81 research outputs found
Connecting Digitally with the Tejas Star Reading List
No full textPresented at CTLC 2020Learn about the Tejas Star Reading List and how you can connect students digitally with the bilingual and Spanish titles on this reading list as well as scheduling virtual author visit
Las singulares tejas de la ermita de Jugachi
No full textSe describen los grabados presentes en las tejas procedentes del tejado de la ermita de Nuestra Señora de Jugachi, situada sobre Jugo. Se describe la ermita, su fiesta, y el lugar donde se encuentra. Se describen los dibujos de las tejas cuya significación es desconocida. Se cree que estos dibujos no fueron hechos sin más, sino que tienen un significadoThe author describes the present engravings in the tiles from the roof of the hermitage of Nuestra Señora de Jugachi, located at Jugo. The author then describes the hermitage, its festivities, and the place where it is situated. The author also describes the drawings on the tiles, the meaning of which is unknown. It is believed that these drawings were not made without a purpose, and that they have a meanin
On Load Balancing Equilibria in Multiqueue Systems with Multiclass Traffic
No full textInternational audienceWe consider a queueing system with two non identical FCFS servers together serving two classes of customers. All customers have i.i.d service requirements. One of the queues may charge an admission price, say c. Arrivals are randomly routed to one of the servers and the routing probabilities are determined centrally to optimise a global objective, or from a local mechanism minimising a local--class or individual-- objective. Our interest is to analyse the use of c to achieve a target distribution of loads among the servers. We first analyse the structure of the optimal allocation and then consider (1) a system with a dispatcher for each class, (2) a non atomic system, and (3) a system where one of the classes has a dispatcher
On the equivalence between multiclass processor sharing and random order scheduling policies
No full textInternational audienceConsider a single server system serving a multiclass population. Some popular scheduling policies for such system are the discriminatory processor sharing (DPS), discriminatory random order service (DROS), generalized processorsharing (GPS) and weighted fair queueing (WFQ). In this paper, we propose two classes of policies, namely MPS (Multi-class Processor Sharing) and MROS (Multi-class Random Order Service), that generalize the four policiesmentioned above. For the special case when the multi-class population arrive according to Poisson processes and have independent and exponential service requirement with parameter µ, we show that the tail of the sojourn timedistribution for a class i customer in a system with the MPS policy is a constant multiple of the tail of the waiting timedistribution of a class i customer in a system with the MROS policy. This result implies that for a class i customer, the tail of the sojourn time distribution in a system with the DPS (GPS) scheduling policy is a constant multiple of the tail of the waiting time distribution in a system with the DROS (respectively WFQ) policy
Performance analysis of workload dependent load balancing policies
No full textAbstract: Load balancing plays a crucial role in achieving low latency in large distributed systems. Recent load balancing strategies often rely on replication or use placeholders to further improve latency. However assessing the performance and stability of these strategies is challenging and is therefore often simulation based. In this paper we introduce a unified approach to analyze the performance and stability of a broad class of workload dependent load balancing strategies. This class includes many replication policies, such as replicate below threshold, delayed replication and replicate only small jobs, as well as strategies for fork-join systems. We consider systems with general job size distributions where jobs may experience server slowdown. We show that the equilibrium workload distribution of the cavity process satisfies a functional differential equation and conjecture that the cavity process captures the limiting behavior of the system as its size tends to infinity. We study this functional differential equation in more detail for a variety of load balancing policies and propose a numerical method to solve it. The numerical method relies on a fixed point iteration or a simple Euler iteration depending on the type of functional differential equation involved. We further show that additional simplifications can be made if certain distributions are assumed to be phase-type. Various numerical examples are included that validate the numerical method and illustrate its strength and flexibility
On a unifying product form framework for redundancy models
No full textInternational audienceIn this paper, we present a unifying analysis for redundancy systems with cancel-on-start () and cancel-on-complete () with exponentially distributed service requirements. With () all redundant copies are removed as soon as one of the copies starts (completes) service. As a consequence, does not waste any computing resources, as opposed to . We show that the model is equivalent to a queueing system with multi-type jobs and servers, which was analyzed in \cite{Visschers12},and show that (under the assumption of i.i.d. copies) can be analyzed by a generalization of \cite{Visschers12} where state-dependent departure rates are permitted. This allows us to show that the stationary distribution for both the and models have a product form. We give a detailed first-time analysis for and derive a closed form expression for important metrics like mean number of jobs in the system, and probability of waiting. We also note that the model is equivalent to Join-Shortest-Work queue with redundancy (JSW()). In the latter, an incoming job is dispatched to the server with smallest workload among randomly chosen ones. Thus, all our results apply mutatis-mutandis to JSW().{Comparing the performance of with that of with i.i.d copies gives the unexpected conclusion (since does not waste any resources) that is worse in terms of mean number of jobs. As part of ancillary results, we illustrate that this is primarily due to the assumption of i.i.d copies in case of (together with exponentially distributed requirements) and that such assumptions might lead to conclusions that are qualitatively different from that observed in practice
Sequential modeling for mortality prediction in the ICU
No full textThesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 85-89).Severity of illness scores are commonly used in critical care medicine to guide treatment decisions and benchmark the quality of medical care. These scores operate in part by predicting patient mortality in the ICU using physiological variables including lab values, vital signs, and admission information. However, existing evidence suggests that current mortality predictors are less performant on patients who have an especially high risk of mortality in the ICU. This thesis seeks to reconcile this difference by developing a custom high risk mortality predictor for high risk patients in a process termed sequential modeling. Starting with a base set of features derived from the APACHE IV score, this thesis details the engineering of more complex features tailored to the high risk prediction task and development of a logistic regression model trained on the Philips eICU-CRD dataset. This high risk model is shown to be more performant than a baseline severity of illness score, APACHE IV, on the high risk subpopulation. Moreover, a combination of the baseline severity of illness score and the high risk model is shown to be better calibrated and more performant on patients of all risk types. Lastly, I show that this secondary customization approach has useful applications not only in the general population, but in specific patient subpopulations as well. This thesis thus offers a new perspective and strategy for mortality prediction in the ICU, and when taken in context with the increasing digitization of patient medical records, offers a more personalized predictive model in the ICU.by Tejas G. Sundaresan.M. Eng
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