now Walt Crawford Chicago, American Library Association, 2011, 76pp. 978‐0‐8389‐1106‐8, pbk and e‐book $45/$36, $53 print and e‐book
Gastrointestinal Endoscopy and Mucosal Biopsy in the First Year of Life
Authors: Volonaki Eleni , Sebire Neil J. , Borrelli Osvaldo , Lindley Keith J. , Elawad Mamoun , Thapar Nikhil , Shah Neil
Published: December 2011

Objectives:

Lower threshold and widening indications for paediatric gastrointestinal endoscopy have resulted in a significant increase in the numbers of endoscopic procedures performed in infants. Despite this, knowledge of gastrointestinal mucosal findings in this age group is limited and data on the clinical usefulness of endoscopy are lacking.

Methods:

All of the children younger than 1 year referred to a single tertiary paediatric gastroenterology unit during the period June 1987 to August 2007 who underwent gastrointestinal endoscopy were identified and the clinical indications and histological outcomes were reviewed.

Results:

A total of 933 gastroesophageal duodenoscopies and 439 colonoscopies were performed in 1024 cases in a total of 823 infants. In order of frequency, clinical indications were diarrhoea (51%), failure to thrive (41.2%), symptoms of reflux (27.1%), and rectal bleeding (8.5%). Mucosal biopsies were insufficient for assessment in only 2.4% of cases. Mucosal histology was normal in 33.8%, whereas histological abnormalities were identified in 63.8%. Specific histological diagnoses included microvillous inclusion disease, autoimmune enteropathy, graft‐versus‐host disease post–bone marrow transplantation, tufting enteropathy, and disaccharidase deficiency. There was only 1 colonic perforation complicating endoscopy in a total of 889 cases for which relevant information was available (0.1%).

Conclusions:

In two‐thirds of cases, histological abnormalities were detected that influenced management following endoscopic examination and mucosal biopsy in infants. Endoscopy with biopsies is a greatly informative test with low failure and complication rates in the first year of life.