bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of Coexistence of Weakly Relaxed Neutral Deep Donor (D°) and DX− States in AlxGa1−xAs:Se Using ICTS under Pressure
Authors: Takarabe K. , Hirano Y. , Minomura S. , Matsuda K. , Ohnishi H. , Fujita K. , Watanabe T. 
Published: July 2007

AbstractThe coexistence of two deep donors in Al2Ga1−xAs:Se with and without a capture barrier is reported. The difference of their nature is found in the dependence of the electron emission process on filling pulse time, temperature, and pressure.
DLTS Investigations of the Distorted Configuration of the EL2 Defect Stabilized under High Hydrostatic Pressure in GaAs1−xPx
Authors: Przybytek J. , Baj M. , Slupiński T. , Li Ming‐Fu 
Published: July 2007

AbstractDLTS measurements of GaAs1−xPx, samples with phosphorus content χ ≈︁ 0.1 to 0.35 have been performed under hydrostatic pressure. When pressure was applied to samples with χ ≈︁ 0.1 and 0.2, we observed the emergence of the DLTS peak at ≈︁90 K. For χ ≈︁ 0.2 the amplitude of this peak increased by three orders of magnitude. We can unambiguously attribute this phenomenon to a spontaneous rearrangement of the EL2 defect to its distorted configuration, enabled by the free electron capture and not by illumination. For samples with χ ≈︁ 0.35 the same peak has been observed without pressure, i.e. in this case the distorted configuration of the defect is stable even at ambient pressure. For samples with χ ≈︁ 0.1 and 0.2, under pressure and below T ≈︁ 80 K, illumination and/or applying a long, positive, filling pulse, caused a long‐time kinetics of the DLTS signal. This process is explained as a slow redistribution of the EL2 defect between both distorted and nondistorted configurations.
Photoionization of the Si‐DX Center in AIGaAs: The Effects of Pressure and Local Configuration
Authors: Piotrzkowski R. , Litwin‐Staszewska E. , Przybytek J. 
Published: July 2007

AbstractWe have studied the optical ionization rate of Si‐DX centers in Al0.15Ga0.85As at 77 K by measuring the time variations of the density of photoexcited free electrons. The experiments were performed under hydrostatic pressure and without pressure, using the pressure to fill the DX centers with electrons. In the main experiment we determined the variation of the occupancies of individual alloy‐split DX levels along the photoionization transient. As a result, the distinct photoionization rates for all four alloy‐split configurations DX0 to DX3were found. This proves that optical ionization energy of Si‐DX center in the alloys is configuration dependent. A blue shift of the photoionization spectra under pressure was found. For the spectra measured without pressure, the dependence of photoionization threshold on the initial filling was found. Such behavior is the consequence of alloy‐splitting of the optical ionization energy.
Metal‐Insulator Transition in GaN Crystals
Authors: Perlin P. , Knap W. , Camassel J. , Polian A. , Chervin J. C. , Suski T. , Grzegory I. , Porowski S. 
Published: July 2007

AbstractBy means of high‐pressure Raman spectroscopy of coupled LO phonon‐plasmon modes, a qualitatively new model of the metal‐insulator transition observed in bulk GaN crystals at pressure around 20 GPa is proposed. This transition was interpreted recently as caused by the emergence of the localized donor state into the energy gap of GaN. Our new experimental evidence suggests that two types of donors can supply electrons to the bulk crystal: the first of a localized character and the second of a shallow character with contributions to the electron concentration of 5 × 1019 and 3 × 1018 cm−3, respectively. The localized state can be associated with the nitrogen vacancy, while the shallow state can be tentatively attributed to impurities such as oxygen. A number of interesting phenomena take place beyond the metal‐insulator transition in bulk GaN and an attempt to explain them will be made in the present work.
Investigation of Dopant Segregation in GaAsAlAs Short‐Period Superlattices by Hall Effect under High Pressure
Authors: Robert J. L. , Bosc F. , Sicart J. 
Published: July 2007

AbstractHydrostatic pressure is a powerful tool in the electrical characterization of large lattice relaxation states (e.g. DX states in III‐V semiconductors). We have applied this method on short‐period superlattices to evidence the dopant segregation resulting from planar Si doping performed during molecular beam epitaxy. The characterization is based on the dependence of the electrical activation energy both on the dopant location in the microstructure and the applied pressure.
Pressure‐Tuned Resonance Raman Scattering in InAs/GaSb Superlattices
Authors: Lyapin S. G. , Lomsadze A. V. , Trojan I. A. , Klipstein P. C. , Mason N. J. , Walker P. J. 
Published: July 2007

AbstractWe have performed a pressuretuned resonance Raman scattering study in short‐period GaSb/InAs SLs in the region of E1 and E1 + Δ1 in GaSb. Resonance profiles for polarized Raman scattering by both LO and elastic interface modes reveal two electronic transitions with two different types of Fröhlich‐interaction‐induced scattering. The LO resonance at the E1 gap displays strong interference and we attribute it to intrinsic intrasubband Fröhlich scattering, which is dipole allowed due to the difference in the degree of localization of the electron and hole wave functions. A new resonance enhancement peak, not present in the bulk, has been observed in between the E1 and E1 + Δ1 gaps of GaSb. This resonance appears to be dominated by extrinsic Fröhlich scattering.
Electronic and Structural Properties of BeSe, BeTe, and BeS: Comparison between ab‐initio Theory and Experiments
Authors: Muñoz A. , Rodríguez‐Hernández P. , Mujica A. 
Published: July 2007

AbstractWe have used first principles total energy pseudopotential techniques to calculate the ground state properties and the relative stabilities of the high pressure phases of the beryllium chalcogenides BeSe, BeTe, and BeS. We study the energy‐volume (E–V) relations of the zincblende, NaCI, CsCI, NiAs, and βSn structures of these compounds. The components of the stress tensor were also calculated and used in the structural relaxation of the tetragonal and hexagonal phases. From the E–V curves of the structures considered and the Gibbs construction we find that these compounds transform under pressure from the zincblende structure (B3) to the NiAs structure (B8), and no fürther transitions are found. Our calculated values of the structural parameters and the B3 → B8 transition pressure for BeSe and BeTe agree well with recent experimental results. Very little is known experimentally for BeSe, and our results for this compound have a predictive character.
Second‐Order Pretransitional Effects in the High Pressure Phase Transition of Indium Nitride
Authors: Besson J. M. , Bellaiche L. , Kunc K. 
Published: July 2007

AbstractIndium nitride, which has the hexagonal wurtzite structure, transforms to an NaCl lattice between 12 and 16 GPa. Prior to this transition nonlinearities occur in the wurtzite phase, particularly steep decrease of the c/a axial ratio. The equation of state and nonlinear behavior of c, a, and c/a of InN under pressure have been calculated by using the first‐principles total‐energy pseudopotential method. The calculations fit with experiment up to the phase transition pressure (15 GPa), which validates their accuracy. Pursuing the calculations in the wurtzite structure above the actual transition pressure the nonlinearities appear to be caused by a virtual second‐order isostructural phase transition between two wurtzite structures with unequal internal positional parameters. This second‐order process is interrupted by the first‐order reconstructive phase transition to the high pressure structure and remains observable only as its precursor.
High Pressure Effects on Optical Properties of CdS
Authors: Kobayashi M. , Iwata H. , Horiguchi T. , Endo S. 
Published: July 2007

AbstractCdS undergoes a reversible phase transition from the wurtzite to the rock‐salt structure at 2.6 GPa. The LO Raman mode of samples retrieved from the high pressure phase shows a remarkable shift towards lower frequency relative to the LO mode of a single crystal. This shift is explained by the formation of nanocrystals and its interpretation in terms of the spatial correlation model yields nanocrystal diameters ranging from 6.7 to 10 nm. The diameter depends on the highest pressure applied. When pressure is applied again to a sample retrieved from a high pressure cycle, the phase transition pressure has been found to increase compared with that of a single crystal sample. These results lead to an explanation for the question why the wurtzite and rock‐salt structures coexist beyond the onset of the phase transition in CdS.
Raman Frequencies and Angular Dispersion of Polar Modes in Aluminum Nitride and Gallium Nitride
Authors: Filippidis L. , Siegle H. , Hoffmann A. , Thomsen C. , Karch K. , Bechstedt F. 
Published: July 2007

AbstractWe performed angular‐resolved Raman‐scattering experiments on AlN and GaN both grown in the wurtzite structure. Our measurements reveal that the transverse polar modes in AlN and GaN show a pronounced angular dispersion. We varied the angle between the phonon‐propagation direction and the optical axis between 41° and 90° and observed a frequency shift of the A1(TO) mode in the range of 28 cm−1 in AlN and of 15 cm−1 in GaN. The experimental values agree well with our theoretical calculations which were carried out using the DFT‐LDA plane‐wave pseudopotential method.
Morphology and Luminescence of p‐Doped Porous Silicon
Authors: zur Mühlen E. , Chang Da , Rogaschewski S. , Niehus H. 
Published: July 2007

AbstractPorous silicon (PS) layers were created with different etching conditions on boron doped silicon wafers. Morphologies of the PS layers and their surfaces were investigated with atomic force and scanning electron microscopy. Low current densities during anodization led to homogeneous layers, while high current densities resulted in strain induced mechanical instabilities. The strain leads to a peeling off of the layer for mitre or mesoporous silicon. In contrast, in macroporous films strain can be relieved laterally leading to the local formation of channels. Luminescence properties of the samples are investigated and related to the PS morphology.
Dynamical Charge and Force Constant Calculations in c‐BN under Pressure
Authors: Badi N. , Bousetta A. , Bensaoula A. , Aourag H. 
Published: July 2007

AbstractA combination of an adjusted pseudopotential method and the bond‐orbital model of Harrison was used to derive the polarity and the force constants of cubic boron nitride (c‐BN) under pressure up to 900 kbar. The results show that the hybrid covalent energy dominates at high pressure and the transverse effective charge changes by less than 3.3% between normal condition and 900 kbar. The idea of taking the free‐atom term values and the 1/d2 formulae for the covalent energy is not a good approximation to estimate the variation of the transverse effective charge under pressure. In fact, this approximation overestimates the relative variation to 10.2% in the same range of pressure.
Paramagnetism and Magnetic Relaxation in Melt‐Textured Grown GdBa2Cu3O6+y4)
Authors: Qin M. J. , Jin X. , Yao X. X. , Rong X. S. , Ni Y. M. , Xiao L. , Fu X. K. , Ren H. T. 
Published: July 2007

AbstractMagnetic measurements have been performed on a melt‐textured grown (MTG) GdBa2Cu3O6+y sample. Because of the paramagnetism of the Gd3+ ions, the magnetization relaxation rate is increased by a factor of 4πχ. The effect of paramagnetism on the U(J) relationship of the sample has also been discussed. At the end, we extraxted the U(J) relationship based on the field sweep rate H, which is in agreement with the one after corrections for paramagnetism.
Temperature Dependence of Nuclear Magnetic Resonance and Transferred Hyperfine Field of 133Cs in a CsMnCl3 Single Crystal
Authors: Lim A. R. , Choh S. H. , Jeong S. Y. 
Published: July 2007

AbstractThe nuclear magnetic resonance of 133Cs in a CsMnCl3 single crystal grown by the Czochralski method has been investigated by employing a Bruker FT NMR spectrometer. The resonance lines of two different Cs(I) and Cs(II) were recorded. The quadrupole coupling constants of Cs(I) and Cs(II) in CsMnCl3 decrease as the temperature increases. The temperature dependence of e2qQ/h is explained with a single torsional frequency of the Cs‐Cl ion by means of the simple Bayer theory. Also, we have investigated the transferred hyperfine interaction due to the transfer of spin density from the Mn2+ ion to the Cs+ ion in the CsMnCl3 single crystal using the magnetic susceptibility and the paramagnetic shift using nuclear magnetic resonance.
Exciton Lineshapes in Weakly Disordered Systems
Authors: Mertsching J. 
Published: July 2007

AbstractExciton absorptison lines are calculated for weakly disordered tight‐binding systems, using the coherent‐potential approximation (CPA). The scaled lineshapes depend only on the dimension of the system. The CPA results are compared with known exact results for chains, and numerical results for finite two‐and three‐dimensional systems.
Defect‐related aspects of Mn‐doped ZnS nanorods and morphological changes revealed from positron annihilation spectroscopy
Authors: Nambissan P. M. G. , Biswas Subhajit , Kar Soumitra , Chaudhuri Subhadra 
Published: July 2007

AbstractManganese‐doped zinc sulfide (Mnx Zn1‐x S) nanorods were synthesized through solvothermal processes and were characterized by x‐ray diffraction and scanning and transmission electron microscopy. Positron lifetime and Doppler broadening measure‐ments were carried out on powdered samples with different dopant concentrations. A transformation from hexagonal to cubic structure was observed almost concomitantly with the filling of Zn2+ vacancies and/or substitution of Zn2+ ions by Mn2+ ions. The lifetime of positrons annihilating at the surfaces of nanorods decreased with increase in their diameter during increased doping by Mn2+ ions. At concentrations above 20%, pyramid‐like coarse crystals of MnS were found coexisting with the ZnS nanostructures. The interior of the nanorods seemed to be free of vacancy‐type defects unlike in the case of ZnS nanoparticles. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Physics with dense positronium
Authors: Cassidy David B. , Mills Allen P. 
Published: July 2007

AbstractOur recent experiment on Ps‐Ps spin exchange quenching represents the first time that two Ps atoms have been observed interacting with each other. The implication is that experimentation on various systems containing more than one Ps atom is now possible, including the Ps2 molecule, the Ps Bose‐Einstein condensate, the Ps atom laser and the annihilation gamma ray laser. Here we describe various aspects of such research, including the development of new techniques, work currently underway and some possible future experiments. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐thermal food processing/preservation technologies: a review with packaging implications
Authors: Morris Caroline , Brody Aaron L. , Wicker Louise 
Published: July 2007

AbstractNon‐thermal food processing/preservation methods interest food and food packaging scientists, manufacturers and consumers because they exert a minimal impact on the nutritional and sensory properties of foods, and extend shelf life by inhibiting or killing microorganisms. They are also considered to be more energy efficient and to preserve better quality attributes than conventional thermally based processes. Non‐thermal processes also meet industry needs by offering value‐added products, new market opportunities and added safety margins.  This study reviewed non‐thermal processing technologies currently available or developmental for the inactivation of microorganisms and thus microbiological shelf life in foods, and to identify packaging interactions that might result. Processes include ultra‐high pressure, ionizing radiation, pulsed X‐ray, ultrasound, pulsed light and pulsed electric fields, high‐voltage arc discharge, magnetic fields, dense phase carbon dioxide and hurdle technologies. Copyright © 2007 John Wiley & Sons, Ltd.
Ensemble‐based chemical data assimilation. II: Covariance localization
Authors: Constantinescu Emil M. , Sandu Adrian , Chai Tianfeng , Carmichael Gregory R. 
Published: July 2007

AbstractData assimilation is the process of integrating observational data and model predictions to obtain an optimal representation of the state of the atmosphere. As more chemical observations in the troposphere are becoming available, chemical data assimilation is expected to play an essential role in air‐quality forecasting, similar to the role it has in numerical weather prediction. Considerable progress has been made recently in the development of variational tools for chemical data assimilation. In this paper we implement, and assess the performance of, a localized ‘perturbed‐observations’ ensemble Kalman filter (LEnKF). We analyse different settings of the ensemble localization, and investigate the joint assimilation of the state, emissions and boundary conditions. Results with a real model and real observations show that LEnKF is a promising approach for chemical data assimilation. The results also point to several issues on which future research is necessary. Copyright © 2007 Royal Meteorological Society
Alignment of resection planes in total knee replacement obtained with the conventional technique, as assessed by a modern computer‐based navigation system
Authors: Belvedere C. , Ensini A. , Leardini A. , Bianchi L. , Catani F. , Giannini S. 
Published: July 2007

AbstractBackgroundTo improve the anatomy‐based alignment of prosthetic components in total knee replacement, surgical navigation systems have recently been developed, based on anatomical reference frame definitions through landmark digitations and functional calibration. In this study, femoral and tibial resection plane alignments, obtained by conventional tecnique, were measured intraoperatively during total knee replacements by a navigation system to quantify potential errors in conventional bone preparation techniques.MethodsFemoral and tibial resection plane alignments, obtained by conventional femoral intramedullary and tibial extramedullary cutting guides, were measured intraoperatively in 25 primary total knee replacements by a navigation system. This system enabled the surgeon to calculate, before definitive bone sawing, the final position and orientation of all resection planes.ResultsThe measurements revealed unsatisfactory alignments in nearly all anatomical planes. Except for tibial varus/valgus, final plane orientations were considerably different from those targeted by the surgeon via the navigation system, respectively 7° , 8° and 10° apart in varus‐valgus and flexion‐extension at the femur, and in flexion‐extension at the tibia.ConclusionModern computer‐aided surgery in total knee replacement, once relevant precision has been established in all femur and tibia anatomical planes, can in the future limit the current critical component misalignments. Copyright © 2007 John Wiley & Sons, Ltd.
Three‐dimensional surface acquisition systems for the study of facial morphology and their application to maxillofacial surgery
Authors: Kau Chung How , Richmond Stephen , Incrapera Angela , English Jeryl , Xia James Jiong 
Published: July 2007

AbstractBackgroundThere has been a growing interest in three‐dimensional (3D) surface imaging devices over the last few years.MethodsThis comprehensive review discusses the various emerging technologies in this field of 3D imaging and applies the use of technology to oral and maxillofacial imaging.ResultsThe paper shows that there is increased awareness and application of technology to the field.Conclusion3D surface acquisition technology is improving at a rapid pace and has a place in oral and maxillofacial surgery. Copyright © 2007 John Wiley & Sons, Ltd.
On J‐Lossless coprime factorizations and H∞ control
Authors: Tsai Mi‐Ching , Postlethwaite Ian 
Published: July 2007

AbstractThis paper presents a relatively simple approach, based on chain scattering descriptions, to the synthesis of internally stabilizing controllers which result in a cost function with H∞ norm strictly less than a prespecified bound. State‐space formulae for a generator of all suboptimal controllers are found by solving two coupled J‐lossless coprime factorizations of a chain scattering matrix description. A mixed‐sensitivity design problem is used to illustrate the solution procedure, and to demonstrate how in certain cases only one algebraic Riccati equation need be solved to get a solution.
Combined ℋ︁∞/LQG control via the optimal projection equations: On minimizing the LQG cost bound
Authors: Mustafa Denis 
Published: July 2007

AbstractThe Optimal Projection equations for combined ℋ︁∞/LQG control are considered. Positive semidefiniteness of the associated Lagrange multiplier is shown to be necessary for the LQG cost bound to be minimal. It follows that all four Optimal Projection equations have a role to play, even in the full‐order case.
H∞‐optimal controller discretization
Authors: Keller J. P. , Anderson B. D. O. 
Published: July 2007

AbstractA redesign method for discretizing a continuous‐time controller is proposed. The resulting hybrid control system, for example with continuous‐time plant and discrete‐time controller, is stable, and performance including the system's inter‐sampling behaviour can be optimized by approximating some chosen reference transfer function of the continuous‐time control system. In order to obtain a tractable problem, the continuous‐time part of the hybrid system and the reference transfer function are approximated by a discrete‐time system with arbitrary fast sampling. After lifting the resulting periodic system, the approximation problem can be formulated as a standard H∞‐problem which is solved using standard software for H∞‐controller design.
H∞ generalized minimum sensitivity control design
Authors: Casavola Alessandro , Mosca Edoardo 
Published: July 2007

AbstractThis paper presents a two‐stage approach to the H∞ generalized sensitivity minimization problem (H∞‐GSM) for SISO, continuous‐time plants. Besides some possible advantages in the control law evaluation with respect to alternative polynomial methods, the proposed approach provides a direct link with the solution of an underlying generalized minimum variance (H2‐GMV) problem and allows one to identify the class of the joint H2/H∞‐GMV (equalizing H2‐GMV) optimal controllers.
Adaptive dynamical variable structure feedback regulation for nonlinear uncertain systems
Authors: Sira‐Ramírez Herbertt , Zribi Mohamed 
Published: July 2007

AbstractIn this article an adaptive discontinuous dynamical feedback strategy is presented for asymptotic output stabilization problems defined on nonlinear controlled systems exhibiting linear parametric uncertainty. A dynamical feedback controller, ideally achieving output stabilization via exact linearization, is obtained by means of output differentiation and sliding mode control ideas. The adaptive version of the dynamical variable structure controller is then obtainable via standard, direct, overparametrized adaptive control techniques available for linearizable systems through static state feedback. An illustrative example from the chemical process control area, including simulations, is provided.