In this paper, the stability problem of sliding mode (SM) controlled buck converters affected by the switching nonlinearity is investigated. In order to deduce the transfer function, the small signal model of buck converters is established in continuous conduction mode. Instead of the traditional time-domain approach based on Lyapunov theorem, the description function (DF) is introduced to realize the linearization of the switching nonlinearity under the direct ON/OFF control of SM controller. By Nyquist stability criterion, the system stability is proved to be determined by the implementation of hysteresis modulation. Comparative simulations with/without hysteresis modulation validate this paper.

In this paper, the frequency analysis of second-order sliding mode (SM) controlled buck converters is investigated by utilizing the description function (DF) approach. The transfer function of the buck converter is established on the basis of the small signal model. Taking the commonly-used super-twisting algorithm as an example, a second-order SM controller is designed, which consists of two nonlinear components. Then by adopting the DF approach, the linearized counterparts of the both can be further deduced, following the block diagram of the whole closed-loop control system. Based on the Nyquist stability criterion, the system stability is studied, which proves the inevitable existence of periodic oscillations caused by the nonlinearity of the controller. Meanwhile, the influence of the controller parameters with the frequency characteristics is investigated. Simulations validate this paper.

We present a design study of the Deep Insights Anywhere, Anytime (DIA2) platform, a web-based visual analytics system that allows program managers and academic staff at the U.S. National Science Foundation to search, view, and analyze their research funding portfolio. The goal of this system is to facilitate users' understanding of both past and currently active research awards in order to make more informed decisions of their future funding. This user group is characterized by high domain expertise yet not necessarily high literacy in visualization and visual analytics-they are essentially casual experts-and thus require careful visual and information design, including adhering to user experience standards, providing a self-instructive interface, and progressively refining visualizations to minimize complexity. We discuss the challenges of designing a system for casual experts and highlight how we addressed this issue by modeling the organizational structure and workflows of the NSF within our system. We discuss each stage of the design process, starting with formative interviews, prototypes, and finally live deployments and evaluation with stakeholders.

For information visualization researchers, eye tracking has been a useful tool to investigate research participants' underlying cognitive processes by tracking their eye movements while they interact with visual techniques. We used an eye tracker to better understand why participants with a variant of a tabular visualization called `SimulSort' outperformed ones with a conventional table and typical one-column sorting feature (i.e., Typical Sorting). The collected eye-tracking data certainly shed light on the detailed cognitive processes of the participants; SimulSort helped with decision-making tasks by promoting efficient browsing behavior and compensatory decision-making strategies. However, more interestingly, we also found unexpected eye-tracking patterns with SimulSort. We investigated the cause of the unexpected patterns through a crowdsourcing-based study (i.e., Experiment 2), which elicited an important limitation of the eye tracking method: incapability of capturing peripheral vision. This particular result would be a caveat for other visualization researchers who plan to use an eye tracker in their studies. In addition, the method to use a testing stimulus (i.e., influential column) in Experiment 2 to verify the existence of such limitations would be useful for researchers who would like to verify their eye tracking results.

Numerical simulations of the strong nuclear force, known as quantum chromodynamics or QCD, have proven to be a demanding, forefront problem in high-performance computing. In this report, we describe a new computer, QCDOC (QCD On a Chip), designed for optimal price/performance in the study of QCD. QCDOC uses a six-dimensional, low-latency mesh network to connect processing nodes, each of which includes a single custom ASIC, designed by our collaboration and built by IBM, plus DDR SDRAM. Each node has a peak speed of 1Gigaflops and two 12,288node, 10+ Teraflops machines are to be completed in the fall of 2004. Currently, a 512 node machine is running, delivering efficiencies as high as 45% of peak on the conjugate gradient solvers that dominate our calculations and a 4096-node machine with a cost of $1.6M is under construction. This should give us a price/performance less than $1per sustained Megaflops.