The impact of antiretroviral therapy on population-level virulence evolution of HIV-1

In HIV-infected patients, an individual''s set point viral load (SPVL) strongly predicts disease progression. Some think that SPVL is evolving, indicating that the virulence of the virus may be changing, but the data are not consistent. In addition, the widespread use of antiretroviral therapy (ART) has the potential to drive virulence evolution. We develop a simple deterministic model designed to answer the following questions: what are the expected patterns of virulence change in the initial decades of an epidemic? Could administration of ART drive changes in virulence evolution and, what is the potential size and direction of this effect? We find that even without ART we would not expect monotonic changes in average virulence. Transient decreases in virulence following the peak of an epidemic are not necessarily indicative of eventual evolution to avirulence. In the short term, we would expect widespread ART to cause limited downward pressure on virulence. In the long term, the direction of the effect is determined by a threshold condition, which we define. We conclude that, given the surpassing benefits of ART to the individual and in reducing onward transmission, virulence evolution considerations need have little bearing on how we treat.     

Mycobacterium bovis shedding patterns from experimentally infected calves and the effect of concurrent infection with bovine viral diarrhoea virus

Concurrent infection of cattle with bovine viral diarrhoea virus (BVDV) and Mycobacterium bovis is considered to be a possible risk factor for onward transmission of bovine tuberculosis (BTB) in infected cattle and is known to compromise diagnostic tests. A comparison is made here of M. bovis shedding (i.e. release) characteristics from 12 calves, six experimentally co-infected with BVDV and six infected with M. bovis alone, using simple models of bacterial replication. These statistical and mathematical models account for the intermittent or episodic nature of shedding, the dynamics of within-host bacterial proliferation and the sampling distribution from a given shedding episode. We show that while there are distinct differences among the shedding patterns of calves given the same infecting dose, there is no statistically significant difference between the two groups of calves. Such differences as there are, can be explained solely in terms of the shedding frequency, but with all calves potentially excreting the same amount of bacteria in a given shedding episode post-infection. The model can be thought of as a process of the bacteria becoming established in a number of discrete foci of colonization, rather than as a more generalized infection of the respiratory tract. In this case, the variability in the shedding patterns of the infected calves can be explained solely by differences in the number of foci established and shedding being from individual foci over time. Should maximum exposure on a particular occasion be a critical consideration for cattle-to-cattle transmission of BTB, cattle that shed only intermittently may still make an important contribution to the spread and persistence of the disease.     

滚筒式采煤机煤岩截割力学特性及测试系统研究

为实现采煤机在煤岩截割过程中滚筒载荷受力的测试与分析,现场建立等比例大型采煤机力学特性分析研究实验平台,采用等效结构惰轮轴传感器测试方法,针对滚筒式采煤机在煤岩截割过程中采煤机滚筒载荷变化进行实时动态在线监测,采用无线信号发射装置实现测试数据的实时传输。现场截割实验结果表明,在采煤机截割煤岩过程中,滚筒x,y,z三向上的载荷峰值差分别为29.941,17.459和7.371kN,载荷变化显著,测试结果符合现场实际工况,为实现采煤机煤岩动态识别以及自动调高控制提供了重要的理论和数值依据。     

Directional velocity estimation using a spatio-temporal encoding technique based on frequency division for synthetic transmit aperture ultrasound

This paper investigates the possibility of flow estimation using spatio-temporal encoding of the transmissions in synthetic transmit aperture imaging (STA). The spatial encoding is based on a frequency division approach. In STA, a major disadvantage is that only a single transmitter (denoting single transducer element or a virtual source) is used in every transmission. The transmitted acoustic energy will be low compared to a conventional focused transmission in which a large part of the aperture is used. By using several transmitters simultaneously, the total transmitted energy can be increased. However, to focus the data properly, the signals originating from the different transmitters must be separated. To do so, the pass band of the transducer is divided into a number of subbands with disjoint spectral support. At every transmission, each transmitter is assigned one of the subbands. In receive, the signals are separated using a simple filtering operation. To attain high axial resolution, broadband spectra must be synthesized for each of the transmitters. By multiplexing the different waveforms on different transmitters over a number of transmissions, this can be accomplished. To further increase the transmitted energy, the waveforms are designed as linear frequency modulated signals. Therefore, the full excitation amplitude can be used during most of the transmission. The method has been evaluated for blood velocity estimation for several different velocities and incident angles. The program Field II was used. A 128-element transducer with a center frequency of 7 MHz was simulated. The 64 transmitting elements were used as the transmitting aperture and 128 elements were used as the receiving aperture. Four virtual sources were created in every transmission. By beamforming lines in the flow direction, directional data were extracted and correlated. Hereby, the velocity of the blood was estimated. The pulse repetition frequency was 16 kHz. Three different setups were investigated with flow angles of 45, 60, and 75 degrees with respect to the acoustic axis. Four different velocities were simulated for each angle at 0.10, 0.25, 0.50, and 1.00 m/s. The mean relative bias with respect to the peak flow for the three angles was less than 2%, 2%, and 4%, respectively.     

A method on modelling and analyzing the power losses in vehicle transmission

The efficiency of transmissions is related directly to the energy consumption in vehicle systems. Hence, it is worth a lot researching the overall power losses inside the transmission, in order to modify the transmission performance or optimize the transmission. In most research works, only how to model the component power losses is considered. It is then necessary to put forward a general or standard method to calculate the overall power losses in the transmissions. In this paper, a general model of overall power losses in transmissions is built up, based on the selection of the submodels of component power losses from literature. With the help of the experimental data from the test bench, the methodology of parameter identification is introduced. As a result, more accurate power loss distribution of the transmission is possible to be obtained, through combining the overall efficiency experimental data and the model of overall power losses. In order to validate the methodology, it is applied into two study cases of different transmissions. Through the results of the two study cases, it is concluded that the methodology of modelling of power losses in transmissions with parameter identification is ready to be extended to other transmission study cases. It is expected that with the help of the methodology in this paper, a platform can be built up to benchmark different production transmissions in the future.     

同期脱冰架空输电导线的动张力特性实验研究

架空输电导线脱冰后,架空导线发生大幅度的非线性震荡,其震荡的位移和导线张力严重威胁架空线路的安全运行。基于档距为40 m的架空导线模型,通过模拟实验的方法对同期脱冰后的架空导线脱冰动张力特性进行研究。实验结果表明:导线最大动张力和最小动张力发生在脱冰震荡的前1—2周期内;同期整档脱冰时,导线动张力变化幅度随覆冰厚度增加而增大,但始终低于相同条件下的静张力的数值;同期局部脱冰的最大动张力随脱冰位置的不同而变化,当架空导线档距中央局部脱冰时,将会引起更大的动张力变化,其最大动张力数值会出现大于相同覆冰条件下的导线静张力情况。     

Generation and analysis of FCG data using a single specimen and Kmax–ΔK testing matrix

A custom method to generate fatigue crack growth (FCG) data requires testing of multiple specimens at different load ratios, R, and the application of a load shedding procedure from pre-cracking level to threshold. In this paper, a novel method of testing has been investigated which utilizing a single specimen and a testing matrix in terms of K_max and ΔK values corresponding to predetermined R-ratios for which FCG data are recorded. Automatic K-controlled tests on 2324-T39 Al alloy were conducted using both increasing and decreasing ΔK procedures while K_max was kept constant. Results show that the increasing ΔK procedure gives less scatter than decreasing ΔK procedure. Also, fatigue crack growth curves near the threshold region obtained from increasing ΔK are above the curves obtained from decreasing ΔK procedure. These differences are explained by means of interaction between cyclic plastic zones and their effect on fatigue damage. The procedure with increasing ΔK demonstrated minimal interaction effects and hence it is recommended for efficient FCG data generation. The proposed procedure reduces testing time, the overall scatter associated with multiple samples and eliminates possible uncertainty linked to the load shedding procedure and its effects on threshold.     

Coded ultrasound for blood flow estimation using subband processing

This paper investigates the use of coded excitation for blood flow estimation in medical ultrasound. Traditional autocorrelation estimators use narrow-band excitation signals to provide sufficient signal-to-noise-ratio (SNR) and velocity estimation performance. In this paper, broadband coded signals are used to increase SNR, followed by subband processing. The received broadband signal is filtered using a set of narrow-band filters. Estimating the velocity in each of the bands and averaging the results yields better performance compared with what would be possible when transmitting a narrow-band pulse directly. Also, the spatial resolution of the narrow-band pulse would be too poor for brightness-mode (B-mode) imaging, and additional transmissions would be required to update the B-mode image. For the described approach in the paper, there is no need for additional transmissions, because the excitation signal is broadband and has good spatial resolution after pulse compression. This means that time can be saved by using the same data for B-mode imaging and blood flow estimation. Two different coding schemes are used in this paper, Barker codes and Golay codes. The performance of the codes for velocity estimation is compared with a conventional approach transmitting a narrow-band pulse. The study was carried out using an experimental ultrasound scanner and a commercial linear array 7 MHz transducer. A circulating flow rig was scanned with a beam-to-flow angle of 60 degrees. The flow in the rig was laminar and had a parabolic flow-profile with a peak velocity of 0.09 m/s. The mean relative standard deviation of the velocity estimate using the reference method with an 8-cycle excitation pulse at 7 MHz was 0.544% compared with the peak velocity in the rig. Two Barker codes were tested with a length of 5 and 13 bits, respectively. The corresponding mean relative standard deviations were 0.367% and 0.310%, respectively. For the Golay coded experiment, two 8-bit codes were used, and the mean relative standard deviation was 0.335%.     

Design and theoretical analysis of throughput enhanced spatial reuse distributed coordination function for IEEE 802.11

The IEEE 802.11 distributed coordination function (DCF) employs a carrier sensing mechanism, a simple and effective mechanism to mitigate collisions in wireless networks. But the carrier sensing mechanism is inefficient in terms of shared channel use because an overcautious channel assessment approach is used to estimate interference at a receiver. A DCF node simply blocks its transmission when it senses that the channel is busy. However, in many cases this channel assessing node?s own transmission may not generate enough interference to disrupt the ongoing transmission at the receiver. This overcautious channel assessment unnecessarily blocks transmission attempts, and thus degrades the overall network throughput. To avoid this unnecessary blocking, the authors propose a spatial reuse DCF (SRDCF), which utilises location information and transmission parameters to make accurate channel assessments and to permit concurrent transmissions by adjusting the transmission power. SRDCF also resolves the contention between opportunistic concurrent transmissions with a secondary backoff counter. Consequently, the proposed scheme improves the overall network throughput because of more concurrent transmissions. The authors theoretically analyse the performance enhancement of SRDCF over the original IEEE 802.11 DCF by using a Markov chain model and verify it through simulations.     

Transmissibility of swine flu at Fort Dix, 1976.

The 1976 outbreak of A/New Jersey/76 influenza in Fort Dix is a rare example of an influenza virus with documented human to human transmission that failed to spread widely. Despite extensive epidemiological investigation, no attempt has been made to quantify the transmissibility of this virus. The World Health Organization and the United States Government view containment of emerging influenza strains as central to combating pandemic influenza. Computational models predict that it may be possible to contain an emergent pandemic influenza if virus transmissibility is low. The A/New Jersey/76 outbreak at the United States Army Training Center at Fort Dix, New Jersey in January 1976 caused 13 hospitalizations, 1 death and an estimated 230 cases. To characterize viral transmission in this epidemic, we estimated the basic reproductive number and serial interval using deterministic epidemic models and stochastic simulations. We estimated the basic reproductive number for this outbreak to be 1.2 (supported interval 1.1-1.4), the serial interval to be 1.9 days (supported interval 1.6-3.8 days), and that the virus had at least six serial human to human transmissions. This places the transmissibility of A/New Jersey/76 virus at the lower end of circulating flu strains, well below the threshold for control.     

School closures reduced social mixing of children during COVID-19 with implications for transmission risk and school reopening policies

School closures may reduce the size of social networks among children, potentially limiting infectious disease transmission. To estimate the impact of K–12 closures and reopening policies on children''s social interactions and COVID-19 incidence in California''s Bay Area, we collected data on children''s social contacts and assessed implications for transmission using an individual-based model. Elementary and Hispanic children had more contacts during closures than high school and non-Hispanic children, respectively. We estimated that spring 2020 closures of elementary schools averted 2167 cases in the Bay Area (95% CI: −985, 5572), fewer than middle (5884; 95% CI: 1478, 11.550), high school (8650; 95% CI: 3054, 15 940) and workplace (15 813; 95% CI: 9963, 22 617) closures. Under assumptions of moderate community transmission, we estimated that reopening for a four-month semester without any precautions will increase symptomatic illness among high school teachers (an additional 40.7% expected to experience symptomatic infection, 95% CI: 1.9, 61.1), middle school teachers (37.2%, 95% CI: 4.6, 58.1) and elementary school teachers (4.1%, 95% CI: −1.7, 12.0). However, we found that reopening policies for elementary schools that combine universal masking with classroom cohorts could result in few within-school transmissions, while high schools may require masking plus a staggered hybrid schedule. Stronger community interventions (e.g. remote work, social distancing) decreased the risk of within-school transmission across all measures studied, with the influence of community transmission minimized as the effectiveness of the within-school measures increased.     

RK‐Slim: embedded Runge–Kutta without the excess baggage

Computationally demanding scientific simulations require numerical integration of large systems of ordinary differential equations (ODEs) in real time. Runge–Kutta (RK) methods with step‐size control are frequently employed because they are accurate and have short execution times. Computational step sizes can be increased while maintaining accuracy if the error generated during each time step is below a predetermined threshold. However, if the error exceeds the threshold, the time step must be re‐computed using a smaller step‐size. In practice, the re‐computation is unnecessary for most equations in the system because violations of the error tolerance are localized and occur in just a few equations. We present an efficient and accurate method for solving ODEs that exploits these observations on step‐size by eliminating many unnecessary computations in embedded RK methods. We demonstrate how our new method can be a valuable tool for practitioners in the field through simulations with real‐world data. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence analysis of system parameters on characteristics of the nutation drive with double circular arc spiral bevel gears

Gear transmission systems are one of the most frequently used systems for power transmission. The characteristics of a gear transmission system have important guiding significance in the design, manufacture and application of transmissions. This paper focuses on the influence of system parameters on the characteristics of a specific type of gear transmission, the nutation drive with double circular arc spiral bevel gears. Based on the transmission ratio analysis of single-stage and two-stage nutation drive systems, the system parameters, including nutation angle, gear spiral angle, pitch angle and cone distance, were defined. An analysis of the influence of system parameters on transmission efficiency was performed. Furthermore, the influence of system parameters on axial misalignment and cone displacement error was investigated. Finally, by changing the input frequency, input load, nutation angle, and spiral angle, variation regularity of the dynamic meshing force was obtained. A transmission performance analysis based on the influence of system parameters was achieved and provides the theoretical basis for better design of the nutation drive with double circular arc spiral bevel gear.     

Cryogenic temperature near-threshold fatigue crack growth rate data for JBK-75 stainless steel

An important structural component of the Westinghouse Large Coil Programme superconducting magnet is the JBK-75 (modified A-286) stainless steel conductor sheath. Because the presence of pre-existing cracks or flaws in the conductor sheath is a potential possibility, the structural reliability of the conductor sheath would be enhanced if a threshold level of stress intensity range (ΔK_th) was established below which fatigue crack growth would not occur. Consequently, near-threshold fatigue growth rate data were generated at two load ratios on JBK-75 stainless steel at room and cryogenic temperatures. No load ratio effect on near-threshold fatigue crack growth rate was observed at cryogenic temperatures.     

基于分层损伤分析的碳纤维增强树脂复合材料-金属传动轴扭转性能

为提高油动四旋翼无人机载重能力,对碳纤维增强树脂复合材料(CFRP)-金属传动轴进行研究。CFRP-金属传动轴扭转强度影响因素为CFRP管制孔质量问题和传动过程中销钉对连接孔的挤压作用。研究导致CFRP管孔入出口分层损伤的力学行为,揭示了CFRP管制孔质量的影响机制并优化了制孔工艺。利用扭转试验对销接式CFRP-金属传动轴和附有内外衬套的混合式CFRP-金属传动轴进行对比分析。结果表明:在CFRP管内外附有铝合金衬套可有效减少制孔时的分层损伤,使孔入口质量提高了4.4%,孔出口质量高了8.3%,同时抑制销钉对连接孔的挤压作用。优化后的传动轴承受扭矩从499 N·m提高到952 N·m。      

生理参数遥测系统无线供能模块的设计

能量供应问题是动物生理参数遥测系统实现长期稳定工作的关键,基于电磁感应的无线供能技术是解决这一问题的有效途径.为向动物生理参数遥测系统提供稳定、安全的能量,从能量传输的稳定性与电磁生物安全性两方面出发,对能量传输模块进行优化设计,实现了由长方形截面发射线圈和三维接收线圈组成的无线供能模块,能够在Φ10.5 mm×11 mm接收空间内提供至少150 mW有效功率,传输效率不小于2.64%.遥测系统的活体实验证实了该供能方式的可行性.     

DVE中按需预取的递进纹理数据传输方法

很多虚拟环境中的3D模型具有高质量的表面纹理。因此，在大的分布式虚拟环境的应用系统中需要传输大量的纹理数据。然而，分布式虚拟环境中大规模的纹理数据传输带来的传输延时令影响系统的真实感和实时性。为解决这个问题用拉普拉斯金字塔算法和哈尔变换算法实现了纹理递进传输。实验结果和测试数据表明，这两种算法都有效地减少了初始传输延时。但是拉普拉斯金字塔算法增加了表示一幅纹理贴图所需的数据量，而哈尔变换算法则保持数据量不变。为了进一步减轻网络负载，可以用均匀标量量化和行程编码等算法进一步减少在此DVE系统中的所需传输的数据总量。     

覆冰输电线路脱冰跳跃及抑制方法研究

将变截面梁用于一种板壳耦合结构的吸振,推导了功率流在各结构上的分配表达式,并对吸振效果进行了仿真。结果表明：梁在共振频率处对板和壳的吸振效果明显;安装位置对梁的吸振效果有决定作用,安装位置处板的响应幅值越大,梁的吸振效果越明显;提高梁的损耗因子有利于提升其吸振效果;本文有关线输入导纳的推导可为其他结构的功率流分析提供借鉴。     

Parallel optical interconnects may reduce the communication bottleneck in symmetric multiprocessors

We start with a detailed analysis of the communication issues in today's symmetric multiprocessor (SMP) architectures to study the benefits of implementing optical interconnects (OI) in these machines. We show that the transmission of block addresses is the most critical communication bottleneck of future large SMPs owing to the need to preserve the coherence of data duplicated in caches. An address transmission bandwidth as high as 200-300 Gb/s may be necessary in ten years from now; this requirement will represent a difficult challenge for shared electric buses. In this context we suggest the introduction of simple point-to-point OIs for a SMP cache-coherent switch, i.e., for a VLSI switch that would emulate the shared-bus function. The operation might require as much as 10,000 input-outputs (IOs) to connect 100 processors, particularly if one maintains the present parallelism of transmissions to preserve a large bandwidth and a short memory access latency. The interest for OIs comes from the potential increase of the transmission frequency and from the possible integration of such a high density of IOs on top of electronic chips to overcome packaging issues. Then we consider the implementation of an optical bus that is a multipoint optical line involving more optical technology. This solution allows multiple simultaneous accesses to the bus, but the preservation of the coherence of caches can no longer be maintained with the usual fast snooping protocols.     

纯电动汽车两挡变速器减振降噪研究

针对纯电动汽车两挡自动变速器在工作过程中存在的振动和噪声问题,通过建立变速箱-电机转子刚柔耦合动力学模型,对变速器系统进行传递误差、齿面接触应力等分析和计算。根据纯电动汽车的常用工况及其特点,以齿轮修形参数为优化变量,传递误差为主要优化目标,综合考虑齿面载荷分布以及齿面接触应力,在多工况下对齿轮进行修形。结果表明修形后达到了优化齿面载荷分布、提高齿轮使用寿命、减小振动、降低噪声的目的,实现了齿轮多目标优化。研究结果对纯电动汽车变速器的开发有一定的借鉴作用。