bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Onset- and Rhyme-Related Distractors on Phonological Processing in Children With Specific Language Impairment
Authors: Seiger-Gardner Liat , Brooks Patricia J.
Published: August 2008

Purpose

This study used the cross-modal picture–word interference task of P. J. Brooks and B. MacWhinney (2000) to compare effects of phonologically related words on lexical access in children with specific language impairment (SLI).

Method

Children (7;1 [years;months]–11;2) named pictures while ignoring auditory distractors. Three stimulus asynchrony conditions varied the timing of distractors relative to the pictures. Experiment 1 presented onset-related (bell–bed), unrelated (clown–bed), neutral (go–bed), and identical (bed–bed) distractors. Experiment 2 presented rhyme-related instead of onset-related distractors (clock–sock).

Results

Children with SLI produced longer reaction times (RTs) and more errors than their typical language development (TLD) peers. For children with SLI, onset-related distractors led to slower RTs than unrelated distractors (inhibition) when presented before the picture, and faster RTs (facilitation) when presented after the picture. Children with TLD showed facilitation from onset-related distractors when presented after the picture but no inhibition when presented before the picture. Both groups failed to show facilitation from rhyme-related distractors.

Conclusions

The priming effects from onset-related distractors and lack of effects from rhyme-related distractors in SLI supports “just-in-time” incremental processing, similar to children with TLD. However, children with SLI experience phonological interference from members of a lexical cohort while accessing words. Results are discussed with respect to observed word finding and word learning difficulties in SLI.
Toward Validation of a Minimal Competence Phonetic Core for African American Children
Authors: Stockman Ida J.
Published: August 2008

Purpose

This study aimed to show (a) whether the minimal competence core (MCC) of consonants used by African American preschoolers in I. Stockman (2006) can be observed in a larger group of children using shorter and more controlled speech samples and (b) whether the MCC pass/fail outcomes are differentially related to performance on selected criterion measures of typical and atypical speech.

Method

Word-initial single and clustered consonants were sampled in the conversational speech of 120 Head Start students who were distributed in a northern (Lansing, Michigan) and a southern (Baton Rouge, Louisiana) regional location.

Results

The data generally corroborated the earlier preliminary report, which was based on just 7 children. More than 80% of the children met criteria for passing the core set of phonetic competencies, which included word-initial consonant clusters and 13 consonant singletons. Pass/fail outcomes were significantly related to suspected clinical delay and the overall Percentage of Consonants Correct–Revised (PCC-R).

Conclusion

The initial consonant core identified in this study is potentially useful for identifying speech delay among young African American children. Clinical and research issues related to its use for diagnostic screening are discussed.
Dislocation description of twins in high-temperature superconductor YBa2Cu3O7−δ
Authors: Boyko V. S.
Published: August 2008

The thin twins theory is consistently applied to the dislocation description of twins in the high-temperature superconductor YBa2Cu3O7−δ (YBCO). Quantitative analysis of the twin shape shows agreement with a theoretical analysis and gives a new method of evaluating the twin boundary energy γtw. The friction stress Sfr acting on a twinning dislocation is also determined. The formation of a twin and twin microstructures are analyzed. The principles of microstructure design by twinning in YBCO crystals for enhanced Jc at high magnetic fields are discussed.
Nanocontact spin-electric effect
Authors: Gurzhi R. N. , Kalinenko A. N. , Kopeliovich A. I. , Yanovskiĭ A. V.
Published: August 2008

It is predicted that a spin signal can be converted into a change of the electric potential. This effect arises when spin-polarized electrons from a nonmagnetic circuit N penetrate into a magnetized magnetic attachment M with Zeeman splitting of the electron spectrum. Since M possesses a high density of spin states with the same direction of the spin, the penetration of spin-polarized electrons into M results in the appearance of an electric double layer at the N–M boundary and therefore a jump in the electric potential between M and N. The predicted effect can be used for direct detection of a spin signal in nonmagnetic metals and semiconductors as well as for solving a number of problems of spintronics because of the ease with which an electric field can be controlled by currents in semiconductors.
Resonance absorption, reflection, transmission of phonons and heat transfer through interface between two solids
Authors: Kosevich Yu. A. , Feher A. , Syrkin E. S.
Published: August 2008

The different mechanisms of resonant transport of phonons between two media in the presence of an impurity intermediate layer are described. Particular attention is focused on the resonance interaction of elastic waves with a two-dimensional defect on the contact boundary between two solids, on the multichannel interface phonon scattering, and on the experimentally observed nonmonotonic temperature dependence of the reduced heat flux. In the cases when there is a direct interaction between edge atoms of the matrix as non-nearest neighbors or when the impurities do not fill completely the 2D interface layer, an additional channel for the transmission of phonons through the interface opens. This additional transmission channel manifests itself as a transmission (or reflection or absorption) peak with an asymmetric line shape (the so-called Fano-like resonance for phonons due to interference between the two transmission channels). Some applications of the Fano-like interference phenomena in magnon heat conductivity are also discussed.
Structure of the vibrational spectrum of a two-component disordered chain with arbitrary composition
Authors: Ivanov M. A. , Molodid V. S. , Skripnik Yu. V.
Published: August 2008

A detailed calculation and analysis of the vibrational spectrum of long disordered linear chains with arbitrary ratios of the concentrations of two components are performed in the isotopic approximation using Dean’s method. Special attention is focused on the case where light atoms predominate. It is shown that a large number of resonance features corresponding to vibrational modes of short chains of light atoms with clamped ends arise in the continuous spectrum. The widths of the dips formed are linear functions of the concentration of the heavy atoms, and the depths of the dips are independent of the concentration and are determined by the ratio of the atomic masses. As this ratio increases, starting with two, the dips systematically transform into forbidden bands whose widths are also linear functions of the concentration of the heavy atoms. New conditions for opening of such bands are found and analyzed, and it is shown that they cannot fall within the spectrum of an ideal chain of heavy atoms. The transition from a quasi-continuous spectrum with a series of dips to a hierarchical structure of local vibrations, which occurs at low concentrations of the light atoms, is traced.
Quantum oscillations of the thermomagnetic coefficients of layered conductors in a strong magnetic field
Authors: Kirichenko O. V. , Kozlov I. V. , Krstovska D. , Peschanskiĭ V. G.
Published: August 2008

The linear response of the electronic system of a conductor to a perturbation in the form of an electric field and a temperature gradient in a quantizing magnetic field B is investigated theoretically. The thermoelectric effect in a layered conductor is analyzed and it is shown that the quasi-two-dimensional character of the dispersion law of the charge carriers results in gigantic oscillations of the thermo-emf.
Unidirectional single-frequency lasing from a ring-spiral coupled microcavity laser
Authors: Wu Xiang , Li Hao , Liu Liying , Xu Lei
Published: August 2008

A ring-spiral coupled microcavity laser was fabricated. The ring resonator works as an oscillator and has a diameter that is slightly less than that of the spiral cavity. The spiral provides wavelength selective feedback and emits light out from the notch. As a result, the coupled cavity generates unidirectional single-frequency laser emission. Its lasing threshold is also significantly lower than a single spiral-shaped microcavity laser.
Model of defect reactions and the influence of clustering in pulse-neutron-irradiated Si
Authors: Myers S. M. , Cooper P. J. , Wampler W. R.
Published: August 2008

Transient reactions among irradiation defects, dopants, impurities, and carriers in pulse-neutron-irradiated Si were modeled taking into account the clustering of the primal defects in recoil cascades. Continuum equations describing the diffusion, field drift, and reactions of relevant species were numerically solved for a submicrometer spherical volume, within which the starting radial distributions of defects could be varied in accord with the degree of clustering. The radial profiles corresponding to neutron irradiation were chosen through pair-correlation-function analysis of vacancy and interstitial distributions obtained from the binary-collision code MARLOWE, using a spectrum of primary recoil energies computed for a fast-burst fission reactor. Model predictions of transient behavior were compared with a variety of experimental results from irradiated bulk Si, solar cells, and bipolar-junction transistors. The influence of defect clustering during neutron bombardment was further distinguished through contrast with electron irradiation, where the primal point defects are more uniformly dispersed.
Investigation of contact-force dependent effects in conductive atomic force microscopy on Si and GaAs
Authors: Brezna W. , Smoliner J.
Published: August 2008

In this work, we systematically investigated the force dependence of conductive atomic force microscopy on n-type Si and n-type GaAs. IV curves were recorded under different tip sample forces and the corresponding Schottky barrier heights were extracted. The force dependent barrier heights of the Si and GaAs samples showed distinct reproducible differences. At low forces, the Schottky barriers decrease with increasing force because the native oxide layer on both the Si and the GaAs sample surface has to be penetrated. At intermediate forces on the GaAs sample, the Schottky barrier showed a large forced dependent increase due to the pressure coefficient of the GaAs band gap. Furthermore, a sudden change in the Schottky barrier increase with tip force was interpreted as the Γ-X band crossover in GaAs.
Quantum anharmonic densities of states using the Wang–Landau method
Authors: Basire M. , Parneix P. , Calvo F.
Published: August 2008

The Wang–Landau sampling method is adapted to the calculation of quantum densities of states for fully coupled anharmonic systems. The accuracy of the method is illustrated against exact counting for two molecules with separable oscillators, namely, the Zundel complex H5O2+ and the Na11 cluster. Application to the fully coupled naphthalene molecule (C10H8) reveals significant deviations in the finite temperature thermodynamical properties that are not captured by simple perturbation theory. There are no limitations in the size of the molecules that can be treated with this method.
R
-matrix theory of quantum transport and recursive propagation method for device simulations
Authors: Mil’nikov Gennady , Mori Nobuya , Kamakura Yoshinari , Ezaki Tatsuya
Published: August 2008

We present a theory of quantum transport based on spectral expansion of Green’s function in an open system. In continuous models, this representation makes it possible to avoid discretization of the device area and achieve a much higher numerical accuracy with a lower computational burden compared to common grid schemes. We formulate a numerical method which enables all the observables of interest to be propagated through the device area so that the major portion of the computation time scales linearly with the device volume. As an illustration, we apply the method to quantum ballistic electron transport in model three-dimensional metal oxide semiconductor field effect transistors.
Synchronization of chaotic systems with delay using intermittent linear state feedback
Authors: Huang Tingwen , Li Chuandong , Liu Xinzhi
Published: August 2008

This paper investigates the synchronization of coupled chaotic systems with time delay by using intermittent linear state feedback control. An exponential synchronization criterion is obtained by means of Lyapunov function and differential inequality method. Numerical simulations on the chaotic Ikeda and Lu systems are given to demonstrate the effectiveness of the theoretical results.
Nonlinear magnetoresistance of an irradiated two-dimensional electron system
Authors: Lei X. L. , Liu S. Y.
Published: August 2008

Nonlinear magnetotransport of a microwave-irradiated high-mobility two-dimensional electron system under a finite direct current excitation is analyzed using a dc-controlled scheme with photon-assisted transition mechanism. The predicted amplitudes, extrema, and nodes of the oscillatory differential resistance versus the magnetic field and the current density are in excellent agreement with the recent experimental observation [Hatke et al. Phys. Rev. B 77, 201304(R) (2008)].
A portable UV-fluorescence multispectral imaging system for the analysis of painted surfaces
Authors: Comelli Daniela , Valentini Gianluca , Nevin Austin , Farina Andrea , Toniolo Lucia , Cubeddu Rinaldo
Published: August 2008

A portable fluorescence multispectral imaging system was developed and has been used for the analysis of artistic surfaces. The imaging apparatus exploits two UV lamps for fluorescence excitation and a liquid crystal tunable filter coupled to a low-noise charge coupled device as the image detector. The main features of the system are critically presented, outlining the assets, drawbacks, and practical considerations of portability. A multivariate statistical treatment of spectral data is further considered. Finally, the in situ analysis with the new apparatus of recently restored Renaissance wall paintings is presented.
First-principles study of structural and energetic properties of A2Hf2O7 (A=Dy, Ho, Er) compounds
Authors: Zu X. T. , Li N. , Gao F.
Published: August 2008

The structural and energetic properties of A2Hf2O7 (A=Dy, Ho, Er) compounds have been investigated by means of ab initio total energy calculations. For Er2Hf2O7 the defect fluorite structure is predicted to be more stable than pyrochlore structure, agreeing well with previous experimental [J. Inorg. Nucl. Chem. 31, 2367 (1969); J. Less Common Met. 14, 435 (1968)] and theoretical [J. Am. Ceram. Soc. 85, 2139 (2002)] investigations. In contrast to Er2Hf2O7 pyrochlore, Dy2Hf2O7 and Ho2Hf2O7 prefer pyrochlore structures, which is consistent with the recent experimental observations of Dy2Hf2O7 compound [J. Solid State Chem. 179, 1990 (2006)].
Mechanisms of unexpected reduction in hole concentration in Al-doped 4H-SiC by 200 keV electron irradiation
Authors: Matsuura Hideharu , Minohara Nobumasa , Ohshima Takeshi
Published: August 2008

The hole concentration in Al-doped p-type 4H-SiC was found to be significantly reduced by electron irradiation when compared to the hole concentration in Al-doped p-type Si; this is an unexpected result. The temperature dependence of the hole concentration p(T) in Al-doped 4H-SiC irradiated with 200 keV electrons at various fluences was measured. Only substitutional C atoms in SiC can be displaced by irradiation with 200 keV electrons. The reduction in p(T) by the electron irradiation was found to be mainly due to a decrease in Al acceptors and not due to an increase in defects (e.g., C vacancies) located around the middle of the bandgap in SiC. Based on the analysis of p(T), two types of acceptor species were detected and the density and energy level of each acceptor species were determined. An equation describing the fluence dependence of each acceptor density is proposed. The results suggest that for the 200 keV electron irradiation, a substitutional C atom bonded to an Al acceptor was more easily displaced than a substitutional C atom bonded to four Si atoms.
Multilevel vibrational coherence transfer and wavepacket dynamics probed with multidimensional IR spectroscopy
Authors: Nee Matthew J. , Baiz Carlos R. , Anna Jessica M. , McCanne Robert , Kubarych Kevin J.
Published: August 2008

Multidimensional infrared (MDIR) spectroscopy of a strongly coupled multilevel vibrational system Mn2(CO)10 (dimanganese decacarbonyl) in cyclohexane solution reveals fully resolved excited vibrational state coherences that exhibit slow 0.25–0.50ps−1 decay constants. Detailed analysis of the waiting-time dependence of certain cross-peak amplitudes shows modulation at multiple frequencies, providing a direct signature of excited vibrational coherences resulting from coherence transfer. A new signature of coherence transfer is observed as temporally modulated cross-peak amplitudes with more than one modulation frequency. The relative importance of different coherence transfer paths is considered in the context of the orientational response of a system which includes two vibrational modes with parallel dipole moments. Since MDIR spectroscopy enables spectral isolation of individual excited vibrational coherences (i.e., coherences between fundamental excitations), these experiments report directly on the frequency-frequency correlation functions of the excited states relative to each other as well as relative to the ground state. These results highlight the rich information contained in fully exploring three-dimensional third-order spectroscopy, particularly regarding chemically relevant slower dynamics and the importance of intramolecular interactions leading to dephasing by optically dark or low-frequency modes of the molecule.
Stranski–Krastanov growth of GaN quantum dots on AlN template by metalorganic chemical vapor deposition
Authors: Zhang J. C. , Meyler B. , Vardi A. , Bahir G. , Salzman J.
Published: August 2008

GaN/AlN quantum dots (QDs) grown on sapphire/GaN substrate have been realized by low-pressure metalorganic chemical vapor deposition. The influence of the growth conditions, postgrowth annealing ambience, and roughness of AlN template surface has been investigated. QDs with 3–10 nm height, 40–100 nm diameter, and density from 1×1011 down to 1×108 cm−2 were achieved by adjusting the growth temperature, V/III ratio, and growth time. For the formation of QDs, the postgrowth annealing in H2 is more favorable than that in NH3; however, it results in a bad surface of wetting layer and therefore is not suitable for device fabrication. When rough-surface templates were used, small-sized dots with the same density as obtained on smooth-surface templates could be found besides some large clusters. An intense photoluminescence peak of QDs is observed at 15 K and up to room temperature.
Variable temperature photoluminescence of pulsed laser deposited ZnO thin films
Authors: Cui J. B. , Soo Y. C. , Thomas A. , Kandel H. , Chen T. P. , Daghlian C. P.
Published: August 2008

Variable temperature photoluminescence of ZnO thin films deposited by a reactive laser ablation of metallic zinc was investigated. Free and bound exciton emissions are absent at cryogenic temperature, and the near band edge (NBE) emission is independent of measurement temperature for the ZnO thin film deposited at room temperature. Annealing at 700 °C results in the removal of defects, reappearance of exciton emission, and a temperature dependent NBE emission. The experimental data suggest that defects play an important role in the band edge emission in terms of both spectra shape and temperature dependence. Our observations will have an impact on device applications using ZnO, especially for optoelectronics that utilizes the exciton emission.
Soft x-ray induced Ag diffusion in amorphous pulse laser deposited As50Se50 thin films: An x-ray photoelectron and secondary ion mass spectroscopy study
Authors: Kalyva M. , Siokou A. , Yannopoulos S. N. , Wagner T. , Krbal  , Orava J. , Frumar M.
Published: August 2008

In the present paper, x-ray photoelectron spectroscopy (XPS) is used to induce and study the Ag diffusion and dissolution in pulsed laser deposited As50Se50 amorphous chalcogenide films. Dynamic secondary ion mass spectroscopy (SIMS) is also employed to investigate the Ag atomic concentration in depth. Dynamic SIMS measurements reveal that even before x-ray irradiation a considerable percentage of the total silver amount diffuses into the matrix forming an ∼70 nm mixed Ag–Se–As layer. XPS analysis shows that x-ray irradiation induces further diffusion of silver into the chalcogenide matrix. At the end of the procedure silver is found to be homogeneously dissolved into the matrix leaving only a 5–7 nm thick surface layer with excess silver concentration. In this surface layer stable Ag2Se clusters existing probably in quasicrystalline form prohibit further diffusion. The origin of the mechanism of the x-ray induced Ag diffusion and dissolution in amorphous chalcogenides is discussed in light of the present results.
Ferromagnetic properties, electronic structure, and formation energy of Ga0.9375M0.0625N (M=vacancy, Ca) by first principles study
Authors: Fan S. W. , Yao K. L. , Liu Z. L. , Gao G. Y. , Min Y. , Cheng H. G.
Published: August 2008

Using the full potential linearized augmented plane wave method based on the spin density functional theory, we investigate the ferromagnetic properties, the electronic structure, and the formation energy of Ga0.9375M0.0625N (M=vacancy, Ca). The calculations indicate that both cases prefer ferromagnetic ground state. The magnetic moments mainly come from the N atoms surrounding the defect centers, which are different from the conventional diluted magnetic semiconductor. High formation energy for the Ga vacancy suggests that the defect concentration is too low to result in the ferromagnetic GaN. The formation energy for the two substitutional (CaGa,CaN) and two interstitial sites (tetrahedral T, Cai−T and octahedral O, Cai−O) doped configurations indicates that Ca prefers the substitutional Ga in GaN. The defect concentrations for the Ga0.9375Ca0.0625N under thermal equilibrium N-rich and N-realistic growth conditions are also discussed, respectively. The calculations show that defect concentration under N-rich condition can readily reach 7%, while under N-realistic growth condition, the maximum defect concentration is as low as 1.71% when the growth temperature increases to 1100 K (melting point of GaN). These results suggest that it would be a little difficult to achieve ferromagnetic state for Ga0.9375Ca0.0625N using the chemical-equilibrium fabrication method, such as chemical precipitation. Using the same method as that for Cu-doped ZnO [L. H. Ye et al., Phys. Rev. B 73, 033203 (2006)], the transition temperature of Ga0.9375Ca0.0625N may be close to room temperature.
Acceptor and donor impurities in GaN nanocrystals
Authors: Echeverría-Arrondo C. , Pérez-Conde J. , Bhattacharjee A. K.
Published: August 2008

We investigate acceptor and donor states in GaN nanocrystals doped with a single substitutional impurity. Quantum dots (QDs) of zinc-blende structure and spherical shape are considered with radius ranging from 4.5 to 67.7 Å. The size-dependent energy spectra are calculated within the sp3d5s∗ tight-binding model, which yields a good agreement with the confinement-induced blueshifts observed in undoped QDs. The computed binding energy is strongly enhanced with respect to the experimental bulk value when the dopant is placed at the center of the smallest QDs. It decreases with increasing QD size following a scaling law that extrapolates to the bulk limit. In order to estimate the degree of localization of the bound carriers, we analyze their wave functions and average radii. The resulting physical picture points to a highly localized acceptor hole, mostly distributed over the nearest-neighbor anion shell, and a much more extended donor electron. We also study off-center impurities in intermediate-sized QDs. The acceptor binding energy is approximately independent of the dopant position unless it is placed within a surface shell of thickness of the order of the bulk Bohr radius, where the ionization energy abruptly drops. On the contrary, the donor binding energy gradually decreases as the impurity is moved away from the center toward the QD surface.
Modeling deflagration-to-detonation transition in granular explosive pentaerythritol tetranitrate
Authors: Sáenz Juan A. , Stewart D. Scott
Published: August 2008

Based on an approach suggested by Stewart et al. [Phys. Fluids 6, 2515 (1994)] we develop a model to simulate deflagration-to-detonation transition (DDT) in pentaerythritol tetranitrate (PETN) powders. The model uses a continuum mechanics formulation of conservation laws for a mixture of solid reactants and gas products, written in terms of mixture quantities plus two independent variables used to account for exothermic conversion of solid reactants into gas products, and compaction associated with pore collapse and grain rearrangement. We propose a simple empirical dependence of the reaction rate on the initial bed compaction that allows us to calibrate the model for a wide range of initial conditions. For the solid reactants we use a wide-ranging equation of state (EOS) developed by Davis and co-workers in a series of papers [Proceedings of the Tenth International Symposium on Detonation, 1993, pp. 369–376; Explosive Effects and Applications (Springer, New York, 1998), Chap. 1, Combust. Flame 120, 399 (2000); Proceedings of the 12th International Symposium Detonation, San Diego, CA, 2002, pp. 624–631; . ONR 333-05-2; Proceedings of the Eighth Detonation Symposium, 1985, pp. 785–795; Proceedings of the 11th International Symposium on Detonation, 1998, pp. 303–308]. The EOS for powder uses the P-α model of Herrmann [J. Appl. Phys. 40, 2490 (1969)] and Carrol and Holt [J. Appl. Phys. 43, 759 (1972)]. To close the system, we suggest phenomenological closure relations, consistent with the limit of a compressible inert material and of a solid fully reactive material, such that the EOS can be posed only in terms of mixture quantities and the reaction and compaction variables. We demonstrate the model’s ability to capture DDT in PETN powders by matching transients typically observed in experiments through simulation. We show that for flows calculated using nonideal EOSs and complex reaction kinetics such as those formulated in our model, it is possible to define a separatrix, i.e., the C+ characteristic that separates the C+ characteristics that evolve into the detonation front from those that evolve away from it. We comment on the effects that the variability in the grain microstructure in PETN explosive powder beds can have on the overall mechanics of DDT and discuss possible ways to model this.
Low-temperature negative thermal expansion of the antiperovskite manganese nitride Mn3CuN codoped with Ge and Si
Authors: Huang Rongjin , Li Laifeng , Cai Fangshuo , Xu Xiangdong , Qian Lihe
Published: August 2008

We have synthesized antiperovskite manganese nitrides Mn3(Cu0.6SixGe0.4−x)N, (x=0–0.2) and investigated their negative thermal expansion (NTE) in the temperature range of 80–300 K. We found that the transition temperature of NTE moves toward lower temperature region and as well the NTE operation-temperature window (ΔT) becomes broader with increasing Si content. Typically, the giant low-temperature NTE coefficient identified in Mn3(Cu0.6Si0.15Ge0.25)N reaches as large as −16×10−6 K−1, and its ΔT reaches as wide as 100 K. The magnetic properties of these compounds were measured and correlated with the broadened NTE operation-temperature window. The present discovery highlights the potential applications of NTE materials in cryogenic engineering.
Quantum-classical Liouville dynamics in the mapping basis
Authors: Kim Hyojoon , Nassimi Ali , Kapral Raymond
Published: August 2008

The quantum-classical Liouville equation describes the dynamics of a quantum subsystem coupled to a classical environment. It has been simulated using various methods, notably, surface-hopping schemes. A representation of this equation in the mapping Hamiltonian basis for the quantum subsystem is derived. The resulting equation of motion, in conjunction with expressions for quantum expectation values in the mapping basis, provides another route to the computation of the nonadiabatic dynamics of observables that does not involve surface-hopping dynamics. The quantum-classical Liouville equation is exact for the spin-boson system. This well-known model is simulated using an approximation to the evolution equation in the mapping basis, and close agreement with exact quantum results is found.
UV polaritonic emission from a perovskite-based microcavity
Authors: Lanty G. , Lauret J. S. , Deleporte E. , Bouchoule S. , Lafosse X.
Published: August 2008

We report on the realization of a molecule-based one-dimensional microcavity emitting in the near UV range at room temperature. The active material is a thin film of the two-dimensional perovskite (C6H5C2H4–NH3)2PbCl4, a molecular compound absorbing and emitting light around 3.6 eV. Angle-resolved reflectivity and photoluminescence measurements show that this microcavity works in the strong coupling regime. The emitting UV polariton is a mixed state between the photon cavity mode and the exciton of the perovskite-type semiconductor.
Spectrum modulation of relativistic electrons by laser wakefield
Authors: Nakanii N. , Kondo K. , Kuramitsu Y. , Mori Y. , Miura E. , Tsuji K. , Kimura K. , Fukumochi S. , Kashihara M. , Tanimoto T. , Nakamura H. , Ishikura T. , Takeda K. , Tampo M. , Takabe H. , Kodama R. , Kitagawa Y. , Mima K. , Tanaka K. A.
Published: August 2008

Energetic electrons were generated by the interaction of a high-intensity laser pulse with a plasma preformed from a hollow plastic cylinder via laser-driven implosion. The spectra of a comparatively high-density plasma ∼1019 cm−3 had a bump around 10 MeV. Simple numerical calculations explained the spectra obtained in this experiment. This indicates that the plasma tube has sufficient potential to convert a Maxwellian spectrum to a comparatively narrow spectrum.
The role of the relative voltage and phase for frequency coupling in a dual-frequency capacitively coupled plasma
Authors: O’Connell D. , Gans T. , Semmler E. , Awakowicz P.
Published: August 2008

Frequency coupling in multifrequency discharges is a complex nonlinear interaction of the different frequency components. An alpha-mode low pressure rf capacitively coupled plasma operated simultaneously with two frequencies is investigated and the coupling of the two frequencies is observed to greatly influence the excitation and ionization within the discharge. Through this, plasma production and sustainment are dictated by the corresponding electron dynamics and can be manipulated through the dual-frequency sheath. These mechanisms are influenced by the relative voltage and also the relative phase of the two frequencies.
Short- and medium-range structure of multicomponent bioactive glasses and melts: An assessment of the performances of shell-model and rigid-ion potentials
Authors: Tilocca Antonio
Published: August 2008

Classical and ab initio molecular dynamics (MD) simulations have been carried out to investigate the effect of a different treatment of interatomic forces in modeling the structural properties of multicomponent glasses and melts. The simulated system is a soda-lime phosphosilicate composition with bioactive properties. Because the bioactivity of these materials depends on their medium-range structural features, such as the network connectivity and the Qn distribution (where Qn is a tetrahedral species bonded to n bridging oxygens) of silicon and phosphorus network formers, it is essential to assess whether, and up to what extent, classical potentials can reproduce these properties. The results indicate that the inclusion of the oxide ion polarization through a shell-model (SM) approach provides a more accurate representation of the medium-range structure compared to rigid-ion (RI) potentials. Insight into the causes of these improvements has been obtained by comparing the melt-and-quench transformation of a small sample of the same system, modeled using Car–Parrinello MD (CPMD), to the classical MD runs with SM and RI potentials. Both classical potentials show some limitations in reproducing the highly distorted structure of the melt denoted by the CPMD runs; however, the inclusion of polarization in the SM potential results in a better and qualitatively correct dynamical balance between the interconversion of Qn species during the cooling of the melt. This effect seems to reflect the slower decay of the fraction of structural defects during the cooling with the SM potential. Because these transient defects have a central role in mediating the Qn transformations, as previously proposed and confirmed by the current simulations, their presence in the melt is essential to produce an accurate final distribution of Qn species in the glass.
A bent electrostatic ion beam trap for simultaneous measurements of fragmentation and ionization of cluster ions
Authors: Aviv O. , Toker Y. , Errit M. , Bhushan K. G. , Pedersen H. B. , Rappaport M. L. , Heber O. , Schwalm D. , Zajfman D.
Published: August 2008

We describe a bent electrostatic ion beam trap in which cluster ions of several keV kinetic energy can be stored on a V-shaped trajectory by means of an electrostatic deflector placed between two electrostatic mirrors. While maintaining all the advantages of its linear counterpart [Zajfman et al., Phys. Rev. A 55, R1577 (1997); Dahan et al., Rev. Sci. Instrum. 69, 76 (1998)], such as long storage times, straight segments, and a field-free region for merged or crossed beam experiments, the bent trap allows for simultaneous measurement of charged and neutral fragments and determination of the average kinetic energy released in the fragmentation. These unique properties of the bent trap are illustrated by first results concerning the competition between delayed fragmentation and ionization of Aln− clusters after irradiation by a short laser pulse.
Controlled reproducible alignment of cone targets and mitigation of preplasma in high intensity laser interactions
Authors: Renard-Le Galloudec Nathalie , Cho Byoung-Ick , Osterholz Jens , Ditmire Todd
Published: August 2008

The use of cone targets in high intensity laser-plasma experiments has been of recent interest because of their potential use in integrated fast ignition experiments. Simpler experiments provide a good avenue for understanding the underlying physics, however precise control of the alignment along with good pointing accuracy is of crucial importance. While on big laser facilities target alignment is done precisely with several microscopes, it is not always the case on smaller facilities. This can have a detrimental effect on the quality of the results. We have developed and characterized a method for accurate alignment of intense laser pulses into a cone target. This, along with optimal positioning of the focus compared to the tip, efficiently uses the shape of the target to microfocus the laser light and concentrates the hot electrons in the tip, and can mitigate preplasma issues.
Magnetically and optoelectronically isolated trigger for pulse-power applications
Authors: Yu Yi , Wen Yi-Zhi , Yu Chang-Xuan , Wan Shu-De , Liu Wan-Dong
Published: August 2008

In this article the design of a magnetically and optically isolated trigger is discussed. Critical issues for trigger design are presented together with some experimental usages. In this trigger, an optical coupler is used to cut off the ground loop between the circuits of the preceding control system and the power supplies of the double functional device KT-5D (as a simple magnetic torus or a tokamak). A magnetic coupler is used to provide a pulse-power output for the silicon controlled rectifier. The output is a 230μs transistor-transistor logic (TTL) with an amplitude of 3.0V. The rising time and the trailing time are no more than 4.0μs. The delay time between the input and the output of the trigger is 6.8±0.2μs. A resistance-capacity branch is integrated into the trigger to provide an adjustable delay time of up to 72ms. The zero quiescent dissipation character endows the trigger with a long lifetime of years dispensing with any charging or replacing batteries. It is observed that the trigger has a good stability even in a high electromagnetic circumstance (at the order of 1T). Using it as a trigger for the silicon controlled rectifier, we realized the compatible operation of the steady state mode and the pulse mode in KT-5D.
Liquid crystal display using combined fringe and in-plane electric fields
Authors: Park Ji Woong , Ahn Young Joo , Jung Jun Ho , Lee Seung Hee , Lu Ruibo , Kim Hyang Yul , Wu Shin-Tson
Published: August 2008

A high performance liquid crystal display using combined fringe and in-plane horizontal electric fields is proposed. The strong electric fields cause more liquid crystals to reorient almost in plane above and between the pixel electrodes. As a result, the operation voltage is lower and transmittance is higher than those of fringe field switching and in-plane switching modes, while preserving a wide viewing angle. Such a high performance device is particularly attractive for large panel liquid crystal displays.
Extraordinary midinfrared transmission of rectangular coaxial nanoaperture arrays
Authors: Yanik Ahmet Ali , Wang Xihua , Erramilli Shyamsunder , Hong Mi K. , Altug Hatice
Published: August 2008

We analyze the extraordinary transmission effect in the periodic and random nanoaperture arrays in optically thick metal films. Experimental studies are combined with simulations to show that extraordinary transmission effect at midinfrared wavelengths is enhanced when the decaying waveguide mode of a single nanoaperture couples through the collective surface plasmon excitations created through periodicity. Transmission characteristics of the individual nanoapertures are investigated by randomizing the apertures. By comparing rectangular to coaxial rectangular nanoapertures, both of which support TE01-like decaying waveguide modes, we study the effect of nanoaperture geometry on the efficiency of the transmission.
Biomimetization of butterfly wings by the conformal-evaporated-film-by-rotation technique for photonics
Authors: Martín-Palma R. J. , Pantano C. G. , Lakhtakia A.
Published: August 2008

Mimetization of biological structures aims to take advantage of their spatial features for the development of devices of tailored functionality. In this work, we replicated the wing of a butterfly at the micro- and nanoscales by implementing the conformal-evaporated-film-by-rotation (CEFR) technique. Chalcogenide glasses were used due to their good optical and mechanical properties. Morphological characterization and optical measurements indicate high-fidelity replication of the original biotemplate; furthermore, the optical properties of the butterfly wings have a structural origin. The CEFR technique might be useful for the fabrication of highly efficient, biomimetic optical devices.
Surface roughness effects on the terahertz reflectance of pure explosive materials
Authors: Ortolani M. , Lee J. S. , Schade U. , Hübers H.-W.
Published: August 2008

We studied the effect of surface roughness on terahertz reflectance spectra of explosives at both quasinormal and oblique incidence by Fourier-transform spectroscopy. The optical constants of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane and 1,3,5 trinitro-1,3,5 triazacyclohexane were determined from the reflectance spectra of pure optically flat pellets and clear spectral signatures were found in the 0.5–8THz range. In the case of a realistic surface roughness of several tens of microns, the observation of the spectral signatures at quasinormal incidence is hindered by the specular reflectance roll-off at terahertz frequencies. On increasing the angle of incidence, the roll-off occurred at higher frequency and the surface roughness was optically measured. Oblique incidence geometries can benefit the development of terahertz standoff detection devices.
Long-time evolution of the photoluminescence in C- and M-plane GaN∕AlN quantum dots upon intense ultraviolet irradiation
Authors: Brandt O. , Flissikowski T. , Schaadt D. M. , Jahn U. , Trampert A. , Grahn H. T.
Published: August 2008

We compare the spontaneous emission of C- and M-plane GaN quantum dots embedded in AlN. C-plane dots are characterized by an intense emission with an exceptionally long decay time up to room temperature. In contrast, M-plane dots exhibit a much weaker emission with a very short decay time. In addition, the emission of the C-plane dots temporally evolves on a timescale of seconds, while the emission of the M-plane dots is stable over time. These findings are correlated with the different growth mode and microstructure of C- and M-plane GaN quantum dots.
Flow-induced melting of condensed domains within a dispersed Langmuir film
Authors: Davoust Laurent , Huang Yu-Lin , Chang Shuo-Hung
Published: August 2008

During phase transition from the liquid-expanded to the liquid-condensed state, a dispersed Langmuir film of pentadecanoic acid is submitted to an annular shear flow of moderate Reynolds number (Re=10–100). The mesoscopic morphology of this two-phase Langmuir film is investigated based on area fraction distribution of the condensed phase after a permanent regime is established. The distribution demonstrates radially inwards packing along the liquid surface induced by centripetal flow originating from centrifugation of the subphase along the rotating floor. For a growing level of centrifugation, a circular Reynolds ridge arises along the liquid surface. The Langmuir film experiences a strong morphological transition driven by a balance between surface shear and reduced line tension. As a result, a shear-induced melting of the condensed domains generates a new patterning which can be described as a regular and monodispersed matrix of tiny condensed droplets.
Polar-drive designs for optimizing neutron yields on the National Ignition Facility
Authors: Cok A. M. , Craxton R. S. , McKenty P. W.
Published: August 2008

Polar-drive designs are proposed for producing symmetric implosions of thin-shell, DT gas-filled targets leading to high fusion-neutron yields for neutron-diagnostic development. The designs can be implemented as soon as the National Ignition Facility (NIF) [E. M. Campbell and W. J. Hogan, Plasma Phys. Control. Fusion 41, B39 (1999)] is operational as they use indirect-drive phase plates. Two-dimensional simulations using the hydrodynamics code SAGE [R. S. Craxton and R. L. McCrory, J. Appl. Phys. 56, 108 (1984)] have shown that good low-mode uniformity can be obtained by choosing combinations of pointing and defocusing of the beams, including pointing offsets of individual beams within some of the NIF laser-beam quads. The optimizations have been carried out for total laser energies ranging from 350kJto1.5MJ, enabling the optimum pointing and defocusing parameters to be determined through interpolation for any given laser energy in this range. Neutron yields in the range of 1015–1016 are expected.
Phase transformations during rapid heating of Al/Ni multilayer foils
Authors: Trenkle Jonathan C. , Koerner Lucas J. , Tate Mark W. , Gruner Sol M. , Weihs Timothy P. , Hufnagel Todd C.
Published: August 2008

We have used self-propagating exothermic reactions in Al/Ni multilayers as a means to explore the effect of rapid heating on phase transformations. Using time-resolved synchrotron x-ray microdiffraction with an extremely fast detector, we were able to examine the reaction sequence in detail at heating rates of ∼106 K s−1. We observed that the intermediate phases formed during the self-propagating reactions are different from those formed at lower heating rates, even though the final phases are the same. In situ characterization is essential, as other means of studying self-propagating reactions (such as quenching the reaction followed by ex situ analysis) provide different—and potentially misleading—results.
Characterization of indirect and direct interband transitions of anatase TiO2 by thermoreflectance spectroscopy
Authors: Ho Ching-Hwa , Tsai Ming-Cheng , Wong Ming-Show
Published: August 2008

We characterize three as-deposited anatase TiO2 (a-TiO2) films with different deposition flux angles of 0°, 53°, and 86° tilted to Si ⟨001⟩ using thermoreflectance (TR) measurement in the temperature range between 30 and 300 K. The TR spectra at low temperature clearly show considerable difference in interband transitions of the tetragonal a-TiO2 with the largely top plane of {001} or the largely side planes of {100} and {010}. The indirect and direct interband transitions of the a-TiO2 are evaluated. The temperature dependences of the interband transition energies of the a-TiO2 are analyzed. The optical-axial anisotropy of the a-TiO2 films is discussed.
High performance indium gallium zinc oxide thin film transistors fabricated on polyethylene terephthalate substrates
Authors: Lim Wantae , Jang Jung Hun , Kim S.-H. , Norton D. P. , Craciun V , Pearton S. J. , Ren F. , Shen H.
Published: August 2008

High-performance amorphous (α−) InGaZnO-based thin film transistors (TFTs) were fabricated on flexible polyethylene terephthalate substrates coated with indium oxide (In2O3) films. The InGaZnO films were deposited by rf magnetron sputtering with the presence of O2 at room temperature. The n-type carrier concentration of InGaZnO film was ∼2×1017 cm−3. The bottom-gate-type TFTs with SiO2 or SiNx gate dielectric operated in enhancement mode with good electrical characteristics: saturation mobility 11.5 cm2 V−1 s−1 for SiO2 and 12.1 cm2 V−1 s−1 for SiNx gate dielectrics and drain current on-to-off ratio >105. TFTs with SiNx gate dielectric exhibited better performance than those with SiO2. This is attributed to the relatively high dielectric constant (i.e., high-k material) of SiNx. After more than 500 h aging time at room temperature, the saturation mobility of the TFTs with SiO2 gate dielectric was comparable to the as-fabricated value and the threshold voltage shift was 150 mV.
The determination of Young’s modulus in noble metal nanowires
Authors: Ao Z. M. , Li S. , Jiang Q.
Published: August 2008

The origin of the size and temperature dependent Young’s modulus (Y) in noble metal nanowires with fcc structure was investigated by considering the size effects on surface bond contraction and melting temperature (Tm) variation. The results show that Y decreases with a shrinking disparity between Tm and the material’s application temperature, while the surface bond contraction results in increase in Y with size reduction. Thus, the variation in Y is the consequence of the subtle interplay and competition between these two factors. This finding indicates that Y of nanowires can be controlled by manipulating the size and the application temperature.
Plasma characterization in a diode with a carbon-fiber cathode
Authors: Vekselman V. , Gleizer J. , Yarmolich D. , Felsteiner J. , Krasik Ya. , Liu L. , Bernshtam V.
Published: August 2008

Results of optical and spectroscopic studies of the plasma formation at the surface of two types of carbon-fiber cathodes in a diode powered by an ∼200 kV accelerating pulse are presented. It was found that during the pulse, generation of the plasma occurs in a form of several millimeter size plasma spots. In the vicinity of the cathode surface the average plasma density and temperature were found to be ∼3×1014 cm−3 and ∼5 eV, respectively, for an electron current density of ∼22 A/cm2. The plasma expansion velocity toward the anode was found to be ∼1.5×106 cm/s during the first 150 ns of the accelerating pulse duration.