bluuebunny/crossref_metadata_2025 huggingface dataset:
Memory Assessment on an Interdisciplinary Rehabilitation Team: A Theoretically Based Framework
Authors: Sander Angelle M. , Nakase-Richardson Risa , Constantinidou Fofi , Wertheimer Jeffrey , Paul Diane R.
Published: October 2007

Purpose

To describe a cognitive neuroscience model of memory that can be used to guide assessment and promote consistent terminology among members of the rehabilitation team, and to relate the model to frequently used assessment measures.

Method

Description of a model of memory, description of how frequently used memory measures relate to the model, and presentation of case studies to exemplify the application of the model to the clinical assessment of memory.

Conclusions

Use of a theoretical framework is important for choosing assessment instruments, interpreting the results of test performance, and communicating with patients, their family members, and other members of the interdisciplinary team. Understanding where in the memory process a breakdown occurs can guide treatment recommendations and feedback to patients and family members.
Perspectives on Treatment for Communication Deficits Associated With Right Hemisphere Brain Damage
Authors: Lehman Blake Margaret
Published: October 2007

Purpose

To describe the current treatment research for communication (prosodic, discourse, and pragmatic) deficits associated with right hemisphere brain damage and to provide suggestions for treatment selection given the paucity of evidence specifically for this population.

Method

The discussion covers (a) clinical decision processes and evidence-based practice; (b) a review of right hemisphere communication deficits and existing treatment studies; (c) accounts of right hemisphere function, right hemisphere deficits, and theoretically motivated treatments; and (d) a guide for exploring and selecting treatments based on deficits rather than etiology.

Conclusions

Controlled treatment studies for communication deficits specifically for adults with right hemisphere brain damage are limited to aprosodia. For other communication deficits, clinicians may select treatments based on current theories of right hemisphere function and right hemisphere deficits, and/or treatments developed for other etiologies for which deficits are similar to those associated with right hemisphere damage.
Self-Administered Cued Naming Therapy: A Single-Participant Investigation of a Computer-Based Therapy Program Replicated in Four Cases
Authors: Ramsberger Gail , Marie Basem
Published: October 2007

Purpose

This study examined the benefits of a self-administered, clinician-guided, computer-based, cued naming therapy. Results of intense and nonintense treatment schedules were compared.

Method

A single-participant design with multiple baselines across behaviors and varied treatment intensity for 2 trained lists was replicated over 4 participants. Two lists of words were treated sequentially. The same methods and equal numbers of treatment sessions were used, but the number of sessions per week differed across word lists: nonintense (2/week) or intense (5/week). Probes of performance on both word lists were carried out to examine acquisition, maintenance, and generalization.

Results

There was strong evidence of improved naming (acquisition) of trained words in 3 of the 4 participants regardless of treatment intensity. There was strong evidence of maintenance for 1 participant and moderate evidence for the remaining 3 participants. Evidence of generalization to untrained words was weak.

Conclusions

Results suggest that self-administered, computer-based, cued naming therapy using a common mixed-cue protocol may be beneficial to a wide range of persons with aphasia regardless of treatment schedule. If results are replicated with a larger sample, treatments such as this may be a low-cost supplement or extension to traditional aphasia therapy.
Pragmatic Language Profiles of School-Age Children With Autism Spectrum Disorders and Williams Syndrome
Authors: Philofsky Amy , Fidler Deborah J. , Hepburn Susan
Published: October 2007

Purpose

To describe and compare the pragmatic language profiles of school-age children with autism spectrum disorders (ASD) and Williams syndrome (WS) on a standardized measure to determine whether a standard pragmatics tool can differentiate between 2 groups of children with opposing social presentations and pragmatic language difficulties.

Method

Twenty-two parents of school-age children with ASD, 21 parents of school-age children with WS, and 19 parents of school-age typically developing children rated their child on the Children’s Communication Checklist—Second Edition (CCC–2; D. Bishop, 2003), a standardized pragmatic language assessment tool.

Results

Both clinical groups demonstrated impairment in overall communication and pragmatic language functioning, but children with WS performed significantly better on overall pragmatic language functioning, and the magnitude of the effect was medium. Profile examination revealed equivalent performances between ASD and WS on most CCC–2 subscales; however, significantly better performances on the Coherence, Stereotyped Language, Nonverbal Communication, and Social Relations subscales were observed in WS.

Conclusions

The CCC–2 appears to provide an effective means to identify and characterize pragmatic language difficulties using a standardized approach in children with ASD and WS.
A Preliminary Examination of Vocabulary and Word Learning in African American Toddlers From Middle and Low Socioeconomic Status Homes
Authors: Horton-Ikard RaMonda , Ellis Weismer Susan
Published: October 2007

Purpose

This study examined the effect of socioeconomic status (SES) on the early lexical performance of African American children.

Method

Thirty African American toddlers (30 to 40 months old) from low-SES (
n
= 15) and middle-SES (
n
= 15) backgrounds participated in the study. Their lexical-semantic performance was examined on 2 norm-referenced standardized tests of vocabulary, a measure of lexical diversity (number of different words) derived from language samples, and a fast mapping task that examined novel word learning.

Results

Toddlers from low-SES homes performed significantly poorer than those from middle-SES homes on standardized receptive and expressive vocabulary tests and on the number of different words used in spontaneous speech. No significant SES group differences were observed in their ability to learn novel word meanings on a fast mapping task.

Conclusion

The influence of socioeconomic background on African American children’s lexical semantic tasks varies with the type of measure used.
The Icarus Paradox: An Analysis of a Totally Destructive System
Authors: Drummond Helga
Published: October 2007

This paper uses a case study to illustrate and further extend the notion of ‘socially destructive systems’. Baskerville and Land define a destructive information system as either coming apart internally or threatening to take their environment apart. Building upon their insights, this paper suggests that destructive systems emerge from the very attributes that attract organisations to information systems in the first place - a phenomenon encapsulated by the so-called ‘Icarus paradox’. Icarus flew so close to the Sun that his wax wings that had enabled him to fly in the first place melted sending him plunging to his death. The case study of an insurance company shows how a system that increased claims processing productivity in the short run resulted in higher costs and lower customer satisfaction in the long run. The paradox is explained by a disconnect between ‘espoused-theory’ and ‘theory-in-use’. Issues for further research include developing techniques of impact analysis to measure recursive losses arising from ‘destructive systems’ and for gauging the level of complexity at which computer-based automation becomes counterproductive. An important recommendation for practice is that computer-based systems are efficient only to a point. For more complex tasks organisations may need to put more emphasis upon developing people.
Longitudinal photons in a relativistic magneto-active plasma
Authors: Tsintsadze N. L. , Rehman Ayesha , Murtaza G. , Shah H. A.
Published: October 2007

This paper presents some aspects of interaction of superstrong high-frequency electromagnetic waves with strongly magnetized plasmas. The case in which the photon-photon interaction dominates the photon-plasma particle interaction is considered. Strictly speaking, the photon and photon bunch interaction leads to the self-modulation of the photon gas. Assuming that the density of the plasma does not change, the dispersion relation, which includes relativistic self-modulation, is investigated. The existence of longitudinal photons in a strong magnetic field has the well-known Bogoliubov-type energy spectrum. The stability of the photon flow is investigated and an expression for Landau damping of the photons is obtained. Finally, it has been shown that the interaction of even a very strong electromagnetic radiation with a plasma does not always lead to instability, but causes only a change in plasma properties, whereby the plasma remains stable.
Electron heat transport comparison in the Large Helical Device and TJ-II
Authors: García J. , Dies J. , Castejón F. , Yamazaki K.
Published: October 2007

The electron heat transport in the Large Helical Device (LHD) [K. Ida, T. Shimozuma, H. Funaba et al., Phys. Rev. Lett. 91, 085003 (2003)] and TJ-II [F. Castejón, V. Tribaldos, I. García-Cortés, E. de la Luna, J. Herranz, I. Pastor, T. Estrada, and TJ-II Team, Nucl. Fusion 42, 271 (2002)] is analyzed by means of the TOTAL [K. Yamazaki and T. Amano, Nucl. Fusion 32, 4 (1992)] and PRETOR-Stellarator [J. Dies, F. Castejon, J. M. Fontdecaba, J. Fontanet, J. Izquierdo, G. Cortes, and C. Alejaldre, Proceedings of the 29th European Physical Society Conference on Plasma Physics and Controlled Fusion, Montreux, 2002, Europhysics Conference Abstracts, 2004, Vol. 26B, P-5.027] plasma simulation codes and assuming a global transport model mixing GyroBohm-like drift wave model and other drift wave model with shorter wavelength. The stabilization of the GyroBohm-like model by the E×B shear has been also taken into account. Results show how such kind of electron heat transport can simulate experimental evidence in both devices, leading to the electron internal transport barrier (eITB) formation in the LHD and to the so-called “enhanced heat confinement regimes” in TJ-II when electron density is low enough. Therefore, two sources for the anomalous electron heat transport can coexist in plasmas with eITB; however, for each device the relative importance of anomalous and neoclassical transport can be different.
Flux tube disconnection: An example of three-dimensional reconnection
Authors: Wilmot-Smith A. L. , Priest E. R.
Published: October 2007

Magnetic reconnection in three dimensions (3D) is fundamentally different in many respects from its two-dimensional counterpart. An analytical example of a global 3D general magnetic reconnection process is presented here, in which a magnetic flux tube has its footpoints rotated in different directions. A localized nonideal region is found in the center of the tube where the field lines are twisted as a result of the footpoint counter-rotation. A qualitative analysis demonstrates how the parameters that determine the strength and geometry of the magnetic field depend on the rotational driving velocity. The reconnection rate measures the rate at which field lines within the entire flux tube are changing their magnetic connections, and is shown to be proportional to the driving velocity imposed on its footpoints. The qualitative estimates are confirmed by an exact kinematic 3D magnetohydrodynamic analytical solution, which possesses a localized three-dimensional current and determines the reconnection rate quantitatively.
Nonlinear polarization and dissipative correspondence between low-frequency fluid and gyrofluid equations
Authors: Scott Bruce D.
Published: October 2007

The correspondence between gyrofluid and low-frequency fluid equations is examined. The lowest-order conservative effects in E×B advection, parallel dynamics, and curvature match trivially. The principal concerns are polarization fluxes, and dissipative parallel viscosity and parallel heat fluxes. The emergence of the polarization heat flux in the fluid model and its contribution to the energy theorem is reviewed. It is shown that gyroviscosity and the polarization fluxes are matched by the finite gyroradius corrections to advection in the long-wavelength limit, provided that the differences between gyrocenter and particle representations are taken into account. The dissipative parallel viscosity is matched by the residual thermal anisotropy in the gyrofluid model in the collision-dominated limit. The dissipative parallel heat flux is matched by the gyrofluid parallel heat flux variables in the collision-dominated limit. Hence, the gyrofluid equations are a complete superset of the low-frequency fluid equations.
Kinetic-ion simulations addressing whether ion trapping inflates stimulated Brillouin backscattering reflectivities
Authors: Cohen B. I. , Williams E. A. , Vu H. X.
Published: October 2007

An investigation of the possible inflation of stimulated Brillouin backscattering (SBS) due to ion kinetic effects is presented using electromagnetic particle simulations and integrations of three-wave coupled-mode equations with linear and nonlinear models of the nonlinear ion physics. Electrostatic simulations of linear ion Landau damping in an ion acoustic wave, nonlinear reduction of damping due to ion trapping, and nonlinear frequency shifts due to ion trapping establish a baseline for modeling the electromagnetic SBS simulations. Systematic scans of the laser intensity have been undertaken with both one-dimensional particle simulations and coupled-mode-equations integrations, and two values of the electron-to-ion temperature ratio (to vary the linear ion Landau damping) are considered. Three of the four intensity scans have evidence of SBS inflation as determined by observing more reflectivity in the particle simulations than in the corresponding three-wave mode-coupling integrations with a linear ion-wave model, and the particle simulations show evidence of ion trapping.
Potential fluctuations and energetic ion production in hollow cathode discharges
Authors: Goebel Dan M. , Jameson Kristina K. , Katz Ira , Mikellides Ioannis G.
Published: October 2007

Ions with energies significantly in excess of the applied discharge voltage have been reported for many years in hollow cathode discharges. Models of dc potential hills downstream of the cathode and instabilities in postulated double layers in the cathode orifice have been proposed to explain this, but have not been substantiated. Measurements of the dc and rf plasma density and potential profiles near the exit of hollow cathodes by miniature fast-scanning probes suggests that turbulent ion acoustic fluctuations and ionization instabilities in the cathode plume significantly increase the energy of the ions that flow from this region. Increases in the discharge current and/or decreases in the cathode gas flow enhance the amplitude of the fluctuations and increase the number and energy of the energetic ions, which increases the erosion rate of the cathode electrodes. The transition from the quiescent “spot mode” to the noisy “plume mode” characteristic of these discharges is found to be a gradual transition of increasing fluctuation amplitudes.
The coaxial gyrotron with two electron beams. I. Linear theory and nonlinear theory
Authors: Liu Shenggang , Yuan Xuesong , Fu Wengjie , Yan Yang , Zhang Yaxin , Li Hongfu , Zhong Renbin
Published: October 2007

The coaxial gyrotron with two electron beams (CGTB) is proposed and investigated in this paper. This paper consists of two parts: the linear theory and nonlinear theory of CGTB are presented in part I and the investigation on the dual frequency operation, a special operation state of CGTB, is given in part II. The magnetron injection gun with two electron beams has been developed, and simulations show that it may work well. It may guarantee that both the electric potential and the ratio of vertical to longitudinal velocities of two electron beams are equal. The results of the calculation show that CGTB has some distinguished advantages: mode competition is improved and output power is enhanced. Thus CGTB may be capable of providing 2–4MW continuous-wave (CW) at 170GHz to meet the demand of very high radio frequency CW power 1–2MW in the ITER [ITER EDA Agreement and Protocol 2 (IAEA, Vienna, 1994)] program and other applications.
Three-dimensional observations of periodically poled domains in a LiTaO3 quasiphase matching crystal by second harmonic generation tomography
Authors: Uesu Yoshiaki , Yokota Hiroko , Kawado Satoshi , Kaneshiro Junichi , Kurimura Sunao , Kato Noritaka
Published: October 2007

Second harmonic generation interference tomography which enables us to obtain three-dimensional images of ferroelectric antiparallel domain structures is devised. Periodically poled domains (PPDs) inside a LiTaO3 quasiphase matching crystal (QPM) are observed by this microscope. Section images perpendicular to the polar z axis show that the PPD structure is maintained throughout the top quarter of the sample but it starts to lose the periodic nature in the bottom half of the sample. Corresponding degradation of the QPM performance is observed along the z direction of the sample.
First-principles study of interaction between H2 molecules and BN nanotubes with BN divacancies
Authors: Hu Shuanglin , Kan Er-Jun , Yang Jinlong
Published: October 2007

The interaction between H2 molecules and boron nitride (BN) single-walled nanotubes with BN divacancies is investigated with density-functional theory. Our calculations reveal that H2 molecules adsorb physically outside defective BN nanotubes, and cannot enter into BN nanotubes through bare BN divacancies because the energy barrier is as high as 4.62eV. After the defects are saturated by hydrogen atoms, the physisorption behavior of H2 molecules is not changed, but the energy barrier of H2 molecules entering into BN nanotubes through the defects is reduced to 0.58eV. This phenomenon is ascribed to hydrogen saturation induced reduction of electrostatic potential around the defects.
An ab initio investigation of the Buckingham birefringence of furan, thiophene, and selenophene in cyclohexane solution
Authors: Rizzo Antonio , Frediani Luca , Ruud Kenneth
Published: October 2007

Using a recently developed quadratic response methodology for the calculation of frequency-dependent third-order properties of molecules in solution, we investigate the Buckingham birefringence of furan, thiophene, and selenophene in cyclohexane solution. These systems are chosen since accurate experimental data are available, allowing for a direct comparison of experimental observations with our theoretical estimates. Our model for describing the solvent effects is based on a dielectric continuum approach for the solvent, and uses a molecule-shaped cavity. Our results show qualitatively different Buckingham constants and effective quadrupole centers calculated with and without the solvent, and only when the solvent is included are the qualitative trends observed experimentally reproduced. It is demonstrated that a significant part of this effect arises from the geometry relaxation of the molecules in the solvent.
Modeling of two-ribbon flares by the fast reconnection mechanism
Authors: Ugai M.
Published: October 2007

The three-dimensional (3D) spontaneous fast reconnection model is applied to explosive heating in the shape of a pair of ribbons observed in the solar chromosphere, where plasma density is much larger than in the solar corona. In accordance with the onset of fast reconnection in the corona, 3D magnetic field dipolarization is caused by the fast reconnection jet, so that an extreme increase in the chromospheric current density suddenly occurs in a pair of local regions near the separatrix layers because of large-scale redistribution of the current system. Accordingly, chromospheric joule heating impulsively occurs in the thin layers, and the joule heating is interpreted to be sustained by a generator in the coronal fast reconnection region, in the form of u∙(J×B)<0, provided by the fast reconnection jet ahead of the magnetic loop. Hence, the chromospheric temperature is drastically enhanced in a pair of local regions, which move away with time, eventually leading to definite chromospheric evaporation; simultaneously, the coronal flare loop is expanding outward. These results are consistent with the well-known morphological features of two-ribbon flares.
Nonequilibrium versus equilibrium molecular dynamics studies of solvation dynamics after photoexcitation of OClO
Authors: Gunnerson Kim N. , Brooksby Craig , Prezhdo Oleg V. , Reid Philip J.
Published: October 2007

The results of our earlier work [C. Brooksby, O. V. Prezhdo, and P. J. Reid, J. Chem. Phys. 119, 9111 (2003)] rationalizing the surprisingly weak solvent dependence of the dynamics following photoexcitation of chlorine dioxide in water, chloroform, and cyclohexane are thoroughly tested. Comparisons are made between equilibrium and nonequilibrium solvent response, equilibrium response in the ground and excited electronic states, as well as the cumulant and direct evaluation of the optical response function. In general, the linear response and cumulant approximations are found to hold, although minor deviations are found with all solvents. The ground state, linear response, and cumulant data show best agreement with experiment, most likely due to the better tested ground-state force field and the robust behavior of the linear response and cumulant approximations. The main conclusion of our earlier work explaining the weak solvent dependence by the domination of the van der Waals interaction component remains intact within the more advanced treatments. However, the molecular origin of this surprising experimental observation is different in water and chloroform compared to cyclohexane.
Laser beat wave excitation of surface plasma wave and material ablation
Authors: Singh D. B. , Tripathi V. K.
Published: October 2007

Two coplanar laser beams of frequencies ω1 and ω2, impinged on a metal surface at angles of incidence θ and −θ, resonantly excite a surface plasma wave (SPW) at the difference frequency ω=ω1−ω2 when ω has a specific value ω=ωR(θ), where ωR depends on ω1,ω2,θ and plasma frequency of the metal. The lasers exert a ponderomotive force on electrons in the skin layer and drive the SPW. The latter heats the electrons efficiently, causing efficient ablation of the material. The reduction in laser pulse lengths results in reducing the efficiency of SPW excitation and ablation.
Intermediate non-Gaussian transport in plasma core turbulence
Authors: Hauff T. , Jenko F. , Eule S.
Published: October 2007

Test particle transport in realistic plasma core turbulence (as described by nonlinear gyrokinetics) is investigated, focusing on the question whether and under what conditions the transport may become “anomalous”; i.e. super- or subdiffusive. While in the presence of stochastic fluctuations, the transport always becomes diffusive for large times, coherent flow components such as zonal flows or poloidal drifts can induce non-Gaussian transport over large intermediate time spans. In order to understand the origin of these phenomena, a simple model employing stochastic potentials is used to complement the analysis based on gyrokinetic turbulence simulations.
Ligand protons in a frozen solution of copper histidine relax via a T1e-driven three-spin mechanism
Authors: Stoll S. , Epel B. , Vega S. , Goldfarb D.
Published: October 2007

Davies electron-nuclear double resonance spectra can exhibit strong asymmetries for long mixing times, short repetition times, and large thermal polarizations. These asymmetries can be used to determine nuclear relaxation rates in paramagnetic systems. Measurements of frozen solutions of copper(L-histidine)2 reveal a strong field dependence of the relaxation rates of the protons in the histidine ligand, increasing from low (g‖) to high (g⊥) field. It is shown that this can be attributed to a concentration-dependent T1e-driven relaxation process involving strongly mixed states of three spins: the histidine proton, the Cu(II) electron spin of the same complex, and another distant electron spin with a resonance frequency differing from the spectrometer frequency approximately by the proton Larmor frequency. The protons relax more efficiently in the g⊥ region, since the number of distant electrons able to participate in this relaxation mechanism is higher than in the g‖ region. Analytical expressions for the associated nuclear polarization decay rate Teen−1 are developed and Monte Carlo simulations are carried out, reproducing both the field and the concentration dependences of the nuclear relaxation.
On the linearization of the Painlevé III–VI equations and reductions of the three-wave resonant system
Authors: Joshi N. , Kitaev A. V. , Treharne P. A.
Published: October 2007

We extend similarity reductions of the coupled (2+1)-dimensional three-wave resonant interaction system to its Lax pair. Thus we obtain new 3×3 matrix Fuchs-Garnier pairs for the third, fourth, and fifth Painlevé equations, together with the previously known Fuchs-Garnier pair for the sixth Painlevé equation. These Fuchs-Garnier pairs have an important feature: they are linear with respect to the spectral parameter. Therefore we can apply the Laplace transform to study these pairs. In this way we found reductions of all pairs to the standard 2×2 matrix Fuchs-Garnier pairs obtained by Jimbo and Miwa [Physica D 2, 407–448 (1981)]. As an application of the 3×3 matrix pairs, we found an integral autotransformation for the standard Fuchs-Garnier pair for the fifth Painlevé equation. It generates an Okamoto-like Bäcklund transformation for the fifth Painlevé equation. Another application is an integral transformation relating two different 2×2 matrix Fuchs-Garnier pairs for the third Painlevé equation.
Dielectric properties and ac conductivities of dense single-phased BiFeO3 ceramics
Authors: Chen Jhih-Cyun , Wu Jenn-Ming
Published: October 2007

Dense single-phase BiFeO3(BFO) ferroelectric ceramics, with a resistivity of ∼1012Ωcm, may be formed by sintering the 450°C-calcined coprecipitated powder at 800–850°C. The ceramics sintered at 750°C contain a second phase of Bi2O3. The conduction loss activation energies at room temperatures of −290 and 350–430°C are 0.126 and 1.26eV, respectively. The ac conductivity thermal variation suggests ∼290°C as the application limit for BFO ceramics. The loss at T<350°C is higher for low frequencies than for high frequencies. In contrast, an opposite effect is found at T>350°C.
Nonvolatile Si∕SiO2∕SiN∕SiO2∕Si type polycrystalline silicon thin-film-transistor memory with nanowire channels for improvement of erasing characteristics
Authors: Chen Shih-Ching , Chang Ting-Chang , Liu Po-Tsun , Wu Yung-Chun , Chin Jing-Yi , Yeh Ping-Hung , Feng Li-Wei , Sze S. M. , Chang Chun-Yen , Lien Chen-Hsin
Published: November 2007

A silicon-oxide-nitride-oxide-silicon type polycrystalline silicon thin-film transistor (poly-Si TFT) with nanowire channels was investigated for both transistor and memory applications. The poly-Si TFT memory device has superior electrical characteristics, such as higher drain current, smaller threshold voltage, and steeper subthreshold slope. Also, the simulation result on electrical field reveals that the electrical field across the tunnel oxide is enhanced and that across the blocking oxide is reduced at the corner regions. This will lead to the parasitic gate injection activity and the erasing speed can be apparently improved in the memory device due to the pronounced corner effect and narrow channel width.
Renormalization group and Ward identities for infrared QED4
Authors: Mastropietro Vieri
Published: October 2007

A regularized version of Euclidean QED4 in the Feynman gauge is considered, with a fixed ultraviolet cutoff, photon mass of the size of the cutoff, and any value, including zero, of the electron mass. We will prove that the Schwinger functions are expressed by convergent series for small values of the charge and verify the Ward identities, up to corrections which are small for momentum scales far from the ultraviolet cutoff.
An invariant analytic orthonormalization procedure with applications
Authors: Abdollahpour M. R. , Bagarello F. , Triolo S.
Published: October 2007

We apply the orthonormalization procedure previously introduced by Bagarello and Triolo [J. Math. Phys. 48, 043505 (2007)] and adopted in connection with coherent states to Gabor frames and other examples. For instance, for Gabor frames, we show how to construct g(x)∊L2(R) in such a way the functions gṉ(x)=eian1xg(x+an2), ṉ∊Z2 and a some positive real number, are mutually orthogonal. We discuss in some detail the role of the lattice naturally associated with the procedure in this analysis.
Active metamaterials: Sign of refractive index and gain-assisted dispersion management
Authors: Govyadinov Alexander A. , Podolskiy Viktor A. , Noginov M. A.
Published: November 2007

We derive an approach to determine the causal direction of wavevectors of modes in optical metamaterials, which, in turn, determines signs of refractive index and impedance as a function of real and imaginary parts of dielectric permittivity and magnetic permeability. We use the developed technique to demonstrate that the interplay between resonant response of constituents of metamaterials can be used to achieve efficient dispersion management. Finally, we demonstrate broadband dispersionless index and impedance matching in active nanowire-based negative index materials. Our work has a potential to open new practical applications of negative index composites for broadband lensing, imaging, and pulse routing.
Mechanical crystallization of Fe-based amorphous alloys
Authors: Sharma Satyajeet , Suryanarayana C.
Published: October 2007

Mechanical alloying of a number of blended elemental powders of Fe-based alloy systems containing four or five components was undertaken to determine if amorphous phases could be produced and also to compare the glass-forming ability achieved by mechanical alloying and that obtained by solidification-processing methods. Amorphous phase formation was achieved in all the alloy systems investigated, the time for the amorphous phase formation being a function of the glass-forming ability of the alloy system investigated. However, in some alloy systems it was noted that on milling, beyond the time required for the formation of the amorphous phase, the amorphous phase started to crystallize, a phenomenon designated as mechanical crystallization. The present paper specifically discusses the results of mechanical crystallization obtained in the Fe42Ge28Zr10B20 and Fe42Ni28Zr10C10B10 alloy systems as representatives of the typical quaternary and quinary (five-component) systems, respectively. In the case of the quaternary system, mechanical crystallization led to the formation of a supersaturated solid solution of all the solute elements in Fe, while in the quinary system, a mixture of the solid solution and intermetallic phases has formed. The possible reasons for mechanical crystallization and the reasons for the differences in the behavior of the quaternary and quinary systems are discussed.
Superconducting array for high-field magnetic resonance imaging
Authors: Wosik J. , Xue L. , Xie L.-M. , Kamel M. R. , Nesteruk K. , Bankson James A.
Published: October 2007

We report on the design of a planar 200MHz superconducting two-resonator array for magnetic resonance imaging (MRI) applications. The array was made out of a double-sided thin YBa2Cu3O7−x film on r-cut sapphire substrate and consists of two 24mm diameter resonators with built-in planar capacitors for coupling to the tuning and matching electronics. Required for the performance of the MRI array, rf isolation of two resonators was accomplished by built-in planar capacitors, and the mechanism of resonator-to-resonator decoupling was analyzed. The signal-to-noise gain as a result of using high-Tc superconductor resonators/arrays was calculated and compared with experimental data.
Analysis of limitations of terahertz p-i-n uni-traveling-carrier photodiodes
Authors: Feiginov Michael N.
Published: October 2007

The uni-traveling-carrier p-i-n photodiodes have been analyzed both in the ballistic and drift modes of operation. The analytical expressions for the terahertz (THz) power achievable with the photodiodes have been derived in the drift-diffusion approximation, the optimum photodiode parameters have been identified and different THz-power limitation mechanisms (space-charge effects, heating, absorption saturation, etc.) have been considered. It has been shown that the THz powers on the level of 300 μW at ≳1 THz, 10 mW at 0.3 THz and 30 mW at 0.1 THz should be achievable. That would give more than an order of magnitude improvement as compared to the present state-of-the-art results. At the lower end of the THz-frequency range, the main limitation mechanisms are the heating and space-charge effects. At the higher frequencies, at ≳1 THz, the latter mechanism should play the major role.
Microscopic and macroscopic dielectric description of mixed oxide thin films
Authors: Ferrer F. J. , Yubero F. , Mejías J. A. , García-Lopez F. J. , González-Elipe A. R.
Published: October 2007

Compact Si–Ti–O and Si–Zr–O mixed oxide thin films are studied by optical characterization (refractive index, band gap energy) and local probes (Auger parameter obtained by x-ray photoelectron spectroscopy). Interpretation of the obtained results is discussed in the framework of the classical dielectric theory that correlates the macroscopic refractive index to the microscopic electronic polarizability of each particular ion in the compound through the Lorentz-Lorenz relationship. Quantum mechanical cluster calculations have also been performed to support the correlations obtained between the experimental findings.
Effect of the density of collision cascades on ion implantation damage in ZnO
Authors: Azarov A. Yu. , Kucheyev S. O. , Titov A. I. , Karaseov P. A.
Published: October 2007

We study structural disorder in ZnO bombarded at room temperature with 1.3 keV∕amu atomic P and cluster PFn (n=2 and 4) ions. Rutherford backscattering/channeling spectrometry results show that the density of collision cascades has a negligible effect on the damage buildup in the crystal bulk in the dose range resulting in ∼1.5−15 displacements per atom. Hence, the amount of stable post-implantation disorder in the bulk can be predicted based on ballistic calculations. In contrast, the cascade density affects radiation damage in the near-surface region. An intermediate defect peak between the expected surface and bulk peaks of disorder forms for ion irradiation conditions with dense cascades.
Influence of the substrate misorientation on the properties of N-polar GaN films grown by metal organic chemical vapor deposition
Authors: Keller S. , Fichtenbaum N. A. , Wu F. , Brown D. , Rosales A. , DenBaars S. P. , Speck J. S. , Mishra U. K.
Published: October 2007

Smooth, high quality N-polar GaN films were realized by metal organic chemical vapor deposition (MOCVD) through growth on misoriented (0001) sapphire substrates and the development of a high temperature nucleation process. Misorientation angles from 0.5° to 4° toward the a and the m plane of the sapphire substrate were investigated. Whereas GaN films grown on substrates with a misorientation angle of only 0.5° or 1° exhibited high densities of hexagonal surface features as commonly observed for N-polar GaN films grown by MOCVD, smooth GaN layers were obtained on sapphire substrates with misorientation angles of 2° or larger. In addition, the structural and optical properties of the GaN films significantly improved with increasing misorientation angle, as evaluated by high resolution x-ray diffraction, atomic force microscopy, transmission electron microscopy, and photoluminescence measurements. The properties of GaN layers grown on (0001) sapphire with a misorientation of 4° were comparable to Ga-polar GaN films grown in the same reactor.
Defect related issues in the “current roll-off” in InGaN based light emitting diodes
Authors: Monemar B. , Sernelius B. E.
Published: October 2007

Defect related contributions to the reduction of the internal quantum efficiency of InGaN-based multiple quantum well light emitting diodes under high forward bias conditions are discussed. Screening of localization potentials for electrons is an important process to reduce the localization at high injection. The possible role of threading dislocations in inducing a parasitic tunneling current in the device is discussed. Phonon-assisted transport of holes via tunneling at defect sites along dislocations is suggested to be involved, leading to a nonradiative parasitic process enhanced by a local temperature rise at high injection.
Stability of pentacene top gated thin film transistors
Authors: Diallo K. , Erouel M. , Tardy J. , André E. , Garden J.-L.
Published: October 2007

We report on the stability of top gated pentacene field effect transistors processed on Kapton™ with Parylene-C as gate dielectric. The influence of bias stress and ambient atmosphere on device characteristics were investigated. Combined influence of moisture and gate bias stress led to an increase of depletion current and subthreshold slope as well as a drift of onset voltage and threshold voltage. We show that devices stressed in the off state exhibit a high stability.
Electrically controllable and polarization-independent Fresnel zone plate in a circularly symmetric hybrid-aligned liquid crystal film with a photoconductive polymer layer
Authors: Lo K.-C. , Wang J.-D. , Lee C.-R. , Mo T.-S.
Published: October 2007

This work reports a Fresnel zone plate in a circularly symmetric hybrid-aligned liquid crystal (LC) film with a photoconductive polymer layer. An ultraviolet-induced electrodelike pattern of polymer layer under a zone plate photomask results in alternating major and minor portions of external voltage dropping on LC layer in conductive and nonconductive regions, respectively. These effects cause the discrepancy in LC reorientation between adjacent zones, generating a Fresnel zone plate. The focusing of the zone plate is electrically controllable and polarization independent. Additionally, the zone plate has advantages of a zero focusing in the voltage-off state and a very small operating dc field range from 0to0.3V∕μm.
Very thin photoalignment films for liquid crystalline conjugated polymers: Application to polarized light-emitting diodes
Authors: Sakamoto Kenji , Miki Kazushi , Misaki Masahiro , Sakaguchi Koichi , Chikamatsu Masayuki , Azumi Reiko
Published: October 2007

Photoaligned polyimide films with different film thicknesses were prepared on quartz substrates, and uniaxially aligned glassy poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) layers were formed on top. The photoluminescence polarization ratio of the PFO layer rapidly increased with increasing polyimide film thickness, and beyond a thickness of 1.6nm, it was saturated at ∼11. This result shows that the 1.6-nm-thick photoaligned polyimide film works as a good alignment layer for PFO. We succeeded in fabricating a polarized light-emitting diode with a polarization ratio of 29 at 459nm and a brightness of 700cd∕m2 by using a 2.8-nm-thick polyimide photoalignment layer.
Highly efficient white organic light-emitting diodes with single small molecular emitting material
Authors: Wang Lei , Lin Mei-Fang , Wong Wai-Kwok , Cheah Kok-Wai , Tam Hoi-Lam , Gao Zhi-Qiang , Chen Chin H.
Published: October 2007

We demonstrate a highly efficient white organic light emitting device with fluorescent small molecule 4,4′-bis(9-(1-naphthyl)anthracene-10-yl)biphenyl (BUBH-3). With a simple device architecture of indium tin oxide/tris 4,4′,4″-tris-N-naphthyl-N-phenylamino-triphenylamine (60nm)∕N,N′-bis-(1–naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (10nm)/BUBH-3 (45nm)∕Alq3 (15nm)∕LiF (1nm)∕Al (150nm), a white light with CIEx,y color of (0.31,0.36) was generated. The device achieved one of the best single-emitting-material electroluminescence performance of white organic light-emitting devices with efficiencies of 7.0cd∕A and 3.17lm∕W at 6.9V.
Spherical aberration correction in nonlinear microscopy and optical ablation using a transparent deformable membrane
Authors: Tsai P. S. , Migliori B. , Campbell K. , Kim T. N. , Kam Z. , Groisman A. , Kleinfeld D.
Published: November 2007

We describe the design and utilization of a deformable membrane to minimize the negative spherical aberration that occurs when a standard water-dipping objective is used to focus within a higher-index sample. In connection with two-photon laser scanning microscopy, we demonstrate twofold improved axial resolution of structures as deep as 1mm in gels and brain tissue. In conjunction with plasma-mediated ablation, we demonstrate enhanced production of optical damage deep within a glass substrate. The present method provides a simple and inexpensive correction for a limited yet important class of optical aberrations.
Micro-photoluminescence characterizations of GaInAsP/InP single quantum wires fabricated by dry etching and regrowth
Authors: Itoh Hirotake , Yoshita Masahiro , Akiyama Hidefumi , Plumwongrot Dhanorm , Maruyama Takeo , Arai Shigehisa
Published: November 2007

We characterized the micro-photoluminescence (micro-PL) of GaInAsP/InP single quantum wires (Q-wires) at 6 K. The Q-wires had 6–39-nm lateral widths and a 6-nm vertical thickness and were fabricated by dry etching and regrowth. Micro-PL spectra were clearly observed for all single Q-wires. The spectra revealed a high degree of uniformity along the Q-wires. The PL peak energy showed a systematic blueshift with the reduction of the Q-wire lateral width. The blueshift was attributed to the lateral quantum confinement and strain from a lateral direction, and was 100 meV in a 6-nm-wide Q-wire. Systematic analysis on the PL widths of the Q-wires showed that the PL spectra were broadened by fluctuations of 3 nm in the lateral width of the Q-wire after the dry etching and the regrowth in addition to the broadening caused by the fluctuation in the vertical thickness during the initial film growth and that caused by ion bombardment through a Ti metal mask in the dry etching process. The decreased PL intensities in narrow Q-wires were also analyzed, and they were attributed to decreased PL quantum yield because of damage to the etched sidewalls of the Q-wires during dry etching, and to the absorption cross-sections of the excitation light.
The mechanism study on transport properties in perovskite oxide p-n junctions
Authors: Han Peng , Jin Kui-juan , Lu Hui-bin , Zhou Qing-Li , Zhou Yue-Liang , Yang Guo-Zhen
Published: October 2007

The drift-diffusion mechanism, the interband Zener tunneling theory, and the trap assisted tunneling model are combined to reveal the transport properties in a multicorrelated system of the p-La0.9Sr0.1MnO3∕n-SrNb0.01Ti0.99O3 junction with various temperatures. The good agreement between the calculated and measured I-V curves reveal that the drift-diffusion mechanism dominates the transport process with forward bias, and the interband Zener tunneling plays an important role for the carrier transport with high reverse bias. In the low reverse bias, the I-V characteristic of oxide device is mainly attributed to the trap assisted tunneling process caused by the oxygen vacancy induced states.
Frequency selective surfaces for high sensitivity terahertz sensing
Authors: Debus Christian , Bolivar Peter Haring
Published: October 2007

An apporach for the sensing of small amounts of chemical and biochemical material is presented. A frequency selective surface made from asymmetric split ring resonators is excited with free space radiation. Due to interference effects a resonance occurs with a steep flank in the frequency response which is shifted upon dielectric loading. Utilizing a strong E-field concentration by selective loading the detection of very small amounts of probe material becomes possible. The functionality is proven by numerical simulation and the optimization of structure and loading is performed.
Monitoring electrically driven cancellation of exciton fine structure in a semiconductor quantum dot by optical orientation
Authors: Kowalik K. , Krebs O. , Lemaître A. , Eble B. , Kudelski A. , Voisin P. , Seidl S. , Gaj J. A.
Published: October 2007

We use optical orientation technique to monitor the degeneracy control of exciton states in a single InAs∕GaAs quantum dot, achieved by applying an in-plane electric field. Under circularly polarized quasiresonant excitation, the exciton photoluminescence shows a pronounced maximum of circular polarization at electric field corresponding to zero fine structure splitting. By analyzing the width of this maximum we are able to determine the homogeneous linewidth of the excitonic transition. This experimental method is shown to be very efficient to test and possibly tune the photonic properties of an individual quantum dot for the emission of entangled photon pairs.
Rb
Cd
F
3
:
Mn
2
+
: A potential ultraviolet dosimeter material
Authors: Dotzler C. , Williams G. V. M. , Edgar A.
Published: October 2007

Optical absorption and optically stimulated luminescence measurements have been made on RbCdF3:Mn2+. We show that there is an ultraviolet (UV) response that covers the UV spectrum and hence this compound is applicable for passive UV detection and dosimetry. There is a fast UV-A and UV-B stimulated luminescence decay when compared with the bleaching of the deep UV induced optical absorption that can be explained in terms of a distribution of carrier traps with different detrapping rates.
Ultrasound surgery with a toric transducer allows the treatment of large volumes over short periods of time
Authors: Melodelima David , N’Djin William A. , Parmentier Hubert , Chesnais Sabrina , Rivoire Michel , Chapelon Jean-Yves
Published: November 2007

Thermal ablation by physical agents is widely used in clinical settings, but it generally results in a small coagulated volume. Here, we report that a technologically advanced high intensity focused ultrasound transducer can significantly enlarge the coagulated volume over short periods of time. Eight ultrasound emitters were created by sectioning a single toric piezocomposite transducer. A single thermal lesion is created when the eight emitters perform alternative and consecutive 5s ultrasound exposures. This paper presents in vivo evidence that the coagulated volume obtained from a 40s total exposure in the liver was 8.6±4.8cm3.
Electron irradiation-induced increase of minority carrier diffusion length, mobility, and lifetime in Mg-doped AlN∕AlGaN short period superlattice
Authors: Lopatiuk-Tirpak O. , Chernyak L. , Borisov B. A. , Kuryatkov V. V. , Nikishin S. A. , Gartsman K.
Published: October 2007

Minority carrier diffusion length in a p-type Mg-doped AlN∕Al0.08Ga0.92N short period superlattice was shown to undergo a multifold and persistent (for at least 1week) increase under continuous irradiation by low-energy beam of a scanning electron microscope. Since neither the diffusion length itself nor the rate of its increase exhibited any measurable temperature dependence, it is concluded that this phenomenon is attributable to the increase in mobility of minority electrons in the two-dimensional electron gas, which in turn is limited by defect scattering. Cathodoluminescence spectroscopy revealed ∼40% growth of carrier lifetime under irradiation with an activation energy of 240meV.