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Sherry Towers

Publications and source records attributed to Sherry Towers.

10 recordsLinked to original sources
arXiv2018

Assessing the impact of non-vaccinators: quantifying the average length of infection chains in outbreaks of vaccine-preventable disease

Analytical expressions for the basic reproduction number, R0, have been obtained in the past for a wide variety of mathematical models for infectious disease spread, along with expressions for the expected final size of an outbreak. However, what has so far not been studied is the average number of infections that descend down the chains of infection begun by each of the individuals infected in an outbreak (we refer to this quantity as the "average number of descendant infections" per infectious individual, or ANDI). ANDI includes not only the number of people that an individual directly contacts and infects, but also the number of people that those go on to infect, and so on until that particular chain of infection dies out. Quantification of ANDI has relevance to the vaccination debate, since with ANDI one can calculate the probability that one or more people are hospitalised (or die) from a disease down an average chain of infection descending from an infected un-vaccinated individual. Here we obtain estimates of ANDI using both deterministic and stochastic modelling formalisms. With both formalisms we find that even for relatively small community sizes and under most scenarios for R0 and initial fraction vaccinated, ANDI can be surprisingly large when the effective reproduction number is >1, leading to high probabilities of adverse outcomes for one or more people down an average chain of infection in outbreaks of diseases like measles.

q-bio.PE↗
arXiv2017

Quantifying the relative effects of environmental and direct transmission of norovirus

Background: Norovirus is a common cause of outbreaks of acute gastroenteritis in health- and child-care settings, with serial outbreaks also frequently observed aboard cruise ships. The relative contributions of environmental and direct person-to-person transmission of norovirus has hitherto not been quantified. Objective: We employ a novel mathematical model of norovirus transmission, and fit the model to daily incidence data from a major norovirus outbreak on a cruise ship, and examine the relative efficacy of potential control strategies aimed at reducing environmental and/or direct transmission. Results: The reproduction number for environmental and direct transmission combined is Rtot = 11.0 [9.4,15.6], and of environmental transmission alone is Renviron = 0.85 [0.18,2.04]. Direct transmission is overwhelmingly due to 0 passenger-to-passenger contacts, but crew can act as a reservoir of infection from cruise-to-cruise. Implications: This is the first quantification of the relative roles of environmental and direct transmission of norovirus. While environmental transmission has the potential to maintain a sustained series of outbreaks aboard a cruise ship in the absence of strict sanitation practices, direct transmission dominates. Quarantine of ill passengers and cleaning are likely to have little impact on final outbreak size, but intensive promotion of good hand washing practices can prevent outbreaks.

q-bio.QM↗
arXiv2017

Advanced geometrical constructs in a Pueblo ceremonial site, c 1200 CE

Summer 2015 marked the 100th anniversary of the excavation by J.W. Fewkes of the Sun Temple in Mesa Verde National Park, Colorado, an ancient complex prominently located atop a mesa, constructed by the ancestral Pueblo peoples approximately 800 years ago. While the D-shaped structure is generally recognized by modern Pueblo peoples as a ceremonial complex, the exact uses of the site are unknown, although the site has been shown to have key solar and lunar alignments. In this study, we examined the potential that the site was laid out using advanced knowledge of geometrical constructs. Using aerial imagery in conjunction with ground measurements, we performed a survey of key features of the site. We found apparent evidence that the ancestral Pueblo peoples laid out the site using the Golden rectangle, Pythagorean 3:4:5 triangles, equilateral triangles, and 45 degree right triangles. The survey also revealed that a single unit of measurement, L = 30.5+/-0.5 cm, or one third of that, appeared to be associated with many key features of the site. Further study is needed to determine if this unit of measurement is common to other ancestral Pueblo sites, and also if geometric constructs are apparent at other sites. These findings represent the first potential quantitative evidence of knowledge of advanced geometrical constructs in a prehistoric North American society, which is particularly remarkable given that the ancestral Pueblo peoples had no written language or number system.

math.HO↗
arXiv2017

Estimate of the reproduction number of the 2015 Zika virus outbreak in Barranquilla, Colombia, and estimation of the relative role of sexual transmission

Background: In 2015, the Zika arbovirus (ZIKV) began circulating in the Americas, rapidly expanding its global geographic range in explosive outbreaks. Unusual among mosquito-borne diseases, ZIKV has been shown to also be sexually transmitted, although sustained autochthonous transmission due to sexual transmission alone has not been observed, indicating the reproduction number (R0) for sexual transmission alone is less than 1. Critical to the assessment of outbreak risk, estimation of the potential attack rates, and assessment of control measures, are estimates of the basic reproduction number, R0. Methods: We estimated the R0 of the 2015 ZIKV outbreak in Barranquilla, Colombia, through an analysis of the exponential rise in clinically identified ZIKV cases (n = 359 to the end of November, 2015). Findings: The rate of exponential rise in cases was rho=0.076 days-1, with 95 percent CI [0.066,0.087] days-1. We used a vector-borne disease model with additional direct transmission to estimate the R0; assuming the R0 of sexual transmission alone is less than 1, we estimated the total R0 = 3.8 [2.4,5.6], and that the fraction of cases due to sexual transmission was 0.23 [0.01,0.47] with 95 percent confidence. Interpretation: This is among the first estimates of R0 for a ZIKV outbreak in the Americas, and also among the first quantifications of the relative impact of sexual transmission.

q-bio.QM↗
arXiv2016

Astronomical Alignments of the Sun Temple site in Mesa Verde National Park

Summer 2015 marked the 100th anniversary of the excavation by J.W. Fewkes of the Sun Temple in Mesa Verde National Park, Colorado; an ancient ceremonial complex of unknown purpose, prominently located atop a mesa, constructed by the Pueblo Indians approximately 1000 years ago. In this analysis we perform a digital survey of the site, and examine the possibility that four key tower-like elements of the complex were used for observation of the rise or set of celestial bodies known to be sacred to the Pueblo Indians. We find statistically significant evidence that the site was used for astronomical observation of the rise and/or set of nearly all such bodies. The Sun Temple appears to represent the most comprehensive prehistoric astronomical observatory yet uncovered.

physics.hist-ph↗
arXiv2016

Some Models for Epidemics of Vector-Transmitted Diseases

Vector-transmitted diseases such as dengue fever and chikungunya have been spreading rapidly in many parts of the world. The Zika virus has been known since 1947 and invaded South America in 2013. It can be transmitted not only by (mosquito) vectors but also directly through sexual contact. Zika has developed into a serious global health problem because, while most cases are asymptomatic or very light, babies born to Zika - infected mothers may develop microcephaly and other very serious birth defects. We formulate and analyze two epidemic models for vector-transmitted diseases, one appropriate for dengue and chikungunya fever outbreaks and one that includes direct transmission appropriate for Zika virus outbreaks. This is especially important because the Zika virus is the first example of a disease that can be spread both indirectly through a vector and directly (through sexual contact). In both cases, we obtain expressions for the basic reproduction number and show how to use the initial exponential growth rate to estimate the basic reproduction number. However, for the model that includes direct transmission some additional data would be needed to identify the fraction of cases transmitted directly. Data for the 2015 Zika virus outbreak in Barranquilla, Colombia has been used to fit parameters to the model developed here and to estimate the basic reproduction number.

q-bio.PE↗
arXiv2014

The Dynamics of Offensive Messages in the World of Social Media: the Control of Cyberbullying on Twitter

The 21st century has redefined the way we communicate, our concept of individual and group privacy, and the dynamics of acceptable behavioral norms. The messaging dynamics on Twitter, an internet social network, has opened new ways/modes of spreading information. As a result cyberbullying or in general, the spread of offensive messages, is a prevalent problem. The aim of this report is to identify and evaluate conditions that would dampen the role of cyberbullying dynamics on Twitter. We present a discrete-time non-linear compartmental model to explore how the introduction of a Quarantine class may help to hinder the spread of offensive messages. We based the parameters of this model on recent Twitter data related to a topic that communities would deem most offensive, and found that for Twitter a level of quarantine can always be achieved that will immediately suppress the spread of offensive messages, and that this level of quarantine is independent of the number of offenders spreading the message. We hope that the analysis of this dynamic model will shed some insights into the viability of new models of methods for reducing cyberbullying in public social networks.

cs.SI↗
arXiv2010

Short-term heterologous immunity after severe influenza A outbreaks

Conventional wisdom holds that influenza A and B are such genetically dissimilar viruses that infection with one cannot confer cross-immunity to the other. However, our examination of the records of the past 25 influenza seasons in the U.S. reveals that almost every time there is an early and severe influenza A outbreak, the annual influenza B epidemic is almost entirely suppressed (and is never suppressed otherwise). Temporary broad-spectrum (aka "heterologous") immunity in the aftermath of influenza infection is the most direct explanation for this phenomenon. We find a remarkably weak degree of temporary cross-immunity is needed to explain these patterns, and that indeed influenza B provides an ideal setting for the observation of heterologous immune effects outside of the carefully controlled environment of a laboratory.

q-bio.PE↗
arXiv2005

A Study of the Leaky Pipeline Phenomenon for Women in Physics Past the Postdoctoral Level, and a Critique of the AIP 2005 report on Women in Physics and Astronomy

The author has recently examined the departmental web pages of the `top 50' physics research universities, as ranked by the National Research Council (NRC). Most of the departmental web pages contained biographical data (ie; year and institute of PhD, etc) of their faculty members. Of the approximately 1750 faculty members at the `top 50' universities that were examined, approximately 100 were female, and around 1425 had available biographical data. Based on this data, the predicted fractions of female faculty members at the `top 50' universities are 0.129, 0.104, and 0.052 at the assistant, associate, and full faculty levels, respectively. The observed fractions are 0.107, 0.109, 0.043, respectively. The overall observed number of women faculty is about 15% less than expected, and the depletion is statistically significant. Unfortunately, the study finds that the "leaky pipeline" is found to be alive and well for women in academic physics above the postdoctoral level, at all stages of the faculty career ladder. This result is stark contrast with the conclusion of the American Institute of Physics (AIP) 2005 report on Women in Physics and Astronomy; the AIP report concludes that women are actually more likely to be hired at the faculty level than their male peers. In this paper, we will discuss the two key flaws in the AIP analysis that led to their faulty conclusion, then describe in detail the analysis performed by the author that corrects these flaws to get an accurate estimate of the `leakiness' of the academic pipeline for women physicists past the postdoctoral level.

physics.soc-ph↗