Effect of manual and digital contact tracing on COVID-19 outbreaks: a study on empirical contact data

Non-pharmaceutical interventions are crucial to mitigate the COVID-19 pandemic and contain re-emergence phenomena. Targeted measures such as case isolation and contact tracing can alleviate the societal cost of lock-downs by containing the spread where and when it occurs. To assess the relative and combined impact of manual contact tracing (MCT) and digital (app-based) contact tracing, we feed a compartmental model for COVID-19 with high-resolution datasets describing contacts between individuals in several contexts. We show that the benefit (epidemic size reduction) is generically linear in the fraction of contacts recalled during MCT and quadratic in the app adoption, with no threshold effect. The cost (number of quarantines) versus benefit curve has a characteristic parabolic shape, independent of the type of tracing, with a potentially high benefit and low cost if app adoption and MCT efficiency are high enough. Benefits are higher and the cost lower if the epidemic reproductive number is lower, showing the importance of combining tracing with additional mitigation measures. The observed phenomenology is qualitatively robust across datasets and parameters. We moreover obtain analytically similar results on simplified models.     

Automated contact tracing: a game of big numbers in the time of COVID-19

One of the more widely advocated solutions for slowing down the spread of COVID-19 has been automated contact tracing. Since proximity data can be collected by personal mobile devices, the natural proposal has been to use this for automated contact tracing providing a major gain over a manual implementation. In this work, we study the characteristics of voluntary and automated contact tracing and its effectiveness for mapping the spread of a pandemic due to the spread of SARS-CoV-2. We highlight the infrastructure and social structures required for automated contact tracing to work. We display the vulnerabilities of the strategy to inadequate sampling of the population, which results in the inability to sufficiently determine significant contact with infected individuals. Of crucial importance will be the participation of a significant fraction of the population for which we derive a minimum threshold. We conclude that relying largely on automated contact tracing without population-wide participation to contain the spread of the SARS-CoV-2 pandemic can be counterproductive and allow the pandemic to spread unchecked. The simultaneous implementation of various mitigation methods along with automated contact tracing is necessary for reaching an optimal solution to contain the pandemic.     

The effect of contact load reduction on the fatigue life of pearlitic rail steel in lubricated rolling–sliding contact

Twin-disc contact simulation tests were carried out to investigate the influence of contact pressure variation on rail steel fatigue life. Both a colloidal suspension of molybdenum disulphide in an oil carrier fluid (similar to a commercial flange lubrication product) and water were used as lubricants. It was found that the reduction from 1500 to 900 MPa of the maximum Hertzian contact pressure (at which a molybdenum–disulphide-lubricated and previously worn rail sample was tested) extended the fatigue life of the rail steel by over five times. For water lubrication a similar reduction in contact pressure produced only a marginal increase in fatigue life. The results were found to be in qualitative agreement with the predictions of the newly developed Three Mechanism (TM) model of rolling contact fatigue, which is introduced here. This model combines the mechanisms of ratcheting and the fracture mechanics-based mechanisms of both shear stress- and tensile stress-driven, fluid-assisted, crack growth.     

Causes of delayed outbreak responses and their impacts on epidemic spread

Livestock diseases have devastating consequences economically, socially and politically across the globe. In certain systems, pathogens remain viable after host death, which enables residual transmissions from infected carcasses. Rapid culling and carcass disposal are well-established strategies for stamping out an outbreak and limiting its impact; however, wait-times for these procedures, i.e. response delays, are typically farm-specific and time-varying due to logistical constraints. Failing to incorporate variable response delays in epidemiological models may understate outbreak projections and mislead management decisions. We revisited the 2001 foot-and-mouth epidemic in the United Kingdom and sought to understand how misrepresented response delays can influence model predictions. Survival analysis identified farm size and control demand as key factors that impeded timely culling and disposal activities on individual farms. Using these factors in the context of an existing policy to predict local variation in response times significantly affected predictions at the national scale. Models that assumed fixed, timely responses grossly underestimated epidemic severity and its long-term consequences. As a result, this study demonstrates how general inclusion of response dynamics and recognition of partial controllability of interventions can help inform management priorities during epidemics of livestock diseases.     

Influencing dynamics on social networks without knowledge of network microstructure

Social network-based information campaigns can be used for promoting beneficial health behaviours and mitigating polarization (e.g. regarding climate change or vaccines). Network-based intervention strategies typically rely on full knowledge of network structure. It is largely not possible or desirable to obtain population-level social network data due to availability and privacy issues. It is easier to obtain information about individuals’ attributes (e.g. age, income), which are jointly informative of an individual’s opinions and their social network position. We investigate strategies for influencing the system state in a statistical mechanics based model of opinion formation. Using synthetic and data-based examples we illustrate the advantages of implementing coarse-grained influence strategies on Ising models with modular structure in the presence of external fields. Our work provides a scalable methodology for influencing Ising systems on large graphs and the first exploration of the Ising influence problem in the presence of ambient (social) fields. By exploiting the observation that strong ambient fields can simplify control of networked dynamics, our findings open the possibility of efficiently computing and implementing public information campaigns using insights from social network theory without costly or invasive levels of data collection.     

The role of heterogeneity in contact timing and duration in network models of influenza spread in schools

Influenza poses a significant health threat to children, and schools may play a critical role in community outbreaks. Mathematical outbreak models require assumptions about contact rates and patterns among students, but the level of temporal granularity required to produce reliable results is unclear. We collected objective contact data from students aged 5–14 at an elementary school and middle school in the state of Utah, USA, and paired those data with a novel, data-based model of influenza transmission in schools. Our simulations produced within-school transmission averages consistent with published estimates. We compared simulated outbreaks over the full resolution dynamic network with simulations on networks with averaged representations of contact timing and duration. For both schools, averaging the timing of contacts over one or two school days caused average outbreak sizes to increase by 1–8%. Averaging both contact timing and pairwise contact durations caused average outbreak sizes to increase by 10% at the middle school and 72% at the elementary school. Averaging contact durations separately across within-class and between-class contacts reduced the increase for the elementary school to 5%. Thus, the effect of ignoring details about contact timing and duration in school contact networks on outbreak size modelling can vary across different schools.     

Assessing the effect of dynamics on the closed-loop protein-folding hypothesis

The closed-loop (loop-n-lock) hypothesis of protein folding suggests that loops of about 25 residues, closed through interactions between the loop ends (locks), play an important role in protein structure. Coarse-grain elastic network simulations, and examination of loop lengths in a diverse set of proteins, each supports a bias towards loops of close to 25 residues in length between residues of high stability. Previous studies have established a correlation between total contact distance (TCD), a metric of sequence distances between contacting residues (cf. contact order), and the log-folding rate of a protein. In a set of 43 proteins, we identify an improved correlation (r² = 0.76), when the metric is restricted to residues contacting the locks, compared to the equivalent result when all residues are considered (r² = 0.65). This provides qualified support for the hypothesis, albeit with an increased emphasis upon the importance of a much larger set of residues surrounding the locks. Evidence of a similar-sized protein core/extended nucleus (with significant overlap) was obtained from TCD calculations in which residues were successively eliminated according to their hydrophobicity and connectivity, and from molecular dynamics simulations. Our results suggest that while folding is determined by a subset of residues that can be predicted by application of the closed-loop hypothesis, the original hypothesis is too simplistic; efficient protein folding is dependent on a considerably larger subset of residues than those involved in lock formation.     

DEM study of the effect of impeller design on mixing performance in a U-shape ribbon mixer

The mixing of powders in a U-shape mixer is significantly influenced by the mixer design, especially impellers, but the studies on the mixing processes are still insufficient. In this study, the effect of impeller designs on mixing performance in an industrial-scale U-shaped ribbon mixer is studied using DEM simulations. Three impeller designs are studied: 2-bladed impeller spiralling in the same direction (i.e., Design I) and the opposite direction (i.e., Design II), and 4-bladed impeller (i.e., Design III). Different particle mixing behaviours in three different impeller designs are studied in aspects of mixing status, particle path line, velocity distribution, and forces. The radial direction has the highest dispersion coefficient while the axial direction has the lowest dispersion coefficient. Most particles in the mixers are imposed a weak force. Design III shows the best mixing performance among the three with the front-by-back and top-by-bottom loading used. Design II shows a better mixing performance used than Design I and III with the side-by-side loading but takes a longer time to reach the stable status. This work evaluates the effect of different impeller designs on the mixing performance in an industrial-scale U-shaped ribbon mixer and provides an effective way to assist industrial design in an economical and safe manner.     

示踪气体混合均匀性的试验研究

为探讨示踪气体与被测气体实现均匀混合的条件,以CO作为示踪气体,以空气作为被测气体,在直径为0.300 m的90°弯曲管道内对示踪气体与空气的混合均匀性进行了试验研究.结果表明,在本试验条件下,当混合气体流速大于3.2 m/s时,在弯管下游的12D(D为管道内径)和15D处,示踪气体的径向和轴向平均体积分数误差小于4%,示踪气体的实测平均体积分数与理论值趋于一致,可认为示踪气体与空气的混合达到了均匀.因此,工业气体的管道输送过程中采用示踪法校准气体流量计时,可在满足上述条件的位置处作为取样点.     

橡胶连续混炼粉料混合均匀性仿真及实验研究

为了提高橡胶连续混炼中混炼胶质量稳定性,实现炭黑等粉体物料精确配比和均匀性混合问题,针对粉体物料在混合和输送过程存在复杂的物理性质,建立了炭黑等混合粉料的球体颗粒模型和Hertz接触力-位移模型,采用EDEM对典型粉体物料混合均匀性进行模拟仿真和粉体物料混合实验,对炭黑等粉体物料在橡胶连续混炼工艺中的混合均匀性进行分析,探求橡胶粉料连续混合和输送机理.研究发现:粉体物料混合仿真与实验测试结果具有较高的拟合性,表明在橡胶连续混炼工艺中可以在保证混合均匀性的前提下实现多粉体混合物的连续称量和输送,同时也验证了运用EDEM数据模拟仿真粉体物料混合的可行性.     

The effect of turbulent mixing on the dynamics of a liquid layer accelerated by a compressed air flow

The influence of a turbulent mixing (TM), developed at the unstable boundary of a liquid layer accelerated by a hot compressed gas flow, on the efficiency of the subsequent energy transfer from the accelerated liquid layer to a gas layer compressed by the liquid was experimentally studied. It was found that the TM development may significantly decrease the energy takeoff by the accelerated liquid layer, which is explained by cooling of the hot compressed gas as a result of the increased heat transfer from gas to liquid in the TM zone. The experimental data indicate that the gas energy losses can reach several tens percent.     

Probabilistic patterns of interaction: the effects of link-strength variability on food web structure

Patterns of species interactions affect the dynamics of food webs. An important component of species interactions that is rarely considered with respect to food webs is the strengths of interactions, which may affect both structure and dynamics. In natural systems, these strengths are variable, and can be quantified as probability distributions. We examined how variation in strengths of interactions can be described hierarchically, and how this variation impacts the structure of species interactions in predator–prey networks, both of which are important components of ecological food webs. The stable isotope ratios of predator and prey species may be particularly useful for quantifying this variability, and we show how these data can be used to build probabilistic predator–prey networks. Moreover, the distribution of variation in strengths among interactions can be estimated from a limited number of observations. This distribution informs network structure, especially the key role of dietary specialization, which may be useful for predicting structural properties in systems that are difficult to observe. Finally, using three mammalian predator–prey networks (two African and one Canadian) quantified from stable isotope data, we show that exclusion of link-strength variability results in biased estimates of nestedness and modularity within food webs, whereas the inclusion of body size constraints only marginally increases the predictive accuracy of the isotope-based network. We find that modularity is the consequence of strong link-strengths in both African systems, while nestedness is not significantly present in any of the three predator–prey networks.     

大规模接触转台系统动力学建模与仿真

在分析了大型柔性转台研制难点的基础上,提出了采用多柔体动力学方法进行大型柔性转台系统的建模与仿真.在解决柔性轴承大规模接触问题建模的前提下,建立了某柔性转台系统的多柔体虚拟样机,基于该虚拟样机获得了转台撑腿、外环、钢珠的位移和应力随时间、空间的变化特性.最后基于多体动力学的仿真分析结果完成了整个转台系统的疲劳寿命仿真分析.本文所建立的大型柔性转台的虚拟样机为其正式产品的工程设计验证提供了有力的技术手段.     

Study of low‐temperature effect on the fracture locus of a 420‐MPa structural steel with the edge tracing method

Quasi‐static tensile tests with smooth round bar and axisymmetric notched tensile specimens have been performed to study the low‐temperature effect on the fracture locus of a 420‐MPa structural steel. Combined with a digital high‐speed camera and a 2‐plane mirror system, specimen deformation was recorded in 2 orthogonal planes. Pictures taken were then analysed with the edge tracing method to calculate the minimum cross‐section diameter reduction of the necked/notched specimen. Obvious temperature effect was observed on the load‐strain curves for smooth and notched specimens. Both the strength and strain hardening characterized by the strain at maximum load increase with temperature decrease down to ?60°C. Somewhat unexpected, the fracture strains (ductility) of both smooth and notched specimens at temperatures down to ?60°C do not deteriorate, compared with those at room temperature. Combined with numerical analyses, it shows that the effect of low temperatures (down to ?60°C) on fracture locus is insignificant. These findings shed new light on material selection for Arctic operation.     

车轮阻尼及接触点位置对轮轨接触过程稳定性的影响

结合S形辐板辗钢整体车轮和60 kg/m钢轨的尺寸与性能要求,利用有限元法和模态试验法建立车轮高频振动模型,并在考虑钢轨断面变形和轨下结构影响的基础上建立钢轨高频振动模型。在改变轮轨接触点位置和车轮模态阻尼比的情况下对轮轨接触系统进行了稳定性分析。结果表明:节圆数为0的车轮模态对系统稳定性的影响最明显;增大横向蠕滑量会使轮轨接触系统容易发生不稳定,并且该蠕滑量在轮缘接触时的影响比在踏面时要大;接触点位置对接触系统稳定性的影响与轮轨偏向角及接触面摩擦系数的大小有关;增大车轮阻尼能明显减少接触系统不稳定频率的个数,并且在偏向角较大时,阻尼的作用对轮缘接触更明显。     

微量稀土对Cu-Ag接触线性能的影响

接触线(又称电车线)是电气化铁路接触网的主要元件。随着电气化列车向高速、重载的发展。对接触线提出了高强度、高导电、耐高温等多方面性能上的更高要求。本文研究了稀土对电气化铁路用接触线Cu-0．1Ag的强度、硬度、导电性和耐高温性等的影响。结果表明：微量稀土元素的加入可以提高银铜接触线的强度、硬度和耐热性．强度可达470MPa．相对于银铜接触线提高了73MPa；而对银铜接触线的导电性影响很小。     

接触角的测量方法与发展

本文探讨了接触角测量的理论依据、常用方法、接触角滞后的影响因素以及Young方程的适用范围;对接触角测量方法的发展进行阐述,着重于动态接触角的测量。     

SNCR过程还原剂与烟气混合特性数值研究

以某台220t/h煤粉锅炉为研究对象,对选择性非催化还原过程中尿素溶液还原剂与烟气的混合问题进行数值研究.计算表明,还原剂液滴喷入炉内1 100℃左右的高温区后,迅速经历加热、沸腾和蒸发过程,液滴的停留时间很短,因此增加还原剂射流穿透深度可有效提高混合程度.以还原剂质量分数的相对标准偏差为混合程度的衡量指标,分析了还原剂喷射速度、流量、液滴粒径以及锅炉等因素的影响,发现降低锅炉负荷、提高还原剂喷射速度和流量均可有效提高混合程度,而液滴粒径对混合具有双重影响,一般存在最佳粒径范围.     

Recognition and classification of single and concurrent unnatural patterns in control charts via neural networks and fitted line of samples

The correct, prompt recognition and analysis of unnatural and significant patterns in Schewhart’s control charts are very important since they remind out-of-control conditions. In fact, pattern extraction increases the sensitivity of charts when identifying out of control conditions. Artificial neural networks have been used to identify unnatural patterns in many research studies due to their high efficiency in pattern recognition. In most of such studies, there is a significant risk of misclassification of highly sensitive patterns. To put it more clearly, the proposed models offered for the recognition of patterns with low parametric coefficients are mistaken. This study, offers a model for the recognition and analysis of basic patterns in process control charts using LVQ and MLP networks along with a fitted line analysis. In this model, not only does risk of misclassification at different levels of sensitivity decrease remarkably, but there will also be the possibility for recognition and analysis when basic pattern occur simultaneously. The efficiency and effectiveness of the model are shown by conducting tests based on simulation.