Promoting deep learning through design - discussion, student activity and assessment

There is widespread evidence that Australia is currently facing falling student participation rates in science and mathematics subjects at secondary school and university undergraduate levels. The future implications of this science-deficit are widely acknowledged. Unfortunately, science teaching itself is also widely seen as being dull, too content-heavy, delivered to mass-audiences and assessed in ways promoting surface approaches to learning. To address these issues, and issues relating to the apparent lack of challenge for very able students in their first year at university, The University of Queensland developed the Advanced Study Program in Science (ASPinS). This initiative offers an enhanced learning experience to a select group of high-achieving students in addition to their existing undergraduate study in a Science-related degree program. ASPinS offers these students the opportunity to interact with leading research scientists, broaden their understanding of important scientific issues, experience new interactive learning opportunities, undertake research projects and obtain an authentic insight into science as a career. This presentation, however, will only focus on the unique first year course offered within the 3 year ASPinS experience – BIOL1017 “Perspectives in Science”. In this course students are encouraged to think about important current scientific issues from different perspectives – both scientific and non-scientific. Panels of expert scientists use their knowledge and experience to present real scientific issues for students to examine and discuss. These panel discussions cover a spectrum of medical, environmental and social issues, covering different viewpoints and possible solutions. Combining this effective panel model with an array of student-led activities provides an ideal environment for learning. Students are made to apply their new knowledge, discuss issues and construct thoughts, opinions and products – depending on the specifically designed activities. Relevant assessment tasks include group-writing activities and oral presentations which enable students to demonstrate their learning through authentic contexts that are carefully designed to influence the way students learn. Authentic assessment tasks enable students to see a purpose for the product (assessment) they are producing while at the same time enabling them to synthesise the various scientific ‘facts’ and issues they have been discussing. This level of assessment activity, by its nature, encourages higher-order learning. Student evaluations have consistently confirmed that the key to the success of each Module within the course lies in the breadth of speakers selected to represent the different angles associated with the topic under discussion and the related activities and assessment tasks. The findings indicate that students value the opportunity to explore the multi-disciplinary nature of science-related issues and to actually discuss the issues. The “Perspectives in Science” course is a model for the success of combining teaching and learning theory and scholarship, to a particular set of objectives, to create a highly effective learning environment and a meaningful student experience

Permanent current from non-commutative spin algebra

We show that a spontaneous electric current is induced in a nano-scale conducting ring just by putting three ferromagnets. The current is a direct consequence of the non-commutativity of the spin algebra, and is proportional to the non-coplanarity (chirality) of the magnetization vectors. The spontaneous current gives a natural explanation to the chirality-driven anomalous Hall effect.Comment: 7 pages, 4 figures on separate pag

Exact ground-state correlation functions of the one-dimensional strongly correlated electron models with the resonating-valence-bond ground state

We investigate the one-dimensional strongly correlated electron models which have the resonating-valence-bond state as the exact ground state. The correlation functions are evaluated exactly using the transfer matrix method for the geometric representations of the valence-bond states. In this method, we only treat matrices with small dimensions. This enables us to give analytical results. It is shown that the correlation functions decay exponentially with distance. The result suggests that there is a finite excitation gap, and that the ground state is insulating. Since the corresponding non-interacting systems may be insulating or metallic, we can say that the gap originates from strong correlation. The persistent currents of the present models are also investigated and found to be exactly vanishing.Comment: 59 pages, REVTeX 3.0, Figures are available on reques

Non-magnetic impurities in two dimensional superconductors

A numerical approach to disordered 2D superconductors described by BCS mean field theory is outlined. The energy gap and the superfluid density at zero temperature and the quasiparticle density of states are studied. The method involves approximate self-consistent solutions of the Bogolubov-de$\,$Gennes equations on finite square lattices. Where comparison is possible, the results of standard analytic approaches to this problem are reproduced. Detailed modeling of impurity effects is practical using this approach. The {\it range} of the impurity potential is shown to be of {\it quantitative importance} in the case of strong potential scatterers. We discuss the implications for experiments, such as the rapid suppression of superconductivity by Zn doping in Copper-Oxide superconductors.Comment: 16 pages, latex, 8 figures( available upon request

Persistent current of two-chain Hubbard model with impurities

The interplay between impurities and interactions is studied in the gapless phase of two-chain Hubbard model in order to see how the screening of impurity potentials due to repulsive interactions in single-chain model will be changed by increasing the number of channels. Renormalization group calculations show that charge stiffness, and hence persistent current, of the two-chain model are less enhanced by interactions than single chain case.Comment: 4 Pages, RevTeX, No figures, Submitted to PR

Local Electronic Structure of a Single Magnetic Impurity in a Superconductor

The electronic structure near a single classical magnetic impurity in a superconductor is determined using a fully self-consistent Koster-Slater algorithm. Localized excited states are found within the energy gap which are half electron and half hole. Within a jellium model we find the new result that the spatial structure of the positive-frequency (electron-like) spectral weight (or local density of states), can differ strongly from that of the negative frequency (hole-like) spectral weight. The effect of the impurity on the continuum states above the energy gap is calculated with good spectral resolution for the first time. This is also the first three-dimensional self-consistent calculation for a strong magnetic impurity potential.Comment: 13 pages, RevTex, change in heuristic picture, no change in numerical result

Re-parameterization Invariance in Fractional Flux Periodicity

We analyze a common feature of a nontrivial fractional flux periodicity in two-dimensional systems. We demonstrate that an addition of fractional flux can be absorbed into re-parameterization of quantum numbers. For an exact fractional periodicity, all the electronic states undergo the re-parameterization, whereas for an approximate periodicity valid in a large system, only the states near the Fermi level are involved in the re-parameterization.Comment: 4 pages, 1 figure, minor changes, final version to appear in J. Phys. Soc. Jp

Extended Impurity Potential in a d_{x^2-y^2} Superconductor

We investigate the role of a finite potential range of a nonmagnetic impurity for the local density of states in a d_{x^2-y^2} superconductor. Impurity induced subgap resonances are modified by the appearance of further scattering channels beyond the $s$--wave scattering limit. The structure of the local density of states (DOS) in the vicinity of the impurity is significantly enhanced and therefore improves the possibility for observing the characteristic anisotropic spatial modulation of the local DOS in a d_{x^2-y^2} superconductor by scanning tunneling microscopy.Comment: 4 pages, Revtex, with 4 embedded eps figures. Submitted to Phys. Rev. Let

Manipulation of P-TEFb control machinery by HIV: recruitment of P-TEFb from the large form by Tat and binding of HEXIM1 to TAR

Basal transcription of the HIV LTR is highly repressed and requires Tat to recruit the positive transcription elongation factor, P-TEFb, which functions to promote the transition of RNA polymerase II from abortive to productive elongation. P-TEFb is found in two forms in cells, a free, active form and a large, inactive complex that also contains 7SK RNA and HEXIM1 or HEXIM2. Here we show that HIV infection of cells led to the release of P-TEFb from the large form. Consistent with Tat being the cause of this effect, transfection of a FLAG-tagged Tat in 293T cells caused a dramatic shift of P-TEFb out of the large form to a smaller form containing Tat. In vitro, Tat competed with HEXIM1 for binding to 7SK, blocked the formation of the P-TEFb–HEXIM1–7SK complex, and caused the release P-TEFb from a pre-formed P-TEFb–HEXIM1–7SK complex. These findings indicate that Tat can acquire P-TEFb from the large form. In addition, we found that HEXIM1 binds tightly to the HIV 5′ UTR containing TAR and recruits and inhibits P-TEFb activity. This suggests that in the absence of Tat, HEXIM1 may bind to TAR and repress transcription elongation of the HIV LTR

Inhibition of HIV-1 replication by P-TEFb inhibitors DRB, seliciclib and flavopiridol correlates with release of free P-TEFb from the large, inactive form of the complex

<p>Abstract</p> <p>Background</p> <p>The positive transcription elongation factor, P-TEFb, comprised of cyclin dependent kinase 9 (Cdk9) and cyclin T1, T2 or K regulates the productive elongation phase of RNA polymerase II (Pol II) dependent transcription of cellular and integrated viral genes. P-TEFb containing cyclin T1 is recruited to the HIV long terminal repeat (LTR) by binding to HIV Tat which in turn binds to the nascent HIV transcript. Within the cell, P-TEFb exists as a kinase-active, free form and a larger, kinase-inactive form that is believed to serve as a reservoir for the smaller form.</p> <p>Results</p> <p>We developed a method to rapidly quantitate the relative amounts of the two forms based on differential nuclear extraction. Using this technique, we found that titration of the P-TEFb inhibitors flavopiridol, DRB and seliciclib onto HeLa cells that support HIV replication led to a dose dependent loss of the large form of P-TEFb. Importantly, the reduction in the large form correlated with a reduction in HIV-1 replication such that when 50% of the large form was gone, HIV-1 replication was reduced by 50%. Some of the compounds were able to effectively block HIV replication without having a significant impact on cell viability. The most effective P-TEFb inhibitor flavopiridol was evaluated against HIV-1 in the physiologically relevant cell types, peripheral blood lymphocytes (PBLs) and monocyte derived macrophages (MDMs). Flavopiridol was found to have a smaller therapeutic index (LD₅₀/IC₅₀) in long term HIV-1 infectivity studies in primary cells due to greater cytotoxicity and reduced efficacy at blocking HIV-1 replication.</p> <p>Conclusion</p> <p>Initial short term studies with P-TEFb inhibitors demonstrated a dose dependent loss of the large form of P-TEFb within the cell and a concomitant reduction in HIV-1 infectivity without significant cytotoxicity. These findings suggested that inhibitors of P-TEFb may serve as effective anti-HIV-1 therapies. However, longer term HIV-1 replication studies indicated that these inhibitors were more cytotoxic and less efficacious against HIV-1 in the primary cell cultures.</p