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ABSTRACT: To describe the epidemiological and clinical characteristics of 2009 H1N1 influenza, particularly the incubation period and the duration of symptoms, and to assess the public health response to this outbreak.
A retrospective cohort study was conducted among all students and employees in a middle school by telephone survey and laboratory inspection.
Nasopharyngeal specimens were collected and tested, and real-time reverse transcriptase polymerase chain reaction testing was performed to confirm the viral infection. The epidemiological and clinical characteristics were obtained through a telephone survey, and the incubation period and the duration of symptoms associated with 2009 H1N1 influenza were estimated by parametric distribution.
In total, 253 cases of influenza-like illness were found among students and employees, and 79 of these cases were confirmed as H1N1 infection through laboratory inspection. The response rate for the telephone survey was 93.48% for the students (2586/2768) and 85.87% for the employees (158/184). The average attack rate was 9.22% (253/2744). The main reported symptoms were fever (100%), cough (74.68%), sore throat (59.49%), headache (56.96%) and myalgia/arthralgia (51.90%). No complications were reported and no deaths occurred. The confirmed and suspected cases had no associated travel history or contact with a confirmed or probable case. The estimated median incubation period was 1.6 days [95% confidence interval (CI) 1.2-2.3]. The duration of symptoms was 3-11 days, and the median duration of symptoms was 7.5 days (95% CI 4.5-10.5).
The results suggest that the outbreak of 2009 H1N1 influenza in this middle school was widespread but not severe. The natural history of 2009 H1N1 influenza virus appears to be similar to that of previously circulating pandemic and interpandemic influenza viruses. The public health response indicates that school closure could have a substantial impact on the spread of 2009 H1N1 influenza.
Public health 02/2012; 126(4):289-94. · 1.26 Impact Factor
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05/2005: pages 280 - 289; , ISBN: 9783527603503
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ABSTRACT: Growth of equiaxed grains ahead of an advancing columnar front leads to the formation of as-cast defects, such as stray grains in single crystals or tree rings in vacuum arc remelting (VAR) ingots. In this study a combined cellular automata-finite difference model was applied to simulate dendrite growth and the formation of equiaxed grains in directionally solidified nickel-based superalloys. Realistic dendritic structures and complex solute concentration profiles at the growth front were simulated. It was observed that the solute interaction between primary dendrites occurs well below their tips, while strong solute interaction occurs between the diffusion fields of secondary and tertiary arms. The influence of thermal gradient and growth velocity on CET was investigated and the results were combined on a CET map, showing that a decrease in thermal gradient and an increase in growth rate favour a CET.
Journal of Materials Science 01/2004; 39(24):7207-7212. · 2.02 Impact Factor
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ABSTRACT: A cellular automaton model of the solid-liquid interface, combined with a finite difference computation of solute diffusion has been developed to simulate single crystal solidification in molds with step changes in geometry. Simulations were carried out for columnar dendrites passing from the narrow airfoil region of a blade into the platform region, which has an increased cross-sectional area. Different shapes of isotherms moving at a constant velocity were considered in the simulations. The change in mold geometry leads to a significant increase in the undercooling in front of the dendrite tips as they spread around the mold corner. The model was applied to geometries investigated by prior authors, correctly predicting the formation of a to boundary observed experimentally.
Journal of Materials Science 10/2003; 38(21):4385-4391. · 2.02 Impact Factor
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ABSTRACT: A scalable, continuous variable, cellular automaton (CA) model for the quantitative simulation of normal grain growth is presented. The CA model is based on a discrete solution of the classical Turnbull rate equation for grain boundary motion on a mesoscopic scale. The domain is discretised using a regular cubic lattice considering the first and second nearest neighbourhoods. CA rules were usedto determine the state of each cellbased on the local driving force. The effects of both the boundary curvature and the misorientation of grains were incorporated. The driving force was used to determine the direction of the movement of each boundary cell, forming the basis of a continuous variable cell transition rule. The use of experimental grain boundary characteristics (e.g. energy and mobility) allows one to make predictions on industrially applicable spatial and temporal scales. The model was applied to quantitatively predict grain growth during the homogenisation heat treatment of vacuum arc remelted Inconel 718.
Materials Science and Technology 06/2003; 19(7):859-865. · 0.77 Impact Factor
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ABSTRACT: This paper presents an adaptive end-to-end protocol for quality of service (QoS)-sensitive transport of real-time MPEG video using packet-level forward error correction in dynamic networks. The objective is to facilitate a user-specified QoS end-to-end — i.e. without special network support — for real-time MPEG video whose timing constraints rule out the use of retransmission-based congestion control and QoS provisioning schemes. The degree of redundancy — overcode in forward error correction — injected into the network is adjusted as a function of network state, decreasing when the network is well-behaved to minimize unnecessary network resource consumption, and increasing when it is not to compensate for adverse network effects so as to maintain an invariant level of end-to-end QoS. We describe an adaptive packet-level forward error correction protocol called AFEC and analyze its properties with respect to optimality and stability. The optimal control problem is nontrivial due to the fact that increased redundancy, beyond a certain point, can backfire resulting in self-induced congestion which impedes the timely recovery of information — MPEG video frames — at the receiver. We experimentally evaluate the efficacy of our end-to-end QoS control by implementing and customizing AFEC to the transport of real-time MPEG video. We realize the system as a transport/application layer protocol running on UNIX workstations, and measure its performance over controlled network environments. We show that AFEC is able to effectively hide potentially adverse network effects such as packet drops and delays stemming from traffic burstiness and nonstationary structural changes using adaptive redundancy control, exporting a constant QoS service commensurate with user-specified QoS.
Computer Communications.
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ABSTRACT: The thermosphere–ionosphere nested grid (TING) model has been successfully coupled with the Lyon–Fedder–Mobarry (LFM) global magnetosphere MHD code. The coupling between these models is two-way: the LFM provides the TING model with global electric fields and precipitating electron energy fluxes, and the TING model feeds ionospheric conductances back to the LFM. This code coupling enables studies of the global energy budget of the magnetosphere–ionosphere–thermosphere system. In this paper, we present simulation results from the coupled magnetosphere–ionosphere–thermosphere (CMIT) model under solar minimum, northern hemisphere summer conditions. The IMF input to the CMIT model changed its direction every 4 h. Comparisons are made between the simulated results of the CMIT model and those of the stand-alone TING model. It is found that the CMIT model predicted higher cross polar cap potential drops than the empirical model used by the stand-alone TING model. The energy input to the upper atmosphere by precipitating electrons, however, was much lower in the CMIT model during the southward IMF interval. The simulated responses of the thermosphere and ionosphere were also significantly different. As a result of the greater Joule heating calculated in the CMIT model, neutral temperatures and winds were significantly enhanced in the CMIT model in comparison with the stand-alone TING model.
Journal of Atmospheric and Solar-Terrestrial Physics.
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ABSTRACT: The paper develops a replacement action decision aid for a key furnace component subject to condition monitoring. A state space model is used to predict the erosion condition of the inductors in an induction furnace in which a measure of the conductance ratio (CR) is used to indirectly assess the relative condition of the inductors, and to guide replacement decisions. This study seeks to improve on this decision process by establishing the relationship between CR and the erosion condition of the inductors. To establish such a relationship, a state space model has been established and the system parameters estimated from CR data. A replacement cost model to balance at any time costly replacements with possible catastrophic failure is also proposed based upon the predicted probability of inductor erosion conditional upon all available information. The well known Kalman filter is employed to derive the predicted and updated probability of inductor erosion level conditional upon CR data to date. This is the first time the condition monitoring decision process has been modelled for real plant based upon filtering theory. The model fits the data well, gives a sensible answer to the actual problem, and is transferable to other condition monitoring contexts. Possible extensions are discussed in the paper.
European Journal of Operational Research.
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ABSTRACT: This paper describes a set of image segmentation algorithms for mineral froth images, based on gray-value valley detection and a kind of image classification. The size, shape, texture and color of froth bubbles are very important pieces of information for production optimization in mineral processing. In order to determine these parameters, bubbles in a froth image first have to be delineated. Froth images display a large variation of image patterns and quality, thus it is difficult to use only a single algorithm for segmenting all images. To achieve successful segmentation the images are first classified into image classes. Then sets of segmentation algorithms are used, based on the different image classes. The segmentation algorithms and classification algorithms have been tested in a laboratory and in industrial on-line systems for froth images, the test results show that they are robust for froth images. The processing speed for the segmentation algorithm is much faster than for a standard morphological segmentation algorithm. The processing accuracy is comparable to manual drawn result. This test shows that the algorithms work satisfactorily.
Minerals Engineering.
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Y. Wu,
S. Zheng,
X. Zhu, W. Wang,
H. Wang,
S. Liu,
Y. Bai,
H. Chen,
L. Hu,
M. Chen,
Huang Q,
D. Huang,
S. Zhang,
J. Li,
D. Chu,
J. Jiang,
Y. Song
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ABSTRACT: The fusion-driven subcritical system (named FDS-I) was previously proposed as an intermediate step toward the final application of fusion energy. A conceptual design of the FDS-I is presented, which consists of the fusion neutron driver with relatively easy-achieved plasma parameters, and the He-gas/liquid lithium–lead Dual-cooled subcritical Waste Transmutation (DWT) blanket used to transmute long-lived radioactive wastes and to generate energy on the basis of self-sustainable fission and fusion fuel cycle. An overview of the FDS-I is given and the specifications of the design analysis are summarized.
Fusion Engineering and Design.
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ABSTRACT: The formation of stray grains during the casting process can severely reduce the performance of single crystal turbine blades. In this study the mechanism by which stray grains form was investigated using a combined cellular automaton-finite difference (CA-FD) model. The model was first validated by a quantitative comparison of solute profiles and dendritic tip undercooling with those obtained from prior models. It was then applied to simulate dendritic growth in the platform region of turbine blades and to study the influence of withdrawal velocity and thermal gradient on the formation of stray grains. The simulation results show that increasing either the withdrawal velocity or the inclination angle of isotherms increases the undercooling within the platform region, which in turn favors the formation and growth of stray grains. Of these two factors, the isotherm angle has a larger influence than withdrawal velocity. The predicted dendritic microstructures show good correlation with prior experimental results and it is demonstrated that the developed CA-FD model offers the capability to understand the casting process for single crystal components of nickel-based superalloys at a microstructural level.
Materials Science and Engineering: A.
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ABSTRACT: The photon cascade emission of Gd3+ ions under 8S7/2 → 6GJ excitation is observed in GdBaB9O16. Under the 202 nm excitation, a red and a near infrared radiative transition from 6GJ states, 6GJ→6IJ and 6GJ→6PJ occur followed by an ultraviolet emission of 6PJ → 8S7/2. The absence of emission from 6DJ and 6IJ states is attributed to the effective multiphonon 6DJ→6IJ and IJ→6PJ relaxation in this lattice.
Journal of Alloys and Compounds.
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ABSTRACT: A combined cellular automaton-finite difference (CA-FD) model has been developed to simulate solute diffusion controlled solidification of binary alloys. Constitutional and curvature undercooling were both solved to determine the growth velocity of the solid/liquid interface. A modified decentered square/octahedron (in two or three dimensions) growth technique was implemented in the cellular automaton to account for the effect of crystallographic anisotropy. The resulting model is capable of simulating the growth of equiaxed and columnar dendritic grains in 2D and 3D, with the <100> directions either aligned or inclined with the grid. The algorithm used can also be used on coarser grids, with a concomitant loss in resolution, allowing simulation of sufficiently large numbers of dendrites in 3D to investigate the distribution of spacings, as well as average behavior.Simulations were performed for directional solidification with a range of withdrawal velocities and nucleation conditions, but a constant thermal gradient. The simulations capture the full microstructural development and primary spacing selection by both branching and overgrowth mechanisms. The model illustrates that there is a range of possible stable spacings, and that the final spacing is history dependent. It was also found that a minimum deviation from the steady state dendrite spacing is required before the spacing adjustment mechanisms are activated. The influence of perturbing the withdrawal velocity upon the stability of the spacing was also investigated. It was found that perturbations significantly reduce the range of stable primary dendrite spacing.
Acta Materialia.
