Inelastic neutron scattering peak in Zn substituted YBa2Cu3O7

The effects of nonmagnetic impurities on the neutron scattering intensity are studied for a model of the copper oxide layers in the normal state. The contribution to the Q=(pi,pi) neutron scattering intensity from processes involving the scattering of the spin fluctuations from an impurity with large momentum transfers are calculated within the random phase approximation. It is shown that this type of scatterings could lead to a peak in the neutron scattering intensity in the normal state.Comment: 4 pages, 4 figure

Good Practices of the Use of Information Communication Technology in a Second Language Classroom: An Alternating Use of Small Group Learning and Computers for Independent Learning

This presentation is going to analyse the good practices of the alternating use of small group learning and independent learning with computers in a second language classroom. It was a weekly Reading and Phonics lesson scheduled in the Language Learning room for the lower form of primary students. The room consisted of two rows of computers along the side and two small tables for group discussion accommodating around ten people including the teacher in the middle of the room. The class was divided into four small groups and each group of 8 students was assigned various tasks in the lesson. Two teachers, a native-English speaker and a non-native English speaker, and one teacher-assistant were in the lesson. Different from the traditional use of computers for second language teaching and learning, the teachers made good use of alternating groups for independent learning and small group learning in the lesson. The use of alternating groups is effective in providing students with different in-class communicative activities which entail self-practice, small group learning, interactions with teachers, consolidations, and independent reading. The presentation will analyse the structure of the lesson and discuss the advantages of the use of alternating groups in a second language classroom. Factors like the reverse roles of teachers and students, dynamic classroom interaction and promotion of individualistic learning will also be examined.published_or_final_versionCentre of Information Technology in Education, University of Hong Kong and Education and Manpower Bureau, the Government of the Hong Kong SA

Sticker systems over monoids

Molecular computing has gained many interests among researchers since Head introduced the first theoretical model for DNA based computation using the splicing operation in 1987. Another model for DNA computing was proposed by using the sticker operation which Adlemanused in his successful experiment for the computation of Hamiltonian paths in a graph: a double stranded DNA sequence is composed by prolonging to the left and to the right a sequence of (single or double) symbols by using given single stranded strings or even more complex dominoes with sticky ends, gluing these ends together with the sticky ends of the current sequence according to a complementarity relation. According to this sticker operation, a language generative mechanism, called a sticker system, can be defined: a set of (incomplete) double-stranded sequences (axioms) and a set of pairs of single or double-stranded complementary sequences are given. The initial sequences are prolonged to the left and to the right by using sequences from the latter set, respectively. The iterations of these prolongations produce “computations” of possibly arbitrary length. These processes stop when a complete double stranded sequence is obtained. Sticker systems will generate only regular languages without restrictions. Additional restrictions can be imposed on the matching pairs of strands to obtain more powerful languages. Several types of sticker systems are shown to have the same power as regular grammars; one type is found to represent all linear languages whereas another one is proved to be able to represent any recursively enumerable language. The main aim of this research is to introduce and study sticker systems over monoids in which with each sticker operation, an element of a monoid is associated and a complete double stranded sequence is considered to be valid if the computation of the associated elements of the monoid produces the neutral element. Moreover, the sticker system over monoids is defined in this study

Piecewise-polynomial associated transform macromodeling algorithm for fast nonlinear circuit simulation

We present a piecewise-polynomial based associated transform algorithm (PWPAT) for macromodeling nonlinear circuits in system-level circuit design. The generated reduced model can provide both global and local accuracies with the most compact dimension. Numerical examples compare it with existing algorithms and verify its superior accuracy in higher order harmonics simulation over traditional Trajectory Piecewise-Linear (TPWL) approach. © 2013 IEEE.published_or_final_versio

On Measuring Condensate Fraction in Superconductors

An analysis of off-diagonal long-range order in superconductors shows that the spin-spin correlation function is significantly influenced by the order if the order parameter is anisotropic on a microscopic scale. Thus, magnetic neutron scattering can provide a direct measurement of the condensate fraction of a superconductor. It is also argued that recent measurements in high temperature superconductors come very close to achieving this goal.Comment: 4 pages, 1 eps figure, RevTex. A new possibility in the underdoped regime is added. Other corrections are mino

A Proposal to Detect Dark Matter Using Axionic Topological Antiferromagnets

Antiferromagnetically doped topological insulators (A-TI) are among the candidates to host dynamical axion fields and axion-polaritons; weakly interacting quasiparticles that are analogous to the dark axion, a long sought after candidate dark matter particle. Here we demonstrate that using the axion quasiparticle antiferromagnetic resonance in A-TI's in conjunction with low-noise methods of detecting THz photons presents a viable route to detect axion dark matter with mass 0.7 to 3.5 meV, a range currently inaccessible to other dark matter detection experiments and proposals. The benefits of this method at high frequency are the tunability of the resonance with applied magnetic field, and the use of A-TI samples with volumes much larger than 1 mm$^3$.Comment: 6 pages, 4 figures. v2 accepted for publication in Physical Review Letters. Many points clarified, some parameter estimates revise

Finite-Size Studies on the SO(5) Symmetry of the Hubbard Model

We present numerical evidence for the approximate SO(5) symmetry of the Hubbard model on a 10 site cluster. Various dynamic correlation functions involving the $\pi$ operators, the generators of the SO(5) algebra, are studied using exact diagonalisation, and are found to possess sharp collective peaks. Our numerical results also lend support on the interpretation of the recent resonant neutron scattering peaks in the YBCO superconductors in terms of the Goldstone modes of the spontaneously broken SO(5) symmetry.Comment: 4 pages, Rev-Tex, includes 2 eps figure

Co-simulation of RFIC with bondwire antenna via retarded PEEC method

We present an antenna modeling method based on partial element equivalent circuit (PEEC) theory. The antenna is modeled as an equivalent circuit of lumped circuit elements, which enables circuit co-simulation between the antenna and circuits in both time and frequency domains. Antenna radiation is captured as an equivalent radiation resistor. For verification, a 2.4-GHz transmitter with bondwire antenna was implemented in a standard digital 0.35μm CMOS technology. Measurement shows good agreement with the proposed model. This model can be applied to any other on-chip electromagnetic structures. © 2012 IEEE.published_or_final_versio