Excitation spectra of the spin-1/2 triangular-lattice Heisenberg antiferromagnet

We use series expansion methods to calculate the dispersion relation of the one-magnon excitations for the spin-(1)/(2) triangular-lattice nearest-neighbor Heisenberg antiferromagnet above a three-sublattice ordered ground state. Several striking features are observed compared to the classical (large-S) spin-wave spectra. Whereas, at low energies the dispersion is only weakly renormalized by quantum fluctuations, significant anomalies are observed at high energies. In particular, we find rotonlike minima at special wave vectors and strong downward renormalization in large parts of the Brillouin zone, leading to very flat or dispersionless modes. We present detailed comparison of our calculated excitation energies in the Brillouin zone with the spin-wave dispersion to order 1/S calculated recently by Starykh, Chubukov, and Abanov [Phys. Rev. B74, 180403(R) (2006)]. We find many common features but also some quantitative and qualitative differences. We show that at temperatures as low as 0.1J the thermally excited rotons make a significant contribution to the entropy. Consequently, unlike for the square lattice model, a nonlinear sigma model description of the finite-temperature properties is only applicable at temperatures < 0.1J. Finally, we review recent NMR measurements on the organic compound kappa-(BEDT-TTF)(2)Cu-2(CN)(3). We argue that these are inconsistent with long-range order and a description of the low-energy excitations in terms of interacting magnons, and that therefore a Heisenberg model with only nearest-neighbor exchange does not offer an adequate description of this material.

Experiments with Bose-Einstein condensates on an atom chip

We describe the production of BECs on a new type of atom chip based on silver foil. Our atom chip is fabricated with thick wires capable of carrying currents of several amperes without overheating. The silver surface is highly reflective to light resonant with optical transitions used for Rb. The pattern on the chip consists of two parallel Z-trap wires, capable of producing two-wire guide, and two additional endcap wires for varying the axial confinement. Condensates are produced in magnetic microtraps formed within 1 mm of surface of the chip. We have observed the fragmentation of cold atom clouds when brought close to the chip surface. This results from a perturbed trapping potential caused by nanometer deviations of the current path through the wires on the chip. We present results of fragmentation of cold clouds at distances below 100 µm from the wires and investigate the origin of the deviating current. The fragmentation has different characteristics to those seen with copper conductors. The dynamics of atoms in these microtraps is also investigated. ©2005 COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The detection and identification of extraneous metals in material conveyance systems

The aim of this work was to design and build an equipment which can detect ferrous and non-ferrous objects in conveyed commodities, discriminate between them and locate the object along the belt and on the width of the belt. The magnetic induction mechanism was used as a means of achieving the objectives of this research. In order to choose the appropriate geometry and size of the induction field source, the field distributions of different source geometries and sizes were studied in detail. From these investigations it was found the square loop geometry is the most appropriate as a field generating source for the purpose of this project. The phenomena of field distribution in the conductors was also investigated. An equipment was designed and built at the preliminary stages of thework based on a flux-gate magnetometer with the ability to detect only ferrous objects.The instrument was designed such that it could be used to detect ferrous objects in the coal conveyors of power stations. The advantages of employing this detector in the power industry over the present ferrous metal electromagnetic separators were also considered. The objectives of this project culminated in the design and construction of a ferrous and non-ferrous detector with the ability to discriminate between ferrous and non-ferrous metals and to locate the objects on the conveying system. An experimental study was carried out to test the performance of the equipment in the detection of ferrous and non-ferrous objects of a given size carried on the conveyor belt. The ability of the equipment to discriminate between the types of metals and to locate the object on the belt was also evaluated experimentally. The benefits which can be gained from the industrial implementations of the equipment were considered. Further topics which may be investigated as an extension of this work are given.

Developments and extensions of Roth's method of double Fourier series with applications to the solution of electromagnetic field problems

The first part of the thesis compares Roth's method with other methods, in particular the method of separation of variables and the finite cosine transform method, for solving certain elliptic partial differential equations arising in practice. In particular we consider the solution of steady state problems associated with insulated conductors in rectangular slots. Roth's method has two main disadvantages namely the slow rate of con­vergence of the double Fourier series and the restrictive form of the allowable boundary conditions. A combined Roth-separation of variables method is derived to remove the restrictions on the form of the boundary conditions and various Chebyshev approximations are used to try to improve the rate of convergence of the series. All the techniques are then applied to the Neumann problem arising from balanced rectangular windings in a transformer window. Roth's method is then extended to deal with problems other than those resulting from static fields. First we consider a rectangular insulated conductor in a rectangular slot when the current is varying sinusoidally with time. An approximate method is also developed and compared with the exact method.The approximation is then used to consider the problem of an insulated conductor in a slot facing an air gap. We also consider the exact method applied to the determination of the eddy-current loss produced in an isolated rectangular conductor by a transverse magnetic field varying sinusoidally with time. The results obtained using Roth's method are critically compared with those obtained by other authors using different methods. The final part of the thesis investigates further the application of Chebyshdev methods to the solution of elliptic partial differential equations; an area where Chebyshev approximations have rarely been used. A poisson equation with a polynomial term is treated first followed by a slot problem in cylindrical geometry.

Intercultural transfer and artistic innovation:German musicians in Victorian Britain

Throughout the nineteenth century, German classical music production was an aesthetic point of reference for British concert audiences. As a consequence, a sizeable number of German musicians were to be found in Britain as performers, conductors, teachers, musicologists and managers. They acted as agents of intercultural transfer, disseminating performance and organisational practices which had a transformative effect on British musical life. This article moves away from a focus on high-profile visiting artists such as Mendelssohn Bartholdy or Wagner and argues that the extent to which transfer took place can be better assessed by concentrating on the cohort of those artists who remained permanently. Some of these are all but forgotten today, but were household names in Victorian Britain. The case studies have been selected for the range of genres they represent and include Joseph Mainzer (choral singing), Carl Rosa (opera), August Manns, Carl Hallé and Julius Seligmann (orchestral music), and Friedrich Niecks (musicology). On a theoretical level, the concept of ‘intercultural transfer’ is applied in order to determine aspects such as diffusion, adaptation or sustainability of artistic elements within the new cultural context. The approach confirms that ‘national’ cultures do not develop indigenously but always through cross-national interaction. Während des neunzehnten Jahrhunderts war die klassische Musikszene Deutschlands ästhetischer Bezugpunkt für das britische Konzertpublikum. Dies hatte zur Folge, dass vermehrt Deutsche als Musiker, Dirigenten, Lehrer, Musikwissenschaftler und Manager in Großbritannien tätig wurden. Sie fungierten als Vermittler interkulturellen Transfers, indem sie aufführungs- und organisationstechnische Praktiken verbreiteten und damit zu einer Transformation des britischen Musiklebens beitrugen. Vorliegender Artikel konzentriert sich weniger auf bekannte Künstler mit kurzfristigen Engagements (z. B. Mendelssohn Bartholdy, Wagner), und argumentiert vielmehr, dass sich das Ausmaß des Transfers besser über solche Musiker feststellen lässt, die sich längerfristig ansiedelten. Einige davon waren allgemein bekannte Persönlichkeiten im Königreich, sind heute aber vergessen. Die Auswahl der Fallstudien gibt einen Überblick über verschiedene Gattungen und beinhaltet Joseph Mainzer (Chorgesang), Carl Rosa (Oper), August Manns, Carl Hallé und Julius Seligmann (Orchestermusik), sowie Friedrich Niecks (Musikwissenschaft). Auf der Theorieebene wird das Konzept des ‘interkulturellen Transfers’ herangezogen, um Aspekte wie Diffusion, Anpassung oder Nachhaltigkeit künstlerischer Elemente im neuen kulturellen Kontext zu beleuchten. Der Ansatz bestätigt, dass sich ‘nationale’ Kulturen nicht indigen entwickeln sondern immer im Austausch mit anderen Kulturen

Molecular detection using metallic nanowires with quantized conductance

This thesis studies the adsorption of molecules with different binding strengths onto copper nanowires with prestabilized conductance values fabricated by an electrochemical method. Since the diameters of these wires are comparable to the wavelength of conduction electrons the conductance of the nanowires is quantized, and the adsorption of even a few molecules onto atomically thin wires changes the conductance from integer values to fractional ones. These changes are proportional to the binding strength of the adsorbed molecules. The decrease in conductance is hypothesized to be caused by the scattering of the conduction electrons by the adsorbed molecules. The sensitivity of molecular adsorption-induced conductance change can be used for the development of a chemical sensor. The stabilized copper nanowires obtained in this thesis may also be used for other purposes, such as interconnecting conductors between nanodevices and digital switches in functional nanoelectronic circuitry.

"Cantata para louvor e glória", de Cleide Dorta Benjamim: preparo para a execução

This study aims to document the preparation process for the implementation of "Cantata To Praise and Glory"(Cantata Para Louvor e Glória), composed in 1985 by composer Cleide Dorta Benjamin (1936 - ), in order to anticipate and address the possible difficulties faced by future conductors, singers and instrumentalists. Issues that relate to the chosen text as well as its structure and importance in the compositional process, are initially addressed through a brief presentation of the work. Consequently, by addressing every detail of the work, solutions to vocal and instrumental execution difficulties, as well as with the conducting gesture, are analyzed, identified and proposed. The work also presents a report that describes all the practical processes of preparation of the Cantata: reissue of the score; selection and profile of singers and instrumentalists; rehearsals; changes and adjustments to the score; and a brief interview with four singers and two musicians who participated in the process. The interaction with the composer throughout a significant part of the work, brings a notable increase of possible clarifications and idea development, enabling a coherent performance of the work.

O gesto regencial para além do compasso: uma discussão acerca das ferramentas da regência e de seus usos para a performance na música do século XX

This work is the result of a master’s program research developed in the post graduation program in music at the Music School of the UFRN ( Federal University of Rio Grande do Norte) under the orientation of Dr. Andre Luiz Muniz de Oliveira which aimed at making a reflexion about regency gestures and its implications about the objective and subjective elements of the performance connected to a number of regency tools concieved in accordance with the tradition of historic music. As a tool for gestual analysis we’ve used the Harold Farbermann PatternCube method. We’ve used videos from conductors Pierre Boulez e Valery Gergiev, both conducting Igor Stravinsky’s Rite of Spring. In the analysis of the videos we’ve observed the technical use of the gestual aparatus instead of the use of musical gestures fundamented in Hatten. The research showed us the importance of the use of analitical tools in helping subsidise a direction in performance in regency.

Templo Central da Igreja Evangélica Assembleia de Deus do Natal/RN: um estudo sobre música e educação musical

This study aims to investigate the music and the existing music education in Central Temple of the Evangelical Assembly of God Church of Natal/RN. The research question asks how are the musical practices, teaching and learning music that happens in this place. I used the qualitative approach conducting a case study. The theoretical framework were Arroyo (1999, 2000a, 2000b, 2002), Kraemer (2000), Souza (1996), Souza (2000, 2008, 2009), Green (1997), Queiroz (2004a, 2004b, 2005, 2007, 2010, 2011, 2013), Geertz (1989), Nettl (1992) and Merrian (1964). I conducted semi-structured interviews and participant observation with the direction of the music department, teaching coordination, students, teachers, musicians and conductors of the church. The study revealed that the relationship between music and education is beyond just a musical training, there are many relationships established as faith, belief in God and devotion. It was found that the views of musicians and conductors think the music teaching in the church to play in worship and praise God. In the musical training of students, he was working not only musical content; It was understood that music is a mediator of meanings that go beyond experiences and musical practices. The worship of God and the worship featuring musical practices and their effects are direct music classes. The research contributes to reflection and understanding of music and music education happens in the evangelical church and a greater understanding in the relationship between music education and the cultural context where it happens.

Numerical Modelling of Eddy Current Probes for CANDU® Fuel Channel Inspection

Multi-frequency Eddy Current (EC) inspection with a transmit-receive probe (two horizontally offset coils) is used to monitor the Pressure Tube (PT) to Calandria Tube (CT) gap of CANDU® fuel channels. Accurate gap measurements are crucial to ensure fitness of service; however, variations in probe liftoff, PT electrical resistivity, and PT wall thickness can generate systematic measurement errors. Validated mathematical models of the EC probe are very useful for data interpretation, and may improve the gap measurement under inspection conditions where these parameters vary. As a first step, exact solutions for the electromagnetic response of a transmit-receive coil pair situated above two parallel plates separated by an air gap were developed. This model was validated against experimental data with flat-plate samples. Finite element method models revealed that this geometrical approximation could not accurately match experimental data with real tubes, so analytical solutions for the probe in a double-walled pipe (the CANDU® fuel channel geometry) were generated using the Second-Order Vector Potential (SOVP) formalism. All electromagnetic coupling coefficients arising from the probe, and the layered conductors were determined and substituted into Kirchhoff’s circuit equations for the calculation of the pickup coil signal. The flat-plate model was used as a basis for an Inverse Algorithm (IA) to simultaneously extract the relevant experimental parameters from EC data. The IA was validated over a large range of second layer plate resistivities (1.7 to 174 µΩ∙cm), plate wall thickness (~1 to 4.9 mm), probe liftoff (~2 mm to 8 mm), and plate-to plate gap (~0 mm to 13 mm). The IA achieved a relative error of less than 6% for the extracted FP resistivity and an accuracy of ±0.1 mm for the LO measurement. The IA was able to achieve a plate gap measurement with an accuracy of less than ±0.7 mm error over a ~2.4 mm to 7.5 mm probe liftoff and ±0.3 mm at nominal liftoff (2.42±0.05 mm), providing confidence in the general validity of the algorithm. This demonstrates the potential of using an analytical model to extract variable parameters that may affect the gap measurement accuracy.

Development of the Oxide Ion Conductor Na0.5Bi0.5TiO3 (NBT) for Solid Oxide Cells

Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material with potential to replace lead zirconate titanate (PZT),1 however high leakage conductivity for the material has been widely reported.2 Through a combination of Impedance Spectroscopy (IS), O2- ion transference (EMF) number experiments and O18 tracer diffusion measurements, combined with Time-of-flight Secondary Ion Mass Spectrometry (TOFSIMS), it was identified that this leakage conductivity was due to oxygen ion conductivity. The volatilization of bismuth during synthesis, causing oxygen vacancies, is believed to be responsible for the leakage conductivity.3 The oxide-ion conductivity, when doped with magnesium, exceeds that of yttria-stabilized zirconia (YSZ) at ~500 °C,3 making it a potential electrolyte material for Intermediate Temperature Solid Oxide Cells (ITSOCs). Figure 1 shows the comparison of bulk oxide ion conductivity between 2 at.% Mg-doped NBT and other known oxide ion conductors.

As part of the UK wide £5.7m 4CU project, research has concentrated on trying to develop NBT for use in Intermediate Temperature Solid Oxide Cells (ITSOCS). With the aim of achieving mixed ionic and electronic conduction, transition metals were chemically doped on to the Ti-site. A range of experimental techniques was used to characterize the materials aimed at investigating both conductivity and material structure (Scanning Electron Microscopy (SEM), IS, X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS)). The potential for NBT as an ITSOC material, as well as the challenges of developing the material, will be discussed.

(1) Takenaka T. et al. Jpn. J. Appl. Phys 1999, 30, 2236.

(2) Hiruma Y. et al. J. Appl. Phys 2009, 105, 084112.

(3) Li. M. et al. Nature Materials 2013, 13, 31.

Development of functionalised multiwalled carbon nanotube/polyaniline composites for electrical applications

Combining intrinsically conducting polymers with carbon nanotubes (CNT) helps in creating composites with superior electrical and thermal characteristics. These composites are capable of replacing metals and semiconductors as they possess unique combination of electrical conductivity, flexibility, stretchability, softness and bio-compatibility. Their potential for use in various organic devices such as super capacitors, printable conductors, optoelectronic devices, sensors, actuators, electrochemical devices, electromagnetic interference shielding, field effect transistors, LEDs, thermoelectrics etc. makes them excellent substitutes for present day semiconductors.However, many of these potential applications have not been fully exploited because of various open–ended challenges. Composites meant for use in organic devices require highly stable conductivity for the longevity of the devices. CNT when incorporated at specific proportions, and with special methods contributes quite positively to this end.The increasing demand for energy and depleting fossil fuel reserves has broadened the scope for research into alternative energy sources. A unique and efficient method for harnessing energy is thermoelectric energy conversion method. Here, heat is converted directly into electricity using a class of materials known as thermoelectric materials. Though polymers have low electrical conductivity and thermo power, their low thermal conductivity favours use as a thermoelectric material. The thermally disconnected, but electrically connected carrier pathways in CNT/Polymer composites can satisfy the so-called “phonon-glass/electron-crystal” property required for thermoelectric materials. Strain sensing is commonly used for monitoring in engineering, medicine, space or ocean research. Polymeric composites are ideal candidates for the manufacture of strain sensors. Conducting elastomeric composites containing CNT are widely used for this application. These CNT/Polymer composites offer resistance change over a large strain range due to the low Young‟s modulus and higher elasticity. They are also capable of covering surfaces with arbitrary curvatures.Due to the high operating frequency and bandwidth of electronic equipments electromagnetic interference (EMI) has attained the tag of an „environmental pollutant‟, affecting other electronic devices as well as living organisms. Among the EMI shielding materials, polymer composites based on carbon nanotubes show great promise. High strength and stiffness, extremely high aspect ratio, and good electrical conductivity of CNT make it a filler of choice for shielding applications. A method for better dispersion, orientation and connectivity of the CNT in polymer matrix is required to enhance conductivity and EMI shielding. This thesis presents a detailed study on the synthesis of functionalised multiwalled carbon nanotube/polyaniline composites and their application in electronic devices. The major areas focused include DC conductivity retention at high temperature, thermoelectric, strain sensing and electromagnetic interference shielding properties, thermogravimetric, dynamic mechanical and tensile analysis in addition to structural and morphological studies.

POLYMER-NANOPARTICLE COMPOSITES FOR APPLICATIONS IN FLEXIBLE ELECTRONICS

The aim of this dissertation was to investigate flexible polymer-nanoparticle composites with unique magnetic and electrical properties. Toward this goal, two distinct projects were carried out. The first project explored the magneto-dielectric properties and morphology of flexible polymer-nanoparticle composites that possess high permeability (µ), high permittivity (ε) and minimal dielectric, and magnetic loss (tan δε, tan δµ). The main materials challenges were the synthesis of magnetic nanoparticle fillers displaying high saturation magnetization (Ms), limited coercivity, and their homogeneous dispersion in a polymeric matrix. Nanostructured magnetic fillers including polycrystalline iron core-shell nanoparticles, and constructively assembled superparamagnetic iron oxide nanoparticles were synthesized, and dispersed uniformly in an elastomer matrix to minimize conductive losses. The resulting composites have demonstrated promising permittivity (22.3), permeability (3), and sustained low dielectric (0.1), magnetic (0.4) loss for frequencies below 2 GHz. This study demonstrated nanocomposites with tunable magnetic resonance frequency, which can be used to develop compact and flexible radio frequency devices with high efficiency. The second project focused on fundamental research regarding methods for the design of highly conductive polymer-nanoparticle composites that can maintain high electrical conductivity under tensile strain exceeding 100%. We investigated a simple solution spraying method to fabricate stretchable conductors based on elastomeric block copolymer fibers and silver nanoparticles. Silver nanoparticles were assembled both in and around block copolymer fibers forming interconnected dual nanoparticle networks, resulting in both in-fiber conductive pathways and additional conductive pathways on the outer surface of the fibers. Stretchable composites with conductivity values reaching 9000 S/cm maintained 56% of their initial conductivity after 500 cycles at 100% strain. The developed manufacturing method in this research could pave the way towards direct deposition of flexible electronic devices on any shaped substrate. The electrical and electromechanical properties of these dual silver nanoparticle network composites make them promising materials for the future construction of stretchable circuitry for displays, solar cells, antennas, and strain and tactility sensors.

Trajetórias do canto coral no Maranhão: FEMACO como referência histórica num processo de continuidades e rupturas

O FEMACO – Festival Maranhense de Coros – teve durante a sua existência (1977-2012) um forte impacto sociocultural em São Luís, capital do Maranhão e contribuiu decisivamente para a formação de diretores corais e educadores musicais nesta região. A presente investigação constitui um levantamento histórico dos 36 anos de existência deste festival e uma reflexão sobre a sua contribuição para a música coral no Estado do Maranhão. Para chegar a estes objetivos foi realizado um levantamento dos materiais impressos que constam do arquivo do próprio Festival, existente na Universidade Federal do Maranhão, nomeadamente dos cartazes e brochuras com os programas do festival, e dos registos existentes nos jornais locais sobre o mesmo. Foram realizadas entrevistas com os autores do projeto FEMACO e foi ainda feito um inquérito, através de um questionário, a professores e regentes que participaram no festival. Sendo este o primeiro registo histórico sobre o FEMACO, um dos festivais de corais mais antigos da região Nordeste do Brasil, pretende-se realizar uma reflexão sobre a sua influência na música coral no Maranhão e fornecer dados que, esperamos, poderão servir como fonte de consulta para futuras investigações.

Teaching Sight-Reading to Undergraduate Choral Ensemble Singers: Lessons from Successful Learners

This study was designed to investigate professional choral singers’ training, perceptions on the importance of sight-reading skill in their work, and thoughts on effective pedagogy for teaching sight-reading to undergraduate choral ensemble singers. Participants in this study (N=48) included self-selected professional singers and choral conductors from the Summer 2015 Oregon Bach Festival’s Berwick Chorus and conducting Master Class. Data were gathered from questionnaire responses and audio recorded focus group sessions. Focus group data showed that the majority of participants developed proficiency in their sight-reading skills from instrumental study, aural skills classes, and through on-the-job training at a church job or other professional choral singing employment. While participants brought up a number of important job skills, sightreading was listed as perhaps the single most important skill that a professional choral singer could develop. When reading music during the rehearsal process, the data revealed two main strategies that professional singers used to interpret the pitches in their musical line: an intervallic approach and a harmonic approach. Participants marked their scores systematically to identify problem spots and leave reminders to aid with future readings, such as marking intervals, solfege syllables, or rhythmic counts. Participants reported using a variety of skills other than score marking to try to accurately find their pitches, such as looking at other vocal or instrumental lines, looking ahead, and using knowledge about a musical style or time period to make more intuitive “guesses” when sight-reading. Participants described using additional approaches when sight-reading in an audition situation, including scanning for anchors or anomalies and positive self-talk. Singers learned these sight-reading techniques from a variety of sources. Participants had many different ideas about how best to teach sight-reading in the undergraduate choral ensemble rehearsal. The top response was that sight-reading needed to be practiced consistently in order for students to improve. Other responses included developing personal accountability, empowering students, combining different teaching methods, and discussing real-life applications of becoming strong sight-readers. There was discussion about the ultimate purpose of choir at the university level and whether it is to teach musicianship skills or produce excellent performances.