Polarization enhancement in compositionally graded vanadium doped bismuth titanate thin films

Compositionally up and downgraded Bi4-x/3Ti3-xVxO12 (x=0.0, 0.012,0.03, 0.06) thin films were grown on Pt coated silicon substrates by pulsed laser deposition technique. Downgraded fabrication showed improved ferroelectric polarization in comparison to upgraded fabrication. Films deposited at 650 and 700 degrees C showed very large remnant polarization (2P(r)) value of 82 mu C cm(-2), which is comparatively large among all bismuth based thin films reported so far. A mechanism based on vanadium enrich seeded layer formation in the downgraded structure is proposed for the improvement. Moreover, frequency independent behavior (100Hz-5kHz) of the graded films ensures its potential application for various microelectronic devices. (c) 2010 American Institute of Physics. [doi :10.1063/1.3431543].

Making Music, Making Muslims : A Case Study of Islamic Hip Hop and the Discursive Construction of Muslim Identities on the Internet

Hip-hopin juuret juontavat 1970-luvulle Yhdysvaltoihin, mutta hip-hop-kulttuuri ja musiikkityyli ovat sen jälkeen levinneet ympäri maailmaa osana globalisaatiokehitystä. Myös monet nuoret muslimit tekevät nykyään hip-hop-musiikkia, ja yhä useampi tuo myös sanoituksiinsa vaikutteita Islamista ja elämästään muslimina. Musiikin asema on islamissa varsin kiistelty, eikä sitä ole selvästi sallittu (halal) tai kielletty (haram) muslimeilta. Muslimien tekemää hip-hoppia on toistaiseksi tutkittu hyvin vähän. Tutkielmassa tarkastellaan diskurssianalyysin keinoin, miten tapaustutkimuksena toimivalla muslimhiphop.com-internetsivustolla argumentoidaan ja konstruoidaan käsityksiä muslimi-identiteetistä. Teoreettisena ja analyyttisenä viitekehyksenä toimii sosiaalikonstruktivistinen näkemys identiteetistä kontekstisidonnaisena sekä puheessa ja teksteissä diskursiivisesti rakentuvana. Tutkielma kyseenalaistaa aiempien tutkimusten oletuksen hip-hopista vaikutuksiltaan yksinomaan positiivisena muslimi-identiteetille sekä muslimeja yhdentävänä tekijänä. Aineisto on kerätty edellä mainitulta sivustolta syksyn 2010 ja kevään 2011 aikana, josta analyysiin on rajattu vain itse sivusto ja sen hip-hoppia käsittelevät osiot. Sivusto ja sen perustaja ovat yhdysvaltalaisia, mutta sivustolla esiteltävien artistien tausta on hyvin monikulttuurinen. Moni on myös maahanmuuttajana nykyisessä kotimaassaan. Aineistossa esiintyviä teemoja ja diskursseja eritellään ja analysoidaan tutkielmassa lainauksien avulla. Sivuston periaatteissa ja artistien esillepääsyn kriteereissä määritellään tarkasti asennoituminen Islamin ja musiikin yhdistämiseen: mikäli sanoitukset ja artistit noudattavat Islamin oppeja, on muslimin sallittua tehdä ja kuunnella tällaista musiikkia. Islam-aiheisen hip-hopin perustellaan olevan ennen kaikkea vaihtoehto valtavirran hip-hopille, jota konstruoidaan aineistossa moraalisesti arveluttavaksi. Hip-hopille sekä muslimeille sallittuja ja kiellettyjä elementtejä erottelevan halal-haram-diskurssin ohella aineistosta nousee esiin opetusdiskurssi. Muslimien tekemän hip-hopin perustellaan edistävän Islamin opettamista erityisesti nuorille muslimeille ja siten vahvistavan positiivista muslimi-identiteettiä. Myös positiivisen muutoksen diskurssia käytetään aineistossa runsaasti liittyen mm. muslimiyhteisöihin sekä muslimeihin kohdistuviin taloudellisiin ja sosiaalipoliittisiin epäkohtiin ja stereotypioihin; musiikin sisältöä ja sen tekemistä perustellaan sen voimalla muuttaa asioita parempaan suuntaan. Monet muslimiartistit kamppailevat yhdistääkseen toisaalta Islamin ja taiteellisen luovuuden ja ilmaisuvapauden, toisaalta menestyäkseen kaupallisesti unohtamatta uskonnollista vakaumustaan. Monilla heistä hip-hop on ollut vahvasti läsnä kasvuympäristössä, mutta sen yhdistäminen Islamin periaatteisiin aiheuttaa kysymyksiä ja kyseenalaistuksia oman musiikillisen ja uskonnollisen identiteetin muodosta ja sisällöstä. Aineiston perusteella monet muslimiartistit ja Islam-aiheista hip-hoppia kuuntelevat muslimit joutuvat jatkuvasti puolustamaan musiikkia siihen kielteisesti suhtautuville muslimeille sekä ei-muslimeille, jotka vierastavat sen uskonnollisuutta. Muslimi-identiteettiä neuvotellaan jatkuvasti, ja se näyttäytyy aineistossa moniulotteisena ja tilanteisesti rakentuvana. Avainsanat: Muslimit, Islam, hip-hop, identiteetti, Internet, diskurssi, diskurssianalyysi

Affine Hall-Littlewood Functions for A(1)((1)) And Some Constant Term Identities of Cherednik-Macdonald-Mehta Type

We study t-analogs of string functions for integrable highest weight representations of the affine Kac-Moody algebra A(1)((1)). We obtain closed form formulas for certain t-string functions of levels 2 and 4. As corollaries, we obtain explicit identities for the corresponding affine Hall-Littlewood functions, as well as higher level generalizations of Cherednik's Macdonald and Macdonald-Mehta constant term identities.

Electrical properties of La-graded heterostructure of Pb1?xLaxTiO3 thin films

La-graded heterostructure films were prepared by sol-gel technique on platinum substrates and electrical properties of these films were compared with those of conventional thin films of similar compositions. X-ray diffraction results indicate the pure perovskite polycrystalline structure of these films. Atomic Force Microscopy analysis revealed a finer grain size and relatively lower surface roughness. Relatively higher values of Pm and Pr (69 and 38 ?C cm?2, respectively) and excellent dielectric properties with lower loss (K=1900, tan ?=0.035 at 100 kHz) were observed for La-graded heterostructure films. Also lower leakage current density (not, vert, similar2.5 nA cm?2) and a higher onset field (not, vert, similar50 kV cm?1) of space charge conduction indicated higher breakdown strength and good leakage current characteristics. The ac electric field dependence of the permittivity at sub-switching fields was analyzed in the framework of the Rayleigh dynamics of domain walls. The estimated irreversible domain wall displacement contribution to the total dielectric permittivity was 17 and 9% for conventional 15 at.% La doped PbTiO3 and La-graded heterostructure films, respectively. The improved dielectric and polarization behavior of La-graded heterostructure films may be attributed to homogenous dopant distribution compared to the conventional 15 at.% La doped PbTiO3 films.

A new beam finite element for the analysis of functionally graded materials

A new beam element is developed to study the thermoelastic behavior of functionally graded beam structures. The element is based on the first-order shear deformation theory and it accounts for varying elastic and thermal properties along its thickness. The exact solution of static part of the governing differential equations is used to construct interpolating polynomials for the element formulation. Consequently, the stiffness matrix has super-convergent property and the element is free of shear locking. Both exponential and power-law variations of material property distribution are used to examine different stress variations. Static, free vibration and wave propagation problems are considered to highlight the behavioral difference of functionally graded material beam with pure metal or pure ceramic beams. (C) 2003 Elsevier Science Ltd. All rights reserved.

Behavior of Sandwich Beams With Functionally Graded Rubber Core in Three Point Bending

The three-point bending behavior of sandwich beams made up of jute epoxy skins and piecewise linear functionally graded (FG) rubber core reinforced with fly ash filler is investigated. This work studies the influence of the parameters such as weight fraction of fly ash, core to thickness ratio, and orientation of jute on specific bending modulus and strength. The load displacement response of the sandwich is traced to evaluate the specific modulus and strength. FG core samples are prepared by using conventional casting technique and sandwich by hand layup. Presence of gradation is quantified experimentally. Results of bending test indicate that specific modulus and strength are primarily governed by filler content and core to sandwich thickness ratio. FG sandwiches with different gradation configurations (uniform, linear, and piecewise linear) are modeled using finite element analysis (ANSYS 5.4) to evaluate specific strength which is subsequently compared with the experimental results and the best gradation configuration is presented. POLYM. COMPOS., 32:1541-1551, 2011. (C) 2011 Society of Plastics Engineers

Multigrid algorithms for symmetric discontinuous Galerkin methods on graded meshes

We study a class of symmetric discontinuous Galerkin methods on graded meshes. Optimal order error estimates are derived in both the energy norm and the L 2 norm, and we establish the uniform convergence of V-cycle, F-cycle and W-cycle multigrid algorithms for the resulting discrete problems. Numerical results that confirm the theoretical results are also presented.

Large reduction of leakage current by graded-layer La doping in (Ba0.5, Sr0.5)TiO3 thin films

A large reduction in the leakage current behavior in (Ba, Sr)TiO3 (BST) thin films was observed by graded-layer donor doping. The graded doping was achieved by introducing La-doped BST layers in the grown BST films. The films showed a large decrease (about six orders of magnitude) in the leakage current in comparison to undoped films at an electric field of 100 kV/cm. The large decrease in leakage current was attributed to the formation of highly resistive layers, originating from compensating defect chemistry involved for La-doped films grown in oxidizing environment. Temperature-dependent leakage-current behavior was studied to investigate the conduction mechanism and explanations of the results were sought from Poole–Frenkel conduction mechanism.

Reactive Interdiffusion: A Method for Making Composition Graded Metal-ceramic Composites

Presented is a new method for making composition graded metal-ceramic composites using reactive inter-diffusion between a metal and a complex ceramic. Composition variation in both metal and ceramic phases with distance along the direction of diffusion is achieved. The design criteria for developing such composites are discussed. The system should exhibit extensive solid solubility in both metallic and ceramic phases, a defined gradation in the stabilities of the oxides, and mobility of electrons or holes in the oxide solid solution. The complex ceramic used for making the composite should be polycrystalline with sufficient porosity to accommodate the volume expansion caused by alloy precipitation. An inert atmosphere to prevent oxidation and high processing temperature to facilitate diffusive transport are required. The process is illustrated using the reaction couples Fe-NiTiO3, Fe-(Mg,Co)TiO3 and Fe-(Ni,Co)TiO3.

Functionally graded hydroxyapatite-alumina-zirconia biocomposite: Synergy of toughness and biocompatibility

Functionally Gradient Materials (FGM) are considered as a novel concept to implement graded functionality that otherwise cannot be achieved by conventional homogeneous materials. For biomedical applications, an ideal combination of bioactivity on the material surface as well as good physical property (strength/toughness/hardness) of the bulk is required in a designed FGM structure. In this perspective, the present work aims at providing a smooth gradation of functionality (enhanced toughening of the bulk, and retained biocompatibility of the surface) in a spark plasma processed hydroxyapatite-alumina-zirconia (HAp-Al2O3-YSZ) FGM bio-composite. In the current work HAp (fracture toughness similar to 1.5 MPa.m(1/2)) and YSZ (fracture toughness similar to 62 MPa.m(1/2)) are coupled with a transition layer of Al2O3 allowing minimum gradient of mechanical properties (especially the fracture toughness similar to 3.5 MPa.m(1/2)).The in vitro cyto-compatibilty of HAp-Al2O3-YSZ FGM was evaluated using L929 fibroblast cells and Saos-2 Osteoblast cells for their adhesion and growth. From analysis of the cell viability data, it is evident that FGM supports good cell proliferation after 2, 3, 4 days culture. The measured variation in hardness, fracture toughness and cellular adhesion across the cross section confirmed the smooth transition achieved for the FGM (HAp-Al2O3-YSZ) nanocomposite, i.e. enhanced bulk toughness combined with unrestricted surface bioactivity. Therefore, such designed biomaterials can serve as potential bone implants. (C) 2012 Elsevier B.V. All rights reserved.

A new method for fracture toughness determination of graded (Pt,Ni)Al bond coats by microbeam bend tests

A novel method is proposed for fracture toughness determination of graded microstructurally complex (Pt,Ni)Al bond coats using edge-notched doubly clamped beams subjected to bending. Micron-scale beams are machined using the focused ion beam and loaded in bending under a nanoindenter. Failure loads gathered from the pop-ins in the load-displacement curves combined with XFEM analysis are used to calculate K-c at individual zones, free from substrate effects. The testing technique and sources of errors in measurement are described and possible micromechanisms of fracture in such heterogeneous coatings discussed.