On-Line File Caching

In the on-line file-caching problem problem, the input is a sequence of requests for files, given on-line (one at a time). Each file has a non-negative size and a non-negative retrieval cost. The problem is to decide which files to keep in a fixed-size cache so as to minimize the sum of the retrieval costs for files that are not in the cache when requested. The problem arises in web caching by browsers and by proxies. This paper describes a natural generalization of LRU called Landlord and gives an analysis showing that it has an optimal performance guarantee (among deterministic on-line algorithms). The paper also gives an analysis of the algorithm in a so-called ``loosely'' competitive model, showing that on a ``typical'' cache size, either the performance guarantee is O(1) or the total retrieval cost is insignificant.Comment: ACM-SIAM Symposium on Discrete Algorithms (1998

Nearly Linear-Work Algorithms for Mixed Packing/Covering and Facility-Location Linear Programs

We describe the first nearly linear-time approximation algorithms for explicitly given mixed packing/covering linear programs, and for (non-metric) fractional facility location. We also describe the first parallel algorithms requiring only near-linear total work and finishing in polylog time. The algorithms compute $(1+\epsilon)$-approximate solutions in time (and work) $O^*(N/\epsilon^2)$, where $N$ is the number of non-zeros in the constraint matrix. For facility location, $N$ is the number of eligible client/facility pairs

A Bound on the Sum of Weighted Pairwise Distances of Points Constrained to Balls

We consider the problem of choosing Euclidean points to maximize the sum of their weighted pairwise distances, when each point is constrained to a ball centered at the origin. We derive a dual minimization problem and show strong duality holds (i.e., the resulting upper bound is tight) when some locally optimal configuration of points is affinely independent. We sketch a polynomial time algorithm for finding a near-optimal set of points.Comment: Cornell ORIE Tech Repor

Improved ranging systems

Spacecraft range measurements have provided the most accurate tests, to date, of some relativistic gravitational parameters, even though the measurements were made with ranging systems having error budgets of about 10 meters. Technology is now available to allow an improvement of two orders of magnitude in the accuracy of spacecraft ranging. The largest gains in accuracy result from the replacement of unstable analog components with high speed digital circuits having precisely known delays and phase shifts

Does PAL work? An exploration of affect amongst First-year HE in FE students

The study evaluates a peer-assisted learning (PAL) scheme as an effective strategy in alleviating levels of negative emotions and, in the process, contributes to explorations of affect in first-year students in an HE in FE environment, with a particular focus on anxiety and related emotions. Various types of anxieties are defined in the context of a student’s experience in HE, followed by an explanation of the present interventional study in an HE in FE institution, including the survey method used to collect data analyzed through SPSS. Surprisingly, the main findings are that overall anxiety and worry increased for students belonging to most faculties with time, regardless of participation in the PAL scheme. A positive finding was nonetheless that anxiety levels increased more steadily for students who belonged to the control group. The PAL scheme may have thus influenced how less anxious PAL students felt, compared to those who did not participate in the PAL scheme who were left feeling more anxious at the end of the semester