Massively parallel algorithms for trace-driven cache simulations

Considers the use of massively parallel architectures to execute a trace-driven simulation of a single cache set. A method is presented for the least-recently-used (LRU) policy, which, regardless of the set size C, runs in time O(log N) using N processors on the EREW (exclusive read, exclusive write) parallel model. A simpler LRU simulation algorithm is given that runs in O(C log N) time using N/log N processors. We present timings of this algorithm's implementation on the MasPar MP-1, a machine with 16384 processors. A broad class of reference-based line replacement policies are considered, which includes LRU as well as the least-frequently-used (LFU) and random replacement policies. A simulation method is presented for any such policy that, on any trace of length N directed to a C line set, runs in O(C log N) time with high probability using N processors on the EREW model. The algorithms are simple, have very little space overhead, and are well suited for SIMD implementation     

Using digital but physical surrogates to mediate awareness, communication and privacy in media spaces

Digital but physical surrogates are tangible representations of remote people (typically members of small intimate teams), positioned within an office and under digital control. Surrogates selectively collect and present awareness information about the people they represent. They also react to people's explicit and implicit physical actions: a person's explicit acts include grasping and moving them, while their implicit acts include how they move towards or away from the surrogate. By responding appropriately to these physical actions of people, surrogates can control the communication capabilities of a media space in a natural way. Surrogates also balance awareness and privacy by limiting and abstracting how activities are portrayed, and by offering different levels of salience to its users. The combination of all these attributes means that surrogates can make it easy for intimate collaborators to move smoothly from awareness of each other to casual interaction while mitigating privacy and distraction concerns.Exploring different surrogate designs and how they work together can be straightforward if a good infrastructure is in place. We use anawareness server based on a distributed model-view-controller architecture, which automatically captures, stores and distributes events. We also package surrogates as physical widgets orphidgets with a well-defined interface; this makes it easy for a programmer to plug a surrogate into the awareness server as a controller (to generate awareness events), or view (to display events that others have produced), or both. Because surrogate design, implementation and use is still a new discipline, we also present several issues and next steps.     

Two heads better than one: pattern discovery in time-evolving multi-aspect data

Data stream values are often associated with multiple aspects. For example each value observed at a given time-stamp from environmental sensors may have an associated type (e.g., temperature, humidity, etc.) as well as location. Time-stamp, type and location are the three aspects, which can be modeled using a tensor (high-order array). However, the time aspect is special, with a natural ordering, and with successive time-ticks having usually correlated values. Standard multiway analysis ignores this structure. To capture it, we propose 2 Heads Tensor Analysis (2-heads), which provides a qualitatively different treatment on time. Unlike most existing approaches that use a PCA-like summarization scheme for all aspects, 2-heads treats the time aspect carefully. 2-heads combines the power of classic multilinear analysis with wavelets, leading to a powerful mining tool. Furthermore, 2-heads has several other advantages as well: (a) it can be computed incrementally in a streaming fashion, (b) it has a provable error guarantee and, (c) it achieves significant compression ratio against competitors. Finally, we show experiments on real datasets, and we illustrate how 2-heads reveals interesting trends in the data. This is an extended abstract of an article published in the Data Mining and Knowledge Discovery journal.     

The back-buffer algorithm: An extension of the radiosity method to dynamic environments

An efficient algorithm is introduced for the production of realistic image sequences of dynamic environments. The practicality of the radiosity method, which computes the interreflection of light within complex diffuse environments independent of viewpoint, is extended to dynamic environments where the paths of moving objects have been predefined. The algorithm takes advantage of the object coherence between static portions of an environment. A preprocessing stage executes once for a given image sequence and precalculates constant geometrical relationships in the environment. When the environment geometry changes, an update stage determines the global illumination using information provided by the preprocessor and the current positions of all moving objects. Test environments show speedups of at least twenty-five times over previous radiosity methods.     

Dbxtool: A window-based symbolic debugger for sun workstations

Dbxtool is a window- and mouse-based debugger for C, Pascal and FORTRAN programs running on Sun workstations. Its use of the mouse as the primary input mechanism eliminates the need to type variables, line numbers, breakpoints and most commands. Its multiple windows provide several qualitatively different perspectives on the debugging problem. Compared to the Unix 4.2 BSD dbx from which it is derived, it has been extended with the abilities to debug multiple-process programs, already-running processes, and the Sun Operating System kernel.     

Learning about tools in infancy.

These experiments explored the role of prior experience in 12- to 18-month-old infants' tool-directed actions. In Experiment 1, infants' use of a familiar tool (spoon) to accomplish a novel task (turning on lights inside a box) was examined. Infants tended to grasp the spoon by its handle even when doing so made solving the task impossible (the bowl did not fit through the hole in the box, but the handle did) and even though the experimenter demonstrated a bowl-grasp. In contrast, infants used a novel tool flexibly and grasped both sides equally often. In Experiment 2, infants received training using the novel tool for a particular function; 3 groups of infants were trained to use the tool differently. Later, infants' performance was facilitated on tasks that required infants to grasp the part of the tool they were trained to grasp. The results suggest that (a) infants' prior experiences with tools are important to understanding subsequent tool use, and (b) rather than learning about tool function (e.g., hammering), infants learn about which part of the tool is meant to be held, at least early in their exposure to a novel tool. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distributed dynamic lane reversal and rerouting for traffic delay reduction

Traffic congestion is a major source of delays in modern road networks. Motivated by this, we propose two distributed algorithms to reduce delays: a dynamic lane reversal algorithm and a rerouting algorithm. When there is a density imbalance on a road, time can be saved by reallocating lanes from the less dense side to the more dense side, which motivates dynamic lane reversal. When a road has greater density than nearby roads, time can be saved by redirecting flow into the least congested roads, this motivates dynamic rerouting. Given a communication system between infrastructure and vehicles on the road, the local state of the network can be approximated and utilised by the algorithms to minimise travel time. In order to provide a better fundamental understanding of the system dynamics, we analyse equilibrium conditions for the system and prove convergence of the lane reversal algorithm to a critical point. Overall performance is also examined in simulation.     

Continuous-time norm-constrained Kalman filtering

This paper considers continuous-time state estimation when part of the state estimate or the entire state estimate is norm-constrained. In the former case continuous-time state estimation is considered by posing a constrained optimization problem. The optimization problem can be broken up into two separate optimization problems, one which solves for the optimal observer gain associated with the unconstrained state estimates, while the other solves for the optimal observer gain associated with the constrained state estimates. The optimal constrained state estimate is found by projecting the time derivative of an unconstrained estimate onto the tangent space associated with the norm constraint. The special case where the entire state estimate is norm-constrained is briefly discussed. The utility of the filtering results developed are highlighted through a spacecraft attitude estimation example. Numerical simulation results are included.     

Color-defective vision and computer graphics displays

A color space defined by the fundamental spectral sensitivity functions of the human visual system is used to assist in the design of computer graphics displays for color-deficient users. The functions are derived in terms of the CIE standard observer color-matching functions. The Farnsworth-Munsell 100-hue test, a widely used color vision test administered using physical color samples, is then implemented on a digitally controlled color television monitor. The flexibility of this computer graphics medium is then used to extend the Farnsworth-Munsell test in a way that improves the specificity of the diagnoses rendered by the test. The issue of how the world appears to color-deficient observers is addressed, and a full-color image is modified to represent a color-defective view of the scene. Specific guidelines are offered for the design of computer graphics displays that will accommodate almost all color-deficient users     

A design for an immersable pressure-capacitance gauge

An immersable pressure-capacitance gauge has been designed which has a linearity over a pressure range, is non-magnetic and has twice the sensitivity of a single diaphragm