Third-order magnetic susceptibility of the frustrated square-lattice antiferromagnet

We present results from our analysis of the finite-temperature properties of the spin 1/2 $J_{1}$-$J_{2}$ Heisenberg model on a square lattice. The analysis is based on the exact diagonalization of small clusters with 16 and 20 sites utilizing the finite-temperature Lanczos method. In particular, we focus on the temperature dependence of the third-order magnetic susceptibility as a method to resolve the ambiguity of exchange constants. We discuss the entire range of the frustration angle $\phi=\tan^{-1}(J_{2}/J_{1})$ parameterizing the different possible phases of the model, including the large region in the phase diagram with at least one ferromagnetic exchange constant.Comment: 2 pages, 2 figure

BIBS: A Lecture Webcasting System

The Berkeley Internet Broadcasting System (BIBS) is a lecture webcasting system developed and operated by the Berkeley Multimedia Research Center. The system offers live remote viewing and on-demand replay of course lectures using streaming audio and video over the Internet. During the Fall 2000 semester 14 classes were webcast, including several large lower division classes, with a total enrollment of over 4,000 students. Lectures were played over 15,000 times per month during the semester. The primary use of the webcasts is to study for examinations. Students report they watch BIBS lectures because they did not understand material presented in lecture, because they wanted to review what the instructor said about selected topics, because they missed a lecture, and/or because they had difficulty understanding the speaker (e.g., non-native English speakers). Analysis of various survey data suggests that more than 50% of the students enrolled in some large classes view lectures and that as many as 75% of the lectures are played by members of the Berkeley community. Faculty attitudes vary about the virtues of lecture webcasting. Some question the use of this technology while others believe it is a valuable aid to education. Further study is required to accurately assess the pedagogical impact that lecture webcasts have on student learning

Extended quantum U(1)-liquid phase in a three-dimensional quantum dimer model

Recently, quantum dimer models, in which the system can tunnel between different classical dimer configurations, have attracted a great deal of interest as a paradigm for the study of exotic quantum phases. Much of this excitement has centred on the claim that a certain class of quantum dimer model, defined on a bipartite lattice, can support a quantum U(1)-liquid phase with deconfined fractional excitations in three dimensions. These fractional monomer excitations are quantum analogues of the magnetic monopoles found in spin ice. In this article we use extensive quantum Monte Carlo simulations to establish the ground-state phase diagram of the quantum dimer model on the three-dimensional, bipartite, diamond lattice as a function of the ratio {\mu} of the potential to kinetic energy terms in the Hamiltonian. We find that, for {\mu}_c = 0.75 +/- 0.04, the model undergoes a first-order quantum phase transition from an ordered "R-state" into an extended quantum U(1)-liquid phase, which terminates in a quantum critical "RK point" for {\mu}=1. This confirms the published field-theoretical scenario. We present detailed evidence for the existence of the U(1)-liquid phase, and indirect evidence for the existence of its photon and monopole excitations. We also explore some of the technical ramifications of this analysis, benchmarking quantum Monte Carlo against a variety of exact and perturbative results, comparing different variational wave functions. The ergodicity of the quantum dimer model on a diamond lattice is discussed in detail. These results complete and extend the analysis previously published in [O. Sikora et al., Phys. Rev. Lett. 103, 247001 (2009)].Comment: 19 pages, 25 figures - we added a new figure and updated the manuscrip

The World Language Teacher Shortage: Taking a New Direction

Since the end of World War II, international leaders have made calls addressing the world language teacher shortage. For almost 70 years, such rhetoric has been advanced, yet world language teacher shortages remain in many countries such as Australia, Canada, Ireland, New Zealand, the United Kingdom, and the United States. In this article, the authors discuss the past and current state of affairs of the shortage before advancing ideas for language teacher recruitment and retention to which a variety of stakeholders (e.g., parents, administrators, language teacher associations) can contribute immediately in order to address the world language teacher shortage in earnest

A quantum liquid with deconfined fractional excitations in three dimensions

Excitations which carry "fractional" quantum numbers are known to exist in one dimension in polyacetylene, and in two dimensions, in the fractional quantum Hall effect. Fractional excitations have also been invoked to explain the breakdown of the conventional theory of metals in a wide range of three-dimensional materials. However the existence of fractional excitations in three dimensions remains highly controversial. In this Letter we report direct numerical evidence for the existence of a quantum liquid phase supporting fractional excitations in a concrete, three-dimensional microscopic model - the quantum dimer model on a diamond lattice. We demonstrate explicitly that the energy cost of separating fractional monomer excitations vanishes in this liquid phase, and that its energy spectrum matches that of the Coulomb phase in (3+1) dimensional quantum electrodynamics.Comment: 4 pages, 4 figures; revised version, new figures; accepted for publication in Physical Review Letter

Upgrading the SR-30 Miniature Turbojet for Adaptable Exhaust

The California Polytechnic State University, San Luis Obispo (Cal Poly, SLO) Aerospace Department is requesting a variable nozzle adaptation for their SR-30 turbojet engine. The nozzle is intended for laboratory use in sophomore and junior level courses to supplement instruction on the effects that exhaust behavior has on the performance of propulsion technologies. Topics covered during a performance study of the SR-30 turbojet engine will include, but are not limited to: Brayton Cycle analysis, turbojet operation in ideal and non-ideal test conditions, instrumentation limitations, and basic nozzle operation. The SR-30 turbojet engine is similar in design and operation to engines used to power full-size jets, but is scaled down in size for practical use in educational laboratories. Current designs for variable area nozzles in the aeronautics industry are tailored for use on large jet engines, rather than small educational engines such as the SR-30 turbojet. Therefore, this senior project seeks to adapt existing technology designs to an appropriate scale, and manufacture a variable-area nozzle that will allow for controlled exhaust-flow restriction. The solution proposed in this document draws on existing fighter jet variable nozzles J85 and F119-PW-100 for inspiration in nozzle flap layout and uses common methods of robotic motion control, including linear electronic actuators and hydraulic actuators. Given the scale of the existing turbojet exhaust pipe, this senior project team, “TurboTRIO”, has determined that a circular nozzle would be difficult to actuate in an accurate, flexible, and durable manner. Similarly, design specifications such as thrust-vectoring capabilities and hydraulic control systems present themselves as unnecessarily complicated for the scope of this project. As such, these were likewise discarded. The proposed design is, consequently, a converging-diverging nozzle with a fixed-area converging duct and throat, and a variable-area diverging duct. The diverging duct will have a rectangular cross-section, and will be composed of two stationary flaps and two independently-actuated flaps controlled via mechanical linear actuation. This design will allow for educational demonstrations and performance analyses of a sonic converging nozzle, supersonic converging-diverging nozzle, and potentially engine thrust vectoring

Neuroimaging for the Affective Brain Sciences, and Its Role in Advancing Consumer Neuroscience

To fully understand the driving behaviour of a car it is absolutely inevitable to investigate all its hidden parts underneath the surface and to find out what their functions are. To fully understand human behaviour we need to complete traditional behavioural measures with neuroimaging data that allow us to look inside the brain. Only via neuroimaging methodology do we have access to underlying brain processes that guide our behaviour without leading to any conscious reportable traces that show up in questionnaires. On top of that, especially when emotion-related explicit responses are required questionnaires provide us with biased responses due to cognitive influences. These responses can be far away from true underlying emotion-related information. The discrepancy between biased and unbiased emotion-related information processing is of utmost interest for both basic affective neuroscience and consumer neuroscience

EFFECTS OF BACKPACK DESIGN AND FATIGUE ON POSTURE IN CHILDREN

The purpose of this study was to determine which hip bell/frame sheet combination reduced postural changes associated with load carriage in children. Thirty-six 10·12 year olds walked 1000m around a track in 3 randomly assigned hip belt and frame sheet conditions. Two strides were digitized at 100 and 900m with mean head and trunk angles, as well as posture across the gait cycle recorded. Hip belt and frame sheet design did not alter head flexion separately, but interaction between the design features indicated less compromise in posture with the Back Balancer. The solid and padded frame sheet reduced counterbalance of the weight in the trunk