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Papers by Steven Phillips

Siam Journal on Computing, 1993

We investigate the all-pairs shortest paths problem in weighted graphs. We present an algorithm|t... more We investigate the all-pairs shortest paths problem in weighted graphs. We present an algorithm|the Hidden Paths Algorithm|that nds these paths in time O(m n+n 2 log n), where m is the number of edges participating in shortest paths. Our algorithm is a practical substitute for Dijkstra's algorithm. We argue that m is likely to be small in practice, since m = O(n logn) with high probability for many probability distributions on edge weights. We also prove an (mn) lower bound on the running time of any path-comparison based algorithm for the all-pairs shortest paths problem. Path-comparison based algorithms form a natural class containing the Hidden Paths Algorithm, as well as the algorithms of Dijkstra and Floyd. Lastly, we consider generalized forms of the shortest paths problem, and show that many of the standard shortest paths algorithms are e ective in this more general setting. real interval 0; 1] or the uniform distribution on the range f1; : : :; n 2 g. The Hidden

Theoretical Computer Science, 1994

We study preemptive, nonclairvoyant scheduling schemes where the scheduler has no knowledge of th... more We study preemptive, nonclairvoyant scheduling schemes where the scheduler has no knowledge of the jobs&amp;#x27; characteristics. We develop a model for evaluating scheduling strategies for single and multiprocessor systems. This model compares the nonclairvoyant scheduler against ...

Journal of Algorithms, 1996

One of the oldest and simplest variants of multiprocessor scheduling is the on-line scheduling pr... more One of the oldest and simplest variants of multiprocessor scheduling is the on-line scheduling problem studied by Graham in 1966. This problem can also be formulated as an on-line load balancing problem, and we will use this formulation throughout this paper. The jobs arrive online and must be immediately and irrevocably assigned to one of m identical machines without any knowledge of future jobs. The size of a job is known on arrival. The load of a machine is the sum of the sizes of the jobs assigned to it. The goal of the load balancer is to minimize the maximum load on any machine.

Virtually all research in scheduling theory has been concerned with clairvoyant scheduling where ... more Virtually all research in scheduling theory has been concerned with clairvoyant scheduling where it is assumed that the characteristics of a job (in particular, its execution time,release time and dependence on other jobs) are known a priori. This assumption is invalidfor scheduling problems that arise in time-sharing operating systems where the schedulermust provide fast turnaround for processes being generated by

Annals of Thoracic Surgery, 1983

Improved technology has allowed us to develop support pumps that can be applied rapidly and safel... more Improved technology has allowed us to develop support pumps that can be applied rapidly and safely. A system utilizing thin-walled (4 mm inner diameter) percutaneously inserted sheaths has been designed for rapid bedside arterial and central venous cannulation to establish femoral arterial and venous cardiopulmonary bypass. The system utilizes two 30-cm-long large-bore, thin-walled (end and side holes) venous cannulas and a single 15-cm-long (end hole) arterial reperfusion cannula, which is connected to a pediatric oxygenator and a vortex pump head. Five patients with refractory cardiac arrest who could not be resuscitated by conventional means were revived with this system. Application time was approximately five minutes. This system appears to be an easily applied and reliable short-term mechanical support device.

Annals of Thoracic Surgery, 1989

Percutaneous cardiopulmonary bypass (CPB) was used in 22 patients: 7 patients with cardiac arrest... more Percutaneous cardiopulmonary bypass (CPB) was used in 22 patients: 7 patients with cardiac arrest due to acute myocardial infarction; 4 patients in cardiac arrest because of failed angioplasty; 1 patient for high-risk elective angioplasty; 1 patient with massive pulmonary emboli; 2 patients with hypothermia; 2 pediatric patients (1 with sepsis and 1 in combination with extracorporeal membrane oxygenator support); 1 patient with refractory arrhythmia; and 4 patients with trauma. Percutaneous CPB involves a modified Seldinger technique that is easily applied. All patients except those with massive mergency cardiopulmonary bypass (CPB) through E surgical exposure of the femoral artery and veins is an accepted technique [1-4]. Although excellent cardiopulmonary resuscitation and support can be accomplished by this approach, it has never achieved widespread popularity for emergency application. Not only does it require a skillful surgical team, but it is difficult to implement in the environment where a patient is undergoing cardiopulmonary resuscitation. Traditional circulatory support systems such as intraaortic balloon pumping [5-111 have achieved popularity because of their effectiveness and ease of emergency application to patients in extremis.

Annals of Thoracic Surgery, 1988

In 1975, 80 patients undergoing revascularization were prospectively randomized to receive either... more In 1975, 80 patients undergoing revascularization were prospectively randomized to receive either a greater saphenous vein (SV) graft (41 patients, Group 1) or a left internal mammary artery (LIMA) graft (39 patients, Group 2) to the left anterior descending coronary artery (LAD). All patients were completely revascularized. The average number of grafts per patient in both groups was 3.2. Patients were followed 10 years; follow-up was 97.5% complete. Group 1 and Group 2 were compared in regard to mortality, treadmill response, myocardial infarction, reoperation, percutaneous transluminal coronary angioplasty, and return to work. Mortality in Group 1 was 17.9% versus 7.7% in Group 2 ( p < 0.05). Treadmill studies were positive in 17 Group 1 patients and 7 Group 2 patients ( p < 0.05). Myocardial infarctions occurred in 8 patients in Group 1 versus 3 in Group 2. The number of reoperations was 2 in Group 1 versus 1 in Group 2. Percutaneous transluminal coronary angioplasty was performed in 3 patients in Group 1 and 2 in Group 2. Repeat studies revealed 76.3% patency of the SV graft to the LAD (Group 1) and 94.6% patency of the LIMA graft to the LAD (Group 2). Cardiac-related mortality in Group 1 was 12.8% at 10 years (5 patients) versus 7.7% in Group 2 (3 patients). Based on this study, the IMA is a superior conduit for bypass to the LAD.

Siam Journal on Computing, 1996

Page 1. Chapter 29 Strongly Competitive Algorithms for Paging with Locality of Reference Sandy Ir... more Page 1. Chapter 29 Strongly Competitive Algorithms for Paging with Locality of Reference Sandy Irani* Anna R. Karlin t Steven Phillips$ Abstract What is the best paging algorithm if one has partial information about the possible sequences of page re-quests? ...

This paper considers the problem of paging under the assumption that the sequence of pages access... more This paper considers the problem of paging under the assumption that the sequence of pages accessed is generated by a Markov chain. The authors use this model to study the fault-rate of paging algorithms, a quantity of interest to practitioners. They first draw on the theory of Markov decision processes to characterize the paging algorithm that achieves optimal fault-rate on any Markov chain. They address the problem of efficiently devising a paging strategy with low fault-rate for a given Markov chain. They show that a number of intuitively good approaches fail. Their main result is an efficient procedure that, on any Markov chain, will give a paging algorithm with fault-rate at most a constant times optimal. Their techniques also show that some algorithms that do poorly in practice fail in the Markov setting, despite known (good) performance guarantees when the requests are generated independently from a probability distribution

Siam Journal on Computing, 2000