scholarly journals Stability, Memory, and Messaging Trade-Offs in Heterogeneous Service Systems

2021 ◽  
Author(s):  
David Gamarnik ◽  
John N. Tsitsiklis ◽  
Martin Zubeldia
Keyword(s):  
Broad Class ◽  
Text Messages ◽  
Current State ◽  
Trade Offs ◽  
Resource Requirements ◽  
Decision Epoch ◽  
Message Exchange ◽  
Service Rates ◽  
Finite Memory ◽  
Heterogeneous Service

We consider a heterogeneous distributed service system consisting of n servers with unknown and possibly different processing rates. Jobs with unit mean arrive as a renewal process of rate proportional to n and are immediately dispatched to one of several queues associated with the servers. We assume that the dispatching decisions are made by a central dispatcher with the ability to exchange messages with the servers and endowed with a finite memory used to store information from one decision epoch to the next, about the current state of the queues and about the service rates of the servers. We study the fundamental resource requirements (memory bits and message exchange rate) in order for a dispatching policy to be always stable. First, we present a policy that is always stable while using a positive (but arbitrarily small) message rate and [Formula: see text] bits of memory. Second, we show that within a certain broad class of policies, a dispatching policy that exchanges [Formula: see text] messages per unit of time, and with [Formula: see text] bits of memory, cannot be always stable.

scholarly journals MULTI-CLASS RESOURCE SHARING WITH BATCH ARRIVALS

2018 ◽  
Vol 33 (3) ◽  
pp. 348-366
Author(s):  
Paul Ezhilchelvan ◽  
Isi Mitrani
Keyword(s):  
Resource Sharing ◽  
Large Scale ◽  
Virtual Machines ◽  
Cloud Provider ◽  
Batch Arrivals ◽  
Large Scale Systems ◽  
Trade Offs ◽  
Resource Requirements ◽  
Partial Blocking ◽  
Fixed Point Iterations

A cloud provider hosts virtual machines (VMs) of different types, with different resource requirements. There are bounds on the total amounts of each kind of resource that are available. Requests arrive in batches of different sizes. Under the ‘complete blocking’ policy, a request is accepted only if all the VMs in its batch can be accommodated. The ‘partial blocking’ policy would accept a request if there is room for at least one of the VMs in the batch. Blocked requests are lost, with an associated loss of revenue. The trade-offs between costs and benefits are evaluated by means of appropriate models, for which novel solutions based on fixed-point iterations are proposed. The applicability of those solutions is extended, by means of simplifications, to very large-scale systems. Numerical examples and comparisons with simulations are presented.

The effect of cover and food on space use by wintering Song Sparrows and Field Sparrows

1997 ◽  
Vol 75 (10) ◽  
pp. 1636-1641 ◽  
Author(s):  
Christopher W. Beck ◽  
Bryan D. Watts
Keyword(s):  
Predation Risk ◽  
Positive Response ◽  
Distribution Patterns ◽  
Microhabitat Use ◽  
Vegetative Cover ◽  
Song Sparrows ◽  
Trade Offs ◽  
Resource Requirements ◽  
Woody Cover ◽  
Species Specific

The distribution of birds among microhabitats may reflect species-specific resource requirements. Both food availability and predation risk have been shown to influence patterns of microhabitat use by sparrows during winter. We investigated the influence of vegetative cover and food on microhabitat use using a 2 × 2 factorial design. Both woody cover and food were manipulated at the plot level. The presence of screening cover (weed stems) was manipulated within plots. Sparrows showed a positive response to the presence of both cover and food. Within plots, sparrows selected areas with screening cover. The distribution of birds between areas with and without screening cover was influenced by the presence of woody cover and food. Conversely, the presence of screening cover reduced the influence of woody cover on the distribution of birds within patches. Song Sparrows (Melospiza melodia) and Field Sparrows (Spizella pusilla) differed in their response to treatments both within and across plots, suggesting that trade-offs between foraging and predation risk may be important in the structuring of winter sparrow assemblages. Additionally, screening cover appears to moderate predation risk and therefore to affect distribution patterns.

scholarly journals The evolution of competitive ability for essential resources

2019 ◽  
Author(s):  
Joey R. Bernhardt ◽  
Pavel Kratina ◽  
Aaron Pereira ◽  
Manu Tamminen ◽  
Mridul K. Thomas ◽  
...  
Keyword(s):  
Competitive Ability ◽  
Community Dynamics ◽  
Species Coexistence ◽  
Resource Competition ◽  
Environmental Gradients ◽  
Light Limitation ◽  
Major Question ◽  
Trade Offs ◽  
Resource Requirements ◽  
Competitive Abilities

AbstractCompetition for limiting resources is among the most fundamental ecological interactions and has long been considered a key driver of species coexistence and biodiversity. Species’ minimum resource requirements, their R*s, are key traits that link individual physiological demands to the outcome of competition. However, a major question remains unanswered - to what extent are species’ competitive traits able to evolve in response to resource limitation? To address this knowledge gap, we performed an evolution experiment in which we exposed Chlamydomonas reinhardtii for approximately 285 generations to seven environments in chemostats which differed in resource supply ratios (including nitrogen, phosphorus and light limitation) and salt stress. We then grew the ancestors and descendants in common garden and quantified their competitive abilities for essential resources. We investigated constraints on trait evolution by testing whether changes in resource requirements for different resources were correlated. Competitive abilities for phosphorus improved in all populations, while competitive abilities for nitrogen and light increased in some populations and decreased in others. In contrast to the common assumption that there are trade-offs between competitive abilities for different resources, we found that improvements in competitive ability for a resource came at no detectable cost. Instead, improvements in competitive ability for multiple resources were either positively correlated or not significantly correlated. Using resource competition theory, we then demonstrated that rapid adaptation in competitive traits altered the predicted outcomes of competition. These results highlight the need to incorporate contemporary evolutionary change into predictions of competitive community dynamics over environmental gradients.

Updating Bayesian(s): A Critical Evaluation of Bayesian Process Tracing

2020 ◽  
Vol 29 (1) ◽  
pp. 58-74
Author(s):  
Sherry Zaks
Keyword(s):  
Qualitative Research ◽  
Ad Hoc ◽  
Critical Evaluation ◽  
Process Tracing ◽  
American Political Science Association ◽  
Opportunity Costs ◽  
Current State ◽  
Trade Offs ◽  
American Political Science ◽  
Science Association

Given the increasing quantity and impressive placement of work on Bayesian process tracing, this approach has quickly become a frontier of qualitative research methods. Moreover, it has dominated the process-tracing modules at the Institute for Qualitative and Multi-Method Research (IQMR) and the American Political Science Association (APSA) meetings for over five years, rendering its impact even greater. Proponents of qualitative Bayesianism make a series of strong claims about its contributions and scope of inferential validity. Four claims stand out: (1) it enables causal inference from iterative research, (2) the sequence in which we evaluate evidence is irrelevant to inference, (3) it enables scholars to fully engage rival explanations, and (4) it prevents ad hoc hypothesizing and confirmation bias. Notwithstanding the stakes of these claims and breadth of traction this method has received, no one has systematically evaluated the promises, trade-offs, and limitations that accompany Bayesian process tracing. This article evaluates the extent to which the method lives up to the mission. Despite offering a useful framework for conducting iterative research, the current state of the method introduces more bias than it corrects for on numerous dimensions. The article concludes with an examination of the opportunity costs of learning Bayesian process tracing and a set of recommendations about how to push the field forward.

Modeling and exploiting spatial locality trade-offs in wavelet-based applications under varying resource requirements

2010 ◽  
Vol 9 (3) ◽  
pp. 1-26 ◽  
Author(s):  
Bert Geelen ◽  
Vissarion Ferentinos ◽  
Francky Catthoor ◽  
Gauthier Lafruit ◽  
Diederik Verkest ◽  
...  
Keyword(s):  
Spatial Locality ◽  
Trade Offs ◽  
Resource Requirements

scholarly journals The FACTS model of speech motor control: fusing state estimation and task-based control

2019 ◽  
Author(s):  
Benjamin Parrell ◽  
Vikram Ramanarayanan ◽  
Srikantan Nagarajan ◽  
John Houde
Keyword(s):  
Motor Control ◽  
Vocal Tract ◽  
Internal State ◽  
State Feedback Control ◽  
Speech Motor Control ◽  
State Estimate ◽  
Somatosensory Feedback ◽  
Current State ◽  
Trade Offs ◽  
Speech Motor

ABSTRACTWe present a new computational model of speech motor control: the Feedback-Aware Control of Tasks in Speech or FACTS model. This model is based on a state feedback control architecture, which is widely accepted in non-speech motor domains. The FACTS model employs a hierarchical observer-based architecture, with a distinct higher-level controller of speech tasks and a lower-level controller of speech articulators. The task controller is modeled as a dynamical system governing the creation of desired constrictions in the vocal tract, based on the Task Dynamics model. Critically, both the task and articulatory controllers rely on an internal estimate of the current state of the vocal tract to generate motor commands. This internal state estimate is derived from initial predictions based on efference copy of applied controls. The resulting state estimate is then used to generate predictions of expected auditory and somatosensory feedback, and a comparison between predicted feedback and actual feedback is used to update the internal state prediction. We show that the FACTS model is able to qualitatively replicate many characteristics of the human speech system: the model is robust to noise in both the sensory and motor pathways, is relatively unaffected by a loss of auditory feedback but is more significantly impacted by the loss of somatosensory feedback, and responds appropriately to externally-imposed alterations of auditory and somatosensory feedback. The model also replicates previously hypothesized trade-offs between reliance on auditory and somatosensory feedback in speech motor control and shows for the first time how this relationship may be mediated by acuity in each sensory domain. These results have important implications for our understanding of the speech motor control system in humans.

scholarly journals Trade Estimates

2020 ◽  
pp. 27-60
Author(s):  
Alex Cobham ◽  
Petr Janský
Keyword(s):  
Future Development ◽  
Step Change ◽  
Data Availability ◽  
Critical Survey ◽  
Financial Flows ◽  
Trade Off ◽  
Current State ◽  
Trade Offs ◽  
Illicit Financial Flows

International trade plays an important role in some of the most prominent studies aimed at estimating the scale of illicit financial flows (IFF). This chapter provides a critical survey of the leading estimates of trade-based IFF, addressing separately the strengths and weaknesses of methodologies that rely on data at the country, commodity and transaction level. The current state of data availability makes a trade-off between coverage and quality of estimation inevitable, and at present no approach in this area yields sufficiently a strong, global series. There are a number of promising areas for future development, but unfortunate trade-offs will remain unless there is a step change in data availability.

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