scholarly journals A Cluster-based Model of COVID-19 Transmission Dynamics

2021 ◽  
Author(s):  
B Shayak ◽  
Mohit Manoj Sharma
Keyword(s):  
Preventive Measures ◽  
Critical Mass ◽  
Mass Effect ◽  
Spreading Rate ◽  
Epidemiological Models ◽  
Successful Management ◽  
Stochastic Effects ◽  
Discrete Population ◽  
Closed Groups ◽  
Case Rate

Many countries have manifested COVID-19 trajectories where extended periods of constant and low daily case rate suddenly transition to epidemic waves of considerable severity with no correspondingly drastic relaxation in preventive measures. Such solutions are outside the scope of classical epidemiological models. Here we construct a deterministic, discrete-time, discrete-population mathematical model which can explain these non-classical phenomena. Our key hypothesis is that with partial preventive measures in place, viral transmission occurs primarily within small, closed groups of family members and friends, which we call clusters. Inter-cluster transmission is infrequent compared to intra-cluster transmission but it is the key to determining the course of the epidemic. If inter-cluster transmission is low enough, we see stable plateau solutions. Above a cutoff level however, such transmission can destabilize a plateau into a huge wave even though its contribution to the population-averaged spreading rate still remains small. We call this the cryptogenic instability. We also find that stochastic effects when case counts are very low may result in a temporary and artificial suppression of an instability; we call this the critical mass effect. Both these phenomena are absent from conventional infectious disease models and militate against the successful management of the epidemic.

scholarly journals Counter-intuitive COVID-19 Trajectories - Explanations, Early Warning Indicator and Mitigation Strategies

2021 ◽  
Author(s):  
B Shayak ◽  
Mohit Manoj Sharma
Keyword(s):  
Social Interactions ◽  
Early Warning ◽  
Critical Mass ◽  
Mass Effect ◽  
Mitigation Strategies ◽  
Contact Tracing ◽  
Epidemiological Models ◽  
Early Warning Indicator ◽  
Small Change ◽  
Parameter Values

The COVID-19 trajectories worldwide have shown several surprising features which are outside the purview of classical epidemiological models. These include (a) almost constant and low daily case rates over extended periods of time, (b) sudden waves emerging from the above solution despite no or minimal change in the level of non-pharmaceutical interventions (NPI), and (c) reduction or flattening of case counts following relaxation of NPI. To explain these phenomena, we add contact tracing to our recently developed cluster seeding and transmission (CST) model. We find no fewer than four effects which make prediction of epidemic trajectories uncertain. These are (a) cryptogenic instability, where a small increase in population-averaged contact rate causes a large increase in cases, (b) critical mass effect, where a wave manifests after weeks of quiescence with no change in parameter values, (c) knife-edge effect, where a small change in parameter across a critical value causes a huge change in the response of the system, and (d) hysteresis effect, where the timing and not just the strength of a particular NPI determines the subsequent behaviour. Despite these effects however, some non-obvious conclusions regarding NPI appear to be robust. In particular, (a) narrowing the circle of one's social interactions can be as effective a measure as reducing interactions altogether, and (b) a good contact tracing program can effectively substitute for much more invasive measures. Finally, we propose the contact tracing capacity ratio - a metric of the load to which the tracers are subject - as a reliable early warning indicator of an imminent epidemic wave.

Risk Planning and Mitigation in Oil Well Fields

2015 ◽  
Vol 4 (4) ◽  
pp. 27-48
Author(s):  
Nediljka Gaurina-Međimurec ◽  
Borivoje Pašić ◽  
Petar Mijić
Keyword(s):  
Preventive Measures ◽  
Drilling Fluid ◽  
Oil Well ◽  
Remedial Measures ◽  
Successful Management ◽  
Lost Circulation ◽  
Wellbore Strengthening ◽  
Lost Circulation Materials ◽  
Industry Experience ◽  
Tools And Methods

Lost circulation presents one of the major risks associated with drilling. The complete prevention of lost circulation is impossible but limiting circulation loss is possible if certain precautions are taken. Industry experience has proved that is often easier and more effective to prevent the occurrence of loss than to attempt to stop or reduce them once they have started. The problem of lost circulation was magnified considerably when operators began drilling deeper and/or depleted formations. A strategy for successful management of lost circulation should include preventative (best drilling practices, drilling fluid selection, and wellbore strengthening materials) and remedial measures when lost circulation occurs through the use of lost circulation materials. In this paper the authors present lost circulation zones and causes, potential zones of lost circulation, excessive downhole pressures causes, preventive measures, tools and methods for locating loss zones and determining the severity of loss, lost circulation materials, and recommended treatments.

scholarly journals Gendered Representation and Critical Mass: Women’s Legislative Representation and Social Spending in 22 OECD Countries

2018 ◽  
Author(s):  
Soon Seok Park
Keyword(s):  
Linear Models ◽  
Critical Mass ◽  
Percent Level ◽  
Mass Effect ◽  
Critical Threshold ◽  
Policy Outcomes ◽  
Social Spending ◽  
Data Set ◽  
Piecewise Regression ◽  
Legislative Representation

To better understand the dynamics of representation of women’s interests such as public expenditure on healthcare, daycare, and education, this study examines statistical evidence for the notion of critical mass. To do so, this study uses the Comparative Welfare Data Set and the piecewise regression method to produce two linear models that best fit to the data for different ranges of the share of seats in parliament held by women. The analysis fails to find consistent support for a threshold below which women legislators have little-to-no impact upon policy outcomes. By adjudicating seven hypothetical thresholds, the analysis also shows that when there is a critical mass effect, the 10 percent level is more a consequential threshold than 15, 20, or 30 percent levels. Findings suggest that we reject the idea of a critical threshold for women’s legislative representation. However, the relationship between the representation and social spending is robust with or without presumed critical mass.

scholarly journals The role of learner and input variables in learning inflectional morphology

2006 ◽  
Vol 27 (2) ◽  
pp. 185-209 ◽  
Author(s):  
PATRICIA J. BROOKS ◽  
VERA KEMPE ◽  
ARIEL SIONOV
Keyword(s):  
Language Learning ◽  
Critical Mass ◽  
Mass Effect ◽  
English Speakers ◽  
Inflectional Morphology ◽  
Vocabulary Size ◽  
Case Marking ◽  
Input Variables ◽  
Learning Trials

To examine effects of input and learner characteristics on morphology acquisition, 60 adult English speakers learned to inflect masculine and feminine Russian nouns in nominative, dative, and genitive cases. By varying training vocabulary size (i.e., type variability), holding constant the number of learning trials, we tested whether learners required a “critical mass” of vocabulary to generalize case marking patterns to new nouns. Cattell's Culture-Fair IQ Test mediated the effect of type variability on success in generalizing case marking to new vocabulary: only participants with above-median Culture-Fair Test scores showed the predicted critical mass effect of better generalization with larger training vocabulary. These results demonstrate how individual differences in central executive functioning and attention allocation capacity can affect adult second language learning.

scholarly journals Does Gender Diversity in the Boardroom Improve Firm Performance? Evidence from Indonesia

2019 ◽  
Vol 65 (1) ◽  
pp. 1
Author(s):  
Pananda Pasaribu ◽  
Masripah Masripah ◽  
Bonnie Mindosa
Keyword(s):  
Firm Performance ◽  
Critical Mass ◽  
Gender Diversity ◽  
Mass Effect ◽  
Listed Firms ◽  
Beneficial Effects ◽  
Board Gender Diversity

This study investigates board gender diversity in Indonesia’s listed firms and its effect on firm performance from 2011–2016. After addressing the endogeneity of diversity, the results in this paper show that the proportion of female in the boardroom marginally improve firm performance. Firms with two or more female in the boardroom have a stronger impact on firm performance than firms with one female in the boardroom, consistent with the critical mass effect. Finally, certain sectors will gain more benefits of appointing females in the boardroom. The results suggest that increasing gender diversity in the boardrooms can have beneficial effects on firm performance, but the benefits may be subject to the critical mass and firm industry.

scholarly journals Gendered Representation and Critical Mass: Women’s Legislative Representation and Social Spending in 22 OECD Countries

2017 ◽  
Vol 60 (6) ◽  
pp. 1097-1114 ◽  
Author(s):  
Soon Seok Park
Keyword(s):  
Linear Models ◽  
Critical Mass ◽  
Percent Level ◽  
Mass Effect ◽  
Welfare States ◽  
Critical Threshold ◽  
Policy Outcomes ◽  
Social Spending ◽  
Data Set ◽  
Legislative Representation

To better understand the dynamics of representation of women’s interests such as public expenditure on healthcare, daycare, and education, this study examines statistical evidence for the notion of critical mass. To do so, this study uses the Comparative Welfare States Data Set and the piecewise regression method to produce two linear models that best fit to the data for different ranges of the share of seats in parliament held by women. The analysis fails to find consistent support for a threshold below which women legislators have little-to-no impact upon policy outcomes. By adjudicating seven hypothetical thresholds, the analysis also shows that when there is a critical mass effect, the 10 percent level is more a consequential threshold than 15, 20, or 30 percent levels. Findings suggest that we reject the idea of a critical threshold for women’s legislative representation. However, the relationship between the representation and social spending is robust with or without presumed critical mass.

Perceived critical mass effect on groupware acceptance

2000 ◽  
Vol 9 (2) ◽  
pp. 91-103 ◽  
Author(s):  
H Lou ◽  
W Luo ◽  
D Strong
Keyword(s):  
Critical Mass ◽  
Mass Effect

Board Gender Diversity in the STEM&F Sectors: The Critical Mass Required to Drive Firm Performance

2018 ◽  
Vol 25 (3) ◽  
pp. 290-308 ◽  
Author(s):  
Carolyn Wiley ◽  
Mireia Monllor-Tormos
Keyword(s):  
Firm Performance ◽  
Divergent Thinking ◽  
Critical Mass ◽  
Gender Diversity ◽  
Mass Effect ◽  
Theoretical Framework ◽  
Corporate Board ◽  
Reverse Causality ◽  
Engineering Mathematics ◽  
Board Gender Diversity

This study investigates the link between board gender diversity (BGD) and firm performance (FP). The analysis is conducted using Fortune 500 firms in the Science, Technology, Engineering, Mathematics, and Finance (STEM&F) sectors covering a period of seven years, from 2007 to 2013. The theoretical framework combines several theories that give shape to the critical mass effect of BGD on FP. This shape shows that below the critical mass threshold, BGD may represent a disadvantage to the board as it may facilitate the formation of subgroups, dysfunctional conflicts, and distrust. However, at or above the critical mass threshold, BGD facilitates better monitoring of management, greater resource provisions, and divergent thinking. To ensure sound results, this study addresses endogeneity concerns regarding omitted variable bias, reverse causality, and dynamic endogeneity. These results support a significant U-shaped relationship between the number of female directors and FP in the STEM&F sectors. That is, BGD yields higher FP when there is a critical mass of women on the board. This finding remains robust when alternative proxies for BGD and FP are employed and is consistent with the predictions of our theoretical framework. Our analysis also reveals that the positive effect of BGD on FP increases when there is at least a critical mass of 30% of women on a corporate board. This finding suggests that boards that have reached a critical mass of 30% of women present a favorable environment to capitalize on innovative ideas arising from BGD.

scholarly journals The Origins of the Second Wave of COVID-19 in India - a Model-based investigation

2021 ◽  
Author(s):  
B Shayak ◽  
Mohit Manoj Sharma
Keyword(s):  
Infectious Disease ◽  
Critical Mass ◽  
Temporal Correlation ◽  
Mass Effect ◽  
Lessons Learned ◽  
Small Scale ◽  
Causal Connection ◽  
Interaction Patterns ◽  
Sequencing Data ◽  
Second Wave

Background. After months of declining or steady rates of daily COVID-19 cases, in April 2021 India experienced the onset of a massive second wave of the epidemic which overstressed its healthcare facilities and caused lakhs of casualties. During the wave, the reproduction number R in some places was 1·8 or greater. The origins of this wave are at best partially understood. Socioeconomic activities had been running at a relatively high level for several months prior to the wave, and there was no relaxation of non-pharmaceutical interventions (NPI) in the immediately preceding days. A causal connection between the second wave and organized gatherings such as election activities, religious festivals and farmers’ protests is impossible to establish due to absence of spatio-temporal correlation. Analysis of genomic sequencing data suggests that the emergence of the double mutant B1.617 and its sub-lineages cannot be the sole cause of the wave as well.Methods and results. In a companion study [1] we have constructed a mathematical model for COVID-19 transmission which accounts for heterogeneity in people’s interaction patterns. This model yields two phenomena of concern which are outside the purview of classical infectious disease dynamical understanding. These phenomena are • cryptogenic instability in which relatively small-scale social gatherings such as marriage functions and birthday parties play a disproportionately high role in driving spread, and • critical mass effect in which very low case counts result in a temporary and artificial suppression of an existing instability.Principal findings. We believe that the above two phenomena are primarily responsible for the suddenness and severity of the second wave of COVID-19 in India. Complacency prevailing in early 2021 and emergence of mutant strain are not root causes of the wave but contributory factors to disease burden. The origins of the wave are complex and multifactorial, being largely governed by infectious disease dynamics which were unknown at the time of its onset. The lessons learned from the experience must be used to guide future course of NPI, not just in India but in other countries as well until significant fractions of their respective populations have been vaccinated.

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