Population Protocols Research Articles

Self-Stabilizing Population Protocols With Global Knowledge

In the population protocol model, many problems cannot be solved in a self-stabilizing manner. However, global knowledge, such as the number of nodes in a network, sometimes enables the design of a self-stabilizing protocol for such problems. For example, it is known that we can solve the self-stabilizing leader election in complete graphs if and only if every node knows the exact number of nodes. In this article, we investigate the effect of global knowledge on the possibility of self-stabilizing population protocols in arbitrary graphs. Specifically, we clarify the solvability of the leader election problem, the ranking problem, the degree recognition problem, and the neighbor recognition problem by self-stabilizing population protocols with knowledge of the number of nodes and/or the number of edges in a network.

Towards efficient verification of population protocols

Population protocols are a well established model of computation by anonymous, identical finite-state agents. A protocol is well-specified if from every initial configuration, all fair executions of the protocol reach a common consensus. The central verification question for population protocols is the well-specification problem: deciding if a given protocol is well-specified. Esparza et al. have recently shown that this problem is decidable, but with very high complexity: it is at least as hard as the Petri net reachability problem, which is TOWER-hard, and for which only algorithms of non-primitive recursive complexity are currently known. In this paper we introduce the class { WS}^3 of well-specified strongly-silent protocols and we prove that it is suitable for automatic verification. More precisely, we show that { WS}^3 has the same computational power as general well-specified protocols, and captures standard protocols from the literature. Moreover, we show that the membership and correctness problems for { WS}^3 reduce to solving boolean combinations of linear constraints over {mathbb {N}}. This allowed us to develop the first software able to automatically prove correctness for all of the infinitely many possible inputs.

The complexity of verifying population protocols

Population protocols (Angluin et al. in PODC, 2004) are a model of distributed computation in which indistinguishable, finite-state agents interact in pairs to decide if their initial configuration, i.e., the initial number of agents in each state, satisfies a given property. In a seminal paper Angluin et al. classified population protocols according to their communication mechanism, and conducted an exhaustive study of the expressive power of each class, that is, of the properties they can decide (Angluin et al. in Distrib Comput 20(4):279–304, 2007). In this paper we study the correctness problem for population protocols, i.e., whether a given protocol decides a given property. A previous paper (Esparza et al. in Acta Inform 54(2):191–215, 2017) has shown that the problem is decidable for the main population protocol model, but at least as hard as the reachability problem for Petri nets, which has recently been proved to have non-elementary complexity. Motivated by this result, we study the computational complexity of the correctness problem for all other classes introduced by Angluin et al., some of which are less powerful than the main model. Our main results show that for the class of observation models the complexity of the problem is much lower, ranging from varPi _2^p to PSPACE.

Enhanced recovery after posterior cervical fusion surgery: A retrospective case series

Enhanced recovery after surgery (ERAS) is a multifaceted strategy, involving all phases of surgical care, intended to mitigate the stress response of surgery and optimize patient outcomes. A growing number of publications have demonstrated the benefits of ERAS protocols in specific populations of spine surgery patients. ERAS protocols have yet to be studied in patients undergoing posterior cervical decompression and fusion (PCDF) surgery. In this study, we compared the length of stay (LOS) and discharge disposition between two groups of patients that had PCDF surgery for degenerative pathologies. The pre-ERAS group consisted of 74 patients that had surgery between 2012 and 2017. The post-ERAS group included 25 patients that had surgery between 2017 and 2019. There were no significant differences between the two groups in terms of age, gender, and diagnosis (p greater than 0.05). The post-ERAS group had statistically non-significant, positive trends for LOS and discharge disposition. Implementation of an ERAS protocol for PCDF patients is feasible, however, future studies are needed to refine ERAS protocols and confirm the benefits.

Simple and fast approximate counting and leader election in populations

We study leader election and population size counting for population protocols: networks of finite-state anonymous agents that interact randomly. We provide simple protocols for approximate counting of the size of the population and for leader election. We show a protocol for leader election that terminates in O(log2⁡nlog⁡m) parallel time, where m is a parameter that belongs to Ω(log⁡n) and O(n), using O(max⁡{log⁡m,log⁡log⁡n}) bits. By adjusting m between log⁡n and n, we obtain a leader election protocol whose time and space can be smoothly traded off between O(log2⁡nlog⁡log⁡n) to O(log⁡n) time and O(log⁡log⁡n) to O(log⁡n) bits. We also give a protocol which provides a constant factor approximation of log⁡n of the population size n, or an upper bound ne which is at most na for some constant a>1. This protocol assumes the existence of a unique leader and stabilizes in Θ(log⁡n) parallel time.

Genetic Diversity of Drug-Related Genes in Native Americans of the Brazilian Amazon.

IntroductionThe genetic admixture of the Brazilian population has considerable relevance to the implementation of the principles of pharmacogenomics (PGx), as it may compromise the extrapolation of data obtained in more homogeneous world populations.PurposeThis study aims to investigate a panel of 117 polymorphisms in 35 pharmacogenes, which contains label recommendations or clinical evidence by international drug regulatory agencies, in Amazonian Native American populations, and compare the results obtained with continental population data from the 1000 Genomes Project Consortium.Patients and MethodsThe study population is composed of 109 Native American individuals from three Brazilian Amazon groups. The genotyping of the PGx polymorphisms was performed by allelic discrimination using TaqMan® OpenArray Genotyping with a panel of 120 customized assays on the QuantStudio™ 12K Flex Real-Time PCR System.ResultsStatistical differences within the Native American populations were observed regarding both genotypes and phenotypes of some genes of the CYP family. The discriminant analysis of principal components (DAPCs) between the NAM group and the continental populations of the 1000 Genomes Project resulted in the clustering of the three Native American populations. Additionally, in general, the NAM group was determined to be closely situated between East Asia, America, and South Asia groups, which enabled us to infer a genetic similarity between these populations. The DAPC analysis further demonstrated that eight polymorphisms and six polymorphisms were more relevant in differentiating the NAM from the continental populations and the NAM populations among themselves, respectively.ConclusionSome investigated polymorphisms show differences among world populations, particularly with populations of European origin, for whom precision medicine protocols are primarily designed. The accumulated knowledge regarding these variations may assist in the design of specific protocols for Native American populations and populations admixed with them.

Mean-field density matrix decompositions.

We introduce new and robust decompositions of mean-field Hartree-Fock and Kohn-Sham density functional theory relying on the use of localized molecular orbitals and physically sound charge population protocols. The new lossless property decompositions, which allow for partitioning one-electron reduced density matrices into either bond-wise or atomic contributions, are compared to alternatives from the literature with regard to both molecular energies and dipole moments. Besides commenting on possible applications as an interpretative tool in the rationalization of certain electronic phenomena, we demonstrate how decomposed mean-field theory makes it possible to expose and amplify compositional features in the context of machine-learned quantum chemistry. This is made possible by improving upon the granularity of the underlying data. On the basis of our preliminary proof-of-concept results, we conjecture that many of the structure-property inferences in existence today may be further refined by efficiently leveraging an increase in dataset complexity and richness.

Broadcast distributed voting algorithm in population protocols

The authors consider the problem of multi-choice majority voting in a network of n agents where each agent initially selects a choice from a set of K possible choices. The agents try to infer the choice in the majority merely by performing local interactions. Extending the popular ‘Population Protocol’ framework for pairwise interactions between agents, in this study, they propose a new model called ‘Broadcasting Population Protocol’. In the proposed model, each agent broadcasts its messages in such a way that all its neighbours will receive the message simultaneously. They design two distributed algorithms for solving the multi-choice majority voting problem in this new model. They show that these algorithms return the correct output, i.e. the choice in the majority. They also analyse their performances in terms of time and message complexities. They establish via simulations that the proposed algorithms improve both time and message complexities significantly with respect to previous algorithms proposed in conventional population protocols, and they can be utilised in networks where messages can be transmitted to a subset of agents simultaneously, such as wireless networks.

Panorama de pesquisas com seres humanos sobre covid-19 no Brasil

Resumo A pandemia de covid-19 desafia instituições de pesquisa pela urgência de responder à morbimortalidade provocada pelo vírus. O objetivo deste estudo foi traçar panorama das pesquisas com humanos sobre essa doença no primeiro trimestre de 2020 no Brasil. Dados oficiais de saúde da população e de protocolos de pesquisa sobre a covid-19, distribuídos por estados brasileiros, subsidiaram a análise temporal. Houve crescimento exponencial da incidência do vírus, principalmente nas regiões Norte e Nordeste, apesar da difusão discreta, lenta e assimétrica das pesquisas, concentradas no Sudeste. Os poucos ensaios clínicos entraram na Fase II. A distribuição geográfica de comitês de ética em pesquisa, instituições de ensino superior, investimentos em ciência e tecnologia e unidades assistenciais básicas e hospitalares gera vulnerabilidades estaduais para enfrentar a doença. Acompanhamento longitudinal atento deve ser realizado diante das iniquidades regionais, em defesa dos preceitos bioéticos e da vida humana.

Enhanced Phase Clocks, Population Protocols, and Fast Space Optimal Leader Election

The model of population protocols refers to the growing in popularity theoretical framework suitable for studying pairwise interactions within a large collection of simple indistinguishable entities, frequently called agents . In this article, the emphasis is on the space complexity of fast leader election in population protocols governed by the random scheduler , which uniformly at random selects pairwise interactions between n agents. One of the main results of this article is the first fast space optimal leader election protocol , which works with high probability. The new protocol operates in parallel time O (log 2 n ) equivalent to O ( n log 2 n ) sequential pairwise interactions with each agent’s memory space limited to O (log log n ) states. This double logarithmic space utilisation matches asymptotically the lower bound ½log log n on the number of states utilised by agents in any leader election algorithm with the running time o ( n \polylog n ); see Reference [7]. Our new solution expands also on the classical concept of phase clocks used to synchronise and to coordinate computations in distributed algorithms. In particular, we formalise the concept and provide a rigorous analysis of phase clocks operating in nested modes. Our arguments are also valid for phase clocks propelled by multiple leaders. The combination of the two results in the first time-space efficient leader election algorithm. We also provide a complete formal argumentation, indicating that our solution is always correct, fast, and it works with high probability.

Time-Optimal Leader Election in Population Protocols

In this article, we present the first leader election protocol in the population protocol model that stabilizes within O(logn) parallel time in expectation with O(logn) states per agent, where n is the number of agents. Given a rough knowledge m of lg n such that m ≥ lg n and m = O(logn), the proposed protocol guarantees that exactly one leader is elected and the unique leader is kept forever thereafter. This protocol is time-optimal because it was recently proven that any leader election protocol requires Ω(logn) parallel time.

Mitigating the Impact of the Novel Coronavirus Pandemic on Neuroscience and Music Research Protocols in Clinical Populations.

The COVID-19 disease and the systemic responses to it has impacted lives, routines and procedures at an unprecedented level. While medical care and emergency response present immediate needs, the implications of this pandemic will likely be far-reaching. Most practices that the clinical research within neuroscience and music field rely on, take place in hospitals or closely connected clinical settings which have been hit hard by the contamination. So too have its preventive and treatment measures. This means that clinical research protocols may have been altered, postponed or put in complete jeopardy. In this context, we would like to present and discuss the problems arising under the current crisis. We do so by critically approaching an online discussion facilitated by an expert panel in the field of music and neuroscience. This effort is hoped to provide an efficient basis to orient ourselves as we begin to map the needs and elements in this field of research as we further propose ideas and solutions on how to overcome, or at least ease the problems and questions we encounter or will encounter, with foresight. Among others, we hope to answer questions on technical or social problems that can be expected, possible solutions and preparatory steps to take in order to improve or ease research implementation, ethical implications and funding considerations. Finally, we further hope to facilitate the process of creating new protocols in order to minimize the impact of this crisis on essential research which may have the potential to relieve health systems.

Time-space trade-offs in population protocols for the majority problem

Population protocols are a model for distributed computing that is focused on simplicity and robustness. A system of n identical agents (finite state machines) performs a global task like electing a unique leader or determining the majority opinion when each agent has one of two opinions. Agents communicate in pairwise interactions with randomly assigned communication partners. Quality is measured in two ways: the number of interactions to complete the task and the number of states per agent. We present protocols for the majority problem that allow for a trade-off between these two measures. Compared to the only other trade-off result (Alistarh et al. in Proceedings of the 2015 ACM symposium on principles of distributed computing, Donostia-San Sebastián, 2015), we improve the number of interactions by almost a linear factor. Furthermore, our protocols can be made uniform (working correctly without any information on the population size n), yielding the first uniform majority protocols that stabilize in a subquadratic number of interactions.

Evaluation Of Maximal Oxygen Uptake Using Verification Phases Of Different Intensities Across Fitness Levels

Confirmation of maximal oxygen consumption (V˙O2max) has relevance in both clinical and exercise settings. Though there are criteria in place to confirm V˙O2max has been attained, they are inconsistently achieved. For example, a plateau in V˙O2 with a corresponding increase in workload is often absent, and other criteria such as a respiratory exchange ratio (RER) ≥1.15 or heart rate (HR) within 10 beats per min (bpm) of age predicted maximum can result in an inaccurate estimate of V˙O2max. Due to these shortcomings, some researchers have suggested the use of a verification phase (VP) to confirm the attainment of V˙O2max. PURPOSE: Therefore, this study aimed to provide further evidence for the need to use a VP with V˙O2max testing protocols in populations of different fitness levels. METHODS: 49 participants (M: 27, F: 22; 21.9±2.6 y, 24.3±2.8 kg·m2) had their V˙O2 and HR measured during three maximal graded treadmill tests with each test followed by a VP of differing intensity (85%, 95%, 105% final workload). Participants were divided into groups based on their V˙O2max using norms adapted from American College of Sports Medicine (ACSM) V˙O2max guidelines (poor, fair, good, excellent) resulting in 7, 19, 18, and 5 participants respectively. V˙O2max from the graded treadmill test was confirmed with the VP and/or an additional test if the highest V˙O2 value achieved was no more than 2 x typical error (TE: 1.9 to 3.7 mL·kg-1·min-1 across groups). RESULTS: Plateau was achieved on 43/147 tests (29%), RER ≥ 1.15 was achieved on 104/147 tests (71%), HR within 10 bpm of age-predicted max was achieved on 83/147 tests (56%), and volitional fatigue was reached on 147/147 tests (100%). The highest V˙O2 value attained on the initial V˙O2max test was not different than either value attained following the VP at 95 or 105% of final V˙O2max test workload or a second repeat test on a separate day (P>0.211). The 85% VP V˙O2 value was lower than the initial V˙O2max test value (P<0.001). CONCLUSION: While traditional criteria to confirm the attainment of V˙O2max were inconsistently achieved, the use of a VP (at 95 or 105%) or a subsequent repeat test on a separate day were able to confirm the V˙O2max value attained. Our data also suggests exercise studies employing only a single V˙O2max test should consider these inconsistencies across a range of fitness levels.

High-intensity Interval Training In Older Adults: A Scoping Review

High-intensity interval training (HIT) is an increasingly popular form of aerobic exercise which includes bouts of high-intensity exercise interspersed with periods of rest. The health benefits and risks as well as the optimal design of HIT are still unclear. Further, most of the research on the effects and benefits of HIT has been done in young and middle-aged adults and as such, the tolerability and effects in senior populations is less well-known. PURPOSE: To characterize HIT research that has been done in older adults including protocols, feasibility and safety as well as to identify gaps in the current knowledge. METHODS: Five databases were searched with variations of the search terms, “high-intensity interval training, high-intensity exercise” and “elderly, older adults.” These searches identified 3377 potential studies which were reviewed for inclusion. Studies were included if they were randomized controlled trials published in English in or after 2009, if the mean age of a treatment group was 65 years or older, and if the exercise protocols being tested were exclusively high-intensity or high-intensity interval training. RESULTS: Of 3377 papers identified in the initial search, 86 met the inclusion criteria. The HIT protocols used varied widely and ranged from a single session of HIT to a year-long program. These studies included both healthy and clinical populations. The greatest number of studies examined HIT in healthy subjects, followed by subjects with cardiac or vascular disease (heart failure, coronary artery disease, hypertension), metabolic dysfunction (Type-2 Diabetes Mellitus, obesity), and chronic obstructive pulmonary disease. Sample sizes ranged from 5 to 618 with 90% of studies including less than 70 subjects. The most common primary outcomes identified in the studies included changes in cardiorespiratory fitness as well as feasibility and safety of the protocols in the target populations. CONCLUSIONS: With a few exceptions, most studies had small sample sizes and many included non-clinical populations. Larger studies are needed to further evaluate the clinical effects of HIT in older adults. Additionally, there is much variety in the modes of exercise as well as the HIT protocols being used. Despite this, HIT was generally reported to be well-tolerated and safe in older populations.

Fault-tolerant simulation of population protocols

In this paper we investigate the computational power of population protocols under some unreliable or weaker interaction models. More precisely, we focus on two features related to the power of interactions: omission failures and one-way communications. An omission failure, a notion that this paper introduces for the first time in the context of population protocols, is the loss by one or both parties of the information transmitted in an interaction. The failure may or may not be detected by either party. In one-way models, on the other hand, communication happens only in one direction: only one of the two agents can change its state depending on both agents’ states, and the other agent may or may not be aware of the interaction. These notions can be combined, obtaining one-way protocols with (possibly detectable) omission failures. We start our investigation by providing a complete classification of all the possible models arising from the aforementioned weaknesses, and establishing the computational hierarchy of these models. We then address for each model the fundamental question of what additional power is necessary and sufficient to completely overcome the model’s weakness and make it able to simulate faultless two-way protocols; by “simulator” we mean a wrapper protocol that, implementing an atomic communication of states between two agents, converts any standard two-way protocol into one that works in a weaker model. We answer this question by presenting simulators that work under certain assumptions (e.g., additional memory, unique IDs, etc.) and by proving that simulation is impossible without such assumptions.

Distributed Computing Column 77 Consensus Dynamics

Overview. In this edition of the column, we have an exciting contribution from Luca Becchetti, Andrea Clementi, and Emanuele Natale, who provide an in-depth algorithmic perspective on emergent complexity. Roughly, this area aims to characterize non-trivial emergent properties of complex systems, composed of large numbers of relatively simple agents, which can cooperate to express complex global behaviours. Interestingly, over the past two decades, fundamental processes such as consensus or opinion-formation dynamics have been studied independently by different research communities: for instance, in the Distributed Computing community, these dynamics have been studied in the context of population protocols via discrete-time analysis, whereas, in the Control and Optimization community, similar (or even identical) dynamics have been analyzed via continuous-time processes. One very useful feature in this column's contribution is the fact that it provides a unified view of these results, along with the mathematical background to understand and differentiate the underlying results.

Standardized epidemiological protocols for populations affected by volcanic eruptions

Standardized epidemiological protocols for populations affected by volcanic eruptions

Loosely Stabilizing Leader Election on Arbitrary Graphs in Population Protocols without Identifiers or Random Numbers

Loosely Stabilizing Leader Election on Arbitrary Graphs in Population Protocols without Identifiers or Random Numbers

Leader Election Requires Logarithmic Time in Population Protocols

This paper shows that every leader election protocol requires logarithmic stabilization time both in expectation and with high probability in the population protocol model. This lower bound holds even if each agent has knowledge of the exact size of a population and is allowed to use an arbitrarily large number of agent states. This lower bound concludes that the protocol given in [Sudo et al., SSS 2019] is time-optimal in expectation.