bluuebunny/crossref_metadata_2025 huggingface dataset:
High-frequency nonlinear optics: from the nonlinear Schrödinger approximation to ultrashort-pulses equations
Authors: Lannes David
Published: April 2011

After a brief introduction and physical motivation, we show how the nonlinear Schrödinger (NLS) equation can be derived from a general class of nonlinear hyperbolic systems. Its purpose is to describe the behaviour of high-frequency oscillating wave packets over a large time-scale that requires us to take into account diffractive effects. We then show that the NLS approximation fails for short pulses and propose some alternative models, including a modified Schrödinger equation with improved frequency dispersion. It turns out that these models have better properties and are quite accurate for short pulses. For ultrashort pulses, however, they must also be abandoned for more complex approaches. We give the main steps for such an analysis and explain one striking fact about ultrashort pulses: their dynamics in dispersive media is linear.
On an open problem of Weidmann: essential spectra and square-integrable solutions
Authors: Qi Jiangang , Chen Shaozhu
Published: April 2011

In 1987, Weidmann proved that, for a symmetric differential operator τ and a real λ, if there exist fewer square-integrable solutions of (τ−λ)y = 0 than needed and if there is a self-adjoint extension of τ such that λ is not its eigenvalue, then λ belongs to the essential spectrum of τ. However, he posed an open problem of whether the second condition is necessary and it has been conjectured that the second condition can be removed. In this paper, we first set up a formula of the dimensions of null spaces for a closed symmetric operator and its closed symmetric extension at a point outside the essential spectrum. We then establish a formula of the numbers of linearly independent square-integrable solutions on the left and the right subintervals, and on the entire interval for nth-order differential operators. The latter formula ascertains the above conjecture. These results are crucial in criteria of essential spectra in terms of the numbers of square-integrable solutions for real values of the spectral parameter.
Solutions on a torus for a semilinear equation
Authors: Allain Geneviéve , Beaulieu Anne
Published: April 2011

We are interested in the positive doubly periodic solutions, which are even in each variable, of a stationary nonlinear Schrödinger equation in ℝ2, with a small parameter. For any pair of periods (2a, 2b), we construct a branch of solutions that concentrate uniformly to the ground-state solution of the equation.
Review of long time asymptotics and collision of solitons for the quartic generalized Korteweg—de Vries equation
Authors: Martel Yvan , Merle Frank
Published: April 2011

We review recent nonlinear partial differential equation techniques developed to address questions concerning solitons for the quartic generalized Korteweg—de Vries equation (gKdV) and other generalizations of the KdV equation. We draw a comparison between results obtained in this way and some elements of the classical integrability theory for the original KdV equation, which serve as a reference for soliton and multi-soliton problems. First, known results on stability and asymptotic stability of solitons for gKdV equations are reviewed from several different sources. Second, we consider the problem of the interaction of two solitons for the quartic gKdV equation. We focus on recent results and techniques from a previous paper by the present authors concerning the interaction of two almost-equal solitons.
Tug-of-war games and PDEs
Authors: Rossi Julio D.
Published: April 2011

We review some recent results concerning tug-of-war games and their relation to some well-known partial differential equations (PDEs). In particular, we will show that solutions to certain PDEs can be obtained as limits of values of tug-of-war games when the parameter that controls the length of the possible movements goes to zero. Since the equations being studied are nonlinear and are not in divergence form, we will make extensive use of the concept of viscosity solutions.
Zero-electron-mass limit of hydrodynamic models for plasmas
Authors: Xu Jiang , Yong Wen-An
Published: April 2011

This paper is concerned with the limit of the vanishing ratio of the electron mass to the ion mass in the hydrodynamic models for plasmas in critical Besov spaces. We give a new construction of approximation solutions and show that periodic initial-value problems of certain scaled hydrodynamic models have smooth solutions in a (finite) time interval where the Euler solution is known to exist. Furthermore, it is justified that, as the electron mass tends to zero, the smooth solutions converge rigorously to solutions of the incompressible Euler equations, and the definite convergence orders are also obtained.
Incidences in Three Dimensions and Distinct Distances in the Plane
Authors: ELEKES GYÖRGY , SHARIR MICHA
Published: April 2011

We first describe a reduction from the problem of lower-bounding the number of distinct distances determined by a set S of s points in the plane to an incidence problem between points and a certain class of helices (or parabolas) in three dimensions. We offer conjectures involving the new set-up, but are still unable to fully resolve them.

Instead, we adapt the recent new algebraic analysis technique of Guth and Katz [9], as further developed by Elekes, Kaplan and Sharir [6], to obtain sharp bounds on the number of incidences between these helices or parabolas and points in ℝ3. Applying these bounds, we obtain, among several other results, the upper bound O(s3) on the number of rotations (rigid motions) which map (at least) three points of S to three other points of S. In fact, we show that the number of such rotations which map at least k ≥ 3 points of S to k other points of S is close to O(s3/k12/7).

One of our unresolved conjectures is that this number is O(s3/k2), for k ≥ 2. If true, it would imply the lower bound Ω(s/logs) on the number of distinct distances in the plane.
BARIATRIC SURGERY IN PREGNANCY: BENEFITS, RISKS AND OBSTETRIC MANAGEMENT
Authors: GIDIRI MUCHABAYIWA F , GREER IAN A
Published: April 2011

Obesity is a growing problem in obstetric practice. A recent study from Glasgow (UK) showed that 50% of women of childbearing age are either overweight (Body Mass Index [BMI] = 24.9–29.9kg/m2) or obese with 18% starting pregnancy as obese. Obesity prevalence has doubled over a decade from the early 1990’s. In the US it is estimated that 30% of reproductive-age women have a BMI greater than 30 kg/m while 7% have a BMI > 40 kg/m2. A recent report from the UK found that 5% of women had a BMI >35 kg/m2, 2% > 40 kg/m2 and 0.2% >50 kg/m2 with an association not only with social deprivation, but also with a higher prevalence of pre-existing medical disorders such as diabetes and hypertension and medical complications of pregnancy such as preeclampsia. Obesity was also associated with increased rates of macrosomia, operative delivery and postpartum haemorrhage. These data highlight the fact that obesity is an increasing health concern particularly in young women of childbearing age. Obesity will expose them to significant pregnancy complications ranging from miscarriage and fetal abnormality through to operative delivery and thromboembolism. There are also challenges for the delivery of maternity care to meet the needs of these women. As obesity is associated with significant pregnancy complications it is important that women enter pregnancy with an optimum body weight. Many complications, such as fetal abnormality occur in the first trimester and so pre-pregnancy weight reduction is preferred. Further, there is insufficient evidence to recommend specific dietary and/or physical activity interventions to reduce weight or moderate weight gain during pregnancy.
What Can Qualitative Research Tell Us about Service User Perspectives of CBT for Psychosis? A Synthesis of Current Evidence
Authors: Berry Clio , Hayward Mark
Published: April 2011

Background: Although recommended in national treatment guidelines, there is much that is still unknown about CBT for psychosis (CBTp) in terms of the process and experience of the therapy. One way to investigate these gaps in knowledge is to explore service users' experiences through qualitative research. Aims: To consolidate existing qualitative explorations of CBTp from a service user perspective. Method: Qualitative synthesis and comparison with previous research findings. Results: Two analytical themes were created from initial descriptive themes common to multiple studies: “The ingredients in the process of therapy” and “What is the process of therapy?” Conclusions: Qualitative synthesis is a useful method for generating new insights from multiple qualitative studies. Service user perspectives on CBTp corroborate existing research and may also offer more novel findings regarding the ingredients and process of therapy. However, qualitative studies are limited in number and do not always maximize the prominence of service user experience.
Evolution as computation: integrating self-organization with generalized Darwinism
Authors: BEINHOCKER ERIC D.
Published: April 2011

Generalized Darwinism and self-organization have been positioned as competing frameworks for explaining processes of economic and institutional change. Proponents of each view question the ontological validity and explanatory power of the other. This paper argues that information theory, rooted in modern thermodynamics, offers the potential to integrate these two perspectives in a common and rigorous framework. Both evolution and self-organization can be generalized as computational processes that can be applied to human social phenomena. Under this view, evolution is a process of algorithmic search through a combinatorial design space, while self-organization is the result of non-zero sum gains from information aggregation. Evolution depends on the existence of self-organizing forces, and evolution acts on designs for self-organizing structures. The framework yields insights on the role of agency and the emergence of novelty. The paper concludes that information theory may provide a fundamental ontological basis for economic and institutional evolution.
Novel wideband slot antenna having notch-band function for 2.4 GHz WLAN and UWB applications
Authors: Shagar Arumugam Chellamuthu , Wahidabanu Shaik Davood
Published: April 2011

In this paper, the design, simulation, and fabrication of a novel printed rectangular slot antenna with a band-notched function suitable for 2.4 GHz wireless local area network (WLAN) and ultra-wideband (UWB) applications is presented and investigated. Two pairs of slits are introduced into the ground plane to realize band-notched function, by tuning the position, length, and width of which a suitable rejected frequency band can be obtained. To improve the impedance matching, a rectangular cut is also made in the ground plane so that the antenna can cover 2–12 GHz frequency range. According to the measured results, the proposed antenna has a large bandwidth totally satisfying the requirement of 2.4 GHz WLAN and UWB systems, while providing the required band-notch function from 5.1 to 5.9 GHz. The study of transfer function and time-domain characteristics also indicates the band-notched function of the antenna. The radiation patterns display nearly omni-directional performance and the antenna gain is stable except in the rejected frequency band (5.1–5.9 GHz). Moreover, group delays are within 1.5 ns except for the notch band. These features make it a promising candidate for UWB wireless applications. Details of this antenna are described, and the experimental results of the constructed prototype are given.
Multi-wavelength radar target detection in an extreme advection duct event
Authors: Marshall Robert E. , Horgan Katherine L.
Published: April 2011

Near sea surface radio frequency (RF) refraction is four dimensional (4D) and can significantly impact the performance of radar systems. The refractivity field is dictated by the vertical thermodynamic structure of the constantly evolving marine atmospheric boundary layer (MABL). Logistical and budgetary restraints on meteorological measurements over water to capture the spatio-temporal structure of refractivity fields influencing radar performance have limited the knowledge of how and why radar performance is azimuth, range, and time dependent. Rapidly increasing computer processing speeds and decreasing memory capacity costs have supported the horizontal and vertical resolution requirements for mesoscale numerical weather prediction (NWP) models to resolve the thermodynamic structure in the MABL. Once modeled, refractivity structure is easily calculated from the thermodynamic structure. Mesoscale NWP models coupled with modern parabolic equation radar performance models can support the prediction of 4D radar performance in challenging non-homogeneous, near surface refractivity fields at the time and location of the modeler's choice. The NWP modeling presented in this paper demonstrates how large-scale offshore flow of warm and dry air over colder seas produces strong near surface RF trapping. Large land-sea temperature differences can produce near shore sea breezes and surface-based ducts. This paper describes modeled radar performance in such a complex ducting structure over the Persian Gulf during large-scale northwest atmospheric flow. The refractivity field was resolved by the Coupled Ocean/ Atmosphere Mesoscale Prediction System (COAMPS® is a registered trademark of the Naval Research Laboratory) and the notional radar performance was modeled by the advanced refractive effects prediction system (AREPS). The results indicate strong spatial and wavelength-dependent enhancements and degradations in radar performance relative to a standard atmosphere.
60 GHz WLAN applications and implementation aspects
Authors: Schulte Benedikt , Peter Michael , Felbecker Robert , Keusgen Wilhelm , Steffen Rainer , Schumacher Hermann , Hellfeld Marcus , Barghouthi Atheer , Krone Stefan , Guderian Falko , Fettweis Gerhard P. , Ziegler Volker
Published: April 2011

Various wireless applications are currently under development for the unlicensed 60 GHz band. This paper describes three examples with different system requirements. The first two are point-to-multipoint wireless networks (in an airplane and in a car) and the third one is a short range point-to-point connection. Special requirements of the applications are a high number of users for the point-to-multipoint connection and a high data rate of 10 Gbit/s for the point-to-point connection system. Implementation aspects are pointed out, which are important to demonstrate the functionality of the system in a relevant environment and are key aspects to develop the related products. For example, integration aspects of the antenna into an airplane passenger seat and the receiver concept of the radio frequency-(RF) front-end to reducing the power consumption at ultrahigh data rates are described. Additionally, to determine the geometrical system architecture, ray-tracing simulations inside an aircraft and inside a car were performed.
In situ location and U‐Pb dating of small zircon grains in igneous rocks using laser ablation–inductively coupled plasma–quadrupole mass spectrometry
Authors: Sack Patrick J. , Berry Ron F. , Meffre Sebastien , Falloon Trevor J. , Gemmell J. Bruce , Friedman Richard M.
Published: April 2011

A new U‐Pb zircon dating protocol for small (10–50 μm) zircons has been developed using an automated searching method to locate zircon grains in a polished rock mount. The scanning electron microscope‐energy‐dispersive X ray spectrum‐based automated searching method can routinely find in situ zircon grains larger than 5 μm across. A selection of these grains was ablated using a 10 μm laser spot and analyzed in an inductively coupled plasma‐quadrupole mass spectrometer (ICP‐QMS). The technique has lower precision (∼6% uncertainty at 95% confidence on individual spot analyses) than typical laser ablation ICP‐MS (∼2%), secondary ion mass spectrometry (<1%), and isotope dilution‐thermal ionization mass spectrometry (∼0.4%) methods. However, it is accurate and has been used successfully on fine‐grained lithologies, including mafic rocks from island arcs, ocean basins, and ophiolites, which have traditionally been considered devoid of dateable zircons. This technique is particularly well suited for medium‐ to fine‐grained mafic volcanic rocks where zircon separation is challenging and can also be used to date rocks where only small amounts of sample are available (clasts, xenoliths, dredge rocks). The most significant problem with dating small in situ zircon grains is Pb loss. In our study, many of the small zircons analyzed have high U contents, and the isotopic compositions of these grains are consistent with Pb loss resulting from internal α radiation damage. This problem is not significant in very young rocks and can be minimized in older rocks by avoiding high‐U zircon grains.
Transient groundwater chemistry near a river: Effects on U(VI) transport in laboratory column experiments
Authors: Yin Jun , Haggerty Roy , Stoliker Deborah L. , Kent Douglas B. , Istok Jonathan D. , Greskowiak Janek , Zachara John M.
Published: April 2011

In the 300 Area of a U(VI)‐contaminated aquifer at Hanford, Washington, USA, inorganic carbon and major cations, which have large impacts on U(VI) transport, change on an hourly and seasonal basis near the Columbia River. Batch and column experiments were conducted to investigate the factors controlling U(VI) adsorption/desorption by changing chemical conditions over time. Low alkalinity and low Ca concentrations (Columbia River water) enhanced adsorption and reduced aqueous concentrations. Conversely, high alkalinity and high Ca concentrations (Hanford groundwater) reduced adsorption and increased aqueous concentrations of U(VI). An equilibrium surface complexation model calibrated using laboratory batch experiments accounted for the decrease in U(VI) adsorption observed with increasing (bi)carbonate concentrations and other aqueous chemical conditions. In the column experiment, alternating pulses of river and groundwater caused swings in aqueous U(VI) concentration. A multispecies multirate surface complexation reactive transport model simulated most of the major U(VI) changes in two column experiments. The modeling results also indicated that U(VI) transport in the studied sediment could be simulated by using a single kinetic rate without loss of accuracy in the simulations. Moreover, the capability of the model to predict U(VI) transport in Hanford groundwater under transient chemical conditions depends significantly on the knowledge of real‐time change of local groundwater chemistry.
BRIF Workshop Minutes
Authors: Mabile Laurence
Published: April 2011

This document is a detailed summary of the presentations and discussions from the BRIF (Bioresource Impact Factor) workshop, held in Toulouse on 17-18 january 2011.
pH responsive self assemblies from an An-core-(B-b-C)n heteroarm star block terpolymer bearing oppositely charged segments
Authors: Iatridi Zacharoula , Tsitsilianis Constantinos
Published: April 2011

A diversity of pH-responsive amphoteric self-assemblies formed by a multisegmented, multiarm star-shaped (PS33)9(P2VP126-b-PAA69)9 terpolymer in aqueous media is reported.
Efficient hydrolytic hydrogenation of cellulose in the presence of Ru-loaded zeolites and trace amounts of mineral acid
Authors: Geboers Jan , Van de Vyver Stijn , Carpentier Kevin , Jacobs Pierre , Sels Bert
Published: April 2011

The hydrolytic hydrogenation of cellulose in the presence of a bifunctional Ru-loaded zeolite and trace amounts of mineral acid shows excellent hexitol yields.
Direct dendronization of polystyrenes using dendritic diarylcarbenium ion pools
Authors: Nokami Toshiki , Watanabe Takashi , Musya Naoki , Morofuji Tatsuya , Tahara Kazukuni , Tobe Yoshito , Yoshida Jun-ichi
Published: April 2011

Dendritic diarylcarbenium ions reacted with unfunctionalized polystyrenes to give dendronized polymers, which were characterized by MALDI-TOF MS and AFM.
Electron density dependence of intensity ratio for FeXXII extreme ultraviolet emission lines arising from different ground levels in electron beam ion trap and large helical device
Authors: Sakaue H. A. , Yamamoto N. , Morita S. , Nakamura N. , Chen C. , Kato D. , Kikuchi H. , Murakami I. , Ohtani S. , Tanuma H. , Watanabe T. , Tawara H.
Published: April 2011

Extreme ultraviolet (EUV) spectra of highly charged iron ions in a wavelength range of 100–300 Å have been observed from two different plasma sources of the Tokyo Electron Beam Ion Trap (Tokyo-EBIT) with a monoenergetic electron beam and a Large Helical Device (LHD) with Maxwellian electron energy. The excitation process of the spectral lines is compared between the two plasmas, and it is found that the excitation process for Fe XIX - Fe XXII ions is clearly different. Namely, the EUV emission lines from the EBIT plasma are only dominated by electron impact excitation connected to the ground state, but the excitation mechanism is not so simple in the LHD plasma. The difference in the excitation process is studied by measuring the intensity ratio of EUV emission lines (114.412 Å [1s22s2p2 2P3/2 → 1s22s22p 2P3/2]/117.144 Å [1s22s2p2 2P1/2 → 1s22s22p 2P1/2]) arising from different ground levels in the Fe XXII ions. The line intensity ratio has an extremely small value of 0.2 in the EBIT plasma with a low beam current of 30 mA and a beam energy of 2 keV, while the ratio varies with the electron density ne in the LHD plasmas, i.e., 0.35 for ne = 1 × 1013 cm−3 and 0.65 for ne = 4 × 1013 cm−3. Here, the electron density of the EBIT plasma is estimated to be smaller than 1012 cm−3 and the electron temperature of the LHD plasmas is 2 keV. The dependence of the line intensity ratio on the observed electron density is analyzed for both the EBIT and the LHD plasmas using several collisional-radiative (CR) models. The present experimental data can easily be reproduced by the analysis when the thermal proton impact excitation is taken into account. The importance of the proton impact excitation is also experimentally verified by injecting an iron pellet into the LHD plasmas and changing the ratio of the proton density to the electron density.
The effects of Si doping on dislocation movement and tensile stress in GaN films
Authors: Moram M. A. , Kappers M. J. , Massabuau F. , Oliver R. A. , Humphreys C. J.
Published: April 2011

Dislocations in undoped GaN move in response to the in-plane tensile stress present during film growth. Dislocation movement during growth relieves tensile stress, produces arrays of a-type dislocations and reduces the overall dislocation density, with preferential reduction of (a+c)-type dislocations. However, Si-doping limits dislocation movement, limiting the relief of the tensile stress that develops during growth and limiting dislocation reduction, probably due to the formation of Si impurity atmospheres at dislocations. Consequently, Si-doped films are under relatively greater tensile stress compared to undoped GaN films grown under similar conditions. Alternative dopants could be chosen to reduce tensile stress development, such as Ge.
Multiband quantum transport simulations of ultimate p-type double-gate transistors: Effects of hole-phonon scattering
Authors: Cavassilas Nicolas , Michelini Fabienne , Bescond Marc
Published: April 2011

A two-dimensional six-band k·p transport simulator has been developed within the nonequilibrium Green function formalism including hole-phonon interactions in the self-consistent Born approximation. Scattering mechanisms are studied in Si versus Ge double-gate p-type metal-oxide-semiconductor transistors. Although the hole-phonon interaction is larger in Ge, its impact on current characteristics is more important in Si. Indeed we obtain a ON current reduction of, respectively, 22% (Si) and 14% (Ge), due to scattering in 7-nm-long transistors. This result is explained by a higher hole-group velocity in Ge that increases the mean-free-path.
Magnetic and transport properties of transparent SrSn0.9Sb0.05Fe0.05O3 semiconductor films
Authors: Prathiba G. , Venkatesh S. , Kamala Bharathi K. , Harish Kumar N.
Published: April 2011

The effect of antimony doping on the structural, magnetic, and electrical properties of transparent SrSn0.9Sb0.05Fe0.05O3 films synthesized by RF sputtering on oxidized Si and quartz substrates has been investigated. A reduction in electrical resistivity by two orders of magnitude compared to 5% Fe doped SrSnO3 film was observed. The electrical conductivity behavior has been analyzed using the Mott’s Variable range hopping model. The nature of magnetic ordering were investigated by field cooled (FC) and zero field cooled (ZFC) magnetization measurements. The applicability of models based on oxygen vacancies to explain the magnetic ordering present in the sample has been discussed.
Anisotropy of the paramagnetic susceptibility of NdGaO3 single crystals
Authors: Steenbeck K. , Habisreuther T. , Mattheis R.
Published: April 2011

The tensor of the paramagnetic susceptibility χ of NdGaO3 single crystals was determined with high accuracy in the temperature range of T = (5-300) K. A vibrating sample magnetometer was used to determine the three main χ tensor components in the diagonal form. Torquemetry was additionally employed as it especially allows for the characterization of small deviations from isotropy. In the (100) plane the anisotropy Δχ was found to be indeed small (about 0.1% at 300 K and 1% at 30 K). It changes nonmonotonically with T, and reverses its sign at 250 K. In the planes (010) and (001) Δχ is much stronger (about 5% at 300 K and 22% at 30 K). Around 100 K it also changes its sign. Our results allow determing the anisotropy Δχ for any desired crystal orientation and temperature (5 K < T < 300 K). Furthermore, the conditions for disappearing magnetic torque (Δχ = 0) are deduced.
Three dimensional simulation of giant magneto-impedance effect in thin film structures
Authors: Li Bodong , Kosel Jürgen
Published: April 2011

In this paper, a three dimensional model for the giant magneto-impedance (GMI) effect in thin film structures is developed using the finite element method (FEM) with a GMI permeability model embedded. One-layer, three-layer, and five-layer thin film structures are simulated. The GMI effect and the sensitivity are calculated as a function of the external magnetic field, driving frequency, and the thickness of the magnetic layers. The results show that the five-layer structure has the best performance, which is in accordance with experimental results. The GMI ratio and the sensitivity first improve with the increasing thickness of the magnetic layer but reach saturation at a certain value of the thickness. In a five-layer structure, saturation of the GMI effect becomes effective at about 3 μm thickness of the magnetic layers, where a GMI ratio of 1125% was obtained, with a corresponding sensitivity of 0.37%/A/m (29.6%/Oe).
Magnetic properties of ceramics from the pyrolysis of metallocene-based polymers doped with palladium
Authors: Thomas K. R. , Ionescu A. , Gwyther J. , Manners I. , Barnes C. H. W. , Steiner U. , Sivaniah E.
Published: April 2011

Solution processing is a facile method to generate magnetic thin films. Polyferrocenylethylmethylsilane (PFEMS) was doped with palladium (II) acetylacetonate using two methods: sublimation of Pd(acac)2 to form Pd nanoparticles in the PFEMS films and direct mixing of Pd with the PFEMS polymer precursor prior to film deposition. These polymer composites all exhibit paramagnetic behavior, with increasing magnetic susceptibility for increasing Pd content. Pyrolysis of the precursors yields ferromagnetic ceramics at room temperature. The effect of the pyrolysis temperature and atmosphere on the magnetic properties, chemical composition, and crystalline structure of the ceramics was explored. For ceramics containing Pd, FePd alloys are observed to form pyrolyzed under argon at 1000 °C. The formation of these alloys results in enhanced coercivity, remanent magnetization, and saturation magnetization of the ceramics.
Magnetic nanoparticles with bulklike properties (invited)
Authors: Batlle Xavier , Pérez N. , Guardia P. , Iglesias O. , Labarta A. , Bartolomé F. , García L. M. , Bartolomé J. , Roca A. G. , Morales M. P. , Serna C. J.
Published: April 2011

The magnetic behavior of Fe3−xO4 nanoparticles synthesized by either high-temperature decomposition of an organic iron precursor or low-temperature coprecipitation in aqueous conditions is compared. Transmission electron microscopy, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and magnetization measurements show that nanoparticles synthesized by thermal decomposition display high crystal quality and bulklike magnetic and electronic properties, while nanoparticles synthesized by coprecipitation show much poorer crystallinity and particlelike phenomenology, including reduced magnetization, high closure fields, and shifted hysteresis loops. The key role of the crystal quality is thus suggested, because particlelike behavior for particles larger than about 5 nm is observed only when the particles are structurally defective. These conclusions are supported by Monte Carlo simulations. It is also shown that thermal decomposition is capable of producing nanoparticles that, after further stabilization in physiological conditions, are suitable for biomedical applications such as magnetic resonance imaging or biodistribution studies.
Development of strong {001}〈210〉 texture and magnetic properties in Fe–6.5wt.%Si thin sheet produced by rolling method
Authors: Liu J. L. , Sha Y. H. , Zhang F. , Yang H. P. , Zuo L.
Published: April 2011

Fe–6.5wt.%Si thin sheets were successfully produced by conventional rolling and annealing methods. The deformation and recrystallization textures were investigated by means of x-ray diffraction and electron backscattered diffraction analysis. It was found that a strong {001}〈210〉 recrystallization texture was obtained and the magnetic property was significantly improved under the appropriate rolling temperature. The formation of the {001}〈210〉 texture was explained in terms of preferred nucleation by the strain-induced boundary migration mechanism and selective growth by grain size advantage established during primary recrystallization.
Influence of magnetostriction on damping constant of NixFe1−x film with various Ni concentrations (x)
Authors: Endo Yasushi , Mitsuzuka Yoshio , Shimada Yutaka , Yamaguchi Masahiro
Published: April 2011

We investigated the influence of magnetostriction on the damping constant (α) of 50-nm-thick NixFe1−x polycrystalline films, with x ranging from 0.66 to 0.86. In the experiments, α and the saturation magnetostriction (λs) were evaluated with high accuracy, which allowed for an interesting finding suggesting a simple relation between α and λs. In the range of positive λs, α slightly increases as x decreases, whereas α increases from 0.009 to 0.012 with increasing x for negative λs values. α reaches a minimum when λs is around zero at x = 0.78. These results demonstrate that different behaviors of α depend on positive or negative values of λs. Therefore, particular attention should be paid to the change in magnetoelastic properties and the deterioration of magnetic softness when adjusting α of magnetically soft films.
Effect of laminated crystalline FeCoB soft magnetic underlayer for perpendicular magnetic recording tape media
Authors: Gomi Shunsuke , Mashiko Yasuhiro , Hirata Ken-ichiro , Matsunuma Satoshi , Inoue Tetsutaro , Doi Tsugihiro , Watanabe Toshiyuki , Nakagawa Shigeki
Published: April 2011

A crystalline FeCoB soft magnetic underlayer (SUL) improves c-axis orientations of the Ru intermediate layer (IML) and the CoPtCr-SiO2 recording layer (RL). (001) orientations of Ru IML and CoPtCr RL are attained by (110) oriented texture of FeCoB SUL. Since good c-axis orientation in CoPtCr-SiO2 RL as well as domain control in the FeCoB SUL is required for high recording density, a laminated FeCoB SUL is prepared as an underlayer of the bilayered Ru/CoPtCr–SiO2 films. A laminated FeCoB SUL results in better (001) orientation in both CoPtCr-SiO2 RL and Ru IML than the single layered FeCoB SUL. This leads to the reduction of media noise in the high recording frequency region. Recording medium layers composed of a laminated FeCoB SUL and bilayered Ru/CoPtCr-SiO2 films deposited on a 4.5-μm-thick Aramid tape show better (001) orientations of Ru and CoPtCr. Media noise of the tape medium with the laminated SUL is lower than that with the single layered FeCoB SUL.
Reduction of surface roughness and Néel coupling in perpendicular magnetic tunnel junctions with L1-FePt electrodes by plasma treatments
Authors: Tsai Wu-Chang , Lee Jian-Wei , Chen Chia-Hsiang , Lai Chih-Huang , Yen Cheng-Tyng , Wang Yung-Hung
Published: April 2011

The plasma treatment with O2/Ar mixture was applied to reduce the surface roughness of the L10-FePt electrode in perpendicular magnetic tunnel junctions. The surface roughness (Rrms) of the L10-FePt layer was decreased from 1.2 nm at the as-deposited state to 0.52 nm after the plasma treatment with the ratio of O2 to Ar equal to 0.5. The low surface roughness accompanying the formation of an oxide layer led to magnetic decoupling between free and reference layers after the plasma treatment on the surface of FePt layer. The existence of the oxide layer was confirmed by using transmission electron microscopy and x-ray photoelectron spectroscopy. The interfacial Pt-oxide layer plays a significant role in the magnetic decoupling.
Poly(caprolactone) based magnetic scaffolds for bone tissue engineering
Authors: Bañobre-López M. , Piñeiro-Redondo Y. , De Santis R. , Gloria A. , Ambrosio L. , Tampieri A. , Dediu V. , Rivas J.
Published: April 2011

Synthetic scaffolds for tissue engineering coupled to stem cells represent a promising approach aiming to promote the regeneration of large defects of damaged tissues or organs. Magnetic nanocomposites formed by a biodegradable poly(caprolactone) (PCL) matrix and superparamagnetic iron doped hydroxyapatite (FeHA) nanoparticles at different PCL/FeHA compositions have been successfully prototyped, layer on layer, through 3D bioplotting. Magnetic measurements, mechanical testing, and imaging were carried out to calibrate both model and technological processing in the magnetized scaffold prototyping. An amount of 10% w/w of magnetic FeHA nanoparticles represents a reinforcement for PCL matrix, however, a reduction of strain at failure is also observed. Energy loss (absorption) measurements under a radio-frequency applied magnetic field were performed in the resulting magnetic scaffolds and very promising heating properties were observed, making them very useful for potential biomedical applications.
Effect of bake/cure temperature of an advanced organic ultra low-k material on the interface adhesion strength to metal barriers
Authors: Vanstreels Kris , Pantouvaki Marianna , Ferchichi Abdelkarim , Verdonck Patrick , Conard Thierry , Ono Yukiharu , Matsutani Mihoko , Nakatani Koji , Baklanov Mikhail R.
Published: April 2011

The interface adhesion strength of an advanced polymeric low-k material to different metal barriers was quantitatively measured using the four-point bending technique. Different sample configurations were tested in order to find the optimal configuration to study the polymer/barrier interface adhesion strength. The asymmetrical sample configuration with the notch at the film stack side was found to be the most suitable approach to study the adhesion strength of this interface. The effect of bake/cure temperature on the adhesion strength between polymer and barrier was investigated in more detail. Higher cure temperatures resulted in a lower amount of triple C-bonds in the polymer and lower polymer/barrier interface adhesion strength, while no differences in optical and mechanical properties were observed. Moreover, it was found that higher amount of Ta–C bonds formed at the interface improved the polymer/barrier interface adhesion, thereby suggesting that the chemical interaction between the polymer and metal barrier plays a major role in the adhesion performance.
Effects of Mn doping on temperature-dependent magnetic properties of L1 FeMnPt
Authors: Xu D. B. , Chen J. S. , Zhou T. J. , Chow G. M.
Published: April 2011

We report the effect of Mn doping on temperature-dependent magnetic properties of L10 FeMnPt (001) epitaxial films. (001) textured L10 Fe50−xMnxPt50 (x = 0, 5, 10, 15, 20 at. %) films were prepared by cosputtering Fe, Pt, and Mn onto MgO single crystal substrates at 550 °C. θ–2θ XRD scans indicated the lattice parameter c increased whereas the ordering parameter S decreased with Mn doping. The thermal magnetic properties measured using a superconducting quantum interference device showed that Curie temperature TC could be reduced to 500 K with 15 at. % Mn doping, but Ku was decreased to 1.6 × 107 erg/cm3. The relation of temperature-dependent anisotropy and saturation magnetization showed that it did not obey the Callen–Callen theory.
Role of Ru vacancies in the magnetism of strain relaxed SrRuO3 films on SrTiO3 substrates
Authors: Bohra Murtaza , Wu C. P. , Yeh H. J. , Cheng Y. H. , Peng C. C. , Chou H.
Published: April 2011

Magnetic properties of Ru-deficient strain relaxed SrRuO3 films have been investigated. The ferromagnetic transitions drop off from 138 to 100 K with expansion of unit cell volume due to the Ru vacancies. A secondary transition starts appearing near to the bulk transition temperature of 155 K, indicating the two different Ru-deficient regions which result in an exchange structure. Anomalous variation of the saturation magnetization with the unit cell volume could be originated from the stabilization of the high spin Ru+4 states due to the Ru-vacancy and the induced crystal lattice distortions from c/a > 1 to c/a < 1.
Magnetic properties of pulsed laser deposition-fabricated isotropic Fe–Pt film magnets
Authors: Nakano M. , Oniki W. , Yanai T. , Fukunaga H.
Published: April 2011

A high-speed pulsed laser deposition method with the deposition rate of several tens of microns per 1 h enabled us to obtain isotropic Fe–Pt thick film magnets. Increase in the laser power enabled us to obtain as-deposited films with L10 ordered phase due to the heat radiation from a target, which means that a substrate heating system and a post-annealing process are not required to achieve hard magnetic properties in the process. Use of an Fe-rich target enhanced the magnetic properties, and as a result (BH)max value exceeded 100 kJ/m3 in an isotropic Fe–Pt film fabricated at the power of 3 W, which was comparable to those of isotropic Fe–Pt thick film magnets prepared by a sputtering method.
Magnetic properties of (Sm,Y)5Fe17 melt-spun ribbons
Authors: Saito Tetsuji , Nishio-Hamane Daisuke
Published: April 2011

An investigation of the synthesis of the (Sm1−xYx)5Fe17 (x = 0 to 0.5) phase and its magnetic properties is presented. (Sm1−xYx)5Fe17 (x = 0 to 0.5) melt-spun ribbons that fully or mainly consisted of the amorphous phase and which showed low coercivity were prepared. Heat treatment of the melt-spun ribbons resulted in the formation of the (Sm,Y)5Fe17 phase. The highest remanence, 50 emu/g, was achieved in the annealed (Sm0.7Y0.3)5Fe17 melt-spun ribbon. However,the annealed (Sm1−xYx)5Fe17 (x = 0.4 to 0.5) melt-spun ribbons did not contain the (Sm,Y)5Fe17 phase and showed low coercivity values.
Optical waveguide circulators based on two-dimensional magnetophotonic crystals: Numerical simulation for structure simplification and experimental verification
Authors: Yayoi Kazuo , Tobinaga Kazuma , Kaneko Yusuke , Baryshev Alexander V. , Inoue Mitsuteru
Published: April 2011

We demonstrate results of a numerical analysis on functionality of waveguide circulators working in the spectral range of optical communication. Studied circulators were silicon-based three-port waveguide splitters where working elements were slabs of two-dimensional magnetophotonic crystals (2D MPCs) with different structural parameters. An optimized circulator had a 2D MPC slab–hexagonal array of cylindrical air holes in silicon with a magneto-optical defect made of bismuth-substituted yttrium iron garnet and demonstrated an insertion loss of 9 dB and an isolation of 16 dB. If compared to circulators reported in Z. Wan and S. Fan [Appl. Phys. B 81, 369 (2005)], the studied circulators are attractive for realization due to the relative simplicity of their designs.
Acceleration of ordering transformation of a new Fe2(Mn,Cr)Si Heusler-alloy film by very high frequency plasma irradiation process during radio frequency sputter deposition
Authors: Yoshimura S. , Kobayashi H. , Egawa G. , Saito H. , Ishida S.
Published: April 2011

A new Heusler alloy, Fe2(Mn,Cr)Si, that is likely to have high spin polarization (P) and high damping constant (α) was proposed to obtain high magneto-resistance ratio and low spin torque noise in a magnetic read head with a current-perpendicular-to-plane (CPP) giant magneto-resistance (GMR) multilayer. A very high frequency (VHF) plasma irradiation process during radio frequency (RF) sputter deposition was investigated to form the highly ordered structure of the Heusler alloy film with low thermal treatment temperature. The main results are as follows: (1) P and magnetic moment of Fe2(Mn0.5Cr0.5)Si with an L21 structure were estimated at 0.99 and 2.49 µB/f.u., respectively, and α was also estimated to be larger compared with the case of Co2MnSi, according to density of states (DOS) calculations. (2) The ordering (at least B2 structure) temperature of Fe2(Mn0.6Cr0.4)Si film decreased from 500 to 300 °C by using the VHF plasma irradiation process with optimized condition. (3) The surface roughness of Fe2(Mn0.6Cr0.4)Si film also reduced from 1.7 to 0.5 nm by using the VHF plasma irradiation process. It is found that the Fe2(Mn,Cr)Si Heusler alloy and the VHF plasma irradiation process with optimized condition seems to be applicable for fabrication of high-performance magnetic read head with CPP-GMR device.
Combined effects of bilayer structure and ion substitutions on bismuth ferrite thin films
Authors: Wu Jiagang , Wang John , Xiao Dingquan , Zhu Jianguo
Published: April 2011

To understanding the combined effects of bilayer structure and ion substitutions on electrical behavior of BiFeO3 thin films, the Bi0.90La0.10Fe0.90Zn0.10O3/Bi0.90La0.10Fe0.90Sn0.10O3 bilayers with different thickness ratios were fabricated on SrRuO3/Pt/TiO2/SiO2/Si(100) substrates by radio frequency sputtering. Their dielectric constant increases and the fatigue endurance becomes better with increasing Bi0.90La0.10Fe0.90Zn0.10O3 thickness ratios. The bilayer with the thickness ratio of 210: 90 exhibits a high remanent polarization, and a better fatigue behavior is induced by higher driving electric fields and frequencies.
Impact of structural defects upon electron mobility in InSb quantum wells
Authors: Mishima T. D. , Santos M. B.
Published: April 2011

The detrimental effects of structural defects, micro-twins (MTs) and threading dislocations (TDs), on electron mobility have been investigated for InSb quantum wells (QWs) at room temperature (RT). The constants that are necessary to calculate the electron-mobility limits of these defects were determined by a least-squares-based method that has an advantage of clear representation of the analytical results in a two-dimensional space. Based on a mathematical consideration, a general method of converting electron-mobility limits into percentage impacts upon the total electron mobility was developed. Percentage-mobility-impact analyses showed that, when InSb QWs grown on on-axis (001) GaAs substrates have a TD density of 8.7 × 108 – 3.2 × 109/cm2, 21–14 and 18–45% of electron-mobility degradation are attributed to MTs and TDs, respectively, at RT. The use of 2° off-axis (001) GaAs substrates reduces MT densities in InSb QWs, resulting in a suppression of the MT mobility impact to 3–2% and a complementary slight increase of the TD mobility impact to 22–51% in the same TD density range. This considerable TD mobility limit indicates that it should be possible to improve RT electron mobility in InSb QWs grown on 2° off-axis (001) GaAs substrates, by means of reducing TD density further (< 8.7 × 108/cm2). Although the mobility impacts due to phonons in InSb QW grown on-axis and 2° off-axis (001) GaAs substrates are 54–36 and 67–42%, respectively, phonon scattering is not a single dominant scattering factor: MTs and TDs have also substantial negative impacts upon RT electron mobilities in InSb QWs.
The equivalent structure and some optical properties of the periodic-defect photonic crystal
Authors: Pei Ting-Hang , Huang Yang-Tung
Published: April 2011

The concept of the effective medium is used to deal with problems of defects in photonic crystals (PhCs) throughout this paper. First, scattering phenomena in PhCs with defects are investigated and can be very well replaced by those in an effective medium with effective defects in interesting frequency region. It is based on the fact that the Bloch wave in the defect-free PhC very approximates to the wave in the effective medium. Then a periodic-defect PhC created by adding periodic defects into the defect-free PhC is proposed. It can be replaced with an effective PhC by utilizing the concept of effective periodic defects embedded into an effective medium. We verify the equivalence between the periodic-defect PhC and the effective PhC by comparing their photonic band structure (PBS) and photonic band gaps (PBGs) as well as transmissions. Next, the effective PhCs instead of the periodic-defect PhCs are used to investigate the variance of the PBGs by applying different periodic defects. The substitution allows us successfully predicting the negative refraction in the periodic-defect PhC through the PBS of the effective PhC. Finally, the field distributions and Fourier coefficients of waveguide modes in the effective PhC and the periodic-defect PhC are equivalent by the supercell method confirmations.
The effect of dielectric spacer thickness on surface plasmon enhanced solar cells for front and rear side depositions
Authors: Pillai S. , Beck F. J. , Catchpole K. R. , Ouyang Z. , Green M. A.
Published: April 2011

The excitation of surface plasmons on metallic nanoparticles has the potential to significantly improve the performance of solar cells, in particular thin-film structures. In this article, we investigate the effect of the dielectric spacer layer thickness on the photocurrent enhancement of 2 μm thick, thin-film poly-Si on glass solar cells, due to random arrays of self-assembled Ag nanoparticles deposited on the front or the rear of the cells. We report a strong asymmetry in the external quantum efficiency (EQE) of the cell for front and rear located particles for different spacer thicknesses, which is attributed to differences in the scattering behavior of the nanoparticles. We find that for random arrays, with spectrally broad scattering resonances, the strength of the driving field and the coupling efficiency are more important for light trapping than the resonance wavelength. For particles located on the front of the cells it is desirable to have a thin dielectric spacer layer to enhance the scattering from the Ag nanoparticles. Additionally, light trapping provided by the random sized particles on the front can overcome suppression of light transmitted in the visible wavelength regions for thin layers of Si, to result in overall EQE enhancements. However, for particles deposited on the rear it is more beneficial to have the particles as close to the Si substrate as possible to increase both the scattering and the coupling efficiency.