Social encounter networks: collective properties and disease transmission

A fundamental challenge of modern infectious disease epidemiology is to quantify the networks of social and physical contacts through which transmission can occur. Understanding the collective properties of these interactions is critical for both accurate prediction of the spread of infection and determining optimal control measures. However, even the basic properties of such networks are poorly quantified, forcing predictions to be made based on strong assumptions concerning network structure. Here, we report on the results of a large-scale survey of social encounters mainly conducted in Great Britain. First, we characterize the distribution of contacts, which possesses a lognormal body and a power-law tail with an exponent of −2.45; we provide a plausible mechanistic model that captures this form. Analysis of the high level of local clustering of contacts reveals additional structure within the network, implying that social contacts are degree assortative. Finally, we describe the epidemiological implications of this local network structure: these contradict the usual predictions from networks with heavy-tailed degree distributions and contain public-health messages about control. Our findings help us to determine the types of realistic network structure that should be assumed in future population level studies of infection transmission, leading to better interpretations of epidemiological data and more appropriate policy decisions.     

Infectious disease control using contact tracing in random and scale-free networks.

Contact tracing aims to identify and isolate individuals that have been in contact with infectious individuals. The efficacy of contact tracing and the hierarchy of traced nodes-nodes with higher degree traced first-is investigated and compared on random and scale-free (SF) networks with the same number of nodes N and average connection K. For values of the transmission rate larger than a threshold, the final epidemic size on SF networks is smaller than that on corresponding random networks. While in random networks new infectious and traced nodes from all classes have similar average degrees, in SF networks the average degree of nodes that are in more advanced stages of the disease is higher at any given time. On SF networks tracing removes possible sources of infection with high average degree. However a higher tracing effort is required to control the epidemic than on corresponding random networks due to the high initial velocity of spread towards the highly connected nodes. An increased latency period fails to significantly improve contact tracing efficacy. Contact tracing has a limited effect if the removal rate of susceptible nodes is relatively high, due to the fast local depletion of susceptible nodes.     

Beyond contact-based transmission networks: the role of spatial coincidence

Animal societies rely on interactions between group members to effectively communicate and coordinate their actions. To date, the transmission properties of interaction networks formed by direct physical contacts have been extensively studied for many animal societies and in all cases found to inhibit spreading. Such direct interactions do not, however, represent the only viable pathways. When spreading agents can persist in the environment, indirect transmission via ‘same-place, different-time’ spatial coincidences becomes possible. Previous studies have neglected these indirect pathways and their role in transmission. Here, we use rock ant colonies, a model social species whose flat nest geometry, coupled with individually tagged workers, allowed us to build temporally and spatially explicit interaction networks in which edges represent either direct physical contacts or indirect spatial coincidences. We show how the addition of indirect pathways allows the network to enhance or inhibit the spreading of different types of agent. This dual-functionality arises from an interplay between the interaction-strength distribution generated by the ants'' movement and environmental decay characteristics of the spreading agent. These findings offer a general mechanism for understanding how interaction patterns might be tuned in animal societies to control the simultaneous transmission of harmful and beneficial agents.     

Spatial analyses of wildlife contact networks

Datasets from which wildlife contact networks of epidemiological importance can be inferred are becoming increasingly common. A largely unexplored facet of these data is finding evidence of spatial constraints on who has contact with whom, despite theoretical epidemiologists having long realized spatial constraints can play a critical role in infectious disease dynamics. A graph dissimilarity measure is proposed to quantify how close an observed contact network is to being purely spatial whereby its edges are completely determined by the spatial arrangement of its nodes. Statistical techniques are also used to fit a series of mechanistic models for contact rates between individuals to the binary edge data representing presence or absence of observed contact. These are the basis for a second measure that quantifies the extent to which contacts are being mediated by distance. We apply these methods to a set of 128 contact networks of field voles (Microtus agrestis) inferred from mark–recapture data collected over 7 years and from four sites. Large fluctuations in vole abundance allow us to demonstrate that the networks become increasingly similar to spatial proximity graphs as vole density increases. The average number of contacts, , was (i) positively correlated with vole density across the range of observed densities and (ii) for two of the four sites a saturating function of density. The implications for pathogen persistence in wildlife may be that persistence is relatively unaffected by fluctuations in host density because at low density is low but hosts move more freely, and at high density is high but transmission is hampered by local build-up of infected or recovered animals.     

Temporal variation of contact networks in granular materials

For analogue granular materials simulated using DEM, contact networks are often drawn by joining the centroids of contacting particles. Although a limited amount of research has been done to characterise the temporal aspects of such contact networks at a micro-scale, many simple questions regarding the duration of contacts in evolving granular systems remain unanswered. This paper addresses this gap in the existing knowledge by using the open-source code LAMMPS to run and analyse nine (3D) triaxial simulations of 20,164 polydisperse spherical particles. Contacts which exist for a long duration are preferentially oriented in the direction of the major principal stress while the fabric anisotropy for contacts with a given duration increases with duration. Regardless of simulation conditions, there is a linear relationship between the percentage of contacts present for a given duration and contact duration, despite the non-linear overall behaviour of the material. The forces transmitted by contacts increase, on average, with increasing duration. The total number of unique contacts which appear during triaxial compression increases linearly after 10 % axial strain, although the number of contacts, both total and subdivided into strong and weak force subnetworks, remains quite stable. The majority of contacts in these evolving granular systems, even those participating in strong force chains, are formed and lost repeatedly.     

Optimal control of the process of heat transmission between bodies in contact

Problems of optimal fast-response control of the process of heat transmission between bodies in contact are considered under constraints on the thermoelastic stresses. Analytic expressions are obtained for the control function — the thermal contact resistance.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 4, pp. 718–723, October, 1978.     

Optimal allocation of multi-state retransmitters in acyclic transmission networks

In this paper, an algorithm for optimal allocation of multi-state elements (MEs) in acyclic transmission networks (ATNs) is suggested. The ATNs consist of a number of positions (nodes) in which MEs capable of receiving and sending a signal are allocated. Each network has a root position where the signal source is located, a number of leaf positions that can only receive a signal, and a number of intermediate positions containing MEs capable of transmitting the received signal to some other nodes. Each ME that is located in a nonleaf node can have different states determined by a set of nodes receiving the signal directly from this ME. The probability of each state is assumed to be known for each ME. The ATN reliability is defined as the probability that a signal from the root node is transmitted to each leaf node.The optimal distribution of MEs with different characteristics among ATN positions provides the greatest possible ATN reliability. The suggested algorithm is based on using a universal generating function technique for network reliability evaluation. A genetic algorithm is used as the optimization tool. Illustrative examples are presented.     

Electromagnetic compatibility analysis of unstructured mains networks for high-speed data transmission: Part 1

Different approaches for the characterisation of relevant parameters of the low-voltage mains network, used for high-speed data transmission (BPL, broadband over power line) are described. Part 1 of the paper depicts the disturbance scenario of these BPL devices and the motivation will be given for the development of a new measurement procedure in CISPR for the estimation of the high-frequency characteristics of AC mains network. The improvements of the measurement method is not restricted to BPL applications, but can also be applied to other wire-based telecommunication systems. Part 2 of the paper shows the definitions and comparisons of different symmetry factors. The transfer of the results on the compliance test for BPL devices will be shown.     

Electromagnetic compatibility analysis of unstructured mains networks for high-speed data transmission: Part 2

Different approaches are described for the characterisation of the low voltage mains network that is used for high-speed data transmission broadband over power line (BPL). Part 1 investigated the disturbance scenario of these BPL devices and importance will be given to develop a new measurement procedure in Comite Internationale Special des Perturbations Radioelectrotechnique (CISPR) to estimate the high- frequency characteristics of AC mains networks. The improvements of the measurement method that can also be applied to other wire-based telecommunication systems will also be presented. Part 2 shows the definitions and comparisons of different symmetry factors. The transfer of the results on the compliance test for BPL devices will also be depicted.     

Dual-band wearable metallic button antennas and transmission in body area networks

A dual-band metallic antenna with the appearance of a button on a pair of jeans for use with wearable computer networks, emergency rescue scenarios and future wireless medical applications is presented. The design operates at 2.4 GHz WLAN and the HiperLAN/2 bands and a parametric study is given to aid the design process together with measurement and simulation of the structure on a body. A study of transmission between pairs of on-body antennas is presented to give insight into on-body propagating line of sight and non-line of sight channels. A term `body gain? is defined to quantify how the body attenuates the channel.     

The design of a variable-step integrator for the simulation of gas transmission networks

The simulation of a large-scale gas transmission network involves the numerical solution of a large system of initial valued, stiff algebraic/differential equations. Rapid changes in the solution are present due to the disturbances generated by the varying consumer demand and the operation of network controlling devices such as compressors. This paper discusses the design of an efficient variable-step integrator for the solution of the problem. Two sets of strategies are presented for implementing the variable-step integrator; one for the implicit numerical method such as the diagonally implicit Runge–Kutta methods, and the other for the linearly implicit Rosenbrock-type method. The performance of the numerical methods implemented are compared with the British Gas simulation program PAN on a number of large, realistic transmission networks.     

脉冲激光信息的同步判断和捕捉

提出了采用面阵CCD,Fabry_Perot标准具测量脉冲激光波长时的同步判断和捕捉方法,其关键是正确选取序列图像的特征值,画出有关该特征值的统计直方图并选择合理算法确定有关该特征值的阈值;编写图像处理的回调函数,实现图像并行处理。根据CCD的PAL工作制式,用内插法重建捕捉到的图像,以利于后续图像处理。     

Lifetime improvement in wireless sensor networks via collaborative beamforming and cooperative transmission

Collaborative beamforming (CB) and cooperative transmission (CT) have recently emerged as communication techniques that can make effective use of collaborative/cooperative nodes to create a virtual multiple-input/multiple-output system. Extending the lifetime of networks composed of battery-operated nodes is a key issue in the design and operation of wireless sensor networks. The effects on network lifetime of allowing closely located nodes to use CB/CT to reduce the load or even to avoid packet-forwarding requests to nodes that have critical battery life are considered. First, the effectiveness of CB/CT in improving the signal strength at a faraway destination using energy in nearby nodes is studied. Then, the performance improvement obtained by this technique is analysed for a special 2D disc case. Further, for general networks in which information-generation rates are fixed, a new routing problem is formulated as a linear- programming problem, whereas for other general networks, the cost for routing is dynamically adjusted according to the amount of energy remaining and the effectiveness of CB/CT. From the analysis and the simulation results, it is seen that the proposed method can reduce the payloads of energy-depleting nodes by about 90% in the special case network considered and improve the lifetimes of general networks by about 10%, compared with existing techniques.     

A shock capturing application of the finite element method

The finite element method is employed for the calculation in Cartesian co-ordinates of uniform flow on a rectangular region which encounters an embedded oblique shock with known turning angle. A modified form of the code so developed is used to obtain preliminary results concerning finite element performance in the calculation of viscous recirculating flow with embedded weak shocks.     

Factors determining the potential for onward transmission of variant Creutzfeldt-Jakob disease via surgical instruments.

While the number of variant Creutzfeldt-Jakob disease (vCJD) cases continues to decline, concern has been raised that transmission could occur directly from one person to another through routes including the transfer of blood and shared use of surgical instruments. Here we firstly present data on the surgical procedures undertaken on vCJD patients prior to onset of clinical symptoms, which supports the hypothesis that cases via this route are possible. We then apply a mathematical framework to assess the potential for self-sustaining epidemics via surgical procedures. Data from hospital episode statistics on the rates of high- and medium-risk procedures in the UK were used to estimate model parameters, and sensitivity to other unknown parameters about surgically transmitted vCJD was assessed. Our results demonstrate that a key uncertainty determining the scale of an epidemic and whether it is self-sustaining is the number of times a single instrument is re-used, alongside the infectivity of contaminated instruments and the effectiveness of cleaning. A survey into the frequency of re-use of surgical instruments would help reduce these uncertainties.     

Renewable energy supply and carbon capture: capturing all the carbon dioxide at zero cost

Clean Technologies and Environmental Policy - Climate change is likely to be (and is) more serious and likely to proceed much more rapidly than was previously thought. This article surveys and...     

On the application of the locality principle in structural dynamics

Summary A complicated mechanical structure as an assemblage of substructures is considered. A method which enables us to find the exact vibrational state of any substructure within the whole structure will be offered. In order to achieve this aim a particular element will be under precise consideration, while the rest of the structure will be described integrally. It is shown that the vibration of a certain particular element of the structure depends mainly upon the composition of the element itself and upon certain generalized properties of the remote elements of the structure, and does not depend upon details of its composition. As a result of a consideration of two examples, the effect of backward influence of the vibration of a particular element on the general vibrational state of a whole structure will become evident. This means that the usual methods of neglecting the existence of a whole structure, and investigating a simplified problem such as a particular element under excitation are not correct in the general case.     

Design of biomimetic fibrillar interfaces: 1. Making contact.

This paper explores the contact behaviour of simple fibrillar interfaces designed to mimic natural contact surfaces in lizards and insects. A simple model of bending and buckling of fibrils shows that such a structure can enhance compliance considerably. Contact experiments on poly(dimethylsiloxane) (PDMS) fibrils confirm the model predictions. Although buckling increases compliance, it also reduces adhesion by breaking contact between fibril ends and the substrate. Also, while slender fibrils are preferred from the viewpoint of enhanced compliance, their lateral collapse under the action of surface forces limits the aspect ratio achievable. We have developed a quantitative model to understand this phenomenon, which is shown to be in good agreement with experiments.     

A performance measuring matrix for capturing the impact of AMT

New approaches are required to successfully justify and implement advanced manufacturing technology (AMT). This paper offers such a new approach by proposing an operational framework for measuring the impact of AMT on productivity gains at the firm level. The approach is a complement to the conventional input/output analysis and is based on the realization that any attempt to capture the benefits of AMT should emphasize the ‘outcome’ or effectiveness of the operation rather than only to accentuate its ‘output’ or efficiency. The framework presented is sufficiently general that it can be used in assessing any form of new technology and its introduction into the firm.