bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tuneable photonic crystals obtained by liquid crystal infiltration
Authors: Kitzerow H.‐S. , Lorenz A. , Matthias H. 
Published: October 2007

AbstractThe unique combination of fluidity and birefringence that is characteristic for liquid crystals is quite suitable in order to tune the optical properties of photonic crystals. Here, some experimental examples are reviewed where colloidal crystals (artificial opals and inverse opals), two‐ and three‐dimensional photonic crystals made of macroporous silicon and photonic crystal fibres have been filled with liquid crystals and the changes of their optical properties due to temperature variation or external fields have been investigated. The performance and limits of state‐of‐the‐art photonic crystals filled with liquid crystals are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ultra‐low refractive index mesoporous substrates for waveguide structures
Authors: Konjhodzic D. , Schröter S. , Marlow F. 
Published: October 2007

AbstractMesoporous silica films were synthesized by dip‐coating. In this process, evaporation induced self‐assembly leads to the formation of an ordered pore structure. Two types of films with different optical properties have been found in dependence on the humidity during the synthesis. The synthesis field has been explored in order to locate optically perfect films. Both film types, denoted as A and B, have been characterized by small angle X‐ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). From these results, the different structures for the two film types have been determined. A‐type films have a stable worm‐like structure, whereas for B‐type films a sustained lamellar structure has been found. A very low refractive index has been measured for A‐type films and its stability has been examined. These films have been used as low‐n supports to realize waveguide structures based on polymers, Ta2O5, and the ferroelectric material PZT. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solitary wave formation in one‐dimensional photonic crystals
Authors: Essig Sabine , Niegemann Jens , Tkeshelashvili Lasha , Busch Kurt 
Published: October 2007

AbstractWe present a variational approach to the problem of solitary wave formation in one‐dimensional nonlinear photonic crystals. In particular, we analyze how an arbitrary initial pulse is reshaped into a stable solitary wave by shedding excess radiation. Owing to the strong Bragg‐scattering near photonic band edges this reshaping results in non‐trivial dynamics and we show that within the variational framework we can quantitatively describe this complex wave dynamics for relatively short times. For longer times, the results become less accurate but still allow a qualitatively correct description. Finally, we discuss how an improved handling of the coupling to radiation modes can lead to an accurate description of the long‐term behavior. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bloch modes and group velocity delay in coupled resonator chains
Authors: Möller Björn M. , Artemyev Mikhail V. , Woggon Ulrike 
Published: October 2007

AbstractCoherently coupled optical microresonators are studied as a concept for guiding and slowing down light. So‐called coupled‐resonator optical waveguides (CROWs) composed of nanocrystal doped microspheres are studied using mode mapping spectroscopy at the diffraction limit and microphotoluminescence spectroscopy. We demonstate coherent photon coupling in one‐dimensional multiresonator chains and show the evolution of individual cavity modes into waveguide modes. A coupled‐oscillator model is developed, which explains the resulting coupled‐resonator mode patterns in finite systems. The potential to slow down the group velocity of light by orders of magnitude is explored. Experimentally, a slowing‐factor S = 31 has been observed. A model for disorder in CROW structures is developed, by which size tuning of individual resonators is found to result in anticrossing relations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Linear and nonlinear effects of light propagation in low‐index photonic crystal slabs
Authors: Iliew R. , Etrich C. , Augustin M. , Kley E.‐B. , Nolte S. , Tünnermann A. , Lederer F. 
Published: October 2007

AbstractWe investigate theoretically and experimentally photonic crystals realised in slab waveguides made of materials with a low refractive index. Although in such systems a two‐dimensional photonic bandgap for TE polarised light can be achieved, the low index imposes several restrictions influencing the performance. We investigate the transmission and dispersion properties of photonic crystal defect waveguides, high‐quality factor microcavities and unusual phenomena of light propagation and localisation in truly periodic systems without defects. This is compared to results obtained in high‐index materials. Furthermore we investigate theoretically frequency conversion and solitons in nonlinear photonic crystals. An optical parametric oscillator in a photonic crystal microcavity and strongly localised solitons in coupled microcavities are proposed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element simulation of radiation losses in photonic crystal fibers
Authors: Pomplun Jan , Zschiedrich Lin , Klose Roland , Schmidt Frank , Burger Sven 
Published: October 2007

AbstractIn our work we focus on the accurate computation of light propagation in finite size photonic crystal structures with the finite element method (FEM). We discuss how we utilize numerical concepts like high‐order finite elements, transparent boundary conditions and goal‐oriented error estimators for adaptive grid refinement in order to compute radiation leakage in photonic crystal fibers and waveguides. Due to the fast convergence of our method we can use it e.g. to optimize the design of photonic crystal structures with respect to geometrical parameters, to minimize radiation losses and to compute attenutation spectra for different geometries. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Linear and non‐linear optical experiments based on macroporous silicon photonic crystals
Authors: Wehrspohn Ralf B. , Schweizer Stefan L. , Sandoghdar Vahid 
Published: October 2007

AbstractMacroporous silicon is a model system for 2D silicon photonic crystals. In this review, we describe our recent theoretical and experimental advances in the macroporous silicon technology as well as in novel near‐field optical experiments concerning modified light emission from photonic crystal cavities and waveguides. We also review our recent work on tuning silicon photonic crystals by free‐carriers or non‐linear effects and compare the two tuning mechanisms. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dispersive properties of photonic crystal waveguide resonators
Authors: Sünner T. , Gellner M. , Scholz M. , Löffler A. , Kamp M. , Forchel A. 
Published: October 2007

AbstractWe have investigated the group delay and the dispersion of light propagating through photonic crystal (PhC) resonators defined in 240 nm thick GaAs membranes. The design of the resonators is based on a PhC heterostructure, which combines waveguide sections with different lattice constants along a PhC waveguide. The measurements were performed by detecting the phase shift of a microwave signal which was modulated onto the light of a tunable laser source. The group delay was found to increase linearly with the quality factor of the resonator, in good agreement with the prediction of a model where the PhC resonator is replaced by an equivalent Fabry–Perot resonator. An alternative analysis of the measurements was performed using a Hilbert transform approach. A maximum group delay of 132 ps was observed for a resonator with a quality factor of 82000. The overall length of this resonator was 10.4 μm, resulting in a propagation speed of 7.88 × 104 m/s (c/3800). The maximum dispersion of the resonator was around 1.7 ns/nm, which is equivalent to 100 km of standard optical fiber. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Negative refraction in 2D photonic crystal super‐lattice: towards devices in the IR and visible ranges
Authors: Neve‐Oz Y. , Golosovsky M. , Frenkel A. , Davidov D. 
Published: October 2007

AbstractWe consider a planar structure consisting of the periodic array of dielectric rods of two different diameters whereas d1/d2 = 2. The rods have the same dielectric constant ε = 4. Such array exhibits structural modulation and forms a two‐dimensional photonic superlattice. This results in a narrow transmission subband (the bandwidth is 15% of the total stopband width) inside the photonic stop‐band. For the frequencies corresponding to this subband we find high transmittivity accompanied by negative refraction. Although we perform our computer simulations for the microwave range, the small dielectric constant of the rods and small insertion loss for the frequencies in the transmission band suggests that scaling to the optical range using similar structures is possible. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photonic crystals based on chiral liquid crystal
Authors: Ozaki M. , Matsuhisa Y. , Yoshida H. , Ozaki R. , Fujii A. 
Published: October 2007

AbstractLiquid crystals including chiral molecule have a self‐organized helical structure with nano‐scaled periodicity, which can be regarded as a one‐dimensional (1D) photonic crystal. We have so far investigated lasing characteristics at an edge of the 1D photonic band gap (PBG) of dye‐doped chiral liquid crystals such as cholesteric liquid crystal (CLC) and ferroelectric liquid crystal (FLC). A band‐edge excitation effect on the CLC lasing has been experimentally demonstrated by matching the excitation laser wavelength to the higher energy‐edge of the PBG of a dye‐doped CLC. The wavelength tuning of the laser action upon changing electric field strength has been achieved in FLC. We have proposed the defect modes characteristic to the helicoidal structure of the chiral liquid crystal and demonstrated the lasing from the chiral defect modes. A twist defect mode in a transmission spectrum of the composite film consisting of two photopolymerized CLC layers has been experimentally demonstrated. A new type of defect mode in a chiral liquid crystal on the basis of the local deformation of the 1D periodic helical structure has also been proposed, and the possibility of the wavelength tuning has been demonstrated in this system. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nanophotonic Materials: Photonic Crystals, Plasmonics and Metamaterials
Authors: Wehrspohn Ralf B. , Kitzerow Heinz‐Siegfried , Busch Kurt 
Published: October 2007

AbstractFollowing the successful launch of the book on 'Photonic Crystals' in 2004 [1], this special issue of physica status solidi again comprises the work of research groups from the corresponding Priority Programme of the German Research Foundation and some of their close collaborators. Three years on, the understanding of photonic crystal properties has improved across numerous materials systems, applications were devised and developed approaching the industrial stage, and attention extended to the new areas of plasmonic crystals and metamaterials. The current issue presents a collection of Feature Articles reporting on the progress in this active field.In the tradition of the first publication, the Cover Picture shows an overlay of a 3D photonic crystal made from macroporous silicon, a simulation of a waveguide splitter, and the lasing modes of a planar photonic crystals laser made from III–V‐compound semiconductors (Picture courtesy of conImago, http://www.conimago.de). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First principles study of structural and electronic properties of Bex Zn1–xS and Bex Zn1–xTe alloys
Authors: Ameri M. , Rached D. , Rabah M. , El Haj Hassan F. , Khenata R. , Doui‐Aici M. 
Published: October 2007

AbstractWe present the results of first‐principles study of the structural and electronic properties of Bex Zn1–x S and Bex Zn1–x Te alloys for different concentrations x. The computational method is based on the full‐potential muffin‐tin orbitals method (FP‐LMTO) in the framework of density‐functional theory (DFT). The exchange and correlation energy is described in the local density approximation (LDA) using Perdew–Wang parameterization. We have investigated the effect of composition on the ground‐state properties, band gap and effective mass. We report the results concerning the variation of the gaps and crossover of the direct, indirect bandgap and the bowing. Using the approach of Zunger and coworkers, the microscopic origins of bandgap bowing have been detailed and explained. A reasonable agreement is found from the comparison of our results with other theoretical calculations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The impact of a home‐based spirituality teaching programme: qualitative exploration of participants' experiences
Authors: Moritz Sabine , Kelly Mary , Angen Maureen , Quan Hude , Toews John , Rickhi Badri 
Published: October 2007

AbstractContext: A growing body of research reports that spiritual well‐being plays a significant role in mental wellness. Findings from a completed randomized controlled trial (RCT) indicate that a home‐based, eight‐week spirituality teaching programme lowers mood disturbance and increases quality of life. In this qualitative exploration the authors set out to understand how participants perceived the programme's impact.Methods: This descriptive, qualitative exploration employed face‐to‐face, in‐depth interviews with 13 individuals from Calgary, Canada. Participants were self‐referred clients suffering from emotional distress and purposively sampled from the study population of the previously conducted RCT. Interviews consisted of open‐ended questions that focused on how the spirituality teaching programme may have affected mood. Interviews were transcribed verbatim and a thematic analysis was undertaken by three of the authors.Results: Clients described how their mood and life changed throughout and subsequent to the spirituality teaching programme. The following six thematic categories were identified: (1) expansion of spiritual beliefs; (2) changed life perspectives; (3) calmness/mental clarity; (4) relief of mood disorder symptoms; (5) improved relationships; (6) renewed physical energy. Interviewees perceived the first three themes, expanded spiritual beliefs, changed life perspective and calmness, as the core changes that led to improvements in interpersonal relationships, mental health and physical energy.Conclusion: The findings suggest that the programme used with these participants impacts on mood by expanding spiritual beliefs and by shifting perspectives of life situations, in terms of both oneself and others. Spiritual teachings and practices could be an innovative and valuable adjunct intervention to improve mood. Copyright © 2007 John Wiley & Sons, Ltd.
Evaluation of diagnostic scores with adjustment for covariates
Authors: Berres M. , Zehnder A. , Bläsi S. , Monsch A. U. 
Published: October 2007

AbstractDiagnostic tests yield measurements on very different types of scales. Quantitative scales may consist of non‐negative integers, either unbounded or bounded, with a fixed number of different values, or they may consist of continuous or percentage values. Remembering a different threshold value for each diagnostic variable would be cumbersome, in particular if covariates have to be taken into account. As a convenient way to overcome such problems we propose to compute z‐scores for all measurements. They will be adjusted for covariates so that any individual can be judged on any test result on one single scale with an appropriate standard normal quantile as threshold. Two issues need to be addressed: Selection of covariates in the regression model which delivers the adjustment and normality of the residuals. The first will be treated by cross‐validation and the latter by applying an appropriate transformation. We apply this methodology to neuropsychological tests and adjust for age, length of education and sex. Normality of residuals is needed on the diagnostically relevant side only. This allows to use parametric transformations, which can be easily implemented, e.g. in database systems. Since we have measurements at baseline and at follow‐up we also analyze change values in a similar manner. For ease of interpretation, we transform the resulting z‐scores back to the original scale. Copyright © 2007 John Wiley & Sons, Ltd.
A non‐inferiority test for diagnostic accuracy based on the paired partial areas under ROC curves
Authors: Li Chi‐Rong , Liao Chen‐Tuo , Liu Jen‐Pei 
Published: October 2007

AbstractNon‐inferiority is a reasonable approach to assessing the diagnostic accuracy of a new diagnostic test if it provides an easier administration or reduces the cost. The area under the receiver operating characteristic (ROC) curve is one of the common measures for the overall diagnostic accuracy. However, it may not differentiate the various shapes of the ROC curves with different diagnostic significances. The partial area under the ROC curve (PAUROC) may present an alternative that can provide additional and complimentary information for some diagnostic tests which require false‐positive rate that does not exceed a certain level. Non‐parametric and maximum likelihood methods can be used for the non‐inferiority tests based on the difference in paired PAUROCs. However, their performance has not been investigated in finite samples. We propose to use the concept of generalizedp‐value to construct a non‐inferiority test for diagnostic accuracy based on the difference in paired PAUROCs. Simulation results show that the proposed non‐inferiority test not only adequately controls the size at the nominal level but also is uniformly more powerful than the non‐parametric methods. The proposed method is illustrated with a numerical example using published data. Copyright © 2007 John Wiley & Sons, Ltd.
Electrical properties and the thermal and photochemical stability of poly(vinyl chloride) films stabilized with some maleyl amide polymers
Authors: Rabie S.T. , Eid M.A.M. 
Published: October 2007

AbstractSome maleyl amide polymers were prepared and evaluated as thermal and photochemical stabilizers for rigid poly(vinyl chloride) (PVC). Thermal degradation was determined by measuring the rate of dehydrochlorination potentiometrically. Also, the degree of discoloration was measured for both the thermally degraded and the photochemically degraded PVC. Dibutyltin maleate heat stabilizer was used for comparison in thermal and photodegradation. The applied polymers showed stabilizing efficiency in both thermal and photodegradation by decreasing the rate of degradation, degree of discoloration, and percentage weight loss. The amide polymer of melamine gave better stabilizing efficiency than those of p‐phenylenediamine and m‐phenylenediamine. A dielectric study was carried out over a frequency range from 100 Hz to 100 kHz at room temperature (∼22°C). The results revealed that the stabilizing effect of these maleyl amide polymers depends on the type of stabilizer and its concentration. The dielectric data for the investigated systems were found to be fitted by two absorption regions using the Fröhlich function. These regions are ascribed to the Maxwell–Wagner effect and to intramolecular motion involving the rotation of various segments of the side group as the main chain motion is restricted. The study led to a conclusion that the greater stabilizing efficiency of the melamine amide polymer may be due to the presence of a free amino group (NH2) that can participate in the stabilization process. J. VINYL ADDIT. TECHNOL., 13:206–214, 2007. © 2007 Society of Plastics Engineers
Enhancing the performance of flexible vinyl by using the formulary approach
Authors: Strepka Arron M. , Arendt William D. , Petrovich Danielle C. , Joshi Makarand 
Published: October 2007

AbstractEach vinyl plastisol processor has different requirements. The features of the finished goods determine the specifications and physical properties that are critical in the manufacturing process. Processors may also have varying equipment limitations that require a specific working range of each plastisol property, such as viscosity, for acceptable processing. Although the benzoate esters have been utilized for many years by plastisol formulators and processors to their advantage, usage of these esters has been limited because of their tendency to yield high‐viscosity plastisols. By utilizing a formulary approach, it is possible to fine‐tune the properties of the plastisol, thus allowing greater latitude. Design of experiment (DOE) was employed to accomplish this objective. For this work, generic resilient‐flooring formulations were selected as the model. The formulary approach was employed to adjust the formulation and processing parameters, thereby allowing plastisol formulators and processors to develop cost‐efficient formulations. J. VINYL ADDIT. TECHNOL., 13:201–205, 2007. © 2007 Society of Plastics Engineers
Starch as antiblocking agent in breathable polyurethane membranes
Authors: Pecku Suven , van der Merwe Thilo L. , Rolfes Heidi , Focke Walter W. 
Published: October 2007

AbstractA breathable polyurethane membrane was manufactured by using a multilayer film extrusion technique. In this process, the monolithic membrane is blown as the inner layer of a three‐layer film in which the outer support layers are polyethylene‐based. The neat membrane surface was unacceptably sticky. It was found that starch was a suitable antiblocking agent outperforming mineral fillers. However, starch incorporation decreased the membrane permeability towards moisture. The experimental permeability results are consistent with the predictions of the Maxwell model for a randomly dispersed, impermeable spherical filler. Fitting the Wagner‐Sillar model indicated a near‐spherical particle shape and confirmed the impermeable nature of the starch particles. This unexpected result can be rationalized by assuming a highly crystalline or glassy nature for the starch domains. J. VINYL ADDIT. TECHNOL., 13:215–220, 2007. © 2007 Society of Plastics Engineers
Copolymerization of aniline and vinyl acetate by using various surfactants in aqueous media
Authors: Eisazadeh Hossein 
Published: October 2007

AbstractPolyaniline/poly(vinyl acetate) (PAn/PVAc) copolymer was prepared in aqueous solution by the copolymerization of vinyl acetate and aniline using a mixture of KIO3 and (NH4)2S2O8 as an oxidant in the presence of the surfactants sodium dodecylbenzenesulfonate, poly(ethylene glycol), and hydroxypropylcellulose. The PAn/PVAc copolymers were characterized in terms of their conductivity, morphology, and structure. The results indicated that the morphology and conductivity of the products were dependent on the type of surfactant used (anionic or nonionic). Furthermore, it was found that adding vinyl acetate monomer to the stirred aqueous solution containing oxidant, surfactant, and aniline monomer had a great effect on the morphology and increased the amount of the product. The structures of the products were determined by FTIR spectroscopy. J. VINYL ADDIT. TECHNOL., 13:229–233, 2007. © 2007 Society of Plastics Engineers