bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic Studies of Liquid Crystalline and Isotropic Vinyl Ester Resins
Authors: Frigione Mariaenrica , Calò Emanuela , Maffezzoli Alfonso , Carfagna Cosimo , Malucelli Giulio
Published: October 2004

Summary: The curing process of a commercial vinyl ester (VE) resin was characterized by calorimetric and spectroscopic techniques. A phenomenological kinetic model, experienced in previous studies, was employed to describe the proceeding of curing reactions. The model is able to describe the behavior of the processing variables, i.e. rate and degree of the reaction, during the curing of the resin under different conditions (heating rates). The effect of diffusion control phenomena on the reaction kinetics, associated with the evolution of the glass transition temperature as a function of the degree of polymerization and cross‐linking, was taken into account in the formulation of the kinetic model. A simpler model was proposed and verified for a liquid crystalline vinyl ester resin, synthesized by the authors. The model, in particular, did not take into account the effects of vitrification. The kinetic parameters were again evaluated by processing the calorimetric data. The kinetic study of the liquid crystalline monomer is performed after isotropization and therefore, the acceleration effect, associated with the cure in liquid crystalline phase is not taken into account for the kinetic analysis. Also in this case, the comparison between theoretical and experimental data was very satisfying.

Experimental (full line) and predicted data (dotted line) of degree of reaction vs. time for the vinyl ester resin.

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Experimental (full line) and predicted data (dotted line) of degree of reaction vs. time for the vinyl ester resin.
Atom Transfer Radical Polymerization of Glycidyl Methacrylate: A Functional Monomer
Authors: Cañamero Pedro Francisco , de la Fuente José Luis , Madruga Enrique López , Fernández‐García Marta
Published: October 2004

Summary: A detailed investigation of the polymerization of glycidyl methacrylate (GMA), an epoxy‐functional monomer, by atom transfer radical polymerization (ATRP) was performed. Homopolymers were prepared at relatively low temperatures using ethyl 2‐bromoisobutyrate (EBrIB) as the initiator and copper halide (CuX) with N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as the catalyst system. The high polymerization rate in the bulk did not permit polymerization control. However, homopolymerization in solution enabled us to explore the effects of different experimental parameters, such as temperature, solvent (toluene vs. diphenyl ether) and initiator concentration, on the controllability of the ATRP process. SEC analysis of the homopolymers synthesized confirmed the importance of solvent character on molecular weight control, the lowest polydispersity indices ($\overline M _{\rm w} /\overline M _{\rm n} < 1.25$) and the highest efficiencies being found when the polymerizations were performed in diphenyl ether in combination with a mixed halide technique. A novel poly(glycidyl methacrylate)‐block‐poly(butyl acrylate) (PGMA‐b‐PBA) diblock copolymer was prepared through ATRP using PGMA‐Cl as a macro‐initiator. This chain growth experiment demonstrated a good living character under the conditions employed, while simultaneously indicating a facile synthetic route for this type of functional block copolymer. In addition, the isotacticity parameter for the PGMAs obtained was estimated using 1H NMR analysis which gave a value of σGMA = 0.26 in agreement with that estimated in conventional radical polymerization.

SEC chromatograms of PGMA‐Cl macroinitiator and PGMA‐b‐PBA diblock copolymer.

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SEC chromatograms of PGMA‐Cl macroinitiator and PGMA‐b‐PBA diblock copolymer.
Fabrication and Characterization of GRIN Plastic Rods Containing Silver Nanoparticles with Novel Surfmers
Authors: Liu Jui‐Hsiang , Wu Dung‐Shin , Tseng Kuei‐Yu
Published: October 2004

Summary: Both novel polymerizable surfactants of 2‐(methacroyloxy)ethyl succinate (MAES) and succinic acid mono{11‐[2‐(2‐methylacryloyloxy)ethoxy]undecyl} ester (SAME‐11) were synthesized in this investigation. A novel method was also developed for the preparation of gradient refractive index (GRIN) plastic rods containing inorganic nanoparticles with the polymerizable surfactants (surfmers). Silver nanoparticles were prepared using W/O (water in oil) reverse micelle technique in the presence of the surfmers. The effect of w values (w = [H2O]/[surfmer]), silver nitrate concentration, surfmer/isooctane/H2O ratio, and initiator concentration on the nanoparticle size was investigated. The optical absorption spectra of the micellar samples were recorded on a spectrophotometer at room temperature in the range of 200–900 nm. The nanoparticle size was confirmed with a transmission electron microcopy (TEM) technique. To introduce the nanoparticles into the GRIN plastic rods, methyl methacrylate (MMA) was used instead of isooctane in the organic phase. Nanoparticles were found to increase the refractive index of plastic rods effectively. Light scattering and an opaque appearance due to the aggregation of nanoparticles and the existence of surfactants were solved using the polymerizable surfmers in this investigation. We estimated both the real image transmission and the three dimensional refractive index distributions of the prepared GRIN plastic rods. The results of this investigation suggested that nanoparticles could be used as a kind of dopant to fabricate GRIN plastic rods and increased its refractive index effectively. Polymerizable surfactant could further raise the refractive index of the core of the GRIN rods leading to an increase of the numerical apertures (NA) and the acceptance angle (θmax) of the plastic rods.

Three dimensional refractive index distribution of GRIN plastic rod prepared in this investigation.

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Three dimensional refractive index distribution of GRIN plastic rod prepared in this investigation.
Poly(acrylamide‐co‐itaconic acid) and Semi‐IPNS with Poly(ethylene glycol): Preparation and Characterization
Authors: Kalagasidis Krušić Melina , Danković Danijel , Nikolić Marija , Filipović Jovanka
Published: October 2004

Summary: A pH‐responsive poly(acrylamide‐co‐itaconic acid) (PAAm/IA) hydrogel and semi‐interpenetrating networks (semi‐IPNs) with 5, 10 and 15 wt.‐% of poly(ethylene glycol) (PAAm/IA/PEG), were synthesized. Their swelling behavior was studied in the pH range from 1.76 to 7.81, as well as their oscillatory swelling behavior at pH = 7.81 and pH = 1.7. Throughout these studies, the gels maintained their mechanical strengths and shape. The shear storage (G′) and loss (G″) moduli, obtained as a function of frequency, for the gels as formed and at equilibrium swelling were higher for the semi‐IPNs than for the copolymer hydrogel. The shear storage moduli of copolymer hydrogel and semi‐IPNs as formed were independent of frequency over the whole experimental range, whereas the values for the gels at equilibrium swelling decreased with increasing degree of swelling, i.e., the PAAm/IA hydrogel which exhibited the largest swelling had the lowest G′ value. The G′ and G″ values also depended on the content of PEG.

Diffusion exponent vs. pH for PAAm, copolymer hydrogel PAAm/IA and semi‐IPN with PEG.

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Diffusion exponent vs. pH for PAAm, copolymer hydrogel PAAm/IA and semi‐IPN with PEG.
Intraoperative magnification: Who uses it?
Authors: Jarrett Paul Max
Published: October 2004

Surgeons over recent decades have made increasing use of intraoperative magnification to enhance the outcome of surgical procedures, yet no published information exists regarding the extent of magnification use within surgical specialties. A sample of surgeons consisting of 148 specialists and senior surgical trainees in the west of Scotland was surveyed by postal questionnaire regarding their frequency and types of magnification use. Patterns of use were similar within each specialty, but varied markedly between specialties. Otolaryngologists and plastic, maxillofacial, and ophthalmic surgeons use both loupes and microscopes frequently. Cardiothoracic and pediatric surgeons tend only to utilize loupes, whereas neurosurgeons tend only to use microscopes. General surgeons, urologists, orthopedic surgeons, and gynecologists are infrequent users or nonusers of magnification, and when required will utilize loupes rather than microscopes. As a clear pattern of magnification use exists, it should be possible to anticipate the equipment needs of surgeons when providing theater services. © 2004 Wiley‐Liss, Inc. Microsurgery 24:420–422, 2004.
176–200‐GHz receiver module using indium phosphide and gallium arsenide MMICs
Authors: Archer John W. , Shen Mei Gan
Published: October 2004

This paper describes an integrated circuit‐based, down‐converting receiver module operating in the 176–200‐GHz range. The multichip module incorporates a cascaded pair of indium phosphide (InP) monolithic microwave integrated circuit (MMIC) amplifiers, providing a combined gain of more than 30 dB over the 176–200‐GHz band. The output from the amplifiers is fed to a subharmonically pumped InP passive‐HEMT block down‐converter that provides an IF output in the 0.5–15‐GHz range with a local oscillator (LO) signal between 46 and 50 GHz. A gallium arsenide (GaAs) medium‐power amplifier provides the LO drive for the mixer. For RF frequencies in the 176–185‐GHz band, the receiver exhibits a typical CW down‐conversion gain between 0 and 3 dB and a typical noise figure of 9 dB when operating at room temperature. For RF frequencies in the 190–196‐GHz band, the receiver exhibits a typical CW down‐conversion gain between 2 and 5 dB and a typical noise figure of 11 dB. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 458–462, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20501
Compact directive antennas with a wire‐medium artificial lens
Authors: Ikonen Pekka , Simovski Constantin , Tretyakov Sergei
Published: October 2004

In this paper, we present the results of numerical and experimental investigations of a prospective antenna which can be used, for example, as a base‐station antenna in cellular telecommunication systems. The antenna is a half‐wavelength dipole surrounded by periodically arranged capacitively loaded wires. Its operation is based on the recently suggested principle of the wire‐medium artificial lens. The development of this concept can possibly lead to the design of compact (0.2–0.5 wavelength in diameter) electrically controllable base‐station antennas. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 467–469, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20503
Design of a new X‐band active resonator oscillator
Authors: Lee Yeon‐Joo , Yun Tae‐Soon , Kim Ki‐Byoung , Lee Jong‐Chul
Published: October 2004

In this paper, a microstrip active resonator oscillator (ARO) for X‐band application is presented. The ARO is implemented on Teflon substrate with relative dielectric constant of 2.52, height of 0.54 mm, and metal thickness of 0.017 mm. The ARO shows 6‐dBm output power at 10 GHz, 2nd‐harmonic suppression of −20.1 dBc, phase noises of −57.27 and −92 dBc/Hz at the offset frequencies of 1 and 100 kHz, respectively, and a frequency tuning range of 43.7 MHz with 0.05% output error. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 472–475, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20505
Generation of 40‐GHz pulse trains from a 5‐GHz dual‐driving rational harmonic mode‐locked semiconductor fiber‐ring laser
Authors: Jong Kim Yun , Ghiu Lee Chung , Jo Hyun‐Jeong , Park Chang‐Soo
Published: October 2004

We present and demonstrate a simple method of generating 40‐GHz repetition‐rate pulse trains from a rational harmonic mode‐locked semiconductor fiber‐ring laser with 5‐GHz dual‐driving signal by using pulse‐amplitude equalization. By adjusting the voltages applied to both arms of the modulator pulse trains with an eight‐times repetition rate are equalized in their amplitudes. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 489–491, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20511
Lens or resonator? Electromagnetic behavior of an extended hemielliptic lens for a sub‐millimeter‐wave receiver
Authors: Boriskin Artem V. , Nosich Alexander I. , Boriskina Svetlana V. , Benson Trevor M. , Sewell Phillip , Altintas Ayhan
Published: October 2004

The behavior of a 2D model of an extended hemielliptic silicon lens of a size typical for THz applications is accurately studied for the case of a plane E‐wave illumination. The full‐wave analysis of the scattering problem is based on the Muller's boundary integral‐equations (MBIE) that are uniquely solvable. A Galerkin discretization scheme with a trigonometric basis leads to a very efficient numerical algorithm. The numerical results related to the focusability of the lens versus its rear‐side extension and the angle of the plane‐wave incidence, as well as near‐field profiles, demonstrate strong resonances. Such effects can change the principles of optimal design of lens‐based receivers. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 515–518, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20520
Development of ground‐penetrating image radar using a novel compact ultra‐wideband monopole antenna
Authors: Kim Kwan‐Ho , Park Young‐Jin , Park Han‐Kyu
Published: October 2004

A compact ultra‐wideband ground‐penetrating radar (UWB GPR) using an impulse waveform is developed. A proper impulse generator is designed and then a novel compact UWB monopole antenna is developed for transmitting the impulse and receiving the reflected signals. For visualization of buried targets, image processing is performed. For verification, a UWB GPR prototype is built. The experimental results show that the system has very good depth and spatial resolution. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 521–524, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20522
A large dynamic‐range self‐adjusting output‐power laser device
Authors: Lu Z. G. , Grover C. P.
Published: October 2004

We investigate a stable semiconductor fiber‐ring laser (SFRL) whose output power can be controlled by external light injection. Based on this SFRL, we develop a novel laser for keeping its output power approximately constant when the input power is changed over a dynamic range of 17 dB. Potential applications are discussed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 532–535, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20525
Finite‐ground‐plane effects on the ultra‐wideband planar monopole antenna
Authors: Su Saou‐Wen , Wong Kin‐Lu , Cheng Yuan‐Tung , Chen Wen‐Shyang
Published: October 2004

Impedance and radiation characteristics of an ultra‐wideband (UWB) planar monopole antenna with a finite circular ground plane are experimentally studied. The significant effects of the ground‐plane size on the lower‐edge frequency of the antenna's impedance bandwidth are observed, and there exists an optimal diameter of the circular ground plane for achieving a maximum impedance bandwidth. Large ground‐plane effects on the radiation pattern and antenna gain are also seen, especially for the lower frequencies in the antenna's UWB impedance bandwidth. Details of the experimental results are presented and discussed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 535–537, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20526
NMR assignments and single‐crystal X‐ray diffraction analysis of deoxyloganic acid
Authors: Teng Rong Wei , Wang De Zu , Wu Yun Shan , Lu Yang , Zheng Qi Tai , Yang Chong Ren
Published: October 2004

7‐Deoxyloganic acid (1), citrusin C (2), 3,4‐dihydroxyl benzoic acid (3) and (E)‐caffeic acid (4) were isolated from the water‐soluble fraction of ethanol extracts of Morina nepalensis var. alba Hand.‐Mazz. and their structures were determined on the basis of spectroscopic evidence. The total assignments of 1H and 13C NMR spectra of 1 in solvents CD3OD, D2O and CDCl3 were reported, in addition to the single‐crystal X‐ray diffraction analysis of its tetraacetate 1a. All compounds were obtained from Morina genus for the first time. Copyright © 2004 John Wiley & Sons, Ltd.
Unilaterally connected large digraphs and generalized cycles
Authors: Gómez José , Canale Eduardo A. , Muñoz Xavier
Published: October 2004

Lower and upper bounds on the order of digraphs and generalized p‐cycles with a specified maximum degree and unilateral diameter are given for generic values of the parameters. Infinite families of digraphs attaining the bounds asymptotically or even exactly are presented. In particular, optimal results are proved for bipartite digraphs (p = 2) and digraphs with unilateral diameter 3. © 2003 Wiley Periodicals, Inc.
On the power of BFS to determine a graph's diameter
Authors: Corneil Derek G. , Dragan Feodor F. , Köhler Ekkehard
Published: October 2004

Recently, considerable effort has been spent on showing that Lexicographic Breadth First Search (LBFS) can be used to determine a tight bound on the diameter of graphs from various restricted classes. In this paper, we show that, in some cases, the full power of LBFS is not required and that other variations of Breadth First Search (BFS) suffice. The restricted graph classes that are amenable to this approach all have a small constant upper bound on the maximum‐sized cycle that may appear as an induced subgraph. We show that, on graphs that have no induced cycle of size greater thank, BFS finds an estimate of the diameter that is no worse than diam(G) − ⌊k/2⌋. © 2003 Wiley Periodicals, Inc.
Loosely woven fabric model with viscoelastic crimped fibres for ballistic impact simulations
Authors: Ivanov Ivelin , Tabiei Ala
Published: October 2004

A computational micro‐mechanical material model of loosely woven fabric for non‐linear finite element impact simulations is presented in this work. The model is a mechanism incorporating the crimping of the fibres as well as the trellizing. The equilibrium of the mechanism allows the straightening of the fibres depending on the fibre tension. The contact force at the fibre crossover point determines the rotational friction dissipating a part of the impact energy. The stress–strain relationship is viscoelastic based on a three‐element model. The failure of the fibres is strain rate dependent. The model is implemented as user defined subroutine in the transient finite element code LS‐DYNA. The ballistic impact simulations with the model are in good agreement with the experimental results. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis and characterization of poly(epoxy‐imide) crosslinked networks
Authors: Yang Seung‐Jin , Lee Choonkeun , Jang Wonbong , Kwon Jinuk , Sundar Saimani , Han Haksoo
Published: October 2004

Poly(epoxy imide)s were prepared by a reaction between a hydroxyl‐group‐containing soluble copolyimide and commercial epoxy resins at 220 °C for 2 h. Poly(epoxy imide) thin films exhibited higher thermal stability and lower dielectric constants than a commercial flip‐chip package material (U300). The thermal stabilities of the poly(epoxy imide)s were 1.4–2.0 times higher than that of U300. The thermal stability increased with increasing crosslink density and with decreasing bulky CF3 groups (which were easily decomposable). The dielectric constants of the poly(epoxy imide)s were 1.1–1.3 times lower than that of U300, and this is highly desirable for the microelectronic packaging industry. The dielectric constant dramatically decreased when bulky CF3 groups were added and when the functionalities of epoxy resins decreased. The residual stresses, slopes in the cooling curves, and glass‐transition temperatures of the poly(epoxy imide)s were measured with a thin‐film stress analyzer. Low residual stresses and slopes in the cooling curves were achieved with a higher crosslink density. However, in the presence of bulky CF3 groups, the copolyimide backbone structure did not affect the residual stress values. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4293–4302, 2004
Sorption and desorption of flumioxazin to soil, clay minerals and ion‐exchange resin
Authors: Ferrell Jason A , Vencill William K , Xia Kang , Grey Timothy L
Published: October 2004

Flumioxazin adsorption kinetics were described using a Greenville sandy clay loam soil. Adsorption kinetics experiments showed that 72% of total herbicide was absorbed after 1 h of continuous shaking and continued to increase to 78% after 72 h. Flumioxazin adsorption was then tested on seven agriculturally important soils throughout the southern USA. Adsorption isotherms for all soils had Kf (Freundlich distribution coefficient) values that ranged from 8.8 to 0.4, with many near 1.5. Soil organic matter content was the parameter most highly correlated with flumioxazin adsorption (r2 = 0.95, P < 0.001). Sorption to clay minerals had Kf values ranging from 50 for bentonite to 4.7 for kaolinite. However, normalizing Kf for sorbent surface area revealed that aluminum hydroxide (gibbsite) possessed the greatest flumioxazin sorption per unit area. Sorption to anionic exchange resin (Kf 676) was greater than cationic exchange resin (Kf 42). Molecular model calculations were performed to elucidate why sorption was greater to anionic exchangers. These calculations indicated that a region of dense electronegativity exists on the 3‐dione moiety of the molecule. This would lead to greater flumioxazin sorption by positively charged surface sites. Desorption isotherms from soil exhibited no effect of hysteresis. Desorption from clay minerals was very rapid and flumioxazin in solution was undetectable after three desorption steps. From these data it was concluded that flumioxazin can become readily available in soil solution with increase in soil water content. Copyright © 2004 Society of Chemical Industry
Pressure tuning of localized and extended vibrational modes in Si:O
Authors: McCluskey M. D.
Published: October 2004

Interstitial oxygen in silicon (Si:O) is a model system for the study of vibrational modes in semiconductors. Hydrostatic pressure has been used to probe the vibrational properties of this defect. In this paper, the results of infrared (IR) spectroscopy experiments on Si:16O and Si:18O are reviewed. As pressure is applied, the oxygen atom buckles outward. This structural change results in a qualitative change in low‐frequency vibrational motion in the [111] plane, as the system transforms from a harmonic oscillator to a rotor. A particularly interesting phenomenon occurs when the Si:18O local vibrational mode (LVM) approaches the two‐phonon continuum. First, the LVM exhibits an avoided crossing with certain combination modes of the defect. Second, when the LVM enters the two‐phonon continuum, the linewidth abruptly broadens, due to a decrease in the lifetime. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Competitive effects on the high‐pressure phase diagram of manganites
Authors: Postorino P. , Sacchetti A. , Capone M. , Dore P.
Published: October 2004

Recent infrared absorption measurements performed at different pressures and temperatures on the La0.75Ca0.25MnO3 manganite provided the insulator‐to‐metal transition temperature TIM(P), i.e. the P–T phase diagram of the manganite. We report an extended data analysis, by considering in detail pressure and temperature dependence of the observed IR active phonon and of the absorption spectral weights N*. The phonon pressure‐dependence, consistently with the P–T phase diagram, indicates the onset of a new localizing interaction above P* = 6–7 GPa. Finally a simple theoretical model will be employed to give a qualitative explanation of the observed high‐pressure behavior and to suggest the relevance of the charge‐localizing super‐exchange magnetic interaction in the very high‐pressure regime. Within this framework the asymptotic regime at high pressure is ascribed to the competition between the magnetic super‐ and double‐exchange interactions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Amplified spontaneous emission measurements in a diamond anvil cell: A tool to investigate laser diode gain under high pressure
Authors: Patel D. , Xu L. F. , Pownall R. , Anton O. , Menoni C. S.
Published: October 2004

In this work we report on results of amplified spontaneous emission measurements on InGaAsP laser diodes from which gain spectra at different biases and as a function of hydrostratic pressure were obtained. From the analysis of the gain spectra, peak net modal gain, internal losses and quasi‐Fermi energy separation are determined. Knowledge of the latter provides a pathway to determine the injected carrier density and henceforth to calculate the rate of change of the peak gain with carrier density (dg/dN), the transparency carrier density and their pressure behaviour. The evolution of these parameters with pressure allows us to develop a comprehensive picture of the behaviour of the laser threshold current of 1.3 μm communication lasers. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman modes in oligophenyls under hydrostatic pressure
Authors: Martin C. M. , Cai Q. , Guha S. , Graupner W. , Chandrasekhar M. , Chandrasekhar H. R.
Published: October 2004

We present a low temperature study of the Raman modes in three oligo(para‐phenylene) materials (p‐terphenyl, 3P; p‐quaterphenyl, 4P; and p‐hexaphenyl, 6P) under hydrostatic pressure up to 80 kbar. The 1220 cm–1 (C–H in plane bend), 1280 cm–1 (C–C interring stretch), 1600 cm–1 (aromatic C–C on‐ring stretch) and 1610 cm–1 (combination mode of 610 cm–1 and 990 cm–1) modes provide indicators of planarization in their frequency and intensity behaviors. In this comparative study of 3P, 4P, and 6P, the most remarkable feature is the clearly defined change in the slope of the 1220 cm–1 in‐plane bending mode upon planarization. In contrast, modes in the 1600 cm–1 region do not have as clear a two‐slope behavior; however, a more sensitive measure of planarization is the frequency difference between the 1610 cm–1 and the 1600 cm–1 modes, which exhibits a distinct drop before planarization, and a gradual increase thereafter. The resonance conditions that are responsible for the 1610 cm–1 mode make the two‐slope behavior less pronounced as compared to the 1280–1220 pair of modes. The intensity of the Raman modes from all three oligophenyls also indicate planarization: the intensity of the 1280 cm–1 mode decreases sharply relative to the 1220 cm–1 mode until the molecule planarizes, and increases slowly thereafter. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydrostatic pressure effects on the donor impurity‐related photoionization cross‐section in cylindrical‐shaped GaAs/GaAlAs quantum well wires
Authors: Correa J. D. , Cepeda‐Giraldo O. , Porras‐Montenegro N. , Duque C. A.
Published: October 2004

Using a variational method the binding energy has been calculated for a shallow donor impurity and the donor‐related photoionization cross‐section in 1D and 0D GaAs low‐dimensional systems. The dependence on the binding energy and the photoionization cross‐section for a hydrogenic donor impurity in the finite potential model are discussed and the results are presented as a function of the radius, polarization of the photon, applied hydrostatic pressure, and photon energy. The calculations for the pressure effects are performed both in the direct and indirect GaAs gap regime. Calculations are presented for an on‐axis (on‐center) impurity in the wire (in the dot). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Light scattering of double wall carbon nanotubes under hydrostatic pressure: pressure effects on the internal and external tubes
Authors: Puech P. , Hubel H. , Dunstan D. J. , Bassil A. , Bacsa R. , Peigney A. , Flahaut E. , Laurent C. , Bacsa W. S.
Published: October 2004

We report high‐pressure Raman light scattering studies up to 10 GPa on double walled carbon nanotubes using two pressure transmitting media. In alcohol, a clear splitting of the G band is observed up to 10 GPa. This splitting is evidence for both discontinuous tangential stress and continuous radial stress. A structural distortion seems to be present at 3 GPa, revealed by a spectroscopic signature at 1480 cm–1. With argon as the pressure transmitting medium, the nanotubes bundles show a transition at 6 GPa which corresponds to a collapse to a flattened structure and removes the splitting. The comparison of the pressure coefficients before the transition for the two pressure transmitting media shows that the ratio of the two coefficients associated with internal and external tubes, is the same but the absolute values are different. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pressure dependence of 2D hole mobility in thermoactivated photoconductivity effect observed in p‐GaAs/Al0.5Ga0.5As heterostructures
Authors: Berman I. V. , Bogdanov E. V. , Ilievsky A. A. , Minina N. Ya. , Kraak W.
Published: October 2004

The temperature dependence of the 2D hole mobility in p‐GaAs/Al0.5Ga0.5As heterostructures has been investigated in dark and illuminated with red light states under uniaxial compression up to 3.4 kbar in the temperature interval 1.5–20 K. From numerical calculations it has been shown that the decrease of the 2D hole mobility below 5.5 K, where the recently observed thermoactivated negative photoconductivity takes place, may be well described by scattering on ionized deep donor‐like traps located in Al0.5Ga0.5As in the vicinity of a heterointerface. According to the calculations, these traps are distributed in the spacer at distances of 7–48 nm from the heterointerface and their contribution to 2D hole scattering strongly increases under uniaxial compression. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties and structural phase transitions of lead‐halide based inorganic–organic 3D and 2D perovskite semiconductors under high pressure
Authors: Matsuishi K. , Ishihara T. , Onari S. , Chang Y. H. , Park C. H.
Published: October 2004

Optical absorption, photoluminescence and Raman scattering of lead‐halide based inorganic–organic perovskite semiconductors were measured under quasi‐hydrostatic pressure at room temperature. For the 3D perovskite semiconductor, (CH3NH3)PbBr3, the free exciton photoluminescence band exhibits red‐shifts with pressure, and jumps to a higher energy by 0.07 eV at 0.8 GPa, which is associated with a phase transition from a cubic to an orthorhombic structure confirmed by Raman scattering. Above the phase transition pressure, the exciton band shows blue‐shifts with further increasing pressure, and eventually disappears above 4.7 GPa. The results are compared with those for the 2D perovskite semiconductor, (C4H9NH3)2PbI4. First principles pseudopotential calculations were performed to investigate changes in octahedral distortion and electronic band structures with pressure. The calculations have explained the origins of the intriguing changes in the electronic states with pressure in view of bonding characters between atomic orbitals in octahedra. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Excitation and pressure effects on low temperature photoluminescence from GaAs/GaInP heterostructures
Authors: Nagata Atsushi , Kobayashi Toshihiko , Prins Andrew D. , Homma Yasuhiro , Uchida Kazuo , Nakahara Jun‐ichiro
Published: October 2004

We report for the first time the results of a study of 11 K photoluminescence (PL) measurements of metal‐organic vapor phase epitaxy grown GaAs/GaInP quantum wells at pressures up to ∼5 GPa and examine the effects of laser excitation energy and intensity. The use of low temperature allows us to study the true nature of a peak at ∼1.46 eV, which dominates instead of the GaAs QW emission, even at very low excitation intensities to pressures well above the Γ–X crossover in GaInP. Our results suggest that the ∼1.46 eV emission is a spatially indirect transition of electrons and holes separated at the interface in a type‐II band alignment. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High pressure Raman study of BaMoO4
Authors: Christofilos D. , Arvanitidis J. , Kampasakali E. , Papagelis K. , Ves S. , Kourouklis G. A.
Published: October 2004

The structural stability of polycrystalline BaMoO4 under hydrostatic pressure has been investigated by means of Raman spectroscopy up to 8 GPa. Raman spectra reveal a pressure induced phase transition at ∼5.8 GPa. Upon pressure release the structure reverts to its ambient pressure scheelite (CaWO4) structure with no observable hysteresis. The large number of Raman active modes of the high pressure phase suggests either an increase of the size of the unit cell and/or a non‐centrosymmetric structure leading to the activation of the ungerade modes of the scheelite structure. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carrier recombination processes in 1.3 μm and 1.5 μm InGaAs(P)‐based lasers at cryogenic temperatures and high pressures
Authors: Sweeney S. J. , Jin S. R. , Ahmad C. N. , Adams A. R. , Murdin B. N.
Published: October 2004

We describe measurements of the threshold current of 1.3 μm and 1.5 μm InGaAs(P)‐based quantum‐well lasers measured at cryogenic temperatures and at high pressures. At low temperatures (∼100 K), we find that the threshold current of the devices increases with increasing pressure consistent with the calculated pressure variation of the radiative current. This is in sharp contrast with their pressure dependence at room temperature (RT), where the threshold current decreases with increasing pressure due to the decrease in importance of Auger recombination. These low‐temperature, high‐pressure results agree well with previous temperature dependence measurements on the same devices, which show a transition from radiative to non‐radiative Auger recombination dominated behaviour as the laser temperature is increased from ∼100 K to room temperature. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pressure dependence of optical transitions in semiconducting single‐walled carbon nanotubes
Authors: Shan W. , Wu J. , Walukiewicz W. , Ager J. W. , Yu K. M. , Haller E. E. , Kissell K. , Bachilo S. M. , Weisman R. B. , Smalley R. E.
Published: October 2004

The effects of applied hydrostatic pressure on the optical transitions in semiconducting single‐walled carbon nanotubes with different diameters and chiralities have been studied using optical absorption and photoluminescence spectroscopy. The excitonic transitions associated with the band‐gap (the first van Hove transition) energies in the carbon nanotubes are found to shift to lower energy at a rate depending on nanotube structure. The excitonic transitions between the first excited confinement states (the second van Hove transitions) are found to be much less sensitive to the applied hydrostatic pressure. All nanotubes show a dependence on their chirality in terms of pressure coefficient of the band‐gap energy, with the larger‐diameter nanotubes exhibiting a higher sensitivity of the band‐gap energy to hydrostatic pressure. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Bayesian operationalization of the resource‐based view
Authors: Hansen Mark H. , Perry Lee T. , Reese C. Shane
Published: October 2004

This paper argues that the gap between the theoretical utility and the practical utility of the resource‐based view (RBV) may be narrowed by operationalizing the theory more consistently with Penrose's original framework. The operationalization proposed here is a twofold approach. First, the RBV may be enhanced by the explicit recognition of Penrose's two classes of resources, namely, administrative resources and productive resources. This distinction suggests a focus on the administrative decisions of managers that lead to economic performance. Second, we argue that the RBV is a theory about extraordinary performers or outliers—not averages. Therefore, the statistical methods used in applying the theory must account for individual firm differences, and not be based on means, which statistically neutralize firm differences. We propose a novel Bayesian hierarchical methodology to examine the relationship between administrative decisions and economic performance over time. We develop and explain a measure of competitive advantage that goes beyond comparisons of economic performance. This Bayesian methodology allows us to make meaningful probability statements about specific, individual firms and the effects of the administrative decisions examined in this study. Copyright © 2004 John Wiley & Sons, Ltd.
Neutron Scattering as a Powerful Tool in Solid State Chemistry. Examples from the Investigations in Crystal Structures and Properties of Metal Hydrogen and Metal Chalcogen Compounds
Authors: Auffermann Gudrun , Müller Paul , Bronger Welf
Published: October 2004

Neutron scattering experiments play a key role in the investigation in crystal structures and properties of solid compounds which is demonstrated with examples from the compound series AxMyXz (A ≙ alkali metal, M ≙ transition metal and X ≙ H, S or Se). Measurements on powdered samples provide as well the hydrogen positions within the crystal structures of ternary hydrides by using the analogous deuterium compounds as the lithium positions in the compounds with A ≙ Li. Ferromagnetic and antiferromagnetic arrangements are investigated by neutron diffraction which lead to the determination of the magnetic moments of transition metal atoms providing information about chemical bonding. Finally, it is demonstrated that inelastic neutron scattering is an independent method used in a complementary way to infrared or Raman spectroscopy, and, due to the interactions of neutrons with the magnetic states of transition metal atoms, to susceptibility or magnetisation.
About Trihalides with TiI3 Chain Structure: Proof of Pair Forming of Cations in β‐RuCl3 and RuBr3 by Temperature Dependent Single Crystal X‐ray Analyses
Authors: Hillebrecht H. , Ludwig Th. , Thiele G.
Published: October 2004

Single‐crystal X‐ray studies on β‐RuCl3 and RuBr3 at different temperatures verified, that both compounds are dimorphic and show reversible phase transitions at 206 K resp. 384 K. In the HT‐forms the Aristo‐type of the hexagonal TiI3‐structure with space group P63/m c m (Z = 2, β‐RuCl3 at 293(2) K: a = 6.121(2) Å, c =5.655(2) Å, RuBr3 at 423(3) K: 6.5215(12) Å, c= 5.8851(13) Å) has been found, in the LT‐forms the RuBr3‐type structure, an orthorhombic distorted variant with space group Pmmn (Z = 4, β‐RuCl3 at 170(3) K: a= 10.576(2) Å, b = 5.634(1) Å, c = 6.106(1) Å, RuBr3 at 293(2) K: a = 11.2561(16) Å, b = 5.8725(12) Å, c = 6.4987(9) Å). A hexagonal closest packing of X‐ anions forms the basis of an arrangement of infinite chains with face‐connected [RuX6/2] octahedra. While in the chains of the hexagonal HT‐forms the Ru‐Ru‐distances are identical (d(Ru‐Ru) = 2.8275(10) Å for β‐RuCl3, d(Ru‐Ru) = 2.9425(6)Å for RuBr3), in the orthorhombic structures the chains are distorted through pairing of the ruthenium(III) atoms (d(Ru‐Ru) = 2.6328(14) Å / 3.0010(15) Å for β‐RuCl3 at 170(3) K, d(Ru‐Ru) = 2.765(1) Å / 3.108(1) Å for RuBr3 at 293(2) K).

The hexagonal metric with a/c= √3 holds also for the orthorhombic LT‐forms. Large crystals and the final products of the phase transition from HT‐ to LT‐forms are pseudomerohedral twins of three twin domains with nearly equal amounts complicating proof and analysis of the LT‐forms.
Die Kristallstrukturen von Ca4Ir8P7 und Ca4Ir8As7 sowie ihre Beziehung zum ThCr2Si2‐Typ
Authors: Löhken Anke , Mewis Albrecht
Published: October 2004

Ca4Ir8P7 (a = 12, 560(9), b = 3, 945(2), c = 13, 042(8) Å, β = 98, 81(5)°) und Ca4Ir8As7 (a = 12, 987(6), b = 4, 070(2), c = 13, 470(4) Å, β = 98, 14(3)°) kristallisieren in einem neuen Strukturtyp monokliner Symmetrie (P21/m; Z = 2). Bei ihm sind sieben der acht kristallographisch unterschiedlichen Ir‐Atome tetraedrisch von Nichtmetallatomen koordiniert. Im Gegensatz zum ThCr2Si2‐Typ sind die Tetraeder nicht zu Schichten verknüpft, sondern zu Bändern unterschiedlicher Breite. Die gegeneinander verkippten Bänder werden über das achte Ir‐Atom miteinander verbunden, das dadurch eine trigonal planare P‐ bzw. As‐Umgebung erhält. Die Ca‐Atome befinden sich in den Lücken des so gebildeten dreidimensionalen Gerüsts. Im Gegensatz zu ähnlichen Rh‐Phosphiden können bei den beiden Ir‐Verbindungen keine bindenden Wechselwirkungen zwischen den Nichtmetallatomen diskutiert werden, es dominieren vielmehr kovalente Ir‐P/As‐ sowie metallische Bindungen. Dargestellt wurden die Verbindungen durch Erhitzen der entsprechenden Elementgemenge auf 1100 °C; die Strukturbestimmung erfolgte röntgenographisch auf der Basis von Einkristalldaten.
New Ternary Iodides of Lanthanum and Cerium, AIIMI4 (A = Sr, Ba, Nd, Sm, Eu; M = La, Ce)
Authors: Gerlitzki Niels , Hammerich Stefanie , Meyer Gerd
Published: October 2004

Black single crystals of nine ternary iodides AIIMI4 (A = Sr, Ba, Nd, Sm, Eu; M = La, Ce) have been obtained from reactions of the metals A with the triiodides of M in sealed tantalum containers at elevated temperatures. They all crystallize isotypically with BaLaI4 (monoclinic, I2/a, Z = 4). The most important structural feature are chains of face‐sharing square antiprisms [MI8] in accord with the formula A[MI8/2]. M‐M distances are, on the average, 370.6 and 367.9 pm for M = La and Ce, respectively. With all M‐M distances equal, these iodides are expected to be one‐dimensional metals according to the formulation (A2+)(M3+)(e‐)(I‐)4 with the excess electron residing in a 5d band.
Reactions of Di(1‐cyclohepta‐2, 4, 6‐trienyl)sulfane, S(C7H7)2, with Derivatives of the Hexacarbonyls, M(CO)6 (M = Cr, Mo, W)
Authors: Herberhold Max , Liu Jinnan , Milius Wolfgang , Tok Oleg , Wrackmeyer Bernd
Published: October 2004

Mononuclear carbonylmetal complexes of chromium, molybdenum and tungsten containing the sulfane S(C7H7)2 (1) have been obtained starting from precursors such as the THF‐stabilized pentacarbonylmetal fragments, [M(CO)5](thf), the acetonitrile intermediates M(CO)6‐x(CH3CN)x (x = 1, 2, 3) (M = Cr, Mo, W) or the η4‐norbornadiene complexes M(CO)4(C7H8) (M = Cr, Mo). In addition to the pentacarbonyls, M(CO)5[S(C7H7)2] (M = Cr (2a), Mo (2b), W (2c)) which contain 1 unchanged as a two‐electron sulfane ligand with two pending cyclohepta‐2, 4, 6‐trienyl substituents, isomeric complexes M(CO)5[S(CH2Ph)(C7H7)] (M = Cr (3a), W (3c)) were obtained at higher temperatures (40‐50 °C) in which one of the two organic groups has been transformed into a benzyl substituent. In the tetracarbonyls, cis‐M(CO)4[S(C7H7)(η2‐C7H7)] (M = Mo (4b), W (4c)), the ligand 1 serves as an olefinic sulfane four‐electron chelate ligand. The reaction of either Mo(CO)6 or (mesitylene)Mo(CO)3 with S(C7H7)2 (1) in boiling THF leads to the sulfur‐free ditropyl complex Mo(CO)3[(η6‐C7H7)‐C7H7] (5b, two isomers). The 1H and 13C NMR spectra of the new complexes 2‐4 reveal various dynamic processes including pyramidal inversion of the sulfur atom and [1, 7]‐sigmatropic shifts at the C7H7 ring. The molecular structures of 2c, 3a, 4b and 4c have been determined by X‐ray crystallography.
Das Subchlorid Bi16PdCl22: Pd@Bi104+‐Polykationen in einem Raumnetzwerk aus Chlorobismutat(III)‐Anionen
Authors: Dubenskyy Vitaly , Ruck Michael
Published: October 2004

Bi16PdCl22 wurde in Form schwarzer, luftempfindlicher Kristalle aus den Elementen durch langsames Abkühlen einer Schmelze von 1270 K auf Raumtemperatur dargestellt. Aus Röntgenbeugungsuntersuchungen an Einkristallen geht hervor, dass die Verbindung in der triklinen Raumgruppe $P{\bar 1}$ kristallisiert mit a = 2047, 7(4) pm, b = 2132, 1(4) pm, c = 2145, 4(4) pm und α = 91, 09(3)°, β = 95, 14(3)°, γ = 93, 16(3)°. In der Kristallstruktur finden sich Polykationen Pd@Bi104+ in Gestalt pentagonaler Archimedischer Antiprismen eingebettet in die Hohlräume eines pseudo‐kubischen Raumnetzwerkes [Bi6Cl22]4‐ aus spitzen‐ und kantenverknüpften Chlorobismutat(III)‐Ionen. Die 2×2×2‐Überstruktur resultiert aus drei verschiedenen Hauptorientierungen der Polykationen, die im Anzahlverhältnis 3 : 3 : 2 auftreten. Die Formulierung als kationische Einschlussverbindung Pd@Bi104+ basiert auf der nur schwachen Wechselwirkung zwischen dem interstitiellen Pd0, das eine abgeschlossene Unterschale aufweist, und dem umgebenden elektronenpräzisen arachno‐Cluster Bi104+.
Synthesis, Crystal Structure Determination and Vibrational Spectra of Indium(II) Indium(III) Oxidephosphate, (In2)4+(In3+)2O2(PO4)2
Authors: Thauern H. , Glaum R.
Published: October 2004

The new indium(II, III)‐oxidephosphate In2O(PO4) has been obtained from In2O3 and phosphorus (n(In) : n(P) = 1 : 0.53, 800 °C, iodine as mineralizer; In2O3 and indium as by products). Colourless single crystals of In2O(PO4) were grown by chemical vapour transport in a temperature gradient (800 → 700 °C) using iodine as transport agent. The crystal structure of In2O(PO4) ($P{\bar 1}$, Z = 2, a = 5.220(3) Å, b = 6.322(3) Å, c = 6.789(3) Å, α = 107.72(5)°, β = 109.21(5)°, γ = 95.56(6)°, is characterised by a three‐dimensional network of [PO4] tetrahedra and [In2O10] groups formed by edge‐sharing octahedra [In3+O6]. Channels within the network (∥ crystallographic b‐axis) contain (In—In)4+ dimers in agreement with the formula (In2)4+(In3+)2O2(PO4)2. IR‐ and Raman‐spectra have been measured to characterise the In‐In bond. The strongest emission in the Raman spectrum at $\tilde {\nu}$ = 163 cm‐1 is attributed to the In‐In stretching vibration. For In3(PO4)2 [structural formula: (In2)4+3(PO4)4] $\tilde {\nu}$‐(In—;In) = 195 cm‐1 is observed.
>La2C3 und seine Reaktion mit Wasserstoff
Authors: Simon Arndt , Gulden Thomas
Published: October 2004

La2C3 ist als homogene Phase mit einem Kohlenstoffgehalt von 56.2 bis 60.2 % beschrieben worden. Mehrwöchiges Tempern bei 1150 K führt jedoch zur Separation in die Randphasen La2C2.7 ($I{\bar 4}{\rm 3}d$, a = 879.88(4) pm) und La2C3 (a = 881.80(5) pm), die scharfe Übergänge zur Supraleitung bei 5.6 K bzw. 13.2 K zeigen. Die Umsetzung von La2C3‐x mit H2 ergibt temperaturabhängig verschiedene Produkte. Bei 450 K entstehen röntgenamorphe Produkte der analytischen Zusammensetzung La2C3‐xH1.5+x. Ausgehend von La2C3 beobachtet man im Temperaturintervall von 620 bis 820 K ein analytisch als La2CH4 charakterisiertes Produkt mit stark verbreiterten Reflexen im Röntgendiagramm ($FM{\bar 3}m$, a = 564.2(1) pm). Die Umsetzung bei 1000 bis 1100 K ergibt La2C2H2 (C2/m, a = 720.6(8), b = 393.2(2), c = 673.9(4) pm, β = 94.66(5) °), für dessen Struktur ein Vorschlag aus der metrischen Ähnlichkeit mit La2C2O2 entwickelt wird.
Quantitative Beschreibung von Kristallstrukturen über die Fern‐Ordnung: Ist das Oxyd RbNa2AuO2 ein “Oxoaurat”?
Authors: Hoppe Rudolf
Published: October 2004

Selbst Oxyde wie BO4Nb mit simplem Aufbau sind nach der Kristallstruktur nicht einzuordnen: Borat? Niobat? Doppeloxyd? Sind daher RbNa2AuO2 und Analoga, z.B. Na3AuO2 etc., wirklich ‘Oxoaurate’, wie behauptet? Eine neue, nur die Fernordnung nutzende quantitative Beschreibung des Kristallaufbaus hilft, diese und andere Fragen zu beantworten! Bereits bei 430 °C entstehen klar durchsichtige, leicht hellbläuliche/farblose Einkristalle von RbNa2AuO2 durch ‘Oxydative Addition’ aus innigen Gemengen RbAu + Na2O2 (Ag‐Bömbchen, Ag‐Konus‐Verschluß, extrem trocken, unter Ar, in Ampullen aus Supremaxglas, 10 d). Wie bei KNa2AuO2 liegen Hanteln [OAuO], gewellte Schichten {O1/2(NaO)O1/2} und PdCl2‐analoge O2/2RbO2/2‐Ketten vor. Zählt man aber zusätzlich, deutlich weiter entfernt, je ein O von zwei Nachbarketten ‘RbO2’ als Liganden mit, dann ist jedoch ein dreidimensionales Gerüst ‘RbO6/3’ vorhanden. Strukturgeometrisch liegt kein Oxoaurat(I), sondern ein Doppeloxyd vor.